Glycerol Ester of Hydrogenated Rosin

In clear packaging tapes and labels, the adhesive layer is visible, so even a small yellow tint from the tackifier shows up on white films, printed graphics or transparent windows. A glycerol ester of fully hydrogenated rosin controlled to Gardner 1 starts very close to water‑clear, and because its conjugated double bonds have been saturated, it picks up much less additional colour during hot‑melt processing at 160–180 °C than typical hydrogenated rosin esters rated at Gardner 3–6. As a result, the finished adhesive stays almost colourless instead of turning amber, helping keep packs looking consistent on shelf and reducing visible differences between early and late rolls in a production run. In practice, basing a transparent hot‑melt PSA on a Gardner 1 grade means you spend less effort compensating for adhesive yellowing with thicker films or heavy printing, and you gain more safety margin in heat‑ageing tests, while still getting the tack and cohesion associated with hydrogenated rosin ester tackifiers.

Hydrogenation saturates the conjugated double bonds in abietic‑type resin acids, removing the sites that both give rosin its yellow‑brown tint and make it easy to oxidise and darken at high temperature (Liu et al., 2020, Polymers). When this more fully hydrogenated rosin is esterified with glycerol, the resulting glycerol ester keeps that saturated backbone, so during hot‑melt processing at around 160–200 °C it takes up much less extra colour than an ester made from only partially hydrogenated rosin. In practice, grades that still meet Gardner 1 after esterification show that most of the conjugated unsaturation has been removed; they tend to stay almost water‑clear in accelerated ageing tests, whereas esters from less hydrogenated feedstocks can climb by two to four Gardner units as they oxidise. For adhesive formulators this difference means a highly hydrogenated, Gardner 1 glycerol ester helps the adhesive keep its original clarity and avoid visible yellowing over its service life, especially in transparent tapes, labels and clear coatings.

Conventional ester gum is based on unmodified gum rosin, whose abietic‑type resin acids oxidise readily and form hydroperoxides and related products that are established contact sensitisers in colophony allergy (Karlberg et al., 1988, Contact Dermatitis). Hydrogenating the rosin before esterification saturates these conjugated double bonds and makes the resin acids much less prone to air oxidation, which significantly reduces the formation of allergenic oxidation products and lowers the sensitisation potential of the rosin backbone (Karlberg et al., 1988; PCPC, 2019). Esterifying this fully hydrogenated rosin with glycerol and controlling the acid value to about 15 mg KOH/g or below further reduces free resin acids, helping to minimise primary skin irritation while retaining the tackifier’s adhesion performance in medical tapes, transdermal systems and hygiene adhesives. In addition, the improved thermo‑oxidative stability of hydrogenated rosin esters means they generate fewer new oxidation byproducts during storage and use, which helps skin‑contact adhesives keep a stable allergen profile over time compared with formulations based on conventional ester gum.

Glycerol esters of hydrogenated rosin such as HG851 mix well with a wide range of adhesive polymers, including natural rubber, chloroprene rubber, styrene‑butadiene rubber, styrenic block copolymers (SIS, SBS, SIBS) and ethylene‑vinyl acetate, so one tackifier grade can cover multiple PSA and hot‑melt product lines instead of needing a different resin for each backbone. In styrenic block copolymer‑based hot‑melt PSAs, its 80–88 °C softening point sits in the typical tackifier window: it softens and plasticises the rubber mid‑block to build tack, while remaining compatible with the styrene end‑block domains that carry cohesive strength. In EVA and rubber‑based hot‑melt adhesives for packaging, bookbinding and hygiene products, this same resin can be used without changing tackifier type, which simplifies formulation maintenance and inventory while still allowing tuning of open time and set speed by adjusting tackifier level. Good solubility in common industrial solvents such as cyclohexane, petroleum ether, toluene, xylene, ethyl acetate and acetone extends this versatility to solvent‑borne systems, so a single hydrogenated rosin ester can support everything from SIS‑based packaging tapes to EVA‑based hot‑melt and SBR‑based solvent adhesives, reducing tackifier SKUs and changeover risk in production.