Thermal transfer recording medium

Details Thermal transfer recording medium Thermal transfer recording medium

1998-11-18

2001-05-15

Schwartz, Pamela R. (Department: 1774)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S195100, C428S354000, C428S3550RA, C428S3550EN, C428S327000

Reexamination Certificate

active

06231973

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a thermal transfer recording medium. More particularly, it relates to a thermal transfer recording medium having a structure wherein an ink layer and an adhesive layer are provided on a foundation in this order.
A typical example of the thermal transfer recording medium of this type has a structure wherein a heat-meltable or heat-softening ink layer is provided on a foundation. There is also known a thermal transfer recording medium having a structure wherein an adhesive layer is further provided on the ink layer of the foregoing recording medium.
When materials exhibiting sufficient adhesion to a receptor, for example, a polyester resin having a softening point of about 60° C., or the like, are used as a material for the adhesive layer of the thermal transfer recording medium of the aforesaid structure, many of them show fair adhesiveness at ordinary temperatures. Consequently, when the thermal transfer recording medium is stored in such a state that it is wound in the form of a roll, the adhesive layer adheres to the back surface of the foundation in contact with the adhesive layer (this phenomenon is generally called “blocking”), so that difficulty arises in unwinding and dispensing the recording medium in an image formation device, injuring the stability of the recording medium in traveling and eventually inviting the deterioration of image quality. It is also known to add inorganic particles or a wax to the adhesive layer in order to prevent the blocking. However, the addition of the inorganic particles or wax to the adhesive layer is likely to reduce the adhesion to a receptor, thereby causing decreased scratch resistance or falling-off of print images.
The thermal transfer recording medium wherein the adhesive layer is composed of a wax or a resin having relatively high polarity, for example, polyester resin, polyamide resin, cellulosic resin, phenol resin, acrylic resin, or the like has the problem that it does not exhibit sufficient adhesion to a receptor made of a resin having a relatively low surface tension such as polyethylene or polypropylene.
In view of the foregoing, an object of the present invention is to provide a thermal transfer recording medium which exhibits sufficient adhesion to various receptors and does not cause blocking.
This and other objects of the present invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
In accordance with a first feature of the present invention, there is provided a thermal transfer recording medium comprising a foundation, and an ink layer and an adhesive layer provided on one side of the foundation in this order, the adhesive layer comprising a binder comprising a thermoplastic resin (A) and particles comprising a thermoplastic resin (B) dispersed in the binder, the adhesive layer having an uneven surface resulting from the particles, the thermoplastic resin (A) and the thermoplastic resin (B) being different from each other and the same at least in their main constitutional units.
In a second feature of the present invention, there is provided the thermal transfer recording medium of the first feature, wherein the thermoplastic resin (B) has a greater average molecular weight than the thermoplastic resin (A) so that the thermoplastic resin (B) has smaller solubility to the solvent of a coating liquid for the adhesive layer than the thermoplastic resin (A), and the particles comprising the thermoplastic resin (B) maintains the particle form in the adhesive layer.
In a third feature of the present invention, there is provided the thermal transfer recording medium of the first feature, wherein the thermoplastic resin (B) has a greater crystallinity than the thermoplastic resin (A) so that the thermoplastic resin (B) has smaller solubility to the solvent of a coating liquid for the adhesive layer than the thermoplastic resin (A), and the particles comprising the thermoplastic resin (B) maintains the particle form in the adhesive layer.
In a fourth feature of the present invention, there is provided the thermal transfer recording medium of the first, second or third feature, wherein the thermoplastic resin (A) and the thermoplastic resin (B) are each a member selected from the group consisting of a propylene resin, an ethylene-vinyl acetate copolymer, an acrylic resin, a polyester resin, a polyethylene resin, a polystyrene resin, a polybutene resin, a rosin resin, a terpene resin, a vinyl chloride resin and an epoxy resin.
In a fifth feature of the present invention, there is provided the thermal transfer recording medium of the first, second, third or fourth feature, wherein the thermoplastic resin (A) and the thermoplastic resin (B) are each a maleic anhydride-modified polypropylene resin, and the maleic anhydride-modified polypropylene resin as the thermoplastic resin (A) has a weight average molecular weight of not less than 2×10
4
to less than 4×10
4
and the maleic anhydride-modified polypropylene resin as the thermoplastic resin (B) has a weight average molecular weight of more than 4×10
4
.
In a sixth feature of the present invention, there is provided the thermal transfer recording medium of the first, second, third, fourth or fifth feature. wherein the thermoplastic resin (A) and the thermoplastic resin (B) are each a maleic anhydride-modified polypropylene resin having an addition ratio of maleic anhydride of 1 to 7% by weight.
DETAILED DESCRIPTION
The thermal transfer recording medium of the present invention is characterized by comprising a foundation, and an ink layer and an adhesive layer provided on one side of the foundation in this order, the adhesive layer comprising a binder comprising a thermoplastic resin (A) and particles comprising a thermoplastic resin (B) dispersed in the binder, the adhesive layer having an uneven surface resulting from the particles, the thermoplastic resin (A) and the thermoplastic resin (B) being different from each other and the same at least in their main constitutional units.
Herein, the concept that the thermoplastic resin (A) and the thermoplastic resin (B) are different from each other and the same at least in their main constitutional units means as follows: The term “constitutional unit” usually refers to recurring unit. In the case of a homopolymer, there is one kind of constitutional unit (recurring unit) and this is the main constitutional unit. For example, two polypropylenes, two polyethylenes, two polystyrenes, two poly(meth)acrylic acid esters or two polyesters (comprising one kind of dicarboxylic acid component and one kind of diol component) which are different from each other in molecular weight fall under the category of the thermoplastic resins (A) and (B). In the case of a copolymer (including polycondensation products), there are two or more kinds of the main constitutional units (recurring units). For example, in the case of chlorinated polypropylenes, the propylene unit and the chlorinated propylene unit are the main constitutional units. Two chlorinated polypropylenes which each comprise these two kinds of constitutional units and are different from each other in polymerization degree or addition ratio of chlorine fall under the category of the thermoplastic resins (A) and (B). Further, the thermoplastic resin (A) and the thermoplastic resin (B) satisfy the requirement so long as at least the main constitutional units of both are same. When this is explained using polypropylene resins for an example, a propylene homopolymer and a propylene copolymer fall under the category of the thermoplastic resin (A) and (B) because the main constitutional units of both are the same, provided that the comonomer unit in the propylene copolymer is minor in quantity.
When the thermal transfer recording medium of the above-mentioned constitution is stored in the state where it is wound in the form of a roll, the particles of the thermoplastic resin (B) projecting from the surface of the adhesive layer reduce the contact area between the surface of the adhesi

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