A METHOD OF DISPERSING A SELF-EMULSIFYING CROSSLINKER, THE OBTAINED CROSSLINKER DISPERSION AND ITS APPLICATON IN E-COAT HAVING LOW BAKING TEMPERATURE

Abstract

Disclosed herein is a method of dispersing a self-emulsifying crosslinker including at least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, and the microstructure of liquid phase of the aqueous acid dispersion (I) is water-in-oil; and ii) adding water into the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), and the microstructure of liquid phase of the aqueous acid dispersion (II) is oil-in-water. Additionally disclosed here is a self-emulsifying crosslinker dispersion prepared by the method and the self-emulsifying crosslinker dispersion has a Z-average particle size in a range of from 50 to 200 nm.

Claims

1. A method of dispersing a self-emulsifying crosslinker comprising at least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of liquid phase of said aqueous acid dispersion (I) is water-in-oil; wherein a solid content of said aqueous acid dispersion (I) in step i) is from 45% to 75% by weight, based on the total weight of said aqueous acid dispersion (I); and ii) adding water into said aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of liquid phase of said aqueous acid dispersion (II) is oil-in-water; wherein a detected maximum temperature (T.sub.max) of said aqueous acid dispersion (II) in step ii) is no more than 40 C.

2. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein said self-emulsifying crosslinker is at least one selected from the group consisting of cationic polyaromatic urethane, cationic polyaliphatic urethane, waterborne amino resin, cationic polyester polyurethane, cationic polyester polyurea, and cationic polycarbonate polyurethane.

3. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein in step i) said aqueous acid dispersion (I) is prepared by mixing the self-emulsifying crosslinker, acid and water under stirring at a rate in a range of from 500 to 2000 rpm and in step ii) said aqueous acid dispersion (II) is prepared under stirring at a rate in a range of from 200 to 1500 rpm.

4. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein the solid content of said aqueous acid dispersion (I) in step i) is from 50% to 70% by weight, based on the total weight of said aqueous acid dispersion (I).

5. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein the solid content of said aqueous acid dispersion (II) in step ii) is in a range of from 20% to 30% by weight, based on the total weight of said aqueous acid dispersion (II).

6. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein the detected maximum temperature (T.sub.max) of said aqueous acid dispersion (II) in step ii) is no more than 30 C.

7. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein the acid used in step i) to prepare said aqueous acid dispersion (I) is at least one selected from the group consisting of diluted hydrochloric acid, diluted sulfuric acid, phosphoric acid, diluted nitric acid, boric acid, perchloric acid, formic acid, acetic acid, lactic acid, oxalic acid, glycolic acid, citric acid, malic acid, adipic acid, succinic acid, propionic acid, fumaric acid, and benzoic acid.

8. The method of dispersing a self-emulsifying crosslinker according to claim 1, wherein the weight percentage of acid in said aqueous acid dispersion (I) is in a range of from 0.1 wt. % to 5.0 wt. %.

9. A self-emulsifying crosslinker dispersion prepared by the method according to claim 1, wherein said self-emulsifying crosslinker dispersion has a Z-average particle size in a range of from 50 to 200 nm.

10. The self-emulsifying crosslinker dispersion according to claim 9, wherein said self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.2.

11. The self-emulsifying crosslinker dispersion according to claim 9, wherein solid content of said self-emulsifying crosslinker dispersion is in a range of from 20% to 30% by weight.

12. The self-emulsifying crosslinker dispersion according to claim 9, wherein said self-emulsifying crosslinker dispersion comprising at least one selected from the group consisting of cationic polyaromatic urethane, cationic polyaliphatic urethane, waterborne amino resin, cationic polyester polyurethane, cationic polyester polyurea, and cationic polycarbonate polyurethane.

13. An e-coat composition comprising at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion according to claim 9.

14. The e-coat composition according to claim 13, wherein said base resin is at least one selected from the group consisting of polyetheramine and polyetheramine-based epoxy resin.

15. The e-coat composition according to claim 13, wherein said e-coat composition has a curing temperature in a range of from 80 C. to 140 C.

16. An e-coat layer obtained from the e-coat composition according to claim 13 after curing at a temperature in a range of from 80 C. to 140 C.

17. A substrate coated with the e-coat layer according to claim 16.

18. A self-emulsifying crosslinker dispersion prepared by the method according to claim 1, wherein said self-emulsifying crosslinker dispersion has a Z-average particle size in a range of from 60 to 160 nm.

19. The self-emulsifying crosslinker dispersion according to claim 9, wherein said self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.1.

Description

DETAILED DESCRIPTION OF THIS INVENTION

[0013] The present invention now will be described in detail hereinafter. It is to be understood that the present invention may be embodied in different ways and shall not be construed as limited to the embodiments set forth herein. Unless mentioned otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0014] Within the context of the present application, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise.

[0015] Within the context of the present application, the terms comprise(s), comprising are to be interpreted in a non-limiting, open manner. That is, further components or elements may be present.

[0016] Within the context of the present application, the term base resin means the main component of e-coat composition that will react with crosslinker to form e-coat binder and one example of base resin is polyetheramine.

[0017] Within the context of the present application, the term self-emulsifying crosslinker means crosslinker that has functional groups that could be emulsified in aqueous solution and be able to react with base resins. One example of self-emulsifying crosslinker is cationic polyurethane.

[0018] Within the context of the present application, the term the detected maximum temperature (T.sub.max) means the detected highest temperature of the dispersion solution during the process of adding solvent (e.g. a mixture of water and acid) with stirring.

[0019] Within the context of the present application, the term container and vessel are used alternatively having the same meaning.

[0020] Self-emulsifying crosslinker is one potential approach for low temperature baking e-coat. Small particle sizes and narrow particle size distribution of dispersed polyurethane crosslinker are necessary for the storage stability. This invention is to find how to fine-tune the important processing parameters in order to get small particle size with narrow particle size distribution. Furthermore, in prior art, the synthesis and dispersion of polyurethane crosslinker are carried out in different vessels, in present invention, it is possible to implement both synthesis and dispersion steps in one vessel, which reduces cost in actual production.

[0021] This invention provides a method of dispersing a self-emulsifying crosslinker comprising at least two steps: [0022] i). preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, and the microstructure of liquid phase of said aqueous acid dispersion (I) is water-in-oil; and [0023] ii). adding water into said aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), and the microstructure of liquid phase of said aqueous acid dispersion (II) is oil-in-water.

[0024] According to the present invention, the dispersion effects are analysed for cationic polyurethane crosslinker and it is found that the average particle size is small (60 nm to 160 nm) and the particle size distribution is very narrow i.e. PDI (Polydispersity Index) is less than 0.2. The average particle size and the particle size distribution are within an acceptable range, which are beneficial for storage stability as well as for evenly depositing of e-coat on metal substrates. It brings great advantage to automotive OEM and ASM markets.

[0025] The dispersing method of this invention is not only applicable for cationic polyurethane crosslinker but also can be used for other crosslinker. There are mainly two significant parameters affecting particle size and particle size distribution of crosslinker's micelles i.e. the solid content of aqueous acid dispersion (I) and the detected maximum temperature (T.sub.max) during dispersion in the step ii). The solid content of aqueous acid dispersion (I) should be at least 45% by weight based on the total weight of aqueous acid dispersion (I). T.sub.max can be influenced by initial temperature of crosslinker and stirring speed. Preferably, T.sub.max should not be higher than 40 C. and more preferably not be higher than 30 C. The key factor of this invention is the dispersion or emulsion of self-emulsifying crosslinker shall have phase inversion from w/o (water-in-oil) to o/w (oil-in-water) during dispersion process. Such phase inversion could be observed since some dough-like matters are seen.

[0026] Furthermore, instead of using two vessels to synthesize and disperse self-emulsifying crosslinkers separately, it is proved in present invention that only one vessel is needed to carry out both polyurethane crosslinker synthesis and dispersion process and small particle size of micelles and narrow particle size distribution are achieved. One vessel with both organic polyurethane crosslinker synthesis and dispersion process would bring a great advantage for saving energy and cost of production. But by using two vessels for a cationic polyurethane dispersion, it is also able to obtain small particle size and narrow particle size distribution through the invented method.

[0027] Examples of said self-emulsifying crosslinkers include cationic polyaromatic urethane, cationic polyaliphatic urethane, waterborne amino resin, cationic polyester polyurethane, cationic polyester polyurea and cationic polycarbonate polyurethane.

[0028] Selected amines are incorporated into crosslinkers to bring self-emulsifying functions and meanwhile reactive to base resins. Examples of said amines include N-methyl diethanolamine, N-butyl diethanolamine, diethanolamine, N,N-dimethylaminopropylamine, Bis-(N,N-dimethylaminopropylamine), 2-[[2-(Dimethylamino)ethyl]methylamino]ethanol, 2-(2-Aminoethoxy)ethanol, Triethanolamine, pyridine diethanolamine, Ethanolamine, diethanolamine, N,N-dimethyl ethanolamine.

[0029] The synthesis of cationic polyurethane crosslinker is known. Saimani Sundar et al. disclosed its preparation method in Aqueous dispersions of polyurethane cationomers: a new approach for hydrophobic modification and crosslinking, Colloid Polym Sci (2004) 283: 209-218.

[0030] Mixtures of water and acid are used to dilute the obtained cationic polyurethane crosslinker, inorganic acids as well as low molecular organic acids could be used here. Examples of inorganic acids include diluted hydrochloric acid, diluted sulfuric acid, phosphoric acid, diluted nitric acid, boric acid and perchloric acid. Examples of organic acids include formic acid, acetic acid, lactic acid, oxalic acid, glycolic acid, citric acid, malic acid, adipic acid, succinic acid, propionic acid, fumaric acid and benzoic acid. Preferably, the acid is added into water in an amount of from 0.1 wt. % to 5.0 wt. % by weight, and more preferably from 0.5 wt. % to 2.0 wt. % based on the total weight of the mixture of water and acid.

[0031] Preferably, the dispersing of said self-emulsifying crosslinker is under a stirring and the stirring speed is preferably in a range of 500 to 2000 rpm in the first step and in a range of 200 to 1500 rpm in the second step. The stirring speed in the second step of dispersion affected the T.sub.max significantly. Higher stirring speed increased T.sub.max of the dispersion and a high T.sub.max tends to result in big particle size and broad particle size distribution.

[0032] Preferably, the initial temperature of said self-emulsifying crosslinker is less than 35 C. When the initial temperature of said self-emulsifying crosslinker is higher than room temperature e.g. 35 C., T.sub.max increased obviously and a high T.sub.max tends to result in big particle size and broad particle size distribution.

[0033] Preferably, the solid content of said aqueous acid dispersion (I) in step i) is from 45% to 75% and preferably from 50% to 70% by weight, based on the total weight of said aqueous acid dispersion (I). And the solid content of said aqueous acid dispersion (II) in step ii) is from 20% to 30% by weight, based on the total weight of said aqueous acid dispersion (II). The solid content of aqueous acid dispersion (I) was important. When the solid content of aqueous acid dispersion (I) was higher than 49% (e.g. 58%), the microstructure of said dispersion was water-in-oil and the viscosity of said dispersion was quite high. As a contrast, when the solid content of aqueous acid dispersion (I) was lower than 49% (e.g. 38%), the microstructure of said dispersion was oil-in-water. The two-phase inversion of the dispersion, i.e. from water-in-oil to oil-in-water in microstructure level, brings smaller Z-average particle size and narrower particle size distribution. If there was no such phase inversion, the obtained dispersions tend to have large particle sizes and broad particle size distribution.

[0034] Preferably, said self-emulsifying crosslinker dispersion has a Z-average particle size of from 50 to 200 nm and more preferably from 60 to 160 nm.

[0035] Preferably, said self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.2 and more preferably less than 0.1.

[0036] Although according to the present invention, it is advantageous to prepare the crosslinker dispersion in one container or vessel, the dispersion of said self-emulsifying crosslinker could be also prepared in more than one container or vessel such as two containers. And the key issue is despite how many container(s) or vessel(s) are used, the two-phase inversion of the dispersion must happen.

[0037] As a comparison, one-step dispersion approach is carried out by using two containers or vessels. The one-step dispersion approach is defined as follows: the self-emulsifying crosslinker was put in one container (the 1.sup.st container) and an aqueous acid solution was prepared in another container (the 2.sup.nd container) and the cationic polyurethane crosslinker in the 1.sup.st container was continuously added into the 2.sup.nd container with a stirring to reach certain solid content. By using two vessels and one-step dispersing approach, the obtained dispersions had large particle sizes and broad particle size distributions. The reason is in one-step dispersing approach, there was no chance for phase inversion i.e. from water-in-oil to oil-in-water, of the dispersions in microstructure level.

[0038] Moreover, the present invention also provides an e-coat composition comprising at least one base resin dispersion and at least one invented self-emulsifying crosslinker dispersion. Said base resin is preferably at least one selected from polyetheramine and polyetheramine-based epoxy resin. Said e-coat composition could be cured at a temperature of from 80 C. to 140 C. to form an e-coat layer. And such layer is formed on various substrates especially metallic substrates.

EMBODIMENT

[0039] Various embodiments are list below. It will be understood that the embodiments listed below may be combined with all aspects and other embodiments in accordance with the scope of the invention.

Embodiment 1

[0040] A method of dispersing a self-emulsifying crosslinker comprising at least two steps: [0041] i). preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of liquid phase of said aqueous acid dispersion (I) is water-in-oil; and [0042] ii). adding water into said aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of liquid phase of said aqueous acid dispersion (II) is oil-in-water.

Embodiment 2

[0043] The method of dispersing a self-emulsifying crosslinker according to Embodiment 2, wherein said self-emulsifying crosslinker is preferably at least one selected from cationic polyaromatic urethane, cationic polyaliphatic urethane, waterborne amino resin, cationic polyester polyurethane, cationic polyester polyurea and cationic polycarbonate polyurethane.

Embodiment 3

[0044] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 2, wherein in step i) it is preferably to prepare said aqueous acid dispersion (I) by mixing the self-emulsifying crosslinker, acid and water under stirring at a rate of from 500 to 2000 rpm and in step ii) it is preferably to prepare said aqueous acid dispersion (II) under stirring at a rate of from 200 to 1500 rpm.

Embodiment 4

[0045] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 3, wherein the solid content of said aqueous acid dispersion (I) in step i) is from 45% to 75% and preferably from 50% to 70% by weight, based on the total weight of said aqueous acid dispersion (I).

Embodiment 5

[0046] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 4, wherein the solid content of said aqueous acid dispersion (II) in step ii) is from 20% to 30% by weight, based on the total weight of said aqueous acid dispersion (II).

Embodiment 6

[0047] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 5, wherein the detected maximum temperature (T.sub.max) of said aqueous acid dispersion (II) in step ii) is no more than 40 C. and preferably no more than 30 C.

Embodiment 7

[0048] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 6, wherein the acid used in step i) to prepare said aqueous acid dispersion (I) is preferably at least one selected from diluted hydrochloric acid, diluted sulfuric acid, phosphoric acid, diluted nitric acid, boric acid, perchloric acid, formic acid, acetic acid, lactic acid, oxalic acid, glycolic acid, citric acid, malic acid, adipic acid, succinic acid, propionic acid, fumaric acid and benzoic acid.

Embodiment 8

[0049] The method of dispersing a self-emulsifying crosslinker according to any one of Embodiments 1 to 7, wherein the weight percentage of acid in said aqueous acid dispersion (I) is from 0.1 wt % to 5.0 wt. % and preferably from 0.5 wt. % to 2.0 wt. %.

Embodiment 9

[0050] A self-emulsifying crosslinker dispersion prepared by the method according to any one of Embodiments 1 to 8, wherein said self-emulsifying crosslinker dispersion has a Z-average particle size of from 50 to 200 nm and preferably from 60 to 160 nm.

Embodiment 10

[0051] The self-emulsifying crosslinker dispersion according to Embodiment 9, wherein said self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.2 and preferably less than 0.1.

Embodiment 11

[0052] The self-emulsifying crosslinker dispersion according to any one of Embodiments 9 to 10, wherein the solid content of said self-emulsifying crosslinker dispersion is from 20% to 30% by weight.

Embodiment 12

[0053] The self-emulsifying crosslinker dispersion according to any one of Embodiments 9 to 11, wherein said self-emulsifying crosslinker dispersion comprising at least one selected from cationic polyaromatic urethane, cationic polyaliphatic urethane, waterborne amino resin, cationic polyester polyurethane, cationic polyester polyurea and cationic polycarbonate polyurethane.

Embodiment 13

[0054] An e-coat composition comprising at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion according to any one of Embodiments 9 to 12.

Embodiment 14

[0055] The e-coat composition according to Embodiment 13, wherein said base resin is preferably at least one selected from polyetheramine and polyetheramine-based epoxy resin.

Embodiment 15

[0056] The e-coat composition according to any one of Embodiments 13 to 14, wherein said e-coat composition has a curing temperature of from 80 C. to 140 C.

Embodiment 16

[0057] An e-coat layer obtained from the e-coat composition according to any one of Embodiments 13 to 15 after curing at a temperature of from 80 C. to 140 C.

Embodiment 17

[0058] A substrate coated with the e-coat layer according to Embodiment 16.

EXAMPLE

[0059] The present invention will be further described by Examples which are not intended to limit the scope of the present invention. And all raw materials used in Examples are commercially available.

[0060] Examples 1 to 3 describe how the cationic polyurethane crosslinker is prepared. LupranateM20S is an oligomeric methylene diphenyl diisocyanate (MDI) from BASF. methylethyl ketoxime (MEKO) acts as a blocking agent, methylisobutyl ketone (MIBK) acts as a solvent, dibutyltin dilaurate (DBTL) as a catalyst. N-methyl diethanolamine, N-butyl diethanolamine, diethanolamine (DEOLA), N, N-dimethylaminopropylamine (DMAPA), Bis-(N, N-dimethylaminopropylamine) (BDMAPA), 2-[[2-(Dimethylamino)ethyl]methylamino]ethanol (DMAEA), 2-(2-Aminoethoxy)ethanol (AEEOL), triethanolamine, pyridine diethanolamine, ethanolamine, diethanolamine, N,N-dimethyl ethanolamine are amines, containing a nitrogen atoms, acts as a neutralizing agent.

Example 1: Preparation of MEKO-Blocked LupranateM20S by Using N, N-Dimethylaminopropylamine (DMAPA) as an Amine Building Block for Neutralization

[0061] A reactor equipped with a condenser, a nitrogen gas inlet and outlet, was charged with 400 parts by weight of LupranateM20S, 126.1 parts by weight of MIBK, and 0.18 parts by weight of DBTL. This initial charge was heated to 30 C. After that, 153.0 parts by weight of Bisphenol A 6EO was being dosed into a reactor in a uniform rate within 60 min with a constant stirring. 378.3 parts by weight of MIBK was then added into the reactor, parallelly cooling the reaction temperature to 30 C. At reaction temperature 30 C., 150.5 parts by weight of MEKO was slowly dosed into the reactor within 20 min. After finishing dosing MEKO, a reaction temperature was raised up to 60 C. and continued the reaction for another 30 min. Then cooling the reaction temperature to 30 C. again and begin a next step by quickly charging 53.0 parts by weight of DMAPA into the reactor. 20 min after finishing charging, set the reaction temperature to 60 C. again and continued stirring for another 30 min. A polyurethane crosslinker was obtained.

Example 2: Preparation of MEKO-Blocked LupranateM20S by Using Bis-(N, N-Dimethylaminopropylamine) or (BDMAPA) as an Amine Building Block for Neutralization

[0062] 500 parts by weight of LupranateM20S, 139.9 parts by weight of MIBK, and 0.23 parts by weight of DBTL were charged into a reactor equipped with a condenser, a nitrogen gas inlet and outlet. This initial charge was heated to 30 C. After that, 30.7 parts by weight of 1,2-propanediol (PD) was being dosed into a reactor in a uniform rate within 60 min with a constant stirring. 419.7 parts by weight of MIBK was then added into the reactor, parallelly cooling the reaction temperature to 30 C. At reaction temperature 30 C., 187.5 parts by weight of MEKO was slowly dosed into the reactor within 20 min. After finishing dosing MEKO, a reaction temperature was raised up to 60 C. and continued the reaction for another 30 min. Then cooling the reaction temperature to 30 C. again and begin a next step by quickly charging 120.9 parts by weight of BDMAPA into the reactor. 20 min after finishing charging, set the reaction temperature to 60 C. again and continued stirring for another 30 min. A polyurethane crosslinker was obtained.

Example 3: Preparation of MEKO-blocked LupranateM20S by Using 2-[[2-(Dimethylamino)ethyl]methylamino]ethanol (DMAEA) as an Amine Building Block for Neutralization

[0063] 500 parts by weight of LupranateM20S, 135.5 parts by weight of MIBK, and 0.23 parts by weight of DBTL were charged into a reactor equipped with a condenser, a nitrogen gas inlet and outlet. This initial charge was heated to 30 C. Afterwards, 30.7 parts by weight of PD was being dosed into a reactor in a constant speed within 60 min with a continuous stirring. 406.4 parts by weight of MIBK was subsequently added into the reactor, parallelly cooling the reaction temperature to 30 C. At reaction temperature 30 C., 187.5 parts by weight of MEKO was slowly dosed into the reactor within 20 min. After finishing dosing MEKO, a reaction temperature was heated up to 60 C. and continued the reaction for another 30 min. Then cooling the reaction temperature to 30 C. again and begin a next step by quickly charging 94.4 parts by weight of DMAEA into the reactor. 20 min after finishing charging, set the reaction temperature to 60 C. again and continued stirring for another 30 min. A polyurethane crosslinker was obtained.

Examples 4 to 14: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 1 in One Container

[0064] Preparing a dispersion of cationic polyurethane crosslinker involves two inversion stages: i). preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of liquid phase of said aqueous acid dispersion (I) is water-in-oil; and ii). adding water into said aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of liquid phase of said aqueous acid dispersion (II) is oil-in-water.

[0065] In Examples 4 to 6, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 60% was put in a plastic container under a room temperature (20-25 C. at 1 atm.). A mixture of 26.84 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase having a solid content of 58% (the 1.sup.st stage). Subsequently, 1723.3 parts by weight of water was added to the container with stirring to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage). The difference between Examples 4 to 6 is the stirring speed in the 2.sup.nd stage, i.e. 500, 1500 and 2500 rpm in Examples 4 to 6 respectively.

[0066] In Example 7, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 60% was put in a plastic container at 35 C. A mixture of 26.84 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase having a solid content of 58% (the 1.sup.st stage). Subsequently, 1723.3 parts by weight of water was added to the container with a stirring speed of 500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0067] In Example 8, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 60% was put in a plastic container at 50 C. A mixture of 26.84 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase having a solid content of 58% (the 1.sup.st stage). Subsequently, 1723.3 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0068] In Example 9, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 26.84 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1723.3 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0069] In Example 10, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 266.6 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1483.5 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0070] In Example 11, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 713.9 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1036.2 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0071] In Example 12, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 24.8 parts by weight of water and 18.7 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1723.3 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0072] In Example 13, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 264.6 parts by weight of water and 18.7 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1483.5 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0073] In Example 14, the cationic polyurethane crosslinker obtained from Example 1 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 711.9 parts by weight of water and 18.7 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1036.2 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

Examples 15 to 20: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 2 in One Container

[0074] In Example 15, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 6.8 parts by weight of water and 41.5 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1910.1 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0075] In Example 16, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 272.6 parts by weight of water and 41.5 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1644.3 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0076] In Example 17, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 768.4 parts by weight of water and 41.5 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1148.5 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0077] In Example 18, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 1.7 parts by weight of water and 46.5 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1910.1 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0078] In Example 19, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 267.5 parts by weight of water and 46.5 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1644.3 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0079] In Example 20, the cationic polyurethane crosslinker obtained from Example 2 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 763.3 parts by weight of water and 46.5 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1148.5 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

Examples 21 to 26: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 3 in One Container

[0080] In Example 21, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 26.0 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1849.6 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0081] In Example 22, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 283.3 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1592.2 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0082] In Example 23, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 763.5 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86 wt. %) was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1112.1 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0083] In Example 24, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 58% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 23.4 parts by weight of water and 23.3 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1849.6 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0084] In Example 25, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 49% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 280.8 parts by weight of water and 23.3 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1592.2 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

[0085] In Example 26, the cationic polyurethane crosslinker obtained from Example 3 having a solid content of 38% was put in a plastic container under room temperature (20-25 C. at 1 atm.). A mixture of 760.9 parts by weight of water and 23.3 parts by weight of acetic acid was added to the container with a stirring speed of 1500 rpm to obtain water-in-oil phase (the 1.sup.st stage). Subsequently, 1112.1 parts by weight of water was added to the container with a stirring speed of 1500 rpm to obtain oil-in-water phase having a solid content of 25% (the 2.sup.nd stage).

Example 27: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 1 by Using Two Containers

[0086] The cationic polyurethane crosslinker obtained from Example 1 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 266.6 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 49% and subsequently, 1483.5 parts by weight of water was added to the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 25%.

Example 28: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 2 by Using Two Containers

[0087] The cationic polyurethane crosslinker obtained from Example 2 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 272.6 parts by weight of water and 41.5 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 49% and subsequently, 1644.3 parts by weight of water was added to the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 25%.

Example 29: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 3 by Using Two Containers

[0088] The cationic polyurethane crosslinker obtained from Example 3 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 283.3 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 49% and subsequently, 1592.2 parts by weight of water was added to the 2.sup.nd container with a stirring speed of 1500 rpm to reach a solid content of 25%.

Examples 30 to 31: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 1 in One Step by Using Two Containers

[0089] In Example 30, the cationic polyurethane crosslinker obtained from Example 1 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1750.1 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

[0090] In Example 31, the cationic polyurethane crosslinker obtained from Example 1 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1748.1 parts by weight of water and 18.7 parts by weight of acetic acid was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

Examples 32 to 33: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 2 in One Step by Using Two Containers

[0091] In Example 32, the cationic polyurethane crosslinker obtained from Example 2 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1916.8 parts by weight of water and 41.46 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

[0092] In Example 33, the cationic polyurethane crosslinker obtained from Example 2 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1911.8 parts by weight of water and 46.5 parts by weight of acetic acid was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

Examples 34 to 35: Preparation of a Dispersion of Cationic Polyurethane Crosslinker Obtained from Example 3 in One Step by Using Two Containers

[0093] In Example 34, the cationic polyurethane crosslinker obtained from Example 3 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1875.5 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86 wt. %) was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

[0094] In Example 35, the cationic polyurethane crosslinker obtained from Example 3 was put in a plastic container (the 1.sup.st container) under room temperature (20-25 C. at 1 atm.) of which the solid content is 60%. A mixture of 1873 parts by weight of water and 23.3 parts by weight of acetic acid was prepared in another container (the 2.sup.nd container). The cationic polyurethane crosslinker in the 1.sup.st container was added into the 2.sup.nd container with a stirring speed of 1500 rpm continuously to reach a solid content of 25%.

Performance Test

<T.SUB.max.>

[0095] T.sub.max is the detected highest temperature of the dispersion solution during the process of adding solvent (e.g. a mixture of water and acid) with stirring. T.sub.max is tested by IKA RET basic S025 including temperature sensor.

<Z-Average Particle Size>

[0096] The Z-average particle size of the dispersion is tested according to the standard DIN ISO 13321 by using Paticle size analyzer, Malvern, Zetasizer Nano zs90 (model ZEN3690).

<PDI>

[0097] PDI (Polydispersity Index) of the dispersion is tested according to the standard DIN ISO 13321 by using Paticle size analyzer, Malvern, Zetasizer Nano zs90 (model ZEN3690).

<Storage Stability>

[0098] The storage stability of each dispersion was evaluated by visually observing the appearance of the dispersion in a transparent container after standing for a period of time at a certain temperature. The dispersion is evaluated as unstable, if a phase separation (serious) or a sedimentation (mild) occurs.

[0099] The performance test results of Examples 4 to 35 are summerized in Table 1.

TABLE-US-00001 TABLE 1 Performance Test Example T.sub.max Z-average particle size PDI Storage stability 4 28 C. 121 nm 0.05 24 hours 5 35 C. 99 nm 0.08 24 hours 6 43 C. 734 nm 0.3 <2 hours 7 39 C. 143 nm 0.05 24 hours 8 52 C. 1006 nm 0.36 <2 hours 9 35 C. 99 nm 0.08 24 hours 10 37 C. 102 nm 0.11 24 hours 11 36 C. 337 nm 0.26 <6 hours 12 39 C. 100 nm 0.13 24 hours 13 38 C. 99 nm 0.12 24 hours 14 35 C. 210 nm 0.21 <6 hours 15 39 C. 92 nm 0.12 48 hours 16 40 C. 88 nm 0.05 48 hours 17 38 C. 278 nm 0.13 <6 hours 18 39 C. 72 nm 0.17 48 hours 19 40 C. 78 nm 0.11 48 hours 20 38 C. 298 nm 0.18 <6 hours 21 35 C. 98 nm 0.13 48 hours 22 35 C. 94 nm 0.05 48 hours 23 36 C. 298 nm 0.14 <6 hours 24 38 C. 101 nm 0.12 48 hours 25 38 C. 86 nm 0.11 48 hours 26 36 C. 365 nm 0.19 <6 hours 27 30 C. 130 nm 0.04 24 hours 28 29 C. 91 nm 0.06 48 hours 29 30 C. 132 nm 0.07 48 hours 30 487 nm 0.52 <2 hours 31 511 nm 0.60 <2 hours 32 1376 nm 0.76 <1 hour 33 2271 nm 0.09 <1 hour 34 549 nm 0.96 <2 hours 35 1481 nm 0.39 <1 hour

[0100] As learnt from Table 1, when the initial temperature of cationic polyurethane crosslinker was at room temperature, increasing stirring speed in the 2.sup.nd stage of dispersion affected the T.sub.max significantly. And when the initial temperature of cationic polyurethane crosslinker was higher than room temperature e.g. 35 C. or 50 C., T.sub.max also increased obviously. As a conclusion, both initial temperature of cationic polyurethane crosslinker and stirring speed in the 2.sup.nd stage directly influence T.sub.max of the dispersion in the 2.sup.nd stage. Higher initial temperature of crosslinker and higher stirring speed increased T.sub.max of the dispersion. High T.sub.max resulted in big particle size and broad particle size distribution e.g. when the stirring speed is 1500 rpm in the 2.sup.nd stage and the initial temperature of crosslinker is 50 C.), the Z-average particle size is 1006 nm and PDI is 0.36.

[0101] When T.sub.max of cationic polyurethane crosslinkers was controlled within a range of from 35 C. to 40 C., the Z-average particle size of the resultant dispersion varies dramatically, especially in the example wherein the solid content of the 1.sup.st stage dispersion was at 38%.

[0102] For cationic polyurethane crosslinker obtained from Example 1 with adding an aqueous formic acid solution to reach the solid contents of 58% and 49% of 1.sup.st stage dispersion respectively, the resultant Z-average particle sizes of 2.sup.nd stage dispersion were 99 nm (with PDI of 0.08) and 102 nm (with PDI of 0.11) respectively. As a contrast, when the solid content of 1.sup.st stage dispersion was at 38%, the resultant Z-average particle size of 2.sup.nd stage dispersion was 337 nm (with PDI of 0.26). And after the aqueous formic acid solution was changed to aqueous acetic acid solution, when the solid contents of 1.sup.st stage dispersion were 58%, 49% and 38% respectively, the resultant Z-average particle sizes of 2.sup.nd stage dispersion were 100 nm (with PDI of 0.13), 99 nm (with PDI of 0.12) and 210 nm (with PDI of 0.21) respectively.

[0103] For cationic polyurethane crosslinker obtained from Example 2 with adding an aqueous formic acid solution to reach the solid contents of 58% and 49% of 1.sup.st stage dispersion respectively, the resultant Z-average particle sizes of 2.sup.nd stage dispersion were 92 nm (with PDI of 0.12) and 88 nm (with PDI of 0.05) respectively. As a contrast, when the solid content of 1.sup.st stage dispersion was at 38%, the resultant Z-average particle size was 278 nm (with PDI of 0.13). And after the aqueous formic acid solution was changed to aqueous acetic acid solution, when the solid contents of 1.sup.st stage dispersion were 58%, 49% and 38% respectively, the resultant Z-average particle sizes of 2.sup.nd stage dispersion were 72 nm (with PDI of 0.17), 78 nm (with PDI of 0.11) and 298 nm (with PDI of 0.18) respectively.

[0104] For cationic polyurethane crosslinker obtained from Example 3 with adding an aqueous formic acid to reach the solid contents of 58% and 49% of 1.sup.st stage dispersion respectively, the resultant Z-average particle size of 2.sup.nd stage dispersion were 98 nm (with PDI of 0.13) and 94 nm (with PDI of 0.05) respectively. As a contrast, when the solid content of 1.sup.st stage dispersion at 38%, the Z-average particle size of 2.sup.nd stage dispersion was 298 nm (with PDI of 0.14). And after the aqueous formic acid solution was changed to aqueous acetic acid solution, when the solid contents of 1.sup.st stage dispersion were 58%, 49% and 38% respectively, the resultant Z-average particle sizes of 2.sup.nd stage dispersion were 101 nm (with PDI of 0.12), 86 nm (with PDI of 0.11) and 365 nm (with PDI of 0.19) respectively.

[0105] The solid content of 1.sup.st stage dispersion was important. When the solid content of 1.sup.st stage dispersion was higher than 49% (e.g. 58%), the microstructure of said dispersion was water-in-oil and the viscosity of said dispersion was quite high. As a contrast, when the solid content of 1.sup.st stage dispersion was lower than 49% (e.g. 38%), the microstructure of said dispersion was oil-in-water.

[0106] The two-phase inversion of the dispersion, i.e. from water-in-oil to oil-in-water in microstructure level, brings smaller Z-average particle size and narrower particle size distribution. If there was no such phase inversion, dispersions having large particle sizes would be obtained.

[0107] Besides, when the aqueous formic acid solution was changed to the aqueous acetic acid solution, cationic polyurethane crosslinkers obtained from Examples 1 to 3 showed similar results in terms of Z-average particle sizes.

[0108] Moreover, although according to the present invention, it is advantageous to prepare the crosslinker dispersion in one container or vessel, the experiments could be also carried out in more than one container or vessel such as two containers. And the key issue is despite how many container(s) or vessel(s) are used, the two-phase inversion of the dispersion must happen.

[0109] Examples 27 to 29 described the preparation of dispersions of cationic polyurethane crosslinkers obtained from Examples 1 to 3 respectively by using two containers and two-step dispersing approach. And their test results showed that these dispersions also had small particle sizes (e.g. in a range of from 60 nm to 160 nm) with a narrow particle size distribution (e.g. less than 0.1). T.sub.max observed in 2.sup.nd dispersion was around 30 C. Two phase inversion was observed during dispersion process. Therefore, by using two-step dispersing approach, dispersions having smaller particle sizes and narrow particle size distribution were obtained, although two containers or vessels are needed.

[0110] As a comparison, one-step dispersion approach is carried out by using two containers or vessels. Examples 30 to 35 described the preparation of dispersions of cationic polyurethane crosslinkers obtained from Examples 1 to 3 by using two containers and one-step dispersing approach. And their test results showed that by using two vessels and one-step dispersing approach, the obtained dispersions had large particle sizes and broad particle size distributions no matter the aqueous formic acid solution or the aqueous acetic acid solution was used. The reason is in one-step dispersing approach, there was no chance for phase inversion i.e. from water-in-oil to oil-in-water, of the dispersions in microstructure level.