Bonding technology of android touch screen
Table of Contents
Android touch screen has experienced several rounds of changes since its development, the most important of change is bonding technology of android touch screen. Let’s take a look at the following:
We generally divide the screen into three parts through the structure of the touch screen, from top to bottom are protective glass, touch screen ,and display screen respectively. These three parts need to be bonded to become a complete screen.
Air bonding is the most common adhesive method in the current application, that is to simply use double-sided adhesive to fix the four sides of the touch screen and the display screen. Because of its low cost and simple implementation, it is favored by small and medium-sized manufacturers. But the disadvantage is that there is an air layer between the display screen and the touch screen, so that the display effect is not satisfactory.
Optical bonding: a technical process of seamlessly and completely bonding the display screen and the touch screen with water glue or optical glue. This technology is regarded as a medium and high-end product. With the popularity of ultra-thin, ultra-narrow frames and other high-definition display screens, it frequently appears in public view. Today, let’s talk about the magic of this technology.
Advantages of air bonding and optical bonding
Optical bonding, also known as non-airgap, is a process that uses solid transparent optical adhesive or liquid transparent optical adhesive to completely and tightly bond the display panel with the touch screen. Compared with the traditional double-sided adhesive air bonding technology, the optical bonding eliminates the air layer between the touch screen and the display module, which has the following advantages:
1. Enhance the display effect. The optical bonding technology replaces the air layer with OCA/OCR layer which is closer to the refractive index of the upper and lower layers, and the interlayer interface reflection is lower, which can reduce the interference of ambient light reflection, increase the light transmittance of the display screen and enhance the contrast ratio of the image.
2. Screen isolation dust and water vapor to ensure the cleanliness of the screen and improve the adaptability of the screen environment.
3. Reduce the screen thickness, reduce the thickness of the whole machine and increase the embedded touch sensitivity.
4. Less signal noise interference, Improve the accuracy and sensitivity of touch operation.
After years of development, optical bonding in the small and medium-size field has almost completely replaced the air bonding technology, and optical bonding has become the general trend. However, in the field of large-size commercial displays, the challenges of optical bonding technology cannot be underestimated: coating materials, processing costs, adhesive equipment, cleanliness of process environment, GAP, the dosage of liquid glue…… The larger the screen size is, the more difficult the process is. It has become an industrial trend that touch panels adopt optical bonding technology. From the current technical classification, air bonding will be phased out gradually.
Optical bonded structural adhesive materials
The two kinds of glue used are OCA and LOCA respectively.
OCA is mainly suitable for small-size product bonding, but the bonding cost is high, and after a long screen time, there will be yellowing, and bubbles are easily generated at the ink segment difference. However, the advantages lie in high production efficiency and simple maintenance.
LOCA is mainly suitable for large size adhesion, curved surface, or relatively complex structure adhesion. The cost is lower than that of OCA.
The bonding optical materials for optical bonded structures are getting higher and higher, requiring colorless and transparent, light transmittance above 98%, good bonding strength, and curing at room temperature or medium temperature, and it has the characteristics of small solidification and shrinkage. This adhesive is called optical adhesive. Organic silica gel, acrylic resin, unsaturated polyester, polyurethane, epoxy resin, and other optical adhesives of different materials.
What is OCA?
OCA (Optically Clear Adhesive) is a kind of double-sided Adhesive tape without substrate material, which is made of optical acrylic glue into non-substrate, and then on the upper and lower bottom layers, and then a layer of release film is bonded respectively, OCA is generally manufactured in the form of double-sided adhesive tape, so it is also called optical adhesive tape or optical double-sided adhesive tape.
Advantages of OCA
High purity, high light transmittance and low haze; The thickness of the adhesive layer is uniform and the flatness is high; The adhesive force is high, and the adhesive strength after bonding is high; Soft to soft, soft to hard, both hard and hard can be bonded, and the adhesive material has wide applicability.
Disadvantages of OCA
With the development of casual flexible screens and large-size screens, more and more screens are applied to harsh environments. The more obvious the shortcomings of OCA are, the details are as follows:
1) optical bonding is easy to produce bubbles, and the larger the size of the adhesion is, the greater the probability of generating bubbles is; The bonded bubbles Yi Fasheng rebound after defoaming;
2) the solid glue has poor flowing performance and poor filling effect on an uneven surface, which is not suitable for full bonding of frame LCD screen;
3) Large size bonding is difficult, adhesion yield and production efficiency are low;
4) poor surface adhesive effect;
5) the bonding stability is not strong, and the bonding strength after bonding gradually decreases with the increase of temperature;
6) after bonding, it is not easy to rework, and the cost of rework is high;
7) It is easy to adsorb dust and impurities to cause secondary pollution;
8) the strength and explosion-proof ability of the screen cannot be effectively increased; After bonding, the explosion-proof effect of the screen is not good, it is not resistant to falling, and the screen is easy to be damaged;
9) each product must be die-cut separately.
What is LOCA?
LOCA, also known as OCR(Optical Clear Resin), is a kind of Optical glue. Because the glue is liquid, it is also called liquid Optical glue and Optical water glue. After curing, the glue is colorless and transparent, with a light transmittance of more than 98%, and has the characteristics of small curing shrinkage and yellowing resistance. In the field of full adhesion, compared with traditional OCA tape, LOCA has unique advantages in the fields of large size, curved surface, harsh environment, etc.
Advantages of LOCA
1) strong applicability, one glue can correspond to multiple adhesive products;
2) liquid glue has strong fluidity, is not sensitive to Ink thickness, and has good filling property;
3) it is suitable for large size bonding and has no limit on the size of bonding products;
4) applicable to surface bonding or complex structure bonding;
5) high adhesive yield and good reworking performance;
6) chemical bonding, bonding is less affected by temperature and has strong bonding stability.
At that time, it is a new opportunity for the development of large-size touch screens. Bonding technology of android touch screen is widely used in commercial display fields of vertical industries such as finance, education, and medical treatment, effectively solve the problems of large size capacitor products, such as difficult optical bonding process and high cost, and greatly improve the products in appearance, performance, experience and other aspects, which are the minds of customers of various brands, A magic weapon to effectively improve market competitiveness. With the improvement of yield and efficiency of the large-size optical bonding process, optical bonding is occupying a higher and higher market share and will become the standard technology of large-size touch display screens in the future.