Application Analysis of Paper Packaging Screen Printing Technology

Screen printing is characterized by rich colors, with a special three-dimensional effect, screen printing paper packaging products are various types of self-adhesive labels, anti-counterfeiting labels, high-grade cigarettes, wine, cosmetics and nutritional packaging.

In order to improve screen printing quality and production efficiency, the screen printing and platemaking equipment used for packaging and printing is also developing in the direction of high speed and automation. For example, some large screen printing companies have adopted automatic roller screen printing machines and automatic Stencil, large format coater, stretcher, and fully automatic processor; used to improve the efficiency of platemaking, the film connecting machine; used in the pre-press design, production of the G3-300 Apple Computer.

Platemaking

1. Production of Positive Film (Original)

Before making, first analyze the original. The original for screen printing is basically not different from other printed manuscripts, and only differs in details. Because the screen printing ink layer is thick and the subtle level performance is low, use the Curves tool in Photoshop to make appropriate adjustments to the fine level of the image and increase the dot size by 1% to 2% to make up for the printing. Loss of 5% of the following outlets during the process. For the soft part of the transition in the image, you can use the "Gaussian blur" in the Photoshop filter tool to soften the image; you can also use the Dodge or Darken tool in the toolbox to make local adjustments; you can also use the eraser, stamp, and other tools to patch the image Partial defects. In the production, the level of the manuscript must be comprehensively grasped, and the percentage of local and maintone halftone dots should be used to accurately determine the effect of printing on the image level and the influence on the subsequent processes.

Under normal circumstances, most of the boxes printed with screen printing are mostly text (Chinese and English) and color blocks. The middle position of the box is the product name that highlights the topic, and the upper side is the registered trademark that represents the product's patent. For text and line type manuscripts, text and lines should be bolded to a half level. If they are too thin, the printed lines will be broken due to the loss of fine levels in the process of printing. Too rough will be blurred due to the extrusion and diffusion of the ink.

In addition, in the production, we must also take into account the special printing effects and post-press processing requirements:

1) Scrub or Ice Print Etching Screen Printing Positive-printed film should be based on the die-cutting knife plate. The indentation line should be 4 to 6 mm apart from the left and right and right to avoid frosting or ice peeling caused by impact force during die-cutting. Product quality.

2) In the multi-color overprinting joint, the line cannot be touched, and the line pressure line should be designed according to the characteristics of the manuscript and the ink coloring mechanism. This is convenient for overprinting so that the printed product does not leak out, and the finished product rate is high.

3) Gold or gold sanding lines on the matte etched plate, with a line width of 1 to 2 mm. The line is too thin, the contour is not clear, not prominent, but also easy to break; but too thick, it also affects the visual effect.

4) Text and overprinting of matte or ice etching are more difficult in mass production. In order to increase the yield, the text can be directly printed on frosted or icy flowers or directly printed on gold and silver card paper. Due to the high cost of paper packaging materials, improving the yield in production is undoubtedly a good way to reduce costs. In addition, it is necessary to avoid the superposition of the color ink and the etching ink over a large area, because the overprinting effect is not obvious, and the ink is wasted, which decreases the ink adhesion fastness.

5) When bar codes, fine texts, patterns, and large-area on-site color printing, taking into account the accuracy of printed products, should be divided and printed. That is, bar code, small text, and pattern are printed on a fine mesh of 300 to 350 mesh, and field printing is performed on a coarse mesh of 200 to 250 mesh. This ensures barcodes, small texts are clear, smooth, and does not deform. The fine details of patterns are not lost. The field is thick and strong in three dimensions. Otherwise, the two can not have both.

2. Network selection and printing

Because the UV light solid matte (fine, medium, coarse sand) or ice flower (large, medium, small) ink particles are larger, in order to improve the over-net performance of the ink, a coarse mesh with a lower mesh number is often selected for printing in the production. With a high number of meshes, the printed products are finely ground and the patterns are precise; the mesh number is low, and the printed sand is coarse and the patterns are sparse. Take screen printing UV matte etching as an example:

Frosted rough pattern: screen mesh 100 to 180 mesh; photoresist film thickness 10μm or less;
Frosted lines: screen 150 to 250 mesh; photo resist thickness 12μm or less;
Frosted fine lines: screen 200 to 300 mesh; photo resist film thickness 16μm or less.
When the photo-resist film is thick, it is necessary to lengthen the exposure time appropriately so that the photo-resist layer is completely hardened, and at the same time, the development time is appropriately lengthened.

3. Proofing

Proofing is the inspection of the quality of plate making, and it is also the key to test the printing applicability of ink adhesion, rheology, etc., determine the curing time and check the correctness of characters and patterns. Only samples confirmed by the customer can be put into mass production.

Printing

1. The choice of paper

1) When printing paper packaging, it is usually based on the customer's requirements and the use of the product to select paper, and according to the cost to determine whether to use gold, silver paper, gold, silver paper. Gold and silver cardboard are made of vacuum aluminum on glass paper. Gold and silver paper are made of vacuum aluminum on white paper. The surface smoothness and stiffness of glass paper is better than that of white paper. The cost is also high.

2) According to the use of the product, choose face paper (250g/m2, 300g/m2, 350g/m2) and backing paper (250~350g/m2 white paper, small corrugated paper or large corrugated paper). General wine box and outer box face paper commonly used 350g/m2 gold, silver paper, wine box paste back paper commonly used 300g/m2 white paper, outer box paste back paper commonly used small corrugated paper or large corrugated paper, in order to increase strength and stiffness.

3) According to the customer's requirements to determine the color of the paper, shades of gold, silver, and paper must have high gloss, high brightness, smooth surface, no foaming, no wrinkles, tensile and flexural strength, toughness, Aluminized film has good fastness and does not fade.

2. Printing

Before the ink is used, it should be fully stirred. When mixing, an appropriate amount of thinner (less than 10%) can be added to ensure that the ink is wet. After mixing, the ink can be printed on the machine. To keep the mesh open, wipe it with a cleaning agent. The ink viscosity should be moderate, too large, easy to stick, too small, no three-dimensional. After printing, use a special washing net water for reuse. After the ink is used, it needs to be sealed immediately. Since the ink contains a photosensitizer, direct sunlight should be avoided during the printing process. It is better to operate under yellow light.
After printing, it must be cured by UV. When the curing is not complete, the ink fastness is reduced, the surface hardness is low, and the hand is touched. The light and solid are excessive, the bottom paper coating layer is easy to damage, the ink layer is resistant to folding, and the abrasion resistance is reduced. That is to say, ink drop, or even paper deformation occurs, resulting in post-processing difficulties, that is, sticking back paper and pasting paper are not close, uneven, wrinkles or open mouth phenomenon, affecting quality and beauty.

3. Meet the needs of post-press processing

The post-press processing of paper packaging includes backing, bronzing, embossing, die-cutting, and gluing.
Since the surface of the gold and silver (paper) paper is an aluminized film and aluminum is an amphoteric metal, at a certain temperature, a chemical reaction occurs between the acid and the alkali, and the aluminum particles gradually oxidize and lose luster. Therefore, from the consideration of post-process, good quality gold and silver card (board) paper should be used.

Paper and backing paper must be stored at the same temperature and humidity, otherwise the paper will be deformed and the backs will not be even. The backing adhesive must be neutral and the compounding temperature should not be too high.

In order to improve the grade of packaging, increase the three-dimensional sense, make products more eye-catching, many packaging but also use embossing process, the name of the product on the packaging box convex, and then die-cutting, therefore, requires the screen printing ink layer to have High folding and abrasion resistance.

Source: "Printing Technology - Equipment and Special Printing"