Room Temperature Vulcanization (RTV) Silicone is a kind of silicone rubber that is generally supplied as a one-part system with a wide viscosity range. It’s comprised of a combination of organic, and inorganic compounds that make it one of the most stable organic adhesive products available on the market. These adhesives and sealants are resistant to high temperatures, and are extremely flexible compared with other industrial adhesives.
How It Works
RTV Silicone adhesives and sealants utilize water and a curing agent, or mechanism to form an adhesive bond or seal. When these materials combine during crosslink, a chemical byproduct is released. Depending on what materials you are using, this byproduct can be acidic (ie. acidic acid), basic (amine), or neutral (oxime/alcohol) in nature. The curing agent that you use will determine the final properties of your adhesive. The relative humidity and temperature of the surrounding environment will also directly determine the cure rate, but typically, RTV silicones tend to cure within a 72-hour period, although the adhesive can continue to strengthen for up to two weeks after setting.
General Properties
RTV Silicone adhesives and sealants have many advantageous properties; their only real limitations are that they cannot be painted over with water base paint, and the fact that water vapor passes relatively easily through cured silicone rubber. Other than that, these adhesives are incredibly flexible (depending on the temperature), and have a wide operating temperature range. They are resistant to harsh weather conditions, humidity, and mold and mildew, and also carry excellent electrical properties. RTV Silicones have a 40-year life span and a high degree of elongation; they are easy to dispense, even in cold temperatures, and are VOC compliant, with excellent UV and thermal stability properties.
Acetoxy Cure and Neutral Cure Silicones
The most commonly used RTV silicones are acetoxy cure silicone and neutral cure (oxime) silicone. Acetoxy cure silicone has a relatively fast curing rate and a short tack-free time, providing a good, quality adhesion, although it is corrosive to metals. This type of RTV silicone releases acidic acid, producing a vinegar smell as a by-product. Oxime, or neutral cure silicone, on the other hand, is non-corrosive and has excellent oil and temperature resistant properties. This type of silicone produces a neutral/non-acidic byproduct that does take longer to cure and has a longer tack-free time. Let’s take a closer look at these two kinds of silicones.
- Acetoxy Cure Silicone
Acetoxy cure is likely the more commonly used of these two types of RTV silicone. It is used extensively in construction-related applications such as window installations and as expansion joints, but also in common DIY projects in residential bathrooms and kitchens. This is owing to its ability to bond to common substrates like wood and tile, and because of its fast tack-free time and resistance to high temperatures. Their non-corrosive properties, however, do place restrictions on what materials it can be used with, such as concrete.
There are several main acetoxy cure products available on the market. These include:
- ASI 502 100% RTV Silicone – food grade, UL recognized sealant, NSF approved
- ASI 504 Multi-Purpose Silicone – bonds to common substrates, general applications
- ASI 600 High-Temp Silicone – red hi-temp resistance temperatures up to 600˚
- ASI 505 Self-Leveling Silicone – fast skinning, self-leveling joint sealant
- ASI Aquarium Sealant – high tensile strength, aquatic life safe silicone
Neutral cure silicone can be used in a wide range of industries and applications owing to its extensive adhesive abilities. Oxime can adhere to concrete among many other substrate surfaces, and is non-corrosive on most metals. It also releases a non-pungent odor during cure, has a long tack-free time, and is resistant to oil and high temperatures. Unlike acetoxy, however, it is not food grade and can discolor copper in confined spaces. For this reason it is not as commonly used for electrical applications.
Like acetoxy, there are several types of oxime cures available on the market. These include:
- ASI 335 Neutral Cure Silicone – advanced adhesion, high performance sealant
- ASI 335 Window Sealant – AAMA approved for use in manufacturing and/or installation
- ASI 306 Self-Leveling Sealant – used in electronic applications, or as a self-leveling joint sealant
- ASI 338 Electronic Grade Silicone – UL recognized for use in encapsulating, bonding, ect.
Disadvantages of RTV Silicones
Although RTV silicones are used in a wide array of applications in many different industries, these adhesives and sealants do have some disadvantages. They are more susceptible to picking up debris like dirt, and have poor tear resistance, low tensile strength, and poor cohesive strength. Because of their corrosive properties, some substrates, like concrete, require that a primer be used to catalyze the process. There is also evidence that the byproduct of the neutral cure process, butan-2-oxime, acts as a skin sensitizer, but in large industrial plants with good ventilation, this is not a problem.
Applicable Industries
As was mentioned before, acetoxy cure and neutral cure silicones are commonly used in construction and DIY home projects. They are also used for automotive and marine equipment assembly and maintenance, and for some electronic applications. These silicones are also used in aerospace engineering and in the production of common consumer products.
For more information on how using RTV silicone adhesives and sealants can help you and your business, contact us or give us a call and speak to one of our professional representatives at 855-437-7700.