Method for dispersing a self-emulsifying crosslinker, the resulting crosslinker dispersion and its application in low bake temperature e-coats

Abstract

The present invention provides a method for dispersing a self-emulsifying crosslinking agent, comprising at least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinking agent, the microstructure of the liquid phase of the aqueous acid dispersion (I) being water-in-oil type, and ii) adding water to the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), the microstructure of the liquid phase of the aqueous acid dispersion (II) being oil-in-water type. The present invention also provides a self-emulsifying crosslinking agent dispersion prepared by the method of the present invention, and the self-emulsifying crosslinking agent dispersion has a Z-average particle size of 50-200 nm, and preferably 60-160 nm.

Description

[Technical field]

[0001] The present invention relates to a method for dispersing self-emulsifying crosslinkers for use in low bake e-coat compositions, particularly e-coats for the automotive industry. [Background technology]

[0002] In the automotive industry, the curing temperature of e-coat is usually higher than 160°C. However, there is a trend towards lower bake temperature for e-coat to save energy and cost, i.e., curing temperature of 80°C~140°C is desired in the OEM (original equipment manufacturing) and ASM (automotive supply metal) markets.

[0003] To achieve low-bake e-coats, the current practice is to encapsulate a crosslinker (e.g., blocked isocyanate) with a base resin (e.g., polyetheramine) and emulsify it in a mixture of water and acid to obtain micelles of the e-coat binder. However, the binders used in e-coats obtained in this way are not stable during storage. The crosslinker and the base resin tend to react with each other in the micelles. So one solution is to separate the crosslinker from the base resin. The crosslinkers used in such solutions are so-called "self-emulsifying crosslinkers". One example of said self-emulsifying crosslinkers is the cationic polyurethane crosslinker (blocked isocyanate).

[0004] When applying e-coat, there are two kinds of micelles to be deposited on the metal substrate, namely, base resin dispersion and self-emulsifying crosslinker dispersion. The particle size of the two dispersions should be in the same range (e.g., 60nm-160nm). Otherwise, the unbalanced ratio will lead to uneven crosslink density of the e-coat film on the metal substrate, which will further lead to defects in the mechanical properties of the e-coat film. Summary of the Invention [Problem to be solved by the invention]

[0005] It is easy to prepare well-dispersed base resin emulsion. However, there is no satisfactory approach in the prior art to obtain good dispersion of self-emulsifying crosslinking agent. Therefore, there is still a need to provide a dispersion method to obtain emulsion of self-emulsifying crosslinking agent with small particle size and narrow particle size distribution. [Means for solving the problem]

[0006] In one embodiment, the present invention provides a method for producing a method for the treatment of a disease comprising at least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of the liquid phase of the aqueous acid dispersion (I) is water-in-oil; and ii) adding water to the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of the liquid phase of the aqueous acid dispersion (II) is an oil-in-water type; The present invention provides a method for dispersing a self-emulsifying crosslinking agent, comprising:

[0007] In another aspect, the present invention provides a self-emulsifying crosslinker dispersion prepared by the method of the present invention, and said self-emulsifying crosslinker dispersion has a Z-average particle size of 50-200 nm, and preferably 60-160 nm.

[0008] In another aspect, the present invention provides an e-coat composition comprising at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion prepared by the method of the present invention.

[0009] In a further aspect, the present invention provides a substrate coated with an e-coat layer, wherein the e-coat layer is formed by at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion prepared by the method of the present invention.

[0010] Surprisingly, it has been found that by using the method of the present invention, self-emulsifying crosslinker dispersions having small particle size and narrow particle size distribution can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below. It should be understood that the present invention can be embodied in various ways and is not limited to the embodiments described herein. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0012] In the context of this application, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0013] In the context of the present application, the terms "comprise(s)" and "comprising" are to be interpreted in an open and open manner, i.e. further components or elements may be present.

[0014] In the context of this application, the term "base resin" refers to the major component of the e-coat composition that reacts with the crosslinker to form the e-coat binder, and one example of a base resin is a polyether amine.

[0015] In the context of this application, the term "self-emulsifying crosslinker" means a crosslinker that has functional groups that can emulsify in an aqueous solution and react with the base resin. An example of a self-emulsifying crosslinker is a cationic polyurethane.

[0016] In the context of this application, the maximum detection temperature (T max The term "temperature" refers to the maximum detected temperature of the dispersion solution during the process of adding a solvent (e.g., a mixture of water and acid) with stirring.

[0017] In the context of this application, the terms "container" and "vessel" are used interchangeably with the same meaning.

[0018] Self-emulsifying crosslinkers are one potential approach for low-bake e-coats. Small particle size and narrow particle size distribution of dispersed polyurethane crosslinkers are necessary for storage stability. The present invention finds how to fine-tune key processing parameters to obtain small particle size and narrow particle size distribution. Furthermore, in the prior art, the synthesis and dispersion of polyurethane crosslinkers are carried out in different vessels, but in the present invention, both synthesis and dispersion steps can be carried out in one vessel, reducing the cost in practical production.

[0019] The present invention comprises at least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of the liquid phase of the aqueous acid dispersion (I) is water-in-oil; and ii) adding water to the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of the liquid phase of the aqueous acid dispersion (II) is an oil-in-water type; The present invention provides a method for dispersing a self-emulsifying crosslinking agent, comprising:

[0020] According to the present invention, the dispersion effect of the cationic polyurethane crosslinker was analyzed and found to have a small average particle size (60nm-160nm) and a very narrow particle size distribution, i.e., PDI (Polydispersity Index) of less than 0.2. The average particle size and particle size distribution are within acceptable ranges which are favorable for both storage stability and uniform deposition of e-coat on metal substrates. This provides great advantages to the automotive OEM and ASM markets.

[0021] The dispersion method of the present invention is not only applicable to cationic polyurethane crosslinkers, but can also be used for other crosslinkers. There are mainly two important parameters that affect the particle size and particle size distribution of the crosslinker micelles: the solids content of the aqueous acid dispersion (I) and the maximum temperature (T max The solids content of the aqueous acid dispersion (I) must be at least 45% by weight, based on the total weight of the aqueous acid dispersion (I). maxis influenced by the initial temperature of the crosslinker and the stirring speed. max should not exceed 40°C, and more preferably not exceed 30°C. The key element of the present invention is that the dispersion or emulsion of the self-emulsifying crosslinker has a phase transition from w / o (water in oil) to o / w (oil in water) during the dispersion process. Such a phase transition can be observed by the appearance of a dough-like mass.

[0022] Moreover, instead of using two vessels to separately synthesize and disperse the self-emulsifying crosslinker, in the present invention, only one vessel is needed to perform both the synthesis and dispersion process of the polyurethane crosslinker, and it has been proven that the small particle size and narrow particle size distribution of the micelles are achieved. The synthesis and dispersion process of the organic polyurethane crosslinker in one vessel brings great advantages in saving energy and cost of production. However, by using two vessels for cationic polyurethane dispersion, small particle size and narrow particle size distribution can also be obtained through the method of the present invention.

[0023] Examples of the self-emulsifying crosslinking agents include cationic polyaromatic urethanes, cationic polyaliphatic urethanes, water-based amino resins, cationic polyester polyurethanes, cationic polyester polyureas, and cationic polycarbonate polyurethanes.

[0024] The selected amine is incorporated into the crosslinker to provide self-emulsifying functionality while being reactive towards the base resin. Examples of said amines include N-methyldiethanolamine, N-butyldiethanolamine, diethanolamine, N,N-dimethylaminopropylamine, bis-(N,N-dimethylaminopropylamine), 2-[[2-(dimethylamino)ethyl]methylamino]ethanol, 2-(2-aminoethoxy)ethanol, triethanolamine, pyridinediethanolamine, ethanolamine, diethanolamine, N,N-dimethylethanolamine.

[0025] Methods for the synthesis of cationic polyurethane crosslinkers are known, and their preparation is disclosed by Saimani Sundar et al. in "Aqueous dispersions of polyurethane cationomers: a new approach for hydrophobic modification and crosslinking", Colloid Polym Sci (2004) 283:209-218.

[0026] To dilute the resulting cationic polyurethane crosslinker, a mixture of water and acid is used, where both inorganic and low molecular weight organic acids can be used. Examples of inorganic acids include dilute hydrochloric acid, dilute sulfuric acid, phosphoric acid, dilute 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 to the water in an amount of 0.1% to 5.0% by weight, and more preferably 0.5% to 2.0% by weight, based on the total weight of the mixture of water and acid.

[0027] Preferably, the dispersion of the self-emulsifying crosslinking agent is carried out under stirring, and the stirring speed is preferably in the range of 500-2000 rpm in the first step and in the range of 200-1500 rpm in the second step. The stirring speed in the second step of dispersion is T max The higher the stirring speed, the greater the T max becomes higher, and T max When the temperature is high, the particle size tends to be large and the particle size distribution tends to be broad.

[0028] Preferably, the initial temperature of the self-emulsifying crosslinking agent is less than 35° C. If the initial temperature of the self-emulsifying crosslinking agent is higher than room temperature, for example 35° C., T max is obviously higher, and T max When the temperature is high, the particle size tends to be large and the particle size distribution tends to be broad.

[0029] Preferably, the solids content of the aqueous acid dispersion (I) in step i) is between 45% and 75% by weight, and preferably between 50% and 70% by weight, based on the total weight of the aqueous acid dispersion (I). And the solids content of the aqueous acid dispersion (II) in step ii) is between 20% and 30% by weight, based on the total weight of the aqueous acid dispersion (II). The solids content of the aqueous acid dispersion (I) was important. When the solids content of the aqueous acid dispersion (I) was higher than 49% (e.g. 58%), the microstructure of the dispersion was water-in-oil and the viscosity of the dispersion was quite high. In contrast, when the solids content of the aqueous acid dispersion (I) was lower than 49% (e.g. 38%), the microstructure of the dispersion was oil-in-water. The two-phase transition of the dispersion, i.e. the transition from water-in-oil to oil-in-water at the microstructure level, results in a smaller Z-average particle size and a narrower particle size distribution. In the absence of such a phase transition, the resulting dispersions tend to have large particle sizes and broad particle size distributions.

[0030] Preferably, the self-emulsifying crosslinker dispersion has a Z-average particle size of 50-200 nm, and more preferably 60-160 nm.

[0031] Preferably, the self-emulsifying crosslinker dispersion has a PDI (polydispersity index) of less than 0.2, and more preferably less than 0.1.

[0032] According to the present invention, it is advantageous to prepare the crosslinker dispersion in one container or vessel, but the dispersion of the self-emulsifying crosslinker can also be prepared in more than one container or vessel, for example two containers. And the important issue is that regardless of the number of container(s) or vessel(s) used, the two-phase transition of the dispersion must occur.

[0033] For comparison, a 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 is placed in one container (first container), and an acid aqueous solution is prepared in another container (second container), and the cationic polyurethane crosslinker in the first container is added continuously to the second container under stirring to reach a certain solid content. By using two vessels and the one-step dispersion approach, the obtained dispersion has a large particle size and a wide particle size distribution. The reason is that in the one-step dispersion approach, there is no opportunity for phase transition at the microstructure level of the dispersion, i.e., from water-in-oil to oil-in-water.

[0034] The present invention further provides an e-coat composition comprising at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion according to the present invention. The base resin is preferably at least one selected from polyetheramines and polyetheramine-based epoxy resins. The e-coat composition can be cured at a temperature between 80°C and 140°C to form an e-coat layer. Such layers can then be formed on various substrates, particularly metal substrates.

[0035] Embodiment Various embodiments are listed below. It will be understood that the embodiments listed below can be combined with any aspect and with other embodiments in accordance with the scope of the present invention.

[0036] EMBODIMENT 1 At least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of the liquid phase of the aqueous acid dispersion (I) is water-in-oil; and ii) adding water to the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of the liquid phase of the aqueous acid dispersion (II) is an oil-in-water type; A method for dispersing a self-emulsifying crosslinking agent, comprising:

[0037] EMBODIMENT 2 The method for dispersing a self-emulsifying crosslinking agent according to embodiment 2, wherein the self-emulsifying crosslinking agent is preferably at least one selected from cationic polyaromatic urethane, cationic polyaliphatic urethane, water-based amino resin, cationic polyester polyurethane, cationic polyester polyurea and cationic polycarbonate polyurethane.

[0038] EMBODIMENT 3 The method for dispersing a self-emulsifying crosslinking agent according to any one of embodiments 1 to 2, in step i), preferably prepare the aqueous acid dispersion (I) by mixing the self-emulsifying crosslinking agent, acid and water under stirring at a speed of 500-2000 rpm, and in step ii), preferably prepare the aqueous acid dispersion (II) under stirring at a speed of 200-1500 rpm.

[0039] EMBODIMENT 4 The method for dispersing a self-emulsifying crosslinking agent according to any one of embodiments 1 to 3, wherein the solid content of the aqueous acid dispersion (I) in step i) is 45% by weight to 75% by weight, and preferably 50% by weight to 70% by weight, based on the total weight of the aqueous acid dispersion (I).

[0040] EMBODIMENT 5 The method for dispersing a self-emulsifying crosslinking agent according to any one of the first to fourth embodiments, wherein the solid content of the aqueous acid dispersion (II) in step ii) is 20% by weight to 30% by weight, based on the total weight of the aqueous acid dispersion (II).

[0041] EMBODIMENT 6 The maximum detection temperature (T max 6. The method for dispersing a self-emulsifying crosslinking agent according to any one of the preceding embodiments, wherein the temperature (C) of the self-emulsifying crosslinking agent is 40° C. or lower, and preferably 30° C. or lower.

[0042] EMBODIMENT 7 The method for dispersing a self-emulsifying crosslinker according to any one of the preceding embodiments, wherein the acid used in step i) for preparing the aqueous acid dispersion (I) is preferably at least one selected from dilute hydrochloric acid, dilute sulfuric acid, phosphoric acid, dilute 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.

[0043] EMBODIMENT 8 The method for dispersing a self-emulsifying crosslinking agent according to any one of embodiments 1 to 7, wherein the mass percentage of the acid in the aqueous acid dispersion (I) is 0.1 mass% to 5.0 mass%, and preferably 0.5 mass% to 2.0 mass%.

[0044] EMBODIMENT 9 9. A self-emulsifying crosslinker dispersion prepared by the method according to any one of embodiments 1 to 8, having a Z-average particle size of 50-200 nm, and preferably 60-160 nm.

[0045] EMBODIMENT 10 10. The self-emulsifying crosslinker dispersion according to embodiment 9, wherein the self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.2, and preferably less than 0.1.

[0046] EMBODIMENT 11 11. The self-emulsifying crosslinking agent dispersion according to any one of embodiments 9 to 10, wherein the solids content of the self-emulsifying crosslinking agent dispersion is 20% by weight to 30% by weight.

[0047] EMBODIMENT 12 12. The self-emulsifying crosslinker dispersion of any one of embodiments 9 to 11, wherein the self-emulsifying crosslinker dispersion comprises at least one selected from cationic polyaromatic urethanes, cationic polyaliphatic urethanes, water-based amino resins, cationic polyester polyurethanes, cationic polyester polyureas, and cationic polycarbonate polyurethanes.

[0048] EMBODIMENT 13 13. 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.

[0049] EMBODIMENT 14 The e-coat composition according to embodiment 13, wherein the base resin is preferably at least one selected from polyetheramines and polyetheramine-based epoxy resins.

[0050] EMBODIMENT 15 15. The e-coat composition of any one of embodiments 13 to 14, wherein the e-coat composition has a cure temperature of from 80°C to 140°C.

[0051] EMBODIMENT 16 16. An e-coat layer obtained from the e-coat composition according to any one of embodiments 13 to 15 after curing at a temperature between 80° C. and 140° C.

[0052] EMBODIMENT 17 A substrate coated with an e-coat layer according to embodiment 16. EXAMPLES

[0053] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited thereto. All raw materials used in the examples are commercially available.

[0054] Examples 1-3 describe the preparation of cationic polyurethane crosslinkers. (登録商標)M20S is oligomeric methylene diphenyl diisocyanate (MDI) from BASF. Methyl ethyl ketoxime (MEKO) acts as a blocking agent, methyl isobutyl ketone (MIBK) acts as a solvent, and dibutyltin dilaurate (DBTL) acts as a catalyst. N-Methyldiethanolamine, N-Butyldiethanolamine, Diethanolamine (DEOLA), N,N-Dimethylaminopropylamine (DMAPA), Bis-(N,N-Dimethylaminopropylamine) (BDMAPA), 2-[[2-(Dimethylamino)ethyl]methylamino]ethanol (DMAEA), 2-(2-Aminoethoxy)ethanol (AEEOL), Triethanolamine, Pyridinediethanolamine, Ethanolamine, Diethanolamine, N,N-Dimethylethanolamine are amines containing nitrogen atoms and act as neutralizing agents.

[0055] Example 1: MEKO Blocked Lupranate with N,N-Dimethylaminopropylamine (DMAPA) as the Amine Building Block for Neutralization (登録商標) Preparation of M20S A reactor equipped with a condenser, nitrogen gas inlet and outlet was charged with 400 parts by weight of Lupranate. (登録商標) M20S, 126.1 parts by weight of MIBK, and 0.18 parts by weight of DBTL were charged. This initial charge was heated to 30 ° C. Then, 153.0 parts by weight of bisphenol A6EO were charged into the reactor at a uniform rate within 60 minutes with constant stirring. Then, 378.3 parts by weight of MIBK were added to the reactor and in parallel the reaction temperature was cooled to 30 ° C. At a reaction temperature of 30 ° C, 150.5 parts by weight of MEKO were slowly charged into the reactor within 20 minutes. After the end of the charge of MEKO, the reaction temperature was increased to 60 ° C and the reaction was continued for another 30 minutes. Then the reaction temperature was cooled again to 30 ° C, and 53.0 parts by weight of DMAPA were quickly charged into the reactor to start the next step. 20 minutes after the end of the charge, the reaction temperature was again set to 60 ° C, and stirring was continued for another 30 minutes. A polyurethane crosslinker was obtained.

[0056] Example 2: MEKO Blocked Lupranate with Bis-(N,N-Dimethylaminopropylamine) or (BDMAPA) as the Amine Building Block for Neutralization (登録商標) Preparation of M20S 500 parts by weight of Lupranate (登録商標) M20S, 139.9 parts by weight of MIBK, and 0.23 parts by weight of DBTL were charged into a reactor equipped with a condenser, nitrogen gas inlet and outlet. This initial charge was heated to 30°C. Then, 30.7 parts by weight of 1,2-propanediol (PD) were charged into the reactor at a uniform rate within 60 minutes with constant stirring. Then, 419.7 parts by weight of MIBK were added to the reactor and in parallel the reaction temperature was cooled to 30°C. At a reaction temperature of 30°C, 187.5 parts by weight of MEKO were slowly charged into the reactor within 20 minutes. After the end of the charge of MEKO, the reaction temperature was increased to 60°C and the reaction was continued for another 30 minutes. Then the reaction temperature was cooled again to 30°C, and 120.9 parts by weight of BDMAPA were quickly charged into the reactor to start the next step. 20 minutes after the end of the charge, the reaction temperature was again set to 60°C and stirring was continued for another 30 minutes. A polyurethane crosslinker was obtained.

[0057] Example 3: MEKO Blocked Lupranate with 2-[[2-(Dimethylamino)ethyl]methylamino]ethanol (DMAEA) as an Amine Building Block for Neutralization (登録商標) Preparation of M20S 500 parts by weight of Lupranate (登録商標)M20S, 135.5 parts by weight of MIBK, and 0.23 parts by weight of DBTL were charged into a reactor equipped with a condenser, nitrogen gas inlet and outlet. This initial charge was heated to 30 ° C. Then, 30.7 parts by weight of PD were charged into the reactor at a constant rate within 60 minutes with continuous stirring. Then, 406.4 parts by weight of MIBK were added to the reactor and in parallel the reaction temperature was cooled to 30 ° C. At a reaction temperature of 30 ° C, 187.5 parts by weight of MEKO were slowly charged into the reactor within 20 minutes. After the end of the MEKO charge, the reaction temperature was heated to 60 ° C and the reaction was continued for another 30 minutes. Then the reaction temperature was cooled again to 30 ° C, and 94.4 parts by weight of DMAEA were quickly charged into the reactor to start the next step. 20 minutes after the end of the charge, the reaction temperature was again set to 60 ° C, and stirring was continued for another 30 minutes. A polyurethane crosslinker was obtained.

[0058] Examples 4-14: Preparation of a one-pot dispersion of the cationic polyurethane crosslinker obtained from Example 1 The preparation of the dispersion of cationic polyurethane crosslinker involves two transition steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinker, wherein the microstructure of the liquid phase of said aqueous acid dispersion (I) is of the water-in-oil type, and ii) adding water to said aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of the liquid phase of said aqueous acid dispersion (II) is of the oil-in-water type.

[0059] In Examples 4-6, the cationic polyurethane crosslinker with a solid content of 60% obtained from Example 1 was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase with a solid content of 58% (first stage). Then, 1723.3 parts by weight of water was added to the container with stirring to obtain an oil-in-water phase with a solid content of 25% (second stage). The difference between Examples 4-6 was the stirring speed in the second stage, i.e., 500 rpm, 1500 rpm and 2500 rpm in Examples 4-6, respectively.

[0060] In Example 7, the cationic polyurethane crosslinker obtained from Example 1 with a solid content of 60% was placed 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase with a solid content of 58% (first stage). Then, 1723.3 parts by weight of water was added to the container at a stirring speed of 500 rpm to obtain an oil-in-water phase with a solid content of 25% (second stage).

[0061] In Example 8, the cationic polyurethane crosslinker obtained from Example 1 with a solid content of 60% was placed 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase with a solid content of 58% (first stage). Then, 1723.3 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solid content of 25% (second stage).

[0062] In Example 9, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 58% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1723.3 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0063] In Example 10, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 49% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1483.5 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0064] In Example 11, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 38% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1036.2 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0065] In Example 12, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 58% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1723.3 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0066] In Example 13, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 49% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1483.5 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0067] In Example 14, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 38% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1036.2 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0068] Examples 15-20: Preparation of a one-pot dispersion of the cationic polyurethane crosslinker obtained from Example 2 In Example 15, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 58% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1910.1 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0069] In Example 16, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 49% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1644.3 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0070] In Example 17, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 38% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1148.5 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0071] In Example 18, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 58% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1910.1 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0072] In Example 19, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 49% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1644.3 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0073] In Example 20, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 38% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1148.5 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0074] Examples 21-26: Preparation of a one-pot dispersion of the cationic polyurethane crosslinker obtained from Example 3 In Example 21, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 58% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1849.6 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0075] In Example 22, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 49% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1592.2 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0076] In Example 23, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 38% was placed in a plastic container at 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% by weight) was added to the container at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1112.1 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0077] In Example 24, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 58% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1849.6 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0078] In Example 25, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 49% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1592.2 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0079] In Example 26, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 38% was placed in a plastic container at 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 at a stirring speed of 1500 rpm to obtain a water-in-oil phase (first stage). Then, 1112.1 parts by weight of water was added to the container at a stirring speed of 1500 rpm to obtain an oil-in-water phase with a solids content of 25% (second stage).

[0080] Example 27: Two-vessel preparation of a dispersion of cationic polyurethane crosslinker from Example 1 The cationic polyurethane crosslinker from Example 1 with a solids content of 60% was placed in a plastic container (first container) at 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% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was added to the second container at a stirring speed of 1500 rpm to reach a solids content of 49%, followed by the addition of 1483.5 parts by weight of water to the second container at a stirring speed of 1500 rpm to reach a solids content of 25%.

[0081] Example 28: Two-vessel preparation of a dispersion of cationic polyurethane crosslinker from Example 2 The cationic polyurethane crosslinker from Example 2 with a solids content of 60% was placed in a plastic container (first container) at 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% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was added to the second container at a stirring speed of 1500 rpm to reach a solids content of 49%, followed by the addition of 1644.3 parts by weight of water to the second container at a stirring speed of 1500 rpm to reach a solids content of 25%.

[0082] Example 29: Two-vessel preparation of a dispersion of cationic polyurethane crosslinker from Example 3 The cationic polyurethane crosslinker from Example 3 with a solids content of 60% was placed in a plastic container (first container) at 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% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was added to the second container at a stirring speed of 1500 rpm to reach a solids content of 49%, and then 1592.2 parts by weight of water was added to the second container at a stirring speed of 1500 rpm to reach a solids content of 25%.

[0083] Examples 30-31: Preparation of the cationic polyurethane crosslinker dispersion from Example 1 in one step using two vessels In Example 30, the cationic polyurethane crosslinker obtained from Example 1 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1750.1 parts by weight of water and 16.68 parts by weight of an aqueous formic acid solution (86% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container at a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0084] In Example 31, the cationic polyurethane crosslinker from Example 1 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1748.1 parts by weight of water and 18.7 parts by weight of acetic acid was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container with a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0085] Examples 32-33: Preparation of the cationic polyurethane crosslinker dispersion from Example 2 in one step using two containers In Example 32, the cationic polyurethane crosslinker obtained from Example 2 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1916.8 parts by weight of water and 41.46 parts by weight of an aqueous formic acid solution (86% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container with a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0086] In Example 33, the cationic polyurethane crosslinker from Example 2 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1911.8 parts by weight of water and 46.5 parts by weight of acetic acid was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container with a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0087] Examples 34-35: Preparation of the cationic polyurethane crosslinker dispersion from Example 3 in one step using two vessels In Example 34, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1875.5 parts by weight of water and 20.7 parts by weight of an aqueous formic acid solution (86% by weight) was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container with a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0088] In Example 35, the cationic polyurethane crosslinker obtained from Example 3 with a solids content of 60% was placed in a plastic container (first container) at room temperature (20-25°C at 1 atm). A mixture of 1873 parts by weight of water and 23.3 parts by weight of acetic acid was prepared in another container (second container). The cationic polyurethane crosslinker from the first container was continuously added to the second container with a stirring speed of 1500 rpm until a solids content of 25% was reached.

[0089] Performance Testing <T max > T max is the detected maximum temperature of the dispersion solution during the process of adding the solvent (for example, a mixture of water and acid) while stirring. T max is tested with an IKA RET basic S025 including a temperature sensor.

[0090] <Z-average particle size> The Z-average particle size of the dispersion is tested using a particle size analyzer, Malvern, Zetasizer Nano zs90 (model ZEN3690), in accordance with the standard specification DIN ISO13321.

[0091] <pdi> The PDI (Polydispersity Index) of the dispersions is tested according to standard DIN ISO 13321 using a particle size analyzer, Malvern, Zetasizer Nano zs90 (model ZEN3690).

[0092] <Storage stability> The storage stability of each dispersion was evaluated by visually observing the appearance of the dispersion in a transparent container after standing at a certain temperature for a certain period of time. If phase separation (major) or settling (minor) occurred, the dispersion was rated as "unstable."

[0093] The performance test results of Examples 4 to 35 are summarized in Table 1.

[0094] [Table 1]

[0095] As can be seen from Table 1, when the initial temperature of the cationic polyurethane crosslinker is room temperature, increasing the stirring speed in the second stage of dispersion increases the T max was significantly affected. Also, when the initial temperature of the cationic polyurethane crosslinker was higher than room temperature, e.g., 35°C or 50°C, T max In conclusion, both the initial temperature of the cationic polyurethane crosslinker and the stirring speed of the second stage significantly increased the T max The higher the initial temperature of the crosslinker and the faster the stirring speed, the higher the T max has risen. T max Higher β-dispersion resulted in larger particle size and broader particle size distribution, for example, when the stirring speed was 1500 rpm in the second stage and the initial temperature of the crosslinker was 50° C., the Z-average particle size was 1006 nm and the PDI was 0.36.

[0096] Cationic polyurethane crosslinker T max When the temperature was controlled in the range of 35°C to 40°C, the Z-average particle size of the resulting dispersion changed dramatically, especially in the case where the solids content of the first stage dispersion was 38%.

[0097] For the cationic polyurethane crosslinker obtained from Example 1, when the solid content of the first stage dispersion reached 58% and 49% by adding the formic acid solution, the Z-average particle size of the second stage dispersion was 99 nm (PDI is 0.08) and 102 nm (PDI is 0.11), respectively. In contrast, when the solid content of the first stage dispersion was 38%, the Z-average particle size of the resulting second stage dispersion was 337 nm (PDI is 0.26). Also, after changing the formic acid solution to the acetic acid solution, when the solid content of the first stage dispersion was 58%, 49%, and 38%, respectively, the Z-average particle size of the second stage dispersion was 100 nm (PDI is 0.13), 99 nm (PDI is 0.12), and 210 nm (PDI is 0.21), respectively.

[0098] For the cationic polyurethane crosslinker obtained from Example 2, when the solid content of the first stage dispersion reached 58% and 49% by adding the formic acid solution, the Z-average particle size of the second stage dispersion was 92 nm (PDI is 0.12) and 88 nm (PDI is 0.05), respectively. In contrast, when the solid content of the first stage dispersion was 38%, the Z-average particle size obtained was 278 nm (PDI is 0.13). Also, after changing the formic acid solution to the acetic acid solution, when the solid content of the first stage dispersion was 58%, 49%, and 38%, respectively, the Z-average particle size of the second stage dispersion was 72 nm (PDI is 0.17), 78 nm (PDI is 0.11), and 298 nm (PDI is 0.18), respectively.

[0099] For the cationic polyurethane crosslinker obtained from Example 3, when the solid content of the first stage dispersion reached 58% and 49% by adding the formic acid solution, the Z-average particle size of the second stage dispersion was 98 nm (PDI is 0.13) and 94 nm (PDI is 0.05), respectively. In contrast, when the solid content of the first stage dispersion was 38%, the Z-average particle size of the second stage dispersion was 298 nm (PDI is 0.14). Also, after changing the formic acid solution to the acetic acid solution, when the solid content of the first dispersion was 58%, 49%, and 38%, respectively, the Z-average particle size of the second dispersion was 101 nm (PDI is 0.12), 86 nm (PDI is 0.11), and 365 nm (PDI is 0.19), respectively.

[0100] The solids content of the first stage dispersion was important. When the solids content of the first stage dispersion was higher than 49% (e.g. 58%), the microstructure of the dispersion was water-in-oil and the viscosity of the dispersion was quite high. In contrast, when the solids content of the first stage dispersion was lower than 49% (e.g. 38%), the microstructure of the dispersion was oil-in-water.

[0101] The two-phase transition of the dispersion, i.e., water-in-oil to oil-in-water transition at the microstructural level, reduces the Z-average particle size and narrows the particle size distribution. In the absence of such a phase transition, dispersions with large particle sizes would be obtained.

[0102] Furthermore, when the formic acid aqueous solution was changed to an acetic acid aqueous solution, the cationic polyurethane crosslinked bodies obtained in Examples 1 to 3 showed similar results in terms of Z-average particle size.

[0103] Furthermore, according to the present invention, it is advantageous to prepare the crosslinker dispersion in one container or vessel, although the experiment may be carried out in more than one container or vessel, for example two containers, and the key issue is that the two-phase transition of the dispersion must occur, regardless of the number of container(s) or vessel(s) used.

[0104] Examples 27-29 described the preparation of dispersions of cationic polyurethane crosslinkers obtained from Examples 1-3 by using two vessels and two-step dispersion approach, respectively, and the test results showed that these dispersions also had small particle size (e.g., in the range of 60 nm to 160 nm) with narrow particle size distribution (e.g., less than 0.1). The T observed in the second dispersion max was about 30 °C. A two-phase transition was observed during the dispersion process. Thus, using a two-stage dispersion approach resulted in dispersions with smaller particle sizes and narrower particle size distributions, although it required two containers or vessels.

[0105] For comparison, a one-step dispersion approach was performed using two containers or vessels. Examples 30-35 described the preparation of the cationic polyurethane crosslinker dispersions obtained from Examples 1-3 using two containers and one-step dispersion approach. And the test results showed that by using two vessels and one-step dispersion approach, the obtained dispersions have large particle size and wide particle size distribution, whether using aqueous formic acid or aqueous acetic acid. The reason is that the one-step dispersion approach did not have the opportunity for phase transition at the microstructure level of the dispersion, i.e., from water-in-oil to oil-in-water.< / pdi>

Claims

1. At least two steps: i) preparing an aqueous acid dispersion (I) of a self-emulsifying crosslinking agent, wherein the microstructure of the liquid phase of the aqueous acid dispersion (I) is water-in-oil, and the solids content of the aqueous acid dispersion (I) in step i) is 45% to 75% by weight, based on the total weight of the aqueous acid dispersion (I); and ii) A step of adding water to the aqueous acid dispersion (I) to obtain an aqueous acid dispersion (II), wherein the microstructure of the liquid phase of the aqueous acid dispersion (II) is an oil-in-water type, and the maximum detectable temperature (T max ) of the aqueous acid dispersion (II) in step ii) is 40° C. or less. A method for dispersing a self-emulsifying crosslinking agent, comprising:

2. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 2, wherein the self-emulsifying crosslinking agent is preferably at least one selected from cationic polyaromatic urethanes, cationic polyaliphatic urethanes, water-based amino resins, cationic polyester polyurethanes, cationic polyester polyureas, and cationic polycarbonate polyurethanes.

3. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein in step i), the aqueous acid dispersion (I) is prepared by mixing the self-emulsifying crosslinking agent, acid and water preferably under stirring at a speed of 500 to 2000 rpm, and in step ii), the aqueous acid dispersion (II) is prepared preferably under stirring at a speed of 200 to 1500 rpm.

4. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein the solids content of the aqueous acid dispersion (I) in step i) is 50% by weight to 70% by weight, based on the total weight of the aqueous acid dispersion (I).

5. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein the solids content of the aqueous acid dispersion (II) in step ii) is 20% by weight to 30% by weight, based on the total weight of the aqueous acid dispersion (II).

6. The maximum detection temperature (T ｍａｘ 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein the temperature of the dispersion is 30° C. or lower.

7. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein the acid used in step i) for preparing the aqueous acid dispersion (I) is preferably at least one selected from dilute hydrochloric acid, dilute sulfuric acid, phosphoric acid, dilute 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. 3. The method for dispersing a self-emulsifying crosslinking agent according to claim 1 or 2, wherein the weight percentage of acid in the aqueous acid dispersion (I) is 0.1% to 5.0% by weight, and preferably 0.5% to 2.0% by weight.

9. 10. A self-emulsifying crosslinker dispersion prepared by the method of claim 1, having a Z-average particle size of 50 to 200 nm, and preferably 60 to 160 nm.

10. 10. The self-emulsifying crosslinker dispersion of claim 9, wherein said self-emulsifying crosslinker dispersion has a PDI (Polydispersity Index) of less than 0.2, and preferably less than 0.

1.

11. 10. The self-emulsifying crosslinker dispersion of claim 9, wherein the solids content of the self-emulsifying crosslinker dispersion is 20% to 30% by weight.

12. 10. The self-emulsifying crosslinker dispersion of claim 9, wherein the self-emulsifying crosslinker dispersion comprises at least one selected from cationic polyaromatic urethanes, cationic polyaliphatic urethanes, water-based amino resins, cationic polyester polyurethanes, cationic polyester polyureas, and cationic polycarbonate polyurethanes.

13. An e-coat composition comprising at least one base resin dispersion and at least one self-emulsifying crosslinker dispersion according to claim 9 or 10.

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

15. The e-coat composition of claim 13, wherein the e-coat composition has a cure temperature of from 80°C to 140°C.

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

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