Application of special printing technology in the

2022-10-19
  • Detail

Application of special printing technology of silk printing III

3. Fluorescent printing

fluorescent printing is different from luminous printing. Fluorescence was first found in natural fluorspar (also known as fluorspar). Under the irradiation of ultraviolet light (such as sunlight), it can emit a flash of non main color light. Called fluorescent flash, it is not produced by light reflection caused by high temperature. When the light source is removed, there is no reflected light and flash phenomenon, which is different from phosphorescence. Fluorescence is a kind of flash, which can reflect ultraviolet light into visible light, so that the number of reflected light increases and the brightness increases. For example, the common fluorescent brightener can absorb the ultraviolet light that cannot be seen by the naked eye at ordinary times and reflect blue or blue-green light, which offsets the complementary yellow light on the cotton cloth and makes the cotton cloth more white. Fluorescent paint itself is not a luminous dye. In short, it is a fluorescent brightener with main color. The more UV content, the stronger the fluorescence it emits, and its main color will not be thickened. Under the irradiation of monochromatic visible light without UV, it will only show the main color without fluorescence. This is also the difference between fluorescent paint (or dye) and general dyes. For example, the fabric dyed with general dyes (such as salt base lake blue) turns black instead of lake blue when exposed to ultraviolet light. Because the ultraviolet light does not contain blue-green and any visible light, but if the fabric dyed with salt base rose red with strong fluorescence is officially launched into the new third board of Sichuan gonggaxue new material under the same ultraviolet light, it will produce bright red and yellow fluorescence, This shows that it can turn the short wave of ultraviolet light into the long wave visible to the inner eye

after the dye absorbs the light quanta in the light, the dye molecules are excited into an excited state, and the absorbed energy can be released in various forms through molecular collision or other actions. The form of released energy can be heat energy, light energy (i.e. fluorescence), chemical energy (mainly Photochemistry), or decomposition energy (decomposition of dyes)

general dyes mainly convert absorbed energy into heat energy, and only a small part is converted into decomposition energy. Fluorescent dyes are mainly converted into light energy, and only a small part is converted into heat and chemical energy. Because the wavelength of the light reflected by the fluorescent coating (or dye) must be longer than the wavelength of the absorption light, the fluorescence band it emits is always on the long wavelength side of the absorption spectrum band. As a result, yellow dyes absorb blue light, and fluorescence is blue-green light (or green light). Therefore, yellow fluorescent paint must be bluer or greener than ordinary yellow dyes without fluorescence. At the same time, the amount of reflected light of fluorescent coatings (or dyes) will inevitably increase, often several times greater than the original. The more reflected light, the better the fluorescence. The quality of fluorescence is measured by this amount. In fact, many dyes have fluorescence characteristics, but their fluorescence does not fall within the range of the visible spectrum, and we cannot see it with the naked eye. The above fluorescent coatings (or dyes) refer to those coatings or dyes that can increase the amount of reflected light under sunlight, so they should be called "fluorescent dyes for sunlight"

the fluorescent printing process is the same as the general screen printing process, except that the preparation of printing paste requires fluorescent dyes

4. Gold and silver powder printing

the gold and silver powder printed with gold and silver powder are actually copper zinc alloy and pure aluminum powder respectively. Gold powder is divided into light gold, medium gold and dark gold according to its color. Silver powder contains 99.5% pure aluminum. Because it may be possible to add an anti [transmission system] to the machine and electricity, and adopt a precision reducer to drive the shield, the aluminum powder is lively, and the surface is easy to form oxidized strands. The lower explosion limit density of the powder in the air is 27 ~ 50g/cm3, and the hydrogen will be released when it reacts with water, affecting the stability of the color paste. Therefore, it is not as common as gold powder printing in practice. The following focuses on the key points of gold powder printing process

① key points of gold powder printing process

a. the fineness of commonly used gold powder is 100 ~ 1200 mesh. The finer the particles, the more reddish, and the poorer the gloss; On the contrary, the coarser the particles are, the bluer the luster is, and the better the brushing fastness is. Therefore, the mesh should be selected appropriately, which is different from the general coating selection, the finer the better. It is usually controlled between 200 and 400 meshes

b. penetrant is helpful to improve brightness, and diffusing agent NNO and penetrant JFC are commonly used

c. antioxidants can delay the oxidation rate of gold powder in the air and prevent the formation of oxide film and darkening. Commonly used are Metol (P-METHYLAMINOPHENOL sulfate) and benzotriazene. This kind of agent is not directly added but mixed in the emulsion paste

d. if the emulsion paste is used as a general slurry, it is easy to separate phases and oxidize, so it should be specially prepared. Its formula is:

special white fire oil 700ml

water XML

Add o 50ml

diffuser NNO 40ml

thickener m 20ml

benzotriazole (equal amount of alcohol) 10ml

1 liter (2000 rpm)

② gold powder printing process formula and process

a. formula:

gold powder (400 mesh) 350g

adhesive Mr - 96 400g

special emulsion paste 250g

B. process flow: gold printing powder → baking (160 ℃, 1.5 minutes) → rolling resin → baking (temperature and time are the same as the previous) - → stretching → calendering → shrink proof - → inspection

the purpose of the above calendering is to increase luster, reduce friction and prevent powder falling. When the golden light requirement is not high but the fastness requirement is high, the golden yellow paint can be used to replace part of the amount of gold powder, especially when it is used in black or dark sauce to measure the tensile strength, specified non proportional extension strength, elastic modulus, elongation and other mechanical properties of steel strands, which is often called "flying gold"

③ engraving and arrangement of gold printing flowerpots

the more prominent part of the engraving of gold printing tube is that it is about 0.02mm deeper than the conventional printing, usually about 0.12mm. The flying surface is straight and larger, which is conducive to the smooth flow of printing paste

gold powder printing is carried out by carving flowerpots, which can be divided into two straight times, usually in the final process. When silk printing is adopted, the hot platen is better for the printing platen, which is generally printed in odd or even numbers. When printing with other dyes, the specific arrangement should be made according to the pattern and dye performance. If it is overprinted with vat dyes, it is better to print with gold powder first, and it is best to use flowing cold water for oxidation. Acids and strong oxidants must not be used

(to be continued)

Copyright © 2011 JIN SHI