Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F299/00—Macromolecular compounds obtained by interreacting polymers involving only carbon-to-carbon unsaturated bond reactions, in the absence of non-macromolecular monomers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/14—Esterification
• • 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
  • C09D133/14—Homopolymers or copolymers of esters of esters containing halogen, nitrogen, sulfur or oxygen atoms in addition to the carboxy oxygen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2810/00—Chemical modification of a polymer
  • C08F2810/20—Chemical modification of a polymer leading to a crosslinking, either explicitly or inherently
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2810/00—Chemical modification of a polymer
  • C08F2810/30—Chemical modification of a polymer leading to the formation or introduction of aliphatic or alicyclic unsaturated groups

Definitions

• the invention relates to a resin for powder coatings for use as a top coat in the automotive industry.
• the invention also concerns top-coated automotive substrates.
• the top coat or finish coat is the coating intended to be the last coat applied in a coating system and is usually applied over a primer, a basecoat or surfaces.
• the clear top coats which, according to the present state of the art in the automotive industry, are used as a two-component system are solvent-containing paint systems based on acrylate resins cured with isocyanates. In order to meet the requirements regarding the reduction in solvent emissions, so-called high-solids systems are already being used. The only way to reduce solvent emissions still further is to use powder coatings for clear automotive coatings (Lattke, E. "Pulverlack am Auto; Aus der reform der Autoindustrie", presented at "Der Pulver Economics '92, January 23, 1992, M ⁇ nchen”; JOT-Verbeck, pages 1-11).
• Powder paint systems for automotive top coats must meet the same stringent performance standards set for the solvent-containing systems. These requirements include for instance flow, chemical resistance, gloss and outdoor durability (Kinza, W. "Pulverklarlack fur die
• the presently available powder resin systems do not satisfy the required combination of properties. Some properties can be obtained with systems based on an acid-epoxy curing reaction, but the required combination of good flow, good chemical resistance, high gloss, high scratch resistance, good mechanical properties and good outdoor durability remains a desired but still elusive objective for powder coatings. With systems based on polymers containing hydroxyl groups and curing agents containing blocked isocyanate groups, too, several of the above-mentioned properties can be obtained. However, the usual temperature (above 170°C) at which these systems must be cured is far too high for application as a (clear) topcoat for automotive applications. It is for example elucidated in the article 'Powder
• the object of the present invention to provide a binder composition which can be cured at relatively low temperatures and which, moreover, gives a combination of said desired properties.
• the powder coating have to result in a clear top coat on exterior parts in the automotive industry.
• the invention is characterized in that the resin is an acrylate polymer having several side chains containing unsaturated groups and the amount of unsaturation in the unsaturated acrylate resin is between 214 and 1400 g per mol unsaturated group.
• this amount of unsaturation is between 350 and 1000 gram per mol unsaturated group.
• the curing can be effected both thermally and via radiation (UV and EB) at temperatures between for example 100°C and 150°C.
• the powder coatings obtained have good flow properties, good mechanical properties, good gloss, good impact resistance, good flexibility, good resistance to chemicals and a very good resistance to petrol.
• the cured coatings are useful as a clear top coat in the automotive industry on exterior parts such as for example the body, hubcaps, wheels and doors.
• Another advantage of the resin according to the invention is that no crosslinking agent need be used. This means that there are no problems arising from use of a toxic or mutagenic crosslinking agent.
• the present invention offers the further important advantage of good outdoor durability of the coating as contrasted with UV-curing coatings which usually have a poor outdoor durability. As appears from for example page 19 of Journal of Radiation Curing (April 1984) this failure often came as a consequence of the individual components used in the formulated coatings.
• the acrylate polymers having several side chains containing unsaturated groups which comprise the present powder coating resin can be obtained via a two-step process.
• a first step an acrylate polymer is prepared in a conventional polymerisation process in which also a certain portion of functional monomer is copolymerised to obtain a functionalized acrylate polymer.
• This functional monomer which is usually present in amounts of between 3 and 60 wt.%, is preferably an epoxy-functional monomer, for example on the basis of glycidyl (meth)acrylate.
• acid-functional monomers for example on the basis of (meth)acrylic acid
• hydroxyl-functional monomers for example on the basis of hydroxyethyl (meth)acrylate
• isocyanate-functional monomers for example on the basis of TMI (benzene,1-(1-isocyanato-l-methylethyl)-4-(1- methylethenyl) from American Cyanamid)
• amine-functional monomers for example on the basis of (meth)acrylamide
• an addition reaction is carried out between the just described functionalized monomer of the acrylate polymer obtained from the first step and a compound containing a group that can react with said functional monomer and that also contains an unsaturated group.
• the compound can contain as group that can react for example (meth)acrylate ester groups, allyl groups, vinyl groups and anhydrides containing unsaturated groups.
• Representative examples include (meth)acrylic acid, glycidyl (meth)acrylate, TMI, allyl glycidyl ether and maleic anhydride.
• the functionalized acrylate resin can be dissolved in a solvent, such as for example toluene, xylene or butyl acetate.
• the compound containing an unsaturated group that can react with the functionalized acrylate polymer is added at temperatures of between for example 50°C and 150°C. Then the mixture is stirred for several hours. The progress of the reaction can be followed via titrations of for example acid groups or isocyanate groups.
• Examples include reactions between an acid group and an epoxy-functional acrylate polymer, a hydroxyl group and an isocyanate-functional acrylate polymer, an isocyanate group and a hydroxyl-functional acrylate polymer, an anhydride group bound to an isocyanate and an amine- functional acrylate polymer, an epoxy group and an acid- functional acrylate polymer or an epoxy group and an amine- functional acrylate polymer.
• the reaction is preferably carried between an epoxy-functional acrylate polymer, such as glycidyl(meth)acrylate polymer, and an acid group, such as (meth)acrylic acid.
• an epoxy-functional acrylate polymer such as glycidyl(meth)acrylate polymer
• an acid group such as (meth)acrylic acid
• the acrylate polymers can also be obtained via a multi-step process.
• a multi-step process for example one of the isocyanate groups of a diisocyanate compound (such as IPDI or H 12 MDI) can react with a hydroxyl-functional
• the compound thus obtained which contains an isocyanate group and a (meth)acrylate group, can then react with a hydroxyl-functional polymer such as an acrylate polymer that contains hydroxyethyl methacrylate as the functional monomer.
• the acrylate polymers according to the invention can be cured for example thermally, via UV radiation or via the electron beam (EB) method. These acrylate polymers are preferably cured with UV radiation.
• a photoinitiator is mixed with the acrylate polymer according to the invention. This may be done both in a solvent or in the melt in the extruder, the latter of which is preferred. Furthermore, auxiliaries such as flow promoting agents may be added. Then the paint can be applied to a plate or can be electrostatically sprayed. In the latter case the plate is placed in an oven and the powder is melted (this may also be effected by means of heating via infrared radiation), after which the panel, which is still hot, is cured under a source of UV light or by EB-curing.
• Suitable photoinitiators include for example IrgacureTM (Ciba Geigy), DarocureTM (Merck) and Lucirine TPOTM (BASF).
• the initiators are solids and are present in amounts of between 0.2 and 6 wt.%.
• a major advantage of this curing procedure is that the softening of the powder paint (through heat) takes place completely separately from the curing reaction (curing through radiation). This means that powder coatings that have extremely good flow properties can be made from the present powder coating composition.
• peroxides such as for example alkyl peroxides, acyl peroxides, peroxyesters or peroxyketals are mixed with the acrylate polymer according to the invention. This can be done in solution or in the melt in the extruder. Furthermore, auxiliaries such as cobalt (for the acceleration of the peroxide decomposition) , flow promoting agents, degassing agents and pigments may be added. After this the resin solution is applied to a plate or the powder is electrostatically sprayed onto a plate and cured in an oven for a certain length of time.
• cobalt for the acceleration of the peroxide decomposition
• flow promoting agents for the acceleration of the peroxide decomposition
• degassing agents and pigments may be added.
• the cured powder coating is hence obtained by causing unsaturated groups in the side chain of the acrylate polymers to react with one another, via for example thermal curing (addition of peroxides), curing with the aid of ultraviolet light (addition of a photoinitiator) or electron-beam curing. That is why no special hardeners are necessary and no volatile components are released during the curing.
• additives such as fillers, flow aids and/or stabilizers and also pigments if desired, can be added to the coating systems, preferably during extrusion.
• Novel top-coated automobile parts comprise a substrate, e.g. a body panel or other top-coatable automobile parts (such as for example wheels, wheelcovers and doors), having, if desired, a pigment layer or layers thereon and a clear top coat over the pigment layer or layers (if present) wherein the top coat comprises a solvent-free powder coating obtained from the binder composition according to the invention.
• the powder coatings obtainable with the resin according to the invention can be applied on body parts, such as for example wheels, wheelcovers, fenders, doors, hoods and the like but can also be used on wood or plastic.
• the powder coatings of the present invention are also useful as industrial top coats for general purposes, for top coats for machinery and equipment, especially top coats for metal, for example cans, household articles and other small pieces of equipment.
• US-A-3974303 relates to a method for forming coating films which comprises coating a powder composition of a resin having unsaturated bonds.
• This resin may be, amongst many others, a vinyl or acrylic polymer having polymerisable unsaturated bonds.
• US-A-3974303 contains no suggestion that precisely the specific resins according to the present invention offer a solution to the aforementioned problems with respect to powder coatings in the automotive industry.
• a hydroxyl-functional acrylate resin 500 g of toluene was added to a 2-litre reactor vessel fitted with a thermometer, a reflux condenser and a stirrer.
• the monomer mixture consisted of 368 g of methyl methacrylate, 232 g of hydroxyethyl methacrylate, 200 g of butyl acrylate and 200 g of cyclohexyl methacrylate in which 30.27 g of AIBN was dissolved.
• a product was obtained that had a viscosity of 425 dPa.s (Emila, 165°C) and a T g of 48°C.
• Table I also indicates the theoretical epoxy equivalent weight (EEW), the viscosity measured with the aid of an Emila rheometer (dPa.s, 165°C) and the glass transition temperature (T g , Mettler TA-3000, 5°C/min).
• EW epoxy equivalent weight
• T g glass transition temperature
• Mn and Mw values were determined with the aid of GPC (gel permeation chromatography) , using polystyrene as a standard.
• the monomer mixture consisted of 180 g of methyl methacrylate, 155 g of TMI (American Cyanamid), 65 g of cyclohexyl methacrylate and 100 g of butyl acrylate in which 14.5 g of tert.-butyl perbenzoate was dissolved.
• the monomer mixture was added to the reactor in 4.5 hours.
• the reaction mixture was kept at reflux temperature and 3 hours after the addition of the monomer mixture 3 g of tert.-butyl perbenzoate was added to the reactor. After 4 hours at reflux temperature a separation vessel was incorporated in the reactor and the solvent was removed by increasing the temperature and creating a vacuum.
• the product had a viscosity (Emila, 165°C) of 100 dPa.s and a T g of 52°C.
• Example VIII Preparation of an acrylate resin containing a glycidyl methacrylate ester group as the unsaturated side chain, through the addition of glycidyl methacrylate to an acid-functional acrylate resin
• Example X Preparation of an acrylate resin containing a vinyl group as the unsaturated side chain, through the addition of TMI to a hydroxyl-functional resin
• Example XII 300 g of resin of Example II was dissolved in 300 g of toluene in the reactor described in the above examples. The reaction mixture was heated to 115°C. 52.5 g of MA was dissolved in 52.5 g of toluene and this solution was added to the reactor in an hour. When free MA was no longer detected (via determination of the acid number) the solvent was removed as described in previous examples. The final product had an acid number of 78 g of KOH/g of resin and a T g of 26°C.
• Example XII 300 g of resin of Example II was dissolved in 300 g of toluene in the reactor described in the above examples. The reaction mixture was heated to 115°C. 52.5 g of MA was dissolved in 52.5 g of toluene and this solution was added to the reactor in an hour. When free MA was no longer detected (via determination of the acid number) the solvent was removed as described in previous examples. The final product had an acid number of 78 g of KOH/
• AN acid number in g of KOH/g of resin
• WPU theoretical equivalent weight in g of resin per unsaturated group
• Mn and Mw were determined via GPC (gel permeation chromatography) using polystyrene as a standard
• the resistance to petrol of the cured powder coatings was determined by placing a wad of cotton wool saturated with petrol on the coating, under a piece of glass, for 2 hours, after which the coating was visually inspected for any effects or discolouration.
• the durability of the cured powder coatings according to example XIII was measured using QUV artificial weathering apparatus (ASTM-G- 53, lamp: UVB-313).
• Example XIII The resin of Example XIII was mixed with 1 wt.% flow promoting agent (BYK 163TM) in an extruder at 110°C.
• the extrudate was processed as described in Example XVIII.
• the powder-coated panels were placed in an oven at 150°C for 15 minutes to fluidize the applied powder, after which the panels, which had a temperature of 100-125°C, were exposed to electron-beam radiation in an ESI electron curtain apparatus using a beam voltage of 180 kilovolt, a beam intensity of 4 ⁇ iA and a cure dose of 15 mrad.
• a well-cured coating with very good flow properties was obtained and the coating was not affected after 100 acetone double rubs. From this it can be concluded that an acrylate resin containing an acrylate ester group as the unsaturated group in the side chain can be cured thermally, via UV radiation and via EB radiation to yield a well-cured powder coating.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Polymers & Plastics (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Materials Engineering (AREA)
• Wood Science & Technology (AREA)
• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Paints Or Removers (AREA)
• Macromonomer-Based Addition Polymer (AREA)

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Cited By (12)

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Citations (4)

• 1992
  • 1992-06-10 BE BE9200542A patent/BE1005993A3/nl not_active IP Right Cessation
• 1993
  • 1993-06-01 TW TW82104362A patent/TW233305B/zh active
  • 1993-06-07 AU AU45878/93A patent/AU4587893A/en not_active Abandoned
  • 1993-06-07 WO PCT/NL1993/000120 patent/WO1993025596A1/en not_active Application Discontinuation
  • 1993-06-07 EP EP93916272A patent/EP0644905A1/en not_active Withdrawn
  • 1993-06-09 CN CN 93108409 patent/CN1082083A/zh active Pending

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