WO1998058107A2

WO1998058107A2 - Method for constructing wind resistant canvas covers

Info

Publication number: WO1998058107A2
Application number: PCT/CA1998/000608
Authority: WO
Inventors: Richard Auger
Original assignee: Texel Inc.
Priority date: 1997-06-13
Filing date: 1998-06-15
Publication date: 1998-12-23
Also published as: CA2208872A1; AU7903798A; WO1998058107A3

Abstract

A method is disclosed for constructing a wind resistant canvas cover to be used in agriculture, said cover having the form of a flexible membrane made from a structural fibre such as polyester fibre. During the manufacture, said structural fibre is combined with at least another absorbent fibre such as an acrylic acid polymer and/or another fibre with capillary action such as viscose. These other fibres are capable of absorbing or adsorbing water and hence retaining a large amount thereof forming a ballast whereof the value, expressed in the form of resistance to wind, can easily be computed.

Description

METHOD FOR CONSTRUCTING WIND REMOVABLE SHEETS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for constructing tarpaulins resistant to wind removal.

The tarpaulins obtained by this method are in the form of a flexible membrane comprising an absorbent material, the nature and quantity of which are chosen according to very precise parameters so as to absorb or adsorb a mass of water sufficient to ballast the tarpaulin and therefore give it wind resistance.

These tarpaulins are particularly usable in the agricultural field although the invention is not limited to this single application.

DESCRIPTION OF THE PRIOR ART In the field of farming, there are situations where surfaces must be covered with a tarpaulin, canvas, membrane or any flexible cover, whether for shade or growth purposes. forced anti-vegetative or anti-erosion barriers.

Often such tarpaulins can be carried by the wind. To avoid this problem, they should be held in place with fasteners or ballast weights. To date, these solutions are the only ones which, in the usual way, have been used.

There are however special conditions which allow alternative solutions. In certain situations, for example in nurseries and horticulturalists, frequent sprinkling wet large areas. If a membrane covering such a surface has the capacity to capture or withdraw and retain a significant amount of water, then this water will be able to provide a significant ballast. This ballasting allows the tarpaulin to hold in place despite winds of significant velocity.

In other situations, for example, when using nonwovens as a barrier to counter weed growth, discs cut from a tarp of nonwovens are placed on the surface of the growing pots. seedlings of trees or shrubs. These discs have a herbicidal function which helps to counter the growth of weeds on the surface of the pots. The use of such devices makes it possible to significantly reduce the labor costs intended for periodic manual weeding and the purchase of herbicides. However, here again, these discs should be ballasted or anchored. As the quantity of pots to be covered is very large, the transport and installation of anchors, fixings or weights for ballasting the discs, pose serious problems of congestion and the cost of labor becomes significant.

A method of construction of tarpaulins has now been discovered which makes the tarpaulins more resistant to removal by the wind, which corrects the drawbacks mentioned.

SUMMARY OF THE INVENTION

The present invention therefore relates to a method for constructing a tarpaulin which is resistant to removal by the wind, this tarpaulin being in the form of a flexible membrane made from a structural fiber. This method is characterized in that, during the manufacture of the flexible membrane, at least one other fiber chosen from the group consisting of fibers called "superabsorbent" and those called "with capillary action" is combined with the structural fiber. are capable of absorbing or adsorbing and thereby retaining a large amount of water to thereby form a ballast.

The present invention also relates to the tarpaulin thus constructed, as well as its use in the field of agriculture.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention requires incorporating into the structure of the sheet at least one fiber having the capacity to absorb or absorb a large amount of water and / or at least one fiber which is capable of exerting a capillary action. The presence of this or these additional fibers makes it possible to ballast the flexible membrane with water. The water can come from a sprinkler system and be captured by the cover or even be, by the action of capillary action, drawn from the ground that the cover covers. This ballast gives the flexible membrane the ability to withstand high velocity winds.

The sheet obtained by the method according to the invention is therefore composed of a mixture of natural or synthetic continuous or discontinuous fibers. These fibers are linked together in a "mechanical" manner, such as by weaving or needling, or by agglomeration using an adhesive. The types of fibers used come from three different categories, respectively:

- structural fibers, namely those having mechanical strength; - super-absorbent fibers; and - fibers capable of exerting a capillary action.

The structural fibers are preferably made of polypropylene, polyester or any type of fibrous material whose tenacity is greater than 3 grams per denier.

The superabsorbent fibers preferably consist of a polyacrylic acid polymer, an alginate or any other type of polymer capable of absorbing a mass of water twenty (20) times greater than its mass of origin when the polymer is dry.

The fibers capable of exerting a capillary action are preferably chosen from the family of synthetic or natural cellulosic polymers such as viscose and rayon, cotton, linen, jute or hemp, or from the family of type fibers. inorganic such as glass or rock wool. In fact, any material can be used as long as it is capable of producing a wetting angle of less than 90 degrees relative to water.

The cover necessarily contains a structural fiber. To this can be combined only a super-absorbent fiber, only a capillary action fiber, or both.

The method of the present invention makes it possible to specify a wind resistance (Rv) as a function of the mass proportion of the two or three types of fibers present in the membrane and of several other parameters making it possible to calculate the mass of water retained by the sheet. in use.

Thus, when using a structural fiber of density ps, denier ds (expressed in g / 9000m) and wetting angle θ _s (expressed in degrees) in a mass proportion ps; in combination with a superabsorbent fiber of density pa, denier da and wetting angle θ _a in a mass proportion pa and / or with a capillary action fiber of density pc, denier of and wetting angle θ _c in a mass proportion pc, it is then possible according to the invention to combine the structural fiber with the super-absorbent fiber and / or with the capillary action fiber so that the flexible membrane has a surface mass M (expressed in g / m ² ), a thickness E (expressed in mm) and a wind resistance Rv (calculated in km / hr) chosen and precalculated from the following equation:

Rv = 1 2.43 + 0.094 (M + Meau) in which M is defined as above and M water is the mass of water retained by the tank (expressed in g / m ^2> .

Meau is obtained from the equation: Meau = E.1 0 OOO.porosity.test in which

E is defined as above, the "porosity" is equal to 1 - db in which: dm

db = M and

1000 E

dm = pa.pa + pc.pc + ps.ps

and the "test" is a number equal to 0 if the capillary rise in water is less than 0, and equal to 1 if the capillary rise is greater than or equal to 0. More precisely, the equations that can be used to calculate the Rv value of the desired wind resistance as a function of a given use are the following:

Fiber parameters Structural fibers ps in g density of the structural fiber cm "ds in denier of the structural fiber

9000m θs in deg wetting angle of the structural fiber

Absorbent fibers pa in _g absorbent fiber density cm "

da denier absorbent fiber 9000m

θa in deg wetting angle of the absorbent fiber

Capillary fibers pc in _cj density of the capillary fiber cm "

of denier of hair fiber 9000 m

θc in deg wetting angle of the structural fiber

Tarpaulin settings

Construction parameters

M in _g areal mass of the tarpaulin m '

in mm sheet thickness Formulation parameters by mass proportion of absorbent fibers

pc mass proportion of hair fibers

ps mass proportion of structural fibers

Tarpaulin properties calculations

Calculation of the porosity of the tarpaulin db = M density of the tarpaulin

E.1,000

dm = pa.pa 1 -pc.pc + ps.ps density of the fibers constituting the tarpaulin

porosity = 1 -djb porosity of the tarpaulin (relative volume of empty dm)

Calculation of the relative surface occupied by the fibers

Ks = 3.536 conversion factor

Its area occupied by absorbent fiber in square meters

Sc = Ks pc.M surface occupied by the capillary fiber ^ dc.pc in square meter

Ss = Ks ps.M surface occupied by the structural fiber l ^~~ ds.ps in square meter

sa = Its proportion of the surface of absorbent Sa + Sc + Ss fibers

sc = Se proportion of the surface of the fibers

Sa + Sc + Ss capillaries

ss = Ss proportion of the surface of the structural Sa + Sc + Ss fibers

dm = = pa.da + pc.de + ps.ds calculation of the average denier of the fibers

df = 1 1.894.10 ° dm approximation of the average diameter of the fibers in meters f (porosity) = (1 -porosity) ^{1 5} . (1 + 56. (1 -porosity) ³ ) auxiliary equation for porosity

Dp = Df 10000 approximation of the average pore diameter 2f (porosity) of the pores in meters

Calculation of capillary rise

2 (72.88) rsa.cos (θa) + (sc.cos (θc) + ss.cos (θs)) l calculation of Dβ 981 la re2 capillary rise

If h≥ 0, test = 1 Otherwise test = 0 water retention test

Wind resistance calculation

Meau = E 1 0 000. porosite.test mass of water retained by the tarpaulin in grams per square meter

Rv = 1 2.43 + 0.094 (M + Meau) calculation of the wind resistance (limit wind velocity to reach the tarpaulin removal) in kilometers per hour

By wetting angle is meant the angle formed between a flat surface and the wall of a drop of liquid deposited on this surface. The smaller this angle, the more wetting. In practice, even the approximate wetting angles are adequate for the calculations. However, it is necessary to be certain that the wetting angle is less than or greater than 90 degrees.

Tarpaulins constructed according to the method of the invention were used in the form of discs covering pots in order to control weeds. These tarpaulins have been tested as will appear on reading the examples above. They withstood the wind very satisfactory. In fact, only 5% of the tarpaulins were removed by the wind, where conventional tarpaulins recorded removal rates of around 50%.

This wind resistance obtained by the method according to the invention makes it possible to significantly reduce the labor costs intended for the installation of anchors, fixings or weights to ballast such a membrane. In addition, the mass serving as ballast is not incorporated into the product during manufacture and therefore does not have to be transported or handled. The ballast is brought to the user, by an already existing distribution system, normally an irrigation system and in some cases by rain.

It will be understood that it is possible to control the importance of a desired ballast by modifying the quantity of super-absorbent fiber contained in the cover, the proportion of fiber with capillary action, the surface mass of the cover as well as its density. This possibility of ballast adjustment makes it possible to produce ranges of products capable of withstanding winds of determined violence.

In practice, the sheet according to the present invention can be rolled up or cut into pieces of various shapes.

The use of such a product is ideal for agriculture including for purposes ^of shade, forced growth, anti-vegetative barrier or silt fence. It performs all the functions of an ordinary tarpaulin while reducing the cost of the labor intended for its installation via, for example, fastening, anchoring or weight systems serving as ballast.

In the foregoing description, only reference has been made to a tarpaulin made of a single membrane made up of at least two types of fibers, including a super-absorbent or capillary action. It will be understood, however, that this same concept could be taken up in a somewhat different form.

Thus, the tarpaulin could be in the form of a composite with three thicknesses. The super-absorbent or capillary action fiber would constitute the central layer and would be covered on both sides by a sheet, for example, of polyester. The polyester sheets could be permeable or waterproof, as desired. In the embodiment using the impermeable sheet, at least one of the two sheets must however be perforated over the entire surface to allow the liquid to penetrate inside the composite and thus allow the absorbent material to absorb the liquid and to produced its ballast effect.

The tarpaulin in the form of a composite could also consist of only two thicknesses. The absorbent material would then form the upper surface of the composite to be in direct contact with the irrigation system. The polyester sheet would then constitute the bottom surface of the composite.

The invention and its advantages will be better understood on reading the following examples given without implied limitation.

EXAMPLE 1

A tarpaulin consisting of a nonwoven type membrane was constructed by needling according to the following specifications:

Construction parameter

Tarpaulin surface area (M): 1 70 g / m ² Tarpaulin thickness (E) 1.5 mm

Tarpaulin formulation

Super-absorbent fiber based on a 10% polyacrylic acid polymer

Denier of polyacrylic fiber (da): 2 deniers

Density of polyacrylic fiber (sa) 1 g / cm ³

Wetting angle (θa) about 30 degrees

0% capillary action fiber

Structural fiber based on polyester 90%

3 denier polyester fiber denier

Density of polyester fiber (c) 1.38 g / cm ³

Wetting angle (θs) about 90 degrees

Formulation parameters

Mass proportion of absorbent fibers (pa) 0.1

Massive proportion of hair fibers (pc) 0

Mass proportion of hair fibers (ps) 0.9

This tarp was cut and placed on a 20 cm (9 inch) diameter earthen pot with a rim about 1 cm high. Once deposited, it was sprayed with water and then subjected to a wind removal test in a wind tunnel where air was injected at an increasing speed in a direction substantially transverse to the pot. The air speed was measured with an anemometer. The results observed and those obtained using the above equations are as follows:

Calculated removal resistance 1 38 km / h Observed removal resistance 1 57 km / h

EXAMPLE 2

Another tarpaulin made of a non-woven type membrane was built and checked using the same method and under the same conditions as the previous tarpaulin.

During this test, again carried out in a wind tunnel, the water necessary for the ballast was introduced into the pot and was sucked up by the capillary action of the tarpaulin. For a transfer of water to be carried out in a useful way from the pot to the tarpaulin, it was necessary to have a capillary rise for the tarpaulin of the order of 10 cm.

This other tarpaulin was built under the following conditions:

Tarpaulin formulation

0% super-absorbent fiber

Viscose-based capillary action fiber 30% ^' Denier of viscose fiber 1.5 denier Density of viscose fiber 1.52 g / cm ³ Wetting angle approximately 30 degrees

Structural fiber based on polyester 70% Denier of polyester fiber 3 denier Density of polyester fiber 1.38 g / cm ³ Wetting angle about 90 degrees

Construction parameters

Tarpaulin surface area 1 77 g / m ² Tarpaulin thickness 0.65 mm

The results observed and those obtained using the above equations are as follows:

Calculated removal resistance 78 km / h Observed removal resistance 78 km / h

EXAMPLE 3 (comparative)

By way of comparison with Example 1, the tests were carried out under the same conditions as above with a tarpaulin of the nonwoven type manufactured without taking account of the method according to the invention, that is to say without adding 10% absorbent fibers based on a polyacrylic acid polymer.

Tarpaulin formulation

0% super-absorbent fiber

0% capillary action fiber 100% polyester-based structural fiber

Denier of polyester fiber 3 denier Density of polyester fiber 1.38 g / cm ³ Wetting angle about 90 degrees

Construction parameters

Tarpaulin surface area 1 70 g / m ⁵ Tarpaulin thickness: 1.5 mm

Calculated removal resistance: 28 km / h

Resistance to removal observed: 31 km / h

Claims

1. Method for constructing a tarpaulin which is resistant to wind removal, said tarpaulin being in the form of a flexible membrane made from a structural fiber, characterized in that, during the manufacture of the flexible membrane , we combine with the structural fiber at least one other fiber chosen from the group consisting of fibers called "super-absorbent" and those called "capillary action" which are capable of absorbing or absorbing water and from there retain a large amount of water to form a ballast.

2. Method according to claim 1, characterized in that: a structural fiber of density ps is used, denier expressed in g / 9000m, and wetting angle θs expressed in degrees in a mass proportion ps; using a super-absorbent fiber of density pa, denier da, and wetting angle θa in a mass proportion pa and / or a capillary action fiber of density pc, denier of and wetting angle θc in a mass proportion pc; and the structural fiber is combined with the super-absorbent fiber and / or the capillary action fiber so that the flexible membrane has a specific mass M expressed in g / m2, a thickness E expressed in mm and a resistance to wind Rv pre-selected and calculated in km / hr from the following equation: Rv = 1 2.43 + 0.094 (M + Meau) in which M is defined as above and Meau is the mass of water retained by the tarpaulin , expressed in g / m ² ;

Meau being obtained from the equation:

Meau = E 1 0 000.porosite.test where E is defined as above, "porosity" is equal to

1 -db in which: dm

db = M and

1,000 E

dm = pa.pa.pc.pc + ps.ps

and "test" is a number equal to 0 if the capillary rise in water is less than 0, and equal to 1 if the capillary rise is greater than or equal to 0.

3. Method according to claim 1 or 2, characterized in that: the structural fiber is chosen from the group consisting of polypropylene fibers and those of polyester having a tenacity greater than or equal to 3 grams per denier; the super-absorbent fiber is chosen from the group consisting of polyacrylic acid polymer fibers, alginates and other fibers capable of absorbing at least 20 times their weight in water; and the capillary action fiber is chosen from the group consisting of viscose, rayon, cotton, linen, jute, canker, glass, stone wool and other absorbent fibers having a wetting angle less than 90 ° to the water.

4. Method according to claim 1, 2 or 3, characterized in that only the structural fiber and the superabsorbent fiber are used.

5. Method according to claim 4, characterized in that the flexible membrane consists of 90% by weight of structural fiber and 10% by weight of super-absorbent fiber.

6. Method according to claim 5, characterized in that the structural fiber is polyester and the super-absorbent fiber is a polymer fiber of polyacrylic acid.

7. Method according to claim 1, 2 or 3, characterized in that only the structural fiber and the fiber with capillary action are used.

8. Method according to claim 7, characterized in that the membrane consists of 70% by weight of structural fiber and 30% by weight of fiber with capillary action.

9. Method according to claim 8, characterized in that the structural fiber is polyester and the capillary action fiber is viscose.

10. Tarpaulin resistant to wind removal, characterized in that it is obtained by the method according to any one of claims 1 to 9.

1 1. Use of a tarpaulin resistant to wind removal as defined in claim 10 in the agricultural field.