JP2731831B2 - Drying method of coated paper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for drying coated paper. More specifically, the present invention relates to a method for drying coated paper for obtaining excellent printability without generating mottling according to the present invention.

[Conventional technology]

In recent years, in the field of paper coated products, quality requirements from the market have become increasingly severe, and excellent white paper gloss, smoothness, and printability have been demanded.

However, conventionally used metaling bars,
It has become difficult to meet this demand in a single-stage coating system using a blade, an air knife, or the like, or in a double coating system in which a base coat is coated with a metaling bar or a blade and an upper coat is coated with an air knife.

Therefore, in recent years, especially in the field of coating paperboard having poor surface smoothness, as a base coat and a top coat of coated paper, a double coating of a blade-on-blade using a blade capable of obtaining better printing surface characteristics has been performed. It is being improved, and an improvement in coating is being attempted.

Generally, paints applied with a coater include pigments such as kaolin, calcium carbonate, organic pigments, latex,
It is composed of a water-soluble polymer adhesive such as starch and various auxiliary chemicals, and has an appropriate solid content depending on the type of coater used. For example, a solid content of 50 to 75% is used for a blade coater.
And then sent to a drying step to be dried and adjusted so as to have a finished moisture content of 3 to 9%.

It is said that during this drying, the print quality of the coated paper, especially the mottling (non-uniform ink deposition), is most significantly affected.

This mottling, even when the base paper is subjected to a calendering process during papermaking and subjected to a process for improving the surface smoothness,
Occurs when the surface smoothness of the base paper is insufficient, and is particularly affected by the coated paper, especially when the thickness of the paper is too thin to obtain good surface smoothness as a thin paper. .

For example, 1986 Coating Conference / TAPPI Proceeding
s, 73-78, in double coating with a pilot blade coater, the coating concentration is critical area (Critical
Solids Range), it is disclosed that mottling occurs when the drying efficiency is increased.
In ctober 26-34 1989, when drying the third zone, where the paint solidifies in the four drying zones during blade coating, mottling occurs, so where this area occurs to allow for gentle drying It is described that it is important to foresee, but no specific means is mentioned.

In addition, “Paper coating (application of polymer latex) (published by the Society of Polymer Publishing, September 1989) 193-219 states that the surface of the coating layer and the structure of the internal voids become pigmented as the drying proceeds. A three-dimensional network structure consisting of latex particles is generated, a pseudocapillary tube is formed on the surface, and the region up to the point where the wet surface gloss starts to decrease (first critical concentration or immobilization point), from which drying proceeds and air Example of applying a coating color to a non-permeable base such as a glass or plastic film, in which a region up to the second critical concentration at which the displacement of water and water begins to occur and a region until a dried void structure is formed are present. It is explained based on.

However, there is no specific means applied in order to predict which parts correspond to these areas, in particular the immobilization points, in a practical operation in which they are continuously coated.

As one means, it is conceivable to calculate the amount of evaporating water from the temperature, air flow and heat of the dryer and estimate the coating film concentration. It is extremely difficult to follow the drying conditions in response to changes in factors.

[Problems to be solved by the invention]

In view of this situation, the present inventors have conducted intensive studies on the drying of the paint when applied to the base paper, and as a result, after the paint is applied to the surface of the base paper, the water evaporates and dries in the drying step. Focusing on the fact that the reflectance of the coated surface due to light changes extremely sharply even when the coated paper is running at a high speed when the concentration exceeds a certain level of concentration in the process, under a large amount of evaporation atmosphere and high temperature Continuously measure the coating concentration on the coating surface using a non-contact type laser surface inspection meter that demonstrates the function,
The drying conditions in the previous drying step are adjusted so that the coating concentration at one dryer inlet (the coating concentration on the coated surface) reaches a specific level, and the coating concentration at the outlet of the dryer is adjusted to another specific It has been found that the mottle of coated paper can be effectively eliminated by adjusting the evaporation rate by changing the temperature and wind speed in the dryer so as to reach the standard, and the present invention has been completed.

Therefore, the present invention, when drying the coated paper in the drying step after coating the coating on the surface of the base paper, continuously measure the coating concentration at the entrance and exit of the drying zone, the drying conditions It is an object of the present invention to provide a method for drying coated paper excellent in printability substantially free of mottling by proper adjustment.

[Means for solving the problem]

In the present invention, when a paint is applied on a base paper and continuously introduced into a drying process and dried, a laser type surface inspection instrument for measuring a coating concentration is installed at an inlet and an outlet of a dryer. Then, the coating film concentration of the coated paper at the inlet and outlet of each dryer is continuously measured, and the coating film concentration at the inlet of one dryer is adjusted so as to reach the range of 74 to 80% by weight in terms of solid content. The drying rate of the dryer is adjusted, and the evaporation rate in the dryer is adjusted to 15 kg / m ² · h or less so that the coating concentration at the outlet of the one dryer is in the range of 80 to 85% by weight in terms of solid content. A method for drying coated paper, characterized in that the method comprises:

Fig. 1 shows the measurement of reflectance using a laser type surface inspection meter (SU-12 coaxial laser beam sensor, manufactured by High Frequency Communication Industry Co., Ltd.) when a paint was applied on a plastic film and dried. It is a graph which shows the relationship of coating film concentration.

As can be seen from the figure, the laser-type surface inspection instrument captures the coating film density as a change in the voltage of the beam meter, and the two show an extremely good correlation. When the coating film concentration is 76% or less, it can be followed by switching the sensor.

In the present invention, this measuring device is installed between the dryer sections in the drying step, that is, on the paper rolls at the entrance and exit of the dryer, and irradiates a laser beam at right angles to the coating surface of the running coated paper to apply the coating surface. It is important that the reflected light can be received. It is also important to adjust the tension of the coated paper with a paper roll so that the vibration on the coated surface when irradiating the laser beam is minimized.

When installing a laser type surface inspection instrument at the entrance and exit of each dryer, of course, adjust the sensitivity of the sensor according to the coating concentration of the coated paper, but if the coating concentration is 90% or more, A known BM meter can be used together.

In the present invention, the drying conditions in the previous dryer are set so that the coating film concentration of the coated paper entering one of the dryers in the aforementioned dryer group can be maintained in the range of 74 to 80%, preferably 77 to 79%. The temperature of the dryer and the air pressure are adjusted so that the coating concentration is maintained at 80-85%, preferably 81-83% at the outlet of the one dryer.
As appropriate over the range from ~220mmAq selected by evaporation rate is 15 kg / m ² ·
h, preferably 5 kg / m ² · h to 13 kg / m ² · h.

When the coating concentration of the coated paper at the inlet of the dryer is 74% or less, when the evaporation rate obtained in the range of the temperature and the wind pressure of the present invention is applied, the water content of the coated paper is high, and a considerably long dryer is not applied. 80% of the coating concentration at the outlet of the dryer
It is uneconomical because it cannot be maintained above, and if the coating concentration at the dryer entrance is 80% or more, it is already too dry, and the desired effect can be obtained even if the evaporation rate of the present invention is applied with the dryer. Is not suitable for the present invention.

At the dryer outlet, if the coating concentration is 80% or less, the drying is insufficient, and it is necessary to apply the drying conditions based on the evaporation rate of the present invention again in the next dryer in order to obtain the desired effect. On the other hand, if the coating film concentration at the outlet is 85% or more, the desired effect can be obtained, but it is uneconomical because it involves heat loss.

In addition, these changes in the coating concentration are affected by the coater speed, coating amount, coating concentration (coater type), etc., but the coating concentration at the entrance of one dryer can be maintained at a desired level. If the coating concentration at the dryer outlet is too low below the desired level, the coating concentration at the subsequent second dryer outlet can be set to the desired level.

The dryer to which the evaporation rate according to the present invention is applied is 3 to
In the drying comprising the group of 6 dryers, it depends on the drying conditions applied, but falls under any of the 2nd to 5th dryers, and these dryers are usually hot air or a combination of an infrared heater and hot air. Can be applied.

According to the present invention, when drying coated paper coated with a paint, the coated paper is passed through a continuous drying zone, and the concentration of the coating film is measured by a non-contact laser type installed at each dryer inlet and / or outlet. Temperature conditions in the previous dryer so that the coating concentration at the entrance of one dryer falls within the range of 74-80% while continuously measuring the coating concentration of the coated paper at each dryer entrance and exit with a surface inspection meter After reaching the coating concentration, the evaporation rate was adjusted to 15 kg by adjusting the temperature and the wind pressure of the dryer so that the coating concentration at the outlet of the dryer was in the range of 80 to 85%.
/ m ² · h or less, it is possible to obtain a coated paper having excellent printability without substantial mottling, and this method is particularly effective for paperboard having a low surface smoothness of the base paper. It is.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these.
In the following, “%” means “% by weight”.

Example 1 Kaolin (Ultra White 90, manufactured by EMC) 80%, calcium carbonate (wet pulverized calcium, average particle size 0.5μ)
m, 20% oxidized starch (Oji Ace B, manufactured by Oji Constarch) and latex (JSR-0692, manufactured by Nippon Synthetic Rubber Co., Ltd.). Weight of 160g / m for 3-layer assembling using
On ² of the base paper, coating amount 17.5 g / m ² by the blade, coating speed 500
Coated at m / min.

The coated paper was dried using a hot-air drier composed of four sections (manufactured by Ishikawajima-Harima Heavy Industries, Inc., arch-shaped hot-air drier, each having a drying length of 6 m).

A laser type surface inspection meter (manufactured by High Frequency Communication Industry Co., Ltd.)
SO-12, coaxial laser beam sensor) and a BM meter at the outlet of the fourth dryer, so that the coating film concentration, coating amount and moisture of the coated paperboard can be monitored.

The temperature and wind pressure in the first and second dryers were adjusted so that the coating concentration at the inlet of the third dryer (the outlet of the second dryer) was 78%, and the coating concentration at the outlet of the third dryer was 82%. Thus, the water evaporation rate in the third dryer was set to 12.8 kg / m ² · h, and finally the drying conditions in the drying zone of the fourth dryer were adjusted to make the finished moisture of the coated paper 6.7%.

In order to evaluate the print mottling, a coated paperboard was printed using a Mitsubishi diamond four-color printing machine, and the degree of mottling (unevenness of the inking ink) was visually measured.
Performed in stages.

A: Very good B: Good B: There is unevenness, but light and there is no practical problem.

・ ・ ・: The occurrence of unevenness is severe and is not suitable for practical use. The evaluation of the obtained coated paperboard with respect to mottling showed extremely slight unevenness, but was not of a degree that would cause a problem in practical use.

Example 2 The same base paper as in Example 1 except that the coating amount was 16.5 g / m ² ,
Coated paper was manufactured under the conditions of paint and coating speed.

The drying conditions were the same as in Example 1, wherein the temperature and wind pressure of the first and second dryers were adjusted so that the coating concentration at the third dryer inlet was 78%, and the coating concentration at the third dryer outlet was The evaporation rate in the third dryer was adjusted to 10.4 kg / m ² · h so as to be 82%.

Finally, the drying of the coated paperboard was adjusted with a fourth dryer, and the finished water content was adjusted to 6.6%.

The evaluation of the resulting coated paperboard with respect to mottling was slightly uneven, but was slight and had no practical problem.

Example 3 A coated paperboard was produced under the same conditions of base paper, paint and coating speed as in Example 1 except that the coating amount was 15.5 kg / m ² .

The drying conditions were the same as in Example 1, wherein the temperature and wind pressure of the first and second dryers were adjusted so that the coating concentration at the third dryer inlet was 78%, and the coating concentration at the third dryer outlet was The evaporation rate in the third dryer was adjusted to 9.4 kg / m ² · h so as to be 82%.

Finally, the drying of the coated paperboard was adjusted with a fourth dryer, and the finished moisture was adjusted to 6.4%.

The evaluation of the obtained coated paperboard with respect to mottling was good with almost no unevenness.

Comparative Example 1 A coated paper was manufactured under the same conditions as in Example 1 except that the coating amount was 17.7 g / m ² .

The drying conditions are such that the film concentration at the entrance of the third dryer is
The temperature and air pressure of the first and second dryers were adjusted to be 77%, and the evaporation rate in the third dryer was set to 18.9 so that the coating concentration at the outlet of the third dryer was 82%.
Adjusted to kg / m ² · h.

Finally, the drying of the coated paperboard was adjusted with a fourth dryer, and the finished moisture content was adjusted to 6.9%.

The evaluation of the resulting coated paperboard with respect to mottling was somewhat severe, and was at a level that could not be used as printing paper.

Example 4 Coating was performed under the same conditions as in Example 1 except that the basis weight of the four-layer paperboard was 260 g / m ^{2 as} the base paper, the coating speed was 300 m / min, and the coating amount was 17.3 g / m ^2. Manufactured paperboard.

The drying conditions were the same as in Example 1 such that the first and second drying conditions were such that the coating concentration at the entrance of the third dryer was 78%.
The temperature and wind pressure of the dryer were adjusted, and the water evaporation rate in the third dryer was adjusted to 10.1 kg / m ² · h so that the coating concentration at the outlet of the third dryer was 82%.

Finally, adjust the drying of the coated paperboard with the 4th dryer,
The finished moisture was 7.5%.

The evaluation of the resulting coated paperboard with respect to mottling was good with almost no unevenness.

Comparative Example 2 A coated paperboard was produced in the same manner as in Example 4.

The drying conditions are such that the temperature and air pressure of the first dryer are adjusted so that the coating concentration at the second dryer inlet (first dryer outlet) is 75%, and the coating concentration at the second dryer outlet is 83%. The evaporation rate in the second dryer was adjusted to 27.3 kg / m ² · h as described above.

The evaluation of the resulting coated paperboard with respect to mottling was such that unevenness occurred violently and was not practical.

Examples 1 to 4 and Comparative Examples 1 and 2
Table 1 shows the drying conditions and the evaluation results used in the test.

As can be seen from the table, the evaporation rate is 15 kg / m ² · h or less when the coating concentration at the entrance of one drying zone is in the range of 74 to 80% and the coating concentration at the exit is in the range of 80 to 85%. The method of the present invention (Examples 1 to 4) yielded coated paperboard substantially free of mottling, with a slightly higher evaporation rate (about 19 kg / m 2) in the drying zone than in the method of the present invention.
^In Comparative Example 1 in which ² · h) was applied, and in Comparative Example 2 in which a considerably high evaporation rate (approximately 27 kg / m ² · h) was applied, the coated paperboard was not practically usable due to marked mottling. .

〔The invention's effect〕

The present invention relates to a drier for a pre-drying process in which a coated paper has a coating film concentration of 74 to 80% at one dryer inlet in a drying process including 3 to 6 drying sections when drying coated paper. The evaporation rate in the drying zone is adjusted to 15 kg / m ² so that the coating concentration of the coated paper at the outlet of the dryer is within the range of 80 to 85%.
By the drying method of h or less, there is an effect that a coated paper having substantially no mottling can be produced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the voltage of a laser type surface inspection meter and the coating film concentration.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor, Isao Kajita 373 Yoshioka, Yonago, Tottori Pref. Yonago Mill Co., Ltd. (56) References JP-A-1-286886 (JP, A) 6280 (JP, B2)

Claims (4)

(57) [Claims] 1. When a paint is applied on a base paper and continuously introduced into a drying step and dried, an instrument for measuring the coating film concentration is installed at an inlet and an outlet of a drier, Continuously measure the coating concentration of the coated paper at the inlet and outlet, and dry the previous dryer so that the coating concentration at the inlet of one dryer reaches the range of 74 to 80% by weight in terms of solid content. The evaporation rate in the dryer was adjusted so that the film concentration at the outlet of the one dryer was in the range of 80 to 85% by weight in terms of solid content.
A method for drying coated paper, characterized in that the coated paper is maintained at kg / m ² · h or less. ^2. The method for drying coated paper according to claim 1, wherein the base paper is a paperboard having a basis weight of 130 to 600 g / m ² . 3. A laser type surface inspection instrument for measuring a coating film concentration provided at an inlet and an outlet of a dryer for maintaining an evaporation rate of 15 kg / m ² · h or less.
The method for drying the coated paper according to the above. 4. The method for drying coated paper according to claim 1, wherein a laser beam is irradiated from a laser type surface inspection meter at right angles to a coated surface of the coated paper running on a paper roll.