EP0546708A1

EP0546708A1 - Ink release sheet

Info

Publication number: EP0546708A1
Application number: EP92310692A
Authority: EP
Inventors: Kevin Anthony Kirk; Conway Francis Shields
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1991-12-10
Filing date: 1992-11-23
Publication date: 1993-06-16
Also published as: CA2083917A1

Abstract

Improved transfer of ink from a reservoir to an ink receptive surface is accomplished by using as the ink transfer surface, which passes the ink from the reservoir to the ink receptive surface, a combination of an synthetic organic resin and wax.

Description

This invention is relates to an ink release sheet. More particularly, the invention is directed to sheets of material which serve as an intermediary to transfer ink from an ink reservoir to an ink- receptive surface.
Ink transfer materials are well known. Perhaps the most commonly known such material is a typewriter ribbon. In the use of a typewriter ribbon, the ink is suitably applied to the ribbon; the ribbon is juxtaposed with an ink receptive surface, with the ink side facing the ink receptive surface; a suitable indicia forming means is impacted on the other side of the ribbon to force ink from the ribbon into intimate contact with the ink receptive surface, in the shape of the indicia forming means; and the ink receptive surface thus becomes imprinted with the ink indicia.
In another type of ink transfer, indicia forming means, such as printing type, are directly coated with ink and then impressed onto the surface of ink receptive means, such as for example paper or plastic film. The ink transfers from the indicia to the ink receptive means thereby forming the indicia on the ink receptive surface. The indicia forming means in this sort of operation has suitably been metal or, more recently, very tough plastic. In this operation, there is no intermediate ink transfer sheet. The ink coats the type, and then, upon contact, is transferred from the type directly to the paper. In this application, the ink is not usually absorbed by the type to any appreciable extent.
It is axiomatic that the quality of the indicia imprinted on the ink receptive surface is a function of many things, including power with which the ink transfer surface holds the ink prior to transfer, and the ease and completeness with which the ink is transferred from the ink transfer means to the ink receptive surface. The clarity with which the transferred ink corresponds to the indicia forming means is a function of all of these things.
The ink must be held onto the surface of the ink transfer means with enough force so that enough of it is carried to make the desired image, and so that it does not readily smudge. At the same time, it must not be held to the surface with so much force that it will not be easily and exactly transferable to the ink receptive surface upon its being juxtaposed to the ink receptive surface. The composition and the physical properties of both the ink and of the surface of the ink transfer means must be taken into account in arriving at a suitable combination of materials which have the desirable properties which are needed for this service.
It has been known to use various materials as the ink transfer means. In the early application of this technology, where there is an intermediate ink transfer sheet, such as a typewriter ribbon or the like, paper was used as the intermediate ink transfer sheet. As time has passed, newer materials have been developed for this service, including plastic films. Almost any material which can hold a given ink sufficiently tightly to keep it on the surface of the intermediate ink transfer sheet means, but will not hold it so tightly that it does not readily release on demand, is suitable for this service. Specifically, polyethylene, regenerated cellulose, cellulose acetate, polypropylene, particularly biaxially oriented polypropylene and polyester films, have been used as intermediate ink transfer sheet means.
Although plastic and paper films have been used as intermediate ink transfer sheets in the past, it is probably more accurate to consider these materials as being substrates which carry the ink in a condition which is temporarily adhered to the surface. Therefore, it is not only a question of the nature of the material which acts as the carrier of the ink, but it is also a question of the nature of the surface of the material which acts as the carrier of the ink. The carrier itself can he chosen for its mechanical strength, heat stability, and flexibility properties, and for the economies of use. The surface of this carrier can then be modified in order to give the required ink adhesion related properties.
In the past the only surface preparations which were used was to corona discharge treat or flame treat the surface. The surfaces thus produced were not consistent.
The adhesive and release characteristics of the inks used have, on occasion, been modified to improve one property at the expense of other properties. Multiple inks could have been used for the same purpose, but this requires the use of specialised equipment at additional cost.
While it is quite well known what sort of properties are desired for the surface of the ink transfer means, providing materials with these properties has not been easy. There does not seem to be any known simple relationship between the desired properties of the ink transfer material surface and the quality of the printed ink indicia. At best, there is the qualitative relationship that it is known that the ink must stick to the ink transfer surface a little bit, but not too much. It appears that this is an empirical relationship.
According to one aspect of the invention, there is provided a process of transferring ink from a reservoir of ink to an ink receptive surface comprising disposing ink on an ink transfer carrying surface, juxtaposing said ink on said ink transfer carrying surface to said ink receptive surface, and transferring said ink from said ink transfer carrying surface to said ink receptive surface, wherein the said ink transfer carrying surface is a composition comprising substantially 0 to 75 weight percent of at least one synthetic resin and substantially 25 to 100 weight percent of at least one wax.
According to another aspect of the invention there is provided an ink transfer carrying surface comprising a composition comprising substantially 0 to 75 weight percent of at least one synthetic resin and substantially 25 to 100 weight percent of at least one wax.
Preferably the synthetic resin is at least one member selected from the group consisting of acrylic resins, surlyn resins, ethylene/acrylic acid reins and polyvinylidene chloride resins.
Preferably the wax is at least one member selected from the group consisting of carnauba wax, paraffin wax, polyethylene wax, and microcrystalline wax.
Desirably the composition comprises substantially 5 to 30 weight percent synthetic resin and substantially 70 to 95 weight percent wax.
Other components may be used in the composition of this invention. For example, silica, silica gel, talc or the like can also be incorporated in this composition. Where these slip agents are used, they should not be present in a proportion of greater than about 1.5, preferably not greater than about 0.1, weight percent, based on the amount of total solids in the coating.
The coating is suitably present on the surface of said ink transfer carrying surface in a proportion of substantially 0.02 to 2 g/1000 square inches (0.02 to 2 g/6450cm²) of surface; and preferably substantially 0.035 to 1.5 g/1000 square inches (0.035 to 1.5 g/6450cm²) of surface.
The coating is suitably present on the surface of said ink transfer carrying surface in such proportions that the wax content thereof is substantially 0.02 to 0.15 g/1000 square inches (0.02 to 0.15 g/6450cm²) of surface; and preferably substantially 0.04 to 0.1 g/1000 square inches (0.04 to 0.1 g/6450cm²) of surface.
Typically, the ink carrying transfer surface would be flexible, as would the coating.
Inks can be solvent or water based using polyamide, nitro- cellulose, polyester, acrylic, styrene, or other resins common to the art. The pigments are conventional and will be well known to those of routine skill in the ink art.
In a preferred embodiment the coating composition comprises 10 parts by weight of a combination of methyl acrylate, methyl acrylate and methacrylic acid; and 90 parts by weight of carnauba wax.
Where the ink is to be transferred onto an ink receptive means through an intermediate ink transfer intermediate sheet, such as a ribbon, the improved ink transfer surface composition of this invention is suitably disposed on the surface of the intermediate ink transfer sheet on which the ink will he disposed. Therefore, in this embodiment, the ink will be carried directly by the instant invented composition.
Where the ink is to be transferred onto an ink receptive means directly from indicia imparting means, such as type, the improved ink transfer surface composition of this invention is suitably disposed directly on the surface of the indicia imparting means. Therefore, in this embodiment, while the underlying support structure is different, the ink is also carried directly by the instant invented composition.
This invention will have application in other transfer processes such as transfer metallization, and printing on fibre glass panels. This invention will also have application in other processes requiring consistent adjustable release of ink.
The synthetic polymer portion of this composition provides the means to adhere the composition to the substrate. It also provides at least some of the surface which actually supports the ink. Therefore, the resin should he one which adheres well to the substrate surface on which the composition is disposed and yet does not have great adherence to the ink The synthetic polymers which are well suited to use in the composition of this invention are described above; a combination of these synthetic polymers may be used. One particular type of synthetic organic polymer is defined as acrylic resins having a glass transition temperature between about 30 and 100 °C.
The wax portion of the composition of this invention provides the means to release the ink from the ink transfer surface to the ink receptive surface. Substantially any wax, which is solid at the temperatures at which the printing will he accomplished, will be suited to use in this invention. Examples of such wax are given above; a combination of these waxes may be used.
Where there is an intermediate ink transfer sheet which is being used in this invention, the instant composition is applied to the surface of the sheet before the ink is applied thereto. Where this intermediate ink transfer film form sheet material is oriented, the composition of this invention can be applied before or after the orientation stretching of the film. It is preferred, however, that where the substrate film is biaxially oriented, the composition of this invention is applied to the surface of the substrate film between the machine direction and the transverse direction orientation operations.
It has been found that the composition of this invention can be put up in any desired manner, such as a solution or an emulsion in a suitable liquid carrier, and the solution or emulsion can then be used in a conventional manner to coat a suitable substrate. Dipping is one of the conventional coating means, as is the use of a doctor blade.
Other suitable means would include reverse direct gravure, offset gravure, direct gravure, meyer rod, and slot die. Upon the fluid form coating having been applied, the carrier is suitably removed, by evaporation or otherwise, leaving the composition of this invention suitably disposed on the surface of the substrate.
It is desired that the composition of this invention be adapted to being dissolved or dispersed in a suitable carrier fluid, such as for example water or an organic solvent. Where needed or desired, suitable surfactants, and/or other ingredients, can be incorporated in the composition of this invention in conventional proportions for their intended purposes.

EXAMPLE

A coating composition, made up of 90 parts by weight of carnauba wax and 10 parts by weight of an acrylic polymer composition containing: 54 % ethyl methacrylate, 42% methyl acrylate, and 4 % methacrylic acid, was dispersed in water to make a 3% solids coating composition. A polyethylene terephthalate polyester sheet was machine direction stretched to three (3) times its original length in order to MD orient the sheet. The coating composition was applied to one surface of the MD stretched sheet via a 45 quad reverse direct gravure in line coater. Then the coated film was stretched in the transverse direction sufficient to increase the width thereof by four (4) times. The finished ink transfer sheet was about 50 gauge and the finished coating weight was up to about 0.1 gms/1000 in².
Ink was applied uniformly to the coated surface of the polyester sheet, and the inked sheet was used in impact printing of a plastic film surface. The quality of the printing was excellent.

Claims

1. A process of transferring ink from a reservoir of ink to an ink receptive surface comprising disposing ink on an ink transfer carrying surface, juxtaposing said ink on said ink transfer carrying surface to said ink receptive surface, and transferring said ink from said ink transfer carrying surface to said ink receptive surface, wherein the said ink transfer carrying surface is a composition comprising substantially 0 to 75 weight percent of at least one synthetic resin and substantially 25 to 100 weight percent of at least one wax.

2. A process according to 1, wherein said synthetic resin is at least one member selected from the group consisting of acrylic resins, surlyn resins, ethylene/acrylic acid reins and polyvinylidene chloride resins.

3. A process according to claim 1 or 2, wherein said wax is at least one member selected from the group consisting of carnauba wax, paraffin wax, polyethylene wax, and microcrystalline wax.

4. A process according to claim 1, 2 or 3, wherein said composition comprises substantially 5 to 30 weight percent synthetic resin and substantially 70 to 95 weight percent wax.

5. A process according to any preceding claim, which further includes not more than substantially 1.5 weight percent of at least one member selected from the group consisting of silica, silica gel and talc.

6. A process according to any preceding claim, wherein said coating is present on the surface of said ink transfer carrying surface in a proportion of substantially 0.02 to 2 g/1000 square inches (0.02 to 2 g/6450cm²) of surface; and preferably substantially 0.035 to 1.5 g/1000 square inches (0.035 to 1.5 g/6450cm²) of surface.

7. A process according to any preceding claim, wherein said coating is present on the surface of said ink transfer carrying surface in such proportions that the wax content thereof is substantially 0.02 to 0.15 g/1000 square inches (0.02 to 0.15 g/6450cm²) of surface; and preferably substantially 0.04 to 0.1 g/1000 square inches (0.04 to 0.1 g/6450cm²) of surface.

8. A process according to any preceding claim, wherein said ink is solvent based or water based.

9. A process according to any preceding claim, wherein said coating composition comprises 10 parts by weight of a combination of methyl acrylate, methyl methacrylate and methacrylic acid; and 90 parts by weight of carnauba wax.

10. An ink transfer carrying surface comprising a composition comprising substantially 0 to 75 weight percent of at least one synthetic resin and substantially 25 to 100 weight percent of at least one wax.

11. An ink transfer carrying surface according to claim 10, wherein said synthetic resin is at least one member selected from the group consisting of acrylic resins, surlyn resins, ethylene/acrylic acid reins and polyvinylidene chloride resins.

12. An ink transfer carrying surface according to claim 10 or 11, wherein said wax is at least one member selected from the group consisting of carnauba wax, paraffin wax, polyethylene wax, and microcrystalline wax.

13. An ink transfer carrying surface according to claim 10, 11 or 12, wherein said composition comprises substantially 5 to 30 weight percent synthetic resin and substantially 70 to 95 weight percent wax.

14. An ink transfer carrying surface according to any of claims 10 to 13, which further includes not more than substantially 1.5 weight percent of at least one member selected from the group consisting of silica, silica gel and talc.

15. An ink transfer carrying surface according to any of claims 10 to 14, wherein said coating is present on the surface of said ink transfer carrying surface in a proportion of substantially 0.02 to 2 g/1000 square inches (0.02 to 2 g/6450cm²) of surface; and preferably substantially 0.035 to 1.5 g/1000 square inches (0.035 to 1.5 g/6450cm²) of surface.

16. An ink transfer carrying surface according to any of claims 10 to 15, wherein said coating is present on the surface of said ink transfer carrying surface in such proportions that the wax content thereof is substantially 0.02 to 0.15 g/1000 square inches (0.02 to 0.15 g/6450cm²) of surface; and preferably substantially 0.04 to 0.1 g/1000 square inches (0.04 to 0.1 g/6450cm²) of surface.

17. An ink transfer carrying surface according to any of claims 10 to 16, wherein said ink is solvent based or water based.

18. An ink transfer carrying surface according to any of claims 10 to 17, wherein said coating composition comprises 10 parts by weight of a combination of methyl acrylate, ethyl methacrylate and methacrylic acid; and 90 parts by weight of carnauba wax.