JP3190472B2 - How to give high smoothness to one side of paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for finishing paper by calendering, and more particularly, to a method for finishing paper used for surface decorative material base paper.

[0002]

2. Description of the Related Art In general, base paper for surface decorative materials is used by printing a wood grain pattern on the surface, providing a protective layer such as urethane resin on the surface, and then bonding the back surface to the base material with an adhesive. Is done. At this time, the base paper is required to have high surface smoothness and bulkiness in order to improve halftone dot reproducibility of gravure printing, and at the same time to have low back surface smoothness in order to improve adhesiveness with the base material. Also, the interlayer strength of the base paper itself is required.
Therefore, such a base paper may be internally added with a paper strength enhancer or the like as necessary at the time of papermaking, or may be subjected to a resin impregnation treatment after the papermaking step, and further subjected to a calendering treatment in the final step to obtain a surface finish. Finished with enhanced smoothness and appearance.
BACKGROUND ART Conventionally, calendering has been known as an effective means for improving the smoothness and appearance of the base paper surface, and one of the generally used methods is super calendering.
The super calender consists of an odd number of nips consisting of a number of alternating rolls of metal and elastic. However, although high smoothness and gloss can be obtained by passing the paper through a series of nips, there is a problem that the smoothness of the back surface increases and the paper bulk decreases. In addition, Tokiko 63-563
For example, there is a soft nip heat calendering process disclosed in Japanese Patent Application Laid-Open Publication No. 60-1985. This utilizes the fact that cellulose becomes more flexible and more moldable when subjected to a pressing force at or above Tg, so that paper is passed through the nip between a metal heat roll and an elastic roll, and the fiber surface is selectively treated. This is a method of heating, plasticizing, and compressing. However, even in this treatment method, the water content is 3 to 7% based on the absolute dry weight of the fiber, especially the water content on the paper surface is extremely low, and in order to obtain higher smoothness, the paper must be treated with a high-temperature and high-pressure nip. No. For this reason, although it is inevitably slightly improved compared to the super calender treatment, there is necessarily a problem that the smoothness of the back surface is increased and the paper bulk is reduced. It is industrially disadvantageous in terms of durability. Further, utilizing the fact that the Tg of cellulose in paper depends on the moisture content of the paper and the higher the moisture content, the lower the Tg,
There has been proposed a pretreatment method of adding moisture immediately before the soft nip heat calendering treatment. For example, Japanese Patent Application Laid-Open No. Sho 62-177
No. 299 discloses a pretreatment method of applying water to a paper surface using a roll coater or the like, and US Pat. A pretreatment method for imparting moisture to the dried base paper,
Japanese Patent Application Laid-Open No. 2-160993 discloses a pretreatment method using heated steam.

[0003]

However, it is difficult to obtain the paper required for the base paper for surface decorative materials by the above pretreatment method. For example, in the pretreatment method of performing water coating on the paper surface using a roll coater or the like, if the amount of water coating is increased to obtain high smoothness, paper scorch or uneven gloss occurs during calendering, which causes a problem in appearance. Occur. The method of drying the surface with an infrared lamp is effective only for coated paper having no fiber in the surface layer. Further, in the pretreatment method using heated steam, it is difficult to impart sufficient moisture, and it is difficult to improve the surface smoothness. In particular, the technology disclosed in the above publication is
It is difficult to improve the surface smoothness and appearance of the target paper, such as a base paper for surface decorative material, whose paper surface is easy to repel water and has low permeability. The present invention has been made to solve the above problems, and an object of the present invention is to suppress the increase in back surface smoothness and the decrease in paper bulk, and to satisfy the high smoothness of the front surface, Another object of the present invention is to provide a method for producing paper satisfying an excellent appearance without gloss unevenness or the like.

[0004]

Means for Solving the Problems The present inventors contacted a water-coated surface with a heated metal roll prior to calendering treatment, so that high water content without causing paper scorch or gloss unevenness. The present inventors have found that it is possible to perform a calendar process at a specific rate, and have reached the present invention. That is, in the present invention, one side of paper is water-coated, and the same side (hereinafter, the water-coated side is referred to as a surface) is brought into contact with a first heated metal roll (hereinafter, referred to as a preheat treatment). Thereafter, paper is passed through the nip between the second heated metal roll and the elastic roll so that the surface thereof contacts the heated metal roll (hereinafter, referred to as soft nip heat calendering).

[0005] The preheat treatment in the present invention has the effect of heating the surface of the paper (water-coated surface) and evaporating a portion of the water to make the surface water uniform, thereby improving the surface smoothness and appearance. Bring. The heating effect and the uniformity of water content are achieved by appropriately setting the amount of water applied and the preheating temperature and time. In addition, since the water gradient is increased in the thickness direction of the paper as compared with the normal soft nip heat calendering treatment, the smoothness of the front surface is high and the back surface of the water-coated surface (hereinafter referred to as the back surface) is smooth. The effect of low (suppression) is remarkably observed. In the preheat treatment in the practice of the present invention, for example, the base paper used in Examples 4 to 6 described below is evaporated to evaporate 1 to 3% of the water content of the paper and finally to the absolute dry weight of the paper. Preferably, the paper moisture, before soft nip heat calendering,
Finally, it is preferable that the total content be 7 to 15% based on the absolute dry weight of the paper. When the amount of evaporation in the preheat treatment is small, the effect of the soft nip heat calender is not obtained and gloss unevenness occurs, but as the amount of evaporation increases, the effect increases and the smoothness improves. However, if the evaporation amount is too large, gloss unevenness occurs, and it is difficult to obtain the effects of the present invention. If the water content before the preheating treatment and before the soft nip heat calendering treatment is too low, the smoothness and appearance are poor, and if too high, the surface smoothness and appearance are similarly poor.

[0006] The soft nip heat calendering treatment in the present invention is performed so that the surface of the paper (water-coated surface) comes into contact with the heated metal roll. Metal roll temperature is 100 ~ 200
C. and a nip pressure (linear pressure) of preferably 50 to 300 kg / cm. When the metal roll temperature is lower than 100 ° C., the smoothness is hardly improved and the appearance is not good. On the other hand, when the temperature is higher than 200 ° C., smoothness is good, but paper burnout and gloss unevenness tend to occur. When the nip pressure exceeds 300 kg / cm, the interlayer strength tends to decrease. Also, 5
If it is less than 0 kg / cm, improvement in surface smoothness cannot be expected. Regarding the number of nips in the soft nip heat calendering process, the higher the number, the higher the smoothness tends to be.
The effect of the present invention can be sufficiently obtained even with one nip or two nips. Furthermore, there is almost no elastic roll which can be used stably for a long time in high temperature and high pressure treatment.

[0007] Regarding the water coating performed before the preheating treatment in the present invention, the water coating amount is determined after the preheating treatment (before the soft nip heat calendering treatment) because the water content of the paper finally becomes absolutely dry. 7-15 in total for weight
% May be set. In particular, when smoothness is difficult to obtain, a water content as high as possible is suitable. However, when the amount of water applied is too large, scorching of the surface and uneven gloss occur. Also, the preheat and heat roll require a large heat capacity,
In terms of operability, wrinkles during winding, blocking after winding, and the like are likely to occur. The effect of the present invention can be obtained by applying a 5% water coating to a paper having a water content of 10% before coating, but it is still more preferable if the water content in the paper before coating is 5% or less. . The coating device may be any device that can uniformly add moisture, and a gravure roll coater, an air knife, a wire bar system, or the like can be used. Further, by adding a small amount of a surfactant or the like to the coating water, the wettability of the paper surface is improved, and the smoothness and appearance of the surface are further improved.

[0008] As described above, the present invention carries out the steps of water coating → preheating → soft nip heat calendering, and this step can be used either on-machine or off-machine, especially on-machine. It will be beneficial if.

[0009]

The present invention will be described below with reference to examples (in all of the following examples, steps from water coating to soft nip heat calendering were continuously performed). The water content indicates the water content based on the absolute dry weight. Also, the evaluation method is that the density is JIS-
P8118, the front and back surface smoothness conformed to JIS-P8119, the interlayer strength conformed to JIS-P8139, the rigidity conformed to TAPPI543pm-84, and the appearance was evaluated mainly by scorching and gloss unevenness as follows. ◎: No burnt gloss unevenness at all, △: Only gloss unevenness is observed by oblique light, ○: Intermediate between ◎ and △, ×: Burnt gloss unevenness is clearly recognized.

Example 1 80 parts by weight of LBKP and 20 parts by weight of NBKP were subjected to 40 SR
Then, 6 parts by weight of titanium dioxide, 4 parts by weight of an acrylic dry paper strength agent, 6 parts by weight of a sulfuric acid band, 1.2 parts by weight of a wet strength agent, and 1 part by weight of a cationic starch were added to form a paper. And dried at 120 ° C. to a moisture content of 2% to obtain a base paper. Using the above-mentioned base paper, one side of the base paper is coated with water by a gravure roll coater so that the total moisture content becomes 15% of the absolute dry weight of the base paper, and then water-coated. (Surface) is preheated at a temperature of 110 ° C., and finally 3% of the absolute dry weight of the base paper
After evaporating the water content, a soft nip heat calender treatment was performed. The calendering treatment is performed by bringing a water-coated surface of the paper into contact with a metal heat roll at a linear pressure of 100 kg / cm in a nip between a smooth metal heat roll at 130 ° C. and a resin roll having a Shore D hardness of 91 degrees. I went in. Table 1 shows the evaluation of the obtained paper.

[0011]

Table 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Density g / cm ³ 0.70 0.96 0.94 0.90 Surface smoothness sec 10 400 450 600 Back surface smoothness sec 10 200 150 80 Interlayer Strength g / 15mm 200 190 190 210 Stiffness mg 40 20 20 30 Appearance-○ ○ ◎ ─────────────────────────────── ─ Comparative Example 4 Comparative Example 5 Comparative Example 6 Example 2 Example 3 Density g / cm ³ 0.74 1.02 1.00 0.93 0.96 Surface smoothness sec 10 400 450 600 1100 Back surface smoothness sec 10 250 200 60 80 Interlayer strength g / 15 mm 210 210 210 240 230 Stiffness mg 60 40 40 50 40 Appearance-○ ○ ○ ◎ In the table, Comparative Examples 1 and 4 are Examples 1 and 2, respectively.
The paper before the soft nip heat calendering process.
In Comparative Examples 2 and 5, the base papers of Examples 1 and 2 were supercalendered. Comparative Example 3,
In Comparative Example 6, the base papers of Example 1 and Example 2 were adjusted to 8% moisture off-line in advance and then subjected to soft nip heat calendering under the same conditions as in Example 1.

Example 2 80 parts by weight of LBKP and 20 parts by weight of NBKP were added to 27 SR
10 parts by weight of titanium dioxide, 4 parts by weight of a sulfuric acid band, and 4 parts by weight of acrylamide resin were added to make a paper, and then, 3 parts by weight of a surfactant was added to 100 parts by weight of an acrylic emulsion in a solid ratio. A resin diluted with water to a solid concentration of 20% by weight was impregnated with 30% by weight of solids based on the absolute dry weight of the paper made, and dried at 120 ° C. with a water content of 2%.
To obtain a base paper. Except for using the above-mentioned base paper,
In the same manner as in Example 1, water coating, preheating treatment, and soft nip heat calendar were performed. Table 1 shows the evaluation of the obtained paper.

Example 3 The same procedure as in Example 2 was carried out except that water containing 0.1% of a surfactant was used instead of water in the water coating of Example 2. Table 1 shows the evaluation of the obtained paper. From Table 1, it can be seen that by applying the present invention, the increase in density, the increase in back surface smoothness and the decrease in rigidity are suppressed, and the surface smoothness and appearance equal to or higher than those of the super calender treatment and the soft nip heat calender treatment can be obtained. I understand.

Examples 4 to 6 All of the procedures were performed in the same manner as in Example 3 except that the amount of water applied, the preheating temperature, and the amount of water evaporated by the preheating were changed as shown in Table 2. Table 2 shows the evaluation of the obtained paper. From Table 2, it can be seen that the examples have improved surface smoothness and appearance as compared with the comparative examples. For example, in the case of the present embodiment, water coating is performed so that the water content of the paper after the preheating process (before the soft nip heat calendering process) is finally 7 to 15% as a whole with respect to the absolute dry weight, Heating at the time of preheating is performed by using a metal heat roll surface temperature of 80 to 1
When performed at 20 ° C., the surface smoothness, appearance and strength are all good. If the amount of coating water or the processing temperature is out of this range, a good appearance cannot be obtained. The amount of water evaporation during preheating is
Finally, the water content in the paper is 1
When it is 特性 3%, it is understood that the characteristics are good.

[0015]

Table 2 Comparative Example 7 Comparative Example 8 Comparative Example 9 Example 4 Example 5 Example 6 Water Coating Amount% 7 7 20 9 15 16 Preheat Temperature ℃ -60 130 110 110 80 Water Evaporation Amount% 0.5 4 2 3 2 Density g / cm ³ 0.91 0.93 0.97 0.93 0.96 0.95 Surface smoothness sec 400 500 400 600 1100 700 Back surface smoothness sec 60 60 60 60 60 80 60 Interlayer strength g / 15mm 240 240 240 240 240 230 240 Stiffness mg 50 50 40 50 40 40 50 Appearance × △ △ ○ ◎ ○ In the table, Comparative Example 7 was not subjected to the preheating treatment after water coating but to the soft nip heat calendering treatment. According to Example 3. The water application amount indicates the water content of the paper at the time of water application.

Examples 8 to 9 The same procedures as in Example 3 were carried out except that the temperature of the soft nip heat calendering treatment and the linear pressure were changed as shown in Table 3. The amount of water evaporation by the preheat treatment was 3
%. Table 3 shows the evaluation of the obtained paper. Table 3 shows that the soft calender treatment was performed at a treatment temperature of 100 to 200.
℃, linear pressure 50-300kg / cm
Good results were obtained in surface smoothness, appearance, and interlayer strength.

[0017]

Table 3 Comparative Example 10 Comparative Example 11 Example 7 Example 8 Example 9 Calender per roll Temperature ° C 80 210 120 120 160 Linear pressure kg / cm 350 40 250 200 100 Density g / cm ³ 0.94 0.941 .04 1.05 0.95 Surface smoothness sec 400 400 1000 900 600 Back surface smoothness sec 80 60 90 90 60 Interlayer strength g / 15 mm 200 200 240 240 230 230 Stiffness mg 50 50 40 50 50 50 Appearance △ △ ◎ ◎ ○ ○

[0018]

As described above, according to the combination of the present invention in which one side of a paper web is subjected to water coating, and the same side is preheated and then subjected to a soft nip heat calendering treatment, the conventional technique is insufficient. Thus, a paper was obtained in which the increase in smoothness on the back surface and the decrease in interlayer strength and paper bulk were sufficiently suppressed, and the smoothness and appearance of the front surface were improved. In the preheat treatment, the water on the coated paper surface is heated and partially vaporized to make the water uniform, thereby improving the smoothness and appearance of the surface. In addition, since the water gradient in the paper is larger than that of the normal soft nip heat calendering treatment, there is an effect of suppressing the smoothness of the back surface compared to the treatment,
The resulting decrease in paper bulk and rigidity is small. Further, a decrease in interlayer strength is suppressed.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) D21G 1/00-9/00 D21H 11/00-27/42

Claims (1)

(57) [Claims] 1. A method for finishing a surface paper for a surface decorative material by a calendering process, wherein one side of the paper is water-coated, and the surface is brought into contact with a first heated metal roll, and then a second heated metal A calendering method in which paper is passed through the nip between the roll and the elastic roll so that the water-coated surface contacts the metal heat roll.