JPH11189992A - Production of surface sizing agent and coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface sizing agent with improved sizing effect and slight tackiness when remoistened, by emulsion copolymerization between each specific hydrophobic monomer and anionic monomer in the presence of a specific (meth)acrylamide-based copolymer. SOLUTION: This surface sizing agent is obtained by emulsion copolymerization between at least one kind of hydrophobic monomer (b1 ) selected from the group consisting of styrene compounds and alkyl (meth) acrylates (e.g. styrene) and at least one kind of anionic monomer (b2 ) selected from the group consisting of α,β-unsaturated monocarboxylic acids and α,β-unsaturated dicarboxylic half esters (e.g. (meth)acrylic acid) in the molar ratio b1 /b2 of (40-80):(60-20) in the presence of a (meth)acrylamide-based copolymer prepared by copolymerization between 40-96 mol.% of (meth)acrylic acid amide, 3-30 mol.% of a hydrophobic monomer and 1-30 mol.% of a carboxylic acid group- contg. monomer at 0.25-5 wt.% based on the total weight of the above (b1 ) and (b2 ) components, followed by neutralization of the resulting copolymer with an alkali.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface sizing agent and a method for producing a coated paper, and more particularly, to a paper having excellent sizing properties, low stickiness when re-wet, and a coating liquid. The present invention relates to a surface sizing agent with less foaming and a method for producing a coated paper obtained by applying the surface sizing agent to paper.

[0002]

2. Description of the Related Art Surface sizing agents for improving the sizing properties and printability of paper include styrene-maleic anhydride copolymers and styrene-acrylic acid. Copolymer, (di) is
Water-soluble salts of o-butylene-maleic acid copolymer are known. When surface coating using these conventional resins,
Foaming of the coating liquid increases, which becomes foam residue and causes operational troubles such as soiling the rolls of the coating machine. Therefore, it is necessary to use a large amount of an antifoaming agent to suppress foaming. As a result, problems such as a reduction in size effect and repelling (a phenomenon in which the portion is not applied when applied later) are caused, and are not satisfactory in actual operation.

JP-A-56-63098 discloses a copolymer obtained by solution polymerization of styrene-methacrylic acid in an organic solvent or emulsion polymerization or suspension polymerization in an aqueous system using sodium lauryl sulfate as an emulsifier. By using an aqueous solution or aqueous dispersion composed of an alkali salt of a polymer, a surface sizing agent that has less foaming during coating and has good sizing performance has been proposed. The surface sizing agent,
Foaming at the time of coating is smaller than conventional sizing agents, and although a sizing effect can be obtained, it is still not satisfactory in practical use.

[0004] Generally, the surface sizing agent is often used in combination with a surface strength agent such as oxidized starch or acrylamide resin. In this case, the size is improved as compared with the case where the surface strength agent is used alone, but the tackiness increases when the paper is rewet. Therefore, when placed in a high humidity condition, the paper is blocked from adhering to each other, and re-moistened by the fountain solution during printing, and the fine fibers (paper powder) on the paper surface adhere to the blanket. In some cases, problems such as blanket contamination may occur.

[0005] Therefore, in order to prevent the generation of paper dust in the printing process, the appearance of a surface sizing agent having low stickiness on the paper surface when re-wet, in addition to an excellent sizing property improving effect, has been awaited.

The present invention provides a surface sizing agent which is excellent in sizing properties of paper, has low stickiness when re-wet, and has little foaming of a coating solution, and also applies the surface sizing agent to paper. An object of the present invention is to provide a method for producing a coated paper that has been processed.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have found that a (meth) acrylamide copolymer containing at least 40 mol% of (meth) acrylamide as a copolymer component. A surface sizing agent comprising an alkali-neutralized copolymer obtained by emulsion polymerization of a specific hydrophobic monomer (b1) and a specific anionic monomer (b2) in the presence of the polymer [A] is excellent. The present invention has been found to have an improved size property, to have low adhesiveness when re-wet, and to have less foaming of the coating liquid, and to complete the present invention.

That is, the present invention relates to (1) styrenes and alkyl (meth) in the presence of a (meth) acrylamide copolymer [A] containing at least 40 mol% of (meth) acrylamide as a copolymer component. A) at least one hydrophobic monomer (b1) selected from the group consisting of acrylates and at least one selected from the group consisting of α, β-unsaturated monocarboxylic acids and half esters of α, β-unsaturated dicarboxylic acids; An alkali neutralized product of a copolymer obtained by emulsion polymerization of a kind of anionic monomer (b2), wherein the solid content of the (meth) acrylamide copolymer [A] is the same as that of the hydrophobic monomer (b1). ) And the anionic monomer (b2) in an amount of from 0.25 to 5% by weight based on the total weight of the monomers. The (meth) acrylamide copolymer [A] is (a1) (meth) acrylamide 40
(Meth) acrylamide-based copolymer obtained by copolymerizing a monomer component of ％ 96 mol%, (a2) 3-30 mol% of hydrophobic monomer and (a3) carboxylic acid group-containing monomer. (1) the surface sizing agent of (1), (3) the (meth) acrylamide-based copolymer [A] is (a1) (meth) acrylamide 40 to 9
5.5 mol%, (a2) 3 to 30 mol% of a hydrophobic monomer, (a3) 1 to 30 mol% of a carboxylic acid group-containing monomer, and (a4) sulfonic acid group-containing monomer 0.5 to 5
(1) a surface sizing agent which is a (meth) acrylamide copolymer obtained by copolymerizing mol% of a monomer component, and (4) a ratio of the hydrophobic monomer (b1) to the anionic monomer (b2). (B1 / b2) is 40 to 80
The surface sizing agent according to any one of (1) to (3), which is mol% / 60 to 20 mol%, and (5) the surface according to any one of (1) to (4). An object of the present invention is to provide a method for producing coated paper, which comprises applying a coating liquid containing a sizing agent to paper.

[0009]

Next, the present invention will be described in detail.

[0010] 1. (Meth) acrylamide copolymer
[A] 1.1 Monomer Composition The (meth) acrylamide-based copolymer [A] used in the present invention is a (meth) acrylamide-based copolymer containing at least 40 mol% of (meth) acrylamide as a copolymer component. It is united. Here, at least 40 mol% of (meth) acrylamide as a copolymer component in the (meth) acrylamide copolymer [A] means that (meth) acrylamide is used in a ratio of 40 to 100 mol%, and the remaining Is to use other copolymerizable monomers. Further, the monomer component other than (meth) acrylamide in the (meth) acrylamide copolymer is not particularly limited.

A preferred (meth) acrylamide copolymer contains (meth) acrylamide, a hydrophobic monomer and a hydrophilic monomer as its monomer components.

More preferred (meth) acrylamide-based copolymers are multi-component copolymers containing (a1) (meth) acrylamide, (a2) a hydrophobic monomer and (a3) a carboxylic acid group-containing monomer as monomer components. (A1) and (a1) (meth) acrylamide and (a)
2) A multicomponent copolymer (A2) containing, as monomer components, (a) a hydrophobic monomer, (a3) a carboxylic acid group-containing monomer, and (a4) a sulfonic acid group-containing monomer. On the other hand, in the presence of the multi-component copolymer (A1), the hydrophobic monomer (b1) and the anionic monomer (b)
2) has the advantage that the alkali neutralized product of the copolymer obtained by emulsion polymerization has a low foaming property and a low tackiness when re-wetted, and the other multi-component copolymer (A2) has In addition to the above advantages, there is an advantage that the mechanical stability of the alkali neutralized product of the copolymer is good.

(Meth) acrylamide copolymer [A]
(A1) (meth) acrylamide used as a copolymer component of (a1) is at least one selected from the group consisting of acrylamide and methacrylamide. There may be.

Acrylamide is preferred as the monomer unit because it is inexpensive and readily available.

(A2) Examples of the hydrophobic monomer include styrene, α-methylstyrene, vinyltoluene,
Styrene derivatives such as divinylbenzene, alkyl (meth) acrylates, cyclic alkyl (meth) acrylates, dialkyl diesters of maleic acid and fumaric acid, vinyl esters such as vinyl acetate and vinyl propionate, N-alkyl (meth) acrylamides, And methyl vinyl ether. One or more of these monomers can be used in combination.

(A3) Examples of the carboxylic acid group-containing monomer include monomers such as (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid and the like. Alternatively, two or more kinds can be used in combination.

(A4) Examples of the sulfonic acid group-containing monomer include monomers such as vinyl sulfonic acid, (meth) allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and sulfonated styrene. One or more of the monomers can be used in combination.

The multi-component copolymer (A1) includes (a)
1) (meth) acrylamide 40 to 96 mol%, (a)
2) A copolymer containing 3 to 30 mol% of a hydrophobic monomer and 1 to 30 mol% of a (a3) carboxylic acid group-containing monomer as a monomer composition is preferable. (A1) (meta)
Acrylamide, (a2) a hydrophobic monomer and (a3)
When the carboxylic acid group-containing monomer is contained at a content within the above range, there is an advantage that the foamability of the alkali-neutralized product of the obtained copolymer is low and the tackiness when re-wet is low. .

The multi-component copolymer (A2) includes (a1)
(Meth) acrylamide 40 to 95.5 mol%, (a
2) A copolymer containing 3 to 30 mol% of a hydrophobic monomer, (a3) 1 to 30 mol% of a carboxylic acid group-containing monomer, and (a4) 0.5 to 5 mol% of a sulfonic acid group-containing monomer as a monomer composition. preferable. (A1) (meth) acrylamide, (a2) hydrophobic monomer, (a
3) When the carboxylic acid group-containing monomer and (a4) the sulfonic acid group-containing monomer are contained at a content within the above range, the copolymer is obtained in addition to the effect exerted by the multicomponent copolymer (A1). Has the advantage that the alkali neutralized product has good mechanical stability.

Also, a (meth) acrylamide copolymer
[A] is a monomer component as described in (a1) to (a4) above.
Other than the above, a vinyl monomer copolymerizable with (a1) to (a4) may be contained in an amount of 20 mol% or less.

Examples of the copolymerizable monomer include monomers having a phosphoric ester group such as acrylonitrile and a phosphoric ester of hydroxyalkyl (meth) acrylate.

1.2 (meth) acrylamide copolymer
Method for Producing [A] As a method for producing the (meth) acrylamide copolymer [A], a conventionally known method can be applied.

For example, the monomers (a1) to (a4) can be used in a lower alcohol such as methyl alcohol, ethyl alcohol or isopropyl alcohol, in a mixture of these lower alcohols and water, or in water.
It is obtained by polymerizing with a radical polymerization catalyst at 60 to 95 ° C. for 1 to 10 hours, and distilling off lower alcohol after completion of the polymerization.

Examples of the radical polymerization catalyst include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; redox polymerization catalysts obtained by combining these persulfates with a reducing agent; and 2,2'-azobisisopropane. Azo catalysts such as butyronitrile and 2,2'-azobis-2-methylpropionamidine dihydrochloride can be mentioned.

If necessary, a known chain transfer agent may be appropriately used in combination.

Examples of the chain transfer agent include water-soluble mercaptans such as mercaptoethanol having 2 or 3 carbon atoms, cysteamine hydrochloride, mercaptopropionic acid (salt), thioglycolic acid (salt) and thioacetic acid (salt); Alternatively, n-octyl mercaptan, n-dodecyl mercaptan, octyl mercaptopropionate, methoxybutyl mercaptopropionate, butyl thioglycolate, methoxybutyl thioglycolate, octyl thioglycolate, thiophenol, thiobenzoic acid, thiosalicylic acid, etc. Hardly water-soluble mercaptans can be exemplified. These may be used alone or in combination of two or more.

The amount of the chain transfer agent used is as described in (a1) to (a) above.
It is preferable to use 0.2 to 3 mol% based on the total mol of the monomer 4).

In the present invention, the (meth)
The monomers charged when synthesizing the acrylamide-based copolymer [A] react substantially 100% to become the monomer units in the (meth) acrylamide-based copolymer [A].

(Meth) acrylamide copolymer [A]
Is 10 to 25% by weight aqueous solution
10,000 centipoise (however, measured at 25 ° C. at 60 revolutions per minute by a Brookfield viscometer)
The viscosity is more preferably 50 to 5000 centipoise.

The amount of the (meth) acrylamide copolymer [A] used is, for example, from 0.25 to 0.25 with respect to the total amount of the hydrophobic monomer (b1) and the hydrophilic monomer, particularly the anionic monomer (b2) described later. 5% by weight, preferably 0.5 to 5%
It is 3% by weight, more preferably 0.5 to 2% by weight.
When two or more (meth) acrylamide copolymers are used in combination, the ratio is preferably set to the above-mentioned ratio with respect to the total amount of the hydrophobic monomer (b1) and the hydrophilic monomer, particularly the anionic monomer (b2). Good.

(Meth) acrylamide copolymer [A]
When the composition ratio, viscosity or amount of the monomer component is within the above range, the hydrophobic monomer (b1) described later
When emulsion polymerization is performed with a hydrophilic monomer, particularly an anionic monomer (b2), uniform emulsion polymerization can be performed without causing aggregation or thickening (creaming) of particles, and the resulting surface size Good sizing performance and low foaming properties

[0032] 2. Hydrophobic monomer (b1) and anionic
Monomer (b2) 2.1 Hydrophobic monomer (b1) Examples of the hydrophobic monomer (b1) used in the present invention include monomers selected from the group consisting of styrenes and alkyl (meth) acrylates. .

Specific examples of the styrenes include styrene, α-methylstyrene, alkyl-substituted α-methylstyrene, vinyltoluene, and divinylbenzene.

As the alkyl (meth) acrylates,
Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n
-Butyl (meth) acrylate, iso-butyl (meth) acrylate, ter-butyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, decyl (meth) acrylate, glycidyl Examples thereof include (meth) acrylate, lauryl (meth) acrylate and stearyl (meth) acrylate.

As the hydrophobic monomer (b1), only one monomer selected from the group consisting of styrenes and alkyl (meth) acrylates may be used.
It is also possible to use two or more kinds in combination.

Among the hydrophobic monomers (b1), styrene, α-methylstyrene, divinylbenzene, vinyltoluene and methyl methacrylate are particularly preferred in view of the effect of improving the size.

2.2 Anionic Monomer (b2) The anionic monomer (b2) is selected from the group consisting of α, β-unsaturated monocarboxylic acids and α, β-unsaturated dicarboxylic acid half-esters. These monomers may be used, and these monomers may be used alone or in combination of two or more.

Specific examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of unsaturated dicarboxylic acid half-esters include maleic acid, fumaric acid, monoalkyl esters of itaconic acid, Specific examples include monomethyl ester, monoethyl ester, monobutyl ester, and monopropyl ester.

Of the anionic monomers (b2), acrylic acid and methacrylic acid are particularly preferred in view of the effect of improving the size.

2.3 Hydrophobic monomer (b1) and anio
The ratio of the hydrophobic monomer (b1) to the anionic monomer (b) is 100 moles of the total of the molar ratio of the hydrophobic monomer (b1) and the anionic monomer (b2). %, It is preferably in the range of 40 to 80 mol% / 60 to 20 mol%, particularly 50 to 70 mol% / 50 to 30 mol%.
Is preferred. When the amount of the anionic monomer (b2) is less than 20 mol% or more than 60 mol%, the effect of improving the size may be insufficient.

[0041] 3. Method for Producing Surface Sizing Agent The surface sizing agent in the present invention can be obtained as an aqueous solution or an aqueous dispersion by neutralizing a copolymer obtained by emulsion polymerization in water with an alkali compound.

The method of adding the monomers at the time of emulsion polymerization in water may be a batch addition polymerization method in which all the monomers are charged into a reaction vessel at a time, and polymerization may be performed while part or all of the monomers are divided into the reaction vessels. A split addition polymerization method may be used, or a continuous drop polymerization method in which polymerization is performed while continuously or partially dropping a part of the monomer.

The monomer concentration during polymerization is usually 15 to 50.
% By weight. Polymerized at less than 15% by weight,
After that, it is possible to obtain a copolymer having a concentration of 15% by weight or more by a concentration operation, but this may not be preferable in terms of economy. When the polymerization exceeds 50% by weight, control of the heat of polymerization may be difficult, which is not preferable. The polymerization initiator is not particularly limited, and a known and commonly used polymerization initiator can be used. Further, the polymerization initiator may be charged together with the monomer into the reaction vessel, or may be continuously dropped.

Specific examples of the polymerization initiator include, for example, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; a redox polymerization catalyst obtained by combining the persulfate with a reducing agent; Examples include azo catalysts such as' -azobisisobutyronitrile and 2,2'-azobis-2-methylpropionamidine dihydrochloride. Two or more of these polymerization initiators may be used in combination.

The amount of the polymerization initiator used can be usually 0.01 to 5 mol% based on the total amount of the monomers used in the present invention.

If necessary, a known and commonly used chain transfer agent (molecular weight modifier) may be used.

The chain transfer agent may be charged together with the monomer into the reaction vessel, or may be continuously dropped.

The chain transfer agent of the present invention is preferably a mercaptan-based chain transfer agent, and specific examples thereof include, for example, n-octyl mercaptan, ter-dodecyl mercaptan, n-dodecyl mercaptan, n-octadecyl mercaptan, and n-octadecyl mercaptan. Water-insoluble chain transfer agents such as hexadecyl mercaptan or water-soluble chain transfer agents such as mercaptoethanol having 2 or 3 carbon atoms, cysteamine hydrochloride, mercaptopropionic acid (salt), thioglycolic acid (salt), thioacetic acid (salt), etc. Can be mentioned.

These chain transfer agents may be used alone or in combination of two or more. The amount of the chain transfer agent used is usually preferably 0.1 to 2% by weight based on the total amount of the monomers used in the present invention.

The polymerization reaction temperature can be usually from 40 to 100 ° C., and the reaction time can be from 1 to 20 hours.

The neutralization reaction of the copolymer can be carried out usually at a reaction temperature of 60 to 100 ° C. and a reaction time of 0.5 to 4 hours.

As the alkali compound used in the neutralization reaction, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine bases such as ammonia, methylamine and dimethylamine can be used.

The use amount of these alkali compounds is preferably 60 to 100% equivalent to the anion equivalent of the anionic monomer (b2) used in the present invention. If the amount is less than 60% equivalent, sufficient water solubility may not be obtained, and as a result, the effect of improving the size may be poor. On the other hand, 100
Even when used in excess of the% equivalent, no further improvement in water solubility is observed.

The surface sizing agent of the present invention has, for example, a solid content of 10 to 50% by weight and a solid content of 15% by weight.
(Brookfield rotational viscometer: 25
C) is 10 to 1,000 cps, and the pH is 6 to 10.

The surface sizing agent of the present invention can be used in combination with a known surface strength agent such as starch, oxidized starch, polyvinyl alcohol and polyacrylamide.
In addition, conventional surface sizing agents, anti-slip agents, preservatives, defoamers,
Additives such as viscosity modifiers and dyes may be used in combination.

The concentration of the coating liquid for applying the surface sizing agent of the present invention to paper is 0.01 to 5% by weight, preferably 0.05 to 2% by weight. The coating temperature is 2
It is preferably carried out at 0-80 ° C. The coating amount of the surface sizing agent can be appropriately set in consideration of the sizing degree of the base paper and other factors.
0.01 to 5 g / m ² , preferably 0.01 to ² g / m ²
It is.

The surface sizing agent of the present invention can be applied to paper by a known method. Examples thereof include size press, film press, gate roll coater, blade coater, calender, bar coater, knife coater, and the like. It is possible to apply using an air knife coater. Also, spray coating can be performed.

The surface sizing agent of the present invention includes newsprint paper, coated base paper, liner, coated ball, white board, wamp, flame-retardant base paper, postcard base paper, printing and writing paper, foam paper, PPC
It can be used for various base papers made from acidic or neutral paper such as paper, ink-jet paper, heat-sensitive paper, and pressure-sensitive paper.

[0059]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. All parts and percentages are by weight unless otherwise specified. Further, the present invention is not limited to the following embodiments. In addition, the evaluation method of the coated paper was performed according to the following measuring methods.

Evaluation of size / drop test: TAPPI 33 (2 μl of water)
The test was carried out according to the test method described above.

The higher the value of the drop test, the lower the water absorption to paper, that is, the better the size.

Adhesion / adhesion during rewetting : Coated paper was cut into a width of 3 cm and a length of 10 cm, and two test pieces were prepared. The two test pieces were immersed in water for 3 seconds, the coated surfaces were overlapped and sandwiched between filter papers,
After removing excess water, the sample was subjected to heat treatment at a surface pressure of 100 kg / cm ² for 2 minutes using a hot press adjusted to a temperature of 60 ° C. to obtain a measurement sample paper. Thereafter, a T-shaped peel test of the sample paper was performed using an extension-type tensile tester (tensile speed: 30 mm / min), and the adhesive strength between the test pieces was measured.

The smaller the value of the adhesive strength, the lower the tackiness of the paper surface when re-wetting.

[0064] foaming and evaluation methods: anti-foaming agents (anti-form DB-31: Dow Corning Co., Ltd., a silicon-based anti-foaming agent) 10ppm
600 g of each of the coating liquids added was applied to an inner diameter of 7 cm and a length of 50 c.
The foaming test was carried out at a temperature of 60 ° C. and a flow rate of a circulation pump of 9 liter / min, and the height (mm) of the foam 3 minutes after the start of circulation was measured.

The lower the value of the foam height, the lower the foamability.

(Meth) acrylamide copolymer [A]
Examples for the production example of (meth) acrylamide copolymer solution prepared 1 (A-1) a stirrer, thermometer, reflux condenser and a nitrogen gas introducing 50% tube into a four-necked flask equipped with a aqueous solution of acrylamide 228
Parts (80 mol%), isobutyl methacrylate 28 parts (10 mol%), acrylic acid 14 parts (10 mol%), ion-exchanged water 136 parts, isopropyl alcohol 218
Part, 0.9 part (0.5 mol%) of thioglycolic acid, n-
2.8 parts (0.7 mol%) of dodecyl mercaptan were charged, and the mixture was stirred under a nitrogen gas atmosphere under a nitrogen atmosphere.
The temperature was raised to 0 ° C. 0.3 parts of AIBN (azobisisobutyronitrile) was added as a polymerization initiator, and the temperature was raised to 80 ° C. and maintained for 5 hours.

Then, isopropyl alcohol was distilled off, and ion-exchanged water was added to the mixture to give a solid content of 35% and a viscosity of 80%.
A 0 centipoise (cps) copolymer solution (G-1) was prepared.

The viscosity was measured at 25 ° C. using a Brookfield viscometer (hereinafter, viscosity measurement conditions are the same).

(Meth) acrylamide for Examples and Comparative Examples
Production Examples 2 to 6 (A-2 to A-6) of a terpolymer-based copolymer solution as shown in Table 1 (meth) acrylamide (a1), a hydrophobic monomer (a2), a carboxylic acid group-containing monomer (a
3) For the Examples (A-2 to A-5), Comparative Example, except that the sulfonic acid group-containing monomer (a4) and the type and amount of the chain transfer agent were changed, and the same operation was performed. For (A-
6) was obtained. Table 1 shows the physical properties of the (meth) acrylamide copolymer solution. In addition, the chain transfer agent and the polymerization initiator used the same amount as A-1.

[0070]

[Table 1]

(Example 1) (Synthesis of surface sizing agent of the present invention) A 1 equipped with a stirrer, a thermometer, a reflux cooling pipe, and a nitrogen introducing pipe.
514 parts of water, styrene 7
5.4 parts (55 mol%), methyl methacrylate 13
2 parts (10 mol%), 80% methacrylic acid aqueous solution
6 parts (35 mol%), n-dodecyl mercaptan 0.6
7 parts, (meth) acrylamide copolymer (A-1)
5.1 parts were charged and heated to 70 ° C. Then, after oxygen in the reaction system was sufficiently removed with nitrogen gas, 10 parts of a 30% ammonium persulfate aqueous solution was added. After 20 minutes, the temperature in the reaction system was raised to 80 ° C, and the reaction was further performed at a temperature of 80 ° C for 2 hours. Thereafter, 282 parts of water and 50.7 parts of a 48.5% aqueous potassium hydroxide solution (neutralization equivalent: 90%) were added, and the pH was 9.3, the solid content was 15.3%, and the viscosity was 25 cp.
s surface sizing agent was obtained.

(Examples 2 to 7, Comparative Example 1) As shown in Table 2, the types and amounts of the (meth) acrylamide copolymer [A], the hydrophobic monomer (b1) component, and the anionic monomer (b2) component Was performed in the same manner as in Example 1 except that the surface sizing agents of Examples 2 to 7 and Comparative Example 1 were obtained. Table 2 shows the physical properties of each surface sizing agent. The same amounts of the chain transfer agent and the polymerization initiator as in Example 1 were used.

(Comparative Examples 2 and 3) Instead of the (meth) acrylamide copolymer [A], a low molecular surfactant or a non-acrylamide polymer emulsifier was used. Example 1 except that the type and amount of the component b1) and the anionic monomer (b2) were changed.
By performing the same operation as described above, surface sizing agents of Comparative Examples 2 and 3 were obtained. Table 2 shows the physical properties of each surface sizing agent. In addition,
The same amounts of the chain transfer agent and the polymerization initiator as in Example 1 were used.

[0074]

[Table 2]

Preparation of Coating Liquid The surface sizing agent obtained in Examples 1 to 7 and Comparative Examples 1 to 3 and acrylamide-based surface paper strengthening agent ST-481H (manufactured by Nippon PMC Co., Ltd .: solid concentration 30%) ) Was used to prepare mixed aqueous solutions having solid contents of 0.4% and 4%, respectively.

Preparation of Coated Paper This coating solution was applied to uncoated newsprint (basis weight 45 g / m ² ).
To, No. 3 bar coater to one side coated with a (surface sizing agent and the solid coating amount of ST-481H, respectively ^{0. 025g / m 2, 0.} 25g / m 2), a drum dryer (80 (C, 50 seconds). After drying, 20
The humidity was controlled for 24 hours in a thermo-hygrostat at 65 ° C. and a relative humidity of 65%. Thereafter, it was subjected to an evaluation test. The results are shown in Table 3.

Table 3 also shows the results of the foaming test of this coating solution.

In Comparative Example 1, the (meth) acrylamide-based copolymer [A] consisting of less than 40% acrylamide was used without using the (meth) acrylamide-based copolymer [A] used in the present invention. This is an example, and the result was that the effect of improving the sizing property was inferior and that the foamability was large.

Comparative Examples 2 and 3 are examples in which the (meth) acrylamide copolymer [A] used in the present invention was not used and a low molecular surfactant and a non-acrylamide high polymer surfactant were used. As a result, the effect of improving the size was inferior and the foamability was high.

[0080]

[Table 3]

As is evident from Table 3, the surface sizing agent of the present invention has an excellent effect of improving the sizing property as compared with the conventional surface sizing agent, has a low tackiness when re-wet, and has a low viscosity. It can be seen that the foamability is low.

[0082]

According to the present invention, there is provided a surface sizing agent which is superior in size-improving effect as compared with conventional ones, has low tackiness when re-wet, and has low foamability of a coating liquid. Provided. By coating the paper with the surface sizing agent provided by the present invention, it is possible to obtain a coated paper having an excellent sizing property improving effect.

Claims (5)

[Claims] 1. At least 40 mol% as a copolymer component
And at least one hydrophobic monomer (b1) selected from the group consisting of styrenes and alkyl (meth) acrylates in the presence of a (meth) acrylamide-based copolymer [A] containing (meth) acrylamide α, β-
Alkali neutralized product of a copolymer obtained by emulsion polymerization of at least one anionic monomer (b2) selected from the group consisting of unsaturated monocarboxylic acids and half esters of α, β-unsaturated dicarboxylic acids Wherein the solid content of the (meth) acrylamide copolymer [A] is such that the hydrophobic monomer (b1) and the anionic monomer (b2)
0.25 to 5% by weight based on the total weight of the monomers. 2. The (meth) acrylamide copolymer [A] according to claim 1, wherein (a1) 40 to 96 mol% of (meth) acrylamide, and (a2) hydrophobic monomer 3 to 3.
0 mol% and (a3) a carboxylic acid group-containing monomer
The surface sizing agent according to claim 1, which is a (meth) acrylamide-based copolymer obtained by copolymerizing 30 mol% of a monomer component. 3. The (meth) acrylamide copolymer [A] according to claim 1, wherein (a1) 40 to 95.5 mol% of (meth) acrylamide and (a2) a hydrophobic monomer 3
To 30 mol%, (a3) carboxylic acid group-containing monomer 1
To 30 mol% and (a4) a sulfonic acid group-containing monomer
The surface sizing agent according to claim 1, which is a (meth) acrylamide-based copolymer obtained by copolymerizing 0.5 to 5 mol% of a monomer component. 4. The ratio (b1 / b1) of the hydrophobic monomer (b1) and the anionic monomer (b2) according to claim 1.
The surface sizing agent according to any one of claims 1 to 3, wherein b2) is 40 to 80 mol% / 60 to 20 mol%. 5. A method for producing coated paper, comprising applying a coating liquid containing the surface sizing agent according to claim 1 to paper.