JP2001073295A - Production of coated paper for offset printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated paper having a slight minute gloss unevenness, an excellent planar state and improved printing surface strength in the production of a multilayer coated paper for offset printing, having an undercoating coated layer and a topcoating coated layer. SOLUTION: In a method for producing a coated paper for offset printing by coating a base paper with an undercoating coating solution containing a pigment and a topcoating coating solution containing an adhesive, the base paper is coated with the undercoating coating solution containing a copolymer latex having 40-85 nm average particle diameter by a coater of film transfer type and then with the topcoating coating solution containing an alkali thickening type copolymer latex having -10 to -50 deg.C glass transition temperature by a coater of blade type.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated paper for offset printing, which has little matte-like fine gloss unevenness of the coated paper, and is excellent in white paper and printing surface feeling and has good printing surface strength.

[0002]

2. Description of the Related Art In recent years, with the diversification of user needs of printing paper, a multi-layer coating method has been widely used in order to manufacture high quality products at lower cost.

In general, when a coated paper is manufactured by a multilayer coating method, the cost can be reduced because an inexpensive pigment can be used for the undercoating liquid. However, in particular, it is hard to say that a multilayer coated paper manufactured by a method of undercoating a pigment coating liquid on-machine is always superior in quality as compared with a single-layer coated paper. Conventionally, when producing a single-layer coated paper, in order to secure the paper interlayer strength of the base paper, a pigment coating solution is applied after surface size coating with starch or the like. On the other hand, when undercoating a pigment on-machine, in order to simultaneously perform the above surface sizing and undercoating pigment coating,
Inevitably, the surface sizing treatment is insufficient, and there is a problem that the printing surface strength is inferior. In addition, the base paper coated with starch in advance in the surface size improves the barrier properties (filling effect), so that when the pigment coating liquid is applied in the next step, the coating liquid does not easily permeate the base paper, There is an advantage that the coatability is improved, and there is little unevenness of the matte-like gloss caused by unevenness of the coating liquid permeation and unevenness of the orientation of the pigment. In recent years, also on the printing side, with the increase in offset printing speed, the on-press tackiness of ink has risen, and the problem of reduced printing surface strength has been increasing. These problems appear as dry picks (printing white spots occurring in solid-colored areas to shadow areas) or wet picks (printing white spots occurring on a printing surface printed immediately after dampening solution is applied) during printing. It becomes a problem.

[0004] Accordingly, higher printing surface strength is required for paper coated with an undercoat pigment on-machine. As a means for improving the printing surface strength, especially the dry pick strength, a method using a latex having a small particle diameter for a coating adhesive has been proposed.

On the other hand, a film transfer type coater such as a gate roll, a blade metalling or a rod metaling size press coater is generally used as an apparatus for applying an undercoat pigment on-machine. When the coater of this type is operated at a high speed, problems that become remarkable are a peeling pattern (a phenomenon in which the paper separation is not stable at the exit of the application roll nip and a uniform pattern-like surface unevenness occurs on the paper surface) and a gum. It is known that there is a problem such as up (a phenomenon in which a coating liquid is solidified by a shear force applied between rolls having different roll diameters and peripheral speeds and adheres to the roll surface). It has been recognized that these problems can be reduced by lowering the coating solution concentration and viscosity, but such treatment increases the penetration of the undercoat pigment coating solution into the base paper, and reduces the amount of coating. At the same time as the control becomes difficult, the coatability of the base paper is reduced, so that there is a lot of pear-skin-like fine gloss unevenness after the application of the topcoat pigment, and there is a quality problem that a blank paper and a printed surface feel are deteriorated.

As described above, when the undercoat pigment is applied on-machine, the base paper covering property is equal to or higher than that of the single-layer coated paper, and excellent white paper with little fine gloss unevenness, printing feeling and printing surface are provided. It was difficult to balance the strength levels.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the present invention relates to a method for producing coated paper for offset printing in which a base paper is coated with an undercoating liquid and then a topcoating liquid is applied. Another object of the present invention is to provide a method for producing coated paper for offset printing, which is excellent in white paper having little satin-like fine gloss unevenness, has a printed surface feeling and good printed surface strength, and is excellent in operability.

[0008]

The inventors of the present invention have conducted intensive studies on these problems, and as a result, have found that offset printing for coating a base paper with a base coat liquid and a top coat liquid containing a pigment and an adhesive, respectively. In a method for producing a coated paper for printing, an undercoating coating solution containing a copolymer latex having an average particle diameter of 40 to 85 nm is applied to base paper by a film transfer type coater, and then has a glass transition temperature of -10. ~
The present invention has been accomplished by applying an overcoating solution containing an alkali-thickened copolymer latex at −50 ° C. with a blade-type coater. As a result, it was possible to obtain a method for producing coated paper for offset printing having little satin-like fine gloss unevenness, good printing surface strength, and excellent operability.

The details of the present invention will be described below. The present inventors,
In JP-A-10-140499, by using a latex having an average particle diameter of 40 to 70 nm for the undercoat layer and using a latex larger than 70 nm and 110 nm or less for the overcoat layer, dry pick strength, We proposed a method to provide coated paper for offset printing with excellent wet pick strength. However, it has not been possible to solve the problem of satin-like fine gloss unevenness caused by insufficient base paper covering property, which is particularly noticeable when the undercoat pigment is applied by a film transfer method.

As a result of various studies on means for improving this matte-like fine gloss unevenness, the glass transition temperature of the top coating layer is in the range of -10 to -50 ° C, preferably -50 ° C or more and less than -20 ° C. It was confirmed that by using the alkali thickening type copolymer latex therein, the fine gloss unevenness for satin finish was improved and the printing surface strength was good.
The reason for this is that the alkali-thickened copolymer latex has a low glass transition temperature to form a bulky coating layer structure, so that the base paper coatability is improved, or has a bulky and excellent cushioning coating layer. Therefore, it is considered that the linear pressure is evenly applied to the uneven portion of the paper during the soft calendering or the super calendering, so that unevenness in the orientation of the pigment is hardly generated. When the glass transition temperature is lower than −50 ° C., the tackiness becomes too high, and scum adheres to the roll surface during the calendering treatment, and the operability is significantly reduced. On the other hand, when the temperature is higher than -10 ° C, the coating properties of the base paper are reduced, the unevenness in fine gloss is increased, and the surface state is reduced. Further, when a copolymer latex of a non-alkali thickening type was used instead of an alkali thickening type, a bulky coating layer structure was not formed, so that a matte-like fine gloss unevenness occurred. The alkali-thickened copolymer latex of the present invention is used for gravure printing.Also, when an alkali-thickened copolymer latex having a glass transition temperature within the above specified range is used, offset printing is also used. When used for applications, there is a problem that the dry pick strength and the wet pick strength are reduced.

Then, as a result of studying a method for improving dry pick and wet topic strength, it was found that it was necessary to use a copolymer latex having an average particle diameter of 40 to 85 nm for the undercoating coating liquid. When the diameter is smaller than 40 nm, the amount of the hydrophilic emulsifier used in the production of the latex increases, and the wet pick strength decreases. 8
If the diameter is larger than 5 nm, the specific surface area of the latex decreases, and the adhesion area with the pigment decreases, so that the dry pick strength decreases.

Further, in the present invention, the gel content of the copolymer latex used in the undercoating coating solution is 30 to 70%.
It is preferable that If it is less than 30%, the dry pick strength tends to decrease. Conversely, if the gel content exceeds 70%, the absorbency of the dampening solution during offset printing tends to decrease, and the wet pick strength tends to decrease.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pigments used in the undercoating and topcoating pigment coating liquids of the present invention are not particularly specified, but heavy calcium carbonate, light calcium carbonate, kaolin, and the like generally used for papermaking. One or more of clay, calcined kaolin, titanium dioxide, talc, silica, satin white, barium sulfate, calcium sulfate, zinc sulfide, and plastic pigment can be used in combination.

The alkali-thickened copolymer latex used in the present invention as an adhesive for the topcoat coating solution is mainly composed of a styrene-butadiene copolymer latex, and styrene, butadiene and unsaturated monomers as monomers. A copolymer commonly used for paper coating, containing carboxylic acids (methacrylic acid, acrylic acid, etc.) and copolymerizing other monomers as necessary or modifying the copolymer by chemical reaction Latex. As the other monomer, an alkyl ester of an unsaturated carboxylic acid such as acrylic acid or methacrylic acid, or a vinyl monomer such as acrylonitrile or vinyl acetate is often used. As the alkali-thickened copolymer latex of the present invention, those in which 5 to 40% by weight of all monomers are unsaturated carboxylic acids are preferred. The amount of the alkali-thickened copolymer latex in the overcoating liquid is preferably 2 to 10 parts by weight based on 100 parts by weight of the pigment. Further, the copolymer latex used as an adhesive for the undercoat coating liquid in the present invention is for offset printing, and is mainly a styrene-butadiene copolymer latex as a composition, and contains styrene and butadiene as monomers. This is a copolymer latex generally used for paper coating, in which another monomer is copolymerized as required or the copolymer is modified by a chemical reaction. Other monomers include acrylic acid,
Vinyl monomers such as methacrylic acid, alkyl esters of acrylic acid or methacrylic acid, acrylonitrile, maleic acid, fumaric acid, and vinyl acetate are often used. The glass transition temperature is -10 to +3
0 ° C. is preferred. Further, the compounding amount of the copolymer latex in the undercoating coating liquid is preferably 2 to 10 parts by weight based on 100 parts by weight of the pigment.

Other adhesives used besides the copolymer latex of the present invention include oxidized starch and urea-phosphorylated starch in order to maintain the water retention of the coating solution and to increase the internal bond strength of the base paper. And etherified starch such as hydroxyethyl etherified starch, enzyme-modified starch and cold water-soluble starch. Further, other cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxymethylcellulose may be used. In the case of a top coating liquid, the compounding amount is preferably 2 to 15 parts by weight per 100 parts by weight of the pigment. In the case of an undercoating liquid, the pigment 100
15 to 35 parts by weight per part by weight is preferred.

In the overcoating and undercoating pigment 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 with ordinary pigments for coated paper are used. You may.

As the base paper used in the present invention, a chemical pulp, a mechanical pulp, a recovered paper pulp, or the like is mixed at an arbitrary ratio, and used as necessary. An internal sizing agent, a retention agent, a paper strength enhancing agent, if necessary. The raw material to which the agent or the like is added is made by a usual fourdrinier or gap-type twin-wire former, or a hybrid former in which the latter half of the four-wire portion is formed by twin wires. The basis weight of the base paper used is preferably 30 to 150 g / m ² .

Regarding the coating method, an on-machine coater of a film transfer system such as a gate roll coater, a blade metalling or a rod metaling size press coater is used for the undercoat pigment coating. In addition, a blade system such as a fountain blade coater or a short dwell blade coater is used for the overcoat pigment coating. In the present invention, the base paper may be coated with the top coating liquid and the under coating liquid once or more, respectively.

The coating amount of the topcoat pigment is preferably in the range of 6 to ²⁰ g / m ^{2 as} a solid content per one side of the base paper. The amount of the undercoat pigment applied is preferably in the range of ² to 10 g / m ² in terms of solid content per one side of the base paper.

The coated paper coated with the top coating liquid and dried is
The surface is finished with a calender (super calender, soft calender, gloss calender, etc.) as usual.

[0021]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited by these examples. In the examples, parts and% indicate parts by weight and% by weight, respectively. <Quality Evaluation Method> (1) Glass transition temperature: 20 ° C., 65% RH. To prepare a latex film, suggesting 20 mg of the latex film with a scanning calorimeter (DSC) at a heating rate of 5 ° C./min and a measuring temperature of 0 to 10
It was determined from a characteristic curve obtained at 0 ° C. (2) Latex average particle diameter: A sample diluted to a concentration of 0.05 to 0.2% was prepared, the absorbance at a wavelength of 525 nm was measured, and determined by a calibration curve created in advance. (3) Gel content of latex: About 0.3 g of latex is spread thinly on a slide glass and dried with a dryer at 50 ° C. until a film is formed. The latex film is immersed in about 50 ml of toluene all day and night, filtered with a glass filter, and the filtrate is dried with a dryer at 105 ° C., and the weight of the toluene-soluble matter is measured. From the weight of the toluene-soluble component obtained here, the gel content is calculated by the following equation.

Gel content (%) = (weight of dry film−weight of soluble matter in toluene) × 100 / weight of dry film (4) Dry pick strength: manufactured by Toyo Ink using a RI-II type printer (manufactured by Mei Seisakusho) Using TV-24, ink amount 0.3
Printing was carried out at a constant rate of 5 ml, and the degree of picking on the printed surface was visually evaluated relative to each other.

＝= Picking hardly occurs ＝= Picking slightly generated ＝= Picking generated frequently X = Remarkably picking generated (5) Wet pick strength: Using a RI-I type printing machine (manufactured by Mei Seisakusho), Apply dampening water, and after 5 seconds, use Toyo Ink's TK High Plus Red Ink.
Printing was carried out at a constant rate of 30 ml, and the print marks attached to the rubber roll were manually transferred to transfer paper, and the degree of picking was visually evaluated relative to each other.

＝= Picking hardly occurs. ＝= Small picking occurred. 多 い = Picking occurred frequently. X = Remarkable picking occurred. (6) Evaluation of fine gloss unevenness: The product after top coating and calendering was visually evaluated.

◎ = No gloss unevenness ○ = Slight gloss unevenness occurs △ = Gloss unevenness occurs a lot × = Gloss unevenness occurs remarkably [Example 1] Sulfuric acid band is added to bleached kraft pulp slurry having a freeness of 320 ml. Alkyl ketene dimer is added at 0.03%, cationized starch and colloidal silica are added as retention aids, and an on-top type twin-wire hybrid former is used. Light calcium carbonate is contained at 8% by weight in paper as an internal filler. To obtain a base paper having a basis weight of 101 g / m ² .

To 60 parts of heavy calcium carbonate having an average particle size of 0.55 μm and 40 parts of light calcium carbonate having an average particle size of 0.80 μm, 0.3 part of a sodium polyacrylate dispersant was added. , Dispersed in water using a Cowles disperser, and phosphated starch 25 as an adhesive.
Parts and a carboxy-modified styrene / butadiene copolymer latex having an average particle diameter of 60 nm and a gel content of 40%.
And an undercoat pigment coating liquid having a concentration of 38% was prepared.
Using this undercoat pigment coating liquid using a gate roll coater,
6 g / m ² is coated on both sides of the base paper and dried, and the basis weight is 1
A coated paper of 07 g / m ² was obtained.

Further, to 33 parts of heavy calcium carbonate having an average particle diameter of 0.51 μm and 67 parts of kaolin having an average particle diameter of 0.42 μm, 0.3 part of a sodium polyacrylate-based dispersant was added. Dispersed in water using a dispersing machine, and blended 2 parts of phosphorylated esterified starch as an adhesive and 7 parts of an alkali-thickened copolymer latex having a glass transition temperature of -40 ° C. A working solution was prepared.

Using a fountain blade coater, this topcoat pigment coating solution was applied on both sides at 23 g / m ² and dried to obtain a coated paper having a basis weight of 130 g / m ² .

Further, a 2-roll / 4-stack soft calender having an elastic roll having a Shore D hardness of 90 ° was used to obtain a temperature of 1
Calendering was performed under the conditions of 30 ° C., a linear pressure of 200 kg / cm, and 4 nips. [Example 2] The copolymer latex used in the undercoat pigment coating liquid had an average particle diameter of 80 nm and a gel content of 60%.
Coated paper in the same manner as in Example 1 except that the copolymer latex used in Example 1 was used, and that the glass transition temperature of the alkali-thickened copolymer latex used in the overcoat pigment coating liquid was -20 ° C. Was manufactured. [Example 3] The copolymer latex used in the undercoat pigment coating liquid had an average particle diameter of 70 nm and a gel content of 50%.
A coated paper was produced in the same manner as in Example 1 except that the latex was used, and that the glass transition temperature of the alkali-thickened copolymer latex used in the overcoat pigment coating liquid was -30 ° C. . Comparative Example 1 A coated paper was produced in the same manner as in Example 1, except that the alkali-thickened copolymer latex used in the overcoat pigment coating liquid had a glass transition temperature of -55 ° C. Comparative Example 2 A coated paper was produced in the same manner as in Example 1 except that the alkali-thickened copolymer latex used in the overcoat pigment coating liquid had a glass transition temperature of -5 ° C. Comparative Example 3 A coated paper was produced in the same manner as in Example 1 except that the copolymer latex used in the undercoat pigment coating liquid had an average particle diameter of 100 nm. Comparative Example 4 A coated paper was produced in the same manner as in Example 1, except that the latex having an average particle diameter of 35 nm was used as the copolymer latex used in the undercoat pigment coating liquid. Comparative Example 5 A coated paper was produced in the same manner as in Example 1 except that a non-alkali thickening type having a glass transition temperature of 0 ° C. was used as the copolymer latex used in the overcoat pigment coating liquid.

The above results are shown in Table 1.

[0031]

[Table 1] As is clear from Table 1, Examples 1, 2, and 3 have little unevenness in glossiness, excellent surface condition, and dry pick strength,
Excellent wet pick strength.

On the other hand, in Comparative Example 1, a large amount of scum adheres to the calender roll, and the operability is extremely poor. Comparative Example 2
Has many fine gloss unevenness and is inferior in surface state. Comparative Example 3 is inferior in dry pick strength. Comparative Example 4 is inferior in wet topic strength. Comparative Example 5 has many fine gloss unevenness and is inferior in surface condition.

[0033]

According to the present invention, in a method for producing a coated paper for offset printing in which an undercoating coating liquid is applied by a film transfer method, there is no fine gloss unevenness for satin finish, excellent white paper, excellent printed surface feeling, and good printed surface strength. Thus, coated paper for offset printing excellent in operability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) D21H 19/82 D21H 19/82 (72) Inventor Toru Otowa 2-2-1-1, Iidacho, Iwakuni-shi, Yamaguchi Prefecture Nippon Paper Industries Co., Ltd. Iwakuni Mill (72) Inventor Masahiro Hirakawa 2-1-1, Iida-cho, Iwakuni City, Yamaguchi Prefecture Japan Paper Mill Co., Ltd. Iwakuni Mill F-term (reference) 4J038 CA041 CA051 GA06 HA216 HA286 HA356 HA366 HA446 HA526 HA536 KA08 MA10 MA14 NA01 PB11 PC10 4L055 AG11 AG12 AG27 AG48 AG63 AG71 AG76 AG89 AG97 AH02 AH37 AJ04 BE09 CH11 CH12 EA16 EA20 EA33 FA12 FA13 GA19

Claims (2)

[Claims] 1. A method for producing a coated paper for offset printing wherein a base paper is coated with a base coat liquid and a top coat liquid containing a pigment and an adhesive, respectively, wherein the average particle diameter is 40 to 85.
After coating an undercoating coating solution containing a copolymer latex having a thickness of 10 nm on base paper with a coater of a film transfer method, the glass transition temperature contains an alkali thickening type copolymer latex of -10 to -50 ° C. A method for producing coated paper for offset printing, comprising applying a top coating liquid with a blade type coater. 2. The method for producing coated paper for offset printing according to claim 1, which is an undercoat coating liquid containing a copolymer latex having a gel content of 30 to 70%.