JPH0532740A - Production of emulsion particle having corecontaining multilayer structure - Google Patents

Abstract

PURPOSE:To provide a simple process for producing emulsion particles having core-containing multilayer structure without using the treatment with a basic substance. CONSTITUTION:The objective emulsion particle can be produced by successively emulsion-polymerizing (a) a vinyl monomer containing 50-99wt.% of an aromatic vinyl monomer and 1-10wt.% of a crosslinking vinyl monomer, (b) a vinyl monomer containing 20-80wt.% of a hydrophilic vinyl monomer selected from methacrylic acid, methacrylamide, 2-hydroxyethyl methacrylate, etc., (c) a vinyl monomer or further (d) another vinyl monomer. An aliphatic hydrocarbon may be added to the system during and/or after the polymerization of the monomer (b).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to general coated paper, paperboard,
Paper coating agent used for lightweight coated paper, ultra-lightweight coated paper, art paper, cast coated paper, etc., paint used for wood, outer wall, inner wall, etc., heat-sensitive such as facsimile paper, heat-sensitive label and other heat-sensitive recording paper. The present invention relates to a method for producing cored multilayer structured emulsion particles having a modified refractive index layer, which is useful as an additive for a coating agent used in a recording material.

[0002]

2. Description of the Related Art In recent years, various particulate polymer polymers have been investigated as additives for coating agents. The most commonly used particles are uniform and solid emulsion-polymerized polystyrene particles having a particle size of 0.2 to 0.5 μm. For example, according to Japanese Patent Application No. 59-59741, an unsaturated carboxylic acid and a vinyl monomer are copolymerized in the presence of an anionic surfactant and / or a nonionic surfactant, and 90% or more of the particles are A copolymer emulsion having a size within the range of 0.20 to 0.28 μm is obtained, and the emulsion particles are used as an organic pigment for applications such as paper coating, paints and heat-sensitive recording materials. However, a common problem in using the solid emulsion particles as an organic pigment is that the hiding property, whiteness and gloss are insufficient, so that practical advantages cannot be recognized unless a large amount is used.

In recent years, in order to improve the hiding power, whiteness and gloss of the solid emulsion particles, an organic material having a uniform morphology after drying and having small holes in the particles instead of the solid emulsion has been proposed. There is. As a representative example, US Pat.
27,836 and Japanese Patent Application No. 61-62510. The former is obtained by emulsion polymerization by adding at least one monoethylenically unsaturated sheath monomer forming a sheath polymer to a polymer dispersion obtained by copolymerizing at least 5% of an unsaturated carboxylic acid as a core substance. The present invention relates to a method for producing an aqueous dispersion liquid in which fine particles are formed in the particles when dried by neutralizing and swelling the core polymer in the emulsion particles with an aqueous volatile base. The latter is a method for producing synthetic resin emulsion particles having small holes inside the particles, which utilizes phase separation between different kinds of polymers at the time of polymerization and volume contraction accompanying the polymerization.

The characteristics of the particles having hollow pores produced by the various methods described above are that the concealing property, whiteness and glossiness are rather effective as compared with the conventional solid type particles, When used for the following purposes, there are the following problems. (1) When particles having hollow holes are used as an organic pigment for paper coating: Compared with conventional solid-type particles, the same added volume is superior in hiding power, whiteness and gloss. However, since the demand for improving the performance for paper coating is increasing further, it is generally used up to the same range as the weight of the solid particles. As a result, although some effects are recognized in terms of hiding power, whiteness, and glossiness, the strength of the coating layer is reduced, and problems such as printability arise. Further, in the calendering process which is performed for the purpose of increasing gloss after applying the coating liquid, it is generally performed to increase either or both of temperature and pressure to increase the smoothness of the coating surface. However, conventional particles having only hollow holes inside the particles are likely to be crushed due to the single structure, and the hiding power and whiteness are significantly lowered. In addition, the above-mentioned insufficient coating layer strength and the deformation of particles due to heat and pressure cause problems such as blocking and adhesion of stains to the calender roll, which is a serious difficulty in practical use.

In order to improve the above-mentioned drawbacks, it is possible to take measures such as changing the particle size of the particles or changing the porosity inside the particles having hollow pores. Regarding the former particle size, in order to maximize the hiding power, whiteness and gloss, the particle size should be about 0.22μ (USP
No. 4,427,836), and even if the porosity inside the particles is changed, it is not effective for the purpose of preventing the occurrence of blocking in the calendar treatment and improving the strength of the coating layer. As described above, it has been difficult to obtain excellent organic pigments for paper coating using particles having hollow holes. (2) When used in paint: Compared with the case where conventional solid particles are used, it has excellent hiding power and whiteness, but has the drawback that the hiding power and whiteness develop slowly in the actual coating operation. It has been pointed out that the desired whiteness cannot be obtained after the application by the operator, so he accidentally over-applyed it and applied it thicker than the intended coating thickness.
In some cases, it becomes uneven. This phenomenon is also a problem that cannot be solved by changing the particle size or the porosity in the particles, as in the case of paper coating. (3) When used as a thermal recording material: The thermal recording material has recently been diversified in information equipment, and the used thermal recording material is colored so as to correspond to high speed recording and low energy of the thermal head and the thermal pen. Improvements in terms of sensitivity, print clarity, whiteness, residue on the head and sticking are required. Japanese Patent Application No. 55-86789 discloses a method of forming an intermediate layer containing fine particles of a synthetic resin between a base material and a thermosensitive coloring layer to obtain a high density and clear image. However, with this method, it is difficult to obtain sufficient sensitivity to withstand the required high-speed recording property. Japanese Patent Application No. 59-143683 discloses a method in which styrene-based crosslinked fine particles are contained in a thermosensitive color developing layer for the purpose of preventing pressure coloring due to sticking of dust, sticking and scratching. However, even with this method, it is impossible to obtain a high-density and clear image, and it is not practical.

In order to effectively apply the heat of the thermal head to the thermosensitive coloring layer, a heat insulating intermediate layer containing particles having a single hollow hole inside the thermoplastic particles is provided between the substrate and the thermosensitive coloring layer. A method of introducing the same to obtain a high density and clear image is disclosed (for example, Japanese Patent Application No. 62-117787 and Japanese Patent Application No. 63-21180). However, with the particles used in these methods, the drying speed of the intermediate layer is slowed down, which causes problems in coating workability and the like when subsequently coating the thermosensitive color developing layer. Further, this method has not solved the problem of sticking of dust to the head and sticking. Further, the heat-sensitive recording material itself lacks the hiding power and whiteness, and has not yet met the demand for higher quality. Similar to the case of using it for a paint, the above problems cannot be solved even by changing the diameter of the particles having hollow holes or the void layer. As a fine particle having a novel structure that solves these problems, the present inventors have previously found an emulsion particle having a core-structured multilayer structure (Japanese Patent Application No. 2-23645). However, due to the treatment with the basic substance, the odor of the emulsion produced when ammonia is used has been a serious problem depending on the application. This problem can be solved by using an inorganic substance such as sodium hydroxide as the basic substance, but the production time becomes very long and the production cost becomes high. Furthermore, a small amount of low-molecular-weight resin solubilized by the treatment with a basic substance was dissolved in the aqueous phase from the internal swelling layer, and problems such as easy foaming of the emulsion were also found, and there is room for improvement in the manufacturing method. It was left.

[0007]

It is an object of the present invention to more simply and easily provide the above-mentioned cored multi-layered emulsion particles useful as an additive for a coating agent used in paper coating agents, paints and heat-sensitive recording materials. Is to provide a manufacturing method in which problems such as foaming do not occur.

[0008]

[Means for Solving the Problems] As a result of intensive studies to solve the above problems, under certain specific polymerization conditions, the cored multi-layered emulsion particles were not treated with the basic substance of the prior application. However, they have found that they can be produced, and have completed a simpler production method of the present invention. That is, the present invention comprises 50 to 99% by weight of an aromatic vinyl monomer, 1 to 10% by weight of a crosslinkable vinyl monomer having two or more polymerizable vinyl groups in the molecule, and (meth) Acrylamide, N-methyl (meth) acrylamide, N, N
-Dimethylacrylamide, N-isopropylacrylamide, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, maleic anhydride, maleic acid monoalkyl ester, fumaric acid monoalkyl ester,
Sodium styrene sulfonate, 2 acrylamido sodium 2-methylpropane sulfonate, 2 hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth)
By emulsion-polymerizing a vinyl monomer (a) containing 0.1 to 9% by weight of one or more hydrophilic vinyl monomers selected from the group of acrylate, glycerol (meth) acrylate and vinylpyrrolidone. A vinyl monomer (b) containing the prepared polymer (A) having a refractive index of 1.50 or more as a core particle and then containing the hydrophilic vinyl monomer in an amount of 20 to 80% by weight.
Is added to the vinyl monomer (a) in an amount of 1 to 10 times by weight and polymerized to form the polymer (B) in the outer layer portion thereof, and the hydrophilic vinyl monomer is added in an amount of 1 to 1 A vinyl monomer (c) containing 9% by weight is added and polymerized in a weight ratio of 2 to 10 times that of the vinyl monomer (b) and polymerized to obtain a polymer having a glass transition point of 50 ° C. or higher. The polymer (C) is further formed on the outer layer portion thereof, or the vinyl monomer (d) is added to the vinyl monomer (c) in an amount of 0.5 to 7 by weight.
A structure in which the polymer (D) is formed in the outermost layer part by adding and polymerizing so as to be doubled, and the particle structure when dried is composed of the core particle and the outer layer part, and having a void layer between the outer layer part and the core particle. Where D is the particle diameter, φ is the core particle diameter, and d is the void layer diameter.
Then, a modified refractive index layer satisfying D = 0.3 to 5.0 μ φ / D = 0.1 to 0.6 (where d> φ) d / D = 0.2 to 0.8 was formed. It is a method for producing cored multilayer structure emulsion particles.

The vinyl monomer (a) used in the preparation of the core particles made of the polymer (A) is an aromatic vinyl monomer.
0 to 99% by weight, 1 to 10% by weight of a crosslinkable vinyl monomer having two or more polymerizable vinyl groups in the molecule, and further (meth) acrylamide, N-methylol (meth)
Acrylamide, N, N-dimethylacrylamide, N
-Isopropylacrylamide, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, maleic anhydride, maleic acid monoalkyl ester, fumaric acid monoalkyl ester, sodium styrene sulfonate, 2 acrylamido 2-methylpropane sulfonate sodium, 2 One or more hydrophilic vinyl monomers selected from the group consisting of hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, glycerol (meth) acrylate and vinylpyrrolidone can be used in an amount of 0. 1-9
%, And combinations of other vinyl monomers.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene and vinyltoluene. The vinyl monomer (a) preferably contains 60 to 97% by weight, more preferably 70 to 95%. It is contained by weight%. Further, examples of the crosslinkable vinyl monomer include divinylbenzene, ethylene glycol di (meth) acrylate, and trimethylolpropane trimethacrylate, and the vinyl monomer (a) is preferably 2 to 8% by weight.
More preferably, it is contained in an amount of 3 to 6% by weight.

Here, the core particles made of the polymer (A) are
Optically, it plays an important role as a scattering site that scatters and reflects the light that has entered through the void (or low density) part to increase the hiding property, whiteness, and gloss of the particles. For this purpose, the refractive index of the polymer (A) needs to be 1.50 or more, preferably 1.55 or more. Also,
The shape is preferably spherical. Here, if the refractive index is less than 1.50, light scattering and reflection by the cored multi-layered emulsion particles obtained by the present production method are weak, and the desired hiding property, whiteness and gloss cannot be obtained.

Further, the glass transition point of the polymer (A) is not particularly limited, but when it is contained in the resin composition for paper coating, the glass transition point is preferably 50 ° C. or higher, It is more preferably 80 ° C or higher. When the glass transition point of the polymer (A) is low, the heat resistance is low, and for example, when the particles are deformed by heat and pressure by calendering in paper coating, the core particles are also easily deformed. It becomes difficult to suppress the deformation from the inside by the core particles, and the hiding property and the whiteness decrease. From the above points, the use of the crosslinkable monomer in the vinyl monomer (a) improves the heat resistance of the core particles themselves.

Further, by using the crosslinkable monomer, the molecular weight of the polymer (A) forming the core is increased, and the diffusion of the polymer (B) chain to be subsequently formed is suppressed, It is also advantageous to form the polymer in the outer layer portion. Further, when an aliphatic hydrocarbon compound having 6 to 12 carbon atoms described later is added as a non-polymerizable solvent, it is not absorbed in the core particle portion and the desired polymer (B) is obtained.
It becomes easy to be absorbed inside. However, when it is used in excess of 10% by weight, the polymerization stability is impaired and aggregates are generated. If it is less than 1% by weight, the effect of addition is not recognized. Similarly, by containing the aromatic vinyl monomer in the vinyl monomer (a), the glass transition point of the polymer (A) becomes high, and at the same time, its refractive index also becomes high. Here, the amount of the aromatic vinyl monomer used is 50% by weight.
If it is less than the above, it becomes difficult to simultaneously satisfy the above-mentioned refractive index and heat resistance. If it is used in excess of 99% by weight, the amount of the crosslinkable vinyl monomer added will be less than 1% by weight, and the effect of adding the crosslinkable vinyl monomer will not be recognized for the above reasons. The above hydrophilic vinyl monomer is used for the purpose of imparting stability to the particles, but when it is used in an amount of more than 9% by weight, the contour of the core particles becomes unclear, and the desired core-containing multilayer emulsion particles. Can't get Also,
If it is less than 0.1% by weight, the stability of the particles is insufficient and smooth polymerization cannot be performed.

Examples of the other vinyl monomer include methacrylic acid esters such as methyl methacrylate, ethyl methacrylate and butyl methacrylate, acrylic acid such as methyl acrylate, butyl acrylate and 2-ethylhexyl acrylate. Esters, vinyl ester monomers such as vinyl acetate, vinyl cyan monomers such as (meth) acrylonitrile, vinyl halide monomers such as vinyl chloride and vinylidene chloride, and diene monomers such as butadiene. However, the combination is not particularly limited.

The vinyl monomer (b) for forming the polymer (B) on the outer layer portion of the core particle composed of the polymer (A) is
(Meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, maleic anhydride, monoalkyl maleate Ester, fumaric acid monoalkyl ester, sodium styrene sulfonate,
2-acrylamido sodium 2-methylpropanesulfonate, 2-hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, glycerol (meth) acrylate, vinylpyrrolidone, one or more selected from the group 20 to 80% by weight of the hydrophilic vinyl monomer and 80 to 20% by weight of the other vinyl monomer. Here, the content of the hydrophilic vinyl monomer is 2
5 to 70% by weight is preferable, and 30 to 60% by weight is more preferable.

It is an important point of the present production method that the hydrophilicity of the polymer (B) to be formed is increased by adding a large amount of this hydrophilic vinyl monomer. Is used in an amount of more than 90% by weight, the polymer (C)
Is very difficult to form in the outer layer portion, and the obtained particles do not form a multilayer structure but become solid particles. On the other hand, if it is used in an amount of less than 20% by weight, the effect of its addition is low and the desired particles cannot be obtained. still,
From the hydrophilicity of the polymer (B) and the ease of subsequent formation of the polymer (C) on the outer layer portion, the hydrophilic vinyl monomer is
Methacrylamide, methacrylic acid, and 2-hydroxyethyl methacrylate are preferably used alone or in combination of two or more.

Other vinyl monomers to be combined with the above-mentioned hydrophilic vinyl monomers include methyl methacrylate, ethyl methacrylate, methacrylic acid esters such as butyl methacrylate, methyl acrylate, butyl acrylate and acryl. Acrylic esters such as 2-ethylhexyl acid, vinyl ester monomers such as vinyl acetate, aromatic vinyl monomers such as styrene, α-methylstyrene and vinyltoluene, vinyl cyan monomer such as (meth) acrylonitrile Body, vinyl halides such as vinyl chloride and vinylidene chloride, and diene monomers such as butadiene, and crosslinkable vinyl monomers such as divinylbenzene, ethylene glycol di (meth) acrylate and trimethylolpropane trimethacrylate. 1 or 2 or more types from What was Align is used. Here, the combination of the above other vinyl monomers is not particularly limited, but from the viewpoint of hydrophilicity of the polymer (B), the aromatic vinyl monomer and the (meth) acryl having an alkyl group of 4 or more carbon atoms are used. The acid ester is preferably used in an amount of 5% by weight or less, and methyl methacrylate is preferably used.

The above-mentioned crosslinkable monomer is usually contained in the vinyl monomer (a) in an amount of 0 to 1% by weight, preferably 0 to 0.5% by weight. By using this crosslinkable monomer, the molecular weight of the polymer (B) is increased, the diffusion of the polymer (C) chain to be subsequently formed is suppressed, and the polymer is formed in the outer layer portion thereof. It is advantageous to let However, if it is used in an amount of more than 1% by weight, agglomerates are likely to be generated during the polymerization, and further, when an aliphatic hydrocarbon having 6 to 12 carbon atoms described later is added as a non-polymerizable solvent, The aliphatic hydrocarbon is extruded to the outer layer portion by heating at that time, and the effect of adding the non-polymerizable solvent is not recognized. The vinyl monomer (b) selected as described above is the vinyl monomer (a)
It is added and polymerized in a weight ratio of 1 to 10 times, preferably 1 to 5 times. Less than 1 time,
Since the amount is too small, solid-type particles are produced. Further, when it is added 10 times or more, aggregates are generated, and the polymerization does not proceed stably.

After the polymer (B) is formed on the outer layer portion of the core particle composed of the polymer (A), the vinyl monomer (c) is further added and polymerized to further form the outer layer of the particle. The polymer (C) is formed on the part. The vinyl monomer (c) used here is (meth) acrylamide, N
-Methylol (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide,
Acrylic acid, methacrylic acid, crotonic acid, fumaric acid,
Itaconic acid, maleic anhydride, maleic acid monoalkyl ester, fumaric acid monoalkyl ester, sodium styrene sulfonate, sodium 2 acrylamide 2-methylpropane sulfonate, 2 hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol 1 to 9% by weight of one or more hydrophilic vinyl monomers selected from the group of (meth) acrylate, glycerol (meth) acrylate and vinylpyrrolidone, and other vinyl monomers 99 to 9
It consists of a combination of 1% by weight.

If the above hydrophilic vinyl monomer is used in an amount of more than 9% by weight, the water resistance of the obtained particles will be lowered, and the development of clear core particles and void layers will be hindered. However, the intended cored multi-layered emulsion particles cannot be obtained. On the other hand, if it is less than 1% by weight, the stability of the particles will be insufficient and it will be difficult to form the polymer (C) in the outer layer portion of the polymer (B), so that the desired particles cannot be obtained. In order to form the polymer (C) on the outer layer portion of the polymer (B) having high hydrophilicity, it is preferable to use 2 to 7% by weight of the hydrophilic vinyl monomer, and especially methacrylic acid is used. Preferably.

Other vinyl monomers to be combined with the above-mentioned hydrophilic vinyl monomer include methyl methacrylate, ethyl methacrylate, methacrylic acid esters such as butyl methacrylate, methyl acrylate, butyl acrylate, acryl. Acrylic acid esters such as 2-ethylhexyl acid,
Vinyl ester monomers such as vinyl acetate, styrene,
Aromatic vinyl compounds such as α-methylstyrene and vinyltoluene, vinylcyan-based monomers such as (meth) acrylonitrile, halogenated vinyl compounds such as vinyl chloride and vinylidene chloride and diene compounds such as butadiene, and divinylbenzene and ethylene. One or two of crosslinkable monomers such as glycol di (meth) acrylate and trimethylolpropane trimethacrylate
A combination of more than one species is used.

The glass transition point of the polymer (C) formed is 50 ° C. or higher, preferably 70 ° C. or higher. If the temperature is lower than 50 ° C, fusion between particles and deformation of the particles themselves are likely to occur, and performances such as target hiding property, whiteness, and gloss are deteriorated. You won't get it. Further, the polymer (C)
Regarding the refractive index of, the preferable conditions are different depending on whether the polymer (D) is subsequently formed on the outer layer portion or not. That is, in the former case, the refractive index is preferably lower than that of the polymer (A) and the polymer (D) in order to increase the light scattering intensity between the layers. On the other hand, in the latter case, it is preferable to increase the difference in refractive index from the internal void layer, and it is preferably 1.50 or more.

The vinyl monomer (c) selected as described above has a weight ratio of 2 to the above vinyl monomer (b).
It is added and polymerized so that it becomes 10 times, but preferably,
3 to 9 times. If it is less than 2 times, the resulting polymer (C) cannot completely cover the outer layer portion of the polymer (B).
The target particles cannot be obtained. On the other hand, if it is added in excess of 10 times, the outer layer portion made of the polymer (C) becomes too thick, so that the desired performance is deteriorated. The cored multi-layered emulsion particles are prepared by a usual emulsion polymerization method. When this emulsion polymerization is carried out, a surfactant is usually added, and examples of the surfactant used in the present invention include sodium alkylbenzenesulfonate, sodium alkylsulfate, sodium dialkylsulfosuccinate, and naphthalenesulfonate formalin condensate. Anionic surfactants; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, ethylene oxide-propylene oxide block copolymers, sorbitan fatty acid esters, which are used alone or in combination, When emulsion particles are used in a heat-sensitive recording material, it is preferable to use an anionic surfactant as the surfactant in order to prevent color fading in the color forming layer and to prevent fading of the color forming part.

The amount of the surfactant used is not particularly limited, but is usually 0.1 to 1 with respect to the amount of the monomers used between the layers.
It is about 0% by weight. The polymerization initiator may be one that is used in ordinary emulsion polymerization, for example, potassium persulfate, sodium persulfate, ammonium persulfate,
And persulfates; organic peroxides such as benzoyl hydroperoxide; azo compounds such as azobisisobutyronitrolyl. If necessary, it can be used as a redox initiator in combination with a reducing agent.

In order to prepare a core particle emulsion composed of the polymer (A), various monomers are collectively, divided or continuously added in the presence of the above-mentioned surfactant, polymerization initiator and buffer. Polymerization is carried out by dropwise addition. At that time, the polymerization is carried out at a polymerization temperature of 20 to 90 ° C. under a nitrogen purge. Using the core particle emulsion composed of the polymer (A) thus produced as seed particles, the vinyl monomer (b) and the vinyl monomer (c) are subsequently batch-divided,
Alternatively, the polymerization is performed by a method of continuously adding. Also,
As a separate step, a core particle emulsion composed of the polymer (A) was produced in advance, and the core particle emulsion was newly charged as a seed particle into a polymerization tank to obtain a vinyl monomer (b) and a vinyl monomer (c). May be added as described above to carry out polymerization. At that time, it is preferable that after the vinyl monomer (b) is almost polymerized, the vinyl monomer (c) is added and polymerized. Alternatively, the vinyl monomer (b) may be added to complete the polymerization, the polymerization vessel may be newly charged, and the vinyl monomer (c) may be added to carry out the polymerization. Such preparation of the polymer (A), the polymer (B) and the polymer (C) may be carried out subsequently in one step, or in a separate step or a combined step. Well, there is no particular limitation. As described above, when dried, an emulsion particle having a core particle inside the particle and further having a void layer in the core particle outer layer part is obtained, the structure of which is the particle itself, and further the cross section of the particle It can be easily confirmed by observing with a microscope.

In the production method of the present invention, the void layer is formed in the outer layer portion of the core particle only when each polymer, particularly the polymer (B) has a specific composition. Although the reason for this is unclear, it is considered that in the emulsion state, the portion that becomes the void layer when dried is the water-containing layer, which makes the polymer (B) highly hydrophilic and the polymer (B) at the time of polymerization. It is also considered that this is due to the fact that the layer consisting of is composed of water. As described above, the target particles are obtained, but for the purpose of increasing the diameter d of the void layer inside the particles and the volume fraction (void ratio) thereof, and further lowering the density of the void layer, During the polymerization of the vinyl monomer (b) and / or the vinyl monomer (c), or the polymer (B)
After formation of vinyl monomer (c) and before polymerization, an aliphatic hydrocarbon compound having 6 to 12 carbon atoms, preferably one or more kinds of fat selected from cyclohexane, octane, isooctane and heptane. The group hydrocarbon compound is preferably added in an amount of 0.1 to 1 times the weight of the vinyl monomer (b).

Here, the added aliphatic hydrocarbon compound is considered to be present in the layer composed of the polymer (B), and when dried, the diameter d of the void layer and its volume are further increased by the volume, or more. It is considered that the density will decrease.
Here, the added aliphatic hydrocarbon compound, depending on the purpose of use, if the mixing of the organic solvent does not matter, may be used as it is, and may be evaporated together with water at the time of drying,
After completion of the polymerization, it can be easily removed by steam distillation or the like. Here, the carbon number of the aliphatic hydrocarbon is 6
Less than 12 and more than 12 are difficult to handle.

After the desired cored multi-layer structure emulsion particles are obtained as described above, the vinyl monomer (d) is further added and emulsion polymerization is carried out to form a modified refractive index layer on the outer layer portion of the particles. It is also possible to form the following polymer (D). Examples of the vinyl monomer (d) used here include aromatic vinyl monomers such as styrene, α-methylstyrene and vinyltoluene, acrylic acid esters such as methyl acrylate, ethyl acrylate and butyl acrylate. , Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate and butyl methacrylate, vinyl cyan monomers such as (meth) acrylonitrile, vinyl ester monomers such as vinyl acetate, vinyl chloride,
Vinyl halide monomers such as vinylidene chloride, diene-based monomers such as butadiene, and divinylbenzene,
Crosslinkable monomers such as ethylene glycol di (meth) acrylate and trimethylolpropane trimethacrylate are used alone or in combination of two or more. further,
For the purpose of imparting stability to emulsion particles, the vinyl monomer (d) can usually contain the hydrophilic vinyl monomer in an amount of 0.1 to 10% by weight. 10
Use in excess of weight% is not preferable from the viewpoint of water resistance of emulsion particles. The crosslinkable monomer such as divinylbenzene is usually contained in an amount of 0 to 20% by weight for the purpose of improving heat resistance and solvent resistance.
If used in excess of 0% by weight, a large amount of aggregates will be generated,
Polymerization does not proceed stably. Incidentally, the above-mentioned diene-based monomer such as butadiene imparts adhesiveness to the particle surface, increases the coating layer strength particularly when used in a resin composition for paper coating, and imparts rubber elasticity to the particle surface. It is used for the purpose of giving.

The refractive index of the polymer (D) obtained from the vinyl monomer (d) selected as described above is 1.50 or more, preferably 1.55 or more, and the refractive index is 1.
If it is less than 50, the light-scattering and reflecting properties are low and the desired performance cannot be obtained. Here, the glass transition point of the polymer (D) is not particularly limited, and the combination of vinyl monomers mentioned above is not particularly limited as long as the refractive index is 1.50 or more. . The monomer (d) is added so that the weight of the monomer (d) is 0.5 to 7 times that of the vinyl monomer (c), and the polymerization is carried out by the emulsion polymerization method described above. Here, if it is used in excess of 7 times, the outermost layer portion made of the polymer (D) becomes too thick and the desired performance cannot be exhibited. On the other hand, if it is less than 0.5 times, the significance of the existence of the polymer (D) is lowered.

The particle diameter D of the cored multi-layered emulsion particles obtained in the present invention is 0.3 to 5.0 μm, preferably 0.4 to 4.0 μm. Further, depending on the application, it is more preferably in the range of 0.5 to 2.0 μ when used as a pigment in paint or paper coating, and in the range of 0.5 to 3.0 μ when used as a thermal recording material. If the outer diameter of the particles is 0.3 μm, the desired cored multi-layered emulsion particles cannot be obtained and solid particles are produced. Further, particles having an outer diameter of more than 5.0 μm cannot be stably prepared. The ratio of the diameter φ of the core particles and the diameter d of the void layer to the particle diameter D is φ / D = 0.1 to 0.6 (where d> φ) d / D = 0.2 to 0.8, respectively. However, preferably, φ / D = 0.2 to 0.4 (where d> φ) d / D = 0.4 to 0.8, respectively.

If d / D is less than 0.2, the desired hiding property, whiteness, gloss and color development sensitivity cannot be obtained because the diameter of the void layer is too small. Further, when d / D exceeds 0.8, the outer layer portion becomes very thin, and thus it is difficult to stably obtain cored multi-layered emulsion particles having a void layer.

Further, when φ / D is less than 0.1, the core particles are too small, so that the light scattering intensity by the core particle portion is lowered and the desired hiding property, whiteness and gloss cannot be obtained. On the other hand, when φ / D exceeds 0.6, the volume occupied by the core particles becomes too large, and therefore, compared with solid-type particles,
Superiority is not recognized in terms of hiding power, whiteness, gloss and color development sensitivity. Here, the diameter φ of the core particles and the diameter d of the hollow holes are directly expressed in terms of their size from the ratio with the particle diameter D. That is, φ is 0.01
To 3.0 μ, and preferably in the range of 0.02 to 2.0 μ. Here, particularly when it is used as a pigment for coating or paper coating, it is preferably in the range of 0.1 to 1.0 μ, more preferably 0.1 to 0.5 μ from the light scattering effect.
Is more preferable.

On the other hand, d is 0.02 to 4.0 μ, and preferably 0.06 to 3.2 μ. When it is used as a pigment in paints or paper coating, it is preferably in the range of 0.2 to 2.0 μ, and more preferably 0.3 to 1.2 μ from the light scattering as in the above φ. Is more preferably in the range. Further, when used in a heat-sensitive recording material, it is preferably in the range of 0.3 to 2.5 µ, and more preferably in the range of 0.5 to 2.0 µ in terms of color development sensitivity, whiteness, and head residue. Is more preferable from the viewpoint of preventing the adhesion of

The particles of the present invention have more excellent hiding power, whiteness, and luster than the emulsion particles having single-hole hollow pores inside the particles. It is considered that the scattering and reflection of the particles of the present invention occur on the outer surface of the particles and the inner surface of the hollow pores, whereas the particles of the present invention are further subjected to scattering and reflection on the surface of the core particles inside and inside the hollow layer.

The void layer interposed between the core particles and the outer layer particles is relatively determined by the position of the core particles and the position of the outer layer particles. For example, in the example shown in FIG. 1, the core particles are located at the center of the outer layer particles, but the core particles may be displaced from the center. Here, it is considered that the polymer (B) is present at a very low density in the void layer. Since it is inferred that the polymer (B) is partially grafted to the polymer (A) constituting the core particles during the polymerization, the core particles are not completely in contact with the inner wall of the outer layer particles. It seems that it exists in a state of being fixed inside the void layer to some extent. Further, the shape of the particles may be deformed from the sphere due to heat treatment or the like in actual use, but in that case, the shape is not limited to that shown in FIG.

[0036]

EXAMPLES Specific examples of the present invention will be described below, but the present invention is not limited thereto. All parts and percentages below are parts by weight and percentages by weight. (Preparation of Core Particles) Core Particle Emulsion-1 A separable flask equipped with a stirrer, a thermometer, and a reflux condenser is charged with 365 parts of water, and the temperature is raised to 70 ° C. under nitrogen with stirring. The internal temperature was kept at 70 ° C., 0.4 parts of potassium persulfate was added as a polymerization initiator, and after dissolution, 40 parts of water, 0.05 part of sodium lauryl sulfate, 92 parts of styrene, 2 parts of methacrylic acid and 1 part of acrylamide were previously prepared. Parts and 5 parts of divinylbenzene were added under stirring to prepare 5% of the total amount of the emulsion prepared in advance in a separable flask,
After polymerization for 1 hour, the remaining emulsion was added and reacted for about 2 hours, and aging was performed for about 2 hours after the addition was completed to prepare a core particle emulsion. This core particle emulsion had a nonvolatile content of 20% and a particle diameter φ of 0.19 μ (core particle No. 1). Table 1 shows the results prepared by changing the composition of the vinyl monomer (a) by the same method.

[0037]

[Table 1] Here, the refractive index n and the glass transition point Tg of the polymer are
Shonsho (POLYMERHANDBOOK 2nd Ed., Ed. By J. BRANDRUP
and EH IMMERGUT, JOHN WILLEY & SONS, 1975), and calculated from the refractive index ni and the glass transition point Tgi of each homopolymer and the weight fraction xi of each homopolymer added during the polymerization according to the following formula. .

N = Σxi · ni (1 / Tg) = Σ (xi / Tgi)

(Preparation of cored multi-layered emulsion particles [1]) Example 1 A separable flask similar to that used for preparation of core particles was charged with 250 parts of the above core particle emulsion 1 and 1020 parts of water and stirred. The temperature is raised to 80 ° C. while purging with nitrogen. The internal temperature was maintained at 80 ° C, 2 parts of ammonium persulfate was added as a polymerization initiator, and after dissolution, 50 parts of water, 57 parts of methyl methacrylate, 0.4 parts of sodium lauryl sulfate, 57 parts of butyl acrylate and 3 parts of methacrylic acid were previously prepared. An emulsion prepared by adding 40 parts under stirring is continuously added over 3 hours to cause a reaction, and aging is carried out for 2 hours after the addition is completed. Then pre-water 25
0 parts, sodium lauryl sulfate 1.0 parts, methyl methacrylate 400 parts, styrene 75 parts, methacrylic acid 20
Part, and 5 parts of 2-hydroxyethyl methacrylate were added with stirring to prepare an emulsion, which was continuously added and reacted for 4 hours, and aging was carried out for 2 hours after the addition was completed. The obtained emulsion has a nonvolatile content of 30% and a particle diameter D of 0.54.
μ, the core particle diameter φ in the particles was 0.21 μ, and the diameter d of the void layer was 0.37 μm. The calculated glass transition point and refractive index of the polymer (C) are 108 and
C., 1.51.

Examples 2 to 3 The core particle emulsion 1 was used in the same manner as in Example 1 except that the composition and the addition amount of the vinyl monomer (b) were changed. 2 shows. Incidentally, in order to unify the final nonvolatile content to about 30%, the amount of water charged in the flask was first adjusted and the polymerization was performed in accordance with the change in the addition amount. Example 4 In Example 1, the core particle emulsion was changed to No. The results prepared by changing to 2 are shown in Table 2 as Example 4.

Comparative Examples 1 to 4 The results of Comparative Example 1 and Example 4 in which the composition of the vinyl monomer (b) in Example 1 was 92 parts of methyl methacrylate, 3 parts of butyl acrylate and 5 parts of methacrylic acid were prepared. The composition of the vinyl monomer (b) in
Parts, butyl acrylate 3 parts, and methacrylic acid 90 parts were prepared, and the addition amount of the vinyl monomer (b) was reduced in Comparative Example 2 and Example 1 to obtain the monomer (a) and the monomer (b). The weight ratio of) was adjusted to 1 / 0.3 and the result was prepared in Comparative Example 3, and the amount of vinyl monomer (b) added in Example 2 was increased to obtain the monomer (a) and the monomer ( The results prepared by adjusting the weight ratio of b) to 1/15 are shown in Table 2 as Comparative Example 4.

Comparative Example 5 In Example 1, the core particle emulsion was replaced with No. The results prepared by changing to 3 are shown in Table 2 as Comparative Example 5.

[0043]

[Table 2]

Examples 5 to 7 The results of Examples 1 and 3 prepared by changing the composition and addition amount of the vinyl monomer (c) are shown in Table 3 as Examples 5, 6 and 7. Comparative Examples 6 to 7 In Example 1, the addition amount of the vinyl monomer (c) was reduced and the weight ratio of the monomer (b) to the monomer (c) was 1 / 0.8.
The result of the preparation of Comparative Example 6 was changed, and the composition of the vinyl monomer (c) in Example 1 was changed to obtain the polymer (C).
The results obtained by lowering the glass transition point of Comparative Example 7 are shown in Table 3 as Comparative Example 7.

[0045]

[Table 3]

Example 8 A separable flask similar to that used in Example 1 was charged with 250 parts of the above core particle emulsion 1 and 990 parts of water, and the temperature was raised to 75 ° C. with nitrogen substitution while stirring. Inner temperature is 80
Kept at ℃, ammonium persulfate 0.3 as a polymerization initiator
After adding and dissolving, 60 parts of water, 0.5 part of sodium lauryl sulfate, 57 parts of methyl methacrylate, 3 parts of butyl acrylate, 40 parts of methacrylic acid and 30 parts of heptane were previously dissolved.
The emulsion prepared by adding the above parts under stirring is continuously added over 4 hours for reaction, and aging is carried out for 2 hours after the completion of the addition. Then, in advance, 250 parts of water, 1.0 part of sodium lauryl sulfate, 400 parts of methyl methacrylate, and 75 parts of styrene.
Parts, 20 parts of methacrylic acid, and 5 parts of 2-hydroxyethyl methacrylate were added under stirring to continuously prepare 4 emulsions.
The mixture is added over a period of time to cause reaction, and aging is carried out for 2 hours after the addition is completed. The obtained emulsion had a non-volatile content of 30%, a particle diameter D of 0.60 μ, and a core particle diameter φ within the particles of 0.
It was 19μ and the diameter d of the void layer was 0.51 micron.
The calculated glass transition point and refractive index of the polymer (C) are the same as in Example 1.

Examples 9 to 11 The results prepared by changing the type and amount of the aliphatic hydrocarbon added in Example 8 are the results obtained in Examples 9 and 10 and Example 1 after polymerizing the polymer (B). Heptane 40
Part (amount of monomer (b) added; 100 parts) was added to the flask, and after stirring for 2 hours, monomer (c) was added to prepare the same method. -4.

[0048]

[Table 4]

(Preparation of cored multilayer structure emulsion particles [2]) Example 12 A separable flask similar to that used in Example 1 was charged with 500 parts of the emulsion prepared in Example 1 and 175 parts of water.
The temperature is raised to 75 ° C. while substituting with nitrogen while stirring. Internal temperature 8
Keeping at 0 ° C., ammonium persulfate as a polymerization initiator 1.
After 5 parts were added and dissolved, 150 parts of water, 1.2 parts of sodium lauryl sulfate and 291 parts of styrene and 9 parts of 2-hydroxyethyl methacrylate were added with stirring to prepare an emulsion, which was continuously applied for 3 hours. Then, the reaction is carried out, and aging is carried out for 2 hours after the completion of the addition. The obtained emulsion had a non-volatile content of 40%, a particle diameter D of 0.86 μ, a core particle diameter φ of the particles of 0.19 μ, and a void layer diameter d of 0.54 μm.

Examples 13 to 16 The results prepared in Example 12 by changing the amount of the monomer (d) to be added, the composition and the type of emulsion charged initially are shown in Table 5 as Examples 13 to 16. Show.

[0051]

[Table 5]

[0052]

EFFECT OF THE INVENTION Due to its novel form, it has very excellent performance as an additive for coating compositions, paper coating compositions and heat-sensitive recording materials. The cored multi-layered emulsion particles having a void layer in the outer layer can be easily produced by the present invention.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the internal structure of cored multilayer emulsion particles of the present invention.

[Explanation of symbols]

D: Particle diameter d: Diameter of internal void layer φ: Diameter of core particles

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08L 33/26 LJV 7242-4J 35/00 LHR 7242-4J 35/02 LJB 7242-4J C09D 7 / 12 PSM 7211-4J D21H 19/20 (72) Inventor So Yanagihara 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (14)

[Claims] 1. 50 to 99% by weight of an aromatic vinyl monomer, 1 to 10% by weight of a crosslinkable vinyl monomer having two or more polymerizable vinyl groups in the molecule, and (meth) acrylamide. , N-methylol (meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, acrylic acid, methacrylic acid, crotonic acid, fumaric acid, itaconic acid, maleic anhydride, maleic acid monoalkyl ester, fumaric acid Monoalkyl ester, sodium styrene sulfonate, sodium 2 acrylamide 2-methylpropane sulfonate, 2 hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, glycerol (meth) acrylate, vinylpyrrolid The refractive index obtained by emulsion polymerization of the vinyl monomer (a) containing 0.1 to 9% by weight of one or more hydrophilic vinyl monomers selected from the group
0 or more of the polymer (A) is used as a core particle, and then the vinyl monomer (b) containing 20 to 80% by weight of the above hydrophilic vinyl monomer is added by weight to the vinyl monomer (a). The vinyl monomer (c) containing 1 to 9% by weight of the hydrophilic vinyl monomer is further added by 1 to 10 times and polymerized to form the polymer (B) in the outer layer portion thereof. Vinyl monomer (b)
A polymer (C) having a glass transition point of 50 ° C. or higher, which is added and polymerized in an amount of 2 to 10 times by weight with respect to
Is further formed on the outer layer portion thereof, or the vinyl monomer (d) is added to the vinyl monomer (c) in a weight ratio of 0.
It is added and polymerized so that the refractive index is 1.5 to 7 times.
A structure in which 0 or more polymers (D) are formed in the outermost layer part, and the particle structure when dried is composed of a core particle and an outer layer part, and has a void layer between the outer layer part and the core particle. Is D, the core particle diameter is φ, and the void layer diameter is d. D = 0.3 to 5.0 μ φ / D = 0.1 to 0.6 (where d> φ) d / D = 0.2 A method for producing cored multi-layered emulsion particles having a modified refractive index layer satisfying the requirement of 0.8 to 0.8. 2. Carbon during the polymerization of vinyl monomer (b) and / or vinyl monomer (c), or after formation of polymer (B), addition of vinyl monomer (c) and polymerization. Number 6 ~
The method for producing cored multilayer emulsion particles according to claim 1, wherein 12 aliphatic hydrocarbon compounds are added. 3. The cored multilayer according to claim 2, wherein the aliphatic hydrocarbon compound is cyclohexane, octane, isooctane, or heptane, and the amount is 0.1 to 1 times the weight of the monomer (b). Method for producing structured emulsion particles. 4. The method for producing cored multilayer emulsion particles according to claim 2, wherein the polymer (A) has a refractive index of 1.55 or more. 5. The method for producing cored multilayer emulsion particles according to claim 1, wherein the glass transition point of the polymer (A) is 50 ° C. or higher. 6. The method for producing cored multilayer emulsion particles according to claim 1, wherein the core particles made of the polymer (A) have a particle size of 0.1 to 1.0 μm. 7. The method for producing cored multilayer emulsion particles according to claim 1, wherein the aromatic vinyl monomer contained in the vinyl monomer (a) is styrene. 8. The method for producing cored multi-layer emulsion particles according to claim 1, wherein the crosslinkable monomer contained in the vinyl monomer (a) is divinylbenzene. 9. The cored multilayer according to claim 1, wherein the vinyl monomer (b) contains 0 to 5% by weight of an aromatic vinyl compound and a (meth) acrylic acid ester whose alkyl group has 4 or more carbon atoms. Method for producing structured emulsion particles. 10. The hydrophilic vinyl monomer contained in the vinyl monomer (b) is methacrylamide, methacrylic acid, 2
1 selected from hydroxyethyl methacrylate
The method for producing cored multilayer structured emulsion particles according to claim 1, which are one kind or a combination of two or more kinds. 11. When the polymer (C) is the outermost layer,
The method for producing cored multilayer emulsion particles according to claim 1, wherein the refractive index is 1.50 or more. 12. When the polymer (D) is the outermost layer,
The method for producing cored multilayer emulsion particles according to claim 1, wherein the polymer (C) has a refractive index lower than that of each of the polymer (A) and the polymer (D). 13. The method for producing cored multilayer emulsion particles according to claim 12, wherein the vinyl monomer (c) contains methyl methacrylate. 14. The method for producing cored multilayer emulsion particles according to claim 1, wherein the vinyl monomer (d) constituting the polymer (D) contains an aromatic vinyl monomer.