Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
This invention relates generally to adhesive backings and
more particularly concerns an adhesive tape for use as a mirror
backing.
BACKGROUND OF THE INVENTION
~ irrors, particularly large mirrors for household use such
as wardrobe mirrors, are subject to breakage and shattering
when struck. Obviously, the risks to persons positioned near
the mirror when it breaks are great if the glass is allowed to
shatter and fly apart, and the resulting debris is difficult to
clean up without injury. In order to protect the users of such
mirrors, an adhesive backing material is provided to the mirror
which prevents the glass from shattering if the mirror is
broken. This adhesive backing material holds the glass
together for a sufficient period to facilitate disposal thereof.
Backings for such mirrors commonly are tested by allowing a
suspended object of a predetermined weight to be swung from a
given distance against a mirror disposed in a generally
vertical orientation. The larger the weight, or the greater
the given distance, the greater the amount of force the backing
must withstand to prevent the glass from shattering. Most
existing adhesive backings used for such purposes will
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withstand only a 100 foot/pound test and are incapable of
withstanding a 400 foot/pound test. In a 100 foot/pound test,
a 100 pound weight is suspended from a point above a vertically
oriented mirror and is allowed to swing about the point towards
the mirror from a distance of one foot. In the 400 foot/pound
test a 100 pound weight is allowed to swing towards the mirror
from a distance of four feet. If the mirror breaks and the
backing tears or separates more than six inches, allowing the
glass to fly apart, the backing has not withstood the required
test.
Most such backings presently used are dispensed as an
adhesive tape from a roll. Such tapes are generally formed as
a single layer of polyethylene having a pressure sensitive
adhesive disposed on one side thereof.
SUMMARY OF THE INYENTION
An object of this invention is to provide an adhesive
backing material for mirrors capable of withstanding a 400
foot/pound test.
A further object of this invention is to provide an
adhesive backing material for mirrors which is capable of
withstanding a 400 foot/pound test, which is easily
dispensed from a roll and which is inexpensively
formed.
A construction in accordance with the
present invention comprises a mirror backing laminate
material with a first outer layer formed of a plastic
material and a second outer layer secured to the
first outer layer, the second outer layer being
formed of a plastic material. A central reinforcing
scrim is disposed between the first and second outer
layers. Normally hardened means is provided for
securing the first outer layer to the second outer
layer and for sealingly capturing the central scrim
therebetween. An adhesive layer is applied to an
outer surface of a selected one of the first and
second outer layers for securing the mirror backing
laminate material to the back of a mirror.
A method in accordance with the present
invention comprises the steps of providing two outer
plastic layers each having a normally hardened heat
sealable coating, inserting a reinforcing scrim
between the two outer layers, and compressing the
scrim between the two outer layers, and simultaneously
with the compressing step, heating the two outer
layers to activate the heat sealable coatings thereon.
In accordance with the above objects, a
mirror backing material capable of withstanding a
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400 foot/pound test is formed as a three layer
laminate. This laminated backing material includes
a central reinforcing layer sandwiched between two
outer layers. The central reinforcing layer typically
is a polyester scrim, while the outer layers are
formed of a plastic material such as polypropylene,
and the scrim is typically heat sealed between the
two layers of polypropylene. An adhesive layer is
provided on the outer surface of one of the poly-
propylene layers.
The mirror backing material of thls inven-
tion is formed by a process and apparatus in which
the polyester scrim is roller fed between two layers
of polyethylene which are then heat sealed together.
Thereafter, the adhesive layer is applied to one
surface thereof, and the resulting tape is accumulated
on a roll and cut to size.
DESCRIPTION OF THE DRAWING
The objects, advantages and features of
this invention will be more clearly appreciated from
the following detailed
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description taken in conjunction with the accompanying drawing
in which:
Fig. 1 is a pictorial representation of the backing
material of this invention in a partially delaminated condition;
Fig. 2 shows the backing material of Fig. 1 as applied to
~he back of a mirror;
Fig. 3 is a diagrammatic representation of apparatus for
forming the backing material of this invention; and
Fig. 4 is a diagrammatic representation of apparatus for
applying an adhesive layer to the backing material of this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference now to Fig. 1 , the mirror backing material
of this invention will be described. Material 1~ includes a
central reinforcing layer 12 sandwiched between two outer
layers 14 and 16. Reinforcing layer 12 typically is a scrim
which may be formed of polyester, and layers 14 and 16 are
secured together to seal reinforcing layer 12 therebetween.
Outer layers 14 and 16 typically are formed of a plastic
material, such as a polypropylene, which can be heat sealed to
itself, or which permits layers 14 and 16 to be secured
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together by means of an adhesive. The outwardly facing surface
of layer 16 is typically provided with a pressure sensitive,
self-crosslinking acrylic adhesive layer 18. Adhesive layer 18
allows material 10 to be readily and securely applied to the
back of a mirror as shown in Fig. 2, and layer 18 allows
material 10 to be stored and dispensed in a roll without loss
of adhesive strength. A release coating such as a silicone
coated paper may also be used in conjunction with the material
to allow storage thereof in other than a roll form. However, a
self releasing adhesive without a release coating is preferred.
Material 10 of this invention is capable of withstanding a
400 foot/pound test. This superior strength is produced by the
laminated nature of the tape as described herein.
Typically, reinforcing layer 12 is a scrim formed of 1000
denier polyester thread woven into a square grid of four warp
and four fill per square inch. In a preferred embodiment,
layer 12 has a tensile strength of about 35 pounds in the
machine direction and about 38 pounds in the cross direction
and can be purchased from Bay Mills Co., Tonawanda, New York.
In this preferred embodiment, layers 14 and 16 are each formed
of a polypropylene film coated with a heat sealable coating and
having a 70 gauge thickness, a tensile strength in the machine
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direction of about 10 pounds and in the cross direction of
about 13 pounds, and a Mullen Burst of 33 to 34. This film can
be obtained from Hercules Corp. of Dover, Delaware. The heat
sealable coating is preferably a thermoplastic resin which
remains normally hardened at room temperatures to prevent
movement of the strands of reinforcing layer 12. A preferred
material for the coating is Surlyn, a trademark product of E.
I. duPont de Nemours & Co. Adhesive layer 18 typically is an
acrylic polymer such as can be obtained from H & N Chemical Co.
of Totowa, New Jersey.
The method and apparatus for forming material 10 will now
be described with particular reference to Figs. 3 and 4.
Laminating apparatus 51 includes supply rolls 30, 32 and 24,
nip rollers 40, oven 42 and master roll 52. Two spaced rolls
30 and 32 of polypropylene film of the desired thickness and
having a heat sealable coating are provided at one end of
machine 36. Disposed between rolls 30 and 32 at the same end
of machine 36 is a third roll 34 of polyester scrim having the
desired pattern, thickness and strength. Film from rolls 30
and 32 and roll 34 are simultaneously fed to heated, powered
nip rollers 40 where the scrim is sandwiched between film from
rolls 32 and 30. Guide rollers 29 are provided for controlling
tension on the polypropylene film dispensed from roll 30, while
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guide rollers 31 and 33 control the tension on the scrim
dispensed by roll 34 and the polypropylene dispensed by roll 32
respectively. This sandwich is heated and compressed by
rollers 40 to activate the heat sealable coating and is then
fed to ovens 42 where the heat sealable coating on the
polypropylene film is cured to seal together the layers of
polypropylene from rolls 30 to 32, sandwiching the scrim
therebetween.
Thereafter, the resulting laminate 50 is accumulated onto a
master roll 52. Guide rollers 54 control tension on laminate
50 as it is fed to roll 52.
Adhesive applying apparatus 59 is shown diagrammatically in
Fig. 4 and includes application drum 60, metering knife 62,
oven 64, accumulating roll 66 and coating head 76. The master
roll 52 is removed from the laminating apparatus 51 and is
placed in line with apparatus 59 on support 6B. Laminate 50 is
fed to drum 60 by rollers 70 and 71 and is advanced from drum
60 to oven 64 by rollers 72 and 73. Rollers 71 and 72 hold
laminate 50 tightly against the top of drum 60 and the desired
adhesive is applied to one surface of laminate 50 through
coating head 76. Metering knife 62 is spaced from drum 60 a
predetermined distance and controls the thickness of the
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adhesive layer on laminate 50 in a known manner as the
laminate, with adhesive thereon passes thereunder. The
laminate having an adhesive layer applied thereto is fed to
drying oven 64 where the solvent for the adhesive is dissipated
and the adhesive is cured. The resulting adhesive coated
laminate is accumulated by roll 66 on a rewind stand 67, and
thereafter, this coated laminate is slit to the desired length
and width by a known rewind type slitter. A suitable rewind
slitter is the Cameron Type 26-3A produced by the Cameron
Division of Midland-Ross Corporation of New Brunswick, New
Jersey~
In view of the above description, it is likely that
modifications and improvements may occur to those skilled in
the art within the scope of this invention. Thus, the above
description is intended to be exemplary only, the scope of the
invention being defined by the following claims and their
equivalents.
