Non-woven fabric producing apparatus and air gun for the production of non-woven fabric

Abstract: Air nozzle and apparatus permitting a stable, fine spinning and capable of discharging fine filaments at a certain degree of dispersion and affording a non-woven fabric of a uniform shape are provided. The air gun comprises an air nozzle and an accelerator tube, the air nozzle having filament inlet and outlet, further having compressed air inlet and outlet, the filaments being discharged from the filament outlet while being pulled by compressed air. The accelerator tube is formed at a specific dimensional ration and it is connected to the air nozzle in the filament discharging direction. The non-woven fabric producing apparatus is provided with a guide tube and a separator nozzle, with an air flow rate regulator being disposed between the guide tube and the separator nozzle, the air flow rate regulator having an exhaust port for exhausting to the exterior a portion of compressed air which is used for carrying the filaments.

Description: The present invention relates to a non-woven fabric producing apparatus and an air gun for the production of non-woven fabrics, particularly to an air gun and a manufacturing apparatus of the type wherein filaments spun from spinning nozzles are taken up at high speed and delivered onto the surface of a collector such as a screen belt while being carried by an air stream. Generally, as a non-woven fabric producing apparatus, particularly a non-woven fabric producing apparatus of the type wherein filaments as spun from spinning nozzles are taken up and delivered onto a screen belt while being carried by an air stream to form non-woven fabric (web), there is known the apparatus shown in Fig. 8. In such non-woven fabric producing apparatus, filaments 2 as spun from spinning nozzles 1 are taken up and delivered onto a screen belt 3 while being carried by an air stream to form non-woven fabric. The filaments 2 from the spinning nozzles 1 are first received into an inlet of an air nozzle 7. The air nozzle 7 is provided laterally with a compressed air inlet 6, and by compressed air supplied from the compressed air inlet 6 the filaments 6 are discharged in an outlet direction of air. In this conventional non-woven fabric producing apparatus, and an air gun for the production of non-woven fabric, particularly as an air gun of the type wherein the filaments 2 as spun from the spinning nozzles 1 are drawn and taken up at high speed and delivered onto the screen belt 3 while being carried by an air stream to form non-woven fabric (web), an accelerator tube 8a having an inside diameter of 6.6 mm and a length of 280 mm is attached to the front end of the air nozzle 7. In the outlet direction of the air from the air nozzle 7, namely, in the filament discharging direction there are disposed the accelerator tube 8a connected to the air nozzle 7 and a guide tube 8b connected to the tube 8a. The filaments 2 pass through these tubes 8a and 8b while being carried by the air. To the front end of the guide tube 8b is connected a separator nozzle 9. The guide tube 8b is for conducting the filaments 2 from the accelerator tube 8a to the separator nozzle 9 together with compressed air and diffusing them toward the screen belt 3. The filaments 2 are dispersed to an appropriate degree by the separator nozzle 9 and are deposited on the screen belt 3, so by moving the screen belt 3 there is formed non-woven fabric. DE-A-2,322,130, on which the preamble of claim 1 is based, discloses producing a stretchable non-woven sheet by introducing fibres into a nozzle by passing air under high pressure through the same nozzle to cause the fibres to extend. The fibres are then blown onto a receiver such that the continuous fibres become entangled to form a bulky web. Once the tension caused by the air stream is removed, the fibres relax to develop loose crimps. There is also known a fibrous web forming process which is described in Japanese Patent Laid-Open No. 151357/85. According to this process, a multifilament yarn is forced to impinge on an impingement plate together with compressed air from an elongated tube and the multifilament yarn thereby formed is collected in the form of sheet onto a conveyor, the compressed air being discharged forcibly from near the lower portion of the said elongated tube in a direction away from the multifilament yarn jet direction. In the production of non-woven fabric according to such spun bond process, it is required to thin the filaments in order to improve the productivity and quality. To this end, heretofore there have been adopted 1 ○ a method wherein the air pressure supplied to the air gun is raised to increase the flow rate of air, thereby pulling the filaments strongly, 2 ○ a method of shortening the distance (spinning distance) from the spinning nozzle to the air gun, 3 ○ a method of reducing the volume of filament discharged from each of many spinning nozzles, and 4 ○ a method of increasing the spinning temperature. But in the case where productivity is the principal object, the above methods 1 ○ and 2 ○ are usually adopted. However, according to the method 1 ○ , as the flow rate of air increases, the filaments are disturbed when discharged from the separator nozzle, resulting in variations in the shape of non-woven fabric deposited on the screen belt and the uniformity of the non-woven fabric being deteriorated. Further, the increase in the flow rate of air causes an increase of the running cost and an increased cost of the product obtained Also, the method 2 ○ involves a problem from the standpoint of stable spinning and it is difficult to practice this method. According to the present invention there is provided an apparatus for forming a non-woven fabric, the apparatus comprising: an air nozzle having a filament inlet for receiving filaments discharged from one or more spinning nozzles, and a compressed air inlet for receiving compressed air to discharge the received filaments via an air outlet; a guide tube connected to the air nozzle to guide the filaments discharged via said outlet; and an air flow rate regulator connected to the discharge end of the guide tube, the regulator having a main outlet, for the passage therethrough of the filaments to form the non-woven fabric and a first portion of the air discharged from the guide tube, and an exhaust port for exhausting to the exterior, from upstream of the main outlet, a further portion of the air discharged from the guide tube; characterised in that the apparatus further comprises: a separator nozzle connected to the main outlet of the air flow rate regulator to receive therefrom the filaments and the first portion of air, the nozzle being provided with an interior surface including a taper towards the outlet of the nozzle from which the filaments are, in use, discharged towards a screen belt, to form the non-woven fabric, together with the first portion of air. Advantageously the guide is connected to the air nozzle through an accelerator tube. It is preferable to have the ratio of the inside diameter to the length of the accelerator tube between 1 to 20 and 1 to 250. It is also beneficial to have the inner surface of the accelerator tube substantially smooth. The exhaust port of the air flow regulator is preferably provided on one side of the regulator. It is also advantageous to be able to adjust the proportion of compressed air exhausted through the exhaust port. Beneficially, this amount would be between 5% and 50% of the compressed air discharged from the guide tube. With the present invention an air gun for the production of non-woven fabric can produce a stable, fine spinning and can afford a non-woven fabric of a uniform shape, without the fear of increase in the running cost. Further, a non-woven fabric producing apparatus may be produced which is not only capable of effecting a stable spinning operation but also capable of discharging filaments at a certain degree of dispersion and producing a non-woven fabric of a uniform shape. The invention will be further understood from the following description when taken together with the accompanying drawings, which are given by way of example only, and in which: Fig. 1 is a schematic view of the entire apparatus; Fig. 2 is an enlarged sectional view of an air nozzle; Fig. 3 is a partially sectional view of a principal portion mainly of an air flow rate regulator; Fig. 4 is a graph showing a relation between the length of an accelerator tube and the filament size (or fineness) in a first working example; Fig. 5 is a graph showing a relation between the pressure of air and the filament size, using different accelerator tubes, in a second working example; Fig. 6 is a graph showing a relation between the accelerator tube length and the yarn tension in both the presence and absence of a guide tube in a third working example; and Fig. 7 is a graph showing a relation between the amount of air exhausted and the uniformity of non-woven fabric. Fig. 8 is a side view showing a conventional non-woven fabric producing apparatus. As shown in Figs. 1 to 3, spinning is performed using a molten synthetic resin. The molten synthetic resin is extruded preferably through one or a large number of spinning nozzles 1 arranged in rows. As spun filaments 2 are usually in straight rows spaced from one another. As examples of synthetic resins employable in the invention for spinning there are mentioned polyolefins such as polyethylene and polypropylene; ethylene-vinyl compound copolymers such as ethylene-vinyl chloride copolymer; styrenic resins; polyvinyl chloride resins such as polyvinyl chloride and polyvinylidene chloride; polyacrylic esters; polyamides; and polyesters such as polyethylene terephthalate. Other synthetic resins suitable for spinning are also employable. These synthetic resins may each be used alone or as a mixture. Appropriate amount of inorganic or organic pigments may be incorporated therein. An air nozzle 7 takes up a bundle of the spun filaments 2 and delivers it onto a screen belt 3. Usually, plural air nozzles 7 are arranged side by side for forming a non-woven fabric having a practical width. Generally, a large number of air nozzles 7 are arranged so that a desired overlapping of traveling paths of the filaments 2 discharged from the air nozzles 7 is attained over the whole width of the screen belt 3. The spun filaments 2 are stretched by being pulled by an air stream and are dispersed, whereby they are deposited in an entangled state on the screen belt 3. A guide tube 8b may be connected to the air nozzle 7 directly, but preferably through an accelerator tube 8a. It is desirable that the inner surface of the accelerator tube 8a be made as smooth as possible to reduce the air resistance. The inside diameter to length ratio of the accelerator tube 8a is in the range from 1:20 to 1:250, preferably 1:50 to 1:100. As a result, finer filaments 2 may be obtained at the same air pressure as in the prior art. But where it is desired to obtain filaments 2 of about the same size as in the prior art, it is possible to use compressed air of a lower pressure, whereby there can be attained an economic improvement. The inside diameter to length ratio of the guide tube 8b is set preferably in the range from 1:50 to 1:300. An air flow rate regulator 10 is interposed between the guide tube 8b and a separator nozzle 9. The air flow rate regulator 10 functions to discharge a portion of compressed air from the guide tube 8b to the exterior through an exhaust port 11. In this case, a suitable amount of compressed air to be discharged is in the range of 5% to 50%, more preferably 10% to 30%, depending on the total amount of compressed air supplied. If this amount is too large, the filaments 2 will stall halfway, thus making it difficult to continue the normal filament depositing operation. On the other hand, if the amount in question is too small, the provision of the air flow rate regulator 10 becomes meaningless. In this apparatus, since the compressed air supplied in the air nozzle 7 is exhausted halfway, the amount of air discharged from the separator nozzle 9 can be kept to about the same degree as in the prior art even if the pressure of the compressed air supplied in the air nozzle is increased. Consequently, not only the filaments can be pulled strongly into finer filaments, but also the filaments can be deposited uniformly onto the surface of the screen belt 3 without disturbing their distribution from the separator nozzle 9. If an air cock capable of continuously adjusting the amount of air to be discharged is mounted to the exhaust port 11, it becomes possible to finely adjust the distribution of the filaments 2 visually which state changes depending on the thickness and the temperature of the filaments, whereby the uniformity of the non-woven fabric obtained can be further improved. The amount of air exhausted can be measured by a flow meter, which is mounted to the exhaust port 11. But it is more convenient to use a handy type flow meter and set to a desired flow rate while adjusting an air cock capable of changing the amount of air to be exhausted. The air flow rate regulator 10 may be located in any position provided it is interposed between the guide tube 8b and the separator nozzle 9. For example, the regulator 10 and the separator nozzle 9 may be spaced from each other through a tube, or both may be connected together in a closely adjacent state. Further, the regulator 10 may be incorporated in the separator nozzle 9. By the air gun for the production of non-woven fabric according to the present invention the filament diameter can be reduced without increasing the air pressure supplied to the air nozzle. Consequently, a good distribution of filaments can be attained and so it is possible to produce a non-woven fabric of a uniform shape. Besides, since it is possible to use an air pressure of the same level as in the prior art, the production can be practised less expensively without increase of the running cost. According to the non-woven fabric producing apparatus of the present invention, the compressed air for the delivery of filaments is exhausted halfway, whereby there can be attained a stable dispersion of the filaments and hence it is possible to obtain a uniform non-woven fabric. Further, since it becomes possible to apply a compressed air of a higher pressure to the filaments, the filaments can be made thinner. In this case, since surplus air can be exhausted by the air flow rate regulator, the travelling path of the filaments discharged from the separator nozzle is not disturbed and it is possible to obtain a non-woven fabric of high quality. An embodiment of the present invention will be described below with reference to Figs. 1 to 9. Such a non-woven fabric producing apparatus as illustrated in Fig. 1 was constituted according to the present invention. As shown in the same figure, an air gun is constituted by an air nozzle 7 for taking up filaments spun from a spinneret 1 as an assembly of spinning nozzles 1, and an accelerator tube 8a connected to the air nozzle 7, and there are further provided a guide tube 8b connected to the accelerator tube 8a of the air gun, and a separator nozzle 9 connected to the front end of the guide tube 8b and functioning to diffuse the filaments 2 discharged from the guide tube 8b together with compressed air toward a screen belt 3 which serves as a collection surface. The spinning nozzle assembly comprises 13,944 nozzles. The filaments 2 dispersed by the separator nozzle 9 are deposited on the screen belt 3 to form a fibrous web. The spinneret 1 as an assembly of spinning nozzles 1 has nine sets of sections each having 108 small holes 0.85 mm in diameter and functions to spin molten resin extruded from an extruder 1a. As shown in Fig. 2, the air nozzle 7 comprises a first nozzle 30 and a second nozzle 40 connected to the first nozzle. The first nozzle 30 has a filament inlet 30a for receiving the filaments 2 discharged from the spinneret 1. The interior continuous to the filament inlet 30a comprises a tapered tube 30b which is reduced in diameter up to an intermediate part toward the front end of the tapered tube, and a straight tube 30c extending at a constant inside diameter from the front end of the tapered tube 30b up to a filament outlet 30e. The straight tube 30c is formed by a nozzle tube 30d and is in a projecting state. In a surrounding relation to the front end of the nozzle tube 30d the second nozzle 40 is connected to the first nozzle 30. The second nozzle 40 has an outlet nozzle 40a which surrounds the front end portion of the nozzle tube 30d. Between the inner surface of the outlet nozzle 40a and the outer surface of the nozzle tube 30d there is formed a slight clearance, which defines a compressed air outlet 40b around the filament outlet 30e at the front end of the nozzle tube 30d. The inner surface of the outlet nozzle 40a is gradually reduced in diameter from the air inlet 40c side until getting over a maximum constriction 40d, then becomes larger in diameter gradually, and thereafter, from the portion corresponding to the filament outlet 30e, the inner surface diameter becomes constant as a straight tube. On the other hand, the second nozzle 40 is provided sideways with a compressed air inlet 6, which is in communication with an air inlet 40c of the outlet nozzle 40a. The air introduced into the outlet nozzle 40a from the compressed air inlet 6 becomes maximum in its flow velocity when passing through the maximum constriction 40d, whereby the air is jetted strongly in the direction of arrow F from the compressed air outlet 40b, resulting in that the filaments 2 passing near the center of the nozzle tube 30d are pulled out strongly. In the air outlet direction from the second nozzle 40, namely, in the delivery direction of the filaments 2, the accelerator tube 8a for conducting the filaments 2 is connected to the second nozzle, and to the front end of the accelerator tube 8a is connected the guide tube 8b. The guide tube 8b is for conducting the filaments 2 to the separator nozzle 9, which nozzle is connected to the front end of the guide tube 8b. The separator nozzle 9 is for diffusing the filaments 2 toward the screen belt 3 which filaments are discharged from the accelerator tube 8a together with compressed air. The inside diameter and length of the accelerator tube 8a will hereinafter be referred to as D and L, respectively. To the front end of the guide tube 8b is connected an air flow rate regulator 10. As shown in Fig. 3, the air flow rate regulator 10 is generally cylindrical and is sideways formed with an exhaust port 11. The regulator 10 has a tapered inner wall surface 10b. On the other hand, an inlet portion thereof continuous to the guide tube 8b is thin-walled at its front end 10a. The exhaust port 11 is in communication with the interior of the air flow rate regulator 10 through an air passage 10c formed between the tapered inner wall surface 10b of the air flow rate regulator 10 and the front end 10a continuous to the guide tube 8b. An air cook 21 is connected to the exhaust port 11 so that the amount of air discharged can be changed continuously. By way of the conection tube 20, the separator nozzle 9 is connected to the end of outlet of the air flow rate regulator 10. The separator nozzle 9 is for diffusing the filaments 2 toward the screen belt 3 which filaments 2 are delivered with compressed air and discharged from the guide tube 8b by means of the air flow rate regulator 10. The interior continuous to the front end of the separator nozzle 9 is formed tapered which is reduced in diameter. The front end of the nozzle base 9a is surrounded by nozzle skirt which is provided at the bottom of the separator nozzle 9. Using the non-woven fabric producing apparatus of the above construction, filaments 2 were directed to the screen belt 3 and the uniformity of the web layer deposited on the same belt was checked to obtain such results as shown in Fig. 7. In this experiment, the amount of the material of the filaments 2 discharged was set at 550 kg/H, the pressure of the air supplied to the air nozzle 7 was set at 7 kgf/cm² gauge, and inside diameter and length of the guide tube 8b were set at 6.6 mm and 280 mm, respectively. As is apparent from the results shown in Fig. 7, best results were obtained at an amount of air exhausted from the exhaust port 11 of 6.3 Nm³/H. This amount of air was about 30% of the total amount of air supplied. The measurement of uniformity was conducted by a punching method whereby the product to be measured is scooped circularly. Measuring Implement Scooping Punch (inside diameter: 13 mm⊘) Measuring Method (1) Cut off into 25 cm length after trimming each sample for measurement. (2) Measure the weight of the sample, then on the basis of the measured weight, calculate an average weight, i.e., an average weight value (A: g/m²) per unit area. (3) Choose five relatively thick-walled points and twenty thin-walled points optionally and visually from the entire sample and punch those portions. (4) Measure the weights of the thick-walled portions and of the thin-walled portions and calculate mean values. (5) Then, calculate an average weight (C: g/m²) of the thick-walled portions and an average weight (B: g/m²) of the thin-walled portions. Uniformity Defining Equation As can be seen from the above equation, that the uniformity is high indicates a value close to zero. 〈First Example〉 Using the non-woven fabric producing air gun of the above construction, filaments 2 were directed to the screen belt 3 and the size of the constituent filaments of the non-woven fabric deposited on the screen belt was observed and measured to obtain the results shown in Fig. 4. This experiment was conducted under the following conditions. Material of the filaments 2: polypropylene, amount of the filaments discharged: 42 kg/H, air pressure supplied to the air nozzle 7: 9 kgf/cm² gauge, inside diameter of the accelerator tube 8a: 7.0 mm. And the length (L) of the accelerator tube 8a was changed like 280 mm, 450 mm, 600 mm. As is apparent from the results shown in Fig. 4, the size of the filaments 2 could be made smaller than 1.8 denier at an accelerator tube 8a length of about 450 mm or larger. In this case, the inside diameter (D) to length (L) ratio of the accelerator tube 8a was 1:64. 〈Second Example〉 An experiment was conducted under the following conditions about the influence of the shape of the accelerator tube 8a upon the fineness of filaments 2. Material of filaments 2: polypropylene, amount of the filaments discharged: 42 kg/H, spinneret construction: seven sets of sections each having 130 small holes 0.85 mm in diameter, spinning distance (spinning nozzle to air nozzle distance): 4.5 m. The results shown in Fig. 5 were obtained, from which it is seen that when the diameter and length of the accelerator tube 8a are 6.6 mm and 280 mm, respectively, ( ○ - ○ line in Fig. 5), the size of the filaments 2 is only 2.4 denier or so even at a pressure of 8 kgf/cm² gauge applied through the air nozzle 7, but that when the diameter and length of the accelerator tube 8a are 7.0 mm and 600 mm, respectively (□ - □ line in Fig. 5), the filaments 2 can be made finer to 1.8 denier or so even at the same pressure of 8 kfg/cm² gauge as above. 〈Third Example〉 With respect to the case where a guide tube 8b 10 mm in inside diameter was connected to the accelerator tube 8a and the case where such guide tube was not connected to the tube 8a, the relation between the change in length of the accelerator tube and the yarn tension (tension applied to filaments) was observed. The results obtained are as shown graphically in Fig. 6. In the same figure, the ○ - ○ line indicates the result obtained using the accelerator tube 8a alone, while the □ - □ line indicates the result obtained using both the accelerator tube 8a and the guide tube 8b connected thereto. It turns out that the longer the accelerator tube 8a, the larger the yarn tension. It is also seen that in comparison with the use of the accelerator tube 8a alone, a combined use thereof with the guide tube 8b results in increase of the pulling force.

Claims: Apparatus for forming a non-woven fabric, the apparatus comprising: an air nozzle (7) having a filament inlet (30a) for receiving filaments (2) discharged from one or more spinning nozzles (1), and a compressed air inlet (6) for receiving compressed air to discharge the received filaments (2) via an air outlet; a guide tube (8b) connected to said air nozzle to guide the filaments discharged via said outlet; and an air flow rate regulator (10) connected to the discharge end of said guide tube, said regulator having a main outlet, for the passage therethrough of the filaments to form the non-woven fabric and a first portion of the air discharged from the guide tube, and an exhaust port (11) for exhausting to the exterior, from upstream of the main outlet, a further portion of the air discharged from the guide tube (8b); characterised in that the apparatus further comprises: a separator nozzle (9) connected to the main outlet of said air flow rate regulator (10) to receive therefrom the filaments and said first portion of air, said nozzle (9) being provided with an interior surface including a taper towards the outlet of the nozzle from which the filaments are, in use, discharged towards a screen belt (3), to form the non-woven fabric, together with said first portion of air. Apparatus according to claim 1, wherein the guide tube (8b) is connected to the air nozzle (7) through an accelerator tube (8a). Apparatus according to claim 2, wherein the ratio of the inside diameter to the length of the accelerator tube (8a) is between 1:20 and 1:250. Apparatus according to claim 2 or claim 3, wherein said accelerator tube (8a) has a substantially smooth inner surface. Apparatus according to any one of the preceding claims, wherein the exhaust port (11) is provided at one side of the air flow regulator (10). Apparatus according to any one of the preceding claims, wherein the exhaust port (11) is adjusted to exhaust between 5% and 50% of the compressed air discharged from the guide tube (8b). Apparatus according to any one of the preceding claims, wherein said exhaust port (11) has an air cock (21). Apparatus according to any one of the preceding claims, wherein said air flow rate regulator (10) is incorporated with said separator nozzle (9). Apparatus according to claim 8, wherein said air flow rate regulator and said separator nozzle are connected together by a connecting tube (20). Apparatus according to any one of the preceding claims wherein the taper of said separator nozzle (9) tapers to form a nozzle seat at the discharge outlet of the nozzle. Apparatus according to any one of the preceding claims, wherein the air nozzle (7) comprises a filament outlet (30e) for discharging the filaments (2) introduced from said filament inlet (30a), and a compressed air outlet (40b), said compressed air outlet (40b) being positioned around said filament outlet (30e) and adapted to discharge compressed air to discharge the filaments (2) from the filament outlet (30e) while applying a pulling force to the filaments (2). Apparatus according to claim 11, wherein said air nozzle (7) comprises a first nozzle (30) and a second nozzle (40) connected to the first nozzle (30), the first nozzle having said air nozzle filament inlet (30a), the interior of the first nozzle (30) being continuous and said filament inlet (30a) comprising a tapered tube (30b) which reduces in diameter up to an intermediate part towards the downstream end of the tapered tube (30b) and a substantially straight tube (30c) of a substantially constant inside diameter extending from the end of said tapered tube (30b) up to the filament outlet (30e), the second nozzle (40) being provided at one end with a compressed air outlet nozzle (40a) in a surrounding relation to a portion of the downstream end of the substantially straight tube (30c) of the first nozzle (30). Apparatus according to claim 12, wherein the substantially straight tube of the first nozzle (30) is formed by a straight nozzle tube (30d). Apparatus according to claim 12 or 13, wherein a clearance (40d) is formed between the inner surface of said outlet nozzle (40a) and the outer surface of said straight tube (30c), and said compressed air outlet (40b) is provided around said filament outlet. Apparatus according to claim 14, wherein said compressed air inlet (6) of the air nozzle (7) is a compressed air inlet of the second nozzle and said air outlet nozzle (40a) of the second nozzle (40) has an air inlet (40c) communicating with said compressed air inlet (6) of the second nozzle, and the clearance (40d) has a maximum constriction halfway along its length. Apparatus according to any one of the preceding claims, wherein the ratio of the inside diameter to the length of said guide tube (8b) is between 1:50 and 1:300.

Inventors: HATA KATSUYA C O MITSUI PETROC, KANEKO AKIRA C O MITSUI PETROC, KOBAYASHI KEIJI C O MITSUI PET, KOBAYASHI YOSHINORI C O MITSUI, HATA, KATSUYA C/O MITSUI PETROCHEMICAL, KANEKO, AKIRA C/O MITSUI PETROCHEMICAL, KOBAYASHI, KEIJI C/O MITSUI PETROCHEMICAL, KOBAYASHI, YOSHINORI C/O MITSUI PETROCHEMICAL
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1991
Main classification: D04H3
IPC codes: D01D5, D04H3