JP2000301823A - Ink jet recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent stain of an image even by continuously recording the image of a high quality level on a recording sheet to be recorded by ink jet on both surfaces by forming a porous ink absorption layer on one surface of a paper base material having a specific basis weight through a hydrophobic resin layer having a specific thickness. SOLUTION: A porous ink absorption layer is provided on one surface of a paper base material having a basis weight of 100 to 300 g/m2 as a support of an ink jet recording sheet through a hydrophobic resin layer having a thickness of 1 to 20 μm. It is prepared that a dry film thickness of the porous layer is set to 30 to 50 μm and a static frictional coefficient between the porous layer and a rear surface becomes 0.8 or below. Further, it is preferred to contain a matting agent having a mean particle size of 5 μm or above in the porous layer. Further, as the porous layer, a porous film having a porous layer formed of inorganic particles and a small amount of hydrophilic polymer is preferably used.

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 (hereinafter, also simply referred to as a recording sheet), and more particularly to an ink jet recording sheet which can print on both sides such as a postcard.

[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.

Various improvements have been made on the recording paper side in order to obtain a print similar to a silver halide photographic print by ink jet recording. In particular, both sides of the paper are coated with a polyolefin resin such as polyethylene as a support. Recording paper that uses a support and has an ink-absorbing layer on it is relatively inexpensive compared to a plastic film, and because of its solid feeling, suppleness, smoothness, and gloss, silver halide Recently, it has begun to be widely used as a high-quality print similar to a photo print.

[0004] Ink-jet recording papers are broadly classified into those in which the support itself is ink-absorbent, such as paper, and those in which an ink-absorbing layer is provided on the support. It is difficult to obtain high-quality prints because a high maximum density cannot be obtained because the ink directly penetrates into the ink, or the support itself absorbs the ink solvent to cause significant wrinkles in an image.

[0005] Further, many ink jet recording papers having an ink absorbing layer provided on a support are also known. However, when the support absorbs an ink solvent, wrinkles are liable to occur. The dye which has been dyed has a drawback that the density tends to decrease due to the permeation into the support gradually during storage.

On the other hand, ink jet recording paper having an ink absorbing layer provided on a non-water-absorbing support in which the support does not absorb ink at all does not have the above-mentioned drawbacks and can provide a high quality ink jet print.

[0007] As the ink absorbing layer provided on the support, a large swelling type ink absorbing layer and a porous ink absorbing layer are known.

[0008] The swellable ink absorbing layer is substantially composed of a hydrophilic polymer such as gelatin, polyvinyl alcohol, polyvinylpyrrolidone or polyethylene oxide.

[0009] There are several types of porous ink-absorbing layers, but a typical one is a layer composed of a small amount of a hydrophilic polymer and a large amount of fine particles, and voids are formed between the fine particles. This is where the ink is absorbed.

The characteristics of the swellable ink absorbing layer are that high gloss can be obtained and that a large amount of ink can be absorbed as long as the polymer can swell because of the use of a swellable polymer. There are advantages of being able to be manufactured.

On the other hand, the characteristics of the porous ink absorbing layer are that the ink absorbing speed is high and unevenness does not easily occur during printing, the surface is apparently dry immediately after printing, and the water resistance as seen in a swollen type ink absorbing layer. For example, there is no dilemma in the ink absorption speed and both can be satisfied at the same time.

At present, both are used according to the selection of the user, but it is preferable from the viewpoint of image quality that the ink is of a void type because of high absorption and high drying properties.

By the way, when the support does not absorb ink and the ink absorbing layer is porous, a high-quality print without wrinkles or unevenness can be obtained. A problem arises when used for recording purposes.

Usually, an ink jet recording liquid contains a low-evaporating, high-boiling organic solvent in addition to water, but when ink-jet recording is performed on recording paper having an ink-absorbing layer provided on a non-water-absorbing support, it is sufficiently dried. Even in this case, since the high boiling point organic solvent remains in the ink absorbing layer, the image tends to bleed when stored for a long time in this state.

In the case of continuously recording a large number of sheets, such as a postcard, the problem is liable to be remarkable because the water is overlapped while not sufficiently evaporated.

A description will be given of an example of a postcard printed by ink jet recording having an ink receiving layer on both sides of a non-water-absorbing support. On an image recording surface, a large amount of ink is used to record an image on a relatively large area. Has a small area but delicate characters. If an image surface that is continuously inkjet-printed and an address surface mainly composed of characters are overlapped, there is a problem that characters tend to bleed in a state where ink solvent remains on the image surface.

Further, in the case of a recording sheet having a non-porous ink absorbing layer provided on a non-water-absorbing support, the drying properties are insufficient, and the recording sheets tend to stick to each other when recording is performed continuously. .

Although such a problem hardly occurs in a recording paper in which the support absorbs the ink solvent, a high-quality print cannot be obtained as described above. In particular, when ink-jet recording is performed on the same location on both surfaces of the water-absorbing support, wrinkles are likely to be noticeably generated on the image-recorded portions on both surfaces of the recording paper.

Japanese Patent Application Laid-Open No. 9-286166 describes an ink jet recording sheet having an ink receiving layer or a coating layer on both sides, and various ink receiving layers or coating layers are described. As the support, both a water-absorbing support and a non-water-absorbing support are described.

However, the recording papers described in the above publications all have the above-mentioned problems, and high-quality prints cannot be obtained or only blurred images can be obtained.

[0021]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the occurrence of wrinkles in a recording sheet on which ink is recorded on both sides. It is an object of the present invention to provide an ink jet recording sheet in which even if high-quality images are continuously recorded, there is no bleeding of the images while they are superposed, and the recording sheets do not stick to each other.

[0022]

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

1. An ink jet recording sheet comprising a paper substrate having a basis weight of 100 to 300 g / m ² and a porous ink absorbing layer on one surface of a paper substrate with a hydrophobic resin layer having a thickness of 1 to 20 μm interposed therebetween.

2. One side of a paper base material having a basis weight of 100 to 300 g / m ² has a porous ink absorbing layer via a hydrophobic resin layer having a thickness of 1 to 20 μm, and a hydrophobic resin on the other side. An ink jet recording sheet having an ink absorbing layer without interposing a layer.

3. 3. The ink jet recording paper as described in 1 or 2, wherein the porous ink absorbing layer has a dry film thickness of 30 to 50 [mu] m.

4. 4. The ink jet recording paper according to any one of the items 1 to 3, wherein a coefficient of static friction between the porous ink absorbing layer and the back surface is 0.8 or less.

5. 5. The ink jet recording paper according to any one of items 1 to 4, wherein the porous ink absorbing layer contains a matting agent having an average particle size of 5 μm or more.

6. The inkjet recording paper according to any one of the above items 1 to 5, wherein the hydrophobic resin layer contains a pigment.

That is, the recording paper of the present invention is a recording paper that can be recorded on the front and back sides by ink jet recording. This is an ink jet recording paper that is a flexible support.

Hereinafter, the present invention will be described in more detail.

In the ink jet recording paper of the present invention, the support is a paper base having a basis weight of 100 to 300 g / m ² . Here, the paper base material is a paper made from wood pulp as a main raw material and using synthetic pulp such as polypropylene or synthetic fiber such as nylon or polyester in addition to wood pulp as necessary. As wood pulp, LBKP,
LBSP, NBKP, NBSP, LDP, NDP, LU
Both KP and NUKP can be used.

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

In 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 may be calendered after the paper making to give high smoothness. The paper density is 0.7 to 1.2 g / m ² (J
IS-P-8118) is common. Further, the stiffness of the base paper is 20 to 400 under the conditions specified in JIS-P-8143.
g is preferred.

A surface sizing agent may be applied to the paper surface. As the surface sizing agent, the same sizing agent as that 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. The basis weight of the paper substrate is 100 to 300 g / m2.
Need to be ² . When it is less than 100 g / m ² , the rigidity of the paper base material is insufficient, and when a porous ink absorbing layer is provided on only one surface via a hydrophobic resin layer, curling is remarkable. This curl is large especially at low humidity.

When the grammage is less than 100 g / m ² , if a large amount of water or a high boiling point organic solvent remains by ink jet recording on the porous ink absorbing layer shown in the table, When a delicate character is printed, the amount of water absorbed by the paper base material is insufficient, and the character bleeds, or the bleeding of a character-like image easily occurs on the opposite image surface.

On the other hand, when the basis weight of the paper base material exceeds 300 g / m ² , the rigidity of the ink jet recording paper is too high and the transportability is reduced, or the surface is combined with a porous layer or a hydrophobic resin layer on the surface. Sometimes the thickness is about 350 μm or more,
Inkjet recording characteristics when the optimum distance between the recording paper surface and the ink nozzle of the inkjet printer is changed easily deteriorate. Preferred basis weight of the paper substrate is 120 to
It is 250 g / m ² .

On the side of the paper substrate on which the hydrophobic resin layer is provided (hereinafter, this surface is referred to as the front surface of the paper substrate, and the opposite side is referred to as the back surface of the paper substrate), for example, for the purpose of providing gloss or hydrophobic resin. A hydrophilic resin layer may be provided for the purpose of improving the adhesiveness with the resin.

The hydrophilic resin layer may contain various kinds of additives such as various kinds of inorganic fine particles, a surfactant, a fluorescent whitening agent and a white background adjusting agent. The thickness of such a hydrophilic resin-containing layer can be provided between 0.1 and 30 μm.

Next, the first substrate provided on one side of the paper substrate
The hydrophobic resin layer having a thickness of about 20 μm will be described.

As the resin used for the hydrophobic resin layer, any resin can be used as long as it does not allow water to pass therethrough during ink jet recording.
Polyvinyl chloride, polyolefin, polystyrene, polyarylate, polyimide, polycarbonate, triacetyl cellulose, cellophane and the like are common.

These hydrophobic resins may be those formed once in the form of a film and laminated on a paper substrate, or those obtained by coating a molten resin on a paper substrate by melt extrusion. Good, furthermore, a resin can be obtained by dissolving a resin in an organic solvent, applying this on a paper base material, and then drying the organic solvent. preferable.

In addition to the above, a hydrophobic film may be formed by coating and drying a polymer latex emulsion to form a film.

Examples of such polymer latex emulsions include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, acrylamide, styrene,
Hydroxylethyl methacrylate, vinyl chloride, vinyl ether, ethene, styrene, divinylbenzene,
It can be obtained by emulsion polymerization of a single copolymerizable monomer such as vinyl acetate and butadiene or two or more monomers.

Among the above-mentioned various hydrophobic resins, polyolefins are particularly preferred from the viewpoints of cost and ease of production.

As the polyolefin, polyolefins such as polyethylene, polypropylene, polyisobutylene, a copolymer 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 also be partially used.

The thickness of the hydrophobic resin layer is from 1 to 20 μm. If the thickness is less than 1 μm, it becomes difficult to form a uniform layer on the paper substrate, and the hydrophobic resin layer is not partially covered with the hydrophobic resin. A portion is generated to cause a difference in ink absorptivity, which tends to cause unevenness of an image, or unevenness in gloss.

On the other hand, if the thickness exceeds 20 μm, curling particularly at low humidity becomes large.

The preferred thickness of the hydrophobic resin layer is 2 to 15 μm.
m, and particularly preferably 2 to 10 μm.

Various additives can be contained in the hydrophobic resin layer. In particular, it is preferable to contain a white pigment for the purpose of improving a white background and obtaining opacity.

Examples of the white pigment include titanium oxide, barium sulfate, zinc oxide and calcium carbonate, and titanium oxide is particularly preferable. As the titanium oxide, rutile-type or anatase-type titanium oxide can be used, and its content is usually 1 to 50% by weight based on the hydrophobic resin.
Preferably it is 2 to 30% by weight.

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

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

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

The laminate obtained by coating the above-mentioned paper base material with a hydrophobic resin has a tensile strength of 2 to 30 kg in the vertical direction and 1 to 20 kg in the horizontal direction at a strength specified by JIS-P-8113.
kg, tear strength is 10 to 200 g in the vertical direction and 20 to 200 g in the horizontal direction according to the method specified by JIS-P-8116.
g, opacity is 90% or more as measured by the method specified in JIS-P-8138, and whiteness is JIS-Z-87.
L ^* , a ^* , b ^* defined by 29 are L ^* = 80 to 95,
^{a * = -3~ + 5, b} * = -6~ + 2, 50~300cm 2/10 Clark stiffness is in the transport direction of the recording sheet
Those which are 0 are preferred.

The surface of the hydrophobic resin may be a surface having high smoothness or a surface having fine particles. 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 inkjet recording paper having a fine grain surface.

When used for glossy paper, the thickness of the hydrophobic resin layer is usually preferably at least 5 μm, more preferably at least 10 μm, and the glossiness of the surface of the hydrophobic resin layer (JIS)
−60-degree specular gloss defined in Z-8741) is 20
~ 90% is preferred.

When used as a fine-grain surface ink jet recording paper, JIS-B-06 of the hydrophobic resin surface is used.
Reference length 2.5 mm, cut-off value 0.
The center line average roughness (Ra) measured at 8 mm was 1.
It is preferably 0 to 5.0 μm, and preferably has irregularities such that the 60-degree specular glossiness according to JIS-Z-8741 satisfies 10 to 40%.

In order to form fine irregularities on the hydrophobic resin layer, the paper base is coated with the hydrophobic resin, and then the surface is pressed against a molding roller to form fine irregularities. Done.

As a method of forming the pattern, there are a method of performing embossing calendering 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 porous ink absorbing layer provided on the hydrophobic resin layer will be described.

The porous ink absorbing layer is preferably a porous film having a porous layer formed of 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 alumina, pseudoboehmite, aluminum hydroxide,
Examples include white inorganic pigments such as 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, it is preferable to use fine particles having an average particle diameter of usually 500 nm or less, particularly preferably 100 nm or less, from the viewpoint of obtaining a particularly preferable fine particle surface.

Further, it is necessary to form fine voids from the viewpoint of obtaining a high density when recording by an jet. Silica or pseudo-boehmite is preferable, and particularly synthesized by a gas phase method having an average particle diameter of 100 nm or less. Silica, colloidal silica and pseudoboehmite are preferred.

The average particle diameter of the inorganic fine particles can be determined by observing the cross section or surface of the particles 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 degree of saponification 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 usually 3 to 10 by weight. Times, preferably 4 to
It is eight times.

When the porous layer contains polyvinyl alcohol as a hydrophilic polymer, it is preferable to add a hardening agent to improve the film forming property of the film and to 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 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 is usually 1 to 60% by weight, preferably 5 to 40% by weight, based on the hydrophilic polymer. %.

Various additives other than those described above can be added to the ink absorbing layer of the ink jet recording paper of the present invention.

Of these, cationic mordants are preferred for improving water resistance and moisture resistance after printing.

As the cationic mordant, a polymer mordant having a primary to tertiary amino group and a quaternary ammonium group is used, but the discoloration and deterioration of light resistance with time are small, and the mordant ability of the dye is sufficient. From the viewpoint of high cost, a polymer mordant having a quaternary ammonium base is preferred.

Preferred polymer mordants are obtained as a homopolymer of the above-mentioned monomer having a quaternary ammonium salt group, as a copolymer with other monomers or as a condensation polymer.

In addition to the above, see, for example, JP-A-57-741.
Nos. 93, 57-87988 and 62-2
UV absorber described in JP-A-61476;
Nos. 74192, 57-87989, 60-7
Nos. 2785, 61-146591, JP-A-1-95091, and JP-A-3-13376, etc .; anti-fading agents; various anionic, cationic or nonionic surfactants; JP-A-59-42993, JP-A-59-52689, and JP-A-62-28006.
9, JP-A-61-228771 and JP-A-Hei.
Fluorescent brighteners described in -219266 and the like;
Known various additives such as a defoaming agent, a lubricant such as diethylene glycol, a preservative, a thickener, an antistatic agent and a matting agent can also be contained.

The dry film thickness of the porous ink absorbing layer is determined by the relationship with the amount of ink absorbed, and is generally 10 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.

In applying the porous ink absorbing layer on the hydrophobic resin layer, a corona discharge treatment is performed for the purpose of increasing the adhesive strength between the surface of the hydrophobic resin layer and the coating layer. It is preferable to provide a subbing layer.

As the binder used for the undercoat layer, those obtained by applying a hydrophilic polymer such as polyvinyl alcohol, gelatin, polyvinyl pyrrolidone or the like and various polymer latex emulsions to form a film are preferably used. The thickness of the undercoat layer is usually 0.01 to 5 μm, preferably 0.02 to 2 μm.

Next, the back surface of the paper substrate will be described.

The ink jet recording paper according to the first aspect of the present invention is used without any coating or treatment on the back side of the paper base material.

In this embodiment, the back surface of the paper substrate can be usually written with a general writing instrument, and printing by ink jet recording is also possible.

Even when ink-jet recording is performed on the back surface, the ink solvent is quickly absorbed into the paper, and does not stick to each other even when continuous printing is performed.

In addition, since an image is formed on the ink absorbing layer on the surface due to having a sufficient paper thickness, even if an ink solvent (water or a high boiling point organic solvent) remains on the ink absorbing layer on the surface, When they are combined, they are gradually absorbed into the paper on the back surface, so that blurring of images and characters is reduced.

In the ink jet recording paper according to the second aspect of the present invention, another ink absorbing layer is provided on the back side of the paper base without interposing a hydrophobic resin layer.

In this case, although the ink absorption speed on the back side is slightly lower than that of the ink jet recording paper of the first aspect of the present invention, most of the solvent of the printed recording liquid is contained in the paper base material. Since it is absorbed quickly, even in continuous printing, there is no practical problem.

By providing an ink-absorbing layer on the back side of a paper base material, it is possible to impart high water resistance and bleeding resistance to images such as characters recorded by ink jet on this surface, and to improve white background. It is also possible to reduce yellowing due to dripping or aging.

Further, there is an advantage that the coefficient of friction between the front and back of the recording paper can be easily controlled when printing continuously.

The ink absorbing layer provided on the back surface of the paper base may be a swelling layer substantially made of a hydrophilic binder, or may be a porous layer provided on the front side of the paper base. However, it is preferably a porous layer because the drying property during continuous printing is good and the probability of sticking to each other is reduced.

The dry film thickness of the ink absorbing layer provided on the back surface of the paper substrate is usually 1 to 2 when the ink absorbing layer is of a swelling type.
0 μm, preferably 2 to 15 μm. In the case of a porous ink absorbing layer, the thickness is usually 2 to 50 µm, preferably 5 to 30 µm.

The recording paper of the present invention is particularly suitable for applications such as postcards, but these are usually printed continuously in most cases. Therefore, it is preferable to provide a characteristic for continuous paper feeding, and it is particularly preferable to set the coefficient of static friction on the front and back to 0.8 or less from the viewpoint of continuous conveyance.

If the coefficient of static friction is 0.8 or less,
Problems that tend to occur when trying to convey and feed one sheet at a time (eg, many sheets are conveyed at once) are unlikely to occur. It is particularly preferable that the coefficient of static friction be 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 reduce the coefficient of static friction between the front and back sides to 0.8 or less, the surface characteristics of the ink absorbing layer on the front side of the paper base material and the surface characteristics of the paper base material (the ink jet recording paper of the invention of claim 1 of the present invention). In the case of (2), or the surface characteristics of the ink absorbing layer provided on the back side of the paper substrate (in the case of the ink jet recording paper of the invention of claim 2 of the present invention).

Specifically, a method of adding a matting agent to make the surface of the ink absorbing layer on the front and back have convex portions, or a wax, It can be adjusted relatively easily by adding a slipping agent such as a silicon compound or a fluorine compound.

A particularly effective means is to use a matting agent. In particular, it is preferable that the porous ink absorbing layer provided on the front side of the paper substrate contains 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 preferable.

The above matting agent having an average particle size 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
３０30 μm.

The matting agent preferably has a relatively uniform particle size distribution and has little gloss reduction. When the particle size distribution is measured, the degree of dispersion (standard deviation divided by average particle size) is 2.
Below, preferably 1.5 or less are preferred.

The amount of the matting agent used depends 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 usually 0.01 to 0.5 g per 1 m ^{2 of} recording paper.

Polymer latex A polymer latex polymerized by an 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.

[0108]

EXAMPLES The present invention will be described below in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the examples, “%” indicates absolute dry weight% unless otherwise specified.

Example 1 Low-density polyethylene containing 10% by weight of anatase type titanium oxide and having a density of 0.92 and a thickness of 8 μm was provided on the front side of a paper base material having a water content of 6.5% by weight and a basis weight of 200 g / m ^2. Then, a support for glossy paper coated with polyethylene by coating by a melt extrusion coating method was prepared. The 60-degree specular glossiness of this surface was 31%.

Next, a corona discharge was applied to the front side to coat a gelatin subbing layer at 0.03 g / m ² .

On a gelatin subbing layer, disclosed in JP-A-11-2
The coating liquid 1-1 described in Example 1 of No. 0306 was applied, and a porous ink absorbing layer having a dry film thickness of 40 μm was provided to obtain a recording paper-1 of the present invention.

Instead of the polyethylene layer on the recording paper-1, a coating solution in which polyvinyl chloride was dissolved in methyl ethyl ketone (containing 10% by weight of anatase type titanium oxide based on polyvinyl chloride) was dried on the above-mentioned paper substrate. Thickness 1
On a support obtained by coating and drying to a thickness of 5 μm,
Recording paper-2 of the present invention provided with an undercoat layer and a porous ink absorbing layer in the same manner as recording paper-1.

In recording paper-1, styrene / methyl methacrylate / t-butyl methacrylate = 40/3
After applying a 0/30 (molar ratio) polymer latex emulsion so that the dry film thickness becomes 15 μm, 1
Heat treatment was performed at 20 ° C. for 30 seconds to obtain a support having a hydrophobic resin layer. Subsequently, a subbing layer and a porous ink-absorbing layer were provided in the same manner as in the case of the recording paper-1, thereby producing a recording paper-3 of the present invention.

Comparative Recording Paper-4 was prepared by providing an undercoat layer and a porous ink absorbing layer on recording paper-1 without providing a polyethylene layer.

A comparative recording paper-5 was prepared by providing a polyethylene layer on the back side of the paper base material on recording paper-1, and providing an undercoat layer and the same porous ink absorbing layer on the front side on the polyethylene layer.

[0116] In the recording paper-1, the porous ink absorbing layer was made of 5.4 g of gelatin and 3.2 parts of polyvinyl alcohol.
Comparative recording paper-6 was prepared in which the swelling layer contained 2.2 g of polyvinylpyrrolidone and 2.2 g of polyvinylpyrrolidone.

Obtained recording paper (each A6 size)
First, using an inkjet printer PM770C manufactured by Seiko Epson Corporation, first, a color image was printed on the front side of the paper base material, and then address letters were printed on the back side. Twenty of each of the obtained prints were superimposed and stored for one day, and the state of sticking on the front and back, the character quality, and the occurrence of wrinkles on the image surface were evaluated. Also,
The same evaluation was performed by printing only characters on the back surface without printing a color image on the front surface.

The evaluation was performed according to the following criteria.

[Character Quality] A: Clear character image B: Slight character blur but readable C: Blurred enough to make character unreadable [Front and back sticking] No change B: The degree of peeling is worse than before printing, but not at a level that poses a practical problem. C: Characters or images are disturbed or the ink absorbing layer is destroyed when peeled [wrinkles] A : No or very little wrinkles B: wrinkles are observed in the image form but practically acceptable level C: many wrinkles and levels not practically acceptable as photographic grades The results obtained are shown in Table 1. .

[0120]

[Table 1]

From the results shown in Table 1, there is no particular problem when only the characters are printed on the back side of the comparative recording paper-4 in which the ink absorbing layer is directly provided on one side of the paper base. Wrinkles are severe when printed.

Comparative recording paper in which a hydrophobic resin layer was provided on both sides of a paper substrate and a porous ink absorbing layer was provided thereon
No. 5 showed no wrinkles and was good, but when a color image was printed on the surface, the characters were remarkably blurred, and sticking between the front and back was recognized.

In Comparative Recording Paper-6 provided with an ink absorbing layer composed of a swelling layer on the surface side of the paper base material, when printed on the front and back, sharp sticking was observed in the character portion.

On the other hand, even when the recording papers 1-3 of the present invention were printed on the front and back sides, no wrinkles or bleeding of characters were observed, and no sticking phenomenon was observed.

Example 2 Recording sheets 11 to 19 were prepared in the same manner as in recording sheet 1 except that the basis weight and the thickness of the hydrophobic resin layer were changed as shown in Table 2. Was prepared.

The obtained recording paper was evaluated for glossiness on the front side, unevenness of gloss, curl, and transportability.

[Glossiness] The 60-degree specular glossiness was measured. [Gloss unevenness] The surface of the recording paper was visually observed. A (no unevenness at all), B (slightly uneven), and C (severe unevenness). Judged.

[Curl] Recording paper at 23 ° C., 20%
Saved the day and averaged the lifting heights of the four corners. + Represents the time when the four corners are higher than the center when the surface is facing up, and-represents the curl in the opposite direction.

[Transportability] 2
Zero sheets were set and continuously fed, and the number of occurrences of multi-feed and feeding failure was evaluated.

[0130]

[Table 2]

From the results shown in Table 2, it is impractical for recording paper -14 using a paper base material having a basis weight of 80 g to have a large amount of low humidity + curl. Further, recording paper-19 having a basis weight of more than 300 g has good curl but poor transportability.

On the other hand, recording paper 13 having a hydrophobic resin layer thickness of more than 20 μm has a large curl at low humidity and is not practical.

Example 3 Recording sheets 21 to 24 were prepared in the same manner as in recording sheet 3 except that the dry film thickness of the hydrophobic resin layer was changed as shown in Table 3. Produced. Example 2
Evaluation was performed in the same manner as described above, and the results shown in Table 3 were obtained.

[0134]

[Table 3]

According to the results shown in Table 3, the recording paper 24 having a thickness of 1 μm or less as the hydrophobic resin layer has large gloss unevenness.

Example 4 A recording paper was prepared except that a coating solution having the following composition was applied to the back surface of the paper substrate used in the recording papers 1 to 4 prepared in Example 1 so that the dry film thickness became 5 μm. Recording papers 41 to 44 were produced in the same manner as in Nos. 1 to 4.

Coating liquid formulation (per liter) Alumina-treated silica (average particle size: 5 μm) 65 g Water-soluble cationic fluorescent whitening agent: Uvitex BAR Liquid (manufactured by CIBA-GEIGY) 1.2 g Polyvinyl alcohol (degree of polymerization = 4000, saponification degree 99%) 14 g Cationic polymer (P-1) 10 g The whole amount is finished to 1 liter with pure water.

Evaluation was performed in the same manner as in Example 1, and the results shown in Table 4 were obtained.

[0139]

Embedded image

[0140]

[Table 4]

From the results in Table 4, it can be seen that the character quality is improved by providing a thin ink absorbing layer on the back surface, but the recording paper-4 having no hydrophobic resin layer on the surface of the paper base material.
In No. 4, the character quality is deteriorated by printing on the front and back sides, and the sticking is also slightly deteriorated. On the other hand, the recording paper of the present invention does not have such a problem.

Example 5 When polyethylene was melt-extruded on the recording paper 41 of Example 4, various kinds of polyethylene were applied to the polyethylene surface while cooling using a cooling roll having irregular irregularities on the surface immediately after melt-extrusion coating. A typing process was performed.

On the fine grain surface, unevenness having a height difference of about 10 μm was formed by 3 m.
This is a fine grain surface in which 11 are regularly arranged at m intervals.

Using this support, a recording paper-51 was prepared in the same manner as the recording paper-41, and evaluated in the same manner as in Example 1. As a result, a paper having almost the same performance as the recording paper-41 was obtained.

Example 6 Recording papers 61 to 64 were prepared by changing the porous ink absorbing layer of recording paper-1 of Example 1 as follows.

The coating solution 1-1 used in Example 1 of JP-A-11-20306 was used under the condition that the dry film thickness was 30 μm, and the coating solution 3-1 used in Example 3 of JP-A-11-20306 was used.
Was simultaneously applied under the condition that the dry film thickness became 10 μm, to produce a recording paper-61. (The coating liquid 1-1 was applied so as to form a lower layer.) On the recording paper 61, a matting agent (polymethyl Methacrylate) to add recording paper-62 to
64 were prepared (the amount of addition was the amount per 1 m ² of recording paper).

Evaluation was performed in the same manner as in Example 2, and the results shown in Table 5 were obtained.

Further, the static friction coefficient when the front and back surfaces of each recording paper were faced was measured and is shown in Table 5.

[0149]

[Table 5]

The results shown in Table 5 indicate that the recording papers 61 to 6
In No. 4, even when continuous printing was performed, no transport failure occurred on both sides.

It can be seen that when the matting agent having an average particle size of 5 μm or more is used and when the degree of dispersion of the particle size distribution is 2 or less, the glossiness is excellent.

[0152]

According to the ink jet recording paper of the present invention, even if a high-quality image in which wrinkles are suppressed is continuously recorded on a recording paper on which ink is recorded on both sides by ink jetting, image bleeding occurs during superposition. And the recording paper does not stick to each other, and has an excellent effect.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 FC06 2H086 BA15 BA16 BA19 BA21 BA24 BA31 BA33 BA45 4L055 AG53 AG57 AG63 AG64 AG71 AG97 AH02 AH37 AJ04 BE09 EA08 EA16 EA27 FA19 FA30 GA09

Claims (6)

[Claims] 1. A paper base material having a basis weight of 100 to 300 g / m ² , wherein a porous ink absorbing layer is provided on one surface of a paper base material via a hydrophobic resin layer having a thickness of 1 to 20 μm. Ink jet recording paper. ^2. A paper base material having a basis weight of 100 to 300 g / m ² , which has a porous ink absorbing layer via a hydrophobic resin layer having a thickness of 1 to 20 μm on one surface, and An ink jet recording sheet having an ink absorbing layer without a hydrophobic resin layer on the side. 3. The ink jet recording paper according to claim 1, wherein the dry ink absorbing layer has a dry film thickness of 30 to 50 μm. 4. The ink jet recording sheet according to claim 1, wherein a static friction coefficient between the porous ink absorbing layer and the back surface is 0.8 or less. 5. The ink-jet recording sheet according to claim 1, wherein the porous ink-absorbing layer contains a matting agent having an average particle size of 5 μm or more. 6. The ink-jet recording paper according to claim 1, wherein the hydrophobic resin layer contains a pigment.