JPS6025541B2 - High-strength nonwoven fabric made of fine fibers and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-strength nonwoven fabric made of fine fibers, and more particularly to a high-strength nonwoven fabric made of fine fibers of a stretched polymer with uniform molecular orientation.

When using non-woven fabric as a separator for electrolytic capacitors, varnish impregnation, or insulating base fabric for mica packing, it is necessary to use a fabric that is delicate, extremely thin with a thickness of 50 mm or 30 mm, and yet has high strength. It is said that

In order to make the nonwoven fabric thinner and thinner, it is effective to make the constituent fibers of the nonwoven fabric thinner.In this case, in order to achieve high strength, the fibers must be short fibers, have molecular orientation, or have no unwoven fibers. Must not be drawn fibers. According to the present invention, a high-strength nonwoven fabric made of drawn continuous fibers with an average fiber diameter of 10 mm or less, particularly 2 mm or less, can be obtained, and a dense and thin fabric with a small basis weight can be easily obtained. The nonwoven fabric is extremely suitable for use as a separator for electrolytic capacitors, insulation material base fabric for varnish impregnation, mica packing, etc., as well as various tape base materials and coating base fabrics.

Conventionally, it has been extremely difficult to obtain a high-strength nonwoven fabric from fine fibers with an average fiber diameter of about 10 mm or less, particularly 2 mm or less.

For example, in the melt-plowing method, which is a technology for producing fine fiber nonwoven fabric using the spunpond method, the melt viscosity of the high molecular weight polymer must be considerably lowered to produce fine fibers. Shots (molten balls) are often generated due to cutting, and the fibers obtained have only low strength without molecular orientation. In addition, when making nonwoven fabrics from fibers using the normal paper yarn method, the processes of spinning, drafting, stretching, cutting, web formation, and web bonding are necessary. Many troubles occur during the process, and it is difficult to produce fine fiber-free fabric with a diameter of about 10 mm or less. A method can be considered in which a web is formed using mixed spun fibers or the like, and then some of the components are rolled out to leave fine fibers, but this method is technically difficult and economically disadvantageous. The present invention has been made in view of the above points, and the manufacturing method of the present invention includes melting a high molecular weight polymer and spinning it from an orifice while injecting high-temperature airflow from the surroundings to transport and finely spun the spun fiber, Next, while the spun fibers still have self-adhesive properties, they are stacked on a moving collecting surface having an inclination angle of 5 to 80 degrees with respect to the weaving yarn injection direction, thereby aligning the fibers in the moving direction of the collecting surface. to form a fibrous web, and then stretch this fibrous web in the same direction.
This is a method for producing a high-strength nonwoven fabric made of fine fibers of a stretched high molecular weight polymer. In other words, in the manufacturing method of the present invention, the spun fibers are thinned to a certain extent by a high-temperature jet air stream, and then the extracted fibers are accumulated using a special bridging means so that they are arranged in a certain direction, and the fibers are self-bonded to form a fiber web. Forming and drawing the fibers into iron threads, which were insufficient
That is, after forming a web with molecular orientation, the web is stretched in the fiber arrangement direction, thereby further stretching the constituent fibers to make them finer and at the same time causing molecular orientation to obtain a strong nonwoven fabric.

According to the manufacturing method of the present invention, the fibers have an average fiber diameter of 10 French or less, are composed of substantially continuous fine fibers stretched so as to have uniform molecular orientation, and most of the fine fibers are A high-strength nonwoven fabric is obtained which is characterized in that the fibers are arranged in a certain direction and the ratio of the strength in the direction in which the fibers are arranged and the strength in all directions perpendicular to the direction is 15 or more.

Next, the present invention will be explained in detail according to the steps.

The polymer used in the present invention may be any polymer that can be melt-spun, such as poly-IJ olefin,
High molecular weight polymers such as polyamide-based and polyester-based high molecular weight polymers, polyvinyl chloride, polystyrene, polycarbonate, mixtures thereof, and various copolymers can be used. These high molecular weight polymers are supplied to an extruder, and in a heated and molten state, they are passed through a number of orifices while high-temperature airflow is ejected from around the orifices, and the spun fibers are made into paper.

In this case, it is preferable to use the so-called melt blowing method, in which a molten polymer is spun through a number of orifices arranged in a straight line, and a high-temperature air stream is blown out from slits in contact with both sides of the orifices. According to this method, the fibers made into paper threads are conveyed in parallel in layers by the airflow, so that they are uniformly thinned. In the present invention, the spun fibers are conveyed by high-temperature airflow, so that the fibers are ponged in a semi-molten state, and the resulting fibers are characterized by being undrawn fibers with no molecular orientation.

This is a factor that facilitates the subsequent drawing of the fibrous web, which is an important step. The point to be careful about in this paper thread process is that when spinning fine fibers, many shots occur due to fiber cutting, which deteriorates not only the appearance but also the strength and other qualities of the final nonwoven fabric. It is a point. This is because this shot causes problems such as uneven stretching and cutting during the subsequent stretching of the fiber web. Therefore, in the paper threading process of the present invention, it is preferable to thread the paper in such a way that shots do not occur, that is, the fibers are not cut during the paper threading process. The fibers graded in this way are conveyed by a high-temperature air stream, and while they still have self-adhesive properties, they are accumulated on a moving collecting surface having an inclination angle of 5 to 80 degrees with respect to the spinning injection direction, so that the fibers are substantially The collection surface is arranged in the direction of movement.

To explain with the figure, while the fibers 1 made into paper threads still have self-adhesive properties, a collecting surface moves in the direction of the arrow having a mirror oblique angle a of 5 to 8 degrees with respect to the ejection direction of the paper threads. 2 to form a fiber web 3.

Here, the fibers must be accumulated while having a good self-adhesive property, so that the fibers lightly adhere to the collection surface at the collision point 4 on the camphori collection surface, and the accumulated fibers must also adhere to each other. This is to prevent the accumulated web from being disturbed by the ejected airflow, and to provide strength to the web so that it can be stretched uniformly in the subsequent stretching process, and to provide excellent strength to the obtained nonwoven fabric. This is to effectively accomplish the purpose of granting.

In order for the fiber to remain self-adhesive even after it has been made into paper yarn from the orifice, the distance from the orifice to the collision point 4 is generally set at 4.
It is preferable to keep it within the range. There is a second purpose to assembling the spun fibers so that they are arranged in a certain direction. 1
One is to obtain a strong nonwoven fabric. In the conventional spunbond method, the fibers are stacked in a random arrangement, and even though they are made of continuous fibers, the fibers are not aligned in the stress direction, so the strength of the fibers themselves is lower than that of nonwoven fabrics. The strength of the team is not fully utilized. One more
The first purpose is to ensure that each of the fibers is uniformly stretched in the next drawing process, and that the width of the weave is hardly stretched at that time. In the case of random arrangement, the degree of stretching of each fiber differs during stretching, and at the same time, a shrinking force acts in a direction perpendicular to the stretching stress, so as the stretching ratio increases, the width of the weave increases, especially at the corners at both ends. There is a drawback that the stretching is non-uniform, such that the area has a larger basis weight and is thicker than the central area. In order to arrange the fibers in the direction of movement of the swallow collecting plane, it is necessary to tilt the gutter collecting plane at an angle of 5 to 80 degrees with respect to the injection direction and to flow the air flow along the swallow collecting plane.

If it is less than 50, the collision point 4 is caused by the airflow and the shaking of the fibers.
The position of the airflow becomes unstable, making it difficult to obtain a uniform directional web, and in some cases, the airflow passes parallel to the construction surface and is not collected at all.

In the case of 800 or more, the fibers are randomly accumulated in the form of loops as in the case of sub-spun bodets, and never become a directional web.

The preferred angle of inclination is 20o to 60o, optimally 2o.
50-400. The material for the collecting surface is preferably air-impermeable because it is necessary to rectify the ejected airflow downward along the oblique angle.

However, it is not necessary that the net be completely impermeable, and the present invention can be carried out as long as it is a fine net of about 20 mesh or more. A preferable material is a heat-resistant, delicate fabric canvas. The thus obtained web with fibers arranged in one direction is then stretched in the direction of fiber arrangement in order to further refine the fibers and improve the strength.

If the self-adhesive strength of the fibers is weak and therefore the strength of the web cannot withstand stretching, it may be pressed using a hot pressure renderer before stretching. Stretching is performed by a known method such as a roller method, and may be cross-stretching or hot stretching.
Accordingly, it is preferable to stretch the film at least twice in the arrangement direction. Although the stretching ratio varies depending on the polymer, it is preferably 3 to 5 times. Since the web is a web in which the fibers are arranged in the drawing direction, each of the fibers is drawn uniformly as described above, and at this time, the web does not become wider or the edges become thicker. Furthermore, by this stretching, it is possible to produce a nonwoven fabric consisting of continuous fibers with an average fiber diameter of 2 mm or less, which was previously impossible due to the occurrence of secondary shot. For example, if a web made of continuous fibers with a diameter of 3.7 mm is stretched four times, a nonwoven fabric of the present invention made of substantially continuous fibers with a diameter of 1.6 mm is obtained. The term "substantially" is used here because when the fibers become this fine, it is inevitable that some of the fibers will be cut due to stretching. However, even if the fibers break, they will not form anything like the shot that occurs when cutting during spinning, and will not reduce the quality or appearance of a nonwoven fabric made of continuous fibers, so this will not reduce the effects of the present invention. isn't it. This stretching causes molecular orientation in the polymer constituting the fibers, achieving high strength.

As is clear from the above description, the high-strength nonwoven fabric of the present invention is a so-called unidirectional nonwoven fabric, in which fibers are arranged in a certain direction, and the fibers are molecularly oriented by stretching, and thus have high strength in a certain direction. It is. In the present invention, the fact that most of the fine fibers are arranged in a certain direction means that the fibers are arranged to such an extent that high strength can be achieved in a certain direction. This is supported by the strength ratio with the perpendicular direction.

This strength ratio varies depending on the polymer used, the oblique angle of the collection plane, the stretching ratio, and the degree of bonding between fibers.
It is preferable to arrange the fibers to such an extent that this strength ratio is 15 or more. In the case of a unidirectional nonwoven fabric made by a conventional carding machine (flowing method), this strength ratio is 4 to 1 degrees, but in the case of the present invention, it is This intensity ratio can be increased to 40-50. The following table shows how the oblique angle and the stretching ratio affect this strength ratio, in other words, the arrangement of the fibers. As is clear from this table, in the case of low magnification stretching, this ratio is influenced by the tilt angle, but as the magnification increases, the influence of the tilt angle becomes less.

After stretching, in order to bond the intersections of the fibers more firmly, the fibers may be hot-pressed at a temperature higher than the softening point of the polymer, or may be impregnated with an adhesive or the like. However, even if the self-adhesive strength of the fibers is weak in the stacking stage, the fusion between the fibers can be further improved by stretching, so that there is almost no need to provide a new adhesive means. However, if thermal dimensional stability is required, it is preferable to heat set the material in a tensioned or relaxed state, or to pass it through a calendar if it is necessary to adjust the thickness. As described above, according to the method of the present invention, it is possible to obtain a high-strength non-dispersed fabric consisting essentially of continuous fibers, even when the average fiber diameter is 10 or less, especially 2 or less, which was considered impossible in the past. Because it is made of fibers, it is possible to obtain lightweight, delicate, and ultra-thin nonwoven fabrics.

In addition, by increasing the molecular orientation and crystallization of each fiber by stretching, many resistances such as heat resistance and chemical resistance are improved.
It also has a very glossy appearance. Furthermore, from an industrial perspective, there is almost no width reduction due to stretching, and the entire width is uniformly stretched, so the quality is extremely stable and the yield is improved, making it a great contribution.
The nonwoven fabric obtained by the method of the present invention is extremely suitable as a separator for electrolytic capacitors, an insulating base fabric for varnish impregnation, mica backing, etc., as well as various tape base materials and coating base fabrics. It is used for.

EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these in any way. Example 1 Polyethylene terephthalate was supplied to an extruder and melted, and the melt was discharged from an orifice heated to a temperature of 280 oo, consisting of 24 solid holes arranged in a straight line with a diameter of 0.3 mm, at a discharge rate of 12 pm/min. At the same time, compressed air heated to a temperature of 350 oo and at a pressure of 1.5 k9/ground is ejected from the 0.4 rib slits in contact with both sides of the orifice to convey and thin the paper fibers in the longitudinal direction. While still sticky, the fibers were collided and piled up on a fine vertical canvas bottle collecting surface inclined at an angle of 3 to the injection direction of the fibers, which was 15 skins away from the collision point.

Since the fibers have self-adhesive properties, they adhere at the intersections of the fibers and adhere to the bottle collecting surface, so that they are folded and arranged in the direction of the flow of the ejected air flow without being disturbed, and are arranged almost in the direction of the bottle collecting surface. A fiber web with a fabric weight of 50 mm was formed in which continuous fibers with an average fiber diameter of 4 mm were arranged in parallel.
Next, this web was peeled off from the Tachibana collection surface, hot pressed in a calendar at a temperature of 75qo, and then stretched 4 times in the fiber arrangement direction using a roller stretching machine at a temperature of 90q0.
Each fiber was stretched and molecularly oriented uniformly over the entire width with almost no width stretching, resulting in a highly photo-selective nonwoven fabric.

This non-woven fabric has a basis weight of 12.8 mm, a thickness of 30 mm (measured with a micrometer), and an average fiber diameter of 2.0 mm, and the fibers are substantially continuous, so the tensile strength of the non-woven fabric is 3.0 mm. It is extremely strong with a rib width of 8k9/15 (fiber alignment direction), and is therefore suitable for use as various tape base materials and coating base materials, as well as IJ bond tape for decoration and packaging because of its light selection and beauty. It was to be done. Note that the strength in the direction perpendicular to the fiber arrangement direction is 0.
The side width was 11k9/15, and the strength ratio was 34.5. In addition, when this nonwoven fabric was further pressed using a heat-pressure renderer, the fibers were so fine that it reached a thickness of 13 mm, which was previously unheard of.
It became an ultra-thin non-woven fabric called Buddha, and was ideal as a base fabric for insulating materials such as mica backing and varnish impregnation.

Comparative Example 1 In the same manner as in Example 1, paper-outed fibers were collided and accumulated on a bottle collecting surface that was perpendicular to the traveling direction of the fibers.

The fibers were randomly accumulated in a loop without any directionality, and a fiber web with a basis weight of 50 mm was formed.
Next, this web was hot-pressed using a calendar at a temperature of 7yo, and then stretched 4 times at one touch using a roller stretching machine at a temperature of 90:00.

However, due to the random web, as with normal film stretching, there is a problem of uneven stretching in which the width is large due to stretching and the ends of both ends become thicker, and at the same time, the degree of stretching of each fiber is different. The physical properties of the obtained nonwoven fabric also varied greatly. The average basis weight of the obtained woven fabric was 15.5 mm, and the average fiber diameter was 2.8 mm.
The average tensile strength was 2.6k9/15 side width (fiber drawing direction). Example 2 Polypropylene was fed into an extruder and melted, and the melt was heated to a temperature 3.
Spinning is carried out at a discharge rate of 20/min from an orifice heated to 1,000 ℃, and at the same time 0.4
Pressure heated to a temperature of 400 oo from the skin slit 1.
The paper fibers are conveyed and woven by blowing out 5 kg/ground of compressed air, and then, while the fibers are still self-adhesive, the paper fibers are blown at 25° to the direction of injection of the fibers, which is 25 degrees away from the pier point. It was collided and accumulated on a delicate cotton canvas collection surface that was tilted at an angle.

Because the fibers have self-adhesive properties, they adhere at the intersections of the fibers and adhere to the collection surface, so that they are folded and arranged in the direction of the flow of the ejected air flow without being disturbed, and almost follow the direction of the collection surface. A fiber web with a fabric weight of 80 mm was formed in which continuous fibers with an average fiber diameter of 7 strands were arranged in parallel to each row. This web is then peeled off from the construction surface and heated to a temperature of 90 oo
After hot pressing in a calendar, the fibers were stretched 4.5 times in the fiber arrangement direction using a roller stretching machine at a temperature of 10,000, and each fiber was stretched and molecularly oriented uniformly over the entire width with almost no width stretching. A highly photosensitive nonwoven fabric was obtained.

This non-woven fabric has a basis weight of 17.9 k/m, a thickness of 56 k/m (measured with a micrometer), an average fiber diameter of 3.5 k/1, and a tensile strength of 4.6 k9/1 since it is made of continuous fibers.
It was extremely strong with 5 ribs (in the direction of fiber arrangement) and was suitable for use as adhesive tape for decoration, packaging, etc. The strength in the direction perpendicular to the fiber arrangement direction is 0.1
The width was 1 kg/15, and the strength ratio was 44.8.
In addition, this nonwoven fabric was treated with polyoxyethylene nonylphenol ether (Emulgen 810 manufactured by Kao Atlas Co., Ltd.) to give it hydrophilic properties and was used as a separator for an aluminum electrolytic capacitor. Furthermore, since it is made of fine fibers, its impedance and tan8 are small, making it extremely suitable for use.

[Brief explanation of the drawing]

FIG. 1 is a process side view of the manufacturing method of the present invention.

Claims (1)

[Claims] 1. Consisting of substantially continuous fine fibers with an average fiber diameter of 10 μm or less and stretched so as to have uniform molecular orientation,
A high-strength nonwoven fabric characterized in that most of the fine fibers are arranged in a certain direction, and the ratio of the strength in the direction in which the fibers are arranged to the strength in a direction perpendicular to the direction is 15 or more. 2. The high-strength nonwoven fabric according to claim 1, wherein the average fiber diameter of the fine fibers is 2 μ or less. 3. While melting the polymer and spinning it from an orifice, a high-temperature air stream is injected from the surroundings to transport and thin the spun fibers, and then, while the spun fibers still have self-adhesive properties, they are The fibers are collected on a moving collection surface having an inclination angle of 5 to 80 degrees to form a fiber web by arranging the fibers in the direction of movement of the collection surface, and then this fiber web is stretched in the same direction. A method for producing a high-strength nonwoven fabric comprising fine fibers of a stretched polymer having an average fiber diameter of 10 μm or less.