JPH0585041A - Thermal recording medium - Google Patents

Abstract

(57) [Summary] [Object] To provide a thermosensitive recording medium having a sufficient contrast and an erasing temperature range of 25 ° C. or more in a recording medium capable of reversibly recording and erasing an image by heating. And [Structure] A thermosensitive recording medium comprising an organic low molecular weight substance dispersed in an organic polymer resin on a support, and a thermosensitive recording layer having a transparency reversibly changed depending on temperature. The low molecular weight substance is a higher fatty acid amide represented by the following general formula (1) or a substitution product thereof R ₁ -CONH ₂ or R ₂ -CONH-R ₃ (1) (where R ₁ is a double bond) A chain hydrocarbon group having, at least one of R ₂ and R ₃ is a chain hydrocarbon having a double bond and the other is an alkyl group)

Description

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of reversible recording used in the present invention.

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a support and a thermosensitive recording layer comprising an organic low molecular weight substance dispersed in an organic polymer resin, the transparency of which reversibly changes depending on temperature. The organic low-molecular-weight substance is a higher fatty acid amide represented by the following general formula (1) or a substitution product thereof, a heat-sensitive recording medium R ₁ -CONH ₂ or R ₂ -CONH-R ₃ (1) (where (R ₁ is a chain hydrocarbon group having a double bond, R ₂ and R ₃ are at least one chain hydrocarbon group having a double bond and the other is an alkyl group) 2. A higher fatty acid amide or a substituted product thereof is oleic acid amide, n-stearyl oleic acid amide, erucic acid amide, n-stearyl erucic acid amide, n-oleylstearic acid amide or n-oleylpalmitic acid amide. The thermal recording medium according to claim 1, wherein at least one kind is selected from the inside. 3. An organic low-molecular substance is dispersed in an organic polymer resin in the form of particles, and the particles have a center value of particle size distribution of 5 μm or less, and 10% or more of particles having a particle size of 1 μm or less are contained. BACKGROUND oF tHE iNVENTION [0001] field of the invention the present invention can thermosensitive recording medium according to claim 1, wherein that reversibly recording an image by heating, to be erased The present invention relates to a recording medium that can be used, and a thermal recording medium that can be used in a thermal printer or the like. In recent years, as a new recording material, a recording material capable of reversibly recording and erasing an image due to a difference in heating temperature and having an image fixing property at room temperature has been proposed. .. (JP-A 55-154198, JP-A 6-
See 1-257883 and JP-A-63-39377. The principle of recording and erasing of the recording material utilizes the change in transparency depending on the temperature of the thermosensitive recording layer. Explaining this principle with reference to FIG. 1, an organic low molecular weight substance dispersed in an organic polymer resin is used. heat-sensitive recording layer mainly composed of, for example previously heated to T3 or more temperatures, fixing at opacification (cloudy) conditions when subsequently cooled to T ₀ or lower. When the opaque thermosensitive recording layer is heated to the state of T _{1 to} T ₂ ,
The maximum transparency is reached via the →→ route, and when cooled from this state, the transparent state is fixed via →. When the transparent heat-sensitive recording layer is heated to a temperature of T ₃ or higher, →→
After reaching the state of being slightly opaque than the maximum transparency, and then cooling from that state, it becomes fixed in the opaque state via →. The heat-sensitive recording layer is provided with a reversible heat-sensitive recording layer on a transparent support such as a glass plate, a polyester film, a vinyl chloride film, a nylon film or a colored or metal-deposited support. By applying a heat history to a part or the entire surface, a transparent portion and an opaque portion are formed, and image information is printed or erased. The recording materials according to the prior art include organic high molecular weight substances such as behenic acid, methyl stearate, docosyl behenate or higher fatty acids or esters thereof in an organic high molecular weight resin such as polyester resin or vinyl chloride resin. It has a dispersed heat-sensitive recording layer, and the transparency of the heat-sensitive recording layer is changed by selecting the heating temperature. Further, even if this recording material is cooled to room temperature after being heated, it can stably maintain a transparent state or a cloudy state, and can reversibly take these states. However, with only the combination of materials proposed so far, the erase temperature range (T _{1 in} FIG.
It was impossible to exceed the clearing temperature width corresponding to the width of ˜T ₂ of 25 ° C.). For this reason, when actually used as a recording medium, it is possible to print with a thermal head in the same way as a normal thermal recording medium for printing, but for erasing, for example, when erasing with a heat roll, the temperature of the roll is controlled to be constant. However, there was a practical difficulty in erasing the recording temperature. Also, in order to widen the erasing temperature range, two kinds of organic low molecular weight substances are mixed and used,
Although it is proposed to add another additive newly,
It did not yet have a sufficient erase temperature range. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and by combining an organic polymer resin with a specific organic low-molecular substance, it has a sufficient contrast. We provide a reversibly printable and erasable thermosensitive recording medium with an erasing temperature range of ℃ or more, reducing the burden on the erasing temperature control of the printing / erasing device,
The purpose is to improve the completeness of the device as a total system and to enhance its practicality. The outline of the present invention is as follows. A thermosensitive recording medium comprising an organic low molecular weight substance dispersed in an organic polymer resin on a support, the transparency being reversibly changed depending on temperature. Is a higher fatty acid amide represented by the following general formula (1) or a substitution product thereof: R ₁ -CONH ₂ or R ₂ -CONH-R ₃ (1) (where R ₁ is a double A chain hydrocarbon group having a bond, at least one of R ₂ and R ₃ is a chain hydrocarbon group having a double bond, and the other is an alkyl group.) The constitution of the thermosensitive recording medium of the present invention will be described below. .. Support: As the support, a synthetic resin film or a paper provided with a colored coating layer on the front surface or the back surface, a synthetic resin film in which a color pigment is kneaded, or the like can be used. For example, a black film in which carbon black is kneaded can be used. .. or,
The support of the present invention comprises an organic polymer film having a light refractive index of 1.4 to 1.7, a light transmittance of 70% or more and a thickness of 3 to 500 μm, for example, vinyl chloride-vinyl acetate copolymer, polyester, polycarbonate. Also used is a film such as polyacetate or polyimide provided with a reflective layer made of a metal layer. These films have a light refractive index of 1.5 to 1.6, a light transmittance of 85% or more, and a thickness of 50 to 30.
It is more preferably 0 μm. As the reflective layer used for the support,
When irradiated with light in the wavelength range of 500 to 600 nm, a specular reflectance of 35% or more is applicable, preferably 50% or more, and a specular reflectance of 70% or more in the wavelength range of 400 to 700 nm. Is more preferable. Here, the specular reflectance is a value obtained by an integrating sphere reflection measurement method using a spectrophotometer, and is a value obtained from the relationship of (total reflectance)-(diffuse reflectance) = (specular reflectance). .. Further, the wavelength region of 500 to 600 nm is the region having the highest luminosity factor for brightness. The material forming the reflective layer includes aluminum, tin, silver, zinc, magnesium,
Metals such as copper, gold and platinum are used, and these can be applied in the form of a thin film layer formed by a vapor deposition method, a sputtering method, an electroless plating method or the like. As the thickness of this thin film layer,
In terms of reflection characteristics and mechanical strength, the metal thin film layer has a thickness of 0.
001 to 5 μm, preferably 0.03 to 1 μm, and in the case of a metal foil, 1 to 50 μm, preferably 5 to 30 μm. Organic polymer resin: As the organic polymer resin, those having good transparency, excellent mechanical strength and good film forming property are preferable. Specific examples thereof include polyvinyl chloride,
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, Examples thereof include vinylidene chloride-acrylonitrile copolymer, polyester resin, polyamide resin, acrylic resin, silicone resin and the like. Among these, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and polyester resin are particularly preferable. Organic low molecular weight substance: As the organic low molecular weight substance in the present invention, a higher fatty acid amide represented by the following general formula or a substituted form of a higher fatty acid amide can be applied. R ₁ -CONH ₂ or R ₂ -CONH-R ₃ (1) (wherein R ₁ is a chain hydrocarbon group having a double bond, R ₂ and R are at least one chain hydrocarbon group having a double bond) The other is an alkyl group, and the carbon number of R ₁ , R ₂ and R ₃ is usually 10 to 4 carbon atoms.
0 applies. Examples of the higher fatty acid amide represented by the above general formula include erucic acid amide CH ₃ (CH ₂ ) ₇ —CH═CH (C
H ₂ ) ₁₁ CONH ₂ oleic acid amide CH ₃ (CH ₂ ) ₇ —CH═CH
(CH ₂ ) ₇ CONH ₂ elaidic acid amide (trans isomer of oleic acid) brassic acid amide (trans isomer of erucic acid) Further, examples of the substitution product of the higher fatty acid amide represented by the general formula include N-stearyl erucic acid. amide _{C 18 H 37 CONH-CH 3} (CH 2) 7 CH = CH (C
H _{2) 11} N-oleyl stearic acid amide _{C 17 H 35 CONH-CH 2} (CH 2) 7 CH = CH (C
H _{2) 7} CH ₃ N- oleyl palmitic acid amide _{CH 3 (CH 2) 14 CONH} -CH 2 (CH 2) 7 CH =
_{CH (CH 2) 7 CH 3} N- stearyl oleic acid amide _{C 18 H 37 CONHCH 3 (CH} 2) 7 CH = CH (CH
₂ ) ₇ N-Elaidylstearic acid amide (trans isomer of N-oleyl stearic acid amide) N-stearyl brassic acid amide (trans isomer of N-stearyl erucic acid amide) is applied to the present invention. This organic low-molecular substance is dispersed in the organic polymer resin in the form of particles, and the particles preferably have a center value of particle size distribution of 5 μm or less and contain 10% or more of particles having a particle size of 1 μm or less. .. If the center value of the particle size distribution is larger than 5 μm and the particles having a particle size of 1 μm or less are contained in less than 10%, the contrast between the opaque portion and the transparent portion of the thermal recording layer becomes insufficient. When the image is formed, the visibility tends to be insufficient. If the thickness of the heat-sensitive recording layer is increased in order to solve this problem, when printing or erasing is performed on the heat-sensitive recording layer, a temperature gradient can be generated in the thickness direction within the heat-sensitive recording layer depending on the time for imprinting thermal energy. The transparent temperature range, that is, the erase temperature range of T1 and T2 in FIG. 1 is apparently narrowed, which is not preferable in practice. The particle size distribution of the organic low molecular weight substance in the heat-sensitive recording layer was determined by taking a cross-sectional photograph of the recording layer and image-processing the image. The organic low molecular weight substance is dispersed in the organic polymer resin, and the mixing ratio thereof is preferably 5 to 100 parts by weight, and particularly preferably 10 to 100 parts by weight with respect to 100 parts of the organic polymer resin. It is preferably about 50 parts. When the amount of the organic low molecular weight substance is less than 5 parts, the heat-sensitive recording layer is not sufficiently opaque (whitened) and it is difficult to obtain contrast. Again 10
When it is more than 0 parts, the film forming property of the heat-sensitive recording layer is deteriorated. The thickness of the heat-sensitive recording layer is preferably in the range of 3 to 30 μm, more preferably 5 to 15 μm. When the thickness is less than 3 μm, the heat-sensitive recording layer is not sufficiently opaque, while when it is thicker than 50 μm, the thermal conductivity at the time of printing / recording and erasing is deteriorated and the sensitivity of the heat-sensitive recording layer is lowered. In the heat-sensitive recording medium of the present invention, the following layers can be provided, if desired. For example,
In the heat-sensitive recording medium of the present invention, a magnetic recording layer can be provided on the surface of the support opposite to the heat-sensitive recording layer. In this case, as the magnetic recording layer, a magnetic material dispersed in an organic polymer material is used. As the organic polymer material,
Thermoplastic or thermosetting resins such as vinyl chloride-vinyl acetate resin, polyester resin, urethane resin, acrylic resin, epoxy resin can be used. An additive such as a conductive filler or an abrasive may be added to the magnetic recording layer. The thickness of the magnetic recording layer can be set appropriately. Further, when recording with a thermal head, in order to improve the heat resistance of the thermal recording layer and to maintain the matching property with the thermal head, a thermoplastic or thermosetting resin such as polymethacrylate is provided on the thermal recording layer. A heat resistant protective layer containing a resin such as a resin, a silicone resin, an acrylic resin, an alkyd resin, or a photo-curable or electron beam-curable urethane-acrylate resin as a main component may be provided. In addition, an intermediate layer between the heat-sensitive recording layer and the protective layer for preventing migration of the organic low-molecular-weight substance in the heat-sensitive recording medium layer to another layer or for enhancing the adhesiveness between the heat-sensitive recording layer and the protective layer. Layers may be provided. Further, in the present invention 0 thermal recording medium, when a magnetic recording layer is provided, in order to prevent abrasion of the magnetic recording layer, a thermoplastic resin or a thermosetting resin, for example, a polymethacrylate resin, on the surface of the magnetic recording layer, A heat resistant coating layer containing a photo-curable or electron-beam curable urethane-acrylate resin or epoxy-acrylate resin such as silicone resin, acrylic resin or alkyd resin as a main component may be provided. Embodiments of the present invention will be described below. The term "parts" indicates the weight ratio. Example 1 A transparent polyester film having a thickness of 188 μm and having aluminum vapor-deposited on one side thereof was used as a support. After coating, the solvent was dried to form a heat-sensitive recording layer having a coating thickness of 10 μm. The organic low molecular weight substance in the heat-sensitive recording layer had a center value of particle size distribution of 2 μm, and contained 20% of particles having a particle size of 1 μm or less. N-oleyl stearic acid amide 20 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 80 parts by weight Tetrahydrofuran 800 parts by weight Example 2 A 188 μm transparent polyester film supported on one side by vapor deposition of aluminum As a body, the following coating material for the thermal recording layer was applied to the side of the support on which aluminum was not vapor-deposited using a Mayer bar, and then the solvent was dried to form a thermal recording layer having a coating thickness of 10 μm. . The organic low molecular weight substance in the heat-sensitive recording layer had a center value of particle size distribution of 2 μm, and contained 20% of particles having a particle size of 1 μm or less. N-stearyl erucic acid amide 20 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 80 parts by weight Tetrahydrofuran 800 parts by weight Comparative Example 1 A 188 μm transparent polyester film supported on one side by vapor deposition of aluminum As a body, the following coating material for the thermal recording layer was applied to the side of the support on which aluminum was not vapor-deposited using a Mayer bar, and then the solvent was dried to form a thermal recording layer having a coating thickness of 10 μm. . 20 parts by weight of behenic acid 80 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer 800 parts by weight of tetrahydrofuran Using a machine, color development and erasing tests were performed under the conditions of pressure of 400 g / m ² and pressing for 1 second. Erase temperature is (1) 130 ° C first
(2) The temperature range in which the plate was erased by pressing a hot plate heated to a predetermined temperature was measured using the above-mentioned thermal gradient tester. The results are shown in Table 1.
It is as follows. [Table 1] According to this, according to the embodiment of the present invention,
The erasing temperature was higher than that of the comparative example, and the erasing temperature range was widened. The present invention can provide a heat-sensitive recording medium having a wide erasing temperature range of 25 ° C. or more and a high contrast between the colored portion and the non-colored portion.