Adhesive polymers solvent-based

The solids contents of these dispersions generally are of the order of 50% to 60%, occasionally even higher, so that one may deposit from a certain thickness of wet adhesive quite a thick dry film of polymer. Solvent-based adhesives generally have lower solids contents (20% to 30%), and since the shrinkage after drying of water-based dispersions also is lower such adhesives can be formulated to fill gaps between materials as well as to bond them. 

One-component reactive adhesives have to be distinguished from the physically setting adhesives described in Chapter 5, which generally occur only in the form of one component, namely, the already finished polymer, for example, in the case of hot-melt adhesives, dispersion adhesives and solvent-based adhesives. They are called one-component adhesives. 

Latex adhesives replace solvent-based adhesives more easily than solution adhesives. Most latex adhesives are produced from polymers that were not designed for use as adhesives. This is why they require extensive formulation in order to obtain the proper appUcation and performance properties. Application methods for latex adhesives include brush, spray, roll coat, curtain coat, flow, and knife coat. The bonding techniques used for latex adhesives are similar to those used for solvent adhesives. The following techniques are popular ... 

In the final paper, Azrak, Joesten and Hale illustrate the effect of reformulation of acrylic contact adhesives from solvent-based to water-based systems. Requirements on the tackifier and polymer latex are discussed which lead to an adhesive with the proper balance of open time and green strength. 

Acetal homopolymer (Delrin ) is a highly crystalline polymer (Du Pont Company, www2.dupont. com) that has excellent solvent resistance. The chemical structure and solvent resistance of homopolymer acetal lead to a relatively poor adhesion of solvent-based paints and cements. This is largely... 

The dominating chemical pretreatment used in Europe for molded automotive TPO components is flame treatment. The effectiveness of the flame treatment is checked by surface tension measurement and should be a minimum of 45 dynes/cm to ensure acceptable adhesion with solvent-based paints. Chemically, the adhesion effect of flaming is based on a controlled oxidization of the CH2-and CH3 units (7). Also, a degradation of the polymer and polymer melting can occur therefore the flaming needs to be carried out within an upper and lower temperature limit. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Free mono- and multilayer films may be adhesive- or extmsion-bonded in the laminating process. The bonding adhesive may be water- or solvent-based. Alternatively, a temperature-dependent polymer-based adhesive without solvent may be heated and set by cooling. In extmsion lamination, a film of a thermoplastic such as polyethylene is extmded as a bond between the two flat materials, which are brought together between a chilled and backup roU. 

New copolymers based on a copolymerization of isobutylene and p-methyl-styrene with improved heat resistance have been reported [64]. Once copolymerization was accomplished, the polymer was selectively brominated in the p-methyl position to yield a terpolymer called EXXPO. In contrast to butyl and halobutyl, the new terpolymer has no unsaturation in the backbone and therefore shows enhanced thermal stability and resistance to oxidation. Useful solvent-based adhesives can be formulated using the new terpolymer in combination with block copolymers [65]. The hydrocarbon nature of the new terpolymer results in excellent compatibility with hydrocarbon resins and oils. 

Since it is not possible to commercially produce a polymer that is based on the cis 1,4 form, commercial polymers are based on the Irons 1,4 form which has a crystalline melting point, Tm, of +75 °C and a Tg of -45 °C. Pure 1,4 trans polychloroprene thus crystallises readily and would normally be considered to be of limited use for a rubber. Such a polymer, however, does not crystallise when dissolved in a solvent, but will do so when the solvent evaporates. This feature is used to good effect in the production of contact adhesives. 

Solvent- and Emulsion-Based Adhesives Solvent-Based Adhesives. Solvent-based adhesives, as the name implies, are materials that are formed by solution of a high molecular weight polymer in an appropriate solvent. Solvent-based adhesives are usually elastomer-based and formulated in a manner similar to pressure-sensitive adhesives. 

To conclude this discussion on zirconium, it is appropriate to look at the adhesion promotion effects of various zirconium compounds in flexographic and gravure ink printed on corona discharge-treated polyolefins and polyester. Flexographic and gravure inks are basically a pigment (often titanium dioxide) suspended in a polymer (normally called the binder) dissolved in a solvent. Actual commercial ink formulations are rather more complicated. These inks are either water-based when acrylic polymers and co-polymers are typically the binders, or solvent-based (usually ethanol-ethyl acetate mixtures) when the binder is typically nitrocellulose or cellulose acetate propionate. 

Solvent-Based Adhesives. In these formulations the polymers comprising the adhesive proper are dissolved in volatile solvents, which evaporate in the course of the transition. 

The ever increasing emphasis on reducing air pollution and on health considerations emphasized by OSHA has provided a strong impetus for adhesive manufacturers to develop water-based emulsion polymer systems to replace the organic solvent-based systems on which the industry was founded. This has been a difficult process. 

Emulsion polymerization is the basis of many industrial processes, and the production volume of latex technologies is continually expanding—a consequence of the many environmental, economic, health, and safety benefits the process has over solvent-based processes. A wide range of products are synthesized by emulsion polymerization, including commodity polymers, such as polystyrene, poly(acrylates), poly (methyl methacrylate), neoprene or poly(chloroprene), poly(tetrafluoroethylene), and styrene-butadiene rubber (SBR). The applications include manufacture of coatings, paints, adhesives, synthetic leather, paper coatings, wet suits, natural rubber substitutes, supports for latex-based antibody diagnostic kits, etc. ... 

Rubber-like polymers (made of polychloroprene, polybutadiene copolymers, SIS, SBS for adhesive bonding of elastomers and as substitutes for solvent-based adhesives)... 

The polymers are dissolved in organic solvents. Such adhesives are called solvent-based adhesives (Section 2.2.3). 

As described above, adhesives on polymer basis have to be transferred into a processible state by using adequate solvents or water. Thus, the important group of solvent-based adhesives develops, in contrast to reactive adhesives processed in the form of monomers, which, due to their mostly liquid or pastelike state, do not require solvents. In the common language use, only products containing organic and, in the majority of cases, combustible solvents in their formulations are called solvent-based adhesives. 

Solvent-based adhesives are adhesives with polymers dissolved or pasted in organic solvents. The solvents or solvent mixtures are only processing aids and have to be removed, either partly or completely, from the applied liquid adhesive layer through evaporation or penetration prior to the fixing of the adherends. The first case is necessary for solvent-impermeable materials (metals, glass, thermosetting plastics), the second case concerns porous and solvent-permeable materials (paper, cardboard, wood, leather). This process can be accelerated by heat supply. Solvents are mainly esters, ketones, if applicable, portions of different alcohols. The total solvent portion ranges between 75-85%. 

Application of surface pressure When processing solvent-based adhesives, it is in any case recommendable to apply equally distributed pressure to the adhesive layer after the fixing of the adherends. This causes the polymer molecules existing on both adherends to get jammed or entangled", which increases the cohesion strength of the adhesive layer. 

The information is limited to the most important materials, metals, plastics, (thermoplastics, thermoset materials, foams), ceramics, glass and their possible combinations. For papers, cardboards, wood, rubber polymers, usually physically setting systems (solvent-based, dispersion, hot-melt adhesives) are utilized. In these cases, the adhesive selection with regard to the manufacturing conditions and demands is of less problematic nature. 

Physically setting adhesives Adhesives already existing in the form of polymers transferred into a liquid form by solvents or water, respectively, by melting, forming an adhesive layer after evaporation or cooling (e.g., solvent-based, dispersion and hot-melt adhesives). 

Solvent-based adhesives Adhesives with adhesive-layer forming substances (polymers) being solved or pasted. Depending on the character of the adherends, the solvents must evaporate completely or partly prior to fixing. 

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