Products and Applications

	Selecting the right crosslinking agent is an important factor in determining the properties of the sealant formulation. Honeywell supplies the sealant industry with the broadest range of Oxime-type, neutral cure crosslinking agents.

Curing agents, or crosslinkers that are used in silicone formulations are typically substances of the type R-Si-X3 or Si-X4 where R can be a methyl, vinyl or phenyl group and X can be acetoxy, alkoxy, enoxy or oxime groups. All of these crosslinkers are water sensitive. On exposure to atmospheric moisture, the X-group is cleaved to form a hydroxysilane and HX. The hydroxysilane reacts with other OH-groups on the silicone base polymer to form a three dimensional polymer network. The by-products of the curing process (HX) will usually be volatile materials such as acetic acid, alcohols, or oximes like MEKO or MIBKO.

Some of the traditional advantages of Oxime crosslinking agents include:

	Non-corrosive to most materials
	Low odor of MEKO silanes
	Very versatile system (cure rates, hardness)
	Consistent formulations
	Good shelf life
	Can make clear formulations
	Good adhesion
	Can be used for low and high modulus systems
	Low Cost

MEKO-Silane Crosslinkers

For many years, methyl ethyl ketoxime (MEKO) has been the most common oxime leaving group. The methyl and vinyl version MEKO silanes have become the workhorse products for sealant compounders. Honeywell is a basic producer of pure MEKO, and we use this product as a raw material for production of our MEKO silane crosslinkers. 

Honeywell offers the following crosslinkers with MEKO leaving groups:

	OS® 1000 crosslinking agent (methyl version, or MOS)
	OS® 2000 crosslinking agent (vinyl version, or VOS)
	OS® 3000 crosslinking agent (tetra version, or TOS)
	OS® 4010 crosslinking agent (blend of TOS in MOS)
	OS® 4015 crosslinking agent (blend of TOS in VOS)
	OS® 4018 crosslinking agent (blend of TOS in MOS)
	OS® 4025 crosslinking agent (blend of TOS in VOS)
	OS® 4037 crosslinking agent (blend of TOS in MOS)
	OS® 9000 crosslinking agent (phenyl version or PhOS)

Non-MEKO-Silane Crosslinkers

Methyl isobutyl ketoxime (MIBKO) is a larger, less volatile molecule than MEKO, and it exhibits less toxicity than MEKO. Honeywell introduced its patented line of MIBKO-silane crosslinkers for users looking for a lower toxicity leaving group. In the EU, certain label statements are not necessary when the free MEKO concentration can be maintained at a level < 1% by weight. This can be accomplished by using MIBKO-silane crosslinkers or by using combinations of MIBKO-silane and MEKO-silane crosslinkers.

Honeywell offers the following crosslinkers with MIBKO leaving groups:

	OS® 1200 crosslinking agent (methyl version)
	OS® 2200 crosslinking agent (vinyl version)
	OS® 3200 crosslinking agent (tetra version)
	OS® 5200 (Methyl, Vinyl, Di-MIBKO version)

Low Odor, Non-MEKO-Silane Crosslinkers

Honeywell has recently commercialized a new line of Oxime crosslinking agents that do not include MEKO and are also low odor. The first product available in this family of products is:

OS® 1600 crosslinking agent (methyl version)

Other Additives

For more details about other sealant additives please contact your Account Manager or send us your inquiry.