JPH06138428A - Production of reloadable thermosensitive recording medium - Google Patents

Abstract

PURPOSE:To enhance the adhesive power between a recording layer and a protective layer and to improve repetitive rewriting resistance by forming the protective layer by coating in a soln. state contg. a solvent capable of solving the high-polymer liquid crystal of the recording layer. CONSTITUTION:The recording layer of the initialized thermosensitive recording medium is heated to a proper recording set temp. of a glass transition temp. (Tg) or above by a thermal printing means, such as thermal printer. The transparent and opaque liq-crystal state is than obtd. This recording medium is cooled down to the glass transition temp. or below to immobilize the high-polymer liquid crystal in the heated part and to discriminate the heated part from a base region which is the non-heated part, by which the recording image is formed. The protective layer is formed by coating the surface of the recording layer with the protective layer coating liquid prepd. by adding proper inorg. pigments and fillers, such as wax, further to the material soln. for which the solvent capable of dissolving the high- polymer liquid crystal is used, and drying the coating in the case of provision of the protective layer on the recording layer. Then, the respective layers are mingled with each other at the boundary between the recording layer and the protective layer, by which the continuous layer is formed. The adhesive power between the recording layer and the protective layer is therefore increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rewritable heat-sensitive recording medium having a recording layer containing a polymer liquid crystal on a support, and particularly improving the adhesion between the recording layer and the protective layer. The present invention relates to a method of manufacturing a heat-sensitive recording medium that can be used.

[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 when the temperature rises 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, a recording layer containing a polymer liquid crystal, and a protective layer on the recording layer for improving the durability of the recording layer. A part of the layer is heated by a thermal printing means such as a thermal printer to a recording set temperature higher than the glass transition temperature (Tg) of the polymer liquid crystal, and the liquid crystal state developed by this heating is rapidly cooled down to the glass transition temperature (Tg) or lower. It is a means for forming a desired recorded image by immobilizing and fixing.

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 the polymer liquid crystal has an advantage that the recorded image can be rewritten as compared with other heat-sensitive recording mediums. The recording layer changes from the solid state to the liquid state each time it is rewritten, and the state repeats again to the solid state, so that a shift stress is apt to act between the recording layer and the protective layer, and further, thermal contraction between the protective layer and the recording layer. Along with 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 the rewriting operation, so a slight difference in speed between the rollers easily causes stress.
Due to these factors, the adhesive strength between the protective layer and the recording layer is lowered, and the durability of the recording layer tends to be lost over time.

The present invention has been made by paying attention to such a problem, and its object is to manufacture a heat-sensitive recording medium excellent in repeated rewriting resistance by increasing the adhesive force between the recording layer and the protective layer. To provide a method.

[0008]

That is, the present invention has at least a recording layer containing a polymer liquid crystal and a protective layer on a support, and a part of the recording layer is a glass transition temperature (Tg) of the polymer liquid crystal. ) In the method for producing a rewritable heat-sensitive recording medium, which forms a recorded image by heating to the above recording set temperature and cooling and fixing the liquid crystal state appearing by the heating to a glass transition temperature (Tg) or less, It is characterized in that the protective layer is applied and formed in a solution state containing a solvent in which the polymer liquid crystal of the recording layer is soluble.

The present invention will be described in detail below. As the support of the present invention, not only paper such as high-quality paper but also plastic film or sheet such as polyester sheet for prepaid card can be applied.

Next, as a material for forming the recording layer, a memory property is exhibited by exhibiting a 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 (Tcl), and , Is a cholesteric polymer liquid crystal that can select any selective reflection wavelength by cholesteric pitch,
And, if it is soluble in a solvent, it is not particularly limited, for example, a copolymer of a nematic monomer and a cholesteric monomer, or a terpolymer of a nematic monomer and a cholesteric monomer, and a monomer having a glycyl group. Can be given. Further, the polymer liquid crystal is soluble in a solvent such as toluene, tetrahydrofuran or benzene.

As the nematic monomer,

[0012]

[Chemical 1]

And the like, and as the cholesteric monomer,

[0014]

[Chemical 2]

The above can be applied.

The polymer liquid crystal formed by polymerizing the monomers has a structure in which a nematic monomer polymerized portion and a cholesteric monomer polymerized portion are bonded to each other. As an example of the nematic monomer polymerized portion, the above chemical formula ( 1) are in the state of being polymerized with each other,

[0017]

[Chemical 3]

As an example of the cholesteric monomer polymerization part, the above chemical formula (2) is in a state of being polymerized with each other,

[0019]

[Chemical 4]

And the like.

However, in the above chemical formulas (1) to (4), X
Is either -O- or -NH-. Further, in chemical formulas (3) and (4), α and β are integers indicating the degree of polymerization of each monomer.

In the above chemical formulas (1) to (4), R ₁
Is a hydrogen atom or a methyl group, and R ₃ is

[0023]

[Chemical 5]

Or

[0025]

[Chemical 6]

[0026]

In the chemical formulas (1) to (4), R ₂ is

[0028]

[Chemical 7]

Or

[0030]

[Chemical 8]

In the above chemical formula (7), R ₄ is any of a methyl group, an ethyl group and a propyl group.

Further, the chemical formulas (5) and (7) to (8)
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.

A recording layer coating solution is prepared by bringing the above-mentioned polymer liquid crystal into a solution state, and is applied on a support by a known coating method such as a gravure coater or a roll coater to form a recording layer.

The material for forming the protective layer is not particularly limited as long as it is soluble in a solvent, capable of forming a film, and excellent in transparency, heat resistance, flexibility and curability. However, examples thereof include polymers or copolymers such as acrylates, or monomers or oligomers such as monofunctional or polyfunctional acrylates, methacrylates, urethane acrylates, and oligoester acrylates. In addition, the above materials are toluene,
It is soluble in solvents such as tetrahydrofuran and benzene.

A coating solution for the protective layer is prepared by bringing the above-mentioned materials and solvent into a solution state, and the protective layer is formed on the support by a known coating method such as a gravure coater or a roll coater. The coating liquid may be cured by drying with warm air, irradiation with ultraviolet rays, or the like.

When the underlayer is formed between the support and the recording layer, the material may be basically the same as the above-mentioned protective layer. The underlayer is formed by preparing a coating solution for the underlayer by bringing the material and the solvent into a solution, and applying the undercoat layer on the support by a known coating method such as a gravure coater or a roll coater.

The recording process using the heat-sensitive 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 (having 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 merely 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 the Polymer Liquid Crystal Does Not Have Selective Reflectivity First, the entire recording layer containing the polymer liquid crystal is once heated to the isotropic phase transition temperature (Tcl) or higher to be in a transparent state and history information is recorded. After erasing, this 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 not lower than the glass transition temperature (Tg) to be in a transparent or cloudy liquid crystal state. Further, this is cooled to a temperature below the glass transition temperature (Tg) to immobilize the polymer liquid crystal in the heated region, and differentiated from the base region which is the unheated region to form a recorded image. In this case, whether the polymer liquid crystal in the heated region 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 region. Incidentally, the method of selectively setting the polymer liquid crystal at the heated portion to a 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 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.

(2) When the polymer liquid crystal has selective reflection ability When the above-mentioned polymer liquid crystal has a chiral component, this polymer liquid crystal has a selective reflection ability 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 more to make it transparent so that history information is erased and the glass transition temperature (T
g) It is cooled below to fix the polymer liquid crystal in a substantially transparent liquid crystal state.

Next, the entire recording layer is heated to a color-developing temperature not lower than the isotropic phase transition temperature (Tcl) and not lower than the glass transition temperature (Tg) to be a proper 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 variation of the recorded images can be expanded.

As in the case of the polymer liquid crystal not having the selective reflection ability, the history information erasing process and the initializing process may be performed in a single 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 to a temperature higher than the glass transition temperature (Tg) and lower than the isotropic phase transition temperature (Tcl), the liquid crystal color state peculiar to the temperature can be fixed, and the 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, and then the above initialization is performed. It is processed and used for writing again.

Next, in these technical means, in order to form the recording layer on the support such as the above-mentioned paper, plastic film or sheet via the underlayer, first, the underlayer coating liquid is applied and dried. After forming the underlayer by applying a recording layer coating solution obtained by dissolving the polymer liquid crystal and a binder in an organic solvent as appropriate, coating means such as bar coating, blade coating, air knife coating, gravure coating, and roll coating. It is possible to form a recording layer by applying the above method and drying it. Further, when a protective layer is provided on the recording layer, a material (polymer / monomer / oligomer) solution using a solvent in which a polymer liquid crystal is soluble, and an inorganic pigment or a filler such as a wax are appropriately added to obtain the protective layer. It can be formed by coating and drying a protective layer coating solution.

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 machine, a hot stamper, a thermal roll and the like.

[0053]

According to the present invention, when a protective layer is further provided on the recording layer, the protective layer is applied in a solution state containing a soluble solvent for the recording layer. Are mixed together to form a continuous layer, so that the adhesive force between the recording layer and the protective layer can be increased.

[0054]

EXAMPLES Next, examples of the present invention will be described in detail. An experiment was conducted using a polymer liquid crystal having the following structure.

[Example 1] A methylmethacrylate copolymer (Mitsubishi Rayon Co., Ltd.) was used as a base and protective layer coating liquid.
(Product name: BR-83 Tg = 105 ° C.) solid content 3
A 3% toluene solution was applied onto PET with a Meyer bar and dried to form a base layer.

Next, the solid content 3 of the polymer liquid crystal shown below
A 3% toluene solution was applied and dried to form a recording layer.

[0057]

[Chemical 9]

Further, the above-mentioned base and protective layer coating liquid was applied onto the recording layer and dried, and then a heat-sensitive recording sheet (rewritable heat-sensitive recording medium) 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), it was confirmed whether the adhesive tape was peeled off and the recording layer was peeled off (that is, whether the recording layer remained), and the evaluation was performed. The results are shown in Table 1.

[Example 2] As an undercoat layer coating solution, a toluene solution of methyl methacrylate copolymer (manufactured by Mitsubishi Rayon Co., Ltd .: trade name BR-83) with a solid content of 33% was added as P.
A base layer was formed by coating and drying on ET with a Meyer bar.

Next, a recording solution was formed by applying a toluene solution of a polymer liquid crystal having a solid content of 33% as in Example 1 above and drying it.

Then, as a protective layer coating liquid, a 1/1 mixture liquid of polyfunctional acrylate (manufactured by Toagosei Kagaku Kogyo Co., Ltd .: trade name Aronix M-8060 and M-260) was added,
A photoinitiator (manufactured by Merck Japan KK: trade name Darocur 1173) was added at 5% to prepare a toluene solution having a solid content of 33%. This coating solution for protective layer was applied onto the recording layer, dried and then cured with ultraviolet rays to obtain a heat-sensitive recording sheet.

Table 1 shows the results of JIS K5400 (cross-cut tape method) described above.

Comparative Example As a base layer coating liquid, a toluene solution of methyl methacrylate copolymer (manufactured by Mitsubishi Rayon Co., Ltd .: trade name BR-83) having a solid content of 33% was PE.
A base layer was formed by applying and drying T on T with a Mayer bar.

Next, a recording layer was formed by coating and drying a toluene solution of a polymer liquid crystal having a solid content of 33% as in Example 1 above.

Next, as a protective layer coating liquid, a 1/1 mixture liquid of polyfunctional acrylate (trade name: Aronix M-8060 and M-260 manufactured by Toagosei Chemical Industry Co., Ltd.) was added,
A photoinitiator (manufactured by Merck Japan KK: trade name Darocur 1173) was added at 5% to prepare a protective layer coating liquid (without solvent). This coating solution for protective layer was applied onto the recording layer, dried and then cured with ultraviolet rays to obtain a heat-sensitive recording sheet.

Table 1 shows the results of JIS K5400 (cross-cut tape method) described above.

[0068]

[Table 1]

“Recording test and repeated rewriting resistance test”
Next, each of the heat-sensitive sheets of Examples 1 to 2 and Comparative Example thus obtained was subjected to an initialization process to set the hue of its base to blue.

The initialization process was carried out by inserting each heat-sensitive recording sheet for 1 second between a pair of heating rollers set to a blue coloring temperature and a contact pressure thereof set to 0.1 kg / cm ^2. It was

Then, the initialized recording layer of the heat-sensitive recording sheet is selectively heated using a thermal simulator manufactured by Toshiba, and the heated portion is 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,
A recorded image was obtained by differentiating from the blue base region which is the non-heated part.

In order to erase this 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 ) 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 for writing again.

Then, it was confirmed that good recording images can be obtained for both the thermal recording sheets according to Examples 1 and 2 and the thermal 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 Table 1 in which the results of the above-mentioned JIS test are described, the heat-sensitive recording sheets of the examples are the heat-sensitive recording sheets of the comparative examples. It was confirmed that it was significantly superior to the seat.

This difference is based on whether or not the coating liquid for the protective layer melts the surface of the recording layer and mixes at the interface to form a continuous layer, and the adhesion between the protective layer and the recording layer. It was confirmed that the force increased and the repeated rewriting resistance improved.

[0076]

According to the method for manufacturing a rewritable thermosensitive recording medium of the present invention, the underlayer and the recording layer and the protective layer are mixed at the respective interfaces to form a continuous layer, thereby forming the underlayer, the recording layer and the recording layer. Since the adhesive force between the protective layers is increased, it has the effect of further improving the rewriting resistance as a thermal recording medium.

Claims (1)

[Claims] 1. A support having at least a recording layer containing a polymer liquid crystal and a protective layer on a support, and heating a part of the recording layer to a recording preset temperature higher than the glass transition temperature (Tg) of the polymer liquid crystal. A method for producing a rewritable heat-sensitive recording medium in which a recording image is formed by cooling and fixing the liquid crystal state developed by this heating to a glass transition temperature (Tg) or lower, wherein the protective layer is a polymer of the recording layer. A method for producing a rewritable heat-sensitive recording medium, characterized in that the liquid crystal is applied and formed in a solution containing a solvent in which the liquid crystal is soluble.