The selection and problem analysis of flexible packaging transparent ink

With the increasing diversity of people's requirements for packaging, packaged cosmetics. The type of out-of-the-box work has been installed on the exterior of the package. The "color" is most likely to attract people's attention. Today, most of the packaging of merchandise on the market tends to be highly transparent, giving people a sense of glittering sparkles. The ultimate goal is to trigger consumers' desire to buy. In the field of flexible packaging, there is an ink that can meet the above requirements. It is a highly transparent transparent ink. In the process of using transparent ink, aluminum film or aluminum foil is often used as the bottom, the effect is very obvious, and the visual effect is also the best. Now transparent ink has been widely used in the flexible packaging industry, specifically in the high-end flexible packaging such as the food industry. In the actual use of the process often occur some quality phenomena, such as transparent ink printed pits, ink uneven, etc., which greatly reduces the expected effect, this article will be combined with the actual nature of the transparent ink and printing issues to be explained.

Transparent ink types and characteristics

Transparent ink is based on high-grade transparent paint and high-grade transparent resin as the main raw material, together with other types of additives made by fine grinding. It can be divided into two types: table printing transparent ink and inward printing (composite) transparent ink. Compared with other types of inks, transparent ink has the characteristics of high viscosity, high transparency, high brightness, bright colors, strong adhesion and strong coloring power. The fineness of the clear ink is generally less than 10urn, so its hiding power and transferability are better than other inks, but the transparent ink is not as good as the high-temperature transparent ink. When designing the packaging bag, the transparent ink is generally not present at the heat-sealing blade pressure. The transparent printing ink is generally resistant to high temperatures at about 120°C. Certain ink manufacturers, of course, have produced transparent inks that are more resistant to high temperatures. It's best not to mix the clear ink printed with different manufacturers or the clear ink in the ink (composite). Often, packaging companies think that they can be mixed when they belong to the same type of ink. As a result, many quality problems often occur.

Transparent ink application

When printing with clear ink, white mat bottom is generally not used under the color scheme, because white plays a role of extinction, which will greatly reduce its use effect and value. Relatively speaking, the transparent ink printing is thinner 0.01 mm than the white ink pad. The transparent ink Ep~, J is inseparable from the aluminized film or aluminum foil, aluminum foil, etc. in order to obtain high brightness and vivid colors, because the transparency of the transparent ink is extremely high, combined with the aluminized film or directly printed to the above materials Changes will occur to reveal the metallic luster and color, making yellow more yellow, green more green, red more red, and excellent results. In terms of transparency, there are several kinds such as clear golden, transparent yellow, transparent light yellow (blue phase), and the like developed from a transparent printing ink. The transparent golden compound is more glittering if it is compounded on the aluminized film. The transparent golden color is highly transparent. It is also often used in self-aligning gold, and can also be lined with gold powder. According to the customer's requirements, it can be selected and formulated. For example, the golden ink formulated with gold powder, gold transfer oil and clear golden color with a ratio of 1:3:2 can not only enhance the brilliance of the gold ink, but also greatly enhance its adhesion. . Its application is as follows:

â–  Create gift wrapping paper with colorful flowers, color bars, ribbons, etc. It is made of transparent ink (red, yellow, green, blue, etc.) in the printed aluminum and then using the aluminized film to form EPN, a single-layer film.

â–  After printing transparent ink. The inner layer is made of a flexible package made of aluminized film or a small inner bag made of aluminized film, such as a conjunctiva, which belongs to two or more layers of film and has been widely used in the food industry.

● It is generally made of high-grade packaging such as carton, carton, and New Year pictures with aluminum plated after printing and then reconstructed on paper. Its printed products have the advantages of waterproof, moisture-proof and so on.

â–  After printing with security materials, printing with clear ink, and then re-launching the laser film, this is conducive to anti-counterfeiting of printed products, while also making the appearance of colorful, full of light. In order to achieve an optimal state effect, it is considered that designing platemaking may not always use a clear ink color scheme, but may be partially printed using clear ink. Better results.

Reasonable choice of transparent ink

About how to choose transparent ink. We can consider the following three aspects:

â–  Printing should use inks that are compatible with the printing materials. For example, when the printing table is printed with aluminum, the transparent ink must be printed. If it is printed BOPP and composite aluminum, you should use composite ink (transparent). Therefore, it can be said that the type of printing materials determines the type of ink used, even if the same type of film material, often due to different varieties and grades vary, so it should not be mistaken.

â–  The correct choice should be based on the sample provided by the customer. The choice of clear ink includes hue and color. When it comes to the deployment of spot color transparent ink, it is necessary to consult with the production supplier. The difficulty of special color matching for transparent ink is obviously higher than that of opaque ink.

â–  The selection should also be made according to the actual situation. Parameters such as high temperature resistance, light resistance, permeation resistance and so on must be included in the consideration of the selection.

Transparent ink printing and failure phenomenon

â–  It is necessary to stir the clear ink before it is printed. If it is in winter, the weather is relatively cold, because the viscosity of the table printing transparent ink is low, it is not suitable to add too much diluent and viscosity. Generally, the 3# cup is controlled in 18-22 seconds, and then the angle of the doctor blade is adjusted according to the depth of the printing plate. The pressure of the impression cylinder and the distance between the squeegee and the embossing point. If the solvent ratio is misaligned, improper viscosity control, or process failures are very likely to cause many failures, so every link can not be sloppy.

â–  It is easy to produce "pitting" when printing transparent ink. After the printed product is coated with aluminum film, the flash effect comes out, but if you look closely, you will find that the surface of the product is pinhole-shaped, as if it is not printed. There are several factors in this factor:

1 The surface of the printing rubber roller is not sufficiently fine or dust and foreign matter and the printing on the top is caused by the top;
2 The plasticizers, lubricants, etc. contained in the film float to the surface to hinder the normal transfer and lubrication of the ink;
3 The viscosity of the ink is too high, the drying is too fast, or the gap is caused by the adhesive, and the wettability is poorly adapted;
4 increase the pressure of the printing rubber roller, generally about 4kg. If there is regularity in the pitting, you should carefully check whether the plate and the rubber roller are defective, re-plate or replace the roller.

â–  Adhesion after printing transparent ink In the high-temperature, high-humility Meiyu season, after the plastic film is gravure-printed, adhesion phenomenon occurs between the winding positions, the transparent ink blocks fall, and even the transparent ink cannot be separated from the lower plastic film. As for causing waste products.

Most of the adhesion factors are due to the stickiness of the ink, the humidity is too high, and the pressure is too high. The specific factors are as follows:

1. Intrinsic factors: The ink itself is poor in heat resistance. When the paint is dry, we cannot see it with the naked eye. Since the residual solvent is difficult to evaporate after the printed matter is rolled up, the resin in the ink cannot be dried and solidified, causing severe blocking of the finished product. The increase of the residual solvent not only affects its firmness, but also is extremely unfavorable to the food and produces odor. In addition, the auxiliaries in the printed material can also cause the ink to become sticky.

2, external factors: due to improper control caused by adhesions. At room temperature, the finished product with no quality problems in the operation and use of the printed product will soften when exposed to high temperatures. Adhesion builds up. Therefore, it is required that both the operating temperature and the use temperature of the printed matter should not exceed 40°C to 50°C. In addition, too tight winding, winding tension will cause adhesion, the solution is to control the printing drying temperature and tension relaxation, winding should not be too tight.

3, other reasons: ink and substrate sticky, such as the ink and the substrate does not have a good bond. After rewinding, it is easy to transfer and produce adhesion. The solution is to select the ink correctly and control the quality of the ink to make it suitable for the substrate. In addition, treating 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. General BOPP surface tension ≥ 38 dyne can be.

The reason why the gloss is not high after brushing transparent aluminum plating composites is as follows:

The ink itself has poor transparency;
The solvent is too fast when printing, the viscosity is too low; the aluminum plating layer is poor in uniformity, resulting in poor anti-gloss:
The squeegee angle is too large, and the plate is shallow. The solution is: a. Replace the ink with good transparency; b. Use slow-drying solvents to increase viscosity; c. Replacement of composite aluminum plating requires that the aluminized layer be uniform without pinholes; d adjust the squeegee blade, generally the angle is controlled at 35 degrees.

When printing transparent ink, you must start from all aspects to get the best results, and you should select and print according to the actual situation.

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