DEVELOPER COMPOSITION FOR PHENOL-FREE DIRECT THERMAL RECORDING MEDIUM
A recording medium has a substrate and a thermally responsive layer disposed on the substrate. The thermally responsive layer includes a leuco dye and at least one developer. The developer comprises an N,N′-diurea derivative of Structure I and an N,N′-diurea derivative of Structure II: wherein each R n is independently a C 1-7 alkyl group.
1 . A recording medium, comprising:
a substrate; and
a thermally responsive layer disposed on the substrate, the thermally responsive layer including a leuco dye and at least one developer;
wherein the developer comprises an N,N′-diurea derivative of Structure I and an N,N′-diurea derivative of Structure II:
wherein each R n is, independently, a C 1-7 alkyl group.
2 . The recording medium of claim 1 , wherein each R n is independently selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, and a tert-butyl group.
3 . The recording medium of claim 2 , wherein each R n is the same and is a methyl group.
4 . The recording medium of claim 1 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative of Structure II are present in the thermally responsive layer in a weight ratio of 10:90 to 60:40 (Structure I:Structure II).
5 . The recording medium of claim 4 , wherein the N,N′-diurea derivative of Structure II is present in the thermally responsive layer in an amount by weight greater than or equal to the N,N′-diurea derivative of Structure I.
6 . The recording medium of claim 5 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative of Structure II are present in the thermally responsive layer in a weight ratio of 20:80 to 50:50.
7 . The recording medium of claim 6 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative of Structure II are present in the thermally responsive layer in a weight ratio of 25:75 to 50:50.
8 . The recording medium of claim 1 , wherein the developer further comprises diphenyl urea (DPU).
9 . The recording medium of claim 8 , wherein the developer comprises from 20 wt % to 60 wt % DPU.
10 . The recording medium of claim 9 , wherein the developer comprises from 40 wt % to 55 wt % DPU.
11 . The recording medium of claim 8 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative II account for at least 50% of the total developer by weight.
12 . The recording medium of claim 1 , wherein the thermally responsive layer has a coat weight of 1.5 g/m 2 .
13 . The recording medium of claim 1 , wherein a print quality of the recording medium when printed with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6 inches per second (ips) is characterized by at least one of:
(a) an initial ANSI value of at least 3.0;
(b) an ANSI value of at least 3.0 after the printed recording medium is exposed to sunflower oil for 4 hours at 40° C.;
(c) an ANSI value of at least 3.0 after the printed recording medium is exposed to sunflower oil for 4 hours at 80° C.;
(d) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 40° C.;
(e) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 80° C.;
(f) an ANSI value of at least 3.0 after the printed recording medium is exposed to olive oil for 4 hours at 40° C.; and
(g) an ANSI value of at least 3.0 after the printed recording medium is exposed to olive oil for 4 hours at 80° C.
14 . The recording medium of claim 13 , wherein a print quality of the recording medium when printed with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6 inches per second (ips) is characterized by at least (e) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 80° C.
15 . The recording medium of claim 14 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative of Structure II are present in the thermally responsive layer in a weight ratio of 20:80 to 50:50.
16 . The recording medium of claim 3 , wherein the N,N′-diurea derivative of Structure I and the N,N′-diurea derivative of Structure II are present in the thermally responsive layer in a weight ratio of 10:90 to 60:40 (Structure I:Structure II).
17 . The recording medium of claim 16 , wherein a print quality of the recording medium when printed with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6 inches per second (ips) is characterized by at least one of:
(a) an initial ANSI value of at least 3.0;
(b) an ANSI value of at least 3.0 after the printed recording medium is exposed to sunflower oil for 4 hours at 40° C.;
(c) an ANSI value of at least 3.0 after the printed recording medium is exposed to sunflower oil for 4 hours at 80° C.;
(d) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 40° C.;
(e) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 80° C.;
(f) an ANSI value of at least 3.0 after the printed recording medium is exposed to olive oil for 4 hours at 40° C.; and
(g) an ANSI value of at least 3.0 after the printed recording medium is exposed to olive oil for 4 hours at 80° C.
18 . The recording medium of claim 17 , wherein the developer further comprises diphenyl urea (DPU).
19 . The recording medium of claim 18 , wherein a print quality of the recording medium when printed with a thermal printer energy setting of 11.7 mJ/mm 2 at a print speed of 6 inches per second (ips) is characterized by at least (e) an ANSI value of at least 3.0 after the printed recording medium is exposed to Crisco® oil for 4 hours at 80° C.
20 . The recording medium of claim 19 , wherein the thermally responsive layer has a coat weight of 1.5 g/m 2 .