JP2002052813A - Sheet for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet for ink jet recording which is excellent in the property of preventing curling in an environment of temperature and humidity of a wide range, in addition to the primary characteristics of ink absorbing properties, a clear image, etc. SOLUTION: The sheet for ink jet recording has an ink receiving layer containing an inorganic pigment and provided on one surface of a paper base constituted mainly of pulp and has a back coating layer on the opposite side to the ink receiving layer. The back coating layer contains a flake silica of 5 mass % or more to the whole mass thereof.

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 capable of suppressing curling in a wide range of environments, in addition to essential properties such as ink absorbency, surface smoothness, and sharpness of an obtained image.

[0002]

2. Description of the Related Art In recent years, with the spread of digital cameras and computers, hard copy technology for recording images on paper or the like has been rapidly developed. The ultimate goal of these hard copies is silver halide photography,
How to bring color reproducibility, image density, surface glossiness, weather resistance, etc. closer to silver halide photography is an issue for development.

There are various types of hard copy recording methods, such as a method of directly photographing a display displaying an image by a silver halide photograph, a sublimation type thermal transfer method, an ink jet recording method, and an electrostatic transfer method.

Among them, the ink jet recording system has advantages such as a relatively small apparatus and a low running cost, and is considered to be the mainstream of the hard copy system together with the sublimation type thermal transfer system and the like. In the ink jet recording method, ink droplets composed of a dye and a large amount of a solvent are ejected from a nozzle toward a recording medium at a high speed. 2. Description of the Related Art Printers based on the ink jet recording system have been rapidly spreading in recent years because they are easy to achieve full color and high speed and have low printing noise.

[0005] With the increase in definition and speed of the ink jet recording system, the use thereof has been expanded and the environment in which it is used has been expanded. Therefore, ink-jet recording sheets are required to have not only intrinsic properties such as ink absorbency, surface smoothness, and clarity of an obtained image, but also properties capable of suppressing curling in a wide temperature and humidity range environment. It became so.

[0006] In particular, in the case of a recording sheet in which the support is made of a paper base material containing pulp as a main component, a change in temperature or humidity causes a difference in expansion and contraction between the ink receiving layer and the paper base material, resulting in a larger curl. Occurs. For the purpose of eliminating such curling, the back surface of the recording sheet may be subjected to humidification treatment by applying water or steam, or a specific coating layer may be provided on the back surface of the recording sheet (JP-A-5-221115). Proposals have been made, but sufficient properties have not yet been obtained. In particular, at present, there is no recording sheet having satisfactory curl suppression when the above-mentioned support is a paper substrate.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ink having high ink absorbency, capable of forming a clear image, having excellent intrinsic properties such as surface gloss and smoothness, and curling in a wide range of environments. An object of the present invention is to provide an ink jet recording sheet having excellent prevention properties.

[0008]

According to the present invention, a paper base mainly composed of pulp has an ink receiving layer containing an inorganic pigment and a binder on one side and a backside coating layer on the other side. An ink jet recording sheet, wherein the back coating layer contains 5% by mass or more of flaky silica with respect to the total mass thereof.

According to the study of the present inventor, the flaky silica having the above specific shape has a very large curl prevention effect in an environment of a wide temperature and humidity range of an ink jet recording sheet, although the mechanism is not always clear. Was found to have. As shown in the examples described below, such scaly silica [eg, Example 3]
Is a material as conventionally proposed (for example, Example 5
Compared with 7), when the thickness of the back surface coating layer of the ink jet recording sheet is the same, it has a remarkably large curl prevention effect, and even when the thickness is reduced by half, it is still equivalent or higher. Has a curling prevention effect. In particular, it has the effects of being able to be used without a binder and of reducing the amount of coating, as compared with conventionally proposed ones using plate-like inorganic particles.

In general, an ink jet recording sheet has a support made of a paper base material mainly composed of pulp, or has a high-quality ink-receiving layer having high ink absorbency and capable of obtaining a clear image. Since curling is more likely to occur in a recording sheet, a back coating layer for preventing curling that has high performance is required.

For this reason, the present invention provides a recording sheet having a paper base as a support, and an ink receiving layer formed of alumina hydrate, particularly boehmite, which is excellent in ink absorbency and image clarity. It is most suitable for the curl prevention of a recording sheet having a quality ink receiving layer. Hereinafter, the present invention will be described in more detail.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a support used in the present invention,
Preferably, a paper base mainly composed of pulp is used. The paper substrate is not particularly limited, and one containing pulp preferably at least 70% by mass, particularly preferably at least 80% by mass is appropriate. For example, acidic paper and neutral paper used in the coated paper field are preferably used.
As the pulp constituting the paper substrate, a natural pulp mainly containing a softwood pulp, a hardwood pulp, or a mixed pulp of a softwood and a hardwood is preferably used. They are used in bleached pulp such as kraft pulp, sulfite pulp and soda pulp. Further, in addition to natural pulp, a paper substrate containing synthetic fibers or synthetic pulp can be used.

[0013] The thickness of the support is selected depending on the application, as the basis weight is preferably from 60~250g / m ^2, in particular, 100~230g / m ² is preferred. The support may contain various additives, for example, a filler, a sizing agent, a paper strength enhancer, a pH adjuster, a retention enhancer, and the like.

Further, the paper substrate in the present invention may be a paper substrate having a pigment coating layer comprising a pigment and a binder on one or both sides thereof, for example, a coated paper.
As coated paper, preferred is, for example, one-sided or two-sided coating of cast coated paper, super art paper, art paper, coated paper, super dull art paper, mat art paper, dull art paper, mat coated paper, dull coated paper, etc. Goods.

In the present invention, an ink-receiving layer containing an inorganic pigment and a binder is formed on one side of the paper base. The inorganic pigment used for forming the ink-receiving layer is an inorganic oxide or an inorganic oxide. The hydrate is used. Preferred specific examples include silica, alumina, alumina hydrate, and silica-alumina composite. Alumina hydrate is preferable because it absorbs and fixes the ink well. In particular, boehmite (Al ₂ O ₃ .nH
₂ O, n = _1~1.5) are preferred. Although various forms of alumina hydrate can be used, it is preferable to use sol boehmite as a raw material because a smooth layer can be easily obtained.

Since the ink receiving layer has sufficient ink absorbency and transparency, the average pore radius of the pore structure is preferably 3 to 25 nm.
Pore volume, preferably suitably have a 0.3~2.0cm ³ / g. By increasing the transparency of the ink receiving layer, particularly the alumina hydrate, the color density can be increased and a clear image can be obtained. Especially, it is preferable that the pore radius is substantially distributed in the range of 1 to 50 nm. Incidentally, the pore radius distribution in the present invention,
It is measured by a nitrogen adsorption / desorption method.

Examples of the binder used in the ink receiving layer include starch or a modified product thereof, polyvinyl alcohol or a modified product thereof, styrene / butadiene rubber latex, nitrile / butadiene rubber latex, hydroxycellulose, hydroxymethylcellulose, methylcellulose and carboxymethylcellulose. And water-soluble polymers such as gelatin, polyvinylpyrrolidone, polyacrylic acid, and polyacrylamide, alcohol-soluble polymers, and mixtures of these polymers.
Among them, in the present invention, use of polyvinyl alcohol or a modified product thereof is preferable because of good ink absorbency and water resistance. The binder is suitably contained in an amount of preferably 1 to 30 parts by mass, particularly preferably 3 to 15 parts by mass with respect to 100 parts by mass of the pigment in the ink receiving layer.

In the present invention, the coating amount of the ink receiving layer provided on the paper substrate is determined based on the ink absorption, the strength of the coating layer,
Although it is selected depending on the use and the like, the coating amount after drying is preferably 1 to 100 g / m ² . If the coating amount is less than 1 g / m ² , the effect as an ink receiving layer is hardly exhibited, while if it exceeds 100 g / m ² , transparency and strength may be reduced, which is not preferable. Above all, the coating amount of the ink receiving layer is 5 to 5.
Suitably, it is 50 g / m ² .

The means for providing the ink receiving layer on the support may be, for example, a slurry prepared by adding a binder to a pigment, a roll coater, an air knife coater, a blade coater, a rod coater, a bar coater, a comma coater, a gravure coater, a die coater. Coater, curtain coater, spray coater, slide die coater, etc.
A drying method can be employed.

The surface of the ink receiving layer thus formed can be subjected to an appropriate surface treatment. As such a surface treatment, a device such as a super calender or a gloss calender is used.
160 ° C., especially 30 to 100 ° C., preferably at a pressure of 50 to 400 kN / m, especially 100 to 250 kN
Gloss may be imparted by calendering by passing between rolls at / m. Such gloss may be imparted by so-called cast coating in which the ink receiving layer is dried and released with its surface in contact with a smooth molding surface when forming the ink receiving layer.

A backside coating layer is formed on the surface of the recording sheet of the present invention opposite to the side having the ink receiving layer, and the backside coating layer contains flaky silica. The term “flaky silica” as used herein refers to extremely thin scaly primary particles having a nano-sized thickness formed of silicon dioxide. Usually, a plurality of such scaly primary particles are overlapped in parallel. It is used in the form of slurry dispersed in water in the form of secondary particles having a laminated structure. When a slurry in which flaky silica particles are dispersed is applied to a substrate and dried, the particles are extremely strongly bound to each other, and have a unique property of self-forming. This is because the amount of silanol groups (-SiOH) per specific surface area of the flaky silica particles has a value several times as large as that of silica gel, and condensation of the silanol groups occurs by drying, and particle binding occurs. Seem.

In the present invention, the scale-like silica is obtained when the thickness is 0.01 to 0.5 μm and the ratio of the maximum length of the scale plate to the thickness (aspect ratio) is 10 or more. It is preferable in terms of efficiency and economy.

For the formation of the backside coating layer, the above-mentioned flaky silica may be used alone, but the content of the flaky silica is determined based on the total weight of the backside coating layer after drying. And 5
It is at least 10 mass%, preferably at least 10 mass%. When the content is smaller than this, the effect of suppressing environmental curl is insufficient, and the effect of the present invention is not achieved. In particular, such a content is particularly preferably from 40 to 100% by mass.

When other pigments are used in combination for forming the back coating layer, examples of such other pigments include kaolin, light calcium carbonate, heavy calcium carbonate, talc, satin white, titanium dioxide, zinc oxide, and carbon dioxide. Zinc, zinc sulfide, barium sulfate, calcium sulfate, calcium silicate,
Inorganic pigments such as magnesium silicate, aluminum silicate, magnesium hydroxide, aluminum hydroxide, magnesium carbonate, hydrohaloysite, silica, alumina, alumina hydrate, urea resin, melamine resin, styrene,
Organic pigments such as acrylic pigments are exemplified.

For forming the back coating layer, it is preferable to use a binder, if necessary. Examples of the binder include homopolymers such as polyisobutylene, chloroprene rubber, and polybutadiene rubber, copolymers of styrene and butadiene, copolymers of acrylonitrile and butadiene, and copolymers of methyl methacrylate and butadiene. And a homopolymer such as polystyrene, polyvinyl chloride, polyethylene and polyvinyl acetate, and a vinyl polymer latex such as acryl, vinyl chloride, vinyl acetate and acrylate copolymers. If necessary, a water-soluble polymer such as starch or a modified product thereof, polyvinyl alcohol or a modified product thereof, methylcellulose, carboxymethylcellulose, hydroxycellulose, hydroxymethylcellulose, polyvinylpyrrolidone, polyacrylic acid, polyacrylamide, etc., together with the above synthetic polymer latex. Coalescence, alcohol-soluble polymers and the like can be used. The binder is preferably contained in an amount of preferably 1 to 30 parts by mass, particularly 3 to 15 parts by mass with respect to 100 parts by mass of the pigment in the back coating layer.

When a back coating layer is formed, especially when a copolymer of styrene and butadiene is used as a latex, the coating solution can be made to have a high concentration, so that it is easy to make a thick coating. It is preferable because it has excellent handling properties.

The means for forming the backside coating layer on the support includes the above-mentioned flaky silica, a binder, and, if necessary, a pigment, an antifoaming agent, etc., as in the formation of the above-mentioned ink-receiving layer. A method of applying a slurry can be employed.

The thickness of the back coating layer provided on the support in the present invention may be generally small since it has a large anti-curl performance as described above. For example, when the thickness of the ink receiving layer is small, a small thickness is used. Above all, from the viewpoint of curling of the recording sheet over a wide range, the coating amount is preferably 1 to 60 g / m 2.
² , especially ² to 40 g / m ² is suitable.

[0029]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the following, Examples 1 to 4 are examples of the present invention, and Examples 5 to 7 are comparative examples. Further, “parts” in the examples indicates parts by mass in terms of solid content unless otherwise specified.

[Example 1] The following ink receiving layer formulation 1 was coated on one surface of a high-quality paper having a basis weight of 157 g / m ² using a bar coater, and the coated amount after drying was 15 g / m ^2. The ink was coated as described above and dried at 120 ° C. for 2 minutes to obtain an ink jet recording sheet having an ink receiving layer.

Ink receiving layer formulation 1: amorphous silica (manufactured by Mizusawa Chemical Co., trade name: P78A): 100 parts, polyvinyl alcohol (manufactured by Kuraray, trade name: R-1130): 3
0 copies. On the back surface of the sheet having the ink receiving layer on one side, the following back coating layer formulation 1 was applied using a bar coater so that the coating amount after drying was 8 g / m ² ,
By drying at 120 ° C. for 2 minutes, a sheet having a coating layer on both sides was obtained.

Back coating layer formulation 1: Light calcium carbonate (trade name: Brilliant-S1 manufactured by Shiraishi Industry Co., Ltd.)
5): 90 parts, flaky silica (manufactured by Dokai Chemical Industry Co., Ltd., trade name: Sun Lovely LFS, surface diameter 2-5 μm, thickness 0.0)
1-0.5 μm, aspect ratio 10-500): 10
Department. Styrene butadiene latex (manufactured by Sumika ABS Latex, trade name: SN-307): 20
Parts, defoamer (manufactured by San Nopco, trade name: Fourmaster JK): 0.05 parts.

Example 2 On the back side of the sheet having the ink receiving layer on one side in Example 1, the following back coating layer formulation 2 was applied:
An ink jet recording sheet having coating layers on both sides was obtained in the same manner as in Example 1, except that the coating amount after drying was 8 g / m ² using a bar coater.

Back coating layer formulation 2: Light calcium carbonate (Shiraishi Industry Co., Ltd., trade name: Brilliant-S1)
5): 70 parts, flaky silica (manufactured by Dokai Chemical Industry Co., Ltd., trade name: Sun Lovely LFS): 30 parts, styrene butadiene-based latex (manufactured by Sumika ABS Latex Co., trade name: SN-307): 20 parts, antifoaming agent (manufactured by San Nopco, trade name: Fourmaster JK): 0.05
Department.

Example 3 On the back side of the sheet having the ink receiving layer on one side in Example 1, the following back layer coating layer formulation 3 was applied:
An ink jet recording sheet having coating layers on both sides was obtained in the same manner as in Example 1 except that the coating amount after drying was 4 g / m ² using a bar coater.

Back coating layer formula 3: Flaky silica (trade name: Sun Lovely LFS, manufactured by Dokai Chemical Industry Co., Ltd.): 100
Department.

Example 4 In Example 1, the following ink receiving layer formulation 2 was used in place of the ink receiving layer formulation 1, and the coating amount after drying using a bar coater was 15 g / m ^2. , And dried at 120 ° C. to form an ink-receiving layer by performing the same procedure as in Example 1 except that the ink-receiving layer was formed. Was.

Ink receiving layer formulation 2: Alumina sol (catalyst AS-3, manufactured by Catalyst Kasei Co., Ltd.): 100 parts
Polyvinyl alcohol (Kuraray, trade name: PVA-
124): 10 parts.

Example 5 The same procedure as in Example 1 was carried out except that the back side of the sheet having an ink receiving layer on one side was coated with the following back coating layer formulation 4
Has a coating amount of 8 g / m ² after drying using a bar coater.
An ink jet recording sheet having a coating layer on both sides was obtained in the same manner as in Example 1 except that coating was performed so as to be as follows.

Backside coating layer formulation 4: Light calcium carbonate (trade name: Brilliant-S1 manufactured by Shiraishi Industry Co., Ltd.)
5) 100 parts styrene butadiene latex (manufactured by Sumika ABS Latex Co., Ltd., trade name: SN-30)
7): 20 parts, antifoaming agent (manufactured by San Nopco, trade name: Fourmaster JK): 0.05 part.

Example 6 The procedure of Example 5 was repeated, except that the coating amount of the backside coating layer was changed to 30 g / m ² instead of 8 g / m ^2. An ink jet recording sheet having a worked layer was obtained.

Example 7 The same procedure as in Example 1 was carried out except that the back surface of the sheet having an ink receiving layer on one side was coated with the following back coating layer formulation 5
Has a coating amount of 8 g / m ² after drying using a bar coater.
An ink jet recording sheet having a coating layer on both sides was obtained in the same manner as in Example 1 except that coating was performed so as to be as follows.

Back coating layer formulation 5: 100 parts of delaminated clay (manufactured by HUBER, trade name: HYDRAPRINT, aspect ratio 30), styrene-butadiene-based latex (manufactured by Sumika ABS Latex, trade name: SN-307) ): 20 parts, antifoaming agent (manufactured by San Nopco, trade name: Fourmaster JK): 0.05 part. With respect to the ink jet recording sheets of Examples 1 to 7, curl evaluation and strength evaluation of the back surface coating layer in each environment were performed, and the results are shown in Table 1.

[Curl Evaluation Method] Under the following three conditions, the ink jet recording sheet was allowed to stand for 24 hours so that the ink receiving layer faced upward. The heights of the four corners of the processed recording sheet from the horizontal plane were measured and averaged. A curl on the ink receiving layer side is defined as + (plus) curl, and a curl on the opposite side is defined as-(minus).
Curled.

[Environmental conditions] Normal temperature and low humidity: 20 ° C, 20% RH (relative humidity) Normal temperature and normal humidity: 20 ° C, 65% RH (relative humidity) High temperature and high humidity: 30 ° C, 80% RH (relative humidity)

[Curl fluctuation range] The difference between the maximum value and the minimum value of the curl value in the above three environments was expressed.

[Strength of Back Coating Layer] Cellotape (registered trademark) was attached to the back surface, and then slowly peeled off. The peeling state of the coating layer was visually evaluated based on the following criteria. ：: There is no peeling of the coating layer. ×: There is peeling of the coating layer.

[0048]

[Table 1]

As shown in Table 1, the sheets of Examples 1 to 4, which are the ink jet recording sheets of the present invention,
It can be seen that the sheet has excellent characteristics of suppressing curling in a wide range of environments as compared with the sheet No.

Further, from the comparison between Example 1 and Example 6, the amount of coating on the back surface that gives the same degree of curl fluctuation is 30 g / m ² of the light calcium carbonate in Example 6, and the present invention of Example 1 According to this, it can be seen that about 1/4 of 8 g / m ² is sufficient.

Further, from the comparison between Examples 1 to 4 and Example 7,
It can be seen that the present invention is also excellent in curl suppressing effect even when compared with the plate-like particles of kaolin in Example 7.

[0052]

According to the present invention, ink absorbency is high,
Provided is an ink jet recording sheet that can form a clear image, is excellent in intrinsic properties such as surface gloss and smoothness, and is excellent in anti-curl properties in a wide temperature and humidity range environment.

Further, the curl suppressing effect can be obtained with a small coating amount as compared with the use of other inorganic pigment particles, and the productivity and economy are excellent.

Claims (4)

[Claims] 1. An ink jet recording sheet having a paper base mainly composed of pulp having an ink receiving layer containing an inorganic pigment and a binder on one surface and a back coating layer on the other surface. The ink jet recording sheet, wherein the back coating layer contains 5% by mass or more of flaky silica with respect to the total mass thereof. 2. The ink jet recording sheet according to claim 1, wherein the flaky silica has an aspect ratio of 10 or more. 3. The ink receiving layer according to claim 1, wherein the average pore radius is 3 to 3.
25 nm and a pore volume of 0.3 to 2.0 cm ³ / g
The inkjet recording sheet according to claim 1, comprising: 4. The ink jet recording sheet according to claim 1, wherein the ink receiving layer contains alumina hydrate as an inorganic pigment and has a thickness of 5 to 50 μm.