GB2061344A

GB2061344A - Paper

Info

Publication number: GB2061344A
Application number: GB8032872A
Authority: GB
Original assignee: Turner and Newall Ltd
Current assignee: Turner and Newall Ltd
Priority date: 1979-10-19
Filing date: 1980-10-10
Publication date: 1981-05-13
Also published as: GB2061344B

Abstract

Non-asbestos paper alternatives to latex-bound asbestos papers comprise vitreous fibres derived from wool-form material, organic web- forming fibres, unfired ball clay and water-insoluble non-fibrous particulate inorganic filler, the whole being bound together by a cured nitrile rubber; said paper being made by dewatering as a layer on a water- permeable conveyor an aqueous slurry whose solids content comprises by weight vitreous wool-form material 20-40%, organic web-forming fibres 5-15%, ball clay 5-20%, nitrile rubber 10-20%, and inorganic non- fibrous filler 5-50%, and compressing and drying the layer of dewatered slurry.

Description

SPECIFICATION Latex-bound paper This invention relates to iatex-bound paper, and provides non-asbestos alternatives to latex-bound asbestos papers.

Latex-bound papers based on asbestos fibres are employed in the manufacture of gaskets and seals for use in motor vehicles, where they must be resistant to water, anti-freeze, oil and petrol and withstand fairly high temperatures, e.g. 1 500 C. They are also used in the chemical industry in making seals resistant to chemical attack. They are commonly made in the form of flexible sheet of thickness 0.1-1.5 mm on conventional paper-making machines such as the Fourdrinier. In the process an aqueous slurry of the ingredients which are to compose the product is progressively dewatered as a layer on a water-permeable conveyor (usually of wire mesh), the dewatered layer being subsequently compressed and dried.

According to the invention, non-asbestos paper comprises vitreous fibres derived from wool-form material, organic web-forming fibres, unfired ball clay and water-insoluble non-fibrous particulate inorganic filler, the whole being bound together by a cured nitrile rubber; said paper being made by dewatering as a layer on a water-permeable conveyor an aqueous slurry whose solids content comprises by weight: vitreous wool-form material 2040% organic web-forming fibre 515% ball clay 520% nitrile rubber 1020% inorganic non-fibrous filler 550% and compressing and drying the layer of dewatered slurry.

The vitreous wool-form fibre employed is preferably glass wool, mineral wool or ceramic fibre wool. If glass wool is used it is preferably employed in a form which has been treated with a silane coupling agent (e.g. gamma-aminopropyltriethoxysilane).

The function of the organic web-forming fibres is primarily to enable the paper to be formed on conventional paper-making machinery, but additionally those fibres impart strength to the total matrix of the finished paper, just as the vitreous fibres derived from wool-form material (the primary reinforcement) do. The organic web-forming fibres are preferably cellulose fibres, but may alternatively be polyethylene or polypropylene fibres of the kind commercially available under the name PULPEX.

The function of the ball clay is to impart handlability to the paper sheet during manufacture. To improve the drainage properties of the ball-clay-containing slurry, it is preferable to include a small proportion of bentonite (up to about 5% by weight of total solids) in the slurry.

The water-insoluble non-fibrous particulate inorganic filler may be of the kind conventionally used in paper manufacture, for example calcium carbonate, talc, calcium sulphate, kaolin, titanium dioxide, magnesium silicate, or barytes (barium sulphate). The use of barytes, which both densifies and improves the oil resistance of the paper, is particularly preferred.

The nitrile rubber, which bonds all the fibrous and non-fibrous particles of the paper together, is introduced during manufacture as a latex, together with a vulcanising (curing) agent of the usual kind.

The paper may contain small amounts (e.g. 0.52.5% by weight) of fibres other than the vitreous fibres derived from wool-form material and the web-forming fibres. Such other fibres may for instance be low modulus carbon fibres or water-dispersible E-glass fibres. Such fibres improve green strength of the paper during manufacture; additionally the low modulus carbon fibres impart lubricity to the finished paper. ("Low modulus" here means a Young's modulus in tension below 1 25GPa.) A melamine-formaldehyde resin, suitably at about 1% by weight, can be included in the slurry that is dewatered, in order to promote bonding between the various fibres and the nitrile rubber.A small quantity (0.0020.01% by dry weight of total solids in the slurry) of a flocculating agent of the kind (e.g. a polyacrylamide polyelectrolyte) ordinarily used in paper making can be included in order to facilitate sheet formation and subsequent dewatering. The invention is further illustrated by the following Example.

EXAMPLE A. Preparation of Stock (i) Lapponia pulp (bleached softwood sulphate pulp) in sheet form was made into an aqueous slurry of solids content about 3% by weight and treated in a disc refiner until its freeness reached the desired value (measured in degrees Schopper Riegler, OSR).

ii The other ingredients for incorporation in the slurry to be dewatered were added to enough water in a beater to bring the total solids content of the mix to about 5% by weight. The order df addition of the materials to the beater was: a. Wood pulp at desired freeness with 1 82 litres of water at 40-450C.

b. Ball clay (passing sieve of aperture 5cm), and bentonite and barytes (both passing sieve of aperture 0.1 5mm).

c. Mineral wool (fibre length 0.25--5mm; and free from 'shot' i.e. granular vitreous material); and E-glass fibre (borosilicate glass containing less than 1% of alkali calculated as Na2O; 12mm fibre length) or carbon fibre (modulus in tension, 25 GPa; fibre length 12mm).

d. Papermakers' alum to reduce pH to 4.

e. Melamine-formaldehyde resin ('MF resin') f. Sodium hydroxide to raise pH to 7-8.

g. Conventional vulcanizing agent dispersion (active ingredients sulphur, zinc oxide and zinc dithiocarbamate) diluted with an equal volume of water.

h. Conventional wax emulsion (function:to improve water resistance of the finished paper) diluted with an equal volume of water.

i. Conventional nitrile rubber latex (aqueous acrylonitrile-butadiene copolymer; butadiene content of copolymer, 55%; particle size 0.1 cm; 40% solids content) diluted with 10 times its volume of water.

j. Alum to reduce pH to 4.5.

NOTE: Where the wood pulp employed was of high OSR, the pulp was added after the final alum addition.

iii The slurry resulting from (ii) was diluted to a solids content of 13% by weight, and flocculating agent was added to it immediately before passage to the paper making machine.

B. Preparation of paper The stocks (slurries) prepared as in A. above from various formulations as set out in tables 1-3 following were made into flexible sheet material in an entirely conventional way on a Fourdrinier flat wire paper machine, such as is described in Chapters 10 and 11 of "Paper and Board Manufacture" by Julius Grant, James H. Young, and Barry G. Watson (Publishers; Technical Division, The British Paper and Board Industry Federation, London, 1978). The slurry is progressively dewatered as it travels on the water permeable conveyor of the machine, and the dewatered material is consolidated by pressing between rollers, and then dried to low moisture content (suitably 2% by weight).

The properties of the paper produced are shown in the Tables.

The cold calendering referred to in Table 1 was carried out as follows: Paper was passed at room temperature between two smooth-faced steel rolls the gap between which was adjustable to control the density of the paper. Two such passes were made on the papers whose properties are reported in Table 1. The hot calendering referred to in Table 1 was carried out as for cold calendering but with the difference that the steel rolls were heated to about a temperature of 1 450C. Again, two such passes were made on the papers whose properties are reported in Table 1. The purpose of hot calendering as opposed to cold calendering on latex-bound papers is to cause some flow of the latex, thus producing greater consolidation and a high density.

The papers all passed a standard test of flexibility. To pass this, a specimen of the paper (50mm x 230mm, with the 230mm side parallel to the grain) should show no evidence of breaking when bent through 1800 around a mandrel of 50mm diameter, with use of just enough force to keep the specimen in contact with the mandrel.

TABLE 1

Containing Glass Fibre Containing Carbon Fibre Dr Wt % Dry Wt % After After After SLURRY Cold Cold . Hot CONSTITUENTS Initial Ca lendering Initial Calendering Ca lendering Mineral Wool 33 33 Lapponia wood pulp 10 10 (Freeness #SR) (20) (20) Ball clay 11.5 10 Bentonite 3 3 Barytes 20 20 MF resin 1 1 Vulcanising dispersion (9% by wt of latex) (9% by weight of latex) Wax emulsion 1 Nitrile rubber latex 19.5 20 'E' glass fibre 1 Carbon Fibre - 2 TEST RESULTS TEST 'RESULTS 1. Thickness (mm) 0.56 0.51 0.89 0.55 0.37 2. Density(Kg/m3) 611 724 663 773 1150 3. Tensile Strength (MPa) a. Machine direction 5.5 5.1 4.0 4.6 4.8 b. Cross direction 2.8 2.8 2.2 3.4 3.9 4. Water Absorption (%) 27 25 27 22 20 5. Fuel Absorption (%) 80 50 79 67 37 TABLE 2

DRY WT % SLURRY CONSTITUENTS (a) (b) Mineral Wool 33 33 Laopponia wood pulp 10 10 (Freeness #SR) (65) (65) Ball clay 12 12 Bentonite 3 3 Barytes 20 19 MF resin 1 1 Vulcanising dispersion (9% by wt of latex) Wax emulsion 1 1 Nitrile rubber latex 19 19 'E' Glass fibre 1 Carbon Fibre - 2 TEST RESULTS 1. Thickness (mm) 0.5 0.5 2. Density (Kg/m3) 640 621 3. Tensile Strength (Machine direction) (MPa) 4.5 4A TABLE 3

DRY WT % SLURRY CONSTITUENTS (a) (b) (c) Mineral Wool 33 33 33 Lapponia wood pulp (i) Freeness 1805R 10 - - (ii)Preeness650SR) - 10 - (iii) Freeness 95'SR) - - 10 Ball clay 12 12 12 Bentonite 3 3 3 Barytes 20 20 20 MF resin 1 1 1 Vulcanising dispersion (9% by wt of latex) Wax emulsion 1 1 1 Nitrile rubber latex 19 19 19 Glass fibre 1 1 1 TEST RESULTS 1. Thickness (mm) 0.5 0.5 0.5 2. Density (kg/m3) 640 621 652 3. Tensile Strength (Machine direction) (MPa) 4.5 4.4 6.5

CLAIMS 1. Non-asbestos paper comprising vitreous fibres derived from wool-form material, organic webforming fibres, unfired ball clay and water-insoluble non-fibrous particulate inorganic filler, the whole being bound together by a cured nitrile rubber; said paper being made by dewatering as a layer on a water-permeable conveyor an aqueous slurry whose solids content comprises by weight vitreous wool-form material 2040% organic web-forming fibres 5-1 5% ball clay 5-20% nitrile rubber 10-20% inorganic non-fibrous filler 5-50% and compressing and drying the layer of dewatered slurry.

2. Non-asbestos paper according to claim 1, in which said vitreous wool-form material is mineral wool.

3. Non-asbestos paper according to claim 1 ,in which said vitreous wool-form material is glass wood.

4. Non-asbestos paper according to any one of claims 1 to 3, in which said organic web-forming fibres are cellulose fibres.

5. Non-asbestos paper according to any one of claims 1 to 4, in which the inorganic non-fibrous filler is barytes.

6. Non-asbestos paper according to any one of claims 1 to 5, which additionally contains carbon fibre of modulus below 125GPa or water-dispersible E glass fibres, said additional fibres being present

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. TABLE 3 DRY WT % SLURRY CONSTITUENTS (a) (b) (c) Mineral Wool 33 33 33 Lapponia wood pulp (i) Freeness 1805R 10 - - (ii)Preeness650SR) - 10 - (iii) Freeness 95'SR) - - 10 Ball clay 12 12 12 Bentonite 3 3 3 Barytes 20 20 20 MF resin 1 1 1 Vulcanising dispersion (9% by wt of latex) Wax emulsion 1 1 1 Nitrile rubber latex 19 19 19 Glass fibre 1 1 1 TEST RESULTS 1. Thickness (mm) 0.5 0.5 0.5 2. Density (kg/m3) 640 621 652 3. Tensile Strength (Machine direction) (MPa) 4.5 4.4 6.5 CLAIMS

1. Non-asbestos paper comprising vitreous fibres derived from wool-form material, organic webforming fibres, unfired ball clay and water-insoluble non-fibrous particulate inorganic filler, the whole being bound together by a cured nitrile rubber; said paper being made by dewatering as a layer on a water-permeable conveyor an aqueous slurry whose solids content comprises by weight vitreous wool-form material 2040% organic web-forming fibres 5-1 5% ball clay 5-20% nitrile rubber 10-20% inorganic non-fibrous filler 5-50% and compressing and drying the layer of dewatered slurry.

6. Non-asbestos paper according to any one of claims 1 to 5, which additionally contains carbon fibre of modulus below 125GPa or water-dispersible E glass fibres, said additional fibres being present in an amount of 0.5-2.5% by weight

7. Non-asbestos paper according to any preceding claim, made by dewatering a slurry which additionally contains bentonite up to 5% by weight of slurry solids.