WO1999056271A1

WO1999056271A1 - Roll of heat-shrinkable tubing

Info

Publication number: WO1999056271A1
Application number: PCT/GB1999/001110
Authority: WO
Inventors: Dennis John Knell; Colin William Diss
Original assignee: Raychem Limited
Priority date: 1998-04-23
Filing date: 1999-04-09
Publication date: 1999-11-04
Also published as: GB9808611D0; AU3433899A

Abstract

A roll of heat shrinkable thin-walled flexible tubing of extruded plastics material, substantially the whole length of the tubing on the roll having a substantially oval open shape whose height is less than its width with air or other fluid deliberately enclosed therein at a pressure and roll winding tension selected to suit the tubing circumference and wall thickness and the flexibility of the tubing material so that gripping pressure applied to opposite ends of the tubing width at intervals along the tubing as it is fed from the roll in use reliably decreases the width and increases the height to open the tubing for placement onto a wire or other elongate object.

Description

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It is understood that "substantially oval" means a generally oval or egg-like open shape, not any exact geometrical shape, although true elliptical shapes are included. The substantially oval shape may include shapes having relatively sharp corners where the radius of curvature approaches zero, as well as the generally preferred rounded corners of an ellipse or similar curved outline where the radius of curvature approaches a minimum but is clearly not zero. The degree of ovality may be understood in terms of the stated height to width ratio, which for a true ellipse is the ratio of the lengths of the shortest and longest chordal lines passing through the centre. For a circle, the ratio is 1 and for a completely flattened tube the ratio is infinity, both of which are excluded from the claimed range of "squashed circle" shapes, where ratio is at least 1: 1.5 and not more than 1:9 or 1:7.5. For oval shapes other than perfect ellipses, for example egg-shaped tubes, the height may be taken as the length of the longest chordal line normal to the longest (width) axis of the shape, which height line will not necessarily be at the mid-point of the longest axis.

For preferred sizes and materials of marker sleeve tubing, the internal fluid (preferably air) is preferably injected into the leading end of the tubing during winding onto a suitable reel or other carrier at a pressure within the range from 5.5 to 12.2 kPa (0.8 to 1.75 psi), preferably 6.9 to 10.4 kPa (1.0 to 1.5 psi). This may be done by any convenient means, for example by attaching the leading end of the tubing to an air- injection nozzle incorporated in the wind-up shaft of the winding equipment. Care must be taken during the initial few turns of the roll to ensure that the tubing does not become pinched, which would stop the air from progressing along the increasing length of wound tubing on the roll, but after that the partial inflation of the tubing tends to be self- maintaining. The finished roll is easily distinguishable by its feel from one into which no such fluid pressure has been introduced, since the air-injected roll feels "squashy" when pressed by a human finger, while the other feels distinctly hard and solid owing to flattening of the tubing.

The suitably-selected internal fluid pressure and winding tension resist crushing of the oval tubing shape, which has been found advantageously well suited to automated processes for printing marker sleeves and subsequently installing them on wires or other substrates. The invention accordingly provides a method of applying heat-shrinkable 3

marker sleeves to elongate objects using equipment (preferably automatic) capable of repeatedly performing the steps (in any order) of printing indicia on the tubing, severing printed lengths from the tubing to form marker sleeves, and gripping the tubing at opposite ends of the said oval shape width with sufficient force to decrease the width and increase the height (preferably by at least 10-20% , followed by placing of successively gripped marker sleeves onto the objects, and preferably subsequently heat shrinking the sleeves onto the objects. The oval shape can thus be gripped across its width with sufficient pressure to transport it through the processing equipment, thus widening the end opening for reliable placement onto a wire or other elongate object, while retaining sufficient flatness for adequate TT printing earlier in the process. Adequate TT printing has been found difficult to achieve on more rounded or circular shaped tubing, whereas flatter or fully-flattened tubing does not open reliably enough for automatic wire insertion.

The height and width, tubing wall thickness, and tubing material flexibility may be varied over considerable ranges within the balance of properties required to achieve and maintain the desired substantially oval shape at convenient internal fluid pressures. Suitably balanced properties for any particular size of tubing may readily be determined by trial and error. When the tubing is provided in the often-preferred form of a roll, preferably surrounding a central carrier, the length of the tubing in the roll being at least 25 metres, preferably at least 50 metres, for example for feeding to automatic processing equipment, it is preferred that the aforementioned internal fluid pressure be provided and suitably low winding tension be used for limiting crushing pressures within the roll so that substantially the whole length of the tubing maintains the said oval shape at least on removal from roll.

A preferred size of tubing for the present invention has a notional inside diameter (when constrained into circular shape) within the range from 5 to 10 millimetres, preferably 6.5 to 7.5 millimetres; a wall thickness, when fully heat shrunk, within the range from 0.5 to 0.9 millimetres, preferably 0.6 to 0.8 millimetres; an internal diameter, when fully heat shrunk, within the range from 1.7 to 2.1 millimetres, preferably 1.8 to 2.0 millimetres; and an expansion ratio (notional inside diameter : fully shrunk diameter) of at least 2: 1, preferably at least 3: 1 , more preferably within the range from 3.5: 1 to 4.5: 1. 4

The heat-shrinkable tubing for this invention may be made using any of the well- known materials and processes for such tubing, preferred tubings including those wherein the plastics material comprises at least 40% (preferably 45 to 55%) by weight of ethylene/methyl acrylate copolymer, as the majority or sole plastics polymer. For example, a preferred compound comprises 50% by weight ethylene/methylacrylate copolymer, 30% flame retardants, and the usual amounts of cross-linking agents, antioxidants and pigments, and may be crosslinked by ionising radiation and then hot expanded in the usual way.

The invention includes the tubing in the form of printed marker sleeves, either before or after application to an elongate object. Also included is the use of the tubing in a method of applying heat-shrinkable marker sleeves to elongate objects using equipment capable of repeatedly performing the steps (in any order) of printing indicia on tubing according to any preceding claim, severing printed lengths from the tubing to form marker sleeves, and gripping the tubing at opposite ends of the said oval shape width with sufficient force to flex the tubing wall and so decrease the width and increase the height, followed by placement of successively gripped marker sleeves onto the elongate objects, and preferably subsequently heat shrinking the sleeves. The equipment itself for performing such a method may be suitably devised by those skilled in such technology. One preferred kind of equipment may be similar to that described in DE-A-4413577 (Helmet Pfletschinger), the disclosure of which is incorporated herein by reference.

The invention is further illustrated by way of example with reference to typical shapes and degrees of open-ness shown in the accompanying schematic drawings, wherein:

Figure 1 shows in outline a substantially elliptical tube shape 10 of height (h) to width (w) ratio 1:4.5, with a typical life-size shape 12 of that h:w ratio beside it;

Figure 2 shows a less regular shape 20 of h:w ratio 1:4.5;

Figure 3 shows a substantially elliptical shape 30 of h:w ratio 1 :3, with corresponding typical life-size shape 32;

Figure 4 similarly shows a shape 40 of h:w ratio 1:2, with life-size shape 42;

Figure 5 similarly shows a shape 50 of h:w ratio 1 :9; Figure 6 shows a shape 60 of generally elliptical form with h:w ratio 1 :7.5 but with flattened ends 62, the thickness of the tubing wall being indicated in order better to illustrate the end flattening; and

Figure 7 shows a printed marker sleeve 70 made from tubing according to the invention gripped across its width by schematically-indicated jaws 72 of the aforementioned automatic handling equipment (not shown), the gripping force of the jaws having increased the opening of the tubing from its original shape 74 of h:w ratio of about 1:5.5. In this opened state, the marker sleeve can readily receive or be placed onto the end of a wire.

In preferred methods of making the rolls of tubing according to the invention, a nip roll is provided to pinch the tubing as it approaches the winding equipment, thus retaining the injected fluid pressure near the wind-up. The pinching action of the nip roll advantageously helps to set the tubing into the desired oval shape.

1. A roll of heat shrinkable thin-walled flexible tubing of extruded plastics material, substantially the whole length of the mbing on the roll having a substantially oval open shape whose height is less than its width with air or other fluid deliberately enclosed therein at a pressure and roll winding tension selected to suit the mbing circumference and wall thickness and the flexibility of the tubing material so that gripping pressure applied to opposite ends of the tubing width at intervals along the tubing as it is fed from the roll in use reliably decreases the width and increases the height to open the tubing for placement onto a wire or other elongate object.

2. A roll of tubing according to claim 1, wherein lengths of the mbing when removed from any part of the roll will have in end view a substantially oval open shape of internal height to width ratio within the range from 1:1.5 to 1:7.5 (or even 1:9), preferably 1:1.75 to 1:4.5, more preferably 1:2 to 1:3.

3. A roll of mbing according to claim 1 or 2, wherein the height, width, wall thickness, and flexibility are preferably also selected so that a length of the tubing resting freely on a horizontal surface substantially maintains the said oval shape.

4. A roll of mbing according to any preceding claim surrounding a central carrier, the length of the mbing in the roll being at least 25 metres, preferably at least 50 metres.

5. A roll of mbing according to any preceding claim, the mbing having a notional inside diameter (when constrained into circular shape) within the range from 5 to 10 millimetres, preferably 6.5 to 7.5 millimetres.

6. A roll of mbing according to any preceding claim, the mbing having a wall thickness, when fully heat shrunk, within the range from 0.5 to 0.9 millimetres, preferably 0.6 to 0.8 millimetres.

Claims

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7. A roll of mbing according to any preceding claim, the mbing having an internal diameter, when fully heat shrunken, within the range from 1.8 to 2.6 millimetres, preferably 2.0 to 2.4 millimetres.

8. A roll of mbing according to any preceding claim, the mbing having an expansion ratio of at least 2: 1, preferably at least 3:1, more preferably within the range from 3.5:1 to 4.5: 1.

9. A roll of mbing according to any preceding claim, wherein the plastics material comprises at least 40% (preferably 45 to 55%) by weight of ethylene/methyl acrylate copolymer, as the majority or sole plastics polymer.

10. A roll of mbing according to any preceding claim, which mbing has been crosslinked, preferably by exposure to ionising radiation.

11. Portions of a roll of mbing according to any preceding claim in the form of printed marker sleeves, either before or after application to a wire or other elongate object.

12. A method of applying heat-shrinkable marker sleeves to elongate substrates using equipment capable of repeatedly performing the steps (in any order) of printing indicia on a roll of tubing according to any preceding claim, severing printed lengths from the mbing to form marker sleeves, and gripping the tubing at opposite ends of the said oval shape width with sufficient force to decrease the width and increase the height, followed by placement of successively gripped marker sleeves onto the substrates, and preferably subsequently heat shrinking the sleeves.

13. A method of producing a roll of mbing according to any of claims 1 to 9, comprising injecting the said air or other fluid into the mbing during winding thereof onto the roll and preferably closing the ends of the mbing on completion of the roll. 1/1

Fig.1 w

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Fig.6. 60

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