Field of the invention
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The present invention relates to rain protection and rain barrier articles like
raincoats, roof liners for buildings or tents and other protection covers intended to
prevent entry of rainwater. According to the present invention the articles are
provided with or by at least one breathable layer of a resilient, three dimensional
web which consists of a liquid impervious polymeric film having apertures. These
apertures form capillaries which are not perpendicular to the plane of the film but
are disposed at an angle of less than 90° relative to the plane of the film and
installed to retard entry of rain.
Background of the Invention
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Primary need of rain barrier or rain protection articles is to prevent passage of
rainwater through the article. For example in the case of roof liners, that is the
material installed on top of the wooden roof construction but below the tiles in
order to prevent exposure of the wooden roof construction to moisture, water
entry can only come from rain water which does always fall from above, (or under
windy conditions with an angle). However no surface of the roof construction
would usually be exposed to rain water from below ( in a gravitational sense ).
The same is of course true for camping tents. Another possible use of barriers is
for walls of buildings which are exposed to rain water seeping through the soil.
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Such barriers are disclosed for example in EP-A-704 297 in which completely
impermeable coatings (oil and water) to outsides of cellar walls are disclosed.
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According to the present invention it has therefore been recognized and utilized in
conceiving the present invention that exposure to rain water will always happen in
a directional sense such that a directionality of a water barrier can be utilized.
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There are other rain barrier or protection articles in which similar considerations
can be applied. In particular rain wear ( reusable or disposable ) for people will
also have regions which are exposed to rain from a constant or almost constant
direction. Another usage for the articles according to the present invention would
be protective covers against directional liquid exposure such as can be found in
the agricultural field when spraying chemicals (fertilizer or other plant treatments).
A further usage situation for the articles according to the present invention would
be disposable outer liners for cars, cycles or shipment packages for example in
the agricultural field or for the transportation industry.
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Rain barrier or protection articles satisfying the above objectives are of course
already known in the form of water impermeable polymeric films. Such films have
the benefit of not being directional i.e. the installation or usage thereof is
independent of the direction from which water will impact. However they also
suffer a tremendous drawback from causing an occlusion to airborne humidity
such as water vapor but also other airborne materials such as dust particles.
Conventionally the occlusion is accepted to achieve protection against rain water
entry. Articles having water vapor transport characteristics such as Gore Tex (RT)
or other microporous film materials are already well known. However they do not
allow free air circulation and therefore have a very slow water vapor transport
capability. On the other hand eliminating occlusion could be achieved by
apertured film materials which are however not satisfactory in respect to their
barrier function.
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Therefore the intended benefit of the rain protection articles according to the
present invention is the ability to allow water vapor and air to freely pass in and
out through the barrier while the rain protection function is kept. It has now been
found that this can be achieved by use of the principles disclosed in WO97/03818,
W097/03795 or US-A-5.897.543 to design the special breathable rain barrier
according to the present invention. It is therefore an objective of the present
invention to provide rain barrier articles which allow free air circulation through
them while at the same time preventing or at least minimizing water transmission
of water deposited primarily in a designated direction, such as rain. At the same
time reapplication of known and proven manufacturing processes and equipment
is desirable for economic reasons. Satisfying this objective as well as other
benefits of the present invention will become readily apparent when considering
the summary of the invention and the detailed description thereof.
Summary of the invention
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The present invention relates to airpermeable rain protection articles. Rain
protection articles are those articles which are intended to protect a wearer or a
thing against becoming wet from rain. Rain protection in this sense also provides
protection from being exposed to chemicals or dirt conventionally contained in
rain or chemicals contained in sprayed liquid having a designated direction ( such
as fertilizer or fungicides in agricultural use). Examples of rain protection articles
are rain coats, roof liners and wall liners in construction, tents, car or packaging
materials in the agricultural field or the transportation industry.
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According to the present invention the rain protection articles can be reusable for
example in rain coats or disposable such as for example in rain protection capes.
They can of course also be intended for longterm, permanent use such as roof
liners or wall liners on buildings.
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The rain protection article according to the present invention has the particular
benefit and characteristic of being airpermeable. Airpermeability is important for
clothing but also for example in the building industry to allow for water vapor to
escape through a roof or wall while still providing the rain protection performance.
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Of course both objectives are not compatible since airpermeability usually also
results in a loss of liquid imperviousness. Therefore the present invention utilizes
the phenomenon of rain water having a designated direction relative to the
surface of the protection material.
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According to the present invention the rain protection article comprises a resilient
three dimensional layer which has a first and a second surface. The second
surface is that which is exposed to rain while the article is used for rain protection.
The layer consists of a liquid impervious polymeric film with apertures which are
formed by capillaries. The capillaries allow the free air exchange between the first
and the second surface of the liquid impervious film. The capillaries have side
walls which extend away from the second surface of the film and the capillaries
have a first opening in the first surface of the film and a second opening at the
end of the capillary which is spaced apart from the second surface of the film.
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According to the present invention the capillaries extend away from the second
surface of the film at an angle which is less than 90° relative to the plain of the
film and the angle points the capillaries away from that direction from where rain
falls during usage of the rain protection article.
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In a preferred embodiment all capillaries in the film are substantially identical and
preferably homogeneously distributed across the film. The angle at which the
capillaries extend away from the second surface of the film is preferably between
85 ° and 20°, more preferably between 65 ° and 25° and most preferably between
55° and 30°. The shape of the capillaries is most preferably such that they form
cones in which the opening in the first surface of the film is larger than at the end
of the capillaries. In an alternative embodiment or in combination with the cones
the capillaries can be curved so as to direct the second opening again towards
the second surface of the film.
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According to the present invention the open area for conducting air through the
film should provide a effective airpermeability. In this respect it is desirable to
have such an open area of at least 5 %, preferably at least 10%, most preferably
at least 15 %, measured on the basis of the area of the first surface of the film for
conducting air between the two surfaces of the film.
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At the same time a reduction of the surface effects within the capillaries retarding
the free airflow can be achieved by minimizing the capillary wall surface area
relative to the cross section area available for airpermeation. That would
conventionally result in circular capillaries or cones having a circular cross
section. Of course the size of the capillaries is important. The first opening of the
capillaries measured within the plain of the film has been found to be preferably in
the range between 1-20 mm2, preferably 3-10 mm2 and most preferably 5-8 mm2.
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The film material alone can most preferably be used as roof liner or for disposable
rain coats or capes. For reusable rain coats a combination with other layers such
as non wovens or woven material has been found more appealing since the direct
skin contact (even with small areas of polymeric film) often causes the sensation
of sweatiness. In this context it is also possible that the film material is
microporous as starting material so as to allow at least water vapor transport in
regions where no apertures are present, thus combining the benefits of air
permeability with water vapor permeability while maintaining rain protection.
Brief description of the drawings
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Figure 1 shows a photocopy representation of the first surface of a film useful in
the articles according to the present invention.
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Figure 2 shows a photocopy representation of the second surface of the film
useful in articles according to the present invention.
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Figures 3 through 7 show particular alternative embodiments of the capillaries
used for the film useful in articles according to the present invention.
Detailed description of the invention
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In the following the air permeable rain protection article according to the present
invention will be exemplified as a disposable rain coat. Other articles as
mentioned above utilize however the same principles for providing air permeability
and rain protection and their detailed construction will be readily apparent to those
skilled in the art.
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According to the present invention suitable airpermeable rain coats comprise a
resilient three dimensional layer which consists of a liquid impervious film which
has apertures and is air permeable. The film is oriented such that it retards or
prevents rain dropes and water running down on the rain coat from passing
towards the inside while allowing free air flow through it.
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According to the present invention any additional layer of the rain coat needs to
provide at least air permeability in order to improve the comfort benefit from the
breathability of the article. In this context suitable water vapour and air permeable
layers include two-dimensional micro- or macro-apertured films, which can also
be micro-or macroscopically expended films, formed apertured films and
monolithic films, as well as nonwovens, or wovens. Such films and film materials
are disclosed in detail e.g. in EPO 293 482 and the references therein, or US 3,
929,135, US 4 637 819 and US 4 591 523.
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The film layer according to the present invention provides air and water vapour
permeability by being apertured. Preferably this layer is made in accordance with
the aforementioned US-A-5,591,510 or PCT WO- 97/03818, WO-97/03795. In
particular, this layer comprises a polymeric film indicated in figure 1 and 2 as layer
(55), having capillaries (54). The capillaries extend away from the second surface
of film (55) at an angle which is less then 90 degrees. In figure 3 through 7
alternative embodiments of such capillaries are shown. Preferably the capillaries
are evenly distributed across the entire surface of the layer, and are all identical.
However, articles having only certain regions provided with apertures, for example
only in the regions which are substantially vertical such as the arm portions of a
coat or excluding zones which are substantially horizontal such as the shoulder
portions, could be provided with a film in which only selected regions have
capillaries according to the present invention or with an additional impermeable
layer in regions where permeability is not desired.
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Methods for making such three-dimensional polymeric films with capillary
apertures are identical or similar to those found in US 3 929 135, US 4 151 240,
US 4 319 868, US 4 324 426, US 4 343 314, US 4 591 523, US 4 609 518, US 4
629 643, US 4 695 422 or WO 96/00548, US 5 591 510 or WO 97/03118 and WO
97/03795. Typically a polymeric film such as a polyethylene (LDPE, LLDPE,
MDPE, HDPE or laminates thereof) is heated close to its melting point and
exposed through a forming screen to a suction force which pulls those areas
exposed to the force into the forming apertures which are shaped such that the
film is formed into that shape and, when the suction force is high enough, the film
breaks at its end thereby forming an aperture through the film. Other film
materials include PVC, polypropylene, polyesthers, polyethers, polyvinyl alcohols
and other such as monolithic polymer film e.g. Hytrel ™ film from DuPont,
Corporation, USA. Films can also be treated to have an increased water
repellency e.g. by Teflon ™, silicone, or other fluoride coatings or by residue
integrated hydrophobicity increasing compounds such as fluoro carbons.
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Various forms, shapes, sizes and configurations of the capillaries are possible
and will be discussed in reference to figures 3 through 7 in the following. The
apertures (53) form capillaries (54) which have side walls (56). The capillaries
extend away from the wearer facing surface of the film (55) for a length which
typically should be at least in the order of magnitude of the largest diameter of the
aperture while this distance can reach up to several times the largest aperture
diameter. The capillaries have a first opening (57) in the plane of the first surface
of the film (55) and a second opening (58) which is the opening formed when the
suction force (such as a vacuum) in the above mentioned process creates the
aperture. Naturally the edge of the second opening (58) may be rugged or
uneven, comprising loose elements (70) extending from the edge of the opening
as shown in Fig. 2 and 3. However, it is preferred that the opening be as smooth
as possible so as not to create a capillary liquid transport force between the
extending elements at the end of the second opening (58) and the capillary (54)
aperture (53).
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As shown in figure 4 the first opening has a center point (157) and the second
opening also has a center point (158). These center points for non-circular
openings are the area center points of the respective opening area. When
connecting the center point (157) of the first opening (57) with the center point
(158) of the second opening (58) a center axis (60) is defined. This center axis
(60) forms an angle (59) with the plain of the film which is the same plain as the
first surface of the film (55). This angle should be preferably in the range between
85 and 20 degrees, more preferably between 65 degrees and 25 degrees, and
most preferably between 55 and 30 degrees.
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It is of course possible to allow the capillaries to take the shape of a funnel such
that the second opening (58) is (substantially) smaller than the first opening (57)
when considering the opening size in a plain perpendicular to the center axis (60).
Such an embodiment is shown in figure 3. In figure 5 another embodiment of the
capillaries useful for the present invention is shown which is curved along its
length towards the second surface of the film (55).
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In figure 6 another preferred embodiment of a capillary according to the present
invention is shown which has a first portion (257) and a second portion (258). The
first portion (257) of the capillary is different in direction than the second portion
(258) of the capillary (54). This difference can also be in shape, size, and form of
the portions of the capillary in order to achieve the desired level of airpermeability
while preventing liquid passage through the film. Such an example is shown in
figure 7. It should be noted that the second opening, in accordance with the
present invention, has to be directed away form the incident direction of rain.
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Without wishing to be bound by theory it is believed that the capillaries according
to the present invention in the film layer of the breathable backsheet allow air and
water vapour permeability which is not hindered by them being slanted at an
angle or by the shape as indicated above. At the same time the slanting and
shaping according to the present invention will prevent or hinder liquid transport
through the capillaries towards the inside of the article due to gravitational force.
Examples
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The polyethylene film shown in figures 1 and 2 was used to compare the rain
resistance relative to an umbrella nylon fabric. The test is conducted in
accordance with ASTM D3379 which is the standard test method for rain wear.
The test was conducted using a water resistance rain tester 35-1994 as a
standard instrument developed by the American Association of Textile Chemist
and Colorist (AATCC). This instrument is also used to investigate umbrella fabrics
which are however usually tested according to ASGM D4112 as the standard test
setup.
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Basically the instrument measures the resistance of a fabric or combination of
fabrics to the penetration of water by impact to predict the rain penetration (or lack
thereof). The water penetration is indicated by the increase in weight of water
penetrating through the test fabric. The test is performed at different head
pressures (rain strength)
- short shower:
- 30 seconds from 60 mm height
- usual rain:
- 2 minutes from 60 mm height
- rain storm:
- 5 minutes from 950 mm height.
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In the table below a combination of two layers of the polyethylene film according
to figure 1/2, one layer of the film according to figure 1/2 together with a
polypropylene nonwoven, a film according to figure 1/2 sandwiched between two
layers of polypropylene nonwoven and an umbrella fabric were tested. The multilayered
structure including the film according to figure 1/2 were laminated without
adhesive between them but just held together along their periphery overlaying
each other.
| film plus film | film plus nonwoven | nonwoven plus film plus nonwoven | Nylon fabric from an umbrella |
the simulated rain was incident onto the: | film | film | nonwoven | conventional umbrella fabric outside |
rain shower | 0 | 0 | 0 | 3g |
usual rain | 0 | 0 | 0 | > 5g * |
rain storm | 0.25 | 0 | 0 | > 5g * |
Results measured according to ASTM D3779 in g, lower values mean lower
barrier function. (*) Results of more than 5 gram are not measured but reported
as failure. |
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When considering breathability it is of course apparent that a completely liquid, air
and water impermeable polymeric film will have best performance for rain
penetration. It would thus be as good as any of the laminates above, however
without providing air breathability. Also the benefit of water vapor permeability as
achieved by microporous films or breathable monolithic films is substantially less
than the water vapor transport achievable through airpermeable surfaces.
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According to the present invention the rain protection article can be used
beneficially in the context of rain coats, roof barriers and all the other articles
mentioned supra. It is therefore apparent to the skilled person that the respective
rain barrier article should also have all those features and parts which are typical
for products in the context of their intended use.
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As an alternative to the above use of the resilient three dimensional polymeric film
it is also possible, particularly in the context of personal rain protection garments,
to have some or all capillaries extend from the first surface of the film. In such a
case the capillaries also allow free air circulation and extend from the first surface
at an angle of less than 90° measured from the plain of the film. However the
angle needs to direct the capillaries in an upward direction i.e., substantially
against the gravitational force vector. Preferably the capillaries are such that the
opening in the second surface, which is exposed to rain is not larger than the
opening at the end of the capillaries in order to prevent a capillary pumping surge
action directed against gravitational forces.
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The primary benefit of this alternative is that the capillaries when extending from
the first surface are on the inside of the rain protection article. Thereby any
internal squeezing of the film surface causes the capillaries to temporarily
collapse and close. Especially for rain coats or caps this allows to provide the
whole article with capillaries e.g. under arms or on shoulders. It also provides a
smooth outside which is appealing and the loose elements pointing to the inside
reduce/prevent the appearance and sensation of plain plastic film touching the
skin (for articles without inner liner) which is otherwise known to cause rejection of
polymeric film garments.