{"id":8271,"date":"2018-06-01T08:00:49","date_gmt":"2018-06-01T14:00:49","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=8271"},"modified":"2024-06-26T08:52:43","modified_gmt":"2024-06-26T14:52:43","slug":"pc-high-solids-resins-lower-voc","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/8271\/pc-high-solids-resins-lower-voc\/","title":{"rendered":"High Solids Resins: Approaches to Lower VOC"},"content":{"rendered":"
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Photo by Alena Koval from Pexels<\/figcaption><\/figure>\n

Companies in coating and ink technology try to lower the VOC<\/strong> (Volatile Organic Compound) content of their systems. The use of powder coatings, water-based systems and UV-curable coatings and inks has increased substantially over the past decades. Another option to reduce the emission of organic solvents is to increase the solids content of solvent-based systems. This article describes a few concepts that are used to adjust the resin system in order to lower the viscosity so that less solvent is needed to bring the paint or ink to application viscosity.<\/p>\n

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Branching<\/h3>\n

A key effect causing high viscosity of resin solutions is that resin molecules of moderate to high molecular weight have long tails that stretch out. This results in chain entanglement<\/strong>: the tails hinder each other just like pieces of spaghetti do. An approach to reduce chain entanglement is to design resin molecules that have a more spherical shape. Such polymeric molecules are more branched<\/strong>.<\/p>\n

\"Branching
Branching of resin molecules to reduce the number of chain entanglements.<\/figcaption><\/figure>\n

Resin molecules that have a higher degree of branching compared to conventional resins are called hyperbranched<\/strong> resins or dendrimers<\/strong>. Such polymers have lower resin viscosity. Therefore, less solvent is needed to obtain application viscosity of the complete system.<\/p>\n

Several innovative companies, like DSM Coating Resins<\/a> and Perstorp<\/a>, are strong in (raw materials for) hyperbranched resins. Boltorn\u2122 H2004<\/a>, for example, is a hyperbranched hydroxyl-functional polymer. Each molecule contains six reactive primary hydroxyl (-OH<\/strong>) groups. Hyperbranched polymers like H2004 can, amongst others, be used as a building block in the synthesis of resins for high-solids systems.<\/p>\n

Chainstopper solvents<\/h3>\n

Intermolecular interactions between different resin molecules create a physical network, which is another phenomenon causing high viscosity of resins that are dissolved in organic solvents. Physical networks<\/strong> that may strongly contribute to viscosity can be temporarily broken down when the interacting groups are blocked, for example by using suitable chainstopper solvents<\/strong>. The solvents evaporate during film formation and the physical network can build up again, thus contributing to physical drying and mechanical properties.<\/p>\n

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Preventing intermolecular resin-resin interactions by using chainstopper solvent.<\/figcaption><\/figure>\n

Most physical networks in paints and inks are based on hydrogen bonding<\/strong>. A useful approach to lower viscosity is therefore to use solvents that are able to form one hydrogen bond with a resin molecule, thus ‘stopping’ the physical network. Solvents that contain a C=O group are able to substantially reduce the viscosity of systems based on alkyds and polyesters. Such solvents can act as hydrogen acceptor. MPA<\/strong>, 1-methoxy-2-propyl acetate, is a solvent that is suitable to lower the solvent content of paints based on polyester resins and alkyd resins.<\/p>\n

\"MPA:
MPA: chainstopper solvent for alkyds and polyesters.<\/figcaption><\/figure>\n

Reactive diluents<\/h3>\n

The viscosity of binder systems can be lowered by combining polymeric resins with reactive diluents<\/strong>. ‘Reactive’ means that the molecules join in the crosslink reaction during film formation. This implies that the molecules must contain reactive groups of the same sort as the resin molecules. The word ‘diluent’ implies that the molecules must be miscible with, and lower the viscosity of, the resin system. Reactive diluents must have a specific chemical structure as well as a low molecular weight in order to comply with these two criteria.<\/p>\n

Reactive diluents must not contribute to VOC, implying that a good reactive diluent does not evaporate during film formation. Reactive diluents are widely used in, for example, 2-component epoxy-amine systems. Epoxy-functional molecules of low molecular weight are combined with conventional epoxy resins to lower the viscosity of the complete binder system.<\/p>\n

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A few examples of epoxy-functional reactive diluents.<\/figcaption><\/figure>\n

The concept of combining resins and reactive diluents to lower the viscosity of a resin system can be used in UV-curable paints and inks as well. Rahn product Miramer M210<\/a> is an example of a di-functional unsaturated reactive diluent for UV systems.<\/p>\n

\"Chemical
Chemical structure of Miramer M210.<\/figcaption><\/figure>\n

The low viscosity of M210 delivers a strong diluting effect. The two reactive groups of the molecule (C=C<\/strong>) participate in the crosslinking of the binder system during film formation.<\/p>\n

Further reading:<\/h3>\n