HK1101328A - Process for the production of melt-processable polyurethanes - Google Patents

Description

Process for producing melt-processable polyurethanes

Technical Field

The present invention relates to a multi-step process for producing melt-processable polyurethanes with improved processing characteristics, in particular improved homogeneity.

Background

Thermoplastic polyurethane elastomers (TPU) have long been known. They are of technical importance because they combine the well-known advantages of high-quality mechanical properties with low-cost melt processability. A wide variety of mechanical properties can be obtained with different chemical compositions. Reviews on TPUs, their properties and applications are described, for example, in the handbook of plastics 68(1978), pp.819 to 825 or in the handbook of raw rubber, plastics 35(1982), pp.568 to 584.

TPUs are composed of linear polyols, usually polyester or polyether polyols, organic diisocyanates and short-chain diols (chain extenders). By means of polyols, a wide variety of property combinations can be established in a targeted manner. In order to accelerate the preparation reaction, catalysts may additionally be used. To achieve these properties, the ingredients may be varied over a relatively wide range of molar ratios. It has proven to be appropriate for the molar ratio of polyol to chain extender to be from 1: 1 to 1: 12. This will yield a product of 60 Shore A to 75 Shore D.

The melt-processable polyurethane elastomers may be synthesized stepwise (prepolymer metering process) or by simultaneous reaction of all components in one step (one-shot metering process).

The TPU can be prepared continuously or batchwise. The most notable industrial preparation processes are the conveyor belt process (GB-A1057018) and the extruder process (DE-A1964834, DE-A2302564 and DE-A2059570).

To improve processing characteristics, rapid release of the injection-molded parts and an increase in the stability of the melt, tubes and profiles, as well as smooth melting of the TPU, are of great interest. The morphology of the TPU, i.e.its particular recrystallization behavior, is decisive for its demolding behavior and stability. In addition, side reactions, in particular on the NCO side (formation of allophanates, biurets and triisocyanurates), should be avoided for good homogeneity.

In EP-A0571830, it is described how TPUs having a significantly increased recrystallization temperature can be obtained in a simple batch process by reaction of 1mol of polyol with 1.1 to 5.0mol of diisocyanate, incorporation of the remaining diisocyanate and subsequent chain extension, compared with TPUs produced by standard processes. In this way, TPUs with improved mold release and bubble stability are obtained. However, the product thus obtained, due to the production method, produces a film having "fish eyes" and is therefore unsuitable for extrusion processing. High melting temperatures are also disadvantageous for processing, especially in the case of the diisocyanate/polyol ratios of 1.5 to 2.0 described in the examples.

In DE-A2248382, a further soft segment prepolymer process is described. By reaction between 1mol or more of a polyol and 0.2 to 0.7mol of a diisocyanate other than 4, 4' -diphenylmethane diisocyanate, a hydroxyl-terminated prepolymer is formed which in the next step will add a chain extender and which is capable of reacting with a diisocyanate different from the diisocyanate in the first step (optionally in 1 or 2 steps). In this way, broadening of the melting range and slight blooming of the low molecular weight oligomers are achieved. The method also fails to achieve an improvement in the ability to recrystallize and, thus, in the stability. The products obtained are therefore suitable for coating and calendering, but not for film processing.

In EP-A0010601, a continuous process for producing polyurethane and polyurethane urea elastomers in a screw machine with special screw elements is described, in which the component metered feed of one or both monomer components is carried out in at least 2 portions. Both NCO prepolymers (NCO excess) and OH prepolymers (OH excess; 0.3 to 0.8mol of diisocyanate per mole of polyol) are used here. Here too, the remaining amount of diisocyanate and chain extender is optionally added in one or more stages. With this method, the reactivity difference in the raw materials will be smoothed and an elastomer can be obtained at a level of reproducibility of the properties and which has improved ultimate bending stress, notched impact strength and resilience.

Therefore, there is a need in the art for a process for producing TPUs with good stability sufficient for processing into uniform shaped articles.

Disclosure of Invention

The present invention therefore provides a process which produces TPUs with excellent stability which can be processed to give homogeneous shaped articles, in particular films.

Surprisingly, this object is achieved by the multistage process according to the invention.

Detailed description of the invention

The invention will now be described for the purpose of illustration, but is not intended to be limited thereto. Except in the operating examples, or where otherwise indicated, all numbers expressing quantities, percentages, hydroxyl numbers, functionalities and so forth in the specification are to be understood as being modified in all instances by the term "about". Equivalent weights and molecular weights in daltons (Da) are number average equivalent weights and number average molecular weights, respectively, unless otherwise indicated.

The present invention provides a process for producing melt processable polyurethane elastomers (TPU) having improved processing characteristics comprising:

A) one or more linear, hydroxyl-terminated polyols a) having a weight-average molecular weight of from 500 to 5,000 and being mixed with organic diisocyanates b) in an equivalent ratio of NCO-reactive groups to NCO groups of from 1.1: 1 to 5.0: 1 in a high-shear energy mixing device,

B) the reaction mixture formed in step A) is reacted at a temperature of more than 80 ℃ to a conversion of more than 90%, based on component b), to form a hydroxyl-terminated prepolymer,

C) mixing the hydroxyl prepolymer produced in step B) with one or more chain extenders c) having a molecular weight of 60 to 490, and

D) reacting the mixture formed in step C) with a certain amount of component b) to form a thermoplastic polyurethane in order to establish an equivalent ratio of NCO groups to NCO-reactive groups of 0.9: 1 to 1.1: 1,

wherein steps A) to D) are optionally carried out in the presence of a catalyst and optionally from 0 to 20% by weight, based on the total amount of TPU, of auxiliary substances and additives are added.

Suitable organic diisocyanates b) are, for example, aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as described, for example, in Justus Liebigs Annalen der Chemie 562, pp.75 to 136.

Specific examples are given below: aliphatic diisocyanates, for example hexamethylene diisocyanate, cycloaliphatic diisocyanates, for example isophorone diisocyanate, 1, 4-cyclohexane diisocyanate, 1-methyl-2, 4-and-2, 6-cyclohexane diisocyanate, together with the corresponding isomer mixtures, 4, 4 ' -, 2, 4 ' -and 2,2 ' -dicyclohexylmethane diisocyanate, together with the corresponding isomer mixtures, and aromatic diisocyanates, 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, 2, 4 ' -diphenylmethane diisocyanate and 4, mixtures of 4 '-diphenylmethane diisocyanates, urethane-modified liquid 4, 4' -diphenylmethane diisocyanates and/or 2, 4 '-diphenylmethane diisocyanates, 4' -diisocyanatodiphenylethane- (1, 2) and 1, 5-naphthalene diisocyanate. Preference is given to using isomer mixtures of diphenylmethane diisocyanates having a 4, 4 ' -diphenylmethane diisocyanate content of greater than 96% by weight, in particular 4, 4 ' -diphenylmethane diisocyanate, hexamethylene diisocyanate and 4, 4 ' -, 2, 4 ' -and 2,2 ' -dicyclohexylmethane diisocyanate, together with the corresponding isomer mixtures. The above diisocyanates can be used individually or in the form of mixtures with one another. They may also be used together in amounts of up to 15% (based on total diisocyanate) but not more than the amount of polyisocyanate sufficient to produce a melt-processable product. Examples are triphenylmethane-4, 4', 4 "-triisocyanate and polyphenyl polymethylene polyisocyanates.

Linear hydroxyl-terminated polyols are used as polyol a). They often contain small amounts of non-linear compounds resulting from their preparation. Therefore, they are often referred to as "substantially linear polyols".

Polyether diols suitable as component a) can be prepared by reaction of one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene radical with starter molecules containing 2 bonded active hydrogen atoms. Examples of alkylene oxides are: 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, alternatively, sequentially or as mixtures. Suitable starter molecules are, for example, water, amino alcohols, for example N-alkyldiethanolamines, such as N-methyldiethanolamine, and diols, for example ethylene glycol, 1, 3-propanediol, 1, 4-butanediol and 1, 6-hexanediol. Mixtures of starter molecules may also optionally be used. Suitable polyether alcohols are also the hydroxyl group-containing polymerization products of tetrahydrofuran. The trifunctional polyethers can also be used in proportions of from 0 to 30% by weight, based on the difunctional polyethers, but not in amounts sufficient to give products which are still melt-processable. The substantially linear polyether diols preferably have a number average molecular weight Mn of from 500 to 5,000. They may be used either individually or in mixtures with one another.

Suitable polyester diols (component a)) can be formed, for example, from dicarboxylic acids having from 2 to 12 carbon atoms, preferably from 4 to 6 carbon atoms, and polyhydric alcohols. Suitable carboxylic acids are, for example, 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 in the form of mixtures, for example in the form of succinic, glutaric and adipic acid mixtures. For the preparation of the polyester diols, it is advantageous to use, instead of the dicarboxylic acids, the corresponding dicarboxylic acid derivatives, for example carboxylic acid diesters having 1 to 4 carbon atoms in the alcohol radical, carboxylic acid anhydrides or carboxylic acid chlorides. Examples of polyhydric alcohols are diols having 2 to 10, preferably 2 to 6, carbon atoms, such as 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. Esters of carboxylic acids with the above diols are also suitable, in particular those having from 4 to 6 carbon atoms, for example 1, 4-butanediol or 1, 6-hexanediol, omega-hydroxycarboxylic acids, for example condensation products of omega-hydroxycaproic acid, or polymerization products of lactones, for example optionally substituted omega-caprolactones. The polyester diols have a number average molecular weight Mn of 500 to 5,000, and can be used individually or in the form of mixtures with one another.

Low molecular weight diols are used as chain extenders c), optionally with small amounts of diamines, aliphatic diols having a molecular weight of from 60 to 490g/mol, preferably from 2 to 14 carbon atoms, such as ethylene glycol, 1, 6-hexanediol, diethylene glycol, dipropylene glycol, in particular 1, 4-butanediol. However, diesters of terephthalic acid with diols having from 2 to 4 carbon atoms, such as diethylene glycol terephthalate or di-1, 4-butanediol terephthalate, hydroxyalkylene 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 isophorone diamine, ethylene diamine, 1, 2-propane diamine, 1, 3-propane diamine, N-methylpropane-1, 3-diamine, N' -dimethylethylene diamine, and aromatic diamines, such as 2, 4-and 2, 6-toluene diamine, 3, 5-diethyl-2, 4-toluene diamine and/or 3, 5-diethyl-2, 6-toluenediamine and primary mono-, di-, tri-and/or tetraalkyl-substituted 4, 4' -diaminodiphenylmethanes are also suitable. Preferred chain extenders are ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol, 1, 4-di (. beta. -hydroxyethyl) hydroquinone or 1, 4-di (. beta. -hydroxyethyl) bisphenol A. Mixtures of the chain extenders mentioned above may also be used. Relatively small amounts of triols can also be added.

In addition, conventional monofunctional compounds may also be used in small amounts, for example, as chain terminators or mold release agents. Alcohols, such as octanol and octadecanol, or amines, such as butylamine and octadecylamine, may be mentioned as examples.

To produce the TPUs in the process of the invention, the components can optionally be reacted in the presence of catalysts, auxiliary substances and/or additives, preferably in small amounts, in such amounts that: the equivalent ratio of NCO groups from component b) to the sum of NCO-reactive groups, in particular OH (or NH) groups of the low molecular weight compound c) and of polyol a), is in the range from 0.9: 1.0 to 1.1: 1.0, in particular from 0.95: 1.0 to 1.05: 1.0.

Suitable catalysts are the conventional tertiary amines known from the prior art, such as triethylamine, dimethylcyclohexylamine, N-methyl-morpholine, N' -dimethylpiperazine, 2- (dimethylaminoethoxy) ethanol, diazabicyclo- [2.2.2] -octane and the like, and, in particular, organometallic compounds, such as titanic esters, iron compounds, tin compounds, such as tin diacetate, tin dioctoate or tin dialkyl salts of aliphatic carboxylic acids, such as dibutyltin diacetate, dibutyltin dilaurate or the like. Preferred catalysts are organometallic compounds, in particular titanic acid esters, iron compounds and/or tin compounds. The total amount of catalyst in the TPU is generally from about 0 to 5% by weight, preferably from 0 to 1% by weight, based on the TPU.

In addition to the reaction components and the catalyst, up to 20% by weight, based on the total amount of TPU, of auxiliary substances and/or additives may also be added. These ingredients can be dissolved in one of the reaction components, preferably in component a), or optionally metered into a downstream mixing device, for example an extruder, after the reaction has been completed.

The following examples may be mentioned: lubricants, for example, 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, in particular fibrous reinforcing agents, for example inorganic fibers, which can be produced according to the prior art and can be provided with a size. Further details concerning the auxiliary substances and additives mentioned above can be found in specialist literature, for example, J.H.Saunders and K.C.Frisch monograph "high Polymer", volume XVI, polyurethanes, parts 1 and 2, International scientific publishers 1962 and 1964, handbook of plastics additives, eds Gachter and H.Muller (Hanser Press, Munich 1990) or DE-A2901774.

Other additives which may be added to the TPU are thermoplastics, for example polycarbonate 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. Commercially available plasticizers, such as phosphates, phthalates, adipates, sebacates, and alkyl sulfonates, are also suitable for incorporation.

The multi-step production process of the present invention may be carried out in a batch mode or a continuous mode.

The components of step A) are blended at a temperature above their melting point, preferably at a temperature of 50 to 220 ℃ in an OH/NCO ratio of 1.1: 1 to 5.0: 1.

In step B), the mixture is converted substantially completely, preferably above 90%, based on the isocyanate component, at a temperature of above 80 ℃, preferably from 100 ℃ to 250 ℃. A hydroxyl-terminated prepolymer was obtained.

These steps are preferably carried out in a mixing device having high shear energy. For example, stirred tanks may be used, or stirred heads or high-speed turbine mixers, jet or static mixers may be used. Static mixers which can be used are described in chemical engineering techniques 52, part 4, pp.285 to 291, and in mixing in the production of plastics and rubbers, VDI-Press, Dusseldorf 1993. So-called SMX static mixers produced by Sulzer can be cited as an example.

In one embodiment of the invention, a tube may also be used as a reactor for the reaction.

In one embodiment of the invention, the reaction can also be carried out in the first stage of a multi-screw extruder, for example a twin-screw kneader (ZSK).

In step C), the OH-terminated prepolymer is vigorously mixed with the low molecular weight chain extender C).

The chain extender is preferably blended in a mixing device operated at high shear energy. Mention may be made, as examples, of mixing heads, static mixers, jet or multi-screw extruders.

In step D), the remaining diisocyanate b) is incorporated under vigorous mixing, so that the reaction to give the thermoplastic polyurethane is completed, and the total equivalent ratio of NCO groups to NCO-reactive groups of 0.9: 1 to 1.1: 1 is established in steps A) to D). Such blending is also preferably carried out in a mixing apparatus operating under high shear energy conditions, for example, a mixing head, a static mixer, a jet or a multi-screw extruder.

The temperature of the extruder barrel should be selected so that complete conversion of the reaction components is achieved, while the above-mentioned incorporation of auxiliary substances and/or other components can be carried out with maximum product protection.

At the end of the extruder, granulation was carried out. Pellets which can be easily processed are thus obtained.

The TPU produced by the process of the invention can be processed to give injection moldings and homogeneous extruded articles, in particular films.

The invention will be further illustrated by, but is not limited to, the following examples.

Examples of the invention

The raw materials are used:

PE1000 polyether, molecular weight Mn 1,000 g/mol;

PES 2250 butanediol adipate, molecular weight Mn 2,250 g/mol;

MDI diphenylmethane 4, 4' -diisocyanate

HDI 1, 6-hexamethylene diisocyanate

TDI toluene diisocyanate

IPDI isophorone diisocyanate

BUT 1, 4-butanediol

Production of TPU (batch):

in the reaction vessel, the polyol was heated to 180 ℃. 0.4% by weight, based on TPU, of ethylene bis-stearamide (wax) is dissolved in this polyol. A portion of 1 amount of diisocyanate was added with stirring (300rpm) (60 ℃). A prepolymer (conversion > 90 mol%) was obtained. According to the data of Table I, the following ingredients were added to the prepolymer with stirring:

a) butanediol, and subsequently, under vigorous intermixing, a partial amount 2 of diisocyanate (examples 2, 3, 4, 6, 10, 11, 12, 13, 14) or

b) Partial amount of 2 isocyanate and, subsequently, butanediol (examples 1, 5, 7, 9) or

c) Part of the amount 2 of diisocyanate and, at the same time, butanediol with vigorous stirring (examples 8 and 15).

In the case of HDI, about 40 to 100ppm dibutyltin dilaurate (catalyst) based on the polyol is used. After about 20 to 60s (depending on the diisocyanate), the reaction mixture is poured onto the coated plate and equilibrated at 120 ℃ for 30 min. The cast sheet was cut and pelletized. The data on the amounts and ratios are given in table I below.

Injection molding:

the pellets were metered into a D60 (32-screw) injection molding machine manufactured by Mannesmann and formed into sheets (125X 50X 2 mm). Hardness was determined in accordance with DIN 53505.

Processing into a film:

the pellets were metered into a 30/25D single screw extruder (PLASTIC CORDER PL 2000-6, manufactured by Brabender) (metered in at 3 kg/h; 230-195 ℃) and extruded through a flat film die into a flat film.

TABLE I

Examples of the invention	1mol of polyol (step A + B)	Mol diisocyanate (step A + B)	OH to NCO ratio (step A + B)	Step C	Step D	TPU hardness (Shao Er A)	Injection molding sheet (homogeneity)	Flat film (homogeneity)
									1*	PES 2250	1.5MDI	0.67	2.1mol MDI	2.6mol BUT	85	Uniformity	Is very inhomogeneous
2	PES 2250	0.67MDI	1.50	2.6mol BUT	2.93mol MDI	85	Uniformity	Uniformity
									3*	PES 2250	0.67TDI	1.50	2.6mol BUT	2.93mol MDI	82	Browning	Can not be processed
4*	PES 2250	0.67MDI	1.50	2.6mol BUT	2.93mol TDI		Can not be processed	Can not be processed
									5*	PE 1000	1.5MDI	0.67	0.5mol MDI	1.0mol BUT	80	Uniformity	Is not uniform
6	PE 1000	0.67MDI	1.50	1.0mol BUT	1.33mol MDI	80	Uniformity	Uniformity
									7*	PE 1000	0.67MDI	1.50	1.33mol MDI	1.0mol BUT	80	Uniformity	Is very inhomogeneous
8*	PE 1000	0.67MDI	1.50	1.33mol MDI1.0mol BUT	-	80	Uniformity	Is not uniform
									9*	PES 2250	1.50mol HDI	0.67	2.1mol HDI	2.6mol BUT	93	Is very inhomogeneous	Is very inhomogeneous
10	PES 2250	0.67mol HDI	1.50	2.6mol BUT	2.93mol HDI	93	Uniformity	Uniformity
									11*	PES 2250	0.67mol HDI	1.50	2.6mol BUT	2.93mol MDI		Is very inhomogeneous
12*	PES 2250	0.67mol MDI	1.50	2.6mol BUT	2.93mol HDI		Is very inhomogeneous
									13*	PES 2250	0.67mol IPDI	1.50	2.6mol BUT	2.93mol HDI		Is very inhomogeneous
14*	PES 2250	0.67mol HDI	1.50	2.6mol BUT	2.93mol IPDI		Can not be processed
									15*	PES 2250	0.67mol HDI	1.50	2.6mol BUT2.93mol HDI	-	94	Is not uniform	Is not uniform

^*Comparative example, not according to the invention.

From the above table I it is clear that uniform films and sheets can only be produced from the TPU produced according to the invention, in contrast to the TPU produced according to the prior art, which either produces inhomogeneous films or is not processable at all.

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 process for producing a melt processable polyurethane elastomer (TPU), comprising the steps of:

A) one or more linear, hydroxyl-terminated polyols a) having a weight average molecular weight of from about 500 to about 5,000 are mixed with an organic diisocyanate b) in an NCO-reactive group to NCO group equivalent ratio of 1.1: 1 to 5.0: 1 in a high shear energy mixing device,

B) the reaction mixture formed in step A) is reacted at a temperature of greater than about 80 ℃ to a conversion of greater than about 90%, based on component b), to form a hydroxyl-terminated prepolymer,

C) mixing the hydroxyl prepolymer formed in step B) with one or more chain extenders c) having a molecular weight of from about 60 to about 490, and

D) reacting the mixture formed in step C) with a quantity of component b) to give a thermoplastic polyurethane, in order to establish an equivalent ratio of NCO groups to NCO-reactive groups of 0.9: 1 to 1.1: 1 taking into account all components,

wherein steps A) to D) are optionally carried out in the presence of a catalyst and optionally from 0 to about 20% by weight, based on the total amount of TPU, of auxiliary substances and additives are added.

2. The process of claim 1 wherein polyol a) is selected from the group consisting of polyester polyols, polyether polyols, polycarbonate polyols, and mixtures thereof.

3. The process of claim 1 wherein component c) is selected from the group consisting of ethylene glycol, butanediol, hexanediol, 1, 4-di (. beta. -hydroxyethyl) hydroquinone or 1, 4-di (. beta. -hydroxyethyl) bisphenol A, and mixtures thereof.

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

5. The process of claim 1 wherein the organic diisocyanate b) is a mixture of isomers of diphenylmethane diisocyanate having a 4, 4' -diphenylmethane diisocyanate content of greater than about 96%.

6. The process of claim 1 wherein the organic diisocyanate b) comprises an aliphatic diisocyanate.

7. The process of claim 1 wherein the organic diisocyanate b) is 1, 6-hexamethylene diisocyanate or 4, 4 ' -, 2, 4 ' -or 2,2 ' -dicyclohexylmethane diisocyanate or the corresponding isomer mixtures thereof.

8. In a process for producing injection molded parts, the improvement comprising one or more melt processable polyurethane elastomers produced by the process of claim 1.

9. In a process for producing an extruded article, the improvement comprising one or more melt processable polyurethane elastomers produced by the process of claim 1.