United States Patent (19)
`Sturtevant et al.
`
`54
`
`75
`
`METHOD OF FORMING ANTSLP
`SURFACES ON THERMOFORMED
`PRODUCTS
`
`Inventors: Thomas M. Sturtevant, South China;
`Edward E. Cullivan, Palermo, both of
`Me.
`
`73
`
`Assignee: Custom Plastics Molding, Inc.,
`Benton, Me.
`
`21
`22)
`51
`52
`
`58)
`
`Appl. No.: 282,219
`Filed:
`Jul. 28, 1994
`Int. Cl. ... B29C 51/02; B29C 51/10
`U.S. Cl. ......................... 264/80; 264/134; 264/510;
`264/512; 264/309; 264/DIG. 72; 296/39.2
`Field of Search ................................. 264/510,511,
`264/512, 134, 309, DIG. 72, 131, 132,
`80; 427/256, 261, 264, 270, 272, 276, 421,
`422,426; 296/39.2
`
`56
`
`References Cited
`U.S. PATENT DOCUMENTS
`73,919 1/1868 Newton.
`1411,912 4/1922 Fisher.
`1,657,687
`1/1928 Schuler.
`2,120,406 6/1938 Hansen .................................... 264/309
`2,576,290 11/1951 Fisher, Jr. ............................... 427/42
`2,793,136 5/1957 Root.
`3,124,807 3/1964 Frenkel et al........................... 264/545
`3,148,103 9/1964 Gallagher ............................... 264/132
`3,450,563 6/1969 Krueger.
`3573,155 3/1971 Mitchell.
`3,598,677
`8/1971 Bergmeister et al. .
`3,629,051 12/1971 Mitchell.
`3,629,380 12/1971 Edwards .................................. 264/132
`3,878,147 4/1975 Craven.
`4,109,041 8/1978 Tellman.
`4,196,259 4/1980 Augustin et al..
`4,329,312 5/1932 Ganz ....................................... 264/309
`4,420,513 12/1983 Coke et al. .
`4,488,918 12/1984 Jofs .......................................... 156/79
`4.592583 6/1986 Dresen et al..
`4,614,686 9/1986 Coke et al. .
`4,692.370 9/1987 Reckziegel et al. .................... 427/286
`
`
`
`US005648031A
`Patent Number:
`Date of Patent:
`
`11
`45
`
`5,648,031
`Jul. 15, 1997
`
`4,693,507 9/1987 Dresen et al. .
`4,721,641
`1/1988 Bailey ....................................... 428/88
`4,745,139 5/1988 Haasl et al..
`4,760,103 7/1988 Kraft et al..
`5,053,253 10/1991 Haenggi et al..
`5,094,902 3/1992 Haenggi et al..
`5,110,657 5/1992 Ainslie.
`5,194,194 3/1993 Kato et al. .............................. 264/510
`5,263,761 11/1993 Hathaway et al. ..................... 296/39.2
`FOREIGN PATENT DOCUMENTS
`850791 10/1960 United Kingdom................... 264/134
`OTHER PUBLICATIONS
`Printing inks, Materials Handbook, 12th ed., Brady et al. ed.
`pp. 406-407 1986.
`Hans Deamer, Printing, Modern Plastics Encyclopedia
`1988, pp. 356-357 Oct. 1987.
`Primary Examiner-Catherine Timm
`Attorney, Agent, or Firm W. G. Fasse; W. F. Fasse
`57
`ABSTRACT
`A process for selectively forming an antislip surface on a
`product thermoformed from a plastic sheet is applied to
`truckbed liners, for example. The surface of the plastic sheet
`of HDPE or other thermoplastic material is cleaned and
`masked, to prepare a good molecular bonding surface on
`selected surface areas. A sprayable or liquid polymer
`selected to achieve desired characteristics of hardness and
`toughness without brittleness, such as a thermosetting elas
`tomeric polymer, is formed into droplets, which are sprayed
`or otherwise applied onto the selected surface area. The
`droplets form a stippled pattern of primarily separate bumps
`across the selected surface area to be treated, occupying
`substantially less than 50% of the exposed area. After partial
`hardening of the bumps, the plastic sheet is thermoformed at
`thermoforming temperatures to produce the thermoformed
`product. Thermoforming tightly bonds the bumps or drop
`lets to the thermoplastic sheet material, hardens the droplets
`forming macroscopic asperities, increases or enhances the
`three dimensional surface relief, and explodes some droplets
`with entrapped air to increase surface roughness.
`
`55 Claims, 4 Drawing Sheets
`
`EX1064
`Yita v. MacNeil
`IPR2020-01139
`
`

`

`US. Patent
`U.S. Patent
`
`Jul. 15, 1997
`Jul. 15, 1997
`
`Sheet 1 of 4
`Sheet 1 of 4
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`5,648,031
`5,648,031
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`10
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`

`

`US. Patent
`U.S. Patent
`
`Jul. 15, 1997
`Jul. 15, 1997
`
`Sheet 3 of 4
`Sheet 3 of 4
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`5,648,031
`5,648,031
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`

`US. Patent
`U.S. Patent
`
`Jul. 15, 1997
`Jul. 15, 1997
`
`Sheet 4 of 4
`Sheet 4 of 4
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`5,648,031
`5,648,031
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`FIG. 7
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`FIG. 7
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`68
`5 88
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`64
`84
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`85
`65
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`66 ¢
`66 82
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`4.
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`

`

`5,648,031
`5,648,031
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`1.
`1
`METHOD OF FORMING ANTISLIP
`METHOD OF FORMING ANTSLP
`SURFACES ON THERMOFORMED
`SURFACES ON THERMOFORMED
`PRODUCTS
`PRODUCTS
`
`TECHNICAL FIELD
`TECHNICAL FIELD
`This invention relates to a method for imparting slip
`This invention relates to a method for imparting slip
`resistant properties to thermoformed plastic surfaces and
`resistant properties to thermoformed plastic surfaces and
`products. The invention is particularly useful for increasing
`products. The invention is particularly useful for increasing
`the friction on load bearing and cargo carrying surfaces such
`the friction on load bearing and cargo carrying surfaces such
`as those of thermoformed pickup truck bed liners. The
`as those of thermoformed pickup truck bed liners. The
`invention selectively increases frictional effect primarily
`invention selectively increases frictional effect primarily
`through enhanced three dimensional macroscopic surface
`through enhanced three dimensional macroscopic surface
`relief and roughness so that it is effective even when the
`relief and roughness so that it is effective even when the
`surface is wet. Composition of the surface is also a factor
`surface is wet. Composition of the surface is also a factor
`contributing to the increased friction. The invention is useful
`contributing to the increasedfriction. The invention is useful
`for a variety of other practical and industrial applications as
`for a variety of other practical and industrial applications as
`well as for games and recreational products. The invention
`well as for games and recreational products. The invention
`provides a hard and tough antislip surface preferably with an
`provides a hard and toughantislip surface preferably with an
`elastomeric component and with a hardness that is notbrittle
`elastomeric component and with a hardness thatis notbrittle
`or sharp. It is suitable, for example, for bare feet applications
`or sharp.It is suitable, for example, for bare feet applications
`Such as Swimming pool Surfaces, showers, bathtubs, walks,
`such as swimming pool surfaces, showers, bathtubs, walks,
`andstairs.
`and stairs.
`
`10
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`15
`15
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`20
`20
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`2
`2
`formed plastic surfaces, which increases frictional forces
`formed plastic surfaces, which increases frictional forces
`and the coefficient of friction for wet as well as dry surfaces.
`andthe coefficient of friction for wet as well as dry surfaces.
`An advantage of the invention is that it imparts a practical
`An advantage of the invention is that it imparts a practical
`coefficient of friction substantially twice that of the closest
`coefficient of friction substantially twice that of the closest
`prior art antislip surface for both wet and dry surfaces.
`prior art antislip surface for both wet and dry surfaces.
`Another object of the invention is to increase the practical
`Another object of the inventionis to increase the practical
`coefficient of friction and frictional force on thermoformed
`coefficient of friction and frictional force on thermoformed
`plastic surfaces by means of increased three dimensional
`plastic surfaces by means of increased three dimensional
`macroscopic surface relief, asperities, and roughness. This is
`macroscopic surface relief, asperities, and roughness.This is
`to be accomplished with hard and tough materials preferably
`to be accomplished with hard and tough materials preferably
`with viscoelastic or elastomeric properties and with a hard
`with viscoelastic or elastomeric properties and with a hard-
`ness that is not brittle or sharp. The new antislip surface
`ness that is not brittle or sharp. The new antislip surface
`imparted by the invention is suitable for bare feet and can be
`imparted by the invention is suitable for bare feet and can be
`applied in both dry and wet environments such as swimming
`applied in both dry and wet environments such as swimming
`pools and Swimming pool areas, bathtubs, showers, and
`pools and swimming pool areas, bathtubs, showers, and
`bathrooms.
`bathrooms.
`A further object of the invention is to impart antislip
`A further object of the invention is to impart antislip
`properties and increase the coefficient of friction on ther
`properties and increase the coefficient of friction on ther-
`moformed plastic surfaces by the composition of the surface
`moformedplastic surfaces by the composition of the surface
`with reduced materials and expense and without the cost of
`with reduced materials and expense and without the cost of
`handling and applying continuous or integral film layers on
`handling and applying continuousor integral film layers on
`a substrate plastic surface. Furthermore, the antislip surface
`a substrate plastic surface. Furthermore, the antislip surface
`can easily be applied very selectively to only portions of the
`can easily be applied very selectively to only portions of the
`thermoformed plastic surface in any shape or configuration
`thermoformedplastic surface in any shape or configuration
`while leaving other areas untreated.
`while leaving other areas untreated.
`DISCLOSURE OF THE INVENTION
`DISCLOSURE OF THE INVENTION
`In order to accomplish the above objects, the invention
`In order to accomplish the above objects, the invention
`provides a new process for selectively forming an antislip
`provides a new process for selectively forming an antislip
`surface on a product thermoformed from a plastic sheet. The
`surface on a product thermoformed from a plastic sheet. The
`plastic sheet may be formed of any suitable thermoplastic
`plastic sheet may be formed of any suitable thermoplastic
`polymer material such as polyethylene, ABS, synthetic
`polymer material such as polyethylene, ABS, synthetic
`rubber, thermoplastic polymers such as polypropylene, and
`rubber, thermoplastic polymers such as polypropylene, and
`e.g. other polyolefin thermoplastic polymers. Typically the
`e.g. other polyolefin thermoplastic polymers. Typically the
`method proceeds by cleaning the surface of the plastic sheet
`method proceeds by cleaning the surface of the plastic sheet
`for removing oils and other contaminants and preparing a
`for removing oils and other contaminants and preparing a
`good bonding surface. The method further proceeds by
`good bonding surface. The method further proceeds by
`masking the plastic sheet for exposing selected surface areas
`maskingtheplastic sheet for exposing selected surface areas
`to be treated with the antislip surface and covering other
`to be treated with the antislip surface and covering other
`areas not to be treated. In some applications the cleaning and
`areas notto be treated. In someapplications the cleaning and
`masking steps are not required.
`masking steps are not required.
`An embodiment of the invention includes atomizing into
`An embodiment of the invention includes atomizing into
`droplets a sprayable polymer, preferably a thermosetting
`droplets a sprayable polymer, preferably a thermosetting
`elastomeric polymer or other polymer having a viscoelastic
`elastomeric polymer or other polymer having a viscoelastic
`or elastomeric component and a relatively rapid reaction
`or elastomeric component and a relatively rapid reaction
`time. Other polymers which harden to a hard tough plastic
`time. Other polymers which harden to a hard tough plastic
`material without brittleness or sharpness can also be used as
`material withoutbrittleness or sharpness can also be used as
`hereafter described. The invention proceeds by flash spray
`hereafter described. The invention proceeds by flash spray-
`ing a mist of the atomized droplets onto the masked plastic
`ing a mist of the atomized droplets onto the masked plastic
`sheet, or otherwise forming and applying the droplets to the
`sheet, or otherwise forming and applying the droplets to the
`selected exposed area of the plastic sheet. The droplets are
`selected exposed area of the plastic sheet. The droplets are
`deposited so that they form a stippled pattern of primarily
`deposited so that they form a stippled pattern of primarily
`separate bumps or pimples across the treated surface area.
`separate bumps or pimples across the treated surface area.
`The method also includes controlling the time duration of
`The method also includes controlling the time duration of
`the flash spraying or otherwise controlling the application of
`the flash spraying or otherwise controlling the application of
`droplets so that the bumps or pimples cover or occupy
`droplets so that the bumps or pimples cover or occupy
`substantially less than 50% of the treated surface area
`substantially less than 50% of the treated surface area
`leaving the underlying plastic sheet substantially exposed
`leaving the underlying plastic sheet substantially exposed
`between the droplets.
`between the droplets.
`By reason of the masking step, the stippled pattern of
`By reason of the masking step, the stippled pattern of
`primarily separate droplets or pimples can be selectively
`primarily separate droplets or pimples can be selectively
`applied over only a portion of the HDPE sheetin any desired
`applied over only a portion of the HDPE sheetin any desired
`shape or area configuration. The treated surface area can
`shape or area configuration. The treated surface area can
`thereby be limited for example to a cargo carrying surface or
`thereby be limited for example to a cargo carrying surface or
`only a portion of the cargo carrying surface. By way of
`only a portion of the cargo carrying surface. By way of
`example, only a fraction of the cargo carrying surface, such
`example, only a fraction of the cargo carrying surface, such
`
`25
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`BACKGROUND ART
`BACKGROUND ART
`Essentially all truck bed liners are thermoformed from
`Essentially all tuck bed liners are thermoformed from
`high density polyethylene (HDPE) sheets. Other materials
`high density polyethylene (HDPE) sheets. Other materials
`such as ABS, synthetic rubber plastic, and other thermo
`such as ABS, synthetic rubber plastic, and other thermo-
`plastic polymers are sometimes used. The thermoplastic
`plastic polymers are sometimes used. The thermoplastic
`sheets are heated to a thermoforming temperature in a
`sheets are heated to a thermoforming temperature in a
`thermoforming oven and are deformed by ambient air pres
`thermoforming oven and are deformed by ambientair pres-
`sure after application of vacuum on one side in a thermo
`sure after application of vacuum on one side in a thermo-
`forming mold to produce the desired product. Many prod
`forming mold to produce the desired product. Many prod-
`ucts other than truckbed liners are also manufactured by this
`ucts other than truck bed liners are also manufactured by this
`process. A disadvantage of the HDPE material howeveris its
`process. A disadvantage of the HDPE material howeverisits
`low coefficient of friction. HDPE surfaces become even
`low coefficient of fiction. HDPE surfaces become even
`more slippery when wet.
`more slippery when wet.
`U.S. Pat. No. 4,693,507 (Dresen et al.) describes a truck
`US. Pat. No. 4,693,507 (Dresen et al.) describes a truck
`bed liner with antislip surface properties. Increased coeffi
`bed liner with antislip surface properties. Increased coeffi-
`cient of friction on the liner surface is achieved by applying
`cient of friction on the liner surface is achieved by applying
`a continuous film or layer of elastomeric material over the
`a continuous film or layer of elastomeric material over the
`HDPE sheet. The thickness of the integral elastomeric layer
`HDPE sheet. The thickness of the integral elastomeric layer
`or film is typically in the range of 25 mills-30 mils
`or film is typically in the range of 25 mils—30 mils
`(625-750). The elastomeric film is preferably coextruded
`(625p—750y). The elastomeric film is preferably coextruded
`over the HDPE sheet which is typically 180 mils-250 mils
`over the HDPE sheet which is typically 180 mils—250 mils
`(4.5 mm-6.2 mm) in thickness. Dresen et al. further state
`(4.5 mm-6.2 mm) in thickness. Dresen et al. further state
`that the elastomeric film layer can alternatively be applied to
`that the elastomeric film layer can alternatively be applied to
`the HDPE sheet by lamination, by adhesive, or by heat
`the HDPE sheet by lamination, by adhesive, or by heat
`application.
`application.
`According to the Dresen et al. scheme, an increased
`According to the Dresen et al. scheme, an increased
`frictional force is therefore achieved primarily by the "plow
`frictional force is therefore achieved primarily by the “plow-
`ing effect” or embedding effect of harder cargo pieces
`ing effect” or embedding effect of harder cargo pieces
`pressing into the softer continuous elastomer film layer. This
`pressing into the softer continuous elastomer film layer. This
`antislip plowing effect is attributable to the continuous film
`antislip plowing effect is attributable to the continuous film
`or layer of the softer elastomer. A disadvantage of the Dresen
`or layer of the softer elastomer. A disadvantage of the Dresen
`et al. Scheme however, is that the frictional force attributable
`et al. scheme however,is that the frictional force attributable
`to the integral elastomeric layer is reduced, and the layer
`to the integral elastomeric layer is reduced, and the layer
`also becomes slippery, when it is wet. Another disadvantage
`also becomesslippery, when it is wet. Another disadvantage
`of the Dresen et al. method is the increase in cost of adding
`of the Dresen et al. method is the increase in cost of adding
`and applying the integral and continuous film layer of
`and applying the integral and continuous film layer of
`elastomeric material by coextrusion, lamination, adhesion,
`elastomeric material by coextrusion, lamination, adhesion,
`or heat application. The elastomer film of Dresen et al.
`or heat application. The elastomer film of Dresen et al.
`generally extends across the entire substrate plastic sheet.
`generally extends across the entire substrate plastic sheet.
`OBJECTS OF THE INVENTION
`OBJECTS OF THE INVENTION
`It is therefore an object of the present invention to provide
`It is therefore an object of the present inventionto provide
`a new method of imparting antislip properties to thermo
`a new method of imparting antislip properties to thermo-
`
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`as one half of the surface, can be treated for a higher
`as one half of the surface, can be treated for a higher
`coefficient of friction while the other half remains as an
`coefficient of friction while the other half remains as an
`HDPEsurface with lower coefficient of friction. Thus the
`HDPE surface with lower coefficient of friction. Thus the
`right half of the truck bed liner surface may be treated to
`right half of the truck bed liner surface may betreated to
`provide an antislip surface for cargo containers while the left
`provide an antislip surface for cargo containers while theleft
`halfpermits sliding of the objects for loading and unloading.
`half permits sliding of the objects for loading and unloading.
`As a further alternative, the stippled pattern of primarily
`As a further alternative, the stippled pattern of primarily
`separate droplets need not be selectively applied and the
`separate droplets need not be selectively applied and the
`masking step can be eliminated. For example, the entire
`masking step can be eliminated. For example, the entire
`HDPE sheet can be treated with the stippled pattern of
`HDPE sheet can be treated with the stippled pattern of
`separate droplets to impart antislip properties over all the
`separate droplets to impart antislip properties over all the
`surfaces of the truck bed liner or other thermoformed
`surfaces of the truck bed liner or other thermoformed
`product.
`product.
`As a next step of the invention, the droplets forming the
`As a next step of the invention, the droplets forming the
`stippled pattern are at least partially hardened, dried and
`stippled pattern are at least partially hardened, dried and
`solidified in an initial drying step. The plastic sheet is then
`solidified in an initial drying step. The plastic sheet is then
`thermoformed according to standard thermoforming proce
`thermoformed according to standard thermoforming proce-
`dures at thermoforming temperatures to produce the prod
`dures at thermoforming temperatures to produce the prod-
`uct. The thermoforming process causes intimate bonding of
`uct. The thermoforming process causes intimate bonding of
`the droplets to the plastic sheet and relative hardening of the
`the droplets to the plastic sheet and relative hardening of the
`droplets to form three dimensional macroscopic asperities
`droplets to form three dimensional macroscopic asperities
`having an enhanced relief and surface roughness, causing a
`having an enhancedrelief and surface roughness, causing a
`relatively higher coefficient of friction over the treated
`relatively higher coefficient of friction over the treated
`surface area.
`Surface area.
`Thus, a feature of the invention is that the process steps
`Thus, a feature of the invention is that the process steps
`produce an antislip surface across the treated surface area
`produce an antislip surface across the treated surface area
`with enhanced relief in the form of three dimensional
`with enhanced relief in the form of three dimensional
`macroscopic asperities and surface roughness. These mac
`macroscopic asperities and surface roughness. These mac-
`roscopic asperities of the antislip surface engage the peaks,
`roscopic asperities of the antislip surface engage the peaks,
`30
`30
`valleys and surface relief of objects placed on the antislip
`valleys and surface relief of objects placed on the antislip
`Surface by interlocking of asperities and macroscopic rough
`surface by interlocking of asperities and macroscopic rough-
`ness on the two surfaces. As a result, the coefficient of
`ness on the two surfaces. As a result, the coefficient of
`friction and frictional force is substantially increased, and is
`friction andfrictional force is substantially increased, and is
`subsequently not substantially reduced when the surfaces are
`subsequently not substantially reduced whenthe surfaces are
`wet. The enhanced surface roughness and macroscopic
`wet. The enhanced surface roughness and macroscopic
`asperities are achieved by several coacting effects of the
`asperities are achieved by several coacting effects of the
`interacting process steps.
`interacting process steps.
`First it has been found that the thermoforming tempera
`First it has been found that the thermoforming tempera-
`tures cause an intimate physical or chemical bond between
`tures cause an intimate physical or chemical bond between
`the thermosetting elastomeric polymer droplets and the
`the thermosetting elastomeric polymer droplets and the
`plastic sheet typically composed of high density polyethyl
`plastic sheet typically composed of high density polyethyl-
`ene. The bonding between the droplets and the HDPE sheet
`ene. The bonding between the droplets and the HDPE sheet
`is apparently as strong as the bonding of polyethylene to
`is apparently as strong as the bonding of polyethylene to
`polyethylene, and the droplets cannot be scraped off without
`polyethylene,and the droplets cannot be scraped off without
`cutting through the bonded materials. This bonding between
`cutting through the bonded materials. This bonding between
`the droplets and the HDPE sheet is enhanced by mixing with
`the droplets and the HDPE sheetis enhanced by mixing with
`the thermosetting elastomer a small amount of an adhesion
`the thermosetting elastomer a small amount of an adhesion
`promoter which bonds or cross links both to the thermoset
`promoter which bondsor cross links both to the thermoset-
`ting elastomer and to the HDPE sheet.
`ting elastomer and to the HDPE sheet.
`Second it appears that the thermoforming temperatures
`Second it appears that the thermoforming temperatures
`cause a relative hardening and thermosetting of the thermo
`cause a relative hardening and thermosetting of the thermo-
`set elastomeric polymer that was sprayed in droplet form
`set elastomeric polymer that was sprayed in droplet form
`and initially hardened, dried and cured on the exposed
`and initially hardened, dried and cured on the exposed
`Surface areas of the plastic sheet. While the thermosetting
`surface areas of the plastic sheet. While the thermosetting
`elastomer retains some elastomeric properties, there is a
`elastomer retains some elastomeric properties, there is a
`hardening relative to its properties prior to heat curing. The
`hardening relative to its properties prior to heat curing. The
`increased coefficient of friction and frictional force effect is
`increased coefficient of friction and frictional force effect is
`therefore achieved not primarily by elastomeric properties
`therefore achieved not primarily by elastomeric properties
`but by the relative hardness of the droplets forming macro
`but by the relative hardness of the droplets forming macro-
`scopic asperities across the treated surface area. Other
`scopic asperities across the treated surface area. Other
`sprayable or liquid polymers that are formable into droplets
`sprayable or liquid polymers that are formable into droplets
`and hardened by the thermoforming process can also be used
`and hardened bythe thermoforming processcan also be used
`as hereafter described.
`as hereafter described.
`Third, the projecting islands, pimples, or projections
`Third,
`the projecting islands, pimples, or projections
`formed by the droplets bonded and hardened across the
`formed by the droplets bonded and hardened across the
`treated surface area are enhanced in relief by an effect
`treated surface area are enhanced in relief by an effect
`
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`4
`4
`referred to by the inventor as the “moth effect”. Thermo
`referred to by the inventor as the “moth effect”. Thermo-
`forming heat is generally applied to both sides of the plastic
`forming heat is generally applied to both sides of the plastic
`sheet by a variety of heater arrangements such as, for
`sheet by a variety of heater arrangements such as, for
`example, infra-red radiant heaters, such as catalytic gas
`example, infra-red radiant heaters, such as catalytic gas
`burners for example. Electrical heating elements with blow
`burners for example. Electrical heating elements with blow-
`ers are also typically used. The inventors have noted that if
`ers are also typically used. The inventors have noted that if
`a moth falls on the plastic sheet before or during heating of
`a moth falls on the plastic sheet before or during heating of
`the sheet, then a corresponding moth-shaped outline or
`the sheet,
`then a corresponding moth-shaped outline or
`plateau rising slightly above the surrounding area of the
`plateau rising slightly above the surrounding area of the
`sheet will be formed during the thermoforming process. It is
`sheet will be formed during the thermoforming process.It is
`believed this effect is due to “shading" or "screening"
`believed this effect is due to “shading” or “screening”
`provided by the moth, which produces a temperature dif
`provided by the moth, which produces a temperature dif-
`ferential. Thereby, the higher temperature areas surrounding
`ferential. Thereby, the higher temperature areas surrounding
`the shaded outline of the moth are subject to differential
`the shaded outline of the moth are subject to differential
`thermoforming and thinning, so that the surrounding areas
`thermoforming and thinning, so that the surrounding areas
`are more greatly vacuum thinned and pulled away from the
`are more greatly vacuum thinned and pulled away from the
`moth shaded area. This causes a slightly differential thick
`moth shaded area. This causes a slightly differential thick-
`ness or enhanced surface relief according to the pattern of
`ness or enhanced surface relief according to the pattern of
`differential temperatures.
`differential temperatures.
`Similarly it has been observed that the droplets forming a
`Similarly it has been observed that the droplets forming a
`stippled pattern across the treated surface area shade or
`stippled pattern across the treated surface area shade or
`screen the spots under the droplets from the heat sources
`screen the spots under the droplets from the heat sources
`used to bring the plastic sheet to thermoforming tempera
`used to bring the plastic sheet to thermoforming tempera-
`tures. The stippled pattern of droplets thus produces a
`tures. The stippled pattern of droplets thus produces a
`corresponding stippled pattern of shading and differential
`corresponding stippled pattern of shading and differential
`temperatures across the surface area to be treated. During
`temperatures across the surface area to be treated. During
`thermoforming, the areas of the plastic sheet surrounding the
`thermoforming,the areas of the plastic sheet surrounding the
`droplets are vacuum formed or thermoformed and pulled to
`droplets are vacuum formed or thermoformed and pulled to
`a lesser thickness than the shaded areas under the droplets.
`a lesser thickness than the shaded areas under the droplets.
`This effect enhances the relief, projection and elevation of
`This effect enhances the relief, projection and elevation of
`the macroscopic asperities, and roughness across the treated
`the macroscopic asperities, and roughnessacrossthe treated
`surface area.
`surface area.
`Finally, some of the droplets atomized from the viscous
`Finally, some of the droplets atomized from the viscous
`thermosetting elastomeric polymer entrap air. The entrapped
`thermosetting elastomeric polymerentrap air. The entrapped
`air may explode through the top of the droplet during
`air may explode through the top of the droplet during
`thermoforming thereby forming rough edges on the droplets
`thermoforming thereby forming rough edges on the droplets
`to increase the coefficient of friction. The increased rough
`to increase the coefficient of friction. The increased rough-
`ness is achieved on the hard, tough pimples without brittle
`ness is achieved on the hard, tough pimples without brittle-
`ness or sharpness.
`ness or sharpness,
`In the preferred example embodiment the process
`In the preferred example embodiment the process
`includes cleaning the surface of the plastic sheet by flame
`includes cleaning the surface of the plastic sheet by flame
`treatment for burning off contaminants and preparing a good
`treatment for burning off contaminants and preparing a good
`bonding surface, applying the droplets, drying and solidify
`bonding surface, applying the droplets, drying andsolidify-
`ing the droplets forming the stippled pattern over the treated
`ing the droplets forming the stippled pattern over the treated
`surface area, and thermoforming the HDPE sheet toform the
`surface area, and thermoforming the HDPE sheet to form the
`final product in the thermoforming temperature range of
`final product in the thermoforming temperature range of
`250°F-550°F, and preferably in the range of 370° F-400°
`250° F.-550° F. and preferably in the range of 370° F—400°
`F. The step of initially drying and solidifying the droplets
`F, Thestep of initially drying and solidifying the droplets
`before thermoforming can be accelerated by heating. The
`before thermoforming can be accelerated by heating. The
`time duration of the flash spraying may be controlled to an
`time duration of the flash spraying may be controlled to an
`interval for example down to a fraction of a second through
`interval for example downto a fraction of a second through
`a spray head at a relatively high pressure, for example in the
`a spray headat a relatively high pressure, for example in the
`range of 1,000–2,000 pounds. Typically the flash spraying is
`range of 1,000-2,000 pounds. Typically the flash sprayingis
`from a spray head at a distance from the HDPE sheet in the
`from a spray head at a distance from the HDPE sheet in the
`range of 2.5–4.5' (0.75 m-135 m).
`range of 2.5'-4.5' (0.75 m-1.35 m).
`According to the preferred examples, the sprayable poly
`According to the preferred examples, the sprayable poly-
`mer is selected to form hard and tough pimples durably
`mer is selected to form hard and tough pimples durably
`bonded over the selected antislip surface after thermoform
`bonded over the selected antislip surface after thermoform