Moulding material and method of forming same

Abstract

A method of separating a composite material stack comprising multiple elements (12) in contact with one another is discloses. Each element (12) comprises reinforcement fibers and an uncured resin matrix, and the method comprises the steps of temperature treating the stack and/or applying a stress to the stack to separate the elements.

Claims

1. A method of forming a sheet moulding compound, comprising the steps of: (a) as a first step, cutting a moulding or laminate of layers of fibrous reinforcement material impregnated with resin matrix to produce a plurality of off-cuts, said off-cuts each being, in the form of uncured composite material stacks comprising multiple uncured elements in contact with one another, each uncured element comprising reinforcement fibers and a resin matrix; (b) thereafter, as a second step, separating, each of said uncured composite material stacks into its constituent elements by at least partially simultaneously temperature treating the uncured composite material stacks and applying at least one stress to the uncured composite material stacks to separate the uncured elements from each other, wherein the at least one applied stress is a stress selected from the group consisting of flexural stress, torsional stress, compression stress, shear stress, peel stress, tensile stress and vibrational stress; (c) randomly distributing the uncured elements and combining to form a sheet moulding compound.

2. The method of claim 1, wherein the at least one stress is applied in one or more directions in relation to the stack.

3. The method of claim 1, wherein more than one stress is applied consecutively or simultaneously.

4. The method of claim 1, wherein temperature treatment comprises cooling the resin matrix.

5. The method of claim 4, wherein the resin matrix is cooled to reduce the tack of the resin to a value which is less than 10% of the tack value of the resin at room temperature.

6. The method of claim 1, wherein the temperature treatment comprises heating of the resin matrix.

7. The method of claim 1, wherein stress application and temperature treatment are cycled or repeated.

Description

DETAILED DESCRIPTION

(1) The invention will now be described by way of example only and with reference to the following drawing in which:

(2) FIG. 1 shows a diagrammatic view of a process for separating a laminate product according to an embodiment of the present invention.

(3) Laminate lay-ups can be formed from combined layers of fibrous reinforcement which are impregnated with a resin matrix. Preferably, the fibrous reinforcement layers comprise unidirectional fiber tows and the layers are arranged in relation to one another to form a quasi-isotropic lay-up. Preferably, the layers are extending in the +90/+45/0/45/90 directions and they may be arranged in multiples thereof.

(4) These lay-ups may be (die) cut into laminate parts which are subsequently processed as compression mouldings. The cutting process results in redundant laminate lay-up material. This redundant material may be usable for another purpose and the present invention seeks to address this as well as to provide improvements generally.

(5) FIG. 1 presents a re-use process 10. Offcuts 12 from die cut laminated prepreg sheets are cut into smaller laminate elements 14 or they may be cut following completion of the process 10. These elements are temperature treated 16,18 by either heating or cooling or by a combination of both temperature treatments. Heating 18 decreases the viscosity of the resin, and increases Tg and can aid separation, whereas cooling reduces the Tg and/or tack of the resin matrix allowing layers to be more easily separated.

(6) Following temperature treatment, the elements are separated by the application of stress 20. The stress may be applied in different directions and/or forms in relation to the laminate elements. Steps 20, 16 and 18 may be combined or conducted partially simultaneously or cyclically until the elements are separated. Following separation 20, randomly distributed single layer prepreg elements 22 are combined together into a sheet form as a sheet moulding compound (SMC) 24. This SMC is then suitable for re-use to produce composite parts.

(7) There is thus provided a method and a moulding compound as hereinbefore described.