Aged tack

Even though phenol formaldehyde tackifying resins are more expensive than most other tackifying resins such as the hydrocarbon type, they are commonly preferred because they impart better aged tack (they retain tack after storage). They are commonly used in the tire industry. 

These phenol formaldehyde resin tackifiers can be replaced by less expensive hydrocarbon resins however, they may not impart adequate aged tack values. 

This is a premium tackifying resin vs. the conventional phenol formaldehyde resins already discussed. However, this more expensive tackifying resin is only used when better aged tack is needed in the factory. 

Under extreme conditions, sometimes this tackifying resin will outperform the phenol formaldehyde resin discussed earlier, especially for imparting better aged tack. 

Hydrocarbon resins from petroleum are commonly used as a less expensive alternative to phenolic tackifying resins. These resins are commonly used in the tire industry however, they do not impart aged tack as good as phenolic tackifier resins. 

Polyterpene resins are commonly used as tackifying resins to impart building tack to rubber compounds, especially if the compound is based on EPDM, which does not possess very much inherent tack. Polyterpene resins do not impart long-term aged tack as good as the phenol formaldehyde resins. 

Adhesives. Acryhc emulsion and solution polymers form the basis of a variety of adhesive types. The principal use is in pressure-sensitive adhesives, where a film of a very low T (<—20 " C) acrylic polymer or copolymer is used on the adherent side of tapes, decals, and labels. Acrylics provide a good balance of tack and bond strength with exceptional color stabiUty and resistance to aging (201,202). AcryUcs also find use in numerous types of constmction adhesive formulations and as film-to-film laminating adhesives (qv). 

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

The BR and PIB adhesives have permanent tack but relatively low cohesive strength. Cohesive strength is provided by adding natural rubber, fillers or tacki-fiers. Furthermore, these adhesives have excellent resistance to chemicals, oils and ageing. 

The G types do not require further acceleration during cure, but exhibit slightly inferior ageing characteristics. Resilience and tack are generally better than with the W types. 

November 1954, K.U. Leuven Archives, Noddack-Tacke Papers, 634. Having applied for a position in Berlin, he writes a letter to I.N. Stranski that his age is not a real obstacle but rather the fact that he had been appointed in Strasbourg during the war. 

Tack is the ability of two rubbery materials to resist separation after bringing their surfaces into contact for a short time under light pressure. The effect of para-tert-octyl phenolic (PTOP) resin on the tack of isoprene/N660 compound has been studied before and after ageing with FTIR spectroscopy [170]. 

This section describes a methodical procedure that allows reliability issues to be approached efficiently. MEMS reveal specific reliability aspects, which differ considerably from the reliability issues of integrated circuits and macroscopic devices. A classification of typical MEMS-failure modes is given, as well as an overview of lifetime distribution models. The extraction of reliability parameters is a Tack of failures situation using accelerated aging and suitable models. In a case study, the implementation of the methodology is illustrated with a real-fife example of dynamic mechanical stress on a thin membrane in a hot-film mass-airflow sensor. 

Morahan ITl change tack and ask about the age-dependent switch between the generalized TB and the re-emergent TB. This has a parallel in type 1 diabetes, where there seems to be a major incidence before the age of 5 and then again around about the age of puberty. Do you have any idea about what it is about the changing nature of the immune response that causes this re-emergence phenomenon ... 

Humidity, test temperature, and the age of the test samples all will affect tack measurements therefore these variables should be controlled in order to assure good test repeatability. Testing in a temperature- and humidity-controlled room is advised. Also, optimal test dwell time and contact pressure should be selected and used as the standard test conditions. Variations in these properties will affect results. 

Ease of modification Most elastomeric adhesives can be readily modified in viscosity, tack, drying time (for solvent-based products), strength properties, heat resistance, aging characteristics and other properties to fit process and... 

Pressure-sensitive or permanent-tack adhesives are, as their name implies, adhesives that remain sticky even when dried or cured. This means that they are capable of bonding to surfaces simply by the application of light pressure. This makes them arguably the most convenient products available today from the end user s viewpoint and undoubtedly, accounts for the success they enjoy. Although figures are hard to come by, a survey by Business Trend Analysts quoted in the June 1990 issue of Adhesives Age shows that pressure-sensitive adhesives grew from 38% of total adhesive sales in the United States in 1980 to 44.6% in 1988, at an annual rate of 12%, to reach a sales value of 4.9 billion in 1989. 

PROPERTIES OF SPECIAL INTEREST Standard emulsion SBR is a general purpose rubber. Most widely used synthetic rubber in the world. Better tire tread-wear and aging properties than natural rubber. Good abrasion resistance and crack initiation resistance. Poor in tack and heat build-up. Physical properties are poor without reinforcing fillers. Solution SBR is a speciality rubber and more expensive than emulsion SBR. Solution SBR with high vinyl and styrene levels is used in high performance tire treads to improve wet traction. Also used as impact modifier in plastics and as thermoplastic elastomers. 

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