JPH06200092A - Biaxially oriented polypropylene film - Google Patents

Abstract

(57) [Summary] [Purpose] Biaxial, excellent in transparency, blocking resistance, appearance, etc., wound films do not stick to each other, bag opening is good, and workability during packaging is good. Provided is a stretched polypropylene film. [Structure] A biaxially stretched polypropylene film comprising a composition of the following component A, component B and component C. Component A: 100 parts by weight of crystalline propylene polymer Component B: 0.01 to 0.2 parts by weight of an inorganic or organic antiblocking agent having an average particle size of 0.5 to 3 μm Component C: at least a part of the end Acid-modified low-molecular-weight polyethylene having a number average molecular weight of 800 to 20,000.
1 to 1 part by weight

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially oriented polypropylene film having excellent properties such as transparency, blocking resistance and appearance.

[0002]

2. Description of the Related Art In recent years, biaxially stretched polypropylene films have been widely used for packaging (including containers) of foods and textiles, and for other purposes. They have a drawback that they are in close contact with each other and the opening property of the bag is deteriorated, so that the workability of the packaging is significantly reduced. For the purpose of obtaining a polypropylene film that solves such problems,
Many studies have been made in the past, and a method of adding inorganic fine particles such as silica and talc (Japanese Patent Publication No. 52-161).
34), a method of adding organic fine particles (Japanese Patent Publication No. 50-36262), and the like.

[0003]

However, in order to impart blocking resistance to the biaxially oriented polypropylene film, it is sufficient to increase the addition amount of the above-mentioned inorganic or organic fine particles as an anti-blocking agent. But,
On the other hand, there is a drawback in that the transparency of the biaxially oriented polypropylene film itself is deteriorated by increasing the amount of the antiblocking agent added. On the other hand, when the average particle size of the anti-blocking agent is increased in order to enhance the anti-blocking performance, voids are generated around the average particle size of the anti-blocking agent as a core, and the appearance of the film is impaired. Had. Therefore, an object of the present invention is to provide a biaxially oriented polypropylene film having transparency, blocking resistance, and excellent appearance.

[0004]

[Means for Solving the Problems]

[Summary of the Invention] As a result of intensive studies conducted by the present inventors in view of the above problems, the use of inorganic and organic antiblocking agents having specific particle sizes in specific amounts, and modification with an acid. The present invention has been completed based on the finding that the above object can be achieved by using low molecular weight polyethylene. That is, the present invention is a biaxially stretched polypropylene film comprising a composition of the following component A, component B and component C. Component A: 100 parts by weight of crystalline propylene polymer Component B: 0.01 to 0.2 parts by weight of an inorganic or organic antiblocking agent having an average particle size of 0.5 to 3 μm Component C: At least a part of the end Acid-modified low-molecular-weight polyethylene having a number average molecular weight of 800 to 20,000.
1 to 1 part by weight

[Detailed Description of the Invention] [I] Composition for Biaxially Stretched Polypropylene Film (1) Constituent Components (a) Crystalline Propylene Polymer (Component A) Crystalline Propylene Polymer Used in the Present Invention Examples thereof include a propylene homopolymer and a copolymer composed of propylene as a main component and other α-olefins such as ethylene, butene, hexene, 4-methylpentene, and octene as auxiliary components. Propylene homopolymer is the most preferable, but among the copolymers, a copolymer of propylene and 40% by weight or less of other α-olefin is preferable,
Further, a copolymer with 30% by weight or less, and particularly 20% by weight or less of ethylene or butene is preferable. The copolymer may be a random copolymer or a block copolymer. These crystalline propylene-based polymers can be used alone or as a mixture of two or more. The crystalline propylene-based polymer preferably has II of 40 or more, particularly 60 or more, and particularly 80 or more. In the case of a propylene homopolymer, a polymer having II of 90 or more, particularly 95 or more is suitable in terms of the firmness of the film. Further, an MFR of 0.5 to 10 g / 10 minutes, particularly 1 to 5 g / 10 minutes is preferable in terms of film characteristics.

(B) Inorganic and Organic Antiblocking Agent (Component B) The antiblocking agent blended in the crystalline propylene polymer has an average particle size of 0.5 to 3 μm, preferably 0.8. It is an inorganic or organic type having a thickness of up to 2.5 μm. Inorganic Antiblocking Agent Examples of the inorganic antiblocking agents include silica, zeolite, talc, kaolin and the like. Of these, silica is preferred. In addition, as the shape, a spherical shape is preferable because it has an excellent effect of improving blocking resistance. Organic Antiblocking Agent Examples of the organic antiblocking agent include non-melting type silicone resin powder, polyamide powder, triazine ring-containing condensation type resin powder, and the like, among which non-melting type silicone is used. Resin powder is preferred.
Also, the shape is preferably spherical like the inorganic antiblocking agent. An inorganic or organic antiblocking agent having an average particle size of less than the above range cannot improve the blocking resistance. Further, in an inorganic or organic antiblocking agent having an average particle size exceeding the above range, even if the component C described later is added, the transparency and the appearance (void) cannot be improved.

(C) Low-molecular-weight polyethylene whose end is at least partially acid-modified (Component C) As the low-molecular-weight polyethylene to be blended with the above crystalline propylene polymer, at least a part is acid-modified at the end. It is a low molecular weight polyethylene having a number average molecular weight of 800 to 20,000, preferably 1,000 to 18,000 (hereinafter sometimes simply referred to as "acid-modified low molecular weight PE"). The acid-modified low-molecular weight PE can be synthesized by chemically adding an unsaturated carboxylic acid and / or its anhydride described below to low-molecular weight polyethylene having a terminal double bond, and has a softening point. Is 90 ~
130 degreeC, Preferably it is 95-120 degreeC, and the acid value is 3.
-60 mg KOH / g, preferably 10-50 mg KO
H / g and melt viscosity at 140 ° C. is 1,000 to 2
10,000 cps, preferably 2,000 to 10,000
It shows 0 cps. The low molecular weight polyethylene having a terminal double bond, which is preferable here, is 1,000.
It has 1 to 10, preferably 2 to 7, terminal double bonds per carbon and has a number average molecular weight of 800 to 20,000, preferably 1,000 to 18,000. If the terminal double bond is less than the above range, desired acid modification cannot be performed. Further, if the terminal double bond exceeds the above range, the heat resistance of the acid-modified low molecular weight PE decreases, which is not preferable. Further, if the number average molecular weight is less than the above range, the blocking resistance of the biaxially oriented polypropylene film cannot be improved. If the number average molecular weight exceeds the above range, sufficient acid modification cannot be performed.

Such acid modification is carried out by a melt grafting method or a solution grafting method. For example, in the melt grafting method, the temperature is usually 80 to 250 ° C., preferably 100 to 230 ° C., and the reaction time is usually 0.5. ~ 30 hours, preferably 1
It is carried out under the condition of -20 hours. The unsaturated carboxylic acid and / or the anhydride thereof obtained by the acid modification is preferably 0.1 to 10% by weight, particularly preferably 1% by weight.
It is desirable that the content is ˜8% by weight. As long as it is such a thing, what was directly acid-modified and diluted with the unmodified thing may be sufficient. Such an acid-modified low molecular weight PE can be appropriately selected and used from commercially available products. Unsaturated carboxylic acid Examples of the unsaturated carboxylic acid include (meth) acrylic acid,
Maleic acid, fumaric acid, itaconic acid and the like can be mentioned. Unsaturated Carboxylic Anhydride Examples of the unsaturated carboxylic acid anhydride include maleic anhydride, itaconic anhydride, citraconic anhydride, allylsuccinic anhydride, and nadic acid anhydride.
Of these, maleic anhydride is preferably used.

(2) Amount Ratio Inorganic or Organic Antiblocking Agent The compounding amount of the inorganic or organic antiblocking agent to be added to the above crystalline propylene polymer as a blocking inhibitor for the component B is crystalline propylene. It is 0.01 to 0.2 part by weight, preferably 0.02 to 0.18 part by weight, relative to 100 parts by weight of the polymer. If the amount is less than the above range, it is difficult to obtain the effect of improving blocking resistance. Further, if the blending amount exceeds the above range, the transparency and the appearance (void) cannot be improved even if the component C is blended. Acid-Modified Low Molecular Weight PE The amount of the acid-modified low-molecular weight PE blended as the component C in the crystalline propylene-based polymer is 0.1 to 1 part by weight based on 100 parts by weight of the crystalline propylene-based polymer. It is preferably 0.2 to 0.8 parts by weight. If the content is less than the above range, the appearance (void) cannot be improved. Further, if the blending amount exceeds the above range, the transparency is deteriorated. In the present invention, in addition to these components, antioxidants, stabilizers, processing aids, antistatic agents, additives such as lubricants, and various compounding materials such as olefin-based rubber that are usually used for polyolefin resins impair the effect. Can be added within a quantitative range.

(3) Production of polypropylene resin composition As a method for obtaining the composition by mixing the above components, a known powder mixer, for example, Henschel mixer,
It is preferable to mix using a ribbon blender or the like and knead with an extruder or the like to pelletize. At this time, there is no problem even if a master batch is prepared by blending the components B and C in a larger amount than a predetermined amount, and the master batch is diluted and used during molding.
However, it is preferable to avoid blending the component B and the component C separately and diluting and using them at the time of molding since the effect is lowered.

[II] Production of Biaxially Stretched Polypropylene Film (1) Biaxially Stretched The biaxially stretched polypropylene film of the present invention is obtained by subjecting the polypropylene resin composition to a conventional method, for example, a simultaneous or sequential biaxial stretching method using a tenter. A biaxially stretched polypropylene film can be produced by processing by the inflation method. Among these, it is preferable to employ the sequential biaxial stretching method in which the longitudinal stretching by utilizing the peripheral speed difference of rolls and the transverse stretching by a tenter are performed as described below. (A) Longitudinal stretching First of the biaxial stretching, the longitudinal stretching is performed by utilizing the peripheral speed difference of the rolls. Specifically, it is normally 90 to 140 ° C., preferably 105 to 135 ° C., and is passed between two rolls having different rotation speeds to rotate the roll in the longitudinal direction.
3 to 8 times, preferably 4 to 6 times. (B) Transverse Stretching Next, this longitudinally stretched film is continuously stretched in the transverse direction in a tenter oven 3 to 12 times, preferably 6 to 11 times. (C) Heat setting Next, this biaxially stretched film is usually 120-170.
It is desirable to heat set at a temperature of ° C.

(2) Other Treatments Further, a corona discharge treatment may be performed for the purpose of promoting printability and bleeding of the antistatic agent.

[III] Biaxially Stretched Polypropylene Film (1) Thickness The thickness of the biaxially stretched film thus obtained is determined according to its application, but is usually 5 to 100 μm, preferably 10 to 50 μm. Is the range.

[0014]

【Example】

[I] Evaluation method (1) Haze Based on ASTM-D-1003, four films were stacked and measured. (2) Blocking property As for the blocking property of the film, the two films are stacked so that the contact area of the ^two films is 10 cm ² , placed between two glass plates, and a load of 50 g / cm ² is applied to the film in an atmosphere of 40 ° C. After standing for 7 days, the sheet was peeled off at a pulling speed of 500 mm / min using a Shopper type tester, and the maximum load was read and evaluated. (3) Appearance of Film The state of void formation inside the film was observed with a phase contrast microscope at a magnification of 100 times, and the degree of occurrence was visually evaluated according to the following criteria. A: No void is generated. ◯: Voids are slightly generated. Δ: Many voids are generated. X: Voids are considerably generated.

[II] Experimental Examples Examples 1 to 3 and Comparative Examples 1 to 2 100 parts by weight of a crystalline polypropylene homopolymer powder having an MFR of 2.3 was added as an antioxidant with BHT 0.1.
2 parts by weight and tetrakis [methylene-3- (2 ', 5'
-Di-t-butyl-4'-hydroxyphenyl) propionate] methane (0.12 parts by weight) and the additives shown in Table 1 were mixed, respectively, and mixed at high speed with a Henschel mixer at room temperature for about 2 minutes, and then an extruder was used. Melted, kneaded and extruded at a temperature of 230 ° C. to obtain a pelletized composition. The obtained pelletized composition was melted at a resin temperature of 260 ° C.
The film was extruded and rapidly cooled with a cooling roll at a temperature of 20 ° C. to obtain a sheet-like film, which was sequentially stretched 5 times in the longitudinal direction and 10 times in the lateral direction to finally obtain a stretched film having a thickness of 30 μm. The obtained biaxially stretched film was evaluated for haze, blocking property and film appearance.

[0016]

[Table 1]

[0017]

EFFECTS OF THE INVENTION The biaxially oriented polypropylene film of the present invention as described above has good transparency and is excellent in blocking property and appearance. Since it has good properties, it has good workability during packaging and is industrially very useful as a packaging film and the like.

Claims (1)

[Claims] 1. A biaxially stretched polypropylene film comprising a composition of the following component A, component B and component C. Component A: 100 parts by weight of crystalline propylene polymer Component B: 0.01 to 0.2 parts by weight of an inorganic or organic antiblocking agent having an average particle size of 0.5 to 3 μm Component C: At least a part of the end Acid-modified low-molecular-weight polyethylene having a number average molecular weight of 800 to 20,000.
1 to 1 part by weight