Paper adhesives and boxes

Abstract

To provide an adhesive that comprises a polyolefin resin and is used for bonding paper to achieve excellent adhesion.SOLUTION: The present invention provides an adhesive having excellent adhesion to even a paper substrate including a coating layer composed of a styrene acrylic resin or the like, and a box having sufficient adhesive strength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a paper adhesive using a modified polyolefin resin and to boxes laminated using the same. [Background technology]

[0002] Polyolefin resins such as polypropylene and polyethylene have excellent mechanical properties such as tensile strength, tear strength, and impact strength, as well as excellent water resistance and chemical resistance. Polyolefin resins also have various excellent properties, such as being lightweight, inexpensive, and easy to mold. Therefore, polyolefin resins are used in a variety of applications, including sheets, films, and molded products.

[0003] Furthermore, in recent years, there has been an increase in applications requiring heat resistance, and it is known that a resin with a relatively high melting point is used to solve this problem (see, for example, Patent Document 1). In the technology described in Patent Document 1, although the inclusion of a high-melting-point resin improves heat resistance, solution stability may decrease. Therefore, modified polyolefin resins that have good solution properties and heat resistance have been proposed (see, for example, Patent Document 2).

[0004] Furthermore, various types of paper containers and packaging materials using a paper base material have been used to package various items. In particular, in recent years, with the trend toward eliminating plastic, there has been a demand for boxes that can replace polystyrene foam, and waterproof liners for manufacturing such boxes have been attracting attention.

[0005] For example, Patent Document 3 describes the provision of a coating layer containing a styrene-acrylic resin to obtain paper with high moisture-resistant and waterproof properties. Patent Document 4 describes a moisture-proof liner having at least two coating layers on at least one side of a base paper, with a coating layer containing an acrylic copolymer and / or a styrene copolymer provided between the outermost coating layer and the base paper. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-210842 [Patent Document 2] Japanese Patent Application Publication No. 2018-150482 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-037839 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-162899 Summary of the Invention [Problem to be solved by the invention]

[0007] Generally, paper containers such as cardboard boxes are used to store heavy objects and for transporting and storing them. However, since the boxes are often stacked, they need to be firmly bonded at the adhesive joints and have sufficient strength. In view of the above circumstances, an object of the present invention is to provide an adhesive for paper that can achieve excellent adhesive properties, and a box made therefrom. [Means for solving the problem]

[0008] The present invention includes, but is not limited to, the following inventions. [1] An adhesive for paper having the following characteristics: Component (A): Polyolefin resin, Component (B): α,β-unsaturated carboxylic acid or its derivative A modified polyolefin resin modified by The modified polyolefin resin has a weight average molecular weight of 10,000 or more and less than 20,000, and a melting point of 50°C or more and less than 100°C. [2] The adhesive according to [1], wherein the modified polyolefin resin is further grafted with component (C): a (meth)acrylic acid ester. [3] Boxes glued together using the adhesives described in [1] or [2]. [4] The box according to [3], characterized in that the paper base material used for the box has a coating layer containing a styrene-acrylic resin. [5] The box according to [3] or [4], characterized in that the coating layer is a waterproof coating layer. [Effects of the Invention]

[0009] According to the present invention, a paper adhesive having sufficient adhesive strength can be obtained. By using the paper adhesive of the present invention to form a box, a box that is resistant to crushing and has high compressive strength can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a photograph showing the results of the peel test in Experiment 1 (left: ◎, center: ○, right: △). DETAILED DESCRIPTION OF THE INVENTION

[0011] The adhesive according to the present invention contains a thermoplastic resin, and when the paper substrate according to the present invention is laminated with a hot melt adhesive containing a thermoplastic resin, it is strongly bonded. [1. Modified polyolefin resin] The modified polyolefin resin of the present invention contains a graft-modified product obtained by graft-modifying component (A): a polyolefin resin (hereinafter also referred to as "component (A)") with component (B): an α,β-unsaturated carboxylic acid or a derivative thereof (hereinafter also referred to as "component (B)"), and component (C): (meth) (hereinafter also referred to as "component (B)").

[0012] The weight-average molecular weight of the modified polyolefin resin of the present invention is 10,000 or more but less than 200,000, preferably 50,000 or more but less than 10,000. When the weight-average molecular weight is 10,000 or more, the coating film after drying exhibits cohesive strength and can provide sufficient adhesion to paper. On the other hand, when the weight-average molecular weight is less than 200,000, sufficient solvent solubility can be ensured.

[0013] In this specification, Mw is a value calculated from measurements made by gel permeation chromatography (standard substance: polystyrene).

[0014] The melting point of the modified polyolefin resin of the present invention is preferably 50° C. or higher but lower than 100° C., more preferably 50° C. or higher but lower than 80° C. If the Tm is 50° C. or higher, sufficient water resistance under high temperature conditions can be further improved. On the other hand, if the melting point is 100° C. or higher, sufficient strength may not be exhibited when laminated to paper.

[0015] In this specification, the melting point measured by DSC is a value measured under the following conditions: In accordance with JIS K7121-1987, a DSC measuring device (manufactured by TA Instruments) was used to heat approximately 5 mg of a sample to 150°C for 10 minutes and maintain the melted state. The sample was then cooled at a rate of 10°C / min and maintained at a stable temperature of -50°C. The sample was then heated to 150°C at a rate of 10°C / min, and the peak melting temperature upon melting was evaluated as Tm. [1-1. Component (A): Polyolefin resin] Component (A) is not particularly limited and may be a homopolymer of one type of olefin or a copolymer of two or more types of olefins. Furthermore, when it is a copolymer, it may be a random copolymer or a block copolymer. The olefin preferably used is an α-olefin. Examples of the α-olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.

[0016] As component (A), polypropylene (propylene homopolymer), ethylene-propylene copolymer, propylene-1-butene copolymer, and ethylene-propylene-1-butene copolymer are more preferably used from the viewpoint of exhibiting sufficient adhesion to non-polar resin substrates such as polypropylene substrates, with ethylene-propylene-1-butene copolymer being particularly preferred.

[0017] Component (A) preferably contains 50 mol% or more of propylene-derived structural units out of 100 mol% of structural units. When the propylene-derived structural units are contained in this range, adhesion to resins contained in waterproof coating layers, such as styrene-acrylic resins, can be ensured. The melting point of component (A) is preferably 50° C. or higher but lower than 100° C., more preferably 50° C. or higher but lower than 80° C. This makes it easy to obtain a modified polyolefin resin having a melting point within the above range. The weight-average molecular weight of component (A) is 10,000 or higher but lower than 500,000, preferably 30,000 or higher but lower than 400,000.

[0018] Component (A) may be used singly or in combination of two or more types, in which case the ratio is not particularly limited. [1-2. Component (B): α,β-Unsaturated Carboxylic Acid or Its Derivative] Component (B) is an α,β-unsaturated carboxylic acid or a derivative thereof. Examples of α,β-unsaturated carboxylic acids and derivatives thereof include maleic acid, maleic anhydride, fumaric acid, citraconic acid, citraconic anhydride, mesaconic acid, itaconic acid, itaconic anhydride, aconitic acid, aconitic anhydride, himic anhydride, (meth)acrylic acid, and (meth)acrylic acid esters. Among these, maleic anhydride is preferred.

[0019] Component (B) may be at least one compound selected from the group consisting of α,β-unsaturated carboxylic acids and their derivatives, and may be a combination of one or more α,β-unsaturated carboxylic acids and one or more α,β-unsaturated carboxylic acid derivatives, a combination of two or more α,β-unsaturated carboxylic acids, or a combination of two or more α,β-unsaturated carboxylic acid derivatives.

[0020] The graft weight of component (B) in the graft-modified product is preferably 1 to 10% by weight, more preferably 2 to 8% by weight, based on 100% by weight of the graft-modified product. When the graft weight is 1% by weight or more, the resulting modified polyolefin resin can ensure adhesion to the resin contained in the waterproof coating layer, such as a styrene-acrylic resin. When the graft weight is 10% by weight or less, the generation of unreacted grafted material can be prevented, and sufficient adhesion to the resin substrate can be ensured.

[0021] The graft weight of component (B) is a value determined by alkali titration. [1-3. (Component (C): (meth)acrylic acid ester)] The (meth)acrylic acid ester has a structure represented by general formula (I), which is as follows: CH2=C(R 1 )COOR 2 (I) R 1 represents a hydrogen atom or a methyl group, and R 2 is C n H 2n+1 where n is an integer of 8 to 18. As the (meth)acrylic acid ester having the structure represented by formula (I), lauryl (meth)acrylate, tridecyl (meth)acrylate, octyl (meth)acrylate, and isodecyl (meth)acrylate are preferred, and lauryl methacrylate, octyl methacrylate, tridecyl methacrylate, and isodecyl (meth)acrylate are more preferred.

[0022] The graft weight of component (C) is preferably 1 to 10% by weight, more preferably 2 to 8% by weight, based on 100% by weight of the modified polyolefin resin. The graft weight of component (C) is, for example, based on the weight of the modified polyolefin resin. 1The grafting weight can be determined by H-NMR. When the grafting weight is 1% by weight or more, the resulting modified polyolefin resin can ensure adhesion to the resin contained in the waterproof coating layer, such as a styrene-acrylic resin. When the grafting weight is 10% by weight or less, the generation of unreacted grafted material can be prevented, and sufficient adhesion to the resin substrate can be ensured. (graft modification) An example of a method for modifying component (A) with components (B) and (C) is graft-modifying component (A) with components (B) and (C) (introducing them by graft copolymerization). The conditions for graft copolymerization are not particularly limited, and the graft copolymerization may be carried out according to a known method such as a melt method or a solution method. The melt method is simple in operation and allows the reaction to proceed in a short time. The solution method produces a uniform graft polymer with few side reactions.

[0023] In the melting method, for example, polyolefin is heated and melted (heat-melted) in the presence of a radical reaction initiator to cause a reaction. The heat-melting temperature may be equal to or higher than the melting point, and is preferably equal to or higher than the melting point and equal to or lower than 300°C. Equipment such as a Banbury mixer, kneader, or extruder can be used for the heat-melting. In the solution method, for example, polyolefin is dissolved in an organic solvent, and then heated and stirred in the presence of a radical reaction initiator to cause a reaction. Aromatic solvents such as toluene and xylene are preferred as the organic solvent. The reaction temperature is preferably 100 to 180°C. Examples of radical reaction initiators used in the melting method and solution method include organic peroxide compounds and azonitriles. Examples of organic peroxide compounds include di-tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, benzoyl peroxide, dilauryl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, cumene hydroperoxide, tert-butyl hydroperoxide, 1,1-bis(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)-cyclohexane, cyclohexanone peroxide, tert-butylperoxybenzoate, tert-butylperoxyisobutyrate, tert-butylperoxy-3,5,5-trimethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyisopropyl carbonate, and cumyl peroxyoctoate. Examples of azonitriles include 2,2-azobis(2-methylbutyronitrile), 2,2-azobisisobutyronitrile, 2,2-azobis(2,4-dimethylvaleronitrile), and 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile).

[0024] (glue) The thermoplastic resin contained in the adhesive of the present invention is not particularly limited as long as it is a polyolefin-based resin, and a mixture of a polyolefin-based resin with another thermoplastic resin may also be used. Examples include polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polyoxymethylene, polymethyl methacrylate, methacrylate-styrene copolymer, cellulose acetate, polycarbonate, polyethylene terephthalate, polyamide, thermoplastic polyurethane, and fluororesins such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polychlorotrifluoroethylene, perfluoroalkoxy fluororesin, ethylene-tetrafluoroethylene copolymer, and polyvinylidene fluoride. In a preferred embodiment, the thermoplastic resin used as an adhesive for bonding paper substrates includes a polyolefin-based polymer when a styrene-acrylic resin is used in the waterproof coating layer. By adopting this combination of a waterproof coating layer and a thermoplastic resin, when bonding paper substrates, it is possible to bond with sufficient strength not only between uncoated surfaces, but also between coated surfaces and between uncoated and coated surfaces.

[0025] The adhesive of the present invention may contain additives such as known plasticizers, tackifying resins, antioxidants, UV absorbers, liquid rubber, and particulate fillers, as long as the additives do not impair adhesive performance. The plasticizers are not particularly limited, and examples include paraffinic process oils, naphthenic process oils, aromatic process oils, liquid paraffin, and hydrocarbon synthetic oils. Examples of tackifying resins include natural rosin, modified rosin, glycerol esters of natural rosin, glycerol esters of modified rosin, pentaerythritol esters of natural rosin, pentaerythritol esters of modified rosin, copolymers of natural terpene, three-dimensional polymers of natural terpene, hydrogenated derivatives of copolymers of natural terpene, terpene resins, and hydrogenated derivatives of phenol-modified terpene resins. Petroleum resins such as C5 petroleum resins, C9 petroleum resins, C5C9 petroleum resins, and dicyclopentadiene petroleum resins, as well as partially hydrogenated and fully hydrogenated petroleum resins obtained by adding hydrogen to these petroleum resins, etc. Antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,4-bis(octylthiomethyl)-o-cresol, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethoxy]-2,4-bis(octylthiomethyl)-o-cresol, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, and 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethoxy]-2,4-bis(octylthiomethyl)-o-cresol. Examples of antioxidants include hindered phenol-based antioxidants such as 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)]phenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)]acrylate, and tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane; sulfur-based antioxidants such as dilauryl thiodipropionate, lauryl stearyl thiodipropionate, and pentaerythritol tetrakis(3-laurylthiopropionate); and phosphorus-based antioxidants such as tris(nonylphenyl)phosphite and tris(2,4-di-t-butylphenyl)phosphite.Examples of UV absorbers include benzotriazole-based UV absorbers such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-t-butylphenyl)benzotriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole; benzophenone-based UV absorbers such as 2-hydroxy-4-methoxybenzophenone; salicylic acid ester-based UV absorbers; cyanoacrylate-based UV absorbers; and hindered amine-based light stabilizers. Examples of liquid rubbers include liquid polybutene, liquid polybutadiene, liquid polyisoprene, and hydrogenated resins thereof. Examples of particulate fillers include, but are not limited to, calcium carbonate, kaolin, talc, titanium oxide, mica, and styrene beads. These plasticizers and additives may be contained alone or in combination. In a preferred embodiment of the present invention, the adhesive used in the present invention contains a tackifying resin in an amount of 25% or less of the total solids contained in the adhesive, in order to further improve adhesion with the styrene-acrylic resin used in the waterproof coating layer.

[0026] (Paper base material) In the present invention, a paper base material is used as the substrate. There are no particular limitations on the pulp used for the paper base material, and various pulps can be used depending on the application. Examples of raw pulp include various pulps derived from wood fibers, such as bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood kraft pulp (LUKP), groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP), as well as non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc.

[0027] In a preferred embodiment, the paper base material contains recycled paper pulp. When recycled paper pulp is contained, for example, the recycled paper pulp content of the total pulp is preferably 10% by weight or more, more preferably 25% by weight or more, even more preferably 50% by weight or more, and most preferably 70% by weight or more. In a preferred embodiment, all of the pulp used in the paper base material can be recycled paper-derived pulp, and kraft pulp may be blended as a pulp other than recycled paper pulp, or the entire paper base material may be kraft pulp. Furthermore, when the paper base material is a multi-layer paperboard having two or more paper layers, the recycled paper pulp content per layer can be as described above, and the recycled paper pulp content in each layer may be different.

[0028] Examples of waste paper pulp that can be used include waste paper pulp obtained by disintegrating unprinted waste paper such as cardboard, white paper, extra white paper, medium white paper, and white damage; waste paper printed on fine paper, fine coated paper, medium paper, medium coated paper, and recycled paper; written waste paper; paper such as discarded confidential documents; and pulp (DIP) obtained by disintegrating and deinking waste paper such as magazines and newspapers.

[0029] Known fillers and internal chemical additives can be added to the paper base material. Examples of fillers include inorganic fillers such as kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, silica, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, barium sulfate, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, zinc oxide, titanium oxide, and amorphous silica produced by neutralizing sodium silicate with a mineral acid; and organic fillers such as urea-formaldehyde resin, melamine resin, polystyrene resin, and phenolic resin. These may be used alone or in combination. Internal chemical additives such as retention aids, bulking agents, dry strength improvers, wet strength improvers, drainage improvers, water retention agents, dyes, sizing agents, and various salts may also be used as needed.

[0030] The paper substrate is produced by a known papermaking method, for example, using a Fourdrinier paper machine, a gap former paper machine, a hybrid former paper machine, an on-top former paper machine, a cylinder paper machine, etc., but is not limited to these.

[0031] The basis weight of the paper substrate is not particularly limited and may be adjusted depending on the application. In the case of single-layer paper, for example, it is 40 to 750 g / m 2 and can be set to 70 to 600 g / m 2 Or 100~500g / m 2 Or 150~400g / m 2 The paper base material may also be a multi-layer paperboard having two or more paper layers, and preferably has, for example, 2 to 7 paper layers, and more preferably has 3 to 5 paper layers. When the paper base material is a multi-layer paperboard having two or more paper layers, the basis weight of all layers in total may be, for example, 70 to 750 g / m 2 and can be set to 100 to 600 g / m 2 Or 150~500g / m 2 It may also be possible to use the following.

[0032] The paper substrate may be a single-layer paper or a multi-layer paperboard processed by laminating or the like. In a preferred embodiment of the present invention, paperboard is used as the paper substrate, more preferably corrugated cardboard. Corrugated cardboard is made by laminating flat paper (liner) and corrugated paper (core) with an adhesive, and is suitable for various uses such as product packaging, cushioning, transporting luggage, and storing goods.

[0033] There are no particular restrictions on the cardboard liner, and kraft liners, jute liners, etc. can be used depending on the application. The basis weight of the liner is also not particularly limited, and for example, the basis weight of the entire liner can be 70 to 550 g / m 2 and can be set to 100 to 500 g / m 2 Or 150~450g / m 2 It may also be possible to use the following.

[0034] There are no particular restrictions on the medium that makes up the corrugated board, and A-flute, B-flute, C-flute, W-flute, E-flute, etc. can be used. There are also no particular restrictions on the basis weight of the medium, and it is up to 120 g / m 2 , 160g / m 2 , 180g / m 2 , reinforced 180g / m 2 , reinforced 200g / m 2 can be suitably used.

[0035] (Waterproof coating layer) The paper substrate according to the present invention has a waterproof coating layer on at least one side thereof, which makes it difficult for water to penetrate the paper substrate even when it comes into contact with water, thereby maintaining the strength of the paper substrate. The waterproof coating layer preferably contains a synthetic resin. The synthetic resin preferably contains at least one of styrene-based resin, acrylic-based resin, butadiene-based resin, polyolefin-based resin, polyvinyl alcohol resin, polylactic acid resin, polyester-based resin, and polyethylene-based resin. The synthetic resin preferably contains a styrene-based resin and / or an acrylic-based resin, and particularly preferably contains a styrene-acrylic resin.

[0036] The styrene-based resin that can be contained in the waterproof coating layer constituting the present invention is a resin in which the copolymerization ratio of a styrene-based monomer having a styrene skeleton in its structure is 50 mass% or more, and may be composed only of a polymer of a styrene-based monomer.

[0037] Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α-methyl-p-methylstyrene.

[0038] Examples of monomers copolymerizable with styrene monomers include alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate, and methylphenyl methacrylate, alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and cyclohexyl acrylate, unsaturated carboxylic acids such as methacrylic acid and acrylic acid, unsaturated dicarboxylic anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, and conjugated dienes such as 1,3-butadiene and 2-methyl-1,3-butadiene. These can be used alone or in combination of two or more.

[0039] The acrylic resin that can be contained in the waterproof coating layer constituting the present invention is a resin in which the copolymerization ratio of acrylic acid, methacrylic acid, and acrylic monomers that are derivatives thereof is 50% by mass or more, and may be composed only of polymers of acrylic monomers.

[0040] Examples of the acrylic monomer include methacrylic acid esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate, and acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and isopropyl acrylate, and the acrylic resin may be a polymer of one or more monomers selected from these acrylic monomers.

[0041] Examples of monomers copolymerizable with acrylic monomers include aromatic vinyl compounds such as styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α-methyl-p-methylstyrene, unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, unsaturated dicarboxylic anhydrides such as maleic anhydride, and unsaturated carboxylic acids such as methacrylic acid and acrylic acid. These may be used alone or in combination of two or more.

[0042] Styrene-acrylic resins are polymers whose structural units contain acrylic and styrene monomers alternately or randomly. In a preferred embodiment, the styrene-acrylic resin is a copolymerized resin in a styrene / acrylic ratio of 10 / 90 to 90 / 10. In a preferred embodiment, the styrene-acrylic resin accounts for 50% by weight or more of the synthetic resin contained in the waterproof coating layer. Examples of acrylic monomer components that make up the styrene-acrylic resin include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, acrylamide, methacrylamide, acrylonitrile, 2-ethylhexyl acrylate, and lauryl methacrylate. Other monomers and polymers can also be incorporated as needed.

[0043] The waterproof coating layer preferably contains wax, as this has the effect of further improving the waterproofness of the paper surface. Examples of wax include polyethylene wax, Fischer-Tropsch wax, synthetic oil-based waxes (fatty acid esters, fatty acid amides, ketones, and amines), synthetic waxes such as hydrogenated oil, and natural waxes such as beeswax, Japan wax, paraffin wax, and microcrystalline wax. These waxes can be used alone or in combination of two or more, with hydrocarbon waxes containing paraffin being particularly preferred.

[0044] The waterproof coating layer provided on the paper substrate according to the present invention may contain other additives as long as they do not impair the waterproofing performance. Various commonly used additives such as pigments, dispersants, thickeners, water retention agents, defoamers, water-resistant agents, dyes, and fluorescent dyes can be used.

[0045] The waterproof coating layer can be formed by applying a coating agent using a known coating method, such as air knife coating, curtain coating, blade coating, gate roll coating, and die coating. Single-layer coating or multi-layer coating may be used. In the case of multi-layer coating, either a dry-on-wet coating method, in which an undercoat layer is applied and then dried before applying a topcoat layer, or a wet-on-wet coating method, in which an upper layer is applied without drying the lower-layer coating, may be used. The coating may be performed using the same coating equipment or a combination of different types of coating equipment. The coating amount is not particularly limited, and the total coating amount is 4 to 30 g / m. 2 However, from the viewpoint of achieving both economical efficiency and waterproof function, it is recommended to use a thickness of 5 to 20 g / m 2 It is preferable to set the following.

[0046] (bonding with adhesive) The paper substrate according to the present invention is bonded with a hot melt adhesive. The type of adhesive is not particularly limited, and examples include water-based, water-dispersed, solution-based, solventless, and solid-based adhesives, and can be appropriately selected depending on the condition of the surface of the paper substrate to be bonded and the components of the waterproof coating layer provided on the paper substrate.

[0047] In a preferred embodiment, the adhesive according to the present invention is a hot melt adhesive containing a thermoplastic resin, has a softening point of 70°C or higher, and softens when heated. In a preferred embodiment, the softening point of the hot melt adhesive according to the present invention is 70 to 150°C.

[0048] The hot melt adhesive can be heated and melted in a tank or the like, pumped under pressure, and then applied using an applicator. The adhesive application method is not particularly limited, and a wide variety of application methods are possible, including point application, line application, surface application, spiral application, slot application, spray application, and roll application. Application can also be performed using a gravure method to create a dotted, uneven surface. In the present invention, a line application method is preferred, in which the adhesive is continuously applied in a line using a single-hole nozzle.

[0049] The amount of adhesive used is not particularly limited as long as sufficient adhesive strength is obtained, but in the case of surface application, it is 0.5 to 2000 g / m 2 It can be 5 to 1500 g / m 2 It may be 10 to 1000 g / m 2 In the case of line application, the application width can be changed appropriately depending on the nozzle diameter of the applicator, the movement speed of the nozzle or paper substrate, the viscosity of the adhesive during application, the width of the paper substrate to be adhered, etc., and the application amount per unit length is not particularly limited, but may be, for example, 0.1 to 30 g / m, 0.5 to 20 g / m, or 1 to 15 g / m.

[0050] When manufacturing a box by forming a paper base material into a box, a box forming machine can be used. There are no particular restrictions on the type of box forming machine used, and for example, a vertical or horizontal box forming machine can be used. [Example]

[0051] The present invention will be described in more detail below using specific examples, but the present invention is not limited to the following specific examples. Furthermore, unless otherwise specified in this specification, concentrations, parts, etc. are by weight, and numerical ranges are stated as including their endpoints.

[0052] Example 1 In a four-neck flask equipped with a stirrer, a condenser, and a dropping funnel, 100 parts of a propylene-butene-ethylene random copolymer [PBE] (60 mol % propylene, 30 mol % butene, 10 mol % ethylene, Tm = 65°C) was heated and dissolved in 400 g of toluene. While maintaining the temperature in the system at 110°C and stirring, 7.0 parts of maleic anhydride, 7.5 parts of tridecyl methacrylate, and 2.0 parts of di-t-butyl peroxide were each added dropwise over 3 hours, and the reaction was continued for another 1 hour.

[0053] After the reaction was completed, the mixture was cooled to room temperature, yielding a reaction product with a weight-average molecular weight of 80,000 and a Tm of 63°C. The reaction product was purified by adding it to a large excess of acetone to produce a polyolefin resin copolymer for use as a paper adhesive. The graft weights of maleic anhydride and tridecyl methacrylate were measured and found to be 5.8% by weight and 6.0% by weight, respectively.

[0054] Experiment 1.Paperboard lamination Three layers combined to form a basis weight of 280 g / m 2 The weight ratio of the surface layer:middle layer:back layer was 15:60:25, and the pulp composition of each layer was as follows: (Surface layer) 70% unbleached kraft pulp and 30% recycled paper pulp (Middle layer) 100% recycled paper pulp (Back layer) 100% recycled paper pulp A styrene-acrylic waterproofing agent (Michelman, VaporCoat 2200) was applied to the surface of the paperboard at a rate of 10 g / m using an air knife coater. 2 A waterproof coating layer was applied to the box liner to produce the box liner.

[0055] Next, the box liner was cut to a specified size, and the test pieces were coated with the previously prepared hot melt adhesive for paper and bonded to the test pieces. Specifically, two test pieces of the same size were prepared, and the thermoplastic resin listed below was applied in a line to the surface of the box liner using a glue gun in the amount and length shown in the table below, and then the back layer of the box liner was bonded to the test piece, making sure that the adhesive did not protrude beyond the test piece. (Hot melt) The above-mentioned polyolefin resin copolymer (softening point: approximately 80°C). As a reference example, a box liner was cut to a specified size and a test piece was coated with the following adhesive, which is not a hot melt adhesive, in a line and then bonded in the same manner. (Crafting adhesive) Vinyl acetate (Konishi Bond for woodworking) (Liquid glue) Polyvinyl alcohol (Yamato, Arabic Yamato) The bonded samples were left in an environment of 5°C or 23°C for 24 hours, then the samples were forcibly peeled off by hand, and the adhesive strength was evaluated based on the appearance of the peeled surface on the outer layer. The evaluation criteria are as follows: ◎: Strong adhesion (when forcibly peeled off, the entire bonded area breaks, Figure 1, left) ○: Good adhesion (when forcibly peeled off, part of the bonded area broke, see Figure 1) △: Weak adhesiveness (the bonded area does not break even when forcibly peeled off, Figure 1 right) As is clear from the results shown in the table below, the present invention was able to bond paper substrates with sufficient adhesive strength.

[0056] [Table 1]

[0057] [Table 2]

[0058] Experiment 2: Cardboard box making Corrugated cardboard sheets for boxes were produced from the paperboard and box liner produced in Experiment 1. Specifically, a box liner with a waterproof coating layer on the surface side of the paperboard was used as the front liner, and paperboard without a waterproof coating layer was used as the back liner, and the front liner and back liner were bonded together via an A-flute core so that the waterproof coating layer was on the outside of the cardboard.

[0059] Next, a type A corrugated cardboard box (external dimensions: 583 × 383 × 190 mm) was manufactured from the cardboard sheet using a box-making machine. Specifically, a hot melt adhesive was applied in a line to the joint on the side of the box using a glue gun (application amount: 10 g / m, application length: 190 mm), and the front liner and back liner of the cardboard sheet were bonded at the joint.

[0060] The adhesive strength of the bonded portion of the obtained cardboard box was evaluated in the same manner as in Experiment 1. That is, the joint portion of the cardboard box was forcibly peeled off by hand, and the adhesive strength was evaluated from the appearance of the peeled surface.

[0061] In addition, a waterproof bag containing 16 kg of ice was placed in a cardboard box and left in an environment of 5°C for 24 hours, after which the box's compressive strength was measured. The box's compressive strength was measured with the contents still in the box in accordance with JIS Z 0212, using the following procedure. 1) Place the sample box in the center of the compression tester. 2) Start the compression testing machine and apply a gradually downward force evenly across the entire top surface of the box. 3) The weight applied when the side of the box is deformed or the joint on the side of the box is peeled off is read and this is the compressive strength of the box.

[0062] The evaluation results are shown in the table below. The corrugated cardboard boxes manufactured according to the present invention had strong adhesive at the joints. In other words, when the joints were forcibly peeled off, breakage of the material was confirmed.

[0063] Furthermore, the box compression strength was also sufficiently high, and the corrugated cardboard boxes manufactured according to the present invention had sufficient strength even when stacked in multiple layers during actual transportation.

[0064] [Table 3]

Claims

1. An adhesive for paper having the following characteristics: The adhesive Component (A): Polyolefin resin, Component (B): α,β-unsaturated carboxylic acid or its derivative and component (C): (meth)acrylic acid ester. A graft-modified polyolefin resin graft-modified by The modified polyolefin resin has a weight average molecular weight of 10,000 or more but less than 200,000, a melting point of 50°C or more but less than 100°C, and contains 50 mol% or more of propylene-derived structural units out of 100 mol% of structural units.

2. A box bonded using the adhesive of claim 1.

3. 3. The box according to claim 2, wherein the paper base material used for the box has a coating layer containing a styrene-acrylic resin.

4. 4. The box according to claim 3, wherein the coating layer is a waterproof coating layer.

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