A carbon fiber modified resin material and preparation method thereof

Abstract

The invention relates to a carbon fiber modified resin material and a preparation method thereof, belonging to the technical field of polymer composite materials. The material comprises, by weight, 100 parts of polypropylene resin, 11-16 parts of modified carbon fibers, 6-9 parts of compatibilizers, 1.8-2.6 parts of lubricants and 0.1-0.15 parts of antioxidants. The modified carbon fibers are based on chopped carbon fibers, and an amide compound containing a double-terminal alkyl chain is formed by reacting an alkyl chloride with a primary amine of diethylenetriamine, i.e., an intermediate. The epoxy group of a silane coupling agent KH-560 and a secondary amine structure of the intermediate are ring-opened, and an ethoxysilane structure is introduced to prepare a modifier. The modifier is hydrolyzed in an acidic alcohol aqueous solution and coupled to a carbon fiber surface, so that the modifier is grafted to the carbon fiber surface. The modified carbon fibers are blended with modified polypropylene to effectively improve the toughness and creep resistance of the composite material, and are beneficial to maintaining the stability of the structure after the material is formed.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer composite materials, and in particular, relates to a carbon fiber modified resin material and a preparation method thereof. Background Art

[0002] Resin-based composite materials have the advantages of high specific strength, high specific modulus, and good chemical stability, and are important materials for modern industry. Polypropylene resin has the characteristics of low density, good rigidity and toughness balance, excellent thermal properties and acid and alkali resistance. Chopped carbon fiber, as an excellent inorganic filler, has the characteristics of high strength, high modulus, excellent corrosion resistance and light weight. Chopped carbon fiber reinforced polypropylene has the advantages of high strength and light weight compared to traditional glass fiber reinforced polypropylene composite materials, and has far-reaching research significance in the field of automobile lightweighting. Using this material to manufacture body panels, roofs and floor components can significantly reduce vehicle weight and improve energy efficiency and performance.

[0003] However, polypropylene is a non-polar resin, and the surface of carbon fiber contains a large number of polar groups, which makes the bonding performance of carbon fiber and polypropylene resin poor. In addition, compared with polypropylene resin, carbon fiber is a hard material, and strong internal stress is formed at the bonding interface, which makes it difficult to fully exert the strengthening effect of carbon fiber. In addition, the stress at the bonding interface is released under the action of external force, which makes the material prone to creep, affecting the structural stability of the composite product and greatly limiting the application of the material. Summary of the invention

[0004] In order to solve the technical problems mentioned in the background technology, the object of the present invention is to provide a carbon fiber modified resin material and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A carbon fiber modified resin material comprises, by weight, 100 parts of polypropylene resin, 11-16 parts of modified carbon fiber, 6-9 parts of a compatibilizer, 1.8-2.6 parts of a lubricant and 0.1-0.15 parts of an antioxidant.

[0007] The modified carbon fiber is prepared by the following method:

[0008] Step A1: diethylenetriamine, alkaline molecular sieves and anhydrous tetrahydrofuran are mixed, dry nitrogen is introduced for protection, the temperature is controlled at 5-15°C in an ice-water bath, stirring is applied at 120-150 rpm, alkyl acyl chloride is slowly added for reaction for 1-1.5 hours, and then the reaction is continued at 40-55°C in a water bath for 2-3 hours. After the reaction is completed, the alkaline molecular sieve is removed by filtration, and tetrahydrofuran is removed by rotary evaporation to obtain an intermediate;

[0009] Furthermore, the dosage ratio of diethylenetriamine, alkyl acyl chloride, alkaline molecular sieve and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 2.5-4 g: 30-50 mL, and the alkaline molecular sieve is used as an acid absorbent to promote the reaction of alkyl acyl chloride with the primary amine of diethylenetriamine to form an amide compound containing a double-terminal alkyl chain;

[0010] Preferably, the alkyl acid chloride is one or more of butyryl chloride, n-valeryl chloride, octanoyl chloride and decanoyl chloride.

[0011] Step A2: The intermediate, silane coupling agent KH-560 and anhydrous acetone are mixed, dry nitrogen is introduced for protection, the temperature is raised to 50-60°C, stirring is applied at 60-90 rpm, dibutyltin dilaurate is added intermittently to react for 6-8 hours, and acetone is removed by rotary evaporation after the reaction is completed to obtain a modifier;

[0012] Furthermore, the usage ratio of the intermediate, silane coupling agent KH-560, dibutyltin dilaurate and anhydrous acetone is 0.1 mol: 0.1 mol: 0.12-0.16 g: 130-180 mL. Under the promotion of dibutyltin dilaurate, the epoxy group of the silane coupling agent KH-560 and the secondary amine structure of the intermediate are ring-opened to introduce the ethoxysilane structure.

[0013] Step A3: immersing the chopped carbon fiber in a nitric acid solution and heating it for 5 hours, filtering and drying to obtain activated carbon fiber, then mixing the modifier and the ethanol solution, acidifying to a pH value of 4-5 and stirring and hydrolyzing for 1-1.5 hours, adding the activated carbon fiber and mixing, standing for 12 hours, filtering, washing, and drying to obtain modified carbon fiber;

[0014] Furthermore, the dosage ratio of activated carbon fiber, modifier and ethanol solution is 50g:3.5-5.2g:80-100mL, the mass fraction of ethanol solution is 50%, the modifier is hydrolyzed in acidic alcohol aqueous solution and coupled with the surface of activated carbon fiber, so that the modifier is grafted to the surface of carbon fiber.

[0015] A method for preparing a carbon fiber modified resin material comprises the following steps:

[0016] Step S1: premixing raw materials other than modified carbon fiber and feeding them from the main feeding port of the extruder, feeding the modified carbon fiber from the side feeding port, extruding and pelletizing, and preparing composite masterbatch;

[0017] Step S2: transferring the composite masterbatch into a mold for hot pressing to obtain a carbon fiber modified resin material.

[0018] Furthermore, the temperature process parameters of extrusion pelletizing are: zone one 155-165°C, zone two 170-180°C, zone three 180-190°C, zone four 190-200°C, zone five 185-195°C, zone six 180-190°C, and die head 190-205°C.

[0019] Furthermore, the temperature of hot pressing is 185-200°C, and the hot pressing pressure is 5.5-6.5MPa.

[0020] Beneficial effects of the present invention:

[0021] The invention uses polypropylene resin as a matrix, and is modified by compounding modified carbon fibers. The modified carbon fibers use commercially available chopped carbon fibers as a matrix, and an amide compound containing a double-terminal alkyl chain is formed by reacting an alkyl chloride with a primary amine of diethylenetriamine, i.e., an intermediate. Then, an epoxy group of a silane coupling agent KH-560 and a secondary amine structure of the intermediate are ring-opened, and an ethoxysilane structure is introduced to prepare a modifier. The modifier is hydrolyzed in an acidic alcohol aqueous solution and coupled with the surface of the carbon fibers, so that the modifier is grafted onto the surface of the carbon fibers. A large amount of alkyl short chains are introduced into the surface of the modified carbon fibers to improve the compatibility of the carbon fibers with the polypropylene matrix. During the process, it is easy to evenly disperse into the matrix to form a spatially interwoven carbon fiber-based reinforcement network. The modifier introduces a large amount of amide structure in the near-surface layer of the carbon fiber, inducing the generation of β-phase crystallization during the molding process, that is, a β-crystal transition layer extending to the polypropylene matrix is ​​formed in the near layer of the carbon fiber. The β-phase crystal has a more orderly arrangement and better toughness than the α-phase crystal of the matrix, which makes the bonding toughness of the heterogeneous carbon fiber and the matrix better, effectively reduces the internal stress between the carbon fiber and the matrix polypropylene, and improves the impact resistance of the composite material. At the same time, it is not easy to produce stress creep under the action of external force, which is beneficial to maintain the stability of the structure after the material is molded. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1, preparation of carbon fiber modified resin material, the specific implementation process is as follows:

[0024] (1) Preparation of modified carbon fiber

[0025] Step A1: diethylenetriamine, alkaline molecular sieve and anhydrous tetrahydrofuran are mixed, dry nitrogen is introduced for protection, the temperature is controlled at 15°C in an ice-water bath, stirring is applied at 150rpm, alkyl acyl chloride is slowly added for reaction for 1h, and then the reaction is continued at 55°C in a water bath for 2h, wherein 13X molecular sieve is used as the alkaline molecular sieve, and the alkyl acyl chloride is selected from decanoyl chloride. The amount ratio of diethylenetriamine, alkyl acyl chloride, alkaline molecular sieve and anhydrous tetrahydrofuran is 0.1mol:0.2mol:4g:50mL. After the reaction is completed, the alkaline molecular sieve is filtered to remove the alkaline molecular sieve, and the tetrahydrofuran is removed by rotary evaporation to obtain an intermediate.

[0026] Step A2: Take the intermediate, silane coupling agent KH-560 and anhydrous acetone and mix them, introduce dry nitrogen protection, heat to 60°C, apply 90rpm stirring, take equal amounts of dibutyltin dilaurate and divide them into four parts, add them intermittently for 1h, continue to stir the reaction at a constant temperature after complete addition, and control the total addition reaction time of dibutyltin dilaurate to be 6h, wherein the amount ratio of the intermediate, silane coupling agent KH-560, dibutyltin dilaurate and anhydrous acetone is 0.1mol: 0.1mol: 0.16g: 180mL. After the reaction is completed, acetone is removed by rotary evaporation to obtain a modifier.

[0027] Step A3: Take short-cut carbon fiber and immerse it in nitric acid solution and heat it to 80°C for 5 hours. After filtering and drying, activated carbon fiber is obtained. Then the modifier and ethanol solution are mixed, acidified with formic acid to pH 4 and stirred for hydrolysis for 1 hour, activated carbon fiber is added and mixed and allowed to stand for 12 hours, wherein the mass fraction of nitric acid solution is 68% commercially available industrial raw materials, the length of short-cut carbon fiber is 3mm, the wire diameter is 7μm, the amount ratio of activated carbon fiber, modifier and ethanol solution is 50g:5.2g:100mL, the mass fraction of ethanol solution is 50%, and then filtered, washed and dried to obtain modified carbon fiber.

[0028] (2) Preparation of carbon fiber modified resin materials

[0029] The raw materials are measured by weight: 100 parts of polypropylene resin, and M1400 raw material is used in the implementation process; 16 parts of modified carbon fiber, which is homemade in this embodiment; 9 parts of compatibilizer, and CMG9801 maleic anhydride grafted polypropylene raw material is used in the implementation process; 2.6 parts of lubricant, and PPW-0903 polypropylene wax raw material is used in the implementation process; 0.15 parts of antioxidant, and antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio in the implementation process.

[0030] Step S1: adding raw materials other than modified carbon fiber into a high mixer and premixing at 800 rpm for 5 min, feeding the mixed material from the main feeding port of the extruder, feeding the modified carbon fiber from the side feeding port, and extruding and pelletizing, wherein the temperature process parameters of the extrusion and pelletizing are: 165°C in zone 1, 180°C in zone 2, 190°C in zone 3, 200°C in zone 4, 195°C in zone 5, 190°C in zone 6, and 205°C in the die head, to obtain a composite masterbatch.

[0031] Step S2: transferring the composite masterbatch into a mold for hot pressing molding, wherein the hot pressing molding temperature is 200° C. and the hot pressing pressure is 5.5 MPa, to obtain a carbon fiber modified resin material.

[0032] Example 2, preparing carbon fiber modified resin material, the specific implementation process is as follows:

[0033] (1) Preparation of modified carbon fiber

[0034] Step A1: diethylenetriamine, alkaline molecular sieve and anhydrous tetrahydrofuran are mixed, dry nitrogen is introduced for protection, the temperature is controlled at 5°C in an ice-water bath, stirring is applied at 120rpm, alkyl acyl chloride is slowly added for reaction for 1.5h, and then the reaction is continued at 40°C in a water bath for 3h, wherein the alkaline molecular sieve is 13X type molecular sieve, the alkyl acyl chloride is selected from butyryl chloride and decanoyl chloride in a molar ratio of 1:3, and the amount ratio of diethylenetriamine, alkyl acyl chloride, alkaline molecular sieve and anhydrous tetrahydrofuran is 0.1mol:0.2mol:2.5g:30mL. After the reaction is completed, the alkaline molecular sieve is filtered to remove the alkaline molecular sieve, and the tetrahydrofuran is removed by rotary evaporation to obtain an intermediate.

[0035] Step A2: Take the intermediate, silane coupling agent KH-560 and anhydrous acetone and mix them, introduce dry nitrogen protection, heat to 50°C, apply 60rpm stirring, take equal amounts of dibutyltin dilaurate and divide them into four parts, add them intermittently for 1h, continue to stir and react at a constant temperature after complete addition, and control the total addition reaction time of dibutyltin dilaurate to be 8h, wherein the amount ratio of the intermediate, silane coupling agent KH-560, dibutyltin dilaurate and anhydrous acetone is 0.1mol: 0.1mol: 0.12g: 130mL. After the reaction is completed, acetone is removed by rotary evaporation to obtain a modifier.

[0036] Step A3: Take short-cut carbon fiber and immerse it in nitric acid solution and heat it to 80°C for 5 hours. After filtering and drying, activated carbon fiber is obtained. Then the modifier and ethanol solution are mixed, acidified with formic acid to pH 5 and stirred for hydrolysis for 1.5 hours, activated carbon fiber is added and mixed and allowed to stand for 12 hours. Among them, the mass fraction of nitric acid solution is 68% commercially available industrial raw materials, the length of short-cut carbon fiber is 3mm, the wire diameter is 7μm, the amount ratio of activated carbon fiber, modifier and ethanol solution is 50g:3.5g:80mL, the mass fraction of ethanol solution is 50%, and then filtered, washed and dried to obtain modified carbon fiber.

[0037] (2) Preparation of carbon fiber modified resin materials

[0038] The raw materials are taken according to weight parts: 100 parts of polypropylene resin, and M1400 raw material is used in the implementation process; 11 parts of modified carbon fiber, which is homemade in this embodiment; 6 parts of compatibilizer, and CMG9801 maleic anhydride grafted polypropylene raw material is used in the implementation process; 1.8 parts of lubricant, and PPW-0903 polypropylene wax raw material is used in the implementation process; 0.1 parts of antioxidant, and antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio in the implementation process.

[0039] Step S1: adding raw materials other than modified carbon fiber into a high mixer and premixing at 800 rpm for 5 min, feeding the mixture from the main feeding port of the extruder, feeding the modified carbon fiber from the side feeding port, and extruding and pelletizing, wherein the temperature process parameters of the extrusion and pelletizing are: 155°C in zone 1, 170°C in zone 2, 180°C in zone 3, 190°C in zone 4, 185°C in zone 5, 180°C in zone 6, and 190°C in the die head, to obtain a composite masterbatch.

[0040] Step S2: transferring the composite masterbatch into a mold for hot pressing molding, wherein the hot pressing molding temperature is 185° C. and the hot pressing pressure is 6.5 MPa, to obtain a carbon fiber modified resin material.

[0041] Example 3, preparing carbon fiber modified resin material, the specific implementation process is as follows:

[0042] (1) Preparation of modified carbon fiber

[0043] Step A1: diethylenetriamine, alkaline molecular sieve and anhydrous tetrahydrofuran are mixed, dry nitrogen is introduced for protection, the temperature is controlled at 10°C in an ice-water bath, stirring is applied at 150rpm, alkyl acyl chloride is slowly added for reaction for 1.2h, and then the reaction is continued at 50°C in a water bath for 2.5h, wherein the alkaline molecular sieve is 13X molecular sieve, the alkyl acyl chloride is selected from n-valeryl chloride and octanoyl chloride in an equimolar ratio, and the amount ratio of diethylenetriamine, alkyl acyl chloride, alkaline molecular sieve and anhydrous tetrahydrofuran is 0.1mol:0.2mol:3.2g:40mL. After the reaction is completed, the alkaline molecular sieve is filtered to remove the alkaline molecular sieve, and the tetrahydrofuran is removed by rotary evaporation to obtain an intermediate.

[0044] Step A2: Take the intermediate, silane coupling agent KH-560 and anhydrous acetone and mix them, introduce dry nitrogen protection, heat to 55°C, apply 90rpm stirring, take equal amounts of dibutyltin dilaurate and divide them into four parts, add them intermittently for 1h, continue to stir and react at a constant temperature after complete addition, and control the total addition reaction time of dibutyltin dilaurate to be 7h, wherein the amount ratio of the intermediate, silane coupling agent KH-560, dibutyltin dilaurate and anhydrous acetone is 0.1mol: 0.1mol: 0.16g: 150mL. After the reaction is completed, acetone is removed by rotary evaporation to obtain a modifier.

[0045] Step A3: Take short-cut carbon fiber and immerse it in nitric acid solution and heat it to 80°C for 5 hours. After filtering and drying, activated carbon fiber is obtained. Then the modifier and ethanol solution are mixed, acidified with formic acid to pH 4 and stirred for hydrolysis for 1.2 hours, activated carbon fiber is added and mixed and allowed to stand for 12 hours. Among them, the mass fraction of nitric acid solution is 68% commercially available industrial raw materials, the length of short-cut carbon fiber is 3mm, the wire diameter is 7μm, the amount ratio of activated carbon fiber, modifier and ethanol solution is 50g:4.5g:90mL, the mass fraction of ethanol solution is 50%, and then filtered, washed and dried to obtain modified carbon fiber.

[0046] (2) Preparation of carbon fiber modified resin materials

[0047] The raw materials are measured by weight: 100 parts of polypropylene resin, and M1400 raw material is used in the implementation process; 14 parts of modified carbon fiber, which is homemade in this embodiment; 7 parts of compatibilizer, and CMG9801 maleic anhydride grafted polypropylene raw material is used in the implementation process; 2.3 parts of lubricant, and PPW-0903 polypropylene wax raw material is used in the implementation process; 0.12 parts of antioxidant, and antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio in the implementation process.

[0048] Step S1: adding raw materials other than modified carbon fiber into a high mixer and premixing at 800 rpm for 5 min, feeding the mixed material from the main feeding port of the extruder, feeding the modified carbon fiber from the side feeding port, and extruding and pelletizing, wherein the temperature process parameters of the extrusion and pelletizing are: 160°C in zone 1, 175°C in zone 2, 180°C in zone 3, 190°C in zone 4, 190°C in zone 5, 180°C in zone 6, and 200°C in the die head to obtain a composite masterbatch.

[0049] Step S2: transferring the composite masterbatch into a mold for hot pressing molding, wherein the hot pressing molding temperature is 190° C. and the hot pressing pressure is 6 MPa, to obtain a carbon fiber modified resin material.

[0050] Comparative Example 1

[0051] This comparative example refers to Example 3, except that the modified carbon fiber is replaced with the same weight portion of chopped carbon fiber, and the rest of the implementation process is exactly the same.

[0052] Comparative Example 2

[0053] This comparative example adopts coupled carbon fiber compounding to prepare carbon fiber modified resin material, and the specific implementation process is as follows:

[0054] Preparation method of coupled carbon fiber: n-octyltriethoxysilane and 50% ethanol solution by mass are mixed, acidified with formic acid to a pH value of 4, stirred and hydrolyzed for 1.5 hours, activated carbon fiber of Example 3 is added and mixed, allowed to stand for 12 hours, filtered, washed, and dried to obtain coupled carbon fiber.

[0055] The specific implementation process is the same as in Example 3, using the same weight portion of coupled carbon fiber to replace the modified carbon fiber.

[0056] Comparative Example 3

[0057] This comparative example refers to comparative example 2, except that 0.4 parts of TMB-5 nucleating agent is added to the raw materials, and the rest of the implementation process is exactly the same.

[0058] The carbon fiber modified resin material prepared as above was tested for tensile strength according to ISO 527-2, with a tensile rate of 10 mm / min; the impact strength was tested according to ISO 179-1, using a type A specimen; the tensile creep test was performed according to GB / T 11546.1-2008, with a stress value of 40% tensile strength, a test temperature of 25°C, a relative humidity of 60%, and a test cycle of 20,000 s; the specific test results are shown in the following table:

[0059]

[0060] It can be seen from the test results in the above table that the carbon fiber modified resin material prepared in the embodiment has excellent toughness and better creep resistance, and is suitable for use in high-strength structural parts.

[0061] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0062] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A carbon fiber modified resin material, characterized in that: The composition comprises, by weight: 100 parts of polypropylene resin, 11-16 parts of modified carbon fiber, 6-9 parts of compatibilizer, 1.8-2.6 parts of lubricant and 0.1-0.15 parts of antioxidant; The modified carbon fiber is prepared by the following method: Step A1: diethylenetriamine, alkaline molecular sieve and anhydrous tetrahydrofuran are mixed, and dry nitrogen is introduced for protection. The temperature is controlled at 5-15°C in an ice-water bath, and alkyl acyl chloride is slowly added with stirring to react for 1-1.5h. Then, the mixture is placed in a water bath and the reaction is continued at 40-55°C for 2-3h. After the reaction is completed, the alkaline molecular sieve is removed by filtration, and tetrahydrofuran is removed by rotary evaporation to obtain an intermediate, wherein the amount ratio of diethylenetriamine, alkyl acyl chloride, alkaline molecular sieve and anhydrous tetrahydrofuran is 0.1mol:0.2mol:2.5-4g:30-50mL; Step A2: The intermediate, silane coupling agent KH-560 and anhydrous acetone are mixed, dry nitrogen is introduced for protection, the temperature is raised to 50-60° C., and dibutyltin dilaurate is added intermittently with stirring for 6-8 hours. After the reaction is completed, acetone is removed by rotary evaporation to obtain a modifier, wherein the amount ratio of the intermediate, silane coupling agent KH-560, dibutyltin dilaurate and anhydrous acetone is 0.1 mol: 0.1 mol: 0.12-0.16 g: 130-180 mL; Step A3: immerse the chopped carbon fiber in a nitric acid solution and heat it for 5 hours, filter and dry it to obtain activated carbon fiber, then mix the modifier and ethanol solution, acidify it to a pH value of 4-5 and stir and hydrolyze it for 1-1.5 hours, add the activated carbon fiber and mix it, let it stand for 12 hours, filter, wash and dry it to obtain modified carbon fiber.

2. A carbon fiber modified resin material according to claim 1, characterized in that: The alkyl acid chloride is one or more of butyryl chloride, n-valeryl chloride, octanoyl chloride and decanoyl chloride.

3. The carbon fiber modified resin material according to claim 1, characterized in that: The usage ratio of activated carbon fiber, modifier and ethanol solution is 50g:3.5-5.2g:80-100mL.

4. The method for preparing a carbon fiber modified resin material according to any one of claims 1 to 3, characterized in that: The steps include: Step S1: premixing raw materials other than modified carbon fiber and feeding them from the main feeding port of the extruder, feeding the modified carbon fiber from the side feeding port, extruding and pelletizing, and preparing composite masterbatch; Step S2: transferring the composite masterbatch into a mold for hot pressing to obtain a carbon fiber modified resin material.

5. The method for preparing a carbon fiber modified resin material according to claim 4, characterized in that: The temperature process parameters of extrusion pelletizing are: zone 1 155-165℃, zone 2 170-180℃, zone 3 180-190℃, zone 4 190-200℃, zone 5 185-195℃, zone 6 180-190℃, and die head 190-205℃.

6. The method for preparing a carbon fiber modified resin material according to claim 5, characterized in that: The temperature of hot pressing is 185-200°C, and the hot pressing pressure is 5.5-6.5MPa.

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