EP0677601A1 - Polyester fibres with improved bulk and process for their production - Google Patents

Abstract

Stretch-oriented polyethylene terephthalate (PET) spun fibres with improved bulkiness and recovery contain (a) 0.01-2 wt.% of a known conventional nucleating agent, i.e. (a1) inorganic substances with a mean particle size of less than 10mu , (a2) monomeric cpds. such as carboxylate salts, benzophenone or alkali aralkylsulphonates or (a3) polyethylene, polypropylene, copolymers of ethylene and unsatd. acids, or styrene/diene copolymers, (b) 0.05-2 wt.% of an ester cpd. of formula (I), and other known conventional processing aids and use-related additives as required; (CH3(CH2)aCO(OCH2CH2)b-O-B)2A (I) A = 1-10C alkylene; B = phenylene; a = 6-20; b = 1-5. Also claimed is a process for the prodn. of this fibre, by mixing PET with a relative viscosity of 1.45-1.68 with all additives etc., spinning the mixt. and stretching the prod.

Description

Polyethylene terephthalate fibers are widely used for all types of textiles because of their excellent physical and good physiological properties.

With the help of special additives or polymeric admixtures and production conditions, polyethylene terephthalate can also be adapted to special requirement profiles. Such fibers with defined performance characteristics, e.g. used as filling fibers for sleeping bags, quilts, padding and similar applications.

Filling fibers are e.g. through special types of crimp, such as the so-called helix shapes, through optimized crimp formation, through special fiber stiffness, which e.g. by high crystallization, by alloying with other polymers or with selected fiber cross sections. They are mostly surface treated, e.g. siliconized to prevent the fibers from sticking together smoothly and to achieve a soft feel.

Despite extensive development work, in particular to develop polyester filler fibers, which in their usage properties come close to natural down, the structural elasticity and the repetitiveness of such fibers are still insufficient and continue to decrease over the period of use.

The most important variables when assessing a filling fiber, e.g. a PET staple fiber for filling pillows, blankets, sleeping bags, cushions etc., are the bulk and the resilience of the fiber. The bulk is the volume, based on the fiber weight, of a filling fleece made from it under a defined area load. The higher the bulk, the less fibers are required and the lighter the finished article becomes, while at the same time providing better thermal insulation through a larger amount of air enclosed in the fleece.

A high (bending) stiffness of the individual fibers is a prerequisite for optimal building behavior, which gives them a high elastic resilience. In order for this to be effective in the nonwoven dressing, the number, angle and shape of the fibers must be optimized so that they are supported against one another as bulky as possible. In order not to hinder the recovery after a load due to friction, the fibers on the surface are also siliconized, which allows the necessary smoothness and a soft grip to be adjusted.

• 1. Vergrößerung der Materialquerschnittsfläche (d.h. des Einzelfasertiters bzw. -durchmessers). Dadurch nimmt aber die Weichheit ab.
• 2. Vergrößerung des mittleren Materialabstandes von der Faserachse (ohne Erhöhung des Titers). Diese Möglichkeit wird bei einer Hohlfaser optimal ausgenützt.
• 3. Erhöhung des Elastizitätsmoduls des Fasermaterials durch entsprechende Wahl oder Modifikation des Polyesters. Der Elastizitätsmodul hängt direkt zusammen mit der Orientierung bzw. dem Kristallinitätsgrad der Makromoleküle der teilkristallinen, thermoplastischen Polymeren.

There are three ways to increase the stiffness of a single fiber. Physically, the so-called bending stiffness is defined as a mathematical product of the modulus of elasticity and the material cross-sectional area moment of inertia. The latter in turn is made up of the cross-sectional area and the square of the radius with respect to the axis. The following measures increase the stiffness:

• 1. Enlargement of the material cross-sectional area (ie the single fiber titer or diameter). However, this reduces the softness.
• 2. Increasing the average material distance from the fiber axis (without increasing the titer). This possibility is optimally used for a hollow fiber.
• 3. Increase the modulus of elasticity of the fiber material by appropriate choice or modification of the polyester. The modulus of elasticity is directly related to the orientation or the degree of crystallinity of the macromolecules of the semi-crystalline, thermoplastic polymers.

These measures are preferably used in combination in order to achieve a maximum effect.

The majority of the crystallization of PET fibers is stress-induced achieved when stretching the originally almost amorphous spinning cable. With a subsequent heat setting, only a small further increase in crystallinity can be achieved. Since the temperature in this molecule-oriented process is relatively low, ie approx. 100 ° C below the crystallite melting point, and the dwell times are only in the range of seconds, this is normally achieved due to the high relaxation times within which a polymer chain can change places in the structure. only moderate degrees of crystallization.

A very different level of knowledge is known about crystallinity-increasing additives to spinnable polymers. On the one hand, Warner and Holt in "Text. Res. Journal" 1983, 486-89 show that the crystallinity in PET granules, which is improved by the addition of pigments, is not effective in the spun material, on the other hand it is known that additives which promote crystallization make the spinning of polymers extremely difficult or impossible do.

Therefore, highly crystalline polymer formulations, as are common for injection molding applications, cannot be processed into fibers or threads.

For example, DE 31 03 192 describes an alkali metal salt of an aromatic sulfonic acid as a crystallization accelerator for injection molding PES types, the advantages of which can be used for PES fiber with very small proportions only if it is stretched immediately after spinning, i.e. the so-called spin-stretch process is used. It is also known that alkali metal sulfate groups increase moisture retention in the polyester. This property is undesirable for fill and wadding fibers.

Plasticizers can increase the chain mobility of the polyester to such an extent that more easily crystallizable order states can form during solidification. During the cooling process, extensive orientation is not only made possible, but also completed.

However, plasticizers usually worsen the mechanical properties, especially the impact resistance, and they also tend to migrate.

The influence of copolyester components on the crystallization, especially the rate of crystallization, is examined by Lasarova and Dimov in "Faserf. Und Textiltechnik" 1976, 27, 237-40, and a plasticizer-like effect for such copolymers is shown. For such modifications, however, the strength, the elastic modulus and the melting point decrease at the same time, i.e. the most important fiber properties.

In addition, the tendency to crystallize even decreases as a result of the incorporation of other co-monomers because the regularity in the structure of the main valence chain is disturbed.

EP 194 808 describes various polyester resins with improved demolding properties due to increased crystallization speed. They contain up to 10% by weight of inorganic nucleating agents, metal salts of carboxylic acids, up to 150% by weight of reinforcing fiber and 0.3 to 10% by weight of plasticizer based on esters, and 1 to 30% by weight of impact modifier.

In addition to the fact that polymers with such amounts of additives are not suitable for spinning, this EP states that the action of the plasticizer according to the invention fails outside the stated limits.

a =

6 - 20

b =

1 - 5

A =

geradkettiger oder verzweigter Alkylenrest mit 1 bis 10 C-Atomen

B =

Phenylrest

sowie wahlweise weitere verarbeitungs- oder verwendungsbedingte Additive.The object of the invention to develop a stretch-oriented polyethylene terephthalate spun fiber with improved bulk behavior and improved resilience was surprisingly achieved by the characterizing features of claim 1. The polyethylene terephthalate contains additives of 0.01 to 2% by weight of at least one nucleating agent and 0.05 to 2% by weight of an ester compound of the formula I.



[CH₃ (CH₂) _a CO (O-CH₂-CH₂) _b -OB] ₂-A I



With

a =

6 - 20

b =

1 - 5

A =

straight-chain or branched alkylene radical with 1 to 10 carbon atoms

B =

Phenyl radical

and optionally other processing or use-related additives.

The upper limit for the nucleating agent and the ester compound is preferably 2.0% by weight, if possible.

Such use-related additives are known in the art, inter alia. Matting agents, pigments, stabilizers, UV brighteners, dirt-repellent and flame-retardant additives. Of the latter, phosphorus compounds are preferably used. Phosphorine compounds have proven particularly useful.

A proportion of the phosphorinane compound SANDOFLAM® 5085 between 3.0 and 10.0% by weight, preferably between 4.0 and 7.0% by weight, is particularly advantageous.

Among the customary, known processing-related additives, in particular glycols, preferably mono-, di- and triethylene glycol to adjust the viscosity are to be mentioned, ethylene glycol being particularly preferred.

The ester compounds, which according to the invention must preferably be present in amounts of only 0.1 to 0.3% by weight and particularly preferably only 0.15 to 0.25% by weight, are per se as plasticizers for PET injection molding -Recipes known. However, you need to do this in a significantly higher Concentration range, namely 0.3 to 10.0 wt .-%, are used (EP 194 808).

Extensive spinning tests, however, have shown that there is a defined narrow range with a relatively low concentration of the ester compound, in which their influence and the action of the nucleating agent complement one another in such a way that unexpectedly the initial bulking value, recovery and crystallinity are significantly higher. The examples are summarized in Table 1. It was also demonstrated that the ester compound according to the invention (abbreviated to the general name Bidieol) only influences the crystallization if nucleating agent is dispersed in the polyester at the same time. As a nucleating agent e.g. the matting agent titanium dioxide already present in matted polyester is used.

The nucleating agents that are suitable for PET, also called nucleating agents, are described, for example, in the "Taschenbuch der Kunststoff-Additive", Carl Hanser Verlag, 3rd edition 1990, page 899.

The nucleating agents used according to the invention are either inert, inorganic substances with an average particle size of less than 10 μm, preferably less than 1 μm, for example talc, kaolin, chalk, carbon black, graphite, quartz powder (SiO₂) and inorganic pigments, for example TiO₂, BaSO₄, ZnS, or suitable monomeric organic compounds such as salts of carboxylic acids, benzophenone or alkali metal alkyl sulfonates, or finally selected organic polymers such as polyethylene, polypropylene, copolymers of ethylene and unsaturated carboxylic acids or copolymers of styrene derivatives with dienes. (R. Vieweg, L. Goerden (ed.): Kunststoffe Handbuch Vol. VIII, Polyester, Hanser Verlag 1973, page 701). The organic compounds or the polymers can be used alone or together with inorganic nucleating agents become. The nucleating agents preferred according to the invention are the types of matting agents used for the production of PET spin granules, in particular titanium dioxide. They are used in amounts of 0.01 to 2.0, preferably 0.1 to 1.5% by weight.

The invention also relates to a method for producing a PET staple fiber according to claim 11, which is characterized in that a polyethylene terephthalate with a relative viscosity (RV) between 1.45 and 1.68 (measured 1% in m-cresol) 20 ° C) with all additives and additives, mixed, then spun and then stretched.

In advantageous variants, the additives and additives are metered into the extruder or into the PET melt using suitable devices, if they have not been previously, e.g. were added to the granules.

The invention further relates to PET staple fibers with improved bulk behavior and improved resilience, which can be produced by this process, and to the use of ester compounds of the formula I for the production of PET staple fibers with improved bulk behavior and improved resilience.

Figure 1 summarizes the results of the bulk test of the PET fibers produced according to Examples 1 to 7. It is shown that not only does the additive concentration have to be in an optimal range for maximum bulk, but that the molecular weight and the relative viscosity of the polyester are also decisive for the bulk recovery force, which is correlated with the crystallinity. As a result of nonlinear relationships with the additives according to the invention, curved effective surfaces with burr formation are evident. In the area under investigation, the initial height of the bulge and the spring-back force behave in opposite directions. Only in a defined area around point G can you get both high values for the initial construction as well as for the return force. These complex relationships in the field according to the invention are new and unexpected compared to the previous state of knowledge.

The following should be noted regarding the optimal, low relative viscosity (RV) of the PET fiber according to the invention in the range from 1.45 to 1.55:

It is known that spinning polyester melt with the low viscosity optimal for the process according to the invention leads to disturbances, therefore it is advantageous to use higher molecular weight polyester, e.g. with RV = 1.60, assuming a corresponding amount of mono-, di- or tri-ethylene glycol, preferably mono-ethylene glycol (EG), for degradation when using granulate in the extruder feed zone or when spinning directly into the melt line RV = approx. 1.50 is added.

The correlation between EG addition and relative viscosity can be seen in FIG. 1.

Virtually no influence on the viscosity was observed for the ester compound. If the viscosity is reduced by other additives added to the polyester or by traces of moisture in the starting granulate or in the additives, the amount of glycol added must be reduced so that the resulting final viscosity is still in the preferred range of RV = 1.45 to 1.55. Such a case occurred in Example 8, where the viscosity was reduced so much by the further addition of a flame retardant that it was possible to dispense with the addition of glycol.

Figure 1 Bulking behavior of matt PET fill fiber

Interpolierte Kurven mit: konstantem Anfangsbausch -----
   konstanter Rückstellkraft ―
Optimaler Bereich = Überschneidungsbereich der hohen Wertedepending on the addition of bidieol and relative viscosity

Interpolated curves with: constant initial lump -----
constant restoring force -
Optimal range = overlap range of the high values

Examples 1-7

Substances used:
- Standard polyethylene terephthalate from EMS-CHEMIE AG with rel. Viscosity 1.60 (measured 1% in m-cresol at 20 ° C) and 0.4 wt .-% TiO₂ (titanium dioxide) <1 µm
Bidieol: bisphenol A diethoxy laurate
Production of the bidieol
Chemicals used:
- Ethoxylated bisphenol A (from AKZO) Melting point: 105-112 ° C Molecular weight: approx. 340 g / mol Hydroxyl number: approx. 350 mg KOH / g
- Lauric acid, (from FLUKA, purum 98%)
- Butyltin acid, mono-n-butyltin oxide (from ACIMA).
Approach:
272 g ethoxylated bisphenol A (0.8 mol)
304 g lauric acid (1.52 mol)
4 g butyltinic acid (as a catalyst)

Execution:

Ethoxylated bisphenol A, lauric acid and butyltinic acid are placed at 22 ° C and heated to 160 ° C with nitrogen flushing and stirring. The pressure is reduced to approx. 7500 Pa (approx. 56 mm Hg). The water of reaction which forms is removed from the mixture for about 6 hours until the acid number has dropped below 5 mg KOH / g. The product is a slightly yellowish, clear liquid with a viscosity of approx. 410 mPas and a density of approx. 1000 kg / m³ (both at 25 ° C).

Spinning and drawing of the PET fibers:

On a melt spinning machine with 0.4% TiO₂ matted standard PET granulate (relative viscosity 1.60 / 1% solution in m-cresol at 20 ° C) was melted and separated according to Table 1 ethylene glycol (EG) and Bidieol in the Granulate inlet of the extruder added (EG and Bidieol are not mixable). Hollow threads were pressed out of a special nozzle plate with 380 bores at a temperature of 262 ° C., cooled with blown air, drawn off at 1000 m / min and placed in a jug. The void fraction of the undrawn threads was approx. 25% (ie the inside diameter was 50% of the outside diameter), the relative viscosity 1.50. The spinning material was then stretched about 3.5 times on a fiber line, then crimped, siliconized, heat-set and cut into staple fibers which had a final titer of 6.5 dtex and a tensile strength of 3.5 cN / dtex at 55% elongation at break. A filler fleece made from it showed bulk values that were significantly higher than those of a commercially available hollow fiber. Table 1 Building return and crystallinity of the finished fiber Examples 1 2nd 3rd 4th 5 6 7 **) Experimental A B / E C. D F G H - Ethylene glycol (% by weight) 0 0 0 0 0.07 0.07 0.07 - Bidieol (% by weight) 0 0.1 0.2 0.3 0.1 0.2 0.3 - Starting bulk From in mm 126 115/113 125 118 125 126 118 121 Spring force R in% 77 79/80 82 85 78 86 81 81 Crystallinity *) K in% 41 44/45 46 47 44 49 46 44 *) Crystallinity after DSC evaluation **) Comparative values of a commercially available hollow fiber

Dasselbe für die Kristallinität: $$\begin{array}{c}\begin{array}{c}\text{K = 19.40 x + 41,59}\\ \text{Korrelationskoeffizient = 0.9926}\end{array}\end{array}$$

Der Einfluß des Bidieols auf Rückstellvermögen und Kristallinität ist damit statistisch gesichert.Linear regression of the resilience (for the linear range without ethylene glycol addition): $$\begin{array}{c}\begin{array}{c}\text{R = 25.50 x + 76.75 (x =\% by weight bidieol)}\\ \text{Correlation coefficient = 0.9952}\end{array}\end{array}$$

The same for crystallinity: $$\begin{array}{c}\begin{array}{c}\text{K = 19.40 x + 41.59}\\ \text{Correlation coefficient = 0.9926}\end{array}\end{array}$$

The influence of the bidie on resilience and crystallinity is thus statistically secured.

The glass transition point fluctuated in all variants by a maximum of only 0.5 ° C. An additional test with 2% by weight of bidieol resulted in a lowering of the glass transition temperature by approx. 3.5 ° C, combined with a significant deterioration in the bulk.

Example 8

Starting from the same standard PET granulate and under the same spinning and stretching conditions as in Examples 1 to 7, hollow fibers were also produced, but with a flame-retardant additive. 0.2% by weight of bidieol (metered into the inlet of the melt extruder) and 5.6% by weight (based on the fiber weight) of the flame retardant SANDOFLAM® 5085 from SANDOZ AG, a phosphorus with a melting temperature of approx. 188 ° C, added. The flame retardant was introduced directly into the PET melt as a pure powder using a device as described in DE 40 39 857. Advantageous further variants of the method are the addition in the form of a masterbatch granulate into the extruder or melted into the PET melt using a suitable pump. Since the viscosity was reduced to the optimum range by the flame retardant and the traces of moisture contained therein, no ethylene glycol had to be added.

The properties of the fibers produced in this way were summarized in Table 2 as a comparison to test variant G (example 6).

For the LOI flame test (Limiting Oxygen Index according to ASTM D 2863), needled nonwovens with a basis weight of approx. 200 g / m² and a thickness of approx. 6 mm were produced from the staple fibers.

It was found that in this way flame-retardant filler fibers with an approximately 35% higher LOI value than the comparison fiber can be produced without a flame-retardant additive, the high bulk according to the invention being retained. The latter is not a matter of course, because of those previously on the market available flame-retardant polyester fibers is known that their structural resilience is impaired by phosphorus-containing flame retardants. This is because the phosphorus compounds are built into the fiber molecule chains and thus there is a copolyester with a reduced melting point and reduced crystallization capacity. Correlating poorer construction properties are measured. For example, a melting point of 247 ° C. (DSC, with 20 ° C./min heating rate) and a crystallinity of approx. 43% were measured on such a PES fiber.

The PET fiber according to the invention according to Example 8 advantageously meets the requirements for flame retardancy with a high bulk and resilience at the same time and also for a fiber melting point of at least 250 ° C according to the DSC measurement conditions mentioned above.

Methodology of building measurement Principle:

A fleece with a defined basis weight is produced by means of a card or card and the resulting fleece height is measured under a defined load of 0.9 to 10 p / cm². The fleece height is a measure of the bulk of the fiber. The initial bulk (Ab) means the initial fleece height under 0.9 p / cm² load. The return force (R) is also measured after the maximum load on the fleece and a defined waiting time below 0.9 p / cm² and expressed in% of the initial bulk.

Action:

150 g at 20 ° C and 60% rel. Moist conditioned filler fibers processed into a fleece with the base area of 35 x 72 cm. This nonwoven body is subjected to the following load for the bulk measurement: The test stamp, a round plate with a diameter of 150 mm, is pressed against the fleece with increasing weight and the resistance of the fleece to load is determined.

One minute after the maximum load of 10 p / cm², the fleece height is determined again with the initial load of 0.9 p / cm². This bulge gives the so-called spring force (R).

Claims (16)

Stretch-oriented polyethylene terephthalate staple fiber with improved bulk behavior and improved resilience, characterized in that the polyethylene terephthalate contains additives of
0.01 to 2% by weight of at least one customary known nucleating agent from the group - inorganic substances with an average particle size below 10 µm, monomeric organic compounds selected from salts of carboxylic acids, benzophenone or alkali metal alkyl sulfonates, - Organic polymers selected from polyethylene, polypropylene, copolymers from ethylene and unsaturated carboxylic acids and copolymers from styrene derivatives with dienes, and 0.05 to 2% by weight of an ester compound of the formula (I)



[CH₃ (CH₂) _a CO (O-CH₂-CH₂) _b -OB] ₂-A (I)



With a = 6 - 20 b = 1-5 A = straight-chain or branched alkylene radical with 1 to 10 C atoms B = phenyl radical, and optionally contains other customary, known processing or use-related additives. PET staple fiber according to Claim 1, characterized in that the ester compound is present in amounts of 0.1 to 0.3% by weight, preferably 0.15 to 0.25% by weight. PET staple fiber according to claim 1 or 2, characterized in that the acid component of the ester compound is lauric acid. PET staple fiber according to claim 1 or 2, characterized in that the alcohol component of the ester compound is ethoxylated bisphenol A, wherein ethers of bisphenol with mono- and / or diglycols, i.e. Alcohol components in which b = 1 and / or 2 are preferred. PET staple fiber according to claim 1 or 2, characterized in that the additives due to use are those from the group of matting agents, pigments, stabilizers, UV brighteners, flame-retardant and dirt-repellent additives. PET staple fiber according to claim 5, characterized in that the melting point is at least 250 ° C, measured by DSC at a heating rate of 20 ° C / minute. PET staple fiber according to claim 1, characterized in that the processing-related additive is selected from the group of mono-, di- or triethylene glycol. PET staple fiber according to any one of claims 1 to 7, characterized in that it is a hollow fiber. PET staple fiber according to any one of claims 1 to 8, characterized in that its relative viscosity, measured as a 1% solution in m-cresol at 20 ° C, is 1.45 to 1.55. PET staple fiber according to any one of claims 1 to 9, characterized in that the nucleating agent is also a matting agent. Process for the production of a PET staple fiber according to any one of claims 1 to 10, characterized in that a polyethylene terephthalate with a relative viscosity between 1.45 and 1.68 mixed with all additives and additives, mixed, then spun and then stretched. Process according to claim 11, characterized in that the additives and additives are metered into the extruder or into the PET melt. A method according to claim 11 or 12, characterized in that the preferred range of the relative viscosity of the PET staple fiber from 1.45 to 1.55 by metering a corresponding amount of mono-, di- or triethylene glycol, preferably monoethylene glycol, in the extruder or in the melt line is set. Process according to any one of claims 11 to 13, characterized in that a matted hollow fiber is obtained as the staple fiber. PET staple fiber with improved bulk behavior and improved resilience, producible by the method according to claim 11. Use of ester compounds of the formula I for the production of PET staple fibers with improved bulk behavior and improved resilience.

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