CA1213112A - Expanded particles of polyolefin resin and process for producing same - Google Patents
Expanded particles of polyolefin resin and process for producing sameInfo
- Publication number
- CA1213112A CA1213112A CA000428024A CA428024A CA1213112A CA 1213112 A CA1213112 A CA 1213112A CA 000428024 A CA000428024 A CA 000428024A CA 428024 A CA428024 A CA 428024A CA 1213112 A CA1213112 A CA 1213112A
- Authority
- CA
- Canada
- Prior art keywords
- particles
- polyolefin resin
- ethylene
- pressure
- container
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/16—Making expandable particles
- C08J9/18—Making expandable particles by impregnating polymer particles with the blowing agent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/34—Auxiliary operations
- B29C44/3461—Making or treating expandable particles
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/14—Saturated hydrocarbons, e.g. butane; Unspecified hydrocarbons
- C08J2203/142—Halogenated saturated hydrocarbons, e.g. H3C-CF3
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
- Y10S264/09—Pre-expansion of foamed polystyrene
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
Abstract
ABSTRACT
The mixture of water and the polyolefin resin particles impregnated with a volatile blowing agent are released from the interior of the pressure-resistant container under a constant temperature and constant pressure preferably keeping the partial pressure of the blowing agent constant, through at least one orifice having an area of 0.07 to 300 mm2, into a low-pressure zone.
This invention gives various advantages when applied to the practical process resulting in expanded particles with superior properties which are free of blocking and remarkably uniform in the degree of expansion , and are useful for molding.
The mixture of water and the polyolefin resin particles impregnated with a volatile blowing agent are released from the interior of the pressure-resistant container under a constant temperature and constant pressure preferably keeping the partial pressure of the blowing agent constant, through at least one orifice having an area of 0.07 to 300 mm2, into a low-pressure zone.
This invention gives various advantages when applied to the practical process resulting in expanded particles with superior properties which are free of blocking and remarkably uniform in the degree of expansion , and are useful for molding.
Description
lZl;~112 TITLE OF THE INVENTION
EXPANDED PARTIC3~ES OF POLYOLEFIN
RESIN AND PROCESS FOR P~ODUCING SAME
' The present invention relates to expanded particles of polyolefin resin which can be made in-to a molded product when heated within a mold with water vapor or like heating medium and to a process for producing such particles.
More particularly, the invention relates to e~panded particles of polyolefin resin which will not agglomerate into blocks, have a uniform and minute cellular structure and are greatly reduced in variations in the degree of expansion, and to a process for producing the same.
Expanded,particles of polyolefin resin like polyethylene resin useful for molding are prepared most widely by heating resin particles containing a volatile blowing agent or thermally decomposable blowing agent. ~owever, this process involves difficulty in obtaining highly expanded particles and further has the drawback that the expanded particles obtained ~ary greatly in the degree of expansion and are prone to shrinkage, It is also known to produce expanded resin particles by dispersing polyolefin resin particles containing a volatile blowing agent in water within a pressure-resistant container, agitating the dispersion at a high temperature and high pressure and thereafter releasing the dispersion into a ~Z1311Z
low-pressure zone, as disclosed in West German Laid-Open Patent Publication No. 2107683, Published Examined Japanese Patent Application No. 1344/1981, etc. This process is efficient in that the starting resin particles can be impregnated with the blowing agent and expanded continuously within the same apparatus, but has problems in that the resin particles are liable to agglomerate within the container since the particles containing the blowing agent are subjected to a high temperature, and that the expanded particles are prone to blocking since the resin particles are released into a low-pressure zone at a high speed. Moreover, the process has the drawback that the expanded particles tend to vary greatly in the degree of expansion and to be uneven in cellular structure among the particles, which impairs the moldability and fails to obtain products with satisfactory properties when molded.
We have carried out intensive research to overcome such drawbacks of the latter process and accomplished a process which is characterized in that a mixture of resin particles and water is released from a pressure-resistant container into a low-pressure zone through an orifice of small diameter while strictly controlling the internal temperature and pressure of the container during the release.
The orifice of small diameter through which the particles are released prevents the particles from contact with one another during the passage therethrough and controls the the speed of release, consequently preventing them from blocking during the release. Furthermore, the control of the internal pressure of the container during the release eliminates variations in the rate of release to give expanded particles which are uniform in the degree of expansion and also in cellular structure among the particles. The release of particles through the small orifice results in the advantage that the interior of the container can be maintaiened under the controlled pressure easily during the release.
Stated more specifically, the present invention provides a process for producing expanded particles of a polyolefin resin characterized by dispersing polyolefin resin particles 0.25 to 10 mm in particle size and a volatile blowing agent in water in the presence of a dispersant within a pressure-resistant container, heating the mixture at a temperature within the range of from the melting point of crystals of the resin minus 25 C to the melting point plus 10 C to impregnate the resin particles with the blowing agent, and releasing the mixture of the particles and water into a low-pressure zone through at least one orifice having an area of n. 07 to 300 m~2 while maintaining the interior of the container at a constant temperature and constant pressure.
The invention also provides such expanded particles of polyolefin resin obtained by the process.
Examples of polyolefin resins useful for the ~Z13~2 present invention are low-density polyethylene, straight-chain low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-prop~lene random copolymer, ethylene-S propylene block copolymer, ethylene-propylene-butene terpol~mer, etc. These resins are used singly, or at least two of them may be used in admixture. Ultraviolet absorbers, antistatic agents, thermal stabilizers, flame retardants, coloring agents and fillers may be admixed with such resins.
Further, polyolefin resins having crosslinked bonds which are produced with a peroxide or by irradiation with electron rays, can also be used.
The process of this invention enables to produce expanded polyolefin resin particles with uniform cell structure among the particles obtained, by the strict control of the internal pressure of the container and with use of small olifice. ~owever, it is further desired that the polyolefin resin particles of the invention contain 0.01 to 5.0 parts by weight, preferably 0.01 to 1 0 part by weight, most preferably 0.01 to 0.5 part by weight, of an inorganic nucleating agent per 100 parts by weight of the resin. The inorganic nucleating agent acts to give expanded resin particles ha~ing fine and uniform cells in each of the particles which are 0.05 to 0.5 mm in diameter. With less than 0.01 part by weight of the inorganic uncleating agent present, it is difficult to obtain fine uniform cells, whereas more than 5.0 parts by weight of the agent, if ~sed, will not produce a correspondingly enhanced effect. Examples lZ~3~1Z
of useful inorganic nucleating agents are talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, kieselguhr, clay, sodium bicarbonate, barium sulfate, bentonite, etc., of which talc and silica are 5 preferable to use.
The polyolefin resin particles to be expanded are preferably 0.25 to 10 mm, more preferably 0.5 to 6 mm, in particle size to assure favorable molding of the resulting product.
Examples of volatile blowing agents useful for the present invention are hydrocarbons and hydrocarbon halides having a boiling point of -50 to 120 C, such as propane, butane, pentane, hexane, heptane, cyclopentane, cyclohexane, monochloromethane, dichloromethane, monochloroethane, trichloromonofluoromethane/ dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, etc. These compounds are used singly, or at least two of them may be used in admixture.
The amount of the volatile blowing agent to be charged in is determined in accordance with the kind of the resin, the kind Gf the blowing agent, the desired degree of expansion and the ratio of the resin within the pressure-resistant container to the vapor-phase space of the container~ ~ith the present invention, the amount of charge is so determined that the polyolefin resin will be impregnated usually with 5 to 40 parts by weight of the blowing agent.
~2131~;~
When dispersing the polyolefin resin particles in water according to the invention, it is desired to use a small amount of dispersant to prevent the resln particles from fusing to one another during heating. Examples of useful dispersants are water-soluble high polymers such as polyvinyl alcohol, methylcellulose and N-polyvinylpyrrolidone; fine powders of inorganic substances which are sparingly soluble in water, such as calcium phosphate, magnesium pyrophosphate and zinc carbonate; and mixtures of such fine powders of inorganic substances and a small amount of sodium alkylbenzene-sulfonate, sodium ~-olefinsulfonate, sodium alkylsulfonate or like anionic surfactant. It is perferable to use inorganic substances since the use of water-soluble high polymers involves problems of water pollution.
However, if the inorganic substance is used in a large amount, the expanded particles obtained will not thermally a~h~r~ to one another effectively when molded, so that it is preferred to use a small amount of anionic surfactant conjointly with the inorganic substance. In this case, 0.1 to 3 parts by weight of the fine powder of sparingly water-soluble inorganic substance and 0.001 to 0.5 part by weightof anionic surfactant are preferably used per 100 parts by weight of the resin.
AGcording to the present process, the mixture of the above~mentioned materials is heated at a temperature not lower than the softening point of the polyolefin resin with the volatile blowing agent contained in the resin. The range of proper heating temperatures varies with the kind of polyolefin resin and the kind of volatile blowing agent. In actually practicing the present invention, however, the heating temperature is determined within the temperature range of from the melting point of crystals of the resin minus C to the melting point plus 10 C, preferably from the melting point minus 20 C to the melting point plus 5 C.
For example, in the case of a low-density polyethylene which is 110 C in the melting point of its crystals, the proper heating temperature is in the range of 85 to 120 C. In the case of ethylene-propylene random copolymer having an ethylene content of 4.5~ by weight and a crystal melting point of 135 C, the proper heating temperature is in the range of 110 to 145 C. If the heating temperature is lower than the specified range, a greatly reduced degree of expansion will result, whereas if the temperature is too high, the expanded particles obtained have a lower ratio of closed cells, hence undesirable.
According to the present invention, the mixture of water and expandable particles of polyolefin resin which are subjected to heat and increased pressure and remain unexpanded within the container is then released into a low-pressure zone through at least one orlfice having an area of ~.~7 r~ to 300 mm . If the orifice is too small, the particles are unable to pass therethrough and plug up the orifice, whereas if i~ is too large, a large number of expandable particles, remaining unexpanded under pressure but softened by heating, are released into the low-pressure zone through the orifice at the same time to thermally adhere to one another during passage through the orifice or thereafter (when expanding), thus undergoing blocking. The size of orifice or orifices to be used in this invention is 0.07 to 300 mm2 in area, and is preferably 0.28 to 120 mm2. The size o orifice should theoretically be at least about as large as the size of the polyolefin resin particles used and actually be at laast 1.2 times as large as the size of the particles. However, in this invention, it is desired that the size of orifice should be as small as possible. Thus, the upper limit of the size of olifice of 300 mm2 was determined so as to be twice as large as lO mm of the size of the largest polyolefin resin particles to be employed in this invention. When such a small olifice is used for passing the resin particles therethrough into the low-pressure zone, the resin particles can be passed through the orifice without contacting one another and can be released in a smaller number per unit time with reduced likelihood of ¦ colliding with one another. Consequently this will reduce the likelihood of thermal adhesion (blocking) of the expanded particles. The orifice is usually circular or elliptical in shape but can be polygonal in some cases. The orifice can be provided, for example, by disposing a pressure-resistant ..
.
lZ~311Z
orifice plate having at least one orifice at the rear end of a release valve with use of flanges.
While it is critical as one of the features of the invention to maintain the interior of the pressure-resistant S container at a specified pressure during the release of particles as will be described below, the use of small orifice, .07 to 300 mm2in area, leads to the advantage that the container internal pressure is controllable with ease.
According to the present invention, the internal temperature and pressure of the container must be kept constant when the mixture of resin particles and water is released into a low-pressure zone.
The internal temperature, if varying, greatly varies the degree to which the resin particles are expanded. Thus it is required to control the temperature as strictly as possi~le. For example, the variation of the temperature during the period from the start of release until the end of release should preferably be not more than 5 C, more preferably not more than 3 C. The temperature is easily controllable, for example, when the pressure-resistnat container is provided with a usual jacket.
As the mixture of resin particles and water is released from the container, the upper space within the con-tainer increases to lower the internal pressure of the con-tainer and reduce the degree of expansion of the particlesreleased~ further permitting expansion within the container ~o - hamper the release of particles, so that there is a need to main-_g_ .
tain the internal pressure of the container at a consta~t level during the release.
It may appear useful to introduce N2, air or like inert gas for the pressure maintenance, but even if such inert gas is used for this purpose, the reduction in the degree of expansion of the resulting particles is still great.
We have conducted research to solve this problem and found that the reduction of the expansion degree is attributable to the fact that as the mixture of resin particles and water is released from the container, the interior upper space (vapor-phase space) of the container enlarges to decrease the partial pressure of the volatile blowing agent in the interior space and permit the resin to release the blowing agent, consequently decreasing the amount of the blowing agent impreganting the resin, even if the internal pressure is maintained by N2, air or like inert gas.
Accordingly expanded particles can he obtained with a minimized variation in the degree of expansion by keeping the total internal pressure and the partial pressure o~ the blowing agent constant. This can be realized for example, by decreasing the interior upper space of the container by an amount correspond-ing to the increase of the space to maintain the space at a constant volume, or by supplying the volatile blowing agent to the container from outside in corresponding relation to , --1 0--~213112 the increase of the space. The need to supply the blowing agent arises when the interior space of the container is not saturated with the agent as usually and the partial pressure of the blowing agent in the container decreases with the release S of particles. Thus, when the interior space of the container is suturated with the blowing agent and excessive blowing agent is exist in liquid, it is not always necessary to supply the blowing agent. In the case of supplying the volatile blowing agent , the blowing agent can be introduced into the container from outside (1) in the form of a vapor, or (2) in the form of a liquid.
The latter mode of supply is simpler and is therefore more preferable. When introduced into the container in the mode
EXPANDED PARTIC3~ES OF POLYOLEFIN
RESIN AND PROCESS FOR P~ODUCING SAME
' The present invention relates to expanded particles of polyolefin resin which can be made in-to a molded product when heated within a mold with water vapor or like heating medium and to a process for producing such particles.
More particularly, the invention relates to e~panded particles of polyolefin resin which will not agglomerate into blocks, have a uniform and minute cellular structure and are greatly reduced in variations in the degree of expansion, and to a process for producing the same.
Expanded,particles of polyolefin resin like polyethylene resin useful for molding are prepared most widely by heating resin particles containing a volatile blowing agent or thermally decomposable blowing agent. ~owever, this process involves difficulty in obtaining highly expanded particles and further has the drawback that the expanded particles obtained ~ary greatly in the degree of expansion and are prone to shrinkage, It is also known to produce expanded resin particles by dispersing polyolefin resin particles containing a volatile blowing agent in water within a pressure-resistant container, agitating the dispersion at a high temperature and high pressure and thereafter releasing the dispersion into a ~Z1311Z
low-pressure zone, as disclosed in West German Laid-Open Patent Publication No. 2107683, Published Examined Japanese Patent Application No. 1344/1981, etc. This process is efficient in that the starting resin particles can be impregnated with the blowing agent and expanded continuously within the same apparatus, but has problems in that the resin particles are liable to agglomerate within the container since the particles containing the blowing agent are subjected to a high temperature, and that the expanded particles are prone to blocking since the resin particles are released into a low-pressure zone at a high speed. Moreover, the process has the drawback that the expanded particles tend to vary greatly in the degree of expansion and to be uneven in cellular structure among the particles, which impairs the moldability and fails to obtain products with satisfactory properties when molded.
We have carried out intensive research to overcome such drawbacks of the latter process and accomplished a process which is characterized in that a mixture of resin particles and water is released from a pressure-resistant container into a low-pressure zone through an orifice of small diameter while strictly controlling the internal temperature and pressure of the container during the release.
The orifice of small diameter through which the particles are released prevents the particles from contact with one another during the passage therethrough and controls the the speed of release, consequently preventing them from blocking during the release. Furthermore, the control of the internal pressure of the container during the release eliminates variations in the rate of release to give expanded particles which are uniform in the degree of expansion and also in cellular structure among the particles. The release of particles through the small orifice results in the advantage that the interior of the container can be maintaiened under the controlled pressure easily during the release.
Stated more specifically, the present invention provides a process for producing expanded particles of a polyolefin resin characterized by dispersing polyolefin resin particles 0.25 to 10 mm in particle size and a volatile blowing agent in water in the presence of a dispersant within a pressure-resistant container, heating the mixture at a temperature within the range of from the melting point of crystals of the resin minus 25 C to the melting point plus 10 C to impregnate the resin particles with the blowing agent, and releasing the mixture of the particles and water into a low-pressure zone through at least one orifice having an area of n. 07 to 300 m~2 while maintaining the interior of the container at a constant temperature and constant pressure.
The invention also provides such expanded particles of polyolefin resin obtained by the process.
Examples of polyolefin resins useful for the ~Z13~2 present invention are low-density polyethylene, straight-chain low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-prop~lene random copolymer, ethylene-S propylene block copolymer, ethylene-propylene-butene terpol~mer, etc. These resins are used singly, or at least two of them may be used in admixture. Ultraviolet absorbers, antistatic agents, thermal stabilizers, flame retardants, coloring agents and fillers may be admixed with such resins.
Further, polyolefin resins having crosslinked bonds which are produced with a peroxide or by irradiation with electron rays, can also be used.
The process of this invention enables to produce expanded polyolefin resin particles with uniform cell structure among the particles obtained, by the strict control of the internal pressure of the container and with use of small olifice. ~owever, it is further desired that the polyolefin resin particles of the invention contain 0.01 to 5.0 parts by weight, preferably 0.01 to 1 0 part by weight, most preferably 0.01 to 0.5 part by weight, of an inorganic nucleating agent per 100 parts by weight of the resin. The inorganic nucleating agent acts to give expanded resin particles ha~ing fine and uniform cells in each of the particles which are 0.05 to 0.5 mm in diameter. With less than 0.01 part by weight of the inorganic uncleating agent present, it is difficult to obtain fine uniform cells, whereas more than 5.0 parts by weight of the agent, if ~sed, will not produce a correspondingly enhanced effect. Examples lZ~3~1Z
of useful inorganic nucleating agents are talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, kieselguhr, clay, sodium bicarbonate, barium sulfate, bentonite, etc., of which talc and silica are 5 preferable to use.
The polyolefin resin particles to be expanded are preferably 0.25 to 10 mm, more preferably 0.5 to 6 mm, in particle size to assure favorable molding of the resulting product.
Examples of volatile blowing agents useful for the present invention are hydrocarbons and hydrocarbon halides having a boiling point of -50 to 120 C, such as propane, butane, pentane, hexane, heptane, cyclopentane, cyclohexane, monochloromethane, dichloromethane, monochloroethane, trichloromonofluoromethane/ dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, etc. These compounds are used singly, or at least two of them may be used in admixture.
The amount of the volatile blowing agent to be charged in is determined in accordance with the kind of the resin, the kind Gf the blowing agent, the desired degree of expansion and the ratio of the resin within the pressure-resistant container to the vapor-phase space of the container~ ~ith the present invention, the amount of charge is so determined that the polyolefin resin will be impregnated usually with 5 to 40 parts by weight of the blowing agent.
~2131~;~
When dispersing the polyolefin resin particles in water according to the invention, it is desired to use a small amount of dispersant to prevent the resln particles from fusing to one another during heating. Examples of useful dispersants are water-soluble high polymers such as polyvinyl alcohol, methylcellulose and N-polyvinylpyrrolidone; fine powders of inorganic substances which are sparingly soluble in water, such as calcium phosphate, magnesium pyrophosphate and zinc carbonate; and mixtures of such fine powders of inorganic substances and a small amount of sodium alkylbenzene-sulfonate, sodium ~-olefinsulfonate, sodium alkylsulfonate or like anionic surfactant. It is perferable to use inorganic substances since the use of water-soluble high polymers involves problems of water pollution.
However, if the inorganic substance is used in a large amount, the expanded particles obtained will not thermally a~h~r~ to one another effectively when molded, so that it is preferred to use a small amount of anionic surfactant conjointly with the inorganic substance. In this case, 0.1 to 3 parts by weight of the fine powder of sparingly water-soluble inorganic substance and 0.001 to 0.5 part by weightof anionic surfactant are preferably used per 100 parts by weight of the resin.
AGcording to the present process, the mixture of the above~mentioned materials is heated at a temperature not lower than the softening point of the polyolefin resin with the volatile blowing agent contained in the resin. The range of proper heating temperatures varies with the kind of polyolefin resin and the kind of volatile blowing agent. In actually practicing the present invention, however, the heating temperature is determined within the temperature range of from the melting point of crystals of the resin minus C to the melting point plus 10 C, preferably from the melting point minus 20 C to the melting point plus 5 C.
For example, in the case of a low-density polyethylene which is 110 C in the melting point of its crystals, the proper heating temperature is in the range of 85 to 120 C. In the case of ethylene-propylene random copolymer having an ethylene content of 4.5~ by weight and a crystal melting point of 135 C, the proper heating temperature is in the range of 110 to 145 C. If the heating temperature is lower than the specified range, a greatly reduced degree of expansion will result, whereas if the temperature is too high, the expanded particles obtained have a lower ratio of closed cells, hence undesirable.
According to the present invention, the mixture of water and expandable particles of polyolefin resin which are subjected to heat and increased pressure and remain unexpanded within the container is then released into a low-pressure zone through at least one orlfice having an area of ~.~7 r~ to 300 mm . If the orifice is too small, the particles are unable to pass therethrough and plug up the orifice, whereas if i~ is too large, a large number of expandable particles, remaining unexpanded under pressure but softened by heating, are released into the low-pressure zone through the orifice at the same time to thermally adhere to one another during passage through the orifice or thereafter (when expanding), thus undergoing blocking. The size of orifice or orifices to be used in this invention is 0.07 to 300 mm2 in area, and is preferably 0.28 to 120 mm2. The size o orifice should theoretically be at least about as large as the size of the polyolefin resin particles used and actually be at laast 1.2 times as large as the size of the particles. However, in this invention, it is desired that the size of orifice should be as small as possible. Thus, the upper limit of the size of olifice of 300 mm2 was determined so as to be twice as large as lO mm of the size of the largest polyolefin resin particles to be employed in this invention. When such a small olifice is used for passing the resin particles therethrough into the low-pressure zone, the resin particles can be passed through the orifice without contacting one another and can be released in a smaller number per unit time with reduced likelihood of ¦ colliding with one another. Consequently this will reduce the likelihood of thermal adhesion (blocking) of the expanded particles. The orifice is usually circular or elliptical in shape but can be polygonal in some cases. The orifice can be provided, for example, by disposing a pressure-resistant ..
.
lZ~311Z
orifice plate having at least one orifice at the rear end of a release valve with use of flanges.
While it is critical as one of the features of the invention to maintain the interior of the pressure-resistant S container at a specified pressure during the release of particles as will be described below, the use of small orifice, .07 to 300 mm2in area, leads to the advantage that the container internal pressure is controllable with ease.
According to the present invention, the internal temperature and pressure of the container must be kept constant when the mixture of resin particles and water is released into a low-pressure zone.
The internal temperature, if varying, greatly varies the degree to which the resin particles are expanded. Thus it is required to control the temperature as strictly as possi~le. For example, the variation of the temperature during the period from the start of release until the end of release should preferably be not more than 5 C, more preferably not more than 3 C. The temperature is easily controllable, for example, when the pressure-resistnat container is provided with a usual jacket.
As the mixture of resin particles and water is released from the container, the upper space within the con-tainer increases to lower the internal pressure of the con-tainer and reduce the degree of expansion of the particlesreleased~ further permitting expansion within the container ~o - hamper the release of particles, so that there is a need to main-_g_ .
tain the internal pressure of the container at a consta~t level during the release.
It may appear useful to introduce N2, air or like inert gas for the pressure maintenance, but even if such inert gas is used for this purpose, the reduction in the degree of expansion of the resulting particles is still great.
We have conducted research to solve this problem and found that the reduction of the expansion degree is attributable to the fact that as the mixture of resin particles and water is released from the container, the interior upper space (vapor-phase space) of the container enlarges to decrease the partial pressure of the volatile blowing agent in the interior space and permit the resin to release the blowing agent, consequently decreasing the amount of the blowing agent impreganting the resin, even if the internal pressure is maintained by N2, air or like inert gas.
Accordingly expanded particles can he obtained with a minimized variation in the degree of expansion by keeping the total internal pressure and the partial pressure o~ the blowing agent constant. This can be realized for example, by decreasing the interior upper space of the container by an amount correspond-ing to the increase of the space to maintain the space at a constant volume, or by supplying the volatile blowing agent to the container from outside in corresponding relation to , --1 0--~213112 the increase of the space. The need to supply the blowing agent arises when the interior space of the container is not saturated with the agent as usually and the partial pressure of the blowing agent in the container decreases with the release S of particles. Thus, when the interior space of the container is suturated with the blowing agent and excessive blowing agent is exist in liquid, it is not always necessary to supply the blowing agent. In the case of supplying the volatile blowing agent , the blowing agent can be introduced into the container from outside (1) in the form of a vapor, or (2) in the form of a liquid.
The latter mode of supply is simpler and is therefore more preferable. When introduced into the container in the mode
(2), the volatile blowing agent immediately vaporizes, The agent may be introduced in continuously or intermittently, depending upon the acceptable variation of degree of expansion of the expanded particles to be obtained. For example, it is introduced through an adjusting valve while so controlling the pressure that the total pressure within the container will be kept constant. The expression "to keep the pressure constant" as used herein also includes to adjust and main-tain the pressure within a range according to the range of permissible variations in the expansion degree of expanded particles-When the mixture of resin particles and water isreleased from the pressure-resistant container into a low-pressure zone, the particles usually immediately expand andthefore spread out through an angle of discharge. Accordingly, in case that a duct or the li}~e is disposed immediately to =11-lZ131~Z
the rear of the discharge orifice, it must be so shaped as to have a space which is larger than the path of discharge of particles which spread out through the angle of discharge.
If a duct of samll diameter or the like is disposed to the -rear of the discharge orifice, the duct will be plugged up with expanded particles, or the expanded particles obtained include a large amount of agglomerates o~ particleg According to the present invention, the mixture of resin particles and water is released through an orifice which is as small as O,Q7 to ~00 ~2in area, so that the angle of discharge of particles is small, and the distance of scattering of the particles is short since they are released at a reduced speed. Thus the path of discharge is compact in . its entirety.
~ith the present process, therefore, the duct or container to be provided to the rear of the release orifice can be compact.
Fig. 1 and Fig. 2 are diagrams showing examples of apparatus useful for the process of the present invention.
. 20 Apparatus for practicing the present process will be described briefly with reference to these drawings, in which like parts are referred to by like reference numerals.
Fig. 1 shows a pressure-resistant container 1 which is equipped with a heater (jac~et) 4, a pressure control valve 5 and a pressure gauge 11. Pol~olefin resin particles 2 as admixed with water 3 are heated in the container 1 under - increased pressure and impregnated with a blowing agent.
. . -; . . ; - . . . .
1213~Z
The mixture of resin particles and water is released through a dicharge valve 6 and an orifice plate 7, such as the one already stated, into a tank 9, whereupon the particles are made into expanded particles 10. While the orifice may be open to the atmosphere (free space), a flaring duct 8 is provided immediately in the rear of the orifice plate 7 in Fig. 1 to render the apparatus compact. The duct 8 has a space larger than the path of discharge of the particles to be released and expanded. Alternatively a usual cylindrical duct is usable insofar as it has a sufficiently larger inside diameter In Fig. 2, the orifice is open to a tank 9 having a space larger than the path of discharge of the particles to be released and expanded. The tank 9 is useful for storing the expanded particles.
The process of the present invention described above gives expanded particles of polyolefin resin which are low in density (high in the degree of expansion), very uniform in density distribution and also uniform in cellular structure among the particles and thus gives articles with superior properties when molded. The expanded particles of polyolefin resin obtained by the present invention are usually used for molding. Useful for molding are expanded resinr particles which are 0.01 to 0.2 g/cc in density. Those having a density of 0.01 to 0.05 g/cc are suited for preparing shock-absorbing materials, packaging materials, heat-insulat-ing materials, etc., while those having a density of O.OS to lZ13~1Z
0.2 g/cc are suitable for structural materials, containers,heat-insulating materials, etc.
According to the process of this invention, it is possible to produce expanded particles having a high ratio.of closed cells, i.e., at least 65%, usually at least 80%, because the present invention assures a high closed cell ratio by strictly controlling the heating temperature within the range of from the crystal melting point of poly-olefin resin minus 25 C to the crystal melting point plus 10 C to thereby control the amount of ~lowing agent impregnating the resin and the viscoelasticity thereof.
The expanded particles are almost free of variations in closed cell ratio because the expandable resin particles are released through a small orifice while the partial pressure of volatile blowing agent is being maintained at a constant level in the vapor phase of the pressure-resistant container during the release. Accordingly the particles can be fused together effectively and are less prone to shrinkage when molded, giving expanded mol~ed articles which have excellent properties. As mentioned above, the process of this invention enables to produce uniform expanded particles with superior properties industrially advantageously, and can also be applied in industrially manufacturing expanded particles of non-crosslinked polyolefin resin which generally has a difficulty to be formed in expanded articles by conventional foaming proces5es because of the narrow range of temperature giving the viscoelasticity suitable for foaming.
i~3~
The invention will be furthex descxibed withreference to an ethylene-propylene random copol~mer as an example, expanded particles of which have better moldability than the polypropylene homopolymer when subjected to the conven.tional mold forming process hereinafter descxibed and gives a useful expanded molded product havi~g hi~her rigity, strength and heat resistance than polyethylene. Preferably the ethylene-propylene random copolymer has an ethylene content of 1 to 15~ by weight and MI (melt flow index, JIS K 6758) of 0.1 to 40. When having an ethylene content of less than 1% by weight, the copolymer resembles poly-propylene homopolymer, failing to have the remarkable advantage of being moldable under widely varying conditions, whereas when exceeding 15% by weight in ethylene content, lS the copolymer is unable-to have high rigidity and strength characteristic of polypropylene and resembles polyethylene.
With MI of less than 0.1, the copolymer exhibitspoor fluidity when expanding and encounters difficulty in expansion. With MI exceeding 40, the resin conversely exhibits exceedingly high fluidity, failing to expand to a high degree, and .bëcomes susceptible to shrinkage after expansion. In Example 7, an ethylene-propylene random copolymer having an ethylene content of 4.5~ by weight and MI of 9 is used to afford expanded particles having a high degree of expansion and ver~ small in the variation of density.
As desribed above, the process of the present invention gives expanded particles of polyolefin resin .
"
which are free of blocking, high in closed cell ratio, u~i'form and fine in cell structure and minimized in the variation of degree of expansion.
The expanded particles thus prepared can be molded by known methods. For example, the expanded particles obtainedare placed into a mold as they are, or after having been aged and dried for a suitable period of time, with or without expanding ability subsequently given, and are thereafter heated with water vapor or like heating medium for molding. As a method of imparting expanding ability to the expanded particles, an increased internal cell pressure can be given to the paxticles by impregnating their cells with N2, air or like inorganic gas, or by compressing the particles. Another method is also useful in which the internal space of the mold is reduced by compression for molding, with the mold filled with expanded particles as prepared or given expanding ability.
In this way, a molded product is obtained which is uniform and fine in cellular structure, uniform in particle size, ~ttractive in appearance and uniform in density distribution and in which the particles are effectively fused together.
The heating conditions for molding differ with' the kind of the resin. When water vapor is used as the heating medium, the expanded material can be heated for about S seconds to 3 minutes with water vapor having a temperature of lOS to 160 C.
The term "closed cell ratio" as used herein ' , . . .
refers to the ratio of closed cells (cells separated and closed by interposed partitions) to the whole cells which is calculated from the following equation.
v w Closed cell ratio (%) = x 100 . V
wherein d: density of the resln (g/cm3), w: weight of the specimen of expanded particles (g), V: volume of the specimen (volume measured in submerged state, cm3) v: true volume of the specimen as measured by specific gravity meter of air comparison type (e.g. Model 930, product of Toshiba Beckman Co., Ltd.) The present invention will be described below in greater detail with reference to the following examples, in which the parts are all by weight.
Example 1 Powdery talc (0.05 part) was admixed with 100 parts of ethylene-propylene random copolymer (0.90 g/cm3 in density, 9 in MI, about 4.5~ by weight in ethylene content), and the mixture was extruded into pellets about 2 mm in size. One hundred parts of pellets (700 g) were dispersed in 300 parts of water in a 4-liter pressure-resistant container equipped with a stirrer, in the presence of 0.5 part of powdery basic calcium tertiary phosphate and 0.025 part of~sodium dodecyl-benzenesulfonate serving as dispersants. Fifty-five parts of dichlorodifluoromethane was added to the dispersion with stirring, and the mixture was heated to 136 C. While subsequently maintaining the internal pressure of ~he container at 30 kg/cm gauge with N2, the mixture of pellets and water was released into the atmosphere through a circular orifice, 3 mm in diameter (7.07 mm ), in an orifice plate attached to the re~r end of a release valve ~5 mm in inside diameter, whereby expanded particles were obtained. The release of the mixture took about 11 seconds. The particles were free of any blocking, 94~ in closed cell ratio, 0.021 g/cm3 in density,and up to 0.2 mm and uniform in cell diameter.
Example 2 The same procedure as in Example 1 was repeated ~with the exception of using an ethylene-propylene random lS copolymer 30 in MI and about 3.5% by weight in ethylene content and heating the mixture at a temperature of 141 C.
The expanded particles obtained were free of any blocking, 93% in closed cell ratio, 0.022 g/cm3 in density, and up to 0.2 mm and uniform in cell diameter.
Example 3 The same procedure as in Example 1 was repeated with the exception of using 40 parts of n-butane as a volatile blowing agent, admixing 0.3 part of talc with the resin and heating the mixture at a temperatu~e of 115 C.
The expanded particles obtained were free of any blocking, 91% in closed cell ratio, 0.016 g/cm in density,and up to 0.2 mm and uniform in cell diameter.
.
~Z1311Z
Example 4 The procedure of Example 1 was repeated with the exception of using a straight-chain low-density polyethylene (0.920 in density, 2.1 in MI) as the resin, adding 0.01 part of talc, using 60 parts of dichlorodifluoromethane and heating the mixture at a temperature of 117 C. The expanded particles obtained were free of any blocking, 94~ in closed cell ratio, 0.034 g/cm in density, and up to 0.2 mm and uniform in cell diameter.
Comparison Example 1 The procedure of Example 1 was repeated except that the mixture of pellets and water was released directly from the release valve 25 mm in inside diameter t491 mm ) without using the orifice plate. The expanded particles ~ncluded blocks of about 2 to about 10 particles.
Example S
The procedure of Example 1 was repeated with the exception of using a flaring duct measuring 50 cm in inside diameter of its rear end and 150 cm in length and disposed in the rear of the orifice plate, and a storage container of metal netting provided at the rear end of the duct for collecting the pre-expanded particles (see Fi~. 1). The pre-expanded particles obtained were free of any blocking, 94% in closed cell ratio, 0.023 g/cm3 in density, and up to 0.2 mm and uniform in cell diameter.
Example 6 and Comparison Exam~e 2 :
lZ1311Z
The procedure of Example 1 was repeated with the exception of using an inorganic nucleating agent (powdery talc . or powdery sllica) in varying amounts (Experiment Nos. 1 to 7) or not using any nucleating agent (Comparison Example 2) as listed in Table 1. The pre-expanded particles obtained were free of any blocking and had the densities and cell diameters listed in Table 1. Those prepared with use of talc or silica were very small and...uniform in cell : diameter, whereas t,hose,.- prepared without using any nucleat-10. ing agent'~-ere larger and uneven-.-in cells in'~a''par~icle~
Table 1 Exp. No. Nucleating Pre-expanded particles Densi~y . . . Uniformity of agent (part) (g/cm~) Cell diaml) cellsin a particle (Ex. 1)Talc (0.05)0.021 A Uniform 1 " (0.02) 0.025 A
2 " (0.1) . 0.020 A "
the rear of the discharge orifice, it must be so shaped as to have a space which is larger than the path of discharge of particles which spread out through the angle of discharge.
If a duct of samll diameter or the like is disposed to the -rear of the discharge orifice, the duct will be plugged up with expanded particles, or the expanded particles obtained include a large amount of agglomerates o~ particleg According to the present invention, the mixture of resin particles and water is released through an orifice which is as small as O,Q7 to ~00 ~2in area, so that the angle of discharge of particles is small, and the distance of scattering of the particles is short since they are released at a reduced speed. Thus the path of discharge is compact in . its entirety.
~ith the present process, therefore, the duct or container to be provided to the rear of the release orifice can be compact.
Fig. 1 and Fig. 2 are diagrams showing examples of apparatus useful for the process of the present invention.
. 20 Apparatus for practicing the present process will be described briefly with reference to these drawings, in which like parts are referred to by like reference numerals.
Fig. 1 shows a pressure-resistant container 1 which is equipped with a heater (jac~et) 4, a pressure control valve 5 and a pressure gauge 11. Pol~olefin resin particles 2 as admixed with water 3 are heated in the container 1 under - increased pressure and impregnated with a blowing agent.
. . -; . . ; - . . . .
1213~Z
The mixture of resin particles and water is released through a dicharge valve 6 and an orifice plate 7, such as the one already stated, into a tank 9, whereupon the particles are made into expanded particles 10. While the orifice may be open to the atmosphere (free space), a flaring duct 8 is provided immediately in the rear of the orifice plate 7 in Fig. 1 to render the apparatus compact. The duct 8 has a space larger than the path of discharge of the particles to be released and expanded. Alternatively a usual cylindrical duct is usable insofar as it has a sufficiently larger inside diameter In Fig. 2, the orifice is open to a tank 9 having a space larger than the path of discharge of the particles to be released and expanded. The tank 9 is useful for storing the expanded particles.
The process of the present invention described above gives expanded particles of polyolefin resin which are low in density (high in the degree of expansion), very uniform in density distribution and also uniform in cellular structure among the particles and thus gives articles with superior properties when molded. The expanded particles of polyolefin resin obtained by the present invention are usually used for molding. Useful for molding are expanded resinr particles which are 0.01 to 0.2 g/cc in density. Those having a density of 0.01 to 0.05 g/cc are suited for preparing shock-absorbing materials, packaging materials, heat-insulat-ing materials, etc., while those having a density of O.OS to lZ13~1Z
0.2 g/cc are suitable for structural materials, containers,heat-insulating materials, etc.
According to the process of this invention, it is possible to produce expanded particles having a high ratio.of closed cells, i.e., at least 65%, usually at least 80%, because the present invention assures a high closed cell ratio by strictly controlling the heating temperature within the range of from the crystal melting point of poly-olefin resin minus 25 C to the crystal melting point plus 10 C to thereby control the amount of ~lowing agent impregnating the resin and the viscoelasticity thereof.
The expanded particles are almost free of variations in closed cell ratio because the expandable resin particles are released through a small orifice while the partial pressure of volatile blowing agent is being maintained at a constant level in the vapor phase of the pressure-resistant container during the release. Accordingly the particles can be fused together effectively and are less prone to shrinkage when molded, giving expanded mol~ed articles which have excellent properties. As mentioned above, the process of this invention enables to produce uniform expanded particles with superior properties industrially advantageously, and can also be applied in industrially manufacturing expanded particles of non-crosslinked polyolefin resin which generally has a difficulty to be formed in expanded articles by conventional foaming proces5es because of the narrow range of temperature giving the viscoelasticity suitable for foaming.
i~3~
The invention will be furthex descxibed withreference to an ethylene-propylene random copol~mer as an example, expanded particles of which have better moldability than the polypropylene homopolymer when subjected to the conven.tional mold forming process hereinafter descxibed and gives a useful expanded molded product havi~g hi~her rigity, strength and heat resistance than polyethylene. Preferably the ethylene-propylene random copolymer has an ethylene content of 1 to 15~ by weight and MI (melt flow index, JIS K 6758) of 0.1 to 40. When having an ethylene content of less than 1% by weight, the copolymer resembles poly-propylene homopolymer, failing to have the remarkable advantage of being moldable under widely varying conditions, whereas when exceeding 15% by weight in ethylene content, lS the copolymer is unable-to have high rigidity and strength characteristic of polypropylene and resembles polyethylene.
With MI of less than 0.1, the copolymer exhibitspoor fluidity when expanding and encounters difficulty in expansion. With MI exceeding 40, the resin conversely exhibits exceedingly high fluidity, failing to expand to a high degree, and .bëcomes susceptible to shrinkage after expansion. In Example 7, an ethylene-propylene random copolymer having an ethylene content of 4.5~ by weight and MI of 9 is used to afford expanded particles having a high degree of expansion and ver~ small in the variation of density.
As desribed above, the process of the present invention gives expanded particles of polyolefin resin .
"
which are free of blocking, high in closed cell ratio, u~i'form and fine in cell structure and minimized in the variation of degree of expansion.
The expanded particles thus prepared can be molded by known methods. For example, the expanded particles obtainedare placed into a mold as they are, or after having been aged and dried for a suitable period of time, with or without expanding ability subsequently given, and are thereafter heated with water vapor or like heating medium for molding. As a method of imparting expanding ability to the expanded particles, an increased internal cell pressure can be given to the paxticles by impregnating their cells with N2, air or like inorganic gas, or by compressing the particles. Another method is also useful in which the internal space of the mold is reduced by compression for molding, with the mold filled with expanded particles as prepared or given expanding ability.
In this way, a molded product is obtained which is uniform and fine in cellular structure, uniform in particle size, ~ttractive in appearance and uniform in density distribution and in which the particles are effectively fused together.
The heating conditions for molding differ with' the kind of the resin. When water vapor is used as the heating medium, the expanded material can be heated for about S seconds to 3 minutes with water vapor having a temperature of lOS to 160 C.
The term "closed cell ratio" as used herein ' , . . .
refers to the ratio of closed cells (cells separated and closed by interposed partitions) to the whole cells which is calculated from the following equation.
v w Closed cell ratio (%) = x 100 . V
wherein d: density of the resln (g/cm3), w: weight of the specimen of expanded particles (g), V: volume of the specimen (volume measured in submerged state, cm3) v: true volume of the specimen as measured by specific gravity meter of air comparison type (e.g. Model 930, product of Toshiba Beckman Co., Ltd.) The present invention will be described below in greater detail with reference to the following examples, in which the parts are all by weight.
Example 1 Powdery talc (0.05 part) was admixed with 100 parts of ethylene-propylene random copolymer (0.90 g/cm3 in density, 9 in MI, about 4.5~ by weight in ethylene content), and the mixture was extruded into pellets about 2 mm in size. One hundred parts of pellets (700 g) were dispersed in 300 parts of water in a 4-liter pressure-resistant container equipped with a stirrer, in the presence of 0.5 part of powdery basic calcium tertiary phosphate and 0.025 part of~sodium dodecyl-benzenesulfonate serving as dispersants. Fifty-five parts of dichlorodifluoromethane was added to the dispersion with stirring, and the mixture was heated to 136 C. While subsequently maintaining the internal pressure of ~he container at 30 kg/cm gauge with N2, the mixture of pellets and water was released into the atmosphere through a circular orifice, 3 mm in diameter (7.07 mm ), in an orifice plate attached to the re~r end of a release valve ~5 mm in inside diameter, whereby expanded particles were obtained. The release of the mixture took about 11 seconds. The particles were free of any blocking, 94~ in closed cell ratio, 0.021 g/cm3 in density,and up to 0.2 mm and uniform in cell diameter.
Example 2 The same procedure as in Example 1 was repeated ~with the exception of using an ethylene-propylene random lS copolymer 30 in MI and about 3.5% by weight in ethylene content and heating the mixture at a temperature of 141 C.
The expanded particles obtained were free of any blocking, 93% in closed cell ratio, 0.022 g/cm3 in density, and up to 0.2 mm and uniform in cell diameter.
Example 3 The same procedure as in Example 1 was repeated with the exception of using 40 parts of n-butane as a volatile blowing agent, admixing 0.3 part of talc with the resin and heating the mixture at a temperatu~e of 115 C.
The expanded particles obtained were free of any blocking, 91% in closed cell ratio, 0.016 g/cm in density,and up to 0.2 mm and uniform in cell diameter.
.
~Z1311Z
Example 4 The procedure of Example 1 was repeated with the exception of using a straight-chain low-density polyethylene (0.920 in density, 2.1 in MI) as the resin, adding 0.01 part of talc, using 60 parts of dichlorodifluoromethane and heating the mixture at a temperature of 117 C. The expanded particles obtained were free of any blocking, 94~ in closed cell ratio, 0.034 g/cm in density, and up to 0.2 mm and uniform in cell diameter.
Comparison Example 1 The procedure of Example 1 was repeated except that the mixture of pellets and water was released directly from the release valve 25 mm in inside diameter t491 mm ) without using the orifice plate. The expanded particles ~ncluded blocks of about 2 to about 10 particles.
Example S
The procedure of Example 1 was repeated with the exception of using a flaring duct measuring 50 cm in inside diameter of its rear end and 150 cm in length and disposed in the rear of the orifice plate, and a storage container of metal netting provided at the rear end of the duct for collecting the pre-expanded particles (see Fi~. 1). The pre-expanded particles obtained were free of any blocking, 94% in closed cell ratio, 0.023 g/cm3 in density, and up to 0.2 mm and uniform in cell diameter.
Example 6 and Comparison Exam~e 2 :
lZ1311Z
The procedure of Example 1 was repeated with the exception of using an inorganic nucleating agent (powdery talc . or powdery sllica) in varying amounts (Experiment Nos. 1 to 7) or not using any nucleating agent (Comparison Example 2) as listed in Table 1. The pre-expanded particles obtained were free of any blocking and had the densities and cell diameters listed in Table 1. Those prepared with use of talc or silica were very small and...uniform in cell : diameter, whereas t,hose,.- prepared without using any nucleat-10. ing agent'~-ere larger and uneven-.-in cells in'~a''par~icle~
Table 1 Exp. No. Nucleating Pre-expanded particles Densi~y . . . Uniformity of agent (part) (g/cm~) Cell diaml) cellsin a particle (Ex. 1)Talc (0.05)0.021 A Uniform 1 " (0.02) 0.025 A
2 " (0.1) . 0.020 A "
3 " (0.5) 0.021 A "
4 Silica (0.1) 0.024 B - A "
" (0.3)0.023 A "
6 " (0.5)0.022 A "
.~
: 7 " (1.0)0.022 A ..
~' G~p. Ex.2 None 0.033 C - B uneven : . . . . .. . . .
.
"` ~2131~2 1) Cell diameters of pre-expanded particles (as measured according to JIS K 6402) Symbol Measurement A Less than 0.2 mm in mean cell diameter.
B 0.2 mm to less than 0.5 mm "
C Not less than 0.5 mm "
Example 7 One hundred parts (225 kg) of pellets the same as those used in Example 1 were dispersed in 300 parts of water in a pressure-resistant container having a capacity of 1000 liters and a stirrer, in the presence of 0.5 part of powdery basic calcium tertiary phosphate and 0.025 part of sodium dodecylbenzenesulfonate serving as dispersants.
The container was evacuated by a vacuum pump with stirring, 30 parts of dichlorodifluoromethane was then added to the dispersion, and the mixture was heated to 136 C. At this time the container had an internal pressure of 26 kg/cm gauge.
Subsequently~ w~ile maintaini~g the inte~.n~ Yr.,perature and pressure at 26 kg/cm by forcing in liquid dichlorodifluoro-methane under the control of a valve, a release valve at the bottom of the container was opened to release the mixture of pellets and water into the atmosphere of normal pressure ~hrough an orifice, 4 mm in diameter (12.57 mm ~,in an orifice plate attached to the rear end of the release valve.
The release of the mixture took about 30 minutes. The 20 expanded particles obtained by the release.were 0.0298 g/cm3 ~, .
1. -' .
12i31~2 in average density, with a predominant portion thereof within the density range of from 0.028 to 0.032 g/cm3, and thus, in other words were minimized in the variation of expansion degree. No reduction of the expansion degree occurred toward the end of the releasing procedure and also no significant variation of cellular structure occured during the procedure.
Comparison Example 3 The procedure of Example 7 was repeated except that the internal pressure of the container was maintained at 26 kg/cm2 by forcing in pressurized N2 in place of liquid diclorodifluoromethane under the control of the valve.
During a period of 30 minutes which was required for the release of particles, the average density of pre-expanded particles increased from 0.0294 g/cm3 to 0.0514 g/cm3 with the variation of the cellular structure, Example 8 The pre-expanded particles O.OZ98 g/cm3 in average density and obtained in Example 7 were dried at 60 C for 24 hours, then subjected to air pressure of 9 kg/cm2 gauge at 60 C, thereafter placed into a mold measuring 950 x 645 x 65 mm and heated for molding with water vapor at a pressure of 2.8 kg/cm gauge. The molded product obtained was 0.0198 g/cm in:density, smooth-surface and attractive in appearance, with the component particles effectively fused together.
" (0.3)0.023 A "
6 " (0.5)0.022 A "
.~
: 7 " (1.0)0.022 A ..
~' G~p. Ex.2 None 0.033 C - B uneven : . . . . .. . . .
.
"` ~2131~2 1) Cell diameters of pre-expanded particles (as measured according to JIS K 6402) Symbol Measurement A Less than 0.2 mm in mean cell diameter.
B 0.2 mm to less than 0.5 mm "
C Not less than 0.5 mm "
Example 7 One hundred parts (225 kg) of pellets the same as those used in Example 1 were dispersed in 300 parts of water in a pressure-resistant container having a capacity of 1000 liters and a stirrer, in the presence of 0.5 part of powdery basic calcium tertiary phosphate and 0.025 part of sodium dodecylbenzenesulfonate serving as dispersants.
The container was evacuated by a vacuum pump with stirring, 30 parts of dichlorodifluoromethane was then added to the dispersion, and the mixture was heated to 136 C. At this time the container had an internal pressure of 26 kg/cm gauge.
Subsequently~ w~ile maintaini~g the inte~.n~ Yr.,perature and pressure at 26 kg/cm by forcing in liquid dichlorodifluoro-methane under the control of a valve, a release valve at the bottom of the container was opened to release the mixture of pellets and water into the atmosphere of normal pressure ~hrough an orifice, 4 mm in diameter (12.57 mm ~,in an orifice plate attached to the rear end of the release valve.
The release of the mixture took about 30 minutes. The 20 expanded particles obtained by the release.were 0.0298 g/cm3 ~, .
1. -' .
12i31~2 in average density, with a predominant portion thereof within the density range of from 0.028 to 0.032 g/cm3, and thus, in other words were minimized in the variation of expansion degree. No reduction of the expansion degree occurred toward the end of the releasing procedure and also no significant variation of cellular structure occured during the procedure.
Comparison Example 3 The procedure of Example 7 was repeated except that the internal pressure of the container was maintained at 26 kg/cm2 by forcing in pressurized N2 in place of liquid diclorodifluoromethane under the control of the valve.
During a period of 30 minutes which was required for the release of particles, the average density of pre-expanded particles increased from 0.0294 g/cm3 to 0.0514 g/cm3 with the variation of the cellular structure, Example 8 The pre-expanded particles O.OZ98 g/cm3 in average density and obtained in Example 7 were dried at 60 C for 24 hours, then subjected to air pressure of 9 kg/cm2 gauge at 60 C, thereafter placed into a mold measuring 950 x 645 x 65 mm and heated for molding with water vapor at a pressure of 2.8 kg/cm gauge. The molded product obtained was 0.0198 g/cm in:density, smooth-surface and attractive in appearance, with the component particles effectively fused together.
Claims (10)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing expanded particles of a polyolefin resin characterized by dispersing polyolefin resin particles 0.25 to 10 mm in particle size and a volatile blowing agent in water in the presence of a dispersant within a pressure-resistant container, heating the mixture at a temperature within the range of from the melting point of crystals of the resin minus 25° C to the melting point plus 10° C to impregnate the resin particles with the blowing agent, and releasing the mixture of the particles and water into a low-pressure zone through at least one orifice having an area of 0.07 to 300 mm2 while maintaining the interior of the container at a constant temperature and constant pressure.
2. A process as defined in claim 1 wherein the orifice is formed in an orifice plate.
3. A process as defined in claim 1 wherein the interior of the container is maintained at constant pressure, and the partial pressure of the volatile blowing agent in the interior vapor-phase portion of the container is also maintained at a constant level.
4. A process as defined in claim 1 wherein a fine powder of sparingly water-soluble inorganic substance and an anionic surfactant are used conjointly as dispersion stabilizers.
5. A process as defined in claim 1 wherein the polyolefin resin is selected from the group consisting of low-density polyethylene, straight-chain low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer and ethylene-propylene-butene terpolymer.
6. A process as defined in claim 5 wherein the polyolefin resin contains 0.01 to 5 parts by weight of an inorganic nucleating agent per 100 parts by weight of the polyolefin resin.
7. A process as defined in claim 5 wherein the polyolefin resin is ethylene-propylene random copolymer having an ethylene content of 1 to 15% by weight and MI of 0.1 to 40.
8. Expanded particles of a polyolefin resin having a closed cell ratio of at least 65% and a density of 0.01 to 0.2 g/cm3 and obtained by dispersing polyolefin resin particles 0.25 to 10 mm in particle size and a volatile blowing agent in water in the presence of a dispersant within a pressure-resistant container, heating the mixture at a temperature within the range of from the melting point of crystals of the resin minus 25° C to the melting point plus 10° C to impregnate the resin particles with the blowing agent, and releasing the mixture of the particles and water into a low-pressure zone through at least one orifice having an area of 0.07 to 300 mm2 while maintaining the interior of the container at a constant temperature and constant pressure and also while maintaining the partial pressure of the volatile blowing agent in the interior vapor-phase portion of the container at a constant level.
9. Expanded polyolefin resin particles as defined in claim 8 wherein the polyolefin resin is selected from the group consisting of low-density polyethylene, straight-chain low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer and ethylene-propylene-butene terpolymer.
10. Expanded polyolefin resin particles as defined in claim 8 wherein the polyolefin resin is ethylene-propylene random copolymer having an ethylene content of 1 to 15% by weight and MI of 0.1 to 40.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP58128258A JPH0610269B2 (en) | 1983-05-12 | 1983-07-13 | Polyolefin foamed particles and method for producing the same |
| JP4015233A JPH072856B2 (en) | 1983-05-12 | 1992-01-30 | Polyolefin foamed particles and method for producing the same |
Applications Claiming Priority (11)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP57081137A JPS58197027A (en) | 1982-05-13 | 1982-05-13 | Prefoaming of thermoplastic resin particles |
| JP81138/82 | 1982-05-13 | ||
| JP81137/82 | 1982-05-13 | ||
| JP57081138A JPS58197028A (en) | 1982-05-13 | 1982-05-13 | Pre-foaming of thermoplastic resin granule |
| JP57082097A JPS58199125A (en) | 1982-05-14 | 1982-05-14 | Prefoaming of expandable thermoplastic resin particles |
| JP8209682A JPS58198540A (en) | 1982-05-14 | 1982-05-14 | Production of expanded polyolefin particle |
| JP82097/82 | 1982-05-14 | ||
| JP82096/82 | 1982-05-14 | ||
| JP57141576A JPS5930836A (en) | 1982-08-13 | 1982-08-13 | Method for preliminarily expanding polyolefin type resin particle |
| JP141576/82 | 1982-08-13 | ||
| CA000542683A CA1290094C (en) | 1982-05-13 | 1987-07-21 | Pre-expanded particles of polyolefin resin and process for preparing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213112A true CA1213112A (en) | 1986-10-28 |
Family
ID=27543363
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000428024A Expired CA1213112A (en) | 1982-05-13 | 1983-05-12 | Expanded particles of polyolefin resin and process for producing same |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4448901A (en) |
| EP (1) | EP0095109B1 (en) |
| AU (1) | AU559244B2 (en) |
| CA (1) | CA1213112A (en) |
Families Citing this family (56)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1225200A (en) * | 1983-04-08 | 1987-08-04 | Tsukasa Yamagishi | Preparation of foam particles of ethylenic resin and foam moldings prepared therefrom |
| JPS6049039A (en) * | 1983-08-26 | 1985-03-18 | Badische Yuka Co Ltd | Manufacture of polyolefin resin expanded beads |
| US4525485A (en) * | 1983-09-08 | 1985-06-25 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Pre-expanding process and apparatus for the same |
| JPS60105503A (en) * | 1983-11-12 | 1985-06-11 | Kanegafuchi Chem Ind Co Ltd | Preforming of thermoplastic resin patticles and apparatus thereof |
| JPS6090229A (en) * | 1983-10-24 | 1985-05-21 | Japan Styrene Paper Co Ltd | Expanded particle of polyethylene based resin |
| JPS60110734A (en) * | 1983-11-21 | 1985-06-17 | Japan Styrene Paper Co Ltd | Pre-expanded particle of uncrosslinked polypropylene resin |
| JPS60123540A (en) * | 1983-12-07 | 1985-07-02 | Japan Styrene Paper Co Ltd | Noncrosslinked polypropylene resin prefoamed particle |
| JPS60168632A (en) * | 1984-02-13 | 1985-09-02 | Japan Styrene Paper Co Ltd | Expanded molding of bridged polypropylene resin |
| US4704239A (en) * | 1984-04-28 | 1987-11-03 | Japan Styrene Paper Corp. | Process for the production of expanded particles of a polymeric material |
| JPS60235849A (en) * | 1984-05-08 | 1985-11-22 | Japan Styrene Paper Co Ltd | Prefoamed particle of polypropylene resin |
| JPS60252636A (en) * | 1984-05-30 | 1985-12-13 | Japan Styrene Paper Co Ltd | Preparation of preexpanded particle |
| EP0337584B1 (en) * | 1984-06-14 | 1994-08-17 | Japan Styrene Paper Corporation | Process for the production of expanded particles of a polypropylene resin |
| US4676939A (en) * | 1984-06-14 | 1987-06-30 | Japan Styrene Paper Corporation | Process for the production of expanded particles of a polypropylene resin |
| US4863475A (en) * | 1984-08-31 | 1989-09-05 | Zimmer, Inc. | Implant and method for production thereof |
| JPH066637B2 (en) * | 1984-09-03 | 1994-01-26 | 住友化学工業株式会社 | Propylene resin foamed particles |
| JPS61115940A (en) * | 1984-11-09 | 1986-06-03 | Mitsubishi Yuka Badische Kk | Polypropylene foam particle |
| JPS61215631A (en) * | 1985-03-20 | 1986-09-25 | Japan Styrene Paper Co Ltd | Propylene random copolymer resin particle and its production |
| US4778829A (en) * | 1985-07-12 | 1988-10-18 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Process for preparing pre-expanded particles of thermoplastic resin |
| JPH0686544B2 (en) * | 1985-07-12 | 1994-11-02 | 鐘淵化学工業株式会社 | Non-crosslinked linear low density polyethylene pre-expanded particles and molding method thereof |
| US4689351A (en) * | 1985-10-08 | 1987-08-25 | Mitsubishi Yuka Badische Co., Ltd. | Process for producing foamed particles of propylene copolymer resin |
| JPH0660258B2 (en) * | 1986-06-26 | 1994-08-10 | 鐘淵化学工業株式会社 | Method for pre-expanding thermoplastic resin particles |
| EP0234320B1 (en) * | 1986-01-30 | 1992-01-22 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Process for preparing pre-expanded particles of thermoplastic resin |
| JPS62177038A (en) * | 1986-01-30 | 1987-08-03 | Kanegafuchi Chem Ind Co Ltd | Production of pre-expanded particle of thermoplastic resin |
| US4695593A (en) * | 1986-02-21 | 1987-09-22 | Japane Styrene Paper Corporation | Prefoamed propylene polymer-base particles, expansion-molded article produced from said particles and production process of said article |
| CA1280549C (en) * | 1986-05-27 | 1991-02-19 | Kyoichi Nakamura | Pre-expanded particles of propylene resin |
| DE3708291A1 (en) * | 1987-03-14 | 1988-09-22 | Basf Ag | METHOD FOR PRODUCING POLYOLEFINE FOAMS |
| JPH082989B2 (en) | 1987-05-11 | 1996-01-17 | 日本スチレンペ−パ−株式会社 | Pre-expansion method of polyolefin resin particles |
| JPH0739501B2 (en) * | 1987-06-23 | 1995-05-01 | 日本スチレンペ−パ−株式会社 | Non-crosslinked linear low density polyethylene pre-expanded particles |
| JPH04500225A (en) * | 1988-08-22 | 1992-01-16 | ザ ダウ ケミカル カンパニー | Improved expandable and expanded alkenyl aromatic polymer particles and methods of making the same |
| JPH0788432B2 (en) * | 1988-08-31 | 1995-09-27 | 鐘淵化学工業株式会社 | Method for producing pre-expanded polyolefin resin particles |
| JP2887291B2 (en) * | 1989-08-30 | 1999-04-26 | 株式会社ジェイエスピー | Method for producing expanded polyolefin resin particles |
| CA2030754C (en) * | 1989-11-24 | 1997-06-03 | Kazuo Turugai | Production method of prefoamed synthetic resin particles |
| DE4012239A1 (en) * | 1990-04-14 | 1991-10-17 | Basf Ag | FOAMS BASED ON AN OLEFIN COPOLYMER |
| US5372764A (en) * | 1990-08-06 | 1994-12-13 | Kanegafuchi Kagaku Kogyo Kabushiki Kaisha | Method of making olefin synthetic resin expansion molded articles |
| DE4211972A1 (en) * | 1992-04-09 | 1993-10-14 | Huels Chemische Werke Ag | Process for the production of foam beads |
| DE4220242A1 (en) * | 1992-06-20 | 1993-12-23 | Basf Ag | Process for the production of expandable thermoplastic polymers by post-impregnation |
| JP2878527B2 (en) * | 1992-06-22 | 1999-04-05 | 鐘淵化学工業株式会社 | Pre-expanded particles of polyethylene resin |
| CA2107157C (en) * | 1992-09-29 | 1998-02-03 | Thomas N. Hall, Iii | Continuous process for expanding thermoplastic minipellets |
| DE4319587A1 (en) * | 1993-06-14 | 1994-12-15 | Huels Chemische Werke Ag | Process for the production of pre-expanded polyolefin particles |
| KR0159801B1 (en) * | 1994-08-06 | 1999-01-15 | 박원배 | Microcellular pre-expanded polyolefin particles and process for preparing thereof |
| US5883144A (en) | 1994-09-19 | 1999-03-16 | Sentinel Products Corp. | Silane-grafted materials for solid and foam applications |
| US5932659A (en) | 1994-09-19 | 1999-08-03 | Sentinel Products Corp. | Polymer blend |
| EP0702032B1 (en) * | 1994-09-19 | 2002-11-27 | Sentinel Products Corp. | Cross-linked foam structures of essentially linear polyolefines and process for manufacture |
| US5929129A (en) * | 1994-09-19 | 1999-07-27 | Sentinel Products Corp. | Crosslinked foamable compositions of silane-grafted, essentially linear polyolefins blended with polypropylene |
| DE19542734A1 (en) * | 1995-11-16 | 1997-05-22 | Huels Chemische Werke Ag | Process for finishing polyolefinic particle foam |
| DE19547398A1 (en) | 1995-12-19 | 1997-06-26 | Huels Chemische Werke Ag | Process for the production of foamable plastic granules |
| CA2203595A1 (en) | 1996-04-26 | 1997-10-26 | Robert F. Hurley | Cross-linked polyolefin tape |
| US5844009A (en) * | 1996-04-26 | 1998-12-01 | Sentinel Products Corp. | Cross-linked low-density polymer foam |
| US5876813A (en) | 1996-07-09 | 1999-03-02 | Senitnel Products Corp | Laminated foam structures with enhanced properties |
| US5882776A (en) * | 1996-07-09 | 1999-03-16 | Sentinel Products Corp. | Laminated foam structures with enhanced properties |
| US5938878A (en) | 1996-08-16 | 1999-08-17 | Sentinel Products Corp. | Polymer structures with enhanced properties |
| US7473750B2 (en) * | 2004-12-07 | 2009-01-06 | Fina Technology, Inc. | Random copolymers and formulations useful for thermoforming and blow molding applications |
| PL2336225T3 (en) * | 2009-12-17 | 2017-01-31 | Basf Se | Process for producing polyolefin foam particles |
| CN108437333B (en) * | 2018-03-26 | 2020-05-19 | 安徽晟源环保新型材料有限公司 | Processing technology of polyurethane insulation board |
| EP3639997A1 (en) * | 2018-10-15 | 2020-04-22 | Linde Aktiengesellschaft | Method for impregnating polymer granulate |
| EP3868537A1 (en) * | 2020-02-20 | 2021-08-25 | Linde GmbH | Device for the impregnation of synthetic granulate with continuous granulate supply |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2107683A1 (en) | 1971-02-18 | 1972-08-31 | Basf Ag | Particulate foamed polyolefin prodn - by expansion with opt halogenated hydrocarbons in presence of water |
| JPS5277174A (en) | 1975-12-24 | 1977-06-29 | Japan Styrene Paper Corp | Process for foaming of polymer particle |
| FR2400423A1 (en) * | 1977-08-15 | 1979-03-16 | Asahi Dow Ltd | POLYOLEFIN RESIN EXPANDED PARTICLE MATERIAL |
| CA1147100A (en) * | 1979-12-10 | 1983-05-24 | Eiya Sato | Expanded cross-linked polyethylene particle, a molded product thereof and the methods thereof |
| JPS5712035A (en) * | 1980-06-25 | 1982-01-21 | Japan Styrene Paper Co Ltd | Production of polyolefin resin molded foam |
-
1983
- 1983-05-05 AU AU14271/83A patent/AU559244B2/en not_active Ceased
- 1983-05-12 CA CA000428024A patent/CA1213112A/en not_active Expired
- 1983-05-13 US US06/494,394 patent/US4448901A/en not_active Expired - Fee Related
- 1983-05-13 EP EP83104738A patent/EP0095109B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU1427183A (en) | 1983-11-17 |
| AU559244B2 (en) | 1987-03-05 |
| EP0095109B1 (en) | 1988-08-10 |
| EP0095109A1 (en) | 1983-11-30 |
| US4448901A (en) | 1984-05-15 |
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| MKEX | Expiry |