GB2101529A

GB2101529A - Decorating articles by transfer printing

Info

Publication number: GB2101529A
Application number: GB08121725A
Authority: GB
Inventors: Terence Arthur Turner
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1981-07-14
Filing date: 1981-07-14
Publication date: 1983-01-19
Also published as: ZA825022B; FR2509668A1; IT8222394A0; DE3225817A1; IT1151850B

Abstract

An article is decorated by applying a dye-receptive coating 28 of a non-linear, cross-linked polyester or a non-linear, cross-linked thermosetting acrylic resin, preferably with added catalyst, and then using a dye diffusion transfer technique to apply a pattern to the coating, the dyestuff being an anthraquinone or quinoline dyestuff modified by addition or substitution of at least one substituted reactive group per molecule, the dyestuff and coating material being so selected as to ensure chemical bonding between them. <IMAGE>

Description

SPECIFICATION Decorated articles This invention relates to decorating articles, and to methods of decorating articles by dye diffusion transfer, that is to say a method in which a carrier web, printed with indicia in sublimable dyestuff, is applied over a coating receptive to such dyestuff on a surface of the article, and the web is held in initmate contact with the coating whilst the article is heated so that at least some of the dyestuff migrates by sublimation into the coating before the web is removed from the article.

In this specification, the term "decoration" means the application of indicia, and "indicia" means any or all of the possible markings (whether visible to the naked eye or not) which may be applied to a substrate by printing, for example decorative patterns, areas of colour, pictures or diagrams, or written information of any kind.

Dye diffusion transfer techniques have long been used in the printing of textile fabrics, which represent the field in which such techniques find their widest application, particularly in respect of synthetic fibre products which include dresses, skirts, household fabrics such as curtain or upholstery materials, and for the personalisation of tee-shirts and sports wear.

Decoration by dye diffusion transfer is also increasingly used for non-textile products to which a suitable coating is first applied. Thus, for example, household products such as hob covers, saucepans, and jackets for toasters and other appliances have been successfully decorated in this way. The materials that can be given a suitable coating and then decorated by dye diffusion transfer are not confined to metals, but can for example include wood or wood products such as chipboard. Dye diffusion transfer can also be used for direct application to certain ceramics.

Some substrate materials are capable of accepting dyes by sublimation of the dyes which remain fast in the substrate without chemical bonding. Examples of such materials are polyester fibres, for which the process has long been extensively used.

The articles to which this invention is applicable may be for any purpose and of any material, but it is of especial interest in connection with the decoration of metal containers, especially metal cans of the so-called "open top" type, commonly used for foodstuffs or for beverages such as beer and soft drinks. These are subjected, after being filled and closed, to heating in order to effect pasteurisation of the contents. From many points of view the use of cans decorated by printing directly on to the can side wall, rather than by application of a paper label, is preferred by canners and consumers alike. There is now a tendency for the so-called two-piece can to supersede the older type of open-top can which had a body built up from flat sheet. Flat metal sheet can readily be printed to a very high quality and with a wide choice of colour and pattern.The bodies of two-piece cans, on the other hand, are made in one piece by drawing from a flat blank, with subsequent re-drawing and/or ironing of the body side wall. The severity of these operations is such that the flat sheet from which the blanks are made cannot be pre-printed (even using distortion printing techniques) with any hope of achieving successful decoration of the finished can body. As a result the bodies, if they are to be decorated by direct printing, must be printed after being formed.

This is commonly done, but by means of conventional printing methods involving direct cold application of wet inks to the can surface. The print quality usually achieved on two-piece cans is notoriously inferior to that commonly found on three-piece cans made from sheet printed flat, for reasons derived simply from the fact that the printing methods have to be adapted for printing at high speeds on small areas of surface which are curved to a relatively small radius. Although improvements are taking place and there have been a number of proposals for adaptations of conventinal techniques tending towards improved print quality in the high-speed decoration of preformed can bodies, these tend to call for the use of sophisticated and rather expensive machinery.In this connection, dye diffusion transfer, although not so far generally used for high-speed printing of non-planar surfaces, offers the possibility of achieving substantially improved print quality on pre-formed can bodies using comparatively simple equipment.

However, such an application of diffusion transfer methods raises at least two problems not generally met in the more usual applications of such methods, viz. the decoration of textiles and or other articles none of which require to be produced at production rates of the same high order of magnitude at which open-top cans are made. These problems are, firstly that very speedy fixing of the dye to its host material is required; and secondly that the resulting decoration must be able successfully to withstand the heating process necessary for pasteurisation. In addition, it is desirable that the host material should be a coating material of a kind already commonly available and used for can bodies, thus being of a kind whose properties are well tried and known.

The requirement for heat resistance especially, makes it desirable that the fastness of the dyes be obtained by chemical fixing (bonding) of the dyes to their host material, which in the case of a can body is the coating on the outer sidewall surface of the body.

Accordingly the invention, in a first aspect thereof, provides a method of decorating an article, including the steps of: applying over a surface of the article a coating in at least one layer comprising an outer layer of translucent organic varnish; causing the coating to set; printing a flexible carrier web with indicia in sublimable dyestuff comprising at least one organic dye; applying the carrier web in intimate contact with the coating;; and heating the container whilst the web remains in said contact so as to transfer at least some of the dyestuff by sublimation into the coating, wherein the step of applying the coating comprises applying at least one layer of a dyereceptive material comprising a non-linear, crosslinked polyester or a non-linear, cross-linked thermosetting acrylic resin, said material having a plurality of reactive groups per molecule, and in the printing step, the or each dye comprises at least one anthraquinone or quinoline dyestuff modified by addition or substitution of at least one substituted reactive group per molecule, the said reactive groups of the or each said dyereceptive material on the one hand, and those of the or each dye on the other, having been so chosen as to effect bonding of the dye or dyes to the dye-receptive coating layer or layers.

Where at least one dye is of the anthraquinone type, it is preferably of the form:

wherein at least two substituted reactive groups have been introduced into saturated or unsaturated side chains appended at molecular positions selected from those numbered 1 to 8, there being one said group appended to position 1 or 8 and another said group appended to position 4 or 5, respecitvely.

Where at least one dye is of the quinoline type, it is preferably of the form:

wherein at least one substituted reactive group has been introduced into a saturated or an unsaturated side chain appended at a molecular position selected from those numbered 1 to 7.

In a method according to the invention, the dyes employed are anthraquinone or quinoline dyestuffs such that suitable reactive groups (typically carboxylic and/or hydroxyl) are introduced into saturated or unsaturated side chains appended to a position or positions consisting of or selected from positions 1 or 8, 2 or 1, 3 or 6,4 or 5 of the anthraquinone molecule, or into positions on either homocyclic or heterocyclic rings in the case of quinoline. The chosen position of substitution in all cases is subject to any groups already in position and to the directive influences of those groups.

Preferably, the reactive groups on the dyestuff molecules are sufficiently remote from the conjugated ring structure as to be unaffected by steric effects (in terms of molecular size), and are available for chemical bonding to the matrix of the can coating (host material) under the conditions of temperature and duration chosen for the sublimation process.

It will be understood that the method of the invention calls for selection of dyestuffs and coating materials together, so as to be mutually compatible and to achieve the degree of dye fastness, heat resistance and speed of fixing required for any particular application.

Considering the coating materials, therefore, these must include at least one organic layer which serves as host material to the transferred dye or dyes; preferably, if there is more than one layer, then each layer is organic. More than one layer is necessary if, for instance, a white base coat is required to achieve the required visual effect of the decoration. In this case the base coat will be applied before the translucent varnish layer; conveniently the base coat may be of the same material as the latter, but with a suitable white pigment added. On the other hand, the requirements of the decoration may be such that the reflective qualities of the metallic surface of the article (if of metal) are to be utilised to achieve metallic effects.In this case the translucent varnish layer will usually be applied direct to the surface of the article, or to those parts of it where the reflective qualities are to be used. The article may have an opaque base coat over all or only part of its surface, the translucent varnish layer being applied over the whole.

The translucent varnish layer preferably has a thickness of at least 0.5 ,u, The coating preferably comprises at least one said dye-receptive material in the form of either a non-linear polyester cross-linked with at least one formaldehyde resin, or a non-linear, thermosetting resin comprising acrylic resin cross-linked with epoxides of the bisphenol "A" type.

Polyester coating materials are very different from polyester fibres in chemical constitution and the mechanism of dye fixing is therefore somewhat different from that found in textile dyeing by diffusion transfer into polyester fibres. First, the polyester coating materials are of highly branched type as opposed to linear, being formed by condensation between polyhydric alcohols and polybasic (polycarboxylic) acids. Such branched polymers have greater availability of reactive groups appended to the polyester backbone which comprises ester linkages.

The cross-linking resin chosen for a polyester coating suitable for use in the method of this invention will be selected according to the requirements of surface hardness or coating flexibility. Examples of such cross-linking resins are melamine formaldehyde and urea formaldehyde. If the former is used, its quantity can be varied to match the dye or dyes chosen, by varying (for example) the degree of methylolation of the melamine, thus varying the number of reactive hydroxyl groups available, after curing of the coating, for reaction with the dyestuff.

Preferably, a suitable acid catalyst such asptoluene sulphonic acid or phosphoric acid is incorporated in at least one organic layer of the coating, to assist in accelerating the curing time needed. At the end of the curing reaction, substantial quantities of the catalyst remain to be available for use where acid catalysis is required for the reaction between the dyestuff and the coating.

According to the invention, in a second aspect, there is provided a decorated article having a coating of a material comprising a non-linear, cross-linked polyester or a non-linear, cross-linked thermosetting acrylic resin, said material having a plurality of reactive groups per molecule, and decoration comprising dyestuff in the coating, the dyestuff comprising at least one dye, and the or each dye comprising at least one anthraquinone or quinoline dyestuff modified by addition or substitution of at least one substituted reactive group per molecule, and the decoration being bonded into the coating by combination between the reactive groups of the coating material and those of the dyestuff.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings hereof, in which Figure 1 is a section through a portion of a coated article immediately prior to receiving decoration by dye diffusion transfer; Figure 2 is a similar section showing it immediately after the dye transfer has taken place; Figure 3 consists of twelve iilustrations (i) to (xii) showing examples of the molecular structure of anthraquinone-based dyes suitable for use in a method according to the invention; and Figure 4 shows the molecular structure of one quinoline dye suitable in a method according to the invention.

Referring to Figures 1 and 2, an article 12 comprises a metal substrate 12 having a whitepigmented organic base coat 24 and an organic, translucent varnish layer 28, 1 u in thickness, overlying the base coat 24. These layers are applied in succession in known manner, the base coat 24 being cured before the layer 28 is applied and the layer 28 being cured before the article is printed.

For the printing operation, a carrier web 46 is printed with dyestuff to represent the required indicia, the dyestuff being held in a binder layer 49 on the paper substrate 47 of the carrier web. The carrier web 46 is applied over the varnish layer 28, and held in intimate contact therewith whilst the article 12 is heated for a predetermined time at a predetermined temperature, typically 30 seconds at 1 800C. This causes some of the dyestuff to migrate, as indicated in Figure 2, by sublimation into the coating of the article. The carrier web 46 is removed from the article (or vice versa) after the article has been cooled or allowed to cool so as to effect or complete fixing of the dyestuff to the coating material. This fixing is achieved at least partly by chemical reaction.

The dye or dyes and the materials of the layers 24, 28 are so chosen that there are available for this reaction sufficient reactive groups in both the dyestuff and the coating layers to combine the one with the other.

The article as seen in Figure 2, i.e. without the carrier web 46, is a decorated article whose coating consists of the two layers 24,28, each of which is of a coating material comprising either a non-linear, cross-linked polyester or a non-linear, cross-linked thermosetting acrylic resin. The dye or dyes providing the indicia fixed in the coating comprise at least one anthraquinone or quinoline dyestuff modified by addition or substitution of at least one substituted reactive group per molecule, these groups being combined with those of the coating material.

In this example, the coating material is a nonlinear polyester cross-linked with melamine formaldehyde whose degree of methylolation is such that the number of reactive hydroxyl groups in the cross-linked polymer molecule is the same, or nearly the same, as the number of reactive groups per molecule of the dye which, of the dyes chosen, has the smallest number of reactive groups per molecule. The coating material also contains an acid catalyst in the form of p-toluene or phosphoric acid, and, in the case only of the material used forthe base coat 24, the white pigment mentioned earlier herein.

The (or each) dye is, in this example, an anthraquinone dyestuff having the form:

with two substituted reactive groups introduced into saturated or unsaturated side chains at the position 1 or 8 and the position 4 or 5, respectively. There may also be further such groups. Several examples of suitable dyestuffs of this type are illustrated in Figure 3.

Alternatively the (or each) dye, or any one or more of the dyes, may be a quinoline dyestuff having the form:-

with at least one substituted reactive group introduced into a saturated or unsaturated side chain in any of the positions 1 to 7. An example of such a dye is the yellow dye illustrated in Figure 4.

Claims

1. A method of decorating an article, including the steps of: applying over a surface of the article a coating in at least one layer comprising an outer layer of translucent organic varnish; causing the coating to set; printing a flexible carrier web with indicia in sublimable dyestuff comprising at least one organic dye; applying the carrier web in intimate contact with the coating;; and heating the container whilst the web remains in said contact so as to transfer at least some of the dyestuff by sublimation into the coating, wherein the step of applying the coating comprises applying at least one layer of a dyereceptive material comprising a non-linear, crosslinked polyester or a non-linear, cross-linked thermosetting acrylic resin, said material having a plurality of reactive groups per molecule, and in the printing step, the or each dye comprises at least one anthraquinone or quinoiine dyestuff modified by addition or substitution of at least one substituted reactive group per molecule.

the said reactive groups of the or each said dyereceptive material on the one hand, and those of the or each dye on the other, having been so chosen as to effect bonding of the dye or dyes to the dye-receptive coating layer or layers.

2. A method according to Claim 1 wherein, in the printing step, at least one said dye comprises an anthraquinone dyestuff having the form:

wherein at least two substituted reactive groups have been introduced into saturated or unsaturated side chains appended at molecular positions selected from those numbered 1 to 8, there being one said group appended to position 1 or 8 and another said group appended to position 4 or 5, respectively.

3. A method according to Claim 1 wherein, in the printing step, at least one said dye comprises a quinoline dyestuff having the form:

4. A method according to Claim 2 or Claim 3, wherein the substituted reactive groups of at least one of the dyes include carboxylic or hydroxyl groups, or both.

5. A method according to any one of Claims 2 to 4, wherein at least one of the substituted reactive groups of each dye is appended in a side chain sufficiently remotely from the conjugated ring structure of the anthraquinone or quinoline (as the case may be) as to be substantially unaffected by steric effects and to be available for reaction with the reactive groups of the dyereceptive material so as to effect chemical bonding of the dye to the dye-receptive coating layer or layers.

6. A method according to any one of the preceding claims, wherein the said dye-receptive material or at least one said material, applied during the coating-applying step, is a non-linear polyester cross-linked with at least one formaldehyde resin.

7. A method according to Claim 6, wherein the formaldehyde resin or resins comprise at least one selected from melamine formaldehyde and urea formaldehyde.

8. A method according to Claim 6, wherein the formaldehyde resin or resins include or consist of melamine formaldehyde in which the degree of methylolation has been chosen to maximise the number of reactive hydroxyl groups for chemical reaction with reactive groups of the dyestuff.

9. A method according to any one of Claims 6 to 8, wherein the said non-linear cross-linked polyester has incorporated with it an acid catalyst to promote both curing of the resin and the subsequent bonding of the dye or dyes to the dyereceptive coating layer or layers.

10. A method according to Claim 9, wherein the catalyst is p-toluene sulphonic acid or phosphoric acid.

11. A method according to any one of Claims 1 to 4 in which a single layer of the coating is applied, or according to any one of Claims 1 to 10 in which more than one layer of the coating is applied, and wherein dye-receptive material applied to form the single layer or, as the case may be, at least one of said layers but not every layer, is a non-linear, thermosetting resin comprising acrylic resin cross-linked with epoxides of the bisphenol "A" type.

12. A method of decorating an article, performed in a manner substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.

13. A method according to any one of the preceding claims, wherein the dye or at least one of the dyes employed is of the molecular structure illustrated in any one of parts (i) to (xii) of Figure 3, or in Figure 4, of the drawings hereof.

14. An article decorated by a method according to any one of the preceding claims.

1 5. A decorated article having a coating of a material comprising a non-linear, cross-linked polyester or a non-linear, cross-linked thermosetting acrylic resin, said material having a plurality of reactive groups per molecule, and decoration comprising dyestuff in the coating, the dyestuff comprising at least one dye, and the or each dye comprising at least one anthraquinone or quinoline dyestuff modified by addition or substitution of at least one substituted reactive group per molecule, and the decoration being bonded into the coating by combination between the reactive groups of the coating material and those of the dyestuff.

16. An article according to Claim 14 or Claim 1 5 in the form of a metal can body.