GB2048150A - Insulated Mould Lining for Use in Foam Production - Google Patents

Abstract

A process for producing a polyurethane or polyisocyanurate foam in which foam forming materials are cured to form a foam, supported during curing on an insulating base formed by a sheet of thin, flexible material backed by a gas-space. Preferably the insulating base is a mould liner comprising closed gas pockets trapped between layers of a laminate of plastics film e.g. polyethylene. The moulding may be a continuous or batch process. Wastage of materials due to collapse of the foam at the base of the mould is reduced by the process of the invention.

Description

SPECIFICATION Foam Products This invention relates to a process for producing resin foams more particularly polyurethane and polyisocyanurate foams, moulds for use in producing such foams and foams prepared by the process of the invention.

Flexible, rigid and semi-rigid polyurethane and polyisocyanurate foams are widely employed in a large number of purposes.

Continuous and batchwise methods for the production of these foams are known and widely used.

It is sometimes desirable that the foam be formed with a thick integral skin. However, where this is ngt desired, the skin which forms and any area of densified foam adjacent the skin is wasted material. The largest amount of waste usually occurs at the base of the mould, which may be stationary or moving. In our co-pending application No. 39910/78 we described a process for making a phenolic foam in which this same problem was largely overcome. We have now found that this process may usefully be used in the moulding of polyurethane and polyisocyanurate foams also.

The formation of polyurethanes and polyisocyanurate foams conventionally generates a considerable amount of heat and the interior of a curing mass of foam may reach a temperature of 1 300 to 1 600C. The outer regions of the mass of curing foam material lose heat to the mould walls and it is thought that this loss of heat may cause a collapse of the foam cell structure.

The present invention provides a process for producing a polyurethane or polyisocyanurate foam which process comprises curing a mixture of polyurethane or polyisocyanate foam forming materials, the mixture being supported during curing on an insulating base formed by a sheet of thin, flexible material backed by a qas-space.

The invention includes a mould for moulding a polyisocyanate or polyisocyanurate foam wherein at least a base moulding surface thereof is formed by a sheet of thin flexible material backed by a gas-space.

The invention also includes foams produced by the above method.

By use of a mould according to the invention, the thickness of the base skin can be decreased.

Preferably, the mixture is further supported by side-walls formed by the thin, flexible sheet material backed by a gas-space.

Preferably, the thin flexible material is backed by a multitude of closed gas pockets.

Preferably, the flexible material is a plastics material.

Preferably, the gas-space is provided by closed gas pockets trapped between layers of a laminate of plastics films.

Preferably, the gas pockets protrude only on the face of the laminate opposite to that supporting the mixture. The laminate may be formed between a smooth sheet of plastics film and a sheet having a multitude of vacuum formed depressions therein. The pockets may be cylindrical and from 10 to 25 mm in diameter, and may be about 2mm tall.

It is found that the plastics film can act as a release aid and can be removed from the cured foam for re-use.

The process of the invention may advantageously be operated in a continuous moulding process but may also be used in batch processes.

The mould used may be an open or closed mould and may be of a conventional kind except for the provision of an insulating liner. The mould itself may be of any conventionally used material, e.g.

wood or metal. This is most preferably of the kind sold under the Trade Mark "Pilloflex" by A. Latter 8 Co. Ltd. of Croydon, although any essentially similar material could advantageously be used.

"Pilloflex" is a laminate formed between a flat sheet of polyethylene film and a sheet of a similar material having a closely packed array of hollow cylindrical projections formed thereon. The top of each such projection has a dimpled appearance. The films are laminated so as to define a multitude of closed air-filled cyindrical sacks projecting from one face only of the laminate.

In using the present invention in batch moulding one may use a mould substantially as described in Application No. 39910/78. An example of a mould for use in continuous moulding of slabstock is shown in the accompanying drawing, in which the figure is a schematic side view of an apparatus including a moving mould according to the invention.

In the figure is shown a conventional moving mould for moulding rigid polyurethane slabstock comprising a belt conveyor 1 of rectangular trough cross-section running over rollers 2,3. In use according to the invention, "Pilloflex" or a similar material 2 is drawn off a roll 3 onto the floor of the conveyor to form a mould according to the invention. If desired, additional rolls of "Pilloflex" can be provided to line the side walls 4 of the conveyor also. Alternatively, the roll 3 can be sufficiently wide that the "Pilloflex" lines the sides as well as the base of the conveyor. The "Pilloflex" is applied smooth side toward the foam. Foam forming materials are dispensed from conventional apparatus 6 onto the "Pilloflex" base of the mould. If the sides of the mould are not covered with "Pilloflex" it may be desirable to cover them with release paper.

The mixture of foam forming materials foams and cures on the conveyor and is removed after passing a cutter 5 as slabstock at the other end of the conveyor. The "Pilloflex" is peeled away as the slabstock leaves the conveyor and may be re-used. It is wound on a reel 7 after being cleaned by a brush 8.

The mixtures from which the polyurethane and polyisocyanurate foams are made can be the same as are conventionally used.

The invention is illustrated by the following Example.

Example A flexible polyurethane slabstock was produced from the following foam forming ingredients:~ Parts by weight Propylan 330 (a 3500 mol. wt. polyoxyalkylene trio having an OH value of 48 mg KOH/g produced by Lankro Chemicals Limited) 100 Water 4.0 Propamine A (dimethylaminoethanol produced by Lankro Chemicals Limited) 0.25 Nuocone 28 (Stannous Octoate-28% active, produced by Durham Raw Materials) 0.25 Tegostab B2370 (a silicone oil produced by Theodore Goldschmidt AG) 1.0 Toluene Diisocyanate to give an NCO index of 110 These ingredients were thoroughly mixed and formed a liquid foam which was introduced into a 1 5x 1 5 inch wooden box mould and allowed to cure. The base of the mould was lined with a single sheet of Pilloflex, smooth side up prior to the introduction of the foam. The foam produced had virtually no base skin. The Pilloflex was easily removable from the solid foam in good re-usable condition.

For comparison, this Example was repeated using an unlined mould of the same dimensions and material. The foam produced had a densified base layer 1 5 mm thick, accounting for 6.5% of the weight of the foam block.

Claims (18)

Claims

1. A process for producing a polyurethane or polyisocyanurate foam which process comprises curing polyurethane or polyisocyanurate foam forming materials, the mixture being supported during curing on an insulating base formed by a sheet of thin, flexible material backed by a gas-space.

2. A process as claimed in claim 1 wherein the mixture is further supported by side-walls formed by the thin, flexible sheet material backed by an air-space.

3. A process as claimed in claim 1 or claim 2 wherein the thin, flexible material is backed by a multitude of closed gas pockets.

4. A process as claimed in any one of claims 1 to 3 wherein the thin, flexible material is a plastics material.

5. A process as claimed in claim 4 wherein the gas-space is provided by closed gas pockets trapped between layers of a laminate of plastics films.

6. A process as claimed in claim 5 wherein the gas pockets protrude only on the face of the laminate opposite that supporting the mixture.

7. A process as claimed in claim 6 wherein the laminate is formed between a smooth sheet of plastics film and a sheet having a multitude of vacuum formed depressions therein.

8. A process as claimed in any one of claims 4 to 7 wherein the pockets are cylindrical and from 10 to 25 mm in diameter.

9. A process as claimed in claim 8 wherein the pockets are about 10 mm in diameter.

10. A process as claimed in any one of claims 5 to 9 wherein the pockets are about 2 mm tall.

11. A process as claimed in any one of claims 4 to 10 wherein the plastics material supporting the mixture is a polyethylene film.

12. A process as claimed in claim 1, substantially as hereinbefore described in the Example.

13. A mould for moulding a polyurethane or polyisocyanurate foam wherein at least a base moulding surface thereof is formed by a sheet of thin, flexible material backed by a gas-space.

14. A mould as claimed in claim 13 wherein both side and base surfaces of the mould are provided by the thin, flexible sheet material backed by a gas-space.

15. A mould as claimed in claim 13 or claim 14 wherein the thin, flexible material is a plastics material.

16. A mould as claimed in any one of claims .13 to 15 wherein the plastics mould surfaces are provided by a laminate as defined in any one of claims 5 to 10.

17. A mould substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

18. A body of foam produced by a process as claimed in any one of claims 1 to 12.