JP5545933B2 - Multilayer shrink film - Google Patents

Description

  The present invention relates to a shrink film using a cyclic olefin resin.

  In recent years, shrink film has been used as an exterior to prevent the contents from fouling, falsification, and display, or for the integrated packaging of products for improving transportation efficiency and sales promotion, and for the contents of packaging items. It is widely used for packaging to avoid direct impact, tight packaging, and label packaging that also serves to protect glass bottles or plastic bottles and display products.

  Among these, the label for PET bottles is used for the purpose of protecting bottles, improving design properties, various displays related to products, etc., and its use is expanding. In this application, since many PET bottles have low heat resistance, it is necessary to shrink at a low temperature, and in addition to various bottle shapes, a beautiful finish that adheres not only to the trunk but also to the neck is obtained. Therefore, a high shrinkage rate is preferred, and it is required to be excellent in transparency and gloss in order to improve the appearance of the product.

  Currently, labels made of polystyrene or polyethylene terephthalate having suitable heat shrinkage properties and excellent appearance are most widely used.

However, with the recent promotion of recycling, problems with these labels have become apparent. That is, the PET bottle is separated and collected and recycled to various products, but since the label is printed, it is necessary to separate it from the bottle. When the label is mixed, the quality is deteriorated at the time of reproduction. Therefore, it is necessary to remove the label from the bottle and recycle it. However, there are actually many cases where the label is collected without removing the label, and it is now necessary for the collector to remove them one by one. This is because polystyrene and polyethylene terephthalate have a small difference in specific gravity with PET bottles, so that floating separation is difficult. Specific gravity separation is industrially very easy. In particular, PET bottles have a specific gravity of about 1.3 or more, whereas specific gravity separation with water is possible if the specific gravity is 1.0 or less. Therefore, if the specific gravity of the material used for the multilayer shrink film is 1.0 or less, even if it is mixed, it can be separated very efficiently, so that the burden at the time of collection can be greatly reduced. .

  As means for solving the above problems, a shrink film containing a cyclic olefin-based resin has been disclosed (see Patent Document 1 and Patent Document 2).

  However, in the shrink films described in Patent Documents 1 and 2, various properties required for the heat-shrinkable film for labels, particularly the heat shrinkage rate and perforation suitability (longitudinal tear propagation strength) which are important properties. ), Prevention of whitening at the time of heat shrinkage of the fingerprint adhesion portion, haze, gloss, waist, impact strength, shrinkage stress, etc. are not all satisfied.

  Then, the multilayer shrink film which improved these characteristics is indicated (refer to patent documents 3).

JP 2001-162725 A JP 2002-234115 A International Publication WO 2004/110750 Pamphlet

  By the way, a multilayer shrink film is obtained by extending | stretching a multilayer sheet. As described above, the multilayer shrink film described in Patent Document 3 has many properties improved, but depending on the type of cyclic olefin resin used, there is a problem that whitening occurs during stretching of the multilayer sheet. .

  In the case of a multilayer shrink film using a cyclic olefin-based resin, there may be a regular thickness variation that occurs in the drawing direction of the film called “draw resonance” when the multilayer sheet is formed before stretching.

  Therefore, there is a demand for improvement measures when the above-mentioned problems of whitening and thickness instability occur when a desired cyclic olefin-based resin is used. That is, there is a need for a technique for applying a cyclic olefin resin to a multilayer shrink film regardless of the material of the cyclic olefin resin.

  The present invention has been made in order to solve the above-described problems. The purpose of the present invention is to reduce the thickness of a multilayer shrink film using a cyclic olefin resin when the multilayer sheet is stretched and when the multilayer sheet is molded. It is an object of the present invention to provide a multilayer shrink film that prevents the occurrence of stability.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the cause of whitening is the haze caused by the difference between the melt tension of the cyclic olefin resin and the melt tension of polyethylene, and the melt tension of the cyclic olefin resin composition is blended with a specific cyclic olefin resin. As a result, the thickness of the multilayer sheet was found to be stable, and the present invention was completed. More specifically, the present invention provides the following.

  (1) A multilayer shrink film comprising at least three layers of a surface layer / intermediate layer / back surface layer, wherein the surface layer and the back surface layer include a cyclic olefin resin (A) containing ethylene as a copolymerization component; A cyclic olefin resin composition containing a cyclic olefin resin (B) having a glass transition point higher than that of the cyclic olefin resin (A) and containing ethylene as a copolymerization component; and a linear low-density polyethylene (C) In the cyclic olefin resin composition, the content of the cyclic olefin resin (A) in the cyclic olefin resin composition is from 40% by mass to 95% by mass, and in the cyclic olefin resin composition The content of the cyclic olefin resin (B) is 5% by mass to 60% by mass, and the melt olefin of the cyclic olefin resin composition is used. ® down is the 1.15 times higher than the melt tension of the linear low-density polyethylene (C), a multilayer shrink film comprising front and back polyolefin resin composition.

  (2) The melt tension of the polyolefin resin composition for front and back surfaces measured at 190 ° C. with a winding speed of 15 m / min is 30 mN or more, and the ring for front and back surfaces at 190 ° C. and a load of 2.16 kg. The multilayer shrink film according to (1), wherein the melt flow rate of the olefin-based resin composition is 0.1 g / 10 min to 1.5 g / 10 min.

  (3) Melt tension of the cyclic olefin resin composition measured at 190 ° C. with a winding speed of 15 m / min, and the linear low-pressure measured at 190 ° C. with a winding speed of 15 m / min. The multilayer shrink film according to (1) or (2), wherein the difference from the melt tension of the density polyethylene (C) is +10 mN to +40 mN.

  (4) The multilayer shrink film according to any one of (1) to (3), wherein the linear low density polyethylene (C) is a linear low density polyethylene polymerized by a metallocene catalyst.

  (5) The melt tension of the linear low-density polyethylene (C) measured at 190 ° C. and a winding speed of 15 m / min is 20 mN to 40 mN, according to any one of (1) to (4) Multi-layer shrink film.

  (6) The multilayer shrink film according to any one of (1) to (5), wherein the glass transition point of the cyclic olefin-based resin (A) is 80 ° C. or lower.

(7) The said cyclic olefin resin composition is a multilayer shrink film in any one of (1) to (6) which has a single glass transition point.

  (8) The multilayer shrink according to any one of (1) to (7), wherein the cyclic olefin resin (A) and / or the cyclic olefin resin (B) is a copolymer composed of norbornene and ethylene. the film.

  According to the present invention, in a multilayer shrink film using a cyclic olefin resin, a cyclic olefin resin composition having a glass transition point higher than the cyclic olefin resin having a low melt tension is added. By using the product, the melt tension of the cyclic olefin resin composition is significantly improved as compared with the low melt tension of the cyclic olefin resin. By improving the melt tension, instability of the thickness at the time of forming the multilayer sheet can be prevented. Furthermore, the value of the melt tension of the cyclic olefin-based resin composition is very high as compared with the melt tension of the linear low-density polyethylene, so that whitening during stretching of the multilayer sheet can be prevented.

  Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment, and may be implemented with appropriate modifications within the scope of the object of the present invention. it can.

  The multilayer shrink film of the present invention comprises at least three layers of a surface layer / intermediate layer / back surface layer, and the surface layer and the back surface layer are composed of a cyclic olefin-based resin composition and a linear low density polyethylene (C). It contains the polyolefin resin composition for front and back which contains.

<Surface layer / Back layer>
The cyclic olefin resin composition contained in the surface layer and the back layer includes a cyclic olefin resin (A) and a cyclic olefin resin (B) having a glass transition point lower than that of the cyclic olefin resin (A).

[Cyclic olefin resin (A)]
The cyclic olefin resin (A) used in the present invention is not particularly limited as long as it contains a cyclic olefin component as a copolymerization component and is a polyolefin resin containing a cyclic olefin component in the main chain. For example, an addition polymer of a cyclic olefin or a hydrogenated product thereof, an addition copolymer of a cyclic olefin and an α-olefin, or a hydrogenated product thereof can be used.

  Moreover, as the cyclic olefin resin (A) containing a cyclic olefin component used in the present invention as a copolymerization component, a polymer obtained by grafting and / or copolymerizing an unsaturated compound having a polar group to the above polymer, Including.

  Examples of the polar group include a carboxyl group, an acid anhydride group, an epoxy group, an amide group, an ester group, and a hydroxyl group. Examples of the unsaturated compound having a polar group include (meth) acrylic acid and maleic acid. Acid, maleic anhydride, itaconic anhydride, glycidyl (meth) acrylate, alkyl (meth) acrylate (carbon number 1-10) ester, maleic acid alkyl (carbon number 1-10) ester, (meth) acrylamide, (meta ) 2-hydroxyethyl acrylate.

  In the present invention, an addition copolymer of a cyclic olefin and an α-olefin or a hydrogenated product thereof can be preferably used.

  Moreover, as the cyclic olefin-based resin (A) containing the cyclic olefin component used in the present invention as a copolymerization component, it is also possible to use a commercially available resin. Examples of the commercially available cyclic olefin-based resin (A) include TOPAS (registered trademark) (Topas Advanced Polymers), Apel (registered trademark) (Mitsui Chemicals), Zeonex (registered trademark) (Nippon Zeon Corporation). Product), Zeonoa (registered trademark) (manufactured by Nippon Zeon Co., Ltd.), Arton (registered trademark) (manufactured by JSR Corporation), and the like.

（式中、Ｒ１〜Ｒ１２は、それぞれ同一でも異なっていてもよく、水素原子、ハロゲン原子、及び、炭化水素基からなる群より選ばれるものであり、Ｒ９とＲ１０、Ｒ１１とＲ１２は、一体化して２価の炭化水素基を形成してもよく、Ｒ９又はＲ１０と、Ｒ１１又はＲ１２とは、互いに環を形成していてもよい。また、ｎは、０又は正の整数を示し、ｎが２以上の場合には、Ｒ５〜Ｒ８は、それぞれの繰り返し単位の中で、それぞれ同一でも異なっていてもよい。） The addition copolymer of cyclic olefin and α-olefin preferably used in the composition of the present invention is not particularly limited. Particularly preferred examples include a copolymer containing [1] an α-olefin component having 2 to 20 carbon atoms and [2] a cyclic olefin component represented by the following general formula (I).

(In the formula, R1 to R12 may be the same or different and are selected from the group consisting of a hydrogen atom, a halogen atom, and a hydrocarbon group, and R9 and R10, and R11 and R12 are integrated. May form a divalent hydrocarbon group, and R9 or R10 and R11 or R12 may form a ring with each other, and n represents 0 or a positive integer, In the case of 2 or more, R5 to R8 may be the same or different in each repeating unit.)

[[1] α-olefin component having 2 to 20 carbon atoms]
The C2-C20 alpha-olefin used as the copolymerization component of the addition polymer of the cyclic olefin component preferably used for this invention and other copolymerization components, such as ethylene, is not specifically limited. For example, the thing similar to Unexamined-Japanese-Patent No. 2007-302722 can be mentioned. These α-olefin components may be used alone or in combination of two or more. Of these, ethylene is most preferably used alone. This is because the viscosity characteristics are improved and the thickness at the time of forming the multilayer sheet is stabilized.

[[2] Cyclic olefin component represented by formula (I)]
In the addition polymer of the cyclic olefin component preferably used in the present invention and another copolymer component such as ethylene, the cyclic olefin component represented by the general formula (I) serving as the copolymer component will be described.

  R1 to R12 in the general formula (I) may be the same or different from each other, and are selected from the group consisting of a hydrogen atom, a halogen atom, and a hydrocarbon group.

  Specific examples of R1 to R8 include, for example, a hydrogen atom; a halogen atom such as fluorine, chlorine and bromine; a lower alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group. They may be different, partially different, or all the same.

  Specific examples of R9 to R12 include, for example, hydrogen atom; halogen atom such as fluorine, chlorine, bromine; methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, hexyl group, stearyl group, etc. A cycloalkyl group such as a cyclohexyl group; a substituted or unsubstituted aromatic hydrocarbon group such as a phenyl group, a tolyl group, an ethylphenyl group, an isopropylphenyl group, a naphthyl group, an anthryl group; a benzyl group, a phenethyl group, Other examples include an aralkyl group in which an alkyl group is substituted with an aryl group, which may be different from each other, partially different from each other, or all the same.

  Specific examples of the case where R9 and R10 or R11 and R12 are integrated to form a divalent hydrocarbon group include, for example, alkylidene groups such as an ethylidene group, a propylidene group, and an isopropylidene group. .

  When R9 or R10 and R11 or R12 form a ring with each other, the formed ring may be monocyclic or polycyclic, may be a polycyclic ring having a bridge, and is a double bond. It may be a ring having a ring or a ring composed of a combination of these rings. Moreover, these rings may have a substituent such as a methyl group.

  Specific examples of the cyclic olefin component represented by the general formula (I) include those similar to those described in JP-A-2007-302722.

  These cyclic olefin components may be used singly or in combination of two or more. Among these, it is preferable to use bicyclo [2.2.1] hept-2-ene (common name: norbornene) alone.

  The glass transition point of the cyclic olefin resin (A) is preferably 120 ° C. or lower, more preferably 30 ° C. to 80 ° C. In addition, the glass transition point (Tg) employ | adopts the value measured by DSC method (method of JISK7121) on the temperature increase rate of 10 degree-C / min conditions. If it is 120 degrees C or less, since the content of the repeating unit derived from a cyclic olefin will decrease, the viscosity characteristic of a cyclic olefin resin composition will improve, and it will be easy to stabilize thickness at the time of multilayer sheet molding. In addition, in this invention, even if it uses resin with much content of the repeating unit derived from a cyclic olefin by mix | blending the cyclic olefin resin (B) mentioned later, melt tension can be raised, The thickness can be stabilized. From the viewpoint of improving the melt tension, even if the glass transition point of the cyclic olefin resin (A) is 120 ° C. or higher, a high effect of improving the melt tension can be obtained. By increasing the melt tension of the cyclic olefin-based resin composition in this way, the difference from the melt tension of the linear low-density polyethylene described later becomes larger, and whitening that occurs during stretching of the multilayer sheet can be prevented.

  The content of the cyclic olefin resin (A) in the cyclic olefin resin composition is 40% by mass to 95% by mass. More preferably, it is 75 mass% to 95 mass%. However, the above range varies somewhat depending on the cyclic olefin resin used. One of the characteristics of the present invention is that the cyclic olefin resin (A) having a low melt tension is blended with the cyclic olefin resin (B) described later with respect to the cyclic olefin resin (A) having a low melt tension. Is to increase the melt tension of the cyclic olefin-based resin composition containing a large amount of. Therefore, the melt tension is increased, the draw resonance at the time of forming the multilayer sheet is improved, and the melt tension of the cyclic olefin-based resin composition becomes larger than that of the linear low density polyethylene due to the improvement of the melt tension. Therefore, if the whitening that occurs during stretching of the multilayer sheet can be suppressed, the content of the cyclic olefin-based resin (A) is preferably as large as possible.

  The present invention can be preferably applied to a multilayer shrink film containing a cyclic olefin-based resin that is susceptible to thickness instability during molding of the multilayer sheet and whitening during stretching of the multilayer sheet. Even when the cyclic olefin-based resin (A) has a melt tension of 40 mN or less, which is likely to cause the above-described problem, by blending the cyclic olefin-based resin (B) described later, By increasing the melt tension and increasing the difference from the melt tension of the linear low-density polyethylene (C), whitening during sheet stretching can be prevented. More specifically, even if the melt tension of the cyclic olefin resin (A) is as low as 5 mN to 35 mN, it can be used in the present invention.

  [1] A method for polymerizing an α-olefin component having 2 to 20 carbon atoms and a [2] cyclic olefin component represented by formula (I) and a method for hydrogenating the obtained polymer are particularly limited. Instead, it can be carried out according to known methods. Random copolymerization or block copolymerization may be used, but random copolymerization is preferred.

  The polymerization catalyst used is not particularly limited, and can be obtained by a known method using a conventionally known catalyst such as a Ziegler-Natta, metathesis, or metallocene catalyst. The cyclic olefin and α-olefin addition copolymer or hydrogenated product thereof preferably used in the present invention is preferably produced using a metallocene catalyst.

  Examples of the metathesis catalyst include molybdenum or tungsten-based metathesis catalysts (for example, described in JP-A Nos. 58-127728 and 58-129003) as a catalyst for ring-opening polymerization of cycloolefin. In addition, the polymer obtained by the metathesis catalyst uses an inorganic carrier-supported transition metal catalyst or the like, and 90% or more of the main chain double bond and 98% or more of the carbon-carbon double bond in the side chain aromatic ring are hydrogenated. It is preferable to add.

[Other copolymer components]
The cyclic olefin-based resin (A) does not impair the object of the present invention other than [1] the α-olefin component having 2 to 20 carbon atoms and [2] the cyclic olefin component represented by the general formula (I). In the range, other copolymerizable unsaturated monomer components may be contained as required.

  The unsaturated monomer that may be optionally copolymerized is not particularly limited, and examples thereof include hydrocarbon monomers containing two or more carbon-carbon double bonds in one molecule. Can be mentioned. Specific examples of the hydrocarbon-based monomer having two or more carbon-carbon double bonds in one molecule include those similar to those described in JP-A-2007-302722.

[Cyclic olefin resin (B)]
The cyclic olefin resin (B) is not particularly limited as long as it has a glass transition point higher than that of the cyclic olefin resin (A). The cyclic olefin resin (B) contains a cyclic olefin monomer as a copolymerization component as in the case of the component (A), and is a polyolefin resin containing a cyclic olefin monomer in the main chain. For example, an addition polymer of a cyclic olefin or a hydrogenated product thereof, an addition copolymer of a cyclic olefin and an acyclic olefin, or a hydrogenated product thereof can be used. For the cyclic olefin component, the α-olefin component, etc., the same ones as described for the cyclic olefin resin (A) can be used.

  The difference in glass transition point between the cyclic olefin resin (A) and the cyclic olefin resin (B) is not particularly limited, but is preferably 10 ° C to 120 ° C, and more preferably 30 ° C to 80 ° C. If it is within the above range, as will be described later, the cyclic olefin-based resin composition has a single glass transition point, and the effect of the present invention is further enhanced.

  The content of the cyclic olefin resin (B) in the cyclic olefin resin composition is 5% by mass to 60% by mass. More preferably, it is 5 to 25% by mass. By adding the cyclic olefin-based resin (B), the melt tension of the cyclic olefin-based resin composition can be improved, and thickness unevenness at the time of multilayer sheet molding can be suppressed. And since the difference of the melt tension of a cyclic olefin resin composition and the melt tension of a linear low density polyethylene becomes larger, it becomes easy to suppress the whitening which arises at the time of multilayer sheet | seat drawing. As a result, a high-quality multilayer shrink film can be obtained. The cyclic olefin-based resin (B) is for increasing the melt tension of the cyclic olefin-based resin composition, and if the desired effect is obtained, the amount is preferably smaller.

[Physical properties of cyclic olefin resin composition]
The melt tension of the cyclic olefin-based resin composition measured by the method described later is preferably 30 mN or more, more preferably from 35 mN to 80 mN. When the melt tension is 30 mN or more, the effect of stabilizing the thickness of the multilayer sheet and the thickness of the fiber is high, and an extremely high quality multilayer shrink film can be obtained. In addition, if the melt tension is 30 mN or more, it becomes a higher value than the melt tension of linear low-density polyethylene (C) described later, and therefore, whitening of the multilayer shrink film that occurs during stretching of the multilayer sheet is suppressed. Can do.

  The melt flow rate of the cyclic olefin-based resin composition at 190 ° C. and a load of 2.16 kg measured by a method according to JIS K7210 is preferably 0.1 g / 10 min to 1.5 g / 10 min. More preferably, it is 0.5 g / 10 minutes to 1.3 g / 10 minutes. If it is 0.1 g / 10 min or more, it is preferable because the fluidity is high and it is easy to mold.

  The glass transition point of the cyclic olefin-based resin composition is preferably 50 ° C to 130 ° C. When the temperature is lower than 50 ° C., the heat resistance of the multilayer shrink film surface decreases, and when heat is applied, the surface becomes sticky. When used as a shrinkable label, the phenomenon that containers are likely to block each other on the mounting line tends to occur. In addition, the natural shrinkage rate tends to be too large. On the other hand, when it exceeds 130 ° C., the thermal shrinkage in the lateral direction tends to be too small. More preferably, it is 65 ° C to 100 ° C. The cyclic olefin-based resin composition may have a plurality of glass transition points, but preferably has a single glass transition point. By increasing the compatibility between the cyclic olefin resin (A) and the cyclic olefin resin (B), draw resonance can be effectively suppressed, and as a result, the thickness and thickness of the molded body are stabilized. As a result, a high-quality molded product can be obtained.

  Here, the single glass transition point means that there is only one peak corresponding to the glass transition point when measured at a temperature rising rate of 10 ° C./min by the DSC method (method described in JIS K7121). Say.

[Linear low density polyethylene (C)]
The linear low density polyethylene (C) is not particularly limited as long as the melt tension is lower than that of the cyclic olefin resin composition, and a conventionally known one can be used. Examples thereof include linear low density polyethylene polymerized using a metallocene catalyst and linear low density polyethylene synthesized using a Ziegler-Natta catalyst. In the present invention, linear low density polyethylene polymerized using a metallocene catalyst is preferred. This is because the compatibility with the cyclic olefin resin is high.

  Ratio of the melt tension of the linear low density polyethylene (C) and the melt tension of the cyclic olefin resin composition measured by the method described later (melt tension of the cyclic olefin resin composition / melt tension of (C)) Is 1.15 or more. The difference between the melt tension of the cyclic olefin resin and the melt tension of (C) is not particularly limited, but is preferably +10 mN to +40 mN. Within the above range, the cyclic olefin-based resin composition and the linear low-density polyethylene extend in the same way when the multilayer sheet is stretched, so that it is possible to suppress the occurrence of haze and suppress the decrease in transparency of the molded product. This is because the effect is enhanced. More preferably, they are 1.3 times to 4.0 times and +10 mN to +30 mN.

  The melt tension of the linear low density polyethylene (C) is preferably 40 mN or less. If the melt tension of the linear low density polyethylene is in the above range, a difference in melt tension is likely to appear when combined with a cyclic olefin resin composition having an increased melt tension, and the moldability is stable as described above. It is because it can improve or suppress whitening of the multilayer shrink film during stretching of the multilayer sheet. More preferably, it is 30 mN or less. However, if the melt tension is too low, the thickness stability and gloss may be deteriorated. For this reason, the melt tension of the linear low density polyethylene (C) is preferably 10 mN or more.

  The melt flow rate of the linear low density polyethylene is preferably 0.5 g / 10 min to 10 g / 10 min. If it is less than 0.5 g / 10 min, kneading and dispersion with the cyclic olefin resin composition is worsened, and a homogeneous blend polymer cannot be obtained, which tends to be a multilayer shrink film having a poor surface condition. . Also, if it exceeds 10 g / 10 min, the melt viscosity becomes too low, the melt viscosity becomes too low, and the steady casting of the molten polymer film discharged from the T-die becomes impossible, and the constant thickness and constant width film Winding is not possible, and film strength and other film physical properties tend to be lowered and the specified value cannot be achieved.

  The mixing method of the cyclic olefin-based resin (A), the cyclic olefin-based resin (B), and the linear low-density polyethylene (C) is not particularly limited, and the raw material may be pre-compounded using an extruder or the like in advance. May be dry blended and directly fed into an extruder or the like for producing a stretched film or a sheet. Alternatively, the cyclic olefin resin (A) and the cyclic olefin resin (B) may be pre-compounded to produce a cyclic olefin resin composition, which may be dry blended with the linear low density polyethylene (C). .

  Moreover, when mixing cyclic olefin resin (A) and cyclic olefin resin (B), it is also possible to distill off a solvent, after carrying out solution mixing using cyclohexane or decalin as a solvent. Furthermore, it is also possible to use a method in which the cyclic olefin resin (B) produced in advance is introduced into the production facility during the solution polymerization of the cyclic olefin resin (A).

  The sheet before stretching of the present invention preferably has a neck-in measured by the method described in Examples of 60 mm or less. Neck-in refers to a phenomenon in which, for example, when a cast film is formed in T-die molding, the end of the cast film shrinks toward the center. When this neck-in occurs, the sheet width becomes small and the thickness of the end portion of the sheet becomes thicker than that of the central portion of the sheet, so that the yield of the product is deteriorated. In the present invention, since a neck-in of 60 mm or less can be realized, the yield of products can be improved.

  The mixing ratio of the cyclic olefin resin composition and the linear low density polyethylene is 55% by mass to 95% by mass of the cyclic olefin resin composition, and 45% by mass to 5% by mass of the linear low density polyethylene, preferably the cyclic olefin. Resin composition 60 mass% to 90 mass%, linear low density polyethylene 40 mass% to 10 mass%, more preferably cyclic olefin resin composition 65 mass% to 90 mass%, linear low density polyethylene 35 From 10% by mass to 10% by mass. When the mixing ratio of the linear low density polyethylene exceeds 45% by mass, the haze (transparency) tends to deteriorate. On the other hand, when the mixing ratio of the linear low-density polyethylene is less than 5% by mass, it tends to be difficult to completely suppress the whitening phenomenon of the fingerprint adhering portion at the time of heat shrinkage, and corona discharge treatment. When it is applied, it tends to be difficult to maintain the lubricity of the surface of the multilayer shrink film.

[Others]
The resin composition of the front surface layer and the back surface layer, that is, the types of the cyclic olefin-based resin composition and the linear low density polyethylene (including the difference in melt flow rate) of the front surface layer and the back surface layer are different even if they are the same. It may be a thing. Moreover, two or more types of them may be included. The resin composition ratio may be the same or different. More preferably, the front surface layer and the back surface layer have the same resin composition and resin composition ratio. In the polyolefin resin composition for front and back surfaces forming the surface layer and the back layer, an antistatic agent, an anti-blocking agent, a lubricant, an anti-ultraviolet agent, a stabilizer, a colorant, within the range not impairing the essence of the present invention. A known material such as low density polyethylene or other resin may be added for the purpose.

<Intermediate layer>
In the multilayer shrink film of the present invention, the intermediate layer is not particularly limited, but the same one as the intermediate film layer described in International Publication WO 2004/110750 is particularly preferable.

<Other layers>
In the multilayer shrink film of the present invention, “consisting of at least three layers of surface layer / intermediate layer / back surface layer” means that when one or more layers are further provided between the surface layer and the intermediate layer, When one or more layers are further provided between the back surface layer, when one or more layers are provided on the surface layer, when one or more layers are further provided on the back surface layer, etc. It may be laminated. Examples of the other layer include an overcoat layer further provided on the front surface layer or the back surface layer in order to impart heat resistance, blocking resistance, and lubricity.

<Method for producing multilayer shrink film>
The film of the present invention can be produced by a known method. For example, it can be produced by the same method as described in International Publication WO 2004/110750 pamphlet.

  A preferred extrusion temperature range for producing the film of the present invention is 170 ° C. to 280 ° C., more preferably 180 ° C. to 240 ° C.

<Multilayer shrink film>
The composition ratio of the thicknesses of the front and back layers and the intermediate layer is preferably surface layer / intermediate layer / back surface layer = 1/2 to 10/1, more preferably surface layer / intermediate layer / back surface layer = 1/3 to 7 /. 1, More preferably, it is surface layer / intermediate layer / back surface layer = 1/3 to 5/1. The total film thickness is usually preferably 30 to 70 μm. In order to improve the adhesion with the printing ink, it is desirable to perform corona discharge treatment on one side of the film. When overcoating the opposite side of the printing surface, it is desirable to perform corona discharge treatment on both sides of the multilayer shrink film. The corona discharge treatment strength is preferably such that the wetting tension can be maintained at 38 to 48 mN / m. When the wetting tension is less than 38 mN / m, the adhesion with the printing ink or overcoat agent tends to be inferior. On the other hand, when the wetting tension exceeds 48 mN / m, the slipperiness of the film tends to deteriorate.

  In the multilayer shrink film of the present invention, the cyclic olefin resin composition and the linear low-density polyethylene (C) are stretched in the same manner at the time of stretching in the production of the present invention, so that no haze is likely to occur. As a result, a highly transparent multilayer shrink film can be obtained. “Transparent” means that the haze (%) measured by the method described later is 20% or less. The multilayer shrink film of the present invention can realize a haze of 20% or less after stretching, and can maintain high transparency.

  The multilayer shrink film of the present invention is also excellent in gloss. “Excellent gloss” means that the gloss (%) measured by the method described later is 110% or more. In the present invention, a surface gloss of 120% to 140% can be realized.

  The multilayer sheet obtained in the production process of the present invention preferably has a neck-in measured by the method described in the examples of 60 mm or less. Neck-in refers to a phenomenon in which, for example, when a cast film is formed in T-die molding, the end of the film shrinks toward the center. When this neck-in occurs, the width of the multilayer sheet becomes smaller and the thickness of the end of the multilayer sheet becomes thicker than that of the central part of the multilayer sheet. In the present invention, a neck-in of 60 mm or less can be realized, and the yield of products can be improved. That is, a high-quality multilayer shrink film can be obtained with high productivity by subsequent stretching.

  The multilayer sheet obtained in the production process of the present invention preferably has a film thickness variation (maximum value−minimum value) of 10 μm or less by the method described in Examples. In the present invention, a multilayer shrink film having a stable film thickness as described above can be obtained by using the above-mentioned cyclic olefin resin composition.

<Material>
[Surface layer / Back layer]
As cyclic olefin resin (A),
“9506F-04” (Topas Advanced Polymers)
"8007F-04" (Topas Advanced Polymers)
As cyclic olefin resin (B),
“6013F-04” (Topas Advanced Polymers)
"8007F-04" (Topas Advanced Polymers)
As linear low density polyethylene (C),
"SP2320" (manufactured by Prime Polymer)
"SP1520" (manufactured by Prime Polymer)
[Middle layer]
Polypropylene (Nippon Polypro Co., Ltd./Batec EG6D)
LLDPE (Evolue SP2040 manufactured by Prime Polymer)
Polyolefin elastomer (Dynalon 1320P manufactured by JSR)

<Manufacture of polyolefin resin composition for front and back surfaces>
In the ratio shown in Table 1, using a twin screw extruder (TEX30 manufactured by Nippon Steel Works), melt kneading at a cylinder temperature of 250 ° C. to obtain the cyclic olefin resin composition pellets of Examples and Comparative Examples, Sheets were prepared and subjected to various evaluations.

  Separately, a cyclic olefin-based resin composition comprising (A) and (B) was obtained under the above extrusion conditions at the ratio of (A) and (B) shown in Table 1, and the cyclic olefin-based resin described below The Tg, MFR and melt tension of the composition were evaluated.

<Measurement of glass transition point>
The glass transition point of the cyclic olefin resin (A), the cyclic olefin resin (B), and the cyclic olefin resin composition composed of (A) and (B) is measured with a differential scanning calorimeter (DSC manufactured by TA Inshalment Co., Ltd.). -Q1000) at a temperature increase rate of 10 ° C./min. The measurement results are shown in Table 1.

<Measurement of melt flow rate (MFR)>
1. MFR of cyclic olefin resin (A), cyclic olefin resin composition comprising (A) and (B), linear low density polyethylene (C) according to JIS K7210 at a temperature of 190 ° C. or 260 ° C. Measurement was performed with a load of 16 kgf. The measurement results are shown in Table 1.

<Measurement of melt tension>
The cyclic olefin resin (A), the cyclic olefin resin composition comprising (A) and (B), and the melt tension of the linear low density polyethylene (C) are measured by a Capillograph 1B (piston diameter 10 mm) manufactured by Toyo Seiki. Using an orifice having an inner diameter of 1 mm and a length of 20 mm, the tension (mN) applied to the fiber when the molten polymer discharged from the orifice at 190 ° C. and an extrusion speed of 10 mm / min is drawn into a fiber at a take-up speed of 15 m / min. ) Was measured.

<Manufacture of multilayer shrink film>
Dry blend of 80% polypropylene (Novatech EG6D manufactured by Nippon Polypro Co., Ltd.), 10% LLDPE (Evolu SP2040 manufactured by Prime Polymer Co., Ltd.) and 10% polyolefin elastomer (Dynalon 1320P manufactured by JSR Co., Ltd.) The solution was put into a layer extruder (32 mmφ single shaft) and extruded at a cylinder temperature of 230 ° C. For the surface layer and the back layer, the polyolefin resin composition for the front and back surfaces of each formulation listed in Table 1 is introduced into the outer layer extrusion equipment (40 mmφ uniaxial) of the multilayer shrink film forming equipment, and the cylinder temperature is 230 ° C. A molten sheet is extruded from a manifold type three-layer T-die (die temperature 230 ° C.) so that the air gap is 100 mm, the take-off speed is 8.5 m / min, and the thickness of the front and back layers is 45 μm and the thickness of the intermediate layer is 210 μm. The screw speed of each extruder was adjusted, and the multilayer sheet was taken up on a chilled roll at 25 ° C. and cooled and solidified. Thereafter, roll stretching of 1.2 times in the MD direction was performed at a preheating roll temperature of 80 ° C., a first nip roll temperature of 85 ° C., a second nip roll temperature of 90 ° C., and a stretching time of 0.25 seconds, followed by preheating at 118 ° C. for 9 seconds. Thereafter, the first stretching zone (stretching zone inlet side) is 90 ° C., the second stretching zone (stretching zone outlet side) is 77 ° C., and the residence time of each film is 5 seconds (hence, the stretching time is 10 seconds). The tenter was stretched 0 times, heat-fixed in the same tenter while relaxing 7% in the TD direction over a period of 6 seconds at a temperature of 75 ° C., and the film was cooled with a cold air of about 25 ° C. and wound up. The thickness of the multilayer shrink film was 8 μm for both the front and back layers, 34 μm for the intermediate layer, and a total of 50 μm.

<Evaluation of multilayer shrink film>
[Evaluation of transparency]
In order to confirm the transparency of the multilayer shrink film obtained by the above production method, haze measurement was performed by a method based on JIS P 8116 with a haze guard measuring machine manufactured by Toyo Seiki (10-point average value). The measurement results are shown in Table 1.

[Gloss evaluation]
The gloss was evaluated by measuring the surface gloss. DR. Using “Reflectometer LMG064” manufactured by LANGE, measurement was performed by a method in accordance with JIS K 7105 (10-point average value).

[Evaluation of heat shrinkage]
A sample of MD direction (film flow direction) × TD direction (film width direction) = 10 mm × 100 mm is cut from the multilayer shrink film. One of the samples is immersed in warm water at 70 ° C. for 10 seconds, taken out immediately and cooled with cold water (about 25 ° C.), and then the length L (mm) in the TD direction is measured. And 100-L is calculated. The same was repeated with the remaining nine samples, and the average value (10-point average value) of a total of 10 sheets was defined as the heat shrinkage rate in the TD direction at 70 ° C. The same evaluation was performed under the temperature conditions of 80 ° C., 90 ° C. and 100 ° C. Table 1 shows the evaluation results.

[Neck-in evaluation]
A multilayer sheet was obtained in the same manner as the multilayer sheet molding in the production of the multilayer shrink film except that the take-up speed was changed to 4 m / min. Here, the neck-in when the width of the T die was L0 and the width (average value) of the formed multilayer sheet was L was evaluated. The evaluation results are shown in Table 1.

[Evaluation of film thickness fluctuation]
A multilayer sheet was obtained by the same method as the multilayer sheet molding in the production of the multilayer shrink film except that the molding was performed at a take-up speed of 8 m / min. The film thickness fluctuation in the multilayer sheet forming direction was expressed by measuring the thickness at 20 locations on a line shifted by 5 cm from the center line, and representing the maximum value, the minimum value, and the difference therebetween. The results are shown in Table 1.

[Evaluation of surface roughness]
Evaluation of the surface roughness of the obtained multilayer shrink film was performed by measuring Ra using a surface roughness measuring instrument (“JV-C624-3D” manufactured by Mitutoyo Corporation). The evaluation results are shown in Table 1.

  As is clear from Table 1, it was confirmed that the multilayer shrink film of the present invention had less haze and higher transparency than Comparative Example 1. And since the multilayer shrink film of this invention was equivalent to the comparative example which is a conventional product in heat shrink rate, it was confirmed that it is preferable also for the use of a shrink film.

  It was confirmed that Comparative Example 2 in which the cyclic olefin resin (A) having a low melt tension was used alone had a large amount of haze after stretching and low transparency. On the other hand, in Example 1 of this invention, melt tension as a cyclic olefin resin composition is added by adding a small amount of cyclic olefin resin (B) to cyclic olefin resin (A) with low melt tension. It was confirmed that the film was greatly improved, the haze after stretching was small, and a highly transparent shrink film was obtained.

  In Comparative Example 3, a cyclic olefin resin having a higher melt tension than the cyclic olefin resin (A) used in Comparative Example 2 is used. For this reason, Comparative Example 3 is more advantageous than Comparative Example 2 in terms of transparency and the like. However, when compared with Examples 1 to 3, it was confirmed that Comparative Example 3 had a rough surface and increased film thickness variation and neck-in. And it was confirmed that the comparative example 3 cannot be preferably used as a shrink film because it is difficult to heat shrink.

Claims (8)

A multilayer shrink film comprising at least three layers of a surface layer / intermediate layer / back layer,
The surface layer and the back layer have a cyclic olefin resin (A) containing ethylene as a copolymerization component and a cyclic olefin resin having a glass transition point higher than that of the cyclic olefin resin (A) and ethylene as a copolymerization component. A polyolefin-based resin composition comprising a cyclic olefin-based resin composition containing a resin (B), and further a linear low-density polyethylene (C),
The content of the cyclic olefin resin (A) in the cyclic olefin resin composition is from 40% by mass to 95% by mass,
The content of the cyclic olefin resin (B) in the cyclic olefin resin composition is 5% by mass to 60% by mass,
The multilayer shrink film containing the cyclic polyolefin resin composition for front and back surfaces whose melt tension of the said cyclic olefin resin composition is 1.15 times or more higher than the melt tension of the said linear low density polyethylene (C).   The melt tension of the polyolefin resin composition for front and back surfaces measured at 190 ° C. and a winding speed of 15 m / min is 30 mN or more, and the cyclic olefin resin for front and back surfaces at 190 ° C. and a load of 2.16 kg. The multilayer shrink film according to claim 1, wherein the melt flow rate of the composition is from 0.1 g / 10 min to 1.5 g / 10 min.   Melt tension of the cyclic olefin-based resin composition measured at 190 ° C. with a winding speed of 15 m / min, and the linear low density polyethylene (190 ° C., measured with a winding speed of 15 m / min) The multilayer shrink film according to claim 1 or 2, wherein a difference from the melt tension of C) is +10 mN to +40 mN.   The multilayer shrink film according to any one of claims 1 to 3, wherein the linear low density polyethylene (C) is a linear low density polyethylene polymerized by a metallocene catalyst.   The multilayer shrink film according to any one of claims 1 to 4, wherein a melt tension of the linear low-density polyethylene (C) measured at 190 ° C and a winding speed of 15 m / min is 20 mN to 40 mN.   The multilayer shrink film according to any one of claims 1 to 5, wherein a glass transition point of the cyclic olefin-based resin (A) is 80 ° C or lower.   The multilayer shrink film according to any one of claims 1 to 6, wherein the cyclic olefin-based resin composition has a single glass transition point.   The multilayer shrink film according to any one of claims 1 to 7, wherein the cyclic olefin resin (A) and / or the cyclic olefin resin (B) is a copolymer composed of norbornene and ethylene.