JPH08332779A - Reversible recording medium - Google Patents

Abstract

PURPOSE: To provide a reversible recording medium bringing a record layer into non-contact with the rear surface of a base material even if the base material spread with the layer by coating the base material is wound round a roll and hence improving the productivity. CONSTITUTION: The reversible recording medium comprises a record layer formed on a plastic film and reversely varying light scattering degree according to an external stimulus, wherein the layer contains release agent. The record layer is preferably obtained by crosslinking polymer having active group by curing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible recording medium capable of repeatedly recording and erasing images by reversibly changing the light scattering degree by external stimuli such as heat, electric field, magnetic field and light. .

[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 techniques, organic low-molecular compound / polymer compound composite materials and polymer liquid crystals whose light scattering degree reversibly changes are regarded as promising materials for recording media because of their excellent durability. (JP-A-59-10930)
Japanese Patent Laid-Open Publication No. Sho 63-223066, Japanese Laid-Open Patent Publication No. Sho 62-62
-14114, 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, and the recording medium is used by forming a protective layer on the recording layer.

Generally, this type of recording medium is shown in FIG.
A recording layer 1 is formed on a base material 2 as shown in FIG.
As shown in FIG. 1 (b), the recording layer 1 and the protective layer 4 are sequentially formed on the base material 2, or as shown in FIG. 1 (c), the light reflection layer 3, on the base material 2, It has a laminated structure including a recording layer 1 and a protective layer 4 sequentially formed. 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. The light reflection layer 3 is a layer for the purpose of improving the light scattering degree of the recording layer, and a metal film of aluminum, silver, tin, magnesium, platinum or the like is formed by vapor deposition or sputtering. It is not necessary when the recording medium is used with transmitted light. The protective layer 4 is a layer formed in order to prevent deterioration of the surface due to repeated use of the recording layer, and is preferably a layer having high heat resistance, high hardness and low friction, such as fluororesin and silicone. A resin, a thermosetting resin, an ultraviolet curable resin, an electron beam curable resin, or the like is used. The protective layer may be composed of a plurality of layers, and the thickness thereof is about 0.1 to 20 μm. To the protective layer, powders of silica, calcium carbonate, barium sulfate and the like are blended, if necessary, in order to improve the contact property with the thermal head during recording.

[0004]

In producing the above-mentioned recording medium, a recording layer is coated on a substrate by using a coating device such as a roll coater, and the coated substrate is sequentially coated. The method of winding is adopted. At that time, in the roll 5 as shown in FIG. 2, a high pressure is applied to the core 6, which is the center of the roll 5 on which the base material is wound. Therefore, since the recording layer on the base material is in contact with the back side of the wound base material, there is a possibility that the recording layer may adhere to the back surface of the base material. In particular, the recording layer is formed of a polymer liquid crystal composed of a polymer of a liquid crystal monomer and a non-liquid crystal monomer having an active group, and the active group of the non-liquid crystal monomer is formed by a polyisocyanate compound. In the case of a product obtained by cross-linking (Japanese Patent Laid-Open No. 6-160825, etc.), a chemical reaction during cross-linking facilitates adhesion to the back surface of the base material, and further the entire roll to accelerate the cross-linking reaction. In the case of heating, there was a problem that there was a higher tendency to adhere more closely to the back surface of the base material. Since the recording medium is no longer usable when it comes into close contact with the substrate to such an extent that it cannot be easily peeled off, the advent of a material in which the recording layer does not come into close contact has been desired. Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to wind a base material having a recording layer formed by coating the base material on a roll, The purpose of the present invention is to provide a reversible recording medium in which the recording layer does not come into close contact with the back surface of the substrate, and therefore the productivity is improved.

[0005]

The reversible recording medium of the present invention is a reversible recording medium in which a recording layer having a light scattering degree reversibly changed by an external stimulus is formed on a plastic film. It is characterized by containing an agent. The recording layer is preferably obtained by crosslinking a polymer having an active group with a curing agent.

Hereinafter, the present invention will be described in detail. In the present invention, a release agent is added to the recording layer as an additive in order to prevent the recording layer of the reversible recording medium from adhering to the back surface of the substrate. As the release agent used in the present invention,
Usually, it is known as an additive for preventing adhesion between articles, and by way of example, it is composed of various materials having low surface free energy such as silicone compounds, fluorine compounds, acrylic compounds. There are oil type, wax type, paste type, emulsion type, resin solution type, resin dispersion type and the like. It is preferable to select, from these releasing agents, those which can be mixed with the recording material and do not cause printing trouble during reversible recording.

Generally, the above-mentioned release agent is applied to the side which comes into contact with an article having adhesiveness, and may be applied to the back surface of the substrate. However, the present invention
In order to shorten the coating process and make the recording layer itself non-adhesive, a release agent is contained in the recording layer. Further, in the case of laminating a protective layer or the like on the recording layer, a strong releasability is not preferable so that the coating agent does not cause a coating failure when the protective layer or the like is applied,
If the release agent is soluble in the solvent of the coating liquid to be laminated thereon, it will dissolve to some extent at the time of coating, so that coating failure will not occur. As the release agent used in the present invention, specifically, a modified silicone oil or a dimethyl silicone compound crosslinked is preferable. The content of the release agent in the recording layer is preferably 0.001 to 0.1% by weight.

As the recording layer material of the present invention, an organic low molecular weight compound / polymeric compound composite material or a polymer liquid crystal in which an organic low molecular weight compound is dispersed in a polymer binder can be used. Hereinafter, the recording layer material used in the present invention will be described in detail. Examples of the organic low molecular weight compound of the organic low molecular weight compound / polymeric compound composite material used in the recording layer of the present invention include fatty acids such as arachidic acid, palmitic acid, stearic acid, behenic acid, lauric acid and dodecyl laurate, and esters thereof. Is mentioned. Examples of the polymer compound (polymer base material) include acrylic resin, polystyrene resin, vinyl chloride resin and copolymers thereof, styrene-butadiene resin, polyester resin, polyamide resin and the like. 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.

In the above material, Japanese Patent Laid-Open No. 3-2276 is used.
As described in JP-A-88, etc., it is preferable to crosslink the polymer base material from the viewpoint of improving durability. As the polymer base material to be cross-linked, one containing a reactive group in the main chain or side chain is used, and utilizing the reactive group, a catalyst or a polyfunctional reactive compound is added if necessary. It is crosslinked. Examples of the reactive group include vinyl group, acrylate group, methacrylate group, epoxy group, and isocyanate group, and other polymerizable groups, hydroxyl group, amino group, acid amide group, thiol group, carboxyl group, and sulfonic acid group. It is preferably a phosphoric acid group, a metal alcoholate group, a magnesium halide (Grignard) group, 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.

As the polymer liquid crystal used in the recording layer of the present invention, there are a main chain type polymer liquid crystal and a side chain type polymer liquid crystal in which a mesogenic group (mesogen molecular group) showing liquid crystallinity is bonded to the main chain or side chain. is there. As the side chain type polymer liquid crystal, one having a repeating structural unit represented by Structural Examples 1 to 3 below is used.

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). ]

[0011]

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

The polymer liquid crystal used in the present invention is disclosed in Japanese Patent Laid-Open No.
As disclosed in JP-A-218024 and JP-A-6-18866, a phase obtained by copolymerizing a non-mesogenic group with a polymer side chain, which is synthesized by copolymerizing a mesogenic monomer and a non-mesogenic monomer. Separated polymer liquid crystals are also used. When such a polymer liquid crystal is used, the contrast of the recorded image is significantly improved, and the heat-sensitive characteristics can be optimized. The mesogen monomer and the mesogen compound capable of addition reaction used in the present invention include biphenyl type, phenylbenzoate type, cyclohexylbenzene type, azoxybenzene type, azobenzene type, azomethine type, phenylpyrimidine type, diphenylacetylene type, biphenylbenzoate type. , Cyclohexylbiphenyl-based, terphenyl-based rigid molecules,
Representative examples include various compounds in which an acrylic acid ester group, a methacrylic acid ester group, and a vinyl group are bonded via an alkyl spacer having a predetermined length.

Representative structural examples of these compounds are shown below. These are typical structural examples, and the present invention is not limited to these. _{CH 2 = C (Ra) -COO-} (CH 2) l -O-A CH 2 = C (Ra) -COO-A CH 2 = CH- (CH 2) l -O-A ( In the formulas, Ra Hydrogen or a methyl group, l represents an integer of 1 to 30, and A is the same as the mesogen group in Structural Example 1).

Examples of the non-mesogenic monomer used in the present invention include alkyl acrylate and its derivatives,
Styrene and its derivatives, vinyl acetate, acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone,
1-hexene, 1-octene, etc. and acrylic acid, a compound having a reactive group for crosslinking, 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,
Examples thereof include N, N-diethylaminoethyl acrylate, glycidyl acrylate, 2-propen-1-ol, 5-hexen-1-ol (each acryl may be methacryl). What is illustrated here is an example, and the present invention is not limited thereto. Plural kinds of the above-mentioned compounds may be used. The copolymerization or co-addition amount 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 preferably crosslinked to improve durability, and crosslinked polymer liquid crystals having a multi-domain structure are particularly preferable. High-speed and stable recording and erasing can be realized 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. 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. Particularly, when the size of the domain in the multi-domain structure is in the range of 0.2 to 2.0 μm in diameter at the maximum of the distribution number of the domain, it is preferable because light is scattered most strongly.

Crosslinking of the above-mentioned polymer liquid crystal is carried out 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 its main chain or side chain is used. As the reactive group, the same one as described in the organic low molecular weight compound / polymeric compound composite material 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 the weather resistance, an antioxidant such as hindered amine or hindered phenol, and in order to improve the display contrast, anthraquinone-based, styryl-based,
Various dichroic dyes such as azomethine and azo, and various fluorescent dyes are added to improve the light scattering property. To efficiently perform thermal writing with laser light, a laser light absorbing dye, for example, 780 to 830 nm
In the case of using the general semiconductor laser of 1), it is also effective to add a near infrared absorbing dye such as phthalocyanine, squarylium or azurenium. The various components listed above are preferably added in an amount of 0.01 to 5% by weight in the composition. In addition, for polymer liquid crystal,
The low molecular weight liquid crystal compound may be added in the range of 1 to 20% by weight.

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 can be performed reversibly 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. Other,
It is also possible to make the initial state transparent and perform cloudy recording. This recording and erasing method can also be performed by using an electric field or a magnetic field.

The present invention will be specifically described below with reference to examples. All "parts" mean "parts by weight".

【Example】

Example 1 As a substrate, a polyethylene terephthalate film (width 40 cm, thickness 75 μm) having a length of 1,000 m vapor-deposited on aluminum was prepared. On the other hand, as a mesogenic monomer, 4-acryloxyhexyloxy-4'-cyano-
Polymerization was carried out using 95 parts of biphenyl, 5 parts of 2-hydroxyethyl methacrylate as a reactive monomer, 3 parts of azobisisobutyronitrile as a polymerization initiator, and 400 parts of 2-butanone as a solvent. The obtained polymer solution was purified by precipitating with methanol as a precipitating solvent to obtain 95 parts of polymer liquid crystal represented by the following structural formula I.

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

To 100 parts of the above-mentioned polymer liquid crystal, 4,4'-diphenylmethane diisocyanate as a cross-linking agent, 4 parts, 2-butanone as a solvent, 150 parts and toluene, 150 parts,
And silicone release agent (KS778, manufactured by Shin-Etsu Chemical Co., Ltd.)
A solution containing 0.01 part was prepared. This solution was continuously applied to the film using a gravure roll coater. After that, it is dried at 80 ° C. for 2 minutes and the film thickness is 6 μm.
m recording layer was formed and wound. 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 scattered light and became cloudy. Then, an ultraviolet curable resin (Aronix, manufactured by Toagosei Co., Ltd.) in which 1% by weight of silica particles having an average diameter of 1 μm is dispersed is applied onto the recording layer by using a gravure roll coater and cured by using a high pressure mercury lamp. A protective layer having a film thickness of 2 μm was formed and wound on a roll.
A sheet of A4 size was cut out from this roll to prepare a recording medium. In order to evaluate the performance of the obtained recording medium, a thermal printer (8 dots / mm, 0.3
When recording was performed using mJ / dot), the printed portion 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 100 times or more.

Comparative Example 1 A recording layer was formed in the same manner as in Example 1, except that the coating solution prepared without adding the silicone-based releasing agent to the polymer liquid crystal solution was used. When this roll was placed in a greenhouse and the film was unwound to apply a protective layer after thermal crosslinking at 60 ° C. for 24 hours, the liquid crystal layer adhered to the back surface of the film and could not be easily peeled off. , The protective layer could not be applied.

Example 2 90 parts of 4-acryloxyhexyloxy-4'-cyano-biphenyl as a mesogenic monomer, 5 parts of 2-hydroxyethyl methacrylate as a reactive non-mesogenic monomer, and 5 parts of butyl acrylate as a non-mesogenic monomer. Is polymerized in the same manner as in Example 1 and purified to obtain a polymer liquid crystal 9 represented by the following structural formula II.
5 parts were obtained.

[Chemical 4] When the physical properties of the obtained polymer liquid crystal were measured, its weight average molecular weight (in terms of polystyrene by GPC) was 50,000, Tg (glass point transfer) was 40 ° C., Ti (liquid crystal phase-isotropic phase transition point). ) Was 90 ° C.

To 100 parts of the above-mentioned polymer liquid crystal precipitated and purified using methanol, 3 parts of hexamethylene diisocyanate which is a polyfunctional isocyanate compound as a cross-linking agent, 150 parts of 2-butanone as a solvent, 150 parts of toluene and a silicone type release agent. (KF410, manufactured by Shin-Etsu Chemical Co., Ltd.)
A solution containing 01 parts was prepared. This solution is applied to a thickness of 10
It was coated on a 0 μm aluminum vapor-deposited polyester film with a roll coater and dried at 80 ° C. for 2 minutes to form a polymer liquid crystal layer with a film thickness of 6 μm. This polymer liquid crystal layer was white turbid due to light scattering. Next, when cross-linking was performed in an oven at 60 ° C. for 24 hours, the polymer liquid crystal layer after cross-linking was cloudy as in the case before cross-linking. Further, a protective layer was formed in the same manner as in Example 1 to prepare a recording medium. The recording medium thus obtained could record and reproduce information as in Example 1.

[0024]

INDUSTRIAL APPLICABILITY The reversible recording medium of the present invention has a constitution in which a releasing agent is blended in the recording layer, so that even if the film substrate on which the recording layer is formed is wound up, the recording layer is a film substrate. Does not adhere to the back side. Therefore, since it is possible to employ a method in which a long raw fabric film is used as a base material and which is wound on a roll to produce a recording medium, the production efficiency of the recording medium can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reversible recording medium.

FIG. 2 is a roll obtained by winding a reversible recording medium.

[Explanation of symbols]

1 ... recording layer, 2 ... substrate, 3 ... light reflecting layer, 4 ... protective layer, 5
… Roll, 6… core.

Claims (2)

[Claims] 1. A reversible recording medium comprising a plastic film and a recording layer whose light scattering degree is reversibly changed by an external stimulus, wherein the recording layer contains a release agent. recoding media. 2. The reversible recording medium according to claim 1, wherein the recording layer is obtained by crosslinking a polymer having an active group with a curing agent.