JP2002201595A - Coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated paper for printing having excellent high flatness and smothness at the surface of coated layer coated by using a transfer roll coater. SOLUTION: At least an upmost layer to be covered of this coated paper for printing comprises a coated layer prepared by coating a base paper with a coating liquid comprising 10-50 wt.% of wet-milling ground calcium carbonate by the transfer roll coater using a coating roll on at least one side of an applicator roll, wherein the coating roll is composed of a polyurethane elastomer prepared by mixing ultra-high molecular weight polyethylene powder having an active group such as an OH group and a COOH group to a polyurethane prepolymer having an NCO group with a crosslinking agent having an NH2 group or an OH group to chemically bond.

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 printing which is excellent in flatness and smoothness on the surface of a coating layer coated using a transfer type roll coater.

[0002]

2. Description of the Related Art In recent years, it has been desired to reduce the weight of printing coated paper and visualize printed matter, and the demand for coated printing paper coated using a transfer type roll coater is increasing. The transfer type roll coater measures the coating amount by the shear stress generated by the peripheral speed difference between the rolls like a gate roll coater.The coating liquid is supplied to the applicator roll, and the coating amount is adjusted by a rod or blade. There is a film transfer type roll coater that weighs, but in any case, the base paper is passed through the nip of the applicator roll, and the coating liquid measured on the applicator roll is transferred to the base paper to transfer the coating surface. It does not change in terms of shaping.

[0003] In the case of coating using a transfer type roll coater, when the coating liquid on the applicator roll is transferred to the base paper, the coating liquid is cleaved between the applicator roll and the base paper. And the smoothness is easily impaired. This is called an "orange peel pattern" and is one of the biggest problems in coated paper manufactured using a transfer type roll coater. In addition, droplets generated when the coating liquid is cleaved fly onto the paper surface, which also causes damage to the coating surface.

[0004] Further, in many cases, double-sided coating is performed by a nip between applicator rolls. However, when performing double-sided coating, when the base paper is pulled by both applicator rolls and the balance between the tensions of both is lost, after coating, The paper flaps, which makes the position where the coated paper is peeled off from the applicator roll unstable, which also causes unevenness in the amount of coating and greatly impairs the appearance and printability of the coated paper.

[0005] Regarding the coating suitability of the above-mentioned transfer type roll coater, conventionally, there have been many cases in which the properties of the coating liquid are changed to cope with the problem. For example, by adding a highly polar water-soluble polymer such as sodium polyacrylate, carboxymethylated cellulose, or sodium alginate to increase the viscosity of the aqueous phase of the pigment coating liquid, Measures have been generally taken to prevent the coating liquid from sticking to the applicator roll after being absorbed.However, due to an excessive increase in the viscosity of the coating liquid, the concentration of the coating liquid could not be increased and the coating amount could not be increased. Since it cannot be ensured, the quality of the coated surface may be reduced.

[0006] Further, by using a coating solution having a high concentration to increase the transfer rate to the base paper to nearly 100%, the surface of the applicator is transferred to the coating surface, and a good surface quality can be obtained. However, it is difficult to always stably separate the base paper from one of the rolls, which causes unevenness in the coating amount.

[0007] Further, there is a concept that the roughness of the surface of the applicator roll is increased to reduce the adhesion of the coating liquid to the applicator roll. However, although the base paper is easily peeled off from the applicator roll, the rough surface of the applicator roll is effective. Is reflected and flatness is impaired.

In addition to the above-mentioned measures, Japanese Patent Laid-Open No. 2000-538
As described in JP-A-55-55, even when a water-repellent modified urethane rubber-coated roll is used, coating unevenness can be improved, but it has not been eliminated.

As described above, in the transfer type roll coater, the surface quality of the coated surface is often impaired due to the resistance when the coating liquid and the base paper are peeled off from the applicator roll. The production of coated paper for printing using a coater is a major issue.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coated paper for printing which has high flatness and excellent smoothness on the surface of a coating layer coated on a base paper using a transfer type roll coater. Is to do.

[0011]

Means for Solving the Problems The present inventors have made intensive studies in view of the above, and as a result, have come to invent the coated paper for printing of the present invention.

That is, the coated printing paper of the present invention is characterized in that at least the outermost coating layer has an ultra-high molecular weight polyethylene powder having an active group such as an OH group and a COOH group with respect to a polyurethane prepolymer having an NCO group. With NH
_A coating roll made of a polyurethane elastomer mixed and chemically bonded with a crosslinking agent having _two or OH groups, and a transfer-type roll coater using the coating roll on at least one applicator roll,
It is characterized in that it is provided with a coating layer obtained by coating a base paper with a coating liquid containing 10 to 50% by weight of wet ground heavy calcium carbonate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the coated paper for printing of the present invention will be described in detail.

The polyurethane elastomer used for the coating roll of the present invention is described in, for example, JP-A-2000-538.
No. 55, a modified urethane rubber and the like.
The coating roll coated with the modified urethane rubber is made of a material in which 3 to 10% by weight of ultra-high molecular weight polyethylene powder is blended with urethane, the water repellency is increased, and the coating liquid is transferred from the applicator roll to the base paper. The transfer rate at the time of transfer increases, and the amount of the coating liquid remaining on the applicator roll after the transfer decreases, so that a decrease in the smoothness of the coated surface due to the cleavage of the coating liquid is suppressed.

[0015] The water repellency of the surface of the applicator roll of urethane containing polyethylene can be said to be a preferable level if the contact angle with water is 90 ° or more. However, if the height is too high, the coating liquid will be repelled on the surface of the applicator roll, causing coating unevenness on the surface of the coated paper. Therefore, the upper limit of the contact angle to water is 140 °.
The water repellency of the surface of the applicator roll varies depending on various factors at the time of roll molding or polishing, but is mainly governed by the surface roughness of the coated surface, and if the surface roughness Rmax is in the range of 10 to 50, the contact angle is reduced 90 ° to 140 °.

The above-mentioned effects are not limited to the composition of the coating liquid as long as they are aqueous coating liquids, but a preferable effect is produced by a combination with the composition of the coating liquid.

That is, 10 kg of wet-pulverized heavy calcium carbonate is added.
By coating the base paper with a coating liquid containing ５０50% by weight, the resistance at the time of paper separation from the applicator roll is suppressed, and the coating unevenness due to the unstable paper separation position is more easily avoided. As a result, The smoothness of the coating layer surface is improved.

Here, when the mixing ratio of the wet-pulverized heavy calcium carbonate exceeds 50% by weight, the water retention of the coating liquid is reduced, and the coating liquid is dehydrated at the nip of the applicator roll to increase the concentration. , The fluidity of the coating liquid decreases,
The flatness of the coating layer surface after cleavage is easily impaired. On the other hand, when the blending ratio of the wet pulverized heavy calcium carbonate is less than 10% by weight, the viscosity of the coating liquid is increased, and also in this case, the fluidity of the coating liquid is reduced, and the surface of the coating liquid after cleavage is reduced. Is easily impaired.

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, DI
Including pulp such as waste paper pulp such as P, various fillers such as light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, sizing agent, fixing agent, retention agent,
It contains various additives such as a cationizing agent and a paper strength enhancer, and is made into an acidic, neutral, or alkaline paper.

As the paper machine to be used, various types of paper machines such as a fourdrinier system, a circular net system, a twin-wire system, a hybrid system, a gap former type and a roll former type can be used.

As the base paper of the present invention, use is made of no-size press base paper, base paper size-pressed with starch, polyvinyl alcohol, or the like, or base paper undercoated with a pigment coating solution. However, basically, since a double-sided transfer type roll coater is often installed in a size press unit of a paper machine, it is often applied to a no-size press base paper.

As the pigment used in the coating layer, a commonly used pigment can be used. Examples of the coated paper pigment used in the present invention include kaolin, calcium carbonate, clay, satin white, talc, titanium oxide, aluminum hydroxide, silica, zinc oxide, activated clay, acid clay, silicon clay, and plastic pigment. Is mentioned.

Examples of the binder of the coating liquid used in the present invention include styrene / butadiene-based binders and styrene / butadiene-based binders.
Acrylic, vinyl acetate / acrylic, ethylene / vinyl acetate /
Various copolymers such as butadiene / methyl methacrylic, vinyl acetate / butyl acrylate and polyvinyl alcohol, maleic anhydride / styrene copolymer, isobutene
Synthetic binders such as maleic anhydride copolymers, acrylic acid / methyl methacrylate copolymers, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and cold-water-soluble starch obtained by flash-drying them, casein, Commonly known binders such as natural binders such as soybean protein are exemplified. Also, if necessary,
Various commonly used auxiliaries such as a lubricant, a dispersant, a thickener, a water retention agent, a defoaming agent, a waterproofing agent, and a coloring agent can be appropriately used.

In the method of coating the base paper according to the present invention, a film transfer system such as a shim sizer and a speed sizer, and a transfer type roll coater such as a gate roll coater are used.

The coated and dried coated paper can be subjected to a calendering treatment such as a super calender, a soft calender, and a machine calender.

The coated printing paper of the present invention can be printed by various printing methods such as sheet-fed offset printing, offset rotary printing, gravure rotary printing, flexographic printing, screen printing, and letterpress printing. In addition, UV curable and EB curable inks can be applied, and can be applied to high-definition offset printing of 300 lines or more.

[0027]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight", respectively.

Various measured values in the examples were obtained by the following methods. 1) Contact angle The contact angle was measured by a screen projection method using a contact angle meter CA-P manufactured by Kyowa Science Co., Ltd. 90 ° to 140 ° is good. (Unit: degree)

2) Smoothness Measured using a smoother smoothness meter (unit: kPa). As an index of flatness and smoothness, the lower the numerical value, the better.

3) Gloss Unevenness on White Paper Surface Gloss unevenness on a white paper surface at a size of several mm to several tens of mm was visually determined in five stages. Stage 3 and above are acceptable levels.

4) Gloss on white paper Measured at an angle of 75 degrees according to JISP8142. The higher the value, the better. (unit:%)

Example 1 <Preparation of base paper><Blending of pulp> LBKP (filtration degree: 350 mlcsf) 30 parts NBKP (filtration degree: 420 mlcsf) 70 parts The base paper was prepared by mixing the above pulp with the following internal additives. It was prepared.

<Blending of Internally Added Chemicals> Light calcium carbonate (average particle size: 3.4 μ, calcite type) 10 parts * Indicated by ash content in base paper. Commercially available alkyl ketene dimer-based internal sizing agent (AKD) 0.03 part Commercially available cationized starch 0.2 part Commercially available cationic polyacrylamide retention aid 0.03 part 60 g / m of the above pulp and internal chemicals A base paper having a basis weight of ² (absolutely dried) was made into a base paper. The paper machine is a Duoformer D type (manufactured by Ishikawajima Heavy Industries, Ltd.).
Papermaking was performed at a papermaking speed of 0 m / min.

<Preparation of Coated Paper> Hardness (JIS) of 89 mm is applied to the top applicator roll and urethane-coated roll of Rmax 20 is applied to the bottom applicator roll using a shim sizer installed after the paper machine pre-dryer. A urethane-coated roll containing Rmax20 and polyethylene 3% was put therein, and a coating solution having the following composition was applied onto the above-mentioned base paper at 6 g / m ^{2 on} one side, and dried with a cylinder dryer.

<Coating solution> (Pigment) 25 parts of wet heavy calcium carbonate (FMT90, manufactured by Fimatec) High-grade primary kaolin (Ultra White 90, manufactured by Engelhardt) 75 parts (Binder and additive) Commercial phosphoric acid esterification Starch (MS4400 manufactured by Nippon Shokuhin Kako Co., Ltd.) 3 parts Styrene butadiene latex (0617 manufactured by JSR) 14 parts Commercially available calcium stearate 0.6 part The pH was adjusted to 9.7 with aqueous ammonia. The solids concentration is 57%.

<Calendar Finish> The coated paper coated under the above conditions was processed under the following conditions immediately after coating and drying using a soft calender having the following specifications to obtain a coated paper for printing.

<Soft calender specification> Number of nips: 2 (a nip is formed so that the rigid roll surface once contacts each side of the coated paper) Rigid roll: diameter 80 cm, forged steel roll (with heating mechanism) Elasticity Roll: 70 cm diameter, synthetic resin (polyether resin) coated roll, Shore D hardness 89 degrees

<Soft calender treatment conditions> Treatment speed: 800 m / min Rigid roll surface temperature: 80 ° C. Linear pressure: 40 kg / cm The characteristics of the coated printing paper manufactured as described above are shown in Table 1 below. .

Example 2 The pigment formulation in Example 1 was as follows. (Pigment) Wet heavy calcium carbonate (Fimatec FMT90) 10 parts High-white first-order kaolin (Engelhard Ultra White 90) 90 parts

Example 3 The composition of the pigment in Example 1 was as follows. (Pigment) 50 parts of wet heavy calcium carbonate (Fimatec FMT90) 50 parts High white grade kaolin (Engelhard Ultra White 90) 50 parts

Comparative Example 1 The pigment formulation in Example 1 was as follows. (Pigment) 5 parts of wet heavy calcium carbonate (Fimatec FMT90) 5 parts High white grade kaolin (Engelhard Ultra White 90) 45 parts

Comparative Example 2 The pigment formulation in Example 1 was as follows. (Pigment) 55 parts of wet heavy calcium carbonate (Fimatec FMT90) 55 parts High-white kaolin (Engelhard Ultra White 90) 45 parts

Comparative Example 3 The bottom applicator roll in Example 1 was a urethane-coated roll having a hardness (JIS) of 87 ° and an Rmax of 20.

Comparative Example 4 The pigment formulation in Comparative Example 3 was as follows. (Pigment) 5 parts of wet heavy calcium carbonate (Fimatec FMT90) 5 parts High white grade kaolin (Engelhard Ultra White 90) 95 parts

Comparative Example 5 The pigment formulation in Example 3 was as follows. (Pigment) 55 parts of wet heavy calcium carbonate (Fimatec FMT90) 55 parts High-white kaolin (Engelhard Ultra White 90) 45 parts

Table 1 below summarizes the conditions of the above Examples and Comparative Examples and the evaluation results of the obtained coated paper for printing.

[0047]

[Table 1]

Evaluation: Examples 1-3 in Table 1 and Comparative Examples 1-2
From the results of the above, the hardness (JI
S) A coating containing urethane-coated rolls containing 87%, Rmax20, and polyethylene of 3% by weight is coated with 10 to 50% by weight of wet pulverized heavy calcium carbonate in all of the smoothness, glossiness of blank surface, and blankness of blank. By applying the liquid, good evaluation results were obtained.

From the results of Example 1 and Comparative Example 4, even when a coating solution containing 10 to 50% by weight of wet pulverized heavy calcium carbonate was applied, a urethane-coated roll containing no polyethylene was obtained. When it was used, the results were inferior in all of the smoothness, gloss unevenness of blank surface quality, and blank gloss.

[0050]

As is apparent from the above, the coated paper for printing of the present invention is obtained by wet-pulverized heavy calcium carbonate using a transfer type roll coater using a urethane-coated roll containing polyethylene as an applicator roll on at least one side. 1
By coating a base paper with a coating liquid containing 0 to 50% by weight, a coated paper for printing excellent in flatness and smoothness of a coating layer surface can be obtained.

Claims (1)

[Claims] At least the outermost coating layer has an ultrahigh molecular weight polyethylene powder having an active group such as an OH group and a COOH group with respect to a polyurethane prepolymer having an NCO group, and has an NH ₂ group or an OH group. A coating roll made of a polyurethane elastomer mixed and chemically bonded together with a cross-linking agent. At least one applicator roll is coated with a transfer-type roll coater using the coating roll. A coated paper for printing, comprising a coating layer obtained by applying a coating liquid containing 50% by weight to a base paper.