JP2000226797A - Hardboard having high light-shielding properties - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hardboard that has high shielding action from the light with wavelength from 250 nm-850 nm, causes no migration of the coloring dyes or pigments to the content in the package and is suitable for the purpose of food packaging. SOLUTION: This hardboard comprises at least the outer layer, the intermediate layer and the back layer where the intermediate layer includes chemical fibers that are colored by kneading inorganic pigments therein. The amount of the colored chemical fibers is 12-60 g/m2 in the intermediate layer and the proportion of the inorganic pigment kneaded is 1-50 wt.% in the chemical fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a paperboard having a high light-shielding property.

[0002]

2. Description of the Related Art Paperboard is widely used in packages such as packaging boxes, cartons and cups. If the paperboard is used in food packaging, light rays may affect the contents by penetrating the paperboard. For example, when the contents are sake, green tea, yogurt, fats or ice cream with high fat, etc., these are susceptible to light rays, causing pigment deterioration and quality deterioration, significantly lowering the commercial value. Sometimes. In order to prevent the deterioration of the contents as described above, it is necessary to suppress the light transmission of the paperboard used (hereinafter, may be referred to as light shielding or light shielding).

[0003] However, the wavelength that causes the quality deterioration of the contents is not specified, and it is necessary to shield wavelengths in the near ultraviolet region and near infrared region including the visible light region. A method of printing black ink or the like on the surface of the paperboard for the purpose of shielding such an area, a method of laminating an aluminum foil (hereinafter referred to as an aluminum foil) on the paperboard, and a method of coloring some layers of the paperboard. 2. Description of the Related Art Paperboard (hereinafter, sometimes referred to as light-shielding paper) having a property is manufactured.

[0004] Among these methods, in the case of a light-shielding paper made by printing on the surface of a paperboard, printing for shielding light is performed, and in order to maintain whiteness, white printing is performed on the light-shielding printing layer. This means that production efficiency is poor. In the case of light-shielding paper made by bonding aluminum foil to paperboard, a sufficient effect can be obtained in light-shielding performance,
Incineration remains unsuitable for incineration, and remains one of the environmental issues.

A light-shielding paper made by coloring a part of a paperboard layer is made of unexposed pulp as disclosed in Japanese Utility Model Application Laid-Open No. Sho 59-103800, or pulp is colored with a dye or a coloring pigment. , Or a combination of them. In the case of paperboard that is shielded from light by unexposed pulp, the paperboard has a drawback that light rays from a high wavelength region of visible light to an infrared region are transmitted, and a sufficient light-shielding effect cannot be obtained. Also, in the case of paperboard colored with a dye, light rays from the high wavelength region of visible light to the infrared region are transmitted as in the case of paperboard shaded by unexposed bleaching pulp, and not only a sufficient light-shielding effect is not obtained, but also Depending on the substance, the dye may dissolve and lower the commercial value of the contents. In the case of a paperboard colored with a coloring pigment, a sufficient light-shielding effect can be obtained, but depending on the contents, there is a risk of adhesion and contamination, and in any case, it is hard to say that the paper is an excellent light-shielding paper.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a food having a high light-shielding property when the wavelength of light is in the range of 250 nm to 850 nm, and a dye or a coloring pigment does not adhere to the contents. An object of the present invention is to provide a paperboard suitable for packaging use.

[0007]

SUMMARY OF THE INVENTION The present invention has been studied intensively to solve the problems of the prior art. As a result, the present invention comprises at least three layers: a surface layer, a middle layer, and a back layer. The inventors have found that the above object can be achieved by a paperboard having a high light-shielding property containing a chemical fiber colored by kneading, and completed the present invention.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. In the present invention, the back layer of the paperboard refers to the outermost layer on the wire side, and the surface layer refers to the outermost layer on the side opposite to the back layer. The middle layer refers to the entire layer between the surface layer and the back layer. The paperboard of the present invention is composed of a front and back layer, which are pulp layers, and a middle layer made of chemical fibers colored by kneading pulp and an inorganic pigment.

The chemical fiber colored by kneading the inorganic pigment mixed into the middle layer is a so-called native fiber (hereinafter, referred to as “fiber”).
Chemical fibers colored by kneading inorganic pigments are referred to as primary fibers). The original fiber is 12
It is preferably 〜60 g / m ² . If the mixing amount in the middle layer is less than 12 g / m ² , sufficient light-shielding properties cannot be obtained. If the mixing amount exceeds 60 g / m ² , the strength of the paper is remarkably reduced and the use as a paperboard becomes difficult. Particularly preferred range is 12~50g / ^{m 2.}

The amount of the inorganic pigment to be kneaded into the soaked fiber is preferably 1 to 50% by weight. If the addition amount is less than 1% by weight, the light-shielding performance is not sufficient, and if it exceeds 50% by weight, single yarn breakage and color unevenness during spinning tend to occur.
More preferably, it is 3 to 40% by weight.

The inorganic pigment to be kneaded into the fiber is carbon black, activated carbon, iron black, mica iron oxide, cobalt oxide, titanium black, cobalt blue, strontium chromate, titanium yellow, ultramarine blue,
Navy blue and the like, and these can be used alone or in combination of two or more. However, the inorganic pigment used preferably shows black in order to sufficiently suppress light transmission, and carbon black, activated carbon, iron black, and titanium black are preferable.

The dyed fiber can be obtained by wet spinning, dry spinning or melt spinning of a stock solution containing an inorganic pigment by a known method.

As the original fibers, regenerated fibers such as rayon fibers and cupra fibers, semi-synthetic fibers such as acetate fibers, and synthetic fibers such as nylon fibers, polyester fibers, polypropylene fibers, vinylon fibers, and acrylic fibers can be used. Preferably, rayon fiber having excellent dispersibility is used.

The cut length of these original fibers is 3 mm to 1 mm.
It is preferably 0 mm. If the cut length is shorter than 3 mm, the strength of the paper is reduced. If the cut length is longer than 10 mm, the formation deteriorates and uniform light-shielding properties cannot be obtained. More preferably, the cut length is 3 mm to 5 mm.

[0015] The cross section of the above-mentioned soaked fiber is an irregular cross section such as a circular cross section, a Y cross section, a U cross section, a T cross section, a star cross section, a triangular cross section, a hollow flat cross section, and a ribbon flat cross section. Either may be used.

The pulp used in the present invention is not particularly limited. For example, wood pulp such as chemical pulp and mechanical pulp, waste paper pulp such as deinked pulp, and non-wood natural pulp such as kenaf, bagasse, hemp and bamboo. And synthetic pulp using polyethylene or polypropylene as a raw material. These may be used alone or in combination of two or more. In addition to the above, it is also possible to mix chemical fibers such as acrylic fiber, rayon fiber and vinylon fiber.

As the additives of the slurry obtained by mixing the above constituent materials, various conventionally used anionic, nonionic, cationic or amphoteric paper strength enhancers, sizing agents, retention improvers and the like can be appropriately used. You can select and use. Specific examples of chemicals that can be used are as follows. Paper strength agent,
Polyacrylamide-based anionic, nonionic, cationic or amphoteric resin, polyethyleneimine and its derivatives, polyethylene oxide, polyamine, polyamide, polyamine polyamide and its derivatives, cationic, and amphoteric starch as a yield improver,
Organic compounds such as oxidized starch, carboxymethylated starch, vegetable gum, polyvinyl alcohol, urea formalin resin, melamine formalin resin, hydrophilic polymer particles, and sulfate band, alumina sol, basic aluminum sulfate, basic aluminum chloride, base Inorganic compounds such as hydrophobic polyaluminum hydroxide, ferrous sulfate, colloidal silica, bentonite and the like can be used in appropriate combination. Examples of the sizing agent include rosin-based, petroleum resin-based, alkyl ketene dimer-based, and alkenyl succinic anhydride-based sizing agents. Further, generally known fillers, for example, mineral fillers such as talc, kaolin, calcined kaolin, clay, diatomaceous earth, heavy calcium carbonate, magnesium carbonate, aluminum hydroxide, and titanium dioxide can be appropriately selected and used. As a papermaking additive, a pH adjuster, a slime control agent, an antifoaming agent, a thickener and the like can be used according to the intended use.

Further, starch, polyvinyl alcohol, polyacrylamide, various surface sizing agents, etc. are applied to paperboard by a coating method such as size press coat, gate roll coat, calender coat, blade coat, roll coat, air knife coat, bar coat and the like. It is also possible to apply a pigment or the like.

Examples of the paper machine used for making the paperboard of the present invention include a circular net type, a short net type, a long net type, and a combination type.

The basis weight of the paperboard of the present invention is 150 to 500 g /
m ² is preferable. Paperboard weight 150g / m
If the ratio is less than ² , when the necessary amount of the soaked fiber is mixed in the middle layer, the soaked fiber becomes transparent and the appearance deteriorates. 50
If it exceeds 0 g / m ² , there is a problem in papermaking properties such as a decrease in dehydration properties and a decrease in drying efficiency. More preferably 230 g / m
² to 400 g / m ² .

The basis weight of the middle layer is 80 to 300 g / m.²Range
It is preferred that 80 g / m ²If less than
The ratio of the indigenous fibers mixed in the middle layer increases,
It may be difficult to use it as a supplementary paperboard. 300g /
m²If it exceeds, the primary fibers mixed into the middle layer
Transparent on the surface, worse on the appearance and lower whiteness
You. More preferably, 100 to 250 g / m²It is.

The paperboard obtained from the constituent materials described above is often subjected to printing and film laminating in the next step. Gravure printing, offset printing,
Flexographic printing can be used. Gravure inks, offset inks, flexo inks, etc., suitable for each printing can be used as the printing inks. Examples of the resin used for the film lamination include various resins such as a polyethylene resin, a polypropylene resin, a polyamide resin, a polyethylene terephthalate resin, and an ethylene-vinyl alcohol copolymer resin, and these resins may be used alone or in a laminate thereof.

[0023]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following, “%” and “part” indicate “% by weight” and “part by weight”.
Hardwood bleached kraft pulp is denoted as LBKP, softwood bleached kraft pulp is denoted as NBKP, and hardwood unbleached kraft pulp is denoted as LUKP. The methods for measuring the light transmittance, discoloration, and tensile strength in the following Examples and Comparative Examples are as follows.

Light transmittance: 250 nm to 8 with a spectrophotometer manufactured by JASCO Corporation
The measurement was performed for a range of 50 nm. Since the absolute value of the light transmittance of the paperboard of the present invention itself is small and difficult to measure, the measurement was performed with reference to the filter paper. The light transmittance T of the paperboard of the present invention is represented by the following equation. That is, the NO. Assuming that the light transmittance of 5C (trade name, manufactured by Toyo Roshi Co., Ltd.) itself is to and the light transmittance of the paperboard itself is ti.

[Equation 1] T = (ti / to) × 100

◎ Discoloration The sample was immersed in water and a 1% citric acid aqueous solution at 20 ° C. for 24 hours, taken out, sandwiched between filter papers, and pressed at a pressure of 5 kg / kg.
Press for 4 hours at cm2. Thereafter, drying was performed at 105 ° C. for 2 hours using a hot air circulation type dryer, and the color adhering to the filter paper was visually determined. A sample without coloring was rated as ○, and a sample with coloring was rated as ×.

The tensile strength was measured according to JIS P-8113.

Example 1 Pulp obtained by mixing 70 parts of LBKP and 30 parts of NBKP was beaten with a Niagara beater at a stock density of 2.5% and a Canadian standard freeness (CSF) of 450 ml to give a pulp slurry. And This pulp slurry is added to a wet paper strength agent WS-570 (trade name, manufactured by Nippon PMC Co., Ltd.).
0.28 parts, alkyl ketene dimer sizing agent AS-
201 (trade name, manufactured by Nippon PMC Co., Ltd.) 0.22 parts,
Hermide EX Copolymerized Polyacrylamide Paper Strengthener
0.3 parts of -370 (trade name, manufactured by Harima Chemicals, Inc.)
0.3 parts of Hoffman-modified polyacrylamide paper strength agent Star Gum KX-12 (trade name, manufactured by Seiko Chemical Co., Ltd.) was added to the pulp to prepare a papermaking raw material for the surface layer and the back layer.

Pulp slurry prepared in the same manner as for the surface layer and the back layer
100% Lee in 4% viscose with carbon black
Colored original rayon fiber seluka added and colored
BR (trade name, manufactured by Kojin Co., Ltd.) at 18 g / m²become
0.28 parts of wet paper strength agent, alkyl ketone
0.22 parts of ten dimer sizing agent, copolymerized polyacryl
0.3 parts of luamide paper strength agent, Hoffman-modified polyac
0.3 parts of a lylamide paper strength agent was added to
Fees. These papermaking raw materials were used on a TAPPI type paper machine.
The back layer, the middle layer, and the surface layer are composed of three layers in this order.
180 g / m ²Paper so that the total basis weight is 30
0 g / m²Was obtained.

Example 2 Pigmented vinylon fiber colored by kneading 10% of carbon black with the pigmented fiber to be mixed into the middle layer (manufactured by Co., Ltd.)
Paper made in the same manner as in Example 1 except that the mixing amount in the middle layer was 36 g / m ² .

Example 3 The raw fiber mixed with the middle layer was viscose and activated carbon pigment was 4
% Paper was made in the same manner as in Example 1 except that the colored rayon fibers were colored by adding so as to obtain a colored original rayon fiber.

The paper in Example 4 dyed rayon fibers to be mixed into the intermediate layer were mixed at a 19 g / ^{m 2,} the entire board, as the basis weight of the middle layer is 127 g / ^{m 2} basis weight 230 g / ^{m 2} Papermaking was performed in the same manner as in Example 1 except for the above.

Table 1 shows the main papermaking conditions of Examples 1 to 4.

[Table 1]

Comparative Example 1 The mixed amount of the soaked rayon fibers to be mixed with the middle layer was 5.4 g /
except that the m ² is paper in the same manner as in Example 1 to obtain a paperboard.

Comparative Example 2 The mixed amount of the raw rayon fiber to be mixed with the middle layer was 144 g /
except that the m ² is paper in the same manner as in Example 1 to obtain a paperboard.

Comparative Example 3 Papermaking was carried out in the same manner as in Example 1 except that the dyed fiber mixed with the middle layer was added to viscose so that activated carbon pigment was added to a concentration of 0.5% to obtain dyed dyed rayon fiber.

COMPARATIVE EXAMPLE 4 100 parts of LUKP were subjected to Canadian standard freeness (CSF) 4
Beat to 50 ml to make a pulp slurry, 0.28 parts of wet paper strength enhancer of Example 1, 0.22 parts of alkyl ketene dimer-based sizing agent, 0.3 parts of copolymerized polyacrylamide-based paper strength enhancer, Hoffman modified A paperboard was obtained in the same manner as in Example 1, except that 0.3 part of a polyacrylamide-based paper strength enhancer was added and adjusted and used as a middle layer papermaking raw material.

Comparative Example 5 The raw materials prepared for the surface layer and the back layer in the same manner as in Example 1
The middle layer and the back layer were used for all layers, and the cationic paper dye Kayacell Black CN-liq (trade name, manufactured by Nippon Kayaku Co., Ltd.) was added to the papermaking raw material for the middle layer in an amount of 20% based on the pulp solid content. Paper was made in the same manner as in Example 1.

The main papermaking conditions of Comparative Examples 1 to 5 are shown in Table 2.

[Table 2]

Tables 3, 4 and 5 show the measurement results of the light transmittance, discoloration and tensile strength of the paperboards obtained in the above Examples and Comparative Examples, respectively.

[Table 3]

[Table 4]

[Table 5]

From the results of the above examples, it can be seen that the composition has a high light-shielding property when the wavelength of light is in the range of 250 nm to 850 nm, does not adhere dyes or color pigments to the contents, and is suitable for food packaging. A suitable paperboard was obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Go Kubota 5-43, Minami-Kasugaoka, Ibaraki-shi, Osaka F-term (reference) 4F100 AA00B AA00H AA37B AA37H AJ05B AK21B AK26A AK26C AK26H BA03 BA06 BA10A BA10C BA13 CA13BDGA DG10C DH00B GB16 GB23 HB00B JL10B JN02 YY00B 4L055 AF10 AF43 AG02 AG96 AH01 AJ01 BD18 EA04 EA32 FA12 GA06

Claims (3)

[Claims] 1. A paperboard having high light-shielding properties, comprising at least three layers of a surface layer, a middle layer and a back layer, wherein the middle layer contains chemical fibers colored by kneading an inorganic pigment. 2. The mixing amount of the colored chemical fiber in the middle layer is 1
The paperboard having high light-shielding properties according to claim 1, wherein the weight is ² to 60 g / m2. 3. The paperboard having high light-shielding properties according to claim 1, wherein an addition ratio of the colored inorganic pigment kneaded into the chemical fiber is 1 to 50% by weight.