JPS606439A - 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 from outside onto the tubular biaxially stretched film composed of a thermoplastic resin and an inorganic filler, 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% an inorganic filler is biaxially stretched along a mandrel of a conical trapezoidal form. The film is then cooled by blowing gas from 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. The thermoplastic resin used includes low- and high-density polyethylenes, etc., and the inorganic filler used in cludes calcium carbonate, calcium oxide, talc, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a 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 thermoplastic resin and an inorganic filler to generate voids that communicate in the thickness direction of the stretched film. ing.

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 two drawbacks: when stretching the film in the transverse direction, the film is held with clips, and the part that is held during the stretching process does not become a product, and the stretching equipment used in this method is very expensive. However, it has the disadvantage that the product cost is high. Furthermore, the methods commonly used commercially have the disadvantage that the mechanical properties of the stretched film are unbalanced because the unstretched film is stretched in separate steps in the longitudinal and transverse directions. There is.

The method of biaxial stretching while maintaining the tubular shape was proposed to solve the above-mentioned drawbacks of the flat shape.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. %a.

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

The internal pressure bubble stretching method is a method of stretching in the longitudinal direction due to the peripheral speed difference between low-speed rolls and high-speed rolls, while stretching in the full direction (circumferential direction) using internal pressure between the rolls.In order to prevent leakage of internal pressure gas, The low speed roll and high speed roll are of the nip roll type. Therefore, when attempting to biaxially stretch a tubular unstretched film made of a composition of thermoplastic (! ■ fat and inorganic filler) using this internal pressure bubble stretching method, the tubular When the unstretched film passes through the low-speed nip rolls, it is pressed into a two-fold state by the nip rolls, so the folded edges on both ends are plastically deformed and the inorganic filler is peeled off from the resin.This locally peeled part is Because the stretching starts at a low stretching stress, the shape of the tubular film changes during stretching, making the stretching unstable. Void unevenness appears in the film as vertical streaks, making it impossible to obtain a breathable film with uniform quality.Furthermore, this internal pressure bubble stretching method confines pressurized gas between the low-speed roll and high-speed roll in the transverse direction. Since this is a method of stretching in the circumferential direction, in breathable films, 0111
Internal pressurized gas leaks from the inside to the outside, making continuous 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. Stretching instability caused by local stretching is improved, and since there is no need to confine pressurized gas, creases due to nip rolls do not occur, and quality defects due to vertical streaks are eliminated. However, since the stretched film is stretched along a truncated conical mandrel, considerable compressive stress acts on the stretched film in the thickness direction, and voids developed by stretching are crushed, making it impossible to obtain a high-quality breathable film. have.

As mentioned above, in the conventional method of manufacturing a breathable film by biaxially stretching an unstretched film made of a composition of a thermoplastic resin and an inorganic filler, the mechanical properties in the longitudinal and transverse directions cannot be balanced. At present, it has not yet been possible to stably produce a film that is removable and has excellent air permeability.

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 turnip filler 58-13%
A tubular unstretched film consisting of a composition of % by volume is biaxially stretched along a frustoconical mandrel, and then
It is characterized in that the film is cooled by blowing gas from the outside of the tubular biaxially stretched film, and the film is penetrated to the outside of the film by continuously blowing gas from the inside of the film.

Here, thermoplastic resins include polymers such as low density polyethylene, high density polyethylene, polyglopylene, etc., polyolefins such as copolymers such as ethylene-propylene copolymer, ethylene-butene-1 copolymer, etc., polyester, It refers to polyamide, etc., and these can be used alone or in a mixed state. Among these, polyolefins, especially high-density polyethylene, ethylene-
It is effective in α-olefin copolymers, and as high-density polyethylene, the density is 0.9401 F/ca or more, preferably Q, 945 S'/cri or more, and MFR
is 1.01F/10 minutes or less, preferably o, lr/l.

It is included in the scope of preparative separation. Also, ethylene-
As an α-olefin copolymer, the density is 0.910~
0.940 r/cr! , preferably 0.916 to 0.
935 S'/-, MFR 0.1-5f/10min,
Preferably it is within the range of 0.1 to 39710 minutes.

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 include:
They are spherical, granular, irregular shapes, etc. other than plate-like, rod-like, and needle-like.
Its average particle size is 0.1-5μ, preferably 0.6-3μ
It is. When the average particle size is less than 0.1μ, the unstretched film loses its elongation during stretching, making biaxial stretching difficult.
If it exceeds 5μ, pinholes are likely to occur in the biaxially stretched film, impairing continuous and stable stretching properties, and the surface becomes more uneven.

Methods for mixing thermoplastic resin and inorganic filler include dynamic or twin-screw extruders, Banbury mixers, Negoo mixers,
Heating crosstalk using mixing rolls, 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 thermoplastic resin and the inorganic filler is such that the thermoplastic resin is 42 to 87% by volume, preferably 55 to 80% by volume, and the inorganic filler is 58 to 13% by volume, preferably 45 to 20% by volume. range. When the inorganic filler becomes 13% undropped, the interface between the thermoplastic resin and the inorganic filler peels off, and the voids that are in contact with each other no longer communicate with each other, making it impossible to obtain air permeability. Moreover, if it exceeds 58 volume %, the unstretched film loses its elongation when stretched on a mandrel, making it difficult to biaxially stretch the unstretched film while maintaining its tubular shape.

The mandrel stretching method in which biaxial stretching is performed along a truncated conical mandrel as used in the present invention refers to the method of biaxially stretching a tubular unstretched film along a truncated conical mandrel, in which one end has a diameter equal to or slightly smaller than the diameter of the tubular unstretched film, and the other end has a diameter equal to or slightly smaller than the diameter of the tubular unstretched film. A truncated conical mandrel whose 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 slanted 6111 plane of the mandrel, the back of the mandrel is Due to 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 method of supporting this mandrel is as follows:
A preferred method is to fix the small diameter end face of the mandrel to a support rod connected to an annular die for extruding the tubular unstretched film.

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 −s o≦ T8≦Tm
-5(C) is suitable.

In the case of low-density polyethylene, high-density polyethylene, etc., Tm -20≦Ts≦Tm-5°C is preferable.

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. By blowing gas into the film, the gas is passed through the outside of 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 ONl/n at °C? · min, preferably 1 to 70 Nt/lr? The diameter is set appropriately within the range of - minutes so that the tubular biaxially stretched film maintains the same diameter as at the end of stretching. While spraying a large amount of cooling gas,
When the amount of gas blown into the film is increased, a breathable film with gradually higher air permeability can be obtained. Moreover, air is the most common gas. In order to blow this gas, a conduit is provided which is connected to an external pressure source, penetrates the annular die, the mandrel support member mentioned above, and opens at the large diameter end face of the mandrel. .

The manufacturing process of the breathable film in the present invention consists of the following five steps. That is, a tubular unstretched film manufacturing process in which a tubular unstretched film is extruded in a molten state through the die lip gap of an annular die, the diameter is equal to or larger than the die lip diameter, the film is cooled and solidified, and then continuously withdrawn; a preheating step in which the heated tubular unstretched film is stretched to an appropriate stretching temperature, a stretching step in which the heated tubular unstretched film is biaxially stretched along the surface of a truncated conical mandrel while receiving surface pressure, and a The firn, which is in a tubular state after being stretched, is cooled by controlled cooling gas from the outside of the tubular film, and controlled pressurized gas is applied from the inside of the tubular film to the outside. It consists of a step of continuously penetrating the entire circumference of the tubular film to impart air permeability 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 type of thermoplastic resin, the particle size, type, and filling ratio of the inorganic filler. ! jI The stretching conditions, such as the stretching temperature, the stretching ratio in the longitudinal and lateral directions, and the blowing of cooling gas, can be freely controlled by blowing gas from the inside. When the thickness of the breathable film is 25 to 150μ, JIS P 811
Air permeability measured at 7 is 25-30000 seconds/1oocc
, moisture permeability measured according to JIS Z0208 is 300-25
000t/rr? -Has a value in the range of 24 hours.

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 0.920t/
cr1%M F R2, OS' 710 minutes, melting point 12
4℃) powder 65% by volume, heavy calcium carbonate (average particle size 1.2μ, irregular shape, not plate-like or rod-like) 35% by volume
, a heat stabilizer (2,6-di-t-butyl-p-cresol) per 100 parts by weight of ethylene-butene-1 copolymer.
After mixing 0.1 part by weight and 1.0 part by weight of a dispersant (oleic acid) with 100 parts by weight of heavy calcium carbonate in a super mixer for 5 minutes, extrusion into a strand at 200°C from a twin-screw extruder After that, it was cut into pellets.

The obtained pellet was screwed with a screw diameter of 509 mm. L/D25
21 from the annular die (4-row spiral die with lip diameter 75c3 and lip gap 111111) attached to the extruder.
After extrusion at 0°C, 5°C water circulates inside the diameter 10
08 cooling mandrel, blow ratio 1.33
Cool and solidify the tubular unstretched film with a thickness of 4
It was picked up at m/min.

After heating this film to 114°C with a 98mm diameter preheating mandrel connected below the cooling mandrel,
The diameter of the end face directly connected to the preheating mandrel is 988 mm, and the diameter of the other end face is 2500 mm, and the cone angle is 90''. Stretched 2.5 times in the transverse direction (circumferential direction) and 3.0 times in the longitudinal direction, and then stretched the lower end of the mandrel around the entire outer circumference of the two-roll stretched film in the tubular state that had left the mandrel. At the position of 50 from
From the air ring, blow air at 15 C for 5 m and 7 seconds, and from the lower tube of the mandrel, blow air at 20 C into the inside of the tubular film.・
By continuously blowing at a rate of 100 min, the film was continuously penetrated in the thickness direction of the film from the inner 11411 to the outside, and was continuously taken up by the Nira roll to obtain a tubular 21111 stretched breathable film.

The appearance and physical properties of the obtained breathable film are shown in Table 1. ib, moisture permeability is JIS z0208, air permeability is JIS
P8117 and tear strength were measured based on JIS Z1702.

Example 2 In Example 1, the cooling air blowing of the tubular biaxially stretched film was 10 m/sec, and the internal air blowing was 4ON.
A breathable film was obtained in the same manner as in Example 1 except that the temperature was set at t/-min.The results of the obtained breathable film are shown in Table 1.Example 3 The preheating temperature and stretching temperature of the tubular unstretched film are set at 112°C, the cooling air blowing rate of the tubular biaxially stretched film is 20 m/sec, and the internal air blowing rate is 4ONt/rr? A breathable film was obtained in the same manner as in Example 1 except that the amount of air permeable film was 100%. The results of the obtained breathable film are also shown in Table 1.

Comparative Example 1 Stretching was carried out in the same manner as in Example 1, except that the air introduced into the tubular film from the conduit at the lower end of the mandrel was stopped. The results of the obtained biaxially stretched film are also shown in Table 1.

Example 4 In Example 1, high density polyethylene (density 0.956t/cI/
1, MF RO-05f / 10 minutes, melting point 135℃)
Pelletized at 270℃ using powder of
The film was extruded as a 150μ tubular unstretched film, the preheating temperature and stretching temperature were 119°C, and the stretching ratio in the longitudinal direction was 2.
．． 5 times, the cooling air blowing of the tubular two@h stretched film was 20 m7 seconds, and the air blowing was 60 Nt/r.
A breathable film was obtained in the same manner as in Example 1 except that the temperature was set to rl·min. The results of the obtained breathable film are also shown in Table 1.

(Margin below)

Claims (1)

[Claims] Thermoplastic resin 42-87% by volume and inorganic filler 58-13%
A tubular unstretched film consisting of a composition of % by volume is biaxially stretched along a frustoconical mandrel, and then
A breathable film characterized in that the film is cooled by blowing gas from the outside of the tubular biaxially stretched film, and the film is penetrated to the outside of the film by continuously blowing gas from the inside of the film. Manufacturing method 0