HK1033143B - A process for the continuous preparation of melt processable polyurethanes with improved softening behaviour - Google Patents

Description

Method for the continuous production of melt processable polyurethanes with improved softening properties

The invention relates to a method for the continuous production of melt-processable polyurethanes with improved softening properties in a static mixer.

Thermoplastic polyurethane elastomers (TPU) are by no means new. They are of great industrial importance owing to the combination of the well-known advantages of high-quality mechanical properties and inexpensive melt processability. Due to the use of different chemical components, a wide variation of mechanical properties can be obtained. A review of TPUs, their properties and applications is given, for example, on pages Kunststoffe 68(1978), 819. quadrature.825 or Kautschuk, Gummi, Kunststoffe 35(1982), 568. quadrature.584.

TPUs are synthesized from linear polyols, usually polyester polyols or polyether polyols, organic diisocyanates and short-chain diols (chain extenders). Additionally, a catalyst may be added to accelerate the formation reaction. These components can be varied within a wide range of molar ratios in order to adjust the properties. Molar ratios of polyol to chain extender of from 1: 1 to 1: 12 have proven suitable. As a result, products ranging from 70Shore A to 75Shore D were obtained.

The synthesis of the melt-processable polyurethane elastomers can be carried out either stepwise (prepolymer metering process) or by simultaneous reaction of all components in one step (one-shot metering process).

The TPUs can be prepared in a continuous or batchwise process. The most widely known industrial processes are the belt process (GB-A1057018) and the extruder process (DE-A1964834, DE-A2302564 and DE-A2059570). In the extruder process, the starting raw materials are metered into a screw reactor, polyaddition is carried out therein, and the product is then converted into a uniform granular form. The extruder process is relatively simple, but has the disadvantage that the homogeneity of the product thus prepared is not sufficient for many applications, since mixing and reaction take place simultaneously. Also, the softening properties of the TPUs and the moldings produced therefrom are limited. Fusible TPUs of the type used for example for hot-melt films or sintered products can be prepared only to a limited extent, if at all, by this process.

Moreover, preparation processes are known from the literature in which the starting materials are initially mixed in a mixing zone at low temperatures at which polyaddition does not occur and are then reacted together in a reaction zone which reaches the desired reaction temperature. The mixing and reaction zone is preferably designed as a static mixer.

In DE-A2823762, homogeneous products are obtained by the "one-shot process". In EP-A747409, the metering is carried out by the prepolymer process, giving homogeneous TPUs with improved mechanical properties.

The object was therefore to provide a simple process with which homogeneous TPUs having improved softening properties can be prepared inexpensively and in an industrially simple manner.

Surprisingly, this object is achieved by the continuous preparation of the TPU in a static mixer, the entire TPU reaction being carried out essentially in a "one-shot metering process" under the particular process conditions. Homogeneous TPU products with much better melting properties can be obtained by this process.

The invention provides a process for the continuous preparation of melt-processable, homogeneous polyurethane elastomers having improved softening properties, in which

One or more polyisocyanates (A) and

mixtures (B) with Zerewitinoff-active hydrogen atoms consisting of the following components in a static mixer for > 500sec^-1And < 50000sec^-1Is homogeneously mixed in at most 1 second at a shear rate of (a), the mixture (B) containing:

B1) 1 to 85 equivalent%, based on the isocyanate groups in (A), of one or more compounds having an average of at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and an average molecular weight Mn of 450-,

B2) 15 to 99 equivalent%, based on the isocyanate groups in (A), of one or more chain extenders having an average of at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and a molecular weight of 60 to 400g/mol, and

from 0 to 20% by weight, based on the total amount of TPU, of other auxiliaries and additives (C),

wherein the components A) and B) are used in a ratio NCO: OH of from 0.9: 1 to 1.1: 1,

the reaction mixture thus prepared is metered into an extruder, optionally via a second static mixer, and optionally with the introduction of auxiliaries and/or further components, characterized in that the polyisocyanate (A) and the mixture (B) each have a temperature of > 170 ℃ and < 250 ℃, the reaction is carried out essentially in the first static mixer to a conversion of > 90%, based on component A), and the reaction mixture leaves the first static mixer at a temperature of > 240 ℃ and < 350 ℃.

Examples of suitable organic polyisocyanates (A) include aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as described, for example, in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136.

More precisely, examples include aliphatic diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic diisocyanates, such as 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 toluene-2, 4-diisocyanate, mixtures of toluene-2, 4-and 2, 6-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 ' -diisocyanatodiphenylethane- (1, 2) and 1, 5-naphthylene-diisocyanate. Mixtures of diphenylmethane diisocyanate isomers having a 4, 4 '-diphenylmethane diisocyanate content of more than 96% by weight and in particular 4, 4' -diphenylmethane diisocyanate and 1, 5-naphthylene diisocyanate are preferably used. 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% (based on the total diisocyanate) but at most only in the amount required to obtain a melt-processable product. Examples are triphenylmethane-4, 4', 4 "-triisocyanate and polyphenyl polymethylene polyisocyanates.

Linear hydroxyl-terminated polyols having an average of from 1.8 to 3.0, preferably 2.2 Zerewitinoff-active hydrogen atoms per molecule and a molecular weight of 450-. For production reasons, it is stated that polyols generally contain small amounts of nonlinear compounds. The term "substantially linear polyol" is therefore often used. Polyester diols, polyether diols, polycarbonate diols or mixtures thereof are preferred.

Suitable polyether diols can be prepared 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 the bonded state. Examples of suitable alkylene oxides include: ethylene oxide, 1, 2-propylene oxide, epichlorohydrin and 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. Examples of suitable starter molecules include: water, amino alcohols such as N-alkyldiethanolammines, for example N-methyldiethanolamine, and glycols such as ethylene glycol, 1, 3-propanediol, 1, 4-butanediol and 1, 6-hexanediol. Optionally, mixtures of starter molecules may also be used. Suitable polyether alcohols are also the polymerization products of tetrahydrofuran which contain hydroxyl groups. It is also possible to use trifunctional polyethers in proportions of from 0 to 30% by weight, based on the bifunctional polyethers, but at most in such amounts that melt-processable products are obtained. The substantially linear polyether diols preferably have molecular weights of 450-5000 g/mol. They may be used alone or in a mixture with one another.

Suitable polyester diols can be prepared, for example, from dicarboxylic acids with dicarboxylic acids of 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric alcohols. Examples of suitable dicarboxylic acids include: aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid and 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 as succinic, glutaric and adipic acid mixtures. For the preparation of the polyester diols, it is also very advantageous to use the corresponding dicarboxylic acid derivatives instead of the dicarboxylic acids, such as carboxylic acid diesters having 1 to 4 carbon atoms in the alcohol radical, carboxylic acid anhydrides or amides. Examples of polyols are diols having 2 to 10 carbon atoms, 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, 2-dimethyl-1, 3-propanediol, 1, 3-propanediol and dipropylene glycol. Depending on the desired properties, the polyols can be used as such or optionally in the form of mixtures. Esters of carbonic acid with the diols mentioned are also suitable, in particular those having from 4 to 6 carbon atoms, such as 1, 4-butanediol or 1, 6-hexanediol, condensation products of omega-hydroxycarboxylic acids, such as omega-hydroxydecanoic acid, and preferably polymerization products of lactones, for example optionally substituted omega-caprolactones. Polyester diols which are preferably used are polyethylene glycol adipate, 1, 4-butanediol adipate, polyethylene glycol-1, 4-butanediol adipate, 1, 6-hexanediol-neopentyl glycol adipate, 1, 6-hexanediol-1, 4-butanediol adipate and polycaprolactone. The polyester diols have a molecular weight of 450-5000g/mol and can be used individually or in the form of mixtures.

Diols or diamines having an average of from 1.8 to 3.0, preferably 2.2, Zerewitinoff-active hydrogen atoms per molecule and a molecular weight of from 60 to 400g/mol are used as component B2), preferably aliphatic diols having from 2 to 14 carbon atoms, for example ethylene glycol, 1, 6-hexanediol, diethylene glycol, dipropylene glycol and in particular 1, 4-butanediol. However, diesters of terephthalic acid and diols having from 2 to 4 carbon atoms are also suitable, for example terephthalic acid-bis-ethylene glycol or terephthalic acid-bis-1, 4-butanediol, hydroxyalkylene ethers of hydroquinone, for example 1, 4-di (. beta. -hydroxyethyl) hydroquinone, ethoxylated bisphenols, for example 1, 4-di (. beta. -hydroxyethyl) -bisphenol A, (cyclo) aliphatic diamines, for example isophorone diamine, ethylene diamine, 1, 2-propane diamine, 1, 3-propane diamine, N-methylpropylene-1, 3-diamine, N, N' -dimethylethylene diamine and aromatic diamines, for example 2, 4-and 2, 6-toluene diamine, 3, 5-diethyl-2, 4-toluenediamine and/or 3, 5-diethyl-2, 6-toluenediamine and primary mono-, di-, tri-and/or tetraalkyl-substituted 4, 4' -diaminodiphenylmethanes. Mixtures of the above chain extenders may also be used. In addition, it is also possible to add smaller amounts of triols.

Furthermore, conventional monofunctional compounds can also be used in relatively small amounts, for example as chain terminators or mold release agents. Examples include alcohols such as octanol and stearyl alcohol or amines such as butylamine and stearylamine.

To prepare the TPUs, these components, optionally in the presence of catalysts, auxiliaries and/or additives, are preferably each reacted in such an amount that the equivalent ratio of NCO groups A) to the sum of the NCO-reactive groups (in particular the OH groups of the low molecular weight diols/triols B2) and polyols B1) 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 are the customary tertiary amines which are well known in the state of the art, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N' -dimethyl-piperazine, 2- (dimethylaminoethoxy) -ethanol, diazabicyclo- (2, 2, 2) -octane and the like, and in particular organometallic compounds, such as titanic acid esters, iron compounds and tin compounds, for example tin diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic carboxylic acids, such as dibutyltin diacetate, dibutyltin dilaurate and the like. Preferred catalysts are organometallic compounds, in particular titanates, iron and/or tin compounds.

In addition to the TPU components and the catalyst, it is also possible for auxiliaries and/or additives C) to be added in amounts of up to 20% by weight, based on the total amount of TPU. They can be dissolved beforehand in one of the TPU components, preferably in component B1), or optionally metered in after reaction has taken place in a downstream reaction apparatus, for example an extruder.

Examples include lubricants, such as fatty acid esters, their metal soaps, fatty acid amides, fatty acid ester-amides and siloxane compounds, antiblocking agents, inhibitors, stabilizers against hydrolysis, light, heat and discoloration, flame retardants, colorants, pigments, inorganic and/or organic fillers and reinforcing agents. Reinforcing agents are, in particular, fibrous reinforcing agents, such as inorganic fibers, which may be prepared according to the prior art and may also have sizing agents applied to their surface. Further details concerning the auxiliaries and additives mentioned can be taken from the technical literature, for example from the monograph by j.h.saunders and k.c.frisch: "high polymers", volume XVI, polyurethane, parts 1 and 2, Verlag Interscience Publishers 1962 and 1964, Taschenbuch fur Kunststoff-Additive, R.G Graprofile and H.M muller, Hanser Verlag, Munich 1990, or DE-A-2901774.

Other additives which may be incorporated into the TPU are thermoplastics, for example, 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. Furthermore, commercial plasticizers such as phosphates, phthalates, adipates, sebacates and alkylsulfonates are suitable for incorporation.

The preparation process according to the invention proceeds as follows:

components A) and B) are heated separately, preferably in a heat exchanger, to a temperature in the range from 170 ℃ to 250 ℃ and then metered simultaneously and continuously in liquid form into a static mixer preferably having a length/diameter ratio of from 5: 1 to 20: 1, most preferably from 8: 1 to 14: 1.

Wherein these components are present at 500-50,000sec^-1Are uniformly mixed and reacted at a shear rate of (1). Homogeneous mixing within the meaning of the present invention means that the concentration distribution of the components and reaction products in the mixture has a relative standard deviation of less than 5%. The residence time in the static mixer is up to 1 second.

The static mixer is adiabatic and is preferably heated to a temperature of 200 ℃ to 260 ℃. Static mixers which can be used according to the invention are mentioned both in chem. -Ing.Techn.52, No.4, pages 285 to 291 and in "Mischen von Kunststoff und Kautschukprodukten", VDI-Verlag, Dusseldorf 1993. Examples include SMX static mixers available from Sulzer.

According to the invention, a conversion of > 90% is obtained in the static mixer, based on the starting component A), the reaction mixture having a temperature of > 240 ℃ and < 350 ℃ on leaving the static mixer.

In a particular embodiment, the reaction mixture is metered, optionally via a second static mixer, directly into a continuously operated kneader and/or extruder (for example a ZSK twin-screw kneader), in which additional auxiliaries are introduced into the TPU at a temperature of between 120 ℃ and 250 ℃.

In the second static mixer, the reaction according to the invention takes place only to a very small extent (< 10%, based on the starting component A)), if present. The granulation is carried out at the end of the extruder.

The TPUs prepared by the process of the invention can be processed to injection-molded articles, extruded articles, in particular hot-melt films, to coatings or sintered types and to fusible coextrusion types, for example of the laminating, calendering and powder-slurry (slush) type. Owing to the good homogeneity, it is characterized primarily by a low softening temperature, which is also the case for moldings produced therefrom.

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

Examples

The TPU formula comprises:

54 parts by weight of poly (1, 4-butylene adipate) (molecular weight: about 820)

7.4 parts by weight of 1, 4-butanediol

37 parts by weight of 4, 4' -diphenylmethane-diisocyanate

Ethylene bis stearamide 0.2 part by weight

Tin dioctoate 200ppm

Example 1

Example 1 (ZSK Process not according to the invention (comparative example)

The polyester, in which 200ppm (based on the polyester) of tin dioctoate as catalyst was dissolved, was heated to 145 ℃ together with butanediol and was then metered continuously into the first barrel of ZSK83 (Werner/Pfleiderer). 4, 4' -diphenylmethane-diisocyanate (130 ℃ C.) and ethylene bisstearamide were metered into the same barrel section. The first 9 barrel sections of the ZSK were not heated (quasi-adiabatic). Temperatures of up to 240 ℃ are obtained due to the liberated heat of reaction. The last 4 barrel sections were cooled. The screw speed was 270 rpm.

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

The results of the relevant product tests are given in the table.

Examples 2 to 7

(static mixer-extruder method):

the polyester-butanediol mixture described above, containing tin dioctoate, is metered continuously into a SMX static mixer from Sulzer¹⁾In (1).¹⁾DN 18: length 185 mm: diameter of 18mm

DN 32: the length is 500 mm: diameter of 32mm

DN 4: length 38 mm: diameter of 4mm

At the same time, the 4, 4' -diphenylmethane diisocyanate was continuously pumped into the static mixer.

The TPU obtained is metered directly into an extruder²⁾Of the first inlet (barrel section 1).²⁾ ZSK 83 (Werner/Pfleiderer)

Welding 3500 (3.5Dual Wonn；Welding Engineers)

Continua 37 (Werner/Pfleiderer)

Ethylene bis stearamide was metered into the same barrel section.

The setting of the ZSK parameters was similar to example 1. The quasi-adiabatic barrel temperature setting revealed that the heat of reaction was released in the ZSK in comparative example 2; in examples 3 and 7, no heat of reaction was released.

This means that only in comparative example 2, the majority of the reaction takes place not in the static mixer but in the extruder.

The two sections of the Welding extruder were heated to 180 ℃. The rate of rotation is 110 rpm.

The Continua extruder was heated to 200 ℃. The rate of rotation was 100 rpm.

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

Preparation of blown films

Starting from the TPUs of examples 1 to 7.

The TPU pellets were melted in a single-screw extruder 30/25 DPlastifier PL 2000-6 (metering rate 3kg/h, 185-.

Preparation of injection-molded articles

Starting from the TPUs of examples 1 to 7.

The TPU pellets were melted in an injection molding machine D60(32 screw) from manninesmann (melt temperature about 225 ℃) and formed into sheets (125 mm x 50 mm x 2 mm).

Kinetic analysis (DMA) as a function of temperature

In each case, the kinetic measurements of the specimens (50 mm. times.12 mm. times.2 mm) cut from the injection-molded sheets of the product were carried out as a function of temperature in a torsion pendulum test, analogously to DIN 53445.

The measurement was carried out with RDA 700 from Rheometrics at 1Hz in the temperature range-125 ℃ to 200 ℃ and at a heating rate of 1 ℃/min. In order to characterize the softening behaviour according to the invention, the temperature at which the memory modulus G' reaches a value of 1MPa (softening temperature) is given in the table below.

Mechanical testing at room temperature

The modulus at 100% elongation was measured on injection-molded test specimens in accordance with DIN 53405.

As a result:

examples	Static mixer/extruder	Yield [ g/min [ ]]	Shear rate in static mixers [ sec-1]	Residence time in static mixer sec]	Temperature of each component A)/B) [ ° C]	In a static mixer1Temperature of the tip of (1 [ ° c)]	100% modulus [ MPa ]]	Softening temperature DMA [ deg.C]
									1*	ZSK 83	10000			130/145		10.3	152
2*	DN 18/ZSK 83	9000	2000	0.4	90/95	160	10.0	153
									3*	DN 18/ZSK 83	9000	2000	0.4	155/185	200	a)	a)
4*	DN 32/Welding	5500	140	5.5	170/170	230	a)	a)
									5	DN 18/Welding	5500	1300	0.6	180/200	285	9.9	143
6	DN 4/Continua	70	1000	0.3	180/180	280	10.1	139
									7	DN 18，DN 18/ZSK 83	9100	2000	0.4	190/180	282	10.8	143

^*Comparative examples not according to the invention

a) After 30 minutes the static mixer was blocked; continuous preparation of the TPU becomes impossible.

Homogeneous blown films were obtained from the entire product.

If all the parameters (temperature, shear rate and residence time) of the static mixer process according to the invention are observed, a product is obtained which has a much lower softening temperature than the product prepared by the standard ZSK process and which has the same mechanical properties at room temperature and equally good film homogeneity.

These melting properties are desirable, especially for TPU hot melt films and sintered parts (sectors).

Claims (6)

1. A continuous process for preparing a thermoplastic, homogeneous polyurethane elastomer having improved softening properties, comprising:

(i) obtaining at least one polyisocyanate (A) at a temperature higher than 170 ℃ and lower than 250 ℃ and a mixture (B) at a temperature higher than 170 ℃ and lower than 250 ℃, containing:

B1) 1 to 85 equivalent%, based on the isocyanate groups in (A), of at least one compound having an average of at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and a number average molecular weight of 450-

B2) 15 to 99 equivalent%, based on the isocyanate groups in (A), of at least one chain extender having an average of at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and a molecular weight of 60 to 400g/mo1, and

(ii) in a static mixer for more than 500sec^-1And less than 50000sec^-1Said (A) and (B) being homogeneously mixed at a NCO: OH ratio of from 0.9: 1 to 1.1: 1 over a period of up to 1 second at a shear rate of (A) to form a reaction mixture having a conversion of more than 90% based on (A) and a temperature of more than 240 ℃ and less than 350 ℃, and

(iii) the reaction mixture is metered into an extruder.

2. The process of claim 1 wherein the reaction mixture additionally comprises up to 20% of other auxiliaries and additives, based on the weight of the polyurethane.

3. The method of claim 1, wherein B1) is at least one selected from the group consisting of polyester polyols, polyether polyols, and polycarbonate polyols.

4. The process of claim 1 wherein B2) is at least one member selected from the group consisting of ethylene glycol, butanediol, hexanediol, 1, 4-bis (β -hydroxyethyl) -hydroquinone and 1, 4-bis (β -hydroxyethyl) bisphenol a.

5. The process of claim 1 wherein A) is an aromatic diisocyanate.

6. The process of claim 5 wherein the aromatic diisocyanate is a mixture of diphenylmethane diisocyanate isomers containing greater than 96% by weight of 4, 4' -diphenylmethane diisocyanate.