JP2012232225A - Method of manufacturing coated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated sheet having a coated layer containing hollow particles uniformly and not having a coating defect, and further to provide a high-resolution recording sheet that does not cause a print failure but exhibits such qualities that a print concentration are stable when the coated sheet is used as a recording sheet.SOLUTION: The method of manufacturing a coated sheet in which a coating solution containing at least hollow particles is coated on a sheet-like support and is dried to form a coating layer is characterized in that the coating solution is fed to a coater head from a coating solution tank through a swirl flow type deaerator, and coating is performed by the coater head.

Description

  The present invention relates to a method for producing a coated sheet in which a coating liquid containing hollow particles is coated on a sheet-like support and dried to form a coating layer.

In recent years, thermal printing has attracted attention, and it is used in various applications, from a single color thermal printer for sales receipts to a photographic dye thermal transfer printer capable of printing clear full-color images. A thermal printer performs printing by coloring a color former contained in a recording sheet by heat, or by melting or sublimating a dye on an ink sheet by heat and transferring it onto a recording sheet. is there.

The recording sheets used in thermal printing are papers mainly made from natural pulp and plastic films such as polyester and polypropylene, but papers are widely used because of their low cost and ease of recycling. ing.

Thermal printing is required to have high speed and low power consumption, and the recording sheet is also required to efficiently use heat given from the thermal printer. For this reason, a coated sheet obtained by coating a paper with a heat insulating material is often used as a recording sheet.

As the heat insulating material, inorganic or organic pigments or hollow particles are used. Among these, the hollow particles have a high heat insulating effect and can provide a high-quality recording sheet (Patent Documents 1 and 2). However, when bubbles are mixed in the coating liquid containing hollow particles, a coating defect occurs after the formation of the coating layer, which causes a printing defect.

As a method for removing bubbles in the coating liquid, a method of irradiating ultrasonic waves has been proposed (Patent Document 3).

Japanese Patent Laid-Open No. 5-573 (2nd page) JP 2004-345289 A (second page) JP 2008-24628 A (second page)

As a result of repeated investigations on improving the uniformity of the coating layer containing hollow particles, the present inventors have removed hollow particles, particularly hollow structures, when removing bubbles in the coating liquid by a method of irradiating ultrasonic waves. The hollow particles formed by the foamed gas have a low specific gravity, so when irradiated with ultrasonic waves, the hollow particles move to the upper part of the coating liquid together with the bubbles, and the uniformity of the paint is lost. We found that the quality of the construction layer is not constant.

This invention is made | formed in view of the above situations, and this invention coats the coating liquid containing a hollow particle on a sheet-like support body, dries, and has a coating layer. In the sheet manufacturing method, the bubbles in the coating liquid are efficiently removed to prevent coating defects, and by maintaining the uniformity of the coating liquid, there are no coating defects and uniformly contain hollow particles. A coating sheet having a coating layer to be provided is provided.

Such a coated sheet can be used as, for example, a recording sheet or a heat insulating layer of a recording sheet. In such a case, there is no coating defect that causes defective printing, and high quality such as printing density is stable. A recording sheet with high image quality can be obtained.

(1) In a method for producing a coating sheet in which a coating liquid containing at least hollow particles is coated on a sheet-like support and dried to form a coating layer, the coating liquid is removed from a coating liquid tank. A method for producing a coated sheet, wherein the coating sheet is fed to a coater head through a swirling flow type defoamer and coated by the coater head.
(2) The method for producing a coated sheet according to (1), wherein the hollow particles are hollow particles enclosing and sealing a gas.
(3) The swirling flow type defoaming machine separates the coating liquid from which bubbles are removed and the coating liquid containing a large amount of bubbles into the coating liquid tank. The manufacturing method of the coating sheet as described in (1)-(2) made to reflux.
(4) A bubble detector is provided between the swirl type defoamer and the coater head, and when the bubble detection frequency exceeds a set numerical value, liquid feeding to the coater head is restricted. (1)-The manufacturing method of the coating sheet of (3) description.

  According to the present invention, it is possible to form a coating layer that contains hollow particles uniformly and has no coating defects.Therefore, when used as a recording sheet, there is no defective printing, a high quality recording sheet having a stable quality such as a printing density, and the like Become.

Hereinafter, the present invention will be described in more detail.
(Composition of coating sheet)
The coating sheet manufactured with the manufacturing method of this invention has a sheet-like support body and the coating layer which contains a hollow particle in the at least one surface of the said support body. This coated sheet may be used as it is as a recording sheet, and a sublimation transfer receiving layer or a heat-sensitive recording layer may be provided on the coated layer. In this case, the coating layer serves as a heat insulating cushion layer.

(Sheet support)
As the sheet-like support used for the coated sheet of the present invention, a film substrate made of polyethylene terephthalate or polyolefin, a nonwoven fabric substrate made of synthetic fiber or natural fiber, a paper substrate made from pulp as a main component, etc. A laminated substrate obtained by bonding these substrates is used.

  For example, as a base material having pulp as a main component, high-quality paper (acid paper, neutral paper), medium-quality paper, coated paper, art paper, and glassine paper can be mentioned. Furthermore, a sheet-like support obtained by resin-laminating the image receiving layer surface side of a base paper mainly composed of pulp, or a sheet-like support obtained by laminating and laminating sheets mainly composed of synthetic resin may be used.

(Coating fluid)
The coating liquid used in the production method of the present invention contains hollow particles, and further contains an adhesive resin for binding the hollow particles. In addition, surfactants, dispersants, antifoaming agents, thickeners, preservatives, colorants, dyes, pigments, and the like used in coated paper paints can be used as appropriate.

(Hollow particles)
Examples of the hollow particles contained in the coating liquid used in the production method of the present invention include foamable hollow particles and hollow emulsions.

  The expandable hollow particles are, for example, acrylonitrile, methacrylonitrile, methyl methacrylate, styrene, vinylidene chloride, vinyl chloride, etc. with a low boiling point hydrocarbon such as n-butane, i-butane, pentane, neopentane, etc. as the core. Monomer resin of monomers or these copolymer resins are used as walls (shells) to encapsulate them, and by heating, low boiling point hydrocarbons are vaporized and expanded to encapsulate and enclose gas in the particles. A space is formed inside.

  A hollow emulsion uses a polymer-forming material as a shell-forming material and a volatile liquid as a pore-forming material, and volatilizes the pore-forming material from microcapsules produced by a microcapsule polymerization method. It is the microcapsule-like hollow particle obtained by making it.

  The volumetric hollow ratio of the hollow particles used in the coated sheet of the present invention is preferably 60 to 97%, more preferably 65 to 90%. By setting the volumetric hollow ratio to 60% or more, when the coated sheet is used as a recording sheet, a recording sheet with high sensitivity and high image quality can be obtained, and by setting the volumetric hollow ratio to 97% or less, the volume is hollow. The strength of the particles is ensured, and a recording sheet with high sensitivity and high image quality can be obtained with stable quality.

The hollow particles used in the coating sheet of the present invention are preferably hollow particles in which the hollow particles enclose and seal a gas, that is, expandable hollow particles. The expandable hollow particles can easily have a volume hollow ratio of 60% or more as compared with the hollow emulsion, and can obtain a stable quality.

  The volume hollowness of the hollow particles indicates the ratio of the volume of the hollow part to the volume of the particles. The volume hollowness ratio of the foamable hollow particles and the hollow emulsion is calculated, for example, from the enlarged image obtained by an electron microscope, and the volume of the hollow portion and the entire volume of the hollow particle are calculated, and (volume of the hollow portion) / (volume of the entire hollow particle) ).

However, when the volumetric hollowness of the hollow particles is high and easily deformed during cross-section sample preparation, or when the shape of the hollow particles is not constant, it is difficult to determine the volumetric hollowness from the enlarged image by the electron microscope. There is. In such a case, the volume hollow ratio of the expandable hollow particles is such that the specific gravity of the hollow particle dispersion composed of hollow particles and a poor solvent, the mass fraction of the hollow particles in the dispersion, and the shell (wall) of the hollow particles are formed. It can obtain | require from the specific gravity of the polymer resin to perform, and the specific gravity of a poor solvent. The poor solvent is a solvent that does not dissolve and / or swell the resin that forms the walls of the hollow particles, and examples thereof include water and isopropyl alcohol.

The coating liquid used in the present invention contains an adhesive resin together with the hollow particles. Examples of the adhesive resin include water-soluble resins and water-dispersible resins.

Examples of the water-soluble resin include polyvinyl alcohol, modified polyvinyl alcohol, modified starch, methyl cellulose, carboxymethyl cellulose, casein, water-soluble polyester and water-soluble polyurethane into which a hydrophilic group such as a carboxyl group or a sulfone group is introduced.

The water-dispersible resin is a so-called latex obtained by emulsifying various resins with various emulsifiers. For example, styrene-butadiene latex, acrylic latex, vinyl chloride-acrylic acid copolymer resin emulsion, vinyl chloride-vinyl acetate copolymer resin. An emulsion etc. are mentioned.

The coating layer containing hollow particles formed in the present invention may also serve as a color former layer in the thermal recording system and a dye receiving layer in the thermal transfer system, and is a heat insulating layer independent of these layers. Also good.

(Coating equipment)
The coating equipment used in the production method of the present invention has at least a coating liquid tank, a swirling flow defoamer, and a coater head, and further includes a bubble detector and the swirling flow defoamer. It is preferable to have a pipe for returning the coating liquid containing a large amount of air bubbles separated by the above to the coating liquid tank.

(Coating liquid tank)
The coating liquid tank is a tank that is stored until the coating liquid is prepared and then fed to the coater head. However, the coating liquid tank may also serve as a preparation tank that inputs, disperses, and the like.
The coating liquid tank is preferably designed to be stirred at a low speed in order to promote the upward movement of bubbles in the coating liquid and the release from the liquid surface to the atmosphere. Specifically, it is preferable to provide a stirring blade capable of low-speed rotation control. When the number of rotations of the stirring blade is too large, air is embraced from the liquid level and warps to increase the bubbles in the coating liquid, and when it is too small, the effect of promoting the release of bubbles into the atmosphere is small. When the nearby paint is dried and solidified and fed as it is, it becomes agglomerated and causes coating defects. The optimum number of rotations of the stirring blade varies depending on the solid content concentration, viscosity, water retention, etc. of the coating solution, and is appropriately adjusted depending on the coating solution used.

(Swirl type defoaming machine)
A swirl type defoamer used in the present invention is a defoamer based on the principle of a cyclone in which a centrifugal force is applied by swirling a coating liquid, thereby separating a liquid and a gas having different specific gravity, for example, , A liquid bubble removing device described in JP-A-2000-176204.

Due to the centrifugal force generated by the swirling motion, the high-density component moves toward the outer peripheral side of the swirling chamber, and the coating liquid whose bubble content is reduced than before the treatment flows out. On the other hand, bubbles with low density gather on the inner peripheral side, repeatedly coalesce while gathering on the inner peripheral side, grow gradually into larger bubbles, and are separated and discharged by the pressure of the newly flowing coating liquid It has become.

If the coating liquid and air bubbles cannot be completely separated by the treatment of the swirl type defoamer, the coating liquid from which the air bubbles have been removed and the coating liquid containing more bubbles than before the treatment To be separated. The coating liquid containing a large amount of bubbles is preferably returned to the coating solution tank and removed by low-speed stirring.

The treatment of the hollow particle-containing coating solution by the swirl type defoamer can continuously remove bubbles without destroying the structure and dispersion state of the hollow particles.
For example, when the hollow particle-containing coating solution is processed using a vacuum decompression type defoamer, the hollow particles burst due to the negative pressure, and a desired high-quality recording sheet cannot be obtained.
In addition, the defoaming method of irradiating with ultrasonic waves raises the temperature of the coating liquid, and the dispersion state of the hollow particles is likely to break and cause aggregation. Further, in the case of expandable hollow particles, the hollow particles are coated together with bubbles. It moves to the top of the liquid, the uniformity of the paint is lost, and a recording sheet with a constant quality cannot be obtained.

It is also possible to arrange a plurality of swirl type defoamers in series.

(Coater head)
Examples of the coater head include known coating machine heads such as blade coaters, air knife coaters, roll coaters, bar coaters, gravure coaters, rod blade coaters, lip coaters, die coaters, curtain coaters, and slide bead coaters. .

The coater head has a pre-weighed coating head that applies a pre-weighed amount of coating liquid on the support and immediately after the amount of coating liquid that exceeds the amount to be applied is applied on the support. There is a weighing type coating head after scraping off excess coating liquid and circulating the scraped coating liquid (return coating liquid) to a tank. The scraped-off coating liquid often entraps bubbles and places a load on the defoamer. Therefore, in the coating system of the present invention, a pre-metering type coating head that does not generate a return coating liquid is preferable. Examples of the pre-weighing type coating head include a lip coater, a die coater, a curtain coater, and a slide bead coater.

(Bubble detector)
As long as the bubble detector can be used in-line, any method can be used. However, the method for measuring the intensity of near-infrared transmitted light and scattered light applied to the coating solution is a high-concentration coating. Since it can be measured even with a working solution, it can be preferably used. As the bubble detector of the above-mentioned type, an appearance monitor manufactured by Sensor Technology Inc. is generally available.
As another type of bubble detector, an ultrasonic measurement type pulsar receiver (manufactured by GNES) may be mentioned.

If the amount of bubbles in the coating liquid sent to the coater head is determined to be large as a result of measurement by the bubble detector, the liquid feeding to the coater head is stopped by a switch such as a three-way valve, and the coating is performed. It is preferable to return to the liquid tank and remove bubbles by low-speed stirring. If the liquid feeding to the coater head is stopped, the coating process will be interrupted, so if the air bubble detection frequency exceeds the set value, restrict the liquid feeding to the coater head. Is more preferable. Specifically, the trend data of the measurement values measured by the bubble detector is monitored, and the separation threshold between the coating liquid from which bubbles are removed and the coating liquid that contains a large amount of bubbles is adjusted according to the increase or decrease in the amount of bubbles. It is more preferable to adjust the setting by changing the setting conditions of the swirl type defoamer and continue the coating process.

  In addition, a plurality of coating liquid supply paths including the coating liquid tank, a swivel defoamer, and a bubble detector are provided in parallel for one coater head, and bubbles are generated in one coating liquid supply path. When it increases, the coating process can be continued by switching to another coating liquid supply path.

The present invention will be described in detail by the following examples, but the scope of the present invention is not limited thereto. In Examples, unless otherwise specified, “%” and “parts” represent “mass%” and “parts by mass” of solid content, except for those relating to solvents.

Example 1
(Adjustment of coating solution)
Feed the raw materials shown in the coating liquid below into a coating liquid preparation tank with an inner diameter of 1.5 m and a capacity of 1.8 m ³ while rotating a propeller mixer with a stirring blade with a rotating diameter of 50 cm at a speed of 200 revolutions per minute. After confirming that all the raw materials were uniformly dispersed, the propeller mixer was adjusted to a speed of 20 revolutions per minute and stirred for 5 hours.

(Coating liquid composition ratio)
Water 200 parts polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray Co., Ltd.) 15 parts polyvinylidene chloride-based foamed hollow particles 35 parts (volume hollow ratio 93%, average particle size 4 μm, maximum particle size 20 μm)
50 parts of styrene-butadiene latex (trade name: PT1004, manufactured by Nippon Zeon)

As a sheet-like support, high-quality paper having a thickness of 150 μm is used, and the coating liquid is applied and dried on one side thereof using the coating equipment shown in FIG. 1, and the film thickness after drying becomes 43 μm. As described above, coating and drying were performed to form a coating layer, and a coated paper was obtained. During the coating, the coating liquid preparation tank was continuously stirred by adjusting the propeller mixer to a speed of 20 revolutions per minute.

(Comparative Example 1)
In Example 1, a coated paper was obtained in the same manner as in Example 1 except that the coating equipment shown in FIG. 2 was used instead of the coating equipment shown in FIG.

(Comparative Example 2)
In Example 1, a coated paper was obtained in the same manner as in Example 1 except that the coating equipment shown in FIG. 3 was used instead of the coating equipment shown in FIG.

(Preparation of dye-sublimation sheet for sublimation thermal transfer coating)
The dye-receiving layer coating solution having the following composition was applied to the coated paper obtained in Example 1 and Comparative Examples 1 and 2 so that the film thickness after drying was 3 μm, dried, and sublimation thermal transfer coating dye-receiving sheet. It was created.

(Dye-receiving layer coating solution)
Polyester resin (trade name: Byron 200, manufactured by Toyobo) 100 parts silicone oil (trade name: KF393, manufactured by Shin-Etsu Chemical Co., Ltd.) 3 parts polyisocyanate (trade name: Takenate D-140N, manufactured by Takeda Pharmaceutical Co., Ltd.) 5 parts Toluene / Methyl ethyl ketone = 1/1 (mass ratio) mixture 400 parts

(Evaluation)
(Image defect)
Sublimation thermal transfer printer (trademark: Trademark: UPC-R35A, manufactured by Sony Corporation) equipped with a dye sublimation dye thermal transfer sheet (trade name: UPC-R35A, manufactured by Sony Corporation) as a dye receiving sheet obtained by the method shown in the preparation of the dye sublimation thermal transfer coating sheet. DR-100 (manufactured by Sony Corporation), and after printing a halftone pattern image in an environment of 20 ° C. and 65% RH, the image quality of the printed material was evaluated according to the following criteria, and the results are shown in Table 1. It was.
○: Image defect is not seen at all and is excellent.
X: Slight white spots are seen in the image and it is not practical.

(Image clarity and print density stability)
Using a commercially available thermal transfer video printer (trade name: UP-DR100, manufactured by Sony Corporation) equipped with a commercially available sublimation dye thermal transfer sheet (trade name: UPC-R35A, manufactured by Sony Corporation) Ten black-and-white check pattern test patterns were printed. The print density of the black print portion of 10 prints was measured with a Macbeth reflection densitometer RD914 and evaluated according to the following evaluation criteria. The results are shown in Table 1.
A: The average value of the print density is 1.80 or more, and the image is clear. In addition, the variation in print density is within 0.05 and is stable.
X: The average value of the print density is less than 1.80, and the image clarity is inferior. In addition, the variation in print density exceeds 0.05 and is unstable.

  As is apparent from Table 1, the sublimation heat transfer coating dye receiving sheet obtained by the recording sheet manufacturing method of the present invention is a high quality sublimation heat transfer coating dye receiving sheet having no printing defects and having a stable printing density. is there.

According to the present invention, it is possible to provide a coating sheet having a coating layer containing hollow particles uniformly and having no coating defects. When the coating sheet obtained according to the present invention is used as a recording sheet, there is no printing defect. It becomes a high-quality recording sheet with stable quality such as density, and is extremely useful.

It is the schematic which shows the coating equipment of this invention. It is the schematic which shows the coating equipment of a prior art. It is the schematic which shows the coating equipment of a prior art.

A: Coating liquid tank B: Pump C1: Swivel type defoamer (trade name: 30, manufactured by Nippon Juntech Co., Ltd.)
C2: Ultrasonic irradiation type deaerator (trade name: GSD600MAT, manufactured by Ginsen)
C3: Batch vacuum depressurization deaerator (Product name: Vertical agitator type B, manufactured by Otsuka Seisakusho)
D: Bubble detector E: Die coater head F: Pipe G: Stirrer H: Hot air dryer I: Web (quality paper)

Claims (4)

In the method for producing a coating sheet in which a coating liquid containing at least hollow particles is coated on a sheet-like support and dried to form a coating layer, the coating liquid is swirled from a coating liquid tank. A method for producing a coated sheet, wherein the coated sheet is fed to a coater head through a defoaming machine and coated by the coater head. The method for producing a coated sheet according to claim 1, wherein the hollow particles are hollow particles enclosing and sealing a gas. Claims that the swirl flow type defoamer separates the coating liquid from which bubbles are removed and the coating liquid containing a lot of bubbles, and returns the coating liquid containing a lot of bubbles to the coating liquid tank. Item 3. A method for producing a coated sheet according to Item 1 or 2. 2. A bubble detector is provided between the swirl flow defoamer and the coater head, and when the bubble detection frequency exceeds a set numerical value, liquid feeding to the coater head is limited. The manufacturing method of the coating sheet of ~ 3.

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