1.Roll-to-roll precision coating technology
It can be used in IC, PCB, optoelectronics, livelihood, medical and other industries. Take 3M as an example. There are tens of thousands of products derived from coating by 3M, ranging from general products (such as stationery tape) to medical tapes. (Beauty, healing) to electronics (IC cutting, PCB solder mask), and optoelectronics (optical film for LCD), etc., are all products developed using the precision coating technology platform.
First, the definition and industrial structure of coating are introduced. Here, the importance of technology can be found. Then, each unit of the coating mechanism is introduced, and the key points of each unit are briefly described.
2. Coating Definition and Industry
First of all, we must define what the coating technology is. 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. Therefore, from the definition point of view, coating covers a wide range. Coating technology is based on roll coating technology.
First, a roll of substrate (such as PP, PET, PI, copper foil, etc.) is coated on the substrate through a coating device, and then the solvent is removed through a drying process, and finally rolled into a roll, which is the finished product or semi-finished products. The simplest example is the production of tape. The production process is to coat the pressure-sensitive adhesive on OPP or PVC, roll it after drying in the oven, and then package it in strips for sale. However, this coating technology is relatively simple ( We call this the traditional coating method).
Domestic tape factories and some other industries mostly use traditional coating methods, such as knife coating (Comma Coating) or roller coating (Roll Coating) for processing, because these methods are simple in structure and easy to operate, but can only produce The unit price of low-value products is less than 10 yuan per square meter, and this type of coating method is an open operation mode, and there is a problem that solvent volatilization affects the health of operators. adjustment.
Advanced foreign manufacturers such as Du Pont, 3M, Kodak, Nitto, etc. all use extrusion coating to develop related businesses. The unit price of products derived from such technology is at least 50 yuan per square meter, and even some can reach It is more than 3,000 yuan per square meter, which is very different from traditional coating products, and we have to pay attention to it.
The substrates for precision electronic products are developed through coating technology, which covers a lot of technologies. If we look at the key technologies, the importance is as follows:
? Quality, Performance (Formulation) 25%
? Coating 35%
? Know-how 25%
? Equipment 15%
Although the material formula is an important source (25%), there are as many as 75% of other processing and post-processes that must be solved. The expression here is not that the process is more important than the formula synthesis. In fact, the formula is the source of all product development. It dominates the development of the subsequent process. Taking the material developed system as an example, the material synthesis development system is inseparable, and Figure 2 can be used to represent the correlation between the two.
Establishing a technical platform for precision coating technology, and then cooperating with various high-functional coatings developed by the Chinese, can be applied to the development of various products, which can be used in a wide range of applications. The description is as follows:
Since the coating technology covers a wide range, there is no real forecast trend of coating output value published. However, from the above product correlation and technology correlation table, it can be seen that if each item is in an upward trend, the overall output value will be very high. amazing.
3. Coating process technology
The previous description has shown that there are a wide variety of products produced by coating processing, ranging from household items to cutting-edge high-tech products. In order to pursue high-yield and high-precision coating products, high-quality design is required at each stage of the production process. The following is an introduction and analysis of the related technologies of the coating process.
01. Coating method
There are many types of coating technologies, which can be mainly divided into two 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.; another type is called wet coating (Wet Coating), that is, a process in which a liquid coating material is applied to the substrate after processing, and then dried and cured to form a film.
Wet method can be mainly divided into two types according to its difference in fluid mechanics, namely Post-Metering and Pre-Metered coating methods, which are described as follows:
Coating Technology Classification
(a) Post-Metering Coating
The common feature of this type of coating method is that the film thickness is affected by the rheological properties of the coating solution and the coating conditions. Among them, dip coating is the most commonly used in the industry. The thickness of the coating film increases with the increase of the coating speed, but it is not proportional. If the speed increases, the thickness will tend to a constant value or instead decreased. Others such as blade type, roller type coating, etc. belong to this type of coating method.
(b) Pre-Metered Coating
The coating film thickness is only set by the infusion system and will not vary due to changes in the rheological properties of the coating solution or the coating speed. The principle of this type is that the coating is transported from a stable supply pump to a precisely designed Extrusion Die to form a wide and uniform thickness film, which is then coated on the substrate, such as shown in Figure 6. Such coating methods include Slot-die Coating, Slide Coating, Curtain Coating and Gravure coating.
Coating Technology Classification
Schematic diagram of extrusion coating method
Since most electronic products are currently developing towards the trend of being light, thin and short, the requirements for precision and uniformity of coating products are gradually increasing. Therefore, in recent years, relevant domestic coating manufacturers have also set off to invest in the research and development of precision coating related technologies. Among them, precision mold coating is the most popular, and applications such as flexible printed circuit boards, dry film photoresists, IC tapes and so on.
Schematic diagram of extrusion coating method
02. Paint conveying system
In terms of application types of conveying systems, solution-based coatings usually use a metering pump, while hot-melt coatings use a Melter or Extruder; the more commonly used metering pumps include There are two types of screw pump and gear pump. Their common features are as follows:
1. It can be delivered continuously with almost no pulsation
2. It can be quantitatively transported from aqueous liquids to high-viscosity liquids of hundreds of thousands of centipoises (cps).
3. High-precision discharge volume, high reliability, and discharge accuracy within ± 1%
4. Use a variable speed motor to change the flow rate range
5. There is no need to use the structural design of the valve, and there will be no blockage
6. Strong self-priming ability, extremely high suction and discharge pressure
7. Can run smoothly without vibration and noise
8. Strive for simplicity in disassembly and maintenance
The coating thickness is completely determined by the feeding system, so the thickness uniformity of the coating film in the machine travel direction (MD) is completely determined by the stability of the pump. The formula of the feeding flow is:
Pump feed flow = (coating width) x (wet film thickness) x (coating speed)
In addition, it is necessary to avoid the pollution of impurities or the generation of air bubbles when the paint is conveyed to prevent the occurrence of defects in the coating process. Therefore, a filter device and a defoaming mechanism will be installed in the process of conveying the paint to ensure the coating quality; in addition, the equipment is also A pressure gauge or digital pressure gauge will be installed for online monitoring to prevent the filtration pressure from being too large and stop work. The schematic diagram of the general paint conveying system is shown in Figure 7. Its main items include De-Gassing, Filter, Static Mixer, Pressure Sensor and so on.
03. Precision mold design
Extrusion die plays a very important role in polymer processing. General die, according to the shape of its exit, can be divided into annular die (Annular Die) for the production of sleeves, and Annular Die for the production of fibers and round rods. Circular Die, Slot Die for Sheet and Film. In addition, it can also manufacture some special-shaped products such as profile die (Profile Die), which can be said to have a wide range of applications.
The Coat-Hanger Die used in the coating industry is a kind of slot die, 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. Since the thickness of the slit is extremely small, the resistance of the liquid to pass through is extremely large, so the polymer liquid will first flow to both ends of the shunt pipe with a larger cross-sectional area, and stay in the width direction of the coating. After uniform distribution, it flows into the slot zone and extrudes to form a uniformly distributed film. The main purpose of mold design is how to design the change of the cross-sectional area of the shunt pipe, so that the coating liquid with different rheological properties or different processing conditions can produce a coating liquid film with uniform thickness in the width direction.
On the whole, the mold design should include the distribution of internal runner geometry, internal and external adjustment mechanisms, heating devices, die geometry design, and mechanical structure, among which the internal runner design has the greatest impact on uniformity. According to the shape of the shunt pipe, it can be divided into two types: T-shaped mold with a fixed cross-section and a hanger-type mold with a cross-section that changes with position. The structure is shown in Figure 8. As for how to determine which mold to use, please refer to Table 2. Compare the differences between the two molds, and compare the basic characteristics.
Comparison of two common molds
04 Oven Design
In the 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 coating product, and its importance is no less than that of the coating technology.
The transfer of heat can transfer heat from the heat source to the object to be heated by conduction, convection and radiation. Both conduction and convection require a heating medium. Radiation directly transfers heat to the surface of the object to be heated without the need for It heats an intermediate medium (eg air), so it 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 coating, increase the fluidity of its water or solvent, and evaporate the water or solvent, and mass transfer is to promote The moisture or solvent inside moves towards the surface for evaporation.
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 uses hot air heating to volatilize the solvent to form a uniform coating film on the surface of the object , Because this heating method needs to evaporate a large amount of solvent, it not only consumes energy, but also causes the solvent to pollute the environment.
The recently developed radiation 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, microwave heating , Ultra Violet Curing (Ultra Violet Curing) and Electron Beam Curing (Electron Beam Curing) all use radiation energy to achieve the purpose of drying.
Among them, the microwave heating efficiency is the highest. The difference between infrared and microwave is that the microwave energy is high and can penetrate the interior of the material for uniform heating. The electron beam hardening method requires high cost and is carried out in an inert gas, which is its disadvantage.
In order to further understand the drying status of the coating film, there are many softwares for calculating the drying status of the coating film on the market. Two products are listed here for reference. One of them is SuperDryer, which is a software developed by TNN Technology in the United States that can design drying systems and calculate drying conditions of ovens. It is a software package available under Microsoft operating system. It is a very useful software for R&D engineers. The scope of application of this software is:
a). Can be used in coating and printing industries
b). It can provide drying system manufacturers and users with a design, modification and evaluation tool.
c). The drying status 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 status of the existing oven, and can calculate: 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 drying process change with drying time and oven position. The range that can be simulated includes:
a). Constant speed drying period and descending speed drying period
b). Drying by combining hot air and infrared rays
c). Can simulate the drying of multi-section oven
05 Clean Room Specifications
A clean room is a specially designed space that controls the temperature and humidity, cleanliness, indoor pressure, airflow velocity and airflow distribution, noise and vibration, lighting and static electricity within a certain range of requirements within a certain space. The function is to control the cleanliness and temperature and humidity of the atmosphere that the product is exposed to, so that the product can be produced and manufactured in a good environmental space, and its design principle is based on the interval design, and the cleanliness is gradually improved from the outside to the inside to strengthen the precision. product requirements.
In the maintenance and management of the clean room, in addition to the standardized management of 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. Only in this way can the specification requirements of precision coating products be met.
06 Other auxiliary equipment
In order to improve product yield, it is recommended to use the following equipment to improve production problems.
a. 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 film thickness stability. This can also reduce production problems. Commonly used instrument principles include infrared, β-ray, γ-ray and other methods.
b. Inspection System
It can ensure all-weather product quality, and can monitor the status of production machines and the stability of production conditions in real time. The items that can be monitored include surface defects, such as scratches, wrinkles, pinholes and spots, etc. Maintain the stability of appearance quality.
c. Data Acquisition System
For example, the 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 by a data acquisition system. In order to grasp the stability of the process.
d. Substrate cleaning device (Web Cleaner)
Dust sticking wheels or ultrasonic dust removal devices can be installed in multiple places on the coating machine to eliminate foreign matter, dust or fibers to improve product yield; the possible sources of foreign matter include substrate raw materials, lamination wheels or idlers caused by an unclean or clean room environment.
e. Gas Detector
The gas concentration detection system can be installed in the places with high concentration of the coating machine (such as the coating area, the front section of the oven and the exhaust gas exhaust) to prevent the danger of excessive concentration due to abnormal exhaust gas.
Wet film coating processes have been used in various fields for a long time.
Coating Technology System Integration
In the field of electronics, the applications in TFT∕LCD panels, which have grown significantly, as well as plastic LCD substrates with promising future prospects, optical components such as near-infrared blocking films, and large-capacity multilayer capacitors, are particularly bright and dazzling. In particular, the increasingly thin and high-definition multilayer film structure is a technological trend in recent years. However, this wet coating film processing technology itself contains cutting-edge technology and professional quality of artistic atmosphere, which cannot be ignored as usual. Of.
In a word, as electronic products continue to be "light, thin and short" as the development goal, the demand for electronic materials is growing day by day. With the development of high-performance substrates and precision coating technology, the thin film has been successfully achieved. area development. At the same time, the functional coating processing of thin films is pervasive and penetrates into various fields. With the excellent properties of thin films, the combination of substrates, coatings and new coating technologies with special properties is bound to develop more and more excellent coatings in the future. film material.
