JP7375338B2 - Wrapping paper and packaging bags - Google Patents

Description

The present invention relates to a wrapping paper having a gas barrier coating applied to a paper base material, and a packaging bag using the same.

A wrapping paper in which a gas barrier coating is applied on a paper base material is disclosed in Patent Document 1. This wrapping paper forms a gas barrier coating layer by applying a coating liquid onto a paper base material and drying it. The coating layer is formed by laminating a first layer placed on a paper base material and a second layer placed on the first layer.

The first layer is formed by applying a coating liquid in which a binder resin having water vapor barrier properties and a pigment are dispersed in a water dispersant. The second layer is formed by applying a coating liquid in which a water-soluble polymeric binder resin and a pigment are dispersed in an aqueous dispersant. As a result, a coating layer consisting of a first layer having high water vapor barrier properties and a second layer mainly having high oxygen barrier properties is obtained.

By laminating the above-mentioned wrapping paper with a thermoadhesive resin, a packaging bag that can be sealed by thermal bonding of the thermoadhesive resin can be formed.

JP 2018-172149 (pages 3 to 12)

However, according to the above conventional wrapping paper, the wrapping paper is folded when the thermally adhesive resin is laminated to form a packaging bag. At this time, there was a problem that cracks were generated on the coating layer and the gas barrier properties of the packaging bag were deteriorated.

An object of the present invention is to provide a wrapping paper that can suppress deterioration of gas barrier properties during bag manufacturing, and a packaging bag formed from the paper with high gas barrier properties.

In order to achieve the above object, the present invention includes a paper base material, a coating layer coated on one side of the paper base material, and a thermally adhesive resin disposed on the other side of the paper base material via an adhesive layer. The wrapping paper is characterized in that the coating layer has gas barrier properties, and the adhesive layer is formed of a gas barrier adhesive.

Further, the present invention provides the wrapping paper having the above structure, in which the gas barrier adhesive comprises a main ingredient consisting of a resin having two or more hydroxyl groups in one molecule, and a curing agent consisting of a polyisocyanate having an isocyanate group having a valence of two or more. It is characterized by being a solvent-free adhesive containing.

Further, the present invention is characterized in that the wrapping paper having the above structure is characterized in that the coating layer contains polyvinyl alcohol and kaolin.

Furthermore, the packaging bag of the present invention is characterized in that it is formed from wrapping paper having each of the above-mentioned configurations.

According to the present invention, a coating layer coated on one side of a paper base material has gas barrier properties, and a thermoadhesive resin layer is disposed on the other side via an adhesive layer made of a gas barrier adhesive. Therefore, even if cracks occur in the coating layer of the wrapping paper that is folded during bag manufacturing, the gas barrier adhesive can suppress the deterioration of the gas barrier properties of the wrapping paper. Therefore, a packaging bag with high gas barrier properties can be obtained.

A perspective view showing a packaging bag according to an embodiment of the present invention A sectional view showing a wrapping paper forming a packaging bag according to an embodiment of the present invention

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a perspective view of a packaging bag of one embodiment. The packaging bag 1 is made into a pillow shape using a laminated wrapping paper 20 (see FIG. 2), and stores contents such as foods, medicines, and supplements.

The packaging bag 1 is sealed by a back seal part 2 and an edge seal part 3. The back seal part 2 is formed by thermally adhering both circumferential ends of a body part 4 in which wrapping paper 20 is arranged in a cylindrical shape. The edge seal portion 3 is formed by thermally bonding both ends of the body portion 4 in the axial direction. The edge of the edge seal portion 3 is formed into a sawtooth shape for opening.

FIG. 2 is a schematic cross-sectional view showing the layer structure of a wrapping paper 20 made of a laminate forming the packaging bag 1. As shown in FIG. The wrapping paper 20 is formed by laminating a heat-adhesive resin layer 28 on a coated paper 26. The coated paper 26 is formed by coating one side of the paper base material 25 with the coating layer 21. The thermoadhesive resin layer 28 is dry laminated on the other surface of the paper base material 25 via the adhesive layer 27.

The paper base material 25 is not particularly limited, but includes high-quality paper, thin imitation paper, bleached kraft paper, unbleached kraft paper, single-gloss kraft paper, heavy-duty kraft paper, pure white roll paper, glassine paper, white paperboard, paper tube base paper, Liner base paper, recycled paper, etc. can be used. The paper base material 25 may be made of single layer paper or multilayer paper. The basis weight of the paper base material 25 is not particularly limited, but may be, for example, about 20 g/m ² or more and 500 g/m ² or less.

Fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers may be added to the paper base material 25. In addition, the paper base material 25 includes a retention improver (sulfuric acid bandate, etc.), a freeness improver, a paper strength enhancer, an internal additive aid for papermaking (internal additive sizing agent, etc.), a dye, a fluorescent whitening agent, and a pH adjuster. A foaming agent, an antifoaming agent, a pitch control agent, a slime control agent, etc. can be added as necessary.

Furthermore, the surface of the paper base material 25 is treated with an agent such as oxidized starch, hydroxyethyl etherified starch, oxygen-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agent, water resistance agent, water retention agent, thickener, lubricant, etc. You may.

The coating layer 21 is formed by applying a coating liquid to one surface of the paper base material 25. The coating layer 21 is formed by laminating a first barrier layer 21a and a second barrier layer 21b, and has gas barrier properties. The first barrier layer 21a has water vapor barrier properties, and the second barrier layer 21b has oxygen barrier properties.

The first barrier layer 21a contains a binder resin and a pigment. Since the first barrier layer 21a has moisture resistance, it is possible to suppress the influence of moisture, and it is also possible to suppress the influence of moisture penetrating from the paper base material 25 on the second barrier layer 21b. Further, by providing the first barrier layer 21a, permeation of the coating liquid forming the second barrier layer 21b into the paper base material 25 is suppressed. Therefore, a uniform second barrier layer 21b can be formed, and deterioration in barrier properties of the second barrier layer 21b can be suppressed.

As the binder resin of the first barrier layer 21a, various copolymers such as styrene/butadiene type, styrene/acrylic type, ethylene/vinyl acetate type, butadiene/methyl methacrylate type, vinyl acetate/butyl acrylate type, maleic anhydride copolymer can be used. Synthetic resins such as acrylic acid/methyl methacrylate copolymers can be used alone or in combination of two or more.

Among these, styrene-butadiene resins with high water vapor barrier properties are more preferred. Styrene-butadiene-based synthetic resins are made by emulsion polymerization of styrene and butadiene as main constituent monomers, combined with various comonomers for the purpose of modification. Examples of comonomers include methyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl acrylate, and unsaturated carboxylic acids such as itaconic acid, maleic acid, and acrylic acid.

The binder resin is used as an emulsion type coating liquid using water as a dispersant. Examples of emulsifiers include anionic surfactants such as sodium oleate, rosin acid soap, sodium alkylallylsulfonate, and sodium dialkylsulfosuccinate. These can be used alone or in combination with a nonionic surfactant. Furthermore, an amphoteric or cationic surfactant may be used if necessary.

In addition, the coating liquid forming the first barrier layer 21a may contain hydrocarbons, silicone resins, fluororesins, fatty acids, and esters of fatty acids and alcohols, within a range where the coating liquid forming the second barrier layer 21b is not repelled. It is possible to contain water repellent components such as.

The pigment contained in the first barrier layer 21a can improve the water vapor barrier properties of the first barrier layer 21a and the adhesion with the second barrier layer 21b. Inorganic pigments and organic pigments can be used as pigments. Inorganic pigments include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin. Examples include white, mica, and montmorillonite. Examples of organic pigments include solid type, hollow type, and core-shell type. These pigments can be used alone or in combination of two or more.

Among these pigments, flat-shaped inorganic pigments such as kaolin are preferred from the viewpoint of improving water vapor barrier properties. In particular, kaolin having an average particle diameter of 5 μm or more and an aspect ratio of 10 or more is more preferable. Since the flat pigment with a large aspect ratio is distributed parallel to the coating layer, water vapor that has penetrated into the first barrier layer 21a is blocked from moving in the thickness direction by the flat pigment and moves in a detour. Therefore, when the aspect ratio of the pigment is large, the water vapor barrier property is improved because the path through which water vapor passes through the first barrier layer 21a becomes longer.

In addition to kaolin, mica and montmorillonite can also be used as flat pigments. However, since mica and montmorillonite dispersions have lower concentrations than kaolin dispersions, it is difficult for pigments to align parallel to the coating layer. Therefore, kaolin, which can be contained in a coating liquid at a high concentration, is more suitable than mica and montmorillonite.

Further, in addition to the flat pigment, a pigment having an average particle diameter of 5 μm or less may be added to the first barrier layer 21a. As a result, the first barrier layer 21a has a structure in which pigments with large particle diameters and aspect ratios exist in a multilayered manner, and pigments with small particle diameters enter gaps between adjacent pigments with large particle diameters. The water vapor bypasses the large particle size pigment and moves along the surface of the pigment, and its movement is blocked by the small particle size pigment in between. Thereby, the water vapor barrier properties of the first barrier layer 21a can be further improved.

As the pigment having an average particle diameter of 5 μm or less, each of the above pigments can be used, but heavy calcium carbonate is more preferable.

Furthermore, the blending ratio of the flat large particle diameter pigment (kaolin) and the small particle diameter pigment (large particle diameter/small particle diameter) is preferably in the range of 50/50 to 99/1 by dry weight. . If the blending ratio is smaller than the above, the distance that water vapor detours through the coating layer becomes shorter, making it impossible to obtain sufficient water vapor barrier properties. If the blending ratio is larger than the above, the voids between the large particle diameter pigments in the coating layer cannot be sufficiently filled with the small particle diameter pigments, so that no improvement in water vapor barrier properties is observed.

The blending amount of the binder resin and pigment in the first barrier layer 21a is preferably in the range of 5 parts by weight or more and 200 parts by weight or less of the binder resin (dry weight) per 100 parts by weight of the pigment (dry weight). More preferably, the binder resin (dry weight) is 20 to 150 parts by weight based on 100 parts by weight of the pigment (dry weight).

Next, the second barrier layer 21b contains a binder resin made of a water-soluble polymer, and has gas barrier properties mainly against oxygen and carbon dioxide. The water-soluble polymer contained in the second barrier layer 21b includes fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymerized polyvinyl alcohol, polyvinylpyrrolidone, starch, modified starch, dextrin, methylcellulose, carboxymethylcellulose, and sodium alginate. etc. can be used. Among these, from the viewpoint of oxygen barrier properties, polyvinyl alcohol and carboxymethyl cellulose are preferred, and polyvinyl alcohol is more preferred.

Further, the second barrier layer 21b may contain a pigment to improve oxygen barrier properties. As the pigment contained in the second barrier layer 21b, the same pigment as in the first barrier layer 21a described above can be used.

Among these, it is preferable to use inorganic pigments from the viewpoint of gas barrier properties. It is more preferable to use an inorganic pigment (particularly kaolin) having an average particle diameter of 3 μm or more and an aspect ratio of 10 or more. It is more preferable to use an inorganic pigment (particularly kaolin) having an average particle diameter of 5 μm or more and an aspect ratio of 50 or more. When the second barrier layer 21b contains a pigment, it has excellent gas barrier properties because gas components such as oxygen bypass the pigment and pass through.

The blending ratio (dry weight) of the pigment and water-soluble polymer contained in the second barrier layer 21b is preferably in the range of 1/100 to 1000/100 (pigment/water-soluble polymer). If the pigment ratio is outside the above range, sufficient gas barrier properties will not be exhibited.

When blending a pigment into a water-soluble polymer, it is preferable to add and mix a slurry obtained by dispersing the pigment in water.

Further, the first barrier layer 21a and the second barrier layer 21b may contain various auxiliary agents such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistance agent, a dye, a fluorescent dye, and a crosslinking agent. May contain.

Since the crosslinking agent causes a crosslinking reaction with the binder resin, the number of bonds (crosslinking points) in the first barrier layer 21a and the second barrier layer 21b increases. Thereby, the first barrier layer 21a and the second barrier layer 21b have a dense structure and exhibit good water vapor barrier properties.

The type of crosslinking agent is not particularly limited, and can be appropriately selected from polyvalent metal salts, amine compounds, amide compounds, aldehyde compounds, hydroxy acids, etc., depending on the binder resin. Polyvalent metal salts include polyvalent metals such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, and titanium, as well as carbonate ions, sulfate ions, nitrate ions, phosphate ions, and silicate ions. A compound in which an ionic substance such as , nitrogen oxide, or boron oxide is bonded can be used.

The number of parts of the crosslinking agent to be blended is not particularly limited as long as it is within the range of coating solution concentration and coating solution viscosity that can be coated. In addition, when using a styrene-based binder resin such as styrene-butadiene-based or styrene-acrylic-based which exhibits excellent water vapor barrier properties, it is preferable to use a polyvalent metal salt from the viewpoint of achieving a crosslinking effect. Furthermore, potassium alum is more preferred.

The amount of the crosslinking agent added is 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the binder resin. More preferably, it is 3 parts by weight or more and 5 parts by weight or less. If it is less than 1 part by weight, sufficient effects cannot be obtained, and if it is more than 10 parts by weight, the viscosity of the coating solution increases significantly, making coating difficult.

Moreover, when adding a crosslinking agent to a coating liquid, it is preferable to dissolve a crosslinking agent in polar solvents, such as an ammonium hydroxide solution, and to add to a coating liquid. By dissolving the crosslinking agent in a polar solvent, the crosslinking agent and the polar solvent form hydrogen bonds. Therefore, even if the crosslinking agent is blended into the coating liquid, a crosslinking reaction with the binder resin does not occur immediately, and thickening of the coating liquid can be suppressed. In this case, after the coating liquid applied to the paper base material 25 dries and the polar solvent component evaporates, a crosslinking reaction between the crosslinking agent and the binder resin occurs, forming a dense first barrier layer 21a.

A coated paper 26 is formed by applying a coating liquid for the first barrier layer 21a on one surface of the paper base material 25 and drying it, and then applying a coating liquid for the second barrier layer 21b and drying it. .

Next, the heat-adhesive resin layer 28 is made of a heat-adhesive resin, and is formed of a low-density polyethylene film, a linear low-density polyethylene film, an unstretched polypropylene film, or the like. The back seal portion 2 and the edge seal portion 3 are formed by overlapping the opposing thermoadhesive resin layers 28 and applying pressure and heat.

The adhesive layer 27 is formed of a gas barrier adhesive, and the paper base material 25 of the coated paper 26 and the film forming the thermoadhesive resin layer 28 are dry laminated. The gas barrier adhesive forming the adhesive layer 27 contains a main agent made of a resin having two or more hydroxyl groups in one molecule, and a curing agent made of a polyisocyanate having an isocyanate group having a valence of two or more. Further, the curing agent is a polycondensate of an aliphatic polycarboxylic acid or anhydride thereof having 8 or less carbon atoms in the portion excluding the carboxyl group, and an aliphatic polyhydric alcohol having 8 or less carbon atoms. It has an ester skeleton derived from polyester.

The gas barrier adhesive forming the adhesive layer 27 is cured by a chemical reaction between a hydroxyl group and an isocyanate group, and has gas barrier properties against oxygen, water vapor, inert gas, alcohol, fragrance components, and the like.

In order to use a polyisocyanate having a divalent or higher valence isocyanate group as the curing agent of the adhesive layer 27, it is preferable that the polyester has a divalent or higher hydroxyl group. It is also possible to obtain the curing agent for the adhesive layer 27 by reacting a monovalent polyester with an isocyanate compound having a valence of 3 or more.

The aliphatic polycarboxylic acid component used to synthesize the curing agent for the adhesive layer 27 is not limited as long as it is an aliphatic polycarboxylic acid having 8 or less carbon atoms in the portion excluding the carboxyl group. Specifically, at least one fat selected from the group consisting of succinic acid, maleic acid, fumaric acid, adipic acid, azelaic acid, sebacic acid, 1,3-cyclopentanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Examples include group polyhydric carboxylic acids or anhydrides thereof.

The aliphatic polyhydric alcohol component used to synthesize the curing agent for the adhesive layer 27 is not limited as long as it is an aliphatic polyhydric alcohol having 8 or less carbon atoms. Specifically, ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, cyclohexanedimethanol, 1,5-pentanediol, 3-methyl-1,5-pentanediol , 1,6-hexanediol, methylpentanediol, dimethylbutanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol. Among these, unbranched aliphatic polyhydric alcohols such as ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol are preferred. A curing agent can be obtained from a polycondensate of at least one aliphatic polyhydric alcohol selected from the group consisting of these and an aliphatic polycarboxylic acid.

In addition, polyhydric alcohols having more than 8 carbon atoms, aromatic polyhydric alcohols, polycarboxylic acids having more than 8 carbon atoms, and aromatic polyhydric alcohols can be used as long as the lamination strength and gas barrier properties of the adhesive layer 27 are not impaired. Small amounts of carboxylic acids may also be used.

The curing agent for the adhesive layer 27 may be a polyisocyanate having an aromatic ring, and is not limited as long as it is a polyisocyanate having an aromatic ring in the molecule and an isocyanate group having a valence of two or more. As the polyisocyanate having an aromatic ring, at least one monomer selected from m-xylylene diisocyanate, toluene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, etc. Mention may be made of those selected from the group consisting of oligomers and reaction products of these isocyanates and alcohols having two or more hydroxyl groups.

Further, as the polyisocyanate having an aromatic ring, an adduct obtained by reacting an excess amount of an isocyanate monomer with a polyfunctional alcohol can also be used. Examples of polyfunctional alcohols include low-molecular active hydrogen compounds (trimethylolpropane, glycerol, pentaerythritol, erythritol, sorbitol, diethanolamine, triethanolamine, etc.) and their alkylene oxide adducts, various polyester resins, and polyether polyols. , polymer active hydrogen compounds such as polyamides, and the like.

Furthermore, it is also possible to use compounds obtained by modifying a portion of the NCO groups of each of the above polyisocyanates with carbodiimide, allophanate compounds derived from these polyisocyanates, and nurate compounds derived from these polyisocyanates. A small amount of aliphatic polyisocyanate may be used as long as the lamination strength and gas barrier properties of the adhesive layer 27 are not impaired.

Among these, it is preferable to use at least one monomer selected from m-xylylene diisocyanate, toluene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, etc. .

The number average molecular weight of the curing agent in the adhesive layer 27 is preferably in the range of 500 to 2,000, more preferably in the range of 500 to 1,000. The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC) under the following conditions.

Measuring device: HLC-8220GPC manufactured by Tosoh Corporation
Column: TSK-GUARD COLUMN SuperHZ-L manufactured by Tosoh Corporation
+TSK-GEL SuperHZM-M×4 manufactured by Tosoh Corporation
Detector: RI (differential refractometer)
Data processing: Multi-station GPC-8020model II manufactured by Tosoh Corporation
Measurement conditions: Column temperature 40℃
Solvent Tetrahydrofuran
Flow rate 0.35 mL/min Standard: Monodisperse polystyrene Sample: 0.2 mass% tetrahydrofuran solution (contains 1 vol% dibutylamine in the solvent) in terms of resin solid content, filtered through a microfilter (100 μL)

The viscosity of the curing agent for the adhesive layer 27 is preferably in the range of 300 to 4,000 mPas, more preferably in the range of 400 to 3,000, and even more preferably in the range of 400 to 2,000 when measured at 60 degrees.

The main agent of the gas barrier adhesive forming the adhesive layer 27 may be one having substantially two or more hydroxyl groups. Examples of the main component of the adhesive layer 27 include polyester polyols, polyether polyols, acrylic polyols, and the like. In order to impart gas barrier properties, polyester polyol is most preferred.

Further, it is preferable that the number average molecular weight (Mn) of the main ingredient of the adhesive layer 27 is in the range of 400 to 3000 because the time required for synthesis is short and handling is easy. The number average molecular weight (Mn) of the base resin can be measured in the same manner as above, and the sample used is a 0.2% by mass tetrahydrofuran solution (calculated as resin solid content) filtered through a microfilter (100 μL). It will be done.

The polyester polyol used as the main ingredient of the adhesive layer 27 is a polycondensate substantially having a plurality of hydroxyl groups obtained by polycondensation reaction of a polyhydric carboxylic acid component and a polyhydric alcohol component. Although there is no particular limitation as long as it can exhibit gas barrier properties, those having aromatic rings are preferred, and those having ortho-oriented aromatic rings are preferred because they have better gas barrier properties.

More specific examples of the polyester polyol having a plurality of hydroxyl groups include, but are not limited to, the following.

(a) Polyester polyol obtained by polycondensing a polyhydric carboxylic acid component containing an aromatic polycarboxylic acid component (more preferably an ortho-oriented aromatic polycarboxylic acid component) and a polyhydric alcohol component (b) 3 pieces A polyester polyol obtained by reacting a polyester polyol having the above hydroxyl groups with a carboxylic acid anhydride or a polycarboxylic acid (c) A polyester polyol having a polymerizable carbon-carbon double bond (d) A polyester polyol having a glycerol skeleton ( e) Polyester polyol having an isocyanuric ring

The number average molecular weight of the main component of the adhesive layer 27 is particularly preferably from 450 to 5,000, since this provides a crosslinking density that provides an excellent balance between adhesive ability and barrier function. More preferably, the number average molecular weight is 500 to 3,000. When the number average molecular weight is less than 450, the cohesive force of the adhesive during application becomes too small. For this reason, problems such as shifting of the film or lifting of the bonded film during lamination are likely to occur. When the number average molecular weight is higher than 5000, problems occur such as the viscosity during coating becomes too high and coating cannot be performed, and the tackiness is so low that lamination cannot be performed.

Further, the adhesive forming the adhesive layer 27 may be a solvent type or a solvent-free type, but if the number average molecular weight of the main ingredient is in the range of 400 to 2,000, the adhesive can be a solvent-free type. By using a solvent-free adhesive, the step of removing the solvent by drying can be omitted, and it is also possible to prevent odor from remaining in the packaging bag 1 (see FIG. 1) due to the organic solvent.

The main ingredient of the adhesive layer 27 may be a polyol whose number average molecular weight is set to 1,000 to 15,000 by urethane extension through reaction with a diisocyanate compound. Since the polyol contains components with a molecular weight above a certain level and urethane bonds, it not only has excellent gas barrier properties but also has excellent initial cohesive strength, making it even more excellent as an adhesive for use in lamination.

The viscosity of the main ingredient of the adhesive layer 27 is preferably 50,000 mPas or less at 60°C. Furthermore, it is more preferable to set the viscosity of the main ingredient of the adhesive layer 27 to 10,000 mPas or less, since this allows the adhesive to be used as a solvent-free adhesive.

The main agent and curing agent of the adhesive layer 27 are preferably blended so that the ratio of hydroxyl groups in the main agent to isocyanate groups in the curing agent is 1/0.5 to 1/10 (equivalent ratio), more preferably 1/1. It is 0.6 to 1/5. If the amount of the curing agent is excessive beyond this range, there is a risk that the excess curing agent will remain and bleed out from the adhesive layer 27 after adhesion. If the curing agent is insufficient, there is a risk that the adhesive strength will be insufficient.

Further, the adhesive forming the adhesive layer 27 may contain various additives within a range that does not impair lamination suitability. Examples of additives include inorganic fillers such as silica, alumina, aluminum flakes, and glass flakes, coupling agents, stabilizers (antioxidants, heat stabilizers, ultraviolet absorbers, etc.), plasticizers, antistatic agents, Examples include lubricants, antiblocking agents, colorants, fillers, crystal nucleating agents, and the like. Moreover, various thermoplastic resins may be blended for the purpose of adjusting the glass transition temperature of the cured coating film. As the thermoplastic resin, acrylic resin, ketone resin, epoxy resin, polyester resin, etc. can be used.

Furthermore, the adhesive may contain an inorganic compound having a flat shape for the purpose of imparting a higher gas barrier function. By containing a flat inorganic compound, the laminate strength and gas barrier properties can be improved.

Flat inorganic compounds include hydrated silicates (phyllosilicate minerals, etc.), kaolinite-serpentine clay minerals (halloysite, kaolinite, endellite, dickite, nacrite, etc., antigorite, chrysotile, etc.), and pyrophyllite. - Talc group (pyrophyllite, talc, kerolae, etc.), smectite group clay minerals (montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, stevensite, etc.), vermiculite group clay minerals (vermiculite, etc.), mica or mica group clay minerals (mica such as muscovite, phlogopite, margarite, tetrasilylic mica, teniolite, etc.), chlorite group (cuckeyeite, sudoite, clinochlore, chamosite, nimite, etc.), hydrotalcite, platy barium sulfate , boehmite, aluminum polyphosphate, etc. These minerals may be natural clay minerals or synthetic clay minerals.

Although the charge between the layers does not directly affect barrier properties, ionic inorganic compounds have significantly poor dispersibility in resins, and increasing the amount added poses problems in coating suitability (thixotropy). On the other hand, uncharged inorganic compounds are more preferred because coating suitability can be ensured even if the amount added is increased.

The particle size of the inorganic compound is preferably 0.1 to 100 μm, more preferably 1 to 40 μm. When the particle size of the inorganic compound is larger than about 1 μm, gas barrier properties are more likely to be exhibited, and when the particle size is smaller than about 1 μm, the gas barrier properties are lowered. Furthermore, if the particle size is too large, coating suitability cannot be obtained because the inorganic compound will not enter the gravure plate during gravure printing or the like.

Further, the aspect ratio of the flat inorganic compound is preferably high in order to improve the barrier ability due to the labyrinth effect of gas component molecules. Specifically, the number is preferably 3 or more, more preferably 10 or more, and most preferably 40 or more. Further, the content of the inorganic compound in the adhesive layer 27 is arbitrary, but is preferably 50% by mass or less. If it exceeds 50% by mass, the lamination operation may become difficult or the adhesive strength may become insufficient.

Examples of methods for dispersing inorganic compounds in resin compositions for adhesives include ultrasonic homogenizers, high-pressure homogenizers, paint conditioners, ball mills, roll mills, sand mills, sand grinders, Dyno mills, Dispermats, nanomills, SC mills, nanomizers, etc. can be mentioned. Even more preferably, examples of equipment capable of generating high shearing force include Henschel mixer, pressure kneader, Banbury mixer, planetary mixer, two rolls, three rolls, and the like. One of these devices may be used alone, or two or more types of devices may be used in combination.

In the wrapping paper 20 having the above structure, the coating layer 21 coated on one side of the paper base material 25 has gas barrier properties, and the heat adhesive resin layer 28 is coated on the other side via an adhesive layer 27 made of a gas barrier adhesive. will be arranged. Therefore, even if cracks occur in the coating layer 21 of the wrapping paper 20 that is folded during bag manufacturing of the packaging bag 1, the adhesive layer 27 made of the gas barrier adhesive can suppress the deterioration of the gas barrier properties of the wrapping paper 20. I can do it. Therefore, a packaging bag 1 with high gas barrier properties can be obtained.

Further, since the wrapping paper 20 does not include a vapor-deposited film having gas barrier properties, the costs of the wrapping paper 20 and the packaging bag 1 can be reduced.

Further, the gas barrier adhesive forming the adhesive layer 27 contains a main ingredient made of a resin having two or more hydroxyl groups in one molecule, and a curing agent made of a polyisocyanate having an isocyanate group having a valence of two or more. Thereby, gas barrier properties of the adhesive layer 27 can be easily achieved. At this time, if the gas barrier adhesive forming the adhesive layer 27 is a solvent-free adhesive, the step of removing the solvent by drying can be omitted, and it is possible to prevent odor from remaining in the packaging bag 1 due to the organic solvent. I can do it.

Moreover, since the second barrier layer 21b of the coating layer 21 contains polyvinyl alcohol and kaolin, the coating layer 21 with high oxygen barrier properties can be easily obtained.

Examples of the packaging bag 1 will be described below. The paper base material 25 of the wrapping paper 20 forming the packaging bag 1 of this example was made of double-sided kraft paper (basis weight 70 g/m ² ).

The coating liquid for the first barrier layer 21a is prepared by adding sodium polyacrylate as a dispersant to large-particle engineered kaolin (Varisurf HX manufactured by Imerys, particle size 9.0 μm, aspect ratio 80 to 100). (0.2 parts of pigment) was dispersed in a Serie mixer to prepare a large-particle kaolin slurry with a solid content concentration of 55%. Styrene-butadiene latex (Nippon Zeon Co., Ltd. PNT7868) was blended into the obtained kaolin slurry at a concentration of 100 parts by weight (solid content) per 100 parts by weight of the inorganic pigment, and coating was carried out at a solid content concentration of 50%. I got the liquid.

The coating liquid for the second barrier layer 21b is an inorganic pigment, large-particle engineered kaolin (Varisurf HX manufactured by Imerys, particle size 9.0 μm, aspect ratio 80-100), with sodium polyacrylate added as a dispersant. (0.2 part of inorganic pigment) and dispersed with a Serie mixer to prepare a large-particle kaolin slurry with a solid content concentration of 55%. Polyvinyl alcohol (PVA117 manufactured by Kuraray Co., Ltd.) was prepared to have a solid content concentration of 10% to obtain a PVA solution. The obtained kaolin slurry and a PVA solution were mixed in a solid content of pigment:PVA=100:100 so that the solid content concentration was 10% to prepare a coating liquid.

The first barrier layer 21a is formed by applying the coating liquid of the first barrier layer 21a to one side of the paper base material 25 using a blade coater at a coating speed of 300 m/min so that the coating amount is 15 g/m ² (dry weight). It was formed by coating and drying. The second barrier layer 21b is formed by applying the coating liquid of the second barrier layer 21b onto the first barrier layer 21a using an air knife coater at a coating speed of 50 m/min so that the coating amount is 4.0 g/m ² (dry weight). It was formed by drying after coating. As a result, a coated paper 26 having a basis weight of 89 g/m ² and a paper thickness of 103 μm was produced.

The thermoadhesive resin layer 28 was formed of a linear low-density polyethylene film, coated with a gas barrier adhesive at 5 g/m ² (dry weight), and dry laminated with the paper base material 25 . The gas barrier adhesive is a solvent-free type that contains a main ingredient mainly composed of polyester polyol and a curing agent mainly composed of m-xylylene diisocyanate, and 30% by mass of an inorganic compound (kaolin) is added.

<Comparative example>
The wrapping paper of the packaging bag 1 of the comparative example was obtained by dry laminating the same coated paper 26 and thermoadhesive resin layer 28 as in the example using a urethane-based dry laminating adhesive. Adhesives for dry lamination do not have gas barrier properties.

The oxygen permeability and water vapor permeability of the wrapping paper 20 of the above Examples and Comparative Examples were measured before and after the wrapping paper 20 was made into a packaging bag 1. Oxygen permeability was measured using an oxygen permeability measuring device (OX-TRAN2/21 manufactured by MOCON) under conditions of 23°C and 0% RH (dry) and 23°C and 85% RH (under high humidity). It was measured using The water vapor permeability was measured using a moisture permeability meter (manufactured by Dr. Lyssy, L80-4000) at a temperature of 40±0.5° C. and a relative humidity of 90±2% (high humidity). The results of each measurement are shown in Table 1.

As shown in Table 1, in this example, the wrapping paper 20 has low oxygen permeability and water vapor permeability before and after bag making, and has high gas barrier properties. On the other hand, in the comparative example, the oxygen permeability and water vapor permeability of the wrapping paper 20 before bag making are low, but the oxygen permeability of the wrapping paper 20 after bag making is high, and the water vapor permeability is within the detection range of the measuring instrument. It has become higher than that.

Therefore, by forming the coating layer 21 with gas barrier properties and forming the adhesive layer 27 with a gas barrier adhesive, it is possible to obtain the packaging bag 1 with high gas barrier properties.

According to the present invention, it can be used for packaging bags for foods, etc.

1 Packaging bag 2 Back seal portion 3 Edge seal portion 4 Body portion 20 Wrapping paper 21 Coating layer 21a First barrier layer 21b Second barrier layer 25 Paper base material 26 Coated paper 27 Adhesive layer 28 Heat-adhesive resin layer

Claims (4)

A wrapping paper comprising a paper base material, a coating layer coated on one side of the paper base material, and a thermoadhesive resin layer disposed on the other surface of the paper base material via an adhesive layer, wherein the coating The layer has gas barrier properties, and the adhesive layer is formed of a gas barrier adhesive,
The gas barrier adhesive is composed of a main resin having two or more hydroxyl groups in one molecule and having a viscosity of 10,000 mPas or less at 60°C, and a polyisocyanate having an isocyanate group having a valence of 2 or more and having a viscosity of 10,000 mPas or less at 60°C. A solvent-free adhesive containing a curing agent with a viscosity of 300 to 4000 mPas , and a flat inorganic compound having an aspect ratio of 40 or more, and the content of the inorganic compound in the adhesive layer is 50% by mass. A wrapping paper characterized by: The wrapping paper according to claim 1, wherein the inorganic compound has a particle size of 1 to 40 μm. The wrapping paper according to claim 1 or 2, wherein the coating layer contains polyvinyl alcohol and kaolin. A packaging bag characterized by being formed from the wrapping paper according to any one of claims 1 to 3.

Images