DK149455B - PROCEDURE FOR THE PREPARATION OF STARCH PRIOR POLYURETHING GLOVES - Google Patents

Description

149455 i

The invention relates to a process for preparing starch-reinforced rigid polyurethane foams, in particular rigid integral polyurethane foams, whereby polyol and polyisocyanate components conventionally used in the production of rigid polyurethane foams are mixed with a starch filler and the mixture is allowed to react under the foaming agent. and curing conditions.

As is well known, molding agents are often added to fillers, the purpose of which is usually primarily to achieve a cost savings while maintaining and / or even improving the desired technical properties of the base material.

Polyurethane foam exhibits a number of excellent properties and, therefore, despite its relatively high cost, has found 15 widespread use. Of course, it was also already tried to stretch them or make them cheaper by the addition of fillers to which a number of organic and inorganic fillers were recommended, including also very finely ground native starch 20 (Rigid Urethane Foam Extended With Starch, Bennett-Otey -

Mehltretter, J. Cellular Plastics, (1967), pp. 369 et seq. DE Publication No. 25 37 859).

With these known fillers it is easy to achieve a more or less significant price reduction, but this 25 usually has to be bought with a drastic deterioration of important application properties.

EP Publication No. 3161 relates to a process for the manufacture of starch-extruded polyurethane foam of all types (see claim 1 in combination with page 1, last paragraph, of the description of EP 3161) and 30 is concerned with improving their unsatisfactory technical properties (see page 2, second paragraph).

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The improvement is achieved by the proposed use of so-called "stabilized starches", ie. according to the principal requirement the addition of a) mixtures of any starch with certain antioxidants or b) starches which have been liberated from oxidizable or oxidized materials by a pretreatment and wherein ground starch is a preferred material.

Thus, rigid polyurethane foams are mentioned in this publication only in the general list of polyurethane foams, which are considered 10. In addition, it can be concluded from page 2, second and third paragraphs, in combination with claim 2, that it is mandatory to subject the "stabilized starch" to a drying process.

The examples in EP 3161 only illustrate the preparation of flexible and highly resilient foams and the experiments show that with these types of polyurethane foams, gelatinized (swollen) starch, if left untreated, does not yield useful results. Furthermore, "stabilized starches" of type (a) in EP 3161 are preferred for economic reasons to those of type (b) (see page 9, lines 20 - 21).

The object of the invention is to provide a process for the production of rigid polyurethane foams, thereby obtaining foams which exhibit, at similarly favorable prices, better technical properties than the known pre-stretched rigid polyurethane foams and are superior in particular to the modulus of elasticity, tensile strength, fracture elongation and / or thermal expansion ratio.

This task is solved according to the invention in the manner specified in the characterizing part of the main claim from the surprising realization that, by foaming and curing, one has from the castings of otherwise usual composition which, instead of native starch, contains a swollen starch. polyurethane foam, which is known in its own way, achieves not only a very low cure rate, but in comparison, both unstretched and native starch polyurethane foams are characterized by significantly better heat expansion properties, ie. lower linear coefficient of thermal expansion, and as a rule also with respect to one or more other application-technical properties, those known with starch 10 are pre-stretched polyurethane foam.

In particular, in contrast to the polyurethane foam reinforced with native starch, according to the invention, no or at least only a significantly smaller degradation of the E-modulus value is found compared to a corresponding unstrengthened polyurethane foam. The same is true with regard to the tensile strength and with respect to the elongation at break. Plastic foam pre-stretched with swell starch in the process of the invention often has even better properties than the corresponding unstrengthened polyurethane foams, while by adding similar amounts of native starch as filler or elastomer, as mentioned above, a drastic reduction in fracture extension must always be included.

From the foregoing, it is clear that the present invention is far from what is known from EP Publication Publication No. 3161 both with respect to the problem being solved and with respect to the proposed solution.

Specifically, the present invention relates to the manufacture of rigid foams which are not equivalent to the other types of polyurethane foams described in EP 3161. For a comparison of the examples of the present application with the Examples, in particular 1 and 2, in EP 3161 shows that a combination of any pregelatinized starch and a rigid foam has good properties, while with flexible foams unsatisfactory properties are obtained unless a treated starch is used.

As "swell starches" within the meaning of the invention, 5 not only so-called "dry starch starches" are considered, but all those in which the native grain structure is degraded by heat treatment of moist starch, including, among other things, extruded starches. Evening starches in the sense of the invention can also be known in that the 10 are essentially free of grains which exhibit a double refractive cross in polarized light.

With regard to the origin of the starches, according to the invention, both starch and root starches as well as flour or fiber particles contaminated with starches are considered.

According to the invention, the starch content, based on the total weight of the polyurethane foam, is between 3 and 40% by weight. These limits are given downwards by the quantities of starch which, purely economically, provide an even more noticeable advantage, ie. causes a considerable reduction of the polyurethane foam.

The improvement of the application properties of the polyurethane foam generally begins to become significant at a starch filler content of about 5%, preferably 25 to 30? Really significant improvements usually occur first from 8 to 0, preferably in the range of 8 to 25 ».

The upper limits are given by the processability of the mixture of polyol, starch and polyisocyanate required for the polyurethane foam. At very high starch contents, the viscosity rises so strongly that a sufficiently homogeneous mixing of the three components within the fixed mixing times of a few seconds is no longer possible. In addition, at extremely high starch content, there is usually a significant deterioration 5 of various application characteristics, so that the choice of the filler content in the upper region regularly constitutes a compromise between the minimum requirements for the application characteristics which the plastic foams must meet for their intended use. and as far back as possible.

According to the invention, starches containing both native and swollen starches can also be used, whereby the swelling starch must be the predominant proportion for its positive effect on the technical properties of the polyurethane foam to be realized. If you increase this mixture's starch content to 80%, then no differences can be observed in relation to pure evening starch.

From 90% evening starch, differences can no longer be ascertained.

Of course, for the fillers to be used in the process of the invention, the rule is that a regular distribution over the total polyurethane foam gives the best results, resulting in the grain size not being too large, and must be as uniform as possible. Still, the invention is in this regard. for as advantageous as evening starches even when compared to native starch relatively coarse grain size, ie. 0.03 - 0.1 mm for "fine" swell starch and 0.1 - 0.5 mm for "coarse" swell starch and 0.01 - 0.025 mm for native corn starch at the same starch content gives the best use with 30 starch polyurethane foam. technical characteristics, such as characterized by the modulus of elasticity or tensile strength. Preferably, at least 50% by weight, and more preferably at least 75% by weight K, and most preferably at least 95% by weight of the swelling starch 35 pass through a screen having an open mesh width of 0.5 mm.

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The water content of polyurethane foam starch fillers affects both their manufacturability and their properties, whereby the high water content of native starches, which is between 12 and 18 weight-X, is particularly negative. This, on the one hand, manifests itself in high initial viscosities of the starch / polyol mixtures, which impede the necessary homogeneous mixing with polyisocyanate, and, on the other hand, in a deterioration of application-technical properties, such as, for example, characterized by the bending breaking stress or modulus of elasticity.

The evening starches used according to the invention are also advantageous in this regard, since even at water contents of up to 15 wt. X, they mostly still lead to technically usable products in terms of processability and the properties of the polyurethane foam thus produced. and in some cases even higher water content can be tolerated.

Significant improvement is achieved by reducing the water content of the starch filler to a maximum of 10 wt.

Preferably 6 weight-X or lower, whereby 2 weight-X

or lower has been found to be particularly advantageous.

While preparing the molding compositions of the process of the invention, the components can be basically mixed with each other in any order, but it is generally advantageous to first mix the filler at least partially with the isocyanate and / or, preferably, the polyol component.

Furthermore, it may be noted that the process according to the invention is well suited for the production of polyurethane foams in general, but that its advantages are particularly evident in the manufacture of integral polyurethane foams.

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The following examples and comparative experiments serve to elucidate the invention and its advantages over the state of the art.

In these examples and comparison experiments, the starch 5 was stirred each time in a polyether polyol having a hydroxyl number of 500 mg KOH / g. Further, the polyol contained dimethylcyclohexylamine as the reaction catalyst, 10 weight S trichloromonofluoromethane as the propellant, and 0.5 weight 50 of a polyethersiloxane foam stabilizer. As the isocyanate component, a polyphenylene polymethylene polyisocyanate was used. The weight ratio of polyol (without additives) to polyisocyanate was 1: 1.56.

Following the mixing of polyisocyanate and polyol blend, the molding material was filled into a heated to 50 ° C, forming the integral polyurethane foam.

EXAMPLE 1

The polyurethane foam contained 20% by weight of starch based on the total weight. The influence of the milling starch milling rate on the linear heat expansion coefficients was 20 as follows:

Starch grinding degree Linear heat expansion (water content <-15o) coefficient (1 / K) 0.03 - 0.1 mm 9.10'6 0.1 - 0.5 mm 15.10 "6 149455 8 EXAMPLE 2

The influence of various humidities of the swelling starch material used on the final properties of the polyurethane foam is shown here in terms of tensile strength. The starch content was 10 and 26% by weight, respectively, calculated on the total weight.

2

Moisture content of the starch Tensile strength (N / mm) (grain size 0.05-0.1 mm) 10 wt. 0 starch 25 wt. Starch <1 * 8.9 6.5 7% 7.3 4.3 Example 3

Here, a polyurethane foam having 20 weight percent starch filler within the grain size range of 0.03 -0.1 mm was prepared. The foam modulus of elasticity and elongation at break depending on the moisture content of the starch were as follows: E-module Elongation at break 2

Moisture content of the starch_ (N / mm) _ (¾) _ <1% 560 2.9 6.7% 350 1.85

Comparative Experiment 1

A polyurethane foam of Examples 1-3 without starch filler was prepared. It had the following characteristics:

Linear heat expansion 46 * 10-6 / K

koefficient_

Tensile strength 10 N / mm

Elongation at break 2.4% E-module 570 N / mm2 149455 9

Comparative Experiment 2

Polyurethane foams of Examples 1-3 were prepared using native starch having a grain size of 0.005 - 0.02 mm and a moisture content of less than 1 µl. They had the following properties: Weight% starch, calculated on the total weight 2 10 Tensile strength 4.5 N / mm 25 "4.0 N / mm2 20 E module 370 N / mm2 20 Elongation elongation 1.2% 20 Linear heat exchanger .

knowledge coefficient 24 * 10-61 / K