JPH07156354A - Multilayer film - Google Patents

Abstract

PURPOSE:To improve low temperature impact resistance, etc., by forming an intermediate layer of a specific propylene random copolymer and both outer layers of polymer selected from a crystalline propylene homopolymer, etc. CONSTITUTION:A multilayer film is formed of a three-layer structure of an intermediate layer and both outer layers in such a manner that a thickness of the intermediate layer is 10-95% of thickness of the entire film. The intermediate layer is formed of a propylene-ethylene crystalline random copolymer for satisfying the formula I. Both the outer layers are formed of at least one type of polymer selected from a crystalline propylene homopolymer having an isotactic index of 95% or more, a propylene/ethylene crystalline random copolymer having xylene soluble content of less than 7wt.% and a comonomer content of less than 2wt.%, and a propylene/ethylene crystalline random copolymer for satisfying the formula II. In the formulae I and II, X=(X1+(X2/3)), X>=3.0 (in the formula I), 2.0 (in the formula II), X1 is ethylene content (wt.%, similar in the followings, X2 is 1-butene content, and Y is xylene soluble content (less than 7 in the formula II).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene-based multi-layer film which is excellent in low-temperature impact resistance, tear strength and blocking resistance and whose transparency is hardly deteriorated with time.

[0002]

2. Description of the Related Art Polypropylene-based multilayer films are excellent in transparency, rigidity and heat seal strength and are used in various industrial fields such as the food packaging field. As a material for the polypropylene film, a propylene / ethylene crystalline random copolymer is mainly used because it is excellent in 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.

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

In recent years, a propylene-based copolymer has been obtained by a gas phase polymerization method because of its high productivity. And, according to this method, it is relatively easy to copolymerize a high concentration of ethylene, and therefore, using the copolymer obtained by this process, a polypropylene film excellent in 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 sometimes abbreviated as “APP”) components produced during polymerization were partially dissolved and removed in the 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. For this reason, the polypropylene film obtained by using the propylene copolymer produced by the gas phase polymerization method has remarkable blocking, and the low molecular weight component and the APP component bleed out over time, resulting in impaired transparency. have. Furthermore, these problems are caused by periodic table IV-V.
It appears remarkably when a Ziegler type catalyst basically composed of a Group I transition metal compound and an organic aluminum compound is used. Therefore, an antiblocking agent such as silica or zeolite is added to solve the blocking problem, but it is necessary to add a considerable amount to improve blocking, resulting in deterioration of transparency of the polypropylene film. Was causing.

[0005]

The object of the present invention is to improve the respective drawbacks of the single-layer polypropylene film produced by the conventional methods such as the gas phase polymerization method, the slurry method and the bulk method, and to improve the low temperature impact resistance and tear resistance. It is to provide a polypropylene film having good strength and blocking resistance, and having extremely little deterioration in transparency over time.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a propylene-based random copolymer having a high xylene-soluble content is used as an intermediate layer and a xylene-soluble content is increased. The inventors have found that the above problems can be solved by specifying the ratio of the thickness of the intermediate layer to the total thickness of the multilayer film with a small amount of propylene-based polymer as both outer layers, leading to the present invention.

That is, the present invention is a multilayer film having at least three layers comprising an intermediate layer (B) and both outer layers (A, C), and the thickness of the intermediate layer (B) is 10 to 10 times the total thickness of the film. 95%, intermediate layer (B) is the following formula ^{(I) Y> 0.083X 2 +} 42X + 2.1 (I) ( where _{Shikichu, X = (X 1 + (} X 2/3)), X ≧ 3 .0
X ₁ represents the ethylene content (wt%), X ₂ represents the 1-butene content (wt%), and Y represents the xylene-soluble component (wt%). ) / Ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random copolymer satisfying the above conditions, and both outer layers (A,
C) is (1) a crystalline propylene homopolymer having an isotactic index of 95% or more, and (2) a xylene-soluble component is 7
Propylene / ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random copolymer having a comonomer content of less than 2% by weight, and (3) the following formula (II) Y <0. ^{.083X 2 + 42X + 1.9 (II} ) ( where _{Shikichu, X = (X 1 + (} X 2 /3)),X≧2.0
X ₁ represents the ethylene content (wt%), X ₂ represents the 1-butene content (wt%), and Y is less than 7 and represents the xylene solubles (wt%). ), A multilayer film comprising at least one polymer selected from the group consisting of a propylene / ethylene crystalline random copolymer and / or a propylene / ethylene / 1-butene crystalline random copolymer.

The present invention will be described in detail below.

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 copolymer satisfying the above formula (I). It is a copolymer. The range represented by the above formula (I) is the portion represented by the slanted line (I) in FIG. 1, and normally a propylene-based random copolymer having such a large xylene-soluble content can be obtained by a gas phase polymerization method. it can. The method for measuring the xylene-soluble component is as follows.

[Method for Measuring Xylene-Soluble Content] A sample is dissolved in heated xylene using an Erlenmeyer flask connected to a reflux condenser, cooled at room temperature, and insoluble matter is filtered. The filtrate is heated to dryness and then vacuum dried at 100 ° C. for 1 hour, and the xylene-soluble component is determined by the following formula. Xylene solubles = ((weight of filtrate after heating to dryness) / (sampled amount)) × 100 xylene soluble components are a part of comonomers, and low molecular weight components and most of APP, It is a function of the comonomer content, and if the comonomer type and the comonomer content are constant, there is a correlation between the xylene-soluble component and the contents of low molecular weight components and APP in the propylene copolymer. Further, the xylene-soluble content differs depending on the type of comonomer, and the contribution rate of the comonomer to the xylene-soluble content is about 1/3 of 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%.

The gas phase polymerization method is a method in which a fine polymerization catalyst is used as it is or in a state where it is dispersed in a small amount of a dispersion medium in the substantial absence of a solvent, or a fine powder carrier such as silica or alumina. It is a method of adhering or dispersing it in a granular polymer bed introduced in advance or produced by the progress of polymerization in a state of being supported on, contacting with a gas phase olefin, and growing the polymer on the catalyst. As the catalyst used in the gas phase polymerization method, for example, a transition metal compound of Group IV to VI of the periodic table, particularly a halogen compound of titanium is generally used, and these compounds are supported on various carriers. Things are also used. Among these, those supported on a carrier containing magnesium halide have high activity and are preferably used. Further, an organoaluminum compound is used as a cocatalyst used together with the above catalyst, and is represented by the general formula AlR _n X _3-n (where R is a hydrogen atom) such as triethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, and diethylaluminum ethoxide. 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) is preferably used. Further, 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 present in a substantially gas phase, and the temperature and pressure conditions below the softening point of the obtained polymer are selected. . Generally, the polymerization temperature is room temperature to 120
° C is preferred, and 20-100 ° C is still more preferred. The polymerization pressure is preferably normal pressure to 100 kg / cm ² · G, and 5
˜50 kg / cm ² · G is more preferred. The molecular weight can be adjusted by the polymerization temperature, the catalyst molar ratio, the comonomer amount, etc., but it is effectively performed by adding hydrogen to the polymerization system. Further, it is possible to carry out a polymerization reaction in two or more stages with different polymerization conditions such as hydrogen concentration, polymerization temperature and comonomer concentration. As a reactor used in the polymerization step, a conventionally known reactor such as a stirred tank reactor or a circulation reactor can be used. The polymerization operation may be a continuous system, a semi-batch system or a batch system.

The above-mentioned method for producing polypropylene by the gas phase polymerization method is known, and is disclosed in, for example, JP-A-48-84.
No. 184, JP-A No. 55-157605, JP-A No. 1-165608, and the like, and catalysts and production methods are described.

Both outer layers (A, C) of the multilayer film of the present invention
The resin used as (1) is a crystalline propylene homopolymer having an isotactic index of 95% or more, (2)
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, and a formula (3) ( It is at least one polymer selected from the propylene / ethylene crystalline random copolymer and / or the 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 or a gas phase polymerization method, and its isotactic index is 95%.
Or more, preferably 96% or more. For polymers with an isotactic index of less than 95%, the intermediate layer (B)
And the effect of preventing the decrease in transparency due to bleeding of the resin used in the intermediate layer (B). The isotactic index means (100- (xylene solubles)).

Further, 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 or 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 or a gas phase polymerization method.

The range represented by the above formula (II) is the portion represented by (II) below the curve 2 in FIG.
The copolymers (1), (2) or those outside this range have no effect of preventing blocking of the intermediate layer and suppressing deterioration of transparency due to bleeding of the intermediate layer resin. When the copolymer (3) is a random copolymer of propylene and ethylene obtained by a gas phase polymerization method, one having a crystal melting point of 135 ° C. or higher has anti-blocking properties and bleed-out prevention with time. Preferably used from

In the present invention, the melt flow rate (J) of the resin used for the intermediate layer (B) and both outer layers (A, C).
IS K6758, 230 ° C., load 2160 g, hereinafter sometimes abbreviated as “MFR”. ) Is not particularly limited, but 1 to 20 g / 10 minutes is preferable in terms of moldability. The density of these (JIS K6758) is 0.8.
It is preferably 9 to 0.90 g / cm ³ .

The "propylene random copolymer" in the present invention is for distinguishing from the generally called "propylene block copolymer", and the chain distribution of propylene and the copolymerization comonomer is strict according to the Bernoulli statistical rule. It does not mean that the copolymer complies with the above, but the composition may have a distribution.

In the present invention, the resin used for the intermediate layer (B) and both outer layers (A, C) is a crystalline resin, and the low crystalline or amorphous resin has a density of 0.89 g / cm ^3.
And the resulting film has insufficient waist 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 film thickness, preferably 30 to.
80%. When 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 when it exceeds 95%, the effect of improving the blocking resistance of the film and the decrease in transparency over time are sufficient. is not.

The thickness of the multilayer film of the present invention is not particularly limited, but 20 to 100 μm is suitable. Two
If it is less than 0 μm, the mechanical strength will be poor, and if it exceeds 100 μm, the cost will increase.

The method for obtaining the multilayer film of the present invention is not particularly limited, and known methods can be adopted.
Specifically, the resin forming the intermediate layer (B) and the outer layer (A,
A method of performing multi-layer coextrusion of the resin constituting C) from a cast molding machine or an inflation molding machine having a multi-layer die to prepare a multi-layer cast film or a multi-layer inflation film, and then stretching if necessary, the above-mentioned multi-layer film manufacturing method. After producing a two-layer film consisting of the intermediate layer (B) and one outer layer (A), 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 the resin film that constitutes both outer layers (A, C) is prepared in advance,
A method of performing sandwich lamination using the resin forming the intermediate layer (B) can be mentioned. Of these, the multi-layer coextrusion method is particularly preferable because of its excellent productivity.

In the resin used for the intermediate layer (B) and both outer layers (A, C) in the present invention, an antioxidant, a light stabilizer, an ultraviolet absorber, an antistatic agent, a catalyst neutralizing agent, an antifogging agent. Agents, anti-blocking agents, lubricants, pigments, dyes, drops,
Additives such as a nucleating agent, a filler, a clarifying agent, and a plasticizer can be added as needed within a range not impairing the object of the present invention.

The intermediate layer (B) of the multilayer film of the present invention
And / or both outer layers (A, C) and / or both outer layers (A, C)
If necessary, a layer made of paper, a metal foil such as an aluminum foil, cellophane, or a thermoplastic resin may be provided on the outer side of C) within a range not impairing the effects of the present invention. 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, 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, etc. Can be mentioned.

[0026]

In the present invention, the propylene copolymer having a high xylene-soluble content shown in the shaded portion (I) of FIG. 1 is used as the intermediate layer (B), and the propylene homopolymer and / or the parallel line portion of FIG. Both outer layers (A, C)
It improves the blocking resistance of the propylene random copolymer film having a high xylene-soluble content and the decrease in transparency over time. Since the propylene-based resin having less 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. Although the reason why the deterioration of transparency due to bleeding is improved by this is not clear, bleeding is suppressed by the difference in crystallinity between the outer layer (A, C) film and the intermediate layer (B) film. Presumed to be. Further, the reason why the multilayer film of the present invention is excellent in low temperature impact resistance and tear strength is considered to be 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). To be

[0027]

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Parts in the 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. according to JIS P8134.

Blocking resistance A load of 1 kg 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 shear-peeled by an autograph was calculated.
It is displayed in units of 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 paper-wrapped state, and the change in film transparency after 1 day and 1 month was visually observed and the following criteria were used. evaluated. 1: No decrease in transparency due to bleed-out etc. was observed. 2: Slightly cloudy. 3: Significant white turbidity is observed. 4: White turbidity is remarkable.

Comonomer Content in Propylene Random Copolymer Polymer Analysis Handbook (edited by Japan Society for Analytical Chemistry and Society for Polymer Analysis Research, published by Asakura Shoten, first edition) P. 256
The measurement was performed according to the quantification method by IR spectrum described in No. 259. The ethylene content in the copolymer is 73
It was determined by the following equation using the characteristic absorption of 3-1 and 722-1. _{(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 (% by weight) = 0.575 {(K'733) c + (K'722) c} where K'a: Apparent extinction coefficient (= A / ρl) K'c: corrected extinction coefficient A: absorbance ρ: density (g / cm ³ ) l: sample thickness (cm) The 1-butene content of the copolymer utilizes the characteristic absorption of 766 ^-1 Sought by. 1-Butene content (% by weight) = 510 (A ₇₆₆ / l ′) 1 ′: 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 under the conditions of the propylene partial pressure, the molar ratio of ethylene to propylene, and the molar ratio of hydrogen to propylene shown in Table 1 in the polymerization vessel.
Ethylene and hydrogen were supplied, and the titanium trichloride catalyst component was continuously supplied at a rate of 8 g / hour, and further, diethylaluminum 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 withdrawn and discharged into a tank. The density, MFR, ethylene content, and xylene-soluble content of the obtained propylene / ethylene random copolymer were measured. The results are shown in Table 1.

Production Examples 4 to 5 (Synthesis of propylene terpolymer for outer layer by vapor phase method) (a) Preparation of solid catalyst component (D) 80 g of magnesium metal powder in a 20 liter reactor equipped with a stirrer (3.29 mol) was added, and 4.0 g of iodine and 2.14 kg of 2-ethylhexanol (1
6.45 mol) and titanium tetrabutoxide 1.12
kg (3.29 mol) and tri-i-propoxyaluminum 1.48 kg (7.24 mol) were added, and the stirring number was 2
The temperature was set to 00 rpm, the temperature was raised to 90 ° C., and the mixture was stirred for 1 hour under a nitrogen blanket while eliminating generated hydrogen gas. Continued 1
The temperature was raised to 40 ° C. and the reaction was carried out for 2 hours to obtain a uniform 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
A solution of (6.58 mol) was added over 2 hours. After adding everything, when the temperature was raised to 70 ° C over 2 hours,
A slurry containing a white solid product was obtained, which was filtered off and washed with hexane.

A total solution of 6.2 kg (32.9 mol) of titanium tetrachloride diluted with 6.2 kg of chlorobenzene was added to the slurry containing the white solid thus obtained, and 364 g (1.38 mol) of diisobutyl phthalate was added. , 100
The reaction was carried out at 0 ° C for 3 hours. The solid portion was collected by filtering the product, and a solution prepared by diluting 6.2 kg of titanium tetrachloride with 6.2 kg of chlorobenzene was added again to 100 ° C.
And stirred for 2 hours. Hexane was added to the product, and the washing operation was sufficiently performed 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 interior of the stainless steel electromagnetic stirring type autoclave having an internal volume of 5 liters was sufficiently replaced with nitrogen, and the solid catalyst component (D) obtained by the above-mentioned method (a) ) 50 g and triethylaluminum 37 g (0.32 mol) were sequentially added, and hexane 3 l was added. Internal pressure of autoclave 0.1 kg /
The internal temperature of the autoclave was adjusted to 20 ° C. to cm ² G, and then stirring was started. 100 g of propylene was supplied for 20 minutes while the internal temperature of the autoclave was maintained at 20 ° C., and the mixture was stirred for 30 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 liquid and drying under a nitrogen atmosphere was 150 g.

(C) Synthesis of ternary copolymer The inside of the polymerization vessel having an internal volume of 3 m ³ was sufficiently replaced with nitrogen, and the propylene partial pressure shown in Table 1 in the polymerization vessel, the molar ratio of ethylene to propylene, and 1 to propylene were used. Butene molar ratio,
Propylene, ethylene, 1-butene and hydrogen were supplied under the condition of a molar ratio of hydrogen to propylene, and the prepolymerization catalyst component obtained by the method (b) was added at a rate of 6 g / hour and triethylaluminum. Al / Ti = 70 mol / mol with respect to titanium in the catalyst, and diphenyldimethoxysilane as an electron donating compound is Si / Al =
It was continuously fed so as to be 0.5 mol / mol. The temperature was adjusted to 75 ° C. The polymerized polymer particles were withdrawn and discharged into a tank. Obtained propylene / ethylene / 1
The density, MFR, ethylene content, 1-butene content and xylene-soluble content of the butene random copolymer were measured.
The results are shown in Table 1.

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 replaced with nitrogen, and the polymerization vessel was filled with propylene partial pressure shown in Table 1 and hydrogen to propylene. Propylene and hydrogen were fed under a molar ratio condition, and the prepolymerization catalyst component obtained by the method of Production Example 2 (b) was mixed with 6 parts.
At a rate of g / hour, triethylaluminum was further added to titanium in the catalyst Al / Ti = 70 mol / mol, and diphenyldimethoxysilane as an electron-donating compound was Si / Si.
It was continuously fed so that Al = 0.5 mol / mol. The temperature was adjusted to 75 ° C. The polymerized polymer particles were withdrawn and discharged into a tank. The density, MFR and xylene solubles of the obtained propylene homopolymer were measured.
The results are shown in Table 1.

[0039]

[Table 1]

Example 1 Pentaerythrityl tetrakis-3 (3,5-di-t-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, 0.1 part of Ciba Geigy Co., Ltd., 0.05 part of calcium stearate as a catalyst neutralizing agent, 0.1 part of oleic acid amide as a lubricant, and 0.15 part of synthetic silica as an antiblocking agent. Henschel mixer
After mixing in the pellets by a single screw extruder, both outer layers (A,
A resin for C) was prepared.

Further, with respect to 100 parts of the crystalline propylene copolymer obtained in Production Example 1, pentaerythrityl tetrakis-3 (3,5-di-t-butyl-) was used as an antioxidant.
0.1 part of 4-hydroxyphenyl) propionate,
0.05 part 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 the three-layer extruder with a diameter of m and a diameter of 65 mm for both outer layers, and a three-layer T-die connected to the extruder, the intermediate layer is 2
Resin temperature of 40 ° C, 250 ° C for both outer layers, processing speed 90m
/ Min, (A) / (B) / (C) = 1/3/1 in the constitution thickness ratio, and coextruded to obtain a film having a total thickness of 30 μm. Table 2 shows the results of evaluation of 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 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 intermediate layer resin. Table 2 shows the results of evaluation of 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 prepared in the same manner as in Example 1 except that the crystalline propylene copolymer obtained in Production Example 3 was used as the intermediate layer resin. Table 2 shows the results of evaluation of 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 4 Implementation was carried out except that the crystalline propylene copolymer obtained in Production Example 2 was used as the intermediate layer resin and the crystalline propylene copolymer obtained in Production Example 4 was used as the outer layer resin. A multilayer film was prepared in the same manner as in Example 1. Table 2 shows the results of evaluation of 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 Implementation was carried out except that the crystalline propylene copolymer obtained in Production Example 2 was used as the intermediate layer resin and the crystalline propylene copolymer obtained in Production Example 5 was used as the outer layer resin. A multilayer film was prepared in the same manner as in Example 1. Table 2 shows the results of evaluation of 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.

Comparative Example 1 Pentaerythrityl tetrakis-3 (3,5-di-t-butyl-4-hydroxyphenyl) as an antioxidant was added to 100 parts of the crystalline propylene copolymer obtained in Production Example 1. ) Propionate (trade name; Irganox 10
10, 0.1 part of Ciba-Geigy Co., Ltd., 0.05 part of calcium stearate as a catalyst neutralizing agent, 0.1 part of oleic acid amide as a lubricant, and 0.15 part of synthetic silica as an antiblocking agent are added. After mixing with a Henschel mixer, the mixture was pelletized with a single screw extruder.

The pellets thus obtained 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. at a processing speed of 90 m / min to obtain a single layer film of 30 μm. Table 2 shows the results of evaluation of 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 deteriorated in transparency over time.

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

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

Comparative Example 3 A monolayer 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 evaluation of various physical properties of the obtained film.

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

Comparative Example 4 A monolayer 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 evaluation of various physical properties of the obtained film.

The monolayer film of this comparative example is excellent in blocking resistance and shows 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 resin for both outer layers, MFR 6.5 g / 10 min, density 0.
Resin pellets for the intermediate layer and both outer layers were produced in the same manner as in Example 2 except that a propylene / ethylene copolymer having 89 g / cm ³ , a comonomer content of 3% by weight, and a xylene-soluble content 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 thickness of the intermediate layer to the total thickness are shown in Table 3.
The results of evaluating various physical properties of the obtained film are shown in Table 3.

The multilayer polypropylene films of Examples 6 and 7 are excellent in impact resistance, tear strength and blocking resistance and show 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 at low temperature, tear strength and blocking resistance, and is not deteriorated in transparency over time, and is suitable as a packaging film for food packaging, pharmaceutical packaging, etc. Used.

[Brief description of drawings]

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

[Explanation of symbols]

1: Y = 0.083X ² + 42X + 2.1 2: Y = 0.083X ² + 42X + 1.9

Claims (1)

[Claims] 1. A multilayer film having at least three layers 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 +} 42X + 2.1 (I) ( where _{Shikichu, X = (X 1 + (} X 2 /3)),X≧3.0
X ₁ represents the ethylene content (wt%), X ₂ represents the 1-butene content (wt%), and Y represents the xylene-soluble component (wt%). ) / Ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random copolymer satisfying the above conditions, and both outer layers (A,
C) is (1) a crystalline propylene homopolymer having an isotactic index of 95% or more, and (2) a xylene-soluble component is 7
Propylene / ethylene crystalline random copolymer and / or propylene / ethylene / 1-butene crystalline random copolymer having a comonomer content of less than 2% by weight, and (3) the following formula (II) Y <0. ^{.083X 2 + 42X + 1.9 (II} ) ( where where each of at _{X = (X 1 + (X} 2 /3)),X≧2.0,
X ₁ is ethylene content (wt%), X ₂ is 1-butene content (wt%), Y is less than 7 and xylene solubles (wt%)
Indicates. Propylene / ethylene crystalline random copolymer and / or propylene / ethylene / 1
-A multilayer film made of at least one polymer selected from butene crystalline random copolymers.