Tukon hardness

Diol/HMMM, w/w Tukon hardness (KHN) Pencil hardness Fwd. impact (in-lb)... 

Film Thickness, Mils Tukon Hardness, KHN25 1.4 1.5... 

Figure 6. Tukon hardness of AH and epoxy acrylate based films.

Figure 8 compares the Tukon hairdness of the melamine and AM 10 films. Films of each material were drawn on primed Bonderite 40 with a 4 blade and cured for 30 minutes at 250° F. Both formulations were catalyzed with 0.8% PTSA on TRS. For the melamine cured films, hardness increases slightly as melamine content is increased from 25 to 40%, but then is reduced at 50% melamine content, probably due to plasticization by unreacted excess melamine functionality. For the acrylated melamine, hardness increases monotonically, probably because of the lower alkoxy functionality and higher Tg of the AM resin compared to the melamine resin. At 40% AM the Tukon hardness is similar to that achieved with a 25% melamine resin. 

Figure 8. Tukon hardness of melamine and AHIO films compared.

Properties Wh. fine powd. sol. In styrene/methyl methacrylate (80/20), glycidyl methacrylate, butyl acrylate, diethylene glycol diacrylate, 1,3-butylene glycol diacrylate sol. hazy in styrene m.w. 16,000 dens. 1.16 kg/l vise. 0.038 poise m.p. 127-142 C Tukon hardness 15 2.0% acetyl, 53% butyryl... 

Properties Wh. fine powd. low odor sol. in 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, tetraethylene glycol diacrylate negligible sol. in water m.w. 25,000 sp.gr. 1.23 vise, 1,52 poise vapor pressure negligible m.p. 188-210 C ref. index 1.475 Tukon hardness 23 100% solids 2.5% acetyl, 45% propionyl... 

Rohm and Haas, Rhoplex AC-35 was selected as a typical flexible acrylic latex. Films of AC-35 on glass or other mineral surfaces are clear, tough and flexible, with a Tukon hardness of about 1, but generally have poor adhesion, especially after soaking in water. Addition of 5% silane (as 50% dispersions in water) to AC-35 generally did not improve wet adhesion to glass. 

The KHT was devised in 1939 by F. Knoop. A Knoop diamond indenter may be used in a Tukon Hardness Tester (or in a Buehler Instrument Model 1600-6400). The indentation produced by the KHT resembles that made by a pyramid-shaped diamond indenter (developed by the U.S. National Bureau of Standards). The apical angles are 130° and 172°. Thus, a narrow, rhombus-shaped indenter is used to produce a rhomboid-shaped impression, as seen in Fig. 1.61. 

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