JP2005179610A - Cycloolefin-based heat-shrinkable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a film that has a low specific gravity and can easily be separated from a PET (polyethylene telephthalate) bottle by specific gravity difference during the recycling process; that is excellent in low-temperature shrink properties and dimensional stability; and that, even when the film having a portion to which oils and fats such as fingerprints adhere is subjected to heat shrinking, does not cause whitening on the adhered portion. <P>SOLUTION: This heat-shrinkable film has at least one resin layer composed mainly of a resin composition produced by adding a plasticizer to a cycloolefin-based resin and has a value Δn of birefringence index of 5.0-8.0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a packaging material excellent in transparency, particularly a cyclic olefin-based heat-shrinkable film, which is useful as a label or cap seal, by preventing occurrence of dirt due to fingerprint adhesion on the front and back surfaces during shrinkage.

  Soft drinks such as juice are sold in containers such as bottles or PET bottles. At that time, in order to differentiate from other products and improve the visibility of the products, a heat-shrinkable label whose inner surface is printed is often attached to the outside of the container. Examples of the label material include polystyrene, polyester, polyvinyl chloride, and polyolefin.

  In addition, when the container is a plastic bottle, the plastic bottle collected after use for recycling is often recycled into flakes and pellets. An outline of this process will be described below. Collected PET bottles (usually with polyethylene caps and heat-shrinkable labels) can be used for other containers such as glass bottles, cans, and PVC bottles by hand, weight separator, X-ray inspection, etc. Sorted out from Next, the PET bottle is pulverized into several mm to 10 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. Desired regenerated pet flakes or regenerated pet 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) and a thing that sinks in water (a heat-shrinkable label or plastic bottle having a specific gravity of 1 or more) The wind power separator is a device that expands the pulverized body and blows the heat-shrinkable label pulverized body by blowing air from below. From each principle, the specific gravity separator has a large throughput per unit time, while that of the wind separator is small. For this reason, a heat-shrinkable label having a specific gravity of less than 1 that can be removed by a specific gravity separator is desired.

  However, among the label materials, the polystyrene label has a large natural shrinkage rate, the polyester label has a large shrinkage rate when thermally contracted, and both are difficult to handle. The polyvinyl chloride label is a harmful gas such as hydrogen chloride when incinerated after use. There is a problem of generating. Further, since each label has a specific gravity greater than 1, there is a problem that it cannot be separated by a specific gravity separator in the recycling process. On the other hand, the polyolefin label has a specific gravity of less than 1, but has a problem that its waist and gloss are insufficient and cannot be produced by center seal processing with an organic solvent. Furthermore, since the polyolefin label does not shrink unless the heat shrink temperature is raised, there is a problem that it has no heat resistance, for example, cannot be used for a non-heat resistant PET bottle.

Therefore, when these problems were examined, a shrink film having a specific gravity of 1 or less in which a layer made of an amorphous resin such as a cyclic olefin resin and a layer made of a polyolefin resin were laminated was found. The heat-shrinkable film made of this cyclic olefin resin is excellent in transparency and gloss, and has an appropriate waist, so that it has been studied as a variety of packaging materials. For example, in Patent Document 1, a layer composed mainly of an olefin resin having a density of less than 0.94 g / cm ³ is used as an intermediate layer, and layers having a cyclic polyolefin resin as a main component are provided on the front and back surfaces to form a laminate. A heat-shrinkable film having a specific gravity of less than 0.96, obtained by stretching the laminate 3-6 times, is disclosed. Further, Patent Document 2 discloses a cyclic polyolefin heat-shrinkable tube having a printed surface as an inner surface, a bonding surface for forming a tube having an excellent appearance, and excellent bonding strength. However, the heat shrinkable film that forms the front and back surfaces with a cyclic olefin-based resin has the problem that when the oil and fat such as fingerprints adheres to the film surface, the oil and fat adhering part is whitened and the appearance is impaired. In many cases, it is not necessarily good as heat shrink packaging suitability.
JP 2000-20951 A JP 2000-211025 A

  The problem to be solved by the present invention is a heat-shrinkable label film using a cyclic olefin-based resin, which has excellent low-temperature shrinkage characteristics and dimensional stability, and can be heat-shrinked in a state where oils such as fingerprints are attached. An object of the present invention is to provide a film that does not cause whitening at the adhered portion.

The inventor has found a heat-shrinkable film that can solve the above problems, and the gist of the film is as follows.
A cyclic olefin having at least one resin layer mainly composed of a resin composition obtained by adding a plasticizer to a cyclic olefin resin, and having a birefringence value Δn of 4.0 to 8.0. The heat-shrinkable film.

  According to the present invention, the function of a heat-shrinkable label is maintained, and even if oil adheres to the surface of the film without heat loss without deteriorating the transparency of the film, whitening does not occur, and a heat-shrinkable film excellent in appearance is obtained. Is possible. Further, when the label has a specific gravity of less than 1, it can be easily separated by a specific gravity separator during recycling.

The present invention will be described in detail below.
The cyclic olefin-based resin of the present invention is a general generic name. Specifically, (a) a polymer obtained by hydrogenating a ring-opened (co) polymer of a cyclic olefin as necessary, and (b) a cyclic olefin. Addition (co) polymer, (c) Random copolymer of cyclic olefin and α-olefin such as ethylene, propylene, (d) The above (a) to (c) were modified with unsaturated carboxylic acid or its derivative, etc. Examples include graft modified products. Specific examples of the cyclic olefin copolymer resin include a product name “ZEONOR” manufactured by Nippon Zeon Co., Ltd., a product name “Apel” manufactured by Mitsui Chemicals, Inc., and a product name “Topas” manufactured by Ticona. be able to. The specific gravity of the cyclic olefin resin is generally 1.00 to 1.05. The cyclic olefin polymers are described in, for example, JP-A-60-168708, JP-A-61-115916, JP-A-61-271308, JP-A-61-252407. Can be produced according to known methods.
Further, in the present invention, the cyclic olefin ring-opening (co) polymer or the hydrogenated product of the cyclic olefin ring-opening (co) polymer is, for example, maleic anhydride, maleic acid, itaconic anhydride, itaconic acid, (meth) acrylic. Graphs and copolymers modified with modifiers of unsaturated carboxylic acids such as acids or anhydrides can also be used.

  The glass transition temperature of the cyclic olefin-based resin is preferably 50 to 105 ° C, more preferably 55 to 90 ° C. If it is less than 50 ° C, the heat shrinkage rate in the main stretching direction at 60 ° C tends to be too large, and if it exceeds 105 ° C, the heat shrinkage rate in the main stretching direction at 70 to 90 ° C tends to be too small.

  The cyclic olefin resin of the present invention and the component to be added are plasticizers that are compatible at such an extent that they do not separate from each other when added, preferably transparent to translucent and have a certain degree of compatibility and are liquid at normal temperature and pressure. Specifically, those commonly known as plasticizers for vinyl chloride resins, namely di-n-butyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisooctyl phthalate, phthalic acid Phthalic acid plasticizers such as octyldecyl, diisodecyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl isophthalate, di-2-ethylhexyl adipate, di-n-decyl adipate, diisodecyl adipate, dibutyl sebacate , Aliphatic ester plasticizers such as di-2-ethylhexyl sebacate, trimellitic acid plasticizers such as trioctyl trimellitic acid and tridecyl trimellitic acid, pyromellitic acid plasticizers such as pyromellitic acid tetraoctyl, phosphorus Tributyl phosphate, tri-2-ethylhexyl phosphate, 2-ethyl phosphate Phosphate ester plasticizers such as tilhexyl diphenyl and tricresyl phosphate, aliphatic dibasic esters such as dioctyl adipate and dioctyl sebacate, epoxidized soybean oil, epoxidized linseed oil, epoxidized castor oil, and epoxidized safflower Epoxy plasticizers such as oil, epoxy stearate ester, epoxyhexahydrophthalate dioctyl, etc., liquid polyisobutylene that is a high-purity isobutylene polymer and a hydrocarbon polymer having an unsaturated double bond at the end of the molecular chain, a small amount Is a copolymer in which some normal butenes mainly composed of liquid butyl rubber, liquid polybutadiene, liquid polyisoprene, and isobutene are reacted. An example of a liquid polybutene It can be. Among these, liquid polybutene is more preferable from the viewpoint of compatibility. In addition, the low molecule here refers to a molecular weight compound having a molecular weight of about 10,000 or less, usually 5000 or less, and may contain two or more kinds.

  When the low molecular weight compound is added, the addition amount is determined by the degree of molecular orientation of the cyclic olefin-based resin composition, and the molecular orientation can be estimated from the birefringence value. In order to prevent soiling due to adhesion of oils and fats, the birefringence value Δn of the molded cyclic olefin resin film is preferably in the range of 5.0 to 8.0, more preferably in the range of 6.0 to 7.0. When Δn is less than 5.0, appropriate heat shrinkage characteristics are often not obtained, and when attached to a bottle, the appearance may deteriorate due to insufficient shrinkage. In addition, since the plasticizer is added in a large amount, the plasticizer bleeds on the film surface, resulting in poor lubricity, the glass transition temperature of the plasticized composition is lowered, and the heat resistance of the film surface is reduced. As a result, the surface becomes sticky by heating. For example, when used as a shrink label, a phenomenon that the containers are blocked on the mounting line tends to occur. On the other hand, when Δn is 8.0 or more, the whitening phenomenon at the time of shrinkage cannot be completely suppressed, and the film appearance may be impaired.

  The film of the present invention can be produced by a known method. The shape of the film may be either flat or tube-like, but it is more flat from the viewpoint of productivity (a few products can be taken in the width direction of the original film) and printing on the inner surface. preferable. 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 vertical direction, and tenter-stretched in the horizontal direction. An example is a method of obtaining a film by winding, annealing, cooling, and winding with a winder (corona discharge treatment is applied to the surface when printing is performed). Moreover, the method of cutting open the film manufactured by the tubular method and making it flat is also applicable.

  In applications where the stretching ratio is contracted in two directions, such as for overlap, the longitudinal direction is 2 to 10 times, the transverse direction is 2 to 10 times, preferably the longitudinal direction is 3 to 6 times, and the transverse direction is about 3 to 6 times. Is desirable. On the other hand, in applications that shrink mainly in one direction, such as for shrink labels, the direction corresponding to the main shrinking direction is 2 to 10 times, preferably 4 to 8 times, and the direction perpendicular to it is 1 to 2 times (1 times is It is desirable to select a magnification ratio of 1.1 to 1.5 times, preferably in the category of uniaxial stretching. Since the film obtained at a normal biaxial stretching ratio also has a large thermal shrinkage rate in the direction perpendicular to the main shrinkage direction, for example, when used as a shrinkage label, the film also extends in the height direction of the container when it is attached to the container. A so-called vertical shrinkage phenomenon that heat shrinks occurs, which is not preferable.

  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 measured value and evaluation which are shown to an Example were performed as follows. Here, the film take-up (flow) direction is described as the “longitudinal” direction, and the direction perpendicular thereto is described as the “transverse” direction.

[Heat shrinkage]
The film was cut into a size of 100 mm in length and 100 mm in width, and immersed in a hot water bath at 80 ° C. for 10 seconds, and the amount of shrinkage was measured. The thermal shrinkage rate was expressed as a ratio (%) of the shrinkage amount to the original size before shrinkage in the lateral direction.

[All haze]
Measurement was performed according to JIS-K-6714 using a film haze haze meter.

[Birefringence]
Using a birefringence Abbe refractometer, the longitudinal refractive index n _MD and the width refractive index n _TD of the uniaxially oriented film were measured and defined by the difference between both values, that is, | n _MD −n _TD |.

[Evaluation of whitening]
The film is cut into a size of 100 mm in length and 210 mm in width, set in a fixed frame having a length of 130 mm, width of 150 mm, and chuck allowance of 10 mm in a state where the film is slackened, rapeseed oil is applied to the film surface, and the fixed frame is 90 ° C. Is immersed in a warm water bath for 10 seconds, and immersed in cold water immediately after soaking, a film in a state of 20% heat shrinkage is collected. The rapeseed oil on the surface of the film after 20% heat shrinkage was wiped off, and the whitening of the part where the rapeseed oil was applied was visually confirmed. The case where no whitening was observed was marked with ◯, the case where whitening was not observed but a mark remained on the coated part was marked with Δ, and the case where whitening was seen was marked with ×.

(Example 1)
Cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. Liquid polybutene having a molecular weight of 500 in 100 parts by weight (manufactured by Nippon Petrochemical Co., Ltd .: “Nippon Polybutene LV100” 3) parts by weight was added and melt kneaded using the same direction twin screw extruder to obtain a pellet of the composition. An unstretched sheet having a width of 200 mm and a thickness of 200 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 100 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. Shrinkage was carried out at 90 ° C. for 10 seconds, but no whitening was observed at the oil and fat adhesion portion, and the film appearance was good.

(Example 2)
Liquid polybutene having a molecular weight of 500 (manufactured by Nippon Petrochemical Co., Ltd .: “Japan” with respect to 100 parts by weight of a cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. Polybutene LV100 ") was added in an amount of 5 parts by weight, and melt kneaded using the same-direction twin screw extruder to obtain pellets of the composition. An unstretched sheet having a width of 200 mm and a thickness of 240 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 95 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. Shrinkage was carried out at 90 ° C. for 10 seconds, but no whitening was observed at the oil and fat adhesion portion, and the film appearance was good.

(Example 3)
Liquid polybutene (manufactured by Nippon Petrochemical Co., Ltd.) having a molecular weight of 500 per 100 parts by weight of a cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. as front and back layers. A composition comprising 3 parts by weight of “Nippon Polybutene LV100”) and a low-density polyethylene (manufactured by Nippon Polychem Co., Ltd .: “LF440HB”) as an intermediate layer, each melted and kneaded using a same-direction twin screw extruder Pellets were obtained. This composition was put into separate extruders, then co-extruded from a three-layer die so that the thickness of each layer would be front / back layer / intermediate layer / front / back layer = 1/4/1, and taken and solidified by a 50 ° C. cast roll. Thus, a two-type three-layer sheet having a thickness of 200 μm was obtained. This was stretched 4 times in a uniaxial direction at a temperature of 100 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. Shrinkage was carried out at 90 ° C. for 10 seconds, but no whitening was observed at the oil and fat adhesion portion, and the film appearance was good.

(Comparative Example 1)
A cyclic olefin-ethylene copolymer having a glass transition point of 70 ° C. (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) was melt-kneaded using the same-direction twin screw extruder to obtain pellets of the composition. An unstretched sheet having a width of 200 mm and a thickness of 240 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 100 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. When contracted at 90 ° C. for 10 seconds, whitening occurred in the oil and fat adhesion portion, and the appearance was remarkably impaired.

(Comparative Example 2)
Cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. Liquid polybutene having a molecular weight of 500 in 100 parts by weight (manufactured by Nippon Petrochemical Co., Ltd .: “Nippon Polybutene LV100” 3) parts by weight was added and melt kneaded using the same direction twin screw extruder to obtain a pellet of the composition. An unstretched sheet having a width of 200 mm and a thickness of 240 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 90 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. When contracted at 90 ° C. for 10 seconds, whitening occurred in the oil and fat adhesion portion, and the appearance was remarkably impaired.

(Comparative Example 3)
Cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. Liquid polybutene having a molecular weight of 500 in 100 parts by weight (manufactured by Nippon Petrochemical Co., Ltd .: “Nippon Polybutene LV100” 5) parts by weight was added and melt-kneaded using a twin-screw extruder in the same direction to obtain composition pellets. An unstretched sheet having a width of 200 mm and a thickness of 240 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 90 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. When contracted at 90 ° C. for 10 seconds, whitening occurred in the oil and fat adhesion portion, and the appearance was remarkably impaired.

(Comparative Example 4)
Cyclic olefin-ethylene copolymer (manufactured by Nippon Zeon Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. Liquid polybutene having a molecular weight of 500 in 100 parts by weight (manufactured by Nippon Petrochemical Co., Ltd .: “Nippon Polybutene LV100” 10) parts by weight was added and melt-kneaded using a twin-screw extruder in the same direction to obtain composition pellets. An unstretched sheet having a width of 200 mm and a thickness of 240 μm was obtained from this composition using a single screw extruder. This was stretched 4 times in a uniaxial direction at a temperature of 100 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. When contracted at 90 ° C. for 10 seconds, no whitening of the oil / fat deposit occurred, but the contraction rate was insufficient.

(Comparative Example 5)
Cyclic olefin-ethylene copolymer (manufactured by ZEON Co., Ltd .: “ZEONOR750R”) having a glass transition point of 70 ° C. serving as the front and back layers, low density polyethylene (manufactured by Nippon Polychem Co., Ltd .: “LF440HB”) serving as the intermediate layer, After feeding into separate extruders, each layer is co-extruded from a three-layer die so that the thickness of each layer is front / back layer / intermediate layer / front / back layer = 1/4/1, and is taken up and solidified by a 50 ° C. cast roll to a thickness of 200 μm. 2 types of 3 layer sheets were obtained. This was stretched 4 times in a uniaxial direction at a temperature of 90 ° C. using a biaxial stretching apparatus (manufactured by TM Long) to prepare a heat-shrinkable film having a thickness of 50 μm. However, the preheating time was 30 seconds and the stretching speed was 3000% / min. The results of this heat shrink film are shown in Table 1. When contracted at 90 ° C. for 10 seconds, whitening occurred in the oil and fat adhesion portion, and the appearance was remarkably impaired.

Claims (4)

Cyclic olefin-based heat shrinkage having at least one resin layer containing a resin composition obtained by adding a plasticizer to a cyclic olefin-based resin, and having a birefringence value Δn of 5.0 to 8.0 Sex film. The cyclic polyolefin resin is a homopolymer of a norbornene polycyclic olefin, a copolymer of a norbornene polycyclic olefin and an acyclic α-olefin, or a homopolymer of a tetracyclododecene polycyclic olefin. The cyclic olefin-based heat-shrinkable film according to claim 1, which is at least one polymer selected from the group consisting of a copolymer of tetracyclododecene polycyclic olefin and acyclic α-olefin. The cyclic olefin-based heat-shrinkable film according to claim 1 or 2, wherein the plasticizer is selected from the group consisting of liquid polybutadiene, liquid polyisoprene, and liquid polybutene. The cyclic olefin-based heat-shrinkable film according to any one of claims 1 to 3, wherein the film is for heat-shrinkable labels and cap seals of containers.