OCR Optical Clear Resin is a special adhesive designed for bonding transparent optical components. It can fill the gaps between panels, transparent protective layers, and LCD modules, effectively suppressing light scattering caused by external light and backlight, and improving the display effect of displays. With the rapid development of the display industry, full fit technology is becoming increasingly mature, and its application areas have evolved from traditional self-service devices, retail terminals/POS machines, education and training, game consoles, industrial control, finance/ATM machines, medical equipment and other industries to emerging industries such as touch laptops, integrated touch devices, and large-sized screens for urban emergency management systems. Organosilicon OCR is a high-performance optical adhesive material with similar refractive index and transmittance to glass, resistance to yellowing, and softness. Its overall performance is superior to that of OCA adhesive, and it plays an extremely important role in the application of full bonding technology. The conventional performance testing methods are introduced as follows:
1. Glue density
Testing the density of organic silicon OCR liquid adhesive before curing is to calculate the amount of adhesive required for bonding.
Test standard GB/T 13354-1992- Determination of density of liquid adhesives - Gravimetric cup method.
2. Viscosity
Viscosity refers to the resistance of a fluid to flow. When organic silicon OCR adhesive flows, a portion of it experiences resistance when flowing on top of another portion, which is the internal friction force of the adhesive. The viscosity of glue is a measure of the magnitude of the internal friction force during the flow of glue
The lower the viscosity, the better the fluidity of the adhesive;
The international standard unit is Pa. s (Pa. s), and commonly used units of measurement include poise (poise) and cps (centropoise);
Conversion of viscosity units: 1 Pa · s=1000 mPa · s=1000 cps;
Testing instrument: rotary viscometer/rheometer;
Related standard: GB 2794-81- Determination of viscosity of adhesives (rotational viscometer method)
3. Refractive index
The refractive index is the ratio of the propagation speed of light in vacuum to the propagation speed of light in organic silicon OCR materials. The refractive index of air is ≈ 1, the refractive index of glass is ≈ 1.5, and organic silicon
The refractive index of OCR material is similar to that of glass, so after using organic silicon OCR, the display part
The overall refractive index is basically the same, reducing the light loss and dryness caused by dispersion and scattering
Disturbance can improve the display effect of the monitor.
Testing instrument: Abbe refractometer;
Related standard: ASTM D1747- Test method for refractive index of viscous materials
4. Curing shrinkage rate
The curing shrinkage rate of organic silicon OCR material refers to the ratio of volume change of OCR material after curing to before curing, expressed as a percentage (%). The smaller the requirement for curing (hardening) shrinkage rate of organic silicon OCR, the better. During use, it is less likely to experience shrinkage, breakage, discoloration, and other phenomena.
Related standard: ASTM C1241-2000 (2005) - Standard test method for volume shrinkage of latex sealants during solidification process
5. Hardness
Hardness refers to the ability of a material to resist the pressure of hard objects on its surface locally. It is an indicator of the softness and hardness of various materials, and a comprehensive indicator of the mechanical properties of materials such as elasticity, plasticity, strength, and toughness. The hardness of organic silicon OCR generally refers to the value after complete curing, and this value is not necessarily higher or lower. The overall performance of the cured product should be comprehensively considered while improving its strength.
Testing instruments: hardness tester/penetrometer;
Related standards: GB/T 531.1-2008 Test method for indentation hardness of vulcanized rubber or thermoplastic rubber;
6. Elongation at break
The ratio of the displacement value of the test material at break to its original length. Expressed as a percentage. The elongation at break of organosilicon OCR is an indicator of the toughness (elasticity) after complete curing. The higher the percentage index, the better the toughness (elasticity) of organic silicon OCR. Testing instrument: Universal material testing machine;
Related standard: GBT13022-1991 Test method for tensile properties of plastic films
7. Adhesive strength
The cohesive force of organic silicon OCR after complete curing, in units of Kgf/cm2; Make the organic silicon OCR sample into the cross lap test sample shown in the right figure. When conducting vertical shear tests, if there is detachment between the adhesive layer and the bonding substrate (glass) interface, it indicates that the adhesive force between the adhesive layer and the substrate is the test value at this time; If only the main body of the adhesive layer is damaged and there is no debonding at the interface between the adhesive layer and the bonding substrate, it indicates that the adhesive force of the adhesive layer on the substrate is greater than the test value obtained at this time. Testing instrument: Universal material testing machine, the bonding substrate used during testing is ordinary sodium silicate glass;
Related standards: GB/T 7124-2008- Determination of tensile shear strength of adhesives (rigid materials vs. rigid materials);
8. Dielectric constant
Also known as permittivity or relative permittivity, it is an important data that characterizes the electrical properties of dielectric or insulating materials, often represented by ε. It refers to the ratio of capacitance in the same capacitor when using the same substance as the dielectric and under vacuum, indicating the relative ability of the dielectric to store electrostatic energy in an electric field. The higher the value, the better the conductivity. The dielectric constant of air at room temperature is ≈ 1, the dielectric constant of glass is about 4-11, and the dielectric constant of OCR is usually between 1.5-3. Therefore, capacitive touch screens using organic silicon OCR are more sensitive. Testing instrument: Dielectric constant tester. Relevant standards: GB/T 1693-2007- Determination of dielectric constant and dielectric loss tangent of vulcanized rubber
9. Optical performance (transmittance, haze, yellow index b *)
Transmittance: The percentage of the light flux passing through a transparent or semi transparent body to its incident light flux, expressed in percentage (%). The higher the transmittance of the adhesive, the higher the contrast of the corresponding touch screen, and the clearer the image;
Haze: The percentage of transmitted light intensity that deviates from the incident light by more than 2.5 ° from the total transmitted light intensity. A higher haze indicates a decrease in the film's gloss and transparency, especially its imaging degree;
Yellow index b: In the CIELab color scheme, the value of b * represents the color range from blue to yellow, b *>0 represents the yellow scheme, and b *<0 represents the blue scheme. In organic silicon OCR adhesive, b * is usually used to measure the degree of yellowing of colorless, transparent, semi transparent, or nearly white polymer materials. The closer b * is to zero, the better. Generally, the b * of organic silicon OCR is ≤ 0.1.
Testing instrument: colorimeter
Related standards: GB/T 2410-2008- Determination of transparency and haze of transparent plastics;
ASTM E313-1998- Standard Operating Procedure for Calculating the White and Yellow Index of Instrument Measurements of Color Coordinates.
