JPH09132893A - Production of coated paper for printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a coated paper for printing, excellent in smoothness, luster and whiteness, and having no difference between the obverse surface and reverse surface (double surface property). SOLUTION: This method for producing a double surface coated paper for printing is to apply an aqueous coating composition containing a pigment and an adhesive as main components, dry and then pass the paper through a high temperature calendar consisting of a metal roll having 100 deg.C surface temperature and an elastic roll for a compressed finishing. Especially, the paper is passed through a compressing nip consisting of the metal roll and the elastic roll having >=88 deg. Shore D hardness and 1-10μm Rmax surface roughness measured according to the JIS B0651, so as to contact each of the surfaces (obverse surface and reverse surface) of the paper with the metal roll surface at least one or more times, and then passed through a nip consisting of two elastic rolls having >=88 deg. Shore D hardness and 3-14μm Rmax surface roughness measured according to the JIS B0651 at least one or more times for finishing.

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 coated paper for printing, and more particularly to a method for obtaining a coated paper for printing which has excellent smoothness, gloss and whiteness and has no difference between front and back (double sided).

[0002]

2. Description of the Related Art In recent years, with the progress of printing technology and the demands of customers, the quality and quality of printed materials have been increasing.
Therefore, there is an increasing demand for further improvement of the gloss and smoothness of the coated layer surface of the coated paper for printing, and further improvement of the ink gloss after printing. In response to these requests for improvement, operations such as a multi-layer coating method using a blade coater, a finishing method using a high temperature calender at 100 ° C. or higher (Japanese Patent Laid-Open No. 54-125712, etc.), or proposals from the finishing surface have been made. There is. Furthermore, in terms of the composition of the coating composition, the use of pigments such as organic pigments and satin white that have a great effect of improving gloss and smoothness,
Alternatively, a high-concentration coating method in which the coating concentration during coating is 65% by weight or more has been proposed.

However, although it is possible to improve the glossiness and smoothness of the coated paper by the improvement of the coating composition of the coating composition and the coating method as described above, the glossiness and smoothness of the coated paper are not improved. The higher the height, the greater the difference between the front and back sides (double-sidedness) in the quality of the coated paper.
The actual situation is that a coated paper for printing with little difference between the front and back sides in terms of gloss and smoothness has not yet been obtained.

That is, a coated paper for printing is coated with a coating composition containing a pigment and an adhesive as main components on a base paper, dried, and then passed through a calender such as a super calender for smoothing. Chemical treatment is applied to finish. In this finishing step, the surface of the coating layer is pressed and finished at the nip portion of the calender by a roll having different surface properties, that is, a metal roll and an elastic roll. For this reason, the surface in contact with the metal roll is mirrored to the mirror surface of the metal roll, resulting in high smoothness and high gloss, but the surface in contact with the elastic roll has a gloss or The smoothness is inferior, and as a result, gloss and smoothness are expressed as a difference between front and back (double-sided).

This difference between the front and back sides is compared with a calender having a large number of nip steps generally called a super calender, which is a so-called gross calender or a soft calender that performs high-temperature pressure treatment with a small number of nips. It is particularly prominent when pressure treatment is performed using a so-called calendar device. This is because the smoothing process is performed with a small number of nips, so usually a metal roll is often heated to operate.
The mechanism of smoothing and gloss development is different from Supercalender, and the thermoplastic material in the coating layer is plasticized under high temperature and high pressure to copy the surface of the heated metal roll and the surface of the elastic roll paired with the metal roll. By doing so, the desired smoothness and gloss can be obtained. Therefore, the difference in surface property between the metal roll and the elastic roll is directly expressed as the difference between the front and back sides of the coated paper.

As a method for eliminating such a difference between the front and back sides,
A method of using an elastic roll whose surface roughness falls within a specific range depending on the hardness of the elastic roll and the surface temperature of the metal roll during operation (Japanese Patent Laid-Open No. 2-175990, 2-200).
No. 888 gazette) has been proposed, but it is the current situation that the difference between the front and the back has not been sufficiently resolved. In addition, the higher the smoothness and glossiness of the high temperature calender, the more transparent and mirror-finished the coating layer, and the less light diffusely reflected from the coating layer, resulting in lower whiteness. There is a difficulty to do it.

[0007]

DISCLOSURE OF THE INVENTION The present invention eliminates the difference between the front and back surfaces, which occurs when a coated paper having a high smoothness and a high gloss is produced by heating calendering, and further flattens it under high temperature and high pressure. It is intended to provide a method for producing a coated paper for printing, which can reduce a decrease in whiteness caused by the treatment.

[0008]

According to the present invention, a base paper is coated with an aqueous coating composition containing a pigment and an adhesive as a main component and dried, and then a metal roll and an elastic roll having a surface temperature of 100 ° C. or more are used. In a method for producing a double-sided coated paper which is passed through a high-temperature calender to finish the pressure, the metal roll and the Shore D hardness are 88 ° or more and JIS B0601 is used.
A pressure nip composed of an elastic roll having a surface roughness Rmax of 1 to 10 μm measured in accordance with the above, so that each side (front and back) of the coated paper is pressed against the surface of the metal roll at least once. After passing the paper, a nip composed of elastic rolls having a Shore D hardness of 88 ° or more and a surface roughness Rmax of 3 to 14 μm measured according to JIS B0601 is passed at least once to finish. A method for producing a coated paper for printing characterized by the above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have made detailed studies on the difference in smoothness and gloss between the front and back surfaces, which are generated by the high temperature calendering treatment as described above. As a result, the difference between the front and back surfaces that is most sensitive to visual observation is a glossiness called "shining", which is the so-called J.
Gloss value measured according to IS P8142 (75 °
It was found that the (value) did not differ significantly between the front and back. further,
As a result of examination, a method was found, in which the above-mentioned 75 ° gloss value (hereinafter, simply referred to as glossiness) was maintained, and the evaluation was performed visually, so that the difference between the front and back sides in so-called shiny feeling could be eliminated, and finally the present invention was achieved. It was completed.

Here, the shine (feeling) is the appearance quality noticeably recognized in cast coated paper, which is the coated paper having the highest smoothness, and the angle of incident / reflected light with respect to the paper surface is high ( It is known to have a high correlation with a 20 ° gloss value (close to the normal direction). In addition, such a high gloss of incident / reflected light is close to a general angle when a person views a printed picture or character. Luster is a quality that is very important for brands that compete for the specularity of coated layers such as cast coated paper,
For general printing coated paper, the 75 ° gloss value is regarded as important.

According to the method of the present invention, first, the double-sided coated paper is passed through a high temperature calender consisting of a metal roll and an elastic roll to impart smoothness and gloss, and then an elasticity having a specific hardness and surface roughness. It is characterized in that the paper is passed through a pressure nip composed of rolls for finishing.

In the present invention, the double-sided coated paper is passed through a calender for finishing. In this case, first, a paper is passed through a high temperature calender consisting of a combination of a heating metal roll and an elastic roll. As the high temperature calender, various calenders such as a super calender, a soft calender, or a gross calender can be used. Then, it is finished by passing through a pressure nip composed of specific elastic rolls, but the nip between the elastic rolls may be incorporated in the calender, or may be an independent separate facility. good. The calender including the nip between these elastic rolls is used in the form of on-machine or off-machine. The metal roll may be surface-treated by hard chrome plating or the like.

Thus, in a high temperature calender comprising a heating metal roll and an elastic roll, the surface temperature of the heating metal roll is 100 ° C. or higher, preferably 100 ° C. or higher, 250
It is desirable to use below ℃. Below 100 ° C,
The high smoothness and high gloss desired by the present invention cannot be obtained. Further, at a high temperature of more than 250 ° C., a part of the components in the coating layer may be discolored and the product may be darkened, which is not preferable.

As the elastic roll paired with the heated metal roll, a roll having a Shore D hardness of 88 ° or more should be used. Incidentally, if it is less than 88 °, the smoothness of the coated paper obtained is inferior, which is not preferable. On the other hand, if the hardness is too high, gloss unevenness and smoothness unevenness due to the base paper and coating unevenness are likely to occur. Therefore, it is preferable to use a roll of 88 ° or more and less than 97 °.

Further, the surface roughness Rmax of the elastic roll paired with the heating metal roll is 10 μm or less, Rmax
Is smaller, the more preferable it is, but practically 1 μm is the minimum value that can be stably obtained. Incidentally, when Rmax exceeds 10 μm, not only the smoothness and glossiness of the coated surface are deteriorated but also a remarkable difference between the front and back surfaces occurs, and the coated paper quality desired by the present invention cannot be obtained.

In the present invention, when the double-sided coated paper is passed through the nip composed of the heated metal roll and the elastic roll,
It is important to pass the coated paper at least once so that each surface of the coated paper is brought into pressure contact with the surface of the metal roll, and then to pass through a nip composed of elastic rolls. Through such a process, the smoothness and the glossiness imparted by the heating calendering treatment are maintained, the occurrence of the difference between the front and the back is eliminated, and further, there is an effect of suppressing the decrease of the whiteness. .

The hardness of the elastic roll forming the nip between the elastic rolls is preferably 88 ° or more in Shore D hardness, like the elastic roll paired with the metal roll in the heating calender. Incidentally, if it is less than 88 °, the surface of the roll is too soft, and the smoothness and glossiness obtained by the heat calender pressing treatment in advance are lowered. On the other hand, when a hard roll having a hardness of more than 97 ° is used, the effect of suppressing the difference between the front and the back may be reduced.
Therefore, the roll hardness in this case is preferably 88 ° or more and 97 ° or less in terms of Shore D hardness.

Further, the surface roughness Rmax of the elastic roll is 3
It is necessary to be in the range of ˜14 μm for eliminating the difference between the front and back and maintaining the whiteness. By the way, Rmax is 3μm
When it is less than 1, the effect of eliminating the difference between the front and back is small, and there is a concern that the whiteness may decrease, which is not preferable. On the other hand, Rmax is 14
When it exceeds μm, the smoothness and gloss imparted by the heat calendering treatment are greatly reduced, which is not preferable.

The material of the elastic roll is not particularly limited, but when the hardness and surface roughness desired in the present invention are maintained and durability is taken into consideration, epoxy, urethane, polyamide, isocyanate, silicone, A resin made of a resin such as vinylidene fluoride or phenol is appropriately used. Of course, these materials may be used alone or in combination of a plurality of resins as appropriate, and the roll may have a single layer structure or a multi-layer structure, and may be continuously formed in the roll thickness direction. The roll can be formed by using resins having different materials and properties.

The surface roughness Rmax of the elastic roll is JI
The elastic roll used in the present invention usually has a roll width of 1 although it is a value measured according to S B0601.
The surface roughness is about 500 to 8500 mm, and the surface roughness Rmax is obtained by measuring at least 10 points in the entire width direction and averaging the obtained values.

The water content of the double-sided coated paper when the nip between the high temperature calender and the subsequent elastic rolls is passed through to finish the surface is preferably 3 to 7% by weight before entering the high temperature calender nip. Paper speed is 100-1
It is adjusted in the range of about 500 m / min.

The pigment which is the main component of the aqueous coating composition (hereinafter referred to as paint) is not particularly limited, and it is one of the known pigments used in the general field of coated paper production.
One kind or two or more kinds are used in an appropriate combination. Specific examples include clay, kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, calcium sulfate, talc, satin white, calcined kaolin, various white carbons, and organic pigments.

The adhesive is also not particularly limited, and one kind or two or more kinds of known adhesives generally used in the field of coated paper production can be used in an appropriate combination. Specific examples thereof include proteins such as casein, various starches such as oxidized starch, thermochemically modified starch, enzyme modified starch, phosphate esterified starch, etherified starch, polyvinyl alcohol, olefin-maleic anhydride resin, and melamine resin. Examples thereof include synthetic resin adhesives such as, and various emulsion (co) polymer latices such as styrene-butadiene copolymers and acrylic polymers. further,
If necessary, various auxiliary agents such as a water-proofing agent, a defoaming agent, a release agent, a flow modifier and a dye are appropriately incorporated into the coating material.

A coating material composed of the above-mentioned materials is generally prepared to have a solid content concentration of 40 to 75% by weight, and in consideration of operability and product quality, 45 to 70% by weight. Known coaters used in the manufacturing field of, for example, blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, gravure coater, chanplex coater, size press coater, etc. An on-machine or off-machine coater provided with a device coats the base paper in one layer or in two or more layers.

When coating the base paper with a coating material, the coating amount is generally 3 to 30 g / m per one side as a dry weight.
² , 8-30 considering the blank quality of the product and printability
Both sides of the base paper are coated at about g / m ² . As a method for drying the wet coating material coated on the base paper, for example, an ordinary drying device such as a steam heating cylinder or a hot air dryer is appropriately used alone or in combination.

The method of making the base paper is not particularly limited, and may be any of acid papermaking, neutral papermaking, and alkaline papermaking, and a medium-quality basepaper containing high-yield pulp can also be used. Of course, various recovered waste paper pulps can also be used. Further, an undercoat base paper preliminarily coated with a water-based paint containing a pigment or an adhesive with a size press, coater or the like can also be used as appropriate.

[0027]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but it is needless to say that the present invention is not limited thereto. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight", respectively, unless otherwise specified. The quality evaluation of the coated paper and the surface roughness Rma of the elastic roll
The measuring method of x is as follows.

(Gloss of Coated Paper) 75 ° gloss was measured according to JIS P8142.

(Shining of coated paper) 20 ° gloss was measured according to JIS Z8741.

(Smoothness of coated paper) The smoothness was measured by a smoother smoothness meter (DSM01 / Toei Denshi KK). The smaller the value, the higher the smoothness.

(Whiteness of Coated Paper) The whiteness was measured according to JIS P8148.

(Difference between front and back of coated paper) The following criteria were visually evaluated. ○: No difference between front and back is observed. Δ: Difference between front and back is recognized.

(Surface Roughness Rmax of Elastic Roll) JIS
Surftest 201 series 178 according to B0601
(Mitoyo Seisakusho Co., Ltd.), the measurement length is 8 mm, the measurement is performed 10 times over the entire width, and the average value is obtained to obtain the surface roughness Rma.
I assumed x.

Examples 1 and Comparative Examples 1 and 2 80 parts of kaolin (UW-90 / Engelhard Co.) as a (coating) pigment, heavy calcium carbonate (FMT-90)
/ Pharmatech Co., Ltd.) and 0.02 part of sodium polyacrylate (solid content) as a dispersant to the pigment, and mixed and stirred using a Choles disperser to prepare a pigment slurry having a solid content concentration of 70%. Prepared. Styrene / butadiene copolymer latex (SN-307 /
Sumitomo Dow Co., Ltd., 15 parts by solid content, oxidized starch (Ace A /
Oji Corn Starch Co., Ltd.) in solid content of 3 parts, Sumireze Resin 703 (Sumitomo Chemical Co., Ltd.) in water content of 0.2 parts in solid content, and calcium stearate (Nopcoat C-104 / San Nopco) as lubricant. 0.1 part by solid content and 0.2 part by fluorescent dye (Kayahor PAS Liquid / Nippon Kayaku Co., Ltd.) were added respectively, and water was added to obtain a coating composition having a solid content concentration of 63%. This coating composition was applied to a high-quality base paper made from neutral paper having a basis weight of 76 g / m ² .
20 g / m ² dry weight per side with blade coater
To obtain a double-sided coated paper having a water content of 5%.

(Calendar finish) The above-mentioned double-sided coated paper was placed in a soft calender consisting of a combination of two-stage and three-stage rolls as shown in FIG. 1 at a speed of 500 m / min and a linear pressure of 250 kg / cm at each nip. Paper was passed under the conditions. In addition,
For the metal roll, use a hard chrome plated finish,
The surface temperature of the metal roll during paper passing was 120 ° C. Tables 1 and 2 show the elastic roll hardness and surface roughness Rmax of the soft calender used in this case, and the quality evaluation results of the coated paper obtained.

In the measurement of glossiness, smoothness and whiteness, the front and the back of the coated paper were the surfaces which first contacted the surface of the metal roll in the soft calender shown in FIG.

Comparative Example 3 In the calender finish of Example 1, an elastic roll composed of the elastic roll (2) and the elastic roll (3) was passed through only the nip composed of the heated metal roll (1) and the elastic roll (2). The finishing was performed in the same manner as in Example 1 except that the nip between them was not passed. Table 2 shows the quality evaluation results of the coated paper thus obtained.

Example 2 and Comparative Example 4 In calender finishing of Example 1, two sets of three-stage rolls and one set of two-stage rolls as shown in FIG. 2 were used for a soft calender at a speed of 500 m / min and linear pressure at each nip. 200 kg / c
A coated paper was obtained in the same manner as in Example 1 except that the paper was passed under the condition of m. The metal roll used was a hard chrome-plated finish, and the surface temperature during paper passing was 120 ° C. Tables 1 and 2 show the elastic roll hardness and surface roughness Rmax of the soft calender used, and the quality evaluation results of the coated paper obtained.

Comparative Example 5 In the calender finishing of Example 2, the three-stage roll 2
A pair of elastic rolls (3) that passes through only a nip composed of a pair of metal rolls (1) and elastic rolls (2)
The finishing was performed in the same manner as in Example 2 except that the nip composed of the two members was not passed. Table 2 shows the quality evaluation results of the coated paper thus obtained.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

EFFECTS OF THE INVENTION According to the method for producing coated paper of the present invention, the difference between front and back is reduced without deteriorating gloss and smoothness.
It was possible to solve the problem, and it was possible to suppress the decrease in whiteness due to the calendar process.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a roll configuration as an example of a calendar device in a manufacturing method of the present invention.

FIG. 2 is a schematic diagram showing a roll configuration as an example of a calender device in the manufacturing method of the present invention.

[Explanation of symbols]

 (1): Metal roll (2): Elastic roll paired with metal roll (3): Elastic roll not paired with metal roll (4): Coated paper

Claims (1)

[Claims] 1. A surface temperature of 100 ° C. after coating and drying an aqueous coating composition containing a pigment and an adhesive as main components on a base paper.
In the method for producing a double-sided coated paper which passes through a high-temperature calender consisting of the metal roll and the elastic roll to finish the pressure, the metal roll and the Shore D hardness are 88 ° or more and conform to JIS B0601. A pressure nip made of an elastic roll having a surface roughness Rmax of 1 to 10 μm measured by means of at least 1 on each side (front and back) of the coated paper.
After passing through the paper so that it comes into pressure contact with the surface of the metal roll more than once, the Shore D hardness is 88 ° or more, and JIS B0601
A method for producing a coated paper for printing, characterized in that a nip composed of elastic rolls having a surface roughness Rmax of 3 to 14 μm measured according to the above is passed at least once to finish.