JP7309167B2 - Polypropylene light-shielding sealant film and its laminate - Google Patents

Description

The present invention relates to a light-shielding sealant film comprising a propylene-ethylene copolymer and produced by an upward air-cooling inflation method, and a laminate thereof. The film is excellent in strength such as impact resistance, has heat resistance capable of being subjected to retort heating, and is also excellent in recyclability.

Polypropylene, like polyethylene, is a resin that is inexpensive and excellent in transparency, heat resistance, flexibility, weather resistance, recyclability, and the like. A film containing polypropylene resin as a main material is also frequently used as a sealant film responsible for hermetic and heat-sealing properties of packaging materials. A general polypropylene sealant film is called CPP, and most of them are formed by a casting method.

In the casting method, a resin having a relatively small molecular weight is used in order to improve the film formability, and therefore the mechanical strength and impact strength are low, and the heat resistance is also insufficient.

On the other hand, polypropylene resin has a lower melt tension and a faster crystallization rate than polyethylene resin, so when producing a sealant film, it is difficult to maintain the shape of the blown bubble with upward air cooling inflation. However, it was difficult to increase the blowing ratio (blow ratio), and it was difficult to obtain a uniform thin film or a wide film. As a result, inflation film formation is usually performed downward by water cooling.

As a method for producing a polypropylene sealant film by an upward air-cooling inflation method, there are methods disclosed in Patent Document 1 and Patent Document 2.

Patent Document 1 discloses a sealant film produced by an air-cooled inflation method using a polypropylene-based resin containing an elastomer component composed of a propylene-based elastomer and/or an ethylene-based elastomer. This invention improves the poor low-temperature heat-sealability of polypropylene resins by adding an elastomer component, and also solves the citrus skin problem that occurs when oil-containing foods are packaged and subjected to high retort treatment.

Patent Document 2 also discloses an invention in which a polypropylene resin composition containing a polypropylene component and a propylene-ethylene copolymer or a polypropylene-α-olefin copolymer as an elastomer component is formed into a film by an air-cooled inflation method. This invention solves the problem that polypropylene has poor impact resistance at low temperatures.

Then, the present applicant devised a blend of polypropylene resin, provided a heat insulating pipe to heat the lower side of the resin bubble discharged from the die, and adjusted the air temperature for air cooling to slowly cool the polypropylene. We have developed a method for obtaining a good sealant film in an upward air cooling system, and filed a patent application for this (Patent Document 3).

This resin contains 1 to 50 parts by mass of an ethylene-α-olefin copolymer per 100 parts by mass of a propylene-based resin composition comprising 70 to 95% by mass of a propylene homopolymer and 5 to 30% by mass of a propylene copolymer elastomer. It is compounded. Further, this sealant film has a three-layer structure of an inner layer, an intermediate layer and an outer layer, and the inner layer and the outer layer comprise 60 to 80% by mass of the resin composition, 15 to 30% by mass of titanium dioxide and 5 to 15% by mass of a propylene random copolymer. A light-shielding sealant film was also developed in which the intermediate layer was composed of 70 to 90% by mass of the resin composition, 10 to 25% by mass of carbon black, and 15 to 30% by mass of propylene random copolymer.

JP-A-2002-331578 Japanese Patent Application Laid-Open No. 2004-27218 JP 2018-90723 A

In the method of forming a polypropylene sealant film by inflation method facing downward, the extruder, which is a heavy machine, must be installed on the floor, and the burden of equipment investment such as raw material supply lines and load-bearing frames was large. Furthermore, it is difficult to form a film of high-molecular-weight polypropylene, and it is difficult to obtain high crystallinity.

On the other hand, the upward air-cooling inflation method is the most economical film-forming method for commercial production of resin films, and polyethylene resin films are produced not only by the casting method but also by this method.

In this upward air-cooling inflation method, the molten bubbles are aligned vertically and horizontally in the take-up (vertical direction) and blow-in (horizontal direction) during film formation, and crystallization progresses and solidifies, resulting in a product with high tearability. . A high tear strength means that the packaging material has high strength, but is "difficult to open" when unsealed by the consumer.

The methods of Patent Documents 1 and 2 improve low-temperature heat-sealability and low-temperature impact resistance, but they do not fundamentally solve the instability and tearability of film formation in the upward air-cooling inflation method. do not have.

The method previously developed by the present applicant solved the instability and tearability of film formation, but since it is a method of blending three kinds of resins from the resin composition, fewer kinds of resins are used. It is desired to develop a method that can be used to produce a polypropylene sealant film in an upward air-cooled inflation process.

On the other hand, light-shielding packaging materials are also frequently used from the viewpoint of maintaining the quality of the items to be packaged. Conventionally, carbon black and aluminum foil have been mainly used to impart this light-shielding property.

When carbon black is used, the packaging material turns black, so it is not suitable for printing because it cannot be printed in colors that show through. With respect to aluminum foil, the collection and recycling of plastics are being promoted from the viewpoint of environmental problems. In addition, if aluminum foil is included, there is also a problem that it cannot be heated in a microwave oven because sparks occur when heated in a microwave oven.

The object of the present invention is to have high physical strength such as mechanical strength and impact resistance, heat resistance to withstand retort heating, printable on the surface, recyclability and light shielding without microwave heating problems. To provide a means for producing a polypropylene sealant film with a simple resin composition by an upward air-cooling inflation method.

The present inventors have made intensive studies to solve the above problems, and found that if inflation film formation is performed while slowly cooling using a propylene-ethylene copolymer containing 2 to 20% by mass of ethylene units among polypropylene resins, , With only propylene-ethylene copolymer and without adding other elastomers or ethylene-α-olefin copolymers, the upward air-cooled inflation method has excellent physical strength such as mechanical strength and impact resistance, and can be retorted. It has been found that a heat-resistant polypropylene sealant film can be produced without the problems of film instability and tearability. Then, if this polypropylene sealant film is made into a three-layer structure, the inner layer and the outer layer contain 15 to 30% by mass of titanium dioxide, and the intermediate layer contains 10 to 25% by mass of carbon black, it is possible to obtain It has been found that a light-shielding polypropylene sealant film can be obtained that maintains quality, provides good light-shielding properties, allows surface printing, is recyclable, and does not cause problems with heating in microwave ovens.

On the other hand, when the present inventor similarly performed retort heat treatment on a cast film, which is a conventional polypropylene sealant film, as a light-shielding film having a three-layer structure of titanium dioxide, carbon black, and titanium dioxide, carbon black and titanium dioxide were not produced. Addition of carbon black and titanium dioxide to conventional cast films resulted in a significant drop in impact resistance and increased offensive odor. rice field.

Accordingly, the present invention comprises an inner layer, an outer layer and an intermediate layer, each layer comprising a propylene-ethylene copolymer containing 2 to 30 mol % of ethylene units, the inner and outer layers containing titanium dioxide, and the intermediate layer comprising To provide a light-shielding polypropylene sealant film containing carbon black and having a transmittance of 0.5% or less for ultraviolet light of 315 to 380 nm and a transmittance of 0.5% or less to visible light of 380 to 760 nm. is.

When this light-shielding polypropylene sealant film is used as a substitute for an aluminum foil laminated film, the gas barrier properties against oxygen gas and water vapor may be insufficient depending on the application. Therefore, in the present invention, the melt flow rate ( MFR ) of the propylene-ethylene copolymer including the inner layer, outer layer and intermediate layer is 10 g/10 min or less, and the elastic modulus of the film is 1500 MPa or more in both MD and TD directions. It also provides the light-shielding polypropylene sealant film according to any one of claims 1 to 3.

According to the present invention, a light-shielding polypropylene sealant that has high physical strength such as mechanical strength and impact resistance, has heat resistance that can withstand retort heating, can be printed on the surface, and has no problems with recyclability or microwave heating. Films can be made with a simple resin composition in an upward air cooled inflation process. By laminating a gas barrier layer and a substrate layer on this light-shielding polypropylene sealant film , a film having light-shielding properties and gas barrier properties comparable to those of an aluminum foil laminated film can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a schematic configuration of an example of an inflation film-forming machine for producing the light-shielding polypropylene sealant film of the present invention; It is a figure which shows the arrangement|positioning of the heat insulation cylinder and a rectification|straightening member. FIG. 3 is a plan view showing the arrangement of three kneaders and dies;

The propylene-ethylene copolymer used for the light-shielding polypropylene sealant film of the present invention preferably has a propylene unit content of about 70 to 98 mol %, preferably about 85 to 95 mol %. Also, the MF R is 10 g/10 min or less, preferably about 0.1 to 8 g/10 min, more preferably about 0.5 to 6.0/10 min. The polymerization form may be either a block copolymer or a random copolymer, but the block copolymer is preferred because of its superior impact resistance. On the other hand, it is preferable to use a masterbatch for blending titanium dioxide and carbon black, and although a block copolymer can also be used as a resin for the masterbatch, a random copolymer is better for dispersing titanium dioxide and carbon black. It is preferable because it has excellent properties. Therefore, the ratio of the block copolymer to the random copolymer in the resin after addition of titanium dioxide or carbon black is 60 to 100% by mass, preferably about 70 to 90% by mass, and the random copolymer The coalescence is about 0 to 40% by mass, preferably about 10 to 30% by mass.

The light-shielding polypropylene sealant film of the present invention is a multi-layer film having three or more layers, in which titanium dioxide is blended in the inner and outer layers and carbon black is blended in the intermediate layer.

Titanium dioxide and carbon black are blended in such an amount that the sealant film as a whole can block ultraviolet light and visible light that degrade the quality of the package, at least to the extent that the quality can be maintained. Specifically, the transmittance of ultraviolet light of 315 to 380 nm is 0.5% or less, preferably less than 0.1%, and the transmittance of visible light of 380 to 760 nm is 0.5% or less, preferably 0.1%. % or less, more preferably less than 0.1%. This transmittance measurement conforms to JIS K 0115.

In order to obtain such a transmittance, the content of titanium dioxide in the inner and outer layers combined is 4 g/m ² or more, usually about 4 to 50 g/m ² , preferably about 6 to 20 g/m ² . is good. As for the content, both the inner and outer layers should be about 5 to 60% by mass, preferably about 10 to 30% by mass. The amount of carbon black in the intermediate layer is 0.3 g/m ² or more, usually about 0.3 to 15 g/m ² , preferably about 0.5 to 5 g/m ² .

The appropriate thickness of each layer is about 5 to 200 μm, usually about 7 to 50 μm, particularly about 10 to 30 μm. This thickness is determined according to the content of titanium dioxide and carbon black in each layer so that the transmittance of ultraviolet light is 0.5% or less and the transmittance of visible light is also 0.5% or less. The light-tight polypropylene sealant film of the present invention is produced by an upward air-cooled inflation process.

The inflation film-forming machine to be used is a normal inflation film-forming machine with a heat-retaining cylinder that covers 30 to 800 mm, preferably 30 to 500 mm above the frost line of resin bubbles in a steady state from the air ring. By attaching this heat-retaining cylinder, the molten resin is kept warm and crystallizes slowly, and as a result, the frost line position rises. In addition, weak molecular orientation is formed mainly in the longitudinal direction of the resin below the frost line, and the tearability of the film is improved. In addition, the heat insulating cylinder eliminates the influence of external air turbulence, etc., and also rectifies the blown air.

It is preferable to use transparent plastic, for example, as the material of the heat insulating cylinder so that the inside can be seen.

It is preferable to provide a rectifying member along the curvature of the blown expansion of the resin bubble inside the heat insulating cylinder. By providing this straightening member, the position and shape of the bottom of the resin bubble can be stabilized. The straightening members are preferably arranged evenly so that the bottoms of the resin bubbles can be stably supported. For example, as shown in FIG. , the shape close to the curvature of the resin bubble blowing expansion, that is, the shape close to the bottom of the resin bubble formed in a substantially bowl shape. The distance between the surface connecting the upper edge of the rectifying member and the bottom of the resin bubble (the distance in the direction perpendicular to the tangential line) is preferably about 1 to 10 mm. The air outlet may be provided near the base of the resin bubble as in a normal air ring. The material of the heat insulating cylinder is not particularly limited, but it is preferable to use, for example, a transparent plastic, which allows easy visual confirmation of the frost line condition and has excellent heat insulating properties.

However, these heat insulation cylinders and rectifying members are not essential, and by controlling the air blowing conditions so that they can be slowly cooled in the same state as they are, upward air cooling inflation can be performed without installing heat insulation cylinders and rectifying members. The light-shielding polypropylene sealant film of the present invention can be produced by the method.

In the inflation film-forming machine, after the resin bubbles are flattened by pinch rolls, multi-stage heat treatment rolls are provided to slowly cool the film. It is possible to avoid problems such as winding squeezing and winding wrinkles of the film wound up. The film traveling path length of the multistage heat treatment roll section is about 1 to 20 m, preferably about 1.5 to 10 m, particularly preferably about 2 to 5 m, and the number of heat treatment rolls is about 3 to 30.

In the method of forming an inflation film using such an upward air-cooled inflation film-forming machine, first, titanium dioxide and a propylene-ethylene copolymer and carbon black and a propylene-ethylene copolymer are kneaded at 190 to 250°C, respectively. Then, masterbatch pellets of titanium dioxide and carbon black are produced. Then, these masterbatch pellets and propylene-ethylene copolymer pellets are put into extruders for the inner layer, the outer layer, and the intermediate layer, respectively, kneaded with a kneader, and extruded from a die at about 160 to 210° C. to form a multilayer tube. Extrude into Then, the tube is inflated with air pressure from the inside, and air is sent from the outside to raise the temperature while keeping it warm. The blow ratio is not particularly limited. The appropriate temperature of this air is 55 to 65°C. If the temperature is higher than 65°C, the film will be overheated and hardening will be hindered. On the other hand, if it is lower than 55°C, it will solidify prematurely. Then, the film is flattened by pinch rolls at the top, and the temperature of the film is lowered by about 20.degree. C. from about 60 to 65.degree. C. to about 40 to 45.degree.

The elastic modulus of the entire sealant film obtained in this manner is about 1500 to 2500 MPa in both MD and TD.

The resulting film has a tensile strength (JIS-Z-1702) in the longitudinal direction of about 35 to 85 MPa, and a tear strength (JIS-Z-1702) (MD) of about 0.05 to 1 N, particularly 0.05 to 0. .2N, impact strength (JIS-K-7124) of 3 kgf or more, and heat resistance up to about 135°C.

The film of the present invention has high tensile strength, and the same strength can be obtained at a thickness of 60 to 80% of that of a conventional cast film (CPP).

Other resins such as polyethylene can be added to the light-shielding polypropylene sealant film of the present invention as long as the characteristics of the present invention can be secured, thereby producing an easily peelable sealant film with arbitrarily adjusted heat seal strength. It is also possible to The blending amount of polyethylene can be, for example, about 5 to 25% by mass of low-density polyethylene, and about 10 to 50% by mass in total. Additives such as antioxidants, ultraviolet absorbers, fillers, and colorants may also be added.

The number of layers of the sealant film is also not limited to three layers, and other functional layers can be arranged between the inner layer, the intermediate layer, and the outer layer, or on the outer side not used as the sealant.

The light-shielding polypropylene sealant film of the present invention can be used as a substitute for an aluminum foil laminated film by laminating a gas barrier layer.

The gas barrier layer enhances the barrier properties against oxygen gas, water vapor, etc., which the light-shielding polypropylene sealant film of the present invention lacks, and is made of a barrier resin film or a vapor deposition film. Barrier resins include vinyl alcohol resins and vinylidene chloride resins, and vinyl alcohol resins include polyvinyl alcohol resins and ethylene-vinyl alcohol copolymer resins. Vinylidene chloride resins include polyvinylidene chloride resins. From the viewpoint of recyclability, the deposited film is preferably deposited with a transparent material, and preferably deposited with aluminum oxide or silica. Vapor-deposited films include polyester, polyamide, polypropylene, and the like. Among these, an ethylene-vinyl alcohol copolymer resin film and a polyethylene terephthalate film deposited with aluminum oxide or silica are preferred.

In addition to the gas barrier layer, the light-shielding polypropylene sealant film of the present invention is preferably further laminated with a substrate layer for the purpose of improving the physical strength and protecting the gas barrier layer.

Films such as polyester, polyamide, polypropylene, and biaxially stretched films thereof can be used for the substrate layer.

As a method for laminating the gas barrier layer and the substrate layer, general dry lamination and extrusion lamination are used, and dry lamination, which is commonly used as a lamination method, is particularly suitable. In this case, it is more preferable that the light-shielding polypropylene sealant film of the present invention is subjected to corona discharge treatment immediately after film formation on the laminated surface. The amount of corona discharge treatment is preferably 37 to 47 dyne/cm in terms of wetting index of the film surface immediately after treatment.

FIG. 1 shows a schematic configuration of a film-forming apparatus used in the examples. This apparatus consists of an inflation film forming machine main body 1, three kneaders connected thereto for melt-kneading and extruding resins for the inner layer, the intermediate layer and the outer layer, and a multistage heat treatment roll group 3.

The inflation film forming machine 1 includes a die for co-extrusion of the resin extruded from the three kneaders into a tubular shape, and a mechanism (not shown) for pressurizing the extruded tubular resin from the inside with air pressure. , a device for air-cooling the resin extruded into a tubular shape from the outside, a guide 5 for gradually folding the resin bubble 4 rising in a tubular shape, and a pinch roll 6 for flattening it.

This device for air cooling from the outside includes a branch pipe 13 that sends air warmed by a warm air fan 9 from a blower 7 to an air ring 10 and an air outlet between multiple cylinders 11 that are rectifying members, and a branch pipe 13 that directs the blown air from the outside world. It consists of an acrylic thermal insulation tube 14 that eliminates the influence. The heat insulating cylinder 14 has a height of 1000 mm from the die and an inner diameter of 1000 mm. As shown in FIG. 2, the multiple cylinders 11 are arranged concentrically with five cylinders each having a slightly higher upper edge. It's becoming Air outlets 12 are arranged at regular intervals on the bottom surface between the cylinders of the multiple cylinders 11 .

A resin supplied from a kneader is extruded in a tubular shape from a die, is inflated by air pressure from the inside, rises, is gradually folded by a guide 5, and is flattened by a pinch roll 6. - 特許庁Then, it passes through guide rolls 15 and 16 and is slowly cooled by a multistage heat treatment roll group (tempering roll) 3 having a running path length of 2.5 m, and is subjected to corona treatment by a surface treatment machine 17 .

The diameter of the resin bubble 4 is 600 to 1000 mm at the portion having the same diameter, and the height of the frost line 18 from the die is 30 to 800 mm.

The following examples were carried out using the film-forming apparatus described above.

<Resin used>
Block PP: propylene-ethylene block copolymer (ethylene 10 mol%,
MFR 2 g/10 minutes, melting point 160°C)
Random PP: 96 mol% polypropylene, 4 mol% ethylene
random copolymer polymerized using a metallocene catalyst of
MF R =8 g/10 min, melting point 140°C
Polyethylene: High density polyethylene (of Comparative Example 8) ( MFR 4 g/10 min, melting point 126°C
Titanium dioxide: average particle size 250 nm
Carbon black: average particle size 100 nm
EVOH: thickness 15 μm, oxygen permeability 0.5 cc/m ² · 24 hr · atm,
Vapor-deposited PET: thickness 12 μm, oxygen transmission rate 0.8 cc/m ² · 24 hr · atm,
PET: thickness 12 μm

The method for measuring each physical property value is as follows.

<Melt flow rate>
JIS K7210-1

<Elastic modulus>
JIS K7127

<Transmittance>
Wavelength range (ultraviolet 315-380nm, visible 380-760nm)
JIS K0115

<Odor>
180 cc of pure water was enclosed in a bag (130 mm×170 mm), subjected to retort treatment (120° C.-30 minutes), kept at 60° C., and evaluated for odor. The odor sensory test was conducted with 5 preselected passers of the odor sensory test.
(odor standard)
4: Strong odor 3: Slightly strong odor 2: Weak odor 1: Slight odor 0: No odor

<Drop strength>
180 cc of water is enclosed in a bag (130 mm x 170 mm), cooled to 0-1°C, and retorted (120°C - 30 minutes). gone.

<Comprehensive evaluation>
◎ (best) to × (bad)

[Examples 1 to 6]
The inner layer is a resin composition containing 80% by mass of block PP, 60% by mass of titanium dioxide, and 20% by mass of a masterbatch consisting of 40% by mass of random PP. The intermediate layer is composed of 80% by mass of block PP and 35% by mass of carbon black. and 20% by mass of a masterbatch composed of 65% by mass of random PP and a resin composition containing 70% by mass of block PP and 30% by mass of a masterbatch composed of 60% by mass of titanium dioxide and 40% by mass of random PP. composition was used.

The above resin composition was put into each kneader of the film forming apparatus shown in FIG. A ^three -layer coextruded film having a thickness shown in Table 1 and a width of 800 mm was prepared at m 3 /min and a film forming speed of 12.8 m/min. The position of the frost line was around 700 mm from the die.

This film exhibited stable seal strength, heat resistance, and impact strength without cohesion failure observed during measurement.

The resulting three-layer coextruded film that had been subjected to corona treatment was coated with the gas barrier layer and the base material layer shown in Table 1 using a urethane-based adhesive as the adhesive, and the adhesive layer was formed by dry lamination. The laminated films of Examples 1 to 6 were obtained by bonding with a thickness of 3 μm.

It was confirmed that a similar three-layer coextruded film could be obtained by controlling the air volume, air temperature, etc. so that the same slow cooling could be achieved by omitting the heat insulating cylinder and the multiple cylinders.

Each physical property value in Table 2 was measured for the laminated films of Examples 1 to 6, and the results shown in Table 2 were obtained.

[Comparative Examples 1 to 4]
A two-layer or three-layer coextruded film was prepared in the same manner as in Examples 1 to 6 with each thickness shown in Table 1, and the gas barrier layer and the base layer shown in Table 1 were formed in the same manner as in Examples 1 to 6. By lamination, laminated films of Comparative Examples 1 to 4 were obtained. For each laminated film, each physical property value in Table 2 was measured, and the results shown in Table 2 were obtained.

As shown in the table, since Comparative Example 1 did not have a carbon black layer, visible light was transmitted and a considerable offensive odor was felt. In Comparative Example 2, since the titanium dioxide layer was too thin, visible light was transmitted and a foul odor was felt. In Comparative Example 3, since the carbon black layer was thin, visible light was transmitted and a foul odor was felt. In Comparative Example 4, since there was no carbon black layer, even if the titanium dioxide layer was thick, visible light was transmitted and a foul odor was perceived.

[Comparative Example 5]
A three-layer coextruded film and a laminate film were produced in the same manner as in Example 2 except for the propylene-ethylene copolymer, and the physical properties were measured. Table 2 shows the results.

In Comparative Example 5, since the molecular weight of the base PP was low, thermal deterioration during film formation was large, a foul odor was generated, and a drop in impact strength was observed.

[Comparative Example 6]
A three-layer coextruded film and a laminate film were produced in the same manner as in Example 2, except that the extrusion temperature was 260° C., and the physical properties were measured. Table 2 shows the results.

In Comparative Example 6, since the film-forming temperature was high, crystallization was difficult to proceed, and thermal deterioration was large, so that an offensive odor was generated and the impact resistance strength was lowered.

[Comparative Example 7]
A three-layer coextruded film and a laminate film were produced in the same manner as in Example 2, except that homo PP was used instead of block PP and random PP. Table 2 shows the results of measuring the physical properties.

In Comparative Example 7, since the base PP was homo-PP, low-temperature brittleness appeared in the molecular structure, and the dispersibility with the colorant was poor, so that the impact resistance strength was greatly reduced.

[Comparative Example 8]
A three-layer coextruded film and a laminate film were produced in the same manner as in Example 2, except that high-density polyethylene was used instead of block PP and random PP, and the physical properties were measured. Table 2 shows the results.

Since the base of Comparative Example 8 was HDPE, the heat resistance was inferior to that of PP, and the retort sterilization caused a large decrease in impact strength.

Table 1 shows an overview of the layer structures of Examples 1-6 and Comparative Examples 1-8.

Table 2 summarizes the results of measuring the physical properties of the laminated films of Examples 1-6 and Comparative Examples 1-8.

The light-shielding polypropylene sealant film of the present invention has high physical strength such as mechanical strength and impact resistance, has heat resistance to withstand retort heating, can be printed on the surface, and has problems of recyclability and microwave heating. Since a light-shielding polypropylene sealant film that does not have a light-shielding film can be produced by an upward air-cooling inflation method with a simple resin composition, it can be widely used as a light-shielding polypropylene sealant film. In particular, if a gas barrier layer is laminated, it can be used as a substitute for aluminum foil laminated films, which have problems with recyclability and microwave heating.

1 Inflation film forming machine main body 3 Multi-stage heat treatment roll group 4 Resin bubble 5 Stabilizer 6 Pinch roll 7 Blower 9 Hot air machine 10 Air ring 11 Multiple cylinder 13 Branch pipe 14 Thermal insulation cylinder 15 Guide roll 16 Guide roll 17 Surface treatment machine 18 Frost line

Claims (7)

It consists of an inner layer, an outer layer and an intermediate layer, each layer has a thickness of 7 to 200 μm, contains 2 to 30 mol % of ethylene units, and contains 70 to 90% by mass of a block copolymer and a random copolymer. The sealant film consists of a propylene-ethylene copolymer of 10 to 30% by mass, has a melt flow rate of 3 to 7 g/10 minutes as a whole, and contains titanium dioxide of 4 to 50 g/m ² in total in the inner and outer layers. The intermediate layer contains 0.3-15 g/m ² of carbon black, and has a transmittance of 0.5% or less for ultraviolet light of 315-380 nm and a transmittance of 0.5 for visible light of 380-760 nm. % or less, a light-shielding polypropylene sealant film . 2. The light-shielding polypropylene sealant film according to claim 1, wherein the content of titanium dioxide in the inner and outer layers is 10-30% by mass, and the content of carbon black in the intermediate layer is 10-25% by mass . 3. The light-shielding polypropylene sealant film according to claim 1, wherein the modulus of elasticity of the film is 1500 MPa or more in both MD and TD directions . 4. The method for producing a light-shielding polypropylene sealant film according to any one of claims 1 to 3, wherein the inner layer, the outer layer and the intermediate layer are co-extruded by an upward air-cooled inflation film forming machine . A laminated film obtained by laminating a gas barrier layer on the light-shielding polypropylene sealant film according to any one of claims 1 to 3 . 6. The laminated film according to claim 5, wherein the gas barrier layer is made of a vapor-deposited film of silica or alumina vapor-deposited or an ethylene-vinyl alcohol copolymer . 7. The laminated film according to claim 5, further comprising a substrate layer .

Images