AU664482B2

AU664482B2 - Powder coating composition with hydroxyalkylamide crosslinker

Info

Publication number: AU664482B2
Application number: AU47631/93A
Authority: AU
Inventors: Marten Houweling; Dirk Armand Wim Stanssens; Wilhelmus Henricus Hubertus A Van Den Elshout
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 1992-07-29
Filing date: 1993-07-21
Publication date: 1995-11-16
Anticipated expiration: 2013-07-21
Also published as: BE1006097A3; TW248568B; WO1994003545A1; AU4763193A; CN1086836A; EP0652911A1

Description

OPI DATE 03/03/94 AOJP DATE 26/05/94 APPLN. ID 47631/93 PCT NUMBER PCT/NL93/00155 AU9347631 INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 94/03545 C09D 5/03, 133/06, 167/02 Al (43) International Publication Date: 17 February 1994 (17.02.94) (21) International Application Number: PCT/NL93/00155 (74)Agent: SCHMEETZ, Marcel, Max, Hubertina, Johanna; Octrooibureau DSM, P.O. Box 9, NL-6160 MA Geleen (22) International Filing Date: 21 July 1993 (21.07.93) (NL).

Priority data: (81) Designated States: AU, FI, JP, NO, US, European patent 9200687 29 July 1992(29.07.92) BE (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).

(71) Applicant (for all designated States except US): DSM N.V.

[NL/NL]; Het Overloon 1, NL-6411 TE Heerlen Published With international search report.

(72) Inventors; and Inventors/Applicants (for US only) STANSSENS, Dirk, Armand, Wim [BE/NL]; Pastoorslindestraat 75 Bl, B-3620 Lanaken VAN DEN ELSHOUT, Wilhelmus, Henricus, Hubertus, Antonius [NL/NL]; Onderstehof 9, NL- 6132 SM Sittard HOUWELING, Marten [NL/ NL]; Engelsmanplaat 113, NL-8032 DX Zwolle 6 4 (54) Title: POWDER COATING COMPOSITION WITH HYDROXYALKYLAMIDE CROSSLINKER (57) Abstract The invention relates to a powder coating composition comprising as a binder a polymer with free carboxylic acid groups and as a crosslinker a compound containing P-hydroxyalkylamide groups. The crosslinker comprises a combination of at least two compounds containing p-hydroxyalkylamide groups and each compound having different 3-hydroxyalkylamide functionalities, the first compound having a P-hydroxyalkylamide functionality of 3 and the second compound having a p-hydroxyalkylamide functionality of 3.

WO 94/03545 PC's/NL93/00155 1 POWDER COATING COMPOSITION WITH HYDROXYALKYLAMIDE CROSSLINKER The invention relates to a powder coating compostion comprising as a binder a polymer with free carboxylic acid groups and as a crosslinker a compound containing 1-hydroxyalkylamide groups.

A powder coating comprising a co-reactable mixture of an amorphous carboxylic acid group containing polyester and a p-hydroxyalkylamide is known from EP-A- 322834. The composition described in this application is cured after application to a substrate by heating the powder to 160-200 0 C so that the powder melts, forming a smooth layer. At that temperature the coating is chemically crosslinked due to an esterification reaction between the acid groups of the polymer and the hydroxy groups of the compound containing B-hydroxyalkylamide groups. According to EP-A-322834, a de-gasifying agent, benzoin (0.5 to 3% by wt. of the powder composition), may be added to the composition. A de-gasifying agent is needed to ensure that the air and/or water entrapped due to melting of the powder (during a curing cycle) are removed from the paint layer as a result of the reaction.

Any gas bubbles that remain in the coating reduce the adhesion of the coating to the substrate and markedly adversely affect the protection obtainable with the coating.

Although coatings of this composition are characterized in EP-A-322834 as having good physical properties, such compositions are unsuitable for preparing a white or crystal-clear coating because the powder coating exhibits some degree of browning after curing, as indicated in Mercurio, New Perspective on Hydroxyamide Crosslinkers, 16th International Conf. in Org. Sci. and Tech. 235-49 (Athens, Greece 1990).

Also, browning appears to intensify upon heating WO 94/03545 PC/NL93/00155 2 the cured powder coating at a temperature of 200 0 C for a prolonged period of time (for example between 30 and minutes). This discolouration upon excessive curing (yellowing on overbake) increases with the amount of benzoin. A lower amount of benzoin, on the other hand, results in a lower blister limit, such as lower than pm, which results in surface defects.

The object of the invention is to provide a powder coating composition in which it is possible to use a small amount of benzoin, for example between 0.05 and 0.8 to obtain the highest possible blister limit, for example higher than 120 pm. Of course, the powder coatings must also retain good mechanical properties, such as, for example, good gloss, toughness and impact resistance and chemical properties such as for example a good chemical resistance.

The invention is characterized in that the crosslinker comprises a combination of at least two compounds containing B-hydroxyalkylamide groups and each compound having different p-hydroxylalkylamide functionalities, the first compound having a A-hydroxyalkylamide functionality of a 3 and the second compound having a 0-hydroxyalkylamide functionality of 5 3.

The functionality stands for the average number of 5-hydroxyalkylamide groups per molecule.

As a result, powder coatings are obtained in which the blister limit has been raised considerably while the desired mechanical and chemical properties are retained.

Suitable compounds containing Bhydroxyalkylamide groups and having a functionality of 3 can be depicted structurally according to formula R3 R 2 O 0 R2 R3 SII II 1 HO C C N C A C N C C H (I)

R

3

R

2 m R R ,R 2

R

3 )n where: WO 94/03545 PCr/NL93/00155 3 A represents a mono- or polyvalent organic group derived from a saturated or unsaturated alkyl group with 1-60 carbon atoms (for example ethyl, methyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, eicosyl, triacontyl, tetracontyl, pentacontyl and hexacontyl); an aryl group, such as for example phenyl, naphthyl; a trialkylene amino group with 1-4 carbon atoms per alkylene group, for example trimethylene amino and triethylene amino; or an unsaturated residue with one or more alkenic groups with 1-4 carbon atoms, such as, for example, ethenyl, 1-methyl ethenyl, 3-butenyl-l,3diyl and 2-propenyl-l,2-diyl, carboxy-alkenyl group, for example 3-carboxy-2-propenyl group, an alkoxy carbonylalkenyl group with 1-4 carbon atoms, such as, for example, 3-methoxy carbonyl-2-propenyl group;

R

1 represents hydrogen, an alkyl group with 1carbon atoms (for example methyl, ethyl, n-propyl, n-butyl, sec. butyl, tert. butyl and pentyl) or a hydroxyalkyl group with 1-5 carbon atoms (for example 2-hydroxyethyl, 3-hydroxypropyl, 2-hydroxypropyl, 4-hydroxybutyl, 3-hydroxybutyl, 2-hydroxy-2-methylpropyl, or the hydroxy derivatives of the pentyl isomers);

R

2 and R 3 are the same or different and each independently represents hydrogen or a straight or branched alkyl group with 1-5 carbon atoms, while one of the groups R 2 and one of the groups R 3 may also form, together with the adjacent carbon atoms, a cycloalkyl group, such as, for example, cyclopentyl and cyclohexyl;

R

2 and R 3 may also be hydroxyalkyl groups, such as, for example, hydroxy (C 1 -Cs)-alkyl groups, hydsixymethyl and l-hydroxyethyl, being preferred among the latter and the p-hydroxyalkylamide functionality is 3.

Preferably, the functionality is 4.

According to a further preferred embodiment of the invention in formula A is an alkyl group with (1-10) carbon atoms,

R

1 represents 2-hydroxyethyl or hydrogen, and

R

2 and R 3 are independent of one another hydrogen WO S14/03545 PCr/NL93/00155 or hydroxy (Cl-C 2 )-alkyl.

Preferably, the first compound having a 0hydroxyalkylamide functionality of a 3 is a compound according to formula (II):

HO-H

2

C-H

2 C 0 0 CH,--CH 2

-OH

l Il r-C-(CH 2 4 -C-N XII)

HO-H

2

C-H

2 C CH 2

-CH

2

-OH

Very suitable compounds having a A-hydroxyalkylamide functionality of 5 3 are compounds according to formula having a A-hydroxyalkylamide functionality of 8 3 or compounds according to formula (III): 0 R 2

R

3 A C N C C OH (III) R 1 2

R

3 1 3 wherein formula (III) A represents a monovalent group as defined for formula where R 1

R

2 and R 3 also have the same meaning as in formula and where m 1 or 2.

R

1 represents 2-hydroxyethyl or hydrogen, and

R

2 and R 3 are independent of one another hydrogen or hydroxy (C 1

.C

2 )-alkyl.

Preferably; the second compound having a phydroxyalkylamide functionality of 5 3 is a compound according to formula (IV): 0 CH 2

CH

2

OH

CH

3 C N (IV)

CH

2 CH2 OH Preferably, the functionality of the second compound having a functionality of 5 3 according to formula is 2.

WO 94/03545 PC/NL93/00155 5 Compounds according to formula are also very suitable as compounds having a functionality of 3: 0 CH 2

CH

2

OH

II H N (V)

CH

2

CH

2

OH

The weight ratio in the crosslinker between is preferably between 90:10 and 10:90 and more preferably between 80:20 and ?0:80. This ratio depends on the functionality of the polymer with free carboxylic groups.

Usually the average functionality of the polymer is between 1.7 and 4.5 and preferably between 2.3 and The weight ratio of the crosslinker to the polymer is usually between 10:90 and 3:97, more preferably between 20:80 and 3:97.

The acid number of the polymer containing carboxyl groups is preferably between about 15 and about 150 mg KOH/gram resin, in particular is between about and about 70 mg KOH/gram resin.

The glass transition temperature, Tg, is preferably between about 30 0 C and about 800C and in particular ranges between about 35 0 C and about 65 0

C.

The viscosity at 165 0 C (Emila, D 17.6 s- 1 is preferably between about 100 and about 1000 dPas and in particular ranges between about 100 and about 800 dPas.

Said parameters influencing powder coating properties and the determination of these parameters is decribed at pages 175-199 and 284-300 of Powder Coatings, Chemistry and Technology by Misev (Wiley and Sons, 1991).

Preferably, the polymer that contains carboxyl groups is a polyester and/or a polyacrylate.

Examples of preferred monomers for polyacrylates that can be incorporated in the main chain of the polymer are unsaturated monocarboxylic acids, such as, for example, acrylic acid, methacrylic acid and crotonic acid, unsaturated dicarboxylic acids, such as, for example, maleic acid, 2-methyl maleic acid, itaconic acid, and WO 94/03545 P(TNL93/00155 6 a-B-methylene glutaric acid, unsaturated anhydrides, such as, for example, maleic anhydride, itaconic anhydride, acrylic anhydride and methacrylic anhydride. The polymer usually also consists of copolymerized esters of (meth)acrylic acid, such as, for example, methyl methacrylate,-butyl acrylate, 2-ethyl hexyl acrylate or acrylonitrile, styrene and other ethylenically unsaturat&d compounds.

Suitable polyesters can be obtained via standard preparation methods from essentially aromatic polycarboxylic acids, such as, for example, phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, trimellitic acid, 3,6-dichloro phthalic acid, tetrachloro phthalic acid, or, if obtainable, the anhydrides, acid chlorides or lower alkyl esters thereof. Usually the carboxylic acid component is composed.at least of 50% by weight, preferably at least 70 mol of isophthalic acid and/or terephthalic acid. Exemplary procedures are described in said reference of Misev at pages 144-162.

The polycarboxylic acids used can also be cycloaliphatic and/or acyclic polycarboxylic acids such as, for example, totrahydro phthalic acid, hexahydro-endomethylene terephthalic acid, hexachloro tetrahydrophthalic acid, azelaic acid, sebacic acid, decane dicarboxylic acid, dimer fatty acid, adipic acid, succinic acid and maleic acid, in amounts of up to not more than 30 mol%, preferably up to not more than 20 mol%, of the total of carboxylic acids. Hydroxy-carboxylic acids and/or, optionally, lactones such as, for example, 12-hydroxystearic acid, E-caprolacto n and the hydroxypivalic acid ester of neopentyl glycol can also be used. In minor amounts, monocarboxylic acids such as, for example, benzoic acid, tert-butylbenzoic acid, hexahydro benzoic acid and saturated aliphatic monocarboxylic acids can also be added during the polyester preparation.

Furthermore, especially suitable in the polyester preparation are aliphatic diols such as, for example, ethylene glycol, 1,2-propanediol, 1,3-propane- WO 94/03545 PCrNL93/00155 7 diol, 1,2-butanediol, 1,4-butanediol, 1,3-butanediol, 2,2dimethyl-1,3-propanediol neopentyl glycol), hexanediol, 1,6-hexanediol, 2,2-[bis(4-hydroxycyclohexyl)]propane, 1,4-dimethylol cyclohexane, diethylene glycol, dipropylene glycol and 2,2-bis[4-(2-hydroxyethoxy)]phenylpropane and smaller amounts of polyols such as glycerol, hexanetriol, pentaerythritol, sorbitol, trimethylol ethane, trimethylol propane and tris(2hydroxyethyl)isocyanurate can be used. Preferably, the alcohol component contains at least 50 mol% of neopentyl glycol and/or propylene glycol.

Additional suitable compounds for reacting with polycarboxylic acids include monoepoxides such as, for example, ethylene oxide, propylene oxide, monocarboxylic acid glycidyl ester (for example Cardura EOT"; Shell) or phenyl glycidyl ether.

The polyesters are prepared, using methods known per se, by esterification or transesterification, optionally in the presence of customary catalysts such as, for example, dibutyl tin oxide or tetrabutyl titanate, a suitable choice of the preparation conditions and of the COOH/OH ratio yielding end products with an acid number between 15 and 150.

Compounds according to formula (III) and (IV) and methods for making them, are described in, amongst others: US-A-4727111, US-A-4788255 and EP-A- 322834. The complete disclosures are incorporated herein by reference.

The preparation and testing of the powder coating can take place in a customary manner, for example as described in Misev, Powder Coatings; Chemistry and Technology (Wiley and Sons, 1991) pp. 225-226.

If desired, the powder coating can also contain mixtures of polyesters and polyacrylates. Furthermore, other resins, such as, for example, an epoxy resin, can also be included in the powder coating composition.

Of course, all the standard additives such as, for example, pigments, fillers, flow-promoting agents, WO 94/03545 PCT/NL9300155 8 stabilizers and catalysts can be added to the coating systems.

Suitable pigments include, for example, inorganic pigments such as titanium dioxide, zinc sulphide, iron oxide and chromium oxide, and organic pigments such as azo compounds.

Suitable fillers include, for example, metal oxides, silicates, carbonates and sulphates.

Compositions according to the invention can be used as coating agents for metal, wood and plastic substrates. Examples are general-purpose industrial top coats, top coats on machinery and equipment, in particular top coats on metal, for example for tins, domestic and other small equipment, cars and the like.

The invention will be elucidated with the following, non-restrictive examples and comparative example.

Example I The preparation of a powder coating based on a combination of a two- and a four-functional B-hydroxyalkv'amide In an extruder (Werner Pfleider, ZSK 30) 570.5 parts by weight of a carboxyl-functional polyester resin (Uralac P 845 PM; DSM Resins with an acid number of mg KOH/g-were mixed at 130 0 C with 20.5 parts by weight of Primid XL 552 TH (compound according to formula Rohm Haas), with 9 parts by weight of n-acetyl diethanol amine (compound according to formula with 300 parts by weight of titanium dioxide (Kronos CL 31 0 with 9 parts by weight of flow-promoting agent (Resiflow PV-5

T

M,

Worlee), and with 2.5 parts by weight of benzoin.

After cooling, the extrudate was subjected to granulation and fine grinding to a particle size of 90 pm.

WO 94/03545 PCT/NL93/00155 9 Example II The preparation of a powder coating based on a two- and a four-functional B-hydroxyalkylamide Example I was repeated, use being made of the listed ingredients in the following amounts by weight (Table I).

TABLE I parts by weight Uralac P 8 4 5 T' 571 Primid XL 5 5 2 n-acetyl diethanol amine 14 TiO 2 300 Resiflow PV-5"T 9 Benzoin Comparative example A The preparation of a powder coating based on a four-functional B-hvdroxvalkylamide The procedure of Example 1 was repeated, to make powder coatings from the ingredients listed in the following table A in the indicated amounts by weight. No acetyl diethanol amine was added.

TABLE A parts by weight Uralac P 8 4 5 TM 570 Primid XL 5 5 2 T" TiO 2 300 Resiflow PV-5" 9 Benzoin WO 94/03545 PC'/NL93/00155 10 The powder coatings according to Examples I, II and Comparative Example A were electrostatically applied to steel panels and cured, during 15 ainutes, at 180 0

C.

The blister limit was determined via electromagnetic induction (see the already cited Misev, Powder Coatings, pp. 295-296).

TABLE II Example blister limit in pm I 120 II 140 A 105 In I, II and A the reverse impact strength (160 inchpound), the acetone resistance (more than 100 rubs full curing), the flow (good, visually determined) and the gloss were good.

The powder coating compositions according to the present invention having the specified combinations of 3hydroxyalkylamides at a constant amount of benzoin yielded coatings having a desirable higher blister limit. The coatings obtained using the powder coating compositions according to the present invention also retained the desired mechanical properties.

Claims

1. Powder coating composition comprising as a binder a polymer with free carboxylic acid groups and as a crosslinker a compound containing B-hydroxyalkylamide groups, characterized in that the crosslinker comprises a combination of at least two compounds containing 3-hydroxyalkylamide groups and each compound having different A-hydroxyalkylamide functionalities, the first compound naving a p- hydroxyalkylamide functionality of a 3 and the second compound having A-hydroxyalkylamide a functionality of 5 3.

2. Powder coating composition according to claim 2, characterized in that the first compound has a functionality of 4 and the second compound has a functionality of 2.

3. Powder coating composition according to any one of claims 1-2, characterized in that the weight ratio between the first compound to the second compound is from 90:10 and 10:90.

4. Powder coating composition according to any one of claims 1-3, characterized in that the polymer is a polyester and/or polyacrylate.

5. Crosslinker for the preparation of v powder coating, characterized in that the crosslinker comprises a combination of at least two compounds containing J-hydroxyalkylamide groups and each compound having different p-hydroxyalkylamide functionalities, the first compound having a p-hydroxyalkylamide functionality of a 3 and the second compound having a A-hydroxyalkylamide functionality of 5 3.

6. Crosslinker according to claim 5, characterized in that the first compound has a functionality of 4 anr the second compound has a functionality of 2.

7. Use of a combination of at least two compounds containing B-hydrcxyalkylamide groups and ?ach compound having different p-hydroxyalkylamide 12 functionalities, the first compound having a P-hydroxyalkylamide functionality of 3 and the second compound having a P-hydroxyalkylamide functionality of 3, as a crosslinker in the preparation of powder coatings.

8. Use according to claim 7, characterised in that the first compound has a functionality of 4 and the second compound has a functionality of 2.

9. Powder coating composition, crosslinker and use according to any one of claims 1-8, characterised in that the first compound having a P-hydroxyalkylamide functionality of 3 is a compound according to formula (III): 0 0 HO-H 2 C-H 2 C I 1 I ,CH 2 -CH 2 -OH SHO 2 N-C-(CH 2 4 (l) "HO-H2C-H2C CH2-CH2-OH 10

10. Powder coating composition, crosslinker and use according to any one of claims 1-9, characterised in that the second compound having a 0-hydroxyalkylamide e functionality of 2 3 is a compound according to formula (IV): *0 O CH 3 -CH 2 -OH CH 3 -C-N IV) CH 3 -CH 2 -OH

11. Powder coating composition comprising as a binder a polymer with free S0,* 15 carboxylic acid groups and as a crosslinker a compound containing P- hydroxyalkylamide groups, substantially as hereinbefore described with reference to any one of the Examples.

12. Use of a powder coating composition according to any one of claims 1-4 or 9-11.

13. A coated substrate, characterised in that the coating material is a powder e* coating according to any one of claims 1-4 or 9-11. S" Dated 27 February, 1995 DSM N.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON IN:\LIBC)00695:ZLA j I I INTERNATIONAL SEARCH REPORT loternational1 Application No PCT/NL 93/00155 1. CLASSIFICATION OF SUBJECT MATER (Of sevrail classification symbols apply, Indicate 911)6 According to International1 Patent assilfication (lPC or to both National Classification and ipc Int.C1. 5 C09D5/03; C09D133/06; C09D167/02 Docanmentation Searched other than Minimum Documentation to the Extent that such Documents ase Included In the Fields Searcheda la. DO CUMIENTS CONSIDERED TO BE RELEVANT9 Category 0 Citation of Documvot, U1 with indication, where appropriate, of the relevant passeages 12 Relevant to ailm No.U A EP,A,0 473 380 (ROHM AND HAAS COMP)

1 4 March 1992 scheme 2 0 Special categories of dited documents 10 Tl' later document published after the International Miing date ocumnt efinng te gnera stae ror priority dateo and not In conflict with the application but A dcumntdefnin te gnerl tat c the ant which is not cited to ndertad the principle or theory undryn the considered to be of particular relevance ivtIonth Er earlier document but published on or after the intmrnational -xV document of particular relevance; the climed Invention filing date cannot be considered novel or canno bo considered to WL document which may throw doubts on priority claims) or Involve an inventive step which Is cited to establish the publication date of another document of particular relevace; the claimed Invention citation or other special reason (a~s specified) cannot be considered to Involve an Inventive step when the document referring to an oaml disclosure, use. exhibition or document Is combined with one or more other such docu- other means ments, such combination being obvious to a person skilled 91' document published prior tc, the International fII~g dateo but In the amt later than te priority date climed document member of the same patent family IV. CERTIFCATION Date of the Actual Completion V~ thin International Search Date of Milling of this International Search Rep" OCTOBER 1993 11, 93 International Seaching Authority Signature of Authorize Officer EUROPEAN PATENT OFFCE Dieter SchUler Porn PURJSA/2IO (mcau mbiI (Jutwy 1"5S3 ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION NO. NL 9300155 SA 77194 Ths annex lis!& the patent family members risaing to the patent documents cited in the above-mentioned international search reporL The members are as contained in the European Patent Office EDP file on The European Patent Office is in no way liable for these particulars which are merely given for the purpose of infornmation. 20/10/93 Patent document Pbcaion Patent family Publication cited in search report daemember~s) date EP-A-0473380 04-03-92 US-A- 5101073 31-03-92 AU-A- 8268991 05-03-92 CA-A- 2049563 28-02-92 JP-A- 4247058 03-09-92 'W For more details about this annex :see Offlii Journal of the European Patent Office, No. 12182