Contact-bond recommended adhesives

Adhesive- bonded Synthetic and glass backed PVDF(60, 90, 118 mils) ECTFE (60, 90) Glass backed ETFE (60, 90 mils) PTFE (80, 120 mils) FEP ( 60, 90 mils) PFA (90, 110 mils) MFA (60, 90 mils) Contact or thermosetting adhesive Weld rod and Cap strip welds Shop or field Pressure OK Full vacuum up to 120°F (49°C) Max Temp 275°F (135°C) None Visual Spark Possible Testing recommended... 

An example of a 100% solid, non-flammable, heat-activated hot-melt adhesive recommended for structural bonding of aluminum, steel, copper, brass, titanium, fabric, and some plastics is 3M Company s Scotch -Weld Thermoplastic Adhesive Film 4060. Strength data are shown in Table 5.5. " Bonding using this clear, amber, unsupported film adhesive takes place rapidly. The speed of bonding is hmited only by the heat-up time required to reach the optimum bonding temperature of 149°C at a pressure sufficient to maintain contact between the surfaces to be bonded. The adhesive... 

Epoxies, urethanes, cyanoacrylates, and thermosetting acrylics will result in bond strengths greater than the strength of the acrylic part. The surface needs only to be clean of contamination. Molded parts may stress crack when in contact with an adhesive containing solvent or monomer. If this is a problem, an anneal (slightly below the heat distortion temperature) is recommended prior to bonding. 

Application of Primers and Sealants A primer solution can be applied to the aluminum surface prior to bonding with the adhesive to improve wet strength. Primers are low viscosity fluids that are typically a 10% solution of the adhesive in an organic solvent, which can wet out the aluminum surface. This leaves a coating on which the adhesive can readily flow and attain intimate contact. Viitually all adhesive suppliers recommend a primer for their paste of film adhesives when they are used to bond aluminura... 

National legislation on adhesives includes German BfR Recommendation XXVIII (Components of adhesives) and US FDA Title 21 Part 175 on adhesives. Part 175.105 deals with adhesives overall and Part 175.125 deals with pressure-sensitive adhesives. In addition, FDA Part 177.1390 permits the use of certain high temperature laminates that may be safely used for food contact at temperatures up to 275 °F, given that only the specified adhesives are used to bond the layers that make up the laminate. Part 177.1395 permits certain laminates that may be safely used at temperatures between 120 °F and 250 °F. However, it does not specify permitted adhesives. 

Polystyrene Although polystyrene is usually bonded by solvent cementing, it can be bonded with vinyl acetate/vinyl chloride solution adhesives, acrylics, polyurethanes, unsaturated polyesters, epoxies, urea-formaldehyde, rubber-base adhesives, polyamide (Versamid-base), polymethylmethacrylate, and cyanoacrylates. The adhesives should be medium-to-heavy viscosity and room-temperature and contact-pressure curing. An excellent source is a Monsanto Company technical information bulletin which recommends particular commercial adhesives for bonding polystyrene to a number of different surfaces. Adhesives are recommended in the fast-, medium-, and slow-setting ranges (10). 

To avoid inner tensions through thermal stress, it is recommended to use only adhesives that cure at room temperature. The adhesive selection is limited by the fact that many applications require an invisible glueline. In such cases, adhesives with fillers are excluded, cyanoacrylates and in particular radiationcuring products (Section 9.3.3) are the suitable choice. If the visual appearance of the bonded joint is not important, two-component reactive adhesives based on expoxides, polyurethanes, methacrylates, contact adhesives and, if required, adhesive tapes are recommended. 

Solvent-based adhesives, hot-melt adhesives (paperboards, cardboards), dispersion adhesives (for further information refer to Section 5.2). Tip For bonding of papers, paperboards, photos and the like, glue-sticks - available for detatchable and nondetachable bonded joints - are recommended because of their convenient application (Section 5.8). Solvent-based adhesives, dispersions, hot-melt adhesives, contact adhesives (for further information refer to Section 9.5). 

Application of activator to both substrates is recommended where one substrate is porous or where gaps more than 20 mils are to be filled. Activator and adhesive may be applied to the same surface, but this initiates the bonding action so that the parts must be joined immediately. For example, in automobile hem bonding, adhesive is applied in "chocolate drops" and activator is sprayed over the drops. The hem is formed immediately, squeezing activator and adhesive into intimate contact. 

Use of contact adhesives is a good solution for a variety of miscellaneous bonding problems in the home where nonporous surfaces are involved and immediate high bond strength is a requirement. The adhesive is applied via paint brush or paint roller, with normal application recommending two coats to be applied to the nonporous surface, chipboard in this case. 

Various etchants have been recommended for the remaining metals of engineering practice, but it is doubtful if sufficient work has been reported to differentiate between them or to assess their effect on the durability of the bonds formed with different adhesives. Strong, durable bonds are uncertain with copper because of the ease with which a weak, friable oxide is formed. Even when coated with an adhesive, oxygen can diffuse to the interface and eventually cause failure. Brass has an oxide film almost entirely of zinc oxide and, as with zinc galvanized iron, it can hydrate or form salts with the tackifiers added to some contact adhesives. Cadmium is met with as a plating if a strong, durable adhesive bond is essential, it should be replaced by chromium, the surface of which can be treated as stainless steel. 

Once the adhesive or sealant has been applied to the substrate or substrates, the joint should be assembled within the allowable open or assembly time, that is, between the minimum and maximum recommended times. With solvent-home contact adhesives, for example, sufficient time for solvent evaporation must be allowed to prevent solvent entrapment, which can lead to premature failure, especially when bonding impermeable substrates. The maximum open time with hot-melt adhesives, which set on cooling, can be very short and should be closely monitored. 

Hart-Smith and Thrall (1985) recommend a visual inspection of the adhesive fillet and surest it is the most effective of all inspection techniques for bonded joints. The state of the fiUet is a good indication of the state of the adhesive at the end of the joint. A porous fiUet indicates too high a heat-up rate or the presence of moisture in the joint. A lack of fillet indicates a lack of pressure and may indicate internal voids. Just as the water-break test is an indicator of the adherend surface, the contact angle of the cured adhesive at the end of the fiUet, formed when the adhesive was liquid, indicates if surface contamination is present. 

Flooring mastics based on nonorboxylated SBR HSL are employed primarily in carpet and mineral fiber or felt-backed vinyl glue-down apphcations over most common sub-floor surfaces. Such SBR based adhesives are not recommended for unbacked vinyl (PVC) applications due to plasticizer migration from PVC to the adhesive and bond loss issues. Conventional felt backings provide an effective barrier to plasticizer migration. In contrast, acrylic copolymer based floorplasticizer resistance is required. 

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