JP2005335288A - Heat shrinkable polyolefin-based laminated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat shrinkable polyolefin-based laminated film which, as suitable for the use of the labels of PET bottles, is excellent in film stiffness (rigidity at ordinary temperature), resistance to fingerprint whitening, finish after shrinkage, transparency, natural shrinkage and suitability for addition for reclamation, and which can be gravitationally separated with satisfactory precision. <P>SOLUTION: The heat shrinkable polyolefin-based laminated film is proposed which comprises a surface layer (layer S) consisting of a mixed resin composition between a cyclic olefin resin and a polyethylene resin, an intermediate layer (layer L) consisting of a polyethylene resin, and an intermediate layer (layer M) consisting of a mixed resin composition between a cyclic olefin resin and a polyethylene resin and which has a specific gravity of <1.00. Particularly, the one that has a tensile modulus of ≥1,200 MPa in the direction orthogonal to the primary shrink direction of the film and that has a heat shrink ratio of ≥20% in at least one direction when dipped into 80°C warm water for 10 sec is especially suitable for the use of labels of PET bottles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable polyolefin-based laminated film, and more specifically, excellent in film stiffness (rigidity at room temperature), anti-fingerprint whitening, shrinkage finish, transparency, natural shrinkage, and regenerative additive properties, and accuracy. The present invention relates to a heat-shrinkable polyolefin-based laminated film that can be well separated in specific gravity, a heat-shrinkable label comprising the film, and a plastic container having the heat-shrinkable label attached thereto.

  Drinking water such as juice is filled in a container such as a bottle or a plastic bottle and sold. At that time, a printed heat-shrinkable label is often attached to the outside of the container in order to differentiate from other products and improve the visibility of the products. As a material for the label film, polystyrene, polyester, polyvinyl chloride, polyolefin, or the like is used.

  In recent years, in label applications for coating PET bottles, in order to improve productivity, it is required that a highly shrink-finished appearance can be obtained at a low temperature in a short time in the label coating process for bottles. At the same time, a film having a small natural shrinkage rate is also required. This natural shrinkage is a phenomenon in which shrinkage occurs gradually at room temperature or in a storage warehouse in the summer. When film dimensions change or rolls are rolled, trouble occurs during packaging or secondary processing due to deformation, etc. There is a case.

  In addition, flakes and pellets are increasingly recycled from PET bottles collected after use for recycling. The outline of this process will be explained. First, the collected plastic bottle (usually in a state with a cap made of polyethylene or a heat-shrinkable label) is placed in a glass bottle by manual labor, mass separator, X-ray inspection or the like. Sort from other containers such as cans and PVC bottles. Next, the PET bottle is pulverized to about several mm to several tens of mm square, and the heat-shrinkable label pulverized body and cap having a specific gravity of less than 1 are removed by a specific gravity separator. Further, the heat-shrinkable label pulverized body having a specific gravity of 1 or more is removed by the wind separator. Recycled pet flakes or pellets are obtained from the PET bottle pulverized body thus obtained.

  The above-mentioned specific gravity separator means that a pulverized body is put in water and floats in water (a heat-shrinkable label or cap having a specific gravity of less than 1.00) and a thing that sinks in water (a heat-shrinkable having a specific gravity of 1.00 or more). Label and plastic bottle pulverized body), and the wind separator is a device that expands the pulverized body and blows the heat-shrinkable label pulverized body by blowing air from below. Since the specific gravity separator has a higher processing capacity per unit time than the wind separator, a heat-shrinkable label having a specific gravity of less than 1.00 that can be accurately separated by the specific gravity separation method is desired.

  Examples of the heat-shrinkable film having a specific gravity of less than 1.00 include stretched films made of polyolefin resins such as polyethylene resins and polypropylene resins. However, conventional heat-shrinkable films have problems such as insufficient film shrinkage (rigidity at room temperature) and low-temperature (about 70 to 90 ° C) shrinkage, a large natural shrinkage rate, and poor shrinkage finish. Had a point.

As an improvement of these problems, for example, in Patent Document 1, a layer composed of a polyolefin resin having a density of less than 0.94 g / cm ³ , a cyclic olefin resin of 70 to 90% by mass, and a crystalline polyolefin resin 30 to 30%. A heat-shrinkable polyolefin-based laminated film obtained by stretching a laminate having a layer composed of 10% by mass is disclosed.

  However, although this film has achieved a specific gravity of less than 1.00 (hereinafter referred to as “low specific gravity”), reduced natural shrinkage, and good shrinkage finish, (Rigidity at normal temperature) is low, so when filmed bags such as PET bottles are covered with a labeling machine etc., there is a problem that the yield tends to decrease due to slanting or folding of the film. It was.

  Patent Document 2 discloses a heat-shrinkable polyolefin film having front and back layers made of a cyclic olefin resin and an intermediate layer made of a resin composition mainly composed of a polyethylene copolymer resin.

  However, although this film has achieved low specific gravity, the film as a whole has low stiffness (rigidity at room temperature), and the cyclic olefin resin of the surface layer is inferior in oil resistance. After touching the surface of the surface with heat, when the oil and fat components such as fingerprints are attached, heat shrinkage causes a phenomenon of whitening and fine cracks (hereinafter referred to as “fingerprint whitening”). However, there were problems such as lowering the product value.

  Furthermore, in patent document 3, the front and back layer which has as a main component the resin composition which mixed linear low density polyethylene resin 60-150 mass parts with 100 mass parts of cyclic olefin resin, and propylene-alpha-olefin random copolymer. A heat-shrinkable polyolefin film having an intermediate layer mainly composed of a polymer is disclosed.

  However, in this film, although the whitening resistance to fingerprints is improved, the phase of the cyclic olefin resin and / or linear low density polyethylene resin of the front and back layers and the propylene-α-olefin random copolymer of the intermediate layer is improved. Due to poor solubility, the transparency of the entire film tends to decrease when recycled resin generated from trimming loss such as film ears is added (hereinafter referred to as “regeneration addition”). In some cases, the interlaminar adhesion strength is insufficient.

JP 2000-20951 A JP 2001-315260 A JP 2002-234115 A

  The object of the present invention is a heat-shrinkable polyolefin-based laminate that is excellent in film stiffness (rigidity at room temperature), anti-fingerprint whitening, shrinkage finish, transparency, natural shrinkage, regenerative additive properties, and capable of separating specific gravity accurately. An object of the present invention is to provide a plastic container equipped with a film and a heat-shrinkable label made of the film.

  As a result of intensive studies, the present inventors have found that a surface layer (S layer) composed of a mixed resin composition of a cyclic olefin resin and a polyethylene resin (A) described later, and an intermediate composed of a polyolefin resin (B). Layer (L layer), a heat-shrinkable laminated film having an intermediate layer (M layer) made of a mixed resin composition of a cyclic olefin resin and a polyethylene resin (C), and a heat-shrinkable label made of the film In addition, the present inventors have found that the above problems can be solved by a plastic container equipped with the heat-shrinkable label, and have completed the present invention.

That is, the present invention is a laminated film having a surface layer (S layer), an intermediate layer (L layer), and an intermediate layer (M layer) in a heat-shrinkable polyolefin-based laminated film having a specific gravity of less than 1.00. The present invention proposes a heat-shrinkable polyolefin-based laminated film characterized in that each layer is composed mainly of the following composition or resin.
(S layer): Polyethylene resin (A) having a cyclic olefin resin of 90 to 50% by mass and a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of 90 ° C. or more and 125 ° C. or less. Mixed resin composition with 10-50 mass%.
(L layer): Polyethylene resin (B) having a crystal melting peak temperature (Tm) measured with a differential scanning calorimeter of 125 ° C. or lower.
(M layer): 95 to 50% by mass of a cyclic olefin resin and a polyethylene resin having a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of more than 125 ° C. and 140 ° C. or less ( C) Mixed resin composition with 5 to 50% by mass.

  The heat-shrinkable polyolefin-based laminated film of the present invention can be used for various applications. Preferably, heat shrinkage is applied to a plastic container such as a plastic bottle by printing on one or both sides of the film. Sex labels can be formed. Also in this case, it is preferable that the specific gravity of the heat-shrinkable label is less than 1.00.

In the present invention, “each layer is composed mainly of the following composition or resin” is intended to allow other components to be contained within a range that does not interfere with the action / effect of the “the following composition or resin”. It is. Although a specific content ratio is not limited, it is general that the “the following composition or resin” occupies 70% by mass or more, particularly 75% by mass or more of the total component of each layer.
In addition, the upper and lower limits of the numerical range in the present invention, even if slightly deviating from the numerical range specified by the present invention, as long as the same effect as in the numerical range is provided. It is included in the equivalent range.

  According to the heat-shrinkable polyolefin-based laminated film of the present invention, it is excellent in film waist (rigidity at room temperature), anti-fingerprint whitening resistance, shrink finish, transparency, natural shrinkage, etc. It can use suitably for. Moreover, since the surface layer (S layer), the intermediate layer (L layer), and the intermediate layer (M layer) are composed of a cyclic olefin resin and / or a polyethylene resin, it has excellent regenerative additivity and has a specific gravity of the film. Therefore, the specific gravity separation with high accuracy is possible in the recycling process of the PET bottle.

  Hereinafter, the present invention will be described in more detail.

  The present invention includes a surface layer (S layer) made of a mixed resin composition of a cyclic olefin resin and a polyethylene resin (A), an intermediate layer (L layer) made of a polyethylene resin (B), and a cyclic olefin type. It is a heat-shrinkable polyolefin-based laminated film having an intermediate layer (M layer) made of a mixed resin composition of a resin and a polyethylene-based resin (C).

  First, the cyclic olefin resin used in the present invention will be described.

The bonding form of the cyclic olefin-based resin is a random copolymer of ethylene and a cyclic olefin represented by the following general formula (1), a cyclic olefin ring-opening (co) polymer, or a cyclic olefin ring-opening (co) polymer. Examples thereof include hydrides and graft modified products of these (co) polymers. In the case of a random copolymer of ethylene and a cyclic olefin represented by the following general formula (1), it contains an α-olefin other than ethylene, or contains a butadiene, isoprene or the like as the third component. May be.
In Formula 1, R _{1 to} R ₁₂ are hydrogen atoms or hydrocarbon groups, and may be the same or different. N is 0 or a positive integer.

  Here, examples of the cyclic olefin represented by the general formula (1) include bicyclohept-2-ene (2-norbornene) of the following formula (2) and derivatives thereof such as norbornene, 6-methylnorbornene, 6- Examples thereof include ethyl norbornene, 6-n-butylnorbornene, 5-propylnorbornene, 1-methylnorbornene, 7-methylnorbornene, 5,6-dimethylnorbornene, 5-phenylnorbornene, and 5-benzylnorbornene.

  Examples of tetracyclo-3-dodecene of the following formula (3) and derivatives thereof include 8-methyltetracyclo-3-dodecene, 8-ethyltetracyclo-3-dodecene, 8-hexyltetracyclo-3-dodecene, Examples include 2,10-dimethyltetracyclo-3-dodecene and 5,10-dimethyltetracyclo-3-dodecene.

  The above-mentioned cyclic olefin resins have various glass transition temperatures depending on the type and content of the cyclic olefin. Specifically, trade names “ZEONOR”, Mitsui Chemicals, Inc., manufactured by Nippon Zeon Co., Ltd. ) Manufactured product name “Apel”, Ticona product name “Topas”, and the like.

  Examples of the cyclic olefin resin include, for example, JP-A-60-168708, JP-A-612012016, JP-A-61-115912, JP-A-61-115916, JP-A-61. -271308, JP-A-61-272216, JP-A-62-252406, JP-A-62-2252407, and the like.

  Examples of cyclic olefin resins include ethylene and cyclic olefin random copolymers, cyclic olefin ring-opening (co) polymers or hydrogenated products of cyclic olefin ring-opening (co) polymers such as maleic anhydride. Graft polymers modified with a modifying agent such as an unsaturated carboxylic acid such as maleic acid, itaconic anhydride, itaconic acid, (meth) acrylic acid, or an anhydride thereof can also be used. These modifiers can be used alone or in combination.

The glass transition temperature (Tg) of the cyclic olefin-based resin is preferably 50 to 140 ° C, more preferably 55 to 130 ° C, and particularly preferably 60 to 110 ° C.
When the glass transition temperature (Tg) is 50 ° C. or higher, natural shrinkage is not excessively large and a film having good dimensional stability is easily obtained, which is practically preferable. On the other hand, if it is 140 degrees C or less, the thermal contraction rate of a practical temperature range (about 70-90 degreeC) can fully be obtained by adding a plasticizer etc. as needed, and is preferable.

  In addition, the glass transition temperature (Tg) used in this invention is the value calculated | required as follows. That is, using a viscoelastic spectrometer DVA-200 (manufactured by IT Measurement Co., Ltd.), measurement was performed at a vibration frequency of 10 Hz, a strain of 0.1%, and a heating rate of 3 ° C./min. The peak value of E ″) was determined, and the temperature at that time was defined as the glass transition temperature (Tg).

  The cyclic olefin resin suitably used in the present invention is amorphous or low crystalline, and the crystallinity measured by X-ray diffraction method is usually 20% or less, preferably 10% or less, Preferably it is 2% or less.

  The cyclic olefin-based resin has an intrinsic viscosity [η] measured in decalin at 135 ° C. of usually 0.01 to 20 dl / g, preferably 0.03 to 10 dl / g, more preferably 0.8. The melt flow rate (MFR) is not particularly limited, but usually MFR (JIS K7210, temperature: 190 ° C., load: 21.18 N) is 0.2 to 10 g. / 10 min, more preferably 0.5 to 5 g / 10 min.

  The cyclic olefin-type resin demonstrated above may be used individually by 1 type or in mixture of 2 or more types.

  The cyclic olefin resin used for the surface layer (S layer) and the intermediate layer (M layer) may be the same resin or different resins. In particular, those having a difference in glass transition temperature (Tg) of the cyclic olefin resin used for the surface layer (S layer) and the intermediate layer (M layer), specifically about 3 to 20 ° C., particularly about 5 to 15 ° C. Those having a difference of Tg are preferable. For example, when a low Tg cyclic olefin resin is used for the intermediate layer (M layer) and a high Tg cyclic olefin resin is used for the surface layer (S layer), or vice versa, the shrinkage behavior is moderate. It is preferable because an effect such as being able to be obtained is obtained.

  Next, the polyethylene resin (A) used in the present invention will be described.

As the polyethylene resin (A), a polyethylene resin having a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of 90 ° C. or more and 125 ° C. or less, preferably 95 ° C. or more and 120 ° C. or less is suitable. Used for.
If the crystal melting peak temperature (Tm) is 90 ° C. or higher, the heat resistance of the film surface is sufficiently maintained, and there is a problem that the films block each other at the time of high temperature heat retention on a bottle mounting line or hot beverage sales. It is preferable because it is difficult to occur. On the other hand, when the temperature is 125 ° C. or lower, the difference in elastic modulus between the cyclic olefin resin and the polyethylene resin (A) is the main cause at the time of stretching, so that unevenness is generated on the film surface or transparency is lowered. This is preferable because problems such as haze are unlikely to occur.

The density of the polyethylene resin (A) is preferably not more than 0.890 g / cm ³ or more 0.940 g / cm ^3.
When the density is 0.890 g / cm ³ or more, the heat resistance of the film surface is maintained, and problems such as blocking of the films between the bottle mounting line and hot beverage sales at hot beverage sales are preferable. On the other hand, if it is 0.940 g / cm ³ or less, the elastic modulus difference between the cyclic olefin-based resin and the polyethylene-based resin (A) is the main cause at the time of stretching, and irregularities are generated on the film surface or the transparency is lowered. (So-called external haze), and further, problems such as difficulty in lowering the specific gravity of the entire film hardly occur, which is preferable. For these reasons, the density of the polyethylene resin (A) is more preferably 0.900 g / cm ³ or more 0.925 g / cm ³ or less.

  The melt flow rate (MFR) of the polyethylene resin (A) used in the present invention is not particularly limited, but usually MFR (JIS K7210, temperature: 190 ° C., load: 21.18 N) is 1 0.015 to 15 g / 10 min, more preferably 1.5 to 10 g / 10 min. Here, the MFR may be selected in consideration of kneading dispersibility and molding processability with the cyclic olefin resin to be used. In order to obtain good transparency and kneading dispersibility, the viscosity at the time of melt kneading is used. It is preferable to select a resin close to the cyclic olefin resin used in the above.

  The method for producing the polyethylene resin (A) is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene system. Examples thereof include a slurry polymerization method, a solution polymerization method, a bulk polymerization method, and a gas phase polymerization method using a single site catalyst typified by a catalyst, and a bulk polymerization method using a radical initiator.

  The polyethylene-based resin (A) is usually called a low density polyethylene resin (LDPE) or a linear low density polyethylene resin (LLDPE). In the present invention, from the viewpoint of stretchability and transparency, A linear low density polyethylene resin is preferably used.

  Here, the linear low density polyethylene resin as the polyethylene resin (A) is a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, preferably 4 to 12 carbon atoms. , Propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene, etc. Illustrated. The α-olefin to be copolymerized may be used alone or in combination of two or more.

  The polyethylene-type resin (A) demonstrated above may be used individually by 1 type or in mixture of 2 or more types. In the present invention, when two or more kinds of polyethylene resins are mixed and used, and have a plurality of crystal melting peak temperatures (Tm), the mixing weight ratio is large and the crystal melting peak temperature of the highest temperature is obtained. And

  Next, the resin composition constituting the main component of the surface layer (S layer) will be described.

It is important that the resin composition constituting the main component of the surface layer (S layer) is a mixed resin composition of 90 to 50% by mass of the cyclic olefin resin and 10 to 50% by mass of the polyethylene resin (A). It is.
If the content of the polyethylene resin (A) is 10% by mass or more, the effect of suppressing the fingerprint whitening phenomenon that occurs during thermal shrinkage is remarkable, and it is easy to achieve a low specific gravity. On the other hand, if it is 50 mass% or less, it is preferable at the point that it is excellent in transparency, it is easy to obtain a film with a small natural shrinkage rate, and the ink adhesiveness at the time of printing on this film becomes favorable. From these facts, the resin composition of the surface layer used in the present invention is a mixed resin composition of the above-described cyclic olefin resin 80 to 60% by mass and the polyethylene resin (A) 20 to 40% by mass. More preferred.

  Next, the polyethylene resin (B) used for the intermediate layer (L layer) will be described.

As the polyethylene resin (B), it is important that the crystal melting peak temperature (Tm) measured using a differential scanning calorimeter is 125 ° C. or lower.
When the crystal melting peak temperature (Tm) is 125 ° C. or lower, it is preferable that the stretchability at low temperatures is maintained and a film having excellent transparency is easily obtained. In addition, since the density of polyethylene is reduced and the specific gravity of the film is low, the specific gravity can be accurately separated when recycling the PET bottle. The lower limit of the crystal melting peak temperature (Tm) is not particularly limited, but if it is 50 ° C. or higher, preferably 70 ° C. or higher, particularly preferably 90 ° C. or higher, the heat resistance and rigidity (waist) of the entire film can be improved. This is preferable because it does not significantly decrease.

The density of the polyethylene resin (B) is preferably 0.940 g / cm ³ or less.
A density of 0.940 g / cm ³ or less is preferred in that the stretchability at a low temperature is maintained and a heat shrinkage rate in a practical temperature range (about 70 to 90 ° C.) can be sufficiently obtained. The lower limit of the density of the polyethylene resin (B) is not particularly limited, but is 0.865 g / cm ³ or more, preferably 0.875 g / cm ³ or more, particularly preferably 0.900 g / cm ³ or more. If it exists, it is preferable because the heat resistance and waist (rigidity at room temperature) of the entire film are not significantly lowered.

  The melt flow rate (MFR) of the polyethylene resin (B) is not particularly limited, but usually MFR (JIS K7210, temperature: 190 ° C., load: 21.18 N) is 1.0 to 15 g. / 10 min, more preferably 1.5 to 10 g / 10 min. Here, in order to obtain a film having a uniform thickness, the MFR is preferably selected to be similar to the viscosity at the time of melting of the (S layer) and (M layer).

  The method for producing the polyethylene resin (B) is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene system. Examples thereof include a slurry polymerization method, a solution polymerization method, a bulk polymerization method, and a gas phase polymerization method using a single site catalyst typified by a catalyst, and a bulk polymerization method using a radical initiator.

  The polyethylene resin (B) is usually called a low density polyethylene resin (LDPE) or a linear low density polyethylene resin (LLDPE). In the present invention, from the viewpoint of stretchability and transparency, A linear low density polyethylene resin is preferably used.

  The linear low density polyethylene resin as the polyethylene resin (B) is a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, preferably 4 to 12 carbon atoms. As the α-olefin, propylene is used. 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene, etc. The The α-olefin to be copolymerized may be used alone or in combination of two or more.

  The polyethylene-type resin (B) demonstrated above may be used individually by 1 type or in mixture of 2 or more types. In the present invention, when two or more kinds of polyethylene resins are mixed and used, and have a plurality of crystal melting peak temperatures (Tm), the mixing weight ratio is large and the crystal melting peak temperature of the highest temperature is obtained. And

  Next, the polyethylene resin (C) used for the intermediate layer (M layer) will be described.

The polyethylene resin (C) is a high-density polyethylene having a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of more than 125 ° C and not more than 140 ° C, preferably not less than 130 ° C and not more than 140 ° C. Based resin (HDPE) is preferably used.
If the crystal melting peak temperature (Tm) exceeds 125 ° C., a film with high stiffness (rigidity at room temperature) can be obtained, and since the difference in refractive index from the cyclic olefin resin is small and the internal haze is small, it is transparent. It is preferable at the point which can maintain favorable property. On the other hand, if it is 140 degrees C or less, it is preferable at the point which the drawability in low temperature is maintained and the heat contraction rate of a practical temperature range (about 70-90 degreeC) can fully be obtained.

Further, the density of the polyethylene resin (C) is preferably higher than that of the polyethylene resin (A) and the polyethylene resin (B). Specifically, the density of the polyethylene resin (C) exceeds 0.935 g / cm ³ . It is preferably 970 g / cm ³ or less.
If the density exceeds 0.935 g / cm ³ , a film with high stiffness (rigidity at room temperature) can be obtained, and since the difference in refractive index from the cyclic olefin resin is small and the internal haze is small, transparency is improved. It is preferable at the point which can be made favorable. On the other hand, if it is 0.970 g / cm < ³ > or less, it is preferable at the point which the drawability in low temperature is maintained and the thermal contraction rate of a practical temperature range (about 70-90 degreeC) can fully be obtained. From these facts, the density of the polyethylene resin (C) is more preferably 0.945 g / cm ³ or more and 0.965 g / cm ³ or less.

  The melt flow rate (MFR) of the polyethylene resin (C) is not particularly limited, but the MFR (JIS K7210, temperature: 190 ° C., load: 21.18 N) is 1.0 to 15 g / 10 min. More preferably, 1.5 to 10 g / 10 min is used. Here, the MFR may be selected in consideration of kneading dispersibility and molding processability with the cyclic olefin resin to be used. In order to obtain good transparency and kneading dispersibility, the viscosity at the time of melt kneading is used. It is preferable to select a resin close to the cyclic olefin resin used in the above.

  The method for producing the polyethylene resin (C) is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene system. Examples thereof include a polymerization method using a single site catalyst typified by a catalyst.

  The polyethylene-type resin (C) demonstrated above may be used individually by 1 type or in mixture of 2 or more types. In the present invention, the crystal melting peak temperature (Tm) when two or more polyethylene resins are mixed and used is the highest crystal melting peak temperature with a large mixing weight ratio.

  Next, the resin composition constituting the main component of the intermediate layer (M layer) will be described.

It is important that the resin composition forming the main component of the intermediate layer (M layer) is a mixed resin composition of 95 to 50% by mass of the cyclic olefin resin and 5 to 50% by mass of the polyethylene resin (C). It is.
If content of polyethylene-type resin (C) is 5 mass% or more, the effect of making the specific gravity of a film low, impact resistance, and economical efficiency can fully be acquired. On the other hand, if it is 50% by mass or less, it is easy to obtain a film having excellent transparency and a small natural shrinkage rate, and can maintain stretchability at a low temperature, and heat shrink in a practical temperature range (about 70 to 90 ° C.). This is preferable because a sufficient rate can be obtained. From these things, the resin composition of the intermediate | middle layer (M layer) used for this invention is a mixed resin composition of 75-50 mass% of above-described cyclic olefin resin and 25-50 mass% of polyethylene-type resin (C). More preferably, it is a product.

  Each layer (S layer), (L layer), and (M layer) constituting the heat-shrinkable polyolefin-based laminated film of the present invention may be any material as long as it contains the above composition or resin as a main component. If necessary, other additives may be added in any one layer or two or more layers.

For example, hydrocarbon resins may be added to the surface layer (S layer) and / or the intermediate layer ((L layer), (M layer)) as necessary.
By adding hydrocarbon resins to the surface layer, the effect of improving glossiness and shrinkage characteristics of the film surface can be obtained, and by adding to the intermediate layer, improvement of stretchability and shrinkage characteristics can be expected. .
The hydrocarbon resins to be added are, for example, cyclopentadiene or an alicyclic petroleum resin from the dimer thereof or an aromatic petroleum resin from the C9 component as a petroleum resin, and as a terpene resin from β-pinene. Examples of the rosin resin include rosin resins such as gum rosin and wood rosin, esterified rosin resins modified with glycerin, pentaerythritol, and the like.
The hydrocarbon resins are known to exhibit relatively good compatibility when mixed with polyolefin resins and the like, but it is preferable to use a hydrogenated derivative from the viewpoint of color tone, thermal stability, and compatibility. .
Specifically, Mitsui Chemicals' product names “Hilets” and “Petrogin”, Arakawa Chemical Industries' product name “Arcon”, Yashara Chemicals' product name “Clearon”, Idemitsu Petrochemical Co., Ltd. ) And trade name “Escolez” of Tonex Co., Ltd. can be used.
Some hydrocarbon resins have various softening temperatures mainly depending on the molecular weight. In the present invention, those having a softening temperature of 100 ° C. or higher and 150 ° C. or lower, preferably 110 ° C. or higher and 140 ° C. or lower are suitable. Used for. If the softening temperature is 100 ° C. or higher, when mixed with the above-described mixed resin composition of cyclic olefin resin and polyethylene resin, the sheet surface bleeds, causing blocking, or the mechanical strength of the entire sheet is increased. It is practically preferable because it does not decrease and easily break. On the other hand, if it is 150 degrees C or less, compatibility with polyolefin-type resin is maintained favorably, it does not bleed on the film surface with time, causing blocking or a decrease in transparency, which is preferable.
The mixing amount of hydrocarbon resins added to the surface layer (S layer) and / or the intermediate layer ((L layer), (M layer)) is a ratio of 2 to 40 parts by mass with respect to 100 parts by mass of the main component of each layer. Is preferably added. When the mixing amount of the hydrocarbon resins is 2 parts by mass or more, the effect of improving the glossiness and shrinkage property of the film surface is remarkable, which is preferable. On the other hand, if it is 40 parts by mass or less, it is preferable because problems such as bleed on the surface over time and the films tend to block each other and impact resistance is reduced are unlikely to occur. From these things, the mixing amount of hydrocarbon resins added to the surface layer (S layer) and / or the intermediate layer ((L layer), (M layer)) is 5 to 100 parts by mass of the main component of each layer. It is more preferable to add at a ratio of 20 parts by mass.

  In addition, the resin composition of the surface layer (S layer) and / or the intermediate layer ((L layer), (M layer)) is molded within the range not significantly impairing the effects of the present invention in addition to the components described above. Recycled resin generated from trimming loss such as film ears (usually added to the intermediate layer for the purpose of improving / adjusting properties, productivity and various properties of heat shrinkable film, etc. In addition to polyolefin elastomers and polyolefin resins, for example, resins such as styrene elastomers, inorganic particles such as silica, talc, kaolin, calcium carbonate, titanium oxide, carbon Black pigments, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, crosslinking agents, lubricants, nucleating agents, plasticizers (liquid polybutene, etc.) It may be appropriately added additives such as antioxidant.

The heat-shrinkable polyolefin-based laminated film of the present invention only needs to have at least four layers of both surface layers (S layer), intermediate layer (L layer), and intermediate layer (M layer). As long as the function of the heat-shrinkable polyolefin-based laminated film is not hindered, other layers may be interposed, or treatment may be appropriately performed, and there is no particular limitation.
For example, a layer having the same composition as the surface layer (S layer) may be formed in the intermediate layer. Further, the intermediate layer (L layer) and the intermediate layer (M layer) may each have at least one layer in the intermediate layer, and may each have two or more layers. In this case, the composition and thickness ratio of each layer may be the same or different.

  As a specific layer structure, for example, a four-layer structure including (S layer) / (L layer) / (M layer) / (S layer), (S layer) / (L layer) / (M layer) / ( Examples include a 5-layer structure consisting of (L layer) / (S layer) or (S layer) / (M layer) / (L layer) / (M layer) / (S layer), and other other layer structures. However, in the present invention, the preferred laminated structure is (S layer) / (L layer) / (M layer) / (L layer) / (S layer) or (S layer) / (M layer) / ( This is a five-layer structure consisting of (L layer) / (M layer) / (S layer). By adopting this five-layer structure, the film waist (rigidity at room temperature) and whitening resistance against fingerprints are the objects of the present invention. Heat-shrinkable polyolefin film that is excellent in heat resistance, shrink finish, transparency, natural shrinkage, regenerative addition properties, and capable of separating specific gravity with high accuracy, can be obtained with higher productivity and economy. . Among them, one of the preferred embodiments is a film having a five-layer structure of (S layer) / (L layer) / (M layer) / (L layer) / (S layer). The thickness ratio may be set in consideration of the effects and actions described above, and is not particularly limited.

  In the present invention, the thickness ratio of the intermediate layer (L layer) to the thickness of the entire film is 5 to 50%, preferably 20 to 40%, and the thickness ratio of the intermediate layer (M layer) to the thickness of the entire film is 40 to 40%. 80%, preferably 50-70%. In addition, the surface layer (S layer) has a function of 2 μm or more, preferably 3 to 15 μm, so that the film waist (rigidity at room temperature), anti-fingerprint whitening, shrink finish, transparency, spontaneous shrinkage, A heat-shrinkable polyolefin-based laminated film that has excellent regenerative additive properties and can be separated with a specific gravity with high accuracy can be obtained in a well-balanced manner.

  The transparency of the heat-shrinkable polyolefin-based laminated film of the present invention is usually preferably 10% or less, more preferably 7% or less, and still more preferably 5% or less in total haze. A total haze of 10% or less is preferable because a clear display effect can be obtained.

Next, it is important that the specific gravity of the heat-shrinkable polyolefin-based laminated film of the present invention is less than 1.00.
In order to reduce the specific gravity of the heat-shrinkable polyolefin-based laminated film to less than 1.00, for example, a cyclic olefin resin and a polyethylene-based resin (A) (B) (C ) May be adjusted by the mixed composition ratio and the thickness constitution ratio of each layer. The density of the cyclic olefin-based resin is usually about 0.99 to 1.05 g / cm ³ , and as described in the specification, the polyethylene-based resin (A) that is suitably used is 0.890 g / cm ^3. 0.940 g / cm ³ or less, polyethylene resin (B) is 0.940 g / cm ³ or less (0.865 g / cm ³ or more) and polyethylene resin (C) exceeds 0.935 g / cm ³ 0.970 g / cm ³ or less, and the density and content may be integrated to design appropriately.
However, the method of setting the specific gravity of the heat-shrinkable polyolefin-based laminated film to less than 1.00 is not limited to such a method.

  In general, the front and / or back of a heat-shrinkable film used for labeling is subjected to a printing process by a known method such as gravure printing, flexographic printing, offset printing, or bar coater. The printing ink used in these is not particularly limited and can be appropriately selected according to the printing method. For example, solvent-based (non-aqueous) or water-based acrylic resin-based or urethane resin-based ink, foamable ink, heat foamable property Ink etc. are mentioned.

The density of the printing layer formed through a printing / drying process that is usually performed at present is larger than 1.05 g / cm ³ , for example, a printing layer formed by silver ink widely used for the label application. The density of the printing layer is 1.55 g / cm ³ , and the density of the printed layer formed of white ink is about 1.40 g / cm ³ . Moreover, the thickness of the printing layer applied to the label application is not particularly limited, but is generally about 0.1 to 10 μm in the case of gravure printing. From these facts, in order to set the specific gravity of the heat-shrinkable label subjected to the printing process to less than 1.00 which is the specific gravity that can be accurately separated in the specific gravity separation process such as a PET bottle, the specific gravity of the heat-shrinkable film is More preferably, it is 0.97 or less.

The waist (rigidity at normal temperature) of the heat-shrinkable polyolefin-based laminated film of the present invention is important that the tensile elastic modulus in the direction orthogonal to the main shrinkage direction of the film is 1200 MPa or more, more preferably 1300 MPa, Preferably it is 1400 MPa or more. Moreover, the upper limit of the tensile elasticity modulus of the heat shrinkable film used normally is about 2500-3000 MPa. If the tensile elastic modulus is 1200 MPa or more, the film as a whole has high stiffness (rigidity at room temperature), especially when the film thickness is reduced, When covering with a labeling machine or the like, it is preferable because it does not easily cause problems such as being covered at an angle or the yield is liable to decrease due to film folding.
In order to set the tensile elastic modulus of the heat-shrinkable polyolefin-based laminated film of the present invention to 1200 MPa or more, for example, a cyclic olefin resin and a polyethylene-based resin (A) (B) mainly used as the whole heat-shrinkable polyolefin-based laminated film. ) The content of (C) may be adjusted by the mixed composition ratio and the thickness composition ratio of each layer. Particularly in the present invention, the thickness ratio of the intermediate layer (M layer) containing the polyethylene resin (C) to the thickness of the entire film is preferably 40 to 80%, and preferably 50 to 70%.
However, the method of setting the tensile elastic modulus of the heat-shrinkable polyolefin-based laminated film of the present invention to 1200 MPa or more is not limited to such a method.

It is important that the heat shrinkable polyolefin-based laminated film of the present invention has a heat shrinkage rate of 20% or more in at least one direction when immersed in 80 ° C. warm water for 10 seconds.
This is an index for determining the adaptability to the shrinking process in a relatively short time (several seconds to about several tens of seconds) such as the use of shrinkage labels for PET bottles. For example, the required shrinkage rate required for a heat-shrinkable film applied to the use of shrinkage labels for PET bottles varies depending on the shape, but is generally about 20 to 70%.

  Further, the shrinkage processing machine that is most commonly used industrially for label mounting of PET bottles is generally called a steam shrinker that uses steam as a heating medium for shrinking. Furthermore, the heat-shrinkable film needs to be sufficiently heat-shrinked at a temperature as low as possible from the viewpoint of the influence of heat on the object to be coated. In consideration of such industrial productivity, a film having a heat shrinkage rate of 20% or more under the above conditions is preferable because it can sufficiently adhere to the object to be coated within the shrinkage processing time. From these, it is more preferable that the thermal shrinkage rate when immersed in warm water at 80 ° C. for 10 seconds is 40 to 70% in at least one direction, usually the main shrinkage direction.

  Further, in shrinkage label use for PET bottles, the thermal shrinkage rate when immersed in 80 ° C. warm water for 10 seconds in a direction orthogonal to the main shrinkage direction is preferably 10% or less, more preferably 7% or less. . If the film has a thermal shrinkage rate of 10% or less in the direction perpendicular to the main shrinkage direction, the dimension itself in the direction perpendicular to the main shrinkage direction after shrinkage may be shortened, or the printed pattern or character distortion after shrinkage may occur. In the case of a square bottle, it is preferable because troubles such as vertical sink are unlikely to occur.

In order to set the heat shrinkage rate of the heat-shrinkable polyolefin-based laminated film of the present invention to the above predetermined% or more, for example, the resin composition of each layer is adjusted and the characteristics of the resin composition used, stretching means, stretching What is necessary is just to adjust suitably according to temperature, the target product form, etc.
However, the method of setting the heat shrinkage rate of the heat-shrinkable polyolefin-based laminated film of the present invention to a predetermined% or more is not limited to such a method.

The natural shrinkage ratio of the heat-shrinkable polyolefin-based laminated film of the present invention is preferably as small as possible, but generally the natural shrinkage ratio of the heat-shrinkable film is, for example, 2.0% under conditions of 30 ° C. and about 30 days. If it is less than this, it is difficult to cause a practical problem. More preferably, it is less than 1.5%.
In order to make the natural shrinkage ratio of the heat-shrinkable polyolefin-based laminated film of the present invention less than 2.0%, for example, a resin having a glass transition temperature (Tg) of a cyclic olefin resin mainly used of 50 ° C. or higher is used. In the resin composition constituting the surface layer (S layer) and the intermediate layer (M layer), particularly the intermediate layer (M layer), the amount of the cyclic olefin-based resin mixed is used (see the description in [0031] above). The content may be adjusted to 50% by mass or more (see the above [0062]) and the characteristics required for the glass transition temperature of the resin composition using the stretching temperature and the heat-shrinkable film. In general, the temperature may be controlled in the range of approximately 60 to 130 ° C., preferably 70 to 110 ° C. (see [0081] above).
The surface layer (S layer) also has a function similar to that of the above-described intermediate layer (M layer) with respect to the natural shrinkage ratio. However, in the present invention, the mixing composition ratio of the surface layer (S layer) Is more important from the viewpoint of ink adhesion when printing on a film.
However, the method of setting the natural shrinkage ratio of the heat-shrinkable polyolefin-based laminated film of the present invention to less than 2.0% is not limited to such a method.

  Next, the manufacturing method of the heat-shrinkable polyolefin-type laminated film of this invention is demonstrated.

  The heat-shrinkable polyolefin-based laminated film of the present invention can be produced by appropriately changing conditions in a conventionally known production method, and the production method is not particularly limited.

The form of the film may be either flat or tube-like, but it is flat from the point of view of productivity (a few products can be taken in the width direction of the raw film) and printing on the inner surface. More preferred.
As a production method in the case of a flat shape, for example, a resin is melted using a plurality of extruders, co-extruded from a T die, cooled and solidified with a chilled roll, roll-stretched in the longitudinal direction, and tenter-stretched in the transverse direction. Then, the manufacturing method can illustrate the film extended | stretched to the uniaxial or biaxial direction by processes, such as annealing, cooling, and a corona discharge process as needed. Moreover, the method of cutting open the film manufactured by the tubular method and making it flat is also applicable. Here, the extrusion molding temperature is appropriately adjusted depending on the flow characteristics and film-forming property of the mixed resin composition, but is generally 260 ° C. or less, preferably in the range of 200 ° C. to 250 ° C. In addition, since cyclic olefin-based resins are liable to generate fish eyes and the like due to shear during extrusion, it is preferable to use a method such as starvation feed extrusion or extrusion with a lubricant added.

  The stretching temperature needs to be changed depending on the glass transition temperature of the resin composition to be used and the properties required for the heat-shrinkable film, but is generally controlled in the range of 60 to 130 ° C, preferably 70 to 110 ° C. The draw ratio is 1.5 to 10 times in the main shrinkage direction, preferably 3 to 7 times, depending on the characteristics of the resin composition to be used, the drawing means, the drawing temperature, the desired product form, and the like. It is determined appropriately in the axial or biaxial direction. Even in the case of uniaxial stretching in the transverse direction, it is also effective to impart weak stretching of about 1.05 to 1.8 times in the longitudinal direction for the purpose of improving the mechanical properties of the film. Next, the stretched film is not relaxed in molecular orientation after heat treatment or relaxation treatment at a temperature of about 50 to 100 ° C. for the purpose of reducing the natural shrinkage rate or improving the heat shrinkage characteristics, if necessary. It is quickly cooled in time to become a heat-shrinkable film.

  The thickness of the heat-shrinkable polyolefin-based laminated film of the present invention is not particularly limited, but is usually 20 to 80 μm, preferably 30 to 70 μm. If the thickness is 20 μm or more, the film is easy to handle. On the other hand, if it is 80 μm or less, the transparency and shrinkage workability are excellent, which is economically preferable. If necessary, surface treatment and surface processing such as corona treatment, printing, coating, and vapor deposition, and bag making processing and perforation processing using various solvents and heat sealing can be performed.

  The heat-shrinkable polyolefin-based laminated film of the present invention is processed from a flat shape to a cylindrical shape or the like by an article to be packaged and provided for packaging. For things that require printing in cylindrical containers such as PET bottles, first print the required image on one side of a wide flat film wound up on a roll, and then cut the printed image to the required width. The center seal (the so-called envelope is attached to the seal portion) may be folded into an inner side to form a cylinder. As the center sealing method, a heat sealing method, an adhesive method, and an impulse sealer method can be considered.

  Here, the heat sealing method may damage the appearance because the seal portion contracts due to heat. Moreover, in the method using an adhesive, it is difficult to apply the adhesive stably. Further, in the method using impulse sealing, the seal portion is likely to be wavy, which may impair the appearance. From these facts, the preferred center sealing method employed in the present invention is a method using an organic solvent.

  The organic solvent is preferably a mixed solvent system of a good solvent in which the cyclic olefin, which is the main component of the surface layer (S layer), dissolves or swells relatively easily at room temperature, and a poor solvent that does not swell but of course dissolve. This is because the mixing ratio of the two can be freely changed and the solubility can be freely changed, so that it is possible to easily cope with the welding in accordance with the traveling speed in the center sealing process.

  Examples of the good solvent include aliphatic cyclic ethers such as tetrahydrofuran (THF) and tetrahydropyran, and C5 to C10 linear or cyclic aliphatic hydrocarbons such as pentane, heptane, cyclohexane and cyclooctane. It is done. On the other hand, examples of the poor solvent include aliphatic ketones such as dimethyl ketone and diethyl ketone, aliphatic alcohols such as methyl acetate and ethyl acetate, and cyclic ethylene dioxides such as 1,3-dioxolane and 1,4-dioxane. Etc.

  The heat-shrinkable polyolefin-based laminated film of the present invention has mechanical strength such as film stiffness (rigidity at room temperature), fingerprint whitening resistance, shrinkage finish, transparency, natural shrinkage, regenerative additive property, breakage resistance, etc. However, the use of the film is not particularly limited, but examples of plastic containers using the film include bottles (blow bottles), trays, lunch boxes, prepared dishes containers, and dairy products containers. Representative examples. Examples of these materials include polyester resins such as polyethylene terephthalate, polystyrene resins, polycarbonate resins, nylon resins, polyvinyl chloride resins, phenol resins, and melamine resins. The heat-shrinkable polyolefin-based laminated film of the present invention can be suitably used as a label for containers having a specific gravity of 1.00 or more, such as a PET bottle made of a polyester-based resin such as polyethylene terephthalate.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In addition, the various measured value and evaluation about the film displayed in this specification were performed as follows. Here, the flow direction from the extruder of the film is called the vertical direction, and the orthogonal direction is called the horizontal direction.

(1) Glass transition temperature (Tg)
A sample was cut into a length of 4 mm and a width of 60 mm, using a viscoelastic spectrometer DVA-200 (manufactured by IT Measurement Co., Ltd.), with a vibration frequency of 10 Hz, a strain of 0.1%, a heating rate of 3 ° C./min, and a chuck spacing of 25 mm. About the horizontal direction, it measured to -50-150 degreeC, the peak value of loss elastic modulus (E '') was calculated | required from the obtained data, and the temperature at that time was made into the glass transition temperature (Tg).

(2) Crystal melting peak temperature (Tm)
Using DSC-7 manufactured by PerkinElmer Co., Ltd., 10 mg of the sample was heated from −40 ° C. to 200 ° C. at a heating rate of 10 ° C./min according to JIS K7121, and held at 200 ° C. for 1 minute. The temperature was lowered to −40 ° C. at a cooling rate of 10 ° C./min, held at −40 ° C. for 1 minute, and then the crystal melting peak temperature (Tm) was obtained from a thermogram when the temperature was raised again at a heating rate of 10 ° C./min. .

(3) Haze (cloudiness value)
The total haze of the film was measured according to JIS K7105.

(4) Film specific gravity The obtained heat-shrinkable film was measured according to JIS K7112.

(5) Tensile modulus According to JIS K7127, the film was measured in a direction (longitudinal direction) perpendicular to the main shrinkage direction of the film under the condition of a temperature of 23 ° C. The results of evaluation based on the following criteria are also shown.
(◎): Tensile modulus is 1400 MPa or more (O): Tensile modulus is 1200 MPa or more and less than 1400 MPa (x): Tensile modulus is less than 1200 MPa

(6) Tensile elongation at break In accordance with JIS K7127, measurement was performed in a direction (longitudinal direction) perpendicular to the main shrinkage direction of the film under the conditions of a temperature of 23 ° C. and a test speed of 200 mm / min.

(7) Low temperature tensile elongation at break In accordance with JIS K7127, measurement was performed in a direction (longitudinal direction) orthogonal to the main shrinkage direction of the film under the conditions of a temperature of 0 ° C. and a test speed of 200 mm / min.

(8) Spontaneous shrinkage A sample having a size of 100 mm in the vertical direction and 1000 mm in the horizontal direction was cut from the obtained heat-shrinkable film and left in a constant temperature bath at 30 ° C. for 30 days, and the main shrinkage direction of the film (lateral direction) ), The amount of shrinkage relative to the original size before shrinkage was measured, and the ratio was obtained as a% value.

(9) Heat Shrinkage A sample having a size of 100 mm in the vertical direction and 100 mm in the horizontal direction was cut from the obtained heat-shrinkable film and immersed in a hot water bath at 70 ° C., 80 ° C., and 90 ° C. for 10 seconds each. The amount of shrinkage in the shrinkage direction (lateral direction) was measured, and the ratio of the shrinkage amount to the original size before shrinkage was obtained as a% value.

(10) Fingerprint whitening resistance A sample having a size of 100 mm in the vertical direction and 100 mm in the horizontal direction was cut from the obtained heat-shrinkable film, and fingerprints (grease of hands) were attached to the film surface. After soaking for 2 seconds, the state of the fingerprint adhering portion was visually evaluated and displayed according to the following criteria.
(○): Whitening (crack) is not noticeable in the fingerprint adhesion part (×): Whitening (crack) is conspicuous in the fingerprint adhesion part

(11) Shrinkage finishing property A film printed with a grid of 10 mm in length and width was cut into a size of 100 mm in the vertical direction and 298 mm in the horizontal direction. This cylindrical film was attached to a 1.5-liter round PET bottle with an internal capacity of 10 seconds without rotating through a steam heating type 3 m-length shrink tunnel. The blowing steam temperature was 99 ° C., and the tunnel atmosphere temperature was 90 to 94 ° C. After coating the film, the shrinkage finish was evaluated according to the following criteria.
(○): Shrinkage is sufficient, wrinkled, no avatar, lattice distortion is practically satisfactory, and film adhesion is good (×): Clearly shrinkage is insufficient or wrinkle Intrusion, avatar, lattice distortion is conspicuous

(12) Specific gravity of printing label On one side of the obtained heat-shrinkable film, gravure ink (manufactured by Dainichi Seika Kogyo Co., Ltd., trade name: OS-M65 white) is printed on the entire surface with a bar coater (# 4) (solid printing) After that, drying was performed at a temperature of 23 ° C. for 24 hours to obtain a printed label having an ink coating film having a density of 1.40 g / cm ³ and a thickness of 3 μm. Using this printed label, measurement was performed according to JIS K7112.

(Example 1)
As shown in Table 1, the constituent component of the surface layer (S layer) is an ethylene-norbornene random copolymer (manufactured by Ticona, trade name: Topas 9506, Tg: 71 ° C., MFR (JIS) as a cyclic olefin resin. K7210, temperature: 190 ° C., load: 21.18 N, hereinafter, unless otherwise specified, measurement conditions of MFR are the same): 1.3 g / 10 min) (hereinafter abbreviated as “annular PO”) 70% by mass A linear low-density polyethylene resin (manufactured by Ube Industries, Ltd., trade name: UMERIT 0540F, density: 0.904 g / cm ³ , Tm: 111 ° C., MFR: 4. 0 g / 10 min) (hereinafter abbreviated as “PE1”) 30% by mass with 100 parts by mass of the mixed resin composition, an antioxidant (Ciba Specialty Chemica) Inc., trade name: Irganox 1010) as a resin composition obtained by adding 0.1 part by weight,
Constituent components of the intermediate layer (L layer) are linear low density polyethylene (manufactured by Mitsui Chemicals, Inc., trade name: evolveSP2540, density: 0.923 g / cm ³ , Tm: 123 ° C.) as the polyethylene resin (B). MFR: 4.0 g / min) (hereinafter abbreviated as “PE2”),
Constituent components of the intermediate layer (M layer) are 60% by mass of cyclic PO as a cyclic olefin resin and a polyethylene resin (C), a high density polyethylene resin (manufactured by Mitsui Chemicals, Inc., trade name: Hi-Zex HZ2200J). , Density: 0.964 g / cm ³ , Tm: 136 ° C., MFR: 5.2 g / 10 min) (hereinafter abbreviated as “PE3”) 40% by mass.

The constituent components of each layer are put into separate single-screw extruders, melted and mixed at a set temperature of 240 ° C., and then the thickness of each layer is (S layer) / (L layer) / (M layer) / (L layer) / ( S layer) = 20 μm / 20 μm / 120 μm / 20 μm / 20 μm Co-extruded from a three-layer die, taken with a cast roll at 50 ° C., cooled and solidified to obtain an unstretched laminated sheet having a width of 300 mm and a thickness of 200 μm. Next, in the tenter stretching facility, the film is stretched 4.0 times in the transverse uniaxial direction at a preheating temperature of 110 ° C. and a stretching temperature of 84 ° C., and then rapidly cooled with cold air to obtain a heat-shrinkable polyolefin laminated film having a thickness of 50 μm. It was.
The results of evaluating the obtained film are shown in Table 1. Moreover, the film which did not have a problem with respect to all the evaluation items was evaluated as (◯), and the film having even one problem was evaluated as (×).

(Example 2)
As shown in Table 1, in Example 1, the thickness of each layer before stretching was (S layer) / (L layer) / (M layer) / (L layer) / (S layer) = 15 m / 35 μm / 100 μm / A heat-shrinkable polyolefin-based laminated film was obtained in the same manner as in Example 1 except that the thickness was changed to 35 μm / 15 μm. The results of evaluating the obtained film are shown in Table 1.

(Example 3)
As shown in Table 1, in Example 1, the mass ratio of the mixed resin composition composed of cyclic PO and PE1 used for the surface layer (S layer) was changed to 60 mass% for cyclic PO and 40 mass% for PE1. Example except that the thickness of each layer before stretching was changed to (S layer) / (L layer) / (M layer) / (L layer) / (S layer) = 13 μm / 47 μm / 80 μm / 47 μm / 13 μm As in Example 1, a heat-shrinkable polyolefin laminated film was obtained. The results of evaluating the obtained film are shown in Table 1.

Example 4
As shown in Table 1, in Example 1, the mass ratio of the mixed resin composition composed of cyclic PO and PE3 used for the intermediate layer (M layer) was changed to 80% by mass for cyclic PO and 20% by mass for PE3. Except for the above, a heat-shrinkable polyolefin-based laminated film was obtained in the same manner as in Example 1. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 1)
As shown in Table 1, in Example 1, except that the mixed resin composition composed of cyclic PO and PE1 used for the surface layer (S layer) and the mass ratio thereof were changed to 100% by mass of cyclic PO. As in Example 1, a heat-shrinkable polyolefin laminated film was obtained. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 2)
As shown in Table 1, in Example 1, the thickness of each layer before stretching was (S layer) / (L layer) / (M layer) / (L layer) / (S layer) = 34 μm / 66 μm / 0 μm / A heat-shrinkable polyolefin-based laminated film was obtained in the same manner as in Example 1 except that the structure was changed to 66 μm / 34 μm and the two-layer / three-layer configuration. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 3)
As shown in Table 1, in Example 1, the mass ratio of the mixed resin composition composed of cyclic PO and PE3 used for the intermediate layer (M layer) was changed to 30% by mass of cyclic PO and 70% by mass of PE3. Except for this, the same procedure as in Example 1 was performed. However, the film could not be stretched due to film breakage.

  From Table 1, the heat-shrinkable polyolefin-based laminated film specified in the present invention is excellent in film stiffness (rigidity at room temperature), anti-fingerprint whitening, shrinkage finish, transparency, and natural shrinkage. It turns out that specific gravity can be achieved (Examples 1-4). On the other hand, regarding the resin composition of the surface layer (S layer), it can be seen that when the polyethylene resin (A) is not mixed, the whitening resistance is inferior (Comparative Example 1). Next, when the intermediate layer (M layer) composed of the mixed resin composition of the cyclic olefin resin and the polyethylene resin (C) is not provided, the specific gravity can be reduced, but the waist of the film (at room temperature) It can be seen that the rigidity (here, tensile modulus) is inferior (Comparative Example 2). In addition, regarding the resin composition of the intermediate layer (M layer), it is understood that when the polyethylene resin (C) is mixed in a large amount at a ratio outside the range specified in the present invention, it is difficult to stretch at a low temperature. (Comparative Example 3).

Claims (6)

In a heat-shrinkable polyolefin-based laminated film having a specific gravity of less than 1.00,
A heat-shrinkable polyolefin, characterized in that it is a laminated film having a surface layer (S layer), an intermediate layer (L layer), and an intermediate layer (M layer), each layer mainly comprising the following composition or resin. Laminated film.
(S layer): Polyethylene resin (A) having a cyclic olefin resin of 90 to 50% by mass and a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of 90 ° C. or more and 125 ° C. or less. Mixed resin composition with 10-50 mass%.
(L layer): Polyethylene resin (B) having a crystal melting peak temperature (Tm) measured with a differential scanning calorimeter of 125 ° C. or lower.
(M layer): 95 to 50% by mass of a cyclic olefin resin and a polyethylene resin having a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of more than 125 ° C. and 140 ° C. or less ( C) Mixed resin composition with 5 to 50% by mass.   (S layer) / (L layer) / (M layer) / (L layer) / (S layer) or (S layer) / (M layer) / (L layer) / (M layer) / (S layer) The heat-shrinkable polyolefin-based laminated film according to claim 1 having a layer structure of   The heat-shrinkable polyolefin-based laminated film according to claim 1 or 2, wherein the specific gravity is 0.97 or less.   A heat-shrinkable label having a specific gravity of less than 1.00, wherein the heat-shrinkable polyolefin-based laminated film according to any one of claims 1 to 3 is subjected to printing treatment on one side or both sides.   A plastic container equipped with the heat-shrinkable label according to claim 4. In a heat-shrinkable polyolefin-based laminated film having a specific gravity of less than 1.00,
A laminated film having a surface layer (S layer), an intermediate layer (L layer), and an intermediate layer (M layer), each layer comprising the following composition or resin as a main component,
The heat shrinkability is characterized in that the tensile elastic modulus in the direction orthogonal to the main shrinkage direction of the film is 1200 MPa or more, and the heat shrinkage rate when immersed in warm water at 80 ° C. for 10 seconds is 20% or more in at least one direction. Polyolefin-based laminated film.
(S layer): Polyethylene resin (A) having a cyclic olefin resin of 90 to 50% by mass and a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of 90 ° C. or more and 125 ° C. or less. Mixed resin composition with 10-50 mass%.
(L layer): Polyethylene resin (B) having a crystal melting peak temperature (Tm) measured with a differential scanning calorimeter of 125 ° C. or lower.
(M layer): 95 to 50% by mass of a cyclic olefin resin and a polyethylene resin having a crystal melting peak temperature (Tm) measured by a differential scanning calorimeter (DSC) of more than 125 ° C. and 140 ° C. or less ( C) Mixed resin composition with 5 to 50% by mass.