Thermal recording media

Details Thermal recording media Thermal recording media

2001-03-09

2002-12-17

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

Having a colorless color-former, developer therefor, or...

C503S226000

Reexamination Certificate

active

06495490

ABSTRACT:

BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to thermal recording media, and more specifically to thermal recording media, each of which has a back layer comprising a polyurethane with fluorine-atom-containing side chains and is useful in heat-melting-type thermal transfer recording and sublimation-type thermal transfer recording.
b) Description of the Related Art
Conventionally-known thermal recording media include heat-melting-type thermal recording media and sublimation-type thermal recording media. A heat-melting-type thermal recording medium is provided with a thermal recording layer (ink layer) formed on one side of a base sheet such as a polyester film by having a dye or pigment carried thereon with a binder resin, and the medium is heated patternwise from the back side thereof such that the ink layer is transferred onto a desired material. On the other hand, a sublimation-type thermal recording medium makes use of a heat-sublimable dye as a dye, and the dye alone is caused to sublimate such that it is transferred likewise onto a desired material.
As these recording methods are each of the type that thermal energy is applied by a thermal head from the side of the back side of a base sheet, the back side of the base sheet of each thermal recording medium for use in such a recording method is required to have sufficient slipperiness, separability, non-tackiness and the like relative to the thermal head so that the thermal head does not stick on the back side. With a view to meeting this requirement, it has been proposed, for example, to form a back layer with a silicone resin, melamine resin, phenol resin, polyimide resin, modified cellulose resin or a mixture thereof on the back side of the base sheet of a thermal recording medium (see JP S58-13359 A, for example).
To form heat-resistant back layers in the above-described thermal recording media, it has been attempted, for example, to thermally crosslink the above-described resins by using a variety of crosslinking agents or to add inorganic fillers, powders of fluorine-containing resins and/or the like to these resins. These measures can provide back layers having heat resistance, but with these resins, the slipperiness and non-tackiness relative to thermal heads are insufficient. Only silicone resin is equipped with slipperiness and non-tackiness. Silicone resin, however, develops a problem that a heating step required to fully crosslink the resin gives damage to the base sheet which is a thin film (generally, 2 to 5 &mgr;m in thickness); or a problem that, if the crosslinking is incomplete, winding of the thermal recording medium into a roll allows the unreacted low-molecular silicone to migrate from the back layer into the ink layer located in contact with the back layer, resulting in formation of obscure pictures or marks.
The present inventors conducted an investigation with a view to developing methods for overcoming these problems, and in JP S61-227087 A, JP S62-202786 A, JP H2-102096 A, etc., proposed that use of various silicone-polyurethane copolymer resins can furnish thermal recording media having excellent back layers which are endowed with heat resistance, slipperiness, non-tackiness and the like. However, keeping in step with the move toward use of hotter thermal heads and thinner base sheets associated with the move toward printing at higher speeds in recent years, still higher heat resistance, slipperiness, non-tackiness and the like are required for back layers.
To meet these requirements, there is an outstanding need for a material which makes it possible to further improve the conventional art and to form back layers with excellent properties by simpler production steps. In response to these requirements, the present inventors also proposed to use perfluoroalkyl-containing polyurethane resins for the formation of back layers (JP S62-251192 A, JP H1-11887 A, etc.). Incidentally, as a process for the preparation of a conventional one-end diol (a compound having two hydroxyl groups at only one end of its molecule) having a perfluoroalkyl group (which will hereinafter be abbreviated as “R
f
group”), a process which proceeds following such a reaction scheme as will be described next is known.
As is appreciated from the foregoing, the conventional processes for the preparation of one-end diols having the Rf group all require many steps. High-purity products of these one-end diols, each of which has the R
f
group, are costly so that these conventional processes have a problem in their practical use on an industrial scale. Further, there is a need to make the content of R
f
groups higher in a field where high performance is required as described above. The back-layer-forming resin, therefore, is so costly that it is not suited for practical use.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to solve the above-described problems of the conventional art and hence, provide a thermal recording medium having a back layer which is formed of an economical material and is excellent in slipperiness, non-tackiness, heat resistance and the like.
The present inventors have proceeded with an extensive investigation to develop an economical process for the preparation of a one-end diol having an group, resulting in development of a novel preparation process. Further, the present inventors have also found that use of a fluorine-containing polyurethane, which employs the R
f
-containing one-end diol available from the process, makes it possible to achieve the above-described object, leading to completion of the present invention.
The above-described object can be achieved by the present invention as will be described hereinafter.
In one aspect of the present invention, there is thus provided a thermal recording medium having a base sheet, a thermal recording layer arranged on one side of the base sheet, and a back layer arranged on an opposite side of the base sheet, wherein the back layer comprises a polyurethane having side chains derived from a fluorine-containing diol represented by the following formula (I):
wherein R
f
represents a perfluoroalkyl or perfluoroalkenyl group having 1 to 20 carbon atoms; X represents a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenylene group represented by —CH═CH—(CH
2
)
n
— in which n stands for an integer of from 1 to 10, or
in which n stands for an integer of from 0 to 6; Y represents a direct bond, —O—, —NH—, or —R
0
—NH— in which R
0
is an alkylene group having 1 to 6 carbon atoms; Z represents a direct bond or —N(R′)R— in which R is an alkylene group having 1 to 20 carbon atoms and R′ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R
1
and R
2
each independently represent a divalent organic group; and R
3
represents a residual group of an aliphatic, alicyclic or aromatic diisocyanate.
Owing to the use of the polyurethane having the side chains, each of which contains the R
f
group represented by the formula (I), for the formation of the back layer, the back layer is excellent in heat resistance, flexibility, the adhesion to the base sheet and also superb in the slipperiness relative to a thermal head. The thermal head, therefore, does not stick the thermal recording medium.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention will next be described in further detail based on certain preferred embodiments.
The thermal recording medium according to the present invention has the thermal recording layer formed on one side of the base sheet and the back layer formed on the other side of the base sheet, and is characterized in that the polymer, which makes up the back layer, comprises the polyurethane having side chains derived from the fluorine-containing diol represented by the formula (I), that is, the R
f
-containing one-end diol. It is to be noted that the term “polyurethane” as used herein collectively means polyurethane, polyurea and polyurethane-polyurea. Such a polyurethane can

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