PROCESS AND PAINT SPRAY DEVICE

The present invention relates to a process of refinishing an automobile and to a spraying device useful for the process. The device comprises a spray nozzle and a feed line between the nozzle and an open end surrounded by a first connection member to connect the open end of the feed line to a corresponding second connection member surrounding an opening of a paint container which is compressible by evacuation.

A solvent-borne isocyanate based moisture-curing coating composition is known from United States Patent US 6245877. This document describes a moisture-cure urethane composition comprising an isocyanate-terminated polymer and a solvent. The composition optionally includes a crosslinking catalyst, which allows curing to occur quickly. The composition can be used as primer and base coat to protect metal, wood, and concrete surfaces such as water tanks, pipes, bridges, and decks.

German patent application DE 3245294 A relates to the use of an isocyanate group-containing copolymer for moisture-curing lacquers. The copolymers are also used as binder in moisture-curing automobile repair lacquers. Added water or atmospheric moisture serves as crosslinker.

US 5143294 discloses a pliant paint container for use with a spray gun. A dip tube from the spray gun is inserted into the pliant container through the opening and sealed therein by means of a frusto conic plug. The pliant container is then placed in a canister, normally used for containing the paint. To use such a pliant container, it must first be opened, thus exposing the paint contained therein to ambient air. Moreover, if the container is exchanged for another pliant container, e.g., one containing a paint with a different colour, the paint in the container is again exposed to air. Subsequently, the bag should be closed again by a screw cap or other suitable closing means. As a consequence, the

replaceable pliant container can only be used for paints which are not affected by the influence of ambient air, such as moisture or oxygen.

US 2003/209573 A describes a spraying device using a collapsible reservoir which can be attached to and detached from a spray gun. The reservoir is equipped with a valve device which has to be opened and closed manually.

The object of the invention is to provide a process of refinishing an automobile or a part thereof in a simple and time-saving fashion, and wherein unused coating material can be used later on for further repair jobs. The invention also seeks to provide a spraying device which allows easy attachment and replacement of a paint container without exposing the contents to ambient air or moisture and without requiring additional steps upon attaching or detaching the paint container.

The object of the invention is achieved by a process of refinishing an automobile wherein a solvent-borne isocyanate based moisture-curing coating composition comprising a polyisocyanate, an organic solvent, and a curing catalyst, which composition cures by the reaction of isocyanate groups and atmospheric moisture, is applied to an automobile surface, wherein the solvent- borne isocyanate based moisture-curing coating composition is provided in a moisture-tight container which allows removal of the coating composition from the container without entry of atmospheric moisture into the container.

The coating composition used in the process according to the invention has a practically unlimited pot life and does not require metering and mixing of its components prior to application. It has surprisingly been found that the applied coating has an acceptable curing speed under various conditions of atmospheric moisture. The cured coating exhibits the properties required for automobile coatings, such as good hardness, scratch resistance, elasticity, durability, resistance to water and solvents, and a good appearance, e.g. gloss.

The cured coatings have also been found to be free of defects caused by gas bubbles.

Suitable polyisocyanates for use in the coating composition are isocyanate- functional compounds comprising at least two isocyanate groups. Preferably, the isocyanate-functional crosslinker is a polyisocyanate, such as an aliphatic, cycloaliphatic or aromatic di-, tri- or tetra-isocyanate. Examples of diisocyanates include 1 ,2-propylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, dodecamethylene diisocyanate, ω,ω'-dipropylether diisocyanate, 1 ,3-cyclo- pentane diisocyanate, 1 ,2-cyclohexane diisocyanate, 1 ,4-cyclohexane diisocyanate, isophorone diisocyanate, 4-methyl-1 ,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate, dicyclohexyl methane-4,4'-diisocyanate (Desmodur ^® W), toluene diisocyanate, 1 ,3-bis(isocyanatomethyl) benzene, xylylene diisocyanate, α,α,α',α'-tetramethyl xylylene diisocyanate (TMXDI ^® ), 1 ,5-dimethyl-2,4-bis(2-isocyanatoethyl) benzene, 1 ,3,5-triethyl-2,4-bis(iso- cyanatomethyl) benzene, 4,4'-diisocyanato-diphenyl, 3,3'-dichloro-4,4'- diisocyanato-diphenyl, 3,3'-diphenyl-4,4'-diisocyanato-diphenyl, 3,3'-dimethoxy- 4,4'-diisocyanato-diphenyl, 4,4'-diisocyanato-diphenyl methane, 3,3'-dimethyl- 4,4'-diisocyanato-diphenylmethane, and diisocyanatonaphthalene. Examples of thisocyanates include 1 ,3,5-triisocyanatobenzene, 2,4,6-thisocyanatotoluene, 1 ,8-diisocyanato-4-(isocyanatomethyl) octane, and lysine triisocyanate. Adducts and oligomers of polyisocyanates, for instance biurets, isocyanu rates, allophanates, uretdiones, urethanes, and mixtures thereof are also included. Examples of such oligomers and adducts are the adduct of 2 molecules of a diisocyanate, for example hexamethylene diisocyanate or isophorone diisocyanate, to a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate to 1 molecule of water (available under the trademark Desmodur N of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of toluene diisocyanate (available under the trademark

Desmodur L of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of isophorone diisocyanate, the adduct of 1 molecule of pentaerythritol to 4 molecules of toluene diisocyanate, the adduct of 3 moles of m-α,α,α',α'-tetramethyl xylene diisocyanate to 1 mole of trimethylol propane, the isocyanurate trimer of 1 ,6-diisocyanatohexane, the isocyanurate trimer of isophorone diisocyanate, the uretdion dimer of 1 ,6-diisocyanatohexane, the biuret of 1 ,6-diisocyanatohexane, the allophanate of 1 ,6-diisocyanatohexane, and mixtures thereof. Furthermore, (co)polymers of isocyanate-functional monomers such as α,α'-dimethyl-m-isopropenyl benzyl isocyanate are suitable for use. Isocyanate-terminated oligomers and polymers are also suitable. Such oligomers or polymers can be prepared by the reaction of an active hydrogen- functional precursor with a stoichiometric excess of a diisocyanate. Suitable active hydrogen-functional groups are hydroxyl groups, thiol groups, and primary or secondary amino groups. Michael donor groups, such as malonates and acetoacetates, can be used as well. The active hydrogen-functional precursor may be a monomer, oligomer or polymer. Examples of suitable hydroxyl-functional precursor oligomers or polymers are hydroxyl-functional polyesters, hydroxyl-functional polyacrylates, or hydroxyl-functional polycarbonates, as well as mixtures or hybrids thereof. In order to obtain sufficient outdoor durability, aliphatic polyisocyanates are preferred over aromatic polyisocyanates, in particular when the coating composition is applied as a top coat in a multi-layer lacquer coating. The aliphatic groups may be acyclic or cyclic.

In addition to the above-described polyisocyanate, the coating composition used according to the invention may optionally comprise other polymeric and/or oligomehc binders and resins, provided that these materials are substantially inert towards the isocyanate groups of the polyisocyanate. This means that the polymers and/or oligomers do not comprise active hydrogen-functional groups capable of reacting with isocyanate groups, such as hydroxyl groups, amino groups or thiol groups. Examples of suitable materials are vinyl polymers, i.e.

polymers which are obtainable by the polymerization of olefinically unsaturated monomers; polyesters; polyamides; polycarbonates; polyurethanes; and modified cellulose based materials.

Examples of suitable organic solvents for the coating composition to be used according to the invention are hydrocarbons, such as toluene, xylene, Solvesso 100; ketones, such as acetone, 2-butanone, methyl amyl ketone, and methyl iso-amyl ketone; terpenes, such as dipentene or pine oil; halogenated hydrocarbons, such as dichloromethane or para-chlorobenzothfluoride; ethers, such as ethylene glycol dimethyl ether, dipropyl ether, dibutyl ether, dipentyl ether, dioctyl ether; esters, such as ethyl acetate, ethyl propionate, n-butyl formate, n-butyl acetate, n-butyl propionate, n-butyl butyrate, the corresponding tert.-butyl, sec-butyl, and iso-butyl esters, esters of linear or branched pentanol, hexanol, or octanol, such as 2-ethyl-hexanol; or ether esters, such as methoxypropyl acetate or ethoxyethyl propionate. Also mixtures of these compounds can be used.

In view of current and future legislation it is preferred that the composition used according to the invention has a low content of volatile organic compounds (VOC). Examples of suitable VOC values are 500 g/l or less, 420 g/l or less, or 250 g/l or less.

In order to achieve an acceptable curing speed of the applied coating, the coating composition contains a curing catalyst which catalyzes the reaction of isocyanate groups and water. Examples of suitable catalysts are organotin compounds in which the tin is tetravalent. Representative of these catalysts are dibutyl tin dilaurate, dibutyl tin diacetate, dibutyl tin di-2-ethlyhexanoate, dibutyl tin dichlohde, dibutyl tin disulfide, and dibenzyl tin di-2-ethlyhexanoate. Other organotin catalysts and metal based catalysts which catalyze the reaction of isocyanate groups and moisture can also be used. Examples of further catalysts include alkaline compounds, such as tertiary amines, alkylated guanidines, and

inorganic bases. Also possible, but less preferred, are acidic catalysts, for example dibutyl phosphate.

The curing catalyst is generally present in the composition in an amount of 0.01 % to 4% by weight, calculated on the non-volatile content of the composition. The curing rate is generally increased by a higher proportion of catalyst, for example at least 0.1 % by weight, at least 0.2 % by weight, or at least 0.4 % by weight, calculated on the non-volatile content of the composition. A too high proportion of catalyst may undesirably deteriorate the storage stability of the composition. Therefore, in order to safeguard a superior storage stability of the composition, the proportion of catalyst suitably does not exceed 3% by weight, preferably 1.5% by weight, calculated on the non-volatile content of the composition. In individual cases, the optimum proportion of catalyst may depend on the specific type of catalyst and on the desired balance of storage stability and curing speed.

The coating composition used according to the invention may further comprise other ingredients, additives or auxiliaries commonly used in coating compositions, such as pigments, dyes, surfactants, pigment dispersion aids, levelling agents, wetting agents, anti-cratering agents, antifoaming agents, antisagging agents, heat stabilizers, light stabilizers, UV absorbers, antioxidants, and fillers.

In the process of refinishing of automobiles according to the invention, the coating composition can be applied to an automobile or a part thereof. The process is suitable for refinishing the entire automobile. Alternatively, it is possible to refinish damaged panels or replacement parts. In still another embodiment, refinishing can be carried out to repair small scratches or dents without refinishing an entire body panel. The latter method is generally referred to as spot repair. Application of the coating composition can be carried out by any method which is suitable for applying a liquid coating composition to a

substrate. Examples of suitable methods are brushing, rolling, and spraying. The best results are frequently obtained when the coating composition is applied by spraying.

Coatings on automobiles generally are multi-layer coating systems. The coating composition can be used according to the invention in any of the layers applied during the process of refinishing. In one embodiment, the coating composition is applied as a top coat in a multi-layer lacquer coating. The top coat may be a pigmented top coat. In this case pigments are included in the moisture curing coating composition. In order to prevent a reaction of isocyanate groups and water during storage, dry pigments should be used. Alternatively, the top coat may be a clear coat. Clear coats are generally applied on top of a colour- and/or effect-imparting base coat layer. In still another embodiment, the coating composition is applied as a primer and/or filler. When applied as a primer and/or filler composition, the coating composition suitably comprises anti-corrosive pigments, optionally in combination with fillers.

After application of the coating composition the coating layer cures under the influence of moisture, generally atmospheric moisture. Curing essentially occurs by reaction of isocyanates with water, which leads to carbamic acid intermediate. The intermediate decarboxylates under formation of an amine group, which subsequently reacts with a further isocyanate group to form a urea linkage. Although the relative atmospheric moisture content is not critical for curing of the coating layer, optimum results are obtained when the relative atmospheric moisture is in the range of 20 to 80%. Although it is not generally required to achieve good results, curing may be carried out in a humidity controlled atmosphere.

Curing is generally carried out in a temperature range of 0°C to 80°C. In one embodiment, curing is carried out at ambient temperature, i.e. in the range of about 15°C to about 25 °C. In another embodiment, curing is carried out in a heated curing chamber, for example at a temperature of 40 °C to 60 °C.

In a particular embodiment, the coating composition is applied with a spraying device comprising a spray nozzle, a feed line, and a compressible paint container, wherein the feed line extends between the spray nozzle and an open end surrounded by a first connection member to connect the open end of the feed line to a corresponding second connection member surrounding an opening of the compressible paint container, characterized in that the paint container is provided with a closing valve to close off the opening of the paint container and in that the first connection member is provided with a member acting on the valve to cause its being opened when the first and second connection members are mutually connected and to cause its being closed when the the first and second connection members are mutually disconnected. This way, the paint contents in the container are effectively protected against open air influences, even when the paint container is temporarily replaced by a paint container containing paint of another type or colour. When the paint container is attached to the spraying device, the valve automatically opens. When the paint container is taken off the spraying device, the closing valve is automatically closed again. Later on, it can be used again to spray out the rest of the paint contents, which are still unaffected by oxygen or moisture. Due to the compressibility or collapsibility of the paint container, it can be emptied without air supply, and so during spraying the paint in the container is not contacted with air or moisture either.

An important advantage of the device according to the invention is that it allows the use of paints based on binder systems which can be cured or crosslinked by crosslinking chemistries induced by exposure to ambient moisture or oxygen.

Typical examples of oxidatively drying binder systems are alkyd binders, which are commonly used in the field of the building industry, joinery, and wood paints. Examples of paint systems curable by ambient moisture are one- component isocyanate paints. Due to their reactivity, such isocyanate paint systems were hard to control and could only be used with appropriate

application machinery. The device according to the present invention allows the use of such crosslinking chemistry with less sophisticated spray guns, such as for instance spray guns used in car repair body shops, where the fast drying properties of such coating compositions are particularly advantageous. The system according to the present invention can also be used for other types of long-shelf-life paints, including one-component physically drying paints, UV- curable paints, heat-cured paints, and the like. In the case of UV-curable paints, the paint container should be made of a light-tight, UV-tight material.

The system according to the invention requires less time to prepare the spraying device before painting. The paint containers, which can be used as disposable cartridges, do not have to be cleaned. Paint which is not sprayed out is left in the air-tight paint container, and since the paint containers can be re- closed in an air-tight fashion, they can be stored for further use next time, so waste and spoiling of paint is minimized.

The closing valve can for example comprise a closing member which is tightly pressed onto an inner ledge or shoulder along the inner diameter of the opening by a resilient member, such as a coil spring. For better closing off of the opening, the closing member can have a convex surface to be pressed against the shoulder. Optionally, the closing member may have the shape of a ball. To open the container, the first connection member can be provided with a protrusion or finger to press the closing member away from the shoulder surrounding the opening of the paint container.

In an alternative embodiment, the closing valve may comprise a nipple with an outer screw thread and a cap with an inner screw thread cooperating with the outer screw thread of the nipple, the nipple having a top end provided with at least one opening and a protrusion which is in register with an opening in the top end of the cap, the opening being dimensioned to fit tightly over the protrusion. The first connection member has an opening to receive the cap.

When the cap is put into the opening in the first connection member, the bag can be turned to screw the nipple out off the cap to open the valve. In order to prevent the cap from being rotated together with the nipple, the connection between the cap and the first connection member may be provided with a stop, or the outline of the cap may be made non-circular, matching a corresponding shape of the opening in the first connection member, or the cap may be held in place by friction. A bayonet catch can be used to prevent removal of the bag while it is still open.

In a further alternative embodiment, the closing valve can include a plug with a central bore leading from an outlet opening to an outer end provided with a narrowing inner diameter and a cap comprising a closed end and an open end defined by a profiled edge apt to form a snap joint in cooperation with the narrowing inner diameter of the plug's outer end, the cap being attached to the plug by flexible spokes. The first connection member at the inlet of the spray gun's feed line can then be provided with a hollow protrusion with a head dimensioned to fit tightly into the plug's cap and radial openings below the head. The hollow protrusion can be provided with a shoulder to cooperate with the narrowing inner diameter in the plug's inner bore to prevent further intrusion of the protrusion than is required for opening the plug's cap.

The first connection member can for example be a collar provided with an outer screw thread apt to cooperate with an inner screw thread of a collar around the paint container opening forming the second connection member. Alternatively, the first connection member can be a collar provided with an inner screw thread apt to cooperate with an outer screw thread of a collar around the paint container opening forming the second connection member. In a further alternative embodiment, the first and second connection members can form a bayonet catch.

The paint container can hang below the air supply line or it can be located on top of it. In the latter case, the paint container may be stabilized by a supporting frame or holder. Alternatively, the paint container itself can be provided with one or more rigid parts to maintain it in the upright position when it is evacuated. If the paint container is used in the upright position, use can be made of gravity feed in addition to suction feed.

The container can be configured as a pouch of two or more walls of foil material, sealed along the outlines, leaving free only the outlet opening. The foil material can be made of polymeric material or of metal foil, such as aluminium, or it can be made of layers of different materials.

Since the paint containers according to the present invention can be temporarily replaced and stored to be used again, the system allows the paint containers to be designed as easily replaceable cartridges. This way, modular sets of cartridges can be used, each cartridge containing a paint of a different type or colour. Such systems can for example include cartridges for a primer or various types of primers, base coats, clear coats, and the like.

The invention is further illustrated by the drawings. In the drawings,

Fig. 1 : shows in perspective a spray gun with a paint container according to the present invention;

Figs. 2A and 2B: show in cross-section a closing valve of a spray gun according to the invention in open and closed positions, respectively; Figs. 3A and 3B: show in cross-section an alternative embodiment of a closing valve of a spray gun according to the invention in open and closed positions, respectively;

Figs. 4A - 4C: show in cross-section a further alternative embodiment of a closing valve of a spray gun according to the invention in open and closed positions, respectively;

Fig. 5 shows an exploded view of a spray gun and a paint container according to the invention with an external holder;

Fig. 6 shows a front view partly in cross-section of a bag container comprising an internal support.

Figure 1 shows a handheld spray gun 1 comprising a spray nozzle 2, a connection member 3, and a paint container 4 having walls 5 of a pliant, collapsible foil material. An internal feed line leads from the paint container 4 to the spray nozzle 2. The spray gun 1 comprises a hand grip 6. A supply line 7 for pressurized air is attached to an inlet 8 below the grip 6. A hingeable trigger 9 serves to actuate a valve actuator 10 to control the flow of pressurized air. Rotary buttons 1 1 , 12 serve to adjust the flow rate and the scope of the conical spray mist. The paint container is provided with a self-closing valve, such as is shown in Figures 2A and 2B.

Figures 2A and 2B show in cross-section a self-closing valve assembly 13 comprising a nozzle 14 defining the outlet opening of the paint container 4, and a ball-shaped closing member 15 dimensioned to be tightly pressed onto an inner ledge 16 along the inner diameter of the nozzle 14 by a resilient coil spring

17. The first connection member 3 is provided with a protrusion or finger 18 to press the closing member 15 away from the ledge 16 surrounding the opening of the paint container. In Figure 2A, the first connection member 3 is screwed over the nozzle 14. The finger 18 presses the closing member 15 down, away from the ledge 16. In this position, paint can flow alongside the closing member

15 and the finger 18 through the opening of the nozzle 14 into the feed line of the spray gun. In Figure 2B the connection member 3 is removed from the cap and the coil spring 17 presses the closing member back to the ledge 16, thus re-closing the paint container.

Figures 3A and 3b show an alternative embodiment of the closing valve. Here, the closing valve comprises a nipple 20 and a cap 21. The nipple 20 has a top end 22 provided with off-centre openings 23 and a protrusion 24. This protrusion 24 is in line with a central opening 25 in the top end 26 of the cap 21. The central opening 25 in the cap's end 26 is dimensioned to fit tightly over the protrusion 24. The cap can be screwed on the nipple 20 between a closed position (Figure 3B), when the protrusion 24 closes off the opening 25 in the cap's top end, and an open position (Figure 3A), when the protrusion 24 is pulled out of the opening 25. The connecting member 3 has an opening fitting tightly over the cap 21. When the cap 21 is pushed into the opening in the connection member 3, the nipple 20 can be screwed out of the cap 21 , thus allowing paint to flow via the openings 23 and 25 into the feed line to the spray nozzle.

In Figures 4A and 4B, a further alternative embodiment of a self-closing valve according to the present invention is shown. This closing valve 30 includes a plug 31 with a central bore 32 leading from an outlet opening 33 to an outer end 34 provided with a narrowing inner diameter 35. A cap 36 comprises a closed end 37 and an open end 38 defined by a profiled edge 39 apt to form a snap joint in cooperation with the narrowing inner diameter 35 of the plug's outer end (see Figure 4C). The cap 36 is attached to the plug 31 by a number of flexible spokes 40. The first connection member 3 at the inlet of the spray gun's feed line is provided with a hollow, cylindrical protrusion 41 fitting tightly into the bore 32 of the plug 31. The protrusion 41 is provided with a head 42 dimensioned to fit tightly into the plug's cap 36. The protrusion 41 has radial openings 43 below the head 42. The hollow protrusion 41 is provided with a shoulder 44 to cooperate with the narrowing inner diameter in the plug's inner bore 32 to prevent the protrusion 41 from being inserted into the opening too deeply, which could damage the cap 36 or break the spokes 40.

In Figure 4A, the protrusion 41 is put into the bore 32, pushing the cap 36 out of the snap joint formed by the narrowed bore diameter 35. In this position, the radial openings 43 in the protrusion 41 form an open connection between the inside of the paint container and the inner side of the protrusion 41. Paint can flow from the paint container through the flexible spokes 40 and the radial openings 43 into the protrusion 41 and further to the feed line and the spray nozzle of the spray gun.

When the protrusion 41 is pulled out of the paint container, as is shown in Figure 4B, it pulls back the cap 36 until it snaps back again onto the ridge formed by the narrowing inner diameter of the plug's central bore 32, thus closing off the paint container in an air-tight fashion.

Figure 5 shows an exploded view of a spray gun and a paint container according to the invention with an external support 50. The support 50 comprises a hollow cylindrical base part 51 with close to one end a slit 52 which cooperates with a protrusion 53 on the connection member 3 to form a bayonet catch. Close to the other end, the base part 51 comprises a recess 54 suitable for receiving in a close fitting the open top end of a bag container 55. The bag container 55 is made of a flexible foil material sealed along its edges 56. The support further comprises a clip 57 made of an L-shaped double wire. The outer end of the short arm 58 of the L-shape is attached to the hollow base part 51. At the outer end of the long arm 59 of the L-shape, the two wire parts join to form a single folded wire. About halfway along the long arm 58 of the L-shape, the wire parts bend toward each other to form a clamp to clamp the sealed edge 55 of the bag container.

Figure 6 shows a front view partly in cross-section of a bag container 60 comprising two walls 61 , 62 of a flexible foil material sealed together along the edges 63. In the drawing, the wall 61 is partly cut away to show an internal support formed by a frame 64 of a rigid material to maintain the bag 60 in the

upright position when it is emptied by a spray gun. When viewed from a direction at right angles with the front view as shown in the drawing, the frame 64 is flat in order to allow the bag 60 to be completely evacuated. The bag comprises an opening 65 closable by a valve assembly 66 as shown in Figures 4A - C. The frame 64 is attached to the valve 66 and comprises two arms 67 extending from the valve 66 to a point near the corners of the side opposite the bag opening 65. The outer ends of the two arms 67 are bridged by a rib 68.

The process of the invention is illustrated by the following Examples:

Raw materials used:

Tolonate HDT-LV A polyisocyanate based on the isocyanurate trimer of hexamethylene diisocyanate, ex Rhodia BYK 331 Wetting agent ex BYK Chemie

Solvesso 150 An aromatic solvent mixture ex Exxon Mobil

DBTL A mixture consisting of 10 parts by weight of dibutyl tin dilaurate and 90 parts by weight of butyl acetate Sikkens Autobase Plus Solvent-borne base coat system ex Akzo Nobel Car

Refinishes

The drying stage of applied coating layers was determined manually, with 10 drying stages being discerned: 1 The still wet coating is easily rubbed off with the thumb.

2 By touching the coating with the thumb, threads of paint may be drawn.

3 The coating is cohesive, but is easily damaged down to the substrate by gentle rubbing with the thumb.

4 Gentle rubbing with the thumb leaves a clear mark. 5 Gentle rubbing with the thumb hardly leaves a mark. A tuft of wadding, dropped on the paint, can be blown off. The coating is dust-dry. 6 Gentle rubbing with the thumb leaves no mark. On gentle rubbing or pushing with the palm of the hand a sticky effect is felt.

7 On gentle rubbing or pushing with the palm of the hand, no stickiness is observed. The coating is tack-free.

8 Firm pushing with the thumb leaves a permanent mark.

9 The mark from firm pushing with the thumb disappears after 1 -2 minutes. The coating is touch-dry.

10 The coating can hardly, or cannot at all, be damaged by scratching with the (human) nail. The coating is hardened through.

The distinctness of image (DOI) of clear coat films was determined with an ATIDOI-meter one day after application of the clear coat. Higher DOI values indicate a better film appearance.

Example 1

A clear coat composition was prepared by mixing the following components:

Tolonate HDT-LV 58.3 g

DBTL 4.0 g

BYK 331 , 10% solution in 3-ethoxy ethyl propionate 0.7 g

Butyl acetate 27.7 g

Solvesso 150 9.3 g

The clear coat composition was spray-applied to metal panels to give a dry layer thickness of 60 μm. The metal panels were precoated with a white coil coating layer on top of which a blue metallic Autobase Plus base coat layer was applied, as prescribed in the technical data sheet of Autobase Plus. In a second series the clear coat composition was applied to metal panels precoated with the white coil coating layer only, i.e. without the blue base coat layer. The clear coats were applied in a humidity- and temperature-controlled spray booth. The temperature during application was 20 °C, the relative humidity was 10%, 35 %, and 60 %.

Directly after spraying the temperature in the spray booth was increased to 60 °C. This temperature was reached after 10 minutes.

The drying times and the distinctness of image of the clear coats are summarized in Table 1 below.

Table 1

a) Relative humidity during application of the clear coat b) The substrate "Base coat" indicates metal panels which were precoated with a white coil coating layer on top of which a blue metallic Autobase Plus base coat layer was applied, the substrate "Coil" indicates metal panels which were precoated with a white coil coating layer without a base coat layer c) Indicated is the time in minutes until drying phase 5 is reached d) Indicated is the time in minutes until drying phase 9 is reached

From the above results it can be inferred that even at low relative humidity the drying speed is only slightly decreased, remaining at a good level. The appearance of the dried clear coats is good without any defects.

The hardness and the resistance to organic solvents and water of all cured clear coats were on a level comparable to the one for commercial two-component clear coats used for refinishing of automobiles.

The clear coat composition described above was stored at 35 °C for two months in a sealed container allowing no access of moisture. After storage, the

viscosity, sprayability, drying time, and appearance of the cured coating were at the same level as for the freshly prepared composition. It can thus be concluded that the composition has very good storage stability.