Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1992-12-22
1995-05-30
Short, Patricia A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523527, 525170, C08L 6706
Patent
active
054201799
DESCRIPTION:
BRIEF SUMMARY
The present invention relates more particularly to compositions consisting of unsaturated polyester resins and of new antishrinkage additives.
Unsaturated polyester resins are employed in many fields of application, in particular for moulding objects reinforced with glass fibres. They are widely employed for the manufacture of motor vehicle components, of bathroom fittings and accessories, of cabinets for electronic apparatus, of kitchen utensils, furniture units, etc. A major disadvantage of the use of unsaturated polyester resins is the fact that these resins exhibit a considerable volume shrinkage during moulding, which is produced as the polyester resin polymerises. This volume shrinkage of polyester resins then results in a rough finished surface which makes it possible to discern the glass fibres which generally appear to project over the surface of the finished product and even allow undulations to be perceived.
The majority of the applications in which unsaturated polyester resins reinforced with glass fibres are involved require impeccable finished surfaces. This is the case, for example, with motor vehicle components. Various techniques have been proposed for improving the surface finish. The sanding technique has, for example, been employed, followed by a filling operation. It has also been proposed to employ coats of polyester resins in the form of gels (gel coat) which enable the glass fibres to be masked. All these techniques, which are arduous to use, have the disadvantages of increasing the costs of manufacture and of reducing the production efficiency.
Antishrinkage additives have also been proposed, including thermoplastic pollers. In particular, C.A. 80, 84093v describes, as antishrinkage additive, a solution of 20 to 30 parts of a thermoplastic copolymer (such as a copolymer comprising 85% of methyl methacrylate, 10% of 2-hydroxyethyl methacrylate and 5% of methacrylic acid) in 70 to 80 parts of styrene containing less than 20% of at least one hydroxyalkyl (meth)acrylate. A composite obtained from an unsaturated polyester in styrene containing this additive exhibits a shrinkage of 3.1%. This additive is insoluble in styrene and immiscible with the unsaturated polyester, probably because of an excessively high molecular weight, which results in an excessively high volume shrinkage.
These known antishrinkage additives have the disadvantage of separating into two layers when added to the polyester resins. That is to say that they form a mixture which is not homogeneous, the constituents being immiscible at room temperature. Furthermore, it is often necessary to pigment the resin compositions, particularly in a dark shade. The use of resinous compositions involving these thermoplastic polymers results in pigmented compositions which are in most cases homogeneous after moulding. From the viewpoint of appearance, they resemble resin compositions without any antishrinkage additive, but they have the disadvantage of not being able to be stored, and this makes it necessary to market them in two parts, that is to say to deliver, on the one hand, the polyester resins and, on the other hand, the additives.
There is therefore a perceived need for developing unsaturated polyester compositions containing antishrinkage additives which can be stored and which, when pigmented, must be homogeneous and must have good mechanical properties. In addition, these additives must have the particular property of being miscible with the unsaturated polyester resins at room temperature. The miscibility, or the homogeneity, of a mixture is established when the latter has one and only one glass transition temperature.
The present invention relates to liquid resinous compositions suitable especially for the moulding of objects reinforced with glass fibres and capable of being homogeneously pigmented, comprising an unsaturated polyester, at least one monomer copolymerisable with the unsaturated polyester, and an at least partially hydroxylated alkyl methacrylate polymer, which are characterised in that the said hydroxyl
REFERENCES:
patent: 3956421 (1976-05-01), Roberts et al.
patent: 4579890 (1986-04-01), Domeier
patent: 4626570 (1986-12-01), Gardner
Chemical Abstract 48205t of South African 6704330.
Chemical Abstract 84093v of S. Hajime et al., Japan Kokai 73 51,090, Jul. 18, 1973.
Chemical Abstract 48653u of S. Hajime et al., Japan Kokai 73 49,884, Jul. 13, 1973.
Fourquier Dominique
Suspene Laurent
Conlin David G.
Corless Peter F.
Cray Valley S.A.
Short Patricia A.
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