JP3792015B2 - Polyolefin film - Google Patents

Description

【００５４】
【表２】

【００５５】
【表３】

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyolefin film, and more particularly to a polyolefin film suitable for a stretch packaging film excellent in transparency, stretch properties, self-adhesiveness, flexibility, cut property, and bottom surface sealability.
[0002]
[Prior art]
As a film suitable for stretch packaging excellent in packaging machine suitability such as transparency, stretchability, self-adhesiveness, flexibility, cut property, and bottom surface sealing property, a film mainly composed of soft polyvinyl chloride is frequently used.
[0003]
However, as environmental problems are highlighted, the generation of harmful gases due to incineration and the shift of plasticizers to packages are regarded as problems, and packaging materials that replace soft polyvinyl chloride have begun to be demanded. As a result, a polyolefin film made of an ethylene-vinyl acetate copolymer, a polyethylene-based resin, a polypropylene-based resin or the like has been attracting attention. However, they have not been sufficiently put into practical use as stretch packaging films, despite being excellent in transparency, flexibility, stretchability and the like and having high strength.
[0004]
The reason is that the overlapping part of the film on the lower surface of the tray is stiff at the time of packaging, and it is difficult to fold and seal the film pieces with sufficient overlap and adhesion (hereinafter, the bottom surface sealing property is poor). And). In this case, the lower surface of the tray rises due to the low adhesiveness of the overlapped portion, causing problems such as tilting of the tray during display at the store. In addition, since the self-adhesiveness between films is inferior, if the lower surface of the tray is not applied to the hot plate for a certain period of time during pillow packaging or stretch packaging, a highly airtight film cannot be sealed and moisture generated from the contents leaks. It was easy to occur.
[0005]
[Problems to be solved by the invention]
Against this background, the present invention provides a polyolefin film that is excellent in packaging machinery such as transparency, stretchability, self-adhesiveness, flexibility, and cutability, and particularly excellent in bottom surface sealing properties and suitable for stretch packaging. With the goal.
[0006]
[Means for Solving the Problems]
The present inventors have continued earnestly research in view of the above problems. As a result, the inventors have found that the above problems can be solved by using a specific polyolefin composition containing liquid paraffin as a film raw material, and have completed the present invention.
[0007]
That is, the present invention provides: a) a propylene-based polymer having a content of monomer units based on propylene of 97 mol% or more, 5 to 70 wt%
b) Propylene-ethylene random copolymer having a content of monomer units based on propylene of 40 to 95 mol% and a content of monomer units based on ethylene of 60 to 5 mol% 95 to 30% by weight %
c) A polyolefin film comprising a polyolefin composition comprising 1 to 20 parts by weight of liquid paraffin with respect to 100 parts by weight of a resin component comprising a) a propylene-based polymer and b) a propylene-ethylene random copolymer.
[0008]
The present invention will be described in detail below.
[0009]
The a) propylene polymer used in the present invention has a content of monomer units based on propylene of 97 mol% or more. Specifically, in addition to a propylene homopolymer, a random copolymer of 97 mol% or more of propylene and 3 mol% or less of another monomer copolymerizable with this can be mentioned. Here, the other monomer is preferably an α-olefin having 2 to 12 carbon atoms such as ethylene, 1-butene, 3-methylbutene, 4-methyl-1-pentene, 1-hexene, and among these, ethylene is particularly preferable. Is good.
[0010]
These propylene polymers can be usually obtained by polymerization in the gas phase or liquid phase in the presence of a transition metal catalyst. These may be used alone or in combination. In addition, when the content of the monomer unit based on propylene is less than 97 mol%, it is not preferable because the cut property of the obtained film is not sufficient and the tightening force at the time of packaging cannot be obtained.
[0011]
The melt index (MI) at 230 ° C. of the propylene polymer is preferably 0.1 to 20 g / 10 min. When the MI is in the above range, the film appearance is hardly deteriorated due to the occurrence of surface roughness during film formation, the transparency is hardly deteriorated, and the strength of the film is hardly lowered.
[0012]
The propylene-ethylene random copolymer used in the present invention has a monomer unit content based on propylene of 40 to 95 mol%, preferably 50 to 80 mol%, and is an ethylene based monomer. The unit content is 60 to 5 mol%, preferably 50 to 20 mol%. These can usually be obtained by copolymerizing propylene and ethylene in the gas phase or liquid phase in the presence of a transition metal catalyst.
[0013]
Here, when the content of the monomer unit based on propylene is less than 40 mol%, the transparency is lowered, and since the self-adhesiveness is too high, blocking occurs during unwinding of the film, and 95 mol% is reduced. When exceeding, since a softness | flexibility, stretch property, and self-adhesion are not enough, it is unpreferable.
[0014]
The propylene-ethylene random copolymer preferably has an MI at 230 ° C. of 0.1 to 20 g / 10 min. When the MI is in the above range, the film appearance is hardly deteriorated due to the occurrence of surface roughness during film formation, the transparency is hardly deteriorated, and the strength of the film is hardly lowered.
[0015]
In the present invention, the above-mentioned a) propylene polymer and b) propylene-ethylene random copolymer are: a) 5 to 70% by weight of propylene polymer, preferably 6 to 60% by weight, b) propylene- The ethylene random copolymer is blended at a ratio of 95 to 30% by weight, preferably 94 to 40% by weight. Here, a) When the blending amount of the propylene-based polymer is less than 5% by weight, the tightening force and the cutting property at the time of packaging become insufficient, and when it exceeds 70% by weight, the stretch property, self-adhesiveness, flexibility, The bottom sealing performance is insufficient.
[0016]
The blending of the a) propylene-based polymer and b) the propylene-ethylene random copolymer may be mechanically blended, but a part or all of each may be microblended by block copolymerization. May be. In particular, from the viewpoint of improving the cut property with a serrated blade during stretch packaging of the resulting polyolefin film, a) the propylene-based polymer accounts for 10 to 80% by weight, preferably 10 to 70% by weight in the component. However, it is preferable that it is mix | blended as a block copolymer with b) propylene-ethylene random copolymer.
[0017]
At that time, the propylene-ethylene block copolymer may be obtained by any known method. Specifically, as described in JP-B-7-53771, first, in the first stage polymerization, a propylene-based polymer containing titanium is produced in the presence of a titanium compound and an aluminum compound, and then, In the second stage polymerization, propylene and ethylene are preferably copolymerized in the presence of the propylene polymer.
[0018]
In the present invention, as the resin component, in addition to the above-mentioned a) propylene polymer and b) propylene-ethylene random copolymer, other resins are used in such an extent that the effects of the present invention are not impaired, preferably in the range of 5% by weight or less. May be blended. Specific examples of other resin components include other polyolefins such as polyethylene and polybutene. These other polyolefins may be blended by block copolymerization with a) a propylene-based polymer or b) a propylene-ethylene random copolymer.
[0019]
Next, as the liquid paraffin used in the present invention, known paraffins are used without limitation. Generally, it consists of saturated hydrocarbons that are colorless and transparent, tasteless and odorless, and highly purified. In the present invention, by blending liquid paraffin in this way, the resulting polyolefin film has improved bottom sealability during stretch wrapping and self-adhesion between films. Here, the density of the liquid paraffin at 15 ° C. is 0.85 to 0.91 g / cm ³ , preferably 0.85 to 0.88 g / cm ³ , and the liquid paraffin has a kinematic viscosity at 20 ° C. of 10 to 10. 600 cSt, preferably 50 to 300 cSt is suitable. When the density and kinematic viscosity of the liquid paraffin are within the above ranges, slipping with the screw does not occur during granulation or film formation, and excessive adhesion due to liquid paraffin does not occur, so that handling is easy, which is particularly preferable. .
[0020]
The blending amount of the liquid paraffin is 1 to 20 parts by weight, preferably 3 to 15 parts by weight, per 100 parts by weight of the a) propylene polymer and b) propylene-ethylene random copolymer. Here, when the blending amount of the liquid paraffin is less than 1 part by weight, the bottom sealing property becomes insufficient, and when it exceeds 20 parts by weight, the film forming property is deteriorated.
[0021]
In the present invention, additives may be added to the above polyolefin composition in order to impart various properties to the film. For example, weathering agents such as antioxidants and ultraviolet absorbers, anti-blocking agents, flame retardants, adhesives, colorants, matting agents, antistatic agents, antifogging agents, oxygen and carbon dioxide gas absorbents, gas adsorbents , Freshness-retaining agents, deodorants, and fragrances.
[0022]
Any known molding method may be used for forming the film using the polyolefin composition. Specifically, methods such as an extrusion casting method, an upward inflation method, a downward water-cooled inflation method, a biaxial tenter method, and a tubular biaxial stretching method can be used without any limitation. The film thus obtained may be unstretched, and may be uniaxially or biaxially stretched after film formation, but the stretch ratio should be in the range of 40 times or less in terms of area magnification. preferable.
[0023]
In the present invention, in order to further improve the self-adhesiveness and bottom surface sealing property of the film, the content of monomer units based on ethylene is 90 to 98 on at least one surface of the polyolefin film made of the polyolefin composition. From an ethylene-vinyl acetate copolymer having a mol%, preferably 92 to 97 mol%, and a monomer unit content based on vinyl acetate of 10 to 2 mol%, preferably 9 to 3 mol%. It is preferable to laminate the surface layer. Here, when the content of the monomer unit based on vinyl acetate in the ethylene-vinyl acetate copolymer is less than 2 mol%, the effect of improving the self-adhesiveness and the bottom surface sealing property is not sufficient, and the single unit based on vinyl acetate. If the content of the monomer unit exceeds 10 mol%, the cutting property and the tightening force at the time of packaging tend to be insufficient, and the self-adhesiveness is too high, so that blocking tends to occur when the film is unwound. .
[0024]
The ethylene-vinyl acetate copolymer preferably has an MI at 190 ° C. of 0.1 to 20 g / 10 min. When MI is in the above range, the deterioration of the film appearance and the deterioration of transparency due to the occurrence of surface roughness during film formation are particularly small, and the decrease in the strength of the film is also small, which is preferable. .
[0025]
In the present invention, additives may be added to the surface layer composed of the ethylene-vinyl acetate copolymer in order to impart various properties to the film. For example, weathering agents such as antioxidants and ultraviolet absorbers, anti-blocking agents, flame retardants, adhesives, colorants, matting agents, antistatic agents, antifogging agents, oxygen and carbon dioxide gas absorbents, gas adsorbents , Freshness-retaining agents, deodorants, and fragrances.
[0026]
Moreover, as a method for laminating the surface layer composed of the ethylene-vinyl acetate copolymer on the polyolefin film, any known laminating method may be used, but a laminating method by coextrusion is general.
[0027]
In the present invention, the thickness of the polyolefin film is preferably 5 to 100 μm, more preferably 7 to 30 μm, from the viewpoints of film strength, transparency, cutability, and bottom sealability. In the case of a laminated polyolefin film in which a surface layer made of an ethylene-vinyl acetate copolymer is laminated on at least one surface of the polyolefin film, the thickness of the entire film is 5 to 100 μm, and the thickness of the surface layer is The thickness of the base material layer made of the polyolefin film is preferably 50% or less from the viewpoints of cutability and tightening force during packaging.
[0028]
【The invention's effect】
The polyolefin film of the present invention is excellent in suitability for packaging machines such as transparency, stretchability, self-adhesiveness, flexibility, and cutability, and extremely excellent in bottom sealability. Therefore, it is extremely useful as a stretch packaging film.
[0029]
【Example】
Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.
[0030]
▲ 1 ▼ MI
Propylene homopolymer, propylene-ethylene random copolymer, and propylene-ethylene block copolymer were measured according to JIS-K7210. On the other hand, the ethylene-vinyl acetate copolymer was measured according to JIS-K6730.
[0031]
(2) Density The density was measured according to JIS-K7112.
[0032]
(3) Kinematic viscosity Measured according to JIS-K2283.
[0033]
(4) Haze Measured according to JIS-K7105.
[0034]
(5) Stretching property Using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., a film having a width of 300 mm was stretched 100%, and the stretchability of the film was evaluated in two stages.
[0035]
○: No breakage occurs during stretching.
[0036]
X: The film breaks during stretching.
[0037]
(6) Adhesive strength (self-adhesive)
One end of a film with a width of 15 mm and a length of 60 mm is overlapped over 10 mm, and is crimped at 23 ° C. and a pressure of 2.5 kPa. The distance between the chucks is 50 mm and the crosshead speed is 50 mm / min so that the crimped portion is in the center of the chuck. Tensile stress was measured by using to determine the adhesive strength.
[0038]
(7) Cut property Using a stretch automatic wrapping machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., an automatic wrapping machine was used to evaluate whether or not the film can be cut with a serrated blade.
[0039]
(Double-circle): It can cut well and a cut end is also smooth.
[0040]
○: Cut is possible, but the cut is not smooth.
[0041]
X: Cut property is insufficient.
[0042]
(8) Bottom sealing property Using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., packaging a Chuo Kagaku C-65 foam tray with 4 pieces of mandarin orange on a 300 mm wide film, The sealability was evaluated in three stages.
[0043]
○: The overlapping portions of the film are sufficiently overlapped, and the seal portion is in close contact.
[0044]
Δ: Although the overlapping portions of the film overlap to some extent, the adhesion of the seal portion is insufficient.
[0045]
X: The overlapping part of the film does not overlap, and therefore the seal part does not adhere.
[0046]
(9) Finishing feeling Using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., a C-65 foam tray made of Chuo Chemical Co., Ltd. with 4 pieces of mandarin orange on a 300 mm wide film was packed, and then the tray was packed. The film tension was evaluated in three stages.
[0047]
○: A film that wraps the tray is stretched and tightened.
[0048]
Δ: Some wrinkles are generated on the film in which the tray is packaged, and the tightening force is reduced.
[0049]
×: Wrinkles are generated on the film in which the tray is packaged, and the film is not tightened.
[0050]
The resin and liquid paraffin used in the present invention are as follows.
[0051]
Resin component P1; propylene homopolymer (MI 2.0 g / 10 min)
R1: propylene-ethylene random copolymer (content of monomer units based on ethylene 2.0 mol%, MI 2.0 g / 10 min)
R2: propylene-ethylene random copolymer (ethylene monomer content 23 mol%, MI 1.5 g / 10 min)
R3: propylene-ethylene random copolymer (content of monomer unit based on ethylene: 35 mol%, MI 1.5 g / 10 min)
B1: propylene-ethylene block copolymer (propylene homopolymer part 7% by weight, propylene-ethylene random copolymer part 93% by weight of ethylene-based monomer unit content 23% by weight, MI 2.0 g / 10 min)
B2: propylene-ethylene block copolymer (propylene homopolymer part 18% by weight, propylene-ethylene random copolymer part having a monomer unit content of 35 mol% based on ethylene, 82% by weight, MI 1.6 g / 10 min)
V1; ethylene-vinyl acetate copolymer (content of monomer unit based on vinyl acetate 5.8 mol%, MI 2.7 g / 10 min)
V2; ethylene-vinyl acetate copolymer (content of monomer unit based on vinyl acetate 8.9 mol%, MI 1.0 g / 10 min)
Liquid paraffin component L1; density 0.86 g / cm ³ , kinematic viscosity 220 cst
L2: density 0.85 g / cm ³ , kinematic viscosity 100 cst
Examples 1-9, Comparative Examples 1-4
The resin component and liquid paraffin shown in Table 1 were mixed at the blending ratio shown in Table 1, and then extruded at 190 ° C. with an annular die. Next, air was blown into the melted cylindrical film, and air was blown in an annular shape from the outside to be air-cooled and solidified. The film was taken up at a blow-up ratio of 6 and a take-up speed of 30 m / min to obtain a single-layer film having a thickness of 13 μm. The results of measuring the physical properties of the obtained film are shown in Tables 2 and 3.
[0052]
Examples 10 and 11
A three-layer inflation die was used. The ethylene-vinyl acetate copolymer shown in Table 1 was extruded from an inner surface layer and outer surface layer extruder. Moreover, the polyolefin composition which mixed the resin component and liquid paraffin shown in Table 1 with the compounding ratio shown in Table 1 was extruded at 180 degreeC from the base material layer extruder. Next, air is blown into the inside of the molten cylindrical film, and air is blown in an annular shape from the outside to be air-cooled and solidified, and taken up at a blow-up ratio of 6 and a take-up speed of 30 m / min. A three-kind three-layer film having a layer thickness of 2 μm was obtained. The results of measuring the physical properties of the obtained film are shown in Table 2.
[0053]
[Table 1]

[0054]
[Table 2]

[0055]
[Table 3]

Claims (5)

A polyolefin film comprising a polyolefin composition comprising 1 to 20 parts by weight of liquid paraffin with respect to 100 parts by weight of a resin component comprising a) a propylene-based polymer and b) a propylene-ethylene random copolymer.
a) 5 to 70% by weight of a propylene polymer having a content of monomer units based on propylene of 97 mol% or more
b) Propylene-ethylene random copolymer having a propylene-based monomer unit content of 40 to 95 mol% and an ethylene-based monomer unit content of 60 to 5 mol% 95 to 30 wt. % The polyolefin film according to claim 1, wherein 10 to 80% by weight of a) the propylene-based polymer is blended as a block copolymer with b) a propylene-ethylene random copolymer. A film for stretch packaging comprising the polyolefin film according to claim 1. The content of the monomer unit based on ethylene is 90 to 98 mol% and the content of the monomer unit based on vinyl acetate is 10% on at least one surface of the polyolefin film according to claim 1 or 2. A laminated polyolefin film obtained by laminating a surface layer made of an ethylene-vinyl acetate copolymer of ˜2 mol%. A film for stretch packaging comprising the laminated polyolefin film according to claim 4.