JP7721882B2 - Vapor-deposited film and method for producing gas barrier film using the same - Google Patents

Description

The present invention relates to a vapor-deposited film as a gas barrier material used in packaging for food, pharmaceuticals, electronics products, etc., and a gas barrier film using the same.

Packaging materials used for packaging food, electronics, and other products are often required to have gas barrier properties that prevent oxygen, water vapor, and other gases that can cause deterioration of the contents from permeating the packaging material, in order to prevent deterioration and maintain the contents' functions and properties. A well-known packaging material with gas barrier properties is vapor-deposited film, which uses a vapor-deposited layer of metal foil such as aluminum, which is less affected by temperature and humidity.

Another known configuration of vapor-deposited film is one in which a vapor-deposited layer of inorganic oxides such as silicon oxide or aluminum oxide is formed on a substrate film made of a polymeric material by vacuum deposition or sputtering (see, for example, Patent Document 1). These gas barrier vapor-deposited films are transparent and have the ability to block gases such as oxygen and water vapor. Polyethylene terephthalate (PET) is commonly used as the substrate film.

Japanese Unexamined Patent Publication No. 60-49934

Due to the characteristics of the contents, packaging materials for powders, electronics products, and other items benefit from antistatic properties. This antistatic property is necessary not only for the inner surface of the packaging that comes into contact with the contents, but is also known to be necessary for materials that do not come into direct contact with the contents. For example, when packaging katsuobushi (dried bonito flakes), the static charge on the outer surface of the packaging affects the contents when they are filled. If an outer packaging material with low antistatic properties is used, the static charge will attract the katsuobushi and cause it to become caught in the packaging seal, resulting in a poor seal. For this reason, outer packaging materials are desired to have both gas barrier properties and antistatic properties. However, when a vapor deposition layer is applied to an antistatic substrate using conventional methods, the action of the antistatic agent prevents sufficient adhesion between the substrate and the vapor deposition layer. This is thought to be because the antistatic agent segregates to the outermost surface of the substrate, inhibiting adhesion with the vapor deposition layer.

To solve this problem, previous attempts have been made to use plasma as an in-line pretreatment to improve the adhesion of metal or metal oxide deposition onto plastic substrates.

The present invention aims to solve the above-mentioned problems by strengthening the adhesion between a substrate made of a polymeric material with antistatic properties and a vapor-deposited film, thereby providing a vapor-deposited film that maintains high adhesion even after hot water treatment and does not cause delamination, and a gas barrier film using the same.

In order to achieve the above object, a first aspect of the present invention is
A vapor-deposited film having an antistatic function, in which a vapor-deposited layer and a coating layer are laminated in this order on the processed surface of a polypropylene substrate,
the surface layer to be machined is a copolymer of propylene and ethylene, or a copolymer containing propylene and ethylene or 1-butene,
the surface resistance of the processed surface layer is 2.0×10 ¹² Ω/□ or more;
The deposited film is characterized in that the adhesive strength between the substrate and the deposited layer after hot water treatment is 1.0 N/15 mm or more.

A second aspect of the present invention is
The method for producing a vapor-deposited film includes the steps of: forming a vapor-deposited layer on the surface of a substrate made of antistatic polypropylene , the surface of the substrate being a copolymer of propylene and ethylene or a copolymer containing propylene and ethylene or 1-butene , and the surface resistance of the surface of the substrate being 2.0 x 10 ¹² Ω/□ or more; and forming a coating layer on the vapor-deposited layer.

The present invention strengthens the adhesion between a substrate made of a polymeric material with antistatic properties and a vapor-deposited film, making it possible to provide a vapor-deposited film that maintains high adhesion even after hot water treatment and does not cause delamination, as well as a gas barrier film using the same.

1 is a schematic cross-sectional view of a gas barrier film according to a simple embodiment of the present invention.

An embodiment of the present invention will now be described with reference to FIG.
1 is a schematic cross-sectional view of a gas barrier film 1 according to this embodiment. The gas barrier film 1 comprises a vapor-deposited film 20, an adhesive layer 50, and a sealant layer 60. The vapor-deposited film 20 comprises a substrate 10, a pretreatment layer 10a, a vapor-deposited layer 30, and a coating layer 40.

The substrate 10 used in the present invention is made of a plastic material with antistatic properties, preferably a transparent film substrate to maximize the transparency of the vapor-deposited thin film layer. Examples of substrates include plastic materials containing at least one of the following: polyethylene, polypropylene, polyamides, polyesters, polycarbonate, polyacrylonitrile, polystyrene, polyvinyl chloride, cellulose, triacetyl cellulose, polyvinyl alcohol, and polyurethanes; plastic materials containing at least one of these copolymers; and plastic materials containing at least one of these chemically modified forms. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate, either alone or as copolymers. The substrate may be stretched or unstretched, and should have mechanical strength and dimensional stability. The plastic material used in the present invention preferably has a surface layer made of a propylene-ethylene copolymer or a copolymer of propylene with ethylene or 1-butene. The substrate 10 can be a single layer of a copolymer of propylene and ethylene, or a copolymer of propylene and ethylene or 1-butene, or a laminated structure in which at least one surface layer of the substrate 10 is a copolymer of propylene and ethylene, or a copolymer of propylene and ethylene or 1-butene, and the other layers are homopolymers.

The substrate 10 used in the present invention is characterized by being a plastic material having an antistatic function, and it is desirable that the surface resistivity is 1×10 ¹¹ [Ω/□] or more. If the surface resistivity is lower than this value, sufficient adhesion between the substrate and the vapor deposition layer cannot be obtained. To impart antistatic function, an antistatic agent can be used in the surface layer of the substrate 10. Examples of antistatic agents include cationic surfactants, anionic surfactants, and nonionic surfactants.

The thickness of the substrate 10 is not particularly limited, and in consideration of its suitability as a packaging material, a film laminated with films of different properties may be used in addition to a single film. In consideration of the processability when forming a primer layer, a vapor-deposited thin film layer made of an inorganic oxide, and a gas barrier coating layer, a practical thickness is preferably in the range of 3 to 200 μm, and more preferably 6 to 30 μm.

Before forming the vapor deposition layer, a coating layer of thermoplastic resin, thermosetting resin, ultraviolet-curable resin, etc. may be applied to the substrate surface as a pretreatment layer 10a to improve gas barrier properties and adhesion, or ion beam treatment, corona treatment, plasma treatment, ozone treatment, flame treatment, etc. may be performed. There are no particular restrictions on the pretreatment layer or its formation method. From the perspective of productivity, plasma treatment, which can be performed in-line, is preferred. Plasma treatment may be performed using a magnet to increase plasma density. The gas used during plasma treatment can be selected from one or more of oxygen, nitrogen, argon, and helium.

The vapor deposition layer 30 is a layer whose main component is aluminum metal, aluminum oxide, or silicon oxide, and exhibits gas barrier properties against certain gases such as oxygen and water vapor. The vapor deposition layer 30 may be either transparent or opaque.

The thickness of the vapor-deposited layer 30 varies depending on the type, composition, and film-forming method of the inorganic compound used, but can generally be set appropriately within the range of 3 to 300 nm. If the thickness of the vapor-deposited layer 30 is less than 3 nm, a uniform film may not be obtained or the film thickness may be insufficient, and the vapor-deposited layer may not fully function. If the thickness of the vapor-deposited layer 30 exceeds 300 nm, the vapor-deposited layer 30 becomes hard, and external factors such as bending or pulling after film formation may cause cracks in the vapor-deposited layer 30, resulting in a loss of gas barrier properties. The thickness of the vapor-deposited layer 30 is particularly preferably within the range of 6 to 150 nm.

There are no limitations on the method for forming the vapor deposition layer 30, and methods such as vacuum deposition, sputtering, ion plating, ion beam deposition, and plasma chemical vapor deposition (CVD) can be used. Combining methods such as plasma-assisted and ion-beam-assisted deposition can result in a denser vapor deposition layer, improving gas barrier properties and adhesion.

The coating layer 40 further enhances the gas barrier properties of the vapor deposition layer 30. The coating layer 40 is formed using a coating agent whose main component is an aqueous solution or water/alcohol mixed solution containing a water-soluble polymer and one or more metal alkoxides or their hydrolysates. For example, the coating agent is prepared by mixing a water-soluble polymer dissolved in an aqueous solvent (water or a water/alcohol mixed) with a metal alkoxide, either directly or after being pre-treated by hydrolysis. The coating agent can be applied to the vapor deposition layer 30 and then dried to form the coating layer 40.

The components contained in the coating agent used to form the covering layer 40 will be described in more detail below. Examples of water-soluble polymers used in coating agents include polyvinyl alcohol (PVA), polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, and sodium alginate. PVA is particularly preferred because it provides excellent gas barrier properties. PVA is generally obtained by saponifying polyvinyl acetate. PVA can be either partially saponified PVA, in which several tens of percent of acetate groups remain, or completely saponified PVA, in which only a few percent of acetate groups remain. PVA that is intermediate between the two may also be used.

The metal alkoxide used in the coating agent is a compound represented by the general formula M(OR ₎ n (M: metals such as Si and Al, R: alkyl groups such as CH3 _{and C2H5} ). Specific examples include tetraethoxysilane [Si( _OC2H5 ) ₄ ] and triisopropoxyaluminum _Al [OCH(CH3) ₂ ] _{3 .} Examples of silane coupling agents include those having an epoxy group such as 3-glycidoxypropyltrimethoxysilane, those having an amino group such as 3-aminopropyltrimethoxysilane, those having a mercapto group such as 3-mercaptopropyltrimethoxysilane, those having an isocyanate group such as 3-isocyanatopropyltriethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate. There are no limitations on the method for applying the coating agent, and any conventionally known method such as commonly used dipping, roll coating, screen printing, spraying, or gravure printing can be appropriately selected.

The thickness of the coating layer 40 varies depending on the composition of the coating agent, application conditions, etc., and is not particularly limited. However, if the dried thickness of the coating layer 40 is less than 0.01 μm, the coating film may not be uniform and sufficient gas barrier properties may not be achieved. If the dried thickness exceeds 50 μm, cracks may easily occur in the coating layer 40. Therefore, the suitable thickness of the coating layer 40 is, for example, in the range of 0.01 to 50 μm. The optimal thickness of the coating layer 40 is in the range of 0.1 to 10 μm.

The sealant layer 60 is a layer that is bonded by heat sealing when the gas barrier film 1 is used to form a bag-shaped package or the like. Examples of materials for the sealant layer 60 include resin materials such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, and metal-crosslinked versions of these materials. The thickness of the sealant layer 60 is determined depending on the purpose, but is, for example, in the range of 15 to 200 μm.

The adhesive layer 50 bonds the sealant layer 60 and the coating layer 40. By using the adhesive layer 50, the resin film that will become the sealant layer 60 can be bonded to the substrate 10 on which the vapor deposition layer 30 and coating layer 40 have been formed by dry lamination. An example of a material for the adhesive layer 50 is a two-component curing polyurethane adhesive. A printed layer, an intervening film, a sealant layer, etc. can be laminated on the coating layer 40 to create a packaging material.

Next, a method for producing the vapor-deposited film 20 of this embodiment having the above-described configuration will be described. First, a vapor-deposited layer 30 is formed on one surface of the substrate 10 (first step). Next, the above-described coating agent is applied to the vapor-deposited layer 30 and dried to form a coating layer 40 on the vapor-deposited layer (second step), thereby producing the vapor-deposited film 20. Furthermore, an adhesive 50 is applied to the coating layer 40 of the vapor-deposited film 20, and a resin film that will become the sealant layer 60 is attached thereto (third step), thereby completing the gas barrier film 1.

The gas barrier film 1 of this embodiment will be further described using examples and comparative examples. The present invention is not limited in any way by the specific content of the examples and comparative examples.

Example 1
A film (thickness: 20 μm, surface resistance: 1.0× ¹⁰ Ω/□) containing an antistatic agent and made by copolymerizing polypropylene and ethylene was used as the substrate 10. Aluminum was evaporated in a vacuum chamber for the substrate 10, and a vapor deposition layer 30 (thickness: 50 nm) made of metallic aluminum was formed by electron beam evaporation.

A coating agent prepared by mixing the following liquids (1) and (2) in a weight ratio of 6:4 was applied onto the vapor deposition layer 30 by gravure coating and dried to form a coating layer 40 with a thickness of 0.4 μm, thereby producing a vapor deposition film 20.
(1) Solution: 10.4 g of tetraethoxysilane was mixed with 89.6 g of hydrochloric acid (0.1 N), and the mixture was stirred for 30 minutes to hydrolyze the mixture, resulting in a hydrolysis solution with a solid content of 3 wt % ( _SiO2 equivalent).
(2) Liquid: 3 wt % water/isopropyl alcohol solution of polyvinyl alcohol (water:isopropyl alcohol weight ratio 90:10).

Finally, an unstretched polypropylene film 60 (70 μm thick) was bonded to the coating layer 40 by dry lamination using a two-component curing polyurethane adhesive 50, thereby obtaining the gas barrier film 1 of Example 1.

Example 2
A gas barrier film 1 of Example 2 was produced in the same manner as in Example 1, except that the deposition material was Al and oxygen was introduced to form a deposition layer 30 made of aluminum oxide and having a thickness of 10 nm.

Example 3
A gas barrier film 1 of Example 3 was produced in the same manner as in Example 1, except that the deposition material was SiO and a deposition layer 30 made of silicon oxide and having a thickness of 30 nm was formed.

Example 4
A gas barrier film 1 of Example 4 was produced in the same manner as in Example 1, except that the substrate was subjected to a plasma treatment with Ar gas as pretreatment 10a (the surface resistance of the substrate changed to 2.0 × 10 ¹² Ω/□) to continuously form aluminum.

Example 5
A gas barrier film 1 of Example 5 was produced in the same manner as in Example 2, except that the substrate was subjected to a plasma treatment with Ar gas as a pretreatment 10a (the surface resistance of the substrate changed to 2.0 × 10 ¹² Ω/□) to continuously form aluminum oxide.

Example 6
A gas barrier film 1 of Example 6 was produced in the same manner as in Example 3, except that the substrate was subjected to a plasma treatment with Ar gas as a pretreatment 10a (the surface resistance of the substrate changed to 2.0 × 10 ¹² Ω/□) to continuously form silicon oxide.

Example 7
A gas barrier film 1 of Example 7 was produced in the same manner as in Example 1, except that a urethane resin layer 50 was formed on the substrate as a pretreatment 10a.

(Example 8)
A gas barrier film 1 of Example 8 was produced in the same manner as in Example 2, except that a urethane resin layer 50 was formed on the substrate as a pretreatment 10a.

Example 9
A gas barrier film 1 of Example 9 was produced in the same manner as in Example 3, except that a urethane resin layer 50 was formed on the substrate as a pretreatment 10a.

Example 10
A gas barrier film 1 of Example 10 was produced in the same manner as in Example 3, except that a substrate 10 having a surface resistance of 1.0×10 ¹² Ω/□ was used.

Example 11
A gas barrier film 1 of Example 11 was produced in the same manner as in Example 3, except that a substrate 10 having a surface resistance of 1.0×10 ¹³ Ω/□ was used.

(Comparative Example 1)
A gas barrier film 1 of Comparative Example 1 was produced in the same manner as in Example 3, except that a substrate 10 having a surface resistance of 1.0×10 ⁹ Ω/□ point was used.

(Comparative Example 2)
A gas barrier film 1 of Comparative Example 2 was produced in the same manner as in Example 3, except that the substrate 10 of Comparative Example 1 was subjected to a plasma treatment with Ar gas as a pretreatment 10a (the surface resistance of the substrate changed to 2.0 × ¹⁰ Ω/□) to continuously form silicon oxide.

(Comparative Example 3)
A gas barrier film 1 of Comparative Example 3 was produced in the same manner as in Example 3, except that a urethane resin layer 50 was formed on the substrate of Comparative Example 1 as a pretreatment 10a.

<Evaluation 1: Adhesion evaluation after hot water treatment>
Two gas barrier films 1 of each example were stacked with the sealant layers 60 facing each other, and three sides were joined by heat sealing to produce a pouch (packaging container) of each example. Each pouch was filled with water as the content, and the open side was sealed by heat sealing. Then, a boiling treatment (90°C for 30 minutes) was performed as a hot water treatment. After the hot water treatment, a test piece was cut out from the part of each pouch that had been in contact with the content in accordance with JIS K6854-2, and measured using an Orientec Tensilon universal testing machine RTC-1250.

<Evaluation 2: Gas barrier property evaluation after hot water treatment>
After the pouches of each example prepared by the above procedure were prepared and subjected to hot water treatment, the pouches were opened and the oxygen permeability (unit: cc/ ^m2 day atm, measurement conditions: 30°C-70% RH) and water vapor permeability (unit: g/ ^m2 day, measurement conditions: 40°C-90% RH) of the gas barrier film 1 were evaluated. The results are shown in Table 1.

Examples 4 to 6 show that the pretreatment plasma treatment increases adhesion and maintains gas barrier properties. Examples 7 to 9 show that the pretreatment thermosetting resin layer increases adhesion and further improves oxygen barrier properties. Examples 1 to 11 show that high adhesion can be achieved when the surface resistivity of the substrate surface is 1.0 x 10 ¹¹ [Ω/□] or more and has antistatic properties. As can be seen from Comparative Examples 1 to 3, when the surface resistivity is lower than 1.0 x 10 ¹¹ [Ω/□], adhesion is significantly reduced and delamination becomes more likely to occur.

From the above, it was found that if the surface resistivity of the substrate surface is 1.0 x 10 ¹¹ [Ω/□] or more and has an antistatic function, sufficient adhesion can be obtained even after hot water treatment, no delamination occurs, and a vapor deposition film 20 and a gas barrier film 1 with high gas barrier properties can be obtained.

DESCRIPTION OF SYMBOLS 1... Gas barrier film 10... Substrate 10a... Pretreatment layer 20... Vapor deposition film 30... Vapor deposition layer 40... Coating layer 50... Adhesive layer 60... Sealant layer

Claims (9)

A vapor-deposited film having an antistatic function, in which a vapor-deposited layer and a coating layer are laminated in this order on the processed surface of a polypropylene substrate,
the surface layer to be machined is a copolymer of propylene and ethylene, or a copolymer containing propylene and ethylene or 1-butene,
the surface resistance of the processed surface layer is 2.0×10 ¹² Ω/□ or more;
A vapor-deposited film, characterized in that the adhesive strength between the substrate and the vapor-deposited layer after hot water treatment is 1.0 N/15 mm or more. 2. The vapor-deposited film according to claim 1, wherein the surface of the processed surface is provided with one of a thermoplastic resin layer, a thermosetting resin layer, and an ultraviolet-curing resin layer, or a surface-treated layer obtained by plasma treatment. 3. The vapor-deposited film according to claim 1 , wherein the vapor-deposited layer contains aluminum, aluminum oxide, or silicon oxide as a main component. 4. The vapor-deposited film according to claim 1, further comprising a composite coating on the vapor-deposited layer, the composite coating containing at least one of a hydroxyl group-containing polymer compound, a metal alkoxide and/or its hydrolysate and/or its polymer. 5. A gas barrier film comprising a vapor-deposited film according to claim 1, and a sealant layer made of a heat-sealable thermoplastic resin laminated on the coating layer via an adhesive layer. 6. The gas barrier film according to claim 5, wherein the oxygen permeability at 30°C and 70% RH after hot water treatment at a temperature of 90°C or higher for 30 minutes or longer is 3 cc/ ^m2 ·day·atm or less, and the water vapor permeability at 40°C and 90% RH is 1 g/ ^m2 ·day or less. A method for producing a vapor-deposited film includes the steps of: forming a vapor-deposited layer on a surface layer of a substrate made of antistatic polypropylene , the surface layer being a copolymer of propylene and ethylene or a copolymer containing propylene and ethylene or 1-butene , and the surface resistance of the surface layer being 2.0 x 10 ¹² Ω/□ or more; and forming a coating layer on the vapor-deposited layer. A method for producing a vapor -deposited film includes the steps of: subjecting a substrate made of antistatic polypropylene , the surface layer of which is to be processed, to a plasma treatment to increase the surface resistance to 2.0 x 10 ¹² Ω/□ or more ; forming a vapor-deposited layer on the plasma-treated surface; and forming a coating layer on the vapor-deposited layer. a step of forming a heat seal layer on the coating layer of the vapor-deposited film produced by the vapor-deposited film production method according to claim 7 or 8 , via an adhesive layer;
A method for manufacturing a gas barrier film.