A halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance

Abstract

The present invention relates to a halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance. The hydrolysis-resistant halogen-free flame-retardant reinforced polyester composite material of the present invention comprises a polyester resin, alkali-free glass fiber, a halogen-free flame retardant, an anti-hydrolysis agent, a buffer, an antioxidant, and a lubricant. The alkali-free glass fiber can improve the mechanical strength and impact resistance of the material. The hydrolysis-resistant halogen-free flame retardant, the anti-hydrolysis agent, and the buffer work together to obtain a polyester composite material with high hydrolysis resistance. The flame retardancy meets the UL-94 standard 0.4mm V-0 rating, and after storage in an 85°C / 85% RH environment for 2000 hours, the tensile strength retains 70%.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance. Background Art

[0002] Polyester resin is a general term for polymer compounds formed by the condensation of diols, dibasic acids, or polyols and polyacids. Polyesters represented by polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT) have excellent properties and are widely used in packaging, electronics, medical care, construction, automobiles and other fields.

[0003] However, polyester materials generally have a disadvantage: they are prone to hydrolysis, which leads to a significant reduction in the service life of polyester products and a significant reduction in the overall performance of the products. Polyester molecular chains contain a large number of ester bonds and terminal carboxyl groups. Under the action of the terminal carboxyl groups, the ester bonds are easily eroded by water or moisture. Especially in high temperature and high humidity environments, the ester bonds easily react with water, resulting in molecular chain breakage and a decrease in molecular weight. It can be seen that there are two main factors that lead to polyester hydrolysis: one is water molecules and the other is the terminal carboxyl groups. Therefore, reducing the water absorption rate (water content) and the terminal carboxyl group content of polyester can effectively enhance its anti-hydrolysis effect. The method currently commonly used is to consume the terminal carboxyl groups in the polyester by adding carbodiimide anti-hydrolysis agents or resins containing epoxy groups, inhibiting the hydrolysis reaction, thereby improving the overall performance and service life of the polyester.

[0004] For example, Chinese invention patent application number 102838850B discloses a method for preparing a hydrolysis-resistant PBT resin. Its composition is: 96% PBT, 3% polycarbodiimide, and 1% antioxidant. The -NCO groups in the polycarbodiimide react with the terminal carboxyl groups in the PBT resin, thereby improving hydrolysis resistance. Chinese invention patent application number 104583290A discloses a method for preparing a melt-stable and hydrolysis-resistant polyester composition. Its composition is: 40-89% polyester resin, 10-50% glass fiber, 0.5-5% hydroxyapatite, 0.5-4% epoxy resin, and 0.5-15% toughening agent. The resulting composition exhibits excellent hydrolysis resistance and maintains stable melt viscosity. Chinese invention patent application number 106832810A discloses a hydrolysis-resistant polyester and its preparation method. The polyester composition comprises 30-99% polyester resin and 1-70% boehmite (γ-AlOOH). This invention avoids the use of carbodiimide additives, is safe and environmentally friendly, exhibits excellent hydrolysis resistance, and maintains good mechanical properties after aging.

[0005] However, research on the hydrolysis resistance of flame-retardant reinforced polyester resins is currently limited. Typically, the introduction of flame retardants degrades the hydrolysis resistance of polyester resins. Conventional methods of improving hydrolysis resistance by adding carbodiimides and epoxies have little effect on flame-retardant systems. Therefore, the present invention provides a method for improving the hydrolysis resistance of flame-retardant reinforced polyester systems with high application value. Summary of the Invention

[0006] The purpose of the present invention is to provide a halogen-free flame retardant reinforced polyester composite material with high hydrolysis resistance in order to solve the problems existing in the prior art.

[0007] The hydrolysis-resistant halogen-free flame-retardant reinforced polyester composite material of the present invention comprises polyester resin, alkali-free glass fiber, halogen-free flame retardant, anti-hydrolysis agent, buffer, antioxidant and lubricant, wherein the alkali-free glass fiber can improve the mechanical strength and impact resistance of the material, achieving a tensile strength of more than 105MPa and a notched impact strength of ≥7kJ / m 2 In flame-retardant systems, a single anti-hydrolysis agent provides minimal improvement in hydrolysis resistance. While the present invention utilizes epoxy resin or carbodiimide-based anti-hydrolysis agents to enhance the material's hydrolysis resistance, the addition of reactive anti-hydrolysis agents increases the material's melt viscosity, severely impacting its fluidity and hindering subsequent processing. The addition of a buffer, on the one hand, absorbs acidic substances in the material, maintaining the pH near neutral and slowing acidic hydrolysis. On the other hand, it addresses the increased melt viscosity caused by the addition of an anti-hydrolysis agent, while maintaining stable melt viscosity and imparting stable processing properties.

[0008] The synergistic effect of a hydrolysis-resistant halogen-free flame retardant, an anti-hydrolysis agent, and a buffer is combined to obtain a polyester composition composite material with high hydrolysis resistance. The flame retardancy has a UL-94 standard 0.4mm V-0 rating, and after storage in an 85°C / 85% RH environment for 2000 hours, the tensile strength has a retention rate of 70%.

[0009] The purpose of the present invention can be achieved by the following solutions:

[0010] The present invention provides a halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance. The halogen-free flame-retardant reinforced polyester composite material comprises the following components in parts by weight:

[0011]

[0012] The polyester resin comprises one of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT), preferably PBT. The polyester resin has a terminal carboxyl content of less than 30 mol / t, preferably less than 20 mol / t, and more preferably less than 15 mol / t. The polyester resin is prepared by a direct esterification method.

[0013] The halogen-free flame retardant is a phosphorus-nitrogen-based flame retardant, prepared by compounding melamine polyphosphate and an alkyl phosphinate in a mass ratio of 2-2.5:1. The alkyl phosphinate includes one or more of methylethyl aluminum hypophosphite, diethyl aluminum hypophosphite, dipropyl aluminum hypophosphite, and isobutyl aluminum hypophosphite; dipropyl aluminum hypophosphite is preferred, and diethyl aluminum hypophosphite is more preferred. The flame retardant in the present invention uses a high-purity, low-ion-precipitation phosphorus-nitrogen-based halogen-free flame retardant, which can reduce the decomposition and precipitation of acidic substances during the damp-heat aging process.

[0014] The glass fiber is an alkali-free hydrolysis-resistant glass fiber surface treated with a coupling agent, and its diameter is preferably 11-15 μm, preferably 15-30 parts; the coupling agent includes one or more of aminosilane, epoxysilane, methacryloxysilane, and monoalkoxy titanate coupling agent.

[0015] The anti-hydrolysis agent includes one or more of an epoxy resin containing epoxy groups and a carbodiimide, preferably in an amount of 0.4 to 1 part. The epoxy component of the epoxy resin containing epoxy groups is preferably a bisphenol epoxy condensation product, more preferably a glycidyl ether, and even more preferably a glycidyl ether of a phenol compound; the carbodiimide includes one or more of dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, and (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), preferably dicyclohexylcarbodiimide, more preferably N,N'-diisopropylcarbodiimide, and even more preferably (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), and polymeric carbodiimides are preferred over monomeric carbodiimides. The anti-hydrolysis agent used in the present invention is an organic substance that can react with the terminal carboxyl groups of the polyester resin.

[0016] The buffer comprises an amphoteric compound and a melt stabilizer (acid absorber), with a mass ratio of 1-2:1. The amphoteric compound comprises one or more of hydroxide and stearate; and the stabilizer (acid absorber) is hydrotalcite.

[0017] The hydroxide includes one or more of aluminum hydroxide and magnesium hydroxide; the stearate includes one or more of zinc stearate, magnesium stearate and calcium stearate; and the hydrotalcite includes one or more of magnesium aluminum hydrotalcite and calcium aluminum hydrotalcite.

[0018] The buffer used in the present invention is a class of amphoteric compounds and acid absorbers that can adsorb small acidic molecules. The buffer stabilizes the material's melt viscosity and regulates its processability. The buffer's ability to regulate acidity and alkalinity significantly impacts the material's hydrolysis resistance. Hydrotalcite, a selected buffer, primarily stabilizes the melt viscosity and can also adsorb acidic substances, preventing them from participating in the material's hydrolysis process. Amphoteric hydroxides react with acidic and alkaline substances, primarily maintaining the material's acidity and alkalinity. Adding only a single component cannot achieve both melt stability and acidity and alkalinity stability. Low amounts of hydrolysis resistance and buffer have little effect on improving the material's water resistance. Only at a certain level can hydrolysis resistance be significantly improved. Epoxy-based anti-hydrolysis agents, in particular, react with terminal carboxyl groups, resulting in chain extension and crosslinking, which can impair fluidity. Melt stabilizers prevent further loss of fluidity.

[0019] The preferred particle size of the buffer is 5-10 μm, more preferably 3-5 μm, and most preferably 2-3 μm. Particle size affects its dispersion in the matrix, and the presence of some metal ions (such as sodium ions) can deteriorate the acid-base balance (aluminum hydroxide and magnesium hydroxide contain metal ions, such as sodium ions). Therefore, the sodium ion content of the hydroxide (purity) in the buffer is preferably <50 ppm, more preferably <20 ppm, and most preferably <10 ppm.

[0020] The surface of the buffer is treated with a coupling agent, which includes one or more of aminosilane, epoxysilane, methacryloxysilane, and monoalkoxy titanate coupling agents. The buffer needs to be formulated based on various performance requirements to optimize the effect.

[0021] The antioxidant is preferably a mixture of a hindered phenol antioxidant and a phosphite antioxidant at a mass ratio of 1-1.5:1. The phosphite antioxidant is preferably pentaerythritol di(2,4-di-tert-butylphenyl) bisphosphite; and the hindered phenol antioxidant is preferably pentaerythritol ester.

[0022] The lubricant is preferably one or more of silicone powder, N,N'-ethylene bisstearamide, and pentaerythritol stearate.

[0023] The present invention also provides a method for preparing a halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance, comprising the following steps:

[0024] (1) Prepare the ingredients according to the following weight parts:

[0025]

[0026] (2) The components in step (1) are fully mixed and extruded into granules to obtain the halogen-free flame retardant reinforced polyester composite material.

[0027] In step (2), the speed of the screw extruder for extrusion granulation is 300-500 rpm and the temperature is 270-290° C. The components are added into a high-speed mixer according to the above weight percentages and then placed in a screw extruder to obtain a highly hydrolysis-resistant halogen-free flame-retardant reinforced polyester composite material.

[0028] The high hydrolysis resistance of the halogen-free flame-retardant reinforced polyester composite material of the present invention is achieved mainly through the combined action of the halogen-free flame retardant, the anti-hydrolysis agent, and the buffer. Traditional halogen-free flame retardants contain a large amount of metal impurities and contain components that are acidic in themselves or after decomposition, which will greatly reduce the hydrolysis resistance of the material. The flame retardant of the present invention uses a high-purity, low-ion-precipitation phosphorus-nitrogen halogen-free flame retardant, which can reduce the decomposition and precipitation of acidic substances during the wet heat aging process of the flame retardant; the anti-hydrolysis agent uses a traditional carbodiimide anti-hydrolysis agent to cap the terminal carboxyl groups of the polyester resin. However, there is a disadvantage in that carbodiimide capping can only cap the terminal carboxyl groups of the polyester resin and cannot cap the acidic small molecules produced by the decomposition of other components in the material, resulting in the acidity of the material itself being uncontrollable and deteriorating the anti-hydrolysis performance. Therefore, a third component, a buffer, needs to be added. The hydrolysis stability of polyester resin under weak alkaline conditions is better than that under acidic conditions. Therefore, the role of the buffer is to adjust the environmental acidity and alkalinity of the matrix polyester resin so that it tends to be between neutral and weakly alkaline, and to adsorb the acidic small molecular substances produced by decomposition, thereby reducing the hydrolysis rate of the polyester resin and improving the material's anti-hydrolysis properties.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) Compared to existing hydrolysis-resistant polyester resin materials, which generally use a single carbodiimide or epoxy resin as a means to improve the hydrolysis resistance of polyester resins, in flame-retardant reinforced polyester resin systems, the use of a single water repellent cannot effectively improve the hydrolysis resistance of polyester resins. Moreover, adding too much water repellent degrades the physical properties of the composite material and seriously affects the processing performance of the material. The present invention addresses the hydrolysis resistance issue of polyester resins by synergistically addressing the carboxyl end groups of the polyester resin and the pH value of the melt.

[0031] 2) Since a certain amount of inorganic materials with acidity and alkalinity adjustment are added to the system, it is beneficial to improve the hydrolysis resistance of the material without reducing the various properties of the material. In addition, thanks to the adjustment effect on acidity and alkalinity, the amount of anti-hydrolysis agent added to the system can be reduced, which reduces costs and improves the processability of the material to a certain extent.

[0032] 3) The addition of anti-hydrolysis agents will lead to a sharp increase in the melt viscosity of the base material and poor fluidity, thereby affecting the subsequent processability of the material. The addition of buffers not only adjusts the acidity and alkalinity of the base material, but also has a beneficial effect on the stability of the melt viscosity, giving the material better processing performance.

[0033] 4) The preparation process of the present invention is simple, and polyester resin materials with stable performance can be produced without the need for precise control of temperature, rotation speed, etc. during the production process. During the production process, no toxic or harmful gases are generated, no pollution is caused to the environment, and the application range is wide. The buffer and anti-hydrolysis agent can stably improve the hydrolysis resistance of the material, and the other components and contents in the formula are widely tolerant and do not require strict restrictions. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, provide detailed implementation methods and specific operating procedures, and will help those skilled in the art to further understand the present invention. It should be pointed out that the protection scope of the present invention is not limited to the following embodiments, and a number of adjustments and improvements made under the premise of the concept of the present invention all fall within the protection scope of the present invention.

[0035] In the Examples and Comparative Examples of the present invention, the material compositions of Table 1 and Table 2 are as follows:

[0036] PBT: purchased from Yizheng Chemical Fiber Company, brand GL236, intrinsic viscosity 1.280 ± 0.030 dl / g; terminal carboxyl content less than 27 mol / t;

[0037] Flame retardant: purchased from Zhejiang Xusen, a halogen-free flame retardant with phosphorus and nitrogen as flame retardant elements, with a mass ratio of melamine polyphosphate and diethyl phosphinate aluminum of 2:1;

[0038] Glass fiber: purchased from Jushi Co., Ltd., brand ECS13-03-534A, diameter 13 μm;

[0039] Anti-hydrolysis agent: Carbodiimide was purchased from LANXESS, brand P400; epoxy resin was purchased from Nan Ya, brand NPES-907;

[0040] Buffer: hydrotalcite (<200 nm), purchased from Chenghe Technology, brand AC-320; zinc stearate (1-2 μm), purchased from FACI, brand ZS-TM;

[0041] Antioxidant: a mixture of hindered phenol and phosphite antioxidants IRGANOX 1010 and IRGAFOS 168 in a weight ratio of 1:1;

[0042] Lubricant: Pentaerythritol stearate, German Corning PETS lubricant LOXIOL P 861 / 3.5.

[0043] Examples 1-7

[0044] A halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance and a preparation method thereof, the method comprising the following steps:

[0045] The raw materials were added into a high-speed mixer according to the weight percentage of the ingredients in Table 1 and mixed thoroughly. The mixture was then placed into a screw machine. The speed of the screw machine was controlled to be 400 rpm and the temperature to be 280°C. The mixture was extruded and granulated to obtain the product.

[0046] Examples 1-7 are products of compounding CTI synergist and polyolefin, Examples 1-3 are used to determine the optimal ratio of CTI synergist and polyolefin, and Examples 4-7 are material formulations at different glass fiber contents.

[0047] Explanation for the compilation of Table 1:

[0048] Examples 1 to 3 are used to demonstrate that carbodiimide anti-hydrolysis and buffering agent jointly improve the hydrolysis resistance of the material, and their addition amount needs to reach a certain threshold. The comprehensive effect is optimal when 0.5 parts and 5 parts are added respectively.

[0049] Examples 6 and 7 are used to demonstrate that high hydrolysis resistance can also be achieved by compounding epoxy resin with a buffer, and the optimal values are when 1 part and 5 parts are added.

[0050] Examples 6 and 7 are used to demonstrate that the compound system of the anti-hydrolysis agent and the buffer can be used in a 15-40 parts glass fiber reinforced PBT composite material system and can stably obtain high hydrolysis resistance.

[0051] Table 1 - Recipe

[0052]

[0053]

[0054] Comparative Examples 1-9

[0055] A halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance has a composition as shown in Table 2 and a preparation method the same as that in the example.

[0056] Comparative Examples 1 to 9 are used to demonstrate that for flame retardant reinforced PBT materials, a single anti-hydrolysis agent or buffer cannot effectively improve the hydrolysis resistance of the material, even if the anti-hydrolysis content is increased to 1%.

[0057] Table 2 - Recipe

[0058]

[0059]

[0060] Performance testing:

[0061] Table 3 and Table 4 are the performance test results. The specific items are as follows:

[0062] Table 3 Test results of comparative examples 1 to 9

[0063]

[0064] Table 4 Test results of Examples 1 to 7

[0065]

[0066]

[0067] The performance test item standards are as follows:

[0068] Charpy notched impact strength: tested in accordance with ISO 179-1:2010 standard;

[0069] Tensile strength: tested according to ISO 527-1:2019 standard;

[0070] MI: Tested according to ISO 1133-1:2011 standard;

[0071] Flame retardant test: tested according to UL-94 standard;

[0072] Tensile strength and retention after hygrothermal aging: Tested in accordance with GB / T 2573-2008. After the test specimens are stored at room temperature for 24 hours, they are tested according to the tensile test standard. Hygrothermal aging conditions: temperature 85°C, humidity 85% RH, time 2000 hours;

[0073] High-pressure steam test tensile strength and retention: Tested according to JEDEC JESD22-A102 standard. After the test specimens are stored at room temperature for 24 hours, they are tested according to the tensile test standard. High-pressure steam test conditions: temperature 121°C, humidity 100% RH, pressure 2atm, time 96 hours;

[0074] Analysis of the test results shows that in Comparative Example 1, without any anti-hydrolysis agent components, the PBT exhibits extremely poor hydrolysis resistance, resulting in a tensile strength retention of only 32% after 2000 hours of damp-heat aging. This severe performance degradation makes it unsuitable for use in harsh damp-heat environments. Comparative Examples 2 and 3, in which 0.1%-0.5% of a carbodiimide anti-hydrolysis agent was added, showed no significant improvement in tensile strength retention after damp-heat aging. Similarly, Comparative Examples 4 and 5, in which 0.5%-1% of an epoxy resin was added, showed no significant improvement in hydrolysis resistance. This demonstrates that simply adding a single anti-hydrolysis component to a halogen-free flame-retardant PBT system is insufficient to effectively improve the material's hydrolysis resistance. Comparative Examples 6 and 7, in which 1%-5% of a buffer was added, also exhibit low tensile strength retention, indicating that the buffer does not effectively reduce the acidic hydrolysis process of PBT, but rather serves only to adjust the pH. To achieve enhanced hydrolysis resistance, it must be combined with other anti-hydrolysis agents.

[0075] Examples 1 and 2 demonstrate that even though the combined effect of an anti-hydrolysis agent and a buffer can produce a higher improvement in hydrolysis resistance, a low addition of an anti-hydrolysis agent still fails to significantly improve hydrolysis resistance. Only when the carbodiimide anti-hydrolysis agent content reaches 0.5% does the hydrolysis resistance improve significantly. Examples 2 and 3 demonstrate that when the buffer content is 5% and the carbodiimide anti-hydrolysis agent content is 0.5%, the hydrolysis resistance of the material is optimal, with a tensile strength retention rate of 59%. This indicates that a certain buffer content is required to more effectively maintain the acid-base balance of the matrix material, thereby improving the hydrolytic stability of the material.

[0076] Examples 4 and 5 demonstrate that epoxy resin and buffering agents can also consistently improve the material's hydrolysis resistance. When 1% epoxy resin and 5% buffering agent are added, the tensile strength retention of the composition reaches 53%. Compared to Comparative Examples 4 and 5, these increases are 8% and 7%, respectively. This demonstrates that the addition of the buffering agent synergistically enhances the hydrolysis resistance of the composition.

[0077] Examples 6 and 7 demonstrate that, even with glass fiber content ranging from 15% to 40%, the addition of an epoxy resin-based anti-hydrolysis agent and a buffer can still yield a PBT halogen-free flame-retardant reinforced material with consistently enhanced hydrolysis resistance. This demonstrates the stable synergistic effect between the anti-hydrolysis agent and the buffer, making it applicable to a wider range of systems.

[0078] By comparing Comparative Example 3, Comparative Example 5, Example 3 and Example 5, it can be determined that the anti-hydrolysis agent and the buffer can effectively improve the hydrolysis resistance of the PBT halogen-free flame retardant reinforced material. When 0.5% carbodiimide and 5% buffer, 1% epoxy resin and 5% buffer are added, tensile strength retention rates of 59% and 53% can be obtained, as well as other excellent comprehensive properties, showing a simple and effective method for preparing halogen-free flame retardant reinforced PBT composite materials with high hydrolysis resistance.

[0079] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A halogen-free flame-retardant reinforced polyester composite material with high hydrolysis resistance, characterized in that: The halogen-free flame retardant reinforced polyester composite material comprises the following components in parts by weight:

2. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The polyester resin includes one of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate.

3. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The halogen-free flame retardant is a phosphorus-nitrogen flame retardant combination, including melamine polyphosphate and alkyl phosphinate.

4. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The glass fiber is alkali-free and hydrolysis-resistant glass fiber with a diameter of 11-15 μm.

5. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The anti-hydrolysis agent includes one or more of epoxy resin and carbodiimide containing epoxy groups.

6. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The buffer comprises an amphoteric compound and a melt stabilizer, with a mass ratio of 1-2:

1.

7. The halogen-free flame-retardant reinforced polyester composite material according to claim 6, characterized in that: The amphoteric compound includes one or more of hydroxide and stearate; the melt stabilizer is hydrotalcite; the hydroxide includes one or more of aluminum hydroxide and magnesium hydroxide; the stearate includes one or more of zinc stearate, magnesium stearate and calcium stearate; and the hydrotalcite includes one or more of magnesium aluminum hydrotalcite and calcium aluminum hydrotalcite.

8. The halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The antioxidant includes hindered phenol antioxidants and phosphite antioxidants; the lubricant includes one or more of silicone powder, methylene bisstearamide, and N,N'-ethylene bisstearamide.

9. A method for preparing a halogen-free flame-retardant reinforced polyester composite material according to claim 1, characterized in that: The steps include: (1) Prepare the ingredients according to the following weight parts: (2) The components in step (1) are fully mixed and extruded into granules to obtain the halogen-free flame retardant reinforced polyester composite material.

10. The preparation method according to claim 9, characterized in that In step (2), the speed of the screw machine for extrusion granulation is 300-500 rpm and the temperature is 270-290°C.

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