Patent Application
20050255996
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-143892 filed on May 13, 2004, the contents of which are incorporated herein by reference.
The present invention relates generally to a thermosensitive recording medium and a method of manufacturing a thermosensitive recording medium, particularly to a method of manufacturing of a high-quality multicolor thermosensitive recording medium that develops a plurality of colors.
Conventionally, there has been proposed a method of recording multicolor images by divisionally forming thermosensitive coloring layers that develop more than one color on a substrate and selectively applying heat to pixels developing a desired color.
For example, in Japanese patent application Kokai publication No. 60-208283, a multicolor thermosensitive recording medium is described in which a plurality of thermosensitive coloring materials developing different colors are divisionally coated on a recording surface of a substrate and images of different colors are formed in the respective regions where thermosensitive coloring materials of different colors are coated.
In Japanese patent application Kokai publication No. 2000-301835, there is described another multicolor thermosensitive recording medium that divisionally develops different colors. This recording medium comprises a support, dye layers containing leuco dyes developing different coloring hues that are formed and arranged in parallel on a substrate without one layer overlapping another, and a developer layer or layers containing a developer formed adjacent to, above or/and beneath the dye layers. This dye layers are formed in stripes by sequentially coating each ink of different colors by means of a printing process (screen printing, gravure printing, and offset printing). By narrowing widths of the respective dye layers and miniaturizing a heat-applying part of a thermal recording head, high-resolution full-color images can be formed.
However, the inventors of the present invention have found that thermosensitive coloring layers and thermosensitive recording mediums that are formed using a printing process involve several problems.
Method of forming plural thermosensitive coloring layers on a thermosensitive recording medium using a printing process is suitable for producing labels having thermosensitive coloring layers of the same form as shown in
Second problem lies during formation of thermosensitive coloring layers. As typical thermosensitive ink for producing a thermosensitive recording medium, water-dispersion thermosensitive ink is widely used, in which pigment components comprising an electron-accepting compound, for example, a developer, an electron-donating compound, for example, a leuco dye, a sensitizer, etc. are dispersed in water using a dispersant such as a surfactant.
By coating this water-dispersion thermosensitive ink using a coating apparatus such as a blade coater, air knife coater, roll coater, bar coater, gravure coater, and lip coater, a film having a uniform thickness can be formed on a substrate.
However, when a thermosensitive coloring layer is formed by coating water-dispersion thermosensitive ink by a printing process that uses a printing plate such as a relief printing plate, engrave plate, and stencil printing plate, thickness of the printed film needs to be largely increased to obtain a fair optical density comparing to a normal printing process for producing literatures using printing ink. The inventors of the present invention confirmed that, when such a thermosensitive recording medium on which water-dispersion thermosensitive ink is thickly coated is heated in an oven or others to dry the medium, a striped pattern is developed. This striped pattern is a phenomenon, called “streaking or streaks,” which emerges as a state of ‘waving’ failing for the water-dispersion thermosensitive ink to spread smoothly over the surface of the medium when a printing plate is separated from a substrate during a printing process. This phenomenon is considered to likely occur to water-dispersion thermosensitive ink containing a pigment relating to own characteristics of this ink.
When an image is formed on a thermosensitive recording medium that forms thermosensitive coloring layers having such a phenomenon by applying heat energy to the medium by a thermal print head, a region corresponding to such a striped pattern appears as an image having an irregular density.
If an organic-solvent based thermosensitive ink that is formulated using an organic solvent in which a leuco dye and developer are dispersed is used in stead of such water-dispersion thermosensitive ink, a striped pattern as in
In view of the above problems, the inventors of the present invention proposed a method of forming a thermosensitive recording medium in Japanese patent application Kokai publication No. 2003-99356 (corresponding U.S. patent application Ser. No. 10/854,413), in which the phenomenon of “streaking” can be alleviated to a practically trouble-free degree by impregnating water-dispersion thermosensitive ink into a substrate and providing an ink receptive layer holding a film thickness that secures a predetermined recording density and lowering a surface tension of water-dispersion thermosensitive ink so as to enhance penetrability into a substrate and leveling characteristic of the ink.
If penetrability and leveling characteristic of water-dispersion thermosensitive ink are boosted, color mixing between thermosensitive coloring layers of different colors adjacent to each other tends to occur. Particularly in engraved printing, the ink makes it hard to remove excess ink with a doctor blade because the water-based inks generally increase friction of a doctor blade comparing to solvent-base inks. Accordingly, water-dispersion thermosensitive inks makes a doctor blade to wear easily, and color mixing between inks adjacent thermosensitive coloring layers of different colors tends to occur owing to boosting of its penetrability and levelling characteristic of the inks in effort to alleviate “streaking.”
According to one aspect of the present invention, there is provided a thermosensitive recording medium that comprises a substrate in a roll, at least a first thermosensitive coloring layer developing a first hue and a second thermosensitive coloring layer developing a second hue different from the first hue, wherein the first and second thermosensitive coloring layers are formed in parallel continuously in a longitudinal direction of the thermosensitive recording medium, the thermosensitive coloring layers of different hues having the respective widths.
According to another aspect of the present invention, there is provided a method of manufacturing a thermosensitive recording medium that comprises a step of preparing a substrate in a roll, a step of preparing a first printing plate for forming a first thermosensitive coloring layer developing a first hue, the first thermosensitive coloring layer continuously extending in a longitudinal direction of the substrate and having a width, a step of preparing a second printing plate for forming a second thermosensitive coloring layer developing a second hue different from the first hue, the second thermosensitive coloring layer continuously extending in a longitudinal direction of the substrate and having a width, a step of ink-coating using the first and second printing plates to form the first and second thermosensitive coloring layers such that the first and second thermosensitive coloring layers are arranged in parallel extending in a longitudinal direction of the substrate, a step of dividing for dividing the thermosensitive recording medium including the first and second thermosensitive coloring layers by cutting the second thermosensitive coloring layer that is formed in the step of ink-coating in a longitudinal direction.
By this structure, there can be provided a recording medium whose length can be flexibly changed and which does not hold “streaking,” which likely occur in a thermosensitive recording medium having a thermosensitive coloring layer formed through a printing process that uses a printing plate. In addition, color mixing that tends to occur on a process of forming thermosensitive coloring layers of different colors on a thermosensitive recording medium can be prevented.
Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. The same numerals are applied to the similar elements in the drawings, and therefore, the detailed descriptions thereof are not repeated.
An embodiment according to the present invention will be described in reference to FIGS. 1 though 3.
In this thermosensitive recording medium 1, there are formed a substrate 2, an ink receptive layer 3 formed on a surface of substrate 2, thermosensitive coloring layers 4a, 4b, and 4c developing different coloring hues that are formed over ink receptive layer 3, and a protective layer 5 that is provided as needed.
Thermosensitive coloring layers 4a, 4b, and 4c having different coloring hues are formed in parallel stripes in a longitudinal direction of the substrate using a printing process, each stripe having a prescribed width. “Longitudinal direction” means a direction of feeding of a continuous paper that is used as substrate 2 during a printing process. This direction conforms to a direction of printing characters in a printer. Substrate 2 is a base material on which thermosensitive coloring layers are formed by coating ink thereon on an ink-coating process and which is divided into several thermosensitive recording mediums being cut in its longitudinal direction.
Thermosensitive coloring layers 4a, 4b, and 4c need to be formed in stripes continuously in the ink-coating direction. Printing process that meets this need of performance is gravure printing.
Using gravure printing, thermosensitive coloring layers 4a, 4b, and 4c are formed integrally with ink receptive layer 3 by making ink penetrate into receptive layer 3, as illustrated in
Thermosensitive recording medium 1 formed in continuous stripes can be used, for example, as shown in
Because thermosensitive coloring layers 4a, 4b, and 4c are provided in continuous stripes, thermosensitive recording medium 1 can flexibly be used by cutting the medium at a desired length according to a length of recording characters, as shown in
As for a combination of thermosensitive coloring layers formed in stripes, thermosensitive coloring layers 4a that develops blue (a third color hue), thermosensitive coloring layers 4b that develops black (a second color hue), thermosensitive coloring layers 4b that develops red (a first color hue) are favored. In this color combination, red thermosensitive coloring layers 4c expresses emphasis and therefore is often used for recording important information. To make it more visually effective, the width of this red layer is better to be formed wider than other layers. First, second, third color hues referred herein denote merely different colors and are not restricted to particular colors.
As for the widths of thermosensitive coloring layers 4 formed in stripes, if they are too narrow, a visual effect of emphasis by different colors becomes diminished. Desirable width may be some 10 mm, considering the accuracy of recording positioning in a printer. Particularly, considering recording of a bar-code that is required in black or blue thermosensitive coloring layers 4, some 10 mm is mostly required. (According to the JAN requirements relating to a bar-code, the height of a bar-code must be 18.29 mm in terms of 0.8 times minimum magnification. Actually, since a bar-code at a height of a half of this height can be readily read by a bar-code scanner, a height of more than 10 mm is preferable.)
Since a multi-color thermosensitive recording medium 1 is mostly used in cases where images or characters need to be visually distinguished, a balance in the respective color hues becomes important. Therefore, the width of stripes of each of the thermosensitive coloring layers is preferably more than one tens of the width of the thermosensitive recording medium. Also, even more preferably, providing generally equal widths in the respective layers makes the images visually more effective.
As materials suitable for substrate 2, there are, for example, paper, plastic film such as of polyethylene terephthalate, metallic foil, etc. However, they are not limited to the above, as long as they do not prevent the object of the present invention.
Ink receptive layer 3 needs to be absorptive for water-dispersion thermosensitive ink to prevent “streaking” on thermosensitive coloring layers 4 that are formed using a printing process, and comprises a pigment as a main component and a binder resin. Pigments usable for this layer include, for example, an inorganic pigment, such as clay, calcined clay, calcium carbonate, titanium oxide, alumina, aluminum hydroxide, silica; organic pigments of beaded hollow resins, such as styrenes, styrene-acrylics, acrylics. Also preferable for use is a porous pigment, which is formed by flocculation of a mass of its primary particles, for example, a calcium carbonate or synthetic silica.
Binder resins usable for ink receptive layer 3 include water-soluble macromolecules and water-soluble macromolecule emulsions. The water-soluble macromolecules include, for example, polyvinyl alcohol, starch and its derivatives, cellulosic derivatives, gelatine, casein, styrene-dihydrogen maleic copolymer salt, styrene-acrylic acid copolymer salt. The water-soluble macromolecule emulsions include emulsions of latex of styrene-butadiene copolymer, vinyl acetate resin, styrene-acrylic ester copolymer, and polyurethane resin, etc. As needed, a lubricant such as zinc stearate, wax, and an additive such as hindered phenols may be added to ink receptive layer 3.
Ink for receptive layer 3 is formulated such that, first, a coating liquid is prepared by dispersing and mixing in water a hydrophilic pigment, binder resin, and some additives if need. As needed, other additive of a pigment dispersant such as sodium polyacrylate, sodium hexamethacrylate, denatured sulfonic polyvinyl alcohol, etc., a defoamer, ultraviolet absorbent, and antiseptic, etc. may be added to the liquid.
Ink receptive layer 3 is formed by coating a coating liquid formulated by a coater over a surface of a substrate in such an amount of the coating liquid that would weigh after dried in a range of 1 to 50 g/m2, preferably 3 to 10 g/m2. As the coater on this process, air knife coater, bar coater, roll coater, blade coater, gravure coater, etc. may be used.
Thermosensitive coloring layers 4a, 4b, and 4c having different coring hues are formed integrally with ink receptive layer 3 using a gravure printing process. A gravure printing apparatus 100, as shown in
In reference to
As appeared in
By selecting widths and lateral positions of the respective cell bands in groups of 117a and 117b, 127a and 127b, and 138a and 138b, thermosensitive coloring layers 4a, 4b, and 4c can be formed without gaps between the layers in the width direction of substrate 2. When different colors are coated using a first print unit 110, a second print unit 120, and a third print unit 130 of a gravure printing apparatus, the individual thermosensitive coloring layers are likely misaligned on their layer edges due to thermal extension/contraction or media transport errors. Occurrence of interspaces between the thermosensitive coloring layers of different colors, if happens somewhat, can be prevented by coating a lighter color ink before a darker ink so that the darker one is superposed over the lighter.
Gravure printing plates 113, 123, and 133 are etched plates having 175 lines and 40 μm in depth. The fewer the number of lines and the greater depth of the cells of a printing plate are, the thicker the thermosensitive coloring layer is formed and more concentrated the developed color appears. Then again, “streaking” and density unevenness likely occur. Therefore, the number of the lines and depth of the cells of a printing plate should be determined on terms of tradeoff between these color density and density unevenness. Thermosensitive recording medium 1 can be produced at desired lengths in a longitudinal direction of ink-coating in a direction (as characters are serially printed in a printer) by forming the thermosensitive coloring layers continuously in stripes.
A sequence of forming thermosensitive coloring layers 4 among them on a printing process is preferably to be determined such that ink of lightest color is coated first, then the second lighter one follows it, and so on. This is based on the following reason. A doctor blade generally tends to wear easier when used with aqueous inks than with other types of inks, and a worn doctor blade likely touches spots other than an intended area so that water-dispersion thermosensitive ink is coated elsewhere. In such a case, when a dark thermosensitive coloring layer is formed after a light color layer even if using such a worn doctor blade, color mixing becomes hard to spot as the dark layer superimposes the lighter one. In other respects, if a worn doctor blade is used with a darker ink, color mixing becomes hardly distinguished because spots of a coloring layer that unintended color ink could be accidentally touched on are not over an ink receptive layer but over a thermosensitive coloring layer of a lighter hue, and hence the amount of a darker ink to be transferred from the printing plate to the coloring layer is a little.
On a process of forming thermosensitive coloring layers 4a, 4b, and 4c as shown in FIGS. 1 though 3, red thermosensitive coloring layer 4c is first formed in ink by first print unit 110 of a gravure printing apparatus, blue layer 4a is next formed by second print unit 120, and lastly black layer 4b is formed by third print unit 130.
On thermosensitive recording medium 1, as shown in
If necessary, a protective layer is provided over the coloring layers, following formation of thermosensitive coloring layers 4a, 4b, and 4c on substrate 2. As shown in
In the case that a number of thermosensitive recording mediums in each of which thermosensitive coloring layer are arranged in the order of 4a, 4b, and 4c as illustrated in
To avoid to produce such unusable areas as shown, thermosensitive coloring layers 4a, 4c, and 4c are formed though a printing process on substrate 2 having ink receptive layer 3 such that the neighboring thermosensitive coloring layers 4a and 4c interposed by split line 150 are united into a common coloring layer. Thermosensitive recording medium 1 is produced by splitting substrate 2 along the cutting line 150 provided over the common thermosensitive coloring layer 4. The common coloring layer is formed having a width of, for example, double normal width, if split thermosensitive coloring layers (from the common layer) would be set to the same width.
In
To form plural thermosensitive recording mediums having the same arrangement order of thermosensitive coloring layers 4a, 4b, and 4c on one substrate, arrangement of thermosensitive coloring layers 4 (119a, 119b, 129a, 129b, 139a, 139b, 139c) of one of neighboring thermosensitive recording mediums 1 is reversed. In actual recording by a thermal printer, images of the same pattern can be recorded by merely changing a direction of data transferring within a printer, since arrangement orders of the coloring layers in neighboring thermosensitive recording mediums 1 are mutually reversed. More specifically, in thermosensitive recording mediums 1 adjacent to each other (for example, 1a and 1b) as shown in
If cutting is made over thermosensitive coloring layers 119b and 129a, positional error of some 1 mm from the center line in the width direction may be allowed in view of recording accuracy of a printer.
Producing multiple thermosensitive recording mediums 1 by cutting in the middle of thermosensitive coloring layer instead of an unusable space yields advantages that narrow gaps 152 that lack thermosensitive coloring layers become unnecessary and occurrences of color mixing caused by a worn doctor blade can be reduced by reduction of boundary areas between thermosensitive coloring layers 4 of different colors.
As a material of substrate 2, paper may be used. When thermosensitive coloring layers 4 are formed by coating water-dispersion thermosensitive ink using a gravure printing machine, a paper is likely cockled. To prevent such cockles when used with a typical photogravure printing machine, a thickness of paper as substrate 2 of 90 g/m2 in terms of basis weight, preferably 100 g/m2, is required.
So far, there has been described an example in which thermosensitive coloring layers in stripes were formed over ink receptive layer 3 that was provided on a continuous substrate 2 by coating in stripes a water-dispersion thermosensitive ink containing an electron-donating compound and electron-accepting compound using a gravure printing plate. As an alternative example, in view of preventing “streak,” it is more effective to form the coloring layers by coating water-dispersion thermosensitive ink containing at least an electron-donating compound over ink receptive layer 3 in which an electron-accepting compound is impregnated.
For the electron-accepting compound, for example, a developer can be used. To be more specific, oxides such as phenols, phenolic metallic salts, carboxylic metallic salts, sulfonic acid, sulfonate, phosphoric acid, phosphoric metallic salts, acid ester phosphate, phosphorous acids, phosphorous acid metallic salts may be used. These materials may be used either alone or mixed as well.
For the electron-donating compound, for example, a leuco dye can be used. To be more specific, usable as a black dye are PSD-150, PSD-184, PSD-300, PSD-802, PSD-290 of Nippon Soda Co., Ltd.; CP-101, BLACK-15, ODB, ODB2 of Yamamoto Chemicals Inc.; BLACK-100, S-205, BLACK-305, BLACK-500 of Yamada Kagaku Co., Ltd.; and TH-107 of Hodogaya Chemical Co., Ltd. Usable as a blue dye are CVL, BLUE-63, BLUE-502 of Yamamoto Chemicals Inc.; BLUE-220 of Yamada Kagaku Co., Ltd.; and BLUE-3 of Hodogaya Chemical Co., Ltd. Usable as a red dye are PSD-HR, PSD-P, PSD-0 of Nippon Soda Co., Ltd.; Red-3, Red-40 of Yamamoto Chemicals Inc.; Red-500, Red-520 of Yamada Kagaku Co., Ltd.; and Vermilion-DCF, Red-DCF of Hodogaya Chemical Co., Ltd. Among the dyes indicated in the above, more than one kind may be mixed.
Dyes usable for other colors are: for green, PSD-3D (Nippon Soda Co. Ltd.), ATP (Yamada Kagaku Co., Ltd.), Green DCF (Hodogaya Chemical Co., Ltd.), etc.; for yellow, F. Color Yellow-17 (Yamamoto Chemicals Inc.); for orange, PSD-0 (Nippon Soda Co. Ltd.), Orange 100 (Yamada Kagaku Co., Ltd.), etc.
In the above, descriptions were made for example of using color combination of blue, black, and red for the respective thermosensitive coloring layers 4a, 4b, and 4c. This color combination is well balanced and suitable for multicolor thermosensitive recording medium 1 as used for a price card. However, colors usable are not limited to this combination.
Usable as the binder resins are water-soluble resins such as starches, celluloses, and polyvinyl alcohols, and latex resins such as polyvinyl acetate, polyurethane, and polyacrylic ester. These materials may be used either alone or mixed as well.
As needed, sensitizers such as waxes, naphthol derivative, biphenyl derivative, polyether derivative, and diester carbonate derivative, print-head abrasion resistance agents and anti-sticking agents such as zinc stearate, amide stearate, and calcium carbonate may be used.
To form thermosensitive coloring layers 4a, 4b, and 4c, first, water-dispersion thermosensitive ink is prepared by dispersing and mixing in water a developer (electron-accepting compound) a leuco dye (electron-donating compound), binder resin, and if necessary, pigments such as a sensitizer, print-head abrasion resistance agent, anti-sticking agent. If needed, various additives such as a modified resin, such as denatured sulfonic polyvinyl alcohol, dispersant such as a surfactant, defoamer, ultraviolet absorbent, antiseptic, may be mixed in the ink.
A sensitizer is used to enhance color developing sensitivity by binding between an electron-accepting compound and an electron-donating compound. Although an ideal material for the sensitizer differs depending on an electron-accepting compound used and electron-donating compound used for thermosensitive coloring layers 4, for example, sensitizer HS-3520, manufactured by Dainippon Ink & Chemicals Co., Ltd. may be used.
In the above example, descriptions have been made that a width of the thermosensitive coloring layer 4 needs to be more than 10 mm and more than one tenth of a width of thermosensitive recording medium 1. However, the width may be smaller than that depending on applications, and those dimensions may be selected accordingly.
In the above example, description has also been made for thermosensitive recording medium roll 10 for recording by a thermal printer (not shown) as an applied form of thermosensitive recording medium 1. Thermosensitive recording medium roll 10 can be transformed to a folded thermosensitive recording medium 11, as shown in
In the above example, one thermosensitive recording medium 1 is provided such that thermosensitive coloring layers each having a color different from other are formed in stripes. If at least two different colors are provided, more than one thermosensitive coloring layers 4 having the same color may be formed.
Hereinafter, specific compositions of thermosensitive recording medium 1 according to the present invention will be described by using examples. However, the invention is not restricted to such examples. In the examples below, unit “part(s)” means “part(s) by weight.”
Formation of Ink Receptive Layer
A pigment dispersion liquid of hydrophilic silica was prepared by dispersing the above components using a homogenizer. Then, a coating liquid for ink receptive layer 3 was prepared by adding the following components to this pigment dispersion liquid and mixing them using a homogenizer.
Ink receptive layer 3 was formed such that the coating liquid prepared in the above process is coated on substrate 2 (a quality paper) having basic weight of 90 g/m2 by a micro-gravure coater at a medium transport speed of 50 meter/minute at drying temperature of 100 degrees C. in an amount of the coating material that would weigh 8 g/m2 after dried.
Formation of thermosensitive coloring layers
This sensitizer dispersion liquid was prepared by dispersing the sensitizer as a dispersant with a 5% GOHSERAN L-3266 (manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) and using a sand mill so as to obtain an average particle size of 0.8 μm.
A calcium carbonate dispersion liquid was prepared by dispersing the sensitizer in water as a dispersant with a 5% GOHSERAN L-3266 (manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) and using a sand mill so as to obtain an average particle size of 0.8 μm.
The water-dispersion thermosensitive inks having different color hues of blue, black, and red were formulated by mixing the above developer dispersion liquid, sensitizer dispersion liquid, lubricant dispersion liquid, recrystalization-inhibitor dispersion liquid, calcium carbonate dispersion liquid, 10%-PVA solution, surfactant, and water with the respective leuco dye dispersion liquids of blue, black, and red.
Each of the water-dispersion thermosensitive inks prepared in the above process was adjusted so that a viscosity of the ink falls in a range between 30 and 40 cps (measured with an E type viscometer of Tokyo Keiki Co., Ltd.) and the surface tension becomes 30 mN/m or lower (measured using a K12-Mk5 surface tension balance, manufactured by Kruss GmbH). The surface tension of the ink needs to be lowered using a surfactant, particularly when printing using an engraved plate, since the ink having a high surface tension makes it difficult to let the ink intrude into dents on a printing plate.
These water-dispersion thermosensitive inks were coated on ink receptive layer 3 using a photogravure printing machine (etched plate having 150 lines in cell density and 40 μm in cell depth), so that thermosensitive coloring layers 4 of thermosensitive recording medium 1 were formed. The etched plate that was used in this process had 150 lines in cell density and 40 μm in cell depth, which permits continuously coating in stripes for the respective color inks as shown in
As it happens normally, wearing of doctor blades 114, 124, and 134 caused hazing in a stripe at a coating length of some 15000 to 20000 meters, which then caused color mixing between thermosensitive coloring layer 4a, 4b, and 4c. However, by coating the inks in the above sequence, this color mixing between thermosensitive coloring layer 4a, 4b, and 4c in stripes did not occur even at some 20000 to 25000 meters of coating, and the number of changing of doctor blades 114, 124, and 134 could be reduced. This is because a thermosensitive coloring layer having dark color overrode a thermosensitive coloring layer having light color so that it became undistinguished even if hazing occurred lightly.
“Hazing” means a phenomenon that water-dispersion thermosensitive ink that remains on the surface of a printing plate without being removed by doctor blade is lightly transferred to a surface of a blank area on a recording medium.
Because regions adjacent to dense color thermosensitive coloring layer 4 that is subsequently coated are not ink receptive layer 3 but other thermosensitive coloring layers in stripes, the amount of transferred water-dispersion thermosensitive ink of dense color having hazing is little, and therefore such color mixing is hardly distinguished.
As can be seen in
A protective layer was formed on thermosensitive recording medium 1 thus obtained, on which thermosensitive coloring layers 4 have previously been formed, by coating OCA-5 of Nippon Kayaku Co., Ltd. with a bar coater in such an amount that the coating after dried would weigh 1 g/m2. The thermosensitive recording medium is slit along cutting line 150 by a slitter as shown in
Since thermosensitive recording medium 1 obtained in this manner is provided with thermosensitive coloring layers 4a (blue), 4b (black), and 4c (red) formed in continuous stripes in an ink-coating direction, a recording length can be flexibly selected.
Because orders of the respective thermosensitive coloring layers at both sides in respect to cutting line 50 are arranged mutually in reversed order, the number of boundaries between different thermosensitive coloring layers can be reduced. Also, by coating ink of light color before coating the darker, the number of replacement of a doctor blade can be reduced.
Since the width of each of thermosensitive coloring layers 4 in stripes is more than one tenth of a total medium width and at least 10 mm, they look well balanced visually. Particularly, when a bar-code is recorded on blue thermosensitive coloring layer 4a or black thermosensitive coloring layer 4b, reading accuracy of bar-codes showed good results.
When thermosensitive recording medium roll 10 is produced by rolling the medium in a predetermined length, since stripe patterns interposed by cutting line 150 are reversed, it is useful to put marks on winding core of the medium that indicates arrangements of the stripe coloring layers.
Thermosensitive recording medium 1 obtained in this example exhibited excellent results in bar-code reading by a scanner and dimensional balancing between thermosensitive coloring layers of different colors, and the same effect as in Example 1 was obtained in respect to color mixing due to a worn doctor blade.
In this example, as shown in
Since this example is the same as Example 2 in the condition except that thermosensitive coloring layer 4d was added, the same effects as in Example 2 were obtained on blue thermosensitive coloring layer 4a, red thermosensitive coloring layer 4b, and black thermosensitive coloring layer 4c. Thermosensitive coloring layer 4d cannot be applied for bar-code recording, but can be used for marking an underline for underscoring characters of recorded contents. In this sense, 10 mm or even less is sufficient for the width of the layer. In respect to color mixing due to a worn doctor blade, the similar effect to Example 2 was obtained. This means that the effect can be obtained even if two thermosensitive coloring layers 4 of the same color are provided on thermosensitive recording medium 1.
In Example 4, as shown in
The process conditions were the same as in Example 1 except of changing leuco dye from CVL to Green DCF (manufactured by Hodogaya Chemical Co., Ltd.) to obtain green thermosensitive coloring layer 4e.
Because the conditions are alike to Example 1 except substitution of blue thermosensitive coloring layer 4a by green thermosensitive coloring layer 4e, thermosensitive recording medium 1 obtained in this example exhibited excellent results in bar-code reading and dimensional balancing between thermosensitive coloring layers of different colors, and the same effect as in Example 1 was obtained in respect to color mixing due to a worn doctor blade.
In Example 5, as shown in
Unlike Example 1, three patterns of thermosensitive recording mediums 1 were separated from one substrate 2. All of these three thermosensitive recording mediums 1 exhibited excellent results in terms of bar-code reading and dimensional balance in thermosensitive coloring layers of different colors, and the same effect as in Example 1 was obtained as to color mixing due to a worn doctor blade.
In this example, since three arrangements of different colors of thermosensitive coloring layers were produced, after separation into thermosensitive recording medium 1 it becomes difficult to distinguish those mediums before developing colors in thermosensitive coloring layers 4. To differentiate these three kinds of thermosensitive recording mediums, when substrate 2 is split and individual thermosensitive recording mediums 1 are rolled at predetermined lengths, it would become convenient if marks are made on surfaces or backs of the respective thermosensitive recording medium 1 at their ends after being rolled on winding cores so that the arrangements of the respective thermosensitive coloring layers 4 can be differentiated.
In Comparative Example 41, as seen in
Because striped thermosensitive coloring layers 4 are discontinuous, its application in a longitudinal direction is limited. Its performances otherwise are the same as those of Example 1. In terms of production, because a gravure printing plates used for the respective thermosensitive coloring layer 4a, 4b, and 4c need to be aligned not only in a width direction but also in a longitudinal direction of substrate 2, quite a little of substrate 2 and water-dispersion thermosensitive inks are wasted for the alignments.
In Comparative Example 2, as seen in
Although performances in respect to bar-code reading, dimensional balance between thermosensitive coloring layers 4 of different colors, and flexibility in a longitudinal direction were the same as Example 1, color mixing occurred earlier due to increased number of boundaries between thermosensitive coloring layers 4a, 4b, and 4c of different colors. In addition, accurate cutting along cutting line 150 was required.
In Comparative Example 3 a sequence of ink-coating on thermosensitive recording medium 1 was changed (the sequence of ink-coating was reversed). Otherwise, the condition was unchanged.
As to bar-code reading and dimensional balance between thermosensitive coloring layers 4 of different colors, the same performance results as in Example 1 were obtained. However, owing to different sequence of ink-coating from that of Example 1, color mixing between neighboring thermosensitive coloring layers 4 likely occurred when even little hazing has occurred as a result of a worn-out doctor blade on the black layer. For this reason, frequency of replacement of the doctor blade increased comparing to Example 1.
In Comparative Example 4, as seen in
In Comparative Example 5, as seen in
Table 1 below is a comparison table between Examples 1 through 4 and Comparative Examples 1 through 5.
Term “continuous” indicated in Table 1 in a cell means a medium sample in which thermosensitive coloring layers are continuously formed in a longitudinal direction, and term “discontinuous” in a cell means that discontinued regions 151 (as shown in
Term “same” under the column of “Arrangement of thermosensitive coloring layers” means that thermosensitive coloring layers of different colors in neighboring thermosensitive recording mediums 1 are arranged in the same order, and term “reciprocal” means that thermosensitive coloring layers of different colors in neighboring thermosensitive recording mediums 1 are arranged mutually in reversed order in a transverse direction.
Term “Position of cutting line” as an item in Table 1 means, a position of cutting line 150 which is placed “over a thermosensitive coloring layer” in Examples 1 through 5, “between neighboring thermosensitive coloring layers 4 in Comparative Example 2, and “on a gap on substrate 2” in Comparative Example 4.
Term “From a light color” under the column of “Ink-coating sequence” in Table 1 means that a light color of a thermosensitive coloring layer is formed prior to a darker color of thermosensitive coloring layer, and “From darker color” means coating inks in any orders other than the “order from a lighter color.”
Term “Freedom of recording length” means a degree of freedom in respect to a recordable length on thermosensitive recording medium 1 when characters or images are recorded by a thermal printer.
Term “Frequency of blade replacement means frequency of replacements of doctor blade on a gravure printing process.
Term “Cutting accuracy” means whether or not cutting of a medium requires a more accuracy than a normal cutting.
Overall judgment was made and ranked at levels of A, B, and C as in the order from “Superior” depending on how much each sample satisfies requirements of the evaluation items above-mentioned.
From results of the comparisons, it can be seen that Examples 1 through 5 are superior to Comparative Examples 1 through 5 in respect to freedom of recording length (“Variable”: variable setting of recoding length possible; “Limited”: length limited), Time of replacement for a doctor blade (“Long”: replacement required due to occurrence of color mixing after its use for 20,000 meters of medium; “Short”: replacement required due to occurrence of color mixing before its use for 20,000 meters of medium), requirement for cutting accuracy (Not required; Required), and overall judgment (based on the performances in Example 1 as A rank, rank B and rank C are subjectively judged in terms of flexibility of recording length, replacement time for a doctor blade, and requirement for cutting accuracy).
In the examples and comparative examples described above, quality papers of 90 g/m2 were used. If substrates having basic weight of less than 90 g/m2 are used, cockles likely occur during a drying process after thermosensitive coloring layers 4 are formed.
Normally, printing apparatus are not provided with a vapor-steaming means that prevents occurrence of cockling on a substrate by applying vapor steam to it from back of a substrate. To obtain a substrate having a stable quality using normal printing apparatus without having cockles, a thickness of some 90 g/m2, preferably 100 g/m2, is needed. It is preferable to use a lower limit as long as cockles are not developed, because increasing its thickness increase its cost. Therefore, some 100 g/m2 is considered optimum.
In the above Examples and Comparative Examples, gravure printing process was used. However, printing process need not be limited to gravure printing, and may also be used as long as they permit continuous coating of water-dispersion thermosensitive ink containing 30% of solid components.
Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the present invention can be practiced in a manner other than as specifically described therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2004-143892 | May 2004 | JP | national |
