What Is a Rosin?
Rosin is a natural resin obtained by refining the oleoresin (pine resin) found in pine trees, making it a renewable biomass material.
In the modern era, a wide range of industrial products is manufactured using synthetic resins derived from petroleum. Resins, originally referring to viscous high-molecular compounds, include natural resins and synthetic resins. Natural resins can be plant-derived, animal-derived, or mineral-derived. Major natural resins include lacquer, rosin, natural rubber, amber, shellac, glue (animal glue), shellac, casein, and natural asphalt.
Powdered rosin has been used since ancient times as an anti-slip agent in sports and applied to string instruments like violin bows. Moreover, it is widely used as an intermediate material to enhance the properties of various industrial products during their manufacturing processes.
Uses of Rosin
Rosin finds applications in various areas, serving as an anti-slip agent in sports, an intermediate material in various industries, and a source material for the production of rosin derivatives used in paper chemicals, synthetic rubber, ink, paint, solder, adhesives, and even chewing gum.
1. Sizing Agents (Ink Anti-Bleeding)
In the paper manufacturing process, sizing agents are used to prevent ink from bleeding and spreading on paper when written or printed. Rosin derivatives are employed as water-based sizing agents, penetrating paper uniformly.
2. Adhesive and Adhesive Resin
To enhance the adhesion and compatibility with various substrates in adhesives, tackifiers (adhesive imparting agents) are used. Rosin derivatives and hydrocarbon resins, like hydrogenated petroleum resin, exhibit wide compatibility with elastomers and synthetic resins, the main components of adhesives.
3. Printing Ink Resin
Resins for printing inks are utilized to improve the dispersion of pigments, express colors effectively, and enhance drying properties (productivity) during printing. Rosin-modified phenolic resins are commonly used in offset printing inks.
4. Synthetic Rubber Emulsifying Agent
As an emulsifying agent for the emulsion polymerization of synthetic rubbers like SBR (Styrene Butadiene Rubber), ABS (Acrylonitrile Butadiene Styrene), and CR (Chloroprene Rubber), disproportionated rosin soap (alkali metal salt aqueous solution) is primarily used. It contributes to improving the adhesive properties and various physical properties of rubber.
5. Solder Flux Resin
Flux is used in soldering to remove the metal oxide film from the substrate electrode, components, and the solder itself, creating a clean surface. Rosin derivatives are included in the flux.
6. Chewing Gum Base
“Estergum,” a food-grade material derived from rosin, is used in chewing gum to adjust the chewing texture. It is registered as a safe food additive and is widely added to both pellet and slab gum.
Properties of Rosin
1. Manufacturing Methods of Rosin
Rosin is produced from pine tree resin. Different manufacturing methods result in various types of rosin, such as gum rosin (colophony), tall oil rosin, and wood rosin.
Gum Rosin: Traditionally, gum rosin is obtained by making incisions in the bark of pine trees and collecting the exuding sap (oleoresin). The remaining substance after distilling volatile oil (turpentine oil) from the oleoresin becomes gum rosin.
Tall Oil Rosin: Tall oil rosin is produced by acid hydrolysis of the skimmings obtained from the caustic soda extraction of black liquor, a byproduct in the Kraft pulping process used to make craft pulp.
Wood Rosin: Wood rosin, also known as tall wood rosin, is extracted from processed chips of pine stumps using solvents. Although this method started in the United States in 1910, it has significantly decreased due to the depletion of stumps.
2. Rosin Derivatives
Rosin derivatives are intermediate materials derived from rosin that support various products essential for daily life. Numerous derivatives extend the applications of rosin.
Rosin Esters
Produced by esterifying rosin with alcohols, rosin esters are used in tackifiers (adhesive imparting agents) for adhesives, as bases for chewing gum, and in applications such as paints, inks, rubber, and paper.
Hydrogenated Rosin
Obtained by adding hydrogen to rosin, hydrogenated rosin is resistant to oxidation by oxygen in the air, exhibiting excellent heat and weather resistance. It is used in solder flux, pigment coatings, inks, paints, rubber, and various other applications.
Disproportionated Rosin
Produced by catalytically disproportionating rosin under the presence of a catalyst, this stabilized rosin derivative serves as an emulsifying agent in the emulsion polymerization of synthetic rubbers. It is used as disproportionated rosin soap (alkali metal salt aqueous solution) for the emulsion polymerization of synthetic rubbers like those used in car tires.
Polymerized Rosin
Obtained by dimerizing rosin in the presence of a catalyst, polymerized rosin has a higher softening point than regular rosin. It is used in hot-melt adhesives and solder flux.
Acid-Modified Rosin
Created by modifying rosin with maleic acid or fumaric acid, acid-modified rosin is widely used in paper sizing agents, resins for paints, and water-based ink.
Rosin-Phenol Resin
Formed by combining the rosin skeleton with resol-type phenolic resin and further esterifying with various polyols, this high-molecular-weight resin possesses both hydrophobic parts from the alkyl chain of alkylphenol and hydrophilic parts from the hydroxyl groups of phenols and polyols. It plays a role in adjusting properties such as solubility in ink solvents, gloss, and drying performance in offset printing.
Acrylated Rosin
Produced by adding acrylic acid to rosin, acrylate rosin is used in adhesives, paints, inks, rubber, and paper.
Ultra-Light Rosin
A resin that successfully achieves light coloration to address the color issues associated with traditional rosin and its derivatives. It has superior initial color and long-term stability, finding wide application in adhesive imparting agents, solder flux resin, and medical adhesive agents.
How to Choose Rosin
When selecting rosin, which is a resin acid primarily composed of abietic acid, several factors should be considered:
1. Origin and Properties of Rosin
Rosin can be derived from various sources, including gum rosin from pine resin, wood rosin from pine stumps, and tall oil rosin from byproducts of the papermaking process. These rosins differ in the type and quantity of resin acids, influencing properties like solubility, hardness, viscosity, color, and stability. It is essential to choose the most suitable rosin based on the intended application.
2. Modification and Additives in Rosin
Various derivatives enhance the performance of rosin. Since different rosin derivatives exhibit distinct properties, it is crucial to choose the appropriate rosin derivative or additive method according to the intended purpose.
3. Price and Availability of Rosin
Being a natural raw material, the price and availability of rosin may fluctuate due to factors such as climate and demand. Caution is required to monitor current prices and ensure a stable supply.
4. Application-Specific Compatibility
Concerning rosin derivatives, it is necessary to use “registered” ones depending on the application. When using it as a chewing gum base, the selection must come from materials registered in the Food Additive Compendium or approved by the FDA (Food and Drug Administration), the United States regulatory agency for food and pharmaceuticals. For applications such as tackifiers (adhesive imparting agents) in medical adhesive patches or as ingredients in pharmaceuticals, quasi-drugs, and cosmetics, one needs to choose from materials registered in pharmaceutical regulations (Pharmacopoeia), quasi-drug regulations (Regulations for Non-Prescription Drugs), and the International Nomenclature of Cosmetic Ingredient (INCI).