Solvent-Based Acrylic Sealants

Solvent-based acrylic sealants are semi-elastomeric because of their thermoplastic nature. The movement accommodation factor is approximately 20%. However, these sealants perform best in the area from 7.5%... 

Table 5.3 Properties of solvent-based acrylic sealants... 

Initially, these sealants exhibit a shore A hardness of 25 to 35, which increases slowly with time. A good solvent-based acrylic sealant does not exceed 55 shore A. A higher hardness limits the movement capability and may result in adhesive or cohesive failure of the sealant. 

Solvent-based acrylic sealants are used for areas where there is limited movement, such as perimeter joints around doors and windows, wood sashes and wood-to-masonry joints, precast joins, panel-to-panel joints and stone cladding. The properties of solvent-based acrylic sealants are summarised in Table 5.3. 

Acrylic adhesives first appeared about 1937 the acrylic resins may be considered as belonging to the vinyl family [1, p. 305], Today, acrylic adhesives appear in many forms as both pressure-sensitive and non-pressure sensitive formulations in organic solvent and emulsion forms as monomer and polymer cements as anaerobics as cyanoacrylates as so-called reactive or honeymoon two-part systems and as radiation curing formulations. Commercial production of acrylic polymers began in the late 1920s, but it was not until 1958 that the first aerylie sealant was developed [10, p. 226]. The solvent-based acrylic sealants were first introdueed to the eonstruction industry in about 1960 ... 

As previously noted, the primary use for this elastomer has been as solvent-based adhesives and sealants. Solvent-based products are losing market share to water-based poly-chloroprenes, to other polymer types such as acrylics and polyurethanes, and to hot melt adhesives. However, where the processing facility is able to contain the vapor emissions, a solvent-based adhesive or sealant is preferred because of better wetting of surfaces, faster drying, and higher performance of the cured or dried product. Many rubber bonding... 

Acrylic sealants are water-based but they may also contain ethylene and propylene glycols, mineral spirits and mineral oil. There are also solvent-based aerylie sealants which contain substantial amounts of solvents sueh as mineral spirits, toluene and xylene. Polysulfide sealants usually contain toluene but methyl ethyl ketone is also used. The group of class B sealants contains substantially more solvents (up to 40% by volume) but there are some exceptions. PVC sealants are based on plastisols and they ean be made without solvents. Butyl rubber based sealants usually eontain hydroearbons (Q-Cn). Styrene-buta-diene-styrene based sealants usually have a large amount of solvents seleeted from a group including toluene, heptane, hexane, methyl ethyl ketone, isobutyl isobutyrate, n-amyl acetate, n-amyl ketone. They are usually processed in solvent mixtures. Polyehloroprene is usually dissolved in a mixture of solvents ineluding ketones or esters, and aromatie and aliphatic hydrocarbons. The list includes naphtha, hexane, aeetone, methyl ethyl ketone, benzene, and toluene. 

High quality, conventional sealants (118) will dominate the industries in the 80 s. Energy-efficient, water-proof, and durable sealants will be in demand by the construction and automotive industries. Commonly used sealants are polysulfides, polyurethanes, silicones, oil-based caulks, butyls, and solvent or latex acrylics. However, judged by their performances and durability (Table 3), the first three will be the most important sealants for this decade. 

Intermediate movement accommodating sealants include solvent-based and emulsion-type acrylic systems, higher quality butyl/PIB blends, neoprene and styrene-butadiene (SBR) based compounds. These have sufficient movement tolerance to be used in joints subject to both settlement and thermally induced movement across the sealant. These intermediate type systems cure by means of solvent evaporation with some auto-oxidation, or a mixture of the two processes. 

In the adhesives, sealants and coatings market, Kraton SBC products primarily compete with acrylics, silicones, solvent-based... 

Finishing the patina. Most patinas on outdoor pieces, like garden furniture or decorative metalwork, will actually help the metal resist further corrosion. However, if you find that your patina runs or streaks with moisture or stains surrounding areas, consider finishing the patina with sealant. Use an acrylic or solvent-based sealer, not urethane or polyurethane. 

Sealants, while sharing many similarities with adhesives, tend to be made from different materials and include those based on polysulfides (often for uses in contact with fuel), silicones, polyurethanes, acrylics in both solvent-based and latex-based materials, and sealants based on butyl and fluorocarbon polymers. In addition to adhesive and sealant types, this chapter reviews methods for testing and qualifying these materials. 

Sealants are divided into groups according to the generic names of polymer base. The main groups include polyurethanes, silicones, acrylics, polysulfide and others (PVC, polybutylene, styrene-butadiene-styrene copolymers, polychloroprene, and several others). The amount of solvent used in sealants is controlled by the standards which previously divided sealants into two groups these below 10% VOC and those above. Recently, a provision was made to include water-based acrylics and the limit of VOC for class A sealants was increased to 20%. Polyurethane sealants and structural adhesives can be made without solvent (the first solvent-free polyurethane sealant was made in 1994). Solvents are added to reduce sealant viscosity and to aid in the manufacture of polymer. Typical solvents used are mineral spirits, toluene, and xylene. A small amount of solvent is emitted from curatives... 

Current inventions show improvements in solvent utilization, as follows. PVC-based adhesive for PVC pipes, typically containing solution of PVC in tetrahydrofuran, was replaced by solution of chlorinated PVC in 1,3-dioxolane and/or its derivatives whieh are far less toxic than THF. Ethanol is used in polyimide adhesive and dental adhesive. Monomer solvent mixture is used in crosslinkable acrylate adhesive, which permits formulation of VOC-free composition. Polyurethane hot-melt adhesive produced from polyacrylates and polyesters does not need solvents for its production and cure which occurs under the effect of moisture. Similar observations can be made for sealants. For example, sealing agent for semiconductor light emitting elements have been made from acrylic monomers without application of solvent. Material for production of printed wiring board was produced and cured without solvent from polymethacrylate. It is clear from these examples that new processes are consciously directed towards less toxic solutions. 

The base polymer for this t5q>e of sealant exists in the form of an emulsion of micron- and submicron-sized partides of the polymer suspended in water. The base polymer formed by free radical polymerization may be a homopolymer of an acrylic monomer but is more likely to be a copolymer of a number of different monomers chosen to provide the correct balance of properties. The polymer latex has to be made more permanent and therefore a nonionic surfactant such as a nonyl phenol/ polyethylene oxide is added to help stabilize the emulsion. Other additives to the sealant formulation include plastid-zers, fillers, solvents, and silanes. A plasticizer is added to the formulation in order to improve upon or maintain the flexibility of the sealant. Solvents (usually a small amount) are added to improve the tooling of the sealant after it is applied. In addition, a solvent could be a material such as ethylene or propylene glycol which can improve the resistance of the packaged sealant to temperatures below freezing. The most widely used filler for this type of sealant is calcium carbonate. Silanes are often added to acrylics to improve the wet adhesion of the sealant to glass. Other additives include antimildew agents (for tub and tile applications) and clay for rheological control. 

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