Problems of Adhesion in Tinplate Printing (II)

In addition, there is no generation of by-products during the curing of the resin, and no bubbles are generated. Therefore, the shrinkage rate is small, and when the curing agent is not added, the resin is a heat-polymerizable resin, does not deteriorate due to heat, and has strong water resistance.
The use of excellent primer paint, but also a scientific and rigorous production process. The paint should be evenly coated on the surface of tinplate. The thickness of the coating should be controlled to about 1.5 to 2 g/m2. If the film is too thin, it will not work. If it is too thick, it will cause shrinkage stress and affect adhesion. The actual baking temperature should be lower than the theoretical standard baking temperature of 10 ~ 15 °C or so, artificially leave some unreacted polar groups in the paint, so that when overprinting the first color ink, the organic solvent in the ink The primer swells to make the interfacial polymer chains of the ink film entangled and enhance the adhesion of the coating.
2. Printing inks should be reasonably selected for ink varieties. The surface of the tinplate is smooth like a pound. Although the surface of the tinplate is coated with a primer before color overprinting, if the adhesiveness of the synthetic resin to the tinplate surface of the connecting material is not taken into consideration, the ink adhesion produced cannot be produced. Satisfy the printability of tinplate. It is generally advisable to use an oil-modified alkyd resin binder-based ink.
Alkyd resins are polyester resins modified with vegetable oils or fatty acids. They can be classified into dry and non-dried properties according to their properties; they can be classified as short, medium, and large according to the amount of vegetable oil or fatty acids. Three kinds of oil length. Dry intoxication resin in the ink mainly soybean oil, dehydrated castor oil and other ingredients, this resin can be dry, it can also join the amino tree and tire combination. The printing ink produced by the high temperature curing, has a strong adhesion, high gloss, strong hydrophobicity, color retention and other characteristics, to meet the printability of tinplate and product processing requirements.
Due to the particularity of its process, tinplate printing often requires multiple color registrations, drying, and non-absorption of the smooth surface. Therefore, the thickness of each ink layer should be controlled during the construction process. Thick ink layer, the cohesion between the ink layer is large. Imperceptibly offsets the adhesion between the primer coating and the tinplate surface, resulting in reduced adhesion of the entire coating layer. In particular, when coating or printing white ink, it is appropriate to maintain the white ink color and maintain the ink because the proportion of dioxy titanium (titanium oxide) pigment in white ink is large and the ink layer thickness should be controlled at (14±2) g/m 2 . Layer adhesion.
3. After the multi-color overprinting of coated gloss tinplate is completed. Also apply a layer of varnish to the surface of the ink. The coated varnish not only adds luster to the appearance of the tinplate product, but also makes it bright and dazzling. Moreover, some of the hydroxyl and ether bonds in the mooring penetrate the ink layer under the effect of the surface tension of the ink, enhancing the flexibility of the ink layer surface. Impact strength, wear resistance, to achieve the ideal adhesion. In addition, the coating film formed by the high-temperature curing of the varnish isolates the ink coating from the outside, so that the surface of the tinplate product is resistant to physical and chemical substances.
The commonly used varnish is mostly epoxy type, alkyd type, acrylate type. Epoxy varnish contains high-polarity aliphatic hydroxyl and ether bonds that are not easily hydrolyzed, making the coating not only has good adhesion to the surface of the article to be coated, but also has high chemical resistance. Due to the alternating arrangement of the rigid benzene core and the flexible hydrocarbon chain, the physical and mechanical properties of the coating film are enhanced. Of course, due to the existence of polar groups, the coating film will have a certain degree of hydrophilicity, which requires the manufacturer of the production of the optical oil material to adjust the formulation, and the good water resistance can also be obtained by the isolation of the cross bond structure.
Inulin resin type varnish containing medium and short chain products of castor oil, coconut oil, and synthetic fatty acids. It is a medium and short oil alkyd resin. High saturation speed, good resistance to oxidation, co-polymerization with nitrocellulose, amino resin, penta-oxide resin, etc., making baked dry coating film with firm adhesion, toughness, heat resistance, solvent resistance, weather resistance, etc. Features. Used in a large amount in tinplate varnish...
Acrylic type varnish, generally used hydroxy acrylic acid such as acrylic acid ethyl ester and acrylic acid copolymerization, the introduction of hydroxyl and carboxyl groups in the resin, amino tree tire as a crosslinking agent. The varnish is not yellowed by high-temperature baking, has good heat resistance, acid and alkali resistance, and water resistance, and is often used for coating on tinplate used for food cans.
All types of Tuoshi Varnish have their own advantages and disadvantages. In actual production, the type of varnish should be used correctly according to the characteristics and application of the printed product. However, no matter which type of varnish is selected, the solid content of the varnish, the purity of the varnish, the viscosity of the coating, the baking temperature and other technical data should be known before use so as to ensure the hardness (abrasion) and luster of the coating film. Degrees and adhesion.
Third, the baking temperature on the impact of tinplate adhesion Tinplate printing, the surface layer of ink is the use of heat-cured form of drying, which is the difference between metal printing and lithographic offset printing one of the main to Temple sign. Since the paint and ink used in each process contain different resins and pigments, the baking temperature is not the same. Strictly controlling the baking temperature of each process is the key to the quality of tinplate products. It will directly affect the adhesion of the entire ink film layer. If the baking temperature is low, the chemical molecular bonds in the resin are not sufficiently cross-linked and cured to form a film. Not only does it have no adhesive force, but it also causes the back of the tinplate to become sticky, and the reverse printing occurs. The next process is due to ink stickiness, which makes the tinplate minute. Difficulties in the sheeting affect the color registration (the back of the tinplate is the inner wall of the container and the presence of sticky stains can contaminate the contents of the container). However, the baking temperature is too high, the chemical breaks down at the bond, the ink film layer becomes brittle and cracks, and can not withstand the mechanical processing and high temperature sterilization. Therefore, it is necessary to strictly control the baking temperature of each process, and regularly check the temperature inside the drying room, and strive to achieve the error between the measured temperature value in the drying room and the temperature value of the drying room temperature display instrument at 13°C. At the same time, during the printing process, the circulating air volume should reach 21600m3/h. The electric heating tube, automatic thermostat, and temperature indicator of the drying room must be normal. The speed of the machine should also be controlled within a certain range to ensure that the ink coating has a suitable baking time.
The printing of tinplate, its adhesion is good or bad, involves many factors, there is an objective existence, but also subjective. This article is only a personal opinion, which has certain deficiencies, but also hope to study and discuss with industry colleagues.