Volume 37, Issue 1, January 2002

While Pilkington was the first to introduce its version of self-cleaning glass, PPG Industries quickly followed suit. Additionally, AFG Industries says it is in the final phase of development prior to the launch of its self-cleaning glass and Guardian Industries says it will introduce a similar product, which the company deems as low-maintenance and not self-cleaning. Guardian says introduction of this product, which may be used in architectural applications, is projected for the fourth quarter of 2002. 

Visteon Float Glass has not yet thrown its hat into the self-cleaning glass ring but a company spokesperson had the following to say: "We at Visteon Float Glass are encouraged to see new value-added products offered to customers of the float glass market. While we don't presently offer self-cleaning glass in our portfolio of tinted and coated products, we will continue to evaluate the                  performance, customer acceptance, customer value and technology of self-cleaning glass along with many other product                   improvements as they become available."                                                                                                                                         

With all of these new products on the market, or soon to be introduced, USGlass decided to offer our readers a glimpse of the different product offerings. We asked each manufacturer to answer a series of questions and their answers are printed below. So, if you've been asking yourself such questions as, "Is self-cleaning glass really self-cleaning?" or "Will the windows ever have to be washed again?" you'll find these answers and many more in the following pages. 

HOUSE Traditional glass used in homes may now be replaced by self-cleaning glass.

Q: Is your company currently manufacturing self-cleaning glass?

AFG: Yes, we are in the final phase of Radiance Ti™ development, prior to product launch. 

Guardian: No, Guardian is manufacturing a low-maintenance product called RainBan hydrophobic glass for automotive applications only. It is important to note that Guardian Industries' product is called low-maintenance, not self-cleaning. Introduction of a product in this category for architectural applications is projected for the fourth quarter of 2002. 

Pilkington: Yes, production of Pilkington Activ™ self-cleaning glass began in December 2000. The official North American launch was in June 2001. Activ has been installed in numerous homes in the United States and Canada, and is specified for various commercial projects. Activ is produced by Pilkington North America's plant in Ottawa, Ill.

PPG: Yes, manufacturing has begun at our Mt. Zion, Ill., plant. Our product is called SunClean self-cleaning glass.

Q: How can interested parties purchase the glass?

AFG: We will make the product available to all current customers.

Guardian: Once the product is introduced, interested customers may request samples and product information from their Guardian sales representative.

Pilkington: Currently, there are eight glass fabricators who offer Activ. There are another 18 window manufacturers who sell directly to consumers and/or sell windows through distributors. In addition, some of the glass fabricators sell insulating glass (IG) units to window manufacturers and distributors. Therefore, it is available from approximately 18 companies for residential products. Fabricators and window manufacturers who want to offer Activ should contact Pilkington. 

PPG: By contacting one of our customers.

Q: In what applications can the glass be used?

AFG: Residential and non-residential glazing applications. 

Guardian: We anticipate the primary application of this product to be as a low-maintenance glass option for the residential window market, typically in conjunction with high-performance low-E. However, the coating could be applied to certain commercial applications as well.

Pilkington: Activ can be used in any residential or commercial fenestration application that is exposed to the outside environment with minimal overhang. Primary applications include residential windows, commercial/ institutional windows and façades, skylights, atriums and sunrooms and as a part of exterior doors.

PPG: It is well-suited for any application in which the exterior surface is exposed to the sun's ultraviolet (UV) light.

Q: How does it work?

AFG: Radiance Ti is a hydrophilic (water-sheeting), photocatalytic (self-cleaning organic particles) product.

: Guardian's low-maintenance coating is extremely hydrophilic (or water-attracting), which means water will sheet across the glass surface, rinsing dirt and debris away and leaving very little spotting behind as the glass dries. The coating is also scratch-resistant, which is a benefit throughout the window fabrication, installation and post-construction clean-up process. 

Pilkington: Activ is a pyrolytic coated-glass product, thus the composition becomes an integral part of the surface, rather than being applied onto the surface after the glass has cooled. Once produced and installed, it never needs to be re-treated. 
The sun's UV rays cause the integrated coating to react chemically with unwanted organic dirt to break down its adherence to the glass surface (photocatalytic effect) gradually and continuously. After installation, the integrated coating of Activ must be exposed to the sun's UV rays for several days to become active. The integrated coating reduces the surface tension of water on the glass surface. This is known as the hydrophilic effect, and causes water to sheet on the glass surface, preventing the formation of separate droplets and ensuring that loose dirt and other particles can be washed away during normal rainy weather.

PPG: SunClean glass is a coated glass product with photocatalytic and hydrophilic properties that combine to make windows easy to maintain. The transparent coating of SunClean glass is applied to hot glass during the forming process, where it forms a strong, durable bond with the glass surface. The photocatalytic property of the coating is triggered by the sun's UV light and works to break down and loosen organic dirt slowly. At the same time, the coating's hydrophilic property breaks down water beads and causes water to sheet over the glass, which helps to rinse away loosened dirt. 

PPG says homeowners can enjoy a clearer view with little hassle with its SunClean self-cleaning glass.

Q: Does it work immediately after being installed?

AFG: Our tests show initial coating hydrophilicity (when UV rays are introduced) at less than 24 hours. More than likely, UV will be introduced in the window manufacturer's process or distribution channel to energize the coating. By the time a fenestration product is glazed into a home or building, the coating will be energized. 

: Like competitive offerings, Guardian's hydrophilic coating must be exposed to UV light for a period of time in order to reach its highest performance potential. However, unlike competitive products, the Guardian low-maintenance glass product maintains peak performance once fully activated whereas competitive products require continual reactivation.
Pilkington: No, before the integrated coating of Activ can work, it needs to be exposed to the sun's UV rays for several days.

PPG: Depending on exposure, it may take up to seven days for the glass to energize. 

Q: Will windows with this glass ever have to be washed again?

AFG: Radiance Ti works on organic dirt. Not all visual obstructions can be considered organic. This is a subjective question as everyone has a different opinion as to how clean his windows need to be. AFG's opinion would be yes, but much less frequently, and in the interim (or between washings), the view through the glass will be clearer than with traditional glass products.

Guardian: A realistic expectation for a low-maintenance glass product is to provide a cleaner and clearer appearance than the product would have without the coating, with low effort and less frequent cleaning than traditional glass products. It is important to set expectations properly. For example, while it may be technically accurate to describe a photocatalytic effect as self cleaning, unless the consumer would describe what they see as self cleaning, they'll be disappointed, even if there is a demonstrable improvement relative to clear glass.

Pilkington: Yes, though not nearly as often as without using Activ. If it has not rained for a significant period of time and the windows have become dirty, simply spray them with water and allow the hydrophilic effect to sheet away any dirt that has yet to be broken down. It is suggested that when spraying Activ glass, the windows should be rinsed from top to bottom. This maximizes the sheeting effect action by ensuring that all the dirt can be washed off and, on heavily soiled windows, reduces streaking issues in drying. 
If there is a heavy buildup of soil on the glass and it does not appear to be breaking down the dirt and/or sheeting it away when sprayed with water, then the integrated coating of Activ has been deactivated (i.e., the dirt has prevented UV rays from reaching the glass surface). Use a standard, but non-abrasive, window cleaner with a lint-free towel to hand-wash the glass. Then, rinse the glass thoroughly and allow several days for the coating to be reactivated by UV rays.

PPG: Yes, the self-cleaning attributes of our product are effective in reducing the everyday dirt and grime that accumulates on the exterior surface, meaning windows will be easier to clean. However, inorganic materials such as paint will continue to require hand cleaning. If the glass becomes heavily soiled or does not become clean under specific exposure conditions and circumstances, then it will be necessary to clean the glass manually. Of course, the interior surface will need to be cleaned like any other window glass. 

In looking at a building through a window, you can see the hydrophilic action of Pilkington Activ™ glass (left) causes water to sheet, rather than streak and spot, as it does on ordinary glass (right). (Note that this photo is for demonstration purposes. Activ has not been installed in this building.)

: What does it look like? Does it have a color?

AFG: Radiance Ti will be neutral in color. There will be slightly more reflectivity looking at the glass from the exterior.

Guardian: The residential market has expressed a strong preference for color-neutral coated products. This preference is particularly relevant in the context of an IG unit that is now likely to include two or even three coated surfaces, providing a full range of value-added performance. Guar-dian considers color-neutrality to be a primary product design attribute and our low-maintenance glass offering meets the color-neutral standard exceptionally well.

: Activ has very much the same appearance as any other clear float glass used in windows and skylights. The only noticeable difference is that it may appear slightly shinier.

PPG: From the exterior, windows with SunClean glass appear brighter. From the inside, they look the same.

Q: What is the composition of the coating?

AFG: This is confidential. 

Guardian: Guardian considers this to be proprietary information. After extensive research Guardian has determined that utilizing traditional deposition technology and materials such as titanium dioxide, it is not possible to fully meet industry requirements for a durable, color-neutral, low-reflecting product.

Guardian's proprietary technology produces a low-maintenance glass product with significantly greater scratch resistance than competitive products, offering color neutrality and low reflectance.

Pilkington: Activ utilizes a proprietary mixture of chemical precursor materials and a proprietary chemical vapor deposition process to form a pyrolytic coating. U.S. and international patents and patent applications related to the precursor materials and the method for depositing the coating have been granted or are pending.

PPG: Titanium dioxide.

Q: How long will the self-cleaning qualities last? 

AFG: Our intentions are to manufacture and sell products that we believe will last for the useful lifetime of the application for which they are intended. Until product rollout, we will not have a finalized warranty.

Guardian: Guardian's low-maintenance coating has undergone rigorous automotive testing successfully. We have observed a high degree of correlation between automotive testing standards and product durability. In any event, the coating is currently undergoing long-term testing targeted to residential applications, and is expected to be permanent.

Pilkington: We guarantee that Activ will last ten years. However, tests indicate that it will last longer.

PPG: Like other PPG coated products, SunClean glass comes with a ten-year warranty. We believe the coating is extremely durable. 

Q: To what surface is the coating applied? 

AFG: The coating is applied to the first surface or outside lite of a window or glazed unit.

Guardian: The key here is configuration flexibility. The low-maintenance coating is intended for the number-one (exterior) surface of an IG unit. With Guardian's low-maintenance product, it is possible to maximize the performance potential of other coatings, such as low-E, that are most effective when placed on the number-two surface. This flexibility is reduced significantly when (as with competitive products) the low-maintenance coating is applied to the atmosphere side of the glass as part of the glass manufacturing process. Because Guardian uses an off-line application process to apply the low-maintenance coating, it is possible to preserve the atmosphere surface of the glass for coatings that are incompatible with the tin (or bottom) surface of the glass. For example, high-performance low-E must be applied to the atmosphere side of the glass, while a low-maintenance coating is compatible with either glass surface. 

Pilkington: The coating is applied to the first surface—the surface that will face outside. 

PPG: It is applied to the exterior surface only. This is because UV light is required to power the self-cleaning properties.

Q: Can the coating be damaged?

AFG: Yes. 

Guardian: It would be very difficult to damage the coating, which is nearly as hard as diamond.

Pilkington: Yes, while the integrated coating of Activ will not rub off, it can be damaged if the surface of the glass is damaged. Also, it may become damaged if an abrasive cleaner or steel wool, razor blade or other metal item is used to try to remove stubborn inorganic marks.

PPG: Yes, that's why proper care and maintenance of the glass are so important.

Q: Is there edge deletion on any surfaces?

AFG: Technical information is not final on this subject.

Guardian: No.

Pilkington: No.

PPG: No, edge deletion is not required.

Q: Are there any special care or cleaning requirements?  Should it be polished?

AFG: Yes, there are special cleaning requirement. No, it should not be polished. 

Guardian: No, in fact the low-maintenance coated surface is substantially more chemically and mechanically durable than clear glass.

Pilkington: Generally, no special care or polishing is required under normal conditions. However, the customer must avoid using any abrasive cleaners or objects such as steel wool or razor blades.
PPG: Yes.

Q: Can the glass be cleaned of scratches or stains? 

AFG: No.

Guardian: Scratches are unlikely due to the unique surface hardness of Guardian's low-maintenance coating. Any surface stain that results from external contamination may be removed safely using any equipment or cleaning agent that is typically used in conjunction with clear glass.

Pilkington: Scratches cannot be removed without removing some of the coating. Stains can be cleaned with acetone, mineral spirits or even Lime-Away.

PPG: No, scratches cannot be cleaned from the surface. Like clear glass, some stains may be removed.

Q: How much does it cost?

AFG: Our pricing is confidential.

Guardian: Price is still being determined. 

Pilkington: Activ cannot be bought by itself. It can only be obtained when purchasing a window (or skylight, door, etc.) that uses Activ. Since the glass is just one component of a window, skylight, door, etc., and those costs are set by the window manufacturer/distributor, Pilkington has little control over the final cost. However, it is estimated that windows with Activ will cost approximately 20 percent more than windows using standard, clear glass.

PPG: We believe uninstalled windows with SunClean glass will cost between 10 and 20 percent more than windows with ordinary glass.

CUTAWAY The photocatalytic action of Pilkington Activ™ self-cleaning glass (upper) gradually breaks down and loosens dirt, while the hydrophilic surface (lower) causes rain to sheet on the glass, leaving an exterior with minimal spotting or streaking. 

Q: How does your product differ from other similar products on the market? 

AFG: Radiance Ti is a hydrophilic photocatalytic product with a spectrally selective low-E coating. It is energy-efficient self-cleaning glass.

Guardian: The Guardian low-maintenance glass product provides comparable or superior water and dirt management properties, while providing superior color-neutrality, optimal IG configuration flexibility and remarkable scratch resistance.

Pilkington: There are no other products like Activ in the North American marketplace, so it is difficult to compare Activ to products which are not available. 

There are sprays and coatings that consumers can purchase to spray on their automotive windshields that cause water to bead which does not work well on vertically glazed applications. In addition, these sprays are only temporary and only affect how water reacts to the glass. These sprays have no self-cleaning properties.

PPG: PPG defines self-cleaning glass as a product that has three distinct characteristics. First, the glass has a durable, long-lasting coating that has been fused into the glass at high temperatures during the glass manufacturing process. Second, the coating exhibits photocatalytic properties (i.e., it will slowly decompose organic material). Third, the same coating also exhibits hydrophilic properties (i.e., it will cause water to sheet over the coated surface and dry with minimal spotting and streaking). Other companies offering self-cleaning glass products should be evaluated as to whether they provide these three distinct characteristics.

Q: Can the glass be used as the inside lite of glass?

AFG: There is no practical application for this.

Guardian: See the question referring to what surface coating can be applied above.

Pilkington: No, the integrated coating of the glass must be exposed to the sun's UV rays to work.
PPG: Yes, on surface number four, but you probably wouldn't want to do that. 

According to PPG, with SunClean, cleaning windows is now as easy as watering the flowers.

Q: Can this be used in interior applications such as shower doors?

AFG: Additional applications are under consideration; the presence of UV light is at issue. 

Guardian: If the coating is used inside, the UV activation may not be as rapid or as thorough when compared to a product that is placed on the exterior surface of an IG unit. Our group is developing a non-UV activated product that would meet customer expectations in an interior application.

Pilkington: No, because glass used in these applications does not receive enough UV rays to activate the Activ coating. Therefore, it can neither break down dirt nor provide sheeting action when water is applied.

PPG: See answer to previous question.

Q: Can the glass be tempered and undergo other glass fabrication or processing (such as lamination)?

AFG: No testing has been completed to evaluate the laminating process. But the glass can be heat-strengthened, tempered and bent. 

Guardian: The glass can be laminated. Once the coating is applied, subjecting the glass to typical heat treatment temperatures will reduce the low-maintenance properties of the glass dramatically. However, the Guardian coating is applied in an off-line operation, which means it is possible to coat annealed or heat-treated glass for high-volume requirements. Guardian has a detailed plan under development to respond to the industry challenge of providing a post-heat treatable product that maintains peak performance when subjected to heat treatment.

: Yes, Activ can be tempered, heat-strengthened, laminated, insulated, bent and cut using standard float glass techniques and no edge deletion is required. 

PPG: Yes, SunClean glass can be heat-strengthened and tempered. We believe it can be bent; we just haven't tried it yet.

Q: When the glass is used on an IG unit, can any type of sealant be used?

AFG: Yes, the self-cleaning feature is on the first surface and not in contact with the sealants used to make insulating glass.

Guardian: While comprehensive testing is still underway, interim analysis of typical IG sealants indicates full compatibility with the Guardian low-maintenance coating.

Pilkington: Yes, Activ has been tested with IG sealants. The coated glass is compatible with the commonly used polysulfide, urethane, two-part silicones and hot-melt butyl materials. During normal production these materials are applied to the number-two and number-three surfaces of an IG unit and are not applied to the outer, number-one surface where the Activ coating is located. The glazing sealants used to supply a weather seal between the number-one surface and the glazing frame or sash should be selected carefully to avoid any compound containing silicone. As with all first-surface-reflective coated glasses, it has been noticed that silicone oils can migrate from silicone sealants, or even from silicone-lubricated rubber-glazing gaskets. Such oils are difficult to remove from coated glass surfaces and can attract and hold visible dirt deposits. 

PPG: IG sealant is not much of a concern if SunClean glass is positioned on surface number one. However, glazing sealants (e.g., silicone) can cause SunClean glass to become ineffective in certain areas.

Q: Will the glass work with all types of frame materials?

AFG: If this question is referring to wood, vinyl, aluminum, fiberglass and composite, then the answer is yes.

Guardian: Yes.

Pilkington: Yes, the frame materials and colors have no impact on how Activ works.

PPG: Testing will be required to determine if there is any material incompatibility risk. Some materials can cause SunClean glass to be rendered ineffective.


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