WO2011031909A1

WO2011031909A1 - Clear coat coating composition and use thereof in the preparation of base coat/clear coat two-layer coatings

Info

Publication number: WO2011031909A1
Application number: PCT/US2010/048335
Authority: WO
Inventors: Claudia Drewin; Carmen Flosbach; Junya Ogawa
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2009-09-10
Filing date: 2010-09-10
Publication date: 2011-03-17
Also published as: JP2011057955A

Abstract

A clear coat with a resin solids consisting of 60 to 70 wt.% binder solids and 30 to 40 wt.% trimeric 1,6-hexane diisocyanate crosslinker, the binder solids comprising 60 to 100 wt.% of a (meth)acrylic copolymer resin A with a calculated glass transition temperature of -15 to +5°C and a weight-average molar mass of 8.000 to 12.000, wherein the monomer composition of the (meth)acrylic copolymer resin A is: a) (meth)acrylic acid in a proportion corresponding to an acid number of the (meth)acrylic copolymer resin A of 5 to 10 mg KOH/g, b) (meth)acrylic monomers with a primary hydroxyl group in a proportion corresponding to a hydroxyl number of the (meth)acrylic copolymer resin A of 120 to 150 mg KOH/g and comprising 50 to 100 mol-% of 1,4-butanediol monoacrylate, relative to the (meth)acrylic monomers with a primary hydroxyl group, c) 15 to 25 wt.% styrene, and d) 15 to 50 wt.% of one or more C4-C12-alkyl (meth)acrylates with at least 4 carbon atoms forming a chain in the alkyl residue.

Description

TITLE OF INVENTION

CLEAR COAT COATING COMPOSITION AND USE THEREOF IN THE PREPARATION OF BASE COAT/CLEAR COAT TWO-LAYER COATINGS

The present invention relates to a clear coat coating composition which can be used in the preparation of the dear coat layer of base coat/clear coat two-layer coatings, in particular in the preparation of a scratch- and acid etch-resistant clear coat layer of automotive base coat/clear coat two-layer coatings.

The present invention satisfies the demand for a (meth)acry!ic copolymer-based clear coat coating composition that is particularly useful for automotive clear coating.

The invention provides a clear coat coating composition of the two- component poiyurethane clear coat type, The clear coat coating composition contains a■hydroxyi-functional (meth)acrylic copolymer resin binder and trimeric 1.S-hexane diisocyanaie (1 _:8-hexane diisocyanaie isocyanurate) as crossiinker.

The clear coat coating composition has a resin solids consisting of 80 to 70 wt.% (weight- ) binder solids and 30 to 40 wt.% trimeric 1,6-hexane diisocyanate crossiinker,

wherein the binder solids comprise 60 to 100 wt.% of a (meth)acrylic copolymer resin A with a calculated glass transition temperature of -15 to +5°C and a weight-average molar mass of 8,000 to 12,000 and 0 to 40 wt.% of one or more further hydroxyi-functional binders,

the sum of the respective wt% equalling 100 wt.%. and

wherein the monomer composition of the (meih)acrylic copolymer resin A is: a) (meth)acrylic acid in a proportion corresponding to an acid number of the (meth)acrylic copolymer resin A of 5 to 10 mg KOH g,

b) (methjacry!ic monomers with a primary hydroxy) group in a proportion corresponding to a hydroxy! number of the (methjacrylic copolymer resin A of 120 to 150 mg KGH/g and comprising 50 to 100 mol-% of 1 ,4-butanedioi monoacryiate, relative to the (meth)acryfic monomers with a primary hydroxyl group,

c) 15 to 25 wt.% styrene, and

d) 15 to 50 wt.% of one or more C4-C12~a!kyl (meth)acrylates with at least 4 carbon atoms forming a chain in the alky! residue.

The term "(meth)acrylic" is used in the present description and the claims. This means acrylic and/or methacryiic.

The term "calculated glass transition temperature" is used in the present description and the claims, it refers to the glass transition temperature (Tg) calculated according to the well-known Fox equation (see, for example, T. Brock, , Grotekiaes and P. Misehke, European Coatings Handbook, 2000, Curt R, Vincentz Ver!ag, Hannover, pages 43-44; Tg values for homopolymers see, for example, Polymer Handbook, 3rd Edition, 1989, .J.Wiley & Sons, New York, page VI-209 and the following).

Ail statements made in the present description and the claims in relation to weight-average molar masses relate to weight-average molar masses determined by GPC (gel permeation chromatography, polystyrene standards, polystyrene gel as stationary phase, tetrahydrofuran as mobile phase).

The (nieth)acryiic copolymer resin A may be prepared by free-radicai copolymerization of a monomer mixture consisting of:

a) (meth)acry!ic acid in a proportion corresponding to an acid number of the {meth)acryitc copolymer resin A of 5 to 10 mg KGH/g,

b) {meth}acryiic monomers with a primary hydroxyl group in a proportion corresponding to a hydroxyl number of the {mefh)acry!ic copolymer resin A of 120 to 150 mg KOH/g and comprising 50 to 100 moi~% of 1 ,4-butaned!Oi monoacryiate, relative to the (meih)acryiic monomers with a primary hydroxyl group,

c) 15 to 25 wt.% styrene, and

d) 15 to 50 wt.% of one or more C4-Cl 2-aikyl (meth)acrylaies with at least 4 carbon atoms forming a chain in the aikyi residue. Examples of (meth)acrylic monomers with a primary hydroxy! grou other than 1 ,4- butanediol monoacrySate include in particular hydroxyefhyi (meth)acrylate and S-hydroxypropyi (meth)acrylate.

Examples of C4~G12-a!kyi (rneih)aerylates with at least 4 carbon atoms forming a chain in the alkyl residue include n-buty! (me.th)acry{ate_f n~ hexyl (rneih}acr late_; 2-eihylhexyl (meth)acryiate, n-decyi (meth)acrylate, n- dodecyi (meth )acry iate

The composition of the monomer mixture, i.e., the ratio between the (meih)acrylic acid, the (meth)acryiic monomers with a primary hydroxy! group, the styrene and the C4-C12-a!kyi (mefh}acryiaies with at least 4 carbon atoms forming a chain in the aikyi residue, is selected in such a manner that the (methjacryiic copolymer resin A has an acid number of 5 to 10 mg KOH/g, a hydroxy! number of 120 to 150 mg KOH/g and a calculated glass transition temperature of -15 to +5*0,

Acid number, hydroxy! number and the calculated glass transition temperature of the (meth)acryiic copolymer A are a direct result of the composition of the monomer mixture. The weighi-average molar mass of the (meih}acrylic copolymer A in the range of 8.000 to 12,000, on the other hand, may be obtained by selecting appropriate conditions and parameters for the free-radical copo!ymerizat!on. The person skilled In free-radical po!ymerization knows such conditions and parameters and how to select and vary those to arrive at the desired weight-average molar mass in said range of 8.000 to 2.000, Examples of such conditions and parameters include in particular the reaction temperature, the manner how monomer mixture and free-radical initiator dosage is performed and type and amount of free-radical initiator used.

The free-radical copolymerization of the monomer mixture may proceed by conventional processes. In this reaction one or more organic solvents are initially introduced into the reaction vessel, heated to the reaction temperature and then the monomer mixture and free-radicai initiators are added.

The free-radicai copolymerization is performed, fo example, at temperatures of 80*0 to 180^oC, preferably at 120°C to 160^¾C, The copoiymerization reaction may be initiated with conventional initiators that are thermally dissociable into free radicals. Examples of free- radical initiators are dia!kyl peroxides, such as di-tert~butyl peroxide, dicumyl peroxide; diacyi peroxides, such as dibenzoyl peroxide, diiauroyi peroxide; hydroperoxides, such as cumene hydroperoxide, tert-butyi hydroperoxide; peresters, such as tert-butyi perbenzoate. ten butyi per-2-ethyihexanoate; peroxy dicarbonates; perketals; ketone peroxides, such as cyciohexane peroxide, methyl isobutyt ketone peroxide and azo compounds, such as azobisisobutyranitrile; C-C-cieaving initiators, such as for example benzopinacoie derivatives.

The free-radica! initiators are in genera! added, for example; in a quantity of 0,1 to 10 wt.%, relative to the tola! quantity of the monomer mixture. The monomers of the monomer mixture may a!so be added separately or with a time delay during the copoiymerization. The monomers or the monomer mixture used may either contain the free-radical initiators, or the free-radical initiators may be added to the monomer mixture optionaiiy with a slight time delay or may be separately added to the reaction medium.

As already mentioned, the binder so!ids of the clear coat coating composition according to the invention may comprise up to 40 wt.%, preferably not more than 20 wt.% of one or more further hydroxyi-functional binders, i.e., hydroxyi-functional binders different from (meth)acrylic copolymer resin A. Examples include hydroxyi-functional (meth)acrylic copolymer resins different from {meth)acrylic copolymer resin A, hydroxyi- functional polyurefhane resins, hydroxyi-functional polyester resins and hydroxyi-functional hybrid binders derived from these resin classes.

in a preferred embodiment, the binder solids of the clear coat coating composition according to the invention consists of the {meth)acrytic copolymer resin A,

The dear coat coating composition according to the invention has a solids content, formed from the resins solids and optionaiiy contained nonvolatile additives, of, for example, 47 to 57 wt.%. It contains, as volatile constituents, one or more organic solvents and, optionally, voiatile additives.

Examples of organic solvents that may be used in the clear coat coating composition of the present invention include glycol ethers, such as, butyl glycol, buty! diglycol, dipropylene glycol dimethyl ether; glycol ether esters, such as, ethyl glycol acetate, butyl glycol acetate, butyl diglycol acetate, methoxypropyl acetate; esters, such as, butyl acetate, isobutyl acetate, amyl acetate; ketones, such as, methyl ethyl ketone, methyl Isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone; alcohols, such as, methanol, ethano!, propane! , butanol; aromatic hydrocarbons, such as, xylene, Solvesso® 100 (mixture of aromatic, hydrocarbons with a boiling range from 155°C to 18.5°C)„ Solvesso® 150 (mixture of aromatic

hydrocarbons with a boiling range from 182°C to 2Q2°C) and aliphatic hydrocarbons.

The clear coat coating composition of the present invention may contain conventional coating additives in amounts of, for example, up to 5 wt-%. for example, leveling agents, rheology influencing agents, such as, pyrogenic silica, urea group-containing reaction products of amines and pol Isocya nates ("sagging control agents"), catalysts, light stabilizers, UV absorbers, antioxidants, substances releasing formaldehyde.

As already mentioned, the clear coat coating composition of the present invention is a clear coat of the two-component po!yurethane dear coat type, it may be prepared by mixing together two components that are stored separately from each other. One of the components comprises the binder solids and the other the trimeric 1 ,6-hexane diisocyanaie crossSinker. Typically, mixing together of the two components happens shortly or directly before the application of the clear coat.

The clear coat coating composition of the present invention is particularly suitable for the preparation of the clear coat layer of base coat/clear coat two-layer coatings, In particular In the preparation of a scratch- and acid etch-resistant clear coat layer of automotive base coat/clear coat two-layer coatings.

The present invention is also directed to a process for the preparation of a base coat/clear coat two-layer coating comprising the steps:

(a) providing a substrate, in particuSar an automotive body or an automotiv body part, provided with a color- and/or effect-imparting base coat layer,

(b) applying a clear coat layer from the dear coat coating composition of the present invention onto the base coat layer and (c) curing the clear coat layer,

it is preferred that the base coat layer on the substrate provided in step (a) has not been cured before the dear coat layer is applied, In other words, it is preferred that step (b) is performed according to the so-called and well-known wet-on-wet coating method and that step (c) of curing the dear coat layer is performed as a step of Jointly curing the base coat iayer and the dear coat Iayer.

In step fb) the clear coat is applied, in particular by spraying, in a dry iayer thickness of, for example, 30 to 50 pm and optionally flashed off briefly at temperatures of, for example, 20 to 4G^*C.

in the following step (c) the dear coat is cured at elevated object temperatures of, for example, 130 to 160°C. Heat curing is in particular performed by baking. As already mentioned, the clear coat curing is preferably performed as a joint curing of base coat and dear coat

Clear coat layers prepared from the clear coat coating composition of the present invention are resistant to chemicals and scratching, in particular acid-resistant and resistant to scratching that occurs when an automobile is washed in a typical commercial car wash.

EXAMPLES

pbw means parts by weight.

general ..procedure):

180 pbw of Solvesso© 100 and 20 pbw of butyl acetate were charged into a flask equipped with stirrer, ihermometer and reflux condenser and heated to 152*0 under stirring.

In a first separate container a monomer mixture was prepared. In a second separate container an initiator mixture was prepared.

The monomer mixture and the initator mixture were simultaneously fed to the heated solvent at 152°C over a period of 8 hours. After the end of the dosing the lines were rinsed with 30 pbw of Solvesso® 100. The reaction mixture wa kept at 152*0 for another two hours. The resin solution was then cooled to below 120^SC and 20 pbw of buiyi acetate were &άύβύ. Table 1 shows type and proportions of monomers and initiators used for preparing the (meth)acryiic copolymer resins 1a, lb and 1c as well as the weight-average molar masses and the caiculated glass transition

temperatures of the copolymers.

Table 1

Clear coat bases were prepared by mixing the following constituents:

Clear coats 3a to 3c were prepared by mixing the bases 2a to 2c in eac case with a poiyisocyanate hardener composed of 68 wt% of hexamethySene diisocyanate isocyanurate and 32 wt.% of Solvesso® 100 in a base : hardener weight ratio of 3 : 1.

(1) Each of the dear coats 3a to 3c was spray-applied in a wedge- shaped gradient to a dry iayer thickness range from 20 to 50 pm on test panels (300x100mm, dear coat wedge in longitudinal direction} provided with a three-layer precoaimg of cathodic elecirodeposition coating primer, primer surfacer and aqueous base coat iayer, the latter having been dried for 0 minutes at 80°C but not cured. After a 10 minute flash-off at 20°C, the dear coat layer was in each case baked for 18 min at 140°C (object temperature). After aging the multi-layer coatings for 24 h, the panels so obtained were tested for the acid resistance of the outer ciear coat layer.

(2) Each of the dear coats 3a to 3c was spray-applied in a dry layer thickness of 40 pm on test panels provided with a three-layer precoating of cathodio eJectrodeposition coating primer, primer surfacer and aqueous base coat layer, the latter having been dried for 10 minutes at 80°C but not cured. After a 10 minute fiash-off at 20°C_S the clear coat layer was in each case baked for 18 min at 140°C (object temperature). After aging the multi-layer coatings for 24 h, the panels so obtained were tested for the scratch resistance of the outer clear coat layer.

Table 2 gives results of technological tests carried out on the multilayer coatings.

Taoie 2

d

by initial gloss of the muiii-!ayer coating, gloss measurement in each case at an angle of illumination of 20°) was measured without refiow and after one hour's refiow at 80°C, Scratching was carried out using the iaboratory-scale Amtec Kistier car wash (cf. Th, Kiimmasch and Th. Engbert, Deveiopment of a uniform laborator test method for assessing the car wash resistance of automotive top coats, in DFO Proceedings 32, pages 59 to 66, Techrsologie- Tage, Proceedings of the Seminar on 29. and 30.4.97 in Cologne, Published by Deutsche Forschungsgeselischaft fur QberflSchenbehandiung e.V.

Adersstra e 94, 40215 Dusseidorf).

2} 500 μi-drops of 40 wt.% sulphuric acid were placed on the wedge- shaped outer clear coat layers of the test panels by using a rnicro-pipefter. Placement of the acid drops was performed in each case aiong the clear coat wedge in 5 pm steps starting wit 30 pm clear coat dry film thickness, i.e. at 30 μιη, 35 pm, 40 ym, 45 pm and 50 pm clear coat thickness. The test panels so provided with the acid drops were put in an oven preheated to 80°C. After 30 minutes at SO^C the test panels were removed from th oven, rinsed with water and dried with a soft cloth. The etching of the spots at the different clear coat fiim thicknesses was judged according to the foilowing ranking;

10 - no change

9 ~ swelling

8 - swelling, some blisters at the collar

7 - swelling; many blisters at the collar

6 - swelling, blisters at the collar and in the center

5 - swelling, many blisters at the collar and in the center

4 - swelling covered with lots of blisters

3 - incipient etching at the collar and blisters in the center

2 - bigger etching at the collar and blisters in the center

1 ~ complete etching

Claims

1. A clear coat coating composition with a resin solids consisting of 80 to 70 wt.% binder solids and 30 to 40 wt.% i imerie 1 ,6-hexane dissocyanate crossiinker,

wherein the binder solids comprise 80 to 100 wt.% of a ( eth)acryi!c copolymer resin A with a calculated giass transition temperature of -15 to +5^SC and a weight-average molar mass of 8.000 to 12.000 and 0 to 40 wt.% of one or more further hydroxyi-functional binders,

the sum of the respective wt.% equalling 100 wt.%, and

wherein the monomer composition of the {meth)acrylie copolymer resin A is; a) (meth)acryilc acid in a proportion corresponding to an acid number of the (rnefhjacrylic copolymer resin A of 5 to 10 mg OH/g_;

b) (meth)acrylic monomers with a primary hydroxyi group in a proportion corresponding to a hydroxy! number of the (meth)acryiic copolymer resin A of 120 to 150 mg KOH/g and comprising 50 to 100 mol-% of 1 ,4- utanediol monoacrylate, relative to the (methjacrylic monomers with a primary hydroxyi group,

c) 15 to 25 wt.% styrene, and

d) 15 to 50 wt. of one or more C4-C12^»aikyi (meth)acrylates with at ieast 4 carbon atoms forming a chain in the aikyl residue.

2. The ciear coat coating composition of claim 1 , wherein the binder solids consists of the (meth)acryiic copolymer resin A.

3. A process for the preparation of a base coat/clear coat two-iayer coating comprising the steps:

(a) providing a substrate provided with a color- and/or effect-imparting base coat layer,

(b) applying a clear coat layer from the clear coat coating composition of claim 1 or 2 onto the base coat layer and

(c) curing the clear coat layer.

4, The process of claim 3_S wherein the substrate is an automotive body or an automotive body part,

5. The process of claim 3 or 4, wherein step (c) is performed as a step of jointly curing the base coat layer and the clear coat layer.