JP2003055479A - Polypropylene film and process for producing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene film that is suitable for use as a heat seal layer of a food packaging material. SOLUTION: The polypropylene film is molded from a propylene/α-olefin block copolymer comprising (a) a polypropylene block and (b) a propylene/2-12C (exclusive of 3) α-olefin copolymer elastomer block wherein the copolymer elastomer block is contained in an amount of 5-30 wt.% based on the total copolymer and the propylene/α-olefin block copolymer that is soluble in xylene at a predetermined temperature has an intrinsic viscosity of 4.0-6.0 dl/g and wherein the copolymer elastomer block has dispersed particles of the characteristics (1)-(3) as follows: (1) the proportion of the dispersed particles with an aspect ratio of 1-3 in the machine direction(MD) is 50-100%; (2) the proportion of the dispersed particles with an average particle size of 0.2 μm or less in the MD is 45-80% and the proportion thereof with an average particle size of 0.4-1 μm is 20-40%; and (3) the proportion of the dispersed particles with a roundness of 1-1.2 in the MD is 60-95% and the proportion thereof with a roundness of 1.2-1.4 is not more than 30%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a film for packaging retort foods, when used as a heat-sealing layer of a packaging material, without causing unevenness (orange peel or yuzu skin) on the film surface due to heat sterilization such as retort sterilization treatment. And a polypropylene film suitable as a food packaging material.

[0002]

2. Description of the Related Art Conventionally, polypropylene films have been used as various food packaging materials and various medical packaging materials by taking advantage of the features such as heat resistance, chemical resistance, and easy heat sealability, which are inexpensive. In the food packaging field, as a packaging material for retort foods and the like, aluminum foil and vinylidene chloride resin and ethylene-vinyl acetate copolymer resin saponification agent and the like as a gas barrier layer, combined with a polyamide resin layer or a polyester resin layer, Polypropylene is used as the heat seal layer. In food packaging, after filling the contents, heat sterilization such as boil sterilization or retort sterilization is performed, and normal temperature storage or low temperature storage is performed. As the polypropylene for this use, for example, a propylene block copolymer or an ethylene-propylene random copolymer is blended with a thermoplastic elastomer, for example, an ethylene-propylene elastomer obtained by a vanadium-based polymerization catalyst and an elastomer component such as polybutene, and molded. Film is used.

[0003] However, when heat sterilization such as retort sterilization is performed, an uneven surface called orange peel or yuzu skin is formed on the surface of the film after heat sterilization, and other substrates are laminated by a laminating method such as dry lamination. When the retort pouch was made by laminating the pouches, there was a problem that the entire pouch was affected and the appearance of the product was significantly impaired. As a method for improving this, for example, a method of blending polybutene-1 (Japanese Patent Publication No. 2-32142), a retort packaging material using an ethylene-α-olefin copolymer polymerized using a specific catalyst. (JP-A-7-266520, JP-A-7-256841, etc.), a production method by a specific multistage polymerization (JP-A-3-44087), a specific laminate (JP-A-3-56570), and the like. Is proposed.

[0004]

However, all of the above methods are still inadequate from the viewpoint of preventing the generation of a scratched skin. An object of the present invention is to provide a polypropylene film which is suitable as a food packaging material in which unevenness on the film surface such as a scratched skin due to heat sterilization such as retort sterilization is less likely to occur.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have made a polypropylene film formed by passing a specific propylene-α-olefin block copolymer in a molten state through a metal fiber filter. It was found that the film can achieve the above object, and the present invention has been completed based on this finding. That is, the present invention includes (a) a polypropylene block, (b) propylene and 2 to 2 carbon atoms.
It is composed of a copolymer elastomer block with 12 (excluding 3) α-olefins, and the copolymer elastomer block accounts for 5 to 30 mass% of the total copolymer, and the xylene-soluble component. Intrinsic viscosity is 4.0-6.0
It is intended to provide a polypropylene film obtained by molding a propylene-α-olefin block copolymer having a dl / g and having dispersed particles of an elastomer block having the following properties (1) to (3). (1) Aspect ratio 1 in the film flow direction (MD)
% To 3% is 50% to 100% (2) Mean grain size 0.2 in the film flow direction (MD)
45-80% and average particle size 0.4-1
Ratio of μm is 20 to 40% (3) Roundness in the film flow direction (MD) 1-1.
The ratio of 2 is 60 to 95% and the ratio of circularity is 1.2 to 1.4 is 30% or less.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Propylene-α-in the present invention
The olefin block copolymer (hereinafter sometimes abbreviated as “BPP”) is (a) a polypropylene block,
(B) A copolymer elastomer block of propylene and an α-olefin having 2 to 12 carbon atoms (excluding 3), and the copolymer elastomer block accounts for 5 to 30 of the total copolymer. It is a copolymer which is mass%. Examples of the polypropylene block (a) of BPP include homopolypropylene or a propylene-α-olefin copolymer in which propylene and other α-olefin are less than 5% by mass. The α-olefin content is preferably 4.5% by mass or less, and particularly preferably 4.0% by mass or less. When the content of α-olefin is 5% by mass or more, the rigidity and heat resistance are impaired, and the amount of low crystalline components increases, and mutual adhesion of the film occurs, which is not preferable.

On the other hand, the (b) copolymer elastomer block of BPP contains propylene and 2 to 12 carbon atoms (however,
(Excluding 3) is a copolymer elastomer with an α-olefin, and the proportion of the copolymer elastomer block (hereinafter sometimes abbreviated as “elastomer”) in all copolymers is 5 to 30% by mass. . The proportion of the elastomer is preferably 10 to 28% by mass, particularly preferably 15 to 25% by mass. If the proportion of the elastomer is less than 5% by mass, the heat seal strength after retort sterilization is largely reduced, and the impact resistance and cold resistance are poor, which is not preferable. On the other hand, if it exceeds 30% by mass, the heat resistance is poor and the films adhere to each other by heat sterilization such as retort treatment, which is not preferable. The copolymerization ratio of the α-olefin is usually 30 to 80% by mass, preferably 35 to 75.
It is a mass%, and particularly preferably 38 to 72 mass%. If the copolymerization ratio is less than 30% by mass, impact resistance is poor.
On the other hand, when it exceeds 80% by mass, impact resistance and heat resistance are deteriorated, which is not preferable. Examples of the α-olefin used in the components (a) and (b) of BPP include ethylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, and 4-methyl-1-. Penten, 4,4-
Dimethyl-1-pentene, vinylcyclopentane, vinylcyclohexane and the like can be mentioned. These α-olefins may be used alone or in combination of two or more. Of these α-olefins, ethylene is preferred.

The BPP used in the present invention is required to have an intrinsic viscosity of xylene-soluble content of 4.0 to 6.0 dl / g. The intrinsic viscosity is preferably 4.1 to 5.5 dl /
g, and particularly preferably 4.2 to 5.0 dl / g. When the intrinsic viscosity is less than 4.0 dl / g, the effect on improving the skin loss after retort sterilization is poor. On the other hand, when it exceeds 6.0 dl / g, gel, fish eyes, eyes and the like are likely to occur and the appearance of the film is deteriorated, which is not preferable. Here, the intrinsic viscosity of the xylene-soluble component is BPP 13
It is the intrinsic viscosity of the polymer that precipitates when it is once dissolved in 5 ° C ortho-xylene and then cooled to 25 ° C. The polymer is dissolved in decahydronaphthalene at a temperature of 1
It is a value when measured under the condition of 35 ° C. Intrinsic viscosities measured by dissolving in decahydronaphthalene at a temperature of 135 ° C. are described by Elliott et al.
App. Poly. Sci, Vol. 14, pp294
The method of 7-2963 (1970) can be adopted.

The propylene film of the present invention is obtained by molding the above BPP, but it is necessary that the dispersed particles of the elastomer block have the following characteristics (1) to (3). (1) Aspect ratio 1 in the film flow direction (MD)
The ratio of 3 to 50 is 50 to 100% (2) The average particle size in the film flow direction (MD) is 0.2.
45-80% and average particle size 0.4-1
Ratio of μm is 20 to 40% (3) Roundness in the film flow direction (MD) 1-1.
The ratio of 2 is 60 to 95% and the ratio of circularity is 1.2 to 1.4 is 30% or less.

The aspect ratio is the ratio of the major axis to the minor axis of the equivalent ellipse (ellipse of the same area and having the same first and second moments) of the elastomer block dispersed particles appearing in the cross section in the film flow direction (long axis). / Minor axis). The ratio of the aspect ratio of 1 to 3 is preferably 60 to 99%, and particularly preferably 70 to 98%. If the ratio of the aspect ratio is 1 to 3 is less than 50%, it is not preferable because a scratched skin is likely to occur.

The average particle size is the average value of the diameters of the elastomer dispersed particles appearing in the cross section in the flow direction during film formation, measured through the center of each particle in increments of 5 degrees. The ratio of the average particle size of 0.2 μm or less is preferably 50 to 78%, and particularly preferably 55 to 75%. Average particle size 0.2
If the proportion of μm or less is less than 50%, it is not preferable because a scratched skin is likely to occur due to the retort sterilization treatment. Further, the ratio of the average particle diameter of 0.4 to 1 μm is preferably 25 to 38%, and particularly preferably 28 to 35%. If the ratio of the average particle size of 0.4 to 1 μm is less than 20%, it is not preferable because the rejuvenated sterilization treatment tends to cause scratched skin. On the other hand, if it exceeds 40%, it may be inferior in terms of skin roughness, rigidity and shrinkage ratio, which is not preferable.

The roundness can be obtained from the following equation from the peripheral length and area of the elastomer block dispersed particles appearing in the cross section in the flow direction during film formation. Roundness = (perimeter) ² / (4 × π × area) The ratio of circularity of 1 to 1.2 is preferably 65 to 93%, and particularly preferably 63 to 90%. Roundness is 1
If the ratio of 1.2 is less than 60%, the heat seal strength may decrease due to the retort sterilization treatment, which is not preferable. On the other hand, if it exceeds 95%, it is not preferable because a scratched skin is likely to occur due to the retort sterilization treatment. The ratio of roundness 1.2 to 1.4 is preferably 28% or less, particularly 2
It is preferably 5% or less. If the roundness is 1.2 to 1.4 and the ratio exceeds 30%, it is not preferable because the rejuvenated sterilization treatment may easily cause discolored skin. The above-mentioned ratio (%) means the ratio of the number of particles.

The above-mentioned properties of the elastomer dispersed particles of the present invention are obtained by image analysis of a photograph obtained using a scanning electron microscope (hereinafter referred to as "SEM") or a transmission microscope (hereinafter referred to as "TEM"). . That is, in the case of SEM, the sample is immersed in xylene at a temperature of 40 to 90 ° C., put in an ultrasonic cleaner, the elastomer component is etched, and a photograph is taken. On the other hand, in the case of TEM, the T
A sample for EM is cut out, dyed with RuO ₂ , and then, an ultrathin section cut by a cutting machine is observed with a TEM and photographed. The obtained photograph is used to determine the aspect ratio, roundness and average particle size using an image analyzer. As the image analysis device, TOSPIX-U type high precision monitor particle analysis package (manufactured by Toshiba Corporation), IMAGE-PRO PLUS
Commercially available products such as an apparatus (manufactured by MEDIA CYBERNETICS Co., Ltd.) can be mentioned.

As a preferred BPP in the present invention, the xylene-soluble component at a temperature of 25 ° C. according to the two-site model is (I) the average propylene content (FP) according to the two-site model is preferably 30 to 70 mol%, It is preferably 35 to 68 mol%, particularly preferably 38 to 65 mol%.
The mole% is 60 to 90 mole% propylene content (P _P) of (II) the copolymer produced in the active sites of polymerization preferentially propylene in two-site model (P _H), preferably 63 ~ 85 mol%, particularly preferably 6
A 5-83 mol%, a further (III) ratio of P _H occupies the copolymer (P _f1) is from 0.30 to 0.70, preferably 0.35-0.65, particularly preferably Is 0.
38 to 0.60. Xylene solubles are B
It is a dissolved content when PP is dissolved in orthoxylene at a temperature of 130 ° C. in an amount of about 1% by weight and then cooled to 25 ° C. Specifically, the component soluble in orthoxylene at a temperature of 25 ° C. of BPP is added to a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene at a temperature of 120% so that the polymer concentration becomes 10% by weight. Dissolve by heating at ℃. This solution is put into a ¹⁰ mmφ glass sample tube and ¹³ C-NMR spectrum is measured.

Here, 2 of propylene-α-olefin
FIG. 1 shows an example of a nuclear magnetic resonance ( ¹³ C-NMR) spectrum of isotope carbon of a propylene-ethylene copolymer for the site model. In the spectrum, 10 peaks shown in (1) to (10) appear due to the difference in chain distribution (arrangement of ethylene and propylene). The name of this chain is Carman.
CJ, et al; Macromolecules, Vol. 10, p536-544 (1977), and the name is shown in Fig. 2. Such a chain is
Assuming the reaction mechanism of the copolymerization, it can be expressed as a reaction probability (P).
The relative intensities of the peaks (1) to (10) can be expressed as a probability equation based on Bernoulli statistics with P as a parameter. For example, in the case of Sαα in (1), if the propylene unit is the symbol p and the ethylene unit is the symbol e, the possible chains are [pppp], [pppe], and [eppe].
And each of them is represented by a reaction probability (P),
Add up. The remaining peaks (2) to (10) can be obtained by formulating equations in the same manner and optimizing P so that the peak intensity actually measured and those 10 equations are closest to each other. . The two-site model is a model that assumes this reaction mechanism. HNCHENG; Jounalof A
pplied Polymer Sience, Vol.35, p1639-1650 (1988). That is, in the model of copolymerizing propylene and ethylene using a catalyst, polymerized preferentially ethylene and propylene content (P _P) of the copolymer generated at the active sites of polymerization preferentially propylene (P _H) Assuming two of the propylene content (P ' _P ) of the copolymer formed at the active point and the ratio of P _H in the copolymer (P _f1 ) as a parameter, the probability equation shown in Table 1 is obtained. .
The relative intensities of the ¹³ C-NMR spectrum described above and Table 1
P _P , _P'P and P
It is obtained by optimizing the three parameters of _f1 . The (I) average propylene content (FP) of the xylene-soluble component in the BPP of the present invention is determined by the following equation using the above three parameters. _{FP = P P × P f1 +} P 'P × (1-P f1) ( mol%) FP obtained by the above formula is 20 to 80 mol%, more preferably 30 to 70 mol%. Further, the (II) P _P of the parameters is preferably 60 to 90 mol%, especially 65 to 85 mol% are preferred.
Further, (III) P _f1 is preferably 0.40 to 0.90, and particularly preferably 0.48 to 0.82.

The BPP of the present invention is copolymerized by using a polymerization tank having two or more stages, and is referred to as high impact polypropylene or impact copolymer and block polypropylene. Known polypropylene, known by T.Ogawa, T.Inaba: J.Appl.Polym.Sc
i., 18,3345-3365 (1974), AJLononte: J.Polym.Sci., Pa
It is described in many documents such as rt A, 2,705-709 (1964).
As an example of the method for producing BPP, homopolypropylene or the polypropylene component (a) of the propylene-α-olefin random copolymer is polymerized in the first-stage reactor, and ethylene-α is used in the second and subsequent reactors. A method of producing the olefin copolymer elastomer block component (b) is used. In addition, the number of reactors is increased to control the molecular weight distribution of the polypropylene phase, and propylene-α
-It is also practiced to impart unique performance by changing the composition of the olefin copolymer.

The polymerization method is not particularly limited and known methods can be used. It can be obtained by either a continuous method or a batch method, and the form of the polymerization reactor is not particularly limited. The BPP is an inert hydrocarbon such as hexane, heptane, kerosene, or liquefied α-such as propylene.
The polymerization is carried out at a room temperature to 130 ° C. by a slurry method in the presence of an olefin solvent or a gas phase polymerization method without a solvent. It is preferably 50 to 90 ° C. The polymerization pressure is 0.
It is performed in the range of 2 to 4.9 MPa. As the reactor in the polymerization step, a reactor generally used in this technical field can be appropriately used. For example, using a stirred tank reactor, a fluidized bed reactor or a circulation reactor, the polymerization operation can be carried out by any of a continuous system, a semi-batch system and a batch system. The obtained BPP slurry or powder is inactivated with alcohol, water or the like, or the residual catalyst is removed, if necessary.
It is dried, melt-mixed with the additive, and provided.

The melt flow rate of BPP used in the present invention (MFR; load of 21.18 in accordance with JIS K7210).
N, measured at a temperature of 230 ° C.) is not particularly limited and may be selected according to the molding method. For example, the MFR used in the T die molding method is usually 0.5 to 10 g / 10 minutes, preferably 0. It is 8 to 8 g / 10 minutes, particularly preferably 1.0 to 5 g / 10 minutes. MFR is 0.5g / 1
If the time is less than 0 minutes, it is not preferable because the eye tends to be generated during molding and the productivity is poor. On the other hand, if it exceeds 10 g / 10 minutes, the degree of decrease in heat seal strength after retort sterilization tends to be large, which is not preferable.

Examples of the method for obtaining the polypropylene film of the present invention include a method in which the BPP in the molten state is filtered using a metal fiber filtration filter and then formed into various films. As the metal fiber filtration filter,
For example, a wire netting filter, a sintered wire netting filter, a porous metal filter, a metal fiber sintered filter, and a combination of these filters may be mentioned. These metal fiber filters are known and widely used for removing and refining gels and fish eyes of polyolefin resin films. It is also used for filtering high viscosity liquids such as fibers and plastics, filtering foreign substances in coating lines, and homogenizing pigments. As described above, the metal fiber filtration filter has been conventionally used for removing gels and fish eyes of a film, and improvement of the yuzu skin can be achieved only by using the BPP of the present invention. BPPs other than those of the present invention have no effect on improving the skin tone even if a metal fiber filtration filter is used.

The metal fiber filtration filter used in the present invention preferably has a filtration accuracy of 5 to 80 μm, more preferably 10 to 60 μm, and particularly preferably 15 to 40 μm, measured according to JIS B8356.
m. If the filtration accuracy is less than 5 μm, the pressure tends to rise during extrusion molding and the moldability is impaired, which is not preferable. On the other hand, if it exceeds 80 μm, the effect of improving the yuzu skin is difficult to be exhibited, which is not preferable.

Examples of the shape of the metal fiber filtration filter include a tube type filter, a pleated type cylindrical filter, a leaf disc filter and a flat type cylindrical filter. Among them, the leaf disk filter is preferable in terms of the effect of improving the skin roughness, pressure resistance and filtration area.
The metal fiber filtration filter is commercially available from Nippon Seisen Co., Ltd. under the "trade name: Naslon filter" and Fuji Filter Industry Co., Ltd. under the "trade name: Fuji Metal Fiber", and these can be preferably used. The temperature of the metal fiber filtration filter installed in the extruder is preferably 200 to 280 ° C., more preferably 210.
To 270 ° C., particularly preferably 220 ° C. to 260 ° C.
Is. If the temperature is less than 200 ° C., the effect of improving the yuzu skin is poor or the extrusion pressure increases, which is not preferable. on the other hand,
If it exceeds 280 ° C., the resin is deteriorated or the effect of improving the skin roughness is not obtained, which is not preferable. Preferably temperature 210 ° C
To 270 ° C, more preferably 220 ° C to 26 ° C.
It is 0 ° C.

The polypropylene film of the present invention can be obtained by a known inflation molding method, T-die molding method or the like. Usually, the die temperature is 220-
280 ° C. The cooling temperature is generally 30 to 90 ° C.
And 50 to 85 ° C is preferable, and 60 to 80 ° C is particularly preferable. The thickness of the polypropylene film of the present invention is usually 20 to 180 μm, preferably 3
0 to 170 μm, particularly preferably 40 to 160 μm
m. When the thickness is less than 20 μm, the heat seal strength is poor, which is not preferable. On the other hand, when it exceeds 180 μm, the impact resistance is inferior, which is not preferable. If the cooling temperature is less than 30 ° C, the effect of preventing the skin damage is poor. On the other hand, if the temperature exceeds 90 ° C., impact resistance and transparency decrease, which is not preferable.

For the polypropylene film of the present invention, a known dry laminate molding machine, extrusion lamination method or the like is used, and further, aluminum foil, metal vapor deposition film, silicon oxide vapor deposition film, vinyl dendrene resin and ethylene-vinyl acetate copolymer are saponified. Other materials such as a gas barrier layer of a material, a polyester resin layer, a polyamide resin layer and a polycarbonate resin layer can be laminated and used.

The heat sterilization referred to in the present invention is a method of killing microorganisms that are the main cause of food spoilage, and it is usually carried out in a temperature range of 60 ° C to 135 ° C, although it depends on the target bacteria. There is. Among these heat sterilization methods, a sterilization method using heated steam or hot water having a temperature of 100 ° C. or higher is called retort sterilization, and is processed at a high temperature for a short time so as not to spoil the taste and flavor of the contents. For details of these heat sterilizations, for example, Isao Shibazaki; “Food Sterilization Engineering” Korin Zensho 24
(Published March 14, 1981), Ushio Shimizu, Rio Yokoyama;
"The theory and practice of retort foods" is described in Koshobo (published on January 15, 1981).

[0025]

EXAMPLES The present invention will now be described in more detail with reference to examples. The methods for measuring various physical properties used in the present invention are shown below. [Heat seal strength] Using a tensile tester (RTA-100 type) manufactured by Orientec Co., Ltd., a sample was pulled at a pulling speed of 30.
The 180-degree peel strength was measured under the condition of 0 mm / min. [Evaluation of skin loss] The surface of the bag after the retort treatment was visually observed for surface irregularities (skin surface), and evaluation was performed according to the following five grades. 1 ... No occurrence of wrinkled skin is observed at all 2 ... ... Use of a slightly wrinkled uneven skin is observed 3 ... ... Use of something where a lot of wrinkled uneven skin is observed 4 … Clear and uneven shape skin that cannot be used because it is seen on the entire surface of the packaging bag. 5… severe uneven shape skin that is visible on the entire surface of the packaging bag and cannot be used [Film Impact Strength] ASTM According to D781, it was measured at a temperature of -5 ° C using a film impact tester manufactured by Toyo Seiki Seisaku-sho, Ltd. [Xylene-insoluble matter and soluble matter] The polymer was once dissolved in ortho-xylene at a temperature of 130 ° C to a concentration of about 1% by weight, then cooled to a temperature of 25 ° C, and the precipitated matter was not ortho-xylene-insoluble matter. The thing was made into the ortho-xylene soluble content, and the weight ratio was calculated. The orthoxylene-soluble component was used for the next measurement of the ¹³ C-NMR spectrum.

[Measurement of ¹³ C-NMR spectrum] Measuring device: JNM-GSX400 manufactured by JEOL Ltd. Measuring mode: Proton decoupling method Pulse width: 8.0 μs Pulse repetition time: 5.0 μs Integration number: 20000 times Solvent: Mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene (75/25% by volume) Internal standard: Hexamethyldisiloxane Sample concentration: 300 mg / 3.0 ml Solvent measurement temperature: 120 ° C

The materials used are shown below. [Propylene-α-olefin block copolymer] BPP1: elastomer block content is 20% by mass,
Xylene-soluble component is 17.3% by mass, xylene-soluble component is F
P is 44.1 mol%, P _P is 74.9 mol%, P _{f 1} is 0.33, MFR is 2.3 g / 10 min, and xylene solubles are dissolved in decahydronaphthalene and measured at a temperature of 135 ° C. Propylene-ethylene block copolymer BPP2 having an intrinsic viscosity of 4.3 dl / g: elastomer block content of 15% by mass,
9.8 mass% xylene solubles, xylene solubles FP
Of 48.5 mol%, P _P of 72.2 mol% and P _f1 of 0.
46, propylene-ethylene block copolymer BPP3 containing an elastomer block having an MFR of 3.4 g / 10 min, an xylene-soluble component dissolved in decahydronaphthalene and an intrinsic viscosity measured at a temperature of 135 ° C. of 4.8 dl / g 20% by mass,
Xylene-soluble component is 17.5% by mass, xylene-soluble component is F
P is 48.1 mol%, P _P is 75.9 mol%, P _{f 1} is 0.36, MFR is 2.8 g / 10 min, and xylene solubles are dissolved in decahydronaphthalene and measured at a temperature of 135 ° C. Propylene-ethylene block copolymer BPP4 having an intrinsic viscosity of 5.3 dl / g: elastomer block content of 20% by mass,
Xylene solubles 17.6% by mass, xylene solubles F
P is 47.5 mol%, P _P is 72.1 mol%, P _{f 1} is 0.38, MFR is 2.6 g / 10 min, and xylene solubles are dissolved in decahydronaphthalene and measured at a temperature of 135 ° C. -Ethylene block copolymer having an intrinsic viscosity of 3.7 dl / g

Examples 1 to 3, Comparative Example 1 After mixing with a tumbler in the types and compounding amounts shown in Table 2, pellets were formed using a twin-screw extruder (KTX37 type, manufactured by Kobe Steel Ltd.). The diameter of each obtained pellet is 1
Using a 15 mmφ and 65 mmφ extruder, a die width of 3,400 mm, a lip width of 0.8 mm, and a feed block type T-die molding machine manufactured by Toshiba Machine Co., Ltd., manufactured by Nippon Seisen Co., Ltd., “Product Name: Naslon Filter ( Filtration accuracy 20
μm) ”was passed through a filter in which 80 sheets / group were set and then supplied to a die (temperature 250 ° C.) to produce a polypropylene film having a thickness of 70 μm. The cross section in the flow direction (MD) of each of the obtained films was observed by TEM,
The state of dispersed particles of the elastomer block was observed. The results are shown in Table 2. Next, each of the obtained films and a polyester film (thickness 12 μm) are laminated by a dry lamination method using a heat sealer manufactured by Tester Sangyo Co., Ltd.,
A laminated film was produced. Each laminated film was heat-sealed with a heat sealer under the conditions of a temperature of 170 ° C., a pressure of 0.2 MPa, and a time of 1 second to produce a pouch, and a commercially available “Aojiru Meishu” made by Ajinomoto Co., Inc. was repacked. Then, the repacked pouch was sterilized by HISAKA CORPORATION (RCS-4
Retort sterilization was performed for 30 minutes at a temperature of 121 ° C. The pimples after the retort sterilization were evaluated for the skin loss. Further, the joint portion of the pouch before retort sterilization and after retort sterilization was cut into a width of 15 mm, and the heat seal strength was measured.

Example 4 Example 4 was repeated except that a metal fiber filter having a filtration accuracy of 80 μm was used.

Example 5 The same procedure as in Example 1 was carried out except that a metal fiber filter having a filtration accuracy of 40 μm was used.

Comparative Examples 2 and 3 Instead of the metal fiber filtration filter, the aperture was 20/60.
The same procedure as in Comparative Example 1 and Example 1 was carried out except that a screen mesh of / 120/60/20 mesh was used. Table 3 shows the above evaluation and measurement results.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

EFFECTS OF THE INVENTION The polypropylene film of the present invention, when used as a heat-sealing layer of a packaging material, has a small decrease in heat-sealing strength due to heat sterilization such as retort sterilization treatment, is excellent in low-temperature impact strength, and causes skin damage. Therefore, it can be usefully used as a food packaging material and a medical packaging material.

[Brief description of drawings]

FIG. 1 is an example of a nuclear magnetic resonance spectrum of a propylene-ethylene copolymer with isotopic carbon.

FIG. 2 is an example showing names of carbons derived from a chain distribution in a propylene-ethylene copolymer.

Continued front page    F-term (reference) 4F071 AA14 AA75 AF59 AH04 BA01                       BB06 BB09 BC01                 4J026 HA04 HB02 HB03 HB04 HB48                       HB49                 4J100 AA02Q AA03P AA04Q AA09Q                       AA17Q AA18Q AA20Q CA04                       GC02 GC37

Claims (3)

[Claims] 1. A polypropylene block (a),
(B) It is composed of a copolymer elastomer block of propylene and an α-olefin having 2 to 12 carbon atoms (excluding 3), and the copolymer elastomer block accounts for 5 to 30 mass% of all copolymers. %, And the xylene-soluble component has an intrinsic viscosity of 4.0 to 6.0 dl / g, which is obtained by molding a propylene-α-olefin block copolymer. ) -The polypropylene film which has the characteristic of (3). (1) Aspect ratio 1 in the film flow direction (MD)
% To 3% is 50% to 100% (2) Mean grain size 0.2 in the film flow direction (MD)
45-80% and average particle size 0.4-1
Ratio of μm is 20 to 40% (3) Roundness in the film flow direction (MD) 1-1.
The ratio of 2 is 60 to 95% and the ratio of circularity is 1.2 to 1.4 is 30% or less. 2. A polypropylene block (a),
(B) It is composed of a copolymer elastomer block of propylene and an α-olefin having 2 to 12 carbon atoms (excluding 3), and the copolymer elastomer block accounts for 5 to 30 mass% of all copolymers. %, And a propylene-α-olefin block copolymer having an intrinsic viscosity of xylene-soluble content of 4.0 to 6.0 dl / g is melt-filtered using a metal fiber filtration filter. Film manufacturing method. 3. The metal fiber filtration filter is JIS B
The filtration accuracy measured according to 8356 is 5 to 80 μm.
The method for producing a polypropylene film according to claim 2, wherein