JP2023001143A - Polypropylene-based laminate film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sealable stretched polypropylene laminate film which has a low shrinkage rate at 150°C comparable to the shrinkage rate of PET and also has high rigidity.

SOLUTION: A polypropylene-based laminate film comprises a substrate layer (A) composed of a polypropylene resin satisfying requirements 1) to 4), and a heat seal layer (B) composed of a polyolefin-based resin, the heat seal layer laminated on one or both faces of the substrate layer, where a lower limit of a plane orientation coefficient of the film is 0.0125. 1) A lower limit of a mesopentad fraction is 96%. 2) An upper limit of a content of comonomer(s) other than propylene is 0.1 mol%. 3) A ratio [mass-average molecular weight (Mw)/number-average molecular ratio (Mn)] is 3.0-5.4 inclusive. 4) A melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.2-9.0 g/10 min inclusive.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a polypropylene-based laminated film having heat sealability. More particularly, it relates to a polypropylene-based laminated film having excellent heat seal strength for use as packaging. More particularly, it relates to a polypropylene-based laminated film that can be suitably used in various fields where dimensional stability and high rigidity at high temperatures are required, and that is excellent in heat resistance, mechanical properties, and heat sealability.

Stretched films made from polypropylene have been used for a wide range of purposes, such as food and various product packaging, electrical insulation, and surface protection films. There is BACKGROUND ART Conventionally, as a heat-sealable polypropylene-based laminated film, a co-extruded laminated polypropylene-based resin film obtained by laminating a low-melting-point polyolefin-based resin on a polypropylene-based resin has often been used.
As one of such heat-sealable films, an oriented polypropylene laminated film has been proposed that has a low shrinkage ratio comparable to that of PET at 150° C. and that can be heat-sealed at high temperatures (see, for example, Patent Document 1). .
However, this film also had room for improvement in mechanical properties.

WO2015/0126165 Pamphlet

The present invention has been made against the background of such problems of the prior art. That is, the object is to provide a polypropylene-based laminated film having excellent heat-sealing strength for use in packaging applications.

The present inventor has completed the present invention as a result of intensive studies to achieve this object. That is, in the present invention, a heat is composed of a base layer (A) in which the polypropylene resin constituting the layer satisfies the following conditions 1) to 4), and a polyolefin resin laminated on one side or both sides of the base layer (A). It is a polypropylene-based laminated film comprising a sealing layer (B) and having a lower limit of the plane orientation coefficient of the film of 0.0125.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.2 g/10 min or more and 9.0 g/10 min or less.

In this case, it is preferable that the film has a thermal shrinkage rate of 8% or less at 150° C. in both the longitudinal and transverse directions.

In this case, it is preferable that the Young's modulus in the MD direction is 2.1 GPa or more and the Young's modulus in the TD direction is 3.7 GPa or more.

Furthermore, the 180 degree peel strength of a 10 mm wide test piece obtained by superimposing the heat seal layer (B) surfaces and performing hot plate sealing at 140 ° C. for 1 second is 8.0 N / 15 mm or more. is preferred.

Furthermore, in this case, the polyolefin resin constituting the heat seal resin (B) is preferably a propylene random copolymer and/or a propylene block copolymer.

According to the present invention, it was excellent for use as packaging and very suitable for heat sealing.
Furthermore, for example, by setting the heat-sealing temperature high, it becomes possible to increase the line speed in the bag-making process, thereby improving the productivity. In addition, the heat seal strength can be improved by increasing the heat seal temperature.
Furthermore, it can be suitably used in various fields where dimensional stability and high rigidity at high temperatures are required. As a result, thinning is possible.

TECHNICAL FIELD The present invention relates to a polypropylene-based laminated film having heat sealability. More particularly, it relates to a polypropylene-based laminated film having sufficient heat-sealing strength for use as packaging.
A feature of the polypropylene-based laminated film of the present invention resides in the state of molecular weight distribution of the polypropylene resin used for the substrate layer (A).

The polypropylene-based laminated film of the present invention comprises a base layer (A) in which the polypropylene resin constituting the layer satisfies the following conditions 1) to 4) and a polyolefin-based resin laminated on one side or both sides of this base layer (A). A polypropylene-based laminated film comprising a heat-seal layer (B) having a lower limit of the plane orientation coefficient of the film of 0.0125.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.2 g/10 min or more and 9.0 g/10 min or less.
Further details are provided below.

(Base layer (A))
A polypropylene resin obtained by copolymerizing 0.5 mol % or less of ethylene and/or an α-olefin having 4 or more carbon atoms can be used as the polypropylene resin used for the substrate layer (A) of the present invention. Such a copolymerized polypropylene resin is also included in the polypropylene resin of the present invention (hereinafter referred to as polypropylene resin). The content of the copolymer component is preferably 0.3 mol % or less, more preferably 0.1 mol % or less, and most preferably a complete homopolypropylene resin containing no copolymer component.
When ethylene and/or α-olefins having 4 or more carbon atoms are copolymerized in excess of 0.5 mol %, the crystallinity and rigidity may be excessively lowered and the thermal shrinkage at high temperatures may increase. A blend of such resins may be used.

The mesopentad fraction ([mmmm]%) measured by ¹³ C-NMR, which is an index of the stereoregularity of the polypropylene resin, is preferably 96 to 99.5%. More preferably, it is 97% or more, and still more preferably 98% or more. When the mesopentad fraction of the polypropylene of the substrate layer (A) is small, the melting point of the crystals becomes low, and the elastic modulus and heat resistance at high temperatures may become insufficient. 99.5% is a realistic upper limit.

Mw/Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 for polypropylene resins. It is more preferably 3.0 to 5.0, still more preferably 3.2 to 4.5, and particularly preferably 3.3 to 4.0.
When the Mw/Mn of the entire polypropylene resin constituting the substrate layer (A) is 5.4 or less, high molecular weight components are present, but their amounts are small, and the thermal shrinkage tends to be small. The presence of high-molecular-weight components promotes crystallization of low-molecular-weight components, but the entanglement between molecules is strengthened, and this is also a factor in increasing the thermal shrinkage even if the crystallinity is high.
Further, when the Mw/Mn of the entire polypropylene resin constituting the base material layer (A) is 5.4 or less, the amount of low-molecular-weight components having a considerably low molecular weight increases, and the elastic modulus tends to decrease. This is because if a low-molecular-weight component having a considerably low molecular weight is present, the entanglement between molecules becomes weak, and the film can be stretched with a low stretching stress.
If the Mw/Mn of the entire polypropylene resin constituting the substrate layer (A) of the present invention is less than 3.0, film formation becomes difficult. Mw means weight average molecular weight and Mn means number average molecular weight.

The weight average molecular weight (Mw) of the polypropylene resin is preferably 180,000 to 500,000. A more preferable lower limit of Mw is 190,000, more preferably 200,000, and a more preferable upper limit of Mw is 320,000, more preferably 300,000, and particularly preferably 250,000.

The number average molecular weight (Mn) of polypropylene resin is preferably 20,000 to 200,000. A more preferable lower limit of Mn is 30,000, more preferably 40,000, particularly preferably 50,000, and a more preferable upper limit of Mn is 80,000, more preferably 70,000, particularly preferably 60,000. be.

When the gel permeation chromatography (GPC) integrated curve of the entire polypropylene resin constituting the base material layer (A) is measured, the lower limit of the amount of the component having a molecular weight of 100,000 or less is preferably 35% by mass, more preferably It is 38% by mass, more preferably 40% by mass, particularly preferably 41% by mass, and most preferably 42% by mass.
On the other hand, the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integration curve is preferably 65% by mass, more preferably 60% by mass, still more preferably 58% by mass, and particularly preferably 56% by mass. and most preferably 55% by mass. Within the above range, stretching is facilitated, thickness unevenness is reduced, stretching temperature and heat setting temperature are easily raised, and heat shrinkage can be suppressed to a lower level.

When the gel permeation chromatography (GPC) integrated curve of the entire polypropylene resin constituting the base material layer (A) is measured, the lower limit of the amount of the component having a molecular weight of 10,000 or less is preferably 1% by mass, more preferably It is 1.5% by mass.
On the other hand, the upper limit of the amount of components having a molecular weight of 10,000 or less in the GPC integration curve is preferably 5% by mass, more preferably 4% by mass, still more preferably 3.5% by mass, and particularly preferably 3% by mass. % by weight.

At this time, the polypropylene resin preferably has a melt flow rate (MFR; 230° C., 2.16 kgf) of 6.2 g/10 minutes to 10.0 g/10 minutes.
The lower limit of the MFR of the polypropylene resin is more preferably 6.5 g/10 minutes, still more preferably 7 g/10 minutes, and particularly preferably 7.5 g/10 minutes. The upper limit of the MFR of the polypropylene resin is more preferably 9 g/10 minutes, still more preferably 8.5 g/10 minutes, and particularly preferably 8.2 g/10 minutes.
When the melt flow rate (MFR; 230° C., 2.16 kgf) is 6.2 g/10 minutes or more, the thermal shrinkage at high temperatures can be further reduced. Furthermore, since the degree of crystallization of the film caused by stretching is increased, the rigidity of the film, particularly the tensile elastic modulus (Young's modulus) in the width (TD) direction is increased. Moreover, when the melt flow rate (MFR; 230° C., 2.16 kgf) is 9.0 g/10 minutes or less, the film can be easily formed without breakage.
The molecular weight distribution of polypropylene resin can be determined by polymerizing components with different molecular weights in multiple stages in a series of plants, by blending components with different molecular weights offline in kneaders, and by blending catalysts with different performance. or by using a catalyst capable of realizing a desired molecular weight distribution.

The polypropylene resin used in the present invention is obtained by polymerizing raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among them, it is preferable to use a Ziegler-Natta catalyst in order to eliminate heterogeneous bonds, and to use a catalyst capable of polymerizing with high stereoregularity.
As a method for polymerizing propylene, known methods may be adopted. For example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of polymerizing a gaseous monomer with a catalyst and polymerizing in a gas phase, or a method of polymerizing by combining these.

The polypropylene resin may contain additives and other resins. Examples of additives include antioxidants, ultraviolet absorbers, nucleating agents, adhesives, antifog agents, flame retardants, inorganic or organic fillers, and the like. Other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers that are copolymers of propylene and ethylene and/or α-olefins having 4 or more carbon atoms, and various elastomers. These are polymerized sequentially using a multi-stage reactor, blended with polypropylene resin in a Henschel mixer, or prepared in advance using a melt kneader and diluted with polypropylene to a predetermined concentration. Alternatively, the entire amount may be previously melted and kneaded before use.

(Heat seal layer (B))
In the present invention, the resin used for the heat seal layer (B) is preferably a propylene random copolymer having a low melting point of 150° C. or lower, or a propylene block copolymer in which an elastomer component containing a comonomer is dispersed. Moreover, these can be used individually or in mixture. As a comonomer, it is preferable to use at least one selected from ethylene or α-olefins having 3 to 10 carbon atoms such as butene, pentene, hexene, octene and decene.

Furthermore, the melting point of the propylene random copolymer forming the heat seal layer (B) is preferably 60 to 150°C. This makes it possible to impart sufficient heat-sealing strength to the oriented polypropylene-based resin laminated film. If the melting point of the propylene random copolymer forming the heat-seal layer (B) is less than 60°C, the heat-sealed portion has poor heat resistance, and if it exceeds 150°C, no improvement in heat-seal strength can be expected. Also, the melting point of the elastomer component contained in the propylene block copolymer is preferably 150° C. or less.
Also, the MFR can be exemplified in the range of 0.1 to 100 g/10 min, preferably 0.5 to 20 g/10 min, more preferably 1.0 to 10 g/10 min.

The polypropylene resin used in the heat seal layer (B) is obtained by polymerizing propylene as a raw material using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among them, it is preferable to use a Ziegler-Natta catalyst in order to eliminate heterogeneous bonds and to use a catalyst capable of highly regular polymerization.
As a method for polymerizing propylene, known methods may be used, including a method of polymerizing in an inert solvent such as hexane, heptane, toluene, and xylene, a method of polymerizing in liquid propylene or ethylene, and a method of polymerizing in gaseous propylene or ethylene. A method of adding a catalyst and polymerizing in a gas phase, or a method of polymerizing by combining these may be mentioned.
The high-molecular-weight components and low-molecular-weight components may be polymerized separately and then mixed, or they may be produced in a series of plants using multi-stage reactors. Particularly preferred is a method in which a plant with multiple reactors is used and the high molecular weight component is first polymerized and then the low molecular weight component is polymerized in its presence.

(Manufacturing method of polypropylene film)
The polypropylene-based laminated film of the present invention may be a uniaxially stretched film in the longitudinal direction (MD direction) or transverse direction (TD direction), but is preferably a biaxially stretched film. Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching.
By using a stretched film, it is possible to obtain a film with a low thermal shrinkage rate even at 150° C., which could not be expected with conventional polypropylene-based laminated films.

A method for producing a film by sequential biaxial stretching of longitudinal stretching and transverse stretching, which is the most preferred example, will be described below.
First, the base layer (A) is melt extruded from one extruder, the heat seal layer (B) is melt extruded by the other extruder, and the polypropylene resin layer (A) and heat are extruded in the T die. The layers are laminated so as to form a sealing layer (B), and are cooled and solidified by cooling rolls to obtain an unstretched sheet. The melt extrusion conditions are such that the resin temperature is set to 200 to 280°C, the resin is extruded into a sheet form from a T-die, and cooled and solidified by a cooling roll having a temperature of 10 to 100°C. Then, the film is stretched 3 to 7 times in the length (MD) direction with stretching rolls at 120 to 165°C, and subsequently in the width (TD) direction at a temperature of 155°C to 175°C, preferably 158°C to 170°C. It is stretched 6 to 12 times.
Furthermore, heat treatment is performed at an ambient temperature of 165 to 175° C., preferably 166 to 173° C., while allowing a relaxation of 1 to 15%.
If necessary, a roll sample can be obtained by applying a corona discharge treatment to at least one side and then winding it with a winder.

The lower limit of the draw ratio in MD is preferably 3 times, more preferably 3.5 times. If it is less than the above, the film thickness may become uneven.
The upper limit of the MD draw ratio is preferably 8 times, more preferably 7 times. If the above is exceeded, it may become difficult to carry out subsequent TD stretching.

The lower limit of the MD stretching temperature is preferably 120°C, more preferably 122°C. If it is less than the above, the mechanical load may increase, the thickness unevenness may increase, and the surface roughness of the film may occur.
The upper limit of the MD stretching temperature is preferably 150°C, more preferably 145°C, still more preferably 135°C, and particularly preferably 130°C. A higher temperature is preferable for lowering the heat shrinkage, but the film may adhere to the rolls and become unable to be stretched.

The lower limit of the TD draw ratio is preferably 4 times, more preferably 5 times, and still more preferably 6 times. If it is less than the above, thickness unevenness may occur.
The upper limit of the TD draw ratio is preferably 20 times, more preferably 17 times, and still more preferably 15 times. If the above is exceeded, the heat shrinkage rate may increase, or breakage may occur during stretching.

The preheating temperature in the TD stretching is preferably set 10 to 15° C. higher than the stretching temperature in order to quickly raise the film temperature to the vicinity of the stretching temperature.

The TD stretching is performed at a temperature higher than that of conventional heat-sealable polypropylene laminated stretched films.
The lower limit of the TD stretching temperature is preferably 157°C, more preferably 158°C. If it is less than the above, it may be broken without being sufficiently softened, or the heat shrinkage rate may increase.
The upper limit of the TD stretching temperature is preferably 170°C, more preferably 168°C. In order to reduce the heat shrinkage, a higher temperature is preferable, but if the temperature exceeds the above range, the low-molecular-weight components may melt and recrystallize, resulting in surface roughness and whitening of the film.

The stretched film is heat set. Heat setting can be performed at a higher temperature than conventional polypropylene films. The lower limit of the heat setting temperature is preferably 165°C, more preferably 166°C. If it is less than the above, the heat shrinkage rate may increase. In addition, a long time is required to reduce the heat shrinkage rate, which may result in poor productivity.
The upper limit of the heat setting temperature is preferably 175°C, more preferably 173°C. If the above is exceeded, the low-molecular-weight components may melt and recrystallize, resulting in surface roughness and whitening of the film.

Relaxation (relaxation) is preferred during heat setting. The lower limit of relaxation is preferably 2%, more preferably 3%. If it is less than the above, the heat shrinkage rate may increase.
The upper limit of relaxation is preferably 10%, more preferably 8%. When the above is exceeded, thickness unevenness may become large.

Furthermore, in order to reduce the heat shrinkage, the film produced by the above steps may be wound into a roll and then annealed off-line.
The lower limit of the offline annealing temperature is preferably 160°C, more preferably 162°C, still more preferably 163°C. If it is less than the above, the effect of annealing may not be obtained.
The upper limit of the offline annealing temperature is preferably 175°C, more preferably 174°C, still more preferably 173°C. When the above is exceeded, the transparency may be lowered and the thickness unevenness may be increased.

The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and still more preferably 1 minute. If it is less than the above, the effect of annealing may not be obtained.
The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, still more preferably 20 minutes. If the above is exceeded, productivity may decrease.

The thickness of the film is set according to each application, but the lower limit of the film thickness is preferably 2 μm, more preferably 3 μm, and still more preferably 4 μm. The upper limit of the film thickness is preferably 300 μm, more preferably 250 μm, still more preferably 200 μm, particularly preferably 100 μm, most preferably 50 μm.

The polypropylene-based laminated film thus obtained is usually formed into a roll having a width of 2,000 to 12,000 mm and a length of 1,000 to 50,000 m, and wound into a roll.
Furthermore, it is slit according to each application and provided as a slit roll having a width of 300 to 2000 mm and a length of about 500 to 5000 m.

The polypropylene-based laminated film of the present invention has the above-mentioned excellent characteristics not found in the prior art.
When it is used as a packaging film, it can be made thin because of its high rigidity, and the cost and weight can be reduced.
In addition, because of its high heat resistance, high-temperature drying is possible when coating or printing, which makes it possible to improve production efficiency and to use coating agents, inks, lamination adhesives, etc., which have been difficult to use in the past. Since there is no need for a lamination step using an organic solvent or the like, it is economical and favorable in terms of impact on the global environment.

(Film properties)
The lower limit of the 150° C. heat shrinkage in the MD direction and the TD direction of the polypropylene-based laminated film of the present invention is preferably 0.5%, more preferably 1%, still more preferably 1.5%, especially Preferably 2%, most preferably 2.5%. If the thickness is within the above range, it may become easier to manufacture realistically from the viewpoint of cost and the thickness unevenness may be reduced.

The upper limit of the 150° C. heat shrinkage in the MD direction is preferably 7%, more preferably 6%, still more preferably 5%. Within the above range, it is easier to use in applications where there is a possibility of being exposed to a high temperature of about 150°C. If the 150° C. heat shrinkage rate is up to about 2.5%, it is possible, for example, by increasing the low molecular weight component and adjusting the stretching conditions and fixing conditions. preferable.
In a conventional oriented polypropylene laminated film, the 150° C. heat shrinkage in the MD direction is 15% or more, and the 120° C. heat shrinkage is about 3%. By setting the heat shrinkage rate within the above range, a polypropylene-based laminated film having excellent heat resistance can be obtained.

The upper limit of the 150° C. heat shrinkage in the TD direction is preferably 8%, more preferably 7%, still more preferably 7%. Within the above range, it is easier to use in applications where there is a possibility of being exposed to a high temperature of about 150°C. If the 150° C. heat shrinkage rate is up to about 2.5%, it is possible, for example, by increasing the low molecular weight component and adjusting the stretching conditions and fixing conditions. preferable.
In a conventional oriented polypropylene laminated film, the 150° C. heat shrinkage in the TD direction is 15% or more, and the 120° C. heat shrinkage is about 3%. By setting the heat shrinkage rate within the above range, a polypropylene-based laminated film having excellent heat resistance can be obtained.

When the polypropylene-based laminated film of the present invention is a biaxially stretched film, the lower limit of Young's modulus (23° C.) in the MD direction is preferably 1.8 GPa, more preferably 1.9 GPa, and still more preferably 2. It is 0 GPa, particularly preferably 2.1 GPa, and most preferably 2.2 GPa.
The upper limit of Young's modulus in the MD direction is preferably 3.7 GPa, more preferably 3.6 GPa, still more preferably 3.5 GPa, particularly preferably 3.4 GPa, and most preferably 3.3 GPa. be. Within the above range, realistic manufacturing may be easy, and the MD-TD balance may be improved.

When the polypropylene-based laminated film of the present invention is a biaxially stretched film, the lower limit of Young's modulus (23° C.) in the TD direction is preferably 4.4 GPa, more preferably 4.5 GPa, still more preferably 4.5 GPa. 6 GPa, particularly preferably 4.7 GPa.
The upper limit of Young's modulus in the TD direction is preferably 8 GPa, more preferably 7.5 GPa, still more preferably 7 GPa, and particularly preferably 6.5 GPa. In the above range, realistic manufacturing may be easy, and the MD-TD balance may be improved.
The Young's modulus can be increased by increasing the draw ratio, and in the case of MD-TD stretching, the MD draw ratio is set lower and the TD draw ratio is increased to increase the Young's modulus in the TD direction. can be done.

The lower limit of the plane orientation coefficient of the polypropylene-based laminated film of the present invention is preferably 0.0125, more preferably 0.0126, even more preferably 0.0127, and particularly preferably 0.0128. As a practical value, the upper limit of the plane orientation coefficient is preferably 0.0155, more preferably 0.0150, still more preferably 0.0148, particularly preferably 0.0145, and more particularly Preferably it is 0.0140. The plane orientation coefficient can be set within a range by adjusting the draw ratio. When the plane orientation coefficient is within this range, the thickness unevenness of the film is also good.

The heat seal strength of the polypropylene-based laminated film of the present invention at 140° C. is preferably 8.0 N/15 mm or more, more preferably 9.0 N/15 mm or more, and further preferably 10 N/15 mm or more. preferable.
Further, the heat seal strength of the polypropylene-based laminated film of the present invention at 110° C. is preferably 1.5 N/15 mm or more, more preferably 2.0 N/15 mm or more, and 2.2 N/15 mm or more. It is even more preferable to have

The lower limit of the impact resistance (23°C) of the stretched polypropylene film of the present invention is preferably 0.6J, more preferably 0.7J. Within the above range, the film has sufficient toughness and is not broken during handling.
The upper limit of the impact resistance is preferably 3J, more preferably 2.5J, still more preferably 2.2J, and particularly preferably 2J from a practical point of view. Impact resistance tends to decrease, for example, when there are many low molecular weight components, when the overall molecular weight is low, when there are few high molecular weight components, or when the molecular weight of the high molecular weight components is low. These components can be adjusted to be within range.

As a practical value, the lower limit of the haze of the polypropylene-based laminated film of the present invention is preferably 0.1%, more preferably 0.2%, still more preferably 0.3%, and particularly preferably 0.3%. 4%, most preferably 0.5%.
The upper limit of haze is preferably 6%, more preferably 5%, still more preferably 4.5%, particularly preferably 4%, most preferably 3.5%. Within the above range, it may be easy to use in applications where transparency is required. For example, haze tends to be worse when the stretching temperature and heat setting temperature are too high, when the cooling roll (CR) temperature is high and the cooling rate is slow, and when the low molecular weight is too large. can do

The lower limit of thickness uniformity of the polypropylene-based laminated film of the present invention is preferably 0%, more preferably 0.1%, still more preferably 0.5%, and particularly preferably 1%.
The upper limit of thickness uniformity is preferably 20%, more preferably 17%, still more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are unlikely to occur during post-processing such as coating and printing, and it is easy to use for applications requiring precision.

EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Methods for measuring physical properties in Examples are as follows.

1) Melt flow rate (MFR, g/10 minutes)
It was measured at a temperature of 230° C. according to JIS K7210.

2) Molecular Weight and Molecular Weight Distribution Molecular weight and molecular weight distribution were determined by monodisperse polystyrene standards using gel permeation chromatography (GPC).
The columns and solvents used in GPC measurements are as follows.
Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMH HR-H (20) HT x 3
Flow rate: 1.0ml/min
Detector: RI
Measurement temperature: 140°C
The number average molecular weight (Mn), mass average molecular weight (Mw), and Z+1 average molecular weight (Mz+1) are each determined by the molecular weight (Mi) at each elution position of the GPC curve obtained through the molecular weight calibration curve (Ni). It is defined by the following formula.
Number average molecular weight: Mn = Σ (Ni · Mi) / ΣNi
Mass average molecular weight: Mw = Σ (Ni · Mi ² ) / Σ (Ni · Mi)
Z+1 average molecular weight: Mz+1=Σ(Ni·Mi ⁴ )/Σ(Ni·Mi ³ )
Molecular weight distribution: Mw/Mn, Mz+1/Mn
Also, the molecular weight at the peak position of the GPC curve was defined as Mp.
If the baseline is not clear, set the baseline in the range up to the lowest point on the high molecular weight side of the elution peak on the high molecular weight side that is closest to the elution peak of the standard substance.
Peak separation was performed on two or more components with different molecular weights from the obtained GPC curve. A Gaussian function was assumed for the molecular weight distribution of each component, and Mw/Mn=4 so as to be similar to the molecular weight distribution of ordinary polypropylene. Each average molecular weight was calculated from the obtained curve of each component.

3) Stereoregularity Mesopentad fraction ([mmmm]%) and meso-average chain length were measured using ¹³ C-NMR. The mesopentad fraction was determined according to the method described in Zambelli et al., Macromolecules, Vol. C. Randall, Polymer Sequence Distribution, Chapter 2 (1977) (Academic Press, New York).
¹³ C-NMR measurement was carried out at 110°C by dissolving 200 mg of a sample in a 8:2 mixture of o-dichlorobenzene and deuterated benzene at 135°C using AVANCE500 manufactured by BRUKER.

4) cold xylene soluble part (CXS, mass%)
After dissolving 1 g of a polypropylene sample in 200 ml of boiling xylene and allowing it to cool, it was recrystallized in a constant temperature water bath at 20° C. for 1 hour. and

5) Thermal shrinkage rate (%)
Measured according to JIS Z1712.
(The stretched film was cut in the MD and TD directions with a width of 20 mm and a length of 200 mm, suspended in a hot air oven at 150 ° C. and heated for 5 minutes. The length after heating was measured, and the shrinkage relative to the original length The thermal shrinkage rate was obtained as a percentage of the length.)

6) Impact resistance Measured at 23°C using a film impact tester manufactured by Toyo Seiki.

7) Young's modulus (unit: GPa)
The Young's modulus in the MD and TD directions was measured at 23° C. according to JIS K7127.

8) Haze (unit: %)
It was measured according to JIS K7105.

9) Plane orientation factor (ΔP)
Measured according to JIS K7142-1996 5.1 (method A) using an Atago Abbe refractometer. Nx and Ny are the refractive indices along the MD and TD directions, respectively, and Nz is the refractive index in the thickness direction. The plane orientation coefficient (ΔP) was obtained by (Nx+Ny)/2−Nz.
When the seal layer is on one side: The surface opposite to the seal layer was measured three times, and the average value was taken.
When the seal layer is on both sides: Each side of the seal layer was measured three times, and the average value was taken.

10) Heat-sealing strength Heat-sealing temperature is 140°C and 110°C, pressure is 1 kg/cm ² , and heat-sealing time is 1 second. A test piece with a width of 10 mm was prepared. The 180 degree peel strength of this test piece was measured and defined as the heat seal strength (N/15 mm).

11) Curling property The degree of curling of the laminated stretched film of the film obtained in the evaluation of 10) was visually measured.
○: No curling △: Slightly curling ×: Significant curling

12) Thickness Unevenness A 1 m square sample was cut out from the wound film roll and divided into 10 equal parts in the MD direction and the TD direction to prepare 100 samples for measurement. A contact-type film thickness meter was used to measure the thickness of the sample for measurement at approximately the center.
The average value of the obtained 100 points of data is obtained, the difference (absolute value) between the minimum value and the maximum value is obtained, and the absolute value of the difference between the minimum value and the maximum value is divided by the average value. and

13) Appearance of heat seal The prepared film and Toyobo Co., Ltd. pyrene film-CT P1128 are overlapped, and a test sealer manufactured by Seibu Kikai Co., Ltd. is used to heat seal by holding at 170 ° C. and a load of 2 kg for 1 second. rice field. The degree of change in appearance due to shrinkage of the film after heat sealing was visually evaluated. The degree of deformation of the heat-sealed portion was small and was within a range that did not affect use.

(Example 1)
Using two melt extruders, the first extruder uses the polypropylene homopolymer PP-1 shown in Table 1 as the polypropylene resin as the base layer (A), and the second extruder uses propylene. - Ethylene-butene random copolymer (PP-7: Pr-Et-Bu, density 0.89 g/cm ³ , MFR 4.6 g/10 min, melting point 128°C) at 85% by weight, propylene-butene random copolymer (PP-8: Pr--Bu, density 0.89 g/cm ³ , MFR 9.0 g/10 min, melting point 130° C.) at 15% by weight of a mixed resin is used as a heat seal layer (B), and the substrate is placed in a die. Material layer (A) / heat seal layer (B), the base layer (A) and the heat seal layer (B) are melted and co-extruded in the order of the T die from the T die at 250 ° C., After cooling and solidifying with a cooling roll at 30°C, it was stretched 4.5 times in the length direction at 125°C, then clipped at both ends, introduced into a hot air oven, preheated at 175°C, and transversely at 160°C. It was stretched 8.2 times in the direction and then heat-treated at 170° C. with a relaxation of 6.7%. Then, one side of the film was subjected to corona treatment and wound up with a winder. The thickness of the film thus obtained was 20 μm, and a laminated stretched film was obtained in which the substrate layer and the heat seal layer had thicknesses of 18 μm and 2 μm, respectively. As shown in Tables 1, 2 and 3, the obtained laminated stretched film satisfies the requirements of the present invention. was also excellent.

(Example 2)
A polypropylene-based laminated film was obtained in the same manner as in Example 1, except that the polypropylene homopolymer PP-2 shown in Table 1 was used as the raw material for the substrate layer (A). As shown in Tables 1, 2 and 3, the obtained laminated stretched film satisfies the requirements of the present invention. was also excellent.

(Comparative example 1)
A polypropylene-based laminated film was obtained in the same manner as in Example 1, except that the polypropylene homopolymer PP-3 shown in Table 1 was used as the raw material for the base layer (A). As shown in Tables 1, 2 and 3, the obtained laminated stretched films were excellent in heat-sealing strength, stiffness and curling properties, but had a large heat shrinkage.

(Comparative example 2)
An attempt was made to obtain a polypropylene-based laminated film in the same manner as in Example 1, except that the raw material used for the base material layer (A) was changed to the polypropylene homopolymer PP-4 shown in Table 1. was torn and no sample was obtained.

(Comparative Example 3)
A polypropylene-based laminated film was obtained in the same manner as in Example 1, except that the polypropylene homopolymer PP-5 shown in Table 1 was used as the raw material for the base layer (A). As shown in Tables 1, 2 and 3, the obtained laminated stretched films were excellent in heat-sealing strength, stiffness and curling properties, but had a large heat shrinkage.

(Comparative Example 4)
The raw material used for the base material layer (A) was changed to the polypropylene homopolymer PP-6 shown in Table 1, the width direction stretching preheating temperature was 170 ° C., the width direction stretching temperature was 158 ° C., and the heat setting temperature was 165. A polypropylene-based laminated film was obtained in the same manner as in Example 1, except that the temperature was changed to °C. As shown in Tables 1, 2 and 3, the obtained laminated stretched films were excellent in heat seal strength, stiffness and curling properties, but had a very large heat shrinkage.

The polypropylene-based laminated film of the present invention was excellent for use in packaging applications and very suitable for heat-sealing.
Furthermore, for example, by setting the heat-sealing temperature high, it becomes possible to increase the line speed in the bag-making process, thereby improving the productivity. In addition, the heat seal strength can be improved by increasing the heat seal temperature.

Claims (4)

A base layer (A) in which the polypropylene resin constituting the layer satisfies the following conditions 1) to 4), and a heat seal layer (B) composed of a polyolefin resin laminated on one or both sides of the base layer. The lower limit of the plane orientation coefficient of the film obtained by (Nx + Ny)/2-Nz is 0.0125 when the refractive indices in the MD direction, TD direction, and thickness direction of the film are Nx, Ny, and Nz, respectively. A polypropylene-based laminated film having a Young's modulus in the MD direction of 2.1 GPa or more and a Young's modulus in the TD direction of 3.7 GPa or more.
1) The lower limit of the mesopentad fraction is 96%.
2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%.
3) The weight average molecular weight (Mw)/number average molecular weight (Mn) is 3.0 or more and 5.4 or less.
4) Melt flow rate (MFR) measured at 230° C. and 2.16 kgf is 6.2 g/10 min or more and 9.0 g/10 min or less. 2. The polypropylene-based laminated film according to claim 1, wherein the heat shrinkage at 150[deg.] C. in the longitudinal and transverse directions of the film is 8% or less. The 180 degree peel strength of a test piece with a width of 10 mm obtained by superimposing the heat seal layer (B) surfaces and performing hot plate sealing at 140 ° C. for 1 second is 8.0 N / 15 mm or more. The polypropylene-based laminated film described. The polypropylene-based laminated film according to any one of claims 1 to 3, wherein the polyolefin-based resin constituting the heat seal resin (B) is a propylene random copolymer and/or a propylene block copolymer.