Reflective sheeting technology

A reflex light reflector comprising a laminate of water-insoluble layers including an internal specular-reflecting metal layer sealed between water-insoluble layers and formed in situ by vapor deposition of metal to a sufficient thickness to constitute a continuous opaque electrically conductive film, and a monolayer of microsphere lens elements of a diameter within the range of 10 to 200 microns overlying the metal layer and bonded by resinous bonding material in optical relationship thereto for reflex light reflection, wherein said metal layer is characterized by being multiply fractured in a random pattern resembling the cracking pattern of a dried mud flat such that it consists of a multiplicity of non-overlapping patches of metal, each fractionally separated from others sufficiently to render said metal layer highly resistant to electrolytic corrosion, each said patch having an area size sufficient to underlie from one up to about thirty of said lens elements, with each said patch having at least one depression therein and each said depression being optically associated with a said lens element.

BACKGROUND OF THE INVENTION 
This invention relates to new and improved reflex light reflectors and new 
and improved methods for making a variety of different reflex light 
reflectors. The new reflex reflecting articles of the invention have a 
layer of microsphere lens elements and an underlying metal layer formed in 
situ by vapor deposition so as to be a continuous layer but which in fact, 
as it exists in the product, consists of a multiplicity of non-overlapping 
patches of metal, each fractionally separated from others sufficiently to 
render the metal layer highly resistant to electrolytic corrosion. These 
improved reflectors are ideally useful for highway and advertising signs 
and markers. 
Especially significant are the new methods or processes taught herein. The 
procedures employed permit reliable and economical manufacture of a 
variety of reflex reflectors. 
Specular reflecting metallic flakes such as aluminum flakes have heretofore 
been employed as reflectors in reflex-reflecting sheeting. The random and 
multiple overlapping relationship of the flakes in the sheeting 
necessarily introduces costly waste of material inasmuch as it is only the 
outer non-overlapped surface portions of the flakes that perform a useful 
reflective function therein. 
The advantages of metal as a specular reflecting layer have long been 
recognized; and structures in the prior art have sometimes heretofore 
employed vapor-deposited metal layers (applied, however, late in the 
process of manufacture after bead or microsphere bonding). Vapor-deposited 
aluminum layers in particular have been so employed. The continuity of 
such vapor deposited layers has contributed to brilliance of reflex 
reflection, but unfortunately, that very continuity as heretofore employed 
(without this invention's fractional space separation at cracks) tends to 
render the vapor-deposited layer highly susceptible to electrolytic 
corrosion as the sheet material is employed in outdoor highway signs and 
markers. 
A major benefit of the present invention is that the advantages of a 
continuous in situ vapor-deposited layer of metal as a specular reflector 
are retained, while the disadvantage of that layer being highly 
susceptible to electrolytic corrosion is essentially obviated. 
Still other benefits and advantages of the invention will be evident as 
this description proceeds. 
SUMMARY OF THE INVENTION 
The invention provides new reflex light reflectors which comprise a 
laminate of water-insoluble layers including an internal 
specular-reflecting metal layer sealed between water-insoluble layers. 
This metal layer is formed by in situ vapor deposition of metal. The term 
"in situ" is considered appropriate inasmuch as the vapor deposition is 
one step in building up the product as a face up structure. Importantly, 
the vapor deposition of metal in these new reflectors is accomplished to a 
sufficient thickness to constitute a continuous electrically conductive 
film, that is, a film having a sufficient continuity for electrical 
conduction (and thus be readily susceptible to electrolytic corrosion). 
Such films are highly efficient opaque specular reflectors, and are to be 
distinguished from semi-transparent vapor deposits which are more or less 
discontinuous in that the deposited molecules are somewhat separated from 
each other and detract from high specularity of reflection (and also lack 
film continuity for electrical conduction). 
Further, the reflectors include a compact monolayer of microsphere lens 
elements of a diameter within the range of about 10 to 200 microns bonded 
by resinous bonding material in optical relationship to the metal layer 
for reflex light reflection. This layer of lens elements overlies (that 
is, is above) the metal layer. Thus, light striking the front or face 
surface of the structure passes through these lens elements on its way to 
the specular reflecting metal layer, and then returns back through lens 
elements on its way toward its source. 
While the metal layer is formed in situ as a continuous layer, it has 
special properties in the reflex light reflectors. Those properties are 
characterized as follows: the metal layer is multiply fractured in a 
random pattern of crack lines resembling the cracking pattern of a dried 
mud flat. Thus, the vapor-deposited metal layer, while in situ vapor 
deposited as a continuous layer, actually consists (in the product) of a 
multiplicity of non-overlapping patches of metal. Each patch is 
fractionally separated from others to a sufficient extent to obstruct 
electrical conductivity between the patches and thus render the metal 
layer highly resistant to electrolytic corrosion. Further, each patch has 
an area size sufficient to underlie at least one and no more than about 
thirty of the lens elements of the structure. Still further, each patch 
has depressions therein and each depression is optically associated with a 
lens element of the structure. 
Reflex light reflectors of the invention may be in the form of sheeting 
having a flat face surface or front face of transparent resinous material 
overlying the lens elements. The teachings of the invention are also 
useful in forming reflex reflectors having a lenticular face surface, that 
is, a face surface formed by lens elements hemispherically exposed (i.e., 
exposed to air and thus having a lens-air interface). 
The preferred method taught herein for making reflex light reflectors 
involves first preparing or forming a special laminate of layers having a 
releasable low-adhesion interface between a removable base structure and a 
product-forming structure. The base structure comprises an 
integrity-maintaining base web which forms one of the outer layers of the 
laminate, plus a deformable cushion layer of thermoplastic resinous 
material carried by the web. The product-forming structure comprises an in 
situ vapor-deposited metal layer having a sufficient thickness of vapor 
deposit to constitute a continuous electrically conductive film, a lens 
element bonding layer of thermoplastic resinous material, and a monolayer 
of microsphere lens elements forming the other outer layer of the 
laminate. The lens elements are lightly tacked in the monolayer on the 
surface of the bonding layer in this laminate. 
The special laminate recited above is then pressure treated or compressed, 
preferably at an elevated temperature. The pressure applied in the 
compression treatment can vary but is always sufficient to press the lens 
elements into the bonding film up to or about at their equator level and 
sufficient to simultaneously form lens-element-associated depressions in 
the metal layer. 
After the pressure treatment, the base structure and product-forming 
structure are stripped apart at the low adhesive interface between the 
same. The product-forming structure is preferably united to an adhesive 
layer carried on a releasable low-adhesion liner. 
Still other refinements of process and product will be covered as this 
description proceeds.

DESCRIPTION OF PREFERRED EMBODIMENTS 
While reflex light reflection has become well known, the illustration of it 
in FIG. 1 as applicable for microsphere lens element structures will serve 
as a reminder. In this type of reflection, the incident beam or ray 10 
striking the face surface 11 of the reflex reflector is returned or retro 
reflected back toward its source in a cone, illustrated by dash lines 12 
and 13, having the incident beam more or less as the axis of the cone. For 
reflex reflectors, this is true even though the incident beam strikes the 
face surface of the structure at varying angles from normal or from 
perpendicular to the face surface. Note that the cone of returned light 
becomes broader or expands as the light is returned or reflex reflected. 
This feature is called divergence. It is a beneficial feature. (If the 
incident headlight rays of an automobile were retro-reflected or 
reflex-reflected perfectly back toward the headlight source, with no 
divergence, reflex-reflecting signs and markers along a highway would not 
appear to be "lighted" and attention-getting to the vehicle occupants, 
whether at close or at long range.) 
However, the very benefit of divergence also tends to reduce the intensity 
of the light returned to the eyes of a viewer as compared to the intensity 
of the ray striking the face of the reflex reflector. This constitutes one 
reason for employing the most efficient of specular-reflecting means in 
these structures. Vapor-deposited metal specular reflectors are considered 
to be highly efficient for return of light focused on them by the 
microsphere lens elements; and amongst the best of these is 
vapor-deposited aluminum, although substantially equivalent results may be 
obtained with other vapor-deposited metals and sometimes the color 
benefits of using different metal vapor deposits will dictate their choice 
over aluminum. Aluminum presents a silvery light return, although this may 
be adjusted by employing transparent colored resinous coatings in the 
structure. 
(The term "specular" as employed in conjunction with reflection is commonly 
understood to refer to that type of reflection characteristic of an 
ordinary mirror, where, as is well known, an incident light beam striking 
the mirror at an angle of about 5.degree. one way from normal will leave 
the mirror at an approximately opposite and equal angle.) 
It is within the ambit of this invention to form microsphere-type reflex 
reflectors of a variety of types. The optical relationships between 
microsphere lens elements and underlying specular reflecting means for 
reflex reflection has been the subject of work by others. This invention, 
however, provides an extraordinarily economical means, and a highly 
reliable means, for gaining the desired optical relationships according to 
the will of operators, with little or no worthless final product, which 
has been a problem where ability to test the optical relationships as they 
are formed in manufacture is handicapped by the nature of the methods 
employed. Most importantly, the new methodology taught herein imparts 
unique characteristics to the vapor-deposited metal layer, with retention 
of its high specularity and yet an astonishing alteration of its otherwise 
disadvantageous characteristics. 
Referring to FIG. 2, the reflex-reflecting sheeting there illustrated is 
characterized as having a flat top, and in this respect is comparable to 
reflex light reflectors described in Palmquist et al U.S. Pat. No. 
2,407,680, issued Sept. 17, 1946, here incorporated by reference. As 
compared to lenticular surfaced reflex reflectors, the occurrence of rain 
or wetting on the surface of a flat-topped structure presents little 
interference with the ability of the structure to reflex reflect incident 
light. The layers of the flat-topped structure illustrated in FIG. 2 are: 
a transparent resinous covering 20 with a flat front face 21, a compact 
monolayer of microsphere lens elements 22, a transparent lens-element 
binder and spacing layer or film 23, a vapor-deposited metal film 24 
having the characteristics for the metal layer as described herein, and 
particularly having lines of rupture as illustrated at 25 between patch 
24-1 and another patch 24-2. Interestingly, the depressions in the metal 
layer assume somewhat of an inverted pyramid character in these structures 
having a spacing layer between the microspheres and the depressions of the 
metal layer. The inverted pyramid analogy should be understood to be a 
reference to angular orientation of a multiplicity of contiguous minute 
planes formed by minute folds and giving an approximately overall cup-like 
shape to the depressions in the metal layer. Behind the metal layer 24 is 
an adhesive layer 26 having a removable temporary liner 27 (shown 
partially removed). The liner is removed at the time cut portions of the 
sheeting are adhesively affixed to a sign or marker. 
In FIG. 3, the reflex reflector illustrated has a lenticular surface formed 
by hemisphere projections of the microsphere lens elements 30 out of their 
bonding film or layer 31. In this lenticular respect, the structure of 
FIG. 3 bears analogy to lenticular surfaced reflex reflectors of Gebhard 
et al U.S. Pat. No. 2,326,634, issued Aug. 10, 1943, here incorporated by 
reference. Underlying the compact monolayer of microsphere lens elements 
30 is an in situ vapor-deposited metal layer 32 having the special 
characteristics taught herein and particularly the line of rupture 35 
separating patch 32-1 from patch 32-3. The microspheres are suitably and 
preferably in direct contact with the metal layer and lie in depressions 
in it, with the metal cupped more or less hemi-spherically about the back 
surface of the microsphere lens elements. Thus, the metal layer 
depressions in these structures are in substantial concave contact about 
the back surface of the lens elements. Underlying the metal layer 32 is an 
adhesive layer 33 and a removable temporary liner 34. 
FIG. 4 illustrates a flat-topped reflex reflector having a transparent 
surface film 40 which may be formed of colored resinous material or formed 
by adhering a film of polyester material such as "Mylar" (polyethylene 
terephthalate) over a transparent resinous covering layer 41. This 
structure illustrates tiny glass beads or microspheres 42 discretely 
coated with a spherical covering of transparent resinous material 43 which 
suitably may serve as the equivalent of the transparent spacing film 23 in 
FIG. 2. Further, to provide a specially colored appearance for daytime 
viewing, interstitial spaces between the spherically covered lens elements 
may be filled with a pigmented resinous layer of material 44. Underlying 
the spherically covered lens elements is the vapor-deposited metal layer 
45 having the characteristics of the invention and including the ruptured 
or fractured characteristic 46 between patches 45-1 and 45-2, as well as a 
substantially concave contact about the space coating 43 of the individual 
microspheres. Underlying the metal film 45 is an adhesive layer 48 and a 
temporary removable liner 47. This structure is offered merely to 
illustrate variable details which may be built into microsphere-type 
reflex reflectors having new features of the invention. Of course, a 
reflex reflective sheeting incorporating a transparent colored film 40 may 
omit the pigmented material layer 44, if desired, and vice versa. The 
important point is that a multitude of possibilities exists for imparting 
a variety of colored effects as those skilled in the art will readily 
appreciate. 
In the structure of FIG. 5, the principle is illustrated that a lenticular 
surfaced reflex reflector may be provided with air cells defined by a grid 
pattern which secures a flat top film 50 over the lenticular surface. For 
such details, reference is made to the general concepts for air cell 
structures as illustrated in McKenzie U.S. Pat. No. 3,190,178, issued June 
22, 1965, here incorporated by reference. Illustratively, a biaxially 
oriented polyester film of transparent nature may be employed, or a film 
of biaxially oriented methyl methacrylate. The film 50 is adhered or fixed 
to the underlying lenticular surfaced reflex reflector along grid lines 
formed by any suitable bond or adhesive material 51. The lines 51 of 
adherence are in a grid pattern so as to form a multiplicity of cellular 
spaces 52 occupied by a multitude of hemispherically exposed lens elements 
53 held in bonding film 54. The exposed hemispherical upper part of the 
lens elements 53 is within air cells of the structure, thus presenting a 
lens-air interface for the optical conditions for high brilliance 
lenticular reflex reflection, as those skilled in the art now readily 
appreciate. Underlying the lens elements 53 is an in situ vapor-deposited 
metal layer 55 having the special characteristics for that layer as 
described above, particularly in connection with FIG. 2. Again, a line of 
rupture 56 is illustrated between patch 55-1 and patch 55-2. An adhesive 
layer 57 with a temporary liner 58 completes the structure. 
It should be emphasized, if not already evident, that the variations of 
structure illustrated, except for the special characteristics of the in 
situ vapor-deposited metal layer in the combination, are at this point in 
time well known to those skilled in the art. Thus but modest 
characterization of suitable materials to employ should suffice. Adhesive 
layers may be formed of either heat-tackifying or permanently 
pressure-sensitive adhesives, with of course a caution that the 
heat-tackified layers should not require so much heat for tackification as 
to destroy optical relationships in the remaining portion of the 
structure. Commonly, plasticizers are mixed with resinous materials to 
lower the temperature for heat tackification. Pressure-sensitive adhesives 
of any well-known type (commonly referred to as rubber-resin type and 
equivalents, especially acrylate pressure-sensitive adhesives) may be 
employed so long as they do not attack either during manufacture or in use 
the characteristics of the vapor-deposited metal layer as a specular 
reflector (or are prevented from so attacking by interposing a thin film 
of protective resin between the adhesive layer and the metal layer). 
Removable liners commonly are formed in an economical manner by coating 
paper with a layer or film of polyethylene or silicone. Such coatings are 
widely known as films from which conventional popular adhesive films or 
layers are readily released without significant transfer of adhesive to 
the coated liner. A suitable bead or microsphere bonding coat or layer may 
be formed by using polyvinylbutyral resin, particularly the vinylbutyral 
resin characterized as XYHL available from the chemicals and plastics 
division of Union Carbide Corporation having an address at 270 Park 
Avenue, New York, N.Y. 10017. Other bead bonding layers of course are 
useful, such as acrylic base polymer resins. These resins or others may be 
employed also as the space coatings for flat-topped reflex reflectors, 
according to principles set forth in the aforementioned Palmquist et al 
patent. As the top coating for the flat-topped reflectors, it is 
preferable to choose a different transparent resin and preferably one 
which can be applied in a manner not solvating or otherwise disturbing the 
optical relationships between the lens elements and the 
specular-reflecting film of a flat-topped structure. For that reason, I 
preferably employ as the top coat transparent resin layer a polyurethane 
such as for example one formed by curing the urethane coating composition 
available from Wyndham Chemical Company, 10640 South Painten Street, Santa 
Fe, Calif. 90670, under the designation WC2176. Application of this 
material is possible without the addition of any solvent, for it is liquid 
in character and is readily cured or polymerized on mild heating to about 
120.degree. C. to form a water insoluble film. Indeed, the materials 
present in all portions of the product are insoluble in water. Especially 
important is the fact that the layers on each side of the specular film 
must be insoluble in water. 
Useful microsphere lens elements for the structures have a diameter within 
the range of about 10 to 200 microns. Preferably, however, the diameter 
range selected for any one structure should be more limited, and most 
preferably, transparent glass beads or microsphere lens elements are 
segregated from a raw batch of the same by passing the batch through sieve 
sizes of varying mesh so as to collect those of the larger size and pass 
those of the smaller and end up with preferred useful batches where the 
largest size is not over about twice the diameter of the smallest size, 
and even preferably not over about 50% the diameter of the smallest size. 
Overall, however, it may be stated as a general proposition that the 
preferred range of sizes for the microsphere lens elements will lie 
between about 25 microns up to about 100 or possibly 125 microns. Again it 
is emphasized that the most preferred size range for any one stretch of 
sheeting should be limited to a range where the largest diameters are not 
in excess of about 50% the smallest diameters, and even most ideally not 
over about 25% greater than those of smallest diameter. 
Referring now to FIGS. 6 through 9 inclusive, a method will be described 
for manufacture of the reflectors in a manner effectively creating unique 
characteristics for the vapor-deposited film. 
The first step of manufacture involves a series of substeps in forming a 
laminate of layers built up on an integrity-maintaining base web 60. By 
integrity-maintaining is meant a web or sheet which does not disintegrate 
or fall apart under the conditions of processing. A suitable web is paper, 
preferably a calendered hard surface paper such as 50-80 pound Fourdrinier 
or equivalent. 
On the base web 60 is coated, as by roll coating, a pressure-deformable 
cushion layer 61 of thermoplastic resinous material. Illustratively, 
polystyrene is suitable to employ, as also is a co-polymer of 
vinylchloride and vinylacetate such as the co-polymer VYHH of Union 
Carbide Corporation. The resin is suitably roll-coated from a solvent 
mixture; and toluene as well as methyisobutylketone have been employed. 
Resin solid content in the solvent for the roll-coating step can vary, but 
approximately 30 to 50% resinous solids by weight is preferred. The dried 
thickness of the coating after solvent removal should be in the range of 
at least 1 mil, preferably at least a couple mils and need not be in 
excess of about 21/2 mils, although it may be as thick as 3 mils, or more 
(as where microspheres of the larger sizes within the range of diameter 
aforenoted are employed). The coating of this cushion layer should be 
accomplished in a manner so as to present, on drying of it, a very smooth 
outer or upper surface. Further, the upper surface of this cushion layer 
must release readily from the next applied layer of the laminate, for the 
base web and cushion layer constitute a removable base structure portion 
of the composite laminate formed at this stage. 
Thus, the resin selected for the cushion layer will normally be one to 
which a vapor deposit of metal will exhibit poor adherence or low adhesion 
and therefore will readily release for removal from the cushion layer. On 
the other hand, if cushion layers to which vapor deposited metal is 
adherent are used, a suitable expedient to create a releasable 
low-adhesion interface between the base structure of layers 60 and 61 and 
the next layer of the laminate is that of employing a strippable film 
coating on the cushion layer (i.e., a film coating exhibiting poor 
adhesion to the cushion layer). Such a strippable film should be 
exceedingly thin, not over about a mil or 25 microns in thickness and 
preferably much less, for it suitably may become but a thin film portion 
of the final reflective product. If desired, reflective pigments or flakes 
may be included in this strippable film, although their function as a 
reflector in the final product would be limited to the minute areas of 
fractional separation between patches of the metal layer. The fundamental 
principle to observe for this laminate is that of creating a low-adhesion 
interface between the contact layer of the base structure (which is later 
removed from the laminate) and the adjacent layer of the product-forming 
portion of the laminate. 
Most preferably, the resin selected for the cushion layer 61, particularly 
when reflecting articles such as illustrated in FIG. 1 are to be formed, 
is from amongst those which, when heat or elevated temperature is employed 
for the later embossing or compression pressure step, will exhibit a 
slightly greater flow or plasticity than the resin selected for the 
spacing layer. Illustratively, temperatures of approximately 180.degree. 
C. (360.degree. F.) have been found to be near ideal for the pressure 
compression step. A cushion layer formed as described functions well with 
other elements of structure, under the pressure treatment to be described, 
to effect the breaking up or fracturing of the aluminum layer, as well as 
to effect fractional separation of patches of it, without destroying its 
specularity performance. 
Remaining layers which form the laminate are product-forming layers. 
Normally, the next layer will be that formed by vapor depositing metal 
directly on the cushion layer. Vacuum deposition techniques as heretofore 
known may be employed. The important consideration is that of applying a 
sufficient thickness of vapor deposit, preferably aluminum, so as to 
create a continuous vapor deposited film or layer 62. This is to be 
distinguished from vapor deposits which are semi-transparent and 
essentially have but discrete particles or molecules of aluminum which may 
give a visual appearance of being continuous but in fact lack density in 
that they permit the transmission of light through the film. The vapor 
deposit of this invention is such that it is opaque and continuous and 
effectively constitutes an electrical conductor, although not the most 
excellent of conductors. Conductivity is achieved as soon as a continuous 
dense opaque deposit is formed, that is, one blocking light transmission. 
Thicker vapor deposits may be employed, if desired, but are generally 
unnecessary after opaqueness is reached. Such a layer presents a highly 
specular reflecting surface. It also appears to be a layer exhibiting more 
brittleness than metal foils, which by comparison are more ductile. 
After the vapor deposit step, two major options present themselves. One is 
that of specially coating a space coat over the metal layer and then 
applying a lens element or bead bonding film over the space coating. The 
other is that of applying a film 63 of resinous material characterized as 
the lens element bonding film and either applying it at a thickness for it 
to function as both a bead bonding layer as well as a spacing layer for a 
flat-topped structure, or applying it as a thinner layer and simply 
employing it for the purpose of hemispherically bonding the lens elements 
without a special spacing relationship to the metal layer 62. In either 
event, a lens element bonding film is applied. It of course may be applied 
in two steps. One may constitute or in essence form the spacing layer 
where a flat-topped sheet structure is to be manufactured; and the other 
or later applied layer may be looked upon as functioning as the lens 
element bonding layer per se. 
Ideally, the lens element bonding film 63 is applied as a single step, 
whether sufficiently thick for spacing purposes as well as lens element 
bonding, or so thin as to simply serve per se as a lens element bonding 
layer. A preferred resin for film 63 is polyvinylbutyral resin (e.g., 
resin XYHL of Union Carbide Corporation). Approximately a 20% solids 
solution of this resin in ethyl alcohol or any other suitable diluent or 
solvent (e.g., including mixtures such as a 50--50 mixture of an alcohol 
and a glycol ether mixture) is satisfactory for roll coating purposes; and 
roll coating is suitably employed, followed by drying. In selecting the 
lens element bonding resin, the important consideration is that it must 
adhere well to the glass microsphere lens elements and in addition exhibit 
sufficient deformability or plasticity at the later pressure compression 
treatment to receive the lens elements up to about their equator into it. 
But the deformability or plasticity of this bonding film 63, when a 
spacing function for it is also to be gained (as where the article of FIG. 
1 is to be made) must be less than the deformability or plasticity of the 
cushion layer 61 under the conditions of later processing, that is, under 
the conditions experienced by each in the processing under the compression 
pressure step. But where microspheres are to be placed contiguously 
against the vapor-deposited film, the plasticity of the cushion layer may 
vary, or even be less than that of the lens element bonding film under the 
conditions employed in the pressure compression step. Preferably, even 
when the microspheres are placed contiguously against the vapor-deposited 
film, the lens element bonding layer will deform (i.e., have less 
plasticity) less readily than the cushion layer. 
Then the next step of the laminate formation is that of applying a 
monolayer of microsphere lens elements 64 on the exposed surface of the 
bonding film 63. Suitably, this is accomplished by passing the entire 
laminate of layers 60, 61, 62, and 63 over a heated cylinder (with the web 
60 next to the cylinder) to elevate the temperature of film 63 up to about 
180.degree. C. so as to tackify it. Simultaneously, the glass beads in the 
nature of microsphere lens elements are sprayed or dropped from a hopper 
onto the tacky surface of the layer 63, with excess beads falling away (as 
by inverting the laminate) to leave essentially a monolayer in rather 
compact form adhering to it. 
Thereafter, this laminate (as illustrated graphically in FIG. 6) is 
promptly passed through the nip of squeeze rollers or between squeeze 
rollers adjusted to pressure such that the microspheres 64 are pressed up 
to about their equator into the film 63; and this is preferably done while 
maintaining elevated temperature conditions, suitably with film 63 at 
about 180.degree. C. The heat from employing a heated drum as one of the 
squeeze rollers is suitable for this purpose; and in this respect it 
should be recognized that a small differential or drop in temperature may 
exist from the web to the bead bond layer 63. Pressure adjustments are 
necessary at this stage to accomplish the optical relationships between 
the lens elements and specular vapor deposited layer, as those 
relationships are well known in the art for microsphere reflex reflectors. 
Such relationships are described, for example, in the aforenoted Palmquist 
et al Patent for a flat-topped structure (where spacing between the layer 
of microspheres and the specular reflecting layer is employed), and in the 
aforenoted Gebhard et al Patent for a lenticular surfaced structure (where 
the microspheres and reflector layer are continuous or contacting). 
Checking the proper optical relationships between the microspheres and the 
specular metal layer is easily accomplished since the structure exiting 
from the pressure treatment may be subjected to examination for its reflex 
reflectivity and, if necessary, the pressure treatment then adjusted 
according to the will of the operator. 
It is this step of pressure treatment, as just discussed, that effects a 
substantial alteration of the vapor-deposited metal layer 62; and the 
results of this alteration are illustrated graphically in FIG. 7 and also 
FIG. 10. One thing that happens is that the metal layer 62 is converted 
from a purely flat layer into one having varying depressions 65 therein, 
with each depression optically associated with and underlying a lens 
element 64. This result appears to be enhanced by employing a bead bonding 
or microsphere lens bonding layer 63, whether thick or thin, having a 
greater bodying strength or resistance to flow under the temperature 
conditions of processing than the layer 61 serving as the cushion layer. 
Another phenomenon that takes place is that the metal layer is multiply 
fractured or ruptured, as at the crack 66 illustrated in FIG. 7 and crack 
lines 66 of FIG. 10. The thickness of vapor deposit, however, is such that 
the fracture lines or cracking pattern is not so frequent as to form a 
discrete platelet of metal under each lens element. The multiple 
fracturing of the metal layer is in a random pattern of lines resembling 
the cracking pattern of a dried mud flat. It consists of a multiplicity of 
non-overlapping depression-containing flake-like or plate-like patches of 
metal. But each patch has an area size sufficient to underlie at least one 
and no more than about thirty of the lens elements. Further, and most 
important, each of the lines 66 illustrated in FIG. 10 represents a minute 
space. Each patch of metal is fractionally separated from the others 
sufficiently to obstruct electrical conductivity between the patches, thus 
rendering the metal layer highly resistant to electrolytic corrosion. 
Additionally, however, the metal layer retains its high specularity of 
reflection and functions as a specular reflector of light striking it (as 
focused on it by the lens elements 64). 
Thus, the metal layer is fundamentally altered in the pressure treatment of 
the special laminate. Magnified examination reveals that the crack lines 
indeed do sometimes occur under the lens elements themselves. What is 
interesting, however, is that the fractional separation of the patches at 
the crack lines is so microscopic as to be but a few microns in width, and 
a width less than the diameter of lens elements at locations optically 
overlying adjacent patches of the metal layer at the crack line 
therebetween. This principle is illustrated in FIG. 10, where lens 
elements 68 overlie a crack line and optically overlie metal of adjacent 
patches of metal. Not over 15% (and usually not over 10%) of the total 
number of lens elements in a monolayer over any significant area of the 
sheeting (i.e., an area of a couple square centimeters or more) are in 
locations of the crack lines, a fact which in retrospect is surprising. 
Generally, one expects fracturing at points of pressure (i.e., at the 
tangent contact between a "pole" of a bead and metal layer), but the 
conditions of processing the special laminate promotes the formation of 
crack or fracture lines between the bead (that is, microsphere) locations. 
Still further, in the most preferred structures, most of the discrete 
patches of the metal layer are of an area size that underlies at least two 
and no more than twenty microsphere lens elements, or even no more than 
fifteen lens elements. Stated another way, 80% of the lens elements in the 
preferred structures are within the area boundary or edge of individual 
patches of metal having at least two and no more than 20 (or no more than 
15) lens elements per discrete patch. They are optically entirely within 
the perimeter edges (area boundary) of such patches. In general, preferred 
structures of this type have greater depths for depressions optically 
associated with the microspheres; and they generally exhibit improved 
angularity of reflex reflection over those having larger areas for the 
patches. By improved angularity is meant an improved reflex reflective 
light return for incident light striking the structure at increasing 
angles from a normal or perpendicular incidence. 
The size of the patches of metal varies randomly, but few exceed 1000 
microns in their largest dimension. For preferred structures, the longest 
dimension of patches generally does not exceed 750 microns and most are 
less, e.g. not over 500 microns. 
After the pressure treatment with results as illustrated in FIG. 7, and 
assuming for the moment that a flat-topped reflex reflector is to be 
formed, the next step is that of applying (see FIG. 8) the flat top 
coating 67; and procedures and materials such as illustrated in the 
forenoted Palmquist et al. U.S. Pat. No. 2,407,680 may be employed. 
Ideally, however, transparent polyurethane resins are employed as the top 
coating resin, as previously noted. They are applied, as by roll coating, 
from a liquid state containing no solvent and are cured in situ by 
heating. Preferably the curing temperature for the resin selected should 
be below that employed for the pressure embossing step. The reason for 
this is to avoid triggering any possible memory reversion of the resin 
layers, and thus the shaped and fractured metal film, back toward a flat 
condition. 
The layers 60 and 61 perform no further useful function in the article 
after the pressure treatment and for that reason are removed, as by 
stripping, so as to reduce the thickness of the final article. Thereafter, 
an adhesive layer carried by a removable liner is laminated to the 
structure of FIG. 9 so as to form a structure as illustrated in FIG. 2. 
Of course, in the event a lenticular surfaced structure is to be formed, 
the step of applying the coating 67 to achieve a flat top will be omitted 
and the lens elements normally pressed into depressed direct contact with 
the metal layer, as illustrated in FIG. 3. 
The specular reflecting metal layer is sealed between water insoluble 
layers. This is most important inasmuch as it is the constant weathering 
to which sheet material on signs and markers is subjected in use that has 
heretofore constituted a problem with respect to corrosive deterioration 
of any continuous specular reflecting metal film, although the continuous 
types are the most efficient. Testing of that corrosion characteristic can 
be accomplished by immersing a sheet sample in a water solution of about 
5% by weight of a metal salt (e.g., copper sulfate) and then cutting the 
sheeting or scratching it through the vapor coat. It is in this test that 
the metal layer of the structures of this invention shows exceedingly high 
resistance to electrolytic corrosion. When tested against otherwise 
comparable sheetings but sheetings which have a continuous specular 
reflecting metal layer, the sheetings of this invention show insignificant 
evidence of corrosion eating in from the cut edges whereas the sheetings 
containing continuous metal layers evidence corrosive degradation of 
substantial distance or width from the cut edges, with consequent loss of 
the reflex light reflection capability as well as development of a poor 
visual appearance. 
Because the optical relationship between microsphere lens elements and 
specular reflecting metal layers may vary depending on the different 
qualities and types of reflex-reflecting sheeting to be manufactured, as 
is well known and well understood and documented in a multitude of earlier 
patents on reflex-reflecting sheeting formed of small glass beads or 
microsphere lens elements, those skilled in the art will readily recognize 
that the principles of this invention may be employed in a wide variety of 
reflex reflectors according to varied optical relationships that are now 
well known. In general, resinous materials exhibit a refractive index (nD) 
around 1.5, with some resins exhibiting refractive indices even lower. 
Useful lens elements should exhibit refractive indices of at least 1.65 
and generally above 1.7. Lenticular surfaced structures having their lens 
elements in pressed contact relationship against the specular reflecting 
metal layer preferably employ lens elements exhibiting refractive indices 
from approximately 1.7 up to approximately 1.9, although microspheres of 
somewhat lower (down to about 1.65) or higher (up to about 1.95) 
refractive indices may be employed for such structures. As microspheres of 
higher and higher refractive indices (up to 2.8 or even possibly 2.9) are 
employed in flat-topped structures, the spacing requirement of the 
microspheres from the specular reflecting metal layer diminishes, and even 
becomes unnecessary, as is now well known. (See principles discussed in 
the aforenoted Palmquist et al U.S. Pat. No. 2,407,680). The prior art 
contains a multitude of teachings dealings with microsphere lens elements 
having refractive indices well over 2.0. These references to the prior art 
are intended to emphasize that the teachings of this invention may be 
incorporated in a variety of reflex light reflectors using conventional 
and now well known optical relationships. 
Accordingly, the invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiments are therefore to be considered in all respects as 
illustrative and not restrictive, the scope of the invention being 
indicated by the appended claims rather than by the foregoing 
descriptions; and all changes which come within the meaning and range of 
equivalency of the claims as construed for validity are therefore intended 
to be embraced thereby.