Optical density question

Here is the question.

I am student of packaging institute presently working in multinational company.please tell me what is the method to find out optical density of metallized film which is laminated to other film and in with print or without print? thank u very much for the information u have display on web.

Answer.

Here are the basic equations used in measuring the optical density

Optical Density    =            log ₁₀ Opacity    =    log ₁₀ 1

                                                                                                  T

Opacity    =     1                                  

                        T

Opacity    =     Incident light                       

                        Transmitted light                                             

Transmittance =    Transmitted light

                                    Incident light

The fact that the light is measured in transmittance means that the OD measured is a combination of the metal coating and the printing.  In order to have a measure of the metal it is necessary to have a measure of the OD with and without the metal present so that the OD of the print can be subtracted from the OD of the combined and thus the OD left will be that of the metal.

The simplest, and most reliable, method is to ask for a sample of the metallized film alone and measure that directly.

I hope this helps you.

CAB

Comments

[Raymon Chan]

Follow the optical density question, I have a similar issue of measuring the density of Ni layer on Tin. Can anyone tell the equipment to be used and give out more the experimental details?
Thank you for your attention.

[m.abdul haq]

at what wave length?

[Eldridge Mount III]

Relative to the Ni layer on Tin, You might be able to do a simple difference technique if the optical density ranges are in a good range. this might also require the use of a higher power light source, perhaps a laser. In principle an elipsometer might be used but might be difficult to use in a chamber and would be an off line measurement. You could also make use of a reflection of a circularly polarized light beam (can be purchased as a laser source) off the Ni layer and measuring the change in polarization which will occur on the reflection, either as a change in intensity or the angle of polarization. It should be possible to develop the correlation between the Ni thickness and the change in the light reflection.

Alternative would to look for interference effects in transmitted or reflected light which would be related to Tin and Ni layer thicknesses and refractive indexes.

[jason]

albedo=s/(s+k)
s scattering coefficient
k absorption coefficient
optical density=(k+s)*Z =log10(1/T) ?
Z is the film thickness
How to calculate the k & s of a film using two reflectance of film over white and over black substrate

Thanks in advance