U.S. patent number RE29,742 [Application Number 05/771,541] was granted by the patent office on 1978-08-29 for retroreflective protective helmet.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Chi Fang Tung.
United States Patent |
RE29,742 |
Tung |
August 29, 1978 |
Retroreflective protective helmet
Abstract
Protective helmets that give a distinctive retroreflective
signal under wet or dry conditions at night or in other darkened
environments are provided by disposing a retroreflective layer
covered by a transparent layer over at least a major portion of the
outer surface of the helmet.
Inventors: |
Tung; Chi Fang (Mahtomedi,
MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (Saint Paul, MN)
|
Family
ID: |
23635011 |
Appl.
No.: |
05/771,541 |
Filed: |
February 24, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
412920 |
Nov 5, 1973 |
03885246 |
May 27, 1975 |
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Current U.S.
Class: |
2/412; 2/422;
359/541 |
Current CPC
Class: |
A42B
3/061 (20130101) |
Current International
Class: |
A42B
3/06 (20060101); A42B 3/04 (20060101); A42B
003/02 (); G02B 005/12 () |
Field of
Search: |
;2/2,410,411,412,422,425,171,171.1,175,185R,192 ;350/97,98,105
;427/163,164,273 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schroeder; Werner H.
Attorney, Agent or Firm: Alexander; Cruzan Sell; Donald M.
Tamte; Roger R.
Claims
What is claimed is:
1. A protective helmet comprising a protective shell adapted to be
worn on a person's head; a retroreflective layer disposed over
substantially all of the outer surface of the protective shell,
comprising a layer of binder material and a monolayer of
transparent glass microspheres that are partially embedded in the
layer of binder material and have a coating of specular reflective
material on their embedded surfaces; and a transparent sheet having
the shape of the protective shell disposed directly over the
retroreflective layer, said sheet being in tight frictional
engagement with said retroreflective layer but without optical
contact to the exposed surfaces of the microspheres and being
attached to the protective shell at least around the periphery of
the retroreflective layer so as to provide an airtight sealed
pocket between the retroreflective layer and the transparent sheet,
whereby the retroreflective layer retroreflects light shined at the
helmet under either wet or dry conditions.
2. A protective helmet of claim 1 in which the retroreflective
layer is carried on a support sheet that has the shape of the
protective shell and is attached over the exterior of the
protective shell. .Iadd. 3. A protective helmet comprising a
protective shell adapted to be worn on a person's head; a support
sheet that has the shape of the protective shell disposed over the
exterior of the protective shell; a retroreflective layer carried
on said support sheet and disposed over substantially all of the
outer surface of the protective shell and comprising a layer of
binder material and a monolayer of transparent glass microspheres
that are partially embedded in the layer of binder material and
have a coating of specular reflective material on their embedded
surfaces; and a transparent sheet having the shape of the
protective shell disposed directly over the retroreflective layer,
said sheet being in tight frictional engagement with said
retroreflective layer but without optical contact to the exposed
surfaces of the microspheres and being attached to the support
sheet at least around the periphery of the retroreflective layer so
as to provide an airtight sealed pocket between the retroreflective
layer and the transparent sheet, whereby the retroreflective layer
retroreflects light shined at the helmet under either wet or dry
conditions. .Iaddend.
Description
The present invention is based on the conception that protective
helmets such as worn by motorcycles, construction workers, or
miners could be a useful tool to provide distinctive
retroreflective signals at night or in other darkened environments.
Others have previously suggested adding retroreflective elements to
protective helmets, as shown by U.S. Pat. No. 3,577,561, but the
retroreflective treatments of these prior suggestions were of
limited value; they did not use the retroreflective signal to
provide a distinctive indication of the presence of a person
wearing a helmet; they did not provide a retroreflective signal of
maximum conspicuity; and they required cumbersome unattractive
attachments to a helmet that were vulnerable to accidental
removal.
The present invention provides smooth-surfaced attractive
retroreflective protective helmets that provide a distinctive
retroreflective signal of excellent brightness and angularity and
that function whether wet or dry. Briefly, a protective helmet of
the invention generally comprises a protective shell adapted to be
worn on a person's head, and a retroreflective layer that is
attached to the shell, is visible from the exterior of the shell,
and extends over at least a major portion (that is, at least half)
of the surface of the shell. The retroreflective layer comprises a
layer of binder material and a monolayer of transparent glass
microspheres that are partially embedded in the layer of binder
material and have specular reflective means underlying their
embedded surfaces. A transparent layer that forms the outer surface
of the helmet is disposed directly over the microspheres to protect
them from contact by moisture, whereby the retroreflective layer
retroreflects light shined at the helmet under either wet or dry
conditions.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a protective helmet of the
invention;
FIG. 2 is a section through a peripheral portion of the protective
helmet shown in FIG. 1 taken along the lines 2--2 of FIG. 1;
FIG. 3 is section through a peripheral portion of a component of a
protective helmet of the invention; and
FIGS. 4 and 5 are sections through peripheral portions of different
helmets of the invention.
DETAILED DESCRIPTION
The illustrative protective helmet of the invention 10 shown in
FIGS. 1 and 2 comprises a protective shell 11 adapted to be worn on
a person's head (usually harness means attached to the inside of
the shell, not shown, engage the person's head); a retroreflective
layer 12 covering the outer surface of the rigid shell, the layer
12 comprising a layer 13 of binder material and a monolayer of
transparent glass microspheres 14 that are partially embedded in
the layer of binder material and have specular reflective means
underlying their embedded surfaces (not shown in the drawings); and
a transparent sheet or layer 15 that has the shape of the
protective shell disposed directly over the retroreflective
layer.
The transparent sheet 15 is attached to the protective shell 11
near the periphery of the shell, as by a layer of adhesive, a
heat-seal, or mechanical fasteners, and that attachment provides an
air-tight sealed pocket between the retroreflective layer and the
transparent sheet. However, over at least most of the
retroreflective layer, the transparent sheet 15 is spaced from the
exposed surfaces of the microspheres 14. The spacing of the
transparent sheet from the microspheres may be quite small, just
sufficient to prevent the sheeting and microspheres from making
optical contact, which would cause the contacted portion of the
microspheres not to refract light to the degree necessary to cause
the desired retroreflection.
As shown in FIG. 3, in some embodiments of the invention the
retroreflective layer is carried on a support sheet 16 that has the
shape of the protective shell, and the support sheet 18 and a
transparent sheet 17 to which the support sheet is attached at the
periphery of the two sheets form a unified article 18 that is
removable from the shell 19. The unified article 18 is like a
sleeve that resiliently and tightly slides onto the shell 19, where
it is held in place either by its own resiliency or by clamps or
other fastening devices. In some embodiments, the layer 20 of
binder material for the retroreflective layer itself constitutes
the support sheet of a unified, sleeve-type article.
In FIG. 4 a layer of binder material 21 is coated onto a shell 22,
a monolayer of transparent glass microspheres 23 is partially
embedded in the layer of binder material, and a transparent layer
24 is disposed directly over the outer surfaces of the
microspheres. The transparent layer 24 engages and makes optical
contact with the surfaces of the microspheres 23 and for that
reason must be of a special index of refraction to permit the
microspheres to retroreflect. Generally, the index of refraction of
the transparent layer 24 and glass microspheres 23 should be in a
ratio of 1.92 to 1.94, so that, if the index of refraction of the
transparent layer 24 is 1.38 (as with certain fluorinated polymers)
the index of refraction of the transparent microspheres 23 should
be 2.65 to 2.67.
A preferred shell for use in a protective helmet of the invention,
as shown in FIGS. 1-4, is a hard rigid material such as a synthetic
polymeric material containing a fibrous reinforcement such as woven
glass cloth. The polymeric material is typically based on a
polyester or epoxy resin.
Another protective shell used in the invention, as shown in FIG. 5,
is of a thicker construction and comprises a cellular material such
as compressed adhered particles of polystyrene foam. A
retroreflective layer 26 on the shell 27 comprises a layer 28 of
binder material directly coated onto the shell, and a monolayer of
transparent glass microspheres 29 that are partially embedded in
the layer of binder material and have specular means underlying
their embedded surfaces. A transparent layer 30, in the form of a
hard rigid removable shell of a material such as polycarbonate, is
slidingly received over the shell and protects the glass
microspheres from contact with moisture. The transparent shell 30
generally is sufficiently resilient so that it can be force-fit
over the protective shell and held in place as a result of the
tight fit. Although the outer transparent shell may contact the
microspheres at some points over the whole surface of the helmet,
at at least most locations it will be spaced sufficiently from the
microspheres to avoid optical contact and to accordingly permit
retroreflection by the microspheres.
The retroreflective layer on a protective helmet of the invention
may be conveniently formed by methods taught in Nellessen et al.,
U.S. Pat. No. 3,420,597, which is incorporated herein by reference.
The retroreflective layer is typically formed from a coating
composition that comprises a liquid vehicle including a
film-forming binder material and volatile thinner, and transparent
glass microspheres that are dispersed in the liquid vehicle and are
covered over their whole surface with specular reflective material
such as vapor-deposited aluminum or chemically deposited silver.
When the coating composition is coated onto a protective shell, the
microspheres tend to settle within the coating until they rest at
or near the bottom of the layer of liquid vehicle and engage the
surface of the shell. The liquid vehicle is generally diluted so
that the vehicle will readily flow off the outer surface of the
microspheres and leave at most a thin coating of binder material on
the microspheres. After the coating has dried, an etching solution
is applied, and it removes both the thin layer, if any, of binder
material on the outer surfaces of the glass microspheres as well as
the aluminum or other coating of specular reflective material on
the outer surfaces of the microspheres. The result is a layer of
dried or cured binder material and a monolayer of transparent glass
microspheres partially embedded in the layer of binder material,
with a cap of specular reflective material on the embedded surfaces
of the microspheres.
A wide variety of binder materials may be used in retroreflective
layers on protective helmets of the invention, including acrylic
and alkyd resins, and elastomeric epoxypolyamine compositions such
as described in U.S. Pat. No. 3,436,359. For embodiments such as
shown in FIG. 3, the support sheet is preferably a flexible
material such as polyvinyl chloride. Support sheets of the desired
shape can be formed by vacuum molding or casting procedures, for
example. Typical materials for the transparent layer disposed over
the retroreflective layer are polyvinyl chloride, polystyrene, and
for the embodiment shown in FIG. 5, polycarbonates. The transparent
layer may be flexible as in the case of the embodiment shown in
FIG. 3, or rigid as in the embodiment shown in FIG. 5. Generally
the transparent sheet will be between 0.005 and 0.25 inch
thick.
Generally the transparent glass microspheres used in this invention
average about 50 microns in diameter, though their average diameter
may range between about 20 to 100 microns in diameter. They are
generally included in the coating composition in an amount
sufficient to provide between about 20 and 90 weight-percent of the
total non-volatile material in the coating composition.
The invention will be illustrated by the following examples.
EXAMPLE 1
A hard rigid smooth-surfaced protective shell of a synthetic
polymeric material reinforced with layers of woven cloth was coated
with a composition having the following formulation.
______________________________________ Parts by Weight
______________________________________ Water-soluble thermosetting
acrylic resin 12 including 40 weight-percent of a solvent mixture
of butoxyethanol, butyl cellosolve, and water (Synthermul 40-552
made by Reichold) Hexamethoxymethylmelamine liquid catalyst 3
(Cymil 301 made by American Cyanamide) Propyleneglycol thinner 15
Transparent glass microspheres having an 70 average diameter of 50
microns and coated with silver.
______________________________________
The coating was allowed to dry at 250.degree. F for 30 minutes,
after which an etching solution that comprised 124 grams of
potassium dichromate, 240 milliliters of 36N sulfuric acid and
15,000 milliliters of water was applied over the coating. Thereupon
the outer surfaces of the microspheres were exposed, so that the
microspheres were embedded to slightly over 50 percent of their
diameter.
Thereupon a transparent sheet was formed by heating a 15
mil-thick-sheet of vinyl chloride until the sheet began to sag, and
then drawing the sheet by vacuum over a helmet-shaped mold. This
transparent sheet was then placed over the coated helmet, and
adhered to the shell by a strip of adhesive applied around the
periphery of the shell.
EXAMPLE 2
A structure as shown in FIG. 5 was prepared by coating a shell of
compressed polystyrene cellular particles with an acrylic latex,
drying the coating to form a smooth base, and then forming a
retroreflective layer over the dry coating in the manner described
in Example 1. A transparent polycarbonate shell was then forced
over the polystyrene shell to achieve a friction fit.
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