JPH0952452A - Reversible recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible recording medium, in which an intermediate layer made of a thermoplastic resin is provided on a recording layer so as to improve the solvent resistance of the recording layer and, at the same time, a protective layer having proper unevenness on its surface is formed. SOLUTION: In a reversible recording medium consisting of a recording layer 1, the degree of light scattering of which is changed in response to external stimulus, is formed on a plastic film and a protective layer 3 formed at the surface of the medium, a spherical powder having a particle diameter, which is 0.5-2.0 times as much as the average film thickness of the protective layer 3, is included in the protective layer 3. In addition, an intermediate layer 5 made of a thermoplastic resin is provided between the recording layer 1 and the protective layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high quality reversible recording medium capable of repeatedly recording and erasing an image by reversibly changing the light scattering degree by an external stimulus such as heat, electric field, magnetic field and light. It is a thing.

[0002]

2. Description of the Related Art In recent years, various kinds of materials capable of reversibly recording and erasing images by an external stimulus, and various types of recording media applying these materials have been proposed. Among these technologies, a composite material of an organic low molecular weight compound and a high molecular weight compound, in which the light scattering degree reversibly changes, and a high molecular weight liquid crystal are promising materials for a recording medium because of their excellent durability. (JP-A-59-109)
No. 30, JP 62-14114, and JP 6
3-223066, JP-A-2-2513, etc.). These materials are formed as a recording layer of a recording medium on a base material such as a plastic film.

In general, this type of recording medium basically has a structure in which a recording layer 1 is formed on a substrate 2 as shown in FIG. 1 (a), and as shown in FIG. 1 (b). The recording layer 1 and the protective layer 3 containing the powder 4 are sequentially laminated on the base material 2 to have a layer structure. As the base material 2 of these recording media, resin films such as polyester, polyether, polyurethane, polyamide, polyimide, polyvinyl chloride, polycarbonate and the like, metal foil, paper, coated paper and the like are used, and the film thickness is 10
It is about 1,000 μm. Further, between the base material and the recording layer, a light reflection layer formed of a metal film of aluminum, silver, tin, magnesium, platinum or the like is provided by vapor deposition, sputtering or the like for the purpose of improving the light scattering degree. May be However, when the recording medium is used in the form of transmitted light, the light reflection layer is unnecessary. Furthermore, the protective layer is formed as a layer that prevents deterioration of the surface due to repeated use of the recording layer.

[0004]

In order to manufacture the above-mentioned recording medium, a base material having a recording layer formed by applying a coating liquid of a recording material onto a base material using a coating device such as a roll coater. The method of sequentially winding is adopted.
When the protective layer is provided on the recording layer, it is necessary that the solvent used for forming the protective layer does not dissolve the recording layer. However, in general, the resin material used for the protective layer has a high heat resistance, a high hardness and a low friction, and as the solvent thereof, a ketone, an ester or an aromatic type is used, There was a problem of dissolving the recording layer. Therefore, in order to form the protective layer, it is effective to interpose an intermediate layer between the recording layer and the protective layer. For the intermediate layer, it is preferable to use a thermoplastic resin that dissolves in a solvent in which the recording layer is difficult to dissolve, such as water, alcohol, or aliphatic hydrocarbon. However, when the intermediate layer made of a thermoplastic resin is interposed, the interface between the intermediate layer 5 and the protective layer 3 becomes uneven as shown in FIG.
Since the surface of the protective layer is smooth, there is a problem that the advantage of dispersing the powder 4 is lost.

Therefore, the present invention has been made to solve the above problems. That is, an object of the present invention is to provide a reversible recording medium in which an intermediate layer of a thermoplastic resin is provided on the recording layer in order to improve the solvent resistance of the recording layer, and a protective layer having appropriate irregularities on the surface is formed. To provide.

[0006]

The reversible recording medium of the present invention is a reversible recording medium having a recording layer having a light scattering degree reversibly changed by an external stimulus and a protective layer formed on the surface thereof on a plastic film. The protective layer contains a spherical powder having a particle diameter of 0.5 to 2.0 times the average film thickness of the protective layer, and an intermediate layer made of a thermoplastic resin is provided between the recording layer and the protective layer. It is characterized by

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The layer structure of the reversible recording medium of the present invention is as shown in FIG. In FIG. 3, 1 is a recording layer, 2 is a base material, 3 is a protective layer, 5 is an intermediate layer, and 6 is a spherical powder. In the present invention, the protective layer 3 has an average film thickness of 0.
By including the spherical powder having a particle size of 5 to 2.0 times, even if the intermediate layer 5 made of a thermoplastic resin is provided between the recording layer 1 and the protective layer 3, the surface of the protective layer 3 becomes uneven. It is formed as a surface. The "spherical powder" is one having a measured value of the Wadell's true spheroidization degree of 0.8 or more.
When the spherical powder has a particle size in the above range, the powder is not buried in the protective layer or the intermediate layer, and thus the irregularities due to the powder can be formed on the surface of the protective layer. If the powder is not spherical, an acute-angled surface is projected on the surface of the protective layer, and since the particle size is random and a large amount of coarse powder is contained, irregularities on the surface of the protective layer become irregular, May be partially exposed on the surface of the protective layer. When such protrusions or irregularities are large, it is difficult to uniformly transfer heat to the recording layer when writing to or erasing from the recording medium, which is likely to cause image defects, which is not preferable. .

For the protective layer of the present invention, it is preferable to use a material having high heat resistance, high hardness and low friction.
Thermosetting type, ultraviolet ray curing type and electron beam curing type fluorine resin, silicone resin, acrylic resin, urethane resin, epoxy resin or the like is used. In the protective layer,
To improve the contact with the thermal head during recording,
Powders of silica, calcium carbonate, barium sulfate, silicone resin and the like are mixed. The thickness of the protective layer is 0.5 to
The thickness is preferably in the range of 5 μm, and when the spherical powder is blended, irregularities are formed on the surface of the protective layer. In the present invention, the particle size of the spherical powder used for the protective layer needs to be 0.5 to 2.0 times the average film thickness of the protective layer. If the particle size is less than 0.5 times, it is difficult to form irregularities on the surface of the protective layer, and if it exceeds 2.0 times, the projections on the surface of the protective layer become too large, resulting in image defects. appear. The average film thickness of the protective layer is an averaged film thickness obtained by smoothing the surface irregularities. To be exact, it can be known by observing the cross section with a transmission electron microscope. It may be an average of measured values obtained by measuring several points with a film thickness meter such as a gauge.

As the thermoplastic resin used in the intermediate layer of the present invention, polyvinyl butyral, polyvinyl acetal,
Polyvinyl alcohol, polyvinyl acetate, alcohol-soluble polyamide, polyacrylic acid copolymer, casein,
Cellulose derivatives and the like, polyurethane,
Emulsions such as polyacrylic acid esters are also possible. The thickness of this intermediate layer is preferably about 0.3 to 3.0 μm.

As the recording layer material of the present invention, a composite material of an organic low molecular weight compound in which an organic low molecular weight compound is dispersed in a high molecular weight binder and a high molecular weight compound, or a high molecular weight liquid crystal can be used. Hereinafter, the recording layer material used in the present invention will be described in detail. In the composite material of the organic low molecular compound and the high molecular compound used in the recording layer of the present invention, as the organic low molecular compound, fatty acids such as arachidic acid, palmitic acid, stearic acid, behenic acid, lauric acid and dodecyl laurate, The ester etc. are mentioned. As the polymer compound (polymer base material), acrylic resin,
Polystyrene resin, vinyl chloride resin and its copolymers,
Examples thereof include styrene-butadiene resin, polyester resin and polyamide resin. The above-mentioned composite material is one in which the organic low-molecular compound is dispersed in a polymer matrix, and the degree of light scattering changes due to changes in crystallinity and the compatibility of the two components due to the difference in heating temperature. As a result, recording and erasing can be repeated.

Further, in order to improve the durability, the polymer base material is required to contain a reactive group in its main chain or side chain as described in JP-A-3-227688 and the like. It is preferable to add a catalyst or a polyfunctional reactive compound in accordance with the above conditions for crosslinking. As the reactive group of the polymer matrix to be crosslinked, a vinyl group, an acrylate group, a methacrylate group, an epoxy group or an isocyanate group, a polymerizable group, a hydroxyl group, an amino group, an acid amide group,
It is preferably a thiol group, a carboxyl group, a sulfonic acid group, a phosphoric acid group, a metal alcoholate group, a magnesium halide group (Grignard reagent), or the like. These reactive groups are preferably introduced into the polymer base material by copolymerizing a monomer having them. As the catalyst, various ultraviolet or thermal polymerization initiators are used, and as the polyfunctional reactive compound, a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a polyfunctional melamine compound, a polyfunctional aldehyde compound, a polyfunctional amine compound. , Polyfunctional carboxyl compounds and the like are used.

The polymer liquid crystal used in the recording layer of the present invention includes a main chain type polymer liquid crystal and a side chain type polymer liquid crystal in which a mesogenic group (mesogen molecule group) showing liquid crystallinity is bonded to the main chain or side chain. However, in particular, Structural Example 1 in which the following mesogenic monomers (1) to (3) are polymerized as a side chain type polymer liquid crystal
What has a repeating structural unit represented by -3 is used. _{(1) CH 2 = C (} R) -COO- (CH 2) n -O
_{-A (2) CH 2 = C} (R) -COO-A (3) CH 2 = C (R) - (CH 2) n -O-A

Embedded image [In the formula, R represents a hydrogen atom or a methyl group, n represents an integer of 1 to 30, and A represents a mesogen group selected from the following (a) to (k). ]

[0013]

Embedded image [Wherein, X and Y are each a single bond, -N = N-,
-N (→ O) = N-, -CH = N-, -N = CH-,-
COO-, -OCO-, represents a group selected from an ethynylene group, R ¹ represents a group selected from an alkoxy group, a halogen atom, a cyano group, a carboxyl group, and an alkyl group, and p is an integer of 1 to 5 Yes, if p is 2 or more,
Each R ¹ may be different. ]

The polymer liquid crystal used in the present invention has a phase-separated type having a non-mesogenic group in the polymer side chain, as disclosed in JP-A-4-218024 and JP-A-6-18866. Polymer liquid crystals are also used. The polymeric liquid crystal is synthesized by copolymerizing a mesogenic monomer and a non-mesogenic monomer, and when such a polymeric liquid crystal is used, the contrast of a recorded image is significantly improved and the thermosensitive property is improved. It is possible to improve.

Examples of the above-mentioned non-mesogenic monomer include alkyl acrylate and its derivatives, styrene and its derivatives, vinyl acetate, acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone, 1-hexane, 1-octene, and crosslinks. Acrylic acid which is a compound having a reactive group, ω-carboxy-polycaprolactone monoacrylate, vinyl sulfonate, hydroxyethyl acrylate, hydroxypropyl acrylate, 2-acryloxyethyl acid phosphate,
2-hydroxy-3-phenoxypropyl acrylate, 2-acryloxyethyl succinate, phthalic acid monoacrylate, 2-acryloxyethyl (2-hydroxyethyl) phthalate, 4-acryloxyalkyloxy-benzoic acid, glyceryl acrylate, Hydroxy group-substituted styrene, acrylamide, N,
N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, glycidyl acrylate, 2-propen-1-ol, 5-hexen-1-ol, etc. (any of these acryl may be methacryl). And a plurality of these may be used. The amount of copolymerization or co-addition of the above compound into the polymer liquid crystal is preferably in the range of 0.1 to 70 mol% as a monomer unit.

The polymer liquid crystal can be produced by using the above-mentioned monomer or reactive compound, by homopolymerization or copolymerization by radical polymerization, ionic polymerization or the like, or by addition to a reactive polymer. The weight average molecular weight of the polymer liquid crystal is 10,000 to 10
It is in the range of 0,000, and particularly preferably in the range of 20,000 to 500,000. These polymer liquid crystals are disclosed in JP-A-6-16.
As described in JP-A-0825, cross-linking is preferable, and cross-linked polymer liquid crystal having a multi-domain structure is particularly preferable. By cross-linking the polymer liquid crystal as a multi-domain structure composed of an aggregate of domains having a specific size having optical anisotropy, high speed and stable recording and erasing can be performed. The multi-domain structure refers to a structure composed of an aggregate of a plurality of minute domains having optical anisotropy (birefringence) and strongly scatters light.
In particular, the diameter of the domain in the multi-domain structure is
It is preferable for the maximum distribution number of domains to be in the range of 0.2 to 2.0 μm because light is scattered most strongly. Crosslinking of the above-mentioned polymer liquid crystal is performed by applying heat, light, an electron beam or the like after forming the polymer liquid crystal as a recording layer. As the polymer liquid crystal to be crosslinked, a liquid crystal containing a reactive group in the main chain or side chain is used, and the reactive group is the one described in the composite material of the organic low molecular compound and the polymer compound. The same can be used.

Components other than the above may be added to the recording layer of the present invention for the purpose of improving its properties. For example, in order to improve weather resistance, an antioxidant such as hindered amine or hindered phenol is added, and in order to improve display contrast, anthraquinone-based, styryl-based, azomethine-based or azo-based dichroic dyes. Is added, and various fluorescent dyes are added to improve the light scattering property. In order to efficiently perform thermal writing with laser light, a laser light absorbing dye, for example, 780 to 830
When a general semiconductor laser having a wavelength of nm is used, it is also effective to add a near infrared absorbing dye such as phthalocyanine, squarylium or azurenium. The addition amount of these components is preferably in the range of 0.01 to 5% by weight in the composition. In addition, a low molecular weight liquid crystal compound may be added to the polymer liquid crystal in the range of 1 to 20% by weight.

Further, when the recording layer is adhered to the back surface of the substrate after the recording layer is applied and the substrate is wound up, it is also effective to add a slight amount of a releasing agent to the recording layer. . Generally used as a release agent is a silicone type,
There are various compounds with low surface free energy such as fluorine type and acrylic type. These are oil type, wax type,
There are paste type, emulsion type, resin solution type, resin dispersion type and the like. Of these, those which can be mixed with the recording material and which do not cause printing trouble during reversible recording may be selected.

Next, the principle of recording and erasing on the reversible recording medium of the present invention using thermal control will be described. In the initial state, the recording layer made of polymer liquid crystal having a multi-domain structure is light-scattered and clouded, but the polymer liquid crystal etc. When it is converted to an isotropic transparent state and then rapidly cooled, the heated portion is fixed in the glass state in the isotropic state and becomes transparent. On the other hand, in the case of erasing, it can be erased by returning to the initial light scattering state by gradually cooling after heating as compared with the time of recording. By repeating the above operation, recording and erasing of the recording layer can be reversibly repeated many times. When a thermal head is used as the heating means, desired conditions can be achieved by controlling the pulse width and energy applied to the thermal head. In addition, it is possible to make the initial state transparent and perform cloudy recording. This recording and erasing method is
It can also be performed by using an electric field or a magnetic field.
The cloudy state is observed as black in transparent light such as OHP.

The present invention will be specifically described below with reference to examples. Note that “parts” means “parts by weight”.

[Example] As a base material, a polyethylene terephthalate film having a length of 1000 m (width 40 cm, thickness 75 μm)
Prepared. On the other hand, as a mesogenic monomer, 4-acryloxyhexyloxy-4'-cyano-biphenyl 9
5 parts and 5 parts of 2-hydroxyethyl methacrylate as a reactive monomer, 3 parts of azobisisobutyronitrile as a polymerization initiator, and 2-butanone 400 as a solvent.
Polymerization was carried out in parts. The obtained polymer solution was purified by precipitating with methanol as a precipitating solvent to obtain 97 parts of a polymer liquid crystal represented by the following structural formula I.

Embedded image When the physical properties of the obtained polymer liquid crystal were measured, the weight average molecular weight (polystyrene conversion by GPC) was 80,000, Tg (glass transition point) was 40 ° C., Ti (liquid crystal phase-isotropic phase transition point). ) Was 115 ° C.

100 parts of the above-mentioned polymer liquid crystal, 4 parts of 4,4'-diphenylmethane diisocyanate as a crosslinking agent, 150 parts of 2-butanone and 150 parts of toluene as a solvent,
And a silicone release agent (trade name: KS778, manufactured by Shin-Etsu Chemical Co., Ltd.) of 0.005 part were added to prepare a solution. This solution was continuously applied to the film using a gravure roll coater. Then, it was dried at 80 ° C. for 2 minutes to form a recording layer having a film thickness of 6 μm, which was wound up. next,
Polyvinyl butyral resin (trade name: B
M1, manufactured by Sekisui Chemical Co., Ltd.) in isopropanol, and dried again at 80 ° C. for 2 minutes to give a film thickness of 1.5 μm.
m of intermediate layers were formed. Next, on this intermediate layer, 1% by weight of spherical silica powder having an average particle diameter of 0.5 μm (trade name: Seahoster, manufactured by Nippon Shokubai Co., Ltd.) was dispersed with a toluene solvent in an ultraviolet curable resin (trade name: Aronix, Toagosei). Was applied by using a gravure roll coater and cured by using a high pressure mercury lamp to form a protective layer having a thickness of 1.0 μm, which was wound up on a roll. This roll was placed in a greenhouse and heat-treated at 60 ° C. for 24 hours to crosslink the polymer liquid crystal. The recording layer of the film thus obtained was light-scattered and turbid, and the surface roughness Ra of the protective layer was 0.3 μm, showing no abnormal protrusions. A4 size sheet was cut out from this film to prepare a recording medium.

In order to evaluate the performance of the obtained recording medium, a thermal printer (8 dots / mm, 0.3 mJ
/ Dot), the printed part became transparent. When the entire recording medium was heated to 130 ° C. and cooled in the air, the entire surface was reproduced again in a cloudy state. This recording and reproduction could be repeated 200 times or more. Furthermore, as spherical silica powder,
Recording and reproduction could be performed in the same manner on recording media prepared using media having average particle diameters of 1.0 μm, 1.5 μm, and 2.0 μm. The surface roughness Ra of the protective layer is 0.4 μm, 0.7 μm, and 1.0 μm, respectively.
m.

Comparative Example 1 When a coating solution for a protective layer was applied on the recording layer without forming an intermediate layer in Example 1, the recording layer was dissolved in a toluene solvent to prepare a recording medium. I couldn't. Comparative Example 2 In Example 1, when a recording medium is manufactured without dispersing the powder in the protective layer, when writing is attempted on the recording medium, the recording medium may get stuck when passing through the thermal head, or may run obliquely. It was not possible to write normally due to a running failure of the. Comparative Example 3 In Example 1, when 1% by weight of amorphous silica powder having an average particle diameter of 0.5 μm was dispersed in the protective layer, the surface roughness Ra of the protective layer was 0.5 μm and 3.0 μm. There were two or more abnormal protrusions per cm ² . The protruding portion did not become transparent even when recording was performed, resulting in defective printing.

Comparative Example 4 In Example 1, when 1% by weight of spherical silica powder having an average particle size of 0.3 μm was dispersed in the protective layer, the surface roughness Ra of the protective layer was 0.1 μm. The same running failure as in Comparative Example 2 occurred. Comparative Example 5 In Example 1, when 1% by weight of spherical silica powder having an average particle diameter of 3.0 μm was dispersed in the protective layer, the surface roughness Ra of the protective layer was 2.0 μm. As a result, a small cloudy portion was present in the transparent portion, and a completely transparent state was not obtained.

[0025]

INDUSTRIAL APPLICABILITY The reversible recording medium of the present invention comprises a protective layer containing spherical powder having a specific particle diameter, and an intermediate layer of thermoplastic resin provided between the recording layer and the protective layer. In addition, it is possible to prevent the recording layer from being dissolved by the solvent at the time of applying the protective layer, and the spherical powder dispersed in the protective layer forms appropriate irregularities on the surface of the protective layer, which may cause printing defects. Therefore, a reversible recording medium of good quality can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of a basic reversible recording medium.

FIG. 2 is a cross-sectional view showing an outline of a conventional reversible recording medium.

FIG. 3 is a cross-sectional view showing an outline of a reversible recording medium of the present invention.

[Explanation of symbols]

1 ... Recording layer, 2 ... Base material, 3 ... Protective layer, 4 ... Powder, 5 ... Intermediate layer, 6 ... Spherical powder.

Claims (1)

[Claims] 1. A reversible recording medium in which a recording layer whose light scattering degree is reversibly changed by an external stimulus and a protective layer is formed on the surface of a plastic film, and the average thickness of the protective layer is 0 in the protective layer. A reversible recording medium containing a spherical powder having a grain size of 0.5 to 2.0 times, and an intermediate layer made of a thermoplastic resin provided between the recording layer and the protective layer.