JP4531739B2 - Inkjet recording paper - Google Patents

Description

  The present invention relates to an ink jet recording paper that is optimal for ink jet recording using an aqueous pigment ink.

  Recording by an ink jet printer is used in many fields because it is low in noise and can be recorded at high speed and can easily be multicolored. Ink used for ink-jet recording contains a large amount of solvent, so it must be quickly penetrated into the paper. Originally, it was mainly used for ink-jet recording paper such as high-quality paper or matte-coated paper. As an image close to a photograph is demanded, high gloss inkjet recording paper such as so-called cast coated paper is also increasing.

  In recent years, digital cameras and inkjet printers have rapidly become popular, and there are applications such as printing images from digital cameras with inkjet printers and creating New Year's postcards, etc. In order to perform offset printing on postal codes and stamps, paper with no printing unevenness is required.

  In addition, with regard to glossiness, a technology to measure so-called image clarity has been developed, which is based on how clear and undistorted the image is displayed when an object appears on the surface of the coating film, rather than the conventional glossiness. It is one of the required qualities.

In Patent Document 1, in order to provide excellent gloss and image clarity, a wet coating layer coated with a gloss layer coating material is gelled by a coagulation treatment such as a coagulation liquid, and is pressed onto a mirror-finished heating drum and dried. In other words, an ink jet recording paper using a so-called gelling cast method (coagulation method) and containing an alumina hydrate in the gloss layer is disclosed. It is also described that the shape of the alumina hydrate is preferably a flat plate shape with good ink absorbability. However, as the resolution of inkjet printers increases, a higher level of image clarity has been demanded.
JP-A-2005-246806

In view of the above situation, the present invention is optimal for inkjet recording, maintains a high level of gloss and image clarity, has high ink absorbency, and reduces the amount of paper dust generated during guillotine cutting and printing. An object of the present invention is to provide an inkjet recording paper that can be used .

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the image clarity can be improved by using a needle-shaped alumina hydrate contained in the gloss layer. However, in this case, the ink absorbability is reduced, and the amount of paper dust generated during guillotine cutting and printing may increase. Although the ink absorbability and paper dust generation amount can be adjusted by increasing or decreasing the amount of binder used, for example, increasing the binder reduces the paper dust generation amount, but the ink absorbability deteriorates. It was difficult. As a result of further diligent research, the present inventors have found that the above problems can be solved by using an acrylic ester resin and a urethane resin as a binder for the gloss layer, and have completed the present invention.

  That is, the present invention provides an inkjet recording paper having at least one ink receiving layer on a substrate and a glossy layer formed on the ink receiving layer, wherein the glossy layer is acicular alumina hydrated. And an acrylic ester resin and a urethane resin as a binder.

  In the present invention, the gloss layer is preferably mirror-finished by a rewet cast method (rewetting method).

  The ink jet recording paper of the present invention is optimal for ink jet recording, maintains a high level of gloss and image clarity, has high ink absorbability, and can reduce the amount of paper dust generated during guillotine cutting and printing. .

  Although it does not specifically limit as a pulp used for a base material, For example, chemicals, such as softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and hardwood bleached kraft pulp (LBKP) Pulp: Thermomechanical pulp (TMP), Chemithermomechanical pulp (CTMP), Refiner mechanical pulp (RMP), Refiner ground pulp (RGP), Chemiground pulp (CGP), Thermogrand pulp (TGP), Groundwood pulp (GP) , Mechanical pulp such as stone grand pulp (SGP) and pressurized stone grand pulp (PGW); chemical pulp such as deinking pulp (DIP) and waist pulp (WP); 1 type from It can be selected and used over seeds. Among these, from the viewpoint of improving whiteness and smoothness, LBKP is preferably used in an amount of 80 to 100% by mass based on the total amount of raw material pulp.

  The Canadian standard freeness of pulp is preferably 350 to 500 ml. If it is less than 350 ml, the cushioning property of the substrate is lowered, and the printability of the anti-glossy surface tends to be lowered. If it exceeds 500 ml, the strength of the substrate will be reduced, and paper dust will be easily generated during guillotine cutting.

  The base material preferably contains a filler so that the ash content according to JIS P 8251 is 10 to 20% by weight. The filler improves unevenness in offset printing by improving smoothness, improves opacity for use as a postcard application, and further suppresses the interfiber bonding of the pulp and creates a void in the base material to provide cushioning properties. It is possible to reduce scratches on the glossy surface due to rubbing between the anti-glossy surface and the glossy surface by perforating by the conveyance gear in the ink jet printer and by pressing the conveyance roll during continuous printing. When the ash content is less than 10% by weight, scratches may be seen on the communication surface. When the ash content exceeds 20% by weight, paper dust tends to adhere to the blanket during anti-glossy surface printing, and paper dust tends to occur during cutting. Become.

  Although it does not specifically limit as said filler, Titanium oxide, clay, talc, calcium carbonate, etc. are mentioned.

From the viewpoint of improving surface strength and reducing paper dust during offset printing, the base material contains various starches such as oxidized starch, acetylated starch, esterified starch, and etherified starch by internal addition and / or surface coating. It is preferable to do. As for content in a base material, 1-10 g / m < ² > is preferable.

  The base material may include known additives such as a paper strength enhancer, an internal sizing agent, an external sizing agent, and a yield improving agent as other additive chemicals.

  On the substrate, at least one ink receiving layer containing a pigment and a binder is provided to absorb and dry the ink.

  The pigment is not particularly limited, and examples thereof include inorganic pigments such as amorphous silica, colloidal silica, alumina, clay, calcium carbonate, talc, magnesium carbonate, barium persulfate, and magnesium silicate. Amorphous silica is particularly preferable because of its large pore volume and good ink absorbability.

  The particle diameter of the pigment is not particularly limited, but an average secondary particle diameter by a coal counter method is preferably in the range of 1 to 10 μm. If the thickness is less than 1 μm, there is no void in the layer and the ink absorbability tends to decrease.

  Although it does not specifically limit as a binder which adheres the said pigment to a base material, For example, polyvinyl alcohol (PVA), ethylene vinyl acetate copolymer (EVA), styrene butadiene copolymer, vinyl acetate, polyvinyl acetal, oxidized starch, ether Examples thereof include a modified starch, an acrylic ester resin, an acrylamide resin, a polyester resin, and a urethane resin, and at least one of them can be selected and used. In particular, PVA and EVA are used in combination, and the binder content in the ink receiving layer is preferably 20 to 70 parts by weight based on the active ingredient with respect to 100 parts by weight of the pigment, from the viewpoints of ink absorbability and surface strength.

The coating amount of the ink receiving layer is not particularly limited, but is, for example, about 5 to 15 g / m ² by dry weight.

  A gloss layer containing a pigment and a binder is provided on the ink receiving layer.

The pigment contains at least acicular alumina hydrate for improving image clarity. In the present invention, alumina hydrate is a compound represented by the formula Al ₂ O ₃ .nH ₂ O (n is an integer of 1 or more). Depending on the difference in composition and crystal form, it is classified into gypsite, vialite, norstrandite, boehmite, boehmite gel (pseudoboehmite), diaspore, amorphous amorphous, etc., but boehmite is preferred because of less ink bleeding. The needle shape means a shape having a major axis / minor axis ratio of 5 to 50, preferably 10 to 30, as observed by a microscope. The size of the acicular alumina hydrate is not particularly limited, but the major axis is about 100 to 200 nm.

  As the pigment other than the acicular alumina hydrate, the same pigment as that of the ink receiving layer can be used, and among them, colloidal silica is preferably used. When acicular alumina hydrate and colloidal silica are used in combination, the mixing ratio (weight basis) of the two is acicular alumina hydrate: colloidal silica = 40-50: 60-50. , Gloss and image clarity can be satisfied.

  As the binder for the gloss layer, an acrylic ester resin and a urethane resin are used in combination in order to prevent deterioration of ink absorbability and paper dust generation due to the use of acicular alumina hydrate as a pigment. When there is no acrylic ester resin, a lot of paper dust is generated when the printer is conveyed, and when there is no urethane resin, the ink absorbability is poor. In the present invention, the acrylic ester resin refers to a polymer obtained by polymerizing an acrylic ester and / or a methacrylic ester as a main monomer, and includes those obtained by copolymerizing vinyl chloride, vinyl acetate, butadiene and the like. The urethane resin means a urethane bond-containing polymer obtained by reacting diisocyanate and dialcohol, and includes those having a network structure by reacting polyol or polyisocyanate.

  Although it does not specifically limit as a compounding part number of both binders, 5-40 weight part is preferable on the basis of an active ingredient with respect to 100 weight part of pigments, and 10-30 weight part is more preferable. If the amount of the acrylic ester resin is too small, a large amount of paper dust may be generated. If the amount is too large, the glossy layer surface may be formed into a film, and the ink absorbability may be poor. The urethane resin is preferably 1 to 8 parts by weight, more preferably 2 to 5 parts by weight based on the active ingredient based on 100 parts by weight of the pigment. If the amount of urethane resin is too small, paper dust may be generated, and the ink absorbability may decrease due to acicular alumina hydrate. On the other hand, if the amount is too large, the surface of the glossy layer may be formed into a film and ink absorbency may be inferior.

  In the range which does not inhibit the effect which this invention show | plays, the said glossy layer may contain binders other than acrylic ester resin and urethane resin.

The coating amount of the gloss layer is not particularly limited, but is, for example, about 5 to 15 g / m ² by dry weight.

  The method for applying the coating liquid for the ink receiving layer and the glossy layer is not particularly limited. For example, the coating liquid may be applied using a known coating machine such as an air knife coater, roll coater, bar coater, comma coater, or blade coater. Can be crafted.

  The ink jet recording paper of the present invention may be mirror-finished so as to have a gloss as high as that of a silver salt photograph. The method is based on a so-called cast coating method in which the coating layer coated with the gloss layer coating is wet while the surface of the coating layer is in a wet state and then dried after being pressed against a heated mirror surface. preferable. In general, the cast coating method includes (1) a wet casting method (direct method) in which a coating layer is in a wet state and is dried by pressure bonding (pressure contact) to a mirror-finished heating drum, and (2) a wet coating method. Rewetting cast method (rewetting method) in which the work layer is once (semi-) dried and then swelled and plasticized (wet) with a rewetting liquid, and pressed onto a mirror-finished heating drum (drying method). Can be divided into three types: a gelled cast method (coagulation method) in which a gel is made into a gel state by a coagulation treatment such as a coagulation liquid, and is pressed onto a mirror-finished heating drum and dried. In the present invention, the rewet cast method is preferable because the gloss layer can be formed without lowering the gloss of the white paper.

  The ink jet recording paper of the present invention can achieve a blank paper glossiness of 85% or more and image clarity of 65% or more, is excellent in ink absorbability, and generates less paper dust in the printer.

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.
Examples 1-10 and Comparative Examples 1-7
1. Substrate 100% hardwood bleached kraft pulp was used as a raw material, and the freeness was 370 ml. A paper strength agent and a sizing agent were each internally added in an amount of 5 kg on the basis of the active ingredient based on 1 t of the absolutely dry pulp, and talc was internally added as a filler so as to have an ash content of 13%. After papermaking and drying with a long paper machine, the oxidized starch was applied to a dry weight of 3.0 g / m ² using a size press to obtain a substrate having a weight of 157 g / m ² .
2. Ink-receiving layer 15 parts by weight of PVA (manufactured by Kuraray, product number: R1130) as a binder and 100 parts by weight of amorphous silica (manufactured by Grace, product number: ED5) and EVA (manufactured by Chuo Rika, product number: DI-1) A coating solution containing 12 parts by weight was prepared, and this was coated on the surface of the substrate with an air knife coater so as to have a dry weight of 10 g / m ² . Each part is a number based on active ingredients. (The same applies to the following)
3. Gloss layer From 45 parts by weight of acicular alumina hydrate (product of Grace, product number: EM5075, major axis / minor axis ratio = 15, major axis 150 nm) and 55 parts by weight of colloidal silica (manufactured by Bayer, product number: Lebasil 100S) Table 1 shows acrylic ester resin (manufactured by Daicel Chemical Industries, product number: Asi-3007) and urethane resin (manufactured by Nikka Chemical Co., product number: Neofix IJ-170) as binders with respect to 100 parts by weight of the pigment. The coating liquid containing the number of parts is adjusted, and this is coated on the surface of the ink-receiving layer after coating and drying with an air knife coater so that the dry weight is 12 g / m ^2. Went.

However, in Example 10, the mirror finish was performed by the gelation cast method, and in Comparative Example 1, flat alumina hydrate (manufactured by Sasol, product number: Disperal HP14, major axis / minor axis ratio) instead of acicular alumina hydrate = 1.2), and for Comparative Examples 2 to 7, instead of acrylic ester resin and urethane resin, PVA (manufactured by Kuraray Co., Ltd., product number: PVA117) and EVA (manufactured by Chuo Rika Co., Ltd., product number: DI-) 1) was used in the number of copies described in Table 1.
Measurement / Evaluation Method The inkjet recording paper produced as described above was measured and evaluated as follows. The results are shown in Table 1 below.
1) White paper gloss The 75 ° white paper gloss was measured in accordance with JIS P 8142.
2) Image clarity Measured according to JIS H 8686-2.
3) Suitability of inkjet printer Evaluation was performed after printing with an inkjet printer (manufactured by Epson, PM-G820).
3-1) Paper dust 100 sheets of continuous printing and guillotine cutting were performed, and the paper dust attached to the roller and cutting blade inside the printer was visually evaluated.
A: Generation of paper dust was not observed.
◯: Slight paper dust was seen.
X: A lot of paper dust was observed.
3-2) Ink Absorbency Solid printing was performed, and after 10 seconds from completion, the ink was bonded to a high-quality paper and visually transferred to the high-quality paper.
A: Transfer to fine paper was not observed.
○: Slightly transferred to high-quality paper.
X: Many transfers to high-quality paper were observed.

表１の結果から、実施例１〜１０では、白色光沢度及び写像性が高く、紙粉の発生量は少なく、かつ、インク吸収性は良好であった。一方、アルミナ水和物として平板状のものを使用した比較例１では、写像性が低下した。また、光沢層のバインダーとしてアクリル酸エステル系樹脂及び／又はウレタン樹脂以外のものを使用した比較例２〜７では、紙粉の発生量が多く見られるか、又は、インク吸収性が低下した。

From the result of Table 1, in Examples 1-10, white glossiness and image clarity were high, the generation amount of paper dust was small, and ink absorptivity was favorable. On the other hand, in Comparative Example 1 in which a flat plate was used as the alumina hydrate, the image clarity was lowered. Further, in Comparative Examples 2 to 7 where a binder other than the acrylic ester resin and / or the urethane resin was used as the binder of the gloss layer, a large amount of paper dust was generated or the ink absorbability was lowered.

Claims (4)

An ink jet recording paper having, on a substrate, at least one ink receiving layer and a gloss layer containing a pigment and a binder formed on the ink receiving layer,
The gloss layer contains acicular alumina hydrate as the pigment ,
Further, 5 to 40 parts by weight of acrylate resin to the pigment 100 parts by weight of the binder, and,
An ink jet recording paper comprising 1 to 8 parts by weight of a urethane resin with respect to 100 parts by weight of the pigment . The inkjet recording paper according to claim 1, further comprising colloidal silica as the pigment. The inkjet recording paper according to claim 2, wherein a mixing ratio (weight basis) of the acicular alumina hydrate and the colloidal silica is 40 to 50:60 to 50. The inkjet recording paper according to any one of claims 1 to 3, wherein the glossy layer is mirror-finished by a rewet cast method (rewetting method).