JP3154830B2 - Method for manufacturing pigment coated 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 producing pigment coated paper, and more particularly to a method for producing pigment coated paper using a curtain coating apparatus.

[0002]

2. Description of the Related Art Conventionally, pigment-coated paper has been widely used as printing paper because of its high smoothness and gloss and uniform ink absorption as compared with uncoated high-quality paper. In particular, in recent years, visualization of printed matter has been advanced, the ratio of color printing has been increased, and the printing speed has been increased, and the demand for printing paper has been further increased.

[0003] There are many requirements for the quality of pigment-coated paper, but it is particularly important that the smoothness is high, the coating surface quality of the surface to be printed is uniform, there is no coating defect, and no printing unevenness occurs. .

[0004] In the production of pigment-coated paper, in recent years, it has been premised to recycle and reuse coated paper, especially in terms of suppressing resource depletion and protecting the environment, but compared to uncoated paper. In the case of reusing coated paper, it is necessary to crush and disperse the formed coating layer. Therefore, it is necessary to increase the amount of a dispersing aid such as a surfactant, which leads to an increase in manufacturing cost. In addition, since a large amount of waste liquid containing a surfactant is generated, the effect on the environment is not negligible. Therefore, in the manufacturing process of the pigment coated paper, it is an essential condition to reduce as much as possible the waste paper of the coated paper which needs to go through the same processing steps as the reuse of the printed product except for the deinking process.

[0005] There are a wide variety of coating methods for printing paper on which pigment is applied, and specific examples include a blade coating method, a rod coating method, an air knife coating method, and a roll coating method. A common feature of these coating methods is that a relatively simple operation can apply a coating liquid containing a pigment as a main component. However, with these coating methods, it was difficult to obtain a high quality printing pigment coated paper.

[0006] That is, the blade coating method or the rod coating method is a post-metering coating method in which an excessive coating liquid is supplied to a web and then excess liquid is scraped off by a blade or a rod. However, in such a coating method,
During the period from the supply of the excess liquid to the measurement, the water or the binder component in the coating liquid infiltrates the web more than necessary, and a high pressure is applied to the coating liquid immediately below the blade during the measurement. Penetration of the binder component into the web proceeds more significantly. For this reason, the binder component is relatively reduced in the pigment coating layer, so that the coating layer strength is low and high gloss is hardly developed. In addition, the composition of the liquid that has been scraped off as a surplus differs from the composition of the liquid before supply, and the composition of the coating liquid changes over time, so that a product of stable quality cannot be obtained.

[0007] Furthermore, the blade coating method or the rod coating method has a disadvantage that the rate of occurrence of waste paper is high.
That is, when the pigment dispersion is applied by such an application method, occurrence of application defects such as streaks and scratches is inevitable.

The air knife coating method is a post-measurement type coating method in which an excessive coating liquid is supplied to a web and then excess liquid is scraped off by wind pressure. In such a coating method, a pattern peculiar to the air knife coating is easily generated in the coating layer, and such a pattern is remarkably seen when the viscosity of the coating liquid is high or when the coating speed is high. As a result, the gloss and smoothness of the surface of the coating layer are remarkably reduced, and not only the quality is reduced, but also a serious obstacle in the printing process. in this way,
The air knife coating method is not suitable for the production of pigment coated paper which requires a relatively high viscosity liquid to be applied at a high speed.

There are various types of roll coating methods depending on the combination of rolls and the like. Basically, a plurality of rolls are combined and the coating liquid is transferred between the rolls to measure the liquid and transfer it to the web. It is a coating method. In such a coating method, when the coating roll surface and the web are separated after transfer, a roll-specific pattern is likely to be generated, and the gloss and smoothness of the coating surface are reduced. difficult.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a blade coating method, a rod coating method, an air knife coating method,
Using an extrusion-type curtain coating head to achieve both high-quality pigment-coated paper production and efficient production, which was impossible with a coating method such as a roll coating method. It is.

[0011]

According to the method for producing pigment-coated paper of the present invention, the distance between the narrowest portions of the flow path through which the coating liquid of the extrusion type curtain coating apparatus passes is 0.10 mm to 0.90 mm. Within this range, the maximum particle diameter of the coating liquid solids containing a pigment as a main component is adjusted to 1/8 or less of the interval of the narrowest part, and the curtain coating device is used for a web running continuously. It is characterized by being applied.

As described above, the blockage of the coating liquid in the flow path of the curtain coating apparatus is suppressed, the frequency of occurrence of waste paper is extremely low, the coating operation can be performed in a stable state, and the coating layer can be uniformly formed. High quality pigment coated paper can be obtained.

The curtain coating method is a pre-measuring type coating apparatus, and since the coating liquid is not scraped off at the time of coating, the coating liquid forms a very uniform so-called contour coating layer along the surface shape of the web. In particular, when coating is performed on a web having excellent smoothness, it is possible to obtain a pigment-coated paper for printing excellent in the smoothness of the coated surface and the uniformity of the coating amount.

As described above, since the curtain coating method is a pre-metering type coating method, the amount of the liquid flowing out of the head is recovered and used, and therefore, the amount of excess liquid is reduced as in the rod or blade coating method. There is no obstacle such as high concentration of the coating liquid due to the collection and circulation of the liquid. Further, in the curtain coating method, foreign matter adhering to the base paper surface does not cause streaks or scratches.

The feature of the extrusion type curtain coating method is that, as shown in FIG. Here, the width of the slit is 0.10 mm to 0.90 mm
Must be within the range. That is, if the width of the slit does not reach 0.10 mm, the flow velocity inside the slit increases, and the flow at the outlet of the lip 3 tends to be turbulent. If the width of the slit exceeds 0.90 mm, The static pressure inside the manifold 6 decreases, and the dynamic pressure distribution of the slits 2 becomes uneven in the width direction, and as a result, the coating amount becomes uneven in the width direction.

In the curtain coating, the liquid flowing out of the lip 3 forms a free surface until it comes into contact with the web 5, so that the flow path is not regulated after flowing out of the slit 2.
On the other hand, in the rod or blade coating method, the minimum gap between the rod or blade and the web where the liquid is measured is usually 0.05 mm or less. Therefore, when a solid having a large particle diameter such as an agglomerate or a foreign substance is present in the liquid, the probability of appearing as a streak is extremely lower in the curtain coating method than in the rod or blade coating method.

As a result of intensive studies by the present inventors, the maximum particle diameter of the solid content contained in the coating liquid is set to 1/8 or less of the interval between the narrowest portions inside the curtain coating head, so that the coating is performed. It has been found that local clogging does not occur inside the head, and as a result, coating defects do not occur.

In the extrusion type coating head, the narrowest part inside the head is usually the slit 2 shown in FIG. In this part, 1/8 of the narrowest gap
When particles having a particle size exceeding the diameter are retained or aggregates are formed, the thickness of the curtain film is affected, and immediately below the retaining portion, the thickness of the liquid film becomes extremely thin, and streak is generated. You will see.

Therefore, a pigment containing particles whose maximum particle diameter exceeds 1/8 of the gap at the narrowest portion inside the coating head is not used in the coating liquid, and the pigment penetrates from the outside reaching such a size. Foreign matter is removed before reaching the coating head, and when the pigment forms an aggregate and reaches such a particle size, it is similarly removed before reaching the coating head or dispersed / dissociated. Measures need to be taken.

As a method for removing particles having a maximum particle diameter exceeding 1/8 of the interval between the narrowest portions inside the coating head, a method using a sieve or a filter can be adopted. There are open-type vibrating sieve, closed-type metal mesh filter, closed-type resin filter, closed-type spiral wire filter, closed-type metal slit filter, etc., and the closed-type filter is preferable because it can be placed immediately before the coating head. It is a method.

Examples of means for dispersing and dissociating aggregates such as pigments include a ball mill, a sand mill, and a homogenizer. Considering reaggregation, it is desirable to dispose the aggregate just before the coating head, like a filter. .

The maximum particle size was measured using a light transmission type particle size distribution analyzer manufactured by Seishin Enterprise, and was defined as the minimum particle size of the residual particles when the transmittance was 99% or more.

As described above, the present invention is characterized in that the coating layer in contact with the web is smeared by a curtain coating method, but the narrowest flow path through which the coating liquid of the extrusion type curtain coating apparatus passes. 0.1
Within the range of 0 mm to 0.90 mm, the maximum particle diameter of the solid content of the coating liquid containing a pigment as a main component is set to 1 / of the narrowest interval.
By applying the coating liquid adjusted to 8 or less,
There has not yet been disclosed any method for obtaining a printing pigment-coated paper having no coating defects and excellent coating layer smoothness.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of a coating apparatus for a pigment-coated paper for printing showing an embodiment of the present invention. The prepared pigment coating liquid is supplied from the coating liquid storage tank 11
The liquid is supplied to the coater head 1 by the liquid supply pump 12.
At this time, since the amount of the applied liquid is proportional to the applied amount of the final product, it is necessary to control the amount of the applied liquid to the coater head 1 with high accuracy. Therefore, a variable flow type non-pulsating constant flow pump is suitable as the liquid supply pump 12.

The inside of the coater head 1 is composed of a manifold 6 and a slit 2, each of which is finished with high precision. The supplied coating liquid is filled in the manifold 6, and in a narrow gap that passes when being sent to the slit 2, the influence of the dynamic pressure due to the liquid feeding of the pump 12 is reduced, and the pressure distribution in the width direction is made uniform, Lip 3
More outflow and vertical curtain film 4 is formed.

The vertical curtain film 4 having a uniform profile in the width direction comes into contact with the continuously running web 5,
It is applied to the web 5. Here, the edge guides 10a, 1
0b is provided not to exceed the width of the coater head 1 and further to exceed the width of the web 5, and the vertical curtain film is formed to exceed the width of the web 5. The vertical curtain film 4 is formed so as to exceed the width of the web 5 in order to prevent thick coating of the coating layer at both ends of the vertical curtain film 4. Web 5
The coating liquid flowing down beyond the width of is collected in the liquid receiving tank 9,
After being returned to the coating liquid storage tank 11, the coating liquid is applied again. Also, when the application is interrupted such as when the web 5 is cut, the application liquid is collected in the liquid receiving tank 9.

At the contact portion between the continuously running web 5 and the vertical curtain film 4 (hereinafter referred to as "coating portion"), the air flow accompanying the web 5 is shielded and the air flow around the curtain is circulated. The web 5 without disturbing the vertical curtain film 4
A wind shield plate 8 is provided so as to reach. The transport direction of the web 5 is changed by a roll 7 immediately before the application section, so that the influence of air accompanying the web 5 on the application section is minimized.

In order to apply the formed vertical curtain film 4 in a stable state, it is necessary to apply the coater head 1 from the web 5.
Although a certain height is required to the lower outflow portion, in the present embodiment, the height can be controlled, and the height suitable for stabilizing the vertical curtain film 4 is 60 to 30.
0 mm, preferably 100 to 250 mm, more preferably 120 to 180 mm.

It is needless to say that the present invention is not limited to the above embodiments, but can be variously modified. In the above-described embodiment, the width of the formed curtain film is larger than the width of the web 5, but this is to prevent an increase in the coating amount at both ends of the coating layer. Or if the problem is not so significant, or if the problem can be solved by adopting a method disclosed in Japanese Patent Publication No. 49-14130 or other methods for preventing an increase in the coating amount, the vertical curtain film may be used as a web 5. It may be equal to or slightly smaller than this width.

Further, it is also possible to add a profile adjusting mechanism or a control mechanism to the curtain head. In particular, if a mechanism for adjusting the opening profile is attached to the slit 2 shown in FIG. 1, a more uniform application amount profile in the width direction can be obtained, especially when the application width is increased.

In the present invention, the coating liquid containing a pigment as a main component is a liquid obtained by dissolving or dispersing a pigment and a binder in water together with other additives. 10 to 70% by weight. The mixing ratio of the pigment and the binder is generally 10
It is desirable that the binder is 5 parts by weight or more, preferably 10 to 70 parts by weight, based on 0 parts by weight.

The pigment for coated paper used in the present invention includes kaolin, clay, calcium carbonate, satin white, titanium oxide, aluminum hydroxide, zinc oxide, barium sulfate, calcium sulfate, silica, activated clay, lake, plastic pigment. And binder pigment.

The binder used in the present invention includes:
Various copolymers such as styrene / butadiene, vinyl acetate / acrylic, ethylene / vinyl acetate, butadiene / methyl methacrylic, vinyl acetate / butyl acrylate, polyvinyl alcohol, maleic anhydride copolymer, isobutene / maleic anhydride Synthetic adhesives such as acid copolymers, acrylic acid / methyl methacrylate copolymers, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and cold water-soluble starch obtained by flash-drying them, casein, Commonly known adhesives such as natural adhesives such as soy protein and the like can be used. If necessary, various auxiliaries such as a thickener, a water retention agent, a water resistance agent, and a coloring agent, which are blended with a general pigment for coated paper, can be appropriately used.

The coating composition of the present invention thus obtained is
A single layer or a multilayer is applied to both sides or one side of the web. A coating device other than the curtain coating device can be used for the application of the lower layer portion in the multilayer coating, and wet-on-wet coating for performing the upper layer coating without drying the lower layer coating portion may be performed.

As the web used in the present invention, generally used high-quality paper, medium-quality paper, paper-changed paper, machine-coated paper,
Including art paper, cast coated paper, synthetic paper, resin coated paper, plastic film, and the like.

[0036] In the present invention, the coating amount of the coating solution mainly composed of pigment on a dry weight standards, 1 g / m ² or more, preferably, suitably 3 to 30 g / m ^2.

[0037]

In the present invention, the interval between the narrowest portions of the flow path through which the coating liquid of the extrusion type curtain coating apparatus passes is in the range of 0.10 mm to 0.90 mm, and the coating liquid solid containing pigment as a main component is used. By applying a coating liquid having a maximum particle diameter of 1/8 or less of the interval between the narrowest parts,
Blockage of the coating liquid in the curtain flow path is suppressed, the frequency of broke is extremely low, the coating operation can be performed in a stable state, and a high quality pigment coated paper with a uniform coating layer can be obtained. be able to.

[0038]

The following examples are provided to further clarify the effects of the present invention. In the examples, all the numbers of parts indicate parts by weight, and unless otherwise specified, the concentration indicates the weight% of the solid concentration, and the coating amount indicates the coating amount after drying.

Example 1 A coating solution having a solid content of 46% and a solid content of 46% was applied to a high quality paper having a basis weight of 60 g / m ² by a gate roll coating apparatus so that the absolute dry coating amount was 2 g / m ^2. As an undercoat liquid
The coating was performed at a coating speed of 1000 m / min to prepare an undercoated base paper.

<Undercoat liquid formulation> Commercial heavy calcium carbonate (Carbital 70) 100 parts Commercial polyacrylic acid-based dispersant 0.2 parts Commercial phosphorylated starch 8 parts Commercial styrene / butadiene latex 7 parts Sodium hydroxide 0. One copy

With the following composition, an overcoating liquid having a solid content of 54% was prepared. At this time, the heavy calcium carbonate was previously pulverized by a sand mill, and the maximum particle diameter (hereinafter, referred to as the maximum diameter) of the solid content contained in the coating solution was set to 28 μm. The obtained coating liquid was applied to the previously obtained base coat base paper at an application speed of 500 m / min using an extrusion type curtain coating apparatus so that the coating amount was 16 g / m ² , followed by drying. Was. At this time, the interval between the narrowest portions through which the coating liquid passes inside the curtain coating head (hereinafter, referred to as a slit interval) is 0.24.
mm, and the maximum diameter / slit interval ratio is 0.117.
And

<Composition of overcoating liquid> Commercial heavy calcium carbonate (special grade of heavy calcium carbonate, manufactured by Sankyo Fine Powder) 10 parts Commercial primary kaolin (Ultra White 90, manufactured by Engelhard) 50 parts Commercial secondary kaolin (Hydrasperse, Engelhard 20 parts Commercial cubic light calcium carbonate (Brilliant 15, Shiraishi Kogyo) 10 parts Aragonite-type calcium carbonate (TP-HGA, Okutama Kogyo) 10 parts Commercial polyacrylic acid dispersant 0.2 part Phosphated starch 3 parts Styrene butadiene latex 16 parts

Example 2 The maximum diameter was changed to 3 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was adjusted to 9 μm, the slit interval was adjusted to 0.33 mm, and the maximum diameter / slit interval ratio was set to 0.118.

Example 3 The maximum diameter was changed to 1 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was adjusted to 7 μm, the slit interval was adjusted to 0.24 mm, and the maximum diameter / slit interval ratio was set to 0.071.

Example 4 The maximum diameter was changed to 1 by changing the conditions for pulverizing heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was set to 3 μm, the slit interval was adjusted to 0.12 mm, and the maximum diameter / slit interval ratio was set to 0.111.

Example 5 The maximum diameter was changed to 5 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was adjusted to 5 μm, the slit interval was adjusted to 0.86 mm, and the maximum diameter / slit interval ratio was set to 0.064.

Comparative Example 1 The maximum diameter was changed to 2 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1, except that the slit diameter was 8 μm, the slit interval was adjusted to 0.21 mm, and the maximum diameter / slit interval ratio was 0.133.

Comparative Example 2 The maximum diameter was changed to 3 by changing the grinding conditions of heavy calcium carbonate.
Pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was 9 μm, the slit interval was adjusted to 0.29 mm, and the maximum diameter / slit interval ratio was 0.134.

Comparative Example 3 The maximum diameter was changed to 2 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was set to 8 μm, the slit interval was adjusted to 0.19 mm, and the maximum diameter / slit interval ratio was set to 0.147.

Comparative Example 4 The maximum diameter was changed to 3 by changing the grinding conditions of heavy calcium carbonate.
Pigment coated paper for printing was produced in the same manner as in Example 1 except that the slit diameter was 9 μm, the slit interval was adjusted to 0.26 mm, and the maximum diameter / slit interval ratio was 0.150.

Comparative Example 5 The maximum diameter was changed to 9 by changing the grinding conditions of heavy calcium carbonate.
A pigment coated paper for printing was produced in the same manner as in Example 1, except that the thickness was set to μm, the slit interval was adjusted to 0.08 mm, and the maximum diameter / slit interval ratio was set to 0.113.

Comparative Example 6 The maximum diameter was changed to 5 by changing the grinding conditions of heavy calcium carbonate.
Pigment coated paper for printing was produced in the same manner as in Example 1, except that the slit diameter was adjusted to 5 μm, the slit interval was adjusted to 0.97 mm, and the maximum diameter / slit interval ratio was set to 0.057.

COMPARATIVE EXAMPLE 7 A blade coating device was used as the coating device, and the overcoating liquid used in Example 1 was used. The undercoating base paper used in Example 1 was coated at a coating speed of 500 m / min at an application amount of 16 g / m2.
Coating and drying were carried out so as to obtain m ² .

Comparative Example 8 A rod coating device was used as a coating device, and the overcoating liquid used in Example 1 was used.
At a coating speed of 500 m / min, the coating amount is 16 g / m ²
Was applied and dried.

Comparative Example 9 An air knife coating device was used as a coating device.
The overcoat solution used in Example 1 was diluted to 49% and used.
Was applied and dried at a coating speed of 250 m / min so that the coating amount was 16 g / m ² .

COMPARATIVE EXAMPLE 10 A reverse roll coating device was used as a coating device, and the overcoat liquid used in Example 1 was diluted to 45%, and a coating speed of 200 m / min was applied to the undercoat base paper used in Example 1. Then, coating and drying were performed so that the coating amount was 16 g / m ² .

The coated sample was evaluated after calendering.

Evaluation Method 1 (Smoothness) The smoothness was measured using a smoother smoothness tester (model SM-6A, manufactured by Toei Electronics Co., Ltd.).

Evaluation Method 2 (Blank glossiness) Using a Murakami gloss meter, the glossiness of the calendered sample was measured with an incident angle of 75 ° -reflection angle of 75 °.

Evaluation method 3 (uniformity of coating layer) The uniformity of the coating layer was determined by dyeing the base paper layer with ammonium chloride and visually evaluating the coatability of the coating layer with the base paper. The evaluation was performed on a five-point scale. A sample in which no unevenness was observed in the coatability was determined as 5, a sample in which slight unevenness was observed was determined as 4, and an unevenness in which the base paper was not exposed was determined as 3, If the exposure of the base paper was observed and the unevenness of the inlay during printing was expected, it was determined to be 2, and if the exposure of the base paper surface was remarkable and the obstruction during printing, such as picking, was expected to be significant, was determined to be 1. .

Evaluation method 4 (coating defect) The coating defect was detected by a defect detecting device installed in the coating device, and evaluated by the length of the defect relative to the coating length.
The coating defect that can be detected by the defect detection device is streak,
It is a defect with an uncoated portion such as a scratch and an over-coated portion such as dirt, and can be detected if the width is 0.3 mm or more. The length of the defect is a length obtained by adding 1 m before and after the defect in consideration of the margin when deleting the defect, for example, even if the actual length of the defect is 0.1 m, The length is 2.1 m. The measurement length was uniformly 10,000 m.

The evaluation results are shown in Table 1 collectively. As shown in the examples, when the curtain coating method is used, the maximum diameter / slit interval ratio is 0.125 (= 1/8) or less, and the slit interval is in the range of 0.10 mm to 0.90 mm. , The paper loss rate is uniformly 0, and the smoothness, glossiness, and uniformity of the coating layer are all high. On the other hand, if the maximum diameter / slit interval ratio exceeds 0.125, the paper loss rate due to the generation of streaks becomes slightly higher. The slit interval is 0.10m
If it is less than m, the stability of the curtain film will be lost, and the smoothness, glossiness, uniformity of the coating layer will be low, and the paper breakage rate will be high. When the slit interval exceeded 0.90 mm, uneven flow rate occurred in the width direction of the curtain film, and the uniformity of the coating layer was reduced. As a coating method other than the curtain coating method, a blade and rod coating method has a high sheet-loss rate due to the generation of streaks. The air knife and the reverse roll coating method are inferior in smoothness, gloss, and coating layer uniformity.

[0063]

[Table 1]

[0064]

According to the present invention, it is possible to carry out a coating operation in a stable state in which the frequency of broke is extremely low and to obtain a high quality pigment coated paper having a uniform coating layer. it can.

[Brief description of the drawings]

FIG. 1 is a schematic view of a curtain coating apparatus using an extrusion type coater head, showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coater head 2 Slit 3 Lip 4 Curtain film 5 Web 6 Manifold 7 Roll 8 Wind shield 9 Liquid receiving tank 10a, 10b Edge guide 11 Storage tank 12 Liquid supply pump

Claims (1)

(57) [Claims] 1. A method for producing a pigment-coated paper, wherein the interval between the narrowest portions of the flow path through which the coating liquid of the extrusion type curtain coating device passes is within a range of 0.10 mm to 0.90 mm, and the pigment is mainly used. The maximum particle diameter of the solid content of the coating liquid as a component is adjusted to 1/8 or less of the interval between the narrowest portions, and the coating is applied to a continuously running web using the curtain coating apparatus. Of producing pigment coated paper.