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PMI foam (quality is equal to Rohacell)

Tasuns Composite Technology Co.,Ltd | Updated: Aug 29, 2017

Owing to the large number of available adhesives and the multitude of substances which may be bonded to foam, it is difficult to provide complete information on the methods and amounts, and application of adhesives, as well as the drying and curing times. However, in case of special problems, we, together with adhesives manufacturers, shall be glad to look for a practical solution. Still, for most bonding problems, Tasuns offers the advantages of solvent resistance and heat distortion resistance for hot curing (epoxy resins up to 180 °C) advantages which should not be underestimated. Practically all commercial adhesives can therefore be used.

It is indispensable that before bonding, the foam surfaces shall be freed from dust by suction or by blowing the dust off with oil-free compressed air.

The adhesives are usually classified in three groups:

1. Solvent-based adhesives

2. Emulsion adhesives

3. Solvent less adhesive systems

Since PMI FOAM is very impervious to solvent diffusion, and great care must be taken when large areas of PMI foam are to be bonded to PMI foam or other diffusion-impervious materials by adhesives of groups 1 and 2, that the adherents dry off well after the adhesive has been applied to both sides before they are joined together under pressure. Joints made with these adhesive systems (generally rubber based) normally remain a little elastic and have good peel-off strength. If it is possible to heat-seal the joint, the quality of the bond can be greatly improved. 

After applying the adhesive to both sides, the adhesive are 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 it should be maintained for 1 - 5 minutes. The bonded materials should be removed at a temperature below 80 °C.

The solvent less system includes hot-melt adhesives, two-component adhesives like epoxy, polyester or methacrylic resins should be allowed to cure under sufficient pressure(0.05-0.3N/mm2) or be very fluid during the application so that the cells of the foam are well filled. The cure can be accelerated by heat (up to 160°C). The joints become very hard and rigid.

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) in order to anchor them firmly in the cut PMI FOAM cells. Two-component adhesive films which 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 in order to avoid air bubbles. For the purpose of better deaeration in difficult cases, prior grooving of the PMI FOAM sheet surfaces will help. Grooves about 1 - 1.5 mm deep and 2 mm wide have proved useful.

 When PMI FOAM 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 adhesives systems.

To obtain perfectly straight sandwich sheets, it is important for both sides of the PMI FOAM 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 PMI FOAM 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 PMI FOAM sheets (0.5 – 1 mm) for bonding skins, and to run the press to firm stop, lest the PMI FOAM curing temperatures, or the dimensions be below the required tolerance through thermo elastics creep.