Prefabricated retroreflective sign

Details Prefabricated retroreflective sign Prefabricated retroreflective sign

1998-05-29

2002-10-29

Davis, Cassandra (Department: 3611)

Card, picture, or sign exhibiting

Illuminated sign

Reflective

C359S530000

Reexamination Certificate

active

06470610

ABSTRACT:

BACKGROUND
The present invention relates generally to retroreflective signs. The invention has particular application to signs that utilize cube corner retroreflective sheeting operating on principles of total internal reflection (TIR).
The term “sign” as used herein refers to a stand-alone article that conveys information, usually by means of alphanumeric characters, symbols, graphics, or other indicia, and that in use is mounted to an object such as a post, bracket, wall, or similar body. Specific examples include signs used for traffic control purposes (STOP, YIELD, speed limit, informational, roadside markers, etc.), street signs, and vehicle license plates. The term “retroreflective” as used herein refers to the attribute of reflecting an obliquely incident light ray in a direction antiparallel to its incident direction, or nearly so, such that it returns to the light source or the immediate vicinity thereof.
Two known types of retroreflective sheeting are microsphere-based sheeting and cube corner sheeting. Microsphere-based sheeting, sometimes called “beaded” sheeting, employs a multitude of microspheres typically at least partially imbedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes, vapor coats) to retroreflect incident light. Illustrative examples are disclosed in U.S. Pat. Nos. 3,190,178 (McKenzie), 4,025,159 (McGrath), and 5,066,098 (Kult). In contrast, cube corner retroreflective sheeting comprises a body portion typically having a substantially planar front surface and a rear structured surface comprising a plurality of cube corner elements. Each cube corner element comprises three approximately mutually perpendicular optical faces that cooperate to retroreflect incident light. Examples include U.S. Pat. Nos. 1,591,572 (Stimson), 4,588,258 (Hoopman), 4,775,219 (Appledorn et al.), 5,138,488 (Szczech), 5,213,872 (Pricone et al.), 5,691,846 (Benson, Jr. et al.), and 5,696,627 (Benson et al.).
Some types of cube corner retroreflective sheeting require the rear structured surface to be maintained in a benign air (or other low refractive index medium) environment. This is particularly true for sheeting that relies upon TIR at the faces of the cube corner elements. Presently, this type of sheeting is generally provided with a seal film as shown in the enlarged fragmentary view of FIG.
1
. Prior art sheeting
10
shown in that figure has a body portion
12
with a front surface
12
a
and a rear structured surface
12
b
, a seal film
14
, a pressure sensitive adhesive (PSA) layer
16
, and a release liner
18
. Sheeting
10
also has a top film or layer
20
which can comprise: an ultraviolet (UV) absorbing material; a patterned ink layer, or other patterned layer such as Electrocut™ film sold by 3M Company, that forms indicia such as alphanumeric characters, symbols, or graphics; or a combination of UV absorbing and patterned or colored layers. Seal film
14
is bonded to structured surface
12
b
in a repeating pattern of closed polygons which form isolated, sealed cells to keep contaminants away from groups of individual cube corners on the structured surface. Boundaries of the polygonal cells are depicted at
14
a
. Heat and pressure used to form the cells destroys or deforms cube corner elements located along the boundaries
14
a.
In order to make a retroreflective sign using the prior art sheeting
10
, a sign board is provided which comprises a rigid mass of metal, wood, plastic, or the like. “Sign board” as used herein means a rigid substrate suitable for mounting in the intended end use application. The retroreflective sheeting
10
is then prepared by removing the release liner
18
so as to expose the PSA layer
16
. Then the sheeting is applied to a smooth, flat front surface of the sign board with the adhesive layer contacting such front surface. Letters, symbols, or other indicia may be added in layers above the body portion
12
either before or after the sheeting
10
is applied to the sign board. Some signs, such as certain road shoulder markers, carry no indicia at all but are merely bolted to a post at the side of the road.
FIG. 2
shows a fragmentary view of another prior art sheeting
22
applied to a substrate
24
such as a sign board. A body layer
26
of sheeting
22
has a rear structured surface which includes both cube corner elements
28
and a plurality of raised sections
30
arranged to define cells enclosing groups of cube corner elements. A seal film
32
, ultrasonically bonded to raised sections
30
, seals off these cells to maintain an air interface at the faces of the cube corner elements
28
. An adhesive layer
34
bonds seal film
32
, and thus sheeting
22
, to substrate
24
.
FIG. 3
shows a fragmentary plan view of the structured surface of FIG.
2
. The structured surface includes cube corner elements
28
and intersecting raised sections
30
, two of which are shown in FIG.
3
.
There is a continuing need to reduce the cost of retroreflective signs and to simplify the manufacture thereof.
BRIEF SUMMARY
As disclosed herein, a retroreflective sign is provided that comprises a rigid sign board and a retroreflective sheeting having a structured surface. The structured surface is bonded directly to the sign board to define a plurality of cells. The cells protect the structured surface from moisture and dirt, which could adversely impact the retroreflective performance of the film. By sealing the structured surface directly to the sign board, rather than to an intermediate seal film and then to the sign board, a simpler, prefabricated sign construction is achieved.
Preferably, the structured surface is bonded to the sign board in a repeating pattern. Raised sections defining the repeating pattern can be employed in the structured surface of the retroreflecting sheeting, or on the surface of the sign board. The raised sections help to maintain a space between at least some cube corner retroreflective elements on the structured surface and the sign board surface. Bonding can alternately be accomplished without raised sections by hot pressing the structured surface against the sign board in the repeating pattern which destroys cube corner elements along the pattern boundary. Various bonding techniques are contemplated, including ultrasonic bonding, heat sealing, and bonding via conventional adhesives.


REFERENCES:
patent: 1591572 (1926-07-01), Stimson
patent: 3190178 (1965-06-01), McKenzie
patent: 3359671 (1967-12-01), Nier et al.
patent: 3684348 (1972-08-01), Rowland
patent: 3843474 (1974-10-01), Golden et al.
patent: 3924929 (1975-12-01), Holmen et al.
patent: 4025159 (1977-05-01), McGrath
patent: 4208090 (1980-06-01), Heenan
patent: 4498733 (1985-02-01), Flanagan
patent: 4588258 (1986-05-01), Hoopman
patent: 4775219 (1988-10-01), Appeldorn et al.
patent: 4875798 (1989-10-01), May
patent: 4983436 (1991-01-01), Bailey et al.
patent: 5066098 (1991-11-01), Kult et al.
patent: 5138488 (1992-08-01), Szczech
patent: 5213872 (1993-05-01), Pricone et al.
patent: 5277513 (1994-01-01), Flanagan et al.
patent: 5442870 (1995-08-01), Kochanowski
patent: 5450235 (1995-09-01), Smith
patent: 5670005 (1997-09-01), Look et al.
patent: 5691846 (1997-11-01), Benson, Jr. et al.
patent: 5696627 (1997-12-01), Benson et al.
patent: 6048069 (2000-04-01), Nagaoka
patent: 15 47 631 (1969-11-01), None
patent: 28 16 346 (1979-10-01), None
patent: 297 07 066 (1997-09-01), None
patent: WO 96/41323 (1996-12-01), None
Advertising literature: “3M Marker Series 280 Durable Raised Pavement Markers With Enhanced Brightness,” 3M Traffic Control Materials Division (1991).
Advertising literature: “3M Scotchlite Reflective Sheetings,” 3M Traffic Control Materials Division (1994).

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