JP2015030955A - Base paper for container and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide base paper for containers excellent in printability, formability of a thermoplastic resin layer, adhesion and suppression of cracking in production and processing and occurrence of paper powder and its production method.SOLUTION: Base paper for containers using a paper substrate has a pigment coating layer which contains a pigment and a water-soluble binder, on the side of the paper substrate to serve as an outside surface of a paper, and the pigment contains light calcium carbonate. The base paper for containers has polyethyleneimine on the side of the base substrate to serve as an inside surface of the container. The content of the water-soluble binder is preferably 2-12 pts.mass to 100 pts.mass of the pigment.

Description

  The present invention relates to a container base paper having a pigment coating layer on the outer surface side as a container of a paper substrate.

  Conventionally, paper base materials have been widely used for containers filled with ice cream, yogurt or the like because they do not break, are lightweight, and can be incinerated. The container base paper is processed into a laminated sheet in which printing is performed on one side and a thermoplastic resin layer is provided on at least the other side. Then, in order to form as a container, the laminated sheet is subjected to folding ruled line processing and punching processing in accordance with the container shape, and is folded and assembled along the ruled line placed in the laminated sheet.

  As described above, since the container is processed through many steps, various properties are required for the container base paper to be used. First, in order to prevent the filled contents from penetrating into the paper base material and leaking, the thermoplastic resin layer is free of cracks, thickness unevenness, and does not peel off from the paper base material. Layer formability and adhesion are required. Further, since the container base paper is subjected to ruled line processing, punching, and bending processing, it is necessary to suppress the generation of cracks and paper dust in these processing. Furthermore, the container surface is printed, but high printability is required in order to enhance product differentiation and advertising functions.

  In order to impart these characteristics, a liquid container base paper has been proposed which is composed of three paper layers and defines the weight ratio of the layers and the internal bond strength (Patent Document 1). However, in this proposal, although there is a possibility that cracking and generation of paper dust can be suppressed with respect to the bending process or the like, a sufficiently satisfactory one in terms of print quality, formability of the thermoplastic resin layer, and adhesion cannot be obtained. .

  In order to improve printing quality, a coated white paperboard provided with two coating layers containing titanium dioxide has been proposed (Patent Document 2). However, in this proposal, although the printing quality is improved, it is not used for processing peculiar to the base paper for containers. Therefore, cracking due to bending, etc., suppression of paper dust, formability of thermoplastic resin layer, adhesion No properties are given.

  In addition, a processed paper for paper use and a paper base paper having a coating layer containing a pigment, a binder and the like to improve printability have been proposed (Patent Documents 3 and 4). However, with these proposals, although there is a possibility that the printing quality may be improved, cracks due to bending and the like, and suppression of paper dust are not sufficient, and the formability and adhesion of the thermoplastic resin layer are satisfactory. You can't get anything.

  As described above, the present situation is that the various characteristics required for the container base paper are not yet obtained in a high dimension.

JP 2009-242999 A JP 2006-328574 JP 9-158089 A JP2005-105467

  The present invention provides a base paper for containers excellent in printability, formability of thermoplastic resin layer, adhesion, and cracking during processing and processing, and suppression of paper dust, and a method for manufacturing the base paper for containers. Main purpose.

  As a result of intensive studies on the printability of the base paper for containers, the formability of the thermoplastic resin layer, adhesion, and cracking during production and processing, and the suppression of paper dust, the present inventors have found that the outer surface of the paper substrate is a container. By having a pigment coating layer containing light calcium carbonate and a water-soluble binder on the side to become, and having polyethyleneimine on the side to become the inner surface as a container for the paper base material, the above problems have been solved. That is, the present invention relates to the following container base paper.

  Item 1: A base paper for a container containing a paper base material, having a pigment coating layer containing a pigment and a water-soluble binder on the outer surface side as a container of the paper base material, wherein the pigment comprises light calcium carbonate A container base paper comprising polyethylene imine on the inner surface side as a container of the paper base material.

  Item 2: The container base paper according to Item 1, wherein the pigment coating layer contains 2 to 12 parts by mass of a water-soluble binder with respect to 100 parts by mass of the pigment.

  Item 3: The container base paper according to Item 1 or 2, wherein the pigment coating layer further contains kaolin, and the mass ratio of kaolin and light calcium carbonate is 35:65 to 60:40.

  Item 4: The container base paper according to any one of Items 1 to 3, wherein the water-soluble binder is at least one selected from starch, derivatives thereof, and casein.

  Item 5: The container base paper according to any one of Items 1 to 4, wherein the paper base material does not contain waste paper pulp.

  Item 6: The paper base material has three or more paper layers, and an intermediate layer formed between the front layer and the back layer contains 350 to 400 ml of Canadian standard freeness (based on JIS P 8121). Container base paper of any one of 1-5.

  Item 7: In the method for producing a container base paper according to any one of Items 1 to 6, the step of forming the pigment coating layer on the outer surface of the paper base material as a container, the paper base material The manufacturing method of the base paper for containers including the process of providing a polyethyleneimine by the calendar coating to the side used as the inner surface of this.

  The container base paper of the present invention has high coating layer strength, and is excellent in printability, thermoplastic resin layer formability, adhesion, and cracking and paper powder suppression during production and processing.

  In general, a container base paper containing a paper base has higher rigidity than ordinary coated paper for printing, and is bent and cracked when formed as a container by heat sealing or the like compared to white paperboard processed into a decorative box, etc. Paper dust becomes a quality problem. Furthermore, when the coating layer is provided on the paper base material constituting the container base paper, the problem of cracking due to bending or the like, the problem of paper dust becomes serious, or the coating layer is formed under severe conditions such as smoothing treatment. There is a problem of dropping off, and it is not easy to provide a pigment coating layer. In the present invention, by having a pigment coating layer containing light calcium carbonate and a water-soluble binder on the outer surface side as a container of a paper base material constituting the base paper for containers, the printability is excellent and the coating layer There is no fear that the coating layer will fall off in the bending process or the like when forming as a container with a high strength or a smoothing process such as a calendar. For this reason, conventionally, when applying or impregnating polyethyleneimine or the like to a paper base material having a pigment coating layer by calendar coating or the like, the components of the coating layer that have fallen off due to pressure and friction are mixed in as a paint cake, Although there was a problem that a mold enters when molded as a container, in the present invention, a base paper for a container that does not cause such a problem can be obtained regardless of means for applying or impregnating.

  The paper base material in the present invention may consist of a single paper layer or a plurality of paper layers. In the present invention, at least when formed as a container, it has a multilayer structure comprising a surface layer on the outer surface side of the container, a back layer on the inner surface side, and an intermediate layer formed between the surface layer and the back layer. Is preferred. By making it into multiple layers, it is possible to improve the interlaminar strength by using a pulp having a relatively high beating degree for the middle layer and prevent delamination. The number of paper layers is preferably 3 or more. However, the upper limit is not particularly limited, and may be about 6 layers. The particularly preferred number of layers is 5 or 6.

The basis weight of the container base paper in the present invention is preferably about 100 to 500 g / ^{m 2,} about 140~470g / ^{m 2} is more preferable. By setting it as 100 g / m < ² > or more, rigidity can be improved and the swelling which becomes a problem when filling the contents after container formation can be suppressed. The moldability as a container can be improved by setting it as 500 g / m < ² > or less.

  Printing is usually performed on the side that becomes the outer surface when formed as a container. Further, printing may be performed on a thermoplastic resin layer provided on the outer surface or the inner surface in order to impart water resistance or acid resistance to the contents, and the uneven pattern on the paper surface is also reflected in the thermoplastic resin layer. For this reason, the paper surface is preferably as smooth as possible. In the present invention, the Parker print surf smoothness based on JIS P 8151 on the surface of the pigment coating layer of the base paper for containers is preferably 2 μm or less, and more preferably 1.5 μm or less. Gravure printing aptitude can be improved by setting it as 2 micrometers or less.

  As the raw material pulp for forming the paper layer of the paper base material in the present invention, various pulps can be used as long as the effects of the present invention are not impaired. Chemical pulp (conifer, hardwood), mechanical pulp, waste paper pulp, non-wood pulp And synthetic pulp. These pulps may be used alone or in combination of two or more.

  The container base paper in the present invention is not particularly limited in use, but it is preferably used for food applications such as hot drinks, cold drinks, ice creams, yogurts by not including waste paper pulp in the paper layer. Can do.

  As the blending ratio of the middle layer pulp, it is preferable that the softwood bleached kraft pulp (hereinafter also referred to as NBKP) is 5 to 30% of the total solid amount of the middle layer pulp. By setting it to 5% or more, interlayer strength can be improved and delamination can be prevented. On the other hand, by setting it to 30% or less, there is no problem that the paper is tightened and the density is increased and the moldability as a container is deteriorated.

  As the pulp blending ratio of the front and back layers, it is preferable that hardwood bleached kraft pulp (hereinafter also referred to as LBKP) is 60% or more of the total solid content of the pulp in the front and back layers. Thereby, the smoothness of the front and back layers can be improved and the cushioning properties can be improved, and excellent gravure printing aptitude can be obtained.

  The mixed freeness of the raw pulp used in the present invention is preferably such that the Canadian standard freeness based on JIS P 8121 is in the range of 350 to 500 ml. By setting the freeness to 350 ml or more, it is possible to avoid troubles due to water retention in the paper making process without significantly reducing the line speed. On the other hand, by setting it to 500 ml or less, unevenness on the paper surface can be reduced, printability can be improved, and paper strength can be increased. In order to avoid troubles in the paper making process, the freeness of the front and back layers is preferably set higher than the freeness of the middle layer. The freeness of the middle layer in the present invention is preferably 350 ml or more and 400 ml or less, more preferably 360 ml or more and 390 ml or less. By setting it as 350 ml or more, the trouble derived from the water retention in a papermaking process can be avoided, without reducing a line speed significantly. On the other hand, by setting it to 400 ml or less, interlayer strength can be improved and delamination can be prevented.

  In the present invention, a softener may be contained in the front and back layers or the middle layer. By containing a softening agent, interfiber bonding can be inhibited and the fiber itself can be softened. Therefore, the effect | action that it becomes easy to bend along the ruled line put into the lamination sheet | seat acts, It becomes possible to respond | correspond to various ruled line shapes, and the moldability as a container can be improved greatly.

  In order to improve flexibility, it is more effective to contain a softener in all layers of the container base paper. However, if it is contained in the front and back layers, the surface strength is greatly reduced, and the front and back surfaces of the container base paper Inadequate adhesion with the thermoplastic resin layer provided on the surface is undesirable. Therefore, it is preferable not to contain a softening agent other than the middle layer.

  The softening agent that can be used in the present invention is not particularly limited as long as it weakly hydrophobizes the pulp fiber surface and can inhibit interfiber bonding. For example, oil-based nonionic surfactants, sugar alcohol-based nonionic surfactants, polyhydric alcohol-type nonionic surfactants, higher alcohols, ester compounds of polyhydric alcohols and fatty acids, higher alcohols or polyoxygens of higher fatty acids Examples include alkylene adducts, polyoxyalkylene adducts of ester compounds of polyhydric alcohols and fatty acids, polyoxyalkylene adducts of higher fatty acid esters, fatty acid polyamidoamines, polyalkylene polyamine fatty acid epichlorohydrin polycondensates and the like.

  In the present invention, various internal chemicals can be used together with the raw material pulp as required. For example, water-repellent agents such as fluorine resins, polyamide resins, wax emulsions, rosin sizing agents, styrene / maleic acid, alkyl ketene dimers, alkenyl succinic anhydrides, natural and synthetic paper additive sizing agents, various types Paper strength enhancers, wet paper strength agents, starch, drainage yield improvers, water resistance agents, antifoaming agents, fillers such as talc, various dyes, and the like can be used as appropriate. However, in the present invention, it is preferable that the paper layer does not contain a fluorescent dye for food applications such as hot drinks, cold drinks, ice creams and yogurts.

  The pH at the time of papermaking in the present invention can be arbitrarily selected as necessary in the neutral papermaking region from about 4.0 which is acidic papermaking to about 6-8.

  The paper machine for producing the container base paper of the present invention is not particularly limited, but a machine capable of making three or more layers is preferable. For example, paper is made by combining with a long net paper machine, a short net paper machine, a circular net paper machine, etc. to produce a base paper for containers.

  In the present invention, although there is no particular limitation, a machine calendar and / or a super calendar, a gloss calendar, a soft nip before and / or after various coating apparatuses such as a coating process for forming a coating layer. By passing the paper through a calendar such as a calendar and performing a smoothing treatment, a product finish excellent in gravure printing suitability can be applied.

  In the present invention, a pigment coating layer containing light calcium carbonate and a water-soluble binder as pigments is provided on the outer surface (paper substrate surface side) as a paper substrate container. As a result, the strength of the pigment coating layer is increased, and there is no fear that the coating layer will fall off due to a smoothing treatment such as a calendar, and it is excellent in gravure printing suitability and crack and paper powder suppression during manufacturing and processing. Container base paper can be obtained. Furthermore, in this invention, since it has a polyethyleneimine in the side used as the inner surface (back side of a paper base material) as a container of a paper base material, it is the opposite side of a paper base material with respect to the back surface process for providing the polyethyleneimine And a pigment coating layer having a strength that the surface side can sufficiently withstand.

  The pigment coating layer can be formed by applying and drying a paint containing light calcium carbonate and a water-soluble binder. For example, when the paper layer of the paper base is composed of three layers, the paint may be applied on the outer surface layer as a container. In the present invention, it is preferable that the pigment coating layer has a multilayer structure including a first coating layer and a second coating layer formed on the first coating layer from the side close to the paper substrate. By making the pigment coating layer into a multilayer structure, it is possible to easily adjust the coating amount within a desired range, and to provide a coating surface free from coating defects (uncoated parts) that significantly impairs the design of the container. Can be obtained. In other words, two or more coating layers may be formed by using one kind of paint, or two or more coating layers may be formed by using two or more kinds of paints for each layer. Since the pigment coating layer in this invention is excellent also in coating suitability, it is preferable that the composition of the coating material which forms each layer is the same.

  The paint forming the pigment coating layer preferably has a B-type viscosity of 100 to 500 mPa · s at a liquid temperature of 25 ° C. and 60 rpm, and a high shear viscosity of 8 to 15 mPa · s at 8800 rpm.

  As a method of adjusting the viscosity of the paint to the above range, in addition to adjusting the solid content concentration of the paint as appropriate, as a constituent of the pigment coating liquid, the blending ratio of various pigments, the type of binder, the blending of pigment and binder Viscosity can be adjusted by blending various auxiliary agents such as ratio and thickening water retention agent. The solid content concentration of the paint is not particularly limited as long as the viscosity of the paint falls within the above range, but the drying load is reduced in the drying process after coating, and the coating speed is increased. From the viewpoint of improving the production efficiency of the base paper for containers, the solid content concentration is preferably 45 to 55% by weight.

  The content ratio of light calcium carbonate in the solid amount of all pigments in the pigment coating layer is preferably 35 to 70% by mass, more preferably 40 to 65% by mass, and still more preferably 45 to 60% by mass. By setting the content to 35% by mass or more, the whiteness can be increased without using a fluorescent dye which is undesirable for food use, and the color developability of the printed matter can be improved. On the other hand, by setting it to 70% by mass or less, insufficient coating layer strength due to excessive refinement of the pigment forming the coating layer is prevented, and the components of the pigment coating layer do not fall off in the smoothing treatment by a calendar or the like. When molded as a container, there is no risk of bending cracks or powder falling.

  In the pigment coating layer in the present invention, kaolin is preferably used as a pigment in combination with light calcium carbonate. The mass ratio of kaolin and light calcium carbonate is preferably 35:65 to 60:40, more preferably 40:60 to 55:45. By setting the kaolin ratio to 35% by mass or more, a highly smooth coated surface is obtained, the gravure printing suitability is excellent, and the glossiness can be increased. On the other hand, whiteness can be raised by setting it as 60 mass% or less.

  As a pigment, another pigment can also be contained in the range which does not impair the effect of this invention. Examples of the other pigments include inorganic pigments such as calcined kaolin, talc, aluminum hydroxide, titanium dioxide, barium sulfate, zinc oxide, satin white, heavy calcium carbonate, and calcium sulfate, and organic pigments such as plastic hollow particles. .

  In this invention, as content of the water-soluble binder in a pigment coating layer, 2-12 mass parts is preferable with respect to 100 mass parts of pigments containing light calcium carbonate, 3-10 mass parts is more preferable, 4- 9 mass parts is still more preferable, and 4-6 mass parts is especially preferable. By setting it as 2 mass parts or more, the water retention of a coating material can be improved, the uniform coating layer without a soaking | uniform-in unevenness can be formed, and gravure printing aptitude can be improved. Further, the strength of the pigment coating layer is increased, and there is no possibility that the coating layer falls off due to a smoothing process such as a calendar or a bending process when forming as a container. On the other hand, by setting it to 12 parts by mass or less, the gravure halftone dot missing rate can be greatly reduced and the gravure printing aptitude can be improved. In addition, an effect of increasing the glossiness can be obtained.

  Various known binders can be used as the water-soluble binder in the present invention. Specific examples of the water-soluble binder include starch and derivatives thereof, partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, modified polyvinyl alcohol, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose and ethylcellulose, and polyacrylic. Acid soda, polyvinylpyrrolidone, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, Casein etc. are mentioned. Among these, from the viewpoint of improving the strength of the coating layer, at least one selected from starch and derivatives thereof and casein is preferable, and starch and derivatives thereof are more preferable. Specific examples of these starches include oxidized starch, positive starch, esterified starch, and dextrin. Among these starches, oxidized starch is preferable.

  In the present invention, it is preferable that a copolymer obtained from latex is contained in the pigment coating layer in combination with a water-soluble binder. The content of the copolymer obtained from the latex is preferably 10 to 25 parts by mass and more preferably 15 to 20 parts by mass with respect to 100 parts by mass of the total pigment containing light calcium carbonate. By setting it as 10 mass parts or more, the intensity | strength of a coating layer can be improved further. On the other hand, since the intensity | strength of a coating layer will be saturated if it contains exceeding 25 mass parts, manufacturing cost can be suppressed by setting it as 25 mass parts or less.

  The mass ratio of the copolymer obtained from the water-soluble binder and latex in the pigment coating layer is preferably in the range of 5:95 to 30:70. By setting the mass ratio of the water-soluble binder to 5 or more, it is possible to increase the water retention of the paint and form a uniform coating layer. On the other hand, by setting it to 30 or less, the gravure halftone dot loss rate can be greatly reduced, and the gravure printing suitability can be improved.

  Specific examples of the latex include conjugated diene copolymer latex such as styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, styrene-methyl methacrylate-butadiene copolymer latex, acrylic acid ester and // Acrylic polymer latex such as polymer or copolymer latex of methacrylic acid ester, vinyl polymer latex such as ethylene-vinyl acetate polymer latex, or these various polymer latexes with functional groups such as carboxyl groups Examples thereof include water-dispersible binders such as a polymer or copolymer latex modified with a containing monomer.

  The latex is a styrene-butadiene having a gel fraction of 70% or more and a glass transition temperature (hereinafter also referred to as Tg) of −35 ° C. or more and 10 ° C. or less from the viewpoint of further improving the strength of the pigment coating layer. It preferably consists of a copolymer latex containing a copolymer.

  The method for forming the coating layer in the present invention is not particularly limited. For example, Mayer bar coating, plain bar coating, air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die An appropriate coating method such as coating can be employed.

  In the present invention, plain bar coating is preferred as the coating method because wear of the Mayer bar or blade due to the pigment in the paint affects the variation in the coating amount.

  When the pigment coating layer has a multilayer structure composed of the first coating layer and the second coating layer formed on the first coating layer from the side close to the paper substrate, the first coating layer is After forming by coating and drying, the second coating layer coating may be applied and dried on the first coating layer to form the second coating layer, or the first coating layer coating and After coating and laminating the coating material for the second coating layer, it may be dried to form the first coating layer and the second coating layer. In the present invention, from the viewpoint of obtaining a coated surface having no coating defects (uncoated portions), after the first coating layer coating is applied, the first coating layer coating is in a wet state without drying. It is preferable to apply the coating material for the second coating layer on the surface to which the first coating layer is applied, and then dry to form the first coating layer and the second coating layer.

The total coating amount of each paint is preferably about 6 to 15 g / m ² by dry weight, and more preferably about 8 to 12 g / m ² . Gravure printing aptitude can be improved by setting it as 6 g / m < ² > or more. On the other hand, by setting it as 15 g / m ² or less, there is no possibility that the coating layer is bent and cracked when formed as a container.

  The container base paper is usually provided with a thermoplastic resin layer on at least the inner surface of the container for the purpose of imparting water resistance and acid resistance to the contents. The thermoplastic resin layer can be provided using a known means such as lamination or coating. Examples of the thermoplastic resin include polyethylenes such as low density polyethylene, medium density polyethylene, and high density polyethylene, and polyolefin resins such as polypropylene. Furthermore, a film made of a saturated polyester resin such as polyethylene terephthalate or polybutylene terephthalate, an ethylene vinyl alcohol copolymer or the like may be provided as an intermediate layer between the container base paper and the thermoplastic resin layer. In addition, an inorganic compound made of silicon oxide, aluminum oxide, magnesium oxide, or the like may be deposited on at least one surface of the film in order to support a gas barrier function.

  In the present invention, at least the container of the paper base material has polyethyleneimine on the inner surface side. Thereby, the excellent formability and adhesiveness of the thermoplastic resin layer can be obtained. In order to impart polyethyleneimine to the inner surface of the paper substrate, it is preferable to perform a backside treatment such as applying or impregnating the backside of the paper substrate with an aqueous solution of polyethyleneimine. Depending on the wettability of the aqueous solution and the type of thermoplastic resin, polyvinyl alcohol, starch, polyacrylamide, acrylic resin, styrene-butadiene resin, styrene-isoprene resin, polyester resin, ethylene-vinyl acetate resin, acetic acid A vinyl-vinyl alcohol resin, a urethane resin, a fluorine resin, or the like can be used in combination.

  In the present invention, by providing a specific pigment coating layer containing light calcium carbonate on the surface of the paper substrate opposite to the surface having polyethyleneimine, there is no possibility of causing a blocking phenomenon in which the front and back are in close contact with each other. The backside treatment using an aqueous solution can be performed without providing a special drying step.

  The backside treatment method using polyethyleneimine is not particularly limited. For example, a bar coater, a blade coater, an air knife coater, a rod coater, a bill blade coater, a bellbaper coater, a gate roll coater, a size press and a calendar size press. Etc.

  Among these methods, the pigment coating layer in the present invention is excellent in strength, and since there is no risk of the coating layer falling off by a smoothing process such as a calendar, the coating process and the smoothing process can be performed simultaneously. Since the aspect which provides polyethyleneimine by the calendering which can be performed can fully exhibit the effect of this invention, it is preferable. In this case, it is preferable to apply water to the pigment coating layer side from the viewpoint of curl correction.

The amount of polyethyleneimine present on the inner surface of the paper base container is not particularly limited, but is preferably about 0.02 to 0.5 g / m ² by dry weight, and 0.04 to 0.2 g / m ^2. The degree is more preferable. By setting it as 0.02 g / m < ² > or more, the formability of a thermoplastic resin layer and adhesiveness can be improved further. On the other hand, if it exceeds 0.5 g / m ² , the formability and adhesiveness are saturated and rather tend to be lowered, so 0.5 g / m ² or less is preferable.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” indicate “part by mass” and “% by mass”, respectively.

Example 1
(Preparation of paper substrate)
As a pulp raw material, 36 parts of NBKP and 64 parts of LBKP were mixed and beaten to obtain a pulp slurry for front and back layers having a Canadian standard freeness of 400 ml. Using the obtained pulp slurry, with respect to 100 parts of the pulp raw material, 0.84 part of polyacrylamide (manufactured by Arakawa Chemical Industries, Polystron 117) as an internal paper strength enhancer, and rosin size as an internal additive sizing agent An agent (Arakawa Chemical Industries, Size Pine N-771) 0.68 part and 2.0 parts of aluminum sulfate were mixed in solid amounts, respectively, to prepare a stock for the front and back layers.

  15 parts of NBKP and 85 parts of LBKP were mixed and beaten as pulp raw materials to obtain a pulp slurry for middle layer of Canadian standard freeness of 380 ml. Using the obtained pulp slurry, with respect to 100 parts of the pulp raw material, 0.3 part of polyacrylamide (manufactured by Arakawa Chemical Co., Ltd., Polystron 117) as an internal paper strength enhancer, and rosin size as an internal additive sizing agent 0.5 parts of the agent (manufactured by Arakawa Chemical Industry Co., Ltd., Size Pine N-771) and 1.9 parts of aluminum sulfate were mixed in solid amounts to prepare a stock for the middle layer.

Using these stocks, paper was made in a five-layer structure to obtain a paper base material for container base paper having a basis weight of 290 g / m ² .

(Preparation of paint for pigment coating layer)
As a pigment, 50 parts of kaolin (manufactured by BASF, Ultra White 90) and 50 parts of light calcium carbonate (manufactured by Okutama Kogyo Co., Ltd., TP123CS) are used, and as a dispersant, 0.4 part of sodium polyacrylate (manufactured by Toagosei Co., Ltd., Aron T50) Were mixed in solid amounts, and a pigment slurry having a solid content concentration of 59% was prepared using a Coreless disperser.

  Using the above pigment slurry, styrene-butadiene copolymer latex with 6 parts of oxidized starch (manufactured by Oji Cornstarch, GRS-T110), 80% gel fraction, and Tg of 7 ° C with respect to 100 parts of the total solid content of the pigment. 19 parts (hereinafter also referred to as latex A) were mixed in solid amounts, and water was further added to prepare a paint having a solid content concentration of 45%.

(Preparation of container base paper)
Using the pigment coating layer paint thus obtained, the paper substrate surface obtained above was coated with a wire bar so as to have a dry mass of 10 g / m ^2, and further dried to obtain a pigment coating. After the construction layer was formed, the paper was passed through a calendar composed of a combination of a metal roll and a wool roll. Furthermore, 0.2 g / m ² of a polyethyleneimine aqueous solution having a solid content concentration of 1% was applied by dry weight on the back surface of the paper substrate using a plain bar to obtain a base paper for containers.

Example 2
A base paper for containers was obtained in the same manner as in Example 1 except that in preparing the pigment coating layer paint of Example 1, the amount of oxidized starch in the paint was changed to 2 parts instead of 6 parts.

Example 3
A base paper for containers was obtained in the same manner as in Example 1 except that the amount of oxidized starch in the paint was changed to 4 parts instead of 6 parts in the preparation of the paint for the pigment coating layer of Example 1.

Example 4
A base paper for containers was obtained in the same manner as in Example 1 except that the amount of oxidized starch in the paint was changed to 12 parts instead of 6 parts in the preparation of the paint for the pigment coating layer of Example 1.

Example 5
In preparation of the paint for a pigment coating layer of Example 1, the amount of kaolin was changed to 60 parts instead of 50 parts, and the amount of light calcium carbonate was changed to 40 parts instead of 50 parts. A container base paper was obtained in the same manner.

Example 6
In preparation of the paint for a pigment coating layer of Example 1, the amount of kaolin was 35 parts instead of 50 parts, and the amount of light calcium carbonate was 65 parts instead of 50 parts. A container base paper was obtained in the same manner.

Example 7
A base paper for containers was obtained in the same manner as in Example 1 except that in the preparation of the paint for the pigment coating layer of Example 1, casein (Nisshi Kyoyoku, Arashid) was used instead of oxidized starch.

Example 8
A base paper for containers was obtained in the same manner as in Example 1 except that the amount of latex A was changed to 14.5 parts instead of 19 parts in the preparation of the pigment coating layer paint of Example 1.

Example 9
A container base paper was obtained in the same manner as in Example 1 except that the amount of latex A was changed to 22 parts instead of 19 parts in the preparation of the pigment coating layer paint of Example 1.

Example 10
In preparation of the pigment coating layer coating material of Example 1, instead of latex A, a styrene-butadiene copolymer latex (hereinafter also referred to as latex B) having a gel fraction of 87% and Tg-34 ° C. was used. Except for the above, a container base paper was obtained in the same manner as in Example 1.

Example 11
In preparing the pigment coating layer paint of Example 1, instead of latex A, a styrene-butadiene copolymer latex (hereinafter also referred to as latex C) having a gel fraction of 56% and Tg of 18 ° C. was used. In the same manner as in Example 1, a container base paper was obtained.

Example 12
Instead of producing the container base paper of Example 1, using the pigment coating layer coating material described in Example 1 and a paper base material, a plain bar having a dry mass of 5 g / m ^{2 on the} paper base material surface was obtained. While the paint is wet, apply the same paint on the coated surface with a plain bar so that the dry mass is 5 g / m ^2, and then dry and apply the pigment. A layer was formed. In addition, a smoothing process was performed with a calendar, and a polyethyleneimine aqueous solution having a solid content concentration of 0.86% was applied to the back surface of the paper substrate by calendar coating to a dry weight of 0.04 g / m ² to obtain a base paper for containers .

Example 13
A container base paper was obtained in the same manner as in Example 1 except that the amount of oxidized starch in the paint was 9 parts instead of 6 parts in the preparation of the paint for the pigment coating layer of Example 1.

Example 14
In the preparation of the paint for a pigment coating layer in Example 1, the amount of kaolin was changed to 55 parts instead of 50 parts, and the amount of light calcium carbonate was changed to 45 parts instead of 50 parts. A container base paper was obtained in the same manner.

Example 15
In the preparation of the paint for a pigment coating layer of Example 1, the amount of kaolin was changed to 40 parts instead of 50 parts, and the amount of light calcium carbonate was changed to 50 parts instead of 50 parts. A container base paper was obtained in the same manner.

Example 16
A container base paper was obtained in the same manner as in Example 1 except that the amount of latex A was changed to 15.0 parts instead of 19 parts in preparing the pigment coating layer paint of Example 1.

Example 17
Container base paper was obtained in the same manner as in Example 1 except that the amount of latex A was changed to 20 parts instead of 19 parts in the preparation of the pigment coating layer paint of Example 1.

Comparative Example 1
In preparing the pigment coating layer coating solution of Example 1, a container base paper was obtained in the same manner as in Example 1 except that the oxidized starch was not added.

Comparative Example 2
In the preparation of the coating liquid for the pigment coating layer of Example 1, the base paper for containers was prepared in the same manner as in Example 1 except that heavy calcium carbonate (manufactured by Pimatech, FMT100) was used instead of light calcium carbonate. Obtained.

Comparative Example 3
In Example 12, a base paper for containers was obtained in the same manner as in Example 12 except that a polyvinyl alcohol aqueous solution having a solid content concentration of 0.86% was used instead of the polyethyleneimine aqueous solution having a solid content concentration of 0.86%. .

Comparative Example 4
In Example 12, except that the solid content concentration 0.86% polyethylenimine aqueous solution was not 0.04 g / m ² coating on a dry weight on the back paper substrate by a calender coating, in the same manner as in Example 12 A container base paper was obtained.

  The container base paper thus obtained was evaluated as follows. The results were as shown in Table 1. The container base paper was pretreated according to JIS P8111.

(Paint water retention)
Using an AA-GWR water retention meter (manufactured by SMT), measurement was performed under conditions of a pore size 0.4 μm filter, a pressure of 100 kPa, and a contact time of 30 seconds. The smaller the value, the better the water retention.

(Coating layer strength)
After printing on the pigment coating layer using an offset ink using an RI printer (Ming Seisakusho), the coating layer strength (degree of picking) was visually evaluated.
○: Excellent coating layer strength, and there is no risk of the coating layer dropping off even under severe conditions such as smoothing or bending. Δ: Slightly superior coating layer strength, smoothing or bending. In use under severe conditions such as processing, there is a slight risk of the coating layer dropping off depending on the conditions. X: Coating layer strength is inferior, and coating is used in severe conditions such as smoothing and bending. There is a risk of falling off the layer

(Suitability for gravure printing)
Gravure printing was performed using a Ministry of Finance gravure printing tester, and the degree of dot missing was visually evaluated according to the following criteria.
○: Almost no halftone dots are observed in all gradation parts. ○ ': Some halftone dots are observed depending on the gradation parts (low gradation parts). Missing dots X: Many missing dots in all gradations

(Adhesion)
A thermoplastic resin layer made of low-density polyethylene was provided on the back surface of the container base paper, and the presence or absence of poor adhesion between the container base paper and the thermoplastic resin layer was visually evaluated.
○: There is no portion with poor adhesion.
X: There exists a part of poor adhesion.

(Whiteness)
The whiteness of the pigment coating layer side was measured according to JIS P 8148 using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd., SC-10WT type).

(Glossiness)
The glossiness on the pigment coating layer side was measured using a glossmeter (GM-26D, manufactured by Murakami Color Research Laboratory) under the conditions of an incident angle / light receiving angle of 75 degrees according to JIS Z 8741.

  Since the container base paper obtained by the present invention is excellent in printability, thermoplastic resin layer formability, adhesion, and cracking during production and processing, paper powder suppression, for general foods, acidic foods, It is suitable for paper containers for liquids and can be suitably used especially for food applications such as yogurt.

Claims (7)

  A container base paper containing a paper base material, having a pigment coating layer containing a pigment and a water-soluble binder on the outer surface side as a container of the paper base material, wherein the pigment contains light calcium carbonate, A base paper for containers having polyethyleneimine on the inner surface as a container of a paper base.   The container base paper of Claim 1 in which the said pigment coating layer contains 2-12 mass parts of water-soluble binders with respect to 100 mass parts of pigments.   The base paper for containers according to claim 1 or 2, wherein the pigment coating layer further contains kaolin, and the mass ratio of kaolin and light calcium carbonate is 35:65 to 60:40.   The base paper for containers of any one of Claims 1-3 whose said water-soluble binder is at least 1 sort (s) chosen from starch, its derivative (s), and casein.   The base paper for containers of any one of Claims 1-4 in which the said paper base material does not contain used paper pulp.   The paper base has three or more paper layers, and an intermediate layer formed between the front layer and the back layer contains 350 to 400 ml of pulp of Canadian Standard Freeness (based on JIS P 8121). The container base paper according to any one of 5.   In the manufacturing method of the base paper for containers of any one of the said Claims 1-6, the process of forming the said pigment coating layer in the side used as the outer surface as a container of the said paper base material, The container of the said paper base material The manufacturing method of the base paper for containers including the process of providing a polyethyleneimine to the side used as an inner surface by calender coating.