JP2024033225A - Multilayer packaging film and packaging materials using it - Google Patents

Abstract

[Problem] The object of the present invention is to provide a multilayer film that can exhibit antibacterial and antifungal properties even when packaging foods with relatively low moisture content, and that can be easily recycled by making it into a monomaterial. The objective is to provide packaging materials that can be used. [Solution] The present invention provides a multilayer film including a sealing layer, wherein the sealing layer contains a water-soluble antibacterial agent, and of the components contained in the multilayer film, propylene resin accounts for 75% by mass or more. The above problems are solved by a multilayer film, characterized in that the content of foreign components other than propylene resin is less than 25% by mass, and the multilayer film has a water vapor permeability of 9.0 g/m2/24 hours or less. [Selection diagram] None

Description

The present invention relates to a packaging material for packaging foods, etc., which has both high antibacterial and antifungal properties even when the contents contain relatively little moisture, and is a monomaterial (single material). The present invention relates to a multilayer film that can extend its edible life and is recyclable, and a packaging material made from the multilayer film.

In recent years, the disposal of foods that have expired or expiration dates and fruits and vegetables that have lost their freshness has become a problem as food loss. Additionally, at home, food packages are sometimes opened and then resealed to preserve leftover food, but mold can grow on such food, and moldy food is discarded. Therefore, there is an increasing demand for packaging materials that maintain the freshness and hygiene of foods and extend the edible period of foods.

Films containing antibacterial agents are being considered as packaging materials that extend the edible life of foods. When adding an antibacterial agent to food packaging materials, the antibacterial agent must be safe enough to cause no problems even if it comes into contact with the food contained inside or the human body.

Patent Document 1 is known as a film containing an antibacterial agent. The antibacterial film of Patent Document 1 is a resin film that includes a sealant layer containing an inorganic antibacterial agent and an adjacent support layer, and has a specified amount of extracted metal ions.

On the other hand, in order to promote recycling and reduce environmental impact in food packaging films, the use of monomaterials (single material) is progressing. In contrast to the conventional multilayer laminate structure of different materials (e.g., a multilayer film of oriented polyethylene terephthalate OPET/unoriented polypropylene CPP), in order to respond to monomaterialization, a multilayer film such as oriented polypropylene OPP/unoriented polypropylene CPP is required. is required.

However, the antibacterial properties of the antibacterial film disclosed in Patent Document 1 have not been studied for foods with relatively low moisture content. In addition, it was based on the premise of laminating multiple other layers, so it was not possible to make it into a monomaterial.

Japanese Patent Application Publication No. 2016-030406

In view of the above circumstances, an object of the present invention is to provide a multilayer film that can exhibit antibacterial and antifungal properties even when packaging foods with relatively low moisture content, and that is easy to recycle by making it a monomaterial. The object of the present invention is to provide a packaging material using this.

The present invention provides a multilayer film including a sealing layer, wherein the sealing layer contains a water-soluble antibacterial agent, and of the components contained in the multilayer film, propylene resin accounts for 75% by mass or more, and the propylene resin The above-mentioned problem is solved by a multilayer film characterized in that the amount of foreign components that are not present is less than 25% by mass, and the multilayer film has a water vapor permeability of 9.0 g/m ² /24 hours or less.

The present invention also provides a packaging material having the above multilayer film, and a packaging material for food packaging.

The multilayer film of the present invention and the packaging material using the same exhibit antibacterial and antifungal properties even when packaging foods with relatively low moisture content, and can extend the edible period of foods. can. Moreover, by making it a monomaterial, it has excellent recyclability and can reduce environmental burden.

Below, each part constituting the multilayer film of the present invention and a packaging material using the same will be explained in detail.

<Seal layer>
The multilayer film of the present invention includes a sealing layer. The sealing layer constitutes the surface layer on one side of the multilayer film of the present invention, and is a layer that comes into direct contact with the food and the like contained therein.
Further, the seal layer contains a water-soluble antibacterial agent and has an antibacterial effect.

The sealing layer of the multilayer film of the present invention preferably contains a propylene resin in order to be made into a monomaterial. Other resins other than propylene resins may be included as long as the content of different components other than propylene resins is less than 25% by mass.

Examples of the propylene-based resin include propylene homopolymers, propylene-ethylene copolymers, propylene-butene-1 copolymers, propylene-ethylene-butene-1 copolymers, and metallocene catalyst polypropylenes. Other α-olefin copolymers may be mentioned. These may be used alone or in combination. Examples of the propylene homopolymer include isotactic polypropylene, syndiotactic polypropylene, and attacktic polypropylene, and among these, isotactic polypropylene is preferred.

Examples of the other α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4-methyl-pentene-1, 4-methyl-hexene-1, etc. may be mentioned, and two or more of these may be copolymerized simultaneously. As for the copolymerization type, either random copolymerization or block copolymerization can be used. Among these, a propylene-ethylene random copolymer is preferred.
Further, the content of the other α-olefin in the copolymer is preferably 2.0 to 23 mol%, more preferably 2.5 to 15 mol%.

Examples of the metallocene catalyst include various metallocene catalysts, such as a metallocene catalyst system such as a combination of a metallocene compound of a group IV or V transition metal of the periodic table, and an organoaluminium compound and/or an ionic compound. In addition, since single-site catalysts such as metallocene catalysts have uniform active sites, the resulting resin has a sharper molecular weight distribution than multi-site catalysts with non-uniform active sites. This is preferable because it results in less precipitation of low molecular weight components and a resin with excellent physical properties such as stability of seal strength and blocking resistance.

The above propylene resin preferably has an MFR (at 230°C) of 0.5 to 30.0 g/10 minutes and a melting point of 120 to 168°C, more preferably an MFR (at 230°C) of 2. 0 to 15.0 g/10 minutes and a melting point of 125 to 162°C. If the MFR and melting point are within the above ranges, the shrinkage of the film during heat sealing will be small and the film formability will also be improved.

When the above-mentioned propylene resin is used in the seal layer used in the present invention, the heat resistance of the film is improved. Among these, it is preferable to use a copolymer of propylene and other α-olefins in the sealing layer, which can increase the heat-sealing strength, so that it can be particularly suitably used as a packaging material for heavy goods. Of all the components constituting the seal layer, the content of the propylene and other α-olefin copolymers is preferably 20% by mass or more, more preferably 45% by mass or more.

Thermoplastic resins can be used as the other resins, and are not particularly limited. Among these, polyethylene resins and cyclic olefin resins are preferred. Examples of the polyethylene resin include low density polyethylene resin and high density polyethylene resin.

The low density polyethylene resin mentioned above may be any polyethylene resin with a density of 0.900 to 0.940 g/cm ³ , such as very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), and low density polyethylene. (LDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) Ethylene copolymers such as copolymers, ethylene-ethyl acrylate-maleic anhydride copolymers (E-EA-MAH), ethylene-acrylic acid copolymers (EAA), ethylene-methacrylic acid copolymers (EMAA), etc. Coalescence; further examples include ionomers of ethylene-acrylic acid copolymers and ionomers of ethylene-methacrylic acid copolymers. Among these, low-density polyethylene and linear low-density polyethylene are preferred because they have a good balance between easy tearability and pinhole resistance.

The low-density polyethylene may be any branched low-density polyethylene obtained by high-pressure radical polymerization, preferably branched low-density polyethylene obtained by homopolymerizing ethylene by high-pressure radical polymerization.

The linear low-density polyethylene is produced by a low-pressure radical polymerization method using a single-site catalyst, with ethylene monomer as the main component, butene-1, hexene-1, octene-1, and 4-methylpentene as comonomers. It is a copolymer of α-olefins such as The comonomer content in LLDPE is preferably in the range of 0.5 to 10 mol%, more preferably in the range of 1 to 7 mol%. In addition, when butene-1 is used as a comonomer, transparency, impact resistance, easy tearability, etc. are improved, so it is preferable, and in this case, the content of the butene monomer is in the range of 1 to 5 mol%. is most preferable.

The density of the low-density polyethylene resin is 0.900 to 0.945 g/cm ³ as described above, but it is more preferably in the range of 0.905 to 0.935 g/cm ³ . If the density is within this range, it will have appropriate rigidity, excellent mechanical strength such as pinhole resistance, and improved film formability and extrusion suitability. Further, the melting point is preferably in the range of 95 to 120°C, more preferably 100 to 130°C. If the melting point is within this range, processing stability will be improved. Furthermore, the MFR (190°C, 21.18N) of the low density polyethylene resin is preferably 2 to 35 g/10 minutes, more preferably 2 to 20 g/10 minutes, and 3 to 10 g/10 minutes. It is more preferable that If the MFR is within this range, the extrusion moldability of the film will improve.

Since the above-mentioned low-density polyethylene resin has low mechanical strength, it is relatively brittle and has good tearability compared to other polyolefin resins. Further, without using an adhesive resin or the like, interlayer adhesive strength with other layers other than the intermediate layer can be maintained, and since it has flexibility, pinhole resistance is also good. Furthermore, when improving pinhole resistance, it is preferable to use linear low density polyethylene.

The high-density polyethylene resin may be any polyethylene having a density of 0.950 g/cm ³ or more, and preferably polyethylene having a density of 0.955 g/cm ³ or more. The high-density polyethylene resin can provide an effect of improving tearability and packaging suitability.

The high-density polyethylene resin may be high-density polyethylene (HDPE), which is generally used in extrusion molding such as film molding, such as high-density polyethylene with good fluidity and an MFR (190°C) of 5 to 20 g/10 minutes. This is preferable because when it is melt-kneaded with the above-mentioned low-density polyethylene resin and extruded, the dispersion is relatively good and a film with a smooth surface and good transparency can be obtained.

Examples of the cyclic olefin resin include norbornene polymers, vinyl alicyclic hydrocarbon polymers, and cyclic conjugated diene polymers. Among these, norbornene polymers are preferred. Norbornene polymers include ring-opening polymers of norbornene monomers (hereinafter sometimes referred to as "COP"), norbornene copolymers made by copolymerizing norbornene monomers with olefins such as ethylene. Coalescence (hereinafter sometimes referred to as "COC"), and the like. Particular preference is given to hydrogenated products of COP and COC. Further, the weight average molecular weight of the cyclic olefin resin is preferably 5,000 to 500,000, more preferably 7,000 to 300,000.

The norbornene polymer and the norbornene monomer used as a raw material are alicyclic monomers having a norbornene ring. Examples of such norbornene monomers include norbornene, tetracyclododecene, ethylidenenorbornene, vinylnorbornene, ethylidetetracyclododecene, dicyclopentadiene, dimetanotetrahydrofluorene, phenylnorbornene, methoxycarbonylnorbornene, and methoxycarbonylnorbornene. Examples include carbonyltetracyclododecene. These norbornene monomers may be used alone or in combination of two or more.

The norbornene copolymer (COC) is a copolymer of the norbornene monomer and a copolymerizable olefin, such as ethylene, propylene, 1-butene, etc. Examples include olefins having 2 to 20 carbon atoms; cycloolefins such as cyclobutene, cyclopentene, and cyclohexene; and nonconjugated dienes such as 1,4-hexadiene. These olefins can be used alone or in combination of two or more.

Further, the content ratio of the norbornene monomer in the norbornene copolymer (COC) is preferably 40 to 90 mol%, more preferably 50 to 80 mol%. If the content ratio is within this range, the rigidity, tearability, and processing stability of the film will improve.

Examples of commercially available ring-opening polymers (COP) of norbornene monomers that can be used as the cyclic olefin resin include "ZEONOR" manufactured by Nippon Zeon Co., Ltd.; Examples of the COC include "APEL" manufactured by Mitsui Chemicals, Inc. and "TOPAS" manufactured by TICONA.

By using the above-mentioned cyclic olefin resin, water vapor barrier properties can be imparted to the multilayer film, and antibacterial properties can be improved.

<Water-soluble antibacterial agent>
The water-soluble antibacterial agent used in the present invention refers to an antibacterial agent that dissolves in an amount of 150 mg or more in 100 g of distilled water at 23°C. Various antibacterial agents can be used as water-soluble antibacterial agents, including antibacterial agents containing calcium hydroxide obtained by hydrating shells or eggshells after firing, and soluble glass carrying antibacterial metal ions. Glass-based antibacterial agents and the like are preferred. Moreover, multiple types of water-soluble antibacterial agents can be used in combination.

When using the antibacterial agent containing calcium hydroxide, the amount of calcium hydroxide contained in the antibacterial agent is preferably 40% by mass or more based on the entire antibacterial agent. When the ratio of calcium hydroxide contained in the antibacterial agent is within the above ratio, a sufficient antibacterial effect can be exhibited.
Examples of the shells used as materials include scallop shells, abalone shells, turban shells, surf shells, sea urchin shells, coral shells, etc., and these may be natural or cultured. Among these, it is preferable to use scallop shells because they have a uniform shell composition and can be supplied in large amounts.

The antibacterial agent containing calcium hydroxide can be produced by methods known to those skilled in the art. For example, an antibacterial agent containing calcium hydroxide can be produced by baking seashells at a high temperature of 850 to 1200°C in a special electric furnace, converting the calcium carbonate contained in the shells into calcium oxide, and then hydrating it. can. Moreover, commercially available antibacterial agents can also be used. Commercially available antibacterial agents containing calcium hydroxide include Scallop Premium, Scallop Premium S, Scallop Premium HK, Scallop Premium R (all manufactured by WM Co., Ltd.), and baked scallop shell powder (Unicera Co., Ltd.). However, it is not limited to this.

When using the above-mentioned glass-based antibacterial agent, it is preferable that metal ions having antibacterial properties are supported in the network structure of soluble glass. Such a metal-supported meltable glass gradually releases metal ions in small amounts in the presence of moisture. The slowly released metal ions are positively charged, and these ions attract negatively charged bacteria and fungi, and by disrupting the electrical balance on the surface of the bacteria and fungi, they can exert an antibacterial effect. In addition, the network structure of soluble glass is very strong, so it is chemically and physically stable and can be used for kneading with any resin. Examples of the antibacterial metal ions supported on the soluble glass include silver ions, zinc ions, copper ions, etc. Silver is preferred because it has high antibacterial activity.

The above-mentioned glass-based antibacterial agent can be produced by methods known to those skilled in the art. For example, it can be carried out by adding an aqueous solution containing the antibacterial metal ions to an aqueous suspension of glass powder, and causing the metals to be present in the glass powder through an ion exchange reaction.
Commercially available products can also be used as the glass-based antibacterial agent. Commercially available glass-based antibacterial agents include Ion Pure WPA (silver-based antibacterial agent), Ion Pure IPI (silver-based antibacterial agent), and Ion Pure WZ (zinc-based antibacterial agent) (all manufactured by Ishizuka Glass Co., Ltd.). However, it is not limited to this.

The amount of the antibacterial agent used in the present invention is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, based on the total mass of the seal layer used in the present invention. , 0.5 to 10% by mass is particularly preferred. By using the antibacterial agent in this range in the sealing layer, it is possible to achieve both excellent antibacterial effects and transparency of the multilayer film of the present invention.

(Particle size of antibacterial agent)
The particle size of the antibacterial agent used in the present invention can be adjusted by pulverizing it with various pulverizers or classifying the powder during the manufacturing process of the antibacterial agent. The preferred particle size range of the antibacterial agent is preferably 0.1 to 1000 μm, more preferably 0.5 to 100 μm, and particularly preferably 2 to 20 μm or more. If the particle size is in a preferable range, mesh clogging is less likely to occur when the antibacterial agent is made into a masterbatch, it can be uniformly dispersed when mixed with resin, and transparency can be maintained when it is made into a multilayer film. It becomes easier.

The particle size of the antibacterial agent is a value measured using a laser diffraction scattering particle size distribution analyzer (Microtrac MT-3300EXII, manufactured by Nikkiso Co., Ltd.). As a specific measurement method, particles of the antibacterial agent are dispersed in IPA solvent in a water tank, and the above-mentioned device is used to measure and analyze the diffraction and scattering intensity distribution of light, and the particle size and volume-based particle distribution are determined. The value of D50, which can be calculated by measuring , is defined as the particle size of the antibacterial agent.

(ratio of seal layer thickness and antibacterial agent particle size)
The ratio of the thickness of the sealing layer used in the present invention to the particle size of the antibacterial agent used in the present invention is preferably such that the thickness of the sealing layer: the particle size of the antibacterial agent = 1:7 to 8:1, and 1: A ratio of 2 to 2:1 is particularly preferred. The reason why the multilayer film of the present invention exhibits a good antibacterial effect when the ratio of the thickness of the sealing layer to the particle size of the antibacterial agent is within a preferable range is not clear, but the inventor speculates as follows. There is. In other words, since the particle size of the antibacterial agent is larger than the thickness of the seal layer, the antibacterial agent in the seal layer protrudes from the seal layer, and the antibacterial agent protrudes onto the seal layer side surface of the multilayer film. It will be distributed. As a result, a high antibacterial effect can be obtained with a small amount of antibacterial agent.

In order to add the antibacterial agent used in the present invention to the film, it is preferable to prepare an antibacterial agent masterbatch mixed with a resin in advance. It is preferable that the resin is a resin used for the seal layer because it facilitates mixing of the antibacterial agent masterbatch and the resin used for the seal layer.
Further, the method of mixing the antibacterial agent masterbatch with the resin used for the seal layer is not particularly limited, and can be mixed by a conventionally known method. For example, dry blending or melt blending may be used. Among these, melt blending is preferable, and specifically, it is preferable to manufacture the antibacterial agent masterbatch by melt blending the antibacterial agent and the resin in a melt kneading device such as an extruder, and pelletizing the compound. Moreover, a commercially available antibacterial agent masterbatch may be used as the antibacterial agent masterbatch. Commercially available antibacterial agent masterbatches include Scarlow Premium Antibacterial Agent PP Masterbatch (WM Corporation), Scarrow Premium Antibacterial Agent PE Masterbatch (WM Corporation), and the like.

(outermost layer)
In addition to the seal layer, the multilayer film of the present invention preferably includes an outermost layer as the other surface layer that is not the seal layer.
The resin used in the outermost layer is preferably a propylene resin. Examples of the propylene resin include propylene homopolymers and copolymers of propylene and other α-olefins. Examples of the propylene homopolymer include isotactic polypropylene, syndiotactic polypropylene, and attacktic polypropylene, and among these, isotactic polypropylene is preferred.

Examples of the other α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4-methyl-pentene-1, 4-methyl-hexene-1, etc. may be mentioned, and two or more of these may be copolymerized simultaneously. As for the copolymerization type, either random copolymerization or block copolymerization can be used. Among these, a propylene-ethylene random copolymer is preferred.
Further, the content of the other α-olefin in the copolymer is preferably 2.0 to 23 mol%, more preferably 2.5 to 15 mol%.

It is preferable to use a propylene homopolymer as the resin used for the outermost layer, since it exhibits water vapor barrier properties and thus enhances the antibacterial effect. On the other hand, it is preferable to use a propylene-ethylene random copolymer as the resin used for the outermost layer because film properties such as impact strength of the multilayer film of the present invention can be ensured and lamination properties can be improved.

The resin used for the outermost layer preferably contains 50% by mass or more of the propylene resin, but within a range that does not impair the effects of the present invention, the propylene resin should be 75% by mass of the components contained in the multilayer film. This is the above, and other resins other than the above propylene resin may be used in combination within the range where the content of foreign components other than propylene resin is less than 25% by mass. Examples of other resins include those similar to the other resins that can be used for the seal layer.

(middle class)
In addition to the sealing layer, the multilayer film of the present invention may include an intermediate layer located between the sealing layer and the outermost layer. There may be only one intermediate layer, or there may be a plurality of intermediate layers. The intermediate layer preferably contains a propylene resin in order to improve recyclability, but among the components contained in the multilayer film, the propylene resin accounts for 75% by mass or more, and the non-propylene resin component accounts for 25% by mass. %, the layer may be composed of a resin other than the propylene resin, or the layer may be a combination of a propylene resin and another resin.

Examples of the propylene resin include the same propylene resins that can be used for the seal layer.

As the resin component of the intermediate layer, it is preferable to use the propylene homopolymer. By using the propylene homopolymer in the intermediate layer, it is possible to exhibit water vapor barrier properties and enhance the antibacterial effect.

A cyclic olefin resin may be used as the resin component of the intermediate layer. When using a cyclic olefin resin in the intermediate layer, in order to improve recyclability, the content of the cyclic olefin resin, which is a different component other than propylene resin, in the multilayer film should be less than 25% by mass. In addition, the thickness ratio of the intermediate layer can be adjusted.

Each layer of the multilayer film of the present invention may contain an antifogging agent, an antistatic agent, a heat stabilizer, a nucleating agent, an antioxidant, a lubricant, an antiblocking agent, a mold release agent, an ultraviolet absorber, Components such as colorants are adjusted within a range that does not impair the purpose of the present invention, and among the components contained in the multilayer film, propylene resin accounts for 75% by mass or more, and non-propylene resin components account for less than 25% by mass. It can be added within a certain range. In particular, in order to provide processing suitability during film molding and packaging suitability for filling machines, the coefficient of friction of the outermost layer and seal layer that forms the surface of the multilayer film is preferably 1.5 or less, particularly 1.0 or less. Therefore, it is preferable to add a lubricant or an anti-blocking agent to the outermost layer and the seal layer as appropriate.

<Multilayer film>
The multilayer film of the present invention includes a sealing layer, the sealing layer contains a water-soluble antibacterial agent, and of the components contained in the multilayer film, a propylene resin accounts for 75% by mass or more, and a non-propylene resin component is less than 25% by weight, and the multilayer film has a water vapor permeability of 9.0 g/m ² /24 hours or less.

<Components contained in multilayer film>
In the multilayer film of the present invention, among the components contained in the multilayer film, propylene-based resin accounts for 75% by mass or more, and foreign components other than propylene-based resin account for less than 25% by mass. The components contained in the multilayer film include not only resin components but also additive components. Furthermore, when the multilayer film of the present invention is constructed by laminating with an adhesive, the adhesive component is also included.
Moreover, the different component other than the propylene resin refers to a component other than the resin listed as the propylene resin. When the amount of the foreign component is less than 25% by mass with respect to the multilayer film, recyclability is improved, leading to a reduction in environmental load. The content of the different component other than the propylene resin is preferably less than 20% by mass of the components contained in the multilayer film, more preferably less than 15% by mass, and when it is less than 10% by mass, the multilayer film of the present invention A packaging material using the above is more preferable because it tends to be a monomaterial.
Note that "the packaging material is a monomaterial" refers to a case in which 90% by mass or more of all components constituting the packaging material is composed of the same component, for example, a propylene resin. As described below, the packaging material may be a bag made of a laminate film using the multilayer film of the present invention, or may be a bag made of the multilayer film of the present invention alone, It may be a combination of the laminate film or the multilayer film and a container, or it may be a bag made of the laminate film or the multilayer film and a film other than the multilayer film.
When the multilayer film of the present invention is used alone, it becomes a monomaterial packaging material because 90% by mass or more of all the components constituting the multilayer film are composed of the same components. On the other hand, when using a laminate film using the multilayer film of the present invention, if 90% by mass or more of all the components constituting the laminate film are composed of the same components, it becomes a monomaterial packaging material. The multilayer film of the present invention itself does not need to be included in the definition of monomaterial. Among the components contained in the multilayer film of the present invention, propylene resin accounts for 75% by mass or more, and foreign components other than propylene resin account for less than 25% by mass. It can be a monomaterial.
Monomaterial packaging materials contain only a small amount of foreign components, making them easy to reuse and reducing environmental impact.

The multilayer film of the present invention preferably contains a propylene homopolymer resin in the intermediate layer or the outermost layer. By including a propylene homopolymer resin in the middle layer or outermost layer, it is possible to achieve monomaterialization while imparting water vapor barrier properties to the multilayer film and lowering the water vapor permeability, which results in antibacterial properties. improves.

In addition, in order to achieve both lamination suitability, recyclability, and the effect of improving antibacterial properties, it is more preferable that the intermediate layer contains a propylene homopolymer and the outermost layer contains a propylene-ethylene random copolymer. It is more preferable that the outermost layer contains 51% by mass or more of a propylene-ethylene random copolymer.

The multilayer film of the present invention preferably contains a cyclic polyolefin resin in the intermediate layer or the outermost layer. By including a cyclic polyolefin resin in the intermediate layer or the outermost layer, it is possible to impart water vapor barrier properties to the multilayer film and lower water vapor permeability, thereby improving antibacterial properties.

<Water vapor permeability of multilayer film>
The water vapor permeability of the multilayer film of the present invention is measured using a water vapor permeability meter (LyssyL80-5000, manufactured by Systech Illinois) under the conditions of 40°C, 90% RH, and 24 hours of measurement time according to JIS K7129A. This is the measurement result. The unit in this case is "g/m ² /24 hours".

The water vapor permeability of the multilayer film of the present invention is preferably 9.0 g/m ² /24 hours or less. When the water vapor permeability is low, the antibacterial effect increases. Although the reason is not clear, when the water vapor permeability is low, it becomes difficult for the water vapor emitted from the contents to escape to the outside of the package of the present invention, and the water vapor emitted from the contents is efficiently absorbed into the water-soluble antibacterial agent. It is speculated that the antibacterial properties increase due to the reaction or elution of metal ions.

(Layer structure of multilayer film)
The multilayer film of the present invention includes a sealing layer. In addition, in the multilayer film of the present invention, in order to prevent the antibacterial agent contained in the seal layer from migrating to the adjacent layer, the layer adjacent to the seal layer is mainly made of a resin having a different crystallinity from that of the seal layer. It is preferable that the layer is a component. Among these, from the viewpoint of water vapor permeability, it is preferable that the layer adjacent to the seal layer is an intermediate layer containing a propylene homopolymer or a cyclic polyolefin resin. The degree of crystallinity is the ratio of crystalline regions in a polymer, and is the value obtained by dividing the heat of fusion of a resin by DSC measurement by the heat of fusion of a completely crystalline body. The heat of fusion measured by differential scanning calorimetry (DSC) is the heat of fusion at the first temperature increase, and is measured using, for example, a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Co., Ltd., DSC7020) according to the following procedure. be able to.
First, about 5.0 mg of a multilayer film for ultrasonic sealing, which is a target sample, is placed in an aluminum sample container, and the sample container is placed on a holder unit and set in an electric furnace. Next, the sample is heated from 30° C. to 200° C. at a heating rate of 10° C./min in a nitrogen atmosphere (first temperature raising), and a DSC curve is measured using a differential scanning calorimeter.
From the obtained DSC curve, use the analysis program of the differential scanning calorimeter to select the DSC curve at the first temperature increase, and calculate the heat of fusion [mJ/mg] at the first temperature increase of the target sample. can.
The value of the heat of fusion of the perfectly crystalline body is 207 [mJ/mg], and by calculating the value obtained by dividing the heat of fusion by the DSC measurement of the resin by the heat of fusion of the perfectly crystalline body (207 [mJ/mg]), Crystallinity can be calculated.

The layer structure of the multilayer film includes, but is not limited to, outermost layer/intermediate layer/seal layer, outermost layer/intermediate layer/intermediate layer/seal layer, and the like.
Further, it is preferable that the layer be laminated with an outermost layer/intermediate layer/seal layer.

As mentioned above, the ratio between the thickness of the sealing layer and the particle size of the water-soluble antibacterial agent used in the present invention is preferably 1:7 to 8:1. Since the particle size of the antibacterial agent is particularly preferably in the range of 2 to 20 μm, the thickness of the sealing layer is preferably 2.5 to 14 μm. In particular, it is preferable that the thickness of the sealing layer is 14 μm or less because the antibacterial agent will easily protrude from the sealing layer and the antibacterial effect will be enhanced.

The thickness ratio of the seal layer is preferably 8 to 40% of the total thickness of the multilayer film of the present invention.
The thickness ratio of the outermost layer is preferably 25 to 80% of the total thickness of the multilayer film of the present invention from the viewpoints of film rigidity, packaging suitability, transparency, surface gloss, and ease of tearing in the transverse direction, More preferably, it is 30 to 75%.
The thickness ratio of the intermediate layer is preferably in the range of 5 to 40%, more preferably 7 to 30% of the total thickness of the multilayer film of the present invention. When the ratio of the thickness of the intermediate layer to the total thickness of the multilayer film is within this range, transparency, tearability, pinhole resistance, and heat sealability are improved.

Furthermore, the multilayer film of the present invention preferably has a film thickness of 15 to 90 μm, more preferably 20 to 80 μm. When the film thickness is within this range, stable sealing strength, suitability for packaging machines, excellent pinhole resistance, easy tearing performance, etc. can be obtained.

(Method for manufacturing multilayer film)
The method for producing the multilayer film of the present invention is not particularly limited, but for example, each resin or resin mixture used for the outermost layer, intermediate layer, and sealing layer is heated and melted in separate extruders, and a coextrusion multilayer die method is used. Examples include coextrusion methods in which the outermost layer/intermediate layer/seal layer are laminated in the order of outermost layer/intermediate layer/seal layer in a molten state by a method such as a feed block method or the like, and then formed into a film by an inflation method, a T-die/chill roll method, or the like. This coextrusion method is preferable because it allows the ratio of the thickness of each layer to be adjusted relatively freely, and a multilayer film with excellent hygiene and cost performance can be obtained. Further, in order to suppress phase separation and generation of gel, a T-die chill roll method is preferred, which allows melt extrusion to be performed at a relatively high temperature.

When the resin mixture is laminated into each layer, the resin mixture can be laminated by directly extruding the dry blended resin mixture using a coextruder. Alternatively, the resin mixture may be melt-blended in advance using a melt-kneading device such as a single-screw extruder, twin-screw extruder, or Brabender mixer, pelletized, and then extruded using a co-extruder to form layers. You can also do it.

Since the multilayer film of the present invention is obtained as a substantially unstretched multilayer film by the above-described manufacturing method, secondary forming such as deep drawing by vacuum forming is also possible.

Alternatively, the seal layer used in the present invention and one or more other layers may be laminated together to form the multilayer film of the present invention. As the lamination method, known methods can be implemented, including dry lamination using a solvent-based adhesive, extrusion lamination, and the like. When an adhesive is used, the adhesive also falls under the category of a different component other than the propylene resin contained in the multilayer film of the present invention, but if the adhesive contains a volatile solvent component, the solvent component is included in the different component. Not applicable.

As the adhesive used for the above-mentioned laminate, a known adhesive can be used, but a two-component curing adhesive of a polyol composition and a polyisocyanate composition is preferable. The two-component curing adhesive may be in either a solvent type or a solvent-free type. In this specification, a "solvent type" adhesive refers to an adhesive that is applied to a base material, heated in an oven, etc. to volatilize the organic solvent in the coating film, and then bonded to another base material. This refers to the form used in the so-called dry lamination method. In addition, "solvent-free" adhesives are a method in which adhesives are applied to a base material and then bonded to other base materials without the process of heating in an oven or the like to volatilize the solvent. Refers to the form of adhesive used in the lamination method.

In the multilayer film of the present invention, the outermost layer is preferably subjected to a surface treatment in order to improve adhesion with printing ink and suitability for lamination. Examples of such surface treatments include surface oxidation treatments such as corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, ozone/ultraviolet treatment, and surface roughening treatments such as sandblasting. Corona treatment is preferred.

<Packaging material>
The multilayer film of the present invention can be used as a packaging material. Furthermore, a laminate film using the multilayer film of the present invention can also be used as a packaging material.

(Laminate film)
The multilayer film of the present invention can also be used by laminating other substrates. The other base material is preferably laminated on the surface resin layer (A) side. The other base material is not particularly limited, and may be a paper base material such as plain paper or coated paper, a plastic film such as unstretched film or stretched film, or a nonwoven fabric, but recyclability is improved by making it a monomaterial. In order to improve this, a propylene resin film is preferable.

As the laminating method, known methods can be used, including dry lamination using an adhesive, extrusion lamination, and the like. As the adhesive used for the laminate, any known adhesive can be used, but a two-component curing adhesive of a polyol composition and a polyisocyanate composition is preferred. The two-component curing adhesive may be in either a solvent type or a solvent-free type.
Further, the mass of the adhesive after drying is preferably 0.1 to 10 g/m ² , more preferably 1 to 6 g/m ² , and even more preferably 2 to 5 g/m ² Although it is preferable, since it is a monomaterial packaging material, it is more preferable to use less adhesive.

The structure of the laminate film is not particularly limited, but for example,
(1) Multilayer film of the present invention/adhesive layer/other base layer (2) Multilayer film of the present invention/adhesive layer/printed layer/other base layer (3) Multilayer film/adhesive of the present invention Layer/Other base layers/Printed layer/Adhesive layer/Other base layers (4) Multilayer film of the present invention/Adhesive layer/First printed layer/Second printed layer/Other base layers (5) Multilayer film/printed layer of the present invention (6) Multilayer film/first printed layer/second printed layer of the present invention, etc.

(Printing layer)
The packaging material using the multilayer film of the present invention may further include a printed layer in which a desired pattern is formed using ink in order to impart cosmetic properties, various information regarding the contents, and functionality. The ink is not particularly limited, and may be a general-purpose solvent-containing ink, a water-based ink, an active energy ray-curable ink, or various inkjet inks. Good too. In order to achieve a monomaterial, it is preferable that the amount of ink in the printing layer is small.

The printing method is not particularly limited, and printing can be performed by gravure printing, flexographic printing, inkjet printing, or the like.
As the cylinder used for gravure printing, known types such as an engraved type and a corroded type are used. The film thickness of the printing ink formed by the gravure printing method or the flexographic printing method is, for example, 10 μm or less, preferably 5 μm or less.

Moreover, the packaging material using the multilayer film of the present invention may have not only one printed layer but also a plurality of printed layers. For example, the multilayer film of the present invention may include a laminate having at least a first printed layer and a second printed layer in this order, or the multilayer film may include at least a first printed layer, a second printed layer, and a third printed layer. A laminate can be made with the layers in this order. Specifically, for example, a first printing layer formed from a printing ink containing a coloring agent, a second white printing layer formed from a liquid ink containing a white pigment as a coloring agent, and a third white printing layer. A printed product can have the printing layers in this order. The first printing layer can form a pattern using a coloring agent, and the second white printing layer formed from liquid ink containing a white pigment and the third printing layer can be used as the background of the pattern. Can be done. If the second or third printing layer is an overprint varnish, it may not contain a colorant.

Printing on the multilayer film of the present invention may be so-called front printing or back printing.

(packaging material)
Examples of the packaging material made of the multilayer film of the present invention include packaging bags and packaging containers used for foods, medicines, industrial parts, miscellaneous goods, magazines, and the like. In order to take advantage of the effects of the present invention, the contents are preferably foods, and particularly preferably foods with relatively low moisture content. The food with relatively low water content refers to food with a water activity value (Aw) of 0.95 or less, and includes, but is not limited to, rice cakes, white bread, fish paste products, rice, and sweets. do not have. The multilayer film of the present invention can exhibit a suitable antibacterial function even for foods with a water activity value (Aw) of 0.95 or less.

The above-mentioned packaging bag is preferably a packaging bag formed by stacking and sealing the sealing layers of the multilayer film of the present invention, or by stacking and sealing the outermost layer and the sealing layer. For example, cut two pieces of multilayer film into the desired packaging bag size, overlap them and seal three sides to form a bag, then fill the contents from one unsealed side and seal. It can be used as a packaging bag by sealing it. Furthermore, it is also possible to form a packaging bag by sealing the ends of a roll of film into a cylindrical shape using an automatic packaging machine and then sealing the top and bottom.

Furthermore, the multilayer film of the present invention can also be used to form a packaging bag or container by stacking and sealing the seal layer used in the present invention with another sealable film. In this case, as the other film, a film such as LDPE or EVA, which has relatively low mechanical strength, can be used. In addition, a film such as LDPE or EVA is bonded to a stretched film with relatively good tearability, such as biaxially stretched polyethylene terephthalate film (OPET), biaxially stretched polypropylene film (OPP), or unstretched polypropylene (CPP). Laminated laminate films can also be used. Among these, in order to obtain a monomaterial packaging material, it is preferable to bond it with a propylene film such as OPP or CPP.

(Sealing method)
The sealing layer of the multilayer film of the present invention has heat sealability. Therefore, the multilayer film of the present invention and the laminate film using the multilayer film of the present invention can be heat-sealed to form a package. The heat-sealing strength of the multilayer film or laminate film may be adjusted as appropriate depending on the mode of use, but for example, the sealing layer surfaces of the multilayer film of the present invention are overlapped, and the heat-sealing strength is 1. After heat sealing for 0 seconds, cut out a 15 mm wide test piece and peel it in a 180 degree direction at a tensile rate of 300 mm/min in a constant temperature room at 23 ° C and 50% RH. The maximum load is 4 N/15 mm or more. It is preferably 6N/15mm or more, and more preferably 6N/15mm or more. Further, the upper limit of the maximum load is preferably less than 20 N/15 mm, more preferably less than 15 N/15 mm. With this peel strength, the multilayer film is less likely to peel or fall off, and the ease of opening the package is particularly favorable.
In addition to heat sealing, ultrasonic sealing can also be applied to the multilayer film of the present invention and the laminate film using the multilayer film of the present invention. There are no particular limitations on the method of ultrasonic sealing, and a known ultrasonic sealing method, a method using a known ultrasonic sealing device, or the like can be appropriately selected depending on the purpose.

In the packaging material using the multilayer film of the present invention, arbitrary tear initiation parts such as V notches, I notches, perforations, micropores, etc. are formed in the sealing part in order to weaken the initial tear strength and improve the ease of opening. It is preferable to do so.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the scope of the claims is not limited thereto.

<Particle size measurement of antibacterial agent>
The particle size of the antibacterial agent was determined by a laser diffraction scattering particle size distribution analyzer (Microtrac MT-3300EXII manufactured by Nikkiso Co., Ltd.). As a specific measurement method, particles of the antibacterial agent are dispersed in IPA solvent in a water tank, and the above-mentioned device is used to measure and analyze the diffraction and scattering intensity distribution of light, and the particle size and volume-based particle distribution are measured. The value of D50, which can be calculated by the following, was taken as the particle size of the antibacterial agent. According to this measurement method, the particle size of Ion Pure WPA (manufactured by Ishizuka Glass Co., Ltd.) is 3.6 μm, the particle size of Scarlow Premium S (manufactured by WM Co., Ltd.) is 5.4 μm, and the particle size of Novaron AG1100 (manufactured by Toagosei Co., Ltd.) is 3.6 μm. The particle size of the product (manufactured by J.D. Co., Ltd.) is 1.9 μm.

<Water solubility evaluation of antibacterial agents>
100 g of distilled water at 23° C. was weighed into a 200 mL glass beaker. Into this beaker, 150 mg of various antibacterial agents were added and stirred for 10 minutes using an ultrasonic cleaning device filled with water. Thereafter, stirring was stopped and the mixture was allowed to stand for 60 minutes, and the dispersion in the beaker was visually observed. Those in which phase separation occurred were judged to be not water-soluble.
As a result of the evaluation, Ion Pure WPA (manufactured by Ishizuka Glass Co., Ltd.) and Scarlow Premium S (manufactured by WM Co., Ltd.) were found to be water-soluble, whereas Novaron AG1100 (manufactured by Toagosei Co., Ltd.) was not water-soluble.

<Manufacture of antibacterial agent masterbatch>
Various antibacterial agents and propylene-ethylene random copolymer (density 0.900 g/cm ³ , MFR 7.0 g/10 min) were added to a melt-kneading device of a single-screw extruder (screw diameter 40 mm) to achieve a specific antibacterial agent concentration. The mixture was melt-blended at a temperature of 220°C, compounded, and pelletized to obtain various antibacterial agent PP masterbatches.

<Manufacture of multilayer film>
(Example 1)
As the resin for the outermost layer, a propylene-ethylene random copolymer (density 0.900 g/cm ³ , MFR 7.0 g/10 min) (hereinafter referred to as COPP) was used. In addition, a propylene homopolymer (density 0.900 g/cm ³ , MFR 8.0 g/10 min) (hereinafter referred to as HOPP) was used as the resin for the intermediate layer. In addition, as a resin for the sealing layer, a resin mixture of 95 parts by mass of COPP and 5 parts by mass of Ion Pure WPA antibacterial agent PP masterbatch (compound product with COPP, antibacterial agent particle size 3.6 μm, antibacterial agent concentration 10% by mass) was used. was used. These resins were each supplied to an extruder for the outermost layer (diameter 50 mm), an extruder for the middle layer (diameter 50 mm), and an extruder for the seal layer (diameter 50 mm) and melted at 200 to 230°C. Co-melt extrusion is performed by supplying the resin to a T-die/chill-roll coextrusion multilayer film manufacturing apparatus having a feedblock (feedblock and T-die temperature: 250°C), so that the layer structure of the film is the outermost layer/middle layer. A multilayer film of Example 1 was obtained, which had a three-layer structure of layer/seal layer and the thickness of each layer was 24 μm/8 μm/8 μm (total 40 μm). The concentration of the antibacterial agent contained in the seal layer is 0.5% by mass.

(Examples 2 to 9)
Multilayer films of Examples 2 to 10 were obtained in the same manner as in Example 1, except that the components used and their ratios were changed as shown in Table 1.

The composition of the sealing layer in Example 1 was 60 parts by mass of COPP and 40 parts by mass of Scarlow Premium Antibacterial Agent PP Masterbatch (compound product with COPP, antibacterial agent average particle diameter 5.4 μm, antibacterial agent concentration: 20% by mass). A multilayer film of Example 10 was obtained in the same manner as in Example 1 except that the mixture was changed to a mixture of .

(Comparative Examples 1 and 3)
Multilayer films of Comparative Examples 1 and 3 were obtained in the same manner as in Example 1, except that the components used and their ratios were changed as shown in Table 2.

(Comparative example 2)
The composition of the seal layer in Example 1 was a mixture of 80 parts by mass of COPP and 20 parts by mass of Novaron AG1100 antibacterial agent PP masterbatch (compound product with COPP, antibacterial agent average particle diameter 1.9 μm, antibacterial agent concentration: 10% by mass). A multilayer film of Comparative Example 2 was obtained in the same manner as in Example 1 except that the following was changed.

<Measurement of seal strength>
The sealing layer surfaces of the multilayer films obtained in Examples and Comparative Examples were overlapped and heat sealed at a temperature of 130°C to 150°C (in 10°C increments) and a pressure of 0.2 MPa for 1.0 seconds, and then sealed to a width of 15 mm. The seal strength was measured by cutting and peeling at 90 degrees at a speed of 300 mm/min using a tensile tester (manufactured by A&D Co., Ltd.) in a constant temperature room at 23° C. and 50% RH.

<Measurement of impact strength>
The multilayer films obtained in Examples and Comparative Examples were allowed to stand for 4 hours in a thermostatic chamber adjusted to 23°C. Thereafter, using a BU-302 film impact tester manufactured by Tester Sangyo, a 1.0-inch head was attached to the tip of the pendulum, and the impact strength was measured by the film impact method.

<Measurement of water vapor permeability>
The multilayer films produced in Examples 1 to 10 and Comparative Examples 1 to 3 were tested at 40°C, 90% RH, and Water vapor permeability was measured under conditions of a measurement time of 24 hours. The measurement results are shown in Tables 1 and 2.

(Creation of packaging bag)
The multilayer films prepared in Examples 1 to 10 and Comparative Examples 1 to 3 were cut into A4 size sheets, folded in half, and heated at 120°C for 1 second at 0.2 MPa and 1 second, leaving one long side. A packaging bag was produced by heat sealing under the following conditions. Two packaging bags were prepared for each type of multilayer film, and the test was conducted with N=2.
A commercially available bread (pack of 6 pieces) was opened and immediately taken out while wearing nitrile gloves, one piece of bread was placed in each packaging bag, and the empty long side was sealed with an impulse seal. Packaging bags containing bread made from the multilayer films of Examples 1 to 10 and Comparative Examples 1 to 3 (N = 2, total of 28 items) were placed on a tray and stored in a constant temperature and humidity room at 23°C and 55%.

<Calculation of mold growth area>
Twelve days after sealing the packaging bag containing the bread, visually observe it, take photos of each side (front and back), and use image analysis software (GIMP) to identify the mold area, which is the mold breeding area. By selecting it and calculating the total number of pixels in the histogram dialog, the ratio of the mold area to the total area of the bread calculated in advance was quantified.
The arithmetic mean value of N=2 was calculated, and the evaluation results are shown in Tables 1 and 2 as mold growth areas.

The raw materials used are as follows.
COPP: Propylene-ethylene random copolymer (density 0.900 g/cm ³ , MFR 7.0 g/10 min)
HOPP: Propylene homopolymer (density 0.900 g/cm ³ , MFR 8.0 g/10 min)
COC: norbornene copolymer of cyclic olefin resin (density 1.010 g/cm ³ , MFR 12.0 g/10 min)
Ion Pure WPA: manufactured by Ishizuka Glass Co., Ltd., particle size 3.6 μm
Scarlow Premium: Manufactured by WM Co., Ltd., particle size 5.4 μm
Novalon AG1100: manufactured by Toagosei Co., Ltd., particle size 1.9 μm

As is clear from the above table, the multilayer films of the present invention of Examples 1 to 10 contain water-soluble antibacterial agents, have water vapor permeability of 9 g/m ² /24 hours or less, and are suitable for breads with relatively low moisture content. It was also found that the effect of inhibiting mold growth is high. In addition, it could be made into a monomaterial and could be easily recycled.
On the other hand, in Comparative Example 1, which did not contain an antibacterial agent, although the water vapor permeability was low, no mold growth inhibiting effect was observed. Furthermore, in Comparative Example 2, which contained Novalon AG1100, which is a non-water-soluble antibacterial agent, in the sealing layer, no mold growth inhibiting effect was observed. Furthermore, Comparative Example 3, which contained a water-soluble antibacterial agent in the sealing layer but had a high water vapor permeability, could not exhibit the effect of inhibiting mold growth.

<Confirmation of antibacterial effect>
Regarding the multilayer films of Examples 1 to 3 and Comparative Examples 1 to 2, test bacteria "Escherichia coli (NBRC 3972, Escherichia coli)" and " Staphylococcus aureus (NBRC 12732, Staphylococcus aureus)" was tested (conducted with n=1) to evaluate antibacterial properties.
As a result, the multilayer films of Examples 1 to 3 were found to have sufficient antibacterial effects. On the other hand, no antibacterial effect was observed in the multilayer films of Comparative Examples 1 and 2.

Claims (6)

A multilayer film including a sealing layer,
the sealing layer contains a water-soluble antibacterial agent,
Among the components contained in the multilayer film, propylene resin accounts for 75% by mass or more, and different components other than propylene resin account for less than 25% by mass,
A multilayer film, wherein the multilayer film has a water vapor permeability of 9.0 g/m ² /24 hours or less. 2. The multilayer film of claim 1, wherein the multilayer film has an intermediate layer and an outermost layer, the intermediate layer or the outermost layer comprising a propylene homopolymer resin. The multilayer film according to claim 1, wherein the ratio between the thickness of the sealing layer and the particle size of the antibacterial agent is 1:7 to 8:1. The multilayer film according to claim 1, wherein the thickness of the sealing layer is 14 μm or less. A packaging material comprising the multilayer film according to any one of claims 1 to 4. The packaging material according to claim 5, which is used for food packaging.