Electromagnetic shielding polyimide film and preparation method thereof

Abstract

The invention discloses a magnetic shielding polyimide film and a preparation method thereof, a polyamide acid solution is prepared from general aromatic diamine monomers and dianhydride monomers, and the polyimide film is prepared from the polyamide acid solution and other additives. The cable has good conductivity, an excellent electromagnetic shielding function and good mechanical performance. The polyimide film can be applied to electromagnetic shielding elements and / or conductive elements, and the preparation method of the polyimide film is simple to operate and can be used for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic shielding polyimide films, in particular to an electromagnetic shielding polyimide film and a preparation method thereof. Background Art

[0002] With the rapid development of the 5G communication market, more and more communication devices and electronic devices have penetrated into every corner of society, providing great convenience for people's daily life.

[0003] While people are enjoying the convenience and comfort of modern life, they are also suffering from increasingly serious harm caused by electromagnetic radiation (electromagnetic radiation refers to the phenomenon of electromagnetic waves generated by the interaction of electric and magnetic fields being emitted or leaked into the air), which has caused a series of social and environmental problems, such as electromagnetic interference between electronic components, electromagnetic information leakage, and harm to the human body caused by electromagnetic waves. Therefore, for the sake of health, data security, and the normal operation of equipment, it is necessary to develop high-performance materials that can absorb or shield electromagnetic waves to eliminate the harm caused by electromagnetic radiation.

[0004] Traditional electromagnetic shielding materials are mostly metal materials containing metal interlayers or doped metal particles. However, metals are expensive, heavy, and easily corroded, and do not meet the requirements of the next generation of electronic components for flexibility, high electromagnetic shielding performance, and lightweight. Therefore, polymer composite materials are used instead of metal-based electromagnetic shielding materials.

[0005] Polyimide film is a type of high-performance polymer with polyimide ring as the main body, which has excellent high temperature resistance, radiation resistance, mechanical properties and solvent resistance. However, due to the insulating properties of polyimide film, it has almost no shielding performance against electromagnetic waves. Therefore, how to build a good conductive network in the polyimide film matrix and give the polyimide film excellent electromagnetic shielding performance has become the top priority for expanding the application of polyimide film in the field of electromagnetic shielding. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a polyimide film with electromagnetic shielding function and a preparation method thereof. The prepared polyimide film has good electromagnetic shielding function.

[0007] In order to solve the above technical problems, the present invention provides a technical solution: a method for preparing an electromagnetic shielding polyimide film, comprising the following steps:

[0008] S1: preparing a polyamic acid resin solution;

[0009] S2: preparing conductive paste;

[0010] S3: adding the conductive paste prepared in S2 to the polyamic acid resin solution and stirring to obtain a modified polyamic acid solution;

[0011] S4: After the polyamic acid solution obtained in S3 is filtered and vacuum degassed, it is evenly squeezed and coated on the surface of a stainless steel belt to form a film;

[0012] S5: The adhesive film obtained in S4 is thermally imidized, and then longitudinally stretched and transversely stretched to obtain a polyimide film having an electromagnetic shielding function.

[0013] Preferably, the polyamic acid resin solution in S1 is prepared by taking an aromatic diamine solution, including mixing and fully dissolving a diamine and a polar aprotic solvent, adding a general aromatic diamine monomer powder under an inert gas atmosphere, stirring at low temperature to form an aromatic diamine solution, taking a general aromatic dianhydride monomer powder, stirring and adding it to the aromatic diamine solution at low temperature and filling it with inert gas protection, and obtaining it through a condensation reaction.

[0014] Preferably, the molar ratio of the diamine to the dianhydride is 1:0.8-1.5; and the polycondensation temperature is -10°C to 10°C.

[0015] Preferably, the general aromatic diamine is one or two of 4,4-diaminodiphenyl ether, p-phenylenediamine, 4,4-diaminodiphenylmethane, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane;

[0016] The general aromatic dianhydride is one or two of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, and 4,4'-(hexafluoroisopropylene) diphthalic anhydride;

[0017] The polar aprotic solvent is one or two of dimethylacetamide, N-methylpyrrolidone and dimethylformamide.

[0018] Preferably, the conductive paste in S2 comprises a conductive filler added into a polar aprotic solvent and uniformly dispersed to prepare a conductive paste.

[0019] Preferably, the conductive filler is one or two of three-dimensional graphene, carbon nanotubes, spiral carbon fibers, and silver nanowires.

[0020] Preferably, a polar aprotic solvent is further added to S3 to adjust and control the viscosity, the viscosity range is 5 Pa·s to 100 Pa·s, and the stirring time is 2 to 4 hours.

[0021] Preferably, the salivation drying temperature in S4 is 150-200° C., and the salivation speed is 3-6 m / min.

[0022] Preferably, the thermal imidization in S5 is carried out by gradient heating at 100-450° C., wherein the ratio of longitudinal stretching is 1:1.1-1.2, and the ratio of transverse stretching is 1:1.1-1.3.

[0023] Another aspect of the invention discloses an electromagnetic shielding polyimide film, comprising a polyamic acid resin solution and a conductive paste, wherein the weight of the conductive filler accounts for 1% to 50% of the weight of the polyimide resin solid, the electromagnetic shielding effect is 70 to 80 dB, and the operating temperature can reach 510°C.

[0024] The advantages of the present invention compared with the prior art are: the polyimide composite film doped with conductive filler provided by the present invention has good electromagnetic shielding performance and mainly realizes electromagnetic shielding in an absorption manner, has good thermal stability and better high temperature resistance and flame retardancy, and the electromagnetic shielding effect reaches a high shielding rate of 70 to 80 dB, and the tolerable working temperature can reach 510°C, and can be applied to electromagnetic shielding elements or conductive elements, and the preparation method of the polyimide composite film is simple to operate and can be mass-produced. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below.

[0026] A polyimide film with electromagnetic shielding function comprises the following raw materials: polyamic acid resin solution and conductive paste.

[0027] The polyamic acid resin solution is prepared by polycondensation of diamine and dianhydride in a polar aprotic solvent.

[0028] The conductive paste is prepared by fully dissolving a conductive filler and a polar aprotic solvent.

[0029] The molar ratio of the diamine to the dianhydride is 1:0.8-1.5, the polycondensation temperature is -10°C-10°C, and the viscosity of the polyamic acid resin solution is 5 Pa·s-100 Pa·s.

[0030] The general aromatic diamine is one or two of 4,4-diaminodiphenyl ether, p-phenylenediamine, 4,4-diaminodiphenylmethane, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane; the general aromatic dianhydride is one or two of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-biphenyl ether dianhydride (ODPA), and 4,4'-(hexafluoroisopropylene) diphthalic anhydride (6FPA); and the polar aprotic solvent is one or two of dimethylacetamide, N-methylpyrrolidone, and dimethylformamide.

[0031] The conductive filler is one or two of three-dimensional graphene, silver nanowires, spiral carbon fibers and carbon nanotubes.

[0032] The weight of the conductive filler accounts for 1% to 50% of the solid weight of the polyimide resin.

[0033] In order to achieve the above object, the present invention provides a polyimide film with electromagnetic shielding function and a preparation method thereof, comprising the following steps:

[0034] In an inert gas atmosphere, a diamine and a polar aprotic solvent are mixed and fully dissolved, a general aromatic diamine monomer powder is weighed, and stirred at low temperature to form an aromatic diamine solution;

[0035] Under the protection of inert gas, a general aromatic dianhydride monomer powder is weighed, and added to the diamine solution in batches under low temperature stirring to obtain a polyamic acid resin solution through low temperature polycondensation;

[0036] Adding a conductive filler into a polar aprotic solvent and dispersing the filler uniformly to prepare a conductive slurry;

[0037] Adding the conductive paste to the polyamic acid resin solution, stirring and dispersing the mixture evenly, to obtain a modified polyamic acid solution, wherein the viscosity of the polyamic acid solution is 5 Pa·s to 100 Pa·s;

[0038] The prepared polyamic acid solution is filtered and vacuum degassed, and then evenly squeezed and coated on the surface of a stainless steel belt to form a film;

[0039] The adhesive film is subjected to thermal imidization, and is longitudinally stretched and transversely stretched to obtain a polyimide film with electromagnetic shielding function.

[0040] The salivation drying temperature is 150-200°C, and the salivation speed is 3-6 m / min.

[0041] The thermal imidization conditions are as follows: a gradient temperature increase at 100 to 450° C., wherein the ratio of longitudinal stretching is 1:(1.1 to 1.2), and the ratio of transverse stretching is 1:(1.1 to 1.3).

[0042] The present invention is further described below in conjunction with embodiments.

[0043] Example 1

[0044] This embodiment provides an electromagnetic shielding polyimide film and a preparation method thereof, and the specific steps are as follows:

[0045] ① Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven at 60°C and dry for 12 hours;

[0046] ② Take 1.2 kg of diaminodiphenyl ether and add it to 12 kg of dimethylacetamide solvent, stir and dissolve it in the reactor for 30 minutes to make the diaminodiphenyl ether completely dissolved, then take 1.55 kg of pyromellitic anhydride and add it under the protection of nitrogen atmosphere, react and stir at a low temperature of 5 ° C for 5 hours to obtain polyamic acid;

[0047] ③ Take 0.145 kg of three-dimensional graphene with a particle size of 40 nm and 0.005 kg of spiral carbon fiber with a particle size of 30 nm, mix them evenly, then add them into the polar aprotic solvent dimethylacetamide, stir them thoroughly for 1 hour at room temperature to prepare a conductive slurry;

[0048] ④ Add the conductive paste to the polyamic acid solution prepared above, stir and disperse for 3 hours to obtain polyamic acid resin, and control the annual of the modified polyamic acid resin to be 70-80 Pa·s;

[0049] ⑤ The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0050] ⑥ The drool-dried composite film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film with electromagnetic shielding function.

[0051] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 15db, the absorption loss is higher than 10db, the reflection loss is about 5db, the tensile strength is 240MPa, and the elongation at break is 80%.

[0052] Example 2

[0053] This embodiment provides an electromagnetic shielding polyimide film and a preparation method thereof, and the specific steps are as follows:

[0054] ① Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven at 60°C and dry for 12 hours;

[0055] ② Take 1.2 kg of diaminodiphenyl ether and add it to 12 kg of dimethylacetamide solvent, stir and dissolve it in the reactor for 30 minutes to make the diaminodiphenyl ether completely dissolved, then take 1.55 kg of pyromellitic anhydride and add it under the protection of nitrogen atmosphere, react and stir at a low temperature of 5 ° C for 5 hours to obtain polyamic acid;

[0056] ③ Take 0.543 kg of three-dimensional graphene with a particle size of 40 nm and 0.017 kg of spiral carbon fiber with a particle size of 30 nm, mix them evenly, then add them into the polar aprotic solvent dimethylacetamide, stir them thoroughly for 1 hour at room temperature to prepare a conductive slurry;

[0057] ④ Add the conductive paste to the polyamic acid solution prepared above, stir and disperse for 3 hours to obtain polyamic acid resin, and control the annual of the modified polyamic acid resin to be 70-80 Pa·s;

[0058] ⑤ The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0059] ⑥ The drool-dried composite film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film with electromagnetic shielding function.

[0060] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 55db, the absorption loss is higher than 40db, the reflection loss is about 15db, the tensile strength is 238MPa, and the elongation at break is 78%.

[0061] Example 3

[0062] This embodiment provides an electromagnetic shielding polyimide film and a preparation method thereof, and the specific steps are as follows:

[0063] ① Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven at 60°C and dry for 12 hours;

[0064] ② Take 1.2 kg of diaminodiphenyl ether and add it to 12 kg of dimethylacetamide solvent, stir and dissolve it in the reactor for 30 minutes to make the diaminodiphenyl ether completely dissolved, then take 1.55 kg of pyromellitic anhydride and add it under the protection of nitrogen atmosphere, react and stir at a low temperature of 5 ° C for 5 hours to obtain polyamic acid;

[0065] ③ Take 0.815 kg of three-dimensional graphene with a particle size of 40 nm and 0.025 kg of spiral carbon fiber with a particle size of 30 nm, mix them evenly, then add them into the polar aprotic solvent dimethylacetamide, stir them thoroughly for 1 hour at room temperature to prepare a conductive slurry;

[0066] ④ Add the conductive paste to the polyamic acid solution prepared above, stir and disperse for 3 hours to obtain polyamic acid resin, and control the annual of the modified polyamic acid resin to be 70-80 Pa·s;

[0067] ⑤ The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0068] ⑥ The drool-dried composite film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film with electromagnetic shielding function.

[0069] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 75db, the absorption loss is higher than 55db, the reflection loss is about 20db, the tensile strength is 236MPa, and the elongation at break is 78%.

[0070] Example 4

[0071] This embodiment provides an electromagnetic shielding polyimide film and a preparation method thereof, and the specific steps are as follows:

[0072] ① Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven at 60°C and dry for 12 hours;

[0073] ② Take 1.2 kg of diaminodiphenyl ether and add it to 12 kg of dimethylacetamide solvent, stir and dissolve it in the reactor for 30 minutes to make the diaminodiphenyl ether completely dissolved, then take 1.55 kg of pyromellitic anhydride and add it under the protection of nitrogen atmosphere, react and stir at a low temperature of 5 ° C for 5 hours to obtain polyamic acid;

[0074] ③ Take 1.083 kg of three-dimensional graphene with a particle size of 40 nm and 0.037 kg of spiral carbon fiber with a particle size of 30 nm, mix them evenly, then add them into the polar aprotic solvent dimethylacetamide, stir them thoroughly for 1 hour at room temperature to prepare a conductive slurry;

[0075] ④ Add the conductive paste to the polyamic acid solution prepared above, stir and disperse for 3 hours to obtain polyamic acid resin, and control the annual of the modified polyamic acid resin to be 70-80 Pa·s;

[0076] ⑤ The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0077] ⑥ The drool-dried composite film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film with electromagnetic shielding function.

[0078] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 80db, the absorption loss is higher than 57db, the reflection loss is about 23db, the tensile strength is 232MPa, and the elongation at break is 70%.

[0079] Example 5

[0080] This embodiment provides an electromagnetic shielding polyimide film and a preparation method thereof, and the specific steps are as follows:

[0081] ① Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven at 60°C and dry for 12 hours;

[0082] ② Take 1.2 kg of diaminodiphenyl ether and add it to 12 kg of dimethylacetamide solvent, stir and dissolve it in the reactor for 30 minutes to make the diaminodiphenyl ether completely dissolved, then take 1.55 kg of pyromellitic anhydride and add it under the protection of nitrogen atmosphere, react and stir at a low temperature of 5 ° C for 5 hours to obtain polyamic acid;

[0083] ③ Take 1.30kg of three-dimensional graphene with a particle size of 40nm and 0.04kg of spiral carbon fiber with a particle size of 30nm, mix them evenly, then add them into the polar aprotic solvent dimethylacetamide, stir them thoroughly for 1h at room temperature to prepare a conductive slurry;

[0084] ④ Add the conductive paste to the polyamic acid solution prepared above, stir and disperse for 3 hours to obtain polyamic acid resin, and control the annual of the modified polyamic acid resin to be 70-80 Pa·s;

[0085] ⑤ The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0086] ⑥ The drool-dried composite film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film with electromagnetic shielding function.

[0087] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 34 db, the absorption loss is higher than 24 db, the reflection loss is about 10 db, the tensile strength is 165 MPa, and the elongation at break is 52%.

[0088] Comparative Example 1

[0089] Place diaminodiphenyl ether and pyromellitic anhydride in a constant temperature and humidity drying oven set at 60°C and dry for 12 hours;

[0090] 1.2 kg of diaminodiphenyl ether was added to 12 kg of dimethylacetamide solvent, and the mixture was stirred and dissolved in a reaction kettle for 30 min to completely dissolve the diaminodiphenyl ether. Then, 1.55 kg of pyromellitic dianhydride was added under nitrogen atmosphere, and the mixture was reacted and stirred at a low temperature of 5 ° C for 5 h to obtain polyamic acid.

[0091] The polyamic acid resin is filtered and vacuum degassed, and the polyamic acid resin is formed into a film under the conditions that the salivation temperature is set to 180-200° C. and the salivation speed is set to 7 m / min.

[0092] The drool-dried film is dehydrated, cyclized and thermally imidized under the condition of a gradient temperature rise of 100 to 450° C., and is longitudinally stretched and transversely stretched. The longitudinal stretching ratio is 1:1.1 and the transverse stretching ratio is 1:1.1 to obtain a polyimide film.

[0093] The electromagnetic shielding effectiveness of the electromagnetic shielding polyimide film obtained in this embodiment is 0, the tensile strength is 245 MPa, and the elongation at break is 83%.

[0094] The basic performance indexes of Examples 1, 2, 3, 4, 5 and Comparative Example 1 were tested, and the results were as follows:

[0095] Table 1 Polyimide film performance test results

[0096]

[0097] It can be seen from the above table that the present invention has good shielding effectiveness when the three-dimensional graphene accounts for 20% to 40% of the total solid content, and the mechanical properties of the electromagnetic shielding composite film have no obvious defects.

[0098] The above descriptions are merely embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure made using the contents of the present invention specification, or directly or indirectly using other related technical fields, are similarly included in the patent protection scope of the present invention.

Claims

1. A method for preparing an electromagnetic shielding polyimide film, characterized in that: The following steps are involved: S1: preparing a polyamic acid resin solution; S2: preparing conductive paste; S3: adding the conductive paste prepared in S2 to the polyamic acid resin solution and stirring to obtain a modified polyamic acid solution; S4: After the polyamic acid solution obtained in S3 is filtered and vacuum degassed, it is uniformly squeezed and coated on the surface of a stainless steel belt to form a film; S5: The adhesive film obtained in S4 is thermally imidized, and then longitudinally stretched and transversely stretched to obtain a polyimide film having an electromagnetic shielding function.

2. The method for preparing an electromagnetic shielding polyimide film according to claim 1, characterized in that: The polyamic acid resin solution in S1 is prepared by taking an aromatic diamine solution, including mixing and fully dissolving a diamine and a polar aprotic solvent, adding a general aromatic diamine monomer powder under an inert gas atmosphere, stirring at low temperature to form an aromatic diamine solution, taking a general aromatic dianhydride monomer powder, stirring at low temperature, adding it into the aromatic diamine solution and filling it with inert gas protection, and obtaining it through a condensation reaction.

3. The method for preparing an electromagnetic shielding polyimide film according to claim 2, characterized in that: The molar ratio of the diamine to the dianhydride is 1:0.8-1.5; and the polycondensation temperature is -10°C-10°C.

4. The method for preparing an electromagnetic shielding polyimide film according to claim 2, characterized in that: The general aromatic diamine is one or two of 4,4-diaminodiphenyl ether, p-phenylenediamine, 4,4-diaminodiphenylmethane, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane; The general aromatic dianhydride is one or two of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, and 4,4'-(hexafluoroisopropylene) diphthalic anhydride; The polar aprotic solvent is one or two of dimethylacetamide, N-methylpyrrolidone and dimethylformamide.

5. The method for preparing an electromagnetic shielding polyimide film according to claim 1, characterized in that: The conductive paste in S2 includes a conductive filler added into a polar aprotic solvent and uniformly dispersed to prepare a conductive paste.

6. The method for preparing an electromagnetic shielding polyimide film according to claim 5, characterized in that: The conductive filler is one or two of three-dimensional graphene, carbon nanotubes, spiral carbon fibers, and silver nanowires.

7. The method for preparing an electromagnetic shielding polyimide film according to claim 1, characterized in that: A polar aprotic solvent is also added to the S3 to adjust and control the viscosity, the viscosity range is 5 Pa·s to 100 Pa·s, and the stirring time is 2 to 4 hours.

8. The method for preparing an electromagnetic shielding polyimide film according to claim 1, characterized in that: The salivation drying temperature in S4 is 150-200° C., and the salivation speed is 3-6 m / min.

9. The method for preparing an electromagnetic shielding polyimide film according to claim 1, characterized in that: The thermal imidization in S5 is specifically carried out by gradient heating at 100-450° C., wherein the ratio of longitudinal stretching is 1:1.1-1.2, and the ratio of transverse stretching is 1:1.1-1.

3.

10. An electromagnetic shielding polyimide film, characterized in that: The invention comprises a method for preparing an electromagnetic shielding polyimide film using any one of claims 1 to 9, wherein the electromagnetic shielding polyimide film comprises a polyamic acid resin solution and a conductive paste, wherein the weight of the conductive filler accounts for 1% to 50% of the solid weight of the polyimide resin, the electromagnetic shielding effect is 70 to 80 dB, and the operating temperature reaches 510°C.

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