JPH03279493A - Pigment coating composition - Google Patents

Abstract

PURPOSE:To obtain the title composition providing a substrate with excellent opacity, containing hollow polymer particles having shell comprising a polymer with a high glass transition temperature as pigment. CONSTITUTION:The object composition containing hollow polymer particles having shell comprising a polymer with >=100 deg.C high glass transition temperature as pigment. The hollow polymer particles are obtained by swelling carboxy modified polymer particles having >=100 deg.C glass transition temperature with a base in the presence of an organic solvent and successively treating the particles with an acid.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pigment coating composition, and more particularly to a pigment coating composition capable of imparting excellent opacity to a substrate.

(Prior Art) It is well known that a pigment coating composition is applied to a substrate such as paper to improve the optical properties of the substrate such as opacity, whiteness, and gloss. Pigment-coated paper such as paper, lightweight coated paper, lightly coated paper, and pigment-coated paperboard such as coated white ball and coated Manila are produced and used in large quantities.

In these coated papers and coated paperboards, the pigment coating composition used for the purpose of improving the above-mentioned optical properties of the base material generally contains a white pigment and an adhesive as main components, but The improvement in properties relies primarily on the white pigment.

Inorganic pigments such as clay, calcium carbonate, titanium white, aluminum hydroxide, and satin white are mainly used as white pigments, but in recent years, inorganic pigments have been used that have a smaller specific gravity than inorganic pigments and are effective in reducing the weight of raw materials and coating materials. Research and development is underway on organic pigments made of polymers such as polystyrene, polymethyl methacrylate, and urea resin.

Among organic polymer pigments, hollow pigments that have a hollow space inside the polymer particle can be made even more lightweight. Pigment-coated paper using this as a pigment component is effective in improving opacity by increasing the refraction of
Pigment-coated paperboard, paints for buildings, equipment, etc. have been put into practical use.

By the way, several methods are known for producing hollow polymer particles for use in coating compositions, but hollow polymer particles produced by these methods are not always suitable in some respects. It's not satisfying.

For example, the method disclosed in JP-A No. 56-32513 involves copolymerizing at least one type of unsaturated carboxylic acid to create core particles, and then producing ethylenic unsaturated particles with a composition different from that of the core particles. Cover polymerization is performed using a monomer mixture to form a particle surface layer (shell), and the resulting particles are neutralized and swollen with a volatile base such as ammonia to obtain hollow polymer particles. It is. In this method, the process is complicated because the polymerization must be carried out in two stages to obtain different polymer compositions in the core and shell.

Furthermore, in this method, it is important to cover-polymerize the ethylenically unsaturated monomer only to the surface layer of the core particle;
It is difficult to control the amount of surfactant, etc., and in many cases there is a problem that new particles are generated or unsaturated carboxylic acid in the core particles migrates to the surface of the final particles.

JP-A No. 61-87734 discloses that after producing capsule-shaped polymer particles containing a monomer component including a wood-philic monomer and a crosslinking monomer and an oily substance therein, hollow particles are formed by removing the oily substance from the capsule-shaped polymer particles. A method of manufacturing particles is described. However, with this method, particles with a partially depressed outer shell may be produced, and hollow particles cannot be obtained unless the oily substance and polymer are completely sealed inside the polymer particles, resulting in porous particles. Therefore, it is necessary to use a large amount of crosslinking monomer, and also a large amount of hydrophilic monomer.
There are many restrictions on the monomers that can be used.

There is also a method of swelling polymer particles with a base in the absence of an organic solvent to obtain hollow polymer particles having at least one cavity (Japanese Unexamined Patent Publication No. 1.56387/1987). Since the glass transition temperature of the products obtained by this method is low, the opacity improvement effect will be diminished if the pigment coating composition is applied to the base material and then subjected to a heating drying process or a heating calendering process. There was a problem.

[Problems to be Solved by the Invention] An object of the present invention is to provide a pigment coating composition whose opacity improvement effect does not deteriorate even after a heat treatment step.

As a result of intensive research to achieve this problem, the inventors of the present invention found that
The inventors have discovered that a pigment coating composition with excellent opacity can be obtained by using specific hollow polymer particles, and have completed the present invention based on this knowledge.

[Means for Solving the Problems] According to the present invention, there is provided a pigment coating composition containing as a pigment hollow polymer particles having a shell made of a polymer having a glass transition temperature of 100° C. or higher. provided.

The hollow polymer particles used in the present invention must have a shell made of a polymer having a glass transition temperature of 100°C or higher, and when the glass transition temperature is less than 100°C, pigment coating with excellent opacity can be applied. Unable to obtain composition. this is,
This is considered to be because the hollow particle structure is destroyed to some extent by the heat treatment.

Further, the hollow polymer particles may be those having one or more hollows, but the larger the number of hollows, the more excellent the pigment coating composition that provides a coated product with excellent optical properties. be able to. Although the reason for this is not clear, it is thought that the more hollows there are in the hollow polymer particles, the more times light passes through the polymer-air interface.

Hollow polymer particles that can be used in the present invention can be heated to 100°C.
It is not limited by the composition or polymerization method as long as the shell is made of a polymer having a glass transition temperature of 100°C or higher, but as a preferable example, carboxy-modified copolymer particles having a glass transition temperature of 100°C or higher are used. Hollow polymer particles having at least one hollow ψ obtained by swelling with a base in the presence of an organic solvent and subsequent acid treatment can be mentioned. Hereinafter, the hollow polymer particles (hereinafter simply referred to as multi-hollow polymer particles) obtained by this method will be explained.

The carboxy-modified copolymer used in the synthesis of the multi-hollow polymer particles may be any copolymer of any monomer composition, as long as it contains a carboxyl group and has a glass transition temperature of 100°C. May be combined. The method of obtaining a polymer containing a carboxyl group is not particularly limited, and examples thereof include a method of copolymerizing a monomer containing a carboxyl group,
A method of introducing a carboxyl group into a copolymer by a known polymer reaction can be shown, but a method using copolymerization is advantageous in terms of production.

Carboxyl group-containing monomers that can be used here include:
Ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid; Ethylenically unsaturated dicarboxylic acids and their monoesters such as itaconic acid, fumaric acid, and maleic acid; and ethylenic acids such as butene tricarboxylic acid. Examples include unsaturated tricarboxylic acids and mono- or diesters thereof, and these carboxyl group-containing monomers may be used alone or in combination of two or more.
The amount of the carboxyl group-containing monomer used is not limited, but is preferably 0.1 to 100 parts by weight of the total monomer mixture.
The amount is preferably 40 parts by weight, more preferably 0.5 to 20 parts by weight. If the amount of the carboxyl group-containing monomer is less than 0.1 parts by weight, it becomes difficult to introduce hollow spaces into the copolymer. On the other hand, if the amount exceeds 401i, a large amount of coagulated material will be generated when the copolymer is obtained by polymerization.

For the synthesis of multihollow polymer particles, one or more monomers copolymerizable with the carboxyl group-containing monomer are used. This monomer is not particularly limited, and specific examples include aromatic vinyl monomers such as styrene, α-methylstyrene, P-methylstyrene, and halogenated styrene; unsaturated nitriles such as (meth)acrylonitrile. ; Methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)
Acrylate.

(Meth)acrylic acid esters such as lauryl (meth)acrylate, glycidyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate: (meth)acrylamide, tomethylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, etc. (Meth)acrylic acid amide and its derivatives: Conjugated diene monomers such as butadiene and isoprene; Carboxylic acid vinyl esters such as vinyl acetate: Vinylidene halides such as vinyl chloride and vinylidene chloride: Vinylpyridine, etc. can.

Further, in the synthesis of the multihollow polymer particles, a crosslinkable monomer can also be used if necessary. Crosslinking monomers that can be used include divinylbenzene, diallyl phthalate,
Allyl (meth)acrylate, ethylene glycol di(
Examples include, but are not limited to, meth)acrylate, trimethylolpropane trimethacrylate, and trimethylolpropane triacrylate.

Two or more types of these crosslinkable monomers may be used.

The amount of crosslinkable monomer used is less than 20 parts by weight, preferably less than 10 parts by weight, based on 100 parts by weight of the total monomer mixture. If the amount of the crosslinking monomer used exceeds 20 parts by weight, a large amount of coagulation may easily occur when the copolymer is obtained by polymerization, or swelling of the copolymer particles may become difficult to occur, resulting in poor formation of the copolymer. It becomes difficult to introduce hollow spaces.

Multi-hollow polymer particles are usually produced by adding a base to a carboxy-modified copolymer latex that does not have a hollow space (this copolymer latex that does not have a hollow space is sometimes referred to as a filled copolymer latex in the present invention). The carboxyl groups are once neutralized to form a salt, and then the latex p
It is synthesized by making H acidic again.

A latex of a carboxy-modified packed copolymer is usually produced by an emulsion polymerization method, but a latex may be made from a copolymer obtained by another polymerization method by a phase inversion method. In these various polymerization methods, any method such as a batch method, a semi-continuous method, or a continuous method may be adopted. Various additives such as agents, chelating agents, and electrolytes can be used.

Furthermore, there is no limit to the polymerization temperature.

There are no restrictions on the type of base used to neutralize the carboxyl groups in the carboxy-modified packed copolymer; specific examples include alkali metal bases such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. Hydroxide; hydroxide of alkaline earth metals such as calcium hydroxide and magnesium hydroxide; Ammonia; Amine compounds such as dimethylamine and jetanolamine; (bi)carbonate of alkali metals such as sodium carbonate and potassium bicarbonate. Salt; (bi)ammonium carbonate salts such as ammonium carbonate can be shown. The base used must be in an amount sufficient to neutralize at least a portion of the carboxyl groups in the carboxy-modified copolymer, and the pH of the carboxy-modified copolymer latex should preferably be 8 or higher, more preferably 10 or higher. This is the amount.

Further, in order to neutralize the carboxyl groups inside the polymer particles with a base, time is required for the base to diffuse into the latex particles, and it is preferable to thoroughly stir the mixture after adding the base. This time varies depending on the carboxyl group content, but is usually 10 minutes or more. Also, mW of latex! When an organic solvent is added at times, the stirring time may be short.

When a base is added to latex to neutralize carboxyl groups, the stability of the latex may decrease and coagulation may occur. To prevent this, if necessary, it is also possible to add an anionic surfactant or a nonionic surfactant to the latex before adding the base.

The acid used to adjust the pH of the latex of the carboxy-modified polymer whose carboxyl groups are neutralized with a base to 7 or less, preferably 5 or less is not particularly limited, and may be a mineral acid such as hydrochloric acid or sulfuric acid. , or an organic acid such as acetic acid or malonic acid.

The addition of these acids is preferably carried out at a temperature at which the copolymer can become flexible.

After adding the acid, stirring is usually continued for 30 minutes or more to ensure that the acid is sufficiently diffused into the copolymer particles. After this, the latex is cooled if necessary.

Furthermore, if necessary, an anionic surfactant or the like may be added before the addition of the acid in order to prevent the stability of the latex from decreasing when adding the acid.

When treating carboxy-modified copolymer particles with a base or acid as described above, in order to quickly diffuse the base or acid into the interior of the polymer particles, it is desirable that the temperature of the latex at that time is high. For this purpose, a temperature higher than the softening point of the copolymer constituting the latex is desirable.

Furthermore, by incorporating an organic solvent into the carboxy-modified copolymer latex, base or acid diffusion can be carried out at a lower temperature. Hollows can be introduced.

The method of incorporating the organic solvent into the carboxy-modified copolymer latex is not particularly limited, but an example thereof is a method in which the organic solvent is added to the latex after it has been obtained by polymerization.

Alternatively, the latex may contain an organic solvent by polymerizing the monomer mixture in the presence of an organic solvent.

In the above method, if the amount of organic solvent is increased, a lower temperature can be used, and if the organic solvent is added at the time of preparing the latex, the amount of organic solvent may be smaller.

The organic solvent that can be used is not particularly limited,
Any material may be used as long as it sufficiently swells the copolymer particles. Specifically, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as ethylbenzene, xylene, and toluene-benzene; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, and dichloromethane; amyl alcohol,
Alcohols such as butyl alcohol, cyclohexyl alcohol, and benzyl alcohol; Phenols such as cresol; Ethers such as diethyl ether; Ketones such as diisobutyl ketone, methyl isopropyl ketone, methyl ethyl ketone, and cyclohexanone; amyl acetate, butyl acetate, propyl acetate, Examples include saturated carboxylic acid esters such as ethyl propionate. It is also possible to use a mixture of two or more of these organic solvents. In addition, when an organic solvent is present at the time of preparing the carboxy-modified copolymer latex, it is also possible to use a polymerizable organic solvent. Specific examples include aromatic vinyl compounds such as styrene, halogenated styrene, and divinylbenzene; unsaturated nitriles such as acrylonitrile; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl ( Examples include (meth)acrylic esters such as meth)acrylate; conjugated dienes such as butadiene and isoprene.

The amount of these organic solvents is 10% of the carboxy-modified copolymer.
It is necessary that the amount is 0.1 to 1000 parts by weight, preferably 10 to 100 parts by weight.
If the amount is less than 0.1 parts by weight, it will be difficult to introduce hollows into the polymer particles, while if it exceeds 1000 parts by weight, the agglomeration of the polymer particles will be severe.

Next, if necessary, the organic solvent is removed from the copolymer latex by a known method such as vacuum distillation or steam distillation, and then the water is removed by a known method to obtain multihollow polymer particles. I can do it.

In the process of acid treatment in the synthesis of the above multi-hollow polymer particles,
Initially, several small pores exist, but as time passes, single hollow particles are formed. It can be controlled by the distribution state of carboxyl groups, the degree of hydrophilicity of the copolymer particles, the neutralization treatment conditions with a base, the acid treatment conditions, the type of organic solvent used, and the amount of acid.

Hollow polymer particles useful as pigments for coated paper compositions or paints have a hollow diameter of 0.1 to 2 μm, preferably 0.2 to 1 μm.

By blending hollow polymer particles obtained by the above-mentioned method or other methods as a raw material with a binder, the pigment coating composition of the present invention, which provides a coated product with excellent optical properties, can be obtained.

In the pigment coating composition of the present invention, known pigments can be used in combination with the hollow polymer particles.

In this case, the proportion of hollow polymer particles is at least 5% by weight, preferably at least 10% by weight, based on the total pigment. If this amount is less than 5% by weight, the effect of improving opacity cannot be obtained. On the other hand, the higher the ratio, the better the optical properties of the coating, but it is not economical when it is in excess.

Conventionally known pigments include mineral pigments such as clay, calcium carbonate, aluminum hydroxide, titanium white, barium sulfate, satin white, and talc; organic pigments such as polystyrene and phenolic resin;
Kaolinite clay is preferred.

In the pigment coating composition of the present invention, binders include water-soluble polymers such as starch, casein, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, and sodium alginate; styrene/butadiene copolymer, methyl methacrylate/butadiene copolymer; , polyvinyl acetate, synthetic latex such as acrylic acid ester copolymer, etc. can be used. The amount of these binders is not particularly limited, but is usually 2 parts by weight per 100 parts by weight of the pigment.
~30 parts by weight.

The pigment coating composition of the present invention also includes pigment dispersants, viscosity modifiers, water retention agents, water resistance agents, dyes, fluorescent dyes, lubricants, p.
H regulators, antifoaming agents, surfactants, preservatives, etc. can be used as necessary.

[Effects of the Invention] Thus, according to the present invention, a pigment coating composition having higher opacity than conventional organic white pigments can be easily and stably obtained.

[Examples] The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto. In addition,
In the present examples, parts and percentages are based on weight unless otherwise specified, and all latexes and blends are expressed in terms of solid content.

All polymerizations were performed in a nitrogen atmosphere, which is an inert gas, and the weight average particle size was measured using a light scattering method (manufactured by Malvern Co., Ltd.).
ode 19800), and the polymerization conversion rate was determined by a gravimetric method.

Reference Example 1 (Synthesis example of seed latex) 300 parts of ion-exchanged water was placed in a four-hole flask equipped with a stirrer, an M-flow condenser, a thermometer, and a dropping funnel, and 95 parts of styrene and 5 parts of methacrylic acid were added. The mixture was heated while stirring.

After the internal temperature reaches 70°C, add 3% potassium persulfate (KPS).
) 17 parts of the aqueous solution was added from the dropping funnel, and a polymerization reaction was carried out to obtain a latex with a polymerization conversion rate of 99%. The solid content concentration was 24% and the pH was 2.3. Moreover, the weight average particle diameter was 160 parts m. This latex is referred to as seed latex [Sco.

Reference Example 2 (Production example of dense polymer latex) [Al1:
518 parts of ion-exchanged water and 2 parts of seed latex [S] were charged into a reaction vessel similar to that used for producing the seed latex and heated. After the internal temperature reaches 85℃, 3% KPS
Thirty parts of the aqueous solution was added to the flask via a dropping funnel.

Next, after washing the dropping funnel with 20 parts of ion-exchanged water,
A monomer mixture consisting of 88 parts of styrene, 5 parts of methyl methacrylate, 6 parts of acrylic acid, and 1 part of ethylene glycol dimethacrylate was added from the dropping funnel over a period of 8 hours. Thereafter, the temperature was maintained at 85° C. for 2 hours to complete the polymerization reaction. The polymerization conversion rate was 97%. The solid content concentration of the obtained latex [Al1] was 15%. The pH and weight average particle diameter of latex [Al1] are shown in Table 1.

[A2]: In a reaction vessel similar to that used for producing the seed latex, 508 parts of ion-exchanged water and 2 parts of the seed latex [S
] and warmed it up. After the internal temperature reaches 85℃,
Thirty parts of a 3% KPS aqueous solution was added to the flask via a dropping funnel. Next, after washing the dropping funnel with 20 parts of ion-exchanged water, a mixed solution of a monomer mixture consisting of 87 parts of styrene, 5 parts of acrylonitrile, 1 part of methacryl W, and 1 part of divinylbenzene and 10 parts of methyl ethyl ketone was added to the dropping funnel. It was added over a period of 8 hours. Thereafter, the reaction system was maintained at 80° C. for 2 hours to complete the polymerization reaction. Regarding the obtained latex [A2], the polymerization conversion rate, solid content concentration, pH, and weight average particle diameter were measured in the same manner as for [Al1], and the results are shown in Table 1.

[A, 3]: Latex [A3] was obtained in the same manner as in the case of [A2], except that the composition of the monomer mixture was 73 parts of styrene, 20 parts of butyl acrylate, and 7 parts of methacrylic acid, and methyl ethyl ketone was not used. The same measurements as for [A2] were performed. The results are shown in Table 1.

[Left below] Table 1 Reference Example 3 (Production example of hollow polymer particles) [B11: In a reaction vessel similar to that used for producing the seed latex, 870 parts of ion-exchanged water and latex [A1110] were added.
0 parts of sodium dodecylbenzene sulfate aqueous solution, 50 parts of methyl ethyl ketone and 33 parts of 10% sodium hydroxide aqueous solution were added and stirred at 80'C for 3 hours. Next, 300 parts of a 1% aqueous hydrochloric acid solution was added, stirred at 80°C for 3 hours, cooled to room temperature, and then the organic solvent was removed under reduced pressure to determine the pH of the latex and the polymer contained therein. The particle diameter of particle [B11 was measured. Furthermore, when the polymer particles were observed using a transmission electron microscope, one or two small pores were confirmed, and their diameters were measured. Furthermore, the glass transition temperature of the polymer particles after drying was measured. These results are also shown in Table 2.

[B11: Hollow polymer particles [B11 was obtained in the same manner as in the production of B11, except that the acid treatment time was 1 hour. Regarding the particles [B11] Table 2 shows the results of the same measurements as for [B11].

[B11: [In a reaction vessel similar to that used in the production of B11, 870 parts of ion-exchanged water, latex [A21100
1 part of an aqueous solution of sodium dodecylbenzene sulfate, 30 parts of benzene and 44 parts of a 10% aqueous potassium hydroxide solution, and stirred at 80° C. for 3 hours. Next, 400 parts of a 1% sulfuric acid aqueous solution was added, stirred at 80°C for 5 hours, and then cooled to room temperature to form hollow polymer particles [B11
I got it. Table 2 shows the results of the same measurements as for B11 regarding this particle.

[C1] (Comparative example): [508 parts of ion-exchanged water, 1 part of sodium dodecylbenzene sulfate aqueous solution, and latex [A2] were placed in a reaction vessel similar to that used in the production of B11, and 33 parts of 10% potassium hydroxide aqueous solution was added. After stirring for 3 hours at an internal temperature of 80° C., the acid addition step was omitted and cooling was performed to obtain polymer particles [C1]. When this particle was observed using a transmission electron microscope, no small pores were observed in the particle.

[C2 Co (Comparative Example)] An experiment similar to the production of [B1] was conducted except that latex [A3] was used in place of Nilatex [A1] and methyl ethyl ketone was not used. Table 2 shows the measurement results for the obtained particles [C2].

[Example 1 (Preparation of pigment coating composition) Polymer particles [B1 co-[B3 co and [C1 co-[c2
] After adjusting the pH of the latex containing either of the following to 7.5 with sodium hydroxide, a pigment coating composition having a solid content concentration of 60% was prepared according to the formulation shown in Table 3.

[Margins below] (Preparation of raw material coated product) The obtained composition was coated onto the base paper to be coated using a wire bar N0010 so that the coating amount was 20 ± 1 g on one side. Immediately thereafter, it was dried with hot air at 120°C for 20 seconds. Next, after conditioning the humidity by letting it stand overnight under constant temperature conditions of 20°C and 65% relative humidity, 50'C1 linear pressure 100
The coated paper obtained by supercalendering twice under the conditions of kg/cm was measured for optical properties and the like. The results are shown in Table 4.

In addition, each characteristic was measured as follows.

[Opacity Konihunter whiteness meter (manufactured by Murakami Color Research Institute)
Using a green filter (540 nm), the contrast ratio of the amount of reflected light between the standard white plate and the standard black plate was measured.

[Whiteness]: The amount of reflected light was measured using a Hunter whiteness meter (manufactured by Murakami Color Research Institute) using a blue filter (457 nm).

[The reflectance was measured between an incident angle of 75 degrees and a reflection angle of 75 degrees using a gloss meter (manufactured by Murakami Color Research Institute).

[Printing gloss]: Perform solid printing using 0.3 ml of offset ink using an RI tester (Mei Seisakusho), leave it for a day and night under constant temperature conditions of 20"C ~ 60% relative humidity, and then use a gloss meter. (manufactured by Murakami Color Research Institute), the reflectance was measured at an incident angle of 75 degrees and a reflection angle of 75 degrees.

[Dry pick]: By RI tester (Mei Seisakusho),
Overprinting was performed six times using the offset ink, and the degree of paper peeling was evaluated with the naked eye on a 5-point scale (5: excellent → 1: poor).

[Wet pick]: Using an RI tester (Mei Seisakusho), water is applied to coated paper using a Molton roll, and then solid printing is performed using offset ink (high tack).
The degree of paper peeling was evaluated with the naked eye on a 5-point scale (5: excellent → 1: poor).

[Ink transferability]: By RI tester (Mei Seisakusho),
After applying water to the coated paper with a Molton roll, perform solid printing using off-cent printing black ink under conditions that do not cause pinking, and check the ink transfer (ink density) to the limit of 5. Evaluation was made using a point system (5: excellent → 1: poor).

[Margin below] As is clear from the results in Table 4, when the pigment coating composition of the present invention is used, it has extremely high opacity,
Coated paper with excellent optical properties such as white paper gloss and printability such as ink receptivity and printing strength can be obtained, whereas pigment coatings obtained using latex of polymer particles without hollow spaces can be obtained. It can be seen that the coated paper obtained using the coating composition is inferior in these properties.

Claims (1)

[Claims] (1) A pigment coating composition containing, as a pigment, hollow polymer particles having a shell made of a polymer having a glass transition temperature of 100° C. or higher.