Лако-красочные материалы — производство

The liquid acrylics form a further group of unsaturated reactive resins and these are now available as two-part mixed or unmixed products. Compared with polyesters they are a relatively recent addition to the range of adhesives potentially suitable for structural joints. Many are based on the monomer methylmethacrylate which is polymerised by the addition of a small quantity of initiator or hardener.

In the two-part mixed versions the amount of hardener added to the monomer can vary between 5% and 50% depending on the formulation. These are suitable as general purpose adhesives capable of filling gaps up to 5 mm in thickness with a usable life of between 10 and 60 minutes. In the unmixed versions the hardener is applied as a thin film to one of the surfaces to be bonded. The monomer is then applied to the opposite surface, the parts immediately fitted together and held under contact pressure. The polymerisation starts instantaneously after the adhesive touches the hardener and requires about 15-20 minutes before the bonded joint can be handled. Although the overall performance is generally better than with the mixed versions, the gap which can be filled is limited to about 0.5 mm.

Many formulations are claimed to be capable of absorbing normal residues of rolling oil on steel surfaces, thus reducing the surface preparation requirements as compared with, say, epoxies. As with epoxies, acrylics can be toughened by the introduction of a rubbery phase within the matrix of the adhesive and they are particularly suitable for polymeric adherends because the surface is compliant.

Three further points are worthy of mention. Firstly, the methyl­methacrylate monomers are highly inflammable with a flash point at about 10 °С. Secondly, oxygen can act as an inhibitor of polymerisation so that the exposed edges of a joint, particularly with thicker bond lines, may never fully cure and may lead to concern over durability along the joint perimeter. Finally, the best acrylics have a distinctive odour and attempts to overcome this invariably lead to a reduction in overall performance.