SI9200092A - Process for preparing a foam sheet of thermoplastic polyurethane and product obtained therefrom - Google Patents

Abstract

A process for preparing a foam film from thermoplastic polyurethane in which the polyurethane is mixed with a blowing agent and shaped continuously or batchwise in a suitable apparatus by means of the action of heat, and the product thus obtainable.

Description

Process for the production of thermoplastic polyurethane foam as well as the product obtainable therefrom

The invention relates to a process for making a foam film of thermoplastic polyurethane as well as to a product obtainable therefrom.

Polyurethanes are formed from the polyaddition reaction of isocyanates with at least two groups of NCOs and diols or. polyols upon formation of the urethane group (RCNH-CO-OR ² ). While used as isocyanate components, they are mainly lower molecular weight diisocyanates, such as TDI (isomeric mixture of 2,4- and 2,6-toluylenediisocyanate), they are like diols or. polyols important predominantly polyester and polyether polyols, i.e., longer chain compounds, also branched, with terminal hydroxyl groups. In special cases, when urea derivatives are formed, lower molecular weight diamines are used to extend the chain.

Today different processes are used to make polyurethane foams:

a) by reaction of isocyanate with water, CO is formed which functions as a foam gas (preferably in the manufacture of soft foam);

b) by the addition of low boiling liquids, the foam is reacted exothermically (preferably in the manufacture of hard foam) by evaporation of the foam. and

c) by blowing or boiling in air, they form a foam during the reaction (preferably in the production of foam coatings).

In doing so, the foaming reaction and the crosslinking reaction with special catalysis must be coordinated with each other so that none overtakes the other.

Although the manufacture of thermoplastic polyurethane elastomers has been known since the 5Os, with high tensile strength and tear strength, high flexibility even at low temperatures, high durability, low durable deformation under static dynamic loading, high abrasion resistance, and wear, high tear strength, high damping, high resistance to oils, fats and many solvents and energy-rich and UV-free, and which have no softeners, have not yet been fortunate enough to obtain foam foils of this kind. Therefore, in areas where foam films are used on a large scale, such as in the automotive industry, they have been linked to the use of soft PVC products, which are questionable from an ecological point of view. Thermoplastic polyurethane, which could replace PVC here, is unknown in the art.

The invention is therefore based on the task of creating a new type of foam based on polyurethane, which can replace the previously known soft foam of PVC.

According to the invention, this task is accomplished in the general process by mixing polyurethane with foam and in a suitable preparation continuously or discontinuously shaped by heat.

Particularly advantageously used as thermoplastic polyurethane aliphatic ahromatic polyurethane based on polyethers, polyesters, polyalkanes, polyalkenes or polyalkines or mixtures thereof.

According to the invention, it is proposed to use as foaming thermally degradable, inorganic hydrogen carbonates.

Alternatively, the thermally degradable salts of organic mono-, di- or polyfunctional acids can be used as a foam.

It is particularly advantageous to use the hydrogen salts as salts.

Particularly advantageous is the addition of inorganic and / or organic acids as an auxiliary foam.

It is further proposed to use diazendicarboxylic acid diamide as a foam.

It is particularly advantageous to add catalysts for the decomposition of diazendicarboxylic acid diamides.

We further propose to use sulfohydrazides as a foaming agent.

Alternatively, it can be used as a foaming sulfonylsemicarbazide.

According to the invention, it is finally proposed to use tetrazoles as foam.

Preferably, foaming of the foil is performed via extrusion.

Polyurethane in the form of granulate and / or powder can be advantageously used.

It is further suggested that foam foil is thermally wetted after formation for 15 to 20 hours at 80 to 120 ° C to achieve the optimum level of its properties. This results in a subsequent chemical reaction of the components. Thermal empowerment is especially important for the return behavior to its original form.

The invention further relates to a foam which can be obtained by the process of the invention.

This is preferably characterized by a hardness of 50 to 90 Shore A, a breaking force in the longitudinal direction from 300 to 600 N, a breaking force in the transverse direction up to 250 to 500 N, a breaking elongation in the longitudinal direction from 1300 to 1800%, and a breaking elongation in the transverse directions from 800 to 1400% at a thickness of about 1.5 mm.

Particularly preferably, it has a hardness of 65 to 75 Shore A, a breaking force in the longitudinal direction from 400 to 500 N, a breaking force in the transverse direction from 300 to 450 N, a breaking elongation in the longitudinal direction from 1400 to 1600%, and a breaking elongation in the transverse direction from 1100 to 1300%.

Finally, the most preferred hardness is about 70 Shore A, a breaking force in the longitudinal direction of about 460 N, a breaking force in the transverse direction of about 360 N, a breaking elongation in the longitudinal direction of about 1550% and a breaking elongation in the transverse direction of about 1200%.

In this case, the foam of the invention is particularly preferably formed with a single-sided closed outer surface, which has a particularly positive effect on its processability with respect to the above-mentioned further processing operations.

As further described below, it has been shown that this type of polyurethane-based foam meets all the requirements to be used as a (in many cases better) substitute for soft PVC foam. While soft PVC foams used hitherto have a hardness of about 60 Shore A, a breaking force in the longitudinal direction of not more than 200 N, a breaking force in the transverse direction also not exceeding 200 N, a breaking elongation in the longitudinal direction of not more than 300% and a breaking elongation up to 300% in the transverse direction, the new polyurethane-based foam of the invention surpasses all these properties. In addition, the new type of foam is resistant to aging, to be molded warmly and to be embossed and lined by various processes (including the embossing calender). Thus, it is a valuable substitute for soft PVC foam films used so far in the automotive industry, which are far superior in ecological terms, since polyurethane-based foams can be recycled far away, without any harmful products being burned and they do not need plasticizers.

Further features and advantages of the foam of the invention as well as further details of the process of the invention are provided in the following description of some embodiments.

EXAMPLE 1

Polymer-polyurethane from Bayer AG, Leverkusen, under the designation Desmopan KA 8550 was used as the starting compound. After pre-drying, the granulate was mixed with 2 wt% of foam consisting of sodium hydrogen carbonate and citric acid and in a conventional nozzle extruder with the wide slit was extruded into foam film about 1.5 mm thick, selecting the temperature zones in the extruder increasing from about 170 ° to about 220 ° C. The extrusion product had a hardness of 65 to 70 Shore A, a breaking force in the longitudinal direction of about 380 N, a breaking force in the transverse direction of about 300 N, a breaking elongation in the longitudinal direction of about 1400%, and a breaking elongation in the transverse direction of about 1150%. Further evaluation of the foil revealed a far-reaching correct distribution of foam bubbles at a slightly irregular bubble size. Workability with a wide-slot nozzle was given, although it was not optimal.

EXAMPLE 2

We used polyester-polyurethane from Elastogran Polyurethan-Elastomere GmbH under the label Elastolan VP 1175 AW as the starting product. About 1% by weight of the chemical foam sold by Bohringer Ingelheim under the Hydroceyrol BH 70 label was added to the previously dried granulate as a white cylindrical granulate on PE wax as a carrier material and with about 70% by weight of the combination of organic acids and carbonates or . their derivatives.

Processing was carried out with the same conventional extrusion with a wide-slot nozzle at approximately the same temperature profile as in Example 1. The foam obtained showed a very uniform bubble distribution at a very uniform bubble size. The workability of the extruded material was very good. The hardness test on freshly extruded foam film gave a mean hardness of 71 Shore A. after about 6 weeks of storage of the film at room temperature, a slight increase to a maximum of 73 Shore A occurred.

We did not perform tensile tests - as in Example 1 - according to DIN standard 53517, but according to the factory standard on 50 mm wide strips at a tensile speed of 100 ml / m. Free length was 20 mm, overall length 140 m. In the case of foam foil about 1.5 mm thick, the mean breaking force in the longitudinal direction was

460 N, mean transverse force in transverse direction of about 360 N, mean transverse elongation in longitudinal direction of about 1550%, and mean transverse elongation in transverse direction of about 1200%. These values characterize the excellent strength of the new foam foil and far surpass the higher priming values of the soft PVC foil.

EXAMPLES 3 TO 11

The starting products and the foams for these experiments are summarized in the following Table I. The processing was performed in all cases in the same conventional wide-slot nozzle extrusion as in cases 1 and 2. The temperature range fluctuated (depending on the starting material). between 150 ° C and 300 ° C.

All foams obtained showed a very uniform bubble distribution with a very uniform bubble size. In any case, the workability of the material had to be characterized as good. Relevant indications of material properties are also shown in Table I.

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The following describes in more detail the experiments we have carried out on new, for example, foamed foils to test their processability, in particular as regards their ability to replace the foamed PVC foils they are currently using.

Experiment 1

In this experiment, we first checked the ability of the foils of Examples 1 and 2 for hot forming. For this purpose, a 100 x 100 mm foil sample was inserted between two round aluminum plates with a round section of 50 mm diameter in the center. The clamped foil was first loaded with a rounded 10 mm diameter mandrel with a feed rate of 10 mm / m. After a draw depth of 30 mm, the tester showed a force of about 10 N. After unloading, the samples spontaneously returned to their original shape. This indicates that the new grade polyurethane-based foams at room temperature exhibit excellent elasticity.

We then pushed an air-circulating oven around the test sample and turned on the heating. After about 20 minutes, both the room temperature and the circulating air temperature were around 120 ° C. The compressive force has now dropped to 3 N. The test specimens were cooled either slowly in air or spontaneously with cold water. Both cooling modes gave a stable hat deformation that had a rubbery character. Upon reheating the deformed film to 81 ° C and subsequent cooling, the film retained its shape.

Experiment 2

The foam sheets made in Example 1 and Example 2 were followed by the embossing experiments described below.

The piece of foil with dimensions of 140 x 200 x 1.5 mm was first heated on a smooth heating surface and stamped with a cold embossing cylinder. Each time, the foam side of the foil was placed for 15 seconds on a pre-heated Teflon coated heating surface. The foil temperature was 220 ° C for the first experiment. For the following experiments, it was increased in steps of 10 ° C each time.

We then removed the foil from the heating surface and placed it upwards with the hot side in the embosser and pushed it under the cold embossing cylinder. The embossing time was 30 seconds, which corresponds to an embossing speed of about 2.5 m / min. Repeated stamping experiments always resulted in a uniform surface. To test how heat-resistant the impression form is, the pieces of the impression film were exposed for 140 hours at 140 ° C. We couldn't detect any change in impression quality. Even when the film was heated to 160 ° C, the impression quality remained the same.

Experiment 3

Attempts to hot lash the adhesion of the foam film to the non-foamed coating film also gave good values of hot lining strength above 170 ° C or. use of special adhesives based on polyurethanes. The composite films made in this way were tested in the following experiments, which in their implementation correspond to Experiments 1 and 2, with respect to their ability for embossing and hot forming. It was also shown that the composite film was also capable of embossing and design-resistant transformation without problems. The lining-created, leather-like surface structure did not harm the processing.

The foams of this invention based on polyurethanes are initially largely colorless and transparent. However, it has been shown that by adding conventional color concentrates made as binders to polyurethane starting products, good color coverage can be obtained which is not adversely affected by extrusion or any subsequent further processing step.

The above description, as well as the claims and drawings described in the features of the invention, both individually and in any combination, may be essential for the realization of the invention in its various embodiments.

Claims (19)

PATENT APPLICATIONS A process for the production of thermoplastic polyurethane foam, characterized in that the polyurethane is mixed with a foam and in a suitable preparation is continuously or discontinuously formed by heat. Process according to claim 1, characterized in that it is used as a thermoplastic polyurethane aliphatic or aromatic polyurethane based on polyethers, polyesters, polyalkanes, polyalkenes or polyalkines or mixtures thereof. Process according to claim 1 or 2, characterized in that it is used as foaming thermally degradable, inorganic hydrogen carbonates. Process according to claim 1 or 2, characterized in that it is used as a foaming agent for the thermally degradable salts of organic mono-, di- or polyfunctional acids. A process according to claim 4, characterized in that it is used as a hydrogen salt. Process according to one of Claims 3 to 5, characterized in that inorganic and / or organic acid is added as an auxiliary foam. A process according to claim 1 or 2, characterized in that diazendicarboxylic acid diamide is used as the foam. Process according to claim 7, characterized in that catalysts for the decomposition of the diazendicarboxylic acid diamides are added. A process according to claim 1 or 2, characterized in that it is used as a foaming sulfohydrazide. A process according to claim 1 or 2, characterized in that sulfonylsemicarbazides are used as foaming agents. A process according to claim 1 or 2, characterized in that it is used as foaming tetrazoles. Method according to one of the preceding claims, characterized in that foam film is formed through an extruder. Process according to one of the preceding claims, characterized in that polyurethane in the form of granulate and / or powder is used. Method according to one of the preceding claims, characterized in that the foam foil is thermally wetted after 80 to 20 hours at 80 to 120 ° C. Foam film obtainable by the process according to any one of claims 1 to 13. Foam film according to claim 15, characterized in that it has a hardness of from 50 to 90 Shore A, a breaking force in the longitudinal direction from 300 to 600 N, a breaking force in the transverse direction from 250 to 500 N, a breaking elongation in the longitudinal direction from 1300 to 1800% and a shear elongation in the transverse direction of 800 to 1400% at a thickness of about 1.5 mm. Foam foil according to claim 16, characterized in that it has a hardness of 65 to 75 Shore A, a breaking force in the longitudinal direction from 400 to 500 N, a breaking force in the transverse direction from 300 to 450 N, a breaking elongation in the longitudinal direction from 1400 to 1600% and a transverse extension in the transverse direction from 1100 to 1300%. Foam film according to claim 17, characterized in that it has a hardness of about 70 Shore A, a breaking force in the longitudinal direction of about 460 N, a breaking force in the transverse direction of about 360 N, a breaking elongation in the longitudinal direction of about 1550%, and a breaking elongation in transverse directions about 1200%. Foam foil according to one of claims 15 to 18, characterized in that it has a one-sided closed outer surface.