How to improve the adhesion of screen printing ink

发布时间：2026/07/06 | 浏览量：0

Screen printing is one of the most commonly used graphic printing processes. So, how to prevent the ink layer from peeling off and dissolving? Adhesion refers to the fastness of ink to the printing surface. If the adhesion is poor and the fixation is not good, without a certain degree of fastness, it will not be resistant to friction, impact, or fatigue, which means there is no printing. To improve the adhesion of ink to the printing substrate, we should mainly focus on the following two aspects: the printability of ink and the printability of printing materials.
1. Ink compatibility control
1. The resin in the ink should match the printing substrate
Resin is the core material of ink vehicle, which directly affects the fastness. For printing on metal substrates, epoxy resin should be used as the vehicle resin in the ink, as it has epoxy groups with reactive activity, forming a cross-linked polymer with strong adhesion. To print on polyethylene plastic, polyethylene should be used as the vehicle; to print on polypropylene, polypropylene should be used as the vehicle, as they have the same polarity and molecular weight. To print on polyurethane materials, polyurethane resin should be used as the vehicle in the ink, as it results in a tough and wear-resistant film layer with good adhesion after printing.
2. The solubility parameters of the resin solvent and the substrate should be similar
Only when the solubility parameters of the resin, solvent, and substrate in the ink are similar can the ink be printed on the substrate. In this way, the solvent will swell on the surface of the substrate, and the colorant in the ink will cross the interface and enter the interior of the substrate, forming a strong adhesion
3. Add appropriate additives
Adding coupling agent: The coupling agent can promote the formation of a coupling complex between the resin and the high molecular weight printing substrate in the ink, thereby enhancing the adhesion effect of the ink.
Adding crosslinking agent: The main function of the crosslinking agent is to form crosslinks in the adhesive, reduce the film-forming temperature of the adhesive, and improve the ink fixation effect. At the same time, the hardness, water resistance, solvent resistance, and drying speed of the ink film are greatly enhanced. Steaming or baking must be performed simultaneously to further improve the fixation effect and enhance the wash fastness.
In recent years, new types of adhesives capable of self-crosslinking have emerged, but they can only crosslink at relatively high temperatures. However, excessively high temperatures can cause brittle damage to fabrics, so the development is now shifting towards self-crosslinking at lower temperatures.
II. Surface treatment of printing substrate
1. Disposal of plastics and plastic films
Plastic film, due to its ease of use, is widely applied in the packaging industry after post-press processing such as glazing and laminating, resulting in bright colors, durability, and firmness. It has become a beautiful landscape in the packaging industry. However, the surface of plastic varies greatly in performance due to differences in molecular structure, density, crystallization degree, and polar groups. Even the same type of plastic can have high, medium, or low density. In addition, the plastic surface is smooth, and stabilizers are added during production, providing certain acid and alkali resistance and oxidation resistance. Therefore, its adsorption of ink is poor, affecting its firmness and wear resistance. Therefore, surface treatment of plastic must be carried out before printing.
The principle of treatment is to change the polarity of the plastic surface. The plastic surface is non-polar. After treatment, the plastic surface is endowed with polar groups, which can connect with the polar groups in the ink binder, thus enabling the ink to firmly adhere to the plastic surface. Common treatment methods include:
A. Corona discharge treatment
The structural composition of the corona treatment device consists of a high-voltage AC motor, an output transformer, and two electrodes. During treatment, the plastic film is passed between the two electrodes. Due to the high voltage, oxygen in the air is highly ionized, generating ozone. This activates the surface of the film, causing electric spark discharge, generating polar groups, increasing molecular polarity, and enhancing surface tension. At the same time, dust is eliminated, and invisible pits are created on the surface, roughening it and enhancing its adsorption of ink. This is a commonly used method at present.
B. Flame treatment method
The principle of this method is to rapidly pass the plastic film through an oxidizing flame, blasting off invisible burrs and greatly improving the adhesion of the ink. The key to this method is “rapidness”, otherwise the surface will be “burned”, reducing the adhesion of the ink and causing the oxidized film treated by the flame to fall off together with the ink. The temperature used during treatment should be lower than the heat distortion temperature of the plastic film. For example, polyethylene commonly used in packaging has a heat distortion temperature of 60-80℃, while polyethylene has a heat distortion temperature of 100-110℃.
C. Plasma treatment
Under the influence of a strong electric field, high temperature, and laser, neutral atoms or molecules in plasma lose their electrons and ionize into ions. These ions contain equal amounts of positive and negative charges, hence the term “plasma”. The principle of the treatment is as follows: a radio frequency generator emits laser energy at a high voltage, generating a characteristic glow discharge phenomenon. This causes the passing gas substances to produce many excited electrons, ions, and atoms, which then bombard the plastic surface. This results in changes to the active groups on the plastic surface or the formation of new groups or radicals, leading to deposition. This achieves the goal of chemical and physical modification of the polymer surface, generating polarity that can dock with the polar groups in the ink vehicle, thereby enhancing the adhesion of the ink.
D. Chemical and Solvent Treatment Methods: Oxidants are used to treat the surface of plastic films, oxidizing the surface to generate hydrophilic groups or other functional groups. These groups can dock with polar groups in the ink, enhancing the adsorption of the ink. For thicker films, solvents can be used for treatment. Common solvents include surfactants or chlorinated solvents such as dichloroethane, pentachloroethane, and trichloroethylene. These treatments can change the wettability of the plastic film surface and destroy the stabilizers (plasticizers, antioxidants, etc.) added to the plastic film before manufacturing. Chemical treatment methods: Apply chemicals such as potassium permanganate, chlorosulfonic acid, and naphthenic chromic acid to the surface of plastic films to chemically corrode the surface and improve the wettability of the ink.
E. Static elimination treatment
Due to the good insulating properties of plastic films, they have high resistance, are prone to static electricity, and are difficult to remove. Therefore, it is necessary to perform static elimination treatment on the plastic before printing to eliminate static electricity, remove dust and foreign matter, and thus enhance the ink’s adsorption. The main method of static elimination is to use static eliminators to remove static electricity. Silicon-based static eliminators: First, use alcohols such as methanol or ethanol to remove oil and moisture, then repeatedly apply the static eliminator with a brush or roller or immerse the plastic film in the static eliminator. Treat it at temperatures ranging from 30 to 40℃ and 60 to 80℃ for 3 hours, dry it after coating, and then print after placing it for 5 hours. Surfactant-based static eliminators: The principle of static elimination in this method is different from that of silicon-based static eliminators, mainly achieved by increasing conductivity and reducing surface resistance. The methods can also be used for roller coating and immersion, which are similar to silicon-based solvent treatments. The above treatment methods are for most plastics, but for a small portion of plastics with polar groups on the surface, rough surface, and low density, such as polystyrene and polyvinyl chloride, they can be printed directly without treatment.
2. Pre-press processing of metal printing materials
With the development of society, the application of metal materials has become increasingly widespread, such as metal tags, three-piece cans, two-piece cans, and other containers.
Due to the application of a layer of anti-rust oil and process lubricating oil during transportation and storage, and the relatively reactive nature of metals, prolonged exposure to air causes the absorption of moisture and oxygen from the air, forming an oxide film. It is precisely because of this layer of anti-rust oil and oxide film that they exhibit repulsion and anti-wetting phenomena towards ink. Therefore, it is necessary to treat the metal surface before printing.
1) Oil removal treatment
Since oils and fats are classified into saponifiable oils (such as vegetable oil) and nonsaponifiable oils (such as Vaseline, paraffin, and engine oil), the methods for removing them differ.
a. The principle of removing saponified oil is to utilize the saponification or emulsification of oil to make it detach from the metal surface. For removing oil from aluminum plates, 3~4% sodium hydroxide is used to react with the oil on the metal surface through saponification. Then, 5% trisodium phosphate is used to make the oil produce saponified substances that turn into tiny droplets dispersed in water. The mixture contains 89~92% water. By removing oil at a temperature of 60~70℃ for 30~60 seconds, the oil will detach from the metal surface.
Chemical degreasing of steel plates, formula: 50g sodium hydroxide, 30g sodium carbonate, 30g trisodium phosphate, 5g sodium silicate, 800g water, temperature 50~80℃, time 5~7 minutes. Function: sodium hydroxide reacts with oil through saponification, sodium carbonate controls the reaction rate; trisodium phosphate and sodium silicate act as emulsifiers, enhancing the activity of oil stains and dispersing them in water.
b. Organic solvent degreasing can remove non-saponifiable oils such as lubricating oil, paraffin, and Vaseline. Commonly used organic solvents include gasoline, kerosene, toluene, propanol, cyclohexanol, and certain chlorinated alkanes and alkanes. The method involves immersing the metal printing substrate in a container filled with organic solvent. This method is effective for removing oil from asphalt blocks and dried grease.
c. Electrochemical degreasing involves hanging the printing substrate on the cathode or anode in an alkaline electrolytic solution. Due to the chemical action of the electrodes, the surface tension at the solution interface is reduced. During electrolysis, hydrogen and oxygen bubbles are released from the electrodes, exerting a strong tearing effect on the ink, reducing the adhesion of the oil and grease, and causing it to detach from the metal surface. This method is thorough and effective in removing oil.
2) Remove oxide film
When metals absorb moisture in the air, they form a layer of oxide films such as ZnO, Al2O3, FeO, Fe2O3, and Zn(OH)3. These naturally formed oxide layers have a loose structure and are highly reactive with acids and alkalis, making it difficult for ink to adhere. Therefore, a dilute solution prepared with sulfuric acid or hydrochloric acid can be applied to the surface of the metal oxide layer to detach it from the metal surface.
3. Glass surface treatment
1) Glass surface condition and printing appropriateness
The main component of glass is SiO2, with silicon primarily located inside the glass and oxygen atoms on the surface. This structure possesses high surface energy, making it prone to interacting with other substances. For instance, upon encountering air, it combines with hydrogen in the air to form hydrophilic groups, such as OH (hydroxyl). These hydrophilic groups float on the surface of the glass, making it difficult for ink to adhere. The glass surface contains alkali ions, forming Na-O bonds. These bonds are easily broken in air and water, making it difficult for ink to adhere. Therefore, the glass surface must be treated before printing.
2) Glass surface treatment methods: a. Lipophilic treatment involves coating various siloxane coupling agents on the glass surface to form lipophilic groups, thereby enhancing the affinity of the glass for ink. One method involves coating the glass surface with a 0.5-1% ethanol solution of coupling agent, which hydrolyzes to form good affinity; another method involves adding 1-5% coupling agent to the ink beforehand, allowing it to self-diffuse onto the glass surface after printing. b. Degreasing treatment removes oil and grease to improve wettability, using acetone, methyl ethyl ketone for cleaning and degreasing, or dichloroethylene vapor for degreasing. c. Strong acid treatment: removes alkali ions to enhance ink adhesion. Prepare the soaking solution: one part chromic acid, 100 parts concentrated sulfuric acid, and 4 parts distilled water. Soak the glass in the solution for 15-20 minutes, then rinse with distilled water and dry at 80-93°C for 20-30 minutes. d. Physical treatment involves mild sandblasting with fine abrasive powder or water sanding to remove surface attachments and enhance ink affinity.