JP3289447B2 - Multilayer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene-based multilayer film having excellent low-temperature impact resistance, tear strength, and blocking resistance, and having extremely little decrease in transparency with time.

[0002]

2. Description of the Related Art Polypropylene-based multilayer films are excellent in transparency, rigidity and heat sealing strength, and are used in various industrial fields such as food packaging. As a material for the polypropylene film, a propylene / ethylene crystalline random copolymer is mainly used because of its excellent low-temperature impact resistance and tear strength. In order to improve the low-temperature impact resistance and tear strength of the polypropylene film, it is necessary to copolymerize propylene with a high concentration of ethylene as a comonomer.

[0003] However, when a propylene-based copolymer is obtained by a slurry method or a bulk method, if the ethylene concentration is increased, low molecular weight components in the polymer are eluted into the polymerization solvent, resulting in poor productivity and high industrial efficiency. It is difficult to copolymerize ethylene at a concentration as a comonomer, and even when using a copolymer obtained by this production, excellent low-temperature impact resistance,
It was difficult to obtain a polypropylene film having tear strength.

In recent years, propylene-based copolymers have been obtained by a gas phase polymerization method because of their high productivity. According to this method, it is relatively easy to copolymerize high-concentration ethylene. Therefore, when a copolymer obtained by this process is used, a polypropylene film having excellent low-temperature impact resistance and tear strength can be obtained. Is possible. However, in the conventional slurry method or bulk method, low-molecular-weight polypropylene and amorphous atactic polypropylene (hereinafter, may be abbreviated as “APP”) components generated during polymerization are partially dissolved and removed in a polymerization solvent. On the other hand, in the gas phase polymerization method, these low molecular weight polypropylene and APP are incorporated into the product polypropylene, and the APP content tends to increase as the comonomer ethylene content increases. Therefore, the polypropylene-based film obtained by using the propylene-based copolymer produced by the gas-phase polymerization method has a disadvantage that the blocking is remarkable, and the transparency is impaired because the low molecular weight component and the APP component bleed out over time. have. In addition, these problems are raised in the Periodic Tables IV to V
It appears remarkably when a Ziegler-type catalyst consisting essentially of a group I transition metal compound and an organoaluminum compound is used. Therefore, an anti-blocking agent such as silica or zeolite is added to solve the blocking problem, but a considerable amount needs to be added to improve the blocking, and as a result, the transparency of the polypropylene-based film deteriorates. Was causing.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the disadvantages of single-layer polypropylene films produced by conventional methods such as the above-mentioned gas-phase polymerization method, slurry method and bulk method, and to provide low-temperature impact resistance and tearing. An object of the present invention is to provide a polypropylene-based film having good strength and blocking resistance and having extremely little decrease in transparency over time.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a propylene-based random copolymer having a high xylene-soluble content was used as an intermediate layer, and a xylene-soluble component was used. The inventors have found that the above problem can be solved by specifying the ratio of the thickness of the intermediate layer to the total thickness of the multilayer film using a small amount of the propylene-based polymer as both outer layers, and have reached the present invention.

That is, the present invention is a multilayer film having at least a three-layer structure including an intermediate layer (B) and both outer layers (A, C), wherein the thickness of the intermediate layer (B) is 10 to 10 times the thickness of the entire film. 95%, intermediate layer (B) is the following formula ^{(I) Y> 0.083X 2 +} 0.42 X + 2.1 (I) ( where _{Shikichu, X = (X 1 + (} X 2/3)) , X ≧ 3.0
X ₁ represents the ethylene content (% by weight), X ₂ represents the 1-butene content (% by weight), and Y represents the xylene-soluble component (% by weight). ) And / or a propylene / ethylene / 1-butene crystalline random copolymer,
C) is (1) a crystalline propylene homopolymer having an isotactic index of 95% or more, and (2) a propylene / ethylene crystalline random copolymer having a xylene-soluble content of less than 7% by weight and a comonomer content of less than 2% by weight. polymer and / or a propylene / ethylene / 1-butene crystalline random copolymer, and (3) the following formula ^{(II) Y <0.083X 2 +} 0.42 X + 1.9 (II) ( where Shikichu, X _{= (X 1 + (X 2} /3)),X≧2.0
In, X ₁ is a ethylene content (wt%), X ₂ is a 1-butene content (wt%), Y represents a xylene solubles (wt%) less than 7. A multilayer film comprising at least one polymer selected from a propylene / ethylene crystalline random copolymer and / or a propylene / ethylene / 1-butene crystalline random copolymer that satisfies (1).

Hereinafter, the present invention will be described in detail.

The resin used as the intermediate layer (B) of the multilayer film of the present invention is a propylene / ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random satisfying the above formula (I). It is a copolymer. The range represented by the above formula (I) is the portion represented by the oblique line (I) in FIG. 1, and a propylene-based random copolymer showing such a large xylene-soluble content can usually be obtained by a gas phase polymerization method. it can. The method for measuring the xylene-soluble content is as follows.

[Measurement method of xylene solubles] A sample is dissolved in heated xylene using a conical flask connected to a reflux condenser, cooled at room temperature, and the insolubles are filtered. After the filtrate is dried by heating, it is vacuum-dried at 100 ° C. for 1 hour, and the xylene-soluble content is determined by the following formula. Xylene solubles = ((weight of filtrate after heating to dryness) / (sample collection amount)) × 100 The components soluble in xylene are part of the comonomer, and most of the low molecular weight component and APP, As well as a function of the comonomer content, if the type of comonomer and the comonomer content are constant, there is a correlation between the xylene solubles and the contents of low molecular weight components and APP in the propylene copolymer. Further, the xylene-soluble component varies depending on the type of comonomer, and the contribution ratio of the comonomer to the xylene-soluble component is 1/3 for 1-butene when ethylene is 1. The comonomer content in the propylene copolymer used for the intermediate layer is not particularly limited, but is generally 0.5 to 25 mol%.

[0011] The gas phase polymerization method refers to a method in which a fine polymerization catalyst is used as it is or in a small amount of a dispersion medium in the absence of a solvent, or a fine powder carrier such as silica or alumina. In this method, the polymer is allowed to adhere or disperse in a granular polymer bed previously introduced or formed by the progress of polymerization while being supported on the catalyst, and brought into contact with a gas phase olefin to grow the polymer on the catalyst. As the catalyst used in the gas phase polymerization method, for example, transition metal compounds of Groups IV to VI of the periodic table, particularly halogen compounds of titanium are generally used, and these compounds are supported on various carriers. Things are also used. Among these, those supported on a carrier containing magnesium halide are particularly preferably used because of their high activity. An organoaluminum compound is used as a cocatalyst to be used together with the above catalyst, and a general formula AlR _n X _3-n such as triethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, diethylaluminum ethoxide, wherein R is a hydrogen atom Or a hydrocarbon group having 1 to 10 carbon atoms,
X represents a halogen atom or an alkoxy group having 1 to 12 carbon atoms, and n represents 1 to 3. The compound represented by the formula (1) is preferably used. Various electron donating compounds such as acid anhydrides, esters, ketones, amines and glycol ethers can be used as the third component of the catalyst. As the polymerization reaction conditions in the gas-phase polymerization method, at least one olefin among the olefins to be polymerized is substantially present in a gas phase, and the temperature and pressure conditions below the softening point of the obtained polymer are selected. . Generally, the polymerization temperature is from room temperature to 120.
C is preferable, and 20 to 100 C is more preferable. The polymerization pressure is preferably normal pressure to 100 kg / cm ² · G,
-50 kg / cm ² · G is more preferred. Although the molecular weight can be adjusted by adjusting the polymerization temperature, the molar ratio of the catalyst, the amount of the comonomer, and the like, it can be effectively adjusted by adding hydrogen to the polymerization system. Further, two or more polymerization reactions under different polymerization conditions such as hydrogen concentration, polymerization temperature, and comonomer concentration can be performed. As a reactor used in the polymerization step, a conventionally known reactor such as a stirred tank type reactor and a circulation type reactor can be used. The polymerization operation may be any of a continuous system, a semi-batch system and a batch system.

A method for producing polypropylene by the gas phase polymerization method as described above is known, and is disclosed, for example, in JP-A-48-84.
184, JP-A-55-157605, JP-A-1-165608 and the like describe catalysts and production methods.

Both outer layers (A, C) of the multilayer film of the present invention
(1) a crystalline propylene homopolymer having an isotactic index of 95% or more;
A propylene / ethylene crystalline random copolymer and / or a propylene / ethylene / 1-butene crystalline random copolymer having a xylene-soluble content of less than 7% by weight and a comonomer content of less than 2% by weight; At least one polymer selected from propylene / ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random copolymer satisfying II).

Crystalline homopolymer of propylene (1)
Is manufactured by a conventionally known method such as a slurry method, a bulk method, a gas phase polymerization method, and has an isotactic index of 95%.
Or more, preferably 96% or more. For polymers having an isotactic index of less than 95%, the intermediate layer (B)
Of the resin used in the intermediate layer (B) and suppressing the decrease in transparency due to bleeding. The isotactic index indicates (100- (xylene solubles)).

The xylene-soluble component is less than 7% by weight;
The propylene crystalline random copolymer (2) having a comonomer content of less than 2% by weight can be produced by a conventionally known method such as a slurry method, a bulk method and a gas phase polymerization method.

Further, the propylene crystalline random copolymer (3) satisfying the formula (II) can be produced by a conventionally known method such as a slurry method, a bulk method and a gas phase polymerization method.

The range represented by the above formula (II) is a portion represented by (II) below the curve 2 in FIG.
Copolymers (1) and (2) or those outside this range do not have the effect of preventing blocking of the intermediate layer and suppressing a decrease in transparency due to bleeding of the resin of the intermediate layer. In the case where the copolymer (3) is a random copolymer of propylene and ethylene obtained by a gas phase polymerization method, a copolymer having a crystal melting point of 135 ° C. or more is preferred in terms of blocking resistance and prevention of bleed out over time. Is preferably used.

In the present invention, the resin used for the intermediate layer (B) and the outer layers (A, C) has a melt flow rate (J).
IS K6758, 230 ° C, load 2160 g, sometimes abbreviated as “MFR”. ) Is not particularly limited, but is preferably 1 to 20 g / 10 min from the viewpoint of moldability. Their density (JIS K6758) is 0.8
9~0.90g / cm ³ is preferable.

The term "propylene random copolymer" in the present invention is used to distinguish it from the so-called "propylene block copolymer", in which the chain distribution of propylene and the comonomer is strictly based on Bernoulli's statistical rule. Does not mean a copolymer according to the formula, and the composition may have a distribution.

In the present invention, the resin used for the intermediate layer (B) and the outer layers (A, C) is a crystalline resin, and the low-crystalline or non-crystalline resin has a density of 0.89 g / cm ^3.
And the resulting film has insufficient stiffness and scratch resistance.

The thickness of the intermediate layer (B) of the multilayer film of the present invention is 10 to 95% of the total thickness of the film, preferably 30 to 95%.
80%. If the thickness of the intermediate layer (B) is less than 10%, the effect of improving the low-temperature impact resistance and tear strength of the film is poor, and if it exceeds 95%, the effect of improving the blocking resistance of the film and the reduction in transparency over time is sufficient. is not.

The thickness of the multilayer film of the present invention is not particularly limited, but is suitably from 20 to 100 μm. 2
If it is less than 0 μm, the mechanical strength is poor, and if it exceeds 100 μm, the cost increases.

The method for obtaining the multilayer film of the present invention is not particularly limited, and a known method is employed.
Specifically, the resin constituting the intermediate layer (B) and the outer layer (A,
(C) a method of co-extrusion of a resin constituting a multilayer die from a cast molding machine or an inflation molding machine having a multilayer die to produce a multilayer cast film or a multilayer inflation film, followed by stretching if necessary; To produce a two-layer film composed of an intermediate layer (B) and one outer layer (A), and then a resin constituting the outer layer (C) is laminated on the intermediate layer side of the two-layer film to form a three-layer film. After preparing a resin film constituting both outer layers (A, C) in advance,
A method of sandwich lamination using a resin constituting the intermediate layer (B) can be used. Among them, the multi-layer coextrusion method is particularly preferred because of its excellent productivity.

In the present invention, the resins used for the intermediate layer (B) and the outer layers (A, C) include an antioxidant, a light stabilizer, an ultraviolet absorber, an antistatic agent, a catalyst neutralizing agent, and an antifogging agent. Agent, anti-blocking agent, lubricant, pigment, dye, dropping agent,
Additives such as a nucleating agent, a filler, a clarifying agent, and a plasticizer can be added as needed as long as the object of the present invention is not impaired.

The intermediate layer (B) of the multilayer film of the present invention
And between the outer layers (A, C) and / or both outer layers (A, C)
A layer made of paper, a metal foil such as an aluminum foil, cellophane, a thermoplastic resin, or the like can be provided on the further outer side of C) as long as the effects of the present invention are not impaired. Examples of the thermoplastic resin include polyethylene, ethylene / vinyl acetate copolymer, polypropylene, ethylene / ethyl acrylate copolymer, ethylene / α-olefin copolymer, ionomer, polyvinyl chloride, polyvinylidene chloride, and polybutene-1. , Poly-4-methylpentene-1, polystyrene, polyacrylate, polyacrylonitrile, nylon, polyethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate / isophthalate copolymer, polyvinyl alcohol, ethylene / vinyl alcohol copolymer, polycarbonate and the like. No.

[0026]

In the present invention, the intermediate layer (B) is made of a propylene copolymer having a high xylene-soluble content shown by the hatched portion (I) in FIG. 1 and is shown by the propylene homopolymer and / or the parallel line portion in FIG. Propylene copolymer is used for both outer layers (A, C)
By using this, the blocking resistance of the propylene random copolymer film containing a large amount of xylene-soluble components and the decrease in transparency over time are improved. Since the propylene-based resin having low xylene-soluble content and excellent blocking resistance is used as both outer layers (A, C) to protect the propylene copolymer intermediate layer (B) having poor blocking resistance, the blocking resistance is improved. Was made. It is not clear why this reduces the aging of the transparency due to bleeding, but bleeding is suppressed by the difference in crystallinity between the outer layer (A, C) film and the intermediate layer (B) film. It is presumed. The reason why the multilayer film of the present invention is excellent in low-temperature impact resistance and tear strength is that the properties of the entire multilayer film are improved by using APP and a propylene copolymer having a large amount of low molecular weight as the intermediate layer (B). Can be

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the invention thereto. Parts in Examples and Comparative Examples are parts by weight. The physical properties in Examples and Comparative Examples were measured according to the following methods.

Low-temperature impact resistance Measured in a temperature atmosphere of 8 ° C. in accordance with JIS P8134.

Blocking Resistance A 1 kg load was placed on two film test pieces of 2 cm × 2 cm, left in an oven at 50 ° C. for 24 hours, and the maximum load when the test pieces were sheared off by an autograph was determined.
It is displayed in kg / (2 cm × 2 cm).

Tear strength Measured according to JIS Z1707.

Change in Transparency with Time The formed film was left in an oven at 80 ° C. in a state of being wound around a paper tube, and the change in film transparency after one day and one month was visually observed. evaluated. 1: No decrease in transparency over time due to bleed-out or the like is observed. 2: A slight cloudiness tendency is exhibited. 3: A considerable cloudiness tendency is observed. 4: The cloudiness is remarkable.

Comonomer Content in Propylene Random Copolymer Polymer Analysis Handbook (edited by the Japan Society for Analytical Chemistry and Polymer Analysis Research Council, published by Asakura Shoten, first edition) 256
The measurement was carried out in accordance with the quantification method using an IR spectrum described in 259. The ethylene content in the copolymer is 73
Using the characteristic absorptions of 3-1 and 722-1, it was determined by the following equation. (K ′ ₇₃₃ ) c = 1 / 0.96 ｛(K ′ ₇₃₃ ) a−0.268 (K ′ ₇₂₂ ) a｝ (K ′ ₇₂₂ ) c = 1 / 0.96 ｛(K ′ ₇₂₂ ) a− 0.150 (K _'733) a} ethylene content (wt%) = 0.575 {(K'733) c + (K'722) c} where K'a: extinction coefficient of apparent (= a / ρl) K'c: Absorption coefficient after correction A: Absorbance ρ: Density (g / cm ³ ) l: Sample thickness (cm) The 1-butene content in the copolymer is expressed by the following formula using the characteristic absorption of 766 ^-1. Determined by 1-butene content (% by weight) = 510 (A ₇₆₆ / l ′) l ′: thickness of sample (mm).

Production Examples 1 to 3 (Synthesis of Propylene Copolymer for Intermediate Layer by Gas Phase Method) Gas phase continuous polymerization was carried out using a polymerization vessel having an internal volume of 3 m ³ .
The inside of the polymerization vessel was sufficiently replaced with nitrogen, and propylene was added to the polymerization vessel under the conditions of a propylene partial pressure, a molar ratio of ethylene to propylene, and a molar ratio of hydrogen to propylene as shown in Table 1.
Ethylene and hydrogen were supplied, and a titanium trichloride catalyst component was continuously supplied at a rate of 8 g / hour, and diethyl aluminum chloride was continuously supplied so that Al / Ti = 20 mol / mol with respect to titanium in the catalyst. The temperature was adjusted to 75 ° C. The polymerized polymer particles were discharged to an extraction tank. The density, MFR, ethylene content and xylene-soluble content of the obtained propylene / ethylene random copolymer were measured. Table 1 shows the results.

Production Examples 4 and 5 (Synthesis of propylene terpolymer for outer layer by vapor phase method) (a) Preparation of solid catalyst component (D) 80 g of metal magnesium powder was placed in a 20 liter reactor equipped with a stirrer. (3.29 mol), and 4.0 g of iodine and 2.14 kg (2-ethylhexanol) were added thereto.
6.45 mol) and titanium tetrabutoxide 1.12
kg (3.29 mol) and 1.48 kg (7.24 mol) of tri-i-propoxyaluminum were added, and the number of stirring was 2
The temperature was raised to 90 ° C. at 00 rpm, and the mixture was stirred for 1 hour under a nitrogen seal while removing generated hydrogen gas. Continue 1
The temperature was raised to 40 ° C., and the reaction was performed for 2 hours to obtain a homogeneous solution (Mg—Ti—Al solution) containing magnesium and titanium. After cooling to 0 ° C., 2.04 kg of i-butylaluminum dichloride diluted to 50% with hexane
(6.58 mol) was added over 2 hours. After adding everything, the temperature was raised to 70 ° C over 2 hours.
A slurry containing a white solid product was obtained, and the solid product was separated by filtration and washed with hexane.

To the slurry containing the white solid thus obtained, a solution prepared by diluting 6.2 kg (32.9 mol) of titanium tetrachloride with 6.2 kg of chlorobenzene was added, and 364 g (1.38 mol) of diisobutyl phthalate was added. , 100
The reaction was carried out at 3 ° C. for 3 hours. The solid portion was collected by filtering the product, and again a solution obtained by diluting 6.2 kg of titanium tetrachloride with 6.2 kg of chlorobenzene was added at 100 ° C.
For 2 hours. Hexane was added to the product, and the product was thoroughly washed until no liberated titanium compound was detected. Thus, a slurry of the solid catalyst component (D) suspended in hexane was obtained. Elemental analysis revealed that the Ti content was 2.8% by weight.

(B) Prepolymerization of solid catalyst component (D) The inside of a 5-liter stainless steel electromagnetically stirred autoclave having an internal volume of 5 liters was sufficiently replaced with nitrogen, and the solid catalyst component (D) obtained by the method (a) was obtained. 50 g) and 37 g (0.32 mol) of triethylaluminum were sequentially added, and 3 l of hexane was added. Autoclave internal pressure 0.1kg /
in cm ² G, the agitation After adjusting the autoclave temperature to 20 ° C. begins, and stirred propylene 100g while maintaining the autoclave temperature inside 20 ° C. supplied for 30 minutes for 20 minutes. Subsequently, the solid content was separated by filtration and sufficiently washed with hexane to obtain a slurry of the prepolymerized catalyst component suspended in hexane. The yield after removing the supernatant and drying under a nitrogen atmosphere was 150 g.

(C) Synthesis of a terpolymer A nitrogen atmosphere was sufficiently substituted in a polymerization vessel having an internal volume of 3 m ³ , and a partial pressure of propylene, a molar ratio of ethylene to propylene, and a Butene molar ratio,
Propylene, ethylene, 1-butene and hydrogen are supplied under the condition of a molar ratio of hydrogen to propylene, and the prepolymerized catalyst component obtained by the above method (b) is further treated with triethylaluminum at a rate of 6 g / hour. Al / Ti = 70 mol / mol with respect to titanium in the catalyst, and diphenyldimethoxysilane was used as an electron-donating compound with Si / Al =
It was continuously supplied at 0.5 mol / mol. The temperature was adjusted to 75 ° C. The polymerized polymer particles were discharged to an extraction tank. The obtained propylene / ethylene / 1
-The density, MFR, ethylene content, 1-butene content and xylene solubles of the butene random copolymer were measured.
Table 1 shows the results.

Production Example 6 (Synthesis of propylene homopolymer for outer layer by gas phase method) The inside of a polymerization vessel having an internal volume of 3 m ³ was sufficiently substituted with nitrogen, and the polymerization vessel was subjected to partial pressure of propylene and hydrogen of hydrogen relative to propylene shown in Table 1. Propylene and hydrogen were supplied under the conditions of the molar ratio, and 6 parts of the prepolymerized catalyst component obtained by the method of Production Example 2 (b) was used.
g / hour, triethylaluminum was Al / Ti = 70 mol / mol with respect to titanium in the catalyst, and diphenyldimethoxysilane was used as an electron-donating compound.
It was continuously supplied so that Al = 0.5 mol / mol. The temperature was adjusted to 75 ° C. The polymerized polymer particles were discharged to an extraction tank. The density, MFR and xylene solubles of the obtained propylene homopolymer were measured.
Table 1 shows the results.

[0039]

[Table 1]

Example 1 Pentaerythrityltetrakis-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate as an antioxidant was added to 100 parts of the propylene homopolymer obtained in Production Example 6. (Product name: Irganox 101
0, Ciba-Geigy Co., Ltd.), 0.05 parts of calcium stearate as a catalyst neutralizer, 0.1 part of oleic amide as a lubricant, and 0.15 part of synthetic silica as a blocking inhibitor. Henschel mixer
And then pelletized by a single screw extruder to form both outer layers (A,
C) was prepared.

Further, pentaerythrityltetrakis-3 (3,5-di-t-butyl-) was added as an antioxidant to 100 parts of the crystalline propylene copolymer obtained in Production Example 1.
0.1 part of 4-hydroxyphenyl) propionate,
0.05 parts of calcium stearate was added as a catalyst neutralizer, mixed with a Henschel mixer, and then pelletized with a single screw extruder to prepare a resin for the intermediate layer (B).

75 m for the intermediate layer using the obtained pellets
Through a total of three extruders and a three-layer T-die connected to the extruder, each having a diameter of 65 mm for both the outer layer and the outer layer, the intermediate layer was 2 mm in diameter.
40 ° C, both outer layers are resin temperature of 250 ° C, processing speed 90m
/ Min, (A) / (B) / (C) = 1/3/1 to obtain a film having a total thickness of 30 μm. Table 2 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene film of this example was excellent in impact resistance, tear strength and blocking resistance, and showed little change in transparency with time.

Example 2 A multilayer film was produced in the same manner as in Example 1 except that the crystalline propylene copolymer obtained in Production Example 2 was used as the resin for the intermediate layer. Table 2 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene film of this example was excellent in impact resistance, tear strength and blocking resistance, and had little change in transparency with time.

Example 3 A multilayer film was produced in the same manner as in Example 1 except that the crystalline propylene copolymer obtained in Production Example 3 was used as the resin for the intermediate layer. Table 2 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene film of this example was excellent in impact resistance, tear strength and blocking resistance, and had little change in transparency with time.

Example 4 The procedure was carried out except that the crystalline propylene copolymer obtained in Production Example 2 was used as the resin for the intermediate layer, and the crystalline propylene copolymer obtained in Production Example 4 was used as the resin for the outer layer. A multilayer film was produced in the same manner as in Example 1. Table 2 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene film of this example was excellent in impact resistance, tear strength and blocking resistance, and had little change in transparency with time.

Example 5 The procedure of Example 5 was repeated except that the crystalline propylene copolymer obtained in Production Example 2 was used as the resin for the intermediate layer, and the crystalline propylene copolymer obtained in Production Example 5 was used as the resin for the outer layer. A multilayer film was produced in the same manner as in Example 1. Table 2 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene film of this example was excellent in impact resistance, tear strength, and blocking resistance, and the change in transparency with time was small.

Comparative Example 1 To 100 parts of the crystalline propylene copolymer obtained in Production Example 1, pentaerythrityltetrakis-3 (3,5-di-tert-butyl-4-hydroxyphenyl) was used as an antioxidant. ) Propionate (trade name: Irganox 10)
10, Ciba Geigy Co., Ltd.), 0.1 part of calcium stearate as a catalyst neutralizer, 0.1 part of oleic acid amide as a lubricant, and 0.15 part of synthetic silica as a blocking inhibitor. After mixing with a Henschel mixer, the mixture was pelletized by a single screw extruder.

The obtained pellets were extruded through a 75 mm diameter extruder and a single layer T die connected to the extruder at a resin temperature of 240 ° C. and a processing speed of 90 m / min to obtain a 30 μm single layer film. Table 2 shows the results of evaluating various physical properties of the obtained film.

The single-layer film of this comparative example was excellent in low-temperature impact resistance and tear strength, but lacked blocking resistance and markedly reduced transparency over time.

Comparative Example 2 A single-layer film was produced in the same manner as in Comparative Example 1 except that the crystalline propylene copolymer obtained in Production Example 2 was used. Table 2 shows the results of evaluating various physical properties of the obtained film.

The single-layer film of this comparative example was excellent in low-temperature impact resistance and tear strength, but lacked blocking resistance and markedly reduced transparency over time.

Comparative Example 3 A single-layer film was produced in the same manner as in Comparative Example 1 except that the crystalline propylene copolymer obtained in Production Example 3 was used. Table 2 shows the results of evaluating various physical properties of the obtained film.

The single-layer film of this comparative example was excellent in low-temperature impact resistance and tear strength, but lacked blocking resistance and markedly reduced transparency over time.

Comparative Example 4 A single-layer film was produced in the same manner as in Comparative Example 1, except that the crystalline propylene homopolymer obtained in Production Example 6 was used. Table 2 shows the results of evaluating various physical properties of the obtained film.

The single-layer film of this comparative example has excellent blocking resistance and little change in transparency with time, but is inferior in impact resistance and tear strength.

[0061]

[Table 2]

Examples 6 to 7 and Comparative Example 5 As resins for both outer layers, MFR 6.5 g / 10 min, density 0.
Resin pellets for the intermediate layer and both outer layers were prepared in the same manner as in Example 2 except that a propylene / ethylene copolymer having a content of 89 g / cm ³ , a comonomer content of 3% by weight, and a xylene-soluble matter of 2.1% by weight was used. . A film was produced in the same manner as in Example 2 except that the total thickness of the multilayer film and the ratio of the intermediate layer thickness to the total thickness were as shown in Table 3.
Table 3 shows the results of evaluating various physical properties of the obtained film.

The multilayer polypropylene films of Examples 6 and 7 are excellent in impact resistance, tear strength and blocking resistance and have little change in transparency with time. On the other hand, the multilayer film of Comparative Example 5 in which the ratio of the thickness of the intermediate layer to the total thickness is less than 10% lacks low-temperature impact resistance and tear strength.

[0064]

[Table 3]

[0065]

Industrial Applicability The multilayer film of the present invention is excellent in impact resistance, tear strength and blocking resistance at low temperatures, and does not decrease in transparency over time, and is suitable as a packaging film for food packaging, pharmaceutical packaging and the like. Used.

[Brief description of the drawings]

FIG. 1 is a view showing a range of a xylene-soluble component of a polypropylene resin used for an intermediate layer and both outer layers in the present invention.

[Explanation of symbols]

^{1: Y = 0.083X 2 + 0.42} X + 2.1 2: Y = 0.083X 2 + 0.42 X + 1.9

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A multilayer film having at least a three-layer structure comprising an intermediate layer (B) and both outer layers (A, C), wherein the thickness of the intermediate layer (B) is 10 to 95% of the total thickness of the film. There, the intermediate layer (B) is the following formula ^{(I) Y> 0.083X 2 +} 0.42 X + 2.1 (I) ( where _{Shikichu, X = (X 1 + (} X 2/3)), X ≧ 3.0
X ₁ represents the ethylene content (% by weight), X ₂ represents the 1-butene content (% by weight), and Y represents the xylene-soluble component (% by weight). ) And / or a propylene / ethylene / 1-butene crystalline random copolymer,
C) is (1) a crystalline propylene homopolymer having an isotactic index of 95% or more, and (2) a propylene / ethylene crystalline random copolymer having a xylene-soluble content of less than 7% by weight and a comonomer content of less than 2% by weight. polymer and / or a propylene / ethylene / 1-butene crystalline random copolymer, and (3) the following formula ^{(II) Y <0.083X 2 +} 0.42 X + 1.9 (II) ( where Shikichu, X _{= (X 1 + (X 2} /3)),X≧2.0
In, X ₁ is a ethylene content (wt%), X ₂ is a 1-butene content (wt%), Y represents a xylene solubles (wt%) less than 7. A multilayer film comprising at least one polymer selected from a propylene / ethylene crystalline random copolymer and / or a propylene / ethylene / 1-butene crystalline random copolymer satisfying (1).