Note: Descriptions are shown in the official language in which they were submitted.
Title of the Invention 2011~55
High-brightness all-weather type pavement marking
sheet material
Background of the Invention
This invention relates to a pavement marking sheet
material and, more particularly, to an all-weather type
pavement marking sheet material having a high brightness
in reflection against light incident at a large angle of
incidence and even during night when it is raining.
There are various prior art pavement marking sheet
materials having a light reflex-reflecting function
which are used for pavement marking purposes such as
providing marking lines and road marks on the roads.
Pavement marking sheet material which are presently used
for pavement marking purposes all have glass
microspheres as reflex-reflecting element dispersed on
the surface thereof or mixed in the material for
affording visibility during night. These pavement
marking sheet materials have the common disadvantage
that, when the surface of the marking material is
covered with a film of water when it is raining, upper
hemisphere portions of the glass microspheres exposed in
air above the surface of the marking material and
performing a light reflecting function are mostly
submerged in the film of water with a result that the
light reflecting function is impaired and visibility
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during night when it is raining becomes extremely poor.
For improving visibility of the pavement marking
sheet materials during night when it is raining, some
proposals have been made in the past. For example, some
publications such as U.S. Patent No. 1,388,359 intend to
improve the visibility during night when it is raining
by providing a multitude of projections and depressions
on the surface of a sheet material in which glass
microspheres are embedded. For another example,
Japanese Patent Application Laid-open No. 211403~1~8~
discloses forming, at intervals in the longitudinal
direction of the base sheet or continuously in the
longitudinal direction of the base sheet in a part of
the base sheet as viewed in the transverse direction of
the base sheet, of an area in which glass microspheres
having refractive index of 2.0 - 2.4 which relatively do
not lose the light reflecting function during night when
it is raining are embedded in the base sheet.
These prior art all-weather type pavement marking
sheet materials have the expected visibility when light
from head lamps of vehicles running during night is
incident at a relatively small angle of incidence with
respect to the pavement marking sheet materials. Light
from head lamps of a vehicle, however, is usually
incident at a very large angle of incidence of 60 - 80
degrees with respcect to the pavement marking sheet
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materials and, at such large angle of incidence,
brightness in reflection of the pavement marking sheet
materials is reduced. The brightness in reflection is
reduced particulary when it is raining due to a film of
water covering the pavement marking sheet materials.
Reduction in the brightness in reflection of a pavement
marking sheet material during night when it is raining
is very dangerous and it has therefore been desired to
improve the brightness in reflection of a pavement
marking sheet material against light which is incident
at such a large angle of incidence.
It is, therefore, an object of the invention to
provide an all-weather type pavement marking sheet
material having a sufficient brightness in reflection
against light which is incident at an incident angle of
degrees or over at which a pavement marking sheet
material is usually used and also having a high
brightness in reflection during night when it is
raining.
Summary of the Invention
For achieving the above described object of the
invention, the high-brightness all-weather type pavement
marking sheet material according to the invention is
characterized in that it comprises a reflex-reflecting
sheet which comprises a layer of glass microspheres of a
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relatively large diameter which are at least partially
exposed in air and bonded to one another by a
transparent resin, a layer of glass microshperes of a
relatively small diameter which are buried and f ixed in
a transparent resin layer behind the glass microspheres
of a large diameter with an interval between the glass
microspheres of a large diameter and the glass
microspheres of a small diameter, and a reflecting layer
consisting of a metallized film or the like material
provided behind the glass microspheres of a small
diameter, and a base sheet made of rubber or synthetic
resin bonded to the lower surface of the reflex-
reflecting sheet.
According to the invention, light incident at a
large angle of incidence of 60 degrees or over is
incident upon the glass microspheres of a relatively
small diameter in the reflex-reflecting sheet through
- the glass microspheres of a relatively large diameter
and the transparent resin, is reflected by the
reflecting layer and is reflex-reflected passing through
the glass microspheres of a relatively small diameter,
the transparent resin and the glass microspheres of a
relatively large diameter. Accordingly, by suitably
selecting and combining the refractive indexes of the
glass microspheres of a relatively large diameter, the
glass microspheres of a relatively small diameter and
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the transparent resin, the diameters of the glass
microspheres of a relatively large diameter and the
glass microspheres of a relatively small diameter, and
the interval between the glass microspheres of a
relatively large diameter and the glass microspheres of
a relativelY small diameter, a sufficiently high reflex-
reflecting characteristic can be obtained at an angle of
incidence of 60 degrees or over.
Moreover, it has been found that, by adopting the
above described structure according to the invention,
the brightness in reflection is not substantially
reduced but is rather increased compared with a dry
state (i.e., a state corresponding to night when it is
fine) even when the exposed portions of the glass
microspheres of a relatively large diameter are covered
with a film of water.
Since the glass microspheres of a relatively large
diameter are at least partially exposed in air, the
amount of light received by the glass microspheres is
large even if the angle of incidence is large so that a
relatively large amount of light reaches the reflecting
layer provided at a lower layer.
Since the base sheet made of unvulcanized rubber,
for example, is provided behind the reflex-reflecting
sheet, shock applied on the glass microspheres provided
on the surface by a passing vehicle is mitigated and the
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likelihood of coming off of these glass microspheres is
reduced.
The invention will be described more fully below
with reference to the accompanying drawings.
Brief Description of the Drawings
In the accompanying drawings,
Fig. 1 is a sectional view of the high-brightness
all-weather type pavement marking sheet material
according to the invention;
Fig. 2 is an enlarged sectional view of a lower
layer section of the reflex-reflecting sheet in the
pavement marking sheet material;
Fig. 3 is a graph showing brightness in reflection
of an embodiment of the invention in comparison with
that of a prior art pavement marking sheet material; and
Fig. 4 is a graph showing relationship between the
thickness of the focus adjusting resin layer and the
brightness in reflection according to the invention.
Detailed Description of the Invention
Referring first to Fig. 1, resin 3 of a reflex-
reflecting sheet 1 is required to have transparency and
have a sufficient strength to hold glass microspheres ~
of a relatively large diameter. Further, since the
pavement marking sheet material is used on the road, the
resin 3 must be selected taking account of resistances
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to wear, staining and cnlor change. As resins
satisfying these requirements, acrylic polymers,
aliphatic urethanes and cross-linked polyester are
preferably used. Thermoplastic resins such as vinyl
polymers and cellulose acetate butylate may also be
used.
Since the pavement marking sheet material of the
invention is so constructed that the glass microspheres
4 of a relatively large diameter are at least partially
exposed in air to receive a large amount of light even
if light is incident at a large angle of incidence so
that the reflecting layer provided as a lower layer can
receive a large amount of light, the larger the diameter
of the glass microspheres 4, the greater is this effect
for reflecting light incident at a large angle of
incidence. However, in view of the fact that the glass
microspheres 4 are used on the road, use of glass
microspheres of a diameter exceeding 2mm is
problematical since they will come off easily. If, on
the other hand, the diameter of the glass microspheres
is less than 0.25 mm, the brightness in reflection is
insufficient for achieving the object of the invention.
It is therefore necessary to select glass microspheres
of a dimater within the range of 0.25 mm - 2 mm as the
glass microspheres 4. Glass microspheres of a diameter
of 0.25 mm - 0.5 mm are found particulary preferable.
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As the glass microspheres 4, glass microspheres of
a refractive index within a range of 1.75 - 2.2 are
preferable. If the refractive index is less than 1.75,
a sufficient brightness in reflection cannot be attained
whereas if the refractive index exceeds 2.2, it is
difficult to manufacture such glass microspheres so that
the cost of manufacture becomes extremely high.
The glass microspheres 4 of a relatively large
diameter are dispersed substantially uniformly over the
resin so that they will cover about 30 - 60~ of the
entire furface area of the reflex-reflecting sheet 1 and
the glass microspheres 4 form a layer.
In the reflex-reflecting sheet 1, glass
microspheres 5 of a relatively small diameter are buried
and fixed in a transparent resin layer behind the glass
microspheres 4 of a relatively large diameter with an
interval between the glass microspheres 4 and the glass
microspheres 5 form a layer. In the rear portion of a
transparent resin layer behind the glass microspheres 5
of a relatively small diameter is provided a reflecting
layer 8 consisting of a metallized film or the like
material. As the glass microspheres 5 of a relatively
small diameter, glass microspheres of a diameter within
a range of 53 ~m - 63 ~m and a refractive index within a
range of 2.0 - 2.2 are preferable. The reflecting layer
8 can be formed by forming a metallized film such as an
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aluminum film by a known method such as a vacuum
deposition in the rear portion of a focus adjusting
resin layer 7 provided behind the glass microspheres 5
and performing a function of adjusting the position of
the reflecting layer 8 so that it coincides with the
focus of the glass microspheres 5.
Further description will be made about an example
in which a lower layer portion a shown in the enlarged
sectional view in Fig. 2 is produced first and then an
upper layer portion b is provided on the lower layer
portion a.
The lower layer portion a comprises a glass
microsphere holding resin layer 6 holding the glass
microspheres 5, a focus adjusting resin layer
adjusting the thickness of the film of resin in
accordance with the focus of the glass microspheres 5
and a reflecting layer 8 made of a metallized film or
the like material and having curved surfaces concentric
with the glass microspheres 5. If necessary, the lower
layer portion a may comprise further a surface resin
layer ~ for reinforcing the glass microsphere holding
resin layer 6. Reference numeral 10 denotes an adhesive
layer made of acrylic resin or the like adhesive
material. The glass microspheres 5 are embedded in
about 20% - 30% of their diameter in the glass
microsphere holding resin layer 6. In case the surface
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resin layer 9 is provided, thickness of about 10 ~m - 30
m is sufficient as the thickness of this layer 9.
The upper layer portion b comprises a transparent
resin layer 3 formed on the lower layer portion a by
suitable means such as coating and this transparent
resin layer 3 holds the glass microspheres 4 of a
relatviely large diameter. As the thickness of this
transparent resin layer 3 for fixing the glass
microspheres 4, a minimum thickness of 20 ~m will be
sufficient. In view of the necessity for holding the
glass microspheres 4 on the roads, however, a thickness
of at least 70 ~m will be necessary. The film thickness
of the resin layer 3 has correlation with the diameter
of the glass microspheres 4 and a preferable film
thickness is half or less of the diameter of the glass
microspheres 4. The film thickness of the resin layer 3
therefore can be within a range of 20~ m - 100 ~ m and
preferably 70 ~m - lOO~m. If the film thickness is less
than 20 ~ m, the strength of the resin layer 3 for
holding the glass microspheres 4 is insufficient whereas
if the film thickness exceeds 100 ~ m, the brightness in
- reflection is reduced.
The method for manufacturing the reflex-reflecting
sheet 1 is of course not limited to the above described
one but the reflex-reflecting sheet 1 may be
manufactured by other method such as making it in
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sequence from the side of the glass microspheres ~ of a
relatively large diameter.
A base sheet 2 bonded at the back of the reflex-
reflecting sheet 1 requires to be made of a material
having excellent conformability to the irregular
pavement surface and durability to various mechanical
forces. The base sheet 2 therefore comprises, as its
main ingredient, unvulcanized synthetic rubber such, for
example, as acrylonitrile-butadiene rubber (NBR),
isobutylene-isoprene rubber (IIR), chloroprene rubber
(CR), chloro-sulphonyl-polyethylene, a urethane rubber
or a synthetic resin such, for example, as polyvinyl
chloride. The base sheet 2 may comprise, if necessary,
additives including a filler such as calcium carbonate
powder and a pigment for providing color to the base
sheet. The mixture of these ingredients is formed into
a sheet with a thickness of 5 mm or less by passing it
through pressure rolls or by other convenient methods.
An adhesive layer 11 of a suitable thickness of 50
~m or more, preferably about 100 ~ m - 200 ~ m, is
provided under the lower surface of the base sheet 2. A
release paper 12 is normally attached to the lower
surface of the adhesive of the adhesive layer 11 but it
may be omitted depending upon the type of the adhesive
employed in the adhesive layer 11.
For making the base sheet, the unvulcanized
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synthetic rubber or synthetic resin which is an
ingredient of the base sheet 2 is added with desired
amount of the filler, pigment and other materials if
required. The mixture is blended and is formed into a
sheet of a thickness of 5 mm or less through heated
pressure rolls and then is wound into a roll. If
necessary, the roll of the base sheet is unwound and an
adhesive coated on a release paper in a thickness of 50
~m or more is superposed on the lower surface of the
base sheet and then the base sheet is wound again.
The base sheet 2 may be composed of two layers,
i.e., a base layer made of the above described
ingredients and a thin colored layer provided on the
base layer. In this two layered structure, the
thickness of the base layer preferably is about 1.0 mm -
1.6 mm and the thickness of the colored layer on the
base layer preferably is about 20 - 25 ~m. The
thickness of the thin colored layer on the base layer is
required to have the same features as those of the base
layer described above, to be adhered integrally to the
base layer and to be colored in a desired color for the
pavement marking purpose so that the same material as,
or a material which is different but has the same
properties as, the unvulcanized synthetic rubber used
for the base layer added with a suitable coloring agent
is preferably employed.
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For forming the colored layer on the base layer,
the base layer which has once been wound into a roll is
unwound and the colored layer is formed thereon by
coating a liquidized material prepared by dissolving an
unvulcanized synthetic rubber material in a solvent and
adding a coloring agent affording a desired color
thereto on the upper surface of the base layer by an
amount sufficient for giving a desired thickness to the
coated film after drying.
The base sheet 2 may be a double layer structure
composed of an upper layer of a relatively hard material
having excellent durability to various mechanical forces
and a lower layer of a relatively soft material having
an excellent conformability to an irregurlar pavement
surface. If the lower layer is made of a material
having JIS K6301 hardness of 30 - l5 and restoration
rate of 50~ or less, the base sheet 2 has an excellent
conformability to the pavement surface and is hardly
separated once it has been adhered to the pavement
surface.
In the case of making the base sheet 2 in such
double layer structure, the above described hardness and
restoration rate can be obtained by, for example, adding
a relatively large amount of plastic material in the
ingredients of the lower layer. The amount of addition
of such plastic material required in the ingredients of
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the lower layer is ~ parts by weight or more. Suitable
plastic materials for this purpose include elastomer,
plasticizers (D.O.P., chlorinated paraffin, epoxi etc.)
and liquid rubber. The two layers comprise, as their
main ingredients, unvulcanized synthetic rubber such,
for example, as acrylonitrile-butadiene rubber (NBR),
isobutylene-isoprene rubber (IIR) and chloroprene rubber
(CR) or a synthetic resin such, for example, as chloro-
sulphonyl-polyethylene, chlorinated polyethylene and
polyvinyl chloride or other material known in the field
of the pavement marking sheet material. The two layers
may comprise, if necessary, additives including a filler
such as calcium carbonate powder and a pigment for
providing color to these layers. The mixture of these
ingredients is formed into a sheet with a thickness of
2 mm or less by passing it through pressure rolls or by
other conventional methods. An adhesive layer of a
suitable thickness of a ~0 ~m or more, preferably 100 ~m
- 200 ~ m, is provided under the lower surface of the
lower layer. The adhesive layer can be formed by
coating adhesive on a release paper in a desired
thickness and superposing it on the lower surface of the
lower layer.
For making the base sheet 2 of this double layer
structure, the unvulcanized synthetic rubber or
synthetic resin which is an ingredient of the upper
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layer and the lower layer is added with desired amounts
of the filler, pigment and other materials if required.
A desired amount of plastic materials is further added
to the material for forming the lower layer. The
respective mixtures are blended and are formed into
sheets of a thickness of 2 mm or less through heated
pressure rolls and the sheets constitute the upper layer
and the lower layer. If necessary, an adhesive coated
on a release paper in a thickness of 50 ~m or more is
superposed on the lower surface of the lower layer.
After preparing the upper layer and the lower layer
in the foregoing manner, the upper layer and the lower
layer are adhered to each other by either coating
adhesive on the upper surface of the lower layer or
softening the upper surface portion of the lower layer
by heating and thereafter superposing the upper layer on
the lower layer. Alternatively, a previously formed
upper layer may be superposed upon a lower layer which
has just been extruded from an extrusion sheet forming
device and thereupon the two layers may be bonded
together by applying pressure by pressure rolls.
Instead of making the upper layer and the lower
layer as separate sheets and superposing one upon the
other and bonding them together, the upper layer and the
lower layer may be formed as a single base sheet from
the beginning by employing the same ingredients as the
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lower layer and the upper layer may be formed by
irradiating electron beam on the upper half portion of
the single base sheet and thereby hardening the upper
half portion whereas the lower half portion of the base
sheet which is not irradiated with electron beam may
constitute the lower layer.
The pavement marking sheet material according to
the invention may be obtained by, for example,
laminating, under heat and pressure, the reflex-
reflecting sheet 1 made in the above described manner
with the base sheet 2 which is separately made in the
above described manner.
Example
An example of the pavement marking sheet material
according to the invention will be described below.
(1) Forming of the lower layer portion a of the reflex-
reflecting sheet 1
- As the resin constituting the surface resin layer
9, a resin which is a mixture of lO0 parts of a modified
acrylic resin and 10 parts of melamine resin or
isocianate as a crosslinker was coated on a carrier film
(polyester film) with a thickness of 10 ~ m - 30 ~ m and
was dried and cured to form the surface resin layer 9.
Then, as the resin constituting the glass
microsphere holding layer 6, a resin which is a mixture
of lOO parts of a modified acrylic resin and 15 parts of
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a crosslinker is coated on the surface resin layer
with a thickness of 10 ~ m - 40 ~ m. In a half-cured
state, glass microspheres 5 having a diameter within
the range of 53 ~m -63 ~m and a refractive index of 2.2
were uniformly dispersed over the resin and the resin
was dried and cured to fix the glass microspheres 5 and
form the glass microsphere holding layer 6.
Nextly, as the resin constituting the focus
adjusting resin layer 7, a resin obtained by dissolving
a mixture of 100 parts of a modified acrylic resin and 5
- 10 parts of a crosslinker in a sovlent which is a
mixture of MIBK and toluen is coated on the side of
the glass microspheres 5 of the glass microsphere
holding layer 6 in a coating amount of 80g/m2 as state
after volatilizing the solvent and was dried and cured
to form the focus adjusting resin layer 7.
The reflecting layer 8 was formed by depositing an
aluminum reflecting film on the exposed surface of the
focus adjusting resin layer 7 by the vacuum deposition
method. An acrylic adhesive was coated on a release
paper and laminated on the aluminum deposited surface
and thereafter the carrier film on the surface resin
layer 9 was removed to complete the lower layer portion
a of the reflex-reflecting sheet 1. The refractive
index of the resin constituting the lower layer portion
a of the reflex-reflecting sheet 1 was 1.52.
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(2) Forming of the upper layer portion b of the reflex-
reflecting sheet 1
As the resin constituting the upper layer portion
b on the lower layer portion a of the reflex-reflecting
sheet 1, a resin which is a mixture of 100 parts of a
modified acrylic resin and 15 parts of a crosslinker was
coated on the surface of the lower layer portion a of
the reflex-reflecting sheet 1 with a thickness of about
~5 m, In a half dried state, glass microspheres 4
having diameters of 350 ~ m - 500 ~ m and refractive
index within the range of 1.90 - 1.92 were dispersed
uniformly over the resin so that these glass
microspheres 4 will occupy 32~ of the entire surface of
the resin. Then the resin was dried and cured to form
the upper layer portion b. The refractive index of the
resin constituting the upper layer portion b was 1.52.
(3) Forming of the base sheet 2
As the base sheet 2, the double layer structure
consisting of the upper layer made of a relatively hard
material having excellent durability to various
mechanical forces and the lower layer made of a
relatively soft material having an excellent
conformability to the irregular pavement surface was
adopted.
For producing the upper layer, 30 parts of NBR, 5
parts of BR, 15 parts of petroleum resin, 30 parts of
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TiO2 and 140 parts of CaCO3 were blended and formed
into a sheet having a thickness of 0.~ mm and a width of
1,000 mm through an extrusion process at a processing
temperature of ~0 C. For producing the lower layer, 30
parts of NBR, 5 parts of BR, 15 parts of petroleum
resin, 30 parts of TiO2, 140 parts of CaCO3 , 5 parts of
liquid rubber, 7 parts of chlorinated polyethylene and 5
parts of D.O.P. were blended and formed into a sheet
having a thickness of 0.7 mm and a width of 1,000 mm
through an extrusion process at a processing temperature
of 90~ C in the same manner as in producing the upper
layer.
An adhesive layer 11 was formed by superposing a
release paper coated with a pressure sensitive adhesive
to a thickness of 100 ~m on the lower surface of the
lower layer. Then, a pressure sensitive adhesive was
coated on the upper surface of the lower layer and then
the upper layer was superposed on the lower layer and
the two layers were bonded together. A release paper
coated with a pressure sensitive adhesive was superposed
on the upper surface of the upper layer whereby the base
sheet 2 was completed.
(4) Completion of the pavement marking sheet material
The release paper laminated on t,he lower surface of
the reflex-reflecting sheet 1 and the release paper
laminated on the upper surface of the upper layer of the
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base sheet 2 were removed. The reflex-reflecting sheet
1 and the base sheet 2 were laminated to each other on
their sides on which the adhesive was coated by pressing
them together under heat whereby the high-brightness
all-weather type pavement marking sheet material
according to the invention was completed.
(5) Measurement of the brightness in reflection
The brightness in reflection of the pavement
marking sheet material of the above described example
was measured with respect to each of a dry state and a
wet state of the glass microspheres with the angle of
incidence being varied between 60 and 80 . For
comparison, the brightness in reflection of the pavement
marking sheet material of the type described in the
above mentioned U.S.Patent No. 4,388,359 (hereinafter
referred to as "prior art A" and the pavement marking
sheet material of the type described in the above
mentioned Japanese Patent Application Laid-open No.
211403/1987 (hereinafter referred to as "prior art B")
was measured under the same measuring conditions as the
example of the present invention. The brightness in
reflection was measured by the brightness measuring
method according to JISZ9117. As to the brightness in
the state in which the glass microspheres are wet with
water, measurement was made in a state in which the
product was completely wet by filling a vessel made of
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an acrylic plate with water and thereafter reduction in
the brightness due to the acrylic plate was adjusted.
Results of the measurement of the respective pavement
marking sheet materials are shown in the following Table
1 and Fig. 3
.
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Table 1
Brightness in reflection of respective sheet
materials (cd/fc/ft~)
Sheet type Present invention Prior art A Prior art B
Ang ~ ,Dry state Wet state Dry state Wet State Dry state Wet state
of inc-\
i~en~ \
60 7.3 9.4 1.00 0.726 1.45 0.967
70 2.69 3.69 0.622 0.553 0.933 0.726
75 1.38 1.90 0.484 0.450 0.691 0.587
80 0.657 0.796 0.380 0.380 0.484 0.450
,
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From the above results of measurement, it will be
understood that the pavement marking sheet material
according to the invention has a higher brightness in
reflection than the prior art products at a large angle
of incidence of 60 - 80 . The results of measurement
show also that the brightness in reflection of the prior
art products is lower when the glass microspheres are
wet than when they are dry whereas the brightness in
reflection of the pavement marking sheet material
according to the present invention is higher when the
~ glass microspheres are wet than when they are dry.
For examining the influence of the film thickness
of the focus adjusting resin layer 7 of the reflex-
reflecting sheet 1 over the brightness in reflection in
the example of the present invention, the brightness in
reflection when the amount of coating of the resin
constituting the focus adjusting resin layer 7 is varied
was measured by employing the same measuring method as
was employed in the measurement described above.
Results of measurement are shown in the following Table
2 and Fig. 4 in which a specimen in which the coating
amount was 23.49 g/m is designa-ted as Sample A, a
specimen in which the coating amount was 2~.77 g~m as
Sample B, a specimen in which the coating amount was
35.38 g/m as Sample C respectively.
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Table 2
Relation between the film thickness of the
focus adjusting resin layer and brightness
in reflection (cd/fc/ft2)
Sheet A(23.49g/m ) B(29.77g/m ) C(35.38g/m )
sample
Angle of Dry state Wet state Dry state Wet state Dry state We~ state
incidence
60 2.64 3.79 6.05 7.69 4.14 5.56
70 1.04 1.56 2.09 2.83 1.46 2.02
75 0.591 0.869 1.01 1.39 0.80 1.08
80 0.347 0.416 0.489 0.628 0.452 0.521
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From the above results of measurement, it will be
understood that, in the pavement marking sheet material
according to the invention, the highest brightness in
reflection is obtained in the case where the film
thickness of the focus adjusting resin layer ~ is that
of the Sample B. The results of measurement show also
that, in all of the Samples A, B and C, a higher
brightness in reflection can be obtained when the glass
microspheres are wet than when they are dry.
