JPH11292992A - Sealant film - Google Patents

Abstract

(57) [Summary] A retort treatment at a temperature of 121 ° C. or more is possible and
Sea run hard to break into bags even when frozen
Provide film. The sealant film has a density of 0.935.
~ 0.965g / cm^ThreeAnd MI at 190 ° C.
Linear low-density polymer in the range of 1-10.0 g / 10 minutes
70 to 98 parts by weight of a styrene resin and a flexural modulus of 50 to
500kg / cm ^TwoHas a melting point in the range of 60 to 90 ° C.
Polyethylene resin or flexural modulus of 500-4
000kg / cm^TwoWith melting point in the range of 130-170 ° C
30 to 2 parts by weight of a certain polypropylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealant film which is excellent in heat resistance, impact resistance, cold resistance, pinhole resistance and the like, and is suitable for heat-resistant packaging bags.

[0002]

2. Description of the Related Art Conventional sealant films are roughly classified into those made of polypropylene resin and those made of polyethylene resin.

As an example of a polypropylene-based resin sealant film, there is an extrusion-formed film of a propylene-ethylene random copolymer or a random polypropylene-type resin composition obtained by mixing an ethylene-based elastomer with the copolymer. This propylene-ethylene random copolymer has, for example, an ethylene content of about 2 to 3% and a melting point of 1%.
It has a melt flow rate (MFR) of about 5 to 10 at about 40 to 145 ° C.

As the ethylene-based elastomer, an ethylene-propylene elastomer and an ethylene-butylene elastomer are often used (JP-A-5-26290).
No. 0).

Another example of a polypropylene-based resin sealant film is an extrusion-formed film of a propylene-ethylene block copolymer or a block polypropylene-type resin composition obtained by mixing an ethylene-based elastomer with the propylene-ethylene block copolymer (Japanese Unexamined Patent Publication (Kokai) No. 2002-282686). See JP-A-59-11512.

On the other hand, as a polyethylene resin sealant film, a high-density polyethylene resin composition obtained by mixing a high-density polyethylene with a polyethylene elastomer or the like is formed by extrusion film formation, or a polymer is formed by a Ziegler-Natta catalyst. There is an extrusion-formed film of a linear low-density polyethylene type resin composition obtained by mixing a high-density polyethylene with the obtained linear low-density polyethylene (see JP-A-8-3383).

[0007]

However, each of the above conventional sealant films has the following problems.

First, a sealant film formed by extruding a random polypropylene-type resin composition into a film has good transparency and heat resistance up to about 125 ° C. (For example, 0 ° C. or less), the impact resistance is poor, and therefore, it is not suitable for the material of bags for frozen distribution.

A sealant film formed by extruding a block polypropylene type resin composition into a film has better impact resistance than a film made of the above random type resin composition, and has heat resistance up to about 135 ° C. Inferior in transparency, high heat sealing temperature, so that the laminated base material is limited to a material having good heat resistance, and also has poor impact resistance at low temperature (for example, 0 ° C. or less), and therefore bags for frozen distribution. Not suitable for materials.

Next, a sealant film formed by extruding a high-density polyethylene type resin composition into a film is
Although it has heat resistance up to about 5 ° C., its impact resistance is not always sufficient.

A sealant film formed by extruding a resin composition of a linear low-density polyethylene type is excellent in impact resistance and does not decrease in impact resistance even at a low temperature.
Since it has heat resistance of only about 5 ° C., its use is limited. (The bag made of this film is difficult to open because the inner surfaces are fused together, and stress is concentrated on the fused part during transportation. Holes and breaks easily occur).

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a sealant film having the following characteristics in view of the advantages and disadvantages of the above-mentioned various retort sealant films.

Heat resistance: Withstands retort treatment at 121 ° C., which is the most common heat treatment temperature.

Impact resistance: comparable to the impact resistance of the conventional linear low density polyethylene type.

Cold resistance: no deterioration in physical properties even at −20 ° C.
It can withstand frozen food packaging.

Pinhole resistance: No pinholes are generated at the time of transportation even at normal temperature or low temperature.

In recent years, demand for processed foods such as canned foods, bottled foods, frozen foods, retort foods and the like has been increasing with the change of lifestyle. In particular, retort foods are widely used not only by ordinary households but also by family restaurants, various types of food service industries such as lunch boxes, etc., because of ease of handling, hygiene, improvement of taste by processing technology, easy disposal, etc. The type and content of the contents are becoming increasingly diversified.

Originally, retort treatment was invented as a means of preserving food for a long period of time, and the original form was canned. However, with the recent development of plastic materials and secondary processing technology, handling has become difficult. Bags (pouches) that are excellent in quality are becoming mainstream.

According to the current Japanese Agricultural Standards, "retort food"
Is a package made of plastic film or metal foil or a multi-layered combination of these in a bag or other shape (limited to air-tight and light-shielding), And sterilized under pressure and heat. " Although there is a description of airtightness and light-shielding property here, this is a necessary item for a preserved food, which enables long-term storage at room temperature. On the other hand, there are cases where food is filled in a transparent bag, although retort treatment is mainly used as a cooking means, although it is out of the agricultural and forestry standard. Such a bag has the advantage that the contents are visible, although the storage stability is reduced.

[0020] In the case of foods which are expected to have a high distribution speed and a short time from production to use, those packaged in a bag of a simple layer structure film of base film (or barrier base film) / sealant film may be used. Many. As the base film, a biaxially stretched film of polypropylene, nylon, polyester, or the like is generally used. To impart gas barrier properties, such a base film is coated with polyvinylidene chloride or an ethylene-vinyl alcohol copolymer layer. And the like are used. The most common sealant film is the above-mentioned random polypropylene type film. This is due to the fact that it shows heat resistance to the most common retort treatment temperature of 120 to 125 ° C., the heat sealing temperature is appropriately low, and the transparency is good. Among the other types of resin films, the linear low-density polyethylene resin film has a shortage of heat resistance, and the block polypropylene resin film has a disadvantage that the sealing temperature is too high and the appearance is slightly inferior.

However, a new type of food distribution method has recently been emerging. That is, this is a method in which the food packed in the bag is retorted and then distributed at a low temperature. According to this, it becomes possible to omit the barrier layer from the film laminated structure of the bag. However, on the other hand, the conventional type has a problem with the sealant film. That is, the polypropylene-type resin film suffers from problems such as bag breakage at the time of low-temperature distribution due to deterioration in physical properties at low temperature, and no linear low-density polyethylene-type resin film has heat resistance of 121 ° C. or more.

In view of the above, an object of the present invention is to provide a sealant film that can be retorted at a temperature of 121 ° C. or higher and hardly causes a bag breakage problem even when frozen and distributed.

[0023]

The present invention has been devised to achieve the above object, and the first sealant film has a density of 0.935 to 0.965 g / cm ³ , 190
Melt index at ° C (hereinafter abbreviated as MI)
Is 0.1 to 10.0 g / 10 min, preferably 0.5 to
70 to 98 parts by weight of a linear low-density polyethylene resin in a range of 3.5 g / 10 minutes, and a flexural modulus of 50 to 500.
kg / cm ² , and 30 to 2 parts by weight of a polyethylene resin having a melting point in the range of 60 to 90 ° C.

The second sealant film has a density
Is 0.935 to 0.965 g / cm ^ThreeAt 190 ° C
MI is 0.1 to 10.0 g / 10 min, preferably 0.1 to 10.0 g / 10 min.
Linear low density polyethylene in the range of 5 to 3.5 g / 10 minutes
70-98 parts by weight of a lene resin and a flexural modulus of 500-
4000 kg / cm^Two, Melting point of 130-170 ° C
30 to 2 parts by weight of polypropylene resin
Things.

As the linear low-density polyethylene resin,
Conventionally generally used linear low-density polyethylenes such as C4, C6 and C8 (C4, C6 and C8 mean the carbon number of the α-olefin comonomer used in the production of the polyethylene-based resin) and high-density polyethylenes A linear low-density polyethylene-based resin containing 50% by weight or less of high-density polyethylene can be used.
It is desirable that the comonomer used has a certain number of carbon atoms.

Further, one of the linear low-density polyethylene resins
The value of MI at 90 ° C. is 0.1 to 10.0 g / 10
Min, preferably 0.5 to 3.5 g / 10 min. If the MI falls below the range of 0.1 to 10.0 g / 10 minutes, there is a problem in film formability, and if the MI exceeds the above range, the resulting film tends to have poor impact strength. The density value of the linear low-density polyethylene resin is 0.935 to 0.9.
It is in the range of 65 g / cm ³ . When the density is lower than the above range, the obtained film tends to be blocked, and when the density is higher than the above range, the pinhole resistance of the film may be inferior.

In the first sealant film, the polyethylene resin has a flexural modulus of 50 to 500 kg / cm.
^{2. It has} a melting point of 60 to 90 ° C. If the flexural modulus of the polyethylene resin exceeds the above range, the obtained film may lack pinhole resistance, and if it is below the above range, blocking may easily occur.

The ratio of the linear low-density polyethylene resin to the polyethylene resin or polypropylene resin is 70 to 98 parts by weight of the former and 30 to 2 parts by weight of the latter.
If the ratio of the latter is more than the above range, the obtained film tends to cause blocking, and if it is less than the above range, the pinhole resistance of the film may not be exhibited.

In the second sealant film, the polypropylene resin has a flexural modulus of 500 to 4000 kg.
/ Cm ² and a melting point of 130 to 170 ° C.
If the flexural modulus of the polypropylene-based resin exceeds the above range, the resulting film may lack pinhole resistance, and if it falls below the above range, there is a risk of blocking.

Mixing of a linear low density polyethylene resin and a polyethylene resin in the first sealant film,
And, the mixture of the linear low-density polyethylene resin and the polypropylene resin in the second sealant film,
It can be made by a usual resin mixing method, and is not particularly limited. For example, both resins may be melt-kneaded by a twin-screw extruder or the like, or pellets of each resin may be dry-blended by a Banbury mixer or the like.

The above resin mixture can be molded by arbitrarily adding commonly used additives as long as the properties of the obtained sealant film are not impaired.

The method for forming a film from the above resin mixture is not particularly limited, and ordinary plastic film forming methods such as inflation extrusion molding and T-die extrusion molding can be applied.

The thus obtained sealant film of the present invention is often used by laminating it with another plastic film or metal foil. For example, when the packaged object dislikes light or requires long-term storage, an aluminum foil is attached to the sealant film. When a higher strength is required for the film, a biaxially stretched film of polypropylene, nylon, polyester, or the like is laminated on the sealant film. When a gas barrier property is required, a film obtained by coating such a biaxially stretched film with polyvinylidene chloride or laminating an ethylene-vinyl alcohol copolymer layer is used. In each case, the sealant film according to the present invention is used to seal the bag at the innermost layer of the bag.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
The present invention is not limited to these examples.

[Example 1] The density was 0.940 g / c.
m ³ , a density of 0.961 g / 60 parts by weight of a linear low-density polyethylene having an MI of 2.0 g / 10 min at 190 ° C. (“MORETECH 0278N” manufactured by Idemitsu Petrochemical Co., Ltd.)
cm ^3, high density polyethylene MI is 1.0 g / 10 min at 190 ° C. (manufactured by Japan Polychem Corporation "Novatec HD · HY540") by mixing 40 parts by weight, density of 0.948g / cm ^3, 190 ℃ Has an MI of 1.6
A linear low-density polyethylene resin having a flow rate of 5 g / 10 minutes was obtained.

This linear low-density polyethylene resin 100
A polyethylene elastomer having a density of 0.870 g / cm ³ , a flexural modulus of 204 kg / cm ² , and a melting point of 69 ° C. (“Engage EG8 manufactured by Dow Chemical Co., Ltd.)
200 ") 10 parts by weight, and the mixture was formed into a film having a thickness of 70 μm using an inflation molding machine.
A sealant film was obtained.

One side of the obtained film was subjected to a corona treatment, and a biaxially stretched nylon film was adhered to the treated surface with a polyester adhesive to obtain a composite film.

Example 2 100 parts by weight of the linear low-density polyethylene resin obtained in Example 1 had a flexural modulus of 1
20 kg by weight of a soft polypropylene resin having a melting point of 164 ° C. and 500 kg / cm ² was mixed, and this mixture was formed into a film having a thickness of 70 μm by an inflation molding machine to obtain a sealant film.

Using the resulting film, a composite film was obtained in the same manner as in Example 1.

Example 3 A composite film was obtained in the same manner as in Example 1, except that the ratio of the polyethylene elastomer to 100 parts by weight of the linear low-density polyethylene resin was changed to 20 parts by weight.

[Comparative Example 1] A density of 0.940 g / c
A linear low-density polyethylene having an m ³ of 190 g and an MI at 190 ° C. of 2.0 g / 10 min was formed into a 70 μm thick film by an inflation molding machine.

Using the resulting film, a composite film was obtained in the same manner as in Example 1.

Comparative Example 2 The linear low-density polyethylene resin obtained in Example 1 was formed into a film having a thickness of 70 μm using an inflation molding machine.

Using the resulting film, a composite film was obtained in the same manner as in Example 1.

Evaluation Test The following items were evaluated for the five types of films obtained in Examples and Comparative Examples by the following test methods.

A) Measurement of retort blocking A bag of 80 × 100 mm was formed from the above laminated film with the sealant film layer as the innermost layer. 3 ml in this bag
Of water, and the mouth was closed with a zem clip to forcibly create a blocking state. Temperature 118
After performing a retort treatment at 30 ° C. or 121 ° C. for 30 minutes, the blocking portion was cut into a strip having a width of 15 mm, and the strength of the obtained test piece was measured according to a tensile test of JIS-K7127.

B) Method for Measuring Dart Impact After the bag sample was allowed to stand for 5 hours at an ambient temperature of −20 ° C., the dart impact was measured according to the method B of JIS-K7127.

C) Method of measuring the number of pinholes Using a test piece of the above laminated film of 200 mm × 300 mm, a bending test of the film (Gerboflex 500 times) was performed according to ASTM-F392. The numerical values in the table represent the number of pinholes after bending (n = 3).

D) Appearance of retort A bag of 150 × 200 mm was formed from the above laminated film with the sealant film layer as the innermost layer. About 1 in this bag
50 ml of water was sealed, and retort treatment was performed at a temperature of 121 ° C. for 30 minutes. After the treatment, the surface appearance of the film was observed and evaluated. The evaluation criteria are as follows.

：: wrinkles are generated Δ: wrinkles are partially observed X: wrinkles are observed almost all over Table 1 shows the evaluation results.

[0051]

[Table 1] As can be seen from Table 1, the bag constituted by using the sealant film according to the present invention has heat resistance and cold resistance to withstand retort treatment, and is excellent in pinhole resistance.

[0052]

According to the present invention, it is possible to provide a sealant film which can be subjected to a retort treatment at a temperature of 121 ° C. or higher and hardly causes a bag breakage problem even when it is frozen and distributed.

Claims (2)

[Claims] (1) a density of 0.935 to 0.965 g / cm;
^{3. A} linear low-density polyethylene resin having a melt index in the range of 0.1 to 10.0 g / 10 min.
Parts by weight, a polyethylene resin 30 having a flexural modulus of 50 to 500 kg / cm ² and a melting point of 60 to 90 ° C.
~ 2 parts by weight of a sealant film. 2. Density of 0.935 to 0.965 g / cm
^{3. A} linear low-density polyethylene resin having a melt index in the range of 0.1 to 10.0 g / 10 min.
Parts by weight and flexural modulus of 500 to 4000 kg / c
a sealant film comprising m ² and 30 to 2 parts by weight of a polypropylene resin having a melting point in the range of 130 to 170 ° C.