WO2007032306A1

WO2007032306A1 - Thermally shrinkable multilayer sheet

Info

Publication number: WO2007032306A1
Application number: PCT/JP2006/317971
Authority: WO
Inventors: Masayuki Yoshino; Yutaka Matsuki
Original assignee: Asahi Kasei Chemicals Corporation
Priority date: 2005-09-15
Filing date: 2006-09-11
Publication date: 2007-03-22
Also published as: JP4954882B2; TWI341790B; TW200732150A; JPWO2007032306A1

Abstract

Disclosed is a thermally shrinkable multilayer sheet having at least three layers composed of both surface layers and an interlayer. Each of the surface layers comprises an ethylene-α-olefin copolymer having a density falling within a specified range. The interlayer comprises a composition comprising an ethylene-α-olefin copolymer having a density falling within a specified range and at least one resin selected from a high-pressure low-density polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-aliphatic unsaturated carboxylic acid copolymer, and an ethylene-aliphatic unsaturated carboxylic acid ester copolymer, in an amount of 50 to 100 wt%. The thermally shrinkable multilayer sheet has the following characteristics (1) and (2): (1) the resin constituting the surface layers has the ratio of the amount of melting heat at 100ºC or lower relative to the total amount of melting heat of 40 to 75% in the second melting behavior in differential scanning calorimetry; and (2) the film has the ratio of the amount of melting heat at 100ºC or lower relative to the total amount of melting heat of 45% or more and the ratio of the amount of melting heat at 110ºC or lower relative to the total amount of melting heat of 70% or more in the second melting behavior in differential scanning calorimetry. The film enables the formation of a packaged article having a beautiful appearance without the need of decreasing the packaging speed. A container formed from the film shows no deformation even after heated with a microwave oven and no film-film cohesion.

Description

Specification

Heat shrinkable multilayer film

Technical field

[0001] The present invention relates to a heat-shrinkable multilayer film which is used by covering a container containing a lunch box container or a side dish with a film, and tensioning the film by heat shrinkage so that the film is in close contact with a package. In particular, it relates to what is reheated in a microwave after packaging.

Background art

[0002] A film for shrink wrapping is characterized in that a plurality of products can be packaged quickly and tightly at the same time, regardless of the shape and size of the package. The resulting shrink-wrapped product has a beautiful appearance, which increases the commercial value and keeps the packaged items hygienic. In addition, since the quality and the like of the article to be packaged can be easily confirmed by external force, the shrink wrapping film is often used for packaging foods, sundries and the like.

[0003] As a typical example of a powerful shrink wrapping method, there is a pillow shrink wrapping in which the film is heat-shrinked with hot air or the like after the contents are primarily packaged with a slight margin. This method generally takes the following scheme. First, the food or other items to be wrapped in a container or tray are covered with a film in a cylindrical shape, and then the film is placed on the back of the item to be wrapped with a center roller sealer or other center sealing device. Heat seal with the ends attached to the palm. Subsequently, both open ends of the tubular film are heat-sealed to form a bag shape, and hot air is blown in a box called a shrink tunnel, and the air is deaerated through holes provided in the film in advance to remove the film. Shrink package by heat-shrinking. In addition to the above, the pillow shrink packaging method includes a method of heat-treating a three-sided seal or a four-side sealed bag-like film. Main examples of the above containers and trays include heat-resistant containers such as polypropylene (PP) made of polystyrene with a lid, polystyrene trays with lids, trays made of expanded polystyrene without lids, PP, paper, etc. Is mentioned. In either case, the container or tray is loosely packaged with a margin in the film, and then the film is shrunk by blowing hot air, so that a beautiful package can be obtained with the film slacking to the corners. [0004] In recent years, there have been moves to reduce carbon dioxide emissions and to increase the speed of packaging lines for reasons such as cost reduction. For this reason, shrink packaging is desired to shrink at a low temperature, and the film should shrink greatly at as low a temperature as possible. However, the reheat temperature of shrink-wrapped packages often reaches 100 ° C in some cases after repackaging in a microwave oven. At this temperature, the container becomes soft due to heat, and the heat-shrinkable film contracts, so the container may be deformed. Especially from the viewpoint of resource saving Containers and trays are becoming thinner, so the containers are easily deformed.

[0005] In order to prevent this container deformation, the film used for packaging should have low shrinkage at 100 ° C or lower. On the other hand, in order to improve the packaging finish, it is better to have high shrinkage at a temperature of 11 ° C. or higher where the heat shrinkage treatment is performed. In the pillow shrink packaging method, if the temperature of the seal bar when sealing the front and back parts of the package is high, the seal part shrinks in the width direction of the film, and small wrinkles remain after shrinkage. There is. For this reason, when considering the finish at the time of packaging, it is more difficult for the flaws to remain on the seal portion after shrinkage when the films are fused at a low temperature. However, if the films are sealed at a low temperature, for example, below the microwave heating temperature, there is a problem that the upper and lower films are fused when the packaging is stacked and heated in a microwave oven. Further, it is preferable that the seal portion of the container edge is positioned below the container edge so that the inside of the container can be seen well when viewed from the top of the package. However, when the film is shrunk at a high temperature, there is a problem that it rises above the edge of the container.

As a low-temperature high-shrinkage film, Patent Document 1 discloses a low-temperature-shrinkable film for packaging containers, such as low-crystalline polyethylene terephthalate, which has low heat resistance. However, since the film has a large shrinkage rate at 100 ° C. or lower, in the application where reheating is performed using the electronic range as in the present invention, the film increases as the temperature of cooked rice or ingredients in the container increases. When the container shrinks and the container is tightened, the container collapses, or when the upper and lower films are fused with each other when stacked and range-heated, there is a problem.

[0006] Patent Document 2 discloses a multilayer crosslinked shrink film using a specific density ethylene oc 1 year old refin copolymer. In this document, the density of the outer layer resin is 0. 913 gZcm ³ ethylene-α-olefin, a film using ethylene _a- olefin with _a density of 0.915 g / cm ³ as an inner layer resin and an ethylene one at-olefin with a density of 0.913 g / cm ³ as an outer layer resin, A film using ethylene a-olefin having a density of 0.926 gZcm ³ and high-pressure low-density polyethylene is exemplified as the inner layer resin. The former has the problem of uneven thickness and low shrinkage at 120 ° C. On the other hand, the latter also needs to increase the shrink tunnel temperature during packaging when the shrinkage rate at 120 ° C is low.

[0007] Patent Document 1: International Publication No. 2005Z049702 Pamphlet

Patent Document 2: Japanese Patent Laid-Open No. 2002-120343

Disclosure of the invention

Problems to be solved by the invention

[0008] The present invention is particularly applicable to a case where a container filled with contents is heated in a microwave oven in a state where the container is shrink-wrapped, and the container is heated in a stacked manner that does not deform the container. An object of the present invention is to provide a shrink film having excellent heat resistance with little fusion between them, low shrinkage at low temperature (100 ° C or lower) and high shrinkage at high temperature (110 ° C or higher). Means for solving the problem

[0009] As a result of intensive investigations to achieve the above-mentioned problems, the present inventor has found that the problems can be solved by the present invention.

That is, the present invention is as follows.

1. At least three layers comprising a surface layer and an inner layer, wherein at least one of the surface layers comprises an ethylene-α-olefin copolymer having a density of 0.900 to 0.918 gZcm ³ Is an ethylene α-olefin copolymer having a density of 0.910 to 0.920 gZcm ³ , a high-pressure low-density polyethylene, an ethylene vinyl acetate copolymer, an ethylene aliphatic unsaturated carboxylic acid copolymer, and an ethylene aliphatic. Unsaturated carboxylic acid ester copolymer 50-: A composition containing at least one resin selected from the group consisting of L00 wt%, and a heat-shrinkable multilayer characterized by the following (1) and (2) the film.

(1) In the second melting behavior of the differential scanning calorimeter, the resin constituting the surface layer has a ratio of the heat of fusion of 100 ° C or less to 45-75% with respect to the total heat of fusion of the surface layer. (2) The film is a differential scanning calorimeter 2nd. In the melting behavior, the ratio of the heat of fusion of 110 ° C or less with the ratio of the heat of fusion of 100 ° C or less to 5% or more of the total heat of fusion of the film Is over 70%

2. The heat-shrinkable multilayer film according to 1 above, wherein the inner layer contains 50 to L00 wt% of a mixture of an ethylene α-olefin copolymer having a density of 0.910 to 0.920 gZcm ³ and a high pressure low density polyethylene.

3. Differential scanning calorimeter of the whole film 2nd. In the melting behavior, the ratio of the heat of fusion below 100 ° C to the total heat of fusion is between 45% and 65%, and melting at 110 ° C or below. 3. The heat-shrinkable multilayer film as described in 1 or 2 above, wherein the ratio of heat release is 70% or more.

4. The heat-shrinkable multilayer film according to 3 above, wherein the shrinkage ratio of the film is 0% or more, less than 30% at 100 ° C, 30% or more at 110 ° C, and 68% or more at 120 ° C.

5. The gel fraction of the resin constituting the surface layer is 1 ~ 20wt%, the gel fraction of the whole film is 5 ~ 50wt%, the specific force of the gel fraction of the surface layer resin and the internal layer resin 5. The heat-shrinkable multilayer film as described in 4 above, which is 2: 1 to 1:20.

6. The heat-shrinkable multilayer film as described in 5 above, wherein the molecular weight distribution (MwZMn) of the ethylene α-olefin copolymer in the surface layer is 3.5 or less.

The invention's effect

[0011] The film of the present invention has a specific resin-constituting force, and is particularly excellent in low shrinkage at low temperatures (100 ° C or lower) and high shrinkage at high temperatures (110 ° C or higher). Therefore, the packaging finish can be improved while maintaining the packaging speed. It also excels in heat resistance, with less container deformation and film-to-film fusion caused by film shrinkage when heated in a microwave oven. Therefore, it is suitable for packaging such as lunch boxes and side dishes.

BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The present invention will be described in detail below with a focus on preferred embodiments.

[0013] The ethylene-at-olefin copolymer used in the film of the present invention is a random copolymer of ethylene and at least one monomer selected from a-olefin monomers having 3 to 18 carbon atoms. . _a —Olefin includes propylene, butene-1, 1, pentene 1, 4—methyl-pentene 1, hexene 1, otaten 1, decene 1, dodecene 1, etc. The polymerization catalyst used for producing the copolymer is not particularly limited, and examples thereof include a multisite catalyst and a single site catalyst. A single-site system is preferred because it increases the slipperiness of the film surface. The ethylene content in the copolymer is preferably 40 to 95 wt%, more preferably 50 to 90 wt%, and even more preferably 60 to 85 wt%, in order to improve sealing properties and transparency. As the polymerization method, it can be produced by a gas phase method or a high pressure method.

[0014] The density of the ethylene α-olefin copolymer used for at least one of the surface layers is 0.

900-0. Is a 918gZcm ^3. When the density of the ethylene- _a -olefin copolymer is 0.900 gZcm ³ or more, moderate hardness can be imparted to the film, and the runnability in the packaging machine is improved, and when it is 0.918 gZcm ³ or less, 110 ° Shrinkage at C or higher improves. It is preferably 0.905 to 0.917 gZcm ³ , more preferably 0.910 to 0.915 gZcm ³ .

[0015] As the surface layer comprising the ethylene α-olefin copolymer, it is preferable to use a surface layer that is easily melted at a low temperature from the viewpoint of suppressing wrinkles around the seal portion and saving power consumption. Heat resistance when using a microwave oven is also necessary. In the present invention, the second melting behavior of the differential scanning calorimeter is used as the index. That is, the ethylene _α- olefin copolymer used for at least one of the surface layers is the ratio of the heat of fusion at 100 ° C or less to the total heat of heat of the surface layer in the second melting behavior of the differential scanning calorimeter. The force should be 0-7 5%. The ratio of the heat of fusion at 100 ° C or less to the total heat of fusion When the force is 0% or more, the low-temperature sealability is improved. Preferably it is 45% or more, more preferably 50% or more. In addition, when the ratio of heat of fusion at 100 ° C or lower is 75% or lower, the film is fused when the package body in which the lidded container containing lunch box or side dish is wrapped with the film is heated in a microwave oven. become. Preferably it is 65% or less, more preferably 60% or less. Further, when the melting property of the surface layer made of the ethylene (X-olefin copolymer of the present invention) is in the above preferred range, the shrinkage balance with the inner layer is good and the transparency after shrinkage is improved. The ratio can be obtained by the following method using an input compensated differential scanning calorimeter, Diamond DSC (trademark), manufactured by Perkin Elma Co., that is, a sample having a mass of 5 to: LOmg from a temperature of 0 ° C. Increase the temperature to 200 ° C in 10 ° CZ (1st melting behavior), hold at 200 ° C for 1 minute, and then decrease to 0 ° C in 10 ° CZ (1st. Crystal) Behavior). Next, the temperature was raised again to 200 ° C in 10 ° CZ minutes (2nd melting behavior). At this time, the heat of fusion at 20 ° C to 100 ° C and 20 ° C to 110 ° C was changed from 20 ° C to the end of melting. It can be obtained by calculating the value (%) divided by the heat of fusion in the temperature range up to.

[0016] If the ratio of the heat of fusion to the total heat of fusion of the ethylene a-olefin copolymer is within the specified range, adjustment is not necessary, but if it is outside the specified range, the ethylene OC-olefin copolymer is added to the high pressure method. Low-density polyethylene, ethylene vinyl acetate copolymer, ethylene aliphatic unsaturated carboxylic acid copolymer, and ethylene aliphatic unsaturated carboxylic acid ester copolymer power To increase or decrease the amount of at least one ethylene polymer selected To adjust within the specified range. As a guideline, for example, when the specific power of the heat of fusion of the ethylene-a-olefin copolymer is lower than 0%, it is sufficient to blend 5-30% of an ethylene polymer having a melting point of 100 ° C or lower. When the ratio of heat of fusion is 75% or more, about 5 to 30% of high pressure low density polyethylene should be blended.

[0017] The molecular weight distribution (MwZMn) of the ethylene a-olefin copolymer used for at least one of the surface layers is measured by a gel permeation chromatography apparatus (hereinafter referred to as GPC). In this molecular weight distribution (MwZMn), MwZMn is not more than 3.5, more preferably not more than 3.2. MwZMn is preferably 1.5 or more, more preferably 2.0 or more, and even more preferably 2.5 or more because of good extrudability.

[0018] The ethylene α-olefin copolymer used in at least one of the surface layers may be a single material or a mixture of ethylene _α -olefin copolymers. Furthermore, another polymer may be mixed within a range of 50 parts by mass or less with respect to 100 parts by mass of the copolymer. For example, with respect to 100 parts by mass of the ethylene-a-olefin copolymer in the surface layer, the high-pressure low-density polyethylene having a density of 0.930 g / cm ³ or less is preferably 1 to 25 parts by mass, more preferably 5 to 20 parts by mass. Addition of a part is preferable because it improves hot tack sealing and transparency. Further, with respect to 100 parts by mass of the ethylene-a-olefin copolymer, ethylene-α-olefin having a density of 0.850 to 0.900 gZcm ³ is preferably 1 to 25 parts by mass, more preferably 5 to 20 parts by mass. Addition of a part is preferable because the sealing performance is improved even at low temperatures. [0019] The thickness ratio of the surface layer is preferably 5 to 50%, more preferably 8 to 30%, still more preferably with respect to the entire film, from the viewpoints of extrudability, sealing properties, transparency, and the like. Is 10-20%.

Film [0020] The present invention, at least one of the two surface layers, wherein the density is 0. 900~0. 91 8gZcm ³ and, in the 2nd. Melting behavior of differential scanning calorimetry, the total melting of the surface layer It is necessary to use an ethylene-a-olefin copolymer that has a specific force of 0 to 75% of the heat of fusion of 100 ° C or less to the heat. However, any other resin can be used for the other surface layer as long as the properties of the film of the present invention are not impaired. It is preferable to use the same resin as the one-side surface layer for the other surface layer because the flatness of the film is improved. Examples of the resin used for the other surface layer include, but are not limited to, forces including ethylene-based resin and polypropylene-based resin.

[0021] When both surface layers are packaged with films composed of different resin configurations, either of the surface layers may be exposed, but the films are prevented from fusing when heated in a microwave oven. Therefore, it is preferable to make the surface layer of the present invention an exposed surface.

[0022] The inner layer has an ethylene α-olefin copolymer having a density of 0.910 to 0.920 gZcm ³ , a high-pressure low-density polyethylene, an ethylene acetate butyl copolymer, an ethylene aliphatic unsaturated carboxylic acid copolymer, and Ethylene Aliphatic Unsaturated Carboxylic Acid Ester Copolymer A composition comprising 50 to LOOwt% of a mixture of at least one ethylene polymer, which is also selected.

[0023] The density of the ethylene ex-one-year-old refin copolymer used for the inner layer is 0.910 to 0.920 gZcm ³ because the film hardness can be sufficiently obtained while the shrinkage is within an appropriate range. It is preferably 0.911 to 0.918 gZcm ³ , more preferably 0.911 to 0.916 gZcm ³ . The melt index range is preferably 0.5 to 7. Og / 10 min at 190 ° C, more preferably 0.5 to 5 because it can be stably stretched without increasing the load during extrusion. OgZlO minutes. The polymerization catalyst used for producing the copolymer is not particularly limited, and examples thereof include a multisite catalyst and a single site catalyst. A single-site catalyst is preferred because sufficient film strength can be obtained.

[0024] The inner layer is made of the above-mentioned ethylene oc-olefin copolymer, and a high-pressure method low-density polymer. Reethylene, ethylene acetate butyl copolymer, ethylene aliphatic unsaturated carboxylic acid copolymer, and ethylene aliphatic unsaturated carboxylic acid ester copolymer power include at least one resin selected from ethylene polymers. By constituting the ethylene _a- olefin copolymer, high-density polyethylene, and ethylene-based polymer force 50 to L00 wt% of the inner layer, high-stretching becomes possible, and the shrinkage characteristics of the present invention can be achieved. Preferably it is 60-100 wt%, More preferably, it is 70-100 wt%.

[0025] When high-pressure low-density polyethylene is added to the inner layer, the film is effectively oriented during molding, so that the film can be given hardness and stretching stability. The range of the density of the high-pressure low-density polyethylene emissions, 0. 915-0. 930g / cm ³ is more preferably preferably instrument 0. 91 6~0. 925gZcm ^3, more preferably 0. 917~0. 923gZcm ³ .

[0026] When the inner layer comprises a blend composition of ethylene α-olefin copolymer having a density of 0.910 to 0.920 gZcm ³ and high-pressure low-density polyethylene, the stretching stability, the high-stretchability, and the extrusion stability Etc. The ethylene a-olefin copolymer gives strength to the film and enables stretching at a high magnification, so that uneven thickness in the transverse direction of the film is less likely to occur. On the other hand, since the high-pressure low-density polyethylene has long-chain branches, the extrusion stability of the unstretched tube is improved, and the thickness unevenness in the flow direction is reduced. "Become. As described above, the above-mentioned effect is remarkably improved by blending and using the ethylene-fluorine copolymer and the high-pressure method low-density polyethylene. The ethylene OC 1-year-old refin copolymer and the high-pressure low-density polyethylene may be used alone or in combination of two or more as long as they satisfy the requirements of the present invention. In order to improve the film strength, the blend ratio of the high-pressure low-density polyethylene to the ethylene-a-olefin copolymer is preferably 70 wt% or less, more preferably 60 wt% or less, and even more preferably 50 wt% or less. . The lower limit is preferably 5 wt% or more, more preferably 10 wt% or more, and even more preferably 15 wt% or more in order to improve the film stretching stability.

[0027] The blend ratio of the ethylene ex-olefin copolymer and the high-pressure low-density polyethylene may be appropriately determined according to the selected resin. For example, when using high-pressure low-density polyethylene with a melt index of less than 1.0, give the film a proper orientation. However, in order to enable the film to be stretched at a high stretch ratio, the blend ratio of high-pressure low-density polyethylene to ethylene _a- olefin is preferably 60 wt% or less, and more preferably 45 wt% or less. . On the other hand, in the case of a high pressure method low density polyethylene having a melt index of 1.0 or more, it is expected that the stretchability can be improved by increasing the blend amount.

[0028] Further, at least one ethylene-based polymer selected from the group consisting of ethylene vinyl acetate copolymer, ethylene aliphatic unsaturated carboxylic acid copolymer, and ethylene aliphatic unsaturated carboxylic acid ester copolymer power is provided in the inner layer. You can use it!

[0029] By using an ethylene vinyl acetate copolymer (EVA) for the inner layer, flexibility and stretch stability can be imparted to the film. Normally, the higher the content of butyl acetate, the lower the melting point and the more flexible. The preferred vinyl acetate content is 1-30 wt%. From the viewpoint of imparting shrinkage of 110 ° C. or higher and thermal stability, it is more preferably 3 to 20 wt%, and even more preferably 5 to 15 wt%.

[0030] Specific examples of the ethylene aliphatic unsaturated carboxylic acid copolymer and the ethylene aliphatic unsaturated rubonic acid ester copolymer include ethylene acrylic acid copolymer (EA A), ethylene-methacrylic acid copolymer Examples thereof include EMAA, ethylene methyl acrylate copolymer (EMA), ethylene ethyl acrylate copolymer (EEA), and ethylene-methyl methacrylate copolymer (EMMA). Like EVA, the more copolymerized components with ethylene, the more flexible and the better the adhesion and shrinkage at 110 ° C and 120 ° C. The preferable range of the Vicat soft spot is 40 to 110 ° C from the viewpoint of thermal stability during processing and low temperature shrinkage, and a more preferable range is 50 to 95 ° C. The Vicat softening point referred to here is a temperature at which the hardness of the polymer substance changes, and is used as an index of heat resistance of the resin. It can be measured by the method described in JIS K-7206. In other words, a needle-shaped indenter is placed vertically on a test piece placed in a heating tub or a heating tank, and the heat transfer medium is heated at a constant speed while applying a predetermined load to the needle-shaped indenter. lmm The temperature of the heat transfer medium when it enters. The load at this time is 10N (Method A), and the heating rate is 50 ° CZhr. Ethylene one _α of the ethylene-based polymer - blend ratio Orefuin is preferably from preferably tool is 10～80Wt% is 20~70wt%. [0031] In the case where an ethylene α-olefin copolymer having a relatively high density of 0.915 to 0.92 OgZcm ³ is used for the inner layer, the above high-pressure low-density polyethylene and ethylene are used. It is preferable to blend a polymer having a relatively low melting point. The blend ratio is preferably 70 wt% or less, more preferably 60 wt% or less.

[0032] Further, the inner layer may contain any resin such as polypropylene resin, styrene resin, polybutene resin in the range of 0 to 50 wt%, as long as the transparency of the film is not impaired. Yes. From the viewpoint of compatibility, ethylene-based resin is preferable.

[0033] Recycled raw materials can be used for the inner layer in the present invention. The recycling raw material is obtained by pulverizing a surplus film or the like after slitting to a predetermined width, melt-extruding, and pelletizing. The use of these raw materials for the inner layer is preferable because it can maintain the transparency of the original film and achieve effects such as resource saving.

[0034] In the second melting behavior of the differential scanning calorimeter of the film of the present invention, the ratio of the heat of fusion to the total heat of fusion is 45% or higher at 100 ° C or lower and 70% or higher at 110 ° C or lower.

[0035] When the ratio of the heat of fusion to the total heat of fusion at 100 ° C or lower is 45% or higher, the shrinkage of the film at 110 ° C or higher is improved. As a result, the wrinkles around the seal and corners after shrinkage are reduced, and the finish after packaging is improved. Preferably it is 48% or more, more preferably 50% or more. The upper limit of the ratio of the heat of fusion at 100 ° C. or less is preferably 65% or less, more preferably 62% or less, and still more preferably 60% or less.

[0036] Further, since the ratio of the heat of fusion to the heat of fusion of 110 ° C or less is 70% or more, the shrinkability of the film of 120 ° C or more is improved. Small wrinkles are reduced, and finishing after packaging is improved. The ratio is preferably 75% or more, more preferably 80% or more. The ratio of the heat of fusion in the 2nd. Melting behavior of the differential scanning calorimeter of the film can be achieved by adjusting the composition of the surface layer and the inner layer within a specified range. The method for measuring the heat of fusion relative to the total heat of fusion of the film is the same as the method described above. As a guideline, for example, if the ratio of the heat of fusion at 100 ° C of the film is lower than 45%, the amount of high-pressure low-density polyethylene or ethylene polymer in the surface layer, Z or inner layer is about 50-80%. It is sufficient to blend. When the ratio of heat of fusion at 110 ° C or lower is lower than 70%, it should be blended about 10 to 50%. Yes.

[0037] The shrinkage ratio of the film of the present invention is represented by an average value of shrinkage ratios in the flow direction and the width direction of the film. At 100 ° C, it is 0% or more and less than 30%, preferably 0% to 28%. At 110 ° C, it is 30% or more, preferably 35% or more, more preferably 38% or more. At 120 ° C, it is 68% or more, preferably 70% or more. The shrinkage rate at each temperature is preferably 95% or less from the viewpoint of practicality. By specifying the shrinkage rate of the film within the above range, the shrink wrapping operation can be improved and the finish of the package can be improved. Furthermore, it becomes possible to suppress container deformation at the time of microwave heating. Here, “increasing the efficiency of the packaging work” means lowering the set temperature of the shrink tunnel and shortening the transit time in the tunnel. “Improving the finish of the package” means to suppress the small wrinkles of the seal part or to position the seal part before and after the package lower than the edge of the container. In order to express the shrinkage rate, the resin of the present invention may be appropriately combined within the conditions of the heat of fusion of the film.

[0038] In the present invention, it is preferable to carry out a crosslinking treatment in order to impart heat resistance and stretching stability. The preferable irradiation dose range for the cross-linking treatment is 40 to 200 kGy, and 50 to 120 kGy is more preferable because it can be stretched at a high magnification while satisfying heat sealability.

[0039] A gel fraction is used as a measure of the degree of crosslinking. The gel fraction is measured by extracting a sample in boiling paraxylene for 12 hours and displaying the proportion of insoluble matter by the following formula.

[0040] Gel fraction (wt%) = (Sample weight after extraction Z Sample weight before extraction) X 100

From the viewpoint of heat sealability, the gel fraction of at least one of the surface layers is preferably 1 to 20 wt%, more preferably 3 to 15 wt%. When the gel fraction of the surface layer is ^% or more, the transparency of the film is improved, and when it is 20 wt% or less, the heat sealability is improved. Is obtained. Further, the gel fraction of the entire film is preferably in the range of 5 to 50 wt%, more preferably in the range of 20 to 40 wt%, since heat resistance can be obtained while securing the high magnification stretchability of the film. From the viewpoint of achieving both heat sealability and stretchability, the ratio of the gel fraction of the surface layer to the inner layer is preferably 2: 1 to 1:20. [0041] Hereinafter, an example of a method for producing the film of the present invention will be described.

[0042] First, the resin is melt-extruded using an extruder so as to have the above layer structure. In melt extrusion, the resin is extruded layer by layer and sequentially joined in an annular die, and joined together in an annular die to obtain a multilayered tube-shaped unstretched raw sheet or sheet. At this time, one extruder per layer may be used, or one extruder force may be divided into two or more layers before the resin flows into the annular die. .

[0043] Next, a cross-linking treatment is performed as necessary on the rapidly solidified product. Thereafter, this is guided into a stretcher and stretched. Stretching is performed at a temperature higher than the melting point of the resin by io ° c or higher and 150 ° C or lower, and air is injected between the rolls with a speed difference. Sequential biaxial stretching or simultaneous biaxial stretching is preferably performed at a magnification of 10 times. In particular, the double bubble inflation method is suitable for stretching a thin film of about 10. The melting point here refers to the peak value at the time of melting in the 2nd melting pattern of the differential scanning calorimeter. When there are two or more peaks, the peak value on the highest temperature side is indicated. By stretching at a melting point or higher of the resin, it can be stretched at a high magnification and a film having a high maximum shrinkage can be obtained. In addition, stretching at 150 ° C or less makes the film surface less susceptible to roughness and improves transparency and gloss.

[0044] The layer structure of the film in the present invention is basically a force composed of at least three layers including both surface layers (X and Z) and an inner layer (M). Any number of layers can be used if used. As long as the characteristics of the present invention are not impaired, one or more layers made of any resin such as polypropylene-based resin and styrene-based resin may be provided as other internal layers. Examples of the layer arrangement include, for example, 3 layers: XZMZZ, 4 layers: XZMI / M2 / Z, 5 layers: XZMlZM2ZM3ZZ, 7 layers: XZM1ZM2ZM3 / M4 / M5 / Z. In addition, it can be composed of 6 layers, 8 layers, and more layers, and other internal layers may be arranged at any position between X and Z. Since the sealing strength is improved, the thickness ratio of the surface layer is preferably 5% or more of the whole film, more preferably 8% or more, and further preferably 10% or more. Since the stretching is stable, the total thickness of the inner layers other than the surface layer is preferably 50% or more, more preferably 55% or more, and still more preferably 60% or more of the entire film. [0045] The obtained film is slit into a predetermined size to obtain a film. The thickness of the film is preferably 5 to 50 m, more preferably 6 m or more for tear resistance during packaging, and 30 μm or less for easy opening after packaging.

[0046] The film of the present invention may contain a surfactant or an antifogging agent. For example, glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, ethylene oxide adduct, and other antifogging agents selected from at least one additive such as liquid paraffin as a plasticizer In the range of 0.1 to 10. Owt%, the processability and the running property of the film during packaging are improved, which is preferable. Especially from the viewpoint of transparency When polyglycerin fatty acid ester, etc. is added to each layer in an amount of 0.5 to 10. Owt%, 0.8 to 6.0% is added from the viewpoint of antistatic properties and slipperiness that are more preferable. Is more preferable. At this time, glycerol fatty acid ester existing on the surface of the unstretched tube will be vaporized at the time of stretching and may volatilize, so the added force to the inner layer more than the surface layer. There are cases.

[0047] In the film used in the present invention, the original characteristics and transparency are not impaired! /, As long as it is within the range, natural silica or synthetic silica, saturated fatty acid amide, unsaturated fatty acid amide, talc as a lubricant. Etc. may be blended. The amount of added force is 0.1 to LOwt%.

[0048] The obtained film is preferably subjected to surface treatment such as corona treatment, ozone treatment or flame treatment because a film suitable for printing applications can be obtained. In this case, it is preferable to add 0.5 to 5. Owt% of glycerin fatty acid ester, etc., perform a corona treatment, and then perform a surface treatment by printing. From the viewpoint of antistatic properties and prevention of ink peeling, the addition amount is more preferably 0.8 to 3. Owt%. Further, as a plasticizer, a tackifier resin may contain petroleum-based resin (for example, Alcon (trademark), Clearon (registered trademark), Imabe (registered trademark), etc.). The addition amount is 0.1 to: If LOwt%, shrinkage and transparency may be improved. Example

[0049] The present invention will be described based on examples.

(1) Measurement of the ratio of heat of fusion

Measurement was performed using an input-compensated differential scanning calorimeter, Diamond DSC (trademark), manufactured by Perkin Elma. Raise approximately lOOmg of film from 0 ° C to 200 ° C in 10 ° CZ minutes. After warming (1st. Melting behavior) and holding at 200 ° C for 1 minute, the temperature was lowered to 0 ° C at 10 ° CZ (1st. Crystallization behavior). Next, the temperature was raised again to 200 ° C in 10 ° CZ minutes (2nd melting behavior), and the heat of fusion at 20 ° C to 100 ° C and 20 ° C to 110 ° C at this time was 20 ° C to melting. The value (%) divided by the heat of fusion within the range until the end was adopted. The sample mass was in the range of 5 to: LOmg.

(2) Measurement of shrinkage rate

A 100 mm square film was placed in an air oven type high-temperature bath set at 100 ° C, 110 ° C, and 120 ° C, and heat-treated for 1 minute each to determine the amount of film shrinkage. The obtained value was expressed as a percentage ratio of the value divided by the original dimension, and the average value in the flow direction and width direction was obtained.

(3) Packaging test

The resulting film was slit to a width of 500 mm, and “FW-3451 A-aV (trade name)” manufactured by Fujikikai Co., Ltd. was used. (Medium) (trade name) "was packed in 30 packs with the film. At this time, heat treatment was performed for 3 seconds in a shrink tunnel set at 130 ° C and 150 ° C, and the packaging finish was evaluated. The temperature of the seal bar at this time was 160 ° C for the upper blade and 120 ° C for the lower blade.

◎ If the package does not have slack in the gutters or corners and the film is completely shrunk, there is no film slack in the corners, and air is trapped between the container lid and the film. The packaging finish is marked as △ if there is a slight sagging of the film on the gavel or corner, or if there is a slight air puddle, and X if there is a slack of the film on the gavel or corner or if the air puddle remains. It was evaluated.

(4) Whitening evaluation of highly contracted parts

Of the packaged body obtained in (3), the corners that are highly shrinkage parts and the periphery of the seal part were observed visually. The transparent one was evaluated as ◯, and the one that was clearly opaque was evaluated as X.

(5) Heat resistance of microwave oven

The package obtained in (3) was refrigerated for 3 hours in a refrigerated showcase at 5 ° C. Next, two of these packages were stacked and heated in a 1600 W commercial microwave oven (manufactured by Sanyo) for 50-60 seconds, and then the microwave oven force was taken out and the fusion between the films was evaluated. “X” indicates that the film is not fused at all, and “X” indicates that the film is fused and the film is torn when peeled off. (6) Container deformation

About 200 g of stew was put in the same container as (3), and the packaged under the same conditions was refrigerated for 3 hours in the refrigerated showcase of (5). Next, the package was heated in a commercial microwave oven (manufactured by Sanyo) for 30 to 40 seconds, and then the deformation of the container was evaluated. The case where the deformation was not at all was evaluated as ◯, and the case where the cover was deformed was evaluated as X.

(7) Measurement of gel fraction

About lOOmg of film was used as a sample, extracted in boiling paraxylene for 12 hours, and the ratio of insoluble content expressed by the following formula was used as a measure of the degree of crosslinking of the film.

Gel fraction (wt%) = (Sample weight after extraction Z Sample weight before extraction) X 100

(8) Molecular weight distribution (Mw / Mn)

As GPC, Nippon Waters GPC equipment 150C type (product name), Tosoh TSK GMH-6 (product name) as column, orthodichlorobenzene (ODCB) as solvent, temperature 135 ° C, flow rate lmlZmin The measurement was performed under the conditions of a concentration of 10 mg ZlOml and a sample flow rate of 500 1 MwZMn was determined from the weight average molecular weight (Mw) and number average molecular weight (Mn) converted from the composition curve of standard polystyrene.

(9) Coffin used in Examples and Comparative Examples

• LL1: Ethylene α-olefin copolymer (polymerized with a single site catalyst), density = 0.913gZcm ³ , MI = 2. OgZlO, melting main peak temperature = 113 ° C, Mw / Mn = 2 . 8

• LL2: Ethylene olefin copolymer (polymerized with a single site catalyst), density = 0.94gZcm ³ , MI = 2. OgZlO content, melting peak temperature = 112 ° C, Mw / Mn = 3. 1

• LL3: Ethylene a-olefin copolymer (polymerized with multisite catalyst), density = 0.916gZcm ³ , melting peak temperature = 121 ° C

• LL4: Ethylene ex-olefin copolymer (polymerized with a single-site catalyst), density = 0.920 gZcm ³ , MI = 1.9 gZl0 min, melting peak temperature = 118 ° C, Mw / Mn = 3. 0

• LL5: Ethylene a-olefin copolymer (polymerized with single site catalyst) Density = 0.915 gZcm ³ , MI = 2. OgZlO min, Main melting peak temperature = 116 ° C, MwZM n = 3.0

• LL6: Ethylene oc-olefin copolymer (polymerized with multisite catalyst), density = 0.926 gZcm ³ , MI = 2. OgZlO content, melting peak temperature = 121 ° C, Mw / M n = 4 . 9

• VL1: Ethylene oc-olefin copolymer (polymerized with a single-site catalyst), density = 0.889 gZcm ³ , MI = 2.2 gZlO, melting main peak temperature = 83 ° C, Mw / Mn = 2. 9

• VL2: Ethylene oc-olefin copolymer (polymerized with a single site catalyst), density 0.888gZcm ³ , MI = 3.6Z10min, melting main peak temperature = 70 ° C, Mw / Mn = 2.1

LD1: High-pressure low-density polyethylene, density = 0.9921 gZcm ³ , MI = 0.4 gZlO, melting main peak temperature = 109 ° C

LD2: High-pressure low-density polyethylene, density = 0.992 gZcm ³ , MI = 1.5 gZl0 min, melting peak temperature = 109 ° C

EVA: Ethylene monoacetate vinylate copolymer, vinyl acetate content = 15 wt%, MI = 1.0 g Z10 min, melting peak temperature = 91 ° C

• EAA: Ethylene-acrylic acid copolymer, comonomer content = 6.5 wt%, MI = 5.5 g ZlO, Vicat soft spot = 85 ° C

• EMA: Ethylene methyl acrylate copolymer, comonomer content = 20wt%, MI = 2.4gZlO min, Vicat softening point = 55 ° C

[Examples 1 to 10]

The resin composition shown in Tables 1-2 was further added with 1.5% by weight of diglycerin fatty acid ester to each layer, and extruded from a circular die as a multilayer raw material. Next, it was cooled and solidified with cold water to produce a tube-shaped original fabric having a folding width of 120 mm and a thickness of 460 m. This was guided to an electron beam irradiation device, irradiated with an electron beam accelerated to 500 kV, and subjected to crosslinking treatment so that the absorbed dose was 80 kGy. While this was reheated in a stretching machine, it was passed between two pairs of differential rolls, and air was injected into the tube material to form bubbles. Stretching The heating temperature at the starting point was set to 140 ° C, and the film was stretched at a magnification of 7 times in the flow direction and 6 times in the width direction to obtain a 11m thick Finolem.

[0052] Both ends of the obtained tube-shaped film were cut and cut into a width of 500 mm to obtain two films. Each piece was wound around a length of 200m with a tension that did not cause wrinkles in a paper roll with a width of 510mm, an inner diameter of 76.2mm, and a thickness of 10mm.

[0053] With the obtained film, each of the PS containers described in (3) is packaged, and the packaging finish (shrinkage of air pockets between the container and the film, small wrinkles, corner residue, etc.) is evaluated, The results are shown in Tables 1 and 2. The obtained package had no corner residue and small wrinkles, and the position of the seal part before and after the package was located below the edge of the container, and it was excellent in transparency even after shrinkage, and a beautiful package was obtained.

[0054] Also, in the microwave heating, there was no deformation of the container without fusion during the two-stage stacking.

[Comparative Examples 1-3]

A film having a thickness of 11 m was obtained in the same manner as in Example 1 with the composition described in Table 3. Evaluation was conducted in the same manner as in Example 1, and the results are shown in Table 4.

[0055] All of the obtained films had a low heat of fusion ratio of 100 to 110 ° C, and the resulting package was insufficiently shrunk at a tunnel temperature of 130 ° C. Even when set to 150 ° C, compared to Examples 1 to 12, there are many small wrinkles and the position of the seal part before and after the package is located above the edge of the container, so that sufficient finish cannot be obtained. I got it.

[Comparative Example 4]

A film having a composition of Table 4 and a thickness of 11 / zm was obtained in the same manner as in Example 1. Evaluation was conducted in the same manner as in Example 1, and the results are shown in Table 4.

[0056] The obtained film had a large melting heat quantity ratio of 100 to 110 ° C, and the obtained packaging body was sufficiently shrunk even at a tunnel temperature setting of 130 ° C, and the packaging finish was also good. However, since the surface layer has a large heat of fusion ratio and is easy to melt, the films are fused when heated in a microwave oven in two layers. In addition, the film had a high shrinkage rate at 100 ° C, so the container was deformed.

[Comparative Example 5]

As shown in Table 4, the same composition as described in Example 7 of Patent Document 1 was used, and Example 1 was used. In the same manner as above, a film having a thickness of 11 m was obtained. Evaluation was carried out in the same manner as in Example 1, and the evaluation results are shown in Table 4.

[0057] The obtained film had a large heat-of-melting ratio of 100 to 110 ° C, and the resulting package was sufficiently shrunk even when the tunnel temperature was set to 130 ° C, and the packaging finish was also good. In order for the heat quantity ratio of the surface layer to satisfy the requirements of the present invention, no fusion between the films was observed even when heated in a microwave oven in two layers. However, due to the large shrinkage of the film at 100 ° C, the container was deformed during microwave heating.

[Comparative Example 6]

A film having a thickness of 11 m was obtained in the same manner as in Example 1 using the same composition as that described in Example 1 of Patent Document 2. The evaluation results are shown in Table 4. The resulting film does not use high-pressure low-density polyethylene, so it is not effectively oriented, and the shrinkage rate of the film at 120 ° C is low. The position of the line was not lowered, and the packaging finish was inferior.

[Comparative Example 7]

As shown in Table 4, a film having a thickness of 11 m was obtained in the same manner as in Example 1 using the same composition as that described in Example 4 of Patent Document 2. Evaluation was carried out in the same manner as in Example 1, and the evaluation results are shown in Table 4.

[0058] Since the obtained film has a high density of the ethylene α-olefin copolymer used for the inner layer, small wrinkles remain on the film after shrinkage, and the position of the seal part before and after the package is the edge of the container. It was located above and the packaging finish was inferior.

[0059] [Table 1]

[] [

] (2006

Industrial applicability

The film of the present invention is suitable for packaging in the field of food packaging, and can be particularly suitably used for packaging such as lunch boxes and side dishes that are reheated in a microwave oven.

Claims

Claims [1] At least three layers comprising a surface layer and an inner layer, wherein at least one of the surface layers comprises an ethylene α-olefin copolymer having a density of 0.900 to 0.918 gZcm3, The inner layer consists of an ethylene a-olefin copolymer having a density of 0.910 to 0.920 g / cm3, a high-pressure low-density polyethylene, an ethylene vinyl acetate copolymer, an ethylene aliphatic unsaturated carboxylic acid copolymer, and an ethylene fat. A heat-shrinkable multilayer characterized by comprising 50 to L00 wt% of the following (1) and (2): a composition comprising at least one resin selected from an aliphatic unsaturated carboxylic acid ester copolymer the film.

(1) The resin constituting the surface layer has a specific force of 0 to 75% of the heat of fusion of 100 ° C or less to the total heat of fusion of the surface layer in the second melting behavior of the differential scanning calorimeter.

(2) The film is a differential scanning calorimeter 2nd. In the melting behavior, the ratio of the heat of fusion of 110 ° C or less with the ratio of the heat of fusion of 100 ° C or less to 5% or more of the total heat of fusion of the film Is over 70%

[2] The heat-shrinkable multilayer polyolefin according to claim 1, wherein the inner layer contains an ethylene α-olefin copolymer having a density of 0.910 to 0.920 gZcm ³ and a high-pressure low-density polyethylene of 50 to L00 wt%.

[3] Differential scanning calorimeter of the whole film 2nd. In the melting behavior, the ratio of the heat of fusion at 100 ° C or lower to the total heat of fusion is 45 to 65% or lower, and the heat of fusion at 110 ° C or lower The heat-shrinkable multilayer film according to claim 1 or 2, wherein the ratio of is at least 70%.

[4] The heat-shrinkable multilayer film according to claim 3, wherein the shrinkage ratio of the film is 0% or more and less than 30% at 100 ° C, 30% or more at 110 ° C, and 68% or more at 120 ° C.

[5] The gel fraction of the resin constituting the surface layer is 1 to 20 wt%, the gel fraction of the entire film is ˜50 wt%, and the gel fraction of the resin of the surface layer and the resin of the inner layer The heat-shrinkable multilayer film according to claim 4, which has a specific force of 2: 1 to 1:20.

6. The heat-shrinkable multilayer film according to claim 5, wherein the molecular weight distribution (Mw / Mn) of the ethylene α-olefin copolymer in the surface layer is 3.5 or less.