JP2012052274A - Low crystalline high strength polyvinyl alcohol-based fiber and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol-based fiber which has low crystallinity and yet high strength by drawing the fiber in a processing time which is far shorter than that of a conventional drawing method.SOLUTION: A polyvinyl alcohol-based fiber has a degree of crystallinity of less than 55% and strength of more than 5 cN/dtex. The polyvinyl alcohol-based fiber may have an orientation of more than 90% and a swelling degree of more than 100%. The polyvinyl alcohol-based fiber may have a dissolution temperature in water of about 60 to 100°C.

Description

  The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having a high fiber strength despite its low crystallinity and a method for producing the same.

  In a PVA fiber composed of a crystal part and an amorphous part, a spinning process of a spun yarn is generally performed to improve fiber strength. In the drawing treatment, the spinning yarn is usually drawn while being heat-treated in a hot air oven. However, in order to sufficiently draw the yarn, the spinning yarn needs to be drawn while being heat-treated over a long time. And in the drawn fiber, the internal crystallinity is improved, and the fiber strength can be improved by the improvement of the crystallinity inside the fiber.

  However, in this case, if the stretching is performed only by external heating, the fibers are heated uniformly, and thus there is a problem that the stretching stress of the amorphous part is lowered. Therefore, in order to solve such a problem, Patent Document 1 (Japanese Patent Laid-Open No. 58-109651) describes a plastic that is continuously stretched while dielectrically heating a crystalline polymer in combination with external heating. A stretching method is disclosed.

  In this document, by using dielectric heating for the amorphous part and using external heating for the crystal part, the fiber can be effectively stretched to achieve high fiber modulus.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 62-152720) discloses a production method for obtaining a polyvinyl alcohol molded article having high strength and high elastic modulus. In this production method, microwave heating is used. Then, when stretching the polyvinyl alcohol molded article, using microwave heating at a stretching temperature of 160 ° C. or less, stretching to a stretching ratio of 8 times, further using microwave heating at a stretching temperature of 170-210 ° C., It is necessary to stretch the draw ratio to at least 15 times or more.

JP 58-109651 A Japanese Patent Laid-Open No. 62-152720

However, in both methods of Patent Documents 1 and 2, it is necessary to increase the crystallinity of the entire fiber in order to increase the strength and elastic modulus of the fiber and the molded product. However, when the crystallinity of the fiber is increased, the fatigue resistance of the fiber is lowered due to this, so that such a fiber cannot be used for applications requiring fatigue resistance. That is, the strength and fatigue resistance of the fiber are inherently incompatible properties, and it is very difficult to achieve both.
Moreover, in these methods, since the heat treatment time becomes long, not only the process time becomes long but also the production cost is regarded as a problem.

Accordingly, an object of the present invention is to provide a PVA fiber having a practical strength despite its low crystallinity and excellent fatigue resistance.
Another object of the present invention is to provide a PVA fiber that not only has practical strength but also has excellent solubility in water.
Another object of the present invention is to provide a method for efficiently producing a fiber having such characteristics in a short time.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have surprisingly been able to perform a specific drawing treatment, that is, dielectric heating, on the spinning yarn obtained by spinning the PVA polymer. And using a combination of stretching processes in a very short time, (ii) the degree of crystallinity of the fiber is (ii) despite the fact that the fiber orientation can be improved by increasing the degree of fiber orientation by stretching. The present invention has been completed by finding that it can be maintained at the same level as before stretching, and (iii) such fibers have both the strength and fatigue resistance of the fibers.

  That is, the present invention is a polyvinyl alcohol fiber (PVA fiber) having a crystallinity of 55% or less and a strength of 5 cN / dtex or more. For example, the degree of orientation of the fiber may be 90% or more, the degree of swelling may be 90% or more, and the dissolution temperature in water may be 60 to 100 ° C.

The present invention also includes a method for producing such a PVA fiber, and the method includes a spinning step of spinning a spinning stock solution containing a PVA polymer to prepare a spinning raw yarn, and the spinning raw yarn comprising: A stretching step of stretching at a stretching ratio of 3 to 15 times under a microwave output under a microwave heat treatment time of 0.1 second or less;
Is included.

  The spinning step can be performed by a known or conventional method, but it is preferable to perform spinning by dry spinning or semi-melt spinning. Moreover, it is preferable that the extending | stretching process under a microwave output is performed by one step extending | stretching.

  According to the present invention, by using a microwave and performing heat treatment in an extremely short time of 0.1 seconds or less and stretching, the film has high strength despite low crystallinity and is resistant to fatigue. An excellent PVA fiber can be obtained. And since such a fiber originates in crystallinity and is excellent in fatigue resistance, it can achieve coexistence with intensity | strength and fatigue resistance.

  Moreover, in the PVA fiber which has solubility in water, since both strength and solubility can be achieved, it can be effectively used as a binder fiber.

  Further, in the present invention, since the drawing can be performed in an extremely short processing time as compared with the conventional drawing method, the process time can be shortened and the manufacturing cost can be reduced.

It is a schematic diagram which shows an example of the extending | stretching process used for this invention.

Hereinafter, the present invention will be described in detail.
The PVA fiber of the present invention can be produced by performing specific drawing on a spinning yarn obtained by spinning a PVA polymer.

(PVA polymer)
The PVA-based polymer is not particularly limited as long as it has a vinyl alcohol unit as a main component, and may have other constituent units (modified units) as desired as long as the effects of the present invention are not impaired. . Examples of such a structural unit include ethylene, vinyl acetate, itaconic acid, vinylamine, acrylamide, vinyl pivalate, maleic anhydride, and a sulfonic acid-containing vinyl compound. These denaturing units can be used alone or in combination. Such a modified unit may be introduced by copolymerization or post-reaction.

  The ratio (molar ratio) of the modified unit to the vinyl alcohol unit is, for example, (vinyl alcohol unit) / (modified unit) = about 85/15 to 100/0, preferably about 88/12 to 100/0, more preferably It may be about 90/10 to 100/0. Of course, as long as the effect of the present invention is not impaired, the polymer may contain additives such as an antioxidant, an antifreezing agent, a pH adjusting agent, a hiding agent, a coloring agent, and an oil according to the purpose. Good. These additives may be included alone or in combination.

  The average degree of polymerization of the PVA polymer constituting the PVA fiber can be appropriately selected according to the purpose and is not particularly limited. However, considering the mechanical properties and dimensional stability of the resulting fiber, The average degree of polymerization determined from the viscosity is preferably about 500 to 4000, more preferably about 1000 to 3500, and still more preferably about 1300 to 3000. If the average degree of polymerization is too high, it is excellent in terms of mechanical properties, but crystallinity is high, fatigue resistance may be impaired, and water-soluble properties such as large shrinkage during dissolution may be impaired. is there. On the other hand, if the average degree of polymerization is too low, the crystallinity is lowered, thereby not only insufficient mechanical properties, but also the fiber is likely to be stuck due to polymer elution during the fiber production process.

  Further, the degree of saponification of the PVA polymer can be appropriately selected according to the purpose and is not particularly limited. However, from the viewpoint of crystallinity of the obtained fiber, for example, 88 mol% or more, preferably 95 mol% or more. More preferably, it may be 98 mol% or more. If the degree of saponification of the PVA polymer is too low, the crystallinity is extremely lowered, which is preferable in terms of imparting fatigue resistance and water solubility at low temperatures. This is not preferable in terms of manufacturing cost.

(Method for producing PVA fiber)
The PVA fiber is prepared by spinning a spinning stock solution containing the PVA polymer to prepare a spinning raw material, and the spinning raw material is processed in a microwave output under a processing time of 0.1 second or less at a draw ratio of 3 It can be obtained by a production method including at least a stretching step of stretching by 15 times.

First, in the spinning process, a spinning stock solution in which a PVA polymer is dissolved in a solvent is prepared.
As the solvent for the spinning dope, various polar solvents can be used, for example, water, organic solvents [sulfoxides such as dimethyl sulfoxide (hereinafter referred to as DMSO); nitrogen such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, etc. Containing polar solvent; polyhydric alcohols such as glycerin and ethylene glycol] and the like. These solvents can be used alone or in combination. Of these, water is preferable from the viewpoints of availability and impact on the environmental load.

  The polymer concentration in the spinning dope varies depending on the composition, degree of polymerization, solvent, and spinning method, but is preferably about 30 to 65% by weight, and more preferably about 35 to 60% by weight. Moreover, as long as the effect of the present invention is not impaired, the spinning dope includes an antioxidant, an antifreezing agent, a pH adjuster, a concealing agent, a colorant, an oil agent, etc., depending on the purpose, in addition to the PVA polymer. The additive may be included.

  The obtained spinning dope can be spun by a known or conventional spinning method such as wet spinning, dry spinning, semi-melt spinning, etc. Among these, the dry spinning method or the semi-melt spinning method is preferably used. In dry spinning, the spinning solution is discharged in air or in an inert gas, and in semi-melt spinning, a semi-molten PVA polymer is discharged from the nozzle into the air or an inert gas. Of these, dry spinning is particularly preferable from the viewpoint of reducing the crystallinity.

  Next, the prepared spinning yarn is subjected to a drawing step of drawing at a draw ratio of 3 to 15 times under a microwave output with a heat treatment time of 0.1 seconds or less.

  Hereinafter, the stretching process will be described with reference to FIG. FIG. 1 is a schematic view showing one embodiment of a PVA fiber drawing step in the present invention. The delivery bobbin 1 is wound with the spinning yarn of the PVA polymer obtained in the spinning process. Then, the spinning raw yarn is fed from the feed bobbin 1 by the feed roller 2, and then introduced into the microwave heating device 3.

  The microwave heating device 3 is particularly limited as long as the introduced spinning yarn can pass through and the spinning yarn introduced in the device can be irradiated with microwaves under predetermined conditions. Instead, it is possible to use a known or conventional microwave heating apparatus.

  In the microwave heating device 3, the spinning yarn is heated in a very short time of a processing time of 0.1 second or less, and then the heated and drawn raw yarn passes through the winding roller 4 to the winding bobbin 5. Rolled up. The draw ratio of the spinning yarn can be determined by adjusting the roller speed between the feed roller 2 and the take-up roller 4.

  The output of the microwave can be appropriately set according to the amount of spinning yarn and the processing time, and can be selected from a wide range of 100 to 7500 W, for example, preferably 300 to 2000 W. In this embodiment, the microwave heating device 3 uses a single mode applicator having a predetermined transmission frequency (2450 MHz) and a maximum output of 1.5 kW. If necessary, a plurality of microwave heating devices can be used in series (that is, in the yarn traveling direction) in accordance with the microwave heating conditions of various fibers.

  The draw ratio is not particularly limited as long as the PVA fiber of the present invention can be obtained. For example, it may be 3 to 15 times, preferably 4 to 13 times, more preferably about 4 to 10 times. May be.

  The heating time needs to be 0.1 second or less, more preferably 0.08 second or less. The notable point of the present invention is that microwave heating is performed in such an extremely short time, and thus the fiber strength is 5 cN while the crystallinity is low crystallinity that is substantially unchanged from that before stretching. Among the general-purpose fibers of at least / dtex, the fibers have high strength properties.

  In addition, as long as the PVA fiber of this invention can be obtained, you may provide various addition means (for example, external heating means) in the manufacturing method of PVA fiber, However, In the said manufacturing method, it is extremely using a microwave. Since the heat treatment is performed for a short time, the spinning yarn can be drawn without using external heating.

  In the method for producing a PVA fiber of the present invention, as long as a predetermined PVA fiber can be produced, even if it is a single-stage stretching, it is a multi-stage stretching (for example, a two-stage stretching) in which a stretching process is performed multiple times. There may be. In the present invention, since a sufficient amount of stretching can be performed by one-stage stretching using a microwave, it is preferable that the stretching process is performed by one-stage stretching from the viewpoint of production efficiency.

  In the case of multi-stage stretching, it is preferable to perform stretching by setting the stretching ratio in the subsequent stage to be lower than the stretching ratio in the preceding stage, and performing stretching by lowering the stretching ratio as the subsequent stretching process is performed. .

(PVA fiber)
The PVA fiber of the present invention obtained by the above production method needs to have a crystallinity of 55% or less, preferably 53% or less, more preferably 50% or less. When the crystallinity of the PVA fiber is higher than 55%, the fatigue resistance of the fiber is lowered. Further, the lower limit of the crystallinity depends on the crystallinity of the spinning yarn of the PVA fiber, but may be about 40%, for example. The crystallinity here is a value measured by the method described in Examples described later.

  The fiber strength of the PVA fiber is required to be 5 cN / dtex or more, and preferably 7 cN / dtex or more. When the fiber strength is less than 5 cN / dtex, it is impossible to develop into a use in which fatigue resistance, which is an object of the present invention, is required performance. The strength of the PVA fiber is preferably as high as possible from a practical viewpoint, but is often 15 cN / dtex or less in view of the crystallinity. The fiber strength here is a value measured by the method described in Examples described later.

  The PVA fiber can be used in any form such as monofilament, multifilament, cut fiber, spun yarn, fabric (nonwoven fabric, woven or knitted fabric), and may be used in combination with other fibers or other materials. The single fiber fineness of the PVA fiber can be set to various values depending on the application, and can be selected from a wide range of 0.1 to 10000 dtex. For example, when used for fatigue resistance Is preferably about 1 to 500 dtex, and preferably about 2 to 100 dtex.

  The degree of orientation of the PVA fiber is preferably 90% or more, and more preferably 95% or more, from the viewpoint of exhibiting strength even when the crystallinity of the PVA fiber is low. In addition, the orientation degree here is a value measured by the method described in the Example mentioned later.

  Moreover, since the degree of crystallinity of the PVA fiber is low, the degree of swelling is high, and the degree of swelling of the PVA fiber may be 90% or more, preferably 100% or more. The degree of swelling here is a value measured by the method described in Examples described later.

  In addition, in the PVA fiber, the dissolution temperature in water may be, for example, about 60 to 100 ° C., and preferably about 70 to 90 ° C., due to its crystallinity. The dissolution temperature in water here is a value measured by the method described in Examples described later.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In the following examples, each physical property value is measured by the following method.

[Fiber strength cN / dtex]
In accordance with JIS L1013, measurement was performed under the conditions of a test length of 20 cm, an initial load of 0.09 cN / dtex, and a tensile speed of 10 cm / min, and an average value of 5 or more points was adopted.

[PVA fiber crystallinity%]
The measurement regarding crystallinity was performed with the measuring apparatus and measuring method as described below.
Measuring device: X-ray diffractometer with two-dimensional detector “D8 Discover with GADDS” manufactured by Bruker AXS
X-ray source: CuKα ray λ = 0.15418 nm
Detector: HiSTAR (two-dimensional PSPC)
Sample setting method: In order to obtain information on the equator line direction, set the yarn vertically. Incident X-ray: Set the goniometer ω angle to 11 ° to be 11 ° Detector position: 2θ = 22 °
Tube voltage: 45kV
Current: 110 mA
Collimator diameter: 0.5mm
Camera distance: 15cm
Exposure time: 300 sec.

The two-dimensional image obtained by the above method was converted into an X-ray diffraction intensity curve by the following method.
Data conversion software: “Bruker Analytical X-ray Systems GADDS for WNT 4.1.23” manufactured by Bruker AXS
2θ range: 5 ° to 38 °
χ range: -150 ° to -30 °
Step width: 0.02 °
Strength normalization method: “Bin normalized”.

  The obtained X-ray diffraction intensity curve was subjected to peak separation by the following curve fitting method, and the crystallinity was determined by the procedure described below. The software used for the analysis was manufactured by MDI: JADE Ver. The profile fitting model was Pseudo-Voigt, and the fitting function was Gauss + Lorentz function.

i) Connect the diffraction intensity of 2θ = 5 ° and the diffraction intensity of 2θ = 38 ° with a straight line to obtain a baseline.
ii) As an amorphous peak, an asymmetric peak is set around 2θ = 18 °. The shape constant = 0.35, the asymmetry = −0.6, and the half width = 9, and the height is adjusted so as to be in contact with the actual measurement curve in the vicinity of 2θ = 15 ° to 17 ° and 30 ° to 35 °.
iii) As crystal peaks, symmetrical peaks are set at 2θ = 11.5 °, 16 °, 20 °, 23 °, 28 °, and 32 °, and the height, half width, and shape constant are variable. To fit.
iv) Fitting with the amorphous peak height, half width, shape constant, and asymmetry being variable.
v) Fitting each peak and 2θ as variable.
vi) Repeat the above steps iii) to v) for fitting.

The crystallinity was calculated from the area (Aa) of the amorphous peak and the area (Ac) of the crystal peak obtained by i) to vi) by the following formula.
Crystallinity (%) = Ac / (Aa + Ac) × 100

[Orientation degree of PVA fiber%]
The measurement regarding the degree of orientation was performed by the measuring apparatus and measuring method described below.
Measuring device: X-ray diffractometer with two-dimensional detector “D8 Discover with GADDS” manufactured by Bruker AXS
X-ray source: CuKα ray λ = 0.15418 nm
Detector: HiSTAR (two-dimensional PSPC)
Sample setting method: Set the thread sideways to obtain meridian direction information. Incident X-ray: Set the goniometer ω angle to 37 ° to be 37 ° Detector position: 2θ = 74 °
Tube voltage: 45kV
Current: 110 mA
Collimator diameter: 0.5mm
Camera distance: 10cm
Exposure time: 300 sec.

The two-dimensional image obtained by the above method was converted into an X-ray diffraction intensity curve in the azimuth direction by the following method.
Data conversion software: “Bruker Analytical X-ray Systems GADDS for WNT 4.1.23” manufactured by Bruker AXS
2θ range: 74 ° to 76 °
χ range: −114 ° to −64 °
Step width: 0.1 °
Strength normalization method: “Bin normalized”.

The half width (w) was obtained from the peak obtained by the above method, and the degree of orientation was calculated by the following formula.
Degree of orientation (%) = (180−w) / 180 × 100

[Swelling degree%]
The fiber was cut to about 1 cm and immersed in water at 30 ° C. for 30 minutes. Thereafter, the fibers were collected by filtration, subjected to centrifugal dehydration for 10 minutes with a centrifuge at a rotation speed of 3000 rpm, and the weight (A) was measured. The dehydrated fiber was left in a dryer at 105 ° C. for 4 hours, completely dried, and the weight (B) was measured. The degree of swelling was calculated by the following formula.
Swelling degree (%) = {weight (A) −weight (B)} / weight (B) × 100

[Solution temperature in water ℃]
A test piece with a weight of 0.9 gf / 500 dtex attached to a PVA fiber tow with a test length of 5 cm was suspended in 500 cc of water (20 ° C.), and the temperature was increased at a rate of temperature increase of 1 ° C./min. The temperature when the fiber was melted was measured as the dissolution temperature in water.

[Example 1]
(1) As a material, a PVA polymer having a polymerization degree of 1780 and a saponification degree of 99.9 mol% was prepared to a concentration of 40%, and a spinning original yarn of PVA fiber was obtained by dry spinning.
(2) A spinning yarn (hereinafter referred to as undrawn yarn) of the PVA fiber (14720 dtex / 213 filament) obtained in (1) above was used as a microwave heating device (transmitting frequency: 2450 MHz, maximum output: 1.5 kW) ), A microwave output of 550 W, a yarn input speed of 30 m / min, a winding speed of 210 m / min, and a heat treatment time of 0.06 seconds. The obtained drawn yarn had a crystallinity of 49%, a fiber strength of 7 cN / dtex, an orientation degree of 95%, a swelling degree of 125%, and a dissolution temperature in water of 77 ° C. This drawn yarn not only has a strength to withstand practical use, but also has excellent fatigue resistance due to its low crystallinity. Moreover, it not only has a high degree of swelling, but also has solubility in warm water.

[Example 2]
The same unstretched yarn of PVA fiber and microwave heating apparatus as in Example 1 were used. The unstretched PVA yarn was drawn under a drawing condition with a microwave output of a microwave heating device of 1800 W, a yarn input speed of 100 m / min, a winding speed of 800 m / min, and a treatment time of 0.02 seconds. The obtained drawn yarn had a crystallinity of 49%, a fiber strength of 9 cN / dtex, an orientation of 96%, a swelling degree of 126%, and a dissolution temperature in water of 73 ° C. This drawn yarn not only has a strength to withstand practical use, but also has excellent fatigue resistance due to its low crystallinity. Moreover, it not only has a high degree of swelling, but also has solubility in warm water.

[Example 3]
The same unstretched yarn of PVA fiber and microwave heating apparatus as in Example 1 were used. The unstretched PVA yarn was stretched under stretching conditions with a microwave output of a microwave heating device of 1600 W, a yarn entry speed of 90 m / min, a winding speed of 900 m / min, and a treatment time of 0.02 seconds. The obtained drawn yarn had a crystallinity of 49%, a fiber strength of 10 cN / dtex, an orientation of 96%, a swelling degree of 91%, and a dissolution temperature in water of 79 ° C. This drawn yarn not only has a strength to withstand practical use, but also has excellent fatigue resistance due to its low crystallinity. Moreover, it not only has a high degree of swelling, but also has solubility in warm water.

[Comparative Example 1]
When unstretched yarn similar to Example 1 was used and stretched at a furnace length of 2.5 m and a hot air oven at a temperature of 235 ° C. with an input speed of 2 m / min, a winding speed of 24 m / min, and a treatment time of 35 seconds, The obtained drawn yarn had a fiber strength of 8.5 cN / dtex, but had a high crystallinity of 65%. Further, the orientation degree of the drawn yarn was 94%, the swelling degree was 12%, and the dissolution temperature in water was 120 ° C. Since this drawn yarn has a high degree of crystallinity, it is inferior in fatigue resistance.

[Comparative Example 2]
When the same undrawn yarn as in Example 1 was used and drawn at a furnace length of 3 m, a plate temperature of 235 ° C., an input speed of 5 m / min, a winding speed of 60 m / min, and a treatment time of 16 seconds, the obtained drawn yarn was The fiber strength was 8.9 cN / dtex, but the crystallinity was as high as 66%.

[Comparative Example 3]
Using the same undrawn yarn as in Example 1, the PVA undrawn yarn was subjected to microwave output of a microwave heating apparatus (transmitting frequency: 2450 MHz, maximum output: 1.5 kW) at 600 W, yarn input speed of 30 m / min, Drawing was performed under a drawing condition with a winding speed of 180 m / min and a treatment time of 0.1 second. The obtained drawn yarn was further drawn at a draw ratio of at least 10 times with a microwave output of 600 W by the above microwave heating apparatus. Was 2 cN / dtex, the degree of orientation was 90%, the degree of swelling was 53%, and the dissolution temperature in water was 96 ° C.

  This is because the yarn stretched at a draw ratio of 6 times under microwave heating was further subjected to two-stage drawing at a draw ratio of 10 times or more under microwave heating, resulting in structural breakage of the fibers. It is thought that this led to an extreme decrease in strength.

  The PVA fiber of the present invention can be used for many applications. For example, the PVA fiber obtained by the present invention can be used as a reinforcing material for various materials used as a reinforcing material, is lightweight, and is desired to have excellent fatigue resistance even at high temperatures. Applicable to usage. In particular, it is useful for a pressure-resistant layer of an oil brake hose of an automobile or a motorcycle that requires high fatigue resistance at high temperatures and high fiber strength.

DESCRIPTION OF SYMBOLS 1 Sending bobbin 2 Sending roller 3 Microwave heating device 4 Winding roller 5 Winding bobbin

Claims (7)

  A polyvinyl alcohol fiber having a crystallinity of 55% or less and a strength of 5 cN / dtex or more.   The polyvinyl alcohol fiber according to claim 1, wherein the degree of orientation is 90% or more.     The polyvinyl alcohol fiber according to claim 1 or 2, which has a swelling degree of 90% or more.   The dissolution temperature in water is 60 to 100 ° C. The polyvinyl alcohol fiber according to any one of claims 1 to 3. A spinning step of spinning a spinning stock solution containing a polyvinyl alcohol polymer to prepare a spinning stock,
A drawing process in which the spinning yarn is drawn at a draw ratio of 3 to 15 times under microwave output with a microwave heat treatment time of 0.1 second or less,
The manufacturing method of the polyvinyl-alcohol-type fiber containing this.   6. The production method according to claim 5, wherein in the spinning step, spinning is performed by dry spinning or semi-melt spinning.   The production method according to claim 5 or 6, wherein the drawing step under microwave output is performed by one-step drawing.

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