JP5216571B2 - Glossy paper for inkjet recording - Google Patents

Description

  The present invention relates to a glossy paper for ink jet recording which does not require the use of a boron compound in the production process, has a high surface glossiness, is excellent in image reproducibility, and is excellent in surface strength and cutting suitability.

  The casting method is widely used as a method for producing glossy paper for ink-jet recording having high gloss on the surface for photographic printing. When producing glossy paper for inkjet recording by the casting method, the coating liquid for the glossy layer that is pressure-bonded to the metal drum is made from pigments and binders in order to have both glossiness and ink absorbability. As a binder for holding the pigment in the coating layer, polyvinyl alcohol having a high film transparency is widely used to clarify the color development upon ink absorption. Yes.

  A casting method in which a coating solution is applied and then gelled by applying a gelling solution to the obtained coating layer, and the coating layer is pressure-bonded to a metal drum while the coating layer is in a wet state is generally gelled. This method is called a casting method and is widely used as a method for producing cast coated paper because of a good balance between productivity and product quality.

  In the gelation cast method, as a gelling agent contained in a gelling liquid applied to a coating layer containing polyvinyl alcohol, a boron compound having a strong gelling power and easy control of the gelation degree Is proposed (Patent Document 1). However, when a boron compound is used in the manufacturing process, there is a problem that process wastewater containing boron is generated. In recent years, concerns about the effect of boron on human health have increased, and in the 2001 revision of the Water Pollution Control Law, the item “boron and its compounds” has been added to the wastewater standards.

  As a method for gelling a coating layer containing polyvinyl alcohol using a gelling agent other than a boron compound, a method using polyacrylic acid has been proposed (Patent Document 2). However, when polyacrylic acid is used as the gelling agent, the gelling power is weaker than that of the boron compound, so that the pressure-bonding of the coating layer to the metal drum is not uniform, and sufficient surface gloss cannot be obtained. There's a problem. In addition, when polyacrylic acid is used as the gelling agent, the acidity of the gloss developing layer of the ink jet recording paper becomes strong (for example, the pH of the paper surface is less than 5). There is a problem that the sharpness of the image is deteriorated.

In addition, ink jet recording paper is required as a necessary physical property that it has high surface strength and is suitable for cutting. When the surface strength is weak, a conveyance scratch is generated in printing with an ink jet printer, and the appearance of the image is impaired. In addition, when the cutting suitability is low, the edge of the image is dropped or fuzzed in edgeless printing, which also impairs the appearance of the image.
Japanese Patent No. 3818573 Japanese Patent No. 3954327

  An object of the present invention is to provide a glossy paper for ink-jet recording that does not require the use of a boron compound in the production process, has high surface glossiness, excellent image reproducibility, and excellent surface strength and cutting suitability. That is.

The present inventors have found that a coating liquid containing polyvinyl alcohol and / or modified polyvinyl alcohol, a gelling liquid containing an alkali metal salt of a polycarboxylic acid as a gelling agent used as a binder, said polycarboxylic acid Was found to be able to solve the above-mentioned problems by being a polymer obtained by homopolymerizing a carboxylic acid monomer having an unsaturated double bond or a copolymer obtained by copolymerizing a combination thereof. I let you.

  One preferred example of the gelling agent used in the present invention is a polycarboxylic acid alkali metal salt having a molecular weight in the range of 3000 to 200000, preferably 3300 to 180000, particularly preferably 5000 to 50000. When the molecular weight is smaller than 3000, the effect of increasing the surface strength and cutting suitability of the glossy surface is reduced, and when the molecular weight is larger than 200000, the sharpness of the inkjet image is lowered. In particular, it has been found from experimental results that a molecular weight of 5,000 provides particularly excellent surface strength and cutting suitability, and a molecular weight of up to 50,000 provides particularly excellent inkjet image sharpness.

  The main reasons for using the alkali metal salt of polycarboxylic acid as the gelling agent of the present invention are the following three points. (1) The carboxylic acid is in a dissociated state in the aqueous solution of the gelling solution, and as a result, it can be strongly bonded to polyvinyl alcohol as compared with the non-dissociated state, and the gelling power is increased. (2) Since the alkali metal forming the alkali metal salt remains in the paper, the pH of the surface of the glossy layer obtained is kept within a certain range, and the inkjet image is not adversely affected. (3) High solubility in water, easy preparation of a gelling solution, and no problems such as insoluble matter remaining on the paper surface.

  As described above, according to the present invention, a glossy paper for inkjet recording that does not require the use of a boron compound in the production process, has high surface gloss, excellent image reproducibility, and excellent surface strength and cutting suitability. Can be obtained.

As the polycarboxylic acid constituting the gelling agent of the present invention, a carboxylic acid monomer having an unsaturated double bond such as acrylic acid, methacrylic acid or maleic acid is polymerized alone or a combination thereof is copolymerized. The polymer can be used. Furthermore, these carboxylic acid monomers can be used together with other monomers having an unsaturated carbon bond such as ethylene, allylamine, acrylic acid ester, vinyl acetate, and vinyl sulfonic acid as long as gelling power and water solubility are not impaired. A copolymer having a polymerized structure can also be used . Moreover, as an alkali metal which comprises the gelatinizer of this invention, there exist lithium, sodium, and potassium, and it is especially advantageous to use sodium and potassium.

  The gelling liquid of the present invention preferably contains the gelling agent in an aqueous solution at a solid content concentration of 1 to 20% by mass, preferably 3 to 10% by mass. More preferred. If the gelled solution solid content concentration is too dilute, sufficient gelling power cannot be obtained, and if the gelled solution solid content concentration is too thick, the sharpness of the inkjet image is reduced.

  Additives such as mold release agents, preservatives, antifoaming agents, dyes, and optical brighteners can be appropriately added to the gelling agent of the present invention. Moreover, it can also use together with other gelling agents, such as a boron compound and an organic type crosslinking agent.

  As the polyvinyl alcohol which is the binder for the glossy layer of the present invention, those having various degrees of polymerization and saponification can be used. In addition, modified polyvinyl alcohols such as cation group modification, carboxyl group modification, silanol group modification and the like can also be used, and their modification degree, polymerization degree and saponification degree can be selected from a wide range. However, it is important for the degree of modification that a necessary amount of hydroxyl groups remain to react when the polycarboxylic acid is dissociated from the alkali metal salt of the polycarboxylic acid in the aqueous gelling solution. Furthermore, a synthetic resin emulsion such as an acrylic resin emulsion or a vinyl acetate resin emulsion, starch and derivatives thereof, a cellulose derivative, etc. are used in combination with polyvinyl alcohol and / or modified polyvinyl alcohol as long as the effects of the present invention are not impaired. Can do.

  Examples of the pigment of the glossy layer of the present invention include colloidal silica, precipitated silica, gel silica, gas phase silica, colloidal alumina, gas phase method alumina, fine particle calcium carbonate, and organic synthetic fine particles. Is not to be done.

  Additives such as a cationic fixing agent, a mold release agent, a preservative, an antifoaming agent, a dye, a fluorescent whitening agent, and a water-proofing agent can be appropriately added to the glossy layer of the present invention.

As a method for applying the glossy layer of the present invention, a known coating machine such as an air knife, a roll coater, a bar coater, a blade coater or the like is used. Amount of coating is, 3~40g / ^{m 2} in terms of solid content, preferably in the range of 5 to 30 g / ^{m 2.} When the coating amount exceeds 40 g / m ² , the productivity is inferior, and when the coating amount is less than 3 g / m ² , it is difficult to obtain sufficient surface gloss.

  As described above, the casting process is performed by a gelled casting method. At that time, by adjusting the time from application to application of the gelling liquid, the time from application of the gelling liquid to crimping by the metal drum, the metal drum temperature, the pressure line speed at the time of crimping, etc. , Higher surface gloss can be obtained. About these various conditions, it is necessary to optimize it by calculating | requiring optimal conditions according to the equipment to be used and a coating material.

  In the glossy paper for ink jet recording of the present invention, one or more ink receiving layers are provided under the glossy expression layer. The ink receiving layer is composed of a pigment and a binder. As the pigment of the ink receiving layer, colloidal silica, precipitated silica, vapor phase silica, colloidal alumina, gel method silica, vapor phase alumina, fine calcium carbonate, organic synthetic fine particles, and the like can be used. As the binder for the ink receiving layer, synthetic resin emulsions such as acrylic resin emulsions and vinyl acetate resin emulsions, polyvinyl alcohol, starch and derivatives thereof, and cellulose derivatives can be used. Furthermore, additives such as a cationic fixing agent, a mold release agent, a preservative, an antifoaming agent, a dye, a fluorescent brightening agent, and a water-proofing agent can be appropriately added to the ink receiving layer of the present invention.

As a method for applying the ink receiving layer of the present invention, a known coating machine such as an air knife, a roll coater, a bar coater or a blade coater is used. The coating amount is not particularly limited. However, when the coating amount is too small, the ink absorbability is inferior, so that it is preferably 3 g / m ² or more in terms of solid content.

  As the base material used in the present invention, a paper base material having air permeability, such as ordinary high-quality paper, medium-quality paper, and white paperboard, is used. Considering the case of recycling as a fuel, it is preferable to use ECF (Elemental Chlorine Free) pulp or TCF (Totally Chlorine Free) pulp having a low chlorine content as raw material pulp. Further, in order to suppress excessive penetration of the paint during the cast coating, it is preferable to use a base paper coated with a water-soluble polymer such as starch or polyvinyl alcohol in a size press.

  The pH of the glossy layer surface of the present invention is preferably in the range of 5-8. If it is less than 5, the image clarity is inferior. If it exceeds 8, there is a problem of causing yellowing of the antioxidant BHT absorbed in the paper from the environment. More preferably, it is in the range of 5.5 to 7.5.

[Example]
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

On one surface of a high-quality paper having a basis weight of 160 g / m ² surface-treated with oxidized starch, 100 parts by mass of synthetic silica (Mizukasil P-78A, manufactured by Mizusawa Chemical Co., Ltd.) as a pigment for the ink receiving layer, polymerized as a binder 10 parts by weight of polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) having a degree of 1700 and 40 parts by weight of ethylene-vinyl acetate (Polysol EVA AD-10, manufactured by Showa High Polymer Co., Ltd.), a cationic polymer (papiogen P) as an ink fixing agent -105, manufactured by Senka Co., Ltd.) A coating solution having a solid content concentration of 22% by mass using 30 parts by mass was coated and dried with an air knife coater so as to have an absolutely dry coating amount of 10 g / m ² . An ink receiving layer was applied.

Next, 100 parts by mass of an aggregate colloidal silica (HS-M-20, primary particle diameter 25 nm, aggregate particle diameter 280 nm, manufactured by Nissan Chemical Industries, Ltd.) as a pigment of the glossy layer, and a saponification degree as a binder 10 parts by mass of polyvinyl alcohol (PVA420, manufactured by Kuraray Co., Ltd.) having a polymerization degree of 78 mol% and 20 parts by mass of a cationic acrylic silicone resin (Aquabrid 922, manufactured by Daicel Chemical Industries, Ltd.), a polyethylene emulsion ( Using 1 part by mass of SN coating 287, manufactured by San Nopco Co., Ltd., a coating solution having a solid content concentration of 20% by mass was obtained. This coating solution was applied with an air knife coater so as to have an absolutely dry coating amount of 10 g / m ² .

  Next, the obtained coating layer is subjected to a gelation treatment by applying a 5 mass% solid dilution of a 3500 molecular weight sodium polyacrylate aqueous solution (Aquaric DL40, manufactured by Nippon Shokubai Co., Ltd.) in water. Then, while the obtained coating layer was in a wet state, it was pressed against a mirror-like metal drum having a surface temperature of 100 ° C. to prepare glossy paper for ink jet recording.

  In the gelation treatment, the same method as in Example 1 was applied, except that a 5% by weight solids concentration aqueous solution of a polyacrylic acid sodium salt aqueous solution having a molecular weight of 5000 (Aquaric DL365, manufactured by Nippon Shokubai Co., Ltd.) was applied. A glossy paper for ink-jet recording was prepared.

  In the gelation treatment, the same method as in Example 1 was applied, except that a 5 wt% solid dilution of a polyacrylic acid sodium salt aqueous solution (AQUALIC DL453, manufactured by Nippon Shokubai Co., Ltd.) having a molecular weight of 50000 was applied. A glossy paper for ink-jet recording was prepared.

  In the gelation treatment, the same method as in Example 1 was applied, except that a 5 wt% solid dilution of a polyacrylic acid sodium salt aqueous solution having a molecular weight of 170000 (Aquaric DL522, manufactured by Nippon Shokubai Co., Ltd.) was applied. A glossy paper for ink-jet recording was prepared.

  In the gelation treatment, the same as Example 1 except that a 5 wt% solids concentration aqueous solution of polyacrylic maleic acid sodium salt aqueous solution (Aron A-6310, manufactured by Toagosei Co., Ltd.) having a molecular weight of 10,000 was applied. By this method, glossy paper for ink jet recording was prepared.

  In the gelling liquid treatment, sodium borate contains a solid content concentration of 1% by mass, and a polyacrylic acid sodium salt aqueous solution having a molecular weight of 5000 (Aquaric DL365, manufactured by Nippon Shokubai Co., Ltd.) contains a solid content concentration of 3% by mass. A glossy paper for inkjet recording was prepared by the same method as in Example 1 except that the mixed aqueous solution was applied.

Comparative Example 1

  In the gelling liquid treatment, the same method as in Example 1 was applied except that a 5 wt% solid dilution of a polyacrylic acid aqueous solution having a molecular weight of 6000 (Aron A-10SL, manufactured by Toagosei Co., Ltd.) was applied. A glossy paper for ink-jet recording was prepared.

Comparative Example 2

  In the gelling solution treatment, the same as in Example 1 except that a water dilution of 5 mass% solid content of an aqueous solution of ammonium polyacrylate having a molecular weight of 6000 (Aron A-30SL, manufactured by Toagosei Co., Ltd.) was applied. By the method, glossy paper for ink-jet recording was prepared.

Comparative Example 3

  A glossy paper for ink-jet recording was prepared in the same manner as in Example 1 except that a 3% by weight aqueous solution of sodium borate in the gelling solution treatment was applied.

  The glossy paper for ink jet recording was subjected to the following test, and the results are shown in Table 1.

(1) Glossiness According to JIS Z 8741: 1997 “Specular Glossiness—Measurement Method”, using a gloss meter (Gloss Meter GM26D, Murakami Color Research Laboratory Co., Ltd.) with an incident / reflection angle of 20 °, The glossiness of the glossy layer surface was measured. A glossiness of 20% or more is evaluated as glossy paper.

(2) Paper surface pH
Using a pH meter for paper quality inspection (manufactured by Kyoritsu Riken), the paper surface pH of the surface of the glossy layer was measured.

(3) Image clarity
ISO standard image (ISO / JIS-SCID high-definition color digital standard image data, image name: portrait, image identification number: N1) is printed using an inkjet printer (PM-900C, manufactured by Seiko Epson Corporation) The printed image was evaluated visually.
A: The recorded image is very clear, the color is very good, and there is no practical problem.
○: The recorded image is clear, the color is good, and there is no practical problem.
X: The recorded image is unclear, the color is poor, and there are practical problems.

(4) Surface strength Using a pencil scratch coating film hardness tester (type NP, manufactured by Toyo Seiki Seisakusho Co., Ltd.), 6B sharpened under conditions adjusted to a pressure of 98.1 mN The scratches on the surface of the glossy layer were visually evaluated.
A: Scratches are not visible at all and there is no practical problem.
○: Scratch scratches are very slight, but there are no practical problems.
X: Scratches are clearly visible and there is a practical problem.

(5) Cutting suitability 30 sheets of A4 size glossy paper for ink-jet recording are placed so that the glossy layer is on the bottom, and using the electric cutting machine (model No. 709, manufactured by Lion Corporation), the short side direction The paper dust generated and the fluff of the cut surface were visually evaluated.
A: Paper dust and fluff are very few and there are no practical problems.
○: There is little paper dust and fluffing and there is no practical problem.
X: There are many paper dusts and fluffs, and there are practical problems.

  From the results of Table 1, in Examples 1 to 5 using a polycarboxylic acid alkali metal salt as a gelling agent, ink jet recording excellent in glossiness and image sharpness without using a boron compound as a gelling agent. Glossy paper was obtained. Further, in Examples 2, 3 and 5 having a molecular weight in the range of 5,000 to 50,000, glossy paper for ink jet recording excellent in all physical properties such as image sharpness, surface strength and cutting suitability could be obtained.

  Example 6 is a gelation containing sodium borate as a gelling agent in order to show the possibility of improving the physical properties of the coating layer even when the polycarboxylic acid alkali metal salt is used in combination with another gelling agent. This is an example in which part of sodium borate in the liquid is replaced with sodium polyacrylate. As a result, glossy paper for ink-jet recording having superior surface strength and cutting suitability was obtained as compared with Comparative Example 3 using only sodium borate.

  In Comparative Examples 1 and 2 using polyacrylic acid / polyacrylic acid ammonium salt as a gelling agent, the paper surface pH was lowered, resulting in poor image sharpness.

Claims (3)

One or more ink-receiving layers are provided on at least one side of a substrate having air permeability, and a coating liquid containing a pigment and a binder is applied as a glossy layer thereon, and then the obtained coating layer is applied. In cast coated paper by gelation cast method, which is made by gelation by applying a gelling solution, and manufactured by pressure-bonding onto a metal drum that is mirror-finished while the coating layer is in a wet state. coating liquid expression layer contains polyvinyl alcohol and / or modified polyvinyl alcohol as the binder, and the gelling liquid containing alkali metal salt of a polycarboxylic acid as a gelling agent, said polycarboxylic acid is not A glossy paper for ink-jet recording, which is a polymer obtained by homopolymerizing a carboxylic acid monomer having a saturated double bond or a copolymer obtained by copolymerizing a combination thereof .   The glossy paper for ink-jet recording according to claim 1, wherein the polycarboxylic acid alkali metal salt constituting the gelling agent has a molecular weight in the range of 3000 to 200000.   The glossy paper for ink-jet recording according to claim 2, wherein the molecular weight of the polycarboxylic acid alkali metal salt constituting the gelling agent is in the range of 5,000 to 50,000.