Soft packaging "concave and soft", what should you pay attention to before printing?

At present, gravure flexible packaging products generally use 150 lines/inch or more of screen lines, while flexo flexible packaging products use 100 to 120 lines/inch of screen lines. If the printing method of a flexible packaging product is changed from gravure printing to flexo printing, the printing effect of color block, line, text, graphic and other information can be basically the same, but in the aspect of mesh image, gradient to absolute network, etc. Flexo printing requires special handling to achieve similar results to gravure to meet customer requirements.

Prepress design considerations

1. Size deformation processing of imposition files

“Concave and soft” PE film flexible packaging activities do not need to worry about the registration problem, as long as the size of the job and the uniformity in the circumferential direction of the plate cylinder, determine the appropriate imposition method and matching plate cylinder size, and do The circumferential and axial tensile deformation treatment of the good imposition document (usually the circumferential dimension is elongated by 0.5% to 2%, and the axial dimension is reduced by 0.3% to 1.2%).

2. Processing of small text, thin lines and barcodes

"Concave and soft" flexible packaging products, pay special attention to the handling of small text, thin lines and barcodes. Under normal circumstances, the small Yang characters of the gravure soft package should be thickened by 0.01mm, and the individual small Yin characters should be processed to be finely processed, and the barcode should be 0.02~0.03mm. If it is converted into a flexo printing process, the processing method is opposite to the gravure printing, in order to prevent the thin and straight pen lines from expanding and thickening, fine and negative lines and small negative words.

In order to ensure the reading level of the barcode, the best processing data under the flexographic process conditions can be determined by testing the barcodes of different colors, the degree of the scale and the proportion, and the anilox rolls of different lines. The following data is for reference: the scaling of the barcode is preferably 90% to 110%, and the left and right safety distance is 4mm left and 3mm right, and the thickness is 0.07~0.1mm, which is suitable for printing with an anilox roller of 500-800 lines/inch. The color is mainly black and dark blue. For fine lines, if a 1016 line/inch anilox roll (BCM value of 2.0) is used for printing, a positive line with a width of 0.018 mm and a negative line of 0.053 mm can be obtained, but this is close to the limit.

3. Trapping and registration

The precision of the registration of satellite flexo printing machines is high, and the flexible packaging products of “concave and soft” should give full play to this advantage. Generally, the offset value of the flexo-printed flexible packaging product is 0.1 to 0.3 mm, and the specific value depends on the product. For example, the size of the trapping value can be determined by combining the distribution rules of the layout image and the imposition.

It should be noted that the circumferential registration is the key point of consideration. If the axially multi-spliced ​​products can be arranged in dislocation on the layout, it is beneficial to register and can alleviate the problem of the bars.

4. Processing of field and dot gradients

Gravure has no worries of increasing dots, and flexo printing must face the problem of dot gain, so special attention must be paid when the field and dot gradient appear on the same layout. The following is a comparative analysis of the gravure and flexo printing processes by taking the monochrome dot gradient as an example.

Gravure process: 150 lines/inch plate, 1% minimum dot, can print the same version in the field and dot, and control the depth of the plate (35~50μm) to achieve the required density in the field. The effect of the field gradual change to the absolute network is also guaranteed, and stable mass production can be achieved.

Flexo printing process: CDI plate making, the number of screens added to the plate is 150 lines/inch, and the minimum dot size is 1%. The solid density of the printed product is mainly determined by the ink storage amount (BCM value) of the anilox roll, and the adhesive tape, the plate material and the ink also have a certain influence on the solid density. In terms of dot grading, flexo should face the problem of dot gain. The minimum dot size increases by 5% to 8% after 1%. If you jump directly to 0, the gap will be visually generated. At the same time, the number of lines of the anilox roller that can match the number of high-net lines and small-sized dots is necessarily high, and the amount of ink stored is bound to decrease, and the density in the gradient pattern on the printed product will also be limited. Therefore, the current 150-inch/inch screen line and 1% minimum dot are generally not used in flexible packaging flexo printing.

The above is a comparative analysis of monochrome flexo and gravure gradients to the absolute web. This problem also exists in the printing of multi-color overprinting of the flexo printing to the absolute printing. It can be said that the current soft underbelly of flexo soft packaging is "gradual to absolute network, dot gain control, and low-screen number printing plate". I have tested flexo-printed hygienic bags, using 120 lines/inch and 150 lines/inch of printing plates, with a minimum dot size of 3%. Using 1016 lines/inch anilox rolls, the flexo proofs are 175 The line/inch gravure proofs are compared. The overall effect of the 150 line/inch flexo proof is very close to that of the gravure proof, but the defect is that the CMYK four colors have limited ink loading and the printed image is generally shallow.

In order to improve the above situation, soft-package flexo printing companies should be flexible in handling the color separation according to the specific conditions of the product (for example, spot color participation in image overprinting, shallow mesh layout, small dots and compact integration + multi-color overprint) You can also try to start with the following aspects: under the conditions of the process conditions, try to use 120 ~ 150 lines / inch of printing plates; at least 4 more than 1000 lines / inch of anilox roll, and the more ink storage The bigger the better; the application of HD Flexo technology (the author's preliminary test that the effect is good, whether it can be used well, it needs to be further verified in practice). In addition, the solvent-based four-color original ink currently used in flexo printing has a higher color density than the gravure ink. If it can continue to greatly increase the color density and stabilize the overprint on the existing basis, it is specially used for the mesh printing of fine products. It will also promote the improvement of flexo packaging technology.

Plate making precautions

The CDI plate making process has been applied in the domestic flexo packaging field for 10 years, the process is mature, and the plate making quality is stable. Flexo packaging requires a thin plate with a thickness of 1.7mm or less. The current 1.14mm laser version is the first choice in the industry. It can produce 175 lines/inch and 1% minimum dot printing plates, but few flexible packaging companies dare. The main reason is that the hardware is insufficient, and the actual printing effect and process control are difficult to guarantee.

The general requirements for the printing plate are flat surface, no residual solvent, moderate viscosity and relief height, sufficient exposure, and sharp and stable dots. In addition, the printing durability of the printing plate is also worthy of attention. In the next few years, flexo printing will adopt high-screen printing plates and new screening technologies, which will put forward higher requirements on the service life of the printing plates. It is recommended that the plate suppliers can consider Introduce thinner plates from abroad to do some preliminary testing. (Editor: Zhang Wei)

Plastic Bags

Made in a woven structure, these bags are much stronger than more common non-woven bags. Additional lamination makes these bags the strongest in its class.Specially structured nylon handles along with PE bottom board make these bags even stronger and more convenient to use.

Moreover, these bags are manufactured from minimum 95% Recycled Plastic. And, don't forget that these bags can be recycled at the end of their life-spans also.

The cover of plastic bags is made of PP material, which can be printed and has publicity effect

Clear Plastic Bags,Plastic Bags,Large Plastic Bags,Custom Plastic Bags

shaoxing chaofeng stationery manufacturing CO.,LTD. , https://www.chaofengstationery.com