JPH0684450B2 - Method for producing microporous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a production method for continuously forming a microporous film having a high porosity necessary for moisture-permeable waterproofing applications and electret filter applications. is there.

[Prior Art] Conventionally, as a method for producing a microporous film, (1) a porosity is obtained by including an inorganic substance and an incompatible substance (polystyrene, polycarbonate, phenoxy resin) in polyolefin, and then extruding and stretching the mixture. Is formed in the range of 5 to 10% (for example, JP-A-50-116561).

(2) A polyolefin containing an inorganic substance and an organic liquid (dioctyl phthalate), which is then subjected to solvent extraction, alkali extraction, and stretching to form a porosity in the range of 30 to 80% (for example, JP 58-59072 publication).

[Problems to be Solved by the Invention] However, the method for producing a microporous film according to the above item (1) is
Since the incompatible substance is added, it is difficult to form an edge after extrusion, and the elongation at break is lowered, so that the film tends to be broken during stretching.

In addition, in order to obtain a film having a high porosity (30 to 80%), the method for producing a microporous film according to the above item (2) is
Extrude and mold three types of raw materials. Then, a long solvent extraction is required to remove the organic liquid. Further, it has a drawback that a complicated process of extracting after extracting with an aqueous solution of sodium hydroxide for a long time to remove inorganic substances and then stretching is required.

[Means for Solving Problems] The present invention is based on 100 parts by weight of a polyolefin, and 10 to 400 parts by weight of an inorganic substance and 0.001 to 10 parts by weight of a β crystal nucleating agent are added,
Melting temperature of polyolefin (Tm) + 20 ℃ or more, [Tm + 10
Melt extruding at a temperature of 0 ° C or lower, and then holding at a temperature lower than the melting crystallization temperature (Tmc) and at a temperature of [Tmc-50 ° C] or higher, and then stretching to obtain a porosity of 30 to 80%. And a method for producing a microporous film.

The polyolefin polymer applied to the present invention is a known polyolefin, specifically polypropylene, polyethylene, polybutene, polystyrene, poly-4-methylpentene-1, and the like, and may be a copolymer or a blend thereof, but particularly Polypropylene is preferred.

The inorganic substance in the present invention may be any substance as long as it does not contain a carbon compound, specifically, diatomaceous earth,
Powder silica, talc, TiO ₂ , BaSO ₄ , glass fiber, glass beads, ground calcium carbonate, alumina hydroxide, etc. are preferable, and one or more of these may be selected and used. . The average particle size of the inorganic material is preferably 0.01 to 10 μm.

The β crystal nucleating agent in the present invention is sodium benzoate, 1.
Alkali or alkaline earth metal salts of carboxylic acids such as potassium 2-hydroxystearate, magnesium succinate and magnesium phthalate, di- or triesters of di- or tribasic carboxylic acids, aromatic sulfonic acids such as sodium benzenesulfonate Compounds such as phthalocyanine compounds such as phthalocyanine blue or pigments such as quinacridone are preferable, and quinacridone is particularly preferable.

The mixing ratio of the inorganic material to 100 parts by weight of the above-mentioned polyolefin is 10 to 400 parts by weight, preferably 20 to 200 parts by weight. If it is less than 10 parts by weight, the porosity is low.

On the other hand, if it exceeds 400 parts by weight, defective molding during extrusion / casting and film tearing during stretching frequently occur during film production.

Further, the mixing ratio of the β crystal nucleating agent is in the range of 0.001 to 10 parts by weight, preferably 0.002 to 5 parts by weight. 0.0
When it is less than 01 parts by weight, the porosity is low and the nitrogen gas permeability and the temperature are low. On the other hand, if it exceeds 10 parts by weight, the elongation at break and the strength at break of the film will be greatly reduced.

Next, the method for producing the film of the present invention will be described by taking sequential biaxial stretching as an example, but the method is not limited to the following methods, unless otherwise specified.

With respect to 100 parts by weight of polyolefin, 10 to 400 parts by weight of an inorganic substance and 0.001 to 10 parts by weight of a β crystal nucleating agent are mixed in a Henschel mixer, and the melting temperature (Tm) of polyolefin is + 20 ° C. or more in a twin-screw extruder. Melt extruding at a temperature of [Tm + 100 ° C.] or lower, cooling and pelletizing. The pellet raw material is supplied to an extruder and extruded into a sheet at [Tm + 20 ° C] or higher. If the temperature is lower than [Tm + 20 ° C], the unevenness of the film thickness is large, and if it exceeds [Tm + 100 ° C], the β crystal nucleating agent does not grow. Then, below the melt crystallization temperature (Tmc), [Tmc-50
℃] or more, the β crystal ratio in the unstretched film is 10 to 90% by molding on a cast drum
Can be adjusted to

After that, it is biaxially stretched. As a method for biaxial stretching, the film is introduced into an ordinary roll-type or oven-type longitudinal stretching machine, heated to a temperature of the film Tm or lower, [Tm-50 ° C] or higher, and longitudinally stretched in a range of 1.5 to 7.0 times. Preferably.
The porosity and average pore size change depending on the draw ratio, but in order to obtain the required porosity, the total draw ratio in the length and width (the product of the mechanical ratios in the length and width) should be 2.25 to 49 times. Is preferred.

Then, heat with a stenter to a temperature below Tm and above [Tm-50 ° C], and transversely stretch in the width direction in the range of 1.5 to 7.0 times, and then perform heat treatment while relaxing 5.0% in the width direction. , Immediately cool to room temperature.

If the stretching temperature is Tm or higher, unevenness in thickness and film breakage may occur due to roll adhesion, which is not preferable. Even if the film can be partially stretched, the film may not be microporous in the thickness direction.

Also, when necking occurs at a temperature lower than [Tm-50 ° C], or even when partially stretched, a microporous film with high porosity and high microporosity cannot be obtained. It is not preferable because there is.

If the total draw ratio is less than 2.25 times, it becomes difficult to obtain a sufficient porosity. On the other hand, if the total draw ratio exceeds 49 times, the elongation at break becomes small and film breakage frequently occurs, which is not preferable for film formation.

The film produced as described above has a porosity of 30 to
It is possible to obtain a microporous film which can be formed in a range of 80% and which has a more uniform pore size than a film containing an inorganic substance and an incompatible substance in polyolefin (Japanese Patent Laid-Open No. 50-1165611). it can. Note that, as mentioned above, in the present invention, good results can be obtained by any stretching method, that is, any method such as uniaxial, biaxial or multistage stretching, but the desired porosity can be easily and effectively obtained. In order to obtain the desired properties, biaxial stretching is preferred.

[Effects of the Invention] The effects of the present invention are listed below.

(1) Since no incompatible polymer is added to the raw material,
Compared to the conventional raw materials in which an inorganic material and an incompatible polymer (phenoxy, polystyrene) are added to polyolefin, the elongation at break of the unstretched film is as high as 800%, and the film breakage during stretching is greatly reduced.

(2) Since no conventional incompatible polymer is added,
A high porosity of 30 to 80% can be easily obtained.

(3) Since it can be made continuous by the conventional sequential biaxial film forming method without requiring complicated steps, it is cost effective.

[Physical property measuring method / Evaluation method] (1) Water vapor permeability is a value measured in accordance with JIS Z-0208 under the conditions of 40 ° C and 90% RH, and is expressed in g / m ² · day / 0.1 mm unit.

(2) Leakage is based on the Bundesmann test method and rainfall is 60
It was carried out at 0 mm / hr for 2 hours.

(3) For the average pore size, determine the area with an image analyzer from the surface and cross-section observation results by SEM,
The average pore size was calculated.

(4) The porosity was calculated by the following calculation after impregnating a unit volume of the microporous film with liquid paraffin.

α = (v / V) × 100 α: Porosity (%) v: Volume of impregnated liquid paraffin V: Apparent volume of film (5) The β crystal ratio is set on the scanning calorimeter DSC-II type. The temperature was raised from room temperature at a heating rate of 20 ° C./min under a nitrogen stream, and the area ratio was calculated by connecting the end point and the time when the temperature rises from the baseline to the endothermic side.

A = {B / (B + C)} × 100 A: β crystal ratio (%) B: β crystal area (Tm peak 146 ° C) C: α crystal area (Tm peak 162 ° C) (6) Water resistance is JISL- Conducted according to 1092.

(7) When the melting temperature (Tm) is set on the scanning calorimeter DSC-II type, the temperature is raised from room temperature at a heating rate of 20 ° C / min under a nitrogen stream, and when the temperature rises from the baseline to the endothermic side. And the end point is the most endothermic position.

(8) Melt crystallization temperature (Tmc), set to scanning calorimeter DSC-II type, heated from room temperature to 280 ° C at a heating rate of 20 ° C / min under a nitrogen stream, then at 20 ° C It is the position where the most heat is generated at the time of rising to the heat generation side and the end point when it is rapidly cooled at a speed of / minute.

(9) Nitrogen gas permeability is 1.0k with a gauge pressure of nitrogen gas from the inlet side of a closed cell with a film area of 12.56 cm ^2.
It was fed under the condition of g / cm ² , and a flow meter was installed on the exit side of the film to measure the nitrogen gas amount.

(10) Intrinsic viscosity [η] was measured in tetralin according to ASTM D 1601 and is expressed in dl / g.

(11) Isotactic index (II) is 720 cm
The absorbance of ^-1 is divided by the absorbance at 731cm ^-1.

[Examples] Next, embodiments of the present invention will be described based on Examples.

Example 1, Comparative Examples 1-2 [η] = 1.85, II = 98, Tm = 165 ° C., Tmc = 120 ° C. polypropylene (“Mitsui Noblen” F from Mitsui Toatsu Chemicals, Inc.)
O-850) 100 parts by weight, the inorganic particle size is 1.7
μm, specific gravity 2.7 heavy calcium carbonate (Kindaira Mining Co., Ltd.)
100 parts by weight of "KS-1300" and β crystal nucleating agent (Toyo Soda Co., Ltd.)
0.1 part by weight of "Rubicron" 400RG) is mixed with a Henschel mixer and pelletized at 240 ° C. After that, the raw material is supplied to a 40 mmφ extruder and extruded from a die at an extrusion temperature of 240 ° C. to grow β crystal type crystals on a casting drum kept at 110 ° C.

As a method of this close contact casting, it is held down with a nip roll.

Continuously, the roll surface temperature was heated to 140 ℃
Double longitudinal stretching is carried out, then introduced into a stenter heated to 155 ° C., stretched 3 times in the width direction, and further heat set at 160 ° C. while relaxing 5% in the width direction. The quality of the microporous film thus obtained (Example 1) is shown in Table 1.

In Comparative Example 1, the raw materials used in Example 1 were mixed and pelletized. Then, the raw material was supplied to the extruder used in Example 1, and a film was formed on a casting drum kept at 50 ° C.

Subsequently, it was stretched under the conditions of Example 1. However, as a result of evaluating the stretched film, the water vapor permeability was 4 g / m ² · day / 0.1 mm.

In Comparative Example 2, the raw materials used in Example 1 were mixed and pelletized. After that, feed the raw material to the 40 mmφ extruder,
The film was extruded from a die at an extrusion temperature of 0 ° C. and evaluated on a casting drum held at 110 ° C. As a result, the water vapor transmission rate was ² g / m ² · day / 0.1 mm.

Example 2, Comparative Examples 3 to 4 [η] = 2.0, II = 97, Tm = 165 ° C., Tmc = 120 ° C. polypropylene (“Mitsui Noblene” FO-, manufactured by Mitsui Toatsu Chemicals, Inc.)
100) 100 parts by weight, as an inorganic material, particle size 2.0μ
100 parts by weight of SiO ₂ (Nippon Talc Co., Ltd. P-2) having a specific gravity of 2.0 and β crystal nucleating agent (Toyo Soda Co., Ltd. “Rubicron” 400RG)
Mix 1.0 part by weight with a Henschel mixer and pelletize at 240 ° C. After that, feed the raw material to the 40 mmφ extruder,
The β crystal is grown on a casting drum extruded from a die at an extrusion temperature of 0 ° C. and kept at 110 ° C.

Then, the roll surface temperature is stretched 5 times by a longitudinal stretching machine heated to 140 ° C, then introduced into a stenter heated to 155 ° C, stretched 6 times in the width direction, and further 5% in the width direction.
While relaxing, heat set at 160 ° C. The film quality thus obtained is shown in Table 1.

In Comparative Example 3, the raw materials used in Example 2 were mixed and pelletized. Then, the raw material was supplied to the extruder used in Example 2 and a film was formed on the casting drum kept at 110 ° C.

Then, using a vertical stretching machine heated to a roll surface temperature of 140 ° C
The film is longitudinally stretched 1.3 times, then introduced into a stenter heated to 155 ° C, stretched 1.5 times in the width direction, and then 5 times in the width direction.
Heat fix at 160 ° C while relaxing%. The quality of the microporous film thus obtained (Comparative Example 3) was as shown in Table 1.

In Comparative Example 4, the raw materials used in Example 2 were mixed and pelletized. Then, the raw material was supplied to the extruder used in Example 2, and a film was formed on a casting drum maintained at 110 ° C.

Then, using a vertical stretching machine heated to a roll surface temperature of 140 ° C
When the film was longitudinally stretched 6.0 times and then introduced into a stenter heated to 155 ° C. and stretched 9.0 times in the width direction, film breakage frequently occurred in the stenter, and film formation was impossible.

Example 3 The same polypropylene as in Example 1 (Mitsui Toatsu Chemicals, Inc.)
"Mitsui Noblene" FO-850) of 100 parts by weight, 50 parts by weight of β-crystal and 50 parts by weight of calcium carbonate (Kinpei Mining Co., Ltd. "KS-1300") having a particle size of 1.7 μm and a specific gravity of 2.7 as an inorganic substance. 0.1 parts by weight of a nucleating agent ("Tubicron" 400RG, Toyo Soda Co., Ltd.) is mixed with a Henschel mixer and pelletized at 240 ° C. After that, it is extruded from a die at an extrusion temperature of 240 ° C. and 90 ° C.
Growth of β-crystals on a casting drum held in place.

Continuously, the roll surface temperature is heated to 135 ° C and stretched 4 times by a longitudinal stretching machine, then introduced into a stenter heated to 155 ° C, stretched 4 times in the width direction and further 5% in the width direction.
While relaxing, heat set at 160 ° C. The film quality thus obtained is shown in Table 1.

Example 4 The same polypropylene as in Example 1 (Mitsui Toatsu Chemicals, Inc.)
"Mitsui Noblene" FO-850) of 100 parts by weight, 200 parts by weight of a heavy calcium carbonate (Kinpei Mining Co., Ltd. "KS-1300") having a particle size of 1.7 μm and a specific gravity of 2.7 as a β crystal. 1.0 part by weight of a nucleating agent ("Rubicron" 400RG, Toyo Soda Co., Ltd.) is mixed with a Henschel mixer and pelletized at 200 ° C. Then, the mixture is extruded from a die at an extrusion temperature of 200 ° C. and held at 120 ° C. Grow β crystals on a drum.

Next, the roll surface temperature is stretched 2.5 times with a longitudinal stretching machine heated to 150 ° C, then introduced into a stenter heated to 155 ° C, stretched 3.5 times in the width direction, and further 3 times in the width direction.
Heat fix at 160 ° C while relaxing%. The film quality thus obtained is shown in Table 1.

Claims (1)

[Claims] 1. To 100 parts by weight of a polyolefin, 10 to 400 parts by weight of an inorganic substance and 0.001 to 10 parts by weight of a β-crystal nucleating agent are added, and the melting temperature (Tm) of polyolefin + 20 ° C. or more, [Tm
Melt extruding at a temperature of + 100 ° C or lower, then holding it at a temperature lower than the melt crystallization temperature (Tmc) and at a temperature of [Tmc-50 ° C] or higher, and then stretching it to obtain a porosity of 30 to 80%. A method for producing a microporous film, comprising: