Solvents film adhesives

The market for polyurethane thermoplastic adhesives is small, but growing. TPU s are used to produce some solvent-borne adhesives and also are used in laminating textiles and films for labels and emblems. In addition, they are being considered as an alternative to solvent-borne adhesives in the shoe market. 

The Solvent Emissions Directive was adopted in March 1999 by the European Council of Ministers and should be implemented by member states within two years. The adhesives industry uses about 130,000 tonnes of solvents in its products annually and has a key role to play in meeting the Directive s targets. The main impact of emissions reduction will be on adhesives coaters because the adhesive film forms through the evaporation of solvent. For adhesives manufacturers, the main issue is the reduction of fugitive emissions. Both oxidation and recovery are well proven abatement techniques. BELGIUM EUROPEAN COMMUNITY EUROPEAN UNION WESTERN EUROPE... 

These differences in film morphology were also reflected as differences in film formation conditions, film adhesion, and in electrochemical properties. The pyrazoline beads readily formed films from solvents such as benzene. For the phenoxy TTF system, however, only CH2Cl2 was effective in forming films. In general, the TTF cross-linked polymers were found to be less adherent to the metallized substrates than the pyrazoline cross-linked polymers. Electro-chemically, it was found that the pyrazoline films showed complete activity after one potential sweep. The TTF polymer films, on the other hand, required from 5 to 20 cycles to reach full electrochemical activity as evidenced by a constant voltammogram with cycling. Furthermore, it was observed that the TTF polymer films were much less electroactive than the pyrazoline materials as shown by optical densities and total coulombs passed which were several times less for the TTF systems. 

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. 

Surface activation of BMI coupons was done by rinsing in organic solvents followed by UVOCS activation for 20 minutes. This was essential for good TiC>2 film adhesion. 

Representative data are shown in Fig. 10.5 for aluminum joints bonded with an epoxy film adhesive and a standard chromate-containing primer. Up until recently, standard corrosion-resistant primers contained high levels of solvent, contributing to high levels of volatile organic compounds (VOCs) and chromium compounds, which are considered to be carcinogens. As a result, development programs have been conducted on waterborne adhesive primers that contain low VOC levels and little or no chrome. Data are presented on several of these primers in Tables 10.8 and 10.9. 

A significant advantage of tape and film adhesives is the greater toughness that is available compared to other adhesive types. This is primarily due to the ease with which resinous modifiers can be added to the formulation via solvent solution. Thus, hybrid epoxy adhesives such as epoxy-nylon, epoxy-phenolic, etc., are often found in tape or film form. 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

TABLE 13.6 Unsupported Film Adhesive Cast from Solvent Solution9... 

Unsupported film adhesive cast from solvent solution... 

The adhesive may be solvent or water-based, hot-melt, coldseal or heatseal and pressure sensitive or chemically reactive. So the solidification process may occur via drying of water or solvent-based adhesives, by cooling of hot-melt and heat-seal adhesives, or by curing of chemically-reactive systems. With two notable exceptions - self-adhesive labels used on items of fruit or vegetables, and heat-sealable layers on packaging films - adhesives are in general not intended to touch the packaged food directly. 

Lawson et al. (2000) examined the migration of constituents from solvent-free adhesives used to bond 12 pm PET film to 45 pm LDPE. The technique of MALDl-MS, a soft ionisation technique capable of looking at sample mixtures over a mass range of 150-500,000 Da without prior separation, was employed. The adhesives studied were based on a solution of mixed isomers of MDl in polymeric MDI with either polyether or polyester-based polyols. Pouch testing of cured laminates with distilled water was undertaken (two hours at 70 °C) with the LDPE surface in contact with the water. 

Effects of surface roughness and coating solvent on film adhesion to tablets. J. Pharm. Sci. 1975, 64, 1554—1557. 142. 

Film adhesive, glue powder, solvent-based adhesive as a reference to the form of supply. 

Film adhesives have to be strictly delimitated from adhesive tapes and adhesive strips (Sections 5.6 and 5.7). Mainly blocked two-component reactive adhesives (Section 3.1.4) are used raw materials. For transport and storage (at low temperatures) they are applied to a - nonadhesive - substrate. Prior to processing they are removed and then applied between the adherends (compounding) and cured under pressure and heat (Sections 3.1.4, 3.2.2 and 4.1.2). Special film adhesives (e.g., phenolic resin nitrile rubber) are also activated by suitable solvents. 

Hot-melt adhesive films (heat sealing), contact adhesives, solvent-based adhesives. 

Minimum drying time In the case of solvent-based adhesives, the time period between the adhesive application and the fixing of the adherends, to enable the evaporation of the major part of the solvent from the liquid adhesive film. 

Type of adhesive Adhesives based on different adhesive raw materials with special processing properties (e.g., hot-melt adhesives, pressure-sensitive adhesives), different purposes of use (e.g., wallpaper paste, wood glue), processing temperatures (e.g., cold glue, heat-curing adhesives), availabilities (e.g., adhesive films, solvent-based adhesive). 

Film adhesives require an outside means such as heat, water, or solvent to reactivate them to a tacky state. Among the film types are some hot melts, epoxies, phenolics, elastomers, and polyamides. Film adhesives can be die cut into complicated shapes to ensure precision bonding of unusual shapes. Applications for this type of adhesive include bonding plastic bezels onto automobiles, attaching trim to both interiors and exteriors, and attaching nameplates on luggage. 

Solvent-based adhesives are made by dissolving suitable solid materials in appropriate organic liquids. The solution is the liquid phase, which carries out the wetting of the substrates then the solvent is removed by evaporation, leaving a solid adhesive film. 

A special type of organic solvent-based adhesive is the so-called contact adhesive. This makes use of the fact that certain elastomeric or rubbery solids (e.g., polychloroprene) have the property of autohesion, i.e., they can stick readily to themselves, especially if compounded with resins and containing small amounts of solvents. The bonding takes place by a diffusion process, the adhesive being applied to both surfaces to be bonded. Thus substrates may be coated with a contact adhesive, the adhesives can be allowed to dry till most of the solvent has evaporated (the dry adhesive film at this point will contain... 

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