新产品·新技术信息

硅烷偶联剂

来源：林中祥胶粘剂技术信息网2011年03月23日

阅读次数：次

Organosilanes ? The Original Chemical Bridge

Adhesion promoters or coupling agents are a group of specialty bifunctional compounds that can react chemically and form a "chemical bridge" either between the adhesive and the substrate or between the adhesive matrix and internal fillers.

Adhesion promoters were originally used to treat glass fibers and other fillers before they are incorporated into liquid resin to make composite materials, and they still have significant use in these applications. Without adhesion promoters, the interfacial resin-to-glass fiber adhesion is weak, and water can diffuse along the interface with catastrophic results on the end-properties of the composite.

The chemical bridge created by the adhesion promoter is also important for adhesives and sealants. They can improve the initial joint strength and prevent delamination of the adhesive from the substrate, even when water, oxygen, and salts migrate to the joint interface. It is well established that the judicious use of the correct adhesion promoter improves the joints durability especially to moist environments.

Over the last 20 years the adhesion promoter marketplace has evolved to include a variety of materials of which organosilanes have secured a prominent position. Each of these adhesive promoter types has a specific set of characteristics (Table 1).

Type	Inorganic Groups	Organic Groups	Molecular Stability	Moisture Sensitivity	Solubility in Solvents
Organosilanes	-OR	Varied	Excellent	Poor	Excellent
Organotitanates	-OR	Varied	Fair/good	Poor	Excellent
Zirconates	-OR	Varied	Fair/good	Poor	Excellent
Zircoaluminates	-OH, -Cl	Varied	Excellent	Excellent	Fair
Alky phosphate ester	-OH	Alkyl/aryl	Good	Fair	Good
Metal organics	-OH	Varied	Excellent	Excellent	Good

Table 1: Characteristics of Various Classes of Adhesion Promoters ¹

All adhesion promoters share several characteristics. They are all bifunctional, surface-active agents that are used in concentrations as low as several parts per hundred of resin solids. Adhesion promoters usually consist of molecules with short organic chains having different chemical composition on either end of the chain. On one end is an organofunctional group that is particularly compatible with the given adhesive material. At the other end of the chain is an inorganic functionality that is especially compatible with a given substrate. Although the best results can be obtained in using adhesion promoters as substrate primers, they can also be added to the adhesive with some effect.

The article reviews the use of organosilanes as adhesive promoters - both as primers and as internal additives in adhesives. The unique chemical structure of the organosilane molecule is examined and its use in a wide variety of adhesive systems is discussed. The possible beneficial performance enhancements provided by silane promoters are described. However, caution in determining the correct silane and the appropriate concentration or method of application is required.

Dont hesitate to react about this Article

Silane Chemistry

Organosilanes are the most common commercial adhesion promoter. They are commonly used to enhance adhesion between polymeric and inorganic materials. Organosilane adhesion promoters usually have the form:

R - Si - (X)3

Silicone (Si) is the center of the organosilane molecule. The organosilane molecule also contains the organofunctional group (R) and a second functional group (X).

X is a hydrolyzable group, typically alkoxy (methoxy or ethoxy). It reacts with water to form silanol (Si - OH) groups. The silanols can further react with themselves, generating oligomeric variations. All silanol variations can react with active surfaces that contain hydroxyl groups. The silanols ultimately form an oxane bond with the inorganic substrate (Si - O - Metal) liberating methanol or ethanol as a byproduct.

R is a nonhydrolyzable organofunctional group that can be vinyl, amino, chloro, epoxy, mercapto, etc.