1. Technical requirements of varnish
In addition to colorless, odorless, strong gloss, fast drying, and chemical resistance, the ideal varnish must also have the following properties.
1. High transparency and no color change
To obtain excellent glazing effect for decorative prints, it depends on the formation of a colorless and transparent film on the surface of the printed sheet, and the graphics and text will not change color after drying. Moreover, it cannot be discolored or yellowed due to sun exposure or long use time.
2. The film layer has certain wear resistance
Some glazed prints require certain abrasion resistance and scratch resistance after glazing. Because the production process of high-speed box making machine, cardboard box packaging machine device, protective cover on books and other lines is used, the surface of the printed matter is subject to friction, so it must be wear-resistant.
3. Has a certain degree of flexibility
The bright film formed by any varnish on the surface of the printed matter must maintain good elasticity in order to be compatible with the flexibility of the paper or cardboard, so as not to be damaged, cracked or peeled off.
4. The membrane layer has better environmental resistance
Some of the printed products after glazing are used to make various packaging cartons. In order to play a good role in protecting the packaged products, the glazing film layer must have good environmental resistance. For example, the packaging of food, cigarettes, cosmetics, clothing and other commodities must have moisture and mildew resistance. In addition, the chemical properties of the dried film should be stable. Do not change performance due to contact with chemical substances such as weak acids or alkalis in the environment.
5. It has a certain adhesion to the surface of the printed matter
Due to the influence of the integrated density value of the graphic ink layer on the surface of the printed matter, the surface stickiness is greatly reduced. In order to prevent the film layer from drying out and cracking in use after drying, the film layer is required to have strong adhesion and various types of Accessories have a certain degree of adhesion.
6. Good leveling and smooth film surface
There are many kinds of printing materials, and the influence of printed graphics and texts, the surface absorption, smoothness, wettability and other differences are very different. In order to make smooth coatings on different product surfaces can form a smooth film, varnish is required Good leveling, smooth film surface after film formation.
7. Wide adaptability for post-press processing
After the printed product is polished, it generally needs to undergo post-process processing, such as molding processing, hot stamping anodized aluminum processing, etc. therefore. It is required that the glaze film layer has a wide adaptability after printing. For example: better heat resistance, after hot stamping of anodized aluminum, there can be no sticking phenomenon; high solvent resistance, after drying, the film layer cannot be blistered, wrinkled and hairy due to the influence of the adhesive in the post-processing Sticky phenomenon.
2. Selection of Varnish
The choice of varnish must comply with the basic principles of science, economy and practicality.
1. Science
The so-called science is to study whether the varnish is suitable for the glazing of the printed matter and the physical and chemical properties in use. For example: the cover or cover of books and periodicals requires varnish not only high transparency, but also good wear resistance and folding resistance; varnish for food packaging must first be non-toxic and have certain moisture resistance and anti-corrosion properties; Varnishing for packaging paper cartons requires high chemical stability. It cannot be discolored or yellowed by placement (under sunlight or light), or sticking together due to stacking.
2. Economy
It means that when choosing varnish, the varnish must be commensurate with the printed matter to avoid the use of high-grade varnish to process medium and low-grade printed matter. For example, for high-end printed products glazing, you can choose higher-cost, better-quality calendering, ultraviolet curing or solvent-based varnishes based on acrylic resin; on the contrary, if the printed products are bulk products such as textbooks, It is appropriate to choose a general solvent-based varnish with moderate cost and quality that can meet the processing requirements.
3. Practical
Refers to the choice of varnish to match the varnish equipment. For example, solvent-based varnishes are only suitable for ordinary varnishing machines; UV-curable varnishes must be used on machines equipped with ultraviolet drying devices; alcohol-soluble or water-soluble varnishes, glazing machines must meet the requirements The drying requirements of varnish (generally requires a drying path of more than 6m and a temperature of more than 65 ° C). In addition, we must consider not only labor and material saving, but also suitable for mechanized mass production, as far as possible to reduce production costs, less input and more output. The selection of varnish must also pay attention to the requirements of safety, hygiene and environmental protection. From the aspect of safety, glazing oil with good storage performance and non-flammability should be selected; from the aspects of hygiene and environmental protection, glazing oil with no smell, non-toxic and tasteless should be selected. The production site and the machine have good ventilation conditions, and the selection range can be appropriately widened. On the contrary, varnishes with aromatic substances as solvents should not be used to prevent affecting the health of the operator and causing pollution to the environment.
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