JPH0647799B2 - Paper coating latex - Google Patents

Description

TECHNICAL FIELD The present invention relates to a latex for paper coating, and in particular, it is possible to obtain coated paper and coated paperboard having good gloss and print gloss development properties, and is good during production. It relates to a latex for paper coating having excellent workability.

2. Description of the Related Art In recent years, a large amount of pigment-coated paper coated with a paper coating composition comprising a pigment and a binder has been used for publication or packaging. The purpose of applying a pigment to such paper is to improve the aesthetic appearance of the paper and to enhance the printing effect to enhance the commercial value. The properties required of the paper coating composition used to achieve such an object are very many, for example, it gives good whiteness, gloss and print gloss as optical properties, and has printability. It must provide good strength, water resistance, and ink transferability, and is also required to have good workability during the production of coated paper.

Of these properties, the gloss that appeals to the visual sense and ultimately determines the value of the product and the gloss after printing are extremely important, and various attempts have been made so far to obtain a high-gloss coated paper. Came.

For example, the gloss of coated paper is as follows:
The friction that occurs in so-called calendering, and the friction generated by this operation imparts smoothness to the surface of the coated paper, and at the same time, orients the pigment particles. The higher the degree of orientation at this time, the higher the gloss.

Therefore, the easiest way to increase gloss in coated paper is to reduce the amount of binder,
In that case, the strength of the coating layer is lowered, and there is a high possibility of causing serious problems such as stains on the calender roll during finishing or picking during printing.

Some notable examples of this attempt are: This is an attempt to improve the gloss by substituting a part or all of the inorganic pigment with an organic pigment, and one using a polystyrene polymer latex is disclosed in Japanese Examined Patent Publication No.
No. 6-6524. This uses a thermoplastic polymer to make it easy to be calendered. By using this pigment, a coated paper having a considerably high gloss can be obtained as compared with the case where only a conventional inorganic pigment is used.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the technique described in the above-mentioned patent publication, a fine part of the coating layer is taken by the calender roll at the time of finishing compared with other pigments, and this is gradually accumulated, so-called calender roll. Easy to get dirty. When stains occur on the calendar roll, naturally the gloss developability decreases,
In addition, workability is extremely reduced due to the removal of dust. In particular, in the case of coated paperboard, a gloss calender is often used, and the calender temperature is considerably increased to 120 to 150 ° C. to improve the gloss development property in many cases. In this case, the tendency of calender stain becomes stronger. Therefore, when such an organic pigment is used, it is necessary to increase the amount of the binder or increase the proportion of natural binders such as starch and casein which have good stain resistance to calender rolls. However, the increase of the binder tends to reduce the gloss development property, and also increases the cost. This is one of the reasons why the range of use of such organic pigments is limited to special fields despite their good performance. Further, an increase in the proportion of the natural binder also has a strong tendency to reduce the gloss, and the obtained print gloss tends to be reduced, which is not desirable.

The present invention has been made against the background of the above-mentioned conventional technical problems, and the purpose thereof is to obtain a coated paper having good gloss and good print gloss expression, and further, a calendar roll at the time of finishing. The object is to provide a paper coating latex which has good resistance to stains. That is, it is intended to provide a latex for paper coating which exhibits good gloss without causing stains on the calendar roll even when the proportion of the binder is not too large and the proportion of the natural binder used is extremely low.

Means for Solving the Problems That is, the present invention comprises the following copolymer latex (A) and copolymer latex (B), and the solid content weight ratio of (A) / (B) is 10 / The present invention provides a latex for paper coating, which is 90 to 60/40.

[Copolymer latex (A)]

Ethylenically unsaturated carboxylic acid monomer; 0.5 to 8 wt% aliphatic conjugated diolefin; 0 to 20 wt% aromatic vinyl monomer; 40 to 99.5 wt% unsaturated acid amide monomer; 0 to 6% by weight (however, the total amount of unsaturated acid amide monomers constituting the copolymer latex (A) and (B) is 1 to 6% by weight)
Is. ) Other mono-olefin monomers: having a copolymer composition of 0 to 59.5% by weight and a glass transition temperature of 30 to 105.
A copolymer latex having a temperature of ℃ and an average particle size of 0.15 to 0.40 μm.

[Copolymer latex (B)]

 Ethylenically unsaturated carboxylic acid monomer; 0.5 to 8% by weight Aliphatic conjugated diolefin; 25 to 55% by weight Unsaturated acid amide monomer; 0 to 6% by weight Other monoolefin monomer; 31 A copolymer latex having a copolymer composition of ˜74.5% by weight.

Hereinafter, the present invention will be described in detail by dividing it into a copolymer latex (A) and a copolymer latex (B).

[Copolymer latex (A)]

Examples of the ethylenically unsaturated carboxylic acid monomer forming the copolymer latex (A) include acrylic acid, itaconic acid,
Methacrylic acid, fumaric acid, crotonic acid, maleic acid and the like are used alone or in combination, and acrylic acid, itaconic acid and methacrylic acid are particularly preferably used. The ethylenically unsaturated carboxylic acid monomer has a function of increasing the adhesion between the pigments or the pigment and the raw material, and a function of improving the stability of the latex as a colloid. It is 5 to 8% by weight, preferably 1 to 5% by weight. If the proportion of the ethylenically unsaturated carboxylic acid monomer in the copolymer latex (A) is less than 0.5% by weight, it is difficult to obtain the above effect, while 8
If it exceeds 5% by weight, the viscosity of the paper coating composition obtained by mixing it with the copolymer latex (A) itself or a pigment becomes too high, which is unsuitable.

Examples of the aliphatic conjugated diolefin constituting the copolymer latex (A) include butadiene, isoprene and chloroprene, and butadiene is particularly preferably used. The amount of the aliphatic conjugated diolefin has a great influence on the gloss, and the proportion thereof is 20% by weight or less, preferably 10 to 20% by weight. When the proportion of the aliphatic conjugated diolefin in the copolymer latex (A) exceeds 20% by weight, the expression of gloss is hindered, and particularly when the calender conditions are relaxed, the effect becomes remarkable. It is also considered that the amount of the aliphatic conjugated diolefin of the copolymer latex (A) exceeds 20% by weight and the amount of the aliphatic diolefin of the copolymer latex (B) is reduced by that amount. If you can't get good gloss. Further, when the proportion of the aliphatic conjugated diolephe in the copolymer latex (A) is 10 to 20% by weight, it is possible to obtain a coated paper which is particularly advantageous in terms of strength as well as good gloss.

Examples of the aromatic vinyl monomer constituting the copolymer latex (A) include styrene, α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxystyrene and 2-hydroxymethyl. Styrene, 4-ethylstyrene, 4-ethoxystyrene,
3,4-dimethylstyrene, 2-chlorostyrene, 3-
Chlorostyrene, 4-chloro-3-methylstyrene, 4
-Tertiary butyl styrene, 2,4-dichlorostyrene,
2,6-dichlorostyrene, 1-vinylnaphthalene, divinylbenzene and the like are mentioned, and styrene is particularly preferably used. The aromatic vinyl monomer affects gloss, and the ratio thereof is 40 to 99.5% by weight, preferably 55.
84.5% by weight.

When the proportion of the aromatic vinyl monomer in the copolymer latex (A) is less than 40% by weight, the gloss of the coated paper obtained is not sufficient.

As the unsaturated acid amide monomer constituting the copolymer latex (A), acrylamide, methacrylamide,
N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethyl acrylamide, N-
Examples thereof include vinylpyrrolidone, and of these, acrylamide and methacrylamide are preferably used.

The unsaturated acid amide monomer is a component necessary for the present invention in order to increase the resistance of the calendar roll to stains and to improve the strength of the coating layer, and the ratio thereof is in the copolymer latex (A). 6% by weight or less, preferably 4% by weight
In the following, the total amount of unsaturated acid amide monomers constituting the copolymer latex (A) and the latex (B) described later is 1 to 6% by weight, preferably 1.5 to 4% by weight.
If less than 6% by weight, the above-mentioned object cannot be achieved, while if more than 6% by weight, the viscosity of the latex (A) and / or (B) or a coating liquid when mixed with a pigment (paper coating composition) Viscosity becomes too high.

The copolymer latex (A) may contain a monoolefin monomer other than these monomers. Examples of the other monoolefin monomer include methyl acrylate and
Methyl methacrylate, hydroxyethyl acrylate,
Examples thereof include acrylic acid or methacrylic acid ester such as acrylonitrile and methacrylonitrile, or ethylene nitrile, and the ratio thereof is 59.5% by weight.
Below, preferably 30% by weight or less is used. When the proportion of the other monoolefin monomer in the copolymer latex (A) exceeds 59.5% by weight, the strength is lowered and the glossiness is deteriorated.

The copolymer latex (A) has a glass transition temperature of 30 to 105 ° C., preferably 30 to 60 ° C., and an average particle diameter of 0.15 to 0.40 μm, in addition to the above conditions.
It preferably has a narrow particle size distribution in the range of 0.15 to 0.30. When the glass transition temperature is lower than 30 ° C. or the average particle size is smaller than 0.15 μm, glossiness is not good. Further, if the average particle size exceeds 0.40 μm, sufficient adhesive strength cannot be obtained.

Especially when the glass transition temperature is in the range of 30 to 60 ° C,
Alternatively, when the average particle size is in the range of 0.15 to 0.30 μm, strength is advantageous in addition to good gloss.

[Copolymer latex (B)]

The kind, purpose of use and amount of the ethylenically unsaturated carboxylic acid monomer constituting the copolymer latex (B) are the same as those of the copolymer latex (A).

Further, the type of the aliphatic conjugated diolefin constituting the copolymer latex (B) is the same as that of the copolymer latex (A), but the proportion thereof is 25 to 55% by weight, preferably 30 to 50% by weight. If it is less than 25% by weight, good strength cannot be obtained. On the other hand, if it exceeds 55% by weight, good gloss cannot be expected and good strength cannot be obtained. .

Further, the type and amount of the unsaturated acid amide monomer constituting the copolymer latex (B) are the same as those of the copolymer latex (A).

Furthermore, the types of the other monoolefin monomers constituting the copolymer latex (B) are the same as those of the copolymer latex (A).

The present invention comprises the copolymer latexes (A) and (B) as described above, and sufficient adhesive strength and good gloss cannot be obtained by the latex (A) or (B) alone. A / weight ratio of solid content represented by (B) is 10 /
90-60 / 40, preferably 10 / 90-40 / 60
The effect can be exhibited for the first time when it is within the range. When the copolymer latex (A) is less than 10% by weight in terms of solid content, not only sufficient gloss is not obtained, but also the printability such as ink receptivity and printing gloss is deteriorated. If it exceeds the above range, sufficient adhesive strength and water resistant adhesive strength cannot be obtained, and workability such as stains on a calendar roll is extremely deteriorated.

The copolymer used in the present invention can be produced by an emulsion polymerization method.

That is, about 50 to 100 while stirring a mixture of water, a monomer mixture, a chain transfer agent, a polymerization initiator, an emulsifier, etc.
It can be polymerized by heating to ° C. In this case, a monomer mixture or the like can be added continuously or intermittently to carry out the polymerization, and in this case, a good result can be obtained with less formation of coagulation.

Specifically, (1) the copolymer (A) by an emulsion polymerization method,
(B)), and then (A) and (B) are mixed within the scope of the present invention, or (2) first, the copolymer latex (A) is polymerized by emulsion polymerization to obtain a polymerization system. A method in which a monomer constituting the copolymer (B) is added and polymerized in the same polymerization system, or (3) the copolymer latex (B) is first polymerized and the copolymer is added to the polymerization system. A latex (A) monomer may be added and polymerized, and the addition order of (2) may be reversed.

The paper-coating latex of the present invention is usually prepared as an aqueous dispersion together with an inorganic pigment or an organic pigment, preferably an inorganic pigment, and a binder and applied to coated paper.

At this time, 5 to 25 parts by weight, preferably 5 to 5 parts by weight of the latex for paper coating of the present invention, relative to 100 parts by weight of the pigment in terms of solid content.
21 parts by weight, other binders 1 to 5 parts by weight, preferably 1 to 3 parts by weight are used, and the solid content concentration in the aqueous dispersion is
Usually 40 to 70% by weight, preferably 45 to 65% by weight
Prepared to a degree.

Examples of the pigment include kaolin clay, talc, barium sulfate, titanium oxide (rutile anatase), calcium carbonate, aluminum hydroxide, zinc oxide, inorganic pigments such as satin white, and organic pigments such as polystyrene latex. These are used alone or as a mixture.

As the binder, a natural binder such as starch, oxidized starch, soybean protein and casein, or a synthetic binder such as polyvinyl alcohol, polyvinyl acetate latex and acrylic latex is used.

To prepare a paper coating composition from the latex of the present invention, other auxiliary agents such as a dispersant (sodium pyrophosphate, sodium hexametaphosphate, etc.), a defoaming agent (polyglycol, fatty acid ester, phosphate ester,
Silicone oil etc.), leveling agent (funnel oil, dicyandiamide, urea etc.), preservative, water resistance agent (formalin, hexamine, melamine resin, urea resin, glyoxal etc.), mold release agent (calcium stearate, paraffin emulsion etc.), Fluorescent dyes, color water retention improvers (carboxymethyl cellulose, sodium alginate, etc.) are added as necessary.

The method for applying the paper-coating composition using the paper-coating latex of the present invention to a coated paper is carried out by a known technique, for example, an applicator such as an air knife coater, a blade coater, a roll coater or an applicator. After application, the surface is dried and finished by calendering.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples.
The present invention is not limited to these examples as long as the gist thereof is not exceeded.

In the examples, all parts and percentages are by weight. Further, the measurement of various physical properties and the production of coated paper in the examples were based on the following methods.

[Average particle size]

 Particle size is measured by electron microscopy.

[Glass transition temperature (Tg)]

 It is measured by a differential scanning calorimeter.

[Preparation of coated paper]

A paper-coating composition is prepared by blending a paper-coating latex, a pigment, an auxiliary agent and the like as shown in Table 2. In this case, the solid content concentration is adjusted to 60%, the coating base paper (basis weight: 240 g) is coated at 150 ± 0.6 g / m ² with a coating rod, and this is dried at 120 ° C. for 10 seconds. Then 12
Gloss calendering was performed under the conditions of 0 ° C. and 70 kg / cm.

The coated paper produced in this manner was evaluated as follows.

[White luster]

Using a Murakami gloss meter, the angle of incidence is 75 ° and the angle of reflection is 75 °.

[Dry adhesion strength]

3 with IPI # 6 ink using RI printing aptitude tester type II
Printing is repeated, and the degree of picking is observed, and no picking is performed.

[Waterproof adhesive strength]

Using the RI printability tester type I, dampening water with IPI # 5 ink, printing, lining, observing the degree of picking, and evaluating the dry adhesion strength on a scale of 5 points. .

[Ink receptivity]

Using the RI printability tester type I, using Toyo King # 617, applying dampening water, printing, lining, observing the state of ink transfer, and similarly evaluating with a maximum of 5 points. .

[Print gloss] Toyo King Ultra 1 using RI printability tester type II
2 After printing using Beni, measure with a Murakami gloss meter.

[Dirty calendar rolls]

After coating the base paper with the coating liquid and drying it, immediately apply the aluminum foil to the coated surface and pass it through a gloss calendar three times, then peel off the aluminum foil and measure the decrease in gloss. The gloss measurement is preferably such that the decrease in gloss is small, and based on the value of decrease in gloss, relative evaluation is performed on the basis of a maximum of 5 points, as in the above evaluation items.

Examples 1 to 5 and Comparative Examples 1 to 11 (1) Production of Copolymer Latex (A) (Production of Copolymer Latex (a) to (g)) Temperature Control with 100 Nitrogen Stirrer In a possible pressurized reactor 85 parts of water, 2 parts of maleic acid, 1.4 parts of potassium persulfate, 1.7 parts of potassium phosphate, 0.06 part of sodium ethylenediaminetetraacetate, 0.03 part of sodium alkylbenzenesulfonate and n -1.0 parts of dodecyl mercaptan was charged and the temperature was raised with stirring.

On the other hand, 15 parts of butadiene, 70 parts of styrene, and 13 parts of methyl methacrylate are charged into a monomer preparation tank, and an aqueous solution of 0.45 parts of sodium alkylbenzenesulfonate dissolved in 45 parts of water is charged into an emulsifier aqueous solution tank. Was sent to an emulsifying apparatus and continuously emulsified to prepare an emulsified monomer.

While maintaining the temperature in the reactor at 70 ° C., the emulsified monomer was continuously introduced into the reactor, and the introduction was completed in 10 hours. The polymerization rate reached 99% after a reaction time of 13 hours. A 5% aqueous potassium hydroxide solution was added to the obtained latex to adjust the pH to 6.0, the residual monomer was removed by steam distillation, and the mixture was further heated under reduced pressure to a solid content concentration of 5
The content was adjusted to 0% to obtain a copolymer latex (a).

Other copolymer latexes (b) to (g) were also synthesized by the same method.

(2) Production of Copolymer Latex (B) (Production of Copolymer Latex (i) to (v)) 85 parts of water in a temperature-adjustable pressure reactor equipped with 100 nitrogen-stirred stirrer, 2.5 parts of itaconic acid, 0.93 parts of potassium persulfate, 0.7 parts of potassium phosphate, 0.06 parts of sodium ethylenediaminetetraacetate, 0.06 parts of sodium alkylbenzenesulfonate and 0.5 parts of n-dodecyl mercaptan are charged. The temperature was increased with stirring.

On the other hand, 37 parts of butadiene, 40.5 parts of styrene and 20 parts of methyl methacrylate are placed in a monomer preparation tank, and 0.45 parts of sodium alkylbenzene sulfonate is added to 4 parts of water.
Charge 5 parts of the aqueous solution into an emulsifier aqueous solution tank,
Both were sent to an emulsification device by a metering pump and continuously emulsified to prepare an emulsified monomer.

While maintaining the temperature in the reactor at 70 ° C., the emulsified monomer was continuously introduced into the reactor, and the introduction was completed in 10 hours. The polymerization rate reached 99% after a reaction time of 13 hours. A 5% aqueous potassium hydroxide solution was added to the obtained latex to adjust the pH to 6.0, the residual monomer was removed by steam distillation, and the mixture was further heated under reduced pressure to a solid content concentration of 5
It was made 0% to obtain a copolymer latex (i).

Other copolymer latexes (IX) to (v) were also synthesized by the same method.

The properties of the copolymer latexes (A) and (B) are shown in Table 1 together.

(3) Evaluation of Paper Coating Composition The copolymer latexes (A) and (B) produced as described above were used as a paper coating composition with the composition shown in Table 2, and a coated paper was prepared using the composition. The compounding ratios of the copolymer latexes (A) and (B) and the evaluation results of the coated paper are shown in Table 3 together.

From Table 3, good workability and dry adhesive strength cannot be obtained when the copolymer latex (A) is 100% (Comparative Example 1), and good white paper is obtained when the copolymer latex (B) is 100%. Gloss and printing gloss are not obtained (Comparative Example 2), and when the Tg of the copolymer latex (A) is lower than 30 ° C., good white paper gloss and printing gloss cannot be obtained (Comparative Example 3). The particle size of the latex (A) is 0.
If it is less than 15 μm, good white paper gloss and printing gloss cannot be obtained (Comparative Example 4), and if the amount of the aliphatic conjugated diolefin monomer of the copolymer latex (A) exceeds 20%, good white paper is obtained. Gloss and print gloss are not obtained (Comparative Example 5), good workability when the solid content ratio of copolymer latex (A) / copolymer latex (B) exceeds 60/40, Dry adhesive strength and the like cannot be obtained (Comparative Example 6), and if the amount of the aliphatic conjugated diolefin monomer of the copolymer latex (B) is less than 25%, good workability and adhesive strength cannot be obtained (Comparison). Example 7), good workability cannot be obtained when the unsaturated acid amide monomer is not used in the copolymer latex (A) or (B) (Comparative Example 8). Amount of aliphatic conjugated diolefin monomer of (B) When the content exceeds 55%, none of white paper gloss, print gloss, adhesive strength, and workability is good (Comparative Example 9), and the unsaturated acid amide monomer is present in both the copolymer latex (A) and (B). It can be seen that when the body is not used and the starch is large, the workability is good but the white paper gloss and the print gloss are not good (Comparative Examples 10 to 11).

EFFECT OF THE INVENTION By using the latex for paper coating of the present invention, coated paper and coated paperboard having good white paper gloss and printing gloss can be obtained. Further, it has extremely good resistance to stains on calendar rolls during production, and has good workability. That is, the conventional paper coating composition having a good gloss development tends to be used by increasing the proportion of the binder or increasing the amount of the natural binder such as starch and casein from the viewpoint of poor workability. The latex for paper coating of the present invention provides a paper coating composition which can obtain good workability without taking such a treatment, and can obtain more excellent gloss and print gloss expression than ever. Can be provided.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Haruhiro Hirai 2-11-24 Tsukiji, Chuo-ku, Tokyo Within Nippon Synthetic Rubber Co., Ltd. (56) Reference JP-A-57-191393 (JP, A) JP Sho 55-45724 (JP, A)

Claims (1)

[Claims] 1. A copolymer latex (A) and a copolymer latex (B) as described below, wherein the solid content weight ratio of (A) / (B) is 10/90 to 60/40. A latex for paper coating characterized by: [Copolymer Latex (A)] Ethylenically unsaturated carboxylic acid monomer; 0.5 to 8% by weight Aliphatic conjugated diolefin; 0 to 20% by weight Aromatic vinyl monomer; 40 to 99.5% by weight % Unsaturated acid amide monomer; 0 to 6% by weight (however, the total amount of unsaturated acid amide monomer constituting the copolymer latex (A) and (B) is 1 to 6% by weight)
Is. ) Other monoolefin monomers; having a copolymer composition of 0 to 59.5% by weight and a glass transition temperature of 30 to 105.
A copolymer latex having a temperature of ℃ and an average particle size of 0.15 to 0.40 μm. [Copolymer Latex (B)] Ethylenically unsaturated carboxylic acid monomer; 0.5 to 8% by weight Aliphatic conjugated diolefin; 25 to 55% by weight Unsaturated acid amide monomer; 0 to 6% by weight Other mono-olefin monomer; a copolymer latex having a copolymer composition of 31 to 74.5% by weight.