JP7698448B2 - Multi-layer biaxially oriented film - Google Patents

Description

The present invention relates to a multi-layer biaxially stretched film, more specifically, to a multi-layer biaxially stretched film useful for packaging films, etc.

It is common for resin products, metal products, glass products, etc. for building materials and optics to have a surface protection film attached to their surfaces to prevent scratches on the surface or the inclusion of foreign matter during transportation, storage, or processing. Surface protection films are required to have various properties depending on the object to be protected, the purpose of protection, the usage environment, etc., in addition to properties such as flexibility and mechanical properties. For this reason, surface protection films are being developed from various perspectives. For example, surface protection films mainly made of polyethylene components (Patent Document 1) and surface protection films made of resin compositions mainly made of polypropylene components and containing oligomers of 4-methyl-1-pentene and 1-decene are being considered (Patent Document 2).

Biaxially oriented polypropylene film is widely used as packaging and industrial material film because of its light weight, thermal stability, and excellent mechanical properties. However, when used as a packaging film, biaxially oriented polypropylene film tends to shrink when heat sealed, and further improvements were required.

Various attempts have been made to use polymethylpentene polymers to obtain films with excellent heat resistance. For example, Patent Document 3 discloses the use of two types of polymethylpentene polymers with different melting points for a wide range of applications such as films and blown molded bodies. However, Patent Document 3 does not specifically disclose a multi-layer biaxially stretched film, and in particular does not disclose any study of the appearance of the seal during heat sealing when the multi-layer biaxially stretched film is used.

Various attempts have been made to combine polypropylene with polymethylpentene polymers. However, it is known that increasing the polymethylpentene content deteriorates biaxial stretchability, and that delamination (interlayer peeling) occurs when the film is made into a multilayer film. Various attempts have been made to overcome this problem.

For example, Patent Document 4 discloses a multi-layer biaxially stretched film that includes a base layer containing polymethylpentene and polypropylene and a seal layer containing polypropylene, and also discloses that this multi-layer biaxially stretched film is capable of suppressing delamination and has good releasability. However, Patent Document 4 does not consider the appearance of the seal when heat-sealed for the multi-layer biaxially stretched film.

Patent Document 5 discloses a multilayer biaxially stretched film including a base layer containing two types of polymethylpentene polymers with different melting points, and a seal layer containing polypropylene. However, the base layer described in Patent Document 5 is mainly composed of polymethylpentene polymer with a lower melting point. Patent Document 5 does not consider the appearance of the seal when heat-sealed for the multilayer biaxially stretched film.

JP 2006-116769 A JP 2010-275340 A International Publication No. 2013/099876 JP 2018-144351 A JP 2019-001139 A

The present invention aims to provide a film that combines good heat resistance and good seal appearance, has good transparency, good stretchability, and is resistant to delamination (interlayer peeling).

As a result of intensive research into solving the above problems, the inventors discovered that a multilayer biaxially stretched film having layers containing multiple specific 4-methyl-1-pentene polymers with different melting points can solve the above problems, and thus completed the present invention.

That is, the present invention relates to the following [1] to [9].
[1]
A multilayer biaxially stretched film comprising an A layer and a B layer laminated together,
Layer A is composed of a resin composition containing a 4-methyl-1-pentene polymer (A1) and a 4-methyl-1-pentene copolymer (A2),
the content of the 4-methyl-1-pentene polymer (A1) in the A layer is 40% by mass or more and 85% by mass or less, based on the total mass of the A layer, and the content of the 4-methyl-1-pentene copolymer (A2) in the A layer is 15% by mass or more and 60% by mass or less, based on the total mass of the A layer;
The 4-methyl-1-pentene polymer (A1) satisfies the following requirements (A1-I) to (A1-III), and the 4-methyl-1-pentene copolymer (A2) satisfies the following requirements (A2-I) to (A2-III),
(A1-I) The content of the structural unit (P1) derived from 4-methyl-1-pentene is 90 to 100 mol %, and the content of the structural unit (Q1) derived from an α-olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene) is 0 mol % to 10 mol %.
(A1-II) The melting point (Tm) measured by DSC is in the range of 200°C to 250°C.
(A1-III) The intrinsic viscosity [η] measured in decalin at 135° C. is 0.5 to 5.0 dl/g.
(A2-I) The content of the structural unit (P2) derived from 4-methyl-1-pentene is equal to or greater than 65 mol% and less than 96 mol%, and the content of the structural unit (Q2) derived from an α-olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene) is greater than 4 mol% and equal to or less than 35 mol%.
(A2-II) The melting point (Tm) measured by DSC is not observed or is in the range of 100°C to 199°C.
(A2-III) The intrinsic viscosity [η] measured in decalin at 135° C. is 0.5 to 5.0 dl/g.
[2]
The multilayer biaxially stretched film according to the above [1], wherein the converted content Y calculated by the following formula A is 3.0 mol% to 11.0 mol%:
Y=(X _Q1 ×W ₁ +X _Q2 ×W ₂ )/(W ₁ +W ₂ +W _O )...Formula A
In the formula A,
_W1 is the mass of the 4-methyl-1-pentene polymer (A1) in the resin composition constituting the A layer;
_W2 is the mass of the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer;
W _O is the total mass content of resins not corresponding to the 4-methyl-1-pentene polymer (A1) or the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer;
X _Q1 represents the content (mol %) of the structural unit (Q1) in the 4-methyl-1-pentene polymer (A1); and
X _Q2 is the content (mol %) of the structural unit (Q2) in the 4-methyl-1-pentene copolymer (A2).
[3]
The multilayer biaxially stretched film according to the above [1] or [2], wherein the structural unit (Q2) is a structural unit derived from an α-olefin having 2 to 4 carbon atoms.
[4]
The multilayer biaxially stretched film according to any one of [1] to [3], wherein the layer B contains polypropylene (B).
[5]
The multilayer biaxially stretched film according to [4], wherein the layer B comprises two or more layers.
[6]
The multilayer biaxially stretched film according to [5], wherein the two or more layers have the same structure.
[7]
The multilayer biaxially stretched film according to [5], wherein the two or more layers include a first layer and a second layer located on the opposite side of the first layer as viewed from the layer A, and the polypropylene (B) constituting the first layer has a melting point equal to or higher than the melting point of the polypropylene (B) constituting the second layer.
[8]
The multilayer biaxially stretched film according to any one of [1] to [7] above, comprising a layer structure consisting of layer A/layer B.
[9]
The multilayer biaxially stretched film according to any one of the above [1] to [8], which is a packaging film.

The present invention provides a film that has good heat resistance and good seal appearance, good transparency, good stretchability, and is not prone to delamination (interlayer peeling) during biaxial stretching.

Specific embodiments of the present invention are described in detail below, but the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the invention.

In this specification, the expression "polymer" is used to encompass homopolymers and copolymers, unless otherwise specified.
In addition, in this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.

Furthermore, in this specification, when referring to a "structural unit derived from X" with respect to a certain monomer X, it means a structural unit corresponding to said monomer X. For example, if the structure of monomer X is R _P R _Q C=CR _R R _S , then the "structural unit derived from X" has a structure represented by -CR _P R _Q -CR _R R _S -. For example, when referring to a "structural unit derived from 4-methyl-1-pentene", it means a structural unit corresponding to 4-methyl-1-pentene (i.e., a structural unit represented by -CH ₂ -CH(-CH ₂ CH(CH ₃ ) ₂ )-). When referring to a "structural unit derived from propylene", it means a structural unit corresponding to propylene (i.e., a structural unit represented by -CH ₂ -CH(-CH ₃ )-).

In addition, in this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, it means the total amount of multiple substances present in the composition, unless otherwise specified.

The multilayer biaxially stretched film of the present invention is formed by laminating layer A and layer B, and layer A is composed of a resin composition containing a 4-methyl-1-pentene polymer (A1) and a 4-methyl-1-pentene copolymer (A2) (hereinafter also simply referred to as copolymer (A2)) having a melting point different from that of the 4-methyl-1-pentene polymer (A1) (hereinafter also simply referred to as polymer (A1)). That is, the multilayer biaxially stretched film of the present invention is
a layer A composed of a resin composition containing a 4-methyl-1-pentene polymer (A1) and a 4-methyl-1-pentene copolymer (A2) having a melting point different from that of the 4-methyl-1-pentene polymer (A1);
and layer B.
The layers A and B will be described in detail below, followed by a description of the layer structure and the film production method.

≪A layer≫
In the multilayer biaxially stretched film of the present invention, Layer A functions as a heat-resistant layer.
The A layer contains a 4-methyl-1-pentene polymer (A1) and a 4-methyl-1-pentene copolymer (A2) having a melting point different from that of the 4-methyl-1-pentene polymer (A1). The content of the 4-methyl-1-pentene polymer (A1) in the A layer is 40% by mass or more and 85% by mass or less, based on the total mass of the A layer, and the content of the 4-methyl-1-pentene copolymer (A2) is 15% by mass or more and 60% by mass or less, based on the total mass of the A layer. The content of the 4-methyl-1-pentene polymer (A1) is preferably 50 to 85% by mass, more preferably 60 to 85% by mass, and even more preferably 70 to 85% by mass, based on the total mass of the A layer. The content of the 4-methyl-1-pentene copolymer (A2) is preferably 15 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 15 to 30% by mass, based on the total mass of the A layer. When the content is within the above range, the 4-methyl-1-pentene polymer (A1) can be finely dispersed in the layer A. When the content of the 4-methyl-1-pentene polymer (A1) is equal to or greater than the above lower limit, the layer A has excellent heat resistance. When the content of the 4-methyl-1-pentene copolymer (A2) is equal to or greater than the above lower limit, the layer A has excellent interlayer strength and is less susceptible to delamination. On the other hand, when the content of the 4-methyl-1-pentene copolymer (A2) is equal to or less than the above upper limit, the obtained multilayer biaxially stretched film has excellent heat resistance and a good appearance after heat sealing.

In addition, as described below, it is believed that when both polymer (A1) and copolymer (A2) contain a specific amount or more of structural units derived from 4-methyl-1-pentene, the compatibility between polymer (A1) and copolymer (A2) is excellent, and the gloss of the resulting film is excellent.

[4-Methyl-1-pentene polymer (A1)]
The following describes the 4-methyl-1-pentene polymer (A1), which is a component constituting layer A. The 4-methyl-1-pentene polymer (A1) satisfies the following requirements (A1-I) to (A1-III).

<Requirements (A1-I)>
The 4-methyl-1-pentene polymer (A1) contains 90 mol % to 100 mol % of a structural unit (P1) (hereinafter, in this specification, may be simply referred to as "structural unit (P1)") derived from 4-methyl-1-pentene. In addition, it contains 0 mol % to 10 mol % of a structural unit (Q1) (hereinafter, in this specification, may be simply referred to as "structural unit (Q1)") derived from an olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene). The olefin having 2 to 20 carbon atoms is not limited to one type, and two or more types may be combined.

In other words, the content of the structural unit (P1) in the 4-methyl-1-pentene polymer (A1) (hereinafter, sometimes referred to as "X _P1 ") is 90 to 100 mol %, and the content of the structural unit (Q1) (hereinafter, sometimes referred to as "X _Q1 ") is 0 to 10 mol %.

From the viewpoint of heat resistance, the 4-methyl-1-pentene polymer (A1) preferably contains 93 mol % or more of the structural unit (P1) derived from 4-methyl-1-pentene.
On the other hand, the 4-methyl-1-pentene polymer (A1) contains up to 10 mol %, preferably up to 7 mol %, of structural units (Q1) derived from an olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene).

Preferred examples of olefins having 2 to 20 carbon atoms that may be contained in the 4-methyl-1-pentene polymer (A1) include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. These olefins having 2 to 20 carbon atoms may be used alone or in combination of two or more. From the viewpoint of imparting an appropriate elastic modulus, flexibility, and pliability, olefins having 8 to 18 carbon atoms (for example, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-heptadecene, and 1-octadecene) are preferred, and 1-decene, 1-hexadecene, and 1-octadecene are more preferred.

The 4-methyl-1-pentene polymer (A1) may contain structural units derived from a polymerizable compound (hereinafter also referred to as a polymerizable compound) other than 4-methyl-1-pentene and an olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene) as long as the object of the present invention is not impaired.

Examples of such polymerizable compounds include vinyl compounds having a cyclic structure such as styrene, vinylcyclopentene, vinylcyclohexane, and vinylnorbornane; vinyl esters such as vinyl acetate; unsaturated organic acids or derivatives thereof such as maleic anhydride; conjugated dienes such as butadiene, isoprene, pentadiene, and 2,3-dimethylbutadiene; 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, and 7-methyl-1,6-octadiene. , dicyclopentadiene, cyclohexadiene, dicyclooctadiene, methylenenorbornene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornadiene, and other non-conjugated polyenes.

The 4-methyl-1-pentene polymer (A1) in the present invention may contain units derived from the polymerizable compound in an amount of 10 mol % or less, preferably 5 mol % or less, and more preferably 3 mol % or less, based on all polymerizable compound structural units contained in the 4-methyl-1-pentene polymer (A1).

<Requirements (A1-II)>
The 4-methyl-1-pentene polymer (A1) in the present invention has a melting point (Tm) measured by DSC in the range of 200 to 250° C., preferably 200 to 245° C., more preferably 200 to 240° C. The melting point (Tm) value varies depending on the stereoregularity of the polymer and the amount of α-olefin copolymerized, and can be controlled and adjusted to a desired composition using an olefin polymerization catalyst described below.
A polymer composition containing a 4-methyl-1-pentene polymer (A1) having a melting point (Tm) within the above range is preferred from the viewpoint of heat resistance.

<Requirement (A1-III)>
The 4-methyl-1-pentene polymer (A1) in the present invention has an intrinsic viscosity [η] measured in decalin at 135° C. of 0.5 to 5.0 dL/g.

Here, the intrinsic viscosity [η] is more preferably in the range of 1.0 to 4.0 dL/g, and further preferably in the range of 1.2 to 3.5 dL/g.
The value of the intrinsic viscosity [η] can be adjusted by the amount of hydrogen added during polymerization when the 4-methyl-1-pentene polymer (A1) is produced.

The 4-methyl-1-pentene polymer (A1) having an intrinsic viscosity [η] within the above range exhibits good fluidity during the production of the resin composition and during various molding processes, has excellent stretchability, and exhibits good dispersibility in the 4-methyl-1-pentene copolymer (A2), resulting in a favorable appearance for the multilayer biaxially stretched film obtained.

<Method for producing 4-methyl-1-pentene polymer (A1)>
The 4-methyl-1-pentene polymer (A1) may be produced by polymerizing olefins, or by thermally decomposing a high molecular weight 4-methyl-1-pentene polymer. In addition, the polymer may be purified by a method such as solvent fractionation for fractionation based on the difference in solubility in a solvent or molecular distillation for fractionation based on the difference in boiling point.

When produced by polymerization reaction, the melting point, stereoregularity, molecular weight, etc. of the obtained 4-methyl-1-pentene polymer (A1) are controlled by adjusting, for example, the amounts of 4-methyl-1-pentene and, if necessary, the α-olefin to be copolymerized, the type of polymerization catalyst, the polymerization temperature, the amount of hydrogen added during polymerization, etc. The production method by polymerization reaction may be a known method. For example, the polymer may be produced by a gas phase method, a solution method, a slurry method, etc. using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst.
The polymer (A1) may be a commercially available polymer such as TPX manufactured by Mitsui Chemicals Inc. in addition to the polymer produced as described above.

[4-Methyl-1-pentene copolymer (A2)]
The 4-methyl-1-pentene copolymer (A2) satisfies the following requirements (A2-I) to (A2-III).

<Requirements (A2-I)>
The 4-methyl-1-pentene copolymer (A2) has structural units (P2) derived from 4-methyl-1-pentene (hereinafter, in this specification, this may be simply referred to as "structural units (P2)") in a proportion of 65 mol % or more and less than 96 mol %, and structural units (Q2) derived from an α-olefin having from 2 to 20 carbon atoms other than 4-methyl-1-pentene (hereinafter, in this specification, this may be simply referred to as "structural units (Q2)") in a proportion of more than 4 mol % and not more than 35 mol %.

In other words, the content of the structural unit (P2) in the 4-methyl-1-pentene copolymer (A2) (hereinafter, sometimes referred to as "X _P2 ") is 65 mol% or more and less than 96 mol%, and the content of the structural unit (Q2) (hereinafter, sometimes referred to as "X _Q2 ") is more than 4 mol% and 35 mol% or less.

The content of the structural unit (P2) is 65 mol% or more and less than 96 mol%, preferably 68 mol% or more and less than 92 mol%, more preferably 68 mol% or more and less than 90 mol%, and particularly preferably 80 mol% or more and less than 88 mol%.

When the content of the structural unit (P2) is 65 mol % or more, the heat resistance is excellent, and the compatibility with the polymer (A1) is excellent, and the gloss of the obtained film is excellent.
The content of the structural unit (Q2) (when there are two or more types of structural unit (Q2), the total content of said two or more types) is more than 4 mol% and not more than 35 mol%, preferably more than 8 mol% and not more than 32 mol%, more preferably more than 10 mol% and not more than 30 mol%, and particularly preferably more than 12 mol% and not more than 20 mol%.

When the content of the structural unit (Q2) in the 4-methyl-1-pentene copolymer (A2) exceeds 4 mol %, the resulting laminate film has excellent interlayer strength and is less susceptible to delamination.
The α-olefin having 2 to 20 carbon atoms other than 4-methyl-1-pentene that forms the structural unit (Q2) is preferably ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-hexadecene, or 1-octadecene, more preferably an α-olefin having 2 to 4 carbon atoms, i.e., ethylene, propylene, or 1-butene, and particularly preferably propylene. In other words, the structural unit (Q2) is preferably a structural unit derived from an α-olefin having 2 to 4 carbon atoms, and particularly preferably a structural unit derived from propylene.

Furthermore, when the polymer (A1) contains the structural unit (Q1), the structural unit (Q2) may be the same as or different from the structural unit (Q1).
The 4-methyl-1-pentene copolymer (A2) may contain other structural units besides the structural unit (P2) derived from 4-methyl-1-pentene and the structural unit (Q2) derived from an α-olefin other than 4-methyl-1-pentene having from 2 to 20 carbon atoms, provided that the effects of the present invention are not impaired. The content of the other structural units is, for example, 0 to 10 mol %.

Monomers that form the other structural units include cyclic olefins, aromatic vinyl compounds, conjugated dienes, non-conjugated polyenes, functional vinyl compounds, hydroxyl-containing olefins, halogenated olefins, etc.

As the cyclic olefin, aromatic vinyl compound, conjugated diene, non-conjugated polyene, functional vinyl compound, hydroxyl group-containing olefin, and halogenated olefin, for example, the compounds described in paragraphs 0034 to 0041 of JP 2013-169685 A can be used.

As the monomers forming the other structural units, vinylcyclohexane and styrene are particularly preferred.
When the 4-methyl-1-pentene copolymer (A2) contains the other structural units, the other structural units may be contained in a single type, or in a combination of two or more types.

The content (mol %) of each structural unit in the 4-methyl-1-pentene copolymer (A2) is measured by ¹³ C-NMR, and the specific measurement method is as described in the Examples section.

<Requirements (A2-II)>
The melting point (Tm) of the 4-methyl-1-pentene copolymer (A2) is not observed or is in the range of 100° C. to 199° C., more preferably not observed or is in the range of 110° C. to 180° C., further preferably in the range of 110° C. to 160° C., and particularly preferably in the range of 125° C. to 150° C. That is, the difference between the 4-methyl-1-pentene copolymer (A2) and the 4-methyl-1-pentene polymer (A1) lies in the melting point (Tm).
The melting point (Tm) of the 4-methyl-1-pentene copolymer (A2) is a value measured by the same method as for the melting point (Tm) of the polymer (A1).

<Requirements (A2-III)>
The intrinsic viscosity [η] of the 4-methyl-1-pentene copolymer (A2) measured in a decalin solvent at 135° C. is 0.5 to 5.0 dl/g, preferably 0.5 to 3.5 dl/g, and more preferably 1.0 to 3.5 dl/g. It is preferable from the viewpoint of moldability that the intrinsic viscosity [η] of the 4-methyl-1-pentene copolymer (A2) is within the above range.

The intrinsic viscosity [η] of the 4-methyl-1-pentene copolymer (A2) is a value measured in the same manner as the intrinsic viscosity [η] of the polymer (A1).
In addition to the above requirements (A2-I) to (A2-III), the 4-methyl-1-pentene copolymer (A2) preferably satisfies one or more of the following requirements:

<Requirements (A2-IV)>
The molecular weight distribution (Mw/Mn) of the 4-methyl-1-pentene copolymer (A2) is preferably from 1.0 to 3.5, and more preferably from 1.1 to 3.0.
The weight average molecular weight (Mw) of the 4-methyl-1-pentene copolymer (A2) is preferably 1×10 ⁴ to 2×10 ⁶ , more preferably 1×10 ⁴ to 1×10 ⁶ , from the viewpoint of formability of the layer made of the composition.
The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the 4-methyl-1-pentene copolymer (A2) are values calculated by the method described in the Examples.

<Requirements (A2-V)>
The melt flow rate (MFR) of the 4-methyl-1-pentene copolymer (A2), measured at 230° C. under a load of 2.16 kg in accordance with JIS K7210, is preferably 0.1 g/10 min to 100 g/10 min, more preferably 0.5 g/10 min to 50 g/10 min, and even more preferably 0.5 g/10 min to 30 g/10 min, from the viewpoint of fluidity during molding of the composition.

<Method for producing 4-methyl-1-pentene copolymer (A2)>
The 4-methyl-1-pentene copolymer (A2) can be synthesized using a conventionally known metallocene catalyst system, for example, by the methods described in WO 2005/121192, WO 2011/055803, WO 2014/050817, etc.

[Configuration of Layer A]
As described above, the resin composition constituting layer A of the multilayer biaxially stretched film of the present invention contains the 4-methyl-1-pentene polymer (A1) and the 4-methyl-1-pentene copolymer (A2) in a specific ratio.

In the present invention, the A layer contains a specific amount of the 4-methyl-1-pentene copolymer (A2) in addition to the 4-methyl-1-pentene polymer (A1), and thus when the multilayer biaxially stretched film is made, it is flexible, has good stretchability, and has excellent heat resistance. Furthermore, by configuring the A layer in this way, heat resistance is imparted, and the resulting multilayer biaxially stretched film has excellent seal appearance when subjected to heat sealing. For example, the multilayer biaxially stretched film of the present invention tends to shrink less when subjected to heat sealing because the amount of the 4-methyl-1-pentene copolymer (A2) in the A layer is equal to or less than a certain amount. Furthermore, the multilayer biaxially stretched film of the present invention tends to shrink less when subjected to heat sealing and has high transparency, compared to a multilayer biaxially stretched film that uses a layer consisting of the 4-methyl-1-pentene polymer (A1) and polypropylene instead of the A layer.

<Other ingredients>
The resin composition constituting the A layer may consist only of the 4-methyl-1-pentene polymer (A1) and the 4-methyl-1-pentene copolymer (A2). However, the resin composition may further contain other components (hereinafter, "other components") that do not fall under either the 4-methyl-1-pentene polymer (A1) or the 4-methyl-1-pentene copolymer (A2). Examples of such "other components" include "other resins" and "additives" described below.

Other Resins The resin composition constituting Layer A of the multilayer biaxially stretched film of the present invention may contain a resin (hereinafter, referred to as "other resins" in the section "Layer A") that does not fall under the above-mentioned 4-methyl-1-pentene polymer (A1) or 4-methyl-1-pentene copolymer (A2) within the scope that does not impair the object of the present invention. As the other resin, for example, it is possible to add a polyolefin polymer such as polyethylene, poly-1-butene, a styrene resin, or an ethylene-α-olefin copolymer.
When the resin composition constituting the layer A contains "other resins", the amount of the "other resins" is preferably 0.01 to 5.0 parts by mass relative to 100 parts by mass of the resin composition.

In the present invention, the value of the converted content Y calculated by the following formula A is preferably 3.0 mol% to 11.0 mol%, more preferably 3.5 mol% to 10.5 mol%, further preferably 4.0 mol% to 10.0 mol%, and particularly preferably 4.5 mol% to 9.5 mol%:
Y=(X _Q1 ×W ₁ +X _Q2 ×W ₂ )/(W ₁ +W ₂ +W _O )...Formula A
In the formula A,
_W1 is the mass of the 4-methyl-1-pentene polymer (A1) in the resin composition constituting the A layer;
_W2 is the mass of the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer;
W _O is the total mass content of resins not corresponding to the 4-methyl-1-pentene polymer (A1) or the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer;
X _Q1 represents the content (mol %) of the structural unit (Q1) in the 4-methyl-1-pentene polymer (A1); and
X _Q2 is the content (mol %) of the structural unit (Q2) in the 4-methyl-1-pentene copolymer (A2).
When the value of the converted comonomer content Y is within the above-mentioned range, the stretchability and the appearance after heat sealing are excellent. In this specification, the converted comonomer content Y may also be referred to as "comonomer content (A1) + (A2)".

In the case where the resin composition constituting the A layer is composed only of a resin component, the content (mass%) of the 4-methyl-1-pentene polymer (A1) in the resin composition and the content (mass%) of the 4-methyl-1-pentene copolymer (A2) in the resin composition are denoted as _C1 and _C2 , respectively.
C ₁ =W ₁ /(W ₁ +W ₂ +W _O )×100
C ₂ =W ₂ /(W ₁ +W ₂ +W _O )×100
Therefore, the formula A can be expressed by the following formula B
Y=(X _Q1 ×C ₁ +X _Q2 ×C ₂ )/100...Formula B
It can also be expressed as:

In addition, when the resin composition constituting the A layer does not contain "other resins", the _WO is 0, and the above formula A is
Y=(X _Q1 ×W ₁ +X _Q2 ×W ₂ )/(W ₁ +W ₂ )...Formula A'
It will be expressed as:

Additives The resin composition constituting Layer A of the multilayer biaxially stretched film of the present invention may contain various additives in addition to or instead of the "other resins" described above, within the scope of the present invention.
Examples of such various additives include weather resistance stabilizers, heat resistance stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, antislip agents, antiblocking agents, antifogging agents, nucleating agents, lubricants, pigments, dyes, antioxidants, hydrochloric acid absorbers, inorganic or organic fillers, organic or inorganic foaming agents, crosslinking agents, crosslinking assistants, adhesives, softening agents, and flame retardants.

As the antioxidant, known antioxidants can be used. Specifically, hindered phenol compounds, sulfur-based antioxidants, lactone-based antioxidants, organic phosphite compounds, organic phosphonite compounds, or combinations of several of these can be used.

Examples of the lubricant include saturated or unsaturated fatty acids such as lauric acid, palmitic acid, oleic acid, and stearic acid, and their sodium, calcium, and magnesium salts, which can be used alone or in combination of two or more. The amount of such a lubricant to be added is preferably 0.1 to 3 parts by mass, and more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the resin composition.

The resin composition constituting the A layer in the present invention may contain a nucleating agent, which is a specific optional component, in order to further improve its moldability, that is, to increase the crystallization temperature and accelerate the crystallization rate. In this case, for example, the nucleating agent is a dibenzylidene sorbitol-based nucleating agent, a phosphate ester-based nucleating agent, a rosin-based nucleating agent, a metal benzoate-based nucleating agent, fluorinated polyethylene, sodium 2,2-methylenebis(4,6-di-t-butylphenyl)phosphate, pimelic acid or its salt, 2,6-naphthalene dicarboxylic acid dicyclohexylamide, etc., and the amount of the nucleating agent is not particularly limited, but is preferably about 0.1 to 1 part by mass per 100 parts by mass of the resin composition. There is no particular limit to the timing of the addition, and the nucleating agent can be added during polymerization, after polymerization, or during molding.
The other components among the various additives exemplified above may be those generally used in the field to which the present invention pertains, and the amounts of these may be appropriately determined.

In addition to the various additives exemplified above, the resin composition may further contain other additives such as secondary antioxidants, natural oils, synthetic oils, waxes, etc., as necessary, within the scope of the present invention. There are no particular restrictions on the amount of the other additives, but the amount is usually 0 to 50 parts by mass, preferably 0 to 30 parts by mass, more preferably 0 to 10 parts by mass, and particularly preferably 0 to 1 part by mass, relative to 100 parts by mass of the resin composition.

When layer A according to the present invention contains the above-mentioned "other components," the above-mentioned definition of the content of component (A1) (5 to 95% by mass) and the definition of the content of component (A2) (5 to 95% by mass) are applied, with the mass obtained by subtracting the "other components" from the total mass of layer A being 100% by mass.

≪B layer≫
The layer B in the multilayer biaxially oriented film of the present invention is a layer provided for the purpose of imparting excellent mechanical properties, for example, excellent sealability, to the multilayer biaxially oriented film of the present invention.
In a typical and preferred embodiment of the present invention, the B layer contains polypropylene (B). When the B layer contains polypropylene (B), the B layer may be composed of a single layer, or may be composed of two or more layers. When the B layer is composed of two or more layers, the two or more layers may have the same configuration, or may be different from each other.

[Polypropylene (B)]
The polypropylene (B) in the present invention is a known polymer mainly composed of propylene, and examples of such polymers include propylene homopolymers, propylene-α-olefin copolymers of propylene and an α-olefin other than propylene (propylene random copolymers such as propylene-ethylene copolymers, propylene-1-butene copolymers, propylene-ethylene-1-butene copolymers, propylene block copolymers, and mixtures thereof). In this specification, when a polymer is described as being "mainly composed of X" and a certain constituent monomer is designated as X, this means that the polymer contains the largest number of constituent units derived from X among all of its constituent units, and for example, a "polymer mainly composed of propylene" refers to a polymer which contains the largest number of constituent units derived from propylene (i.e., constituent units represented by _-CH2 -CH( _-CH3 )-) among all of its constituent units. As the polypropylene, isotactic polypropylene and syndiotactic polypropylene are preferably used, and the isotactic mesopentage fraction (mmmm) or syndiotactic mesopentage fraction (rrrr) showing stereoregularity is preferably 90% or more, more preferably 92% or more, and even more preferably 93% or more. High stereoregularity improves the crystallinity of the resin, and can impart high thermal stability and mechanical properties.

The copolymerization ratio of the α-olefin in the propylene-α-olefin copolymer is preferably 5% by mass or less. The propylene-α-olefin copolymer may be a random copolymer or a block copolymer, and may contain a nucleating agent (crystallization nucleating agent). The nucleating agent is not particularly limited, and examples thereof include α-crystal nucleating agents such as various inorganic compounds, various carboxylic acids or their metal salts, dibenzylidene sorbitol compounds, aryl phosphate compounds, mixtures of cyclic polyvalent metal aryl phosphate compounds and aliphatic monocarboxylic acid alkali metal salts or basic aluminum lithium hydroxy carbonate hydrate, and various polymer compounds. These crystallization nucleating agents can be used alone or in combination of two or more materials.

The MFR of the polypropylene (B) can be measured in accordance with JIS K7210. Specifically, under measurement conditions of a temperature of 230°C and a load of 2.16 kg, it is preferably 0.5 to 25 g/10 min, more preferably 1 to 15 g/10 min, and even more preferably 2 to 10 g/10 min. When the MFR of polypropylene (B) is within the above range, it is suitable for extrusion molding.

The ash content of polypropylene (B) resulting from polymerization catalyst residues, etc. is preferably as low as possible to reduce minute foreign matter (fish eyes), and is preferably 50 ppm or less. More preferably, it is 40 ppm or less. By keeping it at 50 ppm or less, minute foreign matter and defects are significantly reduced, and contamination when used in electronic component applications can be reduced.

When layer B is composed of two or more layers, the two or more layers may include a first layer (hereinafter also referred to as "layer B1") and a second layer (hereinafter also referred to as "layer B2") on the opposite side of layer A from the first layer. Here, the polypropylene (B) (hereinafter "polypropylene (B1)") constituting the first layer (layer B1) and the polypropylene (B) (hereinafter "polypropylene (B2)") constituting the second layer (layer B2) may be the same or different from each other.

When the polypropylene (B1) and the polypropylene (B2) are different from each other, it is preferable that the melting point of the polypropylene (B1) is equal to or higher than the melting point of the polypropylene (B2). In one embodiment of the present invention, the melting point of the polypropylene (B1) is the same as the melting point of the polypropylene (B2). However, depending on the application of the multilayer biaxially stretched film of the present invention, it may be more preferable that the melting point of the polypropylene (B1) is higher than the melting point of the polypropylene (B2). In an exemplary embodiment of the present invention, the polypropylene (B1) is a propylene homopolymer, and the polypropylene (B2) is a propylene random copolymer. However, the polypropylene (B1) is not limited to a propylene homopolymer, and may be a propylene copolymer, as long as it has a melting point equal to or higher than the melting point of the polypropylene (B2).

When layer B contains polypropylene (B), layer B may be a layer consisting of polypropylene (B) alone, or may be a layer consisting of a resin composition containing polypropylene (B). Here, the resin composition forming layer B may contain various additives similar to those listed in the "Additives" section of the "Layer A" section, such as heat stabilizers, antioxidants, lubricants, chlorine traps, and antistatic agents. When layer B is composed of two or more layers, the additives and their blending ratios that may be contained in the two or more layers may be the same or different from each other.

<Multi-layer biaxially oriented film>
The multilayer biaxially stretched film of the present invention contains the above-mentioned layer A and layer B, and in a typical embodiment, contains a layer structure consisting of layer A/layer B. The multilayer biaxially stretched film of the present invention may have only a layer structure consisting of layer A/layer B, or may further contain a layer C that is different from both layer A and layer B.
Here, the layer B may consist of a single layer, or may consist of two or more layers.

In one preferred embodiment of the present invention, the B layer is a single layer (hereinafter, "B0 layer"). In this embodiment, the B layer functions as a seal layer. In this case, the multilayer biaxially stretched film of the present invention includes a two-layer structure consisting of an A layer/B0 layer.
In another preferred embodiment of the present invention, layer B is composed of two or more layers, and for example, the two or more layers may include layer B1 and layer B2 located on the opposite side of layer B1 as viewed from layer A, as described above in the section "layer B". In other words, the multilayer biaxially stretched film of the present invention may have a three-layer structure in which layer A/layer B1/layer B2 are laminated in this order.

In the first of these aspects, the two or more layers constituting layer B have the same structure. In this first aspect, the two or more layers constituting layer B function as a sealing layer. In this first aspect, the two or more layers can be considered as a whole constituting a single layer B, and for example, the B1 layer and the B2 layer can be considered as a whole constituting layer B0.

In the second embodiment, the two or more layers constituting the B layer are different from each other. For example, the B1 layer and the B2 layer may be different depending on the presence and type of components other than the polypropylene (B), or may be different depending on the type of the polypropylene (B). In one preferred embodiment of the present invention, the melting point of the polypropylene (B) constituting the B1 layer (i.e., the polypropylene (B1)) is equal to or higher than the melting point of the polypropylene (B) constituting the B2 layer (i.e., the polypropylene (B2)). In this embodiment, the B2 layer functions as a sealing layer. The B1 layer may be composed of two or more layers having the same structure, and in this case, the two or more layers that can constitute the B1 layer may be considered to constitute one B1 layer as a whole.

In addition, when the multilayer biaxially stretched film of the present invention further includes a layer C different from both the layer A and the layer B, the layer C can be made of a component that does not fall under the category of the 4-methyl-1-pentene polymer (A1), the 4-methyl-1-pentene copolymer (A2), or the polypropylene (B) and that can function appropriately as a sealing layer, such as an ethylene-based resin such as low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, or ethylene-(meth)acrylic acid copolymer, or a blend resin of polyethylene and polybutene. In this case, the multilayer biaxially stretched film of the present invention usually has a three-layer structure in which the layers A, B, and C are laminated in this order.

There are no particular limitations on the method for obtaining such a multilayer film, but it is usually obtained by first forming a raw film (also called a raw sheet) in which layer A and layer B, and other layers as necessary, are laminated, and then biaxially stretching the raw film. Examples of methods for forming the raw film include a method in which a surface layer film previously obtained by T-die molding or inflation molding is laminated by a known lamination method such as extrusion lamination or extrusion coating, or a method in which multiple films are molded independently and then each film is laminated by dry lamination, but from the viewpoint of productivity, co-extrusion molding in which multiple components are fed into a multilayer extruder and molded is preferred.

The thickness of the film before stretching according to the present invention, i.e., the original film, is not particularly limited, but is usually 100 μm to 1000 μm, preferably 150 to 800 μm, and more preferably 200 to 500 μm.

The thickness of one layer A in the raw film is preferably 0.1 to 250% of the thickness of layer B, and more preferably 0.5 to 100%. When the multilayer biaxially stretched film of the present invention contains two or more layers A, the thicknesses of the layers A may be the same or different from each other.

The total thickness of the multilayer biaxially stretched film of the present invention is preferably 3 to 60 μm, more preferably 10 to 50 μm, and even more preferably 10 to 30 μm. By making the total thickness of the film 3 to 60 μm, it is possible to obtain a film with excellent transparency, mechanical properties, and stretchability.

The thickness of one A layer in the multilayer biaxially stretched film of the present invention is preferably 0.1 to 250% of the thickness of the B layer, and more preferably 0.5 to 100%. When the multilayer biaxially stretched film of the present invention contains two or more A layers, the thicknesses of the A layers may be the same or different from each other.

<Manufacturing method of multilayer biaxially stretched film>
As a method for mixing the components to prepare resin composition pellets for layer A or layer B, various known methods can be used, such as a multistage polymerization method, a method for mixing using a plastomill, a Henschel mixer, a V-blender, a ribbon blender, a tumbler, a blender, a kneader-ruder, or the like, or a method for mixing, melt-kneading, for example, at 180 to 300° C., and then granulating or pulverizing using a single-screw extruder, a twin-screw extruder, a kneader, a Banbury mixer, or the like. By this method, it is possible to obtain high-quality resin composition pellets in which the components and additives are uniformly dispersed and mixed.

The raw sheet for the multilayer biaxially stretched film of the present invention can be obtained by melt-extruding the above-mentioned resin composition pellets at a cylinder temperature usually in the range of 180 to 300°C.
To produce a multilayer biaxially stretched film from the raw sheet, a batch-type biaxial stretching method, sequential biaxial stretching immediately after cast molding, or simultaneous biaxial stretching can be used. In sequential biaxial stretching, the cast raw sheet is kept at 100 to 165°C, passed between rolls with a speed difference, stretched 2 to 5 times in the machine direction, and immediately cooled to room temperature. The film is then introduced into a tenter and stretched 5 to 10 times in the width direction at a temperature of 150°C or higher, followed by relaxation, heat setting, and winding.

In the multilayer biaxially stretched film of the present invention, the 4-methyl-1-pentene polymer (A1) and the 4-methyl-1-pentene copolymer (A2) are present in the A layer with high affinity, so that the 4-methyl-1-pentene polymer (A1) and the 4-methyl-1-pentene copolymer (A2) are unlikely to fall off, and the film has excellent blocking resistance over a long period of time.

≪Applications≫
Specific applications of the multilayer biaxially stretched film of the present invention include, for example, the following general film applications.
Packaging films: for example, food packaging films, stretch films, wrap films, shrink films, easy peel films, aluminum vapor deposition films, PVDC coated films, and the like.
Breathable films: for example, films used as disposable diapers, sanitary products, surgical gowns, surgical gloves, surgical down, house wraps (breathable waterproof sheets), disposable hand warmers, household dehumidifiers, desiccants, oxygen absorbers, freshness-preserving agents, composting sheets, simple jumpers, etc.
Anti-rust films: for example, films used as transport packaging, storage packaging, export packaging, etc. for automobile parts, knockdown parts, machinery and machinery parts, iron and chrome products, steel pipes, wire rods, bolts and nuts, bearings, molds, tools, blades, cutting tools, construction tools, etc.
Anti-fog films: for example, films for fruits and vegetables, films for processed foods, etc.
Directional films: films used as twist wrapping for confectionery, agricultural materials, laminate substrates, coin wrapping, electric wire bundling materials, fruit and vegetable wrapping, cardboard cutting tape, detergent refill containers, rice ball wrapping, pillow wrapping, stick wrapping, boiled and retort wrapping, liquid food wrapping, infusion bags, etc.
Self-cleaning films: for example, films used as road signs, general signs, signboards, window glass, road materials, side mirrors, etc.
Separators: for example, battery separators, separators for lithium ion batteries, electrolyte membranes for fuel cells, adhesive/bonding separators, etc.
Stretched films: for example, films for film capacitors, capacitor films, capacitor films for fuel cells, etc.
Semiconductor process films: for example, dicing tape, backgrind tape, die bonding film, films for polarizing plates, surface protective films: for example, protective films for polarizing plates, protective films for liquid crystal panels, protective films for optical components, protective films for lenses, protective films for electrical components and electrical appliances, protective films for mobile phones, protective films for personal computers, masking films, protective films for touch panels, etc.
Films for electronic components: For example, diffusion films, reflective films, radiation-resistant films, γ-ray-resistant films, porous films, etc.
Building material films: for example, window films for building materials, films for laminated glass, bulletproof materials, films for bulletproof glass, heat-shielding sheets, heat-shielding films, etc.
Transfer films: for example, transfer films for automobiles and industry, transfer films for packaging, etc.
Release films: for example, release films for flexible printed circuit boards (FPC), release films for ACM boards, release films for rigid flexible boards, release films for advanced composite materials, release films for curing carbon fiber composites, release films for curing glass fiber composites, release films for curing aramid fiber composites, release films for curing nanocomposite materials, release films for curing filler materials, release films for semiconductor encapsulation, release films for polarizing plates, release films for diffusion sheets, release films for prism sheets, release films for reflective sheets, cushion films for release films, release films for fuel cells, release films for various rubber sheets, release films for urethane curing, release films for epoxy curing (manufacturing process components such as metal bats and golf clubs, etc.), and the like.

In a particularly preferred embodiment of the present invention, the multilayer biaxially stretched film of the present invention is a packaging film. When the multilayer biaxially stretched film of the present invention is used as a packaging film, the sheet has excellent appearance when heat sealed.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, the physical properties were measured as follows.

〔composition〕
The contents (mol %) of 4-methyl-1-pentene and α-olefin in the polymer were measured by ¹³ C-NMR under the following conditions:
Measurement device: Nuclear magnetic resonance device (ECP500 type, manufactured by JEOL Ltd.)
Observed nucleus: ^13C (125MHz)
Sequence: Single pulse proton decoupling Pulse width: 4.7 μs (45° pulse)
Repeat time: 5.5 seconds; Accumulation count: 10,000 or more; Solvent: orthodichlorobenzene/deuterated benzene (volume ratio: 80/20) mixed solvent; Sample concentration: 55 mg/0.6 mL
・Measurement temperature: 120℃
Chemical shift reference value: 27.50 ppm

[Intrinsic viscosity [η]]
The intrinsic viscosity [η] of the polymer was measured at 135° C. in a decalin solvent using an Ubbelohde viscometer as a measuring device. Specifically, about 20 mg of powdered polymer was dissolved in 25 ml of decalin, and then the specific viscosity η _sp was measured in an oil bath at 135° C. using an Ubbelohde viscometer. After diluting the decalin solution by adding 5 ml of decalin, the specific viscosity η _sp was measured in the same manner as above. This dilution operation was repeated two more times, and the value of η _sp /C when the concentration (C) was extrapolated to 0 was calculated as the intrinsic viscosity [η] (unit: dl/g) (see formula 1 below).
[η]=lim(η _sp /C) (C→0)...Formula 1

[Melt flow rate (MFR)]
The melt flow rate (MFR) of the polymer was measured in accordance with JIS K7210 under conditions of 260° C. and a load of 5.0 kg for the polymer A1-1 obtained in Preparation Example 1 below and the polymer A1-2 obtained in Preparation Example 2 below, and under conditions of 230° C. and a load of 2.16 kg for the copolymer A2-1 obtained in Preparation Example 3 below and the polypropylene. The unit is g/10 min.

[Number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw/Mn)]
The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw/Mn) were measured using a Waters gel permeation chromatograph Alliance GPC-2000 model as follows. The separation columns were two TSKgel GNH6-HT and two TSKgel GNH6-HTL, each with a diameter of 7.5 mm and a length of 300 mm, the column temperature was 140° C., the mobile phase was o-dichlorobenzene (Wako Pure Chemical Industries) and 0.025 wt % BHT (Takeda Pharmaceuticals) as an antioxidant, and the flow rate was 1.0 ml/min, the sample concentration was 15 mg/10 mL, the sample injection amount was 500 microliters, and a differential refractometer was used as a detector. The standard polystyrene used was manufactured by Tosoh Corporation for molecular weights of Mw<1000 and Mw>4×10 ⁶ , and was manufactured by Pressure Chemical Company for molecular weights of 1000≦Mw≦4×10 ⁶ .

〔density〕
The density of the polymer was measured in accordance with JIS K7112 (density gradient tube method), and the density (kg/m ³ ) was used as an index of lightness.

[Melting point (Tm)]
The melting point (Tm) of the polymer was measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.) as a measuring device.
Approximately 5 mg of the polymer was sealed in an aluminum pan for measurement and heated from room temperature to 280°C at 10°C/min. In order to completely melt the polymer, it was held at 280°C for 5 minutes and then cooled to -50°C at 10°C/min. After being left at -50°C for 5 minutes, it was heated a second time to 280°C at 10°C/min. The peak temperature (°C) in this second heating was taken as the melting point (Tm) of the polymer.

[Preparation Examples 1 and 2] Production of 4-methyl-1-pentene Polymers A1-1 and A1-2 As Preparation Examples 1 and 2, two types of polymers corresponding to the polymer (A1) were prepared.
In accordance with the polymerization methods described in Comparative Examples 7 and 9 of WO 2006/054613, 4-methyl-1-pentene polymers A1-1 and A1-2 (hereinafter referred to as "Polymer A1-1" and "Polymer A1-2", respectively) having the physical properties shown in Table 1 were obtained as polymer (A1) by changing the ratios of 4-methyl-1-pentene, 1-decene, 1-hexadecene, 1-octadecene, and hydrogen.

That is, polymer A1-1 is a polymer obtained by copolymerizing 4-methyl-1-pentene and 1-decene in the presence of a solid titanium catalyst component, triethylaluminum, and hydrogen, using a solid titanium catalyst component obtained by reacting anhydrous magnesium chloride, 2-ethylhexyl alcohol, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane (BPMP), and titanium tetrachloride as a polymerization catalyst.

Polymer A1-2 is a polymer obtained by copolymerizing 4-methyl-1-pentene and a mixture of equal masses of 1-hexadecene and 1-octadecene in the presence of a solid titanium catalyst component obtained by reacting anhydrous magnesium chloride, 2-ethylhexyl alcohol, 2-isobutyl-2-isopropyl-1,3-dimethoxypropane (BPMP) and titanium tetrachloride as a polymerization catalyst, and in the presence of this solid titanium catalyst component, triethylaluminum and hydrogen.

Preparation Example 3 Production of 4-methyl-1-pentene Copolymer A2-1 Into a 1.5 L capacity SUS autoclave equipped with a stirring blade, which had been thoroughly purged with nitrogen, 300 ml of n-hexane (dried over activated alumina under a dry nitrogen atmosphere) and 450 ml of 4-methyl-1-pentene were charged at 23° C., and then 0.75 ml of a 1.0 mmol/ml toluene solution of triisobutylaluminum (TIBAL) was charged and the stirrer was turned on.

Next, the autoclave was heated until the internal temperature reached 60° C., and pressurized with propylene to a total pressure (gauge pressure) of 0.19 MPa.
Next, 0.34 ml of a toluene solution containing 1 mmol of methylaluminoxane and 0.01 mmol of diphenylmethylene(1-ethyl-3-t-butyl-cyclopentadienyl)(2,7-di-t-butyl-fluorenyl)zirconium dichloride, calculated as Al, which had been prepared in advance, was injected into the autoclave under pressure with nitrogen to initiate the polymerization reaction. During the polymerization reaction, the internal temperature of the autoclave was adjusted to 60°C.

60 minutes after the start of polymerization, 5 ml of methanol was injected into the autoclave with nitrogen to terminate the polymerization reaction, and the autoclave was then depressurized to atmospheric pressure. After depressurization, acetone was added to the reaction solution while stirring the reaction solution, yielding a polymerization reaction product containing the solvent. The resulting polymerization reaction product containing the solvent was then dried under reduced pressure at 130°C for 12 hours to yield 44.0 g of powdered 4-methyl-1-pentene copolymer A2-1 (hereinafter "copolymer A2-1") as copolymer (A2). The measurement results of various physical properties are shown in Table 1.

Example 1
A three-layer biaxially stretched film having an A layer/B1 layer/B2 layer laminated in this order was formed.
First, a resin composition consisting of 85 parts by mass of polymer A1-1 and 15 parts by mass of copolymer A2-1 was prepared as a resin composition for forming layer A. Specifically, polymer A1-1 and copolymer A2-1 were fed to a twin-screw extruder in a ratio of 85 parts by mass:15 parts by mass, and kneaded at 270° C. to prepare a resin composition. The obtained resin composition was used as a raw material for layer A.

As the resin for forming the B1 layer and the B2 layer, Prime Polypro (registered trademark) F113G (propylene homopolymer, density: 910 kg/ ^m3 , MFR (230°C, 2.16 kg load): 3.0 g/10 min, manufactured by Prime Polymer Co., Ltd.) was used. In the following description, this Prime Polypro (registered trademark) F113G may be referred to as "Polymer B".

The obtained resin composition and resin were extruded from the T-die to a thickness of 250 μm (A layer 45 μm/B1 layer 190 μm/B2 layer 15 μm) using a three-type, three-layer T-die sheet molding machine equipped with a T-die with a lip width of 330 mm, three hopper inlets, and a 30 mm diameter screw, with the cylinder temperature of A layer set to 270°C, the cylinder temperatures of B1 and B2 layers set to 230°C, and the die temperature set to 270°C, to cast mold the molten mixture to obtain the original film of Example 1. The thickness of each layer was calculated from the amount of extrusion.

Next, using a Bruckner batch-type biaxial stretching machine KARO IV, the obtained raw film was stretched 2.89 times in the machine direction (MD) and 5.2 times in the width direction (TD) under stretching conditions of a preheating temperature of 160°C, a preheating time of 30 seconds, a stretching temperature of 160°C, a stretching speed of 300%/sec, and heat setting conditions of 162°C, 60 seconds, to obtain a multilayer biaxially stretched film with a total film thickness of 17 μm.
The evaluation results of the obtained multi-layer biaxially stretched film are shown in Table 2-1 below. Specific test methods are as follows.

<Uniformity after stretching>
The multi-layer biaxially stretched film obtained after the multi-layer biaxial stretching was visually inspected. If the surface was smooth and uniform, it was marked with ◯, and if there were wrinkles or other uneven parts, it was marked with ×.

<Delamination during stretching>
In the multilayer biaxially stretched film obtained after the multilayer biaxial stretching, peeling between the A layer and the B1 layer and between the B1 layer and the B2 layer was visually confirmed, and the presence or absence of delamination was confirmed. When there was no delamination, it was marked with ◯, and when there was delamination, it was marked with ×.

<Haze and total light transmittance>
A test piece having a length of 80 mm and a width of 50 mm was taken from the multilayer biaxially stretched film obtained after the multilayer biaxial stretching, and the haze value (unit: %) and the total light transmission amount in air were measured using a Haze Meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: NDH-20D, light source: D65) in accordance with ASTM D1003. This measurement was performed at any three points on the multilayer biaxially stretched film, and the average value of the data at these three points was taken as the measured value.
The total light transmittance was calculated by the following formula.
Total light transmittance (%) = 100 x (total transmitted light amount) / (incident light amount)

<Gross>
The gloss of the multilayer biaxially stretched film obtained after multilayer biaxial stretching was measured under the conditions of an incident angle of 60° and a receiving angle of 60° in accordance with JIS Z8741. This measurement was performed at any five points on the multilayer biaxially stretched film, and the average value of the data at these five points was taken as the gloss.

<Shrinkage after heat sealing>
A test piece having a length of 170 mm and a width of 50 mm was taken from the multilayer biaxially stretched film obtained after the multilayer biaxial stretching. The length direction of the film was the direction corresponding to the flow direction in the film manufacturing process. Using a heat seal tester (thermal gradient heat seal tester TP-701-G, manufactured by Tester Sangyo Co., Ltd.), heat sealing was performed under the conditions of upper temperature 180°C, lower temperature 70°C, seal width 5 mm, seal pressure 0.2 MPa, and seal time 1 second, with the upper part of the heat seal tester (180°C setting point) set so as to contact with layer A of the multilayer biaxially stretched film. At this time, the direction of the seal bar of the heat sealer was parallel to the width direction of the test piece, and heating by the seal bar was performed over the entire width of the test piece.
The shrinkage rate (%) was calculated by the following formula, where the width of the test piece before heat sealing is L0 and the width of the test piece after heat sealing is L1.
Shrinkage rate = (L0 - L1) / L0 x 100 (%)

[Examples 2 to 7, 10 to 12, Reference Examples 8, 9, 13, Comparative Examples 1 to 8]
A multilayer biaxially stretched film was obtained in the same manner as in Example 1, except that the types and blending ratios of the polymers constituting the resin composition forming layer A were changed to those shown in Tables 2-1 to 2-7 below, and the thickness of each layer was changed to those shown in Tables 2-1 to 2-7 below. The evaluation results of the obtained multilayer biaxially stretched film are shown in Tables 2-1 to 2-7 below.
In Tables 2-1 to 2-7, the values shown in the column "Comonomer content (A1)+(A2)" represent the converted comonomer content Y (mol%) calculated according to the following formula B1:
Y=(X _Q1 ×C ₁ +X _Q2 ×C ₂ )/100...Formula B1
In the formula B1,
_C1 is the total content (mass%) of polymer A1-1 and polymer A1-2 in the resin composition constituting layer A,
_C2 is the content (mass%) of copolymer A2-1,
X _Q1 is the sum of the content (mol %) of the structural unit (Q1-1) derived from a comonomer in the polymer A1-1 and the content (mol %) of the structural unit (Q1-2) derived from a comonomer in the polymer A1-2,
X _Q2 is the content (mol %) of the structural unit (Q2-1) derived from the comonomer in the copolymer A2-1.

Claims (8)

A multilayer biaxially stretched film comprising an A layer and a B layer laminated together,
Layer A is composed of a resin composition containing a 4-methyl-1-pentene polymer (A1) and a 4-methyl-1-pentene copolymer (A2),
the content of the 4-methyl-1-pentene polymer (A1) in the layer A is 60% by mass or more and 85% by mass or less, based on the total mass of the layer A, and the content of the 4-methyl-1-pentene copolymer (A2) in the layer A is 15% by mass or more and 40% by mass or less, based on the total mass of the layer A;
The 4-methyl-1-pentene polymer (A1) satisfies the following requirements (A1-I) to (A1-III), and the 4-methyl-1-pentene copolymer (A2) satisfies the following requirements (A2-I) to (A2-III), and
A multilayer biaxially stretched film having a converted content Y value calculated by the following formula A of 3.0 mol % to 10.0 mol % :
(A1-I) The content of the structural unit (P1) derived from 4-methyl-1-pentene is 90 to 100 mol %, and the content of the structural unit (Q1) derived from an α-olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene) is 0 mol % to 10 mol %.
(A1-II) The melting point (Tm) measured by DSC is in the range of 200°C to 250°C.
(A1-III) The intrinsic viscosity [η] measured in decalin at 135° C. is 0.5 to 5.0 dl/g.
(A2-I) The content of the structural unit (P2) derived from 4-methyl-1-pentene is equal to or greater than 65 mol% and less than 96 mol%, and the content of the structural unit (Q2) derived from an α-olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene) is greater than 4 mol% and equal to or less than 35 mol%.
(A2-II) The melting point (Tm) measured by DSC is not observed or is in the range of 100°C to 199°C.
(A2-III) The intrinsic viscosity [η] measured in decalin at 135° C. is 0.5 to 5.0 dl/g.
Y=(X _Q1 ×W ₁ +X _Q2 ×W ₂ )/(W ₁ +W ₂ +W _O )...Formula A
In the formula A,
W1 is the mass of the 4-methyl-1-pentene polymer (A1) in the resin composition constituting the A layer _;
W2 is the mass of the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer _;
W _O is the total mass content of resins not corresponding to the 4-methyl-1-pentene polymer (A1) or the 4-methyl-1-pentene copolymer (A2) in the resin composition constituting the A layer;
X _Q1 represents the content (mol %) of the structural unit (Q1) in the 4-methyl-1-pentene polymer (A1); and
X _Q2 is the content (mol %) of the structural unit (Q2) in the 4-methyl-1-pentene copolymer (A2). The multilayer biaxially stretched film according to claim 1, wherein the structural unit (Q2) is a structural unit derived from an α-olefin having 2 to 4 carbon atoms. The multilayer biaxially stretched film according to claim 1 or 2, wherein the layer B contains polypropylene (B). The multilayer biaxially stretched film according to claim 3, wherein the layer B is composed of two or more layers. The multilayer biaxially stretched film according to claim 4, wherein the two or more layers have the same structure. The multilayer biaxially stretched film according to claim 4, wherein the two or more layers include a first layer and a second layer located on the opposite side of the first layer from the A layer, and the melting point of the polypropylene (B) constituting the first layer is equal to or higher than the melting point of the polypropylene (B) constituting the second layer. The multilayer biaxially stretched film according to any one of claims 1 to 6, which has a layer structure consisting of layer A/layer B. The multilayer biaxially stretched film according to any one of claims 1 to 7, which is a packaging film.