JP2001080208A - Ink jet recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a decrease in a concentration in the cases of double-sided printing by an ink jet and to improve striking through by incorporating cationic compounds in ink absorption layers on both surfaces of a support having an opacity specified according to JIS P 8138 of a specific numeric value or more. SOLUTION: Opacity specified according to JIS P 8138 in a support of the ink jet recording sheet is set to 94% or more, and it is particularly best to set the opacity to 96 to 100%. If the opacity is less than 94%, an image of one side is easily seen through from an opposite surface. As the support having the opacity of 94% or more, a white plastic film, a cloth or the like can be used, and the opacity of 94% or more is performed by increasing a basis weight of paper or adding a white pigment into the paper. As the compound to be contained in the layers provided on both the surfaces of the support, a cationic polymer is used to prevent bleeding of an image or its diffusion in a direction of the support.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording sheet, and more particularly to a double-sided ink jet recording sheet capable of printing high-quality characters and color images on both sides.

[0002]

2. Description of the Related Art With the remarkable technological innovation of ink jet recording in recent years, the print quality is becoming comparable to the print obtained by silver halide photography.

[0003] With the spread of ink jet printers and digital cameras, various color prints have recently been printed by ink jet printers, and the uses of the prints have also become diversified.

[0004] One such application is ink jet recording paper that can print on both sides. Recording paper that can be printed on both sides can be used not only to save resources by reducing the number of sheets, but also to create new color prints in the form of booklets, such as photo albums, and to create postcards and various cards. Suitable to do.

Heretofore, there have been some proposals as recording paper having an ink jet recording layer on both sides of the recording paper.

JP-A-56-148584 discloses that a coating liquid containing porous inorganic pigment particles is prevented from penetrating to the opposite side by a recording paper provided on both sides of a substrate to prevent the ink from penetrating to the opposite side. A method of prevention is described.

Japanese Patent Application Laid-Open No. 2-270588 discloses an ink-jet recording sheet which is excellent in paper quality and does not strike through, in which an ink-absorbing layer is formed on both sides of a paper base to make the ink-absorbing layer thinner to prevent the absorbing layer from peeling off. Is described.

Japanese Patent Application Laid-Open No. 8-174996 discloses a method in which an ink absorbing layer mainly composed of an inorganic pigment and a binder is provided on one surface of a paper base material, and the other surface is impregnated or coated with a cationic substance. A clear image can be recorded on the surface by ink jet recording, and writing can be performed on the opposite surface by ink jet recording or other writing, and an ink jet recording paper on which the ink does not exude on the opposite side can be obtained. This recording paper is mainly used for postcards and cards.

Japanese Patent Application Laid-Open No. 9-286166 describes an ink jet recording sheet in which ink absorbing layers having different dot diameters are provided on both sides of a substrate when ink droplets adhere to the front and back sides. As a result, even when printing on both sides is performed under different printing conditions, it is possible to obtain an ink jet recording paper in which curling or strikethrough does not occur.

The present inventor has studied ink jet recording paper which can print high-quality images on both sides obtained by the methods described in the above publications. As a result, even if the dye fixing property of the ink absorbing layers on the front and back sides is improved. It has been found that so-called strike-through, in which an image recorded on one side is seen through to the other side, is not necessarily sufficiently suppressed.

This strikethrough is likely to occur when a black image (characters or images) is printed on one side and the other side is not printed or printed at a low density.

[0012] Recording is performed using a pigment ink, and an ink is used in which colored pigment particles are substantially fixed on the surface layer of the ink absorbing layer and most of the pigment ink does not penetrate into the ink absorbing layer. Even so, prevention of strikethrough is insufficient.

[0013] By adding an inorganic pigment having a large particle diameter to the ink absorbing layer or by increasing the opacity of the ink absorbing layer by using an inorganic pigment having a high refractive index, this strikethrough can be slightly improved, but ink jet printing is not possible. The decrease in density when printed is large, and it is not possible to sufficiently suppress strikethrough while maintaining good print quality by simply increasing the dye fixing ability of the ink absorbing layer or increasing the opacity of the ink absorbing layer. Was.

The present inventor has studied this point,
The present inventors have found that by improving both the support and the ink absorbing layer, strike-through can be improved without lowering the density printed by ink jet.

[0015]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ink jet recording paper which has a small density reduction when printed on both sides by ink jetting, and in which an image printed on one side is difficult to see through to the other side. To provide.

[0016]

The above object of the present invention is achieved by the following constitution.

(1) An ink jet recording paper comprising an ink absorbing layer containing a cationic compound on both sides of a support having an opacity of 94% or more specified in JIS P 8138.

(2) According to the water absorption test method specified in JIS P 8140, the contact time is 10 seconds, and the Cobb water absorption measured using pure water containing 30% by mass of diethylene glycol is 10 g or less per 1 m ^2. hand,
And the opacity specified in JIS P 8138 is 94
% Of an ink-absorbing layer containing a cationic compound on both sides of a support having a percentage of at least 1%.

(3) The ink jet recording paper as described in (1) or (2) above, wherein the support is a hydrophobic support.

(4) The support is a support in which both sides of a paper substrate are coated with a polyolefin resin, and at least one of the polyolefin resin layers contains a white pigment. 4. The ink jet recording paper according to any one of the items 3.

(5) Each of the above (1), wherein each of the front and back ink absorbing layers has at least one porous layer.
The inkjet recording paper according to any one of Items 1 to 4, wherein

(6) The dot diameters obtained when the ink droplets adhere to the front and back ink absorbing layers are denoted by D1 and D1, respectively.
The ink-jet recording sheet according to any one of the above items 1 to 5, wherein D1 / D2 = 0.90 to 1.1 when 2.

(7) JIS P 8 containing white pigment
138. An ink jet recording paper comprising an ink absorbing layer containing a cationic compound on both sides of a plastic film support having an opacity of 94% or more specified in 138.

(8) A support in which a polyolefin resin containing a white pigment is coated on both sides of a paper base material having a basis weight of 100 to 250 g / m ² , and the opacity specified in JIS P 8138 is 94% or more. An ink jet recording paper comprising an ink absorbing layer containing a cationic compound on both surfaces of a support as described above.

(9) The ink jet recording paper as described in any one of (1) to (8) above, wherein the cationic compound is a compound having a quaternary ammonium base.

Hereinafter, the present invention will be described in detail. The support of the ink jet recording paper of the present invention is JIS P81
It is necessary that the support has an opacity specified in No. 38 of 94% or more.

When the opacity is less than 94%, the image on one side is easily seen through when viewed from the opposite side. Preferably, the opacity of the support is 95% or more, particularly preferably 96% or more and 100% or less.

As a support having an opacity of 94% or more, paper, a white plastic film, cloth, a paper support having both sides or one side of paper coated with a plastic resin, or the like can be used.

The opacity of 94% or more using a paper support can be achieved by increasing the basis weight of the paper or adding a white pigment to the paper. The basis weight of the paper varies depending on the presence or absence of the white pigment is generally 1 m ² per
The range is from 00 to 300 g. When a white pigment is not used, the weight is usually 150 to 300 g, preferably 200 to 300 g.
３００300 g, particularly preferably 220-300 g.

When a white pigment is used, the amount is generally 100 to 250 g, preferably 150 to 200 g, although it greatly varies depending on the amount used.

Examples of the white pigment used in the paper include titanium oxide, barium sulfate, zinc oxide, silica, calcium carbonate and the like.

When a white plastic film is used, a white pigment is added to the film resin to make the opacity 9
It needs to be 4% or more.

Examples of the white pigment include titanium oxide and barium sulfate. In this case, the white pigment itself is used for providing concealing properties, and the white pigment is stretched in the process of forming a film using the white pigment as a core. There are two methods of forming bubbles in the film and providing concealment by scattering by the bubbles.

As the plastic film, polyolefin resins (polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, cellulose triacetate and the like are preferably used. The thickness of these plastic films is approximately 120 to 300 μm, preferably 1 to 300 μm.
It is 50 to 250 μm.

The amount of the white pigment varies widely depending on its particle size and type, but is generally 1 to 50% by mass, preferably 5 to 30% by mass, based on the plastic resin.

The plastic resin film may be a laminate of two or more films, in which case the types may be the same or different.

The support having one or both sides of the paper coated with a plastic resin has a basis weight of 100 to 250 g, preferably 120 to 22 g, in order to make the opacity 94% or more.
A support in which one or both sides of a paper support of 0 g are coated with a plastic resin is used.

As the plastic resin, those used for the above-mentioned plastic film support can be used, but polyolefin resins are preferable because they can be easily produced on a paper support by a melt extrusion method. Is most preferred. Particularly preferred thickness of the resin layer coated with polyethylene is usually 5 to 60 μm, preferably 10 to 50 μm. In this case, the thickness of the front and back polyethylene layers may be the same or different.

In addition to the above, a hydrophobic resin dispersion may be applied on paper to form a hydrophobic film.
Examples of such a hydrophobic resin dispersion include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, acrylamide, styrene, and hydroxyl ethyl. It can be obtained by emulsion polymerization of a single copolymerizable monomer such as methacrylate, vinyl chloride, vinyl ether, ethylene, styrene, divinylbenzene, vinyl acetate, butadiene, or two or more monomers.

In this case, the thickness of the plastic resin is generally 2 to 40 μm, preferably 3 to 20 μm.

In order to increase the opacity to 94% or more, it is preferable to include the above-mentioned white pigment in either paper or plastic resin. Particularly preferred is a case where a white pigment is contained in a plastic resin.

According to the first aspect of the present invention, strike-through is sufficiently suppressed immediately after recording by ink jet. However, when this print is stored for a long time, particularly under high humidity, when a support having sufficient water absorption such as a paper support is used, the dye penetrates into the support and strikethrough occurs. May be noticeable. In order to improve this, it has been found that recording paper using a support having relatively low water absorption is preferable.

Therefore, when the present invention as defined in claims 1 and 2 is used, that is, when a support having a water absorbency of not more than a specific water absorbency is used instead of a normal paper support having a high water absorbability, ink jet recording is performed. Immediately after the print-through, not only the print-through is sufficiently suppressed, but also when the print is stored for a long time, particularly under high humidity, the print-through is less noticeable because the dye penetrates into the support only to a small extent. It is preferable from the viewpoint of. Further, from the same viewpoint, when the support according to the present invention described in claim 2, that is, the non-water-absorbing support is used, penetration of the dye into the support can be prevented, so that strikethrough is further suppressed. Is preferred.

As another effect, claim 1
Ink-jet recording paper using the support according to the present invention described in 2 and 2, after ink-jet recording on one side (front side) and then ink-jet recording on the other side (back side), the front side, of course, It was also found that a high-quality print image with suppressed line unevenness was obtained. Although the reason for this is not clear, the present inventors presume as follows.

Ink-jet recording paper using a normal water-absorbing paper support has the advantage that the support absorbs ink.
Cockling easily occurs when printed on one side.
Having a specific water absorption as described in claims 1 and 2,
Ink-jet recording paper using a support that is relatively hard to absorb water suppresses cockling at the time of printing on one side, so that even when ink-jet printing is to be performed on the back side, the recording paper Since the distance between the printer head and the printer head can be kept constant, uniform printing can be performed and the occurrence of stripe unevenness is suppressed.

From the viewpoints described above, a support having a Cobb water absorption of 5 g / m ² or less is more preferable, and a recording paper using a support having a Cob water absorption of 0 g / m ² is most preferable.

Therefore, according to the recording paper using the non-water-absorbing support according to the second aspect, the occurrence of stripe unevenness is suppressed, and cockling does not occur even after double-sided printing, so that a high-quality print is obtained. It is more preferable from the viewpoint that an image can be obtained.

When a paper support is used, strike-through is sufficiently suppressed immediately after recording by ink jet because the support is water-absorbing.
In particular, when stored under high humidity, the dye penetrates into the support and strikethrough becomes more noticeable. From this viewpoint, the support is preferably a hydrophobic support that does not allow the dye to penetrate.

A preferred hydrophobic support is a support in which both surfaces of a plastic film or paper are coated with a plastic resin, and a paper support in which both surfaces of paper are coated with a polyolefin resin is particularly preferred.

It is preferable that at least one layer of the polyolefin resin contains titanium oxide in order to impart opacity and high whiteness.

Hereinafter, a support in which both surfaces of paper are coated with a polyolefin resin which is particularly preferably used will be described.

The basis weight of the paper is 100 to 250 g /
m ² , particularly preferably 120 to 220 g / m ² .

When the basis weight is 100 g / m ² or more, it is sufficient to make the concentration of the white pigment in the polyolefin resin layer not so high or to make the polyolefin resin layer containing the white pigment not too thick. This is preferable in that a high opacity can be obtained.

When the grammage is 250 g / m ² or less, the rigidity of the support is appropriate, which is preferable from the viewpoint of printer transportability.

The paper is made from 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. LB as wood pulp
KP, LBSP, NBKP, NBSP, LDP, ND
Any of P, LUKP and NUKP can be used.

As the pulp, a chemical pulp containing a small amount of impurities (sulfate pulp or sulfite pulp) is preferably used, and pulp having improved whiteness by a bleaching treatment is also useful.

In the paper, sizing agents such as higher fatty acids and alkyl ketene dimers, white pigments such as calcium carbonate, talc and titanium oxide, starch, polyacrylamide,
Paper strength enhancers such as 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 paper may be used as it is, or it may be calendered after paper making to give high smoothness. Paper density is 0.7 to 1.2 g / m
² (JIS P 8118) is common. Further, the stiffness of the base paper is preferably 20 to 400 g under the conditions specified in JIS P 8143.

A surface sizing agent may be applied to the paper surface. As the surface sizing agent, the same sizing agents as those which can be added to the base paper can be used.

The pH of the paper is preferably 4 to 9 when measured by the hot water extraction method specified in JIS P 8113.

As the polyolefin for coating the paper, polyolefins such as polyethylene, polypropylene, polyisobutylene, copolymers mainly composed of ethylene and propylene are preferable, and polyethylene is most preferable.

The polyethylene is mainly low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE), but other LLDPE, polypropylene and the like can be partially used.

Various additives can be contained in the polyolefin resin layer covering the paper. It is particularly preferable to contain a white pigment for the purpose of obtaining higher opacity.

Examples of the white pigment include titanium oxide, barium sulfate, zinc oxide, calcium carbonate and the like, and titanium oxide is particularly preferable. As the titanium oxide, rutile-type or anatase-type titanium oxide can be used, and the content thereof is 1 to 50% by mass, preferably 2 to 30% by mass based on the polyolefin resin.

The above white pigment can be added to only one or both of the polyolefin resin layers on the front and back of the paper. However, since the higher opacity can be achieved and the sharpness of the image can be improved, the front and back polyolefin resins can be added. It is preferably added to both layers.

In addition to the above, a color pigment having high heat resistance and a fluorescent whitening agent for adjusting the white background can be added to the polyolefin resin layer.

Examples of coloring pigments include ultramarine blue, navy blue, cobalt blue, phthalocyanine blue, manganese blue, cerulean, tungsten blue, molybdenum blue, and anthraquinone blue.

Examples of the fluorescent whitening agent include dialkylaminocoumarin, bisdimethylaminostilbene, bismethylaminostilbene, 4-alkoxy-1,8-naphthalenedicarboxylic acid-N-alkylimide, bisbenzoxazolylethylene, dialkylstilbene And the like.

The support used for the recording paper of the present invention is
Its tensile strength is the strength specified in JIS P 8113, 2 to 30 kg in the vertical direction and 1 to 20 k in the horizontal direction.
g, tear strength is 10 to 200 g in the vertical direction and 20 to 20 in the horizontal direction according to the method specified in JIS P 8116.
0 g, L ^* , whiteness is defined by JIS Z 8729,
a ^* and b ^* are L ^* = 80 to 95, a ^* = − 3 to +5, b ^*
= -6 + 2, Clark stiffness those is preferably 50~300cm ^3/100 in the transport direction of the recording paper.

The support may be a surface having high smoothness or a surface having fine particles formed thereon. When the smoothness is high, the ink jet recording paper is obtained as glossy paper. In the case where it has a fine grain surface, it can be obtained as an ink jet recording paper having a fine grain surface.

When a polyolefin resin layer is provided on the front and back of the paper, the thickness, composition and surface quality of the front and back may be the same or different, but when used for an album print or the like, the surface quality is the same as much as possible. Is more preferable.

On the other hand, when applied to postcards and the like, it is not always necessary to have the same surface quality, and a glossy surface, a fine grain surface, a matte surface, and other surface qualities can be appropriately combined.

In order to obtain a glossy surface, the glossiness of the surface of the polyolefin resin layer (specular glossiness at 60 degrees specified in JIS Z8741) is preferably 20 to 90%. Also,
When used as fine-grain surface inkjet recording paper,
The center line average roughness (Ra) of the polyolefin resin surface measured at a standard length of 2.5 mm and a cutoff value of 0.8 mm specified in JIS B 0601 is 0.8 to 4.0.
μm, and preferably has irregularities such that the 60-degree specular glossiness according to JISZ8741 satisfies 10 to 40%. To obtain a matte surface, the 60-degree specular gloss of the polyolefin resin surface is generally 2 to 10%.

To make such a polyolefin resin layer glossy or to form fine-grained irregularities, the paper is coated with a polyolefin resin and then the surface is pressed against a glossy surface roller or a molding roller to form fine irregularities. This is performed by patterning.

The patterning method includes a method of performing an embossing calender treatment at around room temperature and a method of forming irregularities while cooling using a cooling roll having a pattern engraved on the roll surface immediately after melt extrusion. However, the latter is preferred because it can be molded with a relatively low pressure and can produce a more accurate and uniform molding.

Next, the ink absorbing layers provided on both surfaces of the support will be described. The front and back ink absorption layers contain a cationic compound.

When prints recorded by ink jetting on both sides are superimposed and stored, if printed on the front and back at the superimposed portion, the residual solvent in that portion increases, blurring of the image is enlarged, and printing is performed on one side. It is necessary to further increase the resistance to image dye bleeding.

Examples of the cationic compound used in the present invention include a cationic polymer, a silane coupling agent having a quaternary ammonium salt group, and an inorganic pigment having a cationic surface. Are cationic polymers. By using these cationic compounds, it is possible to prevent bleeding of the image in the ink absorbing layer and diffusion in the direction of the support, and suppress strike-through.

The cationic polymer may be appropriately selected from those conventionally known in ink jet recording paper, and is preferably a cationic polymer having a tertiary amino group or a quaternary ammonium group. , Polyethyleneimine, polyallylamine, dicyandiamide polyalkylenepolyamine, condensate of dialkylamine and epichlorohydrin, polyvinylamine,
Polyvinyl pyridine, polyvinyl imidazole, a condensate of diallyl dimethyl ammonium salt, a quaternized polyacrylate, and the like are included. Particularly preferred are cationic polymers having quaternary ammonium bases. As the polymer having a quaternary ammonium group, a homopolymer of a monomer having a quaternary ammonium group or a copolymer with one or more other copolymerizable monomers is particularly preferable. It has a molecular weight of 2,000 to 100,000, and more preferably 3,000 to 80,000.

The silane coupling agent having a quaternary ammonium base in the molecule may be used by reacting it with inorganic fine particles in advance, or may be given at any stage until the ink absorbing layer is applied and dried. Alternatively, the ink absorbing layer may be formed once and then applied, for example, by overcoating as a solution.

When the surface of the cationic compound is a cationic inorganic pigment, the amount of the cationic compound used per square meter of recording paper is 1 on both sides.
５０50 g, preferably 2-30 g. In the case where the cationic compound is a cationic polymer or a silane coupling agent having a quaternary ammonium base, the weight is 0.1 to 10 g on both sides and preferably 0.2 to 5 g.

On the other hand, examples of the inorganic fine particles having a cationic surface include alumina, pseudo-boehmite, and cation-modified colloidal silica.

The ink absorbing layer is divided into an ink absorbing layer mainly composed of a hydrophilic polymer and a porous ink absorbing layer having a high proportion of inorganic fine particles with respect to the hydrophilic binder.

The former temporarily absorbs the ink by swelling of the hydrophilic binder. After the ink solvent evaporates, the image remains with the pigment retained in the original hydrophilic binder.

The latter absorbs the ink in the porous layer and temporarily retains the ink. However, since the latter has a high ink absorbency, it is difficult to form irregularities in a streak pattern on an image, and moreover, after inkjet recording. The surface becomes dry, which is preferable from the viewpoint of handleability.

In the case of an ink-jet recording paper for recording on both sides, when the ink absorbing layer is of a swelling type, it is necessary to dry the ink-absorbing layer sufficiently so that they can be superposed without sticking even when stored at high humidity. There is. Otherwise, the two-sided prints will easily stick together.

Ink is not suitable for recording paper for double-sided printing because the printing surface usually has a sticky state for a long time because it contains a large amount of a low-evaporating and hygroscopic organic solvent.

The porous ink absorbing layer is formed from inorganic fine particles and a small amount of a hydrophilic polymer. Examples of such 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 Examples include white inorganic pigments such as alumina, pseudoboehmite, aluminum hydroxide, lithopone, and magnesium hydroxide.

Such inorganic fine particles can be used either as primary particles or in a state where secondary aggregated particles are formed.

In the present invention, the average particle diameter is 500 nm from the viewpoint of obtaining a high maximum density and preferable surface quality during printing.
Hereafter, it is particularly preferable to use fine particles of 200 nm or less.

Further, it is necessary to form fine voids from the viewpoint of obtaining a high density when recording by ink jet. Silica or pseudo-boehmite is preferable, and particularly, it is synthesized by a gas phase method having an average particle diameter of 200 nm or less. Silica, colloidal silica and pseudoboehmite are preferred.

The average particle diameter of the inorganic fine particles is determined by observing the cross section or surface of the particles themselves or the void layer with an electron microscope.
The particle size of zero arbitrary particles is obtained, and is obtained as a simple average value (number average). Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

The hydrophilic polymer used for the porous layer can be appropriately selected from known hydrophilic polymers, and a preferred hydrophilic polymer is polyvinyl alcohol.

The polyvinyl alcohol used in the present invention includes, in addition to general polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, polyvinyl alcohol having a cation-modified terminal or anion-modified polyvinyl alcohol having an anionic group. Of modified polyvinyl alcohol.

The polyvinyl alcohol obtained by hydrolyzing polyvinyl 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 500.
0 is preferably used.

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

The ink absorbing layer can be made porous by using a small amount of a hydrophilic binder with respect to the inorganic fine particles. The ratio of the inorganic fine particles to the hydrophilic binder is 3 to 10 times by mass. , Preferably 4 to 8 times.

When the porous layer contains polyvinyl alcohol as a hydrophilic polymer, it is preferable to add a hardener in order to improve the film forming property of the film and increase the strength of the film.

When the hydrophilic binder is a particularly preferred polyvinyl alcohol, the hardener is preferably an epoxy hardener or a borate.

The term "borate" refers to an oxyacid having a boron atom as a central atom and salts thereof, and specifically includes orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid and salts thereof. It is.

The amount of boric acid or a salt thereof can vary widely depending on the amount of the inorganic fine particles and the hydrophilic polymer in the coating solution, but it is generally 1 to 60% by mass, preferably 5 to 40% by mass based on the hydrophilic polymer. It is.

Various additives other than those described above can be added to the ink absorbing layer. For example, Japanese Unexamined Patent Publication No. 57-741
Nos. 93, 57-87988 and 62-2
UV absorber described in JP-A-61476;
Nos. 74192, 57-87989, 60
JP-A-72785, JP-A-61-146591, JP-A-1-95091 and JP-A-3-13376, etc., an anti-fading agent, various anionic, cationic or nonionic surfactants, 1959-4299
No. 3, No. 59-52689, No. 62-280
Nos. 069, 61-242871, and JP-A-4-219266, etc .; fluorescent whitening agents, defoamers, lubricants such as diethylene glycol, preservatives, thickeners, antistatic agents, Various known additives such as a matting agent can be contained.

The dry film thickness of the porous ink absorbing layer is determined in relation to the amount of ink absorbed, and is generally 20 to 70 μm.
m is preferably 30 to 50 μm from the viewpoint that all the ink solvent must be temporarily held. A particularly preferred dry film thickness is 35 to 50 μm.

Each of the ink absorbing layers provided on the front and back of the support may be a single layer or a plurality of layers. In the case of a plurality of ink absorbing layers, the ink absorbing layers may have different compositions, but each of the ink absorbing layers preferably contains a cationic compound.

The composition, thickness and surface quality of the ink absorbing layers on the front and back of the support may be the same or different.

When a color image is mainly printed on one side, such as a postcard or a card, and a character image is mainly printed on the other side, the characteristics of the front and back sides are adjusted so that the ink absorbing layer is optimized for the printing conditions. Is preferably designed.

On the other hand, when used for an album print or the like, the same surface quality, glossiness and white background on the front and back may be the same or different, but it is preferable that the ink absorption characteristics are substantially the same.

In particular, if the ink absorption characteristics are different between the front and the back, even if the same image is ink-jet printed under the same conditions, a print of a completely different color tone can be obtained.

In order to reduce such a thing as much as possible, it is preferable to make the ink jet aptitude on the front and back sides as close as possible. And D2, it is preferable that D1 / D2 = 0.90 to 1.1. The dot diameter referred to here is determined by arranging a single dot on recording paper and forming it on an optical microscope or CCD.
An image is taken with a camera or the like, and the area is measured. Assuming a circle equal to this area, it indicates its diameter. The dot diameter is represented by an average value obtained by measuring arbitrary 20 dots.

If D1 / D2 is less than 0.9 or exceeds 1.1, the spread of ink droplets differs between the front and back sides, so that the color reproducibility of the same print differs between the front and back sides.

To make D1 / D2 fall within the above range,
The configuration of the front and back ink absorbing layers is made substantially the same. Here, the term “substantially the same configuration” means that the same inorganic fine particles, a hydrophilic binder and a cationic compound contained in the ink absorbing layer are used, and the layer configuration is preferably as close as possible.

However, in general, there is almost no influence on the ink absorbency, and a color tone adjusting agent, a fluorescent whitening agent, a matting agent, etc. for giving a subtle difference in color tone can be changed. Further, the ink absorption capacities of the front and back sides can be changed within a range that does not affect the image. Generally, the ratio of the amount of ink absorbed on the front and back sides is generally in the range of 0.8 to 1.2.

The recording paper of the present invention preferably has a static friction coefficient of front and back of 0.8 or less from the viewpoint of continuous conveyance.

When the coefficient of static friction exceeds 0.8, it becomes difficult to feed or feed a large number of sheets at a time. On the other hand, when the coefficient of static friction is 0.8 or less, it is preferable that a situation in which a large number of sheets are conveyed at one time or a sheet is difficult to be fed hardly occurs. In particular, the coefficient of static friction is preferably set to 0.7 or less. The lower limit of the static friction coefficient is not particularly limited, but is generally 0.2 or more.

In order to make the front and back static friction coefficient 0.8 or less, the surface properties (surface quality, binder slipperiness) of the front and back ink absorbing layers are adjusted.

Specifically, a method of adding a matting agent to make the surface of the ink absorbing layer on the front and back surfaces convex, or a wax, a silicon-based compound or It can be adjusted relatively easily by adding a slipping agent such as a fluorine compound. A particularly effective means is to use a matting agent.

As the matting agent, inorganic particles (silica, calcium carbonate, talc, etc.) and organic latex (polystyrene, polyethylene, polymethyl methacrylate, etc.) are used, but organic latex is preferred.

[0118] Such a matting agent having an average particle diameter of 5 µm or more is preferable since it has a relatively small effect on gloss and can improve slipperiness. Particularly preferred matting agents have an average particle size of 7 to 30 μm.

It is preferable that the matting agent has a relatively uniform particle size distribution and has a low gloss reduction. When the particle size distribution is measured, the degree of dispersion (standard deviation divided by average particle size) is 2.
Or less, preferably 1.5 or less.

The amount of the matting agent used varies depending on the particle size of the matting agent and the dry film thickness of the ink absorbing layer to which the matting agent is added, but is generally about 0.01 to 0.5 g per 1 m ^{2 of} recording paper.

The organic latex is a polymer latex polymerized by a polymer latex emulsion polymerization method, and is a polymerizable monomer having at least one unsaturated bond in a molecule, or a copolymer of two or more monomers. .

[0122]

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 mass% unless otherwise specified.

Example 1 On a paper support having the basis weight and opacity shown in Table 1,
The following coating solutions were applied to both sides of the paper support so that the dry solid content was 12 g per 1 m ^{2 of} recording paper, thereby producing recording papers 1 to 6.

Coating solution composition (per liter of coating solution) Polyvinyl alcohol 30 g Cationic colloidal silica 140 g Polyvinylpyrrolidone 5 g Epoxy-based cross-linking agent 2 g Comparative Example 1 In preparing the coating solution prepared in Example 1, instead of cationic colloidal silica Recording papers 4R to 6R were produced in the same manner as recording papers 4 to 6 of Example 1, except that the surface was changed to ordinary colloidal silica having an anionic surface.

The ink jet recording papers produced in Example 1 and Comparative Example 1 were evaluated for strikethrough, bleeding, and line unevenness by the following methods.

<Blankthrough> After solid black printing is performed on one side with an ink jet printer, the reflection density is measured from the opposite side (immediately).

The reflection density was set to 0 when no solid black printing was performed. After storing the printed print at 40 ° C. and a relative humidity of 80% for 2 days, the reflection density was similarly measured from the back surface.

If the reflection density is about 0.05 or less, it is practically acceptable. In particular, if it is 0.03 or less, no problem occurs in most cases.

<Bleeding> A line having a width of about 250 μm is printed on one side with black ink using an ink jet printer, solid printing of magenta ink is performed on another recording paper, and then the printing surfaces are overlapped. 40 ° C, relative humidity 8
Stored at 0% for 2 days.

The line width was measured with a microdensitometer, and the rate of increase of the line width after storage with respect to the line width before storage was determined. If the rate of increase is 1.2 or less, there is no practical problem.

<Evaluation of streak unevenness> After printing on one side (front side) of the recording paper with a K line width of about 0.3 mm using PM750 manufactured by Seiko Epson Corporation, apply it to the opposite side (back side). Was also printed. The streak-like white spots in the printed portion on the back side were visually evaluated according to the following evaluation criteria.

◎: No white streaks (streak unevenness) observed. ○: Slight white streaks (streak unevenness) observed but no problem in practice. There is no upper problem. X: White streaks (streak unevenness) are noticeable. Table 1 shows the results of the recording papers obtained in Example 1 and Comparative Example 1.

[0133]

[Table 1]

From the results shown in Table 1, it is found that the recording papers 4 to 6 having opacity of 94% or more and using cationic colloidal silica for the ink absorbing layer have small strike-through, and the image on the back side is not affected even when printed on both sides. It turns out that it is not affected.

In particular, recording paper having an opacity of 95% or more is particularly good. On the other hand, the recording paper having an opacity of less than 94% has a large strike-through, especially when stored under high humidity, and shows a large strike-through. In addition, the ink absorption using a non-cationic inorganic pigment It can be seen that strike-through is also large when a layer is used.

When the recording paper shown in Table 1 was evaluated for streak unevenness, the streak unevenness was recognized, but was at a level that was not problematic in practical use (evaluation result was Δ).

Example 2 The recording sheet 11 was prepared in the same manner as in Example 1 except that zinc oxide particles were added to the recording sheets 1 to 3 of Example 1.
To 13 were prepared and evaluated. Table 2 shows the results.

[0138]

[Table 2]

From the results shown in Table 2, it can be seen that the addition of zinc oxide in the paper improves the opacity of the support and improves the strike-through even when a thinner paper is used.

When the recording paper shown in Table 2 was evaluated for streak unevenness, the streak unevenness was recognized, but there was no practical problem (evaluation result was at a level).

Example 3 The supports shown in Table 3 (the supports used for recording papers 1A to 4A are the following supports 1 to 4, respectively) were prepared. That is, fine paper (support 1) having a basis weight of 250 g and opacity of 95%, support baryta paper having a basis weight of 250 g and support of 95% opacity (support 2), and art paper having a basis weight of 250 g and opacity of 95% opacity (support 1). 3) and opacity of base paper having a basis weight of 170 g coated with an anatase type titanium oxide-containing polyethylene resin.
A 5% support (Support 4) was prepared. Next, corona discharge was performed on both sides to apply a gelatin subbing layer of 0.05 g / m ² .

<Preparation of Coating Solution 1-1> 180 g of fine-particle silica powder synthesized by a gas phase method having an average primary particle size of about 7 nm was added to 900 ml of pure water while stirring with a high-speed homogenizer. An aqueous dispersion was prepared. Next, 100 ml of a 25% aqueous solution of a mordant Mor-1 (cation mordant) was added to the aqueous silica dispersion,
The mixture was dispersed with a high-speed homogenizer for 1 minute to obtain a pale and clear dispersion. Next, the average degree of polymerization was 300 and the degree of saponification was 88%.
1 ml of a 10% aqueous polyvinyl alcohol solution of
Furthermore, 5% of the average degree of polymerization of 3500 and the degree of saponification of 88%
530 ml of an aqueous polyvinyl alcohol solution (containing 4% by mass of ethyl acetate) was gradually added. Next, 40 ml of a 4% boric acid aqueous solution was added as a hardener, and
Was added, and 50 ml of a 10% aqueous gelatin solution was further added to prepare a coating liquid 1-1 for forming a void-type ink absorbing layer.

[0143]

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<Preparation of Recording Papers 1A to 4A> The coating solution 1-1 was applied to one side of the support prepared as described above.
Is applied, and a porous ink absorbing layer having a dry film thickness of 36 μm is provided.
The recording papers 1A to 4A were prepared by applying the coating so as to have a thickness of μm.

The recording sheets 1A to 4A obtained were evaluated in the same manner as in Example 1, and the results shown in Table 3 were obtained.

[0146]

[Table 3]

From the results shown in Table 3, although the recording paper 1A has a small degree of strike-through and can be used without any practical problem, stripe unevenness is recognized.

The recording paper 2A using a baryta paper having a support having an opacity of 95% and a Cobb water absorption of 12 g / m ² has a small rise in strike-through after storage, but streak unevenness in the back side image is observed.

The recording paper 3A, which is an art paper and uses a support having an opacity of 95% and a Cobb water absorption of 3 g / m ² , has a small rise in strike-through after storage and has good streak unevenness in the back side image.

Both sides of the paper were coated with polyethylene resin.
The recording paper 4A using the support having an opacity of 95% and a Cobb water absorption of 0 g / m ² showed almost no increase in strike-through after storage, and a high-quality print with no streak unevenness of the back side image was obtained.

Example 4 A basis weight of 110 g / m ² and 140 g having a water content of 6.5% by mass.
/ M ² and 170 g / m ² paper were prepared. For each of the papers, the following three types of polyethylene resins were coated on the front and back by a melt extrusion method so as to have a thickness of 30 μm, and nine types of paper supports having both sides coated with polyethylene were produced (Table 4). ).

(A) Polyethylene resin only. (B) Polyethylene resin containing 3% by mass of anatase type titanium oxide. (C) Polyethylene resin containing 8% by mass of anatase type titanium oxide. 55%.

Then, a corona discharge was applied to the front and back sides, and a gelatin subbing layer was coated at 0.05 g / m ² .

On one side of the gelatin subbing layer, Example 3
Is applied, a porous ink absorbing layer having a dry film thickness of 40 μm is provided, and then the same coating solution is applied on the opposite side so that the dry film thickness becomes 40 μm.
To 29 were prepared.

The recording paper obtained was evaluated in the same manner as in Example 1, and the results shown in Table 4 were obtained.

[0156]

[Table 4]

From the results shown in Table 4, it can be seen that the recording paper having the opacity of the support of 94% or more can obtain good images with little strikethrough.

In comparison with Tables 1 and 2, it can be seen that strike-through hardly changes even when stored at high humidity because the support is a hydrophobic support.

The recording papers 21 to 29 were evaluated for streak unevenness. As a result, no streak unevenness was observed in the back side image (evaluation result is ◎), and high-quality prints were obtained.

Example 5 In the nine types of supports prepared in Example 4 which were coated on both sides with polyethylene, after extruding the polyethylene, one side was matted with a 60 ° specular gloss of 8%. Nine types of supports were prepared in which one of the polyethylene layers had a Ra = 3.2 μm fine-grained surface shaped and treated.

Next, a coating solution having the following composition was prepared on the front side. "Preparation of silica dispersion 1" The average particle size of the primary particles is about 0.1.
125 kg of 007 μm fumed silica (A300 manufactured by Nippon Aerosil Co., Ltd.) was added to a jet stream inductor mixer TD manufactured by Mitamura Riken Kogyo Co., Ltd.
After using S to disperse by suction at room temperature in 600 l of pure water adjusted to pH = 3.0 with nitric acid, the total volume was made up to 660 l with pure water.

"Preparation of silica dispersion 2" 1.29 kg of cationic polymer (P-1), 4.2 l of ethanol, n
An aqueous solution containing 1.5 l of propanol (pH = 2.
3) To 15 liters, add 66.0 liters of silica dispersion 1 into the liquid while stirring with a high-speed homomixer, then add boric acid 2
7.0 l of an aqueous solution containing 60 g and 230 g of borax was added to the solution while stirring at a high speed in the same manner as in the case of the silica dispersion liquid 1, and 1 g of an antifoaming agent SN381 (manufactured by Sannobuco) was added. This liquid was further stirred at a high speed of 3000 rpm for 1 hour, then uniformly dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd., and the whole amount was adjusted to 90 l with pure water to prepare a silica dispersion liquid 2.

[0163]

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"Preparation of Fluorescent Whitening Agent Dispersion 1" 400 g of oil-soluble fluorescent whitening agent UVITEX-OB manufactured by Ciba-Geigy Co., Ltd. was added to 4,000 g of diisodecyl phthalate, and an antioxidant (2,4-di-t-amyl) was used. -Hydroquinone-di-n-octyl ether) in 4,000 g and 12 l of ethyl acetate.
0 g, a cationic polymer (P-1) and a saponin 50% aqueous solution containing 6,000 ml of an aqueous solution (65 l) were added and mixed, emulsified and dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd., and ethyl acetate was removed under reduced pressure. 100l total volume
Finished. "Preparation of matting agent dispersion liquid 1" 600 g of methacrylic acid ester-based matting agent MX-1500 manufactured by Soken Kagaku Co., Ltd.
Was added to 7 liters of pure water containing 30 g of PVA235 (polyvinyl alcohol: manufactured by Kuraray Industries Co., Ltd.), and dispersed with a high-speed homogenizer to finish the total volume to 8 liters.

"Preparation of Coating Solution" Coating solutions for the first, second and third layers were prepared by the following procedure. First layer coating solution: 40 ° C. in 560 ml of silica dispersion 2
While stirring at, the following additives were sequentially mixed. 10% aqueous solution of polyvinyl alcohol (Kuraray Industries Co., Ltd .: PVA203) 6 ml Polyvinyl alcohol (Kuraray Industries Co., Ltd .: PVA235) 5% aqueous solution: 260 ml Fluorescent brightener dispersion 1: 22 ml Daiichi Kogyo Co., Ltd. : Latex emulsion AE-803: 24 ml Make up to 1000 ml with pure water.

Coating solution for second layer: 650 of silica dispersion 2
While stirring at 40 ° C. in the ml, the following additives were sequentially mixed. 10% aqueous solution of polyvinyl alcohol (manufactured by Kuraray Industries Co., Ltd .: PVA203) 6 ml Polyvinyl alcohol (manufactured by Kuraray Industries Co., Ltd .: PVA235) 5% aqueous solution: 270 ml Fluorescent brightener dispersion liquid 1: 30 ml manufactured by Daiichi Kogyo Co., Ltd. : Latex emulsion AE-803: 4 ml Make up to 1000 ml with pure water.

Coating solution for third layer: 650 of silica dispersion 2
While stirring at 40 ° C. in the ml, the following additives were sequentially mixed. 10% aqueous solution of polyvinyl alcohol (Kuraray Industries Co., Ltd .: PVA203): 6 ml 5% aqueous solution of polyvinyl alcohol (Kuraray Industries Co., Ltd .: PVA235): 270 ml Silicon dispersion (Toray Dow Corning Silicone Co., Ltd., BY) -22-839): 3.5 ml 50% aqueous solution of saponin: 4 ml Matting agent dispersion liquid 1: 25 ml Make up to 1000 ml with pure water.

The coating solution obtained as described above was filtered with the following filter. 1st layer and 2nd layer: 2 layers with TCP10 manufactured by Toyo Roshi Co., Ltd. 3rd layer: 2 layers with TCP30 manufactured by Toyo Roshi Co., Ltd. On the fine particle side of the above-mentioned support having both surfaces coated with the above 9 kinds of polyolefins , First layer (40 μm), second layer (1
10 μm) and the third layer (30 μm) in this order. The figures in parentheses indicate the respective wet film thicknesses.

Each coating solution was applied at 40 ° C. using a three-layer slide hopper, and immediately after coating, the coating solution was cooled in a cooling zone maintained at 8 ° C. for 20 seconds, and then blown at a temperature of 20 to 30 ° C. for 60 seconds. , 45 ° C for 60 seconds, 50 ° C for 6 seconds
After sequentially drying for 0 seconds, 23 ° C, relative humidity 40-60%
Was conditioned.

Next, the same coating liquid was applied to the opposite mat surface side.
The first layer (50 μm), the second layer (110 μm), and the third layer (20 μm) were applied under the same application and drying conditions as those applied to the fine particle side, to obtain recording papers 31 to 39.

The 60-degree specular gloss of the ink absorbing layer on the fine particle side and the matte side was in the range of about 25 to 27% and 12 to 14%, respectively.

The color difference ΔE between the front and back white backgrounds is 3
Was within. When evaluated in the same manner as in Example 1, the effect of the present invention was obtained, and high-quality prints without print-through were obtained on both sides of a recording sheet having an opacity of the support of 94% or more even when printed on both sides with an inkjet printer. Was done. or,
When streak unevenness was evaluated for the recording papers 31 to 39, no streak unevenness was observed in the back side image (the evaluation result is ◎).
High quality prints were obtained.

Example 6 Using the recording sheet prepared in Example 5, a ruled line frame such as a postal code for use as a postcard was printed on the matte side, and then cut into postcard sizes to prepare a postcard for ink jet recording. did. When characters such as addresses were printed on the matte side with an inkjet printer, and color images were printed on the other side with an inkjet printer. Although remarkable, the recording papers 36, 38, and 39 using the support having an opacity of 94% or more gave a postcard on which high-quality prints with little strike-through were made.

Further, the postcard was subjected to a heat treatment at 40 ° C. and a relative humidity of 3 ° C.
After storage for a few days, the strikethrough was almost unchanged.

Example 7 A plurality of color images were printed on both sides of the recording papers 36, 38, and 39 prepared in Example 5 with an ink jet printer, and the ends were joined together to form an album print. An album with a different surface quality was obtained on the bonding side.

Example 8 In the recording paper 38 prepared in Example 5, only the ink absorbing layer on the mat side was changed as follows.
8 to 78 were produced in the same manner as the recording paper 38. Recording paper 48: Changed to the coating liquid prepared in Example 1. Recording paper 58: Changed to a coating liquid obtained by adding 2 g of a fluorochemical surfactant per liter of the coating liquid prepared in Example 1 Recording paper 68: Recording paper Recording paper 78: the same as the recording paper 38 except that the coating liquid except for the silicon dispersion of the third layer 38 was used. Recording paper 78: The volume of the silicon dispersion of the third layer of the recording paper 39 was tripled.

Printing was performed on both sides of the obtained recording paper by an ink jet printer, and the dot size was examined.

Further, under the condition that a neutral gray with a reflection density of about 0.8 appears on the fine grain surface, printing was performed on the matte surface, and the color difference between the fine grain surface and the image obtained on the matte surface was measured.

Table 5 shows the results. In the table, D1 represents the dot size on the fine grain surface, and D2 represents the dot size on the matte surface.
(Unit: μm)

[0180]

[Table 5]

From the results shown in Table 5, D1 / D2 was set to 0.
When it is within the range of 9 to 1.1, almost the same finish can be obtained even when used for applications such as album printing.

On the other hand, D1 / D2 is less than 0.9 or 1.
If it exceeds 1, the finished color tone differs depending on the printing surface, so that it is not very suitable for applications such as album printing.

However, even for the above-described prints, the difference in color tone between front and back is not a problem for postcard applications.
It was also confirmed that the effects of the present invention were obtained with regard to strikethrough and bleeding for all of the recording papers 38 to 78.

[0184]

According to the present invention, when both sides of a support having an opacity of 94% or more are printed by ink-jet on an ink-jet recording sheet having an ink-absorbing layer containing a cationic compound on both sides, Inkjet recording paper is obtained in which the density decrease is small and the image printed on one side is hard to see through to the other side.

Claims (9)

[Claims] 1. An ink jet recording paper comprising an ink absorbing layer containing a cationic compound on both sides of a support having an opacity of 94% or more specified in JIS P 8138. 2. The Cobb water absorption measured using pure water containing 30% by mass of diethylene glycol in a water absorption test method specified in JIS P 8140 is 10 seconds or less per 1 m ^2. , And J
An ink jet recording paper comprising an ink absorbing layer containing a cationic compound on both sides of a support having an opacity of 94% or more as defined by ISP 8138. 3. The ink jet recording paper according to claim 1, wherein the support is a hydrophobic support. 4. The support according to claim 1, wherein the support is a support in which both surfaces of a paper base are coated with a polyolefin resin, and at least one of the polyolefin resin layers contains a white pigment. 4. The ink jet recording paper according to any one of the items 3. 5. The ink absorbing layers on the front and back sides each have at least one porous layer.
The inkjet recording paper according to any one of the above. 6. D1 / D2 = 0.90 to 1.1, where D1 and D2 are dot diameters obtained by attaching ink droplets to the front and back ink absorbing layers, respectively. The inkjet recording paper according to claim 1. 7. JIS P 8138 containing a white pigment
An ink-jet recording sheet comprising a plastic film support having an opacity of 94% or more as defined in (1) and an ink absorbing layer containing a cationic compound on both surfaces. 8. A polyolefin resin containing a white pigment,
A support coated on both sides of a paper substrate having a basis weight of 100 to 250 g / m ² and having a opacity of 94% or more as defined in JIS P 8138, containing a cationic compound on both sides. An ink jet recording sheet having an ink absorbing layer. 9. The method according to claim 1, wherein the cationic compound is a compound having a quaternary ammonium base.
9. The ink jet recording paper according to any one of the above items 8.