Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/03—Powdery paints
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
  • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
  • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C09D127/16—Homopolymers or copolymers of vinylidene fluoride
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
  • C09D133/04—Homopolymers or copolymers of esters
  • C09D133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/52—Two layers
  • B05D7/54—No clear coat specified
  • B05D7/546—No clear coat specified each layer being cured, at least partially, separately

Definitions

• the present invention relates to powder compositions and their use as primer coatings.
• the present invention relates to powder compositions for obtaining primer coatings for coatings based on poly(vinylidene fluoride) , hereinafter referred to as PVdF, without using solvents.
• the present invention also relates to a process for preparing powder compositions and to a process for coating a substrate with said compositions.
• PVdF is characterized by a series of valuable properties which make its use as binding agent appear desirable. Thus, it is stable towards aggressive chemicals, thermally stable, dirt-repellent, scratch-resistant, weather-resistant and is not broken down by UV irradiation. The durability of PVdF is evidenced by its tough finish as well as its ability to provide a finish that will not craze or chalk with the changing weather conditions.
• PVdF-based coatings are known to be very useful as protective coatings for a variety of substrates, more particularly for building panels and other articles made from metal sheets which are intended for outdoor use.
• the Applicant has developed a process for preparing pigmented PVdF-based powder coating products, as disclosed in EP-A-259290.
• PVdF-based compositions provide a very satisfactory topcoating, they adhere poorly to metal substrates and have less than satisfactory corrosion resistance.
• PVdF-based coatings usually need to be applied on a suitable primer coating, mainly for improving adhesion to the substrate but also in order to improve corrosion resistance of the substrate. This is particularly necessary with metal substrates such as steel and aluminium. For this reason, many different primer coating compositions have been formulated. The composition of the primer depends, among other factors, on the topcoat which will subsequently be applied to it.
• compositions of an acrylic resin, an epoxy resin and an organosilicon or organoaluminium compound As primer for PVdF topcoats, it has already been proposed to use compositions of an acrylic resin, an epoxy resin and an organosilicon or organoaluminium compound; however, these compositions require the latter compounds, which are designed to improve the adhesion to the substrate and are delicate to use.
• EP-A-294755 discloses a PVdF-based liquid coating product, based on a solvent and a ternary polymer mixture of PVdF, a second polymer incompatible therewith, and a compatibilizer, which is to be used as topcoat without primer coating.
• a compatibilizer which is to be used as topcoat without primer coating.
• the preferred choice of an epoxy resin as incompatible polymer considerably reduces the weathering resistance of the resulting coating.
• Still another object of the invention is to provide a process for coating a substrate with a primer coating for PVdF-based topcoats.
• the present invention provides powder products, comprising as binding agent
• thermoplastic resins compatible with PVdF from about 5 to about 15 % by weight, based on the total weight of the product, of one or several thermoplastic resins compatible with PVdF;
• thermosetting binder system preferably epoxy-based.
• present invention also provides the use of the powder products as primer coatings, more particularly as primer coating for PVdF-based top coatings.
• the present invention further provides a substrate coated with the primer and a process for coating a substrate with a primer coating, said primer coating being suitable for later application of a pigmented PVdF-based top coating by applying a pigmented PVdF-based powder on said primer coating and subjecting it to a heat treatment, preferably at a temperature of about 180 to 260°C, said process comprising the steps of :
• the primer products contain from about 5 to about 15 wt %, preferably about 8 wt %, of one or several thermoplastic resins compatible with PVdF, preferably selected from the group consisting of vinylidene fluoride polymers, compatible acrylic polymers, and mixtures thereof.
• the amount of the compatible thermoplastic resin comprised in the powder composition is an amount sufficient to improve the adhesion of the resulting primer coating with PVdF-based top coatings. If part of the thermosetting resin is compatible with PVdF, It is possible to use lower amounts of compatible thermoplastic resin.
• the compatibility of two polymer resins can be detected by any one of a wide variety of methods known in the art (see e.g. "Polymer Blends", D.R. Paul et al., Eds., 1978 and “Polymer-Polymer Miscibility", 0. Olabisi et al., 1979, both from Academic Press, New York).
• one method is most commonly used, namely the determination of the glass transition temperature Tg, which may be carried out using several methods including spectroscopy and calorimetry. Indeed, it is generally accepted that compatible blends are indicated by a single glass transition temperature.
• the preferred method used by the Applicant is differential scanning calorimetry, better known as DSC.
• Polymer blends are obtained by vacuum ( ⁇ 10 Pa) removal of the solvent from a 3% solution in dimethylformamide, first at room temperature then at 100°C, before being slowly cooled to ambient temperature.
• DSC measurements are carried out using three successive cycles of heating at 20°C/min, maintaining at the maximum temperature for 10 minutes, cooling at 20°C/min and maintaining at the minimum temperature also for 10 minutes.
• Tg is defined as the temperature corresponding to the inflection point at half the specific heat difference ⁇ Cp observed with the transition during the second and third heating steps.
• thermoplastic polymers are known in the art to be compatible with PVdF (see e.g. J. Polym. Sci., 27 B. 1195, 1989).
• the compatible thermoplastic resin is preferably selected from the group consisting of vinylidene fluoride polymers, compatible acrylic polymers, and mixtures thereof.
• the vinylidene fluoride polymers which are preferably used in the compositions of the invention are not only the homopolymer of vinylidene fluoride (PVdF) , but also the copolymers prepared from at least 90% by weight of vinylidene fluoride monomers.
• Suitable copolymers include those with fluorinated comonomers such, for example, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, vinylfluoride, and the like.
• the homopolymer is generally used.
• the preferred vinylidene fluoride polymers are those having a molecular weight in the range of about 10,000 to 70,000, most preferably about 30,000 to 50,000, a melting temperature of about 155 to 170°C, a melt flow index (according to ASTM D 1238 (230°C/5kg)) of about 10 to 50 g/10 min, most preferably about 10 to 30 g/10 min, and a melt viscosity (according to ASTM D 3835) of about 600 to 1200 Pa.s at 230°C, most preferably about 700 to 1000 Pa.s.
• the most preferred acrylic resins are copolymers of about 70wt % of methyl methacrylate with about 30wt % of ethyl acrylate which exhibit a viscosity of about 7 to 17 P when in 40 % solution in a solvent mixture which is a 95:5 by weight mixture of toluene and ethylene glycol methyl ether.
• the composition of the powder products of the invention comprises from about 50 to about 90 wt % of a thermosetting binder system.
• thermosetting binder system consists essentially of a thermosetting resin.
• Thermosetting resins contain cross-linking sites; upon the application of heat, and in the presence of an appropriate curing agent if the nature of the cross-linking sites requires it, they cure to the final resin which will be mechanically strong, resistant to chemical attack and adherent to the substrate.
• Such thermosetting resins are usually obtained by copolymerisation with a minor amount of comonomer units containing a cross-linking site.
• Such sites are usually reactive groups like hydroxy, carboxyl, amino and glycidyl groups, which may be cross-linked using a curing agent which is exemplified by polyisocyanate compounds (usually diisocyanates like isophorone diisocyanate, xylylene diisocyanate, or hexameth lene diisocyanate) , dimers and trimers thereof, and blocked isocyanate compounds (blocked at the isocyanate group with a blocking agent such as epsilon-caprolactam, phenol, benzyl alcohol or methyl ethyl ketoxime) .
• polyisocyanate compounds usually diisocyanates like isophorone diisocyanate, xylylene diisocyanate, or hexameth lene diisocyanate
• dimers and trimers thereof dimers and trimers thereof
• blocked isocyanate compounds blocked at the isocyanate group with a blocking agent such as epsilon
• thermosetting resin is not self-curing, a curing agent is required, the amount of which may vary over a considerable range, depending on the particular type of curing agent selected and on the degree of curing desired.
• thermosetting binder systems designed for use in powder coatings, is available. They are known in the art, so that a complete description is not required herein. However, mainly to meet the corrosion resistance requirements, it is preferable to use a system based on a solid epoxy resin with an appropriate curing agent.
• Solid epoxy resins which are useful in the practice of this invention are exemplified by, but not limited to, resins produced by reacting epichlorhydrin and bisphenol A and having an epoxy equivalent weight of from 400 to 1800. Numerous other examples may be found in the prior art, e.g. in US-4255 553-A or in "Handbook of Epoxy Resins" (Lee and Neville, 1967, McGraw-Hill).
• the preferred concentration range for dicyandiamide is of from about 4% to about 10% by weight of the epoxy resin.
• the powder coating composition of the present invention can be admixed according to need with various kinds of additives conventionally formulated in coating compositions.
• additives conventionally formulated in coating compositions.
• the additives compounded with the inventive powder coating composition include pigments, extenders, levelling agents, ultraviolet absorbers, thermal ageing retarders and so on. These additives can be used either singly or as a combination.
• compositions of the invention contain from 0 to about 35 wt % of pigments.
• pigments in the coating composition of the present invention is optional. If no pigment is used, this results in a clearcoat composition; no visual control will be available when applying such clearcoat manually, and the coating thus obtained may be unevenly thick.
• the powder composition preferably contains from 5 to 25 wt % of pigments.
• the powder composition may optionally contain up to 3 wt % of a levelling agent.
• a levelling agent is not essential to the invention, it helps obtain the high quality of coating surface required in the art.
• the amount of levelling agent can vary widely from about 0 to 3 wt % based on the total weight of the mixture, but the amount preferably used is of about 0.7 to about 1 wt % based on the total weight of the mixture.
• the extruding and granulating (pelletising) of the resulting mixture above can be conducted following standard procedures.
• the operating procedures and conditions are easily determined by one skilled in that art.
• the processing temperature is preferably from about 90°C to 140°C with about 100°C being most preferred.
• the dimensions of the pellets are not critical parameters, however the pellets are usually about 3mm in diameter and 2mm in length.
• a master-batch is first prepared with the PVdF-compatible thermoplastic resins and the thermosetting binder resin in a weight ratio of from about 1:1 to 1:4; it is then extruded with the remainder of the components.
• the resulting powder should comprise particles of size and shape suitable for achieving constant flow through the application equipment, mainly in order to obtain a constant thickness of the coating. It is preferred that the shape of the particles be as spherical as possible, because the resulting powder has better flowing properties.
• the grinding step is, if needed, associated with a sieving step for eliminating the largest size particles, i.e. those particles exceeding about three times the desired thickness of the coating.
• excessively small particles i.e. ⁇ 1.5 urn wherein urn stands for micrometer
• the particles of the ground primer powder have an average particle size between about 0.03 and 0.05 mm.
• the grinding step is preferably carried out at room temperature, or at least at a temperature no higher than about + 50°C.
• Compositions containing high amounts of thermoplastic resin should be ground at lower temperatures, i.e. below about + 20"C.
• a particularly useful grinding process would be any process of grinding that includes the removal of ground particles below a predetermined size (to avoid overgrinding) and the retention of larger particles for further grinding.
• the resulting powder can be applied on the substrate by any means suitable for achieving an even distribution of the particles.
• the powder can be applied by any electrostatic spray application apparatus, whereby the charges particles are sprayed onto the oppositely charged substrate.
• Alternative application techniques include, for example cloud chamber, fluidised bed, and even in some cases triboelectric coating, and the like. Such techniques are well known in the art and need not to be described further.
• the heat treatment preferably comprises passing the coated substrate into a heated oven wherein the coating is finally baked at a temperature from about 160 ⁇ C to 240°C.
• the temperature used in this step should be higher than the melting point of the powder, which melting point is easily determined experimentally. On the other hand, excessively high temperatures have an adverse effect on most properties of the primer coating.
• the duration of the heating step is easily determined by one skilled in the art, using known suitable methods.
• the top coating composition is applied thereon and subjected to a suitable second heat treatment which should however not exceed about 240°C.
• coating compositions of the invention are particularly adapted as primer for PVdF-based powder topcoatings, they may also be used in combination with other powder topcoatings or even with liquid (i.e. solvent-based) topcoatings.
• Dicyandiamide designates a commercially available dicyandiamide-type curing agent sold under the name EPIKURE 107 FF by SHELL .
• Solid epoxy resin E designates a commercially available epoxide resin, manufactured from bisphenol A and epichlorhydrin, having an epoxy molar mass (weight per epoxide equivalent) of 775 g and a melting point of about 65°C (sold under the name EPIKOTE 3003 by SHELL; similar products are available from other manufacturers) .
• Levelling agent M designates MODAFLOW POWDER III by MONSANTO Master batches were prepared by one of the following procedures to contain 70 wt % (as verified by a determination of the epoxy number) of solid epoxy resin E and 30 wt% of either a PVdF-compatible resin C or another non-compatible resin Z (for comparative purposes only). a) Melting the two resins together while mixing them, cooling the mixture and granulating the resulting solid. The following master batches have been prepared according to this procedure :
• Master batch A contained as resin C a commercially available thermoplastic methylmethacrylate polymer sold under the name PARALOID A-21 by ROHM AND HAAS and having a T g of 105°C.
• Master batch B contained as resin C a commercially available thermoplastic copolymer of methyl methacrylate with ethyl acrylate sold under the name PARALOID B-44 by ROHM AND HAAS and having a T g of 60°C. b) Extruding the two resins together.
• Master batch K contained as resin C a commercially available thermoplastic vinylidene fluoride polymer having a melting temperature (according to ASTM D 3418) of 165-170°C and a melt viscosity (according to ASTM D 3835) of about 700 Pa.s, sold under the name KYNAR 710 by PENNWALT.
• the extrusion was carried out in a co-rotating twin-screw extruder having a screw diameter of 28 mm and a length/diameter ratio of 30, operated at 50 rpm and giving an output of about 1 kg/h.
• the temperature profile during extrusion of this master batch was of
• the last temperature being the die temperature.
• Master batch L contained as resin Z a commercially available thermoplastic ethylene vinyl alcohol (EVOH) copolymer ( .p. 105-108°C) sold under the name LEVASINT S 31 by BAYER.
• EVOH thermoplastic ethylene vinyl alcohol
• LEVASINT S 31 commercially available thermoplastic ethylene vinyl alcohol copolymer sold under the name LEVASINT S 31 by BAYER.
• the extrusion was carried out in a co-rotating twin-screw extruder having a screw diameter of 28 mm and a length/diameter ration of 30, operated at 50 rpm and giving an output of about 1 kg/h.
• the temperature profile during extrusion of this master batch was of 20/20/50/120/120/120/110°C, care being taken not to exceed 50°C in the third zone.
• Master batch P contained PARALOID B-44 (hereabove described) as resin C.
• the extrusion was carried out in a single screw extruder having a screw diameter of 45 mm and a length/diameter ratio of 30, operated at 70 rpm and giving an output of about 9 kg/h.
• the temperature profile was of 20/130/150/150/160/130°C. Grinding, application and topcoating
• the pelletised primer compositions were ground in a RETSCH laboratory grinding unit before passing through a 0.12 mm sieve.
• the resulting powders were applied by an electrostatic spray process on a 2mm thick chromated aluminium plate, heated 10 minutes at 180°C (object temperature) to give a 50 urn primer coating and topcoated by a 50 urn PVdF-based powder coating as described in Example 1 of EP-A-259290.
• Evaluation of the filiform corrosion resistance :
• test material scratched vertically through the coating to the bare metal according to ASTM D1654 was placed in a controlled environment, where temperature and relative humidity can be varied independently. Corrosive conditions were made more aggressive by introducing an intermittent salt spray, in alternance with acidification of the climate by a continuous dosage of sulphur dioxide (SO2) gas at a concentration of about 100 ppm according to the following 24 hours cycle :
• SO2 sulphur dioxide
• test panels were evaluated for creepage from scratches (scribe) .
• Primer paints containing 8 wt % of PVdF-compatible resin were prepared by extruding and granulating the following ingredients : Ex. 1 Ex. 2
• a primer paint was prepared with the following composition : 71.15 p.b.w. of solid epoxy resin E 8.0 p.b.w. of PARALOID B-44 (hereabove described). 0.8 p.b.w. of levelling agent M. 16.3 p.b.w. of titanium dioxide. 3.75 p.b.w. of dicyandiamide 100.00
• the preparation method used consisted in first mixing all powdered ingredients, except dicyandiamide, in a Herfeld mixer (dry mixing at room temperature) .
• the resulting mixture was extruded in a co-rotating twin-screw extruder having a screw diameter of 28 mm and a length/diameter ratio of 30, operated at 50 rpm and giving an output of about 1 kg/h.
• the temperature profile during extrusion was of 20/95/95/95/95/90/100°C, the latter temperature being the die temperature and the dicyandiamide being injected along the screws at the beginning of the 90°C zone so that its residence time is of less than one minute.
• Primer paints were prepared by extruding the following ingredients according to the procedure of Example 3 :
• Example 4 shows very bad intercoat (between the primer and the PVdF-topcoat) adhesion.
• the properties of the coating of Example 5 are similar to those of Example 3.
• Example 6 The pellets of Examples 6 and 7 (outside the claimed range) have been cryogenically grinded (according to a procedure similar to that described in Example 1 of EP-A-259290) ; after spraying on an aluminium panel and heating as before, the resulting coating systems showed a low flexibility ( ⁇ 1 N.m) but had a good intercoat adhesion.
• Example 8 The pellets of Examples 6 and 7 (outside the claimed range) have been cryogenically grinded (according to a procedure similar to that described in Example 1 of EP-A-259290) ; after spraying on an aluminium panel and heating as before, the resulting coating systems showed a low flexibility ( ⁇ 1 N.m) but had a good intercoat adhesion.
• Example 8 Example 8
• a primer paint was prepared by extruding and granulating the following ingredients :
• the coating system had the same properties as in Example 2 except the reverse impact resistance which was about 2.5 N.m.
• a primer paint was prepared by extruding and granulating the following ingredients :
• Primer paints were prepared by extruding and granulating the following ingredients :
• a primer paint was prepared by extruding and granulating the following ingredients :
• thermosetting binders than of the epoxy type : in this example an isocyanate-cured polyester was used instead of dicyandiamide-cured epoxy resin used in the previous Examples. However, the anti-corrosive properties were not entirely satisfactory.

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• Wood Science & Technology (AREA)
• Organic Chemistry (AREA)
• Paints Or Removers (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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• 1990
  • 1990-06-22 EP EP90909029A patent/EP0479811A1/en active Pending
  • 1990-06-22 KR KR1019910701943A patent/KR100209186B1/ko not_active IP Right Cessation
  • 1990-06-22 RU SU5010878A patent/RU2139308C1/ru not_active IP Right Cessation
  • 1990-06-22 WO PCT/BE1990/000034 patent/WO1990015845A1/en not_active Application Discontinuation
  • 1990-06-22 CA CA002056982A patent/CA2056982C/en not_active Expired - Fee Related
  • 1990-06-22 EP EP19900870099 patent/EP0404752A1/en active Pending
  • 1990-06-22 AU AU58285/90A patent/AU636622B2/en not_active Ceased
  • 1990-06-22 JP JP50857990A patent/JP3276082B2/ja not_active Expired - Fee Related

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