As the earliest printing process, silk screen printing belongs to stencil printing. It is called the four major printing methods together with flat printing, letterpress printing and gravure printing. It is very common in the manufacture of cosmetic packaging materials and plays a pivotal role in it. This article will share The application of screen printing in glass packaging is for your reference.
screen printing of glass
The special physical and chemical properties of glass products determine that the printing of glass products mainly uses silk.
screen printing method. First of all, the glass surface is smooth and hard, and most of its products are transparent, so it is suitable for color printing by soft-touch screen printing. Secondly, glass is an inorganic material with good chemical stability. It has very little binding force with the organic synthetic resin of the binder in the ink, and does not meet the basic requirements of adhesion and durability. Therefore, sintering treatment is often required after printing, which requires the ink layer to have a certain thickness and heat resistance, and the screen printing method can meet this requirement.
Glass screen printing is the use of screen printing plates, the use of glass glaze, decorative printing on glass products. Glass glaze is also called glass ink and glass printing material. It is a paste printing material which is mixed and stirred by coloring material and connecting material. The coloring material is composed of inorganic pigments and low melting point flux (lead glass powder); the connecting material is commonly known as lite oil in the glass screen printing industry. The printed glass products should be placed in a furnace and fired at a temperature of 520~600C, and the glaze printed on the glass surface can be consolidated on the glass to form colorful decorative patterns.
Ink used for glass screen printing
Due to the different printing materials and printing processes, the requirements for the ink used in screen glass printing are also different. First of all, the most important thing in glass printing is to strengthen the bonding force between the ink and the glass surface, so that the ink does not fall off or dissolve during the use of glass products.
Secondly, screen glass printing is dried at high temperature, so the ink used is high temperature resistant ink. The inks used for glass screen printing mainly include the following:
glass glaze
According to the firing temperature, colored glaze can be divided into three types: high temperature, medium temperature and low temperature. Among them, low temperature (550°C) colored glaze is mainly used for the decoration of thinner glass bottles, and medium temperature (580C) colored glaze is widely used in cosmetic bottles, glass bottles, etc. For the printing of glass products such as cups, high temperature (600°C) color glaze is mainly used for the printing of beverage bottles. Because the color glaze contains heavy metal lead, we must pay attention to the selection of high-quality color glaze, especially food packaging.
UV glass ink
The emergence of UV glass ink has solved the drying problem of glass screen printing to a large extent, but it should be noted that excessive curing will cause the embrittlement of the ink film and reduce the adhesion of the ink layer. Two-wave reactive glass ink, this kind of ink is mainly used for the printing of some small glass containers, such as cosmetic bottles.
Special glass ink for thermosetting
This kind of ink belongs to volatilization drying ink, which can be dried after being placed at room temperature for 10 to 15 minutes. In addition, in order to improve the strength of the ink film and its adhesion, it needs to be baked at a temperature of 180C for 10 minutes.
Glass Pigment Inks
Glass pigments contain glass powder with a low melting point, and use a binder (synthetic resin and organic solvent) to adjust the printability of the ink, but this ink has no intermediate color. After this ink is printed, it is sintered in a heating furnace, so that the binder in the ink is evaporated, and the glass powder is softened and fixed on the glass surface after burning.
The binder of the ink is mainly synthetic resin and organic solvent. The basic requirement for the binder is that it can complete the process of evaporation, sublimation and combustion at low temperature, so as to avoid the residue of the binder when the glass powder is melted. Otherwise, the printing surface will be damaged. Foams and loses smoothness. Gold liquid, silver liquid and gold paste are glass inks composed of various metal organic compounds as main components added to the binder of the ink. The metal organic compounds used mainly include metal monosulfide turpentine, metal monothiol and the like. Liquid silver also contains the same organic compounds. In the golden paste, for gold and silver The content is very small, and it is still feasible to use as printing ink.
Matters needing attention in glass screen printing
In order to ensure the quality of glass screen printing, in the printing process of glass screen printing, we should pay attention to the following issues:
Network distance
When printing, the screen should not be attached to the glass substrate, and should be kept at 1cm back to ink，After scraping, gently scrape the ink back, and evenly cover the ink on the graphic part of the screen to avoid dry plate toning. Adjust the ink well before printing, let it stand for about 1 to 2 hours to defoam before use test A small proofing plate is preset, and the adjusted ink is tested after a small area of trial printing, and the printing is started after the expected requirements are met, so as to avoid failures caused by uncertain factors.
Web version
According to different printing materials, different meshes should be selected and different screen tensions should be set. For example: for the printing of colored crystal glass, 180-mesh~200-mesh DPP monofilament mesh cloth should be used, the tension is 20+2 Newton, and the screen plate made of oil-based photosensitive adhesive or water-oil compatible photosensitive adhesive has a high printing durability. Solvent-resistant cleaning performance is good, reducing the cost of use.