Compared with other heat-curing inks, UV inks have the advantages of fast drying and low VOC content. However, on some non-absorbing substrates, UV inks sometimes dry out, sometimes resulting in low adhesion of the UV ink to the substrate. Although the degree of adhesion required depends on the end use environment and application of the printed product, the adhesion of the UV ink to the substrate can be improved after the proper method is adopted.
Corona treatment is a method of improving UV ink adhesion by means of electroshock treatment. The positive and negative poles of the corona device are respectively grounded and induced air nozzles, and the high-voltage and high-frequency waves are used to cause the electric shock molecules to be ejected from the induced air nozzles, and the high-energy free electrons are accelerated toward the positive electrode so that non-absorption can be changed. The polarity of the material is increased and the surface roughness is increased, and the ability to combine with the ink is enhanced, the correct UV ink adhesion is achieved, and the adhesion of the ink layer is improved.
Corrosion-treated materials have poor surface tension, and the corona effect gradually diminishes over time. Especially when stored under high humidity conditions, the corona effect diminishes faster. If a corona-treated substrate is used, it must cooperate with the supplier to ensure that the substrate is fresh. Common corona treatment materials include PE, PP, nylon, PVC, PET and so on.
In many cases, cleaning the substrate with alcohol will increase the adhesion of the UV ink to the substrate. If the adhesion of the substrate to the UV ink is very poor, or the product has a higher requirement for UV ink adhesion, it may be considered to use a primer/UV ink adhesion promoter that promotes UV ink adhesion. Primer, such as HJ5100 UV primer from Huajin Si, USA, can effectively combine with various polar substrate surfaces such as glass, ceramics, various metals and stainless steel polar groups, and quickly form high gloss on the substrate surface. , transparent film. After applying a primer to a non-absorbent substrate, the adhesion of the UV ink can be increased to achieve the desired adhesion. Unlike corona treatment, chemically-primed materials do not contain non-polar, oil-like molecules that can effectively eliminate the problem of unstable corona effects due to the migration of such molecules. However, the scope of application of the primer is selective, and it is better for substrates such as glass, ceramics, metals, acrylics, and PET.
In general, we can observe the poor adhesion of UV inks on non-absorbent substrates when UV inks are not fully cured. To improve the degree of UV ink curing can start from the following aspects:
1) Increase the power of UV curing lamps: On most substrates, increasing the power of UV curing will increase the adhesion of UV inks to the substrate. This is especially important in multi-layer printing: When coating a second layer of UV coating, the first layer of UV ink must be completely cured. Otherwise, once the second layer of UV ink is printed on the surface of the substrate, the underlying UV ink will have no chance to further cure. Of course, over-curing on some substrates can cause the UV ink to break easily when sheared.
2) Reduce the printing speed: The increase in UV lamp power while reducing the printing speed can also increase the adhesion of UV inks. On UV flatbed ink jet printers, printing can also be improved by printing in one direction (rather than printing back and forth). However, heating and deceleration can also cause the substrate to curl on substrates that tend to curl.
3) Prolong curing time: It must be noted that the UV ink will cure after printing. Especially in the first 24 hours after printing, this will increase the adhesion of UV. If possible, postpone the step of trimming the substrate until after 24 hours of UV printing.
4) Check if the UV lamp and its accessories are working properly: if the adhesion on the substrate, which is relatively easy to attach, is reduced, it is necessary to check whether the UV lamp and its accessories are working properly. All UV light curing lamps have a certain useful life (usually the life time is about 1000 hours). When the UV light curing lamp is used for longer than its service life, the electrode gradually decomposes with the use of the lamp, the inner wall of the lamp tube. As deposition occurs, the transmittance of the transparency and UV light gradually decreases, and the power is greatly reduced. In addition, if the reflector of the UV curing lamp is too dirty, the reflected energy of the UV curing lamp will be lost (the reflected energy may account for about 50% of the power of the entire UV curing lamp), which will also cause the power of the UV curing lamp to decrease. . There are also some printers whose UV light curing lamp power configuration is unreasonable. To avoid poor curing of the ink due to insufficient power of the UV light curing lamp, it is first necessary to ensure that the UV light curing lamp operates within an effective service life, and that the UV light curing lamp that has exceeded its service life is to be promptly replaced. And regular cleaning UV curing light to ensure that the reflector clean and reduce the loss of reflected energy.
5) Reducing the thickness of the ink layer: Since the effect of adhesion is related to the degree of photocuring of the UV ink, lowering the amount of UV ink used will promote adhesion to the substrate. For example, in a large-area printing process, due to the fact that the amount of ink is too large and the ink layer is too thick, when the UV light cures and solidifies, the ink surface layer is cured and the bottom layer is not completely cured. Once the ink has dried up, the binding force between the bottom layer of the ink and the surface of the substrate becomes poor, which can cause the ink layer on the surface of the printed product to fall off due to surface friction during the processing of the subsequent process. When printing a large area of ​​live work, it is necessary to pay strict attention to the control of the amount of ink. For some spot color printing situations, it is best to adjust the color darker during ink dispensing so that the printing process can be dark ink and thin printing, so that the ink is fully cured and the firmness of the ink layer is increased.
Heating: In the screen printing industry, it is recommended to heat the substrate prior to UV curing before printing hard-to-adhere substrates. After heating with near-infrared light or far-infrared light for 15-90 seconds, the adhesion of the UV ink to the substrate can be enhanced.
Varnish: If the above recommendations are used, the UV ink still has problems with adhesion to the substrate and can be coated with a protective varnish.
Cut: If there is only adhesion problem when cutting, it is recommended to cut the substrate to the required size before printing. The edge of the cutting tool must be sharp. Rotary cutters will cut better than ordinary straight-edged scissors.
Corona treatment is a method of improving UV ink adhesion by means of electroshock treatment. The positive and negative poles of the corona device are respectively grounded and induced air nozzles, and the high-voltage and high-frequency waves are used to cause the electric shock molecules to be ejected from the induced air nozzles, and the high-energy free electrons are accelerated toward the positive electrode so that non-absorption can be changed. The polarity of the material is increased and the surface roughness is increased, and the ability to combine with the ink is enhanced, the correct UV ink adhesion is achieved, and the adhesion of the ink layer is improved.
Corrosion-treated materials have poor surface tension, and the corona effect gradually diminishes over time. Especially when stored under high humidity conditions, the corona effect diminishes faster. If a corona-treated substrate is used, it must cooperate with the supplier to ensure that the substrate is fresh. Common corona treatment materials include PE, PP, nylon, PVC, PET and so on.
In many cases, cleaning the substrate with alcohol will increase the adhesion of the UV ink to the substrate. If the adhesion of the substrate to the UV ink is very poor, or the product has a higher requirement for UV ink adhesion, it may be considered to use a primer/UV ink adhesion promoter that promotes UV ink adhesion. Primer, such as HJ5100 UV primer from Huajin Si, USA, can effectively combine with various polar substrate surfaces such as glass, ceramics, various metals and stainless steel polar groups, and quickly form high gloss on the substrate surface. , transparent film. After applying a primer to a non-absorbent substrate, the adhesion of the UV ink can be increased to achieve the desired adhesion. Unlike corona treatment, chemically-primed materials do not contain non-polar, oil-like molecules that can effectively eliminate the problem of unstable corona effects due to the migration of such molecules. However, the scope of application of the primer is selective, and it is better for substrates such as glass, ceramics, metals, acrylics, and PET.
In general, we can observe the poor adhesion of UV inks on non-absorbent substrates when UV inks are not fully cured. To improve the degree of UV ink curing can start from the following aspects:
1) Increase the power of UV curing lamps: On most substrates, increasing the power of UV curing will increase the adhesion of UV inks to the substrate. This is especially important in multi-layer printing: When coating a second layer of UV coating, the first layer of UV ink must be completely cured. Otherwise, once the second layer of UV ink is printed on the surface of the substrate, the underlying UV ink will have no chance to further cure. Of course, over-curing on some substrates can cause the UV ink to break easily when sheared.
2) Reduce the printing speed: The increase in UV lamp power while reducing the printing speed can also increase the adhesion of UV inks. On UV flatbed ink jet printers, printing can also be improved by printing in one direction (rather than printing back and forth). However, heating and deceleration can also cause the substrate to curl on substrates that tend to curl.
3) Prolong curing time: It must be noted that the UV ink will cure after printing. Especially in the first 24 hours after printing, this will increase the adhesion of UV. If possible, postpone the step of trimming the substrate until after 24 hours of UV printing.
4) Check if the UV lamp and its accessories are working properly: if the adhesion on the substrate, which is relatively easy to attach, is reduced, it is necessary to check whether the UV lamp and its accessories are working properly. All UV light curing lamps have a certain useful life (usually the life time is about 1000 hours). When the UV light curing lamp is used for longer than its service life, the electrode gradually decomposes with the use of the lamp, the inner wall of the lamp tube. As deposition occurs, the transmittance of the transparency and UV light gradually decreases, and the power is greatly reduced. In addition, if the reflector of the UV curing lamp is too dirty, the reflected energy of the UV curing lamp will be lost (the reflected energy may account for about 50% of the power of the entire UV curing lamp), which will also cause the power of the UV curing lamp to decrease. . There are also some printers whose UV light curing lamp power configuration is unreasonable. To avoid poor curing of the ink due to insufficient power of the UV light curing lamp, it is first necessary to ensure that the UV light curing lamp operates within an effective service life, and that the UV light curing lamp that has exceeded its service life is to be promptly replaced. And regular cleaning UV curing light to ensure that the reflector clean and reduce the loss of reflected energy.
5) Reducing the thickness of the ink layer: Since the effect of adhesion is related to the degree of photocuring of the UV ink, lowering the amount of UV ink used will promote adhesion to the substrate. For example, in a large-area printing process, due to the fact that the amount of ink is too large and the ink layer is too thick, when the UV light cures and solidifies, the ink surface layer is cured and the bottom layer is not completely cured. Once the ink has dried up, the binding force between the bottom layer of the ink and the surface of the substrate becomes poor, which can cause the ink layer on the surface of the printed product to fall off due to surface friction during the processing of the subsequent process. When printing a large area of ​​live work, it is necessary to pay strict attention to the control of the amount of ink. For some spot color printing situations, it is best to adjust the color darker during ink dispensing so that the printing process can be dark ink and thin printing, so that the ink is fully cured and the firmness of the ink layer is increased.
Heating: In the screen printing industry, it is recommended to heat the substrate prior to UV curing before printing hard-to-adhere substrates. After heating with near-infrared light or far-infrared light for 15-90 seconds, the adhesion of the UV ink to the substrate can be enhanced.
Varnish: If the above recommendations are used, the UV ink still has problems with adhesion to the substrate and can be coated with a protective varnish.
Cut: If there is only adhesion problem when cutting, it is recommended to cut the substrate to the required size before printing. The edge of the cutting tool must be sharp. Rotary cutters will cut better than ordinary straight-edged scissors.
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