JP2001262494A - Method for producing coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coated paper for printing, not causing a coating unevenness on the surface of the coated paper resulting from accompanying air. SOLUTION: In this method for producing a coated paper for printing by coating a base paper with a coating solution having a pigment and an adhesive as main components by a coating apparatus of a curtain coating method, the method for producing the coated paper for printing is characterized in that a base paper having <=50 kPa Smooster smoothness and <=5 second Steckigt sizing degree is coated with the coating solution having <=40 dyne/cm surface tension and <=2,000 cps Brookfield viscosity.

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 and a method for producing the same, and more particularly, to a coated paper for printing free from uneven coating and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, pigment coated paper has been used as a coated paper for printing because of its high smoothness and gloss and uniform ink absorption as compared with uncoated fine paper. I have. In particular, in recent years, visualization of printed matter has been advanced, requirements for coated paper for printing have been diversified, and the printing method has also been gravure,
There is a wide variety of web offsets and sheet offsets, and the development of coated printing papers having characteristics suitable for each printing style is in progress. In such a situation, a demand for a coating technique of a printing coated paper for performing a pigment coating is to obtain a product having high surface smoothness and having no coating defects under high productivity.

[0003] There are a wide variety of coating methods for printing coated paper for performing pigment coating, and specific examples thereof include a blade coating method, an air knife coating method, and a roll coating method. However, in these coating methods, the type and shape of the pigment contained in the coating liquid must be restricted in consideration of the quality of the coated product and the stability of the process, and there is a great effect on improving the quality. Therefore, it is inevitable to give up the addition of a pigment having a high-quality printing coated paper.

[0004] That is, in the blade coating method, coating defects such as streaks and scratches tend to occur in the coating operation. If streaks or scratches occur, all of the occurrences will be wasted, resulting in large losses in terms of production efficiency and cost. In addition, the occurrence of these defects becomes more remarkable as the coating speed is increased and the coating concentration is increased, so that the efficiency of production and the improvement of quality are not compatible.

[0005] Further, in such a coating method, since the water or the binder component in the coating liquid enters the web more than necessary between the supply of the excess liquid and the measurement, the liquid scraped off as excess is , Different from the composition of the liquid before supply. Therefore, the composition of the coating liquid changes over time, and a product of stable quality cannot be obtained.

In the air knife coating method, a pattern peculiar to the air knife is easily generated in a coating layer. As a result, the gloss and smoothness of the surface of the coating layer are remarkably reduced, and not only the quality is reduced, but also a serious damage occurs during printing. This tendency becomes remarkable when the coating speed is increased or when the concentration of the liquid is increased, and it is not possible to achieve both efficiency of production and improvement of quality.

[0007] There are various types of roll coating methods depending on the combination of rolls and the like. Basically, a plurality of rolls are combined and the liquid is measured by transferring the coating liquid between the rolls and transferred to the web. It is a coating method. Such a coating method is likely to generate a roll-specific pattern, and also, when peeling after transfer of the coating roll surface and the web, the gloss of the coated surface, the smoothness is reduced, and the quality is reduced,
It is also a serious injury when printing. This tendency becomes remarkable when the liquid concentration or the coating speed is increased.

On the other hand, in the curtain coating method, the coating liquid flows in a restricted flow path only in the slit portion inside the coater head, and the slit width can be selected in a wide range. , 0.2 mm to 1.0 mm. In the curtain coating method, the liquid flowing out of the lip forms a free surface until it contacts the web, so that the flow path is not restricted. On the other hand, in the rod or blade coating method, the minimum gap between the blade and the web where the coating liquid is measured is usually 0.05 mm or less. Therefore,
When aggregates and foreign substances are present in the coating liquid, the probability of appearing as streaks is much lower in the curtain coating method than in the blade coating method.

Further, since the curtain coating method is a pre-measurement type coating method, the amount of the coating liquid flowing out of the head is recovered and used less. On the other hand, the blade coating method is a metering type coating method in which an excess amount of the coating liquid is once supplied and then scraped off and weighed. Many Further, in the blade coating method, when an excessive coating liquid is supplied to the web, water or a binder in the coating liquid is selectively absorbed by the web, and the concentration of the recovered liquid becomes high, so that the coating liquid becomes high. Concentration or foreign matter adhering to the base paper surface accompanies the recovered liquid and causes a streak. Therefore, in the curtain coating method, stable coating can be performed without a change in the concentration of the coating liquid even during long-time operation. Furthermore, since the curtain coating method is not a contact-type coating method in which the base paper and the metering blade are in contact with each other as in the blade coating method, paper breakage is extremely unlikely to occur, and operation is stable. It also has the advantage of being

As described above, the curtain coating method is a pre-measuring type coating apparatus, and since the coating liquid is not scraped off at the time of coating, the coating liquid does not break and the coating liquid follows the surface shape of the web. It forms a very uniform, so-called contour coating layer. This means that even if there are some irregularities in the web, the coating layer is uniform, so there is no occurrence of coating unevenness, especially when coating is performed on a web with excellent smoothness. An ideal coated paper for printing excellent in the smoothness of the coated surface and the uniformity of the coated amount can be obtained.

[0011] However, there are also problems with the curtain coating method. Although the curtain coating method is a coating method with excellent high-speed coating suitability, air is entrained in the web and the coating liquid when the coating speed is further increased to improve productivity. The phenomenon of so-called air entrainment appears. That is, the flow of air carried by the running web collides with the curtain film, and the contact line between the curtain film and the web, causing the curtain film and the contact line to move and entraining air between the web and the coating liquid. When this air entrainment phenomenon occurs, pinhole-shaped uncoated portions appear on the coated coating surface, and the pinhole-shaped uncoated portions become coating unevenness, and after printing, In this case, printing is not performed, and printing unevenness remains.

It is empirically known that such an air entrainment phenomenon becomes more conspicuous as the coating speed is higher, and becomes more pronounced as the smoothness of the web is reduced.

In a coated paper for printing, since such coating defects are fatal, suppressing the occurrence of the air entrainment is an important issue in increasing the coating speed. Is obvious.

[0014]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to produce high-quality products which cannot be realized by an air knife coating method, a blade coating method, and a roll coating method, and to cut the paper. Stable operability that enables long-term production is achieved by using the curtain coating method, and high-quality printing coating that enables high-speed coating without generating coating unevenness due to the air entrainment phenomenon. An object of the present invention is to provide a method for manufacturing paper.

[0015]

In other words, the method for producing a coated paper for printing according to the present invention is a method for coating a base paper with a coating liquid containing a pigment and an adhesive as main components by a curtain coating system. In the method for producing coated paper for coating, the surface tension of the coating liquid is 40
dyne / cm or less, B-type viscosity of the coating liquid is 2000 c
The coating liquid having a smoother smoothness of 50 kPa or less and a Steckigt size of 5 seconds or less is applied to the base paper using the coating liquid of not more than ps.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the coated paper for printing of the present invention will be described in detail. The method for producing a coated paper for printing according to the present invention is a method for producing a coated coated paper for printing that can be stably operated at a high speed without air entrainment in a curtain coating method. Will be described. Regarding air entrainment, various documents and various technical books describe various things. However, the present inventors conducted various experiments on air entrainment, and concluded that the phenomenon occurred due to the following two causes. I attached. That is, 1) that the amount of air taken in physically increases in proportion to the increase in the speed and the roughness of the surface of the base paper. 2) The instant of the coating liquid applied to the base paper as the speed increases. Is that the wettability becomes worse. In terms of the instantaneous wettability of the coating liquid on the base paper, from the viewpoint of the coating liquid, it has been found that if the viscosity of the coating liquid is too high, the wettability on the base paper deteriorates exponentially. It is known that the lower the surface tension of the coating liquid, the more instantaneous wettability can be secured. Further, from the viewpoint of the base paper, it is clear that the smoother the liquid, the more the wet spread immediately after application of the coating liquid is secured, and the greater the penetration of the coating liquid into the base paper, the more this instant Wettability increases. From these conclusions, in the coated paper for printing of the present invention, the B-type viscosity of the coating liquid which greatly affects the wettability of the coating liquid is 2000 cps or less, and the surface tension is 40 dy.
Ne / cm or less, the fluidity of the coating liquid and the wettability to the base paper are very good. The base paper used in the present invention has a smoother smoothness of 50 kPa or less and a Stekitto size of 5 kPa. Seconds or less, sufficient smoothness, sufficient instantaneous wettability to the coating liquid is secured, without causing air entrainment, at high speed,
It is clear that high quality coated paper for printing can be obtained.

The base paper used in the present invention is not particularly limited, and chemical pulp such as LBKP and NBKP,
GP, PGW, RMP, TMP, CTMP, CMP, C
Includes mechanical pulp containing GP, etc., waste paper pulp such as DIP, various fillers such as light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, sizing agent, fixing agent, retention improver, cationizing agent, paper strength It contains various additives such as a strengthening agent and is made into an acidic, neutral or alkaline paper.

A paper machine for producing the base paper is a variety of formers such as a circular net, a long net, and a twin wire, and a paper machine that combines the various formers to perform a lamination.

The coating pigment used in the present invention is not particularly limited. For example, kaolin clay, delaminated clay, calcined clay, heavy calcium carbonate, precipitated (light) calcium carbonate, aluminum hydroxide , Talc, titanium dioxide and the like, but the viscosity of the coating liquid,
From the viewpoint of the quality design of the coated paper for printing, it is preferable that calcium carbonate is contained in the coating liquid in an amount of 20% or more of the total pigment.

The copolymer latex used as the adhesive in the present invention includes a conjugated diene copolymer latex such as a styrene-butadiene copolymer, and a polymer or copolymer of an acrylate ester and / or a methacrylate ester. Acrylic polymer latex such as styrene
Vinyl polymer latex such as vinyl acetate copolymer,
Alternatively, a copolymer latex such as an alkali-sensitive or alkali-insensitive polymer latex obtained by modifying these various polymer latexes with a functional group-containing monomer such as a carboxyl group can be used. In particular, a conjugated diene-based copolymer latex such as a styrene-butadiene copolymer is preferably used in consideration of the pigment binding force, workability, cost, and the like. The average particle diameter of these copolymer latexes is preferably 150 nm or less from the viewpoint that the viscosity of the coating liquid increases when the average particle diameter is too large, and the amount of addition is preferably in terms of quality design as coated paper for printing. Addition of 5 parts by weight or more is preferred.

The starch used as an adhesive in the present invention includes oxidized starch, etherified starch, esterified starch, enzyme-modified starch and natural binders such as cold-water-soluble starch, casein and soy protein obtained by flash-drying them. However, when the amount of added starch is increased, the viscosity of the coating liquid is increased, and the amount is preferably 6 parts by weight or less from the viewpoint of quality design as coated paper for printing.

Other surfactants used in the present invention include anionic surfactants such as carboxylate, sulfonate, sulfate and phosphate, ether type, ether ester type, ester type, and the like. Nonionic surfactants such as nitrogen-containing surfactants, betaine, aminocarboxylates, amphoteric surfactants such as imidazoline derivatives, and the like, but the addition amount of these surfactants, wetting of the coating solution, From the viewpoint of ensuring the stability of the curtain film during operation, it is preferable to add 0.1 parts by weight or more.

Further, other commonly used auxiliaries such as a dispersant, a thickener, an antifoaming agent, a lubricant, a dye, a pH adjuster, and a water retention agent may be appropriately used.

The coating composition of the present invention can be easily adjusted by weighing the above-mentioned components and blending them using, for example, a disperser such as a Coreless disperser or a Keddy mill.

The method of applying the coating composition according to the present invention to base paper is a curtain coating method, and the coating amount on one side or both sides of the base paper is 5 to 20 g / m ^{2 in} absolute dry weight.
, Preferably in the range of 10 to ²⁰ g / m ² , by on-machine and off-machine. If the coating amount is less than 5 g / m ² , the formation of the curtain film is practically unstable, and the coating liquid must be diluted to increase the supply flow rate as a means for stabilizing the curtain film. However, even if the coating liquid is diluted to stabilize the curtain film, if it is 5 g / m ² or less, sufficient covering will not be realized in terms of the coating property of the coating layer rather than air entrainment. A load is imposed on drying, and a satisfactory product cannot be obtained in terms of cost, which is not the object of the present invention.
Further, if it is more than 20 g / m ² , although it is certainly very effective in improving air entrainment, the effect reaches a plateau and is not suitable because the cost is further increased.

[0026]

EXAMPLES The present invention will be described below in detail with reference to examples, but the contents of the present invention are not limited to the examples.

Evaluation of coating unevenness accompanying air entrainment was performed by the following method. The coated layer surface of the manufactured coated paper is image-analyzed, and the area ratio of pinhole-shaped coating defects generated by air entrainment is measured. The degree of occurrence is XX: extremely large, X: many , △: little, ○: almost none,
◎: No evaluation was made. The level that can be satisfied as a printed matter using the coated paper for printing is ○ or more.

Example 1 A base paper was prepared by mixing commercially available LBKP (freeness of 35) with pulp.
0 mlcsf), 30 parts by weight of commercially available NBKP (freeness 4
20 mlcsf) as a pigment to be included in 70 parts by weight,
10% by weight of light calcium carbonate in distribution, 0.03 parts by weight of other alkyl ketene dimer-based filling sizing agent,
A commercially available cationized starch adjusted to 0.02 parts by weight and a commercially available cationic polyacrylamide retention improver adjusted to 0.03 parts by weight were used. The smoother smoothness of the base paper thus prepared was 40 kPa, and the Stechigt size was 4.0 seconds.

Next, heavy calcium carbonate 5 was used as a pigment.
0 parts by weight, 50 parts by weight of kaolin, and 0.4 parts by weight of sodium polyacrylate as a dispersing agent are dispersed in water using a Cores dispersing machine, and a styrene / butadiene copolymer having an average particle diameter of 140 nm is used as an adhesive. 10 parts by weight of the combined latex and 4 parts by weight of the phosphorylated esterified starch were added and stirred. Then, NaOH was added so that the pH became 9.7, and 0.15 parts by weight of acetylene glycol as a surfactant was added. Carboxymethyl cellulose as a water retention agent
After adding 2 parts by weight, water was added to obtain a coating composition having a B-type viscosity and a surface tension value shown in Table 1 below and having a solid content of 60%.

Next, the coating composition was coated at a coating speed of 1000 m.
/ Min using a curtain coater, the coating amount of the felt surface and wire surface, respectively 10 g / m ² and 11g / m ^2,
The coated paper was coated so that the moisture value became 6.0% by weight, and the obtained coated paper for printing having a length of 10,000 m was rolled at a surface temperature of 60 ° C., a linear pressure of 200 kg / cm, and a speed of 400 m / min. Super calendar treatment was performed under the conditions, and coating unevenness accompanying air entrainment was evaluated.

Example 2 The average particle size and the amount of styrene / butadiene copolymer latex, the amount of phosphate esterified starch, and the amount of acetylene glycol as a surfactant were shown in Table 1 below.
The procedure was performed in the same manner as in Example 1 except that the sample was prepared so as to have the numerical values described.

Comparative Examples 1 to 10 The average particle size and amount of styrene / butadiene copolymer latex added, the amount of phosphorylated starch added, and the amount of acetylene glycol added as a surfactant were set forth in Table 1 below.
The procedure was performed in the same manner as in Example 1 except that the sample was prepared so as to have the numerical values described.

[0033]

[Table 1]

As is clear from Table 1, the printing coated paper in the present invention is an excellent printing coated paper free of coating unevenness caused by air entrainment.

Example 3 As a base paper, a coating solution was prepared by changing the amount of a commercially available cationized starch, or changing the speed and linear pressure of a super calender so as to obtain the Stechigt size and smoother smoothness shown in Table 2 below. As a pigment, 20 parts by weight of heavy calcium carbonate, 80 parts by weight of kaolin, 0.4 parts by weight of sodium polyacrylate as a dispersant are dispersed in water using a Coreless disperser, and an average particle diameter is used as an adhesive. Was added with 5 parts by weight of a styrene-butadiene-based copolymer latex and 6 parts by weight of phosphorylated esterified starch, followed by stirring. Then, NaOH was added so that the pH became 9.7, and a surfactant was added. 0.1 parts by weight of acetylene glycol as
After adding 0.02 parts by weight of carboxymethylcellulose as a water retention agent, water was added to prepare a coating composition having a solid content concentration of 60% in the same manner as in Example 1. The coating product had a B-type viscosity of 1950 cp.
s, surface tension was 39 dyne / cm.

Examples 4 to 6 The amount of commercially available cationized starch added was changed so as to obtain the Stechigt size and smoother smoothness shown in Table 2 below.
The procedure was performed in the same manner as in Example 3 except that the speed and the linear pressure of the super calender were changed.

Comparative Examples 11 to 16 The amount of the commercially available cationized starch added was changed so that the Stechigt size and smoother smoothness described in Table 2 below were obtained.
The procedure was performed in the same manner as in Example 3 except that the speed and the linear pressure of the super calender were changed.

[0038]

[Table 2]

As is clear from Table 2 above, the coated paper for printing in the present invention is an excellent coated paper for printing without generation of coating unevenness accompanying air entrainment. Further, as is clear from the comparison between Tables 1 and 2 above, the values of the surface tension and the B-type viscosity of the coating liquid, the smoother smoothness of the base paper, and the Steckigt size were all not found, and the present invention was not considered. It can be seen that the effect of is not obtained.

[0040]

The method for producing a coated paper for printing according to the present invention comprises a coating liquid having a specific surface tension and a B-type viscosity as a coating liquid, and a specific smoother smoothness and a Stechig size as base paper. By coating the base paper with the coating liquid using a coating apparatus of a curtain coating system, thereby producing an excellent printing coated paper free from coating unevenness accompanying air entrainment. Can be done.

Claims (1)

[Claims] 1. A method for producing a coated paper for printing, in which a coating liquid containing a pigment and an adhesive as main components is applied to a base paper by a curtain coating type coating apparatus, wherein the surface tension of the coating liquid is reduced. 40
dyne / cm or less, B-type viscosity of the coating liquid is 2000 c
A method for producing a coated paper for printing, characterized in that a smoother smoothness of 50 kPa or less and a Stechigt size of 5 seconds or less are applied to a base paper using a coating liquid of ps or less.