GB2070637A - Fibrous abrasive products - Google Patents

Abstract

An abrasive product is made by impregnating a bonded non-woven fibrous product including abrasive with a foamable polymerisable material, generally while the body is compressed, and then polymerising the polymerisable material.

Description

SPECIFICATION Fibrous products and their manufacture It is well known to make abrasive products comprising a bonded non-woven fibrous material into which abrasive grit is bonded. Different bonding agents may be used for bonding the fibres together at their intersections to form the bonded fibrous material and for bonding the abrasive grit to the fibres. The product may have a very lofty structure, the product then being particularly useful as a cleaning or polishing material, or may be dense and may be used for abrasion e.g. as a grinding wheel.One method of making a dense product is described in U.S Patent Specification No. 3,020,139 and involves winding the non woven material, while the adhesive is still tacky, into a tight roll and then curing the adhesive, so as to bond the product into a cylindrical homogeneous mass, which can then be cut, for instance into discs.

It is also known to make dense abrasive products, such as grinding wheels, of a foamed polymeric matrix that includes abrasive grains, for instance as described in U.S. Patent Specification No. 2,972,527 and British Patent Specifications Nos. 1,146,037 and 1,245,373. As mentioned in U.S Patent Specification No. 2,972,527 such a product may be made by mixing together foamable polymeric material, abrasive grains and flock fibres and depositing these on a support, and causing foaming and curing.

It has been our object to devise a simple way of forming abrasive products having long life.

In the invention an abrasive product is made by forming a body of mutually bonded fibres which has substantially the dimensions of the desired product, the body being impregnated throughout by foamable polymerisable material and containing abrasive grains, and causing the polymerisable material to foam and polymerise within the body while the body is confined against any substantial change in its dimensions.

The density and hardness of the fibre product obtained by this method can easily be such that the product is useful for grinding metal, e.g. in the form of a grinding wheel. For instance the hardness of the body may be between 15 and 900 Shore A when measured by a Durometer and the density may be from 0.2 to 0.8 g/cm3.

The fibres within the body must initially be bonded with respect to each other and this is conveniently achieved by forming the fibrous body from a non-woven fibrous web which has been prebonded in conventional manner, for instance by application of a bonding agent.

Preferably the fibrous body is built up from a non-woven fibrous web, generally a bonded web, for instance by laminating a plurality of layers of 'the web upon one another. The polymerisation of the polymerisable material will result in the laminated layers becoming firmly secured to one another.

The abrasive grains may be introduced into the body before, with or after the polymerisable material. However most, and usually all, of the grains are preferably bonded to the fibres of the bonded fibrous body, usually before impregnation with the polymerisable material. Accordingly the fibrous body may be formed from a conventional non-woven abrasive lofty product, e.g. of the type described in British Patent Specification No.

884,204.

The fibres used in the invention may be of the types conventionally used in known bonded fibrous abrasive articles including bonded abrasive grains. They are normally flexible, tough, chemically inert materials, such as those mentioned in U.S Patent Specification No.

3,020,139. The material preferably has a high melting point, in order to withstand a wide range of temperatures of use. Polyamide fibres, and particularly aromatic polyamide fibres such as those known as Nomex, are preferred. If the fibres in the web are bonded with a bonding agent before impregnation with the foam and if the abrasive grains are bonded to the fibres then the traditional bonding agents for these purposes may be used, and they may be the same or different. Again suitable materials for these, and as the abrasive grains, are mentioned in U.S. Patent Specification No. 3,020,139.

One convenient way of laminating layers of a non-woven fibrous web is by winding the web around a mandrel to form a body in the shape of a roller the diameter of which is determined by the number of layers of the web in the laminate.

Another convenient method is to lay layers of the web one upon another, for instance on a flat support surface.

The web is generally an open web having a high void volume, e.g. of at least 92%. The void volume may be, for instance, similar to the void volume of domestic scouring pads comprising a bonded web of fibres into which abrasive grains are bonded. The fibrous body is generally compressed before foaming starts so as to reduce the void volume, and the fibres are secured in this compressed state in the final product by the cured and foamed polymer. Even if the fibrous body is not compressed before foaming it is necessary that the body is confined against any substantial change in its dimensions during foaming. This confinement may be achieved at least in part as a result of initial bonding of the fibres within the fibrous body but preferably some external confinement is also provided.When the fibrous body is a roll formed by winding a web around a mandrel the external confinement may simply be a tube around the roller or any means for preventing expansion of the diameter of the roll, for instance tape around the roll or means for securing the outer layer of the web to the adjacent inner layer, for instance a short length of adhesive tape, or entanglement of fibres of adjacent layers.

In some methods, however, confinement is achieved by conducting the foaming while the body is between mould surfaces that press against opposite faces of the body. These surfaces can be the surfaces of a closed mould or they can be opposing plates that press against two faces only of the body.

If the fibrous body is to be compressed then it is generally preferred to impregnate it with the polymerisable foamable material before compression. Thus a preferred method according to the invention comprises impregnating with a foamable polymerisable material a bonded lofty web into which abrasive grains have been bonded, forming the fibrous body of laminating a plurality of layers of this web upon one another and compressing them, and then causing foaming and polymerisation.

Suitable polymerisable materials include phenol-formaldehyde resins, polyvinyl chloride and acrylic resins and these may be converted into a synthetic polymeric foam in known manner, e.g.

~by foaming and curing a preformed polymer or by polymerising and foaming in one stage. Foaming may be brought about by dissolved gas or blowing agents incorporated in the material that is to foam.

Preferably however the synthetic polymeric foam is a polyurethane foam and preferably the material that is caused to react and foam is a prepolymer that will, upon contact with water, polymerise and foam. The prepolymer may be hydrophilic.

Suitable materials are available from W. R. Grace S Co., under the Trade Name "Hypol" foam polymer. With such polymers foaming may be brought about by immersing the fibrous body in water.

The density and other properties of the final product can be varied by appropriate choice of fibre density during the foaming, the amount of foaming agent and the temperature and other conditions under which foaming is conducted. For instance the hardness can be varied particularly by variations in the fibre density, the amount of foamable polymer and the nature of the polymer whilst cell size can be varied by changes in foaming conditions. When foaming is brought about by immersion in water the inclusion of a surfactant may be desirable as a way of controlling cell size. Similarly the use of hot water is sometimes desirable.

We find in particular that the amount of polymerisable material can have a significant effect upon the aggressiveness of the product and upon its working life. In general its working life reaches an optimum once a certain amount of polymerisable material has been introduced and the presence of additional polymerisable material has little or no effect on the working life. However, it is found that increasing the amount of polymerisable material above an optimum can result in a reduction in aggressiveness, i.e. ability of the product to abrade material. Accordingly it is desirable to select the amount of prepolymer such as to obtain maximum aggression, since amounts of prepolymer above or below this optimum will give inferior aggression.Typically the optimum amount of polymerisable material is from 25 to 75%, preferably about 50%, based on the weight of the initial fibrous body, i.e. the bonded web including abrasive grains and bonding agent.

The amount of polymerisable material can be controlled either by controlling the amount of pickup by the web or by saturating the web and controlling instead the concentration and often the viscosity of the solution of polymerisable material with which the web is saturated. When, as is preferred, the polymerisable material is a polyurethane prepolymer, dilution of the solution should be with an organic solvent that is inert to the prepolymer but which is miscible with it, and usually also with water, e.g. a ketone.

Full polymerisation of the polymerisable material will generally include a final curing stage and this can either be completed while the body is still confined, for instance by external tape or mould surfaces, or can be completed after removal from any such confinement since the foamed polymer along will stabilise the dimensions of the fibrous body.

The resultant bonded fibre product can be used as such or can be shaped to any desired shape, for instance by cutting or grinding. Abrasive products according to the invention may be in the form of grinding wheels or discs.

The following are some examples: EXAMPLE 1 A carded cross-lapped web of coarse denier polyamide fibres is lightly needed to intermingle the fibres and is then sprayed with a phenolformaldehyde resin/abrasive grain slurry which is then dried on a hot air drying machine. After passage through this machine the web is reversed and resprayed on the other surface with a similar slurry and is then dried as before.

The bonded, open, fibrous abrasive material is then impregnated with Hypol polyurethane prepolymer and passed through the nip of two plain steel rollers. The leading edge of the wet impregnated material is bonded to a mandrel and the material is wound on the mandrel under tension until a diameter slightly in excess of the desired outer diameter of the final article is achieved. Tape is the wound around the circumference of the roll to prevent the roll becoming unwound, and the roll is immersed in a water bath at 600 C. Polymerisation and foaming start and after 13 minutes immersion the roll is removed from the water bath and is allowed to stand in air for 10 to 15 minutes to allow completion of the reaction. The tape is removed and the roll is allowed to air dry for 2 to 3 days.

The final product may then be cut and ground to the required outer dimensions. lt is a hard resilient roll which can cut metal. For instance if a traditional industrial fibrous abrasive material is used for de-burring the drilled hole of a printed circuit board the abrasive coated fibres will penetrate into the hole and enlarge its diameter, but the product of this example de-burrs the hole without the abrasive entering the hole to an amount sufficient to enlarge the diameter. The product gives a faster and brighter cut than conventional products.

EXAMPLE 2 A bonded abrasive open non-woven product is made, and impregnated with Hypol, as described in Example 1. Several layers of this impregnated product are then laid up to a thickness 1 to 6 times the required thickness. The assembly is then compressed between metal plates and the compressed product immersed in water and allowed to react as in Example 1, the plates being removed before the air drying step. Discs or other shaped products can be stamped from the dry sheet.

EXAMPLE 3 The process of Example 1 is repeated but with varying pickups of the Hypol polyurethane prepolymer. In each instance the fibrous web is saturated with the prepolymer but the concentration of the solution is varied by dilution with methyl ethyl ketone. It is found that increasing the amount of prepolymer up to about 50% by weight of the initial bonded web gives marked increase in the working life of the resultant product but that further increase in the amount of prepolymer makes little difference to the working life.

It is also found that increasing the amount of prepolymer up to 50% by weight of the initial bonded web gives a marked increase in the aggressiveness of the final product. However further increase in the amount of polymerisable material tends to reduce the aggressiveness.

Optimum results are obtainable by saturating the web with a solution of about 100 parts Hypol polyurethane prepolymer, about 35 parts methyl ethyl ketone and 5 parts of a polymerisable monomer, e.g. methylene diisocyanate, intended to give a harder product. The preferred polymer is Hypol FHP3000.

Claims (10)

1. A method of forming an abrasive product, which comprises forming a non-woven body of mutually bonded fibres which has substantially the dimensions of the desired product, the body being impregnated throughout by foamable polymerisable material and containing abrasive grains, and causing the polymerisable material to foam and polymerise within the body while the body is confined against any substantial change in its dimension.

2. A method according to claim 1 in which the foamable polymerisable material is a polyurethane prepolymer which foams and polymerises on contact with water and the foaming and polymerisation is caused by immersing the body in water.

3. A method according to claim 1 or claim 2 in which the amount of polymerisable material is from 25 to 75% by weight of the weight of the body.

4. A method according to any preceding claim in which the abrasive grains are bonded to the fibres of the body.

5. A method according to any preceding claim in which the body is formed by laminating a plurality of layers of bonded non-woven fibrous web.

6. A method according to claim 5 in which the body is made by winding the web around the mandrel and the body is confined against expansion by securing the wound web against unwinding.

7. A method according to claim 5 in which the body is formed by laying layers of a non-woven web upon one another and is confined during foaming by mould surfaces against opposite faces of the body.

8. A method according to any preceding claim in which the fibrous body is compressed before and during foaming and polymerisation and polymerisation of the polymerisable material results in bonding of the fibres in the compressed state.

9. A method according to claim 8 comprising impregnating with the foamable polymerisable material a lofty non-woven fibrous web having abrasive grains bonded to its fibres, laminating and compressing a plurality of layers of the web, and securing the laminated and compressed layers by foaming and polymerising the polymerisable material.

10. A method according to claim 1 substantially as described in any of the Examples.