JPS606442A - Manufacture of gas-permeable film - Google Patents

Abstract

PURPOSE:To balance the mechanical properties of a gas-permeable film by a method in which gas is blown onto the outside of a tubular biaxially stretched film composed of a thermoplastic resin and an inorganic filler of a specific average grain size, and also the gas is continuously blown into the film. CONSTITUTION:A tubular unstretched film composed of 42-87vol% a thermoplastic resin and 58-13vol% mixture of 50-97vol% an inorganic filler of an average grain size of 0.7-4 and 50-3vol% an inorganic filler of an average grain size of 0.05-0.7 (the ratio of the average grain size of the former to the latter is 2-20) is biaxially stretched along a mandrel of a conical trapezoidal form. Gas is then blown onto the outside of the film and also the gas is continuously blown from the inside to the outside of the film in a piercing manner to obtain a gas- permeable film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a thin and uniformly thick breathable film by biaxially stretching an unstretched film made of a composition of a thermoplastic resin and an inorganic filler.

Conventionally, many methods have been proposed for producing a breathable film by biaxially stretching an unstretched film made of a composition of a pus-plastic resin and an inorganic filler to generate communicating voids in the film.

Biaxial stretching methods in this case include a method of biaxial stretching in a flat state and a method of biaxial stretching while maintaining a tubular shape.

The method of biaxial stretching in a flat form has the disadvantages that the film is held and stretched with clips when stretching in the horizontal direction, so the gripped part does not become a product, and the stretching equipment used in this method is very expensive. This has the disadvantage that the product cost is higher. Furthermore, the method normally used commercially has the disadvantage that the mechanical properties of the stretched film are unbalanced because the unstretched film is stretched in separate steps in the machine direction and the transverse direction. There is.

The method of biaxial stretching while maintaining the tubular shape was proposed to solve the above-mentioned drawbacks of the flat shape, and compared to the method of biaxial stretching with the flat shape, the equipment cost is lower.
Since no clips are used, all of the material is stretched without leaving any unstretched parts, making it more efficient to produce products.Furthermore, since the machine is stretched almost simultaneously in the vertical and horizontal directions, its mechanical properties are balanced. It has characteristics.

This biaxial stretching method includes an internal pressure bubble stretching method in which the film is stretched by the internal pressure of pressurized gas, and a mandrel stretching method in which a truncated conical mandrel is inserted into the interior of a tubular unstretched film for stretching.

The internal pressure bubble stretching method is a method in which stretching is performed in the longitudinal direction due to the difference in circumferential speed between low-speed rolls and high-speed rolls, while stretching in the horizontal direction (circumferential direction) due to internal pressure between the rolls. The low-speed roll and high-speed roll are of the nip roll type. Therefore, when an attempt is made to biaxially stretch a tubular unstretched film made of a composition of a thermoplastic resin and an inorganic filler using this internal pressure bubble stretching method, the tubular unstretched film is folded in two by the nip rolls when passing through the low-speed nip rolls. Since the resin is pressed in this condition, the bent tabs at both ends are plastically deformed and the inorganic filler is peeled off from the resin. Since stretching starts at a low stretching stress in this locally peeled area, the shape of the tubular film during stretching changes and the stretching becomes unstable, and at the same time, the stretching ratio becomes locally high in this peeled area. Moreover, void unevenness appears in the stretched film as vertical streaks, making it impossible to obtain a breathable film of uniform quality. Furthermore, this internal pressure bubble stretching method confines pressurized gas between the low-speed roll and the high-speed roll (
Since this is a method of stretching in the J direction (circumferential direction), in the case of breathable films, internal pressure gas leaks from the inside to the outside of the film, making continuous and stable production difficult.

On the other hand, the mandrel stretching method is a method proposed to improve stretching instability and longitudinal streaks as in the internal pressure bubble stretching method. In addition, the instability of stretching due to local stretching is improved, and since there is no need to confine pressurized gas, creases due to nip rolls do not occur, and therefore quality defects due to vertical streaks are eliminated. However, when it is stretched along a truncated conical mandrel,
In order to stretch the stretched film, considerable compressive stress acts in the thickness direction of the stretched film, and voids developed by stretching are crushed, making it impossible to obtain a breathable film of good quality.

On the other hand, attempts are being made to apply this breathable film to sanitary products such as disposable diapers and sanitary products. required. in general,
One possible method for imparting a soft feel is to use a so-called soft thermoplastic resin with low rigidity, but the soft feel, ie, the flexibility of the film, largely depends on the thickness of the film.

By the way, when producing a thin breathable film by stretching an unstretched film made of a composition of a thermoplastic resin and an inorganic filler, when the film becomes thinner, the film may break at the localized necking part that occurs at the start of sagging. This makes continuous stable production difficult. Furthermore, in the case of the tubular biaxial stretching method, the uniformity of the thickness of the unstretched 1111 film is inferior to that of the flat biaxial stretching method.
The uniformity of the thickness of the IA stretched film is also generally inferior to that of the flat biaxial stretching method.

As mentioned above, in the conventional method of producing a breathable film by biaxially stretching an unstretched film made of a composition of a thermoplastic resin and an inorganic filler, it is difficult to maintain a good balance between the longitudinal direction and the transverse direction. At present, it is far too difficult to stably produce a breathable film that is removable, thin, and has a uniform thickness.

In view of the above-mentioned current situation, the present invention was made with the aim of solving the problems in conventional manufacturing methods.
Thermoplastic resin 42-87% by volume and average particle size 0.7-87% by volume
An inorganic filler with a diameter of 4 μ and an inorganic filler with an average particle size of 0.05 to 0.7 μ are combined so that the ratio of the average particle size of the former to the latter is 2 to 2.
Inorganic filler mixture 58-1, in which the former is mixed in an amount of 50 to 97% by volume and the latter is 50 to 3% by volume.
A tubular unstretched film of 3% by volume of the composition is biaxially stretched along a frustoconical mandrel, and the film is subsequently cooled by blowing gas from the outside of the tubular biaxially stretched film. At the same time, it is characterized in that gas is continuously blown from the inside of the film to penetrate the outside of the film.

Here, thermoplastic resins include polymers such as low-density polyethylene, high-density polyethylene, and polypropylene, copolymers such as ethylene-propylene copolymers, ethylene-butene-1 copolymers, etc., polyolefins, polyesters, It refers to polyamide and the like, and these can be used alone or in a warmed state. Among these, polyolefins are particularly effective in high-density polyethylene and ethylene-α-olefin copolymers, and high-density polyethylene has a density of 0.940 f/aC1.
Above, preferably the sail is 945 g/cd or more, and the MFR is 1.
．． 0 f 710 minutes or less, preferably 0.1' tlx
.

It is included in the range of minutes or less. Also, ethylene-
As an α-olefin copolymer, the density is 0.910~
0.940? /Cd, preferably 0.916-0.9
35 f/crl with MFR of 0.1-5 t/
10 minutes, preferably within the range of 7 to 3 f/10 minutes.

Inorganic fillers include calcium carbonate, calcium oxide, talc, clay, silica, titanium oxide, alumina, aluminum sulfate, etc., and two or more of these are used in a mixed state. Preferred forms of the inorganic filler include those having an aspect ratio close to 1, such as spherical, granular, and irregular shapes, other than plate-like, needle-like, and rod-like shapes.

In the present invention, an inorganic filler with a large average particle size is referred to as inorganic filler A, an inorganic filler with a small average particle size is referred to as inorganic filler B, and the average particle sizes of inorganic fillers A and B are respectively D A
Cu>, DB (μ), the average particle diameter DA of the inorganic filler A is 0.7 to 4μ, preferably 8 to 2μ, and the average particle diameter DB of the inorganic filler B is 0.05 to 0. 7μ, preferably in the range of 0.1 to 0.6μ. Furthermore, the average particle diameter DA (μ) of inorganic filler A and the average particle diameter DB (u
) is 2 to 20, preferably 2.5 to 15, and more preferably 3 to 10.

The mixing ratio of inorganic filler A and inorganic filler B is such that inorganic filler A is 50 to 97% by volume, preferably 60 to 95% by volume, and inorganic filler B is 50 to 3% by volume, preferably 40% by volume. ~
5 bodies Ef? % range.

If inorganic filler A is used alone at a mixing ratio that provides air permeability, stretching itself is possible, but if you try to stretch it with a mandrel while maintaining the tubular shape, local necking will occur, resulting in a thin and uniform thickness. Breathable film cannot be obtained. On the other hand, when inorganic filler B is used alone at a mixing ratio that provides air permeability, the tubular unstretched film itself loses its elongation, making it difficult to stretch the film with a mandrel while maintaining its tubular shape. However, although the reason is not clear, mixing inorganic filler A and inorganic filler B reduces the occurrence of local necking, makes it possible to reduce the thickness of the stretched film, and further improves the film thickness. The thickness will also be uniform.

If the average particle size of the inorganic filler A exceeds 4μ, the unevenness on the surface of the stretched film will become large, making it undesirable as a breathable film.Furthermore, it will cause pinholes, making it impossible to create a continuous stretched film with uniform air permeability. It becomes impossible to produce stably. When the average particle size is less than 7μ, the same phenomenon as when inorganic filler B is used alone occurs, and the tubular unstretched film itself loses its elongation, making mandrel stretching while maintaining the tubular shape difficult. Even if the average particle size of the inorganic filler B exceeds 0.7 or becomes less than 0.05 μm, the effect of preventing local necking is lost. Furthermore, if the ratio of average particle diameters exceeds 20, the unstretched tubular film will be less likely to be stretched, and will break when stretched on a mandrel while maintaining its tubular shape. When the ratio of average particle diameters becomes less than 2, the effect of preventing local necking is lost.

Furthermore, when the content of inorganic filler A exceeds 97% by volume, the effect of preventing local necking disappears, and when 50% by volume becomes ungrooved, it slides on the mandrel surface while maintaining its tubular shape and is subjected to surface pressure. When stretching in a stretched state, the film and mandrel surface come into close contact, making continuous and stable production difficult.
It becomes 4.

Methods for mixing inorganic fillers and thermoplastic resins include -screw or twin-screw extruders, Banbury mixers, kneaders,
Heating cross-conducting using a mixing roll, etc. can be used. When heating and cross-fertilizing, commonly used additives such as dispersants, heat stabilizers, ultraviolet absorbers, lubricants, pigments, and antistatic agents can be mixed at the same time. In particular, higher fatty acids having 12 or more carbon atoms give good results as a dispersant. The inorganic filler may be treated with these dispersants or the like before being heated and kneaded.

The composition ratio of the inorganic filler mixture to the thermoplastic resin is 13 to 58% by volume of the inorganic filler mixture, preferably 20 to 45% by volume.
If the thermoplastic resin is in the range of 87 to 42 volume%, preferably 80 to 55 volume%, and the inorganic filler is less than 13 volume%, the interface between the thermoplastic resin and the inorganic filler will peel off. Adjacent voids created by this process no longer communicate with each other, making it impossible to obtain ventilation. If it exceeds 58% by volume, the unstretched film loses its elongation during stretching, making biaxial stretching difficult.

The mandrel stretching method of biaxially stretching along a truncated conical mandrel as used in the present invention refers to a method in which a tubular unstretched film has one end having a diameter equal to or slightly smaller than the diameter of the tubular unstretched film. A truncated conical mandrel whose other end has a diameter approximately equal to the stretching ratio in the lateral direction (circumferential direction) to be stretched is inserted, and while the tubular unstretched film is placed along the sloped side of the mandrel, the mandrel is The force generated when the stretched film, which has been cooled after stretching, is taken off by the take-up nip roll located at the rear, causes the stretched film to be held under pressure on a substantially truncated conical mandrel (direction (circumferential) and longitudinal direction). A method of supporting the mandrel is preferably a binding method or a method of fixing the small diameter end face of the mandrel to a support frame connected to an annular goug from which the tubular unstretched film is extruded.

The stretching temperature in this stretching is the temperature at which orientation occurs due to so-called stretching, and as is known, it usually has a relatively wide temperature range and can be easily determined in the film processing industry. Generally, the temperature range is slightly lower than the melting point, but in the case of mandrel stretching, the stretching is carried out in contact with the mandrel, so if the melting point is Tm ('C) and the stretching temperature is Ts (C), then Tm-50≦ Ts≦Tm −
5(C) is suitable.

Heating to the stretching temperature may be done from the inside via a mandrel or the like, or from the outside, but it is preferable to heat at least the inside for uniform heating.

Further, a stretching ratio of 1.5 to 4 times in both length and width is suitable for stable stretching.

In the present invention, the tubular biaxially stretched film, which has left the mandrel and has substantially finished stretching, is cooled by a known method of blowing gas, generally air, from the outside of the film, and continuously from the inside of the film. The gas is passed through the outside of the film by blowing gas into the film.

The amount of gas blown at this time cannot be determined uniquely because it varies depending on the physical properties and shape of the obtained tubular biaxially stretched film, the stretching speed, the temperature of the cooling gas and the amount of blowing, etc. 0.1 to 15 ONe/nl-min, preferably 1 to 70 Nt/lr?・The setting is appropriately set so that the tubular biaxially stretched film maintains approximately the same diameter as at the end of stretching. By increasing the amount of cooling gas blown and increasing the number of stitches in which this gas is blown, a breathable film with gradually increasing air permeability can be obtained. Air is still the most common gas. In order to inject this gas, a conduit is provided that is connected to an external pressure source, passes through the annular goo, the mandrel support frame, and the mandrel, and opens at the end surface of the mandrel's dog diameter. .

The manufacturing process of the breathable film in the present invention consists of the following five steps. That is, a process for producing a tubular unstretched film in which a tubular unstretched film is extruded in a molten state through the gap between the gougly lips of an annular gouie, the diameter is equal to or larger than the gougly lip diameter, the film is cooled and solidified, and then continuously withdrawn. , the film is properly stretched I' and the pre-stretching process is performed with high-quality heating, and the heated tubular unstretched film is stretched on two wheels while being stretched along the surface of a truncated conical mandrel under surface pressure. During the stretching process, the film in a tubular state that has left the mandrel and has substantially completed stretching is cooled by controlled cooling gas from the outside of the tubular film, and directed from the inside of the film in a tubular state to the outside 9111. It consists of a step of continuously passing a controlled pressurized gas over the entire circumference of the tubular film to impart breathability to the stretched film, and a winding step of cooling the stretched film and then winding it up as a product.

The physical properties of the breathable film produced according to the present invention include the S type of the thermoplastic resin, the particle size, type, and filling ratio of the inorganic filler, the stretching temperature as the biaxial stretching conditions, the stretching ratio in the longitudinal and lateral directions,
The blowing of cooling gas can be freely controlled by adjusting the amount, the amount of gas blown from the inside, etc. When the thickness of the breathable film is 25 to 150 μ, the air permeability 1 measured according to JIS P8117 is 25 to 30,000 sheets/100 ω, JIS
The moisture permeability measured by zo 208 is 300 to 25,000y.
/ sr? - It is desirable to have a value in the range of 24 hours, and the thickness is preferably 60μ or less, particularly preferably 50μ or less.

Examples of the present invention will be shown below together with comparative examples and will be specifically explained. Note that the present invention is not limited to the examples.

Example 1 Ethylene-butene-1 copolymer (density 0.920 flc
65 ft% powder of Rl, MFR1, o y/1o min, Q value 3.4, melting point 124°C) and heavy calcium carbonate (average particle size 1.2μ, non-plate-shaped, rod-shaped, needle-shaped, etc.) A mixture of 35% by volume of an inorganic filler consisting of SO volume% and 20% by volume of precipitated calcium carbonate (average particle size: 3μ, cubic), relative to the ethylene-butene-1 copolymer ioo layered part. 0.1 part by weight of a heat stabilizer (2,6-di-t-butyl-p-cresol) and 1.0 part by weight of a dispersant (oleic acid) are added to 100 parts by weight of the inorganic filler mixture in a super mixer. After mixing for 5 minutes, 2
After extruding into strands at 00°C, the mixture was cut into pellets.

The obtained pellets were
After extrusion at 210°C through an annular die (lip diameter 75e, 4-row spiral die with lip gap of 1) attached to an extruder, it was brought into contact with a cooling mandrel with a diameter of 1008 cm in which water at 5°C circulated, and then blown. A tubular unstretched film having a thickness of 110 μm which was cooled and solidified at a ratio of 1.33 was taken off at a rate of 5 m/min.

After heating this film to 110°C with a preheating mandrel with a diameter of 989 connected below the cooling mandrel, the end face directly connected to the preheating mandrel has a diameter of 9813, the other end face has a diameter of 250e, and its cone angle The material was stretched 2.5 times in the transverse direction (circumferential direction) and 3.0 times in the longitudinal direction along the surface of a truncated conical mandrel at 110° C. whose 90" surface was satin-finished to have an unevenness of 0.5 μm. , Subsequently, the entire outer circumference of the biaxially stretched film in a tubular state away from the mandrel was heated at 15°C for 5 m for 7 seconds from an air ring with a diameter of 3,500 m at a position 50 m from the lower end of the mandrel. Along with blowing the air of
From the conduit at the lower end of the mandrel, there are two
By continuously blowing air at 0°C at a rate of 5 NL/+♂·min, the film is continuously penetrated in the thickness direction from the inner 11 ml to the outside, and then taken up with nip rolls and subjected to biaxial stretching ventilation into a tubular shape. I got a sex film.

Table 1 shows the appearance and physical properties of the obtained breathable film. In addition, the moisture permeability is JIS z0208, and the air permeability is JIS z0208.
P8117 and tear strength were measured based on RJISz1702.

Example 2 In Example 1, the mixture of inorganic filler was mixed with 90% by volume of heavy calcium carbonate (average particle size 1.8μ, irregular shape not plate-like, rod-like, needle-like, etc.) and the sedimentation property of Example 1. A breathable film was obtained in the same manner as in Example 1 except that the inorganic filler mixture was changed to include 10% by volume of calcium carbonate.

The results of the obtained breathable film are also shown in Table 1.

Example 3 In Example 1) 11, instead of the ethylene-butene-1 copolymer, high-density polyethylene (density 0.956?
/ crl, MF RO, 05t/ 10 minutes, Q value 7
, melting point 135°C), pelletized at 290°C, extruded at 260°C as a tubular unstretched film with a thickness of 90μ, and heated with a preheating mandrel and a stretching mandrel for 12
A breathable film was produced by stretching under the same conditions as in Example 1 except that the temperature was changed to 0°C. The results are shown in Table 1. Comparative Example 1 In Example 1, heavy calcium carbonate was stretched at 30° C. volume%,
Stretching was carried out under the same conditions as in Example 1, except that the mixing ratio was changed to 70% by volume of precipitated calcium carbonate. The results are also shown in Table 1.

Comparative Example 2 Stretching was carried out under the same conditions as in Example 1, except that heavy calcium carbonate was 60% by volume and precipitated calcium carbonate having an average particle size of 0.03μ was 40% by volume. The results are also shown in Table 1.

Comparative Example 3 In Example 1, a 130μ thick tubular unstretched film was extruded using heavy calcium carbonate alone as an inorganic filler, and the preheating mandrel and stretching mandrel were heated at 113°C.
The blowing rate of cooling air after stretching was 10 m/sec, and the blowing rate of air inside the tubular film was 40 Nt/rr?
・Stretching was carried out under the same conditions as in Example 1, except that the stretching was carried out in minutes. The results are also shown in Table 1.

Comparative Example 4 In Example 1, a mixture of inorganic fillers was mixed with 80% by volume of heavy calcium carbonate (average particle size 0.9μ, irregular shape not plate-like, rod-like, needle-like, etc.) and heavy calcium carbonate (average Particle size 0
．． 6μ, irregular shape that is not plate-like, rod-like, needle-like, etc.) 20% by volume
Example 1 except that the mixture was changed to an inorganic filler mixture consisting of
A breathable film was obtained in the same manner as above. The obtained results are also shown in Table 1.

(Margin below)

Claims (1)

[Claims] Thermoplastic resin 42-87% by volume and average particle size 0.7-87% by volume
An inorganic filler with a diameter of 4 μ and an inorganic filler with an average particle size of 0.05 to 0.7 μ are combined so that the ratio of the average particle size of the former to the latter is 2 to 2.
Inorganic filler mixture 58-1 in which the former is 50 to 97% by volume and the latter is 50 to 3% by volume.
A tubular unstretched film consisting of a composition with 8 It% of 3-body is biaxially stretched along a truncated conical mandrel, and then the film is cooled by blowing gas from the outside of the tubular biaxially stretched film. In addition, a method for producing a breathable film, characterized in that gas is continuously blown from the inside of the film to penetrate the outside of the film.