Pad Printing Inks

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What is pad printing inks?
Over the period, pad printing is improving.
The main purpose of the ink is to mark or to decorate the parts and product. Inks are made with various combinations of oils, solvent, raisins and pigment. The raisins also called as a binder is a very important component of the ink as properties like adhesion, resistance to abrasion and scratch are largely depends upon them. Pigments are important to give exact shade, brightness and opacity to the ink. Solvents play a role to maintain the viscosity of the ink.

The pad printing inks are more opaque and aggressive in nature. As the plate etching depth is normally in between 20 to 30 microns. The inks form a very thin layer on the product. So in order to be visible from background material colour, the ink should have more pigment, that even with a thin layer, the print stands out.
Also, solvent and raisins used should be such that, they make perfect adhesion on the product with minimal film layer.
Pad printing inks types.
Pad printing inks India has major two types
a) Oil-based inks
b) Solvent-based inks
Recently UV based inks are being used for some of the applications.
Oil-based inks.
Mostly in the past and in some applications presently, oil-based ink will solvent combination are used for pad printing application.
The advantage of this ink is,
1) Quantity of printing is very sharp.
2)  As it dries for a longer period the ink becomes residents to most chemicals.
3) The finish for the ink is high gloss.
4) Cleaning is easily possible if get misprinted.
As the ink contains oil initial drying time is more. Hence may not be suitable for wet-on-wet
printing.

Solvent-based inks
These inks are developed to overcome the problems faced by prints to do wet-on-wet printing. as the solvent dries faster than oil the print becomes touch dry immediately, this makes possible to print the second colour immediately. The main advantage of this ink to print multiple colours at a time, and complete the job in one go.
Ink manufacturers matched all other parameters and now this type of ink is more popular worldwide.

Selecting pad printing ink.

While selecting the inks following factors are important.

1) Application of pad printing ink
In which industry the ink is going to be used.
Automobile, Medical device, food, pharma, ecological, toys each one has its own specifications.

2) Materials
Each industry use different materials or combinations of materials. Some times base material is different and coating for decoration or protection is of a different material.
It can be identified in the major four categories.
A) Plastics: ABS, PVC, SAN, PMMA, Polyester, Polystyrene, Polysorbate
B) Glass, Metals and parts coated with nickel or chrome plating.
C) Other plastics which requires pre-treatment or post-treatment. Such as HDPE, PP LDPE, Polyamide, Polyacetal, Thermoplastic elastomers
D) Other materials like Rubber, wood, leather, cotton, ceramic, Silicon rubber.

4) Testing parameters of the print.
Different industries use different testing procedures on the prints to check the adhesion, colour fade properties, rub resistance, mechanical resistance, Tape Taste, Scratch Test, Abrasion Taste, Alcohol Test
Ink is selected in order to pass the specific desired tests.

5) Compliance with world standards.
Many industries also require inks to comply with certain norms or standards set by various government, industries or trade associations.
Such as RoHS, EuPIA, GADSL, EN 71/3, REACH USP CLASS VI, cGMP GAMPS, FDA etc.

6) Colour Shade.
Ink manufacturers produce ink shades which are standard in colour. Such as Black, White, Red, Yellow, Blue etc. These are used by most of the printers for printing, they also do mixing and matching as per requirement. But many companies, particularly who have spread internationally required the same shade to be printed on their products worldwide. In that case, Pantone and RAL inks shade systems come to help to get the exact shade.
Such information should be kept in mind while selecting the pad printing inks.

7) One or Single component ink and Two component ink

A) Single component ink has the property to bond with material ( have good adhesion) without any other additional chemicals also called hardener.
This ink has a long shelf life and can be used directly for the container. This inks can be kept overnight while production runs.

B) Two-component inks.
Ink and hardner
The raisins in the ink have a chemical reaction with hardner which has to be mixed just before the printing. These inks last normally for six to eight hrs. After that cross-linking takes place and they are no longer usable. So the production is required to be completed within its effective period.
The main advantage of this type of ink is to have good adhesion on substrates which are difficult to print. Substrates like Glass, Metals, Dalrin, Silicon require this type of inks.
These inks must be printed after mixing the hardener. Without hardner they don’t dry completely. While using this inks utmost care require to mixed the ink and hardner in exact proportion as recommended by the manufacturer.
Special care is required when hardner is to be stored as if comes with air or moisture contact it becomes hard and can’t be used.

Pad Printing Ink