JP2010031427A - Copolymer latex for curtain coater, and composition for coating paper for curtain coater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously produce coated paper having excellent quality without coating failure, good foam breaking (anti-foaming property) even if the foam is produced, and no coating defects with less foaming (foam suppressing property) of a coating causing deterioration of operability and coating quality by a curtain coater at a high speed. <P>SOLUTION: The copolymer latex for curtain coaters is obtained by using 0.5-5 pts.wt. of the whole surfactants based on 100 pts.wt. of the sum total of monomers, and 10 wt.% or more of a specific anionic surfactant relative to the whole surfactants, when carrying out emulsion polymerization of the monomers comprising 30-70 wt.% of an aliphatic conjugated diene-based monomer, 0.5-10 wt.% of an ethylenically unsaturated carboxylic acid monomer, and 20-69.5 wt.% (100 pts.wt. of the sum total of the monomers) of other monomers copolymerizable therewith. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a copolymer latex for a curtain coater used in a non-contact curtain coater. Specifically, when creating coated paper with a curtain coater, there is little foaming of the paint that causes deterioration in operability and coating quality (foam suppression), and even if bubbles are generated, the foam is not blown out. The present invention relates to a good (defoaming) curtain coater copolymer latex and a composition for coating a curtain coater paper containing the copolymer latex.

In recent years, coated paper has been used in a large number of printed materials because of its high printing effect. Even in periodicals such as quarterly and monthly papers, the use of coated paper on all pages has increased considerably. In particular, most direct mails and product catalogs in the mail order business use coated paper for all pages.
Coated paper has many advantages such as whiteness, glossiness, smoothness, and printability compared to non-coated paper, but these are mainly used after making the base paper to make clay or calcium carbonate. Paper coating compositions composed of pigment dispersions in which white pigments are dispersed in water, binders for adhering and fixing pigments to base paper, and other additives, blade coaters, roll coaters, etc. It is produced through a coating process.
However, in recent years, a technique for performing high-speed coating using a non-contact type curtain coater from a method of directly applying a paint by blade coating or roll coating has attracted attention. In particular, as an advantage of the non-contact method, an unnecessary load is not applied to the base paper when applying the paint, so that there are no paper breaks and continuous operation is possible.
On the other hand, foam generated in the paint is not a problem because it is crushed by the blade or roll when the direct method is applied, but in the non-contact curtain coating, the foam generated in the paint is applied as it is. The remaining coating defects on the paper greatly affect the quality of the final coated paper product.
For this reason, the key point in curtain coating is how to suppress bubbles in the paint. In general, there is a process of removing bubbles from a paint using a defoaming device before coating. However, if the number of bubbles in the paint increases, it takes time to remove the bubbles, which causes a problem in continuous operation. In addition, it is possible to increase the capacity of the defoaming device itself, but if the scale of the device is increased, the initial investment cost increases, which is not preferable. Moreover, although a foam can be erased using an antifoaming agent, if a large amount of the remaining antifoaming agent is present in the coating layer, problems such as repellency are exhibited. From these things, the design which does not produce a bubble in the coating material in operation as much as possible is desired. Patent Document 1 (Japanese Patent Laid-Open No. 2004-124312), Patent Document 2 (Japanese Patent Laid-Open No. 2004-204389) and Patent Document 3 (Japanese Patent Laid-Open No. 2004-225219) disclose copolymer latexes having a specific structure. However, it is complicated to prepare a latex having these specific structures.
Japanese Patent Laid-Open No. 2004-124312 JP 2004-204389 A JP 2004-225219 A

  As a result of intensive studies to solve the current problems in view of the above-described circumstances, the present inventors have found that a specific anionic surfactant is used in emulsion polymerization of a copolymer latex used for curtain coating. By using, there is little foaming of the paint that causes deterioration of operability and coating quality (foam suppression), and even if foam is generated, the foam is well-off (defoaming), coating The present inventors have found that it is possible to continuously produce coated paper with an excellent quality curtain coater without defects at a high speed, and have completed the present invention.

That is, the present invention
30 to 70% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and 20 to 69.5% by weight of other monomers copolymerizable therewith ( In the case of emulsion polymerization of a monomer composed of 100 parts by weight of the total monomer, the total amount of the surfactant used is 0.5 to 5 parts by weight with respect to 100 parts by weight of the total monomer, and An anionic surfactant represented by the general formula is used in an amount of 10% by weight or more based on the total surfactant, and a copolymer latex for curtain coater is provided.

（Ｒ1は炭素数８〜４０のアルキル基または芳香族を含む炭化水素、Ｒ２は炭素数１〜９のアルキル基、AOは炭素数２〜３のアルキレンオキサイド、ｎは２〜７０の整数、ＭはＮａ、またはＫ、ＮＨ４である。）

(R1 is an alkyl group having 8 to 40 carbon atoms or aromatic hydrocarbon, R2 is an alkyl group having 1 to 9 carbon atoms, AO is an alkylene oxide having 2 to 3 carbon atoms, n is an integer of 2 to 70, M Is Na, or K, NH4.)

  According to the present invention, there is little foaming of the paint that causes deterioration in operability and coating quality (foam suppression), and even if bubbles are generated, the foams are good (defoaming), and coating defects are reduced. This makes it possible to produce coated paper continuously at a high speed using a curtain coater with no outstanding quality.

The present invention is described in detail below.
Examples of the aliphatic conjugated diene monomer in the present invention include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Examples include butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and one or more of them can be used. In particular, the use of 1,3-butadiene is preferred.

  Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. It can be used above.

  Other monomers copolymerizable with the above aliphatic conjugated diene monomer and ethylenically unsaturated carboxylic acid monomer include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers, hydroxy Examples thereof include unsaturated monomers containing an alkyl group, vinyl cyanide monomers, and unsaturated carboxylic acid amide monomers.

Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene and divinylbenzene, and these can be used alone or in combination. In particular, use of styrene is preferable.
Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, Examples thereof include monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like can be used alone or in combination. In particular, the use of methyl methacrylate is preferred.
Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. Or 2 or more types can be used. In particular, the use of β-hydroxyethyl acrylate is preferred.
Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and the like, and one or more of these can be used. In particular, the use of acrylonitrile or methacrylonitrile is preferred.
Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide, and the like, and one or more of these may be used. it can. Particularly preferred is the use of acrylamide or methacrylamide.

The copolymer latex for curtain coater in the present invention is 30 to 70% by weight of the above aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and copolymerizable therewith. It is obtained by emulsion polymerization of 20 to 69.5% by weight of other monomers (total monomer 100 parts by weight).
If the aliphatic conjugated diene monomer is less than 30% by weight, the adhesiveness such as dry pick strength required at the time of printing is inferior, and if it exceeds 70% by weight, copolymer latex and a composition for paper coating are used. This is not preferable because the film-forming property is increased and the curtain head is easily clogged.
If the ethylenically unsaturated carboxylic acid monomer is less than 0.5% by weight, the mechanical stability of the copolymer latex itself and the paper coating composition is poor, and clogging of the curtain head becomes a problem. On the other hand, when the content exceeds 10% by weight, the viscosity of the composition for paper coating increases, and the coating liquid falls freely from the curtain head, which undesirably deteriorates the coating performance such as spreading on the base paper and permeability.

  In the present invention, it is necessary to use 10% by weight or more of an anionic surfactant represented by the following general formula among the surfactants used as an emulsifier in the emulsion polymerization of the monomer.

（Ｒ1は炭素数８〜４０のアルキル基または芳香族を含む炭化水素、Ｒ２は炭素数１〜９のアルキル基、AOは炭素数２〜３のアルキレンオキサイド、ｎは２〜７０の整数、ＭはＮａ、またはＫ、ＮＨ４である。）

(R1 is an alkyl group having 8 to 40 carbon atoms or aromatic hydrocarbon, R2 is an alkyl group having 1 to 9 carbon atoms, AO is an alkylene oxide having 2 to 3 carbon atoms, n is an integer of 2 to 70, M Is Na, or K, NH4.)

In the present invention, if the proportion of the anionic surfactant represented by the above general formula is less than 10% by weight based on the total amount of surfactant used, the effects of antifoaming and antifoaming properties are not sufficient, which is not preferable.
In the present invention, other surfactants such as sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, nonionic surfactants 1 type or 2 types or more of nonionic surfactants, such as an anionic surfactant, such as a sulfate ester of an agent, or an alkyl ester type, an alkylphenyl ether type, an alkyl ether type, etc. of polyethylene glycol can be used. Preferably, a combination of an anionic surfactant represented by the above general formula and an alkylbenzene sulfonate is preferable, and a use ratio of the anionic surfactant represented by the above general formula is 20 to 90% by weight. It is preferable.

  In the present invention, the total amount of surfactant used is 0.5 to 5 parts by weight with respect to 100 parts by weight of the total monomer, but preferably the total amount of surfactant used is 0.5. ~ 2 parts by weight.

The addition method of various components in the present invention is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be adopted. Furthermore, in emulsion polymerization, conventional chain transfer agents, polymerization initiators, hydrocarbon solvents, electrolytes, polymerization accelerators, chelating agents, and the like can be used.
In the present invention, any one of single-stage polymerization, two-stage polymerization, multi-stage polymerization, seed polymerization, power feed polymerization and the like may be employed.

  Examples of chain transfer agents include n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, and other alkyl mercaptans, dimethylxanthogen disulfide, diisopropylxanthogen disulfide, and the like. Xanthogen compounds, terpinolene, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, thiuram compounds such as tetramethyl thiuram monosulfide, phenol compounds such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol, Allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide, α-benzyloxystyrene, α- Examples include vinyl ethers such as benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, α-methylstyrene dimer, and the like. One or more of these can be used.

  As the polymerization initiator, water-soluble polymerization initiators such as potassium persulfate, sodium persulfate, and ammonium persulfate, redox polymerization initiators, and oil-soluble polymerization initiators such as benzoyl peroxide can be appropriately used. In particular, use of a water-soluble polymerization initiator is preferred.

  In the polymerization, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane and cycloheptane, and unsaturated hydrocarbons such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene. Hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and xylene may be used.

Although there is no restriction | limiting in particular about the particle diameter of the copolymer latex for curtain coaters in this invention, It is preferable that it is 50-150 nm in a number average particle diameter.
The gel content is not particularly limited but is 10 to 100% by weight.

Examples of the pigment used in preparing a composition for coating a curtain coater paper using the copolymer latex for curtain coater obtained in the present invention include kaolin clay, talc, barium sulfate, and titanium oxide. Inorganic pigments such as calcium carbonate, aluminum hydroxide, zinc oxide and satin white, or organic pigments such as polystyrene latex are used alone or in combination.
If necessary, modified starch such as starch, oxidized starch and esterified starch, natural binder such as soybean protein and casein, or water-soluble synthetic binder such as polyvinyl alcohol may be used. Furthermore, synthetic latex such as polyvinyl acetate latex and acrylic latex can be used in combination with the copolymer latex of the present invention.
Furthermore, other auxiliary agents such as dispersants, antifoaming agents, leveling agents, preservatives, mold release agents, fluorescent dyes, color water retention agents, wetting agents and the like can be added as necessary.
In particular, as the wetting agent, various surfactants can be suitably used. Examples of the surfactant include fatty acid soap, rosin acid soap, ether carboxylate, alkyl sulfonate, alkyl sulfonate, ester sulfonate, and the like. Is mentioned.

  In the present invention, the above-mentioned coating composition is applied to the surface of the coating base paper by a curtain coating method, preferably at a coating speed of 1200 to 3000 m / min. Manufactured paper can be manufactured. The coating may be performed only on one side of the coated base paper or on both sides. In the present invention, curtain coating can be performed directly on the coated base paper, but a coated base paper provided with an undercoat layer in advance may be used for the purpose of improving the smoothness of the coated base paper. Furthermore, there is no limitation in particular also about the apparatus used for the said curtain coating, It can carry out using a well-known curtain coating apparatus.

The coating amount in curtain coating is not particularly limited, but the coating amount per one side (dry mass basis) is usually 0.1 to 30 g / m 2, preferably 4 to 20 g / m 2.
The pigment coated paper obtained here can be further subjected to calendar processing such as super calender, machine calender, soft nip calender, and the like, as necessary, to control smoothness.

〔Example〕
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples, unless the summary is exceeded. In the examples, parts and percentages indicating percentages are based on weight unless otherwise specified.

Preparation of copolymer latex In a pressure-resistant polymerization reactor, 150 parts of polymerization water, the first-stage emulsifier shown in Table 1, 0.2 part of potassium persulfate and sodium carbonate were charged and stirred sufficiently. The first stage monomer and other compounds shown were added and polymerization was started at 70 ° C., and the polymerization was terminated when the polymerization conversion rate exceeded 95%. Subsequently, pH of the obtained copolymer latex was adjusted to 7 with an aqueous caustic soda solution to obtain a copolymer latex A.
Further, 150 parts of polymerization water, the first-stage emulsifier shown in Table 1, potassium persulfate or sodium persulfate, and 0.2 part of sodium carbonate were charged into a pressure-resistant polymerization reactor, and after stirring sufficiently, Table 1 The first stage monomer and other compounds shown in Fig. 1 were added, and polymerization was started at 70 ° C. When the polymerization conversion of the first stage monomer reached 70%, it was shown in Table 1. Polymerization was further continued by adding the second-stage monomers, and the polymerization was terminated when the polymerization conversion rate exceeded 95%, and copolymer latexes B to G shown in Table 1 were obtained.
Subsequently, pH of each of these copolymer latexes was adjusted to 7 with an aqueous caustic soda solution to obtain copolymer latexes B to G.

Measurement of number average particle diameter of copolymer latex The number average particle diameter of the copolymer latex was measured by a dynamic light scattering method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used.

Measurement of gel content of copolymer latex A latex film is prepared at room temperature. Thereafter, about 1 g of the latex film is weighed and placed in 400 cc of toluene to be dissolved for 48 hours. Thereafter, this was filtered through a 300-mesh wire mesh, and the toluene insoluble portion captured by the wire mesh was dried and weighed, and the ratio of the weight to the weight of the first latex film was calculated as a gel content in wt%.

Preparation and Evaluation of Paper Coating Composition A paper coating composition was prepared according to the following formulation using copolymer latexes A to G according to the formulation shown below.
(Formulation formulation of paper coating composition)
Kaolin clay 70 parts Calcium carbonate 30 parts Starch 3 parts Copolymer latex 12 parts ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・
Solid content 55%

Evaluation of foamability of paper coating composition The solid content concentration of the paper coating composition was adjusted to 55%, and 250 ml of paint was mixed with a home foaming stirrer (home mixer: MultiFunction ULTRA Power Mixer manufactured by Kitchen Aid) KSM-150), and the specific gravity of the paint after stirring for 2 minutes at a stirring speed of 4 was measured.
◎ ... 0.95 or higher (very good)
○ ・ ・ ・ less than 0.95 to 0.90 or more (good)
Δ: Less than 0.90 to 0.85 or more (slightly bad)
× ・ ・ ・ less than 0.85 (bad)

Preparation and Evaluation of Coated Paper Using a lab curtain coater, apply a paper coating composition to a coated base paper (basis weight 55 g / m ² ) so that the coating amount per side is 10 g / m ^2. In a drying furnace at 150 ° C., the coated paper was prepared by drying for 5 seconds with hot air at a temperature of 210 ° C. and a wind speed of 33 m / sec.
Each coated paper obtained was conditioned overnight under conditions of a relative humidity of 65% and a temperature of 20 ° C., and then a linear pressure of 60 kg / cm, a temperature of 50 ° C., a paper passing speed of 7 m / min, and a total of 4 times for each of the front and back surfaces. The paper was processed with a super calender under the conditions of passing papers and used for evaluation of curtain coating suitability and dry pick strength.

Evaluation of Curtain Coating Suitability Coated paper prepared with a lab curtain coater was sampled to A4 size, the state of the coating layer was visually observed, and the number of coating defects was counted.
0-2 coating defects: ○ Good curtain coating suitability 3-10 coating defects: △ Curtain coating suitability slightly poor 11 or more coating defects: × Inferior curtain coating suitability

Evaluation of dry pick strength of coated paper The degree of picking when each coated paper sample was printed at the same time with an RI printer was judged with the naked eye, and was evaluated relatively from ○ (best) to x (worst). .

  As mentioned above, by using the copolymer latex for curtain coater of the present invention, there is less foaming of the paint that causes deterioration in operability and coating quality (foam suppression), and bubbles are temporarily generated. However, it is possible to continuously produce coated paper with a high quality curtain coater with good foaming resistance (defoaming property) and no coating defects at high speed.

Claims (3)

30 to 70% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and 20 to 69.5% by weight of other monomers copolymerizable therewith ( In the case of emulsion polymerization of a monomer consisting of 100 parts by weight of the total monomer, the total amount of surfactant used is 0.5 to 5 parts by weight with respect to 100 parts by weight of the total monomer, and the following general A copolymer latex for curtain coater, wherein an anionic surfactant represented by the formula is used in an amount of 10% by weight or more based on the total surfactant.

(R1 is an alkyl group having 8 to 40 carbon atoms or aromatic hydrocarbon, R2 is an alkyl group having 1 to 9 carbon atoms, AO is an alkylene oxide having 2 to 3 carbon atoms, n is an integer of 2 to 70, M Is Na, or K, NH4.)   The surfactant is a combination of an alkylbenzene sulfonate and an anionic surfactant represented by the above general formula, and the proportion of the anionic surfactant represented by the above general formula is 20 to 90% by weight. 2. The copolymer latex for curtain coater according to claim 1.   A composition for curtain coater paper coating comprising the copolymer latex according to claim 1.