GB2267675A

GB2267675A - Rotational moulding of two-colour products

Info

Publication number: GB2267675A
Application number: GB9210824A
Authority: GB
Inventors: Siu Man Nan
Original assignee: Nanma Manufacturing Co Ltd
Current assignee: Nanma Manufacturing Co Ltd
Priority date: 1992-05-21
Filing date: 1992-05-21
Publication date: 1993-12-15
Anticipated expiration: 2012-05-21
Also published as: GB9210824D0; GB2267675B

Abstract

A moulding process enables two-colour products to be made by preheating the mould, introducing a first coloured plastisol A, waiting a predetermined interval of time before introducing a second coloured plastisol B at room temperature, and rotating and heating the mould in accordance with known rotational moulding techniques to fuse the two plastisols to form a permanently dual-coloured product. Products such as toys and massage devices made by the process are described and are safer than conventionally painted or sprayed dual-coloured moulded plastics products.

Description

MOULDING PROCESS AND PRODUCT DESCRIPTION The present invention relates to a moulding process particularly to a rotational moulding process for polyvinyl chloride resins and to products made by such a process.

In conventional rotational moulding processes, only a single colour article can be made. Additional colour must be added after moulding by spraying or painting, which is unsatisfactory as it tends to wear or peel off.

According to the present invention, there is provided a moulding process comprising introducing into a mould predetermined amounts of two plastisols which have different viscosities and rotating and heating the mould so as to substantially fuse the two plastisols. Preferably this is achieved using them at different temperatures, for example by heating one plastisol to between 800C and 1000C and preferably around 1000C and using the other plastisol at room temperature.

According to a preferred embodiment, the process comprises the steps of preheating a mould, introducing into the mould a predetermined amount of a first plastisol, then, a predetermined interval of time later, introducing a predetermined amount of a second plastisol into the mould Preferably the mould is preheated to about 1000C and the second plastisol is at room temperature when it is introduced into the mould.

The plastisols may be of different colours or of different textures.

The present invention also provides a plastics article, for example a massage device, made by the process of the invention.

The invention will now be described by way of example and with reference to the drawings, in which: Fig. 1 is a flow diagram of a moulding process according to the present invention; and Fig. 2 illustrates a plastics article made by the process of the invention.

In a conventional rotational moulding process a plastisol consisting of a polyvinyl chloride (PVC) resin in a plasticising liquid and a colour pigment is loaded into a mould. The mould is closed and locked then heated while being rotated in two mutually perpendicular planes. The heat gelatinises the plastisol and the rotation builds it up in an even distribution on the interior wall surface of the mould.

Then the mould is cooled by exposure to cool air and water and the moulded article removed.

In a process according to the invention as illustrated in Fig. 1, a mould is preheated, for example to between 80 C and 1000C. A predetermined amount of a first single-pigmented plastisol A is introduced into the mould. After a predetermined time a second plastisol B with a different pigment is introduced at room temperature into the mould.

Then the mould is subjected to traditional rotational and heating conditions as described above causing the plastisols A and B to blend together. The different initial temperatures of plastisols A and B give them different viscosities, flow properties and gelation speeds within the mould and cause them to form a dual colour product wherein the colour is permanent and physically part of the finished article.

Exact amounts, temperatures and timings will depend upon the particular composition of the plastisols, the size and shape of the mould and the effect intended in the final product, but will be evident to or calculable by those working in the field of rotational moulding. It has been found however, that heating the mould to above 1500C to 1700C can give the plastisol too much viscosity resulting in poor flow properties and possible fusing or deformation.

The necessary different viscosities of the two plastisols A and B could alternatively be achieved by formulating the compositions of the plastisols accordingly.

Fig. 2 shows an article 1 according to the invention made by the novel process described above. As can be seen, the pigmented plastisol A is fused in an irregular marble-like pattern with pigmented plastisol B to give a permanent, physically-built dual coloured texture to the article.

The inventive process can be applied in the manufacture of a wide variety of plastics articles, for example children's toys, household equipment and is particularly useful in the manufacture of massage devices. Obviously a permanent dual colour is desirable in such products to avoid the problems of flaking or worn paint.

The process can be used for plastisols of different textures and can be extended to more than two plastisols so as to produce multi-coloured or multi-textured articles.

Claims

1. A moulding process comprising introducing into a mould predetermined amounts of two plastisols which have different viscosities and rotating and heating the mould so as to substantially fuse the two plastisols.

2. A moulding process according to claim 1, wherein the different viscosities of the two plastisols are achieved by different temperature treatments.

3. A moulding process according to claim 1, wherein one plastisol is heated to between 80 C and 1000C and the other is at room temperature.

4. A moulding process according to any one of claims 1 to 3 comprising the steps of preheating the mould, introducing into the mould a predetermined amount of a first plastisol, then, a predetermined interval of time later, introducing a predetermined amount of a second plastisol into the mould, and rotating and heating the mould.

5. A moulding process according to claim 4, wherein the mould is preheated to between 800C and 1000C.

6. A moulding process according to claim 4 or 5, wherein the second plastisol is at room temperature when introduced into the mould.

7. A moulding process according to any one of claims 1 to 6, wherein the first and second plastisols are of different colours.

8. A moulding process substantially as hereinbefore described.

9. A product made by the process of any one of claims 1 to 8.

10. A massage device made by the process of any one of claims 1 to 8

11. A product substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.