HARD COATINGS WITH HIGH CHEMICAL AND MECHANICAL STABILITY

Abstract

The present invention relates to coatings which have high stability with respect to chemical and mechanical impacts. Said coatings are obtainable by crosslinking polyisocyanates with a low oligomer content.

Claims

1.-15. (canceled)

16. A process for producing surface coatings having a high hardness and high mechanical and/or chemical stability, comprising the process steps of a) providing a polyisocyanate composition A), where the isocyanate content is at least 15% by weight; b) applying the polyisocyanate composition A) to a surface; and c) atalytically crosslinking the polyisocyanate composition A) in the presence of a catalyst B), with the proviso that the reaction mixture formed from the polyisocyanate composition A) and the at least one catalyst B) contains not more than 0.2% by weight of organic and inorganic iron, lead, tin, bismuth and zinc compounds.

17. The process as claimed in claim 16, wherein the catalytic crosslinking is effected at a temperature between 10 C. and 35 C.

18. The process as claimed in claim 16, wherein the catalyst is a metal salt of a weak aliphatic or cycloaliphatic carboxylic acid in combination with a crown ether.

19. The process as claimed in claim 16, wherein the catalyst is a metal salt of a weak aliphatic or cycloaliphatic carboxylic acid in combination with a crown ether and the catalytic crosslinking is effected at a temperature between 10 C. and 35 C.

20. The process as claimed in claim 16, wherein the surface coating created has a Knig pendulum hardness of at least 80 seconds.

21. The process as claimed in claim 16, wherein the surface coating created has a Knig pendulum hardness of at least 100 seconds.

22. The process as claimed in claim 16, wherein the surface coating created has elevated chemical stability.

23. The process as claimed in claim 16, wherein the coating is particularly stable to at least one of the agents selected from the group consisting of ethanol, ink, sodium hydroxide solution and HS DOT 4.

24. The process as claimed claim 16, wherein, during the catalytic crosslinking in process step c), the amount of the isocyanurate groups in the polyisocyanate composition A) increases by at least 10% compared to the amount that was present in process step a).

25. The process as claimed in claim 16, wherein the reaction mixture formed from the polyisocyanate composition A) and the at least one catalyst B) contains not more than 0.1% by weight of organic and inorganic iron, lead, tin, bismuth and zinc compounds.

26. The process as claimed in claim 16, wherein the molar ratio of isocyanate-reactive groups to isocyanate groups in the reaction mixture on commencement of process step c) is at most 0.3:1.

27. A surface coating obtainable by the process as claimed in claim 16.

28. A surface coated with a surface coating as claimed in claim 27.

29. The surface as claimed in claim 28, wherein the surface is selected from the group consisting of mineral substances, metal, rigid plastics, flexible plastics, textiles, leather, wood, wood derivatives and paper.

30. The use of a polyisocyanate composition A) which contains oligomeric polyisocyanates and is low in monomeric polyisocyanates, in the presence of at most 0.5% by weight of organic and inorganic iron, lead, tin, bismuth and zinc compounds in the reaction mixture for production of surface coatings having high mechanical and/or chemical stability.

Description

EXAMPLES

[0113] Description of the Test Methods

[0114] Pendulum hardness analogously to DIN EN ISO 1522:2007-04: the pendulum damping test is a method of determining the viscoelastic properties of coatings to DIN EN ISO 1522 in a pendulum damping instrument and is thus a measure of the hardness thereof. It consists of a sample table on which a pendulum can swing freely on a sample surface and a counter. The number of swings in a defined angle range is a measure of the hardness of a coating and is reported in seconds or number of swings.

[0115] Abrasion resistance in the Taber Abraser instrument with CS10 friction rolls (moderate hardness). The coating materials are applied to specimens. After the appropriate curing time, the test is conducted. The specimen (substrate with coating) is weighed and the starting weight is ascertained. The number of friction cycles after which the weight of the specimen and hence the abrasion is weighed is fixed beforehand. The specimen is secured in the sample holder, the friction rolls and suction are applied, and the abrasion test is started. For the determination of abrasion resistance, the weight loss is measured. The specimen is scratched with a fixed number of rotation cycles and the proportion of the sample abraded is ascertained by difference weighing.

[0116] Hardness test by DUR-O-Test: The instrument consists of a sleeve into which a spiral spring has been inserted, which can be set to different tensions with the aid of a slide adjuster. The spring acts on a cemented carbide stylus ( 1 mm), the tip of which projects out of the sleeve. A locking screw fixes the slide adjuster and hence keeps the spring tension constant. In this way, the stylus can be loaded with different force. Three compression springs of different spring force cover a hardness range of 0-20 N. The load that causes a visible scar on the film is ascertained.

[0117] Chemical Stability

[0118] Coating surface stability to test substance: The cured coating films are examined for their stability to test substances (DIN EN ISO 4628-1 to -5:2016-07). The coating film is generally on a glass plate. A small cottonwool bud is soaked with the test substance and placed onto the coating surface. Evaporation of the test substance is prevented by covering it, for example by means of a watch glass or test tube. The cottonwool bud or cellulose does not dry out. After a contact time fixed beforehand, the bud soaked with test substance is removed, the contact site is dried off, and an immediate assessment is made in order to anticipate regeneration of the paint surface. The test surface is checked for changes visually and by touching by hand. An assessment is then made as to whether and what changes have occurred on the test surface.

[0119] Softening and discoloration of the coating surface are assessed.

0=no changes detectable
1=only visible change
2=minor softening/slight change in hue
3=distinct softening/moderate change in hue
4=significant softening/significant change in hue
5=coating completely destroyed without outside action/very significant change in hue

[0120] Anti-Graffiti Properties of Surfaces

[0121] The cured coating films are assessed for their resistance to graffiti and the corresponding detergents. Paint from a spray can (RAL 4005 blue lilac, RAL 6001 emerald green, RAL 9005 black), Edding 3000 Permanent Marker Red and HS-DOT 4 brake fluid are applied to the painted surface and left to dry at 50 C. for 48 hours. After cooling, AGS 221 graffiti remover surfactant is applied by brush and removed after a contact of 5 minutes. The cycle is repeated up to 10 times and the change is assessed visually, with the following classifications:

0=no changes detectable
1=only visible change
2=minor softening/slight change in hue
3=distinct softening/moderate change in hue
4=significant softening/significant change in hue
5=coating completely destroyed without outside action/very significant change in hue [0122] Sample 0: Clearcoat based on the aliphatic polyisocyanate Desmodur N 3300 (97% by weight) and catalyst (3% by weight). The catalyst mixture contained 0.177 g of potassium acetate, 0.475 g of 18-crown-6 and 3.115 g of diethylene glycol. This catalyst mixture was used for all inventive examples.

Example 1.1: Pendulum Hardness

[0123] Coating Formulations: [0124] Sample 1.1: Clearcoat based on the amino-functional resins Desmophen NH 1450 and Desmophen NH 1520 (1:1) crosslinked with the aliphatic polyisocyanate Desmodur N 3300 with an equivalents ratio of 1.5 [0125] Sample 1.2: Clearcoat based on the amino-functional resins Desmophen NH 1450 and Desmophen NH 1520 (1:1) crosslinked with the aliphatic polyisocyanate Desmodur N 3800 with an equivalents ratio of 1.5

[0126] Application:

[0127] The coatings were applied to various substrates by means of a drawdown bar. After a defined curing time and temperature, pendulum hardness and chemical and mechanical film properties are measured.

[0128] Sample 0:

[0129] 80 m of wet coating material with spiral coating bar on glass plate, Q-Panel steel and aluminum; curing at 180 C. for 30 minutes and at RT for 7 days

[0130] Samples 1.1 and 1.2:

[0131] 80 m of wet coating material with spiral coating bar on glass plate, Q-Panel steel and aluminum; curing at RT for 7 days

TABLE-US-00001 TABLE 1 Comparison of various coating formulations Sample 1.1 Desmophen Sample 1.2 NH 1420/ Desmophen Sample 0 NH 1520 NH 1420/ Desmodur Desmodur NH 1520 N 3300 N 3300 N 3800 Pendulum hardness 190 s 200 s 55 s (Knig) after 7 days Scratch resistance 4N 1N <1N (DUR-O-Test) after 28 d Abrasion resistance 8 mg 50 mg 5 mg CS 10, weight 1000 g, 1000 revolutions Chemical stability after 28 days at RT Acetone, 1 min 0 1 3 Ethanol, 5 min 0 1 2 Ethanol, 50% 30 min 0 1 1 Water, 1 h 0 0 0

Example 1.2: Curing at Room Temperature

[0132] Sample 0 from example 1 was applied to glass plates by means of a drawdown bar. After a defined curing time and curing conditions, pendulum hardness has been determined.

TABLE-US-00002 TABLE 2 Properties of the coating materials as a function of drying temperature Coating properties after different drying conditions 50 m, on glass 15 min. 150 C. RT Pendulum hardness (Knig) after 1 d 195 s tacky Pendulum hardness (Knig) after 7 d 205 s 210 s

Example 1.3: Chemical Stability

[0133] The application test compares the coating of the invention with 2-component polyurethane systems that are recommended for high stabilities.

[0134] Coating Materials: [0135] Sample 3.1: 2-component water-based polyurethane clearcoat based on the acrylate polyol Bayhydrol A 2695 crosslinked with the hydrophilized polyisocyanate Bayhydur 304 with an equivalents ratio of 1.5 [0136] Sample 3.2: 2-component water-based polyurethane clearcoat based on the acrylate polyol Bayhydrol A 2695 crosslinked with the hydrophilized polyisocyanate Bayhydur 3100 with an equivalents ratio of 1.5

[0137] Application:

[0138] Sample 0: 50 m of wet coating material by spiral coating bar onto Makrofol; curing at 180 C. for 15 minutes;

[0139] Samples 3.1 & 3.2: 70 m of wet coating material by spiral coating bar onto Makrofol; curing at 60 C. for 30 minutes and at 60 C. for 960 min

[0140] Sample 0 shows no defect in the film even after 10 cycles.

TABLE-US-00003 TABLE 3 Chemical stability of the coating materials Blue Emerald Jet Number lilac green black of RAL RAL RAL Edding cycles 4005 6001 9005 red HS-DOT Sample 0 7 0 0 0 0 0 Sample 3.1 7 0 0 0 1 5 Sample 3.2 7 5 4 5 5 5 Sample 0 10 0 0 0 0 0

Example 2: Comparative Experiment to Determine the Effect of Dibutyltin Laurate on the Properties of the Coating

[0141] The standard temperature is 23 C. All experiments were conducted under standard climatic conditions (SCC), at 23 C. and 50% relative humidity.

[0142] Desmodur BL 3175 SN, Desmodur BL 4265 SN, Desmodur BL 3272 MPA, Desmodur BL 2078/2 SN, Desmodur PL 340 BA/SN and Desmodur PL 350 MPA/SN are commercially available materials from Covestro AG. They are abbreviated hereinafter to BL 3175, BL 4265, BL 3272 MPA, BL 2078/2 SN, PL 340 BA/SN and PL 350 MPA/SN.

[0143] The chemicals used here were sourced from Sigma-Aldrich, unless mentioned otherwise. Commercial products were sourced from the appropriate companies.

[0144] The amounts and quantitative ratios used in the experiments are based on the solids content or solids ratio.

[0145] Preparation of the Catalyst Composition

[0146] Catalyst 1 was prepared by dissolving 1.8 g of 18-crown-6 and 1.2 g of potassium octoate successively in 57 g of methoxypropyl acetate at room temperature. The catalyst was used without further purification.

[0147] The deblocking temperature of blocked polyisocyanates can be lowered by addition of suitable catalysts. Accelerated deblocking inevitably enables faster crosslinking of the polyisocyanates. Table 4 summarizes the results of the studies of catalytic deblocking: the addition of DBTL in the presence of example 1 does not lead to faster crosslinking, but reduces the film hardnesses. This is already true of the addition of 0.1% by weight of DBTL and even more clearly for 1.0% by weight of DBTL.

TABLE-US-00004 TABLE 4 Effect of DBTL as cocatalyst on curing and crosslinking of the polyisocyanurate coating compositions. The sample temperature was 220 C., 10 minutes; oven temperature 250 C. Ratio (BL 3175:BL Amount Knig pendulum No. Sample 4265 Catalyst (% by wt.) damping (s) 1 BL 3175 SN/BL 4265 SN 10:0 Cat. 1 0.1 174 2 BL 3175 SN/BL 4265 SN 9:1 Cat. 1 0.1 159 3 BL 3175 SN/BL 4265 SN 8:2 Cat. 1 0.1 173 4 BL 3175 SN/BL 4265 SN 5:5 Cat. 1 0.1 181 5 BL 3175 SN/BL 4265 SN 2:8 Cat. 1 0.1 191 6 BL 3175 SN/BL 4265 SN 10:0 Cat. 1/DBTL 0.1/0.1 159 7 BL 3175 SN/BL 4265 SN 9:1 Cat. 1/DBTL 0.1/0.1 162 8 BL 3175 SN/BL 4265 SN 8:2 Cat. 1/DBTL 0.1/0.1 140 9 BL 3175 SN/BL 4265 SN 5:5 Cat. 1/DBTL 0.1/0.1 168 10 BL 3175 SN/BL 4265 SN 2:8 Cat. 1/DBTL 0.1/0.1 173 11 BL 3175 SN/BL 4265 SN 10:0 Cat. 1/DBTL 0.1/1 87 12 BL 3175 SN/BL 4265 SN 9:1 Cat. 1/DBTL 0.1/1 135 13 BL 3175 SN/BL 4265 SN 8:2 Cat. 1/DBTL 0.1/1 95 14 BL 3175 SN/BL 4265 SN 5:5 Cat. 1/DBTL 0.1/1 118 15 BL 3175 SN/BL 4265 SN 2:8 Cat. 1/DBTL 0.1/1 164