Monomers and Oligomers for UV/EB Energy Curing

A set of flashcards covering key concepts, materials, formulation components, performance attributes, and safety considerations for UV/EB energy-curable monomers and oligomers.

What are the two main chemistry types used in UV/EB energy curing?

Free-radical polymerization and cationic polymerization.

In free-radical UV/EB curing, polymerization proceeds through which functional groups?

Through carbon–carbon double bonds, most commonly acrylate (and sometimes methacrylate or vinyl) groups.

In cationic UV/EB curing, polymerization proceeds through which groups?

Epoxy groups, typically cycloaliphatic epoxies.

List the five essential components of a typical UV free-radical coating formulation.

Acrylated resin(s), monofunctional monomer(s), multifunctional monomer(s), additives, and a photoinitiator package.

What role do monofunctional monomers play in a UV formulation?

They reduce viscosity and add flexibility to the cured network.

What is the primary purpose of multifunctional monomers in a UV formulation?

To reduce viscosity while supplying crosslink density for faster cure and greater hardness.

Which curing process uses electrons instead of photons and therefore needs no photoinitiator?

EB (electron-beam) free-radical curing.

Why are oligomers considered the “workhorse” of a UV/EB formulation?

They provide most of the mechanical, chemical, and overall performance properties of the cured film or ink.

What is the typical molecular-weight range of acrylated oligomers used in UV/EB systems?

Approximately 500–5,000 Daltons.

What functionality range (number of acrylate groups) is common for UV/EB oligomers?

Typically 2–10 or more acrylate groups per molecule.

Name two oligomer residuals that can affect performance and/or labeling.

Inhibitors and catalysts.

Why are bisphenol-A (BPA) epoxy acrylates under market scrutiny?

Potential BPA migration makes them a concern for food packaging and retailers such as IKEA.

Give two key advantages of basic BPA epoxy acrylates.

They are economical and provide very fast cure response.

What modification to epoxy acrylates improves pigment wetting but slows cure speed?

Fatty-acid modification.

Epoxidized vegetable oils are BPA-free epoxy acrylate alternatives. Name one trade-off.

They provide greater flexibility but lower hardness and chemical resistance.

What advantages do aliphatic urethane acrylate oligomers offer?

High flexibility, toughness, and non-yellowing weatherability.

Which isocyanate yields non-yellowing aliphatic urethane acrylates?

Isophorone diisocyanate (IPDI).

Which diisocyanate often leads to yellowing aromatic urethane acrylates?

Toluene diisocyanate (TDI).

List four compositional variables used to tune urethane acrylate properties.

Polyol type, diisocyanate type, functionality, and urethane content (also MW distribution, HAA type, inhibitor, catalyst).

How does amine modification of acrylated polyether oligomers affect surface cure?

It decreases oxygen inhibition and increases cure speed.

Why are acrylated amine oligomers generally avoided in lithographic inks?

They are incompatible with the acidic fountain solutions used in litho printing.

Why are non-acrylated oligomers sometimes added to UV formulations?

To minimize shrinkage and improve adhesion.

In waterborne UV-PUDs, which component provides colloidal stability and boosts adhesion?

The diol acid segment containing carboxylic acid groups.

Which system—100 % solids UV or UV-PUD—has the higher crosslink density after curing?

The 100 % solids UV system.

What is the principal oligomer for most cationic curing systems?

Cycloaliphatic diepoxide.

During stress/strain testing of cured films, name two key parameters measured.

Tensile strength and percent elongation (modulus is another).

Define a reactive diluent.

A low-viscosity, polymerizable monomer added to reduce formulation viscosity and become part of the cured network.

Give two reasons why monomer choice affects weatherability.

Different monomers vary in UV stability/yellowing and alter flexibility, which impacts chalking or cracking.

How do monofunctional monomers typically affect cure speed relative to multifunctional ones?

They generally lower cure speed.

Why are some monofunctional monomers unsuitable for food-contact coatings?

Their lower reactivity can leave higher residual uncured monomer.

Which monofunctional monomer showed the fastest cure speed (>200 fpm) in the data provided?

N-vinyl-2-pyrrolidone (NVP).

Which difunctional monomer had the highest listed cure speed (200 fpm)?

1,6-Hexanediol diacrylate (HDDA).

Name a trifunctional monomer known for excellent pigment wetting.

Glycerol propoxy triacrylate (GPTA or OTA-480).

Increasing monomer functionality generally has what effect on shrinkage and hardness?

Both shrinkage and hardness increase with higher functionality.

Which monomer functionality class typically gives the greatest flexibility?

Monofunctional monomers.

What concentration of radical scavenger inhibitors is typically used to prevent premature polymerization?

About 200–1000 ppm.

Identify two common inhibitors used in (meth)acrylate systems.

Hydroquinone (HQ) and hydroquinone monomethyl ether (HQMME).

How do oxygenated inhibitor systems generally affect UV cure speed?

They have little or no effect on cure speed.

State one key health & safety characteristic of (meth)acrylates.

They are generally non-toxic but can irritate skin and eyes.

List three pieces of personal protective equipment recommended when handling (meth)acrylates.

Safety glasses, protective gloves, and a lab coat.

What two principal roles do photoinitiators serve in a UV formulation?

They absorb UV light and generate free radicals to start polymerization.

Why are photoinitiators unnecessary in an EB formulation?

High-energy electrons directly create the free radicals required for polymerization.

Name two solvent types commonly used to reduce viscosity in solvent-borne UV systems.

Ketones and acetates (alcohols are also used).

What property makes propoxylated di- or tri-functional monomers attractive for flexible coatings?

They lower surface tension and add chain flexibility, improving substrate wetting.

Why might chlorinated polyester oligomers be phased out despite their good adhesion?

Regulatory pressure against chlorine-containing materials.