JPH0314059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a breathable film having a soft feel, which is obtained by biaxially stretching an unstretched film made of a combination of a polyolefin 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 polyolefin 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 leaving any unstretched parts, 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 difference in circumferential speed between low-speed rolls and high-speed rolls, while stretching in the horizontal direction (middle 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 a polyolefin resin and an inorganic filler using this internal pressure bubble stretching method,
When the tubular unstretched film passes through the low-speed nip rolls, it is pressed into a two-fold state by the nip rolls, so the bent edges 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 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. As described above, in the conventional method of manufacturing a breathable film by biaxially stretching an unstretched film made of a composition of a polyolefin resin and an inorganic filler, the balance of mechanical properties in the direction and the transverse direction is not achieved. At present, it has not yet been possible to stably produce a film with a uniform thickness that is easy to remove and has excellent air permeability. 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. In view of the above-mentioned current situation, the present invention was made with the aim of solving the problems and demands of conventional manufacturing methods. 0.910〜
0.940g/cm ³ , melt flow rate 0.1~5g/
10 minutes, 42 to 87% by volume of an ethylene-α-olefin copolymer with a Q value expressed as the ratio of weight average molecular weight to number average molecular weight of 4 or more and 58 to 87% by volume of an inorganic filler.
A tubular unstretched film made of a composition of 13% by volume 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. It is characterized in that gas is continuously blown from the inside of the film to penetrate the outside of the film. Here, the ethylene-α-olefin copolymer is 1 to 20% by weight, preferably 3 to 15% by weight of α-olefin, which is a C ₃ to _{C 8} molecular skeleton, and 99 to 80% by weight of ethylene. Preferably, it is a linear low-density ethylene copolymer consisting of 97 to 85% by weight, which is formed by an ionic reaction between ethylene and a C ₃ to _{C 8} molecular skeleton using a catalyst that combines a transition metal compound and an organometallic compound. It is a resin produced by copolymerizing one or more α-olefins, and its density is
0.910-0.940g/ ^cm3 , preferably 0.916-0.935
g/cm ³ , melt flow rate (MFR) 0.1-5
g/10 min, preferably 0.1 to 3 g/10 min, Q expressed as the ratio of weight average molecular weight to number average molecular weight
A branched low-carbon compound whose value is in the range of 4 or more, preferably 6 or more, and is produced by polymerizing ethylene through a radical reaction under high pressure using a commonly known oxygen radical as an initiator. Density polyethylene resins have different performance in molecular structure, melting properties, crystallization properties, solid physical properties, and stretching properties. A mixture of ethylene-α-olefin copolymers having different indexes may be used in the present invention as long as the density, MFR, and Q value of the mixture are within the aforementioned limited ranges.
Preferably it is a single copolymer. When the density of this copolymer is less than 0.910 g/cm ³ , uniform stretchability deteriorates, and when it exceeds 0.940 g/cm ³ , the soft feel of the stretched film is impaired. Also,
If the MFR is less than 0.1 g/10 minutes, abnormal flow will occur when the unstretched film is melt-extruded from the die gap, making it impossible to obtain a uniform unstretched film.
If it exceeds g/10 minutes, uniform stretchability will deteriorate. Furthermore, when the Q value is less than 4, uniform stretchability deteriorates and thickness uniformity is impaired. 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 plate-like, rod-like, spherical, granular, and amorphous shapes other than needle-like shapes, and the average particle size thereof is 0.1 to 5 μm, preferably 0.6 to 3 μm. When the average particle size is less than 0.1μ, the unstretched film loses its elongation during stretching, making biaxial stretching difficult; when it exceeds 5μ, the surface of the biaxially stretched film becomes rough, making it undesirable as a breathable film. With,
When producing thin films of 60μ or less, continuous stable stretchability is impaired. As a method for kneading the ethylene-α-olefin copolymer and the inorganic filler, heating kneading using a single-screw or twin-screw extruder, a Banbury mixer, a kneader, a mixing roll, etc. can be employed. 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, as a dispersant, carbon number 12
The above higher fatty acids give good results. The inorganic filler may be treated with these dispersants or the like before being heated and kneaded. The composition ratio of the ethylene-α-olefin copolymer and the inorganic filler is such that the ethylene-α-olefin copolymer is 42 to 87% by volume, preferably 55 to 80% by volume,
The amount of inorganic filler is 58-13% by volume, preferably 45-20% by volume. If the inorganic filler content is less than 13% by volume, adjacent voids formed by peeling of the interface between the ethylene-α-olefin copolymer and the inorganic filler will 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 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 of the tubular biaxially stretched film is set as appropriate so that the diameter is approximately the same as that 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 physical properties of the ethylene-α-olefin copolymer, the particle size, type, and filling ratio of the inorganic filler, the stretching temperature (biaxial stretching conditions), and the longitudinal and lateral stretching conditions. It can be freely controlled by the stretching ratio, the amount of cooling gas blown, the amount of gas blown from the inside, etc. When the thickness of the breathable film is 25-150μ, the air permeability measured according to JIS P8117 is 25-30000 seconds/100c.c., JIS Z
The moisture permeability measured by 0203 is preferably in the range of 300 to 25,000 g/m ² ·24 hours, and the thickness is preferably 60 μm or less in view of the soft feel. 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 weight combination (density 0.923
g/ ^cm3 , MFR0.9g/10min, Q value 11, melting point 121℃)
65% by volume of powder, 35% by volume of heavy calcium carbonate (average particle size 1.2μ, amorphous, not plate-like or rod-like), 100 parts by weight of ethylene-butene-1 copolymer, heat stabilizer (2,6-di -0.1 part by weight of (t-butyl-p-cresol) and 1.0 part by weight of a dispersant (oleic acid) with 100 parts by weight of heavy calcium carbonate were mixed in a super mixer for 5 minutes, and then heated to 200°C using a twin-screw extruder. After extruding it into a strand, 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 130μ. The stretched film was taken off at a rate of 4 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
The diameter of the other end face is 98φ and the diameter of the other end is 250φ, and the surface with a cone angle of 90° is 2.5 times larger in the lateral direction (circumferential direction) while following the surface of a 110℃ truncated conical mandrel that has been satin-finished to have an unevenness of 0.5μ. While stretching, the biaxially stretched film is stretched 3.0 times in the longitudinal direction, and then an air ring with a diameter of 350φ and a lip gap of 3mm is placed around the entire outer circumference of the biaxially stretched film that has left the mandrel and is in a tubular state, at a position 50mm from the lower end of the mandrel. At the same time, air at 15℃ and 10m/sec is blown into the inside of the tubular film through the conduit at the bottom end of the mandrel.
A tubular biaxially stretched breathable film was obtained by continuously blowing at a rate of 40 Nl/m ² ·min to continuously penetrate the film in the thickness direction from the inside to the outside, and then taking it off with a Nippro roll. . Table 1 shows the appearance and physical properties of the breathable film obtained. 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, ethylene-propylene-butene-1 copolymer (density 0.918 g/cm ³ , MFR 0.701 g/cm 3 ) was used instead of ethylene-butene-1 copolymer.
10 minutes, using a powder with a Q value of 6 and a melting point of 123℃,
Cooling air blowing of tubular biaxially stretched film 5
A breathable film was obtained in the same manner as in Example 1, except that the air blowing rate was 20 Nl/m ² ·min. The results of the obtained breathable film are also shown in Table 1. Comparative Example 1 In Example 1, density 0.920g/cm ³ , MFR 1.0
g/10 minutes, using an ethylene-butene-1 copolymer with a Q value of 3.4 and a melting point of 124°C, with the preheating temperature and stretching temperature adjusted.
Stretched under the same conditions as Example 1 except that the temperature was 113°C.
A breathable film was produced. The results are also shown in Table 1. Comparative Example 2 In Example 1, high density polyethylene (density 0.950
g/cm ³ , MFR 0.05 g/10 min, melting point 132°C) was pelletized at 290°C, extruded as a tubular unstretched film at 260°C, and the preheating temperature and stretching temperature were changed to 118°C. The film was stretched under the same conditions as in Example 1 to obtain a breathable film. The results are also shown in Table 1. 【table】

Claims (1)

[Claims] 1 Ethylene-α-olefin copolymer having a density of 0.910 to 0.940 g/cm ³ , a melt flow rate of 0.1 to 5 g/10 min, and a Q value expressed as the ratio of weight average molecular weight to number average molecular weight of 4 or more A tubular unstretched film made of a composition of 42 to 87% by volume and an inorganic filler of 58 to 13% by volume is biaxially stretched along a truncated conical mandrel, and then gas is introduced from the outside of the tubular biaxially stretched film. A method for producing a breathable film, which comprises cooling the film by blowing the film, and penetrating the film to the outside by continuously blowing gas from the inside of the film.