JPH04301238A - Thermoreversible recording medium - Google Patents

Abstract

PURPOSE:To provide the thermoreversible recording material which is wider in a temp. range capable of attaining a transparent state than the conventional recording media, has the higher contrast than the contrast of the conventional media and can prevent the deterioration in the contrast even if images are formed by repeating the transparent state and opaque state. CONSTITUTION:A substrate 1 is prepd. A thermoreversible recording layer 2 formed of a thermoreversible recording material consisting of a matrix material consisting of polyvinyl butyral and satd. carboxylic acid or the deriv. of this carboxylic acid is provided on this substrate 1. Further, a transparent protective layer 3 which prevents the deterioration of the thermoreversible recording material is provided thereon.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoreversible recording medium on which recording and erasing can be repeatedly performed reversibly by thermal means.

0002

2. Description of the Related Art Thermoreversible recording materials have the property that their transparency to visible light changes depending on their thermal history. Therefore, by using thermal means such as a thermal head, it is possible to make the thermal history of a predetermined part of the material different from that of other parts, and to create a display etc. by creating a difference in the transparency of both parts. becomes.

Conventionally, such thermoreversible recording materials have been described, for example, in Japanese Patent Application Laid-Open No. 55-154198. The thermoreversible recording material disclosed in this publication was constructed by dispersing an organic low-molecular compound such as behenic acid in a matrix material made of a polymer or resin such as polyester.

FIG. 3 shows the characteristics of this conventional thermoreversible recording material.
FIG. 3 is a diagram showing a hysteresis curve of transparency change with respect to temperature, with transmittance on the vertical axis and temperature on the horizontal axis. Hereinafter, the characteristics of the conventional thermoreversible recording material will be explained with reference to FIG. A, B, C, and D in FIG. 3 indicate the transmittance at each temperature. That is, A and D are at room temperature RT
B indicates the transmittance at temperature T1, and C indicates the transmittance at temperature T2 or higher.

[0005] This conventional thermoreversible recording material can be stored at room temperature (R
In the vicinity of (T) in Fig. 3, depending on the past thermal history,
It exhibited the characteristics of either A) transmittance (opaque state) or (D) transmittance (transparent state). When this thermoreversible recording material is heated over temperature T0 to temperature T1, the transmittance that was (A) or (D) becomes (B
). Thereafter, when this is cooled to room temperature, the transmittance, which was (B) in any case, is fixed to (D).

On the other hand, near room temperature, the transmittance is (
The thermoreversible recording material that was A) or (D) was heated to a temperature T
0 and exceeds temperature T1 and is heated to temperature T2 or higher, the transmittance that was (A) or (D) reaches its maximum value (
B) In other words, the state changes to (C) through the transparent state. That is, the state becomes a state where the transparency is slightly lower than the transparent state (D). After that, when this is cooled to room temperature, regardless of whether the transmittance is (A) or (D) at the starting point, (C
), the transmittance becomes (A), and this thermoreversible recording material is fixed in the opaque state (A).

As a specific example of this characteristic, the above-mentioned Japanese Patent Application Laid-open No. 1983
JP-A-154198 describes the following examples. ■: A thermoreversible recording material containing a polymeric linear copolyester based on an aromatic dicarboxylic acid and an aliphatic diol and docosanoic acid showed stable transparency when heated to 72°C and cooled. . It could only be returned to the opaque state by reheating to a temperature above 77°C.

■: A thermoreversible recording material containing a copolymer of vinylidene chloride and acrylonitrile, docosanoic acid, and a Fluorad lubricant for improving fluidity is heated to 63°C.
It showed stable transparency when heated to and cooled. It could only be returned to the opaque state by reheating to a temperature above 74°C. ■: A thermoreversible recording material containing a copolymer of vinyl chloride and vinyl acetate and docosanol showed stable transparency when heated to 68° C. and cooled. This is 70
It could only be returned to the opaque state by reheating to a temperature above °C.

■: A thermoreversible recording material containing polyester and docosanoic acid showed stable transparency when heated to 72° C. and cooled. It could only be returned to the opaque state by reheating to a temperature above 77°C.

0010

However, in the conventional thermoreversible recording material, the temperature range for forming a transparent state is (77-72)=5.
℃, 11℃ for ■, 2 for ■
℃, 5℃ for ■, at most 1
The temperature range was only 1°C, which was extremely narrow.

By the way, in order to configure a display device using a thermoreversible recording material and display a display with good contrast, etc., a colored plate is provided on the back side of the display panel made of the thermoreversible recording material. The printed portion of the display board is selectively rendered transparent using thermal means such as a thermal head,
In addition, it is desirable to have a configuration in which display is performed by leaving the background portion in an opaque state so that only the printed portion can be seen through the color of the colored plate.

However, with conventional thermoreversible recording materials, the temperature range for forming a transparent state is narrow as described above, which makes it difficult to control the temperature of thermal means such as a thermal head. However, it was difficult to obtain stable transparency when repeatedly creating images. Further, in conventional thermoreversible recording materials, the transmittance ratio (contrast) between the transparent state and the opaque state is not very large, so further improvements have been desired.

[0013] The present invention has been made in view of the above points, and therefore, an object of the present invention is to achieve a transparent state in a wider temperature range than the conventional technology, a higher contrast than the conventional technology, and a transparent state. An object of the present invention is to provide a thermoreversible recording material that can prevent contrast deterioration even when an image is formed by repeatedly changing the state and the opaque state.

[0014]

[Means for Solving the Problems] In order to solve the above problems, the thermoreversible recording medium of the present invention is provided by preparing a substrate, and on the substrate, a matrix material made of polyvinyl butyral and a saturated carboxylic acid or the saturated carboxylic acid. A thermoreversible recording layer made of a thermoreversible recording material made of a carboxylic acid derivative is provided, and a transparent protective layer is further provided thereon to prevent deterioration of the thermoreversible recording material.

FIG. 1 schematically shows a cross section of the thermoreversible recording medium of the present invention. 1 is a substrate, and for example, a polyethylene terephthalate substrate is preferably used. 2 is a thermoreversible recording layer formed of a thermoreversible recording material made of a matrix material made of polyvinyl butyral and a saturated carboxylic acid or a derivative of the saturated carboxylic acid. 3 is a transparent protective layer for preventing deterioration of the thermoreversible recording material, and normally the matrix material of the thermoreversible recording layer 2, ie, polyvinyl butyral, is suitably used.

Saturated carboxylic acids that can be used in the present invention include, but are not limited to, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, and the like. be. These correspond to saturated carboxylic acids having 10 to 24 carbon atoms. In addition, the derivative thereof is preferably, but not limited to, an amino group, an aldehyde group, a hydroxyl group, etc.

Further, the mixing ratio of the above-mentioned matrix material and the saturated carboxylic acid or its derivative is 1:1 by weight of the saturated carboxylic acid or its derivative to the matrix material.
If the content is more than 1, it will be difficult to form a film of a thermoreversible recording material, and if it is less than 20:1, the thermoreversibility will be reduced, so it is preferably within the range of 1:1 to 20:1.

[0018] Furthermore, the expression "containing a matrix material made of polyvinyl butyral and a saturated carboxylic acid or a derivative of the saturated carboxylic acid" as used herein refers not only to the case of only these materials, but also to the case of a thermoreversible material in addition to these materials. It also means cases where other substances are included, such as a substance that improves the film quality of the recording material and a substance that improves lubricity. In addition, in actual use of the thermoreversible recording material, a coating solution of the thermoreversible recording material is prepared in order to apply the material to a support such as a substrate, film, etc. made of a suitable material. There are cases where At that time, a coating solution is obtained by dissolving the matrix material and the saturated carboxylic acid or its derivative in a solvent. Solvents for this purpose include, but are not limited to, the following:
For example, it is preferable to use one kind selected from tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene, etc., or to use a mixture of two or more kinds. Further, when preparing the coating solution, the solvent may be heated if necessary.

A film made of polyvinyl butyral is used for the transparent protective layer used in the present invention to prevent deterioration of the thermoreversible recording material.

[0020]

[Operation] According to the present invention, as configured as described above, the thermoreversible recording medium of the present invention is capable of storing the thermoreversible recording material of the present invention at a specific temperature T3 (70° C.) or higher as shown in FIG. The thermoreversible recording material of the present invention exhibits maximum transparency by heating to the melting point temperature of the matrix material (200°C) and then cooling to about room temperature, and at temperatures T1 to T3 (within a certain temperature range lower than T3). Minimum transparency is achieved by heating at 57-70°C and then cooling.

[0021] Therefore, the temperature range that forms a transparent state,
A thermoreversible recording material is obtained in which the temperature range in which an opaque state is formed is reversed compared to conventional thermoreversible recording materials. Further, since the transparent protective layer is provided, the thermoreversible recording material is not directly exposed to the surface, and even if images are formed and erased by repeated heating and cooling, the deterioration of characteristics is reduced.

[0022]

[Embodiment 1] Hereinafter, embodiments of the thermoreversible recording material of the present invention will be described with reference to the drawings. First, prepare 5 parts by weight of S-LEC B (trade name, manufactured by Sekisui Chemical Co., Ltd.) as polyvinyl butyral and 3 parts by weight of stearic acid as a saturated carboxylic acid or its derivative, and add these materials to 50 parts by weight of tetrahydrofuran. A coating solution of the thermoreversible recording material was prepared by dissolving it. This is called solution 1.

Next, a coating solution for the deterioration prevention layer was prepared by dissolving 5 parts by weight of S-LEC B (trade name, manufactured by Sekisui Chemical Co., Ltd.) as polyvinyl butyral in 50 parts by weight of ethyl alcohol. This is called solution 2. Solution 1 is applied to a polyethylene terephthalate substrate by a bar coating method, and the substrate is dried and solidified at a temperature of 90°C to form a thermoreversible recording layer. The mixture was dried and solidified to form a deterioration prevention layer, thereby producing a thermoreversible recording medium of the present invention.

Next, as a coating solution for Comparative Example 1, 5 parts by weight of vinyl chloride-vinyl acetate copolymer VYHH (Union Carpenter Copolymer) was used instead of S-LEC B among the materials for the thermoreversible recording layer solution of Example 1. A coating solution of Comparative Example 1 was prepared in exactly the same manner as in the above Example except that a coating solution (manufactured by Baito Co., Ltd. (UCC)) was used. The coating solution of Comparative Example 1 was coated to the same thickness on a polyethylene terephthalate substrate by the bar coating method in the same manner as in the above Examples. Next, the coated substrates were each dried in an air atmosphere at a temperature of 90°C. This drying time is the temperature at which the solvent can be removed, and is approximately 3.
It was set to 0 minutes.

Furthermore, as the coating solution of Comparative Example 2,
The same thermoreversible recording layer solution as in Example 1 was prepared. This coating solution was coated to the same thickness on a polyethylene terephthalate substrate. Next, the substrate after coating was heated to 90°C.
Each was dried in an air atmosphere at a temperature of . The drying time was approximately 30 minutes at a temperature that allowed the solvent to be removed. Note that Comparative Example 2 does not have the deterioration prevention layer of the thermoreversible recording medium of the above Example.

FIG. 2 is a diagram showing a hysteresis curve of the change in transparency with respect to temperature of the sample of this example, with transmittance on the vertical axis and temperature on the horizontal axis. As can be seen from Figure 2, the sample of this example was heated to S-LEC B from 70°C.
When heated to a temperature within the range of 200℃, which is the melting point of
), it becomes fixed in a transparent state. Further, the sample of this example becomes opaque when heated to a temperature within the range of 57 to 70°C, and is fixed in an opaque state when cooled to room temperature.

[0027] Further, the contrast of the sample of this example as shown by the transmittance ratio between the transparent state and the opaque state (in this case, the transmittance ratio for light with a wavelength of 550 nm) was 10.0. For each of the samples of Example, Comparative Example 1, and Comparative Example 2 formed in this manner, the repeatability of the change in transparency with respect to temperature was measured. That is, after repeatedly heating and cooling to form and erase images, each sample is changed into a transparent state and an opaque state in a constant temperature bath, and measured with a spectrophotometer to determine the difference between the transparent state and the opaque state. The contrast expressed as a transmittance ratio (in this case, a transmittance ratio for light with a wavelength of 550 nm) was determined. Repeat this measurement. The results are shown in Table 1.

[0028]

[Table 1]

As can be seen from Table 1, the thermoreversible recording material of the present invention can be repeatedly heated and cooled to record and erase images.
The contrast did not decrease even after repeating the test about 00 times, whereas the contrast of Comparative Example 1 was poor from the first time, and the contrast of Comparative Example 2 was good at first, but as it was repeated, it became worse. As a result, the contrast decreases and the characteristics gradually deteriorate.

[0030]

As described in detail above, according to the thermoreversible recording material of the present invention, the matrix material is polyvinyl butyral, and the matrix material contains a saturated carboxylic acid and a derivative of the saturated carboxylic acid. By forming a transparent protective layer to prevent deterioration of the recording material on a thermoreversible recording material whose transparency changes depending on its characteristic thermal history, the temperature range in which the thermoreversible recording medium can be made transparent is now lower than before. In addition, it was possible to improve contrast deterioration due to repetition.

Therefore, when this thermoreversible recording material is applied to a display device or the like that uses thermal means such as a thermal head and forms a transparent pattern, the temperature of the thermal means can be roughly controlled, so that the device configuration can be improved. This has the effect of making it easier.

[Brief explanation of the drawing]

FIG. 1 schematically shows a cross section of a thermoreversible recording medium of the present invention.

FIG. 2 shows the hysteresis curve of the thermoreversible recording material of the invention.

FIG. 3 shows a hysteresis curve of a conventional thermoreversible recording material.

[Explanation of symbols]

1　　　　　　　　　　Substrate 2 Thermoreversible recording layer 3 Transparent protective layer

Claims (1)

[Claims] Claim 1: (1) a substrate, and (2) a thermoreversible recording material provided on the substrate and comprising a matrix material made of polyvinyl butyral and a saturated carboxylic acid or a derivative of the saturated carboxylic acid. a thermoreversible recording layer;
(3) A thermoreversible recording medium comprising a transparent protective layer provided on the thermoreversible recording layer to prevent deterioration of the recording material.