JP2009101606A - Antifogging multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antifogging multilayer film, which is comparatively thin and which has favorable antifogging properties though the amount added of an antifogging agent is comparatively few, transparency and slipperiness. <P>SOLUTION: This antifogging multilayer film is equipped with a polyolefin base resin multilayer film having at least three layers or an outer surface, an intermediate layer and a core layer, and the fore conditions are satisfied; (1) The contact angle of the surface of the multilayer film is 30°-70°, (2) The surface roughness of the surface of the multilayer film is 5-20 nm, (3) The total content of the antifogging agent included in the multilayer film is 0.1-1.0 wt.% and (4) The thickness of the multilayer film is 5-20 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an anti-fogging multilayer film used for food packaging and the like, and in particular, can be suitably used for the packaging of food distributed, stored and sold at refrigerated temperatures. The present invention relates to an anti-fogging multilayer film excellent in slipperiness.

  Conventionally, as a film used for food packaging such as meat, seafood, fruits and vegetables, sugar beet, a stretch film made of a vinyl chloride resin composition has excellent performance in transparency and self-adhesiveness. Has been used most often. However, since the stretch film made of such a vinyl chloride resin composition uses a large amount of plasticizer, there is a problem that the plasticizer migrates to the packaged object and becomes contaminated. It has safety and health problems such as the generation of toxic gas when blown or incinerated.

  Therefore, in recent stretch films, polyolefin resin compositions are being used in place of vinyl chloride resin compositions. Among polyolefin resin films, in particular, a film made of an ethylene-α-olefin copolymer resin polymerized using a metallocene catalyst is excellent in transparency, impact strength, low-temperature heat sealability, flexibility, and the like. It is known.

However, packaging with stretch films is inconvenient in that the package is finished in a tight manner to increase the commercial value, so that the demand for packaging with shrink films that can provide a tight and beautiful finish is also increasing. As packaging by such shrink film, pillow shrink packaging and stretch shrink packaging are known.
Pillow shrink wrapping is generally made by covering a packaged item such as food contained in a container or tray with a shrink film and then forming it into a bag shape by fusing and sealing. This is a method of heat-shrinking tightly. Stretch shrink wrapping generally uses a shrink film to wrap the package in some tension like conventional stretch wrap, and then folds the end of the shrink film into the bottom of the package. In this method, the folded portion is primarily packaged by self-adhesion between films or heat-sealing or the like, and then subjected to heat shrinkage treatment in the same manner as pillow shrink packaging to remove local film sagging and wrinkles.

  A feature of pillow shrink wrapping is that by using a shrink film that has a high heat shrinkage in both the vertical and horizontal directions as the wrapping film, the film can be applied to the entire surface of the container, even in the shape of a sphere such as a bag. It is possible to make tight packaging with tight corners and inconspicuous corners, and since fusing seals are generally applicable, there is no need to seal the film again, so the area of film used can be less than stretch shrink packaging, etc. It is done. Therefore, pillow shrink packaging is increasingly used in place of stretch shrink packaging.

  As described above, since the shrink film used for pillow shrink packaging is required to have a fusing seal, the resin constituting the surface layer is not an ethylene-vinyl acetate copolymer having a low fusing seal but a linear low In many cases, density polyethylene or the like is used.

Here, although the film using the ethylene-vinyl acetate copolymer as the surface layer has low fusing sealability, the films folded on the bottom surface of the packaged object and overlapped are brought into contact with the hot plate and heat-sealed. It has excellent bottom sealing properties. In addition, the ethylene-vinyl acetate copolymer is excellent in kneadability with an antifogging agent kneaded with a resin at the time of extrusion molding in order to impart antifogging properties, and further, is antifogged from the film to the film surface after molding. It has the property of easily bleeding out the agent.
On the other hand, linear low-density polyethylene is inferior in kneadability with a highly polar antifogging agent compared to an ethylene-vinyl acetate copolymer. However, it is difficult to knead. In addition, linear low-density polyethylene has the ability to bleed out the antifogging agent from the film to the film surface within a short time of several days at a temperature of 30 ° C. or lower compared to the ethylene-vinyl acetate copolymer. Is low.

  Therefore, the surface layer is composed of an olefin resin such as linear low-density polyethylene. This type of film is excellent in that it can be tightly packed by reducing the use area of the film, but ethylene-vinyl acetate. There was a defect that the antifogging property was inferior compared with the film using the copolymer for the surface layer.

On the other hand, the following are known as techniques for imparting antifogging properties to a film using an olefin resin as a surface layer.
JP-A-2002-20553 (Patent Document 1) describes 1.0% of an antifogging agent selected from the group consisting of glycerin fatty acid ester and sorbitan fatty acid ester, and an antifogging agent consisting of polyoxyethylene alkyl ether. A polyolefin resin composition obtained by mixing ~ 5.0 parts by weight is disclosed.
Japanese Unexamined Patent Publication No. 2002-200672 (Patent Document 2) discloses a crosslinked packaging film made of an ethylene polymer resin obtained by adding a glycerin fatty acid ester surfactant to an ethylene polymer resin.
In JP-A-2004-210967 (Patent Document 3), 0.04 to 3.8 parts by weight of (A) diglycerin mixed fatty acid ester with respect to 100 parts by weight of ethylene-α-olefin copolymer resin, B) 0.005 to 0.7 parts by weight of an ethylene oxide 1 to 100 mole adduct of a fatty acid having 8 to 22 carbon atoms, and (C) an average degree of polymerization of polyglycerol of 3 to 10 and a partial ester compound with a fatty acid. The film for food packaging which consists of 0.003-0.7 weight part of polyglyceryl fatty acid ester and (A)-(C) total addition amount is 0.1-4 weight part is disclosed.

Japanese Patent Application Laid-Open No. 2004-216825 (Patent Document 4) discloses at least one monomer selected from a vinyl ester monomer, an aliphatic unsaturated monocarboxylic acid, and the monocarboxylic acid alkyl ester, and ethylene. Or a surface layer made of a mixed resin of at least one copolymer selected from these derivatives and an ethylene-α-olefin copolymer, glycerin fatty acid ester, diglycerin fatty acid ester, tetra Polyolefin-based resin antifogging / heat-shrinkable multilayer containing 0.1 to 5 parts by mass of a surfactant composition comprising glycerin fatty acid ester and polyethylene glycol fatty acid ester with respect to the total mass (100 parts by mass) of all layers A film is disclosed.
Furthermore, JP-A-2005-146184 (Patent Document 5) was selected from polyglycerin fatty acid ester, polyoxyethylene aliphatic alcohol ether and polyoxyethylene fatty acid ester with respect to 100 parts by weight of polyolefin resin (A). 0.1 to 20 parts by weight of surfactant (B) as at least one compound, and compatibilizer (C) 0.05 to 3 having a solubility parameter of 8 to 11 and a molecular weight of 100 to 10,000. A polyolefin resin composition containing parts by weight is disclosed.

  Japanese Patent Laid-Open No. 4-47936 (Patent Document 6) is a multilayer structure film made of an antifogging thermoplastic resin, comprising an inner layer, an intermediate layer and an outer layer, and an antifogging agent for inner and outer layers. By adding 0.07 to 0.20% by weight and adding the antifogging agent in the intermediate layer to 0.35 to 0.50% by weight, the antifogging of the intermediate layer compared to the inner and outer layers. An antifogging multilayer film is disclosed in which the additive amount of the agent is increased and an antifogging agent-containing concentration gradient is provided between the intermediate layer and the inner and outer layers.

JP 2002-20553 A Japanese Patent Laid-Open No. 2002-200672 JP 2004-210967 A JP 2004-216825 A JP 2005-146184 A Japanese Unexamined Patent Publication No. 4-47936

However, in the techniques disclosed in Patent Documents 1 to 5, in order to achieve both good antifogging properties, optical properties, and slipperiness, an antifogging agent is added to the film at a high concentration or specified. There was a disadvantage that an antifogging agent having the composition of
Moreover, in the technique disclosed in the above-mentioned Patent Document 6, there is a disadvantage that good antifogging properties cannot be obtained unless the thickness of the multilayer film is increased and the film is not stored in a constant temperature room at 40 ° C. there were.
The present invention has been made in view of such problems, and has a relatively thin thickness and a relatively small amount of an antifogging agent, but has a good antifogging property, transparency and slipperiness. It aims at providing a property multilayer film.

As a result of intensive studies to solve the above problems, the present inventors have found that the antifogging multilayer film satisfying the following (1) to (4) is relatively thin and the amount of the antifogging agent added is relatively small. However, they have found that they have good antifogging properties, transparency and slipperiness, and have completed the present invention.
That is, the present invention provides the following (I) to (VII).
(I) A polyolefin-based resin multilayer film having at least three layers of a surface layer, an intermediate layer and a core layer, and the following (1) to (5):
(1) The contact angle of the surface of the multilayer film is 30 ° to 70 °;
(2) The surface roughness of the surface of the multilayer film is 5 to 20 nm;
(3) The total content of the antifogging agent contained in the multilayer film is 0.1 to 1.0% by weight in terms of solid content;
(4) The multilayer film has a thickness of 5 to 20 μm;
An anti-fogging multilayer film that meets the requirements.

(II) The multilayer film is obtained by stretching an unstretched multilayer film that has been extruded and melt-molded. The amount of the antifogging agent added during the extrusion melt molding is determined in the surface layer and the core layer. Is 0 to 1.0% by weight, and the intermediate layer is 2.0 to 10% by weight.
(III) The antifogging multilayer film according to (II), wherein the difference in the amount of antifogging agent added between the surface layer and the intermediate layer is 1.0 to 10% by weight.

(IV) The antifogging multilayer film according to any one of (I) to (III), wherein the surface layer contains an ethylene polymer.
(V) The antifogging multilayer film according to any one of (I) to (IV), wherein at least one of the surface layer, the intermediate layer, and the core layer is crosslinked.

(VI) Shrink packaging using the anti-fogging multilayer film according to any one of (I) to (V).
(VII) Pillow shrink packaging using the anti-fogging multilayer film according to any one of (I) to (V).

  According to the present invention, it is possible to provide an antifogging multilayer film having a relatively thin thickness and having a good antifogging property, transparency and slipperiness even though the addition amount of an antifogging agent is relatively small. it can.

Hereinafter, the antifogging multilayer film of this embodiment will be described in detail.
The antifogging multilayer film of this embodiment comprises a polyolefin resin multilayer film having at least three layers of a surface layer, an intermediate layer, and a core layer, and satisfies the above (1) to (4). Such an antifogging multilayer film can be obtained by adjusting the addition amount of the antifogging agent at the time of molding each layer. The preferred embodiment is such that the amount of antifogging agent added during extrusion melt molding of each layer is 0 to 1.0 wt% in the surface layer and the core layer, and 2.0 to 10 wt% in the intermediate layer. is there.
In this way, adjusting the amount of antifogging agent in each layer, in other words, by giving the multilayer film a specific antifogging agent-containing concentration gradient, the amount of antifogging agent bleed out to the surface of the multilayer film, In addition, the distribution state of the antifogging agent on the surface of the multilayer film is modified, and combined with a specific surface roughness and a specific contact angle of the multilayer film, the thickness of the film is thinner than before, and the addition of the antifogging agent Although the amount is small, it is considered that the antifogging property, slipperiness and transparency are significantly improved.

  The feature of such an antifogging multilayer film is that the total content (absolute amount) of the antifogging agent contained in the multilayer film is 1.0 wt% or less in terms of solid content, which is a small amount compared to the conventional case. Nevertheless, it should exhibit good antifogging properties, slipperiness and transparency. As a result of the low total content of the antifogging agent contained in the multilayer film, it is considered that the amount of the antifogging agent present on the surface of the multilayer film is also reduced. However, the antifogging multilayer film of this embodiment has a contact angle of 30. A high value of ° to 70 ° is shown. Therefore, in the anti-fogging multilayer film of this embodiment, it is estimated that favorable anti-fogging property etc. are exhibited because anti-fogging agent exists comparatively uniformly on the film surface.

  The polyolefin resin constituting the multilayer film is a polymer mainly composed of an α-olefin having 2 to 18 carbon atoms, for example, a homopolymer of α-olefin having 2 to 18 carbon atoms, carbon Copolymer of at least 2 kinds of α-olefin having 2 to 18 atoms, at least one kind of α-olefin having 2 to 18 carbon atoms, vinyl ester, unsaturated carboxylic acid ester, unsaturated carboxylic acid and And a copolymer with at least one comonomer selected from ionomers.

  Among the above polyolefin resins, an ethylene copolymer is preferable. Examples of the ethylene copolymer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene and ultra-low-density polyethylene using a Ziegler-based multisite catalyst, and vinyl copolymerizable with ethylene. Examples thereof include a copolymer with a compound and an ethylene polymer using a single site catalyst such as a metallocene catalyst. Among these ethylene copolymers, linear low-density polyethylene and ultra-low-density polyethylene, which are polymers of ethylene and α-olefin using a Ziegler catalyst, and ethylene and α using a single-site catalyst. -A copolymer with an olefin is more preferable, and a copolymer of ethylene and an α-olefin using a single site catalyst is more preferable.

  As the α-olefin that is a comonomer component of the ethylene-α-olefin copolymer, an α-olefin having 3 to 18 carbon atoms is preferable. Specific examples of the α-olefin having 3 to 18 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and the like. Further, hydrocarbons having a polyene structure such as dicyclopentadiene, 1,4-hexadiene, norbornene monomers (for example, ethylidene norbornene) and the like can be suitably used. Although the ethylene content in a copolymer is not specifically limited, Preferably it is 40-95 mass%, More preferably, it is 50-90 mass%, More preferably, it is 60-85 mass%.

  Specific examples of the antifogging agent include glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkyl ether, polyalkylene glycol and the like. Such anti-fogging agents can be suitably used even if a surfactant other than fatty acid esters, antioxidants, antistatic agents, petroleum resins, liquid additives such as mineral oil, and the like are added.

  Examples of the glycerin fatty acid ester include an ester composed of a long-chain fatty acid having 8 to 24 carbon atoms and monoglycerin, an ester composed of a long-chain fatty acid having 8 to 24 carbon atoms and diglycerin, and an 8 to 8 carbon atom. Examples include esters of 24 long chain fatty acids and tetraglycerin. More specifically, for example, monoglycerol monoacetomonolaurate, monoglycerol diacetomonolaurate, monoglycerol monoacetomonomyristate, monoglycerol diacetomonomyristate, monoglycerol monoacetomonopalmitate, monoglycerol diacetmono Palmitate, monoglycerol monoacetomonostearate, monoglycerol diacetomonostearate, monoglycerol monoacetomonooleate, monoglycerol diacetomonooleate, monoglycerol monoacetomonolinoleate, monoglycerol diacetomonolinoleate, diglycerol monooleate , Diglycerin dioleate, diglycerin monolaurate, diglycerin monolaurate, diglycerin dilaurate, diglycerin monostearate, tet Glycerol monooleate, tetraglycerin dilaurate, tetraglycerin monolaurate, tetraglycerin monostearate, hexaglycerin monooleate, hexaglycerin monolaurate, hexaglycerin monostearate, decaglycerin monooleate, decaglycerin monolaurate, tetraglycerin Examples include monocaprylate.

  As the polyglycerol fatty acid ester, for example, a polyglycerol ester of a saturated or unsaturated fatty acid having 12 to 18 carbon atoms is preferable. Specific examples include polyglycerol laurate, polyglycerol myristate, polyglycerol palmitate, polyglycerol stearate, polyglycerol oleate, polyglycerol linoleate and the like.

  These antifogging agents can be used alone or in combination of two or more. When two or more kinds of antifogging agents are used in combination, an effect excellent in the balance between antifogging properties and slipperiness can be exhibited. As a combination of two or more kinds of antifogging agents, for example, an ester composed of a long chain fatty acid having 8 to 24 carbon atoms and monoglycerin and an ester composed of a long chain fatty acid having 8 to 24 carbon atoms and diglycerin. A combination or a combination of an ester composed of a long chain fatty acid having 8 to 24 carbon atoms and monoglycerol and a polyglycerol ester of a saturated or unsaturated fatty acid having 12 to 18 carbon atoms is desirable. More specifically, a combination of glycerin monooleate and diglycerin oleate and a combination of glycerin monooleate and diglycerin laurate are exemplified.

  Said anti-fogging agent is added so that the total content contained in a multilayer film may be 0.1 to 1.0 weight%. The total content here means the total amount in terms of solid content of the antifogging agent contained in the multilayer film. When the total content of the antifogging agent contained in the multilayer film is less than 0.1 wt%, the amount of the antifogging agent that bleeds out and covers the surface of the multilayer film is insufficient, and the antifogging property and slipperiness tend to deteriorate. It is in. On the other hand, when the total content of the antifogging agent contained in the multilayer film exceeds 1.0 wt%, the transparency tends to decrease.

  The layer structure of the anti-fogging multilayer film of the present embodiment is a surface layer, an intermediate layer, a core layer, from the viewpoint of suppression of delamination, a point that does not need to be used separately between the back and the front, and stretch stability. The five layers are preferably laminated in the order of the intermediate layer and the surface layer. However, the intermediate layer disposed between the surface layer and the core layer may be two layers each, for a total of seven layers.

Next, a production example of the antifogging multilayer film of this embodiment will be described.
First, the polyolefin resin constituting each layer is melted by each extruder, coextruded with a multilayer die, and then rapidly solidified to obtain a multi-layer film original fabric of several tens to several hundreds μm. As the extrusion method, a T-die method, a circular method or the like can be used, and the latter is preferable. By adjusting the addition amount of the antifogging agent added to the polyolefin-based resin at the time of molding each layer, it is easy to give the obtained multilayer film a specific antifogging agent-containing concentration gradient.

  Next, the original film obtained as described above is heated and stretched under a temperature condition suitable for imparting orientation, the surface roughness is 5 to 20 nm, and the thickness is 5 to 20 μm. A multilayer film is produced. Examples of the stretching method include a roll stretching method, a tenter method, an inflation method (including a double bubble method), and a method of forming a film by simultaneous biaxial stretching is more preferable from the viewpoint of stretchability and other rationality. The stretching treatment is preferably performed in an area stretching ratio of 3 to 60 times in at least one direction, and more preferably 4 to 60 times. The draw ratio is appropriately selected according to the heat shrinkage required by the intended application. Moreover, you may perform post-processing as needed, for example, the heat set for dimensional stability, lamination with another film, etc.

  Here, the addition amount of the antifogging agent added at the time of forming each layer is preferably 0 to 1.0 wt% in the surface layer and the core layer, and preferably 2.0 to 10 wt% in the intermediate layer. The surface layer and the core layer are 0 to 0.5 wt%, and the intermediate layer is 3.0 to 5 wt%. As an unfavorable case, the addition amount of the antifogging agent in the surface layer and the intermediate layer exceeds 1.0 wt%, the contact angle of the film surface is 30 ° or less, and the antifogging property is high although the wettability is high. The addition amount of the antifogging agent in the low case and the surface layer and the intermediate layer is less than 1.0 wt%, and the contact angle of the film surface exceeds 70 °, but the wettability is low and the antifogging property is also low. Cases are considered. In the former, the cause of the decrease in antifogging property despite high wettability is considered to be that the antifogging agent is not uniformly attached to the multilayer film surface. In the latter case, the cause of the decrease in antifogging property may be that the amount of the antifogging agent covering the surface of the multilayer film is insufficient. On the other hand, when the difference in the addition amount of the antifogging agent between the surface layer and the intermediate layer exceeds 10 wt%, the antifogging property and the transparency tend to decrease. By setting the addition amount of the antifogging agent within such a range, an antifogging multilayer film excellent in antifogging property, slipperiness and transparency tends to be easily obtained.

  Furthermore, the difference in the amount of antifogging agent added between the surface layer and the intermediate layer is preferably 1.0 to 10 wt%, more preferably 2.0 to 5 wt%. Here, when the difference in the addition amount of the antifogging agent between the surface layer and the intermediate layer is less than 1.0 wt%, the antifogging property tends to decrease.

  Furthermore, at least one layer of the antifogging multilayer film of the present embodiment may be crosslinked. The cross-linking treatment is used as necessary for the purpose of further improving heat resistance, heat sealability, particularly sealability in high-speed packaging. Such cross-linking treatment improves the heat resistance and enables film formation by high-magnification stretching at a high temperature, and can impart high heat shrinkability to the resulting antifogging multilayer film. The cross-linked multilayer film may have a uniform degree of cross-linking in the thickness direction or a timely distribution. Moreover, even if only a specific layer is cross-linked, one surface layer is mainly cross-linked and the degree of cross-linking gradually changes in the thickness direction, or both surface layers are mainly cross-linked Good.

  The crosslinking treatment is a method of irradiating an electron beam (for example, having an energy of 50 to 1000 kV), ultraviolet rays, X-rays, α-rays or γ-rays before and after stretching the film raw material, peroxide, etc. (In some cases, a cross-linking aid may be used in the specific layer, and a cross-linking retarder may be used in the specific layer). Processing may be performed. Crosslinking treatment is performed by irradiating one side or both sides of a multilayer film with an electron beam whose penetration depth is controlled to a predetermined value, such as cross-linking distribution in the thickness direction, and the same inclination (for example, only one surface layer is cross-linked). It may be implemented to occur.

In this embodiment, it is preferable to use an inflation method (including a double bubble method) from the viewpoint that a 5 to 20 μm multilayer film can be easily formed, and a 10 μm or less multilayer film is stabilized. From an obtained viewpoint, an unstretched multilayer film having a thickness of 100 to 600 μm crosslinked by an electron beam or the like is stretched at a temperature that is 5 to 50 ° C. higher than the melting point of the resin at an area stretch ratio of 10 to 60 times. Is preferred.
In order to control the surface roughness to 20 nm or less, when stretching an unstretched multilayer film that has not been subjected to crosslinking treatment, it is preferable to stretch the film at a melting point or less of the resin of the surface layer. When stretched at a temperature equal to or higher than the melting point of the resin of the surface layer, the surface roughness may exceed 20 nm. In such a case, the uniformity of the state of adhesion of the antifogging agent to the multilayer film surface is impaired and the antifogging property is reduced. Since it may cause a decrease, it is not preferable. In addition, if the film is stretched above the melting point of the resin of the surface layer, the film surface may be rough, and the film may be whitened due to irregular reflection of light on the surface. In such a case, the transparency of the multilayer film may be impaired. It is not preferable.
On the other hand, the stretching temperature when stretching a cross-linked unstretched multilayer film is preferably stretched at a temperature 5 to 50 ° C. higher than the melting point of the resin of the surface layer. When stretching at a temperature higher than 50 ° C. higher than the melting point of the resin of the surface layer, the surface roughness may exceed 20 nm. In such a case, the uniformity of the state of adhesion of the antifogging agent to the multilayer film surface is impaired. This is not preferable because it may cause a decrease in antifogging property. It is preferable from the viewpoint of film formation stability that the film is stretched at a temperature higher by 5 ° C. or more than the melting point of the resin of the surface layer.
In order to control the surface roughness to 20 nm or less, the amount of the antifogging agent in the surface layer of the multilayer film is included in one surface layer when the thickness ratio of one surface layer of the film exceeds 7%. The concentration of the antifogging agent is preferably 3.5% by weight or less. When the thickness ratio of one surface layer of the film is 7% or less, the average antifogging agent concentration between the surface layer and the intermediate layer adjacent to the surface layer is 3.5% by weight or less. Is preferred. When the average antifogging agent concentration of the film surface layer or the film surface layer and the intermediate layer exceeds 3.5% by weight, the surface roughness may exceed 20 nm. This is not preferable because the uniformity of the state of adhesion to the surface of the multilayer film can be impaired and the anti-fogging property can be lowered.
In addition, when there are many antifogging agents which exist on the surface of the unstretched film at the time of extending | stretching, it exists in the tendency for the fall of the transparency of the stretched film obtained and the increase in surface roughness to generate | occur | produce simultaneously. Therefore, also from such a viewpoint, it is preferable that the total content of the antifogging agent contained in the multilayer film is 0.1 to 1.0% by weight, and as described above, it is added at the time of forming each layer. The addition amount of the antifogging agent is preferably 0 to 1.0 wt% in the surface layer and the core layer and 2.0 to 10 wt% in the intermediate layer.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not specifically limited to these. In the following, “part” and “%” mean “weight” and “% by weight”, respectively.

The measuring method and the evaluation method used in each example and each comparative example are as follows.
(1) Contact angle The contact angle of water is evaluated with a commercially available contact angle meter (CA-W type manufactured by Kyowa Interface Chemical Co., Ltd.). Since the contact angle may be affected by the smoothness of the sample, it is necessary to make the film as flat as possible. Therefore, water vapor is attached to a smooth slide glass, and an antifogging multilayer film is applied to the slide glass. A sample obtained by removing bubbles and creating a flat surface by gradually pasting is used as a measurement sample. When the contact angle is measured, the amount of water dropped at one time is about 3 μl. After the dropping, the droplet is photographed after being held for 1 second, and the angle formed between the antifogging film surface and the water droplet is read. The contact angle is read using the θ / 2 method, 10 contact angle measurements are performed per sample, and the average value is taken as the contact angle of the sample.

(2) Surface roughness Surface roughness is evaluated using a commercially available scanning probe microscope (Nanoscope IV and Nanoscope IIIa manufactured by Veeco). An Si single crystal probe (NCH-10) is used as the probe, the measurement mode is the taping mode, the measurement area is 30 μm square, and the image is captured. For the image after measurement, using the attached analysis software, the flattening process (0th order) is performed once and the planefit process (XY) is performed once as an image process for removing waviness, and then the surface roughness is measured. calculate.

(3) Quantification of antifogging agent Quantitative analysis of the glycerin ester compound added as an antifogging agent is performed by a calibration curve method according to the following procedure. 1 g of powder obtained by freeze-pulverizing an anti-fogging multilayer film sample is precisely weighed and subjected to Soxhlet extraction with 100 ml of chloroform for 8 hours. This extract was dried with an evaporator under reduced pressure at 40 ° C. aspirator, the obtained preparation was dissolved in 2 ml of pyridine, 1 ml of a TMS inducer ({N, O-Bis (trimethylsilyl) acetamide}) was added, and 90 ml was added. Heat at 30 ° C. for 30 minutes to obtain a sample solution. As a standard sample solution for quantification, a solution obtained by dissolving 30 mg of glycerin monooleate and diglycerin monooleate in 2 ml of pyridine (vs. sample concentration: equivalent to 3.0 wt%) and derivatizing TMS in the same manner as above. Is used.
The GC-MS measurement is performed by an electron impact ionization method using a Voyager manufactured by Thermo Electron. DB-1 (inner diameter: 0.25 mm, length: 30 m, film thickness: 0.25 μm) was used as a separation column. The temperature is raised from 60 ° C. at a rate of 10 ° C. per minute and held for 10 minutes after reaching 320 ° C. At that time, the inlet temperature is 320 ° C., the injection method is split (split ratio: 1/15), and the column flow rate is 1.0 ml / min.
Quantitative calculation is calculated by a one-check quantity method by comparing the peak intensity of each sample solution in the ion chromatogram obtained by GC-MS with the peak intensity of the standard sample solution for quantification. As peaks used in this case, two peaks (holding time 19.3 minutes and 19.5 minutes) detected from the standard solution for quantification were obtained for monoglycerin monooleate, and for diglycerin monooleate. Using the four peaks (11.4 minutes, 11.5 minutes, 22.3 minutes, and 22.5 minutes) detected from the standard sample solution for quantification, the total value of each area intensity is the peak of the component. Strength.

(4) Gel fraction A sample was extracted in boiling p-xylene for 12 hours, and the ratio of the insoluble portion calculated based on the following formula was used as the gel fraction, which was used as the degree of crosslinking of the antifogging multilayer film. Used as a scale.
Gel fraction (% by weight) = (sample weight after extraction / sample weight before extraction) × 100

(5) Sliding property The sliding property of the surface of the anti-fogging multilayer film was measured according to ASTM D-1894. In this measurement, evaluation is performed using a coefficient of dynamic friction measured using a 500 g satin metal as a rider used in the measurement.
[Evaluation criteria]
○: 0.15 or more and 0.30 or less: Practical level in pillow shrink packaging by a packaging machine Δ: Less than 0.15 and more than 0.30 and 0.35 or less: considerably difficult to use in pillow shrink packaging by a packaging machine Level ×: Exceeding 0.35: Film tear may occur frequently in pillow shrink packaging by a packaging machine, and is not at a practical level.

(6) HAZE
The HAZE of the antifogging multilayer film before and after heat shrinkage was measured according to ASTM D-1003. Here, when measuring the HAZE of the film after heat shrinkage, the antifogging multilayer film subjected to electron beam crosslinking was subjected to heat shrinkage of 140 ° C. for 3 seconds to heat shrink the film area to 30%. The antifogging multilayer film not subjected to electron beam cross-linking is subjected to 120 ° C. warm air for 3 seconds and the film area is thermally shrunk to 20%.
[Evaluation criteria]
◎: 2.5% or less: The level of the product to be packaged is not beautiful, and the finish is beautiful. ○: Over 2.5%, 3% or less: The level is slightly cloudy but beautifully finished. △: 3% Exceeding 5% or less: Level that is quite difficult to use because it feels cloudy ×: Exceeding 5%: Not practical because it feels whitish

(7) Anti-fogging property About the anti-fogging multilayer film which carried out electron beam bridge | crosslinking, what was heat-shrinked to the film area to 30% at the temperature of 140 degreeC was used as the sample, and anti-fog prevention which has not implemented electron beam bridge | crosslinking The anti-fogging property is evaluated using a film having a film area that has been thermally shrunk to 20% at a temperature of 120 ° C. as a sample. Put water adjusted to 20 ° C into a 500 ml beaker, seal the beaker mouth with a film, store the beaker in a refrigerated showcase adjusted to 2 ° C, and check the state of water droplets adhering to the film surface after 120 minutes. And antifogging properties were evaluated.
[Evaluation criteria]
○: No cloudiness
Δ: Partly cloudy
×: Fully cloudy.

(Examples 1-4)
Using the resins and additives shown in Table 1, three extruders were used, and a five-layer tube consisting of both surface layers, both intermediate layers, and a core layer was melt-extruded from three types and five layers of annular dies, The tube was rapidly cooled using a water-cooled ring to obtain an unstretched tube (film raw fabric) having a thickness of about 500 μm. The additive was added by a master batch method, and kneaded by a twin screw extruder to form a master batch. A single screw extruder was used for forming the unstretched tube, and a dalmage screw was used as the screw. The temperature setting of the extruder was 200 ° C., 230 ° C., 250 ° C., 260 ° C., 260 ° C., 260 ° C. from the resin supply hopper side in the six temperature control blocks in the longitudinal direction. Table 1 shows the layer ratios of the surface layers, the intermediate layers, and the core layer of the unstretched tube.
Next, the obtained unstretched tube was subjected to crosslinking treatment by irradiating with an electron beam accelerated by an acceleration voltage of 500 kV for 4 mega rads. By continuously heating the cross-linked unstretched tube to 140 ° C. by radiant heating with an infrastructure heater, it is stretched seven times in the flow direction by the speed ratio between the two sets of nip rolls, and air is injected into the tube. After extending 7 times in the direction perpendicular to the machine flow direction, the air ring was cooled by applying cold air to the maximum diameter portion of the bubble. Then, the obtained stretched film was folded to obtain an antifogging multilayer film (packaging film) having a thickness of about 10 μm.
After storing each anti-fogging multilayer film in a room adjusted to 25 ° C. for 3 days, based on the measurement method and evaluation method described above, contact angle, surface roughness, quantification of anti-fogging agent, gel fraction, Slip properties, HAZE, and antifogging properties were evaluated. The results are shown in Table 3.

(Examples 5-7)
Using the resins and additives shown in Table 1, three extruders were used, and a five-layer tube consisting of both surface layers, both intermediate layers, and a core layer was melt-extruded from three types and five layers of annular dies, The tube was rapidly cooled using a water-cooled ring to obtain an unstretched tube (film raw fabric) having a thickness of about 400 μm. The additive was added by a master batch method, and kneaded by a twin screw extruder to form a master batch. A single screw extruder was used for forming the unstretched tube, and a dalmage screw was used as the screw. The temperature setting of the extruder was 200 ° C., 230 ° C., 250 ° C., 260 ° C., 260 ° C., 260 ° C. from the resin supply hopper side in the six temperature control blocks in the longitudinal direction. Table 1 shows the layer ratios of the surface layers, the intermediate layers, and the core layer of the unstretched tube.
Next, the obtained unstretched tube is radiantly heated by an infrastructure heater, and while the unstretched tube is heated to 110 ° C., it is stretched 6 times in the flow direction by the speed ratio between the two sets of nip rolls, After injecting air, the film was stretched 5 times in the direction perpendicular to the flow direction of the machine, and then cooled by applying cold air to the maximum diameter portion of the bubble by the air ring. Thereafter, the obtained stretched film was folded to obtain an original fabric of an antifogging multilayer film (packaging film) having a thickness of about 13 μm.
After storing each anti-fogging multilayer film in a room adjusted to 25 ° C. for 3 days, based on the measurement method and evaluation method described above, contact angle, surface roughness, quantification of anti-fogging agent, gel fraction, Slip properties, HAZE, and antifogging properties were evaluated. The results are shown in Table 3.

(Comparative Examples 1-4)
A laminated film was produced in the same manner as in Example 1 except that the resin and additive composition were changed to those shown in Table 2. The results are shown in Table 4.

(Comparative Examples 5-7)
A laminated film was obtained in the same manner as in Example 5 except that the resin and additive composition were changed to those shown in Table 2. The results are shown in Table 4.

なお、上記の表１及び２にて表記したエチレン−α−オレフィン系共重合体における、コモノマー成分であるα−オレフィンは、以下の通りである。
エチレン−α−オレフィン系共重合体（ρ＝０．９１４ ＭＩ＝１．０ Ｃ６系）の場合；１−ヘキセン
エチレン−α−オレフィン系共重合体（ρ＝０．９２６ ＭＩ＝２．０ Ｃ８系）の場合；１−オクテン
エチレン−α−オレフィン系共重合体（ρ＝０．８７０、ＭＩ＝１．０）の場合；１−オクテン

In addition, the alpha-olefin which is a comonomer component in the ethylene-alpha-olefin type copolymer represented by said Table 1 and 2 is as follows.
In the case of ethylene-α-olefin copolymer (ρ = 0.914 MI = 1.0 C6 system); 1-hexene ethylene-α-olefin copolymer (ρ = 0.926 MI = 2.0 C8) 1) -octene ethylene-α-olefin copolymer (ρ = 0.870, MI = 1.0); 1-octene

  The anti-fogging multilayer film of the present invention has a relatively thin thickness and a relatively small amount of anti-fogging agent, but has good anti-fogging properties, transparency and slipperiness. It can be used widely and effectively in industrial films, industrial protective films, agricultural films, and adhesive tapes.

Claims (7)

A polyolefin-based resin multilayer film having at least three layers of a surface layer, an intermediate layer, and a core layer, the following (1) to (4);
(1) The contact angle of the surface of the multilayer film is 30 ° to 70 °;
(2) The surface roughness of the surface of the multilayer film is 5 to 20 nm;
(3) The total content of the antifogging agent contained in the multilayer film is 0.1 to 1.0% by weight in terms of solid content;
(4) The multilayer film has a thickness of 5 to 20 μm;
An anti-fogging multilayer film that meets the requirements. The multilayer film is obtained by stretching an unstretched multilayer film that has been extrusion-melt molded,
The amount of the antifogging agent added during the extrusion melt molding is 0 to 1.0% by weight in the surface layer and the core layer, and 2.0 to 10% by weight in the intermediate layer.
The anti-fogging multilayer film according to claim 1. The difference in the amount of antifogging agent added between the surface layer and the intermediate layer is 1.0 to 10% by weight,
The anti-fogging multilayer film according to claim 2. The surface layer contains an ethylene-based polymer;
The anti-fogging multilayer film according to any one of claims 1 to 3. At least one of the surface layer, the intermediate layer, and the core layer is crosslinked.
The anti-fogging multilayer film according to any one of claims 1 to 4.   Shrink packaging using the anti-fogging multilayer film according to any one of claims 1 to 5.   Pillow shrink packaging using the anti-fogging multilayer film according to any one of claims 1 to 5.