JPH1045922A - Polyethylene packaging film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a polyethylene packaging film prevented from tearing and cracking in crosswise twist wrapping. SOLUTION: This film is obtained by melting and kneading a resin composition comprising 100 pts.wt. blend of 85-50 pts.wt. high-density polyethylene having a density of 0.945-0.970g/cm<3> and a melt index of 0.1-3g/10min and 15-50 pts.wt. linear low-density polyethylene having a density of 0.910-0.938g/cm<3> and a melt index of 0.4-10g/10min, molding the kneaded material, and unidirectionally stretching and heat treating the molded material in a temperature range from 60 deg.C to a temperature 15 deg.C lower than the melting point of the linear low-density polyethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film mainly composed of high-density polyethylene, which is excellent in uniaxially stretched twist packaging. More specifically, in a laterally twisted package having a direction perpendicular to the stretching direction of the film (hereinafter, referred to as a transverse direction) as a twist axis, the film is prevented from tearing or cracking along the stretching direction, and at the same time, has excellent torsion retention. , Transparency, rigidity,
The present invention relates to a film which is excellent in productivity and can be suitably used for twist packaging of candy, rice cracker, cheese, chocolate and the like.

[0002]

2. Description of the Related Art Individual packaging of individual foods such as candy, rice confectionery, cheese, confectionery such as chocolate and the like has become widespread. Among them, packaging in which the product is wrapped with a film and both ends are twisted is preferred because the contents can be easily taken out. As such a film for twist packaging, a cellophane film has been mainly used in the past. However, the cellophane film is disadvantageous in that it is expensive and has poor moisture-proof properties. A uniaxially stretched polyethylene film using a polyethylene resin having a similar appearance and rigidity to that of the above is used.

[0003] However, although the uniaxially stretched polyethylene film is excellent in moisture resistance and transparency, the elongation in the transverse direction of the film is remarkably reduced. However, there are drawbacks such as tearing and cracking easily occurring in the film, and in order to improve such drawbacks, studies have been made to use a resin other than polyethylene in combination, but the compatibility is poor and the productivity is hindered. There are problems such as.

[0004]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied a packaging film which does not crack or break when twisted and wrapped. As a result, a composition containing a specific amount of two specific resins is melt-kneaded and molded, and then the molded product is uniaxially stretched and heat-treated at a specific temperature condition, thereby causing tearing in a horizontally twisted package, The inventors have found that the film becomes a packaging film in which cracks are prevented, and completed the present invention based on this finding. As is apparent from the above description, an object of the present invention is to provide a film for polyethylene packaging which prevents tearing and cracking in side twist packaging.

[0005]

The present invention has the following constitutions (1) and (2). (1) density of 0.945g / cm ³ ~0.970, melt index (JI
S K7210-1976 Test conditions 4190 ° C, 2.16 kg, hereafter abbreviated as MI) 0.1 to 3 g / 10 min, 85 to 50 parts by weight of high-density polyethylene, density 0.910 to 0.938 g / cm ³ , MI 0.4 to 10 g A resin composition in which 15 to 50 parts by weight of a linear low-density polyethylene of 10 minutes is blended so as to make a total of 100 parts by weight is melt-kneaded and molded. A polyethylene packaging film obtained by unidirectional stretching and heat treatment in a temperature range of 15 ° C. lower than the melting point of low density polyethylene). (2) The polyethylene packaging film according to the above (1), wherein the tensile elongation at break in a direction perpendicular to the stretching direction is 100% or more.

The high-density polyethylene used in the present invention is an ethylene polymer having a density of 0.945 to 0.970 g / cm ³ and an MI of 0.1 to ³ g / 10 minutes. Instead, a copolymer of ethylene and another α-olefin, for example, butene-1, pentene-1, hexene-1, or a mixture of these two types can be used. If the density is less than 0.945 g / cm ³ , the strength and rigidity of the resulting film will be insufficient, the twist residual angle at the time of twist packaging will be small, and twistability will be poor. On the other hand, if the thickness exceeds 0.970 g / cm ³ , the resulting film is likely to have a large number of cracks during twist packaging. If the MI is less than 0.1 g / 10 minutes, the extrusion fluidity is poor and the appearance of the film is poor, and the stretchability of the film is poor. If it exceeds 3 g / 10 minutes, the strength and rigidity of the obtained film will be insufficient, and the twist residual angle at the time of twist packaging will be small.

The linear low-density polyethylene used in the present invention is a copolymer containing ethylene as a main component and having a small number of branched chains of the ethylene and an α-olefin other than the ethylene, and having a density of 0.910 to 0.938. g / cm ³ and MI in the range of 0.4 to 10 g / 10 minutes. Preferably density 0.910 ~ 0.935g / cm
^{3. A} copolymer having a small number of branched chains having an MI of 0.5 to 5 g / 10 minutes. As the α-olefin to be copolymerized, for example, propylene, butene-1, pentene-1, hexene-
Examples thereof include 1, octene-1, 4-methylpentene-1, and the like, preferably propylene, butene-1, hexene-1, and octene-1. The α-olefin content of the linear low-density polyethylene is not particularly limited, but is usually 0.5 to 15% by weight. The density is 0.910g /
If it is less than cm ³ , the film obtained using such a linear low-density polyethylene will have insufficient strength and rigidity, and the twist residual angle during twist packaging will be small. Density 0.938g / c
If it exceeds m ₃ , the resulting film will be more likely to break when twisted. If the MI is less than 0.4 g / 10 minutes, the extrusion fluidity is poor, and the resulting film has poor appearance such as rough skin, and poor stretchability such as film breakage during stretching. If it exceeds 10 g / 10 minutes, the strength and rigidity of the obtained film will be insufficient, and the occurrence of film cracking during twist packaging will increase.

In the present invention, each resin is compounded so that the total of 15 to 50 parts by weight of the linear low-density polyethylene is 85 parts by weight to 100 parts by weight of the high-density polyethylene. If the compounding amount of high-density polyethylene exceeds 85 parts by weight, the rigidity of the obtained film is improved, but the film is easily broken at the time of twist packaging, and if it is less than 50 parts by weight, the strength and rigidity of the obtained film are insufficient, Twist residual angle at the time of twist packaging becomes small. The rigidity of the obtained film is improved when the blending amount of the linear low-density polyethylene is less than 15 parts by weight, but the film is easily broken at the time of twist packaging, and the strength of the obtained film exceeds 50 parts by weight, The rigidity is insufficient, and the twist residual angle at the time of twist packaging becomes small.

[0009] The packaging film of the present invention may contain, if necessary, various antioxidants, ultraviolet absorbers, nucleating agents, slip agents, antistatic agents, etc., in the above resin composition. It can be added within a range that does not impair the purpose of the present invention.

The packaging film of the present invention is prepared by forming an unstretched film by a known film forming method, stretching the film in the machine direction (longitudinal direction) by a known stretching method (uniaxially stretching), and subsequently performing heat treatment. It is obtained by applying. As a method for forming an unstretched film, a T-die molding method using a T-die, an inflation molding method using a circular die, and the like are used.
The resin is melted and kneaded by an extruder heated to ℃, and the film-like molten resin discharged from the T-die is cooled and solidified by a cooling roll at 60 to 110 ° C to obtain an unstretched film of 100 to 360 μm. If the temperature of the cooling roll is lower than 60 ° C., the adhesion to the roll is poor, resulting in poor appearance such as gloss and transparency. Also, 110
If the temperature exceeds ℃, the film sticks to the roll, making film formation difficult.

The unstretched film is heated to a predetermined stretching temperature by a roll or an oven or the like, and is stretched in the longitudinal direction by 4 to 12 mm.
Draw twice. Preferably, 5 to 10 by roll stretching
Good draw ratio of 2 times. The stretching temperature is in a temperature range of 60 ° C. to (a temperature 15 ° C. lower than the melting point of the linear low-density polyethylene). If the film is stretched at a temperature lower than 60 ° C., whitening and stretching of the film occur. At a temperature near the melting point of the linear low-density polyethylene, the resulting film cannot have sufficient elongation in the transverse direction, and the film tends to crack during twist packaging. Further, the film cannot be stretched due to sticking to the stretching roll.

After the stretching, heat treatment is performed using a roll or an oven or the like in order to remove the strain caused by the stretching.
The heat treatment temperature is in the temperature range of 60 ° C. to (temperature lower than the melting point of the linear low-density polyethylene by 15 ° C.) at a temperature equal to or higher than the stretching temperature. At a temperature near the melting point of the linear low-density polyethylene, a film obtained in the same manner as the stretching temperature does not have a sufficient elongation in the transverse direction, and the film is frequently cracked during twist packaging. If the heat treatment temperature is lower than the stretching temperature, the film shrinks greatly, causing problems such as curling of the film and tight tightening of the product.
If the temperature is in the range of (a temperature lower than the melting point of the linear low-density polyethylene by 15 ° C.), it is desirable to perform the treatment at a temperature equal to or higher than the stretching temperature.

Further, in order to remove the strain caused by the stretching, it is preferable that the film is relaxed by mechanically setting the speed after the heat treatment to 0 to 20% lower than the film speed before the heat treatment. By relaxing
Shrinkage of the obtained film is reduced, and problems such as tight winding of the product are improved.

[0014] The packaging film of the present invention preferably has a transverse elongation at break of 100% or more.

The packaging film of the present invention may be subjected to surface treatments such as corona discharge treatment, flame treatment, and application of a surfactant, if necessary, to make the film secondary processing such as metal deposition, printability, and antistatic. Can also be improved.

[0016]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Test methods in Examples and Comparative Examples are as follows. 1) Physical properties of high-density polyethylene and linear low-density polyethylene (1) Density: Measured according to JIS K6760. (2) Melt index (MI): 190 ° C, 2.16
The discharge amount of the molten resin for 10 minutes under a kg load is determined by JI
Measured according to SK6760. (3) Melting point: The melting temperature point was measured with a differential scanning calorimeter.
The device used is Perkin-Elmer DSC7 (trade name). 2) Film properties (1) Transparency: The haze (cloudiness) was measured according to ASTM D1003.
Measured according to. (2) Lateral elongation: The tensile elongation at break in the direction (TD) perpendicular to the stretching direction (MD) of the film was measured according to ASTM D882. The distance between the marked lines was 50 mm and the speed was 500 mm / min. (3) Longitudinal rigidity: According to ASTM D882, the load and elongation rate curve (stress-strain curve) of the film in the stretching direction (MD) of the film are determined, and the tensile modulus is determined from the rising gradient. The distance between the tension marks was 50 mm, and the speed was 5 mm / min. (4) Shrinkage: 10 mm width in the stretching direction (MD) of the film
A test piece having a length of 100 mm is placed in an oil bath at 100 ° C. for 15 minutes.
After heating for one minute, the shrinking length of the film was measured and defined as the shrinkage ratio. 3) Suitability for twisting the film (1) Remaining angle: A wooden cube with a piece of 15 mm is used as a sample film, and the rotation direction is perpendicular to the stretching direction (MD) of the film. The twisted one was allowed to stand at 23 ° C. for 1 hour, the returned state was observed, the remaining angle of the film was measured, and the angle was indicated. (2) Cracking rate: In the above (1), the rate of occurrence of cracking in 100 films was expressed in%.

Examples 1 to 13 and Comparative Examples 1 to 13 The high-density polyethylene and the linear low-density polyethylene having the densities shown in Table 1 and MI were mixed in the proportions shown in Table 1 using a conventional mixer. After that, the mixture was extruded at 230 ° C. using a T-die extruder having a diameter of 65 mm to form a film-like material, and cooled and solidified with a cooling roll at 95 ° C. to obtain an unstretched film. Next, the unstretched film is firstly rolled between rolls having different rotation directions and rotation speeds.
The film was stretched 6 times with a roll having a heating temperature shown in the table, and heat-treated with a roll heated to the temperature shown in Table 1 to obtain a uniaxially stretched film having a thickness of 25 μm. The physical properties of the obtained film were measured, and the results are shown in Table 1.

[0018]

The packaging film of the present invention has high rigidity and transparency and is suitable for packaging with improved twist retention, and can be used for individual packaging of candy, rice cracker, chocolate and the like. As the twist packaging film used,
It can be suitably used.

[0019]

[Table 1]

Claims (2)

[Claims] 1. A high density polyethylene having a density of 0.945 to 0.970 g / cm ³ , a melt index of 0.1 to ³ g / 10 min and a density of 0.910 to 0.938 g / cm ³ and a melt index of 85 to 50 parts by weight.
A resin composition in which 0.4 to 10 g / 10 minutes of a linear low-density polyethylene and 15 to 50 parts by weight are blended so as to make a total of 100 parts by weight is melt-kneaded and molded.
(15 ° C lower than the melting point of linear low-density polyethylene)
A polyethylene packaging film obtained by stretching and heat-treating in one direction in the temperature range described above. 2. The polyethylene packaging film according to claim 1, wherein the tensile elongation at break in a direction perpendicular to the stretching direction is 100% or more.