A refinish basecoat composition includes an alkyd resin, at least one pigment dispersed by resin comprising the alkyd resin, and an hydroxyl-functional acrylic polymer. The acrylic polymer has a number average molecular weight of at least about 6000 and is polymerized using at least about 45% by weight cycloaliphatic monomer, based on total monomer weight polymerized. A mixer system that can be used to prepare the refinish basecoat has a plurality of color components, each independently including at least one pigment dispersed by resin including an alkyd resin, and a pigment-free component containing the hydroxyl-functional acrylic polymer.

The present invention relates to automotive refinish compositions and to methods for preparing and using such compositions.
Automotive topcoat finishes today are predominantly basecoat/clearcoat topcoats, in which the topcoat is applied in two layers, a first layer of a pigmented basecoat composition and a second layer of a clearcoat composition. Basecoat/clearcoat coatings are desirable for their high level of gloss and depth of color. In addition, basecoats having special effect pigments, e.g., flake pigments such as metallic and pearlescent pigment, can achieve excellent gonioapparent effect in basecoat coatings.
In order to provide optimum match to the appearance of the original finish, automotive refinish topcoats are also being applied in separate layers of basecoat and clearcoat. Unlike the original finish coating compositions, which are typically cured at temperatures of 110xc2x0 C. or higher, automotive refinish coatings must be formulated as either thermoplastic compositions or thermosetting compositions that cure at relatively low temperatures because many components of a finished vehicle cannot withstand high temperature bakes and because equipment large enough for a baked finish on a vehicle is very expensive. Nonetheless, thermosetting compositions are generally preferred as providing more durable and scratch- and mar-resistant coatings. Thermosetting refinish compositions are usually designed to cure at ambient temperatures. Although not developing full cure for hours or days, it is desirable to have the coating become xe2x80x9cdry to handle,xe2x80x9d that is, not tacky, within a reasonably short time. A coating that is dry to handle in a short time allows shorter processing times, which improves the productivity of the paint shop. Shorter dry to handle times also reduce the chance that the coating could become contaminated with airborne particulates.
It is desirable to have quick drying basecoats in the application of basecoat/clearcoat systems for an additional reason. If the applied basecoat composition layer has not dried sufficiently before the clearcoat composition is applied, then the application of the clearcoat will disturb the basecoat layer and the appearance of the basecoat will be adversely affected. In particular, the metal control of metallic basecoats will suffer due to disturbance of the flake pigment by intermixing of the coating layers at their interface.
In thermosetting automotive refinish coating compositions the curing agent reacts with the main resin or polymer at room temperatures within a reasonable amount of time without heating or with heating at low temperatures of perhaps up to 150xc2x0 F. Given the reactivity between the curing agent and the main resin or polymer at typical storage temperatures, these materials are segregated into separately stored components until just shortly before application of the coating composition to the substrate. This type of coating composition, in which the materials that react to cure the coating are segregated in two separately stored components, is referred to in the art as a xe2x80x9ctwo-componentxe2x80x9d or xe2x80x9ctwo-packagexe2x80x9d or xe2x80x9c2Kxe2x80x9d coating composition. Refinish clearcoat compositions, which are unpigmented, are often two-package compositions. Refinish basecoat compositions, on the other hand, may also be formulated as two-component compositions for each desired each color or may instead be prepared from an intermix system including separately stored color components, a component having the main resin or polymer, a crosslinker component, and possibly other components.
Cost and solvent content are further concerns in formulating automotive refinish coating compositions. For example, cellulose acetate butyrate (CAB) resins have been used to shorten the dry to handle time and as rheology control additives to enhance metal control and other properties in refinish coatings, but coating compositions containing these CAB materials require an undesirably high amount of organic solvent. In addition, these CAB materials are relatively expensive and require added steps in the coatings manufacturing process. Finally, the CAB materials are specialty products that are not widely manufactured.
Certain curing agents, for example polyisocyanate crosslinkers, can be used to shorten tack-free times and for other properties, but are also relatively expensive. Using polyisocyanate crosslinkers in basecoats again increases the complexity in preparing and mixing refinish paints
It would be desirable, therefore, to have a coating composition (or intermix system for preparing such a coating composition) with a short tack-free drying time, good metal control, that is less expensive, and that could be applied with a lesser amount of regulated emissions.
The invention provides a refinish basecoat composition including an alkyd resin, at least one pigment dispersed by the alkyd resin, optionally in combination with one or more further resins, and an hydroxyl-functional acrylic polymer. The hydroxyl-functional acrylic polymer has a number average molecular weight of at least about 6000 daltons and contains at least about 45% by weight of one or more cycloaliphatic monomers. Preferably, the refinish basecoat is free of materials reactive with the acrylic polymer.
The invention further provides an intermix system for preparing the basecoat composition of the invention. The intermix system includes a plurality of color components, each containing at least one pigment dispersed by the alkyd resin, optionally in combination with one or more further resins; a pigment-free component containing the hydroxyl-functional acrylic polymer; and optional further components. An automotive refinish basecoat composition of any desired color can be produced by combining the intermix system components.
Still further, the invention provides a method of refinishing a substrate, which includes steps of applying the basecoat composition of the invention to a desired area of the substrate, allowing the applied basecoat layer to dry for up to about twenty minutes, and then applying over the basecoat layer a clearcoat composition. The clearcoat composition may contain at least one component reactive with the acrylic polymer of the basecoat composition. Reaction between that reactive component of the clearcoat composition and the acrylic polymer of the basecoat promotes intercoat adhesion, even if only a minor portion of the available acrylic polymer reacts. The alkyd of the basecoat may react with oxygen to crosslink and/or may crosslink through hydroxyl functionality.
It is particularly desirable for the clearcoat composition to be thermosetting in order to provide a durable, scratch- and mar-resistant coating. In the composite basecoat/clearcoat coating, the surface properties are provided by the clearcoat layer, thus the basecoat composition is not required to provide a hard, tough coating layer. The basecoat composition dries quickly with relatively low emissions of regulated materials. The composite coating of the basecoat and clearcoat has excellent adhesion to the substrate and excellent intercoat adhesion between the basecoat and clearcoat layers.
The refinish basecoat composition includes an alkyd resin, at least one pigment dispersed by the alkyd resin or a combination of the alkyd resin and one or more further resins, and an hydroxyl-functional acrylic polymer.
First, the basecoat composition includes an alkyd resin. Alkyd resins are prepared using unsaturated oils and may chemically dry by oxidation (i.e., crosslink through the double bonds in the presence of the oxygen in the air). The alkyd resin may also crosslink through hydroxyl functionality with a hydroxyl-reactive component in the basecoat composition or in the clearcoat composition, preferably in the clearcoat composition. Alkyd resins are desirable for a number of reasons. Alkyd resins are relatively inexpensive resins. Because alkyd resins may cure through oxidation, they do not need a separate crosslinking agent that would require separate storage and increase the complexity of an intermix system for preparing the basecoat composition. Thirdly, alkyd resins are good dispersing resins for a wide variety of pigments. It is also important for the alkyd resin to be compatible with the acrylic polymer, particularly in that the alkyd and the acrylic are miscible with each other in solution.
The basecoat may include a metal drier to promote the oxidative cure of the alkyd, optionally in conjunction with one or more further resins. Suitable examples of metal driers include, without limitation, cobalt naphthenate, calcium naphthenate, zinc naphthenate, zirconium naphthenate, and combinations of these.
The basecoat composition further includes one or more pigments dispersed by the alkyd resin. Virtually any organic or inorganic color pigment may be included. Examples of suitable classes of organic pigments that may be used include, without limitation, metallized and non-metallized azo pigments, azomethine pigments, methine pigments, anthraquinone pigments, phthalocyanine pigments, perinone pigments, perylene pigments, diketopyrrolopyrrole pigments, thioindigo pigments, iminoisoindoline pigments, iminoisoindolinone pigments, quinacridone pigments such as quinacridone reds and violets, flavanthrone pigments, indanthrone pigments, anthrapyrimidine pigments, carbazole pigments, monoarylide and diarylide yellows, benzimidazolone yellows, tolyl orange, naphthol orange, and quinophthalone pigments. Examples of suitable inorganic pigments include, without limitation, metal oxide pigments such as titanium dioxide, iron oxides including red iron oxide, black iron oxide, and brown iron oxide, and chromium oxide green; carbon black; ferric ferrocyanide (Prussian blue); ultramarine; lead chromate; and so on.
The color pigment or pigments are dispersed in the alkyd resin or in the combination of resins including the alkyd resin according to known methods. In general, the pigment and alkyd resin (or alkyd resin and other resin(s)) are brought into contact under a shear high enough to break the pigment agglomerates down to the primary pigment particles and to wet the surface of the pigment particles with the alkyd resin. The breaking of the agglomerates and wetting of the primary pigment particles are important for pigment stability and color development. When the pigment dispersion is used to make a color component of the intermix system, then the pigment dispersion may be further adjusted with alkyd resin, solvent, and/or other materials as needed so that the color components of the intermix system can be used together to produce the universe of desired refinish coating colors.
Metallic basecoat colors are produced using one or more special flake pigments. Metallic colors are generally defined as colors having gonioapparent effects. For example, the American Society of Testing Methods (ASTM) document F284 defines metallic as xe2x80x9cpertaining to the appearance of a gonioapparent material containing metal flake.xe2x80x9d Metallic basecoat colors may be produced using metallic flake pigments like aluminum flake pigments, copper flake pigments, zinc flake pigments, stainless steel flake pigments, and bronze flake pigments and/or using pearlescent flake pigments including treated micas like titanium dioxide-coated mica pigments and iron oxide-coated mica pigments to give the coatings a different appearance when viewed at different angles.
Unlike the solid color pigments, the flake pigments do not agglomerate and are not ground under high shear because high shear would break or bend the flakes, diminishing or destroying the gonioapparent effects. The flake pigments are satisfactorily dispersed in the alkyd resin or combination of resins including the alkyd resin by stirring under low shear.
The refinish basecoat composition also includes an hydroxyl-functional acrylic polymer. The hydroxyl-functional acrylic polymer has a number average molecular weight of at least about 6000, preferably at least about 8000, and even more preferably at least about 10,000. The hydroxyl-functional acrylic polymer also preferably has a weight average molecular weight of at least about 17,000, more preferably at least about 19,000, and even more preferably at least about 21,000 Molecular weights may be determined by gel permeation chromatography using polystyrene standards.
The acrylic polymer is polymerized using one or more cycloaliphatic monomers. Suitable examples of cycloaliphatic monomers include, without limitation, cyclohexyl (meth)acrylate, (meth)acrylate esters of alkyl-substituted cyclohexanol, and (meth)acrylate esters of alkanol-substituted cyclohexane, such as 2-tert-butyl and 4-tert-butyl cyclohexyl (meth)acrylate, 4 cyclohexyl-1-butyl (meth)acrylate, and 3,3,5,5,-tetramethyl cyclohexyl (meth)acrylate; isobornyl (meth)acrylate; isomenthyl (meth)acrylate; cyclopentyl (meth)acrylate, (meth)acrylate esters of alkyl-substituted cyclopentanols, and (meth)acrylate esters of alkanol substituted cyclopentanes; adamantanyl (meth)acrylates; cyclododecyl (meth)acrylate; cycloundecanemethyl (meth)acrylate; dicyclohexylmethyl (meth)acrylate; cyclododecanemethyl (meth)acrylate; menthyl (meth)acrylate; and so on, as well as combinations of these. The term (meth)acrylate is used herein to indicated both the acrylate ester and the methacrylate ester. Preferred among these are cyclohexyl (meth)acrylate and isobornyl (meth)acrylate.
The cycloaliphatic monomer units are included in the acrylic polymer in amounts of at least about 45% by weight, preferably at least about 60% by weight, and more preferably at least about 65% by weight of the polymer. It is advantageous for the cycloaliphatic monomer units to be included in the acrylic polymer in amounts of up to about 85% by weight, particularly up to about 80% by weight, and especially up to about 75% by weight of the polymer. The upper limit on the amount of cycloaliphatic monomer unit depends upon factors such as the particular monomer used, the viscosity obtained in the acrylic polymer using the monomer, the amount of hydroxyl monomer and other monomers used, and so on.
The acrylic polymer also has hydroxyl functionality. Hydroxyl functionality can conveniently be introduced to the polymer by copolymerizing at least one hydroxyl-functional monomer. Suitable examples of hydroxyl-functional monomers include, without limitation, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylates, hydroxybutyl (meth)acrylates, and combinations of these. Preferably, at least about 5% by weight hydroxyl-functional monomer is included in the polymer. It is also preferred to include up to about 15% by weight hydroxyl-functional monomer in the polymer. Hydroxyl functionality may also be introduced through thio-alcohol compounds, including, without limitation, 3 mercapto-1-propanol, 3-mercapto-2-butanol, 11-mercapto-1-undecanol, 1 mercapto-2-propanol, 2-mercaptoethanol, 6-mercapto-1-hexanol, 2 mercaptobenzyl alcohol, 3-mercapto-1,2-proanediol, 4-mercapto-1-butanol, and combinations of these. Hydroxyl functionality may also be introduced to the acrylic polymer, for example, by reaction of the polymer with a material that contains or produces hydroxyl functionality, e.g. ring-opening of an epoxide group. In one preferred embodiment, the acrylic polymer has an hydroxyl number of at least about 15 mg KOH/g polymer, more preferably at least about 40 mg KOH/g polymer, yet more preferably at least about 45 mg KOH/g polymer, and still more preferably at least about 50 mg KOH/g polymer. It is also preferred for the acrylic polymer to have an hydroxyl number of up to about 115 mg KOH/g polymer, more preferably up to about 90 mg KOH/g polymer, more preferably up to about 75 mg KOH/g polymer, still more preferably up to about 60 mg KOH/g polymer. The hydroxyl functionality may be incorporated by any method or by any combination of methods.
Other monomers may be copolymerized with the cycloaliphatic monomer and the hydroxyl monomer (and/or the hydroxy thiol compound and/or monomer that provides hydroxyl functionality through further reaction after polymerization). Examples of suitable co-monomers include, without limitation, xcex1,xcex2-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms such as acrylic, methacrylic, and crotonic acids and the esters of those acids; xcex1,xcex2-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms and the anhydrides, monoesters, and diesters of those acids; vinyl esters, vinyl ethers, vinyl ketones, and aromatic or heterocyclic aliphatic vinyl compounds. Representative examples of suitable esters of acrylic, methacrylic, and crotonic acids include, without limitation, those esters from reaction with saturated aliphatic alcohols containing 1 to 20 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, dodecyl, lauryl, and stearyl acrylates, methacrylates, and crotonates; and polyalkylene glycol acrylates and methacrylates. Representative examples of other ethylenically unsaturated polymerizable monomers include, without limitation, such compounds as fumaric, maleic, and itaconic anhydrides, monoesters, and diesters with alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and tert-butanol. Representative examples of co-polymerizable vinyl monomers include, without limitation, such compounds as vinyl acetate, vinyl propionate, vinyl ethers such as vinyl ethyl ether, vinyl and vinylidene halides, and vinyl ethyl ketone. Representative examples of aromatic or heterocyclic aliphatic vinyl compounds include, without limitation, such compounds as styrene, xcex1-methyl styrene, vinyl toluene, tert-butyl styrene, and 2-vinyl pyrrolidone. The co-monomers may be used in any combination. In one preferred embodiment, the acrylic polymer is prepared using a mixture of monomers that includes styrene and methyl methacrylate (at least about 1 % and up to about 20% by weight in combination, based on the total weight of monomers polymerized) and an acrylic or methacrylic ester having at least about six carbon atoms that is not a cycloaliphatic monomer (at least about 0.5% and up to about 20% by weight, based on the total weight of monomers polymerized). The acrylic polymer should be formulated to have a useful viscosity in view of regulatory constraints on volatile organic compounds. The monomers are selected and apportioned so that a 50% by weight solution of the acrylic polymer in n-butyl acetate has a viscosity preferably less than or equal to 6.3 Stokes at 25xc2x0 C., more preferably less than or equal to 5.8 Stokes at 25xc2x0 C., and still more preferably less than or equal to 5.5 Stokes at 25xc2x0 C.
The acrylic polymer may be prepared using conventional techniques, such as by heating the monomers in the presence of a polymerization initiating agent and optionally chain transfer agents. The polymerization is preferably carried out in solution, although it is also possible to polymerize the acrylic polymer in bulk.
Typical initiators are organic peroxides such as dialkyl peroxides such as di-t-butyl peroxide, peroxyesters such as t-butyl perooctoate and t-butyl peracetate, peroxydicarbonates, diacyl peroxides, hydroperoxides such as t-butyl hydroperoxide, and peroxyketals; azo compounds such as 2,2xe2x80x2azobis (2 methylbutanenitrile) and 1,1xe2x80x2-azobis(cyclohexanecarbonitrile); and combinations of these. Typical chain transfer agents are mercaptans such as octyl mercaptan, n- or tert-dodecyl mercaptan; halogenated compounds, thiosalicylic acid, mercaptoacetic acid, mercaptoethanol and the other thiol alcohols already mentioned, and dimeric alpha-methyl styrene.
The reaction is usually carried out at temperatures from about 20xc2x0 C. to about 200xc2x0 C. The reaction may conveniently be done at the temperature at which the solvent or solvent mixture refluxes, although with proper control a temperature below the reflux may be maintained. The initiator should be chosen to match the temperature at which the reaction is carried out, so that the half-life of the initiator at that temperature should preferably be no more than about thirty minutes.
The refinish basecoat composition may contain other materials, including other resins or polymers used in combination with the alkyd resin to disperse the pigments, such as acrylics, polyesters, and/or polyurethanes; and additives such as rheology control agents, matting agents, surfactants, fillers (e.g., talc or barytes), stabilizers, wetting agents, dispersing agents, adhesion promoters, fillers, UV absorbers, hindered amine light stabilizers, and so on. Optionally, the invention may include one or more waxes such as poly (ethylene-vinyl acetate) copolymers or other rheology control agents. Rheology control agents are added to improve the appearance and/or evenness of the basecoat, particularly the metallic appearance of metallic basecoats.
Preferably, the refinish basecoat is free of materials reactive with the acrylic polymer. When there is no crosslinker for the acrylic polymer included in the composition, the basecoat composition may be formulated as a one-component (one-package) paint. Alternatively, the basecoat composition may include a crosslinking agent reactive with the acrylic polymer and optionally with hydroxyl functionality on the alkyd resin, for example a polyisocyanate such as, but not limited to, the isocyanurate of hexamethylene diisocyanate. The crosslinking agent is kept separately from the acrylic polymer until just prior to application, as a two-component (two-package) paint.
In another embodiment, the invention provides an intermix system for preparing the basecoat composition of the invention. The intermix system includes a plurality of color components, each of which independently contains at least one pigment dispersed by at least the alkyd resin; a pigment-free component containing the hydroxyl-functional acrylic polymer of the basecoat composition; and optional further components.
The color components of the intermix system are formulated so that the system can produce the refinish basecoat composition of the invention in any desired color. The intermix system has at least about 30 color components, but may contain as many as 60 or more color components. It is desirable to minimize the number of color components as much as possible for simpler formulation and lower cost, but a sufficient number of color components must be included so that any desired automotive refinish color can be formulated.
The color components may be formulated so that the refinish basecoat composition will generally have substantially the physical properties, e.g. by having substantially the same weight ratio of alkyd resin to acrylic polymer (based on nonvolatile weights) regardless of which color components are needed to prepared the desired basecoat color. The alkyd resin is used to disperse the pigment in the color component, but some pigments or combinations of pigments require more resin to form a stable dispersion of suitable viscosity. The pigments, including flake pigments, may be included in amounts of from about 2% to about 35% by weight of the nonvolatile portion of the color component, depending upon the particular pigment or pigments included. More alkyd resin may be added to color components as needed so that each color component will contribute the desired amount of alkyd resin to the basecoat composition.
The intermix system further includes a pigment -free component containing the hydroxyl-functional acrylic polymer of the basecoat composition, described above. The intermix system may include optional further components, such as a crosslinker component containing a crosslinker reactive with the hydroxyl-functional acrylic polymer and/or a reducing solvent component.
The basecoat composition may include one or more solvents. In general, the solvent can be any organic solvent or solvents suitable for the alkyd and/or acrylic polymer. The solvent or solvents may be selected from aliphatic solvents or aromatic solvents, for example ketones, esters, acetates, toluene, xylene, aromatic hydrocarbon blends, or a combination of any of these.
In the intermix system, the solvent can be included in any of the components , and the intermix system may include an additional solvent-containing component other than the color components and the acrylic polymer-containing component. Generally, each of the components will include one or more kinds of organic solvent.
The refinish basecoat of the invention is applied in a layer to a desired area of the substrate to be refinished. The applied basecoat layer is allowed to dry, and then a clearcoat composition is applied in a layer over the basecoat composition layer. The basecoat composition of the invention provides an advantage in that the clearcoat composition can be applied in as short a time as 5 minutes after application of the basecoat layer. In general, no more than about 20 minutes of dry time is required before the clearcoat composition is applied.
A layer of a clearcoat composition is applied over the layer of dried basecoat. The clearcoat composition may include a material reactive with the acrylic polymer and, optionally, the alkyd of the layer of basecoat composition. For example, the clearcoat composition may include a crosslinker reactive with hydroxyl functionality, such as an isocyanate-functional crosslinking agent, for example and without limitation the isocyanurate of hexamethylene diisocyanate.
After application of the clearcoat layer, the composite coating is cured by at ambient temperatures, by low temperature baking (e.g., typical automotive refinish bake schedule), or by air drying (oxidative cure). Oxidative cure of the alkyd resin of the basecoat may take place over a period of days by diffusion of oxygen through the clearcoat layer.
The refinished substrate may be an automotive vehicle or a component of an automotive vehicle. The coating compositions of the invention may, however, be applied to other articles for which a protective and/or decorative coating is desirable. Such articles may be those having parts or substrates that cannot withstand high temperature curing conditions or that cannot easily be placed in a high-bake oven.

Fast drying alkyd basecoat refinish composition


The present invention is an imaging element which includes a support and at least one imaging layer superposed on the support. The imaging layer includes a scratch resistant outermost layer either overlying the imaging layer or on the side opposite the imaging layer, and is composed of a ductile polymer having a modulus greater than 100 MPa measured at 20xc2x0 C. and a tensile elongation to break greater than 50 percent, and a stiff filler having a modulus greater than 10 GPa at a volume concentration in the scratch resistant layer of 30 to 60%. The scratch resistant layer has a thickness of at least 0.5 xcexcm.

This invention relates to imaging elements having an improved scratch resistant layer. In particular, this invention relates to scratch resistant layers comprising a ductile polymer and a hard filler.
Microscratches are scratches that are on the order of several microns in width and submicron to microns in depth. They are commonly observed on the front and back sides of photographic films, on photoconductor belts, on thermal prints, and on PhotoCD disks. They are caused by sliding contact of imaging products with dirt particles or other asperities that have micron-sized contact radii. These scratches can affect analog or digital image transfer and degrade the output image quality. Their presence on magnetic or conductive backings could lessen the performance of these functional coatings. Thus, scratch resistance protective coatings on the front or back or both sides of an imaging product are commonly required.
Since all imaging products are based on flexible substrates for ease of transport, conveyance, and manufacturing, hard metallic or ceramic tribological scratch resistant coatings are not suitable due to their mechanical incompatibility with the polymeric flexible substrates. This mechanical incompatibility can cause adhesion failure between the coating and the substrate during scratching. Polymeric coatings are thus preferable as the scratch resistant layer for imaging products. However, with the requirements for high light transmission, low material cost, low internal drying stress, and high coating speeds, the thickness of these scratch resistant coatings is preferably about 10 microns or less.
During micro-scratching of a micron-thick coating, complex stress fields develop in the coating, within which high internal shear stress, interfacial shear stress, and surface tensile stress are present. A coating can fail either by shear fracture, delamination, or tensile cracking depending on the relative shear, adhesive, and tensile strengths of the coating. Using a micro-scratching instrument with a single micron-sized stylus, the resistance to scratch damage for a coating can be measured. Combining this instrument with optical microscopy, the failure mode, such as shear fracture, delamination, or tensile cracking, can be determined. All these failure modes produce scratches that are printable and scanable and, thus, unacceptable for imaging products. A permanent scratch track resulting from plastic deformation of a ductile coating without coating failure is also printable and scanable, and thus, not desirable.
Various types of polymeric coatings have been examined as scratch resistant coatings for imaging products. These include coatings comprising brittle, ductile, elastic-plastic, or rubber-elastic polymeric materials. Brittle polymers with elongations to break less than 5%, such as poly(methyl methacrylate) and poly(styrene) are not desirable as scratch resistant coatings for imaging products. Regardless of the coating thickness, the brittleness of these materials leads to printable surface tensile cracks during scratching. Soft elastomers (rubber-elastic materials), such as urethane rubbers, acrylic rubbers, silicone rubbers, are not suitable as scratch resistant coatings since deep penetration of the asperity or stylus occurs in these soft coatings which causes these elastomeric coatings to fail at low loads during scratching. Using stiff fillers to increase the stiffness of these elastomers to reduce stylus penetration does not solve this problem since permanent and printable scratch tracks result in elastomeric coatings containing stiff fillers by the induced coating plasticity under the presence of stiff fillers.
Ductile elastic-plastic coatings with elongations to break greater than 10%, such as glassy polyurethanes, polycarbonate, cellulose esters, etc., exhibit shear-fracture-type scratch damage during scratching that result from plastic flow. Plastic flow in these ductile coatings during scratching is controlled by the coating thickness. For thin coatings of these materials, plastic flow in the coating during scratching is restricted by the coating adhesion to the substrate leading to a premature failure of the coatings at low loads. Thicker coatings for these materials may have improved resistance to coating failure, however, for imaging products these thicknesses may be impractical. In addition, although thick ductile coatings have improved resistance to coating failure during scratching, the low yield strength and modulus for these materials result in the formation of permanent scratch tracks in the coatings at low loads. As an approach to prevent permanent scratch track formation, the yield strength of a ductile coating can be increased with the addition of stiff fillers. However, with the incorporation of stiff fillers, the elongation to break for these coatings are reduced significantly due to constrained plastic flow which is limited by the filler. This means that although the formation of a permanent scratch track can be delayed to higher loads with the addition of stiff fillers, the load required for coating failure is lowered accordingly. The failure mode is also changed from shear fracture to tensile cracking with the addition of stiff fillers. In addition, with the addition of high concentrations of fillers, the coatings may crack during drying due to the high internal drying stresses.
It can be seen that various approaches have been attempted to obtain an improved scratch resistant layer for imaging products. However, the aforementioned methods have met with only limited success. The present invention provides a coating composition with excellent resistance to the formation of permanent scratch tracks and coating failure when an imaging product is exposed to sharp asperities or other conditions that may lead to scratches during the manufacture and use of the imaging product.
The present invention is an imaging element which includes a support and at least one imaging layer superposed on the support. The imaging layer includes a scratch resistant outermost layer either overlying the imaging layer or on the side opposite the imaging layer, and is composed of a ductile polymer having a modulus greater than 100 MPa measured at 20xc2x0 C. and a tensile elongation to break greater than 50 percent, and a stiff filler having a modulus greater than 10 GPa at a volume concentration in the scratch resistant layer of 30 to 60%. The scratch resistant layer has a thickness of at least 0.5 xcexcm.
The imaging elements of this invention can be of many different types depending on the particular use for which they are intended. Such elements include, for example, photographic, electrostatographic, photothermographic, migration, electrothermographic, dielectric recording and thermal-dye-transfer imaging elements. Imaging elements can comprise any of a wide variety of supports. Typical supports include cellulose nitrate film, cellulose acetate film, poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) film, poly(ethylene naphthalate) film, polycarbonate film, glass, metal, paper, polymer-coated paper, and the like.
Details with respect to the composition and function of a wide variety of different imaging elements are provided in U.S. Pat. No. 5,340,676 and references described therein. The present invention can be effectively employed in conjunction with any of the imaging elements described in the ""676 patent.
In a particularly preferred embodiment, the imaging elements of this invention are photographic elements, such as photographic films, photographic papers or photographic glass plates, in which the image-forming layer is a radiation-sensitive silver halide emulsion layer. Such emulsion layers typically comprise a film-forming hydrophilic colloid. The most commonly used of these is gelatin and gelatin is a particularly preferred material for use in this invention. Useful gelatins include alkali-treated gelatin (cattle bone or hide gelatin), acid-treated gelatin (pigskin gelatin) and gelatin derivatives such as acetylated gelatin, phthalated gelatin and the like. Other hydrophilic colloids that can be utilized alone or in combination with gelatin include dextran, gum arabic, zein, casein, pectin, collagen derivatives, collodion, agar-agar, arrowroot, albumin, and the like. Still other useful hydrophilic colloids are water-soluble polyvinyl compounds such as polyvinyl alcohol, polyacrylamide, poly(vinylpyrrolidone), and the like.
The photographic elements of the present invention can be simple black-and-white or monochrome elements comprising a support bearing a layer of light-sensitive silver halide emulsion or they can be multilayer and/or multicolor elements.
Color photographic elements of this invention typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single silver halide emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as is well known in the art.
A preferred photographic element according to this invention comprises a support bearing at least one blue-sensitive silver halide emulsion layer having associated therewith a yellow image dye-providing material, at least one green-sensitive silver halide emulsion layer having associated therewith a magenta image dye-providing material and at least one red-sensitive silver halide emulsion layer having associated therewith a cyan image dye-providing material.
In addition to emulsion layers, the elements of the present invention can contain auxiliary layers conventional in photographic elements, such as overcoat layers, spacer layers, filter layers, interlayers, antihalation layers, pH lowering layers (sometimes referred to as acid layers and neutralizing layers), timing layers, opaque reflecting layers, opaque light-absorbing layers and the like. The support can be any suitable support used with photographic elements. Typical supports include polymeric films, paper (including polymer-coated paper), glass and the like. Details regarding supports and other layers of the photographic elements of this invention are contained in Research Disclosure, Item 36544, September, 1994 and Research Disclosure, Item 38597, September 1996.
The light-sensitive silver halide emulsions employed in the photographic elements of this invention can include coarse, regular or fine grain silver halide crystals or mixtures thereof and can be comprised of such silver halides as silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chorobromoiodide, and mixtures thereof. The emulsions can be, for example, tabular grain light-sensitive silver halide emulsions. The emulsions can be negative-working or direct positive emulsions. They can form latent images predominantly on the surface of the silver halide grains or in the interior of the silver halide grains. They can be chemically and spectrally sensitized in accordance with usual practices. The emulsions typically will be gelatin emulsions although other hydrophilic colloids can be used in accordance with usual practice. Details regarding the silver halide emulsions are contained in Research Disclosure, Item 36544, September, 1994, and Research Disclosure, Item 38597, September 1996 and the references listed therein.
The photographic silver halide emulsions utilized in this invention can contain other addenda conventional in the photographic art. Useful addenda are described, for example, in Research Disclosure, Item 36544, September, 1994 and Research Disclosure, Item 38597, September 1996. Useful addenda include spectral sensitizing dyes, desensitizers, antifoggants, masking couplers, DIR couplers, DIR compounds, antistain agents, image dye stabilizers, absorbing materials such as filter dyes and UV absorbers, light-scattering materials, coating aids, plasticizers and lubricants, and the like.
Depending upon the dye-image-providing material employed in the photographic element, it can be incorporated in the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye-image-providing material can be any of a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers and redox dye-releasers, and the particular one employed will depend on the nature of the element, and the type of image desired.
Dye-image-providing materials employed with conventional color materials designed for processing with separate solutions are preferably dye-forming couplers; i.e., compounds which couple with oxidized developing agent to form a dye. Preferred couplers which form cyan dye images are phenols and naphthols. Preferred couplers which form magenta dye images are pyrazolones and pyrazolotriazoles. Preferred couplers which form yellow dye images are benzoylacetanilides and pivalylacetanilides.
The photographic processing steps to which the raw film may be subject may include, but are not limited to the following:
1.) color developingxe2x86x92bleachxe2x86x92fixingxe2x86x92washing/stabilizing;
2.) color developingxe2x86x92bleachingxe2x86x92fixingxe2x86x92washing/stabilizing;
3.) color developingxe2x86x92bleachingxe2x86x92bleachxe2x86x92fixingxe2x86x92washing/stabilizing;
4.) color developingxe2x86x92stoppingxe2x86x92washingxe2x86x92bleachingxe2x86x92washingxe2x86x92fixingxe2x86x92washing/stabilizing;
5.) color developingxe2x86x92bleach-fixingxe2x86x92fixing washing/stabilizing;
6.) color developingxe2x86x92bleaching bleach-fixingxe2x86x92fixing xe2x86x92washing/stabilizing;
Among the processing steps indicated above, the steps 1), 2), 3), and 4) are preferably applied. Additionally, each of the steps indicated can be used with multistage applications as described in Hahm, U.S. Pat. No. 4,719,173, with co-current, counter-current, and contraco arrangements for replenishment and operation of the multistage processor.
Any photographic processor known to the art can be used to process the photosensitive materials described herein. For instance, large volume processors, and so-called minilab and microlab processors may be used. Particularly advantageous would be the use of Low Volume Thin Tank processors as described in the following references: WO 92/10790; WO 92/17819; WO 93/04404; WO 92/17370; WO 91/19226; WO 91/12567; WO 92/07302; WO 93/00612; WO 92/07301; WO 02/09932; U.S. Pat. No. 5,294,956; EP 559,027; U.S. Pat. No. 5,179,404; EP 559,025; U.S. Pat. No. 5,270,762; EP 559,026; U.S. Pat. No. 5,313,243; U.S. Pat. No. 5,339,131.
The present invention is also directed to photographic systems where the processed element may be re-introduced into the cassette. These systems allow for compact and clean storage of the processed element until such time when it may be removed for additional prints or to interface with display equipment. Storage in the roll is preferred to facilitate location of the desired exposed frame and to minimize contact with the negative. U.S. Pat. No. 5,173,739 discloses a cassette designed to thrust the photographic element from the cassette, eliminating the need to contact the film with mechanical or manual means. Published European Patent Application 0 476 535 A1 describes how the developed film may be stored in such a cassette.
The scratch resistant layer of the invention is the outermost layer on the front or back side of the imaging element and comprises a ductile polymer and a stiff filler. The ductile polymer is further defined as a polymer having a modulus measured at 20xc2x0 C. which is greater than 100 MPa and a tensile elongation to break greater than 50%. The modulus and tensile elongation to break for a polymer film can be conveniently measured by the tensile testing method in accordance with ASTM D882. The stiff filler is defined as a filler material having a modulus greater than 10 GPa. The stiff filler is incorporated in the scratch resistant layer at a volume concentration of 30 to 60%. This combination of a ductile polymer with these modulus and elongation to break values and a stiff filler provide a dried layer having exceptional resistance to the formation of printable, permanent scratch tracks and to scratches caused by complete coating failure during the manufacture and use of the imaging element. In a preferred embodiment, the scratch resistant layer of the invention is applied on the side of the imaging element opposite to the image forming layer.
Ductile polymers that meet the requirements of the present invention include polycarbonate, glassy polyurethanes and polyolefins. Glassy polymers such as polymethyl methacrylate, styrene, and cellulose esters, that have been described for use as scratch resistant layers for imaging elements are not desirable for use in the present invention due to their brittleness, especially when they are used in combination with stiff fillers. Of the ductile polymers useful in the present invention, polyurethanes are preferred due to their availability and excellent coating and film forming properties. In a most preferred embodiment of this invention, the polyurethane is a water dispersible polyurethane.
Water dispersible polyurethanes are well known and are prepared by chain extending a prepolymer containing terminal isocyanate groups with an active hydrogen compound, usually a diamine or diol. The prepolymer is formed by reacting a diol or polyol having terminal hydroxyl groups with excess diisocyanate or polyisocyanate. To permit dispersion in water, the prepolymer is functionalized with hydrophilic groups. Anionic, cationic, or nonionically stabilized prepolymers can be prepared.
Anionic dispersions contain usually either carboxylate or sulphonate functionalized co-monomers, e.g., suitably hindered dihydroxy carboxylic acids (dimethylol propionic acid) or dihydroxy sulphonic acids. Cationic systems are prepared by the incorporation of diols containing tertiary nitrogen atoms, which are converted to the quaternary ammonium ion by the addition of a suitable alkylating agent or acid. Nonionically stabilized prepolymers can be prepared by the use of diol or diisocyanate co-monomers bearing pendant polyethylene oxide chains. These result in polyurethanes with stability over a wide range of pH. Nonionic and anionic groups may be combined synergistically to yield xe2x80x9cuniversalxe2x80x9d urethane dispersions. Of the above, anionic polyurethanes are by far the most significant.
One of several different techniques may be used to prepare polyurethane dispersions. For example, the prepolymer may be formed, neutralized or alkylated if appropriate, then chain extended in an excess of organic solvent such as acetone or tetrahydrofuran. The prepolymer solution is then diluted with water and the solvent removed by distillation. This is known as the xe2x80x9cacetonexe2x80x9d process. Alternatively, a low molecular weight prepolymer can be prepared, usually in the presence of a small amount of solvent to reduce viscosity, and chain extended with diamine just after the prepolymer is dispersed into water. The latter is termed the xe2x80x9cprepolymer mixingxe2x80x9d process and for economic reasons is much preferred over the former.
Polyols useful for the preparation of polyurethane dispersions include polyester polyols prepared from a diol (e.g. ethylene glycol, butylene glycol, neopentyl glycol, hexane diol or mixtures of any of the above) and a dicarboxylic acid or an anhydride (succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, maleic acid and anhydrides of these acids), polylactones from lactones such as caprolactone reacted with a diol, polyethers such as polypropylene glycols, and hydroxyl terminated polyacrylics prepared by addition polymerization of acrylic esters such as the aforementioned alkyl acrylate or methacrylates with ethylenically unsaturated monomers containing functional groups such as carboxyl, hydroxyl, cyano groups and/or glycidyl groups.
Diisocyanates that can be used are as follows: toluene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, ethylethylene diisocyanate, 2,3-dimethylethylene diisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cycopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-phenylene diisocyanate, 4,4xe2x80x2-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 4,4xe2x80x2diisocyanatodiphenyl ether, tetramethyl xylene diisocyanate and the like.
Compounds that are reactive with the isocyanate groups and have a group capable of forming an anion are as follows: dihydroxypropionic acid, dimethylolpropionic acid, dihydroxysuccinic acid and dihydroxybenzoic acid. Other suitable compounds are the polyhydroxy acids which can be prepared by oxidizing monosaccharides, for example gluconic acid, saccharic acid, mucic acid, glucuronic acid and the like.
Suitable tertiary amines which are used to neutralize the acid and form an anionic group for water dispersibility are trimethylamine, triethylamine, dimethylaniline, diethylaniline, triphenylamine and the like.
Diamines suitable for chain extension of the polyurethane include ethylenediamine, diaminopropane, hexamethylene diamine, hydrazine, amnioethylethanolamine and the like.
Solvents which may be employed to aid in formation of the prepolymer and to lower its viscosity and enhance water dispersibility include methylethylketone, toluene, tetrahydofuran, acetone, dimethylformamide, N-methylpyrrolidone, and the like. Water-miscible solvents like N-methylpyrrolidone are much preferred.
Various stiff fillers that have a modulus greater than 10 GPa may be used in the scratch resistant layer of the present invention, representative stiff fillers include colloidal silica, colloidal tin oxide, colloidal titanium dioxide, mica, clays, doped-metal oxides, metal oxides containing oxygen deficiencies, metal antimonates, conductive nitrides, carbides, or borides, for example, TiO2, SnO2, Al2O3, ZrO3, In2O3, MgO, ZnSb2O6, InSbO4, TiB2, ZrB2, NbB2, TaB2, TaB2, CrB2, MoB, WB, LaB6, ZrN, TiN, TiC, and WC. Preferably, the stiff filler has a refractive index less than or equal to 2.1, and most preferably less than or equal to 1.6. For thick scratch resistant coatings, i.e., for dried layer thicknesses between 0.6 and 10 xcexcm containing 30 to 60 volume % stiff filler it is important to limit the refractive index of the filler in order to provide good transparency of the layer. The filler also has a particle size less than or equal to 500 nm, and preferably, less than 100 nm.
At filler concentrations less than 30 volume % there is little improvement in the scratch resistance of the layer while for filler concentrations greater than 60 volume % the layer becomes too brittle and the coating may exhibit cracking due to drying induced stresses. The filler concentration is specified in terms of volume % rather than weight % since the density of the filler particles can vary widely, for example, from about 1.5 g/cm3 to as much as 7 g/cm3.
Layers containing hard fillers for use in imaging elements have been described in the prior art. For example in U.S. Pat. No. 5,204,233, a silica-containing gelatin layer is described which reportedly has reduced sticking propensity. However, since gelatin does not have an elongation to break greater than 50%, the addition of hard fillers such as silica actually embrittles the layer. Backing layers comprising cellulose esters, styrene, or acrylate polymers and colloidal silica or alumina fillers are described in U.S. Pat. Nos. 4,363,871, 4,4427,764, 4,582,784, 4,914,018, 5,019,491, 5,108,885, 5,135,846, 5,250,409, and European Patent Appl. EP 296656, for example. However, these prior art references describe coating compositions comprising polymers with low elongation to break values and/or low modulus values and so they do not obtain the significant improvements in scratch resistance obtained in the present invention. In addition, these aforementioned prior art references do not teach or suggest that the polymers used in these coatings must have specific elongation to break and modulus values in order to optimize the physical properties of the dried layer.
Antistatic layers containing hard, electrically-conductive fillers such as doped-metal oxides, metal antimonates, etc. have been described in, for example, U.S. Pat. Nos. 4,275,103, 4,394,441, 4,416,963, 4,418,141, 4,431,764, 4,495,276, 4,571,361, 4,999,276, 5,122,445, 5,368,995, 5,457,013, 5,340,676, and in commonly assigned copending application Ser. No. 08/847,634. In these antistatic layer compositions, the binder for the conductive filler is typically not critical and various polymers including gelatin, latex polymers prepared from ethylenically unsaturated monomers, and others are described as being useful in the layer. These references do not teach the use of a polymer binder in which the elongation to break and modulus are critical to the performance of the layer. In addition, since these fillers typically have a high refractive index, it is usually desirable to apply these layers as thin as possible to provide good transparency. In commonly assigned copending application Ser. No. 08/937,685 and 08/940,960, antistatic layers containing a smectite clay and a polymer binder are described. Suitable polymers are described as those which exfoliate the clay. These patent applications do not teach the use of polymer binders having specific elongation to break or modulus values to obtain improved scratch resistance.
In addition to the ductile polymer having a modulus greater than 100 MPa and an elongation to break greater than 50% and a stiff filler having a modulus greater than 10 GPa, the scratch resistant layers in accordance with the invention may also contain suitable crosslinking agents including aldehydes, epoxy compounds, polyfunctional aziridines, vinyl sulfones, methoxyalkyl melamines, triazines, polyisocyanates, dioxane derivatives such as dihydroxydioxane, carbodiimides, and the like. The crosslinking agents react with the functional groups present on the ductile polymer. The thickness of the scratch resistant layer is preferably at least 0.5 xcexcm.
Other additional compounds that can be employed in the scratch resistant layer compositions of the invention include surfactants, coating aids, coalescing aids, lubricants, dyes, biocides, UV and thermal stabilizers, and matte particles. Matte particles are well known in the art and have been described in Research Disclosure No. 308, published December 1989, pages 1008 to 1009. When polymer matte particles are employed, the polymer may contain reactive functional groups capable of forming covalent bonds with the ductile polymer by intermolecular crosslinking or by reaction with a crosslinking agent in order to promote improved adhesion of the matte particles to the coated layers. Suitable reactive functional groups include: hydroxyl, carboxyl, carbodiimide, epoxide, aziridine, vinyl sulfone, sulfinic acid, active methylene, amino, amide, allyl, and the like.
Lubricants useful in the coating composition of the present invention include (1) silicone based materials disclosed, for example, in U.S. Pat. Nos. 3,489,567, 3,080,317, 3,042,522, 4,004,927, and 4,047,958, and in British Patent Nos. 955,061 and 1,143,118; (2) higher fatty acids and derivatives, higher alcohols and derivatives, metal salts of higher fatty acids, higher fatty acid esters, higher fatty acid amides, polyhydric alcohol esters of higher fatty acids, etc disclosed in U.S. Pat. Nos. 2,454,043, 2,732,305, 2,976,148, 3,206,311, 3,933,516, 2,588,765, 3,121,060, 3,502,473, 3,042,222, and 4,427,964, in British Patent Nos. 1,263,722, 1,198,387, 1,430,997, 1,466,304, 1,320,757, 1,320,565, and 1,320,756, and in German Patent Nos. 1,284,295 and 1,284,294; (3) liquid paraffin and paraffin or wax like materials such as carnauba wax, natural and synthetic waxes, petroleum waxes, mineral waxes and the like; (4) perfluoro- or fluoro- or fluorochloro-containing materials, which include poly(tetrafluoroethlyene), poly(trifluorochloroethylene), poly(vinylidene fluoride, poly(trifluorochloroethylene-co-vinyl chloride), poly(meth)acrylates or poly(meth)acrylamides containing perfluoroalkyl side groups, and the like. Lubricants useful in the present invention are described in further detail in Research Disclosure No.308, published December 1989, page 1006.
As part of the present invention it is also contemplated to overcoat the scratch resistant layer with a thin lubricant layer. An example of a particularly useful lubricant layer for the purpose of the invention is a layer of camauba wax.
The coating compositions of the invention can be applied by any of a number of well-know techniques, such as dip coating, rod coating, blade coating, air knife coating, gravure coating and reverse roll coating, extrusion coating, slide coating, curtain coating, and the like. After coating, the layer is generally dried by simple evaporation, which may be accelerated by known techniques such as convection heating. Known coating and drying methods are described in further detail in Research Disclosure No. 308, Published December 1989, pages 1007 to 1008.

Scratch resistant layer for imaging elements


A digital joystick control includes an elongated shaft member having a spherical ball at one end thereof. First and second socket members are coupled to the joystick to provide a swivel joint between the ball and the socket members enabling movement of the shaft about the ball in any direction; movement of the joystick effects corresponding movement of the socket members. Each of the socket members is connected to a plate member which moves therewith. The plate members have a patterned surface presenting conductive and non-conductive regions in opposing relation to wiper arms which engage the patterned surfaces. The patterned surfaces are coded in such a manner that the locations of the conductive and non-conductive regions of the patterned surfaces with respect to the wiper arms are changeable in response to movement of the shaft of the joystick whereby a unique digital-coded positional signal is generated for preselected incremental positions of the shaft.

This invention relates to joystick controls for selectively altering electrical signals in accordance with the relative position of the joystick control and, more particularly, to a joystick control which generates digitally-coded signals.
This invention further relates to copending U.S. Patent Application Ser. No. 785,006 by Kastner et al, entitled System for Displaying Character and Graphic Information on a Color Video Display; Ser. No. 785,145, by Burson, entitled A Digital Joystick Control Interface System for Video Games and the Like; and Ser. No. 785,143 by Burson, entitled System to Control Velocity Vector of a Display Cursor, each filed of even date with and assigned to the Assignee of the present invention. This invention also relates to Ser. No. 791,913, by Trenkler et al, entitled Video Game with Portable Control Units, filed Apr. 28, 1977 and assigned to the Assignee of the present invention.
Prior art joystick controls, which alter electrical signals, have been of the analog type in which potentiometers are mounted in controlled relation to the joystick; one of the potentiometers being controlled with joystick movement in the X direction, and the other being controlled with joystick movement in the Y direction. The position of the joystick thereby determines the relative resistances of the two potentiometers which, in turn, alter electrical signals. If a digital signal is required to control a digital processor or the like, an analog-to-digital conversion circuit is required.
It is an object of the invention to provide an improved joystick control.
It is another object of the present invention to provide a digital joystick which directly generates digital-coded signals indicative of the X-Y position of the joystick.