GB2262543A - Calcium silicate board formed by paper-making technique - Google Patents

Abstract

In a calcium silicate papermade board, inorganic fines (calcite, talc, gypsum, kaolin flyash, wollastonite, mica, vermiculite, magnesium hydroxide, aluminium hydroxide, allophane mordenite, magnesium carbonate or the like) are dispersed in a matrix and fibers, the fines comprising 10 to 33% by weight so that the value of the total strain in a bending test is not smaller than 4.0 x 10-3 and the ratio of the plastic strain to the total strain is not smaller than 50%. The board can be easily bent and easily fixed with nails. The fibres may be pulp or synthetic, eg. polypropylene.

Description

CALCIUM SILICATE BOARD FORMED BY PAPER-MAKING TECHNIQUE This invention relates to calcium silicate board formed by paper-making technique. More especially the invention relates to such a board attachable to a curved surface.

Calcium silicate boards, formed by paper-making technique, nave been widely used as non-combustible building materials for interior end exterior decoration.

Such boards have excellent workability because they are lightweight and easy to cut. The boards are highly water and heat resistance and very durable.

However, application to a curved wall or ceiling is very difficult. Application is difficult because the board is vry rigid and a large bending force is required. If the board is bent its elasticity may cause it to spring bacK to the original shape. Alternatively the force applied may break the board . Accordingly calcium silicate boards are seldom fixed to curved surfaces.

Conventionally gypsum boards, formed by papermaking techniue, have been used for attachement on curved surfaces, gypsum boards have however parer workability on account of their high weight. This weight is not only a physical burden to the user but may also limit range of use.

An object of the invention is to provide a calcium silicate board, formed by paper-making technique, for application to a curved surface.

According to the invention there is provided a calcium silicate board formed by paper-making technique, comprising 10 to 33 wt% of inorganic fine powder and 4 to 9 wt% of fibrous material.

According to the invention, the inorganic fine powder have a surface area of no less than 3,000cm2/g.

According to the present invention, there is provided a method for making a calcium silicate board, which comprises: a) preparing a slurry of a mixture of: i silicic acid material ii lime material iii 10 to 33 wt% of inorganic fine powder with water and iv 4 to 12 wt% fibrous material, b) forming the slurry into a raw-board by means of a paper-making technique, c) steaming the raw board, and d) drying the raw board.

The inorganic fine powder may be calcite or talc. Tfle fine powder may comprise a material undergoing endothermic dehydration on heating such as magnesium hydroxide, or endothermic decarbonation on heating such as magnesium carbonate or calcium carbonate.

The inorganic fine powder consists of talc or a mixture of talc and magnesium hydroxide . The fibrous material comprises organic synthetic fibers.

The total strain of the board determined in a bending test as hereinbefore described is not smaller than 4x1O3 and the ratio of plastic strain to total strain determined as hereinbefore described is not smaller than 50%. It is preferable that the total strain is in a range of from 4.0x10-3 to 15x10-3.

The strain value is determined by a bending test.

The test is a three-point bending test to be performed on a sample having moisture content of 4 t 1 8 under the condition that a span is set to 180 mm (the papermaking direction is arranged to be in the direction of spans and the load speed is set to 2 mm/min. In this test, the total strain means strain at the maximum load i=ediatelv before broken, and the plastic strain means the strain generated in a range of plastic deformation beyond a range of elastic deformation, (that is, the total strain - the elastic strain + the plastic strain; see Fig. 1).

Further, the value of the strain is that is obtained through calculation from the quantity A L of bending strain in the bending test in accordance with the following expression.

Strain = ST . LJA L2 (where T represents the thickness of a test piece and L represents a span of the bending test).

In an ordinary rigid calcium silicate papermade board, the total strain in the foregoing bending test is about 3 x 10-3 to 4 x 10-3 and the plastic strain ratio in the total strain is about 408.

A board in accordance with the invention may comparatively readily be bent and has little tendency to revert to the original state.

Although we do not wish to be bound by this theory it is thought that in the paper making process the inorganic fines calcium silicate and fibers form by filtration thin laminated sheets. The fine powders form discontinuous phases in a crystalline calcium silicate matrix with the fine powders slightly concentrated at the boundary surface. The crystalline calcium silicate matrix can therefore form a three dlmensional meshed structure. When the board is bent micro-cracks are readily generated in tha matrix but do not propagate to the whole of the board. As a result when the board is bent the elastic limit is easily exceeded and plastic: deformation occurs.

However if too many microcracks are generated the strength of the board is dramatically reduced and although it is easily bent it has little practical use.

Fibers are thought, although we do not wish to be bound by this theory, to prevent the microcracks from growing into macrocracks of the board per se and hence to widen the range of plastic deformation.

Accordingly if there are too few fibers the reinforcing effect is too small to prevent cracks from spreading. If there are too many fibers the product density is reduced and the product has insufficient strength.

The precise nature of the powders and fibers determines the intensity cf these effects. It is however a matter of routine experimentation for those skilled in the art to devise suitable compositions. Preferably the quantities and kinds of powders and fibers will be selected so that the total strain as determined by the bending test is not smaller than 4.0 x 1 10-3 and the plastic strain ratio is not smaller than 508.

Where the board is used as a building material it is preferable that the board has a bending strength of at least lOOkgf/cm2.

Furthermore the maximum total strain preferably does not exceed about 15 x lO 3 so that the board is neither broken nor clear hammer marks formed during nailing.

A board in accordance with the invention containing magnesium hydroxide, aluminum hydroxide, allophane (1-2 SiO2 ' A1203 5H2O) mordenite (Na2K2CaAl2Si10 024 . 7H20) or magnesium carbonate is not only easily bent but has highly improved fire resistant properties. While we do not wish to be bound by theory we surmise that when the board is heated the contained magnesium hydroxide or other materials undergo an endothermic dehydration reaction which slows the rate of temperature rise.

The board of the invention can be produced by adding the powders and fibers to the other components such as a silicic acid precursor, a lime precursor or selfhardening calcium silicate slurry. The mixture can then be papermade by ordinary papermaking processes and the composition formed into a lamination, The lamination is heat treated in an autoclave to produce a hardened moist calcium silicate material.

The powders should be inert or have low activity and hence function merely as fillers without taking part in any reaction resulting in formation of the calcium silicate. Preferred powders include calcite or other calcium carbonate, talc, gypsum, kaolin flyash, wollastonitew mica and vermiculite. Other preferred powders include magnesium hydroxide, aluminum hydroxide, allophane mordenite and magnesium carbonate which as hereinbefore described may enhance the fire resistant properties of the board. It is preferred that the fine powders having a surface area not less than 3000 cm2/g are used.

Preferred fibers are pulp which improve the papermaking of the mixture. Orgiinic synthetic fibers such as polypropylene may be used instead of or together with pulp.

An excellent product can be obtained using 15 to 25 wt% calcite powder and 6 to 12 wt pulp.

To facilitate production of the board of the invention materials such as fibrous wol lastonite, cementitons material and molding adjuvants such as floculants may be added.

The boards of the invention may be cut and nailed in a similar manner to ordinary calcium silicate boards.

if the water content oS the board is increased, for example by sprinkling with water prior to nailing, the total strain further increases allowing attachment to surfaces wltn smaller radii of curvature.

Embodiments of the invention will be illustrated by reference to the following non-limiting examples.

Ex les 1 - 3 and Comparative Examples 1 - 4 A papermade board having a thickness of 6 mm was produced from the raw materials shown in Table 1. Pulp in the mixture raw materials was subjected to beating so that the Canadian freeness was 350ml. The other powder raw materials were sufficiently dispersed in a suitable quantity of water in an agitation mixing cell. After the thus obtained pulp dispersed composition and powder dispersed composition were mixed with each other, the water content in the mixture was adjusted so that the weight of the water was 20 times that of the powder, and then a board was formed by means of a cylinder papermaking machine.The thus obtained raw board was cured with steam heat at steam pressure of 12 kg/cm2 for 10 hours and dried to obtain a papermade board The obtained board was subjected to density measurement, a bending test, a non-combustibI-lity test, a workability test and a nailing test.

Density Measurement The density was measured by weighing the sample and dividing by the bulk volume of the sample.

Bending Test The bending test hereinbetore described was used.

Noncombustibilits Test Three test pieces are used. Each of the longitudinal and lateral sizes of the test pieces is selected to be within a range cf from 38 mm to 40mm both inclusive, the thickness is selected to be within a range of from 47 mm to 53 mm both inclusive, and the volume is selected to be within a range of from 75 cm3 to 85 cm3 both inclusive. Lf it is necessary to laminate sheets together to obtain the required thickness. The lamination is tightly bound with a thin steel wire without application of any pressure to the lamination so that the lamination can be horizontally inserted into a test piece holder.

The test pieces are cured at 60 = 50C for 24 hours in a dryer and cooled to a room temperature in a desiccator.

The temperature in a furnace is measured with a thermocouple disposed at a center of the height of the furnace wall with a heat contact ot the thermocouple is separated by 10 mm from the inner surface of the furnace wall, Another thermocouple is inserted into a 2 mm diameter hole formed in the central portion of the test piece to thereby measure the temperature of the test piece. The heating furnacer issued one in which the temperature can be stably maintained at 750 + 100C for 10 minutes or more. In the test, the test pieces are inserted into the heating furnace and the temperature is measured with two thermocouples for 20 minutes.

In the test carried out on each of the three test pieces, it is fudged that the test piece comes up to the standard when both the following conditions are satisfied: (1) the temperature measured with two thermocouples after insertion of the test piece becomes not higher by 500C or more than the adjusted temperature of the furnace; and (2) no flame is continuously observed for 10 seconds or more. Samples which pass are assigned value O. Samples which fail are assigned value X.

Nailing test An N38 nail is driven into a corner of board 10 mm from each of the two edges defining it. The board is inspected for cracks and given the following symbol: no cracks are generated.

although small cracks are sometimes generated in part of some boards, there is no problem if nailing is carefully carried out.

even when nailing is carefully carried out, cracks are generated in some boards.

Workability test Frames having curved surfaces with radii of curvature 100 mm in a range of from 300 mm to 2000 mm by 100 mm steps are prepared. A minimum radius of curvature (unit: mm) when a sample papermade board having a moisture content adjusted to be 4 = I is bent without generating any cracks through the board is urged by hands against the molding frame is determined. It is indicated as "workability". . The lower the workability number, the more easily the board can be bent.

The results are shown in Table l.

Table 1 Example of the Invention (l) (2) (3) crushed pieces of calcite 15 20 30 silica 22 19 14 diatomaceous earth 10 10 10 slaked lime 33 31 26 cement 5 5 5 wollastonite 10 10 10 pulp 5 5 6 temperature rise in furnace 450C 440C 450C center temperature rise 230C 90 -170C noncombustibility test density (g/cm3) 0.85 0.87 0.90 bending strength kgf/cm) 120 115 110 total strain 0.0042 0.0048 0.0062 plastic strain ratio 53% 55% 63% workability 900R 800R nailing test Comparative Example (1) (2) (3) (4) crushed pieces of calcite 8 35 20 20 silica 25 11 20 17 diatomaceous earth 10 10 10 10 slaked lime 37 24 32 29 cement 5 5 5 5 wollastonite 10 10 10 10 pulp 7 7 7 10 temperature rise in furnace 500C 450C 400C 600C center temperature rise 85 C 2000 -50C C 1230C noncombustibility x O O x density 0.84 0.80 0.93 0.82 bending strength (kgf/cm) 145 98 115 120 total strain 0.018 0.0019 plastic strain ratio 91 28 workability 300R 2000R nailing test x x As described above, although the calcium silicate papermade board according to the present invention can be bent to an extent that cannot be considered in the conventional calcium silicate papermade board so that it can be easily fixed on a curved surface with nails. The features such as the light weight property, the water resistance, the incombustibility, etc., of the calcium silicate papermade board are little lost. Therefore, curved-surface finishing in a building can be easily performed by using the calcium silicate quality papermade boards according to the present invention in comparison with the conventional papermade boards.

Further, in the case where the papermade board is made to contain, as the inorganic fine grains, a material such as magnesium hydroxide or the like which causes an endothermic reaction so as to be thermally decomposed, the papermade board is not only superior in workability onto a curved surface but remarkably improved in incombustibility.

Fig. 1 is a graph showing a stress-strain curve of the calcium silicate quality papermade board in the bending test.

Claims (17)

CLAIMS:

1. A calcium silicate board formed by paper-making technique, comprising 10 to 33 wt of inorganic fine powder and 4 to 9 wt% of fibrous material.

2. A board as claimed in claim 1, wherein the inorganic fine powder has a surface area of no less than 3,000cm2/g.

3. A board as claimed in claim 1 or claim 2, wherein the inorganic fine powder is calcite.

4, A board as clamped in any one of the preceding claims, wherein the inorganic fine powder is talc.

5. A board as claimed in any one of the preceding claims, wherein the fine powder comprises a material undergoing endothermic dehydration on heating such as magnesium hydroxide, or endothermic decarbonation on heating such as magnesium carbonate or calcium carbonate.

6. A board as claimed in claim 1, wherein the inorganic fine powder consists of talc or a mixture of talc and magnesium hydroxide.

7. A board as claimed in any one of the preceding claims, wherein the fibrous material comprises organic synthetic fibers.

8. A board as claimed in any one of the preceding claims, wherein the fibrous material comprises pulp.

9, A board as claimed in any one of the preceding claims, wherein the total strain of the board determined in a bending test as hereinbefore described is not smaller than 4x10-3 and the ratio of plastic strain to total strain determined as hereinbefore described is not smaller than 50%.

10. A board as claimed in claim 9, wherein the total strain is in a range of from 4.0x10-3 to 15x10-3.

11. A calcium silicate substantially as described herein by reference to any one of Samples I to 3.

12. A method for making a calcium silicate board, which comprises: a) preparing a slurry of a mixture of: i silicic acid material ii lime material iii 10 to 33 wt% of inorganic fine powder with water and iv 4 to 12 wt% fibrous material, b) forming the slurry into a raw-board by means of a paper-making technique, c) steaming the raw board, and d) drying the raw board.

13. A method as claimed in claim 12, wherein the inorganic fine powder comprises calcite or talc.

14. A method as claimed in claim 12, wherein the inorganic fine powder comprises a material which undergoes endothermic dehydration on heating such as magnesium hydroxide, or endothermic decarbonation on heating such as magnesium carbonate or calcium carbonate.

15. A math as claimed in any one of claims 12 to 14, wherein the fibrous material comprises organic synthetic fibers.

16. A method as claimed in any one of claims 12 to 15, wherein the fibrous material comprises pulp.

17. A method of making calcium silicate board substantially as described herein by reterence to any one of Examples 1 to 3.