The full name of organic silica gel is silicone rubber sealant, or silica gel for short. Organic silica gel can be divided into neutral single-component and two-component types, as shown in Figure 1 and Figure 2. One-component organic silica gel is a kind of ointment-like material, and its curing mechanism is: contact with a small amount of moisture in the air, shrink and react to solidify into a tough rubber-like solid material, and release a small amount of small molecules (≤3ppm).
One-component glue + water vapor in the air→cured glue + small molecule substance
Two-component means that the silica gel is divided into two groups, A and B. Any group can not be cured by itself, but the two groups of glue will be cured once they are mixed.
A component + B component → cured glue + small molecule substance
Table 1 shows the comparison of one-component and two-component organic silica gels.
| Single component | Two-component |
| It reacts to solidify with water in the air, and there needs to be enough surface in contact with the air, too deep to solidify | It can be cured without reacting with water in the air, can be cured under airtight conditions, and can be cured deeply |
| Curing is slower than two-component, the speed is not adjustable, and it is easily affected by ambient temperature and humidity | The curing speed is fast and the speed is adjustable. The ambient temperature has a certain influence on it, but the humidity has little influence on it |
| Single package, glue gun construction, no other complicated equipment | Special equipment is required for construction, improper use of equipment is prone to problems |
1. Performance characteristics of neutral one-component silicone sealant
(1) Neutral curing at room temperature, fast deep curing speed.
(2) Good sealing.
(3) High temperature resistance, yellowing resistance, and good compatibility with all kinds of EVA under high temperature and high humidity environment.
(4) Good resistance to degeneration.
(5) Good weather resistance.
(6) Good insulation performance.
2. Quality requirements of neutral one-component silicone sealant
(1) Appearance requirements.
(2) Pressure flow viscosity.
(3) Refers to dry time.
(4) Tensile strength and elongation.
(5) Shear strength.
3. Performance characteristics of two-component silicone sealant
(1) Curing at room temperature, fast curing speed, fast curing by heating, no heat, no corrosion, and small shrinkage during curing.
(2) Maintain rubber elasticity in a wide temperature range (-60°C~250°C), with excellent electrical properties and good thermal conductivity.
(3) Waterproof and moisture-proof, stable chemical performance, resistance to chemical corrosion, resistance to yellowing, weather resistance for more than 25 years.
(4) Good adhesion to plastics, rubber and other materials, meeting environmental protection requirements.
4. Quality requirements of two-component silicone sealant
(1) Appearance requirements before curing: white fluid, with proper viscosity of components A and B.
(2) Operating performance: The operating time is 20~60min, the initial curing time is 3~5h, and the complete curing time is no more than 24h.
(3) Cured indicators: hardness, thermal conductivity, dielectric strength, volume resistivity, linear expansion coefficient.
5. Storage of organic silica gel and precautions
It should be stored in a dry, ventilated, cool warehouse, protected from light, heat (temperature 20°C~25°C), and moisture-proof. The storage period below 25°C is about 1 year.
Precautions:
(1) Construction is not suitable for long-term flooded areas.
(2) It is not compatible with materials that can ooze grease, plasticizers or solvents.
(3) Frost or wet surfaces cannot be bonded.
(4) It cannot be cured in a completely sealed place (single component, requires moisture in the air to cure).
(5) The surface of the substrate is not clean.
6. Organic silica gel inspection
Organic silica gel inspection items are shown in Table 2.
| Test items | Inspection content | Detection method (use tools) |
| Package | Whether the packaging is intact; confirm the manufacturer, specifications, and shelf life | Visual inspection |
| Exterior | In a bright environment, squeeze the product into thin strips for visual inspection. The product should be a fine and uniform paste or viscous liquid, without lumps, gels, or bubbles; the color is generally white or milky white, without irritating odor | Visual inspection |
| Tack-free time | Squeeze the organic silica gel on the test board into a thin strip with a glue gun, and start timing immediately until you touch the rubber strip with your fingers and do not stick to your fingers. The time from squeezing out to not sticking to your hands is 10~30min | Glue gun, experiment board, chronograph |
| Elongation | Extrude a piece of silica gel on the test board and stretch it after it is fully cured (record the curing time, silica gel thickness, original length, and stretched length). The test result shows that the stretch value should not be less than 300% | ruler |
| Bonding strength | Extrude 3 pieces of silica gel on different backplanes, observe the adhesion after curing (use a tensile tester), the tensile force should be greater than 10N | Rally |
| Fluidity | The time required to extrude silicone under a certain pressure | Timer |
| Curing time | Squeeze a piece of silica gel on the test board, and determine the time required for the silica gel to dry completely by observing its cross-section | Timer, visual inspection |
(1) Liquidity.
①Test method:
(A) Place the product under standard test conditions for more than 4 hours. Standard test conditions: temperature is 23℃±2℃, relative humidity is 50±5%.
(B) Driven by the air pressure of 0.3MP, use a nozzle with an aperture of 3.00mm to squeeze out the silica gel.
(E) Record the time (s) it takes to extrude 20g of product.
(D) Take the average of the three experimental data as the test result.
②Requirement: The test result is not less than 7s/20g.
(2) Curing time.
①Test method:
(a) Extrude the sample to be tested on a flat plate with a silicone gun.
(b) The width of the extruded silica gel strip is about 1cm, the thickness is about 1cm, and the length is arbitrary.
(c) Immediately count the time after squeezing the silica gel, and cut off the rubber strip with a knife every 2h.
(d) Observe the cross-section and check whether the silica gel is completely dry.
(e) The time from extrusion to the complete drying of the cross-section of the rubber strip is the curing time.
②Requirement: T curing ≤24h.
(3) Tensile strength.
①Test method:
(a) Extrude the sample to be tested on a flat plate with a silicone gun.
(b) The width of the extruded silica gel strip is about 1cm, the thickness is about 0.5cm, and the length is greater than 20cm.
(c) After the above-mentioned silica gel is completely cured, the silica gel is separated from the plate, and then the tensile strength of the silica gel is tested with a tension meter.
②Requirement: The tensile strength is not less than 0.7MPa.
(4) Elongation.
① Test method.
(a) Extrude the sample to be tested on a flat plate with a silicone gun.
(b) The width of the extruded silica gel is about 1cm, the thickness is about 0.5cm, and the length is greater than 20cm.
(c) After the above-mentioned silica gel is completely cured, separate the silica gel from the plate, and then measure the initial length of the silica gel.
(d) Place the rubber strip close to the ruler, and slowly pull the rubber strip from both ends of the silicone strip with both hands until the rubber strip is broken.
(e) Record the stretched length of the rubber strip at the moment of breaking.
(f) Use the formula to calculate:
Elongation=(| L2﹣L1|)/L1× 100%
②Requirement: The elongation is not less than 250%.
(5) Bonding power.
①Test method:
(a) Use a silicone gun to squeeze the silicone onto the bonding surface to be tested, such as solar glass, aluminum alloy frame, back film, etc. The size of silica gel is about 20cm×1cm×0.5cm.
(b) Paste a piece of backing film material about 1 cm wide on the upper surface of the silica gel.
(c) After the silicone is fully cured, test the adhesive force between the silicone and each bonding surface.
②Requirement: The bonding force is not less than 20N/cm.
(6) Damp heat aging test.
①Test method:
(a) Coat the silica gel sample to be tested on the target glass, back film and aluminum alloy frame. The size of the silica gel is about 20cm×1cm×0.5cm.
(b) After the above-mentioned silica gel sample is completely cured, put it in a high and low temperature test aging box, and set the aging condition as: 85℃, 85%RH.
(c) Continuous aging for 1000h, of which, every 500h, take out and observe the condition of the experimental sample and make a record.
(d) Take it out after 1000h, and inspect the appearance of the sample after damp heat aging, and the bonding strength between the sample and the glass, back film and aluminum alloy.
②Requirements: No yellowing, no embrittlement, no cracks in appearance; compared with before aging, the attenuation of bonding strength must be less than 50%.
(7) Ultraviolet aging test.
①Test method:
(a) Coat the silica gel sample to be tested on a flat plate, the size of silica gel is about 20cm×1cm×0.5cm.
(b) Place the sample on the stage of the UV aging box.
(c) Adjust the ultraviolet radiation parameters: ultraviolet light with a wavelength of 280~385nm, the intensity does not exceed 250W/㎡.
(d) Make the total irradiance of the sample not less than 15kW/(h·㎡), of which the radiation of 280~320nm wavelength is at least 5kW/(h·㎡).
②Requirements: The tested sample shall not be yellowish, brittle, or cracked.