What is an isocyanate adhesive?

Adhesive with polyisocyanate monomer or homopolymer as main raw material. The correct name is polyisocyanate adhesive. Due to the high activity of isocyanate group (-n = c = o), this kind of adhesive can bond wood, metal, plastic and other materials, with high bonding strength, adjustable adhesive layer toughness, aging resistance, good curability at ultra-low temperature and room temperature, but poor heat resistance. Polyisocyanate is a compound containing two or more isocyanate groups in one molecule, which is easy to react with polyol containing active hydrogen to form polyurethane resin. Polyurethane adhesives are generally divided into three categories, and isocyanate adhesives are one of them.

Physical Properties The main physical constants of isocyanate are shown in the following table.

Isocyanate groups react with water to form polyurea;

OCN-R -NCO+H2O-H2N-R-NH2+CO2NOCN-R-NCO+NH2n-R-NH2-OCN449394 RNHCONH449394 NRNNNCO At this time, the isocyanate groups at both ends of polyurea can react like-NCO in the monomer toluene diisocyanate molecule. However, the more water there is, the more NCO is consumed, which means that. Therefore, in the process of particleboard production, it is very necessary to control moisture.

There are many kinds of isocyanate adhesives, such as polyisocyanate solution, rubber modification and water emulsion. Wherein, the aqueous emulsion is a closed isocyanate adhesive. -NCO is protected by phenols and other substances and does not react with water to form emulsion. When bonding, -NCO is released at a certain temperature or under catalytic conditions for reaction.

Compared with traditional wood adhesives, isocyanate adhesives have the advantages of no formaldehyde pollution, high bonding strength and flexible adhesive layer. People are deeply studying and trying to use it to partially or completely replace formaldehyde-based wood adhesives. Can be used for wood sealing, pressing particleboard, etc. Its disadvantages are high cost, high toxicity and easy adhesion to pad or hot pressing plate.

Isocyanate is toxic and can react with human protein. Oral toxicity is relatively light. If it spills into eyes, it can be fully washed with water. The biggest harm of isocyanate to human body is its vapor, which irritates eyes and respiratory mucosa. The workplace must be well ventilated, and the allowable limit in the air is 0.02ppm.

Application in wood industry

Isocyanate adhesive can form chemical bonds with wood, giving wood glued products good water resistance and aging resistance, and there is no harmful free formaldehyde, so it is more and more used in particleboard industry. The sizing amount of particleboard, core layer and surface layer accounts for 5 ~ 6% and 6 ~ 7% of the weight of absolutely dry wood respectively. The total moisture content, including 2% in wood chips, is controlled at 8% in the core layer and 12 ~ 14% in the surface layer. During hot pressing, the hot pressing temperature is 170℃ and the hot pressing time is13s /mm plate thickness. For particleboard with 6% sizing (diphenylmethane diisocyanate), the hot pressing temperature is 175℃ and the hot pressing time is 10 sec /mm thickness. The properties of 12mm thick plate are: density 0.680g/cm3, dry internal bonding strength 0.8 1 MPa and wet internal bonding strength 0.22 MPa (according to the method of V 100).