LED optical lens
Automatic lens production, cutting nozzle ▼
1、 Understanding LED optical lens
Optical lenses are more and more widely used. According to the actual Optical lens manufacturer application requirements, we develop, use optical design and modeling, manufacture molding molds, and obtain suitable lenses through injection molding. In real life, LED optical lenses are the most widely used.
LED optical lens is mainly used for condensing and guiding light of LED cold light source series products. The light distribution curve is designed according to the angles of different LED outgoing light. By increasing optical reflection, the light loss is reduced and the light efficiency is improved (and the aspheric optical lens is set). It can be developed, designed and produced according to user requirements
The LED lens is placed on the LED lamp bead. Its main function is to change the luminous angle of the LED lamp bead and guide light. It is used in conjunction with the LED light source (lamp bead), so as to form a finished lamp suitable for application.
The role of lens in LED lamps is quite obvious: in addition to focusing, Optical lens manufacturer the light source with lens is evenly distributed, and the light is not strong in some places and weak in some places. Without a lens, the scattering is strong and the lamp is dazzling, but the specific target can not be seen clearly due to the scattered light.
⑴ there are four kinds of LED lens materials: silica gel lens, glass lens, PMMA lens and PC lens. Here we focus on PMMA lens and PC lens formed by injection molding
① . PMMA lens refers to the lens produced by injection molding of optical grade PMMA (polymethylmethacrylate, commonly known as acrylic)
Advantages of using optical grade PMMA: high production efficiency; High light transmittance (about 93% at 3mm thickness); Disadvantages: high temperature resistance (thermal deformation temperature 90 ℃);
② . PC lens refers to optical grade PC for lens produced by injection molding of optical grade PC (polycarbonate). Advantages: high production efficiency; High temperature resistance (above 130 ℃); Disadvantages: the light transmittance is slightly lower (87%);
We usually use PMMA and PC for injection molding.
(2) LED lens specification classification
① . penetrating (convex lens)
When the LED light passes through a curved surface of the lens (biconvex has a curved surface), the light line will be refracted and concentrated, and the distance between the lens and the LED can be adjusted, and the angle will also change. The distance is large (small) and the angle is small (large). The curved spot designed by aspheric technology will be very uniform, but due to the limitation of lens diameter, the light on the side of the lens can not be used (light leakage); This lens is generally used in large angle (40-80 degrees) spotlight, such as table lamp, street lamp, indoor lamp, etc;
② . total reflection type (cone type or cup type)
The design of the lens uses penetrating focusing in the front, and the conical surface can collect and reflect all the side light, and the overlapping (same angle) of the two kinds of light can get the most perfect light utilization and beautiful spot effect;
Some changes can also be made on the surface of the conical lens, Optical lens manufacturer which can be designed into mirror, frosted surface, bead surface, stripe surface, threaded surface, convex or concave surface to obtain different spot effects.
③ . LED lens module
Multiple single lenses are combined and arranged to complete a whole through injection molding. According to different needs, it can be designed into 3-in-1, 5-in-1 or even dozens of lens modules; The lens can effectively save the production cost, realize the consistency of product quality, save the space of lamp mechanism, and make it easier to realize the characteristics of "high power".
2、 LED optical lens raw materials
As optical grade products, lenses have different requirements for light transmittance and toughness according to different applications. In principle, we choose optical grade raw materials, such as Mitsubishi PMMA and optical grade PC, such as Diren pc1225z. Of course, there are many raw material brands in the market. Domestic and imported ones are selected according to their own needs.
PMMA has high light transmittance, but has brittle spots. PC has low light transmittance, but good toughness. PMMA or PC shall be selected according to the lamps.
Therefore, first of all, we must master the injection molding process characteristics of its raw materials:
① PMMA (acrylic)
PMMA is a highly transparent and tasteless amorphous thermoplastic, which is characterized by excellent optical properties, which is also the origin of its common name "glass". PMMA has a uniform refractive index, with a light transmittance of 92%, which is higher than inorganic silicate glass. The transparency is better than that of common plastics. The difference between optical grade PMMA and ordinary grade acrylic is higher transmittance. Optical grade PMMA has high transmittance and good transparency. The transmittance of ordinary acrylic is 92%, and that of high transparent acrylic can reach 93%. It is used as LED lens, lamp, lens product and light guide plate. The fluidity of PMMA is worse than that of PS and ABS, and the melt viscosity is sensitive to the change of temperature. In the molding process, the melt viscosity is mainly changed from the injection temperature.
Drying temperature: 80-90 ℃, time: about 2-4 hours.
Melt temperature: 210 ℃ - 270 ℃, depending on the data provided by the supplier.
The mold temperature is 70-100 ℃, depending on the actual situation.
② PC
Optical grade PC plastics have excellent properties, high transparency, good impact toughness, creep resistance and wide temperature range.
Melt temperature: 270 ~ 320 ℃. If the material temperature exceeds 340 ℃, PC will decompose. The fluidity of PC is poor and it is very sensitive to temperature. The melt viscosity decreases significantly with the increase of temperature. Properly increasing the temperature of the barrel is good for the plasticization of PC. It is extremely sensitive to water, so it must be fully dried before injection molding to reduce its water content to less than 0.02%. General drying conditions of PC: 100 ~ 120 ℃ for more than 2-4 hours. Mold temperature control: 85 ~ 125 ℃, generally controlled at 80-125 ℃. For products with complex shape, thin and high requirements, it can also be increased to 100-125 ℃, but it can not exceed the mold thermal deformation temperature. High mold temperature can reduce the difference between mold temperature and PC material temperature, and reduce the internal stress of parts.
3、 LED lens injection molding process
Quality defects and Solutions
1、 Quality inspection standard for LED lens:
No bubble, no depression, no shrinkage mark, no flow mark, welding mark is within the acceptable range (does not affect the packaging and use function), warpage and deformation. The size is within the controllable range (does not affect the assembly or secondary injection molding), the sun textured products have lines, and the surface is not shiny (does not affect the optical effect)
LED lens products are qualified through injection molding. They also follow the five elements of injection molding: pressure, speed, time, temperature and position. They also follow some injection molding laws. But the optical lens has more stringent requirements than ordinary injection molding products.
The following analyzes the problems and solutions that are easy to occur in the injection molding process of LED lens.
2、 Solution to shrinkage
The root cause of shrinkage is uneven wall thickness and plastic condensation can not be supplemented. Lens products are subject to strict optical design and have specific optical shape and light effect. Whether the surface plane, concave convex surface or internal zigzag surface are shrunk, Optical lens manufacturer its light effect will be changed. We need to analyze what causes it, process parameters or mold problems?
PMMA and PC are temperature sensitive plastics.
Process:
Is the material temperature, mold temperature or runner temperature not enough? Or not enough pressure? Is it cool enough? To find out the reasons, the parameters can be adjusted appropriately, such as increasing the pressure holding pressure, prolonging the pressure holding or cooling time, increasing the mold temperature, increasing the material temperature and increasing the plastic fluidity for better filling.
1. If the material temperature is too low, increase the material temperature. For example, for products with wall thickness, increase the material temperature to increase fluidity and reduce shrinkage.
2. Increase the pressure holding pressure and prolong the pressure holding time due to pressure holding in advance or insufficient pressure holding.
3. If the cooling time is not enough, increase the cooling time. For example, for thick wall lens with mirror surface, appropriate long cooling time is beneficial to improve shrinkage.
On die:
If the rubber inlet of the mold is too small and the sprue is too long to be full, the mold needs to be changed.
1. The mold inlet is small, the sprue is long, and it is difficult to glue the plastic. Increase the inlet or improve the glue feeding method.
2. Hot runner mold:
a. Check the hot runner for blockage and glue leakage.
b. Whether the channel temperature is appropriate can appropriately increase the channel temperature and increase the fluidity of plastic in the channel for better filling.
On the machine:
1. The machine is too small, and the pressure and glue amount are not enough.
2. Check whether the three small parts and the barrel are worn and cannot be sealed.
3. Check whether the oil seal of the glue injection cylinder is worn and the glue injection is weak.
Shrinkage is a common problem in LED lens. Its optical design and light effect application determine that shrinkage defects cannot occur, otherwise it is contrary to the original intention of design and application.
3、 Three "patterns"
Three "patterns" → air pattern, water ripple pattern and flow pattern
First, distinguish three patterns:
① Gas grain. It appears as an aerosol on the surface of the lens product, which is generally located at the product inlet, the thick and thin corner of the rib position or the end of the product.
② Water ripple. It is more vivid and floats on the surface of the product, such as wavy folds.
③ Flow lines usually appear at the rubber inlet and wall thickness, and are expressed as a line perpendicular to the material flow direction.
The generation principle of three "patterns":
① Air lines
a. The material is seriously gasified, and the gas is injected into the cavity together with the melt glue, but it is too late to discharge, floating on the product surface (more serious, it is charred).
b. The mold exhaust is poor and the gas cannot be discharged in time. In short, it is concentrated on the exhaust problem.
② Water ripple. In order to fill the insufficient fluidity, the material has cooled and solidified before the cavity is fully filled during the filling process. Usually, due to the low mold temperature, the plastic condenses in advance and then enters the melt to promote the formation.
③ Flow lines usually appear at the rubber inlet and wall thickness. Generally, the flow lines are mostly caused by the injection of plastic melt, which successively enters the mold cavity. When the melt melts are fused, the two temperatures are different, resulting in the flow lines.
After distinguishing the three "patterns" and their generation principles, we can find their solutions:
① Air striation
Treatment direction: reduce material gasification and increase mold exhaust. Specific scheme:
A: On the mold, if the product allows, the exhaust needle can be added or the exhaust slot can be added on the mold. 80% of the poor injection molding is caused by the mold. This is a once and for all method, and the requirements for machine adjustment are low.
B: In terms of technology, it is required to adjust the machine, reduce the material temperature, increase the mold temperature, reduce the injection speed, control the injection speed by sections, and turn to low-speed injection at the position where the gas lines are generated.
② Water ripple
Mainly from the process: improve the mold temperature, increase the injection speed, increase the injection and holding pressure, and improve the material temperature.
③ Flow pattern
The light effect of lens products will be affected by the presence of streaks, especially at the position of luminous holes. At this time, we must inject in sections, find the position where the flow lines appear, and reduce the injection speed slightly in advance. Of course, sometimes the mold temperature is too high and the plastic flow is fast, which can be appropriately reduced.
1. Process:
A: If the mold temperature is high, it will be reduced.
B: If the injection pressure is too high and the injection speed is too fast, the position can be found to reduce the injection pressure and speed.
2. On the mold: the gate is too small or the shape is wrong, resulting in spraying. Trim the gate size and shape (such as opening a fan as appropriate) to prevent spraying.
LED lens has strict requirements for light shape and light effect. Therefore, if there are three "patterns" in injection molding production, there must be no "patterns" to ignore.
4、 Bonding line
The bonding line is also called fusion mark. The bonding line of LED lens products, especially at the position of light-emitting hole, must be improved, otherwise it will affect the light efficiency, cause water seepage of packaged products and affect the service life of products.
There are two cases of bonding line:
1. Two or more melts are formed when the temperature at the flow end of the mold cavity decreases and cannot be well combined.
In this case, the specific countermeasures are:
① Increase the material temperature, mold temperature and injection pressure and speed appropriately, so as to reduce the temperature difference of melt in the cavity, improve the convergence performance of melt and reduce the generation of bonding line.
② The nozzle hole diameter is too small, so that the mold filling speed is slow, and it is easy to produce bonding lines. Therefore, the nozzle with large diameter should be replaced.
2. The melt flows and converges rapidly in the mold cavity, and the poor exhaust of the mold leads to gas accumulation and bond printing.
In this case, the specific countermeasures are:
① . add exhaust on the die to improve the exhaust
② . change the position of the glue inlet or increase the glue inlet to change the bonding position.
③ The raw materials are fully dried. The raw materials are not fully dried, the moisture content is too high, and the volatile content is too high. A large amount of gas is generated after heating, so that the exhaust of is not enough, Optical lens manufacturer resulting in the generation of bonding line.
④ It is improved by adjusting the position and speed of process parameters.
5、 Black spots, yellowing, mixed color
Black spot yellowing and color mixing are absolutely unacceptable defects of lens products. In this case:
① : check whether the material temperature is too high, causing the material to burn black and carbonize in the barrel. Check whether the nozzle flange has clearance and there is accumulated material carbonization in it
② : color mixing: check whether the barrel is cleaned and whether there is miscellaneous material mixed in the material.
6、 The grain surface is shiny or the grain cannot be printed
Some lenses sun print on the lens surface or some part to obtain corresponding optical effect. If the grain is bright, it cannot be printed. It shall:
① : check whether there are any lines on the part of the mold exposed to the sun
② : is the product full?
③ : is the cooling cycle sufficient?
Therefore, the improvement countermeasures are: check the mold grain surface, appropriately increase the glue amount, increase the pressure holding, and provide sufficient cooling time.
7、 Dimensional difference and warpage deformation
Product design is designed for use at the beginning, with its fixed size.
Main factors affecting the size of injection molded products:
① . machining dimension of die. Generally speaking, the qualified die should take into account the error caused by the imbalance between the die manufacturing error and the shrinkage of the formed part.
② . injection molding process parameters. Reasonable process parameters can be effectively improved.
Warping deformation is common in long strip and square lens products, such as module lens such as industrial and mining street lamp. In terms of mold, the main factors affecting plastic deformation are filling, cooling and ejection. The position, quantity, form, single gate or multiple gate glue are used to affect the flow of melt in the mold cavity and the orientation of internal stress. Due to uneven mold temperature, uneven cooling shrinkage of the product, unbalanced ejection and uneven stress of the product will also cause warpage and deformation.
Process: too high injection pressure, too long pressure holding time, too low melt temperature and too fast speed will cause the increase of internal stress and warpage deformation. The mold temperature is too high and the cooling time is too short, so that the parts during demoulding overheat and eject deformation occurs. Reduce the screw speed and back pressure while maintaining the minimum filling amount, and reduce the melt density to limit the generation of internal stress.
Therefore, the dimensional difference and warpage deformation should be solved from the aspects of die, process and post-treatment:
On die:
① Reasonable gate and ejection design can reduce deformation.
② Increase the water transportation of the mold to make the mold temperature uniform and the product cool evenly, which can reduce the deformation.
A: For large (small) size, reduce (increase) pressure holding, increase (decrease) mold temperature. Extend the pressure holding cooling time to maintain dimensional stability.
Process:
① Reasonable holding pressure, time and cooling time can reduce deformation.
② When adjusting the machine, reduce the mold temperature, reduce the injection pressure, glue melting speed and back pressure, and don't make the product full.
③ Using double mold temperature, since the warpage deformation is caused by uneven mold temperature and uneven cooling, two mold temperature machines can be used to control the front and rear mold temperature respectively to form the front and Optical lens manufacturer rear temperature difference, so as to control the warpage deformation. This is also a method.
Post treatment: if necessary, the product can be annealed after fixture setting or demoulding.
8、 Imprint retention
The imprint protection of lens products mostly appears on Sun textured products, usually due to excessive pressure
