HK1064397B - Continuous preparation of thermoplastically processable polyurethanes - Google Patents

Description

Continuous preparation of thermoplastically processable polyurethanes

Technical Field

The invention relates to a multistage process for the continuous preparation of thermoplastically processable polyurethanes.

Background

Thermoplastic Polyurethanes (TPU) have been known for a long time. They are industrially important due to the known advantages of combining high-quality mechanical properties with inexpensive thermoplastic processability. A wide range of variation in mechanical properties can be achieved by using various chemical building components. An overview of TPUs, their properties and uses is given, for example, in pages Kunststoffe 68(1978), 819 and 825 or in pages Kautschuk, Gummi, Kunststoffe35(1982), 568 and 584.

TPUs are made from linear polyols (usually polyester-or polyether-polyols), organic diisocyanates and short-chain diols (i.e. chain extenders). Various combinations of these properties can be established in a targeted manner by means of polyols. A catalyst can additionally be added to accelerate the formation reaction. The constituent components can be varied in a wide molar ratio to establish the desired properties. Molar ratios of polyol to chain extender of from 1: 1 to 1: 12 have proven suitable. These result in products in the range of 75 Shore A to 75 Shore D.

The thermoplastically processable polyurethane elastomers can be produced in steps (for example by the prepolymer metering process) or by simultaneous reaction of all the components in one stage (for example by the one-shot metering process).

The TPU can be prepared continuously or discontinuously. Well-known preparation processes are conveyor belt processes (see, for example, GB-A1057018) and extruder processes (see, for example, DE-A1964834, DE-A2302564 and DE-A2059570). In the extruder process, the starting materials are metered into a screw reactor, where they undergo polyaddition and are converted into a homogeneous particulate form. The extruder process is relatively simple, but the disadvantage is that the homogeneity of the product obtained in this way is not sufficient for many applications, since mixing and reaction take place simultaneously. In addition, variability in the targeted application of the various polyols is limited because of the limited reaction space and the limited metering possibilities.

A two-stage process is described, for example, in EP-A0571828, in which the prepolymer is formed in a targeted manner from polyol and diisocyanate in a tubular reactor before an extruder, an improvement being achieved for the targeted and controlled preparation of TPUs with improved processability. The TPU formation is carried out in a subsequent extruder with the addition of a chain extender. Based on the optimum conditions in the various processing stages, TPUs are thus prepared in a targeted and controlled manner.

However, for many end-uses, it is not sufficient to use only one polyol to make the TPU. A particular compromise in the properties of the TPU can be achieved by the simultaneous use of different polyols. Examples which may be mentioned are the combined use of polyester polyols and polyether polyols and the advantages obtained. By adding special phosphorus-containing polyols which can be reacted in, the flame-retardant properties of the TPU obtained can be improved without the other properties being adversely affected.

If polyols which are in some cases very different in chemical nature are reacted simultaneously, for example by the prepolymer process, or even together with chain extenders, for example by the one-stage process, with diisocyanates in a continuous preparation process, it is possible to obtain viscous, poorly processable TPUs, since the reaction conditions are no longer optimal for the overall starting materials.

The object of the present invention was therefore to provide an economically advantageous continuous process with which it is possible to prepare readily processable, homogeneous, non-tacky TPUs in an industrially simple manner.

Surprisingly, it has been possible to achieve this object by means of a continuous multistage preparation process.

Disclosure of Invention

The present invention provides a multistage process for the continuous preparation of thermoplastically processable polyurethane elastomers (TPU) having a tensile strength of > 30MPa (measured according to EN ISO 527-3). The method of the invention comprises the following steps:

a) prepolymer I was prepared by reacting the following components:

A) at least one organic diisocyanate with

B) Polyol 1 having on average at least 1.8 and not more than 3.0 Zerewitinoff (Zerewitinoff) active hydrogen atoms and a number average molecular weight Mn of 450-10,000,

b) reacting the prepolymer I prepared in a) with

C) Polyol 2, which is different from polyol 1, the polyol 2 having an average of at least 1.8 but not more than 3.0 zerewitinoff active hydrogen atoms and a number average molecular weight Mn of 60 to 10,000, or polyol 2 containing zerewitinoff active hydrogen atoms comprises an organic phosphorus-containing compound having an average of at least 1.5 and not more than 2.5 zerewitinoff active hydrogen atoms and having a number average molecular weight Mn of 100 to 5,000, in an amount of 0.01 to 50 wt.%, based on the total amount of the TPU.

Carrying out a reaction to give a prepolymer II in which an equivalent ratio of NCO to NCO-reactive groups of from 1.2: 1 to 10: 1, based on the reaction components A), B) and C), is established;

c) the prepolymer II prepared in b) is reacted completely with D) in a high-viscosity reactor operated with high shear energy,

D) at least one low molecular weight polyol or polyamine having on average at least 1.8 and not more than 3.0 Zerewitinoff-active hydrogen atoms and a number average molecular weight Mn of from 60 to 400 as chain extender,

wherein steps a) to c) are carried out optionally in the presence of F) catalysts and optionally with the addition of E)0 to 20% by weight, based on the total amount of TPU, of other auxiliary substances and additives, and the overall equivalent ratio of NCO groups to NCO-reactive groups is in the range from 0.9: 1 to 1.2: 1, based on the sum of all reaction components of steps a) to c).

Detailed Description

Suitable organic diisocyanates for use as component A) include, for example, aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, such as those described, for example, in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136.

Specific examples that may be mentioned in detail include aliphatic diisocyanates such as, for example, hexamethylene-diisocyanate; cycloaliphatic diisocyanates such as, for example, isophorone-diisocyanate, 1, 4-cyclohexane-diisocyanate, 1-methyl-2, 4-and-2, 6-cyclohexane-diisocyanate and the corresponding isomer mixtures, 4, 4 ' -, 2, 4 ' -and 2, 2 ' -dicyclohexylmethane-diisocyanate and the corresponding isomer mixtures; and aromatic diisocyanates such as, for example, 2, 4-tolylene-diisocyanate, mixtures of 2, 4-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, urethane-modified liquid 4, 4' -diphenylmethane-diisocyanate and/or 2, 4 '-diphenylmethane-diisocyanate, 4, 4' -diisocyanato-1, 2-diphenyl-ethane and 1, 5-naphthylene-diisocyanate. Diphenylmethane-diisocyanate isomer mixtures having a 4, 4 '-diphenylmethane-diisocyanate content of more than 96% by weight are preferably used, 4' -diphenylmethane-diisocyanate and 1, 5-naphthylene-diisocyanate being particularly useful. The diisocyanates mentioned above can be used individually or in the form of mixtures with one another. They can also be used with up to 15 mol% (calculated for the total amount of diisocyanate) of polyisocyanate, but the polyisocyanate is added at most in such an amount that a thermoplastically processable product is formed. Examples of such polyisocyanates are triphenylmethane-4, 4', 4 "-triisocyanate and polyphenyl polymethylene polyisocyanates.

Compounds suitable for use as component B) in the context of the present invention include, preferably, polyester polyols, polyether polyols or polycarbonate polyols or polyols containing nitrogen, phosphorus, sulfur and/or silicon atoms, or mixtures of these. Among polyols containing heteroatoms, polyols containing phosphate, phosphonate and phosphine oxides are particularly preferred.

Linear hydroxyl-terminated polyols having an average of from about 1.8 to about 3.0 Zerewitinoff active hydrogen atoms per molecule, preferably from about 1.8 to about 2.2 Zerewitinoff active hydrogen atoms per molecule, and having a molecular weight of 450-. Because of their method of production, these linear polyols often contain small amounts of non-linear compounds. Thus, these are often also referred to as "substantially linear polyols".

Suitable polyether diols of component B) according to the invention can be prepared, 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, 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, alternately in succession or as mixtures. Possible starter molecules include, for example: water, amino alcohols including, for example, N-alkyl-diethanolamines such as, for example, N-methyl-diethanolamine; and diols such as, for example, ethylene glycol, 1, 3-propanediol, 1, 4-butanediol and 1, 6-hexanediol. Mixtures of starter molecules are also optionally used. Suitable polyether polyols also include hydroxyl-containing polymerization products of tetrahydrofuran. It is also possible to use from 0 to 30% by weight of trifunctional polyethers, based on the weight of the bifunctional polyethers. The amount of trifunctional polyethers used is limited to an amount which still results in a thermoplastically processable product. The substantially linear polyether diols of the invention preferably have (number average) molecular weights of 450-5,000 g/mol. They can be used individually or in mixtures with one another.

Suitable polyester diols for use as component B) in the present invention 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. Suitable dicarboxylic acids include, for example: aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and 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 is advantageous, where appropriate, to use, instead of the dicarboxylic acids, the corresponding dicarboxylic acid derivatives, such as carboxylic acid diesters having 1 to 4 carbon atoms in the alcohol radical, carboxylic acid anhydrides or carboxylic acid chlorides. Examples of suitable polyols include glycols having from 2 to 10, preferably from 2 to 6, carbon atoms, such as, for example, 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. The polyols can be used independently or optionally as mixtures with one another, depending on the desired properties. Compounds which are also suitable as component B) include esters of carbonic acid with the abovementioned diols, and in particular those having from 4 to 6 carbon atoms, such as 1, 4-butanediol and/or 1, 6-hexanediol, condensation products of omega-hydroxycarboxylic acids, such as omega-hydroxycaproic acid, and preferably polymerization products of lactones, such as, for example, omega-caprolactone, which lactones are optionally substituted. Polyester diols preferably used include polyethylene adipate, 1, 4-butanediol adipate, polyethylene-1, 4-butanediol adipate, 1, 6-hexanediol-neopentyl glycol adipate, 1, 6-hexanediol-1, 4-butanediol adipate and polycaprolactone. These polyester diols preferably have (number average) molecular weights of 450-5,000g/mol and can be used individually or in mixtures with one another.

Linear hydroxyl-terminated polyols having an average of 1.8 to 3.0 Zerewitinoff-active hydrogen atoms per molecule and having a molecular weight of 60 to 10,000g/mol are also used as component C) (polyol 2) according to the invention. The aforementioned compounds described as suitable for component B) can be used, provided that polyol 2 is different from polyol 1.

Polyester polyols, polyether polyols and polycarbonate polyols having a (number average) molecular weight of 100-5,000g/mol and an average of 1.8 to 2.2 Zerewitinoff-active hydrogen atoms/molecule or mixtures of these compounds are particularly preferred as polyols (2).

Particular polyols containing heteroatoms such as, for example, nitrogen-, phosphorus-, silicon-or sulfur-containing polyols are also preferably used. Phosphoric, phosphonic ester-or phosphine oxide-containing polyols having a molecular weight of 100-5,000g/mol and an average of 1.8 to 2.2 Zerewitinoff-active hydrogen atoms/molecule are particularly preferred.

Preferred compounds for use as phosphates are those corresponding to the general formula (I):

wherein:

R¹and R²: may be the same or different, and each independently represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkaryl group having 6 to 30 carbon atoms;

R³，R⁴and R⁵: may be the same or different, and each independently represents a branched or unbranched alkylene group having 1 to 24 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkylene group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkarylene group having 6 to 30 carbon atoms;

and

n: representing a number from 0 to 100.

Preferred compounds for use as phosphonates are those corresponding to the general formula (II):

wherein:

R¹and R²: may be the same or different, and each independently represents a branched or unbranched alkylene group having 1 to 24 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkylene group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkarylene group having 6 to 30 carbon atoms;

R³: represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkaryl group having 6 to 30 carbon atoms;

and

x and y: each independently represents a number from 1 to 50, preferably from 2 to 40.

Compounds which are also preferably used as phosphonates are those corresponding to the general formula (III):

wherein:

R¹and R²: may be the same or different, and each independently represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkaryl group having 6 to 30 carbon atoms;

R³represents a branched or unbranched alkylene group having from 1 to 24 carbon atoms, a substituted or unsubstituted arylene group having from 6 to 20 carbon atoms, a substituted or unsubstituted aralkylene group having from 6 to 30 carbon atoms, or a substituted or unsubstituted alkarylene group having from 6 to 30 carbon atoms;

and

R⁴and R⁵May be the same or different and each independently represents a branched or unbranched alkylene group having 1 to 24 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkylene group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkarylene group having 6 to 30 carbon atoms.

Preferred compounds for use as phosphine oxides are those corresponding to the general formula (IV):

wherein:

R¹represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 24 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkyl group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkaryl group having 6 to 30 carbon atoms;

and

R²and R³May be the same or different and each independently represents a branched or unbranched alkylene group having 1 to 24 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, a substituted or unsubstituted aralkylene group having 6 to 30 carbon atoms, or a substituted or unsubstituted alkarylene group having 6 to 30 carbon atoms.

Chain extenders suitable for use as component D) for use in the present invention include low molecular weight polyols or polyamines having an average of 1.8 to 3.0 Zerewitinoff-active hydrogen atoms per molecule and a (number average) molecular weight of 60 to 400 g/mol. These low molecular weight compounds preferably include aliphatic diols having 2 to 14 carbon atoms such as, for example, ethylene glycol, 1, 6-hexanediol, diethylene glycol, dipropylene glycol and, in particular, 1, 4-butanediol. However, diesters of terephthalic acid with diols having 2 to 4 carbon atoms, such as, for example, bis-ethylene terephthalate or bis-1, 4-butylene terephthalate; hydroxyalkylene ethers of hydroquinone, such as, for example, 1, 4-di (. beta. -hydroxyethyl) -hydroquinone; ethoxylated bisphenols, such as, for example, 1, 4-bis (β -hydroxyethyl) -bisphenol a; (cyclo) aliphatic diamines such as, for example, isophoronediamine, ethylenediamine, 1, 2-propylenediamine, 1, 3-propylenediamine, N-methyl-propylene-1, 3-diamine and N, N' -dimethyl-ethylenediamine; and aromatic diamines, such as, for example, 2, 4-and 2, 6-toluenediamine, 3, 5-diethyl-2, 4-toluenediamine or 3, 5-diethyl-2, 6-toluenediamine, and primary mono-, di-, tri-and/or tetra-alkyl-substituted 4, 4' -diaminodiphenylmethane, are also suitable. Mixtures of the above-mentioned chain extenders may also be used. In addition, smaller amounts of triols can also be added.

Although it is possible, at least theoretically, to use the same compounds as polyol 2 and as chain extender, these compounds are different in practical application.

Conventional monofunctional compounds can additionally be used 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 of the invention, the constituent components, optionally in the presence of catalysts, auxiliary substances and/or additives, are preferably reacted in amounts which require an equivalent ratio of NCO groups from A) to the sum of NCO-reactive groups, in particular the OH (and/or NH) groups of the low-molecular-weight compounds D) and the polyols B) and C), of from 0.9: 1.0 to 1.2: 1.0, and preferably from 0.95: 1.0 to 1.10: 1.0.

Suitable catalysts for use as component F) in the present invention include conventional tertiary amine catalysts known in the art. Examples of suitable catalysts include tertiary amine compounds such as, for example, triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N' -dimethyl-piperazine, 2- (dimethylamino-ethoxy) -ethanol, diazabicyclo- (2, 2, 2) -octane and the like, and, in particular, organometallic compounds such as titanic acid esters, iron compounds or tin compounds, for example tin diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic carboxylic acids, such as dibutyltin diacetate or dibutyltin dilaurate and the like. Preferred catalysts are organometallic compounds, especially titanates and compounds of iron and/or tin.

In addition to the TPU component and the catalyst, auxiliary substances and/or additives, referred to herein as component E), can be present in amounts of up to 20% by weight, based on the total weight of the TPU. These auxiliary substances and/or additives can be dissolved in one of the TPU components, preferably in component B), or they can also optionally be metered in, after the reaction has been completed, in a subsequent mixing apparatus, for example an extruder.

Examples of such auxiliary substances and/or additives 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 include, inter alia, fibrous reinforcing substances, such as, for example, inorganic fibers, which are prepared according to the prior art and can also be added in certain sizes. Further details of auxiliary substances and additives which may be mentioned can be found in the literature, for example in the monograph "HighPolymers" of J.H.Saunders and K.C.Frisch, volume XVI, Polyurethane, part 1 and 2, Verlag Interscience Publishers 1962 and 1964, the Taschenbuch Kunststoff-Additive of R.G Pa-chter and H.M muller (Hanser Verlag Munich 1990) or in DE-A2901774, the disclosures of which are incorporated herein by reference.

Other additives which can be incorporated into the TPU are thermoplastics such as, for example, polycarbonate and acrylonitrile/butadiene/styrene terpolymers, and in particular ABS. Other elastomers, such as rubber, ethylene/vinyl acetate copolymers, styrene/butadiene copolymers and other TPUs, may also be used. In addition, commercially available plasticizers, such as phosphates, phthalates, adipates, sebacates and alkylsulfonates, are also suitable for incorporation.

The preparation process according to the invention is preferably carried out as follows.

The components A) and B) in step a) are continuously mixed at a temperature above their melting point, preferably at a temperature of from 50 to 220 ℃ and reacted to form prepolymer I. This stage is preferably carried out in a mixing apparatus with high shear energy. For example, a mixing head or a high-speed tubular mixer, a nozzle or a static mixer can be used. Static mixers which can be used include those disclosed in chem. -Ing.Techn.52, No.4, pages 285 to 291, and in "Mischen von Kunststoff und Kautschukprodukten", VDI-Verlag, Dusseldorf 1993, the disclosure of which is incorporated herein by reference. The SMX static mixer from Sulzer can be mentioned as an example.

In another embodiment, a tube may also be used as a reactor for the reaction.

The reaction to form prepolymer I in step a) should proceed to substantially complete conversion (for polyol 1). Preferably, more than 85 mol% of the polyol used should be reacted off in this stage. The reaction temperature should be above 100 ℃, preferably between 120 ℃ and 250 ℃. For a continuously operated process, the reactor volume should be such that, in interaction with the reaction temperature and throughput, the desired conversion is ensured.

Preferably, in step B), component B) (i.e.polyol 2), preheated to above its melting point, is continuously mixed into prepolymer I under high shear energy and the mixture is allowed to react to give prepolymer II. The reactors described above may also be used in this stage. A reactor separate from stage a) is preferably used for this stage.

In addition, for step b), the volume of the reactor should be such that, in interaction with the reaction temperature and throughput, a conversion of the amount of polyol 2 of more than 85 mol% is ensured.

In a particular embodiment, this stage can also be carried out in the first section of a multi-screw extruder (e.g. a twin-screw extruder ZSK).

The entire reaction components, i.e.components A), B) and C) of steps a) and B) are added together, preferably with an equivalent ratio of NCO groups to the sum of NCO-reactive groups of 1.2: 1 to 10: 1 being established.

In step c), the prepolymer II is preferably continuously mixed with low molecular weight polyols or polyamines as chain extenders and reacted in a high-viscosity reactor to give the TPU.

Component D), the chain extender, is preferably incorporated by using a mixing apparatus operating with high shear energy. Examples of such apparatus which may be mentioned include mixing heads, static mixers, nozzles or multi-screw extruders. The mixing and reaction of the components at this stage is preferably carried out after step b) in a multi-screw extruder, for example in a twin-screw kneader ZSK.

The reaction stage c) is preferably carried out in a different reactor from the reactors used in steps a) and b) (different type of reactor).

The temperature of the extruder barrel (houseing) is selected such that the reaction components are completely converted and the possible introduction of the abovementioned auxiliary substances or optional components is carried out with the highest possible protection of the product.

At the end of the extruder, the product was pelletized. Pellets are obtained which are easy to process.

The TPU made by the process according to the present invention can be processed into injection molded articles and homogeneous extruded articles.

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

Examples

The following formulation was used in the working examples.

The TPU formula comprises:

polyol 1: terathane ® 100052.3 parts by weight

Polyol 2: exolit ® OP 5605.5 parts by weight

Chain extender: butane-1, 4-diol 6.2 parts by weight

Isocyanate: 35.1 parts by weight of 4, 4' -MDI

Additive: lcemax ® C0.4 weight portion

Irganox ® 10100.5 parts by weight

0.011 part by weight of tin dioctanoate

Terathane ® 1000: a polyether having a number average molecular weight Mn of 1,000 g/mol; du Pont de

Commercial product of Nemours

Isocyanate: diphenylmethane-4, 4' -diisocyanate, commercially available from Bayer AG

Exolit ® OP 560: flame retardants based on diol-phosphonates having a number-average molecular weight Mn of 300 from

Commercially available from Clariant GmbH

Irganox ® 1010 tetrakis (methylene- (3, 5-di-tert-butyl-4-hydroxycinnamate)) -methane, prepared from

Ciba Specialty Chemicals Inc.

Licowax ® C ethylene-bis stearamide, commercially available from Clariant

Example 1 (comparative)

(ZSK one-step process)

Polyol 1, in which tin dioctoate was dissolved as catalyst, was heated to 200 ℃ and metered continuously into the first barrel of ZSK53 (twin-screw extruder from Werner/Pfleiderer) using a gear pump.

Polyol 2(60 ℃) premixed with butane-1, 4-diol, and 4, 4' -diphenylmethane diisocyanate (Desmodur ® 44M) (60 ℃) and Licowax ® C were metered continuously into the same barrel, the first barrel of ZSK 53. The ZSK was heated to 220 to 230 ℃ (barrels 1 to 8). The last 4 sections of the barrel were cooled. The screw speed was 290 rpm.

At the end of the screw, the hot melt is drawn off as a strand, cooled in a water bath and granulated.

Example 2 (comparative)

(ZSK prepolymer metering technique)

This experiment was performed similarly to example 1, except that polyol 2 and butane-1, 4-diol were metered into barrel 7 of the ZSK, rather than into barrel 1 as described above.

Example 3 (comparative) (two-stage process)

This experiment was carried out analogously to example 1, except that polyol 1 and MDI were metered continuously into the static mixer of the static mixer section of 3XDN20 (SMX from Sulzer). This static mixer section leads directly into the cylinder 1 of the ZSK. The remaining components are mixed and/or metered in as in example 1.

Example 4 (according to the invention).

(multistage prepolymer metering Process)

This experiment was carried out analogously to example 3, except that the continuous addition and reaction of polyol 2 were carried out in a reactor consisting of a DN18 static mixer and a tube (length-to-diameter ratio: 80). This reactor was installed directly after the static mixer section of example 3 and led directly into barrel 1 of the ZSK. The remaining components are mixed and/or metered in as in example 3.

The results of the product tests are shown in the table.

Measurement of MVR value (MVR ═ melt volume Rate)

The MVR value of the pellets was measured according to ISO 1133 with a weight of 10 kg.

Manufacture of injection molded articles

The special TPU pellets of examples 1 to 4 were melted in an injection molding machine D60 (32 screw from Mannesmann) (melting temperature approx. 230 ℃) and formed into sheets (125 mm. times.50 mm. times.2 mm).

Pipe extrusion

The special TPU pellets of examples 3 and 4 were melted in a single-screw extruder 30/25D (Plasticorder PL 2000-6 from Brabender) (metering speed 3 kg/h; 230-.

Mechanical testing at room temperature

The modulus at 100% elongation and the tear strength were measured on injection-molded test specimens in accordance with DIN 53405.

Measurement of flame retardancy:

flame retardant performance was determined according to UL 94V at a specimen thickness of 3mm (described in underwriters laboratories Inc. Standard of Safety, "Test for flexibility of Plastic Materials for parts in Devices and applications", p.14 and below, et al, Northbrook 1998 and in J.Triotzsch, "International Plastics flexibility Handbook", p.346 and below, Hanser Verlag, Munich 1990).

The rating of V0 in this test refers to the dripping that is not burning. Products with this rating are therefore indicated as flame retardant. The V2 rating refers to flame dripping, i.e. lack of flame retardancy.

Results

Examples	A reactor: static mixing extruder	Metering of polyol 1	Metering of polyol 2	Metering of chain extender D	Metering of MDI	Granular material	MVR200℃10kg	100% modulus [ MPa ]]	Tear strength [ MPa ]]	UL94 test (3mm)	Tubular extrusion
												1*	ZSK53	Barrel 1ZSK	Barrel 1ZSK	Barrel 1ZSK	Barrel 1ZSK	Viscosity of	20	6.7	39	V2
2*	ZSK53	Barrel 1ZSK	Barrel 7ZSK	Barrel 7ZSK	Barrel 1ZSK	Very sticky; can not be processed	42
												3*	3xDN20/ZSK 53	First DN20	Barrel 1ZSK	Barrel 1ZSK	First DN20	Viscosity of	25	6.2	47	V0	Heterogeneous extrudate
4	3xDN20/1xDN 18/tube/ZSK 53	First DN20	First DN18	Barrel 1ZSK	First DN20	No stickiness and easy granulation	7	6.7	48	V0	Homogeneous extrudate

^*Comparative examples not according to the invention

hous tube (houseing)

ZSK53 ═ (twin screw extruder from Werner/Pfleiderer)

3xDN 20-three DN20 static mixers from Sulzer

1xDN 18-a static mixer DN18 from Sulzer

The TPU pellets made from the one-step process (example 1) were tacky and gave a rating of only V2 in the flame test. The viscosity of the pellets makes their further processing and their handling (e.g., transport, transfer into containers, etc.) difficult.

The products obtained from the ZSK prepolymer process are therefore so sticky that they cannot be processed (example 2).

The TPU product (example 3) made from the two stage prepolymer process is also tacky. A non-uniform extruded tube is obtained from the process.

On the other hand, the pellets produced by the multistage process according to the invention (example 4) are not tacky and can be very easily processed into TPU articles (e.g. extruded pipes) with excellent TPU properties.

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 (9)

1. A multistage process for the continuous preparation of thermoplastically processable polyurethane elastomers having a tensile strength of more than 30MPa (measured according to EN ISO 527-3) comprising

a) Prepolymer I was prepared by reacting the following components:

A) at least one organic diisocyanate,

and

B) polyol 1 having an average of at least 1.8 and not more than 3.0 Zerewitinoff active hydrogen atoms and a number average molecular weight Mn of 450-;

b) reacting the prepolymer I prepared in a) with

C) Polyol 2, which is different from polyol 1, wherein the polyol 2 has an average of at least 1.8 but not more than 3.0 Zerewitinoff-active hydrogen atoms and a number average molecular weight Mn of from 60 to 10,000,

carrying out a reaction to give a prepolymer II in which an equivalent ratio of NCO groups to the sum of NCO-reactive groups of from 1.2: 1 to 10: 1, based on the reaction components (A), (B) and (C), is achieved;

c) reacting the prepolymer II prepared in b) completely with D) in a high-viscosity reactor operated with high shear energy:

D) at least one low molecular weight polyol or polyamine having an average of at least 1.8 and not more than 3.0 Zerewitinoff active hydrogen atoms and a number average molecular weight Mn of from 60 to 400 as chain extender;

wherein steps a) to c) are carried out optionally in the presence of F) catalysts and E) from 0 to 20% by weight, based on the total amount of thermoplastically processable polyurethane elastomer, of other auxiliary substances and additives, and the total equivalent ratio of NCO groups to the sum of NCO-reactive groups is in the range from 0.9: 1 to 1.2: 1, based on the sum of all reaction components of steps a) to c).

2. The process of claim 1, wherein B) polyol 1 and C) polyol 2, both containing Zerewitinoff active hydrogen atoms, are selected from the group consisting of (i) polyester polyols, (ii) polyether polyols, (iii) polycarbonate polyols, (iv) polyols containing nitrogen, phosphorus, sulfur and/or silicon atoms and (v) mixtures thereof.

3. The process of claim 1, wherein D) the low molecular weight polyol containing Zerewitinoff-active hydrogen atoms comprises ethylene glycol, butanediol, hexanediol, 1, 4-bis- (β -hydroxyethyl) -hydroquinone, or 1, 4-bis- (β -hydroxyethyl) -bisphenol A.

4. The method of claim 1 wherein a) the organic diisocyanate comprises an aromatic diisocyanate.

5. The process of claim 4 wherein the aromatic diisocyanate comprises a diphenylmethane-diisocyanate isomer mixture having a 4, 4' -diphenylmethane-diisocyanate content of > 96% by weight.

6. The process of claim 1, wherein C) polyol 2 containing Zerewitinoff active hydrogen atoms comprises an organic phosphorus-containing compound having on average at least 1.5 and not more than 2.5 Zerewitinoff active hydrogen atoms and having a number average molecular weight Mn of from 100 to 5,000 in an amount of from 0.01 to 50% by weight, based on the total amount of thermoplastically processable polyurethane elastomer.

7. The process of claim 1, wherein steps a) and b) are carried out in separate reactors.

8. The process of claim 1 wherein step c) is conducted in a separate reactor from steps a) and b).

9. The process of claim 1, wherein step c) is carried out in a multi-screw extruder.