Apparatus and process for melt-blowing a fiberforming thermoplastic polymer and product produced thereby

• US 4,380,570 A
• Filed: 04/08/1980
• Issued: 04/19/1983
• Est. Priority Date: 04/08/1980
• Status: Expired due to Term

• Current Assignee: Eckhard C.A. Schwarz
• Original Assignee: Eckhard C.A. Schwarz
• Inventors: Schwarz, Eckhard C. A.
• Primary Examiner(s): Woo, Jay H.
• Application Number:
  US06/138,860
• Time in Patent Office: 1,106 Days
• Field of Search: 425/72 S, 425/80.1, 264/176 F, 264/14, 264/12, 156/176, 428/296
• US Class Current: 442/350
• CPC Class Codes: D01D 4/025 Melt-blowing or solution-blowing dies
• CPC Class Codes: D01D 5/0985 by means of a flowing gas (e.g. melt-blowing)
• CPC Class Codes: D04H 1/56 in association with fibre formation, e.g. immediately following extrusion of staple fibres
• CPC Class Codes: Y10T 442/625 Autogenously bonded
• CPC Class Codes: Y10T 442/626 Microfiber is synthetic polymer
• CPC Class Codes: Y10T 442/68 Melt-blown nonwoven fabric

Abstract

There is disclosed a novel apparatus and process for melt-blowing from fiberforming thermoplastic molten polymers to form fine fibers by extruding through orifices in nozzles the molten polymer at low melt viscosity at high temperatures where the molten fibers are accelerated to near sonic velocity by gas being blown in parallel flow through small orifices surrounding each nozzle. The extruded molten polymer is passed to the nozzles through a first heating zone at low incremental increases in temperature and thence rapidly through said nozzles at high incremental increases in temperature to reach the low melt viscosity necessary for high fiber acceleration at short residence time to minimize or prevent excessive polymer degradation.

Claims

1. In a process for producing melt blown fibers from a molten fiberforming thermoplastic polymer and wherein said molten fiberforming thermoplastic polymer is further heated and extruded through orifices of heated nozzles into a stream of hot gas to attenuate said molten polymer into fibers forming a fiber stream and wherein said fiber stream is collected on a receiver surface in the path of said fiber stream to form a non-woven mat, the improvement, which comprises:

(a) passing said molten polymer through an elongated channel and thence through a plurality of sub-channels to a molten polymer feed chamber, said molten polymer having a resident time through said channels of less than 30 seconds;

(b) heating said molten polymer during step (a) to a temperature whereby

space="preserve" listing-type="equation">aΣ

1/Q is smaller than 0.1,

wherein;

a is the thermal diffusivity of said molten polymer,

1 is the length of each polymer channel, and

Q is the polymer flow rate in each polymer channel;

(c) passing said thus heated molten polymer from said feed chamber through a plurality of heated nozzles to form said melt blown fibers, said molten polymer having a residence time in said heated nozzles of less than 2 seconds; and

(d) further heating said thus heated molten polymer, during step (c) to a temperature whereby

space="preserve" listing-type="equation">aΣ

1/Q is greater than 0.07,

wherein;

a is the thermal diffusivity of said molten polymer,

1 is the length of each polymer channel, and

Q is the polymer flow rate in each polymer channel;

said molten polymer forming said melt blown fibers exhibiting an apparent melt viscosity of less than 45 poise, said molten polymer introduced into said elongated chamber being at a temperature of at least 40°

F. lower than the temperature of said melt blown fibers.

2. The improved process as defined in claim 1 wherein said stream of hot gas in blown from gas orifices surrounding each of said molten polymer orifices, said gas orifices having a combined cross section area per each of said orifices of less than 0.5 square millimeter.

3. The improved process as defined in claim 1 where an average fiber diameter in microns forming said non-woven is from 7 to 15 times the square root of the molten polymer flow rate per molten polymer orifice (in cm.³ /minute), and the Number Average Molecular Weight of said fibers is at least 0.4 times the Number Average Molecular Weight of said fiberforming thermoplastic polymer.

4. The improved process as defined in claim 3 wherein the average diameter of said fibers in micron is less than 2.

5. The improved process as defined in claim 1 wherein said non-woven mat is formed from a plurality of said molten polymer orifices arranged in multiple rows.

6. The product produced by the process defined by claims 1, 2, 3, 4 or 5.

7. An improved apparatus for producing melt blown fibers wherein a fiberforming thermoplastic polymer into fibers that form a fiber stream and wherein said fibers are collected on a receiver surface in the path of said fiber stream to form a non-woven mat, the improvement which comprises:

an elongated channel means for passing said molten fiber to a molten polymer feed channel;

means for heating said molten polymer during passage through said channel means to a temperature, whereby

space="preserve" listing-type="equation">aΣ

1/Q is smaller than 0.1,

wherein;

a is the thermal diffusivity of said molten polymer,

1 is the length of said polymer channel means, and

Q is the polymer flow rate in said polymer channel means;

a plurality of heated nozzles means for receiving said molten polymer from said molten polymer feed chamber and for forming fine melt blown fibers;

orifice means surrounding said plurality of heated nozzle means for passing a heated gas at near sonic velocity therethrough to attenuate said molten polymer;

means for heating said gas to a temperature whereby said molten polymer is heated during passage through said nozzle means to a temperature, whereby;

space="preserve" listing-type="equation">aΣ

1/Q is greater than 0.07,

wherein;

a is the thermal diffusivity of said molten polymer,

1 is the length of said polymer channel means, and

Q is the polymer flow rate in said polymer channel means.

8. The apparatus as defined in claim 7 wherein said orifice means are formed by corners of a screen.

9. The apparatus as defined in claim 8 wherein said orifice means is formed by a plate having a plurality of holes therein.

10. An improved die for forming melt blown fibers, which comprises:

an upper plate member having an inlet passageway and a plurality of channels for passing molten polymer therethrough;

an intermediate plate member including a plurality of elongated nozzles and defining with said upper plate member a molten polymer feed chamber for receiving molten polymer from said plurality of channels;

means for heating said molten polymer during passage through said plurality of channels; and

a lower plate member including a plurality of orifices and defining with said intermediate plate member a gas chamber, said elongated nozzles extending into said orifices.

11. The improved die as defined in claim 10 wherein said lower plate member includes a woven metallic screen member defining said plurality of orifices.

12. The improved die as defined in claims 10 or 11 wherein said heating means heats said molten polymers to a temperature whereby

13. The improved die as defined in claim 11 wherein said orifices of said screen member are square-shaped.

14. The improved die as defined in claim 11 wherein said orifices of said screen member are triangularly-shaped.

15. The improved die as defined in claims 13 or 14 wherein said screen member is in contact with said elongated nozzles.