JP6998904B2 - Printing paper - Google Patents

Description

The present invention relates to a printing paper used for printing by an inkjet printing machine, and more particularly to a printing paper suitable for printing by a rotary type inkjet printing machine.

A rotary type inkjet printing machine capable of supporting plateless printing and on-demand printing is known (see, for example, Patent Document 1).

In a rotary type inkjet printing machine, as a printing paper that can suppress cockling and wrinkles during printing and suppress curl even if it is cut into a flat format after printing, a base paper and a pigment on at least one surface of the base paper are used. It has a coating layer containing a binder, the ash content of the base paper is 20% by mass or more and 30% by mass or less, and the specific tensile strength in the CD direction obtained in accordance with JIS P 8113: 2006 of the printing paper. A printing paper having a ratio of 9.0 N · m / g or less and a ratio of (specific tensile strength in the MD direction) / (specific tensile strength in the CD direction) of 1.9 or more and 2.3 or less is known (for example, patent). See Document 2).

A thin printing coated paper with excellent rigidity and printing characteristics, high whiteness but high opacity, excellent print quality such as strike-through, and high surface strength, with an average particle size of 2 to 15 μm. A coated paper for printing containing calcium aluminate monocarbonate, which is a substance, in a pigment coating layer is known (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2011-157168 Japanese Unexamined Patent Publication No. 2016-176170 Japanese Unexamined Patent Publication No. 2010-236148

In a rotary-type inkjet printing press, tension is applied to the printing paper from unwinding to winding for printing. The printing paper undergoes an inkjet printing process and a drying process from unwinding to winding. When inkjet printing is performed under tension, the printing paper may generate wrinkling phenomenon (cockling) and / or wrinkles in a form parallel to the paper transport direction. The reason for this is that the ink used in inkjet printing machines uses solvents such as water and anti-drying agents such as glycerin, compared to inks such as offset printing machines due to the principle of ejecting ink droplets, which is a characteristic of inkjet printing. This is because it contains a relatively large amount. Further, after printing, the printing paper may cause set-off and / or bleeding when it is wound into a roll or cut into a flat shape and stacked on a bar. The reason for this is that the solvent and anti-drying agent of the ink used in the inkjet printing machine are present in the voids inside the printing paper and exude to the surface of the printing paper without being dried in the drying step. The above-mentioned problems become more remarkable as the printing paper has a lower basis weight and / or the printing paper has a smaller thickness.

An object of the present invention is to provide a printing paper capable of suppressing the occurrence of cockling, wrinkles, set-off and bleeding as described above.

The object of the present invention is achieved by the following.
The base paper has a coating layer containing a white pigment and a binder on at least one side of the base paper, and at least one of the white pigments contains calcium aluminate monocarbonate in the coating layer of the calcium aluminate monocarbonate. The content is 30 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the white pigment in the coating layer, and the average particle size of the calcium aluminate monocarbonate is 0.9 μm or more and less than 2 μm, and the coating layer. Is a printing paper containing a water-soluble polyvalent cation salt.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a printing paper capable of satisfactorily suppressing the occurrence of cockling, wrinkles, set-off and bleeding in an inkjet printing machine, particularly a rotary type inkjet printing machine.

Hereinafter, the present invention will be described in detail.
The rotary inkjet printing machines are the large inkjet printing machine "HP T300 Color Inkjet Web Press" equipped with the rotary function of Hulett Packard, the inkjet printing machine "MPJ20 series" of Miyakoshi, and the high-speed color inkjet digital rotary printing of Kodak. It is already on the market as a machine such as "Kodak Prosper 5000XL Press".

The printing paper preferably has a basis weight of 100 g / m ² or less, and more preferably 70 g / m ² or less. This is because the effect of the present invention appears remarkably within this range. The lower limit of the basis weight is not particularly limited, but it is usually a basis weight within a range that can be used for printing paper. The basis weight is preferably 35 g / m ² or more.

The thickness of the printing paper is preferably 70 μm or less. This is because the effect of the present invention is remarkably exhibited when the thickness is in this range. The lower limit of the thickness is not particularly limited, but is usually a thickness within a range that can be used for printing paper. The thickness is preferably 45 μm or more.

The base paper is made by adding a filler such as calcium carbonate to chemical pulp such as LBKP and NBKP, mechanical pulp such as GP, PGW, RMP, TMP, CTMP, CMP and CGP, and used paper pulp such as DIP, and sizing agent and yield agent. , Cationic compound, pigment dispersant, thickener, fluidity improver, defoamer, defoamer, mold release agent, foaming agent, penetrant, coloring dye, coloring pigment, fluorescent whitening agent, ultraviolet absorber , Antioxidant, Preservative, Antifoaming agent, Water resistant agent, Wet paper strength enhancer, Dry paper strength enhancer, etc. It is a paper made in. After the paper is made, the paper may be subjected to calendar processing using a calendar device described later.

The base paper preferably contains at least LBKP and NBKP as pulp. Further, the drainage degree required in accordance with JIS P 811-2: 2012 "Canada Standard Drainage Degree Method" of LBKP and NBKP is preferably in the range of 400 ml or more and 540 ml or less for each of LBKP and NBKP.

The size of the base paper may be any size as long as the desired effect of the present invention is not impaired. The degree of sizing can be adjusted by the amount of the internal sizing agent blended in the paper material and the amount of the surface sizing agent applied to the base paper. Examples of the internal sizing agent include rosin-based sizing agents, alkenyl succinic anhydride, alkyl ketene dimers, neutral rosin-based sizing agents, and cationic styrene-acrylic sizing agents. Examples of the surface sizing agent include a styrene-acrylic sizing agent, an olefin-based sizing agent, and a styrene-maleic acid-based sizing agent.

The ash content of the base paper is preferably 20% by mass or more and 30% by mass or less. The ash content is the ratio (mass%) of the mass of the incombustible material after the base paper is burned at 500 ° C. for 1 hour and the absolute dry mass of the base paper before the combustion treatment. The ash content can be adjusted by the content of the filler.

The printing paper has a coating layer on at least one side of the base paper. The printing paper may also have coating layers on both sides of the base paper.

The coating layer contains a white pigment and a binder. The white pigment in the coating layer contains at least one calcium aluminate monocarbonate.
Calcium aluminate monocarbonate is a crystalline substance having a composition of _3CaO , _{Al2O3 ,} and _{CaCO3 ,} and is in a state of being hydrated with water molecules like 3CaO, _Al2O3 , _CaCO3,11H2O . Usually exists. Calcium aluminate monocarbonate has a layered structure and is composed of hexagonal plate-shaped primary particles similar to kaolin and the like.

The calcium aluminate monocarbonate can be synthesized by a conventionally known method. The method is, for example, a dry method of calcium carbonate and aluminum oxide described in "Journal of the Society of Inorganic Materials Japan (published by The Society of Inorganic Materials, Vol. 4, May (1997), P196-P204, by Itai and Daimon)". A method for reacting anhydrous calcium aluminate _3CaO / _Al2O3 obtained by firing at 1350 ° C. after mixing with calcium carbonate in water at room temperature, as described in JP-A-2008-37664, slaked lime and hydroxylation. Examples thereof include a method of producing calcium aluminate monocarbonate by reacting aluminum and calcium carbonate in the presence of water. Further, calcium aluminate monocarbonate is commercially available from Kotegawa Sangyo Co., Ltd. and can be used in the present invention.

Calcium aluminate monocarbonate has a smaller true specific density than conventionally known fillers such as kaolin and calcium carbonate. The true specific density is a specific gravity measured by a method based on JIS K 5101-11-1 (Pycnometer method). For example, calcium aluminate monocarbonate is 2.10 g / cm ³ , kaolin is 2.60 g / cm ³ , calcium carbonate is 2.70 g / cm ³ , and calcium aluminate monocarbonate itself is bulky. Although the reason why the effect of the present invention is obtained is not clear, the inventor suppresses the occurrence of cockling, wrinkles, set-off and bleeding by the action effect of the calcium aluminate monocarbonate being plate-like and bulky. I think it can be done.

The average particle size of calcium aluminate monocarbonate is 0.9 μm or more and less than 2 μm. If the average particle size is less than 0.9 μm, the occurrence of cockling and / or wrinkles cannot be satisfactorily suppressed. If the average particle size is 2 μm or more, the occurrence of set-off and / or bleeding cannot be satisfactorily suppressed. The average particle size of calcium aluminate monocarbonate is a value based on volume. Here, the average particle size of the present invention is a volume-based average particle size measured by a laser diffraction method, and is, for example, a laser diffraction / scattering type particle size distribution measuring device such as the Microtrac MT3300EX2 manufactured by Nikkiso Co., Ltd. and a Mastersizer manufactured by Malvern Instruments. It can be measured by using a laser diffraction type particle size distribution measuring device or the like.

The coating layer contains a white pigment conventionally known in the field of coated paper, in addition to calcium aluminate monocarbonate. The content of calcium aluminate monocarbonate in the coated layer is 30 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the white pigment in the coated layer. If the content of the calcium aluminate monocarbonate in the coated layer is less than 30 parts by mass, the occurrence of cockling and / or wrinkles cannot be satisfactorily suppressed. When the content of calcium aluminate monocarbonate in the coated layer exceeds 80 parts by mass, the occurrence of set-off and / or bleeding cannot be satisfactorily suppressed.

Examples of white pigments conventionally known in the field of coated paper are kaolin, calcium carbonate, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, and keisou soil. , Calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, aluminum hydroxide, alumina, lithopone, zeolite, magnesium carbonate, magnesium hydroxide and other inorganic white pigments, styrene-based plastic pigments, acrylic-based plastic pigments, styrene- Examples thereof include organic white pigments such as acrylic plastic pigments, polyethylene, microcapsules, urea resins, and melamine resins. The white pigment is preferably one kind or two or more kinds selected from the group consisting of the above.

The binder is preferably at least one or two or more selected from water-dispersible binders and water-soluble binders conventionally known in the field of coated paper. Examples of water-dispersible binders include conjugated diene copolymer latexes such as styrene-butadiene copolymers and acrylonitrile-butadiene copolymers, polymer latexes of acrylic acid esters and methacrylic acid esters, and methyl methacrylate-butadiene copolymers. Acrylic copolymer latex such as coalescence, vinyl copolymer latex such as ethylene-vinyl acetate copolymer and vinyl chloride-vinyl acetate copolymer, and functional group-containing singles such as carboxyl group of these various copolymers. Examples thereof include functional group-modified copolymer latex, polyurethane resin latex, alkyd resin latex, unsaturated polyester resin latex, and heat-curable synthetic resin such as melamine resin and urea resin. Examples of water-soluble binders include starch derivatives such as oxidized starch, etherified starch and phosphate esterified starch, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose and hydroxyethyl cellulose, polyvinyl alcohol derivatives such as polyvinyl alcohol and silanol-modified polyvinyl alcohol, and Casein and gelatin and their variants, soybean protein, purulan, gum arabic, natural polymer resins such as Karaya rubber and albumin and their derivatives, vinyl polymers such as sodium polyacrylate, sodium alginate, polypropylene glycol, polyethylene glycol, anhydrous. Examples thereof include maleic acid and its copolymer.

The coating layer contains a water-soluble polyvalent cationic salt. By containing the water-soluble polyvalent cation salt, the synergistic effect of the calcium aluminate monocarbonate and the water-soluble polyvalent cation salt can satisfactorily suppress the occurrence of set-off and / or bleeding. The content of the water-soluble polyvalent cation salt in the coating layer is preferably 3 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the white pigment in the coating layer.

The water-soluble polyvalent cation salt is a water-soluble salt containing a metal polyvalent cation. That is, the water-soluble polyvalent cation salt is a salt that contains polyvalent cations of a metal and can be finally dissolved in water at 20 ° C. in an amount of 1% by mass or more. Examples of polyvalent cations in metals are divalent cations such as magnesium, calcium, strontium, barium, nickel, zinc, copper, iron, cobalt, tin and manganese; trivalent cations such as aluminum, iron and chromium. ; And tetravalent cations such as titanium and zircon; and their complexions. The polyvalent cation of the metal and the anion forming the salt may be either an inorganic acid or an organic acid, and are not particularly limited. Examples of the inorganic acid include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid and the like. Examples of organic acids include formic acid, acetic acid, lactic acid, citric acid, oxalic acid, succinic acid, organic sulfonic acid and the like. However, the aluminum sulfate band, which has been conventionally used as a fixing agent for sizing agents, is excluded. Among these, the water-soluble polyvalent cation salt is preferably a water-soluble calcium salt. Further, calcium chloride and calcium nitrate are preferable as the water-soluble calcium salt.

In addition to the white pigment, the binder and the water-soluble polyvalent cation salt, the coating layer includes a dye fixer, a pigment dispersant, a thickener, a fluidity improver, a viscosity stabilizer, a pH adjuster, and a surface activity. Agents, defoamers, defoamers, mold release agents, foaming agents, penetrants, coloring dyes, coloring pigments, fluorescent whitening agents, ultraviolet absorbers, antioxidants, leveling agents, preservatives, antibacterial agents, water resistant Additives conventionally known in the field of coated paper such as an agent, a wet paper strength enhancer, and a dry paper strength enhancer can be appropriately contained.

As a method of providing a coating layer on the base paper, a method of applying and drying the coating layer coating liquid is preferable. The coating of the coating layer coating liquid is a method using a conventionally known coating apparatus and is not particularly limited. Examples of coating equipment include air knife coaters, curtain coaters, slide lip coaters, die coaters, blade coaters, bill blade coaters, short dwell blade coaters, gate roll coaters, film transfer coaters, bar coaters, rod coaters, and roll coaters. , Size press, etc. The drying of the coating layer coating liquid is a method using a conventionally known drying device, and is not particularly limited. Examples of the drying device include a hot air dryer such as a straight tunnel dryer, an arch dryer, an air loop dryer and a sine curve air float dryer, an infrared heating dryer, a dryer using microwaves and the like.

After the coating layer is provided, calendar processing can be performed using a machine calendar, a soft nip calendar, a super calendar, a multi-stage calendar, a multi-nip calendar, or the like, if necessary.

The coating layer is one layer or two or more layers. The outermost coating layer located on the outermost side with respect to the base paper may correspond to the coating layer according to the present invention containing a white pigment and a binder. When there is only one coating layer, the coating layer is the outermost coating layer. When the number of coating layers is two or more, the coating layer located between the base paper and the outermost coating layer is not particularly limited in terms of components such as the presence / absence and type of white pigment and the presence / absence and type of binder. From the viewpoint of manufacturing cost, one coating layer is preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. Moreover, the mass part and mass% shown in an Example show the value of a dry solid content or a substantial component. The coating amount indicates the value of the dry solid content.

<Base paper>
As a filler in a pulp slurry consisting of 70 parts by mass of LBKP having a drainage degree of 450 ml and NBKP having a drainage degree of 430 ml, which was determined in accordance with JIS P 811-2: 2012 "Canada Standard Drainage Degree Method". The number of parts by mass of light calcium carbonate that makes the ash content of the base paper 23% by mass, 0.8 parts by mass of amphoteric starch, 0.8 parts by mass of sulfuric acid band, alkyl ketene dimer type sizing agent (size pine K903, manufactured by Arakawa Chemical Industry Co., Ltd.) A paper material mixed with 1 part by mass was machined with a long net paper machine, and then subjected to machine calendar processing to produce a base paper having a basis weight of 45.3 g / m ² .

The printing papers of each example and each comparative example were produced by the following procedure.

<Coating layer coating liquid>
The coating layer coating liquid was prepared according to the following contents.
Calcium Aluminate Monocarbonate The average particle size and number of copies are shown in Table 1. The number of copies of heavy calcium carbonate is shown in Table 1. 10 parts by mass of polyvinyl alcohol 10 parts by mass of phosphoric acid esterified starch 10 parts by mass of water-soluble cation salt The type and number of copies are shown in Table 1. Description A coating liquid having a solid content concentration of 40% by mass was prepared by blending with the above contents and mixing with water as a medium.

<Printing paper>
Using a film transfer coater, the coating layer coating liquid was applied to the base paper on both sides so that the coating amount per side was 5.5 g / m ² , and then dried to prepare a coated paper. Next, the obtained coated paper was subjected to calendar processing to obtain a printing paper for testing. The calendering process was carried out using a device consisting of an elastic roll and a metal roll, and the nip linear pressure was performed in a linear pressure range of 100 to 120 kN / m within a range in which a thickness profile in the width direction could be appropriately obtained. The temperature of the metal roll was 80 ° C.

The obtained printing paper was evaluated by the following method. The evaluation results are shown in Table 1.

<Evaluation of cock ring and wrinkles>
Printing was performed with a rotation-type inkjet printing machine (HP T300 Color Inkjet Web Press) manufactured by Hewlett-Packard Co., Ltd. at a printing speed of 120 m / min and CMYK 4-color ink. A part of the printing paper wound up after printing was arbitrarily cut into a size of 1 m × 1 m, and the cock ring generated on the printing paper was visually observed and sensory evaluated according to the following criteria. If the evaluations are 3 and 4 in the present invention, it is assumed that the printing paper is well suppressed from the occurrence of cockling and wrinkles.
4: Cock ring and wrinkles are hardly observed, and it is good.
3: Cock ring and / or wrinkles are slightly observed, and it is generally good.
2: Inferior to 3 above, some cock ring and / or wrinkles are observed,
It is practical.
1: Cock ring and / or wrinkles are observed, which poses a practical problem.

<Evaluation of set-off and bleeding>
Printing was performed with a rotation-type inkjet printing machine (HP T300 Color Inkjet Web Press) manufactured by Hewlett-Packard Co., Ltd. at a printing speed of 120 m / min and CMYK 4-color ink. The back and front surfaces of the printing paper wound up after printing were visually observed and sensory evaluated according to the following criteria. If the evaluation is 3, 4 and 5 in the present invention, it is assumed that the printing paper is well suppressed from the occurrence of set-off and bleeding.
5: No set-off or bleeding is observed, which is extremely good.
4: It is good with only a slight amount of set-off and / or bleeding.
3: Slight set-off and / or bleeding is observed, but it is generally good.
2: Although it is inferior to 3 above and a little set-off and / or bleeding is observed, it is practical.
1: Set-off and / or bleeding is observed, which poses a practical problem.

From the results in Table 1, it is stated that the printing papers of Examples 1 to 8 corresponding to the present invention can satisfactorily suppress the occurrence of cockling, wrinkles, set-off and bleeding when printed by a rotary type inkjet printing machine. I understand. On the other hand, it can be seen that the printing papers of Comparative Examples 1 to 7 which do not satisfy the configuration of the present invention cannot obtain at least one of the effects of the present invention.

Claims (1)

The base paper has a coating layer containing a white pigment and a binder on at least one side of the base paper, and at least one of the white pigments contains calcium aluminate monocarbonate in the coating layer of the calcium aluminate monocarbonate. The content is 30 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the white pigment in the coating layer, and the average particle size of the calcium aluminate monocarbonate is 0.9 μm or more and less than 2 μm, and the coating layer. Is a printing paper characterized by containing a water-soluble polyvalent cation salt.