JPH08238732A - Multilayer film - Google Patents

Abstract

PURPOSE: To develop a multilayer film which has dirt impact strength, moistureproofness and low-temperature heat sealability. CONSTITUTION: A multilayer film comprises an intermediate layer made of propylene resin composition containing 1 to 95wt.% of polypropylene, 10 to 90mol% of ethylene content and 5 to 99wt.% of ethylene-propylene random copolymer and having 10μm of amorphous rubber particle size, an outer layer made of high-density polyethylene having a density of 0.935g/cm<3> or more, and an inner layer made of low-density polyethylene having a density of 0.935g/cm<3> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer film having excellent dirt impact strength, moisture resistance and low temperature heat sealability.

[0002]

2. Description of the Related Art Generally, polypropylene type single layer films are used as a packaging material because of their excellent chemical and physical properties, but they have a drawback in their dart impact strength. In order to overcome this drawback, an ethylene-propylene random copolymer (hereinafter sometimes referred to as EPR) has been blended with polypropylene, but sufficient strength and low temperature heat sealability cannot be obtained. The moisture resistance of the film was also poor, reducing the commercial value.

[0003]

An object of the present invention is to improve such drawbacks and to develop a multilayer film having dirt impact strength, moisture resistance and low temperature heat sealability.

[0004]

[Means for Solving the Problems] The above-mentioned problems are 1 to 95% by weight of polypropylene and 10 to 90% by mol of ethylene.
An ethylene-propylene random copolymer of 5 to 99% by weight, and an outer surface layer made of a propylene resin composition having an amorphous part rubber particle diameter of 10 μm or less, and 0.935 g.
This can be solved by a multilayer film including an outer layer made of high-density polyethylene having a density of / cm ³ or more and an inner layer made of low-density polyethylene having a density of 0.935 g / cm ³ or less. Hereinafter, the present invention will be described in detail.

The polypropylene used in the propylene resin composition used for the intermediate layer of the multilayer film of the present invention may be any crystalline polypropylene used for films, and has a density of 0.89 to 0.92 g / cm. ³ ,
Melt flow rate (230 ° C.) measured by JIS K6758 is 0.1 to 90 g / 10 minutes, isotactic index (boiling n-heptane extraction residue) is 7
5 to 98% is preferable.

The ethylene-propylene random copolymer has an ethylene content of 10 to 90 mol%,
~ 85 mol% is preferred. Ethylene content is 10 mol%
If it is less than 1, the low temperature brittleness and the low temperature impact strength are poor. If it exceeds 90 mol%, the heat resistance is poor.

Examples of the ethylene-propylene random copolymer include those commercially available under the trade names such as "Tuffmer P-0280" and "Tuffmer P-0480" manufactured by Mitsui Petrochemical Co., Ltd.

The blending ratio of the ethylene-propylene random copolymer in the propylene resin composition is 5 to 99% by weight, preferably 5 to 50% by weight, and particularly preferably 10 to 30% by weight. When the blending amount of the ethylene-propylene random copolymer is less than 5% by weight, the low temperature impact strength is not improved, which is not preferable. On the other hand, the blending ratio is 99
If it exceeds 5% by weight, transparency is significantly impaired, which is not preferable.

The amorphous part rubber particle diameter in the propylene resin composition must be 10 μm or less, preferably 5 μm or less. When the amorphous part rubber particle size exceeds 10 μm, the dirt impact strength of the multilayer film is poor.

To produce a propylene resin composition,
A preferred method is to uniformly mix polypropylene and an ethylene-propylene random copolymer with a solvent and then remove the solvent.

To mix the composition in the solution, a mixing tank capable of controlling a stirring temperature is used, and a solvent capable of dissolving polypropylene and an ethylene-propylene random copolymer is filled to obtain a mixture of polypropylene and ethylene.
A propylene random copolymer is added, and both are uniformly mixed in a state of being dissolved in a solvent. After mixing, the solvent is removed and separated.

When the mixing is carried out in the liquid phase as described above, polypropylene is dissolved at 20 to 250 ° C. as a solvent,
The solvent is not particularly limited as long as it is an inert solvent having no reactivity with the raw materials and the like. Specific examples of such a solvent include aromatic hydrocarbons such as toluene and xylene or halogenated ones thereof, and further saturated aliphatic hydrocarbons such as hexane, heptane and decane and halogenated ones thereof, cyclohexane and the like. And alicyclic hydrocarbons thereof and their halides.

The mixing is usually carried out in the range of 20 to 250 ° C, preferably in the range of 50 to 220 ° C. Further, the mixing is carried out under reduced pressure or under increased pressure, and the mixing pressure is not limited, but from the reduced pressure to 100 kg /
Good over cm ² . However, usually 0-50 kg /
cm ² , preferably in the range of 1 to 10 kg / m ² .
The mixing time is set appropriately in consideration of the mixing temperature and pressure.

In addition, in such mixing, propylene is polymerized to form polypropylene in the first step by using a solution-type sequential polymerization and process, and the solution remains in a state of being dissolved in a solvent. A method of polymerizing a mixture of propylene and ethylene to form an ethylene-propylene random copolymer may be used.

On the contrary, a method may be used in which the ethylene-propylene random copolymer is produced in the first step and remains in the state of being dissolved in the solvent, and then propylene is polymerized to produce polypropylene in the subsequent step. Absent.

According to this method, the amorphous part rubber particle size is 10
It is possible to produce a propylene-based resin composition having a size of μm or less. The propylene-based resin composition obtained by the production method as described above has good dispersibility of the rubber component, and therefore, when used in the intermediate layer of the multilayer film of the present invention, particularly the dart impact strength (index of strength of packaging material ( In method B), a value of 500 g (film having a thickness of 100 μm) or more is shown, and excellent performance is also shown in pinhole resistance.

As the high-density polyethylene used for the outer surface layer of the multilayer film of the present invention, various kinds can be used as long as they contain ethylene as a unit and have a density of 0.935 g / cm ³ or more. In particular,
Homopolymer made of ethylene, copolymer made of ethylene and another monomer (eg propylene, butene-1, hexene-1), or copolymer made of ethylene and a prepolymer made of two or more kinds of monomers And the like.

High density polyethylene has a density of 0.935.
It is necessary to be g / cm ³ or more. Density is 0.9
If it is less than 35 g / cm ³ , the obtained film will have poor properties as a high-density polyethylene film, such as waist strength (Young's modulus) and gas barrier property (moisture proof).

The high density polyethylene preferably has a melt flow rate (190 ° C.) of 1.0 g / 10 minutes or less. As the melt flow rate increases, the strength of the film tends to decrease.

By using high-density polyethylene for the outer layer, the moisture resistance of the intermediate layer is supplemented, and the moisture permeability is 8 g / m ² ·
Values below 24 hours (100 μm thick film) are obtained, giving an excellent multilayer film as a packaging material for contents which need to control moisture.

The low density polyethylene used for the inner surface layer of the multilayer film of the present invention has a density of 0.935 g /
cm ³ or less, 0.900 to 0.930 g / cm ³
Are preferred. When the density is less than 0.900 g / cm ³ , impact resistance and creep resistance are reduced, and 0.930 g / c
If it exceeds m ³ , sufficient low temperature heat sealability (120 ° C. or less) cannot be obtained.

The propylene resin composition, high-density polyethylene and low-density polyethylene forming each layer are
Other commonly used additives such as antioxidants, antistatic agents, ultraviolet absorbers, colorants (pigments) and the like can be added.

In particular, taking advantage of the characteristics of the multilayer film,
When used as a packaging material for a photosensitive material, it is necessary to have a light shielding property. For this purpose, 0.1 to 30% by weight of a light-shielding substance may be contained in any one or more layers of high-density polyethylene, propylene-based resin composition, and low-density polyethylene. , Thickness of colored paper, or aluminum foil or galvanized thin-layer steel plate, etc. 5
Metal foil of 100 μm or more and 50 μm or less or 100 to 1200
A method such as stacking other layers with a light-shielding property such as paper with a metal vapor deposition layer of Å (eg aluminum vapor deposition paper) or metal vapor deposition film (eg aluminum vapor deposition film) or adding light shielding properties by printing You may use.

As a method for producing a multilayer film, a coextrusion method can be preferably adopted, and for example, a multilayer inflation molding method, a multilayer cast molding method or the like can be used.

In the multilayer film of the present invention,
A third layer may be interposed between the intermediate layer and the inner surface layer, but the surface layer must be present on the outermost surface and the innermost surface of the multilayer film. As the third layer, it is preferable to use an adhesive resin layer in order to more firmly bond the intermediate layer and the outer layer.

The thickness of the multilayer film produced by such a method is generally 10 to 400 μm from the viewpoint of ease of use.
And preferably 20 to 200 μm.

In the multilayer film of the present invention, the thickness of the intermediate layer is 30 to 99%, especially 40 to 80% of the thickness of all layers.
It is preferred that When the thickness of the intermediate layer is less than 30%, the low temperature impact strength becomes poor, and when it exceeds 99%, the external film haze of the multilayer film becomes poor.

[0028]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples and comparative examples, each physical property was measured by the following methods. Dirt impact strength ・ ・ ・ Compliant with JIS Z1702 impact strength. Water vapor transmission rate ・ ・ ・ Compliant with JIS Z0208-1976. Heat-sealing property First, cut the film into strips with a width of 15 mm, and seal it with a sealing pressure of 2 kg / cm.
^2. Heat sealing is performed while changing the temperature under the condition that the sealing time is 1 second, and the test piece is peeled at a speed of 300 mm / min to examine the peel strength. As a result, the heat sealing property was represented by the sealing temperature of the test piece having a peel strength of 1 kg. Amorphous part rubber particle size: Measured with an electron microscope (SEM). In order to make the rubber component easy to see, the film was previously dyed with a RuO ₄ aqueous solution.

(Example 1) Isotactic index 96%, melt flow rate (230 ° C) 1.5 g
/ 10 minutes of 160 kg of propylene homopolymer and 40 kg of ethylene-propylene random copolymer having an ethylene content of 30 mol% are stirred in 1000 liter of xylene solvent at 1 kg / cm ² G and 140 ° C. for 2 hours to obtain a solution. After uniformly mixing in the state, the solvent was removed, and the composition was dried under reduced pressure (0.5 Torr or less, 60 ° C.) for 48 hours and then pulverized,
Pelletized. The obtained polypropylene-based resin composition was used for the intermediate layer, and as high-density polyethylene, the density was 0.950 g / cm ³ , and the melt flow rate (190
(° C) of 0.8 g / 10 minutes is used for the outer surface layer, and low density polyethylene having a density of 0.920 g / cm ³ and a melt flow rate (190 ° C.) of 1.0 g / 10 minutes is used as the inner surface layer. A multilayer film was produced by air-cooling inflation molding. In this case, the inflation molding was performed using a three-layer molding machine with three 40 mmφ molding machines under the conditions of a die of 100 mmφ, a discharge rate of 30 kg / H, and a molding temperature of 230 ° C. The total thickness of the film is 1
The thickness ratio of 00 μm, both surface layers, and the intermediate layer was 1: 2: 1. The blow ratio was 2. Table 1 shows the physical properties of the obtained film. From the results in Table 1, it was confirmed that the multilayer film of the present invention has good dispersibility of the rubber component of the intermediate layer and has excellent dirt impact strength.
On the other hand, it can be confirmed that the effect of using high-density polyethylene for the outer layer and low-density polyethylene for the inner layer is sufficiently exerted, and even the multilayer film has a low moisture permeability and excellent moisture resistance and heat sealability. It was

(Examples 2 to 5) In Examples 2 to 5, various polypropylenes and ethylene-propylene random copolymers were used under the same conditions (scale, temperature, pressure, time, etc.) as in Example 1 for propylene series. A resin composition was prepared, and various high-density polyethylene and low-density polyethylene were used, and film formation was performed under the same conditions as in Example 1. The physical properties of the obtained film are shown in Table 1.

(Comparative Example 1) 160 kg of propylene homopolymer having an isotactic index of 96% and a melt flow rate of 1.5 g / 10 min, and an ethylene content of 30.
Mol%, ethylene-propylene random copolymer 40k
g in a Henschel mixer for 5 minutes, L / D = 2
Melt-kneading pelletizing was carried out at 220 by a 40 mmφ extruder of No. 4. The same high-density polyethylene and low-density polyethylene as in Example 1 were used, and film formation was performed under the same conditions as in Example 1. The physical properties of the obtained film are shown in Table 1.

(Comparative Example 2) Comparative Example 1 is also applied to Comparative Example 2.
Melt-kneading pelletization was performed in the same manner as in (1) to form a film. The same polypropylene and ethylene-propylene random copolymer as in Example 3 were used in the same amount as in Example 3, and a propylene resin composition was obtained in the same manner as in Comparative Example 1. The same high-density polyethylene and low-density polyethylene as in Example 3 were used to obtain a multilayer film. The physical properties of the obtained film are shown in Table 1.

Comparative Example 3 Using the polypropylene resin composition used in Example 1 for the intermediate layer and both surface layers, film molding was carried out in the same manner as in Example 1. The physical properties of the obtained film are shown in Table 1.

(Comparative Example 4) The polypropylene resin composition used in Example 1 was used for the intermediate layer and the inner surface layer, the same high-density polyethylene as in Example 1 was used for the outer surface layer, and the same procedure as in Example 1 was performed. Film forming was performed. The physical properties of the obtained film are shown in Table 1.

Comparative Example 5 The polypropylene resin composition used in Example 1 was used for the intermediate layer and the outer surface layer, the same low density polyethylene as in Example 1 was used for the outer surface layer, and the same procedure as in Example 1 was performed. Film forming was performed. The physical properties of the obtained film are shown in Table 1.

[0036]

[Table 1]

[0037]

As described above, the multilayer film of the present invention has flexibility and excellent dispersibility of the rubber component, and thus has excellent dirt impact strength. In addition, it has low moisture permeability, and also has moisture resistance and low temperature heat sealability.

Claims (4)

[Claims] 1. A propylene-based polymer comprising 1 to 95% by weight of polypropylene and 5 to 99% by weight of an ethylene-propylene random copolymer having an ethylene content of 10 to 90 mol% and having an amorphous part rubber particle diameter of 10 μm or less. An intermediate layer made of a resin composition, an outer layer made of high-density polyethylene having a density of 0.935 g / cm ³ or more, and 0.935 g / c
A multilayer film comprising an inner layer made of low density polyethylene having a density of m ³ or less. 2. The dirt impact strength (method B) is 500.
^2. The multilayer film according to claim 1, wherein the multilayer film has a moisture permeability of 8 g / m ² · 24 hours or less and a heat-sealing temperature between inner layers of 120 ° C. or less. 3. The density of polypropylene in the propylene-based resin composition used for the intermediate layer is 0.89 to 0.92 g.
/ Cm ³ , melt flow rate (230 ° C) is 0.1
90 g / 10 minutes, isotactic index (boiling n-heptane extraction residue) is 75-98%, The multilayer film of Claim 1 or Claim 2 characterized by the above-mentioned. 4. The thickness of the intermediate layer is 30 to 9 of the thickness of all layers.
It is 9%, Any one of Claims 1-3 characterized by the above-mentioned.
The multilayer film according to the item.