Retroreflective polymer coated flexible fabric material and method of manufacture

A process and article for a retroreflective polymeric coated flexible fabric material having a retroreflective layer and a polymeric compatibilizing layer welded to a polymeric coated outer surface of a flexible fabric material. The compatibilizing layer provides an intermediate layer between the retroreflective layer and the flexible fabric material creating suitable bond strength between dissimilar polymers.

FIELD OF THE INVENTION 
The invention relates to retroreflective vehicle covers and in particular 
to radio frequency welding retroreflective devices to the vehicle cover. 
BACKGROUND OF THE INVENTION 
Retroreflective conspicuity devices have been developed for use to increase 
safety and visibility especially during periods of reduced visibility. 
Generally, the problems related to attaching retroreflective conspicuity 
sheeting to rigid substrates have been solved. However, difficulties are 
encountered when it is desirable to attach retroreflective markings to a 
polymeric coated fabric material. Retroreflective conspicuity markings 
must be attachable to a flexible substrate, such as fabric material, 
without interfering with the life and function of the substrate. 
Articles which use flexible fabric materials, such as a trailer tarpaulin 
or a roll-up sign, will typically have a life span up to about ten years. 
Flexible vehicles covers are particularly convenient, permitting the 
operator of the vehicle to gain access to the trailers quickly and 
conveniently, and to allow the trailer compartment to maintain reasonable 
weatherproofing abilities. The vehicle operator may open and close a cover 
numerous times each day, therefore the cover should be flexible but 
strong. 
The vehicle cover must withstand harsh weather conditions as well as the 
mechanical demands placed on it by the operator. The covers encounter 
extremes in temperature, chemical challenges from atmospheric pollution 
and road salt, and photo-reaction involving infrared, visible and 
ultraviolet radiation from sunlight. A retroreflective cover must remain 
flexible and weatherproof throughout the expected life span. 
Flexible fabric materials are typically fabrics manufactured from 
polyester, nylon or cotton. The fabric is usually coated with a suitable 
polymer, with the most useful being highly plasticized polyvinyl chloride 
(PVC). 
Highly plasticized PVC is durable and convenient to work with. Highly 
plasticized PVC is normally attachable to itself or some other suitable 
polymers with the use of heat or radio frequency welding. Large fabric 
materials coated with PVC are manufactured by welding smaller panels 
together. Torn or damaged PVC coated fabric materials are often repairable 
while still on the vehicle. However, problems are encountered when 
attempting to use adhesives with PVCs due to the plasticizers which 
migrate from the PVC into the adhesive. This softens the adhesive and 
causes loss of its cohesive strength. Another problem relates to 
mechanical attachment, such as sewing, of materials to PVC flexible 
covers. This form of attachment often interferes with the waterproofing 
characteristic of a polymeric coated fabric material. 
Other means of attaching PVC coated flexible fabrics include use of thermal 
and radio frequency energy. A thermal fusion technique, using heat for 
example from a source such as a hot air gun, increases the thermal kinetic 
motion of all of the atoms in the polymer chains. When the temperature of 
the polymer is increased to the melt temperature, the polymer is able to 
flow adequately to form a bond. For thermoplastic polymers, melting occurs 
at a temperature below the temperature at which degradation occurs. For 
suitable thermal fusion to occur, the polymers to be fused should have 
similar melting temperatures. An example of melting temperature 
compatibility is highly plasticized PVC and polyurethane. An example of 
incompatibility is highly plasticized PVC and polycarbonate, because of 
the substantially higher melting temperature for polycarbonate. 
Radio frequency (RF) welding is an alternative to thermal fusion. RF 
welding accomplishes fusion through the presence of polymer polar groups 
converting the radio frequency energy into kinetic motion which heats the 
polymer. When a radio frequency field is applied to a thermoplastic 
polymer with polar groups, the ability of the polar groups to switch 
orientation in phase with the radio frequency will determine the degree to 
which RF energy is absorbed and converted to kinetic motion of the polar 
group. This kinetic energy is conducted as heat to the entire polymer 
molecule. If enough RF energy is applied, the polymer will heat 
sufficiently to melt. A useful measure in determining the degree to which 
a polymer will absorb energy from an alternating field is the relation of 
the polymer's dielectric constant and the dielectric dissipation factor 
known as the loss factor and is given by the following relationship: 
EQU N=5.55.times.10.sup.-13 (.function.)(.Fourier..sup.2)(K)(tan.delta.); eq. 1 
where N is the electric loss in watts/cm.sup.3 -sec, .function. is 
frequency in Hertzisec, .Fourier. is field strength in volts/cm, K is the 
dielectric constant, and .delta. is the loss angle (tan.delta. is the 
dissipation factor). 
This dissipation factor is the ratio of the in-phase to out of phase power. 
If the polar groups in a thermoplastic polymer have a relative inability 
to switch orientations in the RF field, this results in a phase lag. This 
phase lag is known as the loss factor. The higher the dissipation factor, 
the greater the amount of heat a RF field will generate. Studies with 
thermoplastic polymers and radio frequency welding have demonstrated that 
thermoplastic polymers with dissipation factors of approximately 0.065 or 
higher will form useful welds. For example, PVC has a dissipation factor 
of approximately 0.09 to 0.10 at 1 MHz, nylon caprolactam has a 
dissipation factor of 0.06 to 0.09 and polycarbonate has a dissipation 
factor of only 0.01. The respective dielectric constants for these three 
compounds are 3.5, 6.4, and 2.96 at 1 MHz. 
Polyethylene, polystyrene, and polycarbonate have very low dissipation 
factors and in practical use have poor radio frequency welding capability. 
The polyvinyl chlorides, polyurethanes, nylon, and polyesters have 
reasonably high dissipation factors and have been found in practical use 
to form very functional RF welds. Reference is made to the article "RF 
Welding of PVC and Other Thermoplastic Compounds" by J. Leighton, T. 
Brantley, and E. Szabo in ANTEC 1992, pps. 724-728. These authors did not 
attempt to weld polycarbonate to the other polymers because of the 
understanding in the art that a useful weld, using RF energy, would always 
fail to form. 
Only those polar groups within the RF field will be put into motion. The 
convenience of RF welding is realized by this controlled heating of only 
the molecules within the RF field. The need for thermal insulation is 
obviated by the use of RF welding. 
PCT Application WO 93/10985 published Jun. 10, 1993, discloses attaching 
PVC retroreflective articles to a tarpaulin cloth coated with PVC using RF 
welding. This combination was then hot air fused to a tarpaulin vehicle 
cover also coated with PVC. To thermally weld the PVC coated cloth to the 
PVC coated tarpaulin cover, the two surfaces are heated to approximately 
400 to 600.degree. C. and the surfaces then pressed together to accomplish 
the hot air fusion. The purpose of the intermediate tarpaulin cloth 
attachment was to provide thermal insulation between the hot air and the 
retroreflective article attached to the tarpaulin cloth to prevent thermal 
melting, loss of retroreflection and destruction of the retroreflective 
article. 
Cube corner retroreflective articles constructed from PVC have relatively 
low coefficients of retroreflectivity, generally in the region of 
approximately 250 candelas per lux per square meter or less. A 
retroreflective flexible fabric material using high brightness flexible 
polymer prismatic retrororeflective elements that is relatively simple to 
attach to the flexible fabric would be desirable. 
SUMMARY OF THE INVENTION 
This invention provides a high brightness, flexible, durable, 
retroreflective sheeting compatible for attachment to polymer coated 
flexible fabric material comprising a polymeric prismatic retroreflective 
layer having a high coefficient of retroreflectivity and a polymeric 
compatibilizing layerfor attachement to a flexible polymeric coated fabric 
material. This invention provides a high brightness, flexible, durable, 
retroreflective sheeting compatible for attachment to polymer coated 
flexible fabric material comprising a polymeric prismatic retroreflective 
layer having a high coefficient of retroreflectivity, a polymeric 
compatibilizing layer, and a flexible polymeric coated fabric material. 
The polymeric prismatic retroreflective layer will have a coefficient of 
retroreflectivity greater than about 250 candelas per lux per square meter 
and preferably greater than 400 candelas per lux per square meter. The 
flexible fabric material is suitable for use for personal items of 
fashion, garments, and safety devices, as well as use on vehicles as 
vehicle covers, tarpaulins, and conspicuity markers. A useful flexible 
fabric material is durable as well as flexible. The compatibilizing layer 
is a polymeric material having characteristics suitable for bonding 
between a retroreflective layer and a flexible fabric material under 
conditions using radio frequency welding and/or selective or patterned 
thermal welding. 
A compatibilizing layer is critical in that high brightness retroreflective 
layers use polymeric material that is dissimilar to the polymeric coating 
commonly used on flexible fabric materials. A useful compatibilizing layer 
will form an adequate bond to a retroreflective layer that is 
characterized by a tensile bond greater than 270 Newtons (60 lb.sub.f). 
The compatibilizing layer will adequately bond with the polymeric coated 
outer surface of a flexible fabric material as characterized by a T-peel 
force greater than 8.8 N/cm (5 lbs/in). A useful compatibilizing layer 
overcomes a bonding, or attachment, incompatibility between a high 
brightness polymeric retroreflective layer and the polymeric coated outer 
surface of a flexible fabric material. 
Mechanical durability, visibility, and attachment can be suitably altered 
by providing a suitable polymer film overlay to the retroreflective layer. 
Along with the retroreflective layer the overlay may incorporate 
ultraviolet stabilizers to increase durability and may also carry colored 
or pigmented dyes to further enhance daytime visibility. 
The polymer compatibilizing layer is characteristically a thermoplastic 
polymer having generally a lower melting point in relation to the chosen 
polymer used in the retroreflective layer and will generally have a 
favorable dielectric loss factor. Where flexible fabric materials have 
been coated on their outer surface with PVC polymers plasticized with 
monomeric plasticizers, the compatibilizing layer can be chosen to 
adequately perform as a barrier to plasticizer migration. A suitable 
compatibilizing layer is not limited to a single polymer layer, but may 
also include multiple layers of compatible polymers to accomplish the 
bonding of a high brightness retroreflective layer to a polymeric coated 
flexible fabric material.

DETAILED DESCRIPTION OF TEE INVENTION 
The invention provides useful retroreflective flexible fabric material 
adaptable for use in numerous applications, for example, but not limited 
to, use by humans in articles of clothing for safety or fashion or 
accessories such as a personal bag or back pack, use for articles for pets 
and other animals, as well as articles for use on signs and machinery such 
as road signs, roll up signs, flexible vehicle covers, tarpaulins, warning 
tapes, and conspicuity markings. The retroreflective flexible fabric may 
comprise all or just a portion of any of these articles. These materials 
may also be useful in decorative and structural webbing for displaying 
graphic designs and logos as well as providing patches for attachment to 
such articles. 
The most common flexible fabric material having a polymeric coated surface 
is fabric material using PVC that has been plasticized with monomeric 
plasticizers. Suitable base fabrics are weaves or scrims from nylon, 
polyester, and cotton. Generally, the PVC polymer is coated on at least 
the outer surface of the flexible fabric base and may contain additional 
chemicals for coloring and stabilization of the PVC for improved 
durability, weatherability, and wearability. Often, an additional very 
thin coating of acrylic will be applied over a surface coated with PVC to 
enhance the hardness of the PVC surface without significantly altering the 
physical and chemical properties of the PVC coating. 
The PVC provides good flexibility, resistance to abrasion, stability to 
ultraviolet rays, and performance in cold temperatures. But PVC is also 
highly plasticized with monomeric plasticizers in order to attain good 
flexibility. Typically the PVC will contain up to 30 to 40% by weight of 
monomeric plasticizers. 
An alternate useful polymeric material for coating at least an outer 
surface of a fabric base is ethylene acrylic acid copolymer (EAA). Like 
the PVC polymer, EAA is flexible, durable, and resistent to abrasion but 
maintains flexibility without the need for plasticizers. 
The present invention provides a high brightness retroreflective polymeric 
flexible fabric material by providing a compatibilizing means for 
attaching a high brightness polymeric prismatic retroreflective layer to a 
polymeric coated flexible fabric material. Polymeric prismatic 
retroreflective layers are well known in the art as well as the actual 
geometric configuration of the prismatic elements on a surface of the 
retroreflective layer or sheet. Suitable polymeric materials for use in 
the retroreflective layer provide a high coefficient of retroreflectivity. 
For the purposes of this invention, a high coefficient of retroreflectivity 
is at least about 250 candelas per lux per square meter at 0.2.degree. 
observation angle and -4.degree. entrance angle for the average of 
0.degree. and 90.degree. orientation angles. In the present invention 
polymers useful in the retroreflective layer will meet and preferably 
exceed this level, preferably providing greater than 400 candelas per lux 
per square meter and even more preferably providing greater than 600 
candelas per lux per square meter. This optical performance requirement 
limits the suitability of PVC prismatic elements due to the unsuitability 
of PVC to provide a high coefficient of retroreflectivity for any length 
of time. This is principally due to the use of the monomeric plasticizers 
within the PVC and land layer of the retroreflective layer. The tradeoff 
is the need to provide flexibility using the monomeric plasticizers, but 
at the cost of allowing migration of the monomeric plasticizers causing 
deterioration of the optics in a retroreflective layer using PVC as the 
polymer. The invention provides a compatibilizing layer that performs as a 
barrier to monomeric plasticizer migration form a PVC coated flexible 
fabric and the polymeric prismatic elements. 
The polymeric materials considered useful for the present invention include 
but are not limited to polymers able to transmit at least 70% of the 
intensity of the light incident upon the polymer at a given wavelength. 
More preferably, the polymers that are used in the retroreflective layer 
of the invention have a light transmissibility of greater than 80%, and 
more preferably greater than 90%. The polymeric materials that are 
employed in the prismatic elements may be thermoplastic or cross-linkable 
resins. 
Examples of thermoplastic polymers that may be used in the prismatic 
elements and the retroreflective layer include acrylic polymers such as 
poly(methylmethacrylate); polycarbonates; cellulosics; polyesters such as 
poly(butyleneterephthalate); poly(ethyleneterephthalate); fluoropolymers; 
polyamides; polyetherketones; poly(etherimide); polyolefins; 
poly(styrene); poly(styrene) co-polymers; polysulfone; urethanes, 
including aliphatic and aromatic polyurethanes; and mixtures of the above 
polymers such as a poly(ester) and poly(carbonate) blend, and a 
fluoropolymer and acrylic polymer blend. Background reference for some 
possible aliphatic urethanes is made to U.S. Pat. No. 5,117,304 (Huang et 
al.). 
Additional materials suitable for forming the polymeric prismatic elements 
and the retroreflective layer include reactive resin systems capable of 
being cross-linked by a free radical polymerization mechanism by exposure 
to actinic radiation, for example, electron beam, ultraviolet light, or 
visible light. Additionally, these materials may be polymerized by thermal 
means with the addition of a thermal initiator such as benzoyl peroxide. 
Radiation initiated cationic polymerizable resins also may be used. 
Reactive resins suitable for forming the prismatic elements and the 
retroreflective layer may include blends of photoinitiator and at least 
one compound bearing an acrylate group. Preferably the resin blend 
contains a monofunctional, a difunctional, or a polyfunctional compound to 
ensure formation of a cross-linked polymeric network upon irradiation. 
Examples of resins that are capable of being polymerized by a free radical 
mechanism include acrylic-based resins derived from epoxies, polyesters, 
polyethers, and urethanes, ethylenically unsaturated compounds, aminoplast 
derivatives having at least one pendant acrylate group, isocyanate 
derivatives having at least one pendant acrylate group, epoxy resins other 
than acrylated epoxies, and mixtures and combinations thereof. The term 
acrylate is used here to encompass both acrylates and methacrylates. U.S. 
Pat. No. 4,576,850 (Martens) discloses examples of cross-linked resins 
that may be used in the prismatic elements and the retroreflective layer 
of the present invention. 
Ethylenically unsaturated resins include both monomeric and polymeric 
compounds that contain atoms of carbon, hydrogen and oxygen, and 
optionally nitrogen, sulfur, and the halogens. Oxygen or nitrogen atoms, 
or both, are generally present in ether, ester, urethane, amide, and urea 
groups. Ethylenically unsaturated compounds preferably have a molecular 
weight of less than about 4,000 and preferably are esters made from the 
reaction of compounds containing aliphatic monohydroxy groups, aliphatic 
polyhydroxy groups, and unsaturated carboxylic acids, such as acrylic 
acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, 
maleic acid, and the like. 
Examples of photopolymerization initiators which can be blended with the 
acrylic compounds include the following illustrative initiators: benzil, 
methyl o-benzote, benzoin, benzoin ethyl ether, benzoin isopropyl ether, 
benzoin isobutyl ether, etc., benzylphenone/tertiary amine, acetophenones 
such as 2, 2-diethoxyacetophenone, benzyl methyl ketal, 
1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropin-1-one, 
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 
2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone, 
2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-methyl-1-4(methylthio), 
phenyl-2-morpholino-1-propinone, etc. The compounds may be used 
individually or in combination. 
Cationically polymerizable materials include but are not limited to 
materials containing epoxy and vinyl ether functional groups. These 
systems are photoinitiated by onium salt initiators. Salt initiators such 
as triarylsulfonum, and diaryliodonium salts. 
Preferred polymers for the prismatic elements include poly(carbonate), 
poly(methylmethacrylate), poly(ethyleneterephthalate), aliphatic 
polyurethanes and cross-linked acrylates such as multifunctional acrylates 
or epoxies and acrylated urethanes blended with mono-and multifunctional 
monomers. These polymers are preferred for one or more of the following 
reasons: thermal stability, environmental stability, clarity, excellent 
release from the tooling or mold, and capability of receiving a reflective 
coating. 
Many of the above-mentioned polymers for use in the prismatic elements on 
one surface of the retroreflective layer will not form adequate bonds 
directly to highly plasticized PVC or EAA. Furthermore, these prismatic 
elements may experience interference due to the migration and deposition 
of monomeric plasticizers from the plasticized PVC material either from 
direct contact or as a vapor. 
The present invention provides an article and method of manufacture for 
attaching a high brightness retroreflective layer to a flexible fabric 
material overcoming the incompatibility between high brightness 
retroreflective layers and polymeric coatings on flexible fabric 
materials. The present invention provides for suitable polymeric 
compatibilizing layers that provide for adequate bonding to a 
retroreflective layer having polymer prismatic elements on a surface as 
measured by a tensile bond test described below and also characterized by 
an adequate bonding to a polymeric coating of a flexible fabric material 
as characterized by an adequate T-peel force as measured by a T-peel test 
described below. An additional quality in a suitable polymeric 
compatibilizing layer is to act as a barrier to the migration of monomeric 
plasticizers migrating from a PVC coated flexible fabric material. 
Polymers suitable for use in a compatibilizing layer include the following 
but are not limited to polyurethane, ethylene methyl acrylate copolymer, 
ethylene N-butyl acrylate copolymer, ethylene ethyl acrylate copolymer, 
ethylene vinyl acetate copolymer, polymerically plasticized PVC, and 
polyurethane primed ethylene acrylic acid copolymer. Polymerically 
plasticized PVC is considered a distinctly different polymer from 
monomerically plasticized PVC because the polymeric plasticizers will not 
migrate from this type of PVC. Polymerically plasticized PVC will remain 
flexible and will not cause a deterioration in the optical performance of 
the retroreflective layer. 
The present invention comprises construction of a retroreflective flexible 
fabric material either from the simultaneous application of a 
retroreflective layer, compatibilizing layer and polymeric coated flexible 
fabric or a preconstruction of a retroreflective sheeting comprising a 
retroreflective layer attached to a compatibilizing layer with subsequent 
attachment of the retroreflective sheeting to a polymeric coated flexible 
fabric material. The retroreflective sheeting is constructed so as to 
maintain an excellent degree of flexibility without any cracking or 
mechanical failure. For example, the sheeting may be wrapped around curved 
or otherwise non-planar surfaces without damage. In one test, this 
flexibility was measured by wrapping the retroreflective sheeting around a 
cylindrical mandrel having a 3.2 mm (0.125 inch) diameter. The test was 
performed at 0.degree. C. with good results, i.e. no visible cracking. The 
polymers used for the retroreflective layer, compatibilizing layer and and 
coated flexible fabric may be dissimilar and the polymers used in the 
retroreflective layer and the coated flexible fabric may also be 
incompatible for direct attachment. 
In a first embodiment of construction, a suitable retroreflective layer, 
compatibilizing layer and a polymeric coated flexible fabric material are 
simultaneously attached using radio frequency energy. The frequency of the 
radio frequency energy and the field strength are variable by an operator 
and chosen for suitability dependent upon the polymeric components within 
the retroreflective layer, compatibilizing layer, and polymeric coated 
flexible fabric. The choice depends on such factors as the individual 
polymeric dielectric loss factors, dielectric constants, melting 
temperatures, and layer thickness. The radio frequency energy is delivered 
through antennas mounted within appropriate platens that are pressed onto 
the appropriate surfaces of the retroreflective flexible fabric material 
applying an appropriate amount of pressure and an appropriate duration of 
radio frequency energy. 
An alternate embodiment of the present invention provides for a selected or 
patterned thermal welding of a retroreflective layer, compatiblizing 
layer, and polymeric coated flexible fabric material. In one illustrative 
embodiment the components are passed between a nip roller and an embossing 
thermal roller applying a suitable pressure to the components over a 
raised ridge embossing pattern carried on the surface of the embossing 
roller. The counter-force nip roller is preferably a sufficiently hard 
rubber smooth surfaced roller, for example an 85 durometer roller. The 
embossing roller is patterned to exert pressure into the material being 
welded only at the point of the raised ridges. Both the embossing roller 
and the hard durometer roller are heated to suitable temperatures 
depending upon the composition of polymers used in the retroreflective 
layer, compatibilizing layer, and polymeric coating on the flexible fabric 
material. The embossing pattern may be of several suitable patterns such a 
chain linked pattern as described below. 
In another embodiment, heat for achieving the bond between the 
compatibilizing layer and the substrate is applied from a heating element. 
In an illustrative embodiment of this approach, a heating element is 
positioned between the retroreflective sheeting with compatibilizing layer 
and the substrate, preferably without being in direct contact with either, 
and then the retroreflective sheeting and substrate are moved by the 
heating element and pass between pressure rollers after being heated such 
that a bond between the compatibilizing layer and substrate develops. The 
heating element, sometimes referred to as a hot wedge, can be configured 
such that essentially the entire bottom surface of the compatibilizing 
layer is softened to achieve a universal bond or it may be configured such 
that longitudinal portions of the compatibilizing layer of the 
retroreflective sheeting and the substrate are selectively bonded as they 
pass through, e.g., one or more bands or stripes extending in the 
direction of movement of the retroreflective sheeting and substrate as it 
passes the pressure rollers. In an illustrative embodiment of this 
approach, the hot wedge can be about 10 to 20 millimeters in width, heated 
to about 460.degree. C., the laminating pressure applied at about 1.6 bar, 
and the retroreflective sheeting and substrate passed over the heating 
element and through the roller at about 6 meters/minute. The heating 
element can be configured to heat only one of the compatibilizing layer 
and substrate, but it is usually preferred that both components be heated 
to ensure that a strong attachment is achieved. 
In another embodiment, heat for achieving the bond between the 
compatibilizing layer and the substrate is applied via hot air. A hot air 
source may be used to warm the compatibilizing layer and/or substrate 
sufficiently to achieve a bond and then the two webs laminated under 
pressure. As with the prior embodiment, this technique may be used to 
achieve a bond across substantially the entirety of the compatibilizing 
layer or in only selected portions thereof by controlling flow of hot air 
in such a way that it is directed only to the outer border of the 
retroreflective sheeting. The latter approach permits obtaining a usefull 
bond or weld between the compatibilizing layer and substrate in instances 
where the heat and pressure necessary for a bond are high enough that 
degradation of the retroreflective prismatic elements occurs. As with the 
heating element discussed above, the hot air source can be configured to 
heat only one of the compatibilizing layer and substrate, but it is 
usually preferred that both components be heated to ensure that a strong 
attachment is achieved. 
As will be understood, the temperature, operating speed, and weld 
configuration of all of these techniques should be chosen so as to not 
undesirably degrade the retroreflective sheeting, including its 
compatibilizing layer, and the substrate. 
When a retroreflective sheeting is pre-fabricated prior to its application 
to a polymeric coated flexible fabric material, the present invention uses 
radio frequency welding, patterned thermal welding, adhesive attachment, 
and casting attachment for bonding the compatibilizing layer to the 
retroreflective prismatic element surface. Radio frequency energy and 
patterned thermal welding are as described above. These methods of welding 
attachment may use previously formed compatibilizing layers. These 
previously formed compatibilizing layers may be either cast or extruded. 
Adhesive attachment of a previously formed compatibilizing layer uses 
appropriate adhesives that may be thermal or pressure sensitive and 
suitable for attaining tensile bond strengths as described below. An 
alternate attachment method is a casting method whereby an appropriate 
compatibilizing layer is cast directly onto the prismatic element surface 
of a retroreflective laye. An additional alternate embodiment provides for 
an increased barrier characteristic in which the retroreflective layer has 
a plurality of septa raised on the prismatic surface for attachment of the 
compatibilizing layer. 
FIGS. 1a-d depict various constructions of retroreflective layers as known 
in the prior art. In FIG. 1a, retroreflective layer 20 comprises a land 
portion 22 and a plurality of prismatic elements 24 projecting from a 
surface of retroreflective layer 20. Retroreflective layer 20 represents a 
monolithic construction. FIG. 1b depicts a composite construction for a 
retroreflective layer 26 comprising a body portion 28 and a plurality of 
prismatic elements on one surface of retroreflective layer 26. The 
polymeric materials used for body 28 and prismatic elements 30 are 
different. 
FIG. 1c depicts a construction for a retroreflective layer 32 of monolithic 
construction having a land 34 and a plurality of prismatic elements 36 on 
one surface of retroreflective layer 32 and incorporating an overlay layer 
38 as an integral portion of retroreflective layer 32. 
In FIG. 1d, an additional construction is represented in a retroreflective 
layer 40 comprising a land portion 42, a plurality of prismatic elements 
44 on one surface of retroreflective layer 40, a body portion 46, and an 
overlay 48. The relative percent each portion may represent is variable 
where, for example, land portion 42 may comprise virtually zero percent of 
the retroreflective layer 40. Each type of construction as represented in 
the various FIGS. 1a-d are chosen with considerations for the optical 
performance that will be required for the application the retroreflective 
layers will be used in. 
FIG. 2 depicts construction of a retroreflective sheeting 50 comprising a 
retroreflective layer 52 and a compatibilizing layer 54 which have been 
fused using radio frequency welding energy from platens 56 creating a RF 
weld 58 between retroreflective layer 52 and compatibilizing layer 54. 
FIG. 3 depicts an alternate method of constructing a retroreflective 
sheeting 60 comprising a retroreflective layer 62 and a compatibilizing 
layer 64 passing between an embossing roller 66 and a durometer roller 70. 
Embossing roller 66 comprises a patterned raised ridge 68 whereby using 
heat and pressure between the rollers 66 and 70 a thermal weld 72 is 
formed between retroreflective layer 62 and compatibilizing layer 64 
corresponding to the patterned raised ridge 68. 
In FIG. 4, an embodiment of the present invention is depicted in 
retroreflective flexible fabric material 80 comprising a retroreflective 
layer 82, a compatibilizing layer 84, and a flexible fabric material 86. 
Retroreflective layer 82, compatibilizing layer 84, and flexible fabric 
material 86 are fed between rollers 88 and 92 creating a patterned thermal 
weld 96 corresponding to the raised pattern 90 on the surface of embossing 
roller 88 with a surface defect 94 embossed into flexible fabric 86 
corresponding to the embossing pattern 90 on embossing roller 88. 
FIG. 5 depicts an alternate embodiment of the present invention 
constructing a retroreflective flexible fabric material 100 comprising a 
retroreflective sheeting 102 and a flexible fabric material 104. 
Retroreflective sheeting 102 comprises a retroreflective layer 106 and a 
compatibilizing layer 108 as constructed using radio frequency energy as 
depicted in FIG. 2. This construction method leads to a depressed portion 
surface 110 and a RF weld 112 created by the pressure and heat generated 
by radio frequency welding platens. Retroreflective sheeting 102 and 
flexible fabric material 104 are fused using radio frequency energy 
generated from radio frequency antenna/electrode platens 114 creating a 
radio frequency weld 116. 
An alternate construction for a retroreflective flexible fabric material 
120 is depicted in FIG. 6 comprising a retroreflective sheeting 122 and a 
flexible fabric material 124. Retroreflective sheeting 122 comprises a 
retroreflective layer 126 having an overlay 128 and a compatibilizing 
layer 130 which has been previously constructed using the method depicted 
in FIG. 3 in which retroreflective layer 126 with its overlay 128 was 
passed between a durometer roller and an embossing roller along with 
compatibilizing layer 130 facilitating thermal weld sites 132. 
Retroreflective sheeting 122 and flexible fabric material 124 undergo 
fusion using radio frequency energy from platens 134 at weld points 136. 
FIG. 7 depicts an alternate embodiment of the present invention in a 
retroreflective flexible fabric material 150 comprising a retroreflective 
sheeting 152 and a flexible fabric material 154. Retroreflective sheeting 
152 comprises a retroreflective layer 156 with an overlay 158 and a 
compatibilizing layer 160. Compatibilizing layer 160 comprises a primer 
layer 162 and a carrying layer 163. Retroreflective sheeting 152 is 
constructed in this embodiment using the method as shown in FIG. 3 where 
retroreflective layer 156 with overlay 158 is passed between a durometer 
and an embossing roller along with compatibilizing layer 160 creating a 
thermal weld 164. Retroreflective sheeting 152 is welded to flexible 
fabric material 154 using radio frequency energy from radio frequency 
energy platens 166 creating an RF weld 168. 
FIG. 8 discloses a schematic representation of an embodiment of the present 
invention in which a retroreflective flexible fabric material 180 is 
manufactured having a retroreflective layer 182, a compatibilizing layer 
184, and a flexible fabric material 186. The retroreflective layer 182, 
compatibilizing layer 184, and flexible fabric material 186 are fed 
between an embossing roll 188 and a hard rubber roll 190. Embossing roll 
188 has raised embossing elements 192 on its surface creating a thermal 
weld pattern within retroreflective flexible fabric material 180, 
corresponding to the embossing pattern of raised ridges 192. FIG. 9 
depicts a plan view of a raised ridge embossing pattern 192 on the surface 
of embossing roll 188 showing the pattern dimension measurements A, B, and 
C which are described below. 
The invention also incorporates specularly coated prismatic elements with 
metal and other suitable reflective coatings as a means for altering the 
optical performance of the retroreflective layer. The invention 
anticipates the need to pattern the metallized coatings when using RF 
welding and to constrain the RF welding to those regions that are void of 
any metallization. It is recognized that a portion may comprise all of the 
prismatic element surfaces or less than all of the surfaces. 
Colorants, UV absorbers, light stabilizers, free radical scavengers or 
antioxidants, processing aids such as antiblocking agents, releasing 
agents, lubricants, and other additives may be added to the 
retroreflective layer and, body portion or prismatic elements and overlay, 
if used. The particular colorant selected, of course, depends on the 
desired color. Colorants typically are added at about 0.01 to 0.5 weight 
percent. UV absorbers typically are added at about 0.5 to 2.0 weight 
percent. Examples of UV absorbers include derivatives of benzotriazole 
such as Tinuvin.TM. 327, 328, 900, and 1130, Tinuvin-P.TM., available from 
Ciba-Geigy Corporation, Ardsley, N.Y.; chemical derivatives of 
benzophenone such as Uvinul.TM.-M40, 408, and D-50, available from BASF 
Corporation, Clifton, N.J.; Syntase.TM. 230, 800, and 1200 available from 
Neville-Synthese Organics, Inc., Pittsburgh, Pa.; and chemical derivatives 
of diphenylacrylate such as Uvinul.TM.-N35, and 539, also available from 
BASF Corporation of Clifton, N.J. Light stabilizers that may be used 
include hindered amines, which are typically used at about 0.5 to 2.0 
weight percent. Examples of hindered amine light stabilizers include 
Tinuvin.TM.-144, 292, 622, and 770, and Chimassorb.TM.-944 all available 
from the Ciba-Geigy Corp., Ardsley, N.Y. Free radical scavengers or 
antioxidants may be used, typically, at about 0.01 to 0.5 weight percent. 
Suitable antioxidants include hindered phenolic resins such as 
Irganox.TM.-1010, 1076, 1035, and MD-1024, and Irgafos.TM.-168, available 
from the Ciba-Geigy Corp., Ardsley, N.Y. Small amounts of other processing 
aids, typically no more than one percent by weight of the polymer resins, 
may be added to improve the resin's processibility. Useful processing aids 
include fatty acid esters, and fatty acid amides available from Glyco 
Inc., Norwalk Conn., metallic stearates available from Henkel Corp., 
Hoboken, N.J., and Wax E.TM. available from Hoechst Celanese Corporation, 
Somerville, N.J. 
Bonding strengths of the retroreflective layers are measured using two 
types of tests, a tensile bond test and a T-peel test. The tensile bond 
test is particularly useful in measuring the bonding strength of small 
sealing patterns, such as disclosed in U.S. Pat. No. 4,025,159 (McGrath); 
U.S. Pat. No. 3,924,929 (Holmen); or as used in 3M Brand High Intensity 
Grade reflective sheeting or 3M Brand Diamond Grade reflective sheeting, 
sold by Minnesota Mining and Manufacturing Company of St. Paul, Minn. The 
T-peel test is useful in measuring the bond strengths of a retroreflective 
sheeting attachment to a flexible polymer coated fabric. 
The tensile bond test is based on ASTM D 952-93 in that the specimen to be 
tested is attached between two metal fixtures. For the purposes of the 
following examples, the test is set up using an upper fixture that is a 
cubic block of steel 25.4 mm on each edge presenting a one square inch 
surface. A lower fixture is a 1.6 mm thick plate of aluminum 50 mm wide. 
For the test, a 30 mm square piece of the retroreflective sheeting of this 
invention is covered on the top and bottom with a layer of a suitable 
pressure sensitive tape such as 3M Scotch Brand Adhesive Tape No. 419. The 
sheeting is placed, compatibilizing layer side down on the center of the 
aluminum plate and the metal block is placed on the top side of the 
sheeting. The sheeting is then cut around the edges of the upper block so 
that a 25.4.times.25.4 mm square of the sample is tested. The assembled 
sandwich is then compressed with a force of 1900 Newton (425 lbs.) for 60 
seconds. The steel cube is secured in the upper jaw of a standard tensile 
testing machine and the aluminum plate is secured along 2 sides in a lower 
gripping fixture of the tester. The jaws are rapidly separated at 500 
mm/min (20 in/min) and the force versus displacement curve is recorded and 
the peak force is reported. 
Well bonded compatibilizing layer samples will result in high peak forces, 
i.e., greater than about 270 N (60 lbs) and preferably greater than about 
450 N (100 lbs). The failure mode is typically cohesive (tensile) within 
the compatibilizing layer or at the prismatic element to compatibilizing 
layer interface. In some cases, the specimen may fail adhesively at the 
tape used to secure the compatibilizing layer or the overlay film to the 
metal fixtures, but if high peak forces are developed, the test results 
still indicate a good bond was formed between the compatibilizing layer 
and cube films. Typically a poorly bonded sample will fail adhesively at 
the cube film to compatibilizing layer interface with low peak force. For 
some material pairs, bonding will appear excellent but after soaking the 
sealed sheeting in water for 1 to 10 days the bond strength will decrease 
significantly indicating a lack of moisture resistance and possible 
failure under wet conditions outdoors. After a 10 day water soak, the peak 
force should be greater than about 180 N (40 lbs) and preferably greater 
than about 360 N (80 lbs). 
The T-peel test is based on ASTM D 1876-93 except with the changes noted 
herein. The samples were cut into strips 25.4 mm (1.0 in) wide 
perpendicular to the RF or thermal weld. Jaw separation rate was 305 
mm/min (12 in/min). Peak peel forces are reported, since the bond line is 
only about 5 mm long in the peel direction. 
Features and advantages of this invention are further illustrated in the 
following examples. It recognized, however, that while the examples serve 
this purpose, the particular ingredients and amounts used, as well as 
other conditions and details, are not to be construed in a manner that 
would unduly limit the scope of this invention. In general, for the 
following examples tested according to the T-peel test, the failure mode 
was cohesive at the polymer coating/fabric interface. 
EXAMPLE 1 
Molten polycarbonate resin (Makolon.TM. 2407, supplied by Mobay 
Corporation, Pittsburgh, Pa.) was cast onto a heated microstructured 
nickel tooling containing microcube prism recesses having a depth of 
approximately 89 micrometers (0.0035 inch). The microcube recesses were 
formed as matched pairs of cube corner elements with the optical axis 
canted or tilted 8.15 degrees away from the primary groove, as generally 
described in U.S. Pat. No. 4,588,258 (Hoopman). The nickel tooling 
thickness was 508 micrometers (0.020 inch) and the tooling was heated to 
215.6.degree. C. (420.degree. F.). Molten polycarbonate at a temperature 
of 288.degree. C. (550.degree. F.) was cast onto the tooling at a pressure 
of approximately 1.03.times.10.sup.7 to 1.38.times.10.sup.7 pascals (1500 
to 2000 psi) for 0.7 seconds in order to replicate the microcube recesses. 
Coincident with filling the cube recesses, additional polycarbonate was 
deposited in a continuous layer above the tooling with a thickness of 
approximately 104 micrometers (0.004 inch). A previously extruded 50 
micrometer (0.002 inch) thick aliphatic polyester urethane body layer 
(Morthane.TM. PNO3, supplied by Morton International, Seabrook, N.H.) was 
then laminated onto the top surface of the continuous polycarbonate land 
layer when the surface temperature was approximately 191.degree. C. 
(375.degree. F.). The combined tooling with laminated polycarbonate and 
polyurethane body layer was then cooled with room temperature air for 18 
seconds to a temperature of 71.1 to 87.8.degree. C. (160 to 190.degree. 
F.), allowing the materials to solidify. The laminate sample was then 
removed from the microstructured tool. 
EXAMPLE 2 
The laminate sample from Example 1 was fed into a nip between a steel 
embossing roll and a 85 durometer rubber roll with a previously extruded 
polyurethane compatibilizing layer. The compatibilizing layer was 
protected by a 25 micrometer (0.001 inch) polyester terephthalate film 
next to the steel embossing roll. The laminate sample from Example 1 was 
also protected by a 51 micrometer (0.002 inch) polyester terephthalate 
film next to the rubber roll. The previously extruded compatibilizing 
layer is 51 micrometer (0.002 inch) thick and is a blend of 60% aliphatic 
polyester urethane (Morthane.TM. PNO3, supplied by Morton International, 
Seabrook, N.H.) with 40% of a pigmented aromatic polyester urethane (the 
pigmented aromatic polyester urethane is comprised of 50% aromatic 
polyester urethane, Estane 58810.TM. from B.F. Goodrich Co., Cleveland, 
Ohio, and 50% titanium dioxide, previously compounded in a twin screw 
extruded and pelletized). The embossing pattern is of a chain link 
configuration as shown in FIG. 9. The embossing roll surface temperature 
was 210.degree. C. (410.degree. F.) and the rubber roll surface 
temperature was 63.degree. C. (145.degree. F.). The rolls were turning at 
a surface speed of 6.09 meters/min. (20 feet/min.) and the force on the 
nip was held at 114 N/cm (65 lbs/in). The polyester terephthalate 
protective layers are then removed from the samples. The laminate sample 
including the compatibilizing layer was then tested for bond strength 
according to the tensile test previously described. This example yielded a 
laminate with a tensile bond strength of 400 N (90 lb.sub.f). 
EXAMPLE 3 
A laminate sample from Example 1 was layered together with a polyurethane 
compatibilizing layer as described in Example 2 on top of a plasticized 
PVC coated fabric (Duraskin.TM. B129134, supplied by Verseidag-Indutex 
GMBH, Krefeld, Germany). The sample was welded using a bar shaped die, 3.2 
mm (0.125 inch) in width. Approximately 1.20 kW radio frequency power was 
used at a frequency of 27.12 MHz for a dwell of 2.8 seconds and a pressure 
of 346 N/cm.sup.2 (502 psi) to achieve a satisfactory weld. The welding 
equipment was from Thermatron, Electronics Division of Wilcox and Gibbs, 
New York, N.Y. 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 4 
A laminate sample from Example 1 was layered together with a previously 
extruded ethylene vinyl acetate copolymer (Ultrathane.TM. UE 646-04 
supplied from Quantum, Cincinnati, Ohio) compatibilizing layer of 
thickness equal to 104 micrometers (0.004 inch) and also placed on top of 
a plasticized PVC coated fabric (Duraskin.TM. B129134, supplied by 
Verseidag-Indutex GMBH, Krefeld, Germany) as shown in Figure. The sample 
was welded using an aluminum bar shaped die, 3.2 mm (0.125 inch) in width, 
7.5 cm (3 inches) in length. Approximately 1.28 kW radio frequency power 
was used at a frequency of 27.12 MHz for a dwell of 2.8 seconds and a 
pressure of 346 N/cm.sup.2 (502 psi) to achieve a satisfactory weld using 
the same equipment described in Example 3. 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 5 
The laminate sample described in Example 2 was layered directly on top of a 
plasticized PVC coated fabric as described in Example 3. The sample was 
welded using an aluminum bar shaped die, 3.2 mm (0.125 inch) in width. 
Approximately 1.20 kW radio frequency power was used at a frequency of 
27.12 MHz for a dwell of 2.8 seconds and a pressure of 346 N/cm.sup.2 (502 
psi) to achieve a satisfactory weld using the same equipment described in 
Example 3. 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 6 
A laminate sample was layered together with a polyurethane compatibilizing 
layer on top of a plasticized PVC coated fabric as described in Example 3. 
The sample was thermally bonded using a heated channel shaped die in a 
model PW 220H platen press, supplied by Pasadena Hydraulics, Inc., Brea, 
Calif. The channel shaped die consisted of parallel raised sections with a 
width of about 6.35 mm (0.25 inch). The width of the channel was about 
50.8 mm (2.00 inch). Approximately 690 to 759 N/cm.sup.2 (1000 to 1100 
psi) was applied for about 3 seconds with the top platen at 132.degree. C. 
(270.degree. F.) and the bottom platen at 48.9.degree. C. (120.degree. F.) 
to achieve a satisfactory bond. 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 7 
A laminate sample was layered directly on top of a plasticized PVC coated 
fabric as described in Example 5. The sample was thermally bonded using a 
heated channel shaped die in a platen press under conditions as described 
in Example 6. 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 8 
A laminate sample was layered together with a polyurethane compatibilizing 
layer on top of a plasticized PVC coated fabric as described in Example 3. 
The layered sample was then fed into a nip between a steel embossing roll 
with a chain link pattern and a rubber backup roll as described in Example 
2. The coated fabric side of the layered sample was positioned next to the 
rubber roll. The steel roll surface temperature was 149.degree. C. 
(300.degree. F.) and the rubber roll surface temperature was 26.7.degree. 
C. (80.degree. F.). The rolls were turning at a surface speed of 1.52 
meters/min. (5.0 ft/min.), and the force on the nip was held at 2030 N/cm 
(180 lbs/inch). 
The sample was measured for bond strength in the 180.degree. T-peel mode, 
and the results are shown in Table 1. 
EXAMPLE 9 
The laminate sample from Example 1 was fed into a nip between a steel 
embossing roll and a rubber roll with a previously extruded, polyurethane 
primed, ethylene acrylic acid copolymer compatibilizing layer. The 
compatibilizing layer was protected by a 26 micrometer (0.001 inch) 
polyester terephthalate film next to the steel embossing roll. The 
laminate sample from Example 1 was also protected by a 26 micrometer 
(0.001 inch) polyester terephthalate film next to the rubber roll. The 
previously extruded compatibilizing layer was 52 micrometer (0.002 inch) 
in total thickness and was a dual layer primed film. The first layer 
utilized 26 micrometer (0.001 inch) thick clear ethylene acrylic acid 
copolymer (Primacor.TM. 3440, The Dow Chemical Company, Midland, Mich.). 
An aliphatic urethane primer was applied to the first layer to promote 
adhesion of the compatibilizing layer to the polycarbonate of the laminate 
sample. The primer (Q-thane.TM. QC-4820, K. J. Quinn and Co., Inc., 
Seabrook, N.H.) was solvent coated to form a layer having a final dried 
coating thickness of about 2.5 micrometers (0.0001 inch). The second layer 
was also 26 micrometer (0.001 inch) thick and utilized a blend of 60% 
ethylene acrylic acid copolymer (Primacor.TM. 3440) with 40% of a 
pigmented ethylene acrylic acid copolymer. The second layer was adjacent 
to the polyester terephthalate protection film. The pigmented 
polyethylene-co-acrylic acid was comprised of 50% ethylene acrylic acid 
copolymer (Primacor.TM. 3150) and 50% titanium dioxide, previously 
compounded in a twin screw extruded and pelletized. The embossing pattern 
was of the chain link configuration as in Example 2 . The embossing roll 
surface temperature was 182.degree. C. (360.degree. F.) and the rubber 
roll surface temperature was 49.degree. C. (120.degree. F.). The rolls 
were turning at a surface speed of 6.09 meters/min. (20 feet/min.) and the 
force on the nip was held at 2030 N/cm (180 lbs/inch). 
The laminate sample including the compatibilizing layer was then tested for 
tensile bond strength according to the tensile test previously described 
yielding a value 400 Newtons (93 lbf). 
EXAMPLE 10 
A laminate sample described in Example 9 was layered directly on top of an 
EAA coated fabric, such as that fabric/backing used in manufacturing 3M 
Brand Scotchlite Reflective Roll Up Sign Sheeting Series RS84, and as 
generally described in commonly assigned co-pending application titled 
High Strength Non-Chlorinated Multi-Layered Polymeric Article Ser. No. 
08/082,037, filed Jun. 24, 1993. The sample was thermally bonded using a 
heated channel shaped die in a platen press as described in Example 6 . 
Approximately 690 to 759 N/cm.sup.2 (1000 to 1100 psi) was applied for 
about 3 seconds with the top platen at 149.degree. C. (300.degree. F.) and 
the bottom platen at 48.9.degree. C. (120.degree. F.) to achieve a 
satisfactory bond. 
The laminate sample including the compatibilizing layer was then tested for 
bond strength according to the tensile test previously described and the 
results are given in Table 1. 
TABLE 1 
______________________________________ 
T-Peel Force 
Example Number Newtons/cm 
______________________________________ 
3 19.6 
4 8.9 
5 15.6 
6 29.5 
7 34.1 
8 11.8 
10 30.5 
______________________________________ 
EXAMPLE 11 
To demonstrate the effects of monomeric plasticizer migration, a 
retroreflective layer produced according to the method of Example 1 was 
layered next to a duraskin canvas as described in Example 3 oriented with 
the prismatic element surface next to the gloss side of the polymeric 
coated fabric. This combination was sealed around the perimeter with 
adhesive tape completely enclosing the structure. A second sample was 
prepared similarly but with the inclusion of a 50 micrometer (0.002 inch) 
thick polyurethane film as described in Example 2 placed between the 
prismatic element surface of the retroreflective layer and the PVC coated 
flexible fabric. 
Initial coefficients of retroreflectivity were measured at 0.2.degree. 
observation angle and -4.degree. entrance angle on a retroluminometer, 
Model MCS-7-7.0, from Todd Products Corporation, Farmington, N.Y., 
obtaining values of approximately 1,400 candelas per lux per square meter. 
These samples were then placed in an oven for fourteen days at 70.degree. 
C. (150.degree. F.) to accelerate the migration of monomeric plasticizer. 
This test is estimated to predict performance of two years at room 
temperature. The coefficient of retroreflectivity was measured after this 
exposure. The retroreflective layer in the sample that did not contain the 
compatibilizing layer acting as a barrier to monomeric plasticizer 
migration appeared milky and had a coefficient of retroreflectivity of 4 
candelas per lux per square meter equating to a loss of over 99% of the 
retroreflectivity. In the sample that did include the compatibilizing 
layer acting as a barrier to the migration of monomeric plasticizer, the 
retroreflector layer did not have any milky appearance and retained 100% 
of its original retroreflectivity. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention.