JPH06146197A - Production of lightweight pigment coated paper - Google Patents

Abstract

PURPOSE:To produce lightweight pigment coated paper excellent in print quality of both sides of coated paper, particularly excellent in gloss. CONSTITUTION:In producing pigment coated paper in which pigment coated layer of 1.5-10g/m per side is provided on the one side (surface A) or both sides (surfaces A and B) of support having 27-60g/m<2> absolute dry basis weight, a support having 2-8wt.% water content is pressed to one or more sets of calendering device composed of an elastic roll having 60-88 shore D hardness and a metallic roll before a coating device for the surface A or/and the surface B, to subject the support to smoothing treatment and as necessary, one side or both sides of the resultant coated paper is subjected to supercalendering treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lightweight pigment coated paper. More specifically, the present invention provides a single-sided coating amount of 10 g / m for offset printing or gravure printing.
^It relates to a method for producing a lightweight coated paper having a smoothness and gloss after coating of ² or less.

[0002]

2. Description of the Related Art In recent years, the tendency of visualization and colorization in the printing and publishing industry has become stronger, and the coating amount on one side is 10 to 20 g /
m ² of coated paper, single-sided coating amount 20-25 g / m ² art paper, one-side coating amount 25 g / m ² or more cast-coated paper,
Demand for pigment-coated paper such as medium-quality paper and lightly-coated paper with a total coating amount on both sides of 15 g / m ² or less is growing remarkably, and their applications are expanding in various fields.

In particular, in offset printing paper, among them, a coating layer mainly composed of a pigment composition is provided on a cellulosic support containing 5% or more of mechanical pulp or high yield pulp of 87% or more in yield. The growth of medium-quality coated paper is remarkable, and in particular, there is an increasing demand for medium-quality coated paper with high glossiness and light weight (or low US grammage) for direct mails or publications for publication.

As a general method for increasing the glossiness of pigment-coated paper, (a) a method of increasing the coating layer, (b) an inorganic pigment or a pigment for increasing the glossiness of the coating layer itself. A method of selecting and using an organic pigment, (c) a method of selecting and using a latex compounded in a coating layer that easily develops glossiness, and (d) coating in a glossing device such as a super calendar. Methods for enhancing the surface treatment of layers are known.

In the case of producing a pigment-coated paper having a high glossiness, it is general to carry out the above methods in combination and further improve each method. In the case of a pigment-coated paper having both properties, it is difficult to manufacture the intended pigment-coated paper because the coating layer is increased and the weight is not compatible.

That is, since it is a necessary condition that the pigment coated paper has a low basis weight as a whole, an increase in the coating amount for obtaining a high glossiness results in a reduction in the basis weight of the coating base paper or the support. I have to do it. However, when the basis weight of the base paper is reduced, the strength becomes weak, paper breakage occurs when the pigment coating composition is applied, and the frequency thereof increases, which deteriorates the operability and also causes a problem when printing as a product. However, there is a problem that adverse effects in various fields become noticeable such as paper breakage troubles.

Further, for the purpose of improving the strength of the coated base paper, increasing the blending ratio of chemical pulp, especially kraft pulp (KP) and decreasing the blending ratio of mechanical pulp suppresses the development of glossiness. Or, it causes another problem that the opacity of the base paper is lowered. Therefore, in order to produce a light weight pigment coated paper having a low basis weight and a high glossiness, a coating composition that easily develops the glossiness is used, and a coating layer as small as possible is provided on the base paper. It is therefore clear that it is preferable to secure the basis weight of the base paper as large as possible.

However, although a combination of these techniques has been developed and researched by many engineers, researchers, etc., they sufficiently satisfy the required quality of having high gloss and light weight, and further, the operation. To date, no technology has been developed that satisfies stability and low manufacturing costs.

On the other hand, it is possible to increase the glossiness of the coated surface by improving the smoothness of the coated base paper to improve the uniformity and coverage of the pigment coated surface. This method is described below. Problem exists.

When manufacturing coated base paper for use in an off-machine coater, a machine comprising a combination of a large number of metal rolls installed between a dryer and a winding machine (reel) of a known paper machine. The surface of the coated base paper can be treated with a calendar to improve smoothness.
Although common to both off-machine coater and on-machine coater, it is coated with a breaker stack consisting of a pair of fully polished metal rolls, one at the top and one at the bottom of the dryer zone of the paper machine or at the latter stage. The smoothness of the surface of the base paper can be improved by pressing the base paper, but the coated base paper treated with these metal rolls is caused by unevenness in the texture of the base paper generated at the time of papermaking and variation in basis weight. Unevenness, crushing unevenness due to variations in the surface properties of the metal roll itself easily occur, eventually it becomes difficult to provide a uniform coating layer on the base paper for coating, and a pigment with high glossiness without unevenness Manufacturing coated paper is difficult.

On the other hand, when a so-called soft calender is used, in which one of the pair of rolls is an elastic roll covered with natural rubber, synthetic rubber, cotton or the like, and the other one is a metal roll. There is. Examples of the use of this soft calendar include those used for calendering final products and those applied to breaker stacks of newsprint paper.However, when the coated base paper is manufactured, it is treated with a breaker stack to improve the characteristics of the base paper. The concept to do is described in Pulp and Paper Technology Times, May 1988, page 11, but it is not specifically described, and various problems to be solved still exist.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied the above-mentioned pre-calendering treatment of the coated base paper, and as a result, the soft calender consisting of an elastic roll and a metal roll was replaced with a breaker stack consisting of a pair of conventional chilled rolls. The base paper having a specific moisture content is treated with one or more sets of elastic rolls having a hardness within a specific range and a metal roll, and then a pigment coating layer is provided, which is excellent in a small coating amount. We proposed a method to obtain high quality lightweight coated paper (Japanese Patent Application No. 3-213205).

As a result of further research by the present inventors, when a coating layer is formed on the first side (called A side) of the base paper in single-sided coating or double-sided coating and dried, it is not yet coated. The smoothness of the second surface (the surface opposite to the A surface, referred to as the B surface) is remarkably reduced, and even if a coating layer is formed on the second surface by super calendering to finish the surface, It was found that the glossiness is extremely difficult to increase, and in addition to the soft calender being provided at the breaker stack position, one side of the base paper is coated on one side, and then on the front side of the coating machine for coating on the B side. In addition, if a soft calender consisting of elastic rolls and metal rolls is installed and the surface to be coated is made smooth before coating, the glossiness after coating, especially the glossiness by supercalendering, can be manifested. Noticeable, even higher on both sides on average And we have completed the present invention become known that gloss lightweight pigment coated paper is obtained.

The object of the present invention is to impart smoothness to the surface to be coated before coating on the surface of a support with a soft calender so that the printing quality, especially glossiness, of both sides of the coated paper can be improved. Another object of the present invention is to provide a method for producing a more excellent lightweight pigment-coated paper.

[0015]

[Means for Solving the Problems] The present invention has an absolute dry basis weight of 27.
On one side of the support to 60 g / m ² (A plane) or both sides (A and B side), in the manufacturing method of a pigment coated paper formed by providing a pigment coating layer per side 1.5 to 10 g / m ^2, Before the coating device for the A side and / or the B side, the support has a water content of 2 to 8% by weight, and the support has a Shore D hardness of 60 to 60%.
A method for producing a lightweight pigment-coated paper, which comprises subjecting a smoothing treatment to one or more sets of calendering apparatus composed of 88 elastic rolls and metal rolls.

The present invention is also a method for producing a lightweight pigment coated paper, characterized in that one or both sides of the coated paper coated by the above method is further subjected to a supercalendering treatment.

Cellulose materials usable as the support in the present invention include pressurized stone ground pulp (PGW), thermomechanical pulp (TMP), stone ground pulp (GP), refiner ground pulp ( It is preferable that the mechanical pulp such as RGP) is contained in an amount of 50 to 80% by weight, and the remaining 20 to 50% by weight is softwood or hardwood kraft pulp (KP), deinked waste paper pulp (DI
P) and the like.

The above-mentioned mechanical pulp, chemical pulp, deinked waste paper pulp and the like can be used in the form of bleached pulp or semi-bleached pulp. In addition, paper-strengthening agents, fillers, pigments, coloring dyes, retention aids, sulfuric acid bands, defoaming agents and other paper-making auxiliary chemicals are added to the pulp slurry as necessary, and the base paper ash content is 15% by weight or less, A wet web is formed by making paper in a known paper machine such as Ford linear, twin wire, on-top wire so that the content is preferably 5 to 10% by weight.

In the present invention, the wet web formed as described above is used as a support for coating after drying with a dryer, and the support for coating has an absolute dry basis weight of 27 to
60 g / m ² , density 0.5-1.0 g / cm ³ , preferably 0.
5 to 0.7 g / cm ^3, and have been installed immediately before the coating machine for coating the coating composition on both sides of the coating base papers (A side and B side), is relatively low hardness A calendar consisting of elastic rolls and metal rolls (hereafter called a soft calendar)
The paper is passed through and pressed.

The water content of the support supplied to the soft calender is 2 to 8% by weight, preferably 3 based on the absolute dry weight of the support by adjusting the drying conditions in the dryer.
It is adjusted in the range of 8 wt%. If the water content of the support exceeds 8%, the smoothing effect tends to be obtained, but at the same time, it tends to be crushed, and crushing unevenness is likely to occur due to the variation of water content in the width direction of the paper machine, which is not suitable. Further, if the smoothness is abnormally increased by crushing the support with the soft calender, streaks are likely to occur on the coating layer when the coating composition is applied on the support, and the stiffness of the paper is increased. (Rigidity) decreases, and the negative effects such as lack of waist become remarkable. On the other hand, if the water content is less than 2%, it becomes difficult to obtain the smoothing effect.

For the above reason, the smoothing treatment of the support with the soft calender installed immediately before the coating machine is performed so as to obtain a value in the range of 10 to 60 seconds according to Beck's smoothness (JIS P 8119). The smoothing conditions are adjusted. If the smoothness is less than 10 seconds, the printability of the coated paper after coating will be insufficient, and in order to obtain a smoothness of more than 60 seconds, the nip pressure and the water content of the support must be increased. It is not suitable because uneven crushing tends to occur.

The soft calender installed immediately before each coating machine for coating both sides of the support is composed of a combination of one metal roll and one elastic roll, as described above. As the metal roll, a chilled roll, an alloy chilled roll, a steel roll, a metal roll having a hard chrome-plated roll surface, and the like can be used by appropriately selecting from these, and as the elastic roll,
Natural rubber, styrene rubber, nitrile rubber, chloroprene rubber, chlorosulfonated ethylene rubber, butyl rubber,
Various natural and synthetic rubbers such as polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, aromatic polyamide resin, polyimide resin, polyether resin, polyester resin,
An elastic roll made of various plastic resins such as a polycarbonate resin, cotton, paper, wool, polyethylene terephthalate, nylon, or a mixture thereof can be mentioned and appropriately selected and used.

However, the types of elastic rolls for the present invention include urethane rubber, aromatic polyamide resin, a mixture of paper and wool, a mixture of wool and polyethylene terephthalate, a mixture of wool and nylon, and a mixture of paper and wool. An elastic roll composed of a mixture of nylon and nylon is preferable, and an elastic roll using urethane rubber and an aromatic polyamide resin is particularly easy to handle, has a long roll life, and has the desired effects of the present invention. It is most preferably used because it can be efficiently expressed.

The hardness of the elastic roll preferably used for the present invention is Shore D hardness (ASTM standard, D-2240).
At 60 to 88 degrees, preferably 65 to 85 degrees. If the hardness of the elastic roll is less than 60 degrees, the elastic roll is too soft and the amount of deformation of the roll and heat generation are large. Even if the purpose of smoothing the surface of the metal roll can be achieved, the life of the elastic roll is shortened, which is not suitable. Hardness
If it exceeds 88 degrees, if there is a place with a high basis weight locally due to minute foreign substances mixed in from the raw material system, uneven formation, uneven coating, etc., that part will be extremely crushed,
It is not suitable as it may weaken the coated base paper locally or may make holes in extreme cases. Local defects in this support cause picking by foreign matter in the step of coating the coating composition in the next step, contamination of the backing roll, and further cutting of the support during coating, which is economical and time-consuming. Will result in serious loss.

The elastic roll as described above is softer than an ordinary elastic roll, and the heat generation phenomenon of the roll is likely to occur even when the operation is stably performed, and the tendency is remarkable especially in the elastic roll using urethane rubber. Due to the heat generation phenomenon, the physical properties of the elastic body become unstable.In an extreme case, the elastic body itself may melt due to the accumulated heat and damage the roll. Cooling the roll is a preferred embodiment, and various measures such as external cooling, changing the roll diameter, and changing the wall thickness of the elastic body are appropriately adopted.

On-machine super calendars and on-machine soft calendars composed of metal rolls and elastic rolls are introduced in the Paper and Pulp Technology Times, August 1987 issue, p. 31 and May 1988 issue, p. The number of nips,
Known processing conditions such as nip line pressure, temperature and speed are appropriately selected and used for the present invention.

In the soft calender used in the present invention, even if a minute foreign substance or a locally thick portion is present on the support and this portion is significantly crushed from the periphery, a cutting trouble occurs during coating. Does not reach. When the support is pressed with the soft calender, the smoothness of both sides of the base paper is relatively improved, but the surface of the elastic roll is deformed near the paper and slippage occurs on the metal roll surface. By doing so, the surface of the base paper on the side in contact with the metal roll surface is more smooth than the side in contact with the elastic roll surface.

In the present invention, the action of such a soft calender is applied, and a soft calender is installed in front of the coating machine,
Coating is performed after enhancing the smoothness with a soft calender, but especially during the period of coating and drying the coating composition on the surface A of the support by the first coating machine, the coating has not yet been applied. The smoothness of the B side (the side opposite to the A side) to be worked is remarkably deteriorated. Even if the coating composition is directly applied on it and dried to produce a double-sided coated paper, the smoothness of both sides is reduced. Based on the finding that only coated paper with markedly different properties and glossiness can be obtained, a soft calender is installed in front of the second coating machine, and the support is passed through the soft calender, and then the coating composition is obtained. Thing B
It has been found that a double-sided coated paper having a small difference in smoothness and glossiness on both sides can be obtained because the smoothness and glossiness are improved by coating the surface. Further, the surface of the double-sided coated paper which has been coated and then dried is further treated with a super calender, whereby a double-sided coated paper having even more excellent printability such as smoothness and gloss can be obtained. In this case, when the above-mentioned surface treatment is carried out, the smoothness and glossiness of the B side are more remarkable than those of the A side, and both sides become uniform, which is more preferable as a double-sided coated paper.

Also in the multi-stage coating, the soft calender is installed in front of the coating machine, and the surface to be coated is pressed against the soft calender to increase the smoothness and then the coating is performed.

The pigment to be added to the coating composition of the present invention is not particularly limited, and kaolin, clay, barium sulfate, light calcium carbonate, heavy calcium carbonate, aluminum hydroxide, satin white, dioxide are used. Titanium, calcium sulfite, zinc sulfate, plastic pigments and the like can be mentioned, and these known coating pigments are appropriately selected and used according to the properties of the respective pigments.

As for the adhesive, casein, soybean protein, yeast protein, starch, oxidized starch, esterified starch, etherified starch, cationic starch, modified starch such as enzyme-modified starch, natural adhesives such as cellulose derivatives and the like. Conjugated diene-based copolymer latex such as styrene / butadiene copolymer, methylmethacrylate / butadiene copolymer, acrylic polymer latex such as acrylic or / methacrylic acid ester polymer or copolymer, ethylene / vinyl acetate Examples thereof include synthetic adhesives such as alkali-insensitive or alkali-sensitive synthetic resin emulsions such as vinyl acetate copolymer latex such as copolymers, etc., and these known coating adhesives have the desired paper quality. One or more types are appropriately selected and used accordingly.

The amount of the adhesive compounded is adjusted within the range of 5 to 25 parts by weight with respect to 100 parts by weight of the pigment.
Various auxiliary agents such as a flow modifier, an antifoaming agent, a dye, a lubricant, a water resistant agent, and a water retention agent are appropriately used as necessary.

In the present invention, the coating composition is coated on both sides of the coating base paper in a single layer or multiple layers by an on-machine or off-machine coater so that the coating amount on one side is 1.5 to 10 g / m ^2. It In this case, the coating composition for double-sided coating or multilayer coating can be appropriately changed according to a conventional method. The coating machine is also not particularly limited,
Various coating devices such as an air knife coater, a roll coater, a blade coater having a bevel or vent type blade, various blade coaters such as bill blades, twin blades, and the like are appropriately used for the coating device of the present invention.

As described above, in the present invention, when the coating composition is applied to both sides of the support, or when one side of the support is applied in multiple layers or in multiple stages, the first coating is performed and drying is performed. After that, install a soft calendar in front of the next coating machine,
Water content of the support is 2-8%, Shore D hardness is 60-88
Smoothness and printing gloss were further improved by applying a second coating after pressing the support against one or more sets of the calendering device composed of elastic rolls and metal rolls, followed by smoothing treatment. A lightweight pigment coated paper is obtained.

Further, when the obtained coated paper is subjected to a super calendering treatment, the smoothness and the printing gloss of the second coated surface are remarkably improved, so that a lightweight pigment-coated paper whose both sides are more uniform can be obtained.

[0036]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In the following,% and parts mean% by weight and parts by weight.

Example 1 and Comparative Example 2 Constituent pulp compositions of the softwood bleached kraft pulp (NBKP, freeness 585 ml C.SF) 45%, hardwood bleached kraft pulp (LBKP, freeness 440 mlC.SF) 10%, SG
P (freeness 60 mlC.SF) 5%, PGW (freeness 55 mlC.SF)
SF) to 40%, talc was added so that the ash content in the support was 7%, and a sizing agent (SPG, manufactured by Arakawa Chemical Industry Co., Ltd.) was added at 0.2% per absolute dry pulp weight, and a sulfuric acid band was added at 1.0%.
Cationized starch (Cate 321
0, made by Oji National Co., Ltd.) is added, and a paper machine equipped with an on-machine blade coater capable of making medium-quality paper, gravure printing paper, and newsprint printing paper is used.
In minutes, a coating support a having an absolutely dry weight of 38 g / m ² was produced.

Behind the dryer of this paper machine, that is, in front of the coating device, the top roll is covered with an elastic body of synthetic rubber filled with synthetic stone (Shore D hardness 82).
The bottom roll is a soft calender consisting of a metal roll with a crown control device, and the nip linear pressure is 30 kg / cm while controlling the water content of the support to 4.2%. a is smoothed, and then the surface of the soft calender in contact with the metal roll (A surface)
5 g / m ^{2 of the} coating composition 1 shown below was applied in the blade coater at 1000 m / min to give a water content of 4.7%.
Dry with an after-dryer until dry basis weight 43g / m ²
A medium-quality coated paper for offset printing was manufactured.

Coating Composition 1 Fine particle kaolin (particle size 2 μm or less 94 to 96%, as a pigment,
Az88, Universe Tank Ship) 30 parts and Comalco Kaolin (Comarco) 70 parts are used, and sodium polyacrylate (Aron T-40, manufactured by Toagosei) as a pigment dispersant.
0.1 part was added to 100 parts of the pigment, and the mixture was dispersed with a high-speed stirring deleter (manufactured by Serie) to produce a pigment slurry having a solid content concentration of 70%. Next, styrene-butadiene rubber latex (T-2045F, made by Nippon Synthetic Rubber) as an adhesive was added to this pigment slurry, 12 parts per 100 parts of pigment in the slurry, 4 parts of oxidized starch (Oji Ace, made by Oji Constarch), and further. Water resistance agent (SUMIRETS 636, manufactured by Sumitomo Chemical Co., Ltd.) 0.08 part, lubricant (Nopcoat C-108, manufactured by San Nopco) 0.3 part, preservative (Suraoff AB, Takeda Pharmaceutical Co., Ltd.) 0.04 part, defoamer (DEF1
22NS, manufactured by San Nopco) 0.02 part, and a fluorescent dye (FOL, manufactured by Nippon Kayaku) 0.3 part were added and mixed. Furthermore, caustic soda 0.5
% Solution was used to adjust the pH to 8.5 to produce coating composition 1 having a solid content concentration of 58%.

Next, using the manufactured medium quality coated paper for offset printing, a double-sided coated paper is manufactured on a laboratory scale by coating on the B side (opposite side of A side, uncoated side). For this reason, the water content of the medium-quality coated paper that had been coated only on the A side was adjusted to 6.5%, and as a soft calendar, a resin roll with a Shore D hardness of 77 degrees (Superform, Meiji Rubber Kasei) and a metal roll were used. Composed laboratory calendar (Oji Koei)
At a nip linear pressure of 10 kg / cm and a roll temperature of 20 ° C., the medium-quality coated paper was passed once at 4 m / min so that the B side was in contact with the metal roll. Coating composition 2 shown below was coated with a laboratory blade coater (manufactured by Oji Koei) at 5 g / m ² and dried by a laboratory drum dryer (manufactured by Japo) to produce double-sided coated paper. Example 1). After adjusting the water content of the medium-quality coated paper to 6.5%, the coating composition 2 was applied to the B-side and dried in the same manner as in Example 1 without treating the B-side with the above calendar. A double-sided coated paper was manufactured (Comparative Example 1).

Coating Composition 2 A coating composition was prepared in the same manner as Coating Composition 1 except that it was prepared on a laboratory scale using a laboratory mixer instead of the high speed agitator deleter.

Each of the double-sided coated papers obtained in Example 1 and Comparative Example 1 was conditioned for 12 hours in a constant temperature and humidity room of 20 ° C. and 65% RH, and then elastic roll (Shore D hardness 83 degrees) (Special A super calender for the laboratory consisting of white cotton, Yuri roll machine) and metal rolls, with a speed of 4 m / min.
The coated surface was subjected to a gloss treatment such that the coated surface was pressed against the metal roll twice at a nip linear pressure of 60 kg / cm and 60 ° C. The smoothness and glossiness of the coated papers of Example 1 and Comparative Example 1 were measured and evaluated.

The paper quality test was based on the following measuring instruments and methods. (1) Paper thickness: High bridge micrometer (JIS P 8118) (2) Beck's smoothness: Smoothness tester (JIS P 8119) (3) Gloss: 75 ° specular gloss tester (JIS P 8142) ( 4) Tear strength: Elemendorf tear strength tester (JIS P 8
116) (5) Opacity: Digital Hunter Reflectometer (JIS P 813
8)

Examples 2 and 3 and Comparative Examples 2 and 3 The one side (A side) coated 43 g / m ² medium quality offset printing coated paper obtained in Example 1 was 18 cm wide in the machine direction. length
Cut to 45 cm, laboratory drum dryer (surface temperature 100
Water content adjusted to 4.0% (Example 2) by passing the mixture through a temperature of 20 ° C. and a relative humidity of 65% for 12 hours to adjust the water content to 7.7. % (Example 3), which was passed through the laboratory drum dryer (surface temperature 105 ° C.) to adjust the water content to 1.5% (Comparative Example 2), and allowed to stand in the atmosphere. Four types of water level supports, which were adjusted to a water content of 9.0% (Comparative Example 3), were prepared.

A nip pressure of 10 kg was applied to the above-mentioned support using a laboratory super calender (manufactured by Oji Koei) equipped with an elastic roll having a Shore D hardness of 77 degrees (manufactured by Meiji Kasei, Superform).
/ Cm and a roll temperature of 20 ° C, a smoothing treatment was performed by passing the support once through at a treatment speed of 4 m / min so that the uncoated surface (opposite surface A) of these supports was in contact with the metal roll. 5.0 g / m ^{2 of the} composition 2 was applied to the uncoated surface of these supports, which had been smoothed, with a laboratory blade coater, and dried with a laboratory drum dryer to give a double-sided coated paper. Manufactured. Further, the obtained coated paper was subjected to a glossing treatment in a super calendar as in Example 1 to obtain a medium-quality coated paper for offset printing.

Examples 4, 5, 6 and Comparative Examples 4, 5 One side (A side) coated basis weight obtained in Example 1 43 g / m 2.
² % offset coated medium coated paper with a moisture content of 6.5%
Shore D hardness [55 degrees (Comparative Example 4), 77 degrees (Example 4), 83 degrees (Example 5), 86 degrees (Example 6)) of 5 levels of elastic roll (Meiji Rubber, Superform) , 93 degrees (Comparative Example 5)] are separately used in the laboratory super calender so that the uncoated surface (the side opposite to the A surface) is in contact with the metal roll, the nip pressure is 20 kg / cm, the roll temperature is 20 ° C., and 4 °
After applying a smoothing treatment once at m / min, the coating composition 2 was applied to each uncoated surface in the same manner as in Examples 2 and 3 with a laboratory blade coater (manufactured by Oji Koei Co., Ltd.) at 5.0 g. / M ² coated and dried in a laboratory drum dryer to produce a double coated paper. Further, the obtained coated paper was subjected to a glossing treatment in a super calendar as in Example 1 to obtain a medium-quality coated paper for offset printing.

Evaluation results of the coated papers obtained in Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Tables 1, 2 and 3.

As can be seen from Table 1, according to the method of the present invention, after the first coating is applied to one surface (A surface) of the support, the smoothness of the other surface (B surface) is remarkably deteriorated. If a soft calender is applied before the second coating is applied to the B side, the smoothness of the A side and the B side becomes higher, and if the super calender treatment is further applied, the glossiness is improved (Example 1). On the other hand, in the conventional method in which the soft calender is not applied before the second coating, the smoothness after the B-side coating is poor, and the glossiness cannot be improved to the level of the method of the present invention even if super calendering is applied to this. (Comparative example 1).

As can be seen from Table 2, coating on the A side,
In the method of the present invention in which the water content of the support after drying is within the suitable range (Examples 2 and 3), soft tearing is applied before the second coating on the B side, which causes loss of tear strength. However, the smoothness after coating on the B side can be improved, and the glossiness is improved by the super calendar treatment, but when the water content is low (Comparative Example 2), the soft calendar and the super calendar are used. If the effect of improving the smoothness and gloss is small, and if the water content of the support is too high, soft calendering remarkably improves the smoothness, but the tear strength also decreases remarkably, so it is not suitable for practical use. .

As can be seen from Table 3, the properties of tear strength, opacity and the like are impaired by the method of the present invention (Examples 4, 5 and 6) in which the hardness of the elastic roll is within an appropriate range upon soft calendering. Although the smoothness after the B-side coating and the glossiness after the super calendering can be remarkably improved without using the elastic roll (Comparative Example 4), the smoothness after the B-side coating and the super calendering after the B-side coating are performed. On the other hand, when the resin roll is hard (Comparative Example 5), the effect of improving the smoothness after the B-side coating and the effect of improving the gloss after the super calender treatment are remarkable, but the tear strength and opacity are small. It is not practical because it is accompanied by the decrease of.

[0051]

As described above in detail, according to the present invention, when the pigment coating layer is provided on one side (A side) or both sides (A and B sides) of the support, the support has a water content of 2-8. weight%
Then, the support is pressure-contacted with one or more calender devices composed of elastic rolls having a Shore hardness of D60 to 88 and metal rolls to carry out a smoothing treatment, and further, if necessary, a super calender treatment. , The smoothness and gloss of the coated surface are significantly improved without loss of other properties,
It is possible to produce a lightweight pigment-coated paper having excellent uniformity on both sides.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Emaeda 2-1-1 Ojimachi, Tomakomai City, Hokkaido Oji Paper Co., Ltd. Tomakomai Mill

Claims (2)

[Claims] 1. One side (A side) or both sides (A and B sides) of a support having an absolute dry basis weight of 27 to 60 g / m ² and 1.5 per side.
In the method for producing a pigment-coated paper having a pigment coating layer of 10 g / m ² to 10 g / m ² , in front of the coating device for the A side and / or the B side, the water content of the support is 2 to A method for producing a lightweight pigment-coated paper, which comprises subjecting the support at 8% by weight to a smoothing treatment with one or more sets of calendering equipment composed of elastic rolls having a Shore D hardness of 60 to 88 and metal rolls. 2. A method for producing a lightweight pigment-coated paper, which comprises subjecting one or both sides of the coated paper coated with the method according to claim 1 to a supercalender treatment.