RESINS AND BASE POLYMERS

INTRODUCTION TO RESINS

The term resin comes from resinous, the description of materials that are amorphous, brittle, and yet soft and tacky. Rosin from trees is the easiest example to relate to—gymnasts and baseball players use it for grip. Rosin derivatives form the oldest group of tackifier resins.

The term resin is sometimes used to describe materials like polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS), which do not fit the description used here for tackifier resins as follows:

• Low molecular weight, less than 20,000 Mz, typically less than 5,000 Mz
• Amorphous
• Melting points from liquid to 180°C
• Glass transition temperatures (Tg) from liquid to 130°C
• Colors from water white to brown

Resins are used to modify the bulk rheology and surface adhesion properties of a variety of polymers for many applications, including adhesives, paints, inks, wax compounds, and chewing gum. In some cases, resins provide tackiness and an increase in specific adhesion, and in other cases they provide film forming and reduction in viscosity. When mixed with a polymer, a compatible resin will increase the Tg and reduce viscosity or hardness in contrast to a plasticizer, which generally will not modify Tg.

There are many types of resins available from a range of suppliers. There are also a number of ways that they can be grouped. The most common way is by the feedstock used to produce them: hydrocarbon resins, rosin resins, and terpene resins.

Hydrocarbon resins are generally made from petroleum-based feedstocks, either aliphatic (C5) or aromatic (C9), or dicyclopentadiene (dcpd), or mixtures of these. The monomers are polymerized using catalysts such as AlCl₃ or BF₃, or in the case of dcpd, thermal polymerization can be employed. These resins can be sold as is or after they have been hydrogenated to reduce either color or levels of unsaturation.

Rosin acids are derived from the root (wood rosin) or sap (gum rosin) or from the kraft process (tall oil rosin). Rosin acids can be tackifiers themselves, but it is more common to use their ester derivatives.

Terpene resins are derived from terpene feedstocks, either from wood sources or from citrus fruit. AlCl₃ also polymerizes these resins.

Choosing a Resin

With so many resins available, how does one choose the right one for a particular application? Basic criteria narrow down the choice, and then a number of secondary filters are applied. Resin suppliers really sell two basic properties: compatibility and stability.

In most formulations, especially adhesives, the polymer is the starting point of the mixture, which means that the resin must have a known and understood compatibility with the polymer and with other ingredients. Viscosity, color, and oxidative stability are very important criteria and, if not understood, can affect application and end use properties, resulting in blocked nozzles, poor coatings, and failed or discolored adhesives. Stability is proportional to cost, so choices are made around what stability is really required for the adhesive. With basic criteria of compatibility and stability in place, secondary filters come into play, such as: FDA clearances, odor, color, and cost.

New resins are often developed as a response to market and polymer changes. Trends such as biodegradability and repulpability will result in new polymers with a different structure that will require different resins and other additives. Advances in radiation-curing techniques will also result in new polymers and resins with the required ability to add adhesion and modify rheology without impacting curing mechanisms.

Acrylic Resins

Acrylic resins are prepared by polymerizing acrylate and methacrylate resins. A range of homopolymers and copolymers is available, ranging from simple plastics like polymethylmethacrylate to complex copolymers incorporating several monomers. Uses range from clear plastics and floor polishes to solvent solutions or emulsions used in both pressure-sensitive and liquid adhesives for a wider range of applications, including packaging, carpet manufacture, and construction. The solid resins can also be used as inert thickeners in adhesives like cyanoacrylates and an aerobics.

Acrylic Resins, Acrylic Copolymers

A copolymer is a polymer that is derived from more than one species of monomer. (See also Acrylic Resins.)

Acrylic Resins, Ethylene-Acrylic Ester Copolymers

Copolymer of ethylene and acrylic ester.

Acrylic Resins, Ethylene-Acrylic Ester-GMA Terpolymers

Terpolymer of ethylene, acrylic ester, and glycidyl methacrylate (GMA).

Acrylic Resins, Ethylene-Acrylic Ester-Maleic Anhydride Terpolymers

Terpolymer of ethylene, acrylic ester, and maleic anhydride.

Acrylic Resins, Ethylene-n-Butylacrylate Copolymers

Copolymer of ethylene and n-butylacrylate.

Acrylic Resins, Polymer Emulsions

Polymer emulsions consist of minute particles of polymer dispersed in water.

Acrylic Resins, Solid

Solid acrylic resins are comprised completely of solid content. They can be used as inert thickeners in adhesives like cyanoacrylates and an aerobics.

Acrylic Resins, Solution

(See Acrylic Resins.)

Acrylic Resins, Water-Reducible

Water-reducible resins can be useful for waterborne and solvent-based inks, adhesives, powder coatings, and anti-corrosive coatings.

Alkyd Resins

Alkyd resins are the reaction product of an oil or fatty acid, polyol(s), and polyacids. These polymers are supplied in solvents and can cure by reaction with oxygen or amino-based crosslinking resins to form tough, durable films. The choice and amount of oil in the polymer determines the dry rate and solubility of the polymer in aliphatic solvents.

Long (over 60%) and medium (40-60%) oil alkyds are supplied in low-odor aliphatic solvents and are suitable for architectural and maintenance finishes. Short (under 40%) oil alkyds are supplied in aromatic solvents and are used in fast air-dry and bake finishes. Alkyds can also be modified or co-reacted with many other material types (rosin, phenolic, urethane, vinyl monomers, etc.). The precise combination of the many possible ingredients, together with careful control of the reaction, influences the final properties of the alkyd produced.

Alkyd Resins, Water-Reducible

Water-reducible resins can be useful for waterborne and solvent-based inks, adhesives, powder coatings, and anti-corrosive coatings.

Amorphous Polypropylene

Polypropylene without a clearly defined shape or form.

Block Copolymers

Block copolymers are formed when the two monomers comprising the copolymer form groups (blocks) of repeating units.

Butadiene-Acrylonitrile Rubber

Also known as NBR, a synthetic rubber copolymer of acrylonitrile and butadiene.

Butyl Rubber

Butyl rubber is mainly polyisobutylene, but with about 1-3% polyisoprene added to it so that it is possible to crosslink it by conventional means. It is a little darker in color, with an available molecular weight range of around 350,000-450,000. Thus, much of what is said about polyisobutylene applies to butyl rubber, recognizing the molecular-weight difference between the two. It is also very stable to aging and ultraviolet light.

In addition to standardized grades, some specialized grades are manufactured. Should some specific end use call for a variation from the ordinary, elastomer manufacturers should be contacted. One major source of butyl rubber for underground pipe-wrap tapes was reclaim butyl from automotive inner tubes, but with the advent of tubeless tires this source has been reduced to truck inner-tube reclaim, along with some mechanical goods and one or two other minor sources. Butyl latex has been used as a base for prime-coat formulae for polyolefin films where it shows preferential bonding.²

Chlorinated Rubber

White powder formed by reacting carbon tetrachloride with chlorine.

Cyanoacrylates

Any of a number of cyanoacrylic esters that quickly cure to form a strong bond.

Dispersions

The term dispersion is normally used to describe a solid finely dispersed in a liquid. In contrast to solutions, dispersions are heterogeneous on a microscopic scale. Colloid chemists refer to them as “sols.” In practice, many materials can be supplied as dispersions, including things like polyurethane adhesive dispersions in water.

Dispersions are also used widely in plastics and rubber processing, where companies supply master batches of additives in water, plasticizers, or process oils. Typical additives are colorants, slip aids, antioxidants, polymer accelerators, UV inhibitors, and polymer stabilizers. Some manufacturers of synthetic latex adhesives have started to call their products dispersions to avoid using the term latex. This is to avoid association with the latex allergy issue, which is in fact unique to natural rubber latex.

Epoxy Films and Paste

Epoxy in film or paste form.               

Epoxy Flexibilizers/Diluents

Flexibilizers improve peel and impact strength generally by allowing the adhesive to deform under the application of stress. They reduce mechanical damage by lowering modulus or plasticization, which allows the adhesive to become distorted.

The primary function of a diluent in an epoxy resin formulation is to reduce its viscosity to either make it easier to compound with fillers, improve filler loading capacity, or to improve application properties.

Epoxy Hardeners

A catalytic or reactive agent used to react with the epoxide group on an epoxy resin to promote, enhance, or control the curing reaction and aid in property development of the final epoxy thermoset. The hardener (also called a curing agent) typically has active hydrogen attached to nitrogen, oxygen, or sulfur. Amine curing agents are the most common and can be primary or secondary, aliphatic or aromatic, or cycloaliphatic. The amines typically have greater than three reactive sites per molecule that facilitate the formation of a three-dimensional polymer network when mixed with the epoxy resin.

Epoxies can be cured in several ways. Single-component epoxies usually contain hardeners like dicyanamide and are cured by heating at moderately high temperatures. Two-component systems can be cured at room temperature or higher by a condensation mechanism involving the glicydyl groups of the epoxy resins and primary or secondary amines. Strong acids or acid-generating molecules such as anhydrides can also act as hardeners.

Epoxy Resins

A thermosetting resin based on the reactivity of the epoxide group. One type is made from epichlorohydrin and bisphenol A. Aliphatic polyols such as glycerol may be used instead of aromatic bisphenol A. Molecules of this type have glycidyl ether structures, --OCH₂CHOCH₂, have many hydroxyl groups in the terminal positions, and cure readily with amines. Another type is made from polyolefins oxidized with peracetic acid. These have epoxide groups within the molecule as well as in terminal positions, and can be cured with anhydrides, but require high temperatures.

Many modifications of both types are made commercially. Halogenated bisphenols can be used to add flame-retardant properties. The reactive epoxies form a tight crosslinked polymer network and are characterized by toughness and good adhesion, corrosion resistance, chemical resistance, and dielectric properties.

Epoxy Resins, Liquid/Solution

Liquid hydrocarbon resins are used almost exclusively for solvent-free systems. The main reasons for their application are improved miscibility of polyol and aromatic isocyanate, adjustment of mix ratio, increased moisture resistance, greater water repellent properties, improved adhesion and better flexibilization. (See also Hydrocarbon Resins.)

Epoxy Resins, UV-Curing

Materials that are polymerized and cured by ultraviolet light.

Ethylene-Propylene Rubber

EPM is a type of synthetic elastomer.

Fluoropolymers

Fluoropolymers are synthetic carbon-based resins used in the manufacture of high-performance industrial coatings.

High-Solids Resins

Resins formulated to have a higher concentration of resin and a smaller concentration of volatile organic compounds (VOCs).

Hydrocarbon Resins

Hydrocarbon resins are generally made from petroleum-based feedstocks, either aliphatic (C5) or aromatic (C9),or dicyclopentadiene (DCPD), or mixtures of these. The monomers are polymerized using catalysts such as AlCl₃ or BF₃, or in the case of DCPD, thermal polymerization can be employed. These resins can be sold as is or after they have been hydrogenated to reduce either color or levels of unsaturation. (See also Introduction to Resins, as well as Tackifiers.)

Hydrocarbon Resins, Aliphatic Hydrocarbon Resins

Aliphatic hydrocarbon resins are used primarily in hot-melt adhesives, coatings, and pressure-sensitive adhesives.

Hydrocarbon Resins, Coumarone-Indene

Resins obtained by polymerization of coumarone and indene.

Hydrocarbon Resins, Emulsion

Emulsion-based formulations can enable the reduction of volatile organic compound (VOC) emissions and eliminate the need for flammable solvents, helping companies address end-user requirements for more environmentally friendly materials.

Hydrocarbon Resins, Hydrogenated Hydrocarbon Resins

Materials used as tackifiers in hot-melt and pressure-sensitive adhesives.

Hydrocarbon Resins, Liquid/Solution

Nonvolatile, light-colored reactive diluents for epoxy and other aromatic resin systems.

Hydrocarbon Resins, Pure Monomer Resins

These resins are polymers or copolymers of varying ratios manufactured from pure monomers, such as styrene. (See also Hydrocarbon Resins.)

Hydrocarbon Resins, Solid

Solid hydrocarbon resins are typically found in pastille or flake form.

Hydrocarbon Resins, Terpene

Tackifiers derived from renewable resources.

Isocyanate Resins

A linear alkyd resin lengthened by reaction with isocyanates, then treated with a glycol or diamine to crosslink the molecular chain.

Latex Resins

A milky, aqueous dispersion of a natural or synthetic rubber or resin. This term is also frequently applied to synthetic emulsion polymers.    

Maleic Resins

Resins produced from maleic anhydride monomer, such as styrene maleic anhydride copolymer, an alternating copolymer of styrene and maleic anhydride that is produced by the free-radical polymerization of the mixed comonomers.