Resin: what it is, types, production and applications

Resin is the binder component of paint, coating, composite and adhesive formulations. It is the layer that forms the film, holds the pigment to the surface, and keeps the fibers together in a composite. A formulation's chemical resistance, flexibility, weather resistance and hardness are largely determined by the resin chosen.

What is resin?

Resin is a polymer or oligomer that exists as a viscous liquid or solid at room temperature and forms a continuous network structure when cured. Natural resins (pine gum, rosin, shellac) have been used throughout history as varnishes and glues; today, almost all resins used in industry are synthetic.

Three fundamental properties define a resin: functional group (epoxy ring, hydroxyl, carboxyl, acrylate double bond), molecular weight (which determines viscosity and film hardness), and crosslink density (which sets the balance between durability and flexibility after curing).

How is it produced?

Synthetic resins are mostly produced by step-growth polymerization (polycondensation) or chain polymerization.

• Polyester and alkyd resins: formed by the esterification of a polyfunctional alcohol with a diacid; the chain is extended by continuously removing the reaction water.
• Epoxy resins: obtained by the reaction of bisphenol A with epichlorohydrin under basic conditions; the resulting product carries epoxy rings at its end points.
• Acrylic resins: produced by free radical polymerization of acrylate and methacrylate monomers, either in solvent or in the aqueous phase (emulsion).
• Amino and phenolic resins: produced by the condensation of formaldehyde with urea, melamine or phenol.

Production is a process-control operation carried out in jacketed reactors, where temperature and the degree of reaction (acid value, epoxy equivalent) are monitored very closely; once the target value is reached, the reaction is stopped through cooling and dilution.

Types and varieties

Which sectors use it?

• Paints and coatings: resin is the "binder" phase of paint; pigment and filler are dispersed within this phase.
• Composites: holds glass and carbon fiber in the matrix; wind turbine blades, boat hulls, automotive panels.
• Adhesives and sealants: the base polymer of structural adhesives.
• Electrical–electronics: encapsulation, printed circuit board laminates, insulation.
• Construction chemicals: floor coatings, waterproofing, repair mortar modification.

Turkish market and production

Resin production in Turkey is concentrated mainly on alkyd, unsaturated polyester and acrylic emulsion lines; these three groups largely meet the domestic paint industry's demand from local supply. In epoxy resins and specialty resins, however, the import share is high. The prices of intermediates such as bisphenol A, phthalic anhydride and acrylic monomer, along with freight costs, directly determine the sector's margins.

Notable trends include: bio-based raw materials (vegetable-oil-derived polyols and alkyds), low-VOC and water-based systems, bisphenol-A-free epoxy alternatives (particularly in packaging linings with food contact), and recyclable composite matrices. Developments on these topics can be followed in the current news items below.

Technical specifications

Resins are defined in datasheets by a variety of different parameters; which figure is critical depends on the resin family.

In practice, two values are read together: Tg and crosslink density. A high Tg produces a hard and chemically resistant but brittle film; a low Tg means a flexible film that is prone to scratching. Formulations often strike a balance between these two extremes by blending two different resins.

Points to consider in selection and procurement

• Evaluate the resin together with the system, not in isolation. The same resin can yield a completely different film with a different hardener or additive package.
• Ask about batch consistency. Batch-to-batch variations in acid value, hydroxyl value and viscosity show up in the formulation as shifts in curing behavior.
• Run compatibility tests early. A new resin may not work well with an existing pigment, filler and additive package; flocculation and settling are most often revealed in shelf-life testing.
• Request the VOC and regulatory documentation. For a formulator exporting products, the ingredient declaration is as decisive as the safety data sheet.
• Pay attention to storage temperature. Some resins crystallize in the cold and must be reheated to recover; this information should be known before delivery.

Frequently asked questions

Are resin and polymer the same thing?

Every resin is a polymer or oligomer, but not every polymer is a resin. In industry, the term "resin" describes polymers that serve as the binder in a formulation and generally reach their final form through curing. A thermoplastic pellet (such as polyethylene) is a polymer but is not considered a resin in this sense.

Should epoxy or polyester resin be chosen?

If mechanical strength, adhesion and chemical resistance are the priority, epoxy is preferred; if cost and production speed are the priority, unsaturated polyester is preferred. In applications involving contact with seawater and chemicals, vinyl ester offers a balance between the two. Outdoors, both need to be protected with a topcoat against UV exposure.

What does a resin's curing time depend on?

It is determined by the type and ratio of hardener, ambient temperature, humidity and layer thickness. Roughly speaking, every 10°C increase in temperature accelerates curing; conversely, at low temperatures curing can stall and the surface may remain tacky. This is why the minimum application temperature stated in the manufacturer's datasheet is binding.

Are natural resins still used?

Yes, but in niche areas. Rosin (a derivative of pine resin) continues to be used as a tackifier in hot-melt adhesives and in some printing inks. Growing interest in bio-based raw materials is drawing renewed attention to these products.