WO2012131050A1

WO2012131050A1 - Aqueous, hydroxyl functional acrylic copolymerisate dispersions

Info

Publication number: WO2012131050A1
Application number: PCT/EP2012/055824
Authority: WO
Inventors: Peter Hoffmann; Anthony J. Tye
Original assignee: Basf Coatings Gmbh
Priority date: 2011-04-01
Filing date: 2012-03-30
Publication date: 2012-10-04

Abstract

Aqueous acrylic copolymerisate dispersion, obtainable by the steps of A) subjecting a monomer mixture comprising a) at least one hydroxyl functional vinyl, acrylate or methacrylate monomer, b) at least one acid functional vinyl, acrylate or methacrylate monomer, and c) at least one vinyl, acrylate or methacrylate monomer that is not hydroxyl functional and not acid functional, to free radical polymerisation in the presence of d) 10 - 40 wt.-%, based on the total weight of the monomers a), b) and c), of at least one polyol selected from the group consisting of castor oil and castor oil based polyol derivatives, having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g, yielding an acrylic copolymerisate composition, B) adding a neutralizing agent to the acrylic copolymerisate composition of step A), and C) dispersing the mixture resulting from step B) in water. Process for the production of the aqueous dispersion, coating compositions comprising the aqueous dispersion and substrates coated therewith.

Description

AQUEOUS, HYDROXYL FUNCTIONAL ACRYLIC COPOLYMERISATE DISPERSIONS

BACKGROUND OF THE INVENTION

The invention relates to aqueous hydroxyl functional acrylic copolymerisate dispersions, a process for their production, coating compositions comprising the aqueous dispersions, and substrates coated with these coating compositions.

Aqueous hydroxyl functional acrylic copolymerisate dispersions are known in the art. For example, an aqueous hydroxyl functional polyacrylate dispersion is commercially available from Bayer MaterialScience under the trade name Bayhydrol® XP 2470.

EP 1699835 A1 describes aqueous, hydroxyl functional binder dispersions that can be used in coating materials. The hydroxyl functional binders are prepared by subjecting specific vinyl and/or (meth)acryl monomers to free radical polymerisation in the presence of compounds containing lactone groups.

However, the aqueous, hydroxyl functional acrylic copolymerisate dispersions of the state of the art show the disadvantage of high sensitivity to water of the dried films. This is particularly disadvanteageous since the resultant film must also withstand exterior exposure to rain, moisture and high humidity conditions.

It is thus an object of the present invention to provide aqueous, hydroxyl functional acrylic copolymerisate dispersions that show improved film appearance after water spot introduction.

SUMMARY OF THE INVENTION

The present invention is directed to aqueous hydroxyl functional acrylic copolymerisate dispersions that are prepared by first subjecting a monomer mixture comprising hydroxyl functional, acid functional, and further vinyl, acrylate and/or methacrylate monomers to free radical polymerisation in the presence of castor oil and/or castor oil based polyol derivatives having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g, subsequently adding a neutralizing agent to the resulting acrylic copolymerisate composition and dispersing the mixture in water. The aqueous hydroxyl functional acrylic copolymerisate dispersions of the present invention display reduced water sensitivity of the dried films. The present invention is also directed to a process for the production of the aqueous dispersions, to coating compositions comprising the aqueous dispersions and a method for producing these coating compositions, and to substrates coated with these coating compositions. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides aqueous acrylic copolymerisate dispersions obtained by the steps of

A) subjecting a monomer mixture comprising

a) at least one hydroxyl functional vinyl, acrylate or methacrylate monomer, b) at least one acid functional vinyl, acrylate or methacrylate monomer, and c) at least one vinyl, acrylate or methacrylate monomer that is not hydroxyl functional and not acid functional

to free radical polymerisation in the presence of

d) 10 - 40 wt.-%, based on the total weight of the monomers a), b) and c), of at least one polyol selected from the group consisting of

castor oil and castor oil based polyol derivatives,

having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g,

yielding an acrylic copolymerisate composition,

B) adding a neutralizing agent to the acrylic copolymerisate composition of step A), and

C) dispersing the mixture resulting from step B) in water.

The invention further provides the described process for producing the aqueous dispersions of the invention. It has been found that these aqueous dispersions display reduced water sensitivity of the dried films.

Described is a process to economically produce low solvent content, low volatile organic content (VOC), water-borne (aqueous), hydroxyl functional acrylic copolymerisate dispersions that are suitable for use in a two-component (2K) water- borne coating composition. The process utilizes natural oil polyols selected from castor oil and castor oil based polyol derivatives, having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 1 60 to 400 mg KOH/g, as a portion of the reactor charge during the synthesis of the acrylic copolymerisate by free radical polymerisation. These natural oil polyols reduce the viscosity of the polymerization mass and also act as a hydrophobic polyol diluent to the ultimate coating composition, thereby drastically reducing the need for volatile organic solvents. These natural oil polyols have the additional advantage of being produced from renewable resources. The neutralized and water dispersed finished acrylic copolymerisate binder has the additional advantage of being emulsifier free. The use of emulsifiers to provide water dispersability for a binder copolymerisate generally compromises the water resistance of the cast film. The monomer mixture of step A) comprises a) at least one hydroxyl functional vinyl, acrylate or methacrylate monomer, b) at least one acid functional vinyl, acrylate or methacrylate monomer, and c) at least one vinyl, acrylate or methacrylate monomer that is not hydroxyl functional and not acid functional. The at least one hydroxyl functional monomer a) is needed for introducing hydroxyl functionality to the copolymerisate. The acid functional monomer b) is capable of forming an ionic pair with another compound (e.g. a neutralizing agent) in order to provide hydrophilic groups for water dispersability. The remainder c) of the monomers may have alkyl chains from 1 to 18 carbon atoms, and/or may be aromatic, linear aliphatic, branched aliphatic or cycloaliphatic.

Examples of hydroxyl functional monomers a) include hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate. A preferred hydroxyl functional monomer a) is hydroxyethyl methacrylate.

Examples of acid functional monomers b) include acrylic acid, methacrylic acid, beta- carboxy ethyl acrylate, phosphoric acid methacrylate, and phosphonic acid methacrylate. A preferred acid functional monomer b) is acrylic acid.

Examples of the monomers c) that are not hydroxyl functional and not acid functional include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, isodecyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, isobornyl methacrylate, trimethyl cyclohexyl methacrylate, 2-ethylhexyl methacrylate, ethyl acrylate, n-butyl acrylate, isodecyl acrylate, cyclohexyl acrylate, lauryl acrylate, isobornyl acrylate, 2-ethylhexyl acrylate, styrene and vinyl toluene.

Preferred monomers c) are methyl methacrylate, n-butyl methacrylate, lauryl methacrylate, ethyl acrylate, n-butyl acrylate and styrene.

Optionally a small amount of a divinyl or di(meth)acrylate monomer may be included to increase the molecular weight of the copolymerisate. Examples include divinyl benzene, 1 ,6-hexanediol diacrylate and 1 ,6-hexanediol dimethacrylate.

In an especially preferred embodiment, the at least one hydroxyl functional monomer a) is hydroxyethyl methacrylate, the at least one acid functional monomer b) is acrylic acid, and the monomers c) are selected from methyl methacrylate, n-butyl methacrylate, lauryl methacrylate, ethyl acrylate, n-butyl acrylate and/or styrene.

The free radical polymerization is conducted between 80 °C and 160°C. The free radical source for the polymerization reaction is typically a peroxide initiator, however, it may also be an azo compound. Examples of initiators include t-butyl peracetate, t- butyl per-2-ethylhexanoate, di-t-butyl peroxide and 2,2^'-azobis(methylbutyronitrile).

Optionally a mercaptan based chain transfer agent may be included to reduce the molecular weight of the copolymerisate. Examples include dodecanethiol, 2- mercaptoethanol and 3-mercaptopropionic acid.

The free radical polymerization is conducted in the presence of 10 - 40 wt.-%, based on the total weight of the monomers a), b) and c), of at least one polyol d) selected from the group consisting of castor oil and castor based polyol derivatives, having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g.

The term "10 - 40 wt.-%, based on the total weight of the monomers a), b) and c)" 5 means that if, for example, the sum of the weights of monomers a), b), and c) is 100 g, then 10 to 40 g of the polyol are used.

The number average molecular weight Mn of the polyol d) is determined by gel permeation chromatography using tetrahydrofuran as diluent and polystyrol i o standards.

Examples of suitable castor oil based polyol derivatives include Polycin® M-365, Polycin® T-400 and Polycin® D-265 from Vertellus Corporation.

15 The preferred embodiment of the free radical polymerization step A) is a 2-stage addition process with the first stage preferably low in hydrophilic groups such as acid groups, and the second stage rich in hydrophilic groups. The first stage is polymerized in the presence of solvent and the natural oil polyol. The second stage is then polymerized in the presence of the completed first stage. The ratio of the mass

20 of the first stage to the second stage may vary from 3:1 to 1 :1 . One of the advantages of the two stage process is that a stable water dispersion is possible at a very low hydrophilic group content.

The monomer compositions for each of the stages do not necessarily need to be 25 similar, however preferably, both stages contain at least one hydroxyl functional monomer a).

The organic solvents employed are typically miscible with water although minor amounts of water immiscible solvents may also be used. Glycol ethers as a class are 30 generally preferred as organic solvents. Examples include ethylene glycol monobutyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol mono-n-butyl ether. The organic solvent content of the completed dispersions typically range from 4 to 10 wt.-% of the completed dispersion. After the free radical polymerization step A) has been completed, a neutralizing base, typically an amine, is added to the reactor in step B), followed by a deionized water reduction in step C). The resultant dispersion typically has a translucent to milky- white appearance. The non-volatile content of the resultant dispersion is typically from 45 to 60%. The hydroxyl value of the completed dispersion is typically between 125 and 187 mg KOH/g. The acid value for the non-volatile portion of the dispersion is typically between 7 and 25 mg KOH/g. The number average molecular weight Mn of the dispersed copolymerisates is typically from 3000 to 10000 g/mol.

The non-volatile content of the dispersion is determined by method ISO 3251 for determining the non-volatile content of paints and varnishes.

The number average molecular weight Mn of the dispersed copolymerisates is determined by gel permeation chromatography using tetrahydrofuran as diluent and polystyrol standards.

Examples of suitable amines for use as a neutralizing agent in step B) include N- methylmorpholine, triethylamine, ethyldiisopropylamine, N,N-dimethylethanolamine, Ν,Ν-dimethylisopropanolamine, N-methyldiethanolamine, diethylethanolamine, triethanolamine, butanolamine, morpholine, 2-aminomethyl-2-methylpropanol and isophoronediamine. A preferred neutralizing agent for use in step B) is N,N- dimethylethanolamine. The neutralizing agent, or a mixture of neutralizing agents, is added in step B) in an amount such that in total a theoretical degree of neutralization of the acid groups of the copolymerisate of from 40 to 150% is reached, preferably of from 60 to 120%, and more preferably of from 95 to 105%. The theoretical degree of neutralization is calculated from the ratio of added basic groups of the neutralizing agent of step B) to the acid functional groups of the copolymerisate.

The pH of the aqueous dispersion is typically from 6 to 10, preferably from 7 to 9. The aqueous hydroxyl functional acrylic copolymerisate dispersion can be combined with a crosslinker, and optionally additives, to produce an aqueous, preferably thermosetting coating composition. The crosslinker is typically one that is water dispersible and contains functional groups that are reactive towards hydroxyl groups. Examples include melamine formaldehyde resins and preferably water dispersible polyisocyanate crosslinkers.

Thus, the present invention also provides for a coating composition, and a method of producing a coating composition comprising mixing the aqueous dispersion of the present invention with at least one OH-reactive crosslinker. The OH-reactive crosslinker is preferably a polyisocyanate crosslinker. Preferably, the coating composition is a two-component polyurethane coating composition, comprising at least the aqueous dispersion of the present invention and a polyisocyanate crosslinker.

Preferred crosslinkers are polyisocyanates that can be blocked or unblocked. Such polyisocyanates typically have two or more NCO groups per molecule and are based, for example, on isophorone diisocyanate, hexamethylene diisocyanate, 1 ,4- diisocyanatocyclohexane, bis(4-isocyanatocyclohexane)methane, 1 ,3-diisocyanato- benzene, triisocyanatononane or the isomeric 2,4- and 2,6-TDI and may further contain urethane, isocyanurate and/or biuret groups. Particularly preferred crosslinkers are HDI trimers and hydrophillic modified HDI trimers such as Bayer Material Science Bayhydur XP2600 and 2700 series hardeners. Glasurit SC29-0850 is suitable also.

The coating compositions comprising the aqueous dispersions of the invention are typically employed for producing primers, sealers, surfacers, pigmented or transparent topcoat materials, clearcoat materials and/or high gloss materials. These are typically applied in the field of industrial coating, automotive OEM finishing and automotive refinishing, for example.

The coating compositions can be applied to various substrates by standard application methods, such as e.g. brushing, rolling, knifecoating or spraying. Preferably, the coating compositions are applied to the substrates by spraying techniques, such as e.g. air-pressure spraying, airless spraying or electrostatic spraying, for example, using atomized spray guns.

The substrates are preferably metal or plastic substrates, more preferably metal substrates. In a highly preferred embodiment, the substrates are automotive metal parts. Generally, the substrates may be pre-treated or pre-coated by methods known in the art, e.g. sanding, solvent-cleaning or application of primers or further coatings.

Hardening of the coating compositions of the invention is performed by methods known in the art, e.g. by curing at room temperature or at elevated temperature, depending on the crosslinker used.

The following Examples are to illustrate the present invention without restricting it to the Examples.

EXAMPLES Chemicals used:

Polycin® D-265 (available from Vertellus Corporation) is a castor oil based diol (functionality = 2) having an equivalent weight of 212 and a hydroxyl value of 265 mg KOH/g

Polycin® D-365 (available from Vertellus Corporation) is a castor oil based derivative (functionality = 4) having an equivalent weight of 154 and a hydroxyl value of 365 mg KOH/g.

Dowanol PtB (available from The Dow Chemical Company) is propylene glycol t- butylether.

Dowanol PnP (available from The Dow Chemical Company) is propylene glycol propylether. Example 1

A 3 L reaction vessel with stirring, cooling and heating apparatus is charged with

183.7 g of Polycin D-265 and

50.0 g of Dowanol PtB and this initial charge is heated to 150°C. At that temperature a solution of

120.8 g methyl methacrylate,

103.5 g styrene,

69.2 g lauryl methacrylate,

155.9 g hydroxyethyl methacrylate,

138.3 g n-butyl acrylate,

5.0 g Dowanol PtB and 1 1 .2 g di-t-butyl peroxide are metered in at a uniform rate over 150 minutes. This is followed by a flush with 2.0 g Dowanol PtB and stirring at 150°C for 30 minutes. Thereafter a monomer mixture of

50.6 g methyl methacrylate,

33.7 g ethyl acrylate,

38.9 g hydroxyethyl methacrylate,

23.6 g acrylic acid,

2.8 g Dowanol PtB and 2.8 g di-t-butyl peroxide are metered in at a uniform rate over 150 minutes. This is followed by a flush with 2.0 g Dowanol PtB and stirring at 150°C for 60 minutes.

Afterward, the temperature is lowered to 105°C and a solution of 0.7 g t-butylperoxy- 2-ethylhexanoate and 0.9 g Dowanol PtB is added. This addition is followed by a flush with 2.0 g Dowanol PtB and stirring at 105°C for an additional 120 minutes.

Then the batch is cooled to 80 °C and 29.2 g Ν,Ν-dimethylethanolamine is added followed by stirring at 80 °C for 60 minutes. The dispersion into water is carried out with 650.0 g of deionized water added over the course of 180 minutes at 80 °C with stirring. Example 2

A 3 L reaction vessel with stirring, cooling and heating apparatus is charged with 183.7 g of Polycin M-365 and

81 .2 g of Dowanol PtB and this initial charge is heated to 150°C. At that temperature a solution of

91 .2 g methyl methacrylate,

103.5 g styrene,

69.2 g lauryl methacrylate,

192.9 g hydroxyethyl methacrylate,

130.9 g n-butyl acrylate,

1 1 .2 g Dowanol PtB and 1 1 .2 g di-t-butyl peroxide are metered in at a uniform rate over 150 minutes. This is followed by a flush with 2.0 g Dowanol PtB and stirring at

150°C for 30 minutes. Thereafter a monomer mixture of

43.2 g methyl methacrylate,

31 .9 g ethyl acrylate,

48.1 g hydroxyethyl methacrylate,

23.6 g acrylic acid,

Then the batch is cooled to 80 °C and 29.2 g Ν,Ν-dimethylethanolamine is added followed by stirring at 80 °C for 60 minutes. The dispersion into water is carried out with 935.7 g of deionized water added over the course of 180 minutes at 80 °C with stirring.

This gave a copolymer dispersion having the following data:

Solids content: 47.3% Density: 1 .05 Kg/L

pH: 8.0

Degree of neutralization: 100% (theoretical)

Theoretical OH equivalent weight (without Ν,Ν-dimethylethanolamine) on non- volatiles: 304 g /Eq

Acid number (on non-volatiles): 19.9 mg KOH/g (without N,N-dimethylethanolamine)

Example 3

A 3 L reaction vessel with stirring, cooling and heating apparatus is charged with 183.9 g of light castor oil and

41 .1 g of Dowanol PnP and this initial charge is heated to 150°C. At that temperature a solution of

120.6 g methyl methacrylate,

103.4 g styrene,

69.2 g lauryl methacrylate,

156.5 g hydroxyethyl methacrylate,

138.3 g n-butyl acrylate,

2.0 g Dowanol PnP and 1 1 .2 g di-t-butyl peroxide are metered in at a uniform rate over 150 minutes. This is followed by stirring at 150°C for 30 minutes.

Thereafter a monomer mixture of

50.0 g methyl methacrylate,

33.7 g ethyl acrylate,

39.0 g hydroxyethyl methacrylate,

23.6 g acrylic acid,

2.0 g Dowanol PnP and 2.8 g di-t-butyl peroxide are metered in at a uniform rate over 150 minutes. This is followed by a flush with 2.0 g Dowanol PnP and stirring at 150°C for 60 minutes. Afterward, the temperature is lowered to 105°C and a solution of 0.7 g t-butylperoxy- 2-ethylhexanoate is added. This addition is followed by a flush with 1 .0 g Dowanol PnP and stirring at 105°C for an additional 120 minutes. 29.2 g Ν,Ν-dimethylethanolamine is added followed by stirring at 105°C for 60 minutes and then by cooling to 80 °C. The dispersion into water is carried out with 1059.0 g of deionized water added over the course of 180 minutes at 80 °C with stirring.

This gave a copolymer dispersion having the following data:

Solids content: 44.6%

Density: 1 .03 Kg/L

pH: 8.3

Degree of neutralization: 100% (theoretical)

Theoretical OH content on non-volatiles (without N,N-dimethylethanolamine): 3.5% Theoretical acid number on non-volatiles: 19.3 mg KOH/g (without N,N- dimethylethanolamine)

Viscosity: 2200 mPas (at 23 °C)

Water sensitivity of the dried films of Examples 1 to 3

The water sensitivity of neat films cast from the dispersions obtained in Examples 1 to 3 was evaluated relative to a commercial aqueous hydroxyfunctional polyacrylic dispersion (Bayhydrol® XP 2470, available from Bayer MaterialScience). The test procedure was as follows:

1 . The resin dispersions are drawn down on a cleaned glass plate with a 10 micrometer drawdown bar.

2. The coated plates are placed in an 80 °C forced air oven for 30 minutes.

3. The plates are allowed to cool for one hour at ambient temperatures.

4. Approximately three drops, resulting in a 1 cm diameter spot, of deionized water is placed on each film.

5. Any changes in the film^'s appearance are noted. Film appearance after water spot introduction

Dispersion 2 min 5 min 10 min 15 min 20 min 60 min 120 min

Example 1 clear clear clear clear clear slight severe whitening whitening

Example 2 clear clear clear clear clear slight moderate whitening whitening

Example 3 clear clear clear clear clear clear clear

Bayhydrol® severe

XP 2470 whitening

The aqueous dispersions according to the present invention showed highly improved film appearance after water spot introduction over the commercially available aqueous polyacrylic dispersion.

Claims

CLAIMS What is claimed is:

1 . Aqueous acrylic copolymerisate dispersion, obtainable by the steps of

A) subjecting a monomer mixture comprising a) at least one hydroxyl functional vinyl, acrylate or methacrylate monomer, b) at least one acid functional vinyl, acrylate or methacrylate monomer, and c) at least one vinyl, acrylate or methacrylate monomer that is not hydroxyl functional and not acid functional to free radical polymerisation in the presence of d) 10 - 40 wt.-%, based on the total weight of the monomers a), b) and c), of at least one polyol selected from the group consisting of

castor oil and castor oil based polyol derivatives,

having a number average molecular weight Mn of 600 to 1200 g/mol and an OH value of 160 to 400 mg KOH/g, yielding an acrylic copolymerisate composition, B) adding a neutralizing agent to the acrylic copolymerisate composition of step A), and

C) dispersing the mixture resulting from step B) in water.

2. The aqueous dispersion of claim 1 , having an organic solvent content of less than 10 wt.-%, based on the total weight of the dispersion.

3. The aqueous dispersion of claim 1 , having a non-volatile content of from 45 - 60 wt.-%.

4. Process for the preparation of the aqueous dispersion according to claim 1 by

castor oil and castor oil based polyol derivatives,

C) dispersing the mixture resulting from step B) in water.

5. The process of claim 4, wherein the free radical polymerisation of step A) is performed in two stages.

6. A method of producing a coating composition comprising mixing the aqueous dispersion of claim 1 with at least one OH-reactive crosslinker.

7. The method of claim 6, wherein the coating composition is a two-component polyurethane coating composition, comprising at least the aqueous dispersion of claim 1 and a polyisocyanate crosslinker.

8. A coating composition comprising at least one aqueous dispersion according to claim 1 and at least one OH-reactive crosslinker.

9. The coating composition of claim 8, wherein the OH-reactive crosslinker is a polyisocyanate crosslinker.

10. Substrates coated with a coating composition according to claim 8.