AU734453B2 - Self-adhesive compositions with improved resistance to creepage, usable for coating metal substrates - Google Patents

Description

I .I P/UU/U11 285/91 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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Application Number: Lodged: Invention Title: SELF-ADHESIVE COMPOSITIONS WITH IMPROVED RESISTANCE TO CREEPAGE, USABLE FOR COATING METAL SUBSTRATES The following statement is a full description of this invention, including the best method of performing it known to us

SPECIFICATION

SELF-ADHESIVE COMPOSITIONS WITH IMPROVED RESISTANCE TO CREEPAGE, USABLE FOR COATING METAL SUBSTRATES TECHNICAL FIELD The invention relates to powder self-adhesive compositions with improved resistance to creepage, based on thermoplastic and/or heat-curable resins for coating metal substrates.

PRIOR ART Polyamide, polyolefin, polyester and/or polyurethane resins are commonly employed for coating metal substrates, especially because of their good mechanical properties such as abrasion resistance and impact strength and their chemical inertness towards many products such as hydrocarbons, bases and inorganic acids.

15 However, it is known that the adhesiveness of these resins to metals is generally inadequate because, for example, of poor wettability. To overcome this defect the metal support is coated with an undercoat, called adhesion primer, intended to ensure the bonding and the mechanical anchoring of the polyamide V I.IO powder. In general the adhesion primer which is employed is based on heat-curable 20 resins and is applied in the form of powder, in solution or in suspension in organic or aqueous solvents. Provision must therefore be made for additional plant for possible l o removal of the solvents and for curing the primer before the coating of the substrate thus clad with the polyamide powder. In addition, curing and/or drying the primer significantly increases the duration of the coating operations, and hence their cost.

25 Given the abovementioned disadvantages, it is increasingly being preferred to eliminate the adhesion primer and to improve the direct adhesion of the coating to the substrate.

Thus, in patent EP 412 888 the Applicant has described mixtures of polyamides and of epoxy/sulphonamide resins which can be employed for coating metal substrates without employing any adhesion primer. These mixtures of polyamide and of epoxy/sulphonamide resins in powder form can be applied onto the substrate with an electrostatic gun. It then suffices to introduce the substrate thus clad into an oven to obtain melting of the powder and a uniform coating. The substrate can also be preheated above the melting point of the powder and immersed in a fluidized bed of the powder.

In patent application PCTIFRI95/01740 the Applicant has proposed pulverulent compositions based on polyamide, on ethylene copolymers and on 0 2 unsaturated carboxylic acids or their vinyl or other esters, and optionally on copolymer of ethylene and vinyl alcohol.

However, the adhesion of such existing coatings which are applied without a primer is still inferior to that of the coatings with a primer, especially where resistance to creepage is concerned.

DESCRIPTION OF THE INVENTION The Applicant has now found anticreepage additives for self-adhesive powder compositions, i.e. which are intended to coat metal substrates without any adhesion primer.

The anticreepage additives according to the invention improve the resistance to creepage of the self-adhesive compositions into which they are incorporated, so that the resistance to creepage of the films of coatings which are applied without any primer approaches that of the coating films preceded by a primer. The anticreepage additives are precipitated calcium carbonates (PCC), uncoated, of specific (BET) surface, measured according to ISO standard 9277, of between 7 and 12 m /g and of free-flow apparent specific weight, measured according to ISO standard 903, of between 130 and 180 g/l and preferably equal to approximately 150 g/l.

The compositions of the invention are intimate mixtures based on the resins and the anticreepage additives described above.

The resins or polymers of the coating compositions may be thermoplastic resins or heat-curable resins.

By way of example of thermoplastic resins there may be mentioned polyolefins such as PE, PP and their copolymers or blends 25 PVC aliphatic, cycloaliphatic and/or aromatic polyamides such as PA-11, PA-12, PA-12,12, PA-6, PA-6,6, PA-6,12 and polyamide-based thermoplastic elastomers, by themselves, mixed and/or copolymerized.

By way of example of heat-curable resins there may be mentioned epoxy and epoxy/phenolic resins, epoxy/polyester hybrids.

The acrylic, polyester and polyurethane resins which are also suitable may be either thermoplastic or heat-curable.

Polyesters are intended to mean the resins originating from condensation reactions between mono- and polyfunctional acids with anhydrides, polyols or esters.

Epoxy resins are intended to mean the products originating from the chemistry of the diglycidyl ethers of bisphenol A, which are also called BADGE, and 3 the products originating from the chemistry of the glycidyl ether of novolac resins.

The BADGE resins employed have molecular masses which are generally between 600 and 6000 g/mol.

The coating compositions according to the invention may contain one or several of the resins listed above, but also other resins or polymers improving, for example, adhesion, such as the epoxysulphonamide resins described in EP 412 888, the resins obtained by polycondensation of aromatic sulphonamide compounds and of aldehydes and/or dicarboxylic acids, described in EP 290 342, copolymers of ethylene and of unsaturated carboxylic acids or their vinyl or other esters, and optionally copolymers of ethylene and vinyl alcohol which are described in PCT/FR/95/01740.

Besides the resins and the anticreepage additives indicated above, the coating compositions according to the invention may contain various additives and/or fillers such as pigments or dyes, anticratering, reducing and antioxidant agents and 15 the like, reinforcing fillers: antioxidants like copper iodide combined with potassium iodide, phenol derivatives and hindered amines, fluidizing agents, reinforcing and nucleating fillers like dolomite, calcium carbonates 20 (other than the anticreepage additives according to the invention) and/or magnesium carbonates, quartz, boron nitride, the kaolin sold under the trade name "Frantex®", wollastonite, titanium dioxide, ballotini, talc, mica, which are sold under the names "Dolomie®" (calcium magnesium carbonate), "Plastorit" (mixture of quartz, mica and chlorite), "Minex®" (felspar) or carbon black, 25 UV stabilizers like, for example, resorcinol derivatives, benzotriazoles or salicylates, anticratering agents, or spreading agents, pigments like, for example, titanium dioxide, carbon black, cobalt oxide, nickel titanate, molybdenum disulphide, aluminium flakes, iron oxide, zinc oxide and organic pigments like phthalocyanine and anthraquinone derivatives.

Into the compositions of the invention may be incorporated additives chosen especially from those described above and whose respective proportions remain within the limits usually encountered in the field of the powder compositions for the coating of substrates, especially metallic ones. In general, up to 100 by weight of the said constituents is incorporated, that is to say that these fillers may represent the same weight as the quantity of resin(s).

These additives can be incorporated into the compositions of the 4 invention by any means. The above compositions may be obtained in a known manner by any technique for mixing the constituents in the molten state, such as, for example, extrusion or compounding on a single- or twin-screw extruder, on a cokneader or by any continuous or noncontinuous technique as, for example, with the aid of an internal mixer.

In general, the particle size of the powders in accordance with the invention may be between 5 im and 1 mm.

A first process for obtaining powder compositions according to the invention consists in kneading, in the molten state, resin(s), anticreepage additive(s) and possible additive(s) and/or filler(s) in a kneader of suitable type. The kneading temperature may be between 150 and 300'C and preferably between 180 and 230 0

C.

A master mix or a final product may be prepared.

The final product is ground using the usual techniques to the desired 15 particle size for the coating. A spraying or precipitation process may also be used.

"Another process for preparing these powder mixtures consists in drymixing all or a proportion (in which case a master mix is prepared) of the various components, previously converted into fine powder form. This dry mixing, or dry 0' blending, generally does not require any special equipment; it can be performed at 20 ambient temperature.

As indicated above, the compositions according to the invention are in the oo form of intimate mixtures; in the case of compositions prepared by kneading in the molten state, the quantity of anticreepage additive(s) may represent from 0.1 to and preferably from 1 to 40 of the total mass of the final composition; in the ooo 25 case of compositions prepared by dry mixing, the quantity of anticreepage additive(s) *.i S may represent from 0.1 to 5 and preferably from 0.2 to 3 of the total mass of the final composition.

According to a known technique which in itself does not constitute a subject-matter of the invention, the metal substrate, and especially one made of common steel, aluminium or aluminium alloy, may have been subjected to one or several of the following surface treatments, no limitation being implied by this list: coarse degreasing, alkaline degreasing, scrubbing, shot-blasting or sandblasting, fine degreasing, hot rinsing, phosphating degreasing, iron/zinc/tri-cation phosphating, chromating, cold rinsing and chromic rinsing.

The present invention also relates to the use of the powder compositions as defined above for the coating of metal substrates and to the substrates thus coated. The metal substrate may be chosen from a wide range of products. It may 5 be pieces of plain or galvanized steel, or parts made of aluminium or of aluminium alloy. The metal substrate may be of any thickness (for example of the order of a tenth of a millimetre or, equally, of the order of several tens of centimetres).

Examples which may be mentioned of metal substrates suitable for being coated with a composition according to the invention are: degreased, smooth or shot-blasted steel, phosphated degreased steel, iron or zinc phosphated steel, Sendzimir galvanized steel, zinc-electroplated steel, bath-galvanized steel, cathodic deposition steel, chromated steel, anodized steel, carborundum-sanded steel, degreased aluminium, smooth or shot-blasted aluminium and chromated aluminium.

The composition according to the invention is therefore applied in powder form onto the metal substrate. The application of the composition in powder form can take place according to the application techniques usually employed. Grinding of the o powders may be performed in equipment that is cooled cryogenically or with high air i o input (impeller, hammer or disc mills and the like). The powder particles obtained are 15 selected in suitable equipment to remove the unwanted particle size cuts, for example grains that are too coarse and/or too fine.

S.i The powder application techniques which may be mentioned include electrostatic spraying, dipping in a fluidized bed and the electrostatic fluidized bed (for example that described in patents DD 277 395 and DD 251 510), techniques that 20 are preferred for performing the coating of the substrates according to the invention.

In electrostatic spraying the powder is introduced into a gun, where it is conveyed by compressed air and enters a nozzle raised to a high voltage which is generally between some ten and some hundred kilovolts. The applied voltage may be positive or negative in polarity. The flow rate of powder in the gun is generally 25 between 10 and 200 g/min, and preferably between 50 and 120 g/min. As it passes o through the nozzle, the powder is charged electrostatically. The powder particles conveyed by the compressed air are applied onto the metal surface to be coated, the said surface itself being earthed, that is to say connected to a zero electrical potential. The powder particles are retained on this surface by their electrostatic charge. These forces are sufficient to allow the article, once it is coated with powder, to be moved and then heated in an oven to a temperature which causes the powder to melt.

Electrostatic spraying of the compositions according to the invention, whatever the polarity of application, offers an undoubted advantage, because it will be possible, in particular, to employ the existing standard industrial plant designed for electrostatic spraying of powder coatings with a single polarity; in this case the metal substrate is subjected to a surface preparation.

6 In general a powder of mean particle size of between 5 and 100 irm and preferably between 20 and pm can be employed. The thickness of the coating is preferably of the order of 110 20 gm.

In the case of the process of dipping in a fluidized bed, the metal substrate to be coated, carefully prepared, for example by being subjected to one or several of the surface treatments listed above, is heated in an oven to a specific temperature according especially to the nature of the said substrate, its form, its thickness and the desired coating thickness. Thus heated, the substrate is next immersed in a powder composition according to the invention, which is kept in suspension by a gas circulating in a tank with a porous bottom. The powder melts on contact with the hot metal surfaces and thus forms a deposit whose thickness is a function of the temperature of the substrate and of the duration of its immersion in the powder.

In fluidized bed dip-coating the particle size of the powders used in a fluidized bed may be between 10 and 1000 ptm and preferably between 40 and 160 m. In general the coating thickness may be between 150 and 1000 gm, preferably of the order of 400 50 gm.

2 mea The present invention also relates to a composite material including a 20 metal substrate and a coating in the form of film obtained by melting the powder compositions of the invention.

WAYS OF IMPLEMENTING THE INVENTION Examples 25 1) The following products are employed in the examples: PA-11: denotes a polyamide 11 of molecular mass Mn before application of between 9000 and 15 000.

Terpolymer 1 denotes a copolymer containing ethylene units, 6 by weight of ethyl acrylate units and 3 by weight of maleic anhydride units, with a melt index, measured according to NFT standard 51016, equal to 200 g/10 min, sold under the trade name Lotader® 8200. (This is a resin intended to improve the adhesion of the polyamide resin to the substrate in accordance with the teaching of patent application PCTIFR/95101740.) Terpolymer 2 denotes a copolymer containing 44 mol% of ethylene units, vinyl alcohol units, of melt index, measured according to NFT standard 51016, equal to 12 g/10 min (measured at 2100C under a 2.16 kg load), grafted with 5 of phthalic anhydride (expressed as weight of the terpolymer sold under the trade 7 name Soarnol® A. (This is a resin intended to improve the adhesion of the polyamide resin to the substrate in accordance with the teaching of patent application PCT/FR/95/01740.) Filler 1: precipitated (acicular) calcium carbonate, uncoated, with a specific (BET) surface measured, according to ISO standard 9277, equal to 11 m 2 /g and with a free-flow apparent specific weight, measured according to ISO standard 903, equal to approximately 150 g/l, sold under the trade name Socal 90A. This is an anticreepage additive within the meaning of the present invention.

Filler 2: precipitated (acicular) calcium carbonate, uncoated, with a specific (BET) surface, measured according to ISO standard 9277, equal to 10 m 2 /g and with a free-flow apparent specific weight, measured according to ISO standard 903, equal to 230 g/l, sold under the trade name Socal P3.

Filler 3: nonacicular calcium magnesium carbonate containing 21 by weight of MgO, sold under the trade name Dolomie DRB 4/15 Filler 4: acicular wollastonite (calcium silicate) with a specific (BET) surface, measured according to ASAP standard 2000, equal to 4 m 2 sold under the trade name Nyad 1250 Filler 5: imbrication of mica, of chlorite (magnesium-potassium- 20 aluminium hydrosilicate) and of quartz (Si02 51.1 A1203 23.0 MgO 12.5 FeO 3.6 K20 2.8 relative density 2.75), sold under the trade name Plastorit "Naintsch Filler 6: anhydrous alumina, potassium and sodium double silicate (Si02 61.0 A1203 23.3 Fe203 trace, CaO 0.7 MgO trace, Na20 9.8 K20 4.6 25 specific weight 2.61, mean statistical diameter of the particles 4.5 pm), sold under Sthe trade name Minex 7.

In all that follows and unless shown otherwise, the proportions of the constituents correspond to parts by weight.

The powder compositions based on PA-11, prepared in the examples below are next applied onto metal substrates either by electrostatic spraying (ES) or by immersion The particle size of the compositions applied by ES is chiefly between and 80 pm, and that of the powders applied by immersion chiefly between 40 and 160 pm. In the case of the adhesion-promoting resins (terpolymers 1 and 2) the particle size is smaller than 60 pm.

After the composition has melted, the coating film thickness is of the order of 110 20 pm (ES application) and of the order of 400 50 pm (I application).

-8 Examples 1 to Formulations and characteristics of the powders before application: Table 1 below summarizes the grey-coloured coating compositions typically used with an adhesion primer; they are obtained by mixing the various constituents in a kneader at a temperature of between 190 and 225"C and with a residence time of the order of 30 seconds. The products in Examples 1 to 5 are next ground to the desired particle size for application by the immersion route.

9 Table 1 Example Natural Pigments Antioxidant Filler 1 Filler 2 Filler 3 No. PA-11 (TiO2, carbon and black etc.) spreading agents 1 1000 120 9 2 1000 120 9 3 1000 120 9 4 1000 120 9 1000 120 9 150 Application: Before the surface coating is applied, all the substrates (100x100x3 mm 5 steel panels) as subjected to degreasing followed by shot-blasting. They are then preheated in a ventilated oven for 10 min at 330°C and then dip-coating in the fluidized bed is carried out for 4 s. Thus coated, the substrates cool freely in the ambient air. The thickness of the films is 400 50 pm.

Evaluation: 10 Thus coated, the panels are next evaluated in saline mist according to NF standard X 41 002: a Saint Andrew's cross-shaped incision is made in the films down to the metal and the creepage is measured visually from this injury. A total creepage corresponds to a value of 35 mm.

N.B. The creepage measured (which corresponds to the distance of 15 detachment of the film starting at the injury) is the average of the maximum and minimum value, these being measured on the eight edges of the incision, excluding the "point" effect, where the creepage may be clearly greater owing to the stagnation and the draining of the salty water.

The results obtained after 1000 h of saline mist are collated in Table 2.

10 Table 2 Example No. Creepage measured (mm) 1 (comparative) 2 3 (comparative) 4 (comparative) (comparative) total creepage found after 500 h of test Examples 6 to 9 Formulations and characteristics of the powders before application: Table 3 details compositions produced in a kneader at a temperature of between 190 and 225 0 C and with a residence time of the order of 30 seconds. They are based on pure (also called natural) PA-11 or else white PA-11 (natural PA-11 10 additionally containing 100 parts of white pigments). After kneading, the mixtures are ground in order to obtain a powder of the desired particle size for application by an electrostatic route, that is to say 110 20 pm.

Table 3 Example Natural White Pigments (carbon Filler Filler Filler No. PA-11 PA- black, blue etc.), 1 3 11 antioxidant and spreading agents 6(black) 800 24 125 7(black) 800 24 125 8(white) 1000 14 40 9(white) 1000 14 40 Application: The powders obtained above are deposited at ambient temperature by electrostatic spraying onto a steel panel of the same dimensions as those described above, which has previously been subjected to degreasing and then to a mechanical surface treatment (shot-blasting). During the application the metal surface is at zero potential.

Once coated, the panel next is moved without waiting into a ventilated

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11 oven maintained at 220°C, where it stays for several minutes and is then taken out of the oven and cools freely in air.

The conditions for application by an electrostatic (ES) route are the following: Electrostatic application onto 100x Examples 100x1 mm steel panel 6 to 9 Shot-blasted substrate kV positive ES 4 min melting in ventilated oven at 220°C .00 00 0. Evaluation: The results of the creepage resistance test, obtained after 250 hours of saline mist, are collated in Table 4.

Table 4 Example No. Creepage (mm) 6 (comparative) 7 8 8 (comparative) 9 19 Examples 10 to 16 Formulations and characteristics of the grey powders before application: Tables 5 and 6 below detail the grey-coloured compositions produced in a kneader at a temperature of between 190 and 225°C and with a residence time of the order of 30 seconds.

12 Table

I

Example No.

to 16 Natural PA-11 Terpolymers Pigments (TiO2, carbon black, etc.) Antioxidant and spreading agents Other fillers 1000 2 1 40 80 1 t I 120 9 cf Table 6 L I a Table 6 Example Filler 1 Filler 2 Filler 3 Filler 4 Filler No.

11 12 150 13 150 14 150 150 16 150 After kneading, they are ground to a suitable particle size for application by a dip-coating route and then applied in the same conditions as those of Example 1.

The evaluation is done using the same method as that described in Example 1. The results are combined in Table 7.

Table 7 Example No. Creepage measured at 1000 h (mm) (comparative) 11 16 12 16 13 (comparative) 14 (comparative) (comparative) 16 (comparative) Examples 17 to 13 Formulations and characteristics of the natural and white powders before application: Table 8 below details the compositions produced in a kneader at a temperature of between 190 and 225 0 C and with a residence time of the order of seconds.

Table 8 Terpolymers Example No./ Natural Pigments Filler PA-11 1 colour 2 1 (TiO2, etc) 17/natural 1000 40 18/natural 1000 40 80 150 19/white 1000 40 80 140 20/white 1000 40 80 140 150 After kneading they are ground to a suitable particle size for application by 10 a dip-coating route and then applied in the same conditions as those in Example 1.

The evaluation is done using the same method as that described in Example 1 above. The results are combined in Table 9.

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Table 9 Example No./colour Creepage at 1000 h (mm) 17/natural 18/natural 19/white 31 21 *total creepage found already at 500 h Examples 21 to Formulations and characteristics of the powders before application: Tables 10 and 11 below detail the compositions produced in a kneader at a temperature of between 190 and 225°C and with a residence time of the order of seconds.

14 Table a. a a.

Table 11 Example No. Filler 1 Filler 3 Filler 5 Filler 6 21 50 100 22 50 100 23 100 24 100 100 After kneading, they are ground to a suitable particle size for application by a dip-coating route and then applied in the same conditions as those in Example 1.

The evaluation is done using the same method as that described in Example 1 above. The results are combined in Table 12.

i5 Table 12 Example No.

21 (comparative) 22 Cepage. measured at 1000 h (mm) 23 (comparative) 24 (comparativp) 125 9.

9* 9. .9 9* 9999 9*9* 9 9 9 .9 9 9* 9*

Claims (9)

1. Self-adhesive composition for the coating of metal substrates, based on thermoplastic and/or heat-curable resins, including at least one precipitated calcium carbonate (PCC), uncoated, with a specific (BET) surface, measured according to ISO standard 9277, of between 7 and 12 m2/g and with a free-flow apparent specific weight, measured according to ISO standard 903, of between 130 and 180 g/l and preferably equal to approximately 150 g/l and (ii) which is in the form of powder, for increasing the creepage resistance of the composition.

2. Composition according to claim 1, based on polyamide and preferably based on PA-11 and/or PA-12.

3. Composition according to claim 1 or 2, also including additives such as fillers, pigments, antioxidants, etc.

4. Process for preparing compositions as defined according to any one of claims 1 to 3 by kneading in the molten state and then grinding and/or by dry mixing of the various constituents.

Use of precipitated, uncoated calcium carbonate (PCC) powder, with a specific (BET) surface, measured according to ISO standard 9277, of between 7 and 12 m2/g and with a free-flow apparent specific weight, measured according to ISO standard 903, of between 130 and 180 g/ as anticreepage additive for a metal substrate coating based on thermoplastic and/or heat curable resins.

6. Composite material including a metal substrate and a coating formed of composition as defined in one of claims 1 to 3.

7. Composite material according to claim 5, in which the layer of powders has _been melted to make a coating. 17

8. Self-adhesive composition according to claim 1 and as herein described with reference to the examples.

9. Process according to claim 4 and as herein described with reference to the examples. DATED this 19 th day of June, 2000. ELF ATOCHEM S.A. WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA P4616AU00 LCG/CLR/SIG a oooo oooo a* a oo a a a