DE1729151A1 - Process for the manufacture of injection molded articles from polyurethane - Google Patents

Description

P 17 29 L51.9-16 March 21, 1971

Messrs Aldo Maria Andrea Eniilio Eggers-Lura, NVrrebakken 26, Gentofte,

Per Wolff, l & igrnarken 28, Farura and Henning Kaaber, Kugraarken 28, Farum / Denmark

Process for making injection molded articles

made of polyurethane

The invention relates to a method of manufacturing of injection molded articles made of polyurethane with a cell structure, which have a supporting core made of rigid polyurethane and an elastic upholstery part made of flexible, resilient Have polyurethane foam, in which process initially the load-bearing core made of rigid polyurethane is made by injecting a suitable first reactive Basic substance in a closed mold with a one-part or multi-part top and one one-part or multi-part Lower part, which closed mold has a cavity shaped to match the shape of the supporting core, after which the upper part of the mold is exchanged for a second upper part, which second upper part with the ger Cast core containing lower part of the mold together

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has a second cavity, the shape of which corresponds to that of the desired elastic pad, which from flexible polyurethane foam afterwards is produced by injecting a suitable second reactive matrix into this second cavity.

The core made of rigid polyurethane foam gives the object support and strength and carries the elastic padding. Combinations of this type are used, for example, for furniture, such as upholstered chairs and the like., used.

Both the rigid and the flexible polyurethane foams are made by using diisocyanates can react with polyols in the presence of a suitable foaming agent. The chemistry and technology of these processes are extensively described in the literature.

Toluene diisocyanate is used for flexible polyurethane foam usually used in conjunction with polyether polyols, the are made from ethylene oxide and propylene oxide and have molecular weights on the order of 1,000 to 6,000. Likewise, linear polyesters can be mixed with alcoholic End groups are made to react with diisocyanates to produce flexible Blyurethan foams.

As a foaming agent, water can be used as it reacts with the diisocyanate, releasing carbon dioxide will. Other suitable foaming agents are halogenated ones Low boiling point hydrocarbons that result from the heat of reaction evaporate.

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In general, tertiary amines are used as a catalyst in the reaction, but organo tin preparations and organo lead preparations as catalysts be used.

Rigid polyurethane foam has proven to be very suitable for use in the structural framework of upholstered furniture proven because of the easy formability of the polyurethanes, as well as the rigidity, high compressive strength and the low specific weight of the injection molded body.

For upholstering such a frame work - in the furniture industry So-called shell - with a covering of flexible polyurethane foam, strips of this material are usually used cut in the desired course and attached to the shells by nailing or gluing.

Recently it has been proposed to use the flexible polyurethane foam in place for cushioning to manufacture rigid shells. This can be done by spraying on the reactive basic substance for the Apply flexible polyurethane to the shell using a suitable spray gun, another option is available is to bring the rigid shell in a suitable mold so that a cavity for the desired cushion remains and fill this cavity with flexible polyurethane foam by adding the reactive basic substance introduces and in this way the polyurethane produces and foams in this cavity.

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ΡΛΠ ORiGIMAL

However, considerable difficulties have been encountered in carrying out the latter two methods because of the production and shaping of the flexible Polyurethane foam in place, and especially on thin and uneven bodies, such as those found in upholstered furniture, is difficult and often delivers defective products. The defects that usually occur are specific to different things Weight, uneven cell size, stickiness or wrinkling on the surface of the pavement.

Some of these errors can be avoided by using heated molds. However, on the other hand, this results in the risk that foaming will occur progresses rapidly that at the end of the foaming process, when the cells have to open up to achieve the desired degree of elasticity, the foam is too soft and thereby collapses in places, as a result of which the injection-molded object is cracked. The solidification of the Foam can be accelerated by using a larger amount of an organotin catalyst. This gives in turn, there is often an excess of closed cells, which makes the resulting foam unsuitable for upholstery power.

The object of the present invention is to provide a method for producing injection molded articles in which parts made of rigid polyurethane foam with parts made of flexible polyurethane foam are connected to create which Procedure avoids the difficulties mentioned.

BATH ORIGINAL

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The task is with the method according to the invention solved in that the second reactive base substance for the flexible polyurethane at a time is injected, in which the first reactive basic substance for the rigid polyurethane gels but still contains a considerable part of their exothermic heat of reaction.

It has been shown that, when proceeding in this way, the reactive basic substance what is usually can be used to make thick bodies from flexible polyurethane foam, equally effective and react reliably in the thin seams, as they are generally used for upholstery and linings will. The method according to the invention provides a product that is advantageously not only homogeneous in terms of the cell structure, the specific gravity and the strength and shows no tendency to wrinkle, but rather also adheres excellently to the rigid polyurethane foam.

The surprising effect of the method according to the invention is that when the rigid polyurethane foam cures resulting heat of reaction on the second reactive basic substance, which is used to produce the flexible polyurethane foam is introduced. This heat affects the normal course of the reaction process in an advantageous manner such that an optimal cell size and structure results and an effective one Final curing is achieved which prevents any tendency for the surface to wrinkle or stick.

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A good connection between the rigid and the soft polyurethane parts depends reliably on that the flexible polyurethane foam is formed in the period in which the rigid polyurethane foam is still is warm and in the final hardening stage.

It has been found that the method gives the best results when the time between injections of the two reactive base substances is more than three times the gel time for the first reactive base substance for the rigid polyurethane. This setting time changes depending on the type of basic substance chosen. In general, the commercially available reactive bases for the production of rigid foam have a gel time that varies between 45 and 200 seconds. A shorter period of time between the injection of the two basic substances is the reason "that the rigid polyurethane foam deforms and disintegrates on the surface, is bothering you.

The time between the injection is advantageously of the two reactive base substances less than twenty times the gel time for the first reactive base substance for the rigid polyurethane foam »; -If there is a longer time interval between the two injections, there is a poor connection between the flexible and rigid polyurethane, and the flexible foam is poorly cured and shows poor strength. ■ ■. · ■ ···;: ■; -. '· ..

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The mold for the method according to the invention can be of conventional design with a concave bottom and a convex top. The closed mold contains a cavity of the same shape as the one to be made Injection molded articles.

The following is an example of the method of the present invention described:

Parts by weight of the basic substances for urethane.

A. Pest foam

Propylene RF H (Lankro Chemicals Ltd.) 56

Castor oil 28

Silicon L. 520 (Union Carbide)

Freon Il 20

Dibutyltin dimaleate (Dibutyltindimaleate) 0.05

Dimethylaminoethanol

Diphenylmethane Diisocyanate 87

B. Flexible foam.

Propylene 3 (Lankro Chemicals Ltd.) 100

Tin (preferably divalent) octoate

(Stanno octoate) 0.3

Dabco (triethylenediamine) 0, lk

Silicon L.52O (Union Carbide) water

Toluene Diisocyanate I05

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3t 2 kg of the basic substance A are mixed thoroughly and injected into a mold of a lower concave part and an upper convex part. In the closed state, the mold has a cavity which corresponds to the supporting rigid core of a chair. The mold is made of 10 mm thick glass fiber reinforced epoxy resin.

The foaming time of the basic substance A is 30 seconds and the gel time 90 seconds.

After 7 minutes, the upper part of the mold is exchanged for a second upper part, which has a larger cavity and consists of 2 mm thick glass fiber reinforced epoxy resin and has a top layer of 50 mm rigid polyurethane foam. 2.5 kg of the basic substance B are injected into the mold.

After a further 25 minutes, the casting mold is opened and the injection-molded article, consisting of a rigid core with a flexible pad on one side is taken out.

The specific weight of the rigid core is 45 kg / m and the specific weight of the flexible padding is kO kg / no

The flexible foam is well solidified and has the the following properties:

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- Q -

Elongation at break Tensile strength Adhesive strength at rigid core

ASTM D 638 ASTM D 638

28O %

2.1 kg / cm '1.2 kg / cm'

1Q982RM555

Claims (3)

Patent pending 1. Process for the production of injection molded articles from polyurethane with a cell structure, which have a load-bearing core made of rigid polyurethane and an elastic padding part made of flexible, resilient polyurethane foam, in which method the load-bearing core is first made from rigid polyurethane by injecting a suitable first reactive basic substance in a closed mold with a one-part or multi-part upper and a one-part or multi-part lower part, which closed casting mold has a cavity shaped according to the shape of the supporting core, after which the upper part the casting mold is exchanged for a second upper part, which second upper part and the lower part of the casting mold containing the cast core together form a "wider" Has cavity, the shape of which corresponds to that of the desired elastic Plst era, which is made of flexible polyurethane Foam existing cushions then by injecting a suitable second reactive basic substance into this second cavity is produced, characterized in that the second reactive The basic substance for the flexible polyurethane is injected at a point in time at which the first reactive The basic substance for the rigid polyurethane has gelled, but still contains a considerable part of its exothermic heat of reaction. ORIGINAL INSPECTED 109828/1555 2. The method according to claim 1, characterized in that the time between injections of the two reactive basic substances more than three times the gel time for the first reactive Basic substance for the rigid polyurethane is. 3. The method according to claim 1, characterized in that g e k e η η draws et that the time between the injection of the two reactive basic substances is less than is twenty times the gel time for the first reactive matrix for the rigid polyurethane. 109828/1555