AU779911B2

AU779911B2 - Thermosetting polyester resin

Info

Publication number: AU779911B2
Application number: AU15396/02A
Authority: AU
Inventors: Malcolm Ross Binns; Jenny Anne Maliphant; Jim Viatos
Original assignee: BHP Steel JLA Pty Ltd
Current assignee: BlueScope Steel Ltd
Priority date: 1993-12-24
Filing date: 2002-02-04
Publication date: 2005-02-17
Anticipated expiration: 2014-12-21
Also published as: AU1539602A

Description

-1-

AUSTRALIA

PATENTS ACT 1990 COMPLETE

SPECIFICATION

FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: BHP Steel (JLA) Pty Ltd Actual Inventors: Malcolm Ross Binns and Jim Viatos and Jenny Anne Maliphant Address for Service: BALDWIN SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000 S. CCN: 3710000352 Invention Title: THERMOSETTING POLYESTER RESIN Details of Original Application No. 21397/99 dated 25 Mar 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 34431AUP00 la Title: THERMOSETTING POLYESTER

RESIN

Field of the invention ooo ~The present invention relates to a thermosetting coating composition and more 5 particularly to a crosslinkable polyester resin suitable for coating metal sheets and coils.

S. Background of the invention Desirably, coating compositions for metal sheets and coils should be resistant to sunlight,

UV

radiation, hydrolysis, adverse weather conditions, solvents and should also display good gloss and hardness retention and rapid cure.

The requirements for resistance to colour change and for good gloss retention when exposed to weather are difficult to satisfy and present a particular problem because data obtained by means of a UV-A accelerated weatherometer does not 2 correlate well with data from a UV-B accelerometer and both correlate poorly with actual weather exposure. Sample resins which "pass" in the weatherometer sometimes "fail" on exposure to weather and sample resins which fail in the weatherometer are frequently rejected without further testing.

Thermosetting coatings are generally used as decorative coatings for metal sheet coils. These 10 coatings are typically produced by reacting at elevated temperatures a blend of hydroxyfunctional resin and a crosslinking agent such as a derivative of melamine formaldehyde, benzoguanamine formaldehyde, glycouril formaldehyde, urea formaldehyde or a blocked isocyanate resin.

Hydroxyfunctional resins such as polyester, acrylic S. and alkyd are generally used as the major component of the decorative coatings and of those resins, polyesters are preferred.

20 Hydroxyfunctional polyester resins are generally manufactured by reacting glycols with a mixture of dicarboxylic acid components together with a trifunctional branching component to form a branched polyester. The mixture of dicarboxylic acid components comprises an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid component.

The aromatic dicarboxylic acid component may be, for -3example, orthophthalic acid, terephthalic acid and/or a corresponding anhydride and the aliphatic dicarboxylic acid component may, for example, be sebacic or succinic acid. At least 20 mole and as much as 80 mole of the total acid component is an aliphatic dicarboxylic acid which is employed to prevent crystallization of the product due to inherent crystallinity of aromatic acids and because aliphatic systems tend to be less UV absorbing.

Although many such resins are known there remains a need for resins for use in coating compositions with improved gloss retention, and resistance to colour change on extensive exposure and which are suitable for coating onto metal coil. The latter entails 10 the ability to be applied uniformly in a film thickness of 15 to 25 microns, a capacity for rapid thermal film cure, satisfactory film durability, flexibility, hardness, peel resistance, impact shock resistance and the like.

Object of the invention Accordingly, it is an object of the present invention to provide an improved thermosetting coating composition for metal sheets and coils.

Summary of the invention According to one aspect, the invention provides a polyester resin for use in a thermosetting coating composition said polyester comprising units derived by polymerizing: an acid component, comprising from 90 to 100 mole of aromatic acid, aromatic anhydride, or mixture thereof, and from 0 to 10 mole of a non-aromatic polycarboxylic acid, non-aromatic polycarboxylic anhydride thereof, or mixture thereof; -4an alcohol component comprising at least 60 mole 2-butyl-2-ethyl-1,3-propanediol (BEPD) and 0 to mole neopentylglycol; and (ii) a polyol trifunctional branching agent present in an amount of from to 20 mole of the total alcohol content; and wherein said polyester resin has an acid value of from 0 to 10, a hydroxyl value of 20 to 110 and a number average molecular weight of from 700 to 8000.

Desirably, the BEPD comprises at least 80 mole of the total acid component.

According to a second aspect the invention provides a method of preparing a 10 polyester resin in according to any one of claims 1 to 11, which method comprises reacting, at an elevated temperature, an acid component, comprising from 90 to 100 mole of an aromatic acid, aromatic anhydride, or mixture thereof, and from 0 to 10 mole of a non-aromatic polycarboxylic acid, polycarboxylic anhydride thereof, or mixture thereof; 15 an alcohol component comprising at least 60 mole 2-butyl-2-ethyl-l,3-propanediol (BEPD) and 0 to mole neopentylglycol; and (ii) a polyol trifunctional branching agent present in an amount of from to 20 mole of the total alcohol content.

According to a third aspect the invention provides a thermosetting coating composition comprising a polyester resin according to the first aspect and a cross-linking agent.

4a In a preferred embodiment the crosslinking agent is selected from the groups consisting of a derivative of melamine formaldehyde, benzoguanamine formaldehyde, glycouril formaldehyde, urea formaldehyde and a blocked isocyanate resin.

In a highly preferred embodiment the aromatic acid is isophthalic acid (IPA) but other aromatic 5 acids such as terephthalic acid and orthophthalic acid and the corresponding anhydrides may also be used. For preference, polycarboxylic acids or polycarboxylic anhydrides such as trimellitic acid, adipic acid succinic acid, azelaic acid and sebacic acid and the corresponding anhydrides can be used in the present invention.

Description of preferred embodiments The present invention will now be more 10 particularly described, by way of example only, with reference to various examples.

Generally, the acid component of the composition according to the present invention consists of 90 to 100 mole V of isophthalic acid and 15 preferably from 95 to 100 mole t (based on the weight of the total acid component). The acid or ~anhydride component may also be substituted with one

S*

or more groups such as methyl, ethyl, butyl, propyl etc. However, groups that are prone to hydrolysis are generally not used as this makes the resulting coating composition more resistant to exterior exposure.

2-Butyl-2-ethyl-l, 3-propanediol (BEPD) (R 1 =butyl) is the preferred glycol of the present invention as its esters do not readily hydrolyse, however other glycols such as when R is ethyl and neopentylglycol hydroxy pivalate (HPHP) may also be 6 used as the glycol component. In a preferred embodiment from about 0 to 10 mole of neopentylglycol (NPG) is used together with BEPD or neopentylglycol hydroxy pivalate and isophthalic acid. The glycols may also be derivatives that are generally resistant to hydrolysis. In particular they may be derivatives which contain carbon atoms beta to the hydroxyl substituents that are dialkylated where the dialkylated groups include but are not limited to methyl, ethyl, propyl, butyl etc.

The acid component and glycol component are mixed with suitable branching agents to provide the desired polyester composition. Useful polyester trifunctional branching agents include 15 trimethylolpropane and trimethylolethane. Typically the trifunctional branching agent is present in an amount of from 0 to 20 mole and more preferably from 5 to 15 mole based on the total alcohol content.

Coating compositions based on the hydroxyfunctional polyesters of-the present invention display good gloss retention and resistance to colour change after three years exterior exposure when compared with the prior art hydroxyfunctional polyesters. This finding was not predictable as a result of accelerated testing with a QUV Accelerated Weather Performance Test using 7 standard QUVB-313 ultraviolet lamps from the Q-panel company.

The polyester resin generally has an acid value of from 0 to 10, a hydroxyl value of 20 to 110 and a number average molecular weight of from 700 to 8000.

Solvents, pigments, dispersants and catalysts can optionally be added to the thermosetting polyester resin and processed by conventional methods of manufacture to form a durable surface 10 coating. Surprisingly, it has also been found that the polyester resins of the present invention are soluble in pure aromatic solvents whereas the prior art polyester resins with high aromatic content are not. Suitable pigments of the present invention 15 include, but are not limited to, titanium dioxide, ultramarine blue, phthalocyanine blue, phthalocyanine green, carbon black, black iron oxide, chromium green oxide, ferrite yellow and quindo red.

The thermosetting coating composition may also contain other additives that are typically incorporated into coating compositions such as degassing agents, flow control agents and anti-oxidants.

The thermosetting coating composition displays excellent gloss and hardness retention compared with controls in alkaline and humid environments. The 8 coating composition is suitable for coating metal coils as a topcoat of precoated metal for electric appliances eg, washing machines and dishwashers which are required to have high processability and resistance to alkalis and humidity.

Coatings based on these resins display high initial gloss levels when appropriately formulated.

Various embodiments of the invention will now be exemplified.

Polyester I: 1.66 mol. of isophthalic acid, 1.61 :m tol of 2-butyl-2-ethyl-1,3-propanediol (BEPD) and 0.19 mol of trimethylolpropane were mixed together in a reaction vessel equipped with a nitrogen purge, a stirrer, a thermometer, fractionating column and a 15 water take-off condenser. The reactants were heated up to a temperature of 240 0 C at a rate to maintain the column head temperature at less than 102 0

C.

Once the resin melt had cleared and the water removal rate slowed, the fractionating column and se* 20 water take-off condenser were replaced by a Dean-Stark apparatus. Sufficient xylene was then added to maintain condensation of xylene in the Dean-Stark apparatus and removal of water until the resin achieved an acid value of 6.2.

The polyester was dissolved in Solvesso 150 (Solvent blend I) to give polyester solution

(I)

with solid component 601.

-9- Polyester I: 1.43 mol of isophthalic acid, 0.13 mole of adipic acid, 1.13 mol BEPD, 0.56 mol neopentylglycol hydroxy pivalate and 0.18 mol of trimethylolpropane was processed as above to an acid value of 4.

The polyester was dissolved in a 10:20:70 (by weight) mixture of butanol, Ektapro EEP, Solvesso 150 respectively (solvent blend II) to give a solid component METHOD OF MANUFACTURE OF PAINT 1 A paint suitable for coil coating was produced by the following procedure. 56.8 parts of coloured pigment, 4.9 parts of titanium dioxide and 1.2 parts of Aerosil 972 were dispersed in a mixture of 6.2 parts of a butylated melamine formaldehyde resin (Cymel 10 1156) (98% solids) and 31 parts of solvent blend 28.5 parts of the above millbase were o o 10 combined with 5.6 parts butylated melamine formaldehyde, 47.6 parts of polyester solution, 0.24 parts blocked organic sulphonic acid catalyst, 0.2 parts flow additive (Byk 306), 3 parts silica (Syloid ED5) and sufficient solvent to give a package viscosity of 96s (Ford 4 cup) at 25 0

C.

PAINT 2: 56.8 parts of coloured pigment, 4.9 parts of titanium dioxide and 1.2 parts of Aerosil 972 were dispersed in a mixture of 6.2 part 10 polyester II solution and 31 parts solvent blend (II) to produce a pigmented millbase 28.5 parts of millbase (II) was combined with 51.76 parts of polyester solution 3.59 parts of methylated melamine formaldehyde resin (Cymel 303), 0.15 parts of blocked organic sulphonic acid catalyst, 0.2 parts flow additive (Byk 306), 3 parts silica and sufficient solvent to give a package viscosity of 96s (Ford 4 cup) at 25 0

C.

PAINT 3: Paint 3 was prepared as described for paint 1 with polyester 3 substituted for polyester 1 and solvent blend II substituted for solvent blend I.

PAINT 4: 28.5 parts of millbase II as described above was combined with 51.76 parts of polyester solution 4.48 parts of blocked isocyanate resin (Coronate 2515) (80% solids), 0.8 parts dibutyltin dilaurate, 0.2 parts flow additive 3 parts silica and sufficient solvent to give a 11 package viscosity of 96s (Ford 4 cup) at 250C.

In Table 1, Examplea 1 to 4, 6 to 9, 11 to 13 and 16 are prior art resins while Examples 5, i0, 14 and 15 are resins according to the invention. All the resins are processed by conventional methods of manufacture into a paint composition and the results of gloss retention and other tests are presented in the Table.

The following materials referred to in this :10 specification were obtained a from the suppliers e indicated below: mteial Pigment Mix 329 Shepherd Aerosil R972 Degussa Cymel 1156 Cyanamid Cymel 303 Cyanamid Solvesso 150 Exxon Cycate 600 Cyanamid Coronate 2515 DMEA Aldrich Byk 306 Byk-Chemie Syloid ED-5 W. R. Grace Although the invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art, that the invention may be embodied in many other forms.

D(RABLITY TESTING DIFFXRENT POLYESTER COMPOSITIONS WAHN 14AD8 UP INTO WEATHRRD COPPER PIW4ENMTD PAINTS Exeee I 3 4 5 6 7 a 10 11 12 3 1 Iis 16 Diacidla) 1.4 CHDA) 1,CtHO) 1.4 CHDA 1.4 CHDA IVA 1,4 CHDA 1,3 CHDA 4 1,3 C A P M A A AA A 2 IF& IVA pulyeates 197%) (97V) (99) A& D101l UePo MPG NHP 58P0 CHlC11 BPD 531PD0 1,(CHD BPPD M5PD HPUP HGO BD BB 5PD 7 Reiln NHPM. HPMP.

I MPG, Procesesal1tyl Yes No No No Iy es yee Yes yen Yes yea Yes YomWO yes Yes Yes £3 nesulc 3.14 0.66 1.31 1.99 1 2.08 d.33 2.3t (200 light houre) 2 27 100 33 3 36 loese retention UIA £3 I&*ult s 1.72 3.34 4 01 2.33 0.53 4.13 2.65 1.23 4.74 0.43 5.16 .91 -1.15 (2000light houral 7 3 25 100 15 50 13 4 73 7 4 Gloa. retention No.haepron s 7.13 6.37 '1.64 5.01 0.42 1.73 4.44 6.21 2.6710.74 4.894.15 1.63 Wlos retention 67 0 13 63 6 13 6 4. 35 7, (3 yeas or y wbere asterisk I) All af the above polyesters, except Example 15, also contained a trial 7WP in sufticient quantitIGO to give In each case a Runction.lity/molecule of 3.0. Other target reain parameters were NW-2250i Hydroxyl value-601 acid value 4 10. Nillbame pigment RIX coaprised o Shepherd pgmnt six 321 16.2 parts and titanium dioxide 1.4 part.

2) The polyester imophthalic ecid/neopentylglycol wee no cryscallized that uniform pigmented Ilim could not be prepared for axposure panel prepre loan.

3) l.4-cyclohautnedicaxboxylic acid 4) 1.3-cycbokaaedicaboxylic acid I 1.4-cycloaxaaadimetbanol 6) 3.2.a-trimethyl-l3-pentanedial 71 This polyester also contained trimellitic anhydride mnomer.

3) A paoceaaabbe resin Is defined as one that does not crystallize within 7 days when diluted to 60% solids in Solveemo 150.

9) £1 tbA paints In this table were made up by using melamins-tormaldehyde type croselinkers.

Claims

13- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A polyester resin for use in a thermosetting coating composition said polyester comprising units derived by polymerizing: an acid component, comprising from 90 to 100 mole of aromatic acid, aromatic anhydride, or mixture thereof, and from 0 to 10 mole of a non-aromatic polycarboxylic acid, non-aromatic polycarboxylic anhydride thereof, or mixture thereof; an alcohol component comprising at least 60 mole 2-butyl-2-ethyl-l,3-propanediol (BEPD) and 0 to mole neopentylglycol; and S 10 (ii) a polyol trifunctional branching agent present in an amount of from to 20 mole of the total alcohol content; and wherein said polyester resin has an acid value of from 0 to 10, a hydroxyl value of 20 to 110 and a number average molecular weight of from 700 to 8000. 2. A polyester resin according to claim 1, wherein said BEPD comprises at least 15 mole of the total alcohol component. 3. A polyester resin according to any one of the preceding claims, wherein the aromatic acid is selected from isophthalic acid (IPA), terephthalic acid, orthophthalic acid and trimellitic acid. 4. A polyester resin according to claim 3, wherein the aromatic acid is isophthalic acid in an amount of 90 to 100 mole based on the total weight of the total acid component. A polyester resin according to claim 3, wherein the aromatic acid is isophthalic acid in an amount of 95 to 100 mole based on the total weight of the total acid component. -14- 6. A polyester resin according to any one of the preceding claims, wherein the polycarboxylic acids or polycarboxylic anhydrides thereof are selected from adipic acid succinic acid, azelaic acid, sebacic acid and the corresponding anhydrides thereof. 7. A polyester resin according to any one of the preceding claims, wherein the aromatic acid component is substituted with one or more methyl, ethyl, butyl or propyl groups. 8. A polyester resin according to any one of the preceding claims, wherein the alcohol t* component further comprises up to 30 mole% neopentylglycol hydroxy pivalate (HPHP). 9. A polyester resin according to any one of the preceding claims, wherein the S 10 trifunctional branching agent is either trimethylolpropane or trimethylolethane. A polyester resin according to any one of the preceding claims, wherein solvents, pigments, dispersants and catalysts are optionally added to the resin. 11. A polyester resin according to claim 10, wherein the pigments are selected from titanium dioxide, ultramarine blue, phthalocyanine blue, phthalocyanine green, carbon 15 black, black iron oxide, chromium green oxide, ferrite yellow and quindo red. 12. A method of preparing a polyester resin in according to any one of claims 1 to 11, S which method comprises reacting, at an elevated temperature, an acid component, comprising from 90 to 100 mole of an aromatic acid, aromatic anhydride, or mixture thereof, and from 0 to 10 mole of a non-aromatic polycarboxylic acid, polycarboxylic anhydride thereof, or mixture thereof; an alcohol component comprising at least 60 mole 2-butyl-2-ethyl-l,3-propanediol (BEPD) and 0 to mole neopentylglycol; and (ii) a polyol trifunctional branching agent present in an amount of from to 20 mole of the total alcohol content. 13. A method according to claim 12, wherein from 0 to 10 mole of neopentylglycol (NPG) is used with BEPD and isophthalic acid and reacted with a trifunctional branching agent at elevated temperatures.

14. A method according to claim 12 or claim 13, wherein the trifunctional branching agent is either trimethylolpropane or trimethylolethane. A thermosetting coating composition comprising a polyester resin according to any one of claims 1 to 11 and a crosslinking agent. 10 16. A thermosetting coating composition according to claim 15, wherein the crosslinking agent is selected from melamine formaldehyde, benzoguanamine formaldehyde, glycouril formaldehyde, urea formaldehyde and a blocked isocyanate resin.

17. A method of preparing a thermosetting coating composition which method 15 comprises reacting at elevated temperatures a blend of polyester resin according to any O* one of claims 1 to 11 and a crosslinking agent.

18. A method according to claim 17, wherein the crosslinking agent is selected from a derivative of melamine formaldehyde, benzoguanamine formaldehyde, glycouril formaldehyde, urea formaldehyde and a blocked isocyanate resin.

19. Sheet metal when coated with a thermosetting coating composition according to any one of claims 1 to 11 or claim A polyester resin according to claim 1 wherein the acid component comprises more than 90 mole and from 0 to <10 of a non-aromatic polycarboxylic acid or polycarboxylic anhydride. -16-

21. A polyester resin according to claim 20 wherein the acid component comprises from 91.6 mole to 100 mole of an aromatic acid and from 0 to 8.4 mole of a non- aromatic polycarboxylic acid or polycarboxylic acid anhydride. DATED this 14th Day of January 2003 BHP STEEL (JLA) PTY. LTD. Attorney: CHARLES W. TANSEY Fellow of The Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS o.* *ooooo