JP3035423B2 - Method for producing multilayer emulsion particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing multilayer emulsion particles having through-holes inside the particles, which are useful as additives for coating agents used for paints, paper coatings, information recording papers and the like.

[0002]

2. Description of the Related Art In recent years, various kinds of polymer fine particles prepared by emulsion polymerization have been studied as organic pigments. The most commonly used particles have a particle size of 0.2 to
It is a uniform solid type emulsion-polymerized polystyrene particle having a particle size of 0.5 μm, and is used for paper covering or paint. However, these emulsion particles have sufficient hiding power,
Since whiteness and gloss cannot be obtained and practical advantages cannot be recognized unless used in a large amount, problems such as high cost and weight increase are caused. In recent years, for the purpose of further improving whiteness, hiding properties and gloss, conversion of the above uniform, dense type particles to emulsion particles having small pores has been proposed, and when used as an organic pigment, Even if not sufficient, it has been recognized that the concealing property and the whiteness are improved as compared with the uniform and dense type. In addition, water is present in the minute voids inside the particles, and when the particles are dried, the moisture in the voids evaporates and becomes hollow, but since the moisture has to pass through the wall of the particles, the water is volatilized. Things are difficult.
Also, as the size of the voids increases, the absolute amount of water in the voids increases, resulting in poor drying properties. In addition, when the above particles are used as an organic pigment in paper coating, the ink receptivity is low. No significant improvement is observed in terms of printability such as ink setting property and blister suitability. Japanese Patent Application Laid-Open No. 63-281886 discloses an example in which the above-described particles having minute voids are introduced into the undercoat of thermosensitive recording paper to enhance the heat insulating property and to improve the coloring sensitivity. The thermosensitive recording paper produced by this method has improved coloring sensitivity compared to inorganic pigments and organic urea resins, but does not improve head scum adhesion or sticking.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the object of the present invention is to satisfy physical properties such as improvement of color sensitivity due to heat insulating property and oil absorption, particularly when introduced as a heat-sensitive recording material in a primer of thermosensitive recording paper. An object of the present invention is to provide a method for producing emulsion particles having a multilayer structure, which has excellent properties and has one or more through-holes connecting the surface layer portion to the inside of the particle when dried.

[0004]

As a result of intensive studies to solve the above-mentioned problems, the dried structure has at least one through-hole connecting the surface to the inside of the particle, and the particle diameter is not more than 0.1.
The emulsion particles having a multilayer structure characterized by having a particle size of 15 to 5.0 μm are found to have more excellent oil absorbency,
The present invention has been completed.

That is, according to the present invention, the unsaturated carboxylic acid
In the presence of particles comprising the polymer (A) obtained by emulsion polymerization of a vinyl monomer (a) containing 80% by weight, the vinyl monomer weighs 0.2 to 10 times the weight of the polymer (A) (B)
Is added in an amount of 0.1% of the weight of the polymer (A) per hour.
The polymer (A) is neutralized by treating the multilayered emulsion particles obtained by forming the polymer (B) by adding so that the amount becomes less than 1 to 3 times with a basic substance, After swelling and neutralizing, a vinyl monomer (c) is added in an amount of 1 to 20 times the weight of the total weight of the polymer (A) and the polymer (B), and emulsion polymerization is performed. The structure obtained by forming (C) is characterized in that the structure at the time of drying has one or more through-holes connecting the surface to the inside of the particles, and the particle diameter is 0.15 to 5.0 μm. The present invention also provides a method for producing multilayer emulsion particles.

First, the monomer composition of the polymer constituting each layer of the multilayer emulsion particles of the present invention and the like will be described. In the present invention, a polymer (A) obtained by emulsion polymerization of a vinyl monomer (a) containing an unsaturated carboxylic acid
Are (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate and butyl (meth) acrylate as vinyl monomers (a); styrene, α
-Aromatic vinyl compounds such as methylstyrene and vinyltoluene; vinyl cyanide compounds such as (meth) acrylonitrile; vinyl halide compounds such as vinyl chloride and vinylidene chloride; and one or a combination of two or more such as butadiene. , As an unsaturated carboxylic acid, (meth)
Monobasic or dibasic acids such as acrylic acid, crotonic acid, fumaric acid and itaconic acid; maleic acid alkyl esters,
One or more kinds of dibasic acid monoesters such as alkyl fumarate, and particularly preferably acrylic acid;
Methacrylic acid is used. The amount of the unsaturated carboxylic acid used is preferably 5 parts per 100 parts by weight of the vinyl monomer (a).
It is copolymerized so as to be 80 to 80 parts by weight, more preferably 10 to 50 parts by weight. When the amount of the unsaturated carboxylic acid in the polymer (A) is 5 parts by weight or less, the polymer (A) does not sufficiently swell when treated with a basic substance, and no through-hole is formed. When the amount is more than 80 parts by weight, polymerization stability is impaired, and a large amount of aggregates are generated, so that a stable emulsion cannot be obtained.

In the method for producing the polymer (A), in order to stabilize the emulsion of the polymer (A), an unsaturated sulfonate such as sodium styrenesulfonate; and an unsaturated sulfonate such as dimethylaminoethyl methacrylate are used. Saturated bases; (meth) acrylates such as 2-hydroxymethyl (meth) acrylate and glycidyl (meth) acrylate; or (meth) acrylamide;
A functional monomer such as N-methylol (meth) acrylamide is used as needed. Further, a crosslinkable monomer can be used as a component constituting the polymer (A). The crosslinkable monomer may be any as long as it can be copolymerized with the monomer constituting the polymer (A), and specifically, divinylbenzene, ethylene glycol di (meth) acrylate And a monomer having two or more polymerizable unsaturated bonds in one molecule, such as trimethylolpropane trimethacrylate. The amount of the crosslinkable monomer to be used can be in the range of 0 to 8% by weight, preferably 0.1 to 5% by weight, more preferably, to the monomer constituting the polymer (A). Ranges from 0.2 to 1% by weight.

The use of the crosslinkable monomer increases the molecular weight of the polymer (A) and suppresses the diffusion of the polymer (B) forming the outer layer portion into the inside of the particles. This is advantageous in forming the coalesced (B) in the outer layer of the particles, and also advantageous in suppressing the elution of the polymer (A) into the aqueous phase during the treatment with the basic substance and the accompanying thickening phenomenon. become. However, the amount of the crosslinkable monomer used is 8% by weight.
When the above is satisfied, swelling in the alkali treatment of the polymer (A) with a basic substance is suppressed or inhibited, and thus particles having a desired shape cannot be obtained.

Next, a vinyl monomer (b) is added to the particles comprising the polymer (A) and emulsion polymerization is carried out to form a polymer (B) in the outer layer of the particles (A). Examples of the vinyl monomer (b) used here include (meth)
(Meth) acrylates such as methyl acrylate, ethyl (meth) acrylate and butyl (meth) acrylate; aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene; vinyls such as (meth) acrylonitrile A cyanide compound; a vinyl halide compound such as vinyl chloride and vinylidene chloride; and one or more kinds such as butadiene are used in combination. Also, for imparting stability to the emulsion during production, unsaturated sulfonates such as sodium styrenesulfonate; (meth) acrylates such as 2-hydroxymethyl (meth) acrylate and glycidyl (meth) acrylate; Alternatively, a functional monomer such as (meth) acrylamide or N-methylol (meth) acrylamide may be used as necessary. As described above, in order to impart stability to the emulsion, the vinyl monomer (b) may contain an unsaturated carboxylic acid such as (meth) acrylic acid, crotonic acid, fumaric acid, and itaconic acid. However, it is less than the proportion of unsaturated carboxylic acid in the vinyl monomer (a), and is preferably 0.1% by weight or more and 2% by weight or less. here,
When the proportion of the unsaturated carboxylic acid in the vinyl monomer (a) is larger than the proportion of the unsaturated carboxylic acid in the vinyl monomer (a), the swellability of the polymer (B) is increased, and the polymer has a target through-hole. No particles are obtained.

The vinyl monomer (b) can be copolymerized with the vinyl monomer (b) for the purpose of improving the blocking resistance, heat resistance, solvent resistance and the like of the target particles. Crosslinkable monomers can also be used. Examples of usable crosslinkable monomers include monomers having two or more polymerizable unsaturated bonds in one molecule, such as divinylbenzene, ethylene glycol di (meth) acrylate, and trimethylolpropane trimethacrylate. The effect of adding the crosslinkable monomer is usually in the range of 0 to 3% by weight, preferably 0.1 to 3% by weight, more preferably 0.2 to 2% by weight based on the vinyl monomer, If it is used in an amount of 3% by weight or more, polymerization stability may be impaired, which is not preferable. Combinations of the above-mentioned monomers can be freely selected, but it is preferable to select monomers so that the glass transition temperature of the polymer (B) is 50 ° C. or higher, preferably 70 ° C. or higher. The above-mentioned multilayer emulsion particles are produced by a usual emulsion polymerization method.

In the present invention, the polymer (B) is formed in the outer layer portion of the core particles composed of the polymer (A), and then treated with a basic substance described later, or further during the treatment. By adding the vinyl monomer (c) and performing emulsion polymerization, a polymer (C) is further formed in the outer layer portion of the particles. Examples of the vinyl monomer (c) used herein include aromatic vinyl compounds such as styrene, α-methylstyrene, and vinyl toluene; methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylic. (Meth) such as butyl acid
Acrylic esters; vinyl cyanide compounds such as (meth) acrylonitrile; vinyl halide compounds such as vinyl chloride and vinylidene chloride; and one or a combination of two or more such as butadiene.

In addition, when the vinyl monomer (c) is added and emulsion polymerization is carried out, unsaturated carboxylic acids such as (meth) acrylic acid, crotonic acid, fumaric acid, itaconic acid and the like are added to impart stability to the emulsion. Unsaturated sulfonic acid salts such as sodium styrenesulfonate; (meth) acrylic esters such as 2-hydroxymethyl (meth) acrylate and glycidyl (meth) acrylate; or (meth) acrylamide, N-methylol (meth) acrylamide Functional monomers such as are used as needed. At this time, the functional monomer to be added can be usually used in an amount of 0 to 20% by weight based on the vinyl monomer (b). Preferably 0.1 wt% to 10 wt%, more preferably 0.1 wt%
-5% by weight. Here, the functional monomer is 20
If it is used in an amount of not less than% by weight, secondary particles are likely to be formed, and the water resistance is reduced and the viscosity in the treatment of a basic substance is increased, which is not practical. In addition, the above vinyl monomer (c)
Of these, the unsaturated carboxylic acids are preferably 3% by weight or less or the proportion in the vinyl monomer (b) or less, and when 3% by weight or more is used, they tend to aggregate. Further, as the vinyl monomer (c), a crosslinkable monomer copolymerizable with the vinyl monomer (c) may be used, if necessary. Examples of usable crosslinkable monomers include monomers having two or more polymerizable unsaturated bonds in one molecule, such as divinylbenzene, ethylene glycol di (meth) acrylate, and trimethylolpropane trimethacrylate. At this time, the crosslinking monomer to be added is usually in the range of 0 to 3% by weight, preferably 0.1 to 3% by weight, more preferably 0.2 to 2% by weight based on the vinyl monomer. is there.

The use of a crosslinkable monomer improves blocking resistance, heat resistance, solvent resistance and the like.
The swelling of the polymer (A) is inhibited. When the content is less than 0.1% by weight, the effect of adding the crosslinkable monomer is poor. The combination of the above-mentioned monomers is free, but the glass transition temperature of the polymer (C) is 50 ° C. or higher, preferably 70 ° C.
° C or higher.

Next, a method for forming each layer of the multilayer emulsion particles will be described. The method for forming each layer is generally performed by ordinary emulsion polymerization, in which case, a surfactant and
A polymerization initiator is used. Examples of the surfactant include anionic surfactants such as sodium alkylbenzene sulfonate, sodium alkyl sulfate, sodium dialkyl sulfosuccinate, and condensate of naphthalenesulfonic acid, polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, and ethylene oxide-propylene. Nonionic surfactants such as oxide block copolymers and sorbitan fatty acid esters are used alone or in combination. The amount of the surfactant used is not particularly limited, but is usually 0.1 to 1 with respect to the total monomer amount.
It is about 0% by weight. Any polymerization initiator may be used as long as it is used in ordinary emulsion polymerization.Examples include potassium persulfate, sodium persulfate, persulfates such as ammonium persulfate, and organic peroxides such as benzoyl hydroperoxide. And azo compounds such as azobisisobutyronitrile. If necessary, a redox initiator can be used in combination with a reducing agent.

Next, a method of forming each layer will be described step by step. In order to prepare an emulsion comprising the polymer (A), polymerization is carried out by dropping the monomer (a) at once, dividedly, or continuously in the presence of the surfactant and the polymerization initiator. The polymerization is carried out at 20 DEG to 90 DEG C. under a nitrogen purge. In emulsion polymerization, for the purpose of providing a polymerization field for particles, a method of adding a vinyl monomer of interest in the presence of seed particles is known as a `` seed polymerization method ''. The same method is also possible. The composition of the seed particles is not particularly limited, but the particle diameter is preferably 0.3 μm or less so as not to affect the performance of the finally obtained particles. The particles of the polymer (A) thus produced have a particle size of 0.1.
08 to 2μ, more preferably 0.1 to 2μ.
~ 0.3μ. Here, if the particle size is less than 0.08 μm, the polymer (B) described later is generated inside the particles, and the particles having the intended through-holes cannot be obtained. On the other hand, if it exceeds 2 μm, the polymerization stability is insufficient and secondary particles and aggregates are generated in large quantities, which is not practical. Polymerization is carried out by a method in which the vinyl monomer (b) is subsequently added to the emulsion composed of the polymer (A) in a lump, dividedly or continuously. Alternatively, as another step, an emulsion composed of the polymer (A) may be prepared in advance, this emulsion may be newly charged in a polymerization tank, and the vinyl monomer (b) may be added as described above to carry out polymerization. . That is, the production process of the polymer (A) and the polymer (B) may be performed successively in one step, may be performed in a separate step, or may be performed in a combined step, and there is no particular limitation. . At this time, the weight of the vinyl monomer (b) to be added is 0.2 to 10 times, preferably 1.5 to 5 times, the weight of the polymer (A) , and more preferably 1 to 5. .5-5
And more preferably 2 to 4 times. The amount of the vinyl monomer (b) added per hour is 0.1 to less than 3 times the weight of the polymer (A), preferably 0.2 to 2.5 times. Preferably, the amount is 0.3 to 2 times.

If the amount of the vinyl monomer (b) added per hour is less than three times the weight of the polymer (A), polymerization occurs near the surface layer of the particles composed of the polymer (A). In this case, the particles are not completely covered with the polymer (B), and particles having the intended through-holes can be obtained. However,
The added weight of the vinyl monomer (b) per hour is 0.1.
If it is less than 1 time, the polymer (B) of particles composed of the polymer (A)
The particles having the intended through-holes cannot be obtained due to the incomplete coverage of the particles. On the other hand, if the weight of the vinyl monomer (b) exceeds 10 times, the particles are completely covered with the polymer (B), so that particles having the intended through-holes cannot be obtained. The polymerization at this time uses the persulfate exemplified above, and preferably has a polymerization temperature of 60 to 100.
C., more preferably at 70 to 90C. here,
When the polymerization temperature exceeds 100 ° C., a treatment such as pressurization is required, which is not practical. On the other hand, when the temperature is lower than 60 ° C., the conversion of the vinyl monomer (b) during the polymerization becomes low, so that an emulsion cannot be obtained stably. When a persulfate and an appropriate reducing agent are combined, polymerization can be carried out at a high conversion rate even at around 30 to 50 ° C., but the desired particles having through-holes cannot be obtained. This is presumed to be because the formation of the polymer (B) is carried out near the surface layer of the particles composed of the polymer (A). By treating the emulsion particles obtained as described above with a basic substance, the intended structure at the time of drying has one or more through-holes connecting the surface layer portion to the inside,
And a particle diameter of 0.15 to 5.0 μm, preferably 0.1
Multilayer emulsion particles in the range of 〜1.2 μ are obtained.

In the present invention, after treatment with a basic substance, a vinyl monomer (c) is further added to the polymer (C).
Thus the polymerization of the outermost layer portion made of, has a through hole connecting the internal structure of the dry <br/>燥時of interest from the surface of the particle 1 or more, and the particle diameter 0.15 Multilayer emulsion particles having a size of 5.0μ, preferably in the range of 0.1 to 1.2μ, are obtained. In this case, the weight of the vinyl monomer (c) is 1 to the sum of the weights of the polymers (A) and (B).
It is necessary to be 20 times, preferably 1.5 to 15 times, more preferably 2 to 10 times. Vinyl monomer (c)
Is 20 times or more the sum of the weights of the polymers (A) and (B), the polymer (C) completely covers the polymer (B), It does not occur and the desired particles cannot be obtained.

The treatment of the emulsion particles obtained by forming the polymer (B) with a basic substance is carried out as follows. Examples of the basic substance include inorganic basic substances such as potassium hydroxide and sodium hydroxide; volatile basic substances such as ammonia; and organic basic substances such as dimethylethanolamine and triethylamine. The pH in the treatment of the basic substance is in the range of 7 to 12, preferably 8 to 11. If it is less than 7, swelling becomes difficult and the desired particles cannot be obtained. On the other hand, if it is 12 or more, the stability of the emulsion at the time of processing is greatly impaired, and the processing itself cannot be performed smoothly.

The temperature during the treatment ranges from 50 to 100 ° C., preferably from 70 to 98 ° C., more preferably from 80 to 95 ° C. If the temperature is lower than 50 ° C., sufficient plasticization of the outer layer does not take place, so that sufficient swelling does not take place, and the desired particles having through-holes cannot be obtained. As described above, the structure at the time of drying has one or more through-holes connecting the surface layer portion to the inside of the particle,
And a particle diameter of 0.15 to 5.0 μm, preferably 0.1
Multilayer emulsion particles in the range of 〜1.2 μ are obtained.

The reason for the shape development of the multilayer emulsion particles of the present invention is not clear. However, when the vinyl monomer (b) is polymerized under the above conditions, the polymer (B)
It is considered that the polymer (A) is partially exposed from the inside of the particle to the particle surface without completely covering the polymer (A). For this reason, when the particles are treated with a basic substance, the polymer (A) swells to form through-holes inside the particles, and at the same time, the vinyl monomer (c) is formed on the surface of the polymer (B). It is considered that a polymer (C) is formed by polymerization, and particles having a desired shape can be obtained by leaving the through holes as they are. The structure of the particle can be easily confirmed by observing the particle itself and further, a cross section of the particle with an electron microscope. The diameter of the emulsion particles obtained in the present invention is 0.15 to 5.0 µ , preferably 0.15 to 1.2 µ , more preferably 0.3 to 5.0 µ.
1.0 μ. If the outer diameter of the particles is less than 0.15 μm , even if the inside of the particles has the above-mentioned structure, the organic pigment cannot be used because the hiding property and whiteness are particularly low. or,
Particles having an outer diameter exceeding 5.0 μm cannot be produced stably.

The particles of the present invention have the same or higher hiding power and whiteness as emulsion particles having a hollow structure with a single pore,
In addition, it has excellent oil absorption and gas permeability. The reason for this is not clear, but one or more, usually having up to several through-holes, greatly increases the porosity due to the small holes in the particles, and at the same time, the presence of the through-holes is more excellent. It seems to have oil absorption and gas permeability. For this reason, when the multilayer emulsion particles of the present invention are used in a coating composition, a paper coating composition, or a heat-sensitive recording material, they have more concealing properties and whiteness than the conventional production method particles. It is possible to improve the oil absorbency and gas permeability in addition, and it is possible to partially or entirely replace the pigments such as titanium dioxide, clay and kaolin which are usually added in the above composition, In addition, special functions such as oil absorption and gas permeability can be provided.

[0022]

(Production of multilayer emulsion particles)

Example 1 2500 parts of water was charged into a separable flask equipped with a stirrer, thermometer and reflux condenser, and the temperature was raised to 80 ° C. while replacing with nitrogen for stirring. The internal temperature was maintained at 80 ° C., and 1.5 parts of potassium persulfate was added as a polymerization initiator. After dissolution, 16 parts of styrene and 0.3 part of methacrylic acid were previously added to 7 parts of water and 0.2 part of sodium lauryl sulfate. An emulsion prepared by adding 0.2 parts of divinylbenzene with stirring was charged into a separable flask and polymerized for 1 hour to produce a seed particle emulsion. At this stage, a small amount of the seed particle emulsion was sampled, and the particle diameter of the particle was measured by a dynamic light scattering method to be 0.06 μm. Subsequently, an emulsion prepared by previously adding 55 parts of methyl methacrylate, 5 parts of butyl acrylate, and 40 parts of methacrylic acid as a vinyl monomer (a) to 40 parts of water and 0.3 part of sodium lauryl sulfate under stirring was used. It is added continuously over 1 hour and allowed to react,
After completion of the addition, aging is performed for one hour to obtain a polymer (A).
The particle diameter of the particles composed of the polymer (A) was 0.12 μm (dynamic light scattering method). Subsequently, an aqueous solution obtained by dissolving 1.5 parts of ammonium persulfate in 15 parts of water was added as a polymerization initiator, and 160 parts of water and 0.8 parts of sodium lauryl sulfate were added to methyl methacrylate 312 as a vinyl monomer (b) in advance.
Part, 80 parts of butyl acrylate and 8 parts of methacrylic acid were added under stirring, and the emulsion was continuously added over 2 hours to react. After completion of the addition, aging was performed for 2 hours,
The polymer (B) is obtained on the polymer (A). After completion of the polymerization, 625 parts of the above emulsion (solid content: 100%) was placed in another separable flask equipped with a stirrer, thermometer, and reflux condenser.
Parts) and 279 parts of water, and 7 parts of 28% aqueous ammonia are added with stirring. The pH of the emulsion at this time was 10.0. Next, the internal temperature is raised to 85 ° C., and stirring is continued for 30 minutes to perform treatment with a basic substance. Subsequently, an aqueous solution obtained by dissolving 0.5 part of ammonium persulfate in 5 parts of water was added as a polymerization initiator, and 297 parts of styrene as a vinyl monomer (c) were added to 120 parts of water and 0.6 part of sodium lauryl sulfate in advance. An emulsion prepared by adding 3 parts of acrylonitrile under stirring was continuously added over 90 minutes to react, and after completion of the addition, aging was further performed for 90 minutes to obtain a polymer on the polymer (B). (C) is formed. The obtained emulsion was a particle having a non-volatile content of about 30% and a through hole having a diameter of 0.47 μm.

Example 2 Table 1 shows Example 2 in which the amount and rate of addition of the vinyl monomer (b) were changed. Comparative Examples 1 and 2 Tables 1 and 2 show Comparative Examples 1 and 2 prepared in Example 1 by changing the amount and rate of addition of the vinyl monomer (b). Incidentally, regarding the particles produced in the above,
The oil absorption was measured according to JIS K-5101. The sample powder used was obtained by drying the emulsion at 50 ° C. for 24 hours, pulverizing the emulsion with a mortar, and filtering with a # 150 mesh filter cloth. The results are shown in Table 1.

[0024]

[Table 1]

[Examples of Thermosensitive Recording Material] Examples of thermosensitive recording paper in which paper is used as a base material and the multilayer structure emulsion particles of the present invention are introduced into an intermediate layer are shown below. 1) Preparation of Undercoat Compound Using the emulsions of Example 1 and Comparative Examples 1 and 2 ,
The undercoating compound was prepared by mixing sufficiently the mixture of the emulsion particles (80 parts by weight) and the binder (20 parts by weight), and then mixing the resulting mixture. Kuraray polyvinyl alcohol K117 was used as a binder. 2) Preparation of heat-sensitive recording layer compound A liquid (coloring agent dispersion) and liquid B (color developing agent dispersion) each having the following composition are separately dispersed in a sand mill to prepare a compound. Solution A 3-dimethylamino-6-methyl-7-anilinofluoran 20 parts by weight 20% aqueous solution of hydroxyethyl cellulose 5 parts by weight Water 75 parts by weight Liquid B Bisphenol A 20 parts by weight 20% aqueous solution of hydroxyethyl cellulose 5 parts by weight Petrolite R -50 (microcrystalline wax, manufactured by Hariko Co.) 5 parts by weight Water 70 parts by weight After fully dispersed in a sand mill, 15 parts by weight of liquid A, B
40 parts by weight of liquid, 20 parts by weight of calcium carbonate, 20% aqueous solution of polyvinyl alcohol (K-117, manufactured by Kuraray) 2
Five parts by weight were sufficiently stirred and mixed to obtain a thermosensitive coloring layer composition. 3) Coating on base material The above-mentioned undercoat composition was applied to a commercially available high-quality paper (basis weight: about 50 g / m ² ) using a bar coater so that the coating amount was 15 g / m ^2, and dried. Then, after drying the heat-sensitive recording layer composition, it was coated with a bar coater so that the coating amount was 15 g / m ^2, and dried to obtain a heat-sensitive recording paper. JIS for whiteness of paper
It measured with the Hunter white clock according to P-8123. The color is developed by a thermal printing device (THK, manufactured by Okura Electric Co., Ltd.).
-PMD) under the following conditions, and the density was measured using a Macbeth densitometer. An applied voltage of 24 V, a pulse width of 1.74 ms, an applied energy of 0.34 mJ / dot, and the printing color is developed under the following conditions. The adhesion of the residue was evaluated as 適, ○, Δ, ×, XX as printability. Table 2 shows these results.

[0026]

[Table 2]

[0027]

According to the production method of the present invention, particles having a higher porosity can be obtained from the multilayer emulsion particles having through-holes than those obtained by the conventional production method. For this reason, for example, when used in a thermosensitive recording material, the color development sensitivity is improved because higher heat insulating properties are imparted, and it is possible to further improve the printing characteristics because of having higher oil absorbency, It is useful as a high-performance thermal recording material.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08F 2/22-2/30 C08F 2/44

Claims (1)

(57) [Claims] 1. A method for preparing a polymer (A) in the presence of particles comprising a polymer (A) obtained by emulsion polymerization of a vinyl monomer (a) containing 5 to 80% by weight of an unsaturated carboxylic acid. .2
The addition amount of the vinyl monomer (b) at 10 times the weight per hour is less than 0.1 to 3 times the weight of the polymer (A).
It added to the polymer so that the amount of multi-layer structure emulsion particles obtained by forming a (B), neutralized polymer (A) by treating with a basic substance, to swell, for neutralization Thereafter, the vinyl monomer (c) is added in an amount of 1 to 20 times the weight of the total weight of the polymer (A) and the polymer (B), and emulsion polymerization is performed to obtain a polymer (C). ), Wherein the dried structure has one or more through-holes connecting the surface to the interior of the particles, and has a particle diameter of 0.15 to 5.0 μ. A method for producing structural emulsion particles.