Learn Flexo Packaging Register Overprint Trapping

Learning flexo is fun, maybe for some people in Indonesia. Of course, the flexo printing technique, especially the CI type, sounds foreign. I'm only 6 years old getting to know flexo printing until this article was written, this poses a big challenge for me to know more about it. In this article I want to introduce flexo printing for those who want to learn flexo printing techniques. 

Initially Flexo printing used rubber (like a Stamp) which was then pressed to print the image. The first flexo printing machine was made in 1980 in England by Bibby Baron and Sons, at the same time the same machine was also made in Germany which is named Aniline because it uses Aniline ink.

In 1950 Franklin Moses proposed that the Aniline printing process be renamed be Flexo print.

For the next 30 years the flexo machine is still considered a printing technique for quality low so that it is generally used to print corrugated boxes. But with the discovery of UV ink and its drying, then flexo print using ink UV began to be used to print labels.

Basically the preparation for design and artwork for flexo printing is the same as artwork design work for other printing systems, but there are some differences fundamentals that we must understand. To print flexo what we see on the computer screen and what we see in the proof, may not be the same as the final flexo print.

Proof is made only to see the layout (position of the layout).

A. TERMS IN FLEXO

1. TYPOGRAPHY

Considerations for font size, object ex and line thickness

2. LINE REVERSE / KNOCKOUT

Line object, it is recommended to be limited to no more than 1 color for color

the arrangement.

3. DROP SHADOW

4. REGISTER

5. OVERPRINT

6. CONVERTING TYPE TO OUTLINE

7. TRAPPING

8. DIE LINE

B. HALFTONE SCREENS

Halftone is a collection of small dots that when viewed from a distance will appear

like a stream of gray or colored smelly shadows. The number of the dots must be

enough to be boxy. For color images, there is a stack of dots

consisting of dot colors cyan, magentha, yellow and black (CMYK). The higher the screen

frequency (the more lines per inch), the smoother the image will be. For flexo

quality can be used up to 175 lpi. The defaults are 100, 120, 133, 150 and 175 lpi.

Dot is a dot (circle) that is used to form halftone printing.

The shape of the dot also varies, including round, square, elliptical and octagonal.

In general, a round pacifier is widely used.

The things that cause dot enlargement:

. Excessive ink absorption

. The ink spreads to the material because the viscosity of the ink is too high, making it difficult

spread

. Over-pressed photopolymer (flexo must be with “kiss printing”

. Machine is not good

C. Ink

Flexo ink comparison:

1. Flexo Waterbased Ink

Excess :

- Does not require Exhaust

- Does not cause air pollution

- Excellent absorption, low energy cost for absorbent materials

- No need for explosion proof equipment

- Does not pose a problem for transportation (harmless)

Deficiency :

- If printed on plastic film, it can cause problems with sticking

as well as drying. But for modern machines this problem has been solved.

- Less shiny

- Sometimes foamy

- Cleaning is quite difficult

2. Solvent based flexo ink

Excess :

- Easy to use (set up, cleaning)

- Dries quickly

- Good adhesion to plastic film

- High mechanical resistance

- Stable surface tension

- Anilox is easy to clean (compared to using waterbased inks)

Deficiency :

- Evaporation of solvents causes pollution (harmful to health)

- Air exhaust equipment is required and must be explosion-proof

- There are regulations for the use and storage of solvents and inks

3. UV flexo ink

Excess :

- Does not require Exhaust

- The ink does not dry on the machine

- No need for explosion proof equipment

- Very glossy (glossy)

Deficiency :

- The price of ink is expensive

- Requires a high enough energy, especially if using a cooling roll

- If the temperature changes, the viscosity will also change and can

cause discoloration especially special colors.

- Some materials do not stick well.

by Su-harto

Polymer Structure Polymerization Polycondensation Polyaddition

Most of the advantages and disadvantages of polymers depend on the size of the structure of the individual polymer molecules, the shape and size of the polymers and how they are formed. The characteristics of a polymer molecule are determined by its size, a feature that distinguishes it from other organic chemical compositions. Polymers are long chains of molecules, also called micromolecules or giant molecules, which are formed by polymerization, in other words by the interlocking and crosslinking of different monomers. Monomers are the basic building blocks of a polymer. The word mer comes from the Greek meros meaning part, indicating the smallest unit.

Polymer means many mers or units, generally a repetition of hundreds or thousands of times a chain-like structure. Most monomers are organic materials in which the carbon atoms are joined in covalent bonds with other atoms, such as hydrogen, oxygen, nitrogen, fluorine, chlorine, silicon and sulfur.

To form macromolecular bonds from each thermoplastic material molecule is done in three ways, namely:

a. Polymerization:

Bringing together several similar molecules to form a large molecule Polymerisate. The monomers in polymers can be linked in repeating units that lengthen and enlarge the molecules by a chemical reaction known as a polymerization reaction. Despite the many variations, the two basic processes are Condentation polymer and Polyaddition.

b. Polycondensation;

The bonding of several molecules to form large macromolecules through the process of separating one of the atoms to bind small molecules from water. From this process, a material called Polycondensate is formed

c. Polyaddition;

Namely the union of several basic molecules through the placement of several molecules without separation of the non-fixed parts. The material formed is called "Polyadducf. In this reaction an initiator is added to break the two bonds between the carbon atoms and start the bonding process by adding more monomers to build the chain. For example the Ethylene monomer bonds to produce a polymer known as Polyethylene .

The sum of the molecular weights of the mer-mers in the polymer chain is the molecular weight of the polymer. The higher the molecular weight in a given polymer, the greater the chain length. Since polymerization is a random event, the resulting polymer chains are not all the same length, but the resulting chain lengths are formed in a traditional distribution curve. We determine and express the average molecular weight of a polymer on a statistical basis by averaging. The distribution of the molecular weight distribution is referred to as the molecular weight distribution (MWD). Molecular weight and MWD have a strong influence on polymer properties. For example, fracture and impact strength, resistance to cracking, and viscosity in the liquid state all increase with increasing molecular weight. Most of the polymers traded have molecular weights between 10,000 and 10,000,000.

In some cases, it is easier to describe the size of a polymer chain in Degrees of Polymerization (DP), defined as the ratio of the molecular weight of the polymer to the molecular weight of the repeating unit. For example, Polyvinyl chloride ( PVC) has a mer weight of 62.5, so the DP of PVC which has a molecular weight of 50,000 will be 50,000 / 62.5 = 800. In the polymerization process, the higher the DP, the greater the polymer viscosity, or flow resistance, thus making it easier to formation and overall costs.

During polymerization the monomers are bonded together in a covalent bond, forming a polymer chain. Because of their strength, covalent bonds are also called primary bonds. In addition, polymer chains hold on to secondary bonds such as van der Waals bonds, hydrogen bonds and ionic bonds. Secondary bonds are weaker than primary bonds. In a polymer, the increase in strength and viscosity with molecular weight is partly due to the fact that the longer the polymer chain, the greater the energy required for secondary bonding.

If the repeating units of the polymer chain are of the same type, we call the molecule a homopolymer. However, two or three types of heavy monomers can be combined to obtain special characteristic advantages, such as improved strength and durability. Copolymer consists of two types of polymers such as Styrene-butadine, widely used for car tires. Terpolymer consists of three types such as ABS used for helmets, telephones.

Rotary screen printing an effective way of printing

Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil to receive a desired image. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink into the mesh openings for transfer by capillary action during the squeegee stroke. Basically, it is the process of using a stencil to apply ink onto another material whether it be t-shirts, posters, stickers, vinyl, wood, or any material that can keep the image onto its surface. Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance. Ink is forced into the mesh openings by the fill blade or squeegee and onto the printing surface during the squeegee stroke. It is also known as silkscreen, serigraphy, and serigraph printing. A number of screens can be used to produce a multicolored image or design.

Rotary screen printing - an effective way of printing

Screen printing is ideally suited wherever a high degree of coverage, precise detail and colour intensity are required to obtain a brilliant, high-quality image. Applying a coating allows special relief and other effects to be created. Scented coatings, thermochromatic inks and glitters are just a few examples of screen printing applications.

One particular feature of screen printing is its ability to produce what is known as the no-label look with transparent labels being applied to the packaging. Screen printing also enables Braille to be applied to any label. 

Gallus Rotascreen - performance package

Gallus Rotascreen is a performance package and our contribution to success for labelprinters:

• Gallus Screeny conventional screen printing plates 

• Gallus Screeny digital screen printing plates 

• Know-how transfer, training

• Application know how and combination printing (screen, flexo, offset, hotfoil etc.)

• Technology centre, product development

• Prepress devices

• Test equipment on Gallus site

• Production expertise plating and coating

Attractive illustrations using rotary screen printing in combination with other printing processes.

The Gallus Rotascreen performance package - complete support for the screen printer.