DD148884A3 - METHOD FOR PRODUCING POLYURETHANE PRODUCTS - Google Patents

Abstract

The aim of the invention is to produce homogeneous, non-tacky and by deformation processable polyurethane products after short reaction times of the feedstock. The invention has for its object to develop a two-stage process in which the feedstock be supplied so that the Schmelzviskositaet after short residence times takes very high values. This is achieved by preparing in the first stage from the diisocyanate and the entire low molecular weight diol, a free liquid containing free isocyanate groups Preaddukt. This feedstock is reacted with all of the polyol in the second stage, greatly increasing the melt viscosity of the liquid reaction mixture in the initial period of the second stage reaction. This increase usually takes place to a maximum, which is above the final viscosity of the fully reacted polyurethane, based on the same temperatures. As the reaction progresses, this maximum is broken down. In the ongoing reaction, the melt viscosity is then increased again.

Description

197

Title of the invention: Process for the preparation of polyurethane products Application of the invention

The invention is used in the chemical industry · With the aid of the invention, polyurethane can be produced in the form of granules, films, profiles and the like.

The invention makes it possible to produce polyurethane product G used for injection molding, extrusion and textile coating or as adhesive. The process according to the invention is particularly suitable for soft formulations in the case of thermoplastically deformable polyurethane elastomers. Related to the system 4, 4-diphenylmethane diisocyanate For example, 1,4-butanediol and a polyester of adipic acid, 1,4-butanediol and ethylene glycol relate to a thermoplastically deformable soft polyurethane with hardnesses between 60 and 80 Shore A *.

Characteristic of the known technical solutions

From the German patent 831772 a two-stage process for the preparation of high molecular weight crosslinked plastics is known, in which one reacts organic linear polyesters in the absence of moisture with an excess of organic diisocyanates · In the thus obtained isocyanate polyesters in the second stage, a glycol is fed, where to put this

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Glycol reacts with the isocyanate groups with simultaneous shaping.

Likewise, BRD-OS 2302564 describes a two-stage polyurethane production process in which, in the first stage, an isocyanate group-containing pre-adduct is first formed from the monomeric isocyanates and the polyhydroxyl compound, which then reacts further with the chain extenders in the second stage.

These processes have the disadvantage for soft thermoplastically deformable elastomers, textile coatings and adhesives that the melt viscosity increases only slowly as the conversion progresses. This results in long reaction times until the formation of granular products and continuous granulation immediately after the product preparation process is not or only possible with low reliability.

Furthermore, from the GDR patent specification 115142 a two-stage process for the preparation of thermoplastically deformable polyurethane elastomers is known in which in the first stage from the entire diisocyanate and a part of the low molecular weight diol, a liquid Preaddukt is prepared. This Preaddukt is reacted in the second stage with the remaining part of the low molecular weight diol and the total polyol. This process is mainly suitable for formulations above 90 Shore A hardness · The sales trend is relatively slow. Moreover, the division of the diol into two parts and their separate addition is disadvantageous.

Object of the invention

The aim of the invention is to provide a method by which a homogeneous, non-sticky and workable by deformation polyurethane can be prepared after short reaction times of the feedstock. This method should be characterized by a low cost and expense and good controllability of the reaction.

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Explanation of the essence of the invention

The invention has for its object to develop a two-stage process for the preparation of polyurethane products, in which the feedstock are fed so that high turnover rates occur and the melt viscosity of the reaction products after short residence times takes very high values.

This object is achieved in that in the first stage of the diisocyanate and the entire low molecular weight diol, a free isocyanate-containing liquid Preaddukt is prepared in this reaction between the diisocyanate and the diol, a relatively large amount of heat released, which in the known polyurethane production process completely or partially free only in the second stage. Due to this exothermic reaction, the temperature of the Preadduktes adiabatic driving in the first stage increases to 180 to 230 C in the inventive method, the starting temperatures of the mixture are between 50 to 90 C *

This Preaddukt is then reacted in the second stage with the entire polyol. The melt viscosity of the reaction mixture is hereby increased on the assumption of comparable conditions (same temperatures, same formulations) in the initial period of the reaction of the second stage to values which are two to seven times higher than in the known prepolymer process. Thus, in the initial period of the reaction, the melt viscosity preferably undergoes a maximum, which in isothermal conditions is above 70 % of the final viscosity of the reacted polyurethane. The NCO content of the reaction mixture at the same residence time is the same or "lower than in the known prepolymer process, the reaction time to reach processable products is in this

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Process under comparable conditions only about half the size of the known prepolymer processes

An expedient embodiment of the method provides that in the production of thermoplastically deformable polyurethane elastomers and polyurethane textile coating compositions, the pre-formed in the first stage Preaddukt having a melt viscosity of less than 200 cP at a temperature of 180 to 230 ⁰ C of the second stage is supplied In order to prepare polyurethane adhesives, the prepolymer is also supplied with a melt viscosity lower than 200 cP at a temperature of from 160 to 200 ^° C. of the second stage.

A further improvement provides that in the preparation of polyurethane elastomers or polyurethane textile coating compositions, the reaction in the second stage is carried out at temperatures of 220 to 250 ⁰ C.

In the invention, polyurethane products are understood to mean only thermoplastically deformable polyurethane elastomers, polyurethane textile coating compositions and polyurethane adhesives; polyurethane foams should not be included in the evaluation

When carrying out the process according to the invention, approximately stoichiometric ratios between the NCO groups and the OH groups are generally observed. The NCOtOH ratio will generally be between 0.96 and 1.05.

For the invention, implementing the known organic diisocyanates which are usually used for producing polyurethane products are 1 1,4 · These include, for example, 4,4-diphenylmethane diisocyanate ^§, 2,4-tolylene diisocyanate, 2, 6-toluene diisocyanate, 5-naphthalene diisocyanate, Phenylene diisocyanate and the like in addition to their mixtures of two or more. Preferably, MDI (4,4- ^t- diphenylmethane diisocyanate) is used.

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Polyesters based on adipic acid and diols, such as 1,4-butanediol, 1,6-butanediol, 1,6-hexanediol and ethylene glycol are particularly suitable for carrying out the invention.

The low molecular weight diols serve as chain extenders. As a rule, 1,4-butanediol is used as a chain extender. However, it is also possible to use mixtures of 1,4-butanediol with other chain extenders, for example 1,6-hexanediol. Such mixtures are used in particular in the production of polyurethane adhesives. In the production of heat-resistant polyurethane products, anctatt 1,4-butanediol also uses 1,4 bis (hydroxyethoxy) benzene as a chain extender. In this case, trimethylpropane is also added as crosslinking agent as a further component.

In addition, fillers of active or inactive nature may also be added in the addition reaction. The method is particularly suitable for polyurethane products in which the total amount of diol and the isocyanate below 250 C melt products. Due to the fact that in the processes according to the invention the melt viscosity of the reaction mixture is increased very rapidly, the time after which a deformable product is present is only short. Thus, the throughput through the used for carrying out the method twin-screw extruder is substantially greater than in the known polyurethane production process. The reaction produces high-quality homogeneous products with good injection molding, extrusion, dissolving and melting properties · The product is good and reliable granulation ·

embodiment

The invention will be explained in more detail below with reference to three exemplary embodiments.

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Example 1 (method according to the invention)

In a 1 liter stirred tank, according to an NCO / OH ratio of 1.02 and taking into account the corresponding raw material purities, wherein the water content of the OH-group carrier is compensated by an isocyanate parent, weighed:

156.4 g of 4.4 ^t- diphenylmethane diisocyanate (MDI) with a purity of 98.48 % (1 g of MDI is hereby included to compensate for the water in the diol and polyol)

With stirring, the MDI is heated to 65 ^° C.

To this MDI is added 36.3 g of 1,4-butanediol (99.2% purity, 0.021 % HgO content) at room temperature. A catalyst is not added.

The mass is initially cloudy, but clears up at the beginning of the reaction. With moderate stirring, the temperature rises to 30 - 40 see. rapidly to 220 to 230 ⁰ C, wherein the melt is somewhat viscous and a slight gas evolution begins (CO ₂ due to water content and possibly traces of carbodiimide) · This reaction is the first step of the process · It holds the melt 1 to 2 · min at 225 ⁰ C with gentle stirring and then added in the second stage of the process in one portion 432.4 g of a polyester of adipic acid with 1,4-butanediol and ethylene glycol having a molecular weight of 2160 (having a water content of 0.015%) of t with preheating to 165 ° C. while stirring.

After 20-30 see the viscosity increases strongly; The stirrer is turned off and a part of the mass in a tempered at 190 ⁰ C "Brabender Plastographen" (laboratory kneading machine Fa · Brabender, Duisburg) poured with a mixing chamber volume of 100 cm and kneaded for 30 min · at 100 U / min · the reaction is with respect to the NCO content and the intrinsic viscosity followed by taking samples at specific time intervals · the melt viscosity is continuously by a scribe in units of the ₄ lent plastograph displayed ·

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The time courses of melt viscosity and NCO content are shown in FIGS. 1 and 2.

As can be seen from curve 1 in FIG. 1, a maximum occurs at the melt viscosity after about 3 minutes of reaction. This maximum corresponds to 590 units of the Brabender Plastograph. With increasing reaction time, this maximum is reduced again to 280 units melt viscosity first faster and then slower to reach 320 units after 20 minutes and 335 units after 30 minutes * These changes in melt viscosity are always related to a constant temperature. Thus, the change in melt viscosity is not due to cooling or heating of the melt In both drawings is the technically interesting residence time range according to the recipe according to Examples 1 and 2 (3 to 6 minutes reaction time, the reaction time with the addition of the polyester to de It can be seen that after a reaction time of 6 minutes, the melt viscosity corresponds to 320 units and is therefore exactly as high as after about 20 minutes. After a reaction time of about 5 minutes, there is thus a product which, despite the relatively incomplete conversion, can be granulated immediately.

Example 2 (comparative method)

It is worked with the raw material batches and according to the recipe of example 1. However, the raw materials are added in the order corresponding to the known prepolymer method (comparative method). Again, no catalyst is added. In two stirred tanks

156;, 5 g MDI and

432.4 g of polyester

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heated separately to 100 ^° C. The polyester is added to the MOI in a cast and stirred for 2 minutes. The temper «Stirring increases

Temperature to 110 - 120 ⁰ C on. Now you add under good

36.6 g of 1,4-butanediol

from room temperature to which the temperature further to 160 - 170 ⁰ C increases · After 1.5 to 2 minutes, the viscous mass is and, now in the 190 ⁰ C tempered "Brabender plastograph" and 30 Min · at 100 U / The reaction is monitored with respect to the NCO content and the intrinsic viscosity by sampling at specific time intervals. The melt viscosity is continuously recorded on a recorder in units of the plastograph. The curve 2 in FIG. 1 shows that the melt viscosity in the first 10 - 12 minutes continuously and then the increase gradually decreases. In the technically interesting residence time range (3 to 6 minutes reaction time, starting with the addition of the butanediol to the MDI-polyester mixture), the melt viscosity increases to 125 units of the Brabender Plastagraphen.

The melt viscosity of the reaction mixture is therefore considerably lower in this process after a reaction time of 3-6 minutes than in the process described in Example 1. The maximum difference between the two processes is after a reaction time of 3 minutes. While in Example 1, after this time, the melt viscosity of the reaction mixture corresponds to 590 units, it increases in the method described in this example, only 60 units. At long reaction times (longer than 20 minutes), the melt viscosities of both processes approach a common final value.

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In contrast to the course of the melt viscosity, the processes described in Examples 1 and 2 show an almost identical course of the intrinsic viscosity or of the macromolecule structure. As can be seen from FIG. 2, the rate of turnover of the NCO reaction in both methods is approximately the same. In FIG. 2, the curve corresponding to example 1 is designated by the reference numeral 3 and the curve corresponding to example 2 bears the reference numeral 4 ·

The sales gradients shown in FIG. 2 were determined for uncatalyzed systems. By adding catalysts, the sales curves are clearly shifted to the left due to the acceleration of the reaction.

Example 3 (process according to the invention):

From the same raw material batches as in Examples 1 and 2, a larger amount (about 2 kg) of polyurethane elastomers is produced by the casting process; the mechanical characteristics are determined · 519.0 g MDI are heated in a 3-liter stirred tank at 90 ⁰ C · Add to that in one portion 120.7 g of 1,4-butanediol from room temperature. The ar.fgangs turbid mixture clears after the reaction has started, and the temperature rises within 20 to 30 see · to 230 to 240 C. Once the maximum of the temperature is reached, 1441.0 g of the mixed polyester of adipic acid with 1,4-butanediol and ethylene glycol having a molecular weight of about 2000, which has been preheated to 140 ⁰ C ', a molding added :, stirred for 10 - 20 · lake vigorously and shed immediately to a PTFE-coated film sheet that was preheated to 180 - 190 ⁰ C. On this sheet, the molding is held for 30 minutes, then removed, cooled and zerkleinerteDie granules thus obtained are heat-treated for 2 hours at 100 ⁰ C and then processed on an injection molding machine at 190 ⁰ C Zylinderteraperatur to standard test specimens

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The standardized material tests give the following material characteristics:

tensile strenght kp / cm 350 Tear strength kp / cra 85 elongation % 645 Hardness Shore A 75 ° impact resilience % 38 abrasion nm 30 density g / ml 1.23 ·

Claims (4)

, U-197686 Erfindunqsansprucht 1 · A process for the preparation of polyurethane products from diisocyanates, polyols and low molecular weight diols at temperatures between 50 and 250 ⁰ C in two stages, characterized in that in the first stage of the oiisocyanate and the entire low molecular weight oiol a free isocyanate-containing liquid Preaddukt is producedj which is reacted in the second stage with the entire polyol, wherein the melt viscosity of the liquid reaction mixture in the initial period of the reaction of the second stage is very much increased ', preferably to a maximum, which is above 70 % of the final viscosity of the reacted polyurethane, based on the same temperatures "is · 2 · The method of item 1, characterized in that in the preparation of polyurethane elastomers and polyurethane textile coating compositions, the preadduct is supplied with a melt viscosity of less than 200 cP at a temperature of 190-230 ⁰ C of the second stage · 3 * Process according to item 1 ', characterized in that in the production of polyurethane adhesives, the Preaddukt having a melt viscosity of less than 200 cP at a temper
becomes" Temperature of 160 to 200 ⁰ C supplied to the second stage 4 · A method according to item 1 or 2, characterized in that Wiru carried out in the production of polyurethane elastomers or polyurethane textile coating compositions of the reaction in the second stage at temperatures from 220 to 250 ⁰ C * For this, "" Drawings