GB2578324A - Method of moulding tie strips - Google Patents

Abstract

A contiguous sheet of conjoined tie strips wherein individual strips (figure 2, 6) are arranged in alternating vertical orientations with adjacent strips being interconnected by narrow gating regions (figure 10, 19). The interconnecting gating regions may be formed by overlapping adjacent tie strips (e.g. figure 13, 27). The tie strips may have a repeating cellular design, a ladder-style design or a conventional single-use design. The tie strips may be manufactured from a polymer material by injection moulding. the sheet of contiguous tie strips may be attached to longitudinal 5 or horizontal 46 runner portions, the runner portions incorporating narrow regions of flow such that debris or contaminants (figure 48, 71) can be trapped and filtered out from the molten polymer, and wherein the runner portions mould over grab-pins 62 embedded on one or both sides of the mould.

Description

Method of Moulding Tie Strips

TECHNICAL FIELD OF INVENTION

The present invention relates to the production of tie strips and similar bundling devices, especially 5 by the process of injection moulding.

DOCUMENTS CITED

GB0811973 -SOPACEM, Wrobel 4/1959 DE1079537 -Grzemba 4/1960 US3102311 -Martin et al 9/1963 US3186047 -Schwester et al 6/1965 US3224054 -Lige 12/1965 US3438095 -Evans 4/1969 US3913178 -Ballin 10/1975 US3973610 -Ballin 8/1976 US4045843 -Loose et al 9/1977 US4077562 -Ballin 3/1978 US4150463 -Brown 4/1979 US4473524 -Paradis 9/1984 US4728064 -Caveney 3/1988 US4754529 -Paradis 7/1988 US5685048 -Benoit 11/1997 US5799376 -Harsley 9/1998 US5836053 -Davignon 11/1998 US7337502 -Mermelshtein 3/2008 US7704587 -Harsley 4/2010 US8709568 -Harsley 4/2014 EP2475589 -Mermelshtein 2011 US2013014350 -Lie W02014125241 -Harsley

BACKGROUND ART

Many tie strip designs are described in the prior art, such as the conventional single-use nylon cable tie as typified by GB0811973 (Wrobel), and numerous variations of it such as US3102311 (Martin et al) and US3186047 (Schwester et al). In these inventions, secure latching is achieved by a pawl-like member enclosed in a robust head portion engaging with a flexible tail portion extending from the head. Said tail portion is generally provided with raised latches that mate with the pawl.

An alternative approach is described in, for example US4473524 (Paradis), US4728064 (Caveney), US4754529 (Paradis) and US5685048 (Benoit). In these inventions, the tail portions are multiply-apertured and latching is achieved when a pawl or barb (formed into the head portion) securely penetrates one of the apertures in the tail portion. Beneficially, such tie strips can be manufactured in a compact form and then subsequently stretched out to length, as described in US4754529 (Paradis). It can be noted that US5836053 (Davignon) combines a multiply-apertured tail portion together with raised latches for additional latching security.

More efficient "multiple-use" tie strips are also described in the prior art, such as DE1079537 (Grzemba), U53224054 (Lige), US3438095 (Evans), U53913178 (Ballin), U53973610 (Ballin), US4045843 (Loose et al), US4077562 (Ballin), US4150463 (Brown), US5799376 (Harsley), US7337502 (Mermelshtein), US7704587 (Harsley), US2013014350 (Lie), EP2475589 (Mermelshtein) and W02014125241 (Harsley). Necessarily, such inventions utilise a multiply-apertured tail portion without a specific locking head portion. The tail portion may then be regarded as a repeating sequence of unit cells that are capable of interlocking with each other.

Detailed manufacturing techniques for such tie strips are less commonly explained, with descriptions in the prior art typically suggesting casting, moulding, stamping, pressing, cutting, etc. In general, injection moulding is the preferred industrial technique, especially for non-planar tie strip designs -i.e., anything involving a three-dimensional shape. However, there are moulding practicalities to consider with mass-production. In particular, tie strip designs are relatively long and thin, resulting in a narrow cavity that requires high pressures to fill. This is particularly problematic for multiple-use tie strips because the numerous apertures along the tail portion significantly impede the flow of injected material.

With some tie strip designs (e.g., U53438095 (Evans) and US7704587 (Harsley)), it is possible to join multiple adjacent cavities together. Such a technique is described in US8709568 (Harsley). When fed from a suitable runner, this "side-gating" yields a much shorter flow-path, greatly reducing the required injection pressures (figure 2). More cavities can therefore fit onto an optimally sized mould and machine configuration, lowering production costs.

This technique works well for manufacturing tie strips with laterally projecting wing portions because the cavities for such tie strips can be placed very close together with only the tips of their wing portions being separated by extremely thin wall sections. These wall sections are then adapted into feed gates that interconnect the adjacent cavities, allowing molten polymer to flow between them, the interconnecting gate lengths being small enough such that when individual tie strips are separated from the contiguous sheet (or side runner), only minor gate vestiges remain that do not impede threading or damage the tie strips (figure 4).

Although the resulting thin wall sections are inherently quite weak, they are not extensive, being limited to just the very tips of the projecting wing portions. Furthermore, the narrowest and weakest wall sections are deliberately removed to create the gates that interconnect the cavities. In this manner, cavity separations (and therefore gate lengths) in the order of 200 microns can be obtained without unduly compromising the mould.

However, this technique is unsuitable for tie strip designs with continuous straight sidewalls, such as those described by GB0811973 (Wrobel) and W02014125241 (Harsley). Placing the cavities for these tie strips very close together (figures 5 and 6) creates a continuous narrow wall section between them, and this is inherently fragile.

SUMMARY OF THE PRESENT INVENTION

The present invention allows the injection moulding of contiguous sheets of conjoined tie 45 strips without requiring weak, narrow wall sections to separate adjacent cavities.

This is achieved by placing adjacent cavities on opposite sides of the mould, such that their top edges either overlap or come very close to doing so. In this manner, side-gating of winged or straight-walled tie strips can be successfully implemented, resulting in a sheet of adjacently interconnected ties strips that can be conveniently separated from one another simply by tearing or cutting.

DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying 60 diagrams and drawings in which: Figure 1 shows individual cable tie strips being injection moulded longitudinally from a cold runner at the head end.

Figure 2 shows a sheet of multiple-use cellular tie strips with projecting side wing portions being injection moulded laterally from a cold runner at the side.

Figure 3 shows a sheet as depicted in figure 2 70 being separated into individual tie strips by tearing through the small interconnecting gates.

Figure 4 shows the sidewall damage that can occur during fitting if large gate vestiges remain after separation.

Figure 5 shows a contiguous sheet of conventional cable tie strips interconnected with very narrow longitudinal gate portions.

Figure 6 shows a contiguous sheet of ladder-style multiple-use tie strips interconnected along their 80 side rails with very narrow gate portions.

Figure 7 shows in cross-section the very narrow cavity separation of figure 5.

Figure 8 shows in cross-section the very narrow cavity separation of figure 6.

Figure 9 shows a method of reinforcing the narrow inter-cavity walls between adjacent cavities.

Figure 10 shows a method of avoiding narrow inter-cavity walls between adjacent cavities.

Figure 11 shows a top view of the horizontal tapering of longitudinal inter-cavity gates.

Figure 12 shows a side view of the vertical tapering of inter-cavity gates.

Figure 13a shows in projection the tapering of an external inter-cavity gate along the side of a tie strip with continuous straight sidewalls.

Figure 13b shows in projection the tapering of an 5 internally overlapping inter-cavity gate between two adjacent tie strips with continuous straight sidewalls.

Figure 14a shows in projection a simple overlapping inter-cavity gate between two tie strips with continuous straight sidewalls.

Figure 146 shows in projection the tapering of a simple overlapping inter-cavity gate between two adjacent tie strips with continuous straight sidewalls.

Figure 15 shows in cross-section an external inter-cavity gate between the side rails of two adjacent ladder-style tie strips with opposite vertical orientations.

Figure 16 shows perforated external inter-cavity 20 gates.

Figure 17 shows the localised narrow waist portion of an internally overlapping inter-cavity gate.

Figure 18 shows the preferential separation of the 25 individual tie strips along the localised narrow waist portion.

Figure 19 shows a less focused waist portion resulting from outwardly tapered walls.

Figure 20 shows a more focused waist portion 30 resulting from inwardly tapered walls.

Figure 21 shows an external gate connecting the side rails of two adjacent tie strips.

Figure 22 shows the asymmetric separation of the gate depicted in figure 21 and the resulting gate 35 vestige.

Figure 23 shows a vertically extended external side gate with a localised waist portion.

Figure 24 shows preferential separation through the localised waist portion depicted in figure 23.

Figure 25 shows the improved melt-flow resulting from vertically extended external gates.

Figure 26 shows a contiguous sheet of ladder-style tie strips with alternate vertical orientations being moulded from a longitudinal side runner or 45 discrete top gates.

Figure 27 shows a contiguous sheet of ladder-style tie strips with alternate vertical orientations being moulded from end runners.

Figure 28 shows functional end portions that may 50 be implemented when moulding contiguous sheets of tie strips.

Figure 29 shows the cross-sectional area of individual tie strip cavities.

Figure 30 shows the slightly increased cross-sectional area of conjoined tie strip cavities. Figure 31 shows a sheet of three ladder-style tie strips with alternate vertical orientations and the mould parting-line between them.

Figure 32 shows a sheet of five such ladder-style 60 tie strips.

Figure 33 shows a sheet of nine such ladder-style tie strips.

Figure 34 shows different mould parting-line positions.

Figure 35 shows in cross-section the offset parting-line of a mould cavity for three ladder-style tie strips with alternate vertical orientations. Figure 36 shows a lengthened rung and its larger gating area.

Figure 37 shows the divergent flow produced by a central feed point.

Figure 38 shows a localised strengthening of a small portion of the sidewalls.

Figure 39 shows an extended strengthening of a 75 longer portion of the sidewalls.

Figure 40 shows two gates producing a potentially weak weld line between them.

Figure 41 shows two gates placed closer together to strengthen the resulting weld line.

Figure 42 shows in plan view the orientation of the lateral rungs and the resulting asymmetric flow. Figure 43 shows longitudinally offset gating to compensate for asymmetric flow.

Figure 44 shows in plan view grab-pins engaging with lateral and longitudinal cold runners. Figure 45 shows in side view grab-pins peeling a sheet of tie strips from the mould during opening. Figure 46 shows a portion of the present invention when implemented using cellular tie strips.

Figure 47 shows figure 46 in projection.

Figure 48 shows inclusions of debris embedded in a central longitudinal cold runner.

Figure 49 shows a cross-section of figure 48 with debris trapped at the longitudinal gates.

Figure 50 shows in cross-section multiple thin longitudinal runners trapping debris.

DESCRIPTION OF THE PRESENT INVENTION

Conventional cable tie strips 1 are generally produced as discrete components by the process of injection moulding (figure 1). Molten material is typically introduced 2 at the head end through feed gates 3 into individual mould cavities. It then flows longitudinally 4 to form the resulting tie strips. Because long thin cavities require high injection pressures to fill, the number of tie strips that can be simultaneously produced is limited by the injection-moulding machine's capability. It is common practice to duplicate the cavities on the opposite side of the feed runner to balance the mould and to increase production capacity.

A more efficient moulding method is to produce sheets of conjoined tie strips (figure 2), as taught by US8709568 (Harsley). This technique allows the injected polymer to flow laterally as well as longitudinally, reducing the flow length and thereby the required injection pressure. It is advantageously implemented by introducing material through a feed point 2a into a large diameter cold runner 5 along one side of the conjoined cavities 6. In this configuration, molten polymer readily fills this runner prior to flowing laterally 7 and filling the cavities. Individual strips are then removed from the contiguously moulded sheet and runner (figure 3) by simply tearing or cutting through the small interconnecting gates 8.

With this technique, the interconnecting gate size must be kept to a minimum (figure 4) because any significant gate vestiges 9 can impede threading and/or tear the aperture sidewalls 10 during use. Depending on the physical dimensions of the tie strip, laterally projecting gates of 200-500 microns are considered

acceptable.

Unfortunately, when implemented with tie strips possessing substantially longitudinally straight sidewalls (figures 5 to 8), one or more very thin longitudinal gates 11, 11a are needed to interconnect the adjacent strips 18, and forming such gates requires equally thin wall sections 12 in the mould between adjacent cavities. These are undesirably weak and prone to damage. In particular, should one cavity fail to completely fill, the long and thin separating wall section 12 has to contain the entire pressure experienced inside an adjacent cavity. The pressures needed to fill such cavities are often enough to buckle or fracture any long thin separating walls.

Wider inter-cavity walls 13 (figure 9) can be created on at least one side of the parting-line 14 of the mould 15 by tapering 16 or rounding 17 the sides of the strips. However, this is not a complete solution because the basal portions of such inter-cavity wall sections 13 may still be only a few hundred microns across, especially when producing very narrow tie strips or when using minimally narrow gates.

The alternative solution presented herein avoids narrow wall sections by placing adjacent tie strip cavities 18 on opposite sides of the mould (figure 10). Arbitrarily narrow longitudinal gates 19 may then be inserted between the cavities 18 without being defined by wall sections of comparable size 12, 13 (figures 7 to 9). Indeed, adjacent cavities may even overlap 20, the gating area then being formed by the narrow overlapping region. The parting-line of such a mould configuration may be level with the top of one of the cavities 21, or it may be placed along the centre line 22 of the gates 19, 20, or it may be placed at any other convenient dividing line.

At their simplest, these longitudinal gates perform two functions: Firstly, they have sufficient cross-sectional area to permit adequate material flow between adjacent cavities; Secondly, they are weak enough to allow easy separation of the conjoined tie strips post-moulding by means such as tearing or cutting. Both of these requirements are satisfied by a very narrow separation or a small overlap.

In either implementation, it is advantageous to taper-off the longitudinal interconnecting side gates 19 at one or both ends (figures 11 and 12).

This avoids a step transition 23 at the end of a gate and facilitates easier separation and easier fitting of the tie strips. This tapering can be implemented both horizontally 24 and/or vertically 25, with the terminal end(s) ideally blending fully 50 into the main body of the tie strip 26 to avoid discontinuities.

Such tapering is easier to achieve with non-overlapping cavities (figure 13a) because a small (or even zero) gating area at the lead end 26 can easily be enlarged as required 27. However, when cavities overlap (figure13b), the gate is internal to the cavities rather than external to them, hence avoiding an abrupt end to the overlap must be implemented by tapering one more of the cavities themselves.

Although the full size of the overlapping gate 27 can be seamlessly blended into the cavities 26, the cross-sectional dimensions of the cavities may need to be slightly different at the two ends, typically being smaller at the lead end 28 compared to the overlapping end 29. This condition imposes extra constraints on the geometry of the cavity that may not be desirable. Placing a thin external gate 19 between adjacent cavities 18 (figure 13a) has therefore proven to be the better solution in this respect.

Where overlapping cavities are acceptable, the simplest solution is a small horizontal overlap 20a (figure 14a). The resulting gate area may then be tapered-off by tapering the cavities as described above (figure 14b). This condition may be automatically satisfied when the tie strips are provided with a laterally tapering tongue portion.

The dimensions of such interconnecting gates, whether internally overlapping (figures 13b and 14a) or externally discrete (figures 13a and 15), may be scaled to match the size of the required tie strips. For a typical tie strip of 5-10mm width, longitudinal interconnecting gates with a nominal working cross-sectional area 27 of about 0.05-0.3mm2 have proven successful, although greater or lesser cross-sections may be implemented as required. Typically, the horizontal spacing 30 between adjacent tie strip cavities is around 100300 microns, with a total vertical gate thickness 31 of around 100-300 microns. Similar dimensions may be obtained with overlapping gates 20, 20a (figures 14a and 14b).

The inter-cavity gating area should be as large as practical to reduce injection pressures, however, the gates must also be subsequently cut or torn to separate the individual tie strips. It is therefore advantageous to make them as weak as possible (figure 16). Short perforations 32 are necessary for cellular tie strips with laterally projecting wing portions (figure 2), but are less desirable for tie strips with longitudinally continuous sidewalls.

This is because their intermittent nature results in many gate vestiges that can impede the threading process (c.f. figure 4). Longer perforations 33 may be employed, especially if the resulting gate sections are sufficiently tapered at the ends to avoid threading problems (figure 16). However, in either case perforations reduce the gating area and this is generally undesirable in a longitudinal side-gating configuration.

Another solution (figure 17) is to provide the gating area with a localised waist portion 34 where the diagonal cross-sectional distance is minimal, typically in the order of 100 to 500 microns. Tearing and/or cutting (figure 18) will then preferentially be constrained to this region. Such a waist 34 is generally self-creating in cavities that overlap both horizontally and vertically (figure 17), although it becomes less pronounced if simple one-dimensionally overlapping cavities are employed (figures 13a and 14a). Tapered or rounded sidewalls may be employed to help define the waist (figure 19), although ideally, the outside contact angle of the overlap should be as small as possible (figure 20) to focus the location of the tear. With square-sectioned walls (figure 17), the outside contact angle is 90 degrees, but it increases if the contacting wall surfaces are tapered or rounded inwardly 35 (figure 19). Conversely (figure 20), wall surfaces that are tapered or rounded outwardly will create a more desirable narrower contact angle 36, although constructing a mould with such geometry may be harder to implement.

With non-overlapping adjacent tie strip cavities (figure 21), a waist that is non-localised will form if a simple square or rectangular gate profile 19 is used to conjoin them. With such geometry, the whole gate has a substantially uniform cross-section, hence any cut or tear is not likely to occur in the exact centre of the gate to give a symmetrical separation. In practice (figure 22), cuts and tears will instead preferentially follow one of the sidewalls 37. This leaves a clean edge 38 on one of the separated tie strips, but a pronounced gate vestige on the sidewall of the adjacent strip 39. In a worst-case scenario, the propagating tear may randomly switch between the two sidewalls leaving an irregular gate vestige on both sides. This remaining gate vestige is undesirable, since it may impede the threading process or damage the tie strips (c.f. figure 4).

A much cleaner tear or cut can be created by applying deeper gates 40 onto the sidewalls (figure 23) such that a narrow localised waist 34 is restored. Ideally, these deeper gates should be rounded or tapered at the ends 41 to avoid sharp edges and promote smooth threading when the end user ultimately fits the tie strip. With a 5-10mm wide tie strip, these deeper gates typically extend vertically 300-800 microns 42 on each side of the centre line. Where such gates are formed with sufficiently small outside contact angle they create a highly localised diagonal tear-line (the waist) 34 through which the conjoined tie strips are preferentially (and cleanly) separated (figure 24).

Deeper gates also tend to increase the melt flow through them (figure 25). This is because a simple rectangular gate 19 has a narrow cross-section that extends a relatively long distance horizontally (figure 25a), whereas the narrowest portion of a waisted gate 34 (with identical cross-sectional area) is minimally short (figure 25b). It can also be noted that the direction of melt flow 43 through the gate portion occurs at a more inclined angle with deeper gates 44, resulting in a much smoother flow path (figure 25b).

As with the side-gating technique described by US8709568 (Harsley) (figure 2), a conjoined tie strip cavity (figure 26) can be fed by a central longitudinal cold runner 5, or by such runners on either or both longitudinal sides, or via one or more surface feed points 45 as part of a hot runner system. Where appropriate (figure 27), such a conjoined tie strip cavity can also be filled from one or both ends, typically using short lateral cold runners 46.

Although an end-fed configuration (figure 27) involves an increased overall flow length compared to a side-gating configuration (figure 26), the required pressures are still generally lower compared to filling individual cavities (c.f.

figure 1). This is because the pressure drop per unit length in a channel scales disproportionally with diameter (as given by the Darcy-Weisbach equation and it's simplification, the HagenPoiseuille equation), hence even a very small increase in hydraulic cross-section requires substantially less pressure to sustain the same volumetric flow rate. In the case of individual cavities, the total cross-sectional area 51 (figure 29) is always less that the cross-sectional area 52 of the same cavities when conjoined by longitudinal side gates 19 (figure 30), therefore identical cavities are easier to mould when conjoined. Additionally, individual cavities require a more balanced filling process to prevent shorting and/or flashing of parts, and the handling requirements of multiple separate parts are usually more complicated. Combining multiple cavities through longitudinal side gates into a single contiguous conjoined cavity is therefore generally an advantageous technique.

Due to the benefits of reduced flow-lengths, the lowest injection pressures are obtained when gating from the sides of the conjoined cavity (figure 26), generally with a cold runner 5. (An obvious variation of this technique is a runner feeding a sheet of conjoined tie strips on either side, as described by US8709568 (Harsley).) However, one problematic issue with such a side-gating approach is the substantially lateral melt flow direction. Maximum tensile strength is normally only achieved along the flow axis, and with tie strips, this flow is preferably longitudinal 4 (c.f. figure 1). Hence, conjoined cavities should ideally be fed from the ends (figure 27), and ideally from just one end to prevent the formation of potentially weak weld-lines. With laterally filled cavities (figure 26), tie strips may accordingly suffer from reduced strength and increased stiffness along the more critical longitudinal axis. It is found that these anisotropic effects are most noticeable in stiffer polymers, particularly nylons (polyamides and polycaprolactams), polyurethanes and other materials generally exceeding 60D on the Shore hardness scale. In practice, such anisotropic side-gating effects on strength and flexibility can be reduced by sympathetic design of the component, or by post-curing the parts after moulding to de-stress them. Softer materials are generally not as badly affected, and side-gating through a cold runner has been successfully used in industry for the mass production of tie strips for many years.

In most cases, cold runners are usually removed from the moulded part after production, however it may be appropriate to make them part of the product design by leaving them in place, or by adding similar end portions as required (figure 28). This may facilitate an apertured tag at an end as a method of binding together multiple sheets of tie strips 47; as a method of hanging them in a retail display 48; or simply as a method of neatly retaining the independent tongue ends prior to removal of the individual tie strips from the conjoined sheet (figure 28a). In all instances, small individual gates 50 are required to attach such end portions to the strips. These gates need to be large enough to readily allow molten material to flow through them, but also weak enough to allow their easy separation from the individual tie strips when required. Such gates may be formed automatically by the narrow contact point between a tapered tongue portion and the adjoining end portion 48, or by adding dedicated gates 50. This is often more appropriate, especially at the rear end of the contiguous sheet of tie strips where such gating is generally performed either on the ends of the sidewalls or on the centres of the ultimate rungs. In either case, gating dimensions in the order of 0.5mm to 1.5mm are generally suitable.

These same end portions 47, 48 may also serve as handling areas for extracting the sheets from the mould (either manually or by automatic means), or as overspill areas 49 such that the moulding process does not need to be exact (figure 28b). This is particularly relevant where the mould contains multiple sets of conjoined cavities to simultaneously produce several independent contiguous sheets. In such cases, it may be difficult to balance the melt flow and consistently fill all cavities without flashed or short shots. Said overspill areas 49 do not need to fill completely since they are removed post-moulding, hence deliberate shorting of these overspill areas helps ensure that the tie strip cavities themselves will fill completely but not flash around the edges.

As noted above, an alternative gating method is to provide one or more feed points 45 directly onto the surface of the conjoined sheets, generally using the pin gates formed by the tips of a hot runner system (figure 26). These are advantageously placed onto the centre of the rungs from above (c.f. figure 32), however the available tip gating area 53 may not be very large, especially with thin tie strips below 5mm in width. Extending the length of the gated rungs 54 is a possible solution to providing a larger gating area 55 (figure 36), but there may be practical limits to this approach. More than one feed point may therefore be required to fill the conjoined cavity at acceptably low injection pressures, and the location of such feed points will depend on the exact design of the tie strips and the material of fabrication.

Feed points 45 near to the centre of the conjoined cavity are desirable since they minimise the required flow length (figure 26). However, it can be noted that even when a single feed point 45 is adequate, the resulting flow must radiate outwardly thereof and subsequently bifurcate 56 to longitudinally fill the conjoined cavity towards the front and rear (figure 37). A continuous longitudinal flow along the tie strips cannot therefore be attained with this method, and this may introduce weak spots where the flow diverges from the gating location 45. Such bifurcation zones often have a generally anisotropic morphology and unpredictable physical properties. They are especially problematic along the sidewalls because modification of the tie strip design to compensate for such weak spots has undesirable consequences. Enlarging the sidewalls to strengthen them cannot reasonably be done just locally near to the weak spot 57 (figure 38) since the exact location of the weak spot may vary between moulding cycles due to variations in temperature, pressure, material viscosity etc. Rather, at least a lamer length of the sidewall 58 (typically a few centimetres) must be strengthened (figure 39), and ideally the whole of the sidewall must be so enlarged to maintain a consistent cross-section and uniform longitudinal gates. Such modifications are generally unwanted since they increase the overall width, weight and stiffness of the strip in such regions.

Multiple feed points 45 can be employed to significantly lower injection pressures, especially when located to minimise the flow lengths (figure 40), but they also create more bifurcation zones 56. Additionally, weld-and meld-lines occur where the multiple flow fronts meet 59, and these may also introduce weak spots into the resulting tie strips. As described above, compensating for weak spots in the sidewalls is problematic.

The weld-line issue can be alleviated somewhat by locating the feed points more closely together (figure 41), however additional feed points elsewhere along the length may then be required to fill the cavity at desirable pressures. There is therefore a trade-off between the number of surface feed points, the distances between them, and the acceptability of weak spots in the moulded tie strips. Optimal solutions will vary depending on mould design and material, but it has been found in practice that two centrally located surface feed points with a separation of around 40-80mm will acceptably fill a 400mm long conjoined cavity of at least up to nine 5mm wide tie strips in many thermoplastics. In a balanced configuration such gates would be spaced roughly 200mm apart, and although this configuration has also been successfully proven to work, more pronounced central weld lines are evident. Hence the advantageous offsetting of the feed locations as described above.

An additional complication arises with many tie strip designs, for example those described by US3438095 (Evans), US7704587 (Harsley) and W02014125241 (Harsley). The longitudinal construction of these tie strips is necessarily asymmetric because of the corresponding longitudinal asymmetry of the individual unit cells from which they are constucted. This asymmetry can subtly affect the flow of the molten material during injection, and the effect is particularly noticeable in the more compact tie strips described in W02014125241. It is found in some materials that when flowing towards the tongue end of the strips the melt-flow tends to flow more quickly past the angled rungs 60, whereas when flowing towards the rear of the strip the melt-flow tends to slow down by flow into the rungs 61 (figure 42). Due to the large number of such rungs, this subtle asymmetry in flow can cause one end of the tie strips to fill more rapidly than the other end, hence the feed locations are advantageously moved slightly away from the centre of the conjoined cavity to compensate and restore a more balanced fill (figure 43). As is common in the injection moulding industry, additional balancing of flow can then be obtained by differential adjustment of the feed temperatures.

Another solution to the weld-and meld-line issue described above is two or more surface feed points located towards the outermost strips of conjoined cavities (as shown in figure 26). This horizontal configuration serves to alleviate the sidewall weld-line issues associated with multiple longitudinal feed points, the weld-lines instead being generally formed at the centres of the rungs. Such central weld-lines are often inherent in the manufacture of cellular tie strips, and these are usually compensated for by making the rungs more robust along their centreline. In this respect, rung weld-lines are less problematic than weld-lines occurring along the sidewalls of the tie strips.

In order to facilitate easy extraction of sheets of 95 conjoined tie strips from their mould, it is advantageous to place most of the conjoined cavity on the moving-half. This can be achieved in This technique has the added advantage that a balanced fill can be accomplished because the conjoined cavity is at least symmetrical about its longitudinal centre line. Hence, one or more central feed points 45, 45a may be used to fill the whole cavity. However, the technique is less effective if the conjoined cavity produces a larger number of tie strips. A cavity for producing five tie strips, for example (figure 32), has two strips 66 in the fixed-half and three strips 65 in the moving-half, whereas a cavity for nine strips (figure 33) has four strips 66 in the fixed-half and five strips 65 in the moving-half. Clearly as the number of tie strips increases the difference in geometry between the two sides diminishes, and it becomes less certain that the moulded sheet will correctly remain in the moving-half as needed. In practice, contiguous sheets of at least seven tie strips have been found to consistently remain in 80 the moving-half without difficulty.

two ways. Firstly, a conjoined cavity consisting of an odd number of tie strips (figure 31) is formed such that the one extra strip 65 resides in the moving-half In this manner, there is more material and more surface area in the moving-half of the mould (below the central parting line 22), hence it is more likely for the moulded sheet of conjoined tie strips to remain in this moving-half when the mould is opened. (As is well understood in the injection moulding industry, parts residing in the moving-half of the mould are readily extracted by use of ejection pins embedded therein.) The second means of placing most of the conjoined cavity on the moving-half of the mould is to move the mould parting-line further into the fixed-half (figure 34). The parting-line 21 may be moved to the top edge of the interconnecting gate portions (figure 34a), or even deeper 21a into the fixed-half if required (figure 34b). With this technique, the tie strip cavities must be cut differently in each mould half (figure 35), with more geometry being in the moving-half 63 than in the fixed-half 64. Again, this leads to a tendency for the moulded tie strip sheets to remain on the moving-half when the mould opens.

In addition to these techniques, it is standard practice to add a slight draft angle 73 to any convenient geometry on the fixed-half, and, wherever necessary, a slight undercut 74 to geometry on the moving-half (figure 35). Alternatively, grab-pins may be embedded into one or both sides of the mould to appropriately retain the moulded sheets of tie strips. An effective implementation of this method (figure 44) places grab-pins 62 along a central longitudinal runner 5 on the fixed-half of the mould, and along a horizontal runner 46 on the moving-half. The horizontal runner is placed either at the top or bottom of the sheet of tie strips, with the grab-pins in the horizontal runner possessing a combined greater holding force than those on the longitudinal runner. When such a mould configuration is opened (figure 45), the horizontal runner is preferentially retained on the moving-half 63, and the longitudinal runner, together with the attached moulded sheet of tie strips 67, is subsequently peeled away from the weaker grab-pins embedded in the fixed-half 64. When the mould is fully open, the moulded sheet of tie strips is retained only by the horizontal runner grab-pins, and thereafter may be readily ejected or extracted from the mould. By combining these methods or modifications thereof, contiguous sheets of any number of tie strips can be produced, including those comprising an even number of tie strips.

Returning to figure 31, it can be noted that a cavity for producing sheets of three tie strips as per the preceding description has its central point in the lower (moving-halt) portion of the mould. If material is symmetrically introduced into the mould cavity at this location, the feed point 45a must fit between the sidewalls 68 of the central tie strip cavity. This is also the case with cavities for producing sheets of seven or eleven tie strips (not shown). However, in figure 32 it is seen that a cavity for producing sheets of five tie strips has its central point in the upper (fixed) portion of the mould. The feed point 45 has no sidewalls to avoid with this arrangement, and it is generally an easier mould configuration to manufacture. As is shown in figure 33, the same is true for cavities producing sheets of nine tie strips, and also for sheets of thirteen and seventeen etc. Sheets of other numbers of conjoined tie strips (including even multiples) may be manufactured by offsetting the feed gate locations by one cavity, although this introduces an unbalanced lateral asymmetry that may require additional mould 55 clamping force to compensate. The orientation of the central tie strip is, of course, irrelevant if the cavity is side-gated from a cold runner 5 (figure 26).

After conjoined sheets of tie strips have been moulded and extracted by the methods previously described, tearing by hand is the most convenient means of separating the individual strips when required for use. A secondary cutting process is not required if the gates can be manually broken, and as described above, this is desirable since conjoined sheet-form production and distribution allows for easier handling and packaging compared to working with individual tie strips.

However, larger inter-cavity gates may be needed when moulding viscous materials with poor melt-flow properties, such as biopolymers and polymers containing large amounts of powder or other additives (for example, fire-retardants or elecromagnetic particulates). In these cases, the inter-cavity gates may need to be enlarged to achieve adequate melt-flow, and these gates may then be too difficult to readily tear by hand. Larger gates may also be needed to maintain adequate material flow when moulding larger tie strips, typically those over 10-15mm wide. A secondary manufacturing process may therefore be required to pre-separate the tie strips, with the resulting individual tie strips being packaged for the end user. Such a process may involve mechanical tearing, shearing, slicing or cutting, typically with the conjoined sheets being passed against a fixed or counter-rotating anvil, blade or heated wire.

The manufacturing method herein described can be applied to most types of tie strip, including conventional nylon cable ties as described by GB0811973 (Wrobel) (figure 5). It can be noted that as well as being alternately placed on opposite sides of the mould, such adjacent tie strip cavities also require an alternating longitudinal offset to accommodate their wider apertured head portions. To permit longitudinal gating between adjacent ties, these head portions must be less than twice the width of the tail portions, which is generally the case.

It can also be noted that the short tongue portions at the other ends of such cable tie strips possess little lateral taper and are generally angled vertically downwards of the tail portions.

Accordingly, external longitudinal inter-cavity gates (c.f. figure 13a) are generally preferred for conjoining multiple cavities of such cable tie strips.

When cellular tie strips with laterally projecting wing portions, such as described by US7704587 (Harsley) (figure 3), are manufactured according to the present invention (figures 46 and 47), short longitudinal gating 69 can only occur at the external tips of the wing portions, rather than along the entire length of the tie strip. Since the sidewall geometry of the repeating unit cell portions naturally tapers to point intersections 70 on either side of this gating area (figures 46 and 47), overlapping gates are in this case the preferred method of conjoining such adjacent tie strip cavities (c.f. figures 14a and 17).

As described above, overlapping gates can be arranged to naturally tear cleanly along the waist formed between them (figure 18), hence no significant gate vestiges remain after separation. This is advantageous because gate vestiges are known to cause damage to the interior aperture walls of cellular tie strips during the fitting process (figure 4). For this reason, when such tie strips are moulded according to the method presented by US8709568 (Harsley), the interconnecting gates are necessarily kept as small as possible.

However, such small gates restrict the lateral flow of molten material and require higher injection pressures to successfully fill the conjoined cavity. According to the present invention, the lack of gate vestiges obtained from overlapping adjacent tie strip cavities allows the interconnecting gating areas to be made much lamer, thereby improving the lateral flow across the conjoined tie strips and reducing the required injection pressures.

It has been found that the method of moulding presented herein works successfully with the types of tie strips described above in most desired materials of construction, including polyamides, polycaprolactams, polyolefins, polyurethanes, polyvinyl chlorides, polyethylene-vinyl acetates, polylactic acids, polyvinyl alcohols, common thermoplastic elastomers (e.g., EPDM, TPV, SEBS etc.) and most other polymers and blends of polymers with suitable physical properties. In addition, contaminated materials have been successfully utilised because the narrow inter-cavity gates also serve as particulate filters (figure 48). Inclusions and debris 71 large enough to affect the strength of the individual tie strips, or to blemish their cosmetic appearance, are generally too large to pass through the narrow longitudinal gates 19 or 20. They can therefore be readily trapped, preferably by a feed runner 5 adjacent to the tie strip cavities themselves (figure 49).

An improved filtration system can be formed by interconnecting multiple feed runners 72 with longitudinal gates 20 in the same manner as described above for connecting the tie strip cavities themselves (figure 50). These runners 72 may be narrower than a single feed runner, but generally have a comparable combined cross-sectional area such that longitudinal flow is maintained. A row of such gated presents a more significant barrier to any debris contained within the molten polymer, whilst still allowing the melt to flow laterally and longitudinally therethrough. The erection of similar horizontal or radial barriers, especially around the feed point 45, can also be utilised where appropriate.

The technique is particularly advantageous when recycled or contaminated polymers are being used, such as the PVC reclaimed from cable sleeving that often contains residual wire strands. It should be noted that a practical implementation also requires that the nozzle diameter of the moulding machine, together with the manifold and feed tips of any attached hot runner system, must all be suitably enlarged to allow the free passage of debris without becoming blocked. This debris is then ultimately contained in the filtration runner as described above and can be disposed of as appropriate.

By combining and extending the various gating techniques described herein, much larger contiguous sheets of conjoined tie strips may also be produced, the maximum size being determined by the limitations of the injection moulding machine. In principle, a continuous manufacturing process (such as indexed injection moulding) could manufacture conjoined sheets of tie strips as described above on a continuous roll, and the same methodology may also be adapted for the manufacture of sheets of conjoined tie strips by casting, extruding, stamping, and other suitable manufacturing techniques.

DESCRIPTION OF A

FIRST PREFERRED EMBODIMENT

A contiguous sheet of conjoined tie strips is produced from a suitable polymer wherein the individual strips are formed in alternate vertical orientation such that thin longitudinal gates separate adjacent strips. Where molten polymer is used to form the contiguous sheets, said longitudinal gates allow the melt to flow both laterally and longitudinally through the corresponding conjoined mould cavity.

Advantageously, the method employs a continuous ladder-style design of tie strip of the form presented by W02014125241 (Harsley), typically about 5-10mm wide with substantially square sidewalls typically around 0.8-2.0mm in width and height. Such tie strips generally possess a tapering tongue portion, and these may terminate through small gates onto an end portion that may be used for manufacturing, handling or packaging purposes.

The longitudinal interconnecting gates between adjacent tie strips are formed either by a simple overlapping of the cavities, or preferably by discrete external gates that extend sufficiently upwards along their vertical sidewalls to define a waist portion through which neighbouring tie strips may be easily separated, such as by tearing by hand. Suitable gates are typically about 250 microns wide and extend vertically about 500 microns along each sidewall, terminating with a radiused edge. The vertical overlap of adjacent cavities is about 200 microns, and at its narrowest cross-section, the waist portion extends diagonally about 300 microns.

These longitudinal gates substantially extend into the tongue portions of the tie strips, gradually tapering both horizontally and vertically to seamlessly blend into the sidewalls of the tongues. At the tail end of the tie strips, such tapering is not critical and the gates may extend to the very ends if desired. In this manner, no discontinuities exist along the gates when adjacent strips are separated, hence there are no potentially damaging gate vestiges.

A conjoined sheet of up to at least nine tie strips is favourably produced by injecting molten material from one or more feed points entering when practical onto the centres of horizontal rungs, preferably from above. The feed points are generally located symmetrically of the centre of the cavity, but may be slightly offset longitudinally thereof to mitigate weld-line weaknesses or to compensate for any asymmetric flow present in the cavity design. Where adjacent cold runners are employed in preference to rung-gates, the gates formed by the runners serve to trap unwanted debris or contamination in the molten material and prevent it from entering the tie strip cavities. The runners may also mould over grab-pins embedded on opposite sides of the mould, thereby assisting the extraction of the moulded sheet by peeling it away from the fixed-half.

DESCRIPTION OF A

SECOND PREFERRED EMBODIMENT

A contiguous sheet comprising any number of conventional cable tie strips of the form presented by GB0811973 (Wrobel) is produced substantially as described by the first embodiment above, but with the tie strip cavities on one side of mould being rotated by 180 degrees from the other and longitudinally offset by an amount sufficient to accommodate their head portions.

The width of the head portion being necessarily less than twice the width of the extending tail portion, the tail portions are conjoined by longitudinal interconnecting gates that are preferably external to the individual tie strip cavities such that they may smoothly taper into the individual tie strip cavities at both ends.

DESCRIPTION OF A

THIRD PREFERRED EMBODIMENT

A contiguous sheet comprising any number of cellular tie strips with laterally projecting wing portions of the form presented by US7704587 (Harsley) is produced substantially as described by the first embodiment above, wherein the cavities overlap only at the tips of the wing portions of the cells in a manner that produces an internal waisted gate portion between them, preferably utilising the configurations shown in figures 17 or 23.

Claims (20)

1. Claims 1. A contiguous sheet of conjoined tie strips wherein individual strips are arranged in alternating vertical orientations with adjacent strips being interconnected by narrow gating regions.
2. 2. A contiguous sheet of conjoined tie strips as claimed in claim 1, wherein the interconnecting gating regions are formed by overlapping adjacent tie strips.
3. 3. A contiguous sheet of conjoined tie strips as claimed in claim 2, wherein the region of overlap is typically about 200 to 500 microns.
4. 4. A contiguous sheet of conjoined tie strips as claimed in claim 1, wherein the interconnecting gating regions are formed by a discrete web portion extending between adjacent tie strips.
5. 5. A contiguous sheet of conjoined tie strips as claimed in claim 4, wherein the interconnecting gate portions are formed to define along them a narrower waist region.
6. 6. A contiguous sheet of conjoined tie strips as claimed in claim 5, wherein the waist region narrows to about 200 to 500 microns.
7. 7. A contiguous sheet of conjoined tie strips as claimed in any preceding claim, wherein adjacent tie strips are alternatingly longitudinally oriented.
8. 8. A contiguous sheet of conjoined tie strips as claimed in any of claims 1 to 7, wherein the SO, individual tie strips are of the conventional single-use design generally formed as a long tail portion extending from an apertured head portion.
9. 9. A contiguous sheet of conjoined tie strips as claimed in any of claims 1 to 7, wherein the individual tie strips are of a repeating cellular design with the interconnecting gates connecting CO the adjacent strips at the tips of their cells' wing portions.
10. C\J 10. A contiguous sheet of conjoined tie strips as claimed in any of claims 1 to 7, wherein the tie strips are of a ladder-style design, being generally formed from a pair of substantially uniform longitudinal side rails that are spanned by a plurality of substantially horizontal rungs.
11. 11. A contiguous sheet of conjoined tie strips as claimed in claim 10, wherein the tie strips are typically about 5-10mm wide with side rails typically around 0.8-2.0mm in width and height.
12. 12. A contiguous sheet of conjoined tie strips as claimed in any preceding claim, wherein the individual tie strips possess a generally tapering tongue portion.
13. 13. A contiguous sheet of conjoined tie strips as claimed in claim 12, wherein the tongue portion terminates through a small gate onto an end runner portion.
14. 14. A contiguous sheet of conjoined tie strips as claimed in any preceding claim, wherein adjacent tie strips may be easily separated along the interconnecting gating regions.
15. 15. A contiguous sheet of conjoined tie strips as claimed in claim 14, wherein the interconnecting gating regions transition smoothly into the tie strips such that no discontinuities or gate vestiges are left when adjacent strips are separated.
16. 16. A contiguous sheet of conjoined tie strips as claimed in any preceding claim, wherein the sheet of contiguous tie strips is manufactured from a polymer material.
17. 17. A contiguous sheet of conjoined tie strips as claimed in claim 16, wherein the sheet of contiguous tie strips is manufactured by injection moulding.
18. 18. A contiguous sheet of conjoined tie strips as claimed in claim 17, wherein the sheet of contiguous ties strips is attached to longitudinal and/or horizontal runner portions.
19. 19. A contiguous sheet of conjoined tie strips as claimed in claim 18, wherein the runner portions incorporate narrow regions of flow such that debris or contaminants can be trapped and filtered out from the molten polymer.
20. 20. A contiguous sheet of conjoined tie strips as claimed in claim 18, wherein the runner portions mould over grab-pins embedded on one or both sides of the mould. C)O CO