HK1056186B - A process for the preparation of soft, low-shrinkage, thermoplastic polyurethane elastomers which can be easily released from the mold - Google Patents

Description

Method for preparing soft low-shrinkage thermoplastic polyurethane elastomer easy to demould

Technical Field

The invention relates to a process for preparing soft, low-shrinkage thermoplastic polyurethane molding compositions which are easy to demold and have good low-temperature properties, good mechanical properties and a hardness of 45 to 65 Shore A.

Background

Thermoplastic polyurethane elastomers (TPU) have been known for a long time. TPU's are of industrial importance because of the well-known advantages of high-quality mechanical properties and inexpensive thermoplastic processability. A wide range of mechanical properties can be achieved by using various chemical components. An overview of TPUs and their properties and uses is described, for example, in Kunststoffe 68(1978), 819 or in Kautschuk, Gummi, Kunststoffe 35(1982), 568.

TPUs are formed from linear polyols (usually polyester polyols or polyether polyols), organic diisocyanates and short-chain diols (chain extenders or chain extenders). Additionally, a catalyst may be added to accelerate the formation reaction. To adjust the properties, the composition can be varied within a wide molar ratio. Molar ratios of polyol to chain extender/chain extender of from 1: 1 to 1: 12 have proven suitable. This generally results in a product characterized by a hardness in the range of 80 shore a to 75 shore D.

The hardness of a TPU is established primarily by the ratio of hard segments (chain extender/chain extender + isocyanate) to soft segments (polyol + isocyanate). If the amount of hard segments is reduced beyond the limit of the 80 Shore A hardness, the resulting product is tacky, cures poorly, has poor mold release during injection molding, and shrinks severely.

Such TPUs do not guarantee an economically viable number of injection molding cycles and sufficient dimensional accuracy of the injection molding components. In addition, initial soft segment crystallization at temperatures slightly below room temperature generally results in a significant increase in hardness and a decrease in elastomeric properties at these low temperatures, making such TPUs less valuable for use at low temperatures.

EP-A0134455 shows that by using plasticizers formed from specific phthalates and phosphates, TPUs with a Shore A hardness of from 60 to 80 are obtained. However, these plasticized TPUs have the same disadvantages as all plasticized plastics, owing to the use of plasticizers, for example the problem of bleeding of the plasticizer during the post-hardening and the odor. Stress cracking occurs when they come into contact with rigid thermoplastics.

EP-A1031588 describes soft polyurethane molding compositions with low shrinkage in the range from 76 to 84 Shore A hardness, in which 68 Shore A hardness TPU A is mixed with 85 Shore A hardness TPU B. The harder TPU B used is prepared by a specific prepolymer procedure in which the polyol is reacted with the diisocyanate in a molar ratio NCO: OH of 1: 2.05 to 1: 6.0, so that the shrinkage of the mixture is reduced and good dimensional accuracy is achieved. This method is of course limited at very low shore a values in the range below 75 shore a hardness.

In DE-A19939112, the previously prepared TPUs having a Shore D hardness of 30 to 80 are degraded in the first stage of the extruder with the addition of low molecular weight diols to give large hard segment blocks; a new soft TPU is then prepared in the second stage with addition of isocyanate, polyol and catalyst. These TPUs have good mechanical values and low abrasion. The preparation process is complicated and it is therefore difficult to maintain the TPU properties in a controlled manner. In addition, the ease of mold release in injection molding is not particularly good.

DE-A2842806 describes the production of TPUs in twin-screw kneaders under specific shear conditions, wherein one or both monomer streams are subdivided into at least two portions. TPUs with improved low temperature Izod impact strength and improved toughness, i.e.Shore hardnesses higher than 57 Shore D, are obtained.

DE-A4217367 describes TPUs in the hardness range from 70 Shore A to 75 Shore D, which are obtained by a multistage reaction, characterized in that in a first stage, a macrodiol is reacted with a diisocyanate in a ratio of 1: 1 to 5.0: 1, in a second stage, the remainder of the diisocyanate is added, and in a third stage, the reaction with a chain extender is carried out. The products obtained have improved release properties and improved stability under load, while maintaining the same hardness and low temperature properties. TPUs softer than 70 Shore A cannot be obtained with polyesters and polyethers as described in the examples using the process described in this reference. If the amount of hard segments is reduced below the stated limit of 70 Shore A, the resulting product can retain its hardness range only for a short time due to crystallization of the soft segments and subsequently harden to a large extent upon storage or heating.

It was therefore an object of the present invention to provide a process by which very soft TPUs in the range from 45 to 65 Shore A can be prepared, which at the same time are easy to demould, have a very low shrinkage and, in addition, have a high elasticity at low temperatures.

This object can be achieved according to the process for preparing a thermoplastic polyurethane elastomer of the present invention.

Disclosure of Invention

The invention provides a process for preparing thermoplastically processable polyurethane elastomers which are easy to demould, have a Shore A hardness of from 45 to 65 (measured according to DIN 53505), a tensile strength of greater than 12MPa (measured according to ISO 37), a shrinkage of ≦ 3.5% (measured according to DIN 16770 part 3), and a DMA storage energy at-10 ℃ under tension E modulus of less than 20MPa (the measurement of E modulus will be explained in more detail in the examples section), which comprises reacting, optionally in the presence of a catalyst:

A) one or more hydroxyl terminated linear polyols selected from the group consisting of:

a) polyester polyols having a number average molecular weight of 450-,

b) a mixture of at least two polyester polyols having different number average molecular weights in the range of 450-,

c) a mixture of at least two polyether polyols having different number average molecular weights in the range of 450-,

d) polyether polyol having a number average molecular weight of 450-,

e) a polyether polyol containing an oxyalkylene unit and having a number average molecular weight of 450-1500,

with one or more organic diisocyanates in a molar NCO/OH ratio of from 1.1: 1 to 1.9: 1, preferably from 1.1: 1 to 1.7: 1, to form an isocyanate-terminated prepolymer,

B) the prepolymer obtained in step A) is preferably mixed with the same organic diisocyanate as in step A),

C) reacting the mixture obtained in step B) with one or more glycol chain extenders having a molecular weight of 60 to 400,

wherein the NCO: OH molar ratio of the components used in A), B) and C) is adjusted to 0.9: 1 to 1.1: 1, and wherein the ratio of the hydroxyl groups of the polyol to the hydroxyl groups of the chain extender is 0.3: 1 to 2.0: 1, particularly preferably 0.4: 1 to 1.5: 1.

Detailed Description

Organic diisocyanates which may be used include, for example, aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as described, for example, in Justus Liebigs Annalen der Chemie, 562, pages 75-136.

Diisocyanates which may be mentioned in particular include, for example, aliphatic diisocyanates, such as 1, 6-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 the corresponding isomer mixtures, 4, 4 ' -dicyclohexylmethane diisocyanate, 2, 4 ' -dicyclohexylmethane diisocyanate and 2, 2 ' -dicyclohexylmethane diisocyanate and the corresponding isomer mixtures; aromatic diisocyanates, for example 2, 4-tolylene diisocyanate, mixtures of 2, 4-tolylene diisocyanate and 2, 6-tolylene diisocyanate, 4, 4 '-diphenylmethane diisocyanate, 2, 4' -diphenylmethane diisocyanate and 2, 2 '-diphenylmethane diisocyanate, mixtures of 2, 4' -diphenylmethane diisocyanate and 4, 4 '-diphenylmethane diisocyanate, polyurethane-modified liquid 4, 4' -diphenylmethane diisocyanate or 2, 4 '-diphenylmethane diisocyanate, 4, 4' -diisocyanato-1, 2-diphenylethane and 1, 5-naphthylene diisocyanate, 1, 6-hexamethylene diisocyanate, 1, 4-cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, isomer mixtures of diphenylmethane diisocyanates, where the content of 4, 4 '-diphenylmethane diisocyanate is greater than 96% by weight, 4, 4' -diphenylmethane diisocyanate and 1, 5-naphthalene diisocyanate. The diisocyanates can be used individually or in the form of mixtures. They can also be used with up to 15 mol% (calculated with respect to the total amount of diisocyanate) of polyisocyanate, but the maximum amount of polyisocyanate added is such that a product is formed which is still thermoplastically processable. Examples of polyisocyanates are triphenylmethane-4, 4' -triisocyanate and polyphenyl polymethylene polyisocyanates.

Hydroxyl-terminated linear polyols are used as polyols. These generally contain small amounts of nonlinear compounds due to their preparation. They are also commonly referred to as "substantially linear polyols".

Suitable polyether diols can be obtained, for example, by reacting one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene radical with a starter molecule which contains two active hydrogen atoms in bonded form. Alkylene oxides which may be mentioned include, for example, ethylene oxide, 1, 2-propylene oxide, epichlorohydrin and 1, 2-butylene oxide and 2, 3-butylene oxide. Preference is given to using ethylene oxide, propylene oxide and mixtures of 1, 2-propylene oxide and ethylene oxide. The alkylene oxides can be used individually, alternately in succession or as mixtures. Feedstock molecules that can be used are, for example, water; aminoalcohols, for example N-alkyldiethanolamines, for example N-methyldiethanolamine; diols, such as ethylene glycol, 1, 3-propanediol, 1, 4-butanediol and 1, 6-hexanediol, optionallyA mixture of feedstock molecules. Examples of suitable polyether polyols are furthermore the polymerization products of hydroxyl-containing tetrahydrofuran. It is also possible to use from 0 to 30% by weight, based on the difunctional polyether, of a trifunctional polyether, but in such a maximum amount that a still thermoplastically processable product is formed. Number average molecular weight of substantially linear polyether diolsPreferably 450-.

Polyethers having at least two different alkylene oxide groups are preferably used and can be obtained, for example, by reacting a mixture of ethylene glycol and 1, 3-propanediol, a mixture of ethylene glycol and butanediol, a mixture of 1, 3-propanediol and butanediol, a mixture of butanediol and 1, 5-pentanediol or a mixture of butanediol and neopentyl glycol. The number average molecular weight of these polyethers is preferably 450-.

In addition, mixtures of at least two polyether diols having different number average molecular weights in the range of 450-. Polyethers of different number average molecular weights in the mixture can be obtained with different alcohols and/or from chain lengths when the same alcohol is used.

Polyether diols which contain an alkylene oxide unit and have a number average molecular weight Mn of 450-1500 are also preferred.

Suitable polyester diols can be prepared, for example, from dicarboxylic acids having from 2 to 12 carbon atoms, preferably from 4 to 6 carbon atoms, and polyhydric alcohols. Examples of such 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 can be used individually or as mixtures, for example in the form of succinic, glutaric and adipic acid mixtures. For the preparation of the polyester diols, it may optionally be advantageous to use, instead of the dicarboxylic acids, the corresponding dicarboxylic acid derivatives, for example carboxylic acid diesters having l to 4 carbon atoms in the alcohol radical, carboxylic acid anhydrides or acid chlorides. Examples of polyols are diols having 2 to 10, preferably 2 to 6, carbon atoms, including, for example, ethylene glycol, diethylene glycol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 10-decanediol, 2-dimethyl-1, 3-propanediol, 1, 3-propanediol or dipropylene glycol. The polyols may be used as such or as mixtures, depending on the desired properties. Esters of carbonic acid with the diols, in particular those having 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 optionally substituted omega-caprolactones, are also suitable. Polyester diols preferably used include ethylene glycol polyadipates, 1, 4-butanediol polyadipates, ethylene glycol-1, 4-butanediol polyadipates, 1, 6-hexanediol-neopentyl glycol polyadipates, 1, 6-hexanediol-1, 4-butanediol polyadipates and polycaprolactones.

The number average molecular weight of the polyester diol used450-.

Preference is given to using polyesters which can be prepared from at least two different polyols and one or more dicarboxylic acids having up to 12 carbon atoms, for example ethanediol-1, 4-butanediol polyadipate, 1, 6-hexanediol-neopentyl glycol polyadipate and 1, 6-hexanediol-1, 4-butanediol polyadipate.

It is also possible to use mixtures of polyesters having different molecular weights. Polyesters of different molecular weights in the mixture can be obtained using different polyols and/or dicarboxylic acids and/or by chain length when using the same alcohols and dicarboxylic acids.

Chain extenders or chain extenders useful in the present invention include diols having a molecular weight of 60 to 400, optionally in combination with small amounts of diamines, preferably aliphatic diols having 2 to 14 carbon atoms, such as ethylene glycol, 1, 6-hexanediol, diethylene glycol, dipropylene glycol, ethylene glycol, and particularly 1, 4-butanediol. However, diesters of terephthalic acid with diols having from 2 to 4 carbon atoms, such as, for example, bis-ethylene terephthalate or bis-1, 4-butylene terephthalate; hydroxyalkyl ethers of hydroquinone, such as 1, 4-di (. beta. -hydroxyethyl) -hydroquinone; ethoxylated bisphenols, such as 1, 4-bis (β -hydroxyethyl) -bisphenol a; (cyclo) aliphatic diamines such as isophorone diamine, ethylene diamine, 1, 2-propylene diamine, 1, 3-propylene diamine, N-methyl-propane-1, 3-diamine, and N, N' -dimethylethylene diamine; and aromatic diamines, such as 2, 4-toluenediamine, 2, 6-toluenediamine, 3, 5-diethyl-2, 4-toluenediamine or 3, 5-diethyl-2, 6-toluenediamine or primary mono-, di-, tri-or tetraalkyl-substituted 4, 4' -diaminodiphenylmethanes. Ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol, 1, 4-di (. beta. -hydroxyethyl) -hydroquinone or 1, 4-di (. beta. -hydroxyethyl) -bisphenol A are preferably used as chain lengtheners/extenders. Mixtures of the above chain extenders/chain extenders may also be used. In addition, minor amounts of triols may be added.

Conventional monofunctional compounds may also be added in small amounts, for example as chain terminators or mold release aids. Examples which may be mentioned are alcohols, such as octanol and stearyl alcohol, or amines, such as butylamine and stearylamine.

To prepare the TPUs, the coagent components, optionally in the presence of catalysts, the coagent substances and/or additives may be used in such amounts that the equivalent ratio of NCO groups to the sum of the NCO-reactive groups, in particular the hydroxyl groups of the low-molecular-weight diols/triols and polyols, is from 0.9: 1.0 to 1.1: 1.0, preferably from 0.95: 1.0 to 1.10: 1.0.

Suitable catalysts according to the invention include the customary tertiary amines known in the art, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N' -dimethylpiperazine, 2- (dimethylaminoethoxy) -ethanol, diazabicyclo [2.2.2] -octane and the like, and in particular organometallic compounds, such as titanic acid esters, iron compounds, or tin compounds, such as tin diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic carboxylic acids, such as dibutyltin diacetate or dibutyltin dilaurate, for example. Preferred catalysts are organometallic compounds, in particular titanic acid esters and iron and tin compounds. The total amount of catalyst in the TPU is generally from about 0 to about 5 weight percent, preferably from 0 to 1 weight percent, based on 100 weight percent of the TPU.

In addition to the TPU components and the catalyst, auxiliaries and/or additives may also be added. Some examples which may be mentioned include lubricants, such as fatty acid esters, metal soaps thereof, fatty acid amides, fatty acid ester-amides and silicone compounds, antiblocking agents, inhibitors, stabilizers against hydrolysis, light, heat and discoloration, flame retardants, dyes, pigments, inorganic and/or organic fillers and reinforcing agents. Reinforcing agents are in particular fibrous reinforcing substances, for example inorganic fibers, which are prepared by the prior art and can be added together with the size. Further details regarding said auxiliaries and additives are described in the technical literature, for example in J.H.Saunders and K.C.Frisch "High Polymers", Vol.XVI, Polyurethane, parts 1 and 2, Verlag Interscience publishers 1962 and 1964, the Taschenbuch fur Kunststoff-Additive (Hanse Verlag Munich1990) or DE-A2901774.

Other additives which have been incorporated into TPUs include thermoplastics such as polycarbonates and acrylonitrile/butadiene/styrene terpolymers, in particular ABS. Other elastomers such as rubber, ethylene/vinyl acetate copolymers, styrene/butadiene copolymers and other TPUs may also be used. It is also suitable to incorporate commercially available plasticizers such as phosphates, phthalates, adipates, sebacates and alkyl sulfonates.

The TPU of the invention is adjusted to a shore a hardness of 45-65 by adjusting the molar ratio between the polyol and the chain extender/chain extender.

The TPU is prepared by the following steps.

To form the isocyanate-terminated prepolymer of step A), the relative amounts of the reaction components used are selected such that the NCO/OH ratio of the diisocyanate to the polyol in step A) is from 1.1: 1 to 1.9: 1, preferably from 1.1: 1 to 1.7: 1.

The components are mixed thoroughly and the prepolymer reaction of step a) preferably achieves substantially complete conversion (based on the polyol component).

Then, in step B), an additional amount of diisocyanate, preferably the same diisocyanate as used in step A), is added.

Then, the chain extender/chain extender is thoroughly mixed in step C) to complete the reaction.

The TPUs of the invention may be prepared discontinuously or continuously. The best known industrial preparation processes for this purpose are the belt process (as described, for example, in GB-A1057018, the disclosure of which is incorporated herein by reference) and the extruder process (as described, for example, in DE-A1964834, DE-A2059570 and US-A5795948, the disclosure of which is incorporated herein by reference).

Known mixing devices, preferably those operated with high shear energy, are suitable for preparing TPUs. Examples which may be mentioned for the continuous preparation are co-kneaders, preferably extruders, such as twin-screw extruders, and Buss kneaders.

The TPU may be prepared, for example, on a twin screw extruder, wherein the prepolymer is prepared in a first stage of the extruder, then the diisocyanate is added, and chain extension/chain extension is carried out in a second stage. The addition of the diisocyanate and the chain extender/extender can be carried out in parallel in the same metering opening of the extruder or preferably continuously in two different openings, but according to the invention the metering of the chain extender/extender should take place before the metering of the remainder of the diisocyanate, i.e. the second portion of diisocyanate.

However, the prepolymer can also be prepared outside the extruder in a different preceding prepolymer reactor, discontinuously in a kettle or continuously in a tube with a static mixer or stirred tube (tube mixer).

However, the prepolymer prepared in the separate prepolymer reactor can also be mixed with the diisocyanate by means of a first mixing device, for example a static mixer, and reacted with the chain extender/chain extender by means of a second mixing device, for example a mixing head. The reaction mixture is then continuously fed onto a support, for example a conveyor belt, in a manner similar to the known belt process, where the reaction mixture is reacted until the material has cured to form the TPU, optionally with heating of the belt.

The TPUs prepared by the process of the invention are very soft (45-65 Shore A) and have good mechanical properties. During the injection molding process, the components cure very rapidly and are therefore easily demolded. Due to the low shrinkage, the injection molded components have high dimensional accuracy and good thermal stability.

The TPUs prepared by the process of the invention still have very good elastic properties even at low temperatures (i.e.no crystallization of the soft segment), as indicated by their low modulus level at-10 ℃ in dynamic mechanical analysis (DMA: modulus of elasticity in tension).

The TPU prepared by the process of the invention is used for preparing soft, flexible injection-molded components, such as shoe heels, clamp caps, sealing parts and dust caps. In combination with other thermoplastics, products with satisfactory handling properties (hard-soft combinations) are obtained.

Extruded articles, such as profiles and hoses, can also be prepared therefrom.

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

The invention is illustrated in more detail by the following examples, but is not limited thereto, in which all parts and percentages are by weight unless otherwise indicated.

Examples

The following components were used in the preparation of the TPUs, the relative amounts of the components and the properties of the resulting TPUs being listed in tables 1 and 2.

Preparation of TPU:

step A):

according to table 1, the corresponding polyol (at 190 ℃) and a suitable first portion (i.e. portion 1) of 4, 4' -diphenylmethane diisocyanate (MDI) are heated to 60 ℃ in a reactor with stirring to achieve a conversion of more than 90 mol%, based on the polyol.

In examples 1 and 2, the reaction was catalyzed with 3ppm (based on polyol) Tyzor AA95 (available from Dupont), and in example 7, the reaction was catalyzed with 15ppm Tyzor AA 95.

Step B):

a second portion of MDI (i.e. portion 2) was added to the stirred reaction mixture obtained in step a).

Step C):

the butane-1, 4-diol was then thoroughly mixed into the mixture obtained in step B), and after about 15 seconds the reaction mixture was poured onto a coated metal sheet and post-conditioned at 120 ℃ for 30 minutes.

Table 1: components and relative amounts used to form the TPU

Examples	Polyhydric alcohols	Amount of polyol [ mol ]]	Part 1MDI [ mol [ ]]	Partial 2MDI [ mole ]]	Amount of 1, 4-butanediol [ mol ]]
						1*	2	1	1.90	0	0.90
2	2	1	1.25	0.65	0.90
						3	1	1	1.20	0.20	0.40
4	3	1	1.25	0.65	0.90
						5*	4	1	1.50	0.40	0.90
6	1 and 4	0.5+0.5	1.20	0.20	0.40
						7	5	1	1.25	1.15	1.40
8*	6	1	1.50	0.50	1.00

Comparative examples, outside the scope of the invention

Polyol 1 ═ polytetramethylene ether glycol, molecular weight 1000 (available from Dupont)

Polyol 2 ═ hexanediol-neopentyl glycol adipate, molecular weight 2000 (available from Bayer)

Polyol 3 ═ butanediol-ethanediol adipate, molecular weight 2000 (available from Bayer)

Polyol 4 ═ polytetramethylene ether glycol, molecular weight 2000 (available from Dupont)

Polyol 5 ═ polyether L5050 (obtained from Bayer, polyethylene glycol-propylene glycol, molecular weight 2000)

Polyol 6 ═ Desmophen ® PE 225B (obtained from Bayer, butanediol adipate, molecular weight 2200)

The cast sheet obtained from step C) is cut and granulated. The pellets were melted in an injection molding machine D60 (32-screw from Mannesmann) and formed into rods (molding temperature: 40 ℃ C.; rod size: 80X 10X 4 mm) or sheets (molding temperature: 40 ℃ C.; size: 120X 50X 2 mm).

And (3) detection:

the hardness of the TPUs was determined in accordance with DIN 53505 and the tensile tests in accordance with ISO 37. The shrinkage was likewise determined in accordance with DIN 16770 (part 3), the shrinkage being important for the evaluation of injection molding.

The relative shrinkage of the injection-molded article after conditioning (80 ℃/15 hours) is expressed in% relative to the mold length.

Dynamic mechanical analysis (DMA: storage E modulus in tension)

Rectangular samples (30 mm. times.10 mm. times.2 mm) were taken from the injection-molded sheets. These test sheets periodically simulate small deformations under a constant preload, optionally detected as a function of temperature and simulated frequency, in terms of storage modulus, force acting on the clamp. The additional applied preload serves to keep the sample still in sufficient tension during the negative deformation amplitude. The DMA assay was performed at 1Hz with Seiko DMS type 210 (from Seiko), at a temperature of-150 ℃ to 200 ℃ and a heating rate of 2 ℃/min.

To characterize the performance of the inventive samples at low temperatures, the storage E modulus was measured under tension at-10 ℃ and +20 ℃ for comparison and illustration.

To characterize the thermal stability, the temperature T is indicated when it drops below 2MPa, i.e.the stable form of the injection-molded component is no longer maintained. The higher the temperature value, the more stable the TPU.

The cure performance in the injection molding process is characterized by hardness measurements on the standard test specimens taken directly after demolding (after 0 seconds) and 60 seconds after demolding. The higher these two initial values, the faster the TPU cures and the earlier the release.

Table 2: results

Examples	1*	2	3	4	5*	6	7	8*
									Immediate hardness Shore A	60	62	64	61	64	59	60	85
Hardness Shore A after 4 weeks	60	62	65	61	66	59	60	95
									Shrinkage of the plate%	7.1	2.6	3	1.8	0.7	2.6	1.3	10.3
Injection molding: hardness Shore A after 0 seconds Shore A60 seconds	3235	3437	3743	3739	2945	2830	2628	3843
									And DMA detection: e modulus (-10 ℃ C.) MPaE modulus (20 ℃ C.) MPaT (2MPa) DEG C	9696	106106	97113	127105	759128	166113	96129	280107129
Tensile strength MPa	18	17	32	20	32	23	13	44
									Elongation at break%	765	850	739	813	759	751	880	620

Comparative examples, outside the scope of the invention

Even without the addition of plasticizers, very soft TPUs are obtained directly in a simple manner by the multistage process of the invention.

These TPUs have very good mechanical properties, can be processed and, owing to the high curing speed, are easy to demould. For TPU with low hardness, the injection molded components have very low shrinkage.

The E modulus value of the DMA at-10 ℃ is in the same range as the E modulus value of the DMA at +20 ℃, i.e. the product has good low temperature properties even at low temperatures. No post-hardening occurred (4 weeks). The thermal stability of the TPUs of the invention is good at high temperatures.

When butanediol adipate was used as the polyester, the desired softness range was not reached (comparative example 8) despite the same low calculated hardness, because the soft segment crystallized.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (1)

1. A process for preparing a thermoplastically processable polyurethane elastomer, which is easy to demould, has a shore a hardness of 45-65, measured according to DIN 53505, a tensile strength of more than 12MPa, measured according to ISO 37, a shrinkage of ≤ 3.5%, measured according to DIN 16770 part 3, and a DMA storage E modulus under tension at-10 ℃ of less than 20MPa, said process comprising reacting, optionally in the presence of a catalyst:

A) one or more hydroxyl terminated linear polyols selected from the group consisting of:

a) polyester polyols having a number average molecular weight of 450-,

b) a mixture of at least two polyester polyols having different number average molecular weights in the range of 450-,

c) a mixture of at least two polyether polyols having different number average molecular weights in the range of 450-,

d) polyether polyol having a number average molecular weight of 450-,

e) a polyether polyol containing an oxyalkylene unit and having a number average molecular weight of 450-1500,

with one or more organic diisocyanates selected from the group consisting of 4, 4 '-diphenylmethane diisocyanate, isophorone diisocyanate, 1, 6-hexamethylene diisocyanate, 1, 5-naphthalene diisocyanate, 4' -dicyclohexylmethane diisocyanate, and mixtures thereof, in a NCO/OH molar ratio of 1.1: 1 to 1.7: 1 to form an isocyanate-terminated prepolymer,

B) mixing the prepolymer obtained in step A) with an organic diisocyanate,

C) reacting the mixture obtained in step B) with one or more diol chain extenders having a molecular weight of 60 to 400, selected from the group consisting of ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol, 1, 4-di (. beta. -hydroxyethyl) -hydroquinone and 1, 4-di (. beta. -hydroxyethyl) -bisphenol A,

wherein the NCO: OH molar ratio of the components used in A), B) and C) is adjusted to 0.9: 1 to 1.1: 1, and wherein the ratio of the hydroxyl groups of the polyol to the hydroxyl groups of the chain extender is 0.4: 1 to 1.5: 1.