Light fastness refers to the color stability (COLOR STABILITY) or the sun resistance of pigments exposed to the sun, which will not fade or change color.Paintings with real light resistant pigments are generally not exposed to the open sun. Paintings are placed indoors and will not be directly exposed to the sun.[1]
Light resistance refers to the resistance of polymer materials exposed to sunlight or ultraviolet lightfade, yellowing, blackening, aging and cracking degradation.Polymer materials are easy to absorb ultraviolet high-energy radiation rays in the spectrum, excite its electrons to high levels, and cause a series of reactions such as oxidation, fading and degradation.Almost all polymer materials will change color when exposed to sunlight or ultraviolet light.
test method
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The xenon lamp is usually used as the light source, and the artificial method is used to simulate and strengthen the environmental factors such as light, heat, oxygen, moisture and rainfall in the natural climate, especially light, to accelerate the thermal aging[2]。
Test instrument
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The testing instruments are mainly xenon lamps and test standards. The distribution of xenon lamp light spectrum is close to that of the sun or that of the sun after passing through the glass.After the sample has been exposed for a certain period of time, its appearance shall be checked by visual inspection or instrument to assess the cracks, spots, color changes, dimensional stability, etc. on the surface of the sample, and the mechanical properties and other property changes can also be checked to evaluate the lightfastness of the material.Its measurement is increasingly valued by people.
Light fastness of pigment
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Pigment is a kind of fine powdery colored substance, which is insoluble in water or oil medium, but can be evenly dispersed in the medium, coated on the surface of the object to form a color layer, showing a certain color.Pigment shall have proper hiding power, coloring power, high dispersion, bright color, light stability, etc.According to the source, it can be divided into natural pigments and synthetic pigments.Under the action of light and atmosphere, the color and performance of pigments will change in varying degrees, such as color darkening.The change of pigments under the action of light is caused by chemical reaction or the change of crystalline state of particles.In addition, impurities and moisture of pigments can accelerate or aggravate the darkening phenomenon under the action of light and atmosphere[3]。
Light fastness of pigment refers to the ability of pigment to maintain its original performance without fading, discoloration or chalking under the specified light source. It is also called light fastness (or light fastness). If the light source is sunlight, it is called sunlight fast - ness of pigment. The main way to improve light fastness is to use surface treatment[4]。
Xenon lamp light source
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Because the discharge material in the lamp isinert gasXenon, the difference between its excitation potential and ionization potential is small.The energy distribution of xenon lamp radiation spectrum is close to that of sunlight, and the color temperature is about 6000K.The spectral distribution of the continuous spectral part of xenon lamps is almost independent of the change of lamp input power, and the spectral energy distribution is almost unchanged during the life cycle.Xenon lamp has good consistency in light and electrical parameters, and its working state is less affected by changes in external conditions.Once the xenon lamp is ignited, it can achieve stable light output almost instantaneously;When the light is off, it can be re ignited instantaneously.Xenon lamp has low luminous efficiency and low potential gradient.The xenon lamp light source system is divided into point light source and parallel light source. It is an experimental equipment that uses the xenon lamp light source as the luminous core, and lights up and operates the xenon lamp light source with professional cooling system, stable power supply and trigger device.The point light source is generally connected to the optical fiber for use, so that the simulated sunlight can reach the narrow and dark experimental equipment.The parallel light source is generally a beam of light spot, and the size of the light spot can be adjusted according to the experimental requirements[5]。
Xenon lamp precautions
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1. The ignition position of xenon lamp can be vertical or horizontal. The inclination angle shall not exceed 40 ° when the lamp is horizontally ignited. When the lamp is vertically ignited, the anode is above and the cathode is below.For horizontal ignition, there should be an arc absorption magnetic field in the horizontal direction of the bulb shell to stabilize the arc position, so as to prevent the arc from floating upward.
2. Do not stain the quartz bubble shell. Keep it clean. Wipe it with alcohol cotton before use, and then light the lamp.
3. Special attention must be paid to the positive and negative connections when connecting bulbs. The "+" end of the thick electrode is the anode, and the "-" end of the thin electrode is the cathode. If the connection is reversed, the cathode will be burned out in a few seconds.
4. Due to the large current, the contact between lamp holder and lamp holder must be good, and the contact point must be clean during use.
5. Since the lamp is filled with high-pressure gas, collision shall be avoided during loading, unloading and transportation, especially during installation. During operation, it shall be placed in a cover with good heat dissipation to prevent explosion, strong light and strong ultraviolet rays from burning skin and eyes.
6. Xenon lamp must be used together with special DC power supply and trigger. The ripple coefficient of DC power supply shall not be greater than 7%, and the working current when ignited shall be within the specified range.Otherwise, the life of the lamp will be affected or even destroyed.
