JPH05273529A - Reloadable heat sensitive recording medium - Google Patents

Abstract

PURPOSE:To provide the heat sensitive recording medium which prevents the peeling of a recording layer contg. a high-polymer liquid crystal and is improved in repetitive reloading resistance. CONSTITUTION:This reloadable heat sensitive recording medium has a base and the recording layer laminated via a substrate on this base and contg. the high-polymer liquid crystal and forms a recording image by heating a part of the recording layer to a recording set temp. above the glass transition point (Tg) and cooling the liquid crystal state produced by this heating to the glass transition point (Tg) or below, thereby immobilizing this state. The above- mentioned high-polymer liquid crystal is constituted of a high-polymer liquid crystal having the glycidyl group expressed by formula and the substrate is constituted of a resin having a functional group, such as amino group bondable to this glycidyl group. The functional group in the resin constituting the substrate and the glycidyl group in the high-polymer liquid crystal bond chemically and, therefore, the strength of adhesion between the substrate and the recording layer is increased and the repetitive reloading resistance of the heat sensitive recording medium is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable heat-sensitive recording medium having a recording layer containing a polymer liquid crystal on a support, and more particularly to a heat-sensitive recording capable of improving the adhesive strength between the support and the recording layer. It relates to the improvement of the medium.

[0002]

2. Description of the Related Art A polymer liquid crystal undergoes reversible phase transition behavior from a solid phase to a liquid crystal phase (glass transition temperature: Tg) and from a liquid crystal phase to an isotropic phase (isotropic phase transition temperature: Tcl) upon application of heat energy. The point that is significantly different from the low-molecular liquid crystal is that it has a glass transition point.

Since it has this glass transition point, it can be fixed by rapidly cooling the liquid crystal state that appears due to temperature rise to below the glass transition temperature (Tg). That is, the immobilization of this liquid crystal state in the solid is nothing but the expression of the memory property.

The rewritable thermosensitive recording medium utilizes the thermal characteristics of the polymer liquid crystal. That is, this type of thermal recording medium comprises a support and a recording layer which is laminated on the support via an underlayer and contains a polymer liquid crystal, and the durability of the recording layer on the recording layer is increased as necessary. A protective layer for improving the properties and the like is provided, and a part of the recording layer is heated by a thermal printing means such as a thermal printer to a recording preset temperature higher than the glass transition temperature (Tg) of the polymer liquid crystal, and this is revealed by this heating. It is a means for forming a desired recorded image by rapidly cooling the liquid crystal state to below the glass transition temperature (Tg) and fixing it.

Since the polymer liquid crystal exhibits a reversible phase transition behavior as described above, the recorded image can be rewritten unlike other thermal recording media using a leuco dye or the like.

[0006]

As described above, this type of heat-sensitive recording medium using a polymer liquid crystal has an advantage that the recorded image can be rewritten as compared with other heat-sensitive recording media, but on the other hand, The recording layer changes from the solid state to the liquid state each time it is rewritten, and the state changes repeatedly again to the solid state, so that a shift stress is apt to act between the underlayer and the recording layer, and further thermal contraction between the underlayer and the recording layer. In addition to the stress due to the difference in the rate, usually, the thermal recording medium is conveyed by a pair of heating rollers that rotate during a rewriting operation, so a slight difference in speed between the rollers easily causes stress.
Due to these factors, the adhesive strength between the underlayer and the recording layer is reduced, and as a result, the recording layer easily peels off from the underlayer over time, and a heat-sensitive layer provided with a protective layer on the recording layer. Also in the recording medium, for the same reason, there is a problem that the adhesive strength between the protective layer and the recording layer is lowered and the durability of the recording layer is easily lost with time.

The present invention has been made by paying attention to such a problem, and an object thereof is to provide a thermosensitive recording medium excellent in repeated rewriting resistance by increasing the adhesive strength between the underlayer and the recording layer. To do.

Another object of the present invention is to provide a thermosensitive recording medium in which the adhesive strength between the underlayer and the recording layer and the adhesive strength between the recording layer and the protective layer are increased to further improve the rewriting resistance. is there.

[0009]

That is, the invention according to claim 1 comprises a support and a recording layer which is laminated on the support via an underlayer and contains a polymer liquid crystal. A part of the polymer liquid crystal is heated to a recording preset temperature equal to or higher than the glass transition temperature (Tg), and the liquid crystal state caused by this heating is cooled to below the glass transition temperature (Tg) and fixed to form a recorded image. Assuming a rewritable thermal recording medium, the polymer liquid crystal has a glycidyl group represented by the following chemical formula (1), and the underlayer is made of a resin having a functional group capable of binding to the glycidyl group. It is characterized by being

[Chemical 2] On the other hand, the invention according to claim 2 is based on the heat-sensitive recording medium according to claim 1, and is provided with a protective layer which is laminated on the recording layer and is made of a resin having a functional group capable of binding to a glycidyl group. It is what

The invention according to claim 3 is premised on the thermosensitive recording medium according to claim 1 or 2, wherein the polymer liquid crystal has a glycidyl group and the monomer content thereof is 1 mol% or more and 30 mol or more. % Or less of a monomer, a nematic monomer, and a cholesteric monomer.

In such technical means, as the polymer liquid crystal having a glycidyl group, for example, a copolymer of a monomer having this glycidyl group, a collective monomer, and a nematic monomer can be applied.

Specific examples will be given below. As the above-mentioned glycidyl group-containing monomer,

[Chemical 3] And the like, and as the cholesteric monomer,

[Chemical 4] Etc. can be applied.

Further, as the nematic monomer,

[Chemical 5] Etc. can be applied.

The copolymer composed of these monomers has a structure in which the polymerized part of the monomer having a glycidyl group, the cholesteric monomer polymerized part, and the nematic polymerized part are bonded together, As an example of the monomer polymerization part having a glycidyl group, the chemical formula (2) is in a state of being polymerized with each other,

[Chemical 6] However, as an example of the polymerized portion of the cholesteric monomer, the above chemical formula (3) is in a state of being polymerized with each other,

[Chemical 7] Further, as an example of the nematic polymerizing part, the above chemical formula (4) is in a state of being polymerized with each other,

[Chemical 8] Is mentioned.

However, in the above chemical formulas (2) to (7), the side chain of A has a glycidyl group at its terminal, and X is -O.
Either-or-NH-. Further, in the chemical formulas (5) to (7), α, β, and γ are integers indicating the polymerization degrees of the respective monomers, and the chemical formulas (2) to
In (7), R ₁ is a hydrogen atom or a methyl group, and R ₂ is

[Chemical 9] Or

[Chemical 10] Is.

Further, R in the chemical formulas (4) and (7)
₃ is

[Chemical 11] Or

[Chemical 12] Or

[Chemical 13] Is. In the chemical formula (9), R ₄ is a methyl group,
It is either an ethyl group or a propyl group.

Further, the chemical formulas (8) and (9) to (11)
In the above, m and n indicating the number of methylene groups are integers of 1 to 14, preferably 4 to 6.

This polymethylene group-(CH ₂ ) _n -,-
Specific examples of (CH ₂ ) _m − include a methylene group, a dimethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, a nonamethylene group, a decamethylene group, an untadecamethylene group,
Examples thereof include a tetradecamethylene group.

Here, when the composition ratio of the monomer having a glycidyl group in the copolymer is less than 1 mol%,
When the glycidyl group is insufficient, the adhesive strength between the underlayer and the recording layer and the adhesive strength between the protective layer and the recording layer are insufficiently improved, and when it exceeds 30 mol%, the above copolymer shows a liquid crystal state. It may disappear.

On the other hand, when the composition ratio of the monomer having a glycidyl group is in the range of 1 mol% or more and 30 mol% or less, the above copolymer shows a liquid crystal state, and further, the underlayer and the recording layer and the recording layer. And the adhesion between the protective layer becomes stronger,
There is an advantage that the recording layer is less likely to be peeled off from the underlayer or the protective layer and the rewriting durability is greatly improved.

The invention according to claim 3 is based on such a technical reason. The composition ratio of the monomer having a glycidyl group in the above copolymer is 1 mol% or more and 30% or more.
By setting the content to be not more than mol%, the adhesive strength between the underlayer and the recording layer and between the recording layer and the protective layer is greatly increased while maintaining the performance of the polymer liquid crystal.

When the composition ratio of the cholesteric monomer as the chiral component in the above copolymer is 5 mol% or more and 50 mol% or less, this copolymer is 400 nm to 7 nm.
Since it has selective reflectivity in the visible region of 00 nm,
Color liquid crystal states of various hues can be set by changing the setting of the color development temperature.

On the other hand, as the resin constituting the underlayer and the protective layer and having a functional group capable of binding to the glycidyl group, an amino group, an imino group, an isocyanate group, or
A resin having a glycidyl group or the like can be applied. When a resin having a glycidyl group is used, a curing agent such as an amine for initiating a reaction between the glycidyl group contained in the polymer liquid crystal and the glycidyl group contained in the underlayer is contained in the underlayer. I need to keep it.

Examples of such a resin include an epoxy resin obtained by polymerizing a known epoxy compound and an amine compound under an epoxy compound or an excessive amount of the amine compound, and a known isocyanate compound and a polyol resin. Examples thereof include polyurethane resins obtained by polymerizing the above isocyanate compound under excessive conditions.

Here, in the heat-sensitive recording medium according to any one of claims 1 to 3, the glycidyl group contained in the polymer liquid crystal and the amino group contained in the underlayer and the like are bound to each other to form the recording layer and the underlayer. In order to improve the adhesive strength with the recording layer, the recording layer may also be formed by including a glycidyl group in the underlayer and the protective layer and a functional group capable of binding to the glycidyl group in the polymer liquid crystal. It is possible to improve the adhesive strength between the underlayer and the underlayer.

The inventions according to claims 4 to 5 are created for such technical reasons.

That is, the invention according to claim 4 is provided with a support and a recording layer which is laminated on the support via an underlayer and contains a polymer liquid crystal, and a part of the recording layer is a polymer liquid crystal. Rewritable heat-sensitive recording medium which forms a recorded image by heating to a recording preset temperature above the glass transition temperature (Tg) and fixing the liquid crystal state developed by this heating below the glass transition temperature (Tg). The polymer liquid crystal has a functional group capable of binding to the glycidyl group represented by the chemical formula (1), and the underlayer is made of a resin having a glycidyl group. The invention according to claim 5 is based on the thermosensitive recording medium according to claim 4, and is provided with a protective layer formed on the recording layer and made of a resin having a glycidyl group. Do It is.

Examples of the functional group capable of binding to the glycidyl group include an amino group, an imino group, an isocyanate group, and a glycidyl group as described above, and a polymer having such a functional group. The liquid crystal may be any one of claims 1 to 3.
Similarly to the invention according to, a monomer having the above functional group,
Examples thereof include copolymers of cholesteric monomers and nematic monomers.

Further, as the material applicable to the support in the thermal recording medium according to the first to fifth aspects, not only paper such as high-quality paper but also plastic film or sheet such as polyester sheet for prepaid card is applied. It is possible.

The recording process using the thermal recording medium thus constructed is performed as follows.

There is a slight difference in the recording operation between the case where the polymer liquid crystal has a selective reflection ability (when it has a chiral component) and the case where it does not have a selective reflection ability. Each of these will be described below.

However, the recording method described below is only one example of the recording method using this thermal recording medium, and a recording method different from the recording method described below using the thermal recording medium to which the above-mentioned polymer liquid crystal is applied. Of course it is good even if you take it.

(1) When Polymer Liquid Crystal Does Not Have Selective Reflectivity First, the entire recording layer containing the polymer liquid crystal is once heated to an isotropic phase transition temperature (Tcl) or higher to be in a transparent state and history information is recorded. After erasing, the liquid crystal is cooled to a temperature below the glass transition temperature (Tg) to fix the polymer liquid crystal in a substantially transparent or cloudy liquid crystal state for an initialization process. The method of setting the liquid crystal state to either substantially transparent or cloudy is as follows.
It can be selectively set by appropriately adjusting a pressure means, for example, by adjusting the pressure when inserting between a pair of heating rollers.

Then, a part of the recording layer of the initialized thermal recording medium is heated by a thermal printing means such as a thermal printer to an appropriate recording set temperature higher than the glass transition temperature (Tg) so as to be in a transparent or cloudy liquid crystal state. Further, this is cooled below the glass transition temperature (Tg) to immobilize the polymer liquid crystal at the heated portion, and differentiated from the base region which is the unheated portion to form a recorded image. In this case, whether the polymer liquid crystal in the heated portion is in a transparent or cloudy liquid crystal state is arbitrarily set within a range that can be differentiated from the liquid crystal state in the base region which is the non-heated portion. Incidentally, the method of selectively setting the polymer liquid crystal in the heated portion to the transparent or cloudy liquid crystal state is the same as in the case of the above-mentioned initialization processing, and is arbitrarily set by the recording set temperature and the set pressure when pressurizing the recording layer. it can.

On the other hand, in order to erase the recorded image, first, the entire recording layer on which the recorded image is formed is heated again to the isotropic phase transition temperature (Tcl) or higher to bring it into a transparent state. It is processed and used for writing again.

(2) Polymer Liquid Crystal Having Selective Reflectivity When the polymer liquid crystal has a chiral component, the polymer liquid crystal has selective reflectivity and can form recorded images of various hues. Have advantages.

First, the entire recording layer containing the above-mentioned polymer liquid crystal is once heated to an isotropic phase transition temperature (Tcl) or higher to make it transparent so that history information is erased and the glass transition temperature (T
g) Cooling to below to fix the polymer liquid crystal in a substantially transparent liquid crystal state.

Next, the entire recording layer is heated to a color development temperature not lower than the isotropic phase transition temperature (Tcl) and not lower than the glass transition temperature (Tg) to be an appropriate color liquid crystal state. When cooled below (Tg), the liquid crystal state can be fixed by performing the above-mentioned pressure treatment, and the base state of the specific color, that is, the initialization process is performed.

In this case, if the polymer liquid crystal has a selective reflection ability, it becomes possible to set the color liquid crystal state of various hues due to the difference in the setting of the color development temperature, so that the hue of the base state can be arbitrarily set. Can be set. Therefore, it is possible to form recorded images of various hues by arbitrarily setting the base state, so that there is an advantage that the variations of the recorded images can be expanded.

As in the case of the polymer liquid crystal not having the selective reflection ability, it goes without saying that the history information erasing process and the initializing process may be performed in one operation.

Then, a part of the recording layer of the initialized thermal recording medium is heated by a thermal printing means such as a thermal printer to a recording set temperature higher than the glass transition temperature (Tg), and the liquid crystal state developed by the heating is heated. By cooling to below the glass transition temperature (Tg) and immobilizing, it is possible to differentiate from the base region which is a non-heated portion and obtain a recorded image. in this case,
By setting the recording set temperature appropriately above the glass transition temperature (Tg) and below the isotropic phase transition temperature (Tcl), the liquid crystal color state peculiar to the temperature can be fixed, and the above recording set temperature is isotropic. By setting the phase transition temperature (Tcl) or higher, a substantially transparent liquid crystal state can be fixed.

On the other hand, in order to erase this recorded image, first, the entire recording layer on which this recorded image is formed is heated again to the isotropic phase transition temperature (Tcl) or higher to bring it into a transparent state. It is processed and used for writing again.

Here, as described above, when the composition ratio of the cholesteric monomer as the chiral component in the copolymer constituting the polymer liquid crystal is 5 mol% or more and 50 mol% or less, the copolymer is 400 nm to 400 nm. The above-mentioned treatment is possible because it has selective reflectivity in the visible region of 700 nm.

The method for synthesizing a polymer liquid crystal having selective reflection ability is limited to the above-mentioned copolymerization method of a monomer having a glycidyl group or a monomer having a functional group capable of binding to the glycidyl group, a nematic monomer and a cholesteric monomer. Alternatively, it can be obtained by the following synthesis method. That is, a method of polymerizing a cholesteric monomer obtained by bonding a chiral compound (for example, a compound containing an asymmetric carbon constituting an optical isomer) to a nematic monomer itself, or a nematic monomer and a non-mesogenic chiral monomer. And a copolymerization method and the like. The polymer liquid crystal obtained by such a synthesis method can express a cholesteric phase, and its selective reflection wavelength can be controlled by the composition and composition ratio of the copolymerization.

Next, as a method of forming a recording layer on a support such as the above-mentioned paper, plastic film or sheet through the underlayer by these technical means, for example, an underlayer coating liquid is applied and dried. After forming an underlayer by applying a recording layer coating solution obtained by dissolving the polymer liquid crystal and an appropriate binder in an organic solvent, a coating means such as bar coating, blade coating, air knife coating, gravure coating, and roll coating. And a method of forming a recording layer by drying the same. When a protective layer is provided on the recording layer, it can be formed by applying and drying a protective layer coating solution obtained by appropriately adding a filler such as an inorganic pigment or wax.

The image forming or image erasing means according to the present invention is based on heat, and can be carried out by using, for example, a thermal printer, a thermal reflection copying apparatus, a hot stamper, a thermal roll and the like.

[0047]

According to the invention of claim 1, the polymer liquid crystal is composed of a polymer liquid crystal having a glycidyl group, and the underlayer is composed of a resin having a functional group capable of binding to the glycidyl group. The functional group in the resin constituting the underlayer and the glycidyl group of the polymer liquid crystal are chemically bonded to each other, whereby the adhesive strength between the underlayer and the recording layer can be increased.

On the other hand, according to the second aspect of the present invention, since the protective layer is provided on the recording layer and is made of a resin having a functional group capable of binding to a glycidyl group, the underlayer and the protective layer are provided. The functional groups in the constituent resin and the glycidyl groups of the polymer liquid crystal are chemically bonded to each other to increase the adhesive strength between the underlayer and the recording layer and between the recording layer and the protective layer.

According to the invention of claim 3, the polymer liquid crystal has a glycidyl group and the monomer content is 1
Since it is composed of a copolymer of mol% or more and 30 mol% or less, a nematic monomer, and a cholesteric monomer, the underlayer, the recording layer, and the recording layer can be formed while maintaining the liquid crystal performance of the polymer liquid crystal. The adhesive strength between the protective layers can be increased.

Next, according to the invention of claim 4, the polymer liquid crystal is composed of a polymer liquid crystal having a functional group capable of binding to a glycidyl group, and the underlayer is composed of a resin having this glycidyl group. Therefore, the glycidyl group in the resin forming the underlayer and the functional group of the polymer liquid crystal are chemically bonded to each other, whereby the adhesive strength between the underlayer and the recording layer can be increased, and the invention according to claim 5 According to this, since the protective layer is formed by the resin having a glycidyl group laminated on the recording layer, the glycidyl group in the resin constituting the underlayer and the protective layer and the functional group of the polymer liquid crystal are respectively By chemically bonding, the adhesive strength between the underlayer and the recording layer and between the recording layer and the protective layer can be increased.

[0051]

EXAMPLES Next, examples of the present invention will be described in detail.

Example 1 (Synthesis of Cholesteric Monomer and Nematic Monomer) Before synthesizing a polymer liquid crystal having a glycidyl group,
First, cholesteric monomer and nematic monomer, which are the raw materials, were synthesized.

That is, 1.0 mol of 6-bromocaproic acid represented by the following chemical formula (12) is used for the following chemical formula (1
1.2 mol of cholesterol represented by 3) is dissolved in a solvent such as THF, and 1.2 mol of DDC (N, N'-dicyclohexylcarbodiimide) and N, N-dimethylaminopyridine which is a tertiary amine are added. 1 mol was added, and the above 6-bromocaproic acid and cholesterol were subjected to a condensation reaction at room temperature for 24 hours and purified by a conventional method to obtain a compound represented by the chemical formula (14). The yield was 98%.

[0054]

[Chemical 14] Then, using a solvent such as DMF, the acrylic acid represented by the chemical formula (15) and the compound represented by the chemical formula (14) are added in the presence of triethylamine, and hydroquinone which is a polymerization inhibitor is added in a catalytic amount. The dehydrobromination reaction was carried out under the condition of 8 ° C. for 8 hours, and further purified according to a conventional method to synthesize a cholesteric monomer (Compound 1) represented by the chemical formula (16). The yield was 87%.

[0055]

[Chemical 15] Next, a compound represented by the chemical formula (19) is first synthesized by the same synthetic method, and this compound and acrylic acid are reacted (dehydrobromination reaction) to produce a nematic monomer (compound 2) represented by the following chemical formula (20). ) Was asked.

The yield of the compound represented by the chemical formula (19) was 83%, and the yield of the compound 2 represented by the chemical formula (20) was 97%.

[0057]

[Chemical 16]

[Chemical 17] (Synthesis of Polymer Liquid Crystal) 25 mol% of the cholesteric monomer (Compound 1) represented by the above chemical formula (16) and 50 mol% of the nematic monomer (Compound 2) represented by the above chemical formula (20) thus synthesized And 25 mol% of glycidyl methacrylate (compound 3) having a glycidyl group and represented by the following chemical formula (21) are dissolved in a benzene solution, and α, α′-azobisisobutyronitrile (AIBN) is used as a polymerization initiator. Polymerization reaction was performed for 8 hours at 60 ° C. in a nitrogen atmosphere, and then purified by reprecipitation from methanol to synthesize a polymer liquid crystal of compound 4 represented by the following chemical formula (22).

Regarding α, β and γ in the chemical formula (22), α / β / γ = 25/50/25 (molar ratio).

Further, the glass transition temperature (Tg) and the isotropic phase transition temperature (Tc) of the polymer liquid crystal represented by the chemical formula (22).
1) and liquid crystallinity are shown in Table 1 below.

[0060]

[Chemical 18]

[Chemical 19] Next, using a black plastic sheet as a support, an epoxy resin (trade name E manufactured by Yuka Shell Epoxy Co., Ltd.
P828) 1-cyanoethyl-2-ethyl-4-methylimidazole (product name 2E4MZ-CN manufactured by Shikoku Kasei Co., Ltd.) 5.0 phr as a curing agent for this resin was dissolved to obtain a coating agent obtained under an excessive curing agent condition. The solution was used as an underlayer coating solution, which was applied with a Mayer bar, dried in a hot-air circulation type oven at 70 ° C. for 10 minutes and precured to form an underlayer, and the above-mentioned composition was formed on this underlayer. A toluene solution of the cholesteric polymer liquid crystal (Compound 4) was applied with a Meyer bar and dried at 110 ° C. for 5 minutes to form a recording layer.

Then, a coating solution having the same composition as the above-mentioned undercoat layer coating solution was used as a protective layer coating solution, which was applied onto the recording layer with a Meyer bar and dried at 110 ° C. for 30 minutes to form a protective layer. A heat-sensitive recording sheet was formed and was obtained.

An adhesive tape was attached to the surface of the protective layer of the heat-sensitive recording sheet thus obtained, and JIS K5400 was used.
According to -1990 (cross-cut tape method), whether or not the adhesive tape was peeled off to peel off the recording layer (that is, whether or not the recording layer remained) was confirmed and evaluated. The results are shown in Table 1.

Regarding this evaluation, ○ (good), △
(Approximately good) and x (bad) are displayed.

Example 2 28 mol% of the cholesteric monomer (Compound 1) represented by the above chemical formula (16),
57 mol% of the nematic monomer (compound 2) represented by the chemical formula (20) is reacted with 15 mol% of glycidyl methacrylate (compound 3) having a glycidyl group and represented by the chemical formula (21) to react with the chemical formula (22). ) Is substantially the same as in Example 1 except that a polymer liquid crystal of compound 4 shown in FIG.

In the chemical formula (22), α, β and γ are α / β / γ = 28/57/15 (molar ratio), respectively, and the glass transition temperature (Tg) of this polymer liquid crystal. Example 1 for the isotropic phase transition temperature (Tcl) and liquid crystallinity
The same is shown in Table 1.

The results of JIS K5400 (cross-cut tape method) described above are also shown in Table 1 as in Example 1.

Example 3 32 mol% of the cholesteric monomer (Compound 1) represented by the above chemical formula (16),
63 mol% of the nematic monomer (compound 2) represented by the above chemical formula (20) is reacted with 5 mol% of glycidyl methacrylate (compound 3) having a glycidyl group and represented by the above chemical formula (21) to react with the above chemical formula (22). Example 1 except that a polymer liquid crystal of compound 4 represented by
Is almost the same as.

In the chemical formula (22), α, β, and γ are α / β / γ = 32/63/5 (molar ratio), respectively, and the glass transition temperature (Tg) of the polymer liquid crystal. Example 1 for the isotropic phase transition temperature (Tcl) and liquid crystallinity
The same is shown in Table 1.

The results of JIS K5400 (cross-cut tape method) described above are also shown in Table 1 as in Example 1.

Example 4 33 mol% of the cholesteric monomer (Compound 1) represented by the above chemical formula (16),
66 mol% of the nematic monomer (compound 2) represented by the chemical formula (20) is reacted with 1 mol% of glycidyl methacrylate (compound 3) having a glycidyl group and represented by the chemical formula (21) to react with the chemical formula (22). Example 1 except that a polymer liquid crystal of compound 4 represented by
Is almost the same as.

In the chemical formula (22), α, β and γ are α / β / γ = 33/66/1 (molar ratio), respectively, and the glass transition temperature (Tg) of this polymer liquid crystal is Example 1 for the isotropic phase transition temperature (Tcl) and liquid crystallinity
The same is shown in Table 1.

The results of JIS K5400 (cross-cut tape method) described above are also shown in Table 1 as in Example 1.

Comparative Example 33 mol% of the cholesteric monomer (Compound 1) represented by the chemical formula (16) and 67 mol% of the nematic monomer (Compound 2) represented by the chemical formula (20) were dissolved in a benzene solution. As a polymerization initiator, α, α′-azobisisobutyronitrile (A
Example 1 except that a polymer liquid crystal of compound 5 represented by the following chemical formula (23) was synthesized by performing a polymerization reaction for 8 hours at 60 ° C. under a nitrogen atmosphere using IBN) and then purifying by reprecipitation from methanol. It is almost the same as 1.

The glass transition temperature (T
g), isotropic phase transition temperature (Tcl), and liquid crystallinity are shown in Table 1 as in Example 1 and the above-mentioned JI
The results of S K5400 (cross-cut tape method) are also shown in Table 1.

[0075]

[Chemical 20]

[Table 1] [Example 5] 30 mol% of the cholesteric monomer (compound 1) represented by the chemical formula (16) and the nematic monomer (compound 2) 6 represented by the chemical formula (20) 6
0 mol% and 10 mol% of an acrylic acid amide having an amino group and represented by the following chemical formula (24) (Compound 6) were dissolved in a benzene solution, and α, α′-azobisisobutyi was used as a polymerization initiator. Polymerization liquid crystal of compound 7 represented by the following chemical formula (25) was synthesized by performing a polymerization reaction for 8 hours at 60 ° C. in a nitrogen atmosphere using ronitrile (AIBN), and then synthesizing a polymer liquid crystal of compound 7. Except for this, it is substantially the same as in Example 1.

A thermosensitive recording sheet to which this polymer liquid crystal was applied was also JIS K540 as in Example 1.
An evaluation test of 0 (cross-cut tape method) was performed. The results are shown in Table 2 below. In this table, the higher the evaluation score, the better. In addition, Table 2 also shows the results of the thermal recording sheet according to the comparative example.

[0077]

[Chemical 21]

[Chemical formula 22] Example 6 An allylamine (compound 8) represented by the following chemical formula (26) was applied in place of the acrylic acid amide (compound 6) represented by the chemical formula (24), and the following chemical formula (2
It is substantially the same as Example 5 except that a polymer liquid crystal of the compound 9 shown in 7) was synthesized.

A thermosensitive recording sheet to which this polymer liquid crystal is applied is also JIS K540 as in Example 5.
An evaluation test of 0 (cross-cut tape method) was performed. The results are shown in Table 2 below.

[0079]

[Chemical formula 23]

[Chemical formula 24]

[Table 2] [Recording Test and Repeated Rewriting Resistance Test] Next, the thermal recording sheets of Examples 1 to 6 and Comparative Example thus obtained were each subjected to an initialization treatment and the hue of the base thereof was set to blue.

The initialization process is carried out by inserting each heat-sensitive recording sheet for one second between a pair of heating rollers set to a blue color development temperature and a contact pressure of 0.1 kg / cm ^2. It was

Then, the recording layer of the initialized thermal recording sheet is selectively heated by using a thermal simulator manufactured by Toshiba, and the heated portion is heated to an isotropic phase transition temperature (Tcl).
It is heated to the above to be in a transparent state and is rapidly cooled to a glass transition temperature (Tg) or lower to be fixed in a substantially transparent liquid crystal state,
The recorded image was obtained by differentiating from the blue base region, which is an unheated region.

In order to erase the recorded image, the entire recording layer is once heated to the isotropic phase transition temperature (Tcl) or higher to make it transparent so that the history information is erased, and the glass transition temperature (Tg) is set. ) It is cooled below to fix the polymer liquid crystal in a substantially transparent liquid crystal state. Then, by performing the same processing as the above initialization processing, it becomes possible to use it again for writing.

It was confirmed that good recording images can be obtained for both the heat-sensitive recording sheets according to Examples 1 to 6 and the heat-sensitive recording sheets according to the comparative example, and that the rewriting is possible. It was

Next, regarding the repeated rewriting resistance of these heat-sensitive recording sheets, as is clear from the results of Tables 1 and 2 in which the results of the above-mentioned JIS test are described, the heat-sensitive recording sheets according to Examples 1 to 6 are It was confirmed that the heat-sensitive recording sheet according to the comparative example was significantly superior.

[0085]

According to the first aspect of the invention, the functional group in the resin forming the underlayer and the glycidyl group of the polymer liquid crystal are chemically bonded to each other to increase the adhesive strength between the underlayer and the recording layer. Further, according to the invention of claim 4, the glycidyl group in the resin forming the underlayer and the functional group of the polymer liquid crystal are chemically bonded to each other to increase the adhesive strength between the underlayer and the recording layer. Therefore, it has the effect of improving the repeated rewriting resistance as a thermal recording medium.

On the other hand, according to the second aspect of the present invention, the functional groups in the resin forming the underlayer and the protective layer are chemically bonded to the glycidyl groups of the polymer liquid crystal, respectively, so that the underlayer and the recording layer And the adhesive strength between the recording layer and the protective layer is increased,
Further, according to the invention of claim 5, the glycidyl group in the resin forming the underlayer and the protective layer and the functional group of the polymer liquid crystal are chemically bonded to each other to form the underlayer, the recording layer, and the recording layer. Since the adhesive strength between the protective layer and the protective layer is increased, it has the effect of further improving the repeated rewriting resistance of the thermal recording medium.

Further, according to the invention of claim 3, there is an effect that the adhesive strength between the underlayer and the recording layer and between the recording layer and the protective layer can be improved while surely maintaining the liquid crystal performance of the polymer liquid crystal. There is.

Claims (5)

[Claims] 1. A support, and a recording layer containing a polymer liquid crystal laminated on the support via an underlayer, and a part of the recording layer is a glass transition temperature (Tg) of the polymer liquid crystal. In the rewritable heat-sensitive recording medium which forms a recorded image by heating to the recording set temperature and cooling the liquid crystal state appearing by the heating to a temperature below the glass transition temperature (Tg) to fix it, the polymer liquid crystal is A rewritable heat-sensitive recording medium having a glycidyl group represented by the following chemical formula (1) and the underlayer made of a resin having a functional group capable of binding to the glycidyl group. [Chemical 1] 2. The rewritable thermosensitive recording medium according to claim 1, further comprising a protective layer laminated on the recording layer and made of a resin having a functional group capable of binding to a glycidyl group. 3. The polymer liquid crystal is composed of a copolymer of a monomer having a glycidyl group and having a monomer content of 1 mol% to 30 mol%, a nematic monomer, and a cholesteric monomer. The rewritable heat-sensitive recording medium according to claim 1 or 2. 4. A support and a recording layer which is laminated on the support via an underlayer and contains a polymer liquid crystal, and a part of the recording layer is a glass transition temperature (Tg) of the polymer liquid crystal. In the rewritable heat-sensitive recording medium which forms a recorded image by heating to the recording set temperature and cooling the liquid crystal state appearing by the heating to a temperature below the glass transition temperature (Tg) to fix it, the polymer liquid crystal is A rewritable heat-sensitive recording medium having a functional group capable of binding to the glycidyl group represented by the chemical formula (1), and the underlayer made of a resin having a glycidyl group. 5. The rewritable thermosensitive recording medium according to claim 4, further comprising a protective layer laminated on the recording layer and made of a resin having a glycidyl group.