JPH11189990A - Production of coated paper for offset printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coated paper for offset printings excellent in opacity and printing surface strengths. SOLUTION: In a production of a coated paper for offset printings by coating paper with a coating solution containing a pigment and an adhesive, a filler is added to be included in the raw paper in a content of 4-8 wt.% as needle or columnar light calcium carbonate having 3.5-5.0 μm long diameter and 0.2-0.5 μm short diameter and produced by hydrating quick lime with water or a weak solution in the caustification process of a pulp production by a sulfate method or a soda method, then caustifying with a green solution.

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 a coated paper for offset printing having excellent opacity and printing surface strength.

[0002]

2. Description of the Related Art In recent years, the demand for offset printing paper in the commercial printing field for advertisements and advertisements such as flyers, catalogs, pamphlets and direct mail has been increasing year by year, and the production volume has been steadily increasing. In particular, in recent years, the rate of growth in the production amount of thin coated paper and lightly coated paper is large. This trend in the coated paper market reflects the user's desire to reduce costs by making it thinner. Under such circumstances, demands for thin offset printing paper include high opacity (especially that ink does not escape to the back side during printing), and excellent bulk, rigidity, printing workability, surface properties, and printing surface strength. That is.

[0003] However, a decrease in the amount of coating causes a decrease in printing surface strength and a decrease in opacity especially when the amount is 15 g / m ² or less on both sides. Therefore, the present inventors have recognized that it is effective to incorporate a latex having a small particle diameter or a high-molecular-weight, high-strength starch into a coating liquid in order to prevent a decrease in printing surface strength ( Japanese Patent Application No. 9-5120
6, Japanese Patent Application No. 9-65214, Japanese Patent Application No. 9-77862
issue).

In order to prevent a decrease in opacity, a filler having a large specific surface area (white carbon, finely divided silica, etc.)
Many proposals have been made, such as the use of a high refractive index filler, a pigment (such as titanium dioxide), and a pigment (plastic pigment, delaminated clay, etc.) for forming a bulky coating layer. In recent years, many methods for using light calcium carbonate having a specific shape as a filler or a pigment have been proposed.

[0005] The inventors of the present invention also disclosed in JP-A-6-73695 and JP-A-6-73698 that the use of spindle-shaped or columnar light calcium carbonate as a pigment in a coating solution makes it possible to improve the coated paper. We found a way to improve transparency.

On the other hand, there have been proposed several techniques for using such light calcium carbonate as an internal filler. Japanese Patent Application Laid-Open No. 57-71499 discloses a technique in which the major axis is 0.5 to 3.0 μm and the minor axis is minor. Is disclosed in Japanese Patent Application Laid-Open No. 7-3315.
No. 95 proposes a method in which acicular light calcium carbonate having an average particle diameter of 3 to 6 μm is used as a filler ash in an amount of 8 to 16%. But for the former,
It uses very small light calcium carbonate and is intended to improve opacity and wire abrasion, not printability of coated paper. In the latter case, a material having an extremely large average particle size is highly blended in the base paper, and is not intended to improve the printing surface strength. In recent years, on the printing side, as the offset printing speed has increased, the on-press tackiness of ink has increased, and the dry strength (surface strength of a solid color solid portion) caused by hardwood-specific pipes (vessel pick), pigment pick, etc.
Is reduced. Accordingly, there is a need for a technique for achieving both higher opacity and higher printing surface strength (dry strength).

[0007]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a coated paper for offset printing which is excellent in opacity and printing surface strength, and a method for producing the same.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a pulp production process using a sulfate method or a soda method as a filler during production of a base paper, wherein the base paper is coated with a coating liquid containing a pigment and an adhesive. In the causticizing step, after slaking quicklime with water or a weak liquor, a long diameter of 3.5 to 5.0 μm and a short diameter of 0.2 to 0.5 μm are produced by a causticizing reaction with green liquor.
Wherein the filler is added so that the needle-shaped or columnar light calcium carbonate in the range of 4 to 8% by weight is contained in the base paper. The present inventors have found that by using this manufacturing method, it is possible to obtain, for the first time, a coated paper for offset printing having both high opacity and excellent printing surface strength (particularly dry strength).

When the major axis is smaller than 3.5 μm or the minor axis is smaller than 0.2 μm, not only is the size reduced, but it penetrates into the interstices of the fibers and inhibits the formation of hydrogen bonds between the fibers. The dry strength of the paper also decreases. When the major axis is larger than 5.0 μm or the minor axis is larger than 0.5 μm, the presence of a material having such a large particle size near the base paper surface results in a large pigment pick at the time of offset printing, resulting in a dry strength. Is significantly reduced.

If the amount of needle-like or columnar light calcium carbonate contained in the base paper is lower than 4% by weight, sufficient opacity cannot be obtained. Conversely, if the content is higher than 8% by weight, the opacity is improved, but the interlayer strength of the base paper or the bonding strength between the fibers of the surface layer is hindered by the filler, so that pigment picks and vessel picks during printing frequently occur, and the dry strength decreases. Inferior.

Further, in the present invention, the light lime produced in the causticizing step of the pulp production step is compared with that produced by the reaction of milk of lime and carbon dioxide according to the conventional production method (carbon dioxide method). It was found that both opacity and dry strength were higher when calcium carbonate was used.

Various investigations were made on the reason why the light calcium carbonate produced by the causticizing process of the present invention had higher opacity and dry strength as compared with the case where the light calcium carbonate produced by the conventional carbon dioxide method was used. As a result, a large difference was observed in the wettability of the two with various liquids, and the one obtained by this method had a moderately low wettability with water, and the one manufactured by the carbon dioxide gas method had excessive wettability with water. Turned out to be high. If the wettability with water is too high, a hydrated layer is likely to be formed on the surface of the particles, and when dried in this state, a large capillary pressure acts between the particles and strongly compresses the particles, causing agglomeration and causing optical aggregation. It is believed that the opacity is reduced due to the reduced interface. If the wettability with water is too high, the compatibility with the polymer latex in the coating liquid is poor, so that the adhesiveness at the interface is poor and the dry strength is considered to be low.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Light calcium carbonate having a specific shape as defined in the present invention is produced by a causticizing step of a pulp producing step by a sulfate method or a soda method. In the pulp manufacturing process by the sulfate method or the soda method, wood chips are digested at high temperature and high pressure using a chemical solution in which sodium hydroxide and sodium sulfide are mixed in order to isolate fibrous material in wood. Then, the fibrous fibers are separated and refined as a solid phase into pulp, and elution components other than the fibers from the chemical solution and wood are recovered as black liquor, and concentrated to a concentration that can be burned by the recovery boiler. Further, sodium sulfate is added to supplement sodium and sulfur lost in a series of processes, and then burnt in a recovery boiler. At that time, the organic component in the black liquor is recovered as a heat source, and the inorganic substances are mainly recovered as sodium carbonate and sodium sulfide. These inorganic substances are called smelt and are taken out of the recovery boiler in a molten state. The smelt removed from the recovery boiler is dissolved in water or a weak liquid (a liquid containing a small amount of a white liquor component obtained after washing calcium carbonate with water) to become a green liquor.

The causticizing step is a step for converting sodium carbonate in green liquor into sodium hydroxide as a cooking chemical, a slaking reaction (1) for converting quicklime into slaked lime, and mixing slaked lime and green liquor. And sodium hydroxide and calcium carbonate (2). The sodium hydroxide liquor obtained by the causticization reaction is called white liquor, separated from calcium carbonate, clarified and sent to the digestion step. In the present invention, calcium carbonate that has been separated and recovered and washed sufficiently with water is used.

CaO + H ₂ O → Ca (OH) ₂ (1): slaking reaction Ca (OH) ₂ + Na ₂ CO ₃ → CaCO ₃ + 2NaOH (2): causticizing reaction This calcium carbonate is used as a chemical in the pulp manufacturing process. Since it is a by-product when producing white liquor, it can be produced at a very low cost as compared with light calcium carbonate obtained by a conventional method of reacting milk of lime with carbon dioxide.

Further, the needle-like or columnar light calcium carbonate specified in the present invention is produced according to the following production method. That is, (1) quicklime generated in the causticizing step and / or introduced from outside the causticizing step, and (2)
A liquid (water or weak liquid) having a pH of 5.5 to 14 is added to the quicklime containing 0.1 to 10% by weight of calcium carbonate such that the quicklime concentration becomes 20 to 60% by weight, and the mixture is stirred. Alternatively, the mixture is slaked while mixing, and lime milk and / or
Alternatively, a predetermined amount of green liquor generated in the causticization step and required for producing white liquor is added to the lime milk and / or 0.02-0.5ml (green liquor) / min / g for lime mud
(Quicklime) at an addition rate of 20 to 105.
It is produced by carrying out a causticization reaction at a temperature of ° C.

The filler used in addition to the above-mentioned light calcium carbonate is not particularly limited, but heavy calcium carbonate generally used for base paper, other light calcium carbonate, kaolin, clay, talc, silica, sulfuric acid One or more of barium, calcium sulfate, zinc sulfide, titanium dioxide and the like can be used in combination as long as the effects of the present invention are not impaired.

As the base paper used in the present invention, a mechanical pulp, a chemical pulp, a waste paper recovery pulp and the like are mixed at an arbitrary ratio and used. If necessary, ordinary fillers for papermaking, paper strength enhancers, yields, etc. The papermaking raw material to which the improver, the sizing agent, and the like are added is formed by an ordinary paper machine having a single wire or a twin wire.

In the case of the present invention, a lightweight base paper is particularly effective for a lightweight base paper.
In the case of ５０50 g / m ² , the effect of the present invention is particularly remarkably exhibited.

The starch used in the production and coating of the base paper of the present invention includes, but is not particularly limited to, oxidized starch, self-modified starch, phosphated starch, and hydroxyethylated starch.

The size press method used in the production of the base paper of the present invention is typically a method in which paper is passed between two press rolls and a size press solution is applied from both sides of the paper. Each roll (fountain roll, metering roll, applicator roll from outside), size press liquid is supplied between the fountain roll and the metering roll, transferred from the metalling roll to the applicator roll, and the size on the applicator roll There is a method in which a press liquid layer and paper are applied in contact with each other at a nip of another applicator roll. In addition, there are a tab size press, a calendar size press, and the like, but the method is not particularly limited since it can be used if the starch concentration and viscosity used are appropriately adjusted.

The pigment in the coating solution used in the present invention may be at least one of commonly used heavy calcium carbonate, kaolin, clay, talc, satin white, silica, plastic pigment, titanium dioxide and the like. I do.

As the adhesive used in the coating liquid of the present invention, one or two or more types are selected from latex or other aqueous adhesives as necessary. Examples of the latex include conjugated diene-based copolymer latex such as styrene-butadiene copolymer and methacrylate-butadiene copolymer, and vinyl-based polymer latex such as acrylate and / or methacrylate ester polymer or copolymer. Or those further modified with a monomer containing a functional group such as a carboxyl group. The amount of the latex is preferably 5 to 20 parts per 100 parts of the pigment.

The aqueous adhesive other than latex includes, for example, enzyme-modified starch, cold water-soluble starch,
Starches such as phosphate esterified starch, etherified starch and oxidized starch, proteins such as casein, soybean protein and synthetic protein, and synthetic resin adhesives such as polyvinyl alcohol, polyvinylpyrrolidone, olefin / maleic anhydride resin and melamine resin And ordinary coating adhesives such as cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose and hydroxymethylcellulose. The blending amount is 2 to 20 per 100 parts of the pigment.
Parts are preferred. In the coating liquid of the present invention, various auxiliaries, such as a dispersant, a thickener, a water retention agent, a defoaming agent, and a water-proofing agent, which are blended in a general pigment for coated paper may be used.

The coating composition thus prepared is applied by a general coating apparatus, but it is preferable to use a roll application or a fountain nozzle type blade coater which is particularly suitable for high-speed coating. The concentration of the coating liquid at that time is preferably in the range of 50 to 68%, and a single layer or a multilayer is coated on the base paper.

As described above, the base paper is coated with the coating liquid and dried, and the coated paper is subjected to a normal calendering device (super calender, soft calender, gloss calender, etc.).
Surface finish.

[0027]

The present invention will be described in more detail with reference to the following examples, but it should be understood that the present invention is by no means restricted to such specific ranges. Unless otherwise specified, parts and% in Examples are parts by weight and% by weight, respectively.

<Quality Evaluation Method> (1) Observation of Light Calcium Carbonate Morphology Light calcium carbonate produced by the causticization method was washed with water and filtered.
After drying, the shape and the average value of the major axis and minor axis were measured with a scanning electron microscope (JEOL JSM-5300). In addition, light calcium carbonate produced by the carbon dioxide method does not wash with water,
After filtration and drying, the shape and the average value of the major axis and minor axis were measured with a scanning electron microscope.

(2) Measurement of filler content in base paper The filler content was measured according to JIS P-8128.

(3) Opacity The opacity was measured using a Hunter whiteness meter according to JIS P-8138, Method A.

(4) Dry strength Using a RI-II type printing machine (manufactured by Meisho Seisakusho), using Toyo Ink TV-24, printing at a constant ink amount of 0.35 cc, and visually checking the picking degree of the printing surface. Relative evaluation was performed.

◎ = Not generated at all, ほ と ん ど = Not generated at all, Δ = Produced, X = Remarkable generated [Example 1] Raw materials and chemicals for base paper production LBKP (csf: 320 ml) 80 parts NBKP (csf: 490 ml) 20 parts Sulfuric acid band 0.8 parts Neutral sizing agent (alkyl ketene dimer) 0.03 parts Cationized starch 0.3 parts Cationic polyacrylamide 0.012 parts Bentonite 0.4 parts Acicular light calcium carbonate is produced in the causticizing step of the pulp production process by the sulfate method containing 10% by weight of calcium carbonate based on the weight of quicklime. The pH of the quicklime is adjusted so that the concentration of the quicklime is 30% by weight.
Adding the weak liquid generated in the causticizing step having 13.5,
Milk is produced by slaking while stirring, and then the green liquor is added to the lime milk at 0.02 ml / min / g (quick lime).
At a reaction temperature of 85 ° C. to carry out a caustic reaction.

With respect to the above-mentioned raw material, an internal additive and a major axis of 4.0 were used.
μm, caustic needle-like light calcium carbonate having a minor axis of 0.4 μm was internally added, and the paper was made with an experimental hand-making machine so that the filler content in the base paper was 6% by weight. / M ² of base paper. The base paper is subjected to a surface size treatment using a Hishira copier (one-step processor S-III, manufactured by Mitsubishi Paper Mills), dried at 105 ° C. for 1 minute, and then machined to a density of 0.70 g / cm ^3. was calendered. the adjustment starch concentration of size press starch coating amount performed by diluting adjusted to 3.5 to 4%, the starch coating amount was 1.0 g / m ^2. size base paper after pressing To 65 parts of heavy calcium carbonate and 35 parts of kaolin, 0.3 part of sodium polyacrylate dispersant was added, and the mixture was dispersed in water using a Cowles disperser, and 4 parts of phosphorylated starch was used as an adhesive. And 10 parts of styrene / butadiene copolymer latex, and a topcoat pigment coating liquid having a solid content of 65% was applied on both sides in an amount of 24 g / m ² on a dry basis.
Coating was performed on both sides using a blade coater so that The obtained coated paper was rolled at a temperature of 50 ° C. and the white paper gloss was 55%.
Super calendar treatment was performed to obtain coated paper for printing.

Example 2 A filler having a long diameter of 3.7 μm was used.
m, a coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic columnar light calcium carbonate having a minor axis of 0.25 μm was used and the filler content in the base paper was 7% by weight. .

Example 3 A filler having a long diameter of 4.6 μm was used.
m, a coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having a minor axis of 0.45 μm was used.

Example 4 The filler content in the base paper was 4.5.
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that the amount was changed to% by weight.

Example 5 The filler content in the base paper was 7.5
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that the amount was changed to% by weight.

[Comparative Example 1] As a filler, the major axis was 2.5 μm.
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having a diameter of 0.15 μm and a minor axis of 0.15 μm was used.

[Comparative Example 2] As a filler, the major axis was 6.0 µm.
m, a coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having a minor axis of 0.6 μm was used.

Comparative Example 3 A coated paper for printing was obtained in exactly the same manner as in Example 1 except that the filler content in the base paper was changed to 3% by weight.

Comparative Example 4 A coated paper for printing was obtained in exactly the same manner as in Example 1, except that the filler content in the base paper was changed to 12% by weight.

Comparative Example 5 A coated paper for printing was obtained in exactly the same manner as in Example 1, except that needle-like light calcium carbonate obtained by blowing carbon dioxide gas into a calcium hydroxide aqueous suspension was used. Was.

Comparative Example 6 A long diameter of 2.0 μm obtained by blowing carbon dioxide gas into an aqueous suspension of calcium hydroxide.
m, minor axis 0.2 μm A coated paper for printing was obtained in exactly the same manner as in Example 1 except that commercially available columnar light calcium carbonate Tamapearl TP-123 (manufactured by Okutama Kogyo) was used.

Comparative Example 7 A long diameter of 2.0 μm obtained by blowing carbon dioxide gas into an aqueous suspension of calcium hydroxide.
m, short diameter 0.4 μm A coated paper for printing was obtained in exactly the same manner as in Example 1 except that commercially available spindle-shaped light calcium carbonate Tamapearl TP-121 (manufactured by Okutama Kogyo) was used.

Comparative Example 8 A long diameter of 4.0 μm was used as a filler.
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having a diameter of 0.15 μm and a minor axis of 0.15 μm was used.

Comparative Example 9 A long diameter of 4.0 μm was used as a filler.
m, a coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having a minor axis of 0.6 μm was used.

[Comparative Example 10] As a filler, the major axis was 2.5 μm.
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having an m and a minor axis of 0.4 μm was used.

[Comparative Example 11] The filler had a major axis of 6.0 µm.
A coated paper for printing was obtained in exactly the same manner as in Example 1 except that caustic needle-like light calcium carbonate having an m and a minor axis of 0.4 μm was used.

The above evaluation results are shown in Table 1 for Examples and Table 2 for Comparative Examples.

[0050]

[Table 1]

[Table 2] As is clear from the results of Tables 1 and 2, Examples 1 to 6 are excellent in opacity and dry strength. In contrast, Comparative Examples 1 and 2 had poor dry strength, Comparative Example 3 had poor opacity,
Comparative Examples 4, 5, and 6 have poor dry strength, and Comparative Example 7 has poor opacity and dry strength. Comparative Examples 8 to 11 are inferior in dry strength.

[0051]

According to the present invention, a coated paper for offset printing excellent in opacity and printing surface strength can be obtained.

Claims (1)

[Claims] 1. A coated paper for offset printing in which a base paper is coated with a coating liquid containing a pigment and an adhesive, in a causticizing step of a pulp manufacturing process by a sulfate method or a soda method as a filler during the manufacture of the base paper. Needles in the range of a major axis of 3.5 to 5.0 μm and a minor axis of 0.2 to 0.5 μm produced by slaking quicklime with water or a weak liquor and then performing a caustic reaction with a green liquor. Alternatively, a method for producing a coated paper for offset printing, characterized by adding a filler so that columnar light calcium carbonate is contained in the base paper in an amount of 4 to 8% by weight.