WO2003106134A1

WO2003106134A1 - Improvements in or relating to decoration of plastics articles

Info

Publication number: WO2003106134A1
Application number: PCT/GB2003/002592
Authority: WO
Inventors: Richard Anthony Hann; Andrew Clifton; Stephen Mann
Original assignee: Imperial Chemical Industries Plc
Priority date: 2002-06-18
Filing date: 2003-06-16
Publication date: 2003-12-24
Also published as: GB0213921D0; WO2003106134A8

Abstract

The present invention relates to a method of making a plastics article bearing a printed image, the method comprising printing an image onto a carrier material by means of a digital imaging technique, and forming the article by an injection moulding process involving in-mould decoration to produce an article with the carrier material and image incorporated therein. The method of the invention can enable the production of moulded plastics articles with photographic quality or near photographic quality decoration by use of a digital imaging technique, e.g. thermal dye transfer printing, ink jet printing and electrophotography, to produce the image. Such techniques print good quality images and are more versatile than the printing techniques of the prior art. Images can typically be printed quickly and easily using a digital imaging technique, enabling articles bearing a short-run or one-off image to be produced.

Description

Title: Improvements in or relating to decoration of plastics articles

Field of the Invention

This invention relates to a method of making a plastics article bearing a printed image by an injection moulding process involving in-mould decoration (referred to hereinafter for simplicity and brevity as "IMD") and to a plastics article bearing a printed image.

Background to the Invention

Injection moulding is a well known industrial process for producing 3-dimensional (3D) plastics articles using various types of thermoplastic resins, in a fast and economical manner. The process is described in more detail in text books such as Ossward T.A. and Gramann P., The Injection Molding Handbook, published by Carl Hanser, 2001. Briefly, a molten thermoplastic resin is forced into a cavity in a mould, typically a metal mould known as a tool, at high pressure where it adopts the internal shape of the cavity. Cold water is generally circulated through the body of the mould to reduce the cooling time of the moulding. When cool, the mould is opened and the moulding removed. Typical cycle times are around twenty seconds and several articles or parts of articles can be made from each tool if required. The particular thermoplastic resin used is chosen with regard to cost considerations and the desired mechanical properties required from the final moulded article or part of an article. Typical examples of thermoplastic resins used in injection moulding include acetal, polypropylene, ABS plastics and polycarbonate, which generally have different melt temperatures and melt flow characteristics. For example, acetal has a melt temperature typically between 175-195°C, polypropylene has a melt temperature typically between 200-215°C, ABS has a melt temperature typically between 240-250°C and polycarbonate has a melt temperature of about 300 °C.

A moulded article or part of an article can be coloured or decorated in a variety of ways. The simplest approach is to incorporate a pigment into the thermoplastic resin to produce a coloured moulded article or part. The colour of the article or part will correspond to that of the pigment, and a number of different colours can be produced. The surface of a moulded article or part may also be coloured. This can be achieved by spraying the moulded article or part after moulding. However, this approach is more expensive than simply forming a coloured moulded plastics article or part, as it requires extra process equipment, materials and time. Further, surface colour can only be provided to a particular area. If text or photographic images are required as decoration, other methods can be employed post-mould. These include screen printing, tampo printing and thermal transfer printing. Such methods however tend to leave colorants on the surface of the article or part, so that the images are subject to damage.

Within the last few years, a new decoration technique known as in-mould decoration (IMD) has gained acceptance and use in the moulding industry and solves several of the problems associated with the above mentioned prior art techniques; see for example US 4,059,471, US 4,650,533, US 4,356,230 and US 4,202,663. IMD combines the process of forming an article by injection moulding with decoration of the article. In this method, a plastics carrier sheet, typically of polyester, poly(methylmethacrylate) or polycarbonate, bearing a printed image, is placed in the cavity of an injection moulding tool. Molten thermoplastic resin is then injected into the cavity to contact the carrier sheet. Carrier sheets of polyester may be either crystalline or amorphous, depending on the application. Crystalline polyester carrier sheets have a higher operating temperature and so are tougher, but are difficult to distort. Accordingly, crystalline polyester carrier sheets can be used where the article or part of an article to be moulded is reasonably flat. Amorphous polyester carrier sheets, or the more expensive carrier sheets of poly(methylmethacrylate) or polycarbonate often have to be used for shaped articles or parts of articles, having greater formability. With suitable design of the injection moulding tool, the pre-printed plastics carrier sheet becomes integral to the moulded article or part. This is contrasted with the process described, for example, in EP 0799681, where an image is transferred onto an article during the injection moulding process. The moulding process disclosed in EP0799681 is reaction injection moulding, whereby reactive polymer components are injected into a mould at a relatively low temperature. The reactive components are mixed by injection and undergo a reaction which raises the temperature of the mixture in the mould and produces hardened, thermoset cross-linked polymers. In order to transfer the image to the moulded article, the reaction is interrupted part way through at the gel stage, when the mould is opened and an image applied to a suitable carrier sheet is introduced into the mould. The mould is closed and the reaction is completed. The carrier sheet is then removed from the mould.

IMD is used successfully in producing automative and mobile phone parts with complex decoration. The image is embedded in the part and is protected by the thickness of the carrier sheet, which can have a thickness of between 100-750μm, depending on the design requirements of the part. Recent advances in IMD are described in the following patents and references therein: US 6,331,263; US 6,326,086; US 6,325,607; US 6,270,331; US 6,071,456; US 6,001,292; US 5,945,059 and US 5,925,302.

Several methods are known for producing the print on the carrier sheet; these include gravure printing, screen printing and off-set lithographic printing. These are established printing techniques and are best suited to long runs of the same image, as there are significant set-up costs in changing the artwork and associated tooling such as printing cylinders or screens. These conventional printing methods are thus not suitable to short- run decoration of an article using IMD. A further disadvantage associated with some of these techniques is that they cannot produce true photographic quality images on the plastics carrier sheets used for in-mould decoration.

The presently claimed invention aims to address these shortcomings of the prior art and provide a method for producing e.g. short-run, durable photographic quality, or near photographic quality, decoration of plastics articles.

Summary of the Invention

In one aspect the invention provides a method of making a plastics article bearmg a printed image, the method comprising printing an image onto a carrier material by means of a digital imaging technique, and forming the article by an injection moulding process involving in-mould decoration to produce an article with the carrier material and image incorporated therein.

The method of the invention can enable the production of moulded plastics articles with photographic quality or near photographic quality decoration by use of a digital imaging technique, e.g. thermal dye transfer printing, ink jet printing and electrophotography, to produce the image. Such techniques print good quality images and are more versatile than the printing techniques of the prior art. Images can typically be printed quickly and easily using a digital imaging technique, enabling articles bearing a short-run or one-off image to be produced.

The method of the invention results in the formation of a plastics article incorporating the carrier material bearing an image printed by a digital imaging technique as part of the article. As defined above the article is formed by the process of injection moulding involving in-mould decoration which involves the steps of placing the carrier material bearing a printed image in a cavity having a shape complementary to the shape of the article, injecting molten thermoplastic resin into the cavity to form the article whereby the carrier material bearing the image is incorporated in the article, cooling the mould and separating the decorated plastics article from the mould.

The carrier material is typically in the form of a film or sheet of suitable material. Typical carrier materials include polymeric materials having suitable properties including dimensional stability, optical transparency, translucency or opacity, tensile strength, adhesion characteristics, thermal stability, and hardness, for the intended purpose. Preferably, the carrier material is in the form of a carrier sheet and more preferably a transparent carrier sheet. Transparent polymeric carrier materials suitable for use in the production of transparencies include sheets or films of crystalline polyester, e.g. poly(ethyleneterephthalate) (PET) such as Melinex (Melinex is a Trade Mark of DuPont Teijin Films), amorphous polyester supplied, for example, by European Vinyls Corporation, poly(methylmethacrylate) such as Rohaglas (Rohaglas is a Trade Mark of Cyro Industries), or polycarbonate (PC) supplied, for example, by General Electric USA and Bayer AG. Such transparent sheets typically have a thickness in the range of about 50μm to about 250μm.

The carrier material may optionally support a coating of an appropriate image-receptive composition, hereinafter "the receiver layer", the nature of which is dependent upon the digital imaging technique used to print the image. Typically, the carrier material comprises a receiver layer, although it may be possible to print an image directly onto a surface of, e.g. a polycarbonate sheet.

The receiver layer coating is conveniently formed by mixing coating materials (to be discussed below) which are appropriate to the digital imaging technique used with a suitable solvent or solvent mixture, as is known in the art. The coating materials may be applied by any suitable coating technique, including those known in the field, e.g. by use of a Meier bar, by roller coating, rod coating, slide coating, curtain coating, doctor coating etc.. The receiver layer coating may then be dried in a known manner.

The receiver layer coating may be applied to the entire surface of the carrier material or to selected areas only of the carrier material. In the case of a sheet or film of carrier material, the receiver layer coating will typically be applied to at least one surface.

Drying of the receiver layer coating may be effected by conventional drying techniques, for example by suspending the coated carrier material in a hot air oven maintained at an appropriate temperature. A drying temperature of about 110 to 130°C is usually suitable for a crystalline polyester carrier sheet. Because of their low deformation temperature, amorphous polyester carrier sheets require a drying temperature of about 50°C.

The thickness of the coating when dry may vary over a wide range, but is conveniently in the range lμm to lOOμm, preferably 50μm or less, especially in the range from 2μm to lOμm, for carrier materials for use in thermal dye transfer printing, in the range lOμm to 50μm for carrier materials for use in ink jet printing, and in the range lμm to 5μm for carrier materials for use in electrophotography.

The receiver layer coating desirably includes particulate filler material as described in WO 00/74944, to modify the mechanical properties of the coating and also (for carrier material for use in ink jet printing) to modify the porosity of the coating.

The carrier material may further optionally include one or more back coats (also known as a hard coat) on the side of the carrier material remote from the image-receiving surface. These are generally based on ultraviolet radiation curable polymers, and typically include various types of particulate filler material at different concentrations to deliver different optical and textural finishes to the article. Conventional back coated carrier sheets of polycarbonate and polyester are supplied, for example, by Autotype International of Wantage, UK and Kurz of Furth, Germany.

As described above, the image on the carrier material is produced by digital imaging. Digital imaging is the capture of images in an electronic digital form, e.g. by use of a digital camera, and their subsequent manipulation and printing. Printing techniques used for digital imaging include thermal dye transfer printing, ink jet printing and electrophotography, using an appropriate carrier material in each case. A preferred digital imaging technique for use herein is thermal dye transfer printing.

Thermal dye transfer printing is a generic term for processes in which one or more thermally transferable dyes are caused to transfer from a dyesheet to a receiver in response to thermal stimuli to thereby form an image. Using a dyesheet comprising a thin substrate supporting a dyecoat containing one or more such dyes uniformly spread over an entire printing area of the dyesheet, printing can be effected by heating selected discrete areas of the dyesheet while the dyecoat is pressed against a receiver sheet, thereby causing dye to transfer to corresponding areas of that receiver. The shape of the image transferred is determined by the number and location of the discrete areas which are subjected to heating. Full colour prints can be produced by printing with different coloured dyecoats sequentially in like manner, and the different coloured dyecoats are usually provided as discrete uniform print-size areas in a repeated sequence along the same ribbon-like dyesheet.

High resolution photograph-like prints can be produced by thermal dye transfer printing using appropriate printing equipment, such as a programmable thermal print head or laser printer, controlled by electronic signals derived from video, computer, electronic still camera, or similar signal generating apparatus. A typical high speed thermal print head has a row of individually operable tiny heaters spaced to print six or more pixels per millimetre, using very short hot pulses.

A carrier material for thermal dye transfer printing is generally in the form of a sheet which optionally supports a receiver layer of a dye-receptive composition for receiving an image, containing a material having an affinity for the dye molecules, and into which they can readily diffuse when an area of dyesheet pressed against it is heated during printing in order to provide good colour density. Materials with good dye-affinity are generally thermoplastic polymers, such as polyesters, soluble in common solvents to enable them readily to be coated onto the carrier sheet from solution.

The thermal dye transfer printing temperature and the highest temperature at which a thermoplastic resin is injected during in-mould decoration, is around the same at 300°C, e.g. for polycarbonate. Therefore, it is thought that if a typical thermal dye transfer printing carrier material supporting a receiver layer is used in the method in accordance with the presently claimed invention, an amount of sideways diffusion of dyes in the printed image is likely to occur during the moulding process. In practice, the amount of diffusion or image spread will depend on the temperature distribution during the mouldmg process, as well as the choice of dyes and the composition of the receiver layer. It is known in the art that simple carrier sheets such as unvoided polyester or polycarbonate films can give lower image quality than is obtained from softer, voided carrier sheets. This lower image quality arises because the dye is transferred in a more localised fashion, giving visibly distinct dots in the image. From this point of view, it may be desirable in some cases to have a small amount of sideways migration, as this can hide the existence of the dots and enhance the overall image quality.

Generally, in order to limit the sideways diffusion of dye in a printed image at the high temperatures experienced by the receiver layer during in-mould decoration, the polymeric material of the receiver layer should be selected with regard to its thermal softening point (or Tg) and/or cross-link density.

A receiver layer comprising polymeric material of low Tg will promote lateral dye migration (or "dye bleed") and hence, image degradation during moulding. Raising the Tg of the polymeric material of the receiver layer will reduce the free volume in the layer during moulding and thereby reduce dye bleed. Care should be taken not to raise the Tg of the polymeric material too far as this will result in limited dye penetration and poor initial image quality. Thus, typically, the receiver layer comprises polymeric material having a Tg in the range of 45 °C to 70 °C. Examples of suitable polymeric material include soluble polyesters such as Nitel PE200 (Nitel is a Trade Mark of Goodyear) and Nylon GK880 (Nylon is a Trade Mark of Toyobo).

Dye mobility during in-mould decoration may also be reduced by cross-linking the polymeric material of the receiver layer. The receiver layer is preferably cross-linked with the level of cross-linking being important: if the level of cross-linking is too high, dye penetration is inhibited, thereby reducing the initial image quality, whereas if the level of cross inking is too low the coating is liable to flow and distort the image. The degree of cross-linking is determined by the molecular weight of units between the cross-linkable functional groups and is preferably greater than 500 and less than 10,000.

Suitable polymeric material for the receiver layer includes polycarbonates, polyesters, polyurethanes, polyvinylchloride/polyvinylacetate copolymers, acrylic copolymers and styrene copolymers. The receiver layer may optionally comprise a release agent to reduce adhesion of the coating to the dyesheet such that the receiver layer may be released from the dyesheet after prmting without damage to the printed image or the dyesheet. Suitable release agents include a functional silicone moiety, which can be thermally cross-linked during the coating process to provide a low adhesion surface. Such release agents are described in detail in US 5,229,352. The presence of release agents in the receiver layer can however provide a weak point in the decorated plastics article, possibly resulting in delarαination of the carrier material bearing a printed image from the article during use. This may be prevented, for example, by optimising the amount of silicone material in the receiver layer, using a different release agent such as a high molecular weight alkyd or masking the release layer from the resin used to form the article (as described below).

In ink jet printing, a stream of ink droplets is projected onto an ink receptive carrier material at high velocity, e.g. up to 20 m/s. Movement of the ink jet may be computer controlled, and images may be formed and printed rapidly. By using inks of different colours a full colour image can be produced. In general, ink jet printing inks may be water-based or organic-based compositions that are usually dye-based or pigment-based solutions. Such inks are widely used in a range of ink jet printers, for commercial, office and domestic use including desk-top printers, to produce photographic quality images. A carrier material for use in ink jet printing generally comprises a carrier sheet carrying an ink absorbent layer that typically comprises a polymer or mixture of polymers, e.g. cellulosic polymers such as carboxymethyl cellulose and especially hydroxy ethyl cellulose; gelatins; vinyl polymers such as poly vinyl acetate, poly vinyl alcohol and poly vinyl pyrrolidone; acrylic polymers such as polyacrylic acid; or an open network, known as a microporous system which typically includes inorganic material such as silica, but may also comprise organic polymeric materials.

Unlike thermal dye transfer printing, ink jet printing does not involve the application of heat to transfer ink to a receiver layer. Thus, dye bleed is not thought to be an important consideration for ink jet printing. Of greater significance is achieving good adhesion of the printed image to the carrier material. Poor adhesion between the printed image and carrier material may arise, as there may be small amounts of solvent retained in the printed image from the printing process. For this reason, it is preferred to dry the printed carrier material thoroughly, e.g. in an oven, before use in the injection moulding process. Further, some materials used for the receiver layer in ink jet printing, such as cellulosic polymers for example, have poor intrinsic adhesion to thermoplastic resins such as polycarbonate and polyester used to form the moulded article. It is therefore desirable to select materials which provide good adhesion, as would be known to those skilled in the art. Microporous materials such as those present in ICI Imagedata Ink Jet Product 2PI188 may also entrap air in the receiver layer during the moulding process. Whilst this can produce a decorative effect, the strength of the bond between the thermoplastic resin of the moulded article and the carrier sheet may be reduced. Thus, it is generally preferred not to use this type of ink jet receiver layer.

In electrophotography, a latent image corresponding to the desired final image is initially written onto a photosensitive drum of, for example, a photocopier, a desktop laser printer (such as those supplied by Hewlett-Packard or Canon) or an industrial version thereof known as a digital press (e.g. supplied by Xeikon), by a low power laser. The image is then produced by transferring particles of fusible toner onto an image-receiving carrier sheet. Full colour images can be produced by using toner particles of yellow, magenta, cyan and black.

The toner can come in various forms such as "dry" or "liquid". Liquid toners are used in printers supplied, for example, by Indigo N.V..

It is preferred to use a carrier material in the form of a carrier sheet comprising plastics material, e.g. a crystalline polyester such as Melinex (Melinex is a Trade Mark). The carrier material, preferably a carrier sheet, may comprise a receiver layer on the sheet.^' Such layers are well known in the art and may comprise, for example, acrylic polymers.

As with ink jet printing, dye bleed is not expected to be an important consideration in electrophotography as the dyes and pigments of the toner are not diffused into the receiver layer (if present). A disadvantage associated with using an image printed by dry-toner electrophotography in an injection moulding process involving in-mould decoration is that true photographic quality of the image may be difficult to achieve. Dry-toner electrophotography has neither the continuous tone capability nor small enough pixel sizes to generate photographic quality colour gradation. The images produced by dry-toner electrophotography are therefore described as near photographic quality, but are suitable for a variety of less demanding decorative applications.

The printed image on the carrier material may be incorporated in the plastics article so that the image is on the exterior surface of the article, known as "first surface printing" . Alternatively, the printed image may be embedded within the article with the carrier material providing a protective layer over the image, known as "second surface printing". Each method has its own advantages and disadvantages. For example, in first surface printing the carrier material bonds easily to the injected thermoplastic resin, but the image is exposed to environmental damage. This may be overcome by using second surface printing where the image is protected by the carrier material, but it can be more difficult to obtain good adhesion between the ink or dye of the printed image and the thermoplastic resin and to prevent the ink or dye being damaged by the resin. The choice of method is determined by many factors including the tool design and the application needs of the final article. A particularly preferred method is second surface printing.

If second surface printing is employed, then, typically, the carrier material of generally polyester or polycarbonate on the surface of the article may be prone to damage, e.g. by scratching. This may be alleviated by employing a carrier material including a back coat as described above.

In a preferred embodiment, an overlay typically including one or more pigments is applied to a printed image on the carrier material, having the image printed directly onto the surface of the carrier material or including a receiver layer printed with the image. The overlay may be conveniently applied using a method such as mass transfer printing where a suitable resin, e.g. of polyester, including one or more pigments is coated on an appropriate substrate which has been primed with a releasing subcoat, e.g. of a highly cross-linked polyacrylate. The pigment-coated substrate is then brought into contact with the image-bearing carrier material and the pigment coating transferred onto the printed image via the application of heat, e.g. using a thermal printer. Preferably, the pigment is a white pigment such as titanium dioxide. However, it will be understood that other pigments, such as coloured, metallic, thermochromic, photochromic, luminous, pearlescent or optically variable pigments could be used in place of or in conjuction with, the white pigment. For example, metallic text could firstly be printed onto the image prior to a white pigment coating being applied to the whole image. This could be achieved, e.g. using a compound ribbon containing both dye diffusion transfer and mass transfer panels or separate ribbons of dye diffusion and mass transfer coatings. The mass transfer panel could also have adhesive properties, enhancing the integrity of the plastics articles.

Thus, in a further aspect, the invention provides a method of making a plastics article bearing a printed image, the method comprising printing an image onto a carrier material by means of a digital imaging technique, applying an overlay to the printed image, typically by mass transfer printing, and forming the article by an injection moulding process involving in-mould decoration to produce an article with the carrier material, image and overlay incorporated therein.

The application of an overlay to a carrier material bearing a printed image is particularly advantageous when the image is produced by means of thermal dye transfer printing.

Like all subtractive printing systems, it is not possible to print the colour white by thermal dye transfer printing, e.g. to provide a white background for an image. Accordingly, the thermoplastic resin forming the article can be loaded with a white pigment such as titanium dioxide. Alternatively, an overlay, e.g. of white pigment, can be applied over an image printed by thermal dye transfer printing. In order to facilitate the transfer of the typically white overlay, it is possible to optionally incorporate the overlay when printing the original image, e.g. in the form of an additional panel of material in each sequence of an ink ribbon giving a YMC(W) assembly, or the overlay can be applied from a separate, continuous ribbon. The application of an overlay to the printed image may mask the image from the thermoplastic resin of the article, thereby improving adhesion and reducing the possibility of damage to the image.

An alternative method for protecting the image during the injection moulding process is to interpose a separate film of polymer between the printed image in the carrier material and the interior of the mould. The film may optionally be coloured, e.g. with pigments.

Thus, preferably, a carrier material for use in an injection moulding process involving in- mould decoration, comprises a carrier sheet, e.g. of polycarbonate or polyester, comprising a back coat on the side of the carrier sheet remote from the image-receiving surface, the image-receiving surface of the carrier sheet optionally supporting an appropriate receiver layer, onto which an image is printed and an overlay covering the printed image-receiving surface, possibly a receiver layer.

The invention also includes within its scope a plastics article bearing a printed image produced by a method in accordance with the invention.

The invention will be further described, by way of illustration, with reference to the following examples.

Example 1

A coating solution was prepared having the following composition:

A pol ol in butyl acetate (Trade ref 84-46-008 from PPG Industries) 5.0g

An oligomeric isocyanate in butyl acetate (Trade ref 870-10-002 from PPG Industries) l.Og

Xylene 1.5g The solution was applied with a wire-wound bar at a wet thickness of 36μm to a sheet of 175μm clear PET (supplied by DuPont Teijin Films). The coating was dried in an oven at a temperature of 110° C for 90 seconds to give a clear and colourless coating of about 8μm in thickness. The Tg of the coating was 65 °C.

The carrier sheet so formed was printed with a fine line pattern at 300 dots per inch (d.p.i) (about 118 dots per cm) (sample A) using a standard magenta dye diffusion ribbon from ICI Imagedata (Product Code 102058). A custom-designed laboratory thermal printer was employed to print the carrier sheet, using a thermal print head (Kyocera type KST-100- 12MPL-19MBD) driven at 24 volts where the maximum energy supplied to each individual heating element while transferring dye in one area was 0.8 mJ (commonly referred to as 0.8 mJ per dot).

Example 2

A coating solution was prepared having the following composition:

Methyl ethyl ketone 78 cm³

Toluene 78 cm³

Polyester resin-Nylon GK880 26.44g

Crodakyd 132XP 0.57g

Cymel 692 1.058g

Tegomer 6440 26 mg

Nylon GK880 is a Trade Mark and is an amorphous, soluble polyester resin, supplied by

Toyobo Industries.

Crodakyd 132XP is a Trade Mark and is a long-chain alkyd hydrocarbon, supplied by

Crodapol Limited.

Cymel 692 is a Trade Mark and is an isobutylated melamine formaldehyde polymer in isobutanol (40% by weight), supplied by Dyno Cyanamid Limited.

Tegomer 6440 is a Trade Mark and is a polydimethylsiloxane-caprolactam copolymer, supplied by Goldschmidt Limited. The solution was applied with a wire wound bar at a wet thickness of 50μm to a sheet of 175μm clear PET (supplied by DuPont Teijin Films). The coating was dried in an oven at 110°C for 90 seconds to give a clear and colourless receiver layer of about 8μm thickness.

The carrier sheet so formed was printed with a fine line pattern using a standard magenta dye diffusion ribbon from ICI Imagedata (Product code 102058) on a custom-designed laboratory thermal printer described in Example 1 (sample B).

Example 3

In order to simulate the injection moulding process involving in-mould decoration and evaluate the degree of unwanted sideways diffusion of dye from an image printed on a carrier sheet upon contact with hot thermoplastic resin, the following experiment was carried out.

A lOg sample of a polyester resin with a melting point of 280°C, (B80 ex DuPont Teijin Films (B80 is a Trade Mark), a copolymer consisting of 18% isophthalic acid, was heated in an oven to 300°C until it was molten. A printed carrier sheet from Example 1 (sample A) and a printed carrier sheet from Example 2 (sample B) were each maintained at a temperature of 100 °C on electrically heated hotplates to simulate the temperature within the cavity of an injection moulding machine. Molten polyester was then poured onto the printed image of sample A and separately onto the printed image of sample B. The composite carrier sheet and resin assemblies were then removed from the hotplates and allowed to cool naturally to room temperature.

Each composite sheet and resin was then inspected to evaluate the degree of sideways diffusion compared with the original image. In the original image it was possible to see individual pixels under a x8 eyepiece typical of thermal dye transfer printing. Inspection of samples A and B showed that there had been some degree of sideways diffusion (dot spread) although this was less for sample A than sample B. The degree of dot spread in either sample was not enough to make an image unacceptable in a final moulded article. A certain amount of dot spread can be advantageous in order to maximise the perceived print density by reducing any clear space between adjacent pixels.

It is known that the magenta dyes used in the dyesheet have the greatest mobility. Therefore, the other colours of a typical dye diffusion ribbon, e.g. yellow and cyan, would be expected to have lower dot spread under the same conditions. Further, since 300 °C is the highest moulding temperature used, thermoplastic resins which use lower temperatures would also be expected to result in less dot spread.

As acceptable images are obtained with this "worst case" combination of dye and injection temperature, this demonstrates that the process of combining thermal dye transfer printing with IMD is a viable one, and will enable the economical production of injection moulded plastics articles with hard wearing, photographic quality decoration.

Example 4

A polyester film having a thickness of 6μm was coated with a heat resistant back coat to provide protection from the thermal head during the printing process. The back coat was as described in EP 0547893.

A UN-curable subcoat forming a highly cross-linked acrylic coating upon UN-curing was prepared according to the following composition:

Cyan dye 0.08%

MIBK is methyl iso-butyl ketone. This is the solvent from which the subcoat layer is deposited.

Uvecryl E1354 (Uvecryl 1354 is a Trade Mark) is a hexafunctional aromatic urethane aery late oligomer.

Diakon MG102 (Diakon MG102 is a Trade Mark) is a high molecular weight grade of poly methylmethacrylate.

Irgacure 907, Uvecryl P101, Quantacure ITX and Quantacure EPD catalyse the UN-curing of the Uvecryl E1354. (Irgacure 907, Uvecryl P101 and Quantacure ITX and EPD are Trade Marks).

The subcoat was coated onto the 6μm thick polyester film and the solvent evaporated therefrom, before the coating was cured with ultraviolet radiation to give a dry coat thickness of approximately 0.6μm. The curing was effected by passing the coating under the focus of two medium-pressure mercury arc lamps running at an input power of 10W per mm of length of the tube.

A solution of the following composition was then made up using a high speed laboratory mixer:

Nylon GXW27 5g

Titanium dioxide (grade R-TC30 ex Tioxide Ltd) 5g

Methyl ethyl ketone 25g

Nylon GXW27 is a Trade Mark and is an amorphous, soluble polyester resin, supplied by Toyobo Limited. The solution was applied by hand to the subcoat using a Meier bar to give a wet coat thickness of approximately 50μm. The coating was dried in an oven at 110°C, for 90 seconds. The resulting coating was opaque, white and around 3μm in thickness.

The white coating of the sheet prepared above was placed in contact with the image of a printed carrier sheet from Example 2 (sample B) and both sheets were passed through a thermal printer described in Example 1 where a thermal stimulus was applied over the entire imageable area of the sheets.

The sheets were then separated by hand to reveal that all of the white coating had been transferred to sample B as a result of a mass transfer process. The image was thus now obscured from the original printed side, but could be viewed against the new white background provided by the transferred coating from the opposite side of the 175 μm PET substrate.

The resulting white overlay was treated with molten polyester as described in Example 3. Excellent adhesion of the polyester to the white overlay was shown, and the image could be viewed through the transparent 175μm PET sheet against the integral white background which was now embedded within the polyester.

Example 5

A transparent lOOμm PET sheet of GP840 (ICI Imagedata) with an hydroxypropylmethyl cellulose (HPMC) coating was printed on a Hewlett Packard 990 ink jet printer with an image consisting of fine lines and block colours.

The printed sheet was treated with molten polyester as described in Example 3. Inspection of the image showed that there was no degradation of the image.

Example 6 A transparent lOOμm PET sheet of EP200 (ICI Imagedata) with an amorphous polymer coating and polyethylene filler as described in WO 99/36833 was printed on a Canon CLC1150 colour laser copier/printer with an image consisting of a person's face.

Example 7

A sheet prepared according to the method described in Example 1 was cut to the size of the tool cavity in an standard industrial scale injection moulding machine and placed in the cavity. Molten polycarbonate resin was injected into the tool at 300°C under a pressure of several tonnes. After the cavity had been filled with resin, the tool was split and the moulded article ejected and allowed to cool to room temperature. The total cycle time was in the region of 20 seconds. The moulded article showed good integrity and the image was clearly visible through the article, showing no visible degradation of the quality of the image.

Example 8

A solution of 10 parts of Peox 50 (Peox is a Trade Mark of Dow Chemical Company, and is a poly(ethyloxazoline) in 40 parts of water was prepared. 18 parts of NeoRez 985 (NeoRez is a Trade Mark of NeoResins which is a business unit of Avecia, and is an aqueous dispersion of a polycarbonate diol polyurethane resin) was then added so that the resulting solution contained 40% NeoRez 985 solids and 60% Peox 50 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C.

The carrier sheet so formed was then printed with a test image on an Epson 680 Ink Jet Printer (Epson is a Trade Mark of Seiko Epson Corporation). In order to test the adhesion of the printed image and its ability to deform with the coated carrier sheet, the printed carrier sheet was then deformed by heating in a vacuum mould at 220°C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet.

A carrier sheet prepared in this way also performed well when used in an IMD process as described in Example 7.

Example 9

A solution of 10 parts of Peox 50 in 40 parts of water was prepared. 12.25 parts of NeoRez 985 was then added so that the resulting solution contained 30% NeoRez 985 solids and 70% Peox 50 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C.

The carrier sheet so formed was then printed with a test image on an Epson 680 Ink Jet Printer. In order to test the adhesion of the printed image and its ability to deform with the coated carrier sheet, the printed carrier sheet was then deformed by heating in a vacuum mould at 220 °C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet.

Example 10

A solution of 10 parts of Peox 50 in 40 parts of water was prepared. 28.6 parts of NeoRez 985 was then added so that the resulting solution contained 50% NeoRez 985 solids and 50% Peox 50 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C. The carrier sheet so formed was then printed with a test image on an Epson 680 Ink Jet Printer. In order to test the adhesion of the printed image and its ability to deform with the coated carrier sheet, the printed carrier sheet was then deformed by heating in a vacuum mould at 220°C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet.

Example 11

A solution of 10 parts of Peox 200 in 40 parts of water was prepared. 12.25 parts of NeoRez 985 was then added so that the resulting solution contained 30% NeoRez 985 solids and 70% Peox 200 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C.

Example 12

A solution of 7 parts of Peox 200 in 40 parts of methanol was prepared. 3 parts of Synthetic resin SK (a hydrolysed acetophenone-formaldehyde resin, supplied by Hϋls A.G.) was then added so that the resulting solution contained 30% Synthetic resin SK solids and 70% Peox 200 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C. The carrier sheet so formed was then printed with a test image on an Epson 680 Ink Jet Printer. In order to test the adhesion of the printed image and its ability to deform with the coated carrier sheet, the printed carrier sheet was then deformed by heating in a vacuum mould at 220 °C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet.

Example 13

A solution of 10 parts of Peox 200 in 40 parts of water was prepared. 8.24 parts of Polidene 17 038 (Polidene is a Trade Mark of Scott Bader Company Limited, and is an aqueous dispersion of a self-crosslinking vinylidene chloride acrylic copolymer) was then added so that the resulting solution contained 30% Polidene 17 038 solids and 70% Peox 200 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C.

Example 14

A solution of 10 parts of Peox 200 in 40 parts of water was prepared. 13 parts of Eastek 1100 (Eastek is a Trade Mark of Eastman Chemical Company, and is a sulfopolyester) was then added so that the resulting solution contained 30% Eastek 1100 solids and 70% Peox 200 solids. This solution was then applied to a polycarbonate sheet using a number 6 Meier bar to give a wet coat weight of 60 μm. The polycarbonate sheet bearing the coating was then dried in an oven at 110°C. The carrier sheet so formed was then printed with a test image on an Epson 680 Ink Jet Printer. In order to test the adhesion of the printed image and its ability to deform with the coated carrier sheet, the printed carrier sheet was then deformed by heating in a vacuum mould at 220°C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet.

Example 15

Polidene 17 038 was applied to a polycarbonate sheet using a number 2 Meier bar to give a wet coat weight of 12 μm. The coated carrier sheet was then dried in an oven at 110°C. The carrier sheet so formed was then printed in a Docul2 colour copier from Xerox Corporation. The printed carrier sheet was then deformed by heating in a vacuum mould at 220 °C. The resulting image was free of cracks and adhered adequately to the coated carrier sheet. A sheet made in this way also performed well when used in an IMD process as described in Example 7.

Claims

1. A method of making a plastics article bearing a printed image, the method comprising printing an image onto a carrier material by means of a digital imaging technique, and forming the article by an injection moulding process involving in-mould decoration to produce an article with the carrier material and image incorporated therein.

2. A method according to claim 1, wherein the carrier material is a film or sheet of suitable material.

3. A method according to claim 1 or 2, wherein the carrier material is a transparent carrier sheet.

4. A method according to claim 1, 2 or 3, wherein the carrier material is a transparent carrier sheet of crystalline polyester, amorphous polyester, poly(methylmethacrylate) or polycarbonate.

5. A method according to any one of the preceding claims, wherein the carrier material comprises a receiver layer for receiving an image.

6. A method according to any one of the preceding claims, wherein the carrier material comprises one or more back coats on the side of the carrier material remote from the image-receiving surface.

7. A method according to any one of the preceding claims, wherein an overlay including one or more pigments is applied to a printed image on the carrier material.

8. A method according to claim 7, wherein the overlay is applied by mass transfer printing.

9. A method of making a plastics article bearing a printed image, the method comprising printing an image onto a carrier material by means of a digital imaging technique, applying an overlay to the printed image and forming the article by an injection moulding process involving in-mould decoration to produce an article with the carrier material, image and overlay incorporated therein.

10. A method according to any one of the preceding claims, wherein the digital imaging technique is thermal dye transfer printing, ink jet printing or electrophotography.

11. A method according to claim 9 or 10, wherein the digital imaging technique is thermal dye transfer printing.

12. A method according to claim 11, wherein the carrier material comprises a receiver layer comprising polymeric material having a Tg in the range of 45 °C to 70°C.

13. A method according to claim 12, wherein the carrier material comprises a receiver layer of cross-linked polymeric material.

14. A method according to claim 12, 13 or 14, wherein the polymeric material of the receiver layer is selected from polycarbonates, polyesters, polyurethanes, polyvinylchloride/polyvinylacetate copolymers, acrylic copolymers and styrene copolymers.

15. A method according to any one of the preceding claims, wherein the carrier material, image and optional overlay are incorporated in the article via first surface or second surface printing.

16. A plastics article bearing a printed image produced by a method in accordance with any one of claims 1 to 15.