JP3217417B2 - Hollow emulsion particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vinyl compound having two large and small peaks in a particle size distribution, comprising a group of hollow particles having voids inside the particles when dried and a group of particles smaller than the group.
It relates to particles obtained by emulsion polymerization of monomers (hereinafter, sometimes referred to as emulsion particles ) , and more specifically, general coated paper, paperboard, lightweight coated paper, ultralight coated paper, At the time of drying useful as a pigment for paper coating paint used for art paper and cast coated paper, paint used for wood, outer wall, inner wall, etc., and coating agent used for thermosensitive recording paper such as facsimile paper and thermal label The present invention relates to emulsion particles comprising a group of hollow particles having voids inside the particles and a group of particles smaller than the group, and having two peaks, large and small, in the particle size distribution.

[0002]

2. Description of the Related Art Various studies have been made on hard emulsion particles as additives for coating agents for the purpose of reducing the weight of a coating film and improving gloss, whiteness, opacity and the like.
In the above applications, the amount of use as a “plastic pigment”, particularly as an alternative pigment to inorganic pigments such as kaolin, calcium carbonate, talc, and satin in the field of paper coating, tends to increase industrially.

Heretofore, those generally used as plastic pigments are generally reviewed (for example, Soichi Muroi, “Application of Polymer Latex, Paper Coating”, Polymer Publishing Association (19).
86), p83, Setsuzo Tezuka, Coating time signal, N
o. 166, p13 (1985), etc.), the emulsion particles were made of polystyrene having a uniform particle size of about 0.5 μm. The particle size of the above emulsion particles is reported by B. Alince et al. (J. Colloi
d and Interface Sci., 76 , 182 (1980)). However, in the above emulsion particles,
It has been difficult to meet the requirements of high gloss, opacity, whiteness, and light weight, and furthermore, the heat insulating properties of the heat-sensitive recording material. JP-A-59-59741 discloses a plastic pigment whose particle size distribution is narrow and 90% or more falls within the range of 0.20 to 0.28 µ. However, such a plastic pigment is not practical, although glossiness is slightly improved, but particularly, whiteness and opacity are reduced. As particles that solve such problems, emulsion particles having voids inside the particles during drying, so-called “hollow particles”, have attracted attention.

[0004] As a method for producing the hollow particles, for example, an alkali swelling method (Japanese Patent Publication No. 3-9124,
704, JP-A-64-48805, JP-A-1-185311, etc.), solvent addition method (JP-A-61-86941, JP-A-63-135409, JP-A-1-301730) Various methods such as a volume shrinkage method (Japanese Patent Application Laid-Open No. 62-127336) and a phase separation method (Japanese Patent Application Laid-Open No. 61-62510) can be exemplified.

[0005] Although the hollow particles obtained as described above have different performances depending on the production method, they have higher gloss, opacity, and whiteness than conventional so-called "solid particles" without voids. , Weight reduction, and further improvement in heat insulation are recognized. However, the hollow particles have a serious problem and have not been widely used. First, the first problem is that the viscosity under a high shearing force is remarkably increased in a coating material to which hollow particles are added. For this reason, especially in the field of paper coating in which high-speed coating has been performed in recent years, the coating workability of the above-mentioned coating material has deteriorated, and in many cases, coating cannot be performed.

[0006] The second problem is that, in the emulsion state, since the hollow particles contain water or an organic solvent inside, the volume concentration of the hollow particles is not much different from the conventional solid particles. However, the weight solids concentration is lower than that of conventional solid particles. For example, a commercially available dense particle having a weight concentration of 4
While it is about 8%, the hollow particles depend on the porosity, but are all less than that. For this,
There is a problem that the water content of the paint increases and its drying property decreases. Furthermore, in most cases, the cost is calculated not in terms of the emulsion itself but in terms of its dry weight, and in Japanese business practice, the reduction in the weight solids leads to an increase in cost, and the advantages of hollow particles cannot be used. Has also become.

[0007] The above problems can be improved by reducing the volume of water or organic solvent present inside the hollow particles, that is, reducing the porosity inside the particles during drying.
This means that the weight reduction, gloss,
The opacity, the whiteness, and the heat insulation will be reduced, and the advantage over the solid particles will be lost. The present inventors have found that a cored multilayer structure particle having a different refractive index layer, such as having a core particle inside the particle and having a void layer in an outer layer portion of the core particle, is different from the above-mentioned “hollow particle”. ,
They have found that they are even better than conventional hollow particles in various aspects such as not only opacity and whiteness but also dryness (Japanese Patent Application No. 3-26678). It was not fully resolved.

[0008]

SUMMARY OF THE INVENTION The present invention relates to paper coating paints and woods used for general coated paper, paperboard, lightweight coated paper, ultralight coated paper, art paper, cast coated paper, and the like. Excellent in gloss, opacity, and whiteness as a pigment for coating materials used for paints used on exterior and interior walls, as well as thermal recording paper such as facsimile paper and thermal labels.
It is still another object of the present invention to provide practical emulsion particles excellent in coating workability and drying property.

[0009]

As a result of intensive studies to solve the above problems, the present inventors have paid attention to the fact that emulsion particles used as conventional plastic pigments have a uniform particle size. . This fact is based on the aforementioned B.Al
As described in the report of ince et al., it is thought to be based on the experimental fact that the light scattering ability is reduced in a mixed system of particles having different particle diameters. Even in the above-mentioned hollow particles for which various production methods have been reported, the idea of making the particle diameter uniform is alive, and can be easily inferred from the description and the examples. In the case of the cored multilayer emulsion particles of the prior application of the present inventors, the production method was similarly adjusted so that the particle diameter became uniform. It is a well-known fact that in a dispersion system such as emulsion particles, when the particle size is made uniform, the viscosity increases, and a high concentration cannot be obtained. In particular, hollow particles containing water or an organic solvent inside the particles are known. In this case, the increase in viscosity becomes remarkable.

In view of the above points, the concept of the conventional uniform particle size was reviewed, and it was found that an emulsion system in which small particles were mixed in a hollow particle emulsion having a uniform particle size, surprisingly showed a gloss of the hollow particles. Without reducing the opacity, etc., on the contrary, found that the viscosity under the above high shear force is significantly reduced, further study,
The present invention has been completed. That is, the present invention includes a first
Particles consisting of a particle group and a smaller second particle group
Emulsions with two peaks in size distribution
And the first group of particles are voids inside the particles during drying.
Having a particle diameter D of the first particle group.
0.3 to 5.0 μm, the particle diameter D ′ of the second particle group is 0.
05 to 0.3 μm, and D ′ <D / 2.
The present invention relates to emulsion particles. Ma
In addition, the present invention relates to a first group of particles and a second group of smaller particles.
Two large and small peaks in the particle size distribution
Emulsion particles, wherein said first and second
All particles have voids inside the particles when dried
Emulsion particles comprising hollow particles
It's about the child. By taking such a configuration,
Gloss, opacity, whiteness, and further weight reduction without compromising the advantages of hollow particles such as thermal insulation, it is possible to improve the mentioned problems before such coating workability and drying property.

Regarding the production of emulsion particles having two peaks, large and small, characteristic of the present invention, the following methods can be exemplified. That is, (1) In the conventional method for producing hollow particles, particles having a small particle diameter are generated as secondary particles in the middle of the polymerization. (2) In the conventional method for producing hollow particles, emulsion particles prepared in advance are added in the middle of the polymerization to produce particles having a small particle diameter. (3) In the conventional method for producing hollow particles, emulsion particles prepared in advance after the polymerization is added,
Introduce small particles.

In addition to the methods exemplified above, there is no particular limitation as long as the method can obtain a target particle size distribution having two peaks, large and small. The method (1) for generating particles having a small particle diameter as secondary particles during the polymerization is specifically described as follows. (1) -1. Disrupt the balance between the rate of addition of the vinyl monomer and its polymerization rate so that the rate of addition is much higher than the rate of polymerization, and polymerize the vinyl monomer remaining in the aqueous phase to produce secondary particles. Let it. (2) -2. By reducing the number of particles in the system, that is, by reducing the number or area of polymerization sites of vinyl monomers to be added and polymerized later, new particle nuclei composed of the vinyl monomers are generated, and Generate particles. (1) -3. In the middle of the polymerization, a surfactant is added alone or in excess simultaneously with the vinyl monomer for emulsifying the vinyl monomer, thereby generating new particle nuclei and generating small particles.

[0013] As described above, emulsion particles having two large and small peaks in the particle size distribution, which are composed of a group of hollow particles having voids inside the particles during drying and a group of particles smaller than that, are known hollow emulsion particles. It is produced by appropriately preparing the production method of Regarding the shape of hollow particles,
Although there is no particular limitation, the prior application of the present inventors (Japanese Patent Application No.
26678) having a core particle inside the particle and a cored multilayer structure having a void layer in an outer layer portion of the core particle.

The small particles coexisting with the hollow particle group may be hollow particles, solid particles, or both. Here, as for each particle diameter, the diameter D of the hollow particles is usually 0.3 to 5.0 μm, preferably 0.3 to 3.0 μm.
m, more preferably 0.4 to 1.5 μm,
On the other hand, the diameter D ' of a small particle is usually 0.05 to 0.
3 μm, preferably 0.08 to 0.25 μm, always satisfying D ′ <D, and preferably satisfying D ′ <D / 2.

The emulsion particles of the present invention obtained as described above, comprising hollow particles having voids inside the particles at the time of drying and particles smaller than the particles, having two peaks in the particle size distribution, The object of the present invention is to solve the above-mentioned problems of the conventional hollow particles, and it can be used in various applications, particularly as a plastic pigment. In particular, when the composition is used for a coating composition for paper coating, only a very small amount of small particles is present, and the suitability for high-speed coating is very good. Furthermore, by mixing small particles, an emulsion having a high concentration can be prepared, and the drying property and cost can be improved without impairing the conventional gloss, opacity, whiteness, and the like.

Next, a paper coating containing emulsion particles having two peaks in the particle size distribution, consisting of a hollow particle group having voids inside the particles at the time of drying according to the present invention and a smaller particle group. The coating composition for use is described below. The paper coating composition of the present invention comprises the above-mentioned emulsion particles as a binder, an inorganic pigment and a plastic pigment, and further contains a dispersant, an antifoaming agent, a release agent, a viscosity modifier, and a bluing agent, if necessary. Etc. can be added. Examples of the binder include water-dispersible binders such as styrene-butadiene-based synthetic resin latex, acrylic-based synthetic resin emulsion, acryl-styrene-based synthetic resin emulsion, and vinyl acetate-based synthetic resin emulsion; starch, modified starch, casein, and polyvinyl alcohol. Examples thereof include a water-soluble binder. These binders may be used alone or in combination of two or more. In particular, it is preferable to use a styrene-butadiene-based synthetic resin latex alone or to use starch and casein in combination. Here, the amount of the binder to be used is 4 to 40% by weight, preferably 6 to 40% by weight, based on the total pigment including the inorganic pigment and the plastic pigment composed of the emulsion particles.
20% by weight. When the amount of the binder used is less than 4% by weight, a coating layer having practical strength cannot be obtained. If it exceeds 40% by weight, the desired gloss, opacity and whiteness cannot be obtained. Examples of the inorganic pigment include kaolin, calcium carbonate, talc, satin white, and titanium dioxide.

The amount of the above-mentioned emulsion particles is not particularly limited as long as it is contained in an amount of 1% by weight or more in all the pigments, but is preferably 2 to 70% by weight, more preferably 3 to 30% by weight. It is. If the amount of the emulsion particles is less than 1% by weight, the effect of the addition is not recognized. When blending the binder, the inorganic pigment, and the emulsion particles, the pH is adjusted to 7 or more with a basic substance to stabilize the system. Examples of the basic substance to be used include sodium hydroxide and water. Inorganic basic substances such as potassium oxide are preferred in view of the viscosity of the paint. The paper coating composition containing the plastic pigment of the present invention is coated on paper or paperboard, the coating is a blade coater, a roll coater, a gate roll coater,
It can be performed by a usual method such as an air knife coater and a bar coater.

The emulsion particles of the present invention obtained as described above, which consist of a hollow particle group having voids inside the particles at the time of drying and a particle group smaller than that, have two peaks in the particle size distribution. The coating composition for paper coating contained is excellent in gloss, opacity, whiteness, and furthermore, the conventional hollowness such as a decrease in suitability for high-speed coating due to an increase in viscosity under high shearing force, an increase in moisture in the coating, etc. It has the feature that the problem that particles had was solved.
The composition can be used for general coated paper, paperboard, lightweight coated paper, ultralight coated paper, art paper, super art paper, cast paper and the like.

[0019]

EXAMPLES The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples. In addition, all the following parts and% show a weight part and weight%. Here, the shape and diameter of the prepared emulsion particles, the diameter of the void layer or voids, etc. were all directly measured by a transmission electron microscope.

[I] Preparation of Emulsion Particles Particle Example 1 365 parts of water is charged into a separable flask equipped with a stirrer, a thermometer and a reflux condenser, and the temperature is raised to 70 ° C. while purging with nitrogen while stirring. The internal temperature was maintained at 70 ° C., and 0.4 parts of potassium persulfate was added as a polymerization initiator. After dissolution, 98 parts of styrene and 2 parts of 2 parts of 2-hydroxyethyl methacrylate were previously dissolved in 40 parts of water and 0.05 part of sodium lauryl sulfate. And a vinyl monomer (a) consisting of 5 parts of divinylbenzene was added with stirring, and 5% of the total amount of the previously prepared emulsion was charged into a separable flask, polymerized for 30 minutes, and the remaining emulsion was added. The product was added over about 2 hours and allowed to react. After completion of the addition, aging was performed for about 2 hours to prepare a core particle emulsion having a particle diameter φ of 0.18 μm and a nonvolatile content of about 20%. Next, 137.3 parts of the above-mentioned core particle emulsion and 959 parts of water are charged into a similar separable flask, and the temperature is raised to 78 ° C. while purging with nitrogen while stirring. The internal temperature was maintained at 78 ° C., and 0.1 part of ammonium persulfate was added as a polymerization initiator. After dissolution, 9.6 parts of water and 0.1 part of sodium lauryl sulfate were added in advance.
12.4 parts of methyl methacrylate and 4 parts of methacrylic acid.
One part of the vinyl monomer (b) was added with stirring, and a previously prepared emulsion was continuously added over 30 minutes to react. After completion of the addition, aging was performed for 2 hours. Subsequently, 0.9 parts of ammonium persulfate was added again and dissolved, and vinyl containing 72 parts of water, 0.6 part of sodium lauryl sulfate, 140 parts of methyl methacrylate, 31.5 parts of styrene, and 3.5 parts of methacrylic acid was previously added. The emulsion prepared by adding the monomer (c) under stirring was continuously added over 2 hours to react, and aging was performed for 2 hours after completion of the addition.

After the polymerization, the internal temperature is raised to 90 ° C.
13.9 parts of 8% aqueous ammonia was added under stirring to adjust the pH to 1;
As 0.2, the stirring was continued for 10 minutes. Subsequently, while maintaining the internal temperature at 90 ° C., 4.4 parts of ammonium persulfate were added again, and after dissolution, 870 parts of styrene and acrylamide 9 were added to 360 parts of water and 3.6 parts of sodium lauryl sulfate in advance.
Part of the vinyl monomer (d) was added under stirring, and the emulsion was continuously added and reacted over 2 hours. After completion of the addition, aging was performed for 2 hours. The obtained emulsion particles have a particle diameter D: 0.68 μm and a void layer diameter d:
The cored multilayer emulsion particles having a core particle diameter of 0.50 μ and a core particle diameter φ of 0.18 μ were added to a particle diameter D ′: 0.2 μ and a void diameter of 0.1 μm.
1 μm hollow particles were mixed.

Particle Example 2 In the particle example 1, the addition time of the vinyl monomer (b) was set to 3 hours.
8μ styrene solid particle emulsion (solid content 40%)
Was added and then polymerized in the same manner as in Particle Example 1 except that 28% aqueous ammonia was added. The obtained emulsion particles were obtained by adding cored multilayer structure emulsion particles having a particle diameter D: 0.67 μm, a void layer diameter d: 0.50 μm, and a core particle diameter φ: 0.18 μm to a particle diameter D ′: 0.15 μm. It was a mixture of dense solid particles.

Particle Example 3 In the particle example 2, the charged water was changed from 959 parts to 680 parts, and the amount of the styrene dense solid particle emulsion having a particle diameter of 0.08 μm added after the polymerization of the vinyl monomer (c) was completed. Polymerization was carried out in the same manner as in Particle Example 2, except that the amount was changed to 50 parts. The obtained emulsion was 46.8%, and the particle diameter D ′ was added to a cored multilayer structure emulsion particle having a particle diameter D: 0.66 μm, a void layer diameter d: 0.48 μm, and a core particle diameter φ: 0.18 μm. : Fine particles of 0.21 μ were mixed.

Particle Example 4 Polymerization was carried out as in Particle Example 1 except that the addition time of the vinyl monomer (b) was 3 hours, and the obtained cored multilayer emulsion particles (particle diameter D: 0.69 μm, void layer diameter d) : 0.50
μ, core particle diameter φ: 0.18 μ, solid content 42%) and 100 parts of a styrene dense solid particle emulsion (solid content 45%) having a particle diameter of 0.08 μ are mixed with 100 parts to obtain the emulsion particles of Particle Example 4. Obtained.

Particle Example 5 In a separable flask similar to Particle Example 1, 350 parts of water,
1.5 parts of sodium hydrogen carbonate is charged, and the temperature is raised to 70 ° C. while purging with nitrogen while stirring. The internal temperature was kept at 70 ° C., 3.0 parts of potassium persulfate was added as a polymerization initiator, and after dissolution, 60 parts of vinyl acetate, 80 parts of butyl acrylate were added to 150 parts of water and 0.1 part of sodium lauryl sulfate in advance. An emulsion prepared by adding 52 parts of methyl methacrylate, 4 parts of acrylic acid, and 4 parts of acrylamide under stirring was added continuously over 3 hours to react, and after the addition was completed, aging was performed for 1 hour. Was. Subsequently, 300 parts of water, 5 parts of sodium lauryl sulfate, 250 parts of styrene, 125 parts of butyl methacrylate, 15 parts of acrylic acid, and 10 parts of acrylamide were added under stirring to prepare an emulsion continuously. The reaction was carried out by adding over time, and aging was performed for 2 hours after completion of the addition. After the completion of the polymerization, 41.7% of a 20% aqueous sodium hydroxide solution was added to the obtained emulsion with stirring to raise the pH of the emulsion to 10.5, then the temperature was raised to 95 ° C., and the mixture was stirred for 4 hours. Continued. 100 parts of hollow emulsion particles having a particle diameter D of 0.91 μm, a particle inner diameter of 0.62 μm, and a solid content of 42% obtained as described above were separately prepared with a 0.2 μm-diameter solid styrene particle emulsion having a particle diameter of 0.2 μm ( (50% solid content) and mixed with 50 parts.
4.7% of the emulsion particles of Example 5 were obtained. Comparative particle example 1 In the particle example 1, the addition time of the vinyl monomer (b) was 3
Except for the time, the particle diameter D obtained by carrying out the polymerization in the same manner: 0.69 μm, the void layer diameter d: 0.
Cored multilayer emulsion particles having a particle size of 50 μm and a core particle diameter φ of 0.18 μm were taken as Comparative Particle Example 1. Comparative Particle Example 2 In Comparative Example 5, the case where the styrene non-solid particle emulsion was not added was referred to as Comparative Particle Example 2. Comparative Particle Example 3 In Particle Example 3, the same polymerization was carried out without adding the styrene resin solid particle emulsion. .

[II] Simplified Evaluation of Drying and Hiding Power of Emulsion Particles For the emulsions obtained in Particle Example 3 and Comparative Particle Example 1, an acrylic synthetic resin emulsion (Almatex E-175 manufactured by Mitsui Toatsu Chemicals, Inc.) As a binder,
The obtained emulsion particles were blended so that the weight ratio of the particles to the binder was 3/7 and the solid content was 40%, and applied on a glass plate using an applicator bar so that the dry coating film became 20 μm. The drying process was visually determined under an environment of 20 ° C. and 60% humidity. Judgment was made as follows: The extent to which the No. 4 newspaper type 1 cm behind was visible through the coated glass plate was evaluated as follows.
It was evaluated on a scale.

：: Best (printing is not visible) ○: Good (printing is slightly visible) Δ: Normal (printing is visible) ×: Poor (printing is visible) The results are shown in Table 1.

[0028]

[Table 1]

[III] Preparation of paint composition for paper coating The obtained emulsion particles were used as a plastic pigment for paper coating, and the performance was evaluated by the following model compounding. [Formulation] Dry weight ──────────────────────────────────── Kaolin clay (manufactured by EMC; UW-90) 63 parts Light calcium carbonate (manufactured by Okutama Kogyo; TP-222HS) 27 parts Emulsion particles 10 parts Dispersant (manufactured by Toa Gosei Chemical; Aron T-40) 0.09 parts Phosphated starch (manufactured by Nippon Shokuhin Kogyo; MS) -4600) 3 parts SBR latex (Mitsui Toatsu Chemical; Polylac 755) 13 parts塗料 Paint solid content 62% The paint is prepared by adding Aron T-40 with a solid content of 40% to water, dispersing UW-90 sufficiently with a Cowles mixer, After adding calcium carbonate slurry and dispersing well, -4600, emulsion particles was done with the addition of SBR latex.
The pH of the paint was adjusted to pH 9 with sodium hydroxide.

The obtained coating was measured for high shear viscosity at 8800 rpm with a Hercules rheometer, and at the same time, the coating was dried with an applicator to a dry coating amount of 1%.
5 g / m ² on high quality paper, 120 ° C,
After drying under drying conditions for 20 seconds, paper was passed through a calender roll twice at a roll temperature of 60 ° C., a linear pressure of 70 kg / cm, and a speed of 10 m / min to obtain a coated paper. The following evaluation was performed about the obtained coated paper.・ Hisha viscosity Measured with a Hercules rheometer (8800 rpm).・ White paper gloss 75 ° according to JIS P-8142
Measured reflectance at.・ Print Gloss Toyo Ink New Bright Indigo 0.4
Printed by RI printing tester using cc. After drying, JIS
75 ° reflectance was measured according to P-8142. -Whiteness Measured with a Hunter whiteness meter according to JIS P-8123. -Opacity Measured according to JIS P-8138. Table 2 shows the results.

[0031]

[Table 2]

[0032]

Emulsion particles according to the present invention are characterized by having two peaks, large and small, in the particle size distribution, consisting of hollow particles having voids inside the particles during drying and particles smaller than the particles. Not only excellent in gloss, opacity and whiteness, but also its drying property, weight solids concentration, and when it is contained in a coating composition for paper coating, its viscosity under high shearing force is low, Excellent workability. Such characteristics cannot be obtained with the conventional hollow emulsion particles having a uniform particle diameter.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kosuke Someya 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside of Mitsui Toatsu Chemicals Co., Ltd. (56) References JP-A-2-140272 (JP, A) JP-A-51-125147 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 2/22-2/30

Claims (5)

(57) [Claims] 1. A particle obtained by emulsion polymerization of a vinyl monomer having two large and small peaks in a particle size distribution composed of a first particle group and a second particle group smaller than the first particle group. The first group of particles comprises hollow particles having voids inside the particles when dried, and the particle diameter D of the first group of particles is 0.3 to
5.0 μm, the particle diameter D ′ of the second particle group is 0.05 to 0.5.
A 3 [mu] m, bi, wherein D '<it is D / 2
Particles obtained by emulsion polymerization of a phenyl monomer . 2. The vinyl monomer according to claim 1, wherein each of the first and second particle groups consists of hollow particles having voids inside the particles when dried.
Particles obtained by polymerization . 3. Particles obtained by emulsion polymerization of a vinyl monomer having two large and small peaks in a particle diameter distribution composed of a first particle group and a second particle group smaller than the first particle group. The particles obtained by emulsion polymerization of a vinyl monomer , wherein each of the first and second particle groups comprises hollow particles having voids inside the particles when dried. 4. The particles obtained by emulsion-polymerizing a vinyl monomer according to claim 1, wherein the hollow particles of the first particle group have a cored multilayer structure. 5. A vinyl monomer according to claim 1,
A paper coating composition comprising particles obtained by emulsion polymerization of a monomer .