AU2005201785B2 - Dip tube - Google Patents

Description

Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR.A STANDARD PATENT (ORIGINAL) Name of Applicant: B.M.W. PLASTICS PTY. LTD. and NITE-GLO INNOVATIONS PTY. LTD. Actual Inventor(s): CHARLES HRUBOS Address for Service: SANDERCOCK & COWIE SUITE 8C, 50-54 ROBINSON STREET DANDENONG VIC 3175 Invention Title: DIP TUBE Details of Associated Provisional Application(s): No(s): Australian Provisional Application No. 2004902246 Filed: 2 8 th April, 2004 The following statement is a full description of this invention, including the best method of performing it known to us: - 1 - - la TITLE: DIP TUBE FIELD OF THE INVENTION 5 This invention concerns variable length dip tubes for drums, intermediate bulk containers (IBC) and like containers routinely used for containing chemical liquids with applications in the chemical, agricultural and veterinary fields. The dip tube is connectable to a valve or pump at the drum aperture. 2005-04-28.A:\534bmw.cao.wDd. I -2 BACKGROUND OF THE INVENTION The contents of such containers are frequently of high concentration and hostile to the polypropylene and polyethylene polymers from which the dip tubes are typically made. 5 In particular, the solvents and chemicals can cause a softening and degradation of the polymer, stress-cracking of the polymer, or a combination of both. Tube failures are discussed in the literature and WO 01/62627 Al describes certain grades of polypropylene and high density polyethylene (HDPE), but points out that stress-cracking resistant grades are not essential if particular applications do not involve any particular 10 substance which induces that mode of failure. Our work has shown that combined resistance to solvent attack and stress-cracking is a generally desirable feature when selecting the material for a dip tube of the type described. The bellows component of the dip tube is particularly prone to attack by 15 environmental stress-cracking agents. If the tube reacts to solvent action by swelling significantly, the airtight fit of the tube to the stub of the valve will be lost and pumping efficiency will be compromised or the tube may fall off. Also considerable bending of the tube may result to the extent that a kink may form and the drum will not empty completely. 20 SUMMARY OF THE INVENTION The apparatus aspect of the invention provides a dip tube of the variable length type for use in a container, comprising a tube capable of connection at the upper end to a 25 connector at the container aperture and at the lower end to a moulded bellows and foot component which is a close coaxial fit over the outside of the tube, wherein at least the bellows and foot component is made of a cross-linked grade of polyolefin based on silane-grafted HDPE, MDPE, LLDPE, copolymer olefins, metallocene catalysed olefins or blends of these. 30 Preferably the tube, bellows and foot are made of the same material. If extra flexibility is required in the bellows, it may also be based on blends of any of the previously mentioned polyolefins with other compatible polymers which are co-grafted and then -3 cross-linked. The tube may be of extruded stock while the bellows and foot may be moulded. The components are manufactured by a standard technique using the mixture of polymer beads and cross-linking agent. The degree of cross-linking may be in the range of 50-90%, preferably in the range of 70-85%. The practical test for confirming 5 a satisfactory degree of cross-linking in the polymer is to conduct a hot set test, for example using an adaptation of the test method of AS/NZS 1660.2.2:1998. The same attributes of chemical and environmental stress crack resistance mentioned above apply. 10 The dip tube is made of a cross-linkable grade of ethylene polymer or copolymer compound. Suitable polymers include polyethylene and ethylene or alphaolefin copolymers, for example, high density polyethylene (HDPE), medium density polyethylene (MDPE) and linear low density polyethylene (LLDPE); ethylene butene 15 copolymers, ethylene hexene copolymers and ethylene octane copolymers; or blends of these. The (co)polymers may also be in the forn of metallocene catalysed (co)polymers. Cross-linking of the composition may be achieved by (i) using a silane-grafted ethylene (co)polymer compound; (ii) the addition of cross-linking agents at the moulding process; 20 or (iii) radiation cross-linking. Persons skilled in the art will be familiar with other methods of initiating cross-linking. The invention embraces these methods. 25 The preferred method is the use of a silane-grafted ethylene (co)polymer compounded with other additives such as antioxidants, uv stabilisers, fillers, colourants, etc. At the stage of extrusion and moulding 6f the tube and bellows respectively, a catalyst is used to accelerate the cross-linking process. This is preferably achieved by the use of a catalyst masterbatch which is blended with the silane-grafted ethylene (co)polymer 30 compound directly prior to the extrusion or moulding process. Typically the addition rate for such a catalyst masterbatch is 1-8%. The masterbatch may also contain other additives to confer other specific properties and -4 characteristics to the final components. For dip tubes, additional antioxidant is considered desirable to ensure extended heat stability of the polymer system and thus the long-term life of the product. It is also considered desirable to include a translucent pigment which provides visual confirmation that the catalyst masterbatch had indeed 5 been added into the component (and thus ensure the cross-linking process) and at approximately the correct percentage. When the polymer has subsequently cross-linked, it cannot be reworked back into the extrusion or moulding process because of the nature of the change to its melt index and processability. It is thus useful to also provide colour differentiation to these products so they are easily identified and can be kept apart from 10 the general polyolefin recycling stream in a manufacturing plant. To enable the cross-linking process of silane-grafted ethylene (co)polymer compounds, moisture must also be present. Moisture cross-linking is typically carried out in the presence of water or steam and at temperatures ranging from ambient up to 95 C. The 15 speed and duration of cross-linking will depend on temperature, humidity (if the water is present as water vapour), the thickness of the component, as well as the concentration of the cross-linking catalyst present. Whereas, thick walled components may require a number of hours in hot water at 20 approximately 85-95 C to achieve full cross-linking, it has been established that the relatively thin walled tube and bellows of the dip tube will cross-link fully when held at ambient conditions of temperature and humidity for 2-3 days after the manufacturing step. 25 The bellows is particularly subject to attack by chemical and ESC (environmental stress crack) agents because of the stress concentration points and ongoing flexing and the attributes of the polymer are especially important in providing a satisfactory service life. The cross-linked polymer also confers improved resistance to flex fatigue and thus minimises failure due to cracking in the bellows section. 30 By choosing the same polymer (or a like polymer) for tube and bellows, the choice of fastening techniques may include ultrasonic welding, spin welding, hot air welding, and the like because the heat-softening/bonding characteristics of both surfaces are -5 compatible. The bellows is preferably attached to the tube by an ultra-sonic welding process. Attachment by ultra-sonic welding provides a long-lifejoin that is not unduly susceptible 5 to attack by chemical solvents, elevated temperatures and the like. Other methods such as mechanical clamping and interference fitting are subject to failure as parts are swollen by aggressive solvents and chemicals and then come loose. 10 Ultrasonic welding of PE to itself is normally regarded as providing only a poor to fair bond, however good to excellent bonds are achieved with cross-linking grades of polyolefins of the types previously mentioned. It has been determined that this is the case because of a further degree of cross-linking across the welded interface during the ultra-sonic welding process. 15 The internal diameter of the neck of the bellows is designed to be an interference fit over the tube. This helps to provide an air-tight join between bellows and tube. The manufacturing dimensions and tolerances specified for these parts is such that at minimum tube size and maximum bellows neck size, fitment is almost exact; at 20 maximum tube size and minimum bellows neck size, the bellows is a push-on fit onto the tube, but still within the strain acceptable limits for the specific grade of polymer chosen. A lead-in is provided at the neck of the bellows to assist with insertion of the bellows over the tube. 25 Because the same or a chemically similar polymer has been selected for both bellows and tube, thermal expansion and chemical swell characteristics are identical or very similar, and the air-tight fit will be maintained irrespective of temperature changes or solvent exposure. 30 The ultra-sonic weld may be provided around the full circumference at the neck of the bellows using a specially designed welding horn and multi-step welding. 2005-04-2RAA514hmw-n.wnd5 -6 Such a weld provides an extra degree of integrity of the air-tight fit of bellows over tube. Such air-tight fit ensures that all of the contents of the drum, into which the dip tube is installed, will be capable of being successfully pumped out, with an absolute minimum of residue. 5 The join between the bellows and the tube is an interference fit. The upper end of the tube is an interference fit on the stub which connects to the valve at the drum aperture. The stub may be moulded with a circumferential stop. The tube may be retained on the stub by a circlip or rivet. 10 BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention is now described with reference to the accompanying drawings, in which: 15 Figure 1 is a diagrammatic section of a dip tube. Figure 2 is a section equivalent to Figure 1 but at 900 thereto. 20 DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS Example An extruded tube 2, 730mm long has an o.d of 27.8mm and a wall thickness of 1.3mm. 25 The blow moulded bellows 4 has a pair of feet 6 extending from a cylindrical portion 8, 36mm long. The cylindrical portion is partially closed by flange 10. The diameter of the opening 12 is 24mm. The upper end of the bellows has a lead-in 14. The i.d of the bellows is 27.7mm. This affords'a push on fit to the tube. The coaxial overlap is 10mm at the neck 16. Both parts are manufactured from the same formulation of silane-grafted 30 polyolefin compound. A blended mix of 100 parts of polymer beads EH903298 and four parts of catalyst cross-linking masterbatch EH704366 is supplied to the hopper of the extrusion machine and moulding machine. Both of these materials are made by Compco Pty. Ltd. of Victoria, Australia.

-7 The tubes and bellows are allowed to age for at least three days to ensure cross-linking is substantially completed. In dry weather more days will be added. The overlap zone 16 is subjected to three or four ultrasonic welds 18 disposed at equal 5 angles about the circumference in ajig, The adjustability, namely the vertical movement possible with the tube inside the drum is nominally 30mm. The following tests were conducted to reveal the suitability or otherwise of the tube. 10 1. Chemical Resistance Tests Compression moulded plaques of the polymer, nominally 2mm thick, were subjected to typical solvents used in agricultural herbicide formulations for 30 days at 45'C. Samples were then checked for tensile strength properties, weight 15 gain, and visual observation. Tensile Strength at Yield Results (MPa) EH903298 Cross-linked Standard HDPE (GF7660) 20 Control 18.5 MPa 21.0 MPa NMP 18.6 +0.5% 20.4 -2.9% Exatte 700 17.0 -8.1% 19.2 -8.6% Solvesso 150 15.2 -17.8% 17.9 -14.8% Solvesso 200 15.6 -15.7% 17.7 -15.7% 25 The test results indicate that the reduction in tensile strength at yield is dependent on the particular solvent used in the test. The change in performance for the cross-linked polymer shows broadly similar levels of property reduction to standard HDPE. GF7660 is known to perform acceptably from a mechanical 30 properties' perspective in the dip tube application. 10OSA.-AR A ., -8 Weight Change Results EH903298 Cross-linked Standard HDPE (GF7660) NMP +1.4% +1.4% 5 Exatte 700 +4.3% +4.2% Solvesso 150 +9.3% +7.9% Solvesso 200 +9.7% +9.1% A weight change of 0-5% is regarded as having "no effect" on the polymer in 10 such a test program. A weight change of 5-10% is regarded as having a "minor effect" on the polymer. The cross-linked polyolefin compound is regarded as performing well in the weight change test, with minor effect, at most, from the solvent exposure. Its performance is very similar to standard HDPE for this range of solvents. 15 In studies using PP dip tubes made by other manufacturers, PP has shown weight gains of around 20% when subjected to Solvesso 150 and Solvesso 200 in a similar test program. Such a level of weight gain is rated as "moderate effect" and regarded as being an unacceptable performance by the agricultural chemicals 20 industry. Visual Observation None of the samples showed any evidence of change in colour, cracking, 25 degradation or the like. ' 2. ESCR (Environmental Stress Crack Resistance) Results Tests were conducted at 50'C as per bell test method of ASTM D1639, using 30 Bayer CropScience Basta herbicide (undiluted) which is a water-based glutosinate-ammonium formulation. Results are expressed as the time in which 50% of the test specimens will fail (F 50 ). The F 5 0 result for GF7660 was 166 hours. The F50 result of EH903298 cross-linked polymer was in excess of 1000 I- l ACA A - -- 2A , .... ,,A -9 hours. This result confirms the susceptibility of standard HDPE to ESCR and shows the superior performance conferred by using the cross-linked polyolefin compound. 5 It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive fori, ie. use of the word "comprising" does not exclude the addition of other elements. 10 It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

Claims (9)

1. A dip tube of the variable length type for use in a container, comprising a tube capable of connection at the upper end to a connector at the container aperture 5 and at the lower end to a moulded bellows and foot component which is a close coaxial fit over the outside of the tube, wherein at least the bellows and foot component is made of a cross-linked grade of polyolefin based on silane-grafted HDPE, MDPE, LLDPE, copolymer olefins, metallocene catalysed olefins or blends of these. 10

2. A dip tube as claimed in Claim 1, wherein both the tube and the bellows and foot component are made of the same material.

3. A dip tube as claimed in Claim 1 or 2, wherein the degree of cross-linking is 50 15 90%.

4. A dip tube as claimed in any one of Claims 1-3, wherein the degree of cross linking is 70-85%. 20

5. A dip tube as claimed in any one of Claims 1-4, wherein the tube is made of extruded stock, whereas the bellows and foot are moulded.

6. A dip tube as claimed in any one of Claims 1-5, wherein at least three ultrasonic welds disposed equally around the coaxially overlapped tube and bellows connect 25 the bellows to the tube.

7. A dip tube as claimed in any one of Claims 1-6, wherein a continuous ultrasonic weld around the coaxially overlapped tube and bellows connects the bellows to the tube. 30

8. A dip tube as claimed in any one of Claims 1-7, wherein the bellows has a neck at the upper end thereof which is an interference fit over the lower end of the dip tube. - 11

9. A dip tube substantially as herein described with reference to and as illustrated in Figures 1 and 2. Dated this 2 8 th day of April, 2005. 5 SANDERCOCK & COWIE PATENT ATTORNEYS FOR B.M.W. PLASTICS PTY. LTD. and NITE-GLO INNOVATIONS PTY. LTD. 20f05-04.2R A-\5Mdhm en 11