Water-based acrylic sealants

Water-based acrylic sealants are also referred to as acrylic emulsion sealants or latex sealants. These are one-component gun-grade material with a solid content ranging from 80%-85%. Curing occurs by evaporation... 

Typical areas of application for water-based acrylic sealants are gaps and joints subject to only a limited amount of movement, for example around door and window frames (Figure 5.1), fixtures and fittings and naturally occurring joints between different building materials. They are... 

Table 5.4 Properties of water-based acrylic sealants...

Figure 5.1 Application of water-based acrylic sealant on window frames...

Table 5.1 outlines useful properties, products and application areas of acrylic systems. Key market segments are coatings based on methacrylates as well as emulsions and water-based sealants. Acrylic emulsions and redispersible powders as cement modifiers offer many useful products for several end-uses. However, the high cost of acrylic has limited their use as cement modifiers. The use of water-based acrylic systems is increasing because of their non-toxic and environmentally friendly nature. 

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... 

Acrylic sealants are water-based but they may also contain ethylene and propylene glycols, mineral spirits and mineral oil. There are also solvent-based acrylic sealants which contain substantial amounts of solvents such 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 can be made without solvents. Butyl rubber based sealants usually contain hydrocarbons (Q-C,2). Styrene-buta-diene-styrene based sealants usually have a large amoxmt of solvents selected 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. Polychloroprene is usually dissolved in a mixture of solvents including ketones or esters, and aromatic and aliphatic hydrocarbons. The list includes naphtha, hexane, acetone, methyl ethyl ketone, benzene, and toluene. 

The acrylic monomers preferred in the preparation of UV curable inks and coatings or in the photoprepolymer printing plate procedure are 2-hydroxyethyl acrylate (2-HEA), 2-hydroxypropyl acrylate (2-HPA), 2-hydroxypropyl methacrylate (2-HPMA), 2-hydroxy-ethyl methacrylate (2-HEMA) and 2-ethylhexyl acrylate (2-EHA). Also, 2-HPMA is used in light-sensitive compositions for fissure sealant adhesives or bonding preparations in dentistry and in Napp printing plates. Various mono(meth)acrylates can be used in water-based acrylic latex paints. Plastics dispersions of acrylic polymers are used as binders or thickeners in paints as well as in cosmetic creams. The monomer content is usually less than 0.3% (Bjorkner 1995). 

While silicones, polyurethanes and polysulfides set through a chemical reaction, water based emulsion sealants achieve their functional end state by simple physical drying, i.e. evaporation of the water. The majority of emulsion sealants are composed of acrylic emulsions and to a lesser extent vinylacrylic and other copolymers. 

Latex-based acrylic sealants have the least number of objectionable qualities of any sealant. They dean up with water, have little or no objectionable odor, and have excellent weath-erability. They are then most often sold for use in residential sealing applications. They have found application in sealing windows, tub and tile sealing, and a myriad of other such applications, primarily for the prevention of air infiltration. They have limited movement capability, usually on the order of 7.5%. Latex caulks should not be used for any application in which the sealed joint is to be submersed in water for extended time periods. 

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... 

Chem. Descrip. 3-Glycidoxypropyltrimethoxysilane CAS 2530-83-8 EINECS/ELINCS 219-784-2 Uses Coupling agent for epoxies, urethane, acrylic and polysulfide sealants adhesion promoter for solv., water-based, solventless, and powd. coating systems pigment treatment... 

Uses Tackifier resin for water-based adhesives and sealants based on acrylic, S/B, nat. rubber, neoprene, and PVAc, esp. for pressure-sensitive adhesives, and for coatings Features Solv.-free... 

Acrylics, on the other hand, with good weatherabilities are used mostly for curtain wall panels as a sealant. Water-based (waterbourne) acrylic sealants and adhesives are well known. Use of thermoplastic elastomers is also increasing in various sealants applications. 

Bentonite thickening agents are used in various water based adhesives, caulks and sealants including those based on proteins and starch, polyvinyl acetate emulsions, natural rubber latexes, acrylic emulsions, neoprene emulsions, butyl emulsions, nitrile emulsions, and SBR emulsions. 

The total cauUc and sealant market in North America is estimated 500 000 tons of formulated sealants [80], with acrylic emulsion sealants comprising approximately 15 % of the total market, and 23 000 tons dry acrylic resin. Water based sealants, sold primarily in cartridge tubes, are used predominately in construction applications whereas reactive urethanes and silicones are used in more demanding construction and automotive applications. 

Acrylic latex sealants. Basic acrylic latex sealant formulations were compounded in a sigma blade mixer, as shown in Table 3. The water-borne silanes were then incorporated into a base. Standard wet and dry peel adhesion determinations from various substrates were performed periodically in accordance with ASTM C794-8. 

The exceptionally fast rate of anionic polymerization of cyanoacrylates in the presence of a base, including water, made this class of monomers unique among all acrylic and vinyl monomers. Of the alkyl cyanoacrylate family of monomers, fhe mefhyl- and ethyl-esters are used extensively in industrial and consumer-type adhesives. Meanwhile, the isobutyl, fi-butyl, and n-octyl cyanoacrylate esters are used clinically as blocking agents, sealants, and/or tissue adhesives in different parts of the world due to their much lower toxicity as compared to their more reactive methyl coxmterpart. 

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. 

Direct exposure to moisture may also have adverse effects on the performance of some sealants, either by its effects on the sealant or on the joint substrates." Absorption of water may cause softening of the sealant material, and some acrylic-based sealants are particularly affected in this way. If absorption is followed by prolonged near-freezing temperatures, the sealant may become stiffer, leading to an increase in internal stresses as the joint opens. These stresses tend to promote failures of adhesion at the interface of the sealant and the joint surfaces. The repeated absorption of moisture by components of porous materials, such as concrete, may cause a gradual migration of soluble salts towards the sealant interface, which could lead to adhesion failure. This effect can be reduced by the application of appropriate primers to the joint faces before application of the sealant. It is essential to follow the advice of the sealant manufacturer in this respect. 

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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