JPH07113075B2 - Stretched polypropylene film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a stretched polypropylene film. More specifically, it relates to a stretched polypropylene film having excellent transparency and blocking resistance.

[Problems to be Solved by Prior Art and Invention]

Stretched polypropylene film, especially biaxially stretched polypropylene film is used for food packaging as a film with excellent balance of mechanical properties such as tensile strength and rigidity, transparency, optical properties such as gloss, moisture resistance and the like, and an excellent balance. It is used in a wide range of applications such as fiber packaging.

However, these properties are not sufficiently satisfied depending on the application, and particularly in applications where transparency and transparency are required, the white turbidity and optical unevenness peculiar to stretched polypropylene film become a problem, and the field of use is greatly increased. The fact that it was limited to the above was an obstacle to application development. Conventionally, as a countermeasure against this, a method of improving transparency by adding a certain nucleating agent to ordinary polypropylene as shown in JP-A-58-129036 and JP-A-58-134714, for example. It is known that in this method, the transparency is improved, but the slip property and the blocking resistance are significantly reduced. Therefore, a slip agent such as an organic fatty acid amide or an inorganic anti-blocking agent such as silica / zeolite is used. Must be added, transparency decreases due to bleed-out of slip agent, voids (voids) with inorganic core as a result of stretching
It caused a decrease in see-through feeling due to the frequent occurrence of. Further, as disclosed in JP-A-60-88049, a method has been proposed in which silicone oil is added as an organic silicon compound to improve slipperiness. Silicone oil is used as a film over time. There are problems such as bleeding out on the surface and formation of an oil film to cause blocking, and deterioration of printability and adhesiveness.

[Means for solving problems]

As a result of intensive studies conducted by the inventors to solve these problems, the following findings have been found. That is, the present inventors have previously stretched a blend obtained by adding a metal salt of a specific cyclic aromatic phosphorus compound and a metal salt of a higher fatty acid together to polypropylene, and thereby stretched the film with remarkably excellent transparency and see-through feeling. It was found that a polypropylene film can be obtained, but as a result of various investigations to improve the slipperiness and blocking resistance without further losing this characteristic, the drawbacks of the conventional method by incorporating a small amount of specific organic cured spherical fine particles It was found that a stretched polypropylene film having excellent transparency and see-through feeling, and improved slipperiness and blocking resistance can be obtained.

The gist of the invention is that the general formula (In the formula, R represents a direct bond, a sulfur atom or an alkylidene group, R ₁ and R ₂ each represent a hydrogen atom, an alkyl group or a cycloalkyl group. L and m are 0 or 1, and n is a valence of a metal. And M ₁ represents a metal atom.) 0.005 to 0.1% of a metal salt of a cyclic aromatic phosphorus compound represented by
5 parts by weight and the general formula (R ₃ COO) ₂ M ₂ (II) (wherein R ₃ is an alkyl group or an alkenyl group having 14 to 18 carbon atoms, and M ₂ is a metal belonging to Group II of the periodic table. 0.01 to 0.40 parts by weight of a higher fatty acid metal salt represented by
It is a stretched polypropylene film excellent in transparency and blocking resistance, which is obtained by stretching a compounded mixture containing 0.5 part by weight in at least a uniaxial direction. The present invention will be described in detail below. That is, the polypropylene resin in the present invention is a crystalline propylene homopolymer, a crystalline copolymer of propylene and ethylene or an α-olefin having 4 or more carbon atoms, or a mixture thereof, in which the propylene component is 93 It is preferable that the content is 85% by weight or more, the insoluble portion in boiling n-heptane (residue after extraction for 6 hours) is 85% by weight or more, and the melt flow rate (MFR) is in the range of 0.5 to 10.

General formula added to polypropylene resin in the present invention The metal salt of a cyclic aromatic phosphorus compound represented by the following will be described in detail. Examples of the alkylidene group represented by R include methylidene, ethylidene, isopropylidene, butylidene, hexylidene, octylidene, nonylidene, cyclobenzylidene, cyclohexylidene, cyclo Octylidene is an example.

As R, a compound having the above alkylidene group rather than a direct bond or a sulfur atom is more effective in the present invention in terms of transparency, and is particularly desirable.

Examples of the alkyl group represented by R ₁ and R ₂ include methyl, ethyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, n-amyl, tertiary amyl, hexyl, heptyl, n-octyl, 2 -Ethylhexyl, tertiary octyl nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl groups and the like.
Examples of cycloalkyl groups include cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl groups and the like.

Further, as a metal atom represented by M ₁ , lithium (L
i), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), strontium (Sr),
Barium (Ba), zinc (Zn), aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe) cobalt (C
o), nickel (Ni), etc., of which Li, N
Periodic table group Ia metals such as a and K and periodic table group IIa metals such as Mg, Ca, Sr and Ba are preferable, and periodic table group Ia metals, that is, Li, Na and K are particularly preferable.

Preferred specific examples of the metal salt of the cyclic aromatic phosphorus compound represented by the above general formula (I) used in the present invention include the compounds shown in [Table 1] below. It is desirable to use a powdery material having a small amount of particles, a uniform particle size and shape, and no aggregation.

Among these preferred examples in Table 1, the compound "methylenebis (2,4-di-t-butylphenol) acid phosphate Na salt" shown by No. is most excellent in the transparency improving effect in the present invention, In addition, homogeneity and dispersibility are also good, which is particularly desirable.

The amount of the metal salt of the above cyclic aromatic phosphorus compound in the present invention is 0.005 to 100 parts by weight of the polypropylene resin.
It is 0.15 parts by weight, preferably 0.01 to 0.05 parts by weight.

If it is less than this range, the effect is insufficient, and if it exceeds this range, the dispersion in the polypropylene resin is extremely deteriorated, and a large number of voids (voids) having this compound as a nucleus are generated by stretching, and the void The diameter is large and the appearance of the film is rather deteriorated, which is not preferable.

In the present invention, in order to suppress the voids enlarged by stretching, it is desirable to select the metal salt of the cyclic aromatic phosphorus compound having an average particle size of 10 μm or less. It is also effective in suppressing.

In the present invention, the general formula (R ₃ COO) ₂ M ₂ (II) (wherein R ₃ is an alkyl group or an alkenyl group having 14 to 18 carbon atoms, M ₂ is a metal belonging to Group II of the periodic table) The specific examples of the higher fatty acid metal salt represented by: are higher fatty acids having 14 to 18 carbon atoms such as myristic acid, palmitic acid, and stearic acid such as calcium (Ca), magnesium (Mg), and zinc (Zn). ) And the like, salts of Group II metals, such as zinc stearate, magnesium stearate, calcium stearate, calcium palmitate, calcium 12-hydroxystearate, zinc myristate, and the like. .

The addition amount of the higher fatty acid metal salt in the present invention is 0.01 to 0.40 parts by weight with respect to 100 parts by weight of the polypropylene resin,
It is preferably 0.03 to 0.30 parts by weight.

If the addition amount of this higher fatty acid metal salt does not reach 0.01 parts by weight, a large number of voids (voids) with the metal salt of the above-mentioned cyclic aromatic compound as a nucleus are generated, and the appearance of the film is remarkably deteriorated. Addition in excess of part does not have the effect of increasing the amount, but rather reduces transparency and bleeds whitening, which is not preferable.

The organic cured resin spherical fine particles used in the present invention do not decompose at the processing temperature of crystalline polypropylene, and are preferably 300 ° C.
In the following, it means a resin which is not melted or decomposed and whose shape is spherical fine particles. Fine powders made of organic polymers are widely known for both thermoplastic resins and thermosetting resins, but in the present invention, they are limited to spherical fine particles that do not substantially decompose or deform at the processing temperature of polypropylene.

As the organic cured resin spherical fine particles, specifically, for example, having a “Si—O—Si” bond obtained by hydrolyzing and condensing a hydrolyzable silane as a structural unit and having a methyl group in a side chain, A silicone resin, which is a three-dimensional polymer having an organic group such as a phenyl group, and a condensation type resin having a triazine ring, such as benzoguanamine / formaldehyde resin or benzoguanamine / melamine / formaldehyde resin, are preferable because of excellent heat resistance.

The method for producing the organic cured resin spherical fine particles is described in JP-A-60-1.
It is known in Japanese Patent No. 3813, JP-A No. 52-16954, etc., and spherical particles having a substantially uniform particle diameter and an arbitrary particle diameter can be obtained.

Among them, in the present invention, a trifunctional silane such as methylchlorosilane and methyltrialkoxysilane or a partial hydrolyzate thereof is treated under an aqueous solution of an alkaline earth metal hydroxide, an alkali metal carbonate, ammonia or an amine. Silicone resin composed of spherical polymethylsilsesquioxane obtained by hydrolysis / condensation has a large effect even when added in a small amount, which is particularly desirable.

Here, the true spherical shape means the ratio of the particle diameter when the spherical particle powder is magnified and observed with an electron microscope or the like, where X is the diameter in the major axis direction and Y is the diameter in the minor axis direction, that is, The sphericity represented by X / Y is 1.0 to 1.25, and the capacity is 5
The content is 0% or more, and when the organic cured resin spherical fine particles having such a sphericity are used, a particularly excellent effect is exhibited.

In addition, since the organic cured resin spherical fine particles are not substantially decomposed or deformed, it is extremely important to adjust the average particle size, and in the present invention, the average particle size must be 5 μm or less. A desirable average particle size is 0.1 to 3 µ. If the average particle size exceeds 5 μ, the irregularities on the film surface become too large, and voids (voids) having these fine particles as cores become visible and the transparency is lowered, which is not preferable.

The addition amount of the organic cured resin spherical fine particles is 0.01 to 0.5 parts by weight with respect to 100 parts by weight of the polypropylene resin, there is no improvement effect if less than 0.01 parts by weight, and the improvement effect increases even if added over 0.5 parts by weight. However, it is not preferable because only the transparency and the appearance are deteriorated.

0.02 to 0.05 parts by weight of trace amount is desirable when high transparency and high transparency are emphasized.0.06 when slipperiness and blocking resistance are emphasized.
0.15 parts by weight is desirable.

In the present invention, the polypropylene resin is blended with the metal salt of the cyclic aromatic phosphorus compound, the higher fatty acid metal salt, and the spherical fine particles of the organic cured resin in a method of uniformly dispersing
Any method of mixing may be used, but it is desirable to uniformly disperse the metal salt of the cyclic aromatic phosphorus compound in the form of finer particles without aggregating, and powdery polypropylene as the main component After being weighed, in powder form, it is well mixed with a ribbon blender, Henschel mixer, etc. and uniformly dispersed, and the powder mixture is melt-kneaded using an extruder or the like, then cooled and cut to be used as a pelletized mixture. Is especially desirable.

The metal salt of the cyclic aromatic compound, the higher fatty acid metal salt, and the organic cured resin spherical fine particles are mixed in a masterbatch to prepare a pellet-shaped mixture at a high concentration, and the masterbatch has a high concentration at the time of film production. It is also possible to form a film by mixing the pellets blended with the above and the pellets not added with the blending range used in the present invention.

If necessary, an antioxidant, a slip agent, and other additives may be appropriately added to the polypropylene resin or the compound used in the present invention.

The method for producing a film in the present invention can be obtained by stretching at least uniaxially by a method usually used for industrially producing a stretched film, for example, a stretching method such as roll stretching, tenter stretching or tubular stretching. . Incidentally, in the case of biaxial stretching, the two directions simultaneously,
Either a sequential or multi-stage stretching method can be applied. Further, it is common to perform heat treatment while stretching or relaxing by a few percent after stretching, and thereafter, surface treatment such as corona discharge may be performed in air or in an inert gas.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, and the excellent characteristics of the present invention will be specifically shown by numerical values, but the present invention is not limited to these Examples.
The characteristic values were measured by the following methods and standards.

(1) Melt flow rate (MFR): JIS K6758 polypropylene test method melt flow rate (conditions: 230 ° C, 2.
16kgf).

(2) Haze According to JIS-K6714, a value (unit:%) measured by stacking four films is shown as four haze. A low haze value means excellent transparency.

(3) Permeability: LS value (narrow-angle diffuse transmission value) measured using "visual transparency tester" manufactured by Toyo Seiki Seisakusho. In addition, the sharpness when an object was permeated through the film was visually judged and shown as "visual see-through feeling". Note that
A low LS value means a good perspective.

(4) Appearance determination: 5 sample films of 20 ^cm x 25 ^cm are superposed and visually observed to have a visible nucleated void (a void in the film having a nucleus at the center, the visible void diameter is about 0.
2 mm or more. ) It was judged by the number.

External appearance Number of nuclear voids ◎ None ○ 1 to 3 △ 4 to 9 × 10 to 20 × × 20 or more (5) Slip property (sliding friction coefficient): measured by the method specified in ASTM D1894-63 The coefficient of static friction is shown.

(6) Blocking power: 2 cm (width) x 7 cm (length) sample films of the same surface are piled up over a length of 2 cm, and under a load of 250 g / cm ² , the temperature is 40 ° C and the relative humidity is 90% RH. After standing for 72 hours, the force required for shear peeling of the sample was determined at a speed of 300 mm / min. Using a tensile tester.

(Unit: g / 4cm ² ) The smaller this value, the better the blocking resistance. (Examples 1 to 5 and Comparative Examples 1 to 4) With respect to 100 parts by weight of crystalline propylene homopolymer powder having MFR = 2.3, 0.12 part by weight of BHT and tetrakis [methylene-3- (2'5) as an antioxidant were used. ′ -Di-t-butyl-
4'-hydroxyphenyl) propionate] methane 0.
After blending 12 parts by weight and the additives shown in Table 2 and mixing at high speed for 2 minutes at room temperature with a Henschel mixer, melt, knead, cool and cut into 9 types of pellets using an extruder. A formulation (composition) was obtained.

The pellets were melt extruded at a resin temperature of 260 ° C. and rapidly cooled with a cooling roll at 35 ° C. to form a sheet having a thickness of 0.9 mm. Next, the obtained sheet is vertically stretched at 153 ° C with a pantograph type stretching machine.
Approximately 3% stretched in both directions in both directions 5.5 times at the same time
While relaxing, it was heat-treated at the same temperature for 10 seconds to obtain a biaxially stretched film having a thickness of about 30μ. The characteristic values of the obtained 9 kinds of films are also shown in Table 2.

Among the additives used in Table 2, the silicone resin is
Inorganic solvent represented by the chemical name methylpolysilsesquioxane, non-melting, spherical particles with a sphericity of 1.06 to 1.12 with heat resistance of 300 ℃ or more, benzoguanamine resin is a benzoguanamine-formaldehyde condensate Similarly, the spherical fine particles are insoluble and infusible and have a heat resistance of 300 ° C. or higher and a sphericity of 1.10.

As is apparent from Table 2, a stretched film obtained by simultaneously adding and blending the metal salt of the cyclic aromatic phosphorus compound, the higher fatty acid metal salt and the organically cured resin spherical fine particles to the polypropylene resin of the present invention (Examples 1 to 5). Are excellent in all film properties, but the films of other comparative examples are extremely inferior in any of the film properties. Particularly, when the organic cured resin spherical fine particles are not added (Comparative Example 3), blocking resistance and It can be seen that the slip property is extremely inferior and the effect of the present invention is extremely large.

(Examples 6 to 9 and Comparative Examples 5 to 10) 100 parts by weight of a crystalline ethylene / propylene copolymer powder having MFR = 3.5 and an ethylene copolymerization ratio of 0.3% by weight, and 0.15 parts by weight of BHT as an antioxidant. Parts and tetrakis [methylene-3- (2'5'-di-t-butyl-4'-
Hydroxyphenyl) propionate] methane (0.10 part by weight) and the metal salt of the cyclic aromatic phosphorus compound used in the present invention (average particle size of 4.5 μ in Table 1) are shown in 0.08 part by weight and calcium stearate (0.05 part by weight) and in Table 3. Each of the additives was blended and pelletized according to Example 1 to obtain 10 types of pelletized blends (compositions).

The pellets are melt extruded at a resin temperature of 260 ° C and rapidly cooled with a cooling roll of 40 ° C to form a sheet having a thickness of 1.6 mm. The sheet is stretched in the longitudinal direction by a tenter type sequential biaxial stretching device.
Stretched 4 times at 140 ℃, and then 158 ℃ in the transverse direction.
Stretching 10 times at 155 ° C and relaxing 3% in the transverse direction (relaxation)
Then, the film was immediately heat-treated and air-cooled, and one side of the film immediately obtained was subjected to corona discharge treatment and then wound up to obtain 10 kinds of single-sided biaxially stretched films having a thickness of 40μ. The corona discharge treatment was carried out by adjusting the wetting index measured by the method of JIS K6768 to be 40 dyne / cm.

The characteristics of the single-sided treated biaxially stretched film thus obtained are also shown in Table 3. Among the additives shown in Table 3,
Examples 6 to 9 and Comparative Example 6 are the same resins as those of Examples 1 and 3 described above, except that the average particle size is changed.
In Comparative Example 7, a silicone resin plate-like material was finely pulverized and then subjected to particle size separation, Comparative Examples 8 and 9 are inorganic silicon compounds, and Comparative Example 10 is a liquid silicone oil at room temperature.

As is clear from Table 3, the films of the present invention (Examples 6 to 9) are excellent in transparency (haze), appearance, slip property and blocking resistance, but the films of Comparative Examples have drawbacks. It has, and there is a problem in practical use.

(Example 10) BFR 0.10 part by weight and magnesium stearate 0.15 part by weight with respect to 100 parts by weight of a crystalline ethylene / propylene random copolymer powder having MFR = 1.3 and an ethylene copolymerization ratio of 5.8% by weight. Part, the same metal salt of a cyclic aromatic phosphorus compound as used in Example 6, 0.03 part by weight, and 0.10 part by weight of polymethylsilsesquioxane powder having an average particle size of 1.2 μ and a sphericity of 1.04 were mixed, and Example 1 Pelletized according to.

Next, the pellets were melt extruded at a resin temperature of 270 ° C.
A sheet with a thickness of 0.25 mm is rapidly cooled with a cooling roll at 100 ° C. This sheet is stretched 5.0 times in the machine direction between rolls heated to 100 ° C and heat-treated at 100 ° C while relaxing 3% in the same direction.
It was rapidly cooled with a 5 ° C. cooling roll to obtain a uniaxially stretched film having a thickness of 50 μm. The characteristics of this film are shown in Table 3.

(Comparative Example 11) To the same crystalline ethylene propylene random copolymer powder as that used in Example 10, only 0.10 part by weight of BHT was added, pelletized according to Example 1, and then formed into a sheet, which was stretched in the vertical direction. -Heat treatment and cooling were performed to obtain a uniaxially stretched film having a thickness of 50μ. The characteristics of this film are shown in Table 3.

[Effects of the Invention] As described above, the polypropylene resin of the present invention, the metal salt of the cyclic aromatic phosphorus compound represented by the formula (I), the higher fatty acid metal salt represented by the formula (II), and the organic cured resin spherical fine particles. The stretched film obtained by stretching the composition of is a film which is particularly clear as compared with the examples, is excellent in transparency and see-through feeling, and is sufficiently slippery and blocking resistant. Taking advantage of these excellent properties, it improves workability in food packaging and fiber packaging, enhances commercial value, mold release applications, print lamination (laminating printed matter) applications, adhesive tapes, etc. It is an extremely excellent film that can be suitably used.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C08L 101: 00) (C08K 5/00 5: 098 5: 527)

Claims (5)

[Claims] 1. A general formula for 100 parts by weight of polypropylene resin (In the formula, R represents a direct bond, a sulfur atom or an alkylidene group, R ₁ and R ₂ each represent a hydrogen atom, an alkyl group or a cycloalkyl group. L and m are 0 or 1, and n is a metal valence. And M ₁ represents a metal atom.) 0.005 to 0.1% of a metal salt of a cyclic aromatic phosphorus compound represented by
5 parts by weight and the general formula (R ₃ COO) ₂ M ₂ (II) (wherein, R ₃ is an alkyl group or an alkenyl group having 14 to 18 carbon atoms, and M ₂ is a metal belonging to Group II of the periodic table. 0.01 to 0.40 parts by weight of a higher fatty acid metal salt represented by
A stretched polypropylene film having excellent transparency and blocking resistance, which is obtained by stretching at least uniaxially a composition prepared by adding 0.5 part by weight. 2. The average particle size of the metal salt of a cyclic aromatic phosphorus compound is
The stretched polypropylene film according to claim 1, which has a thickness of 10 μm or less. 3. The stretched polypropylene film according to claim 1, characterized in that the organic cured resin spherical fine particles are substantially non-melting and spherical spherical silicone resin fine particles having a decomposition temperature of 300 ° C. or higher. . 4. The organic cured resin spherical fine particles have an average particle diameter of 0.1.
The stretched polypropylene film according to claim 1, wherein the stretched polypropylene film has a thickness of 3 μm. 5. The organic cured resin spherical fine particles are benzoguanamine formaldehyde resin or benzoguanamine.
The stretched polypropylene film according to claim 1, which is a cured spherical fine particle of a melamine-formaldehyde resin.