A UNIDIRECTIONAL BLOWING SYSTEM AND A METHOD FOR NONWOVEN FABRIC PRODUCTION

Field of the Invention

The present invention relates to a unidirectional blowing system and method for nano-microfiber nonwoven fabric production.

Background of the Invention

Several techniques are used for nonwoven fabric production. Melt blowing, electrospinning, electro blowing, spun bonding, and solution blow spinning methods are the most essentially used methods used for nano-microfiber nonwoven fabric production. The fabrics produced with these methods are used in filtration, energy storage, biomedical applications, sensors, and textile applications.

Melt blowing method is the method wherein the polymer melt is thinned on the movable conveyor in guidance of air jet and the fibrous nonwoven structures are produced. Melt blowing is an old method the first examinations of which were made in 1950s, and it is an industrial process used for fiber in diameter range of 0.5 - 5 μηι in single step.

In an application wherein melt blowing method is used, thermoplastic polymer melt (such as ΡΡ,ΡΕΤ) is passed through specially structured spin dies, and transferred onto the carrier conveyor in guidance of high pressurized air. By this means, fiber diameters in random micron and submicron levels are provided. The nonwoven surfaces which are obtained are transferred via conveyor system and wrapped around the roller. It was observed that fiber dimensions in nanometer diameters could be acquired by adjusting air pressure and polymer flowrate. However, for the webs produced with this method the fiber diameter usually shows deviation under 30%. In good situations, it is expected that the deviation goes under 10% ¹ .

In the industry, two rectangular channels are used in order to produce polymeric fibers in melt blowing process. The air jet going out of the said two channels spray the polymer melt by means of hot air. Spinneret diameter, air channel width, jet width, and air hitting angle are important system parameters affecting the fiber diameter. Polymer melt is formed under the direction between two air jets .

In the current melt blowing technique, industrial production can be realized; however it cannot be decreased under 500nm fiber diameter. Besides, conventional melt blowing system requires high cost investment since it requires sensitive die design and high volume of air at high temperature.

Hovanec in a recent invention aimed to improve nonwoven fabric production by using electro blowing method. (US7846374B2). In the patent, it is disclosed that nonwoven fabric is obtained by using various gases (nitrogen, argon, helium, carbon) and various polymers (polyamide, nylon, polyaramide, polybenzimidazole, polyetherimide, poly aery lonitrile). In the patent, the operating voltage range of the system is given as 1-300 kV and the spinneret pressure range is given as 0.01-200 bars. It is disclosed in the patent that the oxygen concentration in the gas is reduced during blowing and drawing is performed, and thus oxidization is prevented .

Mao Peng et. al. have acquired more regular fibers relative to electro spinning by increasing the drawing efficiency property in the study that they have realized with PMMA solution by using the electroblowing method. The pore diameters of the fibers formed by using electroblowing method were lower. Furthermore, it is

¹ «Melt-blowing die for producing nonwoven mats»

2

H. M. Krutka, R. L. Shambaugh, ve D. V. Papavassiliou, «Effects of die geometry on the flow field of the melt-blowing process*, Ind. Eng. Chem. Res., v 42, no 22, p 5541-5553, 2003.

J. B. Hovanec, Blowing gases in electroblowing process. Google Patents, 2010. stated in this study that fiber can be produced from PMMA solutions which is commercially available ⁴ .

Although nanofiber nonwoven fabric can be produced in electroblowing technique, safety will be an issue since high electric field is used.

In the inventive unidirectional blowing system, drive force is only a pressurized air, therefore there will be no such problem. However, polymer melt or solution can be charged with electrostatic in various positions if it is needed (especially when fiber separation is required).

Spunbond technique which is another method is one of the most commonly used methods used in nonwoven fabric production. In this technique, polymer material in granule form is transformed into nonwoven fabric on a continuous line ⁵ . Generally, in spunbond technique, there are polymer feeding, extruder, spin pump, die assembly, fiber spinning, fiber drawing and collecting, transforming into fabric form, connection unit, winding processes. Spunbond products are commonly used in areas such as single use medical applications, automotive industry, filtration, civil engineering, packaging applications, carpet padding applications, geotextile, long life papers, mattress, pillow, tiling ⁶ .

In spunbond technique, only thick (in size of 5-50 microns) fibers can be produced. Furthermore, in this technique approximately 10 m of height is required in order to draw fiber. For these reasons, spunbond technique is a high cost system which requires a large area.

In solution blow spinning technique, a co-axial spinneret is used and pressurized air is applied on the polymer solution, and technical textiles with nano-microfiber structure are produced. Polymer solution is fed from the inner channel of the

⁴ M. Peng, Q. Sun, Q. Ma, ve P. Li, «Mesoporous silica fibers prepared by electroblowing of a poly (methyl mefhacrylate)/tetraefhoxysilane mixture in< i> N</i>,< i> N</i>-dimethylformamide», Microporous Mesoporous Mater., v 115, no 3, p 562-567, 2008.

⁵ Z. Bo, «Effects of processing parameters on the filament fiber diameter of spunbonded nonwoven fabrics*, Polym. Eng. Set, v 47, no 4, p 510-515, 2007.

⁶ H. Lim, «A Review of Spunbond Process*, J. Text. Appar. Technol. Manag., v 6, no 3, 2010. spinneret. Pressurized air is fed from its outer channel. The pressurized air completely surrounds the polymer solution and it makes possible to obtain nano- microfiber ⁷ .

Yarin et. al. produced fiber in core-shell structure by using solution blow spinning method from PMMA and PAN solutions in a study that they performed in 2010. Then, they removed PMMA in the core by applying thermal treatment. Then, they produced carbon tube with inner diameter of 50-100 nm and outer diameter of 400-600 nm with carbonization process .

Zhuang et.al. used polyethylene oxide (PEO) with normal molecular weight of 50.000 by dissolving in N,N dimethylformamide (DMF) in concentration of 10% by weight. In this study, the solution is fed to the spinneret with peristaltic pump. Then, the pressurized air is sent to the spinneret such that it will surround it, and the polymer solution is forced to go out of the spinneret, then it is sprayed into the collecting surface with web like structure which is 45 cm far away. The inner diameter of the spinneret used in this study is 0.33 mm and its outer diameter is 0.55 mm. Zhuang et.al. stated that nanofiber can be produced at high feed flow rates such as 0.3-0.8 ml/m by using polymer solution in concentration range of 5- 20% ⁹ .

Oliveira et. al. produced fiber with solution blow spinning method by using polylactide (PDLLA) solution, and they examined the effects of the parameters in this study. Polymer concentration, feeding flow rate and air pressure are the parameters examined in this study. Polymer concentration was determined to be the most important parameter. PDLLA fibers having diameter in rage of 70-2000

7

E. S. Medeiros, G. M. Glenn, A. P. Klamczynski, W. J. Orts, and L. H. Mattoso, Solution blow spinning. Google Patents, 2014.

⁸ S. Sinha-Ray, A. L. Yarin, ve B. Pourdeyhimi, «The production of 100/400nm inner/outer diameter carbon tubes by solution blowing and carbonization of core-shell nanofibers», Carbon, v 48, no 12, p 3575-3578, 2010.

⁹ X. Zhuang, X. Yang, L. Shi, B. Cheng, K. Guan, ve W. Kang, «Solution blowing of submicron-scale cellulose fibers*, Carbohydr. Polym., v 90, no 2, p 982-987, 2012. nm were produced. Low polymer concentration results in lumps on the collecting surface. The fibers produced with this method can be collected on any surface such as human skin, non-metallic collectors and fabric. This situation shows that fiber can be produced without forming electric field, and by means of this advantage solution blow spinning method can easily be used in biomedical applications ¹⁰ .

Solution blow spinning method has production speed of 10-30 ml/hour/spinneret. The said method is more advantageous than the other three methods. However, the feeding flow rate is not in a desired level for industrial production since single feeding spinneret is used in the studies.

The inventive unidirectional blowing system and method overcomes the said disadvantages and thus it enables to produce nano-micro fiber nonwoven fabric economically.

Summary of the Invention

The objective of the present invention is to provide a unidirectional blowing system and method for nano-microfiber nonwoven fabric production by using a polymeric solution or melt.

Another objective of the present invention is to provide a unidirectional blowing system and method which operates in low pressure and has low energy consumption by means of high shear force due to the air shear in the unidirectional blowing system.

A further objective of the present invention is to provide a unidirectional blowing system and method wherein the production speed can be increased in level of the channel by feeding the polymer solution from a channel in form of a line.

J. E. Oliveira, E. A. Moraes, R. G. Costa, A. S. Afonso, L. H. Mattoso, W. J. Orts, and E. S. Medeiros, «Nano and submicrometric fibers of poly (D, L-lactide) obtained by solution blow spinning: Process and solution variables*, J. Appl. Polym. Sci, v 122, no 5, p 3396-3405, 2011. Detailed Description of the Invention

The unidirectional blowing system and method developed to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which: Figure 1 is the schematic view of the unidirectional blowing system.

Figure 2 is the steps of the unidirectional blowing method.

The components shown in Figure 1 are each given reference numerals as follows:

1. Unidirectional blowing system

2. Blowing apparatus

3. Air shear

4. Strip spreading apparatus

5. Flat plate

6. Conveyor band

7. Collecting surface

8. Vacuum system

The steps of the method shown in Figure 2 are each given reference numerals as follows:

100. Unidirectional blowing system

101. Sending the polymer melt/solution going out of the strip spreading apparatus (4) to the surface of the flat plate (5)

102. Compressing the polymer melt/solution between the flat plate (5) and the high speed air fed unidirectionally from the air shear (3)

103. Transferring the compressed polymer melt towards the sharp end of the flat plate (5)

104. The polymer melt/solution leaving the flat plate (5) being transformed into fiber form by means of high shear forces originating from the air shear (3)

105. The fibers which are formed being accumulated on the collecting surface (7) and forming the nonwoven fabric structure The unidirectional blowing system (1) developed to fulfill the objective of the present invention comprises

- at least one blowing apparatus (2) where the pressurized air or gases are sent to the polymer melt/solution,

- at least one air shear (3) which is provided on the blowing apparatus (2), which enables the polymer melt/solution to be transformed into fiber form by applying high shear forces,

- at least one strip spreading apparatus (4) which enables the polymer melt/solution to be distributed homogenously, and which has a channel in form of a line,

- at least one flat plate (5) which is comprised of a surfaces wherein the polymer melt/solution going out of the strip spreading apparatus (4) contacting the pressurized air or gas,

- at least one conveyor band (6) which can be actuated in the horizontal direction and which provides the homogeneity of the nonwoven fabric that is formed,

- at least one collecting surface (7) which is provided on the conveyor band (6) and on which the fibers that are produced are collected,

- at least one vacuum system (8) which prevents the fibers on the collecting surface (7) from being dispersed by reducing the turbulence intensity generated by the air shear (3).

In a preferred embodiment of the inventive unidirectional blowing system (1), the blowing apparatus (2) is comprised of single piece or it is comprised by mounting separate parts end to end.

In a preferred embodiment of the inventive unidirectional blowing system (1), hitting angle and the air transfer speed of the air shear (3) can be adjusted.

In a preferred embodiment of the inventive unidirectional blowing system (1), the flat plate (5) is formed of a metal or ceramic material, and it has a tapered form. In a preferred embodiment of the inventive unidirectional blowing system (1), the collecting surface (7) has a perforated lattice structure comprised of a metal material.

The unidirectional blowing method (100) developed to fulfill the objective of the present invention comprises the steps of

-sending the polymer melt going out of the strip spreading apparatus (4) to the surface of the flat plate (5) (101),

-compressing the polymer melt between the flat plate (5) and the high speed air fed unidirectionally from the air shear (3) (102),

-transferring the compressed polymer melt/solution towards the sharp end of the flat plate (5) (103),

-the polymer melt leaving the flat plate (5) being transformed into fiber form by means of high shear forces originating from the air shear (3) (104),

-the fibers which are formed being accumulated on the collecting surface (7) and forming the nonwoven fabric structure (105).

The inventive unidirectional blowing method can be used both in melt blowing method which is used industrially, and in solution blowing method which is used in academic studies.

In the blowing methods known in the state of the art, nano-microfiber nonwoven fabric can be produced by using a co-axial spinneret. Since feeding is made from a single needle in these methods, the production speed is limited to the diameter of the needle. In the suggested method, the polymer solution is fed not from a single needle, but from a line formed channel. By this means, the production line is increased depending on the width of the channel, and 10-30ml/hour/spinneret levels can be achieved.

In the unidirectional blowing method, the energy consumption is low and the system takes smaller place by volume. In addition to these advantages, low fiber diameters (for example about 200 TPU polymer) can be achieved with the invention.