Introduction to several conventional coating methods

1、 Precise slit coating method:

Slot Die Coating is a high-precision coating method that is not only used for coating rolled substrates such as electronic components (FPC, RCC, CSP, LOC, etc.), optical films (brightening film, hardcoat, polarizing film, diffusion film, etc.), battery plates, etc., but also for non continuous substrates such as LCD glass substrate photoresist coating. The operating principle is to pump a certain amount of fluid into a mold that can evenly spread the fluid.

The narrow slit coating die can produce very thin coatings and transparent optical coatings, while keeping the coating amount within a very narrow tolerance range. Unlike the coating system that wipes the coating liquid onto the substrate, our narrow slit coating die belongs to the coating die with relatively large lip gaps (up to 0.0762mm), and the liquid sucked out by the lip gaps can form a coating as thin as 1 μ m. The narrow gap coating die can control the coating amount on the entire width within a tolerance range of ± 2.5% when the coating thickness is only 2 μ m. The slit coating die head lip we produce is fixed, so interchangeable gap control plates can be used to change the thickness and width of the coating. The coating thickness ranges from less than 1 μ m to 254 μ m. This type of mold can process various types of adhesives (including special transparent adhesives), such as batteries, ceramic capacitors, decorative surfaces, electronic display media, filter membranes, flooring, fuel cells, magnetic slurries, medical products, photoresist materials, pressure-sensitive tapes, solar cells, superconductors, tear tapes, and window films.

The lip of the mold head is fixed, and the gap between the lip is adjusted using shims. This type of die does not "apply" the coating material flow to the substrate like an adjustable die. It adheres to the substrate by sucking the material flow out of the relatively large die lip gap. The thickness of this wet coating can be as thin as 2 μ m. Based on this wet coating process, the die system is particularly suitable for ultra-thin or transparent coatings.

Currently, many coating manufacturers use both roller and seam die coating processes simultaneously. Roller coating is a traditional process that indirectly controls the amount of material applied to the substrate through a scraper or pre-set roller gap; Excess coating material is scraped off and sent back to the coating tank; The coating groove itself is open in the workshop. Compared to it, the sewing die head is very different. Firstly, it is a closed system, and secondly, it pre measures the coating material through a precision metering pump. Based on these two points, the seam die has some advantages that roller coating does not have:

The coating weight and overall distribution are more uniform;

● Faster production line speed;

Greatly reduces volatile emissions, coating pollution, raw material waste, and workplace chaos.

Our slit type coating die has a coating width of up to 3m and a wet coating thickness ranging from 2 μ m to 254 μ m. The slit coating die is generally provided as part of a complete system, which includes a locator (maintaining orientation with the idler), a vacuum box (removing air carried by the coating material flow from leaving the die to contacting the substrate surface), and material flow conveying equipment (filters, pumps, drive devices, and air filters). As an option, a mold head operation mechanism called a "hinge" can be added to the locator to enable the operator to quickly disassemble and clean the mold head, replace shims if necessary, and re tighten the mold body.

2、 Micro concave coating method:

At present, there are many coating methods in the field of coating, such as direct gravure coating, reverse gravure coating, reverse roller coating, die extrusion coating, wire scraper coating, knife coating, and so on. But now many customers have reported that the coating methods such as wire scraper and reverse roller have produced some disappointing coating effects, such as the stripe phenomenon caused by wire scraper, the "orange peel" phenomenon caused by reverse roller or concave roller, and other difficult quality issues. The micro gravure coating method was developed to overcome the above coating defects. Micro gravure coating can obtain smooth and uniform stable coatings, which is a simple and reliable coating method with good repeatability stability. Micro gravure coating is relative to traditional gravure coating methods. In traditional gravure coating, the coating roller is a mesh roller with a diameter generally between Φ 150mm and Φ 300mm. The rubber roller serves as a back pressure roller to press the film onto the coating roller, and the rotation direction of the coating roller is consistent with the direction of the film feeding. Micro gravure coating, the coating roller is also a mesh roller with a diameter generally between Φ 20mm and Φ 50mm, so it is called micro gravure coating. It is a reverse and contact coating method, where the rotation direction of the micro coating roller is opposite to the feeding direction of the film, and the film is not pressed on the coating roller by the pressure roller.

The working mode of micro gravure coating

Like the traditional intaglio method, the micro concave coating also requires a scraper, but the use of the scraper in the micro concave coating is different in hardness and angle. Compared with the traditional scraper, the scraper for micro concave is thin and flexible, the pressure of the scraper is light, the angle of the scraper is steep, and the extension line of the scraper will basically pass through the center of the coating roller. The coating roller and scraper come into soft contact, so in micro concave coating, the lifespan of the scraper and coating roller is longer.

In micro concave coating, the micro mesh roller also serves as a coating metering roller, and its line count has a wide range. The mesh roller is installed in a precision bearing seat and is directly driven to rotate by a motor, with the direction of rotation opposite to the feeding direction.

In micro concave coating, the arc on the roller surface from the coating roller leaving the liquid surface to the contact point between the roller and the substrate should be an arc less than 90 degrees. For a coating roller with a diameter of 40mm, the distance between this section should not exceed 30mm.

In micro concave coating, the most important factor (and the main factor controlling the coating amount) is the ratio of the feeding speed to the speed of the micro concave coating roller. The film has a speed, while the coating roller is stationary. At this time, there is no coating amount. As the speed of the coating roller increases, the coating amount will increase and overflow may occur. If the speed increases again, the coating amount will decrease. Experimental determination shows that there will be a "hump" curve in the ratio of coating amount to speed.

The typical coating mode will be the following: (coating roller surface line speed/material line speed)

When the speed ratio is 60%, coating begins; When the speed ratio is approximately 130%, uniform and regular coating is achieved; When the speed ratio is 130% to 200%, the coating amount increases; When the speed ratio is above 200%, the coating amount decreases and instability occurs.

Although the size of the coating amount is related to the mesh capacity of the roller, there is also a window on this curve. Usually, at a ratio of~130%, the thickness or weight of the coating can be effectively controlled, and a uniform and consistent coating surface can be ensured. In practical situations, the coating amount of each coating roller can vary within a range of ± 10%. By using a certain number of coating rollers with different line numbers, different coating amounts can be obtained, achieving relatively economical results. By combining the transmission ratio and adjusting the coating roller, a relatively continuous coating amount can be obtained. For stricter coating, a curve between coating amount and speed ratio can be drawn based on the specifications of the coating roller mesh hole and the rheological properties of the adhesive solution.

Advantages of Micro gravure Coating

Micro gravure coating can apply very thin coatings onto very thin materials. Due to the absence of back pressure rollers, there are no defects such as "offset printing" or wrinkles on the coating surface.

Since there is no back pressure roller, the edge of the film can also be coated with glue without worrying about the glue liquid being applied to the back pressure roller and affecting the coating. The traditional coating method requires changing the back pressure roller width when changing the coating width. Micro concave coating can adapt to different widths of paper, film, textile, metal foil, etc., and the materials that can be coated can range from 2 micron PET to 200 micron metal foil.

Due to the light contact between the scraper and the mesh roller, the wear of both the scraper and the mesh roller is very small.

Due to the small diameter and light weight of the micro concave roller, it is convenient to replace it with different coating amounts.

Reverse coating (similar to shearing) can achieve a relatively smooth coating without the need for a uniform adhesive system. Micro coating rollers are more suitable for volatile solvent based adhesives without worrying about clogged mesh holes. The viscosity of the adhesive suitable for micro concave coating ranges from 1cps to 1000cps (the Brinell viscosity unit is 1cps=1mPa. s, and the viscosity of water at room temperature is generally 1 CPS).

Application case of micro gravure coating

1. Electronic field: Light shielding film, 0.05 micron coating thickness; Scratch resistant thermal ITO conductive film; Insulation and multi-layer conductive circuit board; LCD backlight film assembly; New flat lighting; Transparent conductive resin layer; Storage tapes and storage materials; Hard protective film for touch screen, etc

2. In the field of image materials: digital publishing printing layer; Film film; Automated labeling, etc;

3. Medical materials: self-adhesive tape, medical materials with coatings, such as test materials, etc;

4. Optical field: various optical films, such as reflective films, optical enhancement films, etc; Various glass insulation films, etc

5 Battery Industry: Materials for Lithium Batteries

6. Industrial automation field

Various composite tapes; Thin chemical reaction coating; Other coating materials that alter surface properties.

Such as solar cell backplates, friction resistant materials, PTFE materials, etc

3、 Mesh coating method:

Jinwei Machinery develops various types of online coating equipment according to market demand.

The sheet online coating unit can treat the surface of the sheet through coating, achieving special requirements such as anti-static and anti fog. A special sheet made by compounding nanoscale conductive materials with a coating machine, with a surface resistance of 10E4-10E6 ohms.

Sheet characteristics: high cleanliness, no precipitation, conductivity does not change with temperature and humidity, achieving anti-static, widely used in high cleanliness electronic vacuum packaging.

The methods of sheet coating include mesh roller, micro concave roller, rolling coating, soaking and other coating methods. Applicable to APET PETG.PS.PP.ABS.PE.PC and all other plastics.

The characteristics are as follows:

1. Surface resistance: The ultra-thin conductive treatment layer has a conductivity of 104-109, and the corresponding surface resistance can be made by adjusting the formula according to customer requirements.

2. Sex: Stable conductive function, can be reused or recycled without losing anti-static function due to temperature and humidity changes.

3. Reliability: Polymer synthesis technology avoids adding errors or uneven coating, has good processing performance, and does not affect printing, molding, and other properties after conductive treatment.

4. Cleanliness: No powder or oil stains, environmentally friendly, free of harmful substances, non corrosive and volatile gases, and resistant to cleaning.

5. Flexibility: It can flexibly replace various specifications of coating rollers according to different sheet materials and surface coating requirements. We can customize various types of coating rollers for customers.

4、 Comma scraper coating:

Coating parameters

Viscosity: 1000~20000 CPS

Thickness: 20~300 µ m (wet state)

characteristic

High coating accuracy

Uniform surface quality

Coating thickness

Scraper coating often results in uneven glue application, which is mainly related to the processing accuracy of the scraper, the installation method of the scraper, the angle at which the scraper touches the backing wheel during coating, and the viscosity of the coating;

The flatness and accuracy requirements of the scraper are high, which means that the scraper does not warp, deform or have gaps, otherwise the coating amount error will be large; During coating, the angle between the scraper and the tangent line of the adhesive wheel's contact point is generally between

Between 15 ° and 30 °; If it is too large, it will almost hit the back rubber wheel. When the back rubber wheel runs at high speed, the scraper is prone to vibration, causing uneven coating and large differences in coating amount; In addition, it can also cause unevenness and scratches on the coated film surface, and is also prone to causing

The scraper blade is damaged.

Comma roller coating:

The characteristic of comma roller coating is the combination of blade scraper and roller scraper. The influence of adhesive thickness is smaller than that of blade scraper, and the coating thickness is easy to adjust, which can apply high viscosity adhesive. Large width, adjustable horizontally

advantage:

1. The strength and hardness of the comma scraper are high, and the straightness error of the blade edge is small. A pneumatic fine-tuning mechanism can be used to adjust and control the position of the scraper, and the coating amount control and scraping accuracy are high.

2. Thick coatings can be applied, and during coating, the adhesive flows from top to bottom between the scraper blade and the film, so the adhesive can be fully used without wasting it.

Disadvantages:

The coating quality of comma roller coating is closely related to the operation of its various constituent units, especially the transmission ratio between the driving motor and the rotating pressure roller is difficult to adjust and control, which often leads to uneven coating and the appearance of irregular stripes in the horizontal or vertical direction. During coating, the adhesive liquid is prone to flow out from the gap between the baffle and the transmission pressure roller, and the sealing is not complete enough. In addition, during coating, manual labor is required to constantly stir the adhesive liquid in the storage tank to ensure uniform distribution of the adhesive liquid.

Application case of comma roller coating:

Various optical films, protective films, film films, matte flexible packaging films.