Method for the continous preparation of thermoplastically processible polyurethanes

ES 2 238 951 T3

DESCRIPTION

Procedure for the continuous preparation of thermoplastically processable polyurethanes.

The invention relates to a process for the continuous preparation of thermoplastically processable polyurethanes (with improved softening behavior) in a tubular mixer.

Thermoplastic polyurethane elastomers have been known for a long time. They are of technical importance due to the combination of high quality mechanical properties with the known advantages of inexpensive thermoplastic processability. A wide range of variation in mechanical properties can be achieved through the use of different chemical structural components. An overview of TPUs, their properties and uses is provided, for example, in Kunststoffe 68 (1978), pages 819 to 825 or Kautschuk, Gummi, Kunststoffe 35 (1982), pages 568 to 584.

TPUs are synthesized from linear polyols, usually polyester polyols or polyether polyols, organic diisocyanates, and short chain diols (chain extenders). In addition, catalysts can be added to accelerate the formation reaction. The structural components can vary within relatively wide molar ratios, for adjustment of properties. Molar ratios of polyols to chain extenders of 1: 1 to 1:12 have been found to be appropriate. This results in products in the range of 70 Shore A to 75 Shore D.

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

TPUs can be prepared continuously or batchwise. The most widely known technical preparation processes are the tape process (GB-A 1,057,018) and the extrusion process (DE-A 1964834, DE-A 2302564 and DE-A 2059570). In the extrusion process, the starting materials are metered into an endless screw reactor, the polyaddition reaction is carried out on them and they are converted into a uniform granular form. The extrusion process is comparatively simple, but has the disadvantage that the homogeneity of the products prepared in this way is unsuitable for many uses, due to the simultaneous course of mixing and reaction. Furthermore, the softening behavior of TPUs and that of molded bodies produced therefrom is limited. Low-boiling TPUs, such as those used, for example, for cast sheets or sintered products, cannot be prepared by this process or only to a limited extent.

From the state of the art, preparation processes are also known by which the starting materials are first mixed in a mixing zone at temperatures where polyaddition does not occur, and then reacted with each other in a reaction zone having the desired reaction temperature. The mixing and reaction zones are preferably configured as a static mixer.

According to DE-A-2823762, homogeneous products are obtained by the one-step process. According to EP-A-747409, it is dosed by the prepolymer process and homogeneous TPUs with improved mechanical properties are obtained.

Therefore, the aim was to provide a simple process with which it was possible to prepare homogeneous TPUs with improved softening behavior in an economically and technically simple way.

Surprisingly, it has been possible to achieve this goal by a process in which TPUs are prepared continuously under special process conditions in a stirred tubular reactor (tubular mixer), in which the entire TPU reaction is substantially carried out in the "One-step dosing procedure." With this process, homogeneous TPU products with considerably better melting properties are obtained.

The object of the invention is a one-step dosing process for the continuous preparation of homogeneous thermoplastically processable polyurethanes with improved softening behavior, in which one or more diisocyanates (A) and a mixture (B), which has active hydrogen atoms of Zerevitinov, of

B1) 1 to 85% equivalent, with respect to the isocyanate groups in (A), of one or more compounds with an average of at least ^ 1.8 and a maximum of 2.2 active Zerevitinov hydrogen atoms per molecule and with an average molecular weight Mn from 450 g / mol to 5,000 g / mol,

B2) 15% to 99% in equivalents, with respect to the isocyanate groups in (A), of one or more chain lengthening agents with an average of at least 1.8 and at most 2.2 active hydrogen atoms of Zerevitinov per molecule and with a molecular weight of 60 g / mol to 400 g / mol, as well as

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0% to 20% by weight, with respect to the total amount of TPU, additional adjuvants and additives (C), using components (A) and (B) in an NCO: OH ratio of 0.9: 1 to 1, 1: 1, they are reacted substantially to complete conversion in a tubular reactor with stirring without forced transport, characterized in that the ratio between the circumferential speed of the stirrer (m / s) in the tubular reactor and the mass flow rate (g / s ) exceeds the value of 0.03 (m / g).

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

They can be specifically mentioned, by way of example: aliphatic diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic diisocyanates, such as isophorone diisocyanate, 1,4-cyclohexanediisocyanate, 1-methyl-2,4-cyclohexanediisocyanate and 1-methyl-2,6-cyclohexanediisocyanate as well as the corresponding 4,4'- isomeric mixtures, 2,4'- and 2,2'-dicyclohexylmethane diisocyanate as well as the corresponding isomeric mixtures and aromatic diisocyanates, such as 2,4-toluene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,6-toluene 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, 4,4'-Diphenylmethane diisocyanate and / or 2,4 ' -Liquid urethane-modified diphenylmethane diisocyanates, 4,4'-diisocyanatodiphenylethane- (1,2) and 1,5-naphthalenediisocyanate. Preferably 1,6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, isomeric mixtures of diphenylmethane diisocyanate with a 4,4'-diphenylmethane diisocyanate content of more than 96% by weight and, in particular, 4,4'-diphenylmethane diisocyanate and, in particular, 4,4'-diphenylmethane diisocyanate are used. The diisocyanates mentioned can be used singly or in the form of mixtures with one another. They can also be used together with up to 15% by weight (calculated on total diisocyanate) of a polyisocyanate, but at most in such an amount that a thermoplastically processable product is formed. Examples are triphenylmethane-4,4 ', 4 ″ -triisocyanate and polyphenyl-polymethylene-polyisocyanates.

As component B1) preferably linear polyols with hydroxyl end groups are used, with an average of 1.8 to 3.0, preferably up to 2.2 active hydrogen atoms of Zerevitinov per molecule and with an average molecular weight of 450 to 5,000. For production reasons, these often contain small amounts of non-linear compounds. Therefore, they are often referred to as "substantially linear polyols". Polyesterdiols, polyetherdiols, polycarbonate diols, or mixtures of these are preferred.

Suitable polyetherdiols can be prepared by reacting one or more alkylene oxides with 2 to 4 carbon atoms in the alkylene moiety with a starter molecule containing two attached active hydrogen atoms. As alkylene oxides, mention may be made, for example: 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 separately, alternatively in succession or as mixtures. Suitable starter molecules are for example: water, amino alcohols, such as N-alkyl-diethanolamines, for example N-methyl-diethanolamine, and diols, such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol and 1,6- hexanediol. If necessary, mixtures of starter molecules can also be used. Also suitable polyether polyols are hydroxyl group-containing polymerization products of tetrahydrofuran. Trifunctional polyethers can also be used in amounts of 0 to 30% by weight, relative to bifunctional polyethers, but at most in an amount such that a thermoplastically processable product is formed. The substantially linear polyetherdiols preferably have molecular weights of 450 to 5,000. They can also be used both separately as well as in the form of mixtures with each other.

Suitable polyesterdiols can be prepared, for example, from dicarboxylic acids with 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric alcohols. Examples of suitable dicarboxylic acids are: 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 separately or as mixtures, for example, in the form of a mixture of succinic acid, glutaric acid and adipic acid. For the preparation of the polyesterdiols, it may be advantageous, if necessary, to use the corresponding dicarboxylic acid derivative instead of dicarboxylic acids, such as carboxylic acid diesters with 1 to 4 carbon atoms in the radical alcohol, carboxylic acid anhydrides or chlorides. carboxylic acid. Examples of polyhydric alcohols are glycols with 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 , 2-dimethyl-1,3-propanediol, 1,3-propanediol and dipropylene glycol. The polyhydric alcohols can be used alone or optionally in admixture with one another, depending on the desired properties. Furthermore suitable are the esters of carbonic acid with the mentioned diols, in particular those with 4 to 6 carbon atoms, such as 1,4-butanediol and / or 1,6-hexanediol, condensation products of ω-hydroxycarboxylic acids, for example -hydroxycaproic acid, and preferably polymerization products of lactones, for example substituted ω-caprolactones, if appropriate. As polyesterdiols there are preferably used ethanediol polyadipates, 1,4-butanediol polyadipates, ethanediol-1,4-butanediol polyadipates, 1,6-hexanediol-neopentylglycol polyadipates, 1,6-hexanediol-1,4-butanediol polyadipates and polycaprolactones. Polyesterdiols have average molecular weights from 450 to 5,000 and can be used separately or as mixtures with each other.

As component B2) diols or diamines with an average of 1.8 to 3.0 are preferably used, preferably

ES 2 238 951 T3 up to 2.2 active hydrogen atoms of Zerevitinov per molecule and with an average molecular weight of 60 to 400, preferably aliphatic diols with 2 to 14 carbon atoms, such as ethanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and in particular 1,4-butanediol. However, diesters of terephthalic acid with glycols having 2 to 4 carbon atoms are also suitable, such as, for example, terephthalic acid with bis-ethylene glycol or terephthalic acid with bis-1,4-butanediol, hydroxyalkylene ethers of hydroquinone, such as Example 1,4-di (6-hydroxyethyl) -hydroquinone, ethoxylated bisphenols, such as 1,4-di (6-hydroxyethyl) -bisphenol A, aliphatic (cyclo) diamines, such as isophorone diamine, ethylenediamine, 1,2-propylenediamine , 1,3-propylenediamine and N-methylpropylene-1,3-diamine, N, N'-dimethyl-ethylenediamine, and aromatic diamines, such as 2,4-toluylenediamine and 2,6-toluylenediamine, 3,5-diethyl- 2,4-toluylenediamine and / or 3,5-diethyl-2,6-toluylenediamine, and primary mono-, di-, tri- and / or tetraalkyl-substituted 4,4'-diaminodiphenylmethanes. Mixtures of the chain extenders mentioned above can also be used. In addition, small amounts of triols can also be added.

Furthermore, small amounts of conventional monofunctional compounds can also be used, for example as chain interrupters or mold release aids. For example, alcohols such as octanol and stearyl alcohol, or amines, such as butylamine and stearylamine, are to be mentioned.

For the preparation of the TPUs, the structural components are reacted, optionally in the presence of catalysts, auxiliaries and / or additives, preferably in amounts such that the equivalent ratio of NCO groups A) to the sum of the groups reactive against to NCO, in particular the OH groups of low molecular weight diols / triols B2) and polyols B1), is 0.9: 1.0 to 1.1: 1.0, preferably 0.95: 1.0 to 1.10: 1.0.

Suitable catalysts according to the invention are conventional tertiary amines known from the state of the art, such as, for example, triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N, N'-dimethyl-piperazine, 2 (dimethylamino-ethoxy) -ethanol, diazabicyclo- (2,2,2) -octane, 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. The preferred catalysts are organometallic compounds, in particular titanic acid esters and iron and / or tin compounds.

In addition to the TPU components and the catalysts, adjuvants and / or additives C) can also be added up to 20% by weight, relative to the total amount of TPU. They can be predissolved in one of the TPU components, preferably in component B1), or else, if necessary, metered in in mixing equipment, such as an extruder, connected after the reactor with stirring, after the reaction has been carried out. For example, mention may be made of lubricants, such as fatty acid esters, metal soaps thereof, fatty acid amides, amide-esters of fatty acids and silicone compounds, anti-adhesion agents, inhibitors, stabilizers against hydrolysis, light, heat. and discoloration, flame retardants, colorants, pigments, organic and / or inorganic fillers and reinforcing agents. The reinforcing agents are, in particular, fibrous reinforcing substances, such as inorganic fibers, which can be prepared according to the state of the art and can also be filled with a sizing. More details will be obtained on the adjuvants and additives mentioned in the technical literature, for example the monograph by JH Saunders and KC Frisch “High Polimers”, Volume XVI, Polyurethane, Part 1 and 2, Verlag Interscience Publishers 1962 and 1964, the Taschenbuch für Kunststoff-Additive by R. Gachter and H. Müller (Hanser Verlag Munich 1990) or the document DE-A- 2901774.

Other additives that can 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 as well as other TPUs can also be used. In addition, available plasticizers are suitable for incorporation, such as phosphates, phthalates, adipates, sebacates, and alkylsulfonic acid esters.

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

Components A) and B) are heated separately from each other, preferably in a heat exchanger, to a temperature between 50 ° C and 220 ° C and are simultaneously and continuously metered in liquid form into a tube (tubular mixer ), which is stirred without forced transport with a length / diameter ratio of 1: 1 to 50: 1, preferably 2: 1 to 20: 1.

The agitator mixes the components at a speed of preferably 200 to 5,000 rpm. According to the invention, the agitator speed is adjusted in such a way that the ratio between the circumferential speed of the agitator diameter in m / s and the mass flow rate (sum of the dosages of components A) + B) and the optional C )) in g / s exceed the value of 0.03 m / g. A value greater than 0.06 m / g is preferred.

The agitator is a mechanical agitator, preferably monoaxially rotating, without forced transport. As mixing elements, for example bars, rods, anchors, grates, paddles or propellers can be used.

According to the invention, the TPU synthesis reaction is carried out substantially up to complete conversion, that is to say> 90%, with respect to the starting component A), in the stirred tubular reactor (tubular mixer). The residence time required for this is 2 seconds to 5 minutes, depending on the yield, the raw materials used, the reaction temperatures and the catalyst. For economic reasons, the conditions mentioned

ES 2 238 951 T3 are preferably set to a residence time in the tubular mixer of 5 to 60 s.

The reaction temperatures here reach values ​​of 140 ° C to 300 ° C, preferably above 220 ° C, depending on the initial temperature of the starting components.

The reaction mixture is continuously discharged from the tubular mixer. It can be deposited directly on a conveyor. After heat treatment at temperatures of 60 ° C to 180 ° C and subsequent cooling, the TPU mass can be granulated. In a continuous preparation process, the conveyor is a continuous conveyor belt.

In a particular variant according to the invention, the reaction mixture from the tubular mixer is metered directly into a continuously operating kneader and / or extruder (for example a double-shaft ZSK kneader), in which additional coadjuvants can be mixed in TPU at temperatures from 120 ° C to 250 ° C. At the end of the extruder, it is granulated in the same way.

The TPU prepared by the process according to the invention can be processed into injection molded articles, extruded articles, in particular into cast sheets, into coating compositions or sintering types, and into low melting point coextrusion types, such as types of laminations, calendering and slip casting. With good homogeneity, it is distinguished above all by a low softening temperature, as well as the mold articles produced from it.

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

Examples Examples 1 to 5

TPU formula for examples 1 to 5:

Poly-butane-1,4-diol adipate (approximate molecular weight 820) Butane-1,4-diol

4,4'-Diphenylmethane-diisocyanate Ethylene-bis-stearylamide Tin dioctoate parts by weight

7.4 parts by weight 37 parts by weight 0.2 part by weight 200 ppm

Example 1

ZSK method not according to the invention (comparison example)

The polyester, in which 200 ppm (relative to polyester) of tin dioctoate was dissolved as a catalyst, was heated to 145 ° C with the butanediol and the mixture was metered continuously into the first receptacle of a ZSK 83 (Werner company / Pfleiderer). 4,4'-diphenylmethane-diisocyanate (130 ° C) and ethylene-bis-stearylamide were metered into the same receptacle. The first 9 sockets of the ZSK were not heated (quasi-adiabatic). Temperatures of up to 240 ° C were reached due to the heat of reaction released. The last 4 receptacles cooled down. The rotational speed of the worm was 270 rpm and the throughput was 10,000 g / min.

At the end of the endless screw, the hot melt was collected in the form of a string, cooled in a water bath and granulated.

The results of the particular test product are provided in the table.

Example 2

Tubular Mixer and ZSK Procedure

The above polyester / butanediol blend was metered continuously with the tin dioctoate at the lower end of a tubular mixer. At the same time, the 4,4'-diphenylmethane diisocyanate (130 ° C) was continuously pumped into the adjacent feed point at the lower end of the tubular mixer. The mass flow rate was 9,000 g / min. The tubular mixer, heated to 240 ° C, had a diameter of 7 cm and a length / diameter ratio of 7: 1. The stirrer equipped with rods of the tubular mixer was rotated at 1,800 rpm. The TPU formed was discharged into the upper end of the tubular mixer and metered directly into the first feed point (receptacle 1) of a ZSK 83. Ethylene bis-stearylamide was metered into the same receptacle. The parameters of the ZSK were adjusted analogously to Example 1. The quasi-adiabatic adjustment of the pot temperature showed that no more heat of reaction was released in the ZSK.

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At the end of the worm, the hot runner was drawn off, cooled in a water bath, and granulated.

Examples 3 to 5

Tubular mixer procedure without extruder

This procedure was carried out analogously to Example 2. An unheated tubular mixer with a diameter of 4.2 cm and a length / diameter ratio of 2.7 was used. The yield was 520 g / min and the stirrer speed was 500, 1,000 or 3,000 rpm.

The polyester / butanediol mixture was heated to 170 ° C and the 4,4'-diphenylmethane diisocyanate was heated to 80 ° C.

The conversion at the end of the tubular mixer was 99% equivalent to 4,4'-diphenylmethane diisocyanate.

The TPU was continuously dosed onto a coated metal carrier, after heating at 110 ° C for 30 min, and granulated.

Production of blown sheets from the TPU of examples 1 to 5

The corresponding TPU granules were melted in a 30 / 25D Plasticorder PL 2000-6 single screw extruder from the Brabender company (dosage: 3 kg / h; 185 ° C-205 ° C) and extruded through a sheet blowing head in a tubular sheet.

Production of injection molded articles from the TPU of Examples 1 to 5

The corresponding TPU granules were cast on a Mannesmann company D 60 (32 ° screw) injection molding machine (approx. 225 ° C melt temperature) and molded into sheets (125mm x 50mm x 2mm).

Dynamic-mechanical analysis (ADM) with respect to temperature

A dynamic and mechanical measurement of a specimen (50 mm x 12 mm x 2 mm) extracted from the injection molded sheet was carried out for each of the products, in a torsion pendulum test with respect to temperature, analogous to the DIN 53445 standard.

Measurements were made with the RDA 700 from Rheometrics company with 1 Hz in the temperature range of -125 ° C to 200 ° C, with a heating rate of 1 ° C / min.

For the characterization of the softening behavior according to the invention, the following table indicates the temperature at which the storage modulus G 'reaches the value of 1 MPa (the softening temperature).

Mechanical test at room temperature

The modulus at 100% of elongation was measured in the injection molded specimens, according to DIN 53405.

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Results

<td>Example</td><td>Reactor</td><td>Time of permanence (s)</td><td>Velocity of the agitator (rpm)</td><td>Velocity circumferential/ mass flow (m / g)</td><td>Module to 100% (MPa)</td><td>Temperature of softening ADM (° C)</td>

<td>r</td><td>ZSK</td><td> 30</td><td> 270</td><td> 0,01</td><td> 10,3</td><td> 152</td>

<td> 2</td><td>Mixer tubular</td><td> 10</td><td> 1800</td><td> 0,04</td><td> 9,9</td><td> 149</td>

<td> 3</td><td>Mixer tubular</td><td> 15</td><td> 500</td><td> 0,13</td><td> 10,1</td><td> 135</td>

<td> 4</td><td>Mixer tubular</td><td> 15</td><td> 1000</td><td> 0,25</td><td> 9,8</td><td> 136</td>

<td> 5</td><td>Mixer tubular</td><td> 15</td><td> 3000</td><td> 0,76</td><td> 10,3</td><td> 129</td>

* comparison example not according to the invention

Blown sheets of all products were obtained.

The products produced by the tubular mixer process according to the invention have a considerably reduced softening temperature compared to the product produced by the normal ZSK process, with the same mechanical properties at room temperature and the same good laminar homogeneity.

These melt properties are particularly advantageous for TPU cast sheets and the sintering industry.