GB2275684A

GB2275684A - Semi-rigid foam

Info

Publication number: GB2275684A
Application number: GB9300232A
Authority: GB
Inventors: Edward Francis Cassidy; Ecker Jacobus Margareta Vanden
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1993-01-07
Filing date: 1993-01-07
Publication date: 1994-09-07
Also published as: GB9300232D0

Abstract

Semi-rigid polyurethane foam article having at a side a reinforcement and at the opposite side an integral polyurethane skin. The reinforcement may be a continuous or woven glass mat.

Description

The present invention is concerned with a process for preparing semi-rigid polyurethane articles which have at a side a reinforcement and at the opposite side an integral polyurethane skin.

DE 4005624 discloses integral skin foam (ISF) comprising a glass-mat reinforcement. The articles are made by first spraying the integral skin foam and then connecting it to the supporting part. The density profile shows a sharp increase near the supporting part and in order to prepare the integral skin foam a composition needs to be sprayed with a gradually increasing amount of blowing agent.

US 4298556 discloses the use of a neutral ester for making reinforced foamed articles in a mould. The PU foaming material is poured onto the reinforcement; then the mould is closed densifying the reinforcement fibres.

The PU foaming material can be any material; preferably rigid foam systems are applied.

US 4610835 and US 4664862 disclose the coating of a premolded glass-fibre-mat reinforced PU panel.

French Patent 1528747 discloses a rigid foam panel with a reinforcement.

Canadian Patent 852182 discloses cellular synthetic material having textile web (glass-mat) reinforcement and a decorative skin; the separate skin may be a sheet of fabric, plastic coated fabric or plastic. The cellular material may be of the semi-rigid type. Preferably the glass-mat is at one side and the skin at the other side of the foam.

Surprisingly we have found that semi-rigid polyurethane articles can be made which have a reinforcement at a side and a good quality surface at the opposite side, the articles having superior properties.

Accordingly the process is concerned with making such an article by applying a reinforcement at the inside of a lid of a mould, providing the mould with a reaction mixture for preparing semi-rigid polyurethane foams, closing the mould, allowing the reaction mixture to react under integral skin forming conditions and demoulding the article.

Further the invention is concerned with such articles.

There are several advantages 1) although not essential it is possible to avoid the use of a coating/decorative sheet at the side opposite to the side containing the reinforcement since a good quality surface is obtainable; preferably no coating or sheet is used in preparing the articles according to the invention; 2) the article contains only polyurethane and reinforcement and can therefore be recycled easily; 3) if the integral skin has been damaged it is possible to repair this by applying the article to the inside of the lid of the mould, providing the mould with a little bit of aforesaid reaction mixture preferably without blowing agent and repeating the further steps; it is also possible to cut the integral skin from the article and to provide it with a new one in the same way; 4) the density profile through the article (going from the integral skin side to the reinforced side) is smoother than for articles which have been made by spraying as in DE 4005624, wherein the density gradient (density reinforcement : density core) between the reinforcement and the core of the foam at less than 0.2 mm from the reinforcement is about 5. This density gradient in the article according to the present invention is less than 2.5 and preferably less than 2; 5) the modulus (MPa) of the article according to the present invention is much higher than an article which is made by first impregnating the reinforcement with a polyurethane and then preparing a semi-rigid foam with an integral skin onto the reinforcement; consequently articles of greater dimensions may be prepared; 6) the penetration by the foaming material of the reinforcement is done in situ, in the mould; this provides for improved stiffness and avoids adhesion problems.

The articles may be made in any mould which can be closed and which enables to make integral skin foams (ISF). Generally it will be a mould of steel, aluminium or epoxy-resin.

The preparation of ISF is generally known in the art and requires cooling of the mould at a temperature of 30 to 60it, preferably 40 to 50'C as well as a certain degree of over-packing; in general overpacking is 150 to 500%, overpacking being defined as a - b x x 100%, a wherein a - the amount of reaction mixture used b - the amount of reaction mixture required to just fill the mould once the reaction is complete.

The reinforcement may be of any kind and is preferably selected from a web of material, like a texitle web from jute, sisal, cotton and wool or a glass fibre mat, a continuous or woven glass mat, a graphite mat, a polyester mat, polyaramide mat or a nylon mat. Preferably a continuous or woven glass mat is employed. In the finished article in general less than 50%, preferably less than 20% of the article comprises reinforcement by weight.

The reaction mixture for preparing the semi-rigid foam is containing a polyisocyanate, an isocyanate-reactive compound having an average molecular weight of 1000-10000, preferably 2000-8000, and at least two isocyanatereactive groups, a chain extender or cross-linker having an average molecular weight of 60 to below 1000, preferably 60-500, a blowing agent and optionally additives known in the art such as catalysts, surfactants, fire- and smoke retardants, internal mould release agents, stabilisers and colouring agents.

The polyisocyanates used can be any of the polyisocyanates known in the art.

Preferably aromatic polyisocyanates are used like toluene diisocyanate, methylene diphenylene diisocyanates (MDI) and polymethylene polyphenylene polyisocyanates comprising MDI. Further polyisocyanates which may be used are so-called MDI variants (MDI, crude or polymeric HDI containing urethane, allophanate, carbodiimide, uretonimine, isocyanurate, urea or biuret groups; such variants are commonly known in the art). The preferred polyisocyanates polyisocyanates have an isocyanate functionality of 2 to 3.

The isocyanate-reactive compounds having a molecular weight of 1000-10000 may be selected from polyols, polyamines, polyimines and poly-enamines. In particular from polyether polyamines, polyester polyols and especially polyether polyols. Preferably the polyols have an hydroxyl functionality of 2-6 and more preferably 2-4. Polyether polyols which may be used are especially selected from those having ethylene oxide and/or propylene oxide units.

The chain-extenders or cross-linking agents may have an isocyanate-reactive group functionality of 2-6, in particular 2-4 and may be selected from e.g.

ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerol, trimethylolpropane, pentaerythritol, sucrose, sorbitol, ethanolamine, diethanolamine, triethanolamine, ethylenediamine, diethyltoluenediamine and isophorone diamine.

The weight ratio of high molecular weight isocyanate-reactive compound and chain-extenders/cross-linkers is 30 to 1, preferably 15 to 1 w/w.

The blowing agent may be any physical or chemical blowing agent known in the art. Preferably water is used as the sole blowing agent. The amount of water used is 0.1 to 2.0, preferably 0.2 to 1.5 t by weight calculated on all isocyanate-reactive ingredients, including water, used.

The articles according to the present invention may be made according to the one-shot, the semi-prepolymer or the full-prepolymer technique. Preferably the articles are made either by premixing all the ingredients for making the ISF, then by pouring the mixture into the mould followed by closing the mould or by making a mixture of all ingredients except the polyisocyanate and feeding the polyisocyanate and the mixture independently via a mixing head into the mould, which may be open or closed at the time the ingredients are fed into the mould. Demoulding in general is conducted 1-30 minutes after providing the mould with the ingredients.

The isocyanate index employed is 70 to 130, preferably 95 to 105.

The articles according to the invention can be used for making headrests, armrests, steering wheels, dash-boards and the like. The overall density of the articles is 300-800, preferably 400-700 kg/m3.

The invention is illustrated by the following examples.

Example 1 SUPRASEC VM 10, an MDI based polyisocyanate obtainable from Imperial Chemical Industries PLC (SUPRASEC is a trademark), was mixed with a polyol composition (index 100) and poured into a mould (overpack about 200%) ; the mould (20 x 10 x 3 cm, 1 x w x h) was closed and the reaction allowed to proceed (mould temperature 450C). Demoulding took place four minutes after mixing started.

The inside of the lid of the mould contained one layer of OCF8610 continuous glass mat from Owens Corning.

The polyol composition contained 90 parts by weight of a glycerol initiated EO-PO polyol (16% EO-tip) of MW 4800; 6.5 pbw of ethylene glycol; 0.91 pbw of ISF catalyst (DABCO EG + dibutyl tin dilaurate); 10 pbw of black paste Black N from Bayer and 0.8 pbw of water. A semi-rigid article with an integral skin was obtained having the following physical properties : the overall density was 520 kg/m; the shore A hardness was 60 (DIN 53505) and the modulus was 62 MPa (DIN 53423). The article had a good quality surface without defects.

The density gradient, as outlined before, was less than 2.

Example 2 Example 1 was repeated with the proviso that instead of one layer four layers of glass mat were used. The article had a good quality surface without defects.

The density gradient was less than 2.

Example 3 (comparative) From the article prepared in example 1 a piece was cut having a thickness of 1 cm and comprising the reinforcement (the cut was made parallel to the side comprising the reinforcement). This 1 cm thick part was fixed to the inner side of the lid of the mould used in Example 1 with the cut-side of the piece faced to the lid surface. Then an amount of the mixture of ingredients used in Example 1 was poured into the mould. The amount used was equal to the weight of the piece which was cut off and not fixed to the lid. Then the mould was closed and the reaction was allowed to take place under the same conditions as in Example 1. Demoulding was conducted four minutes after pouring. The article had a good quality surface without defects. The overall density was 506 kg/m3; the modulus was 35 MPa (DIN 53423) and the shore A hardness was 57 (DIN 53505). This shows that stiffness is improved when the article is prepared in one stage.

Example 4 Similar to example 1 an article was made from an MDI/polyether polyol prepolymer having an NCO of 19% by weight and a polyester polyol composition at an index of 95 (overpack about 340%). The article showed a good surface quality without defects and had a very good stiffness. The density gradient was less than two.

Claims

1. Semi-rigid polyurethane foam article having at a side a reinforcement and at the opposite side an integral polyurethane skin.

2. Article according to claim 1 characterised in that the article contains reinforcement and polyurethane only.

3. Article according to claims 1 and 2 characterised in that the ratio of the density of the part of the article comprising the reinforcement and the density of the foam at a distance of 0.2 mm of said part is less than 2.5.

4. Article according to claims 1-3 characterised in that the reinforcement is a continuous or woven glass mat.

5. Process for making an article according to claim 1 by applying a reinforcement at the inside of a lid of a mould, providing the mould with a reaction mixture for preparing semi-rigid polyurethane foams, closing the mould, allowing the reaction mixture to react under integral skin forming conditions and demoulding the article.