JPH0859856A - Biaxially stretched polypropylene film - Google Patents

Abstract

PURPOSE: To obtain a biaxially stretched polypropylene packaging film excellent in handleability in packaging work. CONSTITUTION: This film is formed from a compsn. comprising 100 pts.wt. crystalline propylene polymer. 0.01-1 pt.wt. fine org. polymer particles having an average particle size of 0.3-3μm, and 0-01-2 pts.wt. metal hydroxycarboxylate and has excellent clarity, slip properties, and antiblocking properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polypropylene film having excellent transparency, slipperiness and blocking resistance.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene film is
Since it is very excellent in transparency and mechanical properties, it is widely used as a packaging material for various articles such as foods and textiles. However, it has a drawback that the blocking resistance is poor, the wound films stick to each other, the opening property of the bag is deteriorated, and the workability of the packaging is deteriorated. Conventionally, inorganic fine particles have been added as a method for improving the slipperiness and blocking resistance of polyolefin-based films (for example, Japanese Patent Publication No.
52-16134, JP 3-9938) and organic polymer fine particles added (for example, JP 49-11945, JP 57-64522, JP 62-39219). Gazette) is known. Among these, the method using the organic polymer fine particles is more useful than the method using the inorganic fine particles because a film excellent in transparency and scratch resistance can be obtained, but the transparency and slipperiness and blocking resistance The balance was insufficient, and there was a problem that it had not reached the level of satisfying high-level market demands. That is, when the amount of fine particles is reduced in order to achieve high transparency, slipperiness and blocking resistance deteriorate, and a problem occurs in workability in the manufacturing process and processing process of the film, and conversely,
If the properties of slipperiness and blocking resistance are satisfied, the transparency decreases, and there is no film that has both excellent properties of "transparency" and "slippery and blocking resistance" which are contradictory. The current situation.

[0003]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the prior art, and its object is to provide a biaxially oriented polypropylene film excellent in transparency, slipperiness and blocking resistance. is there.

[0004]

The biaxially stretched polypropylene film of the present invention comprises a crystalline propylene polymer 100.
Part by weight, organic polymer fine particles having an average particle size of 0.3 to 3 μm
The gist is that the composition consists of 01 to 1 part by weight and 0.01 to 2 parts by weight of a metal salt of oxycarboxylic acid. The organic polymer fine particles are (meth) acrylic monomers and /
Alternatively, a polymer composed of a monomer component containing a styrene-based monomer is a preferred embodiment.

[0005]

The crystalline propylene-based polymer used in the biaxially oriented polypropylene-based film of the present invention includes propylene homopolymer, or propylene as a main component and ethylene, butene, hexene, 4-methylpentene or octene as a secondary component. And other α-olefin copolymers. Propylene homopolymer is most preferable, but as the above copolymer, a random copolymer or a block copolymer may be used, and 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 crystalline propylene-based polymer may be used alone or as a mixture of two or more. The crystalline propylene-based polymer has an isotactic index (II) of 40 or more, preferably 60 or more, and particularly 80 or more. In the propylene homopolymer, those having II of 90 or more, particularly 95 or more are preferable. The melt index is 0.5-
It is preferably 10 g / 10 minutes, particularly 1 to 5 g / 10 minutes.

The molecular structure of the organic polymer fine particles used in the present invention is not particularly limited as long as it is non-melting at the melt molding temperature of the polypropylene polymer and has heat resistance capable of withstanding the same temperature. It may be one obtained by any of the addition polymerization method, polycondensation method and polyaddition reaction method. The polymer constituting the fine particles may be a non-crosslinked type or a crosslinked type, but the crosslinked type is recommended from the viewpoint of heat resistance.

The method of micronizing the polymer in the present invention is not limited, but a method of directly micronizing during polymerization using a method such as emulsion polymerization or suspension polymerization is preferable. When these polymerization methods are adopted, a means for copolymerizing a small amount of a polar monomer having a special structure capable of imparting self-emulsifying property may be adopted. The shape of the polymer particles is not particularly limited, but a substantially spherical shape or a rugby ball shape is preferable.

In the present invention, as the organic polymer fine particles,
It is preferable to use polymer fine particles composed of a monomer component containing a (meth) acrylic monomer and / or a styrene monomer, a homopolymer of a (meth) acrylic monomer or a styrene monomer, a copolymer of a (meth) acrylic monomer (copolymer). The above terpolymers are also included. The same applies hereinafter), copolymers of styrenic monomers, copolymers of (meth) acrylic monomers and styrenic monomers, and the like. Of these, cross-linking type (meth) acrylic-ftylene-based copolymers are preferable, and they are excellent in balance of transparency, slipperiness, heat resistance and the like.

Examples of the (meth) acrylic monomer component include acrylic acid, methyl acrylate, ethyl acrylate, acrylic acid such as butyl acrylate, or ester derivatives thereof, methacrylic acid, methyl methacrylate, ethyl methacrylate, methacrylic acid. Methacrylic acid such as butyl or an ester derivative thereof can be mentioned. These monomers may be used alone or in combination of two or more. Further, as long as it is a small amount, a metal salt of (meth) acrylic acid, an amide derivative, an ester derivative having a special structure such as hydroxylethyl ester or dimethylaminoethyl ester may be used.

Examples of the styrene-based monomer component include styrene and its derivatives such as styrene, methylstyrene and α-methylstyrene. Further, a polymerizable vinyl monomer such as vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile or the like may be copolymerized as long as it is 20% by weight or less of the total monomer components. Examples of the cross-linking method include means such as copolymerizing a polyfunctional monomer such as diacrylic acid ester or dimethacrylic acid ester of ethylene glycol with a fine particle polymer, or post-crosslinking after forming the polymer. It is not limited to these. The organic polymer fine particles of the present invention have a water droplet retention time of 1 measured by the following method.
The effect of the present invention is more remarkably exhibited when a highly hydrophilic material having a viscosity of not more than a minute is used.

[Water Drop Holding Time] Organic polymer fine particles are sandwiched between two biaxially oriented polypropylene films on a horizontal and smooth table, and the upper film is lightly pressed by hand to make a smooth organic polymer having a thickness of 2 mm. After forming the fine particle layer,
Gently remove the upper film. Drops of water with a diameter of 3 mm on the surface of the obtained organic polymer fine particle layer with a spid at a height of 1 c
The time required for the water droplets to be dropped from m to be absorbed by the organic polymer fine particle layer and disappear until the water droplets are retained.

In the present invention, the average particle size of the organic polymer fine particles needs to be in the range of 0.3 to 3 μm. 0.
If it is less than 3 μm, the effect of improving the slip property becomes small, which is not preferable. On the contrary, if it exceeds 3 μm, the effect of improving the slipperiness is saturated and the transparency is deteriorated, which is not preferable. The particle size distribution of the organic polymer fine particles is preferably sharp in order to satisfy transparency, slipperiness and blocking resistance. The average particle diameter of the organic polymer fine particles of the present invention is obtained by taking a photograph with a scanning electron microscope, measuring the Feret diameter in the horizontal direction using an image analyzer, and displaying the average value.

In the present invention, the mixing ratio of the organic polymer fine particles in the film is 0.01 to 1 part by weight based on 100 parts by weight of the polypropylene polymer. Preferably 0.02
~ 0.5 parts by weight. The amount of fine organic polymer particles is 0.
If it is less than 01 parts by weight, it is impossible to impart slipperiness and blocking resistance to the film. On the other hand, if it exceeds 1 part by weight, slipperiness and blocking resistance are sufficiently given, but the transparency of the film is improved. Is markedly inhibited, which is not preferable. The optimum value of the average particle diameter and the blending ratio of the organic polymer fine particles described above varies depending on the type of polyolefin, the thickness and configuration of the film, the presence or absence of stretching, etc., and is appropriately set within the above range according to the desired film characteristics. It is good to set it arbitrarily. In the present invention, the oxycarboxylic acid in the metal salt of oxycarboxylic acid is preferably oxystearic acid, and the metal salt of oxystearic acid is the metal acid of stearic acid having one hydroxyl group. 2-, 3-, 4-, 5-,
Although there are 7-, 9-, 11-, 12- and 18-isomers, 12-oxystearic acid is recommended because it can be industrially manufactured at low cost by catalytic reduction of ricinol, which is the main resin acid of castor oil. It is one of the compounds. Examples of the metal salt include alkali metal salts such as Li, Na and K, M
Alkaline earth metal salts such as g, Ca, Sr, Ba, Z
Although there are n salts and the like, the use of Mg and Ca salts is particularly preferable. Further, as the metal salt, a so-called basic metal salt containing a metal in excess of the theoretical value is preferable.

In the polypropylene film of the present invention,
As long as the effect of the present invention is not impaired, organic or inorganic fine particles other than organic polymer fine particles are used in combination, and higher fatty acid amides, higher fatty acid esters, waxes, lubrication of metal soaps other than metal oxystearate, etc. The lubricant is used together to improve the slipperiness, but it can be said that the lubricant is preferably used together. Further, known stabilizers, antistatic agents, ultraviolet absorbers, processing aids, plasticizers and the like which are usually blended in polyolefin films may be used in combination. The method for mixing the organic polymer fine particles, the metal salt of oxystearate, the additive and the like with the polypropylene polymer is not particularly limited, and a V-type blender, a screw-type blender, a dry blender, a ribbon blender, a Henschel mixer. Generally, a method of uniformly mixing with a mixer such as the above and then kneading into pellets is used. The above-mentioned organic polymer fine particles and the metal salt of oxystearate may be kneaded in the extrusion step at the time of film formation, but it is preferable that they are kneaded in a high concentration with respect to the polypropylene polymer in advance, and blended by a so-called masterbatch method. It is an embodiment. Alternatively, the fine particles of the organic polymer and the metal salt of oxystearate may be mixed in advance to form a thin film of the metal salt of oxystearate on the surface of the fine particles of the polymer, and the fine particles may be blended with the polypropylene polymer.

The biaxially stretched polypropylene film of the present invention can be produced by a conventional means such as simultaneous or successive biaxial stretching method using a tenter, or an inflation method using the polypropylene polymer composition. Further, it can be applied to both a single layer structure and a laminated structure of two or more layers,
In the case of a laminated structure, it is preferable to add the organic polymer fine particles and the metal salt of oxystearic acid to the surface layer, but it is not particularly limited. With a laminated structure of two or more layers, and
The method of adding the organic polymer fine particles and the metal salt of oxystearic acid to the surface layer is a particularly recommended embodiment because the effect of the present invention can be more remarkably exhibited. Further, the film of the present invention may be subjected to a surface treatment such as a corona discharge treatment, a plasma treatment, an ultraviolet irradiation treatment or the like to improve the adhesiveness, if necessary. The thickness of the biaxially stretched film of the present invention is determined according to its application, but is usually 5 to 100 μm, preferably
It is in the range of 10 to 50 μm.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification or implementation within the scope of the present invention is within the technical scope of the present invention. Included. The measuring method used in the examples is as follows. (1) Haze tester Haze tester J manufactured by Toyo Seiki Seisakusho according to JIS-K6714
It was measured at. (2) Narrow-angle diffuse transmission value It was measured using a visual transparency tester manufactured by Toyo Seiki Seisakusho. The smaller the measured value, the higher the transparency. (3) Coefficient of friction Measured according to ASTM-D1894 at 20 ° C x 65% RH. (4) Blocking resistance A film is cut into 80 mm x 120 mm with a cutter, and two pieces of the cut pieces are vertically overlapped with each other by shifting 20 mm. Five sets of this sample and type paper are alternately stacked, sandwiched between glass plates, and a weight of 2 kg is applied, and the sample is left to stand in an environment of 50 ° C. for 48 hours. The sample was taken out, allowed to cool, and re-cut in the longitudinal direction with a width of 20 mm to give a test piece. The test piece was measured for shear stress at a pulling speed of 200 mm / min using a tensile tester.

[0017]

Example 1 (1) Manufacture of masterbatch Polypropylene powder with melt index of 2.5 g / 10 min 9
2.5 parts by weight, water drop retention time within 2 seconds and average particle size 1.1
Spherical cross-linked acrylic-styrene copolymer particles having a substantially monodisperse particle size distribution of μm [methyl methacrylate / n
-Butyl acrylate / styrene / divinylbenzene =
36/27/36/1 (weight ratio)] 5 parts by weight and 2.5 parts by weight of basic magnesium 12-hydroxystearate were uniformly mixed using a Henschel mixer, and the mixture was mixed at 200 ° C. using a twin-screw kneading extruder. A melt extruded master batch was obtained. (2) Production of film For 100 parts by weight of polypropylene having a melt index of 2.5 g / 10 min, the master batch produced by the above method 3.1
Using a composition in which 0.3 part by weight of glycerin resin acid ester and 0.3 part by weight of erucic acid amide are mixed, melt extrusion is performed at a resin temperature of 270 ° C, and the mixture is rapidly cooled with a cooling roller at 20 ° C to a thickness of 0.90 mm. To obtain an unstretched sheet. This unstretched sheet was stretched 4.5 times in the machine direction at a stretching temperature of 120 ° C. by utilizing the roll peripheral speed difference of the machine, and was subsequently stretched 8 times in the transverse direction at a stretching temperature of 155 ° C. by a tenter type stretching machine. . Then, heat treatment was carried out at 160 ° C. to obtain a biaxially stretched film having a thickness of about 25 μm, and then one side was subjected to corona treatment. Table 1 shows the compounding recipes of Examples and Comparative Examples, and Table 2 shows the characteristic values of the obtained films.

[0018]

Comparative Example 1 In the same manner as in Example 1, except that in the production of the masterbatch of Example 1, the basic magnesium 12-hydroxystearate was stopped and the amount of polypropylene powder was changed to 95 parts by weight. Masterbatches and films were produced.

[0019]

Comparative Example 2 A masterbatch and a film were produced in the same manner as in Example 1 except that calcium stearate was used in place of the basic magnesium 12-hydroxystearate in the production of the masterbatch of Example 1. The characteristic values of the obtained film are shown in Table 1.

[0020]

Comparative Examples 3 and 4 In the preparation of the masterbatch of Example 1, a film was prepared in the same manner as in Example 1 except that the average particle size of the crosslinked acrylic-styrene copolymer particles was 0.1 μm and 5.0 μm, respectively. Obtained.

[0021]

Comparative Examples 5 and 6 In the preparation of the masterbatch of Example 1, the addition amount of crosslinked acrylic-styrene copolymer particles was 0.05 parts by weight and 1.2 parts by weight, respectively, and the weight loss of the polymer particles was polypropylene powder. A film was obtained in the same manner as in Example 1 except for the cancellation.

[0022]

Example 2 In the method of Example 1, a crosslinked acrylic-
Instead of styrene copolymer particles, spherical cross-linked acrylic polymer particles [composition: methylmethacrylate / trimethylolpropanetri] having an almost monodisperse particle size distribution with an average particle size of 1.7 μm and a water droplet retention time of 2 seconds or less. Methacrylate = 98/2 (weight ratio)] was used, and a film was obtained in the same manner as in Example 1 except that the amount of the masterbatch added was 2.05 parts by weight.

[0023]

[Comparative Example 7] In the preparation of the masterbatch of Example 2, the master was prepared in the same manner as in Example 2 except that the compounding of the basic magnesium 12-hydroxystearate was stopped and the compounding amount of the polypropylene powder was changed to 95 parts by weight. Batches and films were produced.

[0024]

[Example 3] In the production of the masterbatch of Example 1, instead of the crosslinked acrylic-styrene copolymer particles, a substantially monodisperse particle size distribution having a water drop retention time of 2 seconds or less and an average particle size of 1.3 µm was used. Spherical cross-linked polystyrene particles shown [prepared by suspension polymerization: composition; styrene / divinylbenzene = 98
/ 2 (weight ratio)] was used to obtain a film in the same manner as in Example 1.

[0025]

[Comparative Example 8] In the preparation of the masterbatch of Example 3, the master 12 was prepared in the same manner as in Example 3 except that the basic magnesium 12-hydroxystearate was stopped and the polypropylene powder was mixed in an amount of 95 parts by weight. Batches and films were produced.

[0026]

Example 4 As a resin for the base layer, a melt index
0.3 part by weight of glycerin resin acid ester and 0.3 part of erucic acid amide for 100 parts by weight of polypropylene 2.5 g / 10 min
Using the same composition as used in Example 1 as the resin for the surface layer, the lysine for the base layer was melted by a separate extruder, and the melt was merged between the dies to form a base layer. The three-layered melt having surface layers laminated on both sides was rapidly cooled with a chill roll at 20 ° C. to obtain an unstretched sheet with a total thickness of 0.90 mm (surface layer / base layer / surface layer thickness ratio =
1/23/1). This unstretched sheet was biaxially stretched in the same manner as in Example 1 to obtain a film.

[0027]

Comparative Example 9 A film was produced in the same manner as in Example 4 except that the basic magnesium 12-hydroxystearate was stopped in the method of Example 4. The films of the present invention obtained in Examples 1 to 3 all show excellent transparency, good slipperiness and blocking resistance,
It was of very high quality. On the other hand, the films obtained in Comparative Examples 1 and 2 were inferior in transparency and blocking resistance and had low quality. Incidentally, in the "cloudiness value" which is generally used as a method for evaluating transparency, the films of Comparative Examples 1 and 2 are not so different from those of Examples, but have high correlation with transparency by visual observation. It can be seen that the narrow-angle diffuse transmission value is significantly inferior. The films obtained in Comparative Examples 3 and 5 have good transparency, but the sliding properties and blocking resistance are extremely poor, and the films obtained in Comparative Examples 4 and 6 have good sliding properties and blocking resistance. However, the transparency was poor, and the quality was low in all cases. The films obtained in Comparative Examples 7 and 8 were good in slipperiness, but poor in transparency and blocking resistance. The film of the present invention obtained in Example 4 exhibits excellent transparency, good slipperiness and blocking resistance, and is extremely excellent in transparency, and the effect of forming a laminated film is remarkably exhibited. , Extremely high quality. On the other hand, the film of Comparative Example 9 had good transparency and slipperiness, but had poor blocking resistance and low quality.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

EFFECT OF THE INVENTION The polyolefin film of the present invention has a composition in which fine particles of an organic polymer and a metal salt of oxystearic acid are blended in a specific amount, and therefore is excellent in transparency as well as slipperiness and blocking resistance. It can be widely used as a packaging material.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29K 23:00 (72) Inventor Tsutomu Isaka 2-8 Dojimahama, Kita-ku, Osaka-shi, Osaka Toyo Spinning Co., Ltd.

Claims (2)

[Claims] 1. A crystalline propylene polymer 100 parts by weight,
A biaxially oriented polypropylene film comprising a composition comprising 0.01 to 1 part by weight of organic polymer fine particles having an average particle size of 0.3 to 3 μm and 0.01 to 2 parts by weight of a metal salt of oxycarboxylic acid. 2. The biaxially oriented polypropylene according to claim 1, wherein the polymer of the organic polymer fine particles is a polymer polymerized from a monomer component containing a (meth) acrylic monomer and / or a styrene monomer. Series film.