JP2000314095A - Coating liner - Google Patents

Abstract

(57) [Problem] To provide a coating liner which is free from mottling during flexographic printing and has excellent white paper gloss and print gloss. The coating liner has a coating layer mainly composed of a pigment and an adhesive provided on one surface of a base paper, and in particular, has a pressure-type smoothness as a smoothness characteristic of the coating layer surface of the coating liner. The degree of smoothness A when measured under a pressure condition of 5 kgf / cm ² using a degree meter is 3.0 μm or less, and the pressure condition 20
A coating liner that satisfies the following equation (1), where B is the smoothness measured at kgf / cm ² . 0.3 ≦ B / A ≦ 0.8 (1)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated liner, and more particularly, to a coated liner which is free from mottling in flexographic printing and has excellent white paper gloss and printed gloss.

[0002]

2. Description of the Related Art In general, a liner is used as a cardboard box in combination with a core base paper. At that time, the exterior liner is usually subjected to flexographic printing with one or two colors of printing ink. By the way, in recent years, there has been a tendency for cosmetics to be required for printing on corrugated cardboard boxes. Plays one wing. And for printing on white liners that require aesthetics,
Flexographic printing, offset printing, and gravure printing of four or more colors are available. Among them, flexographic printing is currently the most mainstream printing method. In particular, in flexographic printing of four or more colors, the water-based ink needs to be rapidly absorbed, so that there must be sufficient voids on the liner surface to absorb the ink. If the ink absorptivity is low, mottling occurs, which causes the printing effect to be impaired. In addition, in the case of flexographic printing, the pressure applied during printing is extremely low compared to offset printing and gravure printing, and the use of water-based inks with low viscosity compared to offset inks allows the effects of cosmetic printing to be sufficiently improved. To achieve this, smoothness is more important than the printing strength of the liner surface.

In general, liners, including white liners, have low surface smoothness, and when viewed from the viewpoint of flexographic printing suitability, mottling is likely to occur, especially in highlights, where mottling is severe and print finish is significantly reduced. The fact is that they are doing it. Therefore, when performing flexographic printing on a liner, the number of halftone dots is increased or the depth of the plate is increased. Therefore, high-definition multicolor flexographic printing in the state of the liner as described above is impossible, and the advantages of flexographic printing are not fully utilized. Therefore, when high-definition flexographic printing is required, a coating composition containing a pigment is applied, and a smoothing treatment by a calender is usually performed. However, in this case, in order to eliminate or reduce mottling, it is desirable that the coating layer be as porous as possible and have good air permeability. On the other hand, the more porous, the less mottling, but there is a drawback that gloss, especially print gloss, is reduced and the printed image becomes less vivid.

Heretofore, as a measure to improve the above-mentioned difficulty, use of fine-particle clay, increase of the number of coating layers,
Alternatively, a cationic substance has been added. Further, a coating liner having excellent optical properties and printability by applying a coating composition for a liner containing a pigment component composed of a specific inorganic pigment and an organic pigment is disclosed in Japanese Patent Publication No.
No. 5,160,675. However, none of these measures has been effective in improving both the problems of reducing mottling and improving blank gloss and print gloss in multicolor flexographic printing in a well-balanced manner.

[0005]

SUMMARY OF THE INVENTION As described above, the present invention is to solve the problems of the conventional coating liner and to obtain a coating liner stably having excellent multicolor flexographic printing aptitude. is there. That is, an object of the present invention is to provide a coating liner having high white paper gloss and printing gloss, and in particular, free from mottling and excellent in suitability for multicolor and high-definition flexographic printing.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a coating liner having a coating layer mainly composed of a pigment and an adhesive provided on one side of a base paper. Use a pressure type smoothness meter as the degree characteristic, pressurization condition 5 kg
When the smoothness A measured at f / cm ² is 3.0 μm or less and the smoothness measured at 20 kgf / cm ² under pressurized conditions is B, the following formula (1) must be satisfied. It is a coating liner characterized by the following. 0.3 ≦ B / A ≦ 0.8 (1) The present invention includes the following aspects. That is, a coating type liner was used under a pressing condition of 20 k using a pressing type smoothness meter.
The coating liner according to the above, wherein the smoothness B measured at gf / cm ² is 1.5 μm or less, and the coating liner has an air permeability of 3000 seconds or less measured by an Oken-type air permeability meter. The coating liner according to the above, wherein further,
When the coated liner is passed through a soft calender consisting of an elastic roll and a metal roll to finish the paper, the elastic roll has a Shore D hardness of 80 ° or more, and the finishing is performed with a paper passing nip number of two times or less. And a coated liner.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, ordinary coated liners have drawbacks in terms of suitability for flexographic printing, especially for multicolor flexographic printing. More specifically, mottling is likely to occur in multicolor printing, and the printing effect with excellent aesthetics is difficult to obtain because of low smoothness. The present invention relates to a coating liner which has high white paper gloss and print gloss, is free from mottling, has excellent suitability for multicolor and high-definition flexographic printing, and has excellent cosmetic properties.

In general, when the coating layer is bulky and porous, the occurrence of mottling is reduced, but on the other hand, the resin components and the like that contribute to the gloss of the printing ink easily penetrate into the coating layer, so that the gloss is reduced. In particular, print gloss tends to decrease. Therefore, it is usually difficult to make the coating layer bulky to reduce mottling while increasing the gloss of the printed surface. Therefore, the present inventors have intensively studied and studied to solve this difficulty. As a result, the present invention relates to a coating liner provided with a coating layer containing a pigment component, and in particular, as a smoothness characteristic on a surface of the coating layer by a pressing type smoothness meter, the pressing condition is 5 kgf / cm. ² , when A is 3.0 μm or less and B is the smoothness when the pressing condition is 20 kgf / cm ² , 0.3 ≦ B / A ≦ 0. It has been found that the effect desired by the present invention can be obtained by forming a coating liner satisfying the formula (8). More preferably, the pressure condition of the coating liner is 20 kgf / cm ²
The value of the coating liner is 1.5 μm or less, or the air permeability of the coating liner measured by an Oken-type air permeability meter is 3000 seconds or less, and the coating liner is made of an elastic roll and a metal roll. When finishing by passing the paper through a calender, it is preferable to use the coated liner described above, wherein the elastic roll has a Shore D hardness of 80 ° or more and pressure finishing at a paper passing nip number of 2 or less.

[0009] As described above, it is not always clear why satisfying the smoothness characteristics of the coating layer simultaneously improves the elimination of mottling and the improvement of gloss in multicolor flexographic printing with a coating liner in a well-balanced manner. Is inferred as follows. The required properties required for a coated liner for multi-color, high-definition flexographic printing are as follows:
Voids (porosity) for quick absorption of aqueous ink
In addition, in order to transfer the ink efficiently even at a printing pressure as low as flexographic printing, it is necessary that the surface of the coating layer has high smoothness even under a low pressure. From the above viewpoints, as a result of various studies, the index of the porosity of the coating layer was found from the smoothness characteristics of a pressurized smoothness meter. That is, a pressure type smoothness value when the pressure condition 5 kgf / cm ^2, and by differences in pressure type smoothness value in the pressurized condition 5 kgf / cm ² and 20 kgf / cm ^2, the degree of porosity is very correlation I found out that I could grasp it well. In other words, the larger the difference between the pressurized smoothness under low pressure and under high pressure, the more the coating layer has cushioning properties, so-called crushing margin, and is more porous. In addition, the surface smoothness under a low pressure, the pressurizing condition is 5kgf / cm ²
At the time of the pressure type smoothness value.

As described above, according to the present invention, when the pressing condition of the pressing type smoothness is 5 kgf / cm ² , the smoothness A is 3.0 μm or less, and the pressing condition is 20 kgf / c.
Assuming that the smoothness at m ² is B, 0.3 ≦ B /
A coating liner that satisfies the expression A ≦ 0.8,
Further, preferably, the coating liner has a smoothness B of 1.5 μm or less when the coating liner is measured under a pressure condition of 20 kgf / cm ² using a pressure type smoothness meter, and the coating liner Is a coated liner having an air permeability of 3000 seconds or less as measured by an Oken-type air permeability meter. Furthermore, when finishing the coated liner by passing the paper through a soft calender consisting of an elastic roll and a metal roll, the elastic roll has a Shore D hardness of 80 ° or more and a pressure finish at a paper passing nip number of 2 times or less. This is the coating liner to be performed.

If the smoothness A exceeds 3.0 μm when the pressing condition is 5 kgf / cm ² , satisfactory smoothness of the coating layer surface cannot be obtained, and the present invention is desired. An excellent printing effect in flexographic printing cannot be obtained. In addition, the value of the B / A equation exceeds 0.8, that is, the smoothness value under a pressure condition of 5 kgf / cm ² is 20 kgf / cm ^2.
When the smoothness value approaches / cm ² , the cushioning property of the coating layer is low, and a sufficient space for absorbing the ink cannot be obtained, and mottling tends to occur frequently. In addition, since the phenomenon that the measured smoothness at the time of low pressure is higher than that at the time of high pressure is usually impossible, it may be considered that the value of B / A does not exceed 1.0. On the other hand, when the value of B / A is less than 0.3, that is, the value of the smoothness under the pressure condition of 5 kgf / cm ² is large, and the difference between the value of the smoothness at 20 kgf / cm ² and Is large, it generally indicates that the smoothness of the surface of the coating layer under low pressure is low, and the printing ink is not efficiently transferred at the time of flexographic printing, causing white spots and the like. Also, when B exceeds 1.5 μm, the smoothness is inferior, and there is a possibility that satisfactory multicolor flexographic printing suitability may not be obtained, and further, there is a concern that print gloss and print density may be reduced. .

[0012] Here, the mottling is not limited to flexographic printing, but refers to a phenomenon in which fine ink density unevenness, gloss unevenness, etc. are generated on a printing surface due to defective deposition of a plurality of inks, and the so-called printing surface becomes spotted. . When this mottling phenomenon occurs, the printed pattern becomes non-uniform, the aesthetics of the printed matter are impaired, and this is a serious defect especially for wrapping paper for the purpose of advertising the product. Regardless of the printing method, Western paper, or paperboard, the major cause of mottling is due to uneven ink absorption of the paper.However, in the case of uncoated paper, there is a close relationship with the formation of the base paper. is there. on the other hand,
In the case of coated paper, what is directly related to mottling is the uniformity of the coated layer. This is due to uneven penetration of the adhesive in the paint for forming the coated layer into the base paper layer, There is a close relationship with the thickness unevenness, density unevenness, etc. of the coating layer caused by the unevenness. Of course, the influence of the formation of the base paper is also large, and if the unevenness is severe, it is affected similarly to the case of uncoated paper.

In general, the porosity of a coating layer can also be represented by air permeability. In this case, according to the study results of the present inventors, it is desirable that the air permeability of the coating liner be 3000 seconds or less using an Oken type air permeability meter. By the way,
If the time exceeds 3000 seconds, the amount of voids in the coating layer is small and the printing ink cannot be sufficiently absorbed, and as a result, mottling may occur. The lower limit of the Oken-type air permeability is not particularly limited, but is generally 100 to 150 in the state of ordinary base paper (before coating with a paint).
200 seconds in a state where only an aqueous solution (clear liquid) of polyvinyl alcohol, polyacrylamide, or the like is applied for about 2 seconds.
Since it is about 500 seconds, it is estimated that the lower limit is about 100 seconds (it does not become less than 100 seconds).

The method for obtaining the smoothness and air permeability of the coating layer as described above is not particularly limited, but includes, for example, the following methods. That is, as a pigment which is a component of the coating layer, for example, calcined clay,
Structured kaolin, organic pigments, and the like are relatively easy to form a bulky coating layer as compared with other inorganic pigments and the like. (Hereinafter, simply referred to as paint) increases the base paper covering property of the base paper surface, and the smoothing (pressing) treatment increases the coating layer surface having high smoothness and the bulky coating. A layer is easily obtained. Furthermore, after providing the coating layer on the base paper, by performing a slight pressure treatment using a device such as a calender, particularly a soft calender, it is excellent in smoothness without strongly tightening the coating layer. This is a preferred embodiment because a porous coating layer can be obtained.

On the other hand, organic pigments, structured kaolin,
In particular, when an organic pigment is blended, a higher effect can be obtained because the organic pigment which is thermoplastic is easily melted and plasticized. In addition, by performing a smoothing treatment using a calender or the like, the glossiness of white paper is improved, that is, the base of print gloss is increased, and further, the organic pigment absorbs moisture in the ink and swells. Of the air gap decreases,
Excessive penetration of the vehicle involved in the ink gloss is suppressed, so that the print gloss is enhanced. For the reasons mentioned above,
It is considered that a coating liner free of mottling and having high gloss on white paper and a printed surface and excellent in suitability for multicolor flexographic printing can be obtained.

The coating amount of the paint is desirably applied to one side of the base paper at a dry weight of 3 to 12 g / m ² .
Incidentally, in the case of less than 3 g / m ^2, poor flexographic printability in absorption and smoothness of surface of the ink, while when it exceeds 12 g / m ^2, coated in such case of the box put borders at box making There is a fear of causing layer cracking. Also, apply paint to the base paper,
After the drying, if the elastic roll is finished with a soft calender having a Shore D hardness of 80 ° or more as measured according to JIS Z2246, good multicolor flexographic printing suitability can be obtained more effectively. By the way, 80 °
In a soft calender using an elastic roll of less than
There is a possibility that the elastic roll is too soft and high smoothness cannot be obtained.

Although some effects can be obtained by using a machine calender or a super calender instead of a soft calender, a soft calender can perform a hot roll treatment at a high temperature. A state in which the gap is maintained without crushing the coating layer more than necessary by performing a pressure treatment with a lower pressing force as compared with a render (number of multi-stage nips) and the like, specifically, a paper passing nip number of two or less. Is preferred because only the surface can be efficiently smoothed.

If necessary, pigments other than the above-mentioned specific pigments such as ordinary clay, heavy calcium carbonate,
One or more publicly known pigments used in the general coated paper production field, such as light calcium carbonate, titanium dioxide, aluminum hydroxide, silica, satin white, and talc, can be used as appropriate.

Next, the adhesive which is a main component other than the pigment is not particularly limited, and an adhesive used in the production field of general coated paper can be appropriately used. Specifically, for example, starch (various modified starches such as phosphate esterified starch, cationized starch, enzyme-modified starch), polyvinyl alcohol, casein, styrene-butadiene-based copolymer latex, vinyl acetate-based copolymer latex And synthetic resin latex such as acrylic copolymer latex and urethane copolymer latex. These adhesives may be used alone or in combination of two or more. Above all, when an alkali is added, the use of an alkali-swellable styrene-butadiene-based copolymer latex and / or an acrylic-based copolymer latex in which latex particles swell reduces the adhesiveness of scum and further reduces the Tg to -10 ° C. Below, preferably -50 ℃ ~ -15 ℃
Styrene-butadiene copolymer latex and / or
Alternatively, when an acrylic copolymer latex is used, mottling in flexographic printing tends to be able to be reduced very effectively, so that it is more desirable from the viewpoint of eliminating mottling in flexographic printing.

In addition, if necessary, a dispersing agent, a pH adjusting agent such as caustic soda or ammonia water, a defoaming agent, a preservative, a fluorescent dye, a release agent, a dye, a water-proofing agent, a flow modifier, etc. And a coloring pigment or the like can be appropriately added.

The coating apparatus for coating the base paper with the coating material is not particularly limited, and examples thereof include an air knife coater, a blade coater, a rod coater, a bar coater, a roll coater such as a gate roll coater, and a size press. A bill blade coater, a bellbapa coater and the like are appropriately used. Further, before applying the coating material to the base paper, the base paper may be subjected to a smoothing treatment in advance using a machine calender, a soft calender, a Yankee dryer or the like.

The pulp constituting the base paper is not particularly limited, and for example, one kind of chemical pulp, mechanical pulp, waste paper pulp, etc., or a mixture of two or more kinds is used as appropriate. Further, it is also possible to use a base paper having two or more pulp layers to form a multilayer structure. In addition, as necessary, the base paper has a sizing agent, a paper strength agent, a drainage agent,
Auxiliaries such as fillers, colorants, and optical brighteners can also be added as appropriate.

[0023]

The present invention will be specifically described below with reference to examples. Of course, the present invention is not limited to these examples. Unless otherwise specified, parts and% in the examples indicate "parts by weight" and "% by weight", respectively.

Example 1 Dispersant in water (trade name: Aron T-40 / Toa Gosei Co., Ltd.)
Was added with 0.2 part of an active ingredient, 0.1 part of sodium hydroxide as an active ingredient, and 0.1 part of an antifoaming agent (trade name: Nopco 8034L / San Nopco), and further, while stirring with a Coreless stirrer, As a pigment, calcined clay (trade name: Alphatex / ECC International) is 35
Parts, structured kaolin (trade name: Rotoprint / Huba), 60 parts, and hollow organic pigment (trade name:
(Nipol MH-5055 / Zeon Corporation) in an amount of 5 parts each, and the mixture was stirred and dispersed for 30 minutes to prepare a pigment slurry. Then, a copolymer latex (trade name: L-1117: non-alkali swellable styrene-butadiene copolymer latex, T)
g = -2 ° C./Asahi Kasei Co., Ltd.) and 15 parts in terms of solid content, and water were added to prepare a paint having a finished concentration of 45%.

The surface layer is composed of basis weight 50 g / m ² of bleached chemical pulp, a middle core layer and the back layer is made of waste paper (reproduced) pulp, on the surface of the basis weight 170 g / m ² base paper liner, wherein Was dried using a Meyer bar so that the coating amount after drying was 10 g / m ^2, and the coating was dried. The coated liner thus obtained was conditioned for 6 hours in accordance with the conditions of JIS P8111, and then the surface temperature of the chilled roll was adjusted to 15
At 0 ° C., a soft calender having a Shore D hardness of 85 ° of the elastic roll measured according to JISZ2246,
Linear pressure of 110kg / so that the coated surface hits the chilled roll
cm and a paper passing nip number of 1 (one pass) to obtain a coated liner.

Example 2 In Example 1, a hollow organic pigment (Nipol MH-5055 / supra) was used as a pigment in preparing a coating material.
A coating liner was obtained in the same manner as in Example 1, except that 5 parts were changed to 5 parts of titanium dioxide (trade name: Kronos KA-10 / Titanium Industry Co., Ltd.).

Example 3 In Example 1, in the preparation of the paint, 30 parts of delaminated clay (trade name: Newclay / Engelhard Co.) was used as a pigment, and structured kaolin (Rotprint /
60 parts) and a hollow organic pigment (Nip)
olMH-5055 / supra) except for changing to 10 parts,
A coating liner was obtained in the same manner as in Example 1.

Example 4 In Example 1, in preparing a coating material, 15 parts of a copolymer latex (L-1117 / supra) was used as an adhesive in the form of an alkali-swellable styrene-butadiene copolymer latex (trade name: SN- 134C ... Tg = -37 ° C / Sumitomo A &
(Company L) A coating liner was obtained in the same manner as in Example 1 except that the amount was changed to 15 parts.

Embodiment 5 In Embodiment 4, when performing the soft calendering process,
A coated liner was obtained in the same manner as in Example 4, except that the Shore D hardness of the elastic roll was changed from 85 ° to 82 °.

Example 6 In Example 4, the coating amount after drying of the paint was 10 g / m.
^A coating liner was obtained in the same manner as in Example 4, except that the amount was changed from ² to 5 g / m ² .

Embodiment 7 In Embodiment 4, when performing the soft calender processing,
A coating liner was obtained in the same manner as in Example 4, except that the nip number was set to 2 (two passes).

Comparative Example 1 In Example 1, in preparing the coating material, kaolin (trade name: Amazon SD / CADAM) was used as a pigment for 60 hours.
Part, light calcium carbonate (trade name: TP-123-CS
/ Okutama Industry Co., Ltd.) and 10 parts of titanium dioxide (trade name: Kronos KA-10 / Titanium Industry Co., Ltd.), except that the coating liner was obtained in the same manner as in Example 1.

Comparative Example 2 In Example 2, the amount of the copolymer latex (L-1117 / supra) added as an adhesive was 15 when preparing the paint.
Part was increased to 18 parts, and when finishing, the soft calendering process was changed to the paper passing process with a super calender under the conditions of a metal roll surface temperature: 80 ° C, a linear pressure: 350 kg / cm, and 6 nips. Except having changed, it carried out similarly to Example 2, and obtained the coating liner.

Comparative Example 3 In Example 4, when finishing the soft calender,
A coating liner was obtained in the same manner as in Example 4, except that the Shore D hardness of the elastic roll was changed from 85 ° to 78 °.

Comparative Example 4 In Example 4, the coating amount after drying of the paint was 10 g / m
^A coating liner was obtained in the same manner as in Example 4, except that the amount was changed from ² to 2 g / m ² .

Comparative Example 5 A coated liner was obtained in the same manner as in Example 4, except that the paper was passed three times (3 nips) when the paper was passed through the soft calender.

After the coated liner obtained as described above was conditioned for 6 hours under the conditions in accordance with JIS P8111, the mottling was evaluated, and the glossiness of blank paper, pressurized smoothness, and Oken type air permeability were evaluated. did. Table 1 shows the coating composition of the coating layer and the paper passing conditions of the soft calender in each Example and Comparative Example, and Table 2 shows the evaluation results. In addition, each evaluation test was implemented according to the following.

(Motoring): A water-based ink diluted to an appropriate concentration was applied to the coating surface of the coating liner using a Mayer bar, and the state of ink absorption was visually evaluated. ◎: Ink absorption is uniform and there is no uneven absorption.: Absorption unevenness is hardly recognized. △: Slight absorption unevenness. X: Absorption unevenness is severe.

(Blank gloss): The mirror gloss of the coated surface is determined by JI
It was measured according to SP8142.

(Print Gloss): The specular gloss of the solid printed portion was measured at an incident angle of 60 ° according to JIS Z8741.

(Pressure type smoothness): Pressure type smoothness meter (measuring device: Parker Print Surf / Messmer Bu)
pressure is 5 kgf / cm ²
And the smoothness at 20 kgf / cm ² were measured, and were designated as A and B, respectively.

(Oken type air permeability): The air permeability was measured by an Oken type air permeability meter (Asahi Seiko Co., Ltd.).

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

As is evident from Table 2, the coated liner according to the present invention is a coated liner having high white paper gloss and high print gloss, no mottling, and excellent in suitability for multicolor and high-definition flexographic printing. there were.

Claims (4)

[Claims] 1. A coating type liner having a coating layer mainly composed of a pigment and an adhesive provided on one side of a base paper, wherein a pressure type smoothness meter is used as a coating layer surface of the coating liner. And a smoothness A of 3.0 μm or less when measured under a pressurization condition of 5 kgf / cm ² and a pressurization condition of 20 kgf / cm ^2.
A coating liner characterized by satisfying the following expression (1), where B is the smoothness measured at f / cm ² . 0.3 ≦ B / A ≦ 0.8 (1) 2. The coated liner according to claim 1, wherein the coated liner has a smoothness B of 1.5 μm or less when measured under a pressing condition of 20 kgf / cm ² using a pressurized smoothness meter. . 3. The coating liner according to claim 1, wherein the coating liner has an air permeability measured by an Oken-type air permeability meter of 3000 seconds or less. 4. When the coated liner is passed through a soft calender consisting of an elastic roll and a metal roll to finish the paper, the elastic roll has a Shore D hardness of 80 ° or more and a paper passing nip number of 2 times or less. The coating liner according to any one of claims 1 to 3, which performs finishing.