EP2899305A1

EP2899305A1 - Method of manufacturing biodegradable non-woven web and apparatus therefor

Info

Publication number: EP2899305A1
Application number: EP14152696.2A
Authority: EP
Inventors: Jong Soon Park
Original assignee: Glo-one Co Ltd
Current assignee: Glo-one Co Ltd
Priority date: 2014-01-27
Filing date: 2014-01-27
Publication date: 2015-07-29

Abstract

A method of manufacturing biodegradable non-woven web comprises the steps of extruding a polymer material into strands, drawing the strands to form filaments, and arranging and transferring the said filaments to form a non-woven web, wherein the filament-forming step is carried out by colliding the said strands against a heating drum 45 rotating at high speed so that the said strands are scattered by the centrifugal force exerted by the rotating heating drum. The non-woven web may have multi-purpose uses in surgical procedures.

Description

FIELD OF THE INVENTION

The invention relates to a method of manufacturing non-woven web and an apparatus therefor, which includes a process of making monofilaments with diameter preferably less than 1 micrometer. The web can be made from high molecular weight biodegradable polymer such as poly (lactic acid), poly (glycolic acid), and poly (lactic acid-co-glycolic acid). The biodegradable non-woven web can be served to multi-purpose uses for surgical procedures.

BACKGROUND OF THE INVENTION

In surgical procedures, non-woven webs having easily modifiable surface can be used for wide variety of surgical applications. Compared with non-biodegradable materials, biodegradable polymers have advantage in minimizing the side effects in living body because they can be hydrolyzed to become metabolic products such as lactic acid and glycolic acid. Known biodegradable polymers such as lactic acid-based or glycolic acid-based polymers are currently used for absorbable surgical suture, however, biodegradable non-woven web has not been practically used until now.
Generally monofilaments with diameter less than 1 micrometer are needed to manufacture non-woven webs suitable for surgical procedures, and the process to make the monofilaments of biodegradable polymer materials includes melting, extruding, and drawing procedures. In order to produce monofilaments with diameter less than 1 micrometer, polymer material must be extruded in the form of strand with diameter less than some critical value, which is related with the drawing ratio in the drawing procedure. However, since high molecular weight polymers such as lactic acid-based or glycolic acid-based polymers have high viscosity and low drawing ratio in general, conventional monofilament-forming techniques have problems in discharging these polymers out of a narrow orifice of the extruder. So these conventional techniques cannot be practically used for manufacturing monofilaments with diameter less than 1 micrometer.
Two of the well-known techniques for manufacturing non-woven webs are the spun bond method and the melt blown method, of which the latter can yield monofilaments with higher drawing ratio because it uses both the discharge pressure of the extruder and the high-speed air flow during drawing procedure. However, in case of using high molecular weight polymers such as biodegradable polymers, even the melt blown method alone cannot yield monofilaments with sufficiently high drawing ratio because these polymers have very low melt index.
Apparatus and manufacturing methods of making spun bond or melt blown non-woven web intended to increase the productivity and the homogeneity of filament formation are described in US patents Nos. 4,708,619 , 4,813,864 , 4,838,774 , 5,087,186 , 6,427,745 , 6,565,344 . However, even these apparatus and manufacturing methods cannot yield non-woven web of biodegradable polymers appropriate for medical uses because of the above-mentioned problems.
The other method which may be applied to manufacturing biodegradable non-woven web is the manufacturing method of nano fiber. This method includes the procedures of dissolving polymeric substances in solvent, and discharging the polymer solution through a narrow nozzle under intense electrostatic condition. This method, however, yield monofilaments with weak fiber strength, poor shape-stability, and has some problems caused from residual solvent. Moreover, this method is hard to be adopted for mass production.
Described in US Patents Nos. 5,075,161 and 5,260,003 is the use of a Laval nozzle which accelerates the gas speed up to sonic velocity to produce very fine fibers. However, this technique requires complicated equipment and high maintenance cost. Moreover, the non-woven web manufactured by this method is not suitable for medical uses because it generates very fine particles which may be harmful to patients.
Also manufacturing methods of multiple ultrafine fibers are described in Japanese Patent Application Laid-Open Nos. 3-113082 and 6-272114 , and US Patent No. 4,686,074 . However, even this technique is not able to produce monofilaments with diameter less than 2 micrometers.
A manufacturing method of nano fiber is described in PCT/JP2003/013477 , which is a modification of the manufacturing method of sheath multi-core ultrafine fibers. However, according to this method, one must dissolve polymer material in alkaline water or hot water. And a drying procedure must be attended. Moreover, this technique has also a disadvantage due to partial dissolution of polymers and loss of raw materials.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention aim to provide an apparatus and method of manufacturing a biodegradable non-woven web which serves for multi-purpose uses in surgical procedures. One preferred embodiment of the present invention aims is to provide a method of manufacturing monofilament with diameter less than 1 micrometer, which is made from poly (lactic acid), poly (glycolic acid), or poly (lactic acid-co-glycolic acid) having a molecular weight of more than 120,000 and a melt index of less than 5 g/min; and a further object is to provide a manufacturing apparatus therefor.
According to one aspect of the present invention, there is provided a method of manufacturing a non-woven web comprising the steps of extruding a polymer material into strands, drawing the said strands to form filaments, and arranging and transferring the said filaments to form a non-woven web, wherein the filament-forming step is carried out by colliding the said strands against a heating drum rotating at high speed so that the said strands are scattered by the centrifugal force exerted by the rotating heating drum.
Other aspects of the invention are presented in the appended claims.
For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:

Figure 1 is a schematic diagram of an apparatus for manufacturing non-woven web according to an embodiment of the present invention;
Figure 2 is a perspective view of a heating drum assembly for use in an embodiment of the present invention;
Figure 3 is an end view of a heating drum assembly having a different configuration; and
Figure 4 is a side view of a heating drum showing its main surface pattern in an embodiment of the present invention.

In the figures, like references denote like or corresponding parts.
It is to be understood that the various features that are described in the following and/or illustrated in the drawings are preferred but not essential. Combinations of features described and/or illustrated are not considered to be the only possible combinations. Unless stated to the contrary, individual features may be omitted, varied or combined in different combinations, where practical.
Embodiments of the present invention provides a method of manufacturing a biodegradable non-woven web made of monofilaments with diameter less than 1 micrometer. Compared to conventional techniques, embodiments of the present invention can provide a cheaper non-woven web having bio-absorptivity of more than 95%. The non-woven web is also free of residual solvent and does not generate fine particles so that it can be safely used for medical applications.
Manufacturing apparatus may include a heating drum rotating at high speed, which provides the centrifugal force for the strand to be transformed to fine monofilaments with controlled diameter. Also the heating drum may facilitate the feeding of polymer melt with high accuracy together with a metering pump so that it can prevents the generation of fine particles during the manufacturing process of non-woven webs.
Embodiments of the present invention may also use a heating drum having fine grooves on the surface. By adjusting the depth and length of the grooves and the distance between the grooves, we can control the diameter and length of the monofilament. Moreover, we can obtain more homogeneous monofilaments by rocking the rotating heating drum along the axial direction.
The apparatus shown in Figure 1 is intended for manufacturing a non-woven web made of biodegradable polymer resin. The structure includes an extruder 12 with an extruder motor 11, a filter 13, a metering pump 14, a heating drum 45 with a fixed heating block 46, a conveyor belt 17, a pressure roller 18, a calender 19, first driving roller 47, second driving roller 49, a guiding roller 48, a takeout roller 50, and a vacuum chamber 51. The heating roller 45 is connected to a conventional electric motor operating at controlled rotation velocity, which is not shown in this figure.
Biodegradable polymers, such as poly (lactic acid), poly (glycolic acid), or poly (lactic acid-co-glycolic acid), with the melt index of less than 5 g/min is fed into the extruder 12 while rotating the extruder motor 11 to melt the polymer, which is then passed through the filter 13 and the metering pump 14 and then is continuously discharged as strands. The strands have accurately controlled diameter because the metering pump 14 provides an accurately controlled feeding rate. The discharged strands are collided and then guided by the heating drum 45 into a spacing of 10∼100 micrometer between the heating drum 45 and the heating block 46. While being passed through the spacing, the strands are scattered by the heating drum's rotational motion and drawn by the centrifugal force to be transformed to fine monofilaments. The drawn monofilaments fall on the conveyor belt 17 which is driven by the first driving roller 47 and supported by the guiding roller 48. The monofilaments are then arranged in regular or irregular orientations to form the shape of non-woven web with controlled thickness and pattern, and finally are being wound as a roll type by the takeout roller 50.
In order to manufacture monofilaments with diameter of less than 1 micrometer, it is desirable to reduce the viscosity of the molten polymer down to less than 100 Pa·s.
Also the shear stress between the molten polymer and extruder's spinneret needs to be adjusted to be less than 0.2 MPa, which can be calculated by the Hagen-Poiseulle's law.
If the shear stress between the polymer and the spinneret becomes too high in the drawing procedure, it tends to yield monofilaments with largely-deviated diameters.
It is desirable to set the temperature of the spinneret to be more than 20°C above the melting point of the polymer. Performing the drawing process faster tends to increase the drawing efficiency. It is also desirable to set the heating temperature in the drawing process to be above the glass transition temperature of the polymer. In the present embodiment of invention, we need to melt the biodegradable polymer such as poly(lactic acid), poly(glycolic acid), or poly(lactic acid-co-glycolic acid), in the melting region of the extruder 12 with the temperature set at 20∼60°C above the melting point of each polymer, respectively. The polymer melt is then moving through the filter 13 in order to be free of impurities. The metering pump 14 have orifice dies positioned with uniform spacing, which acts as spin packs. The diameter and length of each orifice in the metering pump 14 may be adjusted to be 0.3∼1mm and 0.6∼3mm, respectively. The spacing between the orifices may be adjusted to be 1∼1.5 times of the orifice diameter. The discharge throughput per each orifice may be adjusted to be 0.15∼1.5 g/min, and the shear stress is adjusted to be less than 1 MPa. The distance between the orifice of the metering pump 14 and the heating drum 45 is adjustable within the range of 5∼30 cm according to the polymer's heat capacity.
Operation of the manufacturing apparatus with the said conditions may yield the strands with diameter of 0.05∼0.5 mm, which are then drawn by 800 times by the rotating heating drum 45. The strands are then transformed to monofilaments with diameter of 0.9∼9 micrometers. The temperature of the heating drum 45 may be set to be 30∼50°C above the glass transition temperature of the polymer material. In order to get the centrifugal force strong enough to draw the strands, the diameter of the heating drum 45 need to be more than 900 mm, and its rotation speed need to be more than 900 rpm, and more desirably to be more than 3600 rpm.
A number of grooves 54 may be formed on the surface of the heating drum 45. The grooves 54 help to scatter and rupture the strands which are being continuously collided against the drum's surface. The strand is then transformed to multiple monofilaments with finite lengths. The scattered monofilaments fall on the conveyor belt 17, wherein they are arranged into a shape of a non-woven web.
The conveyor belt 17 is comprised of a net, and the vacuum chamber 51 is placed under the back side of the net in order to prevent the filaments from being squandered away.
During this process, the mass per unit area (g/m²) of the newly-formed web is controlled by the rotation speed of the first driving roller 47. The apparent density of the web can be controlled by the pressure between the first driving roller 47 and the pressure roller 18. The surface condition of the web may be determined by the surface patterns of the calender 19 and the second driving roller as well as the pressure applied between them.
As an example, we consider using a metering pump with the capacity of 20 g/min, of which the orifice diameter is 0.3 mm and the number of orifices is 100, and the length of each orifice die is 100 mm. In this case, the maximum discharge throughput for each orifice is calculated to be 0.2 g/min. However, we can expect the real discharge throughput for each orifice to be about 0.15 g/min, which is within the range of 70∼80% of the maximum throughput value. If the specific gravity of the polymer is 1.24, the throughput of the polymer discharged from each orifice is calculated to be 0.002cc/s. The linear velocity of the discharged polymer strand falling on the heating drum 45 is then calculated to be 0.03 m/s. If the diameter of the heating drum 45 is 900 mm, the linear velocity at the outer surface of the heating drum is calculated to be 42.4 m/s. If we compare the linear velocity of the discharged strand (0.03 m/s) to that of the outer surface of the heating drum 14 (42.4 m/s), we can get the result that the polymer strand would be drawn by 1400 times in length. Therefore, a polymer strand with diameter of 0.3 mm will be transformed into a monofilament with diameter of less than 2 micrometers. Furthermore, if we reduce the discharge throughput by adjusting the metering pump 14, we can obtain monofilament with diameter of less than 1 micrometer.
It is also noteworthy that we can control the length of the monofilament by adjusting the groove pattern of the heating drum as shown in Figure 4. As an example of a desirable configuration, we can form grooves 54 of 0.5 mm depth on the surface of the heating drum 45, and the length of each groove may be adjusted to be about 10 cm, and the distance between the neighboring grooves may be adjusted to be about 1.2 mm.
As shown in Figure 2, a carbon electrode 52 may be installed inside the heating drum 45, which acts as an electric heater. And an oil inlet 53 may be provided inside the carbon electrode 52 in order to secure homogeneous surface temperature distribution. The said structure is well known in this field.
The heating drum 45 may be able to undergo rocking motion along the axial direction, which is driven by a device which is not shown in Figure 1. By adjusting the rocking motion, we can control the orientation of the monofilaments to manufacture non-woven webs with a variety of patterns. The said structure is also well known in this field.
The heating block 45 acts as a flattener member which guides the scattering direction of the newly-formed monofilaments. The spacing between the heating drum 45 and the heating block 46 may be adjusted to 0.1 ∼0.2 mm so that the discharged monofilaments can easily pass through the spacing. The temperature of the heating drum 45 and the heating block 46 may be set to 10∼20 °C above the melting point of the polymer in order to facilitate the drawing process.
Instead of using the heating block 46 as shown in Figure 1, we can also use another heating drum 46 acting as a flattener member as shown in Figure 3.
In this specification, the verb "comprise" has its normal dictionary meaning, to denote non-exclusive inclusion. That is, use of the word "comprise" (or any of its derivatives) to include one feature or more, does not exclude the possibility of also including further features. The word "preferable" (or any of its derivates) indicates one feature or more that is preferred but not essential.
All or any of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all or any of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

A method of manufacturing a non-woven web comprising the steps of extruding a polymer material into continuous strands, drawing the said strands to form monofilaments, and arranging and transferring the said filaments to form a non-woven web, wherein the monofilament-forming step is carried out by colliding the said strands against a heating drum rotating at high speed so that the said strands are scattered by the centrifugal force exerted on the surface of the rotating heating drum.
An apparatus for manufacturing a non-woven web comprising:
an extruder which can be used to make polymer strands;

a heating drum which can rotate at high speed at an elevated temperature, which is used to transform the said strands into monofilaments; and

means for arranging and transferring the said monofilaments to form a non-woven web.
An apparatus as set forth in claim 2, the apparatus further comprising a flattener member for guiding the scattering filament, which is placed at a distance from the said heating drum and maintained at an elevated temperature.
An apparatus as set forth in claim 2, wherein the said heating drum is a pair of drums positioned with spacing, so that the said strands are collided and scattered inside the spacing.
An apparatus as set forth in claim 2 or 3, wherein the spacing is 0.1 ∼0.2 mm wide.
An apparatus as set forth in claim 2, 3, or 4, the said heating drum having a surface with many grooves formed regularly or irregularly, so that the said grooves can be served to break a strand into a set of multiple filaments.
An apparatus as set forth in claim 2, 3, 4, 5, or 6, wherein the said heating drum is able to undergo rocking motion along the axial direction.