Flexo print guide by Gulzar Hussain

FLEXO PRINTING

DEFINITION OF FLEXO PRINTING: Flexographic printing is a printing technique that has a flexible printing plate, uses a variety of inks, prints on a variety of materials, and can be linked to various post-presses.

A BRIEF DESCRIPTION OF THE FIGURE ABOVE: In the above figure, the ink is supplied to the doctor chamber by the motor and the supplied ink is cut by the blade. The ink remaining in the cell of the Anillox roller is transferred to the printing plate and the transferred ink is printed on the printing paper passing between the plate passing tanks.

PRINCIPLE OF INK TRANSFER: The flexible printing plate (the resin plate) is embossed with embossed image, which is a dot, which contains the ink in the cell of the Anilox Laura which contains ink several times smaller than this dot.

FLEXOGRAPHIC PRINTING Flexographic printing is the only letterpress process that is still showing growth, mainly in packaging, label, and newspaper printing. The main feature of flexographic printing is the use of flexible printing plates. Flexo printing is a typographic process that is growing in packaging, labeling and newspaper printing. A key feature of flexo printing is the use of relatively soft and flexible printing plates compared to printing plates used for book printing. It is possible to print on a wide range of absorbent and non-absorbent printing substrates. The principle on which a flexographic printing unit works is illustrated in figure 1.3-9. It can print on a wide range of absorbent and nonabsorbable printing paper by using a flexible (soft) printing plate suitable for printing paper and a suitable ink (low viscosity). The low-viscosity ink is transferred to the printing plate via a roller that is evenly screened with cells, the so-called screen roller / anilox roller (screen width 200-600 lines / cm, ceramic or hard chromed metal surface). The rubber or plastic plate is attached to the printing plate cylinder. Ink is transferred to the printing substrate by the impression cylinder. The use of a blade (together with the ink supply system) on the screen roller has a stabilizing effect on the printing process even from filling the cells on the screen roller. Low-viscosity inks are inked in very fine cell pockets on the so-called screen roller or anilox roller (screen 200-600 lines / cm, ceramic or hard chrome plated metal surface) The ink is transferred to the resin plate (printing plate). Rubber or elastic resin plate is attached to the plate cylinder. Ink is applied between the plate passing-through pressure cylinder and the ink pressure by the thickness of the paper, whereby the ink is transferred again to the paper. By using the doctor blade (ink supply) on the screen roller, the ink is uniformly supplied to the cells of the screen or the Anilox roller. With rubber plates in exclusive use, only a moderate printing quality of solid motifs and rough line drawings could be achieved. "Nyloflex" from BASF and "Cyrel" from DuPont. It is used for printing on packaging, photopolymer wash-off plates, etc. for today's higher-quality requirements. These allow screen resolutions up to about 60 lines / cm. With the rubber lathes that were used in the early days, it was impossible to reproduce only rough lines, not solid motifs or fine lines, not halftones. In today's high-quality packaging printing, DuPont's BASF uses photoplymer plate cleaning devices such as "Nyloflex" and "Cyrel". It reproduces screen resolutions up to 60 lines / cm.

PLATEMAKING The first method uses a light-sensitive polymer . A film negative is placed on the plate, which is exposed to ultra-violet light. The polymer hardens where light passes through the film. The remaining polymer has the consistency of chewed gum. It is washed away in a tank of either water or solvent. Brushes scrub the plate to the "washout" process. The process can be different depending on whether the solid sheets of photopolymer or liquid photopolymer are used, but the principle is still the same. The plate is washed out of the orbital washout unit on a sticky base plate. The plate is washed out in a mixture of water and 1% dishwasher soap, at a temperature of approximately 40 Â° C. The unit is equipped with a dual membrane filter. With this environmental burdening is an absolute minimum. The membrane unit separates photopolymer from the washout water. After addition of absorbent gelatine for example, the photopolymer residue can be disposed of as standard solid waste together with household refuse. The recycled water is re-used without any detergent. [4] The first way to make a plate is to use a polymer that is sensitive to light. Place a negative film on the plate and expose it to ultraviolet light. Ultraviolet light passes through the film and the polymer is cured. It is washed out by putting lightly unbreakable part of ductility into water or a bottle containing a solvent bottle. Rinse the plate using a brush to promote cleaning. This process may vary depending on whether it is a liquid photopolymer or a photopolymer of a solid sheet. But the principle is the same. The plate to be cleaned is fixed to the orbital wash unit on the sticky base plate. The plates are cleaned in a mixer with water and a 1% dishwasher soap that maintains about 40 degrees. This washing unit consists of a filter with two membranes. Thus, the environmental burden can be minimized. The Melbine unit separates the photopolymer from the washed water. For example, the addition of gelatin to form a solid form can be used to dispose of photocopolymer residues as household waste and standard solid waste. The regenerated water can be reused without adding any detergent.

MANUFACTURING PROCESS OF RESIN PLATE

The second method uses a computer-guided laser to etch the image onto the printing plate. Such a direct laser engraving process is called digital platemaking. Companies such as AV Flexologic, Esko, Polymount and Screen from The Netherlands are market leaders in manufacturing this type of equipment. The second method is to use a computer controlled laser to etch the image on the printing plate. This process of direct laser engraving is called digital plate. AV Flexologic, ESCO, Dutch Polymount and screen are the market leaders in creating such equipment.

PLATEMAKING For printing, we have a printing press. We have a printing press. It can be used to copy, print, or print any type of document. To ensure an accurate picture is made, mounting marks are made on the flexographic plates. These mounting marks can be microdots (down to 0.3 mm) and / or crosses. Special machines are made for these plates.

PRINTING A flexographic print is made by creating a positive mirrored master image as a 3D relief in a rubber or polymer material. Flexographic plates can be created with analog and digital platemaking processes.The image areas are raised above the non-image areas on the rubber or polymer plates. The ink is transferred from the ink tank which is partially immersed in the ink tank. Then it transfers to the anilox or ceramic roll (or meter roll) whose texture is a special amount of ink since it is covered with thousands of small wells or cups. (the number of cells per linear inch can vary according to the type of print job and the quality required). [5] To avoid getting a final product with a smudgy or lumpy look, it must be ensured that the amount of ink on the printing plate is not excessive. This is achieved by using a scraper, called a doctor blade. The doctor blade removes excess ink from the anilox roller before inking the printing plate. The substrate is finally sandwiched between the plate and the impression cylinder to transfer the image. [6] The sheet is then fed through a dryer, which allows the inks to dry before the surface is touched again. If a UV-curing ink is used, the sheet does not have to be dried, but the ink is cured by UV rays instead.

BASIC PARTS OF THE PRESS • • • •

Unwind and infeed section - The roll of stock must be held under control. Printing section - Single color station including the fountain, anilox, plate and impression rolls. Drying station - High velocity heated air, specially formulated inks and an after-dryer can be used. Outfeed and rewind section - Similar to the unwind segment, keeps web tension controlled.

OPERATIONAL OVERVIEW 1. FOUNTAIN ROLLER The fountain roller transfers the ink to the second roller, which is the anilox or ceramic roller.

2. PLATE CYLINDER The plate cylinder holds the printing plate, which is soft flexible rubber. Sticky 2-way tape is used to mount the plate to the plate cylinder.

3. DOCTOR BLADE The doctor blade scrapes the anilox roll to insure that the amount of ink delivered is only contained within the engraved cells. Doctor blades have predominantly been made of steel but advanced doctor blades are made of polymer materials.

4. IMPRESSION CYLINDER The impression is the pressure applied to the plate cylinder, where the image is transferred to the substrate.

5. ANILOX (OLD) OR CERAMIC (MODERN) ROLLER This is what makes flexography unique. The anilox or ceramic roller meters have the same thickness and thickness. It has engraved cells that carry a certain capacity of inks that can only be seen with a microscope. These rollers are responsible for transferring inks to the flexible plates that are already mounted on the Plate Cylinders 12

FLEXOGRAPHIC PRINTING INKS The nature and demands of the printing process and the application of the printed product determine the fundamental properties required of the flexographic inks . Measuring the physical properties of inks and understand how these are affected by the choice of ingredients. Formulation of inks requires a detailed knowledge of the physical and chemical properties of the raw materials composing the inks, and how these ingredients affect or react to each other as well as the environment. Flexographic printing inks are primarily formulated to remain compatible with the wide variety of substrates used in the process. Each formulation component will fulfill a special function and the proportion and composition will vary according to the substrate.There are five types of inks that can be used in flexography: solvent-based inks, water-based inks, electron beam curing inks, ultraviolet curing inks and two-part chemically- isocyanate reactions, although these are uncommon at the moment. [7] Water based flexo inks with particle sizes below 5 Îźm may cause problems when deinking recycled paper.

Ink controls The ink is controlled in the flexographic printing process by the inking unit. The inking unit can be either fountain roll system or doctor blade system. The fountain roll system is a simple old system, so if there is too much or too little ink, this system would probably not control a good way. The doctor blade inside the anilox / ceramic roller uses cell geometry and distribution. These blades insure that the cells are filled with enough ink. [2]

PRESSES STACK PRESS Color stations stack up vertically, which makes it easy to access. This press is able to print on both sides of the substrate.

CENTRAL IMPRESSION PRESS All color stations are located in a circle around the impression cylinder. This press release can only be printed on one side. Advantage: excellent registry

IN-LINE PRESS Color stations are placed horizontally. This press prints on both sides, via a turnbar. Advantages: Can print on heavier substrates, such as corrugated boards.

APPLICATIONS Flexo has an advantage over lithography in that it can use a wider range of inks, water based inks, and a variety of different materials like plastic foil, acetate film, brown paper, and other materials used in packaging. Typical products printed using flexography include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, flexible plastics, self-adhesive labels, disposable cups and containers, envelopes and wallpaper. In recent years there has also been a move towards laminates, where two or more materials are bonded together to produce new material with different properties than either of the originals. A number of newspapers now eschew the more common offset lithography process in favor of flexo. Flexographic inks, like those used in gravure and unlike those used in lithography, generally have a low viscosity . This enables faster drying and as a result, faster production, which results in lower costs. Printing press speeds up to 600 meters per minute (2000 feet per minute) are achievable with modern technology high-end printers. Flexo printing is widely used in the converting industry for printing plastic materials for packaging and other end uses. For maximum efficiency, the flexo presses produce large rolls of material that are then slit down to their finished sizes on slitting machines.