3D printing polyurethane mortar floor material and preparation method thereof

Abstract

The application discloses a kind of 3D printing polyurethane mortar floor materials and preparation method thereof, belong to 3D printing floor material technical field.The polyurethane mortar floor material is composed of independently packed A component and B component:A component includes polyether polyol, dimethylol propyl sulfonic acid, rheological agent, defoaming agent, dispersing agent, catalyst A, filler;B component includes polyisocyanate, catalyst B and aggregate;NCO / OH equivalent ratio is 1.05-1.15.The application realizes 10-30 minutes of operable window period by optimizing system component, and solves the contradiction problem of extrudability and buildability of polyurethane mortar in 3D printing.The obtained floor curing compressive strength is greater than or equal to 80MPa, excellent wear resistance, good chemical corrosion resistance and high-low temperature resistance, suitable for 3D printing construction process of industrial floor.

Description

Technical Field

[0001] This invention belongs to the field of 3D printed flooring materials technology, specifically relating to a 3D printed polyurethane mortar flooring material and its preparation method. Background Technology

[0002] Polyurethane mortar flooring is widely used in flooring projects in industrial fields such as food processing, pharmaceuticals, electronics, and chemicals due to its excellent chemical corrosion resistance, high and low temperature resistance, and high impact resistance. Traditional polyurethane mortar flooring is mainly constructed using self-leveling or trowel-applied processes, which require multiple steps and suffer from problems such as high dependence on manual labor, unstable quality, long curing period, and inability to achieve one-time molding of complex structures.

[0003] In recent years, 3D printing technology has seen rapid development in the construction field. For example, patent CN105419306B discloses a 3D printed flooring, which uses polyurethane resin, epoxy acrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, talc powder, and other components to form a 3D printed floor layer by layer through microdroplet jet bonding technology. Another example is patent US20240181673A1, which discloses a mortar composition for forming structures by 3D printing. This mortar composition contains mortar powder (including cement and aggregate), one or more epoxy resins, and a curing agent. The composition has improved fluidity, slump, and consistency, and allows for in-situ reinforcement integration during the printing process.

[0004] Traditional two-component polyurethane mortars are designed for self-leveling or trowel-applied processes. Their formulation logic conflicts with 3D printing in several ways. First, their rheological properties are incompatible. Self-leveling materials require low viscosity and good leveling properties, with a thixotropic index (TI value) typically below 1.5 and a weak shear-thinning effect. However, 3D printing materials require high thixotropy, with a TI value usually above 3.0. Second, there is a contradiction between curing speed and continuous printing. Traditional polyurethane mortars generally use low catalyst dosages or conventional catalysts to extend working time. However, 3D printing requires materials to rapidly build structural strength within minutes of extrusion to support the upper printing layers, but premature curing inside the print head can lead to clogging.

[0005] Therefore, developing a 3D printable polyurethane mortar flooring material that retains the excellent properties of polyurethane mortar while meeting the requirements of 3D printing processes for material rheology, curing speed, and aggregate compatibility has great market application value. Summary of the Invention

[0006] To address the technical challenges of traditional polyurethane mortar materials failing to simultaneously meet the extrudability and constructability requirements of 3D printing processes, and the rapid curing reaction of two-component polyurethane systems leading to short operating windows and easy clogging of printheads, this application provides a 3D-printed polyurethane mortar flooring material and its preparation method. By optimizing the polyurethane resin system, catalyst type, and filler specifications, compared to conventional polyurethane mortar formulations, the prepared 3D-printed polyurethane mortar flooring material exhibits at least a 3-fold increase in thixotropic index, smooth material pumping, and effectively extended operating windows, effectively meeting the needs of continuous 3D printing. The cured flooring also demonstrates excellent compressive strength and chemical resistance.

[0007] To achieve the above-mentioned effects, the technical solution of the present invention is as follows: A 3D-printed polyurethane mortar flooring material, comprising component A and component B, in parts by weight, Component A: 40-60 parts polyether polyol, 2-8 parts dimethylolpropanesulfonic acid, 1.5-4.5 parts rheology modifier, 0.2-0.5 parts defoamer, 0.3-0.7 parts dispersant, 0.05-0.2 parts catalyst A, and 10-25 parts filler; Component B: 30-45 parts of polyisocyanate, 0.02-1 part of catalyst B, and 10-20 parts of aggregate; The NCO / OH equivalent ratio in polyurethane mortar flooring materials is 1.05-1.15. This application introduces sulfonic acid groups into the polyurethane backbone through dimethylolpropanesulfonic acid copolymerization. Its strong hygroscopic properties rapidly capture trace amounts of moisture from the aggregate surface, promoting the formation of a urea bond crosslinking network from free NCO groups, achieving rapid layer stabilization within 30-60 seconds after printing. If the sulfonic acid group content is too low, the triggering speed is insufficient, the printed layer is prone to collapse, and the interlayer strength decreases; if it is too high, the system cures prematurely, leading to blockage, increased water absorption after curing, decreased toughness, and CO2 byproducts causing surface porosity defects. After being embedded in the backbone in a copolymeric form, the sulfonic acid groups are coated with hydrophobic segments, resulting in low exposed hydrophilicity and good durability after curing. Therefore, the sulfonic acid group content needs to be controlled to balance the comprehensive requirements of triggering speed, workability, and post-curing water resistance and toughness. Furthermore, the polyether polyol is polytetrahydrofuran ether diol (PTMG).

[0008] Furthermore, the polytetrahydrofuran ether diol has a weight-average molecular weight of 1000-3000 g / mol and a functionality of 2-3; this molecular weight and functionality range allows the polyurethane mortar to have a better balance between mechanical and rheological properties.

[0009] Furthermore, the rheology modifier includes one or two of fumed silica and organobentonite.

[0010] Preferably, the rheology modifier comprises fumed silica and organobentonite in a ratio of 1-3:0.5-1.5. The two work synergistically to reduce viscosity at high shear rates during printing for smooth extrusion, and to rapidly restore structural strength at low shear rates after extrusion, preventing the printed layer from collapsing. Adding a small amount of fumed silica can increase the system's low-shear viscosity; however, improper dosage can lead to excessively high overall viscosity, resulting in excessively high dynamic yield stress and difficulties in pumping and extrusion. Organobentonite provides structural viscosity at medium to low shear rates, and its slower thixotropic recovery improves anti-settling and anti-sagging properties.

[0011] Furthermore, the defoamer is a polysilane-based defoamer.

[0012] Furthermore, the dispersant is a carboxylic acid dispersant.

[0013] Furthermore, catalyst A is an organotin catalyst, selected from one or more combinations of dibutyltin dilaurate, dibutyltin diacetate, dioctyltin thiolate, and dibutyltin oxide.

[0014] Preferably, the organotin catalyst is dibutyltin dilaurate.

[0015] Furthermore, the filler includes at least one of quartz sand, nano-silica, and chopped polypropylene fibers.

[0016] Preferably, the particle size of the quartz sand is 100-200 mesh, more preferably 150-200 mesh.

[0017] Furthermore, the aspect ratio of the chopped polypropylene fibers is 100-300.

[0018] In some embodiments, the filler comprises 10-25 parts silica sand and 0.5-2 parts nano-silica. Silica sand provides the compressive strength, abrasion resistance, and dimensional stability required for flooring, but its high density and weak interfacial bonding with resin, when used alone, easily lead to aggregate settling, interfacial debonding, and insufficient print conformability. Adding nano-silica suspends the silica sand in the resin by forming a nano-network and enriches it on the silica sand surface, improving interfacial bonding. It can also synergistically enhance the strength of the thixotropic network with rheology modifiers.

[0019] In some embodiments, the filler consists of 10-25 parts of quartz sand and 0.5-1.5 parts of chopped polypropylene fibers. The uniformly dispersed chopped fibers can form a three-dimensional micro-skeleton network within the mortar, preventing the initiation and propagation of microcracks and preventing cracking or even warping of the printed layer due to shrinkage. However, the dosage needs to be controlled to avoid negatively impacting the fluidity of the system.

[0020] In some embodiments, the filler is 10-23 parts of quartz sand, 0.5-2 parts of nano-silica, and 0.5-1.5 parts of chopped polypropylene fibers.

[0021] Furthermore, component A may also include 0.1-0.5 parts of color paste.

[0022] Furthermore, the polyisocyanate is an isophorone diisocyanate (IPDI) trimer or a hexamethylene diisocyanate (HDI) trimer.

[0023] Furthermore, catalyst B is 1,4-diazabicyclo[2.2.2]octane (DABCO). DABCO can efficiently and selectively catalyze the gelation reaction, ensuring that the material rapidly builds structural strength after 3D printing extrusion without collapsing.

[0024] Furthermore, the aggregate is nano-montmorillonite. The layered silicate structure of montmorillonite forms a dynamic cardboard structure in the system, increasing the static yield stress of the material and preventing the printed layer from collapsing under its own weight.

[0025] A method for preparing 3D printed polyurethane mortar flooring material, the method comprising preparing component A and component B respectively according to the following steps: S1. Preparation of component A: Add polyether polyol to the reactor, heat to 40-50℃, add defoamer and dispersant while stirring and mix, then add filler and disperse evenly, cool to below 30℃, add dimethylolpropanesulfonic acid and catalyst and stir evenly, then degas under vacuum and discharge. S2. Preparation of component B: Add polyisocyanate to another reactor, add catalyst to dissolve, add aggregate, stir and disperse evenly, and discharge after vacuum degassing.

[0026] Furthermore, after adding the filler in S1, the stirring speed is set to 1000-1500 rpm, and the dispersion time is 20-40 min.

[0027] Furthermore, the vacuum degree of the vacuum degassing is ≤-0.08MPa, and the degassing time is 10-30min.

[0028] This application also provides a construction method for the aforementioned 3D printed polyurethane mortar flooring material, comprising the following steps: loading component A and component B into two independent barrels of a 3D printing device, delivering component A and component B to a static mixing print head via a metering pump, extruding the mixture from the nozzle, and printing the flooring layer by layer according to a planned path; allowing each layer to stand for 2-5 minutes after printing to allow the material to initially solidify before printing the next layer; and curing at room temperature for at least 24 hours after printing.

[0029] Further, components A and B are mixed according to an NCO / OH equivalent ratio of 1.05-1.15.

[0030] Furthermore, the nozzle extrusion speed is 10-50 mm / s, and the height of each layer is 3-8 mm.

[0031] Furthermore, printing can be performed using continuous loop or zigzag paths.

[0032] Furthermore, the maintenance time is 24-48 hours.

[0033] Preferably, the thixotropic index of the 3D printed polyurethane mortar flooring material is ≥3.5.

[0034] The beneficial effects of this invention are: (1) In this application, sulfonic acid groups are introduced into the polyurethane backbone by copolymerizing dimethylolpropanesulfonic acid. The strong hygroscopic properties of sulfonic acid are used to quickly capture trace amounts of moisture on the surface of aggregates, which promotes the formation of urea bond crosslinking network by free NCO groups, thereby achieving rapid stabilization of the layer shape within 30 to 60 seconds after printing.

[0035] (2) The thixotropic agent system of fumed silica and organic bentonite in this application can make the thixotropic index of the material reach 3.0-5.5, which is about 3 times higher than the thixotropic index of 1.2 of conventional polyurethane mortar formulation. It can be pumped smoothly and extruded easily, and the printed layer does not collapse.

[0036] (3) This application achieves a suitable working window by adding a latent catalyst DABCO, avoiding printhead clogging, and then rapidly crosslinking and curing to ensure rapid strength establishment during continuous printing, thus solving the problem of continuous printing caused by the rapid curing reaction after mixing of two-component polyurethane systems.

[0037] (4) This application achieves automated construction through a two-component online mixing extrusion 3D printing system, reducing the traditional 3-5 person construction team to 1-2 people, increasing construction efficiency by 2-3 times, and the uniformity of floor thickness can be controlled within ±0.5mm, which is far superior to ±2mm or more of manual troweling. It greatly reduces the dependence on the moisture content of the base layer and the ambient temperature and humidity, and can realize one-time molding of complex designs such as gradient colors, irregular structures, and local thickening.

[0038] (5) The cured flooring of this application has high chemical corrosion resistance (resistance to acids, alkalis, greases and solvents), high and low temperature resistance (-40℃ to 130℃), compressive strength ≥80MPa, excellent wear resistance and no VOC emissions.

[0039] (6) The material cost of this application is reduced by more than 30% compared with the photocurable 3D printing flooring resin; the material utilization rate is more than 95% (the traditional self-leveling flooring has only 70-80% due to edge loss); the construction period is effectively shortened and the management cost is reduced. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1 This embodiment provides a 3D printed polyurethane mortar flooring material, comprising component A and component B, in parts by weight. Component A consists of: 50 parts of polyether polyol (Mw=2000g / mol, functionality 2); 5 parts of dimethylolpropanesulfonic acid; Two parts of hydrophobic fumed silica (HB-152, Huifu); 1 part organic bentonite; 0.3 parts of polysiloxane defoamer (Tego 900); 0.5 parts of high molecular weight carboxylic acid dispersant (DA 421A, Yuchang); 0.1 parts of organotin catalyst (dibutyltin dilaurate); 20 parts of 200-mesh quartz sand; 1.5 parts of nano-silica (50nm particle size); 0.2 parts colorant.

[0042] Component B is: 40 parts of isophorone diisocyanate trimer (IPDI trimer, Desmodur Z 4470 MPA / X); 0.05 parts of blocked DABCO catalyst (Evonik DABCO 8154); 15 portions of montmorillonite (HFGEL-200); The equivalence ratio of NCO / OH in the system is 1.08.

[0043] The preparation method of component A is as follows: polyether polyol is put into a reaction vessel, heated to 45°C, and polysiloxane defoamer and high molecular weight carboxylic acid dispersant are added and mixed under stirring. Then nano silica and quartz sand are added and dispersed at high speed of 1200 rpm for 30 min until uniform. The temperature is lowered to below 30°C, dimethylolpropanesulfonic acid and organotin catalyst are added and stirred evenly. After vacuum degassing at -0.08 MPa for 20 min, the material is discharged. S2. Preparation of component B: IPDI trimer is added to another reactor, sealed DABCO catalyst is added to dissolve it, montmorillonite is added, and the mixture is stirred and dispersed evenly. After vacuum degassing at -0.08 MPa for 20 minutes, the product is discharged.

[0044] Example 2 This embodiment provides a 3D printed polyurethane mortar flooring material, comprising component A and component B, in parts by weight. Component A consists of: 60 parts of polyether polyol (Mw=2000g / mol, functionality 2); 8 parts of dimethylolpropanesulfonic acid; Three parts of hydrophobic fumed silica (HB-152, Huifu); 1.5 parts organic bentonite; 0.5 parts of polysiloxane defoamer (Tego 900); 0.7 parts of a high molecular weight carboxylic acid dispersant (DA 421A, Yuchang); 0.2 parts of organotin catalyst (dibutyltin dilaurate); 23 parts of 200-mesh quartz sand; 1.5 parts of nano-silica (50nm particle size); 0.3 parts colorant.

[0045] Component B is: 45 parts of isophorone diisocyanate trimer (IPDI trimer, Desmodur Z 4470 MPA / X); 0.2 parts of blocked DABCO catalyst (Evonik DABCO 8154); 20 portions of montmorillonite (HFGEL-200); The equivalence ratio of NCO / OH in the system is 1.05.

[0046] The preparation method of component A is as follows: polyether polyol is put into a reaction vessel, heated to 45°C, and polysiloxane defoamer and high molecular weight carboxylic acid dispersant are added and mixed under stirring. Then nano silica and quartz sand are added and dispersed at high speed of 1500 rpm for 20 min until uniform. The temperature is lowered to below 30°C, dimethylolpropanesulfonic acid and organotin catalyst are added and stirred evenly. After vacuum degassing at -0.08 MPa for 30 min, the material is discharged. S2. Preparation of component B: IPDI trimer is added to another reactor, sealed DABCO catalyst is added to dissolve it, montmorillonite is added, and the mixture is stirred and dispersed evenly. After vacuum degassing at -0.08 MPa for 20 minutes, the product is discharged.

[0047] Example 3 This embodiment provides a 3D printed polyurethane mortar flooring material, comprising component A and component B, in parts by weight. Component A consists of: 40 parts of polyether polyol (Mw=2000g / mol, functionality 2); Two parts of dimethylolpropanesulfonic acid; One part of hydrophobic fumed silica (HB-152, Huifu); 0.5 parts organic bentonite; 0.2 parts of polysiloxane defoamer (Tego 900); 0.3 parts of high molecular weight carboxylic acid dispersant (DA 421A, Yuchang); 0.1 parts of organotin catalyst (dibutyltin dilaurate); 22 parts of 200-mesh quartz sand; 1.5 parts of nano-silica (50nm particle size); One part of chopped polypropylene fiber (3mm in length, aspect ratio 210); 0.1 parts colorant.

[0048] Component B is: 30 parts of isophorone diisocyanate trimer (IPDI trimer, Desmodur Z 4470 MPA / X); 0.02 parts of blocked DABCO catalyst (Evonik DABCO 8154); 10 parts of montmorillonite (HFGEL-200); The equivalence ratio of NCO / OH in the system is 1.15.

[0049] The preparation method of component A is as follows: polyether polyol is put into a reaction vessel, heated to 50°C, and polysiloxane defoamer and high molecular weight carboxylic acid dispersant are added and mixed under stirring. Then, nano silica, quartz sand and short-cut polypropylene fibers are added and dispersed at high speed of 1000 rpm for 40 min until uniform. The temperature is lowered to below 30°C, dimethylolpropanesulfonic acid and organotin catalyst are added and stirred evenly. After vacuum degassing at -0.08 MPa for 20 min, the material is discharged. S2. Preparation of component B: IPDI trimer is added to another reactor, sealed DABCO catalyst is added to dissolve it, montmorillonite is added, and the mixture is stirred and dispersed evenly. After vacuum degassing at -0.08 MPa for 20 minutes, the product is discharged.

[0050] Application examples A construction method for the aforementioned 3D-printed polyurethane mortar flooring material includes the following steps: a. Load component A and component B into two independent barrels of a two-component extrusion 3D printing system; deliver component A and component B to a static mixing printhead by a metering pump according to the specified NCO / OH molar ratio by volume ratio, wherein the aspect ratio of the static mixing printhead is 18 and the printhead temperature is controlled at 20°C; b. After mixing components A and B in the static mixing printhead, the mixture is extruded from the nozzle and printed layer by layer in a zigzag pattern. The nozzle extrusion speed is 30 mm / s, the layer height is 5 mm, and the nozzle inner diameter is 5 mm. After each layer is printed, it is left to stand for 2 minutes to allow the material to initially solidify before printing the next layer. This process is repeated for 10 consecutive layers. c. After printing, allow to cure at room temperature for 24 hours, then continue curing for another 7 days.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that component A consists of: 50 parts of polyether polyol (Mw=2000g / mol, functionality 2); 5 parts of dimethylolpropanesulfonic acid; 0.3 parts of polysiloxane defoamer (Tego 900); 0.5 parts of high molecular weight carboxylic acid dispersant (DA 421A, Yuchang); 0.1 parts of organotin catalyst (dibutyltin dilaurate); 20 parts of 200-mesh quartz sand; 1.5 parts of nano-silica (50nm particle size); 0.2 parts colorant.

[0052] Comparative Example 2 The difference between this comparative example and Example 1 is that component B consists of: 40 parts of isophorone diisocyanate trimer (IPDI trimer, Desmodur Z 4470 MPA / X); 15 portions of montmorillonite (HFGEL-200).

[0053] Comparative Example 3 The difference between this comparative example and Example 1 is that component A consists of: 50 parts of polyether polyol (Mw=2000g / mol, functionality 2); Two parts of hydrophobic fumed silica (HB-152, Huifu); 1 part organic bentonite; 0.3 parts of polysiloxane defoamer (Tego 900); 0.5 parts of high molecular weight carboxylic acid dispersant (DA 421A, Yuchang); 0.1 parts of organotin catalyst (dibutyltin dilaurate); 20 parts of 200-mesh quartz sand; 1.5 parts of nano-silica (50nm particle size); 0.2 parts colorant.

[0054] Performance testing methods and results: 1. Thixotropic index: The viscosity of the polyurethane mortar formed by mixing components A and B is measured using a rotational viscometer at speeds of 0.5 rpm and 50 rpm. The thixotropic index is the ratio of the two components.

[0055] 2. 7-day compressive strength: determined according to GB / T 50081-2019 standard.

[0056] 3. Abrasion resistance test: Tested according to GB / T 1768-2006 standard, with a load of 1000g and abrasion after 1000 revolutions, the weight loss was measured.

[0057] Table 1

[0058] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A 3D-printed polyurethane mortar flooring material, comprising component A and component B, characterized in that, By weight Component A: 40-60 parts polyether polyol, 2-8 parts dimethylolpropanesulfonic acid, 1.5-4.5 parts rheology modifier, 0.2-0.5 parts defoamer, 0.3-0.7 parts dispersant, 0.05-0.2 parts catalyst A, and 10-25 parts filler; Component B: 30-45 parts of polyisocyanate, 0.02-1 part of catalyst B, and 10-20 parts of aggregate; The NCO / OH equivalent ratio in polyurethane mortar flooring materials is 1.05-1.

15.

2. The polyurethane mortar flooring material according to claim 1, characterized in that, The polyether polyol is polytetrahydrofuran ether diol; the weight-average molecular weight of the polytetrahydrofuran ether diol is 1000-3000 g / mol, and the functionality is 2-3.

3. The polyurethane mortar flooring material according to claim 1, characterized in that, The rheology modifier includes one or two of fumed silica and organobentonite; the defoamer is a polysilane defoamer; and the dispersant is a carboxylic acid dispersant.

4. The polyurethane mortar flooring material according to claim 1, characterized in that, The rheology modifier comprises fumed silica and organobentonite in a ratio of 1-3:0.5-1.5; the catalyst A is an organotin catalyst selected from one or more combinations of dibutyltin dilaurate, dibutyltin diacetate, dioctyltin thiolate, and dibutyltin oxide.

5. The polyurethane mortar flooring material according to claim 1, characterized in that, The filler includes at least one of quartz sand, nano-silica, and chopped polypropylene fibers; the particle size of the quartz sand is 100-200 mesh; and the aspect ratio of the chopped polypropylene fibers is 100-300.

6. The polyurethane mortar flooring material according to claim 1, characterized in that, The filler is 10-25 parts of quartz sand and 0.5-2 parts of nano-silica; or, the filler is 10-25 parts of quartz sand and 0.5-1.5 parts of chopped polypropylene fiber; or, the filler is 10-23 parts of quartz sand, 0.5-2 parts of nano-silica and 0.5-1.5 parts of chopped polypropylene fiber.

7. The polyurethane mortar flooring material according to claim 1, characterized in that, The polyisocyanate is either isophorone diisocyanate (IPDI) trimer or hexamethylene diisocyanate (HDI) trimer.

8. The polyurethane mortar flooring material according to claim 1, characterized in that, Catalyst B is 1,4-diazabicyclo[2.2.2]octane.

9. The method for preparing polyurethane mortar flooring material according to any one of claims 1-7, characterized in that, The preparation method is as follows: Component A and Component B are prepared respectively according to the following steps: S1. Preparation of component A: Add polyether polyol to the reactor, heat to 40-50℃, add defoamer and dispersant while stirring and mix, then add filler and disperse evenly, cool to below 30℃, add dimethylolpropanesulfonic acid and catalyst and stir evenly, then degas under vacuum and discharge. S2. Preparation of component B: Add polyisocyanate to another reactor, add catalyst to dissolve, add aggregate, stir and disperse evenly, and discharge after vacuum degassing.

10. The preparation method according to claim 9, characterized in that, The vacuum degree of the vacuum degassing is ≤-0.08MPa, and the degassing time is 10-30min.

Images