Antifogging multilayer film, laminate, packaging material, lid material, and top seal container

Abstract

Provided is an antifogging multilayer film which has, in the following order, at least a layer (A) that has a linear polyethylene as a main resin component, an adhesive layer (B) that has a linear polyethylene and a polypropylene resin as main resin components and contains an antifogging agent, and a heat seal layer (C) that has a polypropylene resin as a main resin component and contains an antifogging agent, and which has a seal strength of 10-18 N / 15 mm at room temperature and a seal strength of 4-8 N / 15 mm at 100°C. Also provided are a laminate, a packaging material, a lid material, and a top seal container which use the antifogging multilayer film.

Description

Anti-fogging multilayer film, laminate, packaging material, lid material, and top-sealed container

[0001] The present invention relates to a multilayer film that has both anti-fogging properties and easy-open properties and can be suitably used as a lid material for food packaging containers, and a laminate using the same.

[0002] Currently, food packaging containers include top-sealed containers that comprise a plastic container and a film lid (lid material). Top-sealed lid materials are required to have anti-fogging properties to enhance the visibility of the food contents. A known multilayer film for such lid material is a multilayer film that is suitable for this purpose and includes a laminate layer (A) that is primarily composed of linear polyethylene (a) and does not contain an anti-fogging agent, an intermediate layer (B) that contains linear polyethylene (b1) and an anti-fogging agent (b2), and a heat-sealable layer (C) that contains a polypropylene resin (c1) and an anti-fogging agent (c2), laminated in the order (A) / (B) / (C), wherein the combined mass of the anti-fogging agent (b2) and the anti-fogging agent (c2) is in the range of 0.8 to 1.6% by mass relative to the total mass of the multilayer film, the wetting tension of both outer surfaces of the multilayer film is in the range of 35 to 45 mN / m, and the total thickness of the multilayer film is 20 to 100 μm (see, for example, Patent Document 1).

[0003] Recently, however, an increasing number of users have been using microwave ovens to directly heat the top-sealed containers to heat the food inside them. When a top-sealed container is heated in a microwave oven, the contents become hot, posing a risk of burns, etc. In addition, the large amount of heated steam makes it difficult to see the contents even if the container has anti-fogging properties, posing a risk of burns, etc., when opening the container. Furthermore, because the container itself becomes hot, the rigidity of the container decreases, and it becomes difficult to grip the hot lid tightly, making it difficult to open.

[0004] The anti-fogging multilayer film described in Patent Document 1 is not intended to be used as a top-sealed container that is directly heated in a microwave oven, and there is still room for improvement.

[0005] WO2015 / 046131

[0006] The object of the present invention is to provide an anti-fogging multilayer film suitable for use as a lid material for a top-sealed container when heated directly in a microwave oven, a laminate obtained by laminating this multilayer film onto a base film, and a packaging material and a top-sealed container using this laminate.

[0007] The present inventors have discovered an anti-fog multilayer film suitable for use as a lid for a top-sealed container that is directly heated in a microwave oven, which has sufficient seal strength to withstand distribution and allow opening before microwave heating, but during or immediately after heating, the seal strength decreases to a level that allows easy opening even when the container is hot.

[0008] That is, the present invention provides an anti-fog multilayer film comprising, in this order, at least a layer (A) containing linear polyethylene as the main resin component, an adhesive layer (B) containing linear polyethylene and a polypropylene-based resin as the main resin components and containing an anti-fog agent, and a heat-sealable layer (C) containing a polypropylene-based resin as the main resin component and containing an anti-fog agent, and having a seal strength of 10 to 18 N / 15 mm at room temperature and a seal strength of 4 to 8 N / 15 mm at 100°C.

[0009] The present invention also provides a laminate containing the anti-fog multilayer film described above.

[0010] The present invention also provides a packaging material containing the anti-fogging multilayer film described above.

[0011] The present invention also provides a covering material containing the anti-fogging multilayer film described above.

[0012] The present invention also provides a top-sealed container containing the anti-fogging multilayer film described above.

[0013] The present invention provides an anti-fogging multilayer film suitable for use as a lid material for a top-sealed container when heated directly in a microwave oven, and also provides a laminate obtained by laminating this multilayer film onto a base film, as well as a packaging material and a top-sealed container using this laminate.

[0014] (Anti-Fog Multilayer Film) The anti-fogging multilayer film of the present invention comprises, in this order, at least a layer (A) containing linear polyethylene as the main resin component, an adhesive layer (B) containing linear polyethylene and a polypropylene-based resin as the main resin components and containing an anti-fogging agent, and a heat-seal layer (C) containing a polypropylene-based resin as the main resin component and containing an anti-fogging agent. When the anti-fogging multilayer film of the present invention is used as a lid material for a top-sealed container, the heat-seal layer (C) is the layer to be attached to the container, and the layer (A) is the outer layer of the container.

[0015] [Layer (A)] The layer (A) in the present invention has a linear polyethylene (a) as the main resin component (main component). As will be described later, the layer (A) in the present invention does not have to be composed of a single layer, and may have a single layer or a laminate structure of two or more layers. Even in the case of two or more layers, the main resin component is the linear polyethylene (a).

[0016] In the present invention, the term "main resin component (principal component)" means that a specific resin is contained in an amount of 65% by mass or more, preferably 80% by mass or more, based on the total amount of resin components forming the layer.

[0017] (Linear Polyethylene (a)) The linear polyethylene (a) is obtained by copolymerizing ethylene monomer as a main component with an α-olefin such as butene-1, hexene-1, octene-1, or 4-methylpentene as a comonomer by low-pressure radical polymerization using a single-site catalyst. The comonomer content is preferably in the range of 0.5 to 20 mol%, and more preferably in the range of 1 to 18 mol%.

[0018] Examples of the single-site catalyst include various single-site catalysts, such as metallocene catalyst systems that combine a metallocene compound of a transition metal of Group IV or V of the periodic table with an organoaluminum compound and / or an ionic compound. Single-site catalysts have uniform active sites, and therefore, compared with multi-site catalysts with non-uniform active sites, the molecular weight distribution of the resulting resin is sharper, resulting in less precipitation of low-molecular-weight components when formed into a film, and thus providing a resin with excellent physical properties, such as excellent stability of adhesive strength between resin layers.

[0019] The density of the linear polyethylene (a) used in the layer (A) is 0.920 to 0.950 g / cm ３ is preferably 0.925 to 0.945 g / cm ３ More preferably, it is in the range of 0.930 to 0.940 g / cm ３ It is more preferable that the density is in the range of 100 to 200°C. If the density is in this range, the film has appropriate rigidity and excellent mechanical strength such as pinhole resistance, and the film formability, extrusion suitability, and heat resistance are improved. The melting point is preferably in the range of 60 to 130°C, more preferably 70 to 125°C. If the melting point is in this range, the processing stability and the processability when co-extruded with other layers are improved. Furthermore, the MFR (190°C, 21.18N) of the linear polyethylene (a) is preferably 2 to 20 g / 10 min, more preferably 3 to 10 g / 10 min. If the MFR is in this range, the extrusion moldability of the film is improved.

[0020] As described above, the layer (A) is composed mainly of the linear polyethylene (a). However, when laminating with another substrate using an adhesive or when printing, other resins may be used in combination with the layer (A) in order to improve adhesion to adhesives or inks. In this case, the other resins that can be used in combination are preferably ethylene-based resins from the viewpoint of the transparency of the resulting multilayer film. Examples thereof include ethylene-based copolymers such as branched polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-maleic anhydride copolymer (E-MAH), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), and ethylene-methacrylic acid copolymer (EMAA); as well as ionomers of ethylene-acrylic acid copolymers, ionomers of ethylene-methacrylic acid copolymers, and copolymers of ethylene and a monomer having a cyclic olefin structure, such as a norbornene-based monomer, and these may be used alone or in combination of two or more.

[0021] Layer (A) may or may not contain an antifogging agent, which will be described later. When an antifogging agent is contained, the content thereof is preferably in the range of 0.2 to 1.5 mass %, and more preferably in the range of 0.4 to 1.0 mass %, relative to the total mass of layer (A). Antifogging agents will be described later.

[0022] On the other hand, there is a concern that the anti-fog agent may bleed out. As described above, since the layer (A) is the outer layer of the container, it may be laminated or directly printed with ink or the like for display purposes. In this case, the anti-fog agent that bleeds out onto the surface may cause peeling of the laminating adhesive or ink or printing defects. If such a concern exists, it is preferable that the layer (A) be composed of two or more layers, and that the outermost layer does not contain the anti-fog agent.

[0023] Specifically, it preferably contains two layers: a layer (A1) containing linear polyethylene as the main resin component and no antifogging agent, and a layer (A2) containing linear polyethylene as the main resin component and an antifogging agent. In this case, it is preferable that the layer (A1) containing no antifogging agent is the outer layer of the container, and the layer (A2) containing the antifogging agent is located between the layer (A1) and the adhesive layer (B) described below. Hereinafter, the layer (A) containing no antifogging agent may be referred to as "layer (A1)," and the layer containing the antifogging agent may be referred to as "layer (A2)."

[0024] The content of the antifogging agent in the layer (A2) containing the antifogging agent is preferably in the range of 0.5 to 4.0% by mass, and particularly preferably in the range of 1.0 to 3.0% by mass, based on the total mass of the layer (A2). Antifogging agents will be described later.

[0025] The thickness of layer (A) is not particularly limited, but the total thickness of layer (A) is generally in the range of 15 to 70 μm, and more preferably in the range of 20 to 60 μm. When layer (A) is composed of two or more layers, that is, a material layer (A1) not containing the antifogging agent and a layer (A2) containing the antifogging agent, the thickness of layer (A1) is preferably 5 to 40 μm, and the thickness of layer (A2) is preferably 5 to 40 μm.

[0026] [Adhesive Layer (B)] The adhesive layer (B) of the present invention, which contains linear polyethylene and a polypropylene-based resin as main resin components and an antifogging agent, contains linear polyethylene (b1) and a polypropylene-based resin (b2) as main resin components and an antifogging agent.

[0027] (Linear polyethylene (b1)) In the present invention, the linear polyethylene (b1) may be the same as the linear polyethylene (a) used in the layer (A). The density of the linear polyethylene (b1) used in the layer (B) is 0.920 to 0.950 g / cm ３ is preferably 0.925 to 0.945 g / cm ３ More preferably, it is in the range of 0.930 to 0.940 g / cm ３ It is more preferable that the density is in the range of 100 to 200°C. If the density is in this range, the film has appropriate rigidity and excellent mechanical strength such as pinhole resistance, and the film formability, extrusion suitability, and heat resistance are improved. The melting point is preferably in the range of 60 to 130°C, more preferably 70 to 125°C. If the melting point is in this range, the processing stability and the processability when co-extruded with other layers are improved. Furthermore, the MFR (190°C, 21.18N) of the linear polyethylene (a) is preferably 2 to 20 g / 10 min, more preferably 3 to 10 g / 10 min. If the MFR is in this range, the extrusion moldability of the film is improved.

[0028] (Polypropylene Resin) The polypropylene resin (b2) in the present invention is not particularly limited as long as it can be laminated with the above-mentioned layer (A), and examples thereof include propylene homopolymers, propylene-α-olefin random copolymers, such as propylene-ethylene copolymers, propylene-butene-1 copolymers, propylene-ethylene-butene-1 copolymers, and metallocene-catalyzed polypropylenes. These may be used alone or in combination of two or more. Propylene-α-olefin random copolymers are desirable, and as described above, propylene-α-olefin random copolymers polymerized using a metallocene catalyst are particularly preferred.

[0029] The polypropylene resin (b2) preferably has an MFR (230° C.) of 0.5 to 30.0 g / 10 min and a melting point of 110 to 165° C., and more preferably has an MFR (230° C.) of 2.0 to 15.0 g / 10 min and a melting point of 115 to 162° C. If the MFR and melting point are within these ranges, the film shrinks little during heat sealing, and further the film formability is improved.

[0030] The proportion of the linear polyethylene (b1) and polypropylene resin (b2) used in the adhesive layer (B) is preferably in the range of a mass ratio of 90:10 to 50:50, more preferably 80:20 to 60:40, relative to 100 parts by mass of the resin. If the mass ratio is within this range, good adhesive strength can be obtained with both the layer (A) and the heat-sealable layer (C).

[0031] (Anti-Fog Agent) In the present invention, the anti-fogging agent is not particularly limited as long as it is known to be generally added to olefin-based resins to impart anti-fogging properties. For example, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used, and it is preferable to use a nonionic surfactant.

[0032] Specific examples include sorbitan surfactants such as sorbitan monostearate, sorbitan distearate, sorbitan monopalmitate, sorbitan dipalmitate, sorbitan monobehenate, sorbitan dibehenate, sorbitan monolaurate, and sorbitan dilaurate; glycerin surfactants such as glycerin monolaurate, glycerin dilaurate, diglycerin monopalmitate, diglycerin dipalmitate, glycerin monostearate, glycerin distearate, diglycerin monostearate, diglycerin distearate, diglycerin monolaurate, and diglycerin dilaurate; and polyethylene glycol monostearate. and polyethylene glycol-based surfactants such as polyethylene glycol monopalmitate; trimethylolpropane-based surfactants such as trimethylolpropane monostearate; diethanolalkylamine-based and diethanolalkylamide-based surfactants such as lauryl diethanolamine, oleyl diethanolamine, stearyl diethanolamine, lauryl diethanolamide, oleyl diethanolamide, and stearyl diethanolamide; pentaerythritol-based surfactants such as pentaerythritol monopalmitate; polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan distearate, and mono- and distearates of sorbitan-diglycerin condensates. These may be used alone or in combination of two or more.

[0033] The proportion of the antifogging agent in the adhesive layer (B) is preferably in the range of 0.5 to 5.0% by mass, and particularly preferably in the range of 1.0 to 4.5% by mass, based on the total mass of the layer. By using an antifogging agent in this range, even if migration to the aforementioned layer (A) occurs, the antifogging properties of the film can be easily improved. Furthermore, the interlayer strength between the layer (A) and the heat-sealable layer (C) is not affected.

[0034] [Heat-seal layer (C)] The heat-seal layer (C) of the present invention, which contains a polypropylene-based resin as a main resin component and an anti-fogging agent, essentially requires the use of a polypropylene-based resin (c1) from the viewpoint of facilitating the development of heat-sealability when used as a container lid material or a packaging bag.

[0035] The polypropylene-based resin (c1) is not particularly limited as long as it can be laminated with the aforementioned layer (A) and adhesive layer (B), and examples thereof include propylene homopolymers, propylene-α-olefin random copolymers, such as propylene-ethylene copolymers, propylene-butene-1 copolymers, propylene-ethylene-butene-1 copolymers, and metallocene-catalyzed polypropylenes. These may be used alone or in combination of two or more. Propylene-α-olefin random copolymers are preferred, and as mentioned above, propylene-α-olefin random copolymers polymerized using a metallocene catalyst are particularly preferred. By using these propylene-based resins as the resin for the heat-seal layer (C), they can be suitably used as lid materials for packaging containers, particularly those whose sealing surface is a resin layer containing a polypropylene-based resin. Furthermore, the polypropylene-based resin contained in the heat-seal layer (C) preferably contains 10 to 30% by mass of propylene-butene-1 copolymer.

[0036] The polypropylene resin (c1) preferably has an MFR (230° C.) of 0.5 to 30.0 g / 10 min and a melting point of 110 to 165° C., and more preferably has an MFR (230° C.) of 2.0 to 15.0 g / 10 min and a melting point of 115 to 162° C. If the MFR and melting point are within these ranges, the film shrinks little during heat sealing, and further the film formability is improved.

[0037] The proportion of the polypropylene resin (c1) used in the heat seal layer (C) is preferably such that the resin is the main component, and more preferably is 85 mass % or more. Other resins that can be used in combination are the same as those exemplified as the resins that can be used in combination in the layer (A).

[0038] As the antifogging agent used in the heat seal layer (C), any of the antifogging agents exemplified above can be used, and the same applies to the preferred antifogging agents.

[0039] The anti-fogging agent used in the layer (A2) or the adhesive layer (B) may be the same as or different from the anti-fogging agent used in the heat-seal layer (C). When a masterbatch anti-fogging agent is used, from the viewpoint of compatibility, it is preferred that the base resins of the layer (A2) or the adhesive layer (B) be polyethylene-based resins, and that the base resin of the heat-seal layer (C) be polypropylene-based resins.

[0040] The content of the antifogging agent in the heat seal layer (C) is preferably in the range of 1.0 to 6.0% by mass, particularly preferably 2.0 to 5.0% by mass, based on the total mass of the layer. By using the antifogging agent in this range, it becomes easier to obtain a film with good antifogging properties and antifogging durability.

[0041] [Configuration of Anti-Fog Multilayer Film] Specific embodiments of the anti-fogging multilayer film of the present invention are shown below: Layer (A) / Adhesive layer (B) / Heat seal layer (C) Layer (A1) / Layer (A2) / Adhesive layer (B) / Heat seal layer (C)

[0042] [Seal Strength of Anti-Fog Multilayer Film] The anti-fogging multilayer film of the present invention is characterized in that it exhibits different seal strengths at room temperature and at high temperatures. The seal strength decreases at high temperatures. Specifically, under condition (X), the seal strength at room temperature is 10 to 18 N / 15 mm, and the seal strength at 100°C is 4 to 8 N / 15 mm. In the present invention, "room temperature" is defined as the range of 20°C plus or minus 15°C (5 to 35°C) (JIS Z 8703 [4]). Condition (X) is as follows:

[0043] (Condition X) (1) A laminate is prepared by laminating the anti-fog multilayer film of the present invention and a 15 μm biaxially oriented nylon film with a polyurethane adhesive, and aging is performed at 40°C for 48 hours. (2) The heat seal layer (C) of the laminate is placed face-to-face with a 0.3 mm thick polypropylene sheet, and the upper heat seal bar of a heat seal tester, adjusted to a temperature of 180°C, is set so as to be the outermost layer on the side of the laminate opposite the heat seal layer (C). Heat sealing is performed at 0.2 MPa for 1 second. (3) The polypropylene sheet and the laminate are each gripped with a jig in a tensile tester, and the seal strength is measured as the maximum strength when peeled at a speed of 300 mm / min. The peeling surface is between the adhesive layer (B) and the heat seal layer (C), and the seal strength at this interface is measured.

[0044] In the present invention, the polyurethane adhesive (1) used was a urethane reactive adhesive "DIC Dry LX500 / KR90S" manufactured by DIC Corporation. The heat seal tester (2) used was a "Precision Heat Sealer manufactured by Tester Sangyo Co., Ltd."

[0045] A seal strength of 10 to 18 N / 15 mm at room temperature makes it difficult for the contents to leak due to bag breakage during distribution. Furthermore, a seal strength of 4 to 8 N / 15 mm at 100°C makes it particularly easy to open, even if the rigidity of the container decreases at high temperatures after microwave heating or the container or lid cannot be gripped tightly. Furthermore, the risk of spilling the contents due to the increased opening speed caused by a seal strength that is too low can be reduced.

[0046] In the present invention, the cause of the decrease in seal strength of anti-fog multilayer films at high temperatures is presumed to be as follows: Thermoplastic resins such as polyethylene, polypropylene, and their copolymers soften at temperatures above their glass transition points. Therefore, it is known that their seal strength at high temperatures is lower than that at room temperature. It is also known that steam emitted from the contents during microwave heating can reach approximately 100°C. In conventional technologies, seal strength adjustment was often achieved solely with copolymer resins such as propylene-butene-1 copolymer, making it difficult to control the seal strength at room temperature and at high temperatures. By incorporating a heat-resistant polypropylene-based resin into the heat-seal layer or adhesive layer, or both, and by increasing the density of the linear polyolefin in the layers (A) and (B), the anti-fog multilayer films of the present invention are able to suppress the decrease in seal strength at high temperatures and control the strength at room temperature and at high temperatures.

[0047] The total thickness of the anti-fog multilayer film of the present invention is preferably in the range of 20 to 100 μm, more preferably in the range of 25 to 80 μm, because this facilitates lamination when used by laminating it with other substrates and provides favorable heat sealability and anti-fog properties.

[0048] In addition, from the viewpoints of sealability, easy-openability, and lamination properties, it is preferable that the thickness ratio of each layer in the multilayer film is such that the thickness ratio of the layer (A) is in the range of 60 to 90%, the thickness ratio of the adhesive layer (B) is in the range of 5 to 20%, and the thickness ratio of the heat-sealable layer (C) is in the range of 5 to 18%.

[0049] The total amount of the antifogging agent contained in the entire antifogging multilayer film of the present invention is 0.8 to 2.5 mass %, and in particular, a range of 1.0 to 2.0 mass % is preferred from the viewpoints of good film-forming properties, the expression of antifogging properties, and the durability of antifogging properties.

[0050] Each of Layers (A), (B), and (C) of the anti-fog multilayer film of the present invention can contain components such as antistatic agents, heat stabilizers, nucleating agents, antioxidants, lubricants, antiblocking agents, release agents, ultraviolet absorbers, and colorants, within the scope of the invention. In particular, in order to impart processability during film molding and lamination and packaging suitability in packaging machines, the coefficient of friction of the film surface is preferably 1.5 or less, and more preferably 1.0 or less, and therefore, it is preferable to add lubricants, antiblocking agents, and antistatic agents appropriately to the resin layers corresponding to the surface layers of the multilayer film.

[0051] Furthermore, the anti-fog multilayer film of the present invention may be subjected to a corona treatment, if necessary, to impart wettability. Examples of methods for imparting wettability include surface oxidation treatments such as corona discharge treatment, plasma treatment, flame treatment, and ozone / ultraviolet treatment, with corona discharge treatment being preferred. Such surface treatments improve the coatability of ink and adhesive when subsequent processes, such as applying ink or adhesive to layer (A) of the multilayer film and laminating it to a substrate, provide excellent adhesion to ink, adhesive, anchor coating agents, etc., and facilitate avoiding problems such as detachment and delamination of ink, adhesive, or evaporated aluminum. When laminating by extrusion lamination, there is no particular problem even if the surface of layer (A) of the multilayer film is not subjected to a corona treatment. The corona discharge treatment method is not particularly limited, and known methods can be used.

[0052] The method for producing the anti-fog multilayer film of the present invention is not particularly limited, but examples include a coextrusion method in which the resins or resin mixtures used for the layer (A), adhesive layer (B), and heat-seal layer (C) are heated and melted in separate extruders, laminated in the molten state in the order (A) / (B) / (C) or (A1) / (A2) / (B) / (C) by a method such as a coextrusion multilayer die method or a feed block method, and then formed into a film by an inflation method or a T-die chill roll method. This coextrusion method is preferred because it allows relatively free adjustment of the thickness ratio of each layer and produces a multilayer film that is hygienic and cost-effective. Among these, the T-die chill roll method is preferred because it suppresses deterioration of the film appearance when coextruding resins with different melting points and Tg's, facilitates the formation of a uniform layer structure, and facilitates the production of a film with suitable transparency and gloss. The inflation method is also preferred because it requires simple equipment and is suitable for small-lot, high-mix production.

[0053] The anti-fogging multilayer film of the present invention can be obtained as a substantially unstretched multilayer film by the above-mentioned production method, and therefore can be subjected to secondary forming such as deep drawing by vacuum forming or embossing.

[0054] The anti-fog multilayer film of the present invention can also be used by laminating it with another substrate. The other substrate that can be used in this case is not particularly limited, but from the viewpoint of easily achieving the effects of the present invention, it is preferable to use a thermoplastic resin film having high rigidity and high gloss, particularly a biaxially stretched resin film. Furthermore, in applications where transparency is not required, aluminum foil can be used alone or in combination.

[0055] Examples of stretched resin films include biaxially oriented polyester (PET), biaxially oriented polypropylene (OPP), biaxially oriented polyamide (PA), coextruded biaxially oriented polyamide (ONY) with a central layer of ethylene vinyl alcohol copolymer (EVOH), biaxially oriented ethylene vinyl alcohol copolymer (EVOH), coextruded biaxially oriented polypropylene coated with polyvinylidene chloride (PVDC), etc. These may be used alone or in combination.

[0056] The laminate of the present invention is a laminate film obtained by laminating the thermoplastic resin film on the anti-fogging multilayer film obtained as described above, and examples of the lamination method include dry lamination, wet lamination, non-solvent lamination, and extrusion lamination.

[0057] Examples of adhesives used in the dry lamination include polyester-polyurethane adhesives. While various pressure-sensitive adhesives can be used, it is preferable to use a pressure-sensitive adhesive. Examples of pressure-sensitive adhesives include rubber-based adhesives obtained by dissolving polyisobutylene rubber, butyl rubber, or mixtures thereof in organic solvents such as benzene, toluene, xylene, or hexane; rubber-based adhesives containing tackifiers such as abiethylene acid rosin ester, terpene-phenol copolymer, or terpene-indene copolymer; and acrylic-based adhesives obtained by dissolving an acrylic copolymer having a glass transition temperature of −20° C. or lower, such as a 2-ethylhexyl acrylate-n-butyl acrylate copolymer or a 2-ethylhexyl acrylate-ethyl acrylate-methyl methacrylate copolymer, in an organic solvent.

[0058] The use of the laminate of the present invention is not particularly limited, but it can be suitably used as a lid material for packaging containers used for food, medicines, industrial parts, miscellaneous goods, magazines, etc. In particular, it is preferred that the outermost layer of the packaging container (the portion that adheres to the heat seal layer of the multilayer film of the present invention) contains various propylene-based resins from the viewpoint of a balance between ease of opening and seal strength.

[0059] (Lid material) The anti-fogging multilayer film of the present invention and the laminate of the present invention can be used as a container lid material intended for use as a lid material for plastic containers for food, medicine, etc. When used as a lid material, they may be used alone or as a laminate film depending on the contents, the environment of use, and the form of use, and the layer structure may vary. It is preferable that the outermost layer of the packaging container (the part that adheres to the heat seal layer of the multilayer film of the present invention) contains various propylene-based resins from the viewpoint of balancing ease of opening and seal strength.

[0060] (Top-sealed container) A top-sealed container equipped with the anti-fog multilayer film or laminate of the present invention as a sealing lid is a container in which a flange protrudes from the outer periphery of the opening of a container body filled with solid or liquid food contents, and the opening is sealed by the sealing lid via this flange. As described above, the anti-fog multilayer film or laminate of the present invention has sufficient seal strength to withstand distribution and allow opening of the top-sealed container before microwave heating. However, during or immediately after heating, the seal strength decreases to a level that allows easy opening even when the container is hot, thereby reducing the risk of burns to the user and allowing food to be served safely. As for the container material for the top-sealed container, it is preferable that the outermost layer (the portion bonded to the heat-seal layer of the multilayer film of the present invention) contains various propylene-based resins, from the viewpoint of balancing ease of opening and seal strength.

[0061] The present invention will now be described in more detail with reference to examples and comparative examples. Unless otherwise specified, "parts" are by mass.

[0062] (Preparation of Antifogging Agent) The antifogging agent was prepared by mixing 20 parts by mass of the antifogging agent with any one of the resins constituting the layer to be used, and melt-kneading the mixture in an extruder to prepare a master batch.

[0063] (Example 1) A resin for the heat seal layer (C) having a density of 0.885 g / cm ３ 30 parts of propylene-butene-1 copolymer (1) having an MFR (230 ° C) of 7.0 g / 10 min and a density of 0.900 g / cm ３ 50 parts of polypropylene (1) having an MFR (230°C) of 7.0 g / 10 min and 20 parts of an anti-fog agent (1) prepared with polypropylene (1) were mixed and used. The anti-fog agent concentration in the heat seal layer (C) was 4.0 mass%. The resin for the adhesive layer (B) was a propylene copolymer having a density of 0.937 g / cm. ３ 65 parts of LLDPE (1) having an MFR of 4.0 g / 10 min, 15 parts of polypropylene (1), and a density of 0.919 g / cm ３20 parts of an anti-fog agent (2) prepared with LDPE (1) having an MFR of 7.0 g / 10 min was mixed and used. The anti-fog agent concentration in the adhesive layer (B) was 4.0% by mass. 80 parts of LLDPE (1) and 20 parts of LDPE (1) were mixed and used as the resin for the layer (A1) containing no anti-fog agent. Resins were supplied to the extruder for the heat-seal layer (C), the extruder for the adhesive layer (B), and the extruder for the layer (A), respectively, and extruded from a T-die at an extrusion temperature of 250°C by co-extrusion so that the thicknesses of the layers (A) / (B) / (C) were 20 μm / 6 μm / 4 μm, and cooled with a water-cooled metal cooling roll at 40°C. Next, a corona discharge treatment was performed, the film was wound up on a roll, and the film was aged for 24 hours in an aging chamber at 38°C to obtain a multilayer film having a total thickness of 30 µm and a layer structure of (A) / (B) / (C). Thereafter, the obtained coextruded film and a 15 µm biaxially oriented nylon film were bonded together with a polyurethane adhesive [DIC Dry LX500 / KR90S manufactured by DIC Corporation] to obtain a laminate.

[0064] (Example 2) As the resin for the layer (A2) containing the antifogging agent, LLDPE (1), LDPE (1), and antifogging agent (2) were mixed in a mass ratio of 80 / 18 / 2 and used. The concentration of the antifogging agent in the layer (A2) was 0.4 mass%. Except for these, the laminate of Example 2 was obtained in the same manner as in Example 1.

[0065] (Example 3) A resin for the adhesive layer (B) having a density of 0.931 g / cm ３ 65 parts of LLDPE (2) having an MFR of 6.0 g / 10 min, 15 parts of polypropylene (1), and 20 parts of antifogging agent (2) were mixed and used. The antifogging agent concentration in the adhesive layer (B) was 4.0 mass%. As the resin for the layer (A1) not containing an antifogging agent, 80 parts of LLDPE (2) and 20 parts of LDPE (1) were mixed and used. Except for these, the laminate of Example 3 was obtained in the same manner as in Example 1.

[0066] (Example 4) As the resin for the heat seal layer (C), propylene-butene-1 copolymer (1), 58 parts of polypropylene (1), and antifogging agent (1) were mixed in a mass ratio of 30 / 58 / 12 and used. The antifogging agent concentration in the heat seal layer (C) at this time was 2.4 mass%. As the resin for the adhesive layer (B), LLDPE (1), LDPE (1), polypropylene (1), and antifogging agent (2) were mixed in a mass ratio of 63 / 12 / 15 / 10 and used. The antifogging agent concentration in the adhesive layer (B) at this time was 2.0 mass%. As the resin for the layer (A1) not containing an antifogging agent, LLDPE (1) and LDPE (1) were mixed in a mass ratio of 80 / 20 and used. The resin for the antifogging agent-containing layer (A2) was a mixture of LLDPE (1), LDPE (1), and antifogging agent (2) in a mass ratio of 80 / 10 / 10. The antifogging agent concentration in the layer (A2) was 2.0 mass%. The resins were supplied to the extruder for the heat-sealing layer (C), the extruder for the adhesive layer (B), the extruder for the layer (A1), and the extruder for the layer (A2), and extruded through a T-die at an extrusion temperature of 250°C by coextrusion so that the thicknesses of the layers (A1), (A2), (B), and (C) were 10 μm, 12 μm, 4 μm, and 4 μm, respectively. The laminate of Example 4 was obtained in the same manner as in Example 1.

[0067] Example 5: LLDPE (1) was used as the resin for the layer (A1) containing no antifogging agent. As the resin for the layer (A2) containing an antifogging agent, LLDPE (1) and antifogging agent (2) were mixed in a mass ratio of 90 / 10 and used. The antifogging agent concentration in the layer (A2) was 2.0 mass%. A laminate of Example 5 was obtained in the same manner as in Example 4, except for the above.

[0068] (Example 6) A resin for the adhesive layer (B) having a density of 0.944 g / cm ３A mixture of 63 parts of LLDPE (3) having an MFR of 4.0 g / 10 min, 12 parts of LDPE (1), 15 parts of polypropylene (1), and 10 parts of antifogging agent (2) was used. The antifogging agent concentration in the adhesive layer (B) was 2.0% by mass. LLDPE (3) was used as the resin for the layer (A1) not containing an antifogging agent. LLDPE (3) and antifogging agent (2) were mixed at a mass ratio of 90 / 10 and used as the resin for the layer (A2) containing an antifogging agent. The antifogging agent concentration in the layer (A2) was 2.0% by mass. The laminate of Example 6 was obtained in the same manner as in Example 4, except for the above.

[0069] (Example 7) As the resin for the adhesive layer (B), LLDPE (1), LDPE (1), propylene-butene-1 copolymer (2), and antifogging agent (2) were mixed to a mass ratio of 63 / 12 / 15 / 10 and used. The concentration of the antifogging agent in the adhesive layer (B) at this time was 2.0 mass%. Except for these, the laminate of Example 7 was obtained in the same manner as in Example 4.

[0070] (Example 8) As the resin for the heat seal layer (C), propylene-butene-1 copolymer (1), 58 parts of polypropylene (1), and antifogging agent (1) were mixed so as to have a mass ratio of 10 / 78 / 12. The antifogging agent concentration in the heat seal layer (C) at this time was 2.4 mass%. Except for these, the laminate of Example 8 was obtained in the same manner as in Example 4.

[0071] (Example 9) As the resin for the heat seal layer (C), propylene-butene-1 copolymer (1), 58 parts of polypropylene (1), and antifogging agent (1) were mixed so as to have a mass ratio of 15 / 73 / 12 and used. The concentration of the antifogging agent in the heat seal layer (C) at this time was 2.4 mass%. Except for these, the laminate of Example 9 was obtained in the same manner as in Example 4.

[0072] (Comparative Example 1) As the resin for the heat seal layer (C), 88 parts of propylene (1) and 12 parts of the antifogging agent (1) were mixed and used. The concentration of the antifogging agent in the heat seal layer (C) was 2.4 mass%. As the resin for the adhesive layer (B), a propylene (1) having a density of 0.886 g / cm was used. ３A mixture of 48 parts of an ethylene-butene-1 copolymer (1) having an MFR of 4.0 g / 10 min, 42 parts of LDPE (1), and 10 parts of an antifogging agent (2) was used. The antifogging agent concentration in the adhesive layer (B) was 2.0% by mass. Except for these, the laminate of Comparative Example 1 was obtained in the same manner as in Example 4.

[0073] (Comparative Example 2) As the resin for the heat seal layer (C), propylene-butene-1 copolymer (1) and polypropylene (1) were mixed in a mass ratio of 70 / 30 and used. As the resin for the adhesive layer (B), LLDPE (1), LDPE (1), and propylene (1) were mixed in a mass ratio of 65 / 20 / 15 and used. Other than these, a laminate of Comparative Example 2 was obtained in the same manner as in Example 1.

[0074] (Comparative Example 3) A resin having a density of 0.890 g / cm3 for the heat seal layer (C) was used. ３ 88 parts of a propylene-ethylene copolymer (1) having an MFR (230°C) of 7.0 g / 10 min and 12 parts of an antifogging agent (3) prepared with the propylene-ethylene copolymer (1) were mixed and used. The antifogging agent concentration in the heat seal layer (C) was 2.4 mass%. A resin having a density of 0.933 g / cm was used as the resin for the adhesive layer (B). ３ 80 parts of LLDPE (4) having an MFR of 5.0 g / 10 min and a density of 0.905 g / cm ３ 20 parts of an antifogging agent (4) prepared with LLDPE (5) having an MFR of 4.0 g / 10 min was mixed and used. The antifogging agent concentration in the adhesive layer (B) at this time was 4.0 mass%. As the resin for the layer (A2) containing an antifogging agent, 80 parts of LLDPE (4) and 20 parts of the antifogging agent (4) were mixed and used. The antifogging agent concentration in the layer (A2) at this time was 4.0 mass%. LLDPE (4) was used as the resin for the layer (A1) not containing an antifogging agent. Except for these, a laminate of Comparative Example 3 was obtained in the same manner as in Example 4.

[0075] (Comparative Example 4) A resin having a density of 0.890 g / cm3 for the heat seal layer (C) was used. ３ A propylene-butene-1 copolymer (3) having a density of 0.935 g / cm and an MFR (230°C) of 4.0 g / 10 min was used as the resin for the layer (A1) containing no antifogging agent.３ A mixture of 80 parts of LLDPE (6) having an MFR of 4.5 g / 10 min and 20 parts of propylene-butene-1 copolymer (3) was used. The resins were supplied to an extruder for the heat-sealable layer (C) and an extruder for the layer (A1), and extruded from a T-die at an extrusion temperature of 250°C by coextrusion so that the thicknesses of the layers (A1) and (C) were 25 μm and 5 μm, respectively. A laminate of Comparative Example 4 was obtained in the same manner as in Example 1.

[0076] Unless otherwise specified, MFR is a value measured at 190°C.

[0077] (Evaluation Method) (Film Appearance Evaluation) The appearance of a sample of a film extruded from a T-die by coextrusion and aged at 38°C for 24 hours was visually confirmed. ○: No whitening due to bleed-out of the anti-fog agent or the like was observed. ×: Whitening due to bleed-out of the anti-fog agent or the like, resulting in deterioration of film transparency.

[0078] (Laminate Strength Evaluation) The behavior of the laminate strength between the biaxially oriented nylon film and the film obtained by coextrusion was evaluated using a tensile tester (manufactured by A&D Co., Ltd.) at a peeling speed of 300 mm / min, and the state of the film was evaluated according to the following criteria: ○: Sufficient laminate strength was maintained, and strong adhesion was confirmed between the biaxially oriented nylon film and the film obtained by coextrusion. ×: Easy peeling was confirmed between the biaxially oriented nylon film and the film obtained by coextrusion, due to insufficient laminate strength.

[0079] (Confirmation and evaluation of anti-fogging effect after lamination) The obtained laminate was aged at 40°C for 48 hours, then cut into a piece of 8 cm x 8 cm, and heat-sealed to a φ71 injection container (manufactured by Toko Co., Ltd.) containing 30 ml of water at 40°C (pressure 64 kgf / cup, temperature 160°C, time 1.0 second). The laminate was then stored in a low-temperature room at 3°C ​​for 3 hours and visually evaluated for anti-fogging effect using the following criteria: ○: A continuous water film was formed on the film surface, and visibility was good; △: Fine water droplets were attached to the film surface, but visibility was good; ×: Water droplets were attached, and visibility was deteriorated.

[0080] (Confirmation and evaluation of anti-fogging effect after heating in microwave oven) After aging and heat sealing under the above conditions, the obtained laminate was stored at 3°C ​​in a low temperature room for 3 hours, and then part of the lid was opened and heated in a microwave oven (IMB-F186-W manufactured by Iris Ohyama Co., Ltd.) (500W for 1 minute), and the appearance immediately after heating was confirmed. ○: A continuous water film was formed on the film surface, and visibility was good. △: Fine water droplets attached to the film surface were also visible. ×: Water droplets attached, visibility deteriorated.

[0081] (Preparation of Heat-Sealed Samples) The obtained laminate was aged under the above conditions, and then it was overlapped with a 0.3 mm thick polypropylene sheet so that the heat-sealed surface was on the polypropylene sheet side. Using a heat seal tester (Precision Heat Sealer manufactured by Tester Sangyo Co., Ltd.), the upper heat seal bar adjusted to a temperature of 180°C was set so that it was on the outermost layer side of the laminate, and heat-sealed under conditions of 0.2 MPa and 1 second.

[0082] (Evaluation of seal strength) A 15 mm wide strip sample was cut out perpendicular to the heat-sealed portion, and the maximum strength when peeled at a rate of 300 mm / min using a tensile tester (manufactured by A&D Co., Ltd.) was taken as the peel strength. In the test in a 100°C environment, the sample was kept in a thermostatic chamber adjusted to 100°C for 5 minutes, and then the peel strength was measured.

[0083] (Evaluation of Openability After Heating in a Microwave Oven) The obtained laminate was aged and heat-sealed under the above conditions, then stored in a low-temperature room at 3°C ​​for 3 hours, after which part of the lid material was opened and heated in a microwave oven (IMB-F186-W manufactured by Iris Ohyama Co., Ltd.) (500W, 1 minute). Immediately after heating, the lid was opened entirely starting from the previously opened part to check. ○: No film residue or delamination occurred, and the strength was adequate and the lid was easy to open. △: The lid had adequate strength and was strong enough to open, but film residue or delamination occurred in some places. ×: Film residue or delamination occurred, or the opening strength was weak and the lid was opened all at once.

[0084] The layer structure of the anti-fogging multi-layer film and the evaluation results are shown in Tables 1 to 3. Note that blank spaces indicate that no compound was added.

[0085]

[0086]

[0087]

[0088] As a result, it is clear that the anti-fog multilayer films of the examples have sufficient seal strength to withstand distribution and be able to be opened before heating in a microwave oven, but that during heating or immediately after heating, the seal strength decreases to a level that allows the container to be easily opened even when it is hot.

Claims

1. An anti-fog multilayer film comprising, in this order, at least a layer (A) whose main resin component is linear polyethylene, an adhesive layer (B) whose main resin components are linear polyethylene and a polypropylene-based resin and which contains an anti-fog agent, and a heat-sealable layer (C) whose main resin component is a polypropylene-based resin and which contains an anti-fog agent, and which has a seal strength of 10 to 18 N / 15 mm at room temperature and a seal strength of 4 to 8 N / 15 mm at 100°C.

2. The anti-fog multilayer film according to claim 1, wherein the density of the linear polyethylene contained in said layer (A) and said adhesive layer (B) is 0.930 or more, and the density of said layer (A) is higher than the density of said adhesive layer (B) and the density of said heat-sealable layer (C).

3. The anti-fogging multilayer film according to claim 1, wherein the polypropylene resin contained in the heat seal layer (C) is a propylene-butene-1 copolymer in an amount of 10 to 30% by mass.

4. The anti-fog multilayer film according to claim 1, wherein the layer (A) comprises two layers: a substrate layer (A1) whose main resin component is linear polyethylene and which does not contain an anti-fog agent, and a substrate layer (A2) whose main resin component is linear polyethylene and which contains an anti-fog agent.

5. A laminate comprising the anti-fogging multilayer film according to any one of claims 1 to 4.

6. A packaging material containing the anti-fog multilayer film according to any one of claims 1 to 4.

7. A covering material containing the anti-fogging multilayer film according to any one of claims 1 to 4.

8. A top-sealed container containing the anti-fogging multilayer film according to any one of claims 1 to 4.

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