JPH05214179A - Resin composition for wrapping film - Google Patents

Abstract

PURPOSE:To provide a resin composition for wrapping films which are excellent in tack, transparency, mechanical strength, cuttability and hygiene and generate no toxic gas when burned, and to produce such wrapping films using the above resin composition. CONSTITUTION:The objective resin composition virtually free from antioxidant, comprising (A) 97-85wt.% of a low-density polyethylene produced by high- pressure radical polymerization with a density of 0.925-0.940g/cm<3> and melt flow rate of 0.5-15.0g/10min and (B) 3-15wt.% of an ethylene-alpha-olefin copolymer with a density of 0.860-0.890g/cm<3> and melt flow rate of 0.4-20.0g/10min. The other objective wrapping film can be produced by forming the above resin composition at a temperature of >=210 deg.C but below 260 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for a packaging film used for food packaging and a method for producing a wrap film using the composition, and more particularly to cooking or using a microwave oven. The present invention relates to a resin composition for a wrap film suitable for reheating food using a microwave oven and a method for producing a wrap film using the composition.

[0002]

2. Description of the Related Art A wrap film made of polyethylene has been proposed because wrap films made of polyvinyl chloride, polyvinylidene chloride and the like have drawbacks such as generation of harmful gas during combustion. However, density 0.917-0.924 g / cm
The low-density polyethylene of ³ had insufficient heat resistance.

For the purpose of improving the heat resistance of a wrap film obtained by using a low density polyethylene, a method for producing a packaging film using a medium density polyethylene having a specific composition without adding an antioxidant as polyethylene has been proposed ( JP-A-54-11987). However, in this method, since the resin temperature at the time of extrusion must be increased, polyethylene is likely to deteriorate in the apparatus and gel is easily generated, which lowers the commercial value of the film, making continuous operation difficult for a long time. The adhesiveness of the obtained film is not sufficient, so the adhesiveness to the container of food etc. is low, and the film loosens when rewinding the product wound long by the winder into small rolls and the commercial value is impaired. It cannot be said that it is a practical method for producing a wrap film.

As a method for solving the problems of JP-A-54-11987, a density of 0.926 to 0.935 g / cm
³ high pressure polyethylene at a temperature of 200-290 ° C
A method of extruding from a die has been proposed (JP-A-61-100).
432). However, although this method can suppress the generation of gel, burnt burns, and the like, it has a drawback that the wrap film has insufficient tackiness and is difficult to use.

[0005]

DISCLOSURE OF THE INVENTION The present invention is tacky, easily adheres to dishes, donburi, etc., and has excellent hygiene because it comes into direct contact with food, and it can be used in a microwave oven and has high transparency. It is an object of the present invention to provide a resin composition for a wrap film, which is excellent, has appropriate strength, and is excellent in cutting properties, and a method for producing the same.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that a melt flow rate of 0.95 at a density of 0.925 to 0.940 g / cm ³ obtained by a high pressure radical polymerization method can be obtained. Low density polyethylene 97 to 85% by weight of 5 to 15.0 g / 10 minutes and a density of 0.86
Melt flow rate 0.4 at 0 to 0.890 g / cm ³
Of a resin composition for a wrap film which is substantially free of an antioxidant consisting of 3 to 15% by weight of a copolymer of ethylene and α-olefin of 20.0 g / 10 min and a wrap film using the composition It could be solved by the manufacturing method.

The low density polyethylene used in the present invention is obtained by a high pressure radical polymerization method in which a monomer containing ethylene as a main component is polymerized in the presence of a radical generator such as peroxide under a high pressure of 1000 to 3500 atm.

The density of low density polyethylene is 0.925 to
0.940 g / cm ³ is required and 0.9
26 to 0.935 g / cm ³ is preferable. When the density of the low density polyethylene is less than 0.925 g / cm ³ , the heat resistance is insufficient. If it exceeds 0.940 g / cm ³ , flexibility, tackiness and transparency are insufficient, and it is unsuitable for wrap films.

In addition, the melt flow rate (JIS K6
760, and hereinafter referred to as MFR) is 0.
It is necessary to be 5 to 15.0 g / 10 minutes, and 0.9
It is preferably ˜12.0 g / 10 minutes. When the MFR of the low-density polyethylene is less than 0.5 g / 10 min, the thin-wall moldability is poor when the film is molded with a T-die, and the molding at 260 ° C. or higher at which gel or burn is generated is not preferable. Also, the extrusion pressure becomes high and the transparency becomes poor. On the other hand, if it exceeds 15.0 g / 10 minutes, the strength of the film becomes weak, which is not preferable.

The proportion of low density polyethylene must be 97-85% by weight. If it exceeds 97% by weight, the tackiness is insufficient, and if it is less than 85% by weight, the cuttability is poor and a problem arises. It is necessary for this low-density polyethylene to be substantially free of additives such as antioxidants and antifogging agents in terms of hygiene. The term "substantially free from" means that no antioxidant, antifogging agent, etc. are contained at all, but a slight amount of impurities may be contained.

The copolymer of ethylene and α-olefin is a rubber-like substance used for imparting tackiness. Propylene, butene-1, hexene-1 and the like are used as the α-olefin, and the copolymerization ratio is not particularly limited as long as it exhibits rubber-like physical properties.

Although tackifiers such as rosin are generally known for imparting tackiness, these are low-molecular weight compounds, and if contained in the film, they can be transferred to food by contact with food. It is not preferable because Therefore, as a result of diligent examination of a substance that is sticky and has a large molecular weight, and that does not generate a harmful gas when burned, as a result, by adding a certain amount of a copolymer of ethylene and α-olefin, We have found that we can achieve the purpose.

The copolymer of ethylene and α-olefin has short chain branching and unsaturation, weak intermolecular cohesive force, and large molecular mobility, so that it has a large free energy and is compatible with other materials. It is considered to have adhesiveness because strong molecular ends and short chain branches are likely to appear on the surface. Ethylene and α-
Hydrocarbon type rubbers, polybutadiene and polyisoprene, which are structurally similar to the copolymers with olefins, have many unsaturated groups, so an antioxidant is required from the viewpoint of thermal stability during molding. , Does not meet the purpose of the present invention. From the viewpoint of hygiene, it is necessary that the copolymer of ethylene and α-olefin does not substantially contain an additive such as an antioxidant.

The density of the copolymer of ethylene and α-olefin must be 0.860 to 0.890 g / cm ³ . If it exceeds 0.890 g / cm ³ , sufficient tackiness cannot be imparted, and if it is less than 0.860 g / cm ^3, manufacturing is difficult. The MFR needs to be 0.4 to 20.0 g / 10 minutes, and is preferably 0.7 to 15.0 g / 10 minutes. If the MFR is less than 0.4 g / 10 min, the expected adhesive performance cannot be obtained and the transparency is adversely affected, and if it exceeds 20.0 g / 10 min, the molding stability and the film are not uniform, which is not preferable.

The proportion of the copolymer of ethylene and α-olefin in the composition must be 3 to 15% by weight. If it is less than 3% by weight, the tackiness is not sufficiently imparted, and if it exceeds 15% by weight, the tackiness is so strong that the roll-out property is deteriorated and the cut property is unfavorably deteriorated when used as a wrap film.

The resin composition of the present invention is a resin composition prepared by mixing the above-mentioned low-density polyethylene and a copolymer of ethylene and α-olefin in a predetermined amount. The order of addition is not particularly limited, and the components may be added sequentially or simultaneously. Further, not only mixing but also kneading may be carried out for preparation, and as a method thereof, a melt kneading method is preferable. Mixing is carried out using a Henschel mixer or the like, and kneading is usually carried out using a Banbury mixer, single-screw or twin-screw extruder.

In order to produce a wrap film from the resin composition of the present invention, a usual T die film producing apparatus may be used. At this time, the molding temperature is 210 ° C or higher and 260 ° C
It is necessary that the temperature is lower than 220 ° C., and particularly 220 ° C. or higher and lower than 255 ° C. At 260 ° C. or higher, fisheyes and gels are formed due to deterioration of the inside of the extruder and the inside of the die due to burnt burns, and undesired lack of long-term continuous productivity. In addition, the resulting wrap film has an odor, which is not preferable. 21
If the temperature is lower than 0 ° C, the molding speed and the thin-wall moldability are deteriorated, which is not preferable.

[0018]

EXAMPLES The present invention will be described below with reference to examples. still,
The physical properties in the examples were evaluated by the following methods. B) Thickness The thickness of the wrap film was measured with a dial gauge type film thickness meter. The target thickness was 12 μm. (B) Transparency The haze of the wrap film was measured with a digital haze meter manufactured by Murakami Color Research Laboratory in accordance with ASTM-D-1003. C) Strength and Elongation JI
According to S-Z-1702, the film sample has a width of 15 m
It was measured at a strip shape of m and a pulling speed of 500 mm / min. D) Puncture strength JAS (Ministry of Agriculture and Forestry Notification 1)
No. 019) According to Method A, the puncture speed was measured at 50 mm / min. E) Adhesiveness Adhesiveness of the wrap film is 10 cm x 2 films
The area of 10 cm was adhered, and it was shown by the resistance when peeled up and down with a tensile tester. Peeling speed is 100m
It was measured in m / min. ◯ has a resistance of 70 g / 100 cm ²
Above, the adhesiveness is good. X has a resistance of 70 g / 1
Less than 00 cm ^{2 and} lacking in tackiness. F) Feeding-out property Regarding the feeding-out property of the wrapping film, the weight drop of the small winding film was observed when the film end of the small winding film was fixed. ◯ means that the Komaki drops due to its own weight and has good feeding performance. × indicates that Komaki does not drop due to its own weight and its feeding performance is not good. G) Cutting property The cutting property of the wrap film was evaluated by sensory evaluation of the hand cutting property when a small roll was filled in a small box and the wrap film was cut by the metal blade of the small box. ◯ means that the wrap film is easily cut and has good cutting properties. × indicates that the wrap film stretches and the cutting is not smooth, and the cutting property is not good. H) Heat resistance The heat resistance of the wrap film is shown by the melting peak temperature of the film by DSC. I) Odor The odor of the wrap film was evaluated by sensory evaluation. ◯ means that there is no deterioration or burning odor, and that there is no offensive odor. Poor odor has a bad odor or a burning odor or a strange odor. G) Gel The wrap film gel has a length of 5 m in film observation.
The gel mark of m or more was evaluated in terms of the number of 30 small rolls having at least one gel in one small roll having a width of 30 cm and a length of 20 m. ○ is 3 or less. × is 4 or more.

Example 1 Density 0.929 g produced by high pressure radical polymerization method
/ Cm ³ , MFR 7.0 g / 10 min low density polyethylene 95% by weight and density 0.865 g / cm ³ , MFR 2.0 made by using a coordination anionic polymerization catalyst by the medium-low pressure method
g / 10 min of ethylene and 5% by weight of a copolymer of butene-1 were mixed using a Henschel mixer and then pelletized by an extruder. This pellet is 90mm in diameter (L / D = 2
9) Extruder, T-die with 900mm die width and diameter 45
Using a cast film molding machine equipped with two 0 mm cooling rolls and an air knife, a resin temperature of 250 just below the die was used.
A cast film having a thickness of 12 μm was formed at a temperature of 50 ° C./min. The resin extruded from the T-die passes through an air gap of about 45 mm, is pressed against the first cooling roll by an air knife, then passes through the second cooling roll, is cooled, and is wound up. Wound film has a width of 30c
m, 20 m in length, and used for evaluation as a wrap film. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. Both the physical properties of the film and the lap characteristics were satisfactory.

Example 2 Example 2 was carried out except that a copolymer of ethylene and hexene-1 having a density of 0.865 g / cm ³ and an MFR of 3.0 g / 10 min was used as the copolymer of ethylene and α-olefin. A cast film was molded in the same manner as in Example 1. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. Both the physical properties of the film and the lap characteristics were satisfactory.

Example 3 Example 1 was repeated except that an ethylene / propylene copolymer having a density of 0.865 g / cm ³ and an MFR of 1.5 g / 10 min was used as the ethylene / α-olefin copolymer. A cast film was molded in the same manner as in. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. Both the physical properties of the film and the lap characteristics were satisfactory.

Example 4 A density of 0.926 g / cm 3 instead of low density polyethylene
³ , high pressure radical polymerization method with MFR 5.5 g / 10 min 87% by weight low density polyethylene and density 0.880 g / cm
³ , MFR 2.0g / 10min ethylene and butene-1
A cast film was formed in the same manner as in Example 1 except that 13% by weight of the copolymer was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. Both the physical properties of the film and the lap characteristics were satisfactory.

Example 5 A high density radical polymerization low density polyethylene having a density of 0.932 g / cm ³ and an MFR of 7.0 g / 10 min and a density of 0.
A cast film was formed in the same manner as in Example 1 except that a copolymer of ethylene and propylene having a 862 g / cm ³ and an MFR of 3.0 g / 10 min was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. Both the physical properties of the film and the lap characteristics were satisfactory.

Example 6 90% by weight of high-density radical polymerization low-density polyethylene having a density of 0.930 g / cm ³ and an MFR of 12.0 g / 10 min
A cast film was formed in the same manner as in Example 1 except that a copolymer of ethylene and butene-1 having a density of 0.867 g / cm ³ and an MFR of 2.0 g / 10 minutes was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film.
It was shown to. Both the physical properties of the film and the lap characteristics were satisfactory.

[0025] Example 7 Density 0.930g / cm ^3, a high-pressure radical polymerization method is MFR1.5g / 10 min low density polyethylene 90 wt% and density 0.865 g / cm ^3, a MFR15.0g / 10 min Ethylene A cast film was molded in the same manner as in Example 1 except that a copolymer of 10% by weight and butene-1 was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film.
It was shown to. Both the physical properties of the film and the lap characteristics were satisfactory.

Comparative Example 1 A cast film was formed in the same manner as in Example 1 except that a copolymer of ethylene and butene-1 having a density of 0.915 g / cm ³ and an MFR of 2.0 g / 10 min was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. The wrap film was weak in tackiness and resulted in poor lap characteristics.

Comparative Example 2 A cast film was formed in the same manner as in Example 1 except that a copolymer of ethylene and butene-1 having a density of 0.865 g / cm ³ and an MFR of 0.2 g / 10 min was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. The wrap film was low in transparency and weak in tackiness, and generated a lot of gel, which was not preferable as a wrap.

Comparative Example 3 A cast film was molded in the same manner as in Example 1 except that 80% by weight of the low-density polyethylene of Example 1 and 20% by weight of a copolymer of ethylene and butene-1 were used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. The wrapping film had poor pay-out properties and poor cutting properties, resulting in poor lap properties.

Comparative Example 4 High-Pressure Radical Polymerization Method Only Low Density Polyethylene Example 1
A cast film was molded in the same manner as in. Table 1 shows the evaluation results of the physical properties of the obtained wrap film. The wrap film was weak in tackiness and resulted in poor lap characteristics.

Comparative Example 5 A cast film was formed in the same manner as in Example 1 except that high density radical polymerization low density polyethylene having a density of 0.919 g / cm ³ and an MFR of 8.0 g / 10 min was used. Table 1 shows the evaluation results of the physical properties of the obtained wrap film.
The wrap film had poor heat resistance and poor cutting properties, resulting in poor lap properties.

Comparative Example 6 Molding was carried out in the same manner as in Example 1 except that the resin temperature immediately below the die during molding of the cast film of Example 1 was 280 ° C.
Table 1 shows the evaluation results of the physical properties of the obtained wrap film. The wrap film had a bad odor and was inferior in wrap characteristics.

[0032]

[Table 1]

[0033]

[Table 1]

[0034]

EFFECT OF THE INVENTION A resin composition for a wrap film, which is excellent in tackiness, transparency, strength, cutting property, hygiene and does not generate harmful gas upon burning, and a method for producing the wrap film are obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B29K 23:00

Claims (2)

[Claims] 1. Low density polyethylene 97-85% by weight having a density of 0.925-0.940 g / cm ³ and a melt flow rate of 0.5-15.0 g / 10 minutes, which is obtained by a high pressure radical polymerization method, Density is 0.860 to 0.890
Melt flow rate in g / cm ³ 0.4-20.0 g /
Copolymer of ethylene and α-olefin which is 10 minutes 3 ~
A resin composition for a wrap film, which is substantially free of 15% by weight of an antioxidant. 2. Use of the resin composition according to claim 1, 210
A method for producing a wrap film at a molding temperature of not less than 0 ° C and less than 260 ° C.