Standard adhesive application method

Standard adhesive application methods are insufficient when small amounts of adhesive are necessary. Dispenser units, working with air or extruder feed, are often used for the application of the adhesives. Here, the handling of the COTiductive adhesive is often limited because of the particle size. Another technology utilizes shaped adhesive films. This is an attractive way to produce a complex series. Non-shaped films can be used for non-conductive bonding through the use of pressure and heat. 

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

The large standard deviation observed (compared with untreated papers) reflects nonuniformity in sample thickness produced by the above methods of adhesive application. Generally, it was observed that the treated paper ruptured before the adhesive. The double folds to rupture the paper and the double folds to complete rupture of the system are reported. 

This brief summary report describes the state of the art of all types of cellular materials, particularly plastics and elastomers. The report is organized in the form of a handbook and has an Introduction and sections on Types of Foams (Cellular Materials), Methods of Manufacture, Foam Properties, Solvent Cementing and Adhesive Bonding of Foams, Methods of Making Foams Conductive, and Applications. There are two Appendices, one on Standardization Documents (Test Methods, Practices and Specifications) and the other on Definitions. 

Table 2.9 gives a Kst of various adhesives and typical applications in bonding of plastics. This table is not complete, but it does give a general idea of what types of adhesives are used and where. It should be remembered, however, that thousands and thousands of variations of standard adhesives are available off the shelf. The computer may shape up as an excellent selection aid for adhesives. Selection is made according to the combination of properties desired, tack time, strength, method of appKcation, and economics (performance/cost ratio). 

In the selection of a sealant or caulk, the methodology of performance evaluation must be understood. The performance data by the manufacturer must be quantifiable and comparable to other materials. A method must be used to determine the appropriateness of a sealant or caulk in a specific application. Test methods and specifications have been established by the ASTM, Bureau of Standards, Adhesive and Sealant Council, and other agencies. 

As should be apparent from the variety of applications, there are many test methods for hot melts, most of which are application specific. Many such tests were developed by adhesive suppliers and are proprietary to them. The use of standardized testing is most common for PSA tapes and labels. These tests are discussed elsewhere in this volume. 

Pressure-sensitive adhesives are used in a great variety of applications, most commonly for adhesive tapes. In that case, they have to be tested by static shear test or dynamic shear test The difference between these two methods is that in static shear test a standard force is being applied to the test specimen and the adhesive failure is reported as the time it takes for failure to occur. The dynamic shear test involves a force being applied to the PSA tape at a specific rate of speed (typically 0.25 mm or 0.1 in. per minute). The value reported is as the peak force per unit area (Ib/in, also abbreviated as psi, and in SI units MPa) required to cause adhesive failure. The standards for adhesion shear tests are ASTM D3654, ISO EN 1943, and PSTC-107.i i ... 

Flame Treatment. In this the surfaces are flamed, usually by application of a gas burner for a brief period. Factors such as the temperature of the flame (the ratio of gas to air in the fuel), distance of flame from the surface, and speeds of travel of flame and objects, all are critical—and small variations in any of these factors can lead to unsatisfactory results (that is, under-treatment, or overtreatment). Because of this, standardization and consistent results are best achieved through programmed control with robots. Even so it is difficult to treat more complex shapes satisfactorily, and normally such items would be primed after flame treatment—that is, two methods of promoting adhesion vould be used in combination. 

In applications where possible degrading elements exist, candidate adhesives must be tested under simulated service conditions. Standard lap shear tests, such as ASTM D1002, which use a single rate of loading and a standard laboratory environment, do not yield optimal information on the service life of the joint. Important information such as the maximum load that the adhesive joint will withstand for extended periods and the degrading effects of various chemical environments are addressed by several test methods. Table 15.2 lists common ASTM environmental tests that are often reported in the literature. 

The specification writer must try to put into the specification the requirements that, if met, will provide the greatest likelihood of success. These requirements should be standard tests and acceptable test limits that are agreed upon by both the supplier and the user. The tests should be indicative of how the adhesive is used in production and how the finished joint is to be used in service. Tests that are not directly applicable to the specific application should not be included. Tests should not be used simply because they are standard test methods or have been used in the past. 

Numerous standard test methods have been developed by various government, industrial, and university investigators. Many of these have been prepared or adopted under the auspices of the ASTM Committee D 14 on Adhesives or other professional societies. Reference to the appropriate standards will adequately equip one with the background necessary to conduct the test or a version of it. Several of the more common standard tests are described in this section. Numerous variations exist for specific applications or materials. In these descriptions, the emphasis is on understanding of the reasons for the test, its relationship to a specific adhesive property, advantages and limitations of the test, and possible variations or extrapolations of the test method. The detailed description of the test mechanics is kept to a minimum, since they are adequately covered in the existing standards and specifications. 

Results. Phenolic adhesives are usually manufactured with little or no fillers because of their applications. They are soluble in solvents and dilution methods can be readily applied to the analysis of these products but if trace analysis is required for health or environmental reasons destructive methods may be necessary. Excellent results can be obtained for the determination of calcium and copper sulphonate salts added to products using the internal standard method. These low density adhesives can be analysed without resorting to destructive methods (Table 6.22). 

To enable the determination of almost pure strength values for the adhesive layer, the parameters eccentric application of load and adherend extension/ deformation must be eliminated. This is the case in the test piece geometry depicted in Figure 10.4 according to the standard ISO 11003-2 Shear testing method for thick adherends . 

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