JP2020133034A - Black color paper by multilayer paper making - Google Patents

Abstract

To provide a black color paper by multilayer paper making capable of inhibiting color shading and foil color change while comprising a deep black property.SOLUTION: A black color paper by multilayer paper making comprises: the surface and back layers including a wood pulp as a main component and a black pigment; at least one middle layer provided between the surface and back layers; and an impregnation layer formed on at least one surface of the surface and back layers and impregnated by a coating liquid including a color deepening agent and polyvinyl alcohol. The content of the black pigment in the surface and back layers is 2.5 pts.mass or more but 20.0 pts.mass or less based on 100 pts.mass of absolute dry pulp. The color deepening agent includes silicone as a main component, and the surface electric resistance value measured based on IEC61340 is 1×10Ω/square or more but 1×10Ω/square or less under the atmosphere of 23°C and 50%RH. The solid content of the color deepening agent in the impregnation layer is preferably 0.1 g/mor more but 0.5 g/mor less.SELECTED DRAWING: None

Description

The present invention relates to multi-layer papermaking.

In recent years, black paper has been used for wrapping paper, labels, price tags, etc., which require a high-class feel. Such black paper is required to express a glossy and dark black color, and in the prior art, black paperboard having a black pigment content of 10 parts by mass or more with respect to 100 parts by mass of pulp is disclosed. (Refer to Japanese Patent Application Laid-Open No. 2015-148205).

Further, in order to give a high-class feeling to black paper, a method using a heat transfer foil called foil stamping printing or heat transfer of foil by hot stamping is adopted.

Japanese Unexamined Patent Publication No. 2015-148205

In the blackening of paperboard used as a paper container or a packaging material, it is difficult to obtain a dark black color with little color unevenness only by coloring with a black dye. In addition, in order to use a heat transfer foil called thermal transfer of foil by foil stamping or hot stamping in order to give a high-class feeling to black paper, not only the dark blackness is improved, but also the durability of the printed or heat-transferred foil is durable. Is required to improve.

The present invention has been made based on the above circumstances, and is a multi-layered black color that can suppress discoloration of the foil pasted by color unevenness, thermal transfer in hot stamping, foil stamping, etc., while having dark blackness. The purpose is to provide paper.

The invention made to solve the above problems includes a surface layer and a back layer containing wood pulp as a main component and containing a black pigment, one or a plurality of middle layers provided between the surface layer and the back layer, and the surface layer. And an impregnated layer of a coating liquid containing a deepening agent and polyvinyl alcohol formed on at least one surface of the back layer, and the content of the black pigment in the surface layer and the back layer is the absolute dry pulp 100. The surface electrical resistance values measured in accordance with IEC61340 are 23 ° C. and 50 parts, which are 2.5 parts by mass or more and 20.0 parts by mass or less with respect to parts by mass, and the deepening agent is mainly composed of silicone. It is a multi-layered black paper having a value of 1 × 10 ² Ω / □ or more and 1 × 10 ¹² Ω / □ or less in an atmosphere of% RH.

The multi-layer paper is a multi-layer paper when the content of the black pigment in the surface layer and the back layer is 2.5 parts by mass or more and 20.0 parts by mass or less with respect to 100 parts by mass of the absolute dry pulp. The dark blackness of black paper is improved, and discoloration due to rust of the foil due to the black pigment, which is a problem especially when thermal transfer of the foil by hot stamping or foil pressing printing is performed, can be suppressed. Further, the multi-layered black paper is black by providing an impregnated layer of a coating liquid containing a deep colorant containing silicone as a main component and polyvinyl alcohol formed on at least one surface of a front layer and a back layer. While suppressing the content of the pigment, it is excellent in the dark blackness and the effect of suppressing color unevenness, and can impart good strength to the surface of the multilayer black paper. Further, the surface electrical resistance value measured in accordance with IEC61340 is 1 × 10 ² Ω / □ or more and 1 × 10 ¹² Ω / □ or less in an atmosphere of 23 ° C. and 50% RH. Since the black paper has low conductivity and local batteries are less likely to occur, it is possible to suppress discoloration of the foil of a metal layer such as an aluminum vapor deposition layer used for thermal transfer of the foil by hot stamping or foil stamping printing due to rust. Therefore, the multi-layered black paper has dark blackness and can suppress color unevenness and discoloration of the foil attached by thermal transfer, foil stamping, etc. in hot stamping. Here, the "main component" is the most contained. It is a component having a large amount, for example, a component contained in an amount of 50% by mass or more.

The content of the deepening agent in the impregnated layer is preferably 0.1 g / m ² or more and 0.5 g / m ² or less in terms of solid content. When the content of the deepening agent in the impregnated layer is 0.1 g / m ² or more and 0.5 g / m ² or less in terms of solid content, the dark blackness can be improved.

The surface layer and the back layer further contain a black dye, the black dye is an anionic direct dye, and the content of the anionic direct dye in the surface layer and the back layer is based on 100 parts by mass of the absolute dry pulp. It is preferably 2.0 parts by mass or more and 10.0 parts by mass or less. The surface layer and the back layer contain an anionic direct dye as a black dye, and the content of the anionic direct dye is within the above range, so that the multi-layer papermaking black paper suppresses the content of the black pigment. , Dark blackness can be improved.

It is preferable that the middle layer contains the black pigment, and the content of the black pigment in the middle layer is 0.3 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the absolute dry pulp. When the content of the black pigment in the middle layer is in the above range, it supports the black color of the surface layer and the back layer, and can improve the dark blackness.

According to the present invention, it is possible to provide a multi-layered black paper that has dark blackness and can suppress discoloration of a foil attached by thermal transfer, foil stamping, etc. in color unevenness and hot stamping.

Hereinafter, the multi-layered black paper according to the embodiment of the present invention will be described in detail. Unless otherwise specified, the blending amount (internal addition amount) of each material to be blended in the base paper described below refers to the mass ratio to the absolute dry mass of the raw material pulp. Further, the "solid content" refers to a component other than the solvent.

<Multi-layered black paper>
The multi-layered black paper is a coating liquid formed on the surface layer and the back layer, one or a plurality of middle layers provided between the surface layer and the back layer, and at least one surface of the surface layer and the back layer. It includes an impregnated layer.

[Surface and back layers]
The surface layer and the back layer are mainly composed of wood pulp and contain a black pigment.

(Wood pulp)
As the pulp used for each layer of the multi-layer paper, wood bleached chemical pulp is preferable. As the wood bleaching chemical pulp, a combination of softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP) is preferable. The mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is preferably 30/70 or more and 70/30 or less, and more preferably 50/50. When the mass ratio of the softwood bleached kraft pulp to the hardwood bleached kraft pulp is within the above range, the yield of the black pigment is improved, and a uniform and even black color can be obtained.

Further, as each layer of the multi-layered black paper, mechanical pulp such as used paper pulp, crushed wood pulp (GP), thermomechanical pulp (TMP), and bleached chemithermomechanical pulp (BCTMP) may be used, if necessary. Examples of the waste paper pulp include corrugated cardboard waste paper, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, upper white waste paper, Kent waste paper, structural waste paper, and ground ticket waste paper. , Deinking / deinking waste paper pulp, deinking / bleaching waste paper pulp, etc. can be used. Further, if necessary, mechanical pulp such as crushed wood pulp (GP), thermomechanical pulp (TMP), and bleached chemithermomechanical pulp (BCTMP) may be used.

350 ml is preferable as the lower limit of the Canadian Standard Freeness (CSF) of the pulp used for each layer of the multi-layer paper. If the CSF is less than 350 ml, the texture of the paperboard becomes too dense and the water absorption is lowered, so that curling due to moisture absorption may occur. On the other hand, the upper limit of CSF is preferably 450 ml. If the CSF exceeds 450 ml, the interlayer strength decreases, and there is a risk of delamination during punching. Here, the Canadian Standard Freeness (CSF) is made into dissociated pulp by dissociating in accordance with the pulp dissociation method of JIS-P8220-1 (2012), and this dissociated pulp is made into Canada of JIS-P8121-2 (2012). It is a value measured according to the standard freeness test method.

(Black pigment)
The multilayer black paper contains a black pigment. The lower limit of the content of the black pigment in the surface layer and the back layer is 2.5 parts by mass with respect to 100 parts by mass of the absolute dry pulp, preferably 4.0 parts by mass. The upper limit of the content of the black pigment is 20.0 parts by mass with respect to 100 parts by mass of the absolute dry pulp, preferably 18.0 parts by mass. When the content of the black pigment in the surface layer and the back layer is in the above range, the dark blackness of the multi-layer paper is improved, and the foil is rusted when the foil is thermally transferred or stamped. Discoloration can be suppressed.

As the black pigment, carbon black aggregates are preferable. Carbon black aggregates are inexpensive, and by using carbon black aggregates, a more black color tone can be produced. Carbon black aggregates are fused due to differences in particle size due to adjustment of the manufacturing method, spray diameter and temperature distribution of raw material oil, and reaction time distribution, and particles in a soft state collide with each other at a speed close to sound velocity in the manufacturing furnace. After that, it is obtained by undergoing heat treatment and carbonized, and can be selected according to the degree of development of the so-called carbon structure.

ASTM stipulates that carbon black aggregates should be indicated by a 4-digit code based on the chemical composition and particle size. As the carbon black aggregates, carbon black aggregates produced by the furnace method are preferable. is there. The furnace method is a method of continuously spraying liquid raw material oil and thermally decomposing it in an environment of a high temperature atmosphere of 1400 ° C. or higher, which is obtained by introducing fuel and air into a reactor and completely burning them. .. The quality of the carbon black aggregates produced in the reactor can be adjusted by changing the amounts of fuel, air, and feedstock, and by physically dispersing means, and the particle size and the size of the carbon structure can be arbitrarily adjusted.

The primary particle size of the carbon black aggregate is determined by the arithmetic mean diameter obtained by observing the carbon black particles with an electron microscope. The lower limit of the primary particle diameter is preferably 15 nm, more preferably 20 nm. The upper limit of the primary particle diameter is preferably 55 nm, more preferably 35 nm. Generally, the smaller the primary particle diameter, the higher the blackness of the carbon black aggregates, but the stronger the cohesive force between the carbon black particles, and the more difficult it is to disperse. When the range of the primary particle diameter is within the above range, the blackness and dispersibility of the carbon black aggregate can be improved. As an index of the size of the agglomerates of the primary particles of the carbon black agglomerates, the specific surface area obtained by the S-BET formula from the amount of nitrogen adsorbed measured in accordance with JIS-K6217 is generally used. .. In general, the smaller the particle size, the larger the specific surface area of the carbon black aggregate.

According to the study by the present inventors, when the specific surface area of the black pigment contained in the surface layer and the back layer is large, the dispersibility of the black pigment in the raw material pulp slurry decreases, and when the dispersibility decreases, the frequency of color unevenness occurs. Therefore, it becomes difficult to ensure uniform quality when forming the paper layer, and there is a risk that the papermaking equipment will be soiled. The specific surface area lower limit of the black pigment of the present invention contrast, a ^{30m 2 / g, 200m 2 /} g is preferred, the upper limit of the specific surface area is 1500 m ² / g, more preferably 300 meters ² / By setting g, the black pigment in the raw material pulp slurry has a high concentration content of 2.5 parts by mass or more and 20.0 parts by mass or less with respect to 100 parts by mass of the absolute dry pulp. It is possible to achieve a uniform coloring expression with excellent dispersibility. When the specific surface area is small, the fixability to the raw material pulp is lowered, the raw material pulp slurry is likely to fall off, and fine particles generated at the manufacturing site such as dust, dust, dust, and dust due to static electricity are attracted. There is a risk of adhesion.

(Black dye)
The surface layer and the back layer preferably further contain a black dye. As a black dye,
Anionic direct dyes are preferred. By further containing an anionic direct dye in addition to the black pigment in the surface layer and the back layer, the multi-layer papermaking black paper can improve the dark blackness while ensuring low conductivity.

The anionic direct dye was originally produced for the purpose of dyeing cellulose fibers, and is directly dyed on the cellulose fibers from a dyeing bath containing a neutral salt. From the viewpoint of chemical structure, it can be divided into azo, stilbene, thiazole, dioxazine, phthalocyanine and the like. The anionic direct dye is generally composed of an azo dye having an azo group (-N = N-) as a chromophore, but any anionic direct dye can be used.

The lower limit of the content of the anionic direct dye in the surface layer and the back layer is preferably 2.0 parts by mass, more preferably 2.5 parts by mass with respect to 100 parts by mass of the absolute dry pulp of the surface layer and the back layer. The upper limit of the content of the anionic direct dye is preferably 10.0 parts by mass and more preferably 5.0 parts by mass with respect to 100 parts by mass of the absolute dry pulp of the surface layer and the back layer. As described above, when the content of the anionic direct dye in the front layer and the back layer is within the above range, the multi-layer papermaking black paper can improve the dark blackness while ensuring low conductivity.

(Softening agent)
The surface layer and the back layer preferably further contain a softening agent. By adding a softening agent, it is possible to further suppress discoloration of the foil of a metal layer such as an aluminum vapor deposition layer used for thermal transfer of the foil by hot stamping and foil stamping printing due to rust. Further, even if the content of the black pigment is increased, sufficient flexibility can be obtained. Examples of the softening agent include nonionic surfactants and cationic surfactants. Examples of the cationic surfactant include alkylamine (1, 2, and 3) salts, quaternary alkylammonium salts, heterocyclic quaternary ammonium salts, polyalkylene polyamine fatty acid condensate salts, and polyalkylene polyamine fatty acid epichlorohydrin. Examples thereof include polycondensates, alkyl imidazoline salts, and alkyl imidazolinium salts. Specific examples of these include octadecylamine hydrochloride, dilaurylamine acetate, lauryltrimethylammonium bromide, myristyldimethylbenzylammonium chloride, stearylpyridinium chloride, and bisstearoyldiethylenetriamine acetate. Examples thereof include bisstearoyldiethylenetriamine-epichlorhydrin reaction products, 2-pentadecenyl-1-hydroxyethylimidazoline acetate, 2-heptadecenyl-1-hydroxyethyl-1-methylimidazolinium chloride and the like.

The upper limit of the content of the softening agent in the surface layer and the back layer is preferably 0.040 parts by mass in terms of solid content with respect to 100 parts by mass of the absolute dry pulp of the surface layer and the back layer. When the content of the softening agent in the surface layer and the back layer is within the above range, discoloration due to rust of the foil of the metal layer such as the aluminum vapor deposition layer used for thermal transfer of the foil by hot stamping and foil stamping can be further suppressed. ..

[Middle layer]
The multi-layer paper is provided with one or more intermediate layers between the front layer and the back layer. The middle layer preferably contains waste paper pulp as a main component. The flexibility of the middle layer can be improved by using used paper pulp as the main component. The middle-layer waste paper pulp is not particularly limited, but waste paper pulp derived from machine pulp-containing waste paper may be used. When the multi-layered black paper has a plurality of middle layers, the same type of used paper pulp may be used for each middle layer, or different types of used paper pulp may be used.

The middle layer preferably contains a black pigment. Further, as the black pigment, it is preferable to contain carbon black aggregates as in the case of the surface layer and the back layer. When the middle layer contains a black pigment, the lower limit of the content of the black pigment in the middle layer is preferably in a range lower than the content of the black pigment in the surface layer, specifically, 100 mass of absolute dry pulp in the middle layer. 0.3 parts by mass is preferable, and 0.5 parts by mass is more preferable. The upper limit of the content of the black pigment is preferably 3.0 parts by mass and more preferably 2.0 parts by mass with respect to 100 parts by mass of the absolute dry pulp in the middle layer. When the content of the black pigment in the middle layer is in the above range, it supports the black color of the surface layer and the back layer, and can improve the dark blackness.

[Additive]
(Paper power enhancer)
A paper strength enhancer can be added to each layer of the multi-layer paper. By adding a paper strength enhancer, various strengths suitable for use as a paper container or a packaging material can be imparted to each layer.

Examples of the paper strength enhancer include starch-based paper strength enhancers, acrylamide-based paper strength enhancers, vinyl alcohol-based paper strength enhancers, amide epoxy-based paper strength enhancers, and among these, acrylamide-based paper strength enhancers. Is preferable. More preferably, an amphoteric polyacrylamide resin-based paper strength enhancer is preferable. Amphoteric polyacrylamide is a polymer of cationic monomer and anionic monomer with acrylamide, and is directly fixed to the anionic group of pulp fiber, black pigment, and direct dye through its own cationic group, and has its own anionic property. The group can be indirectly fixed to the anion group of the pulp fiber, the black pigment, or the direct dye through the cationic substance of the pigment fixing agent. As described above, since the mechanism of the amphoteric polyacrylamide resin-based paper strength enhancer can be fixed to the fiber, the yield of the black pigment or the direct dye can be increased and the dropout can be prevented. Another characteristic of amphoteric polyacrylamide resin-based paper strength enhancers is that the molecular structure and molecular weight can be controlled. The part of the amphoteric polyacrylamide resin-based paper strength enhancer that contributes to the improvement of paper strength is the high molecular weight range, but by reducing the low molecular weight range at the manufacturing stage, the multilayer paper containing a high concentration of black pigment is used. Paper power can be efficiently improved on black paper. Amphoteric polyacrylamide in the low molecular weight range tends to cause poor fixing of black pigments and anionic direct dyes, and its contribution to improving paper strength tends to be low.

The lower limit of the content of the paper strength enhancer is preferably 0.70 parts by mass and more preferably 0.80 parts by mass in terms of solid content with respect to 100 parts by mass of the absolute dry pulp. The upper limit of the content is preferably 1.10 parts by mass and more preferably 1.00 parts by mass in terms of solid content with respect to 100 parts by mass of absolute dry pulp. By setting the content of the paper strength enhancer in the above range, it is possible to impart various paper strengths such as interlayer strength of multi-layer papermaking black paper and improve suitability for various packages. If the content of the paper strength enhancer is less than the above range, the interlayer strength may not be sufficient. On the other hand, if the content of the paper strength enhancer exceeds the above range, the improvement of the interlayer strength is almost flat, and there is a possibility that the cost will be increased due to excessive addition.

(Other additives)
In the present invention, each layer of the multi-layer papermaking black paper may contain various papermaking additives as long as the effects intended for the present invention are not impaired. For example, sulfuric acid band, sizing agent, pigment fixing agent, yield improver, pigment dispersant, pH adjuster, thickener, fluidity improver, defoaming agent, defoaming agent, mold release agent, penetrant, ultraviolet absorption. Known additives such as agents, antioxidants, preservatives, antibacterial agents, water resistant agents, fluorescent scavengers, pitch control agents, slime control agents and the like can be added alone or in combination of two or more.

[Immersion layer]
The impregnating layer is formed on at least one surface of the surface layer and the back layer. The impregnated layer is an impregnated layer of a coating liquid containing a deepening agent and polyvinyl alcohol. The impregnating layer of the coating liquid containing the deepening agent and polyvinyl alcohol is a so-called clear coating layer. In the impregnated layer, it is considered that the coating liquid is impregnated into the paper layer from at least one surface of the surface layer and the back layer to form an impregnated layer on the surface of the paper layer. The multi-layered black paper is provided with an impregnated layer containing a deepening agent and polyvinyl alcohol formed on at least one surface of the front layer and the back layer, so that the black color is dark while suppressing the content of the black pigment. In addition to being excellent in suppressing color unevenness, it is possible to impart good strength to the surface of the multi-layered black paper.

(Deepening agent)
The deepening agent is a chemical developed for clothing that suppresses color reflection. By containing the above-mentioned deepening agent, the multi-layered black paper has excellent dark black color and color unevenness while suppressing the content of black pigment which may induce discoloration due to rust of the foil if it is contained in a large amount. It is possible to obtain an inhibitory effect on. The deepening agent has a function of reducing surface reflected light by scattering visible light and amplifying color density. Therefore, by using the deepening agent in combination with the black pigment, excellent dark blackness can be obtained. The deepening agent contains silicone as a main component. As the above-mentioned silicone, a weakly cationic modified silicone is desirable from the viewpoint of lowering the refractive index and further reducing the surface reflected light. The deepening agent preferably further contains silica. Since the electric resistivity is improved by containing silica as the deepening agent, it is possible to further suppress discoloration due to rust of the foil of the metal layer such as the aluminum vapor deposition layer used for thermal transfer of the foil by hot stamping and foil stamping printing. It is presumed. The deepening agent may be used alone or in combination of two or more with different contents.

The lower limit of the content of the deepening agent in the impregnated layer is 0.10 g / m ² in terms of solid content, preferably 0.15 g / m ² . The upper limit of the content of the deepening agent is 0.50 g / m ² in terms of solid content, preferably 0.40 g / m ² . When the content of the deepening agent is in the above range, the dark blackness can be improved.

(Polyvinyl alcohol)
When the impregnated layer contains polyvinyl alcohol, the surface strength can be improved. The degree of saponification of polyvinyl alcohol is preferably 90 mol% or more and 99 mol% or less from the viewpoint of improving the surface strength of the multilayer paper. Further, good strength, water repellency and water resistance can be imparted to the surface of the multilayer black paper. Therefore, the suitability of foil stamping printing can be improved, and the quality of the foil can be maintained for a long time.

The lower limit of the content of the polyvinyl alcohol in the impregnation layer is ^{0.10g / m 2, 0.15g / m} 2 is preferred. The upper limit of the content of the polyvinyl alcohol is ^{0.50g / m 2, 0.40g / m} 2 is preferred. When the content of the polyvinyl alcohol is in the above range, the occurrence of aggregation when used in combination with a deep colorant can be suppressed.

(Wax-based sizing agent)
The impregnated layer preferably contains a wax-based sizing agent. As the wax-based sizing agent, a paraffin wax-based sizing agent, a microcrystalline wax-based sizing agent, a carnauba wax (carnauba wax) -based sizing agent, an alkyl keten dimer wax-based sizing agent, and the like can be used. Among the system sizing agents, it is preferable to contain an alkyl keten dimer system sizing agent because the fixability to the pulp is good. By internally adding these wax-based sizing agents, good water repellency and water resistance can be imparted to the surface of the multilayer paper, and the suitability and quality of foil stamping can be improved.

The lower limit of the content of the wax-based sizing agent in the impregnation layer is 0.05 g / ^{m 2} by solid content, 0.10 g / ^{m 2} is preferred. The upper limit of the content of the wax-based sizing agent, was ^{0.50g / m 2, 0.40g / m} 2 is preferred. When the content of the wax-based sizing agent is in the above range, good water repellency and water resistance can be imparted to the surface of the multilayer paper, and the suitability and quality of foil stamping can be improved.

The impregnated layer may be mixed with starch, polyacrylic amide, a surface sizing agent, or the like in addition to polyvinyl alcohol, a deepening agent, and paraffin wax. Further, additives such as a colorant, a water retention agent, a water resistant agent, a fluidity improver, a fungicide, a preservative, and an antifoaming agent can be added to the coating liquid.

The lower limit of the application amount of the impregnated layer, a ^{0.25g / m 2, 0.30g / m} 2 is preferred. The upper limit of the coating amount is ^{1.30g / m 2, 1.20g / m} 2 is preferred. When the coating amount is less than the above lower limit, the surface strength is weakened, the black pigment is likely to fall off from the surface layer and the back layer, and the foil may fall off during foil stamping printing. When the coating amount is equal to or more than the above upper limit, the texture as "paper" is impaired, the surface layer may be easily soiled due to blocking in the processing process, and the cost merit may be lowered. When the coating amount is within the above range, the appearance of the multi-layered black paper as "paper" and the stable attachment of the foil in foil stamping printing can be improved.

[Physical property values of multi-layered black paper]
(Basis weight)
Basis weight is measured according to JIS-P8124 (2011). The basis weight of the surface layer, back layer and middle layer is the absolute dry mass per unit area. The basis weight of each layer of the multi-layer paper is not necessarily equal, and the basis weight of the surface layer, the back layer and the middle layer is not particularly limited, but the lower limit of the basis weight of the surface layer and the back layer is set. , 65 g / m ² is preferable, and 70 g / m ² is more preferable. As the upper limit of the basis weight of the surface layer and the back layer, 85 g / m ² is preferable, and 80 g / m ² is more preferable. When the basis weights of the surface layer and the back layer are within the above range, the texture unevenness of the paper layer containing the black pigment can be suppressed. Further, as the lower limit of the basis weight of the entire middle layer, 220 g / m ² is preferable, and 250 g / m ² is more preferable even in a plurality of middle layer configurations. As the upper limit of the basis weight of the middle layer, 380 g / m ² is preferable, and 350 g / m ² is more preferable.

The lower limit of the multi-layer paper making black paper overall basis weight, preferably from ^{3150g / m 2, 350g / m} 2 is more preferable. The upper limit of the multi-layer paper making black paper overall basis weight, preferably from ^{550g / m 2, 500g / m} 2 is more preferable. When the basis weight of the entire multi-layered black paper is within the above range, it is possible to maintain sufficient processing strength even when used for paper containers and packaging materials.

(Paper thickness)
Paper thickness is measured in accordance with "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P8118 (2014). The lower limit of the thickness of the multilayer paper is preferably 370 μm, more preferably 410 μm. The upper limit of the paper thickness is preferably 580 μm, more preferably 570 μm. When the thickness of the multi-layer paper is in the above range, cracking of the ruled lines can be suppressed.

(PH)
The pH is defined as JAPAN. TAPPI Pulp and Paper Test Method No. It is a value measured according to 49: 2000. Since it is necessary to contain a relatively large amount of black pigment in at least the surface layer and the back layer of the multi-layer papermaking black paper, colorants such as black pigment and black direct dye added to the papermaking raw material are efficiently fixed to the pulp. It is required to make it. When the pH of the multilayer paper is 6 or more and 8 or less, the fixability of the black direct dye and the black pigment to pulp can be improved. In addition, discoloration due to rust on the foil due to acid or alkali can be further suppressed.

(Hue (L ^* value, a ^* value, b ^* value))
The L ^* value is a value measured in accordance with JIS-P8150 (2004). The L value indicates the degree of brightness, and the larger the value, the brighter the image. The upper limit of the L ^* value of the surface layer surface and the back layer surface of the multi-layer paper is preferably 27.0, more preferably 26.0 or less. When the L ^* values of the surface layer surface and the back layer surface are in the above range, the dark blackness can be improved.

The a ^* value is a value measured in accordance with JIS-P8150 (2004). The ^* value indicates the intensity of redness and greenness. A large value on the positive side indicates a strong redness, and a large value on the negative side indicates a strong greenness. The range of the a ^* values of the surface layer surface and the back layer surface is preferably -0.50 or more and 1.30 or less, and more preferably -0.10 or more and 1.00 or less, from the viewpoint of emphasizing the blackness of appearance. ..

The b ^* value is a value measured in accordance with JIS-P8150 (2004). b ^{* The} value indicates the intensity of yellowness and bluishness, and a large value on the plus side indicates a strong yellowness, and a large value on the minus side indicates a strong bluishness. The range of the b ^* values of the surface layer surface and the back layer surface of the multi-layered black paper is -1.00 or more and 1.00 from the viewpoint of suppressing discoloration (yellowing) of the appearance of the multi-layered black paper. The following is preferable, and −0.30 or more and 0.50 or less is more preferable.

(Surface strength)
The surface strength is determined by JAPAN. TAPPI Pulp and Paper Test Method No. It is a value measured according to the surface strength test method using wax of 1. The surface strength of the surface layer and the back layer of the multi-layer paper is preferably 6A or more and 20A or less. When the surface strength is within the above range, there is an effect that paper blurring and black pigments are less likely to fall off during printing on the surface of multi-layer papermaking black paper, and inadvertent foil falloff during foil stamping printing does not occur. ..

(Surface electrical resistance value)
The surface electrical resistance value of the multilayer paper is the resistance per unit area and is measured according to IEC61340.

The lower limit of the surface electrical resistance value of the multilayer paper-made black paper in an atmosphere of 20 ° C. and 10% RH is 1 × 10 ² Ω / □, preferably 1 × 10 ³ Ω / □. The upper limit of the surface electrical resistance value is 1 × 10 ¹² Ω / □, preferably 1 × 10 ¹¹ Ω / □ or less. When the surface electrical resistance value is lower than the above range, discoloration occurs due to rust on the foil of the metal layer such as the aluminum vapor deposition layer used for foil stamping printing with the black pigment, and the glossiness and stain of the surface of the multi-layer papermaking black paper occur. There is a risk. On the other hand, if the surface electrical resistance value of the multi-layer paper is higher than the above range, fine particles generated at the manufacturing site such as dust, dust, dust, and dust due to static electricity may be attracted and adhered. When the lower limit of the surface electrical resistance value of the multi-layer paper is in the above range, the conductivity of the multi-layer black paper is low and local batteries are less likely to occur. Therefore, thermal transfer of foil by hot stamping or It is possible to suppress discoloration due to rust on a metal layer such as an aluminum vapor deposition layer used for foil stamping printing.

(Cub size)
The degree of bump size is measured (measurement time: 10 seconds) in accordance with JIS-P8140 (1998). As the lower limit of the bump size of the multilayer paper, 20 g / m ² is preferable, and 25 g / m ² is more preferable. When the bump size of the multi-layered black paper is less than the above lower limit, when flexo or offset printing is performed on the multi-layered black paper, the dryness of the ink is lowered and printing stains and scratch stains occur. In addition to the risk, there is a risk of improper bonding during processing into paper containers and the like. On the other hand, as the upper limit of the bump size of the multi-layer paper, 45 g / m ² is preferable, and 40 g / m ² is more preferable. When the bump size of the multi-layered black paper is equal to or greater than the above upper limit, the multi-layered black paper may cause wrinkles or wrinkles due to moisture absorption, or the foil may fall off in foil stamping printing.

According to the multi-layered black paper, it is possible to suppress color unevenness and discoloration of the pasted foil due to thermal transfer in hot stamping, foil stamping, etc., while having dark blackness.

[Manufacturing method of multi-layer paper]
The method for producing the multi-layer paper making is not particularly limited, but for example, it can be produced using a known multi-layer paper machine by the following steps.
(1) Additives corresponding to each paper layer are added as necessary to the slurry obtained by dispersing pulp fibers in water and mixed to prepare a paper material for each paper layer.
(2) Next, using these raw material slurries, the surface layer, single layer or multi-layer middle layer and back layer are used in a paper machine in the neutral range so that the pH of the multi-layer paper is 6 or more and 8 or less. Paper is made by combining the above.
The paper making method is not particularly limited, and a known paper machine, that is, a paper machine such as a long net, a circular net, a hybrid former, or a gap former, is used to make a paper with three or more layers. In the papermaking process, an impregnated layer can be formed by applying a coating liquid to the surfaces of the surface layer and the back layer using a coating device such as a size press, a metering size press, or a gate roll coater.
(3) Next, press with a pressure roll to remove water.
(4) Next, it is dried in a dryer cylinder.
After drying, smoothing may be performed using a calender device such as a nip calender, a super calender, a machine calender, or a soft calender. By performing the smoothing treatment, the multi-layered black paper is imparted with high glossiness and can be suitably used for packages, wrapping papers, price tags and the like having a high-class feeling.
(5) Finally, the paper is wound on a reel to obtain a multi-layered black paper.

<Other Embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in various modifications and improvements in addition to the above-described embodiment.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Example 1]
(1) The following raw materials were added to a pulp slurry of 50% LBKP and 50% NBKP with 380 mL of freeness.
(Surface and back layers)
Acrylamide-based paper strength enhancer ("RB-28" by Harima Chemicals, Inc.): 0.70 parts by mass / 100 parts by mass of absolute dry pulp (solid content)
Carbon black ("Grand Black YT-100" from Mikuni Color Co., Ltd.): 7.0 parts by mass / 100 parts by mass of absolute dry pulp Nikka "Direct Paper Black BG": 2.0 parts by mass / as an anionic black direct dye 100 parts by mass of absolute dry pulp (middle layer)
Carbon black ("Grand Black YT-100" from Mikuni Color Co., Ltd.): 2.0 parts by mass / 100 parts by mass of absolute dry pulp

(2) The pulp slurry was made using a long net paper machine. Further, the surface of the surface layer and the back layer is coated with a coating liquid containing polyvinyl alcohol, a deepening agent and paraffin wax so as to have the following coating amount to form an impregnated layer, and the impregnated layer is formed. A multi-layered black paper was obtained.
Polyvinyl alcohol (Nippon Synthetic Chemical Industry Co., Ltd. "Gosenol N-300"): 0.30 g / m ²
Deep color agent (Matsumoto Oil & Fat Co., Ltd. "Bryan DF-2"): 0.30 g / m ²
Paraffin wax (Harima Chemicals'"HaricoatRK"): 0.40 g / m ²
Total coating amount: 1.00 g / m ²

The method for measuring the physical property value is as follows.
[Freeness (mL)]
The obtained multi-layer paper was dissociated according to the method for dissociating the pulp of JIS-P8220-1 (2012) to obtain dissociated pulp, and this dissociated pulp was used as the Canadian standard of JIS-P8121-2 (2012). It was measured according to the water content test method.

[Basis weight (g / m ² )]
The measurement was performed in accordance with "Paper and Paperboard-Basis Weight Measuring Method" described in JIS-P8142 (1998).

[Paper thickness (μm)]
The measurement was performed in accordance with "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P8118 (2014).

[Hue]
Hue (L ^* value, a) with a light source containing ultraviolet light with a color difference meter PF-10 manufactured by Nippon Denshoku Co., Ltd. in accordance with the "method for measuring color of paper and paperboard" described in JIS-P8150 (2004). ^* Value, b ^* value) were measured.

[Cub size]
The measurement was performed according to JIS-P8140 (1998). The degree of bump size referred to in the present invention is a value measured by bringing water into contact with the surface of the surface layer or the back layer on the side where the foil stamping printing is provided for 10 seconds.

[Surface strength]
JAPAN TAPPI No. The measurement was performed according to the surface strength test method using wax of 1.

[PH]
The pH is defined as JAPAN. TAPPI Pulp and Paper Test Method No. Measured according to 49: 2000.

[Surface electrical resistance value (Ω / □)]
The surface electrical resistance value was measured according to IEC61340.

The physical property values of Example 1 were as follows.
Basis weight: (surface layer) 75 g / m ²
(Middle layer) 300 g / m ²
(Back layer) 75 g / m ²
(Overall) 450g / m ²
Paper thickness: 560 μm
L ^* value: 26.8, a ^* value: 0.13, b ^* value: -0.23
Kobusaizu index: the surface 32 g / ^{m 2,} the back surface 34g / ^{m 2}
Surface strength: front surface 11A, back surface 11A
pH: 7.36
Surface ^{resistivity: 1.0 × 10 8 (Ω /} □)

[Examples 2-32 and Comparative Examples 1-3]
Multilayer black papers of Examples 2-32 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 except that the types and contents of the raw materials were as shown in Tables 1 and 2. As the softener, Softon P-400 (cationic surfactant, bisstearoyldiethylenetriamine-epichlorohydrin reaction product) manufactured by Toho Chemical Industry Co., Ltd. was used. Further, in Comparative Example 2, partially saponified PVA: manufactured by Kuraray Co., Ltd.), product number: PVA-405, and saponification degree: 86.5 were used.

[Evaluation]
Each of the obtained multi-layered black paper was evaluated by the following method. Tables 1 and 3 show the measurement results and evaluation results of the physical property values.

[Dark blackness]
The dark blackness was visually evaluated based on the following evaluation criteria. The evaluation criteria were as follows.
1: There is shine and there is almost no depth of black 2: The shade and depth of black are insufficient 3: There is some shine, but it has enough black shade and is practical. Yes 4: Black is deep and has a high-class feel 5: There is no shine, black is very deep and has a very high-class feel

[Discoloration suppression due to foil rust]
The test method was carried out as follows.
(1) A metallic wheel with aluminum vapor deposition, in which a heat-sensitive adhesive such as a hot melt adhesive is thinly applied to the outermost layer, is stamped and printed on a multi-layer paper black paper according to the present invention by a hot stamping method. A test piece was obtained.
(2) The test piece was immersed in distilled water at room temperature for 1 hour and air-dried.
(3) The test piece was placed in a variable humidity chamber (40 ° C. × 90% × 24 hours).
(4) After the test was completed, the inhibitory properties of the multi-layered black paper foils of each Example and Comparative Example against discoloration (coloring) due to rust were evaluated.
The evaluation criteria were as follows.
1: The foil surface is significantly discolored 2: Discoloration is scattered on the foil surface 3: Slight discoloration is seen on the foil surface, but it is practical 4: Almost no discoloration is seen on the foil surface 5: No discoloration on the foil surface

[Color unevenness suppression]
The inhibitory property against color unevenness was visually evaluated based on the following evaluation criteria. The evaluation criteria were as follows.
1: Many color unevenness occurs and the appearance is inferior 2: Some color unevenness occurs and the appearance is slightly inferior 3: Color unevenness occurs slightly, but the appearance is good and practically possible 4: Color unevenness There is almost no color and the appearance is excellent. 5: There is no color unevenness and the appearance is particularly excellent.

As shown in Table 3 above, Examples 1 to 18 of the multi-layer papermaking were good in all of the dark blackness, the inhibitory property against discoloration due to rust of the foil, and the inhibitory property against color unevenness. ..

On the other hand, Comparative Example 1 in which the content of the black pigment exceeds 20.0 parts by mass, the surface electrical resistance value is less than 1 × 10 ² Ω / □, and no deepening agent is contained, is dark black and foil. It was very inferior in all of the effect of suppressing discoloration due to rust and the effect of suppressing color unevenness. In Comparative Example 2 in which the content of the black pigment exceeded 20.0 parts by mass, the effect of suppressing discoloration due to rust on the foil was extremely inferior. In Comparative Example 3 in which the content of the black pigment was less than 2.5 parts by mass and the surface electrical resistance value exceeded 1 × 10 ¹² Ω / □, the dark blackness and the effect of suppressing color unevenness were extremely inferior. Comparative Example 4 containing no deepening agent was extremely inferior in dark blackness and color unevenness suppressing effect.

The multi-layered black paper of the present invention can be suitably used for high-class packages such as jewelry and cosmetics, mounts, wrapping papers, price tags and the like.

Claims (4)

The surface layer and back layer containing wood pulp as the main component and black pigment,
One or more middle layers provided between the surface layer and the back layer,
It is provided with an impregnating layer of a coating liquid containing a deepening agent and polyvinyl alcohol formed on at least one surface of the surface layer and the back layer.
The content of the black pigment in the surface layer and the back layer is 2.5 parts by mass or more and 20.0 parts by mass or less with respect to 100 parts by mass of absolute dry pulp.
The above deepening agent contains silicone as the main component.
Multilayer black paper having a surface electrical resistance value measured in accordance with IEC61340 of 1 × 10 ² Ω / □ or more and 1 × 10 ¹² Ω / □ or less in an atmosphere of 23 ° C. and 50% RH. The multi-layered black paper according to claim 1, wherein the content of the deepening agent in the impregnated layer is 0.1 g / m ² or more and 0.5 g / m ² or less in terms of solid content. The surface layer and the back layer further contain a black dye,
The above black dye is an anionic direct dye,
The multilayer according to claim 1 or 2, wherein the content of the anionic direct dye in the surface layer and the back layer is 2.0 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the absolute dry pulp. Black paper. The middle layer contains the black pigment and
The multilayer abstract according to claim 1, claim 2 or claim 3, wherein the content of the black pigment in the middle layer is 0.3 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of absolute dry pulp. Black paper.