How polyvinyl butyral interlayer is made

The clear film that holds a cracked windshield together is a resin built from polyvinyl alcohol.

stations: 6
things upstream: 14
raw sources: 5
steps from the ground: 5

The short version

Polyvinyl butyral begins when polyvinyl alcohol reacts with butyraldehyde under an acid catalyst. The resin is neutralized, separated, stabilized and dried, then mixed with plasticizer, because alone it is too stiff to soak up a blow. Melted and forced through a long slot die, it becomes a sheet 0.13 to 1.3 mm thick, ready to go between two panes of glass.

React alcohol with aldehyde

Polyvinyl alcohol reacts with butyraldehyde, a chemical made almost entirely from propylene, in the presence of an acid catalyst. Plants can run this in water or in solvent.

Goes in
Polyvinyl alcohol Propylene
Neutralize and dry the resin

The catalyst is neutralized, and the resin is separated, stabilized and dried. It reaches customers as powder or granules. Inks, paints and ceramic binders use it in that form.
Blend in plasticizer

Plain resin would be too rigid for an interlayer, so plasticizer goes in, generally 15 to 50 parts per 100 parts of resin in one patent. Ultraviolet stabilizers and adhesion control salts may join it, and pigments make the colored sheets used for a windshield's blue or green shade band.

Goes in
Plasticizer
Extrude through a sheeting die

Molten, plasticized resin is forced through a wide, narrow die opening shaped to the sheet being made. Some lines instead cast the melt onto a specially surfaced die roll right at the exit.

about 0.13 to 1.3 mm thick
Texture the sheet surface

Valleys and peaks on the die roll leave one side of the sheet rough. The design of the die opening can roughen the other side. Melt temperature and water content offer other ways to control the texture.
Bond between glass panes

Glassmakers lay the sheet between two panes and bond them under heat and pressure. Only then does it turn optically clear, and the sandwich behaves as a single unit.

End of the linePolyvinyl butyral Next it goes into windshield.

Worth repeating

When laminated glass breaks, the fragments tend to stick to the interlayer instead of falling free.
PVB is also used to encapsulate thin-film solar modules.
The same resin works as a temporary binder in technical ceramics.