Assessment of primer content on a print substrate

1. A method for assessing primer composition coat weight on a print substrate, the method comprising:

providing a primed print substrate comprising an organic print substrate material on which a primer layer comprising an organic primer composition is disposed;

spectroscopically analysing the primed print substrate using Fourier transform infrared (FTIR) spectroscopy by attenuated total reflectance (ATR) to produce a FTIR spectrum of the primer layer disposed on the print substrate;

identifying a primer peak in the FTIR spectrum which is characteristic of the organic primer composition;

identifying a print substrate peak in the FTIR spectrum which is characteristic of the organic print substrate material; and

comparing the primer peak and the print substrate peak to assess the primer composition coat weight on the print substrate of the primed print substrate.

2. A method according to claim 1 comprising calculating a parameter of the primer peak and calculating the same parameter of the print substrate peak, and wherein comparing the primer peak and the print substrate peak comprises calculating the peak parameter ratio of the primer peak parameter to the print substrate peak parameter.

3. A method according to claim 2 , wherein comparing the primer peak and the print substrate peak further comprises comparing the calculated peak parameter ratio with a calibration standard to determine the primer composition coat weight on the print substrate of the primed print substrate, the calibration standard being prepared by calculating a peak parameter ratio from FTIR spectra obtained for each of a plurality of primed print substrate samples each comprising a primer layer having a known coat weight of the primer composition disposed on the print substrate material.

4. A method according to claim 3 , wherein the parameter of the primer peak and the parameter of the print substrate peak is the area of the primer peak and the area of the print substrate peak.

5. A method according to claim 1 , wherein the organic primer composition comprises a group having an absorption primer peak in the range of either 2000-1350 cm-1 or 3000-2400 cm′, and the print substrate material comprises a group having an absorption print substrate peak in the other of the range of 2000-1350 cm-1 or 3000-2400 cm′.

6. A method according to claim 1 , wherein the primer composition comprises methylene groups having an absorption primer peak in the range of about 2900-2500 cm-1.

7. A method according to claim 6 , wherein the primer composition comprises a polyethylene imine resin.

8. A method according to claim 1 , wherein the print substrate comprises a synthetic polymeric material, the polymer of the polymeric material comprises carbonyl groups having an absorption print substrate peak in the range of about 1690-1760 cm-1.

9. A method according to claim 8 , wherein the polymer is polyethylene terephthalate (PET).

10. A method according to claim 1 further comprising determining the primer composition coverage on the primed print substrate.