WO1992009744A1

WO1992009744A1 - Non-asbestos flexible sheet material

Info

Publication number: WO1992009744A1
Application number: PCT/GB1991/002061
Authority: WO
Inventors: David Geoffrey Hall; Antony Latkowski
Original assignee: T&N Technology Limited
Priority date: 1990-11-29
Filing date: 1991-11-21
Publication date: 1992-06-11
Also published as: GB9124747D0; GB2250302A; GB2250302B; GB9025983D0

Abstract

Non-asbestos flexible sheet material suitable for use in gaskets for the cylinder head of an internal combustion engine is made by a paper-making process in which the aqueous slurry employed is substantially free from cellulose and contains the following ingredients in the following proportions by dry weight: kaolinitic clay comprising both ball clay and china clay 65-90 %, organic fibres consisting essentially of fibrillated poly(aromatic amide) fibres 5-15 %, polymeric binder, e.g. nitrile rubber 4-10 %.

Description

Non-asbestos flexible sheet material

This invention relates to non-asbestos flexible sheet material suitable for use in gaskets for the cylinder head of an internal combustion engine.

There are described in GB 2 138 854 A and GB 2 138 855 A methods of making such sheet by a paper-making process: that is to say, by dewatering a layer of aqueous slurry and compressing and drying the de atered layer. In both procedures the aqueous slurry employed includes among its essential ingredients ball clay (a kaolinitic clay of high plasticity) as the paper matrix; cellulose fibres to assist the formation of a web on the water-permeable conveyor of the paper-making machine; fibrillated poly(aromatic amide) fibres as reinforcement; and polymer binder. Of the fibrillated fibres of pol (aromatic amide) or "aramid", the cited prior publications state that they assist formation of a web, but not so effectively as the cellulose fibres; they are, however, much better than _

cellulose fibres in their capacity to confer strength at the high temperature (280- 300 deg C) at which the finished gasket has to operate.

The present invention modifies the above procedures with the object of obtaining gasket sheet material of better performance at high temperature, and in particular better able to retain an applied load, as when bolt-clamped between the engine block and cylinder head.

We have now found that this object can be achieved, with¬ out significantly adverse effect on other desirable proper¬ ties of the gasket paper produced, by omitting cellulose fibres from the aqueous slurry submitted to dewatering, by using a kaolinitic clay mixture, and by keeping the ingred¬ ients within certain limits by dry weight of the slurry.

According to the invention, in a method of making non-asbestos flexible sheet material suitable for use in gaskets for the cylinder head of an internal combustion engine, by dewatering a layer of aqueous slurry and compressing and drying the dewatered layer, the aqueous slurry employed is substantially free from cellulose and contains the following ingredients in the following proportions by dry weight: kaolinitic clay 65-90% organic fibres consisting essentially of fibrillated poly(aromatic amide) fibres 5-15% polymeric binder 4-10%

said kaolinitic clay comprising both china clay and ball clay.

The ball clay is employed in the unfired state. The china clay is preferably calcined china clay. Mixtures of ball clay and china clay may be used in which either of them predominates. In working examples 1 and 3 later, ball clay predominates; in example 2, it forms only a minor proportion of a mixture in which calcined china clay predominates. From the examples, it will be apparent that by varying the weight proportion of ball clay to china clay a range of properties (eg of tensile strength, compression and stress relaxation) can be optimised to suit particular applications. Preferably the proportion of ball clay : china clay is in the range 20 : 1 - 1 : 20, particularly 15 : 1 - 1 : 15, and especially 5 : 1 - 1 : 5. Preferably the kaolinitic clay forms not less than 75% by dry weight of the aqueous slurry.

To mask the whiteness that is due to the kaolinitic clay, a dark (and preferably black) pigment may be included in the slurry, suitably in an amount of 1-10% by dry weight. Examples are: black iron oxide; carbon black. The slurry may include a proportion, suitably 1-10% by dry weight, of mineral wool in order to improve drainage of water from the web on the conveyor of the paper-making machine.

The polymeric binder employed is preferably an elastomer, which may be natural rubber but is preferably synthetic, for example an acrylonitrile-butadiene copolymer. The elastomer is conveniently included in the slurry in the form of a latex. A cross-linking agent may optionally be incorporated, along with antioxidant.

The fibrillated poly(aromatic amide) fibres provide essentially the sole organic web-forming fibres in the process, and these are suitably employed at a freeness of 30-70 degrees Schopper Riegler. The fibres also provide reinforcement, both during "wet" stages of the paper- making process and during processing of the paper product into gaskets. Their reinforcing capacity for the kaolinitic clay matrix is particularly well retained at the high temperatures (280-300 degrees C) prevailing during IC engine operation. The material commercially available as Kevlar (registered trade mark) pulp is very suitably used. Preferably, the fibrillated poly(aromatic amide) or "aramid" fibres are used in an amount of 5-12% by dry weight of the aqueous paper-making slurry. From the sheet material produced by the method of the invention gaskets can be made by entirely conventional means, as by lamination onto each side of a metal sheet (plain, perforated, tanged or other); blanking of the laminate into the desired shape with appropriately spaced combustion chamber and other apertures; insertion of eyelets around the chamber apertures; impregnation with a silicone or other polymer to improve resistance to oil and aqueous anti-freeze solution; and coating of the surface to facilitate release from the cylinder head when the head is removed from the cylinder block.

The density of the sheet material product will ordinarily be in the range 700-1500 kg/m³ .

The invention is further illustrated by the following examples

EXAMPLE 1

A paper was prepared from an aqueous slurry having the following composition

% dry weight

Fibrillated poly( aromatic amide) fibres 8

Ball clay 71

Calcined china clay 5

Mineral wool 5

Nitrile rubber 6

Black iron oxide 5

Preparation of Slurry

(i) "Kevlar pulp" (fibrillated poly aromatic amide) in roll form was made into an aqueous slurry of solids content about 2% by weight and treated in a disc refiner at low load to disentangle the fibres without significantly shortening them. The freeness of the resulting pulp was 62 degrees Schopper Riegler.

(ii) The pulp of (i) (1.6 kg dry weight = 80 kg wet weight) was added to 200 litres of water at 60° C in a mixing tank and the diluted pulp was agitated vigorously. (iii) Mineral wool (1 kg dry weight of Swedish Rockwool having an average fibre length of 1.0 mm, water content of 25% and a shot content below 10%) was added to the diluted pulp.

(iv) Ball clay (14.2 kg; 96% < 20 μ , 67% < 2 μ), calcined china clay (1 kg; 90% < 10 u, 50% < 2 μ ) and black iron oxide (1 kg) were dispersed in 20 litres of water at 60° C and added to the pulp with agitation.

(v) The pH of the slurry was adjusted to 9 by the addition of aqueous ammonia.

(vi) 1.2 kg dry weight (= 2.5 kg wet weight) of a commercially available aqueous acrylonitrile- butadiene copolymer latex (pH 10.5, solids content 47%, acrylonitrile content 33%) was added and the mixture was agitated for 2 minutes.

(vii) The pH of the slurry was reduced by the addition of papermaker's alum (aluminium sulphate) until the supernatant liquid was found to be clear, indicating precipitation of the dispersed rubber particles onto the fibres, clay and pigment. Water at 60° C was then added to bring the total volume in the mixing tank to 500 litres, and mixing was continued for 3 minutes.

Preparation of Paper

The slurry of A above was made into flexible sheet material using a conventional Fourdrinier flat wire paper machine. Conventional polyacrylamide flocculating agent and anti-foaming agent were added to assist processing.

The paper was then densified by use of a 2-bowl calender to produce flexible sheet material having the following properties

Thickness 0.78 mm

Mass/unit area 990g/m²

Density 1270kg/m³

Tensile strength Machine direction 6.6 MPa Cross direction 5.1 MPa

Compression @ 10 MPa 15.0%

In addition the stress relaxation behaviour of the material was measured after laminating to plain steel core. A similar method to that described in ASTM F1276 was used, using an annular specimen of internal diameter 14.7 mm and external diameter 34.5 mm. A stress of 58.6 MPa was applied to the specimen and the residual stress was measured after exposure to a temperature of 300° C for 1.75 hours. The loss in stress as a percentage of the initial stress, and after normalisation to a facing thickness of 1.0 mm, was 35%.

EXAMPLE 2

Following generally the procedure of Example 1 , non- asbestos paper was made from a slurry whose composition was

% dry weight

Fibrillated poly(aromatic amide) fibres 8

Calcined china clay 76

Ball clay 5

Nitrile rubber 6

Black iron oxide 5

The calcined china clay, ball clay and black iron oxide were mixed before addition to the diluted pulp, and no pH adjustment was made prior to addition of the nitrile rubber latex. The calcined china clay had a specific surface area (BET) of 12m² /g, particle size 90% <10 μ , 50% < 2 p.

The resulting flexible sheet material had the following properties

Thickness 0.6 mm

Mass/unit area 690g/m²

Density 1160 kg/m³ Tensile strength

Machine direction 3.4 MPa

Cross direction 2.3 MPa

Compression @ 10 MPa 12.0%

The stress relaxation of samples of this material after laminating to plain steel core was 27%.

Gaskets suitable for use on the cylinder heads of automobile engines were produced from the material by the conventional steps: (i) Lamination of the paper onto each side of plain steel core (ii) Blanking of the required gasket shape (iii) Insertion of steel eyelets into the combustion chamber bore holes of the gasket ( iv) Impregnation of the gasket with a silicone (v) Surface-coating with a release agent

The resulting gaskets gave excellent fluid-sealing performance in test engines.

EXAMPLE 3

Following generally the procedure of Example 1, a non- asbestos paper of improved properties can be made from a slurry of the following composition:

% dry weight Fibrillated poly(aromatic amide) fibres 8

Calcined china clay 20

Ball clay 65

Nitrile rubber 6

Carbon black 1

Claims

1 A method of making non-asbestos flexible sheet material suitable for use in gaskets for the cylinder head of an internal combustion engine, by dewatering a layer of aqueous slurry and compressing and drying the dewatered layer, in which the aqueous slurry employed is substantially free from cellulose and contains the following ingredients in the following proportions by dry weight:

kaolinitic clay 65-90% organic fibres consisting essentially of fibrillated poly(aromatic amide) fibres 5-15% polymeric binder 4-10%

the kaolinitic clay comprising both china clay and ball clay.

A method according to claim 1, in which the kaolinitic clay forms at least 75% by dry weight of the slurry.

A method according to claim 1 or 2, in which the kaolinitic clay is predominantly calcined china clay, the rest being ball clay. A method according to claim 1 or 2, in which the kaolinitic clay is predominantly ball clay, the rest being calcined china clay.

A method according to any of claims 1 to 4 , in which the weight proportion ball clay : china clay is in the range 15 : 1 - 1 : 15.

A method according to any of claims 1 to 5 , in which the slurry also contains mineral wool, in an amount of 1-10% by dry weight.

A method according to any of claims 1 to 6, in which the polymeric binder is a synthetic elastomer.

A method according to claim 7, in which the synthetic elastomer is included in the slurry in the form of a latex.

A method according to any of claims 1 to 8, in which the polymeric binder is an acrylonitrile-butadiene copolymer.

A method according to claim 1, substantially as described with reference to Example 1 herein. A method according to claim 1 , substantially as described with reference to Example 2 herein.

A method according to claim 1, substantially as described with reference to Example 3 herein.

A cylinder head gasket comprising non-asbestos flexible sheet material which is substantially free from cellulose, is made according to any preceding claim, and is secured to a metal support.