JPH10166523A - Multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film having excellent heat sealability in the case of forming a composite film by providing excellent impact resistance at a low temperature, excellent heat resistance, transparency and extrusion processability without blushing in retorting treatment. SOLUTION: The multilayer film having a multilayer structure formed of a polyethylene resin at an inner layer side as a sealing surface comprises (a) the inner layer containing resin composition of polyethylene having a density of 0.935g/cm<3> or more and ethylene-a-olefin copolymer having a density of 0.870 to 0.910g/cm<3> , (b) an intermediate layer containing resin composition of ethylene-α-olefin copolymer containing 0.1 to 0.5wt.% of crystal nucleator and a density of 0.935g/cm<3> or more, and (c), an outer layer containing polyethylene having a density of 0.935g/cm<3> or more.

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 improved transparency and whitening, and more particularly, to whitening during retort treatment due to excellent low-temperature impact resistance and excellent heat resistance. Not transparent, yet transparent,
The present invention relates to a multilayer film having excellent extrudability and heat sealability when forming a composite film.

[0002]

2. Description of the Related Art A laminated film for retort food packaging is widely used as a packaging material for food packaging. Conventionally, since the retort treatment conditions are usually around 115 ° C., the sealant film used for the laminate film used for such a purpose must also have heat resistance of 115 ° C. or more. Therefore, a polypropylene resin, a high-density polyethylene resin, or the like, which has excellent heat resistance and sealing properties, has been used as a sealant film.

However, recently, since retort foods are frozen and distributed, impact resistance at low temperatures has become important in order to prevent bag breakage due to falling in a frozen state. For example, when a resin having a low impact strength at a low temperature such as a polypropylene resin is used as a sealant film, there is a problem that the packaging bag is broken at the time of transportation at a low temperature or the like. From the viewpoint of impact resistance at low temperatures, polyethylene is excellent, but polyethylene is inferior in heat resistance and it is necessary to lower the retort temperature because the film is whitened by heating, so sterilization becomes insufficient. There are drawbacks such as long time and poor work efficiency.

Furthermore, when a propylene / ethylene random copolymer resin is used as a sealant film as a polypropylene resin, heat during retort treatment causes the sealant layers to be thermally fused to each other, resulting in a decrease in opening property and a decrease in the content. There is a drawback that it is difficult to take out, and when propylene / ethylene block copolymer resin or high-density polyethylene resin is used as the sealant layer, stable heat sealing is difficult due to the high melting point of these resins, and sealing There is a drawback that a bag breaking trouble or the like due to detachment easily occurs.

On the other hand, linear low-density polyethylene (ethylene / α-olefin copolymer) is excellent in transparency, impact strength at low temperatures, and sealability, and is a sealant conventionally used for boil sterilization up to about 100 ° C. Used as a film. However, since the melting point of linear low-density polyethylene is as low as about 125 ° C., the retort treatment at 115 ° C. makes the sealant layers more easily heat-sealed than in the case of a propylene / ethylene random copolymer.
It could not be used as a sealant layer of a laminated film for retort food packaging.

[0006]

DISCLOSURE OF THE INVENTION The present invention has excellent impact resistance at low temperatures and excellent heat resistance, so that it does not cause whitening during retort treatment, and has a high transparency, extrudability and a composite film. And to provide a multilayer film having excellent heat sealability.

[0007]

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, the inner layer and the intermediate layer have a specific resin composition, and the outer layer has a multilayer resin having a specific resin. Since the film is excellent in impact resistance at low temperatures and excellent in heat resistance, it does not cause whitening in the retort, and is excellent in transparency, extrudability and heat sealability when forming a composite film, and the present invention was found. It was completed.

That is, the present invention relates to a multilayer film having a multilayer structure comprising a polyethylene resin having an inner layer side as a sealing surface, wherein (a) an inner layer of polyethylene having a density of 0.935 g / cm ³ or more (hereinafter referred to as [A ]) And ethylene • α- having a density of 0.870 to 0.910 g / cm ^3.
A resin composition comprising an olefin copolymer (hereinafter, referred to as [B]);
A resin composition containing 0.5% by weight of an ethylene / α-olefin copolymer having a density of 0.935 g / cm ³ or more (hereinafter referred to as [A ']). A multi-layer film comprising 935 g / cm ³ or more of polyethylene [A].

In the present invention, the inner layer (a) comprises the resin composition of [A] and [B], and has a density of 0.9 as [A].
Heat resistance is imparted by using polyethylene of 35 g / cm ³ or more, and film impact resistance and seal are imparted by using an ethylene / α-olefin copolymer as [B].

The intermediate layer (b) contains a nucleating agent of 0.1
A resin composition comprising [A '] containing from 0.1 to 0.5% by weight, and more preferably from [A'] and [B] containing from 0.1 to 0.5% by weight of a nucleating agent. Is a resin composition. The nucleating agent added to this intermediate layer provides transparency and whitening resistance. The outer layer (c) is a layer made of [A] and having a role of preventing bleed out of the crystal nucleating agent added to the intermediate layer (b).

In the present invention, [A] used for the inner layer and the outer layer is a polyethylene having a density of 0.935 g / cm ³ or more, and when a polyethylene having a density of less than 0.935 g / cm ³ is used, a multilayer obtained is used. It is not preferable because the heat resistance of the film deteriorates.

In the present invention, the density is 0.93.
If it is 5 g / cm ³ or more, an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 or more carbon atoms can be used. Such a polyethylene is, for example, a metallocene catalyst described below. Or a conventionally known polymerization method using a conventionally known Ziegler catalyst.

The [A] used in the inner layer and the outer layer in the present invention may be polyethylene having a density of 0.935 g / cm ³ or more, and usually, the upper limit of the density is 0.950 g / cm ³ or less. Things are used. When used for the inner layer and the outer layer, each may be different or the same.

The polyethylene of [A] used in the present invention is excellent in flowability and processability at the time of forming a multilayer film, and has a high film impact resistance of the obtained multilayer film. The melt flow rate measured under a load is preferably in the range of 0.1 to 20 g / 10 minutes.

In the present invention, [A] used for the intermediate layer
'] Is ethylene • having a density of 0.935 g / cm ³ or more.
It is an α-olefin copolymer. The density is 0.935g /
It is not preferable to use an ethylene / α-olefin copolymer having a size of less than ³ cm ³ because the heat resistance of the obtained multilayer film deteriorates.

[B] used in the inner layer and the intermediate layer in the present invention is an ethylene / α-olefin copolymer. [B] used for the inner layer and the intermediate layer in the present invention may be an ethylene / α-olefin copolymer, and when used for the inner layer and the intermediate layer, they may be different or the same.

The α-olefin copolymerized with ethylene of [A ′] and [B] includes those having 3 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene and 1-hexene. Octene, 1-heptene, 4-methylpentene-1, 4-methylhexene-1, 4,4-dimethylpentene-1, octadecene and the like can be mentioned. It is preferable to use 1-hexene, 1-octene, 1-heptene, and 4-methylpentene-1 among these α-olefins, and 1-hexene is particularly preferable. [B] used in the present invention has a density of 0.870 to
It is an ethylene / α-olefin copolymer in the range of 0.910 g / cm ³ .

Further, the ethylene / α-olefin copolymer has a weight average molecular weight (M _w ) measured by gel permeation chromatography (GPC) since a multilayer film having particularly excellent film impact resistance can be obtained. it preferably has a specific number average molecular weight _{(M n) (M w /} M n) is 3 or less.

Further, since the ethylene / α-olefin copolymer has a uniform composition distribution, it is possible to obtain a multilayer film having particularly excellent film impact resistance. Therefore, the ethylene / α-olefin copolymer is measured by a differential scanning calorimeter (DSC). The temperature (T _m (° C.)) at the maximum peak position of the obtained endothermic curve and the number of short-chain branches per 1,000 carbon atoms (SCB) determined from the measurement of ¹³ C-NMR spectrum satisfy the relationship of the formula (1). Preferably, it is

T _m <−1.8 × SCB + 138 (1) As [B] used in the present invention, any ethylene / α-olefin copolymer can be used. In particular, it is preferable to use an ethylene / α-olefin copolymer satisfying the above characteristics.
In such an ethylene / α-olefin copolymer, a ligand having one or two cyclopentadienyl skeletons is bonded to a transition metal belonging to Groups IVb to VIb of the periodic table, for example, titanium, zirconium or hafnium. Catalysts that combine alumoxane with metallocene compounds,
The metallocene compound and the metallocene compound can be produced by using a catalyst system containing a compound capable of ionizing the metallocene compound to generate a cationic metallocene compound as a basic component.

Examples of the method for producing an ethylene / α-olefin copolymer using the above catalyst system include a gas phase method, a slurry method, a solution method, and a high pressure ionic polymerization method. Among them, it is preferable to produce the ethylene / α-olefin copolymer by a solution method in which polymerization is performed at a temperature from the melting point of the produced ethylene / α-olefin copolymer to 280 ° C., and a high-pressure ionic polymerization method, and particularly the ethylene / α-olefin copolymer used in the present invention. as,
It is preferable to produce by a high pressure ion polymerization method. Incidentally, the high pressure ionic polymerization method means that the pressure as described in JP-A-56-18607 and JP-A-58-225106 is 200 kg / cm ² or more, preferably 300 to ² kg / cm ^2.
000 kg / cm ² , temperature 125 ° C. or higher, preferably 1
This is a continuous method for producing an ethylene polymer, which is carried out under a reaction condition of 30 to 250 ° C, particularly preferably 150 to 200 ° C.

In the present invention, the intermediate layer contains a nucleating agent in an amount of 0.1 to 0.5% by weight, preferably 0.15 to 0.35%.
% By weight. The nucleating agent is not particularly limited as long as it acts as a nucleating agent, but usually, an organic crystal nucleating agent can be preferably used. And, for example, as organic carboxylic acid metal salts, sodium benzoate, aluminum benzoate, sodium p-tert-butyl benzoate, aluminum p-tert-butyl benzoate,
Sodium adipate, aluminum adipate, etc., and especially p-tert
Preference is given to using -butyl aluminum benzoate.

When the content in the intermediate layer is less than 0.1% by weight, the resulting multilayer film has insufficient transparency or whitening resistance. On the other hand, if it exceeds 0.5% by weight, there may be a problem that the nucleating agent is more likely to be bleached than the intermediate layer.

Since the multilayer film of the present invention has excellent heat resistance and workability during production, the inner layer in the composition may have [A]: [B] = 90: 10 to 40:60 (weight) Ratio), and preferably comprises a resin composition having a density of 0.930 g / cm ³ or more and a melt flow rate of 0.1 to 20 g / 10 min. When the composition of [A '] and [B] is used for the intermediate layer in the structure, [A']: [B] = 9
A resin composition obtained in a range of 0:10 to 40:60 (weight ratio), wherein the density of the resin composition is 0.930 g / c.
m ³ or more, melt flow - rate is 0.1 to 20 g / 10
It is preferable that the resin composition is a resin composition.

The multilayer film of the present invention may contain commonly used auxiliary additives such as an antioxidant, a lubricant, an anti-blocking agent, an antistatic agent, a neutralizing agent and the like without departing from the object of the present invention. May be.

The multilayer film of the present invention can be obtained by a general film production method.
[B] A multilayer film by melt-mixing a crystal nucleating agent or the like using a single-screw extruder, a twin-screw extruder, a Banbury mixer or the like, forming a resin composition and then subjecting it to inflation film processing or T-die film processing. Can be molded as

The multilayer film of the present invention is used as a sealant multilayer film for lamination since it has particularly excellent sealing properties and film impact resistance.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Synthesis Example Diphenylmethylene (cyclopentadienyl) (fluorenyl) zirconium dichloride: N, N-dimethylaniliumtetrakis (pentafluorophenyl) borate: triisobutylaluminum = 1: 2: 250
(Molar ratio), a polymerization temperature of 150 to 175 ° C. and a polymerization pressure of 900 kgf / cm.
^{In step 2} , ethylene and 1-hexene were copolymerized to obtain an ethylene / 1-hexene copolymer (1) and an ethylene / 1-hexene copolymer (2).

The obtained ethylene / 1-hexene copolymer (1) and ethylene / 1-hexene copolymer (2) were measured by the following method.

Density: The resin component was heat-treated with hot water at 100 ° C. for 1 hour, and measured using a density gradient tube maintained at 23 ° C. in accordance with JIS K6760 (1981).

Melt flow rate (MFR): JIS
It was measured in accordance with K7210 (1976).

Weight average molecular weight (M _w ), number average molecular weight (M _n ): M _w and M _n are 150C manufactured by Nippon Millipore Co., Ltd.
ALC / GPC (Column: GMHHR, manufactured by Tosoh Corporation)
-H (S), three 7.8 mm ID × 30 cm, solvent:
It was measured by gel permeation chromatography (GPC) using 1,2,4-trichlorobenzene, temperature: 140 ° C., flow rate: 1.0 ml / min, and injection concentration of 1 mg / 1 ml (injection amount: 300 μl). The column elution volume was calibrated by universal calibration using standard polystyrene manufactured by Tosoh Corporation.

Number of short-chain branches: Calculated by measuring ¹³ C-NMR spectrum (JNM GX400 manufactured by JEOL Ltd.) using a solution containing orthodichlorobenzene as a solvent at 100 MHz.

Melting point: Measured using a differential scanning calorimeter (DSC) (DSC-7 manufactured by PerkinElmer). D
After melting the sample at 200 ° C. for 5 minutes in the SC furnace,
Solidification (crystallization) by lowering the temperature to 30 ° C at a rate of ° C / min.
The temperature at the maximum peak position (T _m (° C.)) of the endothermic curve obtained by heating the sample at a rate of 10 ° C./min.
Was measured.

The obtained results are shown in Table 1 (ethylene / 1-hexene copolymer (1)) and Table 2 (ethylene / 1-hexene copolymer (2)).

Reference Example Table 3 shows commercially available ethylene / 1-hexene copolymer (3)
(Product name: Nipolon-Z; ZF260-, manufactured by Tosoh Corporation)
1, the density is 0.935 g / cm ³ , and the melt flow rate is 2.0 g / 10 min).

Table 4 shows commercially available ethylene / 1-butene copolymer (4) (trade name LUMITAC; 2 manufactured by Tosoh Corporation).
2-1; density: 0.900 g / cm ³ ; melt flow rate: 2.0 g / 10 minutes).

Example 1 For the inner layer, the ethylene / 1-hexene copolymer (1) and the ethylene / 1-hexene copolymer (2) obtained in the synthesis examples were used as (1) :( 2) = 85: 15, and 0.15 part by weight of an antioxidant (manufactured by Ciba Geigy, trade name Irganox 1076) based on 100 parts by weight of the composition;
Antioxidant (Circa Geigy, trade name Irgafos1
68) 0.10 parts by weight, 0.3 parts by weight of silica as an anti-blocking agent and 0.0 of erucamide as a lubricant
4 parts by weight were melt-mixed to obtain an inner layer resin composition.

The density of the inner layer resin composition is 0.931 g /
cm ³ , and the melt flow rate was 2.3 g / 10 min.

As the intermediate layer, the resin composition 1 for the inner layer was used.
To 00 parts by weight, 0.2 part by weight (0.2% by weight in the resin composition) of aluminum p-tert-butyl benzoate (manufactured by Shell Chemical) as a nucleating agent was melt-mixed to obtain a resin composition for an intermediate layer. Was.

The density of the intermediate layer resin composition is 0.931.
g / cm ³ , and the melt flow rate was 2.3 g / 10 minutes.

For the outer layer, 100 parts by weight of the ethylene / 1-hexene copolymer (1) obtained in the synthesis example was added with an antioxidant (trade name: Irganox 107, manufactured by Ciba-Geigy).
6) 0.15 parts by weight, 0.10 parts by weight of an antioxidant (trade name: Irgafos 168, manufactured by Ciba Geigy), 0.3 parts by weight of silica as an anti-blocking agent, and 0.04 parts by weight of erucamide as a lubricant were added. The mixture was melt-mixed to obtain an outer layer resin composition.

The density of the outer layer resin composition is 0.935 g.
/ Cm ³ , and the melt flow rate was 2.0 g / 10 minutes.

Each of the obtained resin compositions for the inner layer, the intermediate layer and the outer layer was blown up at a processing temperature of 180 ° C. using an inflation multilayer molding machine equipped with a multilayer die having a die diameter of 175 mm and a die slip clearance of 2.0 mm. By forming a film with a ratio of 1.6, a surface tension of 4
A multilayer film having a thickness of 60 μm subjected to a corona treatment of 2 dyn / cm was obtained.

The obtained multilayer film was measured and evaluated by the following methods.

Haze: An index of transparency was measured according to ASTM D1003.

ΔHaze: The following method was used as an index of heat resistance and whitening property.

A biaxially stretched polyamide film having a substrate thickness of 15 μm and the obtained multilayer film (inner layer: intermediate layer: outer layer =
1: 2: 1) with an ester-based adhesive for dry lamination, followed by dry lamination at 40 ° C. in an atmosphere.
The laminate film was obtained by aging for a day. Put the degassed purified water into a 10 cm x 10 cm bag created by heat sealing this laminate film,
It was heat-sealed without air and sealed. Next, the bag filled with purified water is heated in a retort high-temperature and high-pressure steam sterilizer (Hisaka Seisakusho Co., Ltd.), and the retort treatment is performed at 115 ° C. for 30 minutes. The degree of whitening by this operation was represented by the difference in haze before and after the retort (ΔHaze).

The smaller the value of ΔHaze, the smaller the whitening and the better the heat resistance.

Whitening: The deterioration of the transparency of the film (whitening state) was visually evaluated.

Evaluation criteria ：: No whitening phenomenon Δ: Slight whitening phenomenon ×: Whitening phenomenon occurred Fusing resistance: Evaluation was made based on the presence or absence of inner surface fusion.

Evaluation criteria ○: No fusion ×: Fusion occurred Deformation: Evaluation was made based on the presence or absence of film deformation (wrinkles, distortions, etc.).

Evaluation Criteria 変 形: No deformation ×: Deformation Impact resistance at low temperature: 15c prepared by the above method (2)
A saline solution was put into a bag of mx 20 cm, and heat sealed and airtight without air. After adjusting 10 of these bags, they were cooled to 0 ° C.
m was dropped freely onto a concrete floor from a height of m, and the number of drops until all bags were broken was determined. Table 5 shows the measurement results.

Example 2 A multilayer film was obtained in the same manner as in Example 1, except that the ethylene / 1-hexene copolymer (2) was not used in the resin composition for the intermediate layer.

The obtained multilayer film was evaluated and measured in the same manner as in Example 1. Table 5 shows the obtained results.

Comparative Example 1 In Example 1, the same measurement and evaluation as in Example 1 were carried out except that the ethylene / 1-hexene copolymer (2) and the crystal nucleating agent shown in Table 2 were removed from the intermediate layer.

Comparative Example 2 Commercially available ethylene / 1-hexene copolymer (3) (Nipolon-Z; ZF260-1 manufactured by Tosoh Corporation) was used as the resin composition for the inner layer, the intermediate layer and the outer layer. Example 1 except that no nucleating agent was used in the resin composition for the intermediate layer.
A multilayer film was obtained in the same manner as described above.

The obtained multilayer film was evaluated and measured in the same manner as in Example 1. Table 5 shows the obtained results.

Comparative Example 3 The resin composition for the inner layer, the intermediate layer and the outer layer was ethylene / 1
-Instead of hexene copolymer (1), commercially available ethylene
Using 1-hexene copolymer (3) (manufactured by Tosoh Corporation, trade name Nipolon-Z; ZF260-1), ethylene / 1
-Instead of hexene copolymer (2), commercially available ethylene
1-butene copolymer (3) (trade name L, manufactured by Tosoh Corporation)
Using UMITAC 22-1), a multilayer film was obtained in the same manner as in Example 2 except that no crystal nucleating agent was used in the resin composition for the intermediate layer. At that time, the density of the inner layer resin composition was 0.930 g / cm ³ , and the melt flow rate (MFR) was 2.0 g / 10 minutes.

The obtained multilayer film was evaluated and measured in the same manner as in Example 1. Table 5 shows the obtained results.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

[0067]

As described above, the multilayer film of the present invention has excellent impact resistance at low temperatures and excellent heat resistance, so that it does not cause whitening during retort treatment, and has transparency, extrudability and composite film properties. Excellent heat sealability.

[0068]

Claims (6)

[Claims] 1. A multilayer film having a multilayer structure composed of a polyethylene resin having a sealing surface on the inner layer side, wherein (a) the inner layer is polyethylene having a density of 0.935 g / cm ³ or more and a density of 0.870 to 0.910 g / cm ^{3. 3} ethylene ・ α
A resin composition comprising an olefin copolymer, (b) an ethylene / α-olefin copolymer having a density of 0.935 g / cm ³ or more, wherein the intermediate layer contains a crystal nucleating agent in an amount of 0.1 to 0.5% by weight. (C) an outer layer having a density of 0.9
A multilayer film comprising polyethylene of 35 g / cm ³ or more. (B) The intermediate layer contains a nucleating agent in an amount of 0.1 to 0.5.
Ethylene / α-olefin copolymer having a density of 0.935 g / cm ³ or more and a density of 0.870 to
2. The multilayer film according to claim 1, wherein the resin film is a resin composition comprising 0.910 g / cm ^{3 of} an ethylene / α-olefin copolymer. 3. 3. The resin composition of the intermediate layer (b) has a density of 0.9.
Weight ratio of 35 g / cm ³ or more ethylene · alpha-olefin copolymer and a density 0.870~0.910g / cm ³ ethylene · alpha-olefin copolymer 90: 10 to 4
0:60 and the density of the resin composition is 0.9.
The melt flow rate measured at 190 ° C. under a load of 2160 g is 0.1 to 20 g / cm ³ or more.
The multilayer film according to claim 2, wherein the time is 10 minutes. 4. The resin composition according to claim 1, wherein said resin composition has a density of 0.93.
5 g / cm ³ or more polyethylene and density 0.870～
The weight ratio of the ethylene / α-olefin copolymer of 0.910 g / cm ³ is 90:10 to 40:60, and
The density of the resin composition is 0.930 g / cm ³ or more, and the melt flow rate measured at 190 ° C. under a load of 2160 g is 0.1 to 20 g / 10 minutes. 4. The multilayer film according to any one of 3. 5. An ethylene / α-olefin copolymer having a density of 0.870 to 0.910 g / cm ³ , wherein (i) the α-olefin has 3 to 20 carbon atoms, and (ii) 190 ° C.
The melt flow rate measured under a load of 2160 g is in the range of 0.1 to 20 g / 10 minutes, and (iii) the weight average molecular weight (M _w ) and the number average molecular weight (M _w ) measured by gel permeation chromatography (GPC). (M _n ), the ratio (M _w / M _n ) is 3 or less, and (iv) the temperature (T _m (° C.) at the maximum peak position of the endothermic curve obtained from the measurement by the differential scanning calorimeter (DSC). ) And the short-chain branch number (SCB) per 1000 carbon atoms determined from the measurement of the ¹³ C-NMR spectrum are ethylene / α-olefin copolymers satisfying the relationship represented by the following formula (1). The multilayer film according to any one of claims 1 to 4, wherein: T _m <−1.8 × SCB + 138 (1) 6. The multilayer film according to claim 1, wherein the multilayer film is a sealant multilayer film for lamination.