Abstrict An adhesive desiccant deposit comprising a hot melt adhesive and
a desiccant dispersed within the hot melt adhesive. The hot melt
adhesive has sufficient porosity to allow water molecules to pass
into the hot melt adhesive and contact the desiccant. The hot melt
adhesive may optionally contain an additive to increase the porosity
of the hot melt adhesive. One particular application of the deposit
involves an adhesive desiccant tape comprising a substrate, a first
adhesive layer disposed on the bottom of the substrate, a removable
liner disposed on the first adhesive layer on the side of the first
adhesive layer away from the substrate, and an adhesive desiccant
deposit disposed on the top of the substrate.
Claims What is claimed:
1. An adhesive desiccant deposit comprising:
a hot melt adhesive;
a desiccant dispersed within said hot melt adhesive, said desiccant
selected from the group consisting of silica, calcium oxides, activated
carbon, molecular sieves, and combinations thereof; and
a cellulose additive to increase the porosity of said hot melt
adhesive;
said hot melt adhesive having sufficient porosity to allow water
molecules to pass into said hot melt adhesive and contact said desiccant.
2. The desiccant deposit of claim 1 wherein said hot melt adhesive
is selected from the group consisting of vinyl acetate, ethyl vinyl
acetate, polyurethane, and combinations thereof.
3. The desiccant deposit of claim 1 wherein said desiccant is selected
from the group consisting of silica gel, calcium oxide, molecular
sieves, activated carbon, and combinations thereof.
4. The desiccant deposit of claim 1 wherein said desiccant is an
indicating desiccant.
5. The desiccant deposit of claim 1 wherein said desiccant is a
non-indicating desiccant.
6. The desiccant deposit of claim 1 wherein said desiccant is a
reversible desiccant.
7. The desiccant deposit of claim 1 wherein said desiccant is an
irreversible desiccant.
8. The desiccant deposit of claim 1 wherein said desiccant is a
silica gel.
9. An adhesive desiccant tape comprising:
a substrate with a top and a bottom;
a first adhesive layer disposed on said bottom of said substrate;
a removable liner disposed on said first adhesive layer on the
side of said first adhesive layer away from said substrate; and
an adhesive desiccant deposit disposed on said top of said substrate,
said adhesive desiccant deposit comprising a hot melt adhesive which
has both a desiccant and a cellulose additive to increase the porosity
of said hot melt adhesive dispersed within said hot melt adhesive,
said desiccant selected from the group consisting of silica, calcium
oxides, activated carbon, molecular sieves, and combinations thereof;
and said hot melt adhesive having sufficient porosity to allow water
molecules to pass into said hot melt adhesive and contact said desiccant.
10. The desiccant tape of claim 9 wherein said hot melt adhesive
is selected from the group consisting of vinyl acetate, ethyl vinyl
acetate, polyurethane, and combinations thereof.
11. The desiccant tape of claim 9 wherein said desiccant is selected
from the group consisting of silica gel, calcium oxide, molecular
sieves, activated carbon, and combinations thereof.
12. The desiccant tape of claim 9 wherein said desiccant is an
indicating desiccant.
13. The desiccant tape of claim 9 wherein said desiccant is a non-indicating
desiccant.
14. The desiccant tape of claim 9 wherein said desiccant is a reversible
desiccant.
15. The desiccant tape of claim 9 wherein said desiccant is an
irreversible desiccant.
16. The desiccant tape of claim 9 wherein said desiccant is a silica
gel.
Description FIELD OF THE INVENTION
This invention relates to desiccants, and more particularly to
desiccant compositions which are designed to allow easy, efficient,
and precise placement of the desiccant deposit wherever the user
desires.
BACKGROUND OF THE INVENTION
Many applications exist in which it is desired to reduce ambient
moisture by placing a desiccant in or near a particular area. These
applications include such items as medical diagnostic test strips,
food and medicine containers, and packaging materials.
A general method and apparatus used to position a desiccant near
an object which is to be kept moisture-free involves the placement,
near the object, of a pouch which contains a desiccant. In this
conventional method, the pouch is made of a material which is water
vapor permeable, and water vapor is allowed to permeate the pouch
and be absorb ed by the desiccant inside the package. This method
and apparatus allows loose desiccant, however, to exist inside the
pouch. Such loose desiccant raises several potential problems.
The first problem is the risk of spillage of the desiccant if the
pouch were to be punctured. That is particularly problematic where
it is desired that the desiccant and material which is to be kept
dry should not contact one another. It is also problematic where
desiccant grains could interfere with, or contaminate, a nearby
machine or material. A further risk involves ingestion of the desiccant.
This is especially likely if the desiccant pouch application involves
food or medicine. All of these risks are associated with the use
of desiccants loosely contained inside a permeable pouch.
A second potential problem with the above use involves the difficulty
which exists in placing an exact amount of desiccant in close proximity
to the material to be kept dry where the material or its location
is very small and difficult to reach. Often, where pouches of desiccant
material are used, or loose desiccant material is glued to a surface,
packages must be modified to accommodate the bulk desiccant. Where
that arrangement is necessary, packaging inefficiencies are present.
Also, in such cases, alternative methods and devices must be used
to place the desiccant effectively.
Medical diagnostic test strips are used, for example, in a variety
of applications. Such strips are exposed to samples of blood, feces,
or urine, for example, where specific reagents on the test strip
are designed to detect various components in the sample. Medical
diagnostic test strips are specifically used to detect the level
of glucose in a patient's blood. Such test strips must be exposed
to an atmosphere that is substantially moisture-free until moments
before use in testing a sample. The strips are often highly water
absorbent, and absorption of moisture may alter test results.
Accordingly, the known industry practice for keeping the test strips
dry is to contain a plurality of such test strips in a container
or vial. The cap for the container has a desiccant contained in
it to absorb water from the air inside the container. In this manner,
the strips within the container are kept dry. When ultimately used,
a doctor or other testing personnel, including a patient himself
removes the cap from the container, extracts one of the test strips,
and immediately places it in the sample to be tested (or places
a small quantity of the sample to be tested on the test strip).
Exposure of the strips to the ambient atmosphere before use is thus
minimized to reduce water vapor absorption by the test strip.
Potential problems with this are many, but include the difficulty
associated with the placement of the desiccant into the cap. Some
methods which have been developed to achieve desiccant placement
in this configuration include gluing the desiccant gel into a lid,
or actually constructing a cap out of a desiccant-containing plastic.
These methods are specialized, however, and often require difficult
manufacturing techniques.
The deficiencies of the conventional desiccant applications show
that a need still exists for a desiccant technology which allows
precise, controlled, and easy placement of the desiccant in a location
and in an amount which is desired. Therefore, one object of the
present invention is to provide a desiccant technology which allows
easy, precise, and controlled placement of a desiccant into small
areas. Another object of the present invention is to provide a desiccant
technology which allows easy placement of a consistent and controlled
amount of desiccant over a large area. Yet another object of the
present invention is to provide a desiccant technology which allows
a user to apply a desiccant through simple devices. Still another
object of the present invention is to provide a desiccant technology
which allows the use of a desiccant in close proximity to other
materials without the risk of loose desiccant falling free and causing
subsequent problems.
SUMMARY OF THE INVENTION
To achieve these and other objects, and in view of its purposes,
the present invention provides an adhesive desiccant deposit comprising
a desiccant gel dispersed within a hot melt adhesive. The hot melt
adhesive has sufficient porosity to allow water molecules to pass
into the hot melt adhesive and contact the desiccant gel. The hot
melt adhesive may optionally contain additives such as cellulose,
silica, or other suitable materials to increase its porosity. The
adhesive desiccant deposit allows easy, efficient, and precise placement
of controlled amounts of desiccant wherever the user desires. One
particular embodiment of the invention involves an adhesive desiccant
tape comprising a substrate with a top and a bottom, a first adhesive
layer disposed on the bottom of the substrate, a removable liner
disposed on the first adhesive layer on the side of the first adhesive
layer away from the substrate, and an adhesive desiccant deposit
disposed on the top of the substrate. During manufacturing of the
tape, the adhesive desiccant deposit is easily placed along the
top of the substrate by allowing it to flow, while heated, onto
the substrate, and then allowing it to cool. The product is a tape
with a uniform desiccant composition which can be easily applied
to the surface of a container or other material where it is desired
to absorb water.
BRIEF DESCRIPTION OF THE DRAWING
The invention is best understood from the following detailed description
when read in connection with the accompanying drawing. It is emphasized
that the various features of the drawing are not to scale. On the
contrary, the dimensions of the various features are arbitrarily
expanded or reduced for clarity. Included in the drawing is the
following FIGURE:
FIG. 1 is a cross sectional view of the tape according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention involves an adhesive desiccant deposit comprising
a desiccant gel dispersed within a hot melt adhesive. The hot melt
adhesive is selected such that it has sufficient porosity to allow
water molecules to pass into the adhesive matrix and contact the
desiccant contained in the matrix (i.e., the hot melt adhesive is
water permeable). The adhesive desiccant deposit allows easy, efficient,
and precise placement of controlled amounts of desiccant wherever
the user desires. Many applications exist where the combined desiccant
and hot melt adhesive matrix (the desiccant deposit) can be used.
These applications are discussed below, and include the use of the
desiccant deposit in different ways to meet the needs of industry
where improved desiccant technology is particularly needed.
One particular embodiment of the invention is illustrated in FIG.
1. FIG. 1 shows an adhesive desiccant tape comprising a substrate
100 a first adhesive layer 110 disposed on the bottom of the substrate,
a removable liner 120 disposed on the first adhesive layer, and
a desiccant deposit 130 disposed on the top of the substrate. During
manufacturing of the tape, the desiccant deposit 130 is easily placed
along the top of the substrate by allowing it to flow, while heated,
onto the substrate 100 and then allowing it to cool. The product
is a tape with a uniform desiccant composition covering its surface
which can be easily applied to the surface of a container or other
material where water adsorption is desired. The desiccant deposit
on top of the substrate is uniform both with respect to concentration
of desiccant and also overall thickness.
An aspect of the present invention includes an improved process
of manufacturing. The process can be automated and can place exact
amounts of desiccant onto packages or other materials. The ability
of the desiccant deposit to flow when heated allows it to be placed
where it is needed, in the shape in which it is needed, and in the
amount in which it is needed. This ability provides not only improved
space efficiencies in the manufacturing process, but also in the
final product. Less desiccant is wasted when the exact amount which
is needed can be precisely placed.
The present invention also allows the placement of a relatively
thin layer of desiccant over a large area or sheet. Thus, a "flood
coat" may be applied to a large sheet of substrate material,
such as in the case of applying the desiccant deposit to the substrate
during the manufacturing of the tape as discussed above. The thickness
of the layer will vary depending on the application, but a preferred
range for many flood coat applications is 0.001 to 0.05 inches thick.
An even more preferred range is 0.001 to 0.03 inches thick.
The present invention also allows the "printing" of the
desiccant deposit. Standard printing technologies may also be used
in accordance with the desiccant deposit of the present invention.
In such cases, the material printed, usually through a metal screen,
is the desiccant deposit itself.
Another benefit provided by the deposit of the present invention
is the ability to apply it very simply. One such simple application
procedure involves using it in an ordinary glue gun. The user places
the desiccant deposit, in the form of a stick or other suitable
shape, into a glue gun, heats the deposit material, and applies
the deposit where the desiccant is needed.
Still another benefit of the present invention is that it prevents
desiccant from becoming loose (particularly problematic in several
conventional technologies) and contacting, contaminating, or otherwise
interfering with surrounding materials or equipment. The desiccant
deposit of the present invention provides an enclosed polymer matrix
in which the desiccant gel is contained. Thus, water vapor can enter
the matrix and be adsorbed, but the desiccant will not fall free
from the hot melt adhesive.
The desiccant deposit comprises a hot melt adhesive with a desiccant
dispersed within it. Generally, any appropriate hot melt adhesive
and desiccant can be used for this purpose. The adhesive serves
two primary "adhesive" functions. First, the adhesive
contains the desiccant, holding it in place. Second, the adhesive
allows the placement of the desiccant and hot melt adhesive combination
deposit onto a particular surface. Of course, the adhesive serves
other functions, such as limiting, based on size, what molecules
may enter and contact the desiccant. The hot melt adhesive must
be porous enough, of course, to allow water molecules to enter and
move within it. Certain molecules which are larger than water would
be prevented, perhaps, from entering the adhesive, depending on
the particular hot melt adhesive selected.
The hot melt adhesive may optionally include cellulose, silica,
or other suitable materials to increase its porosity. The presence
of such an additive in the matrix impacts the rate of absorption
of water vapor. More particularly, the amount of additive (e.g.
cellulose) can be controlled to achieve a desired overall rate of
absorption. For example, the greater the cellulose concentration,
the faster the overall rate of absorption.
The performance of the present invention is affected by the particular
selection of hot melt adhesives. Some adhesives work better than
others, but one skilled in the art can easily determine which ones
meet the needs of a particular application. Typical examples include
ethyl vinyl acetate, polyurethane and vinyl acetate. For example,
one of the best hot melt adhesives is ethyl vinyl acetate (EVA).
But even within the varying types of EVAs, it has been found that
some work better than others. Optimization of desiccant deposit
performance can be made easily, however, without undue experimentation
by one skilled in the art.
Regarding the size of desiccant selected, consideration should
be given to the desired final thickness of the deposit layer. The
mesh size of a silica gel, for example, should never be larger than
the thickness of the deposit coating. Obviously, if it were, an
uneven surface, and exposed desiccant, could result. Thus, for example,
if a deposit thickness of 0.002 inches were desired, the particular
silica gel selected would have a particle size less than 0.002 inches.
The type of desiccant used can also vary. Silica gels (SiO.sub.2
based compounds), calcium oxides, activated carbon, and molecular
sieves can all be used in accordance with this invention. These
are only some examples of effective desiccants which can be mixed
with the hot melt adhesives. In addition, both indicating and non-indicating
desiccants can be used, and reversible and irreversible desiccants
can be used. Non-indicating desiccants remain the same color (or
clear) no matter what amount of moisture has been absorbed. Indicating
desiccants change color as moisture is absorbed. Reversible desiccants
can be dried and reused. Irreversible desiccants cannot be reused
once saturated. Moreover, selection of desiccant and hot melt adhesive
can be made by one skilled in the art based on particular applications.
The above text has addressed the invention in general terms. The
following specific examples are offered to define the invention
further, but in no way limit the invention. In the embodiments of
the present invention discussed below, particular desiccant and
adhesive combinations are illustrated. Additional desiccants and
adhesives may be combined in any of the embodiments as necessary
for a particular application. |