1. Rationale
Heated vacuum coating machine is a kind of laboratory precision sample preparation equipment that integrates vacuum adsorption, substrate heating and automatic coating functions. The core design idea of the equipment is to flatten the film substrate (such as silicon wafer, glass, polymer film) on the coating platform through negative pressure, and at the same time use the built-in heating system to preheat or dry the substrate, and finally coat the functional slurry into a uniform liquid film by an automatically driven scraper or wire rod. This integrated design of "fixation-drying-forming" mainly solves the technical problems such as substrate folds, uneven solvent volatilization rate and poor film thickness consistency in the conventional coating process.
In terms of operation logic, the equipment follows three synergistic steps: first, in the physical fixation stage, the vacuum pump generates suction through the micropores on the surface of the platform, eliminates the air between the substrate and the platform, and makes the substrate reach the "mirror-level" flatness, which is the premise of ensuring the tolerance of micron-level coating thickness; secondly, the thermal field intervention stage, the heating element under the platform (such as mica heating plate or graphene heating film) provides controllable heat, accelerates the volatilization of solvents in the wet film, and prevents the phenomenon of "orange peel" or "shrinkage" caused by liquid phase migration; Finally, in the film formation stage, the scraper travels at a set constant speed, using shear force to level the slurry and fill the microscopic voids of the substrate to form a wet film.
According to the specification of ASTM D823 standard for the preparation of uniform paint film and varnish-related coatings, the repeatability error of film formation under laboratory conditions is usually controlled within ±5%, which is suitable for high-precision formula verification and rheological research.
2. Core structure
The technical performance of the heated vacuum coating machine is determined by its three core modules, and the accuracy of the cooperation between each module directly determines the quality of the final film formation.
2.1 Vacuum adsorption system
The system consists of a vacuum pump, a buffer bottle and a porous coating plate. The machine processes microholes with a diameter of about 0.8 mm at specific spacing (e.g. 20 mm × 20 mm matrix) on the surface of the coated plate. The key indicators of vacuum adsorption are "flatness" and "response speed". A well-performing device builds up negative pressure in seconds, allowing the substrate to fit snugly without leaving indentations on the substrate surface due to excessive suction. For paper or fabric bases with strong air permeability, it is sometimes necessary to use mechanical fixtures to assist in fixing.
2.2 Intelligent temperature control heating module
The heating methods are mainly divided into bottom contact conduction heating and infrared radiation heating. Bottom-heated coating machines (such as mica sheet heating) are suitable for conventional lithium battery slurries or polymer solutions, and their temperature uniformity is required to be controlled between ±1°C and ±5°C. In some scenarios that require rapid drying or processing of thick films, the equipment will use infrared heating tubes to penetrate the surface of the liquid film with radiant heat to achieve drying from the inside out. The heating module usually has an adjustment range from room temperature to 150°C (or 180°C) and needs to be insulated to avoid high temperature affecting the motion accuracy of the transmission system.
2.3 Coated transmission mechanism
The coating head drive system mostly adopts servo motor with ball screw to ensure that the travel speed is infinitely adjustable between 50mm/s and 300mm/s. According to different coating methods, there are two main categories:
| Coating type | Technical features and precision |
|---|---|
| Scraper type | Large thickness adjustment range (0.1-10mm), suitable for high viscosity slurries, accuracy ± 0.003mm. |
| Rotary | Uses centrifugal force to lay glue, the speed is 500-10000rpm, suitable for ultra-thin photoresist, high uniformity. |
| Wire rod type | Relying on the winding gap to determine the thickness, it is easy to operate, and the thickness accuracy of the wet film can reach ±0.001mm. |
3. Application scenarios
At the laboratory level, heated vacuum coaters are tools for research on new energy, electronics, and functional film materials. In the research of perovskite solar cells, it is used to prepare electron transport layers and hole transport layers, and use vacuum adsorption to ensure the flatness of transparent conductive glass and prevent scratches. In lithium battery R&D, it is used to evenly coat the positive and negative electrode slurry on copper or aluminum foil, and combine it with heating function to quickly evaporate NMP or deionized aqueous solvent to evaluate the areal density and peel strength under different formulations.
When selecting, researchers should focus on the following technical indicators:
Temperature field uniformity:For studies involving heat-induced phase separation or crystallization kinetics, uniformity of temperature distribution on the surface of the coating platform is critical. If the uniformity is poor (such as exceeding ±5°C), it will lead to inconsistency between the drying rate of the membrane edge and the center, resulting in internal stress cracking.
Stroke and substrate size:The coating stroke of the equipment should match the substrate specifications. Common effective coating areas range from 300mm×150mm to 600mm×600mm, large equipment is suitable for pilot volume, and small equipment is suitable for material screening.
Environmental Adaptability:Some equipment supports operation under inert gas protection (such as in the glove box), and the motor is powered by low-voltage DC (such as 24V/50W) and sealed to prevent safety accidents caused by flammable and explosive solvents.
4. Maintenance requirements
With the specification of the test method of electric heating device in the GB/T 10066 series of standards and the update of the general technical conditions of vacuum coating equipment in GB/T 11164, the modern heating vacuum coating machine is developing in the direction of automation and dataization. The new model equipment has been integrated with an automatic feeding system, which uses air pressure to drip the slurry into the front of the scraper according to the set trajectory, avoiding the problem of bubbles mixed in caused by manual pouring. Some high-end models are equipped with PLC touch screens, which can store up to 12 sets of programs, each containing 6 running stages, to achieve segmented variable speed coating to adapt to the rheological characteristics of non-Newtonian fluids during shear thinning.
When it comes to maintenance, vacuum adsorption holes are a key component. Slurry leakage can cause clogging of micropores, so the platform should be cleaned and vacuumed with solvent after each application. Additionally, the wear of the scraper blade directly affects the coating accuracy, and it is recommended to calibrate it regularly with a feeler gauge or film thickness gauge. For heating elements, long periods of air burning at extreme high temperatures should be avoided to prevent uneven heating caused by thermal conductive grease aging.