DD301044A7 - METHOD FOR PRODUCING NON-BLOCKING POLYURETHANE ELASTOMERS - Google Patents

Abstract

The invention relates to a process for the preparation of non-blocking polyurethane elastomers. Thus, sheet-like structures, coatings, pipes, hoses and the like can be produced, which do not adhere to each other when lying on each other. According to the invention, the elastomers comprise from 50 to 98 parts by weight in% of thermoplastic polyester and / or polyether urethanes and from 2 to 50 parts by weight in% of a random copolymer having a particle size of from 0.05 to 0.5 μm, which comprises at least 5% by weight of based on the copolymer, a polar olefinically unsaturated monomer acrylonitrile, acrylic acid or methacrylic acid and at least 20 parts by weight, based on the copolymer, of a low-polarity, olefinically unsaturated monomer from the group consisting of styrene and alpha-methylstyrene, and formed by melt mixing in one Twin-screw reaction extruder having a minimum length of 25 times the screw diameter at a maximum melt temperature of 230 degrees C.

Description

Field of application of the invention

The invention relates to a process for the preparation of thermoplastic polyurethane elastomers which do not block and are thus suitable for sheetlike structures, coatings, hoses, pipes, profiles and threads and other molded parts. This avoids adhesion of superimposed layers.

Characteristic of the known state of the art

Thermoplastic polyurethane elastomers (TPU) are known to be produced in large quantities and in a wide range of grades, especially in terms of hardness. All these types show more or less pronounced appearance typical of this material that superimposed surfaces after a short time are difficult or impossible to solve each other. Formed from the known TPU moldings and semi-finished products adhere so strongly to each other or in the respective forms by the adhesion that they z. B. can be removed from the molds only after prior spraying with release agents. So far there has been no lack of attempts to circumvent this phenomenon by choosing suitable starting materials for the synthesis of the thermoplastic polyurethane. Thus, the patent DE-OS 3504671 describes such a solution, according to which first a relatively high molecular weight, above 260 ⁰ C melting polyaddition product dispersed in the polyol required for polyurethane production and from a thermoplastic polyurethane elastomer is prepared in which the polyaddition product in particle sizes of 0.01 to 25μητ> and in proportions of 0.66 to 15 wt .-% is present. The disadvantage of this process lies in the complicated additional process steps of the synthesis, the polyaddition product which is severely limited by the choice of the substance class and its dispersion in the diol necessary for the preparation of the polyurethane. Another way is mentioned in patent DD-PS 133811.

Thereafter, in order to avoid the blocking tendency of the TPU during the synthesis, release agents in the form of oxidized polyethylene waxes are added. Mi '. Although improvements in e.g. be achieved in the production of flat films of TPU, but this also involves considerable disadvantages, such as lower mechanical properties o.a. Due to the negative effects on the mechanical properties of the additional amount must remain very limited, which only a small antiblock effect is achieved.

Another approach has been to label TPU compounds and other components that are, on the one hand, miscible with the TPU to a limited extent and, on the other hand, reduce the tacking together of TPU surfaces. US Pat. Nos. 3,970,715 and 2,103,584 to US Pat Addition of small amounts of EVA Copolymorisates described. As already stated, due to the incompatibility of the two polymers, only a small amount of ethylene vinyl acetate (EVA) is miscible with TPU, whereby only a small amount of antiblocking agent can be achieved. Larger amounts than 5 parts by weight in% EVA in the TPU lead in any case to a considerable decrease in the mechanical properties, which could be confirmed by our own investigations. A significant improvement in the demolding of moldings and semi-finished products is not achievable.

The patents DD-PS 235457 and DD-PS 222037 describe processes for the preparation of non-blocking thermoplastic polyurethanes, after which this effect is achieved by compounding TPU with microcrystalline cellulose and with starch. Sheets produced from this are characterized by complete block freedom and a so-called "dry grip. However, the described methods have the disadvantages that the slightest contamination and agglomeration of the additives lead to holes in thin films of such compounds and threads can not be produced therefrom.

Object of the invention

The aim of the present invention is a process for the preparation of thermoplastic polyurethane elastomers which, when processed by the injection molding, extrusion, calendering or blow molding process, allow a significantly reduced adhesion to the molds, molds and rolls and thus easy releasability and after processing to products with multiple superimposed surfaces, such as thin tubes, coatings, threads, stacked moldings, etc. have no blocking surfaces and in addition to a good homogeneity a high level of property.

The TPU or semifinished products made from it should be arbitrarily dyeable.

Darling of the essence of the invention

The invention has for its object to develop a method according to which non-blocking thermoplastic polyurethane elastomers with high quality and with little technical effort can be produced. According to the invention, this object is achieved in that a compound of 50 to 98, preferably 60 to 95 parts by mass in% thermoplastic polyester and / or Polyethorurethan and 2 to 50, preferably 5 to 40 parts by mass in% of a random copolymer, which

a) at least 5 parts by mass in%, based on the copolymer, of a polar olefinically unsaturated monomer acrylonitrile, acrylic acid or methacrylic acid and

b) at least 20% by weight, based on the copolymer, of at least one slightly polar, olefinically unsaturated monomer from the groups of styrene and α-methylstyrene

is constructed by melt mixing in a twin-screw extruder. Essential here is the distribution of the copolymer according to the invention in polyurethane with average particle sizes between 0.05 to 5.0 μm, preferably 0.1 to 3 μm. It has been found that this particle size is crucial for a high level of properties of the products made from the compound with simultaneous block fronthitis. It has also been found that for a homogeneous distribution of the copolymer in the TPU high shear action of the extruder screws used fci required, but on the other hand avoided local overheating by shearing in the extruder, ie a maximum melt temperature of 23O ⁰ C, preferably 210 ° C are not exceeded ,

For the production of the TPU compounds according to the invention with a homogeneous distribution of the compound constituent, concurrent, closely intermeshing twin-screw extruders of a minimum length of 25 times the diameter of the screw (25D), preferably at least 35D, are used. The object of the preparation of the described compounds of polyurethane elastomers and copolymers of vinyl-containing aromatics and acrylonitrile with average particle sizes of the disperse phase between 0.05 to 5μιτ>, preferably 0.1 to 3 μπ \, with high quality level and low blocking properties of the compound according to the invention achieved in that a screw geometry is used, which allows a gentle melting of the polyurethane without frictional temperature increases above 230 ⁰ C, preferably 210 ° C. This is, starting from the hopper, achieved by a threaded portion of the screw with steadily decreasing thread pitch (right-hand thread), which extends over at least 12D, preferably 16D. This is followed by a Knetslement having a length of at least 1D, preferably 2 D, consisting of at least 3, preferably 5, eccentric discs, which are arranged offset by 45 ° to 90 'and cause an intensive mixing of the melt. A constant filling of the kneading element is achieved by a subsequent element of 1D length, which has an opposite thread pitch (left-hand thread) as the threaded pieces used in the 1st part of the screws. This is followed again by a threaded part (right-hand thread) of at least 6D, preferably 8D, with a steadily decreasing pitch in order to initially build up a relaxation and then again a pressure in the melt. This thread part is again followed by a kneading element having the same geometry as that first described. A deviation from the geometry of the individual kneading disks in the two kneading blocks is possible in such a way that instead of the 3eckigen and those of elliptical shape are used. Likewise, the thickness of the individual opposing Knetscheibenpaare can be varied. After the second kneading followed by a threaded portion of the screw of at least 4, preferably 6 D, length, which has the task to provide by gradually decreasing pitch for a repressurization and a continuous delivery of the melt.

The feed of the thermoplastic polyurethane elastomers and the copolymer of vinyl-containing aromatics and acrylonitrile into the hopper of the extruder is carried out as a granulate mixture via a suitable metering scale or separately via 2 metering devices. But it is also possible and content of the invention, insüo fondere at high Anteigen of copolymer in the compound to meter the copolymer into the hopper of the extruder and to promote the polyurethane immediately after the 1 .Knetblock in the extruder barrel with known metering devices.

The homogenized melt is pressed at the end of the extruder through a Düsonplatto with holes for forming strands for the production of granules, the strands in bokannte way, z. B. in a water bath, cooled and cut to rleselfähigom granules.

It has also been found that the preparation of the compounds according to the invention of thermoplastically processable polyurethane elastomers and copolymers of vinyl-containing aromatics and acrylonitrile can be combined with the continuous production of pipes, hoses and profiles, if the extruder with suitable molds and corresponding downstream devices for the calibration and the Deduction is equipped. By combining the extruder with a large diameter stranding tool, it is possible to continuously feed a melting roll plant. When equipped with a slot die, other coating systems are to operate continuously. It is also part of the invention to combine the production of thermoplastically processable polyurethane elastomers au 'reaction extruders with the invention described compounding with the specified copolymers, if used for this purpose twin-screw extruder of at least 32 D length and with a solid and melt feed.

It is essential here that the screw geometry allows the formation of a homogeneous, high-quality polyurethane and then a homogeneous distribution of the metered copolymer. The invention described average particle size of the copolymer in the polyurethane of 0.05 to 5, preferably 0.1 to 3 μιη, is achieved in that the screws from the point of supply of the copolymer have approximately the same geometry as the screw geometry described in the invention. By virtue of the presence of the polyurethane as a melt, the initial threaded part can be made substantially shorter with a continuously decreasing thread pitch. In this case, a length of 6D is sufficient.

From the compound granules according to the invention described can be produced completely homogeneous articles which are characterized by non-blocking surfaces, easy releasability of molds, molds and rollers lighter and compared to pure polyurethane significantly improved extrudability and high quality level in terms of mechanical properties. All products are covered as desired and can be colored translucently.

The aur. Due to the good homogeneity and elasticity of the melt, the compounds of TPU and random copolymers of vinylbenzone and acrylonitrile produced by the process according to the invention can be spun into threads from the melt which can be unwound from the roll without problems and can be processed into fabrics.

Ausführungsbeisplele

example 1

95% to 75% by weight of thermoplastically processable polyurethane elastomer having a hardness of Shore D = 60 based on a long-chain polybutylene ethylene adipate with an average molar mass of 2,000,1,4-butanediol, 4,4-diphenylmethane diisocyanate, paraffin oil and 2,2 ' , 6,6'-Diisopropyldiphenylcarbodiimide as a stabilizer were mixed with 15 to 25 parts by mass. in% of a random copolymer of vinylbenzene and acrylonitrile with an average molar mass of 115,000 and an acrylonitrile content of 28% mechanically mixed, placed in the hopper and homogenized in a twin-screw extruder ZSK 30 with concurrent, tightly meshing screws with the following screw geometry. The threaded part, starting from the hopper, has a steadily decreasing thread pitch over 16D (16 times the screw diameter) length. This is followed by a kneading element with a length of 2 D, which consists of 5 eccentric discs and which are arranged offset by 45 to 90 °. For a constant filling of the kneading element ensures a screw part of 1D length with opposite thread pitch. Next element is a threaded part of 8P length with steadily decreasing gear pitch. This is followed again by a kneading element of 2D length of the same construction as the 1st kneading element. After this follows a screw part over 6D length with gradually decreasing pitch for a repressurization and a continuous promotion of the melt. Temperature profile of the extruder:

barrel zones 1 165 ⁰ C 2 205 ° C 3 205 ⁰ C 4 180 ⁰ C 5 195 ⁰ C 6 195 ⁰ C jet 195 ⁰ C

On the basis of electron micrographs, an average particle size of 0.1 to 1.5 μm of the copolymer of vinylbenzene and acrylonitrile in the polyur could be ascertained in the erhal compound. The mass showed a significantly improved extrudability with higher throughputs in a subsequent extrusion to thin tubes compared to the pure zi .ompounding polyurethane used without the walls of the thin tubes and the wound hoses adhered to each other. The mechanical properties of the compound, determined on sprayed test specimens, as well as the block behavior of thin tubes are shown in Table 1. '

Example 2 (comparative example)

From the polyurethane used for the compounding according to Example 1 were injected to determine the mechanical properties under the same conditions as for Example 1 test specimens and thin-walled tubes extruded. The tensile strength was z.T. under the results mentioned in Example 1, z.T. it was comparable (Table 1). The hoses were not separable due to the strong blocking and can be unwound from the winding only by applying force.

Example 3 (comparative example)

A polyester urethane compound having a hardness of Shore D = 60 and a copolymer of vinylbenzene and acrylonitrile in the same compositions as in Example 1 was prepared under the same conditions as in Example 1, but using a screw geometry as described in U.S. Pat Compounding of polymers is common practice and recommended by the machine manufacturer.

The mechanical properties of sprayed test specimens are significantly worse than those shown in Example 1 (Table 3).

Although the thin-walled hoses made from the compound showed less, but still loud, block tendency compared to pure polyurethane.

Example 4

Compounds of polyester urethane and copolymer of vinylbenzene. and acrylonitrile, prepared by the same method as Example 1, and a Shore hardness of the 6OD polyurethane elastomer were injection-molded on a 150 t-die injection molding machine to give moldings of complicated geometry (e.g., softball sticks). With pure Polyosterurethan after 4 cycles, the mold had to be sprayed with release agent. When using the compound according to the invention that was required only after every 12 cycles. The cycle time was reduced by 10%. Stacked parts showed no adherence to adjacent surfaces even after a long service life.

example

Made of a compound consisting of

a) 75 parts by weight in% of a thermoplastically processable polyurethane with eir.dr hardness of Shore A = 90 on the basis of a long-chain polybutylene ethylene adipate with a fine average molar mass of 2000,1,4-butanediol, 4,4 '· diphenylmethane diisocyanate, paraffin oil and 2 , 2 ', 6,6'-Diisopropyldlphenylcarbodiimid as a stabilizer and

b) 25% by weight in percent of a random copolymer of vinylbenzene and acrylonitrile with an average molar mass of 115,000 and an acrylonitrile content of 28% by weight in%,

prepared by melt mixing on a twin-screw extruder ZSK 30 according to the method described according to the invention were spun on a laboratory spinning line at 2 different Abzugsgeschwindigksiten from a nozzle with 0.3 mm diameter threads.

Temperatures of the spinning plant:

Cylinder: 210 ⁰ C

Nozzle including sieve package: 21O ⁰ C

Even at high take-off speeds (~ 400 m / min), no breaks occurred, which can only be achieved by a very good homogeneity and elasticity of the melt.

Table 1 inventively 90 1382 80 70 60 Standard geometry of the 90 80 70 60 screw geometry 54 machine manufacturer 100 10 medium 20 30 40 100 10 20 30 40 polyester urethane (Mass fraction in%) 0 59.5 47.6 39.2 35.7 0 22.4 14.7 17.9 28.4 copolymer 419 244 195 138 430 260 175 152 (Mass fraction in%) 51.8 0.095 0.125 0.195 0.403 0.71 28.7 0.12 0.18 0.36 0.48 Tensile strength (MPa) 348 1219 1540 1486 1640 450 1110 1362 1200 1250 Elongation at break (%) 53 58 63 65 0.08 53 53 64 67 Flexural modulus (GPa) strongly weak Not Not 1180 strongly strongly medium weak Tear propagation resistance (N / cm) 46 Hardness Shore D extreme block behavior

block, block, strong

The properties of the yarns obtained at the drawing speed of 20 and 420 m / min are shown in Table 2. Table 2

Take-off speed (m / min) thread diameter (| jm) breaking force F _H (mN) breaking elongation Eh (%) fineness-related breaking strength (mN / tex)

20 400 93 37 277 71 244 21 21.6 36.6

Claims (4)

1. A process for the preparation of non-blocking polyurethane elastomers, which have a good homogeneity and a high level of properties, characterized in that a compound of 50 to 98 parts by mass in% thermoplastic polyester and / or polyether urethane and 2 to 50 parts by mass in% of a random copolymer which comprises at least 5% by mass, based on the copolymer, of a polar olefinically unsaturated monomer of acrylonitrile, acrylic acid or methacrylic acid and at least 20% by weight, based on the copolymer of a low-polar, olefinically unsaturated monomer from the group of styrene and α-methylstyrene is prepared and prepared by melt mixing in a close-coupled co-rotating twin-screw extruder of a minimum length of 25 times the screw diameter (25D) high shear and a maximum melt temperature of 230 ⁰ C, wherein the copolymer in polyurethane with average Pa particle sizes between 0.05 to 5.0 mm is distributed. 2. The method according to claim 1, characterized in that the polyester and / or polyether urethane and the copolymer metered as granules through a hopper, for gentle melting by a threaded part with steadily decreasing pitch (right-hand thread) of at least 12 D length with subsequent intensive mixing in a kneading element of at least 1D length, consisting of at least 3 eccentric discs in triangular or elliptical shape, each offset by 49 to 90 °, with a steady filling of the kneading element with a threaded portion of 1D length with opposite thread pitch (left-hand thread) reached Subsequently, a threaded portion of at least 6D length and then a kneading element, as ready * is described and then passed through a threaded portion of at least 4D length with steadily decreasing pitch, whereby the Sc melt is continuously conveyed. 3. The method according to claim 1 and 2, characterized in that the copolymer is metered into the hopper and the PoIv ester and / or polyether urethane immediately after the first kneading block. 4. The method according to claim 1 and 2, characterized in that the copolymer is metered in the reaction extruder in the expansion zone and the subsequent melt mixture over at least 6D length is performed.