HK1087397B - Blocked biuretized isocyanates - Google Patents

Description

Blocked biuretized isocyanates

Background

Biuretization of isocyanates is known in the art. U.S. Pat. nos. 3903127 and 396622 describe various biuretizing agents, including primary aliphatic amines. The use of tertiary alcohols or mixtures of water and tertiary alcohols to biuretize isocyanates is described in canadian published application CA 2211025. Finally, U.S. Pat. No. 4220749 describes the use of secondary monoamines as biuretizing agents. All three references describe the use of 1, 6-hexamethylene diisocyanate as the starting isocyanate.

It is also known to use isocyanate curing agents in coating compositions, with polyisocyanates having an isocyanate functionality of 3 or greater being particularly preferred. U.S. patent application publication 2003/0109664 describes the production of high functional polyisocyanates by biuretizing polyisocyanates containing isocyanate groups. Among the starting isocyanates, the trimer of 1, 6-hexamethylene diisocyanate is used. The biuretizing agent used is water. The patent application shows that trimer-containing isocyanates biuretized with water alone exhibit better color when compared to isocyanates biuretized with t-butanol or a mixture of t-butanol and water. The patent application also broadly shows that the isocyanate groups of biuretized isocyanates can be blocked with alcohols, ketimines or oximes, etc. Although the biuretized isocyanates described in this application are an improvement over the prior art biuretized isocyanates, there is still a need to increase the gel content and abrasion resistance of coatings prepared from such isocyanates.

A wide variety of blocking agents are known in the prior art (see, e.g., "Blocked Isocynate in coatings", Potter et al, report on Water-Borne & Higher-Solids Coating Symposium, New Australian well held at 2.1986). Among the blocking agents are i) phenol, cresol and aliphatic long chain substituted phenols (such as isononylphenol), ii) amides (such as epsilon-caprolactam), iii) oximes (such as butanone oxime), iv) compounds containing active methylene groups (such as malonic esters and acetoacetic esters and v) sodium bisulfite. Various capping agents are also described in us patents 4324879, 4439593, 4495229, 4518522, 4667180, 5071937, 5705593, 5780541, 5849855, 6051675, 6060573, 6274693, 6368669 and 6583216.

More recently, secondary amines such as N-benzyl-tert-butylamine (published European patent application 1375551, corresponding to U.S. patent application Ser. No. 10/459033, filed 6 months 2003) and methyl 3-tert-butylaminopropionate (published PCT patent application WO 2005/000936, corresponding to U.S. patent application Ser. No. 10/874716, filed 6 months 2004) have been described as useful capping agents.

Disclosure of Invention

The present invention relates to a blocked biuret group-containing polyisocyanate composition, wherein the blocked isocyanate functionality of the polyisocyanate composition is at least 4 and is prepared by a process comprising the steps of:

A) reacting a polyisocyanate adduct with a biuretizing agent to introduce biuret groups into said polyisocyanate, wherein the polyisocyanate adduct:

a) from aliphatic and/or cycloaliphatic diisocyanates,

b) has an average isocyanate functionality of at least 2.5, and

c) containing an isocyanurate group or a group selected from the group consisting of,

and

B) mixing polyisocyanate containing biuret with malonic acid di-C₁-C₁₂Alkyl and/or alkoxyalkyl esters and acetoacetic acid C₁-C₁₂Capping agents for alkyl and/or alkoxyalkyl esters.

Detailed Description

Suitable starting polyisocyanates for preparing the polyisocyanates according to the invention are the polyisocyanate adducts according to a), b), c):

a) from aliphatic and/or cycloaliphatic diisocyanates, preferably aliphatic diisocyanates, more preferably 1, 6-hexamethylene diisocyanate,

b) having an average isocyanate functionality of at least 2.5, preferably at least 2.8, more preferably at least 3.0; and

c) containing isocyanurate groups.

The NCO content of the starting polyisocyanate adducts is preferably from 10 to 25% by weight, more preferably from 12 to 25% by weight, most preferably from 15 to 25% by weight; the upper limit of the functionality is preferably 8, more preferably 7, most preferably 6. The starting materials for preparing the polyisocyanate adducts preferably contain at least 70% by weight, more preferably at least 80% by weight, most preferably 90% by weight, of aliphatic diisocyanate, most preferably 1, 6-hexamethylene diisocyanate.

The starting isocyanurate group-containing polyisocyanate adducts are known and can be prepared in accordance with the teachings of U.S. Pat. No. 4,4324879, which is incorporated herein by reference. In the present invention, these adducts are generally preferred starting materials. Useful examples of such isocyanurate group-containing polyisocyanate adducts are trimers formed from aliphatic and/or cycloaliphatic diisocyanates. Trimers of aliphatic diisocyanates, such as the trimer of 1, 6-hexamethylene diisocyanate sold under the trade name Desmodur N3390 from Bayer Polymers LLC, are most preferred.

Essentially any aliphatic and/or cycloaliphatic diisocyanate can be used to form the starting polyisocyanate adducts. Useful diisocyanates include, but are not limited to, 1, 6-hexamethylene diisocyanate, dicyclohexyl diisocyanate, 1, 4-cyclohexyl diisocyanate, bis (4-isocyanatocyclohexyl) methane, 3-isocyanatomethyl-3, 5, 5-trimethylcyclohexyl isocyanate ("isophorone diisocyanate"), and the like.

To prepare the biuret group-containing polyisocyanates according to the invention, the starting polyisocyanate adducts are reacted in the presence of biuretizing agents known in the art. Such biuretizing agents include water, secondary monoamines and tertiary alcohols. Water is used as a biuretizing agent as described in us patents 3124605 and 3903127, the disclosures of which are incorporated herein by reference.

The use of secondary monoamines to prepare biuretized isocyanates is described in U.S. patent 4220749, the disclosure of which is incorporated herein by reference. In general, the secondary amines are of the general formula: (R)₁)(R₂) NH wherein R₁And R₂May be the same or different and represents an aliphatic hydrocarbon group having 1 to 20 carbon atoms. Specific useful secondary monoamines include dimethylamine, diethylamine, dipropylamine, dibutylamine, bis (2-ethylhexyl) amine. The isocyanate and amine are reacted at an equivalent ratio of isocyanate to amine of from about 4:1 to about 14:1 to introduce biuret groups into said polyisocyanate. The reaction is carried out at a temperature of about 0 to 140 deg.C, preferably 60 to 140 deg.C, more preferably 70 to 140 deg.C.

Finally, the use of tertiary alcohols and mixtures of tertiary alcohols with water is described in canadian published application CA2211025, the disclosure of which is incorporated herein by reference.

The resulting biuret group-containing polyisocyanates have an isocyanate functionality of at least 4, preferably at least 4.5, more preferably at least 4.8 and an NCO content of from about 8 to about 24 weight percent, preferably from about 10 to about 22 weight percent, more preferably from about 10 to about 20 weight percent, based on the weight of the polyisocyanate. The resulting polyisocyanate preferably has a maximum functionality of 10, more preferably 8, and most preferably 7. The product can be used by appropriate dilution in a solvent.

The molecular weight of the product was calculated by GPC using polystyrene as a standard. The resulting biuret group-containing polyisocyanates have a number average molecular weight of from about 500 to about 10000, preferably from about 500 to about 5000, and most preferably from about 500 to about 3000.

Using the process of the present invention, biuret-containing polyisocyanates can be prepared continuously or batchwise.

The products obtained by the present process are distinguished in particular by their low viscosity and low molecular weight in combination with a high isocyanate functionality and a high reactivity towards binders in coatings which contain isocyanate-reactive groups, for example polyacrylates containing hydroxyl groups. Further advantages are that they are easy to prepare, the volatile isocyanate content does not increase even on prolonged storage, since these compounds are relatively stable and do not decompose into monomers; they contain standard isocyanate groups which do not require further conditioning removal; the product is storage-stable with respect to viscosity increase and the product is substantially colorless, which is particularly important for clear coat systems.

Then, the product obtained by the method is used for preparing the malonic acid di-C₁-C₁₂Alkyl and/or alkoxyalkyl esters and acetoacetic acid C₁-C₁₂Capping with an alkyl and/or alkoxyalkyl ester capping agent. Particularly useful malonates include diethyl malonate, dimethyl malonate, diisopropyl malonate, di-n-propyl malonate, di-n-butyl malonate, ethyl-n-butyl malonate, methyl-n-butyl malonate, and the like. Particularly useful acetoacetates are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, or dodecyl acetoacetate. Preferred alkyl acetoacetates and/or alkoxyalkyl esters are those having 1 to 6 carbon atoms in the alkyl group. Diethyl malonate and ethyl malonate are the most preferred capping agents. Other examples of useful malonates and acetoacetates can be found in, for example, U.S. patents 4439593, 4518522, 46771805071937, 5780541, 5849855, 6060573, and 6274693. Generally, the reaction is carried out at less than 120 ℃, preferably at 40 ℃ to 80 ℃. Adding known catalystsThe agent is allowed to remain slightly exothermic. The reaction is carried out for about 2 to 6 hours after the catalyst addition. The desired material ratio is one equivalent of blocking agent to one equivalent of isocyanate. The actual ratio is 1. + -. 0.05 equivalents of blocking agent per equivalent of isocyanate.

The products of the invention are particularly suitable as curing agents in coating compositions, in particular in automotive coatings. The coating compositions of the present invention generally contain a film-forming binder comprising an isocyanate-reactive oligomer or polymer or a dispersed gel polymer, and a blocked biuret group-containing polyisocyanate curing agent as described above.

As indicated above, the present coating composition is particularly suitable for use as a clear coat in automotive refinishing and finishing, but it may also be pigmented with conventional pigments and used as a monocoat or basecoat or even as an undercoat such as a primer or sealer. These coatings may also be used in non-automotive applications, such as in industrial and construction applications.

Coatings prepared from the blocked isocyanates of the present invention exhibit better curing properties as indicated by increased gel content at low curing temperatures than similar products prepared from other blocking agents. In addition, the coatings from the blocked isocyanates of the present invention exhibit improved abrasion and mar resistance.

In the following examples, all parts and percentages are by weight unless indicated to the contrary, and the following materials were used:

DESMO800desmophen 800-a polyester having an OH content of 8.8%, 100% solids, and a viscosity of about 170000 centipoise, available from Bayer MaterialScience.

CGLCGL-052L 2-hindered amine light absorber based on hydroxy functional triazine, available from Ciba specialty Chemicals, supplied as 60% solids in PM acetate (propylene glycol monomethyl ether acetate).

T-928-Tinuvin-ultraviolet absorber based on hydroxyphenylbenzotriazole, commercially available from Ciba specialty Chemicals.

Bay OL-Baysilone OL-017-polyether modified methylpolysiloxanes, commercially available from Borchers, sold as flow promoters.

n-BA/PMA/EEPN-butyl acetate (CAS #123-86-4), PM acetate (CAS #108-65-6, also known as propylene glycol monomethyl ether acetate) and Ekatapro EEP from Eastman (CAS #763-69-9, also known as ethyl 3-ethoxypropionate) the ratio of 4: 5: 6. .

Examples

In the examples, example 3 is a comparative example.

Polyisocyanate 1To a 5 liter round bottom flask equipped with a stirrer, nitrogen inlet, thermocouple and heater, 2550 parts (13.14 equivalents) of Desmodur N3300 polyisocyanate (a trimer of solvent-free hexane diisocyanate having an NCO content of about 22% by weight and a viscosity of about 2500 mPa.s at 25 ℃ C., available from Bayer MaterialScience LLC), 450 parts of butyl acetate, 0.128 part of dibutyl phosphate catalyst and 16.60 parts (0.92 equivalents) of distilled water were added and mixed until homogeneous. The reaction was heated at 65 ℃ for 1 hour, then at 90 ℃ for half an hour, then at 120 ℃ for half an hour, and finally at 140 ℃ for 7 hours. After the heating period was complete, the reaction was cooled to room temperature. The isocyanate content was 14.52% by weight (theoretical 14.16%). Viscosity was 6800 cps at 25 ℃. The functionality is about 6 isocyanate groups per molecule.

Polyisocyanate 2To a 5 liter round bottom flask equipped with stirrer, nitrogen inlet, thermocouple and heater, 2500 parts (12.88 equivalents) of Desmodur N3300 polyisocyanate, 700 parts of butyl acetate, 5 parts of dibutyl phosphate catalyst and 297 parts (2.30 equivalents) of N, N-dibutylamine were added and mixed until homogeneous. The reaction was heated to 65 ℃ 1For an hour, then at 90 ℃ for half an hour, then at 120 ℃ for 5 hours, and finally at 140 ℃ for 2 hours. After the heating period was complete, the reaction was cooled to room temperature. The isocyanate content was 10.5% by weight (theoretical 10.0%). The viscosity at 25 ℃ was 1980 cps. The functionality is about 6 isocyanate groups per molecule.

Blocked isocyanates 1To a2 liter round bottom flask equipped with stirrer, nitrogen inlet, thermocouple, heater and addition funnel was added 405.0 parts (1.40 equivalents) of polyisocyanate 1, 104.4 parts (0.71 equivalents) of diethyl malonate, 92.9 parts (0.71 equivalents) of ethyl acetoacetate and 142.8 parts of butyl acetate and mixed until homogeneous. When the catalyst (1.72 parts of 30% sodium methoxide in methanol and 10 parts of diethyl malonate) was added dropwise, the reaction mixture was heated to 50 ℃. The reaction exothermed and as a result, the temperature rose to 68 ℃. The reaction was heated to 80 ℃ and held for one and a half hours at which the isocyanate content obtained by titration was zero. 142.7 parts of n-butanol are added. 4 parts of dibutyl phosphate are then added to neutralize the solution. Viscosity at 25 ℃ is 2085 centipoises. The density was 8.81 lbs/gal. The calculated isocyanate content was 7.41% and the equivalent weight of NCO was 567.

Blocked isocyanates 2To a2 liter round bottom flask equipped with stirrer, nitrogen inlet, thermocouple, heater and addition funnel was added 243.4 parts (0.79 equivalents) of polyisocyanate 2, 64.1 parts (0.4 equivalents) of diethyl malonate, 51.4 parts (0.40 equivalents) of ethyl acetoacetate and 120 parts of butyl acetate and mixed until homogeneous. When catalyst (0.96 parts of sodium methoxide at 30% in methanol and 10.95 parts of diethyl malonate) was added dropwise, the reaction was heated to 35 ℃. The reaction exothermed and as a result, the temperature rose to 68 ℃. The reaction was heated to 70 ℃ and held for two and a half hours at which the isocyanate content obtained by titration was zero. 65 parts of n-butanol are added. 4 parts of dibutyl phosphate are then added to neutralize the solution. The viscosity at 28 ℃ was 63 cps. The density was 8.36 lbs/gal. The calculated isocyanate content was 6.08% and the equivalent weight of the NCO was 690.

Blocked isocyanates 3Desmodur BL XP 2434-diethyl malonate blocked trimer (without biuret groups) commercially available from Bayer MaterialScience LLC with a blocked isocyanate group content of 7.0%, an NCO equivalent weight of 600, 65% solids and a viscosity of 3000 cps at 25 ℃.

The coating compositions tested are listed in table 1 below and the results obtained are listed in tables 2 to 5. The composition was applied using a siphon gun type Binks95 to form a wet film having a thickness of about 4 mils. After removing the water for 15 minutes, the panel is cured depending on its desired temperature range.

The tests performed were as follows:

MEK double scrub: the 2 pound spherical hammer was wrapped with several layers of cheesecloth. The cloth was saturated with MEK. The hammer was placed at 90 degrees to the surface and moved back and forth in an area of 4 ". Every 25 rubs of cloth, the MEK was soaked once more. The test was run until the coating was damaged or rubbed up to 200 times. The number of rubs required to damage the coating was recorded.

Gel content: a known weight of uncoated film was placed in a stainless steel wire mesh screen. They were then left in boiling acetone for 7 hours to remove any extractable material. The coating film was then reweighed to determine and report the total weight of solids retained.

Hardness of pendulum collision: the coated glass sheet was placed in a Koenig pendulum hardness tester and the number of pendulum returns of the clock hammer before its deflection angle was too low was recorded. All coatings were compared to the hardness of glass (172- & 185 times).

Rubbing and damage: in a CM-5 Atlas AATCC crockfastness tester. A piece of wool cloth (Atlas14-9956-00) was placed directly on an acrylic finger (acrylic finger). Then a Bon Ami cleaner was applied to the coated side, gently patted off the excess. Rubbing the coated surface back and forth for ten times, and cleaningAnd then drying. Scratch resistance was determined by the percent of 20% gloss retention read from the direction perpendicular to the rubbing direction.

TABLE 1

Examples	1	2	3
				Isocyanates	Blocked isocyanates 1	Blocked isocyanates 2	Blocked isocyanates 3
Parts by weight of isocyanate	468.79	440.85	392.52
				Parts by weight, Desmo800	143	154.32	128.78
Parts by weight CGL6.74	6.74	6.77	6.89
				Parts by weight, T-92840.42	40.42	40.6	41.33
Parts by weight Bay OL	4.17	4.19	4.26
				Parts by weight, n-BA/PMA/EEP	159.48	190.56	249.12

TABLE 2

Examples	1	2	3
				Curing temperature, F, back and forth
175	11	5	4
				194	22	11	18
212	57	28	43
				230	22	29	36
248	66	57	65

[0053] TABLE 3

Examples	1	2	3
				Cure temperature, F, gel
175	58.4	0	0.7
				194	79.8	56.8	47.2
212	87.7	81.6	75.9
				230	94.5	87.3	75.9
248	94.7	94	77

TABLE 4

Examples	1	2	3
				Curing temperature, F, hardness
175	Adhesive bonding	2	9
				194	5	4	32
212	7	4	66
				230	22	5	81
248	31	17	74

TABLE 5

Examples	1	2	3
				Curing temperature, F, friction
175	21.9	0.9	6.7
				194	79.2	82.9	36.6
212	99.4	95.2	78.6
				230	99.8	93.8	82.8
248	99	99.3	79.3

Claims (7)

1. A blocked biuret group-containing polyisocyanate composition wherein the blocked isocyanate functionality of the polyisocyanate composition is at least 4 and is prepared by a process comprising:

A) reacting a polyisocyanate adduct with a biuretizing agent to introduce biuret groups into the polyisocyanate, the polyisocyanate adduct:

a) from aliphatic and/or cycloaliphatic diisocyanates,

b) has an isocyanate functionality of at least 2.5, and

c) containing isocyanurate groups, and

B) mixing polyisocyanate containing biuret with malonic acid di-C₁-C₁₂Alkyl or alkoxyalkyl esters and acetoacetic acid C₁-C₁₂Capping agents of alkyl or alkoxyalkyl esters.

2. The composition of claim 1 wherein the adduct has an isocyanate functionality of at least 2.8.

3. The composition of claim 2 wherein the adduct has an isocyanate functionality of at least 3.0 and an isocyanate functionality of at most 8.

4. The composition of claim 1 wherein component a) is an aliphatic diisocyanate.

5. The composition of claim 1, wherein the biuretizing agent is selected from the group consisting of water, secondary monoamines, and tertiary alcohols.

6. The composition of claim 1, wherein the blocking agent is a malonate selected from the group consisting of diethyl malonate, dimethyl malonate, diisopropyl malonate, di-n-propyl malonate, di-n-butyl malonate, ethyl-n-butyl malonate, methyl-n-butyl malonate.

7. The composition of claim 1, wherein the capping agent is an acetoacetate ester selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl acetoacetate esters.