Tack-free time

When formulating a silicone adhesive, sealant, or coating, based on hydrosilylation addition cure, one must consider the following properties of the uncured product pot life, dispensing technique, rheology, extrusion rate, cure performance. These characteristics directly affect the processing properties of the polymer base or crosslinker parts. The degree of cure conversion at the temperature of interest is determined by properties such as tack free time, cure profile and cure time. Once... 

If the temperature is carefully controlled, the mass will increase in volume until the mass is strong enough or the evolution of gas is low enough to prevent further expansion. This is referred to as rise time. The molecular weight is still increasing at this point. As it increases further, it passes through a point at which it no longer has adhesive character. This is known as tack-free time. If the purpose of polyurethane... 

Type Solid (%) Solvent Catalyst (DBTDL) Tack-free time n (mPa.s) Curing conditions... 

Reactive diluents can be used to reduce the modulus and increase the elongation of the cured waterborne epoxy formulations just as they are often used for 100 percent solids and solvent-borne epoxy adhesives. The reactive diluents become codispersed in the formulation with mechanical and chemical stability similar to that of the base epoxy emulsion. Polyglycidyl ether of caster oil, phenyl glycidyl ether, and diglycidyl ether of neophenyl glycol are examples of mono- and difunctional reactive diluents that have been used to improve flexibility and increase the tack-free time of waterborne epoxy adhesives. 

Test Method for Tack Free Time of Caulking Compounds and Sealants Specification for Nonbituminous Inserts for Contraction Joints in Portland Cement Concrete Airfield Pavements, Sawable Type Specification for Joint Sealant, Hot Poured, Elastomeric Type, for Portland Cement Concrete Pavements... 

D2377 TM for tack-free time of caulking compounds and sealant. C.2.2.2 Waterproofing... 

Physical properties were evaluated using standard DIN or ASTM specifications. The sealants were filled into Teflon molds to form homogeneous test pieces of comparable thickness. The specimens were then moisture cured and conditioned at 25 °C and 50% relative humidity for 14 days before mechanical property testing. The hardness of the cured sealant samples was measured by Shore A. Shelf life at 50 °C was determined for a maximum of 21 days. Tack-free times were determined by finger touch under ambient conditions. For adhesion testing the substrates were first wiped with either methyl ethyl ketone (aluminum, steel, glass, concrete, wood) or methanol (PVC, PMMA, ABS, polystyrene), then washed with detergent, rinsed with distilled water, and allowed to air dry prior to preparation of the test specimens. Specimens were cured for 14 days at ambient conditions. 

The technical terms employed in the figures are as follows Cream Time—the time between the start of the mixing and the point at which the clear mixture turns creamy or cloudy and starts to expand Gel Time—the time interval between the start of mixing and the start of gelation Rise Time—the time interval between the start of mixing and the completion of expansion of the foaming mass and Tack-Free Time— the time interval between the start of mixing and the time to reach a non-sticky state. 

In the case of flexible foams, gelling usually occurs before rise and tack-free times come after rise is completed. In contrast, tack-free times of rigid urethane foams sometimes are needed before rise is completed, although they are usually reached after rise. 

Reactivity, seconds Cream time Rise time Tack-free time Foam Properties... 

Cream time, rise time, gel time and tack-free time are influenced by environment temperature, component temperature, and catalyst level. 

TFT Tack-Free Time—the time required for the mixture to become tack-free while it is rising or has finished rising... 

Figure 6.2.12 Potlife and tack-free time of a high solids polyester/1,6-diisocyanatohexane trimer (isocya-nurate). Potlife is defined as doubling of the viscosity. Tack-free time of a coating is measured. Potlife,...

Figure 3. Device for measuring tack-free time (1) probe (absorbent cotton) (2) timer controlling interval between exposure and activation of probe (3) oscillating stage (4) exposure timer (5) constant temperature bath and circulator (6) air pressure regulator controlling pressure on probe (7) General Electric UA-3 mercury arc, reflector, and shutter (inside enclosure)...

The tack test is administered by a small air-driven piston, to one end of which is attached a probe consisting of a ball of absorbent cotton. Pressure on the probe is controlled by air pressure driving the piston. A tacky coating is readily recognized by the tendency of cotton 1 inters to adhere to it. The number of seconds following exposure for a coating to become hard enough that it does not pull cotton 1 inters from the probe is defined as the "tack-free time". 

Ultraviolet radiation is required only for the first step. The second step, while independent of UV radiation, is influenced by heat. Continuous exposure to a mercury arc to determine tack-free time can influence the course of the polymerization because of an increase in temperature of coating and substrate caused by the intense heat of the mercury arc. To avoid this complication and to maintain control of the temperature of the coating during cure, exposure to the mercury arc was generally limited to two seconds. This proved adequate to give a tack-free condition within one second following exposure for the most reactive epoxides. 

The PM and TPS photoinitiators generally gave shorter tack-free times than DPI and at the lower concentration level, PM was somewhat more effective than TPS. This can be attributed to the more efficient use of the mercury arc radiation by the PM photoinitiator, which has an absorption peak at 313 nanometers (Figure 4), corresponding to a peak in the emission spectrum of the mercury arc. Absorption maxima for DPI and TPS are at the lower end of the spectrum, far removed from the peak output of the high pressure mercury arc. 

Cationic polymerization is terminated by the presence of contaminants, including water. In experiments to note the combined effects of temperature and humidity on tack-free time, temperature of the substrate was controlled by means of the oscillating stage, as described above, and humidity was controlled by conducting the experiments in an environmental chamber. Results are shown in Table XI. 

High humidity (85%) caused a drastic increase in tack-free time when the substrate was maintained at 35°C or less. When the substrate temperature was raised to 45°C, the effect of high humidity on tack-free time was overcome and rapid cure was observed. Under commercial UV curing conditions (i.e., multiple 200 watt per inch lamps and no control of substrate temperature), coatings would ordinarily reach or exceed 45°C on exposure to the mercury arcs and this would tend to obscure the effects of high humidity. 

Table VIII. Tack-Free Time of Various Epoxides Photosensitized with PM, DPI, or TPS...

Table XI. Comparison of Photoinitiators (PM, DPI, TPS)—Influence of Temperature and Humidity on Tack-Free Time...

NCO/OH Ratio Feed Temperature F Mold Temperature F Tack-Free Time Sec. 

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