Analysis of Technical and Common Problems of Aluminum Foil Varnish

First, the technical requirements of polishing oil

Aluminium foil finishes include gloss base coats and gloss finish oils. Polishing primer, also known as the primer coating, varnish oil, also known as varnish or varnish.

1. Aluminum foil primer (also known as base oil and primer)

The primer of aluminum foil is a layer of paint between aluminum foil and ink. Its role is to make the base oil firmly adhere to the aluminum foil and can be combined with the ink. The bottoming is to use the transfer of the roller to evenly apply the coating on the rubber roller (paint or surface oil) to the aluminum foil, or use the texture of the gravure roller to directly transfer to the aluminum foil. The primer coating has the following technical requirements:

1 The paint has a light color (almost colorless after drying) and has a low yellowness:
2 have a certain leveling, suitable drying (or volatilization or thermosetting) and flexibility:
3 has a certain degree of water resistance and magnetic properties;
4 The white base ink has excellent lipophilicity, especially for pure aluminum foil.
5 does not contain substances harmful to human health;
6 The base oil can be used as a scavenger after the filler has been added, or it can be used as an ink base or printed after adding the colorant.

In order to improve the adhesion to aluminum foil, it should be as thin as possible when it is used (usually the base oil thickness of the rubber roller is usually controlled at 20-40μm, and the thickness of the base oil after transfer on the gravure printing machine is generally controlled to be about 10μm. )

2. Aluminum Foil Varnish (also known as cover paint)

The varnish is applied on the surface of aluminum foils that have been completed with all colors or single colors, which can make the surface of the printed products glossy, beautiful, and resistant to acids and alkalis. It can also protect the graphic surface and increase the surface hardness of the product. In addition, it should also have a certain degree of flexibility. Therefore, aluminum foil varnish must have the following technical requirements:

1 Good color retention performance, no migration, no yellowing, no color change or ink ink film falling after a certain temperature drying image:

2 has a certain degree of brightness, firmness and hardness:

3 with white or yellow base oil and ink should have a certain affinity;

4 high solid content, low viscosity, high transparency, especially good leveling, after filming can withstand die-cutting, embossing, punching and Other mechanical impact.

Second, the classification of polishing oil

There are many kinds of varnishes on aluminum foil, which are generally divided into the following four series.

1 Normal temperature (refers to drying with a printer at a lower temperature such as blowing or infra-red) Aluminium foil varnish: Generally, a varnish of a thermoplastic resin or a thermoplastic resin is mainly used, and amphoteric resin is used as a varnish or heat Plastic-based resin, and then add thermosetting resin (to increase its softening point) of the varnish, at a certain temperature will return to sticky, yellowing, discoloration, commonly used in aluminum foil primer system as a binder.

2 general high temperature (refer to 121 ~ 160 °C) aluminum foil varnish: usually based on hot resin. After this type of coating oil approaches or exceeds 180°C, yellowing, discoloration, discoloration, and side lighting are liable to occur, and in particular, chlorine dioxide is easily generated, and it is currently prohibited for use in pharmaceutical packaging printing products.

3 high temperature (refer to 180 ~ 250 °C) aluminum foil Varnish: Most use of amphoteric resin or acrylic resin, then add silicone resin, due to yellowing, plus two polymers or two or more polymers in high temperature Collisions have produced harmful and toxic chlorine monoxide. At present, people have abandoned the use of amphoteric resins in such products. However, due to the high cost, people are exploring the use of amphoteric resins to add chlorinated additives to solve the problem.

4 UV-cured aluminum foil varnish: This varnish mainly consists of a photosensitive resin and an initiator, etc. to form a varnish. Due to poor adhesion, thermoplastic tackifying resins are now introduced. Make up for its deficiencies. It solves the problems of adhesion, back tack, acid and alkali, anti-hot pressing, embossing, punching, cross cutting and so on, and is deeply favored by the packaging printing industry.

Third, all kinds of faults and troubleshooting

1. Pinholes and snowflakes

The main reasons are as follows: (1) The surface of aluminum foil is oily: (2) The plasticizer in the base oil or white coating system is too much plasticizer and the viscosity is too large; (3) The surface of the mechanical roller or the substrate is not smooth.
Remedy: 1 Remove the oil on the surface of the aluminum foil or replace the aluminum foil: 2 Add T12-6X or TH-3 coupling agent to the base oil and white paint: 3 Replace the smooth surface of the roller or replace the printed aluminum foil.
2. Gloss difference

The main reasons are as follows: 1 The surface of the aluminum foil is rough and uneven, and the absorption ink is large; 2 The varnish oil is cloudy and opaque and the quality is poor; 3 The varnish oil has low viscosity and the coating is too thin: 4 The coating temperature and pressure are insufficient.

Remedy: 1 exchange roller roller or air coating after a period of time, and then polishing operations; 2 select transparent and good leveling of the coating oil; 3 select the coating system of high resin content and low viscosity coating Oil: 4 The working temperature is adjusted to near the glass transition temperature of the coating and the roller application pressure is increased.

3. Uneven and glowing

The main reasons are as follows: (1) the adhesion of the coating oil or the base oil to the ink is poor; (2) the viscosity of the coating oil is too low; (3) the ink layer is too thick or the ink film of the printing ink is crystallized.

Remedy: 1 Add appropriate amount of surfactant to the varnish to reduce the surface tension of the varnish; 2 Increase the varnish viscosity or add new varnish to the adjusted varnish: 8 In the varnish Adds TH-3 coupling agent from Tianyang Chemical Factory or roughens printing ink film surface

4. The coating is explosive and does not fold

Main reasons: 1 The temperature in embossing is high, which makes the resin in the printed matter, especially in the varnish ink system, become too brittle after the hardness is too high. 2 The embossing and die-cutting pressure are large, so that the glazing printability and flexibility are good. Deterioration; 3 die cutting, embossing, punching or improper folding: 4 coating oil and ink adhesion is poor.

Remedy: 1 reduce the embossing temperature, or choose a moderate hardness of the varnish: 2 reduce embossing, die-cutting, punching impact pressure: 3 due to improper die-cutting, should be in the packaging printing design plate, as far as possible Longitudinal specifications are used as the basis for production of die cutting, embossing, punching, and folding for printing (the strength of aluminum foil is different depending on the horizontal and vertical direction): 4 Change the base oil or coating oil with good ink affinity, or add Big print pressure.

5. Adhesion

Main reasons: 1The coating oil is too slow or not dry; 2The coating of coating oil is too thick: 3 The blowing is small, the baking path is short, the temperature is low, or the intensity of the UV light is weak: 4 After the coating on the substrate, the substrate is too high .
Remedy: 1 Change to a quick-drying varnish: 2Reduce the amount of varnish to be applied, reduce the thickness of the varnish oil coating; 3Strengthen the blowing or adjust the blowing angle, extend the drying tunnel, increase the temperature of the drying tunnel or UV light Light intensity: 4 Try to avoid stacking of substrates.

6. Pieces of shedding

The main reasons are as follows: (1) The surface of the aluminum foil of the substrate is not flat; (2) The coating oil or the bottom oil is not firmly attached: (3) The printing pressure is not enough or the pressure of the embossing is too high.

Remedy: 1 Select a flat surface of the aluminum foil: 2 Select a good attachment fastness to the base oil or base oil, you can also add 1% to 5% in the matte or base oil mixed additives - PPH or 4011 ;3 Increase the printing pressure or reduce the pressure of embossing .

7. Fading, discoloration and yellowing

Main reasons: 1The PH value of coating oil or base oil is inconsistent with the ink; 2 The process of film drying is too high during oxidative polymerization, resulting in yellowing; 3The coating oil or base oil itself is not resistant to high temperature; 4Printing The color and dye in the ink system are not resistant to high temperatures.

Remedy: 1 Replace the varnish or base oil with the ink PH value: 2 Control the drying temperature of the varnish; 3 Select the high temperature varnish or base oil: 4 Replace the high temperature printing ink or add calcium, silicon, etc. Organic fillers.

(Author/Liu Jiaju)

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