Bonding of Hybo FOAM® Foam
Owing to the large number of available adhesives and the multitude of substances that may be bonded to HyboFOAM®, it is difficult to provide complete information on the methods, amounts, and application of adhesives, as well as the drying and curing times. However, in case of special problems, we, together with adhesives manufacturers, will be glad to look for a practical solution. Still, for most bonding problems, HyboFOAM® offers the advantages of solvent resistance and heat distortion resistance for hot curing (epoxy resins up to 180 °C), which should not be underestimated. As a result, practically all commercial adhesives can be used.
It is indispensable that before bonding, the HyboFOAM® surfaces shall be freed from dust by suction or by blowing the dust off with oil-free compressed air.
The adhesives are usually classified into three groups:
Solvent-based adhesives
Emulsion adhesives
Solventless adhesive systems
Since HyboFOAM® is very impervious to solvent diffusion, great care must be taken when bonding large areas of HyboFOAM® to itself or other diffusion-impervious materials using adhesives from groups 1 and 2. Ensure that the adherents dry thoroughly after the adhesive is applied to both sides before joining them under pressure. Joints made with these adhesive systems (generally rubber-based) typically remain slightly elastic and have good peel-off strength. If heat-sealing is possible, the bond quality can be significantly improved.
After applying the adhesive to both sides, the adhesive is dried off, then placed on top of each other and bonded under pressure at a temperature of 80-120 °C. The pressure may be up to 40% of the maximum compression strength at 20 °C of the particular foam plastic and should be maintained for 1-5 minutes. The bonded materials should be removed at a temperature below 80 °C.
The solventless system includes hot-melt adhesives and two-component adhesives like epoxy, polyester, or methacrylic resins, which should be allowed to cure under sufficient pressure (0.05-0.3 N/mm²) or be very fluid during application to ensure the foam cells are well filled. The cure can be accelerated by heat (up to 160 °C), resulting in very hard and rigid joints.
Adhesive films and hot-melt adhesives need heat for bonding and can therefore normally be applied by heat-sealing. Adhesive films must be sufficiently thick (100-200 g/m²) to anchor them firmly in the cut HyboFOAM® cells. Two-component adhesive films that give off volatile constituents like solvents or, in the case of phenolic resin films, water during the cure, should be warmed through with gentle pressure. Before bonding, the press should be briefly bumped to allow the volatile constituents to escape.
When hot-melt films are used, it has frequently proved useful to perforate them before bonding to avoid air bubbles. For better deaeration in difficult cases, prior grooving of the HyboFOAM® sheet surfaces will help. Grooves about 1-1.5 mm deep and 2 mm wide have proved useful.
When HyboFOAM® is to be bonded to other materials, the adhesive may generally be selected according to its suitability for these materials. For instance, for metals and laminated plastics, epoxy resins, rubber, or PU adhesives; for acrylic glass/methacrylic resins; for wood and paper; or for glass fiber-reinforced polyester sheets, polyester resins, epoxy resins, and PU adhesive systems.
To obtain perfectly straight sandwich sheets, it is important for both sides of the HyboFOAM® sheet to be simultaneously bonded to the skin. Both skins must be of the same material and have the same thickness. Uniform heating and cooling on both sides are other basic conditions for the manufacture of flat sandwich sheets.
If the HyboFOAM® surface is treated with a needle roller before the application of the adhesive, the obtainable bond strength will meet very high requirements.
We recommend, in all cases, the use of oversize HyboFOAM® sheets (0.5-1 mm) for bonding skins and to run the press to a firm stop to avoid overstressing the HyboFOAM® sheet by the molding pressure at high curing temperatures or falling below the required tolerance due to thermoelastic creep.
