March 02 / Preparation and characterization of weather re sistant silicone/acrylic resin coatings were conducted. In order to prepare these coatings, a silicone/acrylic resin (KLD) was first prepared by an addition polymerization reaction of monomers, including n-butyl acrylate, methyl methacrylate, n-- butyl methacrylate, and 3-methacryloxypropyltrimethoxysilane (MPTS). In the preparation of the silicone/acrylic resin, T^sub g^ of the acrylic copolymer was fixed at 40 deg C and the contents of MPTS were varied to be 10, 20, and 30 wt%.

The weather resistant silicone/ acrylic resin coatings were then prepared by blending the synthesized silicone/ acrylic resin and TiO^sub 2^. The viscosity of the synthesized resin decreased with the content of MPTS, whereas the thermal stability at high temperature increased. The prepared coatings exhibited excellent adhesion to various substrates, and various physical properties of the coatings were satisfactory. The weatherability of the coatings was tested three ways: outdoor exposure test, Weather-Ometer (WOM), and QUV accelerated weatherability tester (QUV). The gloss retention, yellowness index difference, color difference, and lightness index difference were improved at high MPTS concentration. The coatings containing 30 wt% MPTS have especially good weather properties.

INTRODUCTION

It is inevitable for a coated film to undergo deterioration with exposure. Weatherability is a property that resists deterioration caused by several environmental factors, such as radiation, temperature, moisture, substrate, and chemicals.1,2 Since the film of a weatherable coating is densely crosslinked and exhibits high hardness, it stands well against the factors causing deterioration of the film. Therefore, there is a growing need for weatherable coatings in various architectural industries.

Since weatherable coatings require special film properties, it has been difficult to meet the needs with common synthetic resins. Since the 1980s, coatings containing fluorine resin which are copolymerized by fluoroethylene and alkyl vinyl ether have been used as weatherable coatings.3 However, coatings containing fluorine resin have some disadvantages, such as being expensive, environmentally pollutive, poor in hardness, and bad in workability. Recently, coatings containing silicone/ acrylic resins have gained recognition as weatherable coatings. Since the coatings containing silicone/ acrylic resins are a composite of organic and inorganic polymeric materials, it is easy to control the film hardness and to apply them to various substrates. There are two types of coatings containing silicone/ acrylic resins: temperature-cured and moisture- - cured at room temperature. Of these two, the type of hardening by moisture at room temperature will be spotlighted because of its good workability and weatherability.

There have been some reports on the coatings containing silicone/ acrylic resins. Rao and Babu4 synthesized a copolymer of vinyltriacetoxysilane and bromomethacrylate and investigated its thermal behavior. Yasuyuki5 reported phase separation of a silicone/ acrylic rubber prepared by grafting silicone emulsion and acryl emulsion. Witucki6 prepared a silicone / acryl emulsion by cold blending an alkoxy silane and acryl emulsion through the following two-step processes. The first step was hydrolysis of an alkoxy functional group, and the second step was the formation of silicone polymer. He reported that the existence of 10% silicone increases gloss retention and decreases chalk phenomenon and color difference. There have been some patents similar to this work. Kanegafuchi Kagaku Kogyo Co. holds two patents7,8 on weather resistant coatings, in which curing catalysts are used. DuPont Co. also holds a patent9 on weather resistant coatings that consist of hydroxyl group- containing acrylic polymer/ hydroxyl or alkoxy group-containing siloxane. The coatings are not the moisture-curing type, but the two- component reactive type. PPG Co.10 also patented weather resistant coatings that use a cure-accelerating catalyst. However, there have been few papers reporting on the synthesis of the silicone / acrylic resin that is cured by moisture at room temperature and its application to weather resistant coatings.

CONCLUSIONS

White coatings were prepared by blending TiO^sub 2^ and silicone / acrylic resin (KLD) synthesized by the copolymerization of n-butyl acrylate, methyl methacrylate, n-butyl methacrylate, and 3- methacryloxypyltrimethoxysilane (MPTS). The physical properties measurements and weatherability tests of the films of the prepared coatings were carried out.

The measured results of the synthesized silicone/ acrylic resin were as follows: M^sub n^, 17200~18800; M^sub w^, 35900~44500; polydispersity, 2.01~2.40; viscosity, 2.4~6.1; and stoke and conversion, 87.7~89.8%. The prepared coatings exhibited excellent adhesion on various substrates, and most physical properties of the films were satisfactory. From the outdoor and accelerated exposure test, it was found that gloss retention, yellowness index difference, color difference, and lightness index difference were improved with the content of MPTS. Especially, SA-4030, containing 30 wt% MPTS and having T^sub g^ of 40 deg C, proved to be a weather resistant coating.

ACKNOWLEDGMENT

This work was supported by the RRC program of Most and KOSEF, and by the Brain Korea 21 Project.

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H.-S. Park**S.-R. Km, HA. Park Y.-C.Kwah and H.-S. Hahm-Myongji University* SA. Kim-Sam-Hwa Paints Ind. Co. Ltd.^

* Dept. of Chem. Eng., Yongin 449-728, Korea.

^Ansan 425-110, Korea.

** Author to whom correspondence should addressed.