JP2019001073A - Shrink film - Google Patents

Abstract

To provide a shrink film having excellent anti-fogging properties and transparency for long time.SOLUTION: A shrink film has a surface layer containing an ethylene-α-olefin copolymer (i), where, after being heated at 120°C and 130°C, when the surface is coated with pure water, its haze value is 0.5-3.0%; and after being heated at 130°C, at least one surface has surface roughness of Ra of 4.0-8.0.SELECTED DRAWING: None

Description

  The present invention relates to a shrink film that can be used for, for example, a food packaging film. For example, in refrigerated storage after packaging moisture-containing food, water condensed on the inner surface of the film becomes a water film, and it is a food packaging film that exhibits antifogging properties that do not impair the visibility of the contents The present invention relates to a shrink film that can be used.

  Films for food packaging improve the wettability of plastic surfaces with low affinity to water by applying or adding surfactants such as glycerin fatty acid esters, etc., depending on their purpose, and anti-fogging May express sex.

  By the way, an ethylene-vinyl acetate copolymer excellent in low-temperature heat sealability has been widely used for the surface layer of the food packaging film on the side in contact with food. However, since problems such as vibration during transportation and peeling of the seal part due to impact (seal puncture) are likely to occur, an ethylene-α-olefin copolymer having excellent heat seal strength and hot tack strength may be used.

  The ethylene-α olefin copolymer has low polarity and poor affinity with anti-fogging agents such as glycerin fatty acid ester, so the anti-fogging agent bleeds out to the surface compared to the ethylene-vinyl acetate copolymer. In addition, the antifogging agent may not be retained on the film surface and it may be difficult to exhibit and maintain the antifogging property.

  Patent Document 1 discloses a heat-shrinkable laminated film that is excellent in antifogging property, in which a glycerin fatty acid ester surfactant is added to an ethylene-α-olefin copolymer resin layer of a surface layer. Is disclosed.

JP 2007-152570 A

  In general, resin films such as polyethylene have poor affinity with water, and when foods containing moisture such as meat and fresh fish are packaged and stored refrigerated, the inner surface of the film is condensed and water droplets are generated. The visibility of the contents may be reduced.

As in Patent Document 1, when an ethylene-α-olefin copolymer resin is used for the surface layer, it is possible to obtain a film with less surface roughness and excellent transparency.
However, on the other hand, the retention effect of the surface layer of the added antifogging agent is low, and the antifogging agent is easily washed away by water adhering to the film surface. There are cases where adhesion of water drops increases.

  Accordingly, there is a demand for a film that can exhibit antifogging properties for a long time by allowing the antifogging agent to remain on the film surface for a long time. Especially for products with a long shelf life set by gas replacement packaging using a barrier film, the number of display days at the store may be extended by about 2 to 5 days compared to normal packaging, so it will be prevented for a long time. It is more strongly required to maintain cloudiness.

  An object of this invention is to provide the shrink film excellent in anti-fogging property and transparency over a long period of time.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors are a shrink film having a surface layer containing an ethylene-α-olefin copolymer, and utilizing a heat shrinking process during shrink packaging, The shrink film which can adjust the surface layer to an appropriate roughness, and the haze value after film surface coating with pure water after heat treatment and the surface roughness of the film after heat treatment can be in a specific range, It has been found that the retention effect of the antifogging agent can be improved, and it is possible to achieve both the antifogging performance and the transparency of the film after heat treatment, that is, after shrink wrapping.

[1]
It has a surface layer containing an ethylene-α-olefin copolymer, has a haze value of 0.5 to 3.0% during surface coating with pure water after heat treatment at 120 ° C. and 130 ° C., and at 130 ° C. A shrink film, wherein the surface roughness Ra of at least one surface after the heat treatment is 4.0 to 8.0.

[2]
The surface layer contains ethylene-α-olefin copolymer (i) 80 to 98% by mass, olefin polymer (ii) 1 to 15% by mass, and antifogging agent (iii) 1 to 10% by mass, [1] Shrink film.

[3]
The crystallization peak temperature (Tc) measured by the differential scanning calorimeter of the olefin polymer (ii) is measured by the differential scanning calorimeter of the ethylene-α-olefin copolymer (i). The shrink film of [2], which is 5 ° C. or more lower than the temperature (Tc).

[4]
The olefin polymer (ii) is an ethylene-vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, an ethylene-unsaturated aliphatic carboxylic acid ester copolymer, a modified polyethylene, a modified polypropylene, and The shrink film of [2] or [3], which is at least one selected from the group consisting of ionomer resins.

[5]
Having a surface layer comprising an ethylene-α-olefin copolymer;
The haze value at the time of surface coating with pure water is 0.5 to 3.0%,
At least one surface roughness Ra is 4.0 to 8.0,
A film characterized by that.

ADVANTAGE OF THE INVENTION According to this invention, the shrink film excellent in anti-fogging property and transparency over a long term can be provided.
Moreover, since the film surface is appropriately roughened after heat shrink packaging, the antifogging agent can be retained on the film surface, so that a uniform water film can be formed over a long period of time, and the transparency is excellent. It is possible to continuously develop the antifogging property.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

The shrink film of the present invention has a surface layer containing an ethylene-α-olefin copolymer, and has a haze value of 0.5 to 3.0 at the time of surface coating with pure water after heat treatment at 120 ° C. and 130 ° C. The surface roughness Ra of at least one surface after heat treatment at 130 ° C. is 4.0 to 8.0.
In the present specification, the surface layer containing the ethylene-α-olefin copolymer may be referred to as “surface layer (A)”. The surface layer is a layer including at least one surface of the shrink film, and the shrink film of the present embodiment may be formed of only the surface layer (A) or two surface layers (A). May be included, and one surface layer (A) and another surface layer may be included.

[Shrink film]
(Haze value)
The shrink film in the present embodiment can be heated in a shrink tunnel set at about 120 to 130 ° C. after packaging to obtain a tight package.
The shrink film of this embodiment has a haze value at the time of surface coating with pure water after heat treatment at 120 ° C. and a haze value at the time of surface coating with pure water after heat treatment at 130 ° C. of 0.5 to 3 respectively. 0.0%. The haze value is more preferably 0.7 to 2.5%, and still more preferably 0.8 to 2.3%. When the haze value exceeds 3.0%, the visibility is deteriorated. The haze value at the time of surface coating with pure water after heat treatment at 120 ° C. and the haze value at the time of surface coating with pure water after heat treatment at 130 ° C. may be the same or different, These may be within the same numerical range in the numerical ranges, or may be within different numerical ranges.
In the shrink film of the present embodiment, the haze value obtained by coating at least one surface with pure water is in the above range, and the haze value when pure water is coated on one surface may be in the above range, or both. The haze value at the time of covering the surface with pure water may be in the above range. Above all, the haze value obtained by coating the surface layer (A) with pure water is preferably in the above range, and the surface layer (A in which the surface roughness Ra is 4.0 to 8.0 (preferably in the following range). It is more preferable that the haze value obtained by coating a) with pure water is in the above range. When the shrink film of the present embodiment is used as a packaging film for contents containing moisture such as food, the haze value on the contents side surface (the surface on which water droplets adhere) is preferably in the above range. .
In addition, the haze value at the time of surface coating | coated with the pure water after heat-processing at 120 degreeC and 130 degreeC can be measured by the method as described in the below-mentioned Example. The said haze value can be suitably adjusted by changing the kind and ratio of the olefin type copolymer contained in a surface layer, for example.

The shrink film of the present embodiment is heat-treated to form irregularities on the film surface such as the food contact side, but the antifogging property is easily maintained over a long period of time by uniformly holding the antifogging agent in the concave portions. Become.
In general, when unevenness occurs on the film surface, the light transmitted through the film is scattered, which reduces visibility, but the moisture contained in food and other contents is condensed after packaging, and the unevenness on the film surface is made uniform by the condensed water. If it can coat | cover, an unevenness | corrugation will be covered with water and visibility will improve.

(Surface roughness (Ra))
After heat-treating the shrink film of this embodiment at 130 ° C., the surface roughness Ra (Ra observed with an atomic force microscope) of at least one surface is 4.0 to 8.0. If it is less than 4.0, the surface unevenness is not sufficient, and the retention of the antifogging agent on the surface may be difficult to maintain. Preferably it is 4.3 or more, More preferably, it is 4.5 or more. When it exceeds 8.0, even if the surface is covered with a water film, the visibility tends to be impaired. More preferably, it is 7.5 or less, More preferably, it is 7.0 or less.
In the shrink film of the present embodiment, the Ra on only one surface may be in the above range, or the Ra on both surfaces may be in the above range. Especially, it is preferable that said Ra of a surface layer (A) is the said range. When the shrink film of this embodiment is used as a packaging film or the like for contents containing moisture such as food, it is preferable that the Ra on the surface on the contents side is in the above range.
In the shrink film of this embodiment, the Ra on one surface is in the above range, and the Ra on the other surface is not particularly limited.
In addition, said Ra can be measured by the method as described in the below-mentioned Example.

The shrinkage rate at 120 ° C. or 130 ° C. of the shrink film of the present embodiment is preferably 20 to 80%, more preferably 30 to 70%, still more preferably 35 to 65%. The heat shrinkage rate is an average value of the shrinkage rate in the flow direction and the shrinkage rate in the width direction of the film.
The shrinkage rate was measured by measuring the length in the flow direction and width direction of the film before heating (before shrinkage) and after heating for 30 minutes in the hot air dryer at each temperature (after shrinkage), and using the measured lengths. The shrinkage rate in each direction can be calculated by the following formula, and the average of the shrinkage rate in the flow direction and the shrinkage rate in the width direction can be obtained.
Shrinkage rate (%) = {(length before shrinkage−length after shrinkage) / length before shrinkage} × 100
The shrink film of this embodiment can be heat-shrinked by heat-processing for 2 to 5 seconds at the temperature of 110-140 degreeC, for example.

(Surface layer (A))
The shrink film of this embodiment has a surface layer (A) containing an ethylene-α-olefin copolymer (i). The surface layer (A) may be provided on one side surface or may be provided on both side surfaces. The surface layer (A) is preferably used on the surface in contact with the contents such as food.

The ethylene-α-olefin copolymer (i) refers to a copolymer of ethylene and at least one monomer selected from α-olefins having 3 to 18 carbon atoms.
Examples of the α-olefin having 3 to 18 carbon atoms include propylene, butene-1, pentene-1, 4-methyl-pentene-1, hexene-1, octene-1, decene-1, dodecene-1, and the like. It is done.

  Although it does not specifically limit as a polymerization catalyst used when manufacturing the said ethylene-alpha-olefin copolymer (i), For example, a multi-site catalyst, a single site catalyst, etc. are mentioned.

  The ethylene-α-olefin copolymer (i) may be used singly or as a mixture of two or more densities and different comonomer types.

The density of the ethylene-α-olefin copolymer (i) is preferably 0.880 to 0.930 g / cm ³ , in terms of imparting heat seal strength and hot tack strength after film formation, more preferably 0.885~0.925g / cm ^3, more preferably from 0.900~0.920g / cm ^3.

The crystallization peak temperature (Tc) of the ethylene-α-olefin copolymer (i) is preferably 76 to 110 ° C, more preferably 78 to 108 ° C.
The crystallization peak temperature (Tc) can be measured in accordance with JIS K7121 using a differential scanning calorimeter. After the sample is completely melted, the temperature is decreased at a rate of 10 ° C./min. The temperature at the top of the obtained crystallization peak was defined as the crystallization peak temperature.

As MFR of the said ethylene-alpha-olefin polymer (i), it is preferable that it is 0.1-10 g / 10min, More preferably, it is 0.5-5.0 g / 10min.
In this specification, MFR means a value measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 2.16 kgf.

  The surface layer (A) is 80 to 98% by mass of the ethylene-α-olefin copolymer (i), 1 to 15% by mass of the olefin polymer (ii), and 100% by mass of the total surface layer (100% by mass). It is preferable to contain 1-10 mass% of anti-fogging agents (iii), ethylene-α-olefin copolymer (i) 80-98 mass%, olefin-based polymer (ii) 1-15 mass%, and anti-fogging It is more preferable that it consists only of 1-10 mass% of agents (iii).

The content of the ethylene-α-olefin copolymer (i) is preferably 85% by mass or more, and more preferably 90% by mass or more, from the viewpoint of heat seal strength and transparency.
The content of the olefin polymer (ii) is more preferably 1 to 10% by mass and further preferably 1 to 8% by mass from the viewpoints of flexibility and transparency.
The content of the antifogging agent (iii) is more preferably 1 to 8% by mass, and still more preferably 1 to 6% by mass from the viewpoint of imparting antifogging properties and preventing the film from being stained.

  The olefin polymer (ii) includes an ethylene-α olefin copolymer, an ethylene-vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, an ethylene-aliphatic non-polymer having a Tc of 75 ° C. or less. It is preferably at least one selected from a saturated carboxylic acid ester copolymer, a modified polyethylene, a modified polypropylene, and an ionomer resin, and two or more may be combined as necessary. The olefin polymer is more preferably an ethylene-vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, an ethylene-aliphatic unsaturated carboxylic acid ester copolymer, a modified polyethylene, a modified polypropylene, And at least one selected from ionomer resins.

Examples of the ethylene-α olefin copolymer having a Tc of 75 ° C. or lower include an ethylene propylene copolymer and an ethylene butene copolymer, and the density is 0.860 to 0.900 g / cm ^3. May be.
As said ethylene-vinyl acetate copolymer, the copolymer etc. whose content rate of the structural unit derived from vinyl acetate is 1-40 mass% with respect to the copolymer total mass (100 mass%) are mentioned.
Examples of the ethylene-aliphatic unsaturated carboxylic acid copolymer include an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer, and the like, and are aliphatic with respect to the total mass (100% by mass) of the copolymer. 1-40 mass% may be sufficient as the content rate of the structural unit derived from unsaturated carboxylic acid.
Examples of the ethylene-aliphatic unsaturated carboxylic acid ester copolymer include an ethylene-ethyl acrylate copolymer and an ethylene-methyl methacrylate copolymer, and the total mass (100% by mass) of the copolymer. 1-40 mass% may be sufficient as the content rate of the structural unit derived from the aliphatic unsaturated carboxylic acid ester with respect to.
Examples of the modified polyethylene include modified polyethylene obtained by modifying polyethylene with maleic acid or the like.
Examples of the modified polypropylene include modified polypropylene obtained by modifying polypropylene with maleic acid or the like.
As said ionomer resin, metal ion substitution bodies, such as potassium, sodium, zinc, etc. are mentioned, for example as an ethylene-methacrylic acid copolymer.

The crystallization peak temperature (Tc) of the olefin polymer (ii) is preferably 100 ° C. or lower, more preferably 30 to 95 ° C.
Tc measured by the differential scanning calorimeter of the olefin polymer (ii) is preferably 5 ° C. or more lower than Tc of the ethylene-α-olefin copolymer (i) used for the surface layer, and is 10 ° C. or more. It is more preferably low, and further preferably 15 ° C. or higher.

  The MFR of the olefin polymer (ii) is preferably 0.1 to 20 g / 10 minutes, and more preferably 0.5 to 10 g / 10 minutes.

  As the olefin polymer (ii), in order to make the unevenness after the heat treatment on the film more effective, the polar resin, that is, the molecule than the nonpolar resin such as ultra-low density polyethylene and amorphous polypropylene is used. A resin having a polar group such as a carboxyl group, a hydroxyl group, and / or an amino group, or a resin in which the carboxyl group is partially neutralized with a metal such as K, Na, or Zn is preferable.

Examples of the antifogging agent (iii) include glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester and the like. In the antifogging agent (iii), the alkyl group may be an alkyl group having 1 to 10 carbon atoms, and the aliphatic ester may be an ester of a fatty acid having 8 to 22 carbon atoms.
Among these, from the viewpoint of thermal stability, one or a combination of two or more selected from the group consisting of glycerin fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkyl ether, and polyoxyethylene glycerin fatty acid ester is preferable.

  The antifogging agent (iii) is preferably added in an amount of 1 to 10% by mass with respect to 100% by mass of the surface layer (A). To 1.5 to 8% by mass is more preferable, and 2 to 6% by mass is even more preferable.

  If necessary, an antifogging agent may be added to other inner layers.

(Other layers)
Examples of layers adjacent to the surface layer (A) include ethylene-propylene random copolymer (EPC), ethylene-α olefin copolymer (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-fat And a layer containing an aliphatic unsaturated carboxylic acid copolymer, an ethylene-unsaturated aliphatic carboxylic acid ester copolymer, a modified polyethylene, a modified polypropylene, an ionomer resin and the like.

  Examples of the layer configuration of the shrink film of the present embodiment include surface layer (A) / EPC / surface layer (A), surface layer (A) / LLDPE / surface layer (A), surface layer (A) / EVA / Surface layer (A), surface layer (A) / EPC / LLDPE, surface layer (A) / LLDPE / EPC, surface layer (A) / EPC / EVA, surface layer (A) / LLDPE / EVA and the like. In addition, the above resins may be sequentially laminated to form a shrink film having four or more layers, and within a range that does not impair the object of the present invention, polymethylpentene 1, polyurethane resin, cyclic olefin resin, polylactic acid, Polybutylene terephthalate or the like may be laminated as a layer other than the surface layer (A).

  Adjacent to the surface layer (A), ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-unsaturated aliphatic carboxylic acid ester copolymer, modified polyethylene, modified polypropylene, ionomer Adhesive resin such as resin is laminated as an adhesive resin layer, and further ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol copolymer (PVA), polyamide resin (PA), polyvinylidene chloride resin (PVDC), One or more layers of a barrier resin such as polyethylene terephthalate (PET) may be laminated to form a barrier shrink film.

  Examples of the layer structure of the barrier shrink film include surface layer (A) / modified polypropylene / EVOH / modified polypropylene / surface layer (A), surface layer (A) / modified polypropylene / PVA / modified polypropylene / surface layer (A ), Surface layer (A) / modified polypropylene / PA / modified polypropylene / surface layer (A), surface layer (A) / EVA / PVDC / EVA / surface layer (A), surface layer (A) / EVA / PET / EVA / surface layer (A), surface layer (A) / modified polypropylene / EVOH / modified polypropylene / EPC, surface layer (A) / modified polypropylene / PVA / modified polypropylene / EPC, surface layer (A) / modified polypropylene / PA / Modified polypropylene / EPC, surface layer (A) / EVA / PVDC / EVA / EPC, surface layer (A) / EVA / PE / EVA / EPC, surface layer (A) / modified polyethylene / EVOH / PA, surface layer (A) / modified polypropylene / PVA / PA, surface layer (A) / modified polypropylene / PA / modified polyethylene / surface layer (A) , Surface layer (A) / EVA / PVDC / EVA / surface layer (A), surface layer (A) / EVA / PET / EVA / surface layer (A), etc. Resin and barrier resin may be sequentially laminated to form a shrink film of 6 layers or more, and within the range not impairing the object of the present invention, polymethylpentene 1, polyurethane resin, cyclic olefin resin, polylactic acid, polybutylene You may laminate | stack terephthalate etc. as layers other than a surface layer (A).

  Furthermore, tackifying resins such as Alcon (trademark), Clearon (registered trademark), Imabe (registered trademark), etc. as a plasticizer in the surface layer (A) or other layers as long as the object of the present invention is not impaired. System resin may be included. As content of the said plasticizer, if it is 0.1-10 mass% with respect to the resin composition which comprises each layer, contractility and transparency may improve.

It is preferable that the thickness of the shrink film of this embodiment is 5-30 micrometers, More preferably, it is 10-25 micrometers.
In the shrink film of the present embodiment, the ratio of the thickness of the surface layer (A) to the thickness of the entire film (100%) is preferably 5 to 50%, more preferably 10 to 35%. In addition, the ratio of the thickness of the surface layer (A) refers to the ratio of the thickness of each surface layer (A). When a plurality of surface layers (A) are included, all the surface layers (A) It is preferable that it is the said range.

The shrink film of the present embodiment is, for example, packaging for moisture-containing contents: use for low-temperature and frozen storage after packaging: use for long-term packaging (for example, 2 days or more): beef, pork, chicken, etc. Used for the purpose of: be able to.
The content containing moisture refers to a content containing moisture to the extent that the content-side surface of the shrink film is covered with water after packaging, for example, food, beverages, reagents, jelly, yokan, etc. containing moisture. Can be mentioned. Although it does not specifically limit as a density | concentration of a water | moisture content, For example, 30 mass% or more may be sufficient with respect to the whole content.

[Shrink film manufacturing method]
Although the manufacturing method of the shrink film of this embodiment is not particularly limited, a method of extruding and stretching the film into a tube shape from an annular die such as a direct inflation method or a double bubble inflation method, or a sheet extruded from a T die, Examples include a method of stretching only in the longitudinal direction using a method, a method of stretching in the longitudinal direction and then biaxially stretching using a tenter, a method of performing simultaneous biaxial stretching in the tenter, and the like.

  Among these, multilayer films and multilayer sheets obtained by the double bubble inflation method are suitable as food packaging films because they are excellent in shrinkage and mechanical strength.

  As an example of a specific manufacturing method, the resin composition constituting each layer is melt-extruded using an extruder, and the layers are sequentially joined together in an annular die, or joined at once in an annular die, The method of obtaining a multilayer tube-shaped unstretched raw material is mentioned. At this time, one extruder may be used per layer, or it may be divided into two or more by the time the resin composition flows from one extruder into the annular die. . This is rapidly cooled and solidified, guided into the stretching machine, the heating temperature at the stretching start point is adjusted according to the purpose, and air is injected between the nip rolls provided with a speed difference, and the flow direction and the width direction are 3 respectively. Stretching by 0 times or more.

  The upper limit of the stretching ratio is preferably 12.0 times or less from the viewpoint of stretching stability, and it is easy to obtain a film having excellent transparency by stretching at a melting point or less of the resin composition constituting the surface layer. When it is desired to perform stretching at a higher magnification, when it is desired to stretch at a melting point or higher of the surface layer, it is possible to maintain the transparency of the surface layer by performing a crosslinking treatment.

[the film]
As a film of this embodiment, it has a surface layer containing an ethylene-α-olefin copolymer, a haze value at the time of surface coating with pure water is 0.5 to 3.0%, and a surface roughness Ra is The film etc. which are 4.0-8.0 are mentioned. In addition, the haze value and surface roughness Ra at the time of surface covering with the pure water in the film of this embodiment can be measured by a method that omits the heat treatment step in the evaluation of Examples described later.
As a film of this embodiment, the film etc. which heat-processed the shrink film of this embodiment (for example, heat processing at 110-140 degreeC) are mentioned.

  The present invention will be described based on examples.

  The measurement methods used in Examples, Reference Examples, and Comparative Examples are described below.

[1] Haze value during surface coating with pure water after heat treatment (1-1)
Put a wooden frame of length 100mm, width 50mm, thickness 10mm on the desk, face down the surface layer (A) of the shrink film obtained in the examples and comparative examples, and put it on the wooden frame with double-sided tape so as not to loosen Fixed.
Shrink tunnel (C-300, manufactured by Kyowa Denki Co., Ltd.) set at 120 ° C or 130 ° C with a wooden frame placed on the PSP tray (FPJ: FLJ-33-23) so that the film application surface is on top ) For 4 seconds.
(1-2)
A metal frame having a hole with a diameter of 50 mm, in which the center of an iron plate having a length of 70 mm, a width of 70 mm, and a thickness of 9 mm was cut in a circle, was placed on a desk. The film heat-treated in (1-1) is cut into a size of 80 mm in length and 80 mm in width with a double-sided tape so that the surface layer (A) faces downward, so that there is no looseness from above the metal frame. Fixed.
(1-3)
The metal frame was turned upside down on a clean table, 0.5 cc of pure water was dropped into the hole of the metal frame with a microsyringe, and the surface layer (A) of the film was covered with pure water. (If the wettability of the film surface is poor and the water film is not uniformly formed, 0.5 cc may be further dropped and the amount of dripping may be increased to a maximum of 10 cc. (It may be used as a measurement sample by sucking water and finally leaving a 0.5 cc water film on the surface.)
(1-4)
While hiding the film surface with pure water, the haze value was measured using a haze meter (NDH-7000, manufactured by Nippon Denshoku Industries Co., Ltd.) according to ASTM D1003, and this value was subjected to heat treatment at the time of surface coating with pure water. It was set as the haze value (%).

[2] Surface roughness Ra after heat treatment at 130 ° C.
Put a wooden frame of length 100mm, width 50mm, thickness 10mm on the desk, face down the surface layer (A) of the shrink film obtained in the examples and comparative examples, and put it on the wooden frame with double-sided tape so as not to loosen Fixed.
Put a wooden frame on the PSP tray (FPJ Co., Ltd .: FLJ-33-23) so that the film sticking surface is on top, and set it at 130 ° C for 4 seconds in a shrink tunnel (Kyowa Denki Co., Ltd. C-300) Heated to prepare a measurement sample.
The surface roughness was measured using an atomic force microscope “Cypher” (manufactured by Oxford Instruments) according to the following procedure.
The measurement sample was cut out to about 5 mm × 5 mm at an arbitrary location of the measurement sample prepared earlier, and the back surface of the surface layer (A) was fixed to the sample fixing disk. These samples were subjected to AC mode imaging (cantilever; Olympus AC200TS, observation field: 2 μm × 2 μm, resolution: 512 × 512 pixels) using an atomic force microscope (manufactured by Oxford Instruments, “Cypher”). The surface morphology was observed to obtain an observation image. For each of the samples, images of arbitrary three fields of view were obtained that did not include voids due to bubbles during extrusion of the resin, voids due to the antifogging agent, and scratches due to scratches during molding. Moreover, as surface roughness Ra evaluation, calculation of arithmetic average roughness Ra of JISB0601 was performed, and surface roughness Ra of the sample of each Example and each comparative example was evaluated. When moisture adhered to the film surface, it was easily affected by the measurement. Therefore, the film was sandwiched between neutral paper having a thickness of 85 μm, stored for 24 hours in a desiccator with a relative humidity of 30% or less, and conditioned.

[3] Antifogging property 200 ml of 20 ° C. water was placed in a polystyrene container (inner dimensions: 145 mm × 90 mm × 55 mm), sealed with a film, and heat treated for 4 seconds in a shrink tunnel heated to 130 ° C. The container is left in a refrigerator at 5 ° C. After 4 hours, 24 hours, 72 hours, 120 hours, and 168 hours, the container is taken out and the cloudiness of the film inner surface is visually checked. The evaluation was made in four stages according to the following criteria.
A (Excellent): A uniform water film is formed on the inner surface of the film, and it is completely transparent and has no fog
○ (Good): The water film has spots but is almost transparent.
Δ (defect): Water film has spots, water droplets having a diameter of 10 mm or more are attached, and the contents are difficult to see.
X (Inferior): Water droplets of 10 mm or less adhere to the entire surface, and the contents cannot be seen.

Resins used in Examples and Comparative Examples are as follows.
LLDPE1: ethylene-α-olefin copolymer, density: 0.904 g / cm ³ , MFR: 2.0 g / 10 min (190 ° C.), Tc = 97.4 ° C.
LLDPE2: ethylene-α-olefin copolymer, density: 0.931 g / cm ³ , MFR: 4.0 g / 10 min (190 ° C.), Tc = 107.4 ° C.
LLDPE3: ethylene-α-olefin copolymer, density: 0.902 g / cm ³ , MFR = 3.5 g / 10 min (190 ° C.), Tc = 78.7 ° C.
EVA1: ethylene vinyl acetate copolymer, VA content = 15% by mass, MFR = 2.0 g / 10 min (190 ° C.), Tc = 76.3 ° C.
EPC1: ethylene-propylene copolymer, density 0.885 g / cm ³ , MFR = 3.6 g / 10 min (190 ° C.), Tc = 71.5 ° C.
EMAA1: ethylene-methacrylic acid copolymer, MAA content = 11% by mass, MFR = 8 g / 10 min (190 ° C.), Tc = 79.2 ° C.
EAA1: ethylene-acrylic acid copolymer, AA content = 9.5% by mass, MFR = 1.6 g / 10 minutes (190 ° C.), Tc = 88.1 ° C.
EEA1: Ethylene ethyl acrylate copolymer: EA content = 15% by mass, MFR = 1.5 g / 10 min (190 ° C.), Tc = 81.0 ° C.
EMMA1: ethylene-methyl methacrylate copolymer, MMA content = 10% by mass, MFR = 2.0 g / 10 min (190 ° C.), Tc = 83.0 ° C.
Ionomer 1: MFR = 3 g / 10 min, Tc = 67.4 ° C., ionic species = sodium Modified PE1: modified polyethylene, MFR = 2.7 g / 10 min (190 ° C.), Tc = 100.3 ° C.
Modified PP1: Modified polypropylene, MFR = 7.7 g / 10 min (190 ° C.), Tc = 101.5 ° C.
PP1: ethylene-propylene copolymer, MFR = 5.3 g / 10 min (230 ° C.), melting point = 150 ° C.
EVOH1: ethylene-vinyl alcohol copolymer, MFR = 4.0 g / 10 min (190 ° C.), ethylene content = 38 mol%

Antifogging agents used in Examples and Comparative Examples are as follows.
Antifogging agent 1: 25% by mass of polyoxyethylene alkyl ether (HLB = 12), 25% by mass of diglycerin oleate (HLB = 5.7), 25% by mass of diglycerin laurate (HLB = 6.3) %, Glycerol monooleate (HLB = 4.7) in a proportion of 25% by mass.

[Examples 1 to 7]
The resin composition shown in Table 1 is extruded as the surface layer 1, PP1 is laminated as the adjacent second layer, and LLDPE1 is laminated as the third layer, and the surface layer 1 / second layer / third layer is 30/40 in this order. An unstretched original fabric having a three-layer structure was extruded from an annular die and adjusted to a layer thickness ratio of / 30, and cooled and solidified to prepare an unstretched tube original fabric having a thickness of 150 μm. This is induced in a stretching machine and reheated to 70 ° C., which is below the melting point of the surface layer, passed between two pairs of differential nip rolls to form bubbles by air injection, 3.3 times in the flow direction, Each film was stretched at a magnification of 3 times in the width direction to obtain a shrink film having an average thickness of 15 μm.

[Examples 8 to 18]
The resin compositions shown in Tables 2 and 3 were extruded as the surface layer 1, and modified PP1 as the adjacent second layer, EVOH1 as the third layer, modified PE1 as the fourth layer, and PP1 as the fifth layer were laminated. The surface layer 1 / the second layer / the third layer / the fourth layer / the fifth layer is adjusted in order of the layer thickness ratio of 30/15/10/15/30, and the five-layer structure is formed from the annular die. The unstretched original fabric was extruded, cooled and solidified to produce an unstretched tube stock having a thickness of 150 μm, and extruded and stretched in the same manner as in Example 1 to obtain a shrink film having an average thickness of 15 μm.

[Comparative Examples 1-3]
Except for changing the surface layer to the resin composition shown in Table 4, the same operation as in Example 1 was performed, and the same operation was performed. Extrusion and stretching were performed in the same manner as in Example 1 to obtain a shrink film having an average thickness of 15 μm. Obtained.

  The shrink film thus obtained was subjected to measurement of haze value and surface roughness and evaluation of antifogging property.

  The evaluation results of Examples 1 to 18 are shown in Tables 1 to 3. Since all the films obtained in Examples 1 to 18 were excellent in pure water-covered haze value after heat treatment, they had good visibility, excellent initial antifogging property after 4 hours, and 7 days (168 hours). ) The result was excellent in the subsequent continuous antifogging property.

The evaluation results of Comparative Example 1 are shown in Table 4. Since Comparative Example 1 did not contain the olefin polymer (ii) and the film surface was smooth, the antifogging agent could not be sufficiently retained, and the antifogging property could not be maintained for a long time.
The evaluation results of Comparative Example 2 are shown in Table 4. In Comparative Example 2, the surface was extremely rough, the surface roughness value was high, the transparency after heat treatment was greatly reduced, and the visibility of the contents was impaired.
The evaluation results of Comparative Example 3 are shown in Table 4. In Comparative Example 3, the Tc difference between the ethylene-α-olefin copolymer (i) and the olefin polymer (ii) was small, and the surface unevenness was not sufficiently obtained even after the heat treatment. The fogging agent could not be retained sufficiently and the antifogging property could not be maintained.

  Since the highly anti-fogging shrink film of the present embodiment forms moderate irregularities on the film surface after heat treatment, it can easily maintain the anti-fogging, and can exhibit excellent anti-fogging properties over a long period of time. The visibility of objects can be maintained for a long time.

Claims (5)

Having a surface layer comprising an ethylene-α-olefin copolymer (i),
The haze value at the time of surface coating with pure water after heat treatment at 120 ° C. and 130 ° C. is 0.5 to 3.0%,
A shrink film, wherein the surface roughness Ra of at least one surface after heat treatment at 130 ° C. is 4.0 to 8.0.   The surface layer contains ethylene-α-olefin copolymer (i) 80 to 98% by mass, olefin polymer (ii) 1 to 15% by mass, and antifogging agent (iii) 1 to 10% by mass, The shrink film according to claim 1.   The crystallization peak temperature (Tc) measured by the differential scanning calorimeter of the olefin polymer (ii) is measured by the differential scanning calorimeter of the ethylene-α-olefin copolymer (i). The shrink film according to claim 2, which is lower by 5 ° C. or more than temperature (Tc).   The olefin polymer (ii) is an ethylene-vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, an ethylene-unsaturated aliphatic carboxylic acid ester copolymer, a modified polyethylene, a modified polypropylene, and The shrink film according to claim 2 or 3, which is at least one selected from the group consisting of ionomer resins. Having a surface layer comprising an ethylene-α-olefin copolymer;
The haze value at the time of surface coating with pure water is 0.5 to 3.0%,
The surface roughness Ra of at least one surface is 4.0 to 8.0.
A film characterized by that.