Classification of pressure-sensitive adhesives according to manufacturing process

An adhesive is any substance that, when applied to the surfaces of materials, binds the surfaces together and resists separation. The basic ingredients are adhesive firming agents (binder), solvents, adhesion enhancing agents (plasticizers, coalescing agents), wetting agents, modifiers and stabilizers. There are many criteria for the distribution of adhesives taking into account their characteristics and purpose, of which the basic division is made according to their chemical base and the method of curing [1]. Pressure-sensitive adhesives (PSAs) represent a system that actually dates back to the invention of the self-adhesive articles in 1935 when R. Stanton Avery produced the first coating unit using a wooden cigar box with two holes cut in the bottom. PSAs can be defined as a special category of adhesive which in dry form are permanently tacky at room temperature [2]. Pressure-sensitive adhesives require certain properties: besides a good surface adhesion, good stability against light, oxygen, moisture and plasticizers, and the adhesion characteristics is constant over a very wide temperature range. They are characterized by the excellent low constant level of peel strength and tack as well as the excellent aging performance at room or higher temperatures. The inherent tackiness of PSAs allow them to wet and adhere quickly under a low pressure on a broad variety of substrates [3]. There are many criteria for the division of PSA taking into account their characteristics and intended use, where the basic division is made according to their chemical base and a method for curing. In practice, the most commonly used criteria for the allocation of adhesives include: form (consistency), methods and fields of application, rate of binding, joint properties, quantities of ingredients, properties of the thermal adhesive layer or the production process [1]. Pressure-sensitive adhesives according to the manufacturing process can be divided into solvent-based, water-borne and solvent-free PSA (Fig. 2) [14–17]. The most commonly used high molecular compounds used in the manufacture of pressure-sensitive adhesives include natural rubber and synthetic copolymers of ethylene and acrylic acid, polisilicones, acrylics, linear polyesters, polyether, polyurethanes. The market and technology of high-performance PSAs are expanding rapidly. A growing market is the result of expansion in both current and new application areas. Self-adhesive polymers possess inherent properties due to their structure that make them unique [15]. The world market for pressure sensitive adhesives was valued at USD 22.70 billion in 2012 and is expected to reach USD 31.64 billion by 2018. The global pressure sensitive adhesives market volume was 1700.5 kilo tons in 2012 and is expected to reach 2208.2 kilotons by 2018 [18]