JP3345978B2 - Latex for offset sheet-fed printing paper coating and composition for offset sheet-fed printing paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an offset sheet-fed printing paper coating composition and a latex used therefor. More specifically, the present invention relates to a composition for coating a sheet-fed offset printing paper for obtaining a coated paper having both a high dry pick strength and a high wet pick strength and having an excellent balance between them, and a latex used therein.

[0002]

2. Description of the Related Art In recent years, with the rapid development of offset sheet-fed printing technology, the performance required for coated paper has become strict. For example, both inconsistent characteristics of dry pick strength and wet pick strength are required. Thus, there is a need for a composition for coating an offset sheet-fed printing paper, which is improved to obtain a coated paper having a good balance. As the latex used for the offset sheet-fed printing paper coating composition, a latex having a high gel content is generally used. As a method for adjusting the gel content of the latex, a method is known in which a monomer is polymerized in the presence of a chain transfer agent such as t-dodecyl mercaptan and α-methylstyrene dimer. However, the coated paper obtained by applying the latex obtained by this method has an insufficient balance between the dry pick strength and the wet pick strength, and either the dry pick strength or the wet pick strength is low, and the above-mentioned demand is not satisfied. Was not fully satisfactory.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an offset sheet-fed printing paper coating composition for obtaining a coated paper having both dry pick strength and wet pick strength and having an excellent balance between them. It is to provide a latex to be used. The present inventors have conducted intensive studies to achieve the above object, and as a result, it has been found that this object can be achieved by using a specific compound as a chain transfer agent and using a copolymer latex obtained by emulsion polymerization. And completed the present invention.

[0004]

Thus, according to the present invention, 20 to 60% by weight of an aliphatic conjugated diene monomer, 5 to 60% by weight of an aromatic vinyl monomer, and an ethylenic monomer copolymerizable therewith. A latex of a copolymer having a gel content of 60 to 90% by weight obtained by emulsion polymerization of a monomer comprising 0 to 75% by weight of an unsaturated monomer in the presence of a chain transfer agent, A latex for offset sheet-fed printing paper, which is obtained by using a tertiary mercaptan having one tertiary butyl group and having a total number of carbon atoms of 7 to 16 as a chain transfer agent. Is provided. Also,
According to the present invention, there is provided an offset sheet-fed printing paper coating composition comprising the latex and pigment as essential components.

[0005] The latex for offset sheet-fed printing paper coating of the present invention uses a tertiary mercaptan having at least one tertiary butyl group and a total number of carbon atoms of 7 to 16 as a chain transfer agent. It is obtained by emulsion polymerization of a monomer comprising an aliphatic conjugated diene monomer, an aromatic vinyl monomer and an ethylenically unsaturated monomer copolymerizable therewith.

[0006] The chain transfer agent used in the present invention is a tertiary mercaptan having at least one tertiary butyl group. The total number of carbon atoms of the chain transfer agent used in the present invention is 7 to 16, preferably 10 to 13. If the carbon number is outside this range, the balance between the dry pick strength and the wet pick strength of the coated paper will be poor.

Specific examples of the chain transfer agent used in the present invention include 2,5,5-trimethylhexane-2-thiol,
2,2,4,6,6-pentamethylheptane-4-thiol, 2,2,4,4,6-pentamethylheptane-6
-Thiol, 2,2,4,6,6,8,8-heptamethylnonane-4-thiol, 2,2,5,8,8-pentamethylnonane-5-thiol, 2,2,5,5 , 6,
8,8-heptamethylnonane-6-thiol and the like.

The amount of the chain transfer agent to be used is generally 0.05 to 4 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of all monomers. Outside this range, the balance between the dry pick strength and the wet pick strength of the coated paper may be poor.

In the present invention, other compounds having a chain transfer effect can be used in combination with the above-mentioned chain transfer agent, if necessary.

Other compounds having a chain transfer effect include n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan (containing no tertiary butyl group), n-hexadecyl mercaptan, and n-tetradecyl. Mercaptan, 2,2,4,6,6-pentamethylheptane-4-methylenethiol, 2,4,6-
Mercaptans such as trimethylnonane-4-thiol;
Xanthogen disulfides such as dimethylxanthogen disulfide, diethylxanthogen disulfide, diisopropylxanthogen disulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide; halogenated hydrocarbons such as carbon tetrachloride and ethylene bromide; pentaphenyl Hydrocarbons such as ethane; α, β-unsaturated aldehydes such as acrolein and methacrolein; allyl alcohol; 2-ethylhexylthioglycolate; terpinolene, α-terpinene, β
-Terpenes such as terpinene, γ-terpinene and dipentene; α-methylstyrene dimers such as 2-4-diphenyl-4-methyl-1-pentene; and 2,5-dihydrofuran. Among these compounds, t-dodecyl mercaptan, terpene and α-methylstyrene dimer are preferably used. The amount of t-dodecyl mercaptan is usually 0.05 to 100 parts by weight of all monomers.
To 3 parts by weight, preferably 0.1 to 1.5 parts by weight,
The amount of the terpene or α-methylstyrene dimer is usually 0.1 to 3 parts by weight, based on 100 parts by weight of all monomers.
Preferably it is 0.5 to 1.5 parts by weight.

The aliphatic conjugated diene monomer used in the present invention includes 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3 -Pentadiene, chloroprene and the like.

The aromatic vinyl monomer used in the present invention includes styrene, α-methylstyrene, vinyltoluene,
Halogenated styrene, divinyl styrene and the like can be mentioned.

The monomers copolymerizable with the aliphatic conjugated diene monomer and the aromatic vinyl monomer include cyano group-containing monomers such as acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile and α-cyanoethylacrylonitrile. Ethylenically unsaturated monomers; ethylenically unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and monoethyl maleate; methyl (meth) acrylate, (meth) acrylic acid Ethylenically unsaturated carboxylic esters such as ethyl, butyl (meth) acrylate and dibutyl maleate;
And ethylenically unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide. These monomers are used in an appropriate combination in order to improve coated paper properties such as adhesive strength and inking property.

The amount of each monomer used in the present invention is such that the aliphatic conjugated diene monomer is 20 to 100 parts by weight of all monomers.
60% by weight, preferably 30 to 55% by weight, 5 to 60% by weight, preferably 15 to 50% by weight of an aromatic vinyl monomer and 75% by weight or less of a monomer copolymerizable therewith;
It is preferably at most 55% by weight. Outside these ranges, the balance of physical properties of the coated paper, such as adhesive strength and inking property, becomes poor.

[0015] The latex for offset sheet-fed printing paper coating of the present invention has a copolymer having a gel content of 60 to 60.
It is 90% by weight, preferably 70-85% by weight. 60
If it is less than 10% by weight, the dry pick strength of the coated paper will be low,
Conversely, if the content exceeds 90% by weight, the wet pick strength decreases.

[0016] The latex for offset sheet-fed printing paper coating of the present invention is obtained by emulsion polymerization of the monomer in the presence of the chain transfer agent. The chain transfer agent is added to the reactor all at once before the start of the polymerization, or added all at once, dividedly or continuously after the polymerization is started. In case of divided addition or continuous addition,
The addition amount can be uniform or constant, and can be changed according to the stage of the polymerization. The chain transfer agent may be added alone as it is, or may be added after being mixed or dissolved in a monomer, water, a polymerization auxiliary material or an organic solvent.

The offset sheet-fed printing paper coating composition of the present invention comprises the above-described offset sheet-fed printing paper coating latex and a pigment as essential components.

The pigment used in the present invention is a powdery substance generally used for paper coating. Specific examples thereof include inorganic pigments such as clay, calcium carbonate, talc, titanium oxide, and satin white; and organic pigments such as plastic pigment.

The ratio of the pigment to the latex for offset sheet-fed printing paper coating is usually such that the latex for offset sheet-fed printing paper coating (solid content) is 5 to 100 parts by weight of the pigment.
It is 40 parts by weight, preferably 10 to 30 parts by weight.

The offset sheet-fed printing paper coating composition of the present invention may further contain, if necessary, other latex binders.
It may be a compound containing a water-soluble polymer, a dispersant, a water-proofing agent, an antifoaming agent, a dye, a lubricant, and the like.

The composition for coating an offset sheet-fed printing paper of the present invention is used by applying it to a base sheet for offset sheet-fed printing.
The method of application is not particularly limited, and the application is performed using an application device such as a blade coater, a roll coater, an air knife coater, and a short dwell coater. The coating amount is usually 3 to 30 g in terms of solid content of the composition.
/ M ² , preferably 5 to 25 g / m ² .

[0022]

According to the present invention, it is possible to obtain an offset sheet-fed printing coated paper which has both high dry pick strength and wet pick strength and is excellent in balance between them.

[0023]

The present invention will be described below in more detail with reference to examples. The parts and percentages in the examples are on a weight basis.

The coated paper obtained by applying the latex and the paper coating composition containing it was evaluated according to the following method. (Evaluation of latex) Gel content After adjusting the pH of the latex to 8.0, it was cast on a glass plate with a frame, left to dry at room temperature, and further dried.
The film was dried under reduced pressure at ℃ to obtain a film. This film 0.
Put 5 g in an 80 mesh wire mesh basket and add
After dipping in 100 ml of tetrahydrofuran at 100 ° C. for 24 hours, the film remaining in the basket of the wire net was dried at 100 ° C. under reduced pressure, and the residual ratio was calculated to determine the gel content. Average particle size Observed with an electron microscope, the particle size of
Zero was measured and the number average was shown.

(Evaluation of Coated Paper) Dry Pick Strength After the printing ink (tack value: 20) was overprinted four times using RI tester (manufactured by Akashi Seisakusho) on the coated paper, the paper surface was peeled off (picking). The state was observed and evaluated by the five-point method.
The higher the score, the higher the dry pick strength. Wet pick strength After applying water to the coated paper using a Molton roll, RI
Using a tester, the printing ink (tack value: 14) was overprinted four times, and evaluated by a five-point method in the same manner as in the evaluation method of dry pick strength. The higher the score, the higher the wet pick strength. Using a RI tester, water was allowed to flow while the space between the metal roll and the rubber roll was slightly opened, and then process ink (manufactured by Toyo Ink Co., Mark V, black) was solid printed. The condition of the printing ink was visually observed and evaluated by a five-point method. The greater the value, the higher the inking property.

Example 1 45 parts of butadiene, 20 parts of styrene, 16 parts of methyl methacrylate, 15 parts of acrylonitrile, acrylamide 1
Parts, itaconic acid 2 parts, acrylic acid 1 part, 2,2,4
6,6-pentamethyl-heptane-4-thiol 0.5
Parts and 0.5 parts of sodium dodecylbenzenesulfonate were added to 50 parts of soft water and stirred and mixed to obtain a monomer emulsion. Separately, 34 parts of soft water were added to an autoclave with a stirrer,
After 0.5 part of potassium persulfate and 1 part of sodium dodecylbenzenesulfonate were charged and heated to 80 ° C., 10% of the monomer emulsion was added to an autoclave and reacted for 1 hour. Next, potassium persulfate 1.0
Parts and 20 parts of soft water were added to the autoclave, then the remaining monomer emulsion was added to the reactor over 4 hours. During this time, the autoclave was kept at 80 ° C. After completion of the addition of the monomer emulsion, the mixture was reacted at 80 ° C. for further 4 hours. Then, unreacted monomers were removed by blowing steam, the mixture was cooled to room temperature, and a 40% aqueous sodium hydroxide solution was added. The pH was adjusted to 8 by addition to obtain a polymer latex A of the present invention having a solid content of 50%. Table 1 shows the evaluation results of this latex.

Next, 70 parts of kaolin clay (UW90, manufactured by Engelhard), 30 parts of calcium carbonate (Escalon # 2000, manufactured by Sankyo Flour Milling Co., Ltd.), and 0.15 part of a dispersant (Alon T-40, manufactured by Toagosei Co., Ltd.) , Sodium hydroxide 0.15 part, oxidized starch 3 parts and polymer latex A
10 parts (solid content) were mixed and stirred to obtain a solid content of 65%.
%, A paper coating composition having a pH of 9.5. This composition was applied to a high-quality paper at a coating amount of 15 g / m ² per one side, and immediately after the application, dried with hot air at 140 ° C. for 4 seconds.
° C, 65% R.C. H. Was left overnight in a constant temperature and humidity room. Thereafter, a super calender treatment was performed twice at a temperature of 40 ° C. and a linear pressure of 40 kg / cm. Table 1 shows the evaluation results of the coated paper.

Examples 2-5 and Comparative Examples 1-2 Polymer latexes B-G were obtained in the same manner as in Example 1 except that the formulations shown in Tables 1 and 2 were used. These latexes were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Further, using polymer latexes B to G, a coating composition was obtained in the same manner as in Example 1, and a coated paper was obtained. These coated papers were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

[0030]

[Table 1]

[0031]

[Table 2]

From Tables 1 and 2, at least one third
When a chain transfer agent other than a tertiary mercaptan having a tertiary butyl group and having a total number of carbon atoms of 7 to 16 was used (Comparative Examples 1 and 2), the dry pick strength and wet pick strength were poor. It turns out that it is enough. On the other hand, it has at least one tertiary butyl group and has 7 to 7 carbon atoms.
It can be seen that when 16 tertiary mercaptans were used (Example), the dry pick strength and wet pick strength were high and the balance was good.

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Claims (2)

(57) [Claims] 1. An aliphatic conjugated diene monomer from 20 to 60% by weight, an aromatic vinyl monomer from 5 to 60% by weight and an ethylenically unsaturated monomer copolymerizable therewith from 0 to 75% by weight. Is a latex of a copolymer having a gel content of 60 to 90% by weight, obtained by emulsion polymerization of a monomer represented by the formula (I) in the presence of a chain transfer agent. A latex for offset sheet-fed printing paper, which is obtained by using a tertiary mercaptan having a group and having a total number of carbon atoms of 7 to 16. 2. An offset sheet-fed printing paper coating composition comprising the latex for offset sheet-fed printing paper coating according to claim 1 and a pigment as essential components.