Claude Nootens – LUERCHEM LLC
Styrene allyl alcohol copolymer (Fig. 1) is a low molecular weight resinous polyol known as a performance enhancer in coating, ink and adhesive applications1. In ink applications, styrene allyl alcohol copolymer (SAA) or some of its derivatives can be used to formulate superior performing inks used in writing (ballpoint) or printing applications such flexography, inkjet, lithography, gravure or xerography (toner) processes.
Thanks to its chemical, physical and rheological characteristics, SAA can be used as a binder or as an additive in various type of non-aqueous, hot melt, or powder ink formulations. Furthermore, SAA derivatives such as carboxylated rosin-based SAA resin and (meth)acrylate SAA monomer have been prepared to incorporate the SAA structure into waterborne and radcure ink formulations respectively.
Several ink properties are significantly improved when SAA (or a derivative) is incorporated into the ink formulation.
The major benefits of SAA are the improvement of properties such as:
– gloss;
– adhesion on papers, metals and plastic (polypropylene, polystyrene, etc.);
– smudge resistance;
– water and chemicals resistance;
– abrasion (smears) resistance;
– viscosity reduction (enabling high solids);
– hardness;
– pigment wetting (increasing colour acceptance and development).
STYRENE ALLYL ALCOHOL COPOLYMER IN WRITING INKS
Water-fast non-aqueous writing inks for ballpoint pens can be prepared with the water-insoluble styrene allyl alcohol copolymer as binder, and a water-insoluble dye, which can be formed in-situ (U.S. Pat. 3,597,244).
These non-aqueous inks have the required viscosity and rheology characteristic for this application and remain stable upon storage.
The writing inks can also be made via the preparation of an intermediary powder obtained by mixing at elevated temperature, a resins mixture with dyes and additives.
The resulting powder-based intermediate can subsequently be dissolved in solvents by the ink user. The resin mixture is composed of styrene allyl alcohol copolymer in combination with an alkyd resin (U.S. Pat. WO 91/17222; UK Pat. GB 2244280; Euro.
Pat. 0 571 672; Euro. Pat. 0 806 461) or in combination with an alkyd resin and a ketone resin, also called ketone-aldehyde resin, ketonic resin or polyketone resin, (U.S. Pat. WO 97/40110).
Additionally, non-aqueous fluorescent writing inks for ballpoint pens can also be formulated with styrene allyl alcohol copolymer as the binder (U.S. Pat. WO 02/16514; U.S. Pat. 6,517,619; Euro. Pat. 1 311 633).
STYRENE ALLYL ALCOHOL COPOLYMER IN PRINTING INKS
In the case of printing inks, non-aqueous inks were formulated using as binder an SAA-based alkyd resin prepared with coconut fatty acid (Euro. Pat. 0 112 995).
Fluorescent inks were prepared with a combination of styrene allyl alcohol copolymer and a long soya oil alkyd resin (U.S. Pat. 3,412,104).
Interestingly, when styrene allyl alcohol copolymer is used as binder in non-aqueous printing inks on curved polystyrene surfaces, it provides printed matter having excellent adhesion, excellent gloss, good scuff resistance, excellent moisture and detergent resistance (U.S. Pat. 3,397,074).
A non-aqueous solution of styrene allyl alcohol copolymer can be used to formulate printing inks that are designed to cohesively fail upon a de-lamination attack, therefore useful for identification documents (U.S. Pat. 7,143,950 (2006); U.S. Pat. 7,819,327). In this case, the adhesion strength is greater than the cohesion strength of the ink.
FLEXOGRAPHIC PRINTING INKS
Waterborne flexographic or gravure printing inks can be formulated with an amine neutralised SAA-based resin as binder (U.S. Pat. 3,929,701). The resin is an esterified styrene allyl alcohol copolymer with a rosin resin or preferably a fortified (maleic or fumaric adduct) rosin, and a fortified drying or semi-drying oil. These inks are low foaming and have low viscosity, enabling them to carry more pigment or filler. Also, they provide good grease and detergent resistance, as well as solvent release, wet rub and gloss properties.
Styrene allyl alcohol copolymer esterified with fortified rosin which has previously been reacted with polyols (preferably a blend of diethylene glycol/glycerol), can be used as ink pigment grinding resin for waterborne flexographic and rotogravure printing inks (U.S. Pat. 5,166,245).
This alkali-soluble amine neutralised resin provides stable, low viscosity pigment dispersions, over a wide range of pH values while maintaining excellent physical properties in the finished inks with maximum colour strength.
INK-JET INKS
For ink-jet application using an aqueous based ink (still containing water-soluble solvent), a non-aqueous solution of styrene allyl alcohol copolymer can be used in a separate cartridge as a one-part fixer system to overcoat a printing page to enhance printing performance such as smear-fastness, smudge-fastness, water-fastness, and light-fastness (Euro. Pat. 1 223 046; U.S. Pat. 7,446,134).
The presence of styrene allyl alcohol copolymer in an ink-jet ink based on a combination of polyvinyl chloride, polyvinyl acetate and hydrogenated rosin ester improves the abrasion resistance of the ink applied on high density polyethylene and polypropylene (U.S. Pat. WO 2022/125767; U.S. Pat. 2024/0043707).
The combination of styrene allyl alcohol copolymer with terpene phenolic resins allows the formulation of non-aqueous thermal ink-jet ink which can be applied for a long time either at low temperature (5° C) or high temperature (40° C) across a wide humidity range, with improved print quality and adhesion (U.S. Pat. WO 2020/223533).
The smears resistance of a waterborne ink-jet ink still containing solvent and formulated with a polyurethane dispersion is improved by the addition of styrene allyl alcohol copolymer (dissolved in di(propylene glycol) methyl ether) (U.S. Pat. 7,176,248). Transparent hot melt ink for use in inkjet application can be prepared using styrene allyl alcohol copolymer, glycerol-modified rosin ester, stearic acid and a glycol ester of fatty acid as transparentising agents (U.S. Pat. 5,185,035; U.S. Pat. WO 91/18065).
The combination of styrene allyl alcohol copolymer with alkylbenzenesulfonamides, allows formulation of hot-melt ink-jet ink with high mechanical strength and the abrasion resistance resulting in high-quality images (U.S. Patent 4,820,346; Euro. Pat. 0 475 707).
RADCURE INKS
The synthesis of the acrylated SAA and its use in UV or EB cure coating applications has been reported some time ago. Recently several patents which are still active have reported its use in UV cure inks (U.S. Pat. WO 2005/021666; U.S. Pat. 2006/0183868; Euro. Pat. 1 660 599; U.S. Pat. 7,423,092).
The presence of acrylated styrene allyl alcohol copolymer in UV-curable inks, such as UV-lithographic inks, provides significant improvement on the ink-water balance (ink-water emulsion stability on press) and on pigment wetting (flow in ink duct). Additionally, depending on the alkoxylated (meth) acrylated monomer, the ink composition can exhibit a very high cure speed.
Styrene allyl alcohol copolymer dissolved in ethoxylated trimethylolpropane triacrylate can be used as gel-like additive in lithographic inks (U.S. Pat. WO 2008/094863). This gel enhances the viscosity, the emulsion capacity, the print transfer and reduced misting of the ink.
Interestingly, the replacement of isobutyl benzoin ether by SAA benzoin ether in the photoinitiator system allows the UV curable ink composition to have a significant improvement in terms of cure speed, gloss, toughness, abrasion resistance and rub resistance (U.S. Pat. 4,201,842; U.S. Pat. 4,334,970).
CONCLUSIONS
Styrene allyl alcohol copolymer (SAA) and several of its derivatives can be used in the ink industry due to imparting a wide range of beneficial properties. Therefore, they serve as an important performance-enhancing resins, allowing ink formulators to adapt and improve the characteristics of their ink formulations.
REFERENCES
1. European Coating Journal, vol. 07/08 2023, page 34; Farbe und Lack, 1/2024, page 53; Pitture e Vernici – European Coatings – Formulation 5 / 2023, page 14; Pitture e Vernici – European Coatings – Formulation 1 / 2025, page 12.
