Yoshiki Nakagawa

New Durable Sealant of Telechelic Polyacrylate

In this paper, we discuss the application possibilities of a novel telechelic acrylic polymer (NTP) which we have been developing as a versatile base polymer for sealants and adhesives. Due to its unique features, our NTP is expected to offer a variety of applications, including the one for sealants applied in contact with self-cleaning glass (SCG). Our discussion here focuses on the possibilities of this particular application. SCG possesses a photocatalyst layer which enables two reactions, i.e., lessening the contact angle of the glass surface and decomposing organic compounds on the glass surface, by reacting with sunlight. The reactions help wash off dust from the glass surface, mainly by rainwater, to maintain the clearness and beauty of the glass used for building windows in particular. Conventional sealants for this application often lack sufficient weatherability or risk, or a combination thereof contaminating the glass surface causing hydrophobicity. The NTP sealants, on the other hand, has no surface-polluting substances such as a low-molecular-weight silicone often contained in silicone sealants, while maintaining high weatherability. We have conducted our research to study the weatherability of the NTP sealants on SCG and the possible contamination of the SCG surface by the sealants. Our studies have found that the NTP sealants retain good adhesiveness after more than 10 000 h of exposure to UV irradiation (in a Super Xenon Weather Meter) at the interface between the sealant and the glass. We also have found almost no contamination on the SCG surface by the NTP sealants, demonstrated by the results of our tests conducted to measure the contact angles of sealant samples to the glass, through outdoor exposure for about two months.

Evaluation of the Durability Potential of Silyl Terminated Polyacrylate Based Construction Sealant

In this paper, we discuss the durability potential of silyl terminated polyacrylate based construction sealants. The durability and performance of a silyl terminated polyacrylate (STPA) based construction sealant have been evaluated in comparison to a typical silyl terminated polyether (STPE) and a silicone sealant in order to demonstrate the potential of the STPA sealant as a high durability, high performance construction sealant that is also suitable for glazing applications. The polyacrylate backbone of STPA polymer has higher durability, especially UV stability and heat resistance, than the polyether one of STPE polymer as shown by accelerated weathering tests using carbon-arc or superhigh irradiance xenon-light sources. Adhesion of the STPA sealant on glass was retained even after 10,000 h exposure to superhigh irradiance xenon-light [180 W/m2 (300–400 nm)]. The performance of the STPA based sealant has been compared to that of the STPE based sealant by testing according to several industrial International Organization for Standardization (ISO) and Japanese Industrial Standard (JIS) standards. The STPA based sealant conforms to a higher durability class specification than the STPE sealant, for example, the requirements of class 10030 are passed with the STPA sealant, while the STPE sealant passes only class 9030 as stipulated in JIS A 5758. Furthermore, a cyclic movement test of the STPA based sealant in a compression-extension machine shows no damage to the sealant even after 200,000 cycles of ±40 % movement at room temperature. This performance is much better than that of sealants based on other materials, such as STPE, polyurethane, polysulfide, and silicone. These evaluations suggest a high potential of STPA based sealant as durable elastomeric joint sealant, which can be used on a glass, including photocatalytic self-cleaning glass, which functions by decomposing organic materials and by providing a superhydrophilic surface.