Temporary adhesive

A few examples are discussed in Chapter 9 wherein the future will see the biosynthesis of biodegradable protein-based thermoplastics, materials to prevent postsurgical adhesions, temporary functional scaffoldings to direct tissue reconstruction, and drug delivery devices for new drug release regimens. 

Gunmetal eccentric strap secured to faceplate using adhesive. Temporary joint while component is machined. Photo courtesy Ted JoUiffe)... 

Acryhc modifiers for cement impact strength and adhesion to substrates are discussed in reference 211. Both water-soluble acryhc and acryhc emulsion polymers are used in the ceramic industry as temporary binders, deflocculants, and additive components in ceramic bodies and glazes (212) (see Ceramcs). 

In the category of industrial appHcations, nylon is the predominant fiber used in the carcass of bias tmck, racing car, and airplane tires because of its exceUent strength, adhesion to mbber, and fatigue resistance. Nylon is used less in the carcass of radial tires for automobiles and in replacement bias and bias-belted tires because of the development of temporary flat spots. For this reason, nylon has lost most of this market to polyester. 

During World War II, polychloroprene was chosen as a replacement for natural rubber because of its availability. Two copolymers of chloroprene and sulphur which contain thiuram disulphide were available (Neoprene GN and CG). One of the first successful applications of these polychloroprene adhesives was for temporary and permanent sole attachment in the shoe industry. However, these polychloroprene cements show a decrease in viscosity on ageing and a black discolouration appears during storage in steel drums. Discolouration was produced by trace amounts of hydrochloric acid produced by oxidation of polychloroprene... 

Solvent-borne NR and quick-grab adhesives are commonly used in the manufacturing of leather footwear for temporary bonding and in rubber footwear... 

Bond strength can vary from a temporary bond (non-curing compound) to a substrate tearing bond (using phenolic-modified curing products). Solvent-borne CR adhesives can be formulated to have very short open times for fast production operations or to retain contact bond characteristics for up to 24 h. Heat and solvent reactivation can be used to re-impart tack to dried surfaces. 

Cheaper raw materials are another way to reduce production costs. This includes, e.g., the minimization of the melamine content in a MUF-resin. An impeding factor can be the (often temporary) shortage of raw materials for the adhesives, as it was the case with sudden price increases for methanol (from which formaldehyde is obtained industrially) and melamine within the last decade. 

A characteristic of the group (a) of resins is that they air-dry solely by solvent evaporation and remain permanently solvent soluble. This fact, combined with the need to use strong solvents, makes brush application very difficult, but sprayed coats can be applied at intervals of one hour. A full vinyl system such as (o) possesses excellent chemical and water resistance. Many members of group (o) have very poor adhesion to metal, and have therefore been exploited as strip lacquers for temporary protection. Excellent adhesion is, however, obtained by initial application of an etching primer the best known of such primers comprises polyvinyl butyral, zinc tetroxy-chromate and phosphoric acid. 

Office supplies and office communication have been revolutionized by the introduction of the 3M product Post-it Notes in 1980. The temporary adhesive of these self-sticking notes actually was initially rejected as a glue by its inventor, 3M chemist Spencer Silver, because of its impermanence. However, 3M researcher Art Fry found a niche for the adhesive—as an adhesive for a temporary bookmark for his choir hymnal. Key to the performance of these removable, repositional adhesive products is the application of the adhesive to the backing of a note sheet via tiny microspheres rather than a continuous film. With an average particle diameter of 25-45 fim, the microsphere adhesives form a discontinuous layer that assists in retaining the ability to re-apply the note to new surfaces. Traditional adhesive tape contains particles of smaller dimension (typically 0.1 to 2.0 pm) that coalesce to form a continuous film that limits removal. ... 

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

Polyelectrolyte-based dental cements or restorative materials include zinc polycarboxylates, glass ionomers, a variety of organic polyelectrolyte adhesives as well as alginate-based impression materials. Dental cements are primarily used as luting (cementing) agents for restorations or orthodontic bands, as thermal insulators under metallic restorations, and as sealents for root canals, pits and fissures. They are also sometimes used as temporary or permanent (anterior) restorations. For further introduction to dental materials the reader is referred to standard texts [122,123]. 

Dispersion forces57 , which result from temporary variations in the distribution of electron density in atoms, can account for up to 90 per cent58 of the adhesion forces between non-polar polymers and metal substrates (bond energy 0.5-5 Kcal/ mole)50 . However, for the adhesion of epoxy resins and other polar polymers to metals, dispersion forces are of secondary importance when compared to the electromagnetic and mechanical interactions discussed above. 

As the continuous ribbon is conveyed from the forming station it may or may not be consolidated by a cold press. This prepressing operation reduces the mat thickness and increases the mat density which improves the handling characteristics of the mat, but does not initiate adhesive polymerization. The continuous ribbon is also trimmed to width and cut into individual mats, the length of which is equal to the length of the hot press. The individual mats are placed in the press loader which serves as a temporary storage area for the mats prior to hot pressing. 

Maki, J.S., Yule, A.B., Rittschof, D., and Mitchell, R., The effect of bacterial films on the temporary adhesion and permanent fixation of cypris larvai, Balanus amphitrite Darwin, Biofouling, 8,121, 1994. 

A detector wafer 14 of HgCdTe is attached to a transmissive temporary substrate 10 of glass, quartz, alumina or sapphire by the use of a removable adhesive 12. The adhesive should not be soluble in the solvents used in the detector delineation and fabrication steps that will follow. Glycol phthalate is mentioned as an usable adhesive. 

HgCdTe chips 21, comprising inspected photodiodes, are mounted on a temporary substrate 22 and the chips are electrically connected by the use of a conductive adhesive 24. 

In a second embodiment, a silicon substrate 42, a layer of silicon dioxide 44, and a thinned silicon layer 46 which includes read-out circuitry are attached to a temporary carrier substrate 50 with a layer of adhesive or wax 48. 

The silicon substrate is removed while the temporary substrate provides mechanical support. Next, the substrate is bonded to a final carrier substrate 54 with a layer 52 of epoxy adhesive. The bonding layer 48 is removed, which also removes the temporary carrier substrate 50. The final carrier substrate is chosen according to the same criteria as described in the first embodiment. Processing continues by forming indium interconnects 34b for later hybridization of the read-out integrated circuit assembly with a detector array. 

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