JPS6343932A - Production of biaxially oriented gas-permeable film - Google Patents

Abstract

PURPOSE:To produce the title highly gas-permeable film, by biaxially orienting a film comprising a composition containing a polyolefin resin and an inorganic filler and orienting the obtained film in the machine direction. CONSTITUTION:A composition is obtained by mixing 42-87vol% polyolefin resin (e.g., ethylene/proplene copolymer) of a density of 0.910-0.940g/cm<3> and an MFR of 0.1-5g/10min with 58-13vol% inorganic filler (e.g., CaCO3) of an average particle diameter of 0.1-5mum and, optionally, a softener, a dispersant, a heat stabilizer, etc. This composition is molded into a film, which is biaxially oriented consecutively at a ratio of 1.2-12 for each direction in a temperature range lower than the m.p. of the resin by 80-20 deg.C. The obtained film is oriented in the machine direction at a ratio of 1.1-5 in a temperature range lower than the m.p. of the resin by 100-25 deg.C to obtain a gas-permeable oriented film of a thickness of 25-150mu and a moisture permeability (JIS Z-0208) of 300-25,000g/cm<2>.24hr.

Description

Detailed Description of the Invention (<Industrial Field of Application) The present invention relates to a method for producing a breathable film by biaxially stretching a film made of a composition of a polyolefin resin and an inorganic filler. The present invention relates to a method for producing a breathable film having a high degree of breathability and suitable for use in sanitary products such as disposable diapers or sanitary products.

(B) Conventional technology Conventionally, a method of manufacturing a breathable film by stretching a film made of a composition of a polyolefin resin and an inorganic filler in uniaxial or biaxial directions to generate voids that communicate with the film. A number of proposals have been made, and attempts are being made to apply this breathable film to sanitary products such as disposable diapers and sanitary products.

However, the breathable film produced by the biaxial stretching method has the problem of large directional properties in terms of mechanical strength, especially the problem of easy tearing in the direction of stretching.On the other hand, the breathable film produced by the biaxial stretching method Although the problem of the directionality in the -axial stretching method has been resolved, there is a problem that the breathability not only does not show the expected value, but is actually inferior to the breathable film produced by the -axial stretching method. .

(c) Problems to be Solved by the Invention As mentioned above, the conventional method of producing a breathable film by biaxially stretching a film made of a composition of a polyolefin resin and an inorganic filler has a high degree of air permeability. At present, it has not yet been possible to produce a breathable film that has good properties, and in view of this current situation, the present invention was made with the aim of solving the problems in conventional manufacturing methods.

B) Means for Solving the Problems The method for producing a biaxially stretched breathable film of the present invention comprises a polyolefin resin of 42 to 87% by volume and an inorganic filler of 58 to 1% by volume.
After a film consisting of a composition with a volume of 3 and 5 is biaxially stretched in the machine direction and the transverse direction simultaneously or sequentially, it is further stretched in the machine direction at a temperature in the range of 100 to 25 °C lower than the melting point of the polyolefin resin. It is characterized by stretching.

Here, the polyolefin resin refers to polymers such as low density polyethylene, high density polyethylene, polypropylene, etc., and ethylene-α-olefin copolymers such as ethylene-propylene copolymer, ethylene-butene-1 copolymer, etc. etc., and these can be used alone or in a mixed state. Among these, ethylene-α-
Olefin copolymers are preferred in terms of imparting a soft feel to the breathable film, especially those with a density of 0.910 to 0.9.
40 f/cd, preferably 0.916-0.935
t/ad, the MFR is preferably in the range of 0.1 to s t/xo minutes, preferably 0.1 to 3 t/xo minutes. Density of ethylene-α-olefin copolymer is 0
．． If it is 910 tlad without grooves, it will be difficult to stretch the film uniformly, and if it exceeds 0.940 f/ad, it will be difficult to impart a soft feel to the breathable film. Also,
If the MFR is less than 0.1 f/10 minutes, abnormal flow occurs when the film is melt-extruded through the goo gap, making it impossible to obtain a uniform film, and if it exceeds st/10 minutes, uniform stretching becomes difficult.

In addition, here, the ethylene-α-olefin copolymer refers to 1 to 2 α-olefins having a C3 to C8 molecular skeleton.
0% by weight, preferably 3 to 15% by weight, 99% by weight of ethylene
A linear low-density ethylene copolymer consisting of ~80% by weight, preferably 97-85% by weight, in which ethylene and C3 to Cs molecules are reacted by ionic reaction using a catalyst containing a combination of a transition metal compound and an organometallic compound. A resin produced by copolymerization containing one or more α-olefins as a backbone.
Branched low-density polyethylene resin, which is produced by polymerizing ethylene through a radical reaction under high pressure using commonly known oxygen radicals as an initiator, is characterized by its molecular structure, melting characteristics, crystallization characteristics, solid physical properties, They have different performance in stretching properties.

Inorganic fillers include calcium carbonate, calcium oxide, talc, clay, silica, titanium oxide, alumina, aluminum sulfate, etc., and can be used alone or in a mixed state.

Preferred forms of the inorganic filler are plate-like, rod-like, spherical other than needle-like, granular, amorphous, etc., and the average particle size is 0.
．． 1 to 51's, preferably 0.6 to 3μ. If the average particle size is less than 0.1μ, the film loses its elongation during stretching, making it difficult to stretch.If it exceeds 5μ, the surface of the stretched film becomes rough, making it undesirable as a breathable film. Continuous stable stretchability is impaired in producing thin films.

The composition ratio of the polyolefin resin and the inorganic filler is 42 to 87% by volume of the polyolefin resin, preferably Fi5
The content of the inorganic filler is 58-13% by volume, preferably 45-20% by volume. 1 inorganic filler
When 3% by volume of the groove is left ungrooved, the interface between the polyolefin resin and the inorganic filler peels off, and adjacent bonds are no longer in communication with each other, making it impossible to obtain papermaking and air permeability. Also, 58
If the volume% is exceeded, the film will not elongate during stretching.9
, stretching becomes difficult.

The polyolefin resin and the inorganic filler are, if necessary, a softening agent such as an aliphatic alcohol-based ester, a low molecular weight hydrocarbon polymer, and a commonly used dispersing agent.
Heat stabilizers, ultraviolet absorbers, lubricants, pigments, antistatic agents, etc. are added to the core, and the extrusion process is carried out using a -screw or twin-screw extruder, Bamba IJ.
The composition is heated and kneaded using a mixer, kneader, mixing roll, etc. to form a paper composition, and then formed into a film by known T-die molding, inflation molding, etc.

In the present invention, the film is biaxially stretched in the machine direction and the transverse direction simultaneously or sequentially, and then further stretched in the machine direction.If the film is not subjected to the post-stretch process in the machine direction, the film has a high degree of air permeability. Therefore, a stretched film having the following properties cannot be obtained.

Here, the biaxial stretching method in the previous stage may be a known method, and specifically, for example, a method of stretching in the longitudinal direction with a roll and then stretching in the transverse direction with a tenter, a method of stretching in the longitudinal direction with a tube shape, etc. simultaneous biaxial stretching, such as a method in which a tenter is used to simultaneously stretch the longitudinal direction and the lateral force direction; and a method in which a tubular shape is simultaneously stretched in the longitudinal and transverse directions. Laws etc.

At this time, the longitudinal stretching temperature in the sequential biaxial stretching method is usually 80° below the melting point of the polyolefin resin used.
℃ to 20℃ lower, the transverse stretching temperature is 40℃ to 0℃ lower than the melting point, and the stretching temperature in the simultaneous biaxial stretching method is usually 80℃ lower than the melting point.
The temperature range is 10°C lower than the average temperature. In addition, the sleep stretch magnification is
It is 1.2 to 12 times, preferably 1.2 to 10 times in both the vertical and horizontal directions.

Further, the longitudinal stretching method in the later stage can also be a known method, specifically, for example, a stretching method using a roll or a tenter, a stretching method using a tube shape, or the like. It is essential that the stretching temperature at this time be in the range of 100°C to 25°C lower than the melting point of the polyolefin resin used, preferably in the range of 90°C to 30°C lower, particularly preferably 85°C.
The temperature should be in the range of 40°C lower than ℃. Further, the stretching ratio is 1.1 to 5 times.

If the stretching temperature is lower than the lower limit, it will be difficult to stretch, while if it is higher than the upper limit, a stretched film with high air permeability will not be obtained.

Note that in order to stabilize the dimensional accuracy of the stretched film, it is usually heat-treated after stretching.

The physical properties of the biaxially stretched breathable film produced according to the present invention can be freely controlled depending on the seed head of the polyolefin resin, the physical properties, the type of inorganic filler, the particle size, the filling ratio, the stretching conditions such as the stretching temperature, the stretching ratio, etc. It is controllable. When the thickness of the breathable film is 25 to 150μ, J Engineering SzO
The moisture permeability measured with 208 is 300 to 25,000? /m1
・It is desirable to have a value in the range of 24 hours, and the thickness is
The thickness is preferably 60μ or less, particularly preferably 50μ or less.

(E) Function The method for producing a biaxially stretched breathable film of the present invention involves biaxially stretching in the longitudinal and transverse directions, and then further stretching in the longitudinal direction at a temperature within a specific range, so that it has a high degree of breathability. A breathable film can be produced.

In addition, the longitudinal stretching in this latter stage is a stretching process caused by setting the temperature of the transverse stretching in the biaxial stretching in the previous stage to a high degree of at least the softening point of the resin and close to the melting point in order to stabilize the stretching. It is thought that it has the effect of releasing voids that are blocked due to softening or melting of the film surface.

(to) Examples Example 1 Ethylene-butene-1 copolymer (butene-1 content 6% by weight, density 0.923 r/, :+(, MFRo, 9f/
10 minutes, melting point 124°C) powder 65% by volume, heavy calcium carbonate (average particle size 1.2μ, irregular shape, not plate-shaped or rod-like) 35% by volume, ethylene-butene-1 copolymer 100%
Heat stabilizer (2,6-di-tert-butyl-p
-cresol) 0.1 part by weight, heavy calcium carbonate 10
1.0 parts by weight of dispersant (oleic acid) per 0 parts by weight,
A total of 11,100 parts by weight of these was mixed with 5 parts of refined castor oil (containing 85% or more of glycerin triline root, manufactured by Ito Oil Co., Ltd.) in a super mixer for 5 minutes, and then heated at 200°C in a twin-screw extruder. After extruding it into a strand, it was cut into pellets.

The obtained pellets were mixed with a screw diameter of 50e1L/D2
After extruding through a T-die attached to the extruder No. 5 at 210° C., the mixture was cooled and solidified using a cooling roll with a surface temperature of 25° C. to form a film with a thickness of 60 μm.

This film was stretched at a temperature of 70°C by a roll stretching method.
The film was stretched in the machine direction at a stretching ratio of 1.2 times, and then stretched in the transverse direction at a stretching temperature of 110° C. and a stretching ratio of 2 times by a tenter method. Thereafter, the film was further stretched in the longitudinal direction by a roll stretching method at a stretching temperature of 60° C. and a stretching ratio of 1.4 times to produce a breathable film having a thickness of +40 μm.

Regarding the obtained breathable film, the tear strength measured based on J Engineering 521702, and J Engineering S z020
Table 1 shows the moisture permeability measured based on No. 8.

Example 2 A breathable film was produced in the same manner as in Example 1, except that the longitudinal stretching temperature in the latter stage was 80°C.

Table 1 shows the measurement results of the tear strength and moisture permeability of the breathable film obtained.

Comparative Example 1 A uniaxially stretched film was produced by stretching an unstretched film obtained by the same method as in Example 1 in the longitudinal direction using a roll stretching method at a stretching temperature of 60° C. and a stretching ratio of 2 times.

Table 1 shows the measurement results of the tear strength and moisture permeability of the obtained uniaxially stretched film.

Comparative Example 2 An unstretched film obtained by the same method as in Example 1 was subjected to paper-stretching using a roll stretching method, at a stretching temperature of 60°C and a stretching ratio of 1.
A semi-biaxially stretched film was produced by stretching the film in the machine direction by a factor of 5 and then stretching in the transverse direction by a tenter method at a stretching temperature of 110° C. and a stretching ratio of 2 times.

Table 1 shows the results of measuring the tear strength and moisture permeability of the nine-biaxially stretched film obtained.

Comparative Example 3.4 The longitudinal stretching temperature in the later stage in Example 1 was changed to 100°C (
Comparative Example 3), 12 QC (Comparative Example 4) A two-wheel stretched film was produced in the same manner as in Example 1, except for using 12 QC (Comparative Example 4).

Table 1 shows the measurement results of the tear strength and moisture permeability of the obtained biaxially stretched film.

In addition, in each example and comparative example, the thickness of the stretched film was 4
The discharge rate of the extruder was controlled so that it was 0μ.

Table 1 Example 3 In place of the ethylene-butene-1 copolymer in Example 1, a propylene-ethylene block copolymer (ethylene content 3%, MFR 9t/10 min, rut point 164°C)
A film was produced in the same manner as in Example 1, except that the extrusion temperature was 230°C.

This film was stretched at a stretching temperature of 100% by roll stretching method.
The film was stretched in the longitudinal direction at a stretching temperature of 160° C. and a stretching ratio of 4 times, and then stretched in the transverse direction by a tenter method at a stretching temperature of 160° C. and a stretching ratio of 8 times. Thereafter, the film was further stretched in the longitudinal direction by a roll stretching method at a stretching temperature of 80° C. and a stretching ratio of 1.4 times to produce a breathable film having a thickness of 40 μm.

Table 2 shows the measurement results of the moisture permeability of the obtained breathable film.

Example 4 A breathable film was produced in the same manner as in Example 3, except that the longitudinal stretching temperature in the latter stage was 120°C.

Table 2 shows the measurement results of the moisture permeability of the obtained breathable film.

Comparative Example 5.6 The longitudinal stretching temperature in the later stage in Example 3 was changed to 140°C (
A biaxially stretched film was produced in the same manner as in Example 3, except that the temperature was 160° C. (Comparative Example 5) and 160° C. (Comparative Example 6).

Table 2 shows the measurement results of the tear strength of the obtained nine-biaxially stretched film.
Shown below.

Table 2 (G) Effects of the Invention The method for producing a biaxially stretched breathable film of the present invention can produce a breathable film having a high degree of air permeability.

Patent applicant: Mitsubishi Yuka Co., Ltd. Agent: Patent Attorney Masahisa Nagatani (1 other person)

Claims (1)

[Claims] Polyolefin resin 42-87% by volume and inorganic filler 5
After biaxially stretching a film consisting of a composition of 8 to 13% by volume in the longitudinal and transverse directions simultaneously or sequentially, it is further stretched longitudinally at a temperature in the range of 100°C to 25°C lower than the melting point of the polyolefin resin. 1. A method for producing a biaxially stretched breathable film, which comprises stretching in a direction.