Analysis of the Application of Transparent Ink in Flexible Packaging

With the continuous improvement of packaging requirements, packaging design has become more and more diversified, and as an important means of attracting attention, the color has attracted people's attention. Most of the packaging of merchandise in shopping malls has high transparency and gives people a feeling of glitter. In the field of flexible packaging, there is an ink to achieve the above effect, which is a transparent ink with high transparency.

Transparent ink is used for aluminum foil or aluminum foil printing, the effect is more obvious, and the visual effect is the best. Nowadays, transparent ink has been widely used in the packaging and printing industry, and is specifically applied to high-grade packaging such as flexible packaging in the food industry, carton packaging in the brewing industry, and carton packaging in the tobacco industry. However, some problems often occur during the actual use of the transparent ink, such as the phenomenon of pitting and uneven ink spreading after the transparent ink is printed, which often fails to achieve the desired effect. In this paper, we will explain the nature of the clear inks and printing matters in the light of actual situation and hope to help colleagues in the industry.

Transparent ink types and characteristics

Transparent ink is made of high-grade transparent pigments and high-grade transparent resin as the main raw material, together with other types of additives made by fine grinding. Transparent ink can be divided into table printing transparent ink and in India (composite) transparent ink two. Compared with other types of inks, transparent inks have the characteristics of low viscosity, high transparency and brightness, bright colors, strong adhesion and strong coloring power. The fineness of clear ink is generally less than 10μm, so its hiding power and transferability are higher than other types of inks. Ink is good. 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, there are also ink manufacturers have produced transparent ink resistant to higher temperatures. Transparent ink selection

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

2. According to the sample provided by the customer, select the transparent ink, including the hue and color of the ink. If it is necessary to mix spot color transparent inks, it is necessary to consult the ink supplier, because spot color transparent inks are harder to formulate than opaque inks.

3. Select according to the purpose of the package. For example, whether it is resistant to heat, light, penetration, etc. Use of transparent ink

The specific application of transparent ink is as follows.

1. Gift gold paper for printing colorful flowers, color bars, ribbons, etc. These wrapping papers are made of transparent ink (red, yellow, green, blue, etc.), printed in aluminum, or printed with an aluminized film, which is a single-layer film.

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

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

4. Printing with anti-counterfeit materials and then printing with transparent ink, and then re-holographic film, is conducive to printing anti-counterfeiting, while making the appearance of colorful, shining. For best results, transparent inks may not be fully used at design time, but only partially transparent inks are used for printing. Transparent ink printing failures and matters needing attention 1. Easy to produce "pitting" phenomenon when printing transparent ink

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, after the plastic film is gravure-printed, it is prone to sticking during winding and placement. The transparent ink is stuck in pieces and the ink is not even separated from the lower plastic film, resulting in a lot of waste products.

Most of the adhesion of printed products is caused by the stickiness of the ink, the high humidity of the environment, and the excessive 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 sticking of the finished product occurs. The large amount of residual solvent not only affects the fastness of the ink, but also causes odor in the package, which is extremely unfavorable for the packaged food.

3 Adhesives in the substrate cause ink stickiness.

(2) External factors

1 The ambient temperature is too high, causing the ink to soften, causing the print to stick. Therefore, it is required that the operation and use temperature of the printed matter should not exceed 40°C.

2 Tightening caused by excessive tightening. Reduce the winding tension.

(3) Other factors

Insufficient adhesion between the ink and the substrate. After winding, it can easily transfer and cause blocking. At this point should be the correct choice of ink, control the quality of the ink to adapt to the substrate. In addition, the treatment of the surface of the substrate to increase its affinity for the ink is also a method of reducing the occurrence of blocking of the ink. The general BOPP surface tension should not be less than 3.8×10-2N/m.

3. Printing 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-drying 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. Blocking phenomenon of transparent ink

This phenomenon generally occurs at lower temperatures. In this case, the ink should be heated at room temperature of 35°C. In order to prevent accidents, it must also be guarded by special personnel.

5. Other considerations

(1) When printing with clear ink, the bottom of white pad is generally not used because the white layer has a matt effect, which greatly reduces its use effect and value. The transparent 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) It is best not to use mixed printing transparent ink or inward printing (composite) transparent ink produced by different manufacturers to avoid quality problems.

(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.

In short, misalignment of solvents, improper control of viscosity, or incorrect process operations are all very likely to cause many failures, so every aspect cannot be sloppy. Therefore, in the use of transparent ink printing, in order to obtain the desired results, all aspects must be strictly controlled.

Reprinted from: Ink Information