JP2000086790A - Production of air permeable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing air permeable film having uniform air permeability over whole width. SOLUTION: In this method for producing an air permeable film of an olefin resin composition containing filler, a film is oriented in such conditions as to have the difference of temperature so that the surface temperature of sheet end in uniaxial orientation becomes higher, preferably by >=5 deg.C than the surface temperature in sheet center part and does not become higher than the melting point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel method for producing a breathable film. For more details, it has extremely uniform air permeability, battery separators, separation membranes such as filtration membranes, packaging materials such as warmers, house wraps, oxygen absorbers, clothing such as air permeable jumpers, sanitary items such as diapers and sanitary products. This is a method for producing a breathable film useful as an article.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a breathable film, a polyolefin resin such as polyethylene or polypropylene is mixed with an inorganic filler, formed into a sheet by a T-die, an inflation molding method or the like, and then uniaxially or biaxially. There is known a method of obtaining an air-permeable film by stretching to cause interfacial separation between a filler and a polyolefin resin. Generally, the breathable film thus obtained is bonded to a backing material such as a woven fabric, a nonwoven fabric, and paper, and is suitably used for the above-mentioned applications.

However, when a gas permeable film is produced by such a method, there is a problem that the gas permeability at the end of the gas permeable film obtained is remarkably deteriorated due to neck-in during extrusion or uniaxial stretching of the sheet. ing.

[0004] In order to solve the above-mentioned problem in terms of a manufacturing method, studies have not been sufficiently conducted, and the present situation is that the problem is solely solved by contriving in use.

For example, Japanese Patent Application No. Hei 7-21337 and Japanese Patent Application Laid-Open No. 9-85868 use a porous film having a variation in air permeability in the width direction of the film. It shows a method to solve the problem by changing the pattern of the gravure roll at the time of lamination so that the adhesive area is increased in the part with good air permeability and the area is reduced in the part with poor air permeability. .

[0006]

[Problems to be Solved] However, in the above method, it is necessary to have a wide variety of gravure rolls due to the unevenness of the air permeability of each porous film, the difference of each specification for each application, and the like. Overlapped, there was a limit in practicality.

[0007] As described above, in the prior art, no method for fundamentally solving the problem that the air permeability varies in the production of a porous film has not been studied at all.
The problem was solved solely by its use.

According to the confirmation by the present inventors, the variation in the air permeability of the air-permeable film is remarkable in the direction perpendicular to the flow direction of the sheet at the time of stretching, particularly the difference in the air permeability between the central portion and the end portion. It is.

Accordingly, it is an object of the present invention to provide a method for manufacturing a breathable film, which reduces variations in air permeability at the center and both ends of the resulting breathable film and makes them uniform.

[0010]

The present inventors have intensively studied to achieve the above object. As a result, it has been found that the cause of the variation in air permeability between the central portion and both end portions of the air permeable film is a neck-in at the time of sheet stretching, which is caused by filling a large amount of the filler.

Based on the findings, further studies have been conducted. As a result, when a sheet made of a polyolefin resin composition containing a filler is stretched in the flow direction in the production of a breathable film, the sheet at the time of stretching is stretched. It has been found that the above object can be achieved by controlling the heating temperature of the end to a specific temperature, and the present invention has been proposed.

That is, the present invention relates to a method for producing a breathable film by uniaxially stretching a sheet of a polyolefin resin composition containing a filler at least in the flow direction of the sheet. A method for producing a breathable film, characterized in that a sheet temperature is set such that a surface temperature of an end portion of a sheet is higher than a surface temperature of a central portion of the sheet and lower than a melting point, and the sheet is stretched.

In the present invention, the term “sheet” does not have a strict meaning with respect to the thickness but indicates a state before stretching to a film.

[0014]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the polyolefin resin constituting the raw material polyolefin resin composition is not particularly limited, but a homopolymer of α-olefin such as ethylene or propylene, or a copolymer thereof may be used. Used without any particular restrictions. For example, high density polyethylene,
Examples include low-density polyethylene, linear low-density polyethylene, polypropylene, and propylene-ethylene copolymer. Of these, the present invention can be particularly suitably applied to linear low-density polyethylene.

The above polyolefin resin has a density of 0.89.
Melt flow rate (MFR) at ~ 0.94 g / cc
Is 0.1 to 10 g / 10 min, preferably 1 to 5 g / 10 min.
Minutes are common.

On the other hand, as the filler, those generally used for producing a porous film using polyolefin can be used without any particular limitation. For example, an inorganic filler or the like can be used. Specifically, calcium carbonate, gypsum,
Calcium sulfite, calcium phosphate, magnesium carbonate, basic magnesium carbonate, magnesium sulfate, hydrated silicic acid, inorganic silicic acid, soda ash, sodium chloride, barium sulfate, clay, various cements, volcanic ash, shirasu, titanium oxide, iron oxide, carbon black, Examples thereof include metal powder, other inorganic substances, and organic metal salts mainly composed of inorganic substances. Of these, calcium carbonate is common.

The particle size of the filler is 50 μm or less, preferably in the range of 0.05 to 30 μm, particularly 0.1 μm.
About 5 μm is preferable.

The filler is a polyolefin resin 100
50 to 400 parts by weight, preferably 60 to 400 parts by weight with respect to parts by weight
It is preferable to use 300 parts by weight.

In the present invention, the sheet comprising the polyolefin resin composition can be obtained by a known method. Generally, it is obtained by molding by T-die molding, air-cooled or water-cooled inflation molding. Further, the thickness of the sheet is appropriately determined depending on the thickness of the target breathable film.

Next, the above sheet is uniaxially stretched at least in the longitudinal direction to obtain a breathable film having a large number of micropores.

The stretching magnification is 1.2 to 1.2 in area magnification.
8.0 times is preferable. The stretching temperature is appropriately set at a suitable temperature for obtaining a predetermined stretching ratio according to a known method. A suitable stretching temperature cannot be unconditionally limited depending on the resin, but is generally not lower than room temperature, preferably 50 ° C.
The temperature is not less than -5 ° C, preferably -20 ° C or less with respect to the melting point of the polyolefin resin.

The most important feature of the present invention is that, when producing a breathable film by the above method, the surface temperature of the sheet edge at the time of stretching in the film flow direction is higher than the surface temperature of the sheet central portion and lower than the melting point. In this case, the stretching is performed with a temperature difference provided.

In the present invention, the central portion of the sheet refers to a direction perpendicular to the film flow direction at the time of film production, that is, the vicinity of the center in the width direction, and the sheet end portion refers to a portion having an appropriate width at both ends of the sheet. . The appropriate width at both ends of the sheet is the width of the sheet corresponding to the range from the point where the air permeability starts to decrease to the edge of the film when the air permeability of the air permeable film obtained by making the stretching temperature uniform is measured in the width direction. Is determined as

The width of the portion where the air permeability decreases at the end of the obtained air-permeable film varies depending on the molding method, molding conditions, resin used, filler used, and each compounding ratio. When producing a breathable film, the film is stretched in advance under the condition that the stretching temperature is made uniform, the range in which the air permeability decreases is confirmed, and the width of the sheet edge, that is, the heating range is determined. Is preferred.

As described above, the width of the end portion of the sheet cannot be unconditionally limited, but is generally about 10 to 45% in total at both ends with respect to the entire width of the film.

In the present invention, the surface temperature of the sheet edge is lower than the melting point of the polyolefin resin, preferably 10 ° C. or lower than the melting point, more preferably 30 ° C. or lower than the melting point, and the surface of the central portion of the sheet. The stretching is performed by setting the temperature higher than the temperature.The set temperature is set to be higher than the surface temperature of the central portion of the sheet by 5 ° C. or more, by setting the film surface temperature during the uniaxial stretching in the film flow direction, The effect of reducing the variation in the air permeability of the obtained air permeable film is further improved, which is preferable.

In order to determine the temperature difference between the center of the film and the edge of the sheet more effectively, an experiment in which the heating temperature of the edge of the sheet is changed in advance is performed, and then the most suitable temperature difference is determined. Is preferred.

In the present invention, the surface temperature of the sheet is the surface temperature of the sheet at the start of stretching. For example, when the sheet is stretched using a pair of stretching rolls, the sheet immediately after passing through the low-speed roll is used. Temperature corresponds to this.
In addition, as a method for measuring the temperature, a known non-contact type means is suitably adopted, but it is particularly preferable to measure the temperature using a non-contact infrared sensor temperature measuring device.

In the present invention, as a specific method of setting the surface temperature of the sheet edge to be higher than the center of the sheet when the film is stretched, any method can be used as long as a predetermined amount of heat is applied to an arbitrary portion and the sheet surface temperature can be controlled. A technique is used. For example, a heater, a hot-air generator, and a heating roll may be used as a heating body, and the sheet edge may be heated immediately before stretching, or an arbitrary temperature and heating width can be varied in the width direction as a low-speed heating roll of uniaxial stretching. Alternatively, both ends of the sheet may be heated to a higher temperature than the center of the sheet by using a material that can be set to a predetermined value.

As described above, in the present invention, a film having uniform air permeability can be obtained by providing a temperature difference so that the edge of the sheet to be stretched is higher in temperature than the center of the sheet.

In the present invention, after the stretching in the sheet flow direction, the stretching in the direction perpendicular to the direction, that is, in the biaxial direction, can be carried out without any particular limitation. Adopted.

[0032]

As will be understood from the above description, according to the method of the present invention, the biggest problem in the method for producing a breathable film by stretching a sheet made of a polyolefin resin containing a high amount of filler is as follows. The difference in air permeability between the central portion and the end portion of the obtained air permeable film could be corrected very effectively, and it became possible to obtain a gas permeable film having uniform air permeability.

The industrial value of the film is extremely high, for example, the problem caused by the variation of the gas permeability of the gas permeable film can be solved.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The air permeability was evaluated according to JIS-P-811.
7 (Gurley air permeability). That is, the measurement was made at a total of nine measurement points at the center of the obtained air-permeable film and at intervals of 100 mm from the center to evaluate the variation in air permeability of the obtained air-permeable film.

Example 1 The following polyolefin resin and filler were used.

(1) Linear low-density polyethylene; Idemitsu Petrochemical 0234CL, melt flow index 2.0
g / 10 min, density 0.92, melting point 123 ° C. (2) Calcium carbonate; BSK- manufactured by Dowa Calfine
5. An average particle size of 1.7 μm A small amount of an antioxidant and a dispersant are added to a mixture of 70 parts of calcium carbonate with respect to 100 parts of the linear low-density polyethylene, and the mixture is stirred and mixed with a Henschel mixer. The mixture was pelletized by a shaft kneader.

Next, the pellets obtained by the above method were formed into a 150 μm sheet by the inflation molding method of a 65 mmφ extruder under the following conditions.

・ Extrusion temperature 170 ° C.-180 ° C.-190 ° C.-180 ° C. ・ Die diameter 400 mm ・ Head and die temperature 180 ° C. ・ Cooling mandrel temperature 40 ° C. ・ Blow-up ratio 2.0 ・ Take-off speed 8 m / min ・ Folding diameter 1200 mm The folded sheet obtained as described above is
Both ends were slit in the take-off direction and divided into two pieces at the folded part.

Next, in order to determine the width of the end portion at which the air permeability is reduced by ordinary stretching, the one divided sheet is subjected to a stretching temperature of 75 ° C. over the entire width of the sheet.
Uniaxial stretching was performed at a stretching magnification of 4 times, and after treatment at 90 ° C. in a heat set, a breathable film having a thickness of 50 μm was obtained. And when the air permeability of the obtained film was measured, a decrease in the air permeability was observed at a width of about 200 mm from the end,
The width was defined as the sheet edge of the present invention.

As a method of providing a temperature difference between the sheet edge and the sheet center, a hot air generator of Takezuna Manufacturing Co., Ltd. is used just before the sheet enters the uniaxially stretched section, and the entire edge is heat-treated. A nozzle having a 200 mm clearance and a 10 mm clearance was prepared, and the surface temperature of the sheet edge was controlled while blowing hot air from the nozzle to a predetermined position of the sheet. That is, the surface temperature at each end of the sheet was set to 80 ° C. while the surface temperature at the center of the sheet was 75 ° C.

The surface temperature of the sheet was measured by a non-contact infrared sensor temperature measuring device, and was measured at the center of the sheet immediately after the film came out of the low-speed heating roll of the uniaxial stretching machine and at the center of each sheet end. Measured at points.

With respect to the air-permeable film obtained by the above method, the air permeability was measured at the center of the film and at a portion centered at an interval of 100 mm from the center. The measurement results are shown in Table 1 together with the ratio to the air permeability at the center.

Example 2 A porous film was obtained in the same manner as in Example 1, except that the surface temperature of the sheet edge was 90 ° C.

Table 1 shows the measurement results of the air permeability of the air permeable film obtained by the above method together with the ratio to the air permeability of the center of the air permeable film.

Example 3 A porous film was obtained in the same manner as in Example 1, except that the surface temperature of the sheet edge was changed to 100 ° C.

Table 1 shows the measurement results of the air permeability of the gas permeable film obtained by the above method, together with the ratio to the air permeability at the center of the gas permeable film.

Comparative Example 1 A porous film was obtained in the same manner as in Example 1, except that the surface temperature of the sheet edge was the same as that of the sheet center.

Table 1 shows the measurement results of the air permeability of the air permeable film obtained by the above method together with the ratio to the air permeability of the center of the air permeable film.

Comparative Example 2 A porous film was obtained in the same manner as in Example 1, except that the surface temperature of the sheet edge was changed to 125 ° C.

Table 1 shows the measurement results of the air permeability of the air permeable film obtained by the above method, together with the ratio to the air permeability at the center of the air permeable film.

[0052]

[Table 1]

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Claims (2)

[Claims] 1. A method for producing a breathable film by uniaxially stretching a sheet of a polyolefin resin composition containing a filler at least in the flow direction of the sheet, wherein the sheet edge portion is stretched in the flow direction of the sheet. And stretching the film so that the surface temperature is higher than the surface temperature of the central portion of the sheet and lower than the melting point. 2. The production method according to claim 1, wherein the sheet is stretched by setting the surface temperature of the sheet edge to be higher than the surface temperature of the sheet center by 5 ° C. or higher and lower than the melting point.