JP5621326B2 - Polypropylene stretched multilayer film - Google Patents

Description

  The present invention relates to a polypropylene stretched multilayer film having an excellent balance between rigidity and heat seal strength.

Polypropylene stretched films are widely used as various packaging materials because they are excellent in transparency and rigidity. As such a polypropylene stretched film, for example, a film obtained by laminating a low melting point resin on a high melting point polypropylene base layer by a co-extrusion method and then stretching, a polyethylene-based resin film or polypropylene on a stretched polypropylene film It is known that a film or the like obtained by laminating a resin-based resin film is a film imparted with heat sealability.
In the film obtained by the method of laminating and stretching by coextrusion, since the heat seal strength is generally weak, there is a problem that it is not suitable for the packaging of heavy objects, and in the film obtained by the method of laminating by lamination In addition, since a laminating process using an organic solvent or the like is necessary, the load on the global environment is large, which is not economically preferable.
In view of this, a method for improving the heat seal strength in a polypropylene-based film obtained by laminating and stretching a heat seal layer by coextrusion has been studied. For example, Patent Document 1 discloses at least a base material layer made of crystalline polypropylene. A laminated film in which a resin layer of 150 ° C. or lower is laminated on one surface by 4 μm or more is described. Patent Document 2 discloses a multilayer using a blend of a propylene homopolymer and a propylene / ethylene copolymer as a base material layer. A film is described.

JP-A-7-329260 JP 2003-170555 A

However, the above-mentioned film does not always have sufficient rigidity and heat seal strength, and further improvement in rigidity and heat seal strength has been demanded.
An object of the present invention is to obtain a polypropylene stretched multilayer film having an excellent balance between rigidity and heat seal strength.

In order to solve the above-mentioned problems, the present inventors have intensively studied and found that the present invention can solve the above-mentioned problems, and have completed the present invention.
That is, the present invention comprises 10 to 90% by weight of a propylene polymer (component (A)) having a melting point of 164 ° C. or higher and a propylene / 1-butene copolymer (component (component (A)) having a melting point of 150 ° C. or higher and 163 ° C. or lower. B)) a base material containing a resin composition (component (C)) comprising 90 to 10% by weight (provided that the total weight of component (A) and component (B) is 100% by weight). A polypropylene stretched multilayer film obtained by stretching a sheet in which a layer containing a propylene / 1-butene copolymer (component (D)) having a melting point of 140 ° C. or lower is laminated on at least one side of the layer, The ratio of the thickness of the layer containing the component (D) to the thickness of the base material layer containing the component (C) (the thickness of the layer containing the component (D) / the thickness of the layer containing the component (C)) is It is characterized by being 0.15 to 0.45 Those according to propylene oriented multilayer film.

  According to the present invention, a polypropylene stretched multilayer film having an excellent balance between rigidity and heat seal strength can be obtained.

Hereinafter, embodiments of the present invention will be described in detail.
The polypropylene stretched multilayer film of the present invention has a propylene polymer having a melting point of 164 ° C. or higher (hereinafter sometimes referred to as “component (A)”) of 10 to 90% by weight, and a melting point of 150 ° C. or higher and 163 ° C. A resin composition (hereinafter referred to as “component (C)”) comprising 90 to 10% by weight of the following propylene / 1-butene copolymer (hereinafter sometimes referred to as “component (B)”). (However, the total weight of the component (A) and the component (B) is 100% by weight.) Propylene having a melting point of 140 ° C. or lower on at least one side of the base material layer. A sheet on which a layer (hereinafter sometimes referred to as “surface layer”) containing a / 1-butene copolymer (hereinafter sometimes referred to as “component (D)”) is stretched is stretched. The thickness of the base material layer containing the component (C) The ratio of the thickness of the layer containing the component (D) to the thickness (the thickness of the layer containing the component (D) / the thickness of the layer containing the component (C)) is 0.15 to 0.45. It is a multilayer film.

The propylene polymer (component (A)) used for the substrate layer has a melting point of 164 ° C. or higher, and if the melting point of the propylene polymer is lower than 164 ° C., the rigidity of the product may be impaired.
Examples of the propylene polymer include a propylene homopolymer, a copolymer of propylene and ethylene and / or an α-olefin having 4 to 12 carbon atoms. Examples of the α-olefin having 4 to 12 carbon atoms include 1-butene, 4-methylpentene-1, 1-octene, 1-hexene and the like, and preferably 1-butene. The α-olefin having 4 to 12 carbon atoms may be used alone or in combination of two or more.
When the propylene polymer is a copolymer of propylene and ethylene and / or an α-olefin having 4 to 12 carbon atoms, the content of structural units derived from propylene contained in the copolymer is usually 90% by weight or more, preferably 95% by weight, more preferably 97% by weight (provided that the total weight of the copolymer is 100% by weight).
The propylene polymer is preferably a propylene homopolymer.

  The MFR of the component (A) is preferably 0.1 to 100 g / 10 minutes, more preferably 1 to 20 g / 10 minutes, and still more preferably from the viewpoint of excellent extrusion characteristics and stretchability of the resin. 1 to 10 g / 10 min. MFR is a value measured at a temperature of 230 ° C. and a load of 2.16 kgf in accordance with JIS K7210.

  The 20 ° C. xylene soluble part amount (CXS, unit: wt%) of the component (A) is preferably 3 wt% or less, more preferably 2 wt% or less, from the viewpoint of excellent rigidity and blocking resistance. More preferably, it is 1% by weight or less.

  The melting point of the propylene / 1-butene polymer (component (B)) used for the base material layer is 150 ° C. or higher and 163 ° C. or lower, preferably 155 ° C. or higher and 162 ° C. or lower, more preferably 156 ° C. The temperature is 162 ° C. or lower. When the melting point is less than 150 ° C., rigidity may be impaired, and when it exceeds 163 ° C., sufficient heat seal strength may not be obtained.

  The content of the structural unit derived from 1-butene contained in the component (B) is usually from 0.1% by weight to 10% by weight, preferably from 1% by weight to 7% by weight, More preferably, they are 1 weight% or more and 4 weight% or less. (However, the total weight of the copolymer is 100% by weight.)

  The MFR of the component (B) is preferably 0.1 to 100 g / 10 minutes, more preferably 1 to 20 g / 10 minutes, and still more preferably from the viewpoint of excellent extrusion characteristics and stretchability of the resin. 1 to 10 g / 10 min. MFR is a value measured at a temperature of 230 ° C. and a load of 2.16 kgf in accordance with JIS K7210.

  The 20 ° C. xylene soluble part amount (CXS, unit: wt%) of the component (B) is preferably 3% by weight or less, more preferably 2% by weight or less from the viewpoint of rigidity and blocking resistance. More preferably 1% by weight or less.

  The melting point difference between the component (A) and the component (B) is preferably 3 ° C. or higher, more preferably 4 ° C. or higher, from the viewpoint of obtaining sufficient rigidity and sufficient heat seal strength.

  The resin composition (component (C)) used for the base material layer is composed of 10 to 90% by weight of component (A) and 90 to 10% by weight of component (B) (however, component (A) and component (B) )) And the total weight is 100% by weight.) The content of component (A) and component (B) contained in component (C) is preferably 10 to 70% by weight of component (A) and 30 to 90% by weight of component (B). More preferably, the component (A) is 10 to 50% by weight and the component (B) is 50 to 90% by weight.

  The MFR of the component (A) is preferably higher than the MFR of the component (B) from the viewpoint of excellent rigidity of the obtained film.

The propylene / 1-butene copolymer (component (D)) used for the surface layer may be used alone, or may be used by blending other copolymers. When blending a copolymer other than component (D), a propylene / ethylene copolymer is preferred.
When a blend of component (D) and propylene / ethylene copolymer is used for the surface layer, the content of component (D) and propylene / ethylene copolymer is the seal strength and low-temperature heat sealability. From the viewpoint, the component (D) is preferably 40% by weight or more and less than 100% by weight, and the propylene / ethylene copolymer is more than 0% by weight and 60% by weight or less, and more preferably, the component (D) is 60 wt% or more and less than 100 wt%, and propylene / ethylene copolymer is more than 0 wt% and 40 wt% or less (however, the total weight of component (D) and propylene / ethylene copolymer is 100 %).

  The content of the structural unit derived from 1-butene contained in the component (D) is preferably 5% by weight or more and 40% by weight from the viewpoint of obtaining sufficient seal strength and low-temperature heat sealability and excellent blocking resistance. It is less than 10% by weight, more preferably 10% by weight or more and less than 35% by weight, and further preferably 15% by weight or more and less than 30% by weight (provided that the weight of component (D) is 100% by weight). ). The ethylene content of the propylene / ethylene copolymer is preferably 1% by weight or more and less than 10% by weight, more preferably 2% by weight or more and less than 7% by weight (provided that the propylene / ethylene copolymer is used). Of 100% by weight).

  The melting point of the component (D) is 140 ° C. or lower, preferably 80 ° C. or higher and 140 ° C. or lower, more preferably 100 ° C. or higher and 135 ° C. or lower. If the melting point exceeds 140 ° C, the heat seal strength and the low temperature heat sealability may be impaired. Moreover, when blending a propylene / ethylene copolymer, the melting point of the propylene / ethylene copolymer is preferably 150 ° C. or lower, more preferably 120 ° C. or higher and 145 ° C. or lower.

  The MFR of the component (D) is preferably 0.1 to 200 g / 10 minutes, more preferably 1 to 150 g / 10 minutes, and still more preferably 1 from the viewpoint of excellent resin extrusion characteristics and the like. ~ 20 g / 10 min. MFR is a value measured at a temperature of 230 ° C. and a load of 2.16 kgf in accordance with JIS K7210.

  The 20 ° C. xylene-soluble component amount (CXS, unit: wt%) of the component (D) is preferably 25 wt% or less, more preferably 20 wt% or less, and even more preferably, from the viewpoint of blocking resistance of the film. Is 15% by weight or less.

  In the present invention, the base material layer and / or the surface layer may contain additives as necessary. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Add an appropriate amount within the range that does not impair the rigidity and heat sealability of the product.

As a manufacturing method of component (A), component (B), and component (D) used by this invention, the method of manufacturing with a well-known polymerization method using a well-known polymerization catalyst is mentioned.
Known polymerization catalysts include, for example, a catalyst system comprising a solid catalyst component essentially containing magnesium, titanium and halogen, an organoaluminum compound, and a third component such as an electron-donating compound used as necessary. A catalyst system comprising a transition metal compound of group IV of the periodic table having a pentadienyl ring and an alkylaluminoxane, or an ionic complex by reacting with a transition metal compound of group IV of the periodic table having a cyclopentadienyl ring. Examples thereof include a catalyst system composed of a compound to be formed and an organoaluminum compound. Preferred is a catalyst system comprising a solid catalyst component essentially containing magnesium, titanium and halogen, an organoaluminum compound, and an electron donating compound. For example, JP-A-61-218606, JP-A-61-287904. No. 1, JP-A-1-319508, JP-A-7-216017, and the like.

  Known polymerization methods include, for example, a slurry polymerization method using an inert hydrocarbon solvent, a solvent polymerization method, a liquid phase polymerization method without a solvent, a gas phase polymerization method, and the like, preferably a gas phase polymerization method, or A method of combining the above polymerization methods and performing them continuously, for example, a liquid phase-gas phase polymerization method and the like can be mentioned.

  Ratio of the thickness of the layer containing the component (D) to the thickness of the base material layer containing the component (C) in the polypropylene stretched multilayer film of the present invention (thickness of the layer containing the component (D) / component (C ) Is 0.15 to 0.45, and preferably 0.20 to 0.40 from the viewpoint of excellent heat seal strength and rigidity.

  The thickness of the base material layer containing the component (C) is preferably 5 μm or more and less than 100 μm, more preferably 10 μm or more and less than 70 μm, and even more preferably 15 μm or more, from the viewpoint of excellent rigidity and stretchability. It is less than 30 μm.

  The thickness of the layer containing the component (D) is preferably 2 μm or more and less than 10 μm, more preferably 3 μm or more and less than 9 μm, and even more preferably 4 μm or more and less than 8 μm from the viewpoint of excellent heat seal strength and rigidity.

  Examples of the method for producing the base material layer and the surface layer include an inflation method, a T-die method, and a calendar method. Examples of the method for producing the multilayer film include an extrusion laminating method, a thermal laminating method, and a dry laminating method.

  The polypropylene stretched multilayer film of the present invention is stretched by a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a sequential biaxial stretching method, a simultaneous biaxial stretching method, or a tubular biaxial stretching method. Among these, the biaxial stretching method is preferable, and the sequential biaxial stretching method is more preferable.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The measuring methods of physical properties used in Examples and Comparative Examples are shown below.

(1) Melt flow rate (MFR, unit: g / 10 minutes)
It measured according to JIS K7210.

(2) Comonomer content (unit:% by weight)
Measurement was carried out by infrared spectroscopy by the method described on page 616 et seq. Of Polymer Analysis Handbook (published by Kinokuniya, 1995).

(3) Melting point (Tm, unit: ° C)
Using a differential scanning calorimeter (Perkin Elmer DSC), about 10 mg of the test piece was held at 220 ° C. for 5 minutes under a nitrogen atmosphere, and then cooled to 150 ° C. at 300 ° C./min. After maintaining at 150 ° C. for 1 minute, the temperature was decreased to 50 ° C. at a temperature decrease rate of 50 ° C./min.
Thereafter, the temperature was held at 50 ° C. for 1 minute, and then the temperature was raised at 5 ° C./min. The fractional peak of the maximum peak of the obtained melting endothermic curve was rounded off to the Tm (melting point). For those with multiple peaks, the peak on the high temperature side was adopted.
In addition, Tm of indium (In) measured at a temperature decrease rate of 5 ° C./min and a temperature increase rate using this measuring instrument was 156.6 ° C.

(4) 20 ° C. xylene soluble component amount (CXS, unit: wt%)
10 g of polypropylene was dissolved in 1000 ml of boiling xylene and then slowly cooled to 50 ° C., then immersed in ice water, cooled to 20 ° C. with stirring, allowed to stand overnight at 20 ° C., and the precipitated polymer was filtered off. Xylene was evaporated from the filtrate, dried under reduced pressure at 60 ° C. to recover a polymer soluble in xylene at 20 ° C., and CXS was calculated from the weight of the recovered polymer.

(5) Heat seal strength (Unit: g / 25mm)
The surfaces of the films were overlapped, and heat sealed by performing pressure bonding for 2 seconds with a load of 2 kg / cm ^{2 using} a heat sealer (manufactured by Tester Sangyo Co., Ltd.) heated to a predetermined temperature. After this sample was conditioned in an atmosphere of 23 ° C. and 50% humidity all day and night, the peel resistance when peeled at a peel rate of 200 mm / min and a peel angle of 90 ° in an atmosphere of 23 ° C. and 50% humidity was heat sealed. Strength.

(6) Rigidity (Young's modulus, unit: MPa)
The test piece having a length of 120 mm and a width of 20 mm was made to coincide with the longitudinal direction (MD) of the film, and the test piece having a length of 120 mm and a width of 20 mm was taken as the transverse direction of the film ( The test specimens were collected in accordance with TD), and an SS curve was obtained for each of the collected specimens under the conditions of a chuck interval of 60 mm and a tensile speed of 5 mm / min. Rate).

[Example 1]
Propylene homopolymer (A1: MFR = 8.0 g / 10 min, melting point = 165 ° C., CXS = 0.3 wt%) 40 wt%, propylene / 1-butene copolymer (B1: MFR) = 2.0 g / 10 min, 1-butene content = 2.0 wt%, melting point = 159 ° C., CXS = 0.4 wt%) 60 wt. Polymers (D1: MFR = 7.1 g / 10 min, 1-butene content = 25 wt%, melting point = 128 ° C., CXS = 9.5 wt%) were used at a resin temperature of 260 ° C. and 230 ° C., respectively. It was melt-extruded with another extruder and fed to a single co-extrusion T-die. The resin extruded from the T-die in a two-kind two-layer configuration (resin for the surface layer on the chill roll side) was cooled with a cooling roll at 30 ° C. to obtain a cast sheet having a thickness of about 1 mm.
The obtained cast sheet was stretched 5 times in the longitudinal direction at 120 ° C. by the difference in peripheral speed between a low speed roll of 2 m / min and a high speed roll of 10 m / min. Subsequently, the film was stretched 8 times in the transverse direction at a preheating temperature of 165 ° C. and a stretching temperature of 157 ° C. in a heating furnace, and the transverse width was relaxed by 13% while performing heat treatment at 165 ° C. The film from the heating furnace is cooled with a 25 ° C. cooling roll, wound up with a winder, and surface layer (layer consisting of D1) / base material layer thickness (layer consisting of a mixture of A1 and B1) = 5 μm / 17. A biaxially stretched multilayer film having a thickness of 5 μm was prepared. Table 1 shows the physical properties of the obtained film. The obtained film was a film having an excellent balance between heat seal strength and rigidity.

[Example 2]
A biaxially stretched multilayer film was prepared in the same manner as in Example 1 except that the surface layer (layer consisting of D1) / base layer thickness (layer consisting of a mixture of A1 and B1) = 4 μm / 18.5 μm. Table 1 shows the physical properties of the obtained film. The obtained film was a film having an excellent balance between heat seal strength and rigidity.

[Example 3]
65% by weight of propylene / 1-butene copolymer (D1) used in Example 1 for the surface layer, propylene / ethylene copolymer (E1: MFR = 7.0 g / 10 min, ethylene content = 4.6) A biaxially stretched multilayer film was prepared in the same manner as in Example 1 except that a 35 wt% blend was used (wt%, melting point = 138 ° C., CXS = 4.0 wt%). Table 1 shows the physical properties of the obtained film. The obtained film was a film having an excellent balance between heat seal strength and rigidity.

[Comparative Example 1]
A biaxially stretched multilayer film was prepared in the same manner as in Example 1 except that the surface layer (layer composed of D1) / base layer thickness (layer composed of a mixture of A1 and B1) = 9.0 μm / 13.5 μm. Table 1 shows the physical properties of the obtained film. The obtained film had insufficient rigidity and was inferior in transparency.
[Comparative Example 2]
A biaxially stretched multilayer film was prepared in the same manner as in Example 1 except that the surface layer (layer consisting of D1) / base layer thickness (layer consisting of a mixture of A1 and B1) = 4.0 μm / 28.0 μm. Table 1 shows the physical properties of the obtained film. The obtained film was a film with insufficient heat seal strength.

[Comparative Example 3]
A biaxially stretched multilayer film was prepared in the same manner as in Example 1 except that the propylene / ethylene copolymer (E1) used in Example 3 was used alone for the surface layer. Table 1 shows the physical properties of the obtained film. The obtained film was a film having insufficient heat seal strength.

[Comparative Example 4]
Propylene homopolymer (A1) 20% by weight for the base material layer, propylene / ethylene copolymer (E2: MFR = 2.2 g / 10 min, ethylene content = 0.7% by weight, melting point = 159 ° C., CXS = (2.7 wt%) A biaxially stretched multilayer film was obtained in the same manner as in Example 1 except that 80 wt% of the blend was used. The obtained film was a film having insufficient rigidity.

[Comparative Example 5]
A biaxially stretched multilayer film was obtained in the same manner as in Example 1 except that the propylene / ethylene copolymer (E2) was used alone for the base material layer. The obtained film was a film having insufficient rigidity.

[Comparative Example 6]
A biaxially stretched multilayer film was obtained in the same manner as in Example 1 except that the propylene / 1-butene copolymer (B1) was used alone for the base material layer. The obtained film was a film having insufficient rigidity.

[Comparative Example 7]
A biaxially stretched multilayer film was obtained in the same manner as in Example 1 except that the propylene homopolymer (A1) was used alone for the base material layer. The obtained film was a film having insufficient rigidity and heat seal strength.

  The polypropylene stretched multilayer film of the present invention has an excellent balance between rigidity and heat seal strength, and can be used for food packaging films and the like.

Claims (2)

Melting point is not less 164 ° C. or higher, MFR is from 1 to 20 g / 10 min, propylene homopolymer polymer 20 ° C. xylene solubles content is 3 wt% or less (component (A)) and 10 to 90 wt%, A propylene / 1-butene copolymer having a melting point of 150 ° C. or more and 163 ° C. or less , an MFR of 1 to 20 g / 10 minutes, and a 20 ° C. xylene soluble part content of 3% by weight or less (component (B)) Only a resin composition (component (C)) consisting of 90 to 10% by weight (however, the total weight of component (A) and component (B) is 100% by weight) is contained as a resin component . On at least one side of the substrate layer,
Only a propylene / 1-butene copolymer (component (D)) having a melting point of 140 ° C. or lower , an MFR of 1 to 20 g / 10 min, and a 20 ° C. xylene soluble component amount of 25 wt% or less , Surface layer contained as a resin component, or component (D) 40 to 100% by weight and a propylene / ethylene copolymer having a melting point of 150 ° C. or less exceeding 0% by weight and less than 60% by weight (provided that component (D) and propylene / the total weight of ethylene copolymer being 100% by weight.) alone, a polypropylene stretched multi-layer film obtained by stretching a sheet table layer laminated containing as a resin component,
Only components (C) to the thickness of the base material layer containing as a resin component, Tables layer containing only the ratio of the thickness of the table layer containing only the component (D) as a resin component ([component (D) as a resin component The thickness of the base material layer containing only the component (C) as a resin component ]) or the thickness of the base material layer containing only the component (C) as a resin component. Ratio of thickness of surface layer containing only ethylene copolymer as resin component ([thickness of surface layer containing only component (D) and propylene / ethylene copolymer as resin component] / [only component (C) as resin component] The thickness of the base material layer contained as)]) is 0.15 to 0.45.   The polypropylene stretched multilayer film according to claim 1, wherein a difference in melting point between the component (A) and the component (B) is 3 ° C or more.