Three-dimensional (3D) printing with discolorable near-infrared absorbing dye

1. A three-dimensional (3D) printing method, comprising: applying a polymeric or polymeric composite build material; selectively applying a fusing agent on at least a portion of the polymeric or polymeric composite build material, the fusing agent including:

a discolorable near-infrared absorbing dye;

a thiol surfactant; a reducing agent; and a balance of water; and

applying near-infrared radiation to the polymeric or polymeric composite build material at a condition that maintains a temperature of the selectively applied fusing agent below a decomposition temperature of the fusing agent and that allows the discolorable near-infrared absorbing dye to harvest near-infrared radiation energy, thereby fusing the portion of the polymeric or polymeric composite build material in contact with the fusing agent to form a layer and initiating discoloration of the discolorable near-infrared absorbing dye in the layer, wherein the discolorable near-infrared absorbing dye has a general formula I:

wherein:

M is a metal selected from the group consisting of nickel, zinc, platinum, palladium, and molybdenum; and

each of W, X, Y, and Z is selected from the group consisting of H, Ph, PhR, and SR, wherein Ph is a phenyl group and R is selected from the group consisting of C n H 2n +1, OC n H 2n +1, and N(CH 3 ) 2 , wherein 2<n<12.

2. The 3D printing method as defined in claim 1 wherein the condition includes:

a predetermined number of radiation exposure passes at a predetermined speed;

a radiation exposure time ranging from about 5 seconds to about 2 minutes;

a build material platform temperature ranging from about 100° C. to about 200° C.; or

combinations thereof.

3. The 3D printing method as defined in claim 2 wherein the condition includes the predetermined number of radiation exposure passes at the predetermined speed, the predetermined number of radiation exposure passes is 2, and the predetermined speed ranges from about 20 inches per second to about 24 inches per second.

4. The 3D printing method as defined in claim 2 wherein the condition includes the predetermined number of radiation exposure passes at the predetermined speed, the predetermined number of radiation exposure passes is 4, and the predetermined speed ranges from about 24 inches per second to about 30 inches per second.

5. The 3D printing method as defined in claim 2 , further comprising altering the condition based on a concentration of the fusing agent that is selectively applied.

6. The 3D printing method as defined in claim 5 wherein the altering of the condition includes one of:

decreasing the radiation exposure time when the concentration of the fusing agent that is selectively applied is increased; or

increasing the radiation exposure time when the concentration of the fusing agent that is selectively applied is decreased.

7. The 3D printing method as defined in claim 1 , further comprising allowing the discolorable near-infrared absorbing dye in the layer to continue discoloration in the absence of the applied near-infrared radiation.

8. The 3D printing method as defined in claim 7 wherein one of:

the fusing agent further includes a colorant, and the layer exhibits a color of the colorant after the discolorable near-infrared absorbing dye in the layer undergoes at least substantial discoloration; or

the fusing agent excludes a colorant, and the layer exhibits a color of the polymeric or polymeric composite build material after the discolorable near-infrared absorbing dye in the layer undergoes at least substantial discoloration.

9. The 3D printing method as defined in claim 1 wherein during the application of the near-infrared radiation, the discolorable near-infrared absorbing dye in the layer undergoes at least substantial discoloration, and after the application of the near-infrared radiation, one of:

the layer exhibits a color of a colorant present in the fusing agent; or

the layer exhibits a color of the polymeric or polymeric composite build material when the fusing agent excludes a colorant.

10. The method as defined in claim 1 wherein the selectively applying of the fusing agent is accomplished by thermal inkjet printing or piezo electric inkjet printing.

11. The method as defined in claim 1 wherein: the reducing agent is a polar aprotic solvent selected from the group consisting of 1-methyl-2-pyrrolidone, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and combinations thereof; and the thiol surfactant is dodecanethiol.

12. The method as defined in claim 11 wherein:

the discolorable near-infrared absorbing dye is present in the fusing agent in an amount ranging from about 1 wt % to about 3 wt % based on a total wt % of the fusing agent;

the thiol surfactant is present in the fusing agent in an amount ranging from about 1 wt % to about 3 wt % based on the total wt % of the fusing agent; and

the polar aprotic solvent is present in the fusing agent in an amount ranging from about 5 wt % to about 50 wt % based on the total wt % of the fusing agent.

13. The method as defined in claim 1 wherein the discolorable near-infrared absorbing dye is selected from the group consisting of a diarylmethane dye, a triarylmethane dye, a tetraryldiamine dye, a nitroso dye, a cyanine dye, a nigrosine dye, an iminium dye, a diimminum dye, a squarilium dye, a croconium dye, a quinone dye, a phthalocyanine dye, an azo dye and an indoaniline dye.