JPH11100789A - Production of coated paper for offset printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coated paper for rotary offset printing, excellent in smoothness, gloss and stiffness and having excellent running stability on a rotary offset press by using a base paper prepared by forming a sheet of the base paper with a paper machine having a gap type twin-wire former. SOLUTION: A sheet of base paper is produced by dehydration at the ratio of dehydration amount (top wire side/bottom wire side) onto both wire sides until the raw material solid concentration attains 2.5 wt.% in a twin-wire former part within the range of >=0.85 and <=1.15 with a wet press device containing one or more presses of a wide nip, and a coating layer is then formed on the base paper. The resultant coated base paper is subsequently threaded through a hot soft calender to carry out the smoothing and finishing treatments in the production of a coated paper for rotary offset printing by coating and drying the formed sheet of the base paper prepared by using a gap type twin- wire former with a water-soluble coating composition consisting essentially of a pigment and an adhesive and finishing the dried coated base paper. The wet press device of the wide nip is a shoe pressing type wet press device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a coated paper for web offset printing. Especially for web offset printing with excellent smoothness, gloss and rigidity and excellent running stability on web offset presses using base paper obtained by papermaking with a paper machine having a gap type twin wire former. The present invention relates to a method for producing a coated paper.

[0002]

2. Description of the Related Art In recent years, in the papermaking industry, paper machines have become wider and faster for the purpose of labor saving and reduction of manufacturing costs.
Many modifications have been made from Fourdrinier formers to on-top type formers. By installing a top wire on the wire of the Fourdrinier and making it an on-top type, insufficient dewatering capacity in the wire part due to high speed, deterioration of formation due to disorder of the raw material surface, It has become possible to suppress the increase in the difference in properties between the front and back of the paper due to the reinforcement. However, when the papermaking speed of the paper machine exceeds 1200 m / min, the on-top type former starts to deteriorate the formation due to the increase in the disorder of the surface of the raw material in the initial fourdrinier part, which causes a deterioration in product quality. So
No further speed increase is possible.

[0003] A gap-type former has been developed in order to enable operation at higher speeds, in which the raw material exiting the headbox is immediately sandwiched between two wires. In the gap former, the raw material exiting the head box is immediately sandwiched between two wires, thereby making it possible to compensate for the shortage of dewatering ability due to the increase in speed. In addition, the free surface of the raw material on the wire can be eliminated, and the dewatering pressure applied to the raw material between the wires can be optimized. For this reason, gap formers were first introduced in the newsprint manufacturing field, and are now the main models.

[0004] However, depending on the reduction of the retention of the raw material on the wet paper web surface due to the strong dewatering of the raw material immediately after leaving the head box on both wire surfaces and the difference in the dehydration ratio from the both wire surfaces, the raw material may be left and right. It also has the disadvantage of causing differences in characteristics. Therefore, manufacturing a coated paper for web offset printing using base paper manufactured by a paper machine having this gap former in the wire part requires smoothness of the surface of the product, deterioration of gloss after printing, and difference between front and back. Cause trouble. For the offset rotary printing coated paper, the reduction in surface smoothness and gloss after printing lowers the value of the product and significantly lowers the user's trust, and is an issue that must be improved promptly.

[0005] In view of the above, Japanese Patent Laid-Open Publication No. Hei 4-222 aims to improve the inherent disadvantages of base paper made by a paper machine having a gap former in the wire part.
Japanese Patent Publication No. 288 discloses a design in which the position of a forming roll of a top wire forming a gap is designed to be adjustable in a vertical direction, and a paper layer forming condition of an on-top former and a gap former can be selected by a single former. It has been proposed to manufacture according to requirements.
However, in paper machines that are increasing speed with the primary purpose of improving production efficiency, it is necessary to significantly change the conditions of the former section in accordance with the type of papermaking machine, and to operate with changes in conditions and adjustments. The wasted time and the resulting reduction in product production is too great to be a viable solution. Therefore, there is a strong demand for finding a method of producing a base paper for coated web for offset rotary printing having better printing characteristics while utilizing the characteristics of the gap former that can be operated at high speed.

[0006] With the flow of multimedia, the need for higher quality, such as visualization and colorization, of printed matter that has been widely used as a medium for publishing, advertising, publicity, etc. has been rapidly increasing. Along with such a change in user demand, switching from conventional uncoated printing paper to printing coated paper is increasing, and demand for printing coated paper is rapidly increasing. In addition, from the printing process, quality requirements for handling properties of printing paper and running stability on a printing press, which lead to improvement in workability and efficiency, have become increasingly severe.

[0007] In response to these quality requirements, a heat soft calender capable of obtaining high smoothness and gloss has attracted attention in recent years (Paper Pulp Technology Times / August 1987, pp. 31-36; Pulp & Paper Intern).
ational / November 1987, 45-47
page). That is, a thermal soft calender usually has one metal roll.
This is a method in which the coated paper is pressed and smoothed by heating it to 00 ° C. or higher. This method has an advantage that a high surface smoothness and a high print gloss can be obtained with a small number of nips as compared with the conventional super calender, and the product rigidity can be maintained at a relatively high value. This is because while passing through a nip consisting of a heated metal roll and an elastic roll, a thermoplastic material such as latex used as an adhesive in the coating layer is plasticized by high temperature and pressure, and the pigment in the coating layer Can be effectively oriented to smooth the surface of the coating layer, and the base paper layer inside can be kept relatively bulky with a small number of nips.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for producing a coated paper for web offset printing using base paper obtained by making a paper machine having a gap type twin wire former. Things.

[0009]

Means for Solving the Problems The present inventors have studied a method of producing a base paper having better characteristics for coated paper than a base paper made with a conventional on-top type former under high-speed operation conditions. In order to do this, we conducted intensive studies on the properties of base paper made with a paper machine having a gap former in the wire part. As a result, we found that the properties of the base paper greatly changed depending on the dewatering conditions and wet pressing conditions in the gap former. Therefore, the present inventors examined the density in the thickness direction of the base paper formed by the gap former and the distribution state of fine fibers in detail, and as a result, dehydration from both wires-surface at the time of low concentration in the gap former. ,
It was found that many fine fibers gathered on the surface layer of the base paper. By combining this with a wet-type shoe-type wide nip press that can arbitrarily change the pressure and nip width at the entrance and exit of the nip, even under high-speed operation conditions, it differs from the base paper conventionally formed by on-top former. It is bulky, the density of both surface portions of the base paper is high, fine fibers are localized in both surface portions, and the difference in characteristics between the front and back surfaces is small, so that it is possible to obtain an excellent base paper for coated paper for printing. I found what I could do.

Further, the inventors of the present invention have made a conventional coated paper for printing by finishing a coated paper for offset printing using the base paper with a coated layer using a thermal soft calender. It has been found that excellent printing characteristics that are unprecedented are imparted, and the present invention has been achieved.

That is, a first aspect of the present invention is offset rotary printing, in which a base paper made by a gap type twin wire former is coated with an aqueous coating composition containing a pigment and an adhesive as a main component and then dried to finish. In the production of coated paper for
The dewatering ratio (top wire side / bottom wire side) of both base wires until the base paper reaches a raw material solid concentration of 2.5% by weight in the twin wire-former section is 0.8.
The base paper is manufactured in a range of 5 or more and 1.15 or less, and is obtained by dewatering with a wet press device including one or more wide nip presses. Apply the aqueous coating composition as a component
After drying and providing the coating layer, smoothness characterized by performing a smoothing finish treatment by passing the paper through a heat soft calender,
This is a method for producing a coated paper for offset rotary printing having excellent gloss and rigidity and having excellent running stability on an offset rotary printing press. The second aspect of the present invention is the method for producing coated web for offset rotary printing according to claim 1, wherein the wide nip press of the wet press device is a shoe press type wet press device.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, paper pulp used for making base paper refers to pulp obtained by subjecting wood and non-wood raw materials to known and publicly used cooking, bleaching and selective treatment, or recovered from the city. Waste paper and pulp obtained by subjecting waste paper and waste paper generated in papermaking and printing plants to defibration, dust removal, selective treatment, and, if necessary, deinking and bleaching. The preparation conditions of the raw material are not particularly limited, and a beating treatment and various papermaking chemicals and additives are appropriately used.

According to the present invention, the raw material thus obtained is made into a paper by a gap former, and then dewatered by a wet press.
After producing a base paper for coated paper with a small difference between the front and back sides, a high density of both surface layers, a high bulk and a high rigidity, and coating and drying an aqueous coating composition containing a pigment and an adhesive as main components, heat By passing the paper through a calender, the smoothness and density of the coating layer are improved, and excellent printing characteristics and running stability are imparted.

The wet press used in addition to the paper machine having the gap former is not particularly limited, but should be a machine that can meet the high-speed papermaking conditions of 1200 m / min or more. is necessary. That is, under high-speed operating conditions of 1200 m / min or more, a conventional roll-type wet press device, that is, a wet press device that passes a wet paper together with felt through a narrow nip formed between rolls to remove water and removes the wet paper, is required. In order to increase the solid content concentration of paper, it is necessary to increase the linear pressure.In the nip, the water pressure near the roll surface increases rapidly, causing breakage between the paper layers and only the fiber density on the felt side. And the density difference between the front and back sides of the base paper becomes very large, making it difficult to obtain high quality coated printing paper. Therefore, as a wet press device attached to a high-speed paper machine having a gap former as in the present invention, a wet press device having a shoe-type wide nip is preferably used in order to obtain a product of excellent quality. .

Further, when the operation is performed by combining a gap former and a wet press apparatus having a shoe-type wide nip, the ratio of the amount of dewatering from the low-concentration raw material to both wires in the gap former part is determined by the wet paper web. It is very important in forming a symmetrical structure, and the ratio of the amount of dehydration to both wires until the solid concentration of the raw material between the wires reaches 2.5% by weight (top wire / bottom wire) Side) is preferably in the range of 0.85 or more and 1.15 or less. By the way, if the ratio of the amount of dehydration to both wire sides (top wire side / bottom wire side) is less than 0.85 and exceeds 1.15, the difference in fiber density between the front and back layers of the base paper becomes too large. As the characteristic difference between the front and back layers of the paper increases, the running stability on an offset rotary printing press gradually becomes unstable. The reason why good base paper properties can be obtained by controlling the ratio of the amount of dehydration to both wires up to a specific solid content concentration as described above is not necessarily clear, but is presumed as follows. That is, although the role of the fine fibers in the paper layer structure on the properties of the paper is very large, the movement of the fine fibers inside the wet paper is easy up to a solid content concentration of about 2.5% by weight. If the concentration exceeds the concentration, it is considered that the movement of the fine fiber is difficult even if the dehydration conditions are largely changed, and it is difficult to form a symmetrical paper structure.
Therefore, it is important to control the dewatering amount ratio up to a solid content concentration of 2.5% by weight.

Further, a water-soluble coating composition containing a pigment and an adhesive as a main component is coated on the base paper thus formed, dried to form a coating layer, and then passed through a hot soft calender. The paper is smoothed. Such coated paper exhibited excellent smoothness and print gloss in addition to excellent running stability on an offset rotary printing press, and thus was found to have better offset printing suitability than before. As described above, the present invention coats an aqueous coating composition containing a pigment and an adhesive as main components on a base paper formed by a paper machine combining a gap press and a wet press apparatus having a wide nip of a shoe type, This is a method for producing a coated paper that has been dried and provided with a coated layer and then subjected to a thermal soft calender finish.

Prior to the formation of the coating layer, an adhesive or the like is appropriately applied to the base paper using various size presses, roll coaters, or the like to perform a surface treatment to reinforce the paper strength or to improve the pigment strength. It is also possible to use a base paper or the like which is preliminarily coated with a paint mainly composed of an adhesive and an adhesive by a roll coater or a blade coater. Further, it is particularly preferable that the base paper is smoothed in advance using an online soft calender before coating, in order to make the coating layer after coating uniform.

As a pigment which is a main component of the coating material, a pigment used in a usual coated paper manufacturing field can be appropriately used. Specifically, kaolin, clay, calcined kaolin, amorphous silica, zinc oxide, aluminum oxide, calcium carbonate,
One or two or more of satin white, aluminum silicate, magnesium silicate, magnesium carbonate, plastic pigment and the like are appropriately mixed and used.

As the adhesive used in combination with the above-mentioned pigments, adhesives used in the ordinary coated paper manufacturing field can be appropriately used. For example, various starches such as starch and oxidized starch, casein, soy protein,
Proteins such as synthetic proteins, polyvinyl alcohol, cellulose derivatives such as carboxymethyl cellulose and methyl cellulose, styrene-butadiene copolymer, conjugated diene-based polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, ethylene-
A vinyl polymer latex such as a vinyl acetate copolymer is used alone or in combination of two or more. The amount of the adhesive is 5 to 50% by weight based on the solid content of the pigment.
More preferably, it is adjusted to 10 to 30% by weight. In addition to the pigments and adhesives in the paint, various auxiliary agents such as dispersants, thickeners, defoamers, coloring agents, antistatic agents, preservatives, etc. used in the field of general coated paper production Can also be added as appropriate.

The coating composed of the above-mentioned materials is generally adjusted to have a solid content of about 30 to 70% by weight, and is coated on the above-mentioned base paper such that the dry weight per side is ² to 40 g / m ^2. Or a blade coater divided into multiple layers,
Coating and drying are performed by various known and publicly used coating apparatuses such as an air knife coater, a roll coater, a brush coater, a chaplex coater, a bar coater, and a gravure coater. When the coating layer is provided in a plurality of layers, the raw materials of the pigment and the adhesive in the upper layer and the lower layer can be changed, and the mixing ratio and the like can be appropriately changed in consideration of the quality characteristics of the final product.

In the present invention, the coated paper obtained as described above is passed through a heat soft calender comprising a metal roll and an elastic roll which are usually heated to 100 ° C. to 300 ° C. to perform pressure finishing. The nip pressure and the number of nips of the calender are not particularly limited. In particular, it is more effective to use a metal roll or the like whose surface is mirror-finished with hard chrome plating or the like. Further, the material of the elastic roll used as a pair with the metal roll of the thermal soft calender is not particularly limited, but generally, urethane resin, epoxy resin, polyamide resin, phenol resin,
A resin roll showing durability at high temperature and high pressure, such as a polyacrylate resin, is preferably used. When the resin roll has a hardness of 85 degrees or more in shear D hardness, excellent surface smoothness can be obtained.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, of course, are not intended to limit the present invention. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified. The amount of dewatering on each wire surface and the concentration of wet paper web between the wires were calculated from the flow rate of white water from each dewatering element of the former part, the solid content concentration, the flow rate of the head box, and the solid content concentration.

Example 1 (Preparation of base paper) Talc was used as a filler in a pulp slurry composed of 90 parts of LBKP and 10 parts of NBKP, and the ash content in the paper was 9%.
Then, 0.1 part of a rosin sizing agent (trade name: Size Pine E / Arakawa Chemical Co., Ltd.) and 2 parts of aluminum sulfate were added as internal sizing agents to 100 parts of the solid content, respectively. To adjust the raw materials. The stock was made with a gap former at an operating speed of 1200 m / min to form a wet paper. At this time, the dehydrating conditions of the forming shoe were set such that the ratio of the dehydration amount on both wire sides (top wire side / bottom wire side) until the solid content concentration of the raw material reached 2.5% by weight was 0.90. . The wet paper was further dehydrated by a wet press device having a shoe-type wide nip press to obtain a base paper. 2 on this base paper
With this roll size press, a 6% concentration of oxidized starch (trade name: Ace A / Oji Cornstarch Co., Ltd.) solution was applied to a solid content of 2 g / m ² (both sides), dried and dried.
8 g / m ² of base paper for coated paper was obtained.

(Preparation of paint) Kaolin (trade name: UW9)
0 / EC) 30 parts, heavy calcium carbonate (trade name:
Pigment and dispersant consisting of 70 parts (FMT-90 / Fimatec) (Aron A9 / Toagosei Co., Ltd.)
Was dispersed using a Coreless disperser to obtain a pigment slurry. An oxidized starch solution (trade name: SN-113) was added to this slurry.
(Manufactured by Sumika A & L) was added to prepare a paint having a solid content of 60%.

(Production of Coated Paper) The thus prepared paint was applied onto the above-mentioned base paper for coated paper at a rate of 15 g / m 2 per side.
Coating was performed on both sides with a blade coater so as to obtain ² .
The obtained double-sided coated paper was applied to a thermal soft calender consisting of a metal roll and a resin roll heated to 180 ° C. with a linear pressure of 200
Under a pressurizing condition of kg / cm, the paper was passed through a total of 4 nips such that one side thereof was in contact with the metal roll and the resin roll twice each to obtain a coated paper for printing.

Example 2 When forming a wet paper web, the ratio of the amount of dewatering to both wire sides until the solid content concentration of the raw material reaches 2.5% by weight (top wire side /
A coated paper for printing was obtained in the same manner as in Example 1 except that the shape of the forming shoe was changed so that the bottom wire side was 1.10.

Comparative Example 1 When forming a wet paper web, the ratio of the amount of dewatering on both wire sides until the solid content concentration of the raw material reaches 2.5% by weight (top wire side /
A coated paper for printing was obtained in the same manner as in Example 1, except that the shape of the forming shoe was changed so that the bottom wire side was 1.30.

Comparative Example 2 When forming a wet paper web, the ratio of the amount of dehydration to both wires until the solid content concentration of the raw material reaches 2.5% by weight (top wire side /
A coated paper for printing was obtained in the same manner as in Example 1, except that the shape of the forming shoe was changed so that the bottom wire side was 0.80.

Comparative Example 3 A coated paper for printing was obtained in the same manner as in Example 1 except that the wet press was changed to only a roll press having no shoe-type press.

Comparative Example 4 Instead of the hot soft calender after coating, a surface temperature of 25 was used.
Except that a total of 10 nips of paper were passed through a super calender composed of a metal roll and a cotton roll at a temperature of 200 ° C. under a linear pressure of 200 kg / cm so that one side was in contact with the metal roll and the resin roll five times each. In the same manner as in Example 1, a coated paper for printing was obtained.

Comparative Example 5 Example 1 was repeated except that the wire part was changed from a gap former to an on-top former, and only the downward dehydration was performed until the raw material concentration reached 2% by weight, and the operation speed was 1000 m / min. A coated paper for printing was obtained in the same manner as described above.
The quality evaluation shown below was performed on each coated paper thus obtained, and the results are shown in Table 1. (Quality Evaluation Method) (Glossiness) Measured according to JIS-P8142. (Stiffness) It was measured using a Clark stiffness tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) in accordance with the method A of JIS-P8143. (Visual Smoothness) The surface smoothness of the coated paper was visually judged according to the following standard. ◎: very good ○: good △: slightly poor (running stability on printing press) 4 with commercial offset printing press
Color printing was performed, and the running conditions such as wrinkles and meandering at that time were comprehensively determined according to the following standard. ◎: very good ○: good △: slightly poor

[0032]

[Table 1]

[0033]

As is clear from the results in Table 1, the coated paper for offset printing obtained by the method of the present invention has a glossiness,
The coated paper is excellent in smoothness and rigidity and extremely excellent in running stability on a printing press.

Claims (2)

[Claims] 1. A method for producing coated paper for offset rotary printing wherein a base paper made by a gap type twin-wire former is coated with an aqueous coating composition containing a pigment and an adhesive as a main component and then dried to finish. The base paper is a twin wire
In the former part, the dewatering ratio (top wire side / bottom wire side) to both wire sides until the raw material solid content concentration reaches 2.5% by weight is produced in the range of 0.85 or more and 1.15 or less, and A base paper obtained by dewatering with a wet press device including at least one wide nip press, and applying and drying an aqueous coating composition containing a pigment and an adhesive as a main component on the base paper; A method for producing a coated paper for offset rotary printing, comprising providing a coated layer and passing the paper through a thermal soft calender to perform a smoothing finish. 2. The method for producing coated web for offset rotary printing according to claim 1, wherein the wide nip press of the wet press device is a shoe press type wet press device.