JP2022113738A - Laminate and packaging bag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate capable of being subjected to high-temperature retort treatment when formed into a packaging bag even if mainly composed of a polyolefin-based film.

SOLUTION: There is provided a laminate which comprises a first base material layer, a second base material layer and a sealant layer in this order, wherein all of the first base material layer, the second base material layer and the sealant layer contain a polyolefin film, the polyolefin film of the first base material layer and the second base material layer comprise an inorganic oxide layer on at least one surface and the heat shrinkage rate in the traveling direction after heating at 120°C for 15 minutes in each of the first base material layer, the second base material layer and the sealant layer satisfies the following expressions: the heat shrinkage rate of the second base material layer≤5% (Expression 1), the heat shrinkage rate of the second base material layer≥the heat shrinkage rate of the first base material layer (Expression 2) and the heat shrinkage rate of the second base material layer≥the heat shrinkage rate of the sealant layer (Expression 3).

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present disclosure relates to laminates and packaging bags.

Laminates are known that include a biaxially oriented PET (polyethylene terephthalate) film having excellent heat resistance and toughness as a base film and a polyolefin film such as polyethylene or polypropylene as a sealant layer (for example, Patent Document 1).

JP 2017-178357 A

By the way, in recent years, due to the heightened environmental awareness stemming from the problem of marine plastic litter and the like, there has been a demand for more efficient separate collection and recycling of plastic materials. In other words, there is a growing demand for monomaterials even in packaging laminates, which have conventionally been designed to achieve higher performance by combining various different types of materials.

In order to realize a mono-material in the laminate, it is necessary to use the same material for the constituent films. However, when a laminate is produced using a polyolefin-based film, there is a possibility that the resulting packaging bag may not withstand high-temperature retorting.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a laminate that can be subjected to high-temperature retort processing when used as a packaging bag, even if it is mainly composed of a polyolefin film. and Another object of the present invention is to provide a packaging bag using the laminate.

One aspect of the present invention includes a first base layer, a second base layer and a sealant layer in this order, and the first base layer, the second base layer and the sealant layer all include a polyolefin film. , the polyolefin film of the first base layer or the second base layer is provided with an inorganic oxide layer on at least one surface, and the first base layer, the second base layer and the sealant layer Provided is a laminate in which the heat shrinkage in the running direction (MD direction) after heating at 120° C. for 15 minutes satisfies the following formula.
Thermal shrinkage rate of the second base material layer ≤ 5% (Equation 1)
Thermal shrinkage rate of the second base layer≧Heat shrinkage rate of the first base layer (Formula 2)
Thermal shrinkage rate of the second base material layer≧Heat shrinkage rate of the sealant layer (Formula 3)
(However, thermal shrinkage rate (%) = (running direction length before heating - running direction length after heating) / running direction length before heating x 100)

In one aspect, the thermal shrinkage rate may satisfy the following formula.
Thermal shrinkage rate of the second base material layer−Heat shrinkage rate of the first base layer≧0.3% (Equation 4)
Thermal shrinkage rate of the second base material layer - Thermal shrinkage rate of the sealant layer ≥ 0.5% (Formula 5)

In one aspect, the thermal shrinkage rate may satisfy the following formula.
Thermal shrinkage rate of sealant layer ≤ 2% (Equation 6)

In one aspect, the polyolefin film of the first substrate layer or the second substrate layer comprises the inorganic oxide layer on at least one surface, and a gas barrier coating layer on the inorganic oxide layer, A composition for forming a gas-barrier coating layer, wherein the gas-barrier coating layer contains at least one selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, silane coupling agents, and hydrolysates thereof. may be formed using

In one aspect, the inorganic oxide layer may comprise silicon oxide.

In one aspect, the laminate may be for retort pouches.

One aspect of the present invention also provides a packaging bag formed by bag-making the laminate.

According to the present invention, it is possible to provide a laminate that can be subjected to high-temperature retort treatment when used as a packaging bag, even if the laminate is mainly composed of a polyolefin film. Moreover, according to this invention, the packaging bag using the said laminated body can be provided.

FIG. 1 is a schematic cross-sectional view showing a laminate according to one embodiment.

Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings as the case may be. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios.

<Laminate>
FIG. 1 is a schematic cross-sectional view showing a laminate according to one embodiment. A laminate 100 shown in FIG. 1 includes a first base material layer 11, a second base material layer 12, and a sealant layer 13 in this order. The first base material layer 11 and the second base material layer 12, and the second base material layer 12 and the sealant layer 13 may be bonded with an adhesive layer S, respectively. The first substrate layer, the second substrate layer and the sealant layer all comprise polyolefin films. The polyolefin film of the first substrate layer or the second substrate layer has an inorganic oxide layer on at least one surface from the viewpoint of improving gas barrier properties against water vapor and oxygen, for example. Since a polyolefin film having an inorganic oxide layer has gas barrier properties, such a first base material layer or second base material layer can be referred to as a gas barrier base material layer. Each layer will be described below.

[First base material layer 11]
A 1st base material layer is a film used as one of a support body, and contains a polyolefin film. A 1st base material layer may consist of a polyolefin film. Examples of polyolefin films include polyethylene film (PE), polypropylene film (PP), polybutene film (PB), and the like. Examples of the polyolefin film include an acid-modified polyolefin film obtained by graft-modifying a polyolefin with an unsaturated carboxylic acid, an acid anhydride of an unsaturated carboxylic acid, an ester of an unsaturated carboxylic acid, or the like.

The polyolefin film that constitutes the first substrate layer may be a stretched film or a non-stretched film. However, from the viewpoint of impact resistance, heat resistance, water resistance, dimensional stability, etc., the polyolefin film may be a stretched film. Accordingly, the laminate can be more preferably used for retort treatment and boiling treatment. The stretching method is not particularly limited, and any method, such as inflation stretching, uniaxial stretching, or biaxial stretching, may be used as long as a film with stable dimensions can be supplied.

The polyolefin film thickness is not particularly limited. The thickness may be 6 to 200 μm depending on the application, but may be 9 to 50 μm or 12 to 38 μm from the viewpoint of obtaining excellent impact resistance and gas barrier properties.

The polyolefin film may be subjected to various pretreatments such as corona treatment, plasma treatment, flame treatment, etc., or may be provided with a coating layer such as an easy-adhesion layer on its lamination surface, as long as the barrier performance is not impaired.

(Adhesion layer)
When the polyolefin film has an inorganic oxide layer, an adhesion layer (anchor coat layer) may be provided on the surface of the polyolefin film on which the inorganic oxide layer is laminated. The adhesion layer is provided on the polyolefin film, and can obtain two effects of improving the adhesion performance between the polyolefin film and the inorganic oxide layer and improving the smoothness of the surface of the polyolefin film. By improving the smoothness, it becomes easier to form an inorganic oxide layer uniformly without defects, and it is easy to develop a high barrier property. The adhesion layer can be formed using an anchor coating agent.

Examples of anchor coating agents include polyester-based polyurethane resins and polyether-based polyurethane resins. As the anchor coating agent, a polyester-based polyurethane resin is preferable from the viewpoint of heat resistance and interlayer adhesive strength.

Although the thickness of the adhesion layer is not particularly limited, it is preferably in the range of 0.01 to 5 μm, more preferably in the range of 0.03 to 3 μm, and particularly in the range of 0.05 to 2 μm. preferable. When the thickness of the adhesion layer is at least the above lower limit, there is a tendency to obtain more sufficient interlayer adhesive strength.

As a method for coating the adhesion layer on the polyolefin film, known coating methods can be used without particular limitation, and examples thereof include a dipping method (dipping method); a method using a spray, a coater, a printer, a brush, and the like. . The types of coaters and printing machines used in these methods and their coating methods include gravure coaters such as direct gravure, reverse gravure, kiss reverse gravure, and offset gravure, reverse roll coaters, and micro gravure. A coater, a coater combined with a chamber doctor, an air knife coater, a dip coater, a bar coater, a comma coater, a die coater and the like can be used.

The coating amount of the adhesion layer is preferably 0.01 to 5 g/m ² , more preferably 0.03 to 3 g/m ² in mass per 1 m ² after the anchor coating agent is applied and dried. is more preferable. When the mass per 1 m ² after coating and drying the anchor coating agent is at least the above lower limit, film formation tends to be sufficient. It tends to be difficult to remain.

The method for drying the adhesion layer is not particularly limited, but a method of natural drying, a method of drying in an oven set to a predetermined temperature, a dryer attached to the coater, such as an arch dryer, floating dryer, drum dryer, etc. A method using an infrared drier or the like can be mentioned. Furthermore, the drying conditions can be appropriately selected according to the drying method. For example, in the method of drying in an oven, it is preferable to dry at a temperature of 60 to 100° C. for about 1 second to 2 minutes.

As the adhesion layer, a polyvinyl alcohol-based resin can be used instead of the polyurethane resin. As the polyvinyl alcohol-based resin, any resin having a vinyl alcohol unit obtained by saponifying a vinyl ester unit may be used, and examples thereof include polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH).

As PVA, for example, vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate are polymerized alone. and then saponified resins. The PVA may be copolymer-modified or post-modified modified PVA. Modified PVA can be obtained, for example, by copolymerizing a vinyl ester and an unsaturated monomer copolymerizable with the vinyl ester, followed by saponification. Examples of unsaturated monomers copolymerizable with vinyl esters include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene; 3-buten-1-ol, 4-pentyn-1-ol; , hydroxy group-containing α-olefins such as 5-hexene-1-ol; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid; acrylonitrile, methacrylonitrile, etc. Nitriles; amides such as diacetone acrylamide, acrylamide, methacrylamide; olefin sulfonic acids such as ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid; alkyl vinyl ethers, dimethyl allyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene Vinyl compounds such as carbonates, 2,2-dialkyl-4-vinyl-1,3-dioquinane, glycerin monoallyl ether, 3,4-diacetoxy-1-butene; vinylidene chloride, 1,4-diacetoxy-2-butene, Vinylene carbonate etc. are mentioned.

The degree of polymerization of PVA is preferably 300-3000. If the degree of polymerization is less than 300, the barrier properties tend to deteriorate, and if it exceeds 3000, the viscosity is too high and the coatability tends to deteriorate. The degree of saponification of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 99 mol% or more. Moreover, the degree of saponification of PVA may be 100 mol % or less or 99.9 mol % or less. The degree of polymerization and degree of saponification of PVA can be measured according to the method described in JIS K 6726 (1994).

EVOH is generally a copolymer of ethylene and an acid vinyl ester such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate. Obtained by saponifying the union.

The degree of polymerization of EVOH is preferably 300-3000. If the degree of polymerization is less than 300, the barrier properties tend to deteriorate, and if it exceeds 3000, the viscosity is too high and the coatability tends to deteriorate. The degree of saponification of the vinyl ester component of EVOH is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 99 mol% or more. Further, the degree of saponification of EVOH may be 100 mol % or less or 99.9 mol % or less. The degree of saponification of EVOH is determined by nuclear magnetic resonance (1H-NMR) measurement and from the peak area of hydrogen atoms contained in the vinyl ester structure and the peak area of hydrogen atoms contained in the vinyl alcohol structure.

The ethylene unit content of EVOH is 10 mol % or more, preferably 15 mol % or more, even more preferably 20 mol % or more, and particularly preferably 25 mol % or more. The ethylene unit content of EVOH is preferably 65 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less. When the ethylene unit content is 10 mol % or more, good gas barrier properties or dimensional stability under high humidity can be maintained. On the other hand, when the ethylene unit content is 65 mol% or less, gas barrier properties can be enhanced. The ethylene unit content of EVOH can be determined by the NMR method.

When a polyvinyl alcohol-based resin is used as the adhesion layer, methods for forming the adhesion layer include coating using a polyvinyl alcohol-based resin solution, multilayer extrusion, and the like.

(Inorganic oxide layer)
When the polyolefin film has an inorganic oxide layer, examples of inorganic oxides contained in the inorganic oxide layer include aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the viewpoint of transparency and barrier properties, the inorganic oxide may be selected from the group consisting of aluminum oxide, silicon oxide and magnesium oxide. In addition, from the viewpoint of excellent tensile stretchability during processing, it is preferable that the inorganic oxide layer is a layer using silicon oxide. By using the inorganic oxide layer, it is possible to obtain a high barrier property with a very thin layer that does not affect the recyclability of the laminate.

The O/Si ratio of the inorganic oxide layer is desirably 1.7 or more. When the O/Si ratio is 1.7 or more, the content of metal Si is suppressed, and good transparency can be easily obtained. Also, the O/Si ratio is preferably 2.0 or less. When the O/Si ratio is 2.0 or less, the crystallinity of SiO becomes high, and the inorganic oxide layer can be prevented from becoming too hard, and good tensile resistance can be obtained. Thereby, it is possible to suppress the occurrence of cracks in the inorganic oxide layer when laminating the gas barrier coating layer. In addition, even after molding into a packaging bag, the polyolefin film may shrink due to heat during boiling or retorting, but the inorganic oxide layer can easily follow the shrinkage because the O/Si ratio is 2.0 or less. , the decrease in barrier properties can be suppressed. From the viewpoint of sufficiently obtaining these effects, the O/Si ratio of the inorganic oxide layer is preferably 1.75 or more and 1.9 or less, and more preferably 1.8 or more and 1.85 or less.

The O/Si ratio of the inorganic oxide layer can be determined by X-ray photoelectron spectroscopy (XPS). For example, the measurement device is an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., trade name: JPS-90MXV), and the X-ray source is non-monochromatic MgKα (1253.6 eV), 100 W (10 kV-10 mA ) can be measured at the X-ray output of A relative sensitivity factor of 2.28 for O1s and 0.9 for Si2p, respectively, can be used for quantitative analysis to determine the O/Si ratio.

The film thickness of the inorganic oxide layer is preferably 10 nm or more and 50 nm or less. When the film thickness is 10 nm or more, sufficient water vapor barrier properties can be obtained. Moreover, when the film thickness is 50 nm or less, it is possible to suppress the occurrence of cracks due to deformation due to the internal stress of the thin film, and to suppress the deterioration of the water vapor barrier properties. If the film thickness exceeds 50 nm, it is not preferable from an economical point of view because the cost tends to increase due to an increase in the amount of material used and an increase in film formation time. From the same viewpoint as above, the film thickness of the inorganic oxide layer is more preferably 20 nm or more and 40 nm or less.

The inorganic oxide layer can be formed, for example, by vacuum deposition. A physical vapor deposition method or a chemical vapor deposition method can be used in vacuum deposition. Examples of the physical vapor deposition method include a vacuum deposition method, a sputtering method, an ion plating method, and the like, but are not limited to these. Examples of chemical vapor deposition methods include thermal CVD, plasma CVD, and optical CVD, but are not limited to these.

In the vacuum film formation, a resistance heating vacuum deposition method, an EB (Electron Beam) heating vacuum deposition method, an induction heating vacuum deposition method, a sputtering method, a reactive sputtering method, a dual magnetron sputtering method, and a plasma chemical vapor deposition method. (PECVD method) and the like are particularly preferably used. However, considering the productivity, the vacuum deposition method is the best at present. As a heating means for the vacuum vapor deposition method, it is preferable to use any one of an electron beam heating method, a resistance heating method, and an induction heating method.

(Gas barrier coating layer)
The polyolefin film may be provided with a gas barrier coating layer on the inorganic oxide layer. The gas barrier coating layer uses a composition for forming a gas barrier coating layer containing at least one selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, silane coupling agents, and hydrolysates thereof. It is a layer formed by

The gas barrier coating layer is a coating layer having gas barrier properties, and is an aqueous solution containing at least one selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, silane coupling agents, and hydrolysates thereof. Alternatively, it is formed using a gas-barrier coating layer-forming composition (hereinafter also referred to as coating agent) containing a water/alcohol mixed solution as a main component. The coating agent preferably contains at least a silane coupling agent or a hydrolyzate thereof, from the viewpoint of more sufficiently maintaining gas barrier properties after hot water treatment such as retort treatment. It is more preferable to contain at least one selected from the group consisting of hydrolysates thereof and a silane coupling agent or a hydrolyzate thereof, a hydroxyl group-containing polymer compound or a hydrolyzate thereof, a metal alkoxide or It is more preferable to contain a hydrolyzate thereof and a silane coupling agent or a hydrolyzate thereof. The coating agent is prepared by, for example, adding a metal alkoxide and a silane coupling agent directly to a solution obtained by dissolving a hydroxyl group-containing polymer compound, which is a water-soluble polymer, in an aqueous (water or water/alcohol mixed) solvent, or by hydrolyzing it in advance. It can be prepared by mixing products that have been subjected to a treatment such as mixing.

Each component contained in the coating agent for forming the gas barrier coating layer will be described in detail. Polyvinyl alcohol, polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, sodium alginate and the like can be mentioned as the hydroxyl group-containing polymer compound used for the coating agent. Among these, when polyvinyl alcohol (PVA) is used as the coating agent for the gas-barrier coating layer, it is particularly preferable because of its excellent gas-barrier properties.

From the viewpoint of obtaining excellent gas barrier properties, the gas barrier coating layer is formed from a composition containing at least one selected from the group consisting of metal alkoxides represented by the following general formula (I) and hydrolysates thereof. is preferred.
M (OR ¹ ) _m (R ² ) _nm (I)
In general formula (I) above, R ¹ and R ² are each independently a monovalent organic group having 1 to 8 carbon atoms, preferably an alkyl group such as methyl or ethyl. M represents an n-valent metal atom such as Si, Ti, Al, Zr. m is an integer from 1 to n. When there are a plurality of R ¹ or R ² , R ^1s or R ^2s may be the same or different.

Specific examples of metal alkoxides include tetraethoxysilane [Si(OC ₂ H ₅ ) ₄ ] and triisopropoxyaluminum [Al(O-2′-C ₃ H ₇ ) ₃ ]. Tetraethoxysilane and triisopropoxyaluminum are preferred because they are relatively stable in aqueous solvents after hydrolysis.

Silane coupling agents include compounds represented by the following general formula (II).
Si(OR ¹¹ ) _p (R ¹² ) _3-p R ¹³ (II)
In general formula (II) above, R ¹¹ represents an alkyl group such as a methyl group or an ethyl group; R ¹² represents an alkyl group, an aralkyl group, an aryl group, an alkenyl group, an alkyl group substituted with an acryloxy group, or a methacryloxy represents a monovalent organic group such as an alkyl group substituted with a group, R ¹³ represents a monovalent organic functional group, and p represents an integer of 1-3. When there are a plurality of R ¹¹ or R ¹² , R ¹¹ or R ¹² may be the same or different. The monovalent organic functional group represented by R ¹³ includes a glycidyloxy group, an epoxy group, a mercapto group, a hydroxyl group, an amino group, an alkyl group substituted with a halogen atom, or a monovalent organic functional group containing an isocyanate group. groups.

Specific examples of silane coupling agents include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ- Examples include silane coupling agents such as methacryloxypropylmethyldimethoxysilane.

Also, the silane coupling agent may be a polymer obtained by polymerizing the compound represented by the general formula (II). The polymer is preferably a trimer, more preferably 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate. This is a condensation polymer of 3-isocyanatoalkylalkoxysilane. It is known that this 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate loses chemical reactivity in the isocyanate portion, but the reactivity is ensured by the polarity of the nurate portion. In general, it is added to adhesives and the like like 3-isocyanate alkylalkoxysilane, and is known as an adhesion improver. Therefore, by adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl group-containing polymer compound, the water resistance of the gas barrier coating layer can be improved by hydrogen bonding. 3-Isocyanatoalkylalkoxysilane has high reactivity and low liquid stability, whereas 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate has a nurate portion that is not water-soluble due to its polarity. However, it is easy to disperse in an aqueous solution and can keep the liquid viscosity stable. Also, the water resistance performance is equivalent between 3-isocyanatoalkylalkoxysilane and 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate.

Some 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates are produced by thermal condensation of 3-isocyanatopropylalkoxysilane, and may contain 3-isocyanatopropylalkoxysilane as a starting material. However, there is no particular problem. More preferred is 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate, and more preferred is 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate. 1,3,5-Tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous because the methoxy group has a high hydrolysis rate and those containing a propyl group are available at a relatively low cost.

In addition, known additives such as isocyanate compounds, dispersants, stabilizers, viscosity modifiers, and colorants can be added to the coating agent as needed, as long as the gas barrier property is not impaired. .

The thickness of the gas barrier coating layer is preferably 50-1000 nm, more preferably 100-500 nm. When the thickness of the gas barrier coating layer is 50 nm or more, it tends to be possible to obtain more sufficient gas barrier properties, and when it is 1000 nm or less, it tends to be able to maintain sufficient flexibility.

The coating liquid for forming the gas barrier coating layer can be applied, for example, by a dipping method, a roll coating method, a gravure coating method, a reverse gravure coating method, an air knife coating method, a comma coating method, a die coating method, a screen printing method, a spray coating method, It can be applied by a gravure offset method or the like. A coating film obtained by applying this coating liquid can be dried by, for example, a hot air drying method, a hot roll drying method, a high frequency irradiation method, an infrared irradiation method, a UV irradiation method, or a combination thereof.

The temperature for drying the coating film can be, for example, 50 to 150°C, preferably 70 to 100°C. By setting the drying temperature within the above range, the occurrence of cracks in the inorganic oxide layer and the gas barrier coating layer can be further suppressed, and excellent barrier properties can be exhibited.

The gas barrier coating layer may be formed using a coating agent containing a polyvinyl alcohol-based resin and a silane compound. Acid catalysts, alkali catalysts, photopolymerization initiators, and the like may be added to the coating agent as necessary.

The polyvinyl alcohol-based resin is as described above. Examples of silane compounds include silane coupling agents, polysilazanes, siloxanes, etc. Specific examples include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, hexamethyl and disilazane.

(Print layer)
A printed layer can be provided on the second substrate layer side of the first substrate layer. The printed layer is provided at a position visible from the outside of the laminate for the purpose of displaying information about the contents, identifying the contents, or improving the design of the packaging bag. The printing method and printing ink are not particularly limited, and are appropriately selected from known printing methods and printing inks in consideration of printability on film, design properties such as color tone, adhesion, safety as a food container, etc. be. Examples of printing methods that can be used include gravure printing, offset printing, gravure offset printing, flexographic printing, and inkjet printing. Among them, the gravure printing method can be preferably used from the viewpoint of productivity and high definition of the pattern.

In order to improve the adhesion of the printed layer, the surface of the first substrate layer on the second substrate layer side is subjected to various pretreatments such as corona treatment, plasma treatment, flame treatment, etc., or a coating layer such as an easy adhesion layer. can be set. Examples of the surface of the first substrate layer on the second substrate layer side include the surface of the polyolefin film (when the first substrate layer is not a gas barrier substrate layer), the surface of the gas barrier coating layer (when the first substrate layer is in the case of a gas barrier substrate layer).

[Second base material layer 12]
For the configuration of the second base material layer, the above description regarding the configuration of the first base material layer can be appropriately referred to. When the first substrate layer is a gas barrier substrate layer, the second substrate layer does not have to be a gas barrier substrate layer. One substrate layer need not be a gas barrier substrate layer.

(Adhesive layer S)
The first base layer and the second base layer can be laminated via the adhesive layer. As the material of the adhesive, for example, polyester-isocyanate resin, urethane resin, polyether resin, or the like can be used. In order to use the packaging bag for retort applications, a two-liquid curable urethane adhesive that is resistant to retort can be preferably used.

[Sealant layer 13]
The sealant layer is a layer that imparts sealing properties by heat sealing in the laminate, and includes a polyolefin film. The sealant layer may consist of a polyolefin film.

Among thermoplastic resins, polyolefin-based resins are generally used as the material for the sealant layer. Specifically, low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin. (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-based resins, blended resins of polyethylene and polybutene, and homopolypropylene Resins (PP), polypropylene-based resins such as propylene-ethylene random copolymers, propylene-ethylene block copolymers, and propylene-α-olefin copolymers can be used. These thermoplastic resins can be appropriately selected depending on the application and temperature conditions such as boiling and retort treatment.

Various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers and tackifiers may be added to the polyolefin film constituting the sealant layer.

The thickness of the sealant layer is determined according to the mass of the contents, the shape of the packaging bag, etc., but the thickness is preferably approximately 30 to 150 μm.

As a method for forming the sealant layer, there is a dry lamination method in which a film-like sealant layer made of the thermoplastic resin described above is laminated with an adhesive such as a one-component curing type or two-component curing type urethane adhesive, or a film-like sealant layer. A non-solvent dry lamination method in which the is laminated using a solvent-free adhesive, an extrusion lamination method in which the above-mentioned thermoplastic resin is heated and melted, extruded in a curtain shape, and laminated. can.

Among the above forming methods, the dry lamination method is preferable due to its high resistance to retort treatment, particularly high-temperature hot water treatment at 120° C. or higher. On the other hand, the lamination method is not particularly limited as long as the packaging bag is used for processing at a temperature of 85° C. or lower.

[Thermal shrinkage of each layer]
In the laminate, the heat shrinkage in the running direction (MD direction) after heating at 120° C. for 15 minutes in each of the first substrate layer, the second substrate layer and the sealant layer satisfies the following formula.
Thermal shrinkage rate of the second base material layer ≤ 5% (Equation 1)
Thermal shrinkage rate of the second base layer≧Heat shrinkage rate of the first base layer (Formula 2)
Thermal shrinkage rate of the second base material layer≧Heat shrinkage rate of the sealant layer (Formula 3)

Here, the thermal shrinkage rate (%) is a value calculated by the following formula.
(Length in running direction before heating - Length in running direction after heating)/Length in running direction before heating x 100
The procedure for measuring the thermal shrinkage rate is as follows.
(1) A 20 cm x 20 cm piece of the layer to be measured is cut out and used as a measurement sample.
(2) Draw a line of 10 cm in the running direction of the measurement sample (running direction length before heating).
(3) Heat the measurement sample at 120° C. for 15 minutes.
(4) Measure the running direction length of the written line (running direction length after heating).
(5) Calculate the thermal contraction rate from the above formula.

The heat shrinkage rate of the second base material layer is 5% or less. As a result, cracks are less likely to occur in the gas-barrier coating layer during barrier processing, resulting in good barrier properties. From this point of view, the heat shrinkage rate can be 4% or less, and may be 3% or less. In addition, since it takes time to heat-set (thermally fix) a film having a very small heat shrinkage, there is a situation that the productivity is greatly deteriorated. From this point of view, the lower limit of the heat shrinkage rate of the second base material layer can be set to 1.5% or more.

The thermal contraction rate of the second base layer is equal to or higher than that of the first base layer and is equal to or higher than that of the sealant layer. By sandwiching and laminating the second base material layer between the first base material layer and the sealant layer having a heat shrinkage rate smaller than that of the second base material layer, the heat shrinkage rate of the laminate is reduced. can be done. As a result, the reduction of the gas barrier function during retort treatment is suppressed, so the barrier properties after retort treatment can be maintained. From this point of view, the thermal shrinkage rate of the second base layer - the thermal shrinkage rate of the first base layer can be 0.3% or more, and may be 0.5% or more. If the thermal shrinkage rate of the second base material layer is larger than the thermal shrinkage rate of the first base material layer by a certain amount or more, it becomes difficult to obtain the effect of reducing the shrinkage rate of the laminate. Since this makes it difficult to suppress the reduction in the gas barrier function, the upper limit of the thermal shrinkage rate of the second base layer minus the thermal shrinkage rate of the first base layer can be set to 1.5% or less. Also, the heat shrinkage ratio of the second base material layer-the heat shrinkage ratio of the sealant layer may be 0.5% or more, and may be 1.0% or more. If the heat shrinkage rate of the second base material layer is larger than the heat shrinkage rate of the sealant layer by a certain amount or more, it becomes difficult to obtain the effect of reducing the shrinkage rate of the laminate. As a result, it becomes difficult to suppress the reduction in the gas barrier function, so the upper limit of the thermal shrinkage rate of the second base material layer - the thermal shrinkage rate of the sealant layer can be set to 3.0% or less.

The heat shrinkage of the sealant layer can be 2% or less. This makes it easier to suppress thermal shrinkage of the laminate. From this point of view, the thermal shrinkage may be 1% or less.

As described above, all the films constituting the laminate can be polyolefin films. Such a laminate can be said to be a (mono-material) packaging material made of a single material with excellent recyclability. From this point of view, the total mass of components other than polyolefin components (for example, adhesive and ink components) can be 10% by mass or less, and may be 7.5% by mass or less, relative to the total mass of the laminate. .

In addition, the laminate can be subjected to high-temperature retort processing when used as a packaging bag, and can be suitably used for retort pouch applications.

<Packaging bag>
A packaging bag is produced by bagging the laminate described above. The packaging bag may be one in which one laminate is folded in two so that the sealant layers face each other, and then heat-sealed on three sides to form a bag shape. After stacking them so that they face each other, the four sides may be heat-sealed to form a bag shape. The packaging bag accommodates contents such as food and medicine as contents, and can be subjected to heat sterilization treatment such as retort treatment and boiling treatment.

Retort processing is a method of autoclave sterilization of microorganisms such as molds, yeasts, and bacteria, generally for the purpose of preserving food, pharmaceuticals, and the like. Usually, a packaging bag containing food or the like is autoclaved at 105 to 140° C. and 0.15 to 0.30 MPa for 10 to 120 minutes. There are two types of retort equipment: a steam type using heated steam and a hot water type using pressurized heated water. Boiling treatment is a wet heat sterilization method for preserving foods, medicines, and the like. Usually, depending on the contents, a packaging bag containing food or the like is subjected to wet heat sterilization at 60 to 100° C. under atmospheric pressure for 10 to 120 minutes. Boiling treatment is usually carried out at 100° C. or less using a hot water bath. As a method, there are a batch method in which the material is immersed in a hot water bath at a constant temperature and taken out after being treated for a certain period of time, and a continuous method in which the material is passed through a hot water bath through a tunnel.

The above packaging bag is particularly suitable for use in retorting at a temperature of 120° C. or higher. A packaging bag using the laminate can maintain excellent barrier properties even when subjected to retort treatment.

The present disclosure will be described in more detail by the following examples, but the present disclosure is not limited to these examples.

<Preparation of First Base Layer and Second Base Layer>
The following stretched polypropylene films were prepared as the first base layer and the second base layer. The term "shrinkage rate" hereinafter means the thermal shrinkage rate in the running direction (MD direction) after heating at 120°C for 15 minutes.
[First base material layer]
OPP (shrinkage rate 2.0%): thickness 20 μm
OPP (shrinkage rate 3.1%): thickness 20 μm
OPP (shrinkage rate 4.1%): thickness 20 μm
EVOH-OPP (shrinkage rate 2.0%): thickness 18 μm. An EVOH layer (adhesion layer) provided on an OPP film.
[Second base material layer]
OPP (shrinkage rate 2.6%): thickness 20 μm
OPP (shrinkage rate 2.6%): thickness 18 μm
OPP (shrinkage rate 3.8%): thickness 20 μm
EVOH-OPP (2.6% shrinkage): thickness 18 μm. An EVOH layer (adhesion layer) provided on an OPP film.

The method for producing the gas barrier substrate layer is as follows.

[Preparation of Composition for Forming Adhesion Layer]
Acrylic polyol and tolylene diisocyanate are mixed so that the number of NCO groups of tolylene diisocyanate is equal to the number of OH groups of acrylic polyol, and the total solid content (total amount of acrylic polyol and tolylene diisocyanate ) was diluted with ethyl acetate to 5% by mass. To the mixed solution after dilution, β-(3,4 epoxycyclohexyl)trimethoxysilane was further added so as to be 5 parts by mass with respect to the total amount of 100 parts by mass of the acrylic polyol and tolylene diisocyanate, and these were mixed. By doing so, a composition for forming an adhesion layer (anchor coating agent) was prepared.

[Preparation of composition for forming gas barrier coating layer]
A composition for forming a gas barrier coating layer was prepared by mixing the following A liquid, B liquid and C liquid at a mass ratio of 65/25/10, respectively.
Solution _A : Solid content of ₅ % by mass ₍ SiO ₂ equivalent) hydrolysis solution.
B solution: 5 mass % water/methanol solution of polyvinyl alcohol (mass ratio of water:methanol is 95:5).
Solution C: 1,3,5-tris(3-trialkoxysilylpropyl) isocyanurate was diluted with a mixture of water/isopropyl alcohol (mass ratio of water:isopropyl alcohol was 1:1) to a solid content of 5% by mass. Hydrolysis solution.

[Production of gas barrier OPP]
The composition for forming an adhesion layer is applied to the corona-treated surface of a stretched polypropylene film by a gravure roll coating method, dried and cured at 60° C. to obtain a polyester-based polyurethane resin having a coating amount of 0.1 g/m ² . An adhesion layer consisting of was formed. Next, a transparent inorganic oxide layer (silica vapor deposition layer) made of silicon oxide and having a thickness of 30 nm was formed using a vacuum vapor deposition apparatus using an electron beam heating system. As the silica vapor deposition layer, a vapor deposition layer having an O/Si ratio of 1.8 was formed by adjusting the vapor deposition material species. The O / Si ratio was determined by an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., trade name: JPS-90MXV), using a non-monochromatic MgKα (1253.6 eV) as the X-ray source, 100 W (10 kV- 10 mA) X-ray power. Quantitative analysis to determine the O/Si ratio was performed using relative sensitivity factors of 2.28 for O1s and 0.9 for Si2p, respectively.

When an alumina deposition layer was formed as an inorganic oxide layer, it was carried out as follows. That is, an AlOx deposition film having a thickness of 10 nm was formed by evaporating aluminum while introducing oxygen by an electron beam vacuum deposition method.

Next, the composition for forming a gas barrier coating layer is applied onto the inorganic oxide layer by a gravure roll coating method, and dried by heating in an oven under conditions of a tension of 20 N/m and a drying temperature of 120°C. A 0.3 μm thick gas barrier coating layer was formed. As a result, a gas barrier film having a laminated structure of film substrate/adhesion layer/inorganic oxide layer/gas barrier coating layer was obtained.

[Production of gas barrier EVOH-OPP]
An inorganic oxide layer (silica deposition layer) was formed in the same manner as above on the EVOH layer (adhesion layer) of the EVOH-OPP film. Next, in the same manner as described above, a gas barrier coating layer was formed on the inorganic oxide layer using the composition for forming a gas barrier coating layer. As a result, a gas barrier film having a laminate structure of film substrate/EVOH layer (adhesion layer)/inorganic oxide layer/gas barrier coating layer was obtained.

<Preparation of sealant layer>
The following polypropylene film was prepared as a sealant layer.
CPP (shrinkage rate 0.2%): thickness 70 μm
CPP (shrinkage rate 1.8%): thickness 70 μm

<Measurement of shrinkage rate of each layer>
The thermal shrinkage rate (%) of each layer was measured according to the following procedure.
(1) A 20 cm×20 cm piece of the layer to be measured was cut out and used as a measurement sample.
(2) A line of 10 cm was drawn in the running direction of the measurement sample (running direction length before heating).
(3) The measurement sample was heated at 120°C for 15 minutes.
(4) The running direction length of the written line was measured (running direction length after heating).
(5) The thermal shrinkage rate was calculated from the following formula.
(Length in running direction before heating - Length in running direction after heating)/Length in running direction before heating x 100

<Production of laminate>
Based on the combinations of layers shown in Table 1, laminates of each example and comparative example were produced. A method for manufacturing the laminate is as follows.
(Example 1)
The first base layer was laminated on the corona-treated surface of the second base layer via a two-component adhesive (trade name: main agent A525/curing agent A52, manufactured by Mitsui Chemicals, Inc.) by a dry lamination method. , and a sealant layer was similarly laminated to the non-corona-treated side of the second substrate layer. The gas-barrier coating layer (barrier surface) of the first substrate layer was on the second substrate layer side. Thus, a laminate having a laminated structure of first substrate layer (gas barrier substrate layer)/adhesive layer/second substrate layer/adhesive layer/sealant layer was produced.
(Example 2)
The first substrate layer is laminated on the gas barrier coating layer of the second substrate layer by a dry lamination method via the two-liquid type adhesive, and a sealant is applied to the non-corona-treated surface of the second substrate layer. The layers were similarly laminated. Thus, a laminate having a laminated structure of first substrate layer/adhesive layer/second substrate layer (gas barrier substrate layer)/adhesive layer/sealant layer was produced.
(Example 7)
A laminate was produced in the same manner as in Example 2, except that the combination of layers was changed as shown in Table 1, and the second substrate layer was laminated so that the gas barrier coating layer was on the sealant layer side.
(Comparative Examples 4 and 5)
Example 2 except that the combination of each layer was changed as shown in Table 1, the second base material layer was laminated so that the gas barrier coating layer was on the sealant layer side, and the first base material layer was not laminated. A laminate was produced in the same manner.
(Other Examples and Comparative Examples)
A laminate was produced in the same manner as in Example 1 or Example 2, except that the combination of each layer was changed as shown in Table 1.

<Production of packaging bags>
The laminate obtained in each example was cut into a size of 15 cm×10 cm, and the two cut packaging films were stacked so that the sealant layers faced each other. After the pouch was impulse-sealed on three sides, 100 ml of tap water was added as the content, and the remaining side was impulse-sealed. Thus, a pouch (packaging bag) sealed on four sides was produced.

<Gas barrier property evaluation>
The pouch obtained in each example was subjected to retort treatment at 0.2 MPa and 121° C. for 30 minutes using a retort device. After the retort treatment, the tap water in the pouch was discarded, and the gas barrier property was evaluated in a sufficiently dried state. Specifically, oxygen transmission rate (OTR) and water vapor transmission rate (WTR) were measured as follows. Table 2 shows the results.
Oxygen permeability:
Oxygen permeability measuring device (manufactured by MOCON, trade name: OX-TRAN2/20)
Measured at a temperature of 30°C and a relative humidity of 70% (JIS K-7126, B method)
Measured values are expressed in units [cc/m ² ·day · MPa].
Water vapor permeability:
Water vapor permeability measuring device (manufactured by MOCON, trade name: PERMATRAN-W 3/33)
Measured at a temperature of 40°C and a relative humidity of 90% (JIS K-7126, B method)
Measured values are expressed in the unit [g/m ² ·day].

The laminate according to the present invention can realize a packaging bag that can be retorted, and the constituent films can be substantially all polyolefin films. Such a laminate can be said to be a (mono-material) packaging material made of a single material, and is expected to have excellent recyclability.

DESCRIPTION OF SYMBOLS 11... 1st base material layer, 12... 2nd base material layer, 13... Sealant layer, S... Adhesive bond layer, 100... Laminated body.

Claims (7)

A first base material layer, a second base material layer and a sealant layer are provided in this order,
The first base layer, the second base layer and the sealant layer all comprise a polyolefin film,
The polyolefin film of the first substrate layer or the second substrate layer has an inorganic oxide layer on at least one surface,
A laminate in which each of the first substrate layer, the second substrate layer, and the sealant layer has a thermal shrinkage rate in the running direction (MD direction) after heating at 120° C. for 15 minutes that satisfies the following formula.
Thermal shrinkage rate of the second base material layer ≤ 5% (Equation 1)
Thermal shrinkage rate of the second base layer≧Heat shrinkage rate of the first base layer (Formula 2)
Thermal shrinkage rate of the second base material layer≧Heat shrinkage rate of the sealant layer (Formula 3)
(However, thermal shrinkage rate (%) = (running direction length before heating - running direction length after heating) / running direction length before heating x 100) The laminate according to claim 1, wherein the thermal shrinkage ratio satisfies the following formula.
Thermal shrinkage rate of the second base material layer−Heat shrinkage rate of the first base layer≧0.3% (Equation 4)
Thermal shrinkage rate of the second base material layer - Thermal shrinkage rate of the sealant layer ≥ 0.5% (Formula 5) The laminate according to claim 1 or 2, wherein the thermal shrinkage ratio satisfies the following formula.
Thermal shrinkage rate of sealant layer ≤ 2% (Equation 6) The polyolefin film of the first substrate layer or the second substrate layer comprises the inorganic oxide layer on at least one surface and a gas barrier coating layer on the inorganic oxide layer,
A composition for forming a gas-barrier coating layer, wherein the gas-barrier coating layer contains at least one selected from the group consisting of hydroxyl-containing polymer compounds, metal alkoxides, silane coupling agents, and hydrolysates thereof. The laminate according to any one of claims 1 to 3, which is formed using The laminate according to any one of claims 1 to 4, wherein the inorganic oxide layer contains silicon oxide. The laminate according to any one of claims 1 to 5, which is for retort pouches. A packaging bag produced by bagging the laminate according to any one of claims 1 to 6.

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