GB2025985A

GB2025985A - Water-dilutable heat curable compositions which provide coatings having a reduced tendency to surface defects such as cissing and pinholing comprise

Info

Publication number: GB2025985A
Application number: GB7920044A
Authority: GB
Original assignee: Vianova Resins AG
Current assignee: Allnex Austria GmbH
Priority date: 1978-06-20
Filing date: 1979-06-08
Publication date: 1980-01-30
Also published as: DE2918067C2; ATA447778A; FR2429247A1; GB2025985B; IT1121795B; DE2918067A1; FR2429247B1; IT7923534A0; AT355693B; ES481683A1; SU1068039A3

Abstract

(1) 40 to 85% by weight of a polymer dispersion based on (meth)acrylate esters and (meth)acrylic acid, optionally styrene and/or alkylstyrenes, (2) 5 to 40% by weight of a water soluble and/or water dispersible partially or completely etherified amine-formaldehyde condensate, (3) 10 to 40% by weight of a solution polymer water soluble upon neutralisation with bases consisting of hydroxyalkyl(meth)acrylates, (meth)acrylates and optionally vinyl aromatic monomers selected on the basis of the glass transition temperatures of their homopolymers, (meth)acrylic acid, and optionally diesters of maleic or fumaric acid with C4-C10 monoalcohols, (4) 0-100% by weight (based on components (1), (2) and (3)) of one or more pigments and/or extenders, auxiliary solvents and additives. m

Description

SPECIFICATION Water-dilutable heat curable coating compositions British Patent Specification number 1,467,879 describes heat hardenable coating compositions based on specific copolymer dispersions and giving highly flexible coatings in admixture with water soluble or water dispersible amine resins. Such highly flexible coatings have good mar resistance, weather resistance, adhesion and surface quality without pinholing. Besides the copolymer dispersions disclosed in this specification, which consist mainly of acrylic monomers in combination with an amine resin, the coating compositions contain as an essential ingredient a pigment paste by means of which the pigments and extenders are introduced into the paint.

According to the above mentioned patent specification the pigment paste may, for example, be a water soluble solution polymer of the acrylic type.

However, it has been shown that in order to obtain optimum performance from the paint, particularly with regard to obtaining a good quality film with higher film thickness, it is not only necessary to carefully select the type and quantity of the monomers which are polymerized to form the copolymer dispersion, the dispersion medium of the pigment paste being also of paramount importance.

It has been discovered that when a suitable dispersion medium is used, the monomers which are polymerised to form the copolymer dispersion, the dispersion medium of the pigment paste being also of paramount importance. It has been discovered that when a suitable dispersion medium is used, the monomers which are polymerised to form the dispersion can be chosen from a much broader range than hitherto. It is then possible to tailor more effectively the properties of the coating composition according to requirements.

It has now been found that binder compositions containing particularly selected solution polymer dispersions and water soluble solution polymers, amine resins and optionally pigments, extenders and/or additives are capable of giving coating compositions having improved performance in practical use.

The present invention is thus concerned with improved water dilutable heat curable coating compositions containing a compatible combination of the following components: (1) 4085% by weight of a polymer dispersion obtained through emulsion polymerisation of the following monomers: 22-89% by weight of acrylic and/or methacrylic acid esters with monoalcohols with from 1 to 18 Catoms, 0-50% by weight of styrene and/or alkyl substituted styrenes, 1-3% by weight of acrylic and/or methacrylic acid, 10-25% by weight monoesters of acrylic or methacrylic acids with glycols or polyalkylene glycols, (2) 540% by weight of a water soluble and/or water dispersible amine-formaldehyde condensation product, the methylol groups of which are either partially or completely etherified with monoalcohols preferably with 1 to 4 carbon atoms, (3) 1 00% by weight of a solution polymer water soluble upon neutralisation with bases and consisting of 1080% by weight, preferably 2535% by weight of hydroxyalkyl(meth)acrylates, the homopolymers of which have glass transition temperatures of below -250C, preferably below 400 C, 8-86% by weight, preferably 60 to 70% by weight of (meth)acrylates, the homopolymers of which have glass transition temperatures of below -400C, preferably below 55C, and 412% by weight, preferably 67% by weight of (meth)acrylic acid and optionally up to 30% by weight of alkyl substituted vinyl aromatic monomers, the homopolymers of which have a glass transition temperature of below-40 C, and/or-of diesters of maleic or fumaric- acid with C4-C10 monoalcohols, (4) 0-1 00% by weight (based on the total weight of components (1), (2) and (3) together) of one or more pigments and/or extenders and conventional auxiliary solvents and additives.

In a special embodiment component (3) may be present in the coating composition as a water soluble partial reaction product with from 2060% by weight of the used quantity of component (2).

The term "compatible combination" as used herein is intended to signify that a clear varnish prepared according to the invention is capable, on stoving, of forming a homogeneous clear film.

The coating compositions of the invention containing the selected component (3) showfurther enhanced levelling compared with the coating compositions according to British Patent Specification number 1,467,879 and, in particular, allow thick coats to be obtained on spray application. Upon adequate flash-offthe coats bake to excellent films without cissing or pinholing. While with the products of the aforementioned patents the critical limit is a film thickness of about 45 ym, with the coemployment of the selected component (3) or its partial reaction product with the amine formaldehyde condensation product, films having a thickness of up to 60 ym can be attained without defects.The coating compositions of the invention moreover, exhibit on application considerably reduced dependence on ambient air humidity as compared to normal paints based on aqueous polymer dispersions. Neither could it have been foreseen that the use of polymer resins having an extremely iow glass transition temperature would influence to such an extent the cissing tendency of paints based on polymer dispersions.

The preparation of the polymer dispersions (component 1) is carried out in known manner by emulsion polymerisation in the presence of anionic and optionally non-ionic emulsifiers and free radical initiators. Suitable anionic emulsifiers are hydrocarbon sulphonates, like dodecyl benzene sulphonate, sodium lauryl sulphate, sodium tridecyl sulphate or the sulphates of ethoxylated fatty alcohols, such as sodium lauryl ethoxylate sulphate or a sulphated octylphenol ethoxylate. Non-ionic emulsifiers such as ethoxylated alkylphenols may be used in mixture with the anionic emulsifiers. Further emulsifiers may be added when the polymerisation is finished to improve the storage stability of the products.

Suitable monomers forming the polymer dispersion are in particular the esters of acrylic or methacrylic acid with straight chain or branched monoalcohols with from 1 to 18 C-atoms, for example methyl-, ethyl-, propyl-, or butyl-acrylates or methacrylates. The polymer dispersions also contain esters of acrylic or methacrylic acid with glycols, such as ethyleneglycol and propylene glycol or with polyalkylene glycols such as di-, tri- or polyethylene glycol or the corresponding polypropylene glycols.

Further monomeric building blocks are styrene or alkyl substituted styrenes, such as vinyl toluene, a-methylstyrene and tert.butylstyrene.

The amine resins (component 2) are crosslinkers conventionally used in the paint industry, such as is amine-aldehyde condensates based on aminotriazines such as melamine, benzoguanamine and urea.

Those types are preferred which are substantially or completely etherified, and they can be used in their monomeric or oligomeric form, an example being hexamethoxymethylmelamine.

Component (3) used according to the invention is a solution polymer with an acid number of at lest 26 mg KOH/g, becoming water soluble upon at least partial neutralisation of the carboxy groups present with inorganic or organic bases. Owing to their constitution, these polymers have extremely low glass transition temperatures.

Suitable monomers, the homopolymers of which have glass transition temperatures as stated in claim 1 are for instance: 1. hydroxyalkylesters of (meth)acrylic acid, the homopolymers of which have a glass transition temperature of below -250C: hydroxyethyl acrylate (30O C) (2)-hydroxypropyl acrylate (-490C) (4)-hydroxybutyl acrylate (-640C) polyethyleneglycol monomethacrylate with a molecular weight of about 220-240 ( < -250C) polypropyleneglycol monomethacrylate with a molecular weight of about 260550 ( < --250C) 2. esters of (meth)acrylic acid, the homopolymers of which have a glass transition temperature of below -400C:: n-propyl acrylate (-450C) n-butyl acrylate (--560C) isobutyl acrylate (-400C) (2)-ethyl-hexyl acrylate (-70DC) n-octyl acrylate G800C) n-decyl methacrylate (-600C) n-dodecyl methacrylate (-650C) isobornyl methacrylate (-1 140C) 3. Alkylsubstituted vinylaromatic monomers, the homopolymers of which have glass transition temperatures of below --400C, such as n-octyistyrene (--450C), n-nonylstyrene (-530C), ndecylstyrene (-65 0C), n-dodecylstyrene (-52 0C) or the corresponding substituted methyl styrenes.

4. Maleic acid and fumaric acid diesters of monoalcohols with from 4 to 10 carbon atoms, for example dibutylmaleate, dibutylfumarate, di-ethylhexylmaleate and dioctylfumarate.

The preparation fo the solution polymers is effected by free-radical polymerisation in inert organic solvents such as ethyl acetate, ethylglycol acetate, butanol, glycol ethers, particularly diethylene glycol monobutylether. Preferably the solvent is first charged to a suitable-reaction vessel and the monomer blend and the initiator are added at reaction temperature. Alternatively, part of the total monomer blend can be charged and the rest can be added in the course of reaction. To render the solution polymers water soluble their carboxy groups are totally or partially neutralised with amines, preferably with tertiary alkyl amines or alkanolamines. To obtain solvent-free solution polymers, the solvent may be removed from the diluted aqueous solution by distillation, optionally with azeotropic means and/or vacuum-stripped.

As pigments and extenders optionally added to the compositions of the invention pigments and extenders normally used in the paint industry are suitable. The ratios to be employed for the various end uses and colour tones are known to those skilled in the art. In preparing pigmented paints the pigments are dispersed in component 3 in normal equipment and are admixed to the dispersion. Normal paint additives such as antifoams, levelling aids, corrosion inhibitors, slip aids, etc. can be added to the paint or to one of the components, as long-as the additive is compatible with the binder and the binder solution.

The following examples illustrate the invention without limiting the scope of it; parts are by weight.

1. Preparation of the polymer dispersions (Component 1) The polymer dispersion used according to the invention are prepared in a known manner according to the emulsion polymerisation process. The dispersions used in the examples have the following composition (parts by weight): Dispersion I Dispersion II 105 styrene 200 styrene 148 methyl methacrylate 200 n-butyl acrylate 272 2-ethyl-hexyl acrylate 40 hydroxyethyl methacrylate 99 n-butyl methacrylate 50 polypropyleneglycol monomethacrylate (MW = 376-434) 141 hydroxyethyl methacrylate 21 methacrylic acid 13 methacrylic acid 1.5 sodium vinyl sulfonate 2.3 t-dodecylmercaptane 3.7 t-dodecylmercaptane 4.4 octylphenol reacted with 2 mols of ethylene oxide and sulfated (28%) 1.5 dodecylbenzenesulfonate 3.9 polyethoxylated octylphenol (16 mols .ethylene oxide) 7.8 polyethoxylated octylphenol (16 mols ethylene oxide) 2.5 ammonium peroxodisulate 1.5 ammonium peroxodisulfate 935 deionised water 500 deionised water 2. Preparation of the solution polymers The solvent is charged into a polymerisation vessel equipped with stirrer, reflux condenser, charging vessel, thermometer and inert gas supply. The monomers, initiator, preferably azobisisobutyronitrile and optionally chain transfer agent are charged to the charging vessel. The solvents warmed to 800C and the blend is continuously added to the solvent over 6 hours while a reaction temperature of 800C is maintained. At the end of the addition more initiator (about 1-3 parts) is added to the batch and the temperature is held at 800C for another 2 hours. Then the batch is held at 1 000C for 1 hour.The solids content of the resins as listed in Table 1 ranges between 45 and 50%.

Key to Table 1 HEA hydroxyethyl acrylate HPA 2-hydroxypropyl acrylate HBA 4-hydroxybutyl acrylate PAMA polyalkyleneglycol monomethacrylate (a) polypropyleneglycol monomethacrylate (MW: 376-434) (b) polyethyleneglycol monometh acrylate (MW: 394-438) BAC n-butyl acrylate EHA 2-ethyl-hexyl acrylate DMA dodecyl methacrylate (laurylmethacrylate) ACS acrylic acid MACS methacrylic acid OST n-octylstyrene DBF dibutylfumarate BDG diethyleneglycolmonobutylether EGA ethyleneglycolmonoethylether acetate BU butanol EXAMPLES 1-5 Paints according to the following formulae were prepared from the solution polymers C, J and K and the dispersions I and II.

The solution polymer (component 3) was blended with dimethylethanolamine, until a sample, diluted 1:1 with deionised water had an approximate pH-value of 9.50 parts of the water-free neutralised resin solution were passed over a three roll mill together with 80 parts TiO2 (Rutile type) and were mixed with 25 parts hexamethoxymethyl melamine. With thorough stirring the blend was admixed to the dispersion which was brought to a pH-value of about 7 with dimethylethanolamine, while optionally deionised water was added for dilution. Upon thorough mixing, 3 parts of a 10% aqueous solution of p-toluene sulfonic acid neutralised with dimethylethanolamine and 0.3 parts of corrosion inhibitors were added. Each paint was diluted with deionised water to a spray viscosity of 20 s (DIN 53 211).The paints were sprayed onto non-treated steel panels and stoved for 30 minutes at 1 600C. TABLE 1 Composition of the solution polymers of the invention (Component 3)

Monomers Solvents HEA HPA HBA PAMA BAC EHA DMA ACS MACS OST DBF BDG EGA BU A 125(a) 220 22 367 B 48(a) 140 12 220 C 125(a) 345 30 511 D 275(a) 195 30 511 E 170 290 40 511 F 170(a) 290 40 511 G 170 300 30 511 H 170 300 30 511 J 68(b) 120 12 230 K 125(a) 198 34 147 511 L 125 215 30 130 511 M 125 215 30 130 511 Table 2 lists the paint formulations 1-5 The evaluation results are listed in Table 3 TABLE 2 Formulation of the paints, Examples 1 - 5 Example 1 2 3 4 5 component 1 1 111 - 111 - 111 11 - 100 - 100 componet 2 HMMM 25 25 25 25 25 component 3 C 50 50 - - J - - 50 bO - K - - - - 50 pigment TiO2-Rutiletype 80 80 80 80 80 pTSA (neutral, 10%) 3 3 3 3 3 corrosion inhibitor 0.3 0.3 0.3 0.3 0.3 TABLE 3 Example 1 2 3 4 5 dry film thickness m 40 40 35 35-40 40 (1) gloss Lange (60 ) 90-98 95 85-90 90 90 (2) pendulum hardness Konig/DIN 53157 80s 755. 85s 70s 90s (3) xylene test, minutes+) 4.5 4 5 3 4,5 (4) Erichsen indentation, mm 5 6.5 5 6.5 5 (5) Erichsen impact++) 50 80 40 80 60 (6) crosshatch DIN 53 151 0-1 0-1 0-1 0-1 1-2 (7) cissing+++) m or over flat 90 70 70 65-70 90 ( dry film) vertical 60 65 50-55 60 60 +) swelling time after which film can be scratched off with fingemails.

++) direct.

+++) 20 min.flash-off at room temperature and 30 min/160 C.

EXAMPLE 6 734 parts solution polymer A are diluted with 1006 parts deionised water and adjusted to a pHvalue of about 8.5 with dimethylethanolamine. The butanol and most of the water is distilled off. A 30% resin solution is obtained the pH-value of which is adjusted to 9 with dimethylethanolamine.

83 parts of the resin solution are ground on a three roll mill with 80 parts of TiO2-Rutile type and 25 parts diethyleneglycolmonobutylether, and then mixed with 25 parts of a substantially methylolated and methanol etherified melamine condensate. This blend was slowly introduced with vigorous stirring into 111 parts of dispersion I, having a pH-value of 7-7.5, adjusted with dimethylethanolamine; optionally deionised water may be added at the same time. After thorough mixing, 3 parts of a 10% aqueous solution of p-toluene sulfonic acid, neutralised with dimethylethanolamine, and 0.3 parts pf corrosion inhibitor were added.

The paint was diluted to a spray viscosity of 20 s (DIN 53 211) with deionised water, was sprayed onto cleaned steel panels and cured at 1 600C for 30 min.

The test results are shown in Table 4.

EXAMPLE 7 Solution polymerJ was mixed with 80 parts of hexamethoxymethylmelamine and held at 1 500C for 5 hours, a small quantity of water and solvent distilling off. The resin thus obtained was neutralised with dimethylethanolamine to the extent that a sample, diluted 1:1 with distilled water, had a pH-value of about 9. About 50 parts of the water free neutralised resin solution were passed over the three roll mill together with 80 parts of TiO2 (Rutile type) and mixed with 11.8 parts of hexamethoxymethylmelamine.

The mixture was slowly introduced into 111 parts of dispersion I, which was stirred vigorously all the while and which was brought to a pH-value of from 7-7.5 with dimethylethanolamine, optionally diluting the blend with deionised water at the same time.

The paint is further processed according to Example 6. The test results are shown in Table 4.

TABLE 4 film Tests according to Table 3 thickness Example im (1) (2) (3) (4) (5) (6) (7) 6 40 90 72s 5.5 5.0 80 0-1 80-90 60 7 37 90 74s 5.5 4.5 70 1-2 55-60 50-55

Claims

CLAIMS:

1. A water dilutable heat curable coating composition containing a compatible combination of the following components: (1) 40 to 85% by weight of a polymer dispersion obtained by emulsion polymerisation of the following monomers: 22 to 89% by weight of esters of acrylic acid and/or methacrylic acid formed with monoalcohols containing 1 to 18 carbon atoms, O to 50% by weight of styrene and/or alkyl substituted styrenes, 1 to 3% by weight of acrylic acid and/or methacrylic acid and 10 to 25% by weight of monoesters of acrylic and/or methacrylic acids with glycols and/or polyalkylene glycols; (2) 5 to 40% by weight of a water soluble and/or water dispersible amine-formaldehyde condensation product, the methylol groups of which are either partially or completely etherified with monoalcohols:: (3) O to 40% by weight of a solution polymer formed by polymerisation of: 10 to 80% by weight of hydroxyalkylacrylates and/or hydroxyalkylmethacrylates the homopolymers of which monomers have glass transition temperatures below 2500, 8 to 86% by weight of acrylates and/or methacrylates the homopolymers of which monomers have glass transition temperatures below -400C, 4 to 12% by weight of acrylic acid or methacrylic acid, O to 30% by weight of alkyl substituted vinylaromatic monomers the homopolymers of which monomers have glass transition temperatures below -400C and/or diesters of maleic or fumaric acids formed with monoalcohols containing 4 to 1 0 carbon atoms: the solution polymer being rendered water soluble by et least partial neutralisation with a suitable base or bases and (4) 0 to 100% by weight (based on the total weight of components (1), (2) and (3) together) of one or more pigments, extenders, solvents or conventional additives.

2. A coating composition as claimed in claim 1 in which the amount of hydroxyalkylacrylates and/or hydroxyalkylmethacrylates in component (3) is 25 to 35% by weight of component (3).

3. A coating composition as claimed in either of claims 1 and 2 in which the hydroxyalkylacrylates and/or hydroxyalkylmethacrylates in component (3) are such that their homopolymers have glass transition temperatures below -4O0C.

4. A coating composition as claimed in any of the preceding claims in which the amount of acrylates and/or methacrylates in component (3) is 60 to 70% by weight of component (3).

5. A coating composition as claimed in any of the preceding claims in which the acrylates and/or methacrylates in component (3) are such that their homopolymers have glass transition temperatures below -550C.

6. A coating composition as claimed in any of the preceding claims in which the amount of acrylic acid or methacrylic acid in component (3) is 6 to 7% by weight of component (3).

7. A coating composition as claimed in any one of the preceding claims in which component (3) is partly reacted with 20 to 60% by weight of Component (2) to form a water soluble partial reaction product.

8. A coating composition as claimed in claim 1 substantially as herein described.

9. A coating composition as claimed.in claim 1 substantially as herein described in any of the examples.