JP2006248148A - Polyolefin multilayer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin multilayer film for food packaging having excellent transparency and shrinkage characteristics. <P>SOLUTION: The multilayer film comprises at least one surface layer (X) and a core layer (Y). The surface layer (X) is composed of a resin composition comprising 50-99 wt% of a polypropylene resin (A) having a melting point of 120-170°C, and 1-50 wt% of propylene α-olefin copolymer (B) having a melting point lower than 120°C and containing 5-50 mol% of α-olefin. The core layer (Y) is composed of an ethylene (co)polymer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyolefin-based multilayer film. In particular, the present invention relates to a polyolefin-based multilayer film having high heat resistance, high transparency, good flexibility and stretchability, and particularly high shrinkage when used as a shrink film, and excellent transparency and gloss after shrinkage. The polyolefin-based multilayer film of the present invention can be suitably used as a food packaging film or a shrink label.

 Polyvinyl chloride and polyvinylidene chloride are used as wrapping films used for household or business use when storing foods. However, since these films contain a large amount of chlorine atoms in the raw material resin, they may cause dioxins depending on the disposal and incineration methods. Development is underway.

 As a polyolefin-based wrap film containing no chlorine atom, a conventional single-layer or multi-layer film comprising at least one film made of a composition comprising low density polyethylene and various resins, a composition comprising polypropylene and various resins, etc. Single-layer or multi-layer films having at least one layer of the above film are known. Moreover, the film obtained by extending | stretching such a film has favorable heat-shrinkability, and is used as a film for stretch shrink packaging.

 These packaging films are required to have transparency and gloss after shrinkage in order to protect the contents and improve the appearance.

JP-A-9-254338 discloses a packaging film having improved low-temperature shrinkage, tear resistance, and puncture resistance by using a resin composition comprising polypropylene and polybutene as a core layer of a multilayer film. Is disclosed. However, the film according to the publication has problems such as inferior heat resistance such as blocking resistance at high temperature and inferior transparency after shrinkage, and the contents to be packaged are limited. (Patent Document 1)
JP-A-9-254338

 An object of the present invention is to provide a polyolefin-based multilayer film excellent in heat resistance, transparency, flexibility, heat sealability, shrinkage characteristics, and transparency after shrinkage.

  The present inventors have found that the above problem can be solved by a multilayer film using a composition comprising a polypropylene resin and a specific propylene / α-olefin copolymer as a surface layer, and have completed the present invention. .

 That is, the present invention relates to a multilayer film comprising at least one surface layer (X) and a core layer (Y), and the surface layer (X) is a polypropylene resin (A) having a melting point of 120 ° C. to 170 ° C., 50 to 99% by weight, And a resin composition comprising 1 to 50% by weight of a propylene / α-olefin copolymer (B) having a melting point of less than 120 ° C. and an α-olefin content of 5 to 50 mol%, and the core layer (Y) is ethylene-based (copolymer). ) A polyolefin-based multilayer film formed from a polymer.

  Furthermore, this invention is a stretched film obtained by extending | stretching the said polyolefin-type multilayer film at least 1.5 times or more in one direction.

The multilayer film of the present invention is formed from at least one surface layer (X) and a core layer (Y).
In the film of the present invention, the surface layer (X) is a polypropylene resin (A) having a melting point of 120 ° C. to 170 ° C., 50 to 99% by weight, and a melting point of less than 120 ° C., and an α-olefin content of 5 to 50 mol%. It is formed from a resin composition comprising 1 to 50% by weight of the olefin copolymer (B).

  The multilayer film of the present invention is excellent in heat resistance, transparency, flexibility, stretchability, heat sealability, shrinkage properties and transparency after shrinkage, and particularly when used as a shrink film, the shrinkage rate is high, after shrinkage. A film having excellent transparency and gloss can be obtained.

Polypropylene resin (A)
Examples of the polypropylene resin (A) of the present invention include a known propylene homopolymer, or a random or block copolymer with ethylene or an α-olefin having 4 to 20 carbon atoms. From the viewpoint of transparency and flexibility, a random copolymer is preferably used. More preferably, the random coordinator having an MFR measured at 230 ° C. (hereinafter abbreviated as MFR ₂₃₀ ) in the range of 0.5 to 100 g / 10 min and a melting point measured by a differential scanning calorimeter (DSC) in the range of 120 to 155 ° C. A polymer, more preferably a random copolymer having an MFR _{230 in} the range of 1 to 20 g / 10 min and a melting point of 125 to 150 ° C. is used. The propylene content of the propylene polymer (A) is 80 to 100 mol%, preferably 85 to 100 mol%, more preferably 90 to 99 mol%.

 Such polypropylene resin (A) typically polymerizes propylene in the presence of a solid titanium catalyst and a catalyst mainly composed of an organometallic compound, or a metallocene catalyst using a metallocene compound as one component of the catalyst. It can be produced by copolymerizing propylene and other α-olefins.

Propylene / α-olefin copolymer (B)
The propylene / α-olefin copolymer (B) used in the film of the present invention is a random copolymer of propylene and ethylene or an α-olefin having 4 to 20 carbon atoms, and is measured by a DSC method. Melting point (endothermic peak when observed when holding at 200 ° C. for 5 minutes, then decreasing to −20 ° C. at a temperature decrease rate of −20 ° C./min and then increasing again to 180 ° C. at 20 ° C./min) It is less than 120 ° C, preferably 30 ° C to 110 ° C, more preferably 35 to 100 ° C, and further preferably 40 to 90 ° C. The MFR ₂₃₀ of the propylene / α-olefin copolymer (B) is in the range of 0.1 to 70 g / 10 min, preferably 0.3 to 50 g / 10 min, more preferably 1.0 to 20 g / 10 min. The α-olefin content is 5 to 50 mol%, preferably 10 to 35 mol%. Examples of the α-olefin component include α-olefins having 4 to 10 carbon atoms, preferably 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, and more preferably 1-butene. Can do.

  Such a propylene / α-olefin copolymer (B) is typically a catalyst mainly composed of a solid titanium catalyst and an organometallic compound, or a metallocene catalyst using a metallocene compound as one component of the catalyst. It can be produced by copolymerizing propylene and α-olefin under pressure.

A preferred specific example of the propylene / α-olefin copolymer (B) is a propylene / α-olefin copolymer obtained using a metallocene catalyst, having a melting point in the range of 40 to 90 ° C., and the melting point Tm ( C) and comonomer constituent unit content M (mol%) determined by 13C-NMR spectrum measurement is 146 exp (-0.022 M) ≧ Tm ≧ 125 exp (−0.032 M).
It is in the range. Such a propylene α-olefin copolymer can be obtained using, for example, a metallocene catalyst as described in International Publication No. WO95 / 14717, but is not limited thereto. In particular, a copolymer obtained by using a metallocene catalyst is desirable since the film has less stickiness. In this case, the molecular weight distribution obtained from gel permeation chromatography (GPC) of the propylene / α-olefin copolymer (B) is in the range of 1 to 3.

 When the physical properties of these propylene / α-olefin copolymers (B) are in the above ranges, films having good transparency and shrinkage characteristics, which are the characteristics of the film of the present invention, can be obtained. When it is out of the above range, the deterioration of transparency and the heat shrinkability of the stretched film are inferior.

Resin Composition The surface layer (X) of the multilayer film of the present invention comprises 50 to 99% by weight of the polypropylene resin (A) and 1 to 50% by weight of the propylene / α-olefin copolymer (B). Preferably, it comprises 55 to 95% by weight of polypropylene resin (A) and 5 to 45% by weight of prolene / α-olefin copolymer (B). In addition, as long as the effect of this invention is not impaired in this resin composition, you may contain other polyolefin resin, such as a polyethylene resin.

An ethylene (co) polymer is used for the ethylene (co) polymer core layer (Y). Specifically, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, other ethylene / α-olefin copolymers, ethylene / vinyl acetate copolymers, ethylene / methacrylic acid copolymers, ethylene / methacrylic copolymers. Examples thereof include ethylene / unsaturated carboxylic acid copolymers such as acid methyl copolymers, ethylene / unsaturated carboxylic acid ester copolymers, and ionomer resins. Among these, since it is excellent in flexibility, transparency, and heat sealability, the density is 0.910 to 0.930 g / cm ³ , low density polyethylene, and the density is 0.910 to 0.930 g / cm ³ . linear low density polyethylene, ethylene-alpha-olefin copolymer having a density of 0.860~0.910g / cm ^3, density of 0.910~0.970g / cm ³ of ethylene-vinyl acetate copolymer, and their These mixtures can be preferably used. Examples of the α-olefin in the ethylene / α-olefin copolymer include α-olefins having 3 to 20 carbon atoms, preferably 3 to 10 carbon atoms.

The MFR (hereinafter abbreviated as MFR ₁₉₀ ) measured at 190 ° C. of the ethylene-based (co) polymer of the present invention is 0.1 to 50 g / 10 min, preferably 0.5 to 30 g / 10 min. The ethylene content of the ethylene-based (co) polymer is 70 to 100 mol%, preferably 75 to 100 mol%.

Multilayer film In the multilayer film of the present invention, the core layer (Y) may form at least one layer. The ethylene (co) polymer used when two or more layers are formed may be the same or different in each layer. For example, two core layers (Y) may be formed with the same resin composition, such as surface layer (X) / linear low density polyethylene / linear low density polyethylene / surface layer (X), or surface layer (X ) / Ethylene / vinyl acetate copolymer / Linear low density polyethylene / Ethylene / vinyl acetate copolymer / Surface layer (X) May be.

  The total thickness of the multilayer film of the present invention is 3 to 500 μm, preferably 5 to 400 μm, from the viewpoints of film strength, flexibility, and transparency. The thickness of the surface layer (X) of the multilayer film of the present invention is 0.5 to 200 μm, preferably 1 to 150 μm, and the thickness of the core layer (Y) is 1 to 300 μm, preferably 2 to 200 μm.

  The film production method of the present invention can be produced using a multilayer T-die molding machine or an inflation molding machine used for ordinary polyolefin film molding.

 A tackifier and a surfactant may be added to the film of the present invention in order to adjust the tackiness and antifogging property. Examples of the tackifier include liquid hydrocarbons such as polybutene and olefin oligomers, liquid paraffin, fatty petroleum resins, alicyclic petroleum resins, and the like. Examples of the surfactant include monoglycerin fatty acid ester, glycerin fatty acid ester, and sorbitan fatty acid ester. These may be used alone or as a mixture of two or more.

The multilayer film of the present invention can be stretched 1.5 times or more in at least one direction to form the stretched film of the present invention.
The stretched film is excellent in heat shrinkability and can be suitably used as a shrink wrapping film or a shrink label. As the stretching method, a known method for producing a polyolefin stretched film can be used. Specific examples include roll stretching, tenter stretching, and tubular stretching. As a draw ratio, it is 1.5-20 times normally, Preferably it is 2-15 times.

EXAMPLES Next, although an Example demonstrates this invention, this invention is not limited to this.
[Evaluation method]
MFR ₂₃₀ : Measured at 230 ° C. under a load of 2.16 kg in accordance with ASTM D1238.
MFR ₁₉₀ : Measured at 190 ° C. under a load of 2.16 kg in accordance with ASTM D1238.
Density: Measured according to ASTM D1505.
Haze: Measured according to ASTM D1003.
Melting point: Measured using a differential scanning calorimeter (DSC) at a temperature elevation rate of 20 ° C./min.

 Thermal shrinkage: The sample film cut to 10 cm square was left in an oven at 120 ° C. for 30 minutes, and the shrinkage was determined by measuring the dimensions after shrinkage.

[Example 1]
The following resin is used as the core layer and the surface layer, and the layer structure (surface layer 60 μm) / (core layer 60 μm) using a 300 mm wide three-layer T-die molding machine equipped with a 50 mmφ extruder. / (Three-layer film) (surface layer 60 μm) was obtained. This film was further biaxially stretched at 105 ° C. at a length of 4.0 times and a width of 4.0 times using a batch type biaxial stretching machine to obtain a stretched film. Table 1 shows the physical properties of the obtained stretched film.
Surface layer resin: MFR ₂₃₀ 3.0 g / 10 min, melting point 140 ° C. random polypropylene 70% by weight, MFR ₂₃₀ 6.5 g / 10 min, melting point 110 ° C., 1-butene content 28 mol% propylene / 1-butene random copolymer A composition comprising 30% by weight of a coalescence (produced with a titanium-based catalyst).
Core layer resin: linear low density polyethylene (manufactured with a metallocene catalyst) with MFR ₁₉₀ 1.0 g / 10 min and density 0.905 g / cm ³ .

[Comparative Example 1]
A stretched film was obtained in the same manner as in Example 1 except that the resin composition described in Table 1 was used as the surface layer resin. Table 1 shows the physical properties of the obtained stretched film.

[Example 2]
A stretched film was obtained in the same manner as in Example 1 except that the surface layer resin composition was changed to the composition shown in Table-1. Table 1 shows the physical properties of the obtained stretched film.

The stretched film obtained by stretching the multilayer film of the present invention is excellent in transparency and heat shrinkability, is suitable as a film for food packaging, and its industrial utility value is extremely high.

Claims (3)

 In the multilayer film composed of at least one surface layer (X) and the core layer (Y), the surface layer (X) is 50 to 99% by weight of the polypropylene resin (A) having a melting point of 120 ° C. to 170 ° C., and the melting point is less than 120 ° C. And a resin composition comprising 1 to 50% by weight of a propylene / α-olefin copolymer (B) having an α-olefin content of 5 to 50 mol%, and the core layer (Y) is formed of an ethylene-based (co) polymer. A polyolefin-based multilayer film characterized by being made. The polyolefin-based multilayer film according to claim 1, wherein the α-olefin in the propylene / α-olefin copolymer (B) is an α-olefin having 4 to 10 carbon atoms. A stretched film obtained by stretching the polyolefin-based multilayer film according to claim 1 or 2 at least 1.5 times in at least one direction.