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Interpretation of reverse polishing process

Time: 2019-05-07

(1) Overview of Reverse UV Technology           

Reverse polishing process can make the same print with mirror high brightness effect and matte or hemp surface non-high brightness effect, form a stronger contrast in brightness, so as to achieve better polishing effect. It is produced by offset printing, so overprinting is very accurate, and it also ensures the printing accuracy of pictures and texts in bright parts.


(2),Reverse UV Principle           

After printing according to normal color sequence, on the basis of thorough drying or curing of ink, a special base oil is printed on the local area without highlighting high brightness by offset printing (or off-line) method, and then coated with UV varnish on the whole surface by full plate method after the base oil is completely dried. In this way, the cohesion reaction occurs in the contact area between UV polishing oil and base oil, forming a small granular ink film, forming a matte or ground surface; while in the UV polishing area of unprinted base oil, a high gloss mirror is formed. Its essence is the result of the copolymerization of two kinds of media, also known as mutually exclusive oil, big impression, etc. It is further developed on the basis of UV offset printing. The core is the polymerization of special base oil and coated varnish under UV light, with fine particles and uniform distribution.


(3)The characteristics of reverse UV           

Local polishing and local matte polishing mode are combined to achieve high contrast effect of local pictures and texts. Therefore, the overprint precision of polishing and printing becomes the key of polishing technology. After printing, the effect of silk screen grinding can be obtained, but it has irreplaceable advantages in efficiency and overprint accuracy.


(4)Advantages of Reverse UV            

Reverse polishing process is adopted to enhance the light resistance of ink, increase the heat and moisture resistance of ink, protect imprinting, beautify products and act as agent for film coating. So that printing can present two different gloss processing.           

Reverse UV synchronization with offset printing has the advantages of small paper deformation, accurate overprinting, high efficiency, relatively low cost and high reproducibility accuracy. The ink layer is relatively thin, similar in effect and environmentally friendly. Widely used: promotional materials, gifts, calendars, crafts, cigarette boxes, wine boxes, food boxes and so on.           


(5)Functions of Reverse UV           

1. Look sideways to see the bright light, change the angle to see the effect change has a certain anti-counterfeiting function.           

2. After printing white and four colors on gold and silver cards, use a set of printing reverse polishing ink (five colors) to go through UV polishing oil online, so that there will be overall matte and local bright effect.

3. Because reverse polishing ink is one color group printing, there is no overprint inaccuracy. The reverse polishing production is exactly the opposite of the background white, or that is to say, the sanded place is on the spot. The bright place is empty.


(6), Reverse UV Process           

1. Conventional printing must be completed before polishing, and the ink must be thoroughly dried or cured.            2. Then, transparent reverse ink is printed on the non-highlighted parts of the design manuscript by offset printing, either online or offline.           

3. Connect again, coat the printing surface with UV varnish and solidify by full plate.           

4. The gloss oil contacts with the previous reverse ink to produce cohesion reaction, forming small granular ink film in the non-bright part to achieve the effect of matte or hemp surface. The bright part without reverse ink forms the high brightness effect of mirror.           

5. Reverse polishing process can make the same print have both mirror high brightness effect and matte or hemp non-high brightness effect, and form stronger contrast in brightness, so as to achieve better polishing effect. At the same time, because offset printing is used for non-bright parts, overprinting is very accurate, and also ensures the printing accuracy of high-bright parts.


(7), how to realize high quality reverse UV Technology           

1. Equipment Requirements           

Ideally, 7-color + 1-UV printing equipment and CTP plate-making system.           

2. Requirements for Special Base Oil and Coating Gloss Oil           

It is necessary to test the matching of printing ink and reverse varnish and the hot stamping performance.           

3. Print Requirements           

Composite paper, white cardboard, copperplate paper and so on are commonly used as the underpinnings of reverse sanding process. It is necessary to pay attention to the best effect of composite paper.           

4. Light Source Requirements           

In practice, it is not necessary to open all lamp tubes at full power. Generally, the open power of dark ink and white ink is larger, which is conducive to rapid drying. The open power of special base oil and coated varnish is between 80% and 95%. The more suitable proportion should be explored in combination with the actual situation.            5. Addition of Auxiliaries           

According to the need to add UV strengthening agent, UV photosensitizer, etc., need to control the amount of added.            6. Detection method of ink adhesion           

Test with 3M600 tape.           

7. Test method for drying degree of ink           

Use bagger knife, 3M600 tape, magnifying glass, pin, pencil, etc.


(8), Requirements of material and process parameters for reverse UV           

1. Smoothness: Selecting paper with smooth surface and rough surface will reduce the glossiness of the printed surface and make the polishing effect not obvious.            

2. Absorption: Paper with poor surface absorptivity is selected. Paper with strong absorptivity makes the polishing effect not obvious.           

3. Paper Material Material: Paper with good surface quality is selected, and its surface is poorly coated and easy to be discolored.           

4. Ink: Choosing ink with strong dyeing power and good toughness can reduce the possibility of discoloration.           

5. Ink Ink Layer Thickness: Special tone deep shallow printing, control the ink layer thickness, can reduce the possibility of discoloration.           

6. Powder spraying quantity: If ordinary ink is used to print documents, it is suggested that on-line polishing should not use powder spraying, or water-borne Varnish can be applied off-line. Too much powder spraying on printed matter affects the polishing of varnish to form mirror surface and particles without contrast, and the effect is not strong.           

7. Ink drying: Printing must be fully dry, surface treatment, in the case of ink drying may cause light oil curing is not complete, no effect.           

8. Material selection: Reverse UV products, materials must be PET light gold and silver cards, not aluminum foil type gold and silver cards, because aluminum foil gold and silver beer molding, explosion of aluminum foil film. The Darin value of the gold and silver film surface must be up to 40. It is no problem to do reverse UV, and there will be no explosion and ink loss.           

9. Paper moisture content: Material with moderate moisture content should be selected. Paper with high moisture content is deformed and curled. Paper with moisture content is easy to break and dry.           

10. Additives: Reverse UV curing products, generally less than 1% of the amount of UV curing agent, is not conducive to reverse UV effect.           

11. Dain value of paper surface: 40 Dain.


(9), Advertisements in Reverse UV Document Making           

1. The pattern needs to be selected and processed. The part of the grinding effect is selected, the background color is filled, the bright place is empty, and the film and publishing list are produced. It is necessary to control the minimum size of Yin and Yang lines.           

2. Documents need to be repaired and exposed, and grinding documents need to be larger than o.3mm (mainly depending on the accuracy of the equipment).           

3. Don't choose small characters or patterns. The font size is very small and easy to paste. The font size is no less than 10.           

4. Anti-white lines must be larger than o.15mm; Anti-white fonts should be larger than 6 fonts and boldface.           

5. Attention should be paid to the rotten images of complex vector files and the jagged edges of bitmap files.           

6. Reverse UV products, when designed, are divided into dumb surface and light surface, dumb surface is printed on the printing base. To use PS version, it is necessary to do a good job of document processing and reverse UV technology, but pay attention to the size of fine lines, generally more than o.15mm lines.


(10), Advertisements for Reverse UV Printing           

1. Printing plate should be baked or used with special UV plate.           

2.The printing press can not be directly illuminated by sunlight.           

3. Keep the temperature in the workshop between 20 and 25 degrees.           

4. The roll gap must be adjusted after replacing the ink rollers.           

5. UV inks should not be printed where solidification, adhesion, odor, preparatory test/food contact is required.           

6. Fineness and roughness of texture, handle and oil sensation are related to the factors such as UV lighting, printing speed, oil thickness and quality, printing pressure and paper smoothness.           

7. Reverse UV oil is surface oil and bottom oil, bottom oil is printing ink roller oil and top oil is gloss oil passing through oil base.           

8. Printers can only be equipped with oil holders one by one, such as 5+1UV printing press, 6+1UV printing press, 7+1UV printing press, 8+UV printing press, etc.