HK1028781B - Nonrigid, thermoplastic moulding compositions - Google Patents

Description

Non-rigid thermoplastic moulding compositions

The invention relates to non-rigid, easily film-moldable molding compositions which comprise thermoplastic polyurethanes and have low shrinkage.

Thermoplastic polyurethane elastomers (TPUs) have been known for a long time. Their industrial importance lies in the combination of their high-grade mechanical properties with the known advantages of thermoplastically, cost-effective processability. The mechanical properties can vary widely with different chemical synthesis components. Reviews on the nature and use of TPUs are disclosed, for example, in Kunststoffe 68(1978), 819, and in Kautschuk, Gummi, Kunststoffe35(1982) 568.

TPUs are synthesized from linear polyols, most of which are polyester-or polyether-polyols, and from organic diisocyanates and short-chain diols (chain extenders). To accelerate the formation reaction, a catalyst may also be added. The molar ratios of the synthesis components can be varied within wide limits in order to adjust the properties of the products formed. Molar ratios of polyol to chain extender of from 1: 1 to 1: 12 have proven suitable and give products having a hardness of from 80 Shore A to 75 Shore D (in accordance with DIN 53505).

TPUs having a hardness of less than 80 Shore A can in principle be obtained in the same way. However, a disadvantage is that such products may encounter processing difficulties in production, as they are difficult to set and cure.

TPUs having such a low hardness exhibit rubber-like elasticity. Thus, the release behavior and dimensional stability of injection molded parts often become unsuitable for processing in the injection molding industry, since their shrinkage is too high.

EP-A0134455 discloses that TPUs having a hardness of from 60 to 80 Shore A can be obtained using plasticizers comprising special phthalates and phosphates.

EP-A0695786 describes the production of non-rigid TPUs based on special polyethers/polyesters in admixture with plasticizers, including alkylsulfonates or benzylbutylphthalate, with the addition of inorganic fillers.

The disadvantage of both these processes is the use of plasticizers which make these TPUs impossible in many applications, the most important of which is the purity of the TPU material or the surface quality of the processed TPU.

The object of the present invention is to provide TPU molding compositions which are non-rigid, easily deformable and thermoplastically processable and have low shrinkage and are free of plasticizers.

This object has been made possible by the TPUs according to the invention.

The invention relates to thermoplastically processable, readily releasable polyurethane molding compositions which have low shrinkage, a shrinkage of less than 2.5% according to DIN 16770(Part 3), a hardness of 65-85 Shore A (according to DIN53505), and the following composition,

A) from 5 to 54 parts by weight of a thermoplastic polyurethane having a hardness of from 60 to 75 Shore A (determined in accordance with DIN53505) from the following sources,

1) an organic diisocyanate which is a mixture of at least one organic diisocyanate,

2) a polyester and/or polyether polyol having a number average molecular weight of 500-

3) A chain extender diol having a molecular weight of 60 to 400, and

B) 95-46 parts by weight of a thermoplastic polyurethane having a hardness of 76-90 Shore A (determined in accordance with DIN53505) are obtained from,

1) an organic diisocyanate which is a mixture of at least one organic diisocyanate,

2) a polyester polyol and/or polyether polyol having a number average molecular weight of 500-

3) A chain extender diol having a molecular weight of 60 to 400, and

4) optionally catalysts, auxiliaries, additives, chain terminators and mold release agents,

wherein B) is obtained by a sequential multistage reaction in which

a) One or more linear, hydroxyl-terminated polyester-and/or polyether polyols are continuously mixed with a portion of an organic diisocyanate in a ratio of 2.0: 1 to 5.0: 1, the shear energy being high (sufficient for good mixing of the components),

b) the mixture formed in step a) is reacted further in the reactor at > 120 ℃ until > 90% of the polyol is converted into an isocyanate-terminated prepolymer,

c) the prepolymer formed in step b) is mixed with residual organic diisocyanate (preferably in an amount of at least 2.5% of the amount of organic diisocyanate in step a)), with an NCO: OH ratio of 2.05: 1 to 6.0: 1 for the sum of steps a) to c) and an NCO: OH ratio of 0.9: 1 to 1.1: 1 for all components from steps a) to f),

d) the mixture resulting from step c) is cooled to < 190 c,

e) the mixture obtained in step d) is continuously and vigorously mixed with one or more chain extender diols for up to 5 seconds, and

f) the mixture obtained in step e) is further reacted in an extruder to give thermoplastic polyurethanes.

Examples of suitable organic diisocyanates 1) include aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, such as those described in Justus Liebigs Annalender Chemie, 562, p.75-p.136.

Detailed examples are cited below: aliphatic diisocyanates such as hexamethylene diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1, 4-cyclohexane diisocyanate, 1-methyl-2, 4-cyclohexane diisocyanate and 1-methyl-2, 6-cyclohexane diisocyanate and mixtures of the corresponding isomers, such as 4, 4 ' -dicyclohexylmethane diisocyanate, 2, 4 ' -dicyclohexylmethane diisocyanate and 2, 2 ' -dicyclohexylmethane diisocyanate and mixtures of the corresponding isomers; aromatic diisocyanates such as toluene-2, 4-diisocyanate, mixtures of toluene-2, 4-diisocyanate and toluene-2, 6-diisocyanate, 2, 4 '-diphenylmethane diisocyanate and 2, 2' -diphenylmethane diisocyanate, mixtures of 2, 4 '-diphenylmethane diisocyanate and 4, 4' -diphenylmethane diisocyanate; urethane-modified liquid 4, 4 ' -diphenylmethane diisocyanate or 2, 4 ' -diphenylmethane diisocyanate, 4, 4 ' -diisocyanatophenylethane (1, 2) and 1, 5-naphthalene diisocyanate. The following are preferred substances: 1, 6-hexamethylene diisocyanate, 1, 4-cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, isomeric mixtures of diphenylmethane diisocyanates containing more than 96% wt/wt of 4, 4' -diphenylmethane diisocyanate; particularly preferred are 4, 4' -diphenylmethane diisocyanate and 1, 5-naphthalene diisocyanate. The diisocyanates mentioned can be used individually or in the form of their mixtures with one another. They may also be used with up to 15 mol% (relative to the total diisocyanate moles) of polyisocyanate. However, the maximum amount of polyisocyanate added must be such that a product is formed which is still thermoplastically processable. Examples of polyisocyanates include triphenylmethane-4, 4', 4 "-triisocyanate and polyphenyl-polymethylene-polyisocyanates.

Linear, hydroxyl-terminated polyols having an average molecular weight M_n500-.Due to their method of production, these materials often contain small amounts of nonlinear compounds. Thus, such materials are also commonly referred to as "substantially linear polyols". These substances are also suitable. Polyester-, polyether-or polycarbonate diols or mixtures thereof are therefore preferably used.

Suitable polyether polyols (polyether diols) can be obtained by reacting one or more alkylene oxides containing 2 to 4 carbon atoms in the alkylene radical with a starter molecule containing two active hydrogen atoms. Examples of alkylene oxides include: ethylene oxide, 1, 2-propylene oxide, chloropropylene oxide, 1, 2-butylene oxide and 2, 3-butylene oxide. Ethylene oxide, propylene oxide and mixtures of 1, 2-propylene oxide and ethylene oxide are preferably used. The alkylene oxides can be used individually or as mixtures. Examples of suitable starter molecules include: water, aminoalcohols, such as N-alkyl-diethanolamine, for example N-methyl-diethanolamine, and diols, such as ethylene ethanol, 1, 3-propanediol, 1, 4-butanediol and 1, 6-hexanediol. Mixtures of starter molecules may also be used with preference. Other suitable polyether alcohols are the polymerization products of tetrahydrofuran, which products contain hydroxyl groups. Trifunctional polyethers can also be used in amounts of 0 to 30% wt/wt, relative to the bifunctional polyethers. However, the maximum amount of trifunctional polyethers used must be such that the products obtained are still thermoplastically processable. The substantially linear polyether diols preferably have an average molecular weight M_n500-. They can be used either individually or in the form of mixtures with one another.

Suitable polyester polyols (polyester diols) can be obtained, for example, from dicarboxylic acids comprising 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric alcohols. Examples of suitable dicarboxylic acids include: aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid, or aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids may be used alone or as mixtures, for example as mixtures of succinic, glutaric and adipic acids. It may be advantageous to produce polyester diols with the corresponding dicarboxylic acid derivatives, such as dicarboxylic acid diesters containing 1 to 4 carbon atoms in their alcohol radical, dicarboxylic acid anhydrides or dicarboxylic acid chlorides, instead of the dicarboxylic acids. Examples of the polyhydric alcohol include glycols having 2 to 10 carbon atoms, preferably glycols having 2 to 6 carbon atoms, such as ethylene glycol, diethylene glycol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 10-decanediol, 2, 2-dimethyl-1, 3-propanediol, 1, 3-propanediol and dipropylene glycol. These polyols may be used alone or in a mixture with one another, depending on the desired properties. Carbonates of said diols are also suitable, in particular those containing from 4 to 6 carbon atoms, such as 1, 4-butanediol or 1, 6-hexanediol, condensation products of omega-hydroxycarboxylic acids, such as omega-hydroxycaproic acid, or polymerization products of lactones, such as polymerization products of omega-caprolactone, which products are optionally substituted. Polyadipates of ethylene glycol, 1, 4-butanediol polyadipates, ethanediol-1, 4-butanediol polyadipates, 1, 6-hexanediol-neo-pentanediol polyadipates, 1, 6-hexanediol-1, 4-butanediol polyadipates and polycaprolactones are preferably used as polyester diols. These polyester diols have an average molecular weight Mn of 500-.

The chain extenders 3) used may be diols or diols with small amounts of diamines having a molecular weight of from 60 to 400. Preferred aliphatic diols contain 2 to 14 carbon atoms, such as ethylene glycol, 1, 6-hexanediol, diethylene glycol, dipropylene glycol and particularly preferably 1, 4-butanediol. However, the maximum amount of diamine used must be such that the product obtained is still thermoplastically processable. Suitable chain extenders also include terephthalic diesters of diols having from 2 to 4 carbon atoms, for example p-phthalic-bis-ethylene glycol ester or p-phthalic-bis-1, 4-butanediol ester, hydroxyalkyl ethers of hydroquinone, such as 1, 4-bis (. beta. -hydroxyethyl) -hydroquinone, ethoxylated bisphenols, such as 1, 4-bis (. beta. -hydroxyethyl) -bisphenol A, (cyclo) aliphatic diamines, such as isophoronediamine, ethylenediamine, 1, 2-propylenediamine, 1, 3-propylenediamine, N-methyl-propane-1, 3-diamine or N, N' -dimethylethylenediamine and aromatic diamines, such as 2, 4-diaminotoluene, 2, 6-diaminotoluene, 3, 5-diethyl-2, 4-diaminotoluene or 3, 5-diethyl-2, 4-diaminotoluene, or primary mono-, di-, tri-or tetra-alkyl-substituted-4, 4' -diaminodiphenylmethane. Ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol, 1, 4-bis (. beta. -hydroxyethyl) -hydroquinone or 1, 4-bis (. beta. -hydroxyethyl) -bisphenol A are preferably used as chain extenders. Mixtures of the above chain extenders may also be used. In addition, small amounts of triols can also be added. However, the maximum amount of triol used must be such that the product obtained is still thermoplastically processable.

Conventional monofunctional compounds may also be added in small amounts, for example as chain extenders or release agents. Examples thereof include alcohols such as octanol and stearyl alcohol or amines such as butylamine and stearylamine.

TPUs may be obtained from the abovementioned synthesis components, optionally in the presence of catalysts, auxiliary substances and/or additives. The reaction of the synthesis components is carried out in such quantities that the equivalent ratio of NCO groups to the total amount of those groups which are reactive with NCO (in particular the OH groups of low molecular weight diols/triols or polyols) is from 0.9: 1.0 to 1.1: 1.0. The preferred ratio is 0.95: 1.0-1.10: 1.0.

Suitable catalysts include the customary tertiary amines known from the prior art, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N' -dimethylpiperazine, 2- (dimethylamino-ethoxy) ethanol, diazabicyclo [2, 2, 2] octane and the like, and in particular metal organic compounds, such as titanates, iron compounds or tin compounds, such as stannous acetate, stannous octoate, stannous laurate or the dialkyltin salts of aliphatic carboxylic acids, such as dibutyltin diacetate or dibutyltin dilaurate or the like. Preferred catalysts are metal organic compounds, in particular titanic acid esters, iron compounds and tin compounds.

Examples of suitable auxiliary substances include internal lubricants such as fatty acid esters and their metal soaps, fatty acid amides, fatty acid ester amides, and silicon compounds, anti-elongation agents, inhibitors, stabilizers against hydrolysis, light, heat and discoloration, flame retardants, colorants, pigments, inorganic and/or organic fillers and reinforcing agents. In particular, reinforcing agents include fibrous reinforcing materials such as inorganic fibers, which may be produced, for example, according to the prior art, or may be coated with a sizing. More detailed materials of the aforementioned auxiliary substances and additives are published in the specialist literature, for example in J.H.Saunders and K.C.Frisch, the "high polymers" polyurethane, volume XVI, parts 1 and 2, Interscience publishers, 1962 and 1964 respectively, and R, Gachter and H.Muller, Taschenbuch fur Kunststoff-Additive (Hanser Verlag Munich 1990) or in the DE-A2901774 patent literature.

Other additives included in the TPU include thermoplastic additives such as polycarbonate and acrylonitrile/butadiene/styrene terpolymer, particularly ABS. Other elastomers may also be included, such as rubbers, ethylene/vinyl acetate copolymers, styrene/butadiene copolymers and other TPUs. Other materials suitable for processing include commercially available plasticizers such as phosphates, phthalates, adipates, sebacates, and alkyl sulfonates.

TPU A) ("non-rigid component") is obtained by adjusting the molar ratio of polyol to chain extender and has a Shore A hardness of from 60 to 75, preferably from 65 to 70.

TPU A) can be produced batchwise or continuously. The most notable industrial processes are the belt transport process (GB-A1057018) and the extrusion process (DE-A1964834, DE-A2059570 and US-A5795948).

TPU B) ("rigid component") is also obtained by adjusting the molar ratio of polyol to chain extender, and has a Shore A hardness of from 76 to 90, preferably from 82 to 88.

TPU B) is produced in a multistage process (analogously to EP-A0816407) as follows:

in step b), the amounts of the reaction components are selected such that the ratio NCO: OH of the fraction 1 of the diisocyanate 1) and of the polyol 2) is from 2.0: 1 to 5.0: 1, preferably the NCO/OH ratio is from 2.05: 1 to 3.0: 1, in order to form a prepolymer. In a processing unit that provides high shear energy, the components are mixed continuously. A mixer head, preferably a high-speed gear-tumbler mixer, a static mixer or a jet mixer can be used.

In step b), the prepolymer reaction is carried out continuously in a reactor, for example in a pipeline reactor. A pipe comprising a static mixer or an agitated pipe (pipe mixer) with a length/diameter ratio higher than 4: 1 is preferably used.

In a particularly preferred embodiment, steps a) and b) are carried out in a jet/pipe apparatus with static mixers, or in a pipe mixer.

According to the invention, the prepolymer reaction in step b) should be carried out to essentially complete conversion, i.e.a conversion of more than 90 mol%, relative to the polyol. The reaction temperature is above 120 ℃, and the preferable reaction temperature is 140-220 ℃.

In step c), part 2 of the diisocyanate 1) is rapidly mixed. To achieve this, one or more static mixers are preferably used in the pipeline. A jet mixer, a mixer head or a mixing element of an extruder may also be used.

The mixture formed in step c) is cooled in step d) to a temperature below 190 ℃, preferably below 170 ℃. Cooled pipes, if necessary, or cooled parts of the extruder with feed parts are also suitable devices for this purpose. Preferably, the cooling is carried out in an extruder with external cooling of the twin screws.

In step e), the chain extender 3) is mixed with the cooled prepolymer mixture within 5 seconds. A mixer unit operating with high switching energy is also preferred for this step. Examples include a mixer head, mixer gun or a small volume high speed peristaltic extruder. The intensive mixing action is preferably carried out by means of mixer elements of the extruder.

In step (f), the reacted mixture is continuously reacted in an extruder, such as a twin screw extruder, to form a thermoplastic polyurethane. The reaction temperature is 140-250 ℃. During this step, the cavity of the extruder is heated or in a second way it is neither heated nor cooled, allowing the direct generation of thermal radiation to the surroundings. This form of temperature control is referred to as a "quasi-adiabatic" approach.

According to the invention, the TPUs A) (non-rigid) and B) (rigid) can be mixed in commercially available powder mixers to give the molding compositions. The TPUs A) and B) can, of course, be mixed in conventional thermoplastic processing steps, for example by extrusion and conversion to homogeneous pulverulent materials, under molten conditions, before the actual further processing.

According to the invention, the molding compositions are very soft (65-85 Shore A) and have good mechanical properties. They are easily demoulded when they are processed by injection moulding. Parts injection molded from them have good mold release stability due to their low shrinkage.

According to the invention, the molding compositions are used for producing non-rigid, flexible injection-molded parts, such as shoe soles, stem caps, expansion bellows and dust caps, and for producing extruded parts, such as plates, films and cut sheets. The molding compositions can also be combined with other thermoplastic materials and processed by multicomponent injection molding and/or coextrusion.

The present invention is illustrated in more detail by the following examples.

Examples

The method comprises the following steps: static mixer/ZSK multistep process

The polyester, in which 150ppm of stannous dioctoate (relative to the polyester) as catalyst had been dissolved, was heated to 150 ℃ and continuously metered into a static mixer (manufactured by Sulzer). Part 1(2.45 mol) of 4, 4' -diphenylmethane diisocyanate (60 ℃) was simultaneously pumped into a static mixer. In the static mixer, 99% (relative to the polyester) conversion to prepolymer was complete within 30 seconds. Part 2(1.09 mol) of 4, 4' -diphenylmethane diisocyanate was mixed with the prepolymer by a first static mixer (manufactured by Sulzer) for 5 seconds. The reaction mixture was metered into the chamber 1 of ZSK83 (manufactured by Werner & Pfleiderer) and cooled therein to about 140 ℃ in the lower chamber. 0.4% wt/wt (relative to TPU) of bis-ethylene-octadecanamide is added to the cavity 1.1, 4-butanediol is added to the chamber 5 and mixed with the prepolymer-MDI mixture in such a way that the mixing action is intensified in a short mixer element located below the chamber 6.

In the final part of the extruder, the reaction components react to form TPU. The reaction temperature was 150 ℃ and 220 ℃. The rotation speed of the worm is 300 rpm.

At the end of the extruder, the hot melt is extruded in the form of threads and cooled in a water bath and then granulated.

The method 2 comprises the following steps: static mixer single step process

The polyester was charged into a vessel containing butanediol and heated to about 200 ℃ and the mixture was continuously fed into a static mixer (manufactured by Sulzer) together with 4, 4' -diphenylmethane diisocyanate heated to 180 ℃. 250ppm (relative to the polyester) of stannous dioctoate was dissolved in the polyester as catalyst. Downstream of the static mixer, where the residence time is about 1 second, the product stream is fed into the first chamber of the Welding extruder (temperature about 200 ℃). 0.8% wt/wt (relative to TPU) of dietheneoctadecanamide was added continuously to the above-mentioned chamber. The rotation speed of the worm is 110 rpm. At the end of the extruder, the polymer melt was pelletized by an underwater pelletizer (manufactured by Gala).

The method 3 comprises the following steps: hybrid head/belt single step process

The polyester, in which 150ppm (relative to the polyester) of stannous dioctoate as catalyst was dissolved, was heated to 150 ℃ and continuously mixed together with butanediol and 4, 4' -diphenylmethane diisocyanate (60 ℃) in the mixing head. The resulting reaction mixture was deposited directly onto a conveyor belt which was continuously passed through a heating zone at 140 ℃ for about 3 minutes. The solidified melt was fed into ZSK83 (temperature: 140 ℃ C.) at the end of the conveyor belt. 0.4% wt/wt (relative to TPU) of bis-ethyleneoctadecylamide is added in the middle of the extruder. The extruder was rotated at a speed of 300 rpm. At the end of the extruder, the hot melt is extruded in the form of threads, cooled in a water bath and granulated.

The method 4 comprises the following steps: ZSK double-step method

A polyol, in which 150ppm (relative to the polyol) of stannous dioctoate as a catalyst was dissolved, was heated to 140 ℃ and continuously added into a first cavity of ZSK83 (manufactured by Wermer/Pfleiderer). All 4, 4' -diphenylmethane diisocyanate (60 ℃) was added to the same chamber. 1, 4-butanediol is continuously added to the chamber 7. The 13 th cavity of the ZSK was gradually heated from 140 ℃ to 240 ℃. The worm has a rotational speed of 300 rpm. The rate of addition was adjusted so that the residence time of the reaction components in the ZSK was approximately 1 minute. At the end of the extruder, the hot melt is extruded in the form of threads, cooled in a water bath and granulated.

The method 5 comprises the following steps: one step stir head/cast plate process

The polyester, in which 20ppm (relative to the polyester) of titanyl acetylacetonate was dissolved as a catalyst, was heated to 180 ℃ and mixed together with butanediol and 4, 4' -diphenylmethane diisocyanate (60 ℃) in a reaction vessel by stirring (2000 rpm). After one minute, the obtained product was cast into a plate and annealed at 140 ℃ for 30 minutes.

The annealed and cooled plate is cut and crushed.

The TPU powders were mixed and processed to injection-molded parts according to the data in Table 2.

Production of injection-molded parts

In a D60 injection molding machine (work 32) from Mannesmann, the TPU powder is melted (material temperature about 225 ℃) and molded into bars (molding temperature; 40 ℃; bar size: 80X 10X 4 mm) or into plates (molding temperature: 40 ℃; 125X 50X 2 mm).

Determination of the experiment

The hardness measurement is carried out in accordance with DIN53505 and the 100% modulus measurement is carried out in accordance with DIN 53504.

The shrinkage, which is important for the evaluation of the processability of injection-molded parts, is determined in accordance with DIN 16770(Part 3).

The relative shrinkage measurements after annealing (80 ℃/15 hours) of the injection molded parts are shown in Table 2 as a percentage of the length of the part.

From the test results it can be seen that non-rigid TPUs for injection-moulded parts having low shrinkage (< 2.5%) can be obtained according to the invention by a mixture comprising TPU B, the rigidity/non-rigidity ratio of which is from 90/10 to 50/50.

Blends with ratios less than 50/50 showed significantly increased shrinkage (comparative examples 4 and 5), which was unacceptable to the injection molding industry.

Mixtures containing TPUs of the same hardness, but not according to the invention (comparative examples 6 and 7) have similar results with an increase in shrinkage. With a Shore A hardness of 75. + -.2, but not a (rigid/non-rigid) TPU mixture (comparative agent 8) also showed an increase in shrinkage.

TABLE 2: test results

Test of	TPU B rigidity	TPU A is not rigid	TPU B/TPU A	Properties of the Molding compositions
										Parts by weight/parts by weight	Hardness (Shore A)	100% modulus [ MPa ]]	Percentage of shrinkage [% ]]
1	TPU 1	TPU 2	90/10	84	5.1	1.1
							2	TPU 1	TPU 2	70/30	76	4.5	1.9
3	TPU 1	TPU 2	50/50	76	3.7	2.3
							4*	TPU 1	TPU 2	45/55	74	3.9	5.8
5*	TPU 1	TPU 2	40/60	75	3.8	7.0
							6*	TPU 3	TPU 2	50/50	82	4.2	2.7
7*	TPU 4	TPU 2	50/50	76	3.7	3.5
							8*			100 TPU 5	73	4.4	2.7

^*Comparative example

TABLE 1: TPUs compositions

TPU	TPU raw material polyester molecular weight [ mol]	Chain extender [ mol ]]Diisocyanate 1		[ mols ] of]	Hardness of	Production method
							1	Butanediol adipate 20001.00 diacid ester	Butanediol 2.5	MDI	3.5	85 Shore A	A multi-step process: method 1
2	Butanediol adipate 14501.00 diacid ester	Butanediol 0.9	MDI	1.9	68 Shore A	One step method: method 2
							3	Butanediol adipate 20001.00 diacid ester	Butanediol 2.4	MDI	3.5	85 Shore A	One step method: method 3
4	Butanediol adipate 22001.00 diacid ester	Butanediol 2.6	MDI	3.6	85 Shore A	The two-step method comprises the following steps: method 4
							5	Butanediol adipate 18001.00 diacid ester	Butanediol 1.6	MDI	2.6	73 Shore A	One step method: method 5

Claims (3)

1. A thermoplastic molding composition having a Shore A hardness of from 65 to 85, as determined in accordance with DIN53505, and a shrinkage of less than 2.5, as determined in accordance with DIN 16770, and comprising, as constituents of a mixture:

A) 5-54 parts by weight of a first thermoplastic polyurethane derived from an organic diisocyanate, a linear polyester polyol and/or a polyether polyol having a number average molecular weight of 500-5000 and a chain extender diol having a molecular weight of 60-400, said first thermoplastic polyurethane having a Shore A hardness of 60-75, and

B) 95-46 parts by weight of a second thermoplastic polyurethane, the continuous process for its preparation comprising,

a) mixing an organic diisocyanate and at least one substantially linear, 5000 number average molecular weight polyol selected from the group consisting of polyether polyols and polyester polyols at an NCO/OH ratio of 2.0: 1 to 5.0: 1 under high shear conditions to form a first mixture, and,

b) reacting the components of said first mixture in a reactor at a temperature above 120 ℃ to a conversion of above 90% relative to said polyol and to form an isocyanate-terminated prepolymer, and

c) said prepolymer being mixed with added organic diisocyanate so that the NCO/OH ratio is from 2.05: 1 to 6.0: 1, to form a second mixture, and

d) cooling said second mixture to a temperature of less than 190 ℃, and

e) continuously mixing said second mixture with at least one chain extender diol having a molecular weight of 60-400 for up to 5 seconds to obtain a third mixture, and

f) continuously reacting the components of said third mixture in an extruder to form said second thermoplastic polyurethane,

said second thermoplastic polyurethane being characterized in that it has an NCO: OH ratio of 0.9: 1 to 1.1: 1 and a Shore A hardness of 76 to 90; said composition is characterized by its easy release from a mold and by low molding shrinkage in the absence of a plasticizer.

2. The composition of claim 1 wherein the organic diisocyanates, both together and independently of each other, are at least one compound selected from the group consisting of: 4, 4 '-diphenylmethane diisocyanate, isophorone diisocyanate, 1, 6-hexamethylene diisocyanate, 1, 5-naphthalene diisocyanate and 4, 4' -dicyclohexyl diisocyanate.

3. The composition of claim 1 wherein both the chain extender diols are, together and independently of each other, at least one compound selected from the group consisting of: 1, 6-hexanediol, 1, 4-butanediol, ethylene glycol and 1, 4-bis (. beta. -hydroxyethyl) -hydroquinone.