JP2001010203A - Ink jet recording paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a curling even when being stored under a condition of a low humidity to a high humidity before and after a printing. SOLUTION: In this ink jet recording paper, the curling degree of a supporting body wherein both surfaces of a paper of which the basic weight is 130 g/m2 or lower, are coated with a polyolefin resin, is -25 to -100. Also, at least on one side of the supporting body, a porous ink absorbing layer containing a hydrophilic binder, of which the dry film thickness is 30 to 45 μm is provided.

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 of photographic quality, and more particularly to an ink jet recording sheet having a relatively small thickness and having improved curl before and after printing and improved transportability.

[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. The print quality obtained by ink-jet recording depends on three factors: printer, ink, and recording paper. However, in terms of image quality, the recent two technical innovations are large, and the difference between recording papers affects the final print quality. Its importance is increasing very much.

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

[0005] The swellable ink absorbing layer is substantially composed of a hydrophilic polymer such as gelatin, polyvinyl alcohol, polyvinylpyrrolidone or polyethylene oxide.

The characteristics of the swellable ink absorbing layer are that high gloss can be obtained, and since a swellable polymer is used, a large volume of ink can be absorbed as long as the polymer can be swollen. It has the advantage that it can be manufactured, but on the other hand, it has low drying property and does not touch the surface immediately after printing, ink droplet absorption speed is slow, and image unevenness due to slow absorption speed when printing at high speed is likely to occur There are drawbacks.

[0007] There are several types of void-type 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 a void is formed between the fine particles. Here, the ink is absorbed.

[0008] The characteristics of this void-type ink absorbing layer are that the ink absorbing speed is high and unevenness is unlikely to occur during printing, the surface is apparently dry immediately after printing, the water resistance and ink absorption as seen in the swollen type ink absorbing layer. There is no speed dilemma and both can be satisfied at the same time. It is particularly preferable to the swelling type ink absorbing layer in terms of high-speed printing characteristics and high image quality.

When the above ink-absorbing layer is provided on a paper support coated on both sides with a hydrophobic resin and printed, high-quality prints can be obtained as described above. There are several weaknesses associated with

One of them is curl.

When the support is non-water-absorbing, all of the ink droplets must be held by the ink absorbing layer, and the ink absorbing layer becomes a much thicker film than the swelling type. When the thickness of the support is thin, curling is likely to occur due to the contraction of the ink absorbing layer when the support is thin.

In general, such a curl is suppressed by providing a binder layer having the same moisture absorption property as that of the ink absorbing layer on the opposite side so that the front and back stretch characteristics when the humidity changes can be matched. Done.

The present inventor has conducted various studies on such points, and as a result, when the back layer is provided using a hydrophilic binder,
It was found that the front and back sides tended to stick together during high-speed printing, or that it was difficult to easily achieve curl balance before and after printing.

When a hydrophilic binder layer is provided on the back layer for the purpose of curling adjustment and the curl balance is maintained under low to high humidity conditions before printing, extreme negative curl (print surface In this case, the curl whose end is lifted is called minus curl, and the curl in the opposite direction is called plus curl).

[0015] This disadvantage is also a problem that, when the substrate is coated with polyethylene on both sides of paper, the problem is more likely to occur as the basis weight of the paper is lower and as the dry thickness of the ink absorbing layer is larger. found.

Further, the basis weight of the paper as described above is small,
In addition, it was also found that when the ink absorbing layer was porous and thick, when the recording paper was stored under high humidity conditions for a long time, the positive curl increased extremely.

The problem is that the paper support has a basis weight of 130 g.
/ M ² or less, or when the thickness of the porous ink absorbing layer is 30 μm or more, it is easy to occur.

If the curl becomes large, not only will it have a serious adverse effect on the print quality, but it will also tend to cause poor paper feed and multiple transport when transported by an inkjet printer.

Such a change in the curl when the environmental humidity changes is caused by a gradual change in the moisture in the paper of the paper support coated with the polyolefin resin, and a change in the rigidity of the paper itself and a change in the curl characteristics. The change may be the cause. The change in water content of the paper usually progresses very slowly on a daily basis, but particularly when the ink absorbing layer is a thick film made of a porous layer, the moisture absorption of the ink absorbing layer is relatively short. Make very complex changes to make rapid changes.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a comparatively thin paper on a support having both surfaces coated with a polyolefin resin. Another object of the present invention is to provide an ink jet recording sheet in which curling is suppressed under low to high humidity conditions before and after printing in an ink jet recording sheet provided with an ink absorbing layer.

[0021]

The above object is achieved by the following recording paper.

1. A support having a basis weight of 130 g / m ² or less and coated on both sides with a polyolefin resin has a curl degree of −25 to −100, and contains a hydrophilic binder on at least one side of the support. Dry film thickness is 30
An ink jet recording paper having a porous ink absorbing layer of up to 45 μm.

2. 2. The ink jet recording paper according to claim 1, wherein the support has a back layer made of a hydrophobic latex polymer on the side opposite to the ink absorbing layer.

Hereinafter, the present invention will be described in detail.

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

As the pulp, a chemical pulp containing 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 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 freeness of the pulp used for papermaking is preferably 200 to 500 cc according to the specification of CSF, and the fiber length after beating is 24 mesh residual weight% and 42 mesh residual weight specified in JIS-P-8207. 30% by weight
To 70% is preferable. The weight percentage of the remaining 4 mesh
Is preferably 20% by weight or less.

The basis weight of the paper is 130 g / m ² or less, but 8
0 g / m ² or more is preferable. If it exceeds 130 g / m ² , it is more preferable in terms of curling, but the rigidity of the entire recording paper is increased or the thickness of the entire recording paper is increased, so that it becomes difficult to obtain various characteristics required for thin recording paper. In addition, 80 g / m
If it is less than ² , it is difficult to adjust the curl, and if the humidity changes, the curl becomes large.

The paper may be calendered at the papermaking stage or after the papermaking to provide high smoothness. Paper density is 0.7
It is generally from 1.2 to 1.2 g / m ² (JIS-P-8118). Further, the rigidity of the base paper is preferably 30 to 150 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 from 5 to 9 as measured by the hot water extraction method specified in JIS-P-8113. Next, the polyolefin resin covering both sides of the paper will be described.

As the polyolefin resin used for this purpose, polyolefins such as polyethylene, polypropylene, polyisobutylene, copolymers mainly composed of ethylene and propylene are preferable, and polyethylene is particularly preferable.

Hereinafter, particularly preferred polyethylene will be described.

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

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

In the polyethylene layer, a pigment having high heat resistance and a fluorescent whitening agent for adjusting the white background can be added.

Examples of the coloring pigment include ultramarine blue, navy blue, cobalt blue, phthalocyanine blue, manganese blue, cerulean, 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 polyethylene-coated paper may be used as a glossy paper, or may be subjected to a so-called embossing process when the polyethylene is melt-extruded and coated on the paper surface to obtain a matte surface or a silk surface which can be obtained by ordinary photographic printing paper. Those having a surface can also be used in the present invention.

The amount of polyethylene used on the front and back of the paper is selected so as to optimize the film thickness of the ink absorbing layer and the curl at low and high humidity after the back layer is provided. It is preferable that the polyethylene layer on the side on which the ink absorbing layer is applied is thinner, and it is preferable that the polyethylene layer be thinner than the opposite side by 2 μm or more. In particular, it is most preferable to make it 4 μm or thinner than the back side.

The preferred polyethylene on the ink absorbing layer side (hereinafter referred to as the surface side) is 5 to 25 μm, and the opposite side is 10 to 3 μm.
The range is 0 μm.

Further, the polyethylene-coated paper support preferably has the following properties.

Tensile strength: 2 to 30 kg in the vertical direction and 1 in the horizontal direction at a strength specified by JIS-P-8113.
It is preferably from 20 to 20 kg.

The tear strength is 10 to 200 g in the vertical direction and 2 in the horizontal direction according to the method specified in JIS-P-8116.
0 to 200 g is preferred.

Compression elastic modulus ≧ 10 ³ kgf / cm ² .

Surface Beck smoothness: JIS-P-811
Although 200 seconds or more is preferable for the glossy surface under the conditions specified in 9, the so-called molded product may be shorter than 200 seconds.

Surface Roughness: It is preferable that the surface roughness specified in JIS-B-0601 has a maximum height of 10 μm or less per 2.5 mm of reference length.

Opacity: 80% or more, especially 85 to 9 when measured by the method specified in JIS-P-8138.
8% is preferred.

Whiteness: L ^* , a ^* , b ^* specified by JIS-Z-8729 are L ^* = 80 to 95, a ^* = − 3 to +
5, it is preferable that b ^* =-6 to +2.

Surface gloss: The 60-degree specular gloss defined in JIS-Z-8741 is preferably 10 to 95%.

[0052] Clark stiffness: support Clark stiffness in the carrying direction is 50~300cm ^2/100 of the recording paper is preferred.

There are various methods for applying a polyethylene resin to a paper substrate, and a method of extruding and applying a molten polyethylene to a paper substrate is particularly preferable. After a polyethylene resin is applied to a paper substrate by an extrusion coating method, a mirror surface or various kinds of rough surface rolls can be used as a cooling roll to change the glossiness of the polyethylene surface or to prepare a support having a clear surface.

The support used in the present invention, in which both surfaces of the paper are coated with a polyolefin resin, preferably has a paper moisture content of 3 to 10% by weight from the viewpoint of the curl variation over time.

Here, the water content of the paper is obtained by multiplying the value obtained by dividing the water content of the paper by the weight of the solid content of the paper by 100 times.

In order to maintain a constant amount of water in the paper, a deliquescent inorganic salt such as calcium chloride or a hygroscopic compound such as glycol can be added.

After being coated with the polyolefin resin, the moisture content does not fluctuate greatly if the support is wound in a roll state, but nevertheless it is kept under extremely high humidity (for example, a relative humidity of 90%) for a long time ( It is better to avoid storing them (for example, more than one month).

The support of the present invention has a curl degree of -25 to 25 in advance.
It was adjusted between -100.

Here, the degree of curl means that a rectangular support sample cut to 1 cm × 5 cm is measured at 23 ° C. and a relative humidity of 80%.
%, When left on a horizontal table for 24 hours and the radius of curvature of the curled sample is dcm, the degree of curl is expressed as 100 / d.

When the sample is allowed to stand, the four corners are left in a lifting direction, and when the four corners are lifted up with the ink absorbing layer surface facing upward, + is when the four corners are lifted with the ink absorbing layer surface side facing down. Display as

Here, the sample is measured in two directions, that is, the papermaking direction of the support and the direction perpendicular to the papermaking direction, and the one having the larger absolute value of the curl degree is used. Usually 1cm in the papermaking direction,
In the case of a cut sample having a size of 5 cm in a direction perpendicular to this, the curl increases.

Here, when a back layer described below is provided, the back layer is included in the support.

In the recording paper of the present invention, the curl of the support is used in the range of -25 to -100. By reducing the curl very much (ie, increasing the negative curl). Even when a thick ink absorbing layer is provided, the curl value is stable against a change in humidity.
Also, relatively little curl is produced even when the humidity changes when printing is performed. The preferred curl degree of the support is-
30 to -90.

As means for adjusting the curl degree of the support within the range of the present invention, there are various methods other than changing the thickness of the front and back polyolefin resins, and the following methods are exemplified.

A curl of the paper support itself is changed by providing a relatively thin coat layer on one or both sides of the paper support and changing the thickness or composition of the coat layer.

Change the composition of the polyolefin resin on both sides (use of polyethylene and polypropylene, polyethylene and polyethylene / vinyl acetate copolymer, etc.).

When a polyethylene resin is used, HD
Change the ratio between PE and LDPE.

These various methods for changing the ratio of the inorganic pigment in the polyolefin resin can be used in an appropriate combination.

A back layer can be provided on the side opposite to the side having the ink absorbing layer of the ink jet recording paper of the present invention to prevent curling and charging.

As the back layer, a layer composed of a hydrophilic binder, a hydrophobic binder, or a mixed binder obtained by combining them is used.

In the back layer made of a hydrophilic binder, curl before printing can be adjusted relatively easily.
It is not preferable to satisfy both curl before and after printing.

As described above, when the back layer is substantially made of a hydrophilic binder, the curl balance can be relatively easily made by giving the same elasticity to the front and back sides to contain the hydrophilic binder. It can be adjusted, but after printing, an extreme minus curl tends to occur when placed in a low-humidity environment due to the solvent remaining in the ink absorbing layer. Further, the image recorded on the surface tends to be easily transferred.

A preferred back layer is made of a hydrophobic binder, and particularly preferred is a back layer coated with a hydrophobic latex polymer.

When a hydrophobic backing layer is provided, the backing layer itself does not have much curl adjusting function, but the addition of an antistatic agent or a matting agent improves slipperiness with the surface and improves transportability in a printer. You.

The hydrophobic latex polymer is a homopolymer or copolymer latex of a polymerizable monomer such as ethylene, vinyl acetate, styrene, butadiene, vinyl chloride, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and divinylbenzene.

In the back layer, an antistatic agent such as a matting agent or a surfactant or a polymer having a quaternary ammonium base for improving the slipperiness, a slipperiness improvement such as a wax, a silicon compound or a fluorine compound, etc. Agents can be included.

The matting agent used in the back layer has a mean particle size of 0.5 to 50 μm, preferably 1 to 30 μm, and includes inorganic particles such as silica and organic fine particles such as methyl methacrylate, polystyrene and polyethylene.

The thickness of the back layer varies depending on the properties of the binder of the back layer. In the case of a hydrophobic binder which is preferably used, 0.01 to 5 per m ^{2 of} recording paper is used.
g, preferably 0.02 to 2 g.

These back layers may be provided in advance, or may be provided after the ink absorbing layer is applied.

Next, the porous ink absorbing layer provided on the support will be described.

The porous ink absorbing layer of the present invention is preferably a porous layer 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 alumina, pseudoboehmite, aluminum hydroxide,
Examples thereof include white inorganic pigments such as lithopone, zeolite, 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, silica or pseudo-boehmite is preferable from the viewpoint of forming fine voids, and silica, colloidal silica and pseudo-boehmite synthesized by a gas phase method having an average particle diameter of 200 nm or less are particularly preferable.

The average particle diameter of the inorganic fine particles is obtained by observing the particles themselves or the cross section or surface of the ink absorbing layer with an electron microscope, calculating the particle diameter of 100 arbitrary particles, and calculating the simple average value (number average). Desired. Here, each particle size is represented by a diameter assuming a circle equal to the projected area.

Examples of the hydrophilic polymer used in the ink absorbing layer include gelatin (eg, an alkali-treated gelatin, an acid-treated gelatin, a derivative gelatin obtained by blocking an amino machine with phenyl isocyanate or phthalic anhydride), polyvinyl alcohol (average polymerization). Degree is preferably 300 to 4000, saponification degree is preferably 80 to 99.5%), polyvinylpyrrolidone, polyethylene oxide, hydroxylethylcellulose, agar, pullulan, dextran, acrylic acid,
Carboxymethylcellulose, casein, alginic acid and the like can be mentioned, and two or more kinds can be used in combination.

A preferred hydrophilic polymer is polyvinyl alcohol whose moisture absorption performance hardly changes when the humidity changes.

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

As the polyvinyl alcohol obtained by hydrolyzing vinyl acetate, those having an average degree of polymerization of 300 or more are preferably used, and those having an average degree of polymerization of 1,000 to 5,000 are particularly preferably used. Saponification degree is 70-100%
Is preferable, and 80 to 99.5% is particularly preferable.

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

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

The proportion of the cation-modified group-containing monomer in the cation-modified polyvinyl alcohol is 0.1 to 10 mol%, preferably 0.2 to 5 mol%, based on vinyl acetate.

The anion-modified polyvinyl alcohol is, for example, a polyvinyl alcohol having an anionic group as described in JP-A-1-2060888, JP-A-61-237681, and JP-A-63-307979.
As described in JP-A-7-285265, copolymers of vinyl alcohol and a vinyl compound having a water-soluble group, and modified polyvinyl alcohol having a water-soluble group as described in JP-A-7-285265 are disclosed. No.

Examples of the nonionic modified polyvinyl alcohol include, for example, a polyvinyl alcohol derivative having a polyalkylene oxide group added to a part of vinyl alcohol as described in JP-A-7-9758, and JP-A-8-25795. And a block copolymer of a vinyl compound having a hydrophobic group and vinyl alcohol described in Japanese Patent Application Laid-Open Publication No. H11-157,086.

Two or more kinds of polyvinyl alcohols such as different degrees of polymerization and different types of modification can be used in combination.

The amount of the inorganic fine particles used is 1 m on a recording sheet.
^{It is 3 to} 50 g per ² and particularly preferably 5 to 30 g. The amount of the hydrophilic polymer used is 0.5 to 10 g, particularly 1 to ⁵ g per 1 m ² of recording paper. The ratio of the inorganic fine particles to the hydrophilic polymer is generally 3 to
It is 10.

The ink absorbing layer contains boric acid or a salt thereof in order to improve the film forming property of the film and increase the strength of the film. The boric acid or a salt thereof refers to an oxyacid having a boron atom as a central atom and a salt thereof, and specifically, orthoboric acid, metaboric acid, hypoboric acid, tetraboric acid, pentaboric acid and salts thereof. Is included.

The amount of boric acid or a salt thereof can vary widely depending on the amount of the inorganic fine particles and the hydrophilic polymer in the coating solution, but is generally about 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 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
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.

In applying the ink absorbing layer on the support, the support is subjected to a corona discharge treatment or a subbing treatment for the purpose of increasing the adhesive strength between the support and the ink absorbing layer. Is preferred.

The ink absorbing layer can be applied by a roll coating method, a rod bar coating method, an air knife coating method, a spray coating method, a curtain coating method or an extrusion coating method using a hopper described in US Pat. No. 2,681,294. It is preferably used.

After the coating liquid for forming the ink absorbing layer is applied on the support, it is dried to obtain a recording paper.
Usually, the coating liquid is applied on a support wound in a roll shape, dried and then wound up again in a roll shape. In the drying process, the moisture in the support hardly fluctuates if it is within a normal drying time (approximately 30 minutes or less).

The drying is preferably performed at a temperature in the range of about 0 to 80 ° C. If the temperature is higher than 80 ° C., the polyolefin resin is softened to make it difficult to convey, or the gloss of the recording layer surface becomes uneven. The preferred drying temperature is from 0 to 70C.

The ink jet recording paper of the present invention can be used both when recording with an ink solution containing a water-soluble dye and when recording with a pigment ink.

[0109]

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

Example 1 A low-density polyethylene having a density of 0.92 was applied on both sides of a photographic base paper having a basis weight of 115 g / m ^{2 by} an extrusion coating method to prepare a support having both sides coated with polyethylene.
The front side contains 5.5% by weight of anatase type titanium oxide.
At this time, the polyethylene on the front side in the range of 10 to 20 g,
Further, by changing the thickness of the back side polyethylene in the range of 10 to 30 g, seven types of supports having curling characteristics were produced.

After a corona discharge was performed on the front side and the gelatin subbing layer was subjected to 0.1 g / m ² , and a corona discharge was also performed on the back side, the styrene / butadiene latex layer was formed to a thickness of 0.4 g / m 2.
² was applied. In the latex layer on the back side, a silica-based matting agent having an average particle size of about 3 μm, a cationic antistatic agent, a silicon-based dispersion and a fluorine-based surfactant are respectively 10% by weight and 5% by weight based on the binder resin. ,
It contains 2% by weight and 3% by weight.

Table 1 shows the degree of curl of the support obtained as described above.

The water content of the support of each recording sheet was in the range of 5 to 6%.

Next, a coating solution for forming an ink absorbing layer was prepared as follows.

[Preparation of Titanium Oxide Dispersion-1] 20 kg of titanium oxide having an average particle size of about 0.25 μm (manufactured by Ishihara Sangyo:
W-10), 150 g of sodium tripolyphosphate having a pH of 7.5, and polyvinyl alcohol (manufactured by Kuraray Co., Ltd.):
PVA235) 500 g, cationic polymer (P-1)
150g and Sannobuco Co., Ltd. Defoamer SN381
Was added to 90 L of an aqueous solution containing 10 g and dispersed with a high-pressure homogenizer (manufactured by Sanwa Kogyo Co., Ltd.).
L to obtain a uniform titanium oxide dispersion liquid-1.

[Preparation of Silica Dispersion-1] 125 kg of fumed silica (A300 manufactured by Nippon Aerosil Co., Ltd.) having an average primary particle size of about 0.007 μm was manufactured by Mitamura Riken Kogyo Co., Ltd. After suction-dispersing in 620 L of pure water adjusted to pH = 2.5 with nitric acid at room temperature using a jet stream inductor mixer TDS, the total amount was 69%.
Finished silica dispersion liquid 1 was adjusted to 4 L with pure water.

"Preparation of silica dispersion-2" 1.29 kg of the cationic polymer (P-1), 4.2 L of ethanol,
An aqueous solution containing 1.5 L of n-propanol (pH =
2.3) 69.4 L of silica dispersion-1 was added to 18 L with stirring, and then 260 g of boric acid and borax 2 were added.
7.0 L of an aqueous solution containing 30 g was added, and 1 g of the antifoaming agent SN381 was added.

This mixture was dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd., and the whole amount was made up to 97 L with pure water to prepare a silica dispersion liquid-2.

[0119]

Embedded image

"Preparation of Fluorescent Whitening Agent Dispersion-1" Oil-soluble fluorescent whitening agent UVITEX-OB.
400 g of diisodecyl phthalate was dissolved by heating in 9000 g of diisodecyl phthalate and 12 L of ethyl acetate.
500 g, cationic polymer (P-1), saponin 50
% Of an aqueous solution containing 6,000 ml, mixed and emulsified and dispersed with a high-pressure homogenizer manufactured by Sanwa Kogyo Co., Ltd., and ethyl acetate was removed under reduced pressure.
L, and a fluorescent brightener dispersion liquid-1 was prepared.

"Preparation of Matting Agent Dispersion-1" Methacrylic acid ester-based matting agent MX-15 manufactured by Soken Kagaku Co., Ltd.
156 g of 000H was added to 7 L of pure water containing 3 g of the PVA235, and dispersed with a high-speed homogenizer to make the total amount 7.8 L, thereby preparing a matting agent dispersion liquid-1.

"Preparation of Coating Solution" Coating solutions for the first, second and third layers were prepared by the following procedure.

Coating solution for first layer: 60 of silica dispersion-2
The following additives were sequentially mixed with 0 ml while stirring at 40 ° C.

10% aqueous solution of polyvinyl alcohol (Kuraray Industries, Ltd .: PVA203): 0.6 ml 5% aqueous solution of polyvinyl alcohol (Kuraray Industries, Ltd .: PVA235): 260 ml Fluorescent brightener dispersion liquid-1: 25 ml Titanium oxide dispersion-1: 33 ml Latex Emulsion AE-803 manufactured by Dai-ichi Kogyo Co., Ltd .: 18 ml Make up to 1000 ml with pure water.

Coating solution for second layer: 65 of silica dispersion-2
The following additives were sequentially mixed with 0 ml while stirring at 40 ° C.

10% aqueous solution of polyvinyl alcohol (Kuraray Industries, Ltd .: PVA203): 0.6 ml 5% aqueous solution of polyvinyl alcohol (Kuraray Industries, Ltd .: PVA235): 270 ml Fluorescent brightener dispersion liquid-1: Make up to 1000ml with 35ml pure water.

Coating solution for third layer: 65 of silica dispersion-2
The following additives were sequentially mixed with 0 ml while stirring at 40 ° C.

A 10% aqueous solution of polyvinyl alcohol (manufactured by Kuraray Industries, Ltd .: PVA203): 0.6 ml A 5% aqueous solution of polyvinyl alcohol (manufactured by Kuraray Industries, Ltd .: PVA235): 270 ml Silicon dispersion (Toray Dow Corning) -BY-22-839 (manufactured by Silicone Co., Ltd.): 15 ml 50% aqueous solution of saponin: 4 ml Matting agent dispersion liquid-1: 10 ml Make up the total amount to 1000 ml with pure water.

The coating solution obtained as described above was filtered with the following filter.

First layer and second layer: 2 layers with TCP10 manufactured by Toyo Roshi Kaisha, Ltd. 3rd layer: 2 layers with TCP30 manufactured by Toyo Roshi K.K. Each layer was applied in order of one layer (45 μm), second layer (90 μm), and third layer (40 μm). The values in the parentheses indicate the respective wet film thicknesses, and the first to third layers were simultaneously applied.

Each coating solution was applied at 40 ° C. using a three-layer slide hopper, and immediately after application, the coating solution was cooled in a cooling zone maintained at 7 ° C. for 20 seconds, and then blown with a wind of 20 to 30 ° C. for 30 seconds. 60 ° C at 45 ° C, 6 ° C at 55 ° C
By drying sequentially for 0 second, recording papers 1 to 7 were obtained.

The dry film thickness of the ink absorbing layer was 35
μm.

Each of the obtained recording papers was stored at 36 ° C. for 3 days to harden, cut into A4 size sheets, and 20 sheets were piled up and wrapped in a polyethylene bag having a thickness of 30 μm.

Each of the obtained recording sheets was evaluated by the following method.

(1) Curling of Raw Sample The unprinted recording paper was taken out of the package at 23 ° C. and a relative humidity of 20% or 80%, and the curl was measured after one hour.

The curl was measured on a horizontal desk, with the print surface up for plus curl and the print surface down for minus curl, and the average of the curl heights at the four corners was measured. It was determined as a value (in mm).

Further, the curl when left in the same environment for 5 days was measured in the same manner.

(2) Curl after printing A4 size samples left for 1 hour under the above two different humidity conditions were solid printed in magenta (15 cm × 24 cm) using an inkjet printer manufactured by Seiko Epson Corporation: PM770C. Area), and after printing, it was left under the environment for 3 minutes, and the curl was measured in the same manner as above.

Even before printing, curling tends to be a fatal problem if it exceeds ± 20 mm, and if it is less than ± 15 mm, it hardly causes a problem in most practical cases.

On the other hand, curl after printing affects print quality, but is preferably within ± 20 mm.

Table 1 shows the obtained results.

[0142]

[Table 1]

From the results shown in Table 1, the curl degree of the support was -2.
For the recording papers 1 and 2 using a support larger than 5, the curl at low humidity before printing and the curl when stored at high humidity for 5 days before printing are +20 mm or more.

In the case of the recording paper 7 in which the degree of curl of the support is -100 or less, the curl after printing or when stored for 5 days in high humidity before printing is -20 mm or less.

On the other hand, it can be seen that the recording papers 3 to 6 of the present invention show good curl characteristics in all cases.

Example 2 Recording sheets 11 to 16 were produced in the same manner as in Example 1 except that the basis weight of the support paper was changed to 85 g. Evaluation was performed in the same manner as in Example 1, and the results shown in Table 2 were obtained.

[0147]

[Table 2]

From the results shown in Table 2, even when the basis weight of the paper was 85 g, the curl degree of the support was -25 to -100.
It can be seen that the recording paper in the range of has good curl characteristics.

Example 3 Recording sheets 21 to 25 were prepared in the same manner as in Example 1 except that the basis weight of the support paper was changed to 70 g in the recording sheets 1 to 5 used in Example 1. Evaluation was performed in the same manner as in Example 1, and the results shown in Table 3 were obtained.

[0150]

[Table 3]

From the results shown in Table 3, the basis weight of the paper support was 8
When the support is not more than 0 g and the curl degree is within the range of the present invention, the curl is ± 20 in any case.
It can be seen that the variation width is larger than that of the first and second embodiments with respect to the change of the environmental humidity. From Examples 1 to 3, it is understood that the basis weight of the paper is particularly preferably 80 g or more.

Example 4 In the recording paper 5 produced in Example 1, the thickness of the ink absorbing layer was increased by 20% and 40% for each layer, and the recording papers 5A and 5B having a total dry film thickness of 42 μm and 49 μm, respectively. Was prepared in the same manner as for recording paper 5.

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

[0154]

[Table 4]

From the results shown in Table 4, it can be seen that as the dry film thickness of the ink absorbing layer is increased, the curl, particularly when stored under high humidity conditions for 5 days, sharply increases.

Example 5 The same support as that of the recording paper 5 was prepared except that the back layer of the recording paper 5 prepared in Example 1 was changed to a latex resin with the following binder.

For recording paper 5C: styrene-ethyl methacrylate latex For recording paper 5D: polyvinyl chloride latex For recording paper 5E: gelatin For recording paper 5F: polyvinyl alcohol Then, in the same manner as in Example 1, an ink receiving layer was applied. Recording papers 5C to 5F were produced.

Evaluation was performed in the same manner as in Example 1, and the results shown in Table 5 were obtained.

[0159]

[Table 5]

From the results shown in Table 5, no significant change in curl characteristics was observed even when the composition of the back layer was changed as described above.

Next, the above-mentioned recording paper was transferred to an A4 size sample using an on-demand type ink jet printer.
As a result of a zero-sheet continuous transport test, it is found that when a hydrophilic binder is used for the back layer, the transportability decreases.

Example 6 As a result of performing a transportability test on the recording paper prepared in Example 1 in the same manner as in Example 5, the results shown in Table 6 were obtained. This indicates the number of sheets on which recording paper is not conveyed when printed by a printer, or is not normally fed by multiple conveyance or the like).

[0163]

[Table 6]

From the results shown in Table 6, recording paper having a large curl is likely to cause conveyance failure.

[0165]

According to the present invention, the basis weight is 130 g / m ^2.
By providing an ink-absorbing layer of a porous layer containing a hydrophilic binder on at least one side of a thin support in which both sides of the following paper are coated with a polyolefin resin, curling before and after printing is excellent. It can be adjusted, and excellent effects can be obtained in terms of transportability.

Continued on the front page F-term (reference) 2C056 EA13 FC06 2H086 BA14 BA15 BA19 BA21 BA24 BA35

Claims (2)

[Claims] 1. A paper having a basis weight of 130 g / m ² or less coated with a polyolefin resin on both surfaces of a support having a curl degree of-
25 to -100, and a dry film thickness containing a hydrophilic binder on at least one side of the support is 30 to
An ink jet recording paper having a 45 μm porous ink absorbing layer. 2. The ink-jet recording sheet according to claim 1, wherein the support has a back layer made of a hydrophobic latex polymer on the side opposite to the ink absorbing layer.