WITH GLASS REINFORCED POLYMERS

TECHNICAL FIELD

[0001] The present invention relates to plastic pipes. More specifically, the present invention relates to glass reinforced polymer corrugated plastic pipes.

BACKGROUND

[0002] Corrugated plastic pipes are commonly used for sewage and drainage applications, as well as, for example, cable ducting and medical, automotive, industrial, and residential uses.

[0003] The outer surface of a pipe is affected by several

external stresses that do not necessarily affect the inner surface. As an example, the outer surface is affected by UV radiation while the internal surface is not .

[0004] In recent years, multilayer plastic pipe technologies have appeared in the market. Multilayer technologies create doubled wall or triple wall pipes, making it possible to use different materials, having different properties, to form the outer and inner walls of the pipe .

[0005] Typically, the materials used to form the layers of the walls are polymers, preferably thermoplastics. Also, it is commonly known that adding glass fibre reinforcement to a polymer increases the polymer' s strength and rigidity .

[0006] An important requirement for pipes used in applications involving high internal pipe pressure is that the pipes have good pressure resistance. Proven methods of improving the pressure resistance of a pipe include adding mass to the pipe, or wrapping the pipe with a special element, such as a reinforcement cover.

However, such additions result in extra material and manufacturing costs, which increase the overall costs of the pipe considerably.

[0007] Another known method of improving the pressure

resistance of pipes is to reinforce pipes with glass fiber reinforced polymers. When thermoplastic pipes are reinforced with glass fibers, the process creates an optimal chemical-coupled bond between the fibers and the thermoplastic. When this reinforcement is accomplished, many of the thermoplastic's physical properties improve. For instance, reinforcement can improve the

thermoplastic' s dimensional stability, its resistance to warpage, its rigidity and its strength. In general, the chemical-coupled thermoplastic with glass fibers enhances the strength characteristics of the

thermoplastic without altering heat resistance, electrical properties or hardness. However, while reinforcing thermoplastic pipes is known, there is a lack of products that specifically target the parts of the pipes that most require reinforcement. As is known, multi-layer pipes have inner and outer walls that may require different properties from each other, especially since these different walls are subject to different stresses .

[0008] It is thus apparent that the need exists for a

corrugated plastic pipe having different properties in the outer wall and the inner wall. Specifically, there would be a benefit to a pipe with an inner and/or outer wall that is stronger and withstands higher pressures.

SUMMARY

[0009] It is an aim of the present invention to provide an

improved corrugated plastic pipe that offers a good balance of strength and flexibility and better

withstands higher pressures (as compared to traditional pipes). Further, the present invention provides a corrugated plastic pipe that is cost-efficient and easy to install.

[0010] The present invention provides a corrugated plastic pipe with an inner wall, an outer wall and, optionally, an outer sheathing layer. Either one or more of the inner wall, the outer wall and the outer sheathing layer may be made of a glass fiber reinforced thermoplastic, while the other walls may be made of the same polymer thermoplastic without reinforcement. The thermoplastic may be any thermoplastic, including for example, PP, PE, or PVC . The corrugated plastic pipe retains comparative advantages of better resistance to high internal pressures . [0011] In a first aspect, the present invention provides a corrugated plastic pipe comprising an inner wall made of a first thermoplastic material and an outer wall made of a second thermoplastic material, wherein at least one of: the first thermoplastic material and the second thermoplastic material is a glass fiber reinforced thermoplastic .

[0012] In a second aspect, the present invention provides a

corrugated plastic pipe comprising an inner wall made of a first thermoplastic material, an outer wall made of a second thermoplastic material and an outer sheathing layer made of a third thermoplastic material, wherein at least one of: the first thermoplastic material, the second thermoplastic material and the third

thermoplastic material is a glass fiber reinforced thermoplastic .

[0013] In a third aspect, the present invention provides a

method for manufacturing a corrugated plastic pipe comprising an inner wall made of a first thermoplastic material and an outer wall made of a second

thermoplastic material, wherein at least one of: the first thermoplastic material and the second

thermoplastic material is a glass fiber reinforced thermoplastic, the method comprising:

(a) providing heat to melt said first thermoplastic

material and said second thermoplastic material;

(b) providing a melted first thermoplastic material to a first extruder and a melted second thermoplastic material to a second extruder; and (c) extruding said melted first thermoplastic material and said melted second thermoplastic material through a mold shape downstream of said first extruder and said second extruder to form the corrugated plastic pipe.

[0014] In a fourth aspect, the present invention provides a method for manufacturing a corrugated plastic pipe comprising an inner wall made of a first thermoplastic material, an outer wall made of a second thermoplastic material and an outer sheathing layer made of a third thermoplastic material, wherein at least one of: the first thermoplastic material, the second thermoplastic material and the third thermoplastic material is a glass fiber reinforced thermoplastic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be described by reference to the following figures, in which identical reference numerals refer to identical elements and in which:

Figure 1 is a perspective view of a corrugated plastic pipe according to an embodiment of the present

invention;

Figure 2 is a front view of the corrugated plastic pipe shown in Figure 1;

Figure 3 is a side view of part of the corrugated plastic pipe shown in Figure 1; Figure 4 is a perspective view of part of the corrugated plastic pipe shown in Figure 1;

Figure 5 is a side view of the corrugated plastic pipe shown in Figure 1;

Figure 6 is a cross-sectional view at B-B of Figure 5;

Figure 7 is a side view of the corrugated plastic pipe drawn in stippled lines; and

Figure 8 is a schematic view of a multi-extruder that may be utilized in manufacturing a corrugated plastic pipe according to a further embodiment of the present invention .

Figure 9 is a schematic view of another multi-extruder that may be utilized in manufacturing a triple-layered corrugated plastic pipe according to another embodiment of the present invention;

Figure 10A is a cross-sectional view of a double-layered cuff;

Figure 10B is a cross-sectional view of a triple-layered cuff ;

Figure 11A is a cross-sectional view of a double-layered bell and spigot assembly;

Figure 11B is a cross-sectional view of a triple-layered bell and spigot assembly;

Figure 12A is a cross-sectional view of a double-layered cuff and pipe assembly; Figure 12B is a cross-sectional view of a triple-layered cuff and pipe assembly.

DETAILED DESCRIPTION

[0016] Figure 1 and Figure 2 show a perspective view of the

corrugated plastic pipe 20 with a reinforced inner wall, and a front view of the corrugated plastic pipe 20 with a reinforced inner wall.

[0017] Figure 3 and Figure 4 show part of the corrugated

plastic pipe 20 to illustrate the shape of the inner wall 21 and the outer wall 22. The plastic pipe 20, with walls having different properties, is manufactured using multi-layer extrusion equipment 10 (as shown in Figure 8) for the inner wall 21 and the outer wall 22 to improve the functionality of the pipe. The use of a multi-layer extrusion system 10 allows the outer wall 22, and the inner wall 21 to be made out of different materials simultaneously.

[0018] Figure 5 shows the corrugated plastic pipe in a side

position and Figure 6 shows a cross-sectional view at line B-B from Figure 5. Figure 7 shows the corrugated plastic pipe 20 drawn in stippled lines to illustrate the shape of the pipe 20, and its two walls: the outer wall 22 and the inner wall 21. The inner wall 21 is made of a first material and the outer wall 22 is made of a second material. Commonly in pipes, the materials used are the same or similar, or the inner wall 21 may be more flexible than the outer wall. However, in the present invention, the inner wall 21 is made from a glass fiber reinforced polymer so that the inner wall 21 is stronger and more rigid than the outer wall 22.

Alternatively, the present invention also provides a pipe with an outer wall 22 that is made from a glass fiber reinforced polymer that is stronger and more rigid than the inner wall 21.

[0019] Figure 8 shows a multi-layer extrusion system 10 for

making double-walled corrugated plastic pipe with walls made of different materials. First pellets made of a first material are fed to a first extruder 1 and second pellets made of a second material are fed to a second extruder 5. Before entering in the extruders, the first and second pellets are melted down. The melted first pellets enter in the first extruder 1, and the melted second pellets enter the second extruder 5. The hot streams of plastic are squeezed through the extrusion head 6 for shaping in the mold region 7 to form the pipe 20. Many different mold shapes for the mold region 7 may be contemplated by the skilled artisan in accordance with the present invention. During the manufacturing of pipe 20, the first and second layers will bond securely, and yet retain the individual properties of their materials (i.e., thermoplastic and glass fiber

reinforced thermoplastic) , including density.

[0020] Figure 9 shows another multi-layer extrusion system 30 for making a triple-layered pipe 40 with walls made of different materials. The first pellets made of a first material are fed to a first extruder 31, second pellets made of a second material are fed to a second extruder 33 and third pellets made of a third material are fed to a third extruder 35. Before entering in the extruders, the first, second and third pellets are melted down. The melted first, second and third pellets each enter in the first extruder 31, the second extruder 33 and the third extruder 35, respectively. The hot streams of plastic from the first extruder 31 and the second extruder 33 are squeezed through the extrusion head 37 to shape in the mold region 7 to form the double-walled pipe 20. The first material forms the inner wall 21 and the second material forms the outer wall 22. The third extruder 35 then extrudes the melted third material to flow around the outside of the outer wall 22 to create an outer sheath 39. During the manufacturing of the triple-layered pipe 40, the first, second and third layers will bond securely, and yet retain the individual properties of their materials (i.e., thermoplastic and glass fiber reinforced thermoplastic) , including density.

[0021] The outer wall 22, the inner wall 21 and the outer

sheath 39 of either the double-walled pipe 20 or the triple-layered pipe 40 may be manufactured from any polymer, including, for instance, polypropylene (PP), polyethylene (PE), or polyvinylchloride (PVC) . Any of the outer wall 22, the inner wall 21 and the outer sheath 39 may be made of a polymer reinforced with glass fibers. The polymers used for the inner wall 21, the outer wall 22 and/or the outer sheath 39 may be the same polymer . [0022] Figure 10A shows an exemplary double-layered cuff 100A made from a first material 101 and a second material 103. Figure 10B shows an exemplary triple-layered cuff 100B made from a first material 101, a second material 103 and a third material 105.

[0023] Figure 11A shows an exemplary double-layered bell 110A

and an exemplary double-layered spigot 111A. The bell 110A and the spigot 111A are each constructed from a first material 101 and a second material 103. Figure 11B shows an exemplary triple-layered bell HOB and a double-layered spigot 111A. The triple-layered bell HOB is made from a first material 101, a second material 103 and a third material 105.

[0024] Figure 12A shows an exemplary double-layered cuff

assembly. Specifically, Figure 12A shows a double layered cuff 100A assembled with a double-walled pipe 20. Figure 12B shows an exemplary triple-layered cuff assembly. Specifically, Figure 12B shows a triple layered cuff 100B assembled with a double-walled pipe 20.

[002 5] A skilled artisan would understand that any of the first material 101, the second material 103, and/or the third material 105 may comprise a polymer reinforced with glass fiber.

[002 6] The typical glass fiber used to reinforce polymer

compounds is known as "E-glass". Other glass

chemistries, such as "D-glass", "C-glass", "R-glass", "S-glass", or "T-glass" can be used to impart different properties to the polymer compound. The glass reinforced polymers used are generally crushed before being

embedded in the thermoplastic and pelletized.

[0027] The pellets may be pre-compounded with up to 70% glass fiber. These pellets may be further diluted to customize the ratio of glass fibers to thermoplastic being loaded into the extruder. Different ratios of glass reinforced polymers and thermoplastic may be used when the glass fibers are embedded.

[0028] Long glass fiber reinforcement thermoplastics (LFRT) provide greater performance improvements than typical fillers because of a parameter known as "aspect ratio". The aspect ratio is the ratio of glass fiber length to fiber diameter of the filament. Embedding glass fibers with longer fibers (relative to a fixed fiber diameter) in a polymer is known to improve the strength properties of that polymer. The introduction of long-fiber reinforcements is well known in the art and it was designed primarily to increase the starting fiber length in pellets from 2-3 mm to 11-12 mm.

[0029] The glass fiber reinforced thermoplastic in accordance with the present invention may also be an inline or direct compounded long glass fiber thermoplastic (D- LTF) . D-LFTs may be formed by feeding glass roving directly into a twin-screw extruder. The twin-screw extruder chops and mixes the glass roving into the thermoplastic before being fed to the extruder. Accordingly, the glass fibers in the glass fiber reinforced thermoplastic may reach lengths of up to 30 mm. [0030] The surfaces of the glass fibers are usually treated to improve the adhesion of the polymer to the glass and frequently coupling agents, like maleic anhydride, are used. The benefits of reinforcement are dependent on the strength of this bond between the polymer and the glass fibers. When the polymer starts to undergo mechanical overload, it transfers load stress to the inherently stronger fibers.

[0031] When the polymer and the glass fibers are chemically bonded, the modulus (i.e., stiffness or rigidity) and the strength of the glass fiber reinforced polymer is increased. The chemical bonding results from a

modification of the backbone chain of the polymer or through the addition of a coupling agent, such as maleic anhydride .

[0032] A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow .