GB2123034A - Making flexible sheet by electrophoretic deposition - Google Patents

Abstract

Flexible sheet material suitable for use as gasket-facing material is made by submitting to electrophoresis an aqueous suspension of an expanded layer silicate e.g. exfoliated vermiculite, which contains a dispersed organic polymeric material such as a butadiene-acrylonitrile copolymer latex, and stripping the coating of electrophoretically deposited material from the support on which it is formed. <IMAGE>

Description

SPECIFICATION Method of making flexible sheet material This invention relates to a method of making flexible sheet material, more particularly flexible sheet material having a content of exfoliated vermiculite or similar expanded layer silicate such as expanded hydrobiotite.

It is disclosed in British Patent Specification 1 593 383 that flexible sheet material composed substantially wholly of lamellae of exfoliated vermiculite adhering together by mutually attractive forces can be made by evaporating certain aqueous suspensions of exfoliated vermiculite while they are in contact with a shaped surface, or alternatively by removing water from the suspensions by absorption into an absorbent part of a shaped surface.

Electrophoretic methods of deposition of the lamellae from the suspension are disclosed as being advantageously used when rapid removal of water is required. After the bulk of the water has been removed by such methods, the vermiculite layer may be stripped from the surface against which it is shaped, or alternatively left in place as a non-combustible coating on the surface. The layer is affected by liquid water, by may be made water-resistant by an ion-exchange proCess after shaping.

- By the present invention we produce flexible sheet material having a content of exfoliated vermiculite or similar expanded layer silicate which has acceptable water-resistance without the use of an ion-exchange procedure.

According to the invention we produce flexible sheet material by submitting to electrophoresis an aqueous suspension of an expanded layer silicate which contains a dispersed organic polymeric material, to deposit on a support a layer or coating which contains from 5 to 90% by dry weight of said polymeric material, and then stripping the electrophoretically deposited coating from the support.

The flexible sheet material thus produced is, by virtue of its water-resistance, cohesiveness and sealing capacity, useful as gasket-facing material, and can be readily secured by conventional adhesives to apertured metal support plates of the type used in gasket manufacture.

Preferably the deposited coating contains not less than one-third by dry weight of layer silicate, and a content of 4080% by weight is particularly preferred.

Suitable polymeric materials are: natural rubber; acrylonitrile butadiene copolymers; polyacrylates; acrylonitrile-butadiene-styrene copolymers; and epoxy resins.

Electrophoresis will usually be carried out at a voltage gradient in the-range 0.05-3 volts/mm.

A preferred range is 0.25-2.5 volts/mm.

Electrophoresis in aqueous suspensions is often accompanied by electrolysis, and this can give rise to gas bubbles, in particular of oxygen, at an electrode (anode) constituted by a metal support. This is specially noticeable when the support is of stainless steel. To avoid this, and the possibility of forming a deposit that is flawed owing to the presence of trapped gas, it is desirable to employ a support whose surface at least is of a metal which suppresses oxygen evolution, preferably zinc, copper, aluminium or very pure iron.

A preferred thickness for the electrophoretically deposited coating is in the range 0.05-0.5 mm when dry.

After formation of the electrophoretic deposit the support is removed from the aqueous suspension employed for electrophoresis and rinsed with water. After any treatment which may be necessary in particular cases to impart green strength to the deposit, the deposit is stripped from the support. To facilitate stripping, the electrode (anode) employed in electrophoresis is preferably of metal that is highly polished.

The expanded layer silicate which is to be present in the electrophoresis medium is preferably an aqueous suspension of silicate which has been exfoliated chemically rather than thermally. Suitable suspensions may be prepared by the methods described in British Patent Specifications 1 016 385, 119 305, 1 593 382 and 1 593 383.

The electrophoresis meduim can contain additional ingredients intended to form part of the coating, for example: pigments and dyes; and additional water-proofing agents such as glyoxal.

The invention is further illustrated by the Examples herein and with reference to the accompanying drawing, which is a diagram showing an eiectrophoresis cell whose anode receives a deposit of material which is later stripped from the anode in the form of flexible sheet.

Example 1 a. A rectangular sheet (50x25 mm) was cut from a highly polished sheet 1 mm thick of pure zinc, and made the anode 1 in an electrophoresis cell 2 containing a slurry 3 made by mixing 90 parts by volume of a slurry of exfoliated vermiculite with 10 parts by volume of an acrylic polymer latex. The slurry of exfoliated vermiculite contains 6.5% by weight of vermiculite of particle size less than 50 ym, and had been prepared following generally the procedure of example 1(A) in British Patent Specification 1 593 382. The acrylic polymer latex was a commercially available material sold under the name Revacryl A275 (an anionic emulsion, 45.5% solids content, of a self-linking acrylic polymer curable at 1 200C; pH4; particle size 0.2 yam).

The cathode 4 of the cell was of perforated tinplate.

The anode 1 had on the side remote from cathode 4, and on its edges, a coating 5 of polyurethane lacquer.

b. Electrophoresis was carried out for 2 minutes at a voltage gradient of 1 volt/mm to form an electrophoretic deposit 6 on the anode 1.

c. The anode 1 was then removed from the electrophoresis cell, rinsed with water, dried at 800C for 1 hour and then heated at 1 200C for 3 minutes to cure the acrylic polymer present in the coating deposited on it. The coating 6 was then stripped from the anode. The highly flexible sheet thus obtained was 0.1 mm thick and contains 35% by weight of acrylic polymer, the rest being exfoliated vermiculite.

Example 2 Following generally the procedure of Example 1 a coating 6 was formed by electrophoretic deposition from a slurry obtained by mixing 225 parts by weight of a slurry of exfoliated vermiculite with 100 parts by weight of the epoxy resin sold under the trademark Grilonit GE38 and 225 parts by weight of the corresponding hardener solution (25% solids content).

The anode was removed from the electrophoresis cell, rinsed with water and dried in a stream of air at ambient temperature until the coating 6 had developed enough green strength to allow it to be stripped from the anode. The film thus detached was then allowed to stand until cure of the epoxy resin component was complete.

The flexible sheet thus obtained contains 11% of epoxy resin.

Example 3 Following generally the procedure of Example 1 a coating 6 was formed by electrophoretic deposition from a slurry obtained by mixing 90 parts by volume of a slurry of exfoliated vermiculite with 10 parts by volume of a commercially available butadiene-acrylonitrile latex (solids content 41%; pH 10.3; particle size 0.13cm).

The flexible sheet obtained contained 81% by weight of butadiene-acrylonitrile copolymer.

Claims (6)

Claims

1. A method of making flexible sheet material comprising submitting to electrophoresis an aqueous suspension of an expanded layer silicate which contains a dispersed organic polymeric material, to deposit on a support a coating which contains 590% by dry weight of said polymeric material, and then stripping the electrophoreticaily deposited coating from the support.

2. A method according to claim 1, in which the deposited coating contains not less than one-third by dry weight of expanded layer silicate.

3. A method according to claim 2, in which the deposited coating contains 4080% by dry weight of expanded layer silicate.

4. A method according to any one of claims 1 to 3, in which the organic polymeric material is an acrylic polymer.

5. A method according to any one of claims 1 to 3, in which the organic polymeric material is an acrylonitrile-butadiene copolymer.

6. A method according to any one of claims 1 to 3, in which the organic polymeric material is of epoxy resin.