JPH0834473A - Bag for liquid - Google Patents

Abstract

PURPOSE:To provide a bag for liquid wherein flexibility is excellent, friction resistance, bending resistance and heat resistance are improved, and heat- sealability is excellent. CONSTITUTION:A bag for liquid is formed by heat-sealing the peripheral edge of a multi-layer film with an internal layer and external layer. The external layer is a polypropylene based resin of which the weight average molecular weight is within the range of 80,000-500,000. Also, the external layer consists of a polypropylene based resin with a composition wherein the resin elution quantity at 0 deg.C or higher and 10 deg.C or lower by the cross fractionation method is 40-70wt.% of the total polypropylene based resin quantity, and the resin elution quantity at 10 deg.C or higher and 65'C or lower is 8-30wt.% of the total polypropylene based resin quantity, and the resin elution quantity at 65 deg.C or higher and 115 deg.C or lower is 15-35wt.% of the total polypropylene based resin quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner bag of a liquid container with a spout or a bag for liquid which is excellent in heat resistance, wear resistance and fold resistance and has excellent flexibility. Is.

[0002]

2. Description of the Related Art Liquid containers having a capacity of 5 liters or more include molded type and heat-sealing film type containers, and have conventionally been containers for drinking water, vinegar, soy sauce, juices, chemicals, agricultural chemicals, etc. Is used as.

In recent years, a back-in box, which is a combination of a heat-sealing film and a cardboard box, has been widely used due to disposal problems and the like. In this case, the film used is required to have excellent flexibility, excellent film strength and strength of the heat-sealed portion, and easy disposal property.

Conventionally, as a film used for a back-in-box, a film containing a polyethylene resin as a main component has been widely used because of its cost and ease of heat fusion.

However, the conventional back-in-box made using only the polyethylene-based resin film has problems in heat resistance, abrasion resistance, and folding resistance, and the outer cardboard box and the film rub against each other during transportation. Film is worn out,
Alternatively, the film is cracked and pinholes are generated, which causes liquid leakage.

[0006]

For this reason, the thickness of the film is thickened, the number of the laminated films is increased, the slippage of the film is improved, and it is combined with another resin film to make up for its drawbacks. It was However, these techniques are not effective because they increase the cost of the film and lengthen the manufacturing process of the film.

In order to solve these problems, for example, Japanese Patent Laid-Open No. 2-69839 proposes to emboss one or both films on both sides of the bag. Further, Japanese Patent Publication No. 3-49820 discloses that
A film has been proposed in which a high-density polyethylene layer obtained by mixing a low-density polyethylene, a copolymer of styrene and butadiene in a specific ratio is laminated.

Further, Japanese Patent Publication No. 4-78467 proposes a multi-layer film comprising a film molded from a composite composition and a film molded from low density polyethylene.

However, even though these films can improve the sliding and impact resistance, they have problems that they are insufficient in abrasion resistance and folding resistance and inferior in heat resistance.

In any case, these methods also have a problem that the cost becomes high, and a liquid bag that sufficiently satisfies the market demand has not been realized.

The present invention solves the above problems and provides a liquid bag having excellent flexibility, improved wear resistance, folding resistance and heat resistance, and excellent heat fusion. The purpose is to provide.

[0012]

The present invention relates to a liquid bag formed by heat-sealing the peripheral portion of a multilayer film having an inner layer and an outer layer, the outer layer having a weight average molecular weight of 80. ，
It is a polypropylene resin in the range of 000 to 500,000, and the resin elution amount by the cross fractionation method at 0 ° C. or higher and 10 ° C. or lower is 40 to 7 of the total polypropylene resin amount.
0% by weight, and the resin elution amount at more than 10 ° C and 65 ° C or less is 8 to 30% by weight of the total polypropylene resin amount, and 6
A liquid bag characterized by comprising a polypropylene-based resin having a composition in which the resin elution amount at a temperature higher than 5 ° C and lower than or equal to 115 ° C is in the range of 15 to 35% by weight of the total polypropylene-based resin.

It is preferable that the inner layer is made of a linear polyethylene resin, and the inner layer and the outer layer are fused.

The present invention will be described in detail below.

The liquid bag of the present invention is a multi-layer film in which an outer layer and an inner layer made of polypropylene resin are laminated, and the peripheral portion of the multi-layer film is heat-sealed.

The thickness of the outer layer is 1 / of the total thickness of the multilayer film.
The range of 3 or less and 1/10 or more is preferable. The thickness of the outer layer is
It is usually 4 to 30 μm.

In the present invention, the weight average molecular weight of the polypropylene resin forming the outer layer can be measured by, for example, high temperature GPC (150 CV) manufactured by WATERS.

The polypropylene resin used in the present invention has a weight average molecular weight of 80,000 to 500,000, preferably 150,000 to 350,000. When the weight average molecular weight is less than 80,000, there is a problem that the strength of the film is insufficient and the impact resistance is poor, and when it exceeds 500,000, the film tends to become cloudy.

The amount of resin eluted by the cross fractionation method used in the present invention is measured as follows.

First, the polypropylene resin is heated to 140 ° C. or at a temperature at which the polypropylene resin is completely dissolved.
It is dissolved in dichlorobenzene, cooled at a constant rate, and a thin polymer layer is formed on the surface of an inert carrier prepared in advance in order of increasing crystallinity and increasing molecular weight. Next, the temperature of the generated polymer layer is continuously or stepwise increased, the concentrations of the components eluted in sequence are detected, and the composition distribution (crystallinity distribution) is measured <temperature rising elution fractionation>. At the same time, the molecular weight and molecular weight distribution of the component are measured by high temperature GPC. For example, the temperature rising elution fractionation (TRE
F = Temperature Rising Elut
ion Fractionation part and high temperature GP
C (SEC = Size Exclusion Chro
cross-fractionation chromatograph <CFC-T150A having a system including
Type: manufactured by Mitsubishi Petrochemical Co., Ltd. can be used.

The polypropylene resin used in the present invention has an elution amount of 40 to 70% by weight of the total polypropylene resin amount at 0 ° C to 10 ° C according to the above cross fractionation method,
It is preferably 50 to 60% by weight. This elution amount is 40
If it is less than 10% by weight, it lacks flexibility and becomes problematic in crease resistance. If it exceeds 70% by weight, it becomes too flexible and its strength is greatly reduced, resulting in impracticality.

Further, by the above-mentioned cross fractionation method, more than 10 ° C. 6
The resin elution amount at 5 ° C. or lower is 8 to 30% by weight of the total polypropylene resin amount.

Further, by the cross fractionation method above 65 ° C. 1
The resin elution amount at 15 ° C or lower is 15 to 35% by weight, preferably 20 to 30% by weight, based on the total amount of polypropylene resin. This is because if it is less than 15% by weight, the heat resistance becomes insufficient, and if it exceeds 35% by weight, the flexibility is lowered and the folding resistance is impaired.

In the polypropylene resin used in the present invention, the elution amount and the weight average molecular weight in each temperature range are within the above ranges, that is, flexibility, heat resistance, abrasion resistance,
It is important for obtaining a film having excellent bending resistance.

The polypropylene resin is produced, for example, by the following multistage polymerization method.

First, as a first step, polymerization is carried out in the presence of a titanium compound catalyst and an aluminum compound catalyst using a propylene monomer and, if necessary, an ethylene monomer or an α-olefin monomer to obtain a first polypropylene resin. . The first polypropylene-based resin may be a propylene homopolymer, a propylene-ethylene copolymer, a propylene-α-olefin copolymer, or the like.

In the second step, the above-mentioned first polypropylene resin containing the titanium compound catalyst and the aluminum compound catalyst and an olefin monomer (eg, ethylene, propylene, or α-olefin) are used.
And are copolymerized to obtain a second polyolefin resin. The second polyolefin resin obtained by this two-step reaction is a propylene-ethylene copolymer or a propylene-α-olefin copolymer, or an ethylene-α
-It can be an olefin copolymer.

Similarly, a multi-step copolymerization reaction can be performed according to the purpose. The feature of this production method is that the polymerization is not completed in one step, but multi-step polymerization of two or more steps is performed. This allows multiple types of polymers to be built up in succession, producing blend-type copolymers at the molecular level, which is quite different from conventional polymer blends.

As a manufacturing method as described above, there is a method described in Japanese Patent Laid-Open No. 4-224809. In this method, as a titanium compound, for example, titanium trichloride and magnesium chloride are co-ground, and this is orthotitanic acid n
A spherical solid titanium catalyst having an average particle diameter of 15 μm obtained by treatment with —butyl, 2-ethyl-1-hexanol, ethyl p-toluate, silicon tetrachloride, diisobutyl phthalate, etc. is used.

In this method, a silicon compound, especially diphenyldimethoxysilane, is added as an electron donor to the polymerization tank, and ethyl iodide is further added. further,
Japanese Unexamined Patent Publication (Kokai) No. 3-977747 discloses that a titanium compound obtained by treating an adduct of magnesium chloride and an alcohol with titanium tetrachloride and an electron donor is used. In addition to these methods, for example, Japanese Patent Laid-Open No.
-96912, 4-96907, 3-
No. 174410, No. 2-170803, No. 2
-170802, 3-205439, 4-153203, and JP 61-4255.
No. 3, for example, describes such a manufacturing method.

In producing the polypropylene resin used in the present invention, any known method as described above can be used. Examples of actual resins obtained by such a production method include "PER" manufactured by Tokuyama Soda Co., Ltd. and "Cataloy" manufactured by Highmont Co., Ltd.

The polypropylene resin includes antioxidants, stabilizers such as ultraviolet absorbers, precipitated barium sulfate,
Fillers such as talc, calcium carbonate, mica and titanium oxide, colorants and the like can be added.

Examples of the resin forming the inner layer of the liquid bag of the present invention include linear low density polyethylene, low density polyethylene, ethylene-vinyl acetate copolymer and the like, and linear low density polyethylene is preferably used. To be Examples of commercially available products include Moretech 0238 (manufactured by Idemitsu Petrochemical Co., Ltd.) and UltoZex 1020 (manufactured by Mitsui Petrochemical Co., Ltd.).
Etc.

The thickness of the inner layer is 2 / of the total thickness of the multilayer film.
It is preferably 3 or more. The thickness of the inner layer is preferably 27 to 60 μm.

In the present invention, a multi-layer film can be obtained by melt-extruding into a sheet by the coextrusion inflation method using the above-mentioned polypropylene resin and the resin forming the inner layer such as linear low-density polyethylene. The multilayer film thus obtained has a thickness of 40 to 9
0 μm is desirable. If it is less than 40 μm, the strength during use may be insufficient, and if it exceeds 90 μm, the flexibility may be poor.

The multilayer film may be colorless and transparent, colored and transparent, or colored and non-transparent.

[0037]

By forming the outer layer of the multi-layer film with the above polypropylene resin, heat resistance, abrasion resistance, bending resistance, strength, etc. are remarkably improved.

Particularly, by forming the inner layer of the liquid bag from a linear polyethylene resin, appropriate heat sealability and seal strength can be secured.

[0039]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 Polypropylene resin (Cataloy KS-052, MF, manufactured by Highmont Co., Ltd.) as an outer layer
R0.8, density 0.90 g / cm ³ ) is used, and linear low-density polyethylene (manufactured by Idemitsu Petrochemical Co., Ltd., Moatech 0238GL, MFR2.1, density 0.918) is used as an inner layer.
g / cm ³ ), a multilayer film having an outer layer / inner layer = 1/3 interlayer ratio and a total layer thickness of 90 μm was produced by a coextrusion inflation method.

The peripheral portion of this film was heat-sealed to obtain a liquid bag.

The results of measuring the physical properties of the film of the obtained liquid bag are shown in Table 1.

The physical properties shown in Table 1 were measured according to the following methods.

Breaking strength and breaking elongation: JIS Z
It was measured according to 1702.

Tear strength: Measured according to JIS Z 1702.

Abrasion coefficient: Measured according to JIS K 7215.

Abrasion resistance: Measured according to JIS L 0849.

Folding endurance: Measured according to JIS P 8115.

Heat resistant temperature: The fusion temperature was measured.

(Embodiment 2) The total layer thickness is 9 by the same method as in Embodiment 1 except that the interlayer ratio of outer layer / inner layer = 1/9.
A 0 μm multi-layer film was produced to obtain a liquid bag.

The results of measuring the physical properties of the produced film under the same conditions as in Example 1 are shown in Table 1.

Comparative Example 1 Ethylene / vinyl acetate copolymer currently used in the market (EVA, vinyl acetate content 1
Table 1 shows the results obtained by measuring the physical properties of a 7%) type single layer film (thickness 90 μm) under the same conditions as in Example 1.

(Comparative Example 2) Linear low-density polyethylene (manufactured by Idemitsu Petrochemical Co., Ltd., Moatech 0238GL, MFR
2.1, density 0.918 g / cm ³ )) was formed into a film having a thickness of 90 μm by the single layer inflation method, and the physical properties thereof were measured under the same conditions as in Example 1 and the results are shown in Table 1.

[0054]

[Table 1]

[0055]

According to the present invention, a liquid bag having excellent flexibility, abrasion resistance, folding resistance and heat resistance can be obtained. Moreover, the thickness of the film is particularly thick as in the past,
Since there is no need to increase the number of layers to be stacked or to improve the slippage of the film, the film can be manufactured at a relatively low cost.

Claims (2)

[Claims] 1. A liquid bag formed by heat-sealing a peripheral portion of a multilayer film having an inner layer and an outer layer, wherein the outer layer has a weight average molecular weight of 80,000 to 500,0.
It is a polypropylene-based resin in the range of 00, and the resin elution amount by the cross fractionation method at 0 ° C or higher and 10 ° C or lower is 40 to 70% by weight of the total polypropylene-based resin amount.
The resin elution amount at more than 0 ° C and less than 65 ° C is 8 to 30% by weight of the total polypropylene resin amount, and the resin elution amount at more than 65 ° C and 115 ° C is 15 to 35% of the total polypropylene resin amount.
A liquid bag comprising a polypropylene resin having a composition within a range of weight%. 2. The liquid bag according to claim 1, wherein the inner layer is made of a linear polyethylene resin, and the inner layer and the outer layer are fusion-bonded to each other.