JP2000015927A - Recording paper and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence of cracks on the surface of an application film by forming a void layer made by applying application liquid containing particles having a specific particle diameter at a specific rate on a support upon manufacturing recording paper including a high glossy void layer. SOLUTION: When recording paper with a void layer provided on a support body is manufactured, a void layer is formed by applying on the support body application liquid containing particles having a particle diameter being a particle diameter of R(μm) or larger expressed by a formula of R=80000/L2 (L is a total of dry film thickness (μm)) by 10 pieces or less/1 ml. The dry film thickness of the void layer is preferably made 25-60 μm. Also, it is preferable to contain fine particles and a hydrophilic binder of 100 μm or lower in application liquid. In addition, it is also preferable to contain hydrophobic latex of a glass transition temperature of 30 deg.C or lower or hydrophobic organic compound grains of a melting point of 30 deg.C or lower in application liquid, and the support body is suitable to be a non water absorptive support body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording paper having a void layer on a support and a method for producing the same, and more particularly, to a recording paper having improved cracks on a coating film surface and a method for producing the same.

[0002]

2. Description of the Related Art In ink jet recording, fine droplets of ink are caused to fly according to various operating principles and adhere to a recording sheet such as paper to record images and characters. It has advantages such as relatively high speed, low noise, and easy multi-coloring. Improvements in nozzle clogging and maintenance, which have been a problem in this method, have been improving in terms of both ink and equipment, and are now rapidly spreading to various fields such as various printers, facsimile machines, and computer terminals. .

The recording paper used in this ink jet recording system has a high density of print dots, a bright and vivid color tone, and the ink absorbs quickly and causes ink to flow or bleed even when the print dots overlap. It is required that the print dots are not unnecessarily large in the horizontal direction and that the periphery is smooth and not blurred.

[0004] In particular, when the ink absorption speed is low, when ink droplets of two or more colors are printed in an overlapping manner, the droplets cause a repelling phenomenon on the recording paper to become uneven, It is necessary for recording paper to have high ink absorbency, because the colors in the boundary area of each other are blurred and the image quality is easily deteriorated.

[0005] To solve these problems, a great many techniques have been proposed. For example, JP
Japanese Patent Application Laid-Open No. Sho 55-582 describes a low-size base paper described in JP-A-2-53012 in which a paint for surface treatment is wetted.
No. 30, a recording paper provided with an ink-absorbing coating layer on the surface of a support, and a recording paper containing non-colloidal silica powder as a pigment in a coating layer described in JP-A-56-157. Japanese Patent Application Laid-Open No. 57-107873, a recording paper using an inorganic pigment and an organic pigment in combination.
A recording paper having two pore distribution peaks described in JP-A-8-110287, a recording paper having two upper and lower porous layers described in JP-A-62-117882,
Recording papers having irregular cracks described in JP-A-59-68292, JP-A-59-123696 and JP-A-60-18383, etc .;
Recording paper having a fine powder layer described in JP-A-1-148092 and JP-A-62-149475;
252779, JP-A-1-108083, 2-1
Nos. 36279, 3-65376 and 3-2797
No. 6 and other recording papers containing pigments having specific physical properties and fine particle silica.
No. 1, No. 60-219083, No. 60-210984
No. 61-20797, No. 61-188183,
JP-A-5-278324, JP-A-6-92011 and JP-A-6-92011
-183134, 7-137431, 7-27
And recording paper containing fine-particle silica such as colloidal silica described in JP-A-6789.
No. 671, No. 3-67684, No. 3-215082
Nos., 3-251488, 4-67986, and 4
Many recording papers and the like containing alumina hydrate fine particles described in JP-A-263983 and JP-A-5-16517 are known.

[0006] In particular, Japanese Patent Application Laid-Open Nos. 3-56552 and 7-56
The recording paper described in JP-A-137434, in which a void layer composed of inorganic fine particles and a hydrophilic binder is provided as an ink absorbing layer, is preferable as a technique capable of simultaneously achieving high ink absorption and glossiness.

In general, it is necessary for the void layer to contain a large amount of fine particles with respect to the binder in order to form voids. Such a void film is a very rigid and hard film. Although this hard film is necessary to obtain high ink absorbency, it has been found that cracks are easily caused by minute foreign matter at the coating and drying stage of the void layer because the flexibility of the film is small, In particular, it has been found that a serious problem occurs in a thick film having a dry film thickness of the gap layer of 25 μm or more as required for ink jet recording.

When producing a recording paper having such a void layer, relatively coarse particles such as coarse particles themselves, aggregates of the fine particles and aggregates of other additives are variously prepared in the step of preparing the coating solution. These coarse particles were found to cause cracks when coated and dried on a support.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a recording paper having a highly glossy void layer. An object of the present invention is to provide a recording sheet in which cracks on a coating film surface due to coarse particles are extremely improved, and a method for manufacturing the same. Another object of the present invention is to provide a recording sheet which can be manufactured at a low cost, and which has high porosity, high water resistance and high gloss, and a method for manufacturing the same.

[0010]

The above objects of the present invention are as follows. Forming a void layer by coating a coating solution containing particles having a particle size of not less than 10/1 ml having a particle size not less than R (μm) represented by the following formula (1) on a support. Characteristic method of manufacturing recording paper, (1) Formula R = 80000 / L ² L represents the total dry film thickness (μm) of the void layer.

2. The dry thickness of the void layer is 25 to 60 μm.
m, wherein:

3. 3. The method for producing a recording paper according to the above 1 or 2, wherein the coating liquid contains fine particles of 100 nm or less and a hydrophilic binder.

4. The recording paper according to any one of claims 1 to 3, wherein the coating liquid contains an emulsified dispersion of a hydrophobic latex having a glass transition temperature of 30 ° C or lower or a hydrophobic organic compound particle having a melting point of 30 ° C or lower. Production method,

5. The method for producing a recording sheet according to any one of the above items 1 to 4, wherein the support is a non-water-absorbing support,

6. The method for producing a recording sheet according to any one of the above items 1 to 5, wherein the coating liquid is filtered through a filter capable of collecting particles having a particle size of R (μm) or more before applying the coating liquid on a support. ,

[7] The number of particles containing inorganic fine particles having an average particle size of 100 nm or less and a hydrophilic binder and having a particle size not less than the particle size R (μm) represented by the above formula (1) is within 5/1 ml. A coating solution for forming a void layer closest to the support, at least one layer containing inorganic fine particles having an average particle diameter of 100 nm or less and a hydrophilic binder;
A method for producing a recording sheet, characterized by forming a void layer by simultaneously applying a plurality of kinds of coating liquids in a multilayer.

8. The method according to any one of the above items 1 to 7, wherein after applying a coating solution for forming the void layer on a support, the coating solution is once cooled to 15 ° C or less, and then dried by blowing air at 20 to 70 ° C. A method for producing a recording sheet according to any of the above,

9. The particle size R (μ) represented by the above formula (1)
m) the number of particles having a particle size of not less than 10/1
ml of a coating liquid, which is applied to a support, and has a void layer formed thereon.

[0019]

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 which has voids in the layer and absorbs the ink mainly by containing the ink in the voids, rather than swelling the binder forming the absorbing layer.

A wide variety of fine particles can be used in the present invention. Fine particles formed of an organic compound or inorganic fine particles may be used, but inorganic fine particles are preferable for forming a good void. For example, various natural or synthetic inorganic fine particles such as silica, calcium carbonate, titanium oxide, zinc oxide, alumina, barium sulfate, magnesium carbonate, calcium silicate and the like can be used.

The fine particles may be single fine particles or fine particles whose surface is coated with various organic compounds, for example, a cationic polymer.

When the recording sheet is an ink jet recording sheet, silica or alumina is preferably used for forming an ink receiving layer of the ink jet recording sheet which requires relatively high transparency due to its low refractive index.

As the silica, colloidal silica, cation-modified colloidal silica, silica synthesized by a gas phase method, and the like are preferably used. In particular, fine particle silica synthesized by a gas phase method and the surface thereof are coated with a cationic polymer. Thus, cationic composite fine particles are preferable because a high porosity can be easily obtained.

Various fine particles can be used as long as they can form a void layer, but the average particle size must be not more than R. In order to obtain the effect of the present invention, it is preferable to use fine particles having an average particle diameter of 100 nm or less. When fine particles of 100 nm or less are used, high glossiness is easily obtained. The lower limit of the fine particles is not particularly limited, but is preferably 5 nm or more, and particularly preferably the average particle size of the fine particles is 5 to 80 nm.

Among the inorganic fine particles forming the ink receiving layer of the ink jet recording paper, fumed silica having an average primary particle diameter of 100 nm or less, particularly preferably 30 nm or less, is preferred. Here, the average particle size of the fine particles is
The particle itself or the cross section of the void layer is observed with an electron microscope, the particle diameter of 100 arbitrary particles is determined, and the particle diameter is calculated as a simple average value (number average). Here, each particle diameter is obtained as a diameter when a projected area is measured and a circle equal to the area is assumed.

It is preferable to use a binder for the void layer, and a hydrophilic binder is particularly preferable. As the hydrophilic binder to be used, various conventionally known hydrophilic binders are used, but the hydrophilic binder preferably used differs depending on whether the inorganic fine particles are anionic or cationic.

When the surface of the inorganic fine particles is anionic, a nonionic binder or an anionic binder is used. When the surface of the inorganic fine particles is cationic, a nonionic binder or a cationic binder is used. . These may be used in combination of two or more.

Examples of the nonionic binder include gelatin, polyvinyl alcohol, polyethylene oxide,
Polyacrylamide, polyvinylpyrrolidone, hydroxyethylcellulose, dextran and the like can be mentioned.

As the anionic hydrophilic binder,
It is a hydrophilic polymer having an anionic group such as a carboxyl group or a sulfo group, and examples thereof include polyacrylic acid, carboxymethyl cellulose, agar, carrageenan, and dextran sulfate.

Examples of the cationic hydrophilic binder include:
Examples thereof include nonionic water-soluble polymers such as cation-modified polyvinyl alcohol and cation-modified polyvinylpyrrolidone, which are cation-modified, and water-soluble polymers having a quaternary ammonium base. The ratio of the fine particles to the hydrophilic binder is generally in the range of 2 to 10 by weight.

In the coating solution for forming the above-mentioned void layer, coarse particles are likely to be formed due to various causes in the manufacturing process.
Some of these factors are based on coarse particles originally contained in the raw materials, but these can be relatively easily removed during the manufacturing process, but the problem is particularly when adjusting the coating solution. This is a coarse foreign substance newly formed at the stage.

The coarse foreign matter formed in the coating liquid preparation step is large, and the aggregate formed by shock generated when mixing the hydrophilic binder and the inorganic fine particle dispersion or other additives, and the surface of the coating liquid And dried foreign matter.

The former is based on a change in the surface charge of the inorganic fine particles that occurs locally when the inorganic fine particles meet the additive solution,
Alternatively, it is often caused by local change in salt concentration during mixing of additives. On the other hand, the dry foreign matter formed on the surface of the latter coating solution generally gradually dissolves with stirring, but tends to be less soluble as the water resistance of the void layer increases.

When the coating is carried out in a state where the above-mentioned coarse foreign matter is contained as it is, it becomes a nucleus for forming larger particles upon drying, and causes cracks in a hard void layer after drying. Cracking greatly depends on the total dry film thickness, and it was found that when the same coating solution was simply applied by changing the film thickness, cracks were more likely to occur rapidly as the total dry film thickness increased.

Therefore, when it is generally necessary to provide a relatively thick void layer as in ink-jet recording paper, it is particularly necessary to control the content of coarse particles in the coating solution. As a result of intensive studies, the present inventors have found the present invention.

When the total dry film thickness is less than about 20 μm, 10
Even when a coating solution containing coarse particles of 0 μm or more is applied, the foreign matter itself remains on the film surface, and although the film surface may be close to a so-called mat state, the foreign matter may not cause cracks in the nucleus. Since there is not much, the print quality is not significantly reduced.

On the other hand, when the total dry film thickness exceeds 50 μm, coarse particles having a size of about 30 μm or more greatly contribute to cracks. Unless foreign matter having a size larger than this is reduced as much as possible, cracks will occur on the entire surface. Although the crack depends on the size of the foreign matter, the crack has a size of about 0.1 to 2 mm, and when this portion is inkjet-recorded, a white spot occurs and print quality is greatly impaired.

In the present invention, by changing the size of the particle size of the coarse foreign matter in the coating solution to be controlled according to the obtained dry film thickness, it is possible to obtain a good coating surface with few cracks. , Especially 25-60 μm as the total dry film thickness
This is preferably applied when forming a void layer having a dry film thickness between m and m.

As described above, when the total dry film thickness is less than 25 μm, cracks due to coarse particles hardly cause a problem, and when used as ink jet recording paper, a product having a small ink absorption amount is used. It is.
On the other hand, when the total dry film thickness exceeds 60 μm, cracks occur due to very fine particles, and it becomes practically difficult to control such fine particles.

In the present invention, it is necessary that the number of coarse particles having a particle size of not less than R μm represented by the formula (1) is equal to or less than 10 in 1 ml of the coating liquid, but it is further required to be equal to or less than 5 Is more preferable, and it is most preferable that the number is particularly three or less.

The recording paper of the present invention is applied to a recording paper in which at least one void layer is coated on a support. When the gap layer is a single layer, as described above, the particle size Rμ represented by the formula (1) in 1 ml of the coating liquid forming the gap layer is as described above.
The number of coarse particles of m or more may be 10 or less.

When the void layer is composed of two or more layers, it is necessary to control the number of coarse particles as the void layer is closer to the support, and the coating solution for forming the void layer closest to the support is required. It is necessary that the number of the coarse particles having a particle size of R μm or more represented by (1) and contained in 1 ml of the particles be within 5 or less. Particularly preferred is no more than two. The coarse particles can be easily measured using a commercially available particle measuring device based on the principle of laser light scattering, for example.

In order to reduce the number of coarse particles having a size not less than the size specified in the present invention to 10 or 5 or less in the coating solution for forming the void layer, it is necessary to use undissolved foreign substances or undispersed particles previously contained in the raw material. In addition to removing the foreign matter before preparing the coating solution, dilute the additive solution so that the liquid surface is as dry as possible during the preparation of the coating solution or the shock during mixing does not occur. It is, of course, necessary to take measures such as adding the addition time slowly.

However, in addition to the above, in order to remove foreign substances that are inevitably generated in the coating solution, a filter that collects particles having a particle size equal to or larger than the cracks specified in the present invention after preparing the coating solution is used. It is particularly preferred to remove them. One such filter may be used, two or more filters may be used in series, and different filters of different particle sizes that can be repaired may be connected in series.

Although the recording paper of the present invention has high gloss and high porosity, it is preferable that the hydrophilic binder is hardened with a hardener in order to reduce cracking. The hardener is generally a compound having a group that can react with the hydrophilic binder or a compound that promotes a reaction between different groups of the hydrophilic binder, and is appropriately selected depending on the type of the hydrophilic binder. Used selectively.

Specific examples of hardeners include, for example, epoxy hardeners (diglycidyl ethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidyl cyclohexane, N , N-diglycidyl-4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc., aldehyde hardeners (formaldehyde, glyoxal, etc.), active halogen hardeners (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 And aluminum alum.

When polyvinyl alcohol and / or cation-modified polyvinyl alcohol is used as a particularly preferred hydrophilic binder, it is preferable to use a hardening agent selected from boric acid and salts thereof and an epoxy hardening agent.

Most preferred are hardeners selected from boric acid and its salts. In the present invention, 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, diboric acid, metaboric acid, tetraboric acid, pentaboric acid, and octanoic acid And their salts.

The amount of the hardener used varies depending on the type of the hydrophilic binder, the type of the hardener, the type of the inorganic fine particles, the ratio to the hydrophilic binder, and the like. Is 10-3
00 mg.

The above-mentioned 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.

In a particularly preferred embodiment in which the void layer is formed of ultrafine silica and polyvinyl alcohol, a hardening agent is added in advance to the coating solution for forming the void layer, and a predetermined time (preferably 10 minutes) is used. As described above, particularly preferably for 30 minutes or more), coating and drying on the support can achieve a higher porosity without deteriorating the brittleness of the film.

Further, in order to further improve the cracking, the recording paper of the present invention contains oil droplets obtained by emulsifying and dispersing a hydrophobic latex having a glass transition temperature of 30 ° C. or lower or a hydrophobic organic compound having a melting point of 30 ° C. or lower. It is preferred to contain.

The hydrophobic latex having a glass transition temperature of 30 ° C. or lower is a polymer latex polymerized by an emulsion polymerization method, for example, styrene-butadiene copolymer latex, polyacrylate latex, polymethacrylate latex. Latex, vinyl acetate latex, ethylene-vinyl acetate latex, silicon latex, and the like are preferably used.

Examples of the above polymer latex include polyvinyl acetate latex, vinyl acetate / ethylene latex (9/1), vinyl acetate / ethyl methacrylate latex (5/5), and vinyl acetate / acrylic acid-n.
-Butyl ester latex (5/5), vinyl chloride /
Butyl acrylate latex (4/6), butyl acrylate latex, ethyl acrylate / butyl methacrylate / styrene (40/55/5), ethyl acrylate /
Examples thereof include butyl acrylate / HEMA (3/6/1), styrene / butyl acrylate / HEMA (15/80/5), and silicon latex. The molar ratio of the copolymer in parentheses is shown, and HEMA is hydroxyethyl methacrylate.

Any type of latex having an average particle size smaller than R (μm) specified in the present invention can be used, but it is preferably 100 nm or less from the viewpoint of the effect of the present invention.

As the hydrophobic compound forming the oil droplet, an organic compound having a melting point of 30 ° C. or lower and usually called a hydrophobic high-boiling organic solvent is used. Examples of such a hydrophobic organic compound include phthalic esters (eg, dibutyl phthalate, di-2-ethylhexyl phthalate, di-isodecyl phthalate), and phosphates (eg, tricresyl phosphate, trioctyl phosphate, etc.). ), Fatty acid esters (butyl stearate, bis (2-ethylhexyl) sebacate, ethylene glycol distearate, etc.), amides (N, N-diethyllauramide, N, N-diethyl-2- (2,
5-di-t-amylphenoxybutanamide)), ethers (ethylene glycol dibutyl ether, decyl ether, etc.), silicone oil, liquid paraffin, hydrophobicity such as poly-2-ethylhexyl methacrylate, poly-n-butyl methacrylamide And the like.

The above-mentioned hydrophobic compound is generally used by emulsifying and dispersing it in a hydrophilic binder, preferably in the presence of a surfactant, using a high-speed rotation homogenizer or a high-pressure homogenizer. At this time, it is preferable to emulsify and disperse in the presence of a low-boiling organic solvent such as ethyl acetate or propyl acetate from the viewpoint of obtaining finer oil droplets.

At this time, other hydrophobic compounds having a melting point of 30 ° C. or higher (for example, ultraviolet absorbers, antioxidants, fluorescent whitening agents,
Colored oil-soluble dyes for white background adjustment) can be used, but the amount used is preferably 50% by weight or less of the hydrophobic organic compound having a melting point of 30 ° C. or less for forming oil droplets.

The average particle size of the hydrophobic latex and the oil droplets emulsified and dispersed is preferably 5 μm or less, particularly preferably 1 μm or less, most preferably 0.05 to 0.5 μm. The amount of addition is from 0.1 to 20% by weight, preferably from 0.2 to 10% by weight, based on the total amount of the inorganic particles. It can also be a layer.

Various additives other than those described above can be added to the void layer and other optional layers of the ink jet recording paper of the present invention. For example,
Various cationic polymers for immobilizing dyes, various cationic or nonionic surfactants, JP-A-57-7
Nos. 4193, 57-87988 and 62-261
No. 476, JP-A-57-7419.
No. 2, No. 58-87989, No. 60-72785,
Discoloration inhibitors described in JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376, and JP-A-59-42993, JP-A-59-52689, and JP-A-59-52989.
Fluorescent brighteners described in 2-280069, 61-242871 and JP-A-4-219266;
Contains various known additives such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate and other pH adjusters, defoamers, preservatives, thickeners, antistatic agents, matting agents, etc. It can also be done.

The void volume of the recording paper of the present invention is approximately 20 to
60 ml / m ² , preferably 50 ml / m ² or more,
The void ratio of the void layer is approximately 0.5 to 0.8.

As the support for the recording paper in the present invention, a paper support, a plastic support, a composite support, etc., which are conventionally known as ink jet recording paper, can be used as appropriate, but in order to obtain a clear image at a higher density. It is preferable to use a non-absorbent support in which a solvent such as water does not penetrate into the support. Examples of the non-water-absorbing support include a transparent or opaque plastic support and a support in which the surface of paper is coated with a plastic resin.

The transparent support is made of, for example, polyester resin, diacetate resin, triacetate resin, acrylic resin, polycarbonate resin, polyvinyl chloride resin, polyimide resin, cellophane, celluloid and the like. Film and the like.
Those having the property of resisting radiant heat when used as HP are preferable, and polyethylene terephthalate is particularly preferable. The thickness of such a transparent support is about 10 to
200 μm is preferred. It is preferable to provide a known undercoat layer on the ink receiving layer side and the back layer side of the transparent support from the viewpoint of the adhesion between the ink receiving layer and the back layer and the support.

As the support used when it is not necessary to be transparent, for example, resin-coated paper (so-called RC paper) having a polyolefin resin-coated layer obtained by adding a white pigment or the like to at least one of the base paper, polyethylene terephthalate A so-called white pet obtained by adding a white pigment to the ink is preferred.

Prior to the application of the ink-receiving layer, for the purpose of increasing the adhesive strength between the support and the ink-receiving layer,
The support is preferably subjected to a corona discharge treatment, an undercoating treatment, or the like. Further, the recording sheet of the present invention does not necessarily need to be colorless, and may be a colored recording sheet.

In the ink jet recording paper of the present invention, the use of a paper support in which both sides of the base paper support are laminated with polyethylene is particularly preferable since the recorded image is close to the photographic quality and a high quality image can be obtained at low cost. preferable.
Such a paper support laminated with polyethylene is 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, using 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 (sulfate pulp or sulfite pulp) having a small amount of impurities is preferably used, and 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 24 mesh residual weight% defined by JIS-P-8207 and 42 mesh calculated. 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. Base paper weight is 3
The amount is preferably from 0 to 250 g, particularly preferably from 50 to 200 g. The thickness of the base paper is preferably from 40 to 250 μm.

The base paper can be calendered at the papermaking stage or after the papermaking to give high smoothness. The 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 preferably from 20 to 200 g under the conditions specified in JIS-P-8143. A surface sizing agent may be applied to the surface of the base paper. As the surface sizing agent, the same sizing agent as can be added to the base paper can be used. The pH of the base paper is preferably 5 to 9 when measured by the hot water extraction method specified in JIS-P-8113.

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 ink receiving layer side is preferably a layer in which rutile or anatase type titanium oxide is added to polyethylene to improve opacity and whiteness as widely used in photographic printing paper. The content of titanium oxide is about 3 to 20% by weight, preferably
１３13% by weight.

The polyethylene-coated paper may be used as a glossy paper, or may be subjected to a so-called molding process when the polyethylene is melt-extruded and coated on the base paper surface, so that the matte surface or the silk-like surface can be obtained on a normal photographic printing paper. Those having a surface can also be used in the present invention.

The amount of polyethylene used on the front and back sides of the base paper is selected so as to optimize the curl under low quality and high humidity after the ink receiving layer and the back layer are provided. Is in the range of 20 to 40 μm, and the back layer side is in the range of 10 to 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 method of applying various hydrophilic layers, which are appropriately provided as necessary, such as a void layer and an undercoat layer, on the support of the recording paper of the present invention can be appropriately selected from known methods. A preferred method is obtained by applying a coating solution constituting each layer on a support and drying it. In this case, two or more layers can be coated simultaneously, and in particular, simultaneous coating 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.

In general, drying after coating the coating solution for forming the void layer on the support is usually performed with hot air drying. In the present invention, the coating solution is cooled to 15 ° C. or less once, particularly after coating. It is preferred that the film be dried quickly by blowing air at 20 to 70 ° C., since liquid is less likely to be generated on the film surface and cracks are less likely to occur.

When hot air or hot air is directly blown without cooling, the viscosity of the coating solution becomes too low, and the sprayed wind tends to cause a local rise in the solution, and cracks occur in portions where the solution becomes excessively thick. Becomes noticeable.

For coating, usually 30 to 50 ° C.
In this case, the viscosity is 5 to 100 c.
By increasing the viscosity of the liquid by cooling the coating film temperature to 15 ° C. or less, the liquid is prevented from being liquid and cracking is suppressed.

After being cooled, even if hot air or hot air is blown, the film temperature does not evaporate so much due to the latent heat of moisture evaporation, so that the liquid can be prevented from being discharged. Drying temperature after cooling is 20-7
It is dried by blowing air at 0 ° C. for preferably 2 to 5 minutes. The wind for drying is preferably blown with a wind from which foreign substances have been removed as much as possible through a filter of an appropriate size so as not to cause cracks on the coating film surface.

When the recording paper of the present invention is used for ink jet recording, when recording an image using the ink jet recording paper, a recording method using an aqueous ink is preferably used. The aqueous ink is a recording liquid including the following colorant, liquid medium, and other additives. As the colorant, a water-soluble dye or a water-dispersible pigment such as a direct dye, an acid dye, a basic dye, a reactive dye, or a food colorant known by inkjet can be used.

Examples of the solvent for the aqueous ink include water and various water-soluble organic solvents, for example, alcohols such as methyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol and isobutyl alcohol; dimethylformamide, dimethylacetamide and the like. Amides; ketones or ketone alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol;
Polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, glycerin, triethanolamine; ethylene glycol methyl ether, diethylene glycol And lower alkyl ethers of polyhydric alcohols such as methyl (or ethyl) ether and triethylene glycol monobutyl ether.

Among these many water-soluble organic solvents,
Preferred are polyhydric alcohols such as diethylene glycol, triethanolamine and glycerin, and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monobutyl ether.

Other additives for the aqueous ink include, for example, a pH adjuster, a metal sequestering agent, a fungicide, a viscosity adjuster,
Surface tension adjusters, wetting agents, surfactants, rust inhibitors, and the like. The aqueous ink liquid is 25 to 60 dy at 20 ° C. in order to improve the wettability on the recording paper.
It preferably has a surface tension in the range of n / cm, preferably 30 to 50 dyn / cm.

[0085]

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 in advance uniformly had an average particle diameter 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 = 2.5, containing 1% by weight of ethanol) was prepared by adding 12% 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)
100 liters were added with stirring at room temperature.

Next, 4 l of a 5% boric acid aqueous solution was gradually added with stirring. Then, the mixture was dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd. at a pressure of 500 kg / cm ² to obtain a uniform and almost transparent dispersion B1. This dispersion is 3
Filtration was performed using a TCP-30 type filter manufactured by Advantex Toyo having a filtration accuracy of 0 μm.

Next, using the above-mentioned dispersion liquid B1, additives were sequentially mixed as follows to prepare a coating liquid (CS1) (a liquid preparation amount was adjusted to 50 liters, Shows the value per liter).

Silica Dispersion B1 620 ml Polyvinyl alcohol (Kuraray PVA203) 10% aqueous solution 5 ml Polyvinyl alcohol (Kuraray PVA235) 5% aqueous solution 265 ml Silicon dispersion (Toray Dow Corning Silicone, BY-22-83) 9) 30 ml latex dispersion (manufactured by Dainippon Ink and Chemicals, Inc., Boncoat SFC-55 (Tg = 0 ° C.)) 20 ml pure water (finish the whole amount to 1000 ml) The silicon dispersion was removed from the above. Except for C
A coating solution CS2 was prepared in the same manner as in S1.

A coating solution CS3 was prepared in the same manner as CS2 except that the hydrophobic latex was further removed from the coating solution CS2.

The hydrophobic latex 2 of the coating solution CS2
Liquid paraffin (liquid state at 20 ° C.) dispersion 2 prepared as follows as a hydrophobic organic compound instead of 0 ml
Coating solution CS in the same manner as CS2 except that 0 ml was added.
4 was adjusted.

(Preparation of Liquid Paraffin Dispersion) A solution prepared by dissolving 10 g of liquid paraffin in 15 ml of ethyl acetate was prepared.
Mix, emulsify, and disperse with 60 ml of water containing 1.8 g of acid-treated gelatin and 1.1 g of saponin.
ml.

Each of the obtained coating liquids was filtered using a filter TCW type manufactured by Advantex Toyo Co., Ltd. (three kinds of pore diameters shown in Table 1 were used), and the coating liquid for single-layer inkjet recording paper was used. I got

The obtained coating solution was diluted 5-fold with pure water, and the resulting coating solution was diluted to 19 μm using No. Sangyo's Hiac / Leuco Intelligent Particle Counter 8000A.
As described above, the number of particles having a particle size of 32 μm or more, 65 μm or more, and 200 μm or more was examined, and the results were converted into the number per 1 ml of the coating solution and shown in Table 1.

[0095]

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[0096]

[Table 1] CS1: Latex = Yes, Silicon = Yes CS2: Latex = Yes, Silicon = No CS3: Latex = No, Silicon = No CS4: mp 30 ° C. or less Hydrophobic organic compound particles = Yes,
Silicon = nothing

Next, the wet thickness of each coating solution was changed to obtain a dry film thickness of 20 μm, 35 μm, 50 μm, and 65 μm, respectively.
m was applied to a support having the following thickness of 240 μm. Support: 170 g / m ² base paper coated on both sides with polyethylene. On the recording surface side of the base paper, a polyethylene layer having a thickness of about 35 μm contains 9% by weight of anatase type titanium dioxide, and the back side of the base paper is coated with a polyethylene layer having a thickness of about 30 μm. Gelatin was applied as a subbing layer on the front and back polyethylene layers at 0.1 g / 1 m ² . The 75 ° glossiness of the support on the recording surface side is 32%, and the glossiness of the back surface is 23%.

Each coating solution was applied by a slide hopper at 40 ° C., and immediately after coating, the coating solution was cooled in a cooling zone maintained at 0 ° C. for 20 seconds to lower the coating temperature to 10 ° C. or lower. Drying was sequentially performed with a wind of ３０30 ° C. for 60 seconds, a wind of 45 ° C. for 60 seconds, and a wind of 50 ° C. for 60 seconds.

The state of cracking of the obtained sample was visually observed and observed with a loupe, and the number of cracks per 0.3 m ^{2 of the} coating film surface was examined. Table 2 shows the results.

The particle sizes related to cracks obtained according to the formula (1) of the present invention at each dry film thickness are as follows. Dry film thickness Particle size (R) 20 μm 200 μm 35 μm 65 μm 50 μm 32 μm 65 μm 19 μm

[0101]

[Table 2]

There is no practical problem if the number of cracks is within about 10 per 0.5 m ² . Table 1,
From the results shown in Table 2 and Table 2, when coating was performed so that the dry film thickness was 20 μm, R ≧ 20 contained in 1 ml of the coating liquid was obtained.
It can be seen that all of the particles having a particle size of 0 μm are 10 or less, and a good film surface can be obtained.

From the results in Tables 1 and 2, the dry film thickness = 35
50 μm or 25 μm when applying to be μm
Coating solution @ CS1 (c) (d)
CS2 (c) (d)｝ is R ≧ 65μ in 1 ml of coating solution
Since the number of particles of m is 10 or less, the number of cracks on the coating surface
Is 10 or less, and a good film surface is obtained. Note that R ≧
Coating solution with 65 μm particles exceeding 10 particles / ml ｛C
Using S1 (a) (b) and CS2 (a) (b)},
In any case, 11 or more / 0.5m on the film surface ^TwoCracks
Alive.

In the samples coated so that the dry film thickness became 50 μm and 65 μm, R ≧ 32 μm,
In any case where the number of particles of R ≧ 19 μm is 10
The number of cracks has increased in all samples.

When the coating solution CS4 containing the hydrophobic organic compound particles according to the present invention was used, the number of cracks was smaller than when the coating solution CS3 containing no hydrophobic organic compound particles was used.
Coating solution CS2 containing hydrophobic latex according to the present invention
When is used, cracking is further reduced, and a very good film surface tends to be easily obtained.

Example 2 The coating solution CS2 used in Example 1 (b), (c),
(D) Using｝, the solution filtered in Example 1 was further 25 μm
｛(B) ', (c)'
(D) The same evaluation as in Example 1 was performed using '｝.
Table 3 shows the number of particles in the coating solution.

[0107]

[Table 3]

Next, in the same manner as in Example 1, it was coated on a support to obtain a recording sheet. The film surface of the recording paper was examined, and the results shown in Table 4 were obtained.

[0109]

[Table 4]

From the results in Tables 3 and 4, it was found that the dry film thickness was 20%.
μm and 35 μm, the corresponding R (200 μm, 65 μm, respectively)
m) The number of coarse particles having a particle diameter of not less than 0 is 1 in 1 ml of the coating solution, and there is no crack on the film surface.

When the coating is performed so that the dry film thickness becomes 50 μm, the number of the corresponding coarse particles of R ≧ 32 μm becomes 10 or less in 1 ml of the coating liquids (c) ′ and (d) ′, and If the number of cracks is 10 or less, the quality becomes acceptable. When the coating liquid (b) ′ is used, the number of coarse particles exceeds 10 in 1 ml of the coating liquid, and the number of cracks increases rapidly.

Example 3 In the silica dispersion B1 prepared in Example 1, the silica was changed to an average particle diameter of primary particles manufactured by Nippon Aerosil Co., Ltd. of 0.00
1: 1 of fumed silica A300 and A200 having a diameter of 7 μm
A silica dispersion B2 was prepared in the same manner as in Example 1 except that the mixture was changed to a mixture of the above.

Next, the following four kinds of coating liquids were prepared to prepare a multilayer ink jet recording paper.

Preparation of Coating Solution for First Layer (Amount per 1 L of Coating Solution) Silica Dispersion B2 650 ml Fluorescent Brightener Dispersion (described below) 30 ml Polyvinyl Alcohol (PVA203 manufactured by Kuraray Co., Ltd.) 10% aqueous solution 5 ml Polyvinyl alcohol ( 5% aqueous solution of Kuraray Co., Ltd.) 270 ml Latex dispersion (Boncoat SFC-55 (Tg = 0 ° C., manufactured by Dainippon Ink and Chemicals, Inc.)) 20 ml Pure water (total volume of 1000 ml)

Coating solution for second layer (amount per liter of coating solution) Silica dispersion B2 650 ml Fluorescent whitening agent dispersion (described below) 30 ml Polyvinyl alcohol (PVA203 manufactured by Kuraray Co., Ltd.) 10% aqueous solution 5 ml Polyvinyl alcohol (Kuraray Co., Ltd.) PVA 235) 5% aqueous solution 270 ml Latex dispersion (Boncoat SFC-55 (Tg = 0 ° C), manufactured by Dainippon Ink and Chemicals, Inc.) 20 ml Pure water (total volume 1000 ml)

Coating solution for third layer (amount per liter of coating solution) Silica dispersion B2 620 ml Fluorescent whitening agent dispersion (described below) 20 ml Polyvinyl alcohol (PVA203 manufactured by Kuraray Co., Ltd.) 10% aqueous solution 5 ml Polyvinyl alcohol (Kuraray Co., Ltd.) PVA 235) 5% aqueous solution 270 ml Latex dispersion (Boncoat SFC-55 (Tg = 0 ° C., manufactured by Dainippon Ink and Chemicals, Inc.)) 10 ml Pure water (total volume 1000 ml)

Coating liquid for fourth layer (amount per liter of coating liquid) Silica dispersion B1 600 ml 10% aqueous solution of polyvinyl alcohol (PVA203 manufactured by Kuraray) 5 ml 5% aqueous solution of polyvinyl alcohol (PVA235 manufactured by Kuraray) 270 ml Surfactant (Saponin) 10% aqueous solution 10 ml Cationic surfactant (S-1) 5% aqueous solution 10 ml Silicon dispersion (BY-22-839, manufactured by Dow Corning Toray Silicone Co., Ltd.) 20 ml Pure water (total volume 1000 ml) )

Fluorescent Whitening Agent Dispersion: An oil-soluble fluorescent whitening agent (UVITEX-OB manufactured by Ciba-Geigy Co., Ltd.) was added to 100 ml of a 3% aqueous solution of acid-treated gelatin (containing 4 g of saponin and 2 g of cationic polymer P-9). ) A solution prepared by heating and dissolving 0.6 g and 12 g of diisodecyl phthalate in 25 ml of ethyl acetate was added, and emulsified and dispersed by an ultrasonic homogenizer.
Make up to 140ml with pure water.

[0119]

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The viscosity of each of the above coating solutions is 30 to 40 ° C.
The viscosity was 10,000 to 20,000 at 40 cp and 15 ° C.

The coating solution obtained as described above was applied on the support used in Example 1 to a total dry film thickness of 20 μm.
m, 35 μm, 50 μm, and 65 μm (the first layer to the fourth layer were coated so that the dry film thicknesses were equal to each other) using the same coating apparatus as in Example 1 and four layers were simultaneously coated under the same drying conditions. did.

Prior to coating, of each coating solution,
The coating liquids of the second to fourth layers have a pore size of 2 used in Example 1.
After filtration twice with a 5 μm filter, filtration was performed once with a 10 μm filter.

On the other hand, the coating solution of the first layer was filtered as shown in Table 5 below. Table 5 shows the maximum number of particles in the coating liquids of the first to fourth layers.

[0124]

[Table 5]

The obtained recording paper was examined for cracks, and the results shown in Table 6 were obtained.

[0126]

[Table 6]

In the case of the recording paper using (e) which is not filtered, even if the dry film thickness is 20 μm, the coating liquid of the first layer is not more than 1 μm.
The number of particles of R ≧ 200 μm contained in the ml was 6, and 14 cracks occurred on the film surface.

When the coating liquid (f) was used, when the dry film thickness was 20 μm or 35 μm, the corresponding R μm
The number of coarse particles (above 200 μm and above 65 μm, respectively) is 5 or less, and cracks on the coated surface are within an allowable range. However, when the dry film thickness is 50 μm and 65 μm, the number of corresponding coarse particles of R μm or more exceeds 5, and
Cracks on the film surface are also outside the allowable range.

When the coating solution (g) was used, the number of coarse particles having a size of R μm or more corresponding to the case of coating with a dry film thickness of 20 μm, 35 μm, and 50 μm was 5 or less,
A good film surface is obtained.

[0130]

According to the present invention, even when a relatively thick void layer is coated on a support, the occurrence of cracking is suppressed, and a recording paper having a good coated film surface can be obtained.

Claims (9)

[Claims] 1. A coating layer comprising a coating liquid containing particles having a particle size of not less than 10/1 ml represented by the following formula (1) and having a particle size of R (μm) or more: Forming a recording paper. (1) Formula R = 80000 / L ² L represents the total dry film thickness (μm) of the void layer. 2. The method according to claim 1, wherein the dry thickness of the gap layer is 25 to 60 μm. 3. The coating liquid according to claim 1, wherein the coating liquid contains fine particles of 100 nm or less and a hydrophilic binder.
Or the method for producing a recording sheet according to 2. 4. The coating liquid according to claim 1, wherein the coating liquid contains a hydrophobic latex having a glass transition temperature of 30 ° C. or lower or an emulsified dispersion of hydrophobic organic compound particles having a melting point of 30 ° C. or lower. 3. The method for producing a recording sheet according to item 1. 5. The method according to claim 1, wherein said support is a non-water-absorbing support. 6. The method according to claim 1, wherein before coating the coating solution on a support, the coating solution is filtered through a filter capable of collecting the particles having a particle size of R (μm) or more. Manufacturing method of recording paper. 7. The content of inorganic fine particles having an average particle diameter of 100 nm or less, a hydrophilic binder, and having a particle diameter of not less than R (μm) represented by the following formula (1) is 5: The coating liquid for forming a void layer closest to the support, which is within 1 ml, is coated with at least one coating liquid containing inorganic fine particles having an average particle diameter of 100 nm or less and a hydrophilic binder in a multilayer simultaneous application. A method for producing a recording sheet, comprising forming a layer. (1) Formula R = 80000 / L ² L represents the total dry film thickness (μm) of the void layer. 8. After applying a coating solution for forming the void layer on a support, the coating solution is once cooled to 15 ° C. or lower, and then cooled.
The method according to any one of claims 1 to 7, wherein the recording paper is dried by blowing air at 0 to 70C. 9. A coating solution comprising particles having a particle diameter of not less than 10/1 ml represented by the following formula (1) and having a particle diameter of R (μm) or more is formed on a support. Recording paper, characterized in that the recording paper has a formed void layer. (1) Formula R = 80000 / L ² L represents the total dry film thickness (μm) of the void layer.