Method of forming traffic markers having short track-free times
United States Patent 3900605
This invention relates to a method of forming traffic markers which, when applied to a traffic-bearing surface, have substantially shorter track-free times than the pigmented organic coating compositions which are utilized in the system. The method comprises applying a coating composition to the substrate and then applying to the coating composition, while it remains wet, light reflecting particulate materials sized so that at least about one-half their mass becomes embedded in the coating composition, while having a diameter greater than the thickness of the paint. The particulate material is applied at such a rate that the individual particles are separated from each other in the marker by less than their average diameter.
US Patent References:
Surfacing for automobile parts and the like
Carlson - April 1927 - 1626508
Reflex light reflector
Gebhard et al. - August 1943 - 2326634
Light reflector sheet
Heltzer et al. - July 1944 - 2354018
Flexible lenticular optical sheet
Palmquist - July 1944 - 2354048
Backless reflex light reflector
Palmquist - July 1944 - 2354049
Surfacing for automobile parts and the like
Carlson - April 1927 - 1626508
Reflex light reflector
Gebhard et al. - August 1943 - 2326634
Light reflector sheet
Heltzer et al. - July 1944 - 2354018
Flexible lenticular optical sheet
Palmquist - July 1944 - 2354048
Backless reflex light reflector
Palmquist - July 1944 - 2354049
Application Number:
05/394587
Publication Date:
08/19/1975
Filing Date:
09/05/1973
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
427/202, 359/540
International Classes:
E01F9/04; G02B5/128
Field of Search:
117/33,9,10 350/15X 427/202,137
US Patent References:
| 2897733 | Traffic marker, material, and method | August 1959 | Shuger | |
| 3036928 | Retroreflective composition and method of applying same | May 1962 | Poole | |
| 3288618 | Colored reflective coating composition | November 1966 | De Vries | |
| 3614199 | REFLEX REFLECTING PRODUCTS, PROCESSES AND DEVICES USEFUL WITH SUCH PRODUCTS | October 1971 | Altman | |
| 3746425 | REFLECTIVE ROAD MARKING MEANS AND AGGREGATE | July 1973 | Eigenmann | |
| 3770483 | NOCTILUCENT REFLECTIVE HELMET | November 1973 | Komine |
Primary Examiner:
Martin, William D.
Assistant Examiner:
Beck, Shrive P.
Attorney, Agent or Firm:
Jones, Tullar & Cooper
Claims:
What is claimed is
1. A method of applying a traffic directing marker to a paved traffic bearing surface which comprises:
2. A method, as in claim 1, where the coating composition dries inherently track-free in about three minutes or less after application and where the particulate material is applied at a rate so that the individual particles in the coating film are in substantial contact with each other.
3. A method, as in claim 1, wherein the light reflective particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand and mixtures thereof.
4. A method, as in claim 2, wherein the light reflective particulate material is applied at a rate of at least about 80 pounds of particulate material per mile to a 4 inch wide strip of coating composition.
5. A method, as in claim 3, wherein the light reflective particulate material is applied at a rate of at least about 100 pounds of particulate material per mile to a four inch wide strip of coating composition.
6. A method, as in claim 5, wherein the applicationn rate is at least 160 pounds of particulate material per mile to a four inch wide strip of coating composition.
7. A method, as in claim 1, wherein the particulate material is applied at a rate of at least about 10 pounds per gallon of coating composition.
8. A method, as in claim 2, wherein the applied traffic directing marker is track-free in less than about 1 minute.
9. A method of applying a traffic directing marker to a paved traffic bearing surface which comprises:
10. A method, as in claim 9, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
11. A method, as in claim 10, where the applied traffic directing marker is track-free in less than about 1 minute.
12. A method, as in claim 10, wherein the wet coating composition has a film thickness of about 10 mils or less.
13. A method, as in claim 12, where the applied traffic directing marker is track-free in less than about 1 minute.
14. A method, as in claim 10, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
15. A method, as in claim 9, where S is about 1.5D or less.
16. A method, as in claim 15, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
17. A method, as in claim 15, where the applied traffic directing marker is track-free in less than about 1 minute.
18. A method, as in claim 15, wherein the wet coating composition has a film thickness of about 10 mils or less.
19. A method, as in claim 15, where the applied traffic directing marker is track-free in less than about 1 minute.
20. A method, as in claim 15, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
21. A method, as in claim 9, where S equals about D or less.
22. A method, as in claim 21, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
23. A method, as in claim 21, where the applied traffic directing marker is track-free in less than about 1 minute.
24. A method, as in claim 21, wherein the wet coating composition has a film thickness of about 10 mils or less.
25. A method, as in claim 21, where the applied traffic directing marker is track-free in less than about 1 minute.
26. A method, as in claim 21, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
1. A method of applying a traffic directing marker to a paved traffic bearing surface which comprises:
2. A method, as in claim 1, where the coating composition dries inherently track-free in about three minutes or less after application and where the particulate material is applied at a rate so that the individual particles in the coating film are in substantial contact with each other.
3. A method, as in claim 1, wherein the light reflective particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand and mixtures thereof.
4. A method, as in claim 2, wherein the light reflective particulate material is applied at a rate of at least about 80 pounds of particulate material per mile to a 4 inch wide strip of coating composition.
5. A method, as in claim 3, wherein the light reflective particulate material is applied at a rate of at least about 100 pounds of particulate material per mile to a four inch wide strip of coating composition.
6. A method, as in claim 5, wherein the applicationn rate is at least 160 pounds of particulate material per mile to a four inch wide strip of coating composition.
7. A method, as in claim 1, wherein the particulate material is applied at a rate of at least about 10 pounds per gallon of coating composition.
8. A method, as in claim 2, wherein the applied traffic directing marker is track-free in less than about 1 minute.
9. A method of applying a traffic directing marker to a paved traffic bearing surface which comprises:
10. A method, as in claim 9, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
11. A method, as in claim 10, where the applied traffic directing marker is track-free in less than about 1 minute.
12. A method, as in claim 10, wherein the wet coating composition has a film thickness of about 10 mils or less.
13. A method, as in claim 12, where the applied traffic directing marker is track-free in less than about 1 minute.
14. A method, as in claim 10, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
15. A method, as in claim 9, where S is about 1.5D or less.
16. A method, as in claim 15, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
17. A method, as in claim 15, where the applied traffic directing marker is track-free in less than about 1 minute.
18. A method, as in claim 15, wherein the wet coating composition has a film thickness of about 10 mils or less.
19. A method, as in claim 15, where the applied traffic directing marker is track-free in less than about 1 minute.
20. A method, as in claim 15, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
21. A method, as in claim 9, where S equals about D or less.
22. A method, as in claim 21, where the wet coating composition has a film thickness of about 15 mils or less and the light reflecting particulate material comprises a material selected from the group consisting of glass spheres, spheroidal sand, and a mixture of glass spheres and spheroidal sand.
23. A method, as in claim 21, where the applied traffic directing marker is track-free in less than about 1 minute.
24. A method, as in claim 21, wherein the wet coating composition has a film thickness of about 10 mils or less.
25. A method, as in claim 21, where the applied traffic directing marker is track-free in less than about 1 minute.
26. A method, as in claim 21, where the coating composition dries inherently track-free in about 3 minutes or less after application and the applied traffic directing marker is track-free in less than about 1 minute.
Description:
STATE OF THE ART
The marking of traffic surfaces, such as asphalt or concrete, with traffic directing paint, for example, lines which delineate traffic lanes, center lines or road edges, is common. Frequently these markings contain light reflecting means, most frequently, glass spheres.
Traffic directing markings are subject to continuous wear and exposure to the elements as well as road chemicals and require periodic reapplication. When traffic directing paints are applied to an area which is travelled there is usually a significant time, during which, if the marker is not protected, the paint which is not firm or dry, can be picked up by the tires of vehicles, for example, and tracked, leaving confusing or unattractive random markings upon the traffic surface, reducing or destroying the effectiveness and/or durability of the traffic marker. To avoid this problem cones or flags or other temporary obstacles are frequently placed to protect the marker until it is no longer subject to tracking. These temporary obstacles, which impede the normal traffic flow, must then be removed in a separate operation.
Various systems have been proposed to provide traffic marker coatings systems which have short track-free times and which can be applied to travelled surfaces without the need for secondary protection. However, these systems involve the use of relatively expensive materials and/or the use of expensive, complex application means.
As previously stated, the majority of traffic marking systems employ the use of a variety of light reflecting or scattering particulate material, preferably glass beads or spheres. The art has examined glass spheres and their use in traffic marker paints extensively, dealing with their optimum reflectivity, the modification of their properties by coating, and the problems of securely embedding the spheres in a paint film.
DESCRIPTION OF THE INVENTION
It has now been found that traffic directing coatings having short track-free times can be rather simply and economically applied to a paved traffic bearing surface.
The traffic marker compositions comprise a pigmented synthetic organic vehicle resin having embedded therein substantial amounts of a relatively large light scattering or reflecting particulate material, the average diameter of the particulate material being greater than the film thickness. The resultant compositions have short track-free times, substantially shorter than the track-free times of the pigmented coating compositions without the particulate material. The track-free times measured in the order of seconds can be achieved employing the compositions and methods of the invention.
In order to obtain the greatest benefit from the invention, the pigmented coating compositions employed in the marker system of the invention should dry track-free in about 6 minutes or less and preferably 3 minutes or less. Drying, as utilized herein, encompasses all the forms referred to a layman that is becoming tack-free by solvent evaporation, cooling, chemical crosslinking, polymerization and the like.
In a preferred embodiment, the marker system comprises a pigmented organic binder, which dries track-free in about 6 minutes or less, at the wet film thickness employed; the organic coating composition being applied in a relatively thin film, for example, at about 15 mils wet film thickness or less, for example, preferably at about 10 mils. The final dry marker system has embedded in the dry coating film relatively large reflecting particulate material, having been incorporated into the coating, for example, by dropping or blowing the particulate material into the wet coating film before it has dried. The reflecting particulate material is of such size that it penetrates substantially the depth of the binder or coating film, so that the base of the particles are in proximity to or substantially resting upon the substrate, the preponderance of the particulate matter forming at least a monolayer of particulate material with at least one-half of the particle embedded in the binder layer, the particles being in close proximity to each other, that is touching or separated only by a very thin paint film which may be adhering to some of the particles, but which appear to the eye as essentially touching. Generally, in the compositions of the invention, the individual particles may be separated by a distance no greater than about the average diameter of the particle.
In another preferred embodiment, a thin, pigmented, fluid paint film is applied to the traffic surface and there is then applied an excess of particulate material, sufficient to fully cover the binder coating. The excess which is not substantially bound to or embedded in the pigmented resinous binder remains at least temporarily to provide additional protection to the marker system, which is track-free so rapidly that even this fugitive protection is of benefit. By substantially bound is meant bound to the extent that the action of a broom sweeping lightly over the surface will not dislodge the particulate material.
The fluid, synthetic organic vehicle resin containing, coating compositions or binder employed in the marker compositions of the invention may vary widely. These compositions are well known in the art and need not be described in great detail. Further, a large number of coating compositions are known as having utility as coatings for materials such as concrete or asphaltic materials or have been described as useful as traffic paints. Virtually any synthetic organic polymeric binder may be employed which has sufficient adhesion to the substrate and to the particulate material to provide mechanical integrity to the marker system, and which when formulated into a pigmented coating composition yields a coating composition which drys track-free in about six minutes or less and preferably three minutes or less. This drying time is the time inherent for the coating composition per se absent the addition of light reflecting particulate material.
The synthetic organic vehicle resin used to formulate the pigmented coating composition may be either thermoplastic or thermosetting and, in addition to the pigment and the organic vehicle resin, the coating composition may contain adjuvants such as solvents, plasticizers, crosslinking agents, catalysts, flow modifiers and the like in accordance to known conventional formulating techniques. Usually the coating composition is solvent based, the solvent being employed to obtain appropriate application viscosities and track-free times. However, the coating composition may be a high solids or solvent-free coating composition such as hot melt coatings, polymer-monomer systems such as an unsaturated polyesterstyrene system or fluid polymer systems which cure upon application such as a polyurethane systems or an epoxy based systems.
Solvent based systems include acrylic resins, vinyl resins, alkyd or polyester resins, epoxy resins, urethane resins, phenoplast and aminoplast resins among others.
The coating composition is pigmented so that the traffic directing marker may be seen under varied conditions. The usual colors employed in traffic paints are yellow and white, although the coating composition may be pigmented to any desired color. Typical pigments include rutile and anatase titanium dioxide, chrome yellow (lead chromate) and the like. The compositions may likewise contain extender pigments such as silica, clay, calcium sulfate, calcium carbonate and magnesium silicate and the like. Coloring of the compositions can be augmented by, or totally produced by, the use of colored light reflecting particulate material.
The pigmented coating composition is applied to the traffic surface in a conventional manner, most preferably by spraying. Preferably it is applied at a wet film thickness of about 15 mils or less, most preferably at about 10 mils or less. Exceptional short track-free times in the order of a few seconds have been obtained with employing wet film thickness of about 10 mils or less.
The reflective or light scattering particulate material embedded in the coating composition may be subject to wide variation. The term light reflective or reflecting particulate material as employed herein is intended to encompass those materials which scatter light such as sand, as well as true retroreflective materials such as glass spheres.
One particular reflective particulate material which is highly useful is glass spheres; these are well known in the art. The spheres commercially available are not homogeneous in size and are usually sold as a material wherein the preponderance of the sphere pass specified mesh size sieve and are retained by a smaller specified sieve size. Thus, when 15 mil spheres are employed, the preponderance of the spheres are about 15 mils but are admixed with some at least slightly smaller spheres. A typical glass sphere composition is one which meets Federal Specification TTB 1325A, Type 1, Class A characterized as follows: 100% passing 20 mesh, 80-100% passing 30 mesh, 18-35% passing 50 mesh.
Another preferred material is a round sand known as Ottawa sand which, unlike ordinary sand, is relatively smooth and spheroidal in shape. Two particularly useful grades are:
A B (Crystal) (Federal Fine) AFS Grain Finess 38 47 Actual Surface Area (CM 2 /gm) 72 97 Base Permeability 246 252 Theoretical Surface Area (CM 2 /gm) 62 80 Coefficient of Area 1.2 1.2 Density (uncompacted) (lb/ft 3 ) 92 91 Density (compacted) (lb/ft 3 ) 97 95 % Retained (U.S. Sieve Nos.) 30 1 -- 40 36 19 50 45 43 70 15 25 100 3 9 140 -- 3 200 -- 1.
Other useful light reflecting particulate materials which can be employed in the marker system of the invention include organic polymeric particles preferably in the form of spheroids or beads. Such materials include polymethylmethacrylate polystyrene, polyvinyl chloride copolymers and vinyl acetate copolymers and the like. The materials can be employed alone or in combination with glass spheres, spheroidal sand, common sand, crushed glass or other mineral particles, for example, of a mesh size between ab out 20 to about 50 mesh.
The light reflecting particulate material should be of such a size so that the preponderance of the particulate material has a diameter greater than the wet film thickness of the coating composition to which it is applied, yet should be of a size small enough so that at least the initial monolayer of particulate material has at least about one-half its mass embedded in the coating composition. Where the material is spheroidal, the circumference of the spheroid should be embedded in the coating composition. While particulate material of substantially the same size can be employed, the typical commercially available materials vary in size over a range, however these materials are readily useful in the marker system of the invention provided that the preponderance of the particulate material is of the desired size. For example, where a 15 mil wet film is applied, the particulate material should be in the range of about 19 mils to 35 mils or about 20 mesh to about 35 mesh.
The weight of the particulate light material applied per unit area necessary to achieve the desired coverage may be readily calculated, assuming a monolayer of beads equally distributed, for example, by the following formula: ##EQU1## where w = weight of spheres (grams)
A = unit area (centimeter 2 )
S = distance between centers of spheres (centimeters)
V = volume of sphere (centimeter 3 ) (0.52 × D 3 )
g = specific gravity of spheres (grams/centimeter 3 )
D = diameter of sphere (centimeter).
For example, for a 929 cm 2 area (1 sq.ft.), employing glass spheres with a diameter of 0.3081 centimeter (0.15 inch) essentially touching each other, about 50 grams/929 cm 2 are employed.
As previously stated, in the composition of the invention, the spheres should be, at a maximum, about one diameter apart and more preferably, the spheres should be about one-half a diameter or less apart. Thus in the above example, at one diameter distance between spheres, S equals 0.0762 centimeter W is about 13 grams; at one-half diameter distance between spheres, S equals 0.0571 centimeter and W is about 24 grams.
The above formula can be used to calculate the necessary weight of a spheroidal material at any size, thus where heavy particles, or larger diameter particles are used the necessary weight is greater. If light weight plastic materials are used the necessary weight will be less.
Where non-spheroidal particles, such as crushed glass or ordinary white beach sand, are employed the diameter may be considered as the average diameter of the particles.
The process of the invention comprises applying to the traffic bearing surface a wet film of the pigmented organic coating composition and then applying the light reflecting particulate material to said coating composition before it dries or increases in viscosity to the point where the light reflecting particulate material will not substantially penetrate the coating film.
The light reflecting particulate material is applied to the surface of the coating composition either by dropping on or preferably by being applied at a substantial velocity, for example, by means of a pressurized spray gun.
The apparatus which can be employed in a preferred embodiment is the type of apparatus heretofore used to apply traffic paints. In its simplest form, it comprises a wheeled vehicle having mounted thereon two separate pressurized vessels, one containing coating compositions, the other light reflecting particulate material. The two materials are supplied under pressure to two separate spray guns which apply the two materials as the vehicle moves forward, in rapid succession, first the paint film and second the particulate material.
In the marker system of the invention the light reflecting particulate material, with a specific gravity the order of glass spheres or sand, is usually applied to a four inch wide strip at a rate of at least about 80 lbs. per mile and preferably 160 lbs. or more per mile.
While it is not intended to limit the invention described herein to any theory, it has been at least tentatively postulated that the rapid track-free times achieved in the marker systems described herein are obtained by avoiding contact of the tires of vehicles with the coating composition before it is actually dry or cured. The dense packing of the particulate material distributes the forces applied and combined with inertia, the force of a vehicle tire does not dislodge sufficient of the light reflecting particles from the coating to allow the vehicle tires to pick-up and track substantial amounts of coating even though it may not be actually dry.
Further, while it would appear that only a monolayer of particulate material of the size employed could be substantially bound to the coating composition, in practice, apparently due to the fact that the particulate material is applied with a lateral force vector, at least some of the coating material is rolled up or perhaps splashed upon the surfaces or rises between the particulate material so that frequently a substantial amount of particulate material in excess of that which forms a closely packed monolayer is substantially bound to the coating film. While some of this particulate material may sometimes become reasonably rapidly dislodged during use, it serves a highly useful initial purpose and contributes to the overall durability of the system.
It is further interesting to note that an added benefit derived from the marker systems disclosed herein is that when employed as crosswalk markers the marker systems of the invention contribute antislip characteristics, especially in wet weather, and increases the useful life of the line as compared to conventional marker systems.
BRIEF DESCRIPTION OF THE DRAWINGS
The four figures graphically present the results of the Examples which follow. In the figures track-free times of the traffic marker compositions of the various examples (Ex) are depicted by plotting track-free time against the amount of particulate material applied to the wet paint film.
The invention is further described in conjunction with the following examples which are to be considered illustrative rather than limiting. All parts and percentages in the examples and throughout the specification are by weight unless otherwise stated.
EXAMPLE 1
The coating composition employed in this example comprised:
Parts by weight ______________________________________ 34% Phthalic Soya-Linseed Alkyd 1958 (60% in toluene) 12% Lead 30 Chrome Medium Yellow 3000 Rutile TiO 2 375 Talc 2625 Cation Modified Clay 40 (Bentone 38) Methanol 95 Calcium Carbonate (50 Micron top size) 3000 40% Chlorinated Paraffin 1128 Chlorinated Rubber, 20 CPS 1500 Methyl Ethyl Ketone 4056 Antiskimming Agent 45 Epicholorhydrin 45 Methyl Amyl Acetate 527. ______________________________________
Paint lines were applied using the above coating composition by means of a commercial crosslink application machine employing a Binks No. 21 spray gun with No. 69D fluid tip and a No. 713 nozzle for the paint and a Binks No. 21 gun with a No. 58 fluid tip and a No. R-30 nozzle for the particulate material, i.e., glass spheres (Federal Specification TT-B-1325A, Type 1, Class A).
The apparatus was operated at a brisk walk, the paint being applied from the first spray gun at a wet film thickness of 17 mils, followed immediately by the application from the second spray gun of the glass spheres. The air temperature was 80°.
No pick-up or track-free times were measured by rolling a rubber vehicle tire over the deposited marker, the rubber tire having approximately the same weight per unit contact area as a passenger sedan tire. The resultant no pick-up, track-free times for varying amounts of glass spheres was plotted and shown in FIG. 1. The quantity of spheres is shown for a solid line four inches wide in pounds per mile as well as grams per square foot and pounds per gallon.
The paint was applied to glass panels to facilitate measurements. Observation of the underside of the glass panel showed numerous relatively color-free areas indicating penetration of the glass spheres through the paint film so that the glass spheres were resting in substantial contact with the substrate.
EXAMPLE 2
Example 1 was repeated with a wet paint film thickness of 10 mils. The results for varying amounts of glass spheres was plotted against time. See FIG. 1. Track-free times as low as 30 seconds were recorded although the paint inherently had a track-free time of 2 minutes.
EXAMPLE 3
The paint employed was that of Example 1.
In an air conditioned building, paint was applied to glass panels using a Bird applicator. The wet film thickness was 10 mils. A preweighed amount of glass spheres (Federal Specification TT-B-1325A, Type 1, Class A) was applied to the wet film by shaking from a salt shaker having 19 holes of 0.055 inch diameter in the top. Distribution of the glass spheres was rapid and as even as possible.
Track-free times were measured in accordance with ASTM No. D-711-67. The results were plotted; see FIG. 1, although the paint per se demonstrated a track-free time of about 5 minutes track-free times as low as 30 seconds were achieved employing the system of the invention.
EXAMPLE 4
Example 3 was repeated except that the light reflecting particulate material was a mixture of one-half glass spheres and one-half Ottawa Sand, Crystal Grade. Track-free times were determined for varying amounts of particulate material and plotted against quantity, see FIG. 2. It has been noted that on a wet road, mixtures of glass spheres and spheroidal sand are more visable than glass spheres, alone.
EXAMPLE 5
Example 3 was repeated except that the particulate material applied was Crystal Grade, Ottawa Sand. Track-free times were determined for varying amounts of sand and plotted against quantity, see FIG. 2.
EXAMPLE 6
Example 3 was repeated except that the light reflecting particulate material applied was a mixture of one-half glass spheres and one-half Del Monte White Beach Sand (30 mesh). Track-free times were determined for varying amounts of particulate material and plotted against quantity, see FIG. 2.
EXAMPLE 7
Example 3 was repeated except that the light reflecting particulate material applied was a mixture of one-half glass spheres and one-half Federal Fine Grade of Ottawa Sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLE 8
Example 3 was repeated except that the light reflecting particulate material applied was Federal Fine Grade Ottawa Sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLE 9
Example 3 was repeated except that the light reflecting particulate material was a mixture of one-half glass spheres and one-half Crystal Grade Ottawa Sand applied in two increments, first the glass spheres being applied and second the sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLES 10-12
Example 4 was repeated except that the paint film was applied at 11, 13 and 15 mils thicknesses, respectively, the particulate material being a mixture of one-half glass spheres and one-half Crystal Grade Ottawa Sand. Track-free times were determined for varying amounts of particulate materials for each film thickness and plotted against quantity as examples 10, 11 and 12; see FIG. 4.
EXAMPLE 13
Equal volumes of plastic spheres; plastic and sand and glass spheres were applied as in Example 3 with similar results. Plastics employed were polystyrene, polyvinyl chloride copolymers and polyvinyl acetate copolymers. No pick-up and no tracking times under 1 minute were obtained when the drop-on materials were applied in the same volume as 180 pounds per mile of glass spheres.
While the traffic markers of the invention have been described primarily as being applied by a two step application process, it is likewise possible to form the compositions of the invention in other ways. For example, a mixture of pigmented fusible resin particles or powder and light reflective particulate material may be applied to the substrate and heat fused to the substrate for example by the use of flame torches which heat the pavement and/or the fusible mixture causing the resin powder to flow and form a film having light reflective particulate material therein.
Other coating compositions, light reflective particulate materials and application techniques, including those described herein, may be substituted for those exemplified to obtain the improvement hereinabove described.
The marking of traffic surfaces, such as asphalt or concrete, with traffic directing paint, for example, lines which delineate traffic lanes, center lines or road edges, is common. Frequently these markings contain light reflecting means, most frequently, glass spheres.
Traffic directing markings are subject to continuous wear and exposure to the elements as well as road chemicals and require periodic reapplication. When traffic directing paints are applied to an area which is travelled there is usually a significant time, during which, if the marker is not protected, the paint which is not firm or dry, can be picked up by the tires of vehicles, for example, and tracked, leaving confusing or unattractive random markings upon the traffic surface, reducing or destroying the effectiveness and/or durability of the traffic marker. To avoid this problem cones or flags or other temporary obstacles are frequently placed to protect the marker until it is no longer subject to tracking. These temporary obstacles, which impede the normal traffic flow, must then be removed in a separate operation.
Various systems have been proposed to provide traffic marker coatings systems which have short track-free times and which can be applied to travelled surfaces without the need for secondary protection. However, these systems involve the use of relatively expensive materials and/or the use of expensive, complex application means.
As previously stated, the majority of traffic marking systems employ the use of a variety of light reflecting or scattering particulate material, preferably glass beads or spheres. The art has examined glass spheres and their use in traffic marker paints extensively, dealing with their optimum reflectivity, the modification of their properties by coating, and the problems of securely embedding the spheres in a paint film.
DESCRIPTION OF THE INVENTION
It has now been found that traffic directing coatings having short track-free times can be rather simply and economically applied to a paved traffic bearing surface.
The traffic marker compositions comprise a pigmented synthetic organic vehicle resin having embedded therein substantial amounts of a relatively large light scattering or reflecting particulate material, the average diameter of the particulate material being greater than the film thickness. The resultant compositions have short track-free times, substantially shorter than the track-free times of the pigmented coating compositions without the particulate material. The track-free times measured in the order of seconds can be achieved employing the compositions and methods of the invention.
In order to obtain the greatest benefit from the invention, the pigmented coating compositions employed in the marker system of the invention should dry track-free in about 6 minutes or less and preferably 3 minutes or less. Drying, as utilized herein, encompasses all the forms referred to a layman that is becoming tack-free by solvent evaporation, cooling, chemical crosslinking, polymerization and the like.
In a preferred embodiment, the marker system comprises a pigmented organic binder, which dries track-free in about 6 minutes or less, at the wet film thickness employed; the organic coating composition being applied in a relatively thin film, for example, at about 15 mils wet film thickness or less, for example, preferably at about 10 mils. The final dry marker system has embedded in the dry coating film relatively large reflecting particulate material, having been incorporated into the coating, for example, by dropping or blowing the particulate material into the wet coating film before it has dried. The reflecting particulate material is of such size that it penetrates substantially the depth of the binder or coating film, so that the base of the particles are in proximity to or substantially resting upon the substrate, the preponderance of the particulate matter forming at least a monolayer of particulate material with at least one-half of the particle embedded in the binder layer, the particles being in close proximity to each other, that is touching or separated only by a very thin paint film which may be adhering to some of the particles, but which appear to the eye as essentially touching. Generally, in the compositions of the invention, the individual particles may be separated by a distance no greater than about the average diameter of the particle.
In another preferred embodiment, a thin, pigmented, fluid paint film is applied to the traffic surface and there is then applied an excess of particulate material, sufficient to fully cover the binder coating. The excess which is not substantially bound to or embedded in the pigmented resinous binder remains at least temporarily to provide additional protection to the marker system, which is track-free so rapidly that even this fugitive protection is of benefit. By substantially bound is meant bound to the extent that the action of a broom sweeping lightly over the surface will not dislodge the particulate material.
The fluid, synthetic organic vehicle resin containing, coating compositions or binder employed in the marker compositions of the invention may vary widely. These compositions are well known in the art and need not be described in great detail. Further, a large number of coating compositions are known as having utility as coatings for materials such as concrete or asphaltic materials or have been described as useful as traffic paints. Virtually any synthetic organic polymeric binder may be employed which has sufficient adhesion to the substrate and to the particulate material to provide mechanical integrity to the marker system, and which when formulated into a pigmented coating composition yields a coating composition which drys track-free in about six minutes or less and preferably three minutes or less. This drying time is the time inherent for the coating composition per se absent the addition of light reflecting particulate material.
The synthetic organic vehicle resin used to formulate the pigmented coating composition may be either thermoplastic or thermosetting and, in addition to the pigment and the organic vehicle resin, the coating composition may contain adjuvants such as solvents, plasticizers, crosslinking agents, catalysts, flow modifiers and the like in accordance to known conventional formulating techniques. Usually the coating composition is solvent based, the solvent being employed to obtain appropriate application viscosities and track-free times. However, the coating composition may be a high solids or solvent-free coating composition such as hot melt coatings, polymer-monomer systems such as an unsaturated polyesterstyrene system or fluid polymer systems which cure upon application such as a polyurethane systems or an epoxy based systems.
Solvent based systems include acrylic resins, vinyl resins, alkyd or polyester resins, epoxy resins, urethane resins, phenoplast and aminoplast resins among others.
The coating composition is pigmented so that the traffic directing marker may be seen under varied conditions. The usual colors employed in traffic paints are yellow and white, although the coating composition may be pigmented to any desired color. Typical pigments include rutile and anatase titanium dioxide, chrome yellow (lead chromate) and the like. The compositions may likewise contain extender pigments such as silica, clay, calcium sulfate, calcium carbonate and magnesium silicate and the like. Coloring of the compositions can be augmented by, or totally produced by, the use of colored light reflecting particulate material.
The pigmented coating composition is applied to the traffic surface in a conventional manner, most preferably by spraying. Preferably it is applied at a wet film thickness of about 15 mils or less, most preferably at about 10 mils or less. Exceptional short track-free times in the order of a few seconds have been obtained with employing wet film thickness of about 10 mils or less.
The reflective or light scattering particulate material embedded in the coating composition may be subject to wide variation. The term light reflective or reflecting particulate material as employed herein is intended to encompass those materials which scatter light such as sand, as well as true retroreflective materials such as glass spheres.
One particular reflective particulate material which is highly useful is glass spheres; these are well known in the art. The spheres commercially available are not homogeneous in size and are usually sold as a material wherein the preponderance of the sphere pass specified mesh size sieve and are retained by a smaller specified sieve size. Thus, when 15 mil spheres are employed, the preponderance of the spheres are about 15 mils but are admixed with some at least slightly smaller spheres. A typical glass sphere composition is one which meets Federal Specification TTB 1325A, Type 1, Class A characterized as follows: 100% passing 20 mesh, 80-100% passing 30 mesh, 18-35% passing 50 mesh.
Another preferred material is a round sand known as Ottawa sand which, unlike ordinary sand, is relatively smooth and spheroidal in shape. Two particularly useful grades are:
A B (Crystal) (Federal Fine) AFS Grain Finess 38 47 Actual Surface Area (CM 2 /gm) 72 97 Base Permeability 246 252 Theoretical Surface Area (CM 2 /gm) 62 80 Coefficient of Area 1.2 1.2 Density (uncompacted) (lb/ft 3 ) 92 91 Density (compacted) (lb/ft 3 ) 97 95 % Retained (U.S. Sieve Nos.) 30 1 -- 40 36 19 50 45 43 70 15 25 100 3 9 140 -- 3 200 -- 1.
Other useful light reflecting particulate materials which can be employed in the marker system of the invention include organic polymeric particles preferably in the form of spheroids or beads. Such materials include polymethylmethacrylate polystyrene, polyvinyl chloride copolymers and vinyl acetate copolymers and the like. The materials can be employed alone or in combination with glass spheres, spheroidal sand, common sand, crushed glass or other mineral particles, for example, of a mesh size between ab out 20 to about 50 mesh.
The light reflecting particulate material should be of such a size so that the preponderance of the particulate material has a diameter greater than the wet film thickness of the coating composition to which it is applied, yet should be of a size small enough so that at least the initial monolayer of particulate material has at least about one-half its mass embedded in the coating composition. Where the material is spheroidal, the circumference of the spheroid should be embedded in the coating composition. While particulate material of substantially the same size can be employed, the typical commercially available materials vary in size over a range, however these materials are readily useful in the marker system of the invention provided that the preponderance of the particulate material is of the desired size. For example, where a 15 mil wet film is applied, the particulate material should be in the range of about 19 mils to 35 mils or about 20 mesh to about 35 mesh.
The weight of the particulate light material applied per unit area necessary to achieve the desired coverage may be readily calculated, assuming a monolayer of beads equally distributed, for example, by the following formula: ##EQU1## where w = weight of spheres (grams)
A = unit area (centimeter 2 )
S = distance between centers of spheres (centimeters)
V = volume of sphere (centimeter 3 ) (0.52 × D 3 )
g = specific gravity of spheres (grams/centimeter 3 )
D = diameter of sphere (centimeter).
For example, for a 929 cm 2 area (1 sq.ft.), employing glass spheres with a diameter of 0.3081 centimeter (0.15 inch) essentially touching each other, about 50 grams/929 cm 2 are employed.
As previously stated, in the composition of the invention, the spheres should be, at a maximum, about one diameter apart and more preferably, the spheres should be about one-half a diameter or less apart. Thus in the above example, at one diameter distance between spheres, S equals 0.0762 centimeter W is about 13 grams; at one-half diameter distance between spheres, S equals 0.0571 centimeter and W is about 24 grams.
The above formula can be used to calculate the necessary weight of a spheroidal material at any size, thus where heavy particles, or larger diameter particles are used the necessary weight is greater. If light weight plastic materials are used the necessary weight will be less.
Where non-spheroidal particles, such as crushed glass or ordinary white beach sand, are employed the diameter may be considered as the average diameter of the particles.
The process of the invention comprises applying to the traffic bearing surface a wet film of the pigmented organic coating composition and then applying the light reflecting particulate material to said coating composition before it dries or increases in viscosity to the point where the light reflecting particulate material will not substantially penetrate the coating film.
The light reflecting particulate material is applied to the surface of the coating composition either by dropping on or preferably by being applied at a substantial velocity, for example, by means of a pressurized spray gun.
The apparatus which can be employed in a preferred embodiment is the type of apparatus heretofore used to apply traffic paints. In its simplest form, it comprises a wheeled vehicle having mounted thereon two separate pressurized vessels, one containing coating compositions, the other light reflecting particulate material. The two materials are supplied under pressure to two separate spray guns which apply the two materials as the vehicle moves forward, in rapid succession, first the paint film and second the particulate material.
In the marker system of the invention the light reflecting particulate material, with a specific gravity the order of glass spheres or sand, is usually applied to a four inch wide strip at a rate of at least about 80 lbs. per mile and preferably 160 lbs. or more per mile.
While it is not intended to limit the invention described herein to any theory, it has been at least tentatively postulated that the rapid track-free times achieved in the marker systems described herein are obtained by avoiding contact of the tires of vehicles with the coating composition before it is actually dry or cured. The dense packing of the particulate material distributes the forces applied and combined with inertia, the force of a vehicle tire does not dislodge sufficient of the light reflecting particles from the coating to allow the vehicle tires to pick-up and track substantial amounts of coating even though it may not be actually dry.
Further, while it would appear that only a monolayer of particulate material of the size employed could be substantially bound to the coating composition, in practice, apparently due to the fact that the particulate material is applied with a lateral force vector, at least some of the coating material is rolled up or perhaps splashed upon the surfaces or rises between the particulate material so that frequently a substantial amount of particulate material in excess of that which forms a closely packed monolayer is substantially bound to the coating film. While some of this particulate material may sometimes become reasonably rapidly dislodged during use, it serves a highly useful initial purpose and contributes to the overall durability of the system.
It is further interesting to note that an added benefit derived from the marker systems disclosed herein is that when employed as crosswalk markers the marker systems of the invention contribute antislip characteristics, especially in wet weather, and increases the useful life of the line as compared to conventional marker systems.
BRIEF DESCRIPTION OF THE DRAWINGS
The four figures graphically present the results of the Examples which follow. In the figures track-free times of the traffic marker compositions of the various examples (Ex) are depicted by plotting track-free time against the amount of particulate material applied to the wet paint film.
The invention is further described in conjunction with the following examples which are to be considered illustrative rather than limiting. All parts and percentages in the examples and throughout the specification are by weight unless otherwise stated.
EXAMPLE 1
The coating composition employed in this example comprised:
Parts by weight ______________________________________ 34% Phthalic Soya-Linseed Alkyd 1958 (60% in toluene) 12% Lead 30 Chrome Medium Yellow 3000 Rutile TiO 2 375 Talc 2625 Cation Modified Clay 40 (Bentone 38) Methanol 95 Calcium Carbonate (50 Micron top size) 3000 40% Chlorinated Paraffin 1128 Chlorinated Rubber, 20 CPS 1500 Methyl Ethyl Ketone 4056 Antiskimming Agent 45 Epicholorhydrin 45 Methyl Amyl Acetate 527. ______________________________________
Paint lines were applied using the above coating composition by means of a commercial crosslink application machine employing a Binks No. 21 spray gun with No. 69D fluid tip and a No. 713 nozzle for the paint and a Binks No. 21 gun with a No. 58 fluid tip and a No. R-30 nozzle for the particulate material, i.e., glass spheres (Federal Specification TT-B-1325A, Type 1, Class A).
The apparatus was operated at a brisk walk, the paint being applied from the first spray gun at a wet film thickness of 17 mils, followed immediately by the application from the second spray gun of the glass spheres. The air temperature was 80°.
No pick-up or track-free times were measured by rolling a rubber vehicle tire over the deposited marker, the rubber tire having approximately the same weight per unit contact area as a passenger sedan tire. The resultant no pick-up, track-free times for varying amounts of glass spheres was plotted and shown in FIG. 1. The quantity of spheres is shown for a solid line four inches wide in pounds per mile as well as grams per square foot and pounds per gallon.
The paint was applied to glass panels to facilitate measurements. Observation of the underside of the glass panel showed numerous relatively color-free areas indicating penetration of the glass spheres through the paint film so that the glass spheres were resting in substantial contact with the substrate.
EXAMPLE 2
Example 1 was repeated with a wet paint film thickness of 10 mils. The results for varying amounts of glass spheres was plotted against time. See FIG. 1. Track-free times as low as 30 seconds were recorded although the paint inherently had a track-free time of 2 minutes.
EXAMPLE 3
The paint employed was that of Example 1.
In an air conditioned building, paint was applied to glass panels using a Bird applicator. The wet film thickness was 10 mils. A preweighed amount of glass spheres (Federal Specification TT-B-1325A, Type 1, Class A) was applied to the wet film by shaking from a salt shaker having 19 holes of 0.055 inch diameter in the top. Distribution of the glass spheres was rapid and as even as possible.
Track-free times were measured in accordance with ASTM No. D-711-67. The results were plotted; see FIG. 1, although the paint per se demonstrated a track-free time of about 5 minutes track-free times as low as 30 seconds were achieved employing the system of the invention.
EXAMPLE 4
Example 3 was repeated except that the light reflecting particulate material was a mixture of one-half glass spheres and one-half Ottawa Sand, Crystal Grade. Track-free times were determined for varying amounts of particulate material and plotted against quantity, see FIG. 2. It has been noted that on a wet road, mixtures of glass spheres and spheroidal sand are more visable than glass spheres, alone.
EXAMPLE 5
Example 3 was repeated except that the particulate material applied was Crystal Grade, Ottawa Sand. Track-free times were determined for varying amounts of sand and plotted against quantity, see FIG. 2.
EXAMPLE 6
Example 3 was repeated except that the light reflecting particulate material applied was a mixture of one-half glass spheres and one-half Del Monte White Beach Sand (30 mesh). Track-free times were determined for varying amounts of particulate material and plotted against quantity, see FIG. 2.
EXAMPLE 7
Example 3 was repeated except that the light reflecting particulate material applied was a mixture of one-half glass spheres and one-half Federal Fine Grade of Ottawa Sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLE 8
Example 3 was repeated except that the light reflecting particulate material applied was Federal Fine Grade Ottawa Sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLE 9
Example 3 was repeated except that the light reflecting particulate material was a mixture of one-half glass spheres and one-half Crystal Grade Ottawa Sand applied in two increments, first the glass spheres being applied and second the sand. Track-free times were determined for varying amounts of particulate material and plotted against quantity; see FIG. 3.
EXAMPLES 10-12
Example 4 was repeated except that the paint film was applied at 11, 13 and 15 mils thicknesses, respectively, the particulate material being a mixture of one-half glass spheres and one-half Crystal Grade Ottawa Sand. Track-free times were determined for varying amounts of particulate materials for each film thickness and plotted against quantity as examples 10, 11 and 12; see FIG. 4.
EXAMPLE 13
Equal volumes of plastic spheres; plastic and sand and glass spheres were applied as in Example 3 with similar results. Plastics employed were polystyrene, polyvinyl chloride copolymers and polyvinyl acetate copolymers. No pick-up and no tracking times under 1 minute were obtained when the drop-on materials were applied in the same volume as 180 pounds per mile of glass spheres.
While the traffic markers of the invention have been described primarily as being applied by a two step application process, it is likewise possible to form the compositions of the invention in other ways. For example, a mixture of pigmented fusible resin particles or powder and light reflective particulate material may be applied to the substrate and heat fused to the substrate for example by the use of flame torches which heat the pavement and/or the fusible mixture causing the resin powder to flow and form a film having light reflective particulate material therein.
Other coating compositions, light reflective particulate materials and application techniques, including those described herein, may be substituted for those exemplified to obtain the improvement hereinabove described.