GB2031786A - Insulated mould lining for use in phenolic resin foam production - Google Patents

Abstract

A process for producing a phenolic resin foam in which a resole resin is reacted with a curing agent in the presence of a foaming agent and the mixture is supported during curing on an insulating base formed by a sheet of thin, flexible material 3 backed by a gas-space. Preferably the insulating base is a mould liner comprising closed gas pockets 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. <IMAGE>

Description

SPECIFICATION Phenolic resin foam production This invention relates to a process for producing phenolic resin foams, moulds for use in producing such foams and foams prepared by the process of the invention.

Phenolic resin foams are widely employed for temperature insulation purposes where flammability resistance is important.

The slow batchwise production of phenolic resin foams gives a product with excellent physical strength characteristics. Also the attendant fine regular cell structures gives a foam with low water absorption characteristics coupled with increased resistance to moisture vapour transmission.

Continuous methods for the production of phenolic foam are known and widely used.

However, with these processes the chemical system must cure quickly and generally these foams have a cell structure more irregular than the foams produced slowly in fixed moulds.

These fast cure foams find application in many diverse areas where strength and moisture vapour transmittance properties are not of prime importance or can be readily overcome by application of moisture vapour barriers.

Whilst the method of the invention may be used in continuous moulding, its main area of application is in batchwise foam production.

In continuous moulding, a rapid cure mixture containing a resole resin, foaming agent and curing agent is deposited from a dispenser onto a moving mould, comprising a base conveyor and side conveyors.

Typically, in the batchwise process of phenolic foam production a resole resin, a cell stabilising agent, a low boiling point liquid to act as a foaming agent and an acidic curing agent are mixed together either by dispensing machines designed for this operation or alternatively by using a high speed propeller type stirrer. Once mixed, the chemicals are poured into a mould of the appropriate shape and design and then the mould is heated until full rise and cure has been achieved. Typically the mould is heated by placing it in an oven at the desired temperature but other forms of mould with inbuilt water, steam or electrical heating can be employed.

Batchwise production of phenolic foam may also be carried out by heating the chemicals before the mixing process. In this way the need to cure the foam in a heated mould is eliminated. For this process to operate effectively the resole resin must be in a more condensed form than resins used in the more conventional heated cure processes. These more viscous resins reduce the severe mixing problems which occur with the lower molecular weight more reactive resins. Using carefully controlled chemical temperatures the foam can be prepared to similar densities as obtained by heat curing (50-70 C) methods. The friability, or resistance to abrasion, is generally very much improved. Usually the resin viscosity is in the region of 5000-10000 centistokes at 25 C with a water content between 18-20%.The resin temperature is generally kept between 30-45 C (depending on the desired foam density) before mixing with the foaming agent, cell stabiliser and the acid curing agent. After intimately mixing the components the procedure is identical to that of the hot cure process except that a heat assisted curing step is not required.

Disadvantages associated with this method include the pumping and transportation of the relatively viscous resis and also the short working life of resole resins held at elevated temperatures.

Another severe disadvantage associated with this method is that the phenolic foam thus formed typically has a characteristic very hard thick outer skin. This skin is probably caused by a collapse of the foam cell structure when the foam comes into contact with the relatively cold walls of the mould which are at ambient temperature. Heated moulds can be used to overcome this problem to a certain extent, but a hot cure system cannot be used in a conventional sense because premature curing of the high molecular weight resin occurs at the foam surface thus resulting in at best a high density foam or, at worst, a cracked foam. The skin is usually hardest at the base of the foam and can be typically 2-3mm thick. Along the edges of the base of the foam this hard unfoamed resin layer can reach thicknesses of 1 Omm or more.

A 3mm skin on the base only of a phenolic foam prepared to the dimensions of 2m long X 1 m length X 0.6m wide at 35 kg/m3 foam density represents almost 10% of total resin materials utilisation. The skin on the sides and top of the foam also tends to reduce foam yield but this skin is usually much thinner than the base layer.

The present invention provides a process for producing a phenolic resin foam which process comprises reacting a resole resin with a curing agent in the presence of a foaming agent, the mixture being supported during curing on an insulating base formed by a sheet of thin, flexible material backed by a gas-space.

The invention includes a mould for moulding a foamed phenolic resin wherein at least a base moulding surface thereof is formed by a sheet of thin flexible material back by a gas-space.

The invention also includes foams produced by the above method.

By the use of a mould according to the invention, the thickness of the hard 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 25mm 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.

Phenolic resole resins suitable for use in the process of the invention are described in our Patent Application No. 26,016/77. These resins are prepared by condensing a phenol, preferably phenol itself, with an excess of formaldehyde, at elevated temperatures in the presence of an alkaline catalyst.

Preferably the resole resin is produced by reacting phenol and excess formaldehyde at a molar ratio of up to 1:2.5.

Many cell stabilising agents are suitable in the production of phenolic foams including siloxane-oxyalkylene copolymers and ethylene oxide adducts with alkylphenols such as nonylphenol.

Foaming agents which can be employed here include "low" boiling point liquids having a boiling point between - 40"C and 90 C. Preferred liquids are alkanes, such as pentane (b.p.

36 C) and halogenated alkanes, such as methylene dichloride (b.p. 40'C), trichloromonofluoromethane (b.p. 23.8 C) and 1,1,2-trichloro-1,2,2-trifluoroethane (b.p. 48 C) and mixtures of these.

The acidic curing agent can be of the mineral acid type or an organic acid or a mixture of these. An example of a suitable mineral acid is sulphuric acid. Suitable aromatic acids are toluene sulphonic acid and phenol sulphonic acid. A sulphonated Novolak resin may be used.

The process of the invention may advantageously be operated in a batch manner.

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. 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.

The nature of "Pilloflex" and the manner of its use according to the preferred practice of the invention can be more easily understood by a consideration of the accompanying drawing in which: Figure 1 shows a plan view of a piece of "Pilloflex" laminate; Figure 2 shows a cross-section through the thickness of the laminate of Fig. 1; and Figure 3shows a mould lined with "Pilloflex".

As shown in Figs. 1 and 2, "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 cylindrical sacks projecting from one face only of the laminate.

In Fig. 3, the laminate has been used to line the walls and base of a mould, (if the mould has a lid this may be lined also). The flat side of the laminate forms the moulding surface of the lined mould. The lining may be retained in place by adhesive or adhesive tape. The mould may be of wood or plastics or of metal.

The invention will be illustrated by the following Example.

EXAMPLE The sides and base of a steel mould of dimensions 2m x 1.2m x 0.6m, which was equipped with a movable lid to achieve a flat topped foam block, were covered with "Pilloflex" which was retained in place with adhesive tape. The cylindrical projections which faced the mould were 1 Omm in diameter.

Preparation of a foamed product without the use of "Pilloflex" Using a Secmer PH380 phenolic foam dispensing machine a foamed product was prepared by intimately mixing the following constituents: Phenolic resole resin 98 parts by weight 1 ,1, 1 2-trichloro-1, 2, 2-trifluoroethane (Freon 113 blowing agent) 7.3 parts by weight cell stabilising agent (silicone oil DC193) 2 parts by weight 50% (w/w) aqueous sulphuric acid 9 parts by weight 98 Kilogrammes of this foaming mixture were dispensed into the mould to produce a foam approximately 1.5 metres high with a foam density of 37 kg/cm3 after a one week conditioning period.

For comparison a similar mixture was charged into a similar but unlined steel mould. The mixture contained 7.9 parts by weight of blowing agent to compensate for the higher foam density expected. 119.5 Kilogrammes of mixture were needed to produce a foam 1.5 metres high with a foam density of 36 kg/m3 after a one week conditioning period.

The base and sides of both foam samples showed an unfoamed skin, but that obtained with the lined mould had a very much thinner skin than the other.

It can be seen that a saving of about 20% by weight of chemicals can be made by the use of polythene sheeting containing entrapped air bubbles as a facing material and release aid within a steel mould.

Claims (25)

1. A process for producing a phenolic resin foam which process comprises reacting a resole resin with a curing agent in the presence of a foaming agent, the mixture being supported during curing on an insulating base formed by a sheet of thin, flexible material backed by a gasspace.

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 25mm in diameter.

9. A process as claimed in claim 8 wherein the pockets are about 1 Omm in diameter.

10. A process as claimed in any one of claims 5 to 9 wherein the pockets are about 2mm 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 any preceding claim wherein the resole resin is the product of reacting, at an elevated temperature, phenol with excess formaldehyde at a molalr ratio of up to 1 to 2:5 in the presence of an alkaline catalyst.

13. A process as claimed in claim 12, in which the curing agent is a mineral acid, aromatic sulphonic acid, or sulphonated Novolac resin or a mixture thereof.

14. A process as claimed in claim 13, in which the acid curing agent is sulphuric acid, toluene sulphonic acid or phenol sulphonic acid or a mixture thereof.

15. A process as claimed in claim 13 or claim 14, in which the foaming agent is a low boiling inert liquid having a boiling point between - 40"C and 90 C.

16. A process as claimed in claim 15, in which the foaming agent is an alkane or halogenated alkane.

17. A process as claimed in any of claims 13 to 16, in which there is additionally employed a cell stabilising agent.

18. A process as claimed in claim 17, in which the cell stabilising agent is a siloxaneoxyalkylene copolymer or a polyethoxylated castor oil.

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

20. A mould for moulding a foamed phenolic resin wherein at least a base moulding surface thereof is formed by a sheet of thin flexible material backed by a gas-space.

21. A mould as claimed in claim 20 wherein both side and base surfaces of the mould are provided by the thin, flexible sheet material backed by a gas-space.

22. A mould as claimed in claim 20 or claim 21 wherein the thin, flexible material is a plastics material.

23. A mould as claimed in any one of claims 20 to 22 wherein the plastics mould surfaces are provided by a laminate as defined in any one of claims 5 to 10.

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

25. A body of foamed phenolic resin produced by a process as claimed in any one of claims 1 to 19.