Can sealant

MAJOR PRODUCT APPLICATIONS cosmetics, pharmaceuticals, mbber, tire, paint, coatings, paper, agriculture, floor covering, crack fillers, primers, films, wire and cable, electrical accessories, can sealants, roofing membranes, syringes, coated fabrics, tennis balls, urethane sealants, foam, gaskets, footwear... 

Zonarez . [Arizona] Polyterpene resins thertnofdastic polymers for adhesives, rubber cements, emulsion adhesives, hot melt adhesives/coadt, can sealants, caulking and general sealants., ink, paints, concrete waterproofing agents, varnishes, chewitig and bubble gum bases. 

NR compounds have better heat ageing characteristics, and hence they are used preferably as seals and gaskets, as food can sealants and teats, and as soothers, as well as for the production of gloves. In food processing equipment, NR compounds are found in the belting and hosing products mostly (for both aqueous and fatty foodstuff), and in dairy hosing milk liners. 

Chem. Descrip. French process zinc oxide CAS 1314-13-2 EINECS/ELINCS 215-222-5 Uses Pigment, filler for latex compds., plastics, can sealants, paint/coat-ing, zinc chems., food can liner coatings Features Prevents discoloration of food from sulfides of iron or tin Properties Free-flowing granular powd. 0.10-0.13 p mean particle size ... 

Zinc Oxide Grade AZO 66USP Zinc Oxide GradeAZO 77USP filler, can sealants... 

Environmental concerns, which have resulted in restrictions on the use of organic solvents, have been the impetus for a strong interest in the use of rubber latexes in the formulation of pressure sensitive tapes and labels, can sealants, and contact adhesives. The availability of suitable rubber latexes and tackifying resin dispersions have made this change pos-... 

The service conditions in these applications can be characterised into two sets. The first is typified by tubing, hosing and belting where a large contact area of rubber is used but which makes only transient contact with a large volume of food or drink. The second type is typified by can sealants where only a small surface area is exposed to the food or drink but for a prolonged period. 

Although the manufacture and sale of adhesives is a worldwide enterprise, the adhesives business can be characterized as a fragmented industry. The 1987 Census of Manufacturers obtained reports from 712 companies in the United States, each of which considers itself to be in the adhesives or sealants business (13) only 275 of these companies had more than 20 employees. The total value of material shipped by these companies approached 4.7 biUion... 

Adhesives are used to transfer loads and are typically designed with much higher tensile and shear strengths than sealants. The most important rating of an adhesive ia many appHcatioas is the determiaatioa of how much load it can handle. Some sealants are used as adhesives and some adhesives as sealants and thus arises the occasional blurring of their roles. If the material s primary function is the exclusion of wiad, water, dirt, etc, it is a sealant. 

Although sealant manufacturer s Hterature commonly reports modulus values, these values must be interpreted carefully. Specimen sizes, test rate, cure conditions, and the time a sealant has been allowed to cure when tested can all have a significant effect on modulus. Therefore, for a tme comparison, sealants should be evaluated by a standard test that examines all sealants by the same procedure. In general, the longer a sealant has been allowed to cure, the more reaUstic the modulus data. 

Wea.ther lbillty. One of the more destmctive elements is exposure to sunlight specifically, ultraviolet (uv) light. AH sealants are affected by weathering, but there is much difference in the effect of weathering on different sealants. Most sHicones are stable with respect to uv exposure. Urethanes and polysulfides show effects of uv exposure, but can be formulated with uv absorbers to provide reasonable lifetimes in most appHcations. However, there are exceptions in aH classes of sealants and specifiers must be carehil to look for test data that has proven a specific sealant s durabHity. The source of the test data is also important data from an independent testing laboratory is generaHy apt to be more reHable. 

Adhesion Life. A second key factor in determining the durabHity of a sealant is the abHity of the sealant to adhere to the substrate through its lifetime. A sealant may have exceHent resistance to uv effects, but if it has poor adhesion performance and faHs adhesively, it is of Httie use. The same can be said of a sealant with superior adhesion characteristics but poor resistance to uv. Either situation results in a short performance life. 

The modulus of elasticity can also influence the adhesion lifetime. Some sealants may harden with age as a result of plasticizer loss or continued cross-linking. As a sealant hardens, the modulus increases and more stress is placed on the substrate—sealant adhesive bond. If modulus forces become too high, the bond may faH adhesively or the substrate may faH cohesively, such as in concrete or asphalt. In either case the result is a faHed joint that wHl leak. 

Another way to determine durabHity is to find successfuHy sealed, existing field instaHations. Sealant manufacturers often have case histories of successful instaHations. Adhesion performance can vary widely with sealant type, substrate type, and cleaning method. Eor this reason, it is important to understand the sealant s sensitivity to cleaning practices. Often with difficult-to-adhere substrates, a primer is used. Sealant manufacturers can provide recommendations as to which substrates require primers, what type of primers should be used, and how they should be appHed. 

Sihcone polymer plasticizers have historically been used in many formulations. These plasticizers (qv) are of the same Si—O backbone as the functional polymers but generally are terrninated with trimethyl groups which are unreactive to the cure system. This nonreactivity means that, if improperly used, the plasticizer can migrate from the sealant and stain certain substrates. Staining has been a widely pubHcized flaw of sihcone sealants, but the potential of a formulation to stain a substrate can be minimized or eliminated with proper formulation work. In general, this is accompHshed by not using plasticizers for formulations developed for stain-sensitive substrates. 

Urethane sealants have good inherent adhesion to most substrates, but silane adhesion promoters are often used to improve this adhesion. Epoxy-, amino-, and mercapto-functional silanes are the most common because of their dual reactive nature. The silane end can react with surface hydroxyls the epoxy, amino, or mercapto end can react with the isocyanate. 

---