GB2407095A - White pearlescent paint compositions and coatings - Google Patents

Abstract

A pearlescent white paint composition comprising a solids material and a film-former, said solids material comprising at least 90% w/w mica, 4-7% w/w TiO2 and 0.2-3.0% w/w particulate metallic Al. The relatively narrow combination of the three solids materials in the defined ratios provides highly desirable white pearlescent finishes at most advantageously relatively thin paint film thickness. The film-former may be selected from the resin group consisting of acrylic, urethane, polyester and melamine/formaldehyde. Also shown is a process for producing a pearlescent white finish on a substrate, preferably a vehicle body.

Description

WHITE PEARLESCENT PAINT

COMPOSITIONS AND COATINGS

FIELD OF THE INVENTION

This invention relates to white pearlescent paints, lacquers and primers; their use in an improved process for creating a white "pearl" finish on a painted or lacquered surface; and substrates, particularly vehicle bodies, obtained by said process with said paint.

BACKGROUND OF THE INVENTION

In the automotive industry, a pearlescent white finish is a desirable and highly prized finish colour for automobiles and truck by reason that a pearlescent white finish has been found to be more popular with purchasers than a flat white finish.

Conventionally, in order to create a pearlescent white finish on a vehicle, a three step application process is necessary after the exposed metal parts have been primed with one or more coats of primer. To create the pearlescent white finish, normally, a base coat of white paint is applied, followed by a coating of pearlescent material usually containing mica, which is not pigmented, but rather contains particles of a highly reflective material to provide the "pearl" finish, and finally, a clear coat to seal the underlying layers. Each coating layer must be applied separately, and suitable drying times, and if necessary baking, must be provided prior to the application of each subsequent layer. Consequently, the production of a pearlescent finish is labour intensive and time consuming.

Whenever coats of two different types of paint are applied to a substrate, it is necessary to allow a longer drying time than is needed between multiple coats of the same type of paint. In order to facilitate the proper setting of a three-coat paint finish, drying times are required to set each of the paint undercoat, pearl coat and clear coat.

The longer drying times are achieved by having the painted vehicles remaining on the assembly line for additional periods of time. It is not feasible to simply run the assembly line more slowly through the painting section of an automobile assembly plant in order to create longer drying times between paint applications. Instead, the entire assembly line must be lengthened to provide the further travel time during which paint drying can occur. It follows that in order to make the assembly line longer, a larger physical plant space is needed through which to run the assembly line.

In manufacturing plants where physical space is at a premium, it may not be possible to set aside additional assembly line length to facilitate multiple times between the application of multiple paint coats. Accordingly, it may not be feasible to offer certain paint finishes on vehicles manufactured at some smaller manufacturing plants.

United States Patent No. 5,871,827 to Jaffe et al. of which the entire subject matter is incorporated herein by reference, discloses two-coat and three-coat automotive finishes and a process for their preparation, wherein polychromism is achieved by incorporating an opaque light interference pigment into the top coat or mid coat. The processes taught by Jaffe involve the use of two coating layers, in which the first contains an opaque white, black or coloured pigment to achieve total hiding, while the second layer, being an interference pigment does not hide the first coating. A clear topcoat is still applied over the pigmented coats in order to complete the finish. The particles of opaque interference pigment taught are multi-layered particles having an opaque layer coated with a transparent dielectric layer, which in turn are coated with a semitransparent layer. This would be a relatively complex and expensive coating process to apply, while the result of the process gives polychromatic paint effects.

United States Patent No. 5,350,509 to Sada et al., of which the entire subject matter is incorporated in by reference, discloses a coating structure that includes a colour base, a first coating layer placed on the colour base, having transparent brilliant members contained in the first coating layer, each brilliant member including an alternate lamination of at least two polymers having different refractive indexes and controlling interference light resulting from reflection interference produced by alternate lamination and transmitted light other than interference light.

United States Patent No. 4,499,143 to Panush, of which the entire subject matter is incorporated herein by reference, discloses a transparent topcoat composition containing low pigment to binder ratio of iron oxide encapsulated in mica particles. The teachings of Panush are particularly addressed to producing coloured finishes having depth, clarity and chromaticity. Although this patent states that mica encapsulated iron oxide pigments have inherent hiding capabilities in addition to being pearlescent, they are said to be additive colours. The desired colour results are stated not to be obtainable with metals, e.g. aluminium, and previous pearlescent natural or synthetic pigments. These so called "colourless and opaque" pigments reduce the value of the true coloured pigments and result in gray-cloudy-low chrome colours. In view of the focus on coloured finishes, this patent fails to recognise and teach the value of aluminium as a pigment and hiding material in pearlescent white finishes.

United States Patent No. 4,615,940 to Panush of which the entire subject matter is incorporated in by reference, discloses an opalescent colour effect on a substrate utilising a multicoat system in which a coloured primer is applied to a surface, followed by a transparent basecoat, and then a clearcoat. This transparent basecoat should tend to have poor hiding qualities, and relatively high light transmittance. In order to compensate for this feature of the basecoat, primers with very effective black and white hiding would be required, and further measures would be necessary to block UV light levels, otherwise there could be significant electrocoat degradation through the transparent basecoat. Additionally, the use of a transparent basecoat requires that the primer layer must be applied carefully and sanded thoroughly, since the transparent basecoat would fail to mask defects in the primer coat.

In the case of conventional titanium dioxide white paint, very large amounts of titanium dioxide pigment are needed in the paint medium in order to achieve adequate hiding power at a reasonable film thickness of, typically, 30 to 50 microns. Such a paint formulation has very little ability to hold more solid particulates, and, therefor, there is little room in the paint mixture left to add a pearlising material, such as particles of mica.

It is known that adding mica to a conventional white titanium dioxide paint does not change the visible appearance of the white paint. Conventional titanium dioxide-based white paint, having a titanium content exceeding 90% w/w of the pigment solids portion, has a "flat" white appearance notwithstanding the presence of a pearlising material.

Solvent-based paints can carry from 40 to 60% w/w pigment, whereas water based paints and primers, on the other hand, which do not dispense the pigment as well, have a lower pigment loading of, for example, in the range of 20 to 35% w/w.

In each case, for conventional white paint, 90 percent of the pigment must be white pigment, generally, titanium dioxide. In consequence, the mica flakes are drowned in the large quantity of titanium dioxide pigment is needed to create conventional white paint, and the pearlised appearance of the mica is lost to the eye.

In order to create a conventional white paint pearlescent finish, it has been necessary to apply a pearl coating of mica or another pearlising material after the white titanium dioxide paint has set in place in order to prevent the "drowning" of the pearlising material, since a conventional mica pearl coat has no hiding power of its own. The pigmented base coat is required for the hiding properties of the finish, so as to cover sand marks and the like on the article and to create the actual colour of the painted article. The pearl coat merely gives the shiny characteristic that converts a "flat" finish into a "pearl" finish. Since the titanium dioxide white base-coat and the pearl coat are two different types of paints, each requires distinct flash times in order to set each of the coats before other substances are applied to the surface. If no flash time is allowed between the application of a pigmented base coat and a pearl coat paint, striking will occur between the coats. Paint striking is a painting flaw which occurs when the dyes or pigments from a previous paint layer become dissolved in the solvents of a newly applied material and seep through to alter the finish colour of the newly applied material. It is caused by the application of two different types of paint coatings without a long enough flash time between the application of the two coatings. The application of the separate mica pearlising coating necessitates a separate application step which requires significant adaptation of automotive production lines and causes a substantial increase in the painting cost of each vehicle produced.

"Hiding Power" is a quantitative factor which is critical in determining the make up of paints. Hiding Power may be quantitatively defined as the property of a paint that enables it to completely hide any background over which it is sprayed.

Generally speaking, it is accepted within the paint industry that complete hiding is achieved when the paint applied over a black background has a reflectance value of 0.98 of that applied in equal thickness over a white background. Thus, Hiding Power is a contrast ratio of the background and the thickness of paint which is required to reduce the contrast difference to 0.02. The standard figure of 0.02 is based upon the Weber-Fechner contrast law which states that differences of less the 2% (0.02) are imperceptible to the human eye in conditions of moderate illumination.

Hiding Power is produced by the light absorbing properties of pigment particles in a film of paint as applied to a painted surface. If much of the light emerges from the top of the surface of the paint film, and the substrate is not obscured, then the film of paint hides poorly. Most pigments are crystalline in nature.

In particular, white pigments when dispersed in a paint medium tend to scatter light strongly. If a single crystal of white pigment were grown sufficiently large, it would be perceived as a shine and transparent glass-like crystal. This light scattering characteristic results in large amounts of light emerging from the surface of the paint film, with corresponding poor hiding power.

Titanium dioxide is the most common white pigment for use in paint.

Unfortunately, this pigment has relatively poor hiding power. In order to maintain the white colour, no coloured pigments, which would by definition have greater hiding power, can be present to improve hiding properties. Accordingly, conventional white base coats are heavily laden with titanium dioxide pigment. Thus, in order to achieve a white paint colour with black and white hiding properties at less than 35 microns, the paint must contain at least 90% w/w titanium dioxide which is approaching the maximum pigment content allowable in a paint formulation to still allow the paint to flow and be effectively sprayed onto a surface. By contrast, other paint colours which contain pigments having more effective hiding power may contain approximately 5% w/w pigment.

PCT/CA02/01810 discloses pigments, pigment formulations, paint formulations and uses thereof for coating surfaces, particularly vehicle bodies to provide white and coloured pearlescent finishes. One embodiment described has a formulation with the following range of solid constituents, namely 0. 1- 15% TiO2, 10- 99% mica, 0. 1-20% aluminium and 0-5% coloured pigment.

Although PCT/CA02/018 10 describes useful paint compositions for providing white pearlescent finishes to substrates, we have surprisingly discovered a much narrower range of white paint formulations which formulations provide a most superior pearlescent white finish of advantageously reduced film thickness relative to prior art two-coat and three-coat white pearl finishes.

Thus, while important strides have been made, to date, to provide improved methods for providing white pearlescent paint finishes and compositions, therefor, there remains a need for better paint compositions of use in improving the appearance and the methods of application of the white pearlescent finishes in a cost effective manner.

SUMMARY OF THE INVENTION

Surprisingly, we have discovered that paint compositions containing solids material comprising relatively specific ratios of components, in admixture with the film former and, optionally, additive ingredients and the like, give greatly improved white pearlescent finishes on substrates, particularly, vehicle bodies.

We have found that a solids material comprising relatively small amounts of a white pigment, namely, titanium dioxide, relatively very small amounts of particulate metallic aluminium, and relatively very large amounts of a pearlising mica with a suitable film former, surprisingly, gives an extremely attractive white pearlescent finish on the substrate, at a relatively extremely thin film thickness.

One aspect of the present invention provides a white pearlescent paint composition of use in giving an improved white pearlescent paint finish on a coated substrate.

A further aspect provides an improved process of using said white pearlescent paint composition to obtain said finish on said substrate.

A yet further aspect provides a method of making said paint composition.

A still yet further aspect provides a substrate, particularly, a vehicle body surface, coated with said paint composition to provide said white pearlescent finish.

In one specific aspect the invention provides a pearlescent white paint composition comprising a solids material and a film-former, said solids material comprising at least 90% w/w mica, 4-7% w/w TiO2 and 0.2-3.0% w/w particulate metallic Al.

Most preferably, the solids material comprises 94.0+ 1% w/w mica, 5.0+ 1% w/w TiO2 and 0.5+ 0.3% w/w Al.

Most preferred embodiments are shown in TABLE I, at the stated % w/w values.

TABLE I

Water Solvent Lacquer

SOLIDS MATERIALS

Titanium dioxide 0.25 0.25 0.25 Aluminium (metallic particulate) 0.025 0. 025 0.025 Mica 4.75 4.75 4.75

RESINS

Acrylic 7.47 18.15 20 Urethane 0.96 Polyester 5.8 Melamine formaldelyde 4. 82 19.4 Microgel 12.91

ADDITIVES

Extender 0.35 0.39 0.35 Rheology additives 0.4 UV Additives 0.19 0.78 0. 78 Catalyst 0.39 0.39 Solvent 17.76 42.95 73.45 Water 57.225 1 00 1 00.00 1 00.00 s A particularly most preferred embodiment is shown in TABLE II, in the relative amounts given in TABLE I.

TABLE II

Polyester resin Bayhydrol D 155 (Bayer) / Polyester resin 5770.84 Cargil) Acrylic 2-Hydroxy ethyl acylate (HEA Dow Chemical / MMMA Methyl methacrylate) Melamine Resin Luwipal 066 (BASF) Urethane U 610 (Alberdingk 8 Boley) Catalyst Nacure X49-110-King Industries) Rehology additive Tego WetZFS 453 UV Additive TinUVin 384/ TinUVin 292 (CibaGeigy) Microgel TEGO Disperss 630 Extender Talc fine grade powder (St.Lawrence Chemical Inc) Titanium Dioxide Ti Pure Dupont Aluminium STAPA IL Hydrolan 2192 55900/G Eckart America L.P Mica Xirralic T 60-10 WNT Crystal silver by Merck We have found that the metallic A1 component in the defined ratios and absolute amounts according to the invention further most advantageously provides an aesthetic sparkle effect and further assists paint flow viscosity control properties. The aluminium particles may be relatively large or coarse particles, having particle sizes ranging in size from 1 to 2 microns in thickness, and 100 to 200 microns in diameter.

Course aluminium is available from Delta Colours Inc. and/or Silberline Mfg. Co., inc. Metallic aluminium for use in paint compositions is generally sold as "aluminium paste-leafing" or "aluminium paste-nonleafing" in a paste according to specific particle size distribution. The aluminium particles may also be fine particles, that is particles having a size range of 0.1 to 1 microns in thickness, and 0.1 to 100 microns in diameter. These particles may, for example, include the pigments commercially available from "Delta colours Inc." and/or Silberline Mfg. Co., Inc., which may be used as supplied or milled or otherwise processed to reduce their size, or size range profile, to suit the application.

The mica compound(s) content is, thus, at least 90% w/w of the solids material, and most preferably, about 94.0+ 1% w/w.

One preferred pearlising mica compound is known under the trade-mark XIRALLIC T60-20 SW Sunbeam Gold, having a particle size of 5-30pm.

Other preferred flaked forms of mica can also be successfully used, either alone, or in combination with the XIRALLIC product. The proportions of mica in different flaked forms can be varied, depending on the pigment properties desired, and upon the tolerance for increased manufacturing costs which result from the use of increased proportions of the preferred XIRALLIC product form.

Other pearlising mica materials may include naturally occurring mica platelets which have been coated with metal oxides, such as alumina or highly refractive metal oxides such as titanium dioxide or iron oxide.

The film dormers of use in the compositions of the invention may be suitably selected from those generally of use in solvent or aqueous bases in paint and lacquer formulations known in the art. Preferably, the film former is selected from those based on acrylic, urethane, polyester, or melamine formaldehyde resins. Preferred acrylic resins are acrylamide, acrylonitride, methyl acrylate, and ethylhexyl acrylate.

A preferred composition comprises about 7-8% acrylic, about 1% urethane, about 6% polyester and about 5% melamine formaldehyde resins on a w/w basis of the total paint composition, as applied to a substrate.

The paint compositions according to the invention may, optionally, further comprise one or more additives selected from UV protestants, extenders, polymerization catalysts, rheology additives and the like.

For the sake of simplicity and clarity, in this specification, the term "solids materials" means the solid materials, namely, TiO2, mica and Al. It does not include any original organic resins or solid material resulting in the film-former or the aforesaid solid additives of use in the paint compositions or cured paint.

In a further aspect, the invention provides a process for producing a pearlescent white finish on a substrate comprising applying a pearlescent white paint composition as hereinabove defined on said substrate; and curing said composition on said substrate.

The substrate may be any desirable, suitable surface of an object or article, but most preferably, the object is an automobile, truck, or like object.

Thus, in a further aspect, the invention provides an aforesaid substrate coated with a pearlescent white finish as hereinabove defined by a process as hereinabove defined.

The pearlescent formulation according to the present invention is, surprisingly, most effective at hiding and also UV blocking, to the extent that the coating may be used to function in the automotive painting process in a manner analogous with a paint layer, not a pearlised clear coat layer. This functional advantage of the formulations according to specific embodiments of the present invention permits the use of a 2-coat painting system instead of a 3-coat painting system to obtain a pigmented pearlised automotive paint finish.

In one embodiment, a paint composition as hereinabove defined, is applied as a base coat to a thickness of approximately 18 to 25 micrometers and may be set or cured by ambient flash dehydration andlor baking in an oven. A clear coat is then, preferably, applied to provide a total overall thickness of approximately 35-45 micrometers, thereon.

In a further embodiment, the invention provides a process for producing a pearlescent white finish on an object comprises the steps of applying to the object at least one base coat of the pearlescent white paint formulation according to the invention, setting the base coat, applying a clear coat to the base coat and setting the clear coat.

The aforesaid basecoat as hereinabove defined may be used, alone, over a primer or Electrocoat, as the final finish on a substrate, without a clearcoat finish.

That such a very small amount of hiding component with such a very low amount of white pigment in such a vast amount of pearlising material can provide such an attractive pearlescent white paint finish is most surprising.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be better understood a preferred embodiment will now be described by way of example only, with reference to the drawing wherein FIGURE 1 represents a comparative graph of the % transmittance at various paint film thicknesses for a two-coat pearlescent white paint according to the invention in comparison with prior art twoand three-coat pearlescent white paint films.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The paint composition given in TABLE II, hereinbefore, was prepared according to standard procedures known in the art as an aqueous formulation in the amount as shown in TABLE I on a % w/w basis, from the film-former precursor and solids material.

The aforesaid paint composition according to the invention was applied above a white primer coat on a simulated car body surface, cured and subsequently coated with a conventional clear coat to give a so-called "two-coat" pearlescent white finish.

Comparative two-coat and three-coat pearlescent white finishes according to the prior art were prepared and compared in FIGURE 1, wherein lines A and B denote two- coat white pearl compositions according to the prior art; line C denotes a three-coat white pearl composition according to the prior art; and line D denotes a two-coat white pearl composition according to the invention. Each of the aforesaid paints has a top clear coat composition.

FIGURE 1 shows the much superior cost-effective film thickness of the cured paint film while providing significantly improved transmittance value.

While the compositions, coatings, methods and substrates hereinabove described are applied with reference to vehicle surfaces, it will be understood that they are also usable on other surfaces, such as those covering a range of industrial and personal products, plastics, metals and the like. Therefore, the above description is not intended to limit the invention entirely to the preferred field of vehicle surfaces.

Further, although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.

Claims (14)

1. Claims 1. A pearlescent white paint composition comprising a solids

   material and a film- former, said solids material comprising at least 90% w/w mica, 4-7% w/w TiO2 and 0.2-3.0% w/w particulate metallic Al.
2. 2. A paint composition as defined in claim 1 wherein said solids material comprises 94.0+ 1% w/w mica, 5.0+ 1% w/w TiO2 and 0.5+ 0.3% w/w Al.
3. 3. A paint composition as defined in claim 1 or claim 2 wherein said filmformer is selected from the resin group consisting of an acrylic, urethane, polyester and melamine/formaldehyde.
4. 4. A paint composition as defined in any one of claims 1 to 3 in a formulation base selected from the group consisting of an aqueous, solvent and lacquer base.
5. 5. A paint composition as defined in claim 3 or claim 4 comprising about 7-8% acrylic, about 1% urethane, about 6% polyester and about 5% melamine formaldehyde resins on a w/w basis.
6. 6. A process for producing a pearlescent white finish on a substrate comprising applying a pearlescent white paint composition as defined in any one of claims 1 to 5 to said substrate; and curing said composition on said substrate to provide a cured said finish.
7. 7. A process as defined in claim 6 further comprising applying a clear coat to said cured finish and curing said clear coat.
8. 8. A process as defined in claim 6 or claim 7 wherein said substrate is a vehicle body.
9. 9. A substrate coated with a cured pearlescent white finish when made by the process as defined in claim 7.
10. 10. A coated substrate as defined in claim 9 wherein said substrate is a vehicle body.

    S
11. 11. A pearlescent white paint composition substantially as hereinbefore described with reference to the accompanying drawing.
12. 12. A process for producing a pearlescent white finish substantially as hereinbefore described with reference to the accompanying drawing.
13. 13. A substrate coated with a cured pearlescent white finish substantially as hereinbefore described with reference to the accompanying drawing.
14. 14. A vehicle body coated with a cured pearlescent white finish substantially as hereinbefore described with reference to the accompanying drawing.