JP3296883B2 - Pigment coated paper and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pigment coated paper and a method for producing the same, and more particularly to a pigment coated paper obtained by a curtain coating apparatus and a method for producing the same.

[0002]

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

[0003] Although there are many requirements for the quality of pigment coated paper, it is important that the thickness and density of the coating layer are uniform, that no coating unevenness occurs, and that no coating defects occur.

[0004] The thickness and density of the coating affect the penetration of the printing ink or dampening solution received by the coating. In other words, when the thickness of the coating layer is non-uniform, the printing ink can be absorbed by the coating layer in relatively thin portions of the coating layer even when the amount of ink received on the coating layer surface is uniform. Because the volume obtained is small, the ink penetrates to the base paper layer,
The amount of ink on the surface of the coating layer is relatively reduced to cause density unevenness, and an obstacle called “show-through” in which the image on the front surface is transparent on the back surface occurs. When the density of the coating layer is non-uniform, the penetration rate becomes slower in the high density part, so that the amount of the printing ink or dampening water on the surface becomes relatively large. In particular, when the surface abundance of the printing ink is large, the ink density becomes relatively high, which causes density unevenness, and when the solidification of the printing ink is insufficient, a back trap motor is generated. . If the amount of dampening solution present on the surface is large, the transfer amount of the printing ink to be transferred next is suppressed, so that density unevenness occurs. Therefore, it is desirable that the thickness and density of the coating layer be uniform when printing quality is considered, and that no coating unevenness occurs.

As a means for satisfying such quality requirements, there is a method of applying a multilayer coating to base paper. In other words, when a single-layer coating layer is applied on a base paper having surface irregularities due to the formation of the base paper layer, a high smoothness on the coating layer surface and a high uniformity in the thickness or density of the coating layer are obtained. It is extremely difficult to simultaneously satisfy the two conditions of obtaining the property. Therefore, by performing the multi-layer coating, the smoothness of the surface of the base paper or the base paper provided with the undercoat layer as the first layer to which the second layer (hereinafter, abbreviated as the second layer) as the uppermost layer is applied is improved. In the second layer, high smoothness and uniform thickness and density can be achieved.

[0006] There are various coating methods for applying the second layer, and specific examples include a blade coating method, an air knife coating method, and a roll coating method. A common feature of these coating methods is that a coating liquid containing a pigment and an adhesive as a main component can be applied by a relatively simple operation. However, in these coating methods, the occurrence of coating defects unique to each coating method is inevitable, and high-quality pigment-coated paper cannot be obtained.

[0007] That is, the blade 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. In the blade coating method, unavoidable coating defects are streaks and scratches.
When performing blade coating on a coated paper (hereinafter, abbreviated as web) smoothed by providing a layer, it is difficult to remove foreign matter that causes such coating defects, and the occurrence of defects becomes remarkable. Since a coating layer is not formed at a portion where a streak or a scratch occurs, it appears as a serious defect on a printed surface. In addition, streaks and scratches can be selected and removed by an online defect detector and finishing process, but the entire front and rear margins including the defective part are broken, resulting in the time and cost required for removal. Is a defect that should be prevented beforehand.

Further, in such a coating method, between the supply of the excess liquid and the measurement, the water or the adhesive component in the coating liquid infiltrates the web more than necessary, and the amount of the water or the adhesive component is high immediately below the blade at the time of the measurement. Because of the application of pressure, the penetration of water or adhesive components in the coating liquid into the web proceeds more markedly. For this reason, since the adhesive component is relatively reduced in the second layer, the coating layer strength is reduced. 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.

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, unevenness in pressure distribution is unavoidable in the air jet, and uneven coating called an air knife pattern in which the thickness of the coating layer is uneven is likely to occur. In addition, in such a coating method, when the coating speed is increased, or when the liquid concentration is increased, it is necessary to increase the wind pressure. Not only becomes more remarkable, but also the turbulence of the flow of the air jet increases, and the noise due to the blowing also becomes remarkable.
Therefore, since the wind pressure cannot be increased unnecessarily, it is not suitable for the production of pigment-coated paper which is required to apply a relatively high-viscosity liquid 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 solution is transferred between the rolls to measure the liquid and transfer it to the web. The application method is general. In this coating method, coating unevenness having a linear pattern having regular intervals peculiar to the roll is likely to occur, and the thickness of the second layer is also uneven when the coating roll surface and the web are peeled off after transfer. Coating unevenness called a split pattern is likely to occur, and it is difficult to satisfy the required quality for printing paper in recent years.

The curtain coating method is a coating method for solving problems inherent in a blade, air knife and roll coating method. However, in the curtain coating method, the wettability of the first layer has a significant effect on the coating property. That is, the first
If the wettability of the layer is low, sufficient wetting does not occur in a region where the curtain film and the first layer are in contact (hereinafter, referred to as a coating line region). In such a case, the curtain film does not uniformly transfer as the second layer, but transfers with uneven coating. If no wetting occurs, no coating layer can be formed, making it impossible to obtain coated paper.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating layer having a uniform thickness and density which is difficult to obtain by a blade coating method, an air knife coating method and a roll coating method which are post-metering coating methods. An object of the present invention is to obtain a pigment-coated paper free from unevenness and coating defects.

[0013]

According to the present invention, there is provided a pigment-coated paper having at least two coating layers mainly composed of a pigment and an adhesive on one side of a base paper, and a method for producing the same, wherein the second layer is coated. The thickness and density of the coating layer are uniform, and the coating layer has a uniform wetting time by a Bristow test method of 0.3 seconds or less and the second layer is coated using a curtain coating apparatus, thereby causing uneven coating and coating defects. It has been found that it is possible to obtain a pigment-coated paper having no pigment.

The Bristow used in the method of the present invention
A test method for measuring dynamic absorption called a test method is described in JA.
PAN TAPPI Paper Pulp Test Method No. 51, here, a support coated with a 25 mm × 1,000 mm first layer is used, and
The wetting time was determined using distilled water colored with 0.1% of dB (manufactured by Nippon Kayaku). In this case, the relationship between the liquid absorption time T (second) and the liquid transfer amount V (ml / m ² ) is B
From the list experiment, it is expressed by the following equation.

[0015]

V = Vr (T ≦ Tw)

[0016]

V = Vr + Ka · (T−Tw) ^1/2 (T> Tw) where V: liquid transfer amount (ml / m ² ) Vr: roughness index (ml / m ² ) Ka: absorption coefficient (Ml / m ² / sec ^1/2 ) T: absorption time (sec) Tw: wetting time (sec)

Here, the term “wetting time” means the time from when the liquid comes into contact with the support and wets the surface until absorption starts. In other words, in the absorption curve in which the square root of the absorption time is on the horizontal axis and the liquid permeation amount is on the vertical axis, the wetting time is a region parallel to the horizontal axis where the liquid transfer amount where absorption is not performed can be regarded as constant, and time Indicates the time at the boundary point of the region where the absorption in which the amount of liquid permeation increases is performed.

That is, in the curtain coating method, since the thickness of the curtain film having a uniform thickness is directly reflected on the thickness of the coating layer, a uniform coating layer can be obtained, and the pigment coating on which printing is performed can be obtained. Preferred characteristics as paper can be obtained. However, if the wettability of the first layer to be curtain-coated is low, there is a problem that coating unevenness occurs or a coating layer cannot be formed at all. Here, in the present invention, the inventors of the present invention have conducted intensive studies on the wettability of the first layer.
By using a dynamic absorption test method called a w test method, the wetting time calculated from this measurement result is highly correlated with the desired effect of the present invention, and the first layer Bristo
By setting the wetting time according to the w test method to 0.3 seconds or less, the second layer does not show any coating unevenness,
It has been found that a pigment coated paper having a uniform layer thickness and density can be obtained.

As described above, the present invention is characterized in that a coating solution containing a pigment and an adhesive as a main component is applied by using a curtain coating apparatus, but the first layer to which the second layer is applied is coated. Wetting time according to the Bristow test method,
Disclosed is a method of obtaining a pigment-coated paper in which the thickness and density of a coating layer are uniform and free of coating unevenness and coating defects, by applying the second layer using a curtain coating apparatus to 0.3 seconds or less. Things are still missing.

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 coating a second layer of a pigment-coated paper according to an embodiment of the present invention. The coating liquid prepared in advance is sent from the coating liquid storage tank 11 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, as the liquid supply pump 12, a variable flow type non-pulsating constant flow pump is suitable.

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 the influence of the dynamic pressure due to the liquid supply of the liquid supply pump 12 is reduced in a narrow gap through which the liquid is supplied to the slit 2, and the pressure distribution in the width direction is made uniform. Then, it flows out of the lip 3 and forms a vertical curtain film 4.

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.

In the coating line area between the continuously running web 5 and the vertical curtain film 4, the air flow accompanying the web 5 is shielded as much as possible, and the vertical curtain film 4 is disturbed by the circulation of air around the curtain. A wind shield 8 is provided to reach the web 5 without any trouble. The transport direction of the web 5 is changed by a roll 7 immediately before the application line area, so that the influence of air accompanying the web 5 on the application line area 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-described 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.

It is also possible to add a profile adjusting mechanism or a control mechanism to the curtain head. In particular, when an opening profile adjusting mechanism is attached to the slit 2 shown in FIG. 1, especially when the coating width becomes large,
A more uniform application amount profile in the width direction can be obtained.

The pigment coated paper in the present invention refers to a base paper provided with at least two layers of coating layers mainly composed of a pigment and an adhesive on one or both sides of a base paper.

The base paper that can be used in the present invention includes, without exception, generally used high-quality paper, medium-quality paper, recycled paper, synthetic paper, plastic film, and the like.

In the present invention, the coating method that can be used for coating the first layer includes a blade, an air knife,
Rods, metering bars, curtains, dies, lips,
Coating methods such as a slide hopper, a comma, a microgravure, a gate roll, a paddle, a gravure roll, and a reverse roll are exemplified. The first layer may be applied to the paper machine by using an on-machine application method or an off-machine application method independently of the paper machine.

In the present invention, the coating method that can be used for the coating of the second layer is limited to the curtain coating method, and the coating method includes an extrusion method and a slide method without exception. Also, the second layer coating device can be installed on a single line, can be of an on-machine type attached to a paper machine, or can be installed on the same line in combination with the first layer coating device. is there.

In the present invention, the coating liquid containing a pigment and an adhesive as main components is a liquid dissolved or dispersed in water together with a pigment, an adhesive and other additives, and includes a pigment, an adhesive and other additives. Has a solid content of 10 to 70% by weight. Generally, the mixing ratio of the pigment and the adhesive is
It is desirable that the amount of the adhesive is 5 parts by weight or more, preferably 10 to 70 parts by weight with respect to 00 parts by weight.

The pigments used in the present invention include kaolin, clay, calcium carbonate, satin white, titanium oxide, aluminum hydroxide, zinc oxide, barium sulfate,
Examples include calcium sulfate, silica, activated clay, lake, plastic pigment, binder pigment and the like.

Examples of the adhesive used in the present invention include various copolymers such as styrene / butadiene, vinyl acetate / acrylic, ethylene / vinyl acetate, butadiene / methyl methacrylic, and vinyl acetate / butyl acrylate, and polyvinyl alcohol. Synthetic adhesives such as alcohol, maleic anhydride copolymer, isobutene / maleic anhydride copolymer, acrylic acid / methyl methacrylate copolymer, oxidized starch, etherified starch,
Commonly known adhesives such as esterified starch, enzyme-modified starch, cold-water-soluble starch obtained by flash-drying them, and natural adhesives such as casein and soybean protein are included. In addition, if necessary, various auxiliaries such as a thickener, a water retention agent, a water resistance agent, and a coloring agent, which are blended in a general pigment coating solution for coated paper, can be used.

The coating composition of the present invention thus obtained is
The volume fraction of pigment particles having a particle diameter of 5 μm or more is adjusted to 10% or less with respect to all the pigments contained in the coating solution, and the pigment is applied as a first layer.
It is applied as a layer.

In the present invention, the coating amount of the coating liquid mainly containing the pigment and the adhesive used for the second layer or the first layer is 1 g / m ² or more, preferably on a dry weight basis,
3 to 30 g / m ² is appropriate.

[0036]

In the present invention, the wetting time of the first layer on which the second layer is applied by the Bristow test method is set to 0.3 seconds or less, and the second layer is applied by using a curtain coating apparatus. Pigment-coated paper having a uniform thickness and density and having no coating unevenness and coating defects can be obtained.

[0037]

The following examples are provided to further clarify the effects of the present invention. In the examples, the number of parts indicates all parts by weight, and unless otherwise specified, the concentration indicates the weight% of the solid concentration, and the coating amount indicates the dry coating amount. The wetting time is a wetting time measured by the Bristow test method.

Example 1 A first layer coating solution having a solid content of 56% and the following composition was applied to a high quality paper having a basis weight of 60 g / m ² by a blade coating device so that the coating amount was 10 g / m ^2. At a coating speed of 100
Application was performed at 0 m / min to produce a web provided with a first layer. At this time, the wetting time of the first layer was 0.15 seconds.

<Composition of First Layer Coating Solution> Commercially available heavy calcium carbonate (Carbital 90) 100 parts Commercially available polyacrylic acid dispersant 0.2 parts Commercially available phosphorylated starch 9 parts Commercially available styrene / butadiene latex 8 parts Ammonia 0 .1 copy

A coating solution for the second layer having a solid content of 48% was prepared according to the following formulation, and a coating amount of the following coating solution was applied to this web at a coating speed of 800 m / min at a coating speed of 800 g / min. The coating was performed so as to obtain m ² and dried to obtain a pigment-coated paper.

<Composition of Second Layer Coating Solution> Commercially available heavy calcium carbonate (Carbital 90) 20 parts Commercially available primary kaolin (Ultra White 90) 70 parts Commercially available satin white 10 parts Commercially available polyacrylic acid dispersant 0.2 part Commercially available Phosphated starch 3 parts Styrene butadiene latex 18 parts

Example 2 The procedure of Example 1 was repeated except that the pigment in the coating solution for the first layer in Example 1 was 70 parts of commercially available heavy calcium carbonate and 30 parts of commercially available kaolin, and the wetting time was 0.06 seconds. In a similar manner, a pigment coated paper was obtained.

Example 3 The procedure of Example 1 was repeated except that the amount of the latex in the first layer coating solution was 14 parts and the wetting time was 0.28 seconds.
In the same manner as in Example 1, a pigment-coated paper was obtained.

Example 4 A pigment-coated paper was obtained in the same manner as in Example 1 except that the web obtained in Example 1 was subjected to a calendering treatment and the wetting time was set to 0.08 seconds.

COMPARATIVE EXAMPLE 1 The pigment in the coating solution for the first layer in Example 1 was replaced with commercially available heavy calcium carbonate (Carbital 75) 100 having a coarse particle diameter.
Example 1 except that the wetting time was 0.33 seconds.
Pigment-coated paper was obtained in the same manner as described above.

Comparative Example 2 The pigment of the first layer coating solution blended in Example 1 was replaced with a commercially available heavy calcium carbonate (Carbital 75) 100 having a coarse particle diameter.
And a web having a wetting time of 0.33 seconds was prepared.
Pigment coated paper was obtained in the same manner as in Example 1 except that the coating amount of the layer coating solution was 20 g / m ² .

Comparative Example 3 The procedure of Example 1 was repeated except that the amount of latex in the coating solution for the first layer was 18 parts and the wetting time was 0.42 seconds.
In the same manner as in Example 1, a pigment-coated paper was obtained.

Comparative Example 4 A web having a wetting time of 0.42 seconds was prepared with the latex blending amount of the first layer coating solution in Example 1 being 18 parts, and the coating amount of the second layer coating solution was 20 g / except that the m ² are in the same manner as in example 1 to obtain a pigment coated paper.

Comparative Example 5 A web was prepared in the same manner as in Example 1 except that the wetting time was 0.35 seconds by calendering a web in which the blending amount of the latex in the first layer coating solution was 18 parts. By the method, a pigment coated paper was obtained.

Comparative Example 6 A pigment-coated paper was obtained in the same manner as in Example 1, except that a blade coating device was used as the coating device for the first layer coating liquid in Example 1.

Comparative Example 7 A pigment-coated paper was obtained in the same manner as in Example 1, except that an air knife coating device was used as the coating device for the first layer coating liquid in Example 1.

Comparative Example 8 A pigment-coated paper was obtained in the same manner as in Example 1, except that a reverse roll coating device was used as the coating device for the first layer coating liquid in Example 1.

The obtained pigment-coated papers were evaluated after calendering under the same conditions.

Regarding the evaluation items of the pigment-coated paper, the uniformity of the thickness and the density of the second layer was determined by visually observing a covering test piece using ammonium chloride, and judged as coating unevenness. The occurrence of coating defects was also confirmed by visually observing the covering test specimen. The unevenness after printing was also visually evaluated after printing.

Evaluation Method for Coating Unevenness and Coating Defects (Covering Test Method) Evaluation of the uniformity of thickness and density is performed by immersing a sample in a 2.5 wt% aqueous solution of ammonium chloride in isopropyl alcohol and then removing an excess solution of the sample. A covering test piece was prepared by absorbing the filter paper and baking the calcium carbonate of the base paper layer and the first layer at 130 ° C., and the distribution of kaolin clay in the second layer was visually evaluated. Regarding coating unevenness, ◎ when the coating layer is uniform over the entire surface, 、 when there is partial unevenness, or when the degree of unevenness is very small,
When slight unevenness was conspicuous, it was judged as Δ, and when unevenness was very noticeable, X was judged. With respect to the coating defect, the type of the coating defect was visually determined.

Evaluation Method of Print Unevenness The print unevenness was evaluated by printing with a four-color printing Roland offset printing machine under the condition of excess dampening solution, and allowed to stand at room temperature all day and night. 50% rate
The printing was performed visually. (Unit: 5 out of 5)

[0057]

[Table 1]

<Evaluation Results> Although the evaluation results shown in Table 1 were obtained, the wetting time of the web coated with the first layer by the Bristow test method was 0.3 seconds or less using a curtain coating apparatus as in the example. In the case of (1), no occurrence of coating unevenness, coating defect, or printing unevenness was observed, and a pigment-coated paper having satisfactory quality was obtained. As shown in Comparative Examples 1 to 5,
When the wetting time exceeds 0.3 seconds, unevenness generated in the coating line region of the curtain is observed on the entire surface. In Comparative Examples 6 to 8,
The occurrence of coating defects unique to coating apparatuses other than the curtain coating apparatus was observed, and it was not possible to obtain coated paper of satisfactory quality.

[0059]

According to the present invention, it is possible to obtain a pigment-coated paper in which the thickness and density of the coating layer are uniform, there is no uneven coating and no coating defects, and no uneven printing occurs.

[Brief description of the drawings]

FIG. 1 is a schematic view of a curtain coating apparatus according to an 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 (2)

(57) [Claims] 1. In a pigment coated paper having at least two coating layers mainly composed of a pigment and an adhesive on one side of a base paper, the wetting time of the first layer to which the second layer is applied by the Bristow test method is as follows: Pigment-coated paper for 0.3 seconds or less, wherein the second layer is applied using a curtain coating device. 2. A method for producing a pigment-coated paper having at least two coating layers containing a pigment and an adhesive as main components on one side of a base paper such that a wetting time by a Bristow test method is 0.3 seconds or less. A method for producing a pigment-coated paper, characterized in that a first layer is coated on a base paper or a base paper provided with an undercoat layer in advance, and a second layer is coated on the first layer using a curtain coating device. .