JPH05154435A - Production of pigment coated paper - Google Patents

Abstract

PURPOSE:To obtain the high-quality pigment coated paper for printing having excellent smoothness and surface quality and does not generate unevenness printing by specifying the Re number in the slit of a coating head expressed by specific general formula to <=30 and specifying the liquid viscosity necessary for calculating the Re number to the viscosity at the shearing speed expressed by other specific general formula. CONSTITUTION:The pigment coated paper is produced by coating the paper with a coating liquid consisting essentially of pigments by using a coater head 1 as a curtain coating head of an extrusion type. The Re number expressed by the formula I (Re denotes Reynolds number; L denotes a slit opening degree; u denotes the average flow velocity of the liquid in the slit; P denotes a liquid density; mu denotes a liquid viscosity) in the slit 2 of the coater head 1 is specified to <=30. The liquid viscosity mu necessary for calculating the Re number is specified to the viscosity at the shearing speed S expressed by the equation (S denotes the shearing speed; L denotes the slit opening degree; u is as mentioned above). As a result, the production of the high-quality pigment coated paper and the efficient production are compatibly obtd.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

There are many required qualities for printing paper, but it is particularly important that the smoothness is high, the coating surface quality on the printing surface is uniform and there is no coating defect, and printing unevenness does not occur.

There are various coating methods for printing paper for pigment coating, and specific examples thereof include a blade coating method, an air knife coating method and a roll coating method. A common feature of these coating methods is that the coating liquid containing a pigment as a main component can be coated by a relatively simple operation. However, with these coating methods, high quality printing paper could not be obtained.

That is, the blade coating method is a post-measurement type coating method in which after the coating liquid is excessively supplied to the web, the excess liquid is scraped off by a blade. However, in such a coating method, water or a binder component in the coating liquid infiltrates into the web more than necessary between the supply of the excess liquid and the measurement, and a high pressure is applied to the coating liquid immediately below the blade during the measurement. Therefore, the infiltration of water or the binder component in the coating liquid into the web proceeds more remarkably. Therefore, since the binder component in the pigment coating layer is relatively small,
The coating layer strength will be low, and high gloss will be difficult to develop. Further, the liquid scraped off as an excess differs from the composition of the liquid before being supplied, and the composition of the coating liquid changes with the passage of time, so that a product of stable quality cannot be obtained. Also,
When the pigment dispersion is applied by such an application method, the occurrence of application defects such as streaks and scratches is unavoidable.

The air knife coating method is a post-measurement type coating method in which an excessive amount of the coating liquid is supplied to the web and the excess liquid is scraped off by wind pressure. Such a coating method tends to generate a pattern peculiar to an air knife in the coating layer, which significantly reduces the gloss and smoothness of the surface of the coating layer, which not only deteriorates the quality but also causes a serious obstacle during printing. Become. Also,
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, but when the wind pressure is increased, the turbulence of the air flow occurs. The noise caused by the blowout will also be significant. Therefore, the wind pressure cannot be unnecessarily increased, and it 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, but 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. Such a coating method easily generates a pattern peculiar to the roll, and
When the coated roll surface and the web are peeled off after the transfer, the gloss and smoothness of the coated surface are deteriorated, and it is difficult to satisfy the required quality for recent printing paper.

The curtain coating method is a coating method which solves the problems in the air knife and blade coating methods. In the curtain coating method, since the coating liquid is supplied to the support, that is, the weighing is performed at the same time before the coating is performed, which is a so-called pre-metering type coating method, the flow rate flowing out from the head is
It is a factor that determines the coating amount together with the coating speed and the solid content concentration of the liquid.

Here, since the solid content concentration of the liquid, which is a factor that determines the coating amount, is an important factor that determines the quality of the coated paper, generally, the optimum coating concentration is determined depending on the product. In many cases

In consideration of productivity, that is, cost, it is desirable that the coating speed be operated at the maximum speed of the apparatus. Therefore, the coating speed is determined by the performance of the coating apparatus.

Therefore, in the case of the curtain coating apparatus, the flow rate flowing out from the coating head is adjusted in order to obtain a desired coating amount. Therefore, when the coating apparatus in recent years has become faster, the outflow rate per unit width is increased.
However, if only the flow rate is increased, the inertial force becomes larger than the viscous force of the liquid, so that the liquid is likely to be disturbed, the coating amount profile is disturbed, and in the worst case, the curtain is broken. Like

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide an air knife coating system, a blade coating system, a roll coating system,
The Re number is used as an index that can form a stable curtain film in the extrusion type curtain coating head to achieve both high quality production of pigment coated paper and efficient production Then, it is realized by setting ideal operating conditions.

[0013]

The present invention provides a method for producing a pigment-coated paper, which comprises applying a coating liquid containing a pigment as a main component by using an extrusion type curtain coating head. The Re number in the slit of the coating head represented by Formula 1) is 30 or less, and the liquid viscosity μ required for calculating the Re number is the viscosity at the shear rate S represented by Formula 4 (Formula 2). Therefore, it has been found that a high-quality pigment-coated paper can be obtained under stable operating conditions.

[0014]

[Formula 3] Re = (L · u · ρ) / μ Re: Reynolds number L: Slit opening u: Average flow velocity of liquid in slit ρ: Liquid density μ: Liquid viscosity

[0015]

## EQU4 ## S = u / L S: Shear rate u: Average flow velocity of liquid in the slit L: Slit opening

Here, the Re (Reynolds) number is the ratio of the inertial force and the viscous force of the fluid, and is widely known as a dimensionless number indicating the flow state. In an extrusion type curtain head, a slit portion is usually provided as a narrow gap for the purpose of rectifying the flow upstream of an outflow portion (hereinafter referred to as a lip). Here, the flow state of the slit portion can be quantitatively shown by the Reynolds number shown in Equation 1. However, destabilization of the curtain film
The flow inside the slit occurs at a Re number lower than the turbulent Re number. This is because the flow at the time of expansion due to pressure release in the lip immediately after flowing out of the slit has a lower Re number inside the slit and transitions to turbulent behavior than the flow inside the slit. In the present invention, with respect to the coating liquid mainly composed of pigments having different viscosities, densities, etc., the flow rate of the coating liquid, the opening of the slit was changed, and the stability of the curtain film was examined. Re
When the value of the number exceeds 30, the curtain film becomes unstable and the coating cannot be performed in a stable state, and the quality of the coated product is remarkably deteriorated. It has been found that the film is stable and a high quality coated product is obtained.

Here, as the viscosity used to calculate the Re number inside the slit, the viscosity value at the shear rate calculated by using the average opening inside the slit as a representative length was used. this is,
This is because the coating liquid containing a pigment as a main component exhibits a thixotropic fluidity in which the viscosity decreases as the shear rate increases, and it is necessary to calculate the viscosity in consideration of the shear rate inside the slit.

Although there are various methods for measuring the viscosity in consideration of the shear rate, the shear rate of the coating solution in the curtain head is in the range of 10 ² to 10 ⁴ sec ⁻¹ , and in this shear rate range. The difference in measurement method among various viscometers such as a cone plate type, a capillary type, and a slit die type has little influence on the measured value. Therefore, these viscometers can be used to measure the liquid viscosity required in the present invention.

As a means for suppressing the turbulence of the coating liquid due to the spreading of the lip, that is, the turbulence of the curtain film in the high Re number region, the opening width from the inside of the slit to the lip is gradually increased in the outflow direction. To form a tapered line. However, although this rectifying means has the effect of rectifying the flow in the lip portion, the coating liquid containing pigment as the main component causes stagnation of the liquid at the low flow velocity portion, causing lip smearing, and The width is preferably uniform.

As described above, the present invention is characterized in that the pigment coating layer that comes into contact with the web is coated by the curtain coating method. However, the Re number is adopted as an index of curtain stability, and the Re number is Disclosed is a method of obtaining a pigment-coated paper for printing which has a coating amount of 30 or less and which can perform a stable coating operation without causing coating defects and has a uniform coating amount and high smoothness. I haven't found it yet.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic view of a coating apparatus for coating a pigment coated paper for printing showing 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 delivery amount of the coating liquid is proportional to the application amount of the final product, it is necessary to accurately control the delivery amount of the coating liquid to the coater head 1. Therefore, a variable flow type non-pulsating constant flow pump is suitable as the liquid supply pump 12.

The interior of the coater head 1 comprises a manifold 6 and slits 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 feeding of the pump 12 is reduced in the narrow gap that passes when being sent to the slit 2, and the pressure distribution in the width direction is made uniform, Lip 3
Further outflow, a 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 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 to exceed the width of the web 5 in order to prevent thick coating of the coating layer on both ends of the vertical curtain film 4. Web 5
The coating liquid that flows 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. Further, even when the coating is interrupted such as when the web 5 is cut, the coating liquid is collected in the liquid receiving tank 9.

The air flow entrained in the web 5 is blocked at the contact portion (hereinafter referred to as the "coating portion") between the web 5 and the vertical curtain film 4 which are continuously running, and the air around the curtain is circulated. Web 5 without vertical curtain film 4 being disturbed
A wind shield 8 is provided to reach the position. Further, the web 7 is configured so that the conveyance direction of the web 5 is changed by the roll 7 immediately before the coating section, so that the influence of air entrained in the web 5 on the coating section is minimized.

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

Needless to say, 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. This is to prevent an increase in the coating amount at both ends of the coating layer, and such an increase in coating amount is small. If it is not a problem, or if it can be solved by adopting the method disclosed in Japanese Patent Publication No. 49-14130, etc., or other method for preventing increase in coating amount, the vertical curtain film is applied to the web 5 The width may be equal to or slightly smaller than this.

It is also possible to attach 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 coating amount profile in the width direction can be obtained especially when the coating width becomes large.

In the present invention, the coating liquid containing a pigment as a main component is a liquid in which the pigment, the binder and other additives are dissolved or dispersed in water, and the concentration of the pigment, the binder and the other additives is 10%. ~ 70% by weight. The mixing ratio of the pigment and the binder is generally 10 for the pigment.
The amount of the binder is 5 parts by weight or more, preferably 10 to 70 parts by weight, based on 0 parts by weight.

Examples of the pigment for coated paper used in the present invention include kaolin, clay, satin white, titanium oxide, aluminum hydroxide, zinc oxide, barium sulfate, calcium sulfate, silica, activated clay, lake, and plastic pigment. Be done.

As the binder used in the present invention,
Various copolymers of styrene / butadiene, vinyl acetate / acrylic, ethylene / vinyl acetate, butadiene / methylmethacrylate, vinyl acetate / butyl acrylate, polyvinyl alcohol, maleic anhydride copolymer, isobutene / maleic anhydride Acid-based copolymers, synthetic adhesives such as acrylic acid / methyl methacrylate-based copolymers, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and cold water-soluble starch obtained by flash-drying them, casein, A commonly known adhesive such as a natural adhesive such as soybean protein can be used. If necessary, various auxiliaries such as a thickener, a water retention agent, a water resistance agent, a colorant and the like, which are mixed with a usual pigment for coated paper, can be appropriately used.

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

As the web used in the present invention, commonly used high-quality paper, medium-quality paper, waste paper, machine-coated paper,
Includes art paper, cast coated paper, synthetic paper, resin coated paper, plastic film, etc.

[0033] 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.

[0034]

In the present invention, in the method for producing a pigment-coated paper by curtain-coating a coating liquid containing a pigment as a main component using an extrusion type curtain coating device, the Re number in the slit of the coating head is When it is 30 or less, a coating operation can be performed without causing coating defects, and a coated pigment-coated paper with a uniform coating amount and high smoothness can be obtained.

[0035]

EXAMPLES Examples will be given below in order to further clarify the effects of the present invention. In the examples, all parts are parts by weight. Unless otherwise specified, the concentration means the weight% of the solid content and the coating amount means the coating amount after drying.

Example 1 A high-quality paper having a basis weight of 60 g / m ² was coated with a gate roll coating device so that the absolute dry coating amount was 2 g / m ² and the coating liquid had a solid content concentration of 46%. As an undercoat liquid,
Coating was performed at a coating speed of 1000 m / min to prepare a base paper for undercoating.

<Undercoating liquid formulation> Commercial heavy calcium carbonate (carbital 90) 70 parts Commercial secondary kaolin (caobrite) 30 parts Commercial polyacrylic acid-based dispersant 0.2 parts Commercial phosphate esterified starch 9 parts Commercial styrene Butadiene latex 8 parts Sodium hydroxide 0.1 part

An overcoating coating solution having a solid content concentration of 48% was prepared with the following formulation, and a curtain coating apparatus was used to coat the undercoating base paper obtained above with a coating speed of 575 m / min and a coating amount of 18 g / m 2. ^It was applied and dried so as to be ² . The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. For the measurement of the liquid viscosity μ, a cone-plate type viscometer (IGK-120 manufactured by Nippon Rheology Instruments Co., Ltd.) was used to measure the liquid viscosity at the shear rate S calculated according to equation 2. μ [g / cm · sec]: 0.136 ρ [g / cm ³ ]: 1.24 L [cm]: 0.06 u [cm / sec]: 58.0 Re [-]: 26.4

<Overcoating liquid formulation> Commercial heavy calcium carbonate (Carbital 90) 10 parts Commercial first grade kaolin (Ultra White 90) 50 parts Commercial secondary kaolin (Caobrite) 20 parts Commercial cubic light calcium carbonate (Brilliant 15) 10 parts Commercial aragonite type calcium carbonate (HGA) 10 parts Commercial polyacrylic acid type dispersant 0.2 parts Commercial phosphoric acid esterified starch 3 parts Styrene-butadiene latex 16 parts

Example 2 To the undercoat base paper obtained in Example 1, an overcoat solution having the same composition as the overcoat composition of Example 1 and having a solid content concentration of 51% was prepared.
The coating amount is 18 g / m ² at the coating speed of 950 m / min.
Was applied and dried. The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured in Example 1
I followed the method I went for. μ [g / cm · sec]: 0.201 ρ [g / cm ³ ]: 1.30 L [cm]: 0.06 u [cm / sec]: 86.0 Re [-]: 27.8

Example 3 To the undercoat base paper obtained in Example 1, was added an overcoat solution having the same formulation as the overcoat formulation of Example 1 and a solid content concentration of 56%.
At a coating speed of 1250 m / min, the coating amount is 18 g / m
^It was applied and dried so as to be ² . The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured in Example 1
I followed the method I went for. μ [g / cm · sec]: 0.380 ρ [g / cm ³ ]: 1.34 L [cm]: 0.06 u [cm / sec]: 100.0 Re [-]: 17.6

Comparative Example 1 The undercoat base paper obtained in Example 1 was coated with the same topcoat solution as used in Example 1 at a coating speed of 675 m / min to a coating amount of 18 g / m ^2. It was applied and dried. The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured according to the method used in Example 1. μ [g / cm · sec]: 0.130 ρ [g / cm ³ ]: 1.24 L [cm]: 0.06 u [cm / sec]: 68.0 Re [-]: 32.4

Comparative Example 2 The undercoat base paper obtained in Example 1 was coated with the same topcoat solution as used in Example 1 at a coating speed of 850 m / min to a coating amount of 18 g / m ^2. It was applied and dried. The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured according to the method used in Example 1. μ [g / cm · sec]: 0.116 ρ [g / cm ³ ]: 1.24 L [cm]: 0.06 u [cm / sec]: 86.0 Re [-]: 46.0

Comparative Example 3 The undercoat base paper obtained in Example 1 was overcoated with the same overcoating composition as in Example 1 but with a solids concentration of 51%.
At a coating speed of 1130 m / min, the coating amount is 18 g / m
^It was applied and dried so as to be ² . The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured in Example 1
I followed the method I went for. μ [g / cm · sec]: 0.194 ρ [g / cm ³ ]: 1.30 L [cm]: 0.06 u [cm / sec]: 102.0 Re [-]: 34.2

Comparative Example 4 An undercoating base paper obtained in Example 1 was coated with an overcoating solution having the same composition as the overcoating composition of Example 1 and having a solid content concentration of 51%.
At a coating speed of 1520 m / min, the coating amount is 18 g / m
^It was applied and dried so as to be ² . The liquid viscosity μ, the liquid specific gravity ρ, the slit opening L, the liquid flow rate u, and the Re number at this time are as follows. The liquid viscosity μ was measured in Example 1
I followed the method I went for. μ [g / cm · sec]: 0.188 ρ [g / cm ³ ]: 1.30 L [cm]: 0.06 u [cm / sec]: 138.0 Re [-]: 47.7

Comparative Example 5 Using the air knife coating device, the same base coat solution as that used in Example 1 was applied to the undercoat base paper obtained in Example 1 by using 4 parts.
Coating and drying were performed at a coating speed of 00 m / min so that the coating amount was 18 g / m ² .

Comparative Example 6 Using the blade coating device, the same undercoating solution as that used in Example 1 was applied to the undercoat base paper obtained in Example 1 11 times.
Coating and drying were performed at a coating speed of 00 m / min so that the coating amount was 18 g / m ² .

<Evaluation Method 1 of Pigment Coated Paper> The smoothness of the coating layer was measured by a smoother smoothness tester (model SM-6A, manufactured by Toei Denshi Kogyo Co., Ltd.). (Unit: mm
Hg)

<Evaluation Method 2 of Pigment Coated Paper> Evaluation of printing unevenness was carried out by printing with a Roland offset printing machine under the condition of excessive water supply of dampening water, and allowed to stand at room temperature for one day. The printed portion having a halftone dot area ratio of 50% was visually observed. (Unit: 5 out of 5 is the best)

<Evaluation Method 3 of Pigment Coated Paper> The quality of the coated surface was evaluated by visually observing an arbitrary part. ◎ when the coating surface quality is completely uniform, and when it is almost good,
◯, when there was some unevenness, it was judged as Δ, and when unevenness was noticeable, it was judged as ×.

[0051]

[Table 1]

<Evaluation Results> The evaluation results as shown in Table 1 were obtained, but when the coating was performed using a curtain coating device with Re number of 30 or less, the smoothness and surface quality were excellent, and printing unevenness did not occur. A high-quality pigment-coated paper for printing can be obtained.

[0053]

EFFECTS OF THE INVENTION According to the present invention, a curtain coating device is used and coating is performed with Re number of 30 or less, whereby high-quality printing pigment coating excellent in smoothness and surface quality and free from uneven printing is produced. The coated paper can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a curtain coating apparatus showing an embodiment of the present invention.

[Explanation 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 feed pump

Claims (1)

[Claims] 1. In a method for producing a pigment-coated paper, which comprises applying a coating solution containing a pigment as a main component using an extrusion type curtain coating head, the method is represented by Formula 1 (Formula 1). Re number in the slit of the coating head is 3
A method for producing a pigment-coated paper, which is 0 or less and a liquid viscosity μ necessary for calculating the Re number is a viscosity at a shear rate S represented by Formula 2 (Formula 2). [Formula 1] Re = (L · u · ρ) / μ Re: Reynolds number L: Slit opening u: Average flow velocity of liquid in slit ρ: Liquid density μ: Liquid viscosity [Formula 2] S = u / L S: Shear rate u: Average flow velocity of liquid in the slit L: Slit opening