CA1050187A - Solid antistatic polymer compositions - Google Patents

Abstract

Abstract of the Disclosure A concentrated antistatic composition adapted for incorporation into olefinic polymers is prepared by admixing a liquid ethoxylated amine antistatic agent, such as an N,N-bis-(2-hydroxyethyl) alkenyl or mixed alkenyl and alkyl (C12 - C18) amine, with polypropylene, polystyrene and copolymers of either or polyphenylene oxide, heating to form a homogeneous liquid and rapidly cooling the mixture to form a solid antistatic agent.
A normally liquid antistatic agent can thus be simply and readily blended into a olefinic polymer such as polyethylene as a dry, solid product to impart antistatic properties and slip properties to the blended resin.

Description

~L050~87 _ack~round of the Inventlon The present invention relates to polymeric materlals, and particularly to those made from ethylenically unsaturated monomers which possess improved antistatic propertles and slip characteristics. It has long been known that various polymers tend to collect electrostatic charges on their SUT-face. This tendency creates difficulty in the handling of the polymers and of articles made therefrom~ for it occurs during stPrage, as well as in the course of processin~ the polymers into shaped forms, such as filaments, sheets, films, and molded plastics.
The charge causes dust and dirt particles to adhere to the plastic surfaces, and also causes the plastic surfaces to adhere to each other or to the equipment used in processing.
Under certain circumstances, the accumulated charges may give rise to sparks, with an attendant fire hazard. The tendency toward the building of electrostatic charges is especially marked in the case of polymers and copolymers made from ethylenically unsaturated monomers, such as polymers and copolymers of vinyl chloride, vinylidene chloride, styrene, and the various polyolefins, such as polyethylene, polypropy-lene, and polybutylene. These are referred to herein as olefinic polymers.
Among the approaches taken in the prior art tD reduce the tendency of plastic materials toward electrostatic charging has been either to coat the plastic material with an anti-static composition, or to incorporate it into the body of the plastlc material. The latter expedient is generally considered to be more effective. Co~pounds which have been proposed for m~p/ -1-~LO51~87 this purpose include polyalkylene glycols and their ester6 and ethers, nnd a wide varlety o~ amines and amldes.
Thus, for example, it has been proposed to incor-porate into an olefinic polymer such as polyethylene, during compounding, molding or fabrication, as an ant:Lstatic additive, a small amount of at least one N,N-(hydroxyalkyl)~alkylamine, and a process of this type is disclosed in U.S. Patent 3,631,162.
It is also known to incorporate into polyolefins, such as polyethylene film, a material which functions as a slip agent, by migrating to the surface in sufficient quantity to provicle thereon a thin film which functions as a lubricant.
Long chain aliphatic amides are usually employed for this purpose, and a system of this type is disclosed, for example, U.S. Patent 3,467,706.
Many of the amine or amide antistatic agents are liquids, which when incorporated into the resin compositions, migrate to the surface at an undesirably rapid rate, causing losses by evaporation, diminished antistatic effectiveness, development of undesirable odors, and adversely affecting the surface properties of the plastic, for example by promoting cracking or crazing. Por example, it was stated in the above-mentioned U.S. Patent 3,631,162 (Table III, Footnote 4) that at 8 parts of N,N-bis (2-hydroxyethyl) alkylamine in 1000 parts of polyethylene~ large amounts of the antistatic agent exuded to the surface. Previous attempts to incorporate a high percentage, i.e. 8reater than about 10%, of a liquid antistatic agent into polymers have been limited by the room temperature solubility of the antistatic agent in the polymer.

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~p/ 2 50~L87 That is, when the solubility in the polymer is exceeded, as by cooling a sol~ltion at high temperatures, two phases will be formed, namely a liquid phase containing some dissolved polymer and a solid phase containing some dissolved liquid.
General Description of the Invention In accordance with the present invention there is provided a novel antistatic and slip improving composition adapted for lncorporation into polymers, and particular]y into olefinic polymers, and a process of preparing the same.
The invention will be described with respect to the treatment of polyethylene, but it is to be understood that this is for purposes of illustration only, and that the practice of the invention is applicable to polyolefins generally, as well as to other olefinic polymers and copoly-mers made from ethenically unsaturated monomers.~
In accordance with the invention, it has been found, surprisingly and unexpectedly, that a liquid amine type anti-static agent can be converted into solid form suitable for incorporation into a polymer by admixing the amine with poly-propylene or copolymer of propylene and ethylene, heating themixture to a temperature such that a homogeneous liquid is formed, and then rapidly cooling the liquid to a solid homogeneous mass. By rapid cooling is meant a reduction in temperature such that the liquid mixture becomes completely solid within a period of time between about 1/2 sec. to about 10 minutes, depending upon the quantity of llquid involved and the cooling means employed, such that a solid material is obtained which does not contain any separate liquid phase therein and wherein the amount o~ normally liquid sntistatic m~p/ ~3-~OS1~
agent incorporated therein is greater ~han the normal solu-bility, i.e. in the range of 10 - 90% by weight of the ~olid polypropylene. In general, it has been found that the cooling rate must be increased as the percentage of antistatic agent that is incorporated into polypropylene is increased.
In practice~ it has been found that the rate of cooling can be controlled so as to obtain the desired results in at least two ways. In the first, a metal plate a~ ambient temperature ~25~C.) is used as a heat sink, and will extract heat from the material at a su~ficien~ rate i~ it is poured rapidly on to the plate in a thin layer. ~est results have been achieved with layers less than 1/4 inches thick, but similar results are observed where layers up to 1/2 inches in thickness are obtained.
- In the second method a rapid cooling rate is achieved by spraying or pouring the solution of liquid polypropylene and antistatic agent into a large amount of water at a temper-ature from 0C. to 75G. The preferred temperature range is from 60C. to 75C. since lower temperatures cause significant amounts of water to be trapped in the globules which can, however, be removed by drying in a vacuum. Globules of a solid combination of antistatic agent and polypropylene having a diameter of 1/8 to 1/16 inches are obtained which are not wet to the touch and do not contain a discreet liquid anti-static agent phase.
It might have been expected that, upon cooling, a liquid phase of the amine would separate containing some dissolved polymer, especially when the normal solubili~y of the amine in the polypropylene is exceeded. It has been m~p/ -4-observed, for example, that if the hot homogeneous mixture of polymer and ll.quid antistatic agent ls stirred cont$nuous-ly while the mixture cools, the mlxture does not cool to a homogeneous solid, but two pha~es do result. ~owever, w-lth rapid cooling of the hot homogeneous mixture of antistatic agent and polypropylene according to the invention, no phase separation occurs. This unexpected behavior takes place even where i~ is known that, merely by mixing, not more than about 10% by weight of antistatic agent could be incorporated into the polypropylene without the separation of a liquid phase.
Thus, the resulting antistatic agent-polypropylene composition contains much more of the antistatlc agent than would be expected from room temperature solubility considerations alone.
The resulting solid mass may be converted to granules or powders of any desired particle size, and readily blended with the olefinic polymer to which it is to be added.
The.principle of the invention is generally appli-cable to antistatic agents which are capable of blending homo-geneously with polypropylene or a copolymer of polypropylene at elevated temperature and forming a solidlsolution therein without phase separation upon cooling. Ordinarily the anti-static agents will be liquid at ordinary temperatures, and the blending step will be performed at a temperature above the softening temperature of the polypropylene or its copolymers.
Advantageously, liquid ethoxylated amines may be employed in the practlce of the invention. These may be derived from primary alkenyl or mixed alkenyl and alkyl amines in which the alkenyl and alkyl moiety has a chain length of between about 12 a~d 18 carbon atoms. ~uch amines are obtained m~p/ -5--` ~LOS~
from distll]ed coco, soya, oleyl or tallow, or mixtures thereof.
The preferred amine antistatic agents are N,N-bls-(2-hydroxyethyl) alkenyl or mixtures of alkenyl and alkyl which are liquid at ordinary temperatures (C1G ~ C18) amines.
Examples of these amines are diethoxylated tallow (mixed alkenyl and alkyl) amine, and diethoxylated coco amine, which are marketed under the trademarks Armostat 310 and Armostat 410, respectively, by Armak Company, Chicago, Illinois. Other known liquid amine antistatic agents could also be used provided they did not degrade upon heating to the temperatures required to render the mixture of polypropylene and antistatic homogeneous.
These and other ethoxylated or alkoxylated amines of similar structure are incorporated into polypropylene in pro-portions ranging from about 10% to about 90% by weight, prefer-ably from about 50% to about 75%, and it is one of the surprising characteristics of the resulting antistatic compositions that as much as 90% of amine can be included in the polypropylene without substantial separation of a liquid phase. The final

2~ . antistatic agent is a dry, stable product which can readily be uniformly incorporated by dry blending into other polymers an in~ernal antistatic agent.
Although polypropylene is preferred as a carrier for the amine or other antistatic agent, copolymers of polypropylene and ethylene may also be employed.
The antistatic compositions of the invention are incorporated into the olefinic polymers to be treated therewith, for example, polyethylene, in antistatically effective propor-tions and are found to be fully comparable ~o the same amoun~

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m~p/ -6-~050~L87 of liquid antista~lc agent incorporated directly into the olefinic polymer. However, the ease and cleanliness of incorporatlng a dry material into the olefinic polymer is much greater than the corresponding liquid agent. Further-more, the solid composition is capable of being added to an olefinic polymer molded by a process, known as rotomolding.
Antistatic agents incorporated both dry or liquid in roto-molded products have been completely ineffective. Effective proportions of antistatic agent represent from about 0.005%
to about 10% of amine agent, by weight, based on the poly-ethylene or other olefinic polymer. The amount employed will depend upon the particular polymer and amine.
Description of the Preferred Embodiments The following examples serve to illustrate the practice of the invention, but are not to be regarded as limiting:
Example 1 A mixture of 50% by weight of N,N-bis-(2 hydroxyethyl) -tallow amine (Armostat 310) and 50% by weight of polypropylene pellets is heated with stirring at 180C. until a clear homo-geneous liquid is obtained. The liquid is then cooled rapidly, within a period of about 10 minutes, to room temperature, whereupon it forms a dry solid mass. The mass is ground to a dry powder and incorporated into molten polyethylene resin at a temperature of about 185C. in an amount equivalent to 0.15%
of amine and 0.15% of polypropylene, respectively, by weight.
A polyethylene product exhibits antistatic and increased slip properties. A sample aged for 6 days, when charged to 800 volts was found to discharge to zero volts ~pl -7-~051D~87 within 45 seconds, a~ compared with a control sample of untreated polyethylene which retained lts charge indeflnltely.
Static coefficients of friction were as follows:
Control sample with no additive 0.70 Sample with amine alone (at 0.1%) 0.50 Sample with amine polypropylene (at 0.15%) 0.36 Example 2 ~he same procedure was followed as in Example 1, except that the proportion of the amine of Example 1 incor-porated into the polypropylene was 75% by weight. The solid material was ground and incorporated into polyethylene in the same proportions as to the amine component as in Example 1, i.e. 0.15% amine and 0.05% polypropylene and evaluated for antistatic and slip properties with the following results: a sample aged for five days when charged to 800 volts was found to discharge to zero volts in 18 seconds. Static coefficient of friction on this sample was found to be 0.51.
Example 3 Following the same procedure as in Example 2, 75% by weight of the amine of Example 2 was incorporated into poly-styrene (crystal grade). In this instance, the temperature was raised to 240C. to dissolve the beads of polystyrene.
Stirring was continued for about five minutes afte$ complete ~olution took place. Then about 1 cc. was poured to a depth of about 1/16 inches on to a flat metal plate and chilled rapidly, i.e. in about flve minutes, to give a brittle, dry ~aterial. A sample of about 50 cc. was poured into a flat dish to a depth of about 1/2 inches and upon cooling it became hard, but was slightly we~ on the top and bottom. A third m~ 8-~S0~7-sample w~s allowed to rem~in in the beaker to a depth o~
about 1 1/2 inches and was cooled by standing. The thlrd portion separated into a liquld and a solld phase.
The dry, brlttle antistatic concentrate prepared above can be lncorporated into an olefinic polymer, for example, molten polys~yrene resin, by adding ground concen--trate in an amount equivalent to 3% of amine by weight and cooling. The antistatic and slip properties of this material are determined in the same manner as in Example 1.
Additional samples of the above were made varying the percentages of amine incorporated in the polystyrene and cooling by pouring the dissolved material into water at various temperatures as indicated in Table I.
TABLE I

Percentage Temp. of Temp. of Sol. Characteristics of of Amine: Water at Time Poured Product Polystyrene (C.) _ (C.) 80:20 0 230 solid, brittle, greasy feel; some trapped H20 230 solid, stained envelope*
sample was placed in 230 solid, stained envelope sample was placed in 75:25 0 230 solid, brittle, slightly greasy; some trapped 25 230 sol:Ld, brittle, stained envelope sllghtly 230 sol:Ld, dry 230 little trapped H20 70:30 0 230 solid, brittle, dry 230 solid9 brittlè, stained envelope very slightly m~p/ _g_ ~al5~ 7 230 solld, brittle, stained envelope very slightly 230 solid, bri~tle, stained envelope very slightly 60:40 0 240 solid, dry 240 solid, dry 240 solid, dry 240 solid, dry *Shows relative amounts of antistat on the surface of the solid material.

Example 4 The same procedure was followed as in Example 3, except that impact grade polystyrene was used. Impact grade polystyrene is actually a copolymer of styrene and butadiene.
The mixture was heated with stirring to a temperature of 235C.
and poured quickly into a chilled stainless-steel pan so that a fllm about 1/16 inches thick was formed which cooled in one minute. The solid material was found to be dry and hard, except for a small amount of condensation on the bottom. A~ter standing overnight, the bottom was found to be dry with no trace of greasiness. Another sample was dissolved at 220~C
and poured on to a 1/64 inch stainless steel plate at room temperature ~25C.) to cool. A hard, dry solid 3/8 inches thick was formed.
Example 5 Following the same procedure as Example 1, a solid dry product was obtained by incorporating 75% by weight, N,N-bis-(2-hydroxye.thyl) coco amine ~Armostat 410) ln 25% by weight of polypropylene. A small amount was cooled on a spatula which was dry to the touch after several hours.

m~ p / -1 O-50~87-Similar antistatic and sllp effects can be obtained by incor-porating the gro~lnd product into polyethylene in an amount equivalent to 0.15% of amine.
E~ample 6 A mixture of 110.6 grams of polypropylene and 64.4 grams of the amine of Example 1 was stirred at 175C. to give a final concentration of 36.8% amine by weight. After cooling, the white, crystalline product was found to be solid and dry.
Example 7 A run similar to Example 3 was made using crystal grade polystyrene. Solution was complete at about 235C. A
portion of the run was cooled by pouring the molten mixture into a chilled stainless steel pan. The material was dry and hard with only a slight wetness at the edges.
Another portion of the molten material was poured into water. On cooling, this product was hard and dry.
Example ô
Following the same procedure as in Example 1, 75% by weight of the amine of Example 1 was incorporated into poly-phenylene oxide, (Noryl~) marketed by General Electric Company.After stirring at 250C. for about five minutes, the mixture was poured into flat dishes to cool. The product was dry and hard with no trace of greasiness.
Example 9 The same procedure was followed as in Example 1, except that 75% by weight of the amine of Example 1 was incor-porated into 25% by weight of a styrene-acrylonitrile copolymer (Tyril~) marketed by Dow Chemical Corporation. Solution began to take place at 255C. and the temperature was then raised to m~p/

:1~5~37 275C. to speed the solution proce~s. One half o~ the solution was poured i.nto a metal sheet to cool and the other half was poured into a flat glass dlsh. Both solutions cooled within about two minutes and formed a hard, brittle solid althou~h some surface wetness was observed.
Example 10 The same procedure was followed as in Example 1, except that the portion of the amine of Example 1 incorporated into the polypropylene was 90% by weight. The mixture was stirred vigorously while heating to a temperature of 200C.
The solution was poured on to a sheet of aluminum foil to a depth of about 50 mills for quick chilling. A solid was obtained that was quite wet. At this proportion of amine, it appears that a small amount of a second phase (liquid) is formed. While thts wet product may be useful for some purposes, to obtain a completely dry product, either a somewhat lower proportion of amine must be used or cooling achieved at a faster rate. It is conte~plated that a faster cooling rate can be achieved in the following manner: feed a metered amount of the heated solution on to a moving, chilled conveyer. The rate of cooling can be controlled by varying the feed rate of polymer so as to control the thickness of the material on the conveyer.
The speed of the conveyer and the temperature of the conveyer plates can also be regulated to achieve different cooling rates.
The conveyer plates themselves can he cooled with a circulating cooling medium, such as air, water, brine solution, Freon, etc.
Example 11 Following the same procedure as in Example 5, 75% by welght of N,N bis-(2-hydroxyethyl) coco amine ~Armostat 410) m~ 12-..

la~50~1L~37 was incorporated into 25% by welght of crystal grade poIy-styr~ne and heated wlth- stirring to 215C. After ætirring Eor ten minutes, the sample was chilled by pouring into a ~lat dlsh. A solid dry material was formed e~cept ~or a sllght wet-ness on the ~ottom and top. The solid material can be ground and incorporated into polyethylene in an amount equivalent to 0.15% amine to obtain similar antistatic slip effects.
Example 12 Following the same procedure as in Example 12, 50%
by weight of the amine of Example 11 was incorporated in 50%
by weight of crystal grade polystyrene at a temperature of 230C. and mixed for a few minutes un~il it became homogeneous.
A sample was poured on to a stainless steel plate at room temperature (25C) to cool in a layer about 3/16 inches thick.
Another sample was cooled by pouring into a Petrie dish at room temperature. Both samples, when cool, were hard and dry.
Example 13 Samples of the solid antistatic agent concentrate prepared in accordance with the preceding examples and contain-ing 75% by weight of the amine of Example 5 and 25% polypropylene were added to powdered charges of high density polyethylene in a "rotomolderl' in amounts equivalent to 0.2% and 0.4% by weight of amine to polyethylene. Rotomolding equipment such as that manufactured by Roto Mold & Die Company, Cuyahoga Falls, Ohio, is well known and available on the market. In the rotomolding process, dry powdered resin is placed in a closed mold and rotated until tha resin charge is evenly distrlbuted around the inside surface thereof. The resLn is then heated to its fusion temperature and thereafter cooled. Xn this example, dry, ~JP/ -13-~L~5~)~8~
pvwdered s~lid an~istati.c a~ent was mi~ed wi~h thc resin nnd charged to the "rotomolder". The antistatic agent imparted good to excellent antlstatic properties to the final molded product as indicated by the half-life, i.eO, the time for the charge to decay to one-half the original value, of the samples in Table II:

Conc. of Amine Initial Charge Half-Life 0.0% (control) 750 volts no decay 0.0% ~control) 750 volts no decay 0.2%2,000 volts 5 seconds 0.2%1,800 volts <l second 0.2% 1,250 volts cl/2 second 0.4% 3,200 volts <l/2 second 0.4% 2,200 volts <l/2 second ~o attempt was made to incorporate other liquid or solid antistatic agents since rotomolders have heretofore been unable to incorporate into rotomolded resins any antistatic agent which proved effect.ive.
Each of the solid products made according to Examples 6 through 12 can be incorporated in polyethylene in an amount equivalent to 0.05~ to 0.3% amine by weight, in polystyrene in an amount equivalent to 2 to 3% of amine by weight or in other olefinic polymers in effective amounts to impart good antistatic and slip characteristics to the blended polymer. The material is readily added to the olefinic polymer in a mixture at a temp-erature above the softening point of the polymer, preferably above about 150C. by adding ground particles of the dry 9 solid polypropylene containing lO - gO~ by weight of the antistatic agent to the molten olefinic polymerO
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m~ p /-14 -

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An ethoxylated antistatic composition adapted for incorporation into olefinic polymers comprising a solid homo-geneous mixture of from 10% to 90% by weight of a normally liquid ethoxylated amine antistatic agent, said amine being derived from primary alkenyl and mixed alkenyl and alkyl amines, or mixtures thereof, in which the alkenyl and alkyl moiety has a chain length between about 12 and 18 carbon atoms, and a polymer selected from the group consisting of propylene and copolymers thereof, poly-styrene and copolymers thereof, and polyphenylene oxide.

2. The composition of claim 1 in which the antistatic agent is N,N-bis-(2-hydroxyethyl) alkenyl or mixed alkenyl and alkyl (C12 - C18) amine.

3. The composition of claim 2 in which the antistatic agent is in a proportion of between about 50% and about 75% by weight.

4. The composition of claim 1 in which the antistatic agent is selected from the group consisting of N,N-bis-(2-hydroxy-ethyl) coco amine and N,N-bis-(2-hydroxyethyl) tallow amine.

5. A process for the preparation of a dry, solid ethoxy-lated antistatic composition adapted for incorporation into ole-finic polymers comprising the steps of admixing a polymer selected from the group consisting of propylene and copolymers thereof, polystyrene and copolymers thereof, and polyphenylene oxide with from about 10% to about 90% by weight of a normally liquid ethoxy-lated amine antistatic agent capable of forming a homogeneous liquid mixture therewith, said amine being derived from primary alkenyl and mixed alkenyl and alkyl amines, or mixtures thereof, in which the alkenyl and alkyl moiety has a chain length between about 12 and 18 carbon atoms, heating the mixture to a temperature such that a homogeneous liquid is formed, and then rapidly cooling the liquid to form a solid homogeneous mass.

6. The process of claim 5 in which polypropylene is used and the mixture is heated to a temperature slightly above the softening temperature of the polypropylene.

7. The process of claim 5 in which said cooling takes place within a period of between about 1/2 second and about 10 minutes of the process of claim 5 in which the antistatic agent is N,N-bis-(2-hydroxyethyl)alkenyl or mixed alkenyl and alkyl (C12 - C18) amine.

8. The process of claim 7 in which said amines is in a proportion of between about 50% and about 75% by weight.

9. The process of claim 5 in which the antistatic agent is N,N-bis-(2-hydroxyethyl) coco amine.

10. The process of claim 5 in which the antistatic agent is N,N-bis-(2-hydroxyethyl) tallow amine.