Unsaturated polyester and silicone resin varnishes (non-baking type) were coated on glass plates and polyethylene films which were about 0.025 mm thick, and then exposed outdoors for 6 months. Changes in weight, gloss and hardness of the films were measured on the films coated on the glass plates as a function of time. IR spectral changes of the films were measured using the coated polyethylene films in the following manner ; the coated film was placed in the position of sample cell of an IR spectrophotometer (double beam type) and another polyethylene film (not coated) in the position of compensate cell, the spectrum of the coated film only was then measured. The results may be summarized as follows.
Unsaturated polyester resin varnish. Since there formed cracks in the coated film on the glass plate after 2 months, the property changes were followed only up to the first 2 months. Weight loss during this period was 3. 8%, gloss decreased to 34% of the initial value and Sward hardness dropped to 12 from the initial value 18. Changes in the quantities of the following groups during 6 months were estimated from the changes in optical densities of the IR spectra.
CH₃- : no change (no change was observed at the 1375 cm^-1 absorption band)
-CH₂- : decrease (considerable decreases were observed at the 2955 cm^-1 and 1452 cm^-1 absorption bands)
-CH=CH- : decrease (both the 1650 cm^-1 absorption band, stretching vibration of ethylene bonds, and the 980 cm^-1 band, out of plain bending vibration of trans ethylene bonds, decreased)
ester groups : no change (only little changes were observed at the 1720 cm^-1, 1295 cm^-1, 1260 cm^-1 and 1240 cm^-1 absorption bands)
-OH : large increase (considerable increases were observed at the 3420 cm^-1 and 1075 cm^-1 absorption bands)
>CO : considerable increase (considerable increases were observed at the 1700 cm^-1 and 935 cm^-1 absorption bands)
-COOH : considerable increase (considerable increases were observed at the 1760cm^-1 and 935cm^-1 absorption bands)
In view of these results it would appear that the degradation of the film of unsaturated polyester resin when exposed outdoors was initiated by the oxidation of-CH₂-and-CH=CH-groups to-OH, >C0 and-COOH groups, while the other groups were not affected at least during this period.
Silicone resin varnish. Cracks were formed in the film of this varnish after 6 months, up to which the measurements were continued. Weight loss during this period was 15.6%, gloss decreased to 66% of the initial value and Sward hardness decreased from 54 to 28.
No detectable changes were observed at the 1428 cm^-1, 1268 cm^-1, 1135 cm^-1, 840 cm^-1, 800 cm^-1 and 750 cm^-1 absorption bands. Thus it appears that the quantities of CH₃-and phenylgroups are unchanged. On the other hand, great changes were observed in the optical densities at the 1025 cm^-1 and 995 cm^-1 absorption bands. Since these bands are due to the Si-O-Si bonding of higher polymers, the observed increases show that the polymerization reaction is being continued even when the film is exposed outdoors.

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Butylated melamine resins are compatible with short oil alkyd resins, their coated films having high gloss and good durability. In general, however, compatibility of two different film formers is not good.
Excessive overbaking of this amino-alkyd resin coatings result in films of poor gloss. The curing of this system is believed to proceed through the co-condensation and self-condensation in the presence of acid catalysts which are supplied by the alkyd resins. Its curing mechanism, however, is not firmly established.
The present work has been performed in an attempt to clarify the effects of alkyd hydroxyl groups on the curing mechanism and viscoelastic properties of the films. Four soya bean oil alkyd with different hydroxyl values were synthesized, where the acid number and molecular weight were kept constant. The dynamic elasticity and tan δ of the films (baked at 120°C for 3 hrs.) were measured at the temperatures between 30° and 200°C by means of a dynamic viscoelastomer (Vibron DDV-I). The melamine/alkyd resin ratios of 9/1 to 1/9 have been covered. The cured films were subjected to extraction with methylene dichloride and then to the infrared analysis. The relation between the composition of and viscoelastic properties were of the films were studies, obtaining the following results.
Film properties.-With increasing hydroxyl value the hardness, the adhesion and the oil resistance are all increased. When the hydroxyl value is very high or very low, poor boiled water and soap resistance are obtained. If the melamine resin content is kept low, the adhesive strength (measured with an adherometer) is increased as the hydroxyl value is increased. If, however, the melamine resin content is kept high, the adhesive strength is decreased as the hydroxyl value is increased.
Viscoelastic properties.-The reactivity of melamine-alkyd resin varnish is enhanced as the hydroxyl value is increased. At the same time the elasticity (E_h') at high temperatures and the temperature (T_g) corresponding to the maximum value of tan δ (tan δ_max) become high, while the value tan δ_max becomes low. A maximum value of E_h' and a minimum value of tan δ_maxa are obtained when the melamine resin content is 70%. The melamine resin content and T_g are not simply correlated. This is because the varnish composition and the film composition are not the same, and because the film is microscopically heterogeneous. The mechanical properties are affected mainly by the properties of the dispersion medium.

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[in Japanese]

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