JP5032283B2 - Cleaning method for twin-screw extrusion kneader - Google Patents

Description

  The present invention relates to a cleaning method for a twin-screw extrusion kneader used in the production of an electrophotographic toner used for developing a latent image formed in an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like.

  In recent years, the tendency to color copying machines and printers has been increasing year by year. As a method for producing a color toner, there is a method in which a toner raw material containing a binder resin and a colorant is melt-kneaded using a biaxial extrusion kneader. Conventionally, when manufacturing color toners of different colors using such an apparatus, the inside of the kneading apparatus is cleaned using a cleaning agent in order to avoid mixing the preceding color toner. However, in the conventional method, after washing with a cleaning agent, in order to sufficiently remove the preceding kneaded product, it is necessary to wipe and wash the inner wall and screw of the kneading apparatus with an organic solvent such as acetone. Since the work is performed manually, it is not necessarily a good working environment.

In Patent Document 1, when the resin composition supplied to the resin kneading apparatus is switched from the high viscosity thermoplastic resin composition to the low viscosity thermoplastic resin composition, the low viscosity thermoplastic resin is extruded after the high viscosity thermoplastic resin composition is extruded. A method of cleaning a resin kneading device by supplying cleaning agents having different melt viscosities step by step into the resin kneading device in order from the highest viscosity before extrusion of the resin composition is disclosed.
JP 2004-17364 A

  However, even if the cleaning method of Patent Document 1 is applied to cleaning a twin-screw extrusion kneading apparatus for melting and kneading a toner raw material containing a binder resin and a colorant, the inner wall of the kneading apparatus can be sufficiently cleaned. Therefore, it is impossible to prevent the mixing of the preceding kneaded product, the decrease in productivity due to the wiping cleaning, and the deterioration of the working environment.

  An object of the present invention is to provide a cleaning method for a twin-screw extrusion kneading apparatus that can be used for the production of color toners, which does not require a complicated post-operation such as wiping and cleaning with an organic solvent, and does not contain the preceding kneaded product. Is to provide.

The present invention relates to a cleaning method for a twin screw extrusion kneader for melt kneading a toner material containing a binder resin and a colorant, and the storage elastic modulus at 180 ° C. is 1.0 × 10 ^{4 to} 4.0 × 10 ⁴ Pa. A cleaning resin composition having a higher storage elastic modulus than the cleaning resin composition used in the first cleaning step after the first cleaning step and the first cleaning step of cleaning the inside of the kneading apparatus using the cleaning resin composition The present invention relates to a cleaning method for a twin-screw extrusion kneader including a second cleaning step for cleaning the inside of the kneader.

  According to the cleaning method of the present invention, the preceding kneaded product can be easily removed from the twin-screw extrusion kneader without performing complicated post-operation such as wiping cleaning with an organic solvent. The twin-screw extrusion kneading apparatus cleaned by the method of the present invention can be suitably used for the production of color toners that require a higher cleaning effect because the mixing of the previous kneaded product has a great influence on the color tone of the toner. .

The present invention is significant in that two types of cleaning resin compositions having different viscosities are used in a specific order when cleaning a twin-screw extrusion kneading apparatus in which a toner raw material containing a binder resin and a colorant is melt-kneaded. Has characteristics. In the present invention, a first cleaning resin composition (hereinafter also referred to as “low viscosity cleaning resin composition”) having a storage elastic modulus at 180 ° C. of 1.0 × 10 ^{4 to} 4.0 × 10 ⁴ Pa, which will be described later, is used. The inner wall of the kneading apparatus and the entire screw can be washed by the washing step, and the washing resin composition has a higher storage elastic modulus than the washing resin composition used in the first washing step (hereinafter also referred to as “high viscosity washing resin composition”). By the second washing step using the kneaded product, the kneaded product fused to the inner wall of the kneading apparatus and the screw can be completely removed together with the extrusion of the high viscosity washing resin composition. The reason why a high cleaning effect can be obtained by the method of the present invention is not clear, but by using a low-viscosity cleaning resin composition, the cleaning resin composition is spread and cleaned to the details of the inner wall of the kneading apparatus, and more firmly melted. About the screw | thread part to which it has worn, it is estimated that a strong share starts in the 2nd washing | cleaning process using a high-viscosity washing resin composition, and the washing | cleaning efficiency in a kneading apparatus further improves.

The first washing step is a step of washing the inside kneading apparatus with a low viscosity cleaning resin composition a storage modulus at 180 ° C. is at ^{1.0 × 10 4 ~4.0 × 10 4} Pa.

The storage elastic modulus of the low-viscosity cleaning resin composition is preferably 1.5 × 10 ^{4 to} 3.0 × 10 ⁴ Pa, more preferably 2.0 × 10 ^{4 to} 3.0 × 10 ⁴ Pa at 180 ° C. from the viewpoint of improving cleaning efficiency. is there.

  The second cleaning step is a step of cleaning the inside of the kneading apparatus using a high viscosity cleaning resin composition having a higher storage elastic modulus than the low viscosity cleaning resin composition used in the first cleaning step. Ratio of storage elastic modulus at 180 ° C. between the cleaning resin composition used in the second cleaning step and the cleaning resin composition used in the first cleaning step (storage elastic modulus at 180 ° C. of the cleaning resin composition used in the second cleaning step / number The storage elastic modulus at 180 ° C. of the cleaning resin composition used in one cleaning step is preferably 1.1 to 20, more preferably 1.2 to 15, and further preferably 1.5 to 10 from the viewpoint of improving the cleaning efficiency.

The storage elastic modulus of the high viscosity cleaning resin composition is preferably 3.3 × 10 ^{4 to} 2.0 × 10 ⁵ Pa, more preferably 3.3 × 10 ^{4 to} 7.0 × 10 at 180 ° C. from the viewpoint of further increasing the cleaning efficiency. ⁴ Pa, more preferably 3.3 × 10 ^{4 to} 6.5 × 10 ⁴ Pa, and still more preferably 3.3 × 10 ^{4 to} 6.0 × 10 ⁴ Pa.

  In the present invention, after the second cleaning step, a third cleaning step of cleaning the inside of the kneading apparatus using a cleaning resin composition having a storage modulus lower than that of the cleaning resin composition used in the second cleaning step may be performed. preferable. Since the clearance between the barrel and the screw is narrow, the screw can be easily pulled out by finishing cleaning with the low viscosity cleaning resin composition.

The storage elastic modulus of the cleaning resin composition used in the third cleaning step is preferably 1.0 × 10 ^{4 to} 4.0 × 10 ⁴ Pa at 180 ° C., similarly to the low viscosity cleaning resin composition used in the first cleaning step. More preferably, it is 1.5 × 10 ^{4 to} 3.0 × 10 ⁴ Pa, and further preferably 2.0 × 10 ^{4 to} 3.0 × 10 ⁴ Pa.

  In the first to third cleaning steps, the cleaning resin composition is cleaned in the kneading apparatus by supplying the cleaning resin composition from the toner material supply port into the apparatus and from the discharge port in the same manner as the melting and kneading of the toner material. It is preferable to carry out extrusion outside the apparatus.

  As a suitable example of the washing method of the present invention, after the extrusion of the preceding melt-kneaded product, the low-viscosity washing resin composition is supplied to the twin-screw extrusion kneader and extruded (first washing step). Then, the high-viscosity cleaning resin composition is supplied into the kneader and extruded (second cleaning step). After the washing, it is preferable to remove the screw and dry the kneading apparatus.

  In each cleaning step, the amount of the cleaning resin composition supplied to the kneading apparatus depends on the capacity of the kneading apparatus.For example, in the case of the twin screw extruder “PCM-43” (manufactured by Ikegai Co., Ltd.), 1 to 20 kg is Preferably, 2 to 10 kg is more preferable.

  In addition, the set temperature of the kneading apparatus in each washing step is preferably 160 to 210 ° C, more preferably 170 to 200 ° C, from the viewpoint of increasing the washing efficiency. The number of rotations of the screw is also preferably 10 to 60 r / min, more preferably 20 to 50 r / min from the viewpoint of increasing the cleaning efficiency.

  As the cleaning resin composition, commonly used cleaning resins can be widely used. Specific examples thereof include styrene resins such as polystyrene, ethylene resins such as polyethylene, propylene resins such as polypropylene, Examples thereof include methyl methacrylate resins such as methyl methacrylate, polyvinyl chloride, polyamide resins, polycarbonates, polybutenes, and the like, and any washing step is not particularly limited as long as the storage elastic modulus is within a predetermined range. In the present invention, those made of an ethylene-based resin such as polyethylene are preferable from the viewpoint of cleaning efficiency.

  Cleaning resin compositions include phenolic, thioether and phosphorus antioxidants, heat stabilizers, light stabilizers, heavy metal deactivators, clearing agents, nucleating agents, lubricants, antistatic agents, Fogging agent, plasticizer, anti-blocking agent, dripping agent, radical generator such as peroxide, flame retardant, flame retardant aid, pigment, halogen scavenger, dispersant, neutralizer, organic and inorganic Antibacterial agent, mica, clay, zeolite, kaolin, bentonite, perlite, diatomaceous earth, silicon dioxide, titanium dioxide, zinc sulfide, barium sulfate, magnesium sulfate, calcium silicate, aluminum silicate, glass fiber, potassium titanate, carbon fiber Various additives such as inorganic fillers such as carbon black and metal fibers, and organic fillers such as wood flour, pulp, synthetic fibers and natural fibers do not impair the purpose of the present invention. It may be contained as appropriate.

Examples of commercially available cleaning resin compositions that can be used in the present invention include, for example, “LioCLEAN-Z” (made by Toyo Ink, polyethylene resin, storage elastic modulus at 180 ° C. as a low-viscosity cleaning resin composition. : 2.2 × 10 ⁴ Pa), “PLACLAIRE” (manufactured by Tokyo Ink Co., polyethylene resin, storage elastic modulus at 180 ° C .: 4.8 × 10 ⁴ Pa) and the like as a high viscosity cleaning resin composition.

  The twin-screw extrusion type kneading apparatus for cleaning by the method of the present invention has a mixture supplied from a raw material supply port engaged with two built-in screws, and a melt-kneaded product discharge port while melt-kneading as the screw rotates. There is no particular limitation as long as it has a mechanism for transporting to a maximum. Examples of the commercially available product include a twin screw extruder “PCM-43” (manufactured by Ikegai Co., Ltd.).

  In the present invention, examples of the binder resin include polyesters, vinyl resins, epoxy resins, polycarbonates, polyurethanes, and the like. Among these, polyesters are preferable because the effects of the present invention can be more remarkably exhibited.

  Polyester is obtained by using a carboxylic acid component and an alcohol component as raw material monomers and subjecting them to condensation polymerization.

  Examples of the alcohol component include polyoxypropylene-2,2-bis (4-hydroxyphenyl) propane and polyoxyethylene-2,2-bis (4-hydroxyphenyl) propane, which are represented by the formula (I):

(In the formula, RO is an oxyalkylene group, R is an ethylene and / or propylene group, x and y represent the number of added moles of alkylene oxide, each being a positive number, and the average of the sum of x and y) The value is preferably 1 to 16, more preferably 1 to 8, and further preferably 1.5 to 4)
Aromatic diols such as alkylene oxide adducts of bisphenol represented by: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6 -Aliphatic diols such as hexanediol, 1,4-butenediol, 1,3-butanediol and neopentyl glycol, and trihydric or higher polyhydric alcohols such as glycerin.

  Examples of carboxylic acid components include oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, etc. Aliphatic dicarboxylic acids; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; trivalent or higher polyvalent carboxylic acids such as trimellitic acid and pyromellitic acid; And anhydrides of these acids, alkyl (1 to 3 carbon atoms) esters; rosins; rosins modified with fumaric acid, maleic acid, acrylic acid, and the like.

  The softening point of the polyester is preferably 80 to 150 ° C, more preferably 85 to 145 ° C, and still more preferably 90 to 145 ° C.

  In the present invention, the polyester may be a polyester modified to such an extent that the characteristics are not substantially impaired. Examples of the modified polyester include grafting and blocking with phenol, urethane, epoxy and the like by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, and the like. And a composite resin having two or more kinds of resin units including a polyester unit.

  As the colorant, all of dyes and pigments used as toner colorants can be used, such as carbon black, phthalocyanine blue, permanent brown FG, brilliant first scarlet, pigment green B, rhodamine-B base, Solvent Red 49, Solvent Red 146, Solvent Blue 35, Quinacridone, Carmine 6B, Isoindoline, Disazo Yellow and the like can be used. The content of the colorant is preferably 1 to 40 parts by weight and more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  The toner material further includes a release agent, charge control agent, magnetic powder, fluidity improver, conductivity modifier, extender pigment, reinforcing filler such as fibrous substance, antioxidant, anti-aging agent, cleaning property Additives such as improvers may be contained as appropriate.

  After melt kneading, the toner can be obtained through known processes such as pulverization and classification.

  The effect of the present invention does not depend on whether the toner raw material is the same or different before and after the cleaning as in the method described in Patent Document 1. Therefore, the cleaning method of the present invention can be applied, for example, to a twin-screw extrusion kneading apparatus used for melt kneading of a color toner raw material in which mixing of the preceding kneaded material greatly affects the color tone of the toner. The present invention can also be applied to a twin-screw extrusion kneading apparatus used for melt kneading when producing a color toner of a plurality of colors while changing the colorant in the toner raw material.

[Softening point of resin]
Using a flow tester (Shimadzu Corporation, CFT-500D), a 1 g sample is heated at a heating rate of 6 ° C / min, and a 1.96 MPa load is applied by a plunger and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. . The amount of plunger drop of the flow tester is plotted against the temperature, and the temperature at which half of the sample flows out is taken as the softening point.

[Glass transition point of resin]
Using a differential scanning calorimeter “DSC210” (manufactured by Seiko Denshi Kogyo Co., Ltd.), the sample was heated to 200 ° C and cooled to 0 ° C at a temperature decrease rate of 10 ° C / min. The temperature of the base line is the temperature at the intersection of the base line extension below the maximum peak temperature of the endotherm and the tangent line indicating the maximum slope from the peak rise to the peak apex.

[Acid value of the resin]
Measured according to the method of JIS K0070. However, only the measurement solvent was changed from the mixed solvent of ethanol and ether specified in JIS K0070 to the mixed solvent of acetone and toluene (acetone: toluene = 1: 1 (volume ratio)).

[Storage elastic modulus of cleaning resin composition]
Measurement is performed using a viscoelasticity measuring device (rheometer) ARES (TA). The measurement equipment conditions are set as follows.

Geometry Type = Parallel Plates (ParaPlate)
Diameter = 25.0 [mm]
Gap = 1.5 to 2.5 [mm]
Read Test Fixture Gap = On
Tool Serial Num = 0000
Tool Inertia = 58.0 [g ・ cm ² ]
Change Gap to Match Tool Thermal Expansion = Off
Tool Thermal Expansion Coefficient = 2.3 [μm / ℃]
Fluid Density = 1.0 [g / cm ³ ]
Fixture Compliance = 0.524 [μrad / g-cm]
------------------------------------
Test Type = Dynamic Temperature Ramp (DTempRamp)
Frequency = 6.28 [rad / s]
Initial Temp. = 200.0 [℃]
Final Temp. = 150.0, 200.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 [℃]
Ramp Rate = 20.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 [℃ / min.]
Computed Ramp Time = 2:30, 10:00, 0, 0, 0, 0, 0, 0 [h: m: s]
Soak Time After Ramp = 300, 0, 0, 0, 0, 0, 0, 0 [s or h: m: s]
Time Per Measure = 24, 12, 0, 0, 0, 0, 0, 0 [s or h: m: s]
Strain = 0.05, 0.05, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 [%]
Computed Test Duration = 17:30 [h: m: s]
Zone Time = 450, 10:00, 0, 0, 0, 0, 0, 0 [s or h: m: s]
Options = ElectroRheology
Steady PreShear = Off
PreShear Mode = Preshear Off
Delay Before Test = Off
Automatically start test when on Temperature = Off
AutoTension Adjustment = On
Mode = Apply Constant Static Force
AutoTension Direction = Compression
Initial Static Force = 10.0 [g]
AutoTension Sensitivity = 10.0 [g]
When Sample Modulus <= 100.0 [Pa]
AutoTension Limits = Default
Max Autotension Displacement = 3.0 [mm]
Max Autotension Rate = 0.01 [mm / s]
AutoStrain = On
Max Applied Strain = 20.0 [%]
Max Allowed Torque = 300.0 [g-cm]
Min Allowed Torque = 1.0 [g-cm]
Strain Adjustment = 20.0 [% of Current Strain]
Strain Amplitude Control = Default Behavior
Limit Minimum Dynamic Force Used = No
Minimum Applied Dynamic Force = 1.0 [gmf]
Measurement Options = Default Delay Settings
Cycles = 0.5
Time = 3 [s or h: m: s]
Correlation: One Cycle Correlate = Off
ElectroRheology Mode = Off
Turn OFF Motor = No
Turn Hold ON = Yes
Turn OFF Temp Controller = No
Set End of Test Temp = Yes
Set End of Test Temp to: = 200.0 [℃]
Oven Air / N2 Switch = Force Air
Dielectric Testing = Off
Steady Stress on Dynamic = 0.0 [Pa]
Analog Data Collection = Off
External Correlation = Off
Measurement Time = 1.0 [s]
Correlation Cycles = 1
Enable External Trigger = Off
Delay before initial trigger = 5.0 [s]
Trigger On Time = 2.0 [s]
Trigger Off Time = 2.0 [s]
Number of On / Off Cycles = 1

Example of resin production 1040 g of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, 10 g of polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane, 199 g of terephthalic acid, and After reacting 4 g of dibutyltin oxide (esterification catalyst) under a nitrogen atmosphere at normal pressure and 230 ° C. for 5 hours, it was further reacted under reduced pressure (70 kPa). The temperature was cooled to 210 ° C., 209 g of fumaric acid and 1 g of hydroquinone were added, reacted for 5 hours, and further reacted under reduced pressure (70 kPa) to obtain Resin A. The obtained resin had a softening point of 107.5 ° C., an acid value of 21.3 mgKOH / g, and a glass transition point of 64.4 ° C.

Production Example 1 of Toner Raw Material Mixture
100 parts by weight of resin A as binder resin, 1 part by weight of charge control agent “Bontron E-81” (manufactured by Orient Chemical Co.), 5 weights of cyan pigment “ECB-301” (manufactured by Dainichi Seika Kogyo Co., Ltd., copper phthalocyanine pigment) Parts and 2 parts by weight of polypropylene wax “NP-055” (manufactured by Mitsui Chemicals) were mixed with a Henschel mixer for 60 seconds to obtain a cyan toner raw material mixture.

Production Example 2 of Toner Raw Material Mixture
A yellow toner raw material mixture was obtained in the same manner as the cyan toner raw material mixture, except that 5 parts by weight of a yellow pigment “Toner Yellow HG” (manufactured by Clariant) was used instead of the cyan pigment as the colorant.

Example 1
40 kg of the cyan toner raw material mixture was supplied to a twin-screw extruder “PCM-43” (manufactured by Ikekai Co., Ltd.) in which the temperature of the extruder was set to 100 ° C. and the rotational speed of the screw was set to 100 r / min, and melt kneaded.

After extrusion of the melt-kneaded product, the setting of the extruder temperature was changed to 180 ° C and the screw rotation speed to 20r / min, and the low-viscosity cleaning resin composition "LIOCLEAN-Z" (Toyo Ink Co., Ltd.) Manufactured, storage elastic modulus at 180 ° C .: 2.2 × 10 ⁴ Pa) 5 kg was supplied to the extruder and extruded (first washing step).

Next, the setting of the temperature of the extruder and the number of rotations of the screw is left as they are, and the high viscosity cleaning resin composition “PLACLAIRE” (manufactured by Tokyo Ink Co., Ltd., storage elastic modulus at 180 ° C .: 4.8 × 10 ⁴ Pa ) 5 kg was supplied to the extruder and extruded (second washing step).

  After washing, the screw was taken out and the inside of the extruder was wiped dry.

  Subsequently, the setting of the extruder temperature was changed to 100 ° C. and the rotation speed of the screw was changed to 100 r / min, and 40 kg of the yellow toner raw material mixture was supplied and melt-kneaded.

  The content of copper contained in the obtained melt-kneaded product was measured with a fluorescent X-ray analyzer “ZSX100e” (manufactured by Rigaku Corporation). Copper in the melt-kneaded material is derived from copper phthalocyanine used as a cyan pigment in the cyan toner raw material mixture. The higher the copper content, the more cyan toner raw material mixture remains after washing. Indicates. The measurement conditions are shown below.

  Using a fluorescent X-ray analyzer “ZSX100e” (manufactured by Rigaku Corporation), the X-ray intensity is measured under the following conditions, and the copper content (ppm) in the measurement sample is calculated.

1) Put about 1.5g of toner into a sample vinyl ring (diameter: 32mm, length: 5mm) and press form with a 10-ton press.
2) Excitation conditions Target: Rh
Tube current: 50mA
Tube voltage: 50mV
Primary filter: OUT
3) Optical system conditions Attenuator: 1/1
Slit: COARSE
Spectroscopic crystal: LiF
Detector: SC
Sample mask diameter: 30mmφ
4) Scanning conditions Spectrum: Cu-Kα
Peak (deg): 45.0
Start (deg): 43
End (deg): 47
Step (deg): 0.02
Scan speed (deg / min): 30

Examples 2 to 4 and Comparative Examples 1 and 2
In the same manner as in Example 1, except that a cleaning process using the cleaning resin composition shown in Table 1 was performed between the melt kneading of the cyan toner raw material mixture and the dry wiping in the extruder, a twin screw extruder was used. After washing, the content of copper in the melt-kneaded mixture of the yellow toner raw material mixture was measured. The results are shown in Table 1.

  From the above results, it can be seen that in Examples 1 to 4, the previous melt-kneaded product was completely removed, and an extremely high cleaning effect was obtained. In contrast, in Comparative Example 1 in which the low-viscosity cleaning resin composition is used after the high-viscosity cleaning resin composition and in Comparative Example 2 in which only the low-viscosity cleaning resin composition is used, the preceding melt-kneaded product is incomplete. I understand that.

  The twin-screw extruder that is cleaned by the method of the present invention is used for the production of toner used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, and the like.

Claims (5)

A cleaning method for a twin-screw extrusion kneader for melting and kneading a toner raw material containing a binder resin and a colorant, and having a storage elastic modulus at 180 ° C. of 1.0 × 10 ^{4 to} 4.0 × 10 ⁴ Pa First cleaning step for cleaning the inside of the kneading apparatus using the composition, and after the first cleaning process, the inside of the kneading apparatus using a cleaning resin composition having a higher storage elastic modulus than the cleaning resin composition used in the first cleaning process A cleaning method for a twin-screw extrusion kneader including a second cleaning step for cleaning   Ratio of storage elastic modulus at 180 ° C. between the cleaning resin composition used in the second cleaning step and the cleaning resin composition used in the first cleaning step (storage elastic modulus at 180 ° C. of the cleaning resin composition used in the second cleaning step / number The washing | cleaning method of Claim 1 whose storage elastic modulus in 180 degreeC of the washing | cleaning resin composition used by 1 washing | cleaning process is 1.1-20.   3. The third washing step of washing the inside of the kneading apparatus with a washing resin composition having a lower storage elastic modulus than the washing resin composition used in the second washing step after the second washing step. Cleaning method.   The cleaning method according to claim 1, wherein the binder resin contains polyester.   The washing | cleaning method in any one of Claims 1-4 whose preset temperature of the twin-screw extrusion-type kneading apparatus in each washing | cleaning process is 160-210 degreeC.