JP2006028681A - Coated paper for gravure printing and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated paper for gravure printing, capable of reducing the falling rate of halftone dots especially in high-speed gravure printing, and providing a printed product having faithful reproducibility and good finish. <P>SOLUTION: The coated paper T for the gravure printing has a coated layer 2 formed on both sides of a paper base 1. The coated layer 2 is formed by using a coating liquid containing (A) a pigment, (B) an adhesive, (C) a water-retaining agent containing a copolymer of an alkyl acrylate and methacrylic acid, and (D) a lubricant containing lecithin. The formulated ratio of the specific copolymer to the lecithin is regulated so as to be within the range of (1:3)-(1:10). The formulated amount of the lecithin is regulated so as to be within the range of 0.1-3.0 pts. wt. based on 100 pts. wt. pigment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coated paper for gravure printing and a method for producing the same.

  Conventionally, various printing methods such as gravure printing and offset printing are known, but gravure printing is excellent in gradation reproducibility, so it can be used in commercial printing fields such as magazines, catalogs, and brochures. It is used. Such gravure printing is a metal roll whose plate is harder than offset printing, and the printing surface is difficult to adhere completely to the substrate during printing. The phenomenon that the phenomenon of not being transferred) is likely to occur. In order to deal with this problem, coated paper for gravure printing is required to have particularly good smoothness and cushioning properties.

  By the way, printing paper used for gravure printing (coating paper for gravure printing) is usually a base paper (paper base material), white pigment such as clay or heavy calcium carbonate, and adhesive such as latex in water. It is manufactured by applying a dispersed slurry-like coating liquid and then drying it. It is often performed that the coating liquid contains a water retention agent such as starch or carboxymethylcellulose (CMC). As a result, the viscosity of the coating solution can be increased to improve the water retention of the coating solution, and as a result, a certain degree of good effect can be obtained against various problems (bleeding, streak, profiling failure) that occur during coating. ing. However, the extensive use of starch and carboxymethylcellulose (CMC) involves the problem that misdots are likely to occur (the dot missing rate tends to be high).

  Development of a water retention agent capable of suppressing the occurrence of misdots while obtaining a water retention effect is desired, and a technique using a synthetic water retention agent such as a copolymer of acrylic acid alkyl ester and methacrylic acid has been proposed (for example, Patent Documents). 1). Such a synthetic water retention agent improves coating properties such as water retention, viscosity, and fluidity in a smaller amount than carboxymethylcellulose (CMC), and can reduce the occurrence of streak and bleeding and also suppress the occurrence of misdots. An effect can be obtained.

JP 2000-328489 A (Claim 2)

  However, with the recent increase in demand for coated paper manufacturing technology, high-speed printing of printed matter, and high quality, even the technology disclosed in Patent Document 1 is said to sufficiently meet the requirements. Under difficult circumstances. For this reason, development of coated paper for gravure printing that can be applied to high-speed coating and high-speed printing and can obtain a high-definition printed matter that is faithfully reproduced and has a high finish is strongly desired.

  The present invention has been made in view of such circumstances, and in particular, it can reduce the dot missing rate in high-speed gravure printing, and can obtain a printed material that is more faithfully reproduced and has a good finish. The purpose is to provide craft paper and its manufacturing method.

The coated paper for gravure printing of the present invention is a coated paper for gravure printing in which a coated layer is formed on at least one side of a paper substrate, and the coated layer includes the following (A) to (D): It is formed using a coating liquid containing ingredients,
(A) Pigment (B) Adhesive (C) Water retention agent containing a copolymer of alkyl acrylate and methacrylic acid (D) Lubricant containing lecithin Alkyl acrylate and methacrylic acid in component (C) And the lecithin in the component (D) and the lecithin in the component (D) are set within a range of 1: 3 to 1:10 by weight. The blending amount is set in the range of 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the pigment as the component (A).

  According to said structure, while using the copolymer of acrylic acid alkylester which is a synthetic water retention agent and methacrylic acid as a water retention agent, and using lecithin as a lubricant, the acrylic acid alkyl ester in said (C) component and The blending ratio of the copolymer with methacrylic acid and lecithin in the component (D) is set in a range of 1: 3 to 1:10 by weight, and in the component (D) The amount of lecithin is set in the range of 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the pigment as component (A). For this reason, ink transfer is performed in a good state during gravure printing.

  In the coated paper for gravure printing, the adhesive as the component (B) contains a latex having a glass transition temperature of −30 to 0 ° C., an average particle diameter of 100 to 170 nm, and a gel content of 80 to 90%. The latex is preferably free of acrylonitrile or has an acrylonitrile content of 10% by weight or less. In this case, it has the advantage that it becomes a coating layer excellent in a weather resistance, stickiness resistance, etc.

The method for producing a gravure coated coated paper of the present invention is a method for producing the above gravure coated coated paper, wherein the coating liquid is applied to at least one surface of the paper base material and dried, and thereafter The surface treatment apparatus includes a plurality of steps of two rolls and one nip by a combination of a metal roll and an elastic roll, and each of the metal rolls has a roll longitudinal direction. Electromagnetic induction having an internal heating mechanism by electromagnetic induction action that can be divided and controlled in the direction, and at least one of the metal rolls facing the outer peripheral surface of the roll and capable of being divided and controlled in the roll longitudinal direction An external heater by action is arranged, and the surface temperature of the metal roll in the vicinity of the nip between the metal roll and the elastic roll is 2 by the internal heating mechanism and the external heater. By passing the paper while being in the range of 0 to 300 ° C., the specular reflection smoothness of the coating layer is characterized in that it is set to 85% or more.
According to said structure, the coating paper for gravure printing which has a coating layer whose regular reflection smoothness is 85% or more using the coating liquid containing said (A)-(D) component is easily manufactured. can do.

According to the coated paper for gravure printing of the present invention, a copolymer of acrylic acid alkyl ester and methacrylic acid, which is a synthetic water retention agent, is used as a water retention agent, and lecithin is used as a lubricant. The blending ratio of the copolymer of acrylic acid alkyl ester and methacrylic acid and lecithin in the component (D) is set in a range of 1: 3 to 1:10 by weight ratio, and Since the blending amount of lecithin in the component (D) is set within a range of 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the pigment as the component (A), a halftone dot is particularly used. The missing rate can be reduced, and a printed matter with a good finish that is reproduced more faithfully can be obtained.
In addition, according to the method for producing a coated paper for gravure printing of the present invention, surface treatment is performed using a specific surface treatment apparatus, so that the dot missing rate is particularly reduced and the finish is more faithfully reproduced. The coated paper for gravure printing which can obtain printed matter can be manufactured easily.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a coated paper for gravure printing according to an embodiment of the present invention.
A gravure coated coated paper (hereinafter simply referred to as “coated paper”) T according to the present embodiment includes a paper substrate 1 and a coated layer 2 formed on both sides thereof. And the regular reflection smoothness of the coating layer 2 is set to 85% or more.

The paper substrate 1 is not particularly limited, and various known materials can be used. Specifically, it may be only a single-layer base paper, or may be a multi-layered structure of two or more layers by overlapping different or similar base papers.
As raw material pulp for base paper, for example, mechanical pulp, kraft pulp, and recycled pulp can be suitably used as main raw materials, but known non-wood pulp such as kenaf, bamboo, hemp, and straw can also be used in combination. These may be used alone or in combination of two or more.
Further, the basis weight of the base paper is not particularly limited, but as the base weight of the coated paper for obtaining the effect of the present invention, specifically, a base paper having a basis weight of about 40 to 130 g / m ² is appropriately used. Used. The paper making method of the base paper is not particularly limited, and a twin wire former machine, a long net machine, and more preferably, from the base paper to the formation of the coating layer and the surface treatment of the coating layer can be performed in a series of steps. A method using an on-line machine that can be used can be appropriately adopted.

The coating liquid used to form the coating layer 2 includes a pigment (component A) and an adhesive (component B) as main components, a water retention agent (component C) and a lubricant (component D) as auxiliary agents, and the like. Contains.
As the pigment (component A), various known materials can be appropriately selected and used according to the application and needs. Specifically, calcium carbonate (heavy calcium carbonate, light calcium carbonate), delaminated clay, calcined clay, satin white, titanium dioxide, aluminum hydroxide, zinc oxide, barium sulfate, calcium hydroxide, calcium sulfate, sulfurous acid Use inorganic pigments such as calcium, magnesium carbonate, magnesium hydroxide, bentonite, sericite, silica, talc, activated clay, and organic pigments such as polystyrene resin fine particles, urea formalin fine particles, fine hollow particles, and porous particles. it can. These can be used alone or in combination of two or more. Of these, calcium carbonate and clay are preferably used.

Moreover, what blended an equal amount of calcium carbonate and clay on a weight basis can be used as a standard pigment, but the weight-based blending ratio of calcium carbonate and clay is 30:70 to 70:30. When it is set within the range, it is particularly preferable since excellent printing glossiness can be obtained, operability is excellent, and coated paper can be produced at a lower cost.
Furthermore, when heavy calcium carbonate is used as a pigment, it is preferable to use esterified starch (particularly carbamic acid starch) because the fluidity of the coating liquid is particularly excellent. Further, when heavy calcium carbonate and clay are used in combination as a pigment, it is preferable because the glossiness of white paper is maintained.
In the coating liquid in the present invention, 30 to 80 parts by weight in terms of solid content is blended as a pigment.

  Although it does not restrict | limit especially as an adhesive agent (B component), A water-soluble adhesive agent is used suitably. Specific examples include oxidized starches, positive starches, esterified starches, starches such as dextrin, synthetic resin adhesives such as polyvinyl alcohol (PVA), proteins such as casein, soy protein, and synthetic proteins. Also, conjugated diene copolymer latex such as styrene-butadiene copolymer, acrylic copolymer latex such as acrylate polymer or copolymer, and vinyl polymer such as ethylene-vinyl acetate copolymer. Latex, or alkali-soluble, alkali-swellable or alkali-insoluble polymer latex obtained by modifying these polymer latexes with a functional group-containing monomer such as a carboxyl group may be used. These adhesives may be used alone or in combination of two or more. And the compounding ratio of an adhesive agent is suitably set by the kind etc. of the adhesive agent to be used, However, It is preferable to set normally in the range of 5-30 weight part with respect to 100 weight part of pigments. This is because if the amount is less than 5 parts by weight, a predetermined adhesive force may not be obtained, and if it exceeds 30 parts by weight, the coatability may be adversely affected.

  Among these, it is a latex that does not contain acrylonitrile as a monomer component or is set to 10% by weight or less even if it is contained, and has a glass transition temperature (Tg) of −30 to 0 ° C., Those having an average particle diameter of 100 to 170 nm and a gel content of 80 to 90% are preferred. This is because latex containing a large amount of acrylonitrile as a monomer component easily yellows in the surface treatment process, and also easily yellows over time.Therefore, there is a problem in weather resistance, which causes variations in color tone in the final product. This is because there is a tendency to end up. However, the inclusion of acrylonitrile as a monomer component has the advantage that the required surface hardness can be imparted to the coated paper while reducing the amount of latex in the coating liquid, and the printing glossiness is increased. Therefore, in order to obtain these advantages, a small amount of 10% by weight or less may be included. Considering these, latexes having an acrylonitrile content of 1 to 10% by weight, more preferably 3 to 8% by weight are more preferably used.

  The reason why the latex has a glass transition temperature (Tg) in the range of -30 to 0 ° C is as follows. That is, when the glass transition temperature (Tg) exceeds 0 ° C., the stickiness resistance deteriorates and the operability tends to deteriorate. More specifically, when the content of acrylonitrile as a monomer component is large, it is possible to suppress the deterioration of stickiness resistance even if the glass transition temperature (Tg) is high, but it is not contained in acrylonitrile or acrylonitrile. This is because, since the latex is contained in a small amount, it is difficult to suppress the deterioration of stickiness resistance unless the glass transition temperature (Tg) is lowered. On the other hand, even if the glass transition temperature (Tg) is lower than −30 ° C., there is almost no difference in the effect of improving the stickiness resistance compared to the case of −30 ° C. For this reason, the glass transition temperature (Tg) is preferably set within the above range. In addition, a glass transition temperature (Tg) produced a latex film at 20 ° C. and 65% (relative humidity), and 20 mg of the film was suggested by a scanning calorimeter (DSC) at a heating rate of 5 ° C./minute, and a measurement temperature of 0 to It can obtain | require from the characteristic curve obtained at 100 degreeC.

  Further, the latex having an average particle diameter in the range of 100 to 170 nm is preferable for the following reason. That is, when the average particle size is less than 100 nm, the coating property tends to be lowered and the coating property by the coating layer 2 tends to be deteriorated. Conversely, when the average particle size exceeds 170 nm, sufficient adhesive strength and surface strength are obtained. This is because the stickiness resistance tends to deteriorate. In other words, when the average particle diameter is within the above range, there are advantages that adhesive strength and surface strength necessary for coated paper can be obtained and good coating properties can be secured. The average particle size is diluted so that the concentration is 0.05 to 0.2%, the absorbance at a wavelength of 525 nm of each diluted sample is measured, and a calibration curve prepared in advance is used. Can be measured.

The reason why the latex gel content is in the range of 80 to 90% is preferable for the following reason. That is, if the gel content is less than 80%, insufficient surface strength is exposed and the operability such as roll dirt tends to deteriorate. On the other hand, even if the gel content is higher than 90%, there is almost no difference in the effect of improving the stickiness resistance compared to the case of 90%. And gel content is an index of adhesive strength, and it is necessary even if acrylonitrile that imparts surface strength to coated paper is not contained or contained in a small amount by setting it within a high range of 80 to 90%. It becomes possible to ensure the surface strength. The gel content is a value calculated by the following mathematical formula (1).
Gel content (%) = (dry film weight−toluene soluble weight) × 100 / dry film weight (1)
Here, the dry film weight is the weight of a dry film obtained by spreading about 0.3 g of latex thinly on a slide glass and drying it to a film with a dryer at 50 ° C. The toluene soluble weight means that the obtained dried film is immersed in about 50 ml of toluene for 24 hours, filtered through a glass filter, separated into a filtrate and a filtrate, and then the filtrate is dried at 105 ° C. It is the value which dried with the machine and measured the weight of toluene soluble part.

  Such a specific latex can be produced by polymerization using monomer components such as butadiene, acrylonitrile, styrene, acrylic acid, butylacrylic acid, methacrylic acid, methylmethacrylic acid, and vinyl acetate as appropriate. Among the latexes thus obtained, copolymer latexes such as styrene-butadiene, styrene-acrylic, vinyl acetate, ethylene-vinyl acetate, butadiene-methyl methacryl, and vinyl acetate-butyl acryl are preferred, and styrene is particularly preferred. -Copolymer latex of butadiene, acrylic or styrene-butadiene-acrylic is preferred.

  And it is preferable that the mixing | blending ratio of the said specific latex is set in the range of 8-15 weight part with respect to 100 weight part of pigments. That is, if it is less than 8 parts by weight, the adhesive strength and surface strength required for the coated paper are insufficient, and the user tends to cause picking troubles (peeling of the coating layer) when printing. Because. On the other hand, if the amount exceeds 15 parts by weight, the absolute amount of acrylonitrile in the coating solution increases, which tends to cause problems such as deterioration in weather resistance and high production costs. In other words, by setting the blending ratio of the specific latex within the above range, a coated paper having excellent weather resistance and the like can be obtained while ensuring the necessary minimum adhesive strength and surface strength. However, it goes without saying that in addition to the specific latex, other adhesives may be used in combination to increase the adhesive strength and surface hardness. In particular, it is preferable to use esterified starch such as urea phosphate esterified starch and carbamic acid starch together with a specific latex. The blending ratio of the esterified starch is preferably set within the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the pigment.

As the water retention agent (component C), a copolymer of acrylic acid alkyl ester (X) and methacrylic acid (Y), which is a synthetic water retention agent, is used.
The alkyl group in the acrylic acid alkyl ester (X) may be linear or branched, but those having 1 to 8 carbon atoms are preferably used. This is because if the carbon number is too large, the water retention tends to decrease. Suitable alkyl acrylate esters (X) include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, pentyl acrylate, 2-methylbutyl acrylate, tert-acrylate Examples thereof include butyl, 2-ethylhexyl acrylate, octyl acrylate, hexyl acrylate, and 2-hydroxyhexyl acrylate. Of these, butyl acrylate is preferred.

  And as for the compounding ratio of acrylic acid alkyl ester (X) and methacrylic acid (Y), methacrylic acid (Y) is 0.5-10 with respect to acrylic acid alkyl ester (X) 20-75, Preferably, 1-7. That is, if too much alkyl acrylate (X) is present, the dispersion stability in the coating solution may be impaired, and sufficient water retention effect may not be obtained. Conversely, if too much methacrylic acid (Y) is present, coating may occur. This is because the viscosity of the working liquid is increased and high-speed coating property may be deteriorated.

In addition, if the content of the specific copolymer that is a synthetic water retention agent is too small, the dispersion stability of the latex is impaired, the water retention of the coating liquid cannot be sufficiently obtained, and the coating property may be deteriorated. This is because there is a decrease in strength of the coating layer. Conversely, if the content ratio of the specific copolymer is too large, the viscosity of the coating solution becomes too high and the paper substrate 1 tends not to be coated uniformly. Of course, in addition to the above specific copolymer, other known water retention agents may be used in combination as long as the object of the present invention is not impaired.
Such a specific copolymer is mixed according to a conventional method, for example, at a predetermined ratio of both, and in an inert organic solvent, a peroxide such as benzoyl peroxide or acetyl peroxide, or bisazoisobutyrate. It can be carried out in the presence of a radical catalyst such as ronitrile.

  Moreover, it is preferable that the weight average molecular weight (Mw) of the copolymer of acrylic acid alkylester (X) and methacrylic acid (Y) is set in the range of 900,000 to 8 million. That is, if the molecular weight is too small, there is a tendency that a sufficient water retention effect cannot be obtained, and conversely, if the molecular weight is too large, the coating liquid may be thickened and the high-speed coating property may be deteriorated. is there.

Lecithin is used as the lubricant (component D). Here, lecithin is a phospholipid mixture extracted from egg yolk, soybean and the like. Since such lecithin has a large number of hydrophilic groups, it is easily dissolved in the coating liquid, and has a higher chemical affinity for the metal roll of the surface treatment device than calcium stearate. Easy to adhere to metal rolls. For this reason, the static / dynamic friction coefficient between the metal roll and the coated paper can be reduced, and as a result, the occurrence of dusting in the surface treatment apparatus can be effectively suppressed.
Moreover, since the high shear viscosity of a coating liquid can be reduced by mix | blending a lecithin with a coating liquid, when coating the preset coating amount (solid content conversion) to the paper base material 1, it coats. The pressure (shearing force) applied to the working fluid decreases. For this reason, the stability of the coating liquid is not impaired, and the occurrence of agglomerates of the coating liquid can be suppressed, so that the occurrence of coating defects such as streaks and scratches can be effectively suppressed.

  And it is preferable that the compounding quantity of a lecithin is set in the range of 0.1-3.0 weight part with respect to 100 weight part of pigments. When the blended amount of lecithin is within such a range, it is possible to effectively suppress the occurrence of dusting of the surface treatment apparatus in the surface treatment process, and coating defects such as streak and scratch at the time of coating. Can be effectively suppressed. If the blended amount of lecithin is less than 0.1 parts by weight, lecithin adhering to the metal roll of the surface treatment device decreases, and components such as pigments and adhesives in the coating liquid adhere to the metal roll. This is because there is a tendency that the dusting of the surface treatment apparatus cannot be effectively suppressed. In addition, since the high shear viscosity of the coating liquid cannot be sufficiently reduced, the occurrence of coating defects such as streaks and scratches during coating tends not to be effectively suppressed. On the other hand, when the blended amount of lecithin is more than 3.0 parts by weight, it effectively suppresses the occurrence of dusting of the surface treatment device, and effectively suppresses the occurrence of coating defects such as streak and scratch during coating. This is because although the surface strength of the coated layer of the coated paper is reduced, troubles such as picking tend to occur during printing. Of course, in addition to the above lecithin, other known lubricants may be used in combination as long as the object of the present invention is not impaired.

  Furthermore, the blending ratio of the copolymer of acrylic acid alkyl ester and methacrylic acid contained in the component (C) and lecithin contained in the component (D) is from 1: 3 to 1: It is preferably set within the range of 10. That is, if the blended amount of lecithin with respect to a specific copolymer is too small, the amount of lecithin attached to the roll surface of a smoothing device such as a surface treatment device such as a thermal soft calender will decrease, and the pigment or adhesion in the coating liquid This is because components such as agents may adhere to the metal roll or resin roll of the thermal soft calender and may cause a problem that causes dusting problems in the surface treatment device. Conversely, the amount of lecithin added to a specific copolymer If the amount is too large, the above problem can be solved, but the problem of reducing the strength of the coated surface of the coated paper may occur, and troubles such as picking during printing may easily occur. In other words, since the specific copolymer and lecithin are blended in the coating liquid in the above specific ratio, both are balanced and the coating property of the coating liquid is improved, so that it is more excellent. This is because the coating layer 2 having both smoothness and cushioning properties is formed.

  In addition to the above-described components, the coating liquid used in the present invention includes various conventionally known auxiliaries such as a dispersant, a thickener, an antifoaming agent, a water-resistant agent, a colorant, and a pH adjuster. Can be appropriately blended according to the purpose of use and needs. Moreover, the solid content concentration of the coating liquid used in the present invention is usually set within a range of 50 to 70%.

The coated paper according to the present embodiment is prepared by, for example, preparing the paper base material 1 and the coating liquid, and then coating the coating liquid on both sides of the paper base material 1 with a predetermined coating amount and drying it. Furthermore, it can manufacture by performing a surface treatment on the conditions from which the regular reflection smoothness of the coating layer 2 formed on the paper base material 1 becomes 85% or more.
Here, the coating treatment can be performed using various known coating apparatuses such as a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, and a curtain coater.
The drying treatment can be performed by various known heating and drying methods such as hot air heating, steam heating, infrared heater heating, gas heater heating, and electric heater heating. In addition, about drying conditions, it adjusts suitably according to a heat drying system, the mixing | blending of a coating liquid, etc.
Furthermore, the surface treatment can be performed using various known surface treatment apparatuses such as a thermal soft calender, a multi-nip calender, and a super calender. In particular, it is preferable to perform surface treatment using a surface treatment apparatus described below.

FIG. 2 is a perspective view schematically showing an example of a preferred surface treatment apparatus. This surface treatment apparatus is a tandem type in which two rolls and one nip stage are arranged in parallel, a metal roll 11 and an elastic roll 12 located on the upstream side, and a metal roll 21 located on the downstream side of the metal roll 11 And an elastic roll 22. The metal roll 11 and the metal roll 21 each have an internal heating mechanism based on electromagnetic induction, and more preferably, outside the metal roll 11 and the metal roll 21, the axial direction of each of the rolls 11 and 21. An electromagnetic induction heating type external heater 14 extending in the same direction is disposed. In the present embodiment, two rolls and one nip stage are arranged in parallel in two stages, but it is needless to say that more stages may be arranged in parallel.
In addition, for on-line surface flattening in high-speed coating of 1300 m / min or more, it is possible to use a multi-nip calender that performs surface flattening by combining multiple stages of metal rolls and elastic rolls. It is suitable from the ease of flattening pressure control of any space and front and back surfaces.

  The internal heating mechanisms in the metal rolls 11 and 21 are both induction coils (not shown) wound around iron cores 11a and 21a extending in the roll longitudinal direction inside cylindrical bodies 11b and 21b formed of various metal materials. Z). Then, by passing an alternating current through the induction coil, a magnetic flux is generated in the induction coil, an induced current is induced inside the cylindrical body, and the cylindrical bodies 11b and 21b themselves self-heat (inductive heating) by the resistance heat. be able to. Such an internal heating mechanism based on electromagnetic induction action divides the induction coil in the longitudinal direction of the roll (for example, 3-6 divisions), and the corresponding induction based on the temperature signal from the temperature sensor disposed in the cylindrical body 11b, 21b. By controlling the amount of alternating current flowing through the coil, it can be divided and controlled in the roll longitudinal direction. With this configuration, the temperature control of the surface temperature of the metal rolls 11 and 21 (the temperature of the outer peripheral surface of the roll) can be performed with high accuracy, particularly in the roll longitudinal direction.

And both the external heaters 14 and 24 arrange | positioned facing the outer peripheral surface of the metal rolls 11 and 21 are those of an electromagnetic induction heating type using the principle of electromagnetic induction heating. Specifically, the external heaters 14 and 24 both have an iron core around which an induction coil is wound inside a shell portion, and a magnetic flux is generated in the induction coil by flowing an alternating current through the induction coil. And an induced current is induced inside the shell portion, and the shell portion itself can be self-heated (inductive heating) by the resistance heat. And the outer peripheral surface of the metal rolls 11 and 21 can be heated with the radiant heat from the heat-generated shell part. The external heaters 14 and 24 are divided into the induction coils in the longitudinal direction of the roll (for example, 3 to 6), and are disposed in the cylindrical bodies 11b and 21b, similarly to the internal heating mechanism using electromagnetic induction. By controlling the amount of alternating current flowing through the corresponding induction coil based on the temperature signal from the sensor, it can be divided and controlled in the roll longitudinal direction. By disposing the external heater 14, the controllability of the paper thickness profile and the temperature controllability of the roll surface temperature can be enhanced. Specifically, only the internal heating mechanism based on the electromagnetic induction action causes stress in the thickness direction on the cylindrical body of the metal rolls 11 and 21, the roll profile is liable to collapse, and the roll surface temperature has a temperature responsiveness per time. Although there is a drawback that it is likely to get worse, it is possible to eliminate this drawback with the external heater 14. Moreover, according to the said structure, the surface temperature of the metal rolls 11 and 21 in the nip vicinity with the elastic rolls 12 and 22 can be made high temperature of 230-300 degreeC. Here, the surface temperature of the metal rolls 11 and 21 is preferably in the range of 250 to 300 ° C, more preferably in the range of 250 to 380 ° C, still more preferably more than 300 ° C and not more than 380 ° C. If surface treatment is performed at a high temperature and low nip pressure, heat transfer to the center (inner layer part) in the thickness direction of the paper can be suppressed as much as possible, resulting in a decrease in bulk and opacity. Can be effectively suppressed. Moreover, the coating layer provided with high regular reflection smoothness can be formed easily.
The internal heating mechanism can be suitably employed not only in a thermal soft calender but also in a multi-nip calender.

  The elastic rolls 12 and 22 have solid or hollow cores 12a and 22a and elastic layers 12b and 22b made of an elastic material such as various rubbers, elastomers, and resins formed on the outer peripheral surface thereof. The elastic layers 12b and 22b having a shear D hardness of 85 to 97, particularly 85 to 94 are preferably used. Thereby, the nip between the metal rolls 11 and 21 and the elastic rolls 12 and 22 can be set to a low nip pressure.

The surface treatment using the surface treatment apparatus can be performed as follows, for example. First, the surface temperature of the metal roll 11 near the nip with the elastic roll 12 is set to a high temperature within a range of 230 to 300 ° C., and the surface temperature of the metal roll 21 near the nip with the elastic roll 22 is set to 230 to 300 ° C. The pressure between both nips is set to a low nip pressure of about 125 to 350 KN / m.
In the study by the present inventors, it has been found that the effect of the present invention in the production at a higher speed can be obtained by increasing the temperature of the surface of the metal roll, more preferably to about 500 ° C. In view of the heat resistance of the elastic roll against the heat resistance and the heat resistance of the heat-generating material in the internal heating device, the operation up to 300 ° C. is preferable in the current facilities from the viewpoint of stability and safety of the operation.
Then, a paper base material T ′ with a coating layer obtained by applying a coating liquid on both surfaces of the paper base material 1 and drying is passed at a paper speed of 400 to 3000 m / min. Thereby, the fine convex part of the coating layer surface after drying can be crushed and smoothed, and as a result, the coated paper T having excellent smoothness in which the regular reflection smoothness is set to 85% or more. Is obtained.

In the coated paper thus obtained, the regular reflection smoothness of the coated layer is set to 85% or more. By providing such a high regular reflection smoothness, it is possible to reduce the dot missing rate, in particular, in combination with the improvement of the coatability. The regular reflection smoothness was measured using a total reflection type printing smoothness meter (Microtopograph manufactured by Toyo Seiki Co., Ltd.).
In the microtopograph, it is possible to read the optical contact rate between the glass surface and the paper 10 milliseconds after the start of pressurization, and regular reflection that is an index of smoothness calculated from the contact rate between the paper and the glass surface. As a result of examining the smoothness and the occurrence rate of missing dots, the specular reflection smoothness 10 milliseconds after the start of pressurization with the setting of the pressurization pressure of 20 kgf / cm ² of the microtopograph has the most correlation with the occurrence rate of the missing dots. I found it expensive.
That is, by finishing the specular reflection smoothness of 85% or more 10 milliseconds after the start of pressurization at a set pressure of 20 kgf / cm ² of the microtopograph, good gravure printing suitability can be obtained, and an unnecessary calendar It is possible to effectively balance gravure printability, appearance as coated paper, and stiffness without losing the appearance of coated paper by strengthening the treatment or reducing the rigidity by crushing too much. It becomes. Incidentally, as a method of obtaining regular reflection smoothness desired by the present invention, smoothing treatment conditions by a thermal soft calender composed of a metal roll and an elastic roll, the coating amount of a coating liquid to be applied to a base paper, A method of changing the amount and type of the pigment to be contained, or adjusting by selecting an auxiliary agent is taken.

  The coated paper according to the present embodiment configured as described above uses a copolymer of acrylic acid alkyl ester and methacrylic acid, which is an acrylic synthetic water retention agent, as a water retention agent (component C), and a lubricant ( Since lecithin is used as the component D), and these are used at a specific blending ratio, both are balanced and the coating property is good, so that the coating layer has both good smoothness and cushioning properties. ing. For this reason, at the time of gravure printing, ink transfer is performed in a good state. Therefore, the dot missing rate particularly in high-speed gravure printing is reduced, and a printed matter with a good finish reproduced more faithfully can be obtained. Moreover, when the said specific latex is used as an adhesive agent (B component), it has the advantage that it becomes a coating layer excellent in a weather resistance, stickiness resistance, etc.

  In addition, this invention is not limited to the said embodiment. For example, the coating layer 2 may be formed not only on both sides of the paper substrate 1 but only on one side. The coating layer 2 is not limited to a single layer, and may have a multilayer structure of two or more layers. In this case, the regular reflection smoothness of the outermost layer may be set to a predetermined value or more. Furthermore, in the surface treatment apparatus (see FIG. 2), the external heater may be arranged to face only the outer peripheral surface of at least one metal roll. However, it is preferable that an external heater is disposed opposite to the outer peripheral surface of all the metal rolls.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.
Example 1
First, 50 parts by weight of heavy calcium carbonate as a pigment (component A), 50 parts by weight of clay, and a styrene-butadiene latex (acrylonitrile content: 5% by weight, Tg: -10) as an adhesive (component B) ° C, average particle size: 130 nm, gel content: 85%) 10 parts by weight, 6 parts by weight of carbamic acid starch (Star Coat # 27 manufactured by Nippon Shokuhin Kako Co., Ltd.), and acrylic acid as a water retention agent (component C) A 0.02 part by weight copolymer of acrylic ester and methacrylic acid (Somalex 270K manufactured by Somaru) and 0.1 part by weight of lecithin as a lubricant (component D) were prepared. Subsequently, these were mixed and diluted with water to obtain a coating solution having a solid content of 65%. Then, using this coating liquid, a dry basis weight of 11 g / m ² was applied to both sides of a base paper having a basis weight of 46 g / m ² using a paper machine size press (rod metering size press), and FIG. The paper was passed through the surface treatment apparatus shown. The surface treatment conditions are as follows: the surface temperature of the metal roll in the vicinity of the nip with the elastic roll is 230 ° C., the pressure between the metal roll and the elastic roll (nip pressure) is 250 KN / m, and the sheet feeding speed is 1500 m / m. Minutes. Thus, the intended coated paper was obtained.

(Examples 2 to 21, Comparative Examples 1 to 18)
Lecithin blending amount (parts by weight), blending ratio of copolymer of acrylic acid acrylic ester and methacrylic acid and lecithin, glass transition temperature (Tg, ° C) of styrene-butadiene latex, average particle diameter (nm), gel Content (%), acrylonitrile content (AN content, weight%), surface temperature of metal roll in the vicinity of elastic roll (° C.), pressure between metal roll and elastic roll (nip pressure, KN / m), The target coated paper was obtained in the same manner as in Example 1 except that the sheet passing speed (m / min) was as shown in Tables 1 to 3 below. In Table 1, Example 1 is also described.

  About the coated paper of the Example and comparative example which were obtained as mentioned above, it measured and evaluated about the following each characteristic. The results are shown in Tables 4 to 6 below.

(Specular reflection smoothness)
It measured using the total reflection type | mold printing smoothness meter (The micro topograph by Toyo Seiki Co., Ltd.).

(Speckle)
It measured using the printing station type | formula gravure printing aptitude test machine (made by Kumagai Riki Kogyo Co., Ltd.). That is, the halftone dot missing state in each 20% halftone part on both sides (F side and W side) of each coated paper was measured as the number of missing parts (number) per 1 cm ² .

(Dry pick strength)
This is an index indicating the surface strength of the coating layer, using a RI-II type printing machine (manufactured by Meisei Seisakusho Co., Ltd.) and using a TV-24 manufactured by Toyo Ink Co., Ltd. The degree of picking of the surface was evaluated visually. As a result, ◎ was given when there was little occurrence of picking, ◯ when there was little occurrence of picking, △ when there was much occurrence of picking, and × when there was significant occurrence of picking.

(Color variation)
Each coated paper obtained was visually evaluated. As a result, it is ◎ that there is no gloss unevenness, ◯ that there is slight gloss unevenness, but there is no problem in practical use, △ that there is a lot of gloss unevenness, and that there is significant gloss unevenness. X was attached.

(Weatherability)
The obtained coated paper was irradiated with visible light and ultraviolet light for 24 hours at an output of 80 W / m ² using a xenon weather meter (manufactured by Suga Test Instruments Co., Ltd.), and then white of a test blank sample under a fluorescent lamp. Were evaluated by visual comparison. As a result, ◎ was given for those in which no change was observed, ◯ for those in which slight change was observed, △ for those in which changes were observed, and × for those in which changes were significant.

(Dusting occurrence evaluation)
The dusting generated on the metal roll constituting the surface treatment apparatus was visually evaluated. As a result, “A” was given for those that did not occur at all, “B” for those that hardly occurred, “B” for those that did not cause any problems in actual use, and “B” for those that occurred.

(Evaluation of occurrence of coating defects)
The occurrence of coating defects such as streaks and scratches during coating was evaluated based on the frequency of streak generated by a transmission type streak detector during coating. That is, the streak length ratio to the total coating flow was evaluated. As a result, the streak rate is less than 0.1%, the streak rate is between 0.1% and less than 0.2%, and the streak rate is between 0.2% and less than 0.3%. A mark was given to those having a streak occurrence rate of 0.3% or more.

(Printing finish)
Using an actual gravure printing machine, gravure printing was performed on the coated papers of the examples and comparative examples. And visual evaluation was performed about the reproducibility of printed matter. As a result, ◎ was reproduced very faithfully, ◯ was slightly inferior but could be reproduced faithfully, and x was not reproduced faithfully.

From the results of Tables 4 to 6, it can be seen that the coated paper of each example has a regular reflection smoothness of 85% or more, a halftone dot loss rate is considerably reduced, and a good print finish. It can also be seen that good results are obtained for each evaluation item such as dry pick strength, color tone variation, weather resistance, dusting occurrence, and coating defects.
Each coated paper of Examples 1 to 4 is obtained by changing the blending amount of lecithin, but the blending amounts of lecithin are 1.0 parts by weight, 2.0 parts by weight, and 3.0 parts by weight. It can be seen that each of the coated papers 2 to 4 is better than the coated paper of Example 1 in which the amount of lecithin is 0.1 parts by weight. Furthermore, the coated papers of Examples 5 and 6 in which the blending ratio of the specific copolymer and lecithin is 1: 3 and 1:10 are slightly inferior in coatability, but comprehensively enough. It can be seen that the dot missing rate is reduced and the print finish is good. In addition, it can be seen that the coated papers of Examples 7 to 9 in which the glass transition temperature of the latex is changed also have a high regular reflection smoothness, a considerably reduced dot missing rate, and a good print finish. In addition, it can be seen that the coated papers of Examples 10 and 11 in which the average particle diameter of the latex was changed also had high regular reflection smoothness, a considerably reduced halftone dot missing rate, and good print finish. Furthermore, it can be seen that the coated papers of Examples 12 and 13 in which the gel content of the latex is changed also have high regular reflection smoothness, the dot missing rate is considerably reduced, and the printing finish is good. In addition, each coated paper of Examples 14 and 15 having a slightly increased acrylonitrile content is slightly inferior in weather resistance (no problem in practical use), but has high regular reflection smoothness and a considerably reduced halftone dot loss rate. It can be seen that the print finish is good. Each of the coated papers of Examples 16 to 21 was produced by changing the surface treatment conditions. However, each of the coated papers had high regular reflection smoothness, the dot missing rate was considerably reduced, and the printing finish was high. It turns out that it is favorable.

On the other hand, the coated paper of Comparative Example 1 did not contain lecithin, and was manufactured at a low nip pressure, so that the dusting was not sufficiently suppressed and the regular reflection smoothness was slightly low. You can see that It can also be seen that the dot missing rate is high and the print finish is insufficient.
The coated paper of Comparative Example 2 did not contain lecithin and was manufactured at a high nip pressure, so that the dry pick strength was poor and the color tone was not uniform, and the dusting was not sufficiently suppressed. You can see that It can also be seen that the dot missing rate is high.
Since the coated paper of Comparative Example 3 does not contain lecithin and was produced at a low roll temperature, the suppression of dusting is insufficient and the specular reflection smoothness is slightly low. Recognize. It can also be seen that the dot missing rate is high.
The coated paper of Comparative Example 4 does not contain lecithin and is manufactured at a high roll temperature, so that the dry pick strength and weather resistance are poor, and the suppression of dusting is insufficient. I understand that. It can also be seen that the halftone dot missing rate is slightly high, and the print finish is slightly worse.
The coated paper of Comparative Example 5 does not contain lecithin and is manufactured at a low paper passing speed, so that the regular reflection smoothness is high, but the suppression of dusting is insufficient. I understand that. It can also be seen that the dot missing rate is high and the print finish is insufficient.
The coated paper of Comparative Example 6 did not contain lecithin, and was manufactured at a high paper feed speed. Therefore, the dry pick strength and weather resistance were poor, and the color tone was not uniform, and dusting occurred. It turns out that suppression is also insufficient. It can also be seen that the dot missing rate is high.

It can be seen that the coated paper of Comparative Example 7 has a low lecithin content and therefore has a poor dry pick strength and an insufficient suppression of dusting. It can also be seen that the dot missing rate is very high.
Since the coated paper of Comparative Example 8 has a high lecithin content, the dot missing rate is low. However, the dry pick strength is insufficient, the color tone varies, and coating defects are observed. I understand that For this reason, it is generally insufficient as coated paper.
Since the coated paper of Comparative Example 9 has a small amount of lecithin with respect to the specific copolymer, the dry pick strength is poor, the color tone is not uniform, and the dusting is not sufficiently suppressed. I understand that. It can also be seen that the dot missing rate is high.
It can be seen that the coated paper of Comparative Example 10 has insufficient suppression of dusting due to the large amount of lecithin added to the specific copolymer. It can also be seen that the dot missing rate is high.
Each of the coated papers of Comparative Examples 11 and 12 does not contain lecithin, and since the latex has a high glass transition temperature, it is found that the weather resistance is inferior and the suppression of dusting is insufficient. . It can also be seen that the dot missing rate is slightly higher.
It can be seen that the coated paper of Comparative Example 13 does not contain lecithin and the average particle diameter of the latex is small, so that the dry pick strength is poor and the suppression of dusting is insufficient. It can also be seen that the dot missing rate is high and the printed finish is insufficient.
The coated paper of Comparative Example 14 does not contain lecithin, and the latex average particle size is large. Therefore, the occurrence of dusting is not sufficiently suppressed, coating defects are observed, and the dry pick strength is insufficient. It turns out that it is enough. It can also be seen that the dot missing rate is high.
It can be seen that the coated paper of Comparative Example 15 does not contain lecithin and the latex gel content is low, so that the suppression of dusting is insufficient. It can also be seen that the dot missing rate is high and the printed finish is insufficient.
It can be seen that the coated paper of Comparative Example 16 does not contain lecithin and has a high latex gel content, so that the suppression of dusting is insufficient. It can also be seen that the dot missing rate is high and the printed finish is insufficient.
Each coated paper of Comparative Examples 17 and 18 does not contain lecithin, and since the acrylonitrile content of the latex is high, the color tone varies, the weather resistance is poor, and the occurrence of dusting is suppressed. It is also understood that is insufficient. It can also be seen that the dot missing rate is high.

It is sectional drawing which shows the coated paper for gravure printing which concerns on one Embodiment of this invention. It is a perspective view which shows typically an example of a surface treatment apparatus.

Explanation of symbols

1 Paper substrate 2 Coating layer T Coated paper for gravure printing

Claims (3)

A coated paper for gravure printing in which a coating layer is formed on at least one side of a paper substrate,
The coating layer is formed by using a coating solution containing the following components (A) to (D), and (A) a pigment (B) an adhesive (C) an acrylic acid alkyl ester, methacrylic acid, Water retaining agent containing a copolymer of (D) Lubricant containing lecithin The blending ratio of the copolymer of acrylic acid alkyl ester and methacrylic acid in the component (C) and lecithin in the component (D), The weight ratio is set within the range of 1: 3 to 1:10,
And the compounding quantity of the lecithin in the said (D) component is set in the range of 0.1-3.0 weight part with respect to 100 weight part of pigments which are the said (A) component, It is characterized by the above-mentioned. Coated paper for gravure printing. The adhesive which is the component (B) contains a latex having a glass transition temperature of −30 to 0 ° C., an average particle size of 100 to 170 nm, and a gel content of 80 to 90%.
The coated paper for gravure printing according to claim 1, wherein the latex contains no acrylonitrile or has an acrylonitrile content of 10% by weight or less. A method for producing a coated paper for gravure printing according to claim 1,
Coating and drying the coating liquid on at least one side of the paper substrate, and thereafter performing a surface treatment with a surface treatment device;
The surface treatment apparatus has a plurality of stages of two rolls and one nip by a combination of a metal roll and an elastic roll,
Each of the metal rolls has an internal heating mechanism by electromagnetic induction that can be divided and controlled in the roll longitudinal direction,
At least one of the metal rolls is provided with an external heater by electromagnetic induction that can be divided and controlled in the roll longitudinal direction, facing the outer peripheral surface of the roll,
By passing the paper in a state where the surface temperature of the metal roll in the vicinity of the nip between the metal roll and the elastic roll is set within a range of 230 to 300 ° C. by the internal heating mechanism and the external heater, A method for producing a coated paper for gravure printing, wherein the regular reflection smoothness is set to 85% or more.

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