Basic knowledge of conventional offset printing inks

Conventional offset printing ink is composed of several key components, each serving a specific purpose to ensure the ink performs well during the printing process and produces high-quality prints. Here is a breakdown of the typical composition of conventional offset printing ink:

Main Components

Pigments:

• Function: Provide color and opacity.
• Types: Organic and inorganic pigments.
• Examples: Carbon black for black ink, titanium dioxide for white ink, and various other pigments for different colors.

Binders (Resins):

• Function: Bind the pigment particles together and to the substrate.
• Types: Natural resins (e.g., rosin), synthetic resins (e.g., alkyd resins, phenolic resins).
• Properties: Affect the gloss, adhesion, and durability of the printed material.

Solvents:

• Function: Dissolve the binders and control the viscosity of the ink.
• Types: Mineral oils, vegetable oils (e.g., linseed oil, soybean oil).
• Properties: Evaporate during drying, impacting drying time and ink behavior on the press.

Additives:

• Function: Enhance specific properties of the ink.
• Types: Waxes (for rub resistance), driers (to speed up drying), plasticizers (to improve flexibility), stabilizers (to prevent settling), and surfactants (to improve wetting).
• Properties: Tailor the ink for specific printing conditions and requirements.

Detailed Breakdown

Pigments:

• Typically constitute 5-30% of the ink.
• Provide the desired color and contribute to the opacity and permanence of the print.

Binders (Resins):

• Usually make up 15-50% of the ink.
• Form a continuous film that holds the pigment in place and adheres to the printed surface.
• Common resins include rosin, alkyds, phenolics, and acrylics.

Solvents:

• Comprise 20-60% of the ink.
• Influence the flow properties and drying behavior.
• Conventional inks often use mineral oils, but vegetable oils are becoming more popular for environmental reasons.

Additives:

• Generally account for 1-10% of the ink.
• Waxes improve scuff and abrasion resistance.
• Driers (e.g., cobalt and manganese compounds) accelerate oxidation and polymerization of the oils.
• Plasticizers enhance flexibility and prevent cracking.
• Surfactants improve the spreadability and leveling of the ink on the substrate.

Example Formulation

A typical formulation for a conventional offset printing ink might look like this:

• Pigment: 20%
• Binder: 25%
• Solvent: 50%
• Additives: 5%

These components work together to ensure that the ink performs well during the printing process, adheres properly to the substrate, and produces vibrant, durable prints.