JP5854543B1 - Heat-shrinkable film, multilayer heat-shrinkable film, and production method thereof - Google Patents

Abstract

A heat-shrinkable film suitable for accumulation packaging of contents (packages), which has excellent heat-shrinkability in the TD direction, exhibits excellent breaking strength, and can be easily manufactured. I will provide a. A heat shrink film containing a total of 100 parts by mass of linear low-density polyethylene and low-density polyethylene and 5 to 100 parts by mass of a cyclic olefin polymer, (1) the linear low-density polyethylene A sea-island structure in which a sea part containing density polyethylene and the low-density polyethylene and an island part containing the cyclic olefin polymer are formed, and (2) the heat-shrinkable film is formed in a film winding direction (MD In the MD cross section formed by cutting in a direction parallel to the direction), the aspect ratio (A) of the island portion and the direction perpendicular to the film winding direction (MD direction) (TD direction) are formed. The ratio (A) / (B) to the aspect ratio (B) of the island part in the TD cross section is 1 or less, and (3) the length in the thickness direction (ZD direction) of the island part in the TD cross section is Heat shrinkable film comprising at 0.5μm or less, that. [Selection figure] None

Description

  The present invention relates to a heat-shrinkable film, a multilayer heat-shrinkable film, and a method for producing them. The heat-shrinkable film can be used, for example, for applications in which accumulated products (can beverages, plastic bottle beverages, paper-packed beverages, etc.) are wrapped and heat-shrinkable film is shrunk by heat treatment and accumulated.

  Conventionally, canned beverages, plastic bottle beverages, paper-packed beverages and the like have been transported in a form that is easy to circulate in units of 24 cans, 6 bottles, etc., and have been opened at retail stores and arranged in stores. However, there is a problem that a large amount of cardboard must be disposed after unpacking. In recent years, there are increasing cases where consumers purchase cardboards at mass merchandise stores and take them home, and disposal of cardboards at home has become a problem.

  In view of the above problems, a method for collecting and packaging products with a heat-shrinkable film that is inexpensive and easy to dispose of has been proposed, but a heat-shrinkable film that satisfies the properties of binding force (heat-shrinkability) and strength has not been obtained. is the current situation.

As the heat shrinkable film, for example, Patent Document 1 discloses that “the core layer is made of a resin composition containing a linear ultra-low density polyethylene resin having a density of 0.860 to 0.910 g / cm ³ , and a surface layer. However, a polyethylene heat-shrinkable film comprising a resin composition containing a linear low-density polyethylene resin having a density exceeding 0.910 g / cm ³ and a cyclic olefin resin is disclosed. This heat-shrinkable film has enhanced binding force by using a resin composition containing a linear low-density polyethylene resin in the surface layer.

  However, when a linear low density polyethylene resin is used, in order to obtain a heat-shrinkable film having a large shrinkage rate, a process of biaxial stretching is required, which requires special equipment and is easy to manufacture. There is a problem that can not be.

  Further, in the formation of a heat-shrinkable film by the inflation method, when a linear low-density polyethylene resin is used, the heat-shrinkability in the TD direction is extremely lowered. The heat-shrinkable film of Patent Document 1 has a problem that the heat-shrinkability in the TD direction, that is, the binding property is not sufficient.

  Furthermore, the heat-shrinkable film of Patent Document 1 has a problem that the breaking strength is not sufficient and it cannot be used for collecting and packing heavy objects.

Japanese Patent No. 4555438

  The present invention has been made in view of the above problems, and is a heat-shrinkable film suitable for stacking the contents (packaged items), having excellent heat-shrinkability in the TD direction, and excellent breaking strength. An object of the present invention is to provide a heat shrinkable film and a multilayer heat shrinkable film that can be easily manufactured.

  As a result of intensive studies to achieve the above object, the present inventor has obtained a heat containing a total of 100 parts by mass of linear low-density polyethylene and low-density polyethylene and 5 to 100 parts by mass of a cyclic olefin polymer. In the shrink film, it has a sea-island structure and is cut in a direction parallel to the film winding direction (MD direction) of the heat shrink film, and the aspect ratio (A) of the island portion in the MD cross section is formed. The ratio (A) / (B) to the aspect ratio (B) of the island part in the TD cross section formed by cutting in the direction (TD direction) perpendicular to the (MD direction) is 1 or less, and in the TD cross section And the length of the island portion in the thickness direction (ZD direction) is 0.5 μm or less, and the dispersion state of the cyclic olefin polymer is controlled, and the above object can be achieved. This has led to the completion of the present invention.

That is, the present invention relates to the following heat shrink film, multilayer heat shrink film, and methods for producing them.
1. A heat-shrinkable film containing a total of 100 parts by mass of linear low-density polyethylene and low-density polyethylene, and 5 to 100 parts by mass of a cyclic olefin polymer,
(1) It has a sea-island structure in which a sea part containing the linear low-density polyethylene and the low-density polyethylene and an island part containing the cyclic olefin polymer are formed,
(2) The aspect ratio (A) of the island part in the MD cross section formed by cutting the heat shrink film in a direction parallel to the film winding direction (MD direction), and the film winding direction (MD direction) A ratio (A) / (B) with an aspect ratio (B) of the island portion in a TD cross section formed by cutting in a direction perpendicular to the direction (TD direction) is 1 or less,
(3) The length in the thickness direction (ZD direction) of the island part in the TD cross section is 0.5 μm or less.
A heat shrinkable film characterized by the above.
2. Item 2. The heat shrinkable film according to Item 1, wherein the cyclic olefin polymer is at least one selected from a cycloolefin homopolymer and an ethylene-cycloolefin copolymer.
3. A multilayer heat shrinkable film having at least one heat shrinkable film according to item 1 or 2,
The multilayer heat-shrinkable film, wherein the thickness of the heat-shrinkable film is 20% or more of the total thickness of the multilayer heat-shrinkable film.
4). A manufacturing method for manufacturing the heat-shrinkable film according to item 1 or 2 or the multilayer heat-shrinkable film according to claim 3 by an inflation method,
The blow ratio is 2 to 6, and the diameter (inner diameter) of the annular die lip is D. The bubble diameter of the heat shrink film or the multilayer heat shrink film at the same height as D from the end of the annular die lip is 2D. Is
The manufacturing method characterized by the above-mentioned.

  The heat-shrinkable film of the present invention has a sea-island structure in a heat-shrinkable film containing a total of 100 parts by mass of linear low-density polyethylene and low-density polyethylene, and 5 to 100 parts by mass of a cyclic olefin polymer, The aspect ratio (A) of the island part in the MD cross section formed by cutting in the direction parallel to the film winding direction (MD direction) of the heat shrink film, and the direction (TD direction) perpendicular to the film winding direction (MD direction) The ratio (A) / (B) to the aspect ratio (B) of the island portion in the TD cross section formed by cutting into TD cross section is 1 or less, and the thickness direction (ZD direction) of the island portion in the TD cross section is 1 or less. Since the length is 0.5 μm or less, it is suitable for accumulation packaging of contents (packaged items), has excellent heat shrinkability in the TD direction, and exhibits excellent breaking strength. Can do.

  The multilayer heat-shrinkable film of the present invention has a configuration in which the heat-shrinkable film has at least one layer, and the thickness of the heat-shrinkable film is 20% or more of the total thickness of the multilayer heat-shrinkable film. Therefore, similarly to the above heat shrink film, it is suitable for accumulation packaging of contents (packages), has excellent heat shrinkability in the TD direction, and can exhibit excellent breaking strength.

  Furthermore, in the production method of the present invention, when the heat shrinkable film and the multilayer heat shrinkable film are produced by an inflation method, the blow ratio is 2 to 6, and the diameter (inner diameter) of the annular die lip is D. Since the bubble diameter of the heat-shrinkable film or multilayer heat-shrinkable film at the same height as D from the end of the film is 2D or less, it is possible to easily produce the heat-shrinkable film and multilayer heat-shrinkable film having the above-mentioned characteristics. is there.

It is a schematic diagram which shows an example of the manufacturing method of the heat shrink film of this invention. It is a schematic diagram of the heat shrink film of this invention in which MD cross section and TD cross section were formed. It is a schematic diagram which shows an example of the manufacturing method of this invention. It is a schematic diagram which shows a cyclic | annular die lip. It is an enlarged photograph by TEM of the MD cross section of the heat-shrink film of Example 2 which performed image processing. It is an enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 2 which performed image processing. It is an enlarged photograph by TEM of the MD cross section of the heat-shrink film of Example 3 which performed image processing. It is an enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 3 which performed image processing. It is an enlarged photograph by TEM of the MD cross section of the heat-shrink film of Example 3 before performing image processing. It is an enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 3 before performing image processing.

The heat shrink film of the present invention is a heat shrink film containing a total of 100 parts by mass of linear low density polyethylene and low density polyethylene, and 5 to 100 parts by mass of a cyclic olefin polymer,
(1) It has a sea-island structure in which a sea part containing the linear low-density polyethylene and the low-density polyethylene and an island part containing the cyclic olefin polymer are formed,
(2) The aspect ratio (A) of the island part in the MD cross section formed by cutting the heat shrink film in a direction parallel to the film winding direction (MD direction), and the film winding direction (MD direction) A ratio (A) / (B) with an aspect ratio (B) of the island portion in a TD cross section formed by cutting in a direction perpendicular to the direction (TD direction) is 1 or less,
(3) The length in the thickness direction (ZD direction) of the island portion in the TD cross section is 0.5 μm or less.

  The heat-shrinkable film of the present invention having the above characteristics is excellent in heat shrinkability because it contains 100 parts by mass of linear low-density polyethylene and low-density polyethylene and 5 to 100 parts by mass of a cyclic olefin polymer. At the same time, it exhibits excellent breaking strength. In the heat shrinkable film of the present invention, the ratio (A) / (B) of the aspect ratio (A) of the island part in the MD cross section and the aspect ratio (B) of the island part in the TD cross section is 1 or less, Moreover, since the length in the thickness direction (ZD direction) of the island portion in the TD cross section is 0.5 μm or less, the heat shrinkability in the TD direction is excellent.

  Further, the multilayer heat shrinkable film of the present invention has at least one heat shrinkable film having the above-described configuration, and the thickness of the heat shrinkable film is 20% or more of the total thickness of the multilayer heat shrinkable film. In the same manner as above, it is suitable for the integrated packaging of contents (packages), has excellent heat shrinkability in the TD direction, and exhibits excellent breaking strength.

  Furthermore, the production method of the present invention comprises producing the above heat shrinkable film or multilayer heat shrinkable film by an inflation method, wherein the blow ratio is 2 to 6, and the diameter (inner diameter) of the annular die lip is D. Since the bubble diameter of the heat-shrinkable film or the multilayer heat-shrinkable film at the same height as D from the end of the film is 2D or less, the island containing the cyclic olefin polymer is oriented in the TD direction, Excellent heat shrinkability. Therefore, according to the production method of the present invention, the heat shrinkable film and the multilayer heat shrinkable film containing the linear low density polyethylene and exhibiting excellent breaking strength are excellent in the heat shrinkability in the TD direction, and the contents It becomes possible to easily manufacture the heat shrinkable film and the multilayer heat shrinkable film suitable for integrated packaging of (packaged items).

  Hereinafter, the heat-shrinkable film, multilayer heat-shrinkable film of the present invention and methods for producing them will be described.

1. Heat Shrink Film The heat shrink film of the present invention contains a total of 100 parts by mass of linear low density polyethylene and low density polyethylene, and 5 to 100 parts by mass of a cyclic olefin polymer.

  The linear low-density polyethylene (hereinafter also referred to as “LLDPE”) can be obtained by copolymerizing ethylene and α-olefin using a single-site catalyst such as a Ziegler catalyst or a metallocene catalyst, The density range can be controlled by adjusting the type and amount of α-olefin.

  Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like. These α-olefins can be used alone or in combination of two or more.

Products with a LLDPE density in the range of 0.870 to 0.945 g / cm ³ are commercially available. The density of the LLDPE is preferably from .900 to .945 / cm ^3, more preferably from 0.910 to 0.945 / cm ^3. In addition, the density in this specification is the value measured on the conditions of JIS K7112: 1999 underwater substitution method (A method) and 25 degreeC.

  Further, if the MFR of LLDPE is too small, the film forming property becomes unstable, and if it is too large, the excellent binding property (heat shrinkability) of the heat shrinkable film cannot be obtained, so 0.05 to 2.0 g / 10 min. Is preferable, and 0.1 to 1.2 g / 10 min is more preferable. In addition, MFR in this specification is the value measured on condition of JISK7210: 1999, A method, 190 degreeC, and load 21.18N.

The low density polyethylene (hereinafter also referred to as “LDPE”) is a polyethylene resin (homopolyethylene) having a density in the range of 0.910 to 0.930 g / cm ³ , for example, a high-pressure radical using a radical initiator. What is manufactured by superposition | polymerization is mentioned. The density of LDPE is preferably from 0.915-.930 / cm ^3, more preferably from 0.920 to 0.930 / cm ^3. Moreover, in order to obtain the excellent binding property (heat shrinkability) and film forming stability of the heat shrinkable film, the melt flow rate (MFR) of LDPE is preferably 0.05 to 2.0 g / 10 min. .1 to 1.2 g / 10 min is more preferable.

  The heat-shrinkable film of the present invention only needs to contain 100 parts by mass of the total of LLDPE and LDPE. For example, the heat-shrinkable film may contain 100 parts by mass of LLDPE without containing LDPE. The structure which contains 100 mass parts of LDPE without doing may be sufficient. That is, the heat-shrinkable film of the present invention may have a content of at least one selected from LLDPE and LDPE of 100 parts by mass.

  The heat-shrinkable film of the present invention preferably contains 30 parts by mass or more, more preferably 35 parts by mass or more of LLDPE. Further, the content of LDPE in the heat shrinkable film of the present invention is preferably 70 mass parts or less, and more preferably 65 mass parts or less.

  As long as the heat shrink film of the present invention contains 100 parts by mass of the total of LDPE and LLDPE, as long as the effects of the present invention are exhibited, the film may contain other polyethylene resins. As such other polyethylene resin, for example, high density polyethylene (HDPE) or the like can be used. Said other polyethylene-type resin can be used individually or in mixture of 2 or more types. In the present specification, the other polyethylene resin means that at least HDPE is included in the concept, and the cyclic olefin polymer described later is not included in the concept.

  In the present invention, it is preferable to use LLDPE alone or a mixture of LDPE and LLDPE.

  The cyclic olefin polymer is not particularly limited as long as it contains a cyclic olefin in the polymer. A cycloolefin homopolymer (hereinafter also referred to as “COP”), an ethylene-cycloolefin copolymer (hereinafter referred to as “COP”). , Also indicated as “COC”). It is more preferable to use COC in that the heat shrinkability in the TD direction of the heat shrink film can be further improved.

The ethylene-cyclic olefin copolymer is not limited, but if the ethylene content as a monomer component is 25% by mass or more and the glass transition point (Tg) is 120 ° C. or less, a polyethylene resin such as LDPE or LLDPE Dispersibility in the TD direction is improved, and heat shrinkability in the TD direction is improved, which is preferable. The density of the ethylene-cyclic olefin copolymer is preferably about 0.95 to 1.05 g / cm ³ , and the MFR measured at 190 ° C. and 21.18 N is preferably about 0.05 to 4.0 g / 10 minutes.

Examples of the cyclic olefin as the monomer component include vinylcycloalkanes and derivatives thereof having a cycloalkane having 3 to 20 carbon atoms, monocycloalkenes and derivatives thereof having 3 to 20 carbon atoms, and bicyclo [2.2. 1] -2-heptene (norbornene) and its derivatives, tricyclo [4.3.0.1 ^2,5 ] -3-decene and its derivatives, tetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene and its derivatives, pentacyclo [6.5.1.1 ^3,6 . 0 ^2,7 . 0 ^9,13] -4-pentadecene and its derivatives, pentacyclo [7.4.0.1 ^2,5. 1 ^9,12 . 0 ^8,13] -3-pentadecene and its derivatives, pentacyclo [8.4.0.1 ^2,5. 1 ^9,12 . 0 ^8,13] -3-hexadecene and its derivatives, pentacyclo [6.6.1.1 ^{3, 6.} 0 ^2,7 . 0 ^9,14] -4-hexadecene and derivatives thereof, hexacyclo [6.6.1.1 ^{3, 6.} 1 ^10,13 . 0 ^2,7 . 0 ^9,14] -4-heptadecene and its derivatives, heptacyclo [8.7.0.1 ^2,9. 1 ^4,7 . 1 ^{11, 17} . 0 ^3,8 . 0 ^12,16 ] -5-eicosene and its derivatives, heptacyclo [8.7.0.1 ^3,6 . 1 ^{10, 17} . 1 ^{12, 15} . 0 ^2,7 . 0 ^11,16 ] -4-eicosene and its derivatives, heptacyclo [8.8.0.1 ^2,9 . 1 ^4,7 . 1 ^{11, 18} . 0 ^3,8 . 0 ^12,17 ] -5- ^Heneicosene and its derivatives, octacyclo [8.8.0.1 ^2,9 . 1 ^4,7 . 1 ^{11, 18} . 1 ^13,16 . 0 ^3,8 . 0 ^12,17] -5-docosene and its derivatives, Nonashikuro [10.9.1.1 ^{4, 7.} 1 ^13,20 . 1 ^{15, 18} . 0 ^2,10 . 0 ^3,8 . 0 ^{12, 21} . 0 ^14,19] -5-pentacosene and its derivatives. The cyclic olefin may be subjected to hydrogenation treatment as disclosed in JP-A-2007-291364.

Examples of the ethylene-cyclic olefin copolymer include ethylene-bicyclo [2.2.1] -2-heptene copolymer, tricyclo [4.3.0.1 ^2,5 ] -3-decene-ethylene copolymer. Polymer, tetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene-ethylene copolymer and the like. In addition, as the ethylene-cyclic olefin copolymer, commercially available products may be used, for example, Apel (trade name) manufactured by Mitsui Chemicals, Inc. TOPAS (trade name) manufactured by Topas Advanced Polymers GmbH, etc. It is done.

The cycloolefin homopolymer is not particularly limited, and if the glass transition point (Tg) is 120 ° C. or less, the dispersibility in polyethylene resins such as LDPE and LLDPE is improved, and the heat shrinkability in the TD direction is improved. Therefore, it is preferable. The density of the cycloolefin homopolymer is preferably about 0.95 to 1.05 g / cm ³ , and the MFR measured at 190 ° C. at 21.18 N is preferably about 0.05 to 4.0 g / 10 minutes.

  Examples of commercially available cycloolefin homopolymers include ZEONOR (trade name) manufactured by Nippon Zeon Co., Ltd., Arton (trade name) manufactured by JSR Corporation, and the like.

  The said cyclic olefin type polymer may be used independently, and 2 or more types may be mixed and used for it.

  In this invention, content of a cyclic olefin type polymer should just be 5-100 mass parts with respect to a total of 100 mass parts of linear low density polyethylene and low density polyethylene, and 20-80 mass parts is preferable. 30-60 mass parts is more preferable. In addition, in the multilayer heat-shrink film of this invention mentioned later, content of a cyclic olefin polymer should just be in the said range in the said heat-shrink film of at least 1 layer which comprises a multilayer heat-shrink film. In this case, when the thickness of the heat-shrinkable film is 20% or more of the total thickness of the multilayer heat-shrinkable film, a more excellent shrinkage rate can be exhibited in the TD direction of the multilayer heat-shrinkable film.

The heat shrinkable film of the present invention has a sea-island structure in which a sea part containing the linear low-density polyethylene and the low-density polyethylene and an island part containing the cyclic olefin polymer are formed. The above-mentioned sea-island structure is obtained by dyeing a heat-shrinkable film with RuO ₄ and then cutting the heat-shrinkable film, and observing the cut surface with a transmission electron microscope (TEM) at an observation magnification of 1000 to 10,000 times. Can be confirmed by shooting. In the TEM image, the cyclic olefin polymer is dyed with RuO ₄ and appears black.

  The sea part may contain other resins as long as it contains linear low-density polyethylene and low-density polyethylene, but preferably contains these resins as main components. In the present specification, the main component means a component having the largest content (preferably a component having a content exceeding 50% by weight). 80 mass% or more is preferable and, as for content of the linear low density polyethylene of a sea part, and the said low density polyethylene, 90 mass% or more is more preferable.

  The island part may contain other resins as long as it contains a cyclic olefin polymer, but preferably contains a cyclic olefin polymer as a main component. 80 mass% or more is preferable and, as for content of the cyclic olefin polymer of an island part, 90 mass% or more is more preferable.

  The heat-shrinkable film of the present invention includes an aspect ratio (A) of the island part in the MD cross section formed by cutting in a direction parallel to the film winding direction (MD direction), and the film winding direction (MD direction). The ratio (A) / (B) to the aspect ratio (B) of the island part in the TD cross section formed by cutting in the vertical direction (TD direction) is 1 or less.

  The MD cross section and the TD cross section will be described with reference to the drawings. FIG. 1 is a schematic view of a production method for producing the heat shrink film of the present invention by an inflation method. In FIG. 1, a heat shrinkable film 1 of the present invention is extruded from the annular die lip of a circular die 2 upward from the bottom of the paper, that is, in the direction of a dotted arrow 3, and wound up in a subsequent process. At this time, the film is stretched in the direction of the dotted line 4 at a specific blow ratio. In the heat-shrinkable film of the present invention, the film winding direction (MD direction) is the direction of dotted line 3, and the cross section formed by cutting in the direction parallel to the MD direction is the MD cross section. In the heat-shrinkable film of the present invention, the direction perpendicular to the film winding direction (MD direction) (TD direction) is the direction of dotted line 4, and the cross section formed by cutting in the TD direction is a TD cross section. is there.

  In FIG. 2, the schematic diagram of the heat shrink film of this invention in which MD cross section and TD cross section were formed is shown. In FIG. 2, the heat-shrinkable film 1 of the present invention is cut in the direction parallel to the dotted line 3 indicating the MD direction to form an MD cross section 5 and is cut in the direction of the dotted line 4 indicating the TD direction to form a TD cross section 6. Has been. In FIG. 2, the heat shrink film 1 of the present invention has a sea-island structure in which a sea part 7 and an island part 8 are formed.

  The heat-shrinkable film of the present invention has an aspect ratio (A) of the island part in the MD cross section formed by cutting in a direction parallel to the film winding direction (MD direction), and the film winding direction (MD direction). The ratio (A) / (B) to the aspect ratio (B) of the island part in the TD cross section formed by cutting in the vertical direction (TD direction) is 1 or less. When the ratio (A) / (B) exceeds 1, the heat shrinkability of the heat shrink film in the TD direction is lowered, and the binding force in the TD direction is not sufficient. The ratio (A) / (B) is preferably 0.9 or less, and more preferably 0.8 or less. The lower limit of the ratio (A) / (B) is not particularly limited, but is preferably 0.1 or more.

  In the heat-shrinkable film of the present invention, the length of the island part in the thickness direction (ZD direction (film thickness direction)) in the TD cross section is 0.5 μm or less. When the length of the island part in the ZD direction in the TD cross section exceeds 0.5 μm, the dispersion of the island part becomes insufficient and the breaking strength is lowered. The length in the ZD direction of the island part in the TD cross section is preferably 0.3 or less, and more preferably 0.2 or less. Moreover, the lower limit of the length in the ZD direction of the island part in the TD cross section is not particularly limited, but is preferably 0.01 or more.

  In this specification, the aspect ratio (A) of the island part in the MD cross section, the aspect ratio (B) of the island part in the TD cross section, and the length of the island part in the ZD direction in the TD cross section are measured by the following measuring methods. The value to be measured.

First, a heat shrink film or a multilayer heat shrink film is dyed with RuO ₄ and then cut. The cut surface is observed with a transmission electron microscope (TEM) at an observation magnification of 1000 to 10,000 times, and an enlarged photograph is taken. The cyclic olefin polymer phase (hereinafter also referred to as “COC phase”) is stained with RuO ₄ and is photographed in black by an enlarged photograph by TEM. At this time, the observation magnification may be adjusted to a magnification at which the dispersed structure of the cyclic olefin polymer can be discriminated and 30 to 500 dispersed phases can be confirmed in the photograph.

  Next, the aspect ratio of the COC phase is calculated in the enlarged photograph. The aspect ratio of the island part of the COC phase is the length of the MD or TD direction passing through the center of gravity of the dispersed phase and ZD (thickness direction) using “WinROOF Ver5.03” which is image processing software made by Mitani Corporation. It can be calculated as a ratio of lengths.

  Using the above “WinROOF Ver5.03”, the aspect ratio (A) of the island part in the MD cross section when the cyclic olefin polymer forms the island part and the LDPE and LLDPE form the sea part, TD cross section A method for calculating the aspect ratio (B) of the island portion in FIG. 3 and the length of the island portion in the ZD direction in the TD cross section will be described in detail below.

First, a pretreatment for accurately extracting the COC phase stained black with RuO ₄ is performed.

(I) Extraction of unstained polyethylene layer The “image processing”, “intensity”, “lookup table conversion”, and “brightness extraction” commands are sequentially executed, and the parameters are set to 128 to 255. The COC phase dyed black by the above command has a density of 0 and is uniformly separated white.

(Ii) Binarization “Binary processing” and “binarization with a single threshold” are executed with the threshold set to 100. This binarizes the COC phase to white and the polyethylene layer to black.

  (Iii) “Image processing”, “emphasis”, and “inversion” commands are executed. As a result, white and black are reversed to change the COC phase to black and the polyethylene phase to white.

(Iv) Noise removal “Binary processing” and “deletion” are executed with the threshold set to 1 or less. Thereby, the noise on the black spots in the polyethylene resin layer is removed. The threshold value is designated while checking the image according to the photographing magnification.

  Subsequently, the process which smoothes the shape of a phase is performed.

  (V) Perform “binary processing” and “expansion” twice. This fills in the blank areas and the indentations in the area.

  (Vi) Perform “binary processing” and “shrink” twice. As a result, the protrusion is removed and returned to the size before expansion.

  Finally, shape analysis is performed to determine the cutting length.

  (Vii) “Measurement” and “shape feature” are performed, and “cutting length” is selected and executed. Thereby, the maximum length and the minimum length passing through the center of gravity of the region are calculated.

In the measurement method, since the film cross section is observed, the minimum length of the island portion is substantially the ZD cut length of the island portion. In the MD cross section, the maximum length of the island portion is the MD cut length of the island portion, TD. In the cross section, the maximum length of the island portion is the TD cut length of the island portion. From the MD cut length, TD cut length, and ZD cut length, the aspect ratio (A) of the island part in the MD cross section and the aspect ratio (B) of the island part in the TD cross section were calculated by the following formulas.
Aspect ratio of island part in MD cross section (A) = MD cut length / ZD cut length Aspect ratio of island part in TD cross section (B) = TD cut length / ZD cut length Setting parameters for binarization of the above COC phase Can be appropriately changed according to the contrast of the enlarged photograph and set so that shape analysis can be performed.

  The calculation of the aspect ratio of the COC phase is performed using “cutting length” as binarization processing and shape analysis prepared in each image processing software even when image processing software other than “WinROOF Ver5.03” is used. This can be done by performing an equivalent measurement. Examples of the image processing software include “analySIS FIVE” commercially available from Olympus Corporation, “Image Pro AMS” commercially available from Nippon Rover, “Image J” commercially available from NIH Image, and Sumitomo. Image processing software such as “particle analysis” commercially available from Metal Technology Co., Ltd. and “general-purpose image analysis software” commercially available from ImageSense.

  20-100 micrometers is preferable and, as for the thickness of the heat shrink film of this invention, 25-80 micrometers is more preferable. If the thickness of the heat-shrinkable film is too thick, the heat-shrinkability may be reduced, and if it is too thin, the breaking strength of the heat-shrinkable film may not be sufficient.

2. Multilayer Heat Shrink Film The multilayer heat shrink film of the present invention has at least one layer of the heat shrink film, and the thickness of the heat shrink film is 20% or more of the total thickness of the multilayer heat shrink film. What was demonstrated above is used as a heat shrink film.

  The multilayer heat-shrinkable film of the present invention is not particularly limited as long as the heat-shrinkable film has the above-mentioned heat-shrinkable film. For example, other layers as inner and outer layers are provided on both sides of the heat-shrinkable film as an intermediate layer. The structure which equips one side of the said heat contraction film with the other layer, the structure provided with the said heat shrink film as an inner layer and an outer layer on both surfaces of the other resin layer as an intermediate | middle layer may be sufficient.

  The other layer laminated with the heat shrink film is not particularly limited, and examples thereof include a layer mainly composed of LDPE, a layer mainly composed of LLDPE, a layer composed of LDPE, a layer composed of LLDPE, and the like. Are preferably used.

  In the multilayer heat shrinkable film of the present invention, the thickness of the heat shrinkable film is 20% or more of the total thickness of the multilayer heat shrinkable film. When the thickness of the heat shrinkable film is less than 20% of the total thickness of the multilayer heat shrinkable film, the heat shrinkability in the TD direction cannot be exhibited sufficiently. The thickness of the heat shrink film is preferably 25% or more, more preferably 30% or more of the total thickness of the multilayer heat shrink film.

  20-100 micrometers is preferable and, as for the total thickness of the multilayer heat shrink film of this invention, 25-80 micrometers is more preferable. If the total thickness of the multilayer heat shrinkable film is too thick, the heat shrinkability may be reduced, and if it is too thin, the breaking strength of the multilayer heat shrinkable film may not be sufficient.

3. Production method of heat-shrinkable film and multilayer heat-shrinkable film The production method of the present invention is a production method for producing the above heat-shrinkable film or multilayer heat-shrinkable film by an inflation method, and has a blow ratio of 2 to 6, and The diameter (inner diameter) of the annular die lip is D, and the bubble diameter of the heat shrink film or the multilayer heat shrink film at the same height as D from the end of the annular die lip is 2D or less. The manufacturing method of this invention is demonstrated using figures. In the following description using FIGS. 3 and 4, the case of the method for producing a heat-shrinkable film will be described as an example, but the method for producing a multilayer heat-shrinkable film is also substantially the same.

  FIG. 3 is a schematic view showing an example of the production method of the present invention, and FIG. 4 is a schematic view showing an annular die lip. In FIG. 3, the heat-shrinkable film 1 of the present invention is extruded from the annular die lip of the circular die 2 from the bottom to the top of the paper, that is, in the direction of the dotted arrow 3, and is wound up in a subsequent step.

  In the manufacturing method of the present invention, as shown in FIG. 4, when the diameter (inner diameter) of the annular die lip of the circular die 2 is D, the same height as D from the end 21 of the die lip in FIG. The diameter of the cylindrical heat-shrink film 1 at the same height as D from the end 21 of the die lip to the upper side of the paper, that is, the bubble diameter L1 is 2D or less. When the bubble diameter exceeds 2D, the heat shrinkability in the TD direction of the heat shrink film and the multilayer heat shrink film is not sufficient. The bubble diameter is preferably 1.8 D or less. The bubble diameter is preferably 1.1D or more. If the bubble diameter is too small, the heat shrinkability of the heat shrink film and the multilayer heat shrink film in the TD direction may not be sufficient. The above “the same height as D” is a position away from the end 21 of the die lip by the same distance as D in the normal direction from the plane including the end 21 of the die lip.

3 and 4, the heat shrink film 1 is stretched in the direction of the dotted line 4 at a blow ratio of 2-6. In addition, the said blow ratio is the circle | round | yen of the circumference (t1) of the heat shrink film 1 in the edge part 21 of a die lip in FIG. 3, and the heat shrink film 1 above a paper surface rather than the frost line L2 in FIG. It is a ratio obtained by calculating the ratio with the circumferential length (t2) by the following equation.
(Blow ratio) = (t2) / (t1)
When the blow ratio is less than 2, the heat shrinkability in the TD direction of the heat shrink film and the multilayer heat shrink film is not sufficient. When the blow ratio exceeds 6, stretching stability is deteriorated, and film breakage or the like occurs. The blow ratio is preferably 2.2 to 5.5, and more preferably 3.0 to 5.5.
The shrinkage ratio in the TD direction of the heat shrinkable film of the present invention is preferably 20% or more in practical use, and the blow ratio is preferably 3.0 or more so that the shrinkage ratio falls within the range. .

  The temperature of inflation molding should just be more than melting | fusing point of LLDPE and LDPE, Preferably, it is melting | fusing point +40 degreeC-melting | fusing point +80 degreeC. Specifically, 160 to 200 ° C. is preferable.

  If the temperature of inflation molding is less than the melting point of LLDPE and LDPE + 40 ° C., these resins may not be in a sufficiently molten state, and there is a possibility that melt film formation by inflation molding cannot be performed. On the other hand, when the temperature of inflation molding exceeds the melting point of LLDPE and LDPE + 80 ° C., melt film formation is possible, but there is a risk that resin degradation will be accelerated. In the present specification, the melting point is a value measured by differential scanning calorimetry in accordance with JIS K7121.

  The heat-shrinkable film and multilayer heat-shrinkable film of the present invention are excellent in heat shrinkability in the TD direction and exhibit excellent breaking strength, and therefore can be suitably used for packaging, particularly for integrated packaging. In particular, it can be suitably used for collecting and packaging relatively heavy articles such as PET bottles and can drinks.

  Moreover, the manufacturing method of this invention can manufacture a heat shrink film and a multilayer heat shrink film provided with the said characteristic easily.

  The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the scope of the examples.

The following raw materials were used as raw materials for preparing the heat-shrinkable film or multilayer heat-shrinkable film, and the heat-shrinkable films or multilayer heat-shrinkable films of Examples and Comparative Examples were prepared by the following method.
(material)
- LDPE (manufactured by Asahi Kasei Corporation, Suntec M2204, MFR = 0.4g / 10 min, density 0.922g / cm ³⁾ · LLDPE (Dow Chemical Elite 5100, MFR = 0.85g / 10 min, density 0.920 g / cm ³⁾ · COC (manufactured by Mitsui Chemicals APL6509T, MFR = 3.5g / 10 min, density 1.02g / cm ³⁾ · COC (Polyplastics Co. TOPAS 9506F-500, MFR = 1g / 10 min, density 1.01 g / cm ³⁾

Examples 1-6 and Comparative Examples 1-5
(Preparation of heat shrink film (single layer))
A single-layer inflation film-forming apparatus was prepared in which one extruder was connected to a circular die having a lip gap of 1.0 mm and a circular inner diameter D of 100 mm via a connector.

  Next, the LDPE, LLDPE and cyclic olefin polymer (COC) in parts by mass shown in Table 1 are mixed, supplied to the extruder, melt-kneaded at 200 ° C., and the molten resin is then added to the circular die. The film was further discharged, and the blow ratio in the horizontal direction was adjusted as shown in Table 1 to form a melt film. The diameter (inner diameter) D of the circular die lip of the circular die was 100 mm. Moreover, the bubble diameter of the heat-shrinkable film at the position extruded 100 mm (the same distance as D) from the end of the annular die lip was adjusted as shown in Table 1.

  By the above, the heat-shrink film (single layer) of Examples 1-6 and Comparative Examples 1-5 with a thickness of 55 micrometers was prepared.

Examples 7-22 and Comparative Examples 6-9
(Preparation of multilayer heat shrink film)
A multilayer inflation film forming apparatus was prepared in which three extruders (for forming each of the inner layer, the intermediate layer and the outer layer) were connected to a circular multilayer die having a lip gap of 1.0 mm via a connector.

  Next, LDPE, LLDPE, and cyclic olefin (COC) in parts by mass shown in Tables 2 and 3 are mixed, supplied to each of the extruders, melt-kneaded at 200 ° C., and the molten resin is added to the circular die. It was further discharged (co-extruded), and the blow ratio in the lateral direction was adjusted as shown in Tables 2 and 3 to form a melt film. The diameter (inner diameter) D of the circular die lip of the circular die was 100 mm. Moreover, the bubble diameter of the heat-shrink film in the position extruded 100 mm (the same height as D) from the edge part of the annular die lip was adjusted as shown in Tables 2 and 3.

  By the above, the multilayer heat-shrink film of Examples 7-22 and Comparative Examples 6-9 with a thickness of 55 micrometers was prepared.

  The following evaluation was performed about the heat-shrink film of Examples 1-6 and Comparative Examples 1-5, and the multilayer heat-shrink film of Examples 7-22 and Comparative Examples 6-9.

<130 ° C shrinkage>
The temperature condition was changed from 120 ° C. to 130 ° C. by a measurement method based on JIS Z1709, and measurement was performed using silicone oil as the heat transfer fluid. The measurement was performed about MD direction and TD direction using the heat-shrinkable film and multilayer heat-shrinkable film before heat shrinkage.

<Tensile strength>
The heat-shrinkable film and the heat-shrinkable film before heat shrinkage were measured according to JIS Z7127.

<Aspect ratio of island part and length of island part in ZD direction>
The aspect ratio (A) of the island part in the MD cross section, the aspect ratio (B) of the island part in the TD cross section, and the length in the ZD direction of the island part in the TD cross section were measured by the following methods.

First, a heat shrink film or a multilayer heat shrink film was dyed with RuO ₄ and then cut. The cut surface was observed with a transmission electron microscope (TEM) at an observation magnification of 5000, and an enlarged photograph was taken. The cyclic olefin polymer phase (hereinafter also referred to as “COC phase”) was stained with RuO ₄ and was photographed in black by an enlarged photograph by TEM. At this time, the observation magnification was able to distinguish the dispersed structure of the cyclic olefin polymer, and 30 to 500 dispersed phases were confirmed in the photograph.

  Next, the aspect ratio of the COC phase was calculated in the enlarged photograph. The aspect ratio of the island part of the COC phase is the length of the MD or TD direction passing through the center of gravity of the dispersed phase and ZD (thickness direction) using “WinROOF Ver5.03” which is image processing software made by Mitani Corporation. Calculated as the ratio of lengths.

  Using “WinROOF Ver5.03”, the aspect ratio (A) of the island part in the MD cross section, the aspect ratio (B) of the island part in the TD cross section, and the length in the ZD direction of the island part in the TD cross section are as follows: Calculated by the method.

First, a pretreatment for accurately extracting the COC phase stained black with RuO ₄ is performed.

(I) Extraction of unstained polyethylene layer The “image processing”, “intensity”, “lookup table conversion”, and “brightness extraction” commands are sequentially executed, and the parameters are set to 128 to 255. The COC phase dyed black by the above command has a density of 0 and is uniformly separated white.

(Ii) Binarization “Binary processing” and “binarization with a single threshold” are executed with the threshold set to 100. This binarizes the COC phase to white and the polyethylene layer to black.

  (Iii) “Image processing”, “emphasis”, and “inversion” commands are executed. As a result, white and black are reversed to change the COC phase to black and the polyethylene phase to white.

(Iv) Noise removal “Binary processing” and “deletion” are executed with the threshold set to 1 or less. Thereby, the noise on the black spots in the polyethylene resin layer is removed. The threshold value is designated while checking the image according to the photographing magnification.

  Subsequently, the process which smoothes the shape of a phase is performed.

  (V) Perform “binary processing” and “expansion” twice. This fills in the blank areas and the indentations in the area.

  (Vi) Perform “binary processing” and “shrink” twice. As a result, the protrusion is removed and returned to the size before expansion.

  Finally, shape analysis is performed to determine the cutting length.

  (Vii) “Measurement” and “shape feature” are performed, and “cutting length” is selected and executed. Thereby, the maximum length and the minimum length passing through the center of gravity of the region are calculated.

In the measurement method, since the film cross section is observed, the minimum length of the island portion is substantially the ZD cut length of the island portion. In the MD cross section, the maximum length of the island portion is the MD cut length of the island portion, TD. In the cross section, the maximum length of the island portion is the TD cut length of the island portion. From the MD cut length, TD cut length, and ZD cut length, the aspect ratio (A) of the island part in the MD cross section and the aspect ratio (B) of the island part in the TD cross section were calculated by the following formulas.
Aspect ratio of island part in MD cross section (A) = MD cut length / ZD cut length Aspect ratio of island part in TD cross section (B) = TD cut length / ZD cut length

  The enlarged photograph by TEM of MD cross section of the heat-shrink film of Example 2 which performed the above-mentioned image processing is shown in FIG. In FIG. 5, the arrow indicates the MD direction. Moreover, the enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 2 which performed the above-mentioned image processing is shown in FIG. In FIG. 6, the arrow indicates the TD direction.

  The enlarged photograph by TEM of the MD cross section of the heat-shrink film of Example 3 which performed the above-mentioned image processing is shown in FIG. In FIG. 7, the arrow indicates the MD direction. Moreover, the enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 3 which performed the above-mentioned image processing is shown in FIG. In FIG. 8, the arrow indicates the TD direction.

  Moreover, the enlarged photograph by TEM of MD cross section of the heat-shrink film of Example 3 before performing the above-mentioned image processing is shown in FIG. In FIG. 9, the arrow indicates the MD direction. Moreover, the enlarged photograph by TEM of the TD cross section of the heat-shrink film of Example 3 before performing the above-mentioned image processing is shown in FIG. In FIG. 10, the arrow indicates the TD direction.

  The results are shown in Tables 1-3.

  The heat-shrinkable film and multilayer heat-shrinkable film of the present invention are excellent in heat shrinkability in the TD direction and exhibit excellent breaking strength, and therefore can be suitably used for packaging, particularly for integrated packaging. In particular, it can be suitably used for collecting and packaging relatively heavy articles such as PET bottles and can drinks.

  Moreover, the manufacturing method of this invention can manufacture a heat shrink film and a multilayer heat shrink film provided with the said characteristic easily.

  DESCRIPTION OF SYMBOLS 1 ... Heat-shrink film, 2 ... Circular die, 3 ... Dotted arrow, 4 ... Dotted line, 5 ... MD cross section, 6 ... TD cross section, 7 ... Sea part, 8 ... Island part

Claims (4)

A heat-shrinkable film containing a total of 100 parts by mass of linear low-density polyethylene and low-density polyethylene, and 5 to 100 parts by mass of a cyclic olefin polymer,
(1) It has a sea-island structure in which a sea part containing the linear low-density polyethylene and the low-density polyethylene and an island part containing the cyclic olefin polymer are formed,
(2) The aspect ratio (A) of the island part in the MD cross section formed by cutting the heat shrink film in a direction parallel to the film winding direction (MD direction), and the film winding direction (MD direction) A ratio (A) / (B) with an aspect ratio (B) of the island portion in a TD cross section formed by cutting in a direction perpendicular to the direction (TD direction) is 1 or less,
(3) The length in the thickness direction (ZD direction) of the island part in the TD cross section is 0.5 μm or less.
A heat shrinkable film characterized by the above.   The heat-shrinkable film according to claim 1, wherein the cyclic olefin polymer is at least one selected from a cycloolefin homopolymer and an ethylene-cycloolefin copolymer. A multilayer heat shrinkable film having at least one layer of the heat shrinkable film according to claim 1 or 2,
The multilayer heat-shrinkable film, wherein the thickness of the heat-shrinkable film is 20% or more of the total thickness of the multilayer heat-shrinkable film. A heat shrink film according to claim 1 or 2, or a multilayer heat shrink film according to claim 3, wherein the heat shrink film is produced by an inflation method.
The blow ratio is 2 to 6, and the diameter (inner diameter) of the annular die lip is D. The bubble diameter of the heat shrink film or the multilayer heat shrink film at the same height as D from the end of the annular die lip is 2D. Is
The manufacturing method characterized by the above-mentioned.