Performance classification and troubleshooting methods for varnish on aluminum foil
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First, the technical requirements of varnish
Aluminum foil varnishes include glazing primers and glazing oils. The glazing oil is also known as the primer, and the glazing oil is also called varnish or varnish.
1. Aluminum foil primer (also known as base oil and base slurry)
The primer for aluminum foil is a layer of coating between aluminum foil and ink that acts to cause the primer to adhere firmly to the aluminum foil and bond to the ink. The bottoming is to use the transfer of the roller to evenly coat the varnish (paint or face oil) on the rubber roller on the aluminum foil, or directly transfer the mesh of the gravure roll to the aluminum foil. The primers have the following technical requirements:
1.1 paint color is light (almost colorless after drying), yellowing is small;
1.2 has a certain leveling, suitable drying (or volatilization or thermosetting) and flexibility;
1.3 has a certain degree of water resistance and magnetic properties;
1.4 white base ink has excellent lipophilicity, especially for pure aluminum foil;
1.5 does not contain substances harmful to human health;
1.6 The base oil can be used as a lightening agent after adding the filler, or can be used as an ink base or printing after adding the coloring material.
In order to improve the adhesion to the aluminum foil, it is as thin as possible at the bottoming (usually the thickness of the base oil of the rubber roller is generally controlled to 20 to 40 μm, and the thickness of the base oil after transfer on the gravure printing machine is generally controlled to about 10 μm. )
2. Aluminum foil varnish (also known as varnish)
The varnish is coated on the surface of the aluminum foil which has completed all the color registration or single color, so that the surface of the printed product has good gloss, beautiful appearance, acid and alkali resistance, and can protect the surface of the graphic and increase the hardness of the surface of the product. In addition, it should have a certain flexibility. Therefore, aluminum foil varnish should have the following technical requirements:
2.1 The color retention performance is good. After drying at a certain temperature, the graphic does not migrate, does not yellow, does not change color, or does not cause ink film to fall off;
2.2 has a certain brightness, firmness and hardness;
2.3 with white or yellow base varnish and ink should have a certain affinity;
2.4 high solid content, low viscosity, high transparency, especially good leveling, can resist mechanical impact such as die cutting, embossing, punching, etc. after film formation.
Second, the classification of glazing oil
There are many types of varnish on aluminum foil, which are generally divided into the following four series.
1 Normal temperature (refers to drying with a lower temperature such as blowing or infrared rays in the printing machine) Aluminum foil varnish: glazing oil generally used as thermoplastic resin or glazing oil mainly based on thermoplastic resin; or amphoteric resin; or heat The varnish, which is mainly composed of plastic resin and then added with thermosetting resin (to increase its softening point), will be sticky, yellowish and discolored at a certain temperature, and is commonly used as a binder in the primer coating system of aluminum foil.
2 generally high temperature (referring to 121 ~ 160 ° C) aluminum foil varnish: usually based on thermal resin. Such varnishes are prone to yellowing, fading, discoloration and sidelighting due to their proximity to or exceeding 180 ° C, especially chlorine dioxide, which is currently prohibited from being used in medical packaging and printing products.
3 high temperature resistance (referring to 180~250 °C) aluminum foil varnish: mostly use amphoteric resin or acrylic resin, and then add silicone resin, due to yellowing, plus two polymers or two or more polymers at high temperature Collision produces harmful toxic chlorine monoxide, and the use of amphoteric resins in such products has been abandoned. However, due to the high cost, people have explored the use of amphoteric resin to add anti-oxidation chlorine to form an auxiliary agent to solve the problem.
4 UV-curable aluminum foil varnish: This glazing oil mainly uses a photosensitive resin and an initiator to form a varnish. Due to poor adhesion, a thermoplastic tackifying resin is now introduced. Make up for its shortcomings. It solves the problems of adhesion, back-sticking, acid and alkali resistance, hot pressing, embossing, punching, cross-cutting, etc., and is favored by the packaging and printing industry.
Third, various types of failures and troubleshooting methods
1. Pinhole and snowflake point
Main reasons: 1 oily surface on aluminum foil; 2 too much plasticizer in the base oil or white paint system, excessive viscosity; 3 mechanical roller or substrate surface is not smooth.
Remedy: 1 Remove the oil stain on the surface of the aluminum foil or replace the aluminum foil: 2 Add T12-6X or TM-3 coupling agent to the base oil and white paint; 3 Replace the smooth surface roller or replace the printed aluminum foil.
2. Poor gloss
Main reasons: 1 rough surface of aluminum foil, large adsorption ink; 2 varnish opaque and poor quality; 3 varnish viscosity is low, coating is too thin; 4 glazing temperature and pressure is insufficient.
Remedy: 1 change the roller or empty coating for a period of time, then varnish operation; 2 select a transparent and leveling glazing oil; 3 select the glazing system with high resin content and low viscosity Oil; 4 The working temperature when glazing is adjusted to be close to the glass transition temperature of the glazing oil and increase the roll coating pressure.
3. Uneven and glowing
Main reasons: 1 The adhesion of the varnish or base oil to the ink is poor; 2 The viscosity of the varnish is too low; 3 The ink layer is too thick or the ink film of the printing ink is crystallized.
Remedy: 1 Add a proper amount of surfactant in the varnish to reduce the surface tension of the varnish; 2 Increase the viscosity of the varnish or add a new varnish in the glazing oil: 3 in the varnish Add TM-3 coupling agent from Tianyang Chemical Plant or roughen the surface of printing ink film.
4. The coating is easy to burst and not resistant to folding
The main reason is: 1 the temperature in the embossing is too high, so that the hardness of the resin in the printed matter, especially the varnish ink system is too high, and becomes brittle; 2 embossing, die cutting pressure is large, so that the printability and flexibility of the printed product after glazing Deterioration; 3 die cutting, embossing, perforation or improper folding; 4 glazing oil and ink adhesion is poor.
Remedy: 1 reduce the embossing temperature, or choose a moderate hardness of the varnish; 2 reduce the impact pressure of embossing, die cutting, punching; 3 due to improper die cutting, should be in the packaging printing design plate, as much as possible Longitudinal specifications are used as the basis for printing die-cutting, embossing, punching and folding (the tensile strength of aluminum foil varies depending on the horizontal and vertical directions); 4 replace the base oil or varnish with good affinity for ink, or add Great printing pressure.
5. Adhesion
Main reasons: 1 varnish drying is too slow or not dry; 2 varnish coating is too thick; 3 small blowing, short drying tunnel, low temperature, or weak UV light; 4 substrate is too high after glazing .
Remedy: 1 Change to dry fast varnish: 2 reduce the coating amount of glazing oil, reduce the coating varnish film layer; 3 strengthen the blowing or adjust the blowing angle, extend the drying tunnel, increase the drying tunnel temperature or ultraviolet The light intensity; 4 try to avoid the stacking of the substrate is too high.
6. Piece detachment
The main reasons are: 1 the surface of the aluminum foil of the substrate is not flat; 2 the varnish or the base oil is not firmly attached; 3 the printing pressure is insufficient or the embossing pressure is too large.
Remedy: 1 select the surface of the aluminum foil; 2 select the coating with good adhesion fastness or base oil, you can also add 1%-5% mixed type of additives in the varnish or base oil - PPH or 4011 ; 3 increase the printing pressure, or reduce the embossing pressure.
7. Fading, discoloration and yellowing
Main reasons: 1 PH value of varnish or base oil is inconsistent with ink; 2 varnish dry film formation process is too high in oxidative polymerization, resulting in yellowing; 3 varnish or base oil itself is not resistant to high temperature; 4 printing The pigments and dyes in the ink system are not resistant to high temperatures.
Remedy: 1 Change the varnish or base oil with the same PH value of the ink: 2 control the drying temperature of the varnish; 3 select the high temperature resistant varnish or base oil; 4 change the high temperature printing ink or add calcium, silicon, etc. Organic filler.