JPH0859855A - Biaxially stretched polyolefin film - Google Patents

Abstract

PURPOSE: To obtain a polypropylene film which has the surface roughened with a homogeneity formerly unattainable and has suitable opacity, light- screening properties, and gloss without detriment to mechanical characteristics, processibility, heat resistance, etc. CONSTITUTION: This film comprises 40-90wt.% crystalline polypropylene having a melt flow rate of 0.5-10 and 60-10wt.% polybutene-1 resin having a melt flow rate of 2-30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matte-like polyolefin film in which crystalline polypropylene is blended with a predetermined amount of polybutene-1 resin having a specific melting index.

[0002]

2. Description of the Related Art In recent years, matte, pearly, or light-shielding films have been used in food packaging, fiber packaging, books, etc.
In the field of office supplies, it is widely used for packaging and packing materials, tapes, ribbons, synthetic papers, etc.

Conventionally, as a method of making a plastic film opaque, a method of adding a white pigment such as titanium oxide, a pearl pigment, an extender pigment, etc., JP-B-63-24532 and JP-A-63-117043 are disclosed. As described, a method of forming a void by stretching after adding a large amount of an inorganic filler is used. However, these methods have a large decrease in fluidity during extrusion due to the addition of a large amount of an inorganic filler such as titanium oxide or calcium carbonate, clogging of the screen back, foaming due to moisture absorption due to the inorganic filler, Trouble is liable to occur during production, for example, it takes a long time to replace the resin. Further, in the above method, the hiding property is high, the contents may be difficult to see in packaging applications, and the appearance of printing may be impaired in print lamination applications. In addition, the obtained film also has drawbacks such as a decrease in glossiness and a film having a significantly roughened surface due to being made porous by stretching.

Further, as described in JP-A-51-32668, a film having a roughened surface is obtained by mixing a large amount of polyethylene. However, this method lacks the degree of roughening in appearance and lacks uniformity, and is not suitable for applications in which appearance is important.

Further, as described in JP-A-52-35272 and JP-B-55-40411, there is a method of obtaining a roughened film using β-crystal isotactic polypropylene. In order to obtain this film, there are severe restrictions on the film forming temperature conditions, and it is difficult to obtain a high-speed and thick film.

Other known methods include a sandblasting method for rubbing the surface of the film with small metal particles to make it rough, and an embossing method for pressing the film with a rough surface roll. Such known methods are already formed films. Since the surface of the film is roughened by rubbing, pressing, etc., it is difficult to obtain a uniform rough film due to unevenness of the rough surface or distortion of the film surface. Further, these methods are generally performed on an unstretched film, and the stretched film is apt to cause troubles such as easy tearing of the film in a manufacturing process or a secondary processing process due to occurrence of small scratches.

[0007]

Therefore, an object of the present invention is to prevent the mechanical properties, workability, heat resistance and the like from being impaired.
An object of the present invention is to provide a polyolefin film which is uniformly roughened and has moderate opacity, light-shielding properties and gloss.

[0008]

As a result of various investigations in order to solve the above-mentioned problems, the present invention provides a crystalline polypropylene which is a commonly used polypropylene biaxially stretched film raw material with a polybutene-1 resin having a specific melt viscosity. It has been found that the intended film can be obtained by using the blended composition, and the present invention has been completed.

That is, according to the present invention, 40 to 90% by weight of crystalline polypropylene having a melt flow rate of 0.5 to 10 is used.
And a biaxially stretched polyolefin film composed of 60 to 10% by weight of a polybutene-1 resin having a melt flow rate of 2 to 30.

The crystalline polypropylene used in the biaxially stretched polyolefin film of the present invention is a homopolymer of propylene, a copolymer of propylene as a main component with other α-olefins, and these homopolymers or copolymers. And the like. In the above copolymer, propylene is 50 mol% or more, and further 90
The amount of the other α-olefin is preferably 50% by mole or more and 50% by mole or less, more preferably 10% by mole or less. Examples of the other α-olefin include ethylene, butene-1, pentene-1, and hexene-1. Etc. can be mentioned.

In the present invention, in order to mold the crystalline polypropylene into a biaxially stretched film, the melt flow rate of the crystalline polypropylene (hereinafter abbreviated as MFR).
Should be 0.5 to 10, and 1 to 4 are more preferable for better moldability.

In the present invention, polybutene-1 resin having an MFR of 2 to 30 is blended with the above-mentioned crystalline polypropylene. Examples of the polybutene-1 resin used here include a homopolymer of butene-1 or a copolymer of butene-1 with another α-olefin, and a blend of these homopolymers or copolymers. be able to. In the above copolymer, butene-1 is preferably 90 mol% or more and the other α-olefin is 10 mol% or less, and the other α-olefin is ethylene, propylene or pentene-1. , Hexene-1 and the like. The polybutene-1 resin in the present invention is more preferably a homopolymer of butene-1.

In the present invention, the polybutene-1 resin is M
FR must be 2 to 30, and 10 to 20 is more preferable for better moldability. When the MFR is less than 2, it becomes almost transparent and a matte tone does not appear, and conversely, when it exceeds 30, the film-forming property becomes unstable, which is not preferable.

The blending amounts of the crystalline polypropylene and the polybutene-1 resin must be 40 to 90% by weight of the crystalline polypropylene and 60 to 10% by weight of the polybutene-1 resin in the proportions of the total amount thereof. I won't. When the amount of the crystalline polypropylene is less than 40% by weight and the amount of the polybutene-1 resin is more than 60% by weight, the matte tone is sufficiently developed, but the strength of the film becomes low, and the film becomes particularly stiff and the secondary processability is poor. Further, if the amount of the crystalline polypropylene is more than 90% by weight and the amount of the polybutene-1 resin is less than 10% by weight, it is not preferable because the matte tone is not sufficiently expressed. Considering these physical properties, the crystalline polypropylene is more preferably in the range of 45 to 70% by weight, further 45 to 55% by weight, the polybutene-1 resin is 55 to 30% by weight, and further 55 to 45% by weight. preferable.

The biaxially stretched polyolefin film of the present invention is biaxially stretched. The degree of stretching is not particularly limited, but in general, it is preferably in the range of 2 to 7 times in the film taking direction and 5 to 12 times in the direction perpendicular thereto.

The thickness of the biaxially stretched polyolefin film of the present invention is not particularly limited, but considering the ease of film formation of the film, the prevention of thickness unevenness, and the application, the thickness is 4 μm to 120 μm. preferable.

Known modifying resins and additives can be added to the above-mentioned crystalline polypropylene and polybutene-1 resin. For example, as the modified resin, polybutene-
Since one resin is soft, it is possible to increase the rigidity of the film by blending a petroleum resin or the like. Further, as the additive, an antioxidant, a crystal nucleating agent, a heat stabilizer, a release agent, a slip agent, an antiblocking agent or an antistatic agent can be used.

Although the biaxially stretched polyolefin film of the present invention has a roughened surface, blocking is unlikely to occur, but when corona treatment is performed, blocking may occur. In this case, examples of the anti-blocking agent include inorganic fine particles typified by silica and organic fine particles such as silicone resin. These fine particles are preferably spherical ones, and more preferably rubber-based ones softer than the polyolefin-based resin. An acrylic resin-based material having a good affinity with the polyolefin-based resin is preferable because it does not impair the transparency inside the film.

As the slip agent, higher fatty acid amides can be used. Generation of static electricity can be suppressed by using 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. The corona treatment is usually performed in an air atmosphere, but a known treatment such as an inert gas atmosphere such as nitrogen gas or carbon dioxide gas may be performed.

The biaxially stretched polyolefin film of the present invention may be manufactured by any method, but it is particularly preferably manufactured by the simultaneous biaxial stretching method or the sequential biaxial stretching method. The sequential biaxial stretching method will be described in detail. First, the crystalline polypropylene and the polybutene-1 resin are mixed in a predetermined composition in advance, or they are supplied to the hopper of the extruder while being weighed. Next, the mixture is melted and kneaded at a temperature of 230 ° C. or higher, preferably 260 to 300 ° C. in an extruder, the molten resin is extruded by a T-type die, and the sheet is placed on a cooling roll at 20 to 80 ° C. It is cooled and solidified into a sheet. The obtained sheet is 120 to 150 with a vertical stretching machine.
After being heated to 0 ° C, it is stretched 2 to 7 times in the machine direction, and subsequently heated to 140 to 160 ° C by a horizontal stretching machine and then stretched 5 to 12 times in the width direction. It is preferable to relax 5 to 15% at a temperature slightly higher than the stretching temperature after the horizontal stretching because the dimensional stability at the time of secondary processing is improved.

The biaxially stretched polyolefin film of the present invention may be a monolayer film or a laminated film having two or more layers. In the case of a laminated film, the resin layer exhibiting a matte tone can be used on one side or both sides depending on the application. However, in the case of a laminated film having three or more layers, it is necessary to allow a resin layer exhibiting a matte tone to be present as the outermost layer. This is because the matte tone can be obtained only when the resin layer is the outermost layer.

By using a laminated film, it is possible to impart properties such as heat-sealing property, different slip property, and gas barrier property. The resin to be laminated is not limited to polyolefin, and a known resin can be adopted depending on the performance to be imparted to the laminated film. For example, in the case of imparting heat sealability, a resin that melts at a lower temperature than the crystalline polyolefin used in the present invention, for example, an ethylene content of 4 to 8% by weight, MFR of 4 to
12 ethylene-propylene random copolymers may be laminated. Further, in the case of imparting different slip properties, a higher fatty acid amide which is a slip agent and an inorganic or organic anti-blocking agent may be added in an appropriate amount to a layer requiring slip properties.

[0023]

EFFECT OF THE INVENTION The matte biaxially oriented polyolefin film of the present invention is uniformly opaque and moderately opaque, unlike the conventional one, without impairing the mechanical properties, processability, heat resistance, etc. of the polypropylene film. Since it has a feeling, light-shielding property and gloss, it can be suitably used for food packaging, fiber packaging, print laminate, adhesive tape, label, ribbon, synthetic paper and the like.

[0024]

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 raw materials and films in the following examples and comparative examples were measured by the following methods.

(1) Melt flow rate (MFR) The melt flow rate was measured according to ASTM-D-1238.

(2) Haze Measured according to JIS-K-6714.

(3) Tensile Strength and Elongation The sample was cut into strips 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 strength and elongation at break were read.

(4) Gloss Measured according to JIS-Z-8741.

(5) Surface roughness (Ra) It was measured according to JIS-B-0601.

(6) Film forming stability Using a sequential biaxial drawing device, the film was drawn 4 times in the vertical direction and 9 times in the horizontal direction at a film forming speed of 50 m / min. The film-forming stability at this time was judged by the following evaluation method. ⊚: The film is stable with no breakage. ◯: Rupture occurs once or twice during the thickness adjustment, but when the thickness accuracy becomes good, the tear disappears. Δ: Occasionally tearing occurs even if the thickness accuracy is improved. X: Tear frequently occurs and continuous production is difficult.

(7) Thickness accuracy Using a sequential biaxial stretching device, the film was drawn 4 times in the vertical direction and 9 times in the horizontal direction at a film forming speed of 50 m / min. The thickness accuracy at this time was judged by the following evaluation method. The thickness accuracy was measured using a dial gauge at 1 cm in the width direction of the film at 5 cm intervals, and the maximum thickness unevenness divided by the average thickness × 100. ⊚: ± 5% or less ○: ± 5% or more and ± 10% or less △: ± 10% or more and ± 20% or less ×: ± 20% or less

Example 1 MFR2 was added to 50% by weight of propylene homopolymer of MFR2.
After dry blending 50% by weight of butene-1 homopolymer of No. 0, the resin melted and kneaded at 280 ° C. by an extruder is extruded from a T-type die having a lip gap of 2 mm, and a thickness of 1 on a cooling roll at 30 ° C. An extruded sheet of 0.3 mm was obtained. The obtained sheet was heated to 145 ° C. by a vertical stretching machine and then stretched 4 times in the machine direction. 155 using a horizontal stretching machine
After heating to 0 ° C, the film was stretched 9 times in the transverse direction and then contracted at 160 ° C in the transverse direction by about 5%. The thickness of the obtained film was 30 μm. The physical properties of the film thus obtained are shown in Table 1.

Example 2 50 wt% of ethylene-propylene copolymer containing 2 wt% of ethylene of MFR2 was dry-blended with 50 wt% of butene-1 homopolymer of MFR20, and then melted at 270 ° C. in an extruder. The kneaded resin is T with a lip gap of 2 mm.
It is extruded from the die and the thickness is 1.
A 3 mm extruded sheet was obtained. The obtained sheet was heated to 140 ° C. by a vertical stretching machine and then stretched 4 times in the machine direction.
Subsequently, it was heated to 150 ° C. by a horizontal stretching machine, stretched 9 times in the transverse direction, and then contracted at 155 ° C. in the transverse direction by about 5%. The thickness of the obtained film was 30 μm. The physical properties of the film thus obtained are shown in Table 1.

Example 3 60% by weight of an ethylene-propylene copolymer containing 2% by weight of ethylene of MFR2 was dry blended with 40% by weight of butene-1 homopolymer of MFR10. Thereafter, the same procedure as in Example 2 was carried out, and the physical properties of the obtained film are shown in Table 1.

Example 4 50 wt% of ethylene-propylene copolymer containing 0.5 wt% of ethylene of MFR8 was dry-blended with 50 wt% of butene-1 homopolymer of MFR20, and then at 240 ° C. in an extruder. Melt and knead resin, lip gap 2mm
Was extruded from the T-type die to obtain an extruded sheet having a thickness of 1.3 mm on a cooling roll at 30 ° C. The obtained sheet was heated to 130 ° C. by a vertical stretching machine and then stretched 4 times in the machine direction. Subsequently, after heating to 150 ° C. by a horizontal stretching machine, the film was stretched 9 times in the transverse direction, and then contracted at 145 ° C. in the transverse direction by about 5%. The thickness of the obtained film was 30 μm. The physical properties of the film thus obtained are shown in Table 1.

Example 5 20% by weight of butene-1 homopolymer of MFR5 was dry blended with 80% by weight of ethylene-propylene copolymer containing 1% by weight of ethylene of MFR1. Thereafter, the same procedure as in Example 1 was carried out, and the physical properties of the obtained film are shown in Table 1.

Comparative Example 1 MFR2 was added to 95% by weight of propylene homopolymer of MFR2.
5 wt% butene-1 homopolymer of 0 was dry blended. Thereafter, the same procedure as in Example 1 was carried out, and the physical properties of the obtained film are shown in Table 1.

Comparative Example 2 70% by weight of butene-1 homopolymer of MFR20 was dry blended with 30% by weight of ethylene-propylene copolymer containing 2% by weight of ethylene of MFR2. Thereafter, the same procedure as in Example 2 was carried out, and the physical properties of the obtained film are shown in Table 1. Although the film has a sufficient matte tone, the strength of the film is low. It is particularly stiff and inferior in secondary workability.

Comparative Example 3 50% by weight of propylene homopolymer of MFR15 was added to MFR.
After 50 wt% of butene-1 homopolymer of 20 was dry blended, the resin melted and kneaded at 250 ° C. by an extruder is extruded from a T-type die having a lip gap of 2 mm, and a thickness of 1 on a cooling roll at 30 ° C. An extruded sheet of 0.3 mm was obtained.
Thereafter, the same procedure as in Example 1 was carried out, and the physical properties of the obtained film are shown in Table 1.

Comparative Example 4 MFR2 was added to 70% by weight of propylene homopolymer of MFR2.
30% by weight of 0 butene-1 homopolymer was dry blended. Thereafter, the same procedure as in Example 1 was carried out, and the physical properties of the obtained film are shown in Table 1.

[0041]

[Table 1]

Claims (1)

[Claims] 1. A biaxially oriented polyolefin film comprising 40 to 90% by weight of crystalline polypropylene having a melt flow rate of 0.5 to 10 and 60 to 10% by weight of polybutene-1 resin having a melt flow rate of 2 to 30.