The bottle exterior printing belongs to the container printing and can be completed with a curved screen printing machine. For the bottles processed from non-polar PE plastic PP plastic materials, such as shampoos, shower gels, cosmetics, insecticides and other bottles, the light curing ink is generally used, so PE plastic PP plastic must be used before screen printing. The external disposal can solve the firm adhesion of ink on it. So, what are the best curing conditions for photo-curable inks? How to polarize PE plastic PP plastic bottles to achieve a good ink effect, on this issue, described in the next.
First, the basic knowledge of UV Varnish
1. Composition of UV Varnish and Its Effect on Ink
Reactive Diluent (also known as Diluent Monomer) A relatively low molecular weight (low molecular weight) chemical that reduces the viscosity, acts as a dispersing and diluting resin, and determines the appearance characteristics of the ink, such as viscosity, hardness, and softness. Sex. Does not volatilize and participates in UV resin curing cross-linking reactions.
2 Additives: including pigments, lubricants, thickeners, fillers, and accelerants, affect the ink color, curing speed, ink thickness and printability and ink weather resistance.
3 Photo-curable resin: The main part of the UV-varnish film, namely the connecting material of UV varnish, determines the gloss and adhesion of the UV varnish. Different inks use different resins to accommodate substrates of different materials.
4 Initiator: A chemical that stimulates the cross-linking reaction. In the photochemical reaction, the initiator becomes excited and excited by photoexcitation and absorbs photons. Radicals are generated, and the energy is transferred to other photosensitive polymers, causing them to undergo a chain reaction and combining single molecules, additives, and photo-curable resins. The formation of a net-like stable structure, the ink conjunctiva firmly attached to the substrate.
2.UV Varnish Curing and Curing System Requirements
1 Types of reflectors: focus type, non-focus type, and multi-faceted reflective type. Commonly used focus, non-focus, and polyhedral types commonly used to cure varnish (inks without colorants)
2 UV Lamps: The power of the UV lamps must meet the requirements for UV light penetration to cure. The maximum lifetime of a UV lamp cannot exceed 1200 hours. It is generally recommended that it should be replaced after 1 000 hours. Clean the lamp at regular intervals. After cleaning, be careful to rotate the lamp counter-clockwise for 1/4 week (repeated three times) and clean the UV lamp.
3 Detection of the system: The energy output of the UV lamp can be measured with an energy meter. The UV image is drawn with a UV IMA P waveform monitor. The curing system is detected based on the UV pattern. If the drawn energy pattern is sharp, it indicates that the curing system is problem-free; if the top is a hump, the reflector has dust; if the top is round Describe the lamp aging, according to the level of aging the replacement should be replaced.
4 Light curing elements:
UV Lamp Power: The amount of UV light emitted, also known as penetrating power, must meet the UV curing ink requirements. If the power of the UV lamp is not enough, even if the lighting time is longer, or the number of times of curing is repeated, the ink cannot be completely cured. . Therefore, when the power of the UV lamp is insufficient, the ink needs to be cured by the high-power lamp because the UV light emitted from the low-power lamp cannot penetrate to the bottom of the ink layer, so that the bottom does not solidify.
Curing speed: Curing speed must be considered from two aspects. One is full cure; the second is cure at the best cure speed. The choice of the best curing speed is to use a UV machine to cure at a certain speed. If it is cured and then speed up, until the ink layer out of the curing machine can not be cured, then the best curing speed can be determined, that is, start Non-curing speed 0.8 = optimum curing speed.
Spectral wavelength range of UV lamps: The spectral sensitivity range of the UV lamp must match that of the UV varnish. General requirements UV lamp wavelength range between l80-420nm.
5 Adhesion test:
After the print is passed through a UV machine and cooled to room temperature, the print can be cut to 6 6mm. Note that only the ink film can be scratched and cannot be damaged. Use 3M-600# tape to test the adhesion. By testing adhesion, the following problems can be explained:
If there is no ink layer on the tape, it means good curing and good adhesion.
If the blots are all transferred to the tape, there are four problems: the ink series is not selected (ie does not match the material of the substrate). The substrate contains a large amount of plasticizer or surface release agent; the surface tension of the substrate is too low. , must be disposed of or has been disposed of without proper handling; poor ink cure.
The imprinted edge does not transfer, and the middle portion is transferred to the tape, indicating that it is not fully cured. This is because the power of the lamp is insufficient or the lamp power is satisfied but the curing speed is too fast.
The blot became a ghost, indicating that the ink was not completely cured.
When overprinting, if the second color has poor adhesion, only the second layer will fall when the tape is tested, indicating that the first color is excessively cured. If the two layers after the overprinting test are lost, the first layer is insufficiently cured. The rule for UV curing during the color printing is 70 30RULE ie 70% cure, 30% uncured, and the final ink layer should be 100% cured.
7 Effect of additives.
The addition of additives can affect some properties of the ink, such as adding an initiator, can increase the adhesion, but it will affect the softness of the ink, and adding too much will immediately lead to cross-linking and can not be printed.
8 Process Conditions:
Screens in UV varnish printing generally use high tension, low elongation, S-grade plain screens or single-sided and double-sided screens. Frame strength is good.
The tension on the screen is the same, the error is ± 2N/cm, the tension is inconsistent, the ink layer is not uniform, and positional deviation can occur.
The net distance is generally between 2-4mm, and the net distance should be adjusted according to the tension.
The hardness of the scraper is 60 ° 90 °, the manual is 70 ° machine printing 80 °
Substrate pretreatment. Due to the different surface conditions of the substrate materials, it is necessary to perform surface treatment on the substrate. This is very important for the adhesion of UV varnish. For plastic films, it can be wiped with a cleaning cloth of tantalum alcohol or isopropyl alcohol to remove the ink floating on the substrate. Plasticizers and impure chemical substances such as dust and grease on the surface; for materials with low external surface tension, such as PP PE PU PET, can be treated by flame or corona according to the thickness and thinness of the printed material to increase Its surface activity improves its adhesion. After surface treatment, the substrate surface tension should be ≥ 45 dyne/cm.
The ink should be fully stirred before use, especially after adding the additives must be stirred evenly, otherwise it will produce some strong adhesion of the curing, and some have not cured or insufficient curing adhesion is poor, the printing will produce adhesion.
The UV lamp power must meet the requirements and adjust the curing speed.
After curing, it was allowed to cool to room temperature and a cross-hatch test was performed using a 3M-600# adhesive tape. Adhesion and solvent resistance were optimized at 24 hours after curing.
Wash the net, wash the net with water, but you can't use alcohol, because alcohol can damage the net template.
9 Climate impact on UV varnish.
Effect of temperature: The temperature is high, the viscosity of the UV varnish becomes low, and the phenomenon of toothiness and stencil is easy to occur after printing. Low temperature, high viscosity, easy to produce incomplete cure. Therefore, it is required that the ink be refrigerated in the summer, and the temperature of the silk screen shop should not be too high; when it is taken in a frozen environment in winter, it should be placed in the temperature of the printing environment in advance, and the curing speed should be appropriately slowed down.
Humidity: Humidity affects the appearance of the substrate and the screen printing performance of the ink on the substrate.
10 effects of color.
Because various colors reflect light differently, the relationship between the reflection wavelength of light and the speed of photo-curing of the seven-color light on the UV curing of the ink varies depending on the color.
Second, the bottle (plastic PE plastic PP plastic PET, etc.) prepress processing requirements and parameters
At present, light-curing inks have not been directly applied to untreated PE plastic plastic bottles. Therefore, to print PE PP bottles, the PE plastic must be polarized before printing. Otherwise, UV inks cannot be firmly attached. So how to polarize?
There are many methods of polarization treatment. The majority of PE plastic plastic plastic and its bottle industry use flame treatment methods. The result of this flame disposal is the use of flames containing free radicals such as O N0 OH and NH, which can turn polymers into polymers. Such as PE plastic PP plastic surface oxygen extracted, followed by a free radical mechanism for surface oxidation and the introduction of some polar oxygen-containing groups break chain reaction, non-polar PE plastic PP polarized to change its surface The wettability ensures the fastness of the ink.
The water surface tension is 72.5 dyne/cm and the oil surface tension is 25-50 dyne/cm.
Flame disposal parameters: At present, most flame treatment units use gas as the combustion source and should control the air: gas = 7 1 to achieve the blue-violet flame, then the flame temperature can reach 1270 C or so, the flame core length is controlled at 6 -19mm Flame core tip to surface is l 0-15mm Contact time is l-4 seconds (1-2 seconds for LDPE, 3-4 seconds for HDPE) Rotation speed 100-150 rev/min, handleable depth of surface at 40 -90A allows PE plastic PP plastic appearance to reach 45 dyne/cm to meet the fastness requirements of ink adhesion.
Detection of polarization after flame treatment of PE plastic PP plastic plastic bottles: When PE plastic PP flame treated, it must reach the original surface tension value of > 45 dyne to ensure that the UV ink is firmly attached, so the flame treatment effect The detection is very important and its method has Dyne test pen (with a mixture of ethylene glycol ether 35% + formamide 65%) for detection and immersion detection. It is generally used to detect by flooding, that is to say, the PE plastic plastic bottle with flame-treated PP is completely immersed in clean water, and then the bottle is removed from the water for a short pause (about 10 seconds or so) to allow excess water to flow out, and then the bottle is viewed. Whether the surface of the treatment site is covered with a uniform layer of water, if it is full of hydrophilicity and lasts for more than 15 seconds, it means that the flame treatment has reached the printable requirements, if the water film on the surface of the bottle is not continuous, even like After the rain leaves the lotus leaf, it is necessary to adjust the flame disposal parameters to meet the requirements, such as the proportion of air and gas combustion, the time and distance of contact between the flame active ingredient and PE PP, and so on.
Third, screen printing process parameters
1. The ink should be thoroughly stirred before printing, and the material splashed on the lid of the ink tank can be completely scraped into the ink and stirred evenly.
2. Screen and screen. Wire mesh: yellow, high strength, low stretch net with a mesh size of >355 mesh/inch. Screen: Tension 18-25N/cm with direct or capillary film, film thickness 15-25 microns.
3. Squeegee: hardness 80 ° polyurethane tip scraping.
4. Screen cleaning with ordinary washing water.
5. Curing conditions: medium/high pressure mercury lamp, wavelength: 280-380nm The peak is better at 365nm. Power: 80-120W/cm or so. Over UV speed: The need to adjust the photocuring energy.
First, the basic knowledge of UV Varnish
1. Composition of UV Varnish and Its Effect on Ink
Reactive Diluent (also known as Diluent Monomer) A relatively low molecular weight (low molecular weight) chemical that reduces the viscosity, acts as a dispersing and diluting resin, and determines the appearance characteristics of the ink, such as viscosity, hardness, and softness. Sex. Does not volatilize and participates in UV resin curing cross-linking reactions.
2 Additives: including pigments, lubricants, thickeners, fillers, and accelerants, affect the ink color, curing speed, ink thickness and printability and ink weather resistance.
3 Photo-curable resin: The main part of the UV-varnish film, namely the connecting material of UV varnish, determines the gloss and adhesion of the UV varnish. Different inks use different resins to accommodate substrates of different materials.
4 Initiator: A chemical that stimulates the cross-linking reaction. In the photochemical reaction, the initiator becomes excited and excited by photoexcitation and absorbs photons. Radicals are generated, and the energy is transferred to other photosensitive polymers, causing them to undergo a chain reaction and combining single molecules, additives, and photo-curable resins. The formation of a net-like stable structure, the ink conjunctiva firmly attached to the substrate.
2.UV Varnish Curing and Curing System Requirements
1 Types of reflectors: focus type, non-focus type, and multi-faceted reflective type. Commonly used focus, non-focus, and polyhedral types commonly used to cure varnish (inks without colorants)
2 UV Lamps: The power of the UV lamps must meet the requirements for UV light penetration to cure. The maximum lifetime of a UV lamp cannot exceed 1200 hours. It is generally recommended that it should be replaced after 1 000 hours. Clean the lamp at regular intervals. After cleaning, be careful to rotate the lamp counter-clockwise for 1/4 week (repeated three times) and clean the UV lamp.
3 Detection of the system: The energy output of the UV lamp can be measured with an energy meter. The UV image is drawn with a UV IMA P waveform monitor. The curing system is detected based on the UV pattern. If the drawn energy pattern is sharp, it indicates that the curing system is problem-free; if the top is a hump, the reflector has dust; if the top is round Describe the lamp aging, according to the level of aging the replacement should be replaced.
4 Light curing elements:
UV Lamp Power: The amount of UV light emitted, also known as penetrating power, must meet the UV curing ink requirements. If the power of the UV lamp is not enough, even if the lighting time is longer, or the number of times of curing is repeated, the ink cannot be completely cured. . Therefore, when the power of the UV lamp is insufficient, the ink needs to be cured by the high-power lamp because the UV light emitted from the low-power lamp cannot penetrate to the bottom of the ink layer, so that the bottom does not solidify.
Curing speed: Curing speed must be considered from two aspects. One is full cure; the second is cure at the best cure speed. The choice of the best curing speed is to use a UV machine to cure at a certain speed. If it is cured and then speed up, until the ink layer out of the curing machine can not be cured, then the best curing speed can be determined, that is, start Non-curing speed 0.8 = optimum curing speed.
Spectral wavelength range of UV lamps: The spectral sensitivity range of the UV lamp must match that of the UV varnish. General requirements UV lamp wavelength range between l80-420nm.
5 Adhesion test:
After the print is passed through a UV machine and cooled to room temperature, the print can be cut to 6 6mm. Note that only the ink film can be scratched and cannot be damaged. Use 3M-600# tape to test the adhesion. By testing adhesion, the following problems can be explained:
If there is no ink layer on the tape, it means good curing and good adhesion.
If the blots are all transferred to the tape, there are four problems: the ink series is not selected (ie does not match the material of the substrate). The substrate contains a large amount of plasticizer or surface release agent; the surface tension of the substrate is too low. , must be disposed of or has been disposed of without proper handling; poor ink cure.
The imprinted edge does not transfer, and the middle portion is transferred to the tape, indicating that it is not fully cured. This is because the power of the lamp is insufficient or the lamp power is satisfied but the curing speed is too fast.
The blot became a ghost, indicating that the ink was not completely cured.
When overprinting, if the second color has poor adhesion, only the second layer will fall when the tape is tested, indicating that the first color is excessively cured. If the two layers after the overprinting test are lost, the first layer is insufficiently cured. The rule for UV curing during the color printing is 70 30RULE ie 70% cure, 30% uncured, and the final ink layer should be 100% cured.
7 Effect of additives.
The addition of additives can affect some properties of the ink, such as adding an initiator, can increase the adhesion, but it will affect the softness of the ink, and adding too much will immediately lead to cross-linking and can not be printed.
8 Process Conditions:
Screens in UV varnish printing generally use high tension, low elongation, S-grade plain screens or single-sided and double-sided screens. Frame strength is good.
The tension on the screen is the same, the error is ± 2N/cm, the tension is inconsistent, the ink layer is not uniform, and positional deviation can occur.
The net distance is generally between 2-4mm, and the net distance should be adjusted according to the tension.
The hardness of the scraper is 60 ° 90 °, the manual is 70 ° machine printing 80 °
Substrate pretreatment. Due to the different surface conditions of the substrate materials, it is necessary to perform surface treatment on the substrate. This is very important for the adhesion of UV varnish. For plastic films, it can be wiped with a cleaning cloth of tantalum alcohol or isopropyl alcohol to remove the ink floating on the substrate. Plasticizers and impure chemical substances such as dust and grease on the surface; for materials with low external surface tension, such as PP PE PU PET, can be treated by flame or corona according to the thickness and thinness of the printed material to increase Its surface activity improves its adhesion. After surface treatment, the substrate surface tension should be ≥ 45 dyne/cm.
The ink should be fully stirred before use, especially after adding the additives must be stirred evenly, otherwise it will produce some strong adhesion of the curing, and some have not cured or insufficient curing adhesion is poor, the printing will produce adhesion.
The UV lamp power must meet the requirements and adjust the curing speed.
After curing, it was allowed to cool to room temperature and a cross-hatch test was performed using a 3M-600# adhesive tape. Adhesion and solvent resistance were optimized at 24 hours after curing.
Wash the net, wash the net with water, but you can't use alcohol, because alcohol can damage the net template.
9 Climate impact on UV varnish.
Effect of temperature: The temperature is high, the viscosity of the UV varnish becomes low, and the phenomenon of toothiness and stencil is easy to occur after printing. Low temperature, high viscosity, easy to produce incomplete cure. Therefore, it is required that the ink be refrigerated in the summer, and the temperature of the silk screen shop should not be too high; when it is taken in a frozen environment in winter, it should be placed in the temperature of the printing environment in advance, and the curing speed should be appropriately slowed down.
Humidity: Humidity affects the appearance of the substrate and the screen printing performance of the ink on the substrate.
10 effects of color.
Because various colors reflect light differently, the relationship between the reflection wavelength of light and the speed of photo-curing of the seven-color light on the UV curing of the ink varies depending on the color.
Second, the bottle (plastic PE plastic PP plastic PET, etc.) prepress processing requirements and parameters
At present, light-curing inks have not been directly applied to untreated PE plastic plastic bottles. Therefore, to print PE PP bottles, the PE plastic must be polarized before printing. Otherwise, UV inks cannot be firmly attached. So how to polarize?
There are many methods of polarization treatment. The majority of PE plastic plastic plastic and its bottle industry use flame treatment methods. The result of this flame disposal is the use of flames containing free radicals such as O N0 OH and NH, which can turn polymers into polymers. Such as PE plastic PP plastic surface oxygen extracted, followed by a free radical mechanism for surface oxidation and the introduction of some polar oxygen-containing groups break chain reaction, non-polar PE plastic PP polarized to change its surface The wettability ensures the fastness of the ink.
The water surface tension is 72.5 dyne/cm and the oil surface tension is 25-50 dyne/cm.
Flame disposal parameters: At present, most flame treatment units use gas as the combustion source and should control the air: gas = 7 1 to achieve the blue-violet flame, then the flame temperature can reach 1270 C or so, the flame core length is controlled at 6 -19mm Flame core tip to surface is l 0-15mm Contact time is l-4 seconds (1-2 seconds for LDPE, 3-4 seconds for HDPE) Rotation speed 100-150 rev/min, handleable depth of surface at 40 -90A allows PE plastic PP plastic appearance to reach 45 dyne/cm to meet the fastness requirements of ink adhesion.
Detection of polarization after flame treatment of PE plastic PP plastic plastic bottles: When PE plastic PP flame treated, it must reach the original surface tension value of > 45 dyne to ensure that the UV ink is firmly attached, so the flame treatment effect The detection is very important and its method has Dyne test pen (with a mixture of ethylene glycol ether 35% + formamide 65%) for detection and immersion detection. It is generally used to detect by flooding, that is to say, the PE plastic plastic bottle with flame-treated PP is completely immersed in clean water, and then the bottle is removed from the water for a short pause (about 10 seconds or so) to allow excess water to flow out, and then the bottle is viewed. Whether the surface of the treatment site is covered with a uniform layer of water, if it is full of hydrophilicity and lasts for more than 15 seconds, it means that the flame treatment has reached the printable requirements, if the water film on the surface of the bottle is not continuous, even like After the rain leaves the lotus leaf, it is necessary to adjust the flame disposal parameters to meet the requirements, such as the proportion of air and gas combustion, the time and distance of contact between the flame active ingredient and PE PP, and so on.
Third, screen printing process parameters
1. The ink should be thoroughly stirred before printing, and the material splashed on the lid of the ink tank can be completely scraped into the ink and stirred evenly.
2. Screen and screen. Wire mesh: yellow, high strength, low stretch net with a mesh size of >355 mesh/inch. Screen: Tension 18-25N/cm with direct or capillary film, film thickness 15-25 microns.
3. Squeegee: hardness 80 ° polyurethane tip scraping.
4. Screen cleaning with ordinary washing water.
5. Curing conditions: medium/high pressure mercury lamp, wavelength: 280-380nm The peak is better at 365nm. Power: 80-120W/cm or so. Over UV speed: The need to adjust the photocuring energy.
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