Fibrous sheet materials

A board product containing glassy inorganic fibre such as mineral wool, in a matrix of a plastic clay such as ball clay. The amounts of clay and inorganic fibre are in the respective ranges 29 to 80 percent by weight and 15 to 55 percent by weight of the product, and its density is at least 500 kg/m.sup.3. The board can replace asbestos millboard and has the advantage of being asbestos-free. It can be made by the standard paper and board-making techniques, when preferred ingredients are pulp fibres e.g. cellulose pulp, and a complementary binder, particularly hydrolyzable starch, the latter enabling the product to be re-mouldable upon moistening with water.

This invention relates to fibrous sheet materials, and in particular to 
sheet materials such as board based on inorganic fibres. 
Conventional asbestos-based millboards consist of 50 to 97% of asbestos 
fibre together with various fillers and binders. They have excellent 
properties owing to the high strength and temperature resistance of 
asbestos fibres and a density of about 1000 kg/m.sup.3. They can be made 
by paper or board making processes in which an aqueous suspension of the 
ingredients is applied to a sieve or filter medium through which the water 
drains to leave a moist tissue or felt. These felts are usually pressed or 
rolled into sheets, either individually or plied together to give a 
laminated structure. Non-flat shapes, which could be difficult to make by 
moulding flat sheets, can be produced directly using foraminous formers of 
the desired shape. 
It is desirable to replace the asbestos fibres in these materials, but 
direct replacement of the fibres is very difficult since asbestos fibres 
can be processed like textile fibres and yet have the temperature 
resistance, non-flammability and strength of mineral fibres. 
The properties demanded from conventional millboards, and which must be 
matched by any replacement, are: 
(1) Good high temperature properties i.e. low organic content to ensure 
non-combustibility and good retention of properties after exposure to 
elevated temperatures. 
(2) Adequate strength and flexibility (tensile and flexural strengths in 
excess of 2 MPa and 4 MPa respectively are usually required). 
(3) A sufficiently low density (e.g. less than 1200 Kg/m.sup.3) to provide 
adequate insulation properties. 
(4) Ideally the ability to soften and reshape the product by moistening. 
(5) A reasonably low price. 
(6) The ability to be rapidly formed into sheets--preferably by a 
continuous process. Ideally this should be possible using existing 
asbestos processing equipment. 
(7) The ability to be punched into various shapes with clean-cut edges and 
without delamination. 
We have now found that by judicious choice of materials and their amounts 
replacement products can be made with very promising properties. 
Thus the present invention provides a board product comprising a matrix of 
a plastic clay reinforced with a glassy inorganic fibre the amounts of 
clay and inorganic fibre being in the respective ranges 29 to 80 percent 
by wt and 15 to 55 percent by weight and the density of the product being 
at least 500 kg/m.sup.3. 
Preferably the board product contains also a complementary binder with 
minimal combustibility. Ball clay is a well-known high-plasticity clay 
which is widely used in the ceramics industry, and is usually fired to 
produce the final product. 
We have found that the plastic clay, such as ball clay, used in this 
invention has several advantages over other types of clay, such as Kaolin 
or china clay, in that it gives better dry strength, improved wet 
mouldability, better interlaminar adhesion during manufacture and better 
interlaminar adhesion when dry. Clearly, for the board product to be 
remouldable, ball clay must not be fired during preparation of the board. 
The preferred glassy inorganic fibres are glassy wools including so called 
glass wool, mineral wool and ceramic fibre. Of these materials mineral 
wool offers the most attractive combination of temperature resistance and 
low cost. As produced, however, mineral wools contain too much non-fibrous 
shot to give a satisfactory board product, and a substantial part of the 
shot must be removed either before or during board production. The glass 
or mineral wool may be given a silane pre-treatment to promote adhesion to 
the binder, and preferably is treated with a dispersing agent, e.g. a 
surfactant. 
The length of the inorganic fibres is usually reduced during the 
manufacture of the board and it is difficult to lay down specific limits 
for the length required. The fibre must be short enough to be initially 
dispersed and to give an even distribution in the product and to avoid 
balling-up of the fibre. On the other hand the fibre should be long enough 
to provide adequate reinforcement in the board. 
These inorganic fibres do not behave like textiles in the same way as 
asbestos fibres. It is preferable to include also an open organic fibre, 
eg in the form of a pulp, to give wet and dry strength, flexibility and 
the ability to use conventional paper or board making machinery. Cellulose 
pulp is preferred, wood pulp with long, fine fibres being the best 
although other pulps can give satisfactory results at less cost. 
The function of the organic fibres is important, in that during board 
making the pulp fibres form a web on a sieve to carry the other materials 
out of slurry, and after the board is formed they give green strength to 
the material before the binder has set. 
The inorganic fibres are a major constituent of the material in terms of 
percentage by weight, 18 to 52 percent by weight preferably being used 
(smaller percentages being used when the fibres are longer), more 
preferably 23 to 42 percent by weight. The organic fibres are to be kept 
to minimum proportions owing to their combustibility and 3 to 7 percent of 
pulp fibres will normally be sufficient. Cellulose fibre is preferred as 
the organic fibre because of its superior web-forming properties in the 
wet state and its low combustibility in comparison with synthetic pulp 
fibres such as polyolefines (e.g. polypropylene, polyethylene). 
The ball clay or other plastic clay is included in the board product to 
keep down cost, to contribute to various properties of the board including 
temperature resistance and mechanical strength both during and after 
manufacture. The ball clay also provides a cohesive matrix in the material 
owing to its plastic nature. 
The ball clay will preferably constitute 34 to 67 percent by weight of the 
board product, depending upon the other binder used, and more preferably 
will constitute 42 to 62 percent by weight of the board product: more clay 
being employed when greater length has permitted reduction in the 
inorganic fibre content. 
Reinforcing fillers such as fibrous wollastonite, mica and waste calcium 
silicate insulation can be included in amounts up to a total of less than 
10% by weight. 
As complementary binder one or more of several types of material may be 
employed. Those used in colloidal or latex form, rather than solution, are 
preferred and typical examples are hydrolysed starch, or finely divided 
clays such as bentonite or montmorillonite. Binders used in the forms of 
true solutions such as soluble cellulose derivatives and sodium silicate 
are not preferred because they are only partly retained in the materials 
in conventional wet processing. The preferred binders are based on starch, 
more preferably Farina starch, which has been found to be most effective. 
Bentonite clay provides a binding effect and also assists in controlling 
the drainage rate of water through a sieve when the layer is being laid 
down on a sieve or filter medium during board production. It may be used 
in an amount up to 5 percent by weight. 
Preferably the binder includes hydrolysable Farina starch in an amount of 
1.5 to 5.0 percent by weight of the board product, since starch gives dry 
strength but softens when wet to facilitate wet mouldability. 
Dry-strength resins of the type used in the paper industry can be used to 
improve the strength of the material although not as sole binder, and only 
in minor quantities eg. up to 0.5% by weight. 
In order to minimize the flammability introduced by the organic 
constituents it may be useful to incorporate small quantities of flame 
retardant. These should be selected to suit the particular organic 
materials employed but ammonium hydrogen phosphates, boric acid or other 
borates, have been found to be effective. 
The fibrous sheet material may be prepared by the same paper or board 
making processes as are used for asbestos-based boards.

The invention is illustrated by the following Examples. 
EXAMPLES 1 TO 7 
Sample boards were made to seven different formulations. In each case the 
boards were prepared by mixing the ingredients as an aqueous suspension 
(each being added in the order shown except the Silane which was applied 
to the mineral wool as a pre-treatment), applying to a sieve, dewatering, 
pressing at 7 MPa pressure and drying at 120.degree.-130.degree. C. The 
seven formulations are tabulated below in Table I. The (dry) density and 
tensile and flexural strengths of the sample boards were measured and the 
results obtained are also tabulated below in Table I. 
TABLE 1 
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Example 1 2 3 4 5 6 7 
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Mineral wool 
35 -- 35 35 30 30 30 
(short fibre -2mm) 
Mineral wool 
-- 16 -- -- -- -- -- 
(long fibre -8mm) 
Ball clay 53.5 77.3 56.5 56.3 56.5 56.5 58.5 
(Hymod BL2) 
Bentonite 2.5 -- 2.5 2.5 2.5 2.5 2.5 
(Wyoming) 
Refined Lapponia 
6 3 3 3 3 3 2 
wood pulp 
Hydrolysed 3 2.5 3 3 3 3 2 
Farina starch 
Mica flake -- -- -- -- 5 -- 5 
Exfoliated -- -- -- -- -- 5 -- 
vermiculite 
Retention aid 
-- 0.05 -- 0.05 -- -- -- 
(Percol 224) 
Dry strength 
-- 0.2 -- 0.2 -- -- -- 
resin 
Boric acid -- 1 -- -- -- -- -- 
Properties 
Density (Kg/m.sup.3) 
1100 1175 815 740 950 843 681 
Tensile Strength 
(MPa) 11.2 4.4 4.2 4.1 7.1 6.7 5.3 
Flexural Strength 
(MPa) -- -- -- 4.5 12 11 3 
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"Percol" is the Registered Trade Mark of Allied Colloids Limited. 
EXAMPLES 8 TO 11 
To investigate the influence of starch content on the mechanical strength 
of the material four different boards were made using different furnishes 
on a pilot-scale Hatscheck board-making machine. In the latter the furnish 
is slurried in water and fed to a vat in which a drum having a surface of 
a fine sieve material such as wire mesh is partially immersed. The drum 
ends are provided with face seals against the sides of the vat, and water 
is withdrawn from the interior of the drum through the drum end so that 
water flows inwardly into the drum depositing a layer of the solids from 
the slurry on the mesh sieve. This is carried out of the vat by rotation 
of the drum and deposited from the drum onto a felt which conveys the 
layer and on which the layer is dewatered. From the felt the layer is 
passed onto a drum upon which it is wound until a predetermined thickness 
has built up. Then the material on the drum is slit and removed as a 
sheet. 
The table II below gives details of the compositions from which the boards 
are made, and their density and tensile strength. Satisfactory boards were 
obtained at all the starch concentrations illustrated (2, 3, 4 and 5 
percent). There is a need to limit the amount of starch needed in order to 
keep down the content of potentially inflammable organic material in the 
board, but a minimum amount is needed to achieve the necessary binder 
function. The preferred content is 1.5% to 5.0% by weight of the board as 
indicated previously. 
Table II 
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Example No. 8 9 10 11 
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Constituent % Dry Wt. 
Wood Pulp 5.0 5.0 5.0 5.0 
Mica 5.0 5.0 5.0 5.0 
Bentonite 2.5 2.5 2.5 2.5 
Ball Clay 55.5 54.5 53.5 52.5 
Swedish Rockwool 
30.0 30.0 30.0 30.0 
Farina Starch 2.0 3.0 4.0 5.0 
"Percol" E24 
(Retention Aid) 
0.005 0.005 0.005 0.005 
Properties 
Density Kg/m hu 3 
995 740 993 985 
Tensile Strength MPa 
4.4 5.4 5.1 6.4 
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EXAMPLES 12 TO 18 
To illustrate the influence of mineral wool content on the mechanical 
strength of boards made on a pilot-scale Hatscheck machine a series of 
boards were made to seven different furnishes. The compositions of the 
seven different furnishes and the density and tensile strength of the 
boards made from them are given in Table III below. As can be seen, the 
most successful compositions were Examples 14, 15 and 16 in the middle of 
the range of compositions tested. Example 12 was a product which could be 
made, but the composition was rather too sticky during manufacture and was 
not preferred. Example 18 gave a product whose strength was rather lower 
than desirable and likewise was not preferred. 
TABLE III 
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Example No. 
12 13 14 15 16 17 18 
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Constituent 
% Dry Wt. 
Wood Pulp 5.0 5.0 5.0 5.0 5.0 5.0 5.0 
Mica 5.0 5.0 5.0 5.0 5.0 5.0 5.0 
Bentonite 2.5 2.5 2.5 2.5 2.5 2.5 2.5 
Ball Clay 69.5 
64.5 
59.5 
49.5 
44.5 
34.5 
29.5 
Swedish Rockwool 
150.0 
20.0 
25.0 
35.0 
40.0 
50.0 
55.0 
Farina Starch 
3.0 3.0 3.0 3.0 3.0 3.0 3.0 
"Percol" E24 
(Retention Aid) 
0.005 
0.005 
0.005 
0.005 
0.005 
0.005 
0.005 
Properties -Density kg/m.sup.3 
900 1010 
1140 
1130 
1080 
970 910 
Tensile Strength MPa 
5.0 4.5 6.5 6.8 5.6 4.8 3.5 
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