JPH04275177A - Reversible thermosensible recording material - Google Patents

Abstract

PURPOSE:To enhance repeating durability, in a recording material wherein a thermosensible layer based on a resin base material and an org. low-molecular substance and reversibly changing in its transparency in dependence on temp. is provided on a support, by adding liquid paraffin oil to the thermosensible layer. CONSTITUTION:A reversible thermosensible recording material is formed by providing a thermosensible layer based on a resin base material and an org. low-molecular substance and reversibly changing in its transparency in dependence on temp. on a support such as a plastic film or a glass plate and the formation and erasure of an image is repeatedly performed many times by utilizing this change in transparency. In this case, liquid paraffin oil with viscosity of 70cps or more at 20 deg.C is added to the thermosensible layer. This fluid paraffin oil means hydrocarbon oil obtained by highly purifying a relatively light lubricant fraction by the washing with sulfuric acid and collorless and odorless alkyl naphthene low in volatility is used. By this constitution, the repeating durability of the formation and erasure of an image due to a thermal head is enhanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible heat-sensitive recording material in which images can be repeatedly formed and erased by utilizing the reversible change in transparency of a heat-sensitive layer depending on the temperature.

0002

BACKGROUND OF THE INVENTION In recent years, reversible thermosensitive recording materials have attracted attention in which temporary images can be formed and the images can be erased when no longer needed. Typical examples include glass transition temperatures (Tg) ranging from 50 to 60°C to 80°C.
Reversible thermosensitive recording materials are known in which low-molecular-weight organic substances such as higher fatty acids are dispersed in a resin matrix such as vinyl chloride-vinyl acetate copolymer with a low glass transition temperature of less than 0°C. 1987-119377, JP-A-55-1
Publications such as No. 54198).

[0003] When a heat roller, a thermal pen, etc. are used as a heating method during image formation and erasing, and only heat is applied without applying much pressure, it is possible to repeatedly form images.
Even after erasing, there is no problem with durability. However, when applying pressure and heating at the same time using a thermal head, etc., the resin matrix around the organic low-molecular substance particles deforms as images are repeatedly formed and erased, resulting in finely dispersed organic low-molecular substance particles. The disadvantage is that the particles gradually become larger in diameter, the light scattering effect becomes less, the white turbidity decreases, and finally the image and contrast deteriorate.

0004

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks and provides a reversible thermosensitive recording material that changes reversibly between a transparent state and a cloudy state depending on the temperature. It is an object of the present invention to provide a reversible thermosensitive recording material which exhibits little decrease in white turbidity even when image formation and erasing are performed using a heating means that simultaneously applies pressure, and which has improved repeat durability.

[0005]

[Means for Solving the Problems] The present invention provides, on a support,
In a reversible thermosensitive recording material, which is provided with a thermosensitive layer whose main component is a resin matrix and an organic low-molecular substance dispersed in the resin matrix and whose transparency changes reversibly depending on the temperature, the thermosensitive layer contains It is characterized by containing liquid paraffin oil, particularly by using liquid paraffin oil having a viscosity of 70 cps or more at 20°C.

That is, a reversible heat-sensitive layer is provided on a support with a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material, and whose transparency changes reversibly depending on the temperature. As a result of intensive studies on the heat-sensitive layer of recording materials, we found that by containing liquid paraffin oil, it is durable against repeated image formation and erasing using a heating means that applies pressure and heats at the same time, such as a thermal head. It has been found that it is possible to obtain a reversible thermosensitive recording material which can form images with high white turbidity and high contrast.

In the present invention, the reason why the durability of repeated image formation and erasure by heating means such as a thermal head is improved by incorporating liquid paraffin oil into the heat-sensitive layer is not clear, but organic low molecular weight It is assumed that this is related to the adsorption of substances to oil. In particular, it is thought that the weak polarity of liquid paraffin oil has a good effect on the adsorption of organic low-molecular substances. Furthermore, since the viscosity of liquid paraffin oil is relatively high, when heating while applying pressure using a thermal head etc., even if the fine particles of the organic low molecular weight substance melt, it is possible to suppress the growth of the particle size of the organic low molecular weight substance. It is thought that this has an effect on repeated durability.

The liquid paraffin oil used in the present invention is a hydrocarbon oil obtained by highly refining a relatively light lubricating oil fraction by washing with sulfuric acid, and is colorless, odorless, has low volatility, and mainly consists of alkylnaphthenes. This is also called white oil. As mentioned above, in the present invention, it is preferable to select and use a liquid paraffin oil having a viscosity of 70 cps or more at 20° C., and a liquid paraffin oil having a viscosity of less than 70 cps has no significant effect on durability and is not preferred. The content of liquid paraffin oil is preferably 3 to 30% by weight, more preferably 5 to 30% by weight based on the organic low molecular weight substance.
It is 20% by weight. Liquid paraffin oil content is 3
If it is more than 0% by weight, the erasability will be poor, and if it is less than 3% by weight, it will be less effective in terms of durability.

The reversible thermosensitive recording material of the present invention utilizes the above-mentioned change in transparency (transparent state, cloudy opaque state), and the difference between the transparent state and the cloudy opaque state is presumed as follows. . In other words, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin matrix are composed of large particles of the organic low-molecular substance, and light incident from one side is not scattered and is scattered in the opposite direction. (ii) In the case of cloudiness, the particles of the organic low-molecular-weight substance are composed of polycrystals, which are aggregates of fine crystals of the organic low-molecular-weight substance, and the crystal axes of the individual crystals are The reason for this is that because the particles face in various directions, light incident from one side is refracted and scattered many times at the interface of the crystals of the organic low-molecular substance particles, resulting in the appearance of white.

In FIG. 1 (which shows the change in transparency due to heat), the heat-sensitive layer whose main components are a resin base material and an organic low-molecular substance dispersed in the resin base material is, for example, T
At room temperature below 0, it is cloudy and opaque. This temperature is T
When heated to 2, it becomes transparent, and even if it is returned to room temperature below T0 in this state, it remains transparent. This is considered to be because the organic low-molecular substance passes through a semi-molten state and crystals grow from polycrystal to single crystal from temperature T2 to below T0. Further heating to a temperature of T3 or higher results in a translucent state intermediate between maximum transparency and maximum opacity. Next, when this temperature is lowered, the liquid returns to its initial cloudy and opaque state without becoming transparent again. This is considered to be because polycrystals precipitate when the organic low-molecular substance is melted at a temperature of T3 or higher and then cooled. Note that when this opaque state is heated to a temperature between T1 and T2 and then cooled to room temperature, that is, a temperature below T0, it can take an intermediate state between transparent and opaque. Moreover, if the material that becomes transparent at room temperature is heated again to a temperature of T3 or higher and then returned to room temperature, it will return to a cloudy, opaque state. That is, it can take both opaque and transparent forms, as well as an intermediate state between them, at room temperature.

[0011] Therefore, by selectively applying heat, it is possible to selectively heat the heat-sensitive layer to form a cloudy image on a transparent background and a transparent image on a cloudy background, and this change can be repeated many times. It is. If a colored sheet is placed on the back side of such a thermosensitive member, it is possible to form an image in the color of the colored sheet on a white background or a white image on the background of the color of the colored sheet. Furthermore, if the image is projected using an OHP (overhead projector) or the like, the cloudy areas become dark areas, and the transparent areas allow light to pass through and become bright areas on the screen.

In order to form and erase images using such a reversible thermosensitive recording material, it is necessary to have two thermal heads, one for image formation and one for image erasing, or to change the applied energy conditions. It is effective to use a single thermal head for forming and erasing images. In the former case, the cost of the device increases because two thermal heads are required, but if the energy application conditions for each thermal head are set separately and the reversible thermosensitive recording material is passed through once, image formation and erasing can be performed. You can do it by doing. In the latter case, since the image is formed and erased using one thermal head, the conditions for applying energy to the thermal head each time the heat-sensitive recording material passes are adjusted depending on the area where the image is to be formed and the area where the image is to be erased. The operation is complicated, as the image on the thermal recording material must be changed in detail, or the image on the thermal recording material must be erased and then run in the opposite direction again to form an image under different energy conditions. Therefore, the equipment cost is low.

In order to make the reversible thermosensitive recording material used in the present invention, generally (1) a resin matrix and two organic low-molecular substances are prepared.
A dispersion liquid in which an organic low-molecular substance is dispersed in the form of fine particles in a solution of dissolved components or (2) a solution of a resin base material (use a solvent that does not dissolve at least one of the organic low-molecular substances) is used as a plastic. A laminated heat-sensitive layer may be formed by coating and drying on a support such as a film, glass plate, or metal plate. Various solvents can be selected as the solvent for preparing the heat-sensitive layer or heat-sensitive recording material depending on the type of the resin base material and the organic low-molecular substance, such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene, etc. Can be mentioned. Of course, when using a dispersion,
In the heat-sensitive layer obtained even when a solution is used, the organic low-molecular substance precipitates as fine particles and exists in a dispersed state.

The resin base material used in the heat-sensitive recording layer is a material that forms a layer in which a low-molecular-weight organic substance is uniformly dispersed and holds, and also influences the transparency at maximum transparency. Therefore, the resin base material is preferably a resin that has good transparency, is mechanically stable, and has good film-forming properties. Such resins 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-vinyl acetate copolymer.
Vinyl chloride copolymers such as acrylate copolymers; vinylidene chloride copolymers such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or Examples include methacrylate or acrylate-methacrylate copolymer; silicone resin, and the like. These resins may be used alone or in combination of two or more.

On the other hand, the organic low-molecular substance may be one that changes from polycrystal to single crystal due to heat in the recording layer (changes within the temperature range T1 to T3 shown in FIG. 1), and generally has a melting point. 30-200℃ preferably 50-150℃
A certain degree is used. Such organic low-molecular substances include alkanols; alkanediols; halogenalkanols or halogenalkanediols; alkylamines; alkanes; alkenes; alkynes; halogenalkanes; halogenalkenes; halogenalkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; Saturated or unsaturated halogenated fatty acids or their esters, amides or ammonium salts; Allylcarboxylic acids or their esters, amides or ammonium salts; Halogenated allylcarboxylic acids or their esters, amides or ammonium salts; Examples include esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or esters, amines or ammonium salts thereof; carboxylic acid esters of thioalcohols. These may be used alone or in a mixture of two or more. The carbon number of these compounds is 10~
60, preferably 10-38, especially 10-30. The alcohol group moiety in the ester may be saturated or unsaturated, or may be substituted with halogen. In any case, the organic low-molecular substance contains at least one of oxygen, nitrogen, sulfur, and halogen in the molecule, such as -OH, -COOH, -CONH, -COOR, -NH.
, -NH2, -S-, -S-S-, -O-, halogen, etc. are preferred.

More specifically, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, arginic acid, and oleic acid; methyl stearate; , esters of higher fatty acids such as tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, dodecyl behenate; and ethers or thioethers. Among these, in the present invention, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, and lignoceric acid are preferred, and higher fatty acids having 16 to 24 carbon atoms are more preferred.

[0017] The thickness of the heat-sensitive layer is preferably 1 to 30 μm,
More preferably, the thickness is from 2 to 20 μm. If the heat-sensitive layer is too thick, heat distribution will occur within the layer, making it difficult to achieve uniform transparency. Furthermore, if the heat-sensitive layer is too thin, the white turbidity will decrease and the contrast will decrease. Furthermore, white turbidity can be increased by increasing the amount of organic low-molecular substances in the heat-sensitive layer. The weight ratio of the organic low-molecular substance to the resin base material in the heat-sensitive layer is preferably about 2:1 to 1:16, more preferably 1:1 to 1:3. If the ratio of the resin base material is less than this, it will be difficult to form a film that holds the organic low molecular weight substance in the resin base material, and if it is higher than this, the amount of the organic low molecular weight substance will be small and the film will become opaque. becomes difficult. Furthermore, in order to widen the range of temperatures at which transparency can be achieved, the organic low molecular weight substances described in this specification may be appropriately combined, or such organic low molecular weight substances may be combined with other materials having different melting points. These include, for example, publications such as JP-A No. 63-39378, JP-A No. 63-130380, and Japanese Patent Application No. 63-1.
4754, Japanese Patent Application No. 1-140109, etc., but the present invention is not limited thereto.

In addition to the above-mentioned components, additives such as surfactants and high boiling point solvents may be added to the heat-sensitive layer in order to facilitate the formation of transparent images. Specific examples of these additives are as follows. Examples of high boiling point solvents; tributyl phosphate, tri-2-phosphate
Ethylhexyl, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate , dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate,
Dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2 azelaic acid
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, acetyl citric acid Tributyl.

Examples of surfactants and other additives; polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkylphenol, higher fatty acid higher alkyl amine, higher fatty acid amide , lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids, sulfuric acid monoesters or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low sulfated oils; poly long-chain alkyl acrylates; acrylic oligomers; poly long-chain alkyl methacrylates; long-chain alkyl methacrylate-amine-containing monomer copolymers ; Styrene-maleic anhydride copolymer; Olefin-maleic anhydride copolymer.

When the image of this recording material is used as a reflective image, by providing a layer that reflects light on the back side of the recording layer, the contrast can be increased even if the thickness of the recording layer is reduced. Specifically, it is possible to evaporate Al, Ni, Sn, etc. (described in JP-A-64-14079).

Furthermore, a protective layer may be provided on the heat-sensitive layer of the present invention in order to prevent the surface from being deformed by the heat and pressure of a heating means using a writing method such as a thermal head and reducing the transparency of the transparent portion. good. A protective layer laminated on the heat-sensitive layer (thickness 0.
1 to 5 μm), silicone rubber, silicone resin (described in JP-A No. 63-221087),
Polysiloxane graft polymer (JP-A-63-317
385), ultraviolet curable resin, or electron beam curable resin (described in JP-A-2-566). In either case, a solvent is used during coating, but it is desirable that the solvent is difficult to dissolve the resin and organic low-molecular substance of the heat-sensitive layer. Examples of solvents that are difficult to dissolve the resin and organic low-molecular substance of the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and alcohol-based solvents are particularly desirable from the viewpoint of cost.

Furthermore, in order to protect the reversible recording material from the solvent, monomer components, etc. of the protective layer forming liquid, an intermediate layer can be provided between the protective layer and the reversible recording material (see Japanese Patent Laid-Open No. 1-133781). (described in the issue). As the material for the intermediate layer, the following thermosetting resins and thermoplastic resins can be used in addition to those listed as the resin base material in the heat-sensitive layer. That is, specific examples thereof include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide, and the like. The thickness of the intermediate layer varies depending on the application, but is preferably about 0.1 to 2 μm. If it is less than this, the protective effect will decrease, and if it is more than this, the thermal sensitivity will decrease.

[0023]

EXAMPLES Next, the present invention will be explained in more detail by giving examples and comparative examples, but the present invention is not limited thereto. All parts and percentages herein are based on weight. Example 1 Behenic acid was deposited on a polyester film with a thickness of about 50 μm and an Al layer with a thickness of about 400 Å.

6 parts eicosane 2 acid

4 parts PVC-vinyl acetate copolymer (VYHH)
30 parts phthalic acid di-
2 ethylhexyl
3 parts Liquid paraffin oil (viscosity 250 cps)
1.5 parts tetrahydrofuran

150 parts toluene

A solution consisting of 15 parts was coated with a wire bar and dried by heating to form a heat-sensitive layer with a thickness of about 5 μm.

Example 2: Behenic acid

6 parts eicosane 2 acid

4 parts PVC-vinyl acetate copolymer (VYHH)
30 parts phthalic acid di-
2 ethylhexyl
3 parts Liquid paraffin oil (viscosity 125 cps)
1.5 parts tetrahydrofuran

150 parts toluene

A solution consisting of 15 parts was coated with a wire bar and dried by heating to form a heat-sensitive layer with a thickness of about 5 μm.

Example 3 Behenic acid was deposited on a polyester film with a thickness of about 50 μm and an Al layer with a thickness of about 400 Å.

6 parts eicosane 2 acid

4 parts PVC-vinyl acetate copolymer (VYHH)
30 parts phthalic acid di-
2 ethylhexyl
3 parts Liquid paraffin oil (viscosity 75 cps)
1.5 parts tetrahydrofuran

150 parts toluene

A solution consisting of 15 parts was coated with a wire bar and dried by heating to form a heat-sensitive layer with a thickness of about 5 μm.

Comparative Examples 1 and 2 A heat-sensitive layer of about 5 μm was provided in the same manner as in Example 1 except that the viscosity of the liquid paraffin oil was changed to 50 cps and 15 cps, respectively. Comparative Example 3 A heat-sensitive layer having a thickness of about 5 μm was provided in the same manner as in Example 1 except that the liquid paraffin oil was removed.

Polyamide resin (CM8000 manufactured by Toray Industries, Inc.) was applied on each of the heat-sensitive layers prepared as described above.
10 parts ethyl alcohol
A solution consisting of 90 parts was applied with a wire bar and dried to a thickness of about 0.5 μm.
A thick intermediate layer is provided on top of which a layer of urethane acrylate ultraviolet curable resin is applied.
5% butyl acetate solution (Unidik C7-15 manufactured by Dainippon Ink Chemical Co., Ltd.)
7) 10 parts toluene

A solution consisting of 10 parts was applied with a wire bar and after heating and drying, 80w/
A reversible heat-sensitive recording material was prepared by curing with an ultraviolet light lamp of 1.5 cm to form a protective layer with a thickness of about 2 μm.

Using the reversible thermosensitive recording material prepared as described above, a forced test was conducted under forced test conditions (applied power 1.0 W, applied pulse width 0.7mse
After printing with c) and making it cloudy, heat roller (80
Transparent and erase was performed at ~85℃, 10 mm/min), and the image area (cloudy area) density and transparent area (background area) density as a result of repeating printing and erasing 10 times under the same conditions using a Magbeth reflection densitometer RD. The measured values measured at =514 are shown in FIGS. 2 to 7. Also, the viscosity of liquid paraffin is 20 with a B-type viscometer.
Measured at ℃. Examples 1, 2, 3 (Figures 2 to 4)
There was no decrease in cloudy density up to 10 times of printing, and high transparency and high contrast were maintained. In Comparative Examples 1, 2, and 3 (FIGS. 5 to 7), almost no clouding occurs after 10 printings.

[0029]

Effects of the Invention As is clear from the description of the examples, the reversible thermosensitive recording material of the present invention contains liquid paraffin oil in the reversible thermosensitive recording layer, so that the liquid paraffin is mixed with the resin base material and the organic solvent. Poor compatibility with molecular substances,
Therefore, a liquid paraffin oil film is formed around the resin film covering the organic low-molecular substance, so even if image formation and erasure are performed using a heating means such as a thermal head that applies heat and pressure at the same time, the organic low-molecular substance remains It has the effect of suppressing the growth of the particle size, and as a result, there is an effect that the decrease in white turbidity is small.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in transparency due to heat of a reversible thermosensitive recording material according to the present invention.

FIG. 2 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Example 1 of the present invention.

FIG. 3 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Example 2 of the present invention.

FIG. 4 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Example 3 of the present invention.

FIG. 5 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Comparative Example 1 of the present invention.

FIG. 6 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Comparative Example 2 of the present invention.

FIG. 7 is a graph showing image density when recording and erasing are repeatedly performed using the reversible thermosensitive recording material of Comparative Example 3 of the present invention.

Claims (2)

[Claims] Claim 1: A reversible photosensitive material, which has a heat-sensitive layer on a support, the main component of which is a resin matrix and an organic low-molecular substance dispersed in the resin matrix, and whose transparency changes reversibly depending on the temperature. A reversible heat-sensitive recording material, characterized in that the heat-sensitive layer contains liquid paraffin oil. 2. The reversible thermosensitive recording material according to claim 1, wherein the liquid paraffin oil has a viscosity of 70 cps or more at 20°C.