GB2041031A - Board - Google Patents

Abstract

A process for producing a fibre- reinforced product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, includes the step of forming the aqueous slurry from water, an inorganic binder and from 1 DIVIDED 2 to 20% by weight of reinforcing fibres 2 (referred to the finished product) together with a minor proportion of auxiliary non- asbestos fibres having a Canadian Standard Freeness in the range 20 to 300 DEG , the reinforcing fibres comprising a non-vitreous non- asbestos reinforcing staple fibres, in particular carbon fibres.

Description

SPECIFICATION Manufacture of Fibre Reinforced Materials This invention relates to the manufacture of fibrous artefacts such as boards, sheets or pipes by processes including the step of forming a layer on the surface of a rotary sieve from an aqueous slurry.

In our U.K. Patent Specification No. 1,521,482 we describe a process in which we use a slurry including vitreous fibre, auxiliary fibre of Canadian Standard Freeness (CSF) less than 3000 and cement, optionally with modifying agents, fillers and the like, which serve to control the density of the final product. In our process, the fibres (e.g. glass and cellulose) and cement are mixed and beaten with a large proportion of water to form a thin slurry, which is then stored while being agitated in a container known as a "stuff chest". This constitutes a reservoir from which supplies of a slurry are taken, diluted with water and fed to one or more vats in each of which a sieve cylinder is rotated.Each of these cylinders picks up the slurry as a continuous, thin wet layer, excess water draining through the meshes of the sieve, and the layer is applied to an endless conveyor belt by which it is carried to a rotating cylinder to which it is transferred and on which it is wound. The coating on the cylinder builds up layer by layer until the required thickness is reached. To make a flat sheet, the layered product on the cylinder (which is then usually known as a forming bowl) is cut axially when it has reached the required thickness. To make pipes, the cylindrical layered product is removed axially from a forming bowl provided with supports which facilitate this operation.

We have now found that the process can be used with advantage to incorporate non-vitreous fibre reinforcements into fibrous artefacts.

Thus according to the present invention, we provide a process for producing a fibre-reinforced product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, the process including the step of forming the aqueous slurry from water, an inorganic binder and from 3 to 20% by weight of reinforcing fibres (referred to the finished product) together with a minor proportion of auxiliary non-asbestos fibres having a Canadian Standard Freeness in the range 20 to 3000, the reinforcing fibres comprising a non-vitreous non-asbestos reinforcing staple fibre.

The expression "Canadian Standard Freeness" (CSF) in this specification refers to the standard sheet forming test as commonly applied through the papermaking industry and wherein, for example, raw cellulose pulp exhibits a CSF of 700-9000 and a very highly opened papermaking cellulose pulp exhibits a CSF of about 3000.

The reinforcing fibres may be for example carbon fibres, particularly the less expensive grades of so called "low modulus" carbon fibres, aromatic polyamide fibres and the like. These fibres may be used in admixture with vitreous fibres such as glass fibre or mineral wool if desired. The term "mineral wool" includes both slag and rock wool. Where carbon fibre is used, the stable length is preferably 25 mm or less, 10 mm being especially preferred. When mineral wool is used in admixture it may be pretreated to reduce its staple length, if necessary, for example by subjecting it to a milling treatment.

The inorganic binder may be a hydraulic binder such as Ordinary Portland (O.F.) cement and in such a case it is preferred that a vitreous fibre, if used be either alkali-resistant or at least treated to reduce its susceptability to alkaline attack. The binder may also include a pulverised fuel ash.

The auxiliary non-asbestos fibre is preferably cellulosic and will usually be in the form of a pulp; if so the process may include a preliminary refining treatment to confer upon the pulp the desired degree of openness equivalent to a Canadian Standard Freeness value in the range 200 to 3000, 1 500 being very suitable in practice. It will be apprnciated that in a conventional papermaking process CSF values of less than 3000 are generally regarded as very low. In contrast, we find that the present process operates well with CSF values of 1 500 or even lower.However, provided that the surface area characteristics of the auxiliary non-asbestos fibre are at least similar to those of asbestos or cellulosic fibre, other materials may be used in the present process such as the synthetic pulps based on fibres of polymers such as polyolefines e.g. polyethylene.

The proportion of organic reinforcing fibre used is dependent upon the degree of noncombustibility which is required. Substantial amounts may be incorporated, e.g. 1 5 to 20 per cent by weight, to give very good reinforcements but combustibility is then substantially increased. Small proportions, e.g. 1 to 1.5 per cent of low modulus carbon fibre, give a useful compromise.

Optionally, the process may also include the step of adding to the slurry density modifying fillers or agents such as perlite, china clay and/or diatomite, so as to bring the density of the finished artefact into the range appropriate for a particular end use.

It is also possible to add free silica-containing materials for the specific purpose of reacting with substantially all of any free lime released when the binder sets. This is particularly relevant to processes using hydraulic cement as the binder and where the binder is caused to set by autoclaving. Free lime would of course tend to degrade any vitreous fibre component of the artefact, if present, if no attempt to minimise its effect was made.

Material stripped from the rotary sieve is naturally in a wet condition and the process will normally include causing the binder to set, for example, by air drying, autoclaving or stoving i.e. heating in an oven to produce the finished product. Optiona!ly, the wet products may be profiled and/or cut or trimmed prior to causing the binder to set. After setting the binder, the boards or sheets may be sanded or otherwise prepared for sale and/or use.

The invention also includes products made by a process according to the invention.

The invention will now be described in more detail by means of specific examples.

Example 1 An aqueous slurry was made from a furnish comprising: % by weight Kg Carbon Fibre (10 mm: low modulus) 1.5 0.75 Bleached Laponia pulp (refined to 1950 CSF) 3.0 1.50* Ordinary Portland cement 90.5 42.25 China Clay 5.0 2.50 The furnish was mixed with water in a pilor plant scale Hollander beater, litres of water being needed for the 50 kg beater charge. *The pulp was in water at 3.0% solids so that 41.66 Kg of the refined pulp was added.

The mixing time was of the order of 10-1 5 minutes, including 2 minutes after adding the carbon fibre to the other ingredients. This was to ensure dispersion of the carbon fibre. The water temperature was in the range of 30-350C.

The slurry was then run on a vat machine and processed into boards which were air matured for twenty seven days. Two sets of samples were then taken, one being placed in water for 24 hours and the other in an oven at 800C for 24 hours.

Both sets of samples were subjected to physical testing. Density, modulus of rupture (M.O.R.) and impact strength of the samples were measured, and the results are given below in Tables I and 11.

Table I Dry Samples Impact Strength Sample M. O.R. (N/mm2) R.M. Density Dry Density Standard (KJ/m2) No. across with (kg/m3) (kg/m3) M,O.R.* across with 1 16.9 14.8 1164 1441 -17.7 4.3 3.1 2 18.0 15.1 1155 1375 18.6 3.4 2.8 3 18.0 14.2 1144 1383 18.3 4.3 2.9 Mean 17.6 14.7 1154 1399 18.2 4.0 2.9 16.2 Table II Wet Samples Impact Strength Sample M.O.R. (N/mm2) R.M.Density Dry Density Standard IKJlm2) No. across with (kg/m3) (kg/m3) M.O.R.* across with 1 15.4 11.3 1131 1338 15.4 13.4 10.8 2 12.8 12.1 1174 1400 13.8 9.9 9.2 3 12.2 10.9 1206 1433 12.5 13.5 6.0 Mean 13.5 11.5 1170 1390 13.9 12.3 8.7 12.5 *Standard M.O.R. is the M.O.R. linearly corrected to an R.M. a density of 1 300 kg/m3.

The durability of the boards was then investigated by immersing samples in water at 500C and testing samples removed after 90 days and 1 80 days respectively. The results of these tests are given below in Table Ill, with the initial values (i.e. the values after 28 days) being included as control.

Table Ill 90 day 180 day Control immersion immersion Wet (wet) (wet) Across 13.5 14.6 1 5.7 Flexural Strength With 11.5 13.3 13.9 (N/mm2) Ratio 1.18 1.10 1.14 MOR 12.5 13.9 14.8 R.M. Density Kg/m3 1170 1272 1220 Table Ill (contd.) MOR at standard R.M. (N/mm2) 13.9 14.2 15.6 Impact Strength Across 12.3 2.8 3.1 With 8.7 2.6 3.3 KJ/m2 Average 10.5 2.7 3.2 Water absorption % 34 26.3 27.2 The results obtained show initial physical properties of the carbon-fibre reinforced board product to be similar to typical values for glass reinforced cement boards at 3.0% by weight glass addition using a similar furnish in the same plant.

The resistance of the carbon-fibre reinforced board to ageing by immersion in water is superior to that which would be expected of comparable glass reinforced board products.

Claims (6)

Claims

1. A process for producing a fibre-reinforced product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, the process including the step of forming the aqueous slurry from water, an inorganic binder and from 2 to 20% by weight of reinforcing fibres (referred to the finished product) together with a minor proportion of auxiliary nonasbestos fibres having a Canadian Standard Freeness in the range 20 to 300 , the reinforcing fibres comprising a non-vitreous non-asbestos reinforcing staple fibres.

2. A process according to claim 1 in which the reinforcing fibre comprises carbon fibres.

3. A process according to claim 1 or 2 in which the reinforcing fibres include also vitreous fibres.

4. A process according to claim 1,2 or 3 in which the auxiliary non-asbestos fibre is in the form of a pulp.

5. A process according to any one of the preceding claims in which the inorganic binder is a hydraulic binder.

6. A process according to claim 5 in which said binder is Portland cement.

6. A process substantially as described herein in the foregoing Example.

7. A fibre reinforced product made by a process as claimed in any preceding claim.

New Claims or Amendments to Claims Filed on 12 Feb 80 Superseded Claims 1,2 and 5 New or Amended Claims:

1. A process for producing a fibre-reinforced product from an aqueous slurry by forming a layer on the surface of a rotary sieve, from which the layer is subsequently removed, the process including the step of forming the aqueous slurry from water, an inorganic binder and from T to 20% by weight of reinforcing fibres (referred to the finished product) together with a minor proportion of auxiliary nonasbestos fibres having a Canadian Standard Freeness in the range 20 to 300 , the reinforcing fibres comprising carbon staple fibres.

2. A process according to claim 1 in which the carbon fibres form 1 to 1.5% by weight of said aqueous slurry.

5. A process according to any one of claims 1 to 4 in which the inorganic binder is a hydraulic binder.