JP2973704B2 - 2-layer coated paperboard - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to paperboard having two coating layers.

[0002]

2. Description of the Related Art White paperboard is a multi-layer cardboard of 3 to 9 layers, and has been used for various packaging boxes and the like for a long time. Waste paper pulp is used for the middle layer because of its cost and resource saving requirements. The middle layer of waste paper pulp is used without deinking. Virgin pulp or deinked pulp with high whiteness is used for the surface layer. The back layer is the same as the surface layer when whiteness is required on both surfaces, and when not necessary, waste paper pulp having low whiteness is used. In order to conceal the color of the middle layer, the surface layer needs to have concealing properties and a certain thickness. However, when concealment is required only for the surface layer,
Because of the cost problem, pulp having a certain degree of whiteness is also used for the lower layer (the layer immediately below the lower layer), and this layer also serves to mask the color of the middle layer. When a more beautiful appearance is required, a paint using a pigment having high whiteness is applied as in the case of a general coated paper for printing. Opacity is also required for pigments to completely hide the color inside the paperboard.

As described above, opacity is often required for a coating layer of paperboard. In such a case, titanium oxide has been conventionally used as a pigment of a paint. Titanium oxide has been widely used because it is the most opaque pigment among pigments. However, because of its high price, pigments that replace it have been developed. Calcined kaolin has been used as a pigment having an opacity similar to or close to that of titanium oxide. The calcined kaolin is obtained by calcining hydrous kaolin at a high temperature of 900 ° C. or more to form a bulky aggregate having a built-in void structure. However, calcined kaolin has a drawback that it is difficult to disperse and that a paint having a high solid content cannot be obtained.

[0004] Therefore, so-called chemically structured kaolin has been developed in which aggregates are formed not by firing but chemically.
In the present specification, chemically structured kaolin is hereinafter simply referred to as structured kaolin. Structured kaolin is also a bulky aggregate having a built-in void structure like calcined kaolin. For structured kaolin, see Paper Pulp Technology Times 199
It is explained on pages 1-9 of the October 2000 issue. In addition, JP-B-59-15944, JP-A-63-500
No. 723, Japanese Unexamined Patent Publication No. 62-1757, Japanese Unexamined Patent Publication No. 62-26
No. 7371 discloses a manufacturing method thereof.

[0005]

However, structured kaolin can replace titanium oxide in terms of simple opacity. However, there is a drawback that whiteness is reduced when an overcoat such as a press coat is applied to a coated paperboard. is there. There is also a disadvantage that surface strength is reduced. The present invention uses structured kaolin to reduce the amount of titanium oxide used, to prevent the whiteness from lowering even when a resin is applied on the coating layer, and to maintain the surface strength. As an issue.

[0006]

As means for solving the above-mentioned problems, the present invention has the following constitution. That is, the present invention relates to a paperboard having two coating layers containing a pigment and a binder as main components, wherein structured paper is contained as a pigment of an undercoat layer of the coating layer, and oxidized as a pigment of an overcoat layer. A two-layer coated paperboard characterized by containing titanium.

The pigment used for the undercoat layer in the present invention contains structured kaolin.
It is necessary to contain 0% by weight or more. If it is less than 30% by weight, the desired opacity cannot be obtained. When other pigments are used in combination, the total amount of the other pigments is 70% by weight or less, and examples thereof include hydrous kaolin (not calcined or structured), talc, heavy calcium carbonate, light calcium carbonate, carbonated carbonate. Magnesium, aluminum hydroxide,
Examples include alumina, silica, zinc oxide, acid clay, activated clay, diatomaceous earth, calcium sulfate, barium sulfate, and satin white.

[0008] The structured kaolin used in the present invention includes urea • kaline described in JP-B-59-15944.
Structural aggregates of clay stabilized by formalin polymer, aggregates obtained by precipitating hydrated metal salt silicate particles described in JP-B-63-500723 on clay, JP-A-62-1775 Kaolin aggregated with the described zirconium compounds
No. 371, for example, hydrated kaolin aggregated with a polyelectrolyte flocculant.

Particularly preferred as another pigment is spindle calcium carbonate. Spindle-shaped calcium carbonate is a precipitated calcium carbonate produced by blowing a gas containing carbon dioxide into an aqueous suspension of calcium hydroxide, and has an average major axis of 1 to 5 μm and a ratio of major axis / minor axis of 3 to 5. Spindle-shaped calcium carbonate. Many methods for producing such spindle-shaped calcium carbonate are known, for example, Japanese Patent Publication No. 54-2.
No. 8399, JP-B-58-43331, and JP-A-3-1
No. 83618 and the like.

The pigment used in the overcoat layer in the present invention contains titanium oxide. Titanium oxide is required in an amount of at least 10 parts by weight of all the pigments, and less than 10 parts by weight makes it difficult to obtain the desired opacity. Pigments used with titanium oxide include hydrous kaolin (unfired or unstructured), talc, heavy calcium carbonate, light calcium carbonate, magnesium carbonate, aluminum hydroxide, alumina, silica, zinc oxide, acid clay, Activated clay, diatomaceous earth,
Examples include calcium sulfate, barium sulfate, and satin white.

In the present invention, the binder used in the undercoat layer and the overcoat layer together with the pigment is 10 to 20 parts by weight, based on 100 parts by weight of the pigment, in terms of solid content. As the binder, a water-soluble polymer such as casein, starch, or polyvinyl alcohol, or a water-dispersible polymer obtained by homopolymerizing or copolymerizing a vinyl monomer such as acrylate, vinyl acetate, styrene, or butadiene is used. . The water-soluble polymer substance and the water-dispersible polymer substance are often used in combination.

The total solid content of the binder and the pigment in the coating material can be appropriately selected from 30 to 80% by weight, but differs depending on the application, the type of the coater, and the like. In the paint of the present invention, a dispersant, a viscosity adjuster, a water retention agent, an antifoaming agent, a waterproofing agent, a dye, a pH adjuster, and the like can be used as necessary.

The reason why the coating layer is composed of two layers in the present invention is that if the structured kaolin is exposed on the surface, the whiteness at the time of press coating and the surface strength are reduced as described above. This is because it is most preferable to use the structured kaolin for the undercoat layer in order to sufficiently exhibit the characteristics of the structured kaolin and to cover the defects. In the present invention,
The coating amount of the undercoat layer is 7 g / m ^{2 to} 10 g /
a m ^2. The coating amount of the overcoat layer is 7 g /
a m ² ~12g / m ^2.

[0014]

According to the constitution of the present invention, even if a resin is applied on the coating layer, the whiteness does not decrease. The reason is considered as follows. Structured kaolin has a bulky structure containing voids inside, and therefore, opacity can be improved, but on the other hand, if voids are filled with resin or the like, opacity is estimated to decrease. . Therefore, it is considered that by using structured kaolin for the undercoat layer and titanium oxide for the overcoat layer, the opacity of the structured kaolin is utilized and the above-mentioned disadvantage is solved.

In the undercoat paint of the present invention, spindle-shaped calcium carbonate is particularly preferable as the pigment in combination with the structured kaolin because, when the pigment concentration is increased, the flowability of the structured kaolin alone deteriorates. This is because mixing the calcium carbonate improves fluidity. The reason is that structured kaolin is bulky, and when it is made to have a high concentration, the particles come into contact with each other and become hard to move, increasing the viscosity.
Spindle-shaped calcium carbonate has a shape that easily rolls in the flowing direction when it flows between structured kaolin particles and when a paint is sheared and flows, and acts like a roller on structured kaolin that is difficult to move. It is presumed to improve the liquidity.

[0016]

The present invention will be specifically described below with reference to examples. Example 1 A paperboard paint was prepared with the following configuration. Undercoat paint Pigment 40 parts by weight of structured kaolin (Ixilon 90 manufactured by Engelhard) 20 parts by weight of spindle calcium carbonate (Tamapearl 121 manufactured by Okutama Industries) 40 parts by weight of heavy calcium carbonate (Ace 25 manufactured by Dowa Mining) Dispersant Polyacrylic acid 0.6 parts by weight of sodium 13 parts by weight of modified styrene / butadiene latex 3 parts by weight of casein The above components were mixed and dispersed by a known coating preparation method so that the total solid concentration was 56%.

Topcoat paint Pigment Special grade kaolin (hydrated type) (Engelhard Co., Ultra White 90) 50 parts by weight Square calcium carbonate (Shiroishi Kogyo Brilliant 15) 36.6 parts by weight Titanium oxide (Tokam Products TCA- 333) 13.4 parts by weight Dispersant Sodium polyacrylate 0.5 part by weight Modified styrene / butadiene latex 15 parts by weight Casein 7 parts by weight A known coating preparation method is used so that the above components have a total solid concentration of 37%. Mixing and dispersion were performed.

The above undercoat paint is applied to a white paperboard having a basis weight of 310 g / m ² at 9 g / m ^{2 in} terms of dry solid content and dried, and then the above top coat paint is applied at 10 g / m ^{2 in} terms of dry solid content. Dried. The whiteness of the obtained coated paperboard was 80%. Press coating was performed on the two-layer coated paperboard thus obtained,
The whiteness was 76%.

(Comparative Example 1) Structured kaolin (Ixylon 90) in Example 1 in place of titanium oxide in the overcoat layer
A coated paperboard was obtained in the same manner as in Example 1 except that was used. The whiteness was 79%. The whiteness after performing a frescoat on it was 74%. The surface strength before press coating was reduced by about 25% as compared with that of Example 1.

[0020]

According to the present invention, even when the amount of expensive titanium oxide is reduced, high opacity of the coated layer is maintained, and as a result, coated white paperboard having high whiteness can be obtained at low cost. If we simply replace titanium oxide with structured kaolin,
Although there is a problem of a decrease in surface strength and a problem of a decrease in whiteness when press-coated on the coating layer, the configuration according to the present invention eliminates such problems.

Claims (1)

(57) [Claims] 1. A paperboard having two coating layers containing a pigment and a binder as main components, wherein the coating layer contains structured kaolin as a pigment of an undercoat layer and oxidized as a pigment of an overcoat layer. A two-layer coated paperboard comprising titanium.