Ultra-clean barrel with multi-layer composite structure and preparation process of ultra-clean barrel

Abstract

The invention relates to an ultra-clean barrel of a multi-layer composite structure and a preparation technology of the ultra-clean barrel, and belongs to the technical field of ultra-clean barrels. The invention provides an ultra-clean barrel of a multi-layer composite structure. The ultra-clean barrel is composed of an outer layer material, a middle layer material and an inner layer ultra-clean material. The outer layer material is prepared by mixing ethylene-vinyl alcohol copolymer and polymethyl methacrylate according to the mass ratio of 3: 1, adding 8-10% of silica powder with the particle size smaller than or equal to 1 micron, and conducting melt blending, water-cooling pelletizing and drying, and it is ensured that the outer layer has the barrier property and rigidity. The material of the middle layer is a high-density polyethylene matrix and provides mechanical support; and the inner layer is made of medical-grade HDPE and is subjected to precise screening treatment, so that the ultra-clean performance is ensured. The three layers are integrally formed through a co-extrusion blow molding process, and the thickness ratio is 20%: 70%: 10%.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-clean barrels and relates to an ultra-clean barrel with a multi-layer composite structure and a preparation process thereof. Background Art

[0002] In the fields of semiconductor manufacturing, biomedicine, and high-purity chemical storage, ultra-clean containers must simultaneously meet stringent requirements for high barrier properties, low pollutant precipitation, excellent mechanical strength, and ultra-low inner wall roughness. While traditional single-layer high-density polyethylene (HDPE) containers are chemically inert, their oxygen permeability is typically higher than 30 cm³·mm / (m²·d·atm) and their water vapor permeability exceeds 5 g·mm / (m²·d), making them difficult to block external gas penetration. This makes stored sensitive materials such as photoresists and high-purity reagents susceptible to oxidation or moisture absorption and deterioration. Furthermore, the compressive strength of single-layer HDPE containers is generally lower than 25 MPa, making them prone to deformation during transportation or stacking. Furthermore, the inner wall surface roughness (Ra>0.5μm) easily absorbs nanoparticles, posing a risk of secondary contamination.

[0003] To improve performance, existing technologies attempt to employ multi-layer composite structures. For example, while introducing a barrier layer (such as ethylene-vinyl alcohol copolymer (EVOH)) into a composite HDPE matrix can reduce oxygen permeability, the polarity difference between EVOH and HDPE leads to insufficient interlayer bonding, resulting in interfacial peel strength typically below 10N / 15mm. This leads to delamination over long-term use and poor impact resistance. Furthermore, insufficient temperature field control precision during blow molding and an imbalance between the blow-up ratio and the pull-off speed during the production process often result in wall thickness deviations exceeding ±10%, compromising sealing reliability.

[0004] In view of the above problems, it is urgent to develop a new type of multi-layer composite structure ultra-clean barrel. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultra-clean barrel with a multi-layer composite structure and a preparation process thereof, which has the characteristics of strong impact resistance.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A super-clean barrel with a multi-layer composite structure, comprising an outer layer material, an intermediate layer material and an inner layer super-clean material. Wherein, the outer layer material includes ethylene-vinyl alcohol copolymer EVOH, polymethyl methacrylate PMMA, and silicon powder; The intermediate layer material is a high-density polyethylene (HDPE) matrix; The inner layer of ultra-clean material is a high-density polyethylene (HDPE) layer; The thickness of the three layers is 20%:70%:10%.

[0007] Furthermore, the outer layer material is prepared by: S1: Ethylene-vinyl alcohol copolymer (EVOH) and polymethyl methacrylate (PMMA) were mixed in a mass ratio of 3:1 to obtain a mixed powder. 8-10% of silicon micropowder was added based on the mass of the mixed powder. The mixture was placed in a high-speed mixer under nitrogen protection and stirred at 600 rpm for 15-20 minutes to obtain a premix. S2: melt-blending the premixed materials through a twin-screw extruder to obtain an extruded melt; S3: The extruded melt is subjected to water-cooling and strand-cutting, with a pelletizing length of 3-5 mm, and dried to obtain a composite material of the outer layer material.

[0008] Furthermore, the particle size of the silicon powder in S1 is ≤1 μm.

[0009] Furthermore, the melt blending process in S2 includes setting four temperature zones: zone 1 at 180°C, zone 2 at 200°C, zone 3 at 220°C, zone 4 at 210°C, a screw speed of 180 r / min, and a melt pressure of 12 MPa.

[0010] Furthermore, the temperature of the cooling water in S3 is 25°C.

[0011] Furthermore, the drying parameters in S3 are drying at 70-80° C. for 12-14 hours, and the moisture content of the material is ≤0.03%.

[0012] A preparation process of an ultra-clean barrel with a multi-layer composite structure, the specific process of the preparation process is as follows: A1: Dry high-density polyethylene (HDPE) pellets at 120-130°C with hot air for 2-3 hours as the middle layer material. A2: Medical-grade high-density polyethylene (HDPE) granules are screened through a 0.45 μm pore size filter to serve as the inner layer ultra-clean material. A3: The outer layer material composite masterbatch, the middle layer HDPE, and the inner layer ultra-clean HDPE are respectively placed into a three-layer co-extrusion blow molding unit. The die head temperature zones are set to 190-200°C for the outer layer, 210-220°C for the middle layer, and 180-190°C for the inner layer. The blow-up ratio is 2.8-3.2, the pulling speed is 6-8 m / min, and the thickness ratio of the three layers is controlled to be 20%:70%:10%. The ultra-clean barrel with the multi-layer composite structure is obtained by blow molding.

[0013] Furthermore, the hot air drying in A1 adopts a hot air circulation drying oven, the wind speed is controlled at 1.5-2.0 m / s, and the moisture content of the HDPE particles after drying is ≤0.02%.

[0014] Furthermore, the inflation molding stage in A3 adopts two-stage pressure control, with a pre-blowing pressure of 0.8~1.2MPa and a holding time of 3~5s; a final blowing pressure of 2.5~3.0MPa and a blowing rate of 15~20L / min.

[0015] The multi-layer composite structure ultra-clean barrel provided by the present invention has unique advantages in terms of intermolecular interaction, material interface bonding and microstructure regulation through precise design of material composition and process parameters.

[0016] In terms of material structure, the ethylene-vinyl alcohol copolymer (EVOH) in the outer layer consists of alternating hydrophobic ethylene segments and hydrophilic vinyl alcohol segments. The ethylene segments form a flexible backbone through van der Waals forces, while the dense hydroxyl groups (-OH) in the vinyl alcohol segments form a network of intra- and intermolecular hydrogen bonds. This dual effect enables EVOH to maintain a dense structure even in polar environments, improving its oxygen barrier performance by over 80% compared to conventional polyethylene. Polymethyl methacrylate (PMMA) acts as a polar compatibilizer. The oxygen atoms of its side chain ester groups (-COOCH3) form dipole-dipole interactions with the EVOH hydroxyl groups through lone pairs of electrons, effectively reducing the interfacial tension between EVOH and the middle layer HDPE during twin-screw extrusion, thus stabilizing the EVOH dispersed phase size at the micron level. The silanol (Si-OH) groups on the surface of the silicon micropowder form hydrogen bond bridges with the hydroxyl groups of EVOH, creating a "rigid-flexible" composite structure within the PMMA matrix. Micron-sized particles (≤1μm) extend the gas diffusion path through a geometric barrier effect, while their high hardness significantly improves the scratch resistance of the outer surface. The high-density polyethylene (HDPE) matrix of the middle layer consists of a dense crystalline structure formed by a highly ordered arrangement of linear molecular chains. During the blow molding process, the shear flow field induces the formation of β-crystals. The spherulites are small in size and tightly bonded at the interface, giving the middle layer excellent compressive strength. The inner layer of ultra-clean HDPE is made from medical-grade raw materials and undergoes precision screening to remove low-molecular-weight substances and impurity particles. The narrow molecular weight distribution stabilizes the melt flowability, and the non-polar hydrocarbon backbone significantly reduces surface energy, effectively inhibiting the adsorption of pollutants.

[0017] The material adopts a three-layer structure with a thickness ratio of 20%:70%:10%, a ratio optimized based on a balance between functional requirements and mechanical properties. The 20% thickness of the outer layer allows the EVOH / PMMA composite layer to form a continuous and dense barrier, thick enough to extend the diffusion path of gas molecules while avoiding the increased brittleness of the material due to excessive thickness. The 70% proportion of the middle layer fully utilizes the mechanical bearing advantages of HDPE. The thick HDPE matrix significantly improves the overall bending strength and impact resistance through the volume effect, and the three-dimensional cross-linked network of the β crystal form effectively disperses external stress. The 10% thin layer design of the inner layer reduces material usage by reducing thickness while ensuring ultra-clean functions. At the same time, the thin layer effect is used to alleviate the interfacial stress caused by the difference in thermal shrinkage between the inner and outer layers. The thickness ratio of the three layers is precisely controlled by temperature zoning in the die head: the higher temperature of the outer layer (190-200°C) reduces the EVOH / PMMA melt viscosity, the highest temperature of the middle layer (210-220°C) promotes the stretching of the HDPE molecular chains, and the lower temperature of the inner layer (180-190°C) maintains the melt strength of the ultra-clean HDPE. The viscosity gradient of the three ensures matching flow rates between layers and achieves precise control of the thickness ratio.

[0018] During material preparation, the process parameters for the outer layer composite material were designed to enhance intermolecular interactions and optimize the microstructure. When EVOH and PMMA are mixed in a 3:1 mass ratio, EVOH becomes the dominant phase, forming a continuous network structure. PMMA, as the dispersed phase, is embedded in the network interstices through the polar interactions of ester and hydroxyl groups. The silicon micropowder addition level is controlled at 8-10%, ensuring uniform dispersion within the matrix while avoiding interfacial defects caused by excessive addition. High-speed mixing (600 rpm) under nitrogen protection breaks up silicon micropowder agglomerates through mechanical shear forces while preventing oxidative deactivation of the hydroxyl groups. The twin-screw extruder's four-zone temperature gradient (180°C → 200°C → 220°C → 210°C) achieves phased material melting and interfacial fusion: low temperature in the first zone prevents premature degradation of EVOH; elevated temperature in the second zone melts the EVOH to form a continuous phase; elevated temperature in the third zone promotes complete melting of PMMA and its penetration into the EVOH interface; and cooling in the fourth zone stabilizes the melt structure. The shear field generated by the screw speed of 180 r / min further refines the dispersed phase size, while the melt pressure of 12 MPa ensures a dense, bubble-free material. The water-cooled strands utilize 25°C cooling water to achieve rapid melt solidification, suppressing the brittleness caused by excessive EVOH crystallinity while simultaneously locking in the dispersed state of the silica powder. The drying process at 70-80°C, below the glass transition temperature of EVOH (Tg=85°C), allows for the limited motion of molecular segments, encouraging the slow diffusion of adsorbed water. After 12-14 hours of drying, the moisture content is reduced to below 0.03%, preventing moisture-induced hydrolysis and breakage of the EVOH molecular chains during subsequent processing.

[0019] The clean barrel preparation process achieves structural integrity through rheological control and molding dynamics optimization. When the middle layer of HDPE is dried with hot air at 120-130°C, the physically adsorbed water in the molecular chain is released through thermal motion. The convection created by the wind speed of 1.5-2.0 m / s accelerates the diffusion of water. After 2-3 hours of drying, the moisture content gradient within the particles tends to equilibrium. After the inner layer of ultra-clean HDPE is screened with a 0.45μm filter, low molecular weight oligomers and ash particles are effectively intercepted. The narrowing of the molecular weight distribution reduces the fluctuation of the melt flow rate, ensuring the surface smoothness of the inner layer during blow molding (Ra≤0.2μm). In three-layer co-extrusion blow molding, the die head temperature zoning setting forms a viscosity gradient: the lower viscosity melt in the outer layer flows preferentially to form a surface coating layer, the moderate viscosity melt in the middle layer builds the main structure, and the higher viscosity melt in the inner layer maintains morphological stability. The combination of a blow-up ratio of 2.8-3.2 and a pulling speed of 6-8 m / min results in biaxial orientation of the material, resulting in orderly alignment of the HDPE molecular chains in both the machine and transverse directions. This increases crystallinity to over 85% and significantly reduces anisotropy. Two-stage pressure blow molding uses a pre-blow (0.8-1.2 MPa) to initially expand the parison and release residual stresses. A 3-5 second hold pressure relaxes the outer layer. A final high-pressure blow (2.5-3.0 MPa) combined with a high-speed airflow (15-20 L / min) ensures rapid mold adhesion of the inner layer. The viscoelastic deformation of the molecular chains allows for the complete reproduction of the fine texture (≤0.5 μm) on the mold surface. During the cooling process, the outer layer preferentially solidifies to form a protective shell, while the middle and inner layers sequentially crystallize and set, ultimately forming a synergistic structural system with a high-barrier outer layer, a high-strength middle layer, and an ultra-clean inner layer. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0021] Example 1

[0022] A super-clean barrel with a multi-layer composite structure, comprising an outer layer material, an intermediate layer material and an inner layer super-clean material. The preparation method of the outer layer material is: S1: Ethylene-vinyl alcohol copolymer (EVOH) and polymethyl methacrylate (PMMA) were mixed in a mass ratio of 3:1 to obtain a mixed powder. 8% of silica powder was added based on the mass of the mixed powder. The mixture was placed in a high-speed mixer under nitrogen protection and stirred at 600 rpm for 20 min to obtain a premix. S2: The premix is ​​melt-blended in a twin-screw extruder at 180°C in zone 1, 200°C in zone 2, 220°C in zone 3, and 210°C in zone 4, with a screw speed of 180 r / min and a melt pressure of 12 MPa to obtain an extruded melt; S3: The extruded melt is water-cooled at 25°C and pelletized into strands with a pellet length of 3 mm. The outer layer material composite material is obtained after drying. The drying parameters are drying at 70°C for 14 hours and the moisture content of the material is ≤0.03%.

[0023] A preparation process of an ultra-clean barrel with a multi-layer composite structure, the specific process of the preparation process is as follows: A1: Use high-density polyethylene (HDPE) granules to dry at 120°C for 3 hours as the middle layer material. Use a hot air circulation drying oven with a wind speed of 1.5m / s. After drying, the moisture content of the HDPE granules should be ≤0.02%. A2: Medical-grade high-density polyethylene (HDPE) granules are screened through a 0.45 μm pore size filter to serve as the inner layer ultra-clean material. A3: The outer layer composite masterbatch, the middle layer HDPE, and the inner layer ultra-clean HDPE were placed separately into a three-layer co-extrusion blow molding unit. The die head temperature zones were set to 190°C for the outer layer, 210°C for the middle layer, and 180°C for the inner layer. The blow-up ratio was 3.0, the pulling speed was 7 m / min, and the thickness ratio of the three layers was controlled to be 20%:70%:10%. The ultra-clean barrel with the multi-layer composite structure was obtained by blow molding. The inflation molding stage adopts two-stage pressure control, with a pre-blowing pressure of 0.8 MPa and a holding time of 5 seconds; a final blowing pressure of 2.5 MPa and a blowing rate of 20 L / min.

[0024] Example 2

[0025] A super-clean barrel with a multi-layer composite structure, comprising an outer layer material, an intermediate layer material and an inner layer super-clean material. The preparation method of the outer layer material is: S1: Ethylene-vinyl alcohol copolymer (EVOH) and polymethyl methacrylate (PMMA) were mixed in a mass ratio of 3:1 to obtain a mixed powder. 10% of silica powder was added to the mixed powder. The mixture was placed in a high-speed mixer under nitrogen protection and stirred at 600 rpm for 15 minutes to obtain a premix. S2: The premix is ​​melt-blended in a twin-screw extruder at 180°C in zone 1, 200°C in zone 2, 220°C in zone 3, and 210°C in zone 4, with a screw speed of 180 r / min and a melt pressure of 12 MPa to obtain an extruded melt; S3: The extruded melt is water-cooled at 25°C and pelletized into strands with a pellet length of 5 mm. The outer layer material composite material is obtained after drying. The drying parameters are drying at 80°C for 12 hours and the moisture content of the material is ≤0.03%.

[0026] A preparation process of an ultra-clean barrel with a multi-layer composite structure, the specific process of the preparation process is as follows: A1: Use high-density polyethylene (HDPE) granules to dry at 130°C for 2 hours as the middle layer material. Use a hot air circulation drying oven with a wind speed of 2.0 m / s. After drying, the moisture content of the HDPE granules should be ≤0.02%. A2: Medical-grade high-density polyethylene (HDPE) granules are screened through a 0.45 μm pore size filter to serve as the inner layer ultra-clean material. A3: The outer layer composite masterbatch, the middle layer HDPE, and the inner layer ultra-clean HDPE were placed into a three-layer co-extrusion blow molding unit. The die head temperature zones were set to 200°C for the outer layer, 220°C for the middle layer, and 190°C for the inner layer. The blow-up ratio was 2.8, the pulling speed was 6 m / min, and the thickness ratio of the three layers was controlled to be 20%:70%:10%. The ultra-clean barrel with the multi-layer composite structure was obtained by blow molding. The inflation molding stage adopts two-stage pressure control, with a pre-blowing pressure of 1.2 MPa and a holding time of 3 seconds; a final blowing pressure of 3.0 MPa and a blowing rate of 15 L / min.

[0027] Example 3

[0028] A super-clean barrel with a multi-layer composite structure, comprising an outer layer material, an intermediate layer material and an inner layer super-clean material. The preparation method of the outer layer material is: S1: Ethylene-vinyl alcohol copolymer (EVOH) and polymethyl methacrylate (PMMA) were mixed in a mass ratio of 3:1 to obtain a mixed powder. 10% of silica powder was added to the mixed powder. The mixture was placed in a high-speed mixer under nitrogen protection and stirred at 600 rpm for 20 min to obtain a premix. S2: The premix is ​​melt-blended in a twin-screw extruder at 180°C in zone 1, 200°C in zone 2, 220°C in zone 3, and 210°C in zone 4, with a screw speed of 180 r / min and a melt pressure of 12 MPa to obtain an extruded melt; S3: The extruded melt is water-cooled at 25°C and pelletized into strands with a pellet length of 3 mm. The outer layer material composite material is obtained after drying. The drying parameters are drying at 70°C for 14 hours and the moisture content of the material is ≤0.03%.

[0029] A preparation process of an ultra-clean barrel with a multi-layer composite structure, the specific process of the preparation process is as follows: A1: Use high-density polyethylene (HDPE) granules to dry at 130°C for 2 hours as the middle layer material. Use a hot air circulation drying oven with a wind speed of 1.5m / s. After drying, the moisture content of the HDPE granules should be ≤0.02%. A2: Medical-grade high-density polyethylene (HDPE) granules are screened through a 0.45 μm pore size filter to serve as the inner layer ultra-clean material. A3: The outer layer composite masterbatch, the middle layer HDPE, and the inner layer ultra-clean HDPE were placed separately into a three-layer co-extrusion blow molding unit. The die head temperature zones were set to 200°C for the outer layer, 210°C for the middle layer, and 190°C for the inner layer. The blow-up ratio was 3.2, the pulling speed was 8 m / min, and the thickness ratio of the three layers was controlled to be 20%:70%:10%. The ultra-clean barrel with the multi-layer composite structure was obtained by blow molding. The inflation molding stage adopts two-stage pressure control, with a pre-blowing pressure of 1.2 MPa and a holding time of 5 seconds; a final blowing pressure of 3.0 MPa and a blowing rate of 20 L / min.

[0030] Comparative Example 1 In this comparative example, PMMA was not added during the preparation of the outer layer material, and the remaining steps were consistent with those in Example 1.

[0031] Comparative Example 2 In this comparative example, silicon powder was not added during the preparation of the outer layer material, and the remaining steps were consistent with those of Example 1.

[0032] Comparative Example 3 In this comparative example, during the preparation of the ultra-clean barrel, the thickness ratio of the three layers was controlled to be 10%:80%:10%, and the remaining steps were consistent with Example 1.

[0033] The impact resistance of the examples and comparative examples was tested according to ASTM D256 at 25°C. The test results are summarized in the following table: Notched impact strength (kJ / m²) Example 1 28.8 Example 2 28.4 Example 3 28.5 Comparative Example 1 15.2 Comparative Example 2 20.7 Comparative Example 3 23.6 It can be seen from experimental data that the ultra-clean barrel with a multi-layer composite structure prepared by the present invention has better impact resistance.

[0034] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A multi-layer composite structure clean barrel, characterized in that: The multi-layer composite structure comprises an outer layer material, an intermediate layer material and an inner layer ultra-clean material, Wherein, the outer layer material includes ethylene-vinyl alcohol copolymer EVOH, polymethyl methacrylate PMMA, and silicon powder; The intermediate layer material is a high-density polyethylene (HDPE) matrix; The inner layer of ultra-clean material is a high-density polyethylene (HDPE) layer; The thickness of the three layers is 20%:70%:10%.

2. The ultra-clean barrel of a multi-layer composite structure according to claim 1, characterized in that: The preparation method of the outer layer material is: S1: Ethylene-vinyl alcohol copolymer (EVOH) and polymethyl methacrylate (PMMA) were mixed in a mass ratio of 3:1 to obtain a mixed powder. 8-10% of silicon micropowder was added based on the mass of the mixed powder. The mixture was placed in a high-speed mixer under nitrogen protection and stirred at 600 rpm for 15-20 minutes to obtain a premix. S2: melt-blending the premixed materials through a twin-screw extruder to obtain an extruded melt; S3: The extruded melt is subjected to water-cooling and strand-cutting, with a pelletizing length of 3-5 mm, and dried to obtain a composite material of the outer layer material.

3. The clean barrel of a multi-layer composite structure according to claim 2, characterized in that: The particle size of the silicon powder in S1 is ≤1 μm.

4. The ultra-clean barrel of a multi-layer composite structure according to claim 2, characterized in that: The melt blending process in S2 includes four temperature zones: zone 1 at 180°C, zone 2 at 200°C, zone 3 at 220°C, and zone 4 at 210°C; a screw speed of 180 r / min; and a melt pressure of 12 MPa.

5. The ultra-clean barrel of a multi-layer composite structure according to claim 2, characterized in that: The temperature of the cooling water in S3 is 25°C.

6. The ultra-clean barrel with a multi-layer composite structure according to claim 2, characterized in that: The drying parameters in S3 are drying at 70-80° C. for 12-14 hours, and the moisture content of the material is ≤0.03%.

7. A process for preparing a clean drum with a multi-layer composite structure, which is realized based on the clean drum with a multi-layer composite structure according to any one of claims 1 to 6, characterized in that: The specific process of the preparation process is as follows: A1: Dry high-density polyethylene (HDPE) pellets at 120-130°C with hot air for 2-3 hours as the middle layer material. A2: Medical-grade high-density polyethylene (HDPE) granules are screened through a 0.45 μm pore size filter to serve as the inner layer ultra-clean material. A3: The outer layer material composite masterbatch, the middle layer HDPE, and the inner layer ultra-clean HDPE are respectively placed into a three-layer co-extrusion blow molding unit. The die head temperature zones are set to 190-200°C for the outer layer, 210-220°C for the middle layer, and 180-190°C for the inner layer. The blow-up ratio is 2.8-3.2, the pulling speed is 6-8 m / min, and the thickness ratio of the three layers is controlled to be 20%:70%:10%. The ultra-clean barrel with the multi-layer composite structure is obtained by blow molding.

8. The process for preparing a super clean barrel with a multi-layer composite structure according to claim 7, characterized in that: The hot air drying in A1 adopts a hot air circulation drying oven, and the wind speed is controlled at 1.5~2.0m / s. After drying, the moisture content of the HDPE particles is ≤0.02%.

9. The process for preparing a super clean barrel with a multi-layer composite structure according to claim 7, characterized in that: The inflation molding stage in A3 adopts two-stage pressure control, with a pre-blowing pressure of 0.8~1.2MPa and a holding time of 3~5s; a final blowing pressure of 2.5~3.0MPa and a blowing rate of 15~20L / min.