JPH0577694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air-permeable porous film,
Specifically, the present invention relates to a porous polyolefin film produced by mixing a polyolefin resin with a thermoplastic polyester resin and stretching the mixture, and a method for producing the same.

(Prior art) Conventionally, as a method for manufacturing a porous film with air permeability, there is a method in which a non-porous film is perforated by electric discharge machining (Method 1), and a method in which calcium carbonate particles are added during film formation to form a film. A method in which calcium carbonate is eluted by acid treatment to form a porous film (Method 2), a method in which inorganic particles such as calcium carbonate are added during film formation to form a film, and the film is stretched uniaxially or biaxially (Method 3). ), a method in which two types of resins with low compatibility are kneaded to form a film, and then uniaxially or biaxially stretched ((Method 4), etc.) are carried out and used as moisture permeable or air permeable films.
Of these, the former two (methods 1 and 2) are unfavorable in terms of productivity, and method 3 is generally used.

(Problems to be Solved by the Invention) However, the porous film obtained by stretching a film added with inorganic fine particles has a high rigidity of filler, and the resulting porous film also tends to have high rigidity. When rubbed, the filler tends to fall off, which not only does not give a good feeling of use, but also has drawbacks such as depending on the application, the fallen filler turns into dust and impairs environmental conditions. Of course, during the manufacturing process, problems with working environment conditions due to inorganic fine particle dust are likely to occur. Further, the inorganic fine particles used are generally calcium carbonate, which has the disadvantage that the waterproof property decreases over time due to the hydrophilic nature of calcium carbonate.

Furthermore, a method (Method 4) of kneading two types of resins with low compatibility to form a film and stretching the film has been proposed in Japanese Patent Publication No. 53-12542 and Japanese Patent Application Laid-open No. 58-198536, but it has various drawbacks.

That is, in the former (Japanese Patent Publication No. 53-12542), 0.05 to 10% by weight of polystyrene is mixed with polypropylene, and the film is formed and stretched to produce a film containing cavities. There are no through holes in the thickness direction of the film, and the film is not breathable or moisture permeable. Further, when polystyrene is added in an amount of 10% or more, cavities are generated from the surface to the inside by stretching, but there are problems such as not only the amount of cavities being generated is small but also difficulty in stretching the product.

Furthermore, in films made by simply kneading the polyolefin resin as the base and the polystyrene resin as the additive resin, the polystyrene resin does not become fine particles, and not only does it have poor stretchability, but even when stretched, the pores generated are large. , only a film with extremely poor waterproof properties can be obtained. Alternatively, even if the polystyrene resin has been formed into suitable particles, if the film forming temperature is not taken into consideration, the polystyrene resin in the particle form will be deformed and its stretchability will deteriorate, and even if it can be stretched, The pore size is too large and the waterproofness is poor.
Alternatively, the pores are layered and not continuous, resulting in a film with low air permeability and low moisture permeability.

On the other hand, the latter (Japanese Unexamined Patent Application Publication No. 1985-198536) has low compatibility with the thermoplastic resin (A) and (A), and has a melting point of (A).
The mixture is melt-kneaded with a thermoplastic resin (b) that is 20°C or more higher than the melting point of the mixture (b), and then formed into a sheet at a temperature that is higher than the melting point of (a) and lower than the melting point of (b). ,
Next, there is a method for producing a moisture-permeable film that is stretched at a temperature lower than the melting point of (a), but (b) tends to agglomerate when formed into a sheet and the particle size tends to increase, resulting in a film with excellent waterproof properties. That's difficult.

In addition, when (a), for example, polyethylene or polypropylene resin is used, and (b), for example, a thermoplastic polyester resin such as polyethylene terephthalate or polybutylene terephthalate, which is normally used for film production, is used, the usual polyethylene or polypropylene resin is used. The stretching temperature is
The glass transition temperatures of polyethylene terephthalate and polybutylene terephthalate are 60-70°C and 40-60°C, respectively. Even if (B) is dispersed in the optimum particle size range and formed into a sheet, if (B) is not crystallized, the stretching temperature is
If it is above the glass transition temperature of
In some cases, the particles in (b) are also stretched and no pores are formed.
The resulting film has only low air permeability and moisture permeability.

In order to overcome these drawbacks, it is possible to improve air permeability and moisture permeability to some extent by promoting crystallization by allowing the film to stay after extrusion film formation, but it has not been possible to improve it sufficiently. If a polyester resin with a small molecular weight is used as (b) to facilitate this crystallization, the viscosity of (b) will become too low during heating and kneading, and the particle size will not be reduced, making it difficult to form a film containing such particles. When stretched, pin poles of 1 mm or more tend to form and are easy to cut. On the other hand, when a resin with a low molecular weight is similarly used as the resin in (a), the stretchability decreases, making it impractical in either case.

(Means for Solving the Problems) As a result of intensive study on methods to eliminate the above-mentioned drawbacks, the present inventors found that the intrinsic viscosity of the particle components is
By using a thermoplastic polyester resin with a low polymerization degree of 0.5 or less and using specific heat-kneading conditions, when the resin is heat-kneaded, particle formation is excellent, and the resulting film has good stretchability, and The present invention was achieved by discovering that the above-mentioned particles effectively act to create vents.

That is, in the present invention, the polyolefin resin (A)
100 parts by weight, 0-50 parts by weight of polyester/polyether type thermoplastic elastomer (B), and thermoplastic polyester resin (C) with a solid viscosity of 0.5 or less.
A resin mixture containing 25 to 90 parts by weight of essential components based on 100 parts by weight of (A) and (B) in total is once heated and melted at a temperature higher than the melting point of (C), and then the crystallization temperature of (C) is Below and below
After cooling the resin composition, which was kneaded at a shear rate of 200/sec or more while applying a negative temperature gradient to a temperature range above the melting point of (A), to below the crystallization temperature of (C), A method for producing a porous film, which comprises forming the film in a temperature range below the melting point of (C) and above the melting point of (A), and stretching the unstretched film obtained by rapid cooling in at least one axis. The present invention relates to a porous film.

Examples of the polyolefin resin (A) used in the present invention include linear low density polyethylene,
High-pressure process low-density polyethylene, high-density polyethylene, polypropylene, polybutylene, ethylene-
These include propylene copolymers, ethylene-vinyl acetate copolymers, ethylene-alkyl (meth)acrylate copolymer resins, ionomer resins, etc., excluding the resins included in the additive resins described below. It is not limited.

The polyester/polyether type thermoplastic elastomer (B) used in the present invention mainly consists of a high-melting-point, high-crystalline polyester component as a hard segment and a polyether segment component as a soft segment. It is a block copolymer, for example, one in which the polyester block is polybutylene terephthalate and the polyether block is polytetramethylene ether glycol. , those substituted with glycol may also be used.

Examples of commercially available elastomers include Pelprene (Toyobo Co., Ltd.), Hytretsu (Toray Dupont), Grilux (Dainippon Ink Chemical), Romotsud (General Electric), Arnitel (Akzo), and the like.

These polyester/polyether type thermoplastic elastomers (B) are polyolefin resins (A)
0 to 50 parts by weight are mixed with 100 parts by weight.
The polyester/polyether type thermoplastic elastomer (B) has an affinity for both the matrix phase polyolefin resin (A) and the dispersed phase thermoplastic polyester resin (C), and is able to bind the two, which have a large viscosity difference. This has the effect of making the dispersed phase finer and preventing reaggregation.

By making the dispersed phase finer and preventing re-agglomeration,
Film appearance and mechanical properties can be improved.

In addition, due to these effects, even if the intrinsic viscosity of the thermoplastic polyester resin (C) and kneading conditions change slightly, it is possible to suppress fluctuations in the dispersed particle size,
The quality of the porous film obtained can be stabilized.

In order to exhibit such an effect, it is preferable to add 1 part by weight or more to 100 parts by weight of the polyolefin resin, and if it is less than 1 part by weight, almost no effect can be expected.

On the other hand, if it exceeds 50 parts by weight, the effect of the above-mentioned affinity (interaction) becomes excessive, making it difficult to generate air permeability even when stretched, which is not preferable.

Examples of the thermoplastic polyester resin (C) used in the present invention include polyethylene terephthalate, polybutylene terephthalate, hexane dimethanol-modified polyethylene terephthalate, and isophthalic acid copolymerized polyethylene terephthalate.

However, the thermoplastic polyester resin used is
Intrinsic viscosity must be 0.5 or less.

Those having an intrinsic viscosity of more than 0.5 are undesirable because the crystallization rate in the temperature range (above the melting point of A and below the crystallization temperature of C) under extrusion film forming conditions is slow and does not reach the required degree of crystallinity. The higher the intrinsic viscosity, the slower the crystallization rate, and it is necessary to take measures such as increasing the residence time during film formation or heat treatment after film formation. This is not preferable because deterioration and crystallization occur concomitantly, leading to a decrease in stretchability and properties such as film strength.

The commonly used thermoplastic polyester resins with a high degree of polymerization (intrinsic viscosity of 0.6 or more) have a low glass transition point and are below the drawing temperature of polyolefin resin (A), making it possible to convert these thermoplastic polyester resins into polyolefin resins. Even if it is dispersed, it is easily deformed during stretching, and pores are difficult to form effectively.

The thermoplastic polyester resin (C) with an intrinsic viscosity of 0.5 or less is a low polymerization degree thermoplastic polyester resin obtained from the steps before and during solid phase polymerization, or a low polymerization degree thermoplastic polyester resin obtained by hydrolyzing a high polymerization degree thermoplastic polyester resin. Polymerization degree thermoplastic polyester resins can be used. Furthermore, it is also possible to hydrolyze and use thermoplastic polyester resin waste produced as a by-product in various industries, and in this case it is advantageous in terms of cost.

Thermoplastic polyester resin (C) is 25 parts by weight per 100 parts by weight of polyolefin resin (A) and polyester/polyether type thermoplastic elastomer (B).
It is necessary to mix in a range of 90 parts by weight. When the amount is less than 25 parts by weight, pores are not formed all the way to the surface, making it difficult to form a porous film.

On the other hand, if it exceeds 90 parts by weight, the probability of re-agglomeration of the dispersed particles increases, so that the particle size tends to increase, resulting in a film with poor waterproofness and mechanical properties.

Furthermore, an inversion phenomenon occurs between the polyolefin resin (A), which should be a matrix phase, and the thermoplastic polyester resin (C), which should be made into fine particles, which not only makes stretching difficult, but also leaves voids even after stretching. is difficult to form, making it impossible to obtain a porous film.

In addition to the above-mentioned components, the present invention further includes liquid or waxy polybutadiene, liquid butene, liquid polyisoprene and derivatives thereof, polybutene-1, ethylene-propylene-diene terpolymer, and ethylene-propylene random copolymer. Additive resins such as polymers, ethylene-butene copolymers, polybutadiene resins, etc. can be used in combination.
These additive resins are used by being added to the polyolefin resin (A) in order to increase the flexibility of the resulting porous film. In addition, by appropriately selecting the viscosity of the additive resin used, it is possible to change the viscosity of the matrix phase and change the viscosity ratio with the thermoplastic polyester resin (C) during the kneading process. The particle size can be adjusted, and the extrusion film forming temperature range can also be changed.

Furthermore, if the amount of the additive resin exceeds 55 parts by weight per 100 parts by weight of the polyolefin resin (A), not only the film forming properties but also the stretchability will deteriorate, making it difficult to efficiently create a porous film. Can not do it.

In addition to the above-mentioned components, if desired, inorganic fine particles such as calcium carbonate, a heat stabilizer, a slip agent, an anti-blocking agent, a coloring agent, and an antistatic agent are used for the purpose of erasing. etc. can also be added as necessary.

The steps for producing a porous film by the method of the present invention will be explained below. In order to efficiently obtain a porous film, it is necessary to micronize the thermoplastic polyester resin (C) by melt-kneading to have an average particle size of 0.05 to 30μ, more preferably 0.05 to 20μ. Furthermore, it is necessary to suppress deformation of the thermoplastic polyester resin that has become particulate during extrusion film formation.

If the average particle size is less than 0.05μ, it is necessary to increase the stretching ratio to obtain practical air permeability.
In this case, the film is easily cut and is not practical. In addition, if it exceeds 30μ, the pore size generated by stretching becomes large and the waterproofness decreases, so low stretching ratio is necessary, but since uniform stretching is difficult at low ratio stretching, it is difficult to achieve an excellent porous film. can't get it.

The average particle size of thermoplastic polyester resin is 0.05~
In order to form fine particles with a particle size of 30μ, the resin mixture is heated above the melting point of the thermoplastic polyester resin (C), which becomes particles, and then heated below the crystallization temperature of the thermoplastic polyester resin (C) and the polyolefin It is necessary to create a negative temperature gradient so that the temperature is higher than the melting point of the system resin (A) and knead at a shear rate of 200/sec or higher. Thermoplastic polyester resin (C) and polyolefin resin (A) are combined into thermoplastic polyester resin (C).
Even if the thermoplastic polyester resin (C) is simply melt-kneaded and extruded at a temperature higher than the melting point of Because the kneading stress is smaller by more than an order of magnitude, in some cases by more than two orders of magnitude, the kneading stress cannot be transmitted, causing slippage and reducing the kneading resistance.
(C) is mostly localized in the form of blocks or strings.

In general, thermoplastic polyester resin (C) melts by heating it above its melting point, and when it is cooled from that state, it begins to solidify and crystallize at a temperature 10 to 50 degrees Celsius lower than its melting point, i.e., the crystallization temperature. do. what if,
Even if uniformly dispersed particles are obtained by melt-kneading at a temperature above the melting point of the thermoplastic polyester resin (C), most of them will remain in a fluid state and cannot be recycled if the temperature is above the crystallization temperature of the thermoplastic polyester resin (C). Particle expansion phenomenon occurs due to aggregation, making it difficult to control the particle size.

On the other hand, when the thermoplastic polyester resin (C) solidifies and crystallizes at the crystallization temperature, its melt viscosity increases significantly.

In other words, if the temperature is kneaded with a negative temperature gradient from above the melting point of the thermoplastic polyester resin (C) to below the crystallization temperature of the thermoplastic polyester resin (C) and above the melting point of the polyolefin resin (A), Within the temperature range, a condition in which the ratio of both melt viscosities is close to 1 can be obtained. However, as mentioned above, a thermoplastic polyester resin with an intrinsic viscosity of 0.5 or less has a significantly low melt viscosity, and the shear rate during kneading during extrusion film formation using a normal screw is insufficient to achieve a dispersed particle size of 0.5 to 30μ. This is insufficient and requires a shear rate of 200/sec or more.

Furthermore, the kneading stress is transmitted through the interaction of the added polyester/polyether type thermoplastic elastomer (B), making it possible to obtain a uniform dispersed particle size. The effect of using the above-mentioned elastomer (B) in combination is revolutionary, and has the effect of narrowing the particle size distribution of dispersed particles and reducing variations in quality due to variations in kneading conditions.

Under the same kneading conditions, the larger the amount of elastomer added, the smaller the dispersed particle size tends to be. By controlling the kneading conditions and the amount of elastomer added, it is possible to obtain a porous film with a predetermined average dispersed particle size. I can do it.

Next, extrusion film formation is performed at a temperature range below the crystallization temperature of the thermoplastic polyester resin (C) and above the melting point of the polyolefin resin (A), and cooled to obtain an unstretched film.

At this time, if the temperature is higher than the crystallization temperature of the thermoplastic polyester resin (C), the thermoplastic polyester resin (C)
is in a molten state and its melt viscosity is extremely low, so deformation occurs due to drawdown during film formation, and furthermore, film breakage occurs due to pulling tension, making it impossible to obtain a good unstretched film. So I don't like it.

In addition, even if the film forming temperature is below the crystallization temperature of the thermoplastic polyester resin (C), if the thermoplastic polyester resin (C) is in a molten state by the time it reaches the die, which is the film forming part, the inside of the die may This is not preferable because the thermoplastic polyester resin (C) separates, solidifies, and accumulates, and falls off over time, forming large particles that impede film formation and stretching.

This phenomenon is significantly observed in the manifold part of the die where the flow rate of the molten resin is slow.

If the thermoplastic polyester resin (C) is cooled to below its crystallization temperature during kneading, the thermoplastic polyester resin (C) is in a solid state and will not melt unless the temperature is raised above its melting point again, making it difficult to form a film. The temperature may be lower than the melting point of the thermoplastic polyester resin (C) and higher than the crystallization temperature. In order to prevent deformation during film formation and stretching, it is preferable to increase the degree of crystallinity of the thermoplastic polyester resin in the dispersed phase. It is preferable to perform extrusion film formation without raising the temperature of the resin stream again.

The unstretched film thus obtained is stretched in at least one direction at a normal stretching temperature range depending on the type of polyolefin resin (A).

Stretching magnification is 1.2 to 10 times, area magnification is 1.2 to 40
The range is preferably twice as large, and is appropriately selected depending on the desired ventilation performance. When the average pore size is less than 0.1μ, the air permeability is low and the usable range is small. Also,
When it is larger than 100μ, waterproofness decreases and water permeability is developed. Porous films used for disposable diapers and the like require waterproofness, so the average pore diameter may be set to 100 μm or less.

Moisture-permeable films containing calcium carbonate as a filler, which are commonly used in disposable diapers, are made up of the hydrophilic properties of calcium carbonate itself and the surface treatment agents of calcium carbonate, such as fatty acids such as stearic acid. Water resistance tends to decrease as the temperature increases.
The pore size must be set small, usually around 0.1 to 10 μm, but the film of the present invention has a low hydrophilicity of the raw materials used, and has excellent waterproof properties even with relatively large pore sizes. is allowed up to 100μ. Needless to say, the smaller the pore diameter, the better the waterproofness.

Furthermore, since the tear strength of the obtained stretched film generally tends to decrease as the stretching ratio increases, the stretching ratio can be set small in order to suppress the decrease in tear strength.

Additionally, the stretched film can be heat set if desired.

Such heat treatment can suppress natural shrinkage of the film itself.

(Functions and Effects) The present invention includes adding a thermoplastic polyester resin and a polyester/polyether type thermoplastic elastomer as essential components to a polyolefin resin, heating and melting the resin, and then kneading the mixture while cooling with a negative temperature gradient. The film is formed below the crystallization temperature of the generated particles,
When the obtained film is stretched at an appropriate temperature, a part of the interface between the matrix resin and the particles is peeled off and that part is opened, resulting in a porous film with micropores. Unlike the porous film production method, inorganic fine powder is not added to the thermoplastic resin, so there is no problem of fine powder scattering during pulverization of the inorganic filler and molding process, and there is no problem in the porous film obtained. Since the dispersed particles are partially in close contact with the polyolefin resin, they do not fall off even when rubbed by hand, and the usability is good.

As described above, the present invention is a method of blending two resins with low compatibility and a large difference in melt viscosity, and the performance can be improved by specific kneading conditions and by adding a third resin that interacts with both resins. This is an innovative method for preventing variations and troubles.
In addition, the hydrophilicity of the materials used is low,
A porous film with excellent breathability and waterproofness can be efficiently obtained.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto.

In addition, each measurement method in this example is shown below.

(1) Melting point; measured by Seiko Electronics Industries Co., Ltd. differential scanning calorimeter (DSC200) at a heating rate of 10°C/min.
Value measured at.

(2) Crystallization temperature; after melting using the same device as above.
The exothermic peak caused by crystallization that appears when the sample is left at 290°C for 10 mm and then cooled at a cooling rate of 5°C/min is defined as the crystallization temperature.

(3) Intrinsic viscosity: Value measured by a conventional method at 30°C using a solvent with a 60/40 weight ratio of phenol/tetrachloroethane.

(4) Moisture permeability: Conforms to JIS Z 0208.

(5) Water pressure resistance: Conforms to the hydrostatic pressure method of JIS L 1092.

(6) Ventilation level: Conforms to JIS P 8117.

Example 1 100 parts by weight of linear low-density polyethylene (melting point 120°C), 60 parts by weight of polyethylene terephthalate (melting point 259°C, crystallization temperature 215°C) with an intrinsic viscosity of 0.35, and polyester/polyether type thermoplastic elastomer (Pelprene P- 40H) were dry blended, heated to 270°C to melt, and immediately kneaded at a shear rate of 400/sec while cooling with a negative temperature gradient from 270°C to 200°C. An unstretched film produced by extrusion while maintaining the resin temperature at 200℃ is uniaxially stretched 5.5 times at 80℃ using a roll stretching machine to a thickness of approximately 40μ.
A porous film was obtained. When the obtained film was observed with a scanning electron microscope, the average particle size of the dispersed particles was about 6 μm, and the average pore size in the MD direction was about 30 μm.

Moisture permeability is 3500g/m ² 24hr. Water pressure resistance is 160cmAq
It was hot. Moreover, the air permeability was 2560 ml/m ² ·sec.

Example 2 100 parts by weight of linear low density polyethylene (melting point 120°C), 65 parts by weight of polyethylene terephthalate (melting point 257°C, crystallization temperature 215°C) with an intrinsic viscosity of 0.26, polyester/polyether type thermoplastic elastomer (Hytrel 4047) 6 parts by weight were heated and melted in the same manner as in Example 1, and immediately kneaded at a shear rate of 500/sec while cooling with a negative temperature gradient from 270°C to 190°C. Furthermore, from the middle of the kneading section, a molecular weight of 25,000 and a hydrogenation rate of 100 parts by weight of linear low density polyethylene are added.
15 parts by weight of 90 mol% liquid hydrogenated polyisoprene was injected and kneaded. After kneading, the resin was extruded from a tubular die while maintaining the temperature at 190° C. to obtain an unstretched tubular film.

The obtained film is guided to a tubular biaxial stretching machine equipped with two sets of take-up nip rolls on the left and right via an introduction side nip roll, a nip roll at the end of folding, and a guide roll, and a gap is created between the nip rolls at the end of folding. While supplying compressed air into the bubble through the gap from the compressed air blow-off nozzle located on the nip roll at the end of folding, the bubble is heated with a heating heater, and then the bubble is cut into two pieces with a cutting knife attached to the compressed air blow-off nozzle. It was opened and taken off to the left and right by two sets of take-up rolls on the left and right.

At this time, the speed of the nip roll on the introduction side is set low, and the nip roll at the end of folding and the take-up nip roll are set at high speed, and simultaneous biaxial stretching is carried out at 80°C to a longitudinal magnification of 3.3 times and a horizontal magnification of 2.5 times, resulting in a thickness of approximately 40 μm. A porous film was obtained.

When the obtained film was observed with a scanning electron microscope, the dispersed particles had an average particle size of about 7 μm and an average pore size of about 15 μm. Moisture permeability is 5700g/ ^m2・
24hr, air permeability 7600ml/ ^m2・sec, water pressure resistance 130cm
Aq, and was a white, finely porous film with balanced length and width.

Example 3 100 parts by weight of high-pressure low density polyethylene (melting point 110°C), 60 parts by weight of polybutylene terephthalate (melting point 224°C, crystallization temperature 212°C) with an intrinsic viscosity of 0.35, polyester/polyether type thermoplastic elastomer (Pelprene P -30B) 5 parts by weight and 10 parts by weight of polybutene-1 (melting point 125°C, MI2.0) were dry blended, heated to 240°C, and immediately after melting, the negative temperature was adjusted from 240°C to 175°C in the extrusion section. The mixture was kneaded at a shear rate of 400/sec while being cooled to create a temperature gradient, and then extruded from the extrusion port at a resin temperature of 175°C to form a film and rapidly cooled to obtain a substantially unstretched film. This film was uniaxially stretched 5 times at 80° C. using a roll stretching machine. The average particle diameter of the obtained film was approximately 7μ, the diameter of the vent in the MD direction was approximately 30μ,
Moisture permeability 3400g/ ^m2・24hr・Water pressure resistance is 155cmAq.
Moreover, the porous film had an air permeability of 2500 ml/m ² ·sec, and had excellent air permeability, moisture permeability, and water resistance.

Example 4 100 parts by weight of linear low density polyethylene (melting point 120°C) was dry blended with 50 parts by weight of polyethylene terephthalate (melting point 259°C, crystallization temperature 215°C) having an intrinsic viscosity of 0.3, heated to 270°C and melted. ,right away
The mixture was kneaded at a shear rate of 380/sec while cooling with a negative temperature gradient from 270°C to 200°C. Resin temperature 200
An unstretched film produced by extrusion at 80° C. was uniaxially stretched six times using a roll stretching machine to obtain a porous film with a thickness of about 40 μm.

When the obtained film was observed with a scanning electron microscope, the average particle size of the dispersed particles was about 15 μm, and the average pore size in the MD direction was about 50 μm.

Moisture permeability is 3200g/m ² 24hr, water pressure resistance is 110cmAq,
The air permeability was 2300ml/m ² ·sec.

Example 5 100 parts by weight of propylene homopolymer (melting point 170°C), 60 parts by weight of polyethylene terephthalate with an intrinsic viscosity of 0.35 (melting point 259°C, crystallization temperature 215°C) and polyester/polyether type thermoplastic elastomer (Pelprene P-40H) Dry blend 10 parts by weight, heat and melt at 270℃, and after melting from 270℃
The mixture was kneaded at a shear rate of 1000/sec while cooling with a negative temperature gradient to 200°C. An unstretched film produced by extrusion while maintaining the resin temperature at 200°C was uniaxially stretched 5.5 times at 85°C using a roll stretching machine to obtain a porous film with a thickness of 40 μm. The obtained film has a moisture permeability of 2800 g/m ²・24hr, an air permeability of 2230 ml/m ²・sec,
The water pressure resistance was 157 cmAq, and it was an excellent porous film.

Example 6 Polyethylene terephthalate with an intrinsic viscosity of 0.26 (melting point 257°C, crystallization temperature 215
Dry blend 65 parts by weight of polyester and 5 parts by weight of polyether type thermoplastic elastomer (Pelprene P-40H), heat to 270°C, and immediately after melting, create a negative temperature gradient from 270°C to 200°C. The mixture was kneaded at a shear rate of 450/sec while cooling. A flat unstretched film was obtained by extrusion film formation while maintaining the resin temperature at 200°C. The obtained unstretched film was cut and stretched using a biaxial stretching machine manufactured by Iwamoto Seisakusho.
Simultaneous biaxial stretching was carried out at 80° C. to a longitudinal magnification of 3 times and a longitudinal magnification of 2.5 times to obtain a porous film with a thickness of about 40 μm.

The dispersed particle size was about 7μ and the average pore size was about 17μ. The moisture permeability is 4200g/m ² 24hr, and the air permeability is 3300.
ml/m ² sec, water pressure resistance was 170 cmAq, and it was an excellent porous film.

Comparative Example 1 An unstretched film was obtained in the same manner as in Example 1, except that the polyester/polyether thermoplastic elastomer (Perprene P-40H) was used in an amount of 60 parts by weight. Although stretching was carried out in the same manner as in Example 1, a netting phenomenon occurred and uniform stretching was difficult. Furthermore, when the stretched film was observed with a scanning electron microscope, the interface between the dispersed particles and the matrix phase was unclear, there were few pores, and the water vapor permeability was 890 g/m ² · 24 hours.
The air permeability was as low as 96 ml/m ² ·sec.

Comparative Example 2 100 parts by weight of linear low-density polyethylene (melting point 120°C), 55 parts by weight of polyethylene terephthalate (melting point 259°C, crystallization temperature 185°C) with an intrinsic viscosity of 0.71, and polyester/polyether type thermoplastic elastomer (Pelprene P- 30B) 5 parts by weight were dry blended, heated to 270°C to melt, and then formed into a film so that the resin temperature immediately after die-out was 230°C.
The dispersed particle diameter of the obtained film was several hundred microns or more, and many pinholes of several millimeters were formed due to stretching.

Comparative Example 3 A film having the same composition as Comparative Example 2 was kneaded and cooled to 170° C. in the same manner as in Example 1 to form a film.

Although the dispersed particle size was small at about 8μ, Example 1
The moisture permeability of the stretched film obtained in the same manner as
It was small at 650 g/m ² for 24 hours, and when observed with a scanning electron microscope, deformation of the dispersed particles was observed, and the pores formed were extremely small.

Comparative Example 4 Example 1 except that the temperature after kneading was 230°C.
Although kneading and film formation were carried out in the same manner as above, during film formation, the film frequently broke due to drawdown, and an unstretched film could not be obtained.

Comparative Example 5 An unstretched film was obtained in the same manner as in Example 1, except that the shear rate during kneading was 180/sec.

The dispersed particle size of the obtained film was about 100 μm, and when it was stretched, there were many pinholes of just under 1 mm.

Comparative Examples 6 and 7 Example 4: 100 parts by weight of linear low-density polyethylene (melting point 120°C) and 20 and 95 parts by weight of polyethylene terephthalate (melting point 258°C, crystallization temperature 225°C) having an intrinsic viscosity of 0.31. A film was formed in the same manner.

The former had a good dispersed particle size of about 14μ, but the water vapor permeability of the film stretched in the same manner as in Example 4 was low at 300 g/m ² 24 hr and the air permeability was 16 ml/m ² sec. The dispersed particle size is large, approximately 40μ,
When stretched, pinholes of several mm were generated frequently, and a satisfactory porous film could not be obtained in either case.

Claims (1)

[Claims] 1. 100 parts by weight of polyolefin resin (A), polyester/polyether type thermoplastic elastomer
(B) is 1 to 50 parts by weight, and (A) is a particulate thermoplastic polyester resin (C) with an intrinsic viscosity of 0.5 or less.
and (B) in an amount of 25 to 90 parts by weight based on the total of 100 parts by weight, and (C) having an average particle size of 0.05 to 30μ, stretched in at least one direction. A porous film obtained by 2 The average pore diameter of the holes penetrating in the thickness direction is 0.1~
2. The porous film according to claim 1, wherein the porous film has a thickness of 100μ. 3 Moisture permeability is 2000g/ ^m2・24hr or more, water pressure resistance is 80
2. The porous film according to claim 1, wherein the porous film has a porous film of cmAq or more. 4 100 parts by weight of polyolefin resin (A), polyester/polyether type thermoplastic elastomer
(B) is 1 to 50 parts by weight, and thermoplastic polyester resin (C) with an intrinsic viscosity of 0.5 or less is the sum of (A) and (B).
A resin mixture containing 25 to 90 parts by weight as an essential component per 100 parts by weight is once heated and melted above the melting point of (C), and then melted at a temperature below the crystallization temperature of (C) and above the melting point of (A). A resin composition is kneaded at a shear rate of 200/sec or more while cooling with a negative temperature gradient so that the crystallization rate is below the crystallization rate of (C). A method for producing a porous film, which comprises forming the film in a temperature range equal to or higher than the melting point of (A), and stretching an unstretched film obtained by rapid cooling in at least one axis.