CN1326491A - Coating composition - Google Patents

Abstract

A coating composition comprising a solvent, an alkyd resin and a vinyl star polymer comprising residues of a polyfunctional thiol compound having at least three functionalized thiol groups and at least three vinyl chains, each vinyl The chain comprises the residue of at least one monofunctional ethylenically unsaturated monomer. Vinyl star polymers are soluble in alkyd resin solutions and give relatively low viscosity solutions compared to linear acrylic polymers.

Description

coating composition

The present invention relates to coating compositions, especially coating compositions containing alkyd resins, for example for use in solvent-borne paints.

Alkyd resins are polyesters derived from polyols and acids (normal (linear) long alkyl chain fatty acids), often obtained from naturally occurring oils and alcohols such as glycerol. They are widely used in many coating applications, for example as wood coatings or industrial lacquers. Alkyds are often modified with other compounds such as phenolics for increased hardness and solvent resistance, epoxies for improved adhesion and silicones for improved heat and thermal shock resistance. A more detailed description of modifiers for alkyds can be found in "Encyclopaedia of Polymer Science and Technology", first edition, Vol. 1, p. 663 (Wiley 1964). Acrylic compounds are also used as alkyd modifiers, for example to improve durability, enhance color and color retention, improve gloss and gloss retention and reduce the drying time of the resulting coatings. In order to obtain the modification effect, the modified resin must be miscible in the alkyd and soluble in the carrier system, such as lacquer solvent or xylene. Among the thermoplastic acrylic resins, low molecular weight linear polyisobutyl methacrylate polymer resins are known to have good solubility in lacquer solvents and miscibility with alkyds. It is preferred for industrial use over resins.

It is an object of the present invention to provide an alternative resin suitable for use in alkyd resin systems.

In accordance with the present invention, the inventors provide a coating composition comprising a solvent, an alkyd resin, and a vinyl star polymer comprising a polymer having at least three functionalized thiol groups and at least three vinyl chains. Residues of functionalized thiol compounds, each vinyl chain comprising at least one residue of a monofunctionalized vinylically unsaturated monomer such as an alkyl acrylate or an alkyl (alk)acrylate.

In a second aspect of the present invention, the inventors provide a vinyl star polymer comprising residues of a polyfunctional thiol compound having at least three functionalized thiol groups and at least three vinyl chains as Use of a component of a coating composition based on an alkyd resin system, wherein each vinyl chain contains at least one monofunctional ethylenically unsaturated monomer such as an alkyl acrylate or an alkyl (alk)acrylate Residues.

In a third aspect of the present invention, the present inventors provide a method of producing a coating composition comprising the steps of forming a solution or dispersion of an alkyd resin in a solvent, and then adding a compound comprising at least three functionalized thiol groups and at least three (each containing at least one monofunctional ethylenically unsaturated monomer such as the residue of an alkyl acrylate or (alk)acrylate) vinyl chain polyfunctional thiol compound residue based vinyl star polymer and mixing the resulting mixture to obtain a solution of acrylic polymer.

Polymers of this composition are referred to as "star" polymers because they have a star morphology resulting from at least three acrylic chains arranged around a thiol-derived central portion. Star polymers are described in WO-A-96/37520. However their compatibility with alkyd resins and thus their use as modifiers for alkyd resin systems has not been described before and was therefore unpredictable. The star polymer has improved solubility in solvents used to process alkyds (such as lacquer solvents, white spirit), and also provides improved miscibility with alkyd resins, unlike some known acrylic alkyds Resin-modified compounds compared. These features can provide performance advantages, such as coating formulations with low application viscosities or with high acrylic modifier loadings in alkyd resins.

The vinyl polymer comprises a central moiety generated from a multifunctional thiol compound. The central portion includes a core group X and at least three linking groups YS. X is preferably the residue of a tri- to hexafunctional alcohol such as glycerol, sorbitol, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, pentahydroxypentane, triquinone and inositol at least part of . The linker Y is preferably an alkyl, especially a C _2-10 alkyl and especially a C _2-6 alkyl.

The central moiety is preferably the residue of a tri- to octa-functionalized and especially a tri- to hexa-functionalized thiol. Such thiols may be esters formed from alcohols and _{thioC2-10alkanoic} acids, especially _{thioC2-8alkanoic} acids. Examples of suitable acids are 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, 5-mercaptopentanoic acid, 6-mercaptocaproic acid and 10-mercaptodecanoic acid. The acid is preferably 2-mercaptoacetic acid or 3-mercaptopropionic acid.

Examples of multifunctional thiols include trimethylolethane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetramercaptoacetate, trimethylolethane trimercaptoethane Ester, Trimethylolpropane Tris(3-Mercaptopropionate), Trimethylolpropane Trimercaptoacetate, Pentaerythritol Tetramercapto Lactate, Pentaerythritol Tetramercaptobutyrate, Dipentaerythritol Hexa(3-Mercapto propionate), dipentaerythritol hexathioglycolate, tripentaerythritol octa(3-mercaptopropionate), tripentaerythritol octathioglycolate.

Mixed polymer systems can be produced by selecting more than one central compound, for example by combining more than one polyfunctional thiol compound or one or more polyfunctional thiol compounds with one or more monofunctional or Acrylic monomers are polymerized in the presence of a difunctional thiol compound to form chains. Suitable monofunctional thiol compounds include propyl mercaptan, butyl mercaptan, hexyl mercaptan, octyl mercaptan, dodecyl mercaptan, mercaptoacetic acid, mercaptopropionic acid, 2-ethylhexyl acetate , mercaptoethanol, mercaptoundecanoic acid, thiolactic acid and thiobutyric acid. Suitable difunctionalized compounds include ethylene dimercaptoacetate, polyethylene glycol bis(3-mercaptopropionate), ethylene bis(3-mercaptopropionate), polyethylene glycol dimercaptoacetate .

Mixtures of star polymers can be formed from such hybrid polymerizations or simply by combining more than one preformed star polymer resin or one or more preformed star polymer resins with one or more Two linear vinyl polymers are mixed together to form. The vinyl chain of each vinyl polymer or linear polymer may be formed from a vinyl monomer composition which may be the same as or equal to every other vinyl star polymer or linear polymer in the mixture. different.

The vinyl polymer chain is formed from at least one monoethylenically unsaturated monomer which may be selected from any of the monoethylenically unsaturated monomers known in the art.

Suitable monofunctional ethylenically unsaturated monomers may be selected from acrylic monomers such as acrylic acid, methacrylic acid and chloroacrylic acid (ie _CH2 =CHClCO.OH), acrylamide and methacrylamide, acrylonitrile and methacrylic acid Acrylonitriles, alkoxyalkylacrylamides, hydroxyalkylacrylamides and methacrylamides, such as N-methylolacrylamide and methacrylamide and methacrylamide, metal acrylates and methacrylates , and esters of acrylic acid, methacrylic acid, and chloroacrylic acid with alcohols and phenols; vinylaromatic compounds, such as styrene and its substituted derivatives, such as its halogenated derivatives, and vinyltoluene; vinyl esters, such as vinyl acetate , and vinylpyrrolidone.

Preferred monofunctional ethylenically unsaturated monomers include acrylic or methacrylic acid and their esters having the formula _CH2 =C(R) ^CO.OR2 , where R is H, methyl or butyl, especially methyl radical, isobutyl and n-butyl, and ^R is optionally substituted hydrocarbyl (for example, optionally halogen or hydroxy substituted hydrocarbyl) and especially C _1-8 alkyl, C _6-10 cycloalkyl or C _6-10 aryl. Specific examples of these monomers include unsubstituted esters of acrylic acid and methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, Isobutyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, benzyl methacrylate, phenyl methacrylate and isobornyl acrylate and substituted esters of acrylic and methacrylic acid such as methacrylic acid Hydroxyethyl and Hydroxypropyl Methacrylate. More particularly, the monofunctional ethylenically unsaturated monomer is a C _1-8 alkyl methacrylate. Methyl methacrylate, isobutyl methacrylate and n-butyl methacrylate are especially preferred monomers.

At least three vinyl polymer chains can be formed from a mixture of monofunctional ethylenically unsaturated monomers, such as the mixtures of monomers described above.

Each vinyl polymer chain is generally formed from 10-1500, eg 25-1500 monomer units and preferably 20-800 and especially 300-800 such units. When mixtures of monomeric units are used, the copolymers may be block or random copolymers of such units. The copolymer is preferably a random copolymer produced by ordinary free radical polymerization methods.

The individual vinyl polymer chains can be formed by polymerization methods commonly used in the preparation of poly(methacrylates) using polythiols as chain transfer agents. These methods include bulk, solution, emulsion and suspension polymerization of acrylic polymer chains. Preferred methods are suspension polymerization and bulk polymerization methods.

When used, the suspension polymerization process is generally carried out (at least initially) in the range of 10-120°C, preferably in the range of 50-110°C, especially in the range of 70-110°C and more especially about 75-100°C . A suitable bulk polymerization process is carried out at a temperature in the range 70-130°C.

Preferred methods are bulk, solution, emulsion and suspension polymerization methods using free radical initiators.

Suitable free radical initiators include organic peroxides, hydroperoxides, persulfates and azo compounds. Examples of these initiators are methyl ethyl ketone peroxide, benzoyl peroxide, cumene hydroperoxide, potassium persulfate, azobisisobutyronitrile (AIBN), lauroyl peroxide, 2,5-bis Methyl-2,5-bis(tert-butylperoxy)hexane, diethyl peroxide, dipropyl peroxide, dilauryl peroxide, dioleyl peroxide, distearyl peroxide, di (tert-butyl) peroxide, di(tert-amyl) peroxide, tert-butyl hydroperoxide, tert-amyl hydroperoxide, acetyl peroxide, propionyl peroxide, lauroyl peroxide, hard peroxide Fatty acyl, malonyl peroxide, succinyl peroxide, phthalyl peroxide, acetylbenzoyl peroxide, propionyl benzoyl peroxide, ascaridin, ammonium persulfate, sodium persulfate, Sodium Percarbonate, Potassium Percarbonate, Sodium Perborate, Potassium Perborate, Sodium Superphosphate, Potassium Superphosphate, Tetralin Hydroperoxide, Tert-Butyl Diperphthalate, Tert-Butyl Perbenzoate, Peroxide 2,4-dichlorobenzoyl, urea peroxide, octanoyl peroxide, p-chlorobenzoyl peroxide, 2,2-bis(tert-butylperoxy)butane, hydroxyheptyl peroxide.

Preferably, the ratio of initiator to polythiol is lower than 6:1 (by molar basis), for example in the range of 6:1 to 1:6, and it is especially preferred that the ratio of initiator to polythiol Below 3:1 (on a molar basis), for example in the range of 3:1-1:3. Preferably, the molar ratio of polythiol to monomer is in the range of 1:30 to 1:3000, and especially preferred, the molar ratio of polythiol to monomer is in the range of 1:25 to 1:1500 In the range.

When the polymerization method is an emulsion polymerization method, the emulsifier may be selected from those generally used in this technical field. These emulsifiers include fatty acid soaps, rosin soaps, sodium lauryl sulfate, polyethoxylated alkylated phenols, sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate.

When the polymerization method requires a solvent, such solvent may be selected from those commonly used in this technical field, such as benzene, toluene, xylene, aliphatic esters, aliphatic ethers, aliphatic ketones and aliphatic alcohols.

The molecular weight of the polymer is controlled by the thiol used to form the center of the star polymer. The molecular weight (Mw) is normally 4,000-80,000 Daltons, preferably 8,000-60,000 D.

The acrylic polymer may be present in the coating composition at a concentration in the range of 1-80 wt%, preferably 1-60 wt%. The ratio (by weight) of acrylic polymer to alkyd resin is generally in the range of 1:8 to 1:2.

Coating compositions generally contain ingredients other than alkyd resins, acrylic resins and solvents. These other components are well known in the art of solvent-borne coating formulations. These components generally include dry components such as salts of cobalt, lead, zinc, zirconium or calcium normally present at concentrations between 0.1 and 1.0 wt% of the alkyd resin component of the paint. Coatings may also contain pigments and opacifiers such as titanium dioxide. When present, pigments are generally used in concentrations to give a pigment to binder ratio of between 1:20 and 1.2:1 by weight.

The solvent used in these paints is mineral spirits. The total solids level (ie, all non-volatile components) in the mineral spirits is generally between 40-50 wt%.

The coating composition may also contain other components not mentioned above, but which are known in the art of formulating solvent-borne coatings.

The invention is further described in the following examples.

The preparation of embodiment 1 mixed star polymer

While sparging with nitrogen and stirring gently, 4.5 g of suspending agent (Natrol HEC 250LR available from Aqualon Inc., a division of Hercules Inc.) was dissolved in a 5 liter flask by heating in the range of 40-50° C. for 30 minutes contained in 2.0L of deionized water. From 500g of isobutyl methacrylate and 1.75phm each of dodecyl mercaptan (DDM), trimethylolpropane tris(3-mercaptopropionate) (TRIMP) and Pentaerythritol tetrakis(3-mercaptoacrylate) (PETMP) forms the monomer phase premix. While maintaining a nitrogen blanket and water-cooled reflux, 5.0 g of AIBN initiator was flushed into deionized water using a pre-mixer. The temperature was raised to 76°C and the mixture was stirred at 1500 rpm. Polymerization was carried out until almost complete conversion of the monomer into polymer, and then the supply of cooling water to the condenser was stopped. The polymer was then heat treated by raising the temperature to a temperature in the range of 90-95°C for 30 minutes to complete the polymerization and to separate unreacted monomers. After heat treating the polymer, the nitrogen atmosphere was removed, and the polymer was air cooled. The cooled polymer was then filtered, washed in deionized water and dried.

Polymer molecular weights were measured by gel permeation chromatography (GPC) using chloroform as solvent and polymethyl methacrylate standards. The results are shown in Table 1. The dissolution of the polymers in the lacquer solvent and the viscosity of the resulting solutions were evaluated and the results are given in Table 2. Dissolution was also measured for a commercially available thermoplastic solid polyisobutylmethacrylate alkyd modifier resin (designated CR in the table below) with measured molecular weights Mw = 9550 and Mn = 4750, and was used to show and compare with Example 1 Performance of known acrylic alkyd modifiers compared to polymers of 2.

The preparation of embodiment 2 medium molecular weight star polymer

The method of Example 1 was carried out, except that DDM was omitted.

The preparation of embodiment 3 (contrast) linear polymer

The procedure of Example 1 was followed except that the only thiol used was DDM at 1.75 phm.

The results show that the polymers described in Examples 1 and 2 are soluble in lacquer solvents and give rise to relatively low viscosity solutions at concentrations up to 30% w/w. In contrast, the linear control (Example 3) was not completely soluble in the lacquer solvent. It can also be seen that for a given solution viscosity, the resins of Examples 1 and 2 have the additional advantage of being soluble to higher solids levels than the polyisobutyl methacrylate resin (eg, to achieve low solvent usage).

Table 1 Example 1 Thiol mw mn d 1 1.75phm each of DDM, TRIMP and PETMP 9450 5250 1.79 2 1.75phm each of TRIMP and PETMP 14100 8700 1.63 3 (comparison) 1.75phm of DDM 15500 7650 2.03 CR 9550 4750 2.00

Table 2 Brookfield viscosity at room temperature (cP) polymer 10%w/w 20%w/w 30%w/w Example 1 2.5 5 14.5 Example 2 4.5 8 23.5 Example 3 incompletely dissolved CR 9 twenty three 152.5

Example 4 - Compatibility with Alkyd Resins

1.0 g each of the polymers prepared in Examples 1-3 and the polyisobutyl methacrylate resin were added to 9.0 g each of the various commercially available alkyd resin solutions. Each sample was then placed in a 90°C water bath with occasional rotation for 6 hours. After cooling to room temperature, the solubility was assessed visually and classified as follows:

A: Clear solution - insoluble particles observed.

B: Clear solution - few insolubles.

C: Cloudy solution - a small amount of insoluble resin deposits

D: Cloudy solution - copious deposits of insoluble resin

The results are shown in Table 3.

table 3 Alkyd type Alkyd commercial grade solvent type acid value polymer CR 1 2 3 long chain soybean oil Wresino1AS62l 65% solution in lacquer solvent 10max D. B A C long chain linseed oil Wresinol AL668 65% solution in lacquer solvent 10max A A A B medium chain soybean oil Wresinol AS483 50% solution in lacquer solvent 14max B A C C short chain soybean oil Blagden Chemicals K674-50x 50% solution in xylene 30max D. B D. D. long chain soybean oil Blagden Chemicals1426 65% solution in lacquer solvent 10max A A B C medium chain linseed oil Blagden Chemi cal830-40 40% solution in lacquer solvent 10max B A B C These results show that the star and partial star polymers in Examples 1 and 2 have a miscibility with the alkyd resin used that is at least as good as the known polyisobutylmethacrylate alkyd modifier . The linear polymer of Example 3 is generally poorly miscible with these alkyds.

Claims (12)

1. A coating composition comprising a solvent, an alkyd resin and a vinyl star polymer comprising residues of a polyfunctional thiol compound having at least three functionalized thiol groups and at least three vinyl chains, Each vinyl chain comprises at least one residue of a monofunctional vinylically unsaturated monomer. 2. A coating composition as claimed in claim 1, wherein said thiol compound comprises a central moiety having a core group X and at least three linking groups Y-S, wherein X is at least Moiety and linker Y are alkylates. 3. The coating composition as claimed in claim 2, wherein said multifunctional alcohol is selected from the group consisting of glycerin, sorbitol, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, pentahydroxypentane alkanes, triquinone groups and inositol. 4. A coating composition as claimed in claim 2, wherein the linker Y is a _C2-10 alkylate. 5. A coating composition as claimed in any preceding claim, wherein said vinyl star polymer is a mixture of more than one vinyl star polymer, each polymer comprising at least three functionalized thiols group and residues of different multifunctional thiol compounds of at least three vinyl chains, wherein the vinyl chains of each vinyl star polymer are formed from vinyl monomer components, each vinyl star polymer Same or different from every other vinyl star polymer. 6. A coating composition as claimed in any preceding claim, wherein said coating composition additionally comprises a linear vinyl polymer comprising residues of vinyl monomer components which form the The vinyl monomer components of the vinyl star polymer or the vinyl chains of the vinyl star polymers are the same or different. 7. A coating composition as claimed in claim 6, wherein said linear vinyl polymer comprises the residue of at least one thiol compound having one or two functionalized thiol groups. 8. A coating composition as claimed in any preceding claim, wherein said at least one monofunctional ethylenically unsaturated monomer is selected from the group consisting of acrylic monomers, acrylamides, methacrylamides, acrylonitriles, Methacrylonitrile, alkoxyalkylacrylamides and methacrylamides, hydroxyalkylacrylamides and methacrylamides, metal acrylates and methacrylates, acrylic, methacrylic and chloroacrylic acids with alcohols and phenols Esters; group of compounds of vinylaromatic compounds and their substituted derivatives and vinyl esters, or mixtures of the foregoing. 9. A coating composition as claimed in claim 8, wherein said at least one monofunctional ethylenically unsaturated monomer is selected from acrylic or methacrylic acid and its compounds having the formula _CH2 =C(R)CO.OR ² , wherein R is H, methyl or butyl, and ^R is optionally substituted C _1-8 alkyl, C _6-10 cycloalkyl or C _6-10 aryl. 10. A coating composition as claimed in claim 9, wherein said at least one monofunctional ethylenically unsaturated monomer is a mixture of at least two acrylic or methacrylate esters. 11. Vinyl star polymers comprising residues of multifunctional thiol compounds having at least three functionalized thiol groups and at least three vinyl chains as coating compositions based on alkyd resin systems Use of components, each vinyl chain contains the residue of at least one monofunctional ethylenically unsaturated monomer such as an alkyl acrylate or an alkyl (alk)acrylate. 12. A method of producing a coating composition comprising the steps of forming a solution or dispersion of an alkyd resin in a solvent and then adding a polyfunctional compound comprising at least three functionalized thiol groups and at least three vinyl chains Vinyl star polymer of residues of thiol compounds and mixing the resulting mixture optionally with other components selected from drying compounds, pigments, modifiers, opacifiers to obtain a solution of acrylic polymer, each The vinyl chain contains the residue of at least one monofunctional vinylically unsaturated monomer.