JP2014070078A - Hollow polymer particle, aqueous fluid dispersion, coated composition, and coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hollow polymer particle that imparts a coated paper that is excellent in opacity and water absorption.SOLUTION: Provided is a hollow polymer particle that includes: a core polymer layer (A); at least one shell layer (B) that substantially enclosures the core polymer layer (A); and at least one air gap that is formed by neutralizing at least one portion of an acidic group included in a core polymer particle. The hollow polymer particle is characterized in that a layer that enclosures the air gap includes two or more projection parts that project toward an inside of the air gap and in which a height is at least 50 nm, and forms an uneven structure.

Description

  The present invention relates to hollow polymer particles, an aqueous dispersion, a coating composition, and a coated paper obtained by using these, which give a coated paper excellent in opacity and water absorption.

  In recent years, printing methods for printed materials such as publications such as books and magazines; commercial advertisements such as flyers, brochures, and posters have been diversified. From the viewpoint of adaptability to single-color printing and multicolor printing in a wide range of applications, improvement in opacity and water absorption of coated paper is required.

  Conventionally, coating compositions containing hollow polymer particles have been used in the manufacture of coated paper. For example, in Patent Document 1, a base is added to an aqueous dispersion containing polymer particles having a three-layer structure of a core polymer particle (A), a shell layer (B), and a shell layer (C) to adjust the pH. By setting it to 7 or more, at least a part of the acidic groups contained in the core polymer particles (A) is neutralized, and voids are formed inside the core polymer particles (A). A method for producing an aqueous dispersion is disclosed.

  However, the coated paper obtained by using the aqueous dispersion of hollow polymer particles obtained by the method of Patent Document 1 does not have sufficient opacity and water absorption, so that monochromatic printing and multicolor in a wide range of applications. From the viewpoint of further improving adaptability to printing, further improvements in opacity and water absorption have been demanded.

JP 2009-144029 A

  An object of the present invention is to provide hollow polymer particles, an aqueous dispersion and a coating composition that give a coated paper excellent in opacity and water absorption, and a coated paper obtained using these. .

  As a result of intensive studies to solve the above problems, the present inventors have found that a core polymer layer composed of a predetermined monomer unit, a shell layer composed of a predetermined monomer unit, In the hollow polymer particles including the voids formed in the layer, the layer surrounding the voids is formed with a concavo-convex structure having a plurality of protrusions with a height of 50 nm or more protruding toward the inside of the voids. The inventors have found that the above object can be achieved and have completed the present invention.

That is, according to the present invention, a monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated carboxylic acid monomer and 40 to 80% by weight of another monomer copolymerizable therewith is obtained. A core polymer layer (A) formed by neutralizing at least a part of acidic groups contained in the copolymerized core polymer particles, and at least one void;
Monomer mixture comprising 0 to 15% by weight of ethylenically unsaturated carboxylic acid monomer, 20 to 100% by weight of aromatic vinyl monomer and 0 to 80% by weight of other monomers copolymerizable therewith ( b) having at least one shell layer (B) formed by copolymerizing and substantially surrounding the core polymer layer (A),
A hollow polymer particle is provided in which the layer surrounding the void has a plurality of protrusions having a height of 50 nm or more protruding toward the inside of the void to form an uneven structure.

According to the present invention, an aqueous dispersion in which the hollow polymer particles are dispersed in an aqueous solvent is provided.
Moreover, according to the present invention, there is provided a coating composition comprising the hollow polymer particles and an inorganic pigment, wherein the content of the hollow polymer particles is from 1 to 30 with respect to 100 parts by weight of the inorganic pigment. A coating composition that is parts by weight is provided.
Furthermore, according to this invention, the coated paper formed by coating the said coating composition on a base paper is provided.

  According to the present invention, it is possible to provide hollow polymer particles, an aqueous dispersion, and a coating composition that give a coated paper excellent in opacity and water absorption. Moreover, according to this invention, the coated paper obtained using these and excellent in opacity and water absorption can be provided.

FIG. 1 is a diagram for explaining a method for measuring the height of a protruding portion protruding toward the inside of a gap in the present invention. FIG. 2A is a SEM photograph of the cut surface of the hollow polymer particles of the example of the present invention, and FIG. 2B is a SEM photograph of the cut surface of the hollow polymer particles of the comparative example.

Hollow polymer particle The hollow polymer particle of the present invention is a monomer comprising 20 to 60% by weight of an ethylenically unsaturated carboxylic acid monomer and 40 to 80% by weight of another monomer copolymerizable therewith. A core polymer layer (A) formed by neutralizing at least some of the acidic groups contained in the core polymer particles obtained by copolymerizing the mixture (a) and at least one void;
Monomer mixture comprising 0 to 15% by weight of ethylenically unsaturated carboxylic acid monomer, 20 to 100% by weight of aromatic vinyl monomer and 0 to 80% by weight of other monomers copolymerizable therewith ( b) having at least one shell layer (B) formed by copolymerizing and substantially surrounding the core polymer layer (A),
The layer surrounding the void has a plurality of protruding portions with a height of 50 nm or more protruding toward the inside of the void to form a concavo-convex structure.

Core polymer layer (A)
The core polymer layer (A) is a monomer mixture (a) comprising 20 to 60% by weight of an ethylenically unsaturated carboxylic acid monomer and 40 to 80% by weight of another monomer copolymerizable therewith. It is a layer formed by neutralizing at least a part of the acidic groups contained in the core polymer particles obtained by copolymerizing.

  The ethylenically unsaturated carboxylic acid monomer is not particularly limited, and specific examples thereof include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid and cinnamic acid; itaconic acid Ethylenically unsaturated polyvalent carboxylic acid monomers such as maleic acid, fumaric acid and butenetricarboxylic acid; ethylenically unsaturated polyvalent carboxylic acids such as monobutyl fumarate, monobutyl maleate and mono-2-hydroxypropyl maleate And a partial ester monomer. These monomers can be used alone or in combination of two or more. Among these, an ethylenically unsaturated monocarboxylic acid monomer is preferable, and methacrylic acid is more preferable.

  The content ratio of the ethylenically unsaturated carboxylic acid monomer in the monomer mixture (a) is 20 to 60% by weight, preferably 30 to 50% by weight. When the content ratio of the ethylenically unsaturated carboxylic acid monomer is too small, it becomes difficult for the base to penetrate into the core polymer particles in the neutralization step described later, and it becomes difficult to form voids. On the other hand, when the content ratio is too large, the core polymer layer (A) may not be sufficiently surrounded by the shell layer (B), the stability of the production process is lowered, and aggregates are easily generated in the production process. End up.

  Other monomers copolymerizable with the ethylenically unsaturated carboxylic acid monomer are not particularly limited, and specific examples thereof include styrene, α-methylstyrene, p-methylstyrene, halogenated styrene and the like. Aromatic vinyl monomers; Ethylenically unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl Ethylenically unsaturated carboxylic acid ester monomers such as (meth) acrylate, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate; (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl ( Ethylene such as (meth) acrylamide Saturated carboxylic acid amide monomers; Conjugated diene monomers such as butadiene and isoprene; Carboxylic acid vinyl ester monomers such as vinyl acetate; Vinyl halide monomers such as vinyl chloride; Vinylidene halides such as vinylidene chloride And vinyl pyridine. These monomers can be used alone or in combination of two or more. Among these, an ethylenically unsaturated carboxylic acid ester monomer is preferable, and methyl (meth) acrylate and butyl (meth) acrylate are more preferable.

  The content ratio of the other copolymerizable monomer in the monomer mixture (a) is 40 to 80% by weight, preferably 50 to 70% by weight.

  In the present invention, it is preferable to use a combination of methyl methacrylate, butyl acrylate, and methacrylic acid as each monomer constituting the monomer mixture (a). 77 wt%, butyl acrylate 3-15 wt% and methacrylic acid 20-50 wt%, preferably methyl methacrylate 42-71 wt%, butyl acrylate 4-13 wt%, and methacrylic acid 25-45 wt% More preferably, methyl methacrylate is 45 to 65% by weight, butyl acrylate is 5 to 12% by weight, and methacrylic acid is 30 to 43% by weight.

  In the monomer mixture (a), a crosslinkable monomer such as divinylbenzene, diallyl phthalate, allyl (meth) acrylate, or ethylene glycol di (meth) acrylate may be blended. However, if the amount of the crosslinkable monomer used is too large, it becomes difficult to form voids inside the core polymer layer (A), and therefore the amount used is preferably within a range where stable void formation can be maintained. . The amount of the crosslinkable monomer used in the monomer mixture (a) is preferably 20% by weight or less, more preferably 10% by weight or less, and particularly preferably 1% by weight or less.

  The copolymerization of the monomer mixture (a) is usually performed in an aqueous medium. Therefore, the core polymer obtained by copolymerization is usually obtained in the state of an aqueous dispersion. As the aqueous medium, water is usually used, and a water-soluble organic solvent such as methanol and ethanol may be used in combination as long as the dispersion stability of the polymer particles during production is not impaired. The usage-amount of an aqueous medium is 100-1000 weight part normally with respect to 100 weight part of monomer mixtures (a), Preferably it is 200-600 weight part. If the amount of aqueous medium used is too small, the amount of aggregates generated during polymerization tends to increase, and if the amount of aqueous medium used is too large, the productivity of hollow polymer particles tends to be poor.

  The copolymerization method of the monomer mixture (a) is not particularly limited, but is usually an emulsion polymerization method. The polymerization method may be any of batch, semi-continuous and continuous methods. The polymerization pressure, polymerization temperature, and polymerization time are not particularly limited, and known conditions are employed. In emulsion polymerization, various additives such as surfactants, polymerization initiators, chain transfer agents, chelating agents, electrolytes, oxygen scavengers and the like that are commonly used in emulsion polymerization reactions may be used as polymerization auxiliary materials. it can.

As the surfactant used in the emulsion polymerization, generally known surfactants can be used. Specifically, rosinates such as potassium rosinate and sodium rosinate; potassium oleate, potassium laurate, lauric acid Anionic surfactants such as sodium fatty acid salts such as sodium, sodium stearate, potassium stearate; sulfates of fatty alcohols such as sodium lauryl sulfate; alkylaryl sulfonic acids such as sodium dodecylbenzenesulfonate; polyoxyethylene Alkyl ether sulfates such as sodium alkyl ether sulfate; nonionic surfactants such as alkyl esters of polyethylene glycol, alkyl ethers or alkylphenyl ethers, polyacrylic acid, polymethacrylic acid, polyvinyl sulfonic acid, Dispersion stabilizers such as hydrophilic synthetic polymer materials such as livinyl alcohol, polyvinyl pyrrolidone and polyethylene glycol; natural hydrophilic polymer materials such as gelatin and water-soluble starch; hydrophilic semi-synthetic polymer materials such as carboxymethyl cellulose; Is mentioned. These surfactants can be used alone or in combination of two or more. Of these, alkyl ether sulfates such as sodium polyoxyethylene alkyl ether sulfate are preferred because of good polymerization stability.
The amount of the surfactant used is preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight, based on the total amount of the monomer mixture (a). If the amount of the surfactant used is too small, aggregates may be easily generated during polymerization. On the other hand, if the amount is too large, the void ratio of the resulting hollow polymer particles may be reduced, and various characteristics may be deteriorated. is there.

  The copolymerization of the monomer mixture (a) is preferably carried out in the presence of a seed, and the use of the seed makes it easy to control the particle diameter of the produced core polymer particles.

  The polymerization conversion rate of the monomer mixture (a) in emulsion polymerization is usually 90% by weight or more, preferably 97% by weight or more. Moreover, the composition of the copolymer to be produced is usually substantially the same as the composition of the monomer mixture (a).

  In addition, the method of adding the surfactant in performing the emulsion polymerization is not particularly limited, and the surfactant can be added to the reaction system all at once, in a divided manner or continuously, A method of continuously adding to the reaction system is preferable from the viewpoint of suppressing the generation of aggregates during polymerization. The monomer mixture (a) and the surfactant may be mixed and added to the reaction system, or may be added separately to the reaction system, but the monomer mixture (a) It is preferable to mix the surfactant and the surfactant together with the aqueous medium and add them to the reaction system as an emulsion.

  In addition, in emulsion polymerization, an inorganic salt may be added to the reaction system, and copolymerization may be performed in the presence of the inorganic salt. In particular, when a surfactant and an inorganic salt are used in combination, aggregates at the time of polymerization may be used. Generation can be effectively suppressed, and the particle size distribution can be narrowed. Although it does not specifically limit as an inorganic salt, Specifically, it is alkali such as sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, sodium phosphate, sodium tripolyphosphate. Metal salts; alkaline earth metal salts such as calcium chloride and barium sulfate; aluminum sulfate and aluminum chloride. Among these, alkali metal salts are preferable, and sodium tripolyphosphate is more preferable. The amount of the inorganic salt used is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight, based on the total amount of the monomer mixture (a). If the amount of the inorganic salt used is too small, the effect of addition tends to be difficult to develop. On the other hand, if the amount used is too large, aggregates may be easily generated during polymerization. Moreover, it does not specifically limit as an addition method of an inorganic salt, It can add to a reaction system collectively, divided | segmenting, or continuously.

  The volume average particle diameter of the core polymer particles obtained by emulsion polymerization is preferably 100 to 600 nm, more preferably 250 to 500 nm. If the volume average particle size is too small, it tends to be difficult to produce hollow polymer particles having a high porosity and a large particle size. On the other hand, when the volume average particle diameter is too large, it becomes difficult to coat the core polymer particles with the shell layer (B), and it is difficult to form voids in the core polymer particles.

  And in this invention, a core polymer layer (A) is formed by neutralizing at least one part of the acidic group contained in the core polymer particle obtained in this way by the neutralization process mentioned later. be able to. Details of the neutralization step will be described later.

Shell layer (B)
The shell layer (B) is a layer that substantially surrounds the core polymer layer (A), and contains 0 to 15% by weight of an ethylenically unsaturated carboxylic acid monomer and 20 to 100% by weight of an aromatic vinyl monomer. And a monomer mixture (b) composed of 0 to 80% by weight of other monomers copolymerizable therewith.

The ethylenically unsaturated carboxylic acid monomer is not particularly limited and can be the same as the core polymer layer (A) described above, but an ethylenically unsaturated monocarboxylic acid monomer is preferable, Methacrylic acid is more preferred.
The content ratio of the ethylenically unsaturated carboxylic acid monomer in the monomer mixture (b) is 0 to 15% by weight, preferably 0 to 5% by weight, more preferably 0.1 to 2% by weight. is there.

  The aromatic vinyl monomer is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, and halogenated styrene, and styrene is preferable. The content ratio of the aromatic vinyl monomer in the monomer mixture (b) is 20 to 100% by weight, preferably 50 to 100% by weight, more preferably 80 to 99.9% by weight. If the content of the aromatic vinyl monomer is too small, the viscosity of the aqueous dispersion of hollow polymer particles may become too high, making it difficult to handle. On the other hand, if the content ratio is too large, a large amount of coarse aggregates are generated during emulsion polymerization, and stable production may not be possible.

  Although it does not specifically limit as another monomer copolymerizable with an ethylenically unsaturated carboxylic acid monomer and an aromatic vinyl monomer, The thing similar to the core polymer layer (A) mentioned above should be used. Can do. The content of other copolymerizable monomers in the monomer mixture (b) is 0 to 80% by weight, preferably 0 to 50% by weight, more preferably 0 to 19.9% by weight. is there.

  Moreover, in this invention, it is preferable to use together methacrylic acid and styrene as each monomer which comprises a monomer mixture (b), These content ratios are 0.1-2 weight of methacrylic acid. % And styrene 98 to 99.9% by weight, and more preferably 0.1 to 1% by weight methacrylic acid and 99 to 99.9% by weight styrene.

  The method for forming the shell layer (B) in a state where the monomer mixture (b) is copolymerized and substantially surrounds the core polymer layer (A) is not particularly limited, but the above-described monomers Examples thereof include a method in which the monomer mixture (b) is emulsion-polymerized in the presence of core polymer particles obtained by copolymerizing the mixture (a). Specifically, the aqueous dispersion of core polymer particles in which the shell layer (B) is formed is obtained by emulsion polymerization of the monomer mixture (b) in the aqueous dispersion of core polymer particles. be able to. As the polymerization method, any of batch method, semi-continuous method and continuous method may be used, and the polymerization pressure, polymerization temperature and polymerization time are not particularly limited, and known conditions can be adopted.

  In addition, in the emulsion polymerization of the monomer mixture (b), the auxiliary materials for polymerization exemplified in the production of the core polymer particles obtained by copolymerizing the monomer mixture (a) can be used.

  In the present invention, when the monomer mixture (b) is copolymerized to form the shell layer (B), one of the monomer mixtures (b) used for forming the shell layer (B). Part is added to the reaction system, after copolymerization in the presence of the core polymer particles obtained by copolymerizing the monomer mixture (a), followed by neutralization treatment in the neutralization step described below, The remainder of the monomer mixture (b) used for forming the shell layer (B) is preferably added to the reaction system and copolymerized in the presence of neutralized polymer particles. In this case, the ratio of the monomer mixture (b1) to be copolymerized before the neutralization treatment (hereinafter referred to as “pre-added monomer mixture (b1)” as appropriate) and the copolymerization after the neutralization treatment are carried out. The ratio of the monomer mixture (b2) (hereinafter referred to as “post-added monomer mixture (b2)” as appropriate) is “pre-added monomer mixture (b1): post-added monomer mixture ( b2) "in a weight ratio of (100: 70) to (100: 500), preferably (100: 80) to (100: 300), more preferably (100: 90) to (100: 200). It is. In the present invention, by setting these ratios in the above range, the fine structure of the obtained hollow polymer particles has a height of 50 nm at which the layer surrounding the void protrudes toward the inside of the void, as will be described later. It can be set as the structure which forms the uneven structure which has two or more above protrusion parts.

In addition, the pre-added monomer mixture (b1) and the post-addition monomer mixture (b2) may have the same monomer composition, or the contained monomer compositions may be different from each other. Although different from each other, it is preferable that the monomer compositions contained are different from each other from the viewpoint that the fine structure of the resulting hollow polymer particles can be better controlled, It is particularly preferable that the post-addition monomer mixture (b2) has a higher content of the aromatic vinyl monomer than the body mixture (b1).
In the following, the shell layer (B) formed by the pre-added monomer mixture (b1) is referred to as “inner shell layer (B1)”, and the shell layer formed by the post-addition monomer mixture (b2). (B) may be expressed as “outer shell layer (B2)”.

Middle layer (C)
In the present invention, an intermediate layer (C) that substantially surrounds the core polymer layer (A) may be further provided between the core polymer layer (A) and the shell layer (B). In this case, the hollow polymer particles of the present invention have a three-layer structure having a core polymer layer (A), an intermediate layer (C), and a shell layer (B) from the inside.

  The intermediate layer (C) is, for example, a core polymer particle obtained by copolymerizing the monomer mixture (c) for forming the intermediate layer (C) with the monomer mixture (a) described above. It can be formed by copolymerization in the presence. The monomer mixture (c) is not particularly limited, and is composed of 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 90 to 99% by weight of another monomer copolymerizable therewith. Is preferably used.

  Although it does not specifically limit as an ethylenically unsaturated carboxylic acid monomer, The thing similar to the core polymer layer (A) mentioned above can be used, Especially, an ethylenically unsaturated monocarboxylic acid monomer is used. Preferably, methacrylic acid is more preferable. The content ratio of the unsaturated carboxylic acid monomer in the monomer mixture (c) is preferably 1 to 10% by weight, more preferably 3 to 9% by weight.

  In addition, the other monomer copolymerizable with the ethylenically unsaturated carboxylic acid monomer is not particularly limited, but the same one as the above-described core polymer layer (A) can be used. , Ethylenically unsaturated carboxylic acid ester monomers are preferred, and methyl (meth) acrylate and butyl (meth) acrylate are more preferred. The content ratio of the other copolymerizable monomer in the monomer mixture (c) is preferably 90 to 99% by weight, more preferably 91 to 97% by weight.

  The method for forming the intermediate layer (C) in a state in which the monomer mixture (c) is copolymerized and substantially surrounds the core polymer layer (A) is not particularly limited, but the above-mentioned monomers Examples thereof include a method in which the monomer mixture (c) is emulsion-polymerized in the presence of core polymer particles obtained by copolymerizing the mixture (a). Specifically, the aqueous dispersion of core polymer particles formed with the intermediate layer (C) is obtained by emulsion polymerization of the monomer mixture (c) in the aqueous dispersion of core polymer particles. be able to. As the polymerization method, any of batch method, semi-continuous method and continuous method may be used, and the polymerization pressure, polymerization temperature and polymerization time are not particularly limited, and known conditions can be adopted.

  In addition, in the emulsion polymerization of the monomer mixture (c), the auxiliary materials for polymerization exemplified in the production of the core polymer particles obtained by copolymerizing the monomer mixture (a) can be used.

  When forming the intermediate layer (C), the shell layer (B) described above is a layer that substantially surrounds the intermediate layer (C) in addition to the core polymer layer (A). Therefore, in this case, when the shell layer (B) is formed, the monomer mixture (b) is emulsion-polymerized in the presence of the core polymer particles surrounded by the intermediate layer (C). Is desirable.

In the present invention, the weight ratio of the monomer mixture (a) for forming the core polymer layer (A) and the monomer mixture (b) for forming the shell layer (B) is: The weight ratio of "monomer mixture (a) / monomer mixture (b)" is preferably (5-50) / (95-50), more preferably (5-30) / (95- 70), particularly preferably (8-20) / (92-80).
When the intermediate layer (C) is further formed, the weight ratio of the monomer mixture (c) for forming the intermediate layer (C) is “monomer mixture (a) / single amount”. Body mixture (c) / monomer mixture (b) ”(2-25) / (2-25) / (96-50), more preferably (3-15) / (3 To 15) / (94 to 70), particularly preferably (6 to 13) / (6 to 13) / (88 to 74).

Neutralization Step Next, the neutralization step in producing the hollow polymer particles of the present invention will be described. In the neutralization step, the acidic dispersion contained in the core polymer particles obtained by copolymerizing the monomer mixture (a) by neutralizing the aqueous dispersion containing the core polymer particles. This is a step of forming at least one void inside the core polymer particle by neutralizing at least a part of the group. At the same time, at least a part of the acidic groups contained in the core polymer particles is neutralized to form the core polymer layer (A) having at least one void therein. Become.

  Although it does not specifically limit as the neutralization processing method in a neutralization process, For example, the method of adding a base to the aqueous dispersion containing a core polymer particle is mentioned suitably. The base may be either a volatile base or a non-volatile base. Specific examples of the volatile base include ammonia, ammonium hydroxide, morpholine, trimethylamine, and triethylamine. Specific examples of the non-volatile base include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; sodium carbonate, Examples include alkali metal (bi) carbonates such as potassium bicarbonate; (bi) ammonium carbonate salts such as ammonium carbonate and ammonium bicarbonate. Among these, volatile bases are preferable, and ammonia and ammonium hydroxide are more preferable.

  In the present invention, the neutralization treatment is performed by adding the pre-added monomer mixture (b1) to the reaction system among the monomer mixture (b) forming the shell layer (B). For the polymer particles obtained by emulsion polymerization in the presence of core polymer particles (including those in which the intermediate layer (C) is formed) obtained by copolymerizing the mixture (a) After the neutralization treatment, the post-added monomer mixture (b2) is preferably added to the reaction system and subjected to emulsion polymerization. That is, in the present invention, in the monomer mixture (b) that forms the shell layer (B), a neutralization treatment is performed by adding a base at the stage where the pre-added monomer mixture (b1) is copolymerized. After that, it is preferable to form the shell layer (B) by adding the remaining post-addition monomer mixture (b2) to the reaction system and carrying out emulsion polymerization, and according to the present invention, The fine structure of the obtained hollow polymer particles can be configured such that the layer surrounding the voids has a predetermined concavo-convex structure as described later.

  In the present invention, as described above, the base is added to perform neutralization treatment, and the post-added monomer mixture (b2) is added to the reaction system and emulsion polymerization is performed, whereby the core polymer layer ( An aqueous dispersion of hollow polymer particles comprising A), a shell layer (B), and, if necessary, an intermediate layer (C) can be obtained.

In addition, the usage-amount of a base in a neutralization process should just be taken as the quantity which can neutralize at least one part of the acidic group of the core polymer particle obtained by copolymerizing a monomer mixture (a). However, it is preferable that the pH of the aqueous dispersion containing polymer particles is 7 or more. And it is preferable to set it as the quantity from which the pH of the aqueous dispersion containing a polymer particle will be 12 or less.
Moreover, it is preferable to add a base in the state of aqueous solution from a viewpoint of suppressing generation | occurrence | production of the aggregate at the time of a neutralization process, The density | concentration becomes like this. Preferably it is 0.5-20 weight%, More preferably, it is 1-. 10% by weight. Moreover, in a neutralization process, you may add an anionic surfactant and / or a nonionic surfactant before adding a base from a viewpoint of suppressing generation | occurrence | production of the aggregate at the time of a neutralization process.

  Further, the treatment time in the neutralization step may be a time required for the base to sufficiently diffuse in the core polymer particles obtained by copolymerizing the monomer mixture (a). 5 to 120 minutes, preferably 10 to 90 minutes. The temperature in the neutralization step is preferably not less than the temperature at which the core polymer particles are sufficiently softened from the viewpoint of diffusibility of the base, and particularly preferably 70 to 95 ° C.

Fine structure of hollow polymer particle The hollow polymer particle of the present invention has at least one void formed by neutralizing at least a part of the acidic group contained in the core polymer particle, and the void The layer surrounding the surface forms a concavo-convex structure having a plurality of protrusions having a height of 50 nm or more protruding toward the inside of the void.
In addition, the height of the protruding portion having a height of 50 nm or more protruding toward the inside of the void is preferably 300 nm or less, more preferably 200 nm or less, and particularly preferably 100 nm or less.

  In the present invention, the hollow polymer particles have voids therein, and the voids have the above-described configuration, whereby the hollow polymer particles of the present invention are coated with excellent opacity and water absorption. Paper can be given.

  In the present invention, the method for measuring the presence or absence of a protrusion having a height of 50 nm or more protruding toward the inside of the void is not particularly limited. For example, the hollow polymer particles are dried until moisture is completely removed. It can be determined by polishing the dried hollow polymer particles using a cross section polisher to expose the cut surface and measuring the height of the protruding portion present on the exposed cut surface. In the present invention, as shown in FIG. 1, the straight line connecting the rising positions of the protrusions is a reference line, and the length from the reference line to the apex of the protrusion is the height of the protrusion. it can.

  Further, in the present invention, the hollow polymer particles may have a plurality of protrusions having a height of 50 nm or more protruding toward the inside of the void, but the height is 50 nm with respect to the entire surface area of the layer surrounding the void. The area ratio of the protrusions is preferably 50% or more, and more preferably 80% or more. By making the area ratio of the protrusions having a height of 50 nm or more with respect to the entire surface area of the layer surrounding the voids within the above range, the effect of improving opacity and water absorption can be further enhanced. In addition, the area ratio of the protrusions having a height of 50 nm or more with respect to the entire surface area of the layer surrounding the void is the same as described above, and the hollow polymer particles are dried by drying until the moisture is completely removed. 100 hollow polymer particles were subjected to an operation for exposing the cut surface by polishing with a cross section polisher and determining the ratio of protrusions having a height of 50 nm or more in the region passing through the exposed cut surface. Can be obtained by performing a simple averaging process.

Furthermore, in the present invention, the hollow polymer particles have an average height of 30 nm or more of protrusions protruding toward the inside of the voids (including those having a height of less than 50 nm, but not including those having a height of less than 5 nm). It is preferable that it is 50 nm or more. The average height is preferably 200 nm or less, particularly preferably 100 nm or less.
When the average height of the protrusions is in the above range, the effect of improving opacity and water absorption can be further enhanced. Note that the average height of the protrusions is obtained by polishing the dried hollow polymer particles using a cross section polisher to expose the cut surface, and the height of the protrusions present on the exposed cut surface. It can be determined by measuring and simply averaging.

  Moreover, the number average particle diameter of the hollow polymer particles of the present invention is preferably 600 to 1500 nm, more preferably 800 to 1400 nm, and still more preferably 900 to 1300 nm. The number average particle diameter can be determined by measuring the maximum particle diameter of each of the 200 hollow polymer particles with a transmission electron microscope and simply averaging the particle diameters.

  Furthermore, the porosity of the hollow polymer particles of the present invention is preferably 30 to 80%, more preferably 40 to 70%, and still more preferably 40 to 60%. The void ratio of the hollow polymer particles is determined by measuring the maximum particle diameter and the maximum diameter of each of the 200 hollow polymer particles with a transmission electron microscope, and simply averaging the void ratio calculated from these values. Can be determined by

Aqueous dispersion The aqueous dispersion of the present invention is one in which the hollow polymer particles of the present invention are dispersed in water. The solid content concentration in the aqueous dispersion of the present invention is preferably 5 to 50% by weight, particularly preferably 10 to 40% by weight. The aqueous dispersion of the present invention can be obtained by the method described above.

Coating Composition The coating composition of the present invention is a composition comprising the above-described hollow polymer particles of the present invention and an inorganic pigment, and is usually an aqueous dispersion. In this case, as the aqueous medium, an aqueous medium contained in an aqueous dispersion of hollow polymer particles can be used, and the aqueous medium can be additionally added as appropriate.

  The content ratio of the hollow polymer particles in the coating composition of the present invention is preferably 1 to 30 parts by weight and more preferably 2 to 15 parts by weight with respect to 100 parts by weight of the inorganic pigment. When the content ratio of the hollow polymer particles is too small, the white paper gloss, whiteness, opacity and bulkiness of the resulting coated paper tend to decrease, while when the content ratio of the hollow polymer particles is too large, The fluidity of the coating composition tends to decrease.

  The inorganic pigment is not particularly limited, and examples thereof include calcium carbonate, clay, barium sulfate, calcium carbonate, talc, titanium oxide, satin white, aluminum hydroxide, silica, and mica.

  In addition, the coating composition of the present invention, if necessary, a pH adjuster, a dispersant, a water resistant agent, an antifoaming agent, a dye, a lubricant, a thickener, a water retention agent, an antioxidant, an antiseptic, Arbitrary compounding agents such as an antibacterial agent, a conductive treatment agent, an ultraviolet absorber, and a water repellent can be appropriately blended.

  The method for preparing the coating composition of the present invention is not limited. For example, in a container equipped with a stirrer, the inorganic pigment, the hollow polymer particles of the present invention, and optional compounding agents used as necessary are mixed. The method to be used may be used.

Coated paper The coated paper of the present invention is obtained by coating the above-described coating composition of the present invention on a base paper to form a surface coating layer. The surface coating layer may be a single layer that is in direct contact with the base paper, or may be the uppermost layer on another undercoat layer.

The base paper is not particularly limited, and base paper made of pulp such as mechanical pulp, chemical pulp, and waste paper pulp can be used. Moreover, the basic weight of a base paper is not specifically limited, Usually, it is 40-220 g / m < ² >.

The coating layer may be formed by a normal coating method, for example, blade coater, roll transfer coater, air knife coater, bar coater, rod blade coater, short dwell coater, curtain coater, bill blade coater, die coater. For example, it can be coated on the base paper using a conventionally known coating means. Among these, it is preferable to use a coating method suitable for high-speed coating such as a blade coater, an air knife coater, a curtain coater, or a bill blade coater. Further, laydown is coated composition per side in terms of solid content, preferably 3 to 30 g / ^{m 2,} more preferably in the range to be 5 to 25 g / ^{m 2.}

  Moreover, after forming a coating layer, it is preferable to dry, and it does not specifically limit as a drying method, Methods, such as vapor | steam drying, hot air drying, electric heater drying, can be employ | adopted suitably. The drying temperature and drying time vary depending on the coating speed and the like, but are usually 80 to 180 ° C. and about 0.03 to 10 seconds.

Further, the coated paper obtained in this manner can be finished through a calendering process as necessary, so that the gloss of the white paper can be further increased. An apparatus for performing the calendar process is not particularly limited, and the calendar process is performed by various calendar apparatuses such as a super calendar, a gloss calendar, and a soft calendar. The conditions for the calendar are not particularly limited, and are usually 30 to 200 ° C. and a linear pressure of 50 to 200 kg / cm ² .

  Since the coated paper of the present invention contains the above-described hollow polymer particles of the present invention, it is excellent in opacity and water absorption. Therefore, the coated paper of the present invention can be suitably used for publications such as books and magazines, and commercial printed materials such as flyers, brochures, and posters, taking advantage of such characteristics.

Hereinafter, the present invention will be described in detail with reference to examples. In the following, “part” is based on weight unless otherwise specified.
Moreover, the test and evaluation were performed by the following method.

Volume average particle diameter of the core polymer particles The volume average particle diameter of the core polymer particles is determined by using a dynamic light scattering particle measuring device (trade name “N4”, manufactured by Coulter, Inc.). Based on the particle size distribution, it was obtained as an average particle size (referred to as “volume average particle size”) calculated by arithmetic averaging.

The number average particle diameter of the number-average particle diameter hollow polymer particles of the hollow polymer particles, transmission electron microscope (trade name "H-7500", manufactured by Hitachi, Ltd.) maximum particle size for the hollow polymer particles 200 respectively by Was obtained by measuring and simply averaging the measurement results.

The porosity of the hollow polymer particles is measured by measuring the maximum particle diameter and the maximum diameter of the voids for each of the 200 hollow polymer particles with a transmission electron microscope (trade name “H-7500”, manufactured by Hitachi, Ltd.). Using these values, the porosity of each hollow polymer particle was determined by the following formula (1), and a value obtained by simply averaging the voids was defined as the porosity of the hollow polymer particles.
Porosity (%) = {(Maximum diameter of voids) ³ / (Maximum particle diameter) ³ } × 100 (1)

Presence / absence of uneven structure in voids inside hollow polymer particles 7.5 g of an aqueous dispersion of hollow polymer particles adjusted to a solid content concentration of 20% by weight with ion-exchanged water is placed in an aluminum dish, temperature 20 ° C., relative humidity It was dried in a 65% constant temperature and humidity room until moisture completely disappeared. Next, the dried hollow polymer particles were exposed to a cut surface using a cross section polisher (trade name “SM-09010”, manufactured by JEOL Datum), and the cut surface was scanned using a scanning electron microscope (trade name “S4700”). And manufactured by Hitachi High-Technologies Corporation) at a magnification of 40000 times. And 100 hollow polymer particles cut | disconnected by the cross section polisher were observed at random, the height of the protrusion part on a cut surface was measured, and the following references | standards evaluated.
There are multiple protrusions with a height of 50 nm or more:
There is only one protrusion with a height of 50 nm or more: Δ
There are no protrusions with a height of 50 nm or more: ×

Area ratio of protrusions having a height of 50 nm or more In the same manner as described above, using a cross section polisher, the cut surfaces of the hollow polymer particles were exposed, and the cut surfaces were scanned using a scanning electron microscope (trade name “S4700”, (Manufactured by Hitachi High-Technologies Corporation). Then, 100 hollow polymer particles cut by the cross section polisher were observed at random, and the area ratio of the protrusions having a height of 50 nm or more was 1 particle with respect to the total area inside the hollow polymer particles per particle. The ratio of the area of the protrusions having a height of 50 nm or more existing inside the hollow polymer particle was calculated for each particle, and the area ratio of the protrusions having a height of 50 nm or more was calculated by simple averaging.

Average height of protrusions Using a cross-section polisher, the cut surfaces of the hollow polymer particles were exposed in the same manner as described above, and the cut surfaces were scanned using a scanning electron microscope (trade name “S4700”, manufactured by Hitachi High-Technologies Corporation). ) At a magnification of 40000 times. Then, 100 hollow polymer particles cut by a cross-section polisher were observed at random, and protrusions (including those having a height of less than 50 nm, but less than 5 nm included in the hollow polymer particles per particle) The average height of the protrusions was calculated by measuring the height of the projections and calculating a simple average.

Opacity phosphate esterified starch (trade name “MS-4600”, manufactured by Nippon Food Processing Co., Ltd.) 2.5 parts, and carboxyl-modified styrene-butadiene copolymer latex (trade name “Nipol LX407F”, manufactured by Nippon Zeon Co., Ltd.) 9 parts, and Kaolin clay ((trade name “HG90”, manufactured by Huber): 40 parts, (trade name “KCS”, manufactured by Imeris): 20 parts) 60 parts and calcium carbonate (trade name “FMT90”, 100 parts of inorganic pigment consisting of 40 parts (manufactured by Phimatech Co., Ltd.) is mixed, and then an aqueous dispersion containing 8 parts of the hollow polymer particles obtained in each Example and Comparative Example, and ion-exchanged water are added thereto Then, a composition for coated paper having a solid content concentration of 61% by weight was obtained by stirring and mixing.
Then, the resulting coated paper composition, the base paper one surface having a basis weight of 65 g / m ^2, was applied in an amount of 14 g / m ² (solid basis) and dried at 120 ° C., coated paper Got.
And the opacity of the obtained coated paper was measured using a spectral color whiteness meter (trade name “PF10”, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS P8138-1976. It can be determined that the greater the numerical value, the better the opacity.

Drop Water Absorption Coated paper obtained in the same manner as described above was cut into 2 cm long and 10 cm wide to obtain sample pieces. Next, 5 μl of an aqueous solution containing 6% by weight of isopropyl alcohol was dropped on the side of the obtained sample piece on which the coated paper composition was applied, using a microsyringe. Then, the instant of dropping was set as the starting point, and the end point was reached when the aqueous solution containing 6% by weight of isopropyl alcohol was completely absorbed by the sample piece. The determination when the aqueous solution containing 6% by weight of isopropyl alcohol was completely absorbed by the sample piece and disappeared was made visually. The time (sec) from the start point to the end point was measured with a stopwatch. It can be determined that the shorter the time (sec) from the start point to the end point, the better the water absorption.

Example 1
Production of core polymer particles In a reaction vessel equipped with a stirrer, 50 parts of methyl methacrylate, 10 parts of butyl acrylate, 40 parts of methacrylic acid, 0.9 part of sodium polyoxyethylene alkyl ether sulfate, 0.15 part of sodium tripolyphosphate and An emulsion of the monomer mixture (a-1) for forming the core polymer particles was prepared by charging 80 parts of ion-exchanged water and then stirring.

  Next, separately from the above, 800 parts of ion-exchanged water, 100 parts of methyl methacrylate, 5 parts of sodium dodecylbenzenesulfonate and 5 parts of potassium persulfate were charged into a reaction vessel equipped with a stirrer and stirred, and the reaction vessel was heated to 80 ° C. The seed latex (S-1) having a volume average particle size of 82 nm was obtained by raising the temperature to 2 ° C. and performing a polymerization reaction.

  Then, 0.28 parts (in terms of solid content) of the seed latex (S-1) obtained above and 40 parts of ion-exchanged water are charged into a reaction vessel equipped with a stirrer and stirred, so that the seed latex (S- After obtaining the aqueous dispersion of 1), the temperature was raised to 85 ° C. Next, 1.63 parts of a 3 wt% aqueous potassium persulfate solution was added to the reaction vessel, and then the emulsification of the monomer mixture (a-1) obtained above was performed while maintaining the reaction temperature at 85 ° C. Of the total amount of the product, an amount corresponding to 7% by weight was continuously added to the reaction vessel over 3 hours, and then reacted for another hour.

  Next, 250 parts of ion-exchanged water and 18.6 parts of a 3% by weight aqueous potassium persulfate solution were added to the reaction vessel, and while maintaining the reaction temperature at 85 ° C., the monomer mixture (a- The remainder of the emulsion from 1) was continuously added to the reaction vessel over 3 hours, and then reacted for another 2 hours. Thereafter, the reaction vessel was cooled to room temperature to obtain an aqueous dispersion containing the core polymer particles. The polymerization conversion rate was 99% by weight or more, and the volume average particle size of the core polymer particles was 420 nm.

Preparation of each monomer mixture In a reaction vessel equipped with a stirrer, 100 parts of monomer (methyl methacrylate 78% by weight, butyl acrylate 16% by weight, methacrylic acid 6% by weight), polyoxyethylene alkyl ether sodium sulfate 0.2 part Then, 160 parts of ion-exchanged water was charged and then stirred to prepare an emulsion of the monomer mixture (c-1) for forming the intermediate layer (C).

  Separately from the above, in a reaction vessel equipped with a stirrer, 100 parts of monomer (99.3% by weight of styrene, 0.7% by weight of methacrylic acid), 0.44 parts of sodium polyoxyethylene alkyl ether sulfate and 144 parts of ion-exchanged water were added. The emulsion of the monomer mixture (b1-1) for inner shell layer (B1) formation was prepared by charging and then stirring.

  Further, separately from the above, in a reaction vessel equipped with a stirrer, 100 parts of monomer (99.7% by weight of styrene, 0.3% by weight of methacrylic acid), 0.44 parts of sodium polyoxyethylene alkyl ether sulfate, and 144 ion-exchanged water An emulsion of the monomer mixture (b2-1) for forming the outer shell layer (B2) was prepared by charging the parts and then stirring.

Formation of the intermediate layer (C) and the inner shell layer (B1) , and an aqueous dispersion containing 130 parts of ion-exchanged water and the core polymer particles obtained above in a reaction vessel equipped with a stirrer Charge was made so that the weight of the particles was about 10 parts by weight (so that the amount of the monomer mixture (a) used was 10 parts by weight), and then the temperature was raised to 85 ° C. Next, 10 parts of a 4% by weight aqueous potassium persulfate solution was added to the reaction vessel, and then 10 weights of the emulsion of the monomer mixture (c-1) for forming the intermediate layer (C) while maintaining the temperature at 85 ° C. Part (solid content conversion) was continuously added to the reaction vessel over 20 minutes to polymerize to form an intermediate layer (C).

  Next, while maintaining the temperature at 85 ° C., 35 parts by weight (in terms of solid content) of the emulsion of the monomer mixture (b1-1) for forming the inner shell layer (B1) was added to the reaction vessel over 45 minutes. Was continuously added to form a polymerized inner shell layer (B1).

Neutralization Step After forming the inner shell layer (B1) by the method described above, 25 parts by weight of 5% ammonia water is added to the reaction vessel and neutralized at 90 ° C. for 1 hour to obtain voids. And the core polymer layer (A) were formed. The pH of the reaction solution was 7 or more and 12 or less over 1 hour during the neutralization treatment.

Formation of outer shell layer (B2) Next, the temperature was returned to 85 ° C., and 10 parts of a 4% by weight aqueous potassium persulfate solution and a monomer mixture (b2-1) for forming the outer shell layer (B2) were added to the reaction vessel. ) Was added continuously to the reactor over 75 minutes to form an outer shell layer (B2). And the aqueous dispersion liquid of the hollow polymer particle was obtained by cooling a reaction container to room temperature. The polymerization conversion rate of all monomers used was 99% by weight or more.

  And each evaluation mentioned above was performed using the obtained hollow polymer particle. The results are shown in Table 1.

Example 2
When forming the inner shell layer (B1), the addition amount of the emulsion of the monomer mixture (b1-1) for forming the inner shell layer (B1) was changed from 35 parts to 45 parts (solid content conversion). The time for continuously adding the emulsion to the reaction vessel was changed from 45 minutes to 60 minutes, and the outer shell layer (B2) was formed when the outer shell layer (B2) was formed. The addition amount of the emulsion of the monomer mixture (b2-1) is changed from 55 parts to 45 parts (in terms of solid content), and the time for continuously adding the emulsion to the reaction vessel is from 75 minutes to 60 minutes. Except for the point changed to minutes, hollow polymer particles were obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 1
In a reaction vessel equipped with a stirrer, 130 parts of ion-exchanged water and an aqueous dispersion containing core polymer particles obtained in the same manner as in Example 1 are added so that the weight of the core polymer particles is about 10 parts by weight. (The amount of the monomer mixture (a) used was 10 parts by weight) was charged, and then the temperature was raised to 85 ° C. Next, 10 parts of a 4 wt% aqueous potassium persulfate solution was added to the reaction vessel, and then the monomer mixture for forming the intermediate layer (C) obtained in the same manner as in Example 1 while maintaining the temperature at 85 ° C. The intermediate layer (C) was formed by polymerization by continuously adding 10 parts by weight (in terms of solid content) of the emulsion (c-1) to the reaction vessel over 20 minutes.

  Next, while maintaining the temperature at 85 ° C., 90 parts by weight of the emulsion of the monomer mixture (b1-1) for forming the inner shell layer (B1) obtained in the same manner as in Example 1 (in terms of solid content) was obtained. ) Was continuously added to the reaction vessel over 2 hours to polymerize to form the inner shell layer (B1).

  Next, after forming the inner shell layer (B1), 25 parts by weight of 5% ammonia water was added to the reaction vessel and neutralized at 90 ° C. for 1 hour to form voids and core weight. The combined layer (A) was formed. The pH of the reaction solution was 7 or more and 12 or less over 1 hour during the neutralization treatment.

  Thereafter, the temperature was returned to 85 ° C., 10 parts of a 4 wt% aqueous potassium persulfate solution was added to the reaction vessel, and the reaction was further continued for 2 hours. And the aqueous dispersion liquid of the hollow polymer particle was obtained by cooling a reaction container to room temperature. The polymerization conversion rate of all monomers used was 99% by weight or more.

  And each evaluation mentioned above was performed using the obtained hollow polymer particle. The results are shown in Table 1.

Comparative Example 2
When forming the inner shell layer (B1), the addition amount of the emulsion of the monomer mixture (b1-1) for forming the inner shell layer (B1) is changed from 35 parts to 65 parts (in terms of solid content). The time for continuously adding the emulsion to the reaction vessel was changed from 45 minutes to 87 minutes, and for forming the outer shell layer (B2) when forming the outer shell layer (B2). The addition amount of the emulsion of the monomer mixture (b2-1) was changed from 55 parts to 25 parts (in terms of solid content), and the time for continuously adding the emulsion to the reaction vessel was changed from 75 minutes to 33. Except for the point changed to minutes, hollow polymer particles were obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

From Table 1, when the hollow polymer particles have voids inside, and the layers surrounding the voids have a plurality of protrusions with a height of 50 nm or more and form a concavo-convex structure, The coated paper obtained was excellent in both opacity and drop water absorption (Examples 1 and 2).
On the other hand, when the hollow polymer particles have voids inside, but the protrusions having a height of 50 nm or more are not formed in the layer surrounding the voids, the resulting coated paper has opacity and drop water absorption. (Comparative Examples 1 and 2).
2A shows an SEM photograph of the hollow polymer particles of Example 1, and FIG. 2B shows an SEM photograph of the hollow polymer particles of Comparative Example 1. As is clear from FIGS. 2 (A) and 2 (B), in Example 1, a plurality of uneven structures are formed in the voids of the hollow polymer particles, whereas in Comparative Example 2, such unevenness is formed. It can be confirmed that no structure is formed.

Claims (4)

Core polymer obtained by copolymerizing monomer mixture (a) comprising 20 to 60% by weight of ethylenically unsaturated carboxylic acid monomer and 40 to 80% by weight of another monomer copolymerizable therewith A core polymer layer (A) formed by neutralizing at least some of the acidic groups contained in the particles and at least one void;
Monomer mixture comprising 0 to 15% by weight of ethylenically unsaturated carboxylic acid monomer, 20 to 100% by weight of aromatic vinyl monomer and 0 to 80% by weight of other monomers copolymerizable therewith ( b) having at least one shell layer (B) formed by copolymerizing and substantially surrounding the core polymer layer (A),
The hollow polymer particle characterized in that the layer surrounding the void has a plurality of protrusions having a height of 50 nm or more protruding toward the inside of the void to form an uneven structure.   An aqueous dispersion in which the hollow polymer particles according to claim 1 are dispersed in an aqueous solvent. A coating composition comprising the hollow polymer particles according to claim 1 and an inorganic pigment,
The coating composition whose content rate of the said hollow polymer particle is 1-30 weight part with respect to 100 weight part of inorganic pigments.   Coated paper obtained by coating the base paper with the coating composition according to claim 3.

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