JPH0314057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a film made by biaxially stretching an unstretched film made of a composition of a thermoplastic resin and an inorganic filler.
The present invention relates to a method for manufacturing a breathable film that is thin and has a uniform thickness. 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 communicating with 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 gripped with a clip and stretched in the horizontal direction, so the gripped part does not become a product, and the stretching equipment used in this method is very expensive. Than,
The disadvantage is that the product cost is high. Furthermore,
The methods commonly used commercially have the disadvantage that the unstretched film is stretched in separate steps in the machine direction and in the transverse direction, resulting in unbalanced mechanical properties of the stretched film. 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 and it uses clips. Since it is not stretched at all, it is fully stretched without remaining in the unstretched area, resulting in high efficiency in turning it into a product.Furthermore, because it is stretched almost simultaneously in the longitudinal and transverse directions, its mechanical properties are well-balanced. are doing. This biaxial stretching method includes an internal pressure bubble stretching method in which the film is stretched using 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 of stretching in the longitudinal direction due to the peripheral speed difference between low-speed rolls and high-speed rolls, while stretching in the horizontal direction (circumferential direction) using internal pressure between the rolls. The low-speed roll and high-speed roll are of the nip roll type. Therefore, if an attempt is made to biaxially stretch a tubular unstretched film made of a composition of a thermoplastic resin and an inorganic filler by this internal pressure bubble stretching method, the tubular unstretched film will be biaxially stretched by the niproll when it passes through the low-speed niproll. Since it is pressed into a folded state, the bent end edges 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 part, the shape of the tubular film during stretching changes and the stretching becomes unstable, and the stretching ratio locally increases in this peeled part. Moreover, void unevenness appears as vertical streaks in the stretched film, making it impossible to obtain a breathable film of uniform quality. Furthermore, this internal pressure bubble stretching method is a method in which pressurized gas is confined between low-speed rolls and high-speed rolls and stretched in the transverse direction (circumferential direction). The internal pressurized gas leaks, 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. 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 longitudinal stripes 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 the voids developed by stretching are crushed, making it impossible to obtain a high-quality breathable film. have. On the other hand, attempts are being made to apply this breathable film to sanitary products such as disposable diapers and sanitary products, and in this case, a breathable film that has a soft cloth-like feel is required instead of a paper-like paper-like feel. be done. Generally, a method of imparting a soft feel is to employ a so-called soft thermoplastic resin with low rigidity, but the soft feel, that is, 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 localized netting parts that occur at the start of stretching. This makes continuous stable production difficult. Furthermore, in the case of the tubular biaxial stretching method, the uniformity of the thickness of the unstretched film is inferior to that of the flat biaxial stretching method. It is generally inferior to the stretching method. As described 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 balance in the longitudinal and lateral directions can be maintained. At present, it has not yet been possible to stably produce a thin and uniformly thick breathable film. In view of the above-mentioned current situation, the present invention was made with the aim of solving the problems in the conventional manufacturing method. ~87% by volume
and an inorganic filler with an average particle size of 0.7 to 4 μ and an inorganic filler with an average particle size of 0.05 to 0.7 μ, the ratio of the average particle size of the former to the latter is 2 to 20, and the former is 50 to 97% by volume. A tubular unstretched film made of a composition of 58 to 13 volume % of an inorganic filler mixture in which the latter is mixed at 50 to 3 volume % is biaxially stretched along a truncated conical mandrel, Subsequently, the film is cooled by blowing gas from the outside of the tubular biaxially stretched film, and 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, polypropylene, etc., copolymers such as ethylene-propylene copolymer, ethylene-butene-1 copolymer, etc., polyolefin, polyester, It refers to polyamide, etc., and these can be used alone or in a mixed state. Among these, polyolefins are particularly effective for high-density polyethylene and ethylene-α-olefin copolymers, and high-density polyethylenes with a density of 0.940
g/cm ³ or more, preferably 0.945 g/cm ³ or more,
The MFR is within the range of 1.0 g/10 minutes or less, preferably 0.1 g/10 minutes or less. In addition, as an ethylene-α-olefin copolymer, the density is
0.910-0.940g/ ^cm3 , preferably 0.916-0.935
g/cm ³ and MFR of 0.1-5 g/10 min, preferably
It is included in the range of 0.1 to 3 g/10 minutes. In addition, as inorganic fillers, calcium carbonate,
Calcium oxide, talc, clay, silica, titanium oxide, alumina, aluminum sulfate, etc.
Two or more of these are used in a mixed state. Preferred forms of the inorganic filler include plate-like, needle-like,
Other than rod-like shapes, the aspect ratio is close to 1, spherical shapes, granular shapes, irregular shapes, etc. 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 DA (μ). , DB (μ), the average particle diameter DA of the inorganic filler A is 0.7 to 4μ, preferably
0.8~2μ, average particle size DB of inorganic filler B is 0.05~
It is 0.7μ, preferably in the range of 0.1 to 0.6μ. Furthermore,
Average particle size ratio DA/DB between the average particle size DA (μ) of inorganic filler A and the average particle size DB (μ) of inorganic filler B
is from 2 to 20, preferably from 2.5 to 15, more preferably from 3 to 10. The mixing ratio of inorganic filler A and inorganic filler B is
Inorganic filler A is 50-97% by volume, preferably 60-95%
The amount of inorganic filler B is in the range of 50 to 3% by volume, preferably 40 to 5% by volume. When inorganic filler A is used alone at a mixing ratio that provides air permeability, stretching itself is possible, but
If an attempt is made to stretch the film with a mandrel while maintaining its tubular shape, netting will occur locally, making it impossible to obtain a thin and uniformly thick breathable film. 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, surprisingly, although the reason is unclear, inorganic filler A and inorganic filler B
By mixing, the occurrence of local netting is reduced, and the thickness of the stretched film can be reduced.
Furthermore, the thickness of the film becomes uniform. If the average particle size of the inorganic filler A exceeds 4μ, the surface of the stretched film will have large irregularities, making it undesirable as a breathable film.Furthermore, it will cause pinholes, and the stretched film with uniform air permeability will not be continuous. Stable production will no longer be possible. Average particle size is 0.7μ
If it is less than that, the same phenomenon as when inorganic filler B is used alone occurs, and the tubular unstretched film itself loses its elongation, making it difficult to stretch the film with a mandrel while maintaining its tubular shape. Even if the average particle size of the inorganic filler B exceeds 0.7 or becomes less than 0.05μ, the effect of preventing local netting is lost. Furthermore, if the average particle size ratio exceeds 20, the elongation of the tubular unstretched film decreases, and it will break when stretched on a mandrel while maintaining its tubular shape. When the ratio of average particle diameters is less than 2, the effect of preventing local netting is lost. Furthermore, if the inorganic filler A exceeds 97% by volume,
When the local netting prevention effect disappears and the amount becomes less than 50% by volume, the film and the mandrel surface will come into close contact when the film is stretched while maintaining its tubular shape and is subjected to surface pressure by sliding on the mandrel surface. Continuous and stable production becomes difficult. As a method for kneading the inorganic filler and thermoplastic resin, heat kneading using a single or twin screw extruder, Banbury mixer, kneader, mixing roll, etc. can be adopted. During heating and kneading, commonly used additives such as dispersants, heat stabilizers, ultraviolet absorbers, lubricants, pigments, and antistatic agents can be kneaded 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 and the thermoplastic resin is 13 to 58% by volume of the inorganic filler mixture, preferably
20-45% by volume, thermoplastic resin in the range of 87-42% by volume, preferably 80-55% by volume. If the inorganic filler content is less than 13% by volume, adjacent voids created by peeling at the interface between the thermoplastic resin and the inorganic filler will no longer communicate with each other, making it impossible to obtain air permeability. If it exceeds 58% by volume, the unstretched film loses its elongation during stretching, making biaxial stretching difficult. The mandrel stretching method in which biaxial stretching is carried out 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. Lateral direction (circumferential direction) in which the end is trying to stretch
A truncated conical mandrel having a diameter approximately equal to the stretching ratio is inserted, and while the tubular unstretched film is placed along the slanted side of the mandrel, it is stretched and cooled by a take-up roll located behind the mandrel. This is a method in which the film is stretched in the transverse direction (circumferential direction) and the longitudinal direction while being subjected to surface pressure on a substantially truncated conical mandrel due to the force generated when the film is taken off. As a method for supporting this mandrel, it is preferable to fix the end face of the mandrel with a small diameter 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, 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 done in contact with the mandrel, so the melting point is Tm (℃) and the stretching temperature is Ts (℃).
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 that 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, the amount of blown gas, etc. 0.1~150Nl/℃
m ² ·min, preferably in the range of 1 to 70Nl/m ² ·min,
The diameter 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 amount of this gas blown, a breathable film with gradually increasing air permeability can be obtained. Moreover, air is the most common gas. In addition, for this gas injection,
A conduit is provided that is connected to an external pressure source, passes through the annular die, the aforementioned mandrel support rod, and the mandrel, 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 process for manufacturing a tubular unstretched film 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 heated 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 under surface pressure; The film, 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 continuously applied from the inside of the tubular film to the outside. It consists of a step of 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 by the present invention include the type of thermoplastic resin, the particle size of the inorganic filler,
Type, filling ratio, stretching temperature (biaxial stretching conditions),
It can be freely controlled by adjusting the stretching ratio in the longitudinal and lateral directions, the amount of cooling gas blown, the amount of gas blown from the inside, etc. The thickness of the breathable film is 25~
In the case of 150μ, the air permeability measured by JIS P8117 is 25~
Moisture permeability measured by JIS Z0208 at 30000 seconds/100c.c.
It is desirable to have a value in the range of 300 to 25000 g/m ² ·24 hours, and the thickness is preferably 60 μm or less, particularly preferably 50 μm 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
g/ ^cm3 , MFR1.0g/10min, Q value 3.4, melting point 124℃)
64% by volume of powder, and heavy calcium carbonate (average particle size 1.2μ, irregular shape not plate-shaped, rod-shaped, needle-shaped, etc.)
80% by volume and precipitated calcium carbonate (average particle size
35% by volume of an inorganic filler mixture consisting of 20% by volume (0.3μ, cubic), ethylene-butene-1 copolymer
Heat stabilizer (2,6-di-t-
After mixing 0.1 part by weight (butyl-p-cresol) and 1.0 part by weight of a dispersant (oleic acid) with 100 parts by weight of the inorganic filler mixture in a super mixer for 5 minutes, strands were heated at 200℃ using a twin-screw extruder. After extruding into a shape, it was cut into pellets. The obtained pellets were passed through a screw with a screw diameter of 50φ, L/
An annular die (lip diameter) attached to a D25 extruder
After extruding at 210℃ through a 75φ, 4-row spiral die with a lip gap of 1mm, it is brought into contact with a 100φ diameter cooling mandrel in which water at 5℃ circulates, and is cooled and solidified at a blow ratio of 1.33 to form a tubular blank with a thickness of 110μ. The stretched film was drawn at a rate of 5 m/min. After heating this film to 110℃ with a preheating mandrel with a diameter of 98φ connected below the cooling mandrel, the diameter of the end face directly connected to the preheating mandrel is
Stretch 2.5 times in the transverse direction (circumferential direction) while following the surface of a 110°C truncated conical mandrel with a 98φ diameter and a cone angle of 90° and a satin finish of 0.5 μm. Then, an air ring with a diameter of 350φ and a lip gap of 3 mm was placed around the entire outer circumference of the biaxially stretched film, which was in a tubular state after leaving the mandrel, at a position 50 mm from the lower end of the mandrel. At the same time, air at 20°C is blown inside the tubular film from the conduit at the lower end of the mandrel.
By continuously blowing at a rate of 5 Nl/m ² ·min, the film was continuously penetrated from the inside to the outside in the thickness direction of the film, and taken up with a nip roll to obtain a tubular biaxially stretched breathable film. Table 1 shows the appearance and physical properties of the breathable film obtained. In addition, the moisture permeability is JIS Z0208, and the air permeability is
JIS P8117 and tear strength were measured based on JIS Z1702. 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 precipitated carbonic acid 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. The results of the obtained breathable film are also shown in Table 1. Example 3 In Example 1, high density polyethylene (density
0.956g/ ^cm3 , MFR0.05g/10min, Q value 7, melting point
135℃) was pelletized at 290℃, extruded at 260℃ as a tubular unstretched film with a thickness of 90μ, and a preheating mandrel and a stretching mandrel were used.
A breathable film was produced by stretching under the same conditions as in Example 1 except that the conditions were changed to 120°C. The results are also shown in Table 1. Comparative Example 1 Stretching was carried out under the same conditions as in Example 1, except that the mixing ratio was changed to 30% by volume of heavy calcium carbonate and 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 tubular unstretched film with a thickness of 130μ was extruded using heavy calcium carbonate alone as an inorganic filler, the preheating mandrel and stretching mandrel were heated to 113°C, and cooling air was blown after stretching. Stretching was carried out under the same conditions as in Example 1, except that the stretching speed was 10 m/sec and the air blowing inside the tubular film was 40 Nl/m ² ·min. 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, amorphous shape not plate-like, rod-like, needle-like, etc.) and heavy calcium carbonate (average particle size). A breathable film was obtained in the same manner as in Example 1, except that the inorganic filler mixture was changed to a mixture of 20% by volume of an inorganic filler (diameter: 0.6μ, amorphous (not plate-like, rod-like, needle-like, etc.)). The obtained results are also shown in Table 1. 【table】

Claims (1)

[Claims] 1 Thermoplastic resin 42-87% by volume and average particle size
An inorganic filler with an average particle diameter of 0.7 to 4μ and an inorganic filler with an average particle diameter of 0.05 to 0.7μ, the ratio of the average particle diameter of the former to the latter is 2 to 20, and the former is 50 to 97% by volume and the latter is 50 to 3.
A tubular unstretched film made of a composition with an inorganic filler mixture of 58 to 13% by volume is biaxially stretched along a truncated conical mandrel, and then tubular biaxially stretched. A method for producing a breathable film, which comprises cooling the film by blowing gas from the outside of the film, and penetrating the outside of the film by continuously blowing gas from the inside of the film.