GB2236982A

GB2236982A - Decorated moulded products

Info

Publication number: GB2236982A
Application number: GB8923723A
Authority: GB
Inventors: Norman Perry David Darby
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-10-20
Filing date: 1989-10-20
Publication date: 1991-04-24
Also published as: GB8923723D0

Abstract

There is disclosed a method of decorating a moulded article comprising applying a screen printed or formed decoration to the surface of a mould whereby the decoration will be bonded to the surface of the moulded article during moulding and thereafter moulding the article characterised in that the decoration is screen printed or formed onto a backing sheet and is applied as a preformed item to the surface of the mould. <IMAGE>

Description

DECORATED MOULDED PRODUCTS This invention relates to a method of decorating a moulded product and to decorative moulded products so formed.

It is known to apply decoration to the surface of a moulded product by silk screening the decoration onto the surface of the mould immediately before the moulding operation is performed. The disadvantage of this procedure is that the mould cycle is extended to allow the silk screen operation to be performed on the surface of the mould and then to allow the silk screened decoration to dry or set. This procedure prevents the use of the mould during the printing operation and increases the 'down time' or preparation time in the moulding operation, thereby increasing costs.

A second disadvantage of using the screen printing technique directly onto the mould is that there are limitations on the size of the decoration that can be applied and on the positions on the surface of the product to which the decoration can be applied. Thus, any screen printing technique requires a frame around the screen and the frame necessarily takes up space within the mould preventing the application of the decoration to those areas of the surface of the mould over which the frame is located during the screen operation. Furthermore, by the nature of the frame the decoration cannot be applied on any surface other than flat surfaces and cannot be applied around curved and angular sections of the mould or of the product to be moulded.

These disadvantages can be overcome by the present invention.

According to a first aspect, the present invention provides a method of decorating a moulded article comprising applying a screen printed or formed decoration to the surface of a mould whereby the decoration will be bonded to the surface of the moulded article during moulding and thereafter moulding the article characterised in that the decoration is screen printed or formed onto a backing sheet and is applied as a preformed item to the surface of the mould.

By screen printing or forming the decoration on a backing sheet as a separate operation the delay involved in applying the decoration to the mould is greatly reduced. The preformed or preprinted decorations can be made by a separate process weeks or months ahead of the moulding operation and the preformed decorations can be stored and used only when needed. The storage time will, of course, be sufficient so as to avoid the need for further delay in the premoulding operation normally associated with screen printing techniques within the mould.

According to a first embodiment, the decoration to be applied to the surface of the mould is produced as a preformed item by a process comprising printing or otherwise forming the decoration using a pigmented hardenable liquid material onto a backing sheet and then coating the pigmented hardenable liquid material on the backing sheet with a layer of a transparent hardenable resin composition. The thus-produced preformed decorated item has a layered structure comprising a backing sheet on the surface of which there is provided a continuous or discontinuous layer of pigmented material and provided, at least, over the layer of pigmented material is a layer of a transparent hardenable resin composition.This preformed decorated item may be applied to the surface of the mould, prior to the moulding operation, by firstly coating the surface of the mould with a layer of a transparent hardenable resin composition and then placing the preformed decorated item on the coated surface of the mould such that the layer of transparent hardenable resin composition on the preformed item is in intimate contact with the layer of transparent hardenable resin composition provided on the mould surfae. After allowing the layers of transparent hardenable resin composition to undergo crosslinking, the backing sheet may be peeled off in readiness for the moulding operation.

According to a second embodiment, the decoration to be applied to the surface of the mould is produced as a preformed item by a process comprising printing or otherwise forming the decoration using a pigmented hardenable liquid material onto a backing sheet which is typically provided with a layer of an adhesive on the underside thereof. Preferably, a layer of a transparent hardenable resin composition is provided between the surface of the backing sheet and the pigmented material.

This preformed decorated item may be applied to the surface of the mould, prior to the moulding operation, by bringing the adhesive undersurface of the backing sheet into intimate contact with the mould surface. After the moulding operation, the decoration is transferred to the surface of the moulded article while the backing sheet remains bonded to the mould surface.

The technique of screen printing is well known; the technique uses a cloth, such as silk or a fine mesh synthetic material, (e.g. nylon), through which liquid material is squeezed. Such screening techniques enables thin, even layers less than 100 microns in thickness and more particularly less than 50 microns in thickness to be applied to a surface. In contrast, alternative techniques such as spraying or painting apply much thicker layers.

The pigmented hardenable liquid material used in the various embodiments of the invention may be any liquid material that is capable of hardening which contains one or more pigments, dyes or other colouring matter and which is capable of being applied to a surface by a technique such as screen printing or by utilizing stencils. In general, resin-containing inks (for instance, PVC ink) can be used although care has to be taken in ensuring compatibility between an ink and the transparent hardenable resin composition with which it comes into contact in the performance of the invention. Preferably, however, the pigmented material will be a hardenable resin composition containing one or more pigments etc. Examples of suitable/resin compositions include polyester resins, acrylic resins and phenol-formaldehyde resins, with unsaturated polyester resins being especially preferred.

The present invention enables the application to a moulded article of a decoration obtained by printing with a resin loaded with a significant amount of pigment, typically containing more than 10% by weight but not exceeding 90% by weight of pigment. The use of such high loadings of pigment in a resin is discouraged in the art since it is generally believed that at pigment loadings greater than 10% by weight the resin will not set. If a pigmented resin can not set properly, any printed image using the pigmented resin will, likewise, not set properly and may be liable to premature breakdown. By using the present invention a decoration formed by a pigmented resin having a high pigment content can be provided on a moulded article which decoration is protected by a hard resin layer obtained by the hardening of the hardenable resin composition. It is believed that the layer of hardenable resin composition overlying the decoration on the surface of the moulded article may contribute towards the setting of the decoration by the chemical crosslinking of the pigmented material and the hardenable resin composition.

The pigmented material is applied to the surface of a backing sheet to produce the desired decoration. By "decoration", I mean not only decorative designs applied for the purpose of mere ornamentation but also letters, words, symbols, logos and other types of presentation of visual information which it may be desired to apply to a moulded article. The decoration is preferably applied by a conventional screen printing technique or a stencilling technique to the surface of the backing sheet.

In the case of the second embodiment described above, it is particularly preferred that a layer of transparent hardenable resin composition is applied on the backing sheet prior to the decoration printing or forming step. Obviously, because of the way in which the preformed decoration is applied in the case of the second embodiment, the pigmented material will be printed or formed on the backing sheet in the mirror image of the desired decoration to be applied to the moulded article.

The backing sheet is preferably flexible since it enables, as has already been described, the application of the design to mould surfaces which are not flat. Any backing sheet can be used which retains its integrity during the manufacture of the preformed decoration and during the application of the decoration to the moulded article. Typically, the backing sheet will be a transparent plastics sheet although it is equally possible to use sheets which are opaque if they are to be removed during the process of applying the preformed decoration to the moulded article. I have achieved good results using, as the backing sheet, a sheet of poly(ethylene terephthalate) which is available commercially under the name "Melinex" ("Melinex" is a registered trade mark).In order to facilitate the removal of the backing sheet from the preformed decoration during the process of applying the preformed decoration to the moulded article, the surface of the backing sheet should preferably be precoated with a layer of release agent. Release agents and coatings are widely available and the choice of such for use in the present invention is not critical.

According to the second embodiment described above, the backing sheet will advantageously be provided with an adhesive layer on its reverse side.

The transparent hardenable resin composition used to prepare the preformed decorated item in the present invention preferably comprises a resin which is chemically similar to the resin used in the pigment material since it may then be possible for cross-linking to take place between the pigmented resin layer and the transparent resin layer. Examples of suitable resins include phenolic resins, acrylic and polyester resins used together with their appropriate hardener systems. Especially preferred for use in the present invention are unsaturated polyester resins which are, in general, prepared by reacting mixtures of unsaturated and saturated dibasic acids (for example, maleic acid, phthalic acid and isophthalic acid) or their anhydrides with dihydric alcohols (for example, ethylene glycol, propylene glycol and diethylene glycol) in styrene monomer.Such unsaturated polyester resins will generally be in the form of a 'gel coat' which contains a catalyst/activator system and one or more wax additives. Such gel coats form, after application, gels wherein the polymer is partially cross-linked. Typically, catalyst/activator systems for unsaturated polyester resins comprise a peroxide initiator such as methyl ethyl ketone hydroperoxide and a styrene-soluble multivalent metal salt activator such as cobalt naphthenate or cobalt octoate.

According to a preferred embodiment, the pigmented resin composition comprises a pigmented unsaturated polyester resin composition and the transparent hardenable resin composition is an unsaturated polyester resin 'gel coat' composition.

In the first described embodiment of the invention,the method typically comprises applying to the surface of the mould in the area of the mould which is to carry the decoration a coating of a transparent hardenable resin composition and, thereafter, applying the decoration to the coated area. It is highly preferred that the transparent hardenable resin composition used to precoat the mould surface is chemically similar to the transparent resin composition which overlies the pigment layer in the preformed decoration since then it is possible for the two layers, when in intimate contact with each other, to cross-link together. For this reason, the transparent hardenable resin composition used to coat the mould surface will typically be an unsaturated polyester resin 'gel coat' of the type described above.Preferably the method of the first embodiment of the invention comprises applying the preformed decoration on the backing sheet over the coated area of the mould surface with the hardenable resin layer of the preformed decoration in contact with the coating, pressing the backing sheet against the mould surface to expel any air and form a close uninterrupted bond between the coating on the mould and the preformed decoration, allowing the hardenable resin layer of the preformed decoration and the hardenable resin in the mould coating to cure, peeling the backing sheet form the decoration now bonded to the coated area and moulding the article.Release tape may be placed on the mould surface, prior to the coating thereof with the transparent hardenable resin, to form a frame around the area of the surface to which the resin is to be applied, followed by applying the resin inside the frame so formed and applying to the coated surface a decoration preformed on a backing sheet of size and form sufficient to extend over the frame whereby the subsequent release of'the backing sheet is facilitated.

In the second described embodiment of the invention, the method preferably comprises bonding adhesively to the surface of the mould the backing sheet which preferably has on its other, i.e. non-bonded, side a release agent which is coated with a layer of a transparent unsaturated polyester resin 'gel coat' composition onto which is provided a continuous or discontinuous coating of pigmented unsaturated polyester resin composition.

According to both the first and second described embodiments, the material to be moulded to produce the decorated article will preferably be a glass fibre reinforced polyester resin having a surface coating of a polyester 'gel coat' composition which is compatible with and which is capable of crosslinking with the polyester 'gel coat' composition utilized in the preformed decoration. According to this, during the moulding operation, the polyester 'gel coat' of the preformed decoration bonds to the polyester 'gel coat' on the surface of the moulded article whereby, after curing, the decoration becomes permanently bonded into the surface layer of the moulded article.

According to a further aspect, the present invention provides a method of decorating a moulded article comprising the steps: (a) providing a preformed decoration comprising a backing sheet coated on one surface thereof with a layer of a transparent hardenable resin composition, said layer having a decoration printed or formed thereon using a pigmented hardenable liquid material; (b) applying, to a surface of a moulded article, a layer of an optionally pigmented hardenable resin composition; (c) placing the preformed decoration onto the layer of hardenable resin composition on the surface of the moulded article such that the pigmented material of the preformed decoration is in intimate contact with the layer of hardenable resin composition on the surface of the moulded article; (d) allowing the layers of hardenable resin composition to cure; and (e) peeling off the backing sheet to leave a decorated surface layer on the moulded article.

This further aspect of the invention utilizes the general concept of preforming a decorated item and applying the same to a moulded article, as described above. The backing sheet, the pigmented material and the hardenable resin compositions may be as described earlier in connection with the first and second embodiments of the invention.

Preferably, in order to improve the bond between the surface of the moulded article and the layer of hardenable resin composition (which may be clear or pigmented), the surface of the moulded article may be prior etched or abraded. By this technique, it is possible to produce raised areas on the article surface which enables the production of a three-dimensional decorative effect. Typically, the site on the article surface to be provided with the preformed decoration will be framed using a release tape, the framed area is then abraded, the hardenable resin composition is then applied in the framed area and the preformed decoration is then placed on the site with the pigmented material of the decoration in intimate contact with the layer of hardenable resin on the article surface.As in the case of the second embodiment described above, the pigmented material will have been printed or formed on the preformed item in the mirror image of the desired final decoration.

After curing of the surface layers on the article, the backing sheet is peeled off.

The invention also includes a moulded product decorated by the methods set forth above.

The invention will now be described with reference to the accompanying drawings wherein: Figure 1 illustrates diagrammatically a simple mould in which a decoration is applied by the method of the first embodiment set forth above, and, Figure 2 illustrates the mould of Figure 1 after the decoration has been applied.

Referring to the drawings, a simple mould 10 is provided with a rectangular moulding recess 11 within which is to be moulded a simple rectangular plate in glass fibre with a surface moulded in polyester resin.

Where it is intended that the moulded article is to be decorated on its surface it would be usual to decorate the corresponding surface of the mould, in this case the base 12 of the mould, by a silk screen technique in a manner such that the silk screened decoration will bond to the surface of the article to be moulded within the mould thereby forming a decorative moulded product.

The problem associated with silk screening within the mould is that the decoration can only be applied within the frame of the silk screen and cannot, for example, be applied onto the corners or around curved surfaces of the mould but can only be applied in a relatively central area within the mould. Furthermore, the silk screen technique itself delays the moulding process by increasing the preparation time both for the printing and for any curing which must take place before the moulding operation can commence.

In the method according to the present invention a 'Melinex' film approximately 50 microns thick and shown in the Figures at 13 is coated by a silk screen technique with a decoration 14 formed from a pigmented unsaturated polyester resin. An approximately 50 micron coating forming the decoration, in this case a letter "B", is applied to the sheet 13 a separate operation some weeks before the moulding operation. The printing decoration is coated with a clear isophthalic acid-based polyester gel coat supplied by West & Senior Limited under their reference WS196#A. Again that coating is applied to a depth of about 50 microns. A series of such decorated sheets can be prepared and stored for weeks or months until needed in the moulding process.By coating the screened decoration with cross-linking top gel coat the pigmented resin will partially cure and remain ready for use for extended periods of time.

The surface 12 of the mould has applied thereto a frame of double sided polypropylene tape 15 the purpose of which is to facilitate the release subsequently of the film 13 when it is peeled from the surface of the mould.

The rectangular frame of tape 15 defines the area on the surface of the mould within which the decoration is to be applied. Within that frame a coating of the same gel coat as previously used in coating the decoration on backing sheet 13 is applied by brushing onto the surface of mould 12. Thereafter the backing sheet 13 is placed over the area within tapes 15 with the decoration 14 face down such that the clear coating on the decoration comes into contact with the coating on the surface of the mould.

Using a roller or other suitable appliance, the film 13 is rolled and squeezed such as to exclude all air which may be disposed between the film 13 and the surface 12 of the mould and to ensure that a firm bond exists between the gel coat forming the coating on the surface 12 and the gel coat covering the pigmented polyester resin forming the preformed decoration 14.

The film is left in position on the surface 12 of the mould for about 20 minutes at 200C to ensure that the coatings have completely cross-linked and set.

Thereafter, the film 13 is peeled away from the surface 12. The tape 15 facilitates this removal by forming the discontinuity and a well defined edge at the inner edge of the tapes.

Thereafter the tape 15 is removed from the surface 12 leaving, as shown in Figure 2, the pigmented polyester resin forming the decoration 14 bonded to the coating on the mould surface.

Thereafter the article is moulded within the mould 10 using, for example, glass fibre material with the surface coating of a polyester gel coat which is compatible with and cross-links with the gel coat covering the pigmented polyester resin forming decoration 14.

Thus, a bond will be formed during the moulding operation between the polyester gel coat surrounding the decoration 14 and the polyester gel coat upon the surface of the article to be moulded whereby the decoration becomes permanently bonded to the surface of the moulded article.

The technique for decorating the moulded product may be used in the manufacture of signs and articles formed of plastics materials, such as glass fibre reinforced plastics products and polypropylene and provides greatly reduced processing times by avoiding the need for screen printing within the mould immediately prior to moulding. By screen printing the decoration as a separate step and storing the screen printed decoration ready for use the processing time at the mould can be greatly reduced.

Furthermore, by mounting the screen printing decoration on a flexible sheet the decoration can be placed around the curved surfaces and corners which could not normally be reached by the frame of a screen printed technique where it is applied within the mould.

Although described by reference to screen printing techniques, it will be appreciated that any appropriate screen can be used, not only silk but also synthetic material such as nylon and, furthermore, any stencilling technique could be employed provided thin layers of material can be produced.

Claims

CLAIMS:

1. A method of decorating a moulded article comprising applying a screen printed or formed decoration to the surface of a mould whereby the decoration will be bonded to the surface of the moulded article during moulding and thereafter moulding the article characterised in that the decoration is screen printed or formed onto a backing sheet and is applied as a preformed item to the surface of the mould.

2. A method according to claim 1, wherein the decoration to be applied is produced as a preformed item by a process comprising printing or forming the decoration using a pigmented hardenable liquid material onto a backing sheet and then coating the pigmented hardenable liquid material with a layer of a transparent hardenable resin composition.

3. A method according to claim 2, wherein, prior to applying the preformed decoration, the surface of the mould is coated with a transparent hardenable resin composition.

4. A method according to either claim 2 or claim 3, wherein the transparent hardenable resin composition comprises an unsaturated polyester resin, a catalyst/activator system and at least one wax additive.

5. A method according to claim 3 or claim 4, wherein the preformed decoration is applied such that the hardenable resin layer of the preformed decoration is brought into contact with the coating of transparent hardenable resin composition on the surface of the mould, applying pressure to the backing sheet so as to expel any air and to form a close uninterrupted bond between the coating and the preformed decoration, allowing the hardenable resin layer of the preformed decoration and the hardenable resin in the mould coating to cure and then peeling away the backing sheet from the preformed decoration bonded to the coating.

6. A method according to claim 1, wherein the decoration to be applied is produced as a preformed item by a process comprising coating a backing sheet with a layer of a transparent hardenable resin composition and then printing or forming on the layer of resin a decoration using a pigmented hardenable liquid material and wherein the preformed item is applied to the surface of the mould by adhesively bonding the reverse side of the backing sheet to the mould surface.

7. A method according to claim 6, wherein the backing sheet has a layer of adhesive on the underside thereof.

8. A method according to any one of claims 1 to 7, wherein the pigmented hardenable liquid material is a pigmented resin composition which is capable of undergoing cross-linking with the transparent hardenable resin composition.

9. A method according to claim 8, wherein the pigmented resin composition is a pigmented unsaturated polyester resin composition and the transparent hardenable resin composition is an unsaturated polyester resin composition containing a catalyst/activator system for the resin and one or more wax additives.

10. A method according to any one of claims 1 to 9, wherein the backing sheet is a flexible sheet of a transparent plastics material.

11. A method according to any one of claims 1 to 10, wherein the surface of the backing sheet is precoated with a layer of release agent prior to the application thereto of the pigmented material and/or hardenable resin composition.

12. A method of decorating a moulded article comprising the steps: (a) providing a preformed decoration comprising a backing sheet carrying on one surface thereof a decoration printed or formed thereon using a pigmented hardenable liquid material; (b) applying, to a surface of a moulded article, a layer of an optionally pigmented hardenable resin composition; (c) placing the preformed decoration onto the layer of hardenable resin composition on the surface of the moulded article such that the pigmented material of the preformed decoration is in intimate contact with the layer of hardenable resin composition on the surface of the article; (d) allowing the layer of hardenable resin composition to cure: and (c) peeling off the backing sheet to leave a decorated surface layer on the moulded article.

13. A method according to claim 12, wherein the preformed decoration comprises a backing sheet coated on one surface thereof with a layer of transparent hardenable resin composition, said layer having a decoration printed or formed thereon using a pigmented hardenable liquid material.

14. A moulded article decorated according to a method claimed in any preceding claim.