JPH0665897A - Coated paper for offset printing - Google Patents

Abstract

PURPOSE:To provide a coated paper for offset printing having high pick resistance durable to high-speed web offset printing and excellent operability. CONSTITUTION:This coated paper for offset printing has >=2 coating layers per one surface of the base paper. The coating composition to be used in the primer coating layer closest to the base paper contains wet-pulverized calcium carbonate having an average particle diameter of 1.0-4.0mum as a pigment component and contains an aqueous solution of a cationic starch satisfying a specific condition as an adhesive component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel offset printing coated paper, and more particularly to an offset printing coated paper having excellent printability, especially high pick resistance.

[0002]

2. Description of the Related Art In recent years, the speed of printing, especially offset printing, has increased, and a coated paper capable of withstanding the demand has been required. In particular, coated paper that can withstand high-speed printing requires high pick strength, blistering suitability that is resistant to blistering caused by high-temperature drying during high-speed offset rotary printing, and reproducibility of image information in the market in recent years. The demand for high printing gloss and high ink inking property are increasing.

To meet these requirements, starch,
By increasing the amount of adhesive such as synthetic polymer latex, offset printing suitability, especially pick strength can be improved. However, if the adhesive strength such as starch and synthetic polymer latex is increased significantly to improve the pick strength, the adhesive layer becomes thicker, which lowers the water vapor permeability inside the coated paper. Conversely, the blister suitability decreases. Furthermore, the viscosity of the coating solution increases due to the increase in the amount of starch, and the coating suitability in a coater decreases, so the coating solution concentration must be reduced, and the glossiness of white paper and the gloss after printing decrease,
In addition, the inking property of the offset printing ink is reduced. Also, when the amount of synthetic polymer latex is greatly increased, the adhesive layer forms a film, and the inking property of the offset printing ink deteriorates. This decrease in printability, especially pick strength, is because the base paper is anionic due to the hydroxyl groups and carboxyl groups of the pulp fibers, and the coating liquid is anionic due to the carboxyl groups of the adhesive. It is promoted by penetrating the base paper. In order to prevent this, some measures have been taken to improve the water retention of the coating liquid. For example, a water-soluble polymer such as carboxymethyl cellulose that makes the aqueous solution extremely high in viscosity may be added to the coating composition. However, the effect of such a water retention agent is limited, and since the viscosity of the coating liquid increases, the concentration of the coating liquid during coating may rather decrease and the printability may not improve.

Further, as reported in the May 1991 issue of Paper and Paper Cooperative Magazine "Study of Blister Resistance by Analyzing Coating Layer Structure", it is suitable for offset printing without deteriorating the coating liquid property. In order to improve the blister suitability of, the low gel amount latex has been developed, but these latexes have the effect of lowering the crosslink density, which lowers the pick strength and requires an increase in the amount of adhesive. Does not improve.

Further, as disclosed in Japanese Patent Application Laid-Open No. 1-97296, since the pulp fiber surface constituting the base paper is anionically charged, the polarity of the coating liquid is set to be cationic to apply the base paper. There is also an idea to prevent the permeation of the liquid and improve the offset printing suitability. However,
When the coating liquid is cationized in this way, the viscosity of the coating liquid is considerably increased, the coating concentration is rather lowered during coating, and printability may not be improved. In addition, when kaolin is used as a pigment, a large amount of a cationizing agent must be used in order to block the anionic groups, which not only increases the cost but also deteriorates the liquidity. For this reason, calcium carbonate or the like becomes the main component of the pigment, and as a result, the glossiness of the white paper becomes low.

Further, by forming a coating layer by performing multi-layer coating, the printability of the top coating layer can be improved and the production efficiency can be increased. For this reason, multilayer coated paper, especially double coated paper, has become popular. However, when starch is mainly used as an adhesive for the undercoating liquid in the case of multilayer coating, the air permeability is lowered due to the film formation of the undercoating layer, and the blister suitability is often deteriorated. Further, by mixing latex in the undercoat layer coating liquid as a main component, air permeability can be improved, but by adding latex in the undercoat layer coating liquid as a main component, the surface strength of the undercoat paper is inferior to that of starch, Since it is necessary to increase the blending amount, the air permeability is not improved so much and the blister suitability is not improved so much.

[0007]

In view of the above situation, an object of the present invention is to provide a multi-layer coated paper having high offset printing suitability, particularly high pick strength during offset rotary printing, and excellent blister suitability, and high operability. Is to get under.

[0008]

The coated paper for offset printing of the present invention comprises two or more coating layers on one side of the base paper, and the coating composition of the undercoat layer closest to the base paper contains a pigment. Component and an adhesive component, and the average particle diameter of the pigment component is 1.0 to 4.0 μm by wet pulverization.
And calcium carbonate, and a cationic starch aqueous solution satisfying the condition of the formula 1 is contained in the adhesive component.

[0009]

0.63 ≦ F × ln (η) <1.28 (Equation 1) F: Ratio of cationic starch to total solids in coating composition ln (η): concentration 20%, at 50 ° C. Natural Logarithmic Value of B-Type Viscosity of Cationic Starch Aqueous Solution under Various Conditions

Further, the cationic starch aqueous solution has a nitrogen content of 0.15% or more and has a B content of 30 to 1000 cps.
It is characterized in that it has a mold viscosity range.

When the average particle size of the wet-ground calcium carbonate in the pigment component of the present invention is less than 1.0 μm, the surface strength of the undercoat layer itself is remarkably reduced, so that the pick strength during offset rotary printing is sufficient. Not only that, but further, when the undercoat layer is coated, the pigment is detached on the roll in the drying step due to the influence of the lowering of the surface strength of the undercoat layer itself, and the workability is deteriorated. Also, when the average particle size exceeds 4.0 μm and becomes large, the pick strength at the time of offset rotary printing is satisfactory, but the smoothness of the undercoat layer deteriorates, and therefore the fine convex portions of the undercoat layer become a resistance, and the drying process The workability and quality are deteriorated due to the detachment of the pigment on the roll.

The cationic starch of the present invention is V (B as an aqueous starch solution excluding the pigment in the undercoating liquid at 20 ° C.).
The relationship between the logarithm of the mold viscosity), that is, ln (V) and CS (concentration as an aqueous starch solution excluding the pigment in the undercoating liquid) is a straight line (FIG. 1). Further, generally, since a large amount of the adhesive is present in the undercoat layer, a film is easily formed, and as a result, the blister suitability is lowered. Particularly, phosphate esterified starch is
The relationship of n (V) is not a straight line, and ln
(V) rises sharply. For this reason, as the water in the aqueous phase is absorbed by the base paper at the interface of the base paper, the concentration is increased, the viscosity is rapidly increased near the interface between the base paper and the undercoat layer, and a film is easily formed. On the other hand, in the case of the cationic starch of the present invention, an increase in viscosity at the interface is suppressed and the aqueous starch solution penetrates into the base paper layer, so that a film is hard to form and high blister suitability is obtained. Further, even with anionic starch, the permeability can be maintained in the low viscosity region, but the adhesive strength at the coating layer interface with the overcoat layer is reduced. On the other hand, even if the cationic starch penetrates into the base paper layer, it cross-links with the anionic binder of the overcoat layer, so that the adhesive strength at the interface of the coating layer can be maintained and the pick strength does not decrease so much.

If the concentration (CS) of the starch-excluding aqueous solution in the undercoating liquid is constant, the logarithm of V which is the B-type viscosity of the starch-excluding aqueous solution of the undercoating liquid in which the starch is removed is 20 ° C. In (V) is proportional to F, which is the ratio of the cationic starch to the total solids in the coating composition, and the logarithmic value ln (η) of η, which is the inherent viscosity of the cationic starch. Since the viscosity of the undercoat coating liquid is influenced by the flow characteristics of the pigment, it does not directly correspond to ln (V).
As described above, using the cationic starch of the present invention, ln
When (V) is within the predetermined range, good blister suitability and pick strength can be obtained. The product of F (the ratio of the cationic starch to the total solid content in the coating composition) of the present invention and ln (η) (the natural logarithmic value of the B-type viscosity of the cationic starch at a concentration of 20% and 50 ° C). Is less than 0.63, either or both of F and ln (η) are too small, so that sufficient pick strength cannot be obtained during offset rotary printing. And when it becomes 1.28 or more, F
Since either or both of In and η (η) are too large, the pick strength at the time of rotary offset printing is sufficient, but the film formation is too large and the blister suitability deteriorates. In addition, the viscosity of the coating liquid during coating increases significantly,
It becomes difficult to control the coating amount, and further the split pattern on the GRC coater increases, so that the coating surface quality deteriorates.

When the adhesive in the coating composition of the present invention is anionic starch or cationic starch having a nitrogen content of less than 0.15%, the pulp fiber of the base paper is anionic,
The undercoating liquid permeates into the base paper layer so much that sufficient pick strength cannot be obtained during offset printing unless the amount of binder is significantly increased. Furthermore, since the amount of the binder is large, the formation of a film that is less likely to transmit water vapor in the undercoat layer is increased, and the blister suitability is reduced.

If the B-type viscosity of the cationic starch used in the present invention is less than 30 cps, the pick strength during offset printing will be too low, and if it exceeds 1000 cps, the viscosity will be remarkably increased. The coating suitability also deteriorates, and the blister suitability also deteriorates.

The binder of the present invention may be a cationized acrylic emulsion, cationized styrene-butadiene latex, cationized ethylene-vinyl acetate copolymer, cationized styrene-acrylic copolymer, cationized vinyl acetate-acrylic copolymer, if necessary. Polymers, cationized butadiene-methylmethacryl copolymer, cationized vinyl acetate-butyl acrylate copolymer, cationized polyvinyl alcohol, cationized soybean protein and the like are used. As a raw material of the cationic starch, corn starch, tapioca, horse mackerel, etc. can be used.
It is prepared by converting to a tertiary amine type by using diethylaminoethyl chloride or the like, or by converting to a quaternary ammonium salt type by reacting 2,3 epoxypropyltrimethylammonium chloride or the like.

By smearing the cationized coating composition of the present invention on a base paper which has been made up as an undercoat layer, the adhesive strength between the base paper and the undercoat layer and the surface strength of the undercoat layer itself are increased. Furthermore, since various anionic water-soluble adhesives and the like are contained in the composition of the usual overcoat coating composition for offset printing, the top coating composition is solidified at the interface with the undercoat layer. , The adhesive strength between the topcoat layer and the undercoat layer increases.
As described above, since the printed coated paper of the present invention has high pick strength, it is possible to reduce the blending amount of the adhesive of the undercoat coating composition. Furthermore, by cationizing the undercoat layer, the internal bond strength of the base paper layer is increased, so that the blister resistance during offset rotary printing is further improved.

Other adhesives used in the present invention include synthetic binders such as polyvinyl alcohol, oxidized starch, etherified starch, esterified starch, enzyme-modified starch, and cold water-soluble starch and casein obtained by flash-drying them. Examples include natural adhesives such as soybean protein, and those obtained by cationizing these adhesives. These are also various kinds of commonly used auxiliary agents such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistant agent, and a colorant, and cationized ones of these various auxiliary agents, if necessary. Can be used as appropriate.

The pigment for coated paper used in the present invention is mainly composed of wet-ground calcium carbonate, but if necessary, kaolin, clay, satin white, talc, titanium oxide, aluminum hydroxide, silica, calcined. Kaolin, zinc oxide, activated clay, acid clay, silicon earth, lake, plastic pigment and the like are used. A cationic dispersant is required for dispersion, and in some cases it is necessary to add a low-molecular weight cationic activator to block the anionic groups.

The base paper used in the present invention is LBKP, N
Chemical pulp such as BKP, GP, PGW, RMP, TM
Mechanical pulp such as P, CTMP, CMP, CGP, DIP
Including used pulp such as, pulp such as light calcium carbonate, heavy calcium carbonate, talc, clay, various fillers such as kaolin, sizing agents, fixing agents, retention agents, cationizing agents, paper strengthening agents, etc. It contains various additives, and is made acidic, neutral and alkaline. As the base paper of the present invention, a non-size press base paper, a base paper size-pressed with starch, polyvinyl alcohol, or the like is used.

The method of applying the coating composition according to the present invention to a base paper is not particularly limited, and various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters and short dowels are used. Two or more layers are smeared using various ordinary coating equipment such as a coater. The smear paper is dried each time each layer is smeared or after smearing two or more layers. The coated and dried coated paper is subjected to a super calender, gloss calender, soft calender treatment and the like.

[0022]

EXAMPLES The effects of the present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In addition, "part" and "%" in an Example show "weight part" and "weight%", respectively. The various measured values in the examples are obtained by the following methods.

1) Average particle diameter: Measured with a Microtrac 7995-30SPA model manufactured by Leads & Northrop Co., and a volume-weighted average particle diameter was determined. 2) Viscosity of coating liquid: Measured under the conditions of a temperature of 25 ° C. and 60 rpm using a B type viscometer of BL type manufactured by Tokyo Keiki Seisakusho. 3) White paper glossiness: Measured at an angle of 75 degrees in accordance with JIS P8142 (unit:%). 4) Multicolor printing glossiness: A sample was printed by a Roland offset printing machine, left at room temperature for one day and night, and a black, magenta, cyan, and yellow four-color overprinted solid print part of the sample was printed at an angle of 60 degrees. The gloss was measured.
(Unit:%) 5) Pick strength: IP using RI printing machine (Ming Seisakusho)
Printing was performed with the I ink, and the degree of picking on the printed surface was visually determined. 5 is the best level on a 5-point scale. The allowable limit is rank 3. 6) Blister resistance: A commercial offset rotary printing ink was printed on both sides of the test piece by an RI printing machine, the test piece was wrapped in aluminum foil, and put in silicone oil at 250 ° C for 5 seconds, and the blister was ejected. One was visually evaluated. 5
A grade of 5 is the best level. 7) Degree of detachment of pigment: A rank of 5 was obtained by evaluating the degree of stains on the roll in the drying step after coating the undercoat coating liquid on a scale of 5
Was the highest standard. The allowable limit is rank 3. 8) Degree of coating pattern: After coating the undercoating liquid, a commercially available offset ink is printed on the undercoating paper with an RI printer,
The uniformity of the printed surface was visually judged and evaluated on a scale of 5 to rank 5 as the best level. The allowable limit is rank 3.

Examples 1 to 8 and Comparative Examples 1 to 7 <Base paper formulation> LBKP (water flow degree 350 mlcsf) 30 parts NBKP (water flow rate 420 mlcsf) 70 parts <Internal additive> Calcium carbonate (* in terms of ash content in base paper) * 10 parts Commercially available alkyl ketene dimer internal additive sizing agent (AKD) 0.03 parts Commercially available cationic polyacrylamide retention aid 0.03 parts Pulp and internal additives are formulated with the above-mentioned composition and 50 g / m
A base paper having a basis weight of ² (extremely dried) was produced. To this base paper, a gate roll coater was used to apply an undercoating composition shown in Tables 1 and 2 at a coating solution concentration of 40% and a coating amount per side of 3 g /
m ² smeared and dried.

Examples 1 to 8 and Comparative Examples 1 to 7 <Preparation of Wet Grinding Pigment Slurry> Calcium carbonate before grinding is A grade manufactured by Sankyo Seiko Co., Ltd. (specific surface area 700
0 cm ² / g) and 0.4% of modified polyacrylamide containing (trimethyl ethyl ammonium chloride) methacrylate monomer as a cationic dispersant.
Used. The wet crushing mill is an agitator mill LME20 type manufactured by Ashizawa Co., Ltd., and the crushing conditions are: bead packing rate 80%, rotation speed 960 rpm, beads: zirconia beads (average diameter 1.0 mm), processing flow rate: 1.0-6. 0l
The pigment slurry was treated at a solids concentration of 65% under the condition of / min.

<Composition of Undercoat Layer> Cationized starch is
Using corn as a raw material, it is converted into a quaternary alkylammonium with a nitrogen content of 0.4% and the B type viscosity of a 20% aqueous solution at 50 ° C is 25 CPS, 33 CPS, 180 CPS, 980 CPS, 1240 CP.
A starch of S and a starch having a nitrogen content of 0.1% and a quaternary alkylammonium of 0.15% and converted into a 20% aqueous solution at 50 ° C. having a B-type viscosity of 180 CPS were used.

A coating liquid having the following composition was smeared on the undercoat layer-coated paper with a blade coater at 13 g / m ² on one side,
Dried. <Overcoat coating liquid formulation> Commercially available primary kaolin (Ultra White 90) 30 parts Commercially available secondary kaolin (Ultra Coat) 40 parts Commercially available wet heavy calcium carbonate (Carbital 90) 30 parts Commercially available polyacrylic acid-based dispersant 0.1 part Commercially available phosphate esterified starch 4 parts Commercially available styrene butadiene latex (JSR0617) 12 parts Calcium stearate 0.3 parts Sodium hydroxide 0.15 parts Coating solution solid content concentration 60% This smear paper was supercalendered under the following conditions. .

<Super calendar condition> Number of steps: 10
Step: Rigid roll, chilled roll, outer diameter 400mm; elastic roll, cotton roll, outer diameter 420mm; processing speed, 400m
/ Min; linear pressure, 220 kg / cm; formulation of coating liquid for topcoat layer, coating method, supercalender conditions are in accordance with the above conditions. The results of each Example and Comparative Example are summarized in Table 1 and Table 2.

Comparative Examples 8 and 9 A base paper produced under the same composition and production conditions as in Examples 1 to 8 was coated with the following undercoat layer coating solution at a coating amount of 3 g / m ² on one side with a gate roll coater. Smeared and dried. <Undercoating liquid formulation> As a pigment, Softon 2200 made by Bihokuhokuka Kogyo Co., Ltd. of dry heavy calcium carbonate was used.
It was prepared by using 0.6 parts of a commercially available polyacrylic acid-based dispersant as a dispersant without wet pulverization and using a commercially available phosphate esterified starch having a B-type viscosity of 130 CPS at 50 ° C. and a 20% concentration as the starch. The number of parts of phosphoric esterified starch is shown in Table 2.
Of the cationic starch. Further, the number of parts of dry heavy calcium carbonate was also inserted in the part of calcium carbonate in Table 2. <Overcoating liquid formulation and supercalender conditions> The above-mentioned undercoated coating paper was treated under the same overcoat layer coating liquid formulation, coating method and supercalendering conditions as in Examples 1 to 8. The quality characteristics of Comparative Examples 8 and 9 are summarized in Table 2. Compared with Examples 1 to 8, the pick strength is low, and the level is such that offset rotary printing cannot be endured. Further, the degree of pigment loss is significant, which causes a problem in operation.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As is apparent from the examples, the coated paper for offset printing of the present invention has high offset printing suitability, particularly excellent pick resistance and blister suitability, and has good coating suitability and operability. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the natural logarithm of the B-type viscosity of an aqueous cationic starch solution and the concentration of the aqueous starch solution excluding the pigment in the undercoating liquid.

Claims (2)

[Claims] 1. A coated paper for offset printing, wherein two or more coating layers are provided on one side of a base paper, and a coating composition of an undercoat layer closest to the base paper contains a pigment component and an adhesive component. In addition, the pigment component contains calcium carbonate having an average particle size of 1.0 to 4.0 μm by a wet pulverization treatment, and the adhesive component contains a cationic starch aqueous solution satisfying the condition of several 1. A coated paper for offset printing, which is characterized by: 0.63 ≦ F × ln (η) <1.28 (Equation 1) F: Ratio of cationic starch to total solids in coating composition ln (η): concentration of 20%, at 50 ° C. Natural Logarithmic Value of B-Type Viscosity of Cationic Starch Aqueous Solution under Various Conditions 2. The coated paper for offset printing according to claim 1, wherein the cationic starch aqueous solution has a nitrogen content of 0.15% or more and a B-type viscosity range of 30 to 1000 cps. .