JP2006188783A - Coated paper for printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide bulky coated paper for printing having high white paper glossiness. <P>SOLUTION: The coated paper for printing comprises a coating layer containing a copolymer latex having ≥2 glass transition temperatures, ≤-5°C lowest glass transition temperature, ≥10°C highest glass transition temperature and 100-200 nm average particle diameter and ≥30 wt.% of styrene content in an amount of 4-15 pts.wt. based on 100 pts.wt. of the coating layer. The figure is a schematic block diagram of a soft calender apparatus as follows. Numerals 1 indicate each a metallic roll; numerals 2 indicate each an elastic roll and numerals 3 indicate each an external induction heating apparatus. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coated paper for printing.

  Due to the demand for full-color printing due to recent progress in visualization, demand for coated paper with good printability and good print quality has increased, and further improvement in print quality is desired. In particular, high-quality art printing, catalogs, brochures, calendars, etc. have been demanding a high-class feeling in the printed finish, and the whiteness, hue, white paper glossiness of coated paper, Demands for printing glossiness and the like are becoming strict, and high whiteness and high white paper glossiness are required. Furthermore, in addition to these qualities, color tone and image area reproducibility and high gloss are required. Among the evaluation items for reproducibility, particularly, the blank paper glossiness and the print glossiness are determined and evaluated most strictly.

As a general method for increasing the glossiness of coated paper, a method of selecting and using an inorganic pigment or an organic pigment is known in order to increase the glossiness of the coating layer itself. For example, Patent Document 1 discloses an inorganic extender pigment containing cubic calcium carbonate fine particles having a primary particle diameter of 0.1 to 1.0 μm, preferably 30 parts by weight or more as a pigment of a coating agent. It is described that it can be used as a cast paper that maintains high glossiness and can be produced at a high speed (see Patent Document 1).
JP 59-216996 A

However, in the present invention, a large amount of calcium carbonate particles having a shape close to a spherical shape rather than a flat shape is used, and as a result, the glossiness of blank paper decreases as the proportion of the total pigment increases.
In addition, as another method for increasing the glossiness of the coated paper, (a) a method of increasing the thickness of the coating layer, and (b) a latex that is easy to express glossiness as a latex to be mixed in the coating layer is used. And (c) a method of strengthening the surface treatment of the coating layer by a pressurizing device such as a super calendar.
However, these methods (a) to (c) have the following problems.
In the method (a), the print gloss can be increased by using a large amount of a water-soluble or water-dispersible polymer material such as polymer latex as a binder for the pigment, but the coating layer has less voids. The orientation of the pigment by the calendar process is hindered, and the gloss of the white paper is lowered.
The method (b) is a method in which two or more polymer latexes having different minimum film-forming temperatures are used in combination and dried, and smoothed with a calendar if necessary. By drying in combination, fine cracks are produced on the coated paper surface, and good ink absorbability can be obtained without impairing gloss. In this case, however, careful attention must be paid to the drying conditions. That is, it is necessary to set the drying conditions such that the latex having a relatively low minimum film forming temperature is completely melted, but the latex having a relatively high minimum film forming temperature is partially melted.
When the surface of the coating layer is pressurized and smoothed to increase the glossiness by the method (c), the gap in the coating layer is crushed inevitably, so the printing gloss is improved, but the paper stiffness is reduced. As a result, the printing workability deteriorates.

  In this way, in coated paper, the type and composition of pigments and adhesives, the amount of paint applied, the degree of smoothing, etc. are determined so that the white paper gloss and the print gloss are reasonably balanced. In the prior art, it is not possible to obtain a high-gloss paper having better printability.

  In view of the above situation, an object of the present invention is to provide a coated paper for printing having a high white paper glossiness and high bulk.

The printing coated paper of the present invention is provided with a coating layer mainly composed of a pigment and an adhesive on at least one surface of a base paper, and the surface of the coating layer is flattened by a thermal calendar. In the coated coated paper being processed,
The coating layer has two or more glass transition points, the lowest glass transition point is −5 ° C. or less and the highest glass transition point is 10 ° C. or more, and the average particle diameter is 100 nm to 200 nm, Copolymer latex having a styrene content of 30% by weight or more is contained in an amount of 4 to 15 parts by weight with respect to 100 parts by weight of the coating layer,
The 75 degree specular gloss is 75% or more, and the density is 0.7 to 1.1 g / m ³ .

By blending the copolymer latex having two or more glass transition points in the coating layer, the 75 ° specular gloss is 75% or more and the density is 0.7 to 1.1 g / m ³ . A coated paper for printing could be easily produced. The reason can be guessed as follows. By setting the lowest glass transition point to −5 ° C. or lower, the adhesive strength can be increased, the coating layer is easily crushed, and the orientation of the pigment by calendering is improved. Is likely to be maintained. In addition, by setting the highest glass transition point to 10 ° C or higher, it is possible to prevent the adhesiveness of the coating liquid from being excessively increased, the operability on the super calendar and coater is improved, the paper is high, and the blister suitability is improved. Is also expected to improve. And the synergistic effect of the said advantage resulting from each glass transition point can be acquired by using two or more glass transition points. When the average particle size is within the above range, if it is smaller than 100 nm, the air permeability may be deteriorated and blisters may be generated. If it is larger than 200 nm, the film-forming property is lowered, and the surface strength of the coating layer may be lowered. Because there is. The reason why the styrene content is in the upper range is that when the styrene content is less than 30% by weight, it may be difficult to set the glass transition point of the copolymer latex to the above temperatures.
Moreover, the content of the copolymer latex is within the above range because if it is less than 4 parts by weight, the effect of containing the latex is not sufficiently exhibited, and if it exceeds 15 parts by weight, the ink setting property is excessively large. It is because it may worsen or a blister may arise.

  In the above coated paper for printing, after the coating layer is coated on the paper substrate, the moisture content of the coated paper is adjusted to 3 to 8% by weight by drying, and then the on-machine thermal calendar It is preferable that the surface is flattened at a temperature of 130 ° C. or higher. The reason why the moisture content of the coated paper before calendering is in the above range is that if it is less than 3% by weight, sufficient smoothness may not be obtained even by calendering, and if it exceeds 8% by weight. This is because workability may deteriorate due to roll contamination during calendar processing. Further, by setting the temperature to 130 ° C. or higher, it is possible to increase the smoothness while maintaining the bulkiness. Furthermore, by using the on machine, the productivity of the coated paper is improved as compared to the off machine.

Furthermore, in the coated paper for printing, the thermal calender is a soft calender composed of a metal roll provided with a heating means and an elastic roll, and can be divided and controlled in the roll width direction inside the metal roll. An internal heating device by electromagnetic induction is provided, and an external heating device by electromagnetic induction that can be divided and controlled in the roll width direction and / or a cooling device that can be divided and controlled in the roll width direction are provided outside the metal roll. The surface of the coating layer is flattened at a roll surface temperature of 130 ° C. or higher while the temperature in the roll width direction is divided and controlled by this thermal calender device, so that the 75 ° specular gloss is 75% or higher. , Preferably having a density adjusted to 0.7 to 1.1 g / m ³ .

  By using a soft calendar, it becomes easy to achieve both smoothness and bulkiness. In addition, by controlling the temperature with each of the heating devices that can be divided and controlled in the roll width direction, the uniformity of the temperature distribution in the roll width direction can be improved, and the uniformity of glossiness and density in the paper width direction can be improved. In addition, the cooling device divided and controlled in the roll width direction can prevent yellowing of the paper due to excessive heating, and can improve uniformity in the roll width direction.

  As described above, according to the present invention, by using a predetermined copolymer latex having two or more glass transition points as an adhesive, a coated paper for printing having a high glossiness and a relatively bulky shape is obtained. It becomes possible.

Hereinafter, the present invention will be described in more detail.
The coating layer of the coated paper for printing of the present invention has two or more glass transition points, and the lowest glass transition point (Tg) is −5 ° C. or lower and the highest glass transition point. A copolymer latex having a temperature of 10 ° C. or higher is used. As such a copolymer latex, latex particles have a core-shell structure, a copolymer having a Tg of −5 ° C. or less exists in the core portion, and a copolymer having a temperature of 10 ° C. or more exists in the shell portion. What has a structure can be illustrated. In order to produce a copolymer latex having such a core-shell structure, in the presence of the copolymer (X) having a Tg of −5 ° C. or lower, a single monomer constituting the copolymer (Y) having a Tg of 10 ° C. or higher is produced. The polymer may be polymerized.

  Monomers constituting the copolymer (X) having a Tg of −5 ° C. or lower include aliphatic conjugated diene monomers, vinyl cyanide monomers, ethylenically unsaturated carboxylic acid monomers, aromatics. Group vinyl monomers, alkyl (meth) acrylates, and the like are used. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, chloroprene and the like, and 1,3-butadiene is particularly preferably used. Examples of the vinyl cyanide monomer include acrylonitrile and methacrylonitrile. Examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid and methacrylic acid. Examples of the aromatic vinyl monomer include styrene and vinyl toluene. Among these, styrene is particularly preferably used. Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate, and among these, methyl (meth) acrylate is particularly preferable. Used. As the monomer constituting the copolymer (X) having a Tg of −5 ° C. or lower, two or more of the above can be used in appropriate combination. And the kind and compounding ratio of a monomer should just be selected suitably so that Tg of copolymer (X) which consists of these monomers may be -5 degrees C or less.

  As the monomer constituting the copolymer (Y) having a Tg of 10 ° C. or higher, as in the case of the copolymer (X), an aliphatic conjugated diene monomer, a vinyl cyanide monomer, ethylene An unsaturated carboxylic acid monomer, an aromatic vinyl monomer, an alkyl (meth) acrylate, and the like are used, and a particularly suitable monomer is the same as that of the copolymer (X). And as a monomer which comprises copolymer (Y) whose Tg is 10 degreeC or more, 2 or more types can be used in combination suitably among said each monomer. And the kind and compounding ratio of a monomer should just be selected suitably so that Tg of the copolymer (Y) which consists of these monomers may be 10 degreeC or more.

  In addition, as a method for polymerizing the monomer, emulsion polymerization can be employed. In this case, polymerization can be performed using an emulsifier, a polymerization initiator, or the like in an aqueous medium by a known method. In addition, as an emulsifier, 1 type, or 2 or more types can be used suitably among each well-known anionic surfactant, nonionic surfactant, amphoteric surfactant, etc. Furthermore, what is used by normal emulsion polymerization, such as a molecular weight modifier, can be used suitably. In the polymerization, first, the copolymer (X) having a Tg of −5 ° C. or lower is polymerized in another system in advance, and then the copolymer (Y) in the presence of the copolymer (X). It is preferable to polymerize each monomer used as a raw material.

The average particle diameter of the copolymer latex is 100 nm to 200 nm. If the thickness is smaller than 100 nm, the air permeability may be deteriorated and blisters may be generated. If the thickness is larger than 200 nm, the film forming property is lowered, and the surface strength of the coating layer may be lowered.
The average particle size is one of the colloidal properties that greatly affects workability and physical properties of coated paper, and is one of the major factors that govern workability. The high shear viscosity, which is an indicator of paint fluidity, decreases with decreasing particle size. For coated paper properties, latex particle size is determined by the number of adhesion points, pore size, and binder migration during drying. The adhesive strength, gloss, ink acceptability, and the like.
Moreover, the average particle diameter was calculated | required by the conventional method using the laser light scattering particle size measuring instrument "LPA-3100PAR-3" by Otsuka Electronics.

  The copolymer latex has a styrene content of 30% by weight or more. Therefore, styrene is used as a monomer for at least one of the above-described copolymer (X) having a Tg of −5 ° C. or lower or the copolymer (Y) having a Tg of 10 ° C. or higher. For example, if the content ratio of butadiene is large, the Tg becomes excessively low, so it may be difficult to set the Tg as defined in the present invention. It becomes easy to set it as 10 degreeC or more. Moreover, Tg can be adjusted by changing the content ratio of styrene. Therefore, when 30% by weight or more of styrene is contained, Tg can be easily set at the desired temperature.

  The content (solid content) of the copolymer latex is 4 to 15 parts by weight with respect to 100 parts by weight of the coating layer in the finished coated paper. In addition to the latex having the two Tg described above, another latex may be added to the coating layer. Moreover, you may add starch, modified starch, PVA, carboxymethylcellulose (CMC), casein, soybean protein etc. as adhesives other than latex, for example. Among these, as the modified starch, oxidized starch, phosphate esterified starch, hydroxyethyl etherified starch, enzyme-modified starch and the like can be exemplified.

The pigment contained in the coating layer is not particularly limited. For example, kaolin, heavy calcium carbonate, light calcium carbonate, calcined kaolin, delaminated kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, Inorganic pigments such as magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, smectite, polystyrene resins, styrene-acrylic copolymer resins, urea resins, melamine resins, acrylic resins, vinylidene chloride resins The organic pigment may be a hollow organic pigment, a solid organic pigment, a through-hole organic pigment, or the like. Moreover, 1 type, or 2 or more types can be suitably selected from these.
Furthermore, you may use together various adjuvants, such as a dispersing agent, a thickener, a water retention agent, an antifoamer, and a water resistance agent, in the coating layer of this invention.

According to the present invention, a 75% specular gloss is 75% or more, a white paper gloss is relatively high, and a density is 0.7 to 1.1 g / m ³ , and a relatively bulky coated coated paper is produced. Easy to do. The 75-degree specular gloss is measured based on JIS P 8142.

  Any heat calender can be used as long as it has a heating mechanism, but it is preferable that the roll surface temperature be 130 ° C. or higher. In addition, a thermal calendar having a nip composed of a metal roll and an elastic roll is preferable because it is easy to achieve both bulkiness and flatness.

  More preferable as the heat calender is a soft calender composed of a metal roll and an elastic roll provided with heating means. An internal heating device with electromagnetic induction action that can be divided and controlled in the roll width direction is provided inside the metal roll, and an external part by electromagnetic induction action that can be divided and controlled in the roll width direction is provided near the outside of the metal roll. It is particularly preferable to provide a heating device and / or a cooling device that can be divided and controlled in the roll width direction. By using a soft calendar, it becomes easy to achieve both smoothness and bulkiness. The heating device may be provided either inside or outside the metal roll, and may be provided either outside or inside. However, if it is provided both outside and inside as described above, temperature control is performed. This is preferable because the accuracy of the is improved. Also, by controlling the temperature with the above heating devices and cooling devices that can be divided and controlled in the roll width direction, the uniformity of the temperature distribution in the roll width direction is improved, and the uniformity of the glossiness and density in the paper width direction is improved. Can do.

  As a mechanism for heating and controlling the surface temperature of the metal roll, in addition to the above-described electromagnetic induction action, for example, a method of circulating hot water or oil inside the metal roll can be adopted, but the accuracy of temperature control is For reasons such as a high heating temperature range and a wide heating temperature range, a heating device that is provided inside or outside the metal roll and causes the metal roll itself to generate heat by electromagnetic induction is preferable.

  As an internal heating device using electromagnetic induction, a cylindrical shell that forms the outer shell portion of a metal roll, an iron core that is coaxial with the shell and is provided inside the roll, and a periphery of the iron core And an induction coil wound around, and generating a magnetic flux by passing an alternating current through the induction coil to generate heat in a cylindrical shell covering the iron core. In this case, the induction coil is divided (for example, 3 to 6 divisions) in the roll width direction (axial direction of the roll), and on the shell side, the shell (metal roll surface) at a position corresponding to each divided portion of the induction coil By providing a temperature sensor that can measure the temperature of the metal roll, and controlling the amount of alternating current flowing through the corresponding induction coil based on the temperature signal from each temperature sensor, an internal heating device that can be divided and controlled in the roll width direction of the metal roll is provided. it can.

  Moreover, as a heating device that is provided outside the metal roll and heats the metal roll, a hot air device that blows hot air heated from the outside of the metal roll, or a heating device that induces heat generation of the metal roll itself by electromagnetic induction action Etc. are exemplified. In this case, the heating device and the induction coil are divided and provided in the width direction of the metal roll, and on the metal roll side, a temperature sensor that can measure the temperature of the surface of the metal roll at a position corresponding to each divided portion is provided. By controlling the corresponding heating device based on the temperature signal from the temperature sensor, the heating device can be divided and controlled in the roll width direction of the metal roll.

  Also, as a cooling device that can be divided and controlled in the roll width direction of the metal roll, which is considered to be adopted as a measure for preventing yellowing of the paper due to excessive heating, it is provided outside the metal roll and blows cold air on the metal roll. An example of a cool air device that can be used. As this cold air apparatus, the thing similar to the principle of a normal air conditioner etc., and the thing provided with the heat exchanger which used refrigerant gas and the compressor together is illustrated. As a preferable specification of the cold air device, one that can be adjusted in the range of the cold air temperature in the range of 0 ° C. to 25 ° C. and the cold air speed in the range of about 5 to 60 m / s is preferable. And, for example, a plurality of the cold air devices that can be controlled independently are juxtaposed in the roll width direction, and the cold air temperature of each cold air device is determined based on a temperature signal from a temperature sensor provided corresponding to the position of each cold air device. By controlling the cold air speed, a cooling device that can be divided and controlled in the roll width direction of the metal roll can be obtained.

A soft calendar device which is a preferred embodiment of the thermal calendar of the present invention will be described with reference to the drawings.
The soft calendar device 10 of FIG. 1 illustrates the internal induction heating device and the external induction heating device described above. As shown in FIG. 1, each of the metal rolls 1 includes an external induction heating device 3 as an external heating device that can cause the metal roll 1 itself to generate heat by electromagnetic induction. FIG. 2 is an enlarged view of the vicinity of the external induction heating device 3, and an AC power source (for example, a high frequency of 3 to 20 kHz) is supplied to the work coil 4 from an AC power source (inverter) 5 and is indicated by an arrow in FIG. 2. ) To generate self-power generation by generating eddy currents on the surface of the shell 6 of the metal roll 1. The surface of the work coil 4 facing the shell 6 is a curved surface along the outer peripheral surface of the shell 6, and the shell 6 and the work coil 4 are separated by about 2 to 20 mm. This separation distance is preferably 2 to 5 mm. As described above, the external induction heating device 3 is divided and provided in the roll width direction, or the work coil 4 of the external induction heating device 3 is divided in the roll width direction so as to be divided in the roll width direction. It is possible.

  Further, inside each metal roll 1 of the soft calender device 10, an internal induction heating device 7 is provided as an internal heating device that can self-heat the metal roll 1 itself by electromagnetic induction and can be divided and controlled in the roll width direction. ing. The internal induction heating device 7 is wound around the iron core 8 and a cylindrical iron core 8 provided coaxially with the shell 6 inside the cylindrical shell 6 constituting the outer shell of the metal roll 1. And an induction coil 9. Between the induction coil 9 and the shell 6, there is a predetermined gap that divides the shell 6 that is a rotating portion and the iron core 8 and the induction coil 9 that are non-rotating portions. The induction coil 9 is connected to an AC power source 11, and the shell 6 self-heats when an AC current is passed through the induction coil 9. Inside the shell 6, there are provided jacket paths 12 that are paths extending in the axial direction (longitudinal direction of the shell 6). The jacket paths 12 are, for example, 10 to 90 at predetermined intervals in the circumferential direction. The heating medium is enclosed in the inside and communicated with a separately provided jacket path (not shown) extending in the circumferential direction. The axial jacket path 12 and the circumferential jacket path (not shown) absorb heat due to self-heating of the shell 6, and the temperature distribution of the shell 6 is uniform in the axial direction (roll width direction) and the circumferential direction. To play a role. As described above, the induction coil 9 is divided in the roll width direction (not shown), and each divided induction coil 9 is controlled, whereby division control in the roll width direction is possible.

  In addition, as an elastic roll used for a heat | fever calendar, it is preferable to set it as plastics, such as modified urethane type | system | group, epoxy type | system | group, and polyether type | system | group excellent in heat resistance, The hardness is 85-97 in Shore D hardness, Especially 85-85. It is preferably about 94. The nip pressure between the elastic roll and the metal roll is preferably set to about 125 to 350 KN / m. By setting these hardness and nip pressure within the above ranges, it becomes easy to achieve both bulkiness and flatness.

  The method of applying the coating liquid is not particularly limited, and a method of applying by a roll coater (gate roll coater), a blade coater (bill blade coater), a bar coater, a rod coater, an air knife coater, a spray or the like is adopted. Can do. However, the use of a blade coater is preferable in that high-speed coating at 1000 m / min or more is facilitated, and even a high-concentration and high-viscosity coating can be applied efficiently and with high accuracy. The coating liquid preferably has a solid amount of 50% or more of the total solid amount of the coating liquid combined with the pigment and the adhesive.

(Examination by example etc.)
The effects of the present invention were verified by preparing and evaluating examples and comparative examples of the present invention.
All examples and all comparative examples (hereinafter also referred to as all examples) include wire part, press part, (pre) dryer part, coater part, (after) dryer part, calendar part, reel part, winder part. It is manufactured by the papermaking process included in order. Of these, in the calendar part, two rolls and one nip stage are formed, and each of the two metal rolls 1 is provided with an external induction heating apparatus and an internal induction heating apparatus as described with reference to FIGS. A tandem type soft calendar device was used on-machine, and the coated surface of the paper web was passed through so as to face the metal roll. At this time, paper was passed while controlling the temperature distribution in the roll width direction to be as constant as possible by performing division control in the roll width direction using the external induction heating device and the internal induction heating device. In the coater part, coating was performed using a chip type (bevel type) blade coater. The coating amount was 30 g / m ^{2 in} solid amount.

  In all examples, a coating liquid containing a copolymer latex having two glass transition points was applied in the coater part, and then the moisture content of the coated paper was adjusted by drying in the (after) dryer part. . This moisture content was measured before the calendar part. The moisture content was measured with a BM meter.

  In all examples, the pulp composition of the base paper is the same. Specifically, the chemical pulp is 80% by weight, the mechanical pulp is 10% by weight, and the used paper pulp is 10% by weight. 50 parts by weight of Hydrocurve 90 manufactured by Powdered Industries Co., Ltd. was mixed with 100 parts by weight of the solid content of the coating layer. In all examples, the coating layer of each example contains kaolin, phosphate esterified starch, dispersant, water retention agent and water resistance agent in addition to the copolymer latex and pigment having two Tg's. did.

Tables 1 and 2 show the specifications and evaluation results of the examples and comparative examples. Except as noted in each table, the specifications in all examples are the same.

Each item in the table will be described.
The copolymer latex (A) to (G) used in each example was a styrene butadiene latex. The styrene butadiene latex is not particularly limited as long as it is a latex having styrene and butadiene as basic constituent monomers, but in order to obtain sufficient initial adhesiveness, the glass transition point (Tg) is −5 ° C. or lower. It is preferable. The styrene butadiene latex may be a polymer obtained by polymerizing a monomer that can be copolymerized with a styrene monomer and a butadiene monomer. Examples of the monomer copolymerizable with the styrene butadiene latex include methyl methacrylate, acrylonitrile, acrylamide, and hydroxyethyl acrylate.

  About each copolymer latex of these (A)-(G), it was left to dry for 20 hours, heating at 100 degreeC in vacuum, and produced the dry film. This dry film was obtained by a conventional method using a differential scanning calorimeter (DSC) “EXTRE6000” manufactured by Seiko Denshi Kogyo Co., Ltd. As a result, two glass transition points (two of the highest Tg and the lowest Tg described in Tables 1 and 2) were observed for any of (A) to (G).

  The “average particle size” in the table is the average particle size (nm) of each of the copolymer latexes (A) to (G) measured by the method described above. The “styrene content” in the table is the weight percent of styrene in each copolymer latex (solid content). The “latex content” is the weight part of the solid content of the copolymer latex (A) to (G) in 100 parts by weight of the coating layer in each example. The “moisture content” is the moisture content (%) of the coated paper after the (after) dryer part and before the calendering treatment, measured by the method described above. The calender temperature is the surface temperature (° C.) of the metal roll in the soft calender process in the production process of each example. In each example, the 75-degree specular gloss (%) based on JIS P 8142 and the density based on JIS P 8118 were measured.

“Paper waist” in the table was evaluated in terms of the touch, texture, and ease of turning by a total of 20 evaluators of 10 males and 10 females, each of which was evaluated according to the following criteria. A: Excellent, B: Good, B: There is a problem. Then, the most frequent evaluation was taken as the evaluation of the example.
“Blister suitability” in the table indicates that the coated paper of a predetermined size is sufficiently immersed in an oil bath at 150 ° C. to 200 ° C., and the blistering state (blister) generated on the coated paper surface The three-level evaluation was performed as follows. A: No blister, B: Less than 3 blisters, X: 3 or more blisters.
The “RIDRY pick” in the table was printed with IPI ink (No. 8) using an RI test printing machine (manufactured by Meisei Seisakusho), and the peel strength of the printed surface was visually evaluated in the following three stages. A: Good, B: Acceptable, ×: Impossible.

As shown in the table, in all examples, the 75 ° specular gloss was 75% or more, the density was in the range of 0.7 to 1.1 (g / m ³ ), and the glossiness of the white paper was high. It became a bulky coated paper for printing.

It is a partial cross section perspective view which shows schematic structure of the soft calender apparatus which is an example of the thermal calendar in this invention. It is an enlarged view of the vicinity of an external heating device of the soft calendar device of FIG.

Explanation of symbols

1 Metal roll 2 Elastic roll 3 External induction heating device (external heating device)
7 Internal induction heating device (internal heating device)
10 Soft calendar device

Claims (3)

In the coated paper for printing, a coating layer mainly composed of a pigment and an adhesive is provided on at least one surface of the base paper, and the surface of the coating layer is flattened by a thermal calendar. ,
The coating layer has two or more glass transition points, the lowest glass transition point is −5 ° C. or less and the highest glass transition point is 10 ° C. or more, and the average particle diameter is 100 nm to 200 nm, Copolymer latex having a styrene content of 30% by weight or more is contained in an amount of 4 to 15 parts by weight with respect to 100 parts by weight of the coating layer,
A coated paper for printing, having a 75 ° specular gloss of 75% or more and a density of 0.7 to 1.1 g / m ³ .   After the coating layer is applied on the paper substrate, the moisture content of the coated paper is adjusted to 3 to 8% by weight by drying, and then flattened at a temperature of 130 ° C. or higher with an on-machine thermal calendar. The coated paper for printing according to claim 1, wherein the coated paper is printed. The thermal calender is a soft calender composed of a metal roll provided with heating means and an elastic roll, and an internal heating device by electromagnetic induction that can be divided and controlled in the roll width direction is provided inside the metal roll. The outside of the metal roll is provided with an external heating device by electromagnetic induction that can be divided and controlled in the roll width direction and / or a cooling device that can be divided and controlled in the roll width direction.
By flattening the surface of the coating layer at a roll surface temperature of 130 ° C. or higher while dividing and controlling the temperature in the roll width direction with this thermal calender device, the 75 ° specular gloss is 75% or higher and the density is The coated paper for printing according to claim 1, which is adjusted to 0.7 to 1.1 g / m ³ .

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