JP6661098B1 - Laminated polytetrafluoroethylene porous membrane and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated PTFE porous membrane which has high strength, good water resistance, air permeability and collection performance and does not peel off, and a method for producing the same. A laminated PTFE porous membrane according to the present invention is composed of a laminated body of three or more layers including three layers of a first layer to a third layer, and the first layer and the third layer have an average molecular weight of 300. Is a PTFE porous membrane layer made of 10,000 or more PTFE emulsion-polymerized particles and having micropores formed by fibrils and nodes, the second layer being located between the first layer and the third layer, It is characterized in that it is a modified fibrillated modified PTFE porous membrane layer made of PTFE emulsion-polymerized particles containing a polymerizable modifier. [Selection diagram] None

Description

  The present invention relates to a laminated polytetrafluoroethylene (hereinafter, “polytetrafluoroethylene” is simply referred to as “PTFE”) porous film and a method for producing the same.

  In the present specification, PTFE that has not undergone a step of heating to 340 ° C. or higher is referred to as unfired PTFE. Incidentally, the melting point of PTFE is 340 ° C., and the melting point of calcined PTFE is 327 ° C.

  In recent manufacturing processes in the semiconductor industry, precision industry, biotechnology, etc., a highly purified space and a highly purified chemical are required. Particularly, in the semiconductor industry, with the recent high integration, it is required to highly clean the atmosphere inside the device, such as removal of fine particles. In order to solve these problems, a porous PTFE membrane is used as a filter material in a high-performance air filter or a filter for removing fine particles in a chemical solution. It is important to form a high-magnification stretched porous membrane with PTFE fine powder having a crystallinity of 98% or more obtained by emulsion polymerization. The fibril increases as the stretching ratio in the longitudinal direction along the extrusion direction (hereinafter, referred to as “MD direction”) and the width direction orthogonal to the extrusion direction (hereinafter, referred to as “TD direction”) is increased. However, the number of nodes decreases, the thickness decreases, and the hole diameter can be reduced. This phenomenon brings about a favorable result in the filter medium in that fine particles are removed and the permeation flow rate is increased.

  The PTFE porous membrane is generally manufactured as follows. That is, a paste-like preform is prepared by adding a solvent such as a petroleum solvent as a molding aid to PTFE fine powder obtained by emulsion polymerization of PTFE, and this preform is used as a cylinder for forming an extrusion mold. To load. Then, when the paste-like preform is extruded into a rod shape or a sheet shape from a nozzle portion provided at the tip of the extrusion mold, a paste-like extruded product is produced. The steps so far are referred to as “paste extrusion” or simply “paste extrusion” in this specification.

  Next, the extruded body is processed into an unfired PTFE film having a thickness of 50 to 1000 μm by a rolling roll including a pair of metal rolls. A molding aid is mixed in the unfired PTFE film at this stage. In the present specification, the unfired PTFE film in which the molding aid has been mixed is referred to as a “molding aid mixed film”.

  When the molding aid is removed by volatilizing and drying the film, an unfired PTFE film from which the molding aid has been removed is produced. In the present specification, the unfired PTFE film from which the molding aid has been removed is referred to as a “molding aid removed film”.

  The film for removing a molding aid is used for applications such as a sealing tape at a joint screw portion to which a pipe such as a gas pipe is connected, a wire covering material for insulating electricity, and a material for forming a flat cable.

  The above-mentioned molding aid-removed film is heated to a temperature lower than the melting point of PTFE, ie, a temperature lower than 340 ° C., and the film is stretched in the MD direction, further stretched in the TD direction, and then stretched to a temperature equal to or higher than the melting point of PTFE. After the heat treatment, a PTFE porous membrane is produced.

  This porous PTFE membrane is used for ski wear, mountain climbing clothing, camping tents, car lamps, air bends for hard disks, etc., chemical liquid filters and air filters.

  By the way, when the thickness of the PTFE porous membrane is reduced, the mechanical strength is weakened, so that discharge damage occurs due to charging at the time of processing, and oil mist or the like adheres to the porous membrane, which deteriorates air permeability and particle collection performance. When the PTFE porous membrane is compressed in the thickness direction by the action of liquid pressure or the like, the gap decreases and the flow rate decreases, and there is a problem that breakage occurs in bending during pleating. In the apparel field, a breathable garment has a problem that when a surfactant comes into contact with the fabric, the water resistance decreases, and when the oil such as sebum contacts, the breathability decreases.

  The invention described in Patent Literature 1 below has been proposed to solve the above problems. That is, the porous PTFE article according to Patent Document 1 provides a combination of high strength, low flow resistance, and small pore size.

  However, in the method of Patent Document 1, a rolled film from which the auxiliary agent has not been removed is first stretched in the TD direction, and then the film is laminated, rolled again and integrated, and then the auxiliary agent is dried. This is a method in which the film is removed, the film is stretched in the MD direction, then stretched in the TD direction, and then sintered, and the first-half integration step is not simple.

  Patent Literature 2 below proposes alternately stacking a PTFE porous membrane having fine pores and a PTFE porous membrane having a size of 5 μm or less, which is slightly larger than the pore diameter, in order to increase the particle collection efficiency.

  However, the method of Patent Document 2 has a difficulty in alternately stacking a plurality of thin and rigid PTFE porous membranes, and also has a problem that the porous membrane is easily peeled off.

  The above-mentioned method of laminating a porous PTFE membrane can be solved by a multilayer extrusion method proposed by the present inventor shown in Patent Documents 3 and 4 below.

  That is, Patent Literature 3 below discloses a method of manufacturing a laminate of a porous PTFE membrane, in which a PTFE paste for obtaining a first layer is placed in a layered manner on a lower mold in a box-shaped mold. Press with. Thus, a compressed first layer is formed. Next, the upper mold is removed, a PTFE paste is added to form a second layer, and the PTFE paste is compressed using the upper mold to form a second layer on the first layer. Thereafter, the PTFE paste for the third layer is further added and pressed by the upper mold. In this way, a multilayer preform having the first layer, the second layer, and the third layer and having a size to be accommodated in the cylinder of the paste extrusion die is obtained. Using this multilayer preform, a PTFE porous membrane multilayer is produced by the above-described procedure for producing a PTFE porous membrane.

  Patent Document 4 discloses, as a combination of layers forming a PTFE porous membrane multilayer body, a combination of PTFE fine powders having different average molecular weights or a PTFE containing a non-fibrous material such as a low molecular weight polymer. Fine powder combinations are shown.

Japanese Patent Publication No. 2009-501632 JP 2012-120969 A JP-A-4-118212 JP-A-3-17938

  However, in Patent Document 4, a layer in which PTFE fine powders having different average molecular weights are combined or a layer of PTFE fine powder containing a non-fibrous material such as a low molecular weight polymer is interposed as an intermediate layer. However, the above problems have not yet been solved.

  Therefore, the present inventor has prepared a film material constituting a polygonally expanded node layer in the intermediate layer of at least three layers from the stage of a preformed body before paste extrusion. It has been found that the above-mentioned problems can be easily solved by performing the usual steps, that is, the production of the sheet by paste extrusion, the rolling of the sheet, the drying and removal of the auxiliary agent, the longitudinal stretching and the transverse stretching by the conventional methods. .

  The greatest feature of the present invention is that, in a multilayer structure, that is, a laminated structure composed of at least three layers or more, a modified PTFE fine powder layer containing 0.5% or less of a comonomer is disposed in an intermediate layer, The upper and lower layers are PTFE fine powders having a crystallinity of 98% or more, and the rolled and auxiliary-removed film is stretched 5 times or more in the MD direction and 20 times or more in the TD direction. In the structure of the membrane.

  The laminated porous PTFE membrane obtained by such a configuration is a membrane in which the modified PTFE polymer of the intermediate layer hardly forms fibrils, but only a node, and has a large pore diameter. Furthermore, the rate of thickness reduction is much smaller than that of the upper and lower surfaces, thereby increasing the overall thickness.

The first laminated porous PTFE membrane according to the present invention is composed of a laminate of three or more layers including three layers of a first layer to a third layer, and the first layer and the third layer have a number average molecular weight of 300. A polytetrafluoroethylene porous membrane layer made of 10,000 or more polytetrafluoroethylene emulsion polymerized particles and having micropores formed by fibrils and nodes, wherein the second layer is formed of a first layer and a third layer. A non-fibrillated modified polytetrafluoroethylene porous membrane layer made of polytetrafluoroethylene emulsion polymerized particles containing a copolymerizable modifying agent, wherein the first and second layers are formed by nodes; It is a modified polytetrafluoroethylene porous membrane layer having a pore size larger than the fine pores formed in the three layers .

In the second laminated PTFE porous membrane according to the present invention, in addition to the configuration of the first laminated PTFE porous membrane, the thickness of the first and third polytetrafluoroethylene porous membrane layers is The thickness is smaller than the thickness of the modified polytetrafluoroethylene porous membrane layer.

The first method for producing a laminated porous PTFE membrane according to the present invention comprises the steps of: forming a PTFE emulsion-polymerized particle mixed with a molding aid for forming a first layer in the first laminated PTFE porous membrane; A modified PTFE emulsion-polymerized particle mixed with a molding aid for forming a second layer in the membrane, and a PTFE emulsion-polymerized particle mixed with a molding aid for forming a third layer in the first laminated PTFE porous film. One layer, the second layer, and the third layer are laminated in this order to prepare a preform, and the preform is loaded into an extrusion die, and the loaded preform is extruded from the extrusion die. After preparing an extruded body, rolling and drying the extruded body to form a molding aid removal film, stretching the molding aid removal film 5 times or more in the extrusion direction, and stretching in the extrusion direction, In the direction perpendicular to the extrusion direction Extend 0 times or more, characterized in that to produce a drawn film, to produce said first or second multilayer polytetrafluoroethylene porous membrane by baking the stretched film at a temperature above the melting point of polytetrafluoroethylene And

In the second method for producing the laminated porous PTFE membrane according to the present invention, after forming the forming aid removing film in the first producing method for the laminated PTFE porous film, the forming aid removing film is removed from a pair of two rolls. One is a metal roll, and the other is narrowed by a nip roll composed of a rubber roll coated with rubber on a metal shaft core to produce a high-density unfired film, and extrude the produced high-density unfired film. After stretching in the direction of extrusion and stretching in the extrusion direction, stretching in the direction perpendicular to the extrusion direction by 20 times or more to produce a high-density stretched film, the high-density stretched film is at least the melting point of polytetrafluoroethylene. And producing the first or second laminated polytetrafluoroethylene porous membrane.

  The laminated porous PTFE membrane configured as described above has improved mechanical strength, and has sufficient water resistance, air permeability, and particle collection performance.

  In addition, in the laminated porous PTFE membrane, pinholes due to electrostatic discharge are reduced.

  Furthermore, since the laminated PTFE porous film can secure a sufficient thickness, consolidation due to external force is suppressed. Since the film is a completely integrated film, peeling and the like do not occur, and handleability is improved.

  Furthermore, when the laminated PTFE porous film is laminated with another fabric with an adhesive, there is no possibility that the adhesive is absorbed by the laminated PTFE porous film and the adhesive oozes out onto the surface of the fabric.

  Further, the laminated porous PTFE membrane has an effect of suppressing deterioration in air permeability due to contact with a surfactant, sebum, or the like.

2 is a surface photograph in which a part of a laminated porous PTFE membrane in Example 1 of the present invention is peeled off so that an inner layer can be confirmed. It is an enlarged surface photograph of layer B in Example 1 of the present invention. The left figure in the figure is a surface photograph showing the state where oil was dropped on the laminated PTFE porous film of Example 1, and the right figure is a surface photograph showing the state where oil was dropped on the laminated PTFE porous film of Comparative Example 1. . The left figure in the figure is a photograph showing the state of the oil that was dripped onto the colored paper laid below by dropping oil onto the laminated PTFE porous membrane of Example 1, and the right figure is the laminated PTFE porous membrane of Comparative Example 1. 5 is a photograph showing the state of oil that has been dripped into colored paper laid under the oil by dropping the oil. 9 is a photograph of the surface immediately after oil was dropped on the laminated porous PTFE membrane of Comparative Example 2. 10 is a photograph of the surface of the laminated PTFE porous membrane of Comparative Example 2 after oil was dropped for 10 minutes. 9 is a photograph showing the state of oil that was dropped onto colored paper laid below by dropping oil onto the laminated porous PTFE membrane of Comparative Example 2.

  The laminated PTFE porous membrane has a multilayer in the thickness direction of a layer A (first layer), a layer B (second layer), and a layer C (third layer) or more.

  The A layer and the C layer are layers formed of fine powder of PTFE emulsion polymerized particles which are easy to form a porous film by fibrils and nodes, and in which fine pores are formed. The A layer and the C layer may be fine powders of the same PTFE emulsion polymerized particles or different PTFE emulsion polymerized particles. PTFE that easily forms micropores by fibrils and nodes that form the A layer and the C layer is composed of PTFE emulsion polymerized particles having a number average molecular weight of 3,000,000 or more.

  The B layer is an intermediate layer interposed between the A layer and the C layer and does not form micropores. The layer B is a layer having a vein-like streak-like polygonal structure whose structure viewed from the surface of the membrane is several millimeters. The layer B is composed of fine powder of PTFE emulsion polymerized particles containing 0.5% or less of a copolymerizable modifier and hardly fibrillated. In addition, hexafluoropropene, ω-hydroperfluoroolefin, trifluorochloroethylene, and perfluoroalkyltrifluoroethylene having 3 to 10 carbon atoms can be suitably used as the copolymerizable modifier.

  The A layer, the B layer and the C layer are formed into layers at once from the stage of preforming, and a laminated PTFE porous film is manufactured from the rolled and dried film.

  The laminated PTFE porous film is manufactured at a draw ratio of 5 times or more in the MD direction and 10 times or more in the TD direction, and is heat-treated at a temperature of the melting point or more.

  Before producing a laminated porous PTFE membrane, the unfired film may be densified by nip rolls and then stretched.

  Note that a structure in which another PTFE porous film is laminated between the A layer, the B layer, and the C layer or outside the A layer and the C layer may be adopted.

[Production of laminated PTFE porous film]
22 parts by weight of Solvent Isopar H (manufactured by ExxonMobil Corporation) was mixed with fine powder F-106 (manufactured by Daikin Industries, Ltd.) composed of PTFE emulsion polymerized particles as a forming aid (hereinafter, this mixture was referred to as “PTFE mixed with forming aid ”). Emulsion polymerization particles A ").

  20 parts by weight of a solvent Isopar H (manufactured by ExxonMobil Corporation) as a molding aid was mixed with fine powder F-205 (manufactured by Daikin Industries, Ltd.) composed of modified PTFE emulsion polymerized particles (hereinafter, this mixture was referred to as “Molding aid”). Agent-modified PTFE emulsion polymerized particles B ”).

  To be inserted into a 70 mm square paste extrusion cylinder, the A layer and the C layer made of the PTFE emulsion polymer particles A mixed with the molding aid, and the modified PTFE emulsion polymer mixed with the molding agents, according to the production method of Patent Document 3 described above. A layer B composed of particles B is filled in a ratio of 1/3 in the order of A, B and C in a preforming mold so that the A layer and the C layer are arranged vertically and the B layer is arranged in the middle. Thus, a multilayer preform was prepared.

  The extrusion die has a die outlet, that is, the opening of the nozzle portion has a narrow rectangular shape of 250 mm × 2 mm, and the multilayer preform has a sheet extruded from the extrusion die in a thickness direction of 3 mm. An extruded mold was filled into layers so as to form a sheet-shaped extruded body.

  A sheet-like extruded product obtained by extruding a paste with an extrusion mold was rolled to 200 μm using a calendar roll, and then the solvent was removed by heating to prepare a film from which a molding aid had been removed.

  The molding aid-removed film prepared above was stretched 5 times in the MD direction between rolls at 300 ° C, and then stretched 20 times in the TD direction at 200 ° C using a tenter device. The heat setting zone of the tenter was 380 ° C.

  The film formed by removing the molding aid from a pair of two rolls, one of which is a metal roll, and the other of which is sandwiched and compressed by a nip roll composed of a rubber roll coated with rubber on a metal shaft. A laminated PTFE porous film may be produced by stretching and heat fixing a densified unfired PTFE film reduced in thickness only.

[Physical properties of laminated PTFE porous film]
For the measurement of the weight of the laminated PTFE porous membrane, the central portion of the laminated PTFE porous membrane was cut with a 50 mm square mold to prepare five samples, and the weight of each sample was measured using an electronic balance (effective digit: 1/1000 g, The sample was weighed with an Aspro Electronic Balance ASP 213 manufactured by As One Corporation, and the average value was defined as the weight of one laminated PTFE porous membrane.

  The thickness of the laminated PTFE porous film was measured by superimposing five samples on a dial thickness gauge (SM-112 manufactured by TECLOCK Co., Ltd.), and dividing the measured value by 5 to obtain a thickness of one sheet. As a result, the thickness of one laminated PTFE porous film was about 30 μm.

  In addition, a sample was prepared after MD / TD stretching and before sintering, an adhesive tape was stuck on both sides, and as shown in FIG. 1, the A layer and the C layer were peeled off, and measurement was performed using the above-mentioned micrometer. As a result, the total thickness of the original layers A to C was 30 μm, the thickness of the layers A and C was about 5 μm, respectively, and the thickness of the layer B was about 20 μm.

  The gas permeability of the laminated porous PTFE membrane was calculated by measuring the pressure loss and the particle removal efficiency of the laminated porous PTFE membrane of Example 1.

  That is, the pressure loss was measured by setting the measurement sample of the laminated PTFE porous membrane of Example 1 in a filter holder having an inner diameter of 100 mm, pressurizing the inlet side with a compressor, and measuring the flow rate of air permeation with a flow meter at 5.3 cm / sec. Was adjusted. Then, the pressure loss at this time was measured with a manometer.

  In addition, the collection efficiency was determined according to the method described in JIS B9928, Annex 5 (Regulation), Method for Generating NaCl Aerosol (Pressure Spraying Method), by using an NaCl particle generated by an atomizer and an electrostatic classifier (manufactured by TSI). ), The particles are classified to a particle diameter of 0.1 μm, the particles are neutralized with Americium 241, the permeation flow rate is adjusted to 5.3 cm / sec, and a particle counter (TSI, CNC) is used. The number of particles before and after the laminated porous PTFE membrane of Example 1 as a measurement sample was determined, and the collection efficiency was calculated by the following equation.

CO = number of particles of NaCl 0.1 μm collected by the measurement sample CI = number of particles of NaCl 0.1 μm supplied to the measurement sample Collection efficiency (%) = (CO / CI) × 100
Pressure loss and trapping efficiency are important as the characteristics of the porous PTFE membrane. However, it is difficult to balance these two characteristics because one tends to increase and the other tends to decrease. As an index for evaluating the balance between the pressure loss and the collection efficiency, a PF value obtained by the following equation is used.

PF value = {− log ((100−collection efficiency (%)) / 100)} / (pressure loss / 1000)
The test results are as shown in Table 1 below.

  Regarding the measurement of the pore size of the laminated PTFE porous film, since the 0.1 μm NaCl particles shown in Table 1 are almost 100% collected, the pore sizes of the A layer and the C layer are about 0.1 μm. It could be estimated.

As for the layer B, as shown in FIG. 2, 1 cm ² was selected from a stereoscopic photograph and its weight was measured. A portion having a relatively small hole diameter and a portion having a relatively large hole diameter were cut out, and the weight was measured. Was measured, and the weight was converted to the area. The hole diameter was calculated using the area as the area of a circle. The results are as shown in Table 2 below, and it was estimated that the pore size of the layer B was approximately 22 μm to 120 μm.

  Regarding the fluid permeability of the laminated PTFE porous membrane, color paper is spread under the laminated PTFE porous membrane, and 70 g of extra virgin olive oil (J-Oil Mills Co., Ltd., Ajinomoto sales) is used to mix the olive oil with the laminated PTFE porous membrane. The measurement was performed by dropping one drop (about 0.025 g) on the film. First, the weight of the colored paper before the olive oil was dropped was measured, and the weight of the colored paper 10 minutes after the olive oil was dropped was measured, and the difference was defined as the permeation amount.

[Comparative Example 1]
As Comparative Example 1, a porous film made of only PTFE emulsion polymer particles A mixed with a molding aid was prepared by the same production method as in Example 1 by paste extrusion, rolling, and biaxial stretching.

[Comparative Example 2]
As Comparative Example 2, two porous films of Comparative Example 1 each having a thickness of 15 μm were stacked to form a porous film having a thickness of 30 μm .

[Test results]
When the above-mentioned measurement was performed for Example 1, Comparative Meter 1 and Comparative Example 2, the results shown in Table 3 below were obtained.

  As shown in Table 3 above, Example 1 had almost no difference in weight from Comparative Example 1, but Example 1 had twice the thickness.

  As a result of a penetration test, olive oil was dropped on the porous membrane of Example 1 and the porous membrane of Comparative Example 1 as shown in FIG. 3, and as shown in FIG. In No. 1, the permeation amount was visibly small, and in Comparative Example 1, the permeation amount was large. Numerically, as shown in Table 3, the amount of permeation of Example 1 was very small.

Furthermore, as shown in FIG. 5, when dropping a porous membrane olive oil of Comparative Example 2, after lapse of 10 minutes in a state as shown in FIG. 6, for the color paper, as shown in FIG. 7 and Table 3 In addition, the permeation amount was not much different from that of Comparative Example 1, and it was found that the permeation amount was considerably large even when two porous membranes of Comparative Example 1 were stacked. Also, the permeation rate was not different from that of the single sheet of Comparative Example 1. That is, it was found that the amount of penetration and the rate of penetration did not change depending on the thickness .

  From the above, it was confirmed that the layer B in Example 1, that is, the porous membrane layer composed of the modified PTFE emulsion polymer particles B mixed with the molding aid became a space layer and had an effect of collecting liquid and blocking permeation. .

  Although the embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

Claims (4)

It is composed of a laminate of three or more layers including three layers of a first layer to a third layer,
The first layer and the third layer are a polytetrafluoroethylene porous membrane layer having a number average molecular weight of 3,000,000 or more and made of polytetrafluoroethylene emulsion polymerized particles and having fine pores formed by fibrils and nodes,
The second layer is located between the first layer and the third layer, and is a fibrillated modified polytetrafluoroethylene porous membrane layer made of polytetrafluoroethylene emulsion polymerized particles containing a copolymerizable modifier. And a modified polytetrafluoroethylene porous membrane layer formed by the node and having a larger pore diameter than the fine pores formed in the first layer and the third layer. . The thickness of the first layer and the third layer porous polytetrafluoroethylene film layer of laminate according to claim 1, characterized in that is smaller than the thickness of the modified polytetrafluoroethylene porous membrane layer of the second layer polytetra Fluoroethylene porous membrane. A polytetrafluoroethylene emulsion polymer particle mixed with a molding aid for forming the first layer according to claim 1, and a modified polytetrafluoroethylene mixed with a molding aid for forming the second layer according to claim 1. The emulsion polymerization particles and the polytetrafluoroethylene emulsion polymerization particles mixed with a molding aid for forming the third layer according to claim 1 are laminated in the order of a first layer, a second layer, and a third layer. Make a preform,
Loading the preform into an extrusion mold,
The loaded preform is extruded from the extrusion mold to produce an extruded body,
Rolling and drying the extruded body to produce a molding aid removal film,
The molding aid-removed film is stretched 5 times or more in the extrusion direction,
After stretching in the extrusion direction, stretched 20 times or more in the direction perpendicular to the extrusion direction to produce a stretched film,
The laminated film is fired at a temperature equal to or higher than the melting point of polytetrafluoroethylene to produce the laminated polytetrafluoroethylene porous film according to claim 1 or 2.
A method for producing a laminated polytetrafluoroethylene porous membrane, comprising: After producing the molding aid removal film according to claim 3,
The molding aid-removed film is composed of a pair of two rolls, one is a metal roll, and the other is a high-density unfired film that is narrowed by a nip roll composed of a rubber roll having a metal shaft covered with rubber. And make
The produced high-density unfired film is stretched 5 times or more in the extrusion direction,
After stretching in the extrusion direction, stretched 20 times or more in the direction perpendicular to the extrusion direction to produce a high-density stretched film,
3. The laminated polytetrafluoroethylene porous film according to claim 1 or 2, wherein the high-density stretched film is fired at a temperature not lower than the melting point of polytetrafluoroethylene to produce the laminated polytetrafluoroethylene porous film according to claim 1 or 2 . Manufacturing method.