Introduction to several conventional coating methods

1. Precise slit coating method:

Slot Die Coating is a high-precision coating method, which is not only used for the coating of electronic fabrics (FPC, RCC, CSP, LOC, etc.), optical films (brightness enhancement film, hardcoat, polarizing film, diffusion film, etc.), battery plates and other coiled substrates, but also for the photoresist coating of discontinuous substrates such as LCD glass substrates. The principle of operation is to pump a certain amount of fluid into a mold that can evenly unfold the fluid.

Unlike coating systems, where the coating fluid is wiped onto the substrate, our slit coating dies are coating dies with relatively large lip gaps (up to 0.0762 mm), from which the liquid drawn from the lip gap can form coatings as thin as 1 μm. The narrow slit coating die can control the amount of coating over the entire width within a tolerance range of about 2.5% ± with a coating thickness of only 2 μm. The lip of the slit coating dies we produce is fixed, so the thickness and width of the coating can be varied with interchangeable gap control plates. Coating thicknesses ranging from less than 1 μm to 254 μm. These dies can process various types of adhesives (including special transparent adhesives) 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 die lip of the die head is fixed, and the gap between the die lip is adjusted with a gap filler. Instead of "spreading" the coated stream onto the substrate like an adjustable die, the die bonds the stream to the substrate by sucking it out of a relatively large lip gap. This wet coating thickness can be as thin as 2 μm. Based on this wet coating process, the die system is particularly suitable for ultra-thin or clear coatings."

At present, many coating manufacturers use both roller and seam die coating processes. Roller coating is a traditional process in which the amount of material applied to the substrate is indirectly controlled by a scraper or a pre-set roll gap; The excess coating material is scraped off and sent back to the coating tank; The coating tank itself is open in the workshop. In contrast, seam dies are very different. Firstly, it is a closed system, and secondly, it is pre-metered with a precision metering pump. It is based on these two points that seam dies offer some advantages that roller coating does not have:

●The coating weight and overall distribution are more uniform;

●The production line speed is faster;
● Minimizes volatile emissions, coating contamination, raw material waste, and workplace chaos.

Our slit coating dies are available in coating widths up to (3 m) and wet coating thicknesses from 2 μm to 254 μm. Slit coating dies are typically supplied as part of a packaged system, but others include positioners (to maintain precise orientation to the rollers), vacuum chambers (to remove air entrained in the coating stream from the distance from leaving the die to contacting the substrate surface), and material flow delivery equipment (filters, pumps, drives, and airers). As an option, a die operation mechanism called a "hinge" can be added to the positioner to allow the operator to quickly disassemble and clean the die, replace the gap filler if necessary, and re-tighten the mold.

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 roll coating, die extrusion coating, wire scraper coating, knife coating, etc. However, many customers now report that coating methods such as wire scrapers and reverse rollers have produced some disappointing coating results, such as the streak phenomenon caused by the wire scraper, the "orange peel" phenomenon caused by the reverse coating roller or concave pressure roller, and other difficult quality problems. The microgravure coating method was developed to overcome the above coating defects. Microgravure coating results in a smooth, homogeneous and stable coating that is simple and reliable with excellent repeatability. Microgravure coating is relative to the traditional gravure coating method. Traditional gravure coating, the coating roller is a anilox roller, the diameter is generally between Φ150mm~Φ300mm, the rubber roller is used as a back pressure roller, the film is pressed on the coating roller, and the rotation direction of the coating roller is consistent with the direction of the material film. Microgravure coating, the coating roller is also an anilox roller, the diameter is generally between Φ20mm~Φ50mm, so it is called micro gravure, it is a reverse, contact coating method, that is, the rotation direction of the micro coating roller is opposite to the direction of the material film, and the film is not pressurized on the coating roller by the pressure roller.

How microgravure coating works

As with the traditional gravure method, a scraper is required for gravure coating, but the use of a scraper in a gravure coating differs in hardness and angle. Compared with traditional scrapers, the slightly concave blades are thin and flexible, the pressure of the scraper is light, the angle of the scraper is steep, and the extension line of the scraper basically passes through the center of the coating roller. The coating roller is in gentle contact with the scraper, so in micro-concave coating, the life of the blade and coating roller is longer.

In micro-concave coating, the role of the micro anilox roller is also to coat the metering roller, and the number of lines also has a wide range. The anilox roller is installed in the precision bearing seat and is directly driven by the motor to rotate, and the direction of rotation is opposite to the direction of material feeding.

In concave coating, the arc on the roll surface should be less than 90 degrees from the time the coating roll leaves the liquid surface to the point where the roll contacts with the substrate. For a coating roller with a diameter of 40 mm, the distance between this section should not exceed 30 mm.

In concave coating, the most important (and the main factor that controls the coating amount) is the ratio of the feed speed to the speed of the concave coating roller. The film has a speed, and the coating roller is stationary, then there is no coating weight, as the coating roller speed increases, the coating amount will increase, and there will be overflow, and the rotation speed will increase again, and the coating amount will decrease. The test determined that the ratio of coating weight to velocity showed a "hump" curve.

Typical coating patterns will be the following: (Coating Roll Surface Linear Velocity / Material Linear Speed)

When the speed ratio = 60%, the coating begins; When the speed ratio = 100%~130%, uniform and regular coating; When the speed ratio = 130%~200%, the coating amount increases; When the speed ratio = 200% or more, the coating amount decreases and instability occurs.

Although the size of the coating amount is related to the cavity capacity of the mesh roller, there is also a window on this curve, usually when the ratio is 100%~130%, the thickness or weight of the coating can be effectively controlled, and a uniform coating surface can be guaranteed. In practice, the coating amount of each coating roll can vary by ± 10%. Through a certain number of coating rollers with different thread numbers, different coating amounts can be obtained, and more economical results can be achieved. Combined with the transmission ratio, adjust the coating roller, and basically obtain a relatively continuous coating amount. For more stringent coating, the curve between the coating amount and the speed ratio can be drawn by combining the specifications of the coating roller cavity and the rheological properties of the glue.

Advantages of microgravure coating

1 Microgravure coating, which allows a very thin coating to be applied to a very thin material. Since there is no back pressure roller, there are no defects such as "offset printing" and wrinkles on the coating surface.

2 Since there is no back pressure roller, the edge of the film can also be coated with glue, without worrying about the glue being applied to the back pressure roller and affecting the coating. The micro-concave coating can adapt to different widths of paper, films, textiles, metal foils, etc., and the materials that can be coated can range from 2 micron PET to 200 micron metal foil.

3 Since the scraper lightly touches the anilox roller, the wear of the scraper and the mesh roller is very small.

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

5 Reverse coating (similar to shear) results in a relatively flat coating without the need for a homogenizing system. Micro coating rollers are more suitable for volatile solvent-based adhesives without worrying about clogging the meshes. The viscosity of the adhesive suitable for coating is from 1cps to 1000cps (cps Brinell viscosity unit 1cps = 1mPa.s, and the viscosity of water at room temperature is generally 1 cps).

Application examples of microgravure coatings

1. Electronics: shading film, 0.05 micron coating thickness; Scratch-resistant thermal ITO conductive film; insulated and multi-layer conductive circuit boards; LCD backlight film stack; new flat lighting; transparent conductive resin layer; storage tapes and storage materials; Hard protective film for touch screen, etc

2. Image material field: digital publishing printing layer; film films; automated labeling, etc.;

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

4. Optical field: all kinds of optical films, such as reflective films, brightening films, etc.; Heat insulation film for various glasses, etc

5 Battery industry: materials for lithium batteries

6 Industrial automation field

various adhesive tapes for lamination; Thin chemically reactive coatings; Other coating materials that alter surface properties.

Such as solar cell backsheet, friction resistant material, Teflon material, etc. 、

3. Anilox coating method:

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

The sheet online coating unit can treat the surface of the sheet by means of coating, which can realize special requirements such as permanent anti-static and anti-fogging. A special sheet made of nano-scale conductive materials compounded with sheets by 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, to achieve permanent anti-static, widely used in high cleanliness electronic blister packaging.

Sheet coating methods: anilox roller, micro-concave roller, calendering coating, soaking and other coating methods. It can be applied to all plastics such as APET.PETG.PS.PP.ABS.PE.PC.

The characteristics are as follows:
1. Surface resistance: ultra-thin conductive treatment layer, conductivity is 104~109, and the corresponding surface resistance can be made by adjusting the formula according to customer requirements.

2. Permanent: Stable conductive function, can be reused or recycled without losing the anti-static function without changing with temperature and humidity.

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 and oil precipitation, environmental protection, no harmful substances, no corrosive and volatile gases, and cleaning resistance.

5. Flexibility: Coating rollers of various specifications can be flexibly replaced according to different sheets and different surface coating requirements. All kinds of coating rollers can be customized for customers.

Fourth, comma scraper coating:

Coating parameters

Viscosity: 1,000~200,000cps
Thickness: 20~300μm (wet)

Features:
High
coating accuracy, uniform
surface quality, and thick coating

Scraper coating often has uneven gluing, which is mainly related to the processing accuracy of the scraper, the angle of scraping to the adhesive wheel during scraping and the viscosity of the coating.
The flatness accuracy of the scraper is required to be high, which means that the scraper is not warped or notched, otherwise the coating amount error is large; During coating, the angle between the tangent of the scraper and the rubber roller is generally between
15°~30°; If it is too large, it scrapes almost against the adhesive wheel, and the scraper is easy to cause vibration when the adhesive wheel runs at high speed, causing uneven coating and large difference in coating amount; In addition, it will cause unevenness and scratches on the coated film surface, and it is also easy to cause
damage to the blade blade.
Comma Roller Coating:
Comma Roller Coating is characterized by a combination of blade and roll scraper. The effect of glue thickness is less than that of blade scrapers, and the coating thickness is easy to adjust, enabling the application of high-viscosity glue. The width is large and can be adjusted
horizontally:
1. The comma scraper has high strength and hardness, and the straightness error of the cutting edge is small, and the 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. Thicker coating can be applied, and when coating, the glue flows from top to bottom between the scraper edge and the material film, so the glue can be fully used, and there is basically no waste of glue.
Disadvantages:
1. The coating quality of the comma roller coating has a large relationship with the operation of its various constituent units, especially for the transmission ratio between the drive motor and the rotating pressure roller is difficult to adjust and master, which often causes uneven coating, easy to appear transverse or longitudinal irregular stripes, when coating, the glue is easy to flow out in the gap between the baffle plate and the transmission pressure roller, the sealing is not complete, and when coating, manpower is required to continuously stir the glue of the rubber storage tank. In this way, the glue is evenly distributed.

Comma Roll Coating Application Examples:

All kinds of optical films, protective films, film films, matte flexible packaging films.