Acrylic adhesives applications

Although the acrylate adhesives are readily available and studies have shown that they can produce reasonable bonding properties, they have the disadvantages of having high shrinkage, high fluid absorption, and low service temperatures. Acrylate adhesive applications would be limited. The development of EB-curable epoxy adhesives would have applications in the aerospace and automotive industry and potential wider uses. The most immediate application for these resin systems is composite repair of commercial and military aircraft. 

Acrylic adhesives can also be used in automotive assembly. For example, the hem flanges between the inner and outer panel of automotive doors can be bonded with acrylic adhesives [153]. There are many smaller industrial assembly applications where acrylic adhesives are applicable. An interesting recent example is the bonding of cable splice enclosures, using a borane initiated adhesive [154]. 

Table 3 lists the selected properties [16] that we have measured for several commercially available acrylate resins manufactured by the Sartomer Company and the Rohm and Haas Company. The resins were cured in an AECL Gammacell Model 240. The temperature rise was measured for an 8-g sample using Acsion s (formerly AECL Radiation Applications Branch) Gamma Calorimetry method [17]. All of this information is being used to evaluate the applicability of EB-cured acrylate adhesives for repairing composite structures. Combinations of these adhesives can be used to create electron-curable adhesives suitable for composite repair. 

Surfactants act as wetting agents by lowering the surface tension of the waterborne epoxy. Silanes can be used to increase adhesion to certain substrates and fillers, as shown in Table 14.4, formulation C. Water-compatible thickeners and protective colloids such as polyvinyl alcohol, substituted cellulosics and sugars, and some acrylics improve application properties and offset viscosity decrease seen with water dilution. 

Paste adhesives are supplied as either one- or two-component adhesive systems. They can be used in applications where pressure cannot be applied. Some two-part pastes cure at room temperature after the appropriate proportions are mixed. Epoxy, urethane, and acrylic adhesives are all available as paste adhesives. 

One of the most important features of SBC adhesives is their versatility. Because they are thermoplastic materials of carefully controlled molecular weight, they can be applied both as hot melts and from solvent. More importantly, adhesive manufacturers can tailor their properties to match a wide range of applications. The primary competitors for SBCs in the pressure-sensitive adhesive market are acrylic copolymers. While acrylics have better specific adhesion to polar materials, adhesive manufacturers cannot easily formulate them for varied adhesion applications. 

The photographs in Fig. 2 show the stratum cor-neum cells removed by the PSA after 0.5 hr of application to the forearm. Acrylic oil-gel has a formulation as described above, whereas original acrylic is the same acrylic adhesive without IPM and cross-linker. It is clear that on removal, substantially fewer cells were removed by the acrylic oil-gel compared with the original acrylic. 

AMS dimer was used to prepare a macromonomer of 2-ethylhexyl methacrylate. Copolymerization of the resulting macromonomer with butyl acrylate and acrylic acid gave a polymer backbone with Tg less than 10 °C that is useful in adhesive applications.486 The adhesive is better than the same composition made without the intermediacy of the macromonomer. 

Gelva [Solutia], TM for a family of acrylic multipolymer products designed for high-performance, pressure-sensitive adhesive applications where skin adhesion, high temperature and/or diffi-cult-to-adhere-to surface are involved. Provided for both solvent and water based grades. 

In the second example (Table 2), two acrylic adhesive formulations are compared. The first contains a hydrogenated rosin ester tackifier, which shows relatively good UV stability. This tackifier can be replaced by one of lower stability (and lower cost), such as the nonhydrogenated rosin ester, by the incorporation of the appropriate light stabilizers. As these data show, some improvement in stability is seen when a BTZ is used at 0.5% (or a combination of BTZ/HALS at 0.25%/0.25%), but the best stability is achieved when the adhesive is stabilized with a HALS at the same level (0.5%). It should be pointed out that BTZs are commonly used in films and coatings (e.g., automotive clear coats) when the objective is to protect the material below the film. Similar applications can be imagined where UVA-containing adhesive films are used to screen and protect other substrates. 

Most acrylic adhesives are supplied as two high viscosity liquids or pastes that are mixed together, called Mix-in Accelerator systems. Some types can also optionally be cured by no-mix accelerator lacquers. Accelerators are low viscosity liquids which are brush or spray applied to one or both of the substrates being bonded. Following accelerator application, the unmixed adhesive is applied to the primed substrate. This method eliminates the need for premixing the adhesive and accelerator, which eliminates pot life concerns. 

Another advancement in acrylic adhesives has been in the area of acrylics with improved low temperature properties, sometimes called HI or high impact acrylics. These variants of the technology not only offer outstanding low temperature properties, but also significant heat resistance makes them ideal for applications where product performance over a wide temperature range is required. Formulators have also further advanced the art in the use of ingredients that are nonflammable and have little or no odor. 

The no-mix or honeymoon type acrylic adhesives are unique in that polymerization is adequately achieved after the A component of the adhesive is applied to one substrate to be bonded, and the B component is applied to the other substrate to be bonded. When these two halves are joined together, as shown in Fig. 6 previously, enough free radicals are generated to initiate and complete the cure. The no-mix technology is unique in that it has found extensive use in the electronics industry, and is a very useful technique in bonding magnets for electrical motors where the fast cure and easy application technique have found extensive utility. 

The new generation of acrylic adhesives show their versatility in other electronic assembly applications. 

Apart from underbody coating (usually PVC based), which is not explained further, the majority of bonding and sealing products in the paint shop are also PVC compounds. Acrylate plastisols are not often used and polyurethane-based sealants are rarely found. The main applications are in seam sealing and antiflutter bonding. On a small scale there are adhesive applications to bond and seal caps and to fix sound deadeners. In addition, foams and butyls as well as bituminous or acrylic-based sealants are used to fill car body holes. 

This type of application sounds ideal for a UV- or light-cured acrylic adhesive that can be cured by irradiating through the glass. Full bond strength can be achieved in a few seconds. These adhesives are expensive and require lamps for the irradiation, but the increase in productivity is tremendous. 

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