JP2000027093A - Recording paper, its production, water-based coating composition, its coating method and coated product therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain recording paper that has a good void layer with high uniformity and evenness, even when the supporter is coated with a dried thick layer, by preparing a coating composition of specific properties from fine particles, a hydrophilic binder and a viscosity thickener. SOLUTION: A hydrophilic binder, for example, a poly(vinyl alcohol) binder, is combined with an inorganic fine particles, for example, fine particles of silica synthesized via the vapor phase process, at a weight ratio of 3-10, in addition, with a viscosity thickener, for example, boric acid or (its salt) whereby the objective coating composition is prepared that has a viscosity of 10-100 cp. at 40 deg.C and a viscosity at 15 deg.C that is substantially more than 20-fold higher that at 40 deg.C and is substantially free from gelatin with a pH of 3.5-6.0. The substrate is coated with the resultant composition with a viscosity of 10-100 cp, then cooled down so that the temperature becomes lower than 20 deg.C at the coating face to increase the viscosity of the coated layer more than 20-fold. Then, the coated layer is blown with the wind higher than 20 deg.C whereby the objective recording paper having the void layer with 30-60 μm thickness on the dry basis is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording paper, a method for producing the same, an aqueous coating composition, a method for applying the same, and a coated product, and more particularly to a recording paper having a void layer, and particularly suitable for high-speed coating and rapid drying. The present invention relates to a recording paper, a method for producing the same, a coating composition suitable for high-speed coating and rapid drying, a method for applying the same, and a coated article.

[0002]

2. Description of the Related Art In recent years, the image quality of ink-jet recording has been rapidly improving, and the image quality is approaching that of photographs. In order to achieve such photographic image quality by ink jet recording, improvements have been made in terms of recording paper.
Recording papers provided with a void layer having minute voids as an ink absorbing layer on a highly smooth support described in JP-A-56552 and JP-A-7-137434 must have high ink absorption and high drying properties. Is becoming one of the closest to photographic quality.

Incidentally, a support that does not absorb ink, such as a polyester film, a polyolefin film, or a paper support coated with a polyolefin, is generally used as the high-smoothness support. In providing an ink-absorbing void layer on such a non-ink-absorbing support, it is necessary to provide a thick coating layer in order to absorb ink sufficiently. Usually, when a void layer is applied on such a non-ink-absorbing support, it is necessary to apply the dry layer to a thickness of 30 μm or more, preferably 35 μm or more.

In the case where the void layer is coated so as to have a dry thickness of 30 μm or more, the wet thickness of the coating solution is 100 μm.
It is necessary to apply with a high wet film thickness of not less than m, usually not less than 130 μm.

[0005] Problems when applying a water-based coating solution on a support with such a high wet film thickness include disadvantages that it takes a long time to dry and that unevenness due to liquid twist during drying is apt to occur.

[0006] Since water, which is the main solvent of the aqueous solution, has a high boiling point, it requires a remarkably long drying time when drying only by heat treatment, and requires an enormous drying zone.

On the other hand, during drying over such a long drying time, the applied liquid locally moves due to various causes, causing so-called liquid twist, resulting in an uneven coating film surface. . When liquid twisting occurs, not only the coating film surface becomes non-uniform, but also the thickened portion causes poor drying and may be wound up, causing serious manufacturing trouble.

As an example of applying the aqueous coating solution at a thick wet film thickness, there is an application of a silver halide photographic emulsion using gelatin as a hydrophilic binder. An aqueous gelatin solution is generally in the form of an aqueous solution at about 30 ° C. or higher,
Below, it has the property of gelling. Utilizing this property,
After applying an aqueous solution containing gelatin on a support, gelling it by cooling, it can be dried by blowing strong wind at a relatively low temperature (about 20 to 60 ° C.). This allows gelatin to dry in a relatively short time despite its high wet film thickness.

In the case of a coat layer in which gelatin can be used, rapid drying is possible by utilizing the above-mentioned properties of gelatin, but in the case of the coating solution for forming the void layer, gelatin is mainly used. It cannot be used as a suitable hydrophilic binder.

In other words, when gelatin is used as a main binder of the void layer, the ink immediately closes the void due to swelling of the gelatin during ink jet recording, so that the characteristics of the void cannot be utilized.

There is no known technique for coating a void layer having a high thickness uniformly and with high productivity without substantially using gelatin. Further, since the coating liquid for forming the void layer contains a large amount of fine particles, lumps are easily generated during the preparation of the coating liquid, and clogging of the filter for filtration or
Also, it was found that high-speed coating easily causes clogging in the coating apparatus.

[0012]

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a recording paper having a good void layer surface and a method for producing a recording paper suitable for forming a void layer by high-speed coating and rapid drying. A second object of the present invention is to provide a coating composition suitable for rapidly drying and coating a thick dry film, and a coating having a good film surface using the coating composition. An object of the present invention is to provide a coating method capable of forming a coating film surface which is uniform and free from unevenness without liquid twist.

[0013]

The above objects of the present invention are as follows. A recording comprising a support having a void layer formed from a coating composition having a viscosity at 40 ° C of 10 to 100 cp and a viscosity at 15 ° C of 20 times or more the viscosity at 40 ° C. Paper,

2. The recording paper according to the above 1, wherein the coating composition is substantially free of gelatin.

3. The void layer has a dry film thickness of 30 to 60 μm
The recording paper according to the above 1 or 2, wherein

4. The recording paper according to any one of the above 1 to 3, wherein the coating composition is a coating composition containing fine particles, a hydrophilic binder and a viscosity increasing agent.

5. The recording paper according to any one of the above 1 to 4, wherein the coating composition is an aqueous coating composition containing inorganic fine particles, polyvinyl alcohol and boric acid or a salt thereof and substantially containing no gelatin.

6. The recording paper according to the above 5, wherein the inorganic fine particles are fine particle silica synthesized by a gas phase method,

[7] The aqueous coating composition has a pH of 3.5 to 3.5.
6. The recording paper according to the above 5 or 6, wherein the recording paper is 6.0.

8. The recording paper according to any one of the above 5 to 7, wherein the ratio of the inorganic fine particles to polyvinyl alcohol is 3 to 10 by weight.

9. An aqueous coating composition containing inorganic fine particles, polyvinyl alcohol and boric acid or a salt thereof, and substantially free of gelatin, having a viscosity at 40 ° C. of 10
１００100 cp and the viscosity at 15 ° C. is 2
An aqueous coating composition characterized by being at least 0 times,

10. A coating, wherein the water-based coating composition according to the above 9 is coated on a support,

11. In the method for producing a recording sheet having a void layer, the viscosity at 40 ° C. is 10 to 100 cp,
A method for producing a recording paper, comprising applying a coating composition having a viscosity at 5 ° C of 20 times or more the viscosity at 40 ° C to form a void layer;

12. In a method for producing a recording paper having a void layer formed by applying a coating composition on a support,
The coating composition is applied to the support at a viscosity of 10 to 100 cp, and then the viscosity of the applied coating composition is adjusted to 20 at the time of application.
A method for producing a recording paper, wherein the method is adjusted before the drying step so as to be twice or more,

13. The method for producing a recording sheet according to the above item 11 or 12, wherein the coating composition contains fine particles, a hydrophilic binder and a viscosity increasing agent,

14. The coating composition according to 9 above,
The method is applied on a support at 50 ° C., cooled to a film surface temperature of 20 ° C. or less, and then dried by blowing a wind of 20 ° C. or more on the support.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The void layer of the present invention is an absorbing layer of a coloring material such as ink,
This is a layer that has voids in the layer and absorbs the ink mainly by containing the ink in the voids, rather than causing the color material to be absorbed by the swelling of the binder. The void volume is approximately 20-60 ml / m ² and 25 ml
/ M ² or more, more preferably 45 ml / m ² or more. The porosity of the void layer is approximately 0.5 to 0.8.

The coating composition of the present invention preferably contains fine particles. The fine particles may be fine particles made of an organic compound or inorganic fine particles. Examples of inorganic fine particles include light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, hydrotalcite. , Aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, alumina, colloidal alumina, pseudoboehmite, aluminum hydroxide, lithopone, zeolite, white inorganic pigments such as magnesium hydroxide and the like. Can be.

Such inorganic fine particles can be used as primary particles, or can be used in the form of secondary aggregated particles formed by aggregation of primary particles. In the present invention, as the inorganic fine particles, fine particle silica synthesized by a gas phase method is particularly preferable because the viscosity is easily increased at a low temperature.

The fine particle silica synthesized by the gas phase method is usually a silica powder having a primary particle diameter of 5 to 500 nm obtained by burning silicon tetrachloride at a high temperature together with hydrogen and oxygen.
In the present invention, those having a primary particle diameter of 50 nm or less are particularly preferable from the viewpoint of glossiness. Examples of such commercially available fumed silica include various types of Aerosil manufactured by Nippon Aerosil Co., Ltd. Silica synthesized by the above-mentioned gas phase method may be one whose surface is cationically modified, or may be Al, Ca, Mg and B
It may be one treated with a or the like, or one having a part of its surface rendered hydrophobic.

The fine particles may have any particle size as long as they can be used to form a layer on the support, but the viscosity change can be made large with respect to the temperature change of the coating solution. So that the average particle size is 1μ
m or less, and particularly preferably 0.2 μm or less. The lower limit of the particle size is not particularly limited, but is preferably approximately 3 nm or more, particularly preferably 6 nm or more from the viewpoint of particle production.

In the above description, the average particle diameter of the fine particles is determined as a simple average value (number average) by observing the cross section or surface of the particle itself or the void layer with an electron microscope, obtaining the particle diameter of 100 arbitrary particles, and calculating the particle diameter. Can be Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

The content of the fine particles in the coating composition is generally from 3% by weight to 20% by weight, particularly from 5% by weight, from the viewpoint of increasing the viscosity at a low temperature and maintaining an appropriate viscosity at the time of coating. 15% by weight is preferred.

The coating composition of the present invention preferably contains a binder. Particularly hydrophilic binders are preferred,
For example, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, dextran, dextrin, carrageenan (λ, ι, λ, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose, etc. No. Among them, polyvinyl alcohol is most preferable. The polyvinyl alcohol used in the present invention includes, in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohol such as polyvinyl alcohol having a cation-modified terminal or anion-modified polyvinyl alcohol having an anionic group. Is also included.

The polyvinyl alcohol obtained by hydrolyzing vinyl acetate preferably has an average degree of polymerization of 300 or more, and particularly preferably has an average degree of polymerization of 1,000 to 4,000.

The saponification degree is preferably from 70 to 100%, particularly preferably from 80 to 99.5%.

As the cation-modified polyvinyl alcohol, for example, a tertiary amino group or a quaternary ammonium group as described in JP-A-61-10483 can be used in the main chain or side chain of the polyvinyl alcohol. Which is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamido-2,2-dimethylethyl) ammonium chloride and trimethyl- (3-acrylamido-3,3-dimethylpropyl). Ammonium chloride, N-vinylimidazole, N-vinyl-2-methylimidazole, N
-(3-dimethylaminopropyl) methacrylamide,
Hydroxyethyltrimethylammonium chloride,
Trimethyl-(-methacrylamidopropyl) ammonium chloride, N- (1,1-dimethyl-3-dimethylaminopropyl) acrylamide and the like.

The ratio of the cation-modified polyvinyl alcohol-cation-modified group-containing monomer is 0.1 to vinyl acetate.
It is 1 to 10 mol%, preferably 0.2 to 5 mol%.
Anion-modified polyvinyl alcohol is described in, for example,
Polyvinyl alcohol having an anionic group as described in JP-2060888, JP-A-61-2376
Copolymers of vinyl alcohol and a vinyl compound having a water-soluble group, as described in JP-A-81-63 and JP-A-63-307979, and water-soluble groups as described in JP-A-7-285265 And a modified polyvinyl alcohol having the formula:

Examples of the nonionic modified polyvinyl alcohol include polyvinyl alcohol derivatives described in JP-A-7-9758, in which a polyalkylene oxide group is added to a part of vinyl alcohol, and JP-A-8-25795. And a block copolymer of a vinyl compound having a hydrophobic group and a vinyl alcohol. Polyvinyl alcohol may be used in combination of two or more kinds, such as different degrees of polymerization and types of modification.

The content of the binder such as polyvinyl alcohol in the aqueous coating composition of the present invention can vary widely depending on the type of binder, the type and amount of fine particles, and the like.
It is generally from 0.1 to 10% by weight, with 0.3 to 5% by weight being particularly preferred.

The weight ratio of the fine particles to the binder is preferably 3 to 10. If it is less than 3, the thickening at low temperatures will be small, and if it exceeds 10, the coated film will be too brittle and it will be difficult to obtain a good coated surface.

Even when polyvinyl alcohol is contained as the main binder in the coating composition of the present invention, other hydrophilic binders may be used as long as they do not adversely affect the effect of the present invention, that is, increase in low-temperature viscosity. it can.
Examples of such a hydrophilic binder include gelatin, polyethylene oxide, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, dextran, dextrin, and carrageenan (λ, ι, λ
Etc.), agar, pullulan, water-soluble polyvinyl butyral,
Hydroxyethyl cellulose, carboxymethyl cellulose and the like can be mentioned. Further, when forming a void layer, gelatin may be contained as long as the void is not blocked. Preferably, the content of the hydrophilic binder is about 20% by weight or less, especially 10% by weight or less based on polyvinyl alcohol.

The coating composition of the present invention preferably contains a viscosity increasing agent in order to increase the viscosity at a low temperature.
Any viscosity increasing agent may be used as long as it increases the viscosity under certain conditions, and a hardener is particularly preferably used.
The hardener is generally a compound having a group capable of reacting with a hydrophilic binder or a compound that promotes a reaction between different groups of the hydrophilic binder.
It is appropriately selected and used depending on the type of the hydrophilic binder. Specific examples of the hardener include, for example, epoxy hardeners (diglycidylethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidylcyclohexane, N, N- Diglycidyl-4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc., aldehyde hardener (formaldehyde, glyoxal, etc.), active halogen hardener (2,4-dichloro-4-hydroxy-1) ,
3,5, -s-triazine, etc.), active vinyl compounds (1,3,5-trisacryloyl-hexahydro-s)
-Triazine, bisvinylsulfonylmethyl ether, etc.), boric acid and its salts, borax, aluminum alum and the like.

A particularly preferred hardener is boric acid or a salt thereof. The boric acid or a salt thereof refers to an oxyacid having a boron atom as a central atom and a salt thereof, and specifically, orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid and salts thereof. Is included.

The amount of boric acid or a salt thereof can vary widely depending on the concentration, pH, etc. of the inorganic fine particles and polyvinyl alcohol in the coating solution, but is generally 1 to 60% by weight, preferably 5 to 40% by weight, based on polyvinyl alcohol. % By weight.

In the water-based coating composition of the present invention, inorganic fine particles, polyvinyl alcohol, and boric acid or a salt thereof are preferred components for increasing the viscosity at low temperature.

In this case, the reason why the increase in viscosity at low temperature occurs rapidly has not been completely elucidated, but the present inventors believe that it is probably due to the following reason. That is, the hydrogen bond between the oxygen atom or hydrogen atom of the inorganic fine particles and the hydrogen atom or oxygen atom of the hydroxyl group of polyvinyl alcohol, and the relatively weak bond between polyvinyl alcohol and boric acid or a salt thereof are complicated. It is considered that entanglement causes a relatively strong bond between molecules at a low temperature to cause an increase in viscosity, and that at a high temperature, the bond becomes weak and the viscosity decreases. Therefore, in this case, inorganic fine particles, polyvinyl alcohol,
Without one of boric acid or a salt thereof, it is difficult to obtain a sudden increase in viscosity at low temperatures as obtained in the present invention. Generally, the viscosity of an aqueous coating composition is increased by lowering the temperature.
When compared between 5 ° C. and 40 ° C., it is about 10 times at most.
In this case, the pH of the aqueous coating composition has a relatively large effect on the surface charge state of the inorganic fine particles, the degree of hydration of the hydroxyl group of polyvinyl alcohol, or the dissociation of boric acid.
Preferably, the pH is in the range of ~ 6.0.

When the pH is less than 3.5, the width of thickening at a low temperature is reduced, and when the pH is more than 6, the interaction in the coating solution becomes too strong to cause agglomeration. Gelation easily occurs even in a high temperature state. A particularly preferred pH range is 3.5 to 5.5.

Compounds for adjusting the viscosity of the aqueous coating composition of the present invention include surfactants, water-miscible organic solvents, and polymer tex. Among them, the surfactant and the water-miscible organic solvent are used as means for lowering the viscosity of the coating composition. On the other hand, the polymer latex is used as a means for increasing the viscosity.

The surfactant may be a cationic surfactant or a nonionic surfactant when the coating composition is cationic, or a nonionic surfactant or anionic surfactant when the coating composition is anionic. Used. The amount of the surfactant varies widely depending on the viscosity to be adjusted, but is generally 0.01 to 10 g per liter of the coating composition.

As the water-miscible organic solvent, methanol,
Alcohols such as ethanol, n-propanol and i-propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and propyl acetate;
Examples include amides such as N-dimethylformamide, and polyols such as ethylene glycol, diethylene glycol, and glycerin. The amount of the water-miscible organic solvent used is generally 0.1 to 20 ml per liter of the coating composition.

As the polymer latex, various latexes such as silicone oil, acrylic latex and urethane latex can be used. However, since the above-mentioned means changes both the high-temperature state and the low-temperature state viscosity, appropriate conditions must be selected from the above-mentioned means in order to maintain the viscosity ratio of both.

The coating composition of the present invention has a viscosity in the range of 10 to 100 cp at 40 ° C. by the above viscosity adjusting means, and increases in viscosity as it is cooled.

Here, the viscosity indicates a viscosity measured by a B-type viscometer. In order to obtain the effect of the present invention, the viscosity at the time of cooling is set to 15 ° C. or more than 20 times the viscosity at 40 ° C.
Although it is necessary in the present invention to have
It is at least 0 times, particularly preferably at least 100 times.

The coating composition of the present invention can be applied to various uses. For example, any layer (for example, photosensitive layer, intermediate layer, protective layer, subbing layer, etc.) of various silver halide photographic materials, ink receiving layer of ink jet recording paper, receiving layer of thermal transfer recording paper, diffusion transfer It can be applied to a dye receiving layer of a photographic light-sensitive material. Accordingly, examples of the recording paper of the present invention include a silver halide photographic light-sensitive material, an ink jet recording paper, a thermal transfer recording paper, and a diffusion transfer photographic light-sensitive material. In particular, when applied to an ink receiving layer of an ink jet recording paper, it is particularly preferably used because a thick coating layer having a high gap layer without cracking and coating unevenness and having high ink absorbability can be obtained.

Various additives other than those described above can be added to the coating composition of the present invention. Above all, a cationic mordant is preferable for improving water resistance and moisture resistance after printing.
As the cationic mordant, a polymer mordant having a primary to tertiary amino group and a quaternary ammonium group is used, and the discoloration and deterioration of light resistance with time are small, and the mordant ability of the dye is sufficiently high. Therefore, a polymer mordant having a quaternary ammonium base is preferred. Preferred polymer mordants are obtained as a homopolymer of the above-mentioned monomer having a quaternary ammonium salt group, as a copolymer with other monomers, or as a condensation polymer.

Other than the above, for example, Japanese Patent Application Laid-Open No. 57-7419
No. 3, No. 57-87988, and No. 62-26147
UV absorber described in No. 6, JP-A-57-74192.
No. 57-87989, No. 60-72785, No. 61-146591, JP-A-1-95091 and JP-A-3-13376, various kinds of anionic, cationic or nonionic Surfactants, JP-A-59-42933, JP-A-59-52689, and JP-A-62-259.
Nos. 280069 and 61-242871 and JP-A-Hei.
Various known additives such as a fluorescent brightener, an antifoaming agent, a diluent such as diethylene glycol, a preservative, a thickener, an antistatic agent, a matting agent, etc. described in JP-A-219266 and the like can be contained. .

Next, a method of manufacturing a recording sheet according to the present invention will be described. The viscosity of the coating composition is 10 to 100 at the time of coating.
cp, which makes it easy to handle and suitable for high-speed coating. In order to carry out drying quickly, it is efficient and preferable to blow air at a controlled temperature.
Before the drying step, the viscosity of the applied coating composition should be at least 20 times that of the applied coating so that the coating liquid will move locally due to the wind, causing liquid twisting and causing an uneven coating film surface. is necessary. Preferably it is 50 times or more, more preferably 100 times or more.

As a method of adjusting such a viscosity,
Although a known method is used, it is preferable to cool the coated film after application to lower the surface temperature, and to use a hardener in order to easily cause an increase in viscosity. In this case, the hardener may be added to the coating liquid for forming the void layer and / or to the coating liquid for forming another layer adjacent to the void layer when the coating liquid for forming the void layer is applied. Alternatively, on a support on which a coating solution containing a hardener has been applied in advance, a coating solution for forming the void layer may be applied, or a hardener-free coating solution for forming a void layer may be further applied. The hardener can be supplied to the gap layer by overcoating the hardener solution after coating and drying, but preferably, from the viewpoint of manufacturing efficiency, the coating solution for forming the gap layer or the layer adjacent thereto is preferably used. It is preferable to add a hardening agent to the coating solution and supply the hardening agent at the same time as forming the void layer. There is also a method in which the coating composition is heated to a high temperature at the time of application, and then returned to room temperature after the application.

Next, a method of coating and drying on a support using the coating composition of the present invention will be described. As the support to be used, any known supports can be used, but preferred supports are those which do not absorb the moisture of the coating composition.

Examples of such non-water-absorbing supports include polyester films, diacetate films, triacetate films, acrylic films,
Polycarbonate film, polyvinyl chloride film, polyimide film, transparent film made of a material such as cellophane or celluloid, or resin-coated paper having a polyolefin resin coating layer obtained by adding a white pigment or the like to at least one of base paper (so-called RC Paper), and a translucent or opaque support such as a so-called white pet obtained by adding a white pigment such as titanium oxide or barium sulfate to polyethylene terephthalate.

In applying the coating composition of the present invention to the support, the support is subjected to a corona discharge treatment, an undercoating treatment or the like for the purpose of increasing the adhesive strength between the surface and the coating layer. Is preferred. Further, the recording sheet of the present invention is not necessarily colorless, and may be a colored support.

The support particularly preferably used in the present invention is a transparent polyester film, an opaque polyester film, an opaque polyolefin resin film, and a paper support in which both sides of a base paper support are laminated with polyethylene. Particularly preferred is a paper support laminated with polyethylene, as described below.

The base paper used for the paper support is made of wood pulp as a main raw material, and if necessary, in addition to wood pulp, is made of synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester. As wood pulp, LBKP, LBSP, NBKP, NBSP, LD
Any of P, NDP, LUKP, and NUKP can be used, but LBKP, NBSP, and LBS containing a large amount of short fibers
It is preferable to use more P, NDP, and LDP.
However, the ratio of LBSP and / or LDP is preferably 10% by weight or more and 70% by weight or less.

As the pulp, a chemical pulp containing less impurities (sulfate pulp or sulfite pulp) is preferably used.
Further, pulp having improved whiteness by performing a bleaching treatment is also useful.

In the base paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, paper strength agents such as starch, polyacrylamide and polyvinyl alcohol, fluorescent whitening agents, Water retention agents such as polyethylene glycols, dispersants, and softening agents such as quaternary ammonium can be appropriately added.

The freeness of the pulp used for papermaking is preferably 200 to 500 ml according to the CSF standard, and the fiber length after beating is calculated based on 24 mesh residual weight% defined by JIS-P-8207 and 42 mesh. 30% by weight
~ 70% is preferred. In addition, it is preferable that the weight% of the 4 mesh residue is 20% by weight or less.

The basis weight of the base paper is preferably 30 to 250 g,
Particularly, 50 to 200 g is preferable. Base paper thickness is 40-2
50 μm is preferred. The base paper may be calendered at the papermaking stage or after papermaking to provide high smoothness. Base paper density is 0.7 to 1.2 g / m ² (JIS-P-8118)
Is common. Further, the rigidity of the base paper is JIS-P-8143.
20 to 200 g is preferred under the conditions specified in (1).

A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, the same sizing agent as that which can be added to the base paper can be used. Base paper pH is JIS-
When measured by the hot water extraction method specified in P-8113, it is preferably 5 to 9.

The polyethylene covering the front and back surfaces of the base paper is mainly composed of low-density polyethylene (LDPE) and / or
Or high density polyethylene (HDPE) but other L
LDPE, polypropylene and the like can also be partially used.

In particular, the polyethylene layer on the coating layer side is preferably one in which rutile or anatase type titanium oxide is added to polyethylene to improve opacity and whiteness, as is widely practiced in photographic printing paper. The content of titanium oxide is approximately 3 to 20% by weight, preferably 4 to 13% by weight, based on polyethylene.

The polyethylene-coated paper may be used as a glossy paper, or may be subjected to a so-called embossing process when the polyethylene is melt-extruded onto the base paper surface to perform a coating process. Those having a surface can also be used in the present invention.

The amount of polyethylene used on the front and back of the base paper is selected so as to optimize the film thickness of the aqueous coating composition and the curl under low and high humidity conditions after the back layer is provided. The polyethylene layer on the side to which the coating composition is applied is 20
４０40 μm, and the thickness of the back layer is 10-30 μm.

Further, the polyethylene-coated paper support preferably has the following characteristics. Tensile strength: The strength specified in JIS-P-8113 is preferably 2 to 30 kg in the vertical direction and 1 to 20 kg in the horizontal direction. Tear strength: preferably 10 to 200 g in the vertical direction and 20 to 200 g in the horizontal direction according to the method defined by JIS-P-8116. Compression elasticity ≧ 10 ³ Kgf / cm ² Surface Beck smoothness: 20 seconds or more is preferable as a glossy surface under the conditions specified in JIS-P-8119, but may be less than this for so-called molded products. Opacity: Under the measurement conditions of linear light incidence / diffuse light transmission conditions, the transmittance for visible light rays is preferably 20% or less, particularly preferably 15% or less.

The coating composition of the present invention may have one layer on the same surface of the support, or may have two or more layers.
When there are multiple layers, one of them may not be a void layer, but when coated simultaneously, it has the property of thickening or gelling at a low temperature similarly to the coating composition of the present invention from the viewpoint of coating. It is preferably formed from a coating composition.

The method of applying the coating composition of the present invention can be appropriately selected from known methods. A preferred method is obtained by applying a coating solution constituting one or more layers on a support and drying the coating solution. In the case of a multi-layer structure, two or more layers can be applied simultaneously, and in particular, simultaneous application in which all the hydrophilic binder layers need only be applied once is preferable.

The coating method is preferably a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method or an extrusion coating method using a hopper described in US Pat. No. 2,681,294. Used.

The coating composition of the present invention preferably has a viscosity of 35 to 50 ° C. when coated, and has a viscosity of 36 to 4 ° C.
It is particularly preferred to use a liquid at 8 ° C. The viscosity of the coating composition of the present invention is relatively low at the time of coating, and a viscosity in the range of 10 to 100 cp at 40 ° C. is necessary from the viewpoint of high-speed coating. After applying the coating solution of the present invention on a support, it is necessary to cool the coating solution to significantly increase the viscosity.

The cooling temperature is preferably set to about 20 ° C. or less, more preferably to 15 ° C. or less. Cooling can be achieved by passing the coated sample through a cooling zone of preferably 10 ° C. or lower for a certain period of time (preferably 5 seconds or longer). At the time of this cooling, it is preferable not to blow a very strong wind because liquid twisting does not occur.

After cooling once, even if a strong wind is blown, the liquid is hardly twisted due to thickening of the coating solution itself, and even if a strong wind is blown, the generation of the liquid twist can be suppressed. Also,
The temperature of the strong wind to be blown can be a wind of 20 ° C. or more, but it is preferable to gradually raise the temperature of the wind. The drying time depends on the wet film thickness, but generally within 10 minutes.
It is particularly preferred that the time be within minutes.

The coating speed depends on the wet film thickness and the drying ability of the equipment, but is generally 10 to 1000 m, preferably 20 to 500 m per minute.

On the side opposite to the side to which the aqueous coating composition of the present invention is applied, various types of back layers may be provided in order to prevent curling, to further improve sticking when superimposed immediately after printing, and to further improve ink transfer. preferable. Although the configuration of the back layer varies depending on the type and thickness of the support and the configuration and thickness of the front side, generally, a hydrophilic binder or a hydrophobic binder is used. The thickness of the back layer is usually in the range of 0.1 to 10 μm. The surface of the back layer can be roughened in order to prevent sticking to other recording papers, improve writing properties, and further improve transportability in an ink jet recording apparatus. Organic or inorganic fine particles having a particle size of 2 to 20 μm are preferably used for this purpose. These back layers may be provided in advance, or may be provided after applying the coating composition of the present invention.

[0084]

The present invention will be described below with reference to examples of the present invention.
The present invention is not limited to these examples. In addition,
In Examples, "%" indicates absolute dry weight% unless otherwise specified.

Example 1 The primary particles dispersed uniformly in advance had an average particle size of about 0.1.
012 μm fumed silica (manufactured by Nippon Aerosil Co., Ltd .:
A200) of 450 liters of a 20% aqueous solution A1 (pH = 2.3, containing 1% by weight of ethanol) was prepared by adding 14% by weight of the cationic polymer P-1, 5% by weight of n-propanol,
And an aqueous solution C1 containing 2% by weight of ethanol (pH =
2.5, containing 2 g of Sannobuco's antifoaming agent SN381)
110 liters were added with stirring at room temperature.

Next, 42 liters of a 1: 1 weight aqueous solution D of boric acid and borax (each having a concentration of 3% by weight) was gradually added with stirring.

Then, the mixture was dispersed at a pressure of 500 kg / cm ² with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd.
After finishing to 30 liters, an almost transparent dispersion B1 was obtained. This dispersion was filtered using a TCP-30 type filter manufactured by Advantex Toyo having a filtration accuracy of 30 μm.

[0088]

Embedded image

Next, in the dispersion liquid B1, the mixed liquid D of boric acid and borax was not added (instead of using an equal amount of pure water).
Dispersion B2 was prepared in the same manner as B1.

Next, the following additives were sequentially mixed with the above dispersion to prepare a coating liquid (CS1).

Silica Dispersion B1 580 ml Polyvinyl alcohol (Kuraray PVA203) 10% aqueous solution 5 ml Polyvinyl alcohol (Kuraray PVA235) 5% aqueous solution 250 ml Silicon dispersion (Toray Dow Corning Silicone, BY-22-83) 9) 30 ml latex dispersion (AE803, manufactured by Showa Kogaku Kogyo KK) 20 ml ethanol 8.5 ml pure water (to make the total amount 1000 ml) The pH of CS1 of the obtained coating composition was 4.2 at 40 ° C. The viscosity of this coating solution at 40 ° C. and 15 ° C. was measured, and the values shown in Table 1 were obtained.

Next, the dispersion B1 or B2 was used, and the amount of B1 or B2 and polyvinyl alcohol (PVA)
235) was changed as shown in Table 1, and coating compositions CS2 to 9 were prepared in the same manner as CS1. However, the total amount was adjusted with pure water so as to be 1 liter, and the pH was adjusted with an aqueous solution of nitric acid or potassium carbonate so that the pH was the same as CS1. 40 of each coating solution
The viscosity at 15 ° C. and 15 ° C. was measured, and the results are shown in Table 1.

CS7 was prepared by adding polyethylene oxide (average molecular weight: about 100,000) in an equal weight instead of polyvinyl alcohol.

Next, each coating solution was filtered three times with a 25 μm filter, and then applied onto a paper support (thickness 240 μm) coated on both sides with polyethylene so that the wet film thickness was 200 μm. Drying is performed in two cooling zones maintained at 0 ° C.
After passing the film for 0 seconds to lower the temperature of the film surface to 13 ° C., the film was blown at 30 ° C. for 60 seconds, and at 45 ° C. for 60 seconds, for 5 seconds.
This was carried out for 60 seconds in a wind of 0 ° C. to obtain an ink jet recording paper. The state of the obtained film surface was measured visually, and the results shown in Table 1 were obtained.

The coating film surface was: ◎: no unevenness due to liquid twisting ：: partial blow-off unevenness at the end but no problem other than that △: unevenness is slightly observed on the entire surface, but practical Above is a level that does not cause a major problem. ×: Visible unevenness is not enough for practical use.

[0096]

[Table 1]

F / C represents the weight ratio of silica particles to polyvinyl alcohol. In CS9, no unevenness occurred, but crack-like coating failure and film peeling partially occurred.

From the results shown in Table 1, CS1 to CS3 whose viscosity at 15 ° C. is 20 times or more higher than the viscosity at 40 ° C. have greatly reduced unevenness due to liquid twisting as compared with a coating solution of less than 20 times. . In particular, CS1, 2, and 9 which are 50 times or more have good unevenness due to blowing and are 100 times or more.
Nos. 1 and 9 are the best in terms of blow-off unevenness. In addition, no lumps were generated at the time of coating, and there was no problem of clogging of a filter or a coating device at the time of adjusting the coating liquid. But,
In CS9, the ratio of the inorganic fine particles was high, and the coating film surface slightly cracked.

On the other hand, any of inorganic fine particles, polyvinyl alcohol and boric acid are used, but CS4 whose viscosity at 15 ° C. is less than 20 times that at 40 ° C. and CS5 which does not use inorganic fine particles. CS7 using polyethylene oxide instead of polyvinyl alcohol,
In CS8 not using boric acid, the thickening effect at low temperature was not obtained, and the unevenness due to blowing was large.

Example 2 Coating solutions CS10 to 15 were prepared from the coating composition CS1 prepared in Example 1 by adjusting the pH of the coating solution with an aqueous solution of nitric acid or potassium carbonate so as to be as shown in Table 2. . Table 2 shows the viscosity of the obtained coating solution. Also,
In the same manner as in Example 1, the film was coated on a support and dried to determine the state of the film surface. Table 2 shows the results.

[0101]

[Table 2]

Among the coating solutions having a viscosity at 15 ° C. of 20 times or more that of the viscosity at 40 ° C., CS11, CS12, and CS13 provided good film surfaces with little unevenness in blow-off, but CS10 having a viscosity less than 20 times was used. In that case, the storm was intense.
Although the viscosity ratio is sufficient, the viscosity at 40 ° C. is 45%.
In CS14 with 0 cp, application was not possible when the wet film thickness was 200 μm. In addition, CS11, 12, and 13 did not generate lumps at the time of coating, and did not cause a problem of clogging in the filter or the coating device.

Example 3 In preparing CS1 used in Example 1, the whole amount was 92
0 ml of the coating solution (CS20) and a solution in which saponin was added as an activator to the coating solution in an amount of 2% by weight (C
S21) was prepared and evaluated in the same manner as in Example 2. Table 3 shows the results.

[0104]

[Table 3]

From the results shown in Table 3, it can be seen that the concentration of the CS1 coating solution greatly increases the viscosity as a whole, but the addition of the activator provides the same coating solution viscosity as CS1. There was no problem of clogging in the filter or the coating device.

Example 4 Using the coating solution CS1 prepared in Example 1, coating was performed under the following drying conditions. (A) After application, hot air of 60 ° C. is directly blown for 3 minutes to dry. (B) After coating, air is blown at 40 ° C. for 5 minutes and dried. (C) After coating, air is blown at 30 ° C. for 10 minutes and dried. (D) After coating, air is blown at 25 ° C. for 20 minutes and dried. (E) After coating, the film was passed through a 0 ° C. zone for 10 seconds to lower the film surface temperature to 17 ° C., and then dried under the same conditions as in Example 1. (F) After coating, the film was passed through a 0 ° C. zone for 5 seconds to adjust the film surface temperature to 22 ° C., and then dried as in Example 1. (G) Drying was carried out under the same conditions as in (E) except that the temperature of the coating solution was raised from 40 ° C. to 50 ° C. After passing through the 0 ° C. zone for 10 seconds, the film surface temperature was 24 ° C. The above film surfaces were examined and are shown in Table 4. Table 4 shows the temperature when the surface temperature of the film surface during drying was the lowest.

[0107]

[Table 4]

In the application (D), the minimum film surface temperature was lowered to 18 ° C., but a little roughening occurred during that time. In the coatings (A) to (C), (F), and (G), the minimum film surface temperature did not become lower than 20 ° C., and all of the coatings were slightly blown and uneven. In coating (E), the temperature of the coating film surface is 1
The temperature has dropped to 7 ° C, there is almost no unevenness,
The effect of the present invention is remarkably exhibited.

[0109]

As described above, according to the present invention, even when applied with a thick dry film thickness, there is no liquid twist and a uniform and uniform coating film surface can be obtained at a high coating speed and drying speed. Further, a recording paper having a good void layer surface can be obtained by high-speed coating and rapid drying.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09D 5/00 C09D 129/04 A 129/04 D21H 19/38 D21H 19/38 B41J 3/04 101Y

Claims (14)

[Claims] 1. The method according to claim 1, wherein the viscosity at 40.degree.
A recording paper having a cp and a void layer formed from a coating composition having a viscosity at 15 ° C of 20 times or more the viscosity at 40 ° C. 2. The recording paper according to claim 1, wherein said coating composition contains substantially no gelatin. 3. The recording paper according to claim 1, wherein the gap layer has a dry film thickness of 30 to 60 μm. 4. The recording paper according to claim 1, wherein said coating composition is a coating composition containing fine particles, a hydrophilic binder and a viscosity increasing agent. 5. The coating composition according to claim 1, wherein said coating composition is an aqueous coating composition containing inorganic fine particles, polyvinyl alcohol and boric acid or a salt thereof and substantially containing no gelatin. Recording paper described in. 6. A recording sheet according to claim 5, wherein said inorganic fine particles are fine particle silica synthesized by a gas phase method. 7. The aqueous coating composition having a pH of 3.5 to 6.
The recording paper according to claim 5, wherein the recording paper is zero. 8. The recording paper according to claim 5, wherein the weight ratio of said inorganic fine particles to polyvinyl alcohol is 3 to 10. 9. An aqueous coating composition containing inorganic fine particles, polyvinyl alcohol and boric acid or a salt thereof, and substantially free of gelatin, having a viscosity of 10 to 1 at 40 ° C.
An aqueous coating composition having a viscosity of 00 cp and a viscosity at 15 ° C. that is 20 times or more the viscosity at 40 ° C. 10. A coated article, wherein the aqueous coating composition according to claim 9 is applied on a support. 11. A method for producing a recording sheet having a void layer, wherein the viscosity at 40 ° C. is 10 to 100 cp,
A method for producing a recording paper, comprising applying a coating composition having a viscosity of at least 20 times the viscosity at 40 ° C. to form a void layer. 12. A method for producing a recording paper having a void layer formed by applying a coating composition on a support, wherein the coating composition is applied to the support at a viscosity of 10 to 100 cp and then applied. A method for producing a recording paper, wherein the viscosity of a coating composition is adjusted before the drying step so as to be at least 20 times the viscosity at the time of coating. 13. The method according to claim 11, wherein the coating composition contains fine particles, a hydrophilic binder, and a viscosity increasing agent. 14. The coating composition according to claim 9, wherein the coating composition is 35 to 5
A method for applying a coating composition, comprising applying the composition on a support at 0 ° C., cooling the film surface temperature to 20 ° C. or lower, and then blowing by blowing air at 20 ° C. or higher.