GB1577505A

GB1577505A - Method and apparatus for producing long-fibre nonwoven fibrics

Info

Publication number: GB1577505A
Application number: GB1830/78A
Authority: GB
Original assignee: Unitika Ltd
Current assignee: Unitika Ltd
Priority date: 1977-05-26
Filing date: 1978-01-17
Publication date: 1980-10-22
Also published as: FR2392159B3; JPS53147875A; DE2821823C2; FR2392159A1; DE2821823A1; JPS5851541B2

Description

(54) METHOD AND APPARATUS FOR PRODUCING LONG-FIBER NON-WOVEN FABRICS (71) We, UNITIKA LIMITED, a Company organised under the laws of Japan, of 50, Higashi Hommachi 1-chome, Amagasaki-shi, Hyogo-ken, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

The present invention relates to a method and apparatus for producing long-fiber non-woven fabrics by sucking continuous bunched filaments by an ejector and accumulating them on a collecting surface to form a web.

In methods of producing long-fiber non-woven fabics by sucking continuous bunched filaments by an ejector and accumulating them on a collecting surface to form a web, in order to produce broad non-woven fabrics, it is necessary that (a) the ejector, i.e., the suction jet from the ejector be transversely moved in a direction at right angles with the direction of movement of a web collecting device, i.e., widthwise of the web or (b) a number of ejectors be arranged in one or more rows widthwise of the web over the entire width of the non-woven fabric being produced.

However, in the former (a) method, a complicated device for transversely moving the elector, i.e., the jet from the ejector is required, and under the condition for production which sets the rate of travel of the collecting surface at, .e.g., several meters or several tens of meters per minute, the production of a board, uniform web necessitates transversely moving the ejector at a considerable speed which would make the production practically impossible.

On the other hand, in the latter (b) method it is possible to produce a broad uniform web without limitations on the rate of travel of the collecting surface and without requiring a complicated device as in the former method. However, the strength of the non-woven fabric produced as measured in the direction of travel of the web, i.e., the longitudinal strength is higher than the strength thereof as measured in a direction at right angles with the direction of tavel of the web, i.e., the transverse strength. Thus, the disadvantage is that the non-woven fabric obtained is unisotropic in that there is a difference between the longitudinal and transverse strengths.

We have made intensive research into the cause for which it is possible to obtain only a unisotropic non-woven fabric whose longitudinal strength is higher than the transverse strength in the method using a number of ejectors arranged in one or more rows, as described in (b) above. Our research has revealed that the cause is due to the fact that when the air blown from each ejector reaches the collecting surface, it collides with the walls of air from transversely adjacent ejectors rather than describing a homogeneous circular pattern, so that the spreading of the air transversely of the collecting surface is obstructed, resulting in the reduction of the extent of transverse spreading and interlacing of the filaments constituting the web. That is, when air jets form elliptic patterns on the collecting surface, the filaments will be spread parallel with the major axis without being interlaced in the direction of the minor axis.

More specifically, in forming a web by using a known ejector for accumulating filaments on a web collecting surface, the filaments can be spread over the boundary region of the free air jet from the ejector, but the distribution of the filaments within the jet is not uniform, with the amount of filaments accumulated increasing as the center is approached.

Therefore, in order to obtain a non woven fabric having no variations in the density (the weight per unit area) over the entire width of the non-woven fabric by the method using a number of ejectors arranged side by side in the direction of width of the web, it is necessary and actually practiced to dispose the width-wise arranged ejectors so that the spacing between adjacent ejectors is so short that the boundary regions of free air jets from the ejectors overlap each other to a substantial degree. If they are arranged in that way, however, the jet from each ejector collides with the walls of jets from adjacent ejectors, obstructing the spreading of the filaments transversely of the web collecting surface. As a result, there is formed an elliptic pattern with its major axis extending in the direction of travel of the collecting surface. In the web obtained according to such pattern, the amount of spreading and interlacing of the filaments in the direction of minor axis of the pattern, i.e., transversely of the web is small and hence the resulting non-woven fabfic is unisotropic in that its longtiduinal strength is higher than its transverse strength.

On the other hand, in order to avoid such a problem, even if the production is carried out under the particular condition that the spacing between adjacent ejectors is increased to the extent that the boundary regions of the free air jets therefrom do not so much overlap each other, the result obtained would be only that the transverse strength of the non-woven fabric is not very high as compared with the longitudinal strength of the non-woven fabric, so that there is little merit for the fact that the troublesome change of the condition, i.e., the change of the spacing is involved. This is because although the increase of the ejector spacing reduces the interference between the jet from each ejector and the jets from adjacent ejectors so that the pattern described on the web collecting surface by each air jet approximates a circle, the result is opposite to the object of producing a uniform non-woven fabric free from widthwise density variations, since the distribution of the accumulated filaments inside the pattern is not uniform, as described bove. Thus, this offers no solution of the problem.

Further, even if two or more rows of ejectors are arranged widthwise of the collecting surface in such a manner as to compensate for density variations, i.e., in zigzags, the amount of interlacing of filaments between adjacent rows is small. Also, even if the spacing between djacent rows is reduced, the interlacing of filaments obtained is in the direction of travel of the web, i.e., the longitudinal direction of the non-woven fabric. As a result, the longitudinal strength can only be improved and the resulting non-woven fabric is not an isotropic one in which the longitudinal-transverse strength ratio is nearly 1.

According to the present invention there is provided an apparatus for producing long-fiber non-woven fabtics, comprising a plurality of ejectors for feeding continuous bunched filaments onto a collecting surface of a moving web, the ejectors being arranged above the level of the collecting surface in one or more rows transversely to the moving direction of the collecting surface, the apparatus being characterized in that a spreading device is fitted on a cylindrical outer periphery of the lower end of a spout tube of each ejector in such a manner that the amount of relative insertion of the lower end of the spout tube into the spreading device is adjustable, said spreading device having an inner surface the cross section of which smoothly varies from cylindrical at an inner axial end thereof fitting or the spout tube, to a slot-like outlet port at the other outer axial end thereof and whose cross-sectional area gradually increases as it extends from said inner axial end toward said outer axial end, the longeraxis of said cross-sectional area at the outlet port extending along the direction of arrangement of the ejectors.

The usually employed ejector has its fluid spouting port circular,-so that the filaments are accumulated within the boundary region of the free air jet from each ejector while describing a circular pattern, as shown in Figure 1. In the case where a number of ejectors are arranged in a row in a direction at right angles with the direction of travel of the web collecting surface, the filaments collide with the walls of jets from adjacent ejectors, so that as shown in Figure 2 they are accumulated while describing an elliptic pattern having a major axis extending in the direction of travel of the web (indicated by an arrow in the figure). Therefore, in order to cause the filaments to describe a circular pattern as shown in Figure 1 or an elliptic pattern having a major axis extending in a direction at right angles with the direction of travel of the web as shown in Figure 3 when a number of ejectors are arranged in a row, this may be achieved by causing the jet from each ejector to describe an elliptic pattern as shown in Figures 3. To this end, the jet from each ejector spout tube in accordance with the present invention has a cross-sectional shape which is oblong in the direction of arrangement of the ejectors.

Thus, the spreading device is attached so that the major axis of the spout port at the front outer end thereof extends in a direction at right angles with the direction of travel of the web collecting surface, i.e.along the direction of arrangement of the ejectors.

If a web is produced by such method, in the case where the angle of opening of the spreading device attached to the ejector, i.e., an angle defined by those generating lines of the inner peripheral surface of the spreading device which face each other in the direction of the major axis, is large, the pattern described on the web collecting surface by the jet from each ejector is an elliptic pattern having a major axis extending in a direction at right angles with the direction of travel of the web. Therefore, a non-woven fabric in which the transverse strength is higher than the longitudinal strength is produced. On the other hand, if the angle of opening is small, the pattern described on the web collecting surface by the jet from each ejector is nearly a circle. Therefore, an isotropic non-woven fabric in which the transverse strength is nearly equal to the longitudinal strength is produced.

Now, the angle of opening of the spreading device is determined by the desired longitudinal-transverse strength ratio of an intended non-woven fabric, the pressure of filament feeding high-pressure air to the ejectors, and the inner diameter of the ejector spout ports. If the intended longitduinal-transverse strength ratio or the air pressure to be fed to the ejectors must be varied, the adjustability of the apparatus according to the invention enables this to be easily achieved.

According to a desirable embodiment of this apparatus, the spreading device is fixed by screw means to the spout tube in such a manner that the amount of relative insertion of the lower end of the spout tube into the spreading device can be adjusted. Preferably, the length of the spreading device from the inner axial end to the outer axial end is such that when said amount of relative insertion is at a minimum the boundary of the free air jet coincides with said angle of opening of the spreading device.

Other numerous features and merits of the present invention will be readily understood from the following description of preferred embodiments of the invention with reference to the accompanying drawings.

Figure I is a view showing a pattern of accumulation on a web collecting surface when a known ejector having a circular fluid spouting port is used alone; Figure 2 is a view similar to Figure 1 but showing a pattern obtained when ejectors similar to that shown in Figure 1 arranged in a row in a direction at right angles with the direction of travel of the web collecting surface are used; Figure 3 is a view similar to Figure 1 but using apparatus in accordance with the present invention; Figures 4a, 4b illustrate a preferred embodiment of the invention, wherein Figure 4a is a front view in longitudinal section and Figure 4b is a side view in longitudinal section; and Figures 5(a) - (d) are cross-sectional views showing examples of the spreading device.

Figures 4a and 4b show an example of the spreading device and ejector used in the present invention, wherein filaments are sucked through an ejector inlet port 2 by the action of high pressure air being fed from the high pressure air feed port 1 of the ejector and is passed through an ejector spout tube 3 and accumulated on a web collecting surface below through a spout port 4. A spreading device 5 is fitted on the lower portion of the ejector spout tube 3, i.e., it is relatively inserted, and fixed in position in such a manner that the length of the portion of the spout tube inserted in the inner recess 6 of the spreading device can be adjusted. Designated at 7 is a screw for setting the spreading device 5. The character 6 designates the angle of opening of the spreading device 5; W designates the inner surface width thereof; D designates the amount of insertion of the ejector spout tube 3 into the speading device 5; L designates the length of the spreading device; d designates the inner diameter of the ejector spout tube 3; and a designates an apparent angle of opening when the spreading device 5 is relatively inserted on the ejector spout tube 3 by the length D.

Figure 5 shows examples of the cross-sectional shape of the spreading device 5 as viewed in the direction in which air is spouted. In practice, it is not always necessary for said cross-section to be oblong as shown at (a), and various shapes which are longer in one direction, as shown at (b), (c) and (d) may be used.

Under the condition that the ejector spout tube 3 is not at all inserted into the inner recess of the spreading device 5, i.e., D = 0, the spreading device presents a spread which is determined by the angle of opening (3 and a pattern which is the most oblong in this spreading device is formed on the web collecting surface, so that the transverse strength of the non-woven fabric obtained is substantially higher than its longitudinal strength. That is, the longitudinal-transverse strength ratio is substantially smaller than 1.

The optimum value of the angle of opening (3 is determined by the volume rate of flow and pressure of air to be spouted from the ejector spout tube, and practically it is fluid-dynamically determined by the pressure of high pressure air to be fed into the ejector.

However, in practice, various factors, including the resistance to flow of the inner surface of the spreading device and the jet of gas being a mixed gas containing filaments, come in, and after all, under usual working conditions i.e., when the pressure of high pressure air to be fed into the ejector is between 1.5 kg/cm3G and 6 kg/cmzG it is most effective for the angle of opening (3 to have a value between 4" and 32". Further, in this case, the inner surface width W of the spreading device is substantially equal to the outer diameter of the ejector spout tube for the purpose of causing the jet to be as oblong as possible, and the length L of the spreading device should not exceed the value necessary for the spreading device to faithfully present its angle of opening 0, i.e., it should not 4exceed the minimum length which provides the condition for the greatest spread when the angle of opening is set at 0.

This is because if the L is longer than is necessary, the spread which is determined by the angle of opening 0 will be presented even if the ejector spout tube 3 is inserted in the inner recess 6 of the spreading device 5, so that the control of spread intended by the invention is difficult. Also, the longer the L, the larger the cross-sectional area of the outlet of the spreading device, so that the sudden-decrese in the speed of the filament-carrying air currents increases, thus making it difficult to achieve a satisfactory accumulation of filaments. Therefore, the optimum length L of the spreading device varies with its angle of opening 0, but usually it is desirably 3-7 times the inner diameter of the ejector spout tube.

If the ejector spout tube 3 is inserted in the interior of the spreading device 5 by D under such conditions, since the spreading device does not have a sufficient length to function its angle of opening 0, despite the fact that seemingly there is the same effect as when a spreading device having an angle of opening a which is greater than the angle of opening 6, is used the ejector jet does not follow the excessive angle of opening a of the spreading device and instead it becomes a so-called peeled jet, separating from the inner wall of the spreading device and becoming a narrow jet, contrary to the expectation. Therefore, despite the use of the same spreading device, it presents only a spread as if a separate spreading device having a smaller angle of opening were used. As a result, the pattern described on the web collecting surface by the filaments ejected from the ejector is more nearly circular than when D = O. As a result, the transverse strength of the non-woven fabic obtained is nearly equal to the longitudinal strength thereof. That is, said fabric is isotropic in that the longitudinal-transverse strength ratio is nearly 1.

If the D is further increased until the spout tube 3 of the ejector passes through the inner surface recess of the spreading device 5 to be positioned below the level of the spreading device outlet, i.e., if D > L, the sprading device will exert no influence whatever, and the same effect is obtained as when the spreading device is not used. Therefore, the longitudinal strength of the resulting non-woven fabric is higher than the transverse strength. Thus, a non-woven fabric whose longitudinal-transverse strength ratio is greater than 1 is obtained. Therefore, it follows that a non-woven fabic whose longitudinaltransverse strength ratio has any desired value can be readily obtained, without changing the angle of opening of the spreading device, i.e., without changing the angle of opening of the spreading device, i.e., without the trouble of exchanging the spreading device, by simply inserting the ejector spout tube in the spreading device and changing the amount of insertion.

The invention will be described by giving examples.

Example 1 24 filaments were sucked into a single ejector with an ejector feed air pressure of 4 kg/cm2G to provide a total of 144 deniers and accumulated on a web collecting surface moving at a speed of 2 m/min. The inner diameter d of the ejector spout tube was 10 mm and the lower end of said spout tube was inserted in a spreading device disposed so that its major axis extends widthwise of the web collecting surface. The amount of insertion of the ejector spout tube into the spreading device, D= 0 mm; the length of the spreading device, L = 50 mm; and the inner surface width W = 12 mm. Under these conditions, the accumulation widths of webs with respect to various angles of opening were measured and the result is shown in the table below.

Angle of opening of Accumulation width spreading device 0 of web No spreading device 140 mm 4" 170 8 190 16 210 24 220 32 180 40 140 48 140 From this table, it has been found that the range of angle of opening which is useful for the spreading device is between 4" and 32".

Example 2 10 ejectors were arranged in a single row transversely of the web collecting surface and 8 filaments were sucked into each ejector with a feed air pressure of 3 kg/cm G to provide a total of 24 deniers and accumulated on the web collecting surface. Each ejector spout port was inserted in a spreading device disposed with its major axis extending widthwise of the web collecting surface and having an inner surface width W of 12 mm, an angle of opening 6 os 16 and a length L of 50 mm. Non-woven fabrics were produced by varying the amount of insertion D into the spreading devices when the inner diamter d of the ejector spout tubes was 10 mm. They were examined for their tensile strength and the result is shown in the following table.

Longitudinal Transverse Longitudinal/ D strength of web strength of web transverse strength ratio Omm 5.4kg/3cm width 8. lkg/3cm width 0.67 1 7.2 7.9 0.91 6 7.7 6.8 1.13 13 8.1 7.3 1.11 20 8.7 7.1 1.23 30 7.8 5.9 1.32 35 8.0 5.8 1.38 40 8.4 6.2 1.35 60 7.9 5.3 . 1.49 80 8.2 3.9 2.10 According to this table, when the ejector spout tubes are not inserted in the inner surface recesses of the spreading devices, i.e., D = 0, the transverse strength is higher than the longitudinal strength, but if the ejector spout tubes are inserted in the inner surface recesses of the spreading devices, the transverse and longitudinal strengths become close to each other, and as the D is further increased, the longitudinal strength becomes greater than the transverse strength. When D = 80, the ejector spout tubes pass completely through the spreading devices to establish the same condition as when there are no spreading devices, so that the longitudinal strength becomes much greater than the transverse strength.

Example 3 12 filaments were sucked into a single ejector with an ejector feed air pressure of 4 kg/cm2G to provide a total of 144 deniers and accumulated on the web collecting surface moving at a speed of 2 m/min. the inner diameter d of the ejector spout tube was 10 mm, and the lower portion of said spout tube was inserted in a spreading device disposed with its major axis extending widthwise of the web collecting surface and having an inner surface width W of 12 mm and an angle of opening 0 of 16". By varying the length L of the spreading device and the amount of insertion D of the ejector spout tube into the spreading device, the filaments were accumulated on the web collecting surface and the accumulaton width was measured, the result being shown in the following table.

Relation between L, D and accumulation width Dmm 0 5 10 15 20 30 Lmm 20 21cm 21 21 21 21 21 30 24 23 22.5 21.5 21 18 50 30 28 27 26 24 20 70 37 34 32 31 30 23 90 *43 *43 *43 *39 36 33 ( * Large sudden-decrease in speed) According to this table, with the L being less than 30 mm, even if the amount of insertion D of the ejector spout tube is varied, there is no variation in the accumulation width.

Therefore, it is impossible to control the longitudinal-transverse strength ratio of the web to be obtained. Further, in the case of the L exceeding 70 mm, even if the ejector spout tube is more or less inserted in the spreading device, there is no variation in the accumulation width and the sudden-decrease in the speed of the jet is large, so that no satisfactory web can be formed.

From the foregoing, it has been found that when the inner diameter d of the ejector spout tube is 10 mm, in the case of the spreading device having an angle of opening 0 of 16 , the optimum length L is between 30 mm and 70 mm, i.e., it is about 3-7 times the inner diameter d of the ejector spout tube.

WHAT WE CLAIM IS 1. An apparatus for producing long-fiber non-woven fabrics, comprising a plurality of ejectors for feeding continuous bunched filaments onto a collecting surface of a moving web, the ejectors being arranged above the level of the collecting surface in one or more rows transversely the moving direction of the collectjing surface, the apparatus being characterized in that a spreading device is fitted on a cylindrical outer periphery of the lower end of a spout tube of each ejector in such a manner that the amount of relative insertion of the lower end of the spout tube into the spreading device is device is adjustable, said spreading device having an inner surface the cross section of which smoothly varies from cylindrical at an inner axial end thereof fitting on the spout tube, to a slot-like outlet port at the other outer axial end thereof and whose cross-sectional area gradually increases as it extends from said inner axial end toward said outer axial end, the longer axis of said cross-sectional area at the outlet port extending along the direction of arrangement of the ejectors.

2. An apparatus for producing non-woven fabrics as set forth in claim 1, further comprising screw means for fixing the spreading device to the lower end of the spout tube in such a manner that the amount of relative insertion of the lower end of said spout tube into the spreading device is adjustable.

3. An apparatus for producing non-woven fabrics as set forth in claim 1 or 2 wherein an angle of opening defined by those generating lines of the inner peripheral surface of said spreading device opposed to each other in the direction of the major axis is 4-32".

4. An apparatus for producing non-woven fabrics as set forth in claim 3, wherein the length of said spreading device from the inner axial end to the outer axial end is such that when said amount of relative insertion is at a minimum the boundary of the free air jet conincides with said angle of opening of the spreading device.

5. An apparatus for producing non-woven fabrics as set forth in claim 4, wherein said length of said spreading device is 3-7 times the inner diameter of the spout tube of the ejector.

6. A method of producing long fibre non-woven fabrics substantially as described herein with reference to the examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Relation between L, D and accumulation width Dmm 0 5 10 15 20 30 Lmm 20 21cm 21 21 21 21 21 30 24 23 22.5 21.5 21 18 50 30 28 27 26 24 20 70 37 34 32 31 30 23 90 *43 *43 *43 *39 36 33 ( * Large sudden-decrease in speed) According to this table, with the L being less than 30 mm, even if the amount of insertion D of the ejector spout tube is varied, there is no variation in the accumulation width.

Therefore, it is impossible to control the longitudinal-transverse strength ratio of the web to be obtained. Further, in the case of the L exceeding 70 mm, even if the ejector spout tube is more or less inserted in the spreading device, there is no variation in the accumulation width and the sudden-decrease in the speed of the jet is large, so that no satisfactory web can be formed.

From the foregoing, it has been found that when the inner diameter d of the ejector spout tube is 10 mm, in the case of the spreading device having an angle of opening 0 of 16 , the optimum length L is between 30 mm and 70 mm, i.e., it is about 3-7 times the inner diameter d of the ejector spout tube.

WHAT WE CLAIM IS 1. An apparatus for producing long-fiber non-woven fabrics, comprising a plurality of ejectors for feeding continuous bunched filaments onto a collecting surface of a moving web, the ejectors being arranged above the level of the collecting surface in one or more rows transversely the moving direction of the collectjing surface, the apparatus being characterized in that a spreading device is fitted on a cylindrical outer periphery of the lower end of a spout tube of each ejector in such a manner that the amount of relative insertion of the lower end of the spout tube into the spreading device is device is adjustable, said spreading device having an inner surface the cross section of which smoothly varies from cylindrical at an inner axial end thereof fitting on the spout tube, to a slot-like outlet port at the other outer axial end thereof and whose cross-sectional area gradually increases as it extends from said inner axial end toward said outer axial end, the longer axis of said cross-sectional area at the outlet port extending along the direction of arrangement of the ejectors.
2. An apparatus for producing non-woven fabrics as set forth in claim 1, further comprising screw means for fixing the spreading device to the lower end of the spout tube in such a manner that the amount of relative insertion of the lower end of said spout tube into the spreading device is adjustable.
3. An apparatus for producing non-woven fabrics as set forth in claim 1 or 2 wherein an angle of opening defined by those generating lines of the inner peripheral surface of said spreading device opposed to each other in the direction of the major axis is 4-32".
4. An apparatus for producing non-woven fabrics as set forth in claim 3, wherein the length of said spreading device from the inner axial end to the outer axial end is such that when said amount of relative insertion is at a minimum the boundary of the free air jet conincides with said angle of opening of the spreading device.
5. An apparatus for producing non-woven fabrics as set forth in claim 4, wherein said length of said spreading device is 3-7 times the inner diameter of the spout tube of the ejector.
6. A method of producing long fibre non-woven fabrics substantially as described herein with reference to the examples.
7. Apparatus for producing non-woven fabrics substantially as described herein with

reference to and as illustrated in Figures 3, 4a, 4b, and Sa to Sd of the accompanying drawings.