Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1999-11-01
2001-01-16
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C427S152000, C427S385500, C428S195100, C428S500000, C428S913000, C428S914000
Reexamination Certificate
active
06174607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermal transfer recording media, particularly to thermal transfer recording media with excellent printing quality and oil resistance.
PRIOR ART
Recently, bar code images have been indispensable for control of circulation and costs in the field of, for example, groceries. The most well known method for generating such bar code images is the thermal transfer recording technique using thermal transfer recording media.
A thermal transfer recording medium generally comprise an ink layer mainly based on a wax having a relatively low melting point or softening point formed on a polyester film, wherein said ink layer is transferred to a sheet such as a label, paper, tag, etc. by heat generated in the thermal head in a printer.
There have previously been demands for the use of labels bearing printed bar code images for controlling containers for oils and chemicals or in manufacturing processes using great quantities of oils and chemicals. However, bar code images for these uses are required to have good oil and chemical resistances, because they are often liable to contamination with oils spilled from containers during handling or splashed during manufacturing processes.
In order to satisfy these demands, some thermal transfer recording media have been proposed. For example, JPA No. H2-38094 describes a transfer sheet formed of a release layer, a protective layer, a colorant layer and an adhesive layer, which involves a curing reaction after transfer to give a transferred image with excellent solvent resistance.
JPA No. H3-166993 describes a thermal transfer sheet obtained by forming a release layer and a protective layer in that order consisting of a resin curable by ionizing radiation, which involves positive irradiation with ionizing radiation after transfer to give a print with excellent solvent resistance.
Our investigation on the above thermal transfer recording media showed that they certainly had succeeded in improving solvent resistance of prints. However, the above prior art examples have the disadvantages that they require means for curing the prints and that the prints can not be used immediately after print operation.
Moreover, any curing step after print operation can not be applied to some kinds of sheets that may be denatured by heating or other means.
JPA No. H2-160584 describes a heat-sensitive transfer recording medium having an ink layer consisting of a colorant, a thermoplastic polyol, and a curing agent, which remarkably improves chemical resistance of images.
Our investigation on said thermal transfer recording medium showed that it certainly had succeeded in improving chemical resistance of images.
However, the curing agent used therein is a so-called aluminium chelate compound such as (ethyl acetoacetate) aluminium-diisopropionate, which had the crucial disadvantage that it readily reacts with moisture in the air or moisture in the solvent used for forming the ink layer to cure the ink, thus failing in continuous application of a long ink layer on said thermal transfer recording medium.
As to the type of oils, neither the above nor other prior art documents have proposed any thermal transfer recording media having a sufficient solvent resistance to highly hygroscopic and non-volatile oils such as brake oils.
In order to solve the above problems of the prior art, the present invention aims to provide a thermal transfer recording medium, which can transfer images to any type of sheets to generate prints with sufficient oil resistance even when they are used immediately after print operation.
Another object of the present invention is to provide a thermal transfer recording medium, which can generate bar code images free from contamination with even highly hygroscopic and non-volatile oils such as brake oils.
Still another object of the present invention is to provide a thermal transfer recording medium wherein the ink layer can stably be prepared over a long length without inducing any sudden reaction.
DISCLOSURE OF THE INVENTION
As a result of our careful studies to solve the above problems, we accomplished the present invention on the basis of the finding that oil resistance of thermal transfer recording media is improved by precuring the ink layer on the substrate (i.e. on the release layer) before transfer.
The present invention based on this finding relates to a thermal transfer recording medium comprising a release layer and an ink layer in that order formed on a substrate, wherein the ink layer contains at least a colorant (A), a curing agent (B) and a bonding resin (C) and the ink layer is cured on the substrate.
The thermal transfer recording medium of the present invention can be prepared by applying a composition for forming a release layer on a substrate, applying a composition for forming an ink layer containing at least a colorant (A), a curing agent (B) and a bonding resin (C) thereon and then performing a curing step at a given temperature.
According to the present invention, thus precured ink layer is not readily mixed with the release layer during transfer to prevent deterioration of solvent resistance of the thermal transfer recording medium and to improve oil resistance.
According to the present invention, any curing step is not necessary after print operation, whereby prints can be used immediately after print operation and images can be printed even on substrates that may be denatured by heating or other means.
The curing step should preferably take place at a temperature not higher than the melting point of the composition for forming a release layer for 12 to 36 hours.
Although a curing step of an ink layer before transfer generally lowers transferability of the ink layer, we were interested in the fact that brake oils are usually alcoholic solvents (for example, polyglycol ether) and found that the use of an ink layer comprising a polyvinyl chloride resin and an isocyanate compound maintains transferability of the ink layer even if it is subjected to a precuring step before transfer.
Namely, the ink layer according to the present invention may contain an isocyanate compound (b) and a vinyl chloride resin (c) capable of reacting with the isocyanate compound.
According to the present invention as described above, printing can take place with relatively low printing energy because the bonding resin (c) is highly adhesive and fast and brittle(The ink is easy to cut.). The images formed on substrates from the ink layer are so resistant that they are free from contamination with brake oils to show sufficient oil resistance.
In addition, this combination of an isocyanate compound and a vinyl chloride resin can continuously form a ink layer for a long time because it does not suddenly begins to set.
On the other hand, we found that an ink layer containing the isocyanate compound and vinyl chloride resin improves oil resistance even if it is not subjected to a precuring step before transfer.
Accordingly, the present invention also relates to a thermal transfer recording medium comprising a release layer and an ink layer in that order formed on a substrate, wherein the ink layer may contain at least a colorant (A), an isocyanate compound (b) and a vinyl chloride resin (c) capable of reacting with the isocyanate compound.
The thermal transfer recording medium here can be prepared by applying a composition for forming a release layer on a substrate, applying a composition for forming an ink layer containing at least a colorant (A), a curing agent (B) and a bonding resin (C) thereon, and then allowing the ink layer to stand at a given temperature for a given period of time (for example, at normal temperatures for 200 hours or more).
In the present invention, the amount of the isocyanate compound (b) added into the ink layer can be in the range from 2 to 60 parts by weight based on 100 parts by weight of the vinyl chloride resin (c) capable of reacting with the isocyanate compound.
THE MOST PREFERRED EMBODIMENTS OF THE INVENTION
Some embodiments of thermal transfer recording media of the present
Sugita Junichiro
Takahashi Hideaki
Hess Bruce H.
Oliff & Berridg,e PLC
Sony Chemicals Corp.
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