JP2011020289A - Thermal recording method, thermal recording object, and thermal recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording method which can acquire a clear gray level image excellent in the storage stability of a recording part irrespective of a type of a thermal recording medium, and a thermal recorder and a thermal recording object printed by the method concerned. <P>SOLUTION: In the thermal recording method, the gray level image is recorded on a thermal recording medium by conveying the thermal recording medium in a direction perpendicular to the arrangement direction of heating elements while making the heating elements generate heat by pressing the thermal recording medium to a thermal head in which a plurality of heating elements are arranged in line. The gray image is formed by dot printing by changing the number of the heating elements to generate heat. The energy value which makes a plurality of heating elements generate heat is desirable to be constant. The energy value is desirable to be such a value as to attain saturated color development density in the thermal recording medium. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thermal recording method capable of printing a dark and light image on a thermal recording medium, and in particular, a thermal recording method capable of obtaining an image excellent in image quality and storage stability without being affected by the type of the thermal recording medium. The present invention also relates to a thermal recording apparatus that executes the recording method, and a thermal recording material recorded by the recording method.

The heat-sensitive recording medium is mainly composed of a light leuco dye, a colorant capable of acting as an electron acceptor of the leuco dye, and an adhesive on at least one side of a support generally made of paper, synthetic paper, or a plastic film. A heat-sensitive color developing layer is provided.
When heat energy is applied to the heat-sensitive recording medium, the leuco dye and the colorant react to produce a color-coded recording image.

Such thermal recording is used for facsimiles, word processors, POS registers, POS labels, CRT medical images, automatic ticket machines, various computers and the like because the recording device is compact and easy to maintain.
Conventionally, thermal recording has been used only for recording mainly for printing numbers, letters, symbols, etc., except for CRT medical images, but in recent years, with the aim of visual effects such as product advertisements, There is an increasing demand for thermal recording to print high-precision images such as graphic images.

  Conventionally, thermal recording of a CRT medical image has been known as a print of an image in which a colored portion is shaded by thermal recording. An image thermal printer that outputs a CRT image for medical measurement as a hard copy obtains a photographic image by controlling gradation of the color density by controlling the thermal energy value of the thermal head.

  In order to obtain a clear grayscale image, it is desired that the contrast due to the grayscale is clear. On the other hand, in the thermal recording method in which the gradation of the color density is changed based on the magnitude of the thermal energy value, the amount of thermal energy applied to form the light color image portion is relatively small. There is a problem that unevenness is likely to occur, and the storability of the recording part is also inferior to that of the dark part.

  As a method for obtaining a clear ultrasonic diagnostic image by thermal recording, for example, Japanese Patent No. 3929234 proposes to devise a method for controlling the preheating of the thermal head that gives thermal energy to the thermal recording medium.

  Japanese Patent Application Laid-Open No. 2007-176058 focuses on the fact that an image free from defects and color unevenness can be obtained at the time of printing by obtaining a uniform coated surface with no coating defects such as coating surface unevenness on the thermal recording medium. Thus, it has been proposed to apply a composition for a heat-sensitive recording layer after the surface of the film support has been subjected to static elimination treatment.

  Japanese Laid-Open Patent Publication No. 2007-268832 relates to a method of performing thermal transfer by heating the back of the ink ribbon with a thermal head. However, the deterioration of image quality is faint due to lack of energy in the highlight portion, and the thermal in the shadow portion. Assuming that there is a cause of image collapse due to excessive energy due to the heat stored in the head, it is proposed that the gradation value of each pixel of the read image data is subjected to heat accumulation correction and printing is performed based on the corrected image data Has been.

Japanese Patent No. 3929234 JP 2007-176058 A JP 2007-268832 A

The idea of the thermal recording medium itself causes an increase in the price of the thermal recording medium. In addition, in a thermal recording apparatus, a method of adding a new control method such as data correction or preheating control causes an increase in the price of the thermal recording apparatus.
Furthermore, since the improvement by data correction and thermal head heat storage control only improves the image quality immediately after printing, there is a case where the effect on the storage stability of the light part is small and the good image quality cannot be maintained.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a clear gray-scale image excellent in storage stability of a recording portion regardless of the type of the thermal recording medium. A thermal recording method, a thermal recording apparatus, and a thermal recording material printed by the method.

  In the thermal recording method of the present invention, a thermal recording medium is pressure-bonded to a thermal head in which a plurality of heating elements are arranged in a line, and the heating recording element generates heat while the thermal recording medium is orthogonal to the arrangement direction of the heating elements. In the thermal recording method of recording an image having a gray level on the thermal recording medium by transporting in the direction of the image, the image having a gray level is formed by dot printing by changing the number of heating elements that generate heat. To do.

  The energy value for generating heat from the plurality of heating elements is preferably constant, and the energy value is preferably an energy value for achieving a saturated color density in the thermal recording medium.

The heat-sensitive recorded material of the present invention is a heat-sensitive recorded material that has been heat-recorded by the above-described method of the present invention. Specifically, it is a recorded matter in which a gray image having a dark portion and a light portion is thermally recorded on a heat-sensitive recording medium, and the image is drawn by a set of dots colored by heat-sensitive recording. The number of dots per unit area differs between the portion and the light portion.
It is preferable that the density immediately after recording of each dot constituting the dark part and the light part is substantially equal, and the total area of the plurality of dots constituting the light part is at least 15% or more per unit area It is preferable.

The thermal recording apparatus of the present invention is a thermal recording apparatus capable of recording a light and dark image on a thermal recording medium, and a thermal head in which a plurality of heating elements are arranged in one direction, and thermal recording on the thermal head. A unit for pressing the medium; a transport unit for transporting the thermal recording medium in a direction perpendicular to the arrangement direction of the heating elements; and a control unit for individually heating the heating elements. By controlling the number of heat-generating elements that generate heat, the dark image is colored on the heat-sensitive recording medium.
The control means preferably includes selection means for selecting the arrangement and number of heating elements that generate heat so as to correspond to the shading of the image.

The heat-sensitive recording method of the present invention is excellent in the storage stability of the recording portion because the coloring portion is colored at a density close to the saturated coloring density even in the light portion. Since the density is expressed depending on the number of dots that form the color development portion with excellent storage stability, a clear gray image with excellent storage stability of the recording portion can be obtained.
In addition, since the thermal recording apparatus of the present invention simply sets the energy value of the heating element and selects the position and the number of the heating elements that generate heat, it is possible to heat a clear gray image with a simpler control means than before. Can be recorded.

1 is a schematic diagram showing a configuration of an embodiment of a thermal recording apparatus of the present invention. It is a schematic diagram for demonstrating the structure of the heat generating element part of a thermal head. It is a flowchart explaining the thermal recording method of this invention. It is a graph which shows the measurement result (relationship with respect to an initial recording density | concentration and a storage rate) of the heat-and-moisture resistance obtained in the Example. It is a graph which shows the measurement result (relationship with respect to an initial recording density and a storage rate) of the plasticizer resistance obtained in the Example. It is a graph which shows the measurement result (relationship with respect to an initial recording density and a storage rate) of the water resistance obtained in the Example.

[Thermal recording method and thermal recording apparatus]
The thermal recording apparatus and thermal recording method of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of an embodiment of the thermal recording apparatus of the present invention.
In FIG. 1, M is a heat-sensitive recording medium, and is conveyed by a pair of rollers 1 and 1 serving as transfer means.
The conveyed thermal recording medium M is pressed and pressure-bonded to the thermal head 4 by the platen roller 3 which is a pressing means.

  In the thermal recording medium M, a color development reaction occurs in a portion to which thermal energy from the thermal head 4 is applied, and so-called thermal recording is performed. In FIG. 1, the heat-sensitive recording medium after heat-sensitive recording is represented as a heat-sensitive recording material M ′ in distinction from the heat-sensitive recording medium M used for heat-sensitive recording.

As shown in FIG. 2, the thermal head 4 has n heating elements (H _{1 to} H _n ) arranged in one direction, and the arrangement direction of the heating elements is orthogonal to the transport direction of the thermal recording medium M. As described above, the thermal head 4 is installed. The thermal head 4 is connected to a control unit 5 having control means, and the control unit 5 controls the heat generation pattern of these heat generating elements.

As the heating element, a resistor that generates heat upon application of a voltage is generally used. An electrode is formed on each heating element (H _{1 to} H _n ), and energization is performed based on the result from the control unit 5.

  Although it does not specifically limit as the thermal head 4 used by this invention, Usually, for example, the heat generating element was arranged on the ceramic substrate which consists of an electrically insulating material excellent in heat resistance, such as alumina ceramics in which glaze was formed. Things are used. The ceramic substrate is generally a base made of a metal plate such as aluminum laminated on the surface opposite to the glaze, and a metal such as aluminum fixed on the other surface of the base and having a number of heat fins. A thing provided with the heat sink made from is used.

  The type and structure of the thermal head 4 are not particularly limited, and any of a flat type, an end face type, a corner type, and a near edge type can be used in relation to the pressing means (platen roller) 3.

  The thermal recording apparatus of the present invention having the above-described configuration records a grayscale image by controlling the number of heating elements that generate heat per unit area of the thermal recording medium. Specifically, the control unit 5 includes a data processing unit that analyzes image data and converts it into density gradations, and a selection unit that selects a heating element and a number to generate heat based on the data processing result.

The control method of the thermal recording apparatus of the present invention, that is, the thermal recording method of the present invention will be described based on the flow as shown in FIG.
Data relating to an image to be printed is input to the control unit 5. The control unit 5 performs density analysis of the input image data, and calculates and determines a density gradation for each density unit area.
In accordance with the density analysis result of the acquired image data and the density gradation of the image, the position and number of heating elements that generate heat for each line (the number of dots per unit area) are selected. A voltage is applied to the selected heating element to generate heat. The heat-sensitive recording medium pressed against the thermal head by the pressing means undergoes a color reaction in the heat-sensitive recording layer at the portion pressed against the heating element portion that has generated heat by energization, and is printed with dots.

The applied energy value is not particularly limited, but is preferably an energy value that achieves the saturated color density of the thermal recording medium.
Here, the energy value means applied energy obtained by the following formula when the heating element is a heating resistor.
Applied energy (mj / dot) = Applied power (w / dot) x Pulse width (msec)

  The energy value that achieves the saturated color density of the thermal recording medium refers to the energy value at which the color density of the thermal recording medium reaches saturation. For example, in the thermal recording medium, the energy value reaching saturation is calculated by recording the thermal recording medium by changing the applied energy using the thermal printing test apparatus TH-PMD (manufactured by Okura Electric) and measuring the recording density. The energy value at which the density reaches saturation is defined as the energy value at which the color density of the thermal recording medium used in the present invention reaches saturation.

In the method of the present invention, the element (resistor) that generates heat may be energized with a predetermined voltage applied to the head throughout the pulse width. Therefore, since the resistance value of the resistor used is constant, it is sufficient that the applied energy calculated by the above equation of the thermal head to be used is set to the saturation energy value.
On the other hand, an element corresponding to a dot that does not cause color development is merely energized (E ₀ ) that is not energized or that cannot produce color on the thermal recording medium.

In this way, in one line where the thermal recording medium is in contact with the thermal head, the heating element selected according to the density gradation is applied with energy capable of achieving a saturated color density by energization, and the other heating elements are The energy required for color development is not applied. As a result, a color development reaction occurs in the portion pressed against the heat generating element that has generated heat, and no color is generated in the portion pressed against the heat generating element to which the applied energy is applied only below the energy that does not generate color. That is, in one line where the thermal head of the thermal recording medium is pressure-bonded, a colored portion (dot) and a non-colored portion (uncolored portion) are formed.
The ratio of the colored portion per unit area (the number of dots per unit area) is determined according to the density gradation.

  Here, a dot is a portion where one dot develops color corresponding to one heating element of the thermal head. That is, in the thermal recording method of the present invention, the number of dots corresponds to the color density (recording density) of the thermal recording medium, and thus corresponds to the density of the image.

  The pulse width of the voltage application pattern, that is, the period of the voltage pulse may be the same as the thermal head pressing time. The density gradation is not controlled by the heat energy value of the heating element, that is, the energization time as in the conventional case, but whether or not each heating element is energized, that is, by on / off control, is saturated with respect to a predetermined voltage. A simple energization pattern having a period of a pulse width that can obtain energy capable of achieving the color density can be employed.

  In this regard, in the conventional density gradation control method according to the magnitude of the energy value, the period (pulse width) is changed so that the current value to be energized or the energization time can be appropriately changed according to the density gradation. It is necessary to perform complicated control such as dividing the power supply.

  In the thermal recording method of the present invention, the dot density of the thermal head used is not particularly limited. Usually, the effective recording width (the length of the portion where the heating element is attached) is 50 to 250 mm, and the dot density (dot / mm, corresponding to the number of elements per unit area) is 8 to 36. In the recording method of the present invention, the density gradation depends on the number of heating elements of the thermal head used. Therefore, it is desirable to achieve a gradual density gradation in order to obtain a more precise image. For this purpose, it is preferable to increase the density gradation. The larger the number of heating elements attached to the thermal head, that is, the higher the dot density of the thermal head to be used, the more it is possible to set gradations in multiple stages, which is preferable.

  In the thermal recording method of the present invention, the shading is controlled by the number of dots per unit area. The dark portion is a case where all the heat generating elements generate heat, and the light portion reduces the number of dots to be colored per unit area. Therefore, if the color density (the number of dots per unit area) in the thermal recording medium is too small, an image like a stippling is formed, which is not preferable in terms of image quality. Therefore, in order to obtain high image quality, the number of dots per unit area should be set at a level that cannot be visually recognized as an aggregate of dots, that is, a density that can recognize the colored portion as uniform even in the light portion. It is preferable to do so. Specifically, it is preferable to set the color development area per unit area to be 15% or more even for the light part. This is a level that exceeds 1 dot / mm (about 13%) when an 8 dot / mm head is used.

Based on the thermal recording method of the present invention as described above, complicated energization control, that is, pulse width control is not required, and only the selection of the heating element to be applied is required, so that the thermal recording apparatus for obtaining a gray image can be controlled. Can be simple.
In addition, the color development portion (dot) obtained is set to an energy value that can achieve the saturation color development density, so that the storage stability of the recording density of each color development portion is increased. This means that the storage stability is high even in the light part.

A printing method for adjusting the density gradation by controlling the number of dots is employed in laser printers, ink jet printers, and the like. However, in the method of recording by adsorbing ink to the exposed portion of the medium, for example, as described in JP-A-8-317209, it is actually due to an overlapping portion of adjacent dots. In this patent document, the density value is input according to the density change taking into account the dot shape and recorded. The solution is achieved by providing input means for supplying the means.
In this respect, in the thermal recording method and the thermal recording apparatus of the present invention, only the portion where the heating element is pressure-bonded is colored, so that overlapping of adjacent dots does not cause a problem. In particular, by setting the energy for color development to an energy value that achieves the saturated color density, unevenness of the color development portion can be reduced, so that a control means for correcting the density of the color development portion is not required.

  However, the thermal recording apparatus of the present invention may further include a storage unit that stores the acquired image data, processed image data, image processing parameters, and the like. In addition to determining the density gradation, the image processing unit may perform resolution conversion processing, heat storage correction processing, and the like as necessary.

<Thermal recording material>
The heat-sensitive recorded material of the present invention is printed and printed by the above-described heat-sensitive recording method of the present invention. In particular, the features of the present invention are conspicuous when a dark and light image is printed on a thermal recording medium.
Specifically, the thermal recording material of the present invention is an aggregate of dots in which the image is colored by thermal recording, and the dark portion and the light portion have different numbers of dots per unit area.
Here, the dark part means a dark part of the image, and the area occupied by the dots that are colored per unit area is high, specifically, the part where 60% or more per unit area is colored. Say. In addition, the light portion refers to a portion having a low density in the image, and the area occupied by dots that are colored per unit area is low, and specifically, a portion where the colored portion per unit area is less than 60%. .

  The darkest portion (the darkest portion) of the dark portion is the case where heat is generated by energizing all the heat generating elements arranged in the head, and the heat sensitive recording method by the conventional energy value control is used. Similar to the dark portion in the case of recording, the entire coloring portion is solid and saturated. However, in the light part thermally recorded by the thermal recording method of the present invention, when magnified by a magnifying glass or the like, it can be confirmed that the dots are in an aggregated state, and further the dots are uniformly colored. A colored portion that looks uniform and has excellent image quality can be obtained. In this regard, in the conventional method in which the density is controlled by the energy value, since low energy is applied to all the heating elements, heat is generated even in the light part, and the colored dots are densely present as in the dark part. As expected, an uncolored portion is seen in the dot, and as a result, it is difficult to obtain a colored portion excellent in image quality visually.

This is considered as follows. In the thermal recording material of the present invention, since the density immediately after recording of each dot constituting the dark portion and the light portion is substantially equal since the energy applied to each heating element is equal, the dots constituting the light portion Even so, the color can be uniformly developed as in the dark portion.
On the other hand, in the heat-sensitive recorded material that is heat-recorded by the conventional method of controlling the density by the heat energy value, the recording density of each dot is low in the light part because the density of the color developing part is proportional to the energy value. . For this reason, when the type of thermal recording medium or a thermal recording medium with low sensitivity is used, the color of the light portion recorded by the conventional thermal recording method becomes insufficient, and a white portion is formed, It is thought that the clearness of the image is impaired. Further, in the light part of the conventional thermal recording material, the color density of each dot itself is low, or there is an uncolored part in each dot. In this case, the coloring portion may not be recognized.

  Of the light part of the heat-sensitive recording material of the present invention, the part having the lowest density gradation (the lightest part) preferably has a total dot area of about 15% to 25% developed per unit area. If it is less than 15%, the image quality is inferior, for example, there are too few dots in the lightest part, the uncolored portion is conspicuous, and an image observed visually is recognized as a stippling.

  The thermal recording medium constituting the thermal recording material of the present invention, that is, the thermal recording medium to which the thermal recording method of the present invention can be applied is not particularly limited. The thermal energy applied to develop the color of the heat-sensitive recording layer is the same in the dark portion and the light portion where the recording density is high, and even in the light portion, the energy for achieving the saturated color density in the heat-sensitive recording medium is high. Therefore, a desired grayscale image can be obtained without selecting a combination of a highly sensitive leuco dye and a colorant or using a heat-sensitive recording medium with a special treatment on the recording surface.

  Therefore, the heat-sensitive recording medium to which the heat-sensitive recording method of the present invention can be applied is not limited to a specific heat-sensitive recording medium such as conventional ultrasonic diagnostic heat-sensitive recording paper, and a conventionally known heat-sensitive recording medium can be used. it can. The following description of the thermal recording medium is an example (typical example) of the thermal recording medium that can be used in the present invention, and is not limited thereto.

  Specifically, the heat-sensitive recording medium has a heat-sensitive recording layer containing a leuco dye, a colorant, and an adhesive on a support.

  Although it does not specifically limit as a support body, For example, neutral or acidic quality paper, a synthetic paper, a transparent or translucent plastic film, a white plastic film etc. are mentioned. Although the thickness of a support body is not specifically limited, Usually, it is about 20-200 micrometers.

  The leuco dye contained in the heat-sensitive recording layer is various kinds of known leuco dyes that are usually used in heat-sensitive recording media. Specifically, for example, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalic acid. Blue, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-dibenzylamino-benzo [α] fluorane, etc. Chromogenic dye; 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluor Green chromophoric dyes such as orane; 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, Red coloring dyes such as diethylamino-6,8-dimethylfluorane; 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N- (Cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane, 3- (N-ethyl- p-Toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6 -Black coloring dye such as chloro-7-anilinofluorane; 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5 , 6,7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7 And dyes having an absorption wavelength in the near infrared region such as -chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide. These may be used alone or in combination of two or more.

  The colorant contained in the heat-sensitive recording layer is selected from those having the property of being liquefied or dissolved by an increase in temperature and having the property of developing a color by contacting the dye precursor. Can be used phenolic compounds, aromatic carboxylic acids, or organic acidic substances such as salts of these compounds and polyvalent metals. Such a colorant is usually preferably used in a proportion of 30 to 2000 parts by mass, more preferably 50 to 200 parts by mass with respect to 100 parts by mass of the leuco dye.

  Typical colorants include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidenediphenol, 4-phenylphenol, 4,4′-dihydroxydiphenylmethane, 4,4'-isopropylidene diphenol, 4,4'-dihydroxydiphenyl ether, 4,4'-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) -ethane, 1,1-bis (4- Hydroxyphenyl) -1-phenylethane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenylsulfone, 2,4'- Dihydroxydiphenyl sulfone, 4-hydroxy-4 Phenolic compounds such as isopropoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, and bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, 4 -Methyl hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoate-sec-butyl, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate Phenolic compounds such as 4,4'-dihydroxydiphenyl ether, or benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropyl Aromatic carboxylic acids such as pyrsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and zinc, magnesium, for example Organic acid substances such as salts with polyvalent metals such as aluminum and calcium.

  Examples of the adhesive include polyvinyl alcohol and derivatives thereof, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester Water-soluble polymer materials such as polymers, acrylamide-acrylic acid ester-methacrylic acid ester copolymers, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, casein, gelatin and derivatives thereof, and , Polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer Emulsions and styrene body such as - butadiene copolymer, styrene - butadiene - can be given latex water-insoluble polymer such as an acrylic copolymer.

  In the heat-sensitive recording layer of the heat-sensitive recording medium, in addition to the above leuco dye, color former, adhesive, surfactant, antifoaming agent, crosslinking agent, wax, metal soap, colored dye, colored pigment, And fluorescent dyes and the like may be contained. Furthermore, an image stabilizer may be used to improve the storage stability of the obtained recorded image. Examples of such an image stabilizer include 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane and 1,1,3-tris (2-methyl-4-hydroxy-). 5-tert-butylphenyl) butane, 1,1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4 ′-[1,4-phenylenebis (1-methylethylidene) ] Phenolic compounds such as bisphenol and 4,4 '-[1,3-phenylenebis (1-methylethylidene)] bisphenol, 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxy Propyloxy) phenylsulfone, 4- (2-methyl-1,2-epoxyethyl) diphenylsulfone, and 4- (2-ethyl-1,2-epoxy) At least one selected from epoxy compounds such as (til) diphenylsulfone and isocyanuric acid compounds such as 1,3,5-tris (2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl) isocyanuric acid. Can be used. Of course, the image stabilizer is not limited to these, and two or more kinds of compounds may be used in combination as required.

  Furthermore, a sensitizer may be contained. Examples of the sensitizer include compounds conventionally known as sensitizers for heat-sensitive recording materials, such as parabenzylbiphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, and di-o adipate. -Chlorobenzyl, 1,2-diphenoxyethane, 1,2-bis (3-methylphenoxy) ethane, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, 1,2-bis (3 , 4-dimethylphenyl) ethane, 1,3-bis (2-naphthoxy) propane, metaterphenyl, diphenyl, benzophenone, and the like.

  Furthermore, in order to improve the whiteness of the thermosensitive coloring layer and improve the uniformity of the image, a fine pigment having a high whiteness and an average particle size of 10 μm or less may be contained. For example, calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface treated inorganic pigments such as calcium carbonate and silica In addition, organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, and polystyrene resin can be used. In order to prevent residue adhesion and sticking to the thermal head, it is preferable to use a pigment having an oil absorption of 50 ml / 100 g or more. The amount of the pigment blended is preferably an amount that does not lower the color density, that is, 50% by mass or less with respect to the total solid content of the thermosensitive coloring layer.

  Furthermore, in order to improve the water resistance of the thermosensitive coloring layer, as a crosslinking agent for three-dimensionally curing the adhesive, for example, aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamides Resins, melamine resins, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, and inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate, or boric acid, boric acid triester, boron The polymer may be contained in an amount of about 1 to 10 parts by mass with respect to 100 parts by mass of the total solid content of the thermosensitive coloring layer.

The heat-sensitive recording medium used in the present invention has a heat-sensitive recording layer containing the above components laminated on a support. An undercoat layer is provided between the support and the heat-sensitive recording layer. It may be formed. As the adhesive component used in the undercoat layer, a resin used in the heat-sensitive recording layer can be used. Examples of the inorganic pigment contained in the undercoat layer include metal oxides such as aluminum oxide, magnesium hydroxide, barium sulfate, and aluminum silicate, metal compounds such as metal hydroxide, sulfate, and carbonate; amorphous silica, calcined kaolin And inorganic white pigments such as talc.
Further, a protective layer containing a water-soluble polymer material and a pigment as used in a conventionally known thermosensitive recording material may be provided on the thermosensitive coloring layer. The protective layer is formed by coating and drying a composition prepared by mixing and stirring an adhesive component, a pigment, and, if necessary, an auxiliary agent. As the adhesive component, pigment, and auxiliary agent used in the protective layer, those that can be used in the heat-sensitive recording layer can be used.

  Furthermore, a gloss layer may be provided on the protective layer. The glossy layer can be formed by applying a coating liquid containing an electron beam or an ultraviolet curable compound as a main component and then irradiating and curing with an electron beam or ultraviolet light. Furthermore, an antistatic layer may be provided on the back side of the support.

In the following examples, “part” means “part by mass”.
[Thermal recording]
(1) Gradation recording thermal printing test apparatus TH-PMD (manufactured by Okura Electric Co., Ltd.) with recording density control, and thermal head (BHP 4312WS, resistance value 767Ω, manufactured by TDK) with a recording density of 8 dots / mm, one line recording time : 1.25 msec / line, the sub-scanning line density: 8 lines / mm, applied energy: by 0.36mJ / dot conditions, 4 dots ^/ mm ² the recording ^{density, 16dot / mm 2, 24dot /} mm 2, 32dot / mm ^{2, 48dot / mm 2, 64dot} / mm 2 and was conducted while changing gradation recording.

(2) One-line recording time using a thermal recording test apparatus TH-PMD (manufactured by Okura Electric Co., Ltd.) and a thermal head (BHP 4312WS, resistance value 767Ω, manufactured by TDK) with a recording density of 8 dots / mm, by means of energy value control. : 1.25 msec / line, sub-scanning line density: 8 lines / mm, recording density of 64 dots / mm ² , applied energy was 0.09 mj / dot, 0.10 mj / dot, 0.13 mj / dot,. Gradation recording was performed by changing to 16 mj / dot, 0.22 mj / dot, and 0.36 mj / dot.

[Measurement evaluation method]
(1) Recording density The density of the recording part of the thermosensitive recording material obtained above was measured in a visual mode of a Macbeth densitometer (trade name: RD-914 type, Macbeth Co.).

(2) Heat and humidity resistance of the recording part The density of the recording part after the heat-sensitive recording material colored as described above was allowed to stand for 24 hours in an atmosphere of 40 ° C. and 90 RH% was measured with a Macbeth densitometer. The preservation rate was determined.
Storage rate (%) = measured value (recording density) ÷ recording density before processing × 100

(3) Plasticizer resistance of the recording portion The heat-sensitive recording material colored as described above is wrapped in three layers on a polycarbonate pipe (40 mmΦ) with a wrap film (trade name: High Wrap KMA-W, manufactured by Mitsui Chemicals). Each color-recorded heat-sensitive recording material was placed on it, and a wrap film was wrapped in triplicate on it and left at room temperature for 4 hours. The density of the recorded part was measured with a Macbeth densitometer, and the storage rate of the recorded part was similarly determined. The calculation was made based on the above formula.

(4) Water resistance of the recording part The density of the recording part after the heat-sensitive recording material colored as described above is immersed in water and allowed to stand at room temperature for 24 hours is measured with a Macbeth densitometer. The rate was determined.

(5) Image quality (5-1) Color development status The color development status of the color development portion was observed using a microscope and evaluated as follows.
A: The dots are uniformly colored and there is no shading unevenness.
○: Slightly uncolored portions of dots are seen, but at a level that does not cause any problems.
Δ: A clear dot non-colored portion is observed, and the unevenness in density is large even in visual evaluation, and there is a problem in practical use.
X: There are many dot non-colored portions, and shading unevenness is intense.

(5-2) Image homogeneity The colored portion was visually observed and evaluated as follows.
A: The colored portion appears to be uniformly colored.
○: The colored portion is not slightly homogeneously colored, but since the dots constituting the colored portion appear to be uniformly distributed, there is no problem as an image.
X: In the colored portion, the distribution of the constituent dots is non-uniform, the color is not uniformly colored, and the image is damaged.

[Manufacture of thermal recording media]
(1) Preparation of coating liquid for undercoat layer 90 parts of spherical resin particle dispersion (trade name: Grosdale 130S, composition: styrene, average particle size: 0.8 μm, manufactured by Mitsui Chemicals, solid content concentration 53 mass%) 120 parts of a 50% aqueous dispersion (average particle size: 0.6 μm) of calcined kaolin (trade name: Ansilex, Engelhard), styrene-butadiene latex (trade name: L-1571, manufactured by Asahi Kasei Chemicals, A composition comprising 10 parts of a solid content concentration of 48% by weight, 50 parts of a 10% aqueous solution of oxidized starch, and 20 parts of water was mixed and stirred to obtain a coating solution for an undercoat layer.

(2) Preparation of heat-sensitive recording layer coating solution and preparation of leuco dye dispersion (preparation of solution A)
100 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 50 parts of a 20% aqueous solution of polyvinyl alcohol having a saponification degree of 60 mol% and a polymerization degree of 200, 5 20 parts of emulsion and 52 parts of water are mixed and processed by a sand mill so that the median diameter (trade name: SALD2200, 50% value by Shimadzu Corporation) is 0.8 μm. A liquid A was obtained.

・ Preparation of colorant dispersion (liquid B)
40 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and 20 parts of water are mixed, and a laser diffraction particle size measuring instrument is used by a sand mill. The B media was obtained by processing so that the median diameter (trade name: SALD2200, 50% value by Shimadzu Corporation) was 1.2 μm.

・ Sensitizer dispersion (liquid C)
Mix 100 parts of di-p-methylbenzyl oxalate ester, 50 parts of 20% aqueous solution of polyvinyl alcohol having a saponification degree of 88 mol% and a polymerization degree of 300, 20 parts of a 5% emulsion of natural fat and oil-based antifoaming agent, and 52 parts of water. Then, it was processed by a sand mill so that the median diameter (trade name: SALD2200, 50% value manufactured by Shimadzu Corporation) by a laser diffraction particle size measuring device was 1.5 μm, and a liquid C was obtained.

-Preparation of coating solution for heat-sensitive recording layer 25 parts of leuco dye liquid (A liquid), 45 parts of colorant dispersion liquid (B liquid), 80 parts of sensitizer dispersion liquid (C liquid), particulate amorphous silica (trade name) : Mizukaseal P-603, manufactured by Mizusawa Chemical Co., Ltd.) 20 parts, a composition consisting of 40 parts of a 25% aqueous solution of polyvinyl alcohol having a saponification degree of 98 mol% and a polymerization degree of 1000, and 60 parts of water was mixed to produce a thermosensitive recording layer. A coating solution was prepared.

(3) Production of thermosensitive recording medium On one side of a high-quality paper (neutral paper) of 64 g / m ² , the undercoat layer coating liquid prepared above is dried so that the weight after drying is 8 g / m ^2. An undercoat layer is formed by coating and drying, and then the thermal recording layer coating solution prepared above is applied onto the undercoat layer and dried so that the weight after drying is 4 g / m ^2. After the formation, a super calender was applied to produce a thermal recording medium.

[Preparation of thermal recording material]
The thermal recording medium prepared above was subjected to gradation recording by recording density control or gradation recording by energy value control in accordance with the above method to obtain a thermal recording material.
With respect to the obtained heat-sensitive recording material, the initial density was measured according to the above evaluation method, and further, heat and humidity resistance, plasticizer resistance, water resistance and image quality were measured and evaluated. Table 1 shows the evaluation results of the thermal recording material by the recording density control, and Table 2 shows the evaluation results of the thermal recording material by the energy value control. Moreover, the relationship between the initial concentration in a heat-and-moisture resistance, a plasticizer resistance, and a water resistance test and a storage rate is shown in FIGS.

From Table 2, in the recording method based on the energy value control, the color development state was poor and the uniformity was poor because the heat generation energy value was low in the low to medium density portions of the initial color density. This means that the image quality of the light part and, as a result, the image quality of the entire image is inferior.
On the other hand, from Table 1, in the recording method by recording density control, since the saturation energy value is adopted as the energy of each dot, there is no problem in the color development situation even in the case where the initial color density is low to medium density. As for the homogeneity, when the printing density was 16 dots / mm ² or more, the same excellent results as in the dark portion were obtained.

  In the initial density, the recording density control tends to have a smaller initial density at a lower gradation. This is because the number of dots is small and the measured value is low in the target color development portion. However, it can be seen that the recording density control is superior in terms of image quality because there is no uncolored portion (coloring unevenness) that causes image quality degradation even in the light portion. However, in order to achieve a high image quality that can be recognized as a uniform color in the recording density control, it is preferable that the dot occupation area in the lightest part is 15% or more.

  Furthermore, from Tables 1 and 2 and FIGS. 4 to 6, the heat-sensitive recorded material obtained by controlling the recording density is superior in storage stability (heat-resistant moisture resistance, plasticizer resistance, water resistance) of the color development portion. I understand that. Therefore, even when storage stability is taken into consideration, the thermal recording method based on the recording density control can provide an image that can maintain a clear image quality even in a light portion.

  The thermal recording method of the present invention can achieve high image quality without complicated control, without using special dyes or colorants, or without using high-cost thermal recording media with special surface treatment. Can be used for recording images including medical photographs, advertisements, etc. using thermal recording.

DESCRIPTION OF SYMBOLS 1 Transfer means 3 Press means 4 Thermal head 5 Control means

Claims (9)

A thermal recording medium is pressure-bonded to a thermal head in which a plurality of heating elements are arranged in a line, and while the heating element is heated, the thermal recording medium is conveyed in a direction perpendicular to the arrangement direction of the heating elements, In the thermal recording method for recording a gray image on the thermal recording medium,
A heat-sensitive recording method, wherein a dark and light image is formed by dot printing by changing the number of heating elements that generate heat. The thermal recording method according to claim 1, wherein an energy value for generating heat from the plurality of heating elements is constant. The thermal recording method according to claim 1, wherein the energy value is an energy value for achieving a saturated color density in a thermal recording medium. On a heat-sensitive recording medium, a recorded matter in which a gray image having a dark portion and a light portion is heat-recorded,
The image is drawn by a set of dots colored by thermal recording,
The dark portion and the light portion are thermal recording materials in which the number of dots per unit area is different. The thermal recording material according to claim 4, wherein the density immediately after recording of each dot constituting the dark part and the light part is substantially equal. The heat-sensitive recorded matter according to claim 4 or 5, wherein the total area of the plurality of dots constituting the light portion is at least 15% or more per unit area. A heat-sensitive recorded matter that has been heat-recorded by the method according to claim 1. A thermal recording apparatus capable of recording a gray image on a thermal recording medium,
A thermal head in which a plurality of heating elements are arranged in one direction, a pressing unit that presses the thermal recording medium against the thermal head, and a transfer unit that conveys the thermal recording medium in a direction perpendicular to the arrangement direction of the heating elements; Control means for individually heating the heating elements,
A thermal recording apparatus that controls the number of heating elements that generate heat per unit area of the thermal recording medium so that a gray image is colored on the thermal recording medium. The thermal recording apparatus according to claim 8, wherein the control unit includes a selection unit that selects an arrangement and the number of heating elements that generate heat so as to correspond to the density of an image.

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