For printing on non-absorbent plastic film, many printing suitability problems need to be solved compared to paper printing. The biggest problem is the adhesion and affinity of plastic film to printing ink:
The basic materials of plastic films currently used are mainly polypropylene (PP), polyhexene (PE), polyvinyl chloride (PVC), polyester (PET), etc. The surface characteristics are due to the polar groups of the molecular structure substrate, The degree of crystallinity and the chemical stability of plastics are different and very different. These factors have a great influence on the adhesion fastness of the printing ink layer. For example, polyethylene material has a molecular structure of ∈CH2-CH2∈n, because it does not Contains polar groups, high chemical stability, can withstand the corrosion of triacid, dibasic, or even hydrofluoric acid. It is soluble in ordinary organic and inorganic solvents at room temperature, but it has poor stability to hydrocarbons and oils. It can cause swelling or discoloration. It can be dissolved in a small amount of solvents such as chlorinated hydrocarbons and tetralin at above 70 ° C. In addition, it is polymerized from ethylene to polyethylene. In the process of manufacturing polyethylene pellets, a certain amount of additives is incorporated according to different requirements. Agents, additives, lower opening agents, when the film is set, these additives float on the surface of the film, forming an oil layer that is invisible to the naked eye, which can make the film anti-aging, transparency, gloss, and flexibility, but these Printing is not at all Of the adhesive film surface is not easy. Therefore, before printing, other materials should be treated according to different plastic surface characteristics to determine whether they need to undergo surface treatment to improve the adhesion of their printing inks.
For PS (polystyrene) and PVC, which are polar structures, surface pretreatment is not required before printing, but for PP, PE, PET, etc. whose surface structure is nonpolar, their chemical stability is extremely high and it is not easy to be large Most ink solvents penetrate and dissolve, and the bonding fastness with ink printing is very low, so it must undergo surface treatment before printing. The purpose of surface treatment is to activate the plastic surface to generate new chemical bonds to roughen the surface, thereby improving the ink and plastic Surface adhesion fastness.
Under normal circumstances, the common methods of plastic surface treatment are as follows:
1. Chemical method: It is a method of strong oxidation. The carbonyl (> C = 0) bond is formed due to the erosion of the membrane surface. In chemical oxidation treatment, the film is degreased by carbon tetroxide, and then immersed in H2SO4 88.5%, K2Cr207 4.4% or H2CrO4 7.1% solution for several minutes. After being washed with water and air dried, it is sent to printing as soon as possible.
2. Solvent treatment: Use some organic solvents or chlorohydrocarbons to scrub the surface to make the non-crystalline part of polyolefin melt in varying degrees to form a rough surface, and then dry it with hot air, usually using the following several Surface treatment of various solvents: 50% xylene mixed with 50% ethanol, containing a certain concentration of dibenzoyl peroxide, etc.
3. Corona treatment:
â‘ The principle and method of corona treatment: Corona treatment is often used in the film blow molding temperature line, because plastic films are often added with antioxidants and slip agents and other additives. These additives are time-effective. After corona treatment, Printed immediately, the best effect. The corona treatment device includes a high-voltage AC motor, an output transformer and two electrodes; one of the electrical stages is connected to a high-voltage metal pole (withstand voltage 10-40KV) and a high-frequency generator (1-4KHZ); the other electrode is Grounding steel wheel or blade, it keeps a distance of 1.5--3mm from the high-voltage electrode, the width of the metal electrode plate is slightly narrower than the width of the film to be processed 5--10mm, to avoid direct discharge short circuit, the processed film is continuous Feeding between the two electrodes, the high-voltage electricity ionizes the oxygen in the air to produce ozone, which oxidizes the surface of the film. Ozone is a strong oxidant that can oxidize the membrane surface and generate a polar base at the active site. It is easy to accept the ink, the treated surface is polarized, electrostatic adsorption occurs, and a slight roughening effect is generated on the film surface, thereby changing the chemical and mechanical combination of the film surface and the printing ink. The effect of corona treatment mainly depends on the output power of the oscillator, the distance between the electrode and the surface of the film, the material of the film and the speed of the film through the electrode, and the intensity of the corona discharge is adjusted to form a cloud-like purple-dark spark as Best state.
â‘¡The effect and effect of corona treatment on the film surface.
A. Surface oxidation: Oxygen is ionized by corona machine to deal with high voltage electricity to form ozone (03). Ozone is a strong oxidant, it can immediately oxidize polyethylene molecules, and can produce carbonyl groups and unsaturated bonds on polyethylene. Nitriding in the air can also be ionized into ions and interact with polyethylene molecules, forming amine groups on the polyethylene molecular chain, and can continue to be oxidized to produce a series of oxides. As a result of surface oxidation, the polyethylene film is converted into polar, from low surface energy to high surface energy, which increases the wettability and adhesion of the printing ink, thereby improving the print fastness of the printed matter.
B. Surface polarization: under the action of high-frequency electric field, the non-conductive plastic film causes displacement of the charge in the molecule, and the induced charge is formed on the surface. The existence of this sensed charge can produce warehouse absorption in polar ink molecules. .
C. Surface observation roughing: The surface of the film is roughened after corona treatment. Observation with scanning microphotograph shows that the friction coefficient of the plastic film surface increases, which can change the smooth shape of the original film surface, which is conducive to the drying and adhesion of film printing Fastness.
③ 〠Corona surface effect identification method:
A. Wetness test method: Because the surface is roughened after oxidation, if water or ink is dropped on the treated surface at this time, it will quickly spread from the surface.
B. Sealing by heat sealing: The treated film feels particularly sticky. The stickiness of thermal insulation paper (such as glass) is proportional to the fastness.
C. Scatch adhesive bag test method: pressurize the pressure-sensitive adhesive tape firmly to the film printing surface, and then quickly pull apart and note the amount of ink transfer. Generally, the amount of ink migration does not exceed 1%. If it is considered qualified, an adhesive tape or adhesive tape may also be used to perform a stick-pull test on the printing ink surface to check the processing effect.
D. Wrinkle test: The printed surface is to be rubbed or wrinkled, and the ink should not be brittle or peeled off into small pieces, otherwise it indicates that the fastness of the ink to the film surface is unsatisfactory.
E. Wetting force test method of film corona treatment effect. The printing process stipulates that the product quality should be fast-drying and the ink is thick and the level is clear. However, sometimes the printing film will be discolored and the ink layer will be adhered during printing. The wetting force test method can be used to check the film corona effect The method is to dip a mixture of formamide and ethylene glycol ether with a cotton ball stick on the surface of polyethylene or polypropylene plastic film, and apply a thick layer to the film to be tested. Then use the following mixed liquid test with high surface tension. When the liquid film breaks into small droplets within two seconds, use the following mixed liquid test with low surface tension to select the appropriate surface tension of the mixed liquid as the wetting tension. Sample. The film has a large wetting tension, indicating good adhesion to the ink. When printing small-area patterns, the wetting tension of the plastic film is preferably 360un / cm. When printing large color blocks, the wetting tension of the solid film is 380un /. cm before is better.
Proportioning table of polyolefin wetting tension measuring liquid:
Formamide (%) Ethylene glycol ether (%) Wetting tension (un / cm) Remarks 19 81 330 At 50% -5% relative humidity, temperature 23 ℃ + 2 ℃ 26.5 73.5 340
35 65 350
42.5 57.5 360
48.5 51.5 370
In order to make the ink wet on the surface of polyethylene and other films, and improve the fastness of its imprint, it must be corona treated to increase its surface tension from 310un / cm to 380un / cm, so that the ink remains non-marking and firm. ; That is, if the surface tension of the polyethylene film does not reach the value of the surface tension of the ink, the ink will fade, corona treatment of the plastic film with low ink transfer performance, thereby oxidizing the active radicals generated on the surface It produces an oleophilic layer to further improve the transferability of the ink. Due to the polarized and roughened surface caused by the discharge, the transfer performance of the ink can be improved.
The basic materials of plastic films currently used are mainly polypropylene (PP), polyhexene (PE), polyvinyl chloride (PVC), polyester (PET), etc. The surface characteristics are due to the polar groups of the molecular structure substrate, The degree of crystallinity and the chemical stability of plastics are different and very different. These factors have a great influence on the adhesion fastness of the printing ink layer. For example, polyethylene material has a molecular structure of ∈CH2-CH2∈n, because it does not Contains polar groups, high chemical stability, can withstand the corrosion of triacid, dibasic, or even hydrofluoric acid. It is soluble in ordinary organic and inorganic solvents at room temperature, but it has poor stability to hydrocarbons and oils. It can cause swelling or discoloration. It can be dissolved in a small amount of solvents such as chlorinated hydrocarbons and tetralin at above 70 ° C. In addition, it is polymerized from ethylene to polyethylene. In the process of manufacturing polyethylene pellets, a certain amount of additives is incorporated according to different requirements. Agents, additives, lower opening agents, when the film is set, these additives float on the surface of the film, forming an oil layer that is invisible to the naked eye, which can make the film anti-aging, transparency, gloss, and flexibility, but these Printing is not at all Of the adhesive film surface is not easy. Therefore, before printing, other materials should be treated according to different plastic surface characteristics to determine whether they need to undergo surface treatment to improve the adhesion of their printing inks.
For PS (polystyrene) and PVC, which are polar structures, surface pretreatment is not required before printing, but for PP, PE, PET, etc. whose surface structure is nonpolar, their chemical stability is extremely high and it is not easy to be large Most ink solvents penetrate and dissolve, and the bonding fastness with ink printing is very low, so it must undergo surface treatment before printing. The purpose of surface treatment is to activate the plastic surface to generate new chemical bonds to roughen the surface, thereby improving the ink and plastic Surface adhesion fastness.
Under normal circumstances, the common methods of plastic surface treatment are as follows:
1. Chemical method: It is a method of strong oxidation. The carbonyl (> C = 0) bond is formed due to the erosion of the membrane surface. In chemical oxidation treatment, the film is degreased by carbon tetroxide, and then immersed in H2SO4 88.5%, K2Cr207 4.4% or H2CrO4 7.1% solution for several minutes. After being washed with water and air dried, it is sent to printing as soon as possible.
2. Solvent treatment: Use some organic solvents or chlorohydrocarbons to scrub the surface to make the non-crystalline part of polyolefin melt in varying degrees to form a rough surface, and then dry it with hot air, usually using the following several Surface treatment of various solvents: 50% xylene mixed with 50% ethanol, containing a certain concentration of dibenzoyl peroxide, etc.
3. Corona treatment:
â‘ The principle and method of corona treatment: Corona treatment is often used in the film blow molding temperature line, because plastic films are often added with antioxidants and slip agents and other additives. These additives are time-effective. After corona treatment, Printed immediately, the best effect. The corona treatment device includes a high-voltage AC motor, an output transformer and two electrodes; one of the electrical stages is connected to a high-voltage metal pole (withstand voltage 10-40KV) and a high-frequency generator (1-4KHZ); the other electrode is Grounding steel wheel or blade, it keeps a distance of 1.5--3mm from the high-voltage electrode, the width of the metal electrode plate is slightly narrower than the width of the film to be processed 5--10mm, to avoid direct discharge short circuit, the processed film is continuous Feeding between the two electrodes, the high-voltage electricity ionizes the oxygen in the air to produce ozone, which oxidizes the surface of the film. Ozone is a strong oxidant that can oxidize the membrane surface and generate a polar base at the active site. It is easy to accept the ink, the treated surface is polarized, electrostatic adsorption occurs, and a slight roughening effect is generated on the film surface, thereby changing the chemical and mechanical combination of the film surface and the printing ink. The effect of corona treatment mainly depends on the output power of the oscillator, the distance between the electrode and the surface of the film, the material of the film and the speed of the film through the electrode, and the intensity of the corona discharge is adjusted to form a cloud-like purple-dark spark as Best state.
â‘¡The effect and effect of corona treatment on the film surface.
A. Surface oxidation: Oxygen is ionized by corona machine to deal with high voltage electricity to form ozone (03). Ozone is a strong oxidant, it can immediately oxidize polyethylene molecules, and can produce carbonyl groups and unsaturated bonds on polyethylene. Nitriding in the air can also be ionized into ions and interact with polyethylene molecules, forming amine groups on the polyethylene molecular chain, and can continue to be oxidized to produce a series of oxides. As a result of surface oxidation, the polyethylene film is converted into polar, from low surface energy to high surface energy, which increases the wettability and adhesion of the printing ink, thereby improving the print fastness of the printed matter.
B. Surface polarization: under the action of high-frequency electric field, the non-conductive plastic film causes displacement of the charge in the molecule, and the induced charge is formed on the surface. The existence of this sensed charge can produce warehouse absorption in polar ink molecules. .
C. Surface observation roughing: The surface of the film is roughened after corona treatment. Observation with scanning microphotograph shows that the friction coefficient of the plastic film surface increases, which can change the smooth shape of the original film surface, which is conducive to the drying and adhesion of film printing Fastness.
③ 〠Corona surface effect identification method:
A. Wetness test method: Because the surface is roughened after oxidation, if water or ink is dropped on the treated surface at this time, it will quickly spread from the surface.
B. Sealing by heat sealing: The treated film feels particularly sticky. The stickiness of thermal insulation paper (such as glass) is proportional to the fastness.
C. Scatch adhesive bag test method: pressurize the pressure-sensitive adhesive tape firmly to the film printing surface, and then quickly pull apart and note the amount of ink transfer. Generally, the amount of ink migration does not exceed 1%. If it is considered qualified, an adhesive tape or adhesive tape may also be used to perform a stick-pull test on the printing ink surface to check the processing effect.
D. Wrinkle test: The printed surface is to be rubbed or wrinkled, and the ink should not be brittle or peeled off into small pieces, otherwise it indicates that the fastness of the ink to the film surface is unsatisfactory.
E. Wetting force test method of film corona treatment effect. The printing process stipulates that the product quality should be fast-drying and the ink is thick and the level is clear. However, sometimes the printing film will be discolored and the ink layer will be adhered during printing. The wetting force test method can be used to check the film corona effect The method is to dip a mixture of formamide and ethylene glycol ether with a cotton ball stick on the surface of polyethylene or polypropylene plastic film, and apply a thick layer to the film to be tested. Then use the following mixed liquid test with high surface tension. When the liquid film breaks into small droplets within two seconds, use the following mixed liquid test with low surface tension to select the appropriate surface tension of the mixed liquid as the wetting tension. Sample. The film has a large wetting tension, indicating good adhesion to the ink. When printing small-area patterns, the wetting tension of the plastic film is preferably 360un / cm. When printing large color blocks, the wetting tension of the solid film is 380un /. cm before is better.
Proportioning table of polyolefin wetting tension measuring liquid:
Formamide (%) Ethylene glycol ether (%) Wetting tension (un / cm) Remarks 19 81 330 At 50% -5% relative humidity, temperature 23 ℃ + 2 ℃ 26.5 73.5 340
35 65 350
42.5 57.5 360
48.5 51.5 370
In order to make the ink wet on the surface of polyethylene and other films, and improve the fastness of its imprint, it must be corona treated to increase its surface tension from 310un / cm to 380un / cm, so that the ink remains non-marking and firm. ; That is, if the surface tension of the polyethylene film does not reach the value of the surface tension of the ink, the ink will fade, corona treatment of the plastic film with low ink transfer performance, thereby oxidizing the active radicals generated on the surface It produces an oleophilic layer to further improve the transferability of the ink. Due to the polarized and roughened surface caused by the discharge, the transfer performance of the ink can be improved.
Church Chairs,Portable Folding Chair,Plastic Camping Chairs,Wedding Tables And Chairs
ZHEJIANG HUZOLI METAL PRODUCTS CO.,LTD , https://www.zlplasticfurniture.com