The shadowless adhesive (UV adhesive) is also called photosensitive adhesive and UV curable adhesive. The shadowless adhesive is a kind of adhesive that can only be cured by ultraviolet light. It can be used as an adhesive, or as an adhesive for paints, coatings, inks, etc. UV is the abbreviation of Ultraviolet Rays, that is, ultraviolet light. Ultraviolet (UV) is invisible to the naked eye. It is a section of electromagnetic radiation outside the visible light, with a wavelength of 10~400 nm. The curing principle of shadowless adhesive is that the photoinitiator (or photosensitizer) in the UV curing material absorbs the UV light under the irradiation of ultraviolet light and produces living free radicals or cations, which initiate monomer polymerization and cross-linking chemical reactions, so that the adhesive can be converted from liquid to solid in a few seconds.
Main components:
Monomer: 40-60% Photoinitiator: 1-6%
Auxiliary agent: 0.2~1%
Prepolymers include epoxy acrylate, polyurethane acrylate, polyether acrylate, polyester acrylate, acrylic resin, etc.
Monomers include: monofunctional (IBOA, IBOMA, HEMA, etc.), bifunctional (TPGDA, HDDA, DEGDA, NPGDA, etc.), trifunctional and multifunctional (TMPTA, PETA, etc.)
Initiators include: 1173184907, benzophenone, etc
Additives can be added or not. They can be used as adhesives, as well as as adhesives for paints, coatings, inks, etc.
Product features:
Universal products have a wide range of applications, and the bonding between plastics and various materials has excellent bonding effect; The adhesive strength is high. The plastic body can be cracked without degumming through the test of damage test. The UV glue can be positioned in seconds and reach the highest strength in a minute, greatly improving the working efficiency; After curing, it is completely transparent, and the product will not yellowing and whitening for a long time; Compared with the traditional instant adhesive bonding, it has the advantages of environmental resistance, non whitening, good flexibility, etc; The damage test of P+R button (ink or electroplating button) can tear the silicone rubber skin; Excellent resistance to low temperature, high temperature and high humidity; It is convenient to operate by automatic mechanical dispensing or screen printing.
advantage:
Environment/Safety
● No VOC volatiles, no pollution to ambient air;
● There are few restrictions or prohibitions on adhesive composition in environmental protection regulations;
No solvent, low flammability
Economy
● Fast curing speed, curing can be completed in seconds to tens of seconds, which is conducive to automatic production line and improving labor productivity
● Testing and handling can be carried out after curing, saving space
Curing at room temperature can save energy. For example, the energy required to produce 1g light cured pressure-sensitive adhesive is only 1% of the corresponding water-based adhesive and 4% of the solvent based adhesive. It can be used for materials that are not suitable for high temperature curing. Compared with heat curing resin, the energy consumption of UV curing can be saved by 90%
● Curing equipment is simple, requiring only lamps or conveyor belts, saving space
● Single component system, without mixing, easy to use
Compatibility
● Temperature, solvent and moisture sensitive materials can be used
● Cure control, waiting time and curing degree can be adjusted
● Repeated sizing and multiple curing
● The ultraviolet lamp can be easily installed on the existing production line without major changes
usage method:
Operating principle
During the gluing process of the shadowless glue, the shadowless glue is also called ultraviolet glue. It can only be cured when the glue solution is irradiated by ultraviolet light. That is, the photosensitizer in the shadowless glue will be bonded with the monomer when it is exposed to ultraviolet light. Theoretically, the shadowless glue will almost never be cured when there is no ultraviolet light source.
There are two sources of ultraviolet light: natural sunlight and artificial light source. The stronger the ultraviolet ray is, the faster the curing speed is. Generally, the curing time is 10-60 seconds. For natural sunlight, the ultraviolet ray in sunny weather will be stronger and solidify faster. However, when there is no strong sunlight, only artificial ultraviolet light source can be used. There are many kinds of artificial ultraviolet light sources, and the power difference is also huge. The small power can be as small as a few watts, and the large power can reach tens of thousands of watts.
Operation guidance
1. One of the two objects to be bonded is transparent and the surface is clean, dry and free of grease;
2. Apply the UV shadowless adhesive on one of the surfaces, close the two planes, and use an appropriate wavelength (usually 365-400nm) and energy ultraviolet lamp or high-pressure mercury lamp for illumination. When lighting, it should be from the center to the periphery, and confirm that the light can really penetrate to the bonding part;
3. It is recommended that the residual glue on the workpiece be removed and re illuminated to fully solidify after about 6s of illumination and initial positioning;
4. The curing time shall be different according to different preparation materials, glue thickness and UV intensity. It is recommended that users purchase an ultraviolet intensity tester and conduct light intensity test before bonding to reduce the scrap rate;
5. The temperature also has a little influence on the activity of the glue, and the curing time should be appropriately extended when the temperature is low;
6. During operation, the materials to be bonded shall not be squeezed and repeatedly rubbed, and it is recommended to use fixed tools;
7. During plastic bonding, the content of ultraviolet absorber in the plastic should be considered. Higher content will seriously affect the transmission rate of ultraviolet light, and thus have a significant impact on the curing efficiency of the glue, even lead to the inability of the glue to cure;
8. Low viscosity products are recommended for large area bonding. If conditions are available, it is better to purchase vacuum equipment and stick it in a vacuum environment to remove bubbles and improve the yield;
9. The above instructions are for reference only, and the specific operation needs to be properly adjusted by the customer according to the specific situation
Disadvantages:
● High raw material cost, no low-cost solvent and filler, high adhesive price
● The penetration of UV light to some plastic or translucent materials is weak, the curing depth is limited, the geometry of curable products is limited, and the opaque parts and dead corners that cannot be irradiated by UV light are not easy to cure
● Common UV adhesives can only be used to bond light transmitting materials, and other technologies should be used to bond light transmitting materials, such as optical delay (cation) curing, photothermal dual curing, and optical moisture dual curing
common problem:
① Why does UV glue turn white after curing?
This phenomenon often occurs in the glass industry. The whitening phenomenon is actually the tiny bubbles generated by the adhesive layer itself, because the adhesive will shrink during the curing process. If the thickness of the adhesive layer is uneven or the hardness is too high, the internal stress generated by the shrinkage cannot be released, and the tiny bubbles will appear after a long time, that is, the whitening phenomenon we see until the bonding material falls off. One way to solve this problem is to choose UV glue with flexible formula; The second is to control the adhesive layer evenly; Third, low power UV lamps are used during initial curing, which slows down the curing speed of glue. After positioning, high power UV equipment is used for deep curing. Because the curing speed of glue is too fast, the shrinkage rate of glue will increase.
② Why is the glue still dry after a long time?
After the glue is solidified, the colloid surface contacts the air. Due to the inhibition of the air, the colloid surface cannot be debonded, which is also a sticky phenomenon.
The solutions to this problem are:
1. Use higher ultraviolet intensity
2. Use a higher photosensitive dose
3. Use a fast reaction sensitizer system
4. Use an ultraviolet light source with a wavelength of 365nm
③ Is UV glue toxic? Why is the skin red, swollen and itchy with UV glue?
UV glue is a green, environment-friendly, economic and chemical product. It does not contain any organic solvent and contains 100% solid glue. It will not cause any toxic, carcinogenic, pathogenic and degenerative hazards to human body. The main components of UV glue are oligomers of acrylate series and some monomers of acrylate series. Acrylate monomers have certain volatility and are irritating to the skin. In the case of initial contact, direct contact under improper protection or long-term exposure to high concentration environment may cause skin allergy, such as red eyes, rashes and itching. But after a period of adaptation, it will not cause allergies, skin rashes and other phenomena.
measures:
1. Keep a good ventilation environment
2. Operators must wear protective clothing, glasses, masks, gloves or finger cots
3. Wash hands frequently and change clothes and gloves frequently
4. Once the glue touches the skin or any other part of the body, immediately wash it with plenty of water, and then rinse it with soap water.
5. For operators with poor physical resistance, please take oral anti allergic drugs such as chlorpheniramine, phenergan, sismin, and kairuitan for about two weeks when they first contact with glue. For operators who have caused allergy, do not grasp with hands at the initial stage of allergy to prevent infection of other body parts. First, take some antiallergic drugs or give antiallergic injections, and the general allergy will disappear soon. Don't panic.
6. For people with allergic skin or poor resistance, it is recommended to change their jobs and do not use UV glue.
matters needing attention:
1. Is the curing speed of the shadowless adhesive related to the quality of the glue? SGS quality report of shadowless adhesive
The curing speed of shadowless adhesive, especially the positioning speed, has always been a data that consumers are concerned about. There are many ways to measure the quality of the shadowless adhesive: positioning time, curing depth, strength, film flexibility, etc. We believe that the faster the positioning speed is, the greater the internal stress generated when the glue is solidified. This may cause the aluminum disc to fall off. Generally, the positioning speed should be 6 to 10 seconds. Therefore, it is wrong to judge the quality of shadowless adhesive only by its curing speed.
2. Is the more glue applied, the better?
The more the shadowless adhesive is applied, the better. The experiment proved that the thinner the adhesive layer, the higher the strength. Generally speaking, it is best that the thickness of the adhesive film does not exceed 0.2 μ m.
3. Many consumers have found that the shadowless adhesive sometimes turns white when they use it. How can the whitening phenomenon of the shadowless adhesive be detected quickly and accurately?
Whitening of shadowless adhesive is a common problem, but it is generally difficult to find it because the whitening is not serious and the adhesive film is relatively thin. This problem exists more or less in the glass to metal shadowless adhesive on the market. Take a glass plate, drop the glue on it, and then shine it under the light for 12 minutes. Take it out for observation, so that the whitening phenomenon of the shadowless glue can be quickly detected. The degree of whitening is directly related to the thickness of adhesive film. The degree of glue whitening has nothing to do with the strength!
4. Viscosity of shadowless adhesive?
When a liquid moves under the action of an external force, the friction resistance between its molecules is measured, which is called viscosity. The greater the friction resistance, the greater the viscosity; The smaller the friction resistance, the smaller the viscosity. In the International System of Units, the unit of viscosity is mPa. s. The viscosity of water is 1.14 mPa. s.
5. Is the lower the viscosity, the lower the strength?
There is no direct relationship between viscosity and strength of shadowless adhesive. It is wrong to understand viscosity as strength, which is a misunderstanding.
6. What is the chemical composition of shadowless glue?
It is composed of oligomer, monomer, photoinitiator and auxiliary agent;
7. Performance characteristics of shadowless glue:
Fast curing and controllable reaction; No solvent and pollution; Suitable for automatic operation; Wide adhesive range, high adhesive strength and wide application; Excellent optical performance; The colloid is colorless and transparent, and the transparency rate after curing is 90%; Excellent weather resistance, no yellowing; Curing principle and curing conditions of shadowless glue; The photoinitiator (photosensitizer) in the shadowless glue absorbs ultraviolet light under the irradiation of ultraviolet light to produce living radicals or cations, which initiate monomer polymerization, cross-linking and branching chemical reactions, so that the adhesive can be transformed from liquid to solid in a few seconds; The shadowless glue must be cured under the ultraviolet radiation with the wavelength of 200nm~400nm;
8. What is the difference between shadowless glue and other glue?
The shadowless glue is initially solidified in 1-5 seconds under ultraviolet radiation, and can be bonded in 20-30 seconds. After irradiation, it can reach high strength, which can meet the needs of automatic production line rhythm; The second generation acrylic structural adhesive is initially solidified in 1-10 seconds, and can reach the highest strength in 24 hours; The epoxy structural adhesive cured at room temperature takes 10-120 minutes for initial curing, and reaches the maximum strength after 7 hours.
Bubble generation:
usage method
1. Pay attention to the amount of shadowless adhesive. When applying shadowless adhesive, do not apply too much. If it is too much, a thick adhesive layer will be produced. This layer of adhesive is not easy to cure, and bubbles will also be generated during the curing process. It is recommended to keep the thickness between 0.04 and 0.06 mm.
2. Glue coating tools should be used properly. During the use of shadowless adhesive, certain irradiation tools should be used. Everyone knows that shadowless adhesive can only be cured under the irradiation of ultraviolet light. Therefore, we inevitably need irradiation tools when using shadowless adhesive. When applying shadowless glue, you'd better use some sizing tools.
3. Before use, the shadowless adhesive may have bubbles during transportation. If you find bubbles in it during use, you'd better put it in a cool place. It can be used for about 24 hours.
There are many manufacturers of shadowless adhesive. The characteristics of shadowless adhesive are also different, and there are many advantages in using it. However, if you want to give full play to the best performance of the shadowless adhesive, you need to pay more attention in the use process. If you have any questions about the shadowless adhesive, you should also consult the seller in time to ensure the use quality of the shadowless adhesive.
Quality improvement:
Poor quality shadowless glue is easy to generate bubbles, mainly because the glue is too thin, and it is OK when the glue just cools the meter. Bubbles are generated by lighting, so high-quality shadowless glue can avoid this phenomenon. UV shadowless adhesive for ice crystal painting can not be seen after curing, which will not affect the appearance of adhesive products. The adhesive strength is strong, and it is not corrosive to various inks; It can withstand low or high temperature, and the tolerance range is - 50 to+120 degrees; Waterproof, aging resistant and yellowing resistant; The shadowless adhesive is suitable for bonding all kinds of printing paper and glass, such as paper, PP, waterproof PP, gold sand, silver sand, jade sand, full transparent, semi transparent, etc; After curing, there will be no internal stress cracking, and the low and high temperature resistance is excellent.
Common sense:
How to remove shadowless glue overflow?
Soft cloth and paper towel can be used to gently wipe the glue overflow, which can be dipped in acetone alcohol. It is easy to remove after positioning, and it needs to be scraped off with a knife after it is completely cured.
Why is the shadowless glue overflowing or the glue surface exposed during fixation sticky and dry?
The surface drying problem is the weakness of UV curable adhesives, which is caused by oxygen polymerization inhibition. High power light source can be used for rapid curing or curing under nitrogen protection.
Why is UV glue for bonding glass metal easy to fall off in summer?
Summer is the season of frequent UV glue accidents. In summer, when it rains or the weather is wet, the glass surface is very easy to absorb water, and many customers can't remove the water film just by wiping with a cloth, which leads to strength attenuation until falling off. The glass can be dried with a hair dryer to maintain a long adhesion.
Why do you feel the bonding strength of some adhesives decreases in winter?
When the temperature of UV adhesive drops in winter, the adhesive film will become hard and brittle, resulting in a decrease in sensory strength. In winter in low temperature areas, the adhesive formula needs to be adjusted to make it have better low-temperature toughness.
How long does UV glue take to cure completely?
According to the difference between the specific UV glue and the curing lamp used by the customer, it cannot be generalized and needs to be determined by experiment. If the UV light intensity is high and the irradiation time is short, it can be cured, and vice versa. Generally, it can be cured in about 1 min under appropriate UV light intensity.
How to separate or remove objects bonded with UV glue?
If the bonding is not good, it is necessary to separate or remove the adhesive for re bonding. According to the specific adhesive and the adhesive, the methods can be used: heating by hair dryer, boiling, steam fumigation, soaking in acetone or ethanol, or soaking in water for a long time.