JPH07241906A - Biaxially oriented polyolefin film - Google Patents

Abstract

PURPOSE:To obtain a polyolefin film which is excellent in setability of bags in bag making operation, excellent in bag-breaking resistance of a sealed part by using in packing operation, and difficult to be broken as the bag even by vibration, impact, dropping, etc., when a package is transferred or handled. CONSTITUTION:A biaxially oriented polyolefin film is composed of ethylene- propylene copolymer of 1 to 4wt.% in ethylene content or ethylene-butene- propylene copolymer of 0.5 to 3.0wt.% in ethylene content and 4 to 15wt.% in butene-1 content. Its elongation percentage at 5kg/mm<2> tensile strength in MD direction is 30 to 150%, and preferablly 80 to 130%, and mts tensile modulus of elasticity in MD direction is 80 to 130kg/mm<2>, and preferablly 90 to 120kg/mm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in bag-breaking resistance of a fusion-cut seal portion and in bag-making workability and filling workability.
Moreover, the present invention relates to a biaxially oriented polyolefin film which is excellent in transparency and gloss and can be suitably used for packaging textile products, general merchandise, envelopes of catalogs and magazines, and heavy fruits and vegetables.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene film (hereinafter referred to as OPP film) is widely used as a representative of polyolefin films for packaging in the packaging of textile products and miscellaneous goods. . This is because the OPP film is excellent in transparency and gloss, and has high mechanical strength, so that it is excellent in printability, bag-making property, and filling workability. However, since the OPP film has a very small elongation at break of 10% or less in the fusing and sealing part, it is easy to break the bag during the filling work of the contents, and when transferring, handling or dropping the package. It has been mentioned as a drawback that it is easy to break the bag even with vibration and shock.

As a method of increasing the elongation of the OPP film, a method of reducing the stretching ratio can be considered. The longitudinal stretching ratio is 40 by using a normal raw material for the OPP film.
When the content is 0% or less, a stretched film portion and an unstretched portion are mixed to form a mottled state, and uniform stretching cannot be performed. Therefore, it is difficult to produce a low-magnification biaxially stretched film in the OPP film.

An unstretched polypropylene film (hereinafter referred to as a CPP film) is a packaging film having excellent bag-breaking resistance. The CPP film has a feature that it is difficult to tear the bag because the stretch ratio of the fused cut portion is very large, but the CPP film has a problem in printability because the stretch ratio is large. In addition, since the film is very soft, bag alignment is poor in bag manufacturing work. Similarly, in filling work, there is a problem that it is difficult to automate the filling machine because of lack of rigidity in the film and it is difficult to automate.

As a conventional technique, Japanese Patent Publication No. 5-81604
JP-B No. 5-82416 and JP-B No. 5-82416 disclose a polyolefin film using an olefin-based copolymer resin having a tensile elastic modulus in the longitudinal and transverse directions of 15 to 50 kg / mm ² . This polyolefin film is
It is a film with excellent flexibility, transparency, and mechanical strength that can replace vinylon film. However, this polyolefin film exhibits a tensile elastic modulus close to that of the CPP film described above, and is insufficient in terms of bag-making workability and filling workability by the fusion cutting and sealing machine which the present inventor aims.

[0006]

In view of the above circumstances, the present inventor has found that the sealing portion of the bag in the fusing and sealing machine is excellent in bag puncture resistance in at least one direction, and has good printability and bag making work. Has been researched for the purpose of obtaining a polyolefin film which is excellent in transparency and filling workability, is flexible, and is excellent in transparency and gloss. As a result, they succeeded in achieving the above object and completed the present invention.

That is, the present invention has an ethylene content of 1 to 4
% Ethylene-propylene copolymer, or ethylene-butene-propylene copolymer having an ethylene content of 0.5 to 3.0% by weight and butene-1 content of 4 to 15% by weight. The biaxially stretched polyolefin film is characterized in that it has an elongation of 30 to 150% at a tensile strength of 5 kg / mm ² and a tensile modulus of elasticity in the MD direction of 80 to 130 kg / mm ² .

The biaxially stretched polyolefin film of the present invention is an ethylene-propylene copolymer having an ethylene content of 1 to 4% by weight, or an ethylene content of 0.5 to 3.0.
It is composed of an ethylene-butene-propylene copolymer having a butene-1 content of 4 to 15% by weight (hereinafter, simply referred to as a polyolefin-based copolymer). The ethylene-propylene copolymer used in the present invention is a random copolymer having an ethylene content of 1 to 4% by weight, preferably 1.5 to 2.5% by weight, and an ethylene-butene-propylene copolymer. The polymer has an ethylene content of 0.5-3.
It is a random copolymer having 0% by weight and a butene-1 content of 4 to 15% by weight, preferably an ethylene content of 1.0 to 2.0% by weight and a butene-1 content of 7 to 10% by weight. .

In the above ethylene-propylene copolymer and ethylene-butene-propylene copolymer,
When the amount of ethylene or the amount of butene-1 is less than the above range, not only a uniform stretched film cannot be obtained as in the OPP film, but also the blow-cut resistance of the fusion-cut seal portion is deteriorated, which is not preferable. Further, when the ethylene amount or the butene-1 amount is larger than the above range, the mechanical strength of the film becomes insufficient and, in the same manner as in the case of the CPP film, bag forming workability and filling workability become insufficient. Not preferable.

The polyolefin-based copolymer used in the present invention is in a range that does not impair its physical properties, for example, 5
Α-other than ethylene, butene and propylene within mol%
An olefin may be included as a copolymerization component. Also, a mixture of the above polyolefin copolymers or a mixture of the above polyolefin copolymers with other polyolefins can be used. When the polyolefin-based copolymers are mixed with each other, the mixing ratio is arbitrary. When the polyolefin-based copolymer and the other polyolefin are mixed, it is preferable that the content of the polyolefin-based copolymer is 70% by weight or more and the content of the other polyolefin is 30% by weight or less in order to obtain the effects of the present invention. . Examples of other polyolefins include polyethylene, polypropylene and polybutene.

The melt index of the polyolefin copolymer and the mixture thereof used in the present invention is not particularly limited, but in order to impart good film moldability, it is 0.5 to 10 g / 10 minutes, and further 1 to The range is preferably 5 g / 10 minutes.

The biaxially stretched polyolefin film of the present invention has an elongation at MD tensile strength of 5 kg / mm ² of 30 to 150%, preferably 80 to 130%.
The tensile elastic modulus in the MD direction is 80 to 130 kg / mm ² , preferably 90 to 120 kg / mm ² . In addition, MD
The direction is the winding direction of the biaxially stretched polyolefin film. If the elongation at MD tensile strength of 5 kg / mm ² is less than 30%, or the tensile elastic modulus in MD is greater than 130 kg / mm ² , the fracturing resistance of the fusing seal is inferior. Is not preferable. On the other hand, if the elongation at MD tensile strength of 5 kg / mm ² is greater than 150% or the tensile elastic modulus in MD is less than 80 kg / mm ² , the mechanical strength of the film becomes insufficient and Similar to the case of the CPP film, it is not preferable in terms of bag making workability and filling workability, which is not preferable.

The biaxially stretched polyolefin film of the present invention is biaxially stretched. The stretching ratio is not particularly limited, but is preferably 2 to 4 times in the MD direction,
More preferably, it is 3.5 to 3.8 times. Also,
It is preferably 8 to 12 times in the TD direction,
More preferably, it is in the range of 9.0 to 10.5.

The thickness of the biaxially stretched polyolefin film of the present invention is not particularly limited, but in consideration of the bag breakage resistance, bag making workability and filling workability of the fusion-cut seal portion, it is 1
It is preferably 5 to 120 μm, and more preferably 25 to 60 μm.

The biaxially stretched polyolefin film of the present invention may be a monolayer film or a laminated film having two or more layers. By using a laminated film,
Physical properties such as heat-sealing property, different slip property, and gas barrier property can be imparted. In the case of a laminated film, it is preferable that the thickness of the film laminated on the biaxially oriented polyolefin film of the present invention is 20% or less of the laminated film because the performance is not impaired.

At this time, the resin to be laminated is not limited to polyolefin, and a known resin can be adopted depending on the physical properties imparted to the laminated film. For example, in the case of imparting heat sealability, a resin that melts at a temperature lower than that of the polyolefin-based copolymer used in the present invention, for example, an ethylene content of 4 to 8 wt% and a melt index of 4 to 12 is used.
A g / 10 min ethylene-propylene random copolymer may be laminated.

Further, in a laminated film of 2 to 3 layers,
By adding more lubricant to the inner layer than to the outer layer, it is possible to reduce the lubricity of the inner surface of the film and increase the lubricity of the outer surface, and it becomes possible to easily fill the contents and Regardless of the presence or absence, it is possible to prevent the bags from collapsing when stacked.

Further, in order to impart a gas barrier property, an ethylene-vinyl alcohol copolymer, for example, "EVAL" manufactured by Kuraray Co., Ltd., is used on one side of the film by an adhesive resin by a coextrusion method or the like. It can also be laminated. In this case, it is preferable that the surface on which the ethylene-vinyl alcohol copolymer is laminated is the outer surface in order not to impair the effects of the present invention.

Known additives such as antioxidants, crystal nucleating agents, heat stabilizers, release agents, slip agents, antiblocking agents and antistatic agents should be used for various resins used in the present invention. You can As the antiblocking agent, silica, natural zeolite, synthetic zeolite, kaolin, talc, silicone resin, silicone rubber, fused silica,
Fine particles such as melamine resin and acrylic resin may be used. These fine particles are preferably spherical, and more preferably rubber-based, which is softer than the polyolefin-based copolymer. As the slip agent, higher fatty acid amide type can be used, but it should be noted that if added in a large amount, there is a risk of whitening of the film and loss of transparency and gloss. Generation of static electricity can be suppressed by adding an appropriate amount of antistatic agent. When the corona treatment is performed, the effect is further improved and printability and laminating processability can be imparted.
When an appropriate amount of anti-fog agent is added, the polyolefin-based copolymer used in the present invention easily exhibits an anti-fog effect, and the inner surface of the bag has excellent anti-fog effect even without corona treatment, and can be sufficiently used for packaging of fruits and vegetables. Become.

The biaxially stretched polyolefin film of the present invention can be manufactured by the following method. First, a polyolefin-based copolymer is melted and kneaded with an extruder, and the melted resin is cooled and solidified into a sheet on a cooling roll with a T-type die. The obtained sheet is heated by a longitudinal stretching machine and stretched 2 to 4 times, and subsequently heated by a transverse stretching machine and then 8 to 8 in the width direction.
Stretch 12 times. It is preferable to relax 5 to 15% at a temperature slightly higher than the stretching temperature after the transverse stretching because the shrinkage of the fusion-cut seal portion can be improved.

[0021]

The biaxially stretched polyolefin film of the present invention is excellent in bag alignment during bag-making work, and also has excellent bag breakage resistance of the fusing seal portion during filling work, and
Difficult to tear the bag against vibration, shock and drop when transferring or handling the package. In addition, it has excellent performance in terms of transparency and gloss, which is not inferior to conventional films.
Therefore, the biaxially oriented polyolefin film of the present invention can be suitably used as a general packaging film,
It can be suitably used as textiles and miscellaneous goods, envelopes for catalogs and magazines, and packaging bags for heavy fruits and vegetables.

[0022]

EXAMPLES Examples and comparative examples are given below to specifically describe the present invention, but the present invention is not limited to these examples. The physical properties of the films in the following examples and comparative examples were measured by the following methods.

(1) Tensile strength and elongation The sample was cut into a strip with a width of 10 mm, and the measurement length was 40 mm.
Was recorded on a chart paper at a tensile speed of 300 mm / min and a chart speed of 300 mm / min. The elongation of 5 kg / mm ² was read from the base point.

(2) Tensile modulus The sample was cut into strips with a width of 10 mm, and the measurement length was 20 mm.
The rising angle was recorded on the chart paper by a tensile tester at a tensile speed of 20 mm / min and a chart speed of 2000 mm / min. A perpendicular line was drawn at a point 20 mm from the base point, the strength at the intersection with the tangent line was read, and the tensile elastic modulus was calculated by the following formula.

Tensile modulus (kg / mm ² ) = [strength (k
g) x sample length (mm) x chart speed (mm / min)] ÷
[Pulling speed (mm / min) × 20 mm × Film thickness (mm) × Film width (mm)] (3) Drop bag breakage rate Kyoei Co., Ltd. PP-500 type For fusion cutting sealer equipped with fusing blade for OPP film The fusing seal temperature 38
Bag size 250 x 30 under conditions of 0 ℃ and bag making speed of 80 sheets / min
A 0 mm bag was produced. 1 kg of potatoes was placed in this bag and naturally dropped on the floor from a height of 0.75 m. The floor was made of PVC tile manufactured by Toyo Rinorum Co., Ltd. As the evaluation method, the same bag was dropped up to 15 times, and the number of drops until the bag was broken was measured. The number of tests was set to 10 and the bag breakage rate was calculated by the following formula.

Bag breakage rate (%) = [15-number of drops until bag breakage] ÷ 15 × 100 In the case of OPP film, the fusing seal temperature is 400 ° C. and in the case of CPP film, the optimum strength is obtained. Similarly, the same conditions were used except that the fusing seal temperature was changed to 230 ° C.

(4) Bag-making workability In a PP-500 type bag-making machine manufactured by Kyoei Co., Ltd., bag dimensions (W × L) of 250 × 300 mm were obtained under the conditions of fusing seal temperature of 380 ° C. and bag-making speed of 120 sheets / min. Continuous bag making. A bag 1 made by a person skilled in this work
When the 00 pieces are neatly aligned, the case where the bag alignment is completed by the time the next 100 sheets are manufactured is marked with ◯, and the case where the bag alignment is not completed is marked with x.

Example 1 Ethylene content 2.2% by weight, melt index 2.
100 parts by weight of an ethylene-propylene copolymer of 2 g / 10 minutes, 0.2 parts by weight as an antioxidant (BHT), glycerin monostearate and N, N 'as an antistatic agent.
0.1 parts by weight of bis (2-hydroxyethyl) stearylamine, 0.01 parts by weight of erucic acid amide, 0.04 parts by weight of calcium stearate, and 0.1 parts by weight of silicone rubber fine particles having an average particle diameter of 2 μ were added. And melt-kneaded to obtain a raw material for a biaxially stretched film. This raw material was melt-extruded at 260 ° C. using a T-die type extruder, and a 1.35 mm sheet was formed on a casting roll at 40 ° C. This sheet was preheated with a heating roll at 125 ° C. and stretched 3.5 times in the machine direction. Then, the film was stretched 9 times in the transverse direction in a transverse stretching machine heated to 145 ° C., and then relaxed in the transverse direction by 7% at 150 ° C. in a heat setting zone of the transverse stretching machine. The thickness of the obtained film was 40 μm. Table 1 shows the strength, elongation, tensile modulus of elasticity of the film thus obtained, and the bag-making workability and bag-breaking test result of the bag made by the fusing and sealing machine.

Example 2 Ethylene content 1.3% by weight, butene-1 content 7.0
% By weight and 100 parts by weight of ethylene-butene-1-propylene copolymer having a melt index of 5.0 g / 10 min.
Same as Example 1 except that the resin containing the same additives as in Example 1 was melt extruded at 240 ° C. using the same T-die type extruder to form a sheet of 1.02 mm on a casting roll at 30 ° C. Biaxial stretching was performed under the conditions. The thickness of the obtained film was 30 μm. The performance of the film thus obtained was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3 Ethylene content 2.5% by weight, melt index 6.
A mixture of 80 parts by weight of an ethylene-propylene copolymer at 0 g / 10 minutes and 20 parts by weight of a propylene homopolymer at a melt index of 2.0 g / 10 minutes with the same additives as in Example 1 was also subjected to T-die type extrusion. Melt extruding at 250 ° C using a machine and 1.3 on a casting roll at 35 ° C.
Biaxial stretching was performed under the same conditions as in Example 1 except that a 5 mm sheet was used. The thickness of the obtained film is 40 μm
Met. The performance of the film thus obtained was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 Ethylene content 2.2% by weight, melt index 2.
70 parts by weight of an ethylene-propylene copolymer at 2 g / 10 minutes, an ethylene content of 1.3% by weight, a butene-1 content of 7.0% by weight, and a melt index of 5.0 g / 10 minutes of ethylene-butene-1-. A mixture of 30 parts by weight of the propylene copolymer and the same additives as in Example 1 was mixed with T
Biaxial stretching was performed under the same conditions as in Example 1 except that melt extrusion was performed at 260 ° C. using a die-type extruder, and a 1.35 mm sheet was formed on a casting roll at 40 ° C. The thickness of the obtained film was 40 μm. The performance of the film thus obtained was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 The same additives as in Example 1 were blended except that 100 parts by weight of a propylene homopolymer having a melt index of 2.0 g / 10 min was added with 1.0 part by weight of an antistatic agent, and Biaxial stretching was performed under the same conditions as in Example 1 except that melt extrusion was performed at 280 ° C. using a T-die type extruder and a 1.35 mm sheet was formed on a casting roll at 35 ° C. However, since the obtained film has insufficient longitudinal stretching ratio, MD
The thickness in the direction was as large as 30 to 120 μm, and unevenness was partially mixed in a mottled area, and a film that could be used practically was not obtained.

Comparative Example 2 A resin similar to that of Comparative Example 1 was biaxially stretched in a longitudinal stretching ratio of 5
The same procedure as in Example 1 was performed except that the film was stretched to 00%. The thickness of the obtained film was 40 μm. The performance of the film thus obtained was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 3 Ethylene content 1.3% by weight, butene-1 content 7.0
% Of ethylene-butene-1-propylene copolymer having a melt index of 5.0 g / 10 min and the same additives as in Example 1 were blended, and the same T-die type extruder was used at 210 ° C. Melt extrusion was carried out to obtain a 40 μm unstretched film on a casting roll at 30 ° C. The performance of the film thus obtained was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 4 Propylene-butene-containing 26.5 mol% butene-1 described in Example 1 of JP-B-5-82416.
50% by weight of random copolymer and ethylene content of 5.8
A mixture with 50% by weight of propylene-ethylene random copolymer of mol% was melt extruded using a T-die type extruder at 230 ° C. and 1.35 on a casting roll at 40 ° C.
mm sheet. This sheet was preheated with a heating roll at 120 ° C. and stretched 3 times in the machine direction. Then 120 ° C
After being stretched 3 times in the transverse direction in the transverse stretching machine heated to 1, it was relaxed in the transverse direction by 7% at 120 ° C. in the heat setting zone of the transverse stretching machine. The thickness of the obtained film was 40 μm. The performance of this film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0036]

[Table 1]

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29L 7:00

Claims (1)

[Claims] 1. An ethylene-propylene copolymer having an ethylene content of 1 to 4% by weight, or an ethylene content of 0.5.
-3.0 wt% and butene-1 content 4-15 wt% ethylene-butene-propylene copolymer, MD
Direction tensile strength 5kg / mm ² elongation of 30 ~
It is 150% and the tensile elastic modulus in the MD direction is 80 to 130.
A biaxially stretched polyolefin film, characterized in that it is kg / mm ² .