WO2006124179A1

WO2006124179A1 - Greenhouse panels

Info

Publication number: WO2006124179A1
Application number: PCT/US2006/014598
Authority: WO
Inventors: Paul D. Haemhouts
Original assignee: Dow Global Technologies, Inc.
Priority date: 2005-05-13
Filing date: 2006-04-19
Publication date: 2006-11-23
Also published as: IL186796A0; KR20080013908A; EP1903854A1; TW200638866A; CN101175399A; JP2008540879A; CA2607613A1; BRPI0612478A2

Abstract

Disclosed are light transmissive panels in general and, in particular, extruded multi-walled thermoplastic sheet structures having corrugated shaped wall(s) and/or surface(s) for use as roof and wall elements in greenhouses, said sheet structures having increased light transmission with combination of improved durability, good insulating properties and reduced maintenance requirements.

Description

GREENHOUSE PANELS

FIELD OF THE INVENTION

This invention relates to light transmissive panels in general and, in particular, to panels for use as roof and wall elements in greenhouses having increased light transmission with a combination of improved durability, good insulating properties and reduced maintenance requirements.

BACKGROUND OF THE INVENTION

Greenhouse cultivation is controlled, for certain types of agriculture products, by truly industrial criteria. The profitability of these cultivations depends sometimes on a narrow margin of benefit. Thus, the farmer must optimize all factors, one of the factors being the amount of sunshine. Increasing the luminosity inside the greenhouse is especially important in that it is known that a 1 percent reduction in light corresponds to a reduction of production in the order of: 1.2 percent for vegetables, 0.9 percent for flowers to be cut, and 0.6 percent for ornamental plants. It is therefore advantageous to increase the average transparency of the walls and roof panels of such greenhouses while reducing the sizes of the elements which form the framework which form opaque surfaces.

The rays of the sun not only illuminate the interior of a green house, but heat it as well. It is desirable for the walls and roof of a greenhouse to have good insulating properties to control heat loss and gain sufficiently to be able to economically heat in the winter and cool in the summer. Another important problem concerns the resistance of the roof and wall panels to the weather. The mechanical characteristics of the covering material must be able to withstand the weather and maintain itself in all conditions. Thus, the combination of the covering material and panel design must be able to withstand elements, such as hail, without shattering or otherwise becoming damaged. The design of roof panels should also facilitate drainage from rain and melting snow. Further, the luminescence of roof panels which collect and retain dust, dirt, and other particulates decreases dramatically as compared to a clean panel.

Thus, it would be desirable to provide a panel for use as roof and wall elements in greenhouses having increased light transmission with a combination of good insulating properties, improved durability, and reduced maintenance requirements.

SUMMARY OF THE INVENTION

The present invention is such a greenhouse panel having increased light transmission with a combination of good insulating properties, improved durability, and reduced maintenance requirements. In one embodiment, the present invention is an extruded thermoplastic multi-walled sheet structure which comprises (i) a thermoplastic polymer, (ϋ) at least two generally parallel walls, each wall having a first and a second surface, which walls are separated apart from one another wherein at least one of said walls has a corrugated shape, one or more corrugated surfaces, or combinations thereof and (iii) the walls are separated from one another by ribs extending the length of the sheet in the direction of extrusion.

In a further embodiment, the sheet structure of the present invention comprises two walls, a first and a second wall, each wall having an interior and an exterior surface, wherein one or both of the walls have a corrugated shape.

In a further embodiment, the sheet structure of the present invention comprises two walls, a first and a second wall, each wall having an interior and an exterior surface, wherein one or more of the surfaces on one or more of the walls is corrugated. In a further embodiment, the sheet structure of the present invention having one or more wall(s) with a corrugated structure defined by a sine wave having a pitch between from about 0.1 mm to about 50 mm.

In a further embodiment, the sheet structure of the present invention having one or more wall(s) with one or more corrugated surface defined by a sine wave having a pitch between from about 0.01 mm to about 10 mm.

In a further embodiment, the sheet structure of the present invention comprises a thermoplastic selected from the group of PC, PET, PETG, and PMMA, preferably PC.

In another embodiment, the sheet structure of the present invention the sheet structure of the present invention wherein the thermoplastic polymer comprises one or more of a UV absorber, a thermal stabilizer, a colorant, a dye, a processing aid, a lubricant, a filler, or a reinforcing aid.

In another embodiment, the sheet structure of the present invention further comprising a laminated or a coextruded layer of one or more thermoplastic or thermoset resins to provide abrasion/scratch resistance, chemical resistance, ultra violet (UV) radiation resistance, light scattering reduction, light reflection reduction, dirt accumulation reduction, condensation reduction, antimicrobial, protection from discoloration, protection from haze formation, or protection from cracking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view along the direction of extrusion of a double-walled sheet structure according to the prior art comprising perpendicular ribs.

FIGS. 2A through 2F represent rib structures of various prior art multi-wall sheet structures. FIG. 3 and 3A show a cross-section of a double-walled sheet structure according to the present invention comprising a wall with a corrugated shape. FIG. 4 shows an alternative embodiment of a cross-section of a double-walled sheet structure according to the present invention comprising a wall with a corrugated shape.

FIG. 5 shows an alternative embodiment of a cross-section of a double-walled sheet structure according to the present invention comprising two walls with corrugated shapes.

FIG. 6 and 6A show an alternative embodiment of a cross-section of a double-walled sheet structure according to the present invention comprising a wall with a corrugated surface. FIG. 7 and 7A show an alternative embodiment of a cross-section of a double-wailed sheet structure according to the present invention comprising walls with corrugated surfaces.

DETAILED DESCRIPTION OF THE EMBODIMENTS

When a multi-wall sheet is viewed in cross-section (cut across or perpendicular to the plane of extrusion as shown in FIG. 1) with the sheet flat and having the longest dimensions (length and width) in the horizontal plane, there are two or more generally parallel, horizontal walls, also referred to as "layers" or "faces" 10 and a series of ribs 20 that run between the layers along the length direction and separate the layers. These ribs 20 are also sometimes referred to as "webs" or "slats". The known and commercially available structures of this type having rib structures shown in FIGS. 2A to 2F can be seen to have rib structures which are perpendicular 21, diagonal 22 or combinations of perpendicular and diagonal between and separating the parallel faces.

As illustrated in FIGS. 2A to 2D, the prior art sheet usually has flat horizontal walls shown as 11 (first or upper wall) and 12 (second or lower wall). These sheet structures have two or more layers, generally with smooth surfaces, and are collectively referred to as "multi-walled" sheet. For example, as shown in FIGS. 2E and 2F, in the case of three horizontal layers (referred to as "triple wall" sheet), there are two external walls (11 and 12) and one internal wall 13. Each external wall as an exterior surface 14 and an interior surface 15. For multi-walled sheet with three or more walls, the interior wall's surfaces are designated as the interior upper surface 16 or interior lower surface 17. For example in FIG 2E, the third wall 13 has an interior upper surface 16 and an interior lower surface 17.

The key aspect of this invention is the surprising discovery that by obtaining an optimize wall structure on at least one wall, light transmittance through the sheet is improved. A preferred optimized wall structure is (1) a corrugated shaped wall, such as illustrated in FIGS. 3 and 4, (2) a wall with one or more corrugated surfaces, such as illustrated in FIGS. 6 and 7, or (3) combinations thereof. As used herein, corrugated means having alternating ridges 30 and grooves 32. Preferably, the corrugation is in the direction of extrusion sometimes referred to as the machine direction or the length of the extruded sheet. An alternate preferred embodiment of the present invention is a sheet structure wherein both external walls have a corrugated shape, see FIG. 5.

Not to be held to any particular theory or theories, we believe the corrugated shaped wall/surface improves light transmission by reducing the reflection of light reaching the sheet structure at low angles. Alternatively, or in addition to, the corrugated shaped wall/surface may cause light reflected from one part of the corrugated surface to be captured by another part of the corrugated surface where the light reaches the surface at a more favorable angle where it can be transmitted through the sheet structure rater than reflected away from it.

In the embodiment where only one wall has a corrugated shape or only one wall has a corrugated surface, the preferable orientation of the sheet of the present invention when employed in a greenhouse roof or wall is with the corrugated shaped wall/surface on the exterior or outside of tne greennouse so tnat me sun's rays pass through the corrugated shaped wall/surface from outside the greenhouse through the sheet into the interior of the greenhouse.

The peak or center of a corrugated ridge is referred to as the crest 31. The center of the bottom of the corrugated groove is called a trough 33. Each ridge has a first 34 and a second 35 surface which meet at the crest 31. Each groove has a first 35 surface and a second 36 surface which meet at the trough 33. The first and second surfaces of a groove are the first surfaces of two adjoining ridges. The first and second surfaces of a ridge are the first surfaces of two adjoining grooves. The crest and the trough are rounded, in other words the point of intersection of the first and second surface of a ridge and a trough is not defined by an angle, it is defined by a radius. The requirement that the corrugated crests be rounded improves the overall durability of the sheet structure, in particular improves toughness. For example, in the case of notch sensitive thermoplastic polymer, such as polycarbonate, a sharp corner (as defined by an angle) acts as a stress concentrator and may significantly lower the ductility, for example, impact resistance, specifically notched impact resistance, of the polymer. The requirement that the corrugated troughs be rounded decreases the potential for dirt, dust, and other particulate to collect and be retained in the bottom of the groves. The distance from the crest to the trough is referred to as the height of the ridge 37. Sometimes, the distance from the crest to the trough is referred to as the depth of the groove 37. The distance between two adjoining crests and/or two adjoining troughs is referred to as the pitch 38. The radius that defines the crest of a ridge may be the same or different as the radius that defines an adjoining trough. The height and pitch may independently vary from one ridge to another across the width (perpendicular to the direction of extrusion) of the sheet of the present invention. For instance, the pitch between each ridge across the sheet may be constant while the height of the ridges may vary. The height of the ridges may vary randomly or in a set pattern. Alternatively, the height between each ridge across the sheet may be constant while the pitch between the ridges may vary. The pitch of the ridges may vary randomly or in a set pattern. Alternatively, the height and pitch of the ridges may both vary across the width of the sheet, either randomly or in a set pattern. Preferably, the radii of the crests and troughs are the same, the height of the ridges across the sheet are constant and the pitch between ridges across the sheet are constant. When the radius of the crests and troughs are the same, the height and the pitch are both constant the repeating pattern for the corrugation is the same across the width of the sheet and can be described as a periodic wave. A preferable wave description is that of one for a sine wave.

In one embodiment, the wave shape of the corrugated surface may be defined by the following equations:

Z = 0.25 - (0.25² - x²)¹'² for 0<= x <= 0.25 or z = 0.25 + (0.25² - (X - 0.5)²)^1/2 for 0.25 <= x <= 0.5

where x = Vz pitch and z = height. For a corrugated shaped and non-corrugated shaped wall, the thickness is defined as the distance from a first surface of a wall to a second surface of the wall. The thickness 50 of a corrugated upper wall 18 and the thickness 51 of a non-corrugated lower wall 12 are shown in FIG. 3. The thickness 52 for a wall with a corrugated surface 40 is defined as the distance from the non-corrugated surface 41 to a crest of a ridge on the opposing corrugated surface 42. The thickness 52 for a wall with a single corrugated surface 40 is shown in FIG. 6A. The thickness 53 for a wall with two corrugated surfaces 43 is defined as the distance from a crest on a ridge on a first corrugated surface of the wall 45 to a crest of a ridge on the opposing second corrugated surface 46. The thickness 53 for a wall with two corrugated surfaces 43 is shown in FIG. 7A. In one embodiment, one or more of the walls have a corrugated shape as exemplified in

FIGS. 3 to 5. When a multi-walled sheet of the present invention has one or more walls with a corrugated shape, preferably defined as a sine wave, the corrugated wall pitch is equal to or greater than about 0.1 mm, preferably equal to or greater than about 0.5 mm, more preferably equal to or greater than about 0.75 mm, and most preferably, equal to or greater than about 1 mm. When a multi-walled sheet of the present invention has one or more walls with a corrugated shape defined as a sine wave, the corrugated wall pitch is equal to or less than about 50 mm, preferably equal to or less than about 30 mm, more preferably equal to or less than about 15 mm, and most preferably equal to or less than about 5 mm.

In another embodiment, one or more of the walls have one or more corrugated surfaces as exemplified in FIGS. 6 and 7. When a multi-walled sheet of the present invention has one or more walls with one or more corrugated surfaces, the corrugated surface pitch is equal to or greater than about 0.05 mm, preferably equal to or greater than about 0.01 mm, more preferably equal to or greater than about 0.05 mm, and most preferably, equal to or greater than about 0.1 mm. When a multi-walled sheet of the present invention has one or more walls with one or more corrugated surfaces, the corrugated surface pitch is equal to or less than about 10 mm, preferably equal to or less than about 5, more preferably equal to or less than about 2 mm, and most preferably equal to or less than about 1 mm.

The wall thickness of the walls of a multi-walled sheet of the present invention independently are equal to or greater than about 0.1 mm, preferably, equal to or greater than about 0.3 mm, and most preferably, equal to or greater than about 0.5 mm. The wall thickness of the walls of a multi-walled sheet of the present invention independently are equal to or less than about 10 mm, preferably equal to or less than about 5 mm, and most preferably equal to or less than about 1 mm.

The rib thickness of a multi-walled sheet of the present invention is equal to or greater than about 0.1 mm, preferably, equal to or greater than about 0.3 mm, and most preferably, equal to or greater than about 0.5 mm. The rib thickness of a multi-walled sheet of the present invention is equal to or less than about 8 mm, preferably equal to or less than about 4 mm, and most preferably equal to or less than about 0.8 mm.

A multi-walled sheet of the present invention has a thickness equal to or greater than about 2 mm, preferably, equal to or greater than about 6 mm, and most preferably, equal to or greater than adout iu mm. A multi-waned sπeet of the present invention has a thickness equal to or less than about 100 mm, preferably equal to or less than about 50 mm, and most preferably equal to or less than about 16 mm.

A preferable extruded thermoplastic sheet structure of the present invention comprises a corrugated shaped wall and/or surface such that the edge of the sheet can be assembled into standard, commercially available aluminum or plastic frameworks that are used in the greenhouse market. There are, for example, commercially available pyramidal-shaped or prism-shaped multi- walled sheet, sometimes referred to as Zigzag sheet, which do not fit into standard aluminum or plastic frameworks. The Zigzag sheet requires special, more expensive, framework which is more difficult, time consuming, and costly to install. Further, the Zigzag sheet is less durable and prone to fracturing because of sharp corners at the apex and base of the pyramids. Dirt accumulation in the sharp corners at the base of the pyramids is also difficult to wash out.

The desired overall sheet thickness, the number of walls (that is, layers or faces) and the spacing between walls or layers (for example, height of perpendicular ribs) can be selected accordingly to provide desired sheet performance properties. Preferably, in sheet thicknesses up to about 40 mm, two or three spaced apart layers are employed (that is, twin- or triple-walled sheet). If three layers are used (first or upper, second or lower, and third or center layers) the center layer can be located equal distance from the upper and lower layers (centered) or closer to one layer or another. The number and design of the ribs is dependent on the structural requirements of the sheet.

The ribs may be vertical 21 (that is, perpendicular the sheet walls), diagonal 22 (including crossing diagonals 23), or combinations thereof. When vertical and diagonal ribs are both employed, the diagonal ribs may intersect the wall(s) at the same point that where the vertical ribs intersect 24 or at different points 25 and 26. As recognized by the skilled practitioner, depending upon the need for rigidity, thermal insulation, light transmission, and weathering resistance, these types of structures can be prepared from a broad range of plastic resins. Preferably, the multi-walled sheet of the present invention is prepared from one of the known rigid thermoplastic resins including polycarbonate (PC), polypropylene (PP), polystyrene (PS), polystyrene-acrylonitrile copolymer (SAN), butadiene modified SAN (ABS), poly(methyl-methacrylate) (PMMA), poly(ethylene-terephthalate) (PET), glycol-modified PET (PETG), and polyvinyl chloride (PVC), more preferably the sheet structures are prepared from PC, PET, PETG, and PMMA and most preferable the sheet structure is prepared from PC.

The structures according to the invention can also contain or have laminated or coextruded thereto further layers of other thermoplastic or thermoset resins to provide desired performance results, particularly where it is desired to modify the surface(s) of the sheet structure in some fashion, such as for abrasion/scratch resistance, chemical resistance, ultra violet (UV) radiation resistance, light scattering reduction, light reflection reduction, dirt accumulation reduction, condensation reduction, antimicrobial, protection from discoloration, protection from haze formation, protection from cracking, or the like. The thermoplastic resin may contain the normal type of additives used for their known purposes for these types of resins and structures, including, but not limited to stabilizers such as UV absorbers or thermal stabilizers, colorants such as dyes, processing aids such as lubricants, fillers, reinforcing aids, optical brighteners, fluorescent additives, and the like. Such additives can be added to the resins that are used to prepare these structures and/or any layers that may be laminated or coextruded thereto for their known purpose. The multi-walled sheet structures of the present invention are prepared by the known process of extrusion through profile dies. Corrugated surfaces may be produced on multi-walled sheet structures of the present invention during the extrusion process for example by using a corrugated calibrator unit or by post embossing the sheet by using an embossing roller. In another embodiment a corrugated film is laminated or coextruded onto one or more surfaces of one or more walls of a multi-walled sheet.

While the invention has been disclosed in its preferred forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims.

Claims

CLAIMS:

1. An extruded thermoplastic multi-walled sheet structure which comprises:

(i) a thermoplastic polymer, (ii) at least two generally parallel walls, each wall having a first and a second surface, which walls are separated apart from one another wherein at least one of said walls has a corrugated shape, one or more corrugated surfaces, or combinations thereof, and (Hi) the walls are separated from one another by ribs extending the length of the sheet in the direction of extrusion.

2. The sheet of Claim 1 comprising two walls, a first wall and a second wall, each wall having an interior surface and an exterior surface, wherein the first wall has a corrugated shape.

3. The sheet of Claim 2 wherein the second wall has a corrugated shape.

4. The sheet of Claim 1 comprising two walls, a first wall and a second wall, each wall having an interior surface and an exterior surface, wherein the first wall has a corrugated exterior surface.

5. The sheet of Claim 4 wherein the first wall has a corrugated interior surface.

6. The sheet of Claim 4 wherein the second wall has a corrugated exterior surface.

7. The sheet of Claim 5 wherein the second wall has a corrugated exterior surface.

8. The sheet of Claim 7 wherein the second wall has a corrugated interior surface.

9. The sheet of Claim 2 wherein one or more surfaces are corrugated.

10. The sheet of Claim 3 wherein one or more surfaces are corrugated.

11. The sheet of Claims 2 or 3 wherein the corrugation is defined by a sine wave having a pitch of from between about 0.1 mm to about 50 mm

12. The sheet of Claims 5, 6, 7, or 8 wherein the corrugation is defined by a sine wave having a pitch of between from about 0.1 mm to about 50 mm

13. The sheet of Claims 9 and 10 wherein the corrugation for the wall(s) and surface(s) are defined by sine waves having a pitch for the corrugated wall(s) between from about 0.1 mm to about 50 mm and the pitch on the corrugated surface(s) between from about 0.01 mm to about 10 mm.

14. The sheet of Claim 1 having a thickness between from about 2 mm to about 100 mm.

15. The sheet of Claim 1 comprising three or more walls.

16. The sheet of Claim 1 wherein the thermoplastic is PC, PET, PETG, or PMMA.

17. The sheet of Claim 1 wherein the thermoplastic polymer is PC.

18. The sheet of Claim 1 wherein the thermoplastic polymer comprises one or more of a UV absorber, a thermal stabilizer, a colorant, a dye, a processing aid, a lubricant, a filler, or a reinforcing aid.

19. The sheet of Claim 1 further comprising a laminated or a coextruded layer of one or more thermoplastic or thermoset resins to provide abrasion/scratch resistance, chemical resistance, ultra violet (UV) radiation resistance, light scattering reduction, light reflection reduction, dirt accumulation reduction, condensation reduction, antimicrobial, protection from discoloration, protection from haze formation, or protection from cracking.