GB2153368A - Liquid moulding compositions - Google Patents

Abstract

A pre-filled, pre-reinforced unsaturated resin moulding composition has a liquid composition so that it may be injection moulded at low temperatures and pressures. The length of the reinforcement fibres should not exceed 6mm.

Description

SPECIFICATION Liquid Moulding Compositions Many types of moulding compositions based on unsaturated polyester and similar resins are known. They range in consistency from doughs, through sheet materials to dry pellets. They all contain polyester resin, monomer, filler, reinforcement and catalyst and are characterised in that they all need heat and pressure to be transformed into cured moulded products. The heat is necessary not only to activate the cure but also to reduce the viscosity so that the material flows readily and fills the mould cavity into which it is placed or forced.

Polyesters can also be used in liquid form in vacuum or pressure assisted filling of closed moulds into which reinforcement is placed before closing the moulds. This is the resin injection process and moulding takes place at ambient temperatures or slightly above.

The present invention provides a readily flowable liquid composition already containing reinforcement which is capable of being injected into low pressure, low cost tools using simple low cost equipment.

The basic ingredients of these liquid, storage stable, compositions are: A. unsaturated polyester or similar resin dissolved in vinyl type monomer, B. inorganic filler, C. 'reinforcement, D. free radical catalyst, However, the free radical catalyst need not be in the composition as sent out from the factory.

Owher ingredients which may be included are internal mould release agents, accelerators, inhibitors, rubbery or thermoplastic polymer to increase toughness and reduce cure shrinkage, blowing agents and pigments.

A. Resin Component Unsaturated polyesters which may be used are those made by polyesterification of a ss unsaturated dicarboxylic acids or anhydrides, with or without saturated dicarboxylic acids or anhydrides and one or more glycols. The polyesters thus formed may, prior to blending with the modifying polymer, be dissolved in a vinyl type monomer with the incorporation of one or more inhibitors to give storage stability.

Typical ingredients that can be used to manufacture such polyester resin composition are: (i) Unsaturated dicarboxylic acids-maleic an hydride fumaric acid, itaconic acid.

(ii) Saturated dicarboxylic acids-phthalic anhydride isophthalic acid, terephthalic acid, tetrahy drophthalic anhydride, hexahydro-phthalic an hydride, endomethylene tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, chlorendic acid, succinic acid, adipic acid, azelaic acid, sebacic acid.

(iii) Glycols-ethylene, diethylene, propylene, dipropylene, neopentyl and dibromoneopentyl glycol.

1,3-propane-diol, butanediols, 1.6-hexanediol, hydrogenated Bisphenol A, ethylene and propylene oxide aducts of Bisphenol A and similar 4,4-diphenols, 2,2,4-trimethyl-1 ,3 pentane-diol. 1,4-cyclohexane dimethanol or compounds with an oxirane group behaving as glycols e.g. ethylene oxide, propylene oxide, glycidyl ethers.

(iv) Vinyl monomers-styrene, vinyl toluene, chlorostyrene bromostyrene, a methyl styrene, t butyl styrene, p methylstyrene, methyl methacrylate, diallyl phthalate.

(v) Inhibitors -hydroquinone and ring substituted hydroquinones, benzoquinone and ring substituted benzoquinones, 1,4 naphthaquinone, copper naphthenate, quaternary com pounds.

Minor quantities of mono and poly function hydroxyl and carboxyl containing compounds such as benzoic acid, penta-erythritol, trimethylol propane, glycerol, trimellitic acid may be incorporated into the unsaturated polyester during manufacture thereof. Dicyclo-pentadiene may also be added during manufacture.

Suitable vinyl ester polymer resins are, for example, made by an addition between epoxide resins and acrylic or methacrylic acids again dissolved in a vinyl monomer.

Other resins which are usable are urethane acrylate resins, i.e. those containing both urethane linkages and acrylic groups and again dissolved in vinyl type monomer.

B. Typical fillers that can be used are clays, natural or synthetic calcium carbonates, silica, talcs, alumina hydrate, antimony oxide, dolomite, and these can be surface treated. Expanded fillers e.g. hollow glass spheres can also be utilised as can be waste products such as fly ash.

Combinations of two or more fillers can be used and if required mixtures of various particle sizes can be employed.

C. The reinforcement is preferably glass fibre either hammer milled or chopped fibre of up to 5-6mm length. Other reinforcements such as carbon fibre, KEVLAR(g), etc. can be used wholly or in part.

D. The free radical catalyst can be selected from the wide range of peroxide, hydroperoxide, perester, perketal types available on the market according to the temperature at which cure is to occur. Azo compounds yielding free radicals can also be used.

Amongst the optional materials that may be incorporated in the compositions are: Mould release agents e.g. zinc stearate accelerators e.g. tertiary aromatic amines. metal salts, inhibitors such as TopanolG) O, Rubbery or thermoplastic polymers such as LP60 (Union Carbide) modified styrene/butadiene copolymers, blowing agents e.g. CelogenO XP100 (Uniroyal).

The amount of filler used is between 25 and 1 50 pphr preferably 50-100 pphr and the amount of reinforcement depends on the length of the fibres but varies between 0 and 60% preferably between 5 and 40%.

The viscosity of the composition must be such that it is sufficiently fluid to be injected into a closed, vented, mould at relatively low pressures and should be below 500 poise preferably 50-150 poise when measured using a capillary extrusion rheometer constructed according to Zlochower, Das and Hudson 34th SPI Conference 1979, Section 11 C. Such viscosities will be referred to as being "as herein defined".

In order to fully cure the moulded articles in a reasonable time it is necessary to have a mould heated to betwen 80"C and 200"C preferably 120"-150"C. At these temperatures mould residue times of 60-120 seconds are possible. Although single pot injectable liquid systems are described in Examples l-VI below it is possible to use two or more pot systems and lower temperatures e.g. a catalysed resin and an accelerated resin. both filled and reinforced, injected into a mould at ambient temperatures. Again a blowing agent may be incorporated such that expansion occurs when the injectable composition meets the hot mould and curing subsequently occurs.

Examples Six resins are used in the examples below and these are made by standard polycondensation methods from the following.

Type 1. maleic anhydride 3 mole phthalic anhydride 1 mole propylene glycol 4.4 mole styrene monomer to non volatile content of 63%.

Type 2. fumaric acid 3 mole isophthalic acid 1 mole propylene glycol 4.25 moles styrene monomer to 63% non volatile content.

Type 3. maleic anhydride 1.4 mole isophthalic acid 1 mole neopentyl glycol 2 mole propylene glycol 0.5 mole styrene monomer to 65% non volatile content.

Type 4. as Type 3 but terephthalic acid used in place of isophthalic acid.

Type 5. as Type 4 but neopentyl glycol 1.875 moles and 0.625 moles diethylene glycol.

Type 6. maleic an hydride 1 mole phthalic anhydride 1 mole diethylene glycol 1.03 mole propylene glycol 1.02 mole styrene to non volatile content of 65%.

In all cases about 1 50 ppm of inhibitor was included.

Example 1 The following composition was prepared: Resin Type 1 100 pbw Omya BLH (Calcium carbonate filler) 76 pbw Hammer milled glass fibre 33 pbw 1.5mm chopped glass fibre (Fibreglass WX 6450) 6.7 pbw Zinc stearate (release agent) 4 pbw Trigonox(E) 21S (free radical catalyst) 2 pbw 20% Topanol(E) O in styrene 0.15 pbw This mix has a viscosity of 50 poise* and was injected into a mould heated to 120"C. After 90 seconds the moulding was released cleanly and was free from crazing and cracks with a smooth surface appearance.

Example 2 A similar composition to Example 1 was used except that 20 pbw hammer milled glass and 20 pbw 3mm chopped glass fibres were used. This composition had a viscosity of 1 25 poise* and like Example 1 gave good mouldings.

*Measured as previously described.

Example 3-7 These were similar to Example 1 except that the resins used were those previously described as numbers 2-5. The results are given in the Table attached.

TABLE

I Example Number 1 2 3 4 5 6 7 Resin Type 1 1 2 3 4 5 6 H.D.I of resin OC 110 - 130 98 105 80 81 Tensile Strength MPa 28 16 22 22 37 33 31 Tensile Modulus cPa 8.6 3.7 8.4 6.6 8.4 7.8 7.0 Elongation 4'0 0.46 0.6 0.41 o.g3 0.56 0.6 1.0 Bend Strength MPa 64 7 38 63 72 78 70 65 I Bend Modulus GPa 6.6 4.2 6.5 6.6 7.2 6.3 6.4 Charpy Impact kJm2 7.18 11.1 4.8 6.0 6.0 5.9 7.0 Izod Impact Jm-1 76.2 130 67.1 53 58.3 50.1 51.0

Claims (8)

1. A liquid moulding composition including (a) an unsaturated resin dissolved in a vinyl monomer (b) an inorganic filler (c) a reinforcement which is fibres of up to 6mm in length.

2. A liquid moulding composition according to claim 1, including also (d) a free-radical catalyst.

3. A liquid moulding composition according to claim 1 or claim 2, wherein the reinforcement fibres are up to 5mm in length.

4. A liquid moulding composition according to any one of the preceding claims wherein the fibres are hammer milled or chopped glass fibres.

5. A liquid moulding composition according to any one of the preceding claims having a viscosity of below 500 poise as herein defined.

6. A liquid moulding composition according to claim 5, wherein the viscosity is between 50-150 poise as herein defined.

7. A liquid moulding composition substantially as herein described and exemplified.

8. A method of injection moulding an article comprising injecting a composition according to any one of the preceding claims at low temperatures and pressure into a closed, vented mould.