METHOD AND FORMULATION FOR ROTOMOULDING RECYCLED POLYMER AND PRODUCTS THEREOF

Abstract

A rotomoulded product and a method of making a rotomoulded product via rotational moulding, the rotomoulded product including at least two layers of material that form a wall of the product, at least one of the layers including post-consumer recyclate (PCR), and at least one of the layers including virgin PE.

Claims

1. A rotomoulded product comprising at least two layers of material that form a wall of the product, a first layer of the at least two layers of material comprising PCR PE and a second layer of the at least two layers comprising virgin PE.

2. The rotomoulded product as claimed in claim 1, wherein the first layer and second layer are fused or combined in a monolithic wall structure.

3. The rotomoulded product as claimed in claim 2, comprising a third or subsequent layer(s), wherein the third or subsequent layer(s) is/are comprised of virgin PE and/or PCR PE.

4. The rotomoulded product as claimed in claim 2, wherein the product is a multilayered product.

5. A rotomoulded product comprising: a first, outermost layer comprised of PCR PE; and a second inner layer comprised of virgin PE; and optionally a third or subsequent inner layer(s) comprised of virgin PE and/or PCR PE.

6. The rotomoulded product as claimed in claim 1, wherein the PCR PE layer has a thickness in the range of 1 mm to 12 mm, and wherein the virgin PE layer has a thickness in the range of 1 mm to 5 mm.

7. A formulation for rotomoulding a product, the formulation comprising: a first component comprising PCR PE for forming a first layer of the rotomoulded product and a second component comprising virgin PE for forming a second layer of the rotomoulded product; or a first component comprising virgin PE for forming a first layer of the rotomoulded product and a second component comprising PCR PE for forming a second layer of the rotomoulded product; wherein the first layer and the second layer together form a monolithic wall in the rotomoulded product.

8. The formulation for rotomoulding the product as claimed in claim 7, the formulation comprising a third component comprising virgin PE and/or PCR PE for forming a third or subsequent layer(s) of the rotomoulded product; wherein the first layer, second layer, third layer or subsequent rotomoulded layers together form a monolithic rotomoulded wall of the product.

9. The formulation as claimed in claim 7, wherein each PCR PE component comprises a singular LLDPE or blend of at least two of HDPE, LDPE and LLDPE.

10. The formulation as claimed in claim 7, wherein each PCR PE component and/or each virgin PE component has one or more additives selected from one or more UV stabilizers and one or more antioxidants.

11. A method of manufacturing a product by rotational moulding, the method including steps of: (a) adding to a cavity of a mould, a predetermined amount of PCR material comprising a PCR PE; (b) heating the mould whilst rotating the mould until the PCR material adheres and forms a first layer on an internal surface of the mould; (c) after forming the first layer on the internal surface of the mould, adding to the mould, a predetermined amount of virgin PE material; (d) continuing to heat the mould whilst rotating the mould until the virgin PE forms a second layer fusing and/or adhering to the first PCR layer; (e) cooling the mould until the first PCR layer and second virgin PE layer solidify to form a monolithic wall of the product; and (f) removing the product from the cavity of the cooled mould.

12. A method of manufacturing a product by rotational moulding, the method including steps of: (a) adding to a cavity of a mould, a predetermined amount of virgin PE material; (b) heating the mould and rotating the mould until the virgin PE material forms a first layer adhering to an internal surface of the mould; (c) after forming the first layer on the internal surface of the mould, adding to the cavity of the mould, a predetermined amount of PCR material comprising a PCR PE; (d) heating the mould and rotating the mould until the PCR material adheres and forms a second layer fused and/or adhered to the first layer in the mould; (e) cooling the mould until the first layer and second layer solidify to form a monolithic wall of the product; and (f) removing the product from the cavity of the cooled mould.

13. A method of manufacturing a product by rotational moulding, the method including the steps of: (a) adding to a cavity of a mould, a predetermined amount of virgin PE material; (b) heating the mould whilst rotating biaxially until the virgin PE material melts and forms a first virgin PE layer adhering to an internal surface of the mould; (c) after forming the first virgin PE layer on the internal surface of the mould, adding to the mould, a predetermined amount of PCR material comprising a PCR PE; (d) heating the mould whilst rotating biaxially until the PCR material adheres and forms a second PCR layer adhered to the first virgin PE layer in the mould; (e) after forming the second PCR layer, adding to the mould, a predetermined amount of virgin PE material; (f) continuing to heat the mould with biaxial rotation until the virgin PE material melts and forms a subsequent virgin PE layer adhering to the second PCR layer; (g) cooling the mould until all layers solidify to form a monolithic wall of the product; and (h) removing the product from the cavity of the cooled mould.

14. A method of manufacturing a product by rotational moulding, the method including steps of: (a) adding to a cavity of a mould, a predetermined amount of PCR material comprising a PCR PE; (b) heating the mould whilst rotating the mould until the PCR material forms a first PCR layer adhering to an internal surface of the mould; (c) after forming the first PCR layer on the internal surface of the mould, adding to the mould, a predetermined amount of virgin PE material; (d) heating the mould whilst rotating until the virgin PE material forms a second layer fused/adhered to the first PCR layer in the mould; (e) after forming the fused second layer, adding to the mould, a predetermined amount of PCR material comprising a PCR PE; (f) continuing to heat the mould with rotation until the PCR material forms a subsequent PCR layer adhering to the second virgin PE layer; (g) cooling the mould until all of the layers solidify to form a monolithic wall of the product; and (h) removing the product from the cavity of the cooled mould.

15. The method as claimed in claim 11, wherein the PCR material is a singular LLDPE or a blend formed from a combination of at least two of HDPE, LDPE and/or LLDPE.

16. The method as claimed in claim 13, wherein further layers are formed by repeating steps (e) and (f) with virgin PE and/or PCR PE materials, as required.

17. The rotomoulded product of claim 6, wherein the PCR layer has a thickness in the range of 3 mm to 10 mm.

18. The rotomoulded product of claim 6, wherein the virgin PE layer has a thickness in the range of 2 mm to 3 mm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0084] Further disclosures, objects, and aspects of preferred and other embodiments of the present application may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which:

[0085] FIG. 1 illustrates a method of manufacturing a product by rotational moulding according to an embodiment of the invention, and

[0086] FIG. 2 illustrates a method of manufacturing a product by rotational moulding according to another embodiment of the invention.

DETAILED DESCRIPTION

[0087] FIG. 1 of the drawings depicts steps involved in a method of manufacturing a product by rotational moulding according to one embodiment of the present invention. Multilayer rotomoulding has been known for many years. Generally, in rotomoulding a mould is provided that can be opened to reveal a cavity (101). The mould is typically a separable cast, machined, or fabricated mould. A predetermined amount of material comprising PCR PE, preferably in powdered, granular or pellet form, is introduced or placed into the cavity of one part of the mould (103) and the mould is then closed. The mould is heated to a required processing temperature (105), usually whilst rotating the mould biaxially. In this regard, the mould may be heated in an oven without applying pressure or centrifugal force. Heat is transferred through the mould wall causing the PCR PE material to melt and adhere to form a first layer on an internal surface of the mould (105).

[0088] A predetermined amount of virgin PE, again preferably in powdered, granular or pellet form, is then added to the mould (107). This may be achieved by a variety of methods, such as:

[0089] Method 1—Removing the mould from the heat source and pouring the virgin PE material into the mould via fill port using gravity or dense phase conveyance; or

[0090] Method 2—Without interrupting the process, discharging the virgin PE material in powdered/granular form from a holding vessel (known as a ‘dropbox”) via a mechanically activated fill port, e.g., allowing the PE to discharge into the mould under gravity. The virgin PE material is substantially prevented from heating prior to its discharge by thermally insulating the dropbox;

[0091] Method 3—Whilst maintaining heating but stopping the biaxial rotation, feeding the (powdered) virgin PE material into the mould via a feeding lance entering the mould through a fill port and discharging via gravity or dense phase conveyance.

[0092] Other methods, including any other means known in the art for creating multiple layers during rotomoulding. For example, multiple layers can be prepared by the manual introduction of material during the moulding process, or by use of a drop-box. Manual addition involves moving the mould from the oven, removing a vent tube or plug that creates an opening in the part providing access to the mould cavity and adding more material using, for example, a funnel. By contrast a drop-box typically contains a single material layer and it is an insulated container that holds material until it is released at the appropriate time during the process. The signal for release of material is usually transmitted as a pressure pulse via an airline through an arm of the rotomoulding machine. The dropbox must be kept cool to prevent the material inside the box from melting. A feeding tube may be used with the assistance of gravity or pressure.

[0093] The mould is then heated at the required processing temperature (109) whilst rotating the mould biaxially. In this regard, there are two notable factors:

(1) the temperature at which the second or subsequent layer is added: it is important for determining the wall thickness of the previous layer formed and how well the two layers may fuse, bond or be bound together; and
(2) the time elapsed before addition of the second or subsequent layer of material: if the mould is at rest for too long, the material that has already adhered to the wall may sag.

[0094] The mould continues to be heated with biaxial rotation until the virgin PE layer adheres to the PCR layer and forms a second layer adhering to the first layer (109).

[0095] After the layers have formed, heating is ceased and the mould is cooled, for example, by moving the mould out of the oven while biaxial rotation continues. Still air, moving air from a fan, or water are typically used to cool the mould and start solidification of the two layers forming the product (111). Once the product inside the mould has cooled to a state of sufficient rigidity the mould is opened and the product is removed from the cavity of the mould (113).

[0096] A rotomoulded PCR products can have poor mechanical properties for various reasons. These may include, for example, poor sintering due to under-curing or damage to the polymer structure due to over-curing, poor quality feedstock material, and/or lack of processing additives, such as antioxidants or stabilizers. Poor mechanical properties may manifest as any one or more of multiple void spaces (high porosity) within a wall section of the product, an uneven inner surface, and/or possible formation of voids which can lend themselves to forming crack initiators from which cracks may, in turn, propagate and become visible on the surface of the moulded product.

[0097] Without wishing to be bound by theory, it is believed that the virgin inner layer of the above embodiment inhibits crack propagation. Loads applied primarily against the outer layer are protected by the inner layer, and loads applied against the inner layer (which alone might be compromised) are, in turn, supported by the outer layer. The inner layer is thus particularly important at that part of the wall at which the load is expected to be applied.

[0098] Polymers will degrade over time, particularly when located outdoors. Polymer stabilisation additives are thus added in order to slow onset of degradation. Antioxidants are used to protect the polymer from thermal degradation due to the moulding process as well as due to heat from the sun. UV stabilisers function to protect the polymer from photo-oxidation through combined exposure to sunlight and the effect of oxygen.

[0099] Polyethylene from post-consumer sources has a similar polymer structure to virgin PE used in the manufacture of many rotomoulded products used in agricultural, industrial, automotive and marine applications. This means that such products are required to have long term durability and performance that is appropriate for their end use. One of the main differences between PCR polyethylene and traditional rotomoulding polyethylene grades, however, is that PCR PE products are often created for single use, disposable applications and therefore may not need to be stabilised against the kind of thermal or UV degradation caused by years of outdoor exposure. As noted above, a rotomoulding grade PE will usually contain one or more specially designed stabilisers and/or other additives to protect the final rotomoulded product and make it suitable for use in an outdoor environment for the extent of its service life (e.g., years or even decades). For this reason, in order to ensure that the PCR PE has the same weathering characteristics as traditional rotomoulded products, an appropriate combination of chemical additives (known as an ‘additives package’) is desirably be used. This additive package is melt-compounded into the PCR PE to ensure complete distribution of the protective additives, throughout the PCR PE to form a well stabilized PCR PE.

[0100] The PCR PE may be selected, depending on the type of feedstock needed, to provide recycled feedstock material which substantially does not contain contaminants of other polymer types which could adversely affect performance. Stabilisation agents will need to be added typically in the melt-compound process. The rotomoulding PE grade consumed may contain additives providing an elevated level of UV protection to provide even further protection to the final PCR PE moulded product against the elements.

[0101] FIG. 2 of the drawings depicts steps involved in a method of manufacturing a product according to another embodiment of the invention. Multilayer rotomoulding has been known for many years. Generally, in rotomoulding a mould is provided that can be opened to reveal a cavity (101). The mould is typically a separable cast, machined or fabricated mould. A predetermined amount of material comprising virgin PE, preferably in powdered, granular, or pellet form, is placed in the cavity of one part of the mould (103) and the mould is then closed. The mould is then heated to the required processing temperature (105), whilst rotating the mould biaxially. The mould is typically heated in an oven without applying pressure or centrifugal force. Heat is transferred to the PE material through the mould causing the virgin PE material to melt and adhere to form a first layer on an internal surface of the mould (105).

[0102] A predetermined amount of PCR PE, again preferably in a powdered, granular or pellet form, is then added to the mould (107) for forming a second layer. This may be achieved by various methods such as:

[0103] Method 1—Removing the mould from the heat source and pouring the PCR PE material into the mould via fill port using gravity or dense phase conveyance; or

[0104] Method 2—Without interrupting the process, discharging the PCR PE material in powdered/granular form from a holding vessel (known as a ‘dropbox’) into the mould under gravity via a mechanically activated fill port. The PCR PE material is substantially prevented from heating prior to discharge by thermally insulating the dropbox;

[0105] Method 3—Whilst maintaining heating but stopping the biaxial rotation, feeding the (powdered or granular) PCR PE material into the mould via a feeding lance entering the mould through a fill port and discharging via gravity or dense phase conveyance.

[0106] Other methods, including any other means known in the art for creating multiple layers during rotomoulding. For example, multiple layers can be prepared by the manual introduction of material during the moulding process, or by use of a drop-box. Manual addition involves moving the mould from the oven, removing a vent tube or plug that creates an opening in the part providing access to the mould cavity and adding more material using, for example, a funnel. By contrast, a drop-box typically contains a single material layer and it is an insulated container that holds material until it is released at the appropriate time during the process. The signal for release of material is usually transmitted as a pressure pulse via an airline through an arm of the rotomoulding machine. The dropbox must be kept cool to prevent the material inside the box from melting. A feeding tube may be used with the assistance of gravity or pressure.

[0107] The mould is then heated at the required processing temperature (109) whilst rotating the mould biaxially until the second PCR layer fuses or adheres to the first virgin PE layer. In this regard, there are two notable factors:

(1) the temperature at which the second or subsequent layer is added: it is important for determining the wall thickness of the previous layer formed and how well the two layers may fuse or be bound together; and
(2) the time elapsed before addition of the second or subsequent layer of material: if the mould is at rest for too long, the material that has already adhered to the wall may sag.

[0108] A predetermined amount of material comprising virgin PE, e.g., in a powdered, granular or pellet form, is added to the mould (110a) in order to form a third layer. The mould is then heated again, whilst rotating the mould biaxially at the required processing temperature (110b). The mould is typically heated in an oven without applying pressure or centrifugal force. Further layers can be added by repeating steps 110a and 110b with virgin PE material and/or PCR PE material. Heat is transferred through the mould wall causing the PE material (in powdered, granular or pellet form) to melt and fuse or adhere to the second layer and form a third layer on an internal surface of the mould (110b).

[0109] After the layers have formed, heating is ceased and the mould is cooled, for example, by moving the mould out of the oven while biaxial rotation continues. Still air, moving air from a fan, or water are typically used to cool the mould and start solidification of the layers forming the product (111). Once the product inside the mould has cooled to a state of sufficient rigidity the mould is opened and the product is removed from the cavity of the mould (113).

Examples

[0110] The present invention will be further described with reference to the following non-limiting example of PCR formulations suitable for use in the first, outer layer of the present rotomoulding invention.

[0111] Table 1 lists thirteen PCR formulations for use in a PCR layer in a rotomoulded product according to the present invention. Each comprises at least one LLDPE or two of HDPE, LDPE and LLDPE. The thirteen formulations were devised to be used in the rotomoulding method described with reference to FIG. 1 or FIG. 2 to form the PCR PE layer(s). Other layer(s) comprise virgin PE. One preferred result is provided by the Formulation 9—a 50:50 blend of HDPE and LDPE.

[0112] In general, the PCR PE material should be designated by PE type, MFI, and density and is derived from sources such as garbage and waste collection bins and is of relatively consistent composition. The PCR material comprises many different types of PCR PE material from a wide range of sources and the composition varies.

[0113] In Table 1, below, the following abbreviations are used:

[0114] LLDPE—Linear low-density polyethylene

[0115] HDPE—High-density polyethylene

[0116] LDPE—Low-density polyethylene

[0117] PCR PE—Post Consumer Recyclate polyethylene

[0118] MFI is measured at 2.16 kg at 190° C. (See standards ASTM D1238 and ISO 1133)

[0119] Density is measured in kg/m.sup.3

TABLE-US-00001 TABLE 1 Recycle Blend Options Formulation PCR PE Density MFI Ratio 1 LLDPE 938 3 100 2 LDPE 923 2 70 LDPE 922 0.3 30 LDPE 923 1.1 100 3 LLDPE 938 3 70 LDPE 922 0.3 30 LLDPE/LDPE 933 1.5 100 4 LLDPE 938 3 85 LDPE 922 0.3 15 LLDPE/LDPE 935 2.1 100 5 HDPE 956 7 70 LDPE 922 0.3 30 HDPE/LDPE 945 2.7 100 6 HDPE 956 7 60 LDPE 922 0.3 40 HDPE/LDPE 942 2 100 7 HDPE 956 7 70 LDPE 923 1.1 30 HDPE/LDPE 946 4 100 8 HDPE 956 7 60 LDPE 923 1.1 40 HDPE/LDPE 942 3.4 100 9 HDPE 956 7 50 LDPE 923 1.1 50 HDPE/LDPE 939 2.8 100 10 HDPE 956 7 50 LDPE 922 0.3 50 HDPE/LDPE 939 1.5 100 11 HDPE 955 4.5 50 LDPE 922 0.3 50 HDPE/LDPE 939 1.16 100 12 HDPE 955 4 50 LDPE 922 0.3 50 HDPE/LDPE 939 1.1 100 13 HDPE 956 10 50 LDPE 922 0.3 50 HDPE/LDPE 939 1.73 100

[0120] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations, uses, or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[0121] Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by persons skilled in the art that a variety of alternative and/or equivalent implementations exist. It should be appreciated that the exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[0122] Thus, various modifications and equivalent arrangements are intended to be included within the scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures.

[0123] Throughout this specification, unless the context requires otherwise, the terms “comprise”, “comprising”, “include”, “including”, “contain”, “containing”, “have”, “having”, and variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense so as to imply the inclusion of a stated step, integer, feature, or element, or group of steps, integers, features, or elements but not the exclusion of any other step, integer, feature, or element, or group of steps, integers, features, or elements.