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Comparison of plastic Cosmetic Tube offset and screen printing

2021-06-06

In the past 10 years, plastic Cosmetic Tube packaging from cosmetic tube manufacturer has been popular among consumers in the cosmetic, pharmaceutical, food and other industries due to its light weight, ease of use, high quality and low price. More and more makekup brands are looking for wholesale custom cosmetic tubes.


As the name implies, Plastic Cosmetic Tube is made of plastic or, more specifically, mainly polyethylene. Depending on the structure, the packaging of Cosmetic Tube can be divided into single, multi-layer and composite tubes with a variety of materials. As far as packaging is concerned, the most attractive part of customers should be the printing pattern. Therefore, this article from cosmetic tube supplier mainly introduces the printing and processing of plastic cosmetic tube.

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The most common cosmetic tube printing processes are: dust removal - surface pretreatment - printing (UV ink) - polishing - UV curing (or heat curing) of gloss tube. A single Cosmetic Tube printing machine, such as those made by Polytype in Switzerland and Hinterkof in Germany, can accomplish almost all of this process.



Step 1 Dust removal

A common problem of plastic raw materials is that they are prone to generate static electricity. In the process of producing cosmetic tube, polyethylene raw materials constantly contact and rub with the metal mould, which makes the surface of the tube generate static electricity, which makes the surface of the tube easy to absorb dust. Therefore, dust removal should be carried out before printing.


The second step is surface pretreatment

Because polyethylene is a non-polar material, surface pretreatment is required before printing. There are two main ways of treatment from cosmetic tube supplier, one is corona treatment, the other is flame treatment, these two ways can achieve the purpose of ink and varnish adhesion firm.


The main factors that affect the corona treatment effect are the discharge power, the distance between the electrode and the surface to be treated, and the speed of the corona tube passing through the corona processor.


The main variables that affect the effect of the flame treatment are the air/fuel gas ratio, the distance between the surface being treated and the visible blue top of the flame, and the speed at which the tube passes through the flame.


It is generally required that the surface tension of the tube be 3.6×10-2N/m or above, depending on the characteristics of the ink and varnish used. A simple way to check the effect of surface treatment is: The treated tube is placed in the water and lifted from the water to see if there is an even film of water on the surface of the tube. If the film is even then the surface of the tube is considered to be well treated, otherwise the factors affecting the effect of the surface treatment should be adjusted appropriately.

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Step 3 Printing

Currently, there are two printing methods commonly used by the Plastic Cosmetic Tube in cosmetic tube manufacturer's production base. One is offset printing, where the ink is transferred to the plate through a set of rollers, and the plate transfers the ink from the printed pattern to the blanket, which then transfers the complete print pattern to the substrate in one go.


The offset tube printing press is different from what is normally referred to as an offset press. Usually referred to as offset lithography, the principle of ink insoluble ink supply plate, and then transferred to the blanket by the plate, although now has developed waterless offset printing, but the plate is still lithography or gravure. The offset printing used for the Cosmetic Tube printing is a relief printing and is therefore more accurately referred to as a relief printing.


Cosmetic Tube offset plates are usually made from a light-cured resin plate that has undergone a process of primary exposure, development, rinse, drying, and post-exposure. The production time of a printing plate is about 30 ~ 40 minutes, and the printing resistance reaches more than 100,000. Since this printing plate is a resin plate and the graphic part has a high raise (about 0.5 ~ 0.6mm), when making the screen adjustment, only more than 5% of the dot can be retained on the highlight part, therefore, the printing pattern on the tube is not as fine as the offset printing and it is for this reason, There was the appearance of labeling the packaging of the Cosmetic Tube instead of printing the logo or other iconic image directly on the Cosmetic Tube.

Now the speed of Cosmetic Tube offset printing is up to 12,000 units per hour and the process is getting easier. The increase in production speed and the decrease in offset printing cost have made offset printing widely used for cosmetic tube printing.


Another way that Cosmetic Tube prints is traditional screen printing. Multicolor screen printing machines produced in China are usually composed of several single-color screen printing machines connected together, which covers a large area and is covered by long tube transmission routes, and the positioning accuracy between colors is worse than offset printing and the printing speed is lower, making their costs higher. In Europe, screen printing machines have been developed and produced for Cosmetic Tube printing, such as Lisson, which have greatly improved the printing accuracy and printing speed, with production speed up to 5,400 PCS/h, overprinting accuracy up to ±0.2mm and printing color up to 6 colors. Due to the thick ink layer of screen printing, it is currently mainly used for the printing of colored Cosmetic Tube or partial uncoated varnish products.


In the case of the Cosmetic Tube printing, it is possible to combine the above two printing methods. A fully automated Cosmetic Tube production line, that is, a combination of offset printing and screen printing, enables Cosmetic Tube to print 12 colours.

With the spread and improvement of UV-curing technology, UV-curing ink was widely used for both Cosmetic Tube offset and screen printing, making the control of the ink easier.


The fourth step is glazing

On both the Cosmetic Tube offset press and the screen press, a set of polishing devices consisting of two steel rolls and one rubber roll are installed. The adhesion fastness of varnish is also directly related to the size of the tension after the pretreatment of the plastic surface. Varnish is usually UV curing varnish, there are many types of light oil and matte oil. Also available are heat curing varnish and 3 in 1 varnish for Cosmetic Tube post-offset glazing.


The fifth step is varnish curing

For UV curable varnish, varnish curing degree and UV lamp emitted by the wavelength and UV intensity has a great relationship. For subsequent processing such as hot stamping products, the degree of curing of varnish will have a great impact on the quality of subsequent processing.


Q&A

In the case of Cosmetic Tube printing, there are several problems that may occur and the solutions are as follows.

1. The problem of light oil and ink adhesion is mainly related to the surface pretreatment of printing materials. The surface tension can reach 3.6×10-2N/m by increasing the power of corona treatment and the ratio of air to combustion gas treated by flame. But the surface tension is not the bigger the better, some ink in the surface tension of 4.0×10-2N/m, there will also be poor adhesion phenomenon, so for different ink should look for the best surface tension value.

2. The image and text appear ink phenomenon

This phenomenon is usually caused by excessive printing pressure. There are two points of pressure on the tube press that would affect the printing quality of the final product, namely, pressure from the ink roller against the plate and pressure from the plate against the blanket. If the pressure is too large, the ink in the middle position of the text and text will be squeezed to the edge of the text and text, making the edge of the printing pattern appear ink and dot bigger. Therefore, we must ensure that the printing pressure is moderate.


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