“UVC” yellowing resistance test for polyurethane
Most of the polyurethane resin is prepared by the reaction of MDI (diphenylmethane diisocyanate) containing benzene ring with polyester or polyether polyol, which belongs to aromatic polyurethane resin; Some polyurethane resins are prepared by the reaction of benzene-free HDI (hexamethylene diisocyanate) and IPDI (isophorone diisocyanate) with polyester or polyether polyols, which are aliphatic polyurethane resins. The cost of aromatic polyurethane products is relatively low, and the mechanical properties are good, but the light is easy to change color and the aging resistance is poor; Aliphatic polyurethane products have higher raw material costs and mechanical properties are not as good as aromatic products, but their light fastness is good and it is not easy to yellow. The photodegradation of polyurethane includes two formation mechanisms: the first mechanism, after the polyurethane absorbs light with a wavelength greater than 340 nm, the methylene group on the MDI oxidizes to form an unstable hydroperoxide, which in turn forms the chromophore monoquinimide structure, which causes the polyurethane to turn yellow, and then further oxidizes to form a diquinonimide structure, and finally becomes amber.
In the second mechanism, after the polyurethane absorbs light with a wavelength of less than 340 nm, Photo-Fries rearrangement occurs, generating aromatic amines, which are further degraded to produce yellowing. Aliphatic polyurethane resin does not contain double bond structures such as benzene rings, so aliphatic polyurethane products have good light resistance and are not easy to yellow.
At present, the mainstream UV aging yellowing test methods are: Q-SUN xenon lamp aging test and QUV UV lamp (including UVA, UVB and UVC) aging test.
The Q-Sun xenon arc lamp aging test is considered to be the most simulated test method for the full solar spectrum, which can continuously expose the tested sample to the equivalent of summer noon light, and its average light intensity is stronger and the average daily exposure time is longer than the actual outdoor environment. The device is capable of lightfastness testing while simulating changes in ambient temperature and humidity. Therefore, the Q-Sun xenon lamp aging test can be very objective and accurate to reflect the color change and aging of materials in the natural environment. Since xenon lamp aging equipment is more expensive and the test conditions are relatively harsh, this method is mainly used in the field of light aging testing of polyurethane products with high requirements such as automotive interiors.
QUV UV aging equipment is based on the principle of short-wave ultraviolet radiation, because short-wave ultraviolet light is considered to be the primary factor for serious damage to plastics exposed to outdoors, QUV UV lamps include: UVA/UVB/UVC three.
- UVA lamps: can well simulate sunlight in the critical shortwave region of sunlight from 365nm to 295nm. UVA-340+ lamps are capable of testing at or above a maximum irradiance of 1.70 W/m2/nm, which meets the highest irradiance values required in the main test standards. The UVA-351 lamp simulates the ultraviolet part of the window glass where sunlight passes through. Cool white lamps can also be used to simulate office environments.
- UVB lamps: UVB-313EL (formerly QFS-40) lamps produce short-wave ultraviolet light stronger than the sun's ultraviolet rays that usually irradiate the earth's surface, UVB-313 lamps are mainly used for quality control and product development, or to test extremely weather-resistant materials. The UVB-311EL+ lamp also provides the most demanding fluorescent UV testing with high irradiance levels. When using UVB lamps, care should be taken to ensure the authenticity of the failure mechanism.
- UVC lamp: UV lamp produces ultra-strong short-wave ultraviolet light of 254nm, which is far below the limit of sunlight. This represents the most common UVC UV radiation used for surface disinfection. While UV effectively kills these pathogens, UV light can also cause degradation of plastics, paints and fabrics. UVC lamps reproduce this destructive irradiance to assess the durability of materials exposed to UVC UV.
The above data is taken from the official Q-LAB manual
In the polyurethane industry, TPU shoe materials, PU synthetic leather and other products, according to ASTM-D1148 test standards, solar lamp method (A method) and ultraviolet lamp method (B method) are often used.
- Method A (bulb method):
According to light-colored or white products, in the natural sunlight long-term exposure is prone to color yellowing phenomenon, with sunlamps and heating temperature control devices to simulate the natural environment, in the specified time, observe the color change of the sample surface, determine the degree of color change of the sample, so as to determine the yellowing resistance of the material under solar radiation.
The light source in the test chamber is a solar bulb, and the light emitted is similar to sunlight, which can be considered as a simplified version of the xenon lamp aging device, which does not control the temperature and humidity of the test product.
The bulb is generally OSRAM's ULTRA VITALUX 300W UV-A UV-A bulb, and the relevant specifications are as follows:
- B method (lamp method):
According to light-colored or white products, the phenomenon of color yellowing is easy to occur in long-term ultraviolet irradiation, and the sample is irradiated with ultraviolet rays, and the color of the sample surface is observed within the specified time to determine the degree of discoloration of the sample, so as to determine the ability of the material to resist yellowing under ultraviolet radiation.
The light source in the test chamber is an ultraviolet lamp, and the light emitted is ultraviolet light. THE LAMP IS GENERALLY USING TWO UV-B LAMPS OF SANKYO DENKI CO., LTD. (UVB-B LAMP 15W G15T8E) UVB LAMP (AS SHOWN IN THE FIGURE), ITS SPECTRAL ENERGY DISTRIBUTION IS BETWEEN 280~360nm, AND THE PEAK IS CONCENTRATED AT 306NM (UVB-313NM SIMILAR TO Q-LAB). UVB lamp is also commonly used to accelerate the artificial climate aging test lamp, it is faster than UVA lamp to destroy the material, because its wavelength is shorter than the UVA lamp wavelength, under the same irradiance (light intensity), it will cause many materials to deviate from the actual test results.
The G15TE lamp has a color-changing fluorescent coating inside the tube, which is white
THE ABOVE DATA IS TAKEN FROM THE OFFICIAL SANKYO DENKI MANUAL
In the Fujian Jinjiang shoe leather market generally use UVB lamp yellowing tester (such as Taiwan high-speed rail GT-7035UB lightfastness tester), but due to the mistakes of equipment manufacturers, many companies use the same type of instruments are not standard UVB lamps, but two UVC lamps with a wavelength of 253.7nm, model SANKYO DENK Germicidal UV-C lamp15W G15T8, using UVC lamps for lightfastness detection results, It does not correctly reflect the actual lightfastness of the product.
The G15T8 lamp is transparent and can be clearly distinguished from the G15T8E
THE ABOVE DATA IS TAKEN FROM THE OFFICIAL SANKYO DENKI MANUAL
SANKYO DENK G15T8E and G15T8 two specifications of lamps, the model difference is only one letter, but the ultraviolet band emitted is completely different, UVB lamp (G15T8E) can be used for polyurethane products B method to test the yellowing effect, UVC lamp (G15T8) high energy in the low band of 253.7nm, so that aromatic polyurethane can not improve its UVC yellowing effect by adding ultraviolet absorbers, nor can it simulate the yellowing resistance of polyurethane products under actual application conditions, the specifications of the two lamps are as follows:
THE ABOVE DATA IS TAKEN FROM THE OFFICIAL SANKYO DENKI MANUAL
At present, UVC germicidal lamps are mainly used to test products that need to be sterilized by ultraviolet light, such as polyolefin medical products.
In summary, polyurethane products for "UVC" yellowing resistance test, is actually UVB lamp (B method: G15T8E) test, and QUV-313nm test is basically the same, so it is necessary to add ultraviolet absorber that absorbs the UVB band (such as UV312) to achieve "UVC" yellowing resistance requirements, UV312 absorption spectrum is as follows:
Add UV312 renderings to the customer's TPU polymer end
For the yellowing resistance test of method A and method B of polyurethane industry, B419 developed by our company can take into account the absorption of UVA and UVB bands, and is widely used in polyurethane shoe materials and other products, blank TPU and ultraviolet absorption spectrum of adding B419 are as follows:
In the TPU industry, ultraviolet absorbers are mostly added at the polymerization end, and the effect of front-end addition is better than that of back-end addition, but the modified end also has more yellowing resistance requirements. We mix B419 with TPU particles (AVALON 85AE with polyester grade HUNTSMAN and IROGRAN 85P4394 with polyether grade HUNTSMAN) and then injection molding, using Q-LAB's QUV/SE type UV lamp aging tester, UVA-340nm lamp, 0.78W/㎡, 45°C conditions, respectively test the yellowing value YI and chromatic difference △E, have reached the industry-leading level, the test results are as follows:
If you have any questions related to polyurethane yellowing resistance, please feel free to contact: little@syntholution.com Thank you!
Post time: Dec-06-2022