How to Choose the Right Ink for Different Materials?

Solvent-Based Inks (MEK / Acetone)

How they work: The solvent evaporates or is absorbed into the substrate, leaving the pigment or dye bound to the surface. MEK-based inks dry fastest due to high vapor pressure.

Best for: Non-porous surfaces — plastics (PE, PP, PET, PVC), metal, glass, coated paper, rubber, cables.

Limitations: Strong odor, flammable, may attack or craze certain plastics (polycarbonate, acrylic, polystyrene).

Alcohol-Based Inks (Ethanol / IPA)

How they work: Milder solvents that dry through evaporation. Slower drying than MEK but much gentler on sensitive substrates.

Best for: Porous and semi-porous surfaces — paper, cardboard, wood, some coated papers, and plastics sensitive to MEK attack.

Limitations: Poor adhesion on non-porous surfaces like untreated glass or metal. Slower line speeds.

Water-Based Inks

How they work: Uses water as the primary carrier. Dries primarily through absorption into the substrate, with some evaporation.

Best for: Highly porous surfaces — corrugated cardboard, uncoated paper, bread bags, egg cartons, some textiles.

Limitations: Very slow drying on non-porous surfaces. Freeze-sensitive. Requires careful pH and conductivity control. Not suitable for non-absorbent substrates.

Pigment-Based Inks

How they work: Solid pigment particles (typically carbon black) suspended in the carrier. The carrier evaporates, leaving pigment on the surface.

Best for: Applications requiring high UV resistance, heat resistance, or rub resistance — automotive parts, outdoor cables, industrial piping, steel, high-temperature environments.

Limitations: Pigment settling over time requires ink circulation and agitation. More expensive than dye-based inks.

Low-Migration / Food-Grade Inks

How they work: Specially formulated with low-migration photoinitiators and pigments that comply with food contact regulations (EU 10/2011, FDA 21 CFR, Swiss Ordinance).

Best for: Food packaging — plastic films, foil, coated paper used for direct food contact or where ink may migrate through packaging.

Limitations: Strict supply chain controls required. Higher cost. Limited color options (typically black or white only).

Plastics

Plastics are the most challenging category because surface energy varies widely:

• Polyethylene (PE) / Polypropylene (PP): Low surface energy. Requires MEK or acetone-based solvent ink. Surface treatment (corona, flame, plasma) is often needed for adhesion.
• PET / Polyester: Moderate surface energy. Standard solvent inks work well. Pigment inks for high-temperature resistance.
• PVC / Vinyl: Good adhesion with most solvent inks. Some plasticizer migration can cause ink to soften over time.
• Polycarbonate / Acrylic: High risk of solvent attack (crazing/cracking). Use alcohol-based or specialized low-aggression inks.
• Nylon / Polyamide: Absorbs some solvents. Standard solvent or alcohol inks work but may require heat resistance testing.

Metal and Glass

Non-porous, high-surface-energy materials. Adhesion relies entirely on the ink's ability to wet the surface and form a mechanical or chemical bond:

• Aluminum, steel, tin: MEK/acetone solvent inks for fast drying and high adhesion. Pigment inks for outdoor/abrasion resistance. Pre-cleaning to remove oils is critical.
• Glass: Requires specialized glass inks with adhesion promoters. Standard solvent inks will wipe off easily. White or colored pigment inks for contrast on transparent surfaces.
• Powder-coated surfaces: Challenging due to low surface energy of the coating. Often requires corona treatment or specialized high-adhesion inks.

Paper and Cardboard

Porous substrates that absorb ink. The choice depends on coating and speed:

• Uncoated paper / corrugated: Water-based or alcohol-based inks. Fast absorption, no drying issues. Lowest cost option.
• Coated paper / glossy: Coating reduces absorption. Use MEK/acetone solvent inks for surface drying. Alcohol inks may smear.
• Kraft paper: Highly absorbent. Water-based inks work well but may cause fiber swelling. Solvent inks give sharper characters.

Rubber and Elastomers

Tires, rubber hoses, silicone gaskets. The ink must flex with the substrate without cracking:

• Natural rubber / EPDM: Fast-drying solvent inks with plasticizer-resistant formulation.
• Silicone: Extremely low surface energy. Requires specialized silicone-marking inks or surface treatment (corona/UV). Standard inks will bead up.
• Tire rubber (carbon-filled): High-temperature pigment inks that withstand vulcanization and road wear.

Cables and Wire Insulation

High-speed production with specific durability requirements:

• PVC insulation: Standard solvent inks. Must resist plasticizer migration.
• XLPE (cross-linked polyethylene): High-temperature pigment inks for power cables that undergo heat curing.
• PTFE / Teflon: Requires specialized etching treatment + high-adhesion ink. Standard inks will not bond.
• Fiber optic coatings: Low-aggression alcohol-based inks to avoid damaging the coating.

Food Packaging Materials

Regulatory compliance is the primary driver:

• Plastic films (BOPP, PET, PE): Low-migration inks required for direct food contact or where ink is on the non-printed side.
• Aluminum foil: Low-migration solvent inks with high heat resistance for retort and sterilization processes.
• Coated paperboard: Low-migration or standard inks depending on whether the printed area contacts food.

Surface Energy (Wettability)

For ink to adhere, its surface tension must be lower than the substrate's surface energy. Measured in dynes/cm. Low-energy materials (PE ~30 dynes/cm, PP ~29, silicone ~22) require either surface treatment or specially formulated inks. A simple dyne pen test can determine if your substrate needs treatment.

Drying Speed and Line Speed

The ink must dry before the product reaches the next handling point (packing, stacking, conveying). High-speed lines (200+ products/min) on non-porous substrates demand fast-evaporating MEK or acetone inks. Porous substrates give more flexibility with alcohol or water-based inks. Always match ink drying time to your line speed — wet codes smudge and get rejected.

End-Use Environment

Consider what the printed product will encounter:

• Heat: Baking, sterilization, hot-fill → pigment or heat-resistant inks
• Moisture/Chemicals: Condensation, washing, chemical exposure → solvent or pigment inks with high chemical resistance
• Abrasion: Shipping, handling, friction → fast-drying solvent inks or pigment inks with rub resistance
• UV exposure: Outdoor storage, sunlight → pigment inks (carbon black is naturally UV-resistant)
• Food contact: Direct or indirect → low-migration inks only

Substrate Contamination

Oils, dust, mold release agents, antistatic coatings, and moisture on the substrate surface are leading causes of ink adhesion failure. In many cases, the "wrong ink" diagnosis is actually a contamination problem. Pre-cleaning with isopropyl alcohol or using in-line corona treatment resolves most of these issues.

Color and Contrast

Black ink is standard for most applications, but white, blue, red, yellow, and green are available. White pigment ink is essential for dark substrates (black cables, dark plastics, colored metal). Ensure the ink opacity is sufficient for your substrate color — a single pass of white ink may not be enough on dark backgrounds without special formulation.

Regulatory Compliance

Different industries and regions have specific requirements:

• Food packaging: EU 10/2011, FDA 21 CFR 175.300, Swiss Ordinance
• Pharmaceuticals: EU GMP, FDA cGMP, traceability requirements
• Automotive: OEM-specific specifications for solvent resistance and durability
• Electronics: RoHS, REACH, low-halogen requirements
• Cosmetics: EU Cosmetic Regulation, FDA Cosmetic Labeling

Using MEK ink on polycarbonate or acrylic

MEK aggressively attacks polycarbonate and acrylic, causing visible crazing (micro-cracks) that weakens the material and ruins appearance. Always use alcohol-based or specially formulated low-aggression inks for these plastics.

Assuming "solvent ink" means it works on all plastics

PE and PP require fast-evaporating ketone-based solvents (MEK, acetone). Slower solvent inks may bead up or take too long to dry on these low-energy surfaces. Each plastic type has different solvent compatibility.

Ignoring surface contamination

Many ink adhesion failures blamed on the ink are actually caused by invisible mold release agents, antistatic coatings, or process oils on the substrate. A simple IPA wipe test can reveal whether contamination is the issue.

Overlooking line speed constraints

An ink that works perfectly at 50 products/min may fail at 200 products/min because the drying time is too long. Always test at actual production speed, not in slow-motion lab conditions.

Choosing ink based solely on price

The cheapest ink that "sort of works" will cost more in the long run through rejected products, line stoppages to clean printheads, and customer complaints about illegible codes. The correct ink for your substrate is always the most cost-effective choice.