CA2240300A1 - Printing paper coated with water absorption resistivity controlling composition and method of producing same - Google Patents

Abstract

Printing paper such as newspaper printing paper, the water absorption resistivity of which is controlled at a water droplet absorption degree of no less than 60 seconds by coating material for controlling water absorption resistivity on the surface of base paper, wherein the coating material contains component A which is at least one water-soluble polyacrylamide selected from nonionic polyacrvlamides, cationic polyacrylamides, and water-soluble polyacrylamides, and component B which is water-soluble anionic polymers of monomers having hydrophobic substitute(s) and monomers having at least carboxyl group(s) or sulfone group(s). The coating is formed by gate roll coating at a coating speed of 1,100-1,800 m/min and is preferably in the range of 0.1-0.3 g/m2 for one side.

Description

PRINTING PAPER COATED WITH WATER ABSORPTION RESISTIVITY
CONTROLLING COMPOSITION AND METHOD OF PRODUCING SAME
BACKG ROU N D
Field of the Invention The present invention relates to printing paper having a coating layer, particularly to printing paper, e.g., newsprint paper, with a coating layer, which contains mechanical pulp at high ratios, and which exhibits, e.g., improved water absorption resistivity, and to the manufacturing method thereof.
Back~eround of the Art Recently, printing technology has developed trends to off-set printing, color printing, high-speed high-quantity printing, automated printing, or the like. Inaccordance with the trends, printing paper, especially newspaper paper, requiresimprovement on various characteristics with respect to workability and applicability to printing.
In general, newsprint paper (paper for printing newspaper, a roll of newsprint) is mainly composed of mechanical pulp and de-inked pulp (hereinafter "de-inked pulp" is referred to as "DIP") and is classified as medium-grade paper or low-grade paper. Newsprint paper is, however, required to satisfy quality requirements stricter than those for general printing paper, since a specified number of newspapers must be printed in a specified duration of time in a specified time zone with certainty in newspaper printing. Newsprint paper is special paper fromsuch a viewpoint, thus a special classification is applied to it. In addition, since a reduction in weight, an increase in content of DIP, etc. are further required for newsprint paper, improvement to satisfy all these needs is required. Thus, improvement of newsprint paper requires a much higher level of technology as compared with that of general printing paper.
Recently, in the field of printing technology for newspapers, transition from relief printing to off-set printing has rapidly proceeded together with the introduction of computer systems into printing of newspapers, in order to respond to the necessity of an increase in printing speed, coloring of the paper, various kinds of printing, and automation, for example.
Newsprint paper used for off-set printing is required to have different qualities from those used for relief printing. These quality requirements include that S (1 ) paper should retain adequate water absorption resistivity, and should have wet strength and not suffer from water break; (2) paper should have low adhesion strength (neppari strength); and (3) paper should not generate paper powders.
Among these quality requirements, improvement on maintaining water absorption resistivity, i.e., control over water absorption resistivity, is a particularly critical 1 0 target.
In the above, newsprint paper having a high content of mechanical pulp and general printing paper having a low content of mechanical pulp but a high content of a broad-leaved tree breached kraft pulp ("broad-leaved breached kraft pulp" is hereinafter referred to as "LBKP") are different in terms of difficulty and ease in water absorption resistivity control (i.e., in rendering sizing properties). When the content of mechanical pulp is high, the surface of base paper is rough, whereas when the content of LBKP is high, the surface of base paper is fine. Further, paper having a fine surface is considered to require low amounts of coating of an external sizing agent, whereas paper having a rough surface is considered to require highamounts of coating of an external sizing agent.
Water absorption resistivity has been conventionally controlled in general printing paper by using means to add agents such as sizing agents into the inside of paper (internal addition sizing) or to add the agents to the outside of paper(external addition sizing). Internal addition is a means of adding agents to pulp slurry at a so-called "wet-end" and make the agents to be contained in the inside of paper simultaneously with paper manufacturing. External addition is a means of coating sizing agents onto the surface of paper using coating machines represented by a two-roll size press and a gate roll coater following paper manufacture.
As sizing agents for internal addition, rosin sizing agents, emulsion-type sizing agents, synthetic sizing agents, etc. are known for acid paper, and alkylketene dimers (AKD) and alkenyl succinic anhydride (ASA) etc. for neutral paper. For example, Japanese Patent Application Laid-Open No. 60-88196 and No. 4-363301 disclose sizing agents comprising cationized starch and alkylketene dimers.
As sizing agents for external addition (also called as surface sizing agents), anionic polymers such as styrene-maleic acid copolymers and styrene-acrylic acid5 copolymers; anionic low molecular weight compounds such as alkyd resin saponification products of rosin, tall oil, and :phthalic acid and saponification products of petroleum resin and rosin; cationic polymers such as styrene polymers and isocyanate polymers are known. The external sizing agents are targeted to beused in paper having high contents of LBKP, such as higher-grade printing paper 10 and paper for inkjet printing, which requires different water absorption resistivity and paper-making conditions from paper having low contents of LBKP or high contents of mechanical pulp.
In contrast, under existing state of the art, in paper having a high content of mechanical pulp, such as newsprint paper, water absorption resistivity control is achieved predominantly by internal addition of, e.g., sizing agents and water resistance agents.
However, among measures for controlling water absorption resistivity of newsprint paper, when means of internal addition of agents such as sizing agentsgenerally employed for general printing paper (internal sizing) was introduced, it 20 was difficult to control the amounts of agents to be added so that addition of excessive amounts was required to maintain effective levels, because there were many problems such as: (1 ) agents should be added to pulp slurry of low concentration; (2) amounts of agents to be fixed on pulp sheet are not constant (amounts of agents fixed are low); (3) parallel operation of sizing-required paper-25 making and sizing-non-required paper-making could not be conducted because a circulatory white water common to plural paper-making machines was normally employed; t4) the effects of yield-improvement agents fluctuated, and when the yield was improved, DlP-based color impurities, for example, were incorporated in paper; (5) water absorption resistivity is changed with a lapse of time; (6) in high-30 speed paper-making of pH-neutralized or light-weighted newsprint paper, the yield of internal sizing agents tended to be decreased, and thus it was difficult to maintain its water absorption resistivity; and (7) when making newsprint paper containing 80% or higher of DIP at a speed as high as 1,000 m/min or higher, theyield of internal sizing agents tended to be decreased, and thus it was difficult to maintain its water absorption resistivity. Such excessive àddition tends to cause a reduction in paper strength, machine trouble, noticeable stain of white water system, etc., and is problematic in cost, quality, operation condition etc.
When the; internal sizing agents did not work well, the addition of the internal sizing agents became excessive, likely resulting in decreasing paper strength, causing machine troubles, and making white water dirty due to adhesionand accumulation of hydrophobic sizing agents, i.e., there were problems in relation to the cost, quality, and operation. Alteration of the composition of raw materials could be applied only as short-term measures, but it was not appropriate for long-term measures, because, for example, noticeable alteration of raw materials might occur in actual machines. In particular, in pH-neutralized or lightweight paper-making, maintaining or improving the quality of paper as compared to the conventional newsprint paper is the important technological target for newsprintpaper manufacturers.
As means of controlling water absorption resistivity of newsprint paper, application of external addition of agents used for general printing paper (external addition sizing) is also considered. However, because of a problem in that sufficient water absorption resistivity cannot be obtained at reasonable costs, the external addition of sizing agents is not conducted at full-scale.
On-machine coating has been generally employed for coating surface-treatment agents onto the surface of newsprint paper for economic reasons and a gate roll coater using a coating formation and transcription system, whichenables high-speed coating, has commonly been used. Characteristics of the gate roller coating method is simply summarized in, for example, Japan TAPPI Journal 43 (4), p. 36, 1989 and Paper Pulp Technology Times Vol. 36, No. 12, p. 20, 1993.
The method enables coating liquid to be retained on the surface of paper and is more effective for improvement of paper surface, as compared with a conventionaltwo-roll size press method. In the two-roll size press method, since base paper passes through a pond (liquid pool) of coating liquid, the coating liquid penetrates into base paper very deeply. However, in the gate roll coating method, since coating liquid preforms the coating, which is then transcribed, coating liquid does not substantially penetrate into base paper. Thus, in the gate roll coating method, 5 coating material tends to remain on the surface of base paper and efficient improvement of paper surface can be achieved.:
SUMMARY OF THE INVENTION
However, the present inventors discovered through experiments that, even using the gate roll coating method, an ideal water absorption resistivity barrier layer 10 could not be formed and impregnation of a coating solution into the interior of base paper could not fully be prevented, when the paper was unsized newsprint paper with high contents of mechanical pulp, which paper had a spot water absorbing capacity of no more than 10 seconds according to the water droplet absorption degree test mentioned below, especially at a speed of 300-1,000 m/min and in an 15 amount of the applied coating composition of 0.3 g/m2 or less per side of the paper.
That is, even though surface sizing agents, which are likely to be applied predominantly only on the surface of base paper, are used, and a coating is formed by the gate roll coating method, there is a problem in that sufficient sizing effects (effects to render water absorption resistivity) cannot be exhibited, especially in an 20 amount of the applied coating composition of 0.3 g/m2 or less per side of the paper.
The present invention has exploited a printing paper with agents only externally added to base paper, which printing paper has an improved water absorption resistivity (sizing property). An objective of the present invention is to provide a printing paper with a coating, having improved water absorption 25 resistivity, i.e., a spot water absorbing capacity (water droplet absorption degree) of no less than 60 seconds, even in as a low amount of the applied coating composition as 0.3 g/m2 or less per one side of paper, without sacrificing well-balanced surface strength and peelability.
Namely, the present invention is to provide a printing paper, preferably a 30 newsprint paper, having a water droplet absorption degree of no less than 60 seconds as measured by determining the time required to absorb 1 ~l of water dropped on the surface of paper, comprising: a base paper for printing paper containing at least 30% by weight of mechanical pulp and having a water droplet absorption degree of no more than 10 seconds as measured by determining the time required to absorb 1 ,ul of water dropped on the surface of paper; and a coating layer formed on said base paper by gate roll coating at a coating speed of 1,100-1,800 m/min, said coating layer comprising a water absorption resistivity controlling composition, preferably in the range of 0.1 0.3 g/m2 for one side, said composition comprising: component A which is water-soluble polyacrylamide; and component B which is water-soluble anionic copolymer of monomer having at least one hydrophobic substituent and monomer having at least one of carboxyl group and sulfone group.
By applying the water absorption resistivity controlling composition of the present invention on printing paper by gate roll coating at a paper-making speed of 1,100-1,800 m/min, printing paper, in which water absorption resistivity is improved and surface strength and peelability are well balanced, can be obtained.
In particular, newsprint paper suitable for high-speed offset printing can be obtained. Further, with the newsprint paper according to the present invention, sizing properties can be given only by the external addition of a water-absorbency controlling compound according to the present invention without the need for internally added sizing, and consequently the problems involved with the internal addition of chemicals can be solved. Furthermore, by optional modification of the amount of coating, mixing ratio and type of material, the present invention is applicable to a wide variety of uses.
The present invention can equally be adapted for a method for producingthe above printing paper. This technology is illustrated for use in newsprint paper hereinafter, since the technology is effective especially for newsprint paper. The present invention, however, is not restricted to newsprint paper, since this technology is applicable to general printing paper.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Printing paper, especially newsprint paper with improved water absorption resistivity according to the present invention can be obtained by using a coater to coatthewaterabsorption resistivitycontrollingcomposition ofthe present inventionon one or both sides of base paper for printing.
Water Absorption Resistivity of Newsprint Paper and Pre~iminary Experiments Although coating nonionic polyacrylamides, cationic polyacrylamides (for example, water-soluble polyacrylamides with tertiary-amine group(s) and/or quaternary ammonium base(s)), or amphoteric polyacrylamides alone on base paper for newsprint paper can improve surface strength, water absorptivity cannot be improved. For example, if oxidized starch is coated on newsprint paper in amounts in a range of 0.5-1.0 g/m2, the level of water absorption resistivity of the coated paper corresponds to approximately several seconds according to a spot water absorbing capacity test method mentioned below, and is insufficient.
A coating of copolymers with anionic hydrophobic group(s) alone is insufficiently effective for improving surface strength, generates a lot of foams, and cannot render water absorption resistivity equivalent to a spot water absorbing capacity of no less than 60 seconds.
Further, the above surface-treatment agents could not improve water absorption resistivity when coated in amounts not adversely affecting peelability of the coated product.
The effects of the water absorption resistivity controlling layer of the presentinvention are considered to depend on such an ionic complex. Application of suchan ionic complex to agents for paper is described, for example, in Japan TAPPI
Journal Vol. 45, No. 2, pp. 245-249, 1991, which discloses a method in which paper strength reinforcing agents are added to pulp slurry, wherein an ionic complex of high molecular weight was formed by mixing anionic paper strengthening agents and cationic paper strengthening agents. This method is, however, basically a method of internal addition of agents, and it does not aim at improving water absorption resistivity. Japanese Patent Application Laid-Open No.
60-119297, for example, describes a method of sizing paper by using anionic hydrophobic sizing agents and cationic retaining agents. However, this method isalso a method of internal addition of agents, and thus it cannot solve the above-mentioned problems associated with internal addition.

On the other hand, Japanese Patent Application Laid-Open No. 52-148211, No. 56-118995, No. 3-54609, etc. disclose methods of surface sizing using coating liquid containing anionic resins and cationic resins. In particular, lapanese Patent Application Laid-Open No.52-148211 describes a method-of producing reinforced 5 core paper for corrugated paper using coating liquid containing anionic resins and cationic resins. This method, however, aims rriainly at improving compressive strength and rigidity but not at improving water absorptivity. In examples of the specification, the agents were coated in an amount of about 10 glm2, which levelis far from that applicable to general printing paper. Japanese Patent Application Laid- Open No. 56-118995 describes a method of manufacturing oil-proof paper using surface sizing agents comprising, for example, oxidized starch, vinylidenechloride-acrylamide copolymers, and polyethyleneimine. Although oil-proof paper is required to have resistance against oil, the printing paper of the present invention is required to have absorptivity for ink (in other words, oil) to cope with high-speed 15 printing in off-set printing. Therefore, the technology disclosed in the above-mentioned specification is quite opposite to that disclosed in the presentinvention, and thus it is impossible to apply the technology to the present invention. Japanese Patent Application Laid-Open No.56-118995 discloses surface sizing agents comprising three components, namely, ketene dimers, cationized 20 starch, anionic polymers, but the surface sizing agents had a problem of a reduction in a friction coefficient.
Japanese Patent Appl ication Laid-Opens No.62- 122781 and No.62-146674 disclose recording material for ink jet recording with an ink-accepting layer containing polymer complexes comprising basic polymers and acidic polymers. In 25 this technology, however, since both polymers are dissolved in organic solvents such as dimethylformamide and employed as coating liquid, it is difficult to apply to printing paper having a high content of mechanical pulp. Further, almost no mechanical pulp is used in paper for ink jet recording, and the paper has a highcontent of LBKP. In addition, material for ink jet recording is required to have30 acceptability (in other words, absorptivity) for ink jet printing ink comprising a mixture of water and polyalcohols, and it cannot satisfy the requirements of water absorption resistivity of the present invention.
The present inventors found that newsprint paper in which water absorption resistivity is improved and surface strength and peelability are also improved in a 5 good balance could be obtained by forming a coating layer containing a combination of two components, that is, specific polyacrylamides and polymers with anionic hydrophobic group(s) on newsprint paper with a gate roll coater(s) at a speed of 1,100-1,800 m/min, thereby completing the present invention.
Water Absorption Resistivity Controlling Composition The present invention relates to printing paper, especially newsprint paper provided with a coating layer containing a water absorption resistivity controlling composition, mainly comprising two Components A and B mentioned below, on the surface of paper.
Component A: Water-soluble polyacrylamide.
Component B: Water-soluble anionic copolymer(s) comprising monomer(s) with hydrophobic substituent(s) and monomers with carboxyl group(s) or sulfonate group(s).
Water absorption resistivity controlling composition of the present invention is mainly constituted with the Components A and B.
Components A
The Components A employed in the water absorption resistivity controlling composition of the present invention are cationic polyacrylamides ("polyacrylamides" is abbreviated as "PAM" hereinafter) including nonionic PAMs,cationic PAMs, and amphoteric PAMs.
As for the nonionic PAMs employed as the Components A, (meth)acrylamide polymers or copolymers (when "meth" is designated, the designation means that (meth~ compounds may exist, thus "(meth)acrylamide" means "methacrylamide and/or acrylamide", the same hereinafter), and copolymers comprising nonionic monomers copolymerizable with (meth)acrylamide and (meth)acrylamide can be exemplified. These PAMs are essentially nonionic, but a part of the amide structure exists in a form of amidinium ion (-CONH3+), thus they are slightly cationic.

g Therefore, nonionic PAMs can be employed as the Components A in the present invention.
In brief, the cationic PAMs and the amphoteric PAMs employed as the Components A are PAMs containing cationic monomer units, desirably those containing tertiary-amine group(s) (or tertiary-amine base(s)) and/or monomer units with quaternary ammonium base(s) as cationic rr~onomer units. Also, in principle, PAMs which do not contain-anionic monomer units other than cationic monomer units are cationic monomers, while PAMs containing anionic monomer units in addition to cationic monomer units are amphoteric PAM.
Cationic Monomers Furthermore, the cationic monomer units shown by the following general formulae [1] and [2] are particularly preferable:
[General formula 13 R
I

- , CH2--C
I

C=O
Y--Z--N--R ~1 [General formula 2]

R

C=O ~R
Y~N--R2 ~ g ~: 2 \ R3 -1 o-wherein, R represents a methyl group or a hydrogen atom; Y represents NH or an oxygen atom; Z represents CH2CH(OH)CH2 or an alkylene group containing 1-4 carbon atoms; R1, R2, and R3 represent an alkylene group containing 1-18 carbon atoms, benzyl group, or a hydrogen atom; R1, R2, and R3, however, may be the 5 same or different: X ion represents a negative ion and a halogen atom ion (chlorine ion, bromine ion, or iodine ion, etc.), sulfate ion, alkylsulfate ion (methylsulfate ion, - ethylsulfate ion, etc.), alkylsulfonate ion, arylsulfonate ion, acetate ion, etc.).
Methods of introducing cationic monomer units into PAMs are, for example, (a) a method to modify various PAMs through Mannich reaction; (b) a method to modify various PAMs through Hoffman degradation reaction; (c) a method to copolymerize monomers with tertiary-amine group or quaternary ammonium base(s); and (d) a method in which monomers with tertiary- amine group(s) are copolymerized followed by conversion to quaternary ammonium base(s) through alkylation, arylation, etc.
For example, it is sufficient to copolymerize (meth)acrylamide and cationic monomers (monomers containing tertiary-amine group(s) or quaternary-ammonium base(s)) or (meth)acrylamide derivatives and cationic monomers in the method of copolymerization mentioned in (c). In the other words, in the present invention,copolymers comprising (meth)acrylamide and cationic monomers mentioned below can be employed as the Components A.
Monomers with tertiary-amine group(s) employed in this method are, for example, N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminohydroxypropyl(meth)acrylate, N-methyl, N-ethylaminoethyl(meth)acrylate, N,N-diphenylaminoethyl(meth)acrylate, N, N,-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, 2-vinylpyridine, 4-vinylpyridine, and 2-methyl-5-vinylpiridine.
Monomers contain ing quaternary-ammon i um base(s) wh ich can be employed include (meth)acroyloxyethyltrimethylammonium chloride, (meth)acroyloxyethyldimethylbenzylammonium chloride, (meth)acroyloxyethyltriethylammonium chloride, (meth)acroyloxyethyldiethylbenzylammonium chloride, (meth)acrylamidepropyltrimethylammoumiun chloride, (meth)acrylamidepropyltriethylammonium chloride, (meth)acrylamidepropldimethylbenzylammonium chloride, diallyldimethylarnmonium chloride, diallyldiethylammonium chloride, and (meth)acroyloxyethyltrimethylammonium sulfate.
In addition, monomers which can be copolymerized with (meth)acrylamide or cationic monomers mentioned above can be employed in this copolymerization method to the extend that no adverse effect is exhibited. That is, in the present invention, copolymer(s) comprising (meth)acrylamide, cationic monomers, and copolymerizable monomers mentioned below can be used as the Components A.
The copolymerizable monomers which can be employed in this method include ethylene, butadiene, styrene, a-methylstyrene, isoprene, propylene, vinyl acetate, vinyl carbazole, vinyl pyrrolidone, (meth)acrylonitrile, (meth)acrylic esters, N-methylol-(meth)acrylamide, methylene bis-acrylamide, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-sulfoethyl(meth)acrylate, ethylene-di(meth)acrylate, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, muconic acid, crotonic acid, allylglycidylether, glycidyl(meth)acrylate, sodium ethylenesulfonate, sodium p-styrenesulfonate, sulfonium salt of vinylbenzyl, and phosphonium salt of vinylbenzyl. Amphoteric PAMs can be obtained using anionic monomers such as acrylic acid and itaconic acid among these monomers.
Alkylating agents employed in the method of converting tertiary-amine group(s) to quaternary ammonium base(s) in the method (d) are dimethyl sulfate, methyl chloride, methyl bromide, methyl iodide, benzyl chloride, benzyl bromide,etc.
Characteristics of PAMs In the present invention, cationic PAMs and amphoteric PAMs are employed more preferably than nonionic PAMs as the Components A to control water absorption resistivity and to provide water absorption resistivity, because nonionic PAMs have very weak cationic properties derived from the amidinium structure partially existing and thus they are only slightly effective for providing waterabsorption resistivity. In cationic PAMs and amphoteric FAMs, a ratio of cationic monomer units is desirably not less than 0.1 mol%. If a ratio of cationic monomer units is less than 0.1 mol%, the water absorption.Tesistivity controlling effect tends to decrease slightly. If higher water absorption resistivity is desired, cationic PAMs are more preferably employed than amphoteric PAMs.
Each PAM of the Components A can be obtained by polymerizing or copolymerizing corresponding monomers by means of conventional, known methods, such as water solution polymerization, solvent polymerization, reverse-phase emulsion polymerization, sedimentation polymerization, and suspension polymerization.
In the present invention, one PAM alone or a mixture of two or more PAMs may be employed as the Components A.
Weight average molecular weight of PAMs employed as the Components A
suitably is in a range of 200,000-4,000,000. If average molecular weight is lessthan 200,000, sufficient coating layer cannot be formed and water absorption resistivity and surface strength are insufficient. However, if average molecularweight is higher than 4,000,000, viscosity becomes so high that problems in operation may occur and peelability of coated products is not acceptable.
Accordingly, it is considered that higher average molecular weight is preferablefrom the viewpoints of providing water absorption resistivity and improving surface strength, whereas lower average molecular weight is preferable from the viewpoint of peelability of coated products. Therefore, average molecular weight of PAMs may be optionally determined according to the required specification within the range mentioned above. Considering water absorption resistivity, surface strength, and peelability comprehensively, average molecular weight of PAMs is preferably in a range of 500,000-3,000,000, more preferably in a range of 700,000-1,200,000.
Components B

The Components B employed in the water absorption resistivity controlling composition of the present invention are copolymers comprising monomers with hydrophobic substituent(s) and anionic monomers (monomers with carboxyl group(s) or sulfonate group(s)).
Although the hydrophobic substitutents mentioned above are those containing not less than 6 carbon atoms and they are not particularly restricted, they may be determined considering the problem of foaming of coating material, the required degree of water absorption resistivity, etc. Alkyl groups containing not less than 6 carbon atoms, alkenyl groups containing not less than 6 carbon atoms, cycloalkyl groups containing not less than 6 carbon atoms, aryl groups containing not less than 6 carbon atoms, and aralkyl groups containing not less than 7 carbon atoms can be mentioned as substitutents.
Hydrophobic Substituent-Containing Monomers and Anionic Monomers The above-mentioned monomers containing hydrophobic substituent(s) include, for example, styrene-type monomers (such as styrene, a- methylstyrene, chlorostyrene, and cyanostyrene), olefin-type monomers (such as hexene, octene, and decene), (meth)acrylic esters, and maleic esters. They are described in detail in "Polymer Handbook: Basis" edited by the Japanese Association of Polymer, Baifu-kan (1986) (examples of styrene-type monomers are listed in Table 5-1 in p.
47, those of olefin-type monomers in Table 1-1 in p. 2, those of acrylic esters in Table 10-1 in p. 105, maleic esters in Table 14-1 in p. 162), among which monomers with hydrophobic substitutents may be selected.
Anionic monomers (monomers with carboxyl group(s) or sulfonate group(s)), the remaining constituents of the Components B are, for example, acrylic acid-type monomers (such as acrylic acid, methacrylic acid, chrotonic acid, isochrotonic acid, 2-ethylacrylic acid, and 3-tertiary-butylacrylic acid), maleic acid-type monomers (such as maleic acid, methylmaleic acid, phenylmaleic acid, chloromaleic acid, fumaric acid, itaconic acid, and muconic acid), 2-acrylamidepropanesulfonic acid, 2-acrylamide-n-butanesulfonic acid, 2-acrylamide-n-hexanesulfonic acid, 2-acrylamide-n-octanesulfonic acid, 2-acrylamide-n-dodecanesulfonic acid, 2-acrylamide-2-methylpropanesulfonicacid, 2-acrylamide-2-phenylpropanesulfonic acid, 2-acrylamide-2,4,4-trimethylpentanesulfonic acid, 2-acrylamide-2-(4-chlorophenyl)propanesulfonic acid, 2-methacrylamide-n-tetradecanesulfonic acid, sodium 4-methacrylamidebenzenesulfonate, 2-sulfoethylmethacrylate, p-vinylbenzenesulfonic acid, styrenesulfonic acid, and ethylenesulfonic acid.
In the copolymers of the Components B, a ratio of the above-mentioned monomers with hydrophobic group(s) to the above-mentioned anionic monomers is preferably in a range of 90:10 - 40:60. It is sufficient to employ at least one monomer each with hydrophobic substituent(s) and anionic monomer.
In addition, a small amount of anionic or nonionic monomers which can be polymerized with the monomers with hydrophobicsubstituent(s) and/orthe anionic monomers may be copolymerized as far as they do not disturb the present invention .
Methods of manufacturing the copolymers of the Components B include, for example, water solution polymerization, solvent polymerization, reverse- phase emulsion polymerization, sedimentation polymerization, and suspension polymerization .
Characteristics of Copolymers The copolymers of the Components B are anionic hydrophilic polymers and have an acid value preferably in a range of 50-500, and more desirably, further restricted to a range of 100-300. If an acid value is less than 50, water-solubility of copolymers is insufficient. If an acid value is larger than 500, anionic strength of copolymers is so strong that it is not suitable for the present invention.
The copolymers of the Components B may have weight-average molecular weight ranging from 1,000 to 1,000,000, more desirably ranging from 1,000 to 100,000. If average molecular weight is less than 1,000, copolymers of the Components C cannot sufficiently form a coating layer and it is not desirable from the viewpoints of surface strength and water absorption resistivity control. If molecular weight i5 higher than 1,0~0,000, problems in operation resulting from high viscosity of coating liquid may occur.

Accordingly, the copolymers of the Components B are specifically styrene-acrylic acid copolymer, styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic ester copolymers, styrene-maleic halfester copolymers, styrene-maleic acid copolymer, styrene-maleic ester copolymers, styrene-2-acrylamide 5 propanesulfonate copolymer, (meth)acrylic acid-(meth)acrylic ester copolymers,a-olefin-maleic acid copolymers, and olefin-acrylk acid copolymers. Among them, styrene-acrylicacid copolymer, styrene-(meth)acrylicacid copolymer, styrene-maleic acid copolymer, and a-olefin-maleic acid copolymers are particularly preferable for providing water absorption resistivity, and styrene-acrylic acid copolymer and 10 a-olefin-maleic acid copolymers are desirable due to the excellent balance between hydrophilic substituent(s) and hydrophobic substituent(s). Thus, styrene-acrylic acid copolymer is the most preferable, taking both factors into consideration comprehensively.
Combination of Components A and B and Other Additives In the water absorption resistivity controlling composition of the present invention mainly composed of the Components A and B, a composition ratio of each component (weight ratio) is, if restricted, such as that a ratio of the Components A to the Components B (A:B) may be in a range of 20:80 - 80:20, more desirably, from an economic viewpoint, in a range of 40:60 - 60:40, although the ratio cannot always be restricted since it depends on the level of required water absorption resistivity or peelability of newsprint paper manufactured or a coating amount of this composition.
It is sufficient that the water absorption resistivity controlling composition employed in the present invention basically consists only of the Components A and B. Excellent peelability can be obtained when the composition is coated in amounts in the range mentioned above, probably because the Components B affect peelability. In order to further improve peelability or as measures against adhesion trouble, a small amount of adhesion preventing agents or releasing agent may be added at levels not adversely affecting water absorption resistivity or not causing foaming upon coating layer. As releasing components, for example, monoalkenyl succinate described in Japanese Patent Publication No. 63-58960, adhesion preventing agents comprising organic fluoro compounds described in Japanese Patent Application Laid-Open No. 6- 57688, and adhesion preventing agents containing substitutentd succinic acid and/or succinic acid derivatives as effective components described in Japanese Patent Application Laid-Open No. 6-192995.
The adhesion preventing agents are added suitably at levels not higher than 10%
(wt%) based on the solid weight of the total of (~omponents A and B. If they areadded at levels exceeding 10%, problems such foaming upon coating may occur.
The water absorption resistivity controlling composition of the present invention may sometimes contain a small amount (e.g., ... - ... % by weight based 10 on the solid weight of the total of Components A and B) of other binder components at levels not adversely affecting peelability, for example. Other binder components are, for example, celluloses such as methylcellulose, ethylcellulose,and carboxymethylcellulose; latex such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, and styrene-butadiene-acrylic ester copolymers; PVAs such 15 as completely saponified PVA, partially saponified PVA, amide-modified PVA, carboxy-modified PVA, and sulfonate-modified PVA; PAMs such as anionic PAMs;
silicone resin, petroleum resins, terpene resin, ketone resins, and coumarone resins.
Since PVAs have a tendency towards increasing adhesion strength of moistured paper when coated on paper, special attention should be paid to the amount 20 employed in combination.
The water absorption resistivity controlling composition of the present invention may include additives such as preservatives, anti-foaming agents, UV-preventing agents, discoloration preventing agents, fluorescent brighteners, viscosity stabilizers, antislipping proofing agents, and fillers as far as they do not 25 affect the present invention.
Newsprint Paper Although base paper of the present invention is not necessarily restricted to that for newsprint paper, the effects of the present invention are clearly observed for base paper for newsprint paper. Thus, the use of the present invention for 30 newsprint paper is illustrated hereinafter.

Base paper for newsprint paper employed in the present invention is base paper manufactured using mechanical pulp (MP) such as grand pulp (GP), - thermo-mechanical pulp (TMP) and semichemical mechanical pulp, and chemical pulp (CP) represented by kraft pulp (KP), and deinked pulp (DIP) obtained by deinking used paper containing the above- mentioned pulp, and recycling pulp obtained by disaggragating loss paper generated from a paper manufacturing process, etc. alone or in a form of a mixture thereof in any ratio. In the above, if a DIP is manufactured from used paper approximately 100% composed of mechanical pulp, such a DIP is considered to be mechanical pulp. The effects of the present invention are exerted especially on paper containing, as pulp, mechanical pulp in an amount of 30% or higher by weight, wherein base paper having a basis weight of preferably 37 43 g/m2 is used. If base paper has a basis weight no less than 46/m2, its surface strength is sufficient and a change in size and a reduction in strength due to wetting with water during offset printing are negligible, thus it is not necessary for such paper to improve water absorption resistivity and surface strength simultaneously by external addition of agents.
The composition ratio of DIP in base paper employed in the present invention may be in any range (0-70%), and preferably in a range of 30-70% owingto the recent trend towards increasing the content of DIP.
The base paper for newsprint paper may contain filler for paper making such as white carbon, clay, silica, talc, titanium oxide, calcium carbonate, synthetic resins (vinyl chloride resins, polystyrene resins, urea-formalin resins, melamine resins, styrene-butadiene copolymer resins); paper strength reinforcing agents such as polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, urea-formalin resins, and melamine-formalin resins; freeness or yieid improving agents such as salts of acrylamide-aminomethylacrylamide copolymers, cationized starch,polyethyleneimine, polyethylene oxide, and acrylamide-sodium acrylate copolymers; adjuvants such as aluminum sulfate, UV preventing agents, and discoloration preventing agents. These agents should be added at levels not deteriorating water absorption resistivity controlling effects of the water absorption resistivity controlling composition of the present invention. In any case, base paper should have physical properties enabling printing by an offset printing press, and it is sufficient for base paper to possess physical properties such as tensile strength, tear strength, elongation, etc. comparable to those of usual base paper for newsprint paper.
Although base paper subjected to internal addition of sizing agent can be used as base paper for newsprint paper, the effects of the present invention can be more clearly exhibited when base paper without internal addition of them is employed, since an object of the present invention is to solve problems associated with internal addition. External addition of the water absorption resistivity controlling composition of the present invention can provide water absorption resistivity similar to or better than that obtained by internal addition sizing, even without subjecting to internal addition sizing. The water absorption resistivitycontrolling composition of the present invention can be sufficiently applied to newsprint paper with a spot water absorbing capacity of, e.g., less than 10 seconds according to the water droplet absorption degree test mentioned below.
The base paper for newsprint paper may be acid paper base, pH-neutral base paper, or alkaline base paper.
Determination of Water Absorbency Rate of Paper Two methods are known for evaluation of water absorption degree of paper with low sizing properties such as newsprint paper. One is a water droplet absorption degree test according to Japan TAPPI No. 33, in which 1 ~l of water is dropped on the surface of paper and the time required to absorb the water drop is then determined. Another method is to determine the contact angle (contact anglemethod). In the present invention, 5 ,ul of water was dropped and the contact angle of the water drop was determined after a predetermined length of time (5 seconds) had passed. According to these evaluation methods, as water absorbency becomes higher (water absorption capacity becomes higher), the time required to absorb becomes longer in the spot water absorbing capacity test method and the contact angle becomes greater and is maintained for a longer period in the contact anglemethod. Japan TAPPI No. 33 (J. TAPPI PAPER PULP TEST METHOD NO. 33-80, enacted: 1980) is as follows:

Deferminafion of WaterAbsorbency Rate of Bibulous Paper (Water Drop Method) 1. Applicable Range This test method defines a method for determination of the water absorbency rate of non-sized paper or bibulous paper such as toilet paper, papertoweling, and absorbing paper.
2. Devices (1) Dropping Device: A pipet, buret, micropipet, or microcylinder can be used.
(2) Test Piece-Supporting Member: This member is composed of a test piece-supporting ring having in the center a hole with a diameter of approximately 40 mm, and a holding ring for papering a test piece over the supporting ring with slight tension (see Commentary).

(3) Light Source: This light is used for observing the paper's changing state when water drops dropped on the test piece are being absorbed into the test piece.
Brightness equivalent to two 20W-fluorescent lights is sufficient.
The light source is placed approximately 400 mm above the test piece, and it is preferable to observe the test piece at an angle of 45 degrees with respect to the surface of the test piece.

(4) Stop Watch.
(S) Water: Distilled water.
3. Test Piece A test piece is sampled from test paper that has been pre-treated in accordance with JIS P8111 (Pre-treatment of Test Paper). At least five pieces, which have a size such that the pieces can be uniformly papered over the supporting ring with slight tension, are prepared.
If the test paper in use is composed of plural sheets stacked together (for example, a stack of two sheets), a test piece is sampled in the same stacked formation as the test paper.
4. Operation:
Tests are conducted under standard conditions in accordance with JIS
P8 1 1 1 .

(1) The volume of water drops is 0.01 ml, 0. 1 ml, and 1.0 ml for paper used for toilet paper, paper toweling, and absorbing paper, respectively.
~2) The test piece is papered over the supporting ring using the holding ring and is kept under slight tension.
(3J The dropping device is filled with water having a temperature of 20~ 2~C.
(a) For 0.01 ml and 0.1 ml Water Drops: While the end of the dropping device is kept vertical, 0.01 ml or 0.1 ml of water is directly dropped on the test piece. Waterproof grease is preferably applied on the end of the dropping device.
(b) For 1.0 ml Water Drops: The dropping device is kept at an angle of 30-45~ with respect to the horizontal surface, and the end of the dropping device is made close to and in slight contact with the center of the test piece. A predetermined volume of water is dropped on the test piece within six seconds. While dropping water, the end of the device remains unmoved from the original position.
(4) The stop watch is activated at the time water touches the test piece, and time is measured at intervals of 0.1 second until the water drops are completelyabsorbed, i.e., until no reflection of light is observed.

(5) Attention should be paid in order to avoid heating of the test piece by the light during a test or to avoid strong air streams affecting the outcome of the test.
The above measurment is repeated at least 4-5 times.
5. Report The absorbency speed is reported by rounding the average values (seconds) in accordance with JIS Z540 1 (method for rounding values) to obtain values to one decimal place. In the report, the number of stacked layers of the test piece, the number of tests conducted, and the volume of water drops are indicated.
incidentally, the maximum and minimum absorbency speeds are indicated as necessary.
Related Standards (1) TAPPI Standard T 433 su-72 Water Absorbency of Bibulous Papers.
(2) JIS P8 141 Method of Water Absorbency of Paper based on Clem Method.
(3) J. TAPPI Test Method for Paper Pulp No. 32, Water Absorbency Rate and Absorbed Water Volume of Bibulous Papers (SubmergingMethod).
Commentary on Test Piece-Supportin~ Member In TAPPI Standard T 432 su-72 Water Absorbency of Bibulous Papers, there is a conceptual description "A test piece-supporting member which is an approximately 100 mm x 100 mm square made of metal or non-absorbent material having in the center a hole with a diameter of approximately 40 mm, and a ring for papering and holding a test piece over the supporting member.n In practice, in Japan, in an example, a test is easily conducted using an embroidery frame (approximately 150 mm in diameter).
Although the TAPPI indicates that the test piece-supporting member is made of metal or non-absorbent material, the requirement can be otherwise satisfied if water dropped on the test piece does not reach the frame before the water is completely absorbed, i.e., if a frame such as an embroidery frame has a diameteras big as approximately 150 mm, the above certainly does not occur. Further, embroidery frames are readily available, and they can be used as is, and thus, the use of the frames is very convenient.
Thus, in this text, the description is made based on the concept that any supporting member suitable for the test purpose, including the above, can be used.
Incidentally, in any event, test piece-supporting rings and holding rings each . preferably have a height of at least 10 mm in order to avoidproblems even when the test piece sags due to swelling upon absorbing water.
(Figure omittedJ
According to the present invention, water absorption resistivity can be controlled within a broad range, for example, 10 seconds to 300 seconds according to the water droplet absorption degree test, by providing a coating layer containing the water absorption resistivity controlling composition of the present invention on newsprint paper. According to the contact angle method, water absorption resistivity can be controlled in a range of 75~-95~. Water absorption resistivity of the newsprint paper thus manufactured can be controlied at a predetermined levelby varying components and composition ratios of the composition of the present invention and amounts of the composition of the present invention to be coated.
Formation of Coating Layer Printing paper, especially newsprint paper with improved water absorption resistivitv according to the present invention can:be obtained by using a coater to coat the water absorption resistivity controlling composition of the present invention on one or both sides of base paper for printing at a coating speed of 1,100-1,800 m/mln.
Amounts of the water absorption resistivity controlling composition of the present invention to be coated should be determined according to a level of water absorption resistivity required for printing paper to be manufactured and are not specifically restricted. However, based on the object of the present invention, the composition of the present invention exerts effects efficiently when it is coated at 0.1-0.3 g/m2 (a total of solid components of the Components A and B) per one side of paper. If the composition of the present invention is coated in amounts less than 0.1 glm2, water absorption resistivity cannot significantly be improved, probably because a sufficient barrier layer cannot be formed by the composition. On the other hand, if an amount to be coated exceeds 0.3 g/m2, peelability merkedly deteriorates (the "neppari phenomenon" occurs). Further, it is economically inefficient to use such an amount. However, the range of 0.05-2.0 g/m2 (for one side) may be employed and may still exhibit improvement of water absorption resistivity to a certain degree. When application of the composition of the present invention to newsprint paper is considered, it is necessary to improve water absorption resistivity, surface strength, and peelability in a good balance. Taking these three factors into consideration comprehensively, it is preferable to coat the water absorption resistivity controlling composition of the present invention at0.1 0.3 g/m2 per side of paper.
The water absorption resistivity controlling composition of the present invention can be coated on base paper for printing paper preferably by using coaters for coating transcription such as a gate roll coater and a blade rod metalling coater. The effects of the present invention is significantly exerted especially when a gate roll coater is employed. The gate role coater method has a defect in thatsufficient effects for providing water absorption resistivity cannot be attained using conventional surface sizing agents. However, the com'position of the present invention coated in amounts in the above-mentioned range at a paper-making speedof 1,100-1,800 m/min can improve water absorption resistivity efficiently, even using this systern Coating liquid mainly comprising the water absorption resistivity controlling composition of the present invention is very suitable for a gate roll coater. When oxidized starch alone is coated using a gate roll coater, striped patterns generally appear on the coated layer. On the other hand, when the coating liquid of the composition of the present invention is coated, these striped patterns are hardly observed and the coating liquid can be coated more evenly.
When the water absorption resistivity controlling composition of the present invention is applied to base paper for newsprint paper, it is desirable to coat the composition by a gate roll coater. In such a case, coating by an on-machine coater is preferable from the viewpoint of productivity.
The water absorbency controlling composition of the present invention may be coated on both sides of base paper for newsprint paper at 0.1-0.3 g/m2 per side by a gate roll coater.
For base paper for newsprint paper, although it is said to be difficult due to unevenness of the surface of the base paper to provide a water absorptive barrier layer on the surface of the base paper by external addition (especially by a gate roll coater system) even in amounts falling into a range of relatively small amounts, the water absorption resistivity controlling composition of the present invention can exert its effect in attaining water absorption resistivity with relatively small amounts of coating, with as high productivity as a coating speed of 1,100-1,800 m/min.
When a coating layer of the water absorption resistivity controlling composition of the present invention is formed on the surface of printing paper, a reduction in the friction coefficient does not occur. It is known that coating of anionic styrene-acidic monomer copolymers on paper by size press reduces the dynamic/static friction coefficient. The water absorption resistivity controlling composition of the present invention, however, does not have such a tendency, and when a coating tayer containing the water absorption resistivity controlling composition of the present invention is provided on the surface of printing paper, the friction coefficient is not decreased and special addition of antislipping agents is not necessary. The dynamic friction coefficient of newsprint paper is preferably in a range of 0.40-0.70. According to the present invention, the dynamic friction coefficient can be maintained in the above range without antislipping agents.
The water absorption resistivity controlling composition of the present invention can better improve water absorption resistivity of a felt side than that of a wire side with a small amount of coating.
The newsprint paper using the water absorption resistivity controlling composition of the present invention can control the level of water absorbency within a broad range, thus it can cope with various kinds of ink used in printing.
For example, it is thought that the water absorption resistivity controlling component of the present invention can be fully applied to printing using special ink such as emulsion ink in which damping water is mixed in oily ink, and ink with high tackiness for waterless lithography.
In general, improvement of newsprint paper is more difficult than that of general high-grade printing paper. Therefore, it is difficult to directly apply technology for general printing paper to that for newsprint paper. However, application of technology for newsprint paper to that for general printing paper is relatively easy. Thus, the water absorption resistivity controlling composition of the present invention can be applied not only to newsprint paper but also to generalprinting paper, and similar effects (e.g., improvement on water absorption resistivity or improvement on surface strength) can be exhibited.
With the use of the water absorption resistivity controlling composition of the present invention, printing paper of a variety of brands with different sizing properties can be easily manufactured without the necessity of internal additionsizing, which is apt to cause operational problems, and surface strength can be improved at the same time.

Paper with improved water absorption resistivity may be obtained by coating the water absorption resistivity controlling composition of the present invention at 0.05-2.0 glm2 (for-one side) on base paper for printing paper by gate roll coating.
Furthermore, newsprint paper suitable for high-speed offset printing in which water 5 absorption resistivity, surface strength, and peelability are all improved in a good balance can be obtained by applying the composition of the present invention at 0.1-0.3 glm2 (for one side) on newsprint paper by gate roll coating at a paper-making speed of 1,100-1,800 m/min. Although the mechanism of the exerted effects of the present invention has not been clarified, it is deduced as follows.
It is thought that the water absorption resistivity controlling composition of the present invention can control water absorbency by forming a hydrophobic complex coating layer when coated on base paper and then dried. The Components A (cationic PAMs) and the Components B (anionic water-soluble polymers with hydrophobic group(s)) form an ionic complex, and finally form a coating in which the hydrophobic substituent(s) are oriented outward to provide a hydrophobic barrier layer on the surface of paper.
If improvement solely in water absorption resistivity is sought, it is thought sufficient to use only the Components B. However, it is thought that the Components A effectively retain the Components B ionically or chemically on the surface of paper, thus the Components A work very advantageously on coating formation, leading to improvement of water absorption resistivity.
In addition, it is thought that the Components A largely contribute to improvement of surface strength as well as to retainment of the Components B.
However, importantly, when the water absorption resistivity controlling composition of the present invention is applied on paper by a gate roll coater at a coating speed of 1,100 m/min or lower, sufficient water absorption resistivity was lacking. In contrast, when coating was conducted at a coating speed of 1,100 m/min or higher, sufficient water absorption resistivity, i.e., a spot water absorbing capacity of no less than 60 seconds, was achieved even in as low a coating rangeas 0.1-0.3 g/m2. The reason for the above is assumed as follows: by applying a coating at a high speed, the water absorption resistivity controlling composition is dry before being impregnated inside the interior of the base paper, thereby increasing the proportion of the water absorption resistivity controlling composition existing on the surface of the base paper.
EXAMPLES
Hereinafter, referring to synthetic examples, examples and comparative examples, the present invention will be described in detail, but it is not limited to these. Parts and % in the description denote weight parts and weight %.
< Synthesis of PAM >
After putting 80% methacryloyloxyethyl trimethylammonium chloride (7.8g), 40% acrylamide aqueous solution (168.6g) and ion exchange water (300g) into a four-neck flask provided with a reflux condenser and heating the mixed solution to 60~C in an atmosphere of nitrogen, 1 % ammonium persulfate aqueous solution (lOg) and 1% sodium hydrogensulfite aqueous solution (2g) were added to the reaction solution and allowed to react at 85~C for an hour. Then, after cooling, a polymer (PAM-3) was obtained. The weight-average molecular weight of this polymer was 740,000.
< Preparation of Coating Liquid >
By adding the aqueous solution of each PAM (Component A) relevant to the present invention and that of an anionic copolymer with hydrophobic substituent(s) (Component B) together at a predetermined ratio, a coating liquid of water absorbency control compound according to the present invention can be easily prepared. A coating liquid that generates an insoluble precipitate in mixing is unfavorable for the present invention.
<Making a newsprint base paper>
35 parts of DIP (deinked pulp), 30 parts of TMP (thermomechanical pulp), 20 parts of GP (grand pulp) and 15 parts of KP (kraft pulp) were mixed and macerated to regulate the freeness at CSF 200 ml. This mixed pulp was manufactured into an unsized and uncalendared newsprint base paper at the rate of 1,100-1,800 rn/min by using a Bervet former paper machine. This base paper was 43g/m2 in weight, 0.65 in density, 51 % in brightness, 60 sec in smoothness,0.45 in static friction coefficient and 0.56 in dynamic friction coefficient, and its paper properties (e.g., strength), other than water absorption resistivity, wereequivalent to those of a general newsprint paper. Further, this base paper - contained no added internal sizing agent and exhibited a water absorbency of 5 sec by the water droplet absorbency degree test method.
< Preparing a newsprint paper >
Examples 1 to 5 By adding an aqueous solution of a copolymer of styrene and acrylic acid (weight average molecular weight: 39,000, and oxidation value: 230) to an aqueous solution of the cationic PAM at a mixing rate of 1 :1 (solid portion weight ratio) and further adding a separating component (sodium salt of an C10- to C16-alkenyl succinate UaPan Patent Laid- Open No. 63-58960 Publication)), a coating solutionwas prepared. The obtained coating solution was applied to the F surface of the above newsprint paper by using a gate roll coater at coating speeds of 1,100 m/min, 1,200 m/min, 1,300 m/min, 1,500 m/min, and 1,800 m/min. After application, newsprint paper was obtained by supercalendaring.
Mixing ratio: PAM/styrene-acrylic acid copolymer/separating agent =
1/1/0.05 Comparative Examples 1 to 5 By adding an aqueous solution of the copolymer of styrene and acrylic acid used in Examples 1-5 to an aqueous solution of the cationic PAM at a mixing rateof 1:1 (solid portion weight ratio) and further adding a separating component (sodium salt of an C10- to C16-alkenyl succinate ~apan Patent Laid- Open No.
63-58960 Publication)), the same coating solution as in Examples 1-5 was prepared.
As in Examples 1-5, the obtained coating solution was applied to the F surface of the above newsprint paper by using a gate roll coater at coating speeds of 300 m/min, 600 mJmin, and 1,000 m/min. Further, coating was conducted at various coated amounts. After application, newsprint paper was obtained by supercalendaring.
On the newsprint papers of Examples 1 to 5 and Comparative Examples 1 to 5, the coated amount, the water droplet absorption degree, the contact angle, and the neppari strength (adhesion strength) were measured according to the methods indicated below. The results are summarized in Table 1.
Measuring Amounts of Coating Each newsprint paper was cut, placed in a decompc~sition tube, and allowed to stand for several minutes after adding concentrated sulfuric acid to the decomposition tube. A hydrogen peroxide aqueous solution and a decomposing agent were added to the tube to conduct heat decomposition. The resulting reaction solution was diluted to a given concentration and introduced to a Kjeldahl analyzer to measure the nitrogen content. From the nitrogen content, the solid weight of coating PAM was calculated.
Measuring Water droplet Absorption Degree As described earlier, according to lapan TAPPI No. 33 (Test Method for Water Absorbing Rate in an Absorbent Paper), tests were carried out by using 1 ~l of water droplet amount.
Measuring Neppari Strength After cutting two 4 x 6 cm sheets from a newsprint paper and soaking the coated surface in water at a temperature of 20~C for 5 sec, both sheets were closely adhered on mutual coated surfaces. Newsprint base papers were overlaid on both outer surfaces, passed between the rollers under a pressure of 50 kg/m2 and humidified at 25~C and 60% RH for 24 hours. After a 3 x 6 cm test piece was prepared, measurement was performed at 30 mm/min tensile speed by a tensile tester.
A higher measured value signifies greater difficulty in peeling (namely, a stronger adhesion). With a newsprint paper according to the present invention, papers whose neppari strength is 30.0 g/3 cm or less were classified as those of"good separability".
"Broken" means that no separation occurred on the adhered surface in separating a sample by a tensile tester but an inter-layer separation phenomenon of the sample itself occurred. This means that the adhesion strength is so high that it cannot be measured by this method.
Table 1 Coating Coated Droplet Neppari speed Amount Water Strength m/min g/m2 Absorption g/3cm Degree sec Ex.1 1,100 0.113 80 23 Ex. 2 1,200 0.133 245 30 Ex. 3 - 1,300 0.146 267 28 Ex. 4 1,500 0.150 264 26 Ex. 5 1,800 0.160 266 2J
Comp.Ex.1 300 0.200 10 45 Comp.Ex.2 600 0.200 11 50 Comp.Ex.3 1,000 0.110 51 20 Comp.Ex.4 1,000 0.250 112 70 Comp.Ex.5 300 0.461 300 Broken As shown in Table 1, by applying a coating in the coating speed range of 1,100-1,800 m/min, coating was conducted efficiently even at low coated amounts,and water absorption resistivity was improved to as a high degree as a water droplet absorption degree of 80 sec or higher at low coated amounts. In contrast, at coating speeds of 300-1,000 m/min, coating was not conducted efficiently even athigh coated amounts, and water absorption resistivity, i.e., the water droplet absorption degree, was not improved. Further, at coating speeds of 300-1,000 m/min, if the water droplet absorption degree was increased by increasing the coated amounts, the neppari strength increased, i.e., the quality of the paper suffered.
It will be understood by those of skill in the art that numerous various and modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention .

Claims (6)

1. A printing paper having a water droplet absorption degree of no less than 60 seconds as measured by determining the time required to absorb 1 µl of water dropped on the surface of the paper, comprising:
a base paper for printing paper containing at least 30% by weight of mechanical pulp and having a water droplet absorption degree of no more than 10 seconds as measured by determining the time required to absorb 1 µl of water dropped on the surface of the paper; and a coating layer formed on said base paper by gate roll coating at a coating speed of 1,100-1,800 m/min, said coating layer comprising a water absorption resistivity controlling composition comprising:
component A which is water-soluble polyacrylamide; and component B which is water-soluble anionic copolymer of monomer having at least one hydrophobic substituent and monomer having at least one of carboxyl group and sulfone group.

2. The printing paper according to Claim 1, wherein said printing paper is a newsprint paper.

3. The printing paper according to Claim 1, wherein said component A
is cationic or amphoteric polyacrylamide having at least one of tertiary amine group and quaternary ammonium base.

4. The printing paper according to Claim 2, wherein said base paper has a basis weight of 37-43 g/m2.

5. The printing paper according to Claim 1, wherein said component B
is water-soluble anionic copolymer of styrene monomer and acrylic acid monomer.

6. The printing paper according to Claim 1, wherein the solid weight ratio of said component A to said component B is in the range of 20:80 to 80:20.7. The printing paper according to Claim 1, wherein said printing paper has a water droplet absorption degree in the range of 100-500 seconds.
8. The printing paper according to Claim 1, wherein said printing paper has a contact angle in the range of 80° to 95° when determined 5 seconds after 5 µl of water is dropped.

9. The printing paper according to Claim 1, wherein the amount of said water absorption resistivity controlling composition is in the range of 0.1-0.3 g/m2 for one side.
10. A method for producing a printing paper having a water droplet absorption degree of no less than 60 seconds as measured by determining the timerequired to absorb 1 µl of water dropped on the surface of the paper, comprising the step of applying a water absorption resistivity controlling composition comprising:
component A which is water-soluble polyacrylamide; and component B which is water-soluble anionic copolymer of monomer having at least one hydrophobic substituent and monomer having at least one of carboxylgroup and sulfone group, on a base paper for printing paper containing at least 30%
by weight of mechanical pulp and having a water droplet absorption degree of no more than 10 seconds as measured by determining the time required to absorb 1 µl of water dropped on the surface of the paper, to form a coating layer on said base paper by gate roll coating at a coating speed of 1,100-1,800 m/min.
11. The method according to Claim 10, wherein said printing paper is a newsprint paper.
12. The method according to Claim 10, wherein said component A is cationic or amphoteric polyacrylamide having at least one of tertiary amine group and quaternary ammonium base.
13. The method according to Claim 12, wherein said base paper has a basis weight of 37-43 g/m2.
14. The method according to Claim 10, wherein said component B is water-soluble anionic copolymer of styrene monomer and acrylic acid monomer.
15. The method according to Claim 10, wherein the solid weight ratio of said component A to said component B is in the range of 20:80 to 80:20.
16. The method according to Claim 10, wherein said printing paper has a water droplet absorption degree in the range of 100-500 seconds.

17. The method according to Claim 10, wherein said printing paper has a contact angle in the range of 80° to 95° when determined 5 seconds after 5 µl of water is dropped.
18. The method according to Claim 10, wherein the amount of said water absorption resistivity controlling composition is in the range of 0.1-0.3 g/m2 for one side.