Aqueous Cationic Polyurethane Dispersions

Abstract

An aqueous polyurethane resin dispersion, the polyurethane resin having a polyalkylene oxide in a side chain thereof and is obtainable by reacting in an organic solvent, a polyisocyanate with a 1,2 or 1,3 polyether diol and with a polymeric diol selected from the group consisting of polyester diol, polyether diol, polycarbonate diol, polyacrylate diol and polyolefin diol and by adding a cationic surfactant or cationic surfactant precursor to the organic solvent.

Claims

1-14. (canceled)

15. An aqueous polyurethane resin dispersion, the polyurethane resin having a polyalkylene oxide in a side chain thereof and is obtainable by reacting in an organic solvent, a polyisocyanate with a 1,2 or 1,3 polyether diol and with a polymeric diol selected from the group consisting of polyester diol, polyether diol, polycarbonate diol, polyacrylate diol, and polyolefin diol and by adding a cationic surfactant or cationic surfactant precursor to the organic solvent.

16. The aqueous polyurethane resin dispersion of claim 15, wherein the cationic surfactant comprises a quaternized ammonium group or a tertiary amine group.

17. The aqueous polyurethane resin dispersion of claim 15, wherein the cationic surfactant is according to Formula II ##STR00033## wherein R1 is a hydrogen or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; R2 and R3 are each independently a substituted or unsubstituted alkyl group having between 1 carbon atom and 18 carbon atoms or a benzyl group; and R4 is a substituted or unsubstituted alkyl group having at least 8 carbon atoms.

18. The aqueous polyurethane resin dispersion of claim 16, wherein the cationic surfactant is according to Formula II ##STR00034## wherein R1 is a hydrogen or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; R2 and R3 are each independently a substituted or unsubstituted alkyl group having between 1 carbon atom and 18 carbon atoms or a benzyl group; and R4 is a substituted or unsubstituted alkyl group having at least 8 carbon atoms.

19. The aqueous polyurethane resin dispersion of claim 15, wherein the cationic surfactant is added after the reacting is completed.

20. The aqueous polyurethane resin dispersion of claim 15, wherein the cationic surfactant comprises reactive groups capable of reacting with polyisocyanate.

21. The aqueous polyurethane resin dispersion of claim 16, wherein the cationic surfactant comprises reactive groups capable of reacting with polyisocyanate.

22. An aqueous treatment liquid for inkjet printing comprising the polyurethane resin dispersion of claim 15 in an amount of from 1 wt. % to 30 wt. % with respect to the total weight of the treatment liquid.

23. An aqueous treatment liquid for inkjet printing comprising the polyurethane resin dispersion of claim 16 in an amount of from 1 wt. % to 30 wt. % with respect to the total weight of the treatment liquid.

24. An aqueous treatment liquid for inkjet printing comprising the polyurethane resin dispersion of claim 17 in an amount of from 1 wt. % to 30 wt. % with respect to the total weight of the treatment liquid.

25. The aqueous treatment liquid for inkjet printing of claim 22, further comprising a flocculant.

26. The aqueous treatment liquid for inkjet printing of claim 24, further comprising a flocculant.

27. The aqueous treatment liquid for inkjet printing of claim 22, further comprising a pigment.

28. The aqueous treatment liquid for inkjet printing of claim 27, wherein the pigment comprises titanium dioxide.

29. The aqueous treatment liquid for inkjet printing of claim 25, wherein the flocculant is a multivalent metal salt.

30. The aqueous treatment liquid for inkjet printing of claim 26, wherein the flocculant is a multivalent metal salt.

31. An aqueous inkjet ink comprising the polyurethane resin dispersion of claim 15 in an amount of from 1 wt. % to 30 wt. % with respect to the total weight of the ink and a pigment dispersion, the pigment dispersion comprising at least one dispersing agent having the Formula III ##STR00035## wherein R.sub.1 is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, and a substituted or unsubstituted (hetero)aryl group; L represents a divalent linking group comprising 2 to 10 carbon atoms; R.sub.2, R.sub.3, and R.sub.4 are each independently selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group, and a substituted or unsubstituted (hetero)aryl group; R.sub.5 represent a hydrocarbon group comprising at least 8 carbon atoms; X.sup.− represents an anion to compensate the positive charge of the ammonium group; and any of R.sub.1, R.sub.2, R.sub.3, R.sub.4, and L may be combined to form a five to eight membered ring.

32. A method of preparing an aqueous polyurethane resin dispersion, the method comprising: (i) reacting a polyisocyanate with a 1,2 or 1,3 polyether diol and a polymeric diol selected from the group consisting of polyester diol, polyether diol, polycarbonate diol, polyacrylate diol, and polyolefin diol in an organic solvent in the presence of a cationic surfactant to form a solution of a polyurethane resin; (ii) adding water to the solution to form a polyurethane resin dispersion; and (iii) removing the organic solvent from the dispersion.

33. A method of preparing an aqueous polyurethane resin dispersion, the method comprising: (i) reacting a polyisocyanate with a 1,2 or 1,3 polyether diol and a polymeric diol selected from the group consisting of polyester diol, polyether diol, polycarbonate diol, polyacrylate diol, and polyolefin diol in an organic solvent to form a solution of a polyurethane resin; (ii) adding a cationic surfactant to the solution; (iii) adding water to the solution to form a polyurethane resin dispersion; and (iv) removing the organic solvent from the dispersion.

34. An inkjet recording method, the method comprising: (i) providing a substrate; (ii) forming a pre-treated substrate by applying the treatment liquid of claim 15 on a surface of the substrate, optionally drying the substrate; and (iii) printing an image by jetting an ink jet ink on the pre-treated substrate.

Description

EXAMPLES

1. Measuring Methods

1.1. Average Particle Size

[0102] Samples of the PU dispersion were diluted 10 times with a 0.005 M NaCl aqueous solution. A diluted PU dispersion of 1.0 mL was brought in a disposable polystyrene cuvette (DTS0012), and its z-average particle size was measured with Malvern Zetasizer Nano S 3 times at 23° C. after 30 seconds of stabilization time.

1.2. Colloidal Stability at Increased pH

[0103] The colloidal stability of the aqueous cationic polyurethane dispersion at increased pH is determined by adding to 3 ml of the dispersion, 1 drop of a 10 wt. % solution of NaOH in a test tube. The formation of precipitation, agglomeration or aggregation is visually evaluated and a figure is attributed to it as tabulated in Table 4.

TABLE-US-00004 TABLE 4 Visual observation of aqueous PU dispersion Scale No difference observed 0 Clear dispersion with 1 slight precipitates Slightly blurry dispersion 2 Severe blurry dispersion 3 Formation of 4 agglomerates Severe formation of 5 agglomeration

2. Materials

[0104] All materials used in the following examples were readily available from standard sources such as Sigma-Aldrich (Belgium) and Acros (Belgium) unless otherwise specified. The water used was demineralised water. [0105] Acetone is acetone p.a. supplied by R International [0106] Dynacoll 7150 is a polyester diol supplied by Evonik [0107] Ymer N120 is 1,3 diol polyether supplied by Perstorp [0108] Reaxis C708 is a catalyst supplied by Reaxis BV, The Netherlands [0109] DBTL is dibutyl tin laurate (KEVER- A T DBTL 162) supplied by Brenntag [0110] IPDI is Desmodur I, a polyisocyanate supplied by Covestro [0111] BD is 1,4-butane diol [0112] Triethylamine is triethylamine [0113] SP-8 is benzyl dimethyl dodecyl ammonium chloride [0114] S-13 dodecyl(benzyl)diethanolammonium chloride=benzoxonium chloride provided by Sachem under the tradename BEXOC [0115] AS-5.HCL: dodecyldiethanolammonium chloride is obtained by protonation of Ethomeen C12 as supplied by Akzo, (CAS registry number 61791-31-9), ie. N,N-Bis(2-hydroxyethyl)(coconut oil alkyl)amine: In an Erlenmeyer of 100 mL, 8.79 g of Ethomeen C12 was dissolved in 25.25 mL of 1.2 M HCl(aq.) at ambient temperature under atmosphere pressure. To prepare a solution of N,N-bis(2-hydroxyethyl)(coconut oil alkyl)ammonium chloride which was further used in the preparation of PU dispersion, 34.75 mL of demineralized water was added to the mixture, and the mixture was stirred overnight. [0116] SURF-1 is Capstone FS3100, a surfactant from Dupont [0117] PYR is 2-pyrrolidone [0118] HD is 1,2-hexanediol [0119] COL is CAB-O-JET 450C, a cyan colorant from Cabot [0120] PU-9 dispersion is a reproduction of the PU-9 dispersion disclosed in the published patent application: WO2018/077624 having a solid content of 41.9 wt. % [0121] SURF-2 is Tego Wet 270, a surfactant from Evonik Industries

3. Synthesis of the Aqueous Polyurethane Dispersions According to the Invention

PU-I1

[0122] In an Erlenmeyer of 500 mL 111.73 g of Dynacoll 7150 and 174.02 g of acetone were weighed. The solution of Dynacoll 7150 in acetone was stirred at room temperature during 60 minutes by using a magnetic stirrer to obtain a colorless and clear solution. The poly ether diol, Ymer N120, was preheated in an oven at 80° C. to obtain a liquid product, and 16.40 g of Ymer N120 was added to the solution. The resulting polyol mixture was then stirred during 15 minutes by using a magnetic stirrer, in order to obtain the polyol mixture which is used in the reaction. In a 500 mL three-necked round-bottom flask equipped with a coiled condenser and an overhead stirrer the polyol mixture was added under a continuous flow of nitrogen, and the Erlenmeyer was flushed with 19.78 g of acetone. A solution of 1.07 g of Reaxis C708 in 7.84 g of acetone was further added to the reaction mixture. The reaction mixture was warmed up to 55° C. during 30 minutes. Subsequently 19.69 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount of isocyanate is in excess towards the hydroxyl amount, ie. NCO/OH=1.53. After adding IPDI the addition funnel was flushed with 7.84 g of acetone, and the reaction mixture was stirred at 55° C. during 2 hours. Subsequently a solution of 2.77 g of BD in 3.92 g of acetone was added. The reaction mixture was reacted over 20 hours at 48° C. and then heated at 55° C. during 1 hour in order to reach full conversion.

[0123] A mixture of 326.10 g of the formed nonionic prepolymers was weighed in a stainless steel vessel. Subsequently the water based dispersion was made by using Disperlux equipment through adding water during high shear mixing. A solution of 10.35 g of SP-8 in demineralized water 60 mL was added to the prepolymer mixture under stirring at 700 RPM using a 5 cm diameter dissolver during 20 minutes. To have a dispersion with a 35 wt. % solid content, 207.47 g of water was added for further mixing under stirring at 1000 RPM during 20 minutes. After further stirring at 900 RPM during 35 minutes, the emulsion was transferred to a 2 L round bottom flask to give 502.70 g of a viscous dispersion. During the mixing already part of the solvent had evaporated. The residual volatile solvent was removed from the emulsion at 40° C. by rotary vacuum evaporation under reduced pressure. The evaporation was started at a pressure of 400 mbar and the pressure was decreased gradually till 60 mbar to obtain 368.70 g of a viscous dispersion. Estimating the amount of the evaporated water, 42.80 g of demineralized water was added to get a 35 wt % dispersion. The solids content was measured of the resulting dispersion, ie. 36.85 wt %. The pH of the obtained dispersion is 5.53. The average particle size in a Malvern particle sizer measured is 59.88 nm.

PU-I2

[0124] In an Erlenmeyer of 500 mL 111.73 g of Dynacoll 7150 and 94.92 g of acetone were weighed. The solution of Dynacoll 7150 in acetone was stirred at room temperature during 60 minutes by using a magnetic stirrer to obtain a colorless and clear solution. The poly ether diol, Ymer N120, was preheated in an oven at 80° C. to obtain a liquid product, and 16.40 g of Ymer N120 was added to the Dynacoll solution. The resulting polyol mixture was then stirred during 15 minutes by using a magnetic stirrer. in order to obtain the polyol mixture which is used in the reaction. In a 500 mL three-necked round-bottom flask equipped with a coiled condenser and an overhead stirrer 10.35 g of SP-08 and 78.60 g of acetonitrile were subsequently added under a continuous flow of nitrogen. The reaction mixture was warmed up to 60° C. and stirred during 30 minutes. While the surfactant dissolved in acetonitrile, the mixture of Dynacoll and Ymer was added to the reaction solution via an addition funnel. The reaction solution was slightly turbid in the beginning and became clear while adding the polyol mixture during 30 minutes. After the addition of polyols, the funnel was flushed with 15.82 g of acetone. A solution of 1.07 g of Reaxis C708 in 7.84 g of acetone was further added to the reaction mixture. Subsequently 19.69 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount of isocyanate is in excess towards the hydroxyl amount, ie. NCO/OH=1.53. After adding IDPI the addition funnel was flushed with 7.86 g of acetonitrile, and the reaction mixture was stirred at 55° C. during 2 hours. Subsequently a solution of 2.77 g of 1,4-butane diol in 3.92 g of acetone was added. The reaction mixture was reacted over 20 hours at 48° C. and then heated at 55° C. during 1 hour in order to reach full conversion.

[0125] A mixture of 348.10 g of the formed non-ionic prepolymers was weighed in a stainless steel. Subsequently the water based dispersion was made by using Disperlux equipment through adding water during high shear mixing. Under stirring at 900 RPM using a 5 cm diameter dissolver stirrer, 276.69 g of water was added to the prepolymer mixture during 20 minutes. Further stirred during 30 minutes under stirring at 800 RPM, the emulsion was transferred to a 2L round bottom flask to give 556.50 g of a viscous dispersion. The residual volatile solvent was removed from the emulsion at 40° C. by rotary vacuum evaporation under reduced pressure. The evaporation was started at a pressure of 400 mbar and the pressure was gradually decreased till 60 mbar to obtain 377.70 g of a viscous dispersion. Estimating the amount of the evaporated water, 48.0 g of demineralized water was added to the viscous dispersion to get a 35 wt. % dispersion. The solids content was measured of the resulting dispersion, ie. 36.60 wt. %. The pH of the obtained dispersion is 5.82. The average particle size is 55.34 nm.

PU-I3

[0126] In an Erlenmeyer of 500 mL 110.54 g of Dynacoll 7150 and 174.02 g of acetone were weighed. The solution of Dynacoll 7150 in acetone was stirred at room temperature during 60 minutes by using a magnetic stirrer to obtain a colorless and clear solution. The polyether diol, Ymer N120, was preheated in an oven at 80° C. to obtain a liquid product, and 16.23 g of Ymer N120 was added to the solution. The resulting polyol mixture was then stirred during 15 minutes by using a magnetic stirrer, in order to obtain the polyol mixture which is used in the reaction. In a 500 mL three-necked round-bottom flask equipped with a coiled condenser and an overhead stirrer the polyol mixture was added under a continuous flow of nitrogen, and the Erlenmeyer was flushed with 19.78 g of acetone. A solution of 1.07 g of Reaxis C708 in 7.84 g of acetone was further added to the reaction mixture. The reaction mixture was warmed up to 55° C. during 30 minutes. Subsequently 19.48 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount of isocyanate is in excess towards the hydroxyl amount, ie. NCO/OH=1.53. After adding IDPI the addition funnel was flushed with 7.84 g of acetone, and the reaction mixture was stirred at 55° C. during 2 hours. Subsequently a solution of 2.74 g of BD in 3.92 g of acetone was added. The reaction mixture was reacted over 20 hours at 48° C. and then heated at 55° C. during 1 hour in order to reach full conversion.

[0127] A mixture of 318.20 g of the formed nonionic prepolymers was weighed in a stainless steel. Subsequently the water based dispersion was made by using Disperlux equipment through adding water during high shear mixing. A solution of 11.92 g of S-13 in demineralized water 60 mL was added to the prepolymer mixture under stirring at 800 RPM using a 5 cm diameter dissolver during 20 minutes. To have a dispersion with a 35 wt. % solid content, 202.37 g of water was added for further mixing under stirring at 900 RPM during 20 minutes. After further stirring at 900 RPM during 35 minutes, the emulsion was transferred to a 2 L round bottom flask to give 477.00 g of a viscous dispersion. During the mixing already part of the solvent has evaporated. The residual volatile solvent was removed from the emulsion at 40° C. by rotary vacuum evaporation under reduced pressure. The evaporation was started at a pressure of 400 mbar and the pressure was gradually decreased till 60 mbar to obtain 365.80 g of a viscous dispersion. Estimating the amount of the evaporated water, 37.80 g of demineralized water was added to get a 35 wt. % dispersion. The solids content was measured of the resulting dispersion, ie. 37.69 wt. %. The pH of the obtained dispersion is 5.39. The average particle size is 57.37 nm.

PU-I4

[0128] In an Erlenmeyer of 500 mL 112.07 g of Dynacoll 7150 and 174.02 g of acetone were weighed. The solution of Dynacoll 7150 in acetone was stirred at room temperature during 60 minutes by using a magnetic stirrer to obtain a colorless and clear solution. The polyether diol, Ymer N120, was preheated in an oven at 80° C. to obtain a liquid product, and 16.45 g of Ymer N120 was added to the solution. The resulting polyol mixture was then stirred during 15 minutes by using a magnetic stirrer, in order to obtain the polyol mixture which is used in the reaction. In a 500 mL three-necked round-bottom flask equipped with a coiled condenser and an overhead stirrer the polyol mixture was added under a continuous flow of nitrogen, and the Erlenmeyer was flushed with 19.78 g of acetone. A solution of 1.07 g of Reaxis 0708 in 7.84 g of acetone was further added to the reaction mixture. The reaction mixture was warmed up to 55° C. during 30 minutes. Subsequently 19.65 g of IPDI was added dropwise via an addition funnel with pressure equalization arm during 20 minutes. The amount of isocyanate is in excess towards the hydroxyl amount, ie. NCO/OH=1.53. After adding IDPI the addition funnel was flushed with 7.84 g of acetone, and the reaction mixture was stirred at 55° C. during 2 hours. Subsequently a solution of 2.77 g of BD in 3.92 g of acetone was added. The reaction mixture was reacted over 20 hours at 48° C. and then heated at 55° C. during 1 hour in order to reach full conversion.

[0129] A mixture of 314.60 g of formed non-ionic prepolymers was weighed in a stainless steel. Subsequently the water based dispersion was made by using Disperlux equipment through adding water during high shear mixing. A solution of 60 mL of AS-5.HCL was added to the prepolymer mixture under stirring at 600 RPM using a 5 cm diameter dissolver during 20 minutes. To have a dispersion with a 35wt. % solid content, 207.92 g of water was added for further mixing under stirring at 900 RPM during 20 minutes. After further stirring during 35 minutes at 1000 RPM, the emulsion was transferred to a 2 L round bottom flask to give 485.50 g of a viscous dispersion. During the mixing already part of the solvent has evaporated. The residual volatile solvent was removed from the emulsion at 40° C. by rotary vacuum evaporation under reduced pressure. The evaporation was started at a pressure of 400 mbar and decreased the pressure gradually till 60 mbar to obtain 349.20 g of a viscous dispersion. Estimating the amount of the evaporated water, 47.60 g of demineralized water was added to get a 35 wt. % dispersion. The solids content was measured of the resulting dispersion, ie. 39.38 wt. %. The pH of the obtained dispersion is 5.59. The average particle size is 52.46 nm.

4. Synthesis of Comparative Aqueous Polyurethane Dispersions

[0130] The comparative PU dispersion (PU-C1) corresponds to the dispersion PU-2 mentioned in the patent application WO2019/105786.

[0131] The comparative PU dispersion (PU-C2) corresponds to the dispersion PU-4 mentioned in the patent application WO2019/105786.

5. Resistance to pH Increase

[0132] The change in colloidal stability at a pH increase to simulate the application of an inkjet ink onto an applied pre-treatment liquid is determined according to method 1.2. The results of the tests are summarized in Table 5.

TABLE-US-00005 TABLE 5 Cationic surfactant added PU-resin Invention/ to organic solvent before/ Colloidal stability dispersion comparative after reaction after pH increase PU-I1 Inv after 1 PU-I2 Inv before 1 PU-I3 Inv after 0 PU-I4 Inv after 1 PU-C1 Comp N.a. 4

[0133] As can be seen from the results of Table 5, the PU-resin dispersions according to the invention show a better colloidal stability at increased pH, thus showing that they preserve better their cationic character which leads to an improved color fixing power if used in a pre-treatment of the substrate before inkjet printing.

Example 2

[0134] This example shows that treatment liquids wherein the PU-resin dispersion according to the invention is combined with white pigments show an excellent storage stability.

Preparation of a White Pigment Dispersion (WIT-1)

[0135] 275 g of white pigment (TRONOX CR 834) was added to a mixture of 68.75 g of Disperbyk 190 and 2.2 g of Proxel K in 204.05 g of water under high shear by means of a Disperlux for 30 minutes. 200 g 0.4 mm yttrium stabilized zirconia beads (“high wear resistant zirconia grinding media” from TOSOH Co.) was added and the white pigment was milled for 75 minutes in a Dynomill Research Lab at a flow of 4500 t/min. The zirconia beads were removed by filtration and the dispersion was filtered over a 0.7 pm filter. The dispersion WIT-1 had an average particle size of 183 nm.

Preparation of the Treatment Liquids PTL-1 and PTL-2

[0136] Treatment liquids PTL-1 and PTL-2 were prepared by mixing the compounds given in Table 6. All weight percentages are relative to the total weight of the liquid.

TABLE-US-00006 TABLE 6 PTL-1 PTL-2 Compound Content in wt. % Content in wt. % PU-C2 33.43 — PU-I4 — 30.47 WIT-1 22.00 22.00 PYR 15.0 15.0 HD 15.0 15.0 SURF-1 0.8 0.8 Water To complete to 100% To complete to 100%

[0137] PTL-2 shows no aggregates nor flocculation when visually inspected by means of an optical transmission microscope after storage in normal conditions (temperature, pressure, light) for 1 month. This shows that the PU-resins according to the invention can be combined with white pigments without causing stability problems in the treatment liquid.

Example 3

[0138] This example illustrates the fixing power of the cationic polyurethane binder in the treatment liquid according to the invention towards colorants.

Preparation of the INK-1

[0139] A cyan ink INK-1 was prepared by mixing the compounds given in Table 7. All weight percentages are relative to the total weight of the inkjet ink.

TABLE-US-00007 TABLE 7 INK-1 Compound Content in wt. % PU-9 dispersion 28.64 PYR 20.00 HD 20.00 SURF-2 0.60 COL 20.00 Water To complete to 100%

Evaluation and Results

[0140] The treatment liquids PTL-1 and PTL-2 were coated with a spiral bar coater (from Elcometer) using an automatic film applicator (Elcometer 4340 from Elcometer) at a speed of 20 mm/s and a wet thickness of 20 μm on a piece of black leather that was cut from a black dyed crusted bovine leather coated with a black pigmented layer from Conceria Nuti Ivo S.P.A. (Italy). After drying the coated layer at 60° C. in an oven for 5 minutes, the treated substrate sheets were coated with INK-1 by means of the same 20 μm spiral bar. The coated samples were dried at 60° C. for 5 minutes.

[0141] The reflectance spectrum of each coated sample after drying was measured two times with a X-Rite™ eXact spectrophotometer in the range from 400 up to 700 nm in steps of 10 nm. The CIEL*a*b* coordinates were determined for a 2° observer and a D50 light source.

[0142] The formula below relates to a measured color difference to a known set of CIEL*a*b* coordinates. Given two colors in CIEL*a*b* color space, (L.sub.1, a.sub.1, b.sub.1) and (L.sub.2, a.sub.2, b.sub.2), the CIE76 color difference formula is defined as:

ΔE=√{square root over ((L.sub.1−L.sub.2).sup.2+(a.sub.1−a.sub.2).sup.2+(b.sub.1−b.sub.2).sup.2)}

[0143] A value for ΔE≥2.3 corresponds to a JND (just noticeable difference), as explained in Sharma, Gaurav (2003). Digital Color Imaging Handbook (1.7.2 ed.). CRC Press. ISBN 0-8493-0900-X.

[0144] In table 8, the L*a*b* values are summarized. The lower the a* value and the lower the b* value, the more cyan the colour.

TABLE-US-00008 TABLE 8 Treatment Sample no liquid Inkjet ink L* a* b* 1 (COMP) PTL-1 INK-1 24.13 −3.96 −29.36 2 (INV) PTL-2 INK-1 24.45 −5.19 −32.33

[0145] From Table 8 it can be seen that the color print with the use of a pre-treatment liquid according to the invention (PTL-2+INK-1) gives more cyan color value than with the use of a pre-treatment liquid not containing the polyurethane dispersion according to the invention. In addition, one can calculate the delta E 76 between the two samples and observe that it is equal to 3.24, which represents a significant visual color difference.