AU620697B2 - Two-phase cathodic electrocoat - Google Patents

Abstract

The substrate coated with a two-phase coating is obtainable by cathodic electro-coating of an electrically conducting substrate with a composition comprising A) an aqueous cationic dispersion of a chain growth polymerisation, polycondensation or polyaddition product B) an aqueous cationic dispersion of a chain growth polymerisation, polycondensation or polyaddition product in which the polymer on which the dispersion is based has a glass transition temperature of between -80 and 20 DEG C and in which the polymers on which dispersions (A) and (B) are based are incompatible with one another and C) a crosslinking agent, a pigment paste, additives and/or auxiliaries, followed by stoving.

Description

COMMONWEALTH OF AUSTRAUA 2 0 6 9 7 PATENTS ACT 1952-69 COMPLETE SPECIFICATION (ORICiiAL) Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art E Related Art: t 6 er 1 Name of Applicant 1 6 6 44 4 *Address of Applicant B I 4 II BASF LACKE FARBEN AKTIENGESELLSCHAFT, D-4400 Muenster, Federal Republic of Germany.

THOMAS SCHWERZEL, HANS SCHUPP, KLAUS HUEMKE, ULRICH

HEIMANN.

WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Actual Inventor ddress for Service t Address for Service Complete Specification for the invt in entitled: TWO-PHASE CATHODIC ELECTROCOAT The following statement is a full description of this invention, including the best method of performing it known to :-U

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t* la O.Z. 0062/02083 0 4 o000o0 o 0 00 0 o *o ,ie o OtSt 0 t 11 (i i Two-phase cathodic electrocoat The present invention relates to a two-phase cathodic electrocoat obtainable by depositing a mixture of two aqueous cationic dispersions of mutually incompatible polymers on an electrically conductive substrate and then baking.

Many of the present-day cathodic coating systems take the form of a dispersion comprising an ionically charged mixture of an organic binder and a crosslinking agent. Instead of this resin mixture it is of course also possible to use a self-crosslinking innically charged resin. The binders for cathodic electrocoating compositions are usually basic nitrogen resins converted into dispersible polymers by protonation with an acid. Resins 15 which have sulfonium or phosphonium groups are also known. Besides these basicity characteristics, the resin must also have functional groups which are capable of reacting with the crosslinking component. Examples of such groups are acidic hydrogen atoms, eg. NH and OH groups, unsaturated olefin-c double bonds, dienophiles and dienes. The resirs can be prepared by polymerizing or copolymerizing unsaturated compounds which carry at least partly basic atoms. A frequent choice are polyaddition compounds formed by reacting epoxy resins with compounds 25 which are reactive toward oxirana groups. The basic groups are frequently introduced by using primary, secondary or tertiary amines or permanent charges in the form of quaternary ammonium salts. Furthermore, the epoxy resins thus modified are reacted with flexibilizing 30 compounds.

The addition of dispersed polymers has also been described. For instance, Moriarity in EP-A-70 550 describes dispersions obtained from reaction products of polyepoxies with polyoxyalkylenepolyamines. These reaction products confer good flow and higher flexibility on the coating compositions and also a higher cratering resistance. WO 86/05196 describes a reaction product of t to O 0 O Ot Cc

O

O 0*0 0* 4 0 06 0 40

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2 a polyoxyalkylenepolyamine with a monoepoxy for use in cathodic electrocoating.

In EP-A 253,404 Mclntyre et al describe a mixture of a cationic epoxy resin formed from a reaction product of a polyol diglycidyl ether with at least one bifunctional phenol and an optional blocking reagent, with subsequent conversion of some excess oxirane groups into cationic groups and a further epoxy-based cathodic electrocoating resin. The advantage of these mixtures is that they enable the thickness of the applied coating, particularly in the case of high-build systems, to be adjusted as desired.

It is a feature common to all prior art systems that the flexibilizing 1 0 component which increases the elasticity of the paint film also reduces the glass transition temperature of the baked paint film. This has a disadvantageous effect on the temperature-dependent properties. For instance, corrosion protection is greatly impaired, particularly after a severe cyclical exposure test using different sets of climatic conditions, for example the cyclical exposure test according to VDA 621-415 15 which is carried out at a maximum temperature of 400 C, or the GM scab test (Fisher Body Division TM 54-26) which is carried out at a maximum temperature of 600 C.

It was the object of the present invention to develop coatings which afford S good corrosion protection in cyclical exposure tests using different sets of climatic Sconditions, even at elevated temperature, but which are also highly elastic.

2 0 This object has been able to be achieved with coatings having a two-phase structure.

The present invention relates to a two-phase cathodic electrocoating composition comprising a mixture containing: an aqueous cationic dispersion of a polycondensation or polyaddition product, which contains primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups, an aqueous cationic dispersion of an aminoepoxy resin obtained by reacting tI l a butadiene/acrylonitrile copolymer which contains primary and/or secondary amino groups with an epoxy resin having an average molecular weight of from 140 to 10,000 3 0 and containing on average fom 1.5 to 3 epoxy groups per molecule, this aminoepoxy resin having a glass transition temperature of from -80 to 200C, the polymers of dispersions and being mutually incompatible.

Optionally a crosslinking agent, a pigment paste, auxiliaries and/or additives may be added to the composition.

Regarding the components of the mixture, the following remarks should be made: i ;i

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9 3 Component is an aqueous dispersion of a polymerization, polycondensation or polyaddition product. In particular, component contains primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups and preferably has an average molecular weight of from 200 to 20,000, such as aminoepoxy resins, aminopoly(meth)acrylate resins and/or amirivpolyurethane resins. The use of aminoepoxy resins is preferred to basecoats affording a high level corrosion protection. The amino resins advantageously have amine numbers of from to 150. The lower limit of the amine number should be 35, preferably 50, and the upper limit should be 120, preferably 100. Examples of aminoepoxy resins are reaction 1 0 products of epoxy-containing resins having preferably terminal epoxy groups with saturated and/or "uisaturated secondary and/or primary amines or aminoalcohols. These reaction products can be modified at the alkyl moiety by at lease one primary and/or secondary hydroxyl group, by a mono- or dialkylamino group and/or by a primary amino group which is at least temporarily protected by ketiminization.

1 5 Any desired epoxy resin can be used, provided it has an average molecular weight of from 300 to 6000 and contains, on average, from 1.0 to 3.0 epoxy groups per molecule, preferably a compound having 2 epoxy groups per molecule. Preference is given to epoxy resins having average molecular weights of from 350 to o o eo 0000 9 0 *o 00 0 O 0 909 0 o 0 0* 0 0 0 00000 1 I 4 4 O.Z. 0062/02083 000 o 4 0 0 0 0 o o 0Q 0 0D 0 5000, in particular from 350 to 2000. Particularly preferred epoxy resins are for example glycidyl ethers of polyphenols which on average contain at least two phenolic hydroxyl groups in the molecule and which are preparable in a conventional manner by etherification with an epihalohydrin in the presence of alkali. Aromatic polyepoxies having a higher epoxy equivalent weight can be prepared from those having a lower epoxy equivalent weight and polyphenols or else by a suitable choice of the ratio of phenolic OH groups to epihalohydrin.

The amino groups can be introduced in a conventional reaction as known to those skilled in the art and as described for example in EP 134 983, EP 165 556 and EP 166 314.

By introducing groups which are capable of crosslinking, eg. blocked isocyanates, it is possible to render the amino resins self-crosslinking, as described for example in US 4 692 503, US 3 935 087 and EP 273 247.

The glass transition temperatures of the amino resins are advantageously within the range from 20 to 100°C, preferably from 20 to 80 0 C, particularly preferably from 25 to 45 0

C.

The amino resins can be converted into a watersoluble or water-dispersible form by protonation with an acid. A suitable acid is phosphoric acid, but it is preferable to use an organic acid, eg. formic acid, acetic acid, propionic acid or lactic acid. It is also possible to add the resin to a water/acid mixture. In general, the dispersions used have a solids content of from 20 to 45% by weight, preferably from 30 to 40% by weight. Coc:rolecS A suitable compenent is an aqueous dispersion of a polycondensation or polyaddition product which has a glass transition temperature of from -80 to 20 0

C,

preferably from -70 to 0 C, particularly preferably from to -10 0 C, and is incompatible with the polymer of dispersion The word "incompatible" means that a *000 o o 0 0 0 0 0o o o o o I~ 5 Z. 0062/02083 mixture of the polymers of dispersions and will separate and form two phases.

ITr,\ pgE o t icar n Sp) C r Suitabl-Olyaddition -produGts-a-re-4 E-examp1ethe reaction product' of butadiene/acrylonitrile copolymer' which contain primary and/or secondary amino groups with epoxy resins. Suitable butadiene/acrylonitrile copolymers have acrylonitrile contents of from 5 to by weight, preferably from 10 to 30% by weight, and butadiene contents of from 55 to 95% by weight, preferably from 70 to 90% by weight, and contain on average from 1.4 to 3.0 primary and/or secondary amino groups per molecule with or without tertiary amino groups. The average molecular weight (Mn) of the copolymers is advantageously from 500 to 15,000, preferably from 2000 15 to 8000.

The amino-containing copolymers are obtainable for example by reacting carboxyl-containing butadiene/ acrylonitrile copolymers with diamines. Such copolymers are commercially obtainable, for example under the designation HYCAR* 1300 x ATBN and HYCAR 1300 x 16 ATBN (from B.F. Goodrich), containing 10% by weight and 16.5% by weight of acrylonitrile respectively.

It is also possible to obtain amino-containing butadiene/acrylonitrile copolymers by partial hydrogena- S 25 tion of butadiene/acrylonitrile copolymers or by addition of primary amines to epoxy-containing butadiene/acxylonitrile copolymers.

Sk Suitable epoxy resins are those which have an average molecular weight (Mn) of from 140 to 10,000 and contain on average from 1.5 to 3 epoxy groups, preferably 2 epoxy groups, per molecule.

Preferred epoxy compounds are glycidyl ethers of aliphatic diols such as butanediol or hexanediol or polyetherols or glycidyl ethers of polyphenols which contain on average two or more phenolic hydroxyl groups and are preparable in a conventional manner by etherification with an epihalohydrin in the presence of alkali.

6 O.Z. 0062/02083 Examples of suitable phenol compounds are 2,2-bis(4hydroxyphenyl)propane (bisphenol 4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)ethane, 1,l-bis(4hydroxyphenyl)isobutane, 2,2-bis(4-hydroxy-tert-butylphenyl)propane, bis(2-hydroxynaphthyl)methane and dihydroxynaphthalene. It is desirable in some cases to use aromatic epoxy resins having a higher molecular weight. They can be obtained by reacting the abovementioned diglycidyl ethers with a polyphenol, for example 2,2-bis(4-hydroxyphenyl)propane, and then further reacting the resulting product with epichlorohydrin to prepare polyglycidyl ethers.

(The weight ratio of the butadiene/acrylonitrile S* copolymer to the epoxy resin is in general determined in 15 such a way that from 1.05 to 20 moles, preferably from .c 1.2 to 4.0 moles, of NH groups of the amino-containing butadiene/acrylonitrile copolymer are used per mole of epoxy group of the epoxy resin.

The reaction is in general carried out by reacting the butadiene/acrylonitrile copolymer with an epoxy resin in an organic solvent or solvent mixture which is inert not only toward amino groups but also toward epoxy groups, at 20-150"C, preferably 50-110C. The reaction S 2 time can be up to 20 hours.

S 25 The polymeric reaction products thus obtained have amine numbers of from 20 to 150 mg of KOH/g of solid i( substance, preferably 40-100 mg of KOH/g of solid sub- So oo stance.

S o By introducing groups capable of crosslinking, eg. blocked isocyanates, it is possible to render the amino resins self-crosslinking, as described for example in US 4 692 503, US 3 935 087 and EP 273 247.

The amino groups of these acids can be wholly or partly neutralized with an acid and the protonated resin dispersed by the addition of water. A suitable acid is phosphoric acid, but it is preferable to use an organic L> acid such as formic acid, acetic acid, propionic acid or

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ir' 7 O.Z. 0062/02083 lactic acid. It is also possible to add the resin to a water/acid mixture. Thereafter the organic solvents may be distilled off.

In general, the dispersions used have a solids content of from 5 to 40% by weight, preferably from 15 to by weight.

Optional component comprises customary crosslinking agents, pigment pastes, auxiliaries and/or additives.

Suitable crosslinking agents are for example aminoplast resins such as urea-formaldehyde resins, S, melamine resins and benzoguanamine resins, blocked isocyanate type crosslinking agents, crosslinking agents which cure by esteraminolysis and/or transesterification, 15 eg. p-hyd7oxyalkyl ester type crosslinking agents as *described in EP 40 867 and carbalkoxymethyl ester type (I crosslinking agents as described in DE 3 233 139. Further possible crosslinking agents are phenolic Mannich bases as described for example in DE 3 422 457.

If either or both of components and is I self-crosslinking, no crosslinking agent need be used.

"l "Besides customary pigment pastes it is also possible to use auxiliaries and/or additives such as solvents, flow control agents, defoamers or curing catalysts.

Components or can be used within a Swide weight ratio. It is advantageous to use S from 10 to 90% by weight, preferably from 40 to 75% by weight, of component I 30 from 10 to 50% by weight, preferably from 5 to 20% by weight, of component and from 0 to 50% by weight, preferably from 20 to 40% by weight, of component the weight percentages of jomponents and (C) adding up to 100% by weight.

Besides using components and as aqueous cationic dispersions it is also possible to use their

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C 8 O.Z. 0062/02083 starting resins for preparing the mixture by for example neutralizing an amino-containing resin wholly or partly with an acid and dispersing the protonated resin by the addition of water. The second protcnated resin can then be dispersed in the dispersion of the first protonated resin. However, it is also possible to protonate the two resins and to disperse them together. Suitable acids are the acids mentioned for the preparation of the cationic dispersions and It is also possible to disperse the resins individually in succession or together in an acid/water mixture.

0 0 o 0 01100 o oo 00 0 r* 0 0000 o 0 09 0 0 00 00 0 000 0 15 Component can be added before, during or after the preparation and mixing of components and o00o 0 0 0o a 0 00 D 0 0 00 a 1 0 40 0 0 For cathodic electrocoating, the solids content of the electrocoating bath is in general set to 5-30% by weight. Deposition customarily takes place at from 15 to in the course of from 0.5 to 5 minutes and at a pH of from 4.0 to 8.5, preferably a neutral pH, at a voltage of from 50 to 500 volts. In cathodic electr. -sing, the electrically conducting object to be coated is connected as the cathode. The deposited film is cured at above 100"C in the course of about 20 minutes.

The cured films have two phases and, from DSC measurements, two glass transition temperatures. The glass transition temperature which is assignable to the crosslinked polymer of starting component is in general within the range from 50 to 150 0 C, preferably from 70 to 110 0 C, particularly preferably from 80 to 110"C. The glass transition temperature which is assignable to the polymer of starting component is -it-, gener within the range from -80 to +20*C, preferably from -70 to 0°C. particularly preferably from -50 to -10 0

C.

The advantage of these systems, which on baking form two phases, is that the hard polymer matrix, which I1IU-LI 9 O.Z. 0062/02083 is responsible for such important properties as for example corrosion protection and sandability, is preserved, whereas the soft phase distinctly improves the elasticity of the coatings.

EXAMPLES 1 TO 7 Preparation of polymeric reaction products according to the present invention General method In all the Examples, the butadiene/acrylonitrile component used was a copolymer having an average molecular weight Mn of 3500-3800, obtainable by reacting aminoethylpiperazine with carboxyl-terminated butadiene/ S' acrylonitrile copolymers having an acrylonitrile content of 16% by weight (Hycar 1300 x 16 ATBN).

S 15 In Examples 1 to 5, the epoxy resin used was a polytetrahydrofuran diglycidyl ether having an epoxy equivalent weight (EEW) of 840. In Example 6, a polypro- 'c pylene oxide diglycidyl ether (EW 330) was used. In Example 7, a bisphenol-A diglycidyl ether (EEW 188) was used.

The butadiene/acrylonitrile copolymer was dis- 1 I t t solved in toluene, admixed with the epoxy resin and c t stirred at 80°C for several hours (see Table I) until the epoxy value was virtually zero. Thereafter, the reaction 1, t, 25 mixture was diluted with ethylene glycol monobutyl ether and isobutanol and cooled down to 40 0 C. Acetic acid was then added, followed by deionized water in the course of V an hour.

Thereafter, some of the organic solvents and 1 30 water was distilled off under reduced pressure, and the Ssolids content listed in the table was then set with deionized water.

The details of these experiments are given in Table I.

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10 O.Z. 0062/02083 o o o o 80 0 boo 0 0060 o o 9004 0* 0 0 00 0 000 a TABLE I Example 1 2 3 4 5 6 7 Bu/AN copolymer 359.8 359.8 359.8 359.8 Z59.8 172.9 359.8 Epoxy resin 23.1 46.3 52.9 61.7 70.7 27.4 9.2 Toluene 164.1 174.0 176.9 180.6 184.5 85.8 158.1 Ethylene glycol monobutyl ether 62.9 68.4 68.2 62.4 59.4 41.4 86.0 Isobutanol 97.1 16.0 119.0 112.0 111.0 73.2 125.3 Acetic 15 acid 5.9 6.4 6.3 5.8 5.5 3.8 Water [ml] 1463 1588 1588 1452 1452 960 2000 Reaction tine 12 10 10 10 11 10 19 Solids content 17 19 17 18 18 18 17 Anmine number [ng of KCH/g of solid sub- 25 stance] 65.0 61.2 60.3 58.4 57.4 59.8 59.4 Electrocoating baths a) Preparation of the base resin al) A mixture of 5800 g of hexamethylenediamine, 7250 g of dimeric fatty acid and 1400 g of linseed oil fatty acid was slowly heated to 195 0 C while the water formed (540 g) was distilled off. The mixture was then cooled down to 100 0 °C and diluted with 5961 g of toluene to a solids content of 70% by weight, The product had an amine number of 197 mg of KOH/g.

a2) In a second stirred vessel, 10 equivalents of a diglycidyl ether based on bisphenol A and epichlorohydrin having an equivalent weight of 485 were dissolved in a S0004 0 6 e<; 4 *4 *Oet, t C 8 1 8 (8 1

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11 O.Z. 0062/02083 aott 0 00 010 I2 C solvent mixture of 1039 g of toluene and 1039 g of isobutanol by heating. The solution thus formed was cooled down to 60 0 C and admixed with 300.4 g of methylethanolamine and 128 g of isobutanol the temperature rising to 78"C in the course of 5 mi.tes. Thereafter, 1850 g of the condensation product obtained by al) were added, and the mixture was heated at 80°C for 2 hours.

b) Preparation of the pigment paste To 525.8 g of the binder obtained by a) were added 168.7 g of butylglycol, 600 g of water and 16.5 g of acetic acid. This was followed by 800 g of titanium dioxide, 11 g of carbon black and 50 g of basic lead silicate, and the mixture was ball-milled to a particle size of less than 9 Mm. Thereaft-r, a solids content of 47% by weight was set with water.

c) Preparation of the crosslinking agent A mixture of 1.32 kg of toluene, 0.42 kg of trimethylolpropane and 0.72 kg of bisphenol A was stirred at 0 C until a homogeneous solution had formed. This solution was added to a hot mixture of 3.45 kg of isophorone diisocyanate, 0.86 kg of toluene and 0.0034 kg of dibutyltin dilaurate at 60"C. The mixture was maintained at 60°C for 2 hours and then admixed with 2.0 kg of dibutylamine, the rate of addition being such that the 25 temperature of the reaction mixture did not exceed 1.11 kg of toluene were then added, and the mixture was maintained at 80"C for a further hour.

d) Preparation of the electrocoating baths 700 g of the binder obtainable by a) and 300 of crosslinking agent c) were dispersed by the addition of 19 g of acetic acid with sufficient water to form a dispersion having a solids content of 31% by weight.

Organic solvents were then distilled off azeotropically, and thereafter the dispersion was adjusted with water to a solids content of 35% by weight.

The dispersion thus obtained was mixed with 775 g of the pigment paste obtainable by b) and with varying 0000 o o a 00 o 'w a o o o a 0 VO 12 0062/02083 amounts of the dispersion according to the present invention~ and made up with water to a volume of 5000 ml.

The electracoating baths were stirred at 30*C for 168 hours. Cathodes comprising zinc phosphatized test panels of~ steel were coated with paint films in the course of 120 seconds. Tha~se paint films were then baked at 160*C for 20 minutes.

The compositions of the baths, the coating conditions and the test results are summarized in Table Ii.

0,00 0.

0 1 3 o.0 00 o00060 00 000 at I 0 0 00 V--77 d I ,P nrf*

LI~L

C CC a a r )LF L1 (I a 0 4 a a ae 4 40 a a TABLE II Bath Electro- Dispersion coating acc. to dispersion pres. inv. /No.

[gl 19[g] U ID Erichsen IV] [pmn] scratch test [nm] RI 480 h SST CET Tgl Tg2 0 C [N1n] [mIn] [nm] 1836 1653 1653 1653 1791 1745 1653 1653 1653 1653 403 372 408 94 187 374 368 376 415 2.3 101l 10.1 13.5 2.3 4.5 >18.1 >18.1 11.3 18.1 -54 -54 -53 -56 -54 -52 -52 -51

U:

ID:

RI:

480hSST:

CT:

Tg1, Tg2: Deposition voltage Layer thickness Reverse impact test; determined with a mandrel imupact tester frcmn Gardner in accordance with ASTM D 2794 480 hours of salt spray test on treated steel, subpenetration in n in accordance with DIN 50021 10 cycles of cyclical exposure test in accordance with VDA 621-415, subpenetration in mn Glass transition temperatures of the two phases, measured by DSC in accordarce with Ij i

Claims (5)

1. A two-phase cathodic electrocoating composition comprising a mixtue containing: an aqueous cationic dispersion of a polycondensation or polyaddition product, which contains primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups, an aqueous cationic dispersion of an aminoepoxy resin obtained by reacting a butadiene/acrylonitrile copolymer which contains primary and/or secondary amino groups with an epoxy resin having an average molecular weight of from 140 to 10,000 and containing on average from 1.5 to 3 epoxy groups per molecule, this aminoepoxy resin having a glass transition temperature of from -80 to 200C, the polymers of dispersions and being mutually incompatible. eoo 0 o Go

2. A two-phase cathodic electrocoating composition as claimed in claim 1, containing a crosslinking agent, a pigment paste, auxiliaries and/or additives. 00 0 p poop Se. 3. A two-phase cathodic electrocoating composition as claimed in claim 1 or O* 2, comprising a mixture containing: 90% by weight of component 50% by weight of component and 0 50% by weight of a component said component being a o o component selected from the group comprising a crosslinking agent, a pigment paste, auxiliaries and additives a the percentages of components and adding up to 100% by S..weight. 0 o

4. A two-phase coating as claimed in any of claims 1 to 3 obtained by using an aqueous cationic dispersion of an aminoepoxy resin as component A two-phase coating as claimed in any of claims 1 to 3, wherein the phase containing component has a glass transition temperature of from 50 to 15000 and the phase containing component has a glass transition temperature of from -80 to +200C.

6. A two phase coating as claimed In any of claims 1 to 3, wherein the phase containing component has a glass transition temperature of from 70 to 1100C and the phase containing component has a glass ransition temperature of from -70 to 0°C. INT

7. A two-phase coating as claimed in any of claims 1 to 4, wherein the phase containing component has a glass transition temperature of from 80 to 110°C and the phase containing component has a glass transition temperature of from -60 to C. DATED this 29th day of October, 1991. BASF LACKE FARBEN AKTIENGESELLSCHAFT WATERMARI PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRAUA i I 'I,