In-situ evaluation of curing of ink compositions via absorbance spectroscopy

• US 10,385,144 B2
• Filed: 07/28/2017
• Issued: 08/20/2019
• Est. Priority Date: 07/28/2017
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Kanungo, Mandakini, LeStrange, Jack T., Knausdorf, Peter, Yang, Xin, Condello, Anthony S.
• Primary Examiner(s): Feggins, Kristal
• Application Number:
  US15/662,573
• Publication Number:
  US 20190031791A1
• Time in Patent Office: 753 Days
• CPC Class Codes: B41J 11/00214 using UV radiation
• CPC Class Codes: B41M 7/0081 using electromagnetic radiation or waves, e.g. ultraviolet radiation, electron beams
• CPC Class Codes: C08F 2/50 with sensitising agents
• CPC Class Codes: C09D 11/101 Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
• CPC Class Codes: C09D 11/322 Pigment inks
• CPC Class Codes: G03F 7/029 Inorganic compounds; Onium compounds; Organic compounds having hetero atoms other than oxygen, nitrogen or sulfur
• CPC Class Codes: G03F 7/031 Organic compounds not covered by group G03F7/029

Abstract

A method for evaluating curing in an ink composition comprises depositing an ink composition on the surface of an object via a direct-to-object inkjet printing system to form a film thereon, the ink composition comprising a photoinitiator capable of initiating a free radical polymerization process in the ink composition upon the absorption of light to cure the deposited film; exposing, in-situ, the deposited film to light generated by a first source of light under conditions which initiate the free radical polymerization process to cure the deposited film; exposing, in-situ, the cured film to light generated by a second source of light under conditions which induce light absorption by unreacted photoinitiator in the cured film; measuring the absorbance of the cured film; and determining a degree of cure in the cured film from the measured absorbance and predetermined calibration data.

Claims

1. A method for evaluating curing in an ink composition, the method comprising:

(a) depositing an ink composition on the surface of an object via a direct-to-object inkjet printing system to form a film thereon, the ink composition comprising a photoinitiator capable of initiating a free radical polymerization process in the ink composition upon the absorption of light to cure the deposited film;

(b) exposing, in-situ, the deposited film to light generated by a first source of light under conditions which initiate the free radical polymerization process to cure the deposited film;

(c) exposing, in-situ, the cured film to light generated by a second source of light under conditions which induce light absorption by unreacted photoinitiator in the cured film;

(d) measuring the absorbance of the cured film; and

(e) determining a degree of cure in the cured film from the measured absorbance and predetermined calibration data.

2. The method of claim 1, wherein the object is a finished, post-manufactured commercial article.

3. The method of claim 1, wherein the ink composition further comprises one or more types of acrylate oligomers, one or more types of acrylate monomers, and a pigment.

4. The method of claim 1, wherein the photoinitiator is selected from methyl 2-benzyl benzonate, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), 1-Hydroxycyclohexyl-1-phenyl methanone, 1-Butanone, 2-(dimethylamino)-2-(4-methylphenyl)methyl-1-4-(4-morpholinyl)phenyl-, and combinations thereof.

5. The method of claim 1, wherein the conditions which induce light absorption by unreacted photoinitiator also minimize further curing by the light generated by the second source of light.

6. The method of claim 5, wherein the light generated by the second source of light comprises a wavelength which substantially overlaps an absorption maximum of the photoinitiator and further wherein the intensity of the light generated by the second source of light or the length of time of exposure to the light generated by the second source of light or both are selected to minimize further curing by the light from the second source of light.

7. The method of claim 1, wherein the predetermined calibration data comprises a set of predetermined absorbance values and associated predetermined degree of cure values, the predetermined degree of cure values generated using solvent extraction.

8. The method of claim 1, wherein the predetermined calibration data is fit to an equation and the degree of cure is calculated using the measured absorbance and the equation.

9. The method of claim 1, further comprising repeating step (b) one or more times to further cure the cured film until a predetermined target degree of cure is achieved.

10. The method of claim 1, wherein the direct-to-object printing system comprises:

an array of printheads, the array comprising one printhead configured to eject the ink composition and one or more additional printheads configured to eject one or more additional ink compositions;

a support member positioned parallel to the array of printheads;

an object holder configured to hold the object such that the surface of the object faces towards the array of printheads, the object holder moveably mounted to the support member;

the first source of light;

the second source of light;

an actuator operatively connected to the object holder to move the object holder relative to the array of printheads, the first source of light, and second source of light; and

a controller operatively connected to the array of printheads, the actuator, the first source of light, and the second source of light, the controller configured to operate the array of printheads, the actuator, the first source of light, and the second source of light.

11. The method of claim 10, wherein the second light source is part of a spectrophotometer operatively connected to the controller.

12. The method of claim 10, wherein the first source of light is a light-emitting diode and the second source of light is a lamp.

13. The method of claim 10, wherein the controller comprises a processor and a non-transitory computer-readable medium comprising instructions that, when executed by the processor, cause the controller to calculate the degree of cure using the measured absorbance and an equation fit to the predetermined calibration data.

14. The method of claim 13, wherein the instructions, when executed by the processor, further cause the controller to compare the calculated degree of cure to a predetermined target degree of cure and to carry out step (b) an additional time if the calculated degree of cure is outside a predetermined threshold value.