JP2612281B2 - Reversible thermosensitive recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reusable reversible thermosensitive recording medium capable of repeating image formation and erasure many times by changing temperature.

Prior art JP-A-54-119377 and JP-A-55-154198 disclose a plastic thermosensitive recording having a thermosensitive layer in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin base material such as a vinyl chloride resin. The body has been proposed.

Image formation and erasing with this type of recording material is based on the reversible change in transparency of the heat-sensitive layer due to temperature.When performing image formation with a thermal head, when the applied energy is large or the platen pressure is high, There is a disadvantage that the surface of the heat-sensitive layer sticks to the thermal head and a uniform image cannot be formed.

Objective The present invention overcomes the drawbacks of the prior art, and can form a uniform and clear projected image by the heat of the thermal head,
It is another object of the present invention to provide a reversible thermosensitive recording medium capable of repeatedly forming and erasing an image.

The reversible thermosensitive recording material of the present invention comprises a resin base material and an organic low-molecular substance dispersed in the resin base material as main components,
A reversible thermosensitive recording medium having a reversible thermosensitive recording layer and a substrate whose transparency reversibly changes depending on temperature, characterized in that the reversible thermosensitive recording layer contains a polyether-modified silicone oil. is there.

The present inventors, in the conventional reversible thermosensitive recording material,
When the heat-sensitive layer further contains a polyether-modified silicone oil, the polyether-modified silicone oil migrates to the heat-sensitive layer surface when heated and dried to form a heat-sensitive layer,
The present inventors have found that since the frictional resistance of the surface is small and the compatibility with other resins is good, it does not completely separate from the heat-sensitive layer and does not peel off from the surface, thereby achieving a desired object. Reached.

The difference between the transparent state and the cloudy opaque state in the present invention is presumed as follows. That is, in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered, and Appears transparent because of transmission. In the case of cloudiness, the particles of the organic low-molecular-weight substance are composed of polycrystals in which fine crystals of the organic low-molecular-weight substance are aggregated, and since the crystal axes of the individual crystals are oriented in various directions, they are incident from one side. Light is refracted many times at the interface between the crystals of the organic molecular substance particles, and is scattered, so that it looks white.

Next, a change in transparency due to heat according to the present invention will be described with reference to the drawings.

In FIG. 1, the main components are a resin base material, an organic low-molecular substance dispersed in the resin base material, and a substance that controls the crystal growth of the organic low-molecular substance added as necessary. thermosensitive element is in the cloudy opaque state at room temperature, for example T ₀ or less. When this is heated to a temperature between T _{1 and} T ₂ , it becomes transparent, and in this state, it remains transparent even if it is returned to room temperature of T ₀ or lower. This is considered for the crystalline low-molecular organic material before reaching the T ₀ or less from the temperature T ₁ through T ₂ is to monocrystalline polycrystalline via a semi-molten state grows. Upon further heating to T ₃ or higher,
It becomes a semi-transparent state intermediate between the maximum transparency and the maximum opacity. Next, when the temperature is lowered, the film returns to the original cloudy and opaque state without taking the transparent state again. This is probably because the polycrystals precipitated by an organic low-molecular material is cooled after melting at a temperature T ₃ or more. When the opaque state is heated to a temperature between T _{0 and} T ₁ and then cooled to room temperature, that is, a temperature lower than T _0, a state between transparent and opaque can be obtained. In addition, the above-mentioned transparent at room temperature is heated again to a temperature of T ₃ or higher, and returned to room temperature,
It returns to cloudy and opaque again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken.

Therefore, by selectively applying heat, the heat-sensitive element can be selectively heated to form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times. If a colored sheet is arranged on the back side of such a heat sensitive body, a color image of the colored sheet on a white background or a white image on a colored background of the colored sheet can be formed.
Further, when the light is projected by an overhead projector or the like, the white turbid portion becomes a dark portion, the transparent portion transmits light, and becomes a bright portion on a screen.

In order to prepare the composite thermosensitive recording medium of the present invention, generally, a polyether-modified silicone oil was added to a solution in which a resin base material and a low-molecular organic substance, and, if necessary, a substance controlling the crystal of the low-molecular organic substance were dissolved. It is prepared by applying a solution on a support such as a plastic film, a glass plate, a metal plate and the like and drying to form a heat-sensitive layer. The solvent for forming the heat-sensitive layer can be variously selected depending on the type of the base material and the organic low-molecular substance. For example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform,
Examples thereof include carbon tetrachloride, ethanol, toluene, and benzene. In the obtained heat-sensitive sheet, the organic low-molecular substance is precipitated as fine particles and exists in a dispersed state.

The resin base material used for the heat-sensitive recording layer is a material that forms a layer in which an organic low-molecular substance is uniformly dispersed and held, and that affects the transparency at the time of maximum transparency. For this reason, the base material is preferably a resin which has good transparency, is mechanically stable, and has good film-forming properties. Examples of such a resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. Vinyl chloride copolymers such as polyvinylidene chloride;
Vinylidene chloride-based copolymers such as vinylidene chloride-vinyl chloride copolymer and vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate or acrylate-methacrylate copolymer, and silicone resin. These may be used alone or as a mixture of two or more.

On the other hand, the organic low-molecular substance may be appropriately selected according to the selection of the temperatures T _{0 to} T ₃ in FIG.
° C, particularly preferably about 50 to 150 ° C. Such organic low molecular weight substances include alkanol; alkane diol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyl; halogen alkane; halogen alkene; halogen alkyne; cycloalkane; cycloalkene; cycloalkyne; Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; Acids or their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; Carboxylic acid esters of o alcohol. These may be used alone or in combination of two or more. These compounds preferably have 10 to 30 carbon atoms. The alcohol group in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, organic low molecular weight substances contain oxygen,
At least one of nitrogen, sulfur and halogen, such as -OH,
-COOH, -CONH, -COOR, -NH - , - NH 2, -S -, -
It is preferred that the compound contains SS-, -O-, halogen and the like.

More specifically, these compounds include lauric acid, dodecanoic acid, limistinic acid, pentadecanoic acid, palmitic acid,
Stearic acid, behenic acid, nonadecanoic acid, arachiic acid,
Higher fatty acids such as oleic acid; esters of higher fatty acids such as methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, docosyl behenate; C ₁₆ H ₃₃ -C ₁₆
H ₃₃ , C ₁₆ H ₃₃ -S-C ₁₆ H ₃₃ , C ₁₈ H ₃₇ -S-C ₁₈ H ₃₇ , C ₁₂ H _{25-
S-C 12 H 25, C} 19 H 39 -S-C 19 H 39, C 12 H 25 -S-S-C 12 H
₂₅ , And ether or thioether. Among them, in the present invention, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms, such as palmitic acid, stearic acid, behen and lignoceric acid, are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

The ratio between the organic low-molecular substance and the resin base material in the heat-sensitive layer is preferably about 2: 1 to 1:16 by weight, more preferably 2: 1 to 1: 5. If the ratio of the base material is less than this, it becomes difficult to form a film holding the organic low-molecular substance in the base material, while if the ratio is higher, the amount of the organic low-molecular substance is small, so that the opacity is reduced. It will be difficult.

Examples of the polyether-modified silicone oil added to reduce the frictional resistance of the surface of the heat-sensitive recording material include organopolysiloxanes having a polyoxyalkylene group, and the surface of the heat-sensitive recording material has smoothness, lubricity, etc. Any silicone oil that can be applied and reduces the frictional resistance of the surface may be used, and a silicone oil modified with ethylene oxide, propylene oxide or the like is particularly preferable.

The amount of the polyether-modified silicone oil in the heat-sensitive layer is preferably about 0.05% to 3% based on the total solid content of the heat-sensitive layer. If the amount of the modified silicone oil is less than this, the surface frictional resistance will not be reduced,
If the amount is larger than this, the transmittance in the transparent state decreases.

The thickness of the heat-sensitive layer is generally from 1 to 30 μm, but the brightness can be increased by increasing the amount of the fatty acid.

Further, in the present invention, a substance that controls crystal growth of the organic low-molecular substance can be used in combination. Examples include those that can expand the range, those that promote the movement of the crystal, and the like.

For example, those generally used as surfactants include polyhydric alcohol higher fatty acid esters; polyhydric alcohol higher alkyl ethers; polyhydric alcohol higher fatty acid esters, higher alcohols, higher alkyl phenols,
Higher fatty acid higher alkylamines, higher fatty acid amides, oils or lower olefin oxide adducts of polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids;
Ca, Ba or Mg salts of aromatic carboxylic acids, higher aliphatic sulfonic acids, aromatic sulfonic acids, mono- or di-sulfates or mono- or di-phosphates; low sulfated oils; poly long chain alkyl acrylates; Oligomer; poly long-chain alkyl methacrylate; long-chain alkyl methacrylate
Amine-containing monomer copolymer; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer, and the like. Tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, and diheptyl phthalate used as plasticizers for the film , Di-n-phthalate
-Octyl, di-2-ethylhexyl phthalate, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-adipate-
2-ethylhexyl, alkyl 610 adipate, di-2-ethylhexyl azelate, dibutyl sebacate,
Di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-
Examples thereof include ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, and acetyl tributyl citrate.

In addition, one of the above-mentioned organic low-molecular substances can be used as an organic low-molecular substance, and another type of organic low-molecular substances can be used as a substance for controlling crystal growth. For example, stearic acid is used as a low-molecular organic substance, and stearyl alcohol is used as a substance for controlling crystal growth.

The weight ratio of the organic low-molecular substance and the substance controlling the crystal growth of the organic low-molecular substance is preferably 1: 0.01 to 1: 0.8. If the substance that controls the crystal growth of the organic low molecular substance is below this range, the temperature range or energy range where it becomes transparent cannot be widened, and if it exceeds this range, the opacity decreases.

Hereinafter, the present invention will be described in more detail with reference to Examples.
All parts are parts by weight.

Example 1 On a 75 μm thick polyester film, behenic acid 8 parts stearyl stearate 2 parts vinyl chloride-vinyl acetate copolymer (VYHH manufactured by UCC) 28
Part Polyether-modified silicone oil (ST102PA, manufactured by Toray Silicone Co., Ltd.) 0.2 part Tetrahydrofuran 140 parts Toluene 17 parts
By providing a heat-sensitive layer having a thickness of μm, a white opaque plastic heat-sensitive recording medium was prepared.

Comparative Example 1 A plastic thermosensitive recording material was prepared in the same manner as in Example 1 except that the polyether-modified silicone-oil was not used.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the polyether-modified silicone oil was dimethyl silicone oil (SH200 manufactured by Toray Dow Corning).

Next, each recording material was reheated and cooled at 65 ° C. to make the whole transparent. These recording samples were used to form cloudy images with CUVAX MC-50 (manufactured by Ricoh Co., Ltd.), and the image densities were measured immediately after the formation and after standing at room temperature for one week. The rate of decrease in image density one week after immediately after was calculated by the following equation, and the above is shown in the following table.

Effect The reversible thermosensitive recording medium of the present invention contains polyether-modified silicone oil, so that the frictional resistance of the surface can be reduced, and since it does not stick even when heated by a thermal head, there is an advantage that a uniform and clear image can be formed.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the transparency of the heat-sensitive layer and the temperature.

Claims (1)

(57) [Claims] 1. A reversible thermosensitive recording layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as main components, and a reversible thermosensitive recording layer whose transparency reversibly changes depending on temperature and a substrate. A reversible thermosensitive recording material, wherein the reversible thermosensitive recording layer contains a polyether-modified silicone oil.