JPH04370299A - Highly smooth delustered coated paper - Google Patents

Abstract

PURPOSE:To provide the title coated paper loaded with a coating layer such as of a pigment, having specific physical properties of its surface after smoothing treatment, excellent in smoothness, ink acceptability and printability despite of the blank paper gloss, thus useful for gravure printing etc. CONSTITUTION:The objective coated paper can be obtained by providing a base paper such as tissue paper with coating layers consisting of 5-20g/m<2> per one surface of a coating agent comprising (1) 100 pts.wt. of a pigment such as clay and (2) 3-30 pts.wt. of an adhesive such as PVA. For the present coated paper, the surface after smoothing treatment has the following characteristics: (A) Oken-type smoothness: >=500; (B) blank paper gloss: >=30%; and (C) ratio Oken-type smoothness/blank paper whiteness: >75. For said pigment, it is preferable that the volume distribution mean particle size be 2.5-30 micron and the coefficient of variation for the particle size <=0.6.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to matte coated paper, and in particular, it is a matte coated paper that has low gloss, high smoothness, excellent ink receptivity, and good printability. It concerns matte coated paper.

0002

[Prior Art] Matte coated paper gives printed matter an elegant and calm feel compared to coated paper with high white gloss.
Also, because there is less light reflection, printed characters are easier to read. For this reason, they are used in a wide range of applications, from monochrome printed matter such as text paper to multicolored printed matter such as posters, catalogs, and magazine covers.

However, conventional matte coated paper uses a coating containing main pigments such as heavy calcium carbonate and agglomerated pigments, which have larger particle sizes than normal coated paper, in order to keep the white paper gloss low. After the composition is coated on a base paper, it is dried and then subjected to a very light treatment such as a supercalender, or is produced without any treatment. For this reason, the surface of conventional matte coated paper has extremely low smoothness and poor printability.Conversely, when processing to increase smoothness is performed to improve printability, the paper becomes blank at the same time. There was a drawback that the gloss level was high.

On the other hand, gravure printing, which is currently widely used, has good reproducibility of photographs, paintings, etc. and forms a beautiful printed surface, but if the surface of the paper on which it is printed is not smooth, it may cause miss dots or halftone dots. Poor reproduction is likely to occur, which significantly reduces the printing effect.Also, even in offset printing, if the ink receptivity is poor due to the low smoothness of the surface, the gloss of the ink will become uneven in the solid printed area of multicolor printing. This results in extremely poor quality printing. Therefore, conventional matte coated paper has a drawback in that the paper surface has low smoothness and poor ink receptivity, so that high-quality printed matter cannot be obtained by gravure printing or offset printing.

[0005] In order to solve such problems, Japanese Patent Application Laid-Open No. 199897 and Japanese Patent Publication No. 3-
No. 69693 discloses matte coated papers coated with a coating composition containing a specific heavy calcium carbonate, but these matte coated papers also improve smoothness while keeping white paper gloss low. It's still not enough in terms of improvement.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a matte coated paper that has a low white paper gloss level, a high smoothness, and good printability. .

[0007]

[Means for Solving the Problems] As a result of conducting research to solve the above problems, the inventors of the present invention have found that by using a pigment having a specific particle size and coefficient of variation, white paper gloss can be reduced. The present invention has been completed based on the discovery that a matte coated paper with high smoothness can be obtained. The present invention is a coated paper in which a coating layer mainly composed of pigment and adhesive is provided on a base paper, and the surface of the coated paper after smoothing treatment is as follows (a).
) to (c); (a) Oken type smoothness is 500 seconds or more; (b) white paper gloss is 30% or more; (c) ) Oken type smoothness/white paper gloss >75.

More specifically, the present invention provides a matte coated paper in which a coating layer mainly composed of pigment and adhesive is provided on a base paper, and the volume distribution of the pigment constituting the coating layer is A coated paper having an average particle size of 2.5 to 30 microns and a coefficient of variation of pigment particle size of 0.6 or less, and further comprising (a)
White paper glossiness is 30% or less, (b) Oken method smoothness is 500 seconds or more, (c) Oken method smoothness/white paper glossiness>7
The present invention provides a matte coated paper characterized in that:

The term "volume distribution average particle size of pigment" as used herein refers to the sum of the volumes of individual pigment particles divided by the total number of particles. The volume distribution average particle size (MV) obtained by measurement using a truck particle size analyzer (Nikkiso Co., Ltd.) is used. The volume distribution average particle size of this pigment can be calculated based on the following formula: Volume distribution average particle size (MV) = Σ(Vi × di )/Σ
Vi, where Vi = volume ratio di in each particle size category
=Representative diameter of the particle size in each particle size category In addition, the term "coefficient of variation" in the specification of this application refers to the volume distribution average particle diameter (MV
) divided by the standard deviation (SD) of the volume particle size distribution and can be calculated based on the following formula: Coefficient of variation = MV/SD.

[0010] This coefficient of variation is a coefficient that can remove the influence of the average particle size and compare the variation in particle size; the smaller the value, the more uniform the particle sizes are.
Indicates that there is little variation. In the present invention, the reason why the volume distribution average particle size of the pigment constituting the coating layer is set to 2.5 to 30 microns and the coefficient of variation of the particle size of the pigment is set to 0.6 or less is as follows.

[0011] The inventors investigated and analyzed the paper quality of more than 100 types of commercially available matte coated papers, and found the following relationship between the smoothness of these matte coated papers and the white paper glossiness. I discovered something. S/G≦75 However, S: Oken type smoothness (seconds) G: White paper glossiness (%) Also, most matte coated papers have S/G<30.

This means that in general commercially available matte coated paper, if the white paper gloss is low, the smoothness will be low, and on the other hand, if the white paper gloss is increased, the white paper gloss will be high. In order to solve the above-mentioned problems, the present inventors investigated and researched, paying particular attention to the particle size and distribution of the pigment constituting the coating composition, and found that the volume distribution average particle size is relatively large. 2.
By using a specific pigment with a uniform particle size that has a coefficient of variation of particle size distribution of 0.6 or less, even if the particle size is 5 to 30 microns, it will remain stable even after finishing processes such as super calendering and gloss calendering. It was possible to obtain a matte coated paper for printing, which has a low glossiness, a coated layer with high smoothness, and excellent printability.

[0013] Pigments having such characteristics of large particle size and uniform particle size can be produced relatively easily by classifying conventionally known pigments using various methods and by controlling the production process. Obtainable. Further, the pigment particles may be primary particles or may be structures such as aggregates formed by chemical or physical treatment. This white paper has low gloss,
The effect of increasing smoothness is that by using a pigment with a large particle size, white paper gloss decreases, and on the other hand, by using a pigment with a uniform particle size, the pigment particles are easier to arrange in the coating layer, which increases bulk. This is thought to be due to the fact that a coating layer with large voids is obtained. Furthermore, due to the arrangement of the pigments, even if the particle size increases, the surface smoothness after supercalendering or gloss calendering treatment hardly deteriorates. By the way,
If the particles of the pigment with a variation coefficient of 0.6 or more are irregular, a low white paper gloss may be obtained, but since the constituent particles include coarse particles, sufficient surface smoothness cannot be obtained, and the coating will be difficult to coat. Since the pigment easily fills the voids in the layer and forms a dense coating layer, the glossiness of the white paper tends to increase.

[0014] In order to obtain a matte effect with a white paper gloss level of 30% or less, the average particle size must be 2.5 microns or more, and it is difficult to achieve this objective if the average particle size is 2.5 microns or less. Furthermore, if a pigment with a large particle size of 2.5 microns or more is used, the printability is usually significantly reduced, but as mentioned above, even if the pigment has a uniform particle size with a coefficient of variation of 0.6 or less, The printability will not deteriorate in any way.
On the contrary, printability is improved.

Pigments used in the present invention include clay, talc, kaolin, calcined kaolin, aluminum hydroxide,
Light calcium carbonate, heavy calcium carbonate, titanium oxide, magnesium carbonate, alumina, activated clay, acid clay,
Examples include diatomaceous earth, synthetic silica, zinc oxide, barium sulfate, calcium sulfate, satin white, lake, plastic pigment, and binder pigment, and these can be used alone or in combination of several types.

[0016] As for the adhesive constituting the coating layer of the present invention, any known adhesive can be used without particular limitation.
For example, styrene/butadiene, styrene/acrylic, vinyl acetate/acrylic, ethylene/vinyl acetate,
Various copolymers such as butadiene/methyl methacrylate, vinyl acetate/butyl acrylate, and alkali-sensitive or alkali-insensitive adhesives such as polyvinyl acetate, as well as polyvinyl alcohol, maleic anhydride,
Synthetic adhesives such as styrene copolymers, isobutene/maleic anhydride copolymers, acrylic acid/methacrylate copolymers, oxidized starches, etherified starches, esterified starches, enzyme-modified starches, and flash-dried Cold water-soluble starch, casein, soybean protein, etc. can be appropriately selected and used.

[0017] The ratio of adhesive used is 100% pigment
The solid content is 3 to 50 parts by weight, preferably 5 to 20 parts by weight. In addition, if necessary, a dispersant,
Viscosity modifier, water retention agent, antifoaming agent, water resistance agent, lubricant, dye,
Various auxiliary agents such as pH adjusters and the like can also be blended as appropriate. In preparing the coating composition, various mixers, mixers, kneaders, ball mills, and other mixing agitators can be appropriately selected and used depending on the type of coating composition.

The coating composition for forming the coating layer is prepared by adding 100% of the pigment while mixing with a mixing agitator.
This is carried out by sequentially adding parts by weight, 3 to 30 parts by weight of the adhesive, and, if necessary, additives such as a dispersant. The solid content of the paint is generally selected between 30 and 80% depending on the purpose. The coating layer constituting the matte coated paper of the present invention is coated in a single layer or in multiple layers on both sides or one side of the coated base paper. In this case, the formulation of the coating composition applied to both sides and the coating composition constituting each layer in multilayer coating can be appropriately changed according to a general method. The coating method is not particularly limited, and examples include air knife coaters, roll coaters, bar coaters, rod coaters, bevel or bent blade coaters, and various blades such as bill blades and twin blades. Various known coating devices such as coaters and short dwell coaters can be used as appropriate.

[0019] The coating amount is 3 to 30 g/m2, preferably 5 to 20 g/m2 per side after drying.
It is generally finished using a finishing device such as a super calender or a gloss calender. The reason why the coating amount is specified in this way is that if the coating amount is less than 3g/m2, the coating effect will not be sufficiently obtained, and if the coating amount is less than 30g/m2,
This is because the effect of coating becomes saturated.

[0020] Furthermore, the base paper used in the present invention is not particularly limited, and it is possible to use paper made from various wood pulps and synthetic pulps alone or by mixing them, and it is applicable to everything from thin paper to paperboard. It is.

[0021]

EXAMPLES The present invention will be explained in detail below based on Examples, but the present invention is of course not limited to the scope of these Examples. In addition, “part” and “
%" means "parts by weight" and "% by weight," respectively, unless otherwise specified. A medium-quality coated base paper with a weight of 41 g/m2 was used as the base paper for manufacturing the matte coated paper. Coating liquid preparation pigment
100 parts styrene-butadiene latex 10 parts modified starch

3-part sodium polyacrylate dispersant
0.5 part pH adjuster (sodium hydroxide)
Using 0.1 part of the above ingredients, paint solids content: 5
A coating liquid was prepared to have a coating content of 6 to 68%. Formation of Coating Layer Using a Mayer bar, the coating liquid was applied and dried on one side of the base paper so that the coating amount after drying was 20 g/m2, and the surface was further treated with a super calender to form each layer. A matte coated paper was obtained.

Based on the above method, Examples 1 to 4 and Comparative Examples 1 to 3 were carried out to obtain matte coated papers. The pigments used are as follows. (Example 1) Commercially available heavy calcium carbonate was classified by a centrifugal method as a pigment, and particles having a uniform particle size were used. (Example 2) Light calcium carbonate with very large cubic crystal particles was used as the pigment. (Example 3) An aggregate of light calcium carbonate was used as a pigment. (Example 4) Titanium oxide (rutile type) having an extremely large particle size was used as a pigment. (Comparative Example 1) As a pigment, commercially available heavy calcium carbonate, which was classified and used in Example 1, was used without treatment. (Comparative Example 2) Commercially available heavy calcium carbonate having a large volume distribution average particle diameter was used as a pigment. (Comparative Example 3) Commercially available light calcium carbonate was used as a pigment.

[0023] For each of the matte coated papers produced in Examples and Comparative Examples, the white paper glossiness, Oken type smoothness, and number of missing halftone dots were measured, and the obtained results are shown in Table 1. The air permeability is also listed for reference. [Evaluation Method] The conditions for measurement and evaluation were as follows. (1) White paper glossiness: Angle 7 according to JIS-P8142
Measured at 5 degrees. (2) Smoothness: J. The smoothness was measured according to TAPPI No5 Oken method. The larger the value, the higher the surface smoothness. (3) Air permeability: J. The air permeability was measured according to the TAPPI No. 5 Oken method and was used as an index of voids in the coating layer. The lower the number, the higher the air permeability and the more voids there are. (4) Missed dots: After black printing, the number of defective ink transfers per 6.5 cm 2 in a 20% gradation area was measured using a gravure printing tester from the Printing Bureau of the Ministry of Finance. The ink (Toyo Ink Manufacturing Co., Ltd. OG-91 ink) was adjusted to a viscosity of 15 seconds using a #3 Zahn cup. (5) Halftone dot reproducibility: The halftone dot shape of the sample printed by the above method was visually evaluated.

0024] ◎ Excellent 〇 Good
△ Slightly inferior × inferior

[0025]

[Effect] As is clear from the results in Table 1, by specifying the average particle size of the pigment and making the coefficient of variation of the pigment particle size 0.6 or less, smoothness can be achieved while maintaining low white paper gloss. A matte coated paper for printing with high and excellent printability was obtained.

[0026]

[Table 1]

Claims (2)

[Claims] Claim 1: A coated paper in which a coating layer mainly composed of pigment and adhesive is provided on a base paper, and the surface of the coated paper after smoothing treatment is one of the following (a) to ( Highly smooth matte coated paper characterized by satisfying the conditions c); (a) Oken style smoothness of 500 seconds or more, (b) white paper gloss of 30% or more, and (c) Oken style Smoothness/white paper gloss>75. 2. A matte coated paper in which a coating layer containing a pigment and an adhesive as main components is provided on a base paper, wherein the volume distribution average particle diameter of the pigment constituting the coating layer is 2.5 to 2.5. A matte coated paper having a pigment particle diameter of 30 microns and a variation coefficient of 0.6 or less.