JP6764750B2 - Printing paper and its manufacturing method - Google Patents

Description

The present invention relates to printing paper and a method for producing the same.

As printing paper, there is a growing demand for paper that has a relatively low density, is thick, has excellent flexibility, and is less likely to be cut off by a printing press. In this highly flexible paper, the addition of a softener such as a surfactant weakens the bond between the pulp fibers and separates the fibers to secure a large number of voids between the paper layers and increase the paper thickness, so-called base paper. The bulkiness effect is concomitantly enhanced along with the flexibility by lowering the density of the above (see JP-A-2004-131922).

However, when such a softener is used, the bond between the pulp fibers is weakened as described above, so that the paper strength such as tensile strength, tearing, and Z-axis strength is lowered. Therefore, in particular, paper (printing paper) that has strength that can withstand high-speed offset printing in recent years, flexibility that suppresses the generation of blister (blisters) during drying and heating after printing, and paper strength is desired. It is rare.

Japanese Unexamined Patent Publication No. 2004-131922

The present invention has been made based on the above circumstances, and an object of the present invention is to ensure sufficient inking property as a printing paper while having flexibility, and to have a sufficient Z capable of supporting high-speed offset printing. It is an object of the present invention to provide a printing paper having axial strength and capable of suppressing the generation of blister during heat-drying after printing, and a method for producing the same.

The invention made to solve the above problems is that the raw material pulp contains a raw material pulp, an amidamine compound and a polyacrylamide-based paper strength enhancer, the raw material pulp contains 75% by mass or more of broadleaf kraft pulp, and the freeness of the raw material pulp is improved. An impregnated layer containing 400 mL or more of base paper, impregnated from the front and back surfaces of the base paper, and formed of a surface sizing agent containing starch and a styrene-based sizing agent as main components, and laminated on at least one outer surface of the impregnated layer. A printing paper having a coating layer containing a pigment and an adhesive, having a peeling strength in the Z-axis direction of 600 kPa or more, and a blister generation temperature of 170 ° C. or more.

According to the printing paper, by incorporating a predetermined raw material pulp, an amidoamine compound, and a polyacrylamide-based paper strength enhancer into the base paper, flexibility and paper strength can be enhanced, and both sides of the base paper can be further improved. By forming the impregnated layer by impregnating the impregnated liquid containing a predetermined component from the above, the strength can be further increased and the generation of blister can be suppressed. In particular, the printing paper has a high Z-axis strength with a peeling strength of 600 kPa or more in the Z-axis direction. Further, the printing paper can be provided with sufficient inking property and the like by having the above structure.

The content of the amidoamine compound with respect to the raw material pulp is 2 kg / pulp t or more and 10 kg / pulp t or less in terms of solid content, the polyacrylamide-based paper strength enhancer is amphoteric, and the polyacrylamide-based paper strength enhancer is The content of the raw material pulp is 0.4 kg / m or more and 1.6 kg / t or less, and the solid content per one side of the impregnated layer is 0.4 g / m ² or more and 1.2 g / m. It is preferably ² or less, and the impregnated layer is formed over the entire thickness direction of the base paper.

By using an amidamine compound and a polyacrylamide-based paper strength enhancer with such a content and setting the amount of the impregnated layer within the above range, flexibility is ensured and the paper strength is lowered due to the inclusion of the amidamine compound. It is possible to ensure flexibility and paper strength while achieving both the properties of hardening paper and the contradictory properties of improving paper strength by adding a polyacrylamide-based paper strength enhancer.

It is preferable that the base paper further contains an internal sizing agent, and the internal sizing agent is a cationic alkyl ketene dimer sizing agent. In addition to the above configuration, by adding an alkyl ketene dimer sizing agent internally, it is possible to further achieve both the contradictory effects of flexibility and paper strength.

It is preferable that the styrene-based sizing agent is an anionic styrene acrylate sizing agent. By using such a styrene-based sizing agent, the paper strength can be further increased.

Another invention made to solve the above problems is that the raw material pulp contains a raw material pulp, an amidamine compound and a polyacrylamide-based paper strength enhancer, and the raw material pulp contains 75% by mass or more of broadleaf kraft pulp, and the raw material pulp A step of papermaking a raw material pulp slurry having a freeness of 400 mL or more, and an impregnating solution containing a surface sizing agent containing starch and a styrene-based sizing agent as main components from the front and back surfaces of the base paper obtained through the above papermaking step. This is a method for producing printing paper, comprising a step of impregnating the entire thickness direction of the base paper by a roll size press and a step of laminating a coating layer containing a pigment and an adhesive on at least one side of the base paper that has undergone the impregnation step.

According to this manufacturing method, it has sufficient Z-axis strength that can be used for high-speed offset printing while ensuring sufficient weight reduction and sufficient fillability as printing paper, and blister generation during heat drying after printing is generated. It is possible to obtain a printing paper that can suppress the above. In particular, by using a 2-roll size press, an impregnated layer having a sufficient content can be formed, and printing paper having high Z-axis strength can be efficiently produced.

The "main component" refers to the component having the highest solid content on a mass basis. Further, the content of each component in the raw material pulp can be regarded as the same as the amount added to the raw material pulp in the slurry of the raw material pulp at the time of production.

According to the present invention, while ensuring flexibility and sufficient fillability as printing paper, it has sufficient Z-axis strength capable of high-speed offset printing, and blister generation during heat drying after printing is generated. It is possible to provide a printing paper that can be suppressed and a method for producing the same.

FIG. 1 is a schematic cross-sectional view of a printing paper according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a printing paper according to an embodiment different from that of FIG.

Hereinafter, the printing paper according to the embodiment of the present invention and the manufacturing method thereof will be described in detail with reference to the drawings as appropriate.

<Printing paper>
The printing paper according to the embodiment of the present invention has a base paper, an impregnated layer impregnated from the front and back surfaces (both sides) of the base paper, and a coating layer laminated on at least one outer surface of the impregnated layer.

<Base paper>
The base paper contains raw material pulp (pulp fiber) as a main component, and at least contains an amidoamine compound and a polyacrylamide-based paper strength enhancer. The base paper is obtained by making a slurry of raw material pulp to which an amidoamine compound, a polyacrylamide-based paper strength enhancer and, if necessary, other additives are added.

(Raw material pulp)
As the raw material pulp, one containing 75% by mass or more of hardwood kraft pulp (NKP) and having a freeness of 400 mL or more is used. As the pulp used as the raw material pulp, for example, virgin pulp, used paper pulp, and a combination thereof can be appropriately used.

As virgin pulp, in addition to coniferous kraft pulp (NKP), chemical pulp such as broadleaf kraft pulp (LKP), broadleaf sulfite pulp, and conifer sulfite pulp; stone ground pulp (SGP), pressurized stone ground pulp (TGP), chemi Mechanical pulps such as ground pulp (CGP), crushed wood pulp (GP), thermomechanical pulp (TMP); various known known pulps such as pulps chemically or mechanically produced from non-wood fibers such as kenaf, hemp and reeds. Pulp is an example.

Examples of used paper pulp include tea waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, upper white waste paper, Kent waste paper, imitation waste paper, and ground ticket waste paper. Examples include ink waste paper pulp (DIP), dissociation, deinking, and bleached waste paper pulp.

As described above, the raw material pulp contains 75% by mass of LKP. The content of this LKP is preferably 80% by mass or more, more preferably 85% by mass or more. The content of this LKP may be 100% by mass, but is preferably 95% by mass or less. Further, it is preferable to use NKP as the raw material pulp other than LKP. The content of NKP is preferably 5% by mass or more. The content of NKP is preferably 20% by mass or less, more preferably 15% by mass or less. By using such raw material pulp, it is possible to make the interfiber voids, interfiber bonds, density and the like in the base paper in a well-balanced and suitable state, and it is possible to improve both flexibility and printability.

The lower limit of the freeness of the raw material pulp is 400 mL, preferably 450 mL, more preferably 470 mL. On the other hand, the upper limit may be, for example, 600 mL, preferably 550 mL. By setting the freeness (water freeness) of the raw material pulp within the above range, there is a tendency that low density and the like can be improved in a well-balanced manner while ensuring the flexibility and strength of the printing paper. Further, by using the raw material pulp made of fibers having relatively high freeness and less defibration, there is an advantage that the gaps between the fibers are increased and low density can be easily obtained due to flexibility and accompanying effects. Fibers that originally have less defibration tend to have a smaller specific surface area and lower fixability of amidamine compounds and polyacrylamide-based paper strength enhancers. However, according to the findings of the present inventors, the raw material pulp and the surface of the base paper are impregnated. By using the ionicity of various functional agents to be allowed in a desired combination, the fixability of the amidoamine compound and the polyacrylamide-based paper strength enhancer can be enhanced. When the raw material pulp having a relatively high freeness is used as described above, the strength of the paper usually tends to decrease. However, in the printing paper, the use of various functional agents in combination with the desired ionicity is used. Sufficient strength can be maintained by providing a specific impregnated layer. Freeness refers to Canadian standard freeness measured in accordance with JIS-P-8121 (1995).

The method for adjusting the freeness is not particularly limited, but the raw material pulp is beaten as necessary so as to have a predetermined freeness with or without using various beaters such as a disc type and a conical type. The method and the like can be mentioned.

(Amidamine compound)
The amidoamine compound is added to impart good flexibility and low density as an incidental effect. Further, the amidoamine compound has lower foamability than other surfactants and softeners of fatty acids, and can perform efficient papermaking. Examples of the amidoamine compound include a compound represented by the following formula (1) or a salt thereof.

In the formula (1), R ¹ CO is an acyl group having 10 to 24 carbon atoms. R ² is an alkylene group having 2 to 4 carbon atoms. R ³ and R ⁴ are independently alkyl groups having 1 to 4 carbon atoms.

Examples of the acyl group having 10 to 24 carbon atoms include a structure derived from a fatty acid. Examples of this fatty acid include chain saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, araquinic acid, bechenic acid and lignoceric acid, branched fatty acids such as isoparmic acid and isostearic acid, palmitic acid and oleic acid. Examples thereof include unsaturated fatty acids such as acid, lignoic acid, lignoceric acid, elaidic acid, and erucic acid. Of these, a carboxylic acid having 16 to 22 carbon atoms is preferable.

Examples of the alkylene group (alkanediyl group) having 2 to 4 carbon atoms include an ethylene group, a propylene group and a butylene group, and a propylene group is preferable.

Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group and the like. Of these, an ethyl group is preferred.

The salt of the compound represented by the above formula (1) can be obtained by neutralizing the above compound with an acid. Examples of this acid include inorganic acids such as hydrochloric acid, sulfuric acid, carbonic acid, nitric acid, and phosphoric acid, formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, lactic acid, gluconic acid, salicylic acid, hydroxyvaleric acid, astragic acid, and glutamate. Examples thereof include organic acids such as taurine and sulfamic acid. Of these, formic acid, acetic acid, glycolic acid, lactic acid, and gluconic acid are preferred. When the amidamine compound is used in the form of such a salt, it exists as a cation, which enhances the fixability to anionic pulp. Examples of commercially available amidamine compounds include "Nichiyumar AC-1" manufactured by NOF CORPORATION.

The content of the amidoamine compound in the base paper is not particularly limited, but for example, as the lower limit with respect to the raw material pulp, the solid content is preferably 2 kg / pulp t, more preferably 4 kg / pulp t. On the other hand, as the upper limit, the solid content is preferably 10 kg / pulp t, more preferably 9 kg / pulp t. By setting the content of the amidoamine compound in the above range, the flexibility, density, strength and the like can be balanced and improved. In addition, "kg / pulp t" indicates the mass in terms of solid content per absolute dry pulp (the same applies hereinafter).

(Polyacrylamide-based paper strength enhancer)
As the polyacrylamide-based paper strength enhancer, any of anionic polyacrylamide, cationic polyacrylamide, and amphoteric polyacrylamide can be preferably used.

In the above polyacrylamide, the viscosity of the 10% aqueous solution at 25 ° C. is preferably 3,000 mPa · s or more and 20,000 mPa · s or less. When this viscosity is less than 3,000 mPa · s, the aggregation effect of fine fibers by polyacrylamide becomes insufficient, and the water solubility and the yield decrease in the papermaking process. On the other hand, when the viscosity exceeds 20,000 mPa · s, the aggregation effect of the fine fibers becomes too large, and the uniformity of the paper surface is lowered. The viscosity is a value measured by a 10% by mass aqueous solution of polyacrylamide at 25 ° C. with a B-type viscometer (Rotor No. 4, 30 rpm).

Among polyacrylamides, examples of anionic polyacrylamide include copolymers of acrylamide with anionic monomers such as acrylic acid and methacrylic acid, and partial hydrolyzates of polyacrylamide. Examples of cationic polyacrylamide include Mannich modified products of polyacrylamide, Hofmann decomposition products, copolymers of acrylamide and cationic monomers, and the like. Examples of the cationic monomer include dimethylaminoethyl methacrylate, diallyldimethylammonium chloride, diallyldiethylammonium chloride, metaacryloxyethyltrimethylammonium methylammonium methylsulfate, metaacryloxyethylammonium methyl chloride, and metaacrylamidepropyltrimethylammonium chloride. Can be mentioned. Examples of amphoteric polyacrylamide include copolymers of acrylamide and the above-mentioned anionic and cationic monomers, Mannig-modified products of copolymers of acrylamide and the above-mentioned anionic monomers, and Hofmann decomposition products. Among these, cationic polyacrylamide and amphoteric polyacrylamide are preferable from the viewpoint of improving the supple feel and suppressing the decrease in strength.

According to the findings of the present inventors, amphoteric polyacrylamide is particularly preferable, and since amphoteric polyacrylamide has a self-fixing function, even if it is added to improve the inter-paper strength, there is no excess of cations. , The charge in the papermaking system can be stably maintained, and the surface strength and printability can be improved to a extent that cannot be achieved by simply adding cationic acrylamide or anionic acrylamide, which is the constitution of the present invention. When used in combination with an amide amine compound, it is possible to obtain low density, which is an incidental effect, while obtaining good flexibility, and high-speed offset printing while ensuring the problematic flexibility and sufficient fillability as printing paper. It is possible to provide a printing paper having sufficient Z-axis strength corresponding to the above and capable of suppressing the generation of blister during heating and drying after printing, and a method for producing the same.

The lower limit of the content of the polyacrylamide-based paper strength enhancer in the raw material pulp may be, for example, 0.1 kg / pulp t in terms of solid content, but 0.4 kg / pulp t is preferable, and 0.6 kg / pulp t is preferable. More preferred. On the other hand, as the upper limit, the solid content may be, for example, 2 kg / pulp t, but 1.6 kg / pulp t is preferable, and 1.4 kg / pulp t is more preferable. By setting the content of the polyacrylamide-based paper strength enhancer in the above range, it is possible to exhibit good strength while having appropriate flexibility.

(Internal sizing agent)
It is preferable that the base paper further contains an internal sizing agent. By containing the internal sizing agent, the hydrophobicity of the pulp fiber is enhanced, and the flexibility can be further enhanced.

The internal sizing agent is not particularly limited, and examples thereof include a rosin-based sizing agent, an alkyl ketene dimer (AKD) -based sizing agent, an alkyl succinic anhydride (ASA) -based sizing agent, and an alkyl ketene dimer sizing agent. it can. Of these, alkyl ketene dimer sizing agents are preferred. The strength can be further increased by adding an alkyl ketene dimer sizing agent internally.

In the findings of the inventors, the present invention is further advantageously achieved, especially by using a cationic alkyl ketene dimer as the sizing agent. The cationic alkyl ketene dimer can be used at the same time as the amidoamine compound to improve its yield, and further, it should be used in combination with a polyacrylamide-based paper strength enhancer, particularly an amphoteric polyacrylamide-based paper strength enhancer. Is desirable.

The interposition of anionic and cationic groups of the amphoteric polyacrylamide-based paper strength enhancer brings out the flexibility and low density of the amidoamine compound, while achieving both the paper strength improving effect and the size. Printing paper that has sufficient Z-axis strength for high-speed offset printing and can suppress the generation of blister during heat-drying after printing, while ensuring sufficient weight reduction and sufficient fillability as printing paper. , And a method for producing the same.

As the content of the internal sizing agent in the base paper, for example, 0.1 kg / pulp t or more is preferable, and 0.2 kg / pulp t or more is more preferable. The content of the internal sizing agent is preferably 2 kg / pulp t or less, more preferably 1 kg / pulp t or less, further preferably 0.5 kg / pulp t or less, and particularly preferably 0.4 kg / pulp t or less. preferable. By setting the content of the internal sizing agent in the above range, it is possible to further increase the strength while maintaining the low density.

The mass ratio of the polyacrylamide-based paper strength enhancer and the internal sizing agent is preferably 1: 4 or more and 1: 2 or less. By setting the mass ratio of the polyacrylamide-based paper strength enhancer and the internal sizing agent within the above range, low density and strength can be improved in a more balanced manner. As the ratio of the polyacrylamide-based paper strength enhancer increases, the low density tends to decrease, and as the ratio of the internal sizing agent increases, the paper strength tends to decrease.

(Other papermaking aids, etc.)
Other papermaking aids may be added to the base paper as long as the effects of the present invention are not impaired. Examples of other papermaking aids include internal paper strength enhancers other than polyacrylamide-based paper strength enhancers, yield improvers (coagulants, coagulants), filling amount and the like. In order to reduce the weight, it is preferable not to positively add a filling amount to the raw material pulp.

Examples of the internal paper strength enhancer include natural polymer-based paper strength agents such as cationized starch. Examples of the yield improver include a sulfate band (aluminum sulfate), anionic polyacrylamide, starch, carboxymethyl cellulose, colloidal silica and the like.

<Impregnated layer>
The impregnated layer is formed by impregnating the impregnating liquid from both sides of the base paper. The strength of the printing paper can be increased by this impregnated layer. Further, it is possible to suppress the sinking of the pigment into the base paper, and as a result, it is possible to improve the flexibility, flatness, printability (filling property) and the like of the printing paper.

Regarding the impregnated layer, the impregnated layer 12 may be formed over the entire thickness direction of the base paper 11 as in the printing paper 10 shown in FIG. 1, or two impregnated layers as in the printing paper 20 shown in FIG. 22a and 22b may be formed so as to exist separately on each side of the base paper 21. Further, a coating layer 13 is formed on both outer surfaces of the impregnated layer 12 of FIG. 1, and a coating layer 23 is formed on each of the outer surfaces of the impregnated layers 22a and 22b of FIG. In addition, in FIGS. 1 and 2, in order to show the degree of impregnation, the impregnation layers 12, 22a and 22b are not formed on both ends of the base papers 11 and 21, but the edges of the base paper are usually used. The impregnated layer is formed up to the part. Further, a part of the impregnated layer may not be impregnated in the base paper.

In the printing paper 10 of FIG. 1, as a result of impregnating the entire base paper with the impregnating liquid from both sides of the base paper, the impregnation layer 12 is formed on the entire base paper 11. As described above, since the impregnated layer 12 is formed over the entire thickness direction of the base paper 11, the strength can be further increased. When the impregnated layer is not formed over the entire thickness direction of the base paper, the total average thickness of the two impregnated layers is preferably 50% or more, preferably 90% or more of the average thickness of the base paper.

The impregnated layer contains starch and a surface sizing agent containing a styrene-based sizing agent as a main component. By forming the impregnated layer containing such a component, it is possible to increase the strength of the printing paper whose strength between fibers is weakened by an amidoamine compound or the like.

(starch)
As the starch, various unprocessed or processed starches such as corn starch (corn starch), potato starch, sweet potato starch, tapioca starch and the like can be used.

Further, as the starch, oxidized starch, cationized starch, carboxymethylated starch, pregelatinized starch, acetic acid esterified starch, urea phosphate-modified starch, unmodified starch and the like can be used, and among these, oxidized starch and unmodified starch can be used. Esterified starch is preferred. By using oxidized starch or cationized starch, the impregnation property in the base paper is enhanced, and the strength of the obtained printing paper can be further enhanced.

The content of the starch is preferably 10 kg / pulp t or more and 50 kg / pulp t or less with respect to the raw material pulp of the base paper. By setting the starch content in the above range, the strength of the obtained printing paper and the like can be improved.

(Surface size agent)
The surface sizing agent contains a styrene-based sizing agent as a main component. The styrene-based sizing agent has good impregnation property into the base paper, and can effectively exhibit sizing property. Examples of the styrene-based sizing agent include styrene / acrylic acid copolymer, styrene / (meth) acrylic acid copolymer, styrene / (meth) acrylic acid / (meth) acrylic acid ester copolymer, and styrene / maleic acid copolymer. Examples thereof include coalescence, styrene / maleic acid semi-ester copolymer, styrene / maleic acid ester copolymer and the like.

As the surface sizing agent, a styrene acrylate sizing agent is preferable among the styrene-based sizing agents described above. The styrene acrylate sizing agent refers to a sizing agent which is a copolymer of styrene and (meth) acrylic acid or (meth) acrylic acid ester. By using such a sizing agent, more effective sizing and the like can be exhibited by the effect of the combination of the amidoamine compound and the polyacrylamide-based paper strength enhancer, and the printing suitability and the like can be improved. Can be done.

As the surface sizing agent, only a styrene-based sizing agent may be used, but it may be used in combination with other sizing agents. Examples of other sizing agents include acrylate-based sizing agents and alkyl ketene dimers.

According to the findings of the inventors, styrene-based sizing agents are used as surface sizing agents, and in particular, by using anionic styrene-based sizing agents, amidoamine compounds and polyacrylamide-based paper strength enhancers embedded in the substrate are used. It has sufficient Z-axis strength for high-speed offset printing while ensuring weight reduction and sufficient inking property as printing paper, which are issues due to ionic bonding with, and during heat drying after printing. It is possible to provide a printing paper capable of suppressing the generation of blister and a method for producing the same.

The content of the surface sizing agent (styrene-based sizing agent) is preferably 0.1 kg / pulp t or more and 1 kg / pulp t or less with respect to the raw material pulp of the base paper. By setting the content of the surface sizing agent in the above range, it is possible to effectively suppress the sinking of the pigment into the base paper.

The mixing ratio of starch and the surface sizing agent in the impregnated layer or impregnated liquid is preferably 1:20 to 20: 1 by weight. If the amount of starch exceeds this range, the water absorption resistance decreases. Further, if the amount of the styrene-based sizing agent exceeds this range, the strength decreases. That is, if it is within this mixing ratio, it has sufficient Z-axis strength that can be used for high-speed offset printing while ensuring weight reduction and sufficient inking property as printing paper, and heating after printing. It is suitable for providing a printing paper capable of suppressing the generation of blister during drying, and a method for producing the same.

The impregnated layer may contain components other than the starch and surface sizing agent described above. Examples of such other components include paper strength of polyacrylamide (PAM), polyvinyl alcohol (PVA), acrylic resin, polyamide / polyamine resin, urea / formalin resin, melamine / formalin resin, polyethyleneimine and the like. Examples include enhancers.

As the lower limit of the mass (coating amount or content) per one side of the impregnated layer, 0.4 g / m ² is preferable, and 0.6 g / m ² is more preferable. On the other hand, as the upper limit, 1.2 g / m ² is preferable, and 1.0 g / m ² is more preferable. The mass per one side of the impregnated layer is, for example, as shown in FIG. 2, when the impregnated layer is separated into the impregnated layer 22a and the impregnated layer 22b on each surface side, the mass per unit area of each impregnated layer. It is the mass. Further, as shown in FIG. 1, when the impregnated liquid impregnated from both sides is impregnated as a whole to form one impregnated layer 12, the mass per suitable unit area of the impregnated layer 12 is the mass per one side. Is twice as much as. By setting the mass of the impregnated layer per one side in the above range, it is possible to further increase the strength while maintaining low density.

<Coating layer>
The coating layer contains a pigment and an adhesive, and usually contains the pigment and the adhesive as main components. When the printing paper has such a coating layer, it is possible to exhibit sufficient inking property as the printing paper. The coating layer is usually laminated by applying a coating liquid to the base paper on which the impregnated layer is formed. The coating layer is laminated on at least one side of the base paper, but may be laminated on both sides of the base paper. The "coating layer containing a pigment and an adhesive as main components" means that the coating layer contains the pigment and the adhesive in an amount of 50% by mass or more, preferably 70% by mass or more, in terms of solid content with respect to the entire coating layer. More preferably, it is contained in an amount of 80% by mass or more. The coating layer may optionally contain other coating aids other than pigments and adhesives as long as the effects of the present invention are not impaired.

(Pigment)
Examples of the pigments include calcium carbonate, clay, talc, kaolin, satin white, calcium sulfite, gypsum, barium sulfate, white carbon, calcined kaolin, structured kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide. , Silica, magnesium hydroxide, zinc hydroxide, zinc oxide, magnesium oxide, bentonite, sericite and other inorganic pigments, polystyrene resin fine particles, urea formalin resin fine particles, fine hollow particles, porous fine particles and the like. Among these, calcium carbonate and clay are preferable. By using calcium carbonate and clay, it is possible to provide a printing paper having high smoothness and excellent flexibility and printability.

(adhesive)
By containing an adhesive in the coating layer, the pigment can be fixed on the surface of the base paper. The adhesive is not particularly limited, and known adhesives can be used. For example, proteins such as casein and soybean protein; conjugated diene latex such as styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, styrene-methyl methacrylate-butadiene copolymer latex; acrylic acid ester and / or Acrylic latex such as polymer latex or copolymer latex of methacrylic acid ester; Vinyl latex such as ethylene-vinyl acetate polymer latex; These various copolymer latex are made of functional group-containing monomer such as carboxyl group. Latexes such as modified alkali partially soluble or insoluble latex; synthetic resin adhesives such as olefin-maleic anhydride resin, melamine resin, urea resin, urethane resin; oxidized starch, cationized starch, esterified starch , Natural polymer-based adhesives such as dextrin; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose can be mentioned.

Among these, natural polymer-based adhesives such as starch and latex-based adhesives are preferable, and latex-based adhesives containing a polymer obtained from a monomer containing butadiene are more preferable. When such an adhesive is used, the flexibility of the coating layer is increased, and the flexibility of the printing paper can be increased. Further, when butadiene is contained as a monomer, the obtained polymer has flexibility.

As for the content of the adhesive with respect to 100 parts by mass of the pigment, the content of the adhesive with respect to 100 parts by mass of the pigment is preferably 13 parts by mass or less, more preferably 8 parts by mass or more and 12 parts by mass or less. By setting the content of the adhesive to the pigment in the above range in this way, a flexible coating layer can be obtained, and as a result, the paper strength tends to be increased while maintaining the flexibility of the printing paper. There is. If the content of the adhesive to the pigment exceeds the above upper limit, the flexibility of the printing paper may decrease. If the content of the adhesive to the pigment is less than the above lower limit, the adhesive strength may be inferior and the flexibility of the printing paper may be deteriorated.

(Other coating aids)
Other coating aids are not particularly limited, and examples thereof include fluorescent whitening agents, antifoaming agents, coloring agents, and water retention agents.

The raw materials used in the present invention may be used alone or in combination of two or more as long as the effects of the present invention are not impaired.

<Physical properties of printing paper>
The peel strength in the Z-axis direction of the printing paper is 600 kPa or more, preferably 700 kPa or more, and more preferably 750 kPa or more. When the printing paper has such a high peel strength, the compatibility with high-speed offset printing is enhanced. The upper limit of the Z-axis strength is, for example, 1,500 kPa. Here, the peel strength in the Z-axis direction refers to a value measured in accordance with TAPPI T 541. The peel strength (kPa) in the Z-axis direction of the printing paper can be measured by using "L & W ZDTENSILE TESTER" (ZDT method) manufactured by Lorentzen & Wettre in accordance with TAPPI T 541. The peel strength can be adjusted by the amount of the impregnated layer applied, the type of raw pulp, the freeness, the amount of other various additives added, and the like.

The density of the printing paper is preferably 0.7 g / cm ³ or more and 0.9 g / cm ³ or less. By setting the density of the printing paper in the above range in this way, the flexibility and printability (filling property, etc.) of the printing paper can be exhibited in a well-balanced manner. If the density of the printing paper exceeds the above upper limit, the flexibility decreases. If the density of the printing paper is less than the above lower limit, the strength of the printing paper is lowered, and the printability and the ease of turning are lowered.

The thickness of the printing paper is not particularly limited, but the lower limit is preferably 70 μm, more preferably 90 μm. On the other hand, the upper limit is preferably 200 μm, more preferably 160 μm. By setting the paper thickness of the printing paper within the above range, even when the paper thickness is high as described above, the flexibility is adjusted so that the printing paper tends to have both flexibility and printability. is there. If the thickness of the printing paper exceeds the above upper limit, the flexibility of the printing paper may decrease. If the paper thickness of the printing paper is less than the above lower limit, the low density of the printing paper may decrease.

The basis weight of the printing paper is not particularly limited, but is preferably 50 g / m ² or more and 150 g / m ² or less. By setting the basis weight of the printing paper in the above range in this way, the flexibility and printability of the printing paper tend to be exhibited in a well-balanced manner, for example, the flexibility can be easily adjusted. If the basis weight of the printing paper exceeds the above upper limit, the flexibility of the printing paper may decrease. If the basis weight of the printing paper is less than the above lower limit, the paper strength of the printing paper may decrease.

The blister generation temperature of the printing paper is 170 ° C. or higher, preferably 200 ° C. or higher. Since the blister generation temperature is high as described above, the blister generation during heating and drying after printing is effectively suppressed. The blister generation temperature refers to a value measured by the method in the examples described later. The upper limit of the blister generation temperature may be, for example, 220 ° C. or 240 ° C. The blister generation temperature can be adjusted by the amount of coating of the impregnated layer and the coating layer, the type of raw material pulp, freeness, the amount of other various additives added, and the like.

The printing paper has an air permeability of 4 to 12 seconds, preferably 5 to 10 seconds, more preferably 6 to 8 seconds, measured based on the Garley method described in JIS-P-8117 (2009). Therefore, it is possible to further suppress the generation of blisters while having sufficient strength. If the air permeability is less than the above lower limit, blisters may easily occur. On the contrary, when the air permeability exceeds the above upper limit, the strength or the like may decrease. The air permeability can be adjusted by adjusting the freeness of the raw material pulp, the amount of the impregnated layer coated, and the like.

Further, by applying a flattening treatment to this coated paper, the coated paper having further excellent image quality can be obtained. These flattening can be performed by a flattening facility that can be generally used for papermaking, and can be adjusted by a linear pressure, a speed, or the like using, for example, a super calendar or a soft calendar. If the air permeability exceeds 12 seconds, even if further flattening is performed, the ink absorption and drying property will only reach a plateau, which is economically unfavorable. Even when the smoothness is adjusted with the super calendar, the flexibility and strength of the paper are impaired due to the excessive linear pressure, and the accompanying effect of low density may also be reduced. If the air permeability is less than 4 seconds, there are many voids on the coated surface, and the ink absorption and drying property during printing tends to decrease.

The ash content of the printing paper is preferably less than 8% by mass, more preferably 5% by mass or less, and even more preferably 3% by mass or less. Since the printing paper has such a low ash content, it is possible to suppress a decrease in interfiber bond due to the presence of a filler, and it is possible to provide high Z-axis strength while ensuring low density. The lower limit of the ash content of the printing paper may be, for example, 0.5% by mass or 1% by mass. The ash content is a value measured according to "Paper, paperboard and pulp-ash content test method-525 ° C. combustion method" described in JIS-P-8251 (2003).

As described above, the printing paper has sufficient Z-axis strength capable of high-speed offset printing while ensuring sufficient weight reduction and sufficient inking property as printing paper, and is used during heat drying after printing. The generation of blister can be suppressed. Therefore, the printing paper can be suitably used for applications requiring these characteristics, particularly as printing paper for mooks and the like.

<Manufacturing method of printing paper>
The printing paper manufacturing method is not particularly limited, but can be obtained by a known printing paper manufacturing method, and the preferred manufacturing method is as follows. That is, the method for manufacturing printing paper according to the embodiment of the present invention is
A step of making a raw material pulp slurry containing raw material pulp, an amidamine compound and a polyacrylamide-based paper strength enhancer, the raw material pulp containing 75% by mass or more of broadleaf kraft pulp, and the freeness of the raw material pulp being 400 mL or more.
A step of impregnating the front and back surfaces of the base paper obtained through the above papermaking process with an impregnating solution containing starch and a surface sizing agent containing a styrene-based sizing agent as a main component by a 2-roll size press over the entire thickness direction of the base paper. A step of laminating a coating layer containing a pigment and an adhesive is provided on at least one side of the base paper that has undergone the impregnation step.

The manufacturing method can be carried out using a known papermaking apparatus. In addition to the amidoamine compound and the polyacrylamide-based paper strength enhancer, various additives such as an internal sizing agent are added to the raw material pulp slurry used in the papermaking process. After papermaking of the raw material pulp slurry, the base paper can be obtained through, for example, a press part and a pre-dryer part. In the production of the base paper, the dehydration method in the press part is not particularly limited, but dehydration can be performed by, for example, pressurizing between the rolls three or four times and letting the felt absorb the water.

In addition to starch and a surface sizing agent, the impregnating liquid may contain other components forming an impregnating layer. In the impregnation step, by impregnating the impregnating liquid with a two-roll size press, the impregnating liquid can be sufficiently impregnated into the base paper, and the strength of the obtained printing paper can be effectively increased. After impregnation with a 2-roll size press, an impregnated layer is formed by performing a flattening treatment and a drying treatment as necessary.

Lamination of the coating layer is usually performed by coating with a coating liquid. The above coating method is not particularly limited, and can be performed by a known method using a blade coater, a bar coater, a gate roll coater, a rod coater, an air knife coater, or the like. After coating, a coating layer is formed by performing a flattening treatment and a drying treatment, if necessary.

According to this manufacturing method, it has sufficient Z-axis strength that can be used for high-speed offset printing while ensuring sufficient weight reduction and sufficient fillability as printing paper, and blister generation during heat drying after printing is generated. It is possible to obtain a printing paper that can suppress the above.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The measurement method and evaluation criteria of each measured value in Examples and Comparative Examples are as described below.

[Peeling strength in the Z-axis direction (kPa)]
The measurement was performed using a ZDT tester "L & W ZDTENSILE TESTER" manufactured by Lorentzen & Wettre in accordance with TAPPI T 541.

[Blister generation temperature]
The printing paper (test piece) is prepared at a flow direction of 2 cm and a width direction of 10 cm, and after adjusting the humidity for 24 hours under the conditions of 23 ° C. and 50% RH, it is immersed in an oil bath (silicon oil) adjusted to a constant temperature for 4 seconds. It was. This test was performed three times, and the lowest temperature at which blister (breakage of the paper layer) occurred was defined as the blister generation temperature.

[Air permeability (seconds)]
The measurement was performed in accordance with the Garley method described in JIS-P-8117 (2009).

[Ash content (mass%)]
The measurement was performed in accordance with "Paper, paperboard and pulp-ash content test method-525 ° C. combustion method" described in JIS-P-8251 (2003).

[Density (unit: g / cm ³ )]
The measurement was performed in accordance with "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P-8118 (1998).

[Stiffness ^(unit: cm 3/100)] (Flexibility: Clark stiffness)
The vertical and horizontal rigidity was measured according to the "paper-stiffness test method-Clark stiffness tester method" described in JIS-P-8143 (2009).

[Meat]
Using an offset printing machine (“Komori SYSTEMC-20” manufactured by Komori Corporation), 10000 copies were continuously printed with ink (“News Zet Naturalis (ink)” manufactured by Dainippon Ink and Chemicals Co., Ltd.). The sharpness and unevenness of shading of the printed matter were visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
5: The image is clear, there is no unevenness in shading, and the ink penetration property is excellent.
4: The image is clear, there is almost no unevenness in shading, and the ink penetration property is good.
3: There are some areas where the image is not clear and uneven shading.
2: There are some areas where the image is not clear and uneven shading, and the ink penetration property is not good.
1: Overall, the image is unclear, uneven shading is remarkable, and the ink penetration property is inferior.

The chemicals used in each Example and Comparative Example are as follows.
(Softener)
-Amidamine compound: NOF's "Nichiyumar AC-1"
-Fatty acid ester compound: Kao's "KB210"
-Fatty acid amide compound: "Pelemin TS-218" from Miyoshi Oil & Fat Co., Ltd.
-Polyamine compounds: "DKS Tafflon NT-350J" from Dai-ichi Kogyo Seiyaku Co., Ltd.
(Paper power enhancer)
・ Amphoteric polyacrylamide: Harima Chemicals' amphoteric "Harmide DN760")
-Nonion polyacrylamide: Harima Chemicals'"HarmideDN420"
-Anion polyacrylamide: "Polymaset 500" from Arakawa Chemical Co., Ltd.
(Internal sizing agent):
-Cationic alkyl ketene dimer (AKD): "FK34" of Toho Chemical Industry Co., Ltd.
-Neutral alkenyl succinic anhydride (ASA): "Size Pine SA864" by Arakawa Chemical Co., Ltd.
-Anionic rosin-based sizing agent: "Size Pine E" manufactured by Arakawa Chemical Co., Ltd.
(Starch and other surface paper strength enhancers)
-Oxidized starch: "MS3800" from Nihon Shokuhin Kako
-Amphoteric starch: "Cato 3210" from NSC Japan
-Cationized starch: "EX-3" from Nissho Chemical Co., Ltd.
-Cationic urea phosphate esterified starch: "Star Coat 14" manufactured by Nihon Shokuhin Kako Co., Ltd.
-Cationized tapioca starch: "Amylofax T-2600" from Abebe Japan
-Polyacrylamide (PAM): Harima Chemicals'"HaricoatG51"
-Polyvinyl alcohol (PVA): "P7400" from Nippon Synthetic Chemistry Co., Ltd.
(Surface size agent)
-Anion-styrene surface sizing agent (styrene acrylate emulsion sizing agent): "SE2066" from Seiko PMC Corporation
-Anion-alkyl ketene dimer-based surface sizing agent: "AD1635" from Seiko PMC Corporation
-Cation / alkyl ketene dimer-based surface sizing agent: "Size Pine K921" from Arakawa Chemical Industry Co., Ltd.
-Cation-styrene surface sizing agent: "Polymaron 360" from Arakawa Chemical Industry Co., Ltd.
-Anion-olefin sizing agent: "SS2550" from Seiko PMC

[Example 1]
Hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP) were blended in a mass ratio of 98: 2 to obtain a raw material pulp having a freeness of 500 mL. With respect to this pulp (absolute dry amount), each solid content is 6 kg / pulp t of amidoamine compound as a softening agent, 0.4 kg / pulp t of polyacrylamide as a paper strength enhancer, and alkyl as an internal sizing agent. Ketene dimer 0.35 kg / pulp t was added to obtain a pulp slurry.

Next, use a papermaking system that includes a wire part, press part, pre-dryer part, undercoater part (2-roll size press), after-dryer part, pre-calendar part, top coater part, scuff dryer part, and reel part. I got the printing paper.

Specifically, the pulp slurry was first made into a paper by a wire part and then used in a press part and a pre-dryer part to produce a base paper having a basis weight of 74.5 g / m ² . Next, in a 2-roll size press as an undercoater part, an impregnating solution containing oxidized starch and a styrene-based surface sizing agent in a mass ratio of 75:25 was impregnated from both sides so as to be 0.8 g / m ² per side. And dried in the after-dryer part. After that, at the top coater part, the coating liquid (heavy calcium carbonate as a pigment), delaminated clay (product name: Contour 1500 parts, laser method average particle size 3.4 μm) and clay were mixed at 60:30:10. A coating liquid containing 8 parts by mass of latex and 2 parts by mass of starch as an adhesive with respect to 100 parts by mass of pigment as an adhesive) is top-coated on both sides so as to be 11 g / m ² per side. Worked. Next, the drying treatment was performed in the dryer part, and the printing paper was used in the winder part to obtain printing paper having a basis weight of 95.5 g / m ² . All of the above parts used an on-machine papermaking system.

[Examples 2-27, Comparative Examples 1-16]
Blending ratio of raw material pulp, freeness of raw material pulp, type and amount of softener, type and amount of paper strength enhancer, amount of internal sizing agent, type and amount of starch or its substitute in impregnating solution, in impregnating solution Examples 2 to 27 and Comparative Examples 1 to 16 are the same as in Example 1 except that the type of surface sizing agent, the amount of the impregnating liquid applied, and the coating method are as shown in Tables 1 and 2. Each printing paper was obtained.

[Evaluation]
For each of the obtained printing papers, the rigidity, the peel strength in the Z-axis direction, the blister generation temperature, the air permeability, the ash content and the density were measured by the above method, and the incarnationability was evaluated. The results are shown in Table 3. Further, when the cross sections of the obtained printing papers of Examples 1 to 27 were observed under a microscope, it was confirmed that the impregnated layer was formed over the entire thickness direction of the base paper.

As shown in Table 3, each printing paper of the example has excellent flexibility, low density, sufficient inking property, high Z-axis strength (peeling strength), and generation of blisters. It can be seen that it is suppressed.

The printing paper of the present invention has sufficient inking property as a printing paper while having flexibility, has sufficient Z-axis strength for high-speed offset printing, and is a blister during heat drying after printing. The occurrence of is suppressed. Therefore, the printing paper can be suitably used for applications requiring these characteristics, particularly as printing paper for mooks and the like.

10, 20: Printing paper 11, 21: Base paper 12, 22a, 22b: Impregnated layer 13, 23: Coating layer

Claims (5)

A base paper containing raw material pulp, an amidamine compound and a polyacrylamide-based paper strength enhancer, the raw material pulp containing 75% by mass or more of hardwood kraft pulp, and a base paper having a freeness of 400 mL or more of the raw material pulp.
An impregnated layer formed from the front and back surfaces of the base paper and formed from a surface sizing agent containing starch and a styrene-based sizing agent as main components,
It has a coating layer that is laminated on at least one outer surface of the impregnated layer and contains a pigment and an adhesive.
Printing paper with a peel strength in the Z-axis direction of 600 kPa or more and a blister generation temperature of 170 ° C or more. The solid content of the amidoamine compound with respect to the raw material pulp is 2 kg / pulp t or more and 10 kg / pulp t or less.
The polyacrylamide-based paper strength enhancer is amphoteric, and the solid content of the polyacrylamide-based paper strength enhancer with respect to the raw material pulp is 0.4 kg / pulp t or more and 1.6 kg / pulp t or less.
The solid content per side of the impregnated layer is 0.4 g / m ² or more and 1.2 g / m ² or less.
The printing paper according to claim 1, wherein the impregnated layer is formed over the entire thickness direction of the base paper. The printing paper according to claim 1 or 2, wherein the base paper further contains an internal sizing agent, and the internal sizing agent is a cationic alkyl ketene dimer sizing agent. The printing paper according to claim 1, claim 2 or claim 3, wherein the styrene-based sizing agent is an anionic styrene acrylate sizing agent. A step of making a raw material pulp slurry containing raw material pulp, an amidamine compound and a polyacrylamide-based paper strength enhancer, the raw material pulp containing 75% by mass or more of broadleaf kraft pulp, and the freeness of the raw material pulp being 400 mL or more.
A step of impregnating the front and back surfaces of the base paper obtained through the above papermaking process with an impregnating solution containing starch and a surface sizing agent containing a styrene-based sizing agent as a main component by a two-roll size press over the entire thickness direction of the base paper. A method for producing printing paper, which comprises a step of laminating a coating layer containing a pigment and an adhesive on at least one side of the base paper that has undergone the impregnation step.

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