阅读说明：本技术 用于浸涂导电基材的包含铋和锂的水性涂料组合物 (Aqueous coating composition comprising bismuth and lithium for dip coating electrically conductive substrates ) 是由 T·格尔布里希 P·凯尔 A·赫内 A·布罗斯特 J·米尔迈尔 S·赫姆克尔 P·托博尔 于 2020-03-20 设计创作，主要内容包括：本发明涉及一种用于以电涂材料至少部分涂覆导电基材的水性涂料组合物(A),其包含(A1)至少一种可阴极沉积的树脂基料,(A2)至少一种交联剂、(A3)基于涂料组合物(A)总重量为至少100ppm的铋,和(A4)呈溶解于(A)中的形式的锂,其中基于涂料组合物(A)的总重量,该锂的比例不超过300ppm。本发明还涉及一种制备(A)的方法、一种涂覆方法和一种可通过该方法获得的至少部分涂覆的基材。(The invention relates to an aqueous coating composition (A) for at least partially coating an electrically conductive substrate with an electrocoating material, comprising (A1) at least one cathodically depositable resin binder, (A2) at least one crosslinker, (A3) at least 100ppm of bismuth, based on the total weight of the coating composition (A), and (A4) lithium in a form dissolved in (A), wherein the proportion of lithium does not exceed 300ppm, based on the total weight of the coating composition (A). The invention also relates to a method for producing (A), to a coating method and to an at least partially coated substrate obtainable by the method.)

1. An aqueous coating composition (a) for at least partially coating an electrically conductive substrate with an electrocoating material, comprising:

(A1) at least one cathodically depositable resinous binder,

(A2) at least one cross-linking agent, wherein,

(A3) at least 100ppm of bismuth, based on the total weight of the coating composition (A),

wherein:

(A4) the coating composition comprises lithium in a form dissolved in (A), the proportion of lithium not exceeding 300ppm, based on the total weight of the coating composition (A).

2. Aqueous coating composition (a) according to claim 1, wherein the proportion of (a4) lithium is from 2.5 to 250ppm, preferably from 12.5 to 70ppm, more preferably from 12.5 to 30ppm, based on the total weight of the coating composition (a).

3. An aqueous coating composition (a) according to claim 1 or 2, comprising a bismuth-based crosslinking catalyst.

4. An aqueous coating composition (A) according to claim 3, comprising a bismuth-based crosslinking catalyst in component (A3).

5. An aqueous coating composition (A) according to claim 3 or 4, wherein the proportion of (A5) phosphorus is in an amount of not more than 100ppm, preferably 45ppm, based on the total weight of the coating composition (A).

6. An aqueous coating composition (A) according to any one of claims 1 to 5, comprising (A6) copper.

7. An aqueous coating composition (A) according to claim 6, wherein (A6a) copper is contained in dissolved form in (A) and the amount of (A6a) is from 5 to 1000ppm, based on the total weight of coating composition (A).

8. An aqueous coating composition (A) according to any one of claims 1 to 7, wherein coating composition (A) comprises at least 300ppm total amount of bismuth, based on the total weight of coating composition (A), comprising:

(A3a) at least 100ppm, based on the total weight of the coating composition (A), of bismuth in the form present in the coating composition (A) as a solution, and

(A3b) at least 200ppm of bismuth in a form not present in the coating composition (a) as a solution, based on the total weight of the coating composition (a).

9. Aqueous coating composition (a) according to any of claims 1 to 8, wherein the total amount of bismuth present in the coating composition (a) is from at least 500ppm to 20000ppm and the coating composition (a) comprises at least one at least bidentate complexing agent (A3aa) suitable for complexing bismuth.

10. A method for at least partially coating an electrically conductive substrate with an electrocoating material, comprising at least step (1):

(1) contacting an electrically conductive substrate as a cathode connection with an aqueous coating composition (A) according to any one of claims 1 to 9,

wherein step (1) is carried out in at least two successive stages (1a) and (1b), i.e.

(1a) Voltage application at an applied voltage of 1-50V for a duration of at least 5 seconds, and

(1b) under an applied voltage of 50-400V, provided that the voltage applied in phase (1b) is at least 10V higher than the voltage applied in phase (1 a).

11. The method according to claim 10, wherein the voltage applied in phase (1a) is applied for a duration of at least 5 to 300 seconds, and the voltage applied in phase (1b) of 50-400V is carried out in a time interval of 0-300 seconds after the implementation of phase (1a) and is maintained at a value of said voltage range of 50-400V for a duration of 10-300 seconds.

12. The method according to claim 11 or 12, wherein the electrically conductive substrate has different regions in terms of metal type, more particularly at least one region is steel-based and at least one further region is aluminum-based.

13. The process according to claim 12, wherein aqueous coating composition (a) comprises lithium (a4) in a form dissolved in (a) and copper (A6a) in a form dissolved in (a) and the proportion of (a4) is 12.5 to 70ppm, preferably 12.5 to 50ppm, more preferably 12.5 to 40ppm and the proportion of (A6a) is 20 to 250 ppm.

14. A coated substrate coated by the method of any one of claims 10-13.

15. A part or article, more particularly an automotive body, comprising the coated substrate of claim 14.

Inventive and comparative examples

Preparation of the aqueous coating composition of the invention and of the comparative coating composition

Obtained from BASF for preparing exemplary coating compositions of the invention and comparative coating composition V1 below800 the pigment paste comprises basic bismuth nitrate. The preparation of such pigment pastes is known to the person skilled in the art from, for example, DE 102008016220A1 (page 7, Table 1, variant B).

Comparative coating composition (A) V1

2129g of base and crosslinker (a product commercially available from BASF)800, solids content 38.0% by weight), 302g of pigment paste (product commercially available from BASF)800 having a solids content of 65.5% by weight), 1258g of water, and 1309.5g of an aqueous solution of Bicine (N, N' -bis (2-hydroxyethyl) glycine) (59.5g of Bicine +1250g of water) were mixed to form comparative coating composition (A), V1. In this case, the Bicine solution is first prepared and then added to the initial charge comprising the base and paste. The mixture was stirred at 18-23 ℃ for 24 hours.

Coating composition (A) E1

Coating composition (A) E1 was prepared as (A) V1 except that 250g of an aqueous solution of lithium acetate dihydrate (7.2 g of lithium acetate dihydrate in 892.8g of water, then 250g of the solution) was additionally mixed and the amount of water added was reduced by a corresponding 250 g. Thus, the proportion of lithium (a4) in (a) E1 corresponds to a proportion of 27ppm, based on the total amount of (a) E1.

Coating composition (A) E2

A coating composition (A) E2 was prepared as (A) E1, except that 250g of an aqueous solution of copper (II) nitrate trihydrate (7.6g of copper (II) nitrate trihydrate +992.4g of water, then 250g of this solution) were additionally mixed and the amount of water added was correspondingly reduced by 250 g. (A) The proportion of copper (A6A) in E2 therefore corresponds to a proportion of 100ppm, based on the total amount of (A) E2.

For all three of the coating compositions, the amount of lithium dissolved (a4), the amount of phosphorus dissolved (a5) (for control), the amount of copper dissolved, and the amounts of bismuth (A3a) and (A3b) were determined. Table 1a provides a summary of the resulting inventive coating compositions (A) E1 and (A) E2 and comparative coating composition (A) V1. Where appropriate, pH and conductivity are also described. If measured, the respective pH and conductivity values of Table 1a are determined at a temperature of about 20 ℃.

TABLE 1a

	(A)V1	(A)E1	(A)E2
				Ratio (A3 a).)	980ppm	980ppm	980ppm
Ratio (A3 b).)	1520ppm	1520ppm	1520ppm
				Proportion (A4)	-	27ppm	27ppm
Proportion (A5)	-	-	-
				Proportion (A6a)	-	-	100ppm
pH	5.44	5.58	5.47
				Electrical conductivity of	2.03mS/cm	2.26mS/cm	2.26mS/cm

Using the amount determined, for example, for (a) E2; (A) precisely the same amounts of V1 and (A) E1 and the proportions of the bismuth-containing components.

Preparation of other coating compositions with different ratios of lithium (A4)

Other coating compositions were prepared as (A) E2, but with varying proportions of lithium (A4). For this purpose, an aqueous solution of the above-mentioned lithium acetate dihydrate (7.2 g of lithium acetate dihydrate in 892.8g of water) was mixed in correspondingly different amounts. By varying the proportion of water added, the total amount of sample produced was again kept constant.

Table 1b provides an overview of the coating compositions prepared. For easier comparison, coating composition (a) E1 is also shown.

TABLE 1b

	(A)E2	(A)E1	(A)E3	(A)E4	(A)E5	(A)V2
							Proportion (A4)	17ppm	21ppm	27ppm	38ppm	49ppm	350ppm
pH	5.24	5.34	5.58	5.60	5.58	5.96
							Conductivity [2 ]mS/cm]	2.47	2.47	2.26	2.40	2.58	4.55

Preparation of other coating compositions with different lithium and phosphorus ratios

Other coating compositions were prepared as in (a) E1, but using lithium phosphate instead of an aqueous solution of lithium acetate dihydrate. Here, lithium phosphate is introduced as an ingredient of the pigment paste by grinding. Table 1c provides a summary of these coating compositions. For easier comparison, coating composition (a) E1 is also shown.

TABLE 1c

n.d. ═ not determined

2. Preparation of a coated electrically conductive substrate with one of the coating compositions (A)

The aqueous coating compositions described in 1. are each applied as a dip-coat to various substrates. Here, each composition was applied to various substrates immediately after preparation as described above.

Three metal test panels were used, these being T1 (hot dip galvanized steel (HDG)) and T2 (aluminum (ALU)) and T3 (cold rolled steel (CRS)).

First, the panels were each cleaned by immersing them in a bath containing an aqueous solution comprising Gardoclean S5160, a product commercially available from Chemetall, and water (97.7 wt%) for 2 minutes at a temperature of 60 ℃.

The substrate cleaned in this way is subsequently rinsed with water.

Immediately thereafter, one of the aqueous coating compositions used according to the invention was applied to each panel T1, T2 or T3, the respective panel being immersed in a respective dip bath comprising one composition in each case. The dip coating bath had a corresponding temperature of 30 ℃.

Here, the coating in the dip coating bath is carried out by a two-stage deposition step and a coating step, which provides two stages (1a) and (1b), in which first of all a current intensity of 0.02 to 0.32A or a voltage of 4V in a constant current manner is applied in each case for a duration of 120 seconds (corresponding to stage (1 a)).

Thereafter, for the substrate obtained after stage (1a), stage (1b) of step (1) of the process of the invention is carried out, in which a voltage of 4V is applied potentiostatically or a current of 0.12-0.28A is applied galvanostatically, in each case continuously linearly increasing in stage (1b) by a voltage ramp to a voltage of 200-220V in each case for a duration of 30 seconds. The respective voltage was then held for a duration of 90 seconds (holding time) to give (after subsequent curing) a coating of the respective substrate with a dry film thickness of 17 to 22 μm. The test panels were then cured in an oven (175 ℃, unless explicitly stated otherwise) for 25 minutes.

3. Investigation of the Corrosion protection Effect of coated substrates

Substrates coated with a coating composition were investigated by the measurement method described earlier above.

3a investigation of coatings prepared using the coating compositions listed in Table 1a

The corrosion resistance of coatings prepared using the coating compositions listed in table 1a was investigated. It should be noted that outstanding corrosion resistance is obtained, with an average failure of about 1 mm. Furthermore, the absolute range difference of about 1mm is technically difficult to evaluate and therefore meaningless. Table 3a shows the results.

TABLE 3a

The results show that system b (a) E shows slightly improved corrosion resistance on the steel substrate compared to system b (a) V1. Although the aluminium destruction performance of both b (a) E1 and b (a) V1 is very good, in the case of b (a) V1 the number of delamination points on the plate is very high, which means that there are many nuclei for further corrosion attack. In contrast, the number of such delamination points in the B (A) E1 system is very small. The system of the invention B (A) E2 is further improved in corrosion inhibition performance.

In summary, it has been found that the system of the present invention is ideally suited to provide outstanding corrosion protection in relation to common metal types-steel and aluminium, and therefore ideally suited to substrates in which both metals are present.

3b investigation of coatings prepared using the coating compositions listed in Table 1b

The surface structure/surface quality of coatings prepared using the coating compositions listed in table 1b was investigated. Table 3b shows the results.

The coating composition (A) V2 can be deposited by electrophoretic deposition coating method. However, the result is a disturbed surface with many holes, which is not acceptable.

TABLE 3b

Coating composition

(A)E2

(A)E1

(A)E3

(A)E4

(A)E5

(A)V2

Coating layer

B(A)E2

B(A)E1

B(A)E3

B(A)E4

B(A)E5

B(A)E6

Proportion (A4)

17ppm

21ppm

27ppm

38ppm

49ppm

350ppm

Surface quality

1

1-2

1-2

2-3

3-4

5

In addition, the surface quality of coating b (a) V1 was studied and rated as a1 ratio.

In addition, many of the corrosion resistance studies described in 3a have also typically been performed on coatings b (a) E2, b (a) E3, b (a) E4, and b (a) E5. The results show that there is a corresponding corrosion resistance in the region of coating b (a) E1 and therefore better than the corrosion resistance of coating b (a) V1.

In summary, the results show that the addition of lithium (a4) to the coating composition leads on the one hand to a significantly improved corrosion resistance. On the other hand, an increase in the ratio of (a4) leads to a decrease in surface quality. At a ratio of 388ppm (A4), electrophoretic deposition was even no longer possible.

3c investigation of coatings prepared using the coating compositions listed in Table 1c

The crosslinking performance of coatings prepared using the coating compositions listed in table 1c was investigated. Table 3c shows the results.

TABLE 3c

	(A)E1	(A)E6	(A)E7	(A)E8	(A)E9
						Ratio of lithium phosphate	-	100ppm	150ppm	250ppm	350ppm
Proportion (A4)	27ppm	18ppm	27ppm	n.d.	n.d.
						Proportion (A5)	-	27ppm	40ppm	67ppm	93.5ppm
Initial temperature	147℃	148℃	150℃	157℃	155℃
						Offset time, 160 deg.C	30 minutes	30 minutes	36 minutes	43 minutes	46 minutes
Offset time, 175 deg.C	20 minutes	20 minutes	22 minutes	27 minutes	28 minutes
						Offset time, 190 deg.C	15 minutes	15 minutes	18 minutes	19 minutes	18 minutes
Tg(CRS)	88	80	77	56	52
						Tg(HDG)	86	76	64	57	56
Tg(ALU)	87	84	56	49	48

The results show that for a preferred system of coating compositions (a) comprising a bismuth-based catalyst, the proportion of phosphorus present in the composition should preferably be very low. The reason is that the higher the proportion of phosphorus, the poorer the crosslinkability (as is evident from the higher onset temperature, the longer offset time and the lower glass transition temperature).