Application of transparent ink on flexible packaging

With the continuous improvement of packaging requirements, packaging design tends to be diversified, and colors are attracting people's attention. Most of the product packaging is highly transparent, giving people a feeling of dazzling. In the field of flexible packaging, transparent inks with high transparency are becoming more and more popular.

Transparent inks are printed on aluminum foil or aluminum foil, which is more effective. Now transparent ink has been widely used in the packaging and printing industry, specifically in high-grade packaging such as food flexible packaging, wine-making carton packaging, and tobacco carton packaging. However, some problems often occur in the actual process of transparent ink, such as: After the printing of transparent ink, there are pitting, uneven ink, and other phenomena, and can not achieve the desired effect.

Transparent ink types and characteristics

Transparent ink uses high-grade transparent paint and high-grade transparent resin as the main raw material, and various types of additives are made by fine grinding. Transparent ink is divided into table printing transparent ink and in India (composite) transparent ink. Compared with other inks, transparent ink has the characteristics of low viscosity, high transparency and brightness, bright colors, strong adhesion and strong coloring power. The fineness of transparent ink is generally less than 10μm, and its hiding power and transferability are better than other inks. However, the transparent printing ink is not as good as the printing ink transparent ink. When the packaging bag is designed, the transparent sealing ink is generally used in the heat sealing position. In India transparent ink is generally resistant to high temperatures around 120 °C.

Transparent ink selection

1. According to the different choices of printing materials to adapt to ink. Such as the table printed aluminized twist film must be selected transparent ink printing, printing BOPP film and composite aluminum film, you should use printed transparent ink. The type of printing materials determines the ink used, and even the same type of film material will vary depending on the brand and grade.

2. Transparent inks are selected based on the samples provided by the customer, including the hue and color of the ink. If you need to deploy spot color transparent ink, it is necessary to consult the ink supplier, because the deployment of spot color transparent ink is more difficult than the opaque ink.

3. Choose according to the purpose of the package. For example, whether it is resistant to heat, light, penetration, etc.

Use of transparent ink

1. The gold paper used for printing colorful flowers, color bars, ribbons, etc. is printed in transparent ink (red, yellow, green, blue, etc.) or printed with aluminum film. It is a single layer. film.

2. After the transparent ink is printed, the inner layer of the aluminized film is made into a soft packaging bag or printed with an aluminized film and then made into a twisted film. This is a film with more than two layers and is widely used in the food industry.

3. After printing, aluminizing and re-applied to paper to make cartons, cartons, New Year pictures and other high-grade packaging printing products, with waterproof, moisture-proof advantages.

4. After printing with security materials and printing with clear ink, covering the holographic film is conducive to printing products security, while making the appearance of colorful, shining. For best results, transparent inks may not be used at design time, but only partially transparent inks are used for printing.

Transparent ink printing failures and precautions

1. Printing transparent ink produces "pitting" phenomenon

Cause Analysis:

(1) The surface of the embossing roller is not sufficiently delicate or has foreign matter such as dust, which causes the ink to be thick enough here.

(2) Plasticizers, lubricants, etc. contained in the film float to the surface, preventing normal transfer and lubrication of the ink.

(3) Ink viscosity is too high, drying is too fast, or lack of adhesive causes ink transfer and poor wetting.

(4) The printing pressure is too small or the printed version is defective.

Solution:

(1) Wipe clean the surface of the imprint roller.

(2) Before the printing, the plastic film is preheated, and the film is heated or replaced with a plastic film.

(3) Reduce the viscosity of the ink and use a slow-drying solvent.

(4) Increase the printing pressure, generally around 4kg.

(5) If the pits are more regular, the plates and embossing rollers should be carefully inspected for defects. If any, re-plate or replace the rollers.

2. Adhesion after printing transparent ink

In the high-temperature, high-humidity rainy season, the plastic film is gravure-printed, and it is prone to sticking when placed on a roll, transparent ink is stuck by the salty block, and cannot be separated from the lower plastic film, resulting in a lot of waste products. Most of the adhesions of printed products are caused by ink stickiness, high ambient humidity, and high pressure, as follows.

(1) Intrinsic factors

1 The ink itself is poor in heat resistance and produces greater viscosity under high temperature conditions.

2 The residual solvent in the ink is too much. After winding, severe adhesion of the finished product occurs. The large amount of residual solvent not only affects the fastness of the ink, but also causes the packaging to be different, which is extremely unfavorable to the packaged food.

3 Adhesives in printing materials cause the ink to stick.

(2) External factors

1 The ambient temperature is too high, causing the ink to soften, causing the print to stick. Requirements print operation and use temperature does not exceed 40 °C.

2 Overtightening causes adhesions. Reduce the winding tension.

(3) Other factors

Insufficient adhesion between the ink and the substrate. After rewinding, migration is likely to occur and adhesion may occur. At this point the correct choice of ink, so that the ink quality to adapt to the substrate. The surface treatment of the substrate improves the affinity for the ink. The general BOPP surface tension should not be less than 3.8×10-2N/m.

3. Printed transparent ink, aluminized composite gloss is not high

Cause Analysis:

(1) The ink itself has poor transparency.

(2) The solvent is too volatile or the viscosity of the ink is too low during printing.

(3) Poor uniformity of the aluminum plating layer causes poor light reflectivity.

(4) The squeegee angle is too large, and the plate is shallow.

Solution:

(1) Replace the ink with good transparency.

(2) Use slow-thousands of solvents to increase ink viscosity.

(3) The replacement of the aluminized film requires a uniform surface and no pinholes.

(4) Adjust the squeegee angle, generally 35 ° is appropriate.

4. Transparent ink caking phenomenon

This phenomenon generally occurs at lower temperatures. Place the ink at 35°C and heat it at room temperature. To prevent accidents, it must be guarded by a specialist.

5. Other considerations

(1) When printing with clear ink, the bottom of the white pad is not used below, because white plays a role of extinction and greatly reduces the use effect. The clear ink printed pattern is thinner by 0.01 mm than the white ink pad bottom.

(2) Select the appropriate diluent according to the type of clear ink.

(3) Because of the low viscosity of transparent ink, it is not appropriate to add too much thinner, and the viscosity is generally controlled within 18-22 seconds (3# Zahn Cup).

(4) Do not use mixed transparent printing ink or printing (composite) transparent ink produced by different manufacturers.

(5) Adjust the angle of the squeegee and the pressure of the impression cylinder, and the distance between the squeegee and the embossing point according to the depth of the plate.