JPH02127041A - Film for twist wrapping - Google Patents

Abstract

PURPOSE:To prevent tearing at the time of lateral twist by thermocompression- bonding a straight chain low-density polyethylene film with a high-density polyethylene group film and forming a film for a twist wrapping through monoaxial stretching. CONSTITUTION:A high-density polyethylene filmy article extruded from a mold at 180-280 deg.C is cooled and solidified on a chill roll at 60-100 deg.C, thus shaping a film not oriented. The film not oriented is heated by a preheating roll at 80-120 deg.C, a previously film-formed straight chain low-density polyethylene film is heat-bonded between a pair of pinched metallic roll and rubber roll, and a thermal adhesive film is monoaxial-stretched at drawing speed of 30-12m/min and a draw ratio of 4-10 times, thus acquiring a film for twist wrapping. The film acquired has ductility, vertical tearing is prevented, lateral twist holding properties are improved, and excellent packaging-machine aptitude is obtained.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a twist packaging film that is uniaxially stretched after thermally adhering a linear polyethylene film to high-density polyethylene or a film mainly composed of high-density polyethylene. Regarding film.

More specifically, in horizontal twist packaging with the film stretching direction as the twist axis, packaging that prevents tearing along the film stretching direction, has excellent horizontal twist retention, and has transparency, slipperiness, and heat sealability. The present invention relates to a packaging film that can be suitably used for candy, rice crackers, etc.

[Conventional technology]

For twist wrapping of candy, rice crackers, etc., cellophane,
Paper has been used, but cellophane is expensive and hygroscopic, and paper has poor twistability, so in recent years uniaxially stretched high-density polyethylene film has been commonly used in place of these films. . However, uniaxially stretched high-density polyethylene film has a weak strength against cracks in the stretching direction of the film, so tearing occurs when angular contents such as chocolate are used in horizontal twist packaging where the film stretching direction is the twist axis. , could not be used for horizontal twist packaging.

There are many reports on twist packaging films using high-density polyethylene.
No. 137 exists, but it is still not sufficient in terms of tearing.

[Problems to be Solved by the Invention] An object of the present invention is to provide a twist packaging film that, unlike the prior art, has lateral twist suitability (a twist retaining property that prevents tearing during lateral twisting).

[Means to solve the problem]

As a result of intensive research to obtain a twist packaging film that prevents tearing during horizontal twist packaging, the inventors of the present invention found that in order to prevent tearing and obtain a film that is suitable for horizontal twisting, a uniaxially stretched film has a suitable rigidity. It was found that it is essential to have elongation in the direction perpendicular to the stretching direction. To achieve this, after thermally adhering a film made of linear low-density polyethylene to a specific high-density polyethylene film or a film mainly composed of high-density polyethylene, the uniaxially stretched film has excellent twistability. The present invention was completed based on the discovery that it is possible to prevent tearing in the stretching direction.

That is, the present invention is a twisted packaging film characterized in that a linear low-density polyethylene film is thermally bonded to a high-density polyethylene film and then uniaxially stretched.
It is also a twisted packaging film which is made by heat bonding a linear low density polyethylene film to a uniaxially stretched high density polyethylene film and then uniaxially stretching it.

In the above twisted packaging film, the thickness ratio of the film is 40 to 90% in the high density polyethylene film part.
%, and the linear low density polyethylene film part is 10
60%.

The high density polyethylene used in the present invention has a density of 0.9
41 =0.956g/cc, melt index (
(hereinafter referred to as M1) is 0.5 to 10. It is an ethylene-based polymer with a ratio of h/10 min, and may be a copolymer or a blend as long as it falls within this range. Density is 0.94
If it is less than 1 g/cc, the stretched film will have insufficient strength and poor twistability, and if it exceeds 0.956 g/cc, it will easily tear. Moreover, if Ml is less than 0.5 g/10 minutes, the workability and transparency will be poor (while if it exceeds 10.0 g/10 minutes, it will become brittle and a good twist packaging film cannot be obtained).

The linear low density polyethylene used in the present invention has a density of 0.
．． 889~0.945g/cc, M+ is 0.4~
It is polyethylene with few branched chains copolymerized with α-olefin in the range of 10.0 g/10 minutes. Density is 0.88
If it is less than 9, the strength will be insufficient when it is made into a stretched film, and the twistability will be poor, and if it exceeds 0.945 g/cc, it will be easy to tear. Moreover, if Ml is less than 0.4 g/10 min, workability and transparency will deteriorate, and if it exceeds 10.0 g/l min, it will become brittle and a good twist packaging film cannot be obtained.

Examples of the α-olefin to be copolymerized include propylene, butene-1, pentene-J, hexene-11octene-1,4-methylpentene-1, etc., but preferably butene-11 and hexene-1. . The α-olefin content of the polyethylene is not particularly limited, but is usually 0.5 to 10% by weight. α-olefin content is 0
．． If the amount is less than 5% by weight, there is little effect of preventing longitudinal tearing of the film, and if it exceeds 10% by weight, the film becomes stiff and its packaging suitability deteriorates.

High-density polyethylene films and linear low-density polyethylene films can be obtained as unstretched films by known film forming methods such as the T-die method and the inflation method.

A method for producing a twist packaging film will be explained below by giving an example.

The temperature of the molten high-density polyethylene resin is 180~
A film extruded from a mold at 280°C is heated to a temperature of 6
It was cooled and solidified on a chill roll at 0 to 100°C to obtain an unstretched film with a thickness of 80 to 500 μm.

Then, this unstretched film was heated to a temperature of 80 to 120'C.
A linear low-density polyethylene film, which had been formed in advance by heating with a preheating roll, is thermally bonded between a pair of pinched metal rolls and a rubber roll. The thermally bonded film was stretched using a known stretching method between a pair of rolls with different surface speeds at a stretching speed of 30 to 12 m/min and a stretching ratio of 4 to 10.
The film is uniaxially stretched at a double speed to obtain a twisted packaging film.

Alternatively, an unstretched film obtained by cooling and solidifying a film-like material discharged from a mold on a chill roll is heated to a temperature of 80°C.
It is heated to ~120°C, stretched 2 to 10 times between a pair of metal rolls with different surface speeds, and then heated again with hot rolls.

A linear low-density polyethylene film previously formed on this heated film is adhered between a pair of pinched metal rolls and a rubber roll, and stretched 1. The film is stretched again by 1 to 5 times to obtain a twisted packaging film.

The thickness of the twist packaging film of the present invention is 5 to 70 μm
, preferably in the range of 10 to 60III11; if the thickness is less than 5 μm, the strength of the film is poor, and the thickness is 70 μm.
If it exceeds μm, workability and packaging suitability will deteriorate.

The thickness ratio of the high-density polyethylene film and the linear low-density polyethylene film of the twist packaging film of the present invention is in the range of 40 to 90% for the high-density polyethylene film and 60 to 10% for the linear low-density polyethylene film. is preferred. If the thickness ratio of the high-density polyethylene film is less than 40% and the thickness ratio of the linear low-density polyethylene film exceeds 60%, the untwisting becomes large; The thickness ratio of the chain low density polyethylene film is 10
If it is less than %, cracking becomes easy.

The twist packaging film of the present invention can also be subjected to surface treatments such as corona discharge treatment and surfactant coating, if necessary. The base material of the film, i.e., the high-density polyethylene and the linear low-density polyethylene that is thermally bonded and provides tear prevention, is pretreated with antioxidants, antiblocking agents, antistatic agents, nucleating agents, colorants, and other additives. Additives such as polymers, modifiers, etc. may be added, and the use of these additives is not limited to (and) as long as they do not satisfy the characteristics of the present invention.

〔Example〕

Hereinafter, the present invention will be specifically explained based on Examples. Note that the evaluation of the present invention was performed by the following method.

(1) M I: Discharge amount of molten resin for 10 minutes at 190°C, 12 kg, under a load of 16 kg, according to JIS 6.
Measured in accordance with 758.

(2) Haze: The transparency of the film sample is
(Haze) measured in accordance with ASTM 01003.

(3) Rigidity: The tensile modulus of the film sample in the stretching direction was determined according to ASTM 0882 and was defined as the rigidity. The tensile speed was 500 m and 7 minutes.

(4) Elongation (TD): Measure the tensile elongation at break in the direction (TD) perpendicular to the stretching direction of the film in accordance with ASTM D882. The tensile speed was 500 ms/min.

Twisting property: The number of pieces torn is displayed after twisting the packaging 14 times.

The residual angle is determined by twisting the candy twice (720"), leaving it at 23°C for 1 hour, observing the return state, and displaying the angle.6 Example 1 High-density polyethylene shown in Table 1 was attached to a T-die. φ65n+
The resin was extruded using an n+ extruder at a resin temperature of 230'C, and cooled and solidified using a chill roll at a temperature of 90°C to obtain an unstretched film. This unstretched film was then heated to a temperature of 110°C.
Linear ethylene, which is preheated with heating rolls and formed into a film in advance.
A film of hexene-1 copolymer was thermally bonded between a pair of rubber rolls and a metal roll, and stretched 7 times at a stretching speed of 70-7 minutes. and a thickness of 25 μm with 40% linear ethylene/hexene-1 copolymer film.
A uniaxially stretched film of steel was obtained. The results of measuring the transparency (Haze), rigidity, and elongation (TO force direction and twisting suitability) of the obtained uniaxially stretched film are shown in Table 1.

Example 2 High-density polyethylene shown in Table 1 was made with a T die of φ65 mm.
Extruded using an extruder at a resin temperature of 230°C, temperature 90°
It was cooled and solidified using a chill roll (C) to obtain an unstretched film. Next, the film was preheated with a heating roll at a temperature of 110°C, and stretched 5 times with a stretching roll at a speed of 70 rpm to obtain a uniaxially stretched film. Furthermore, this stretched film was heated to a temperature of 1
A film of linear ethylene/hexene-1 copolymer prepared in advance is preheated with a heating roll at 20°C and thermally bonded between a pair of rubber rolls and a metal roll, and this thermally bonded film is then heated to a temperature of 1.5 times. A uniaxially stretched film having a thickness of 25 μm was obtained by stretching, and the ratio of the film thickness after stretching was 60% of the high density polyethylene film and 40% of the linear ethylene/hexene-1 copolymer film. Table 1 shows the physical properties of the obtained uniaxially stretched film.

Example 3 A °ζ film was produced in the same manner as in Example 1, except that the linear low-density polyethylene used in Example 1 was replaced with an ethylene-butene-1 copolymer. The results are shown in Table 1.

Examples 4 to 14 High-density polyethylene shown in Table 1 was made with a T die of φ65 mm.
Extruded using an extruder at a resin temperature of 230°C, temperature 90°
It was cooled and solidified using a chill roll (C) to obtain an unstretched film. Then, the film was preheated with a heating roll at a temperature of 110°C, and stretched 5 times with a stretching roll at a speed of 7011/min.
A uniaxially stretched film was obtained. Further, this stretched film was preheated with a heating roll at a temperature of 120'C, and the first film formed in advance was
The linear low-density polyethylene film shown in the table was thermally bonded between a pair of rubber rolls and a metal roll, and this thermally bonded film was further stretched 1.5 times, so that the ratio of the film thickness after stretching was that of a high-density polyethylene film. 60%, straight ethylene/hexene-1 copolymer film 40%
A uniaxially stretched film with a diameter of 25 μm was obtained. Table 1 shows the physical properties of the obtained uniaxially stretched film.

Example 15.16, Comparative Example 1.2 Using high-density polyethylene and linear low-density polyethylene shown in Table 1, the film thickness after stretching was in the ratio shown in Table 1 in the same manner as in Example 2. A uniaxially stretched film was obtained. The film of Comparative Example 1 has a large twist return and a small residual angle. The film of Comparative Example 2 was rejected as a horizontal twist packaging film because the film was torn due to the contents during twist packaging. These physical properties are shown in Table 1.

Example 17 High-density polyethylene film with a density of 0.95
6 g/cc, M I of 0.9 g/10 min high density polyethylene 80 parts, density 0.890 g/cc,
M l is 1. 1.7 wt% comonomer at og/10 min
A uniaxially stretched film was obtained in the same manner as in Example 14, except that 20 parts of the linear ethylene-butene-1 copolymer of 20% was mixed in a blender. The physical properties are shown in Table 1.

Comparative Example 3 Instead of linear low density polyethylene, density is 0.92
A low density polyethylene film of 0 g/cc and Ml of 1.5 g/10 min was thermally bonded in the same manner as in Example 2.
Uniaxial stretching was performed to obtain a uniaxially stretched film in which the thickness ratio of the high density polyethylene film was 60% and the low density polyethylene film was 40%. This film had poor transparency and tearing occurred in parallel to the stretching direction, making it unacceptable for horizontal twist packaging. The physical properties are shown in Table 1.

Comparative Example 4 Using the high-density polyethylene resin shown in Table 1, an unstretched film was obtained in the same manner as in Example 2. Then, this unstretched film was preheated with a heating roll at a temperature of 110'C, and a speed of 70 m/min was obtained. A uniaxially stretched film was obtained by stretching the film by a factor of 7 using a stretching roll for 10 minutes. The physical properties of this film are shown in Table 1.

Although the haze and twist residual angle were good, tearing occurred in parallel to the stretching direction, and the film was rejected as a horizontally twisted packaging film.

〔Effect of the invention〕

Films whose thickness ratios are outside the range of the present invention and films obtained by replacing linear low-density polyethylene with low-density polyethylene have insufficient elongation (TD force direction), resulting in longitudinal tearing and horizontal twist packaging. It is not possible to obtain a suitable film.

By thermally bonding a linear low-density polyethylene film to the high-density polyethylene film of the present invention and uniaxially stretching, or by thermally bonding a linear low-density polyethylene film after stretching the high-density polyethylene film. ,
The film obtained by uniaxial stretching can maintain appropriate rigidity and elongation (TD force direction, good transparency, and prevent longitudinal tearing) by controlling the thickness ratio of each film to be bonded. This is a uniaxially stretched film for twist packaging that has good horizontal twist retention and excellent suitability for packaging machines, and is suitable as a twist packaging film used for packaging rice crackers, candy, etc.

Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) A twisted packaging film characterized in that a linear low-density polyethylene film is thermally bonded to a high-density polyethylene film and then uniaxially stretched. 2) A twisted packaging film characterized in that a linear low-density polyethylene film is thermally bonded to a uniaxially-stretched high-density polyethylene film and then uniaxially stretched. 3) In the twist packaging film according to claim 1 or 2, the thickness ratio of the film is 40 to 90% in the high density polyethylene film part,
A twisted packaging film characterized by having a linear low density polyethylene film portion of 10 to 60%.