JPH0533674B2 - - Google Patents

Description

[Detailed description of the invention] (A) Industrial application field The present invention relates to a novel thermal imaging method.

More specifically, a thermal pattern is applied to a heat-sensitive material that is non-adhesive at room temperature but becomes adhesive when heated to develop an image-like adhesive area, and then the powder is brought into contact with the heat-sensitive material. The present invention relates to a method of forming a thermal image, which involves bringing the powder into contact with the background and removing the powder from the background to produce an image contrast with the background, that is, development.

(B) Prior Art Various methods have been known as thermal image forming methods, and although it will not be necessary to discuss all of them,
At present, the so-called dye coloring type heat-sensitive recording method has become mainstream and is showing remarkable popularity. This method uses a colorless or light-colored leuco dye and an organic solid acid as powders and applies a thermal pattern to a heat-sensitive recording material (heat-sensitive recording sheet) coated in layers on a support using a binder. A visible image is obtained by a color reaction at the heated site.

The image obtained by this method therefore provides contrast due to the difference in visible light absorption (absorbance) between the background containing the uncolored dye and the colored dye image area.

Additionally, Konishiroku Photo Industry Co., Ltd. previously announced a thermal copying method that utilizes supercooling. This method utilizes supercooling development after hot melting of organic crystals such as acetanilide, phenacetin, benzotriazole, etc., and utilizes the property of supercooled liquids of these substances to adhere solid fine powders for development. However, since the adhesion force is small, the image fixability is not sufficient and the image easily peels off.

(C) Problems to be Solved by the Invention As mentioned above, the most widely used thermal image forming method today is a dye coloring type, so the recorded images are subject to discoloration and fading due to decomposition, which is the fate of organic dyes. Moreover, since it is based on an acid-base reversible reaction type coloring mechanism, image areas will be discolored by basic substances, and non-image areas (background) will exhibit undesirable color development by acidic substances. That is, the stability and archival life of recorded images are insufficient.

However, thanks to the development of technology for thermal pattern application mechanisms such as thermal heads, thermal recording systems such as high-speed facsimile machines are expected to become increasingly important, and improvements in the stability of recorded images are strongly desired. It is a place where you can

Therefore, the problem to be solved by the present invention is, first of all, to significantly improve the stability, or archival life, of images formed by a heat-sensitive mechanism.

Next, in the dye-colored type, only one type of heat-sensitive recording sheet can obtain light absorption (i.e., hue) based on the dye present in the heat-sensitive recording sheet, and lacks flexibility. By simply using a recording sheet and selecting the powder at the development stage, not only can images with various desired hues be obtained, but also physical properties other than light absorption (e.g.
It becomes possible to draw patterns whose characteristics (magnetism, electrical properties, optical properties other than absorption, etc.), chemical properties, and even biological properties are different from the background.

Furthermore, in electrophotography (xerography) and electrostatic recording paper technology, development has been carried out by applying colored powder (so-called toner; there are dry and wet types) to electrostatic latent images. However, the toner used had to be made with great care so that its electrostatic properties were sufficient for this imaging method. Therefore, its production required great difficulty and high economic sacrifice (cost). However, since the powder (developing powder) used in the image forming method of the present invention only needs to be adhered to the area of the recording material that exhibits adhesive properties, no technical considerations regarding static electricity are required. Its production is easy and economically burdensome.

It has been pointed out that in the above-mentioned thermal copying method that utilizes the supercooling phenomenon of organic crystals, the powder adhesion of the latent image generated by heating is weak, resulting in poor mechanical robustness of the powder image against scratches, etc. However, the present invention essentially solves this problem. This also greatly contributes to improving archival life.

(D) Means to solve the problem Current highly developed thermal pattern application technology,
For example, while using thermal pens, dot-shaped thermal heads (flying spot method and parallel array method), and even infrared rays (normal light and laser light), the images obtained will not discolor, fade, or peel off. That is, as a method that has a sufficiently long archival life and is capable of obtaining not only optical images but also other significant images, the present inventor has developed an adhesive polymer, a tackifier, and a plasticizer that is solid at room temperature. A heat-sensitive adhesive composition, which basically consists of a three-part adhesive agent, imparts a thermal pattern to the heat-sensitive material present on the support to develop adhesive contact areas in an imagewise manner, and is then brought into suitable contact. Here, we have invented a method for forming a thermal image, which comprises firmly adhering the powder to a site where adhesive properties are developed.

First, the heat-sensitive material used in the heat-sensitive image forming method of the present invention will be described.

This does not simply utilize the solid fine powder adhesion of the supercooled liquid after thermally melting the organic crystal as described above, but rather uses an adhesive polymer that has particularly excellent adhesion to various adherends and its polymer. A tackifier (also known as tackifier), which significantly promotes adhesive development, and a tackifier that is solid at room temperature, but melts when heated and acts as a solvent for the adhesive polymer and tackifier, dissolving both to create a thick, high-concentration product. Essentially, it utilizes the strong adhesive force created by the cooperation of three parties, including a plasticizer that can cause a molecular solution to appear and develop semi-permanent adhesive properties.

Examples of the adhesive polymer include vinyl acetate polymer, acrylic polymer, vinyl chloride polymer, vinylidene chloride polymer, natural rubber type, synthetic rubber type, polyurethane type, polyester type, polyamide type, vinyl acetate-acrylic acid ester copolymer, Famous as an adhesive for vinyl acetate-ethylene copolymer, vinylpyrrolidone-styrene copolymer, styrene-acrylic acid ester copolymer, vinylpyrrolidone-acrylic acid ester copolymer, olefin-based (co)polymers such as ethylene or propylene, polyvinyl butyral-based, etc. Select and use polymeric materials. Of course, two or more types may be used in combination.

Tackifiers include indene resin, ethyl cellulose, petroleum resin, terpene resin, rosin or rosin derivatives (polymerized rosin, hydrogenated rosin, polyhydric alcohol ester of rosin, resin acid dye, etc.). Polymers and organic materials with small molecular weights (ie, so-called resins) are preferably used.

Plasticizers that are solid at room temperature include various diesters of phthalic acid or isophthalic acid such as dicyclohexyl phthalate, diphenyl phthalate, dicresyl phthalate, dihexyl phthalate, dihydroabiethyl phthalate, and dimethyl isophthalate, and catechol dibenzoate. , dicarboxylic acid esters of catechol such as di(cyclohexanecarboxylic acid)catechol, di(phenylacetic acid)catechol, ditoluic acid catechol, benzyl parahydroxybenzoate, n-propyl parahydroxybenzoate, isopropyl parahydroxybenzoate, parahydroxy Various esters of parahydroxybenzoic acid such as n-butyl benzoate and isobutyl parahydroxybenzoate; various esters of 2-acyloxybenzoic acid such as phenyl 2-acetoxybenzoate and phenyl 2-benzoyloxybenzoate; - Various esters of 2-sulfonyloxybenzoic acid such as phenyl benzenesulfonyloxybenzoate, phenyl 2-p-toluenesulfonyloxybenzoate, and N-cyclohexylbenzenesulfonamide, N-cyclohexyl-p
-Toluenesulfonamide, sucrose benzoate, ethylene glycol dibenzoate, trimethylolethane tribenzoate, glyceride tribenzoate,
It is selected from pentaerythritol tetrabenzoate, sucrose octaacetate, tricyclohexyl citrate, dehydroabiethylamine carbonate, methoxyethyl stearate-urea complex, and the like.

Furthermore, antioxidants, ultraviolet absorbers, inorganic pigments, and others may be appropriately contained as additives.

These materials are usually mixed and coated in a layer on a planar support, typically paper or film.

When heat is applied image-wise to the heat-sensitive material thus obtained, an adhesive image is produced.

As a means of applying heat, a method of contacting a high-heat member such as a known heat pen or a thermal head;
A method (so-called thermal copying method) can be used in which the original is irradiated with infrared rays and the heat generated in the image area is utilized. Further, when infrared rays (ordinary light or laser light) are directly applied to the heat-sensitive material, an infrared-absorbing substance such as a metal oxide, metal sulfide or carbon may preferably be present in or under the heat-sensitive layer.

If a powder suitable for the purpose is applied to the adhesive image pattern generated by heat application, it will adhere there, and for example, in the case of colored pigments, a visible image will be obtained.

It is natural to remove the excess powder present in the background area by applying vibration or brushing.

The powder used here is not limited to colored pigments,
It may be colorless powder, conductive powder, magnetic powder, etc., or microorganism powder. In short, the present invention is effectively used when creating an image or pattern that has some properties different from the background.

(E) Example In this example, "parts" represent "parts by weight."

Example 1 First, water was added to 50 parts of dicyclohexyl phthalate (a plasticizer that is solid at room temperature with a melting point of 64°C), 3 parts of polyvinyl alcohol, and 3 parts of a nonionic surfactant to make the plasticizer concentration 50% (w/w).
Wet milling was performed using a ball mill to obtain an aqueous suspension of plasticizer fine particles.

Next, 10 parts (solid content) of an aqueous emulsion of ethylene-vinyl acetate copolymer (adhesive polymer), 5 parts (solid content) of an aqueous emulsion of polymerized rosin polyhydric alcohol ester (tackifier), and 15 parts (solid content) of the above-mentioned aqueous suspension of dicyclohexyl phthalate. (solid content) to form an aqueous coating liquid with a total solid content concentration of 50%.

Apply this to the surface of high-quality paper with a basis weight of 60 g/m ² and
Dry at ℃. The coating weight after drying was 25 g/m ² .

Regarding the heat-sensitive sheet obtained in this way, the current application time was
A standard test pattern was thermally printed onto the heat-sensitive sheet on the receiving side using a commercially available thermal facsimile machine with a 3.3 x 10 ^-3 second thermal head by entering it on the sending side. The heated area (printed area) developed adhesive properties, and visually the image was more glossy and transparent than the background.

Dry black toner used in electrophotographic copying machines was sprinkled on top of this, and excess toner was removed with a brush. As a result, a black reproduction image that was faithful to the original image was obtained with strong contrast against the white background.
This black line was firmly adhered and could not be removed even when rubbed with fingers. Since the black toner used here was mainly made of carbon powder, no image deterioration such as discoloration or fading was observed, and the archival life was sufficient.

(F) Effects of the invention As mentioned above, the present invention uses a thermal printer or the like to print a heat-sensitive layer basically consisting of an adhesive polymer, a tackifier (tackifier), and a plasticizer that is solid at room temperature. The archival life of the recorded image can be extended by applying a method of applying a thermal pattern to produce an adhesive image, and then applying a suitable powder to provide contrast against the background. ) can be made semi-permanent, and by selecting the powder appropriately, it is also possible to create patterns that show not only optical images but also significant physical, chemical, or biological contrast. It became like that. Moreover, thanks to the excellent adhesive polymer, the image had excellent adhesion, or in other words, excellent fixation, and strongly resisted scratching.

Claims (1)

[Claims] 1. A heat-sensitive adhesive composition basically consisting of an adhesive polymer, a tackifier, and a plasticizer that is solid at room temperature imparts a thermal pattern to a heat-sensitive material present on a support to form an image. A thermal image forming method comprising developing an adhesive site and then contacting powder to adhere the powder to the adhesive site.