Patent Publication Number: US-8119202-B2

Title: Method of applying a thermally settable coating to a patterned substrate

Description:
RELATED APPLICATION 
     This application claims priority on pending international application No. PCT/CA02/01864 filed 3 Dec. 2002 which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This application relates to a method of applying a thermally settable coating to a patterned substrate, such as an imprinted asphalt surface. The coating may be applying by placing one or more pre-formed thermoplastic sheets on the substrate and heating the sheets in situ to conform to the thermoplastic material to the underlying pattern. 
     BACKGROUND 
     Various methods for forming patterns in asphalt surfaces and other substrates are known in the prior art. The Applicant is the owner of U.S. Pat. No. 5,215,402 which describes a method of forming a pattern in an asphalt surface using a removable template. The template is compressed into a pliable asphalt surface to imprint a predetermined pattern simulating, for example, the appearance of bricks, cobblestones, interlocking paving stones or the like. The template is then lifted clear of the asphalt surface and the asphalt is allowed to harden. 
     In one embodiment of the &#39;402 invention a thin layer of a cementitious coating may be applied to the imprinted asphalt to enhance the brick and mortar or other desired visual effect. The decorative coating may be applied, for example, by applying concrete powder and a colorant in the form of a slurry which is spread throughout the asphalt surface and allowed to harden. This is a relatively time consuming and labour-intensive process. Various other acrylic, epoxy or latex-based protective coatings may similarly be applied to the imprinted surface after the impression step to seal the surface and enhance its visual appeal. 
     One drawback to the &#39;402 method is that the decorative coating may wear off over time, particularly in high traffic areas. Further, as mentioned above, application of coatings in a liquid form is time consuming and poses technical difficulties. For example, if the coating is not spread to a consistent depth an unappealing visual effect may result. The need has therefore arisen for improved methods for coating asphalt surfaces by application of heat to pre-formed thermoplastic sheets. 
     It is known in the prior art to impress patterns in thermoplastic coatings on-site for functional or decorative purposes. For example, Prismo Universal Corporation has used and described a process for applying a relative thick layer (i.e. approximately 15 mm) of thermoplastic to an underlying substrate in a heated, pliable form. The thermoplastic is then manually stamped in the desired pattern by applicators wearing insulated, heat-protective clothing. The process is very labour-intensive and potentially dangerous. Since the stamping is performed manually, it is difficult to apply consistently render complicated patterns over large surface areas. Moreover, the stamping is intended to impress patterns in the thick thermoplastic layer rather than the underlying substrate. 
     The need has therefore arisen for improved methods and materials for applying a thermally settable coating to a patterned substrate, such as an imprinted asphalt surface. 
     SUMMARY OF INVENTION 
     In accordance with the invention, a method of applying a coating to a substrate is provided comprising (a) forming a first pattern in the substrate; (b) placing a pre-formed thermally settable sheet on the substrate; and (c) heating the sheet in situ to a temperature sufficient for the sheet to adhere to the substrate in a configuration conforming to the first pattern. 
     Preferably the sheet is formed of a thermoplastic material and the substrate is an asphalt surface. The sheet may include a first surface in contact with the asphalt surface and a second surface not in contact with the asphalt surface. The sheet preferably has a thin profile so that the thermoplastic is coated on the asphalt surface in a thickness between 30-150 mil., or more preferably between 50-125 mil. 
     The first pattern may be formed in the asphalt surface when it is in a pliable state. For example, the first pattern may be formed in a recently formed asphalt surface comprising hot asphalt or in a preexisting, re-heated asphalt surface. In one embodiment the first pattern is formed by placing a template on the asphalt surface while it is in a pliable state; imprinting the template into the asphalt surface to form the first pattern; and removing the template from the asphalt surface to expose the pattern. 
     The step of heating the sheet in situ may comprise gradually increasing the temperature of the sheet by providing a heating apparatus having a support frame extending over the sheet, the apparatus having at least one heater which is mounted for movement on the support frame in a travel path which periodically passes over the sheet. The sheet may be heated to a temperature between approximately 150-450° F., or more preferably 300-400° F. 
     The sheet may be subdividable into a plurality of discrete sections. Additionally or alternatively, a plurality of separate sheets may be provided which may be aligned adjacent one another to cover the asphalt surface. The size, shape, color and texture of the sheets may be selected for functional and/or decorative purposes. For example, each sheet may be formed in a second pattern which matches the first pattern formed in the asphalt surface. 
     In an alternative embodiment of the invention the first pattern may be formed in the thermoplastic sheet and the substrate simultaneously. In this embodiment the pre-formed thermally settable sheet is placed on an unpatterned substrate. The sheet in then gradually heated in situ to a temperature sufficient for the first surface of the sheet to adhere to the substrate. The sheet and the substrate are then imprinted to form the first pattern, such as by compressing a template placed on the second, exposed surface of the sheet. Prior to placing the template on the sheet second surface, the second surface may be treated with a bond reduction agent or coolant to minimize adherence between the template and the hot thermoplastic material of the pre-formed sheet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In drawings which illustrate embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way, 
         FIG. 1  is an perspective view of a template for forming a pattern in a pliable asphalt surface. 
         FIG. 2  is a diagrammatic side view of the template of  FIG. 1  being compressed into an asphalt surface with a drum roller. 
         FIG. 3  is a perspective view of an apparatus comprising reciprocating infrared heaters for gradually heating a work site. 
         FIG. 4  is an exploded, perspective view of a pre-formed thermoplastic sheet being placed on a patterned asphalt surface. 
         FIG. 5  is a perspective view showing the heaters of the apparatus of  FIG. 3  passing over the pre-formed sheet of  FIG. 4 . 
         FIG. 6  is a perspective view showing the thermoplastic material of the sheet of  FIGS. 4 and 5  melted on the patterned asphalt surface to form a coating thereon. 
         FIG. 7  is a cross-sectional view showing the coating conforming to the contour of the patterned asphalt surface. 
         FIG. 8  is a an exploded, perspective view of a pair of pre-formed thermoplastic sheets being placed in alignment on a patterned asphalt surface. 
         FIG. 9  is a perspective view showing the heaters of the apparatus of  FIG. 3  passing over the pre-formed sheets of  FIG. 8 . 
         FIG. 10  is a perspective view of an alternative embodiment of the invention comprising placement of a pre-formed thermoplastic sheet on an unpatterned asphalt surface and bonding of the sheet to the surface using the heaters of  FIG. 3 . 
         FIG. 11  diagrammatically illustrates the step of applying a bond reduction agent or a coolant to the exposed surface of the thermoplastic sheet. 
         FIG. 12  is a perspective view illustrating the step of simultaneously forming a pattern in the thermoplastic coating and underlying asphalt surface using a removable template. 
     
    
    
     DESCRIPTION 
     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     This application relates to a method of applying. a thermally settable coating  10  to a patterned substrate, such as an asphalt surface  12 . As shown in  FIGS. 4-6 , coating  10  may be initially applied to asphalt surface  12  in the form of one or more pre-formed sheets  14 . Sheets  14  are then gradually heated in situ as described below until a consistent bond is achieved between sheets  14  and asphalt surface  12 , thereby forming coating  10 . The heating process causes sheets  14  to conform to a pattern formed  22  in the underlying surface  12  to thereby enhance its decorative or functional effect ( FIGS. 6 and 7 ). 
     As used in this patent application the term heating “in situ”refers to heating pre-formed sheets  14  at the installation site rather than applying hot thermoplastic in a liquid form in a conventional manner directly to asphalt surface  12  and allowing it to harden. As used in this patent application “asphalt” means a paving compound for constructing roads, driveways, walkways and the like which consists of a combination of bituminous binder, such as tar, and an aggregate, such as sand or gravel. As will be appreciated by a person skilled in the art, applicant&#39;s method could also be applied to other types of patterned substrates, such as concrete or other materials capable of receiving and adhering to settable coating  10 . 
     As shown best in  FIG. 4 , each pre-formed sheet  14  has a first surface  16  which is placed in contact with asphalt surface  12  and a second, exposed surface  18  which is not placed in contact with asphalt surface  12 . In one embodiment of the invention the thickness of each sheet  14  between surfaces  16 ,  18  is within the range of approximately 30-150 mil in thickness, or more particularly 50-125 mil in thickness. Sheets  14  may be formed from thermoplastic material and are available from various suppliers, such as Lafarge Road Markings, Flint Trading, Inc. and Avery Dennison Corporation. Sheets  14  may be selected for functional purposes, such as traffic markings or corporate logos, or may be purely decorative. As shown in  FIG. 8  , a plurality of sheets  14  may be juxtaposed together in a non-overlapping arrangement to completely cover asphalt surface  12 . In an alternative embodiment, edge portions of adjacent sheets  14  could be partially overlapping. In another alternative embodiment sheets  14  may be arranged to only partially cover asphalt surface  12 , such as by maintaining gaps between adjacent sheets  14 . Further, each sheet  14  may either be continuous or discontinuous. For example, each sheet  14  could include openings or slots formed therein. As will be apparent to a person skilled in the art, the shape and configuration of sheets  14  may vary without departing from the invention. 
     A pattern may be formed in asphalt surface  12 , for example, according to the method of the Applicant described in U.S. Pat. No. 5,215,402 which is hereby incorporated by reference. More particularly, a template  20  is placed on asphalt surface  12  ( FIGS. 1 and 2 ) while it is in a pliable state (i.e. after being freshly rolled with hot asphalt or after surface re-heating). Template  20  is then compressed into asphalt surface  12  with a drum roller  21  or some other compaction apparatus to form pattern  22  therein. For example, pattern  22  may be an impression simulating the appearance of bricks and mortar or some other decorative appearance. Template  20  is then removed from surface  12  to expose pattern  22  ( FIG. 1 ). In alternative embodiments, pattern  22  could consist of protrusions rather than impressions formed in surface  12 , or some other surface texturing. Other similar means for forming pattern  22  in asphalt surface  12  may be envisaged. 
     One means for heating sheets  14  in situ is shown in  FIG. 3  and is described in WO 03/048458 A1 which is hereby incorporated by reference. In this embodiment, a portable surface heating apparatus  26  is provided for heating asphalt surface  12  and sheets  14  placed thereon. Preferably asphalt surface should be dry before the heating procedure commences. In the illustrated embodiment apparatus  26  includes a support frame  28  and a plurality of infrared heaters  30  supported for movement on support frame  28 . For example, support frame  28  may include elongated rails  30  which are supported above asphalt surface  12  by support legs  32  and housing  34 . A heater truck  36  is provided for reciprocating movement on rails  31 . Truck  36  supports a bank of heaters  30  at positions close to surface  12  (e.g. approximately 2 inches above the ground). 
     As shown in  FIGS. 4 and 5 , after pre-formed thermoplastic sheet  14  is placed on asphalt surface  12  overlying pattern  22 , infrared heaters  30  are reciprocated over sheet  14  to gradually melt the thermoplastic material (in  FIG. 5 , only the portion of apparatus  26  comprising heaters  30  is illustrated to aid in clarity). An important advantage of the heating method of  FIG. 1  is that a relatively large sheet  14 , or group of sheets  14 , and underlying asphalt surface  12  can be heated gradually and evenly. This approach avoids the disadvantages of hand-held torch heaters which cannot easily be used to evenly heat large areas and have a tendency to scorch the thermoplastic material and/or the underlying substrate. For example, depending upon their composition, some thermoplastic sheets  14  and/or asphalt surfaces  12  can scorch when subjected to sustained temperatures above approximately 325° F. In accordance with one embodiment of Applicant&#39;s heating method, asphalt surface  12  and thermoplastic sheet  14  are allowed to partially cool after each heating cycle. Thus the temperature of surface  12  (and sheet  14  applied thereto) increases gradually with successive heating cycles until the desired temperature suitable for thermoplastic/asphalt adhesion is achieved. The asphalt surface  12  is thereby subjected to a relatively slow heat soak to permit heat to gradually penetrate through and around sheet  14  below the uppermost surface layer of the asphalt. In accordance with one embodiment of the invention surface  12  and sheet  14  are gradually heated to a temperature within the range of 150-450° F. and most preferably within the range of approximately 150-450° F. 
     As shown in  FIGS. 6 and 7 , when sheet  14  is heated to a sufficiently high temperature it melts and conforms to pattern  22  formed in asphalt surface  12 , forming a coating  10  thereon. The heat source is then removed and coating  10  is allowed to harden. In further embodiments of the invention colorants or additives may be applied to coating  10  while it is still tacky to create further surface texturing or augment the decorative effect. As shown in  FIG. 6 , coating  10  may be applied to all or part of the surface pattern  22  depending upon the visual effect desired. If multiple sheets  14  are employed ( FIGS. 8 and 9 ), sheets  14  may be aligned edge to edge or gaps between adjacent sheets  14  may be maintained (i.e. portions of surface  12  imprinted with pattern  22  may remain uncoated). 
       FIGS. 10-12  show an alternative embodiment of the invention where pattern  22  is formed in both asphalt surface  12  and sheet(s)  14  simultaneously rather than sequentially. In this embodiment a pre-formed sheet  14  is place on an unpatterned asphalt surface  12 . Surface  12  may be in a freshly rolled, reheated or unheated state. As in the embodiment of  FIG. 5 , infrared heaters  30  may reciprocated over sheet  14  to gradually melt the thermoplastic material ( FIG. 10 ). Once sheet  14  has been gradually heated to a sufficiently high temperature for adhesion to the underlying asphalt surface  12 , a bond reduction agent is applied to the exposed surface  18  of sheet  14  ( FIG. 11 ). For example, the bond reduction agent may be a particulate bond breaker  40 , such as sand, or a liquid spray  42 , such as water coolant, applied to layer  18 . The purpose of the bond reduction agent is to minimize adhesion between layer  14  and the pattern forming device. 
     As shown in  FIG. 12 , the pattern forming device may comprise a removable template  20 . In the illustrated embodiment, template  20  is used to simultaneously impress pattern  22  into both sheet  14  and underlying asphalt surface  12 . The bond reduction agent referred to above minimizes adhesion between template  20  and the exposed surface  18  of sheet  14  while not affecting adhesion between surface  16  of sheet  14  and asphalt surface  12 . The result is a patterned asphalt surface  12  having a thin thermoplastic coating  10  thereon ( FIG. 12 ). 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.