WO2017125341A1

WO2017125341A1 - Branched hydroxy-functional (meth)acrylate copolymers having anti-sag properties

Info

Publication number: WO2017125341A1
Application number: PCT/EP2017/050775
Authority: WO
Inventors: Sarav JHAVERI; Donald H Campbell; Colin Wade
Original assignee: Basf Coatings Gmbh
Priority date: 2016-01-22
Filing date: 2017-01-16
Publication date: 2017-07-27

Abstract

Branched, hydroxy-functional (meth)acrylate copolymers having anti-sag properties are disclosed. The copolymers are used in clearcoat applications as a replacement for fumed silica and cellulose butyrate acetate.

Description

BRANCHED HYDRO XY-FUNCTIONAL (METH)ACRYLATE

COPOLYMERS HAVING ANTI-SAG PROPERTIES

FIELD OF THE INVENTION

[0001] The present invention relates to branched (meth)acrylate copolymers as rheology modifiers for use in coating applications. The (meth)acrylate copolymers can be used as a substitute for fumed silica and cellulose butyrate acetate (CAB) in clearcoat applications.

BACKGROUND OF THE INVENTION

[0002] Coating systems for automobiles normally comprise a multiplicity of coatings applied to a steel substrate. Typically, steel is treated with a rust-proofing layer, then a cathodic electrocoat primer for additional corrosion protection is applied. A primer- surf acer then is used to smooth the surface for topcoating and provide stone chip resistance to the coating system during the normal course of driving. Next, a top-coat system is applied, typically as a basecoat with solid color or flake pigments followed by a transparent protective clearcoat to protect and preserve the esthetic qualities of the finish on the vehicle, even after prolonged exposure to the environment or weathering.

[0003] Sag resistance is an important characteristic in automotive coatings for vertical vehicle parts, especially clearcoats, where flow of the coating should be minimized prior to or during crosslinking. Sag resistance is especially important when using high film thickness coatings. A coat having a low sag tolerance prevents additional coating composition from being applied. A thicker clearcoat layer also allows for lower wave numbers, which results in an enhanced appearance. However, if a coating is applied above its sag threshold, unsightly sag lines may appear.

[0004] Typical materials used to prevent sagging are fumed silica and fast evaporating solvents. However, each of these alternatives exhibits negative side effects. Fumed silica is an expensive material that decreases appearance. In addition, fumed silica is an inorganic material that must be milled before use, dispersed in a composition, therefore adding an additional process step. Fast evaporating solvents also are generally expensive, increase volatile organic content (VOC), and can reduce resistivity.

[0005] Cellulose mixed esters also have been used to impart sag resistance to a coating composition. However, cellulose esters also present disadvantages, such as increasing the brittleness of a cured coating, reducing gloss and appearance, causing formulation incompatibilities, increasing cost, and are not as effective as fumed silica. [0006] Accordingly, a need still exists in the art for improved materials that impart anti-sag properties to a coating composition, without an adverse effect on the esthetics and film properties of the cured coating. The present invention is directed to providing such improved anti-sag materials.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to branched hydroxy- functional (meth)acrylate copolymers that demonstrate anti-sag properties. More particularly, the present invention is directed to the synthesis and use of novel branched (meth)acrylate-based polymers as rheology modifiers for coatings applications. The present branched/lightly crosslinked (mefh)acrylic polymers exhibit anti-sag properties equivalent to fumed silica and cellulose butyrate acetate (CAB) in clearcoat applications, and accordingly can be used as a substitute for these materials.

[0008] A present (meth)acrylate copolymer possesses a hydroxyl functionality and possesses the following properties:

[0009] (a) a weight average molecular weight (Mw) of at least 5,000;

[0010] (b) a number average molecular weight (M_n) of about 1,500 to about 20,000;

[0011] (c) a polydispersibity index (PDI) of about 2 to about 15;

[0012] (d) a glass transition temperature (T_g) of about 50°C to about 110°C; and

[0013] (e) a film thickness of about 38 to about 46 μπι at 8 mm in the keyhole test.

[0014] The present (meth)acrylate copolymers have a hydroxyl functionality, and comprise about 10% to about 50%, by weight, of a hydroxyalkyl (meth)acrylate. A present

(mefh)acrylate copolymer is a branched/lightly crosslinked copolymer containing about 1% to about 10%, by weight, of a crosslinking monomer.

[0015] In other embodiments, in order to provide a desired T_g and film hardness, a present (mefh)acrylate copolymer comprises 0% to about 70%, by weight, of a Ci^alkyl

(meth)acrylate. In another embodiment, a present (meth)acrylate copolymer comprises 0% to about 60%, by weight, of a C6-isalkyl (mefh)acrylate.

[0016] Yet another embodiment of the present invention is to provide a coating composition comprising a present branched hydroxy-functional (meth)acrylate copolymer. In preferred embodiments, the composition is free of a fumed silica and a cellulose mixed ester. [0017] Still another embodiment is to provide a method of coating a substrate by applying a composition comprising a present branched hydroxy-functional (meth)acrylate copolymer to the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A present (meth)acrylate copolymer has a hydroxyl-functionality, is

branched/lightly crosslinked, and has the following properties:

[0019] (a) a weight average molecular weight (Mw) of at least 5,000;

[0020] (b) a number average molecular weight (M_n) of about 1,500 to about 20,000;

[0021] (c) a polydispersibity index (PDI) of about 2 to about 15;

[0022] (d) a glass transition temperature (T_g) of about 50°C to about 110°C; and

[0023] (e) a film thickness of about 38 to about 46 μιη at 8 mm in the keyhole test.

[0024] The present hydroxy-functional (meth)acrylate copolymers exhibit anti-sag properties and are useful as a substitute for current anti-sag materials, such as fumed silica and cellulose esters. A present (meth)acrylate copolymer provides an alternative to prior anti-sag materials because a present copolymer is a viscous, branched copolymer that improves the rheology of a coating composition. The use of the present branched copolymer is inexpensive compared to the fumed silica approach.

[0025] The present copolymers possess a low T_g for reflowability, are lightly crosslinked for anti-sag, and contain a crosslinkable functionality (i.e., hydroxy groups). These properties provide scratch resistance and hardness in addition to being a cost effective material. A present (meth)acrylate copolymer can be used in single crosslinker (IK) and dual crosslinker (2K) clearcoats. With 2K clearcoats, an increase in hardness and scratch resistance is attained, while retaining appearance and reflowability. For IK clearcoats, the hydroxyl groups can be modified in order to increase urethane linkages when reacted with melamines. Such a modification further enhances sag resistance as a result of increased hydrogen bonding.

[0026] A present (meth)acrylate copolymer contains a hydroxyalkyl (meth)acrylate in an amount of about 10% to about 50%, by weight, of the copolymer, and preferably about 15% to about 45%, by weight. In most preferred embodiments, the copolymer contains about 20% to about 40%, by weight, of the hydroxyalkyl (meth)acrylate. [0027] The hydroxyalkyl (meth)acrylate can be a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate, or a mixture thereof. The alkylene group of the hydroxyalkyl (meth)acrylate contains 1 to about 6 carbon atoms. Examples of the hydroxyalkyl (meth)acrylate include, but are not limited to, 2-hydroxyethyl methacrylate (HEMA), 4-hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,

2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, and mixtures thereof.

[0028] A present (meth)acrylate copolymer is a branched/lightly crosslinked polymer containing about 1% to about 10%, and preferably 1.5% to about 9%, by weight of the copolymer, of a crosslinking monomer. In most preferred embodiments, the (meth)acrylate copolymer comprises about 2% to about 8%, by weight of the copolymer, of a crosslinking monomer. The crosslinking monomer contains at least two carbon-carbon double bonds, i.e., vinyl moieties, and polymerizes with the hydroxyalkyl (meth)acrylate and other monomers via a free radical reaction to form a present (meth) acrylate copolymer.

[0029] The crosslinking monomer can contain two, three, or four vinyl moieties.

Typically, a crosslinking monomer contains two vinyl moieties. In some embodiments, a combination of crosslinking monomers is used, i.e., a crosslinking monomer containing two vinyl monomers is used in conjunction with one or more crosslinking monomer containing three or four vinyl moieties.

[0030] The crosslinking monomer provides a high molecular weight, substantially non- gelled branched copolymer, alternatively referred to as "branched", "highly branched", and "hyper-branched". The branched copolymers of the present invention have a lower viscosity than their linear analogs.

[0031] The selection of a particular crosslinking monomer or crosslinking monomers, and their amounts, relates to the degree of branching/crosslinking desired in the (meth)acrylate copolymer and is readily determined by persons skilled in the art. The amount of crosslinking monomers present in a (me h)acrylate polymer is sufficient to provide a weight average molecular weight of at least 5,000.

[0032] Crosslinking monomers useful in the present (meth) acrylate copolymers are not limited, and include, but are not limited to, 1 ,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate,

1 ,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, 1,10-decanediol diacrylate, neopentyl glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,

N,N'-methylenebisacrylamide, Ν,Ν'-methylenebismethacrylamide, and mixtures thereof.

[0033] Preferred crosslinkers are 1,6-hexanediol diacrylate (HDD A), 1 ,6-hexanediol dimethacrylate, 1,10-decanediol diacrylate, 1,4-butanediol diacrylate, 1 ,4-butanediol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, neopentyl diacrylate, and mixtures thereof.

[0034] To achieve a predetermined or desired property, such as glass transition

temperature and film hardness, a present (meth)acrylate copolymer comprises 0% to about 70%, by weight, of a Ci-4alkyl (meth)acrylate. In preferred embodiments, a present copolymer comprises about 20% to about 65%, by weight, of the Ci-4alkyl (meth)acrylate. To achieve the full advantage of the present invention, the Ci-4alkyl (meth)acrylate is present in an amount of about 40% to about 60%, by weight, of the copolymer.

[0035] The Ci-4alkyl (meth)acrylates include, but are not limited to, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, t-butyl acrylate, t-butyl methacrylate, and mixtures thereof. A preferred

Ci-4alkyl (meth)acrylate is methyl methacrylate.

[0036] A present (meth)acrylate copolymer also comprises 0% to about 60%, by weight, and preferably about 8% to about 60%, by weight, of a C<5-i8alkyl (meth)acrylate. In more preferred embodiments, the (meth)acrylate copolymer comprises about 10% to about 60%, by weight, of the C6-i8 (meth)acrylate. Among the C6-i8alkyl(meth)acrylates, the Ce alkyl (mefh)acrylates are preferred.

[0037] The C6 isalkyl (mefh)acrylates include, but are not limited to, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, isodecyl acrylate, isobornyl acrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, isodecyl methacrylate, isobornyl methacrylate, and mixtures thereof. Preferred C6-i8alkyl

(meth)acrylates are 2-ethylhexyl acrylate, cyclohexyl acrylate, and hexyl acrylate.

[0038] In other embodiments, a present (meth) acrylate copolymer can contain one or more additional monomer having a carbon-carbon double bond, i.e., a vinyl moiety. The additional monomers are polymerized via a free radical mechanism and modify the copolymer or a property of the copolymer. Nonlimiting examples of additional monomers are ureido methacrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, and methyl vinyl ether. In yet other embodiments, the additional monomer is a styrenic compound having a formula:

[0039] wherein R is hydrogen or a Ci-6alkyl group, and wherein the phenyl ring optionally is substituted with one to four Ci-4alkyl and/or hydroxy groups. Specific examples of the styrenic monomers include, but are not limited to, styrene, a-methylstyrene, p-methylstyrene, t-butyl styrene, and the like, and mixtures thereof.

[0040] The additional monomers are included in an amount of 0% to about 10%, by weight, of the (meth)acrylate copolymer, and preferably in an amount of 0% to about 8%, by weight. In some embodiments, the (meth) acrylate copolymer contains about 2% to about 5%, by weight, of the additional monomer.

[0041] In the preparation of a present (meth)acrylate copolymer, the monomers are solubilized or dispersed in a solvent. The solvent is organic and has a boiling point sufficiently high such that an exothermic free radical polymerization can be conducted.

Typical solvents are aromatic hydrocarbons and acetate esters. Preferably, the solvent is an aromatic solvent having a boiling point of about 100°C to about 200°C. One nonlimiting example of an aromatic solvent is Solvesso™ 100, available from ExxonMobil, Houston, TX. The concentration of monomers in the monomer solution or dispersion is about 40% to about 70%, by weight, of the solution or dispersion.

[0042] Additional solvents include, but are not limited to, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl propyl ketone, 2-propoxyethanol, 2- butoxyethanol, ethyl 3-ethoxypropionate, ethanol, methanol isopropyl alcohol, diacetone alcohol, ethylene glycol monobutyl ether acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, n-aryl acetate, isobutyl acetate, diethylene glycol ethyl ether, propylene glycol methyl acetate, ethylene glycol butyl acetate, propylene glycol monomethyl ether, diethylene glycol methyl ether, propylene glycol monombutyl ether, diethylene glycol ethyl ether, propylene glycol monopropyl ether, ethylene glycol monobutyl ether, N- methylpyrrolidone, ethyl 3-ethoxypropionate, and other volatile inert solvents typically used in coating compositions.

[0043] The monomer solution or dispersion also contains at least one initiator. The initiator or combination of initiators is present in a sufficient amount to provide a present (meth)acrylic copolymer having a desired weight average molecular weight.

[0044] Any of the various polymerization initiators known for use in a free radical polymerization of vinyl-containing monomers can be used in the present invention.

Examples of useful initiators include, but are not limited to, t-butyl hydroperoxide; di-t-butyl peroxide; t-butyl perbenzoate; t-butyl peroxy isopropyl carbonate; l,l-di-t-butylperoxy-3,3,5- trimethylcyclohexane; benzoyl peroxide, dicumyl peroxide; caprylyl peroxide; acetylacetone peroxide; methyl ethyl ketone peroxide; cumene hydroperoxide; tert-amyl perpivalate; tert- butyl perpivalate; tert-butyl perneohexanote; tert-butyl perisobutyrate; tert-butyl per-2- ethlhexanoate; tert-butyl perisononanoate; tert-butyl permaleate; tert-butyl perbenzoate; tert- butyl per-3,5,5-tri-methylhexanoate; and tert-amyl perneodecanoate.

[0045] Thermal initiators also are useful. Nonlimiting examples of thermal initiators include, but are not limited to, azobisisobutyronitrile; 4-t-butylazo-4'-cyanovaleric acid; 4,4'- azobis(4-cyanovaleric acid); 2,2'-bis(2-amidinopropane) dihydrochloride; 2,2'-azobis(2,4- dimethylvaleronitrile); dimethyl 2,2'-azobisisobutyrate; 2,2'-azodimethyl bis(2,4- dimethylvaleronitrile); (1-phenylethyl) azodiphenylmethane; 2,2'-azobis(2- methylbutyronitrile) ; 1 , l'-azobis( 1 -cyclohexanecarbonitrile) ; 2-(carbamoylazo)

isobutyronitrile; 2,2'-azobis(2,4,4-trimethylpenta-2-phenylazo-2,4-dimethyl-4- methoxyvaleronitrile; 2,2'-azobis (2-methylpropane); 2,2'-azobis

(N,N'dimethyleneisobutyramidine) dihydrochloride; 4,4'azobis (4-cyanopentanoic acid); 2,2'- azobis(2-methyl-N-[ 1 , 1-bis (hydroxymethyl)-2-hydroxyethyl]propionamide); 2,2'-azobis(2- methyl-N-[l,l-bis(hydroxymethyl)ethyl]propionamide); 2,2'-azobis[2-methyl-N- (hydroxyethyl)propionamide] ; 2,2'-azobis(isobutyramide)dihydrate; and other thermal initiators known to persons skilled in the art.

[0046] Initiators can be used singularly or in suitable combination. The initiators can be used together with a chain transfer agent to control the molecular weight of the

thermochromic copolymer. Typically chain transfer agents are sulfur-containing compounds, such as dodecyl mercaptan, 2-mercaptoethanol, n-octyl mercaptan, and butyl mercaptan.

[0047] A present (me h)acrylate copolymer is prepared by forming a solution or dispersion of the hydroxyalkyl (meth)acrylate, C₆ lsalkyl (meth)acrylate, crosslinking monomer, optional additional monomer, and optional Ci-4alkyl(meth)acrylate in a suitable solvent. The resulting solution or dispersion then is subjected to a free radical polymerization to yield a present (meth)acrylate copolymer.

[0048] A present branched (meth)acrylate copolymer possesses a combination of properties such that an anti-sag feature is achieved in a coating composition containing the copolymer. The present (mefh)acrylate copolymers have a weight average molecular weight (Mw) of at least 5,000, as determined by gel permeation chromatography using polystyrene as a standard, preferably about 7,000 to about 100,000, and more preferably about 10,000 to about 80,000.

[0049] The present (meth)acrylate copolymers also exhibit a number average molecular weight (M_n) of about 1,500 to about 20,000, preferably about 2,000 to about 15,00, and more preferably about 2,500 to about 10,000. The copolymers have a polydispersity index (PDI) of about 2 to about 15, preferably about 2.25 to about 12, more preferably about 2.5 to about 10.

[0050] The glass transition temperature of a present (meth)acrylate copolymer is about 50°C to about 110°C, preferably about 55°C to about 105°C, and more preferably about 60°C to about 100°C.

[0051] Further, as disclosed below, a present (mefh)acrylate copolymer also exhibits a film thickness of about 38 to about 46 μιη, preferably about 40 to about 45 μιη, and more preferably about 42 to about 45 μιη at 8 mm sag, in the key hole test.

[0052] A present (meth)acrylate copolymer is included in a coating composition in a sufficient amount to impart an anti-sag property to the coating composition when the composition is applied to a substrate. The (meth)acrylate copolymer typically is included in the coating composition in an amount of about 1% to about 25%, by weight of the composition, and preferably in an amount of about 2% to about 20%, by weight of the composition. In other preferred embodiments, the (meth)acrylate copolymer is included in the coating composition in an amount of about 5% to about 20%, by weight of the composition. The above weight parts are based on the copolymer and exclude solvents.

[0053] A coating composition of the present invention therefore comprises:

[0054] (a) about 1% to about 25%, by weight, of a present (mefh)acrylate copolymer;

[0055] (b) about 1% to about 90%, by weight, of one or more of a resin selected from the group consisting of polyesters, polyester-amides, cellulose esters, alkyds, polyurethanes, epoxy resins, polyamides, acrylics, vinyl polymers, polyisocyanates, melamines, phenolics, urea resins, urethane resins, and polyamides; and

[0056] (c) a solvent, preferably an organic solvent, or a solvent mixture;

[0057] wherein the total weight of (a), (b), and (c) equals 100%.

[0058] Optionally, a present coating composition can include 0% to about 10%, by weight of the composition of (d) additional additives, including, but not limited to, flow additives, leveling additives, wetting and dispersing agents, defoamers, adhesion promoters, slip aids, pigments, anti-skinning agents, UV stabilizers, biocides, mildewcides, fungicides, and others, wherein the total weight of (a), (b), (c), and (d) equals 100%.

[0059] The (meth)acrylate copolymers of the present invention contain hydroxyl functionalities and therefore can easily be used with crosslinking agents such as melamines, isocyantes, and compounds having a plurality of -N(CH20R)2 functional groups, wherein R is C1-C4 alkyl, preferably methyl. Nonlimiting examples of melamine and melamine-type crosslinkers include, but are not limited to hexamethoxymethylamine, tetramethoxymethyl- benzo-guanamine, tetramethoxymethylurea, mixed butoxy/methoxy substituted melamines, and the like. The most preferred melamine crosslinking agent is hexamethoxymethylamine.

[0060] Typical, non-limiting isocyanate crosslinking agents and resins include

hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene diisocyanate (MDI), and toluene diisocyanate (TDI).

[0061] A coating composition of the present invention is prepared by admixing the composition ingredients according to methods well known and used in the art to provide a homogenous composition. The order of adding ingredients into the composition is not necessarily limited.

[0062] To prepare coated articles, a coating composition comprising a present

(meth)acrylate copolymer is applied to a substrate, and the composition is allowed to dry or is cured on the substrate. The substrate can be, for example, wood; plastic; metal, such as aluminum or steel; cardboard; glass; and various blends containing, for example,

polypropylene, polycarbonate, polyesters, such as polyethylene terephthalate, acrylic sheeting, as well as other solid substrates.

[0063] The following examples illustrate present (mefh)acrylate copolymers and their method of preparation. EXAMPLE 1

[0064] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, aromatic solvent Solvesso® S-100 (450 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing methyl methacrylate (MMA) (398 g), hydroxyethyl methacrylate (HEMA) (157.6 g), 2-ethylhexyl metacrylate (2-EHMA) (150 g), hexanediol dimethacrylate (HDD A) (14.4 g), and tert-butylperoxy-2-ethyl hexanoate (23.11g). The mix was fed into the flask with stirring over 90 minutes, followed by addition of n-butyl acetate (43 g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert-butylperoxy-2-ethyl hexanoate (0.5g) and n-butyl acetate (26.65g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled by addition of n-butyl acetate (300 g) and filtered at 60°C.

[0065] The resulting branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour was 47.6%, and molecular weight by GPC (using a styrene standard) was: M_w = 24,730; M_n =7,292; PDI = 3.39.

EXAMPLE 2

[0066] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, aromatic solvent Solvesso® S-100 (450 g) and n-butyl acetate (300 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing MMA (398 g), HEMA (157.6 g), 2-EHMA (150 g), HDDA (14.67 g) and tert-butylperoxy-2-ethyl hexanoate (23.11g). The mix was fed into the flask with stirring over 135 minutes followed by addition of n-butyl acetate (36.82g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert-butylperoxy-2-ethyl hexanoate (0.5g) and n-butyl acetate (26.5 g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled and filtered at 60°C.

[0067] The resulting branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour was 47.3% and molecular weight by GPC: M_w = 14,234;

EXAMPLE 3

[0068] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, n-amyl acetate (650 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing MMA (398 g), HEMA (157.6 g), 2-EHMA (150.9 g), HDDA (14.40 g), and tert-butylperoxy-2-ethyl hexanoate (23.1 lg). The mix was fed into the flask with stirring over 120 minutes followed by addition of n-amyl acetate (32.95 g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert- butylperoxy-2-ethyl hexanoate (0.5 g) and n-amyl acetate (26 g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled and filtered at 60°C.

[0069] The branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour was 51.5%, and molecular weight by GPC was: M_w = 20,108; M_n =6,409; PDI = 3.14.

EXAMPLE 4

[0070] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, n-amyl acetate (650 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing MMA (383.6 g), HEMA (158 g), 2-EHMA (150 g), HDDA (28.8 g), and tert-butylperoxy-2-ethyl hexanoate (23.11 g). The mix was fed into the flask with stirring over 170 minutes followed by addition of n-amyl acetate (25.61 g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert-butylperoxy-2-ethyl hexanoate (0.5 g) and n-amyl acetate (26.64 g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled and filtered at 60°C.

[0071] The branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour was 51.4% and molecular weight by GPC was: M_w = 56,505; M_n =8,134; PDI = 6.95.

EXAMPLE 5

[0072] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, n-amyl acetate (650 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing HEMA (288 g), 2-EHMA (403.2 g), HDDA (28.8 g), and tert-butylperoxy-2-ethyl hexanoate (23.1 lg). The mix was fed into the flask with stirring over 120 minutes followed by addition of n-amyl acetate (17.11 g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert-butylperoxy-2-ethyl hexanoate (0.5 g) and n-amyl acetate (13.1 g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled and filtered at 60°C. [0073] The branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour was 52.2% and molecular weight by GPC was: M_w = 28,567; M_n -6,819; PDI = 4.19.

EXAMPLE 6

[0074] In a four-neck round bottomed flask equipped with stirrer and under a nitrogen atmosphere, n-amyl acetate (650 g) was added and heated to 120°C. An initiator and monomer mix feed was prepared by mixing MMA (375.2 g), HEMA (216 g), cyclohexyl methacrylate (CHMA) (71.2 g), HDDA (57.6 g), and tert-butylperoxy-2-ethyl hexanoate (69.33g). The mix was fed into the flask with stirring over 120 minutes followed by addition of n-amyl acetate (20.6 g) as a rinse. The reaction mixture was held for 5 minutes, then a mixture of tert-butylperoxy-2-ethyl hexanoate (0.5 g) and n-amyl acetate (26.73 g) was added over 5 minutes. The resulting reaction mixture was held for 60 minutes at 120°C, then cooled and filtered at 60°C.

[0075] The branched polymer solution was characterized for non-volatiles (solids determination) and molecular weight by GPC. The total non-volatile solids obtained by heating sample at 130°C for 1 hour were 53.1%, and molecular weight by GPC was: M_w = 17,619; Mn =2,944; PDI = 5.99.

[0076] Table 1 summarizes the weight percent of monomers used in Examples 1-6.

Amounts of monomers were varied to increase or decrease Tg, to increase

crosslinking/branching, or to increase the hydroxy functionality, for example.

TABLE 1

' Amyl acetate solvent

[0077] The hydroxy- functional (meth)acrylate copolymers of the present invention were tested in an automotive clearcoat formulation to determine the anti-sag properties of the copolymers. In particular, the branched copolymer solutions of Examples 1-6 were tested as replacements for fumed silica in a commercial clearcoat formula.

[0078] In each case, a copolymer of Examples 1-6 was substituted for the fumed silica presently used in the commercial formulation. The six tested formulations were compared both to the commercial formulation containing fumed silica, and to a control sample of the commercial formulation free of fumed silica and a copolymer of the present invention.

[0079] The commercial clearcoat formula contains fumed silica for anti-sag, solvents, hydroxyl and carbamate functional polymer resins, isocyanate and melamine crosslinkers, catalysts, and other additives for weathering stability and flow and levelling. The fumed silica solution added into the formula is a 37% solids material and is added at a level of 11.76% (by weight) on the total formulated paint. The branched polymer solutions of Example 1 -6 were added at same weight percent levels as a substitute for the fumed silica.

[0080] To test for anti-sag properties of the clear coat formulation, a clearcoat wedge was sprayed onto panels with keyholes, with the dry clearcoat thickness varying from about 30 to 60μιη. The wedge of the clearcoat formulations were sprayed on a black basecoat for appearance and on an E-coat panel for testing sag. The sprayed panels were subjected to a 10 minute ambient flash, followed by a 15 minute bake at 285°F to cure the clearcoat.

[0081] The resulting panels were measured for sag and appearance. The sag threshold was based on how thick a clearcoat could be applied until a keyhole sag of 8 mm is reached. The 8mm distance is measured visually as the distance the clearcoat moved or sagged from the keyholes on a panel at various film thicknesses. The keyhole size was approximately 7.5 mm. The panels were measured for sag, based on how high in thickness of clearcoat paint can be applied until the sag threshold of 8mm is reached. Film thickness measured were the dry film thickness of the clearcoat. The clearcoat containing fumed silica gave a 8mm sag at a 41μιτι film thickness, while clearcoats with the branched copolymers of the present invention gave the same 8 mm sag at film thicknesses ranging from 36-42μιη. A control panel of clearcoat sprayed without any anti-sag agent gave a sag at 8mm film thickness of 25 μηι. The results are summarized in Table 2. TABLE 2. Film-thickness at 8mm Sag of Clearcoats with Different Anti-sag agents

[0082] In addition, a clearcoat formulation sprayed on the black basecoat gave larger film thickness numbers at 8 mm sag compared to when they were sprayed on Ecoat panels.

Thickness numbers of 44 μηι and 48 μηι were observed for clearcoat formulations containing fumed silica and the branched polymer of Example 1, respectively.

[0083] A similar improvement was observed using a present (meth)acrylate copolymer using a different solvent system and a different copolymer composition.

[0084] The panels sprayed with the fumed silica-containing formulation lacked esthetic appeal.

[0085] The hydroxy-functional, branched (mefh)acrylates of the present invention exhibit excellent anti-sag properties and can replace inorganic fumed silicas as anti-sag/rheology modifiers in clearcoats and other coating formulations. The present anti-sag modifiers provide additional advantages over fumed silica, including improved film properties and cost- effectiveness compared to fumed silica, which requires dispersing prior to use. In addition, improper milling/dispersing of fumed silica leads to large fumed silica particle sizes which results in the generation of craters in clear coats.

Claims

WHAT IS CLAIMED:

1. A hydroxy-functional (meth)acrylate having

(a) a weight average molecular weight (Mw) of at least 5,000;

(b) a number average molecular weight (M_n) of about 1,500 to about 20,000;

(c) a polydispersibity index (PDI) of about 2 to about 15;

(d) a glass transition temperature (T_g) of about 50°C to about 110°C; and

(e) a film thickness of about 38 to about 46 μιη at 8 mm in the keyhole test.

2. The (meth)acrylate of claim 1 comprising:

(a) about 10% to about 50%, by weight of a hydroxyalkyl (meth)acrylate;

(b) about 1% to about 10%, by weight, of a crosslinking monomer;

(c) 0% to about 70%, by weight, of a Ci-₄alkyl (meth)acrylate;

(d) 0% to about 70%, by weight, of a Ce-18 alkyl (meth)acrylate;

(e) 0% to about 10%, by weight, of an additional monomer,

wherein at least one of (c), (d), and (e) is present in the (mefh)acrylate.

3. The (meth)acrylate of claim 2 comprising about 15% to about 45%, by weight, of the hydroxyethyl (meth)acrylate.

4. The (meth)acrylate of any preceding claim 2-3 comprising about 1.5% to about 9%, by weight, of the crosslinking monomer.

5. The (meth)acrylate of any preceding claim 2-4 comprising about 20% to about 65%, by weight, of the Ci-₄ alkyl (meth)acrylate.

6. The (meth)acrylate of any preceding claim 2-5 comprising about 8% to about 60%, by weight, of the C₆-i8 (meth)acrylate.

7. The (meth)acrylate of any preceding claim 2-6 comprising 0% to about 8%, by weight, of additional monomer (e).

8. The (meth)acrylate of any preceding claim 2-7 wherein the additional monomer (e) comprises one or more of n-butyl acrylate, n-butyl methacrylate, ethyl acrylate, isopropyl acrylate, isopropyl methacrylate, n-propyl methacrylate, ethyl methacrylate, isobutyl acrylate, t-butyl acrylate, t-butyl methacrylate, methyl acrylate, hexyl acrylate, 2- ethylhexyl acrylate, cyclohexyl acyrlate, ureido methacrylate, benzyl methacrylate, phenyl acrylate, phenyl methacrylate, methyl vinyl ether, a styrenic compound having a formula:

wherein R is hydrogen or a Ci-6alkyl group, and wherein the phenyl ring optionally is substituted with one to four Ci-4alkyl and/or hydroxy groups, and mixtures thereof.

9. The (meth)acrylate of any preceding claim 2-8 having a film thickness of about 40 to about 45μπι at 8 mm sag in a key hole test.

10. A coating composition comprising

(a) about 1% to about 25%, by weight, of a hydroxy- functional (me h)acrylate copolymer of claim 1;

(b) about 1% to about 90%, by weight, of one or more of resin selected from the group

consisting of polyesters, polyester-amides, cellulose esters, alkyds, polyurethanes, epoxy resins, polyamides, acrylics, vinyl polymers, polyisocyanates, melamines, phenolics, urea resins, urethane resins, and polyamides; and

(c) a solvent, preferably an organic solvent, or a solvent mixture;

wherein the total weight of (a), (b), and (c) equals 100%.

11. The coating composition of claim 10 further comprising 0% to about 10%, by weight of (d) one or more additional additive selected from the group consisting of flow additives, leveling additives, wetting and dispersing agents, defoamers, adhesion promoters, slip aids, anti-skinning agents, UV stabilizers, biocides, mildewcides, fungicides, and others, wherein the total weight of (a), (b), (c), and (d) equals 100%.

12. The coating composition of claim 10 which is free of fumed silica and cellulose esters.

13. A coating on a substrate, wherein the coating comprises a dried or cured composition of claim 10.

14. The coating of claim 13 wherein the substrate is selected from the group consisting of wood, plastic, metal, aluminum, steel, cardboard, glass, polypropylene, polycarbonate, polyesters, polyethylene terephthalate, and acrylic sheeting.

15. A method of coating a solid substrate comprising applying a coating composition of claim 10 to the substrate, and allowing the composition to dry on the substrate and/or curing the composition on the substrate.