JPH04299180A - Reversible thermosensitive recording sheet - Google Patents

Abstract

PURPOSE:To improve the repetition of recording and erasing of information by coating the surface of a recording layer with polyimide having heat resistance as a protective layer in a reversible thermal recording sheet for reversibly changing the transparency of the recording layer composed of matrix polymer in which organic crystalline particles are dispersed. CONSTITUTION:Polyimide soluble in an organic solvent is used as a protective layer 1 having heat resistance. This soluble polymide is formed by coating on the surface of a reversible thermal recording layer 2 formed on a backing sheet 3 into a reversible thermal recording sheet. Because the polyimide excellent in heat resistance and wear resistance is used as the protective layer, this reversible thermal recording sheet has excellent performance both thermally and mechanically to realize a reversible thermal record being satisfactory in repetition characteristics.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording sheet capable of recording and erasing information reversibly by heating, for example, capable of displaying rewritable thermosensitive displays.

0002

2. Description of the Related Art Conventionally, many photochromic materials such as spiropyran compounds that develop and discolor when irradiated with light have been studied as compositions for recording layers that can reversibly record and erase information. However, this material has problems with its stability against light and heat and its durability against repeated use, so it has not been put to practical use.

[0003] On the other hand, as materials that are light-resistant and can be used repeatedly, there are polymer compositions that can thermally change the transparency or opacity of the recording layer to reversibly record or display information. It is disclosed in JP-A-54-119377. This composition is a composite composition in which a relatively low-molecular-weight crystalline organic compound is dispersed in a matrix polymer in the form of particles, and can be made transparent depending on the heating temperature range.
It is possible to create a cloudy and opaque state, and it is possible to perform recording in which the state has changed reversibly. Each state corresponds to the single crystal state and polycrystal state of the organic compound in the particle, and transmits and scatters light depending on the difference in crystal size. As one of the configurations for use,
It is used in the form of a sheet formed by coating a recording layer on a support sheet, and a card formed by punching the same.

Writing and erasing information on this thermosensitive reversible recording sheet is normally performed using a thermal head. When recording or erasing by heating with a thermal head, repeated heating causes physical deterioration of the recording state due to damage to the recording layer, and deterioration of the thermal characteristics of the head due to adhesion of the recording layer composition to the thermal head. . Therefore,
A protective layer is formed on the recording layer by coating and used. The protective layer needs to have mechanical strength and flexibility in addition to thermal stability, and is also required to have optical transparency in order to read out information from the recording layer well. In general, the materials for the protective layer include cellulose resin, styrene resin or styrene copolymer resin, acrylic resin or methacrylic resin or their copolymer resin, polyester resin, butyral resin, polyvinyl chloride resin, polyvinyl acetate resin, and vinyl chloride. /Vinyl acetate copolymer resin, polyurethane resin, acrylate radiation-curable resin, etc. are used, and the recording layer coated on the support sheet is further coated.

[0005]

[Problems to be Solved by the Invention] As the material for the protective layer, a material that is durable against mechanical deterioration such as damage and physical deterioration due to heating is selected. However, if the thermal head is repeatedly heated for recording and erasing, slight deterioration of the surface of the protective layer accumulates, causing information to remain unerased. Further, when the recording layer matrix polymer is subjected to thermal stress such as thermal contraction, even the surface of the protective layer is deformed, resulting in optical diffuse reflection, resulting in a thin layer remaining and a poor recording state. The prior art had problems with durability as described above.

[0006] In order to solve the problems of the prior art described above, the present invention aims to propose a protective layer with better mechanical and thermal properties and to improve the repeatability of reversible thermosensitive recording.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the reversible thermosensitive recording sheet of the present invention is made of a polymer composition in which organic crystal particles are dispersed in a matrix polymer, and the sheet is made of a polymer composition in which organic crystal particles are dispersed in a matrix polymer. A reversible thermosensitive recording sheet whose transparency changes reversibly upon coagulation for recording and erasing, characterized in that the surface of the recording layer is coated with a heat-resistant polyimide resin as a protective layer.

In the above structure, it is preferable that the polyimide resin forming the heat-resistant protective layer is a soluble polyimide resin that is soluble in an organic solvent.

Further, in the above structure, it is preferable that the soluble polyimide resin contains at least one type of molecular structure represented by the above (Chemical formula 1).

Furthermore, in the above structure, it is preferable that the organic solvent for dissolving the soluble polyimide resin is dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, or cresol.

[0011]

According to the structure of the present invention, it is possible to provide a protective layer with excellent heat resistance and mechanical strength, and to obtain highly reliable repeated recording/erasing characteristics. That is, polyimide resin is a resin that is not only excellent in heat resistance, mechanical properties, and chemical resistance, but also excellent in moldability. In particular, regarding heat resistance, common aromatic polyimides have
The glass transition temperature is 200°C or higher, the maximum actual operating temperature is 200°C to 300°C, and the heat distortion temperature related to thermal head deterioration is 2
It has excellent properties at 300°C or higher compared to 30°C. Mechanically, it has excellent properties such as wear resistance, tensile strength, bending strength, and compressive strength. In the present invention, by using this polyimide resin as a protective layer, a reversible thermosensitive recording sheet with excellent repeatability of recording and erasing can be produced.

According to a preferred configuration of the present invention in which the polyimide resin forming the heat-resistant protective layer is a soluble polyimide resin that is soluble in an organic solvent, a solution of the soluble polyimide resin is coated on the recording layer. After that, since an imidization reaction is unnecessary, the treatment may be heating at a relatively low temperature to remove the organic solvent and treatment under reduced pressure. Therefore, deterioration of the matrix polymer of the recording layer can be prevented. Furthermore, since no condensation water is generated due to imidization reaction and voids are less likely to occur, the protective layer can be produced as a homogeneous film.

[0013] Furthermore, according to a preferred configuration of the present invention in which the soluble polyimide resin contains at least one kind of molecular structure represented by the above (Chemical formula 1), the recording state will not deteriorate due to repeated heating for recording and erasing. It is less susceptible to mechanical damage caused by the thermal head, and reversible thermosensitive recording with good repeatability can be achieved.

Further, the organic solvent for dissolving the soluble polyimide resin is dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide,
According to a preferable configuration of the present invention in which the resin is one of cresols, the polyimide resin can be preferably dissolved, and it can be coated easily.

[0015]

[Example] First, the present invention will be explained with reference to FIG. The basic structure of the reversible thermosensitive recording sheet of the present invention is shown in FIG. After forming the reversible thermosensitive recording layer 2 on the support sheet 3 by coating, the protective layer 1 is coated using a solution of soluble polyimide resin. After coating with a protective layer, heat treatment and vacuum drying treatment are performed to remove the solvent before use. Next, the principle of reversible thermosensitive recording used in the present invention will be explained using (FIG. 2). This heat-sensitive recording layer is in a cloudy, opaque state at room temperature below T0. When heated to a temperature range of T1 to T2, it becomes transparent,
It maintains its transparent state even when returned to room temperature. Also, T3
When heated to the above temperature range, it changes to a translucent state, and when the temperature is returned from this state to room temperature, it returns to a cloudy, opaque state. By using the difference in transparency due to the difference in heating temperature range, reversible thermal recording can be performed using the transparent and opaque states as information.

Each component will be explained below. When forming a film using poly(pyromellit)imide, such as DuPont's "Kapton" (trade name), as a protective layer, it is insoluble in organic solvents, so its precursor solvent cannot be used. It is coated with soluble polyamic acid and then heat-treated to form polyimide. At this time, since the heating temperature for the imidization reaction needs to be 300° C. or higher in order to carry out a sufficient imidization reaction, it is necessary to be careful about thermal deterioration of the recording layer that occurs during this treatment. Furthermore, there is a problem in that voids are formed by water generated during dehydration condensation by imidization reaction, making it difficult to produce a homogeneous film.

Accordingly, in the present invention, the above-mentioned problem can be overcome by forming the protective layer from a soluble polyimide resin that dissolves in an organic solvent. That is, after coating a solution of soluble polyimide resin on the recording layer,
Since an imidization reaction is unnecessary, the treatment may be heating at a relatively low temperature to remove the organic solvent and treatment under reduced pressure. Therefore, deterioration of the matrix polymer of the recording layer can be prevented. Furthermore, since no condensation water is generated due to imidization reaction and voids are less likely to occur, the protective layer can be produced as a homogeneous film.

The present invention, which uses polyimide resin as a protective layer, has excellent thermal and mechanical performance, unlike the case where a conventional polymer resin is coated on the recording layer. It is not affected by thermal stress such as thermal contraction during heating by a layered matrix polymer thermal head. Therefore, it is less susceptible to deterioration in the recording state due to repeated heating during recording and erasing and to mechanical damage caused by the thermal head, making it possible to realize reversible thermosensitive recording with good repeatability.

In the present invention, a heat-resistant polyimide resin is used as the protective layer, and a soluble polyimide resin is selected in order to form a particularly excellent protective layer. Heat-resistant polyimide resin is formed by the polycondensation reaction of aromatic tetracarboxylic acid anhydride and aromatic diamine, and because it is usually not soluble in organic solvents in the polyimide state, it is necessary to prepare the polyimide precursor in the first step. It is coated in the form of polyamic acid and then heat-treated to form polyimide. In the case of a soluble polyimide resin, a polyimide resin solution can be obtained by selecting a solvent in which the polyimide resin is soluble as an organic solvent during polymerization. Also, the first
There is a method in which polyamic acid is removed in the form of polyamic acid by reprecipitation, heat treatment is performed to imidize the acid, and then the polyamic acid is dissolved in an organic solvent to obtain a polyimide resin solution.

As the molecular structure of the soluble polyimide resin, the resin shown in Chemical Formula 1 can be used. The main skeleton of the aromatic molecular structure of the tetracarboxylic anhydride component is biphenyl, biphenyl ether, benzophenone, and di(trifluoro)diphenylmethane, and the aromatic diamine component includes phenylene diamine, oxydianiline, and methylene dianiline. Molecules with a molecular skeleton such as , diaminobiphenyl, and tolidine are used. A soluble polyimide resin polymerized by a combination of these or a soluble polyimide resin copolymerized with another structure such as pyromellitic anhydride can be used as the protective layer.

Suitable organic solvents for dissolving these soluble polyimide resins include dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, and cresol, which are used in the polymerization of polyimide resins. However, any organic solvent that dissolves the polyimide resin can be used to form the protective layer.

Next, the material of the support sheet is selected in consideration of conditions such as strength and rigidity. Plastics such as nylon, cellulose acetate resin, polystyrene, polyethylene, polypropylene, polyester, polyimide, polycarbonate, and polyvinyl chloride can be used alone or in combination, and polyester and polyvinyl chloride are practical as the support. It also requires sufficient thickness to hold the sheet structure together with mechanical strength. The film thickness is often about 0.005 to 5 mm. A reflective layer is often formed on the support sheet to improve the contrast of the recording layer. Furthermore, as a support sheet,
An information recording layer, such as a magnetic recording layer, may be formed using a method other than heat-sensitive recording.

The matrix polymer constituting the recording layer for reversible thermosensitive recording must hold an organic crystalline low-molecular-weight compound uniformly dispersed in the form of particles, and must also have high transparency in a transparent state. Therefore, it is preferable to use a material that has good film-forming properties, excellent mechanical stability, and optical transparency. Such resins include polyvinyl chloride,
Polyvinyl acetate, polyvinylidene chloride, vinyl chloride/vinyl acetate copolymer resin, vinyl chloride/vinyl acetate/vinyl alcohol copolymer resin, vinyl chloride/vinyl acetate/maleic acid copolymer resin, vinyl chloride/acrylate copolymer resin, chloride Vinyl/vinylidene chloride copolymer resin, vinylidene chloride/acrylonitrile copolymer resin, polyester resin, polyamide resin, polyacrylic resin, polymethacrylic resin, acrylic/methacrylic copolymer resin, silicone resin, nylon resin, butyral resin, styrene/butadiene Copolymer resin etc. can be applied. These resins may be used alone or in combination of two or more.

The organic crystalline particles constituting the recording layer for reversible thermosensitive recording are compounds that exhibit the temperature characteristics shown in FIG. 2 when dispersed in a matrix polymer, and depending on their selection, the transparent temperature range and the opaque temperature range can be adjusted. A range is selected. The melting point of the compound is preferably 30° C. to 200° C., particularly 50° C. to 150° C., taking into consideration the thermal properties of the thermal head and the matrix polymer material. Considering the ease of crystallization, organic compounds constituting organic crystalline particles should contain at least one heteroatom, oxygen,
Preferably, it is a compound containing nitrogen, sulfur, halogen, etc. For example, -O-, -OH, -COOH, -CON
H-, -COOR, -CO-, -NH-, -NH2-
, -S-, -SH, -S-S-, halogen, etc., including alkanol, alkanediol, alkylamine, alkylammonium salt, alkane, alkene, alkyne, cycloalkane, cycloalkene or alkyne, saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, or ammonium salts; aromatic carboxylic acids or their esters, amides, or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amides, or Examples include ammonium salts, carboxylic acid esters of thioalcohols, and halides of these compounds. These compounds may be used alone or in a mixture of two or more. Further, the carbon number of these compounds is 10 to 60, preferably 10 to 38,
A range of 10 to 30 is particularly preferred.

Specific compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, and oleic acid. Alcohols include hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, eicosanol, and docosanol. Higher fatty acid esters include methyl stearate, ethyl stearate, tetradecyl stearate, octadecyl stearate,
Octadecyl laurate, Tetradecyl palmitate,
Examples of ethers or thioethers include didodecyl ether, didodecyl thioether, and octadecyl thioether.

The composition ratio of the organic crystalline particle compound constituting the reversible thermosensitive recording layer and the matrix polymer is preferably in the range of 1:0.5 to 1:20 by weight. If the ratio of the matrix polymer is less than this, the amount of the compound in the organic crystalline particles increases, making it difficult to uniformly coat the recording layer. Conversely, when the ratio of matrix polymer increases, the amount of organic crystalline particles decreases, making it difficult to make the image opaque, resulting in poor information contrast. Next, the present invention will be explained in more detail using Examples.

Example 1 As the support sheet 3, a white polyethylene terephthalate sheet having a thickness of 200 μm and having a dark brown magnetic recording layer of γ-Fe2 O3 formed on its surface was used. Recording layer 2 contains 2 g of behenic acid as an organic crystal particle compound, 0.1 g of phenolic antioxidant as an antioxidant, and 8 g of vinyl chloride/vinyl acetate copolymer as a matrix polymer.
was uniformly dissolved in 100 ml of tetrahydrofuran, and then applied to a thickness of 1 on the surface of the magnetic recording layer of the support sheet 3.
It was formed by coating with a thickness of 2 μm. As the heat-resistant soluble polyimide resin of the protective layer 1, polyimide having the structure shown in Chemical Formula 2 (manufactured by Ube Industries, Ltd., Upilex R) was used.

[0028]

[Case 2]

Using m-cresol as the organic solvent, 5 g of polyimide was dissolved in 100 ml of m-cresol, and then coated on the surface of the recording layer 2 to a thickness of 8 μm to form a pale yellow transparent protective layer 1. Thereafter, the solvent was removed at 150° C. for 5 hours and then in a vacuum dryer for 12 hours to obtain a reversible thermosensitive recording sheet having the structure shown in FIG. The transparent temperature range of this reversible thermosensitive recording sheet is approximately 7
The temperature ranged from 0°C to 80°C. Therefore, the head energy of the thermal head was adjusted to 85° C. on the surface of the recording layer to make the recording layer cloudy and opaque, and recording was performed on the reversible thermosensitive recording sheet that had been made transparent at the beginning. Further, the head energy was adjusted to 75° C., and the cloudy and opaque recording area was made transparent and erased.

As a result of recording 10 numbers from 0 to 9 as character information on this reversible thermosensitive recording sheet, the characters could be displayed in white on the dark brown surface of the magnetic recording layer and could be recognized well. As a result of repeatedly recording and erasing this character display, it was possible to stably perform the repetition over 3000 times. Furthermore, the surface of the protective layer 1 that was in contact with the thermal head did not show any residue due to thermal or mechanical damage.

Comparative Example 1 As the support sheet 3, a white polyethylene terephthalate sheet having a thickness of 200 μm and having a dark brown magnetic recording layer of γ-Fe2 O3 formed on its surface was used. On this support sheet 3, a recording layer 2 having the same composition as in Example 1 was coated and formed. 2 g of behenic acid as an organic crystal particle compound, 0.1 g of a phenolic antioxidant as an antioxidant, 8 g of vinyl chloride/vinyl acetate copolymer as a matrix polymer, and 100 m of tetrahydrofuran.
After uniformly dissolving in 100 ml of water, it was coated to a thickness of 12 μm. Further, on the surface of the recording layer 2, a prepolymer of ultraviolet curable acrylic resin was coated with a thickness of 20 μm as a protective layer 1, and then ultraviolet rays were irradiated to obtain a reversible thermosensitive recording sheet.

As a result of repeatedly recording and erasing characters on this reversible thermosensitive recording sheet, it was possible to repeat the recording more than 1,000 times, but white remaining characters were observed on the surface of the protective layer. This is diffuse reflection caused by mechanical abrasion caused by the thermal head, or by surface distortion caused by thermal contraction of the recording layer itself or the protective layer due to thermal stress on the recording layer.

Example 2 As the support sheet 3, a white polyethylene terephthalate sheet with a thickness of 180 μm was used, on which a reflective layer of vapor-deposited aluminum was formed with a thickness of 0.2 μm. The recording layer 2 contains 2 g of behenic acid, 0.3 g of stearic acid, and 0.2 g of docosanoyl alcohol as compounds of organic crystal particles.
0.1 g of phenolic antioxidant as an antioxidant, 10 g of vinyl chloride/vinyl acetate/acrylamide copolymer as a matrix polymer, and 10 g of tetrahydrofuran.
After uniformly dissolving in 0 ml, it was coated on the reflective layer of the support sheet 3 to a thickness of 20 μm.

As the heat-resistant soluble polyimide resin of the protective layer 1, a polyimide resin having a fluorine-containing structure shown in Chemical Formula 3 was used. This polyimide resin was soluble in N-methylpyrrolidone, and a colorless and transparent protective layer 1 could be formed.

[0035]

[Chemical formula 3]

After coating the recording layer 2 to a thickness of 20 μm, it was heated at 200° C. for 1 hour and vacuum dried for 12 hours.
A reversible thermosensitive recording sheet was formed. The transparent temperature range of this reversible thermosensitive recording sheet is approximately 70°C to 90°C.
It was ℃. Therefore, the head energy of the thermal head was adjusted to 95° C. on the surface of the recording layer to make the recording layer cloudy and opaque, and recording was performed on the reversible thermosensitive recording sheet that had been made transparent at the beginning. Further, the head energy was adjusted to 75° C., and the cloudy and opaque recording area was made transparent and erased.

[0037] This reversible thermosensitive recording sheet is sized 54mm x 86mm.
As a result of evaluating the repeatability of recording and erasing of reversible thermosensitive recording using a card reader/writer with a thermal head punched out to the size of a telephone card of mm, the results showed that it could be repeatedly repeated over 5,000 times, and there was no residue left after erasing. I couldn't see it.

Example 3 As the support sheet 3, a polyvinyl chloride sheet with a thickness of 700 μm was used.

As the reflective sheet, a polyethylene terephthalate film having a thickness of 15 μm and deposited with aluminum was used. On this aluminum reflective layer, a monomolecular layer of a silane coupling agent of γ-(2-aminoethyl)aminopropyltrimethoxysilane was adsorbed in isopropyl alcohol to improve the adhesion with the protective layer 1. . Next, on the polyethylene terephthalate surface of the reflective sheet,
Approximately 5 μm of epoxy resin adhesive was coated and laminated to the support sheet.

The recording layer 2 contains 2 g of behenic acid, 0.2 g of stearic acid, and 0.2 g of arachidic acid as compounds of organic crystal particles.
After uniformly dissolving 2 g of vinyl chloride/vinyl acetate copolymer as a matrix polymer in 100 ml of tetrahydrofuran, on the reflective layer surface of the support sheet 3,
It was coated to a thickness of 15 μm.

Next, as the heat-resistant soluble polyimide resin of the protective layer 1, a copolymer using biphenyltetracarboxylic anhydride and pyromellitic anhydride as the aromatic tetracarboxylic anhydride and orthotolidine as the aromatic diamine is used. A combined polyimide resin was used. m-cresol was used as the organic solvent, and a thickness of 10 μm was formed on the recording layer 2.
A reversible thermosensitive recording sheet was manufactured by coating with The polyimide resin film thus produced could be formed as a homogeneous protective layer without voids.

The transparent temperature range of this reversible thermosensitive recording sheet was about 80°C to 110°C. Therefore, the head energy of the thermal head is adjusted to 120° C. on the surface of the recording layer to make the recording layer cloudy and opaque, and recording is performed on the reversible thermosensitive recording sheet that is initially made transparent. Further, the head energy is adjusted to 90° C., and the cloudy and opaque recording area is made transparent for erasing. As a result of evaluating the repetition of recording and erasing of reversible thermosensitive recording, it was possible to stably perform over 5,000 repetitions, and no residue was observed on the protective layer.

[0043]

As described above, the present invention provides a reversible thermosensitive recording sheet consisting of organic crystal particles and a matrix polymer in which a soluble polyimide resin is used as the protective layer, thereby providing a protective layer with excellent heat resistance and mechanical strength. We were able to obtain highly reliable recording/erasing repeatability.

As described above, the present invention has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the structure of a reversible thermosensitive recording sheet according to the present invention.

FIG. 2 is a diagram showing the recording principle of the reversible thermosensitive recording sheet of the present invention.

[Explanation of symbols]

1 Protective layer made of soluble polyimide resin 2 Recording layer 3 Support sheet

Claims (4)

[Claims] 1. A reversible thermosensitive recording sheet comprising a polymer composition in which organic crystal particles are dispersed in a matrix polymer, and whose transparency can be reversibly changed by melting and solidification of the organic crystal particles to record and erase information, comprising: 1. A reversible thermosensitive recording sheet, characterized in that the surface of the recording layer is coated with a heat-resistant polyimide resin as a protective layer. 2. The reversible thermosensitive recording sheet according to claim 1, wherein the polyimide resin forming the heat-resistant protective layer is a soluble polyimide resin soluble in an organic solvent. 3. The reversible thermosensitive recording sheet according to claim 1, wherein the soluble polyimide resin contains at least one kind of molecular structure represented by the following (Chemical formula 1). [Chemical 1] (However, X = None, O, CO, C(CF3)2, Y = None, O, CO, C(CF3)2, m=0, 1, 2 or R represents various aromatic molecular structures.) 4. The organic solvent for dissolving the soluble polyimide resin is dimethylformamide, dimethylacetamide, N
- The reversible thermosensitive recording sheet according to claim 1 or 2, which is any one of -methylpyrrolidone, dimethylsulfoxide, and cresol.