Definition - What does Hardener mean?

Hardener is a substance mixed with paint or other protective covering to make the finish harder or more durable. It is a curing agent for epoxies or fiberglass.

An agent which does not enter into the reaction is known as a catalytic hardener or catalyst. A reactive curing agent or hardener is generally used in much greater amounts than a catalyst, and actually enters into the reaction.

Hardener is usually classed as a corrosive, and as an irritant when in contact with the skin or by inhalation.

Corrosionpedia explains Hardener

Hardener is a curing agent for epoxy resin. Epoxy resins require a hardener to initiate curing. It is also called the catalyst, the substance that hardens the adhesive when mixed with resin. It is the specific selection and combination of the epoxy and hardener components that determine the final characteristics and suitability of the epoxy coating for a given environment.

In general, uncured epoxy resins have poor chemical, mechanical and heat-resistance properties. However, good properties may be achieved by reacting the linear epoxy resin with suitable curatives to form three-dimensional cross-linked thermoset structures known as curing. Curing of epoxy resins is an exothermic reaction, and in some cases produces sufficient heat to cause thermal degradation if not controlled.

Curing may be achieved by reacting an epoxy with itself or by forming a copolymer with polyfunctional curatives or hardeners. In principle, any molecule containing a reactive hydrogen may react with the epoxide groups of the epoxy resin. Common classes of hardeners for epoxy resins include:

  • Amines
  • Acids
  • Acid anhydrides
  • Phenols
  • Alcohols
  • Thiols

Optimum levels of a hardener are used to formulate epoxy coatings. The ratio differs from product to product. The use of an improper hardener may result in an undercatalyzed or overcatalyzed product. Many epoxy coatings require a specified induction time to fully compatibilize the epoxy resin and the hardener.

High-performance hardener is used to protect memory chips on a printed circuit board (PCB) laminate. A bisphenol novolac is utilized as a hardener to provide the high cross-link density with the glass fiber.

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