First, into a precision coating roll ( Roll-to-Roll Precision Coating's) technology

It can be applied to various industries such as IC, PCB , optoelectronics, people's livelihood, medical treatment, etc. Taking 3M as an example, there are tens of thousands of products derived from coating by 3M , from general products (such as stationery tape) to medical tape (Beauty, healing) to electronics ( IC cutting, PCB soldering), and optoelectronics ( LCD optical film), etc., are products developed using precision coating technology platforms, 3M is high value and high innovation every time Of brand-new products sell well all over the world.

First introduce the coating definition and industrial structure, where the importance of technology can be found, and then introduce each unit of the coating mechanism, briefly describing the focus of each unit.

2. Coating definition and industry

First of all, it is necessary to define the coating technology. The so-called broad definition of coating is described in the original text as follows : Replace a new material of the air on the substrate. The coating technology is mainly roll coating technology.

First, a roll of substrate (such as PP, PET , PI , copper foil, etc.) is coated on the substrate through the coating device, then the solvent is removed through the drying process, and finally it is wound into a roll, which is the finished product Or semi-finished products. The simplest example is the production of adhesive tape. The production process is to coat pressure-sensitive adhesive on OPP or PVC , dry it in an oven, rewind it, and then sell it in separate packaging. However, this coating technology is relatively simple ( We call it the traditional coating method).

Most domestic tape factories and some other industries use traditional coating methods, such as Comma Coating or Roll Coating , because these methods are simple in structure and easy to operate, but can only be produced. Low-value products, the unit price of which is less than 10 yuan per square meter , and this type of coating method is an open operation mode, which has the problem of solvent evaporation affecting the health of the operator. Especially today, environmental awareness is becoming more and more important, it is necessary to make appropriate Adjustment.

Advanced foreign manufacturers such as Du Pont, 3M , Kodak , Nitto, etc. all develop related businesses through Extrusion Coating . The unit price of products derived from such technologies is at least 50 yuan per square meter , or even some More than 3,000 yuan per square meter is very different from traditional coating products, so we have to pay attention to it.

Precision electrical sub-products with the substrate through the coating technology development, which covers a lot of technology, if the key technical point of view, the importance of the following :

• Quality, performance ( Formulation )  25%

• Coating technology ( Coating ) 35% 

• Delivery technology ( Know-how ) 25%

• Equipment technology ( Equipment ) 15%

Although the material formula is an important source ( 25%), other processing and post-processes must be solved as much as 75 %. The expression here is not that the process is more important than formula synthesis. In fact, the formula is the source of all product development It dominates the development of the following processes. Taking the system developed by materials as an example, the material synthesis development system is inseparable. Figure 2 can be used to express the correlation between the two.

Establish a technical platform for precision coating technology, and cooperate with various high-performance coatings developed by the Chinese themselves, that is, they can be applied to the development of various products, and the application range is very wide. The description is as follows:

Due to the wide range of coating technology, there is no real forecast trend of coating output value, but from the above product association and technology association table, if each single item is a growth upward trend, then the overall output value will be very amazing.

3. Coating process technology

The description in the previous paragraph has shown that there are many types of products produced by coating processing, ranging from household products to cutting-edge high-tech products. In order to pursue high-yield and high-precision coating products, each stage of the manufacturing process needs to be completed with high-quality design. The following introduces and analyzes the related technologies of the coating process.

1.  Coating method

There are many types of coating technology, which can be divided into two major categories, as shown in Figure 5. The first category is called Dry Coating, such as Vacuum Deposition or Chemical Vapor Deposition Method ( Chemical Vapor Deposition ), etc .; the other kind is called wet coating ( Wet Coating ), that is, the process of liquid coating material on the substrate through the processing process, and then dried to solidify the film.

The wet method can be divided into two major types according to its hydrodynamic differences, which are the post-metering ( Pre- Metering) and the pre-metering ( Pre-Metered ) coating methods, which are described as follows:

Coating technology classification

(a) metered coating ( Post-Coating's Metering )

The common feature of this type of coating method is that the thickness of the coating film is affected by the rheological properties of the coating liquid and the coating conditions. Among them, the most commonly used in the industry such as dip coating ( Dip Coating), the thickness of the coating film becomes thicker with the increase of the coating speed, but it is not proportional to the relationship, and then increase the speed, the thickness will tend to a fixed value or Instead it decreases. Others, such as doctor blade and drum coating, all belong to this type of coating method.

(b) pre-metered coating ( PreS-Metered Coating's )

The thickness of the coating film is only set by the infusion system, and will not be different because of the rheological properties of the coating liquid or the change of the coating speed. This type of principle, the coating system from the stable feed pump ( Pump) delivered to the sophisticated design of the extrusion mold ( Extrusion Die ), to form a broad uniform film thickness, and then applied to a substrate, such as Figure 6 shows. Examples of such coating methods include slot die coating ( Slot-die Coating ), inclined coating ( Slide Coating ), curtain coating ( Curtain Coating ), and engraved wheel coating ( Gravure ).

Schematic diagram of extrusion coating method

Since most electronic products are currently trending towards lightness, thinness and shortness, the precision and uniformity requirements of coating products have gradually increased. Therefore, in recent years, domestic related coating manufacturers have also launched R & D on precision coating related technologies. Among them, precision mold coating is the most popular, such as flexible printed circuit boards, dry film photoresists, IC tapes, etc.

2.  Paint delivery system

On the application type of delivery system, the use of solution-type coatings are typically metered pump ( Metering Pump), and the hot-melt using a melt coating machine ( Melter ) or the extruder ( Extruder ); wherein the more commonly used metered pump comprising There are two types of screw pumps ( Screw Pump ) and gear pumps ( Gear Pump ). Their common features are as follows:

1. Can be continuously conveyed in a state of almost no pulsation

2. From aqueous liquid to hundreds of thousands of centipoise ( cps ) high viscosity liquid can be quantitatively delivered

3. The discharge amount of the high precision, high reliable, the ejection accuracy ± . 1% or less

4. Use variable speed motor to change flow range

5. No need to use the valve structure design, no blocking

6. Strong self-priming ability, extremely high suction and discharge pressure

7. Can run smoothly without vibration and noise

8. Disassembly, assembly and maintenance strive for simplicity

The coating thickness is completely determined by the feeding system, so the uniformity of the thickness of the coating film in the machine travel direction ( MD) depends entirely on the pump stability.

Pump feed flow = (coating width) x (wet film thickness) x (coating speed)

In addition, when the paint is transported, it is necessary to avoid contamination by impurities or the generation of air bubbles to prevent defects in the coating process. Therefore, a filter device and a defoaming mechanism are added during the process of transporting the paint to ensure the coating quality; in addition, the equipment also A pressure gauge or digital pressure gauge will be installed for online monitoring to prevent the filter pressure from being too large and shutting down. The schematic diagram of the general paint delivery system is shown in Figure 7. The main items include de-gassing mechanism ( De-Gassing), filter ( Filter ), static mixing device ( Static Mixer ), pressure sensor ( Pressure Sensor )

3.  Precision mold design

Extrusion Die ( Extrusion Die) plays a very important role in the polymer processing process. According to the shape of its export, general molds can be divided into annular molds ( Annular Die ) for the production of sleeves . Circular die ( Circular Die ), slit die for making sheet ( Sheet ) and film ( Film ). In addition, it can also manufacture profile dies ( Profile Die ) of some products with special shapes , which can be said to have a wide range of applications.

Coat-Hanger Die ( Coat-Hanger Die) used in the coating industry is a kind of slit-type mold, and its interior is mainly divided into two parts: Manifold and Slot Section ; The fluid to be processed flows in from the entrance of the mold. Because the thickness of the slit is extremely small, the resistance of the liquid to pass is extremely large, so the polymer liquid will first flow to both ends of the shunt tube with a larger cross-sectional area, waiting to be coated in the width direction After the distribution is uniform, it flows into the slit area and extrudes to form a uniformly distributed film. The main purpose of the mold design is how to design the change of the cross-sectional area of ​​the shunt tube, so that the coating liquid of different rheological properties or different processing conditions can produce a coating liquid film with a uniform thickness in the width direction.

Overall, the mold design should include the internal runner geometry distribution, internal and external adjustment mechanisms, heating devices, die geometry design, and mechanical structure, with the internal runner design affecting the uniformity the most. According to the shape of the shunt tube, it can be divided into two types: a T-shaped mold with a fixed cross-section and a hanger-type mold with a cross-section that changes with position. The structure can be seen in Figure 8. Compare the differences between the two molds and compare the basic characteristics.

Figure 8 Comparison of two common molds

4.  Oven design

In coating engineering, the drying procedure is one of the important steps to determine the quality of the coating film. Regardless of the drying technology or the design of the equipment, it has a significant impact on the quality of the coated product, and its importance is no less important than the coating technology.

The heat transfer can transfer heat from the heat source to the heated object by conduction, convection and radiation. Both conduction and convection require a heating medium. Radiation transfers heat directly to the surface of the heated body without Heating intermediate media (such as air) is the most energy-efficient heating method.

In the process of heating and drying, there are two phenomena of heat transfer and mass transfer at the same time. Heat transfer is to increase the temperature of the paint, increase the fluidity of its moisture or solvent, and evaporate moisture or solvent, and mass transfer is to promote The internal moisture or solvent moves to the surface to evaporate.

The general drying method is not affected by the coating method, but it must be adjusted according to the type of coating liquid. The traditional hot air drying method is to evaporate the solvent by the hot air heating method to form a uniform coating film on the surface of the object Because of this heating method, a large amount of solvent needs to be evaporated, which not only consumes energy, but also causes solvent pollution to the environment.

The recently developed radiant drying method has many advantages such as fast heating, high thermal efficiency and greatly shortened drying time. Compared with the traditional hot air drying method, it saves energy and occupies less space. Among them, infrared (Infrared) heating and microwave heating , Ultraviolet curing ( Ultra Violet Curing ) and Electron Beam Curing ( Electron Beam Curing ) are all using the method of radiant energy to achieve the purpose of drying.

Among them, microwave heating has the highest efficiency. The difference between infrared and microwave is that microwave energy is high, which can penetrate through the inside of the substance for uniform heating. The electron beam hardening method requires higher cost and is performed in an inert gas, which is its disadvantage.

In order to further understand the drying status of the coating film, there are many softwares on the market that calculate the drying status of the coating film. Two products are listed for reference. One of them is SuperDryer, which is a software developed by TNN Technology in the United States that can design a drying system and calculate the drying condition of the oven. R & D engineer is a very practical software. The applicable scope of this software is :

a). Can be applied in coating and printing industry

b). Can provide a design, modification and evaluation tool for the manufacturer and user of the drying system.

c). The drying condition of the drying system can be analyzed

The other is the simulation software developed by Gutoff (Precision Coating Consultant). The main function is to predict and estimate the drying condition of the existing oven. It can be calculated : the final temperature of the coating, the final solvent content of the coating And the temperature and solvent content of hot air and paint during the drying process change with the drying time and the position of the oven. Its simulable range includes:

a). Constant speed drying period and decreasing speed drying period

b). Combination of hot air and infrared drying

c). Can simulate the drying of multi-section oven

5.  Clean room specifications

The clean room is to control the temperature and humidity, cleanliness, indoor pressure, air velocity and air distribution, noise and vibration, lighting and static electricity within a certain range of space within a certain range of requirements. The function is to control the cleanliness, temperature and humidity of the products exposed to the atmosphere, so that the products can be produced and manufactured in a good environmental space, and the design principle is to design the interval, and gradually improve the cleanliness from outside to inside to strengthen precision Product requirements.

In the maintenance and management of clean rooms, in addition to the need to regulate the personnel entering and leaving the clean room, the entry and exit of raw materials and equipment must also pass through the clean room management procedures, so as not to affect the cleanliness of the clean room. This is the only way to meet the specifications of precision coating products.

6.  Other ancillary equipment

In order to improve product yield, it is recommended that the following equipment can be used to improve production problems.

a. line film thickness measuring instrument ( the On-Line Thickness Gauge )

The film thickness stability is often affected by factors such as the slit gap of the mold, the coating gap, the feed pump, the filtration pressure and the transmission speed. Therefore, a film thickness measuring instrument can be installed online to monitor the stability of the film thickness. This can also reduce the occurrence of production problems. Among the commonly used instrument principles are infrared, β- ray , and γ- ray .

b. Appearance Inspection System ( Inspection System )

It can ensure the quality of the products around the clock, and can monitor the status of the production machine and the stability of the production conditions in real time. The items that can be monitored include surface defects such as scratches, wrinkles, pinholes and spots, etc., and are recorded and marked to Maintain a stable appearance quality.

c. Data Acquisition System ( Data Acquisition System )

For example, all process parameters such as transmission speed, substrate tension, oven temperature, solvent concentration in the oven, coating film thickness and pump supply are all important factors that affect the product, so they need to be recorded and analyzed using a data acquisition system. To master the stability of the process.

d. Substrate cleaning device ( Web Cleaner )

Sticky wheels or ultrasonic dust removal devices can be installed at multiple places on the coating machine to eliminate foreign materials, dust or fibers to improve the product yield ; the sources of foreign materials that may occur include raw materials of the substrate, pressing wheels or idlers Caused by an unclean or clean room environment.

e. Concentration detection system ( Gas Detector )

A gas concentration detection system can be installed at the higher concentration of the coating machine (such as the coating area, the front section of the oven and exhaust gas exhaust) to prevent the risk of excessive concentration due to abnormal exhaust.

Film wet coating processing has long been used in various fields.

                               Coating technology system integration

In the field of electronics, the performance of TFT / LCD panels with remarkable growth , as well as optical components such as plastic LCD substrates with promising future prospects , near-infrared blocking films, and large-capacity multi-layer capacitors is particularly dazzling. Especially the thinner high-definition multi-layer film structure is a technical trend in recent years, but this wet coating film processing technology itself contains professional qualities of cutting-edge technology and artistic atmosphere, which cannot be ignored like previous general experience. Of it.

In short, as electronic products continue to take "light, thin and short" as the development goal, the demand for electronic materials is growing day by day. With the high-functionalization of substrates and the progress of precision coating technology, the thinning of thin films has been successfully achieved, and the trend towards thin, large Area development. At the same time, the functional coating process of the film is permeable in various fields. With the superiority of the film, in the future, combining substrates, coatings with special properties and new coating technologies will inevitably develop more and more excellent Thin film material.