Explanation of the Application of Reverse UV Process in Printing

Principle: The reverse UV process utilizes the "mutual exclusion" principle between coating-type Uv Varnish and base UV varnish (ink fountain type UV varnish) to achieve a combination of embossed texture and different gloss effects in one step. That is, applying varnish on areas without base varnish to create a glossy effect, and applying varnish on areas with base varnish to achieve a matte effect. This process can control the amount of UV base varnish or the size of the halftone dots to achieve variations in brightness (or the strength of wrinkling and contraction) after UV varnishing.

There are mainly three recommended printing sequences for the reverse varnishing process:

• UV color ink printing - UV irradiation curing - UV base varnish printing - UV irradiation curing - Uv Varnish Coating - UV irradiation curing;
• UV color ink printing - UV irradiation curing - UV base varnish printing - UV varnish coating - UV irradiation curing (without intermediate irradiation);
• UV color ink printing - UV irradiation curing + (offline secondary printing) + UV base varnish printing - UV varnish coating - UV irradiation curing.

Advantages:

Using the reverse varnishing process enhances the light resistance of the ink, increases the ink's ability to resist heat and moisture, and serves to protect the print, beautify the product, and replace lamination. It allows printed materials to present two different gloss processing effects.

Process Flow:

• Conventional printing must be completed first, and it must be ensured that the ink has completely dried or cured;
• Then, using offset printing, print the transparent reverse ink on the non-high-gloss areas of the design in a connected or disconnected manner;
• Next, in a connected manner, apply UV varnish to the entire printed surface and cure it.
• The varnish comes into contact with the previously applied reverse ink, causing a cohesive reaction, forming a granular ink film on the non-high-gloss areas, achieving a matte or sand-like effect. The high-gloss areas without reverse ink form a mirror-like high-gloss effect.
• Using the reverse varnishing process can make the same printed product have both mirror-like high-gloss effects and matte or sand-like non-high-gloss effects at the same time, creating a stronger contrast in brightness and achieving better varnishing effects. At the same time, because the non-high-gloss areas are printed using offset printing, the registration is very accurate, ensuring the printing precision of the high-gloss areas.

Material Requirements:

• Smoothness

Select paper with a higher surface smoothness. Poor paper quality or a rough surface that absorbs a large amount of oil will reduce the gloss of the printed surface and make the varnishing effect less noticeable.

• Powder Spraying Amount

When using ordinary ink for printing documents, it is recommended not to use powder spraying for online varnishing processing, or to apply water-based varnish offline. Excessive powder spraying on printed materials can affect the formation of a mirror surface and the contrast of particles, resulting in a weak effect.

• Ink Drying

Surface treatment must be carried out when the printing is thoroughly dried. Applying varnish on an undried ink layer may cause the varnish to cure incompletely and have no effect.

• Prepress Production

The pattern needs to be selected and processed. The parts that will have a frosted effect should be selected and filled with a solid color, while the glossy areas should be left blank. This should be done when outputting films and printing plates.

• Absorbency

Select paper with poor surface absorbency. Paper with strong absorbency will have an inconspicuous varnishing effect.

• Paper Quality

Select paper with good surface quality. Paper with poor surface coating may easily show color exposure.

• Additives

For reverse UV process products, generally add less UV curing agent, not exceeding 1% of the amount, as it is not conducive to the reverse UV effect.

• Paper Moisture Content

Choose materials with moderate moisture content. High moisture content can cause paper deformation and curling, while low moisture content can make the paper dry and brittle.

Printing Precautions:

• Printing plates need to be baked or UV-specific plates should be used.
• The printing press should not be directly exposed to sunlight.
• The workshop temperature should be maintained between 20-25 degrees.
• After replacing the ink rollers, the roller clearance must be adjusted.
• Conduct tests for curing properties, adhesion, odor, etc. Uv Ink should not be printed on areas that come into contact with food.
• The fineness and coarseness of the texture, the feel, and the oiliness are related to factors such as the opening of UV lights before and after, printing speed, ink thickness and quality, printing pressure, and the flatness of the paper:

The effect of opening UV lights before and after: If UV lights are turned on after OP varnish and before varnish, the texture will have a frosted feel, with obvious patterns and a white effect, and the sand eyes (areas where varnish is not exposed) will not be visible (dry and wet reaction); if UV lights are turned on at the delivery end, the texture will have an oily feel, with an inconspicuous frosted feel, and the sand eyes will be more visible (wet and wet reaction).

The effect of printing speed: Faster speed results in coarser texture and larger sand eyes; slower speed results in finer texture and smaller sand eyes.

The effect of ink thickness: Thicker ink results in finer texture; thinner ink results in coarser texture.

Different ink qualities and brands will have different effects.

Different printing pressures will have different effects.

Different surface flatness of the printed material will have different effects: better surface flatness results in more obvious texture; poorer surface flatness results in less obvious texture.

• Reverse UV varnish - is divided into surface varnish and base varnish; base varnish is the ink roller varnish, and surface varnish is the varnish that passes through the varnish seat.
• Printing press - only a printing press with a varnish seat can be used.

Film Output Precautions:

• When creating files, it is necessary to perform trapping processing. For frosted files, enlarge by 0.3mm (mainly depending on the precision of the equipment).
• Do not choose small text or small patterns. Extremely small fonts are prone to blurring, and the font size should not be less than 10-point. Lines should be greater than 2mm.
• Reverse white lines must be greater than 0.5mm; reverse white fonts should be greater than 6-point font, bold.

Reverse Varnishing Precautions:

• The printed material must be completely dried or cured.
• The OP varnish must be completely cured.
• The printing press speed should be at a speed that allows the UV light to operate at full power.
• The amount of UV varnish applied: 150L/IN - 200L/IN.
• The compatibility between the applied UV varnish and OP varnish.
• The power level of the printing press UV curing system.
• The surface smoothness and gloss of the printed material.
• The design of colors and lines.

Precautions for Reverse UV Process Products:

• For reverse UV process products, the material must be PET light gold and silver cards, not aluminum foil type gold and silver cards, because the aluminum foil gold and silver cards are prone to burst the aluminum foil film during啤 The dyne value of the surface of the gold and silver film must reach 40 to ensure that there are no problems with the reverse UV process, and no color bursting or ink dropping phenomena will occur.
• For reverse UV process products, the surface of the PET light gold and silver cards must be flat, because the better the flatness, the better the reverse UV process effect, and the finer the reverse texture.
• When designing reverse UV process products, if there are matte and glossy areas, the matte areas are printed with the printing seat and PS plates should be used. The files should be well prepared to handle the reverse UV process, but attention should be paid to the size of the fine lines, which should generally be more than 0.15mm. The glossy areas are covered with full UV varnish and do not require film output.
• Generally, reverse UV process products should avoid gold stamping processes. If gold stamping is necessary, it must be done before the reverse UV process. However, during gold stamping, it is essential to test the adhesion of the gold stamping paper. Use a 3mm adhesive pull test and an air pressure test on the printing press to check the adhesion of the gold stamping paper. If it comes off, it is not acceptable. It must be ensured that the gold does not come off. If the gold comes off, either change the gold stamping paper or increase the pressure to make it recessed, which will prevent the gold from coming off during printing.
• Generally, reverse UV process products should use less UV curing agent, not exceeding 1% of the amount, as it is not conducive to the reverse UVeffect; if there is a gold stamping process, the gold stamping must be done before the reverse UV process. During printing, a UV curing agent must be added, and it should have a slippery feel to prevent scratching or sticking during gold stamping. However, the glossy surface of the reverse UV process may not be achieved or may not turn out well, in which case a silk screen UV process must be added.
• For reverse UV process products, when gluing the edges, it is crucial to select the right adhesive. Gluing or adding a toothed knife should only be done halfway through; or if the glued edge is exposed without reverse UV varnish, it is generally difficult to achieve this effect. To do so, one might need to cut the rubber blanket or use a paper pad under the rubber blanket, but this is quite challenging to get right. During imposition, try to align the glued edges in a straight line; or sand the edges before applying glue; or choose a good UV adhesive, test it thoroughly before production, and increase the pressing time to ensure a good bond. It is best to use hot melt adhesive, but when operating in production, the timing must be quick and precise.

Process Identification: The differences between reverse UV process, frosted UV process, frosted embossing process, and silk screen snowflake UV:

• Reverse UV process: The surface is glossy and has an oily feel, and it can be easily scraped off with a blade; it is a printing UV process.
• Frosted UV process: The surface has a whitish effect and a frosted feel, and it can be easily scraped off with a blade; it is a silk screen UV process.

Frosted embossing process: The surface has a matte effect and a frosted feel, and it cannot be scraped off with a blade; it is an embossing machine process. The method to distinguish between the three processes of reverse UV, frosted UV, and frosted embossing: First, scrape with a blade: if it can be scraped off, it is either a reverse UV or frosted UV process; if it cannot be scraped off, it is a frosted embossing process. The difference between reverse UV and frosted UV is to observe the surface appearance: if there is a whitish effect, a sandy feel, and the gloss is not bright, it is a frosted UV process; if the surface is glossy and has an oily feel, it is a reverse UV process.