GB2258235A

GB2258235A - Thermosetting resin composition for fibre reinforced products

Info

Publication number: GB2258235A
Application number: GB9116394A
Authority: GB
Inventors: Godfrey Brian Clegg
Original assignee: FILON PRODUCTS Ltd
Current assignee: FILON PRODUCTS Ltd
Priority date: 1991-07-30
Filing date: 1991-07-30
Publication date: 1993-02-03
Anticipated expiration: 2011-07-30
Also published as: GB9116394D0; GB2258235B

Abstract

A plastics composition, for forming into sheet, comprises at least one thermosetting resin, at least one low density filler in the form of hollow glass microspheres, preferably of mean particle size 10 to 100 mu , and at least one higher density filler in particulate form, e.g. alumina, china clay and/or other aluminious materials, and of smaller particle size than the microspheres, preferably of mean particle size 1 to 10 mu , the weight ratio of the higher to lower density fillers in the composition before the addition of fibres being at least 2:1. The plastics composition can be combined with glass or other reinforcing fibres, e.g. a glass fibre mat, to produce a thermoset sheet product which is surface-blemish free. The resin is preferably an unsaturated polyester.

Description

IMPROVEMENTS IN OR RELATING TO FIBRE-REINFORCED PLASTICS COMPOSITIONS This invention relates to thermo-setting polymer compositions, suitable for use in making fibre-reinforced plastics sheet materials, and sheet materials incorporating such compositions.

When formulating plastics compositions of this type there is a need to retain structural strength and integrity while reducing weight per unit area and retaining a blemish-free surface on the resulting sheet product. Thus it is desirable to produce a reasonably thick sheet product of good structural strength but of lower density than conventional products but without cracking or imperfections of the surface. The incorporation of a proportion of hollow microspheres into the formulation provides an effective means of reducing the density of the composition but can cause, during curing, internal microcrazing and surface cracking, with consequent strength reduction and poor sheet finish.

It is already known (GB 1,498,755) to use low-density fillers (e.g. glass microspheres) in the context of an extrudable, fibre-reinforced vinyl resin composition. This specification further suggests the use of a mineral filler, such as calcium carbonate, in combination with the glass spheres. The stated purpose is here to reduce tangling of glass-fibres during the extrusion of an existing (GB 1,498,450) vinyl thermo-plastic composition which contains mineral filler.

The sheeting produced according to the invention is a thermo-setting laminate and possesses heat stability which derives fundamentally from the crosslinked molecular structure of a thermo-set compared with the substantiallylinear polymerisation of thermo-plastic compositions. Thermo-sets have greater strength and ridigity-retention under variable temperature conditions.

The microspheres are incorporated to reduce composition density and the mineral fillers specifically to prevent any cracking occasioned by the sphere inclusion.

It is also known (EP 21563B) to formulate a thermo-setting resin composition from a granular thermo-setting resin and hollow particles so that the solid fused mass, formed by thermo-setting, has an apparent density of less than 0.5 g/ml.

However, such a composition is primarily intended for cavity filling, does not contain particulate mineral fillers and would not possess the physical properties required of the sheet material of this invention.

The present invention in one aspect consists of a plastics composition for forming into sheets, comprising at least one thermo-setting resin, at least one low density filler in the form of hollow glass microspheres, at least one higher density filler in particulate form and of lower particle size than the microspheres, wherein the weight ratio of higher density filler to lower density filler in the composition (before the addition of fibres) is at least 2:1.

Preferably the resin is of the polyester type.

Preferably the glass microspheres have a mean particle size within the range of 10y to 100cm (micrometers). Preferably the higher density filler is selected from alumina, china clay and other alumina - based or aluminacontaining fillers. Its mean particle size should be within the range 1y to 10 y. The preferred components of the thermo-setting composition (before the addition of fibres) are as follows; (percentages by weight).

Glass Microspheres 2.0 - 8.0% (wt) Alumina 5.0 - 15.0% (wt) China Clay 0.5 - 1.5% (wt) Thermo-setting Resin 92.5 - 75.5%(wt) In a second aspect the invention consists of a laminated sheet material formed by combining a resin composition, as defined above, with glass or other reinforcing fibres to produce a thermo-set structurally-strong sheet product.

Preferred weight limits of the components of such a sheet product are as follows: Glass Microspheres 1.7 - 6.0% (wt) Alumina 4.3 - 11.3 % (wt) China Clay 0.4 - 1.1% (wt) Resin Blend 78.5 - 56.6% (wt) Glass Fibres 15.0- 25.0%(wit) The incorporation of the higher density mineral filler is contrary to the principle of reducing laminate density (to build up thickness) and this is added to stabilize the mix and to reduce surface imperfections (cracks) in the sheet product.

The invention will be further described by reference to the following non limiting example which describes a resin formulation and procedure for producing a sheet product according to the invention.

Example A resin mix was made up from: Component Source and Type 2.45 Kg of mixed BP 8025/8026 resins Obtainable from BIP Chemicals Limited; and which are general purpose grade unsaturated polyester resins, consisting of alkyd reaction products of polybasic acids or acid anhydrides with polyfunctional alcohol dissolved in styrene monmer.

The resins are light-stabilised to improve weather resistance.

0.10 Kg of glass microspheres B23/500 hollow glass microspheres from 3M United Kingdom plc, and having a particle size distribution within the range of about 10y to 100y, and a mean particle size of about 40,u.

0.32 Kg granular alumina Suitable grades of alumina include the product FRF-80 from BA Chemicals Limited or 4608 from Croxton & Garry Limited, which products have a mean particle size of about it, and a particle size distribution in the range of about 2y to 10.

0.025 Kg china day Supreme china clay from ECC International Limited having a mean particle size of about 1y with a maximum particle size of up to 2y.

The glass microspheres were mixed into the resin with recirculation of particles in a current of air, so as to produce a homogeneous mixture. This mix was then laminated with 0.72 Kg of glass fibres (consisting of 2400 tex E-glass roving, chopped into 50mm lengths and randomly distributed to form a reinforcing matt, from Owens-Corning Fibreglass Limited) on a conventional g.r.p laminating production line to produce a 3mm thick panel of glass-reinforced plastics which was thermo-set to produce a structurally strong and essentially surface - blemish free sheet of fibre-reinforced polyester resin. The constituents of one square metre of panel can be summarised as follows: Glass Microspheres 0.11 Kg Alumina Particles 0*32 Kg Glass Fibres 0.72 Kg China Clay Particles 0.025 Kg Polyester Resin 2.45 Kg

Claims

Claims 1. A plastics composition, for forming into sheet, comprising at least one thermo-setting resin, at least one low density filler in the form of hollow glass microspheres, and at least one higher density filler in particulate form and of smaller particle size than the microsphere, wherein the weight ratio of higher density filler to lower density filler in the composition (before the addition of fibres) is at least 2:1.
2. A composition as claimed in Claim 1 wherein the resin is of the polyester type.
3. A composition as claimed in Claims 1 or 2 wherein the microspheres have a mean particle size within the range of 10,u to 100tic.
4. A composition as claimed in Claims 1,2 or 3 wherein the higher density filler is selected from alumina, china clay and other aluminious materials.
5. A composition as claimed in Claim 4 wherein the mean particle size of the higher density filler is between Ite and 10cm.
6. A composition as claimed in Claim 1 which comprises the following percentages of components (by weight) before the addition of fibres: Hollow Glass Microspheres 2.0 - 8.0% (wt) Granular Alumina 5.0 - 15.0% (wt) China Clay 0.5 - 1.5% (wt) Thermo-setting Resin 92.5 - 75.5%(wit)
7. A laminated sheet material formed by combining a resin composition as claimed in Claims 1-6 with glass or other reinforcing fibres to produce a thermo-set structurally-strong sheet product.
8. A sheet material as claimed in Claim 7 which comprises the following components within the ranges specified: Glass Microspheres 1.7 - 6.0% (wt) Granular Alumina 4.3 -11.3% (wt) China Clay 0.4 - 1.1% (wt) Resin Blend 78.5 - 56.6% (wt) Glass Fibres 15.0 - 25.0% (wt)
9. A resin composition for producing a sheet product substantially as hereinbefore described.
10. A sheet material substantially as hereinbefore described with reference to the example.