DE2400254A1 - PROCESS FOR PRODUCING INJECTION MOLDED PARTS FROM POLYURETHANE FOAM - Google Patents

Description

Process for the production of injection molded parts from poly urethane foam

The invention relates to a method for the production of injection molded parts from polyurethane foam, which is entirely with a Skin of the same material are coated.

Polyurethane foam fully covered with a skin parts have gained increasing importance in various fields over the past few years. In the preparation of of shoes that are partially or entirely made of plastic, the use of completely especially skinned polyurethanes because of the various advantages these foams possess Interesting. Fully skinned foams are beneficial in the manufacture of Used ski boots whose upper part or outer parts are made entirely of plastic. Such a Upper, which can be undivided or consist of two or more parts, is combined with the sole in a single one Mold injection molded in a one-step process.

In the case of injection molding of parts made of polyurethane foam that are completely covered with a skin, the problem is high

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Dimensions desirable to achieve a surface - contains ²¹ --- and is free of surface defects and no pores or air bubbles just below the surface of the skin?. In practice this encounters difficulties because, according to the known and customary injection molding processes, air bubbles or pores are often and unpredictably formed so close under the surface of the skin that they are clearly visible. Such an accumulation of pores very seriously damages the appearance of the foamed article and thereby limits its uses.

For example, in a known injection molding process for producing foams with an outer skin, the Surface temperature of the casting mold in the range from -lo ° C to about + 70 ° C, preferably between 20 and 70 ° C and below special conditions in the range of about 20 to 55 ° C. If by the exothermic reaction of the to be foamed Material higher temperatures occur, the Forr. cooled to the temperature of the wall surface in the. mentioned Keep area. These temperature ranges are maintained because of the assumption that at temperatures beyond the upper limit the foam structure of the interior of the Injection molded part is destroyed and no foam with an outer skin is achieved.

Therefore, in the known and customary methods, zuir. Manufacture of injection molded parts from polyurethane foam ir.it an outer skin, care has been taken to ensure that no temperatures occur in the mold which are higher than that caused by the chemical reaction in the mold.

It has now surprisingly been found that injection molded parts

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of polyurethane foam which has no pores or air bubbles are completely covered with a skin und.die have virtually immediately under the surface of the skin can be prepared by a process which consists in that one a polyurethane reaction _s mixture containing one completely covered with a skin coated foam forms, injected into a mold which is held at a temperature above the maximum temperature that takes the shape through the reaction of the mixture, and that the mixture is then allowed to react to produce a foam part.

Therefore, it is contrary to known and customary procedures for the production of injection molded parts from polyurethane foams with an outer skin according to the invention Process heat added. The skin surfaces produced by the process according to the invention are uniform smooth and flawless. Although any injection molded parts can be manufactured using the method described, ski boots are particularly suitable for production by the injection molding process according to the invention.

Another advantage of heating the mold is that the reaction rate of the foamable mixture and the curing of the reaction product can be accelerated. In known and customary injection molding processes the reaction and hardening of the material at the points that come into contact with the mold walls are delayed because of their relatively low temperatures. Therefore, the method according to the invention performs the heating of the injection mold to a much higher production rate.

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2 ^ 00254

The inventive method can be used with any known or the usual mixture for the production of foams with an outer skin. However, it is particularly advantageous to use a reaction mixture which has the following composition in parts by weight:

a) 45 to 70% of an additive compound of a polyol and an alkylene oxide, the alkylene oxide at least partly consists of ethylene oxide and the aforementioned Additxonsverbxndung 2 to 6 predominantly primary Has hydroxyl groups and a molecular weight of at least 25o,

b) 5 to 15% of a compound that has a different reaction rate than the Additxonsverbxndung a) has, has a molecular weight of less than 500 and at least two polyfunctional groups with active hydrogen of the following groups: primary hydroxyl, secondary

Hydroxyl, primary amine, secondary amine groups and /

Has

or mixtures of these groups ^ and otherwise

c) an organic polyisocyanate as well

d) a catalyst for the reaction between the isocyanate and the hydroxyl groups and

e) a blowing agent composed of water, a halogenated aliphatic hydrocarbon or a mixture thereof.

If this reaction mixture in the inventive Injection molding is used to obtain polyurethane foam parts that have a dense surface skin that is pore-free and relatively impermeable to vapor and has a relatively uniform thickness and is practically free of pores immediately below it

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Surface is. This dense surface skin is a solid associated component of the practically uniform, low-density foam that it completely envelops.

The addition compound of a polyol and an alkylene oxide, which can be used advantageously in the process according to the invention can be obtained by reaction of an alkylene oxide, such as ethylene oxide or propylene oxide, made with a diol, a triol, a tetrol or a higher polyol will. If an oxide other than ethylene oxide is used, the primary addition product is left in a second reaction step react with the ethylene oxide so that an addition compound is obtained which predominantly has primary hydroxyl groups.

As examples of the polyfunctional compounds with a molecular weight of less than 500, which can advantageously be used in the process according to the invention, are the aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol; Alkylene glycols such as diethylene glycol, triethybnglycol, etc .; Reaction products of a lactone, such as · =. -Caprolactone with Alkylene glycols, etc .;

Polyesters with hydroxyl groups, for example the derivatives of polycarboxylic acids and polyalcohols, diethylene glycol adipate, etc .; Amines, such as the aromatic N-alkylated Amines or aromatic amines with a negative substituent on the aromatic nucleus, such as, for example, N, N'-dime thy Imethylendx ani lin and 4,4'-methylenebis (2-chloroaniline) (MOCA). ■

As organic polyisocyanates, for example, the

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Use isomers of diphenylmethane diisocyanate or their derivatives, such as prepolymerized products and others.

The catalysts used are advantageously catalysts based on a tertiary amine and metallic catalysts, all of which are well known to those skilled in the art are used. A particularly suitable catalyst consists of one. Mixture of organic tin compounds and tertiary amines, with the tin catalyst as the primary catalyst and the tertiary amine act as a secondary catalyst. The catalyst or catalysts can be used in a ratio nis from ο, οοοΐ to 5, ο%, based on the total weight of the reaction mixture can be used.

As a blowing or foaming agent, for example, water can advantageously be added to the reaction mixture in small amounts, e.g. to 0.5 to 5.0%, based on the total weight of the Reaction mixture, halogenated aliphatic hydrocarbons with a boiling point between -4o and + 7o ° C, those below or at the same temperature as the foams Boil mass, such as trichloromonofluoromethane, dichlorodifluoromethane, Dichloromonofluoromethane, dichloromethane, trichloromethane, Chloromethane, 1, 1-dichloro-l-fluoroethane, etc., or add low boiling point hydrocarbons such as butane, pentane, hexane, etc., as well as carbon dioxide.

The amount of blowing agent used depends on the desired density of the foamed product. In general it can be said that for 100 g of reaction mixture with an average NCO / OH ratio of about

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1: 1 approx. 0.05 to 0.3 moles of gas are required to achieve densities from 13.6 to ο.454 kg / o.283 cm.

The reaction mixture can contain, inter alia, foam stabilizers or compounds that increase the size of the cells control, for example surface-active systems based on siloxaneoxyalkylene copolymers. However, it is not absolutely necessary to end such a connection Add reaction mixture. Examples of such Compounds are "Silicones L 52o" (Union Carbide Corporation) , "Dow Corning I9o Surfactant" (Dow Corning Corporation) etc.

The foam stabilizer can be added up to about 0.5%, based on the total weight of the reaction mixture.

You can also use other known and common additives for Add polyurethane foams, for example fillers such as fuller's earth or diatomaceous earth, and dyes.

The following table shows examples of the invention usable reaction mixtures given. The amount of each additive is given in% by weight.

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[Component

, Composition of the reaction mixture 1

A. B!
i Addition connection
made of polyol and aluminum
kylene oxide (a) Addition compound propylene
oxide / ethylene glycol with after
subsequent addition of ethylene
oxide, hydroxyl number 44.7 85.4o jbifunctional ver
bond with molecule
larweight under
5oo (b) Diethylene glycol 14.6o
J
ϊ I.
; Polyisocyanate
i Mixture of diphenylmethane
diisocyanates I.
i
62, oo catalyst N, N, N), N'-tetramethyl-1,3-
butanediamine (catalyst I)
and dibutyltin dilaurate
(Catalyst II) o, 4o
o, o7 Blowing agent water o, 65

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CD CD CXJ K) to

σ -j cn

2 A. B. 3 A. B. 4th A. B. ■
5 B. as in 1 88, ο as in 1 8o, oo as in 1 87.5o A ■ 87, oo 1,4-butanediol 12, ο Triethylene glycol 2o, oo 1,5-pentane
diol 12.5o as in 1 13, oo as in 1 61.3o as in 1 62, oo as in 1 57.71 1, 6-hexane
diol 54.35 Catalyst I.
■ and o, 4o Catalyst I. o, 4o Catalyst I. ο, 4o as in 1 o, 4o Catalyst II o, o5 • Catalyst II o, o7 Catalyst II 0.06 Catal
gate I 0.06 as in 1 o, 65 as in 1 o, 65 as in 1 o, 65 Catal
gate II o, 65 water

Lp

tv) cn

- Io -

Io

as in as in

-J in to

as in catalyst I.

and catalyst IE

as in

85 ₇ 4o 14.6o

, oo ο, 4o

o, o7 o, 65

as in as in

85.4o 14.6o

as in 1 j62, oo

Catalyst o, 4o tor I

and

Catalyst o, o7 tor II

Water and 0.65 trichloromonofluoromethane

as in 1

1, 3-propanediol

as in 1

Catalyst I.

and

Catalyst II

as in 1

9o, oo Io, oo

61, oo o, 4o

o, Io o, 65

as in 1

Reaction product of ethylene glycol and £. - caprolactone

as in 1

Catalyst I.

and

Catalyst II

water

δο, οο as in 1 86, ο

2ο, oo N-methyl diethanol

< ami n

52.9

D, 4θ

ο, ο6

as in I.

Catalyst II

Trichlorotrifluoroethane

14, ο

46.2

o, oil

lo, o

240025A

- li -

The temperature of the mold must be above the maximum temperature, achieved by the exothermic reaction alone. This can be done advantageously according to known and conventional methods, such as by a heating coil with steam heating, oil heating or by a resistance heater. Temperatures in the range from 9o to 12o ° were found to be particularly favorable for the invention Procedure established.

The mixture of polyol and isocyanate can be stored separately until immediately before mixing. Here can one or both of the compounds are maintained under pressure and at elevated temperatures. For example the polyol can be kept under pressure and at temperatures of 70 ° C in a vessel. The isocyanate compound, which contains trichlorofluoromethane as a blowing agent should be used at temperatures above the boiling point of the blowing agent be stored at the storage pressure and preferably at about 3o to 4o ° C. So that the blowing agent is in the storage tank does not expand prematurely, it will be under pressure of about 3

Maintained 2 to 4 kg / cm.

When the two ingredients are mixed in a mixing nozzle or other device in the desired ratio the reaction mixture formed is also kept under pressure so that the blowing agent does not expand can. Immediately after entering the cavity of the mold, the pressure is reduced somewhat, and immediately and on accelerated way the foam is formed by the blowing agent. The foaming continues due to the relative

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high temperature caused by the preheated components and the heated injection mold on the foaming agent acts before the crosslinking reaction of the reaction components begins.

Because of the preheating of the reaction components and thus also of the reaction mixture itself, the reaction continues Components immediately. On the other hand, because of the preheating of the mold, the reaction proceeds instantly at an increased rate also on the outer parts of the form.

It has also proven advantageous to reduce the pressure in the immediately after the reaction mixture has been injected Increase shape. For example, in the injection molding of ski boots according to the method according to the invention, a result

2 increasing the pressure from 3 to 4 kg / cm in the mold especially good results. The increased pressure helps avoid pores or cells in the surface of the skin. A Means for increasing the pressure consists in that the bottom of the mold is formed like a punch and so by pressing it upwards of the bottom creates a pressure inside the injection mold. The speed and distance that the Floor is moved in the form of a stamp, can be adapted to the special needs.

The amount of material injected in liquid form into the injection mold of a given volume behaves according to another embodiment of the invention so that a material with a density of about 0.3 after the reaction and foaming to a density of at least about 0.85 in the injection mold under the operating conditions employed accepts. This increase in density corresponds to

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a "compression" of the material by 2oo to 3oo%. The injected reaction liquid thus becomes in the mold kept under pressure and so first forms a liquid foam until it hardens through a crosslinking reaction. Man This gives the desired foam structure and a skin with a smooth and flawless surface.

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Claims (7)

Claims [ Ι.ΐ Process for the production of injection molded parts from polyurethane Jethane foam which is completely covered by a skin made of the same material, the skin having no pores immediately below its surface, characterized in that a polyurethane reaction mixture is placed in an injection mold, which can form a foam completely covered with a skin, while maintaining the mold at a temperature above the maximum temperature assumed by the reaction of the mixture, and allowing the mixture to react to form a foam. 2. The method according to claim 1, characterized in that the reaction mixture contains: a) 45 to 70% by weight of an addition compound of a polyol and an alkylene oxide, the alkylene oxide at least partially consisting of ethylene oxide and the reaction product 2 to 6 for the most part being primary
Contains hydroxyl groups and has a molecular weight of at least 25o, b) 5 to 15% by weight of a compound which has a different reaction rate as the addition compound a) and has a molecular weight of less than 500 and at least two polyfunctional groups with active hydrogen from the group: primary hydroxyl, secondary Hydroxyl, primary amine, secondary amine groups and Has
Mixtures of these groups, / and otherwise c) an organic polyisocyanate, d) a catalyst for the reaction between the iso- 509829/0759 cyanate and the hydroxyl groups, and e) a blowing agent, namely water, a halogenated aliphatic Hydrocarbon or a mixture thereof. 3. The method according to claim 1 or 2, characterized in that the temperature of the injection mold is kept at 9o to 12o ° C. 4. The method according to claim 1 to 3, characterized in that da3 the pressure in the mold is increased immediately after the reaction mixture has been injected. 5. The method according to claim 4, characterized in that one the pressure in the injection mold to a value of -3 to 4 2 kg / cm increased. 6. The method according to claim 2, characterized in that the Addition compound a), the polyfunctional compound b) and the other constituents of the reaction mixture together at elevated temperature and at a pressure which is sufficient, the transition of one of the constituents into the gas state to prevent at the elevated temperature. 7. The method according to claim 1 or 2, characterized in that such an amount of the reaction mixture is injected that a Material with a density of about 0.3 after the reaction and foam formation a density of at least 0.85 in the Injection mold assumes under the process conditions used. 509829/0 7 59