Glazing Caused by PE masking Tape on PMMA sheet

Is the all over or just where the tape was, or where the tape was absent? Was the whole sheet covered? Not sure of coverage. If it was on areas covered by the tape it could be a reaction between the adhesive and the PMMA brought on by the UV exposure. You don't say how long the exposure period was (8 Hours?). Nor do you say what sort of UV you used. It is well known that UV light can break the chemical bonds in plastic films. The wave length can interact at a molecular level. Many plastic polythene suffers badly in sun light. So does un-stabalised PVC. I take it you have used PMMA before without any problem?

Crazing was only found the surface of the PMMA sheet where PE tape had covered. The exposure through the UV tunnel(80watt lamp) on the PE Tape was a mere 2 second(300-400mJ/cm.sq of UV dosage) to cure the printing ink on the 1st surface. I was trying to print our company logo on the PE tape by using a UV cured ink. The PE tape was left mostly over night after printing and discovered the crazing the next morning, probably about 8-12 hours I would say. This is the 1st time I had see this problem but not with PC sheet. Yes, the UV could have broken down the chemical bonds on the adhesive layer of the PE tape, but how did it happen what chemical reaction actually taken place?? My understanding of tape adhesive system and chemistry are very limited and since I had switch to solvent based ink I'm no longer have any crazing issue on my PMMA sheets. But out of curosity I just would like to find out the answer ?? Thank for the contribution.

Hello, It is the photochemical reaction of the UV light that severs the chemical bonds. This is brought about by the high energy interaction as the UV light passes through the material it displaces electrons and the molecular structure is torn apart. It is very like when neutrons emmited from a radio active source blast into and through a substance they carry enough energy to be destructivly interactive. Chemistry is largely about the electron and how they are linked between any two or more atoms. Elements behave according to how their out shell is made up some lack an electron to complete their outer shell others have a spare electron. The outer most shell is known as the valency shell as it contains the valence electrons. If the outer shell has extra electrons it has a negative charge if it lacks an electron it has positive charge. Atoms like to be stable so any that can obtain or loose an electron will do so. If you can get hold of Collins dictionary of science it explains this in more detail under (Bond).

Hi Brainwave,

Very interesting explanation but still why it is affecting only PMMA and not PC? Thank for the contribution plse keep its coming!

I shall have to look into it.

It is possible that the original adhesive was an acrylic that had some residual monomer. These residual materials, or the any low MW materials that were generated when exposed to UV, may have solubilized the surface of the PMMA. The PC is more solvent/chemical resistant. Your new adhesive may be rubber based, a higher MW acrylic or contain UV stabilizers that eliminate the problem.

OK so now we have it. Poly(Methyl Methacrylate) Made by the free radical vinyl polymerization process. this means it is susceptible to a large dose of UV radiation.

See Google entry PMMA second in the list under the Wiki entry. It shows up the way this plastic is formed. It is a polymer that is to say it is composed of lots of smaller bits monomers joined up. Because of this particular structure it is week when enough light energy is taken to it. The site is a gold mine of info. Take your time and take the tour.

Hi All,

Thank again for the kind contribution ! I have checked with manufacturer and indeed the adhesive was acrylate based !

There you go, now we know.