Acrylic adhesive for plastics without stress cracking or marking Bostik SAF Ultimate

      Acrylic adhesive for plastics without stress cracking or marking Bostik SAF Ultimate

Bostik SAF Ultimate is a two-part methacrylate acrylic adhesive formulated to bond plastics without causing stress cracking or leaving a mark on the visible face. This is the defect that most often ruins an otherwise sound assembly: the joint holds, then crazing appears around the bead after a few weeks, on a PMMA or a polycarbonate already under tension. Adezif is a distributor of Bostik / Born2Bond adhesives.

Stress cracking does not come from poor adhesion but from the chemistry of the product: an aggressive monomer penetrates the plastic and releases the internal stresses frozen in at moulding or machining. The SAF Ultimate is formulated to avoid it while keeping a shear strength of 12 to 18 MPa, so a genuinely structural bond.

Bostik presents it as a patented methacrylate adhesive for dissimilar substrates — metals, plastics and composites — and highlights its resistance to ageing in aggressive environments: the joint stays tough after ageing instead of hardening and breaking. That is what counts on a plastic part exposed to sunlight or to thermal cycling, where cracking often appears months after assembly. The formulation is non-sag, so it can be applied vertically.

Its strengths:

• No stress cracking or marking on the plastic
• High impact strength, 65 to 120 % elongation depending on the grade
• Resistance to ageing in aggressive environments
• Four fixture times from 6 to 25 minutes
• Minimal surface preparation and vertical application possible

      What are the applications of the SAF Ultimate adhesives?

Bonding PMMA and polycarbonate on the visible face

On a PMMA or polycarbonate panel, the bonded face is often the one you see: a display case, a clear cover, a machine panel. The SAF Ultimate bonds without crazing or haze around the bead, where an aggressive adhesive leaves a permanent mark. As soon as the part is clear or coloured through, this is the criterion to check before strength itself. If the bond can be cured under a lamp, the Born2Bond LC177 UV adhesive answers the same need with a set in seconds.

Plastic to metal assemblies under impact

With 65 to 120 % elongation depending on the grade, the joint absorbs impact instead of failing in a brittle way, and takes up the differential expansion between a metal bracket and a plastic part. The four grades cover workshop throughput: the SAF Ultimate 5 fixtures in 6 minutes on a small part, the SAF Ultimate 25 leaves 18 minutes of open time to coat a large surface.

Bonding plastics without heavy preparation

The range calls for minimal surface preparation, which shortens the bonding station: degreasing is enough where other technologies require a primer. On low surface energy plastics such as polypropylene and polyethylene, the 3M DP 8010 is the one to look at, formulated for polyolefins.

      Applying the SAF Ultimate acrylic adhesive

The SAF Ultimate is applied from a two-part cartridge of 50 ml or 415 to 490 ml, with a two-component dispensing gun fitted with a static mixing nozzle that handles metering and mixing in a single operation. The ratio is 10:1 for grades 5, 10 and 25, and 4:1 for grade 15. The thixotropic rheology holds the bead and allows vertical bonding.

Degrease with isopropyl alcohol to remove grease and oxides; some plastics also need light abrasion, even though the range needs lighter surface preparation than other technologies. Purge the first few centimetres until the colour is even, coat the part, assemble before the end of the open time, then hold in position until the fixture time.

Curing takes place between 18 and 28 °C with no post-cure, final strength being reached after 24 hours. Store between 15 and 25 °C in a closed container, with a shelf life of 9 months in the unopened original packaging.

      Technical data of the SAF Ultimate adhesives

Patented two-part methacrylate acrylic base, non-sag thixotropic rheology on all four grades, hardness 55 to 70 Shore D, full cure in 24 h between 18 and 28 °C with no post-cure.

• Substrates: steel, powder-coated steel, stainless steel, aluminium, polyester, vinylester, epoxy, acrylic Elium, PMMA, PC, ABS, PS, PVC.
• Pack sizes: 50 ml and 415 to 490 ml cartridges depending on the grade.

Typical Bostik values, to be confirmed on the technical data sheet of the chosen grade.