Page 75 - Handbook of Surface Improvement and Modification

70 Tack-free Surface

sample was measured, it was subjected to a measurable compression force for a controlled
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holding time. Also separation speed was preset. The Instron machine was used for the
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measurements and the results were obtained in a form given in Figure 5.2. The results
agreed in ranking with the presently used test, as follows “To determine the tackiness of a
surface, the index, middle, and ring fingers were lightly pressed onto the surface at an
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angle of about 15°. The resistance felt during the subsequent lifting of the fingers was
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regarded as a measure of tack.” Although, the instrumental method may still require more
practice and evaluation it provides means for objective testing of this important property. 2
Without an objective test, not much progress can be expected in the field.
The powdery epoxy resins such as bixylenol diglycidyl ether and triglycidyl isocya-
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nurate are desirable because they permit the development of tack-free coating films. If the
amount of the thermosetting component exceeds 40 wt%, it becomes difficult to obtain a
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tack-free coating film.
The polyurethane coating compositions provide transparent, abrasion-resistant, and
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water-washable anti-fog coatings. The polyurethane coating compositions should have
the ability to dry to a tack-free state at temperatures below 100°C when applied as a coat-
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ing to an article. Clean-room conditions are not always practical in the higher temperature
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commercial ovens used for the final curing. Coatings which do not dry tack-free can pick
up dust or other airborne debris present in these non-clean-room higher temperature cur-
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ing ovens, thereby reducing the quality and cosmetic appearance of such coatings. Drying
the coatings to a tack-free condition in clean-room ovens at lower temperatures (e.g., tem-
peratures below 100°C) before moving the articles to the higher temperature non-clean
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room ovens provides advantages over coating compositions which do not dry tack-free. A
higher molecular weight of the polyurethane polymer structure improves the ability of the
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polyurethane coatings to dry tack-free. Reacting unblocked multi-functional isocyanates
with polyols provides a higher molecular weight polyurethane polymer structure as com-
pared to reacting wholly or partially blocked multi-functional isocyanates with such poly-
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ols.
The printing of the high-opacity laminating ink image-wise onto a surface of a poly-
meric substrate and forming a dried ink image on a surface of the substrate is performed. 5
The image is tack-free, firmly adherent to the surface of the substrate, and undergoes no
picking, blocking, or decaling when contacted under pressure at ambient temperatures to a
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second surface of the same or another substrate.
A photoinitiator composition comprising a combination of aminoalkyl phenone,
thioxanthone, and multifunctional amino benzoate synergist for use in printing inks and
coatings that are curable using UV radiation, particularly from LED lamps provides inks
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with the ability to cure in a single pass at a rate of 99 m/minute.
The curable dental restoration composition comprises a resin system containing a
free-radical polymerizable semi-crystalline resin having a molecular weight no greater
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than 2000 g/mole and at least 50 wt% of nanocluster filler. The hardenable compositions
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are free from tack.
The epoxy resin and hardener are matched to each other so that the epoxy resin sys-
tem at a fixed temperature is tack-free, the precoated components can be prefabricated and
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sold.