JP2005047182A - Multilayer heat-shrinkable oriented film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer heat-shrinkable oriented film having a high elastic modulus and excellent heat shrinkability and excelling in transparency and perforation tear properties. <P>SOLUTION: The multilayer heat-shrinkable oriented film has at least five layers, including a multilayer constitution wherein intermediate layers (B) are formed on the opposite outer sides of a central layer (C) and further surface layers (A) are formed on the opposite outer sides. The two surface layers (A), the two intermediate layers (B) and the central layer (C) are constituted of specific resin compositions respectively and the ratios of the total thickness of the two surface layers (A), the total thickness of the two intermediate layers (B) and the thickness of the central layer (C) to the whole film thickness of 100 are in the ranges of 30-45 : 5-15 : 40-65 respectively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable stretched film obtained by stretching a polyolefin resin composition, and more particularly to a heat-shrinkable stretched film for shrink labels.

The outside of plastic bottles such as PET bottles and glass bottles are often equipped with heat-shrinkable shrink labels printed on the inside, and the material of the shrink labels is polyvinyl chloride, polystyrene, There are polyester type and polyolefin type.
Among these shrink labels, there is an increasing need for polyolefin labels, which are light materials with a specific gravity of less than 1, especially when the containers to be installed are PET bottles, during the PET bottle recycling process. This is because, in a liquid specific gravity separation process for the purpose of separating the label material, etc., a label having a specific gravity of less than 1 enables high-precision separation from a PET resin having a specific gravity of more than 1, and has recently been recycled. The background is that high purity of PET-based resins is required.

Polyolefin-based shrink labels with a specific gravity of less than 1 include uniaxially stretched films made of polyethylene resin or polypropylene resin, but stretched films made of these resins have three main problems with respect to polystyrene and polyester films. there were.
The first problem is inferior in low-temperature shrinkability, and in particular, sufficient shrinkage does not appear in a temperature range of 70 to 90 ° C., which is a mounting temperature in the case of a general PET bottle.
The second problem is that the film has a low elastic modulus and lacks rigidity. Specifically, there is a problem that the film is broken or wrinkled if the rigidity of the mounting machine for mounting on a container such as a bottle or bottle is insufficient.

The third problem is that the longitudinal and lateral tear strength of the film is too high.
First, this problem will be described with respect to the vertical direction. In some cases, the film may be perforated in advance so that consumers can easily separate it from the state of being attached to a bottle or container. This is a problem that is difficult to cut along the perforation due to the high tear strength and the difficulty of tear propagation.
Next, to explain the lateral direction, there is a process of cutting the film into a cylindrical shape and then continuously cutting it for labeling of individual bottles and containers by supplying it to a mounting machine for mounting on bottles and containers. Due to the high tear strength in the lateral direction of the film and the difficulty of tear propagation, the cutting may not be linear in the vicinity of the final cutting position.

As a film for improving the shortage of low-temperature shrinkage, which is the first problem of the above-mentioned polyolefin-based shrink label, JP 2000-159946 A discloses that the surface layer is an amorphous material such as a cyclic olefin resin. A shrink label having a three-layer structure in which a resin layer and a central layer are made of a polyolefin resin is disclosed, and an amorphous material such as a cyclic olefin resin having a glass transition point (Tg) in a specific range is disclosed. It is described that the use of a resin imparts a characteristic that the thermal shrinkage increases rapidly even in a mounting temperature range of 90 ° C. or less.
However, the lack of rigidity, which is the second problem described above, is solved because the thickness ratio of the central layer where the elastic modulus is relatively low is high and it is difficult to ensure sufficient rigidity of the entire film. It has not been.

Furthermore, there remains a problem that the tear strength is too high, which is the third problem described above, and in particular, it is a problem that is not easily cut when cutting along the perforations described above. That is, it is thought that this is mainly due to the fact that the adhesive strength between the surface layer and the center layer is insufficient, so that peeling between the layers occurs and the center layer having a high tear strength is stretched and remains.
A three-layered shrink label having a mixed resin composition mainly composed of a cyclic olefin resin as a surface layer is disclosed in JP-A Nos. 2000-209511 and 2001-219503. As with the shrink labels described in these publications, the problem is that the film is inferior in rigidity, and the adhesive strength between the surface layer and the center layer is not sufficient. The problem that was difficult to be cut was left.

JP 2000-159946 A JP 2000-20951 A JP 2001-219503 A

  The present invention has a high elastic modulus of 900 Mpa or more and a heat shrink property that adheres to a container in a low temperature range of 70 to 90 ° C., and a multilayer heat shrink suitable for polyolefin-based shrink labels excellent in transparency and perforation tearing properties. It is an object to provide a stretchable film.

  In order to solve the above problems, the present inventor has a surface layer composed of a specific resin composition mainly composed of a cyclic olefin-based resin, a center composed of a specific resin composition composed mainly of a propylene-α-olefin copolymer. Solving the problems by using a multilayer structure consisting of at least five layers consisting of an intermediate layer made of a specific resin composition located between the layers and a specific stretch ratio in the machine direction and the transverse direction As a result, the present invention has been found.

That is, the present invention is as follows.
1. A multilayer heat-shrinkable stretched film comprising at least five layers including a multilayer structure in which an intermediate layer (B) is formed on both outer surfaces of the center layer (C) and a surface layer (A) is formed on both outer surfaces, The resin composition in which the surface layer (A) satisfies the following (A) or (B), the resin composition in which both the intermediate layers (B) satisfy the following (C), and the center layer (C) satisfy the following (D) The ratio of the total thickness of both surface layers (A): the total thickness of both intermediate layers (B): the thickness of the central layer (C) is 30 to 45 respectively for the total film thickness 100. A multilayer heat-shrinkable stretched film in the range of 5-15: 40-65.

(A) Amorphous cyclic olefin-based resin (a1) 50 to 85% by weight, propylene-α-olefin copolymer (b1) 10 to 25% by weight having a melting point in the range of 120 to 150 ° C., and a softening point A resin composition comprising 5 to 25% by weight of petroleum resins (d1) at 80 to 140 ° C.
(B) Petroleum having an amorphous cyclic olefin resin (a1) of 50 to 85% by weight, a polyethylene resin (c1) having a density of less than 0.94 of 10 to 25% by weight, and a softening point of 80 to 140 ° C. A resin composition comprising 5 to 25% by weight of resins (d1).
(C) Amorphous cyclic olefin-based resin (a2) 20 to 50% by weight, propylene-α-olefin copolymer (b2) having a melting point within the range of 120 to 150 ° C. (b2) 25 to 50% by weight, and a softening point A resin composition comprising 10 to 40% by weight of petroleum resins (d2) at 80 to 140 ° C.
(D) Containing 1 to 40% by weight of petroleum resins (d3) mainly composed of a propylene-α-olefin copolymer (b3) having a melting point in the range of 120 to 150 ° C. and having a softening point of 80 to 140 ° C. Resin composition.

  2. A substantially uniaxially stretched film having a transverse stretching ratio (t) of 5 to 12 and a relational expression with a longitudinal stretching ratio (m) of 20m-20 ≦ t ≦ 60m-60.

  The multilayer heat-shrinkable stretched film of the present invention has a specific gravity of less than 1 and can obtain a highly pure PET resin in the PET bottle recycling process, and has high rigidity based on the high elastic modulus of the film. Can be mounted on bottles and containers without causing film breaks or wrinkles, and tear strength is not too high, so labels after mounting can be easily cut from perforations, and has good transparency Film suitable for shrink labels.

Hereinafter, the present invention will be specifically described focusing on its preferred form.
First, the resins used in the present invention will be described.
The amorphous cyclic olefin-based resins (a1) and (a2) are a copolymer (a-1) of an α olefin and a cyclic olefin, a ring-opening polymer or a copolymer (a-2) of a cyclic olefin, ( It is selected from the hydrogenated product (a-3) of a-2) and the graft modified product (a-4) of any one of (a-1) to (a-3).
Examples of the cycloolefins, bicyclo [2.2.1] -2-heptene, tetracyclo [4.4.0.1 ^2,5 .1 ^7,10] -3- dodecene, hexacyclo [6.6.1.1 ^{3, 6} .1 ^{10 13} .0 ^2,7 .0 ^9,14] -4-heptadecene, and octacyclo ^{[8.8.0.1 2,9 .1 4,7 .1 11,18 .1} 13,16 .0 3,8 .0 12, ¹⁷ ] -5-docosene and the like, or derivatives obtained by substituting hydrocarbon groups and / or halogen atoms for these polycyclic olefins.

Copolymer (a-1) of α olefin and cyclic olefin generally uses α olefin such as ethylene, propylene, 1-butene, and 1-hexene and the above cyclic olefin in a hydrocarbon solvent as a catalyst. The ring-opening polymer or copolymer (a-2) of cyclic olefin is generally metathesis polymerized using the cyclic olefin using a catalyst such as a tungsten compound. Or a polymer obtained by copolymerizing the polymer and the α-olefin.
The hydrogenated product (a-3) is a polymer or copolymer obtained by further hydrogenation of the ring-opening polymer or copolymer (a-2) of the above-mentioned cyclic olefin, and graft modification The product (a-4) is a modified product obtained by graft-modifying any of the aforementioned polymers or copolymers (a-1) to (a-3) with an unsaturated carboxylic acid or a derivative thereof.

A ring-opening polymer or copolymer (a-2) of a cyclic olefin used in the amorphous cyclic olefin-based resins (a1) and (a2), a hydrogenated product (a-3) of (a-2), The graft modified product (a-4) of any one of (a-1) to (a-3) preferably has a glass transition point of 40 to 100 ° C, and more preferably 50 to 90 ° C. If the glass transition point is less than 40 ° C., the film tends to spontaneously shrink at a room temperature of 40 ° C. or less, and if it exceeds 100 ° C., it is difficult to develop heat shrinkability that adheres to the container in a low temperature region of 70 to 90 ° C.
The amorphous cyclic olefin-based resins (a1) and (a2) may be different types or the same type, or two or more types may be mixed.

The propylene-α olefin copolymers (b1) to (b3) are copolymers obtained by random copolymerization of propylene and 1 to 20 mol% α olefin, and the α olefin is ethylene or an α having 4 to 20 carbon atoms. Examples of preferred propylene-α olefin copolymers that are olefins include ternary random copolymerized propylene polymers in which the α olefin is ethylene and 1-butene.
The melting points of the propylene-α olefin copolymers (b1) to (b3) are in the range of 120 to 150 ° C, and more preferably in the range of 125 to 145 ° C. When the melting point is less than 120 ° C., the film tends to spontaneously shrink at a room temperature of 40 ° C. or less, and the rigidity is low, so the elasticity of the entire film is low, so it is difficult to use. When the temperature exceeds 150 ° C., the heat shrinkability that is in close contact with the container in a low temperature range of 70 to 90 ° C. is hardly exhibited.

The melting point is determined by holding the resin sample at 200 ° C. for 5 minutes in the differential scanning calorimeter, then lowering the temperature to 23 ° C. at a rate of 10 ° C./min, and further increasing the temperature to 200 ° C. at a rate of 10 ° C./min. In the obtained heat of fusion curve, the temperature indicates the main peak of heat of fusion.
The melt flow rate (MFR * 1: ASTM D1238, measurement 230 ° C., load 2.16 kg) of the propylene-α-olefin copolymers (b1) to (b3) is 0.2 to 15 g / 10 min. preferable.
(B1) to (b3) may be different types or the same type, and each may be a mixture of two or more types.

The polyethylene-based resin (c1) is an ethylene homopolymer or a copolymer of ethylene and α-olefin in which ethylene is a main component. The α-olefin is an α-olefin having 3 to 20 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene and 1-octene. As an example of a preferable polyethylene resin, the α olefin is 1-butene. Examples thereof include a linear low density polyethylene resin of an ethylene-butene copolymer and a linear low density polyethylene resin of an ethylene-hexene copolymer in which the α-olefin is 1-hexene.
The density (ASTMD-1505) of the polyethylene resin (c1) is less than 0.94, but is more preferably in the range of 0.915 to 0.935. When it is 0.94 or more, it is difficult to use the film because the specific gravity of the film is less than 1, making it difficult to use.

The melt flow rate (MFR * 2: ASTM D-1238, measurement 190 ° C., load 1.95 kg) of the polyethylene resin (c1) is preferably 0.2 to 15 g / 10 minutes, and further the melting point is 115 to 140. It is preferable to be in the range of ° C. If the melting point is less than 115 ° C, the film may easily shrink spontaneously at a room temperature of 40 ° C or less, and if it exceeds 140 ° C, it is difficult to develop heat shrinkability that adheres to the container in a low temperature region of 70 to 90 ° C. There is a case.
Petroleum resins (d1) to (d3) are petroleum resins derived from petroleum unsaturated hydrocarbons or higher olefin hydrocarbons such as cyclopentadiene, hydrogenated petroleum resins obtained by hydrogenating the petroleum resins, and terpene carbonization. A hydrogen resin, a modified product of the terpene hydrocarbon resin, and a hydrogenated terpene resin obtained by hydrogenating the terpene hydrocarbon resin. Examples of preferable petroleum resins include a hydrogenated terpene resin. Can be mentioned.

The softening points of petroleum resins (d1) to (d3) are in the range of 80 to 140 ° C, and more preferably in the range of 90 to 135 ° C. When the softening point is less than 80 ° C., the film is likely to block, and when the softening point exceeds 140 ° C., the effect of exhibiting heat shrinkage that adheres to the container in a low temperature region of 70 to 90 ° C. is weakened and each layer is firmly The effect of adhering to is also reduced.
(D1) to (d3) may be different types or the same type, and each may be a mixture of two or more types.
In addition, the said softening point is the softening point temperature measured based on JISK-2207.

Next, the composition which comprises a surface layer (A) in the film of this invention is demonstrated.
Among the compositions of the surface layer (A), the first one is (i) an amorphous cyclic olefin resin (a1) of 50 to 85% by weight, and a propylene-α-olefin having a melting point of 120 to 150 ° C. A resin composition comprising 10 to 25% by weight of a copolymer (b1) and 5 to 25% by weight of a petroleum resin (d1) having a softening point of 80 to 140 ° C. The second is an amorphous cyclic Olefin resin (a1) 50 to 85% by weight, polyethylene resin (c1) 10 to 25% by weight with a density of less than 0.94, and petroleum resins (d1) 5 to 5 with a softening point of 80 to 140 ° C. It is a resin composition comprising 25% by weight.

The amorphous cyclic olefin-based resin (a1) functions to impart low temperature shrinkage to the entire film and increase the elastic modulus, so the surface layer (A) requires a content of 50% by weight or more, and 50% If it is less than 1, transparency may be poor. If it exceeds 85% by weight, the heat shrinkability of the intermediate layer and the center layer can be different, and the film tends to curl at a portion where there is a difference in thickness between the front side and the back side.
If the petroleum resin (d1) is less than 5%, the adhesion to the intermediate layer is poor, and if it exceeds 25% by weight, blocking of the film surface tends to occur.
The propylene-α-olefin copolymer (b1) or the polyethylene resin (c1) is obtained from the requirements for the mixing ratio of the amorphous cyclic olefin resin (a1) and the petroleum resins (d1). In order to maintain good transparency, the ratio to the class (d1) is in the range of 1: 2.5 to 5: 1, so that it is in the range of 10 to 25% by weight.

The total thickness of both surface layers (A) needs to be 30 to 45 with respect to the total film thickness 100. Since the surface layer (A) is a layer mainly composed of an amorphous cyclic olefin resin (a1) that functions to impart low-temperature shrinkage and increase the elastic modulus of the entire film, The function of is not fully demonstrated. On the other hand, if it exceeds 45, the amorphous cyclic olefin-based resin is generally a resin having a specific gravity of more than 1, so it may be difficult to make the specific gravity of the entire film less than 1. Moreover, it is preferable that the distribution of thickness to both surface layers is close to the same amount.
Next, the composition constituting the intermediate layer (B) in the film of the present invention will be described.

The resin composition constituting the intermediate layer (B) is an amorphous cyclic olefin-based resin (a2) 20 to 50% by weight, and a propylene-α-olefin copolymer (b2) having a melting point of 120 to 150 ° C. A resin composition comprising 25 to 50% by weight and 10 to 40% by weight of petroleum resins (d2) having a softening point of 80 to 140 ° C.
The intermediate layer (B) is composed of an intermediate composition of the surface layer (A) and the central layer (C), and mainly functions to suppress the change of the composition between the layers and improve the adhesion between the layers. The requirements for the mixing ratio of the resins (a2), (b2), and (c2) are obtained as a range in which good adhesive strength is expressed. Good adhesion can be confirmed by the fact that no delamination phenomenon occurs in the tear strength measurement test in both the vertical and horizontal directions.

Since the intermediate layer (B) is a layer having poor transparency with respect to the surface layer (A) and the center layer (C), the ratio of the total thickness to the total film thickness 100 needs to be as thin as 15 or less. If it is less than 5, it may be difficult to maintain a homogeneous layer, so that the thickness ratio is 5 or more is also a requirement of the present invention. Moreover, it is preferable that the distribution of the thicknesses to both intermediate layers is close to an equal amount.
Next, the composition which comprises a center layer (C) in the film of this invention is demonstrated.
The resin composition constituting the central layer (C) is a petroleum resin (mainly composed of a propylene-α-olefin copolymer (b3) having a melting point in the range of 120 to 150 ° C. and a softening point of 80 to 140 ° C. ( It is a resin composition containing 1 to 40% by weight of d3).

The center layer (C) serves as a base material layer in which the elastic modulus and the heat shrinkability are appropriately balanced while the density of the whole film is less than 1, and the propylene-α-olefin copolymer (b3) is mainly used. However, the petroleum resins (d3) are effective as an auxiliary additive for enhancing the heat shrinkability in a low temperature range of 70 to 90 ° C. However, when the mixing ratio of petroleum resins (d3) exceeds 40% by weight, in addition to the decrease in elastic modulus, there arises a processing problem that makes it difficult to stably feed in the central layer extrusion kneader. There is a case.
The thickness of the center layer (C) needs to be 40 to 65 with respect to the total film thickness 100. This is a requirement inevitably determined from the thickness ratios as the requirements of the surface layer (A) and the intermediate layer (B) as described above.

One feature of the stretched film of the present invention is that it is a multi-layer film of 5 or more layers having a specific resin composition and configuration, each layer having a function as described above.
In the resin composition which comprises each layer, you may mix | blend another polymer within the range which satisfy | fills each requirement described above. Similarly, as long as the properties of the film of the present invention are not impaired, known additives (thermal stabilizer, antioxidant, crystal nucleating agent, transparent nucleating agent, antistatic agent, antifogging agent, lubricant, inorganic fine powder, Organic fine powders, pigments, UV absorbers, light stabilizers, flame retardants, plasticizers, etc.) may be further added.
The mixing method of the resin composition in the present invention may be a conventionally known blending method, and preferred examples include a melt kneading method such as a monoaxial or biaxial extrusion kneader, an open roll, a continuous kneader with a biaxial rotor, and the like. .

The film of the present invention is stretched by generally used stretching equipment, for example, tenter stretching after molding with a multilayer T die or the like, bubble stretching after molding with a multilayer annular die or the like. Since it is substantially a uniaxially stretched film, the preferred stretching method is that it is formed into a sheet by a multilayer T-die, then weakly stretched 1.6 times or less in the machine direction by roll stretching, and transverse by tenter stretching. The method of extending | stretching 5 to 12 times is mentioned.
The film of the present invention preferably has a stretching ratio (t) in the transverse direction of 5 to 12 times, and the relational expression with the stretching ratio (m) in the longitudinal direction satisfies 20m-20 ≦ t ≦ 60m-60. In particular, it is a uniaxially stretched film.

  If it is complete lateral uniaxial stretching without longitudinal stretching, the tear strength in the longitudinal direction is too high, and when a perforation is provided, the label after mounting cannot be easily cut from the perforation. In order to achieve a tear strength of 18 N / mm or less, which is a standard that can be easily cut as found by the inventors' research, in the multilayer film having the specific resin composition and constitution of the present invention, t It is preferable to perform weak stretching in the machine direction so as to satisfy ≦ 60 m−60. On the other hand, if the longitudinal stretch ratio is too high, the heat shrinkage rate in the longitudinal direction becomes high, so that distortion caused by so-called vertical sink occurs at the time of mounting on a bottle or bottle, and the tear strength in the longitudinal direction is as low as less than 6 N / mm. Therefore, there is a case where partial breakage is caused by the heat shrinkage force remaining after mounting, and therefore, it is preferable to suppress the longitudinal stretching in a range of 20 m−20 ≦ t. That is, the preferable range of the tear strength in the vertical direction is in the range of 6 to 18 N / mm.

In addition, regarding the heat shrinkability in the vertical direction, it is preferable that the heat shrinkage rate at 85 ° C. is 1 to 10%, and if it is less than 1%, the slack in the vertical direction occurs when being attached to a bottle or bottle. Lateral wrinkles are likely to occur, and if it exceeds 10%, distortion due to vertical sink marks tends to occur at the time of wearing.
On the other hand, with respect to stretching in the transverse direction, if the draw ratio is less than 5 times, the effect of improving the elastic modulus due to stretching is reduced, and the tensile modulus of elasticity in the longitudinal and transverse directions tends to be less than 900 MPa. When the pressure is 900 MPa or more, the film breaks due to lack of rigidity in a mounting machine that is mounted on a container such as a bottle or bottle even if the label product is generally the same area and weight equal to or less than that of a polystyrene film. And wrinkles are less likely to occur. In addition, when the draw ratio exceeds 12 times, uneven thickness of the film is likely to occur, and when the difference between the elastic modulus in the vertical direction and the horizontal direction becomes too large, wrinkles are likely to occur in the film wound in a roll state. May cause problems.

In view of the above, the preferred range of tensile modulus in the transverse direction is in the range of 900 to 1450 MPa. To achieve this, the transverse draw ratio is preferably 5 to 12 times, and 6 times as mentioned above. More preferably, it is more than 10 times less.
As for the heat shrinkability in the lateral direction, the heat shrinkage rate at 85 ° C. is preferably 30 to 55%, and if it is less than 30%, the heat shrinkability to adhere to the container in a low temperature region of 70 to 90 ° C. is insufficient. If it exceeds 55%, it will shrink too quickly when attached to a bottle or bottle, and label distortion and wrinkles are likely to occur.
Furthermore, since the film of the present invention has a specific resin composition and configuration, it is a film having practically good transparency as a shrink film, particularly a shrink label, and has a haze value of less than 10% in terms of thickness of 60 μm. Although less than 9% is more preferable.

The present invention will be described by way of examples and reference examples, but these are only a part of specific examples and do not limit the scope of the invention.
First, measurement methods and evaluations performed in Examples and Comparative Examples will be described below.
(1) Tensile elastic modulus: measured in accordance with JISK-7127-1989, using a tensile tester under conditions of a length between chucks of 50 mm, a film sample width of 10 mm, and a tensile speed of 10 mm / min. For each of the vertical and horizontal directions of the film, an average value of 5 samples was obtained, and a numerical value obtained by rounding off the decimal point in the unit of Mpa was calculated. The average value in the vertical direction and the horizontal direction was calculated by averaging the numerical values in the respective directions and rounding off the decimals in the unit of Mpa.
The evaluation was made as follows according to the average value of the tensile modulus in the machine direction and the transverse direction.
○: 900 to 1450 MPa
Δ: 800 to less than 900 MPa or more than 1450 MPa ×: less than 800 MPa

(2) Thermal shrinkage: A film having a size of 100 mm × 100 mm is immersed in a hot water bath at 85 ° C. for 10 seconds and then immediately immersed in cold water at 20 ° C. for 10 seconds. The ratio (%) of the contraction of the length with respect to the thickness (100 mm) was determined, and a numerical value obtained by rounding off the decimal point in the unit of% was calculated.
Evaluation of the heat shrinkage rate in the vertical direction was determined as follows.
○: Vertical direction: 1 to 10%
Δ: Longitudinal direction: −1 to less than 1% or more than 10% to less than 13% ×: Longitudinal direction: less than −1% or 13% or more Evaluation of the thermal shrinkage in the transverse direction was determined as follows.
○: Horizontal direction: 30 to 55%
Δ: Lateral direction: less than 25-30% or more than 55% and less than 70% ×: Lateral direction: less than 25% or 70% or more

(3) Tear strength: Measured in the longitudinal and lateral directions in accordance with ASTM D-1922. The numerical value is divided by the thickness to obtain the strength (N / mm) per unit thickness (mm). The numerical value rounded off to two digits was calculated.
Evaluation of the tear strength in the longitudinal direction was determined as follows.
○: 6 to 18 N / mm
Δ: Less than 3-6 N / mm or more than 18 N / mm and less than 21 N / mm ×: Less than 3 N / mm or more than 21 N / mm Evaluation of the tear strength in the transverse direction was made as follows.
○: 0.8 to 1.8 N / mm
Δ: Less than 0.5 to 0.8 N / mm or more than 1.8 N / mm and less than 2.1 N / mm ×: Less than 0.5 N / mm or 2.1 N / mm or more

(4) Haze: Measured according to JISK-7105, converted to a film thickness of 60 μm, and calculated by rounding off the decimal point in units of%.
Evaluation was determined as follows according to the haze value.
○: 0 to less than 9% Δ: 9 to less than 15% ×: 15% or more

(5) Specific gravity of the film: A film sample having a size of 6 mm × 2 mm is measured by the float / sink method according to JISK-7112, and the numerical value is rounded off to the second decimal place by rounding off the third decimal place. Obtained as an effective value.
Evaluation was determined as follows according to specific gravity.
○: Specific gravity of 0.97 or less △: Specific gravity of 0.98 to 0.99
X: Specific gravity is 1.00 or more

In the evaluations (1) to (5) above, ◯ is a range in which it is determined that there is no practical problem and is a good characteristic, and Δ is a characteristic that can be used practically but may be improved. It is a range to be determined, and x is a range to be determined that there is a practical problem.
Next, resins and additives used in Examples and Comparative Examples will be described.
(COC-1): “APL8008T (trade name)” manufactured by Mitsui Chemicals, Inc .: cyclic olefin-ethylene copolymer, glass transition point 90 ° C., density 1.02

(PP-1): “ADSYL7221 (trade name)” manufactured by Sun Allomer Co., Ltd .: ternary random copolymer polypropylene, melting point 134 ° C., melt flow rate (MFR * 1) 0.9, density 0.9
(PP-2): “Wintech WFX4T (trade name)” manufactured by Nippon Polychem Co., Ltd .: Metallocene-catalyzed polymerized random copolymerized polypropylene, melting point 125 ° C., melt flow rate (MFR * 1) 7.0, density 0.90
(PP-3): “Novatec FL6CK (trade name)” manufactured by Nippon Polychem Co., Ltd .: polypropylene homopolymer, melting point 159 ° C., melt flow rate (MFR * 1) 2.4, density 0.90

(PE-1): “NUCG-5225 (trade name)” manufactured by Nippon Unicar Co., Ltd .: ethylene-butene copolymer linear low density polyethylene resin, melting point 119 ° C., melt flow rate (MFR * 2) 2.0, Density 0.921
(PB-1): “Tafmer BL2281 (trade name)” manufactured by Mitsui Chemicals: 1-butene / α-olefin copolymer, melting point 74 ° C., melt flow rate (MFR * 2) 2.0, density 0.90
(T-1): “Clearon P125 (trade name)” manufactured by Yasuhara Chemical Co., Ltd .: hydrogenated terpene resin, softening point 125 ° C.

(K-1): “Nihon Rika Co., Ltd.” “Gelall DH (trade name)”: Composite crystal nucleating agent (K-2): Ciba Specialty Chemicals Co., Ltd. “Irganox 1010 (trade name)”: Phenol series Antioxidant (K-3): “Irgaphos 168 (trade name)” manufactured by Ciba Specialty Chemicals Co., Ltd .: Phosphate-based antioxidant (K-4): Magnesium stearate

Next, the resin compositions used in Examples and Comparative Examples will be described.
(PP-based composition-1): propylene-α-olefin copolymer (PP-1) 99.6% by weight, nucleating agent (K-1) 0.2% by weight, antioxidant (K-2) 0. 08% by weight, antioxidant (K-3) 0.08% by weight, and magnesium stearate (K-4) 0.04% by weight are mixed with a tumbler and melt-kneaded in a 40 mmφ co-rotating twin screw extruder. A polypropylene composition was obtained by pelletizing.
(PP-based composition-2): A polypropylene-based composition is obtained by melt-kneading and pelletizing in the same manner as (PP-based composition-1) except that (PP-2) is used instead of (PP-1). It was.
(PP-based composition-3): Melt-kneaded and pelletized in the same manner as (PP-based composition-1) except that (PP-3) was used instead of (PP-1) to obtain a polypropylene-based composition. It was.

Next, the film manufacturing methods in Examples and Comparative Examples are described.
In the following examples and comparative examples, each of the surface layer, the intermediate layer, and the center layer is extruded into a sheet form using an extrusion line of a 5-layer T die that is a 40 mmφ single screw extruder, and is described in each example. After stretching in the longitudinal direction at the roll temperature (longitudinal stretching temperature) and the stretching ratio (longitudinal stretching ratio), the tenter in the transverse direction at the temperature (transverse stretching temperature) and stretching ratio (transverse stretching ratio) described in each example Stretched to obtain a stretched film of 60 μm.
The resin composition used for each layer was previously uniformly mixed with a tumbler.
The stretching ratio in the machine direction is a ratio of the surface speed of the roll immediately after being extruded from the T-die and the surface speed of the final roll in the longitudinal stretching zone, and the stretching ratio in the transverse direction is between the clips at the tenter entrance. The ratio of the length between the clips at the outlet.

In the comparative example, a three-layer film produced a three-layer film without operating the intermediate layer extruder.
Regarding the thickness ratio of each layer extruded from the T die, the amount of extrusion from each extruder is adjusted so as to be the ratio described in each example, and finally, regarding the thickness of the sheet extruded from the T die, It adjusted so that the thickness of a stretched film might be set to 60 micrometers.

[Example 1]
As shown in Table 1, the resin composition of the surface layer is composed of 65% by weight of amorphous cyclic olefin resin (COC-1), 20% by weight of propylene-α-olefin resin (PP-1), and hydrogenated terpene. A mixed resin composition of 15% by weight of resin (T-1) was obtained. As shown in Table 1, the resin composition of the intermediate layer was composed of 35% by weight of amorphous cyclic olefin resin (COC-1), 35% by weight of (PP composition-1), and hydrogenated terpene resin (T -1) A mixed resin composition of 30% by weight was obtained. As shown in Table 1, the resin composition of the central layer was (PP-based composition-1) 70% by weight, 1-butene / α-olefin copolymer (PB-1) 5% by weight, and hydrogenated terpene resin. (T-1) A mixed resin composition of 25% by weight was prepared.
As shown in Table 1, the thickness ratio of each layer is adjusted to be 19: 4: 54: 4: 19, and the stretching conditions are as shown in Table 1, with a longitudinal stretching temperature of 90 ° C. and a longitudinal stretching ratio. A 5-layer stretched film having a thickness of 60 μm was obtained at 1.2 times, a transverse stretching temperature of 90 ° C., and a transverse stretching ratio of 7.0 times.
The film obtained in Example 1 is a film that satisfies all the requirements of the present invention, and good evaluation results were obtained for any of the evaluation items as shown in Table 2.

[Examples 2 to 4]
Also in Example 2 and Example 3, as in Example 1, the resin composition of each layer, the thickness ratio, and the stretching conditions were carried out as described in Table 1, and each five-layer stretched film was obtained.
The evaluation results of these examples are also shown in Table 2 in the same manner as in Example 1, and all of the films satisfy the requirements of the present invention, and good results were obtained for any of the evaluation items.

[Example 5]
A 5-layer stretched film was obtained in the same manner as in Example 3 except that the longitudinal stretch ratio was 1.05.
Although favorable evaluation is obtained as shown in Table 2, the tear strength in the longitudinal direction is a slightly high value although it is a level that can be practically used, and when compared with Example 3, the stretching ratio in the longitudinal direction This is a result suggesting that it is preferable to make the height higher.

[Comparative Example 1]
The resin composition of the center layer is (PP-based composition-3) 70% by weight, 1-butene / α-olefin copolymer (PB-1) 5% by weight, and hydrogenated terpene resin (T-1) 25% by weight. A five-layer stretched film was obtained in the same manner as in Example 1 except that the mixed resin composition was used and the longitudinal stretching temperature and the transverse stretching temperature were 95 ° C.
The evaluation results are shown in Table 2. The polypropylene resin used for the center layer was a polypropylene homopolymer (P-3) having a melting point exceeding 150 ° C., and the heat shrinkability was inferior.

[Comparative Example 2]
Except omitting the intermediate layer in Example 2, the same resin composition of the surface layer and the center layer as in Example 2 was used, and the thickness ratio of each layer was 22:56:22. A three-layer stretched film was obtained according to the stretching conditions.
Although the evaluation results are shown in Table 2, there is a range in which the interlaminar peeling phenomenon is observed in the longitudinal tear strength measurement and the tear strength is increased and it can be determined that the intermediate layer is eliminated and the interlaminar adhesive strength is reduced. The result exceeded.

[Comparative Example 3]
A three-layer stretched film was obtained in the same manner as in Comparative Example 2 except that the thickness ratio of each layer was 8: 84: 8.
The evaluation results are shown in Table 2. As in Comparative Example 2, in addition to the fact that the longitudinal tear strength is too high, the elastic modulus of the film is less than 900 MPa on average in the vertical and horizontal directions, and it can be determined that the rigidity is insufficient. .

  The film of the present invention is particularly preferably used as a film for shrink labels.

Claims (2)

A multilayer heat-shrinkable stretched film comprising at least five layers including a multilayer structure in which an intermediate layer (B) is formed on both outer surfaces of the center layer (C) and a surface layer (A) is formed on both outer surfaces, The resin composition in which the surface layer (A) satisfies the following (A) or (B), the resin composition in which both the intermediate layers (B) satisfy the following (C), and the center layer (C) satisfy the following (D) The ratio of the total thickness of both surface layers (A): the total thickness of both intermediate layers (B): the thickness of the central layer (C) is 30 to 45 respectively for the total film thickness 100. A multilayer heat-shrinkable stretched film in the range of 5-15: 40-65.
(A) Amorphous cyclic olefin-based resin (a1) 50 to 85% by weight, propylene-α-olefin copolymer (b1) 10 to 25% by weight having a melting point in the range of 120 to 150 ° C., and a softening point A resin composition comprising 5 to 25% by weight of petroleum resins (d1) at 80 to 140 ° C.
(B) Petroleum having an amorphous cyclic olefin resin (a1) of 50 to 85% by weight, a polyethylene resin (c1) having a density of less than 0.94 of 10 to 25% by weight, and a softening point of 80 to 140 ° C. A resin composition comprising 5 to 25% by weight of resins (d1).
(C) Amorphous cyclic olefin-based resin (a2) 20 to 50% by weight, propylene-α-olefin copolymer (b2) having a melting point within the range of 120 to 150 ° C. (b2) 25 to 50% by weight, and a softening point A resin composition comprising 10 to 40% by weight of petroleum resins (d2) at 80 to 140 ° C.
(D) Containing 1 to 40% by weight of a petroleum resin (d3) mainly composed of a propylene-α-olefin copolymer (b3) having a melting point in the range of 120 to 150 ° C. and having a softening point of 80 to 140 ° C. Resin composition.   It is a substantially uniaxially stretched film in which the transverse draw ratio (t) is 5 to 12 times, and the relational expression with the longitudinal draw ratio (m) satisfies 20m-20 ≦ t ≦ 60m-60. The multilayer heat shrinkable stretched film according to claim 1.