GB2061967A

GB2061967A - Process for the manufacture of shrink articles

Info

Publication number: GB2061967A
Application number: GB8031323A
Authority: GB
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1979-10-08
Filing date: 1980-09-29
Publication date: 1981-05-20
Also published as: EP0031868A3; FI802956A; DK157480C; AU540996B2; AR223545A1; DK157480B; NO802983L; NO158747C; DK425780A; EP0031868A2; NO158747B; AU6305880A; GB2061967B

Description

1 GB 2 061 967 A 1

SPECIFICATION

Process for the manufacture of shrink articles The present invention relates to the manufacture of shrink articles, such as shrink tubes, shrink sleeves, 5 shrink caps and the like from extrudable materials, in which a parison is first injection-moulded and/or extruded, is then crosslinked and in this crosslinked state is distended, and, by cooling this distended shaped article, the distended state of the latter is fixed by freezing-in.

For the manufacture of shrink tubes from thermo-plastic compositions, it is already known (Austrian 10,Patent Specification 188,510) to heat the extruded or injection- moulded tube having a fairly small diameter, 10 to distend it by means of compressed air and to press it against the internal wall of a tunnel which determines the larger diameter. In a cooling zone located behind this, the tube which has been distended in this way is cooled so that it retains the diameter it has assumed. However, as far as the materials are concerned, it is disadvantageous in this process that such shrink tubes made from thermoplastics, for example also from polyvinyl chloride, are not adequately heat-resistant for present-day requirements and, in 15 addition, do not have the desired "elastic memory", that is to say in the course of the shrinking process no longer assume their original form in all its details.

A remedy is provided in this case by a similarly known technique for the manufacture of heat-shrink products marketed underthe tradename Thermafit, in which a polyolefine material of high density is used for the injection-moulding of shaped parts. These parts are then exposed to a high-intensity electron irradiation, 20 so that a crosslinked, three-dimensional network of the molecules is achieved. This gives a mechanically resistant shaped part which is creep-resistant, does not split and has an "elastic memory". If, for example, a shrink tube processed in this way is drawn over the article to be coated, it shrinks back rapidly into its original form and dimensions when briefly heated above the crystallite melting point, in a known case above 1350, and a firm and resistant coating is formed. 25 Any desired base polymers, including modified polymers, can be employed for the process described above, depending on the special requirements relating to their use. A prerequisite in every case is, however, the crosslinking produced by irradiation, before the shaped articles are distended or stretched in a warmed state. This requires great care (protection from radiation) and also a large outlay on apparatus, as a result of which manufacture is made more difficult and thus more expensive.

However, the known manufacturing process described initially also has production disadvantages insofar that materials with a tendency to adhesion, in particular, cannot be employed or can only be employed if the friction between the surface of the tube and the inner surface of the tunnel is reduced by means of parting agents or if other precautions are taken to avoid contact between the tunnel and the tube. However, owing to the decisive, and indeed also desired, shaping action of the tunnel, this is not possible. Even if there is no damage to the tube, in this manufacturing process surface roughnesses at least must certainly be expected andthese, apart from their unsatisfactory appearance, can be points of attack for corrosion phenomena caused by later effects of the environment.

The invention is therefore based on the object of finding a possible means which similarly permits'the manufacture of shrink articles having "elastic memory" together with equivalent or at least comparable properties, without being dependent on the very expensive radiation crosslinking, and of simplifying and so arranging the manufacturing process that shrink articles can be manufactured in a satisfactory quality.

This abject is achieved in accordance with the invention by using, as the base materials for the shrink articles, polymers which, after grafting on crosslinking auxiliaries, such as organo-silanes, are crosslinked under the influence of moisture before or during the shaping.of the parison. In this connection it is also essential that the influence of moisture is effected by means of a special device, placed downstream of the manufacture of the parison, or can already take place as a result of the quantities of moisture adhering to the polymers and additives from the start in the mould or, finally, can also be achieved by simply storing under the influence of the surroundings.

The invention is in fact based on the realisation that, in contrast with the peroxidic crosslinking under the 50 -influence of heat which has been known for a long time and is used, for example, in cable technology, as a result of grafting reactive low-molecular compounds, for example organosilanes, as crosslinking agents onto the macromolecules of the base materials, which in turn, in the course of secondary reactions, leads to -a polyfunctional chain linking, "bundle-like" points of crosslinkage are formed, several macromolecules being fixed to one another simultaneously via a cross-linking node. This particular chemical crosslinking 55 mechanism leads to high bond strengths in the molecular sphere, which, although admittedly loosened in a thermoplastic state when warmed and thus permit a distension, for example, of the shaped article, re-assume their original shape after being warmed again and rapidly shrunk.

Shrink articles manufactured from such materials also have, accordingly, an -elastic memory" and they are therefore suitable for any desired possible uses, for example as tubes and caps, say for closing the ends 60 of electrical cables in a pressure-tight and moisture-resistant manner, or as one-piece or composite sleeves for the protection of junctions or connection points in electrical cables or cables consisting of a bank of tubes.

Their properties do not differ or, if so, not in essentials, from those of shrink articles which have been crosslinked by radiation; but the manufacturing process itself is substantially simplified.

In carrying out the invention it has proved advantageous to effect the crosslinking of the parison during the 65 2 GB 2 061 967 A 2 influence of moisture at elevated temperatures between WC and 20WC, preferably 140' and 1800C. The distension to the state at which freezing is to take place is then carried out immediately afterwards, that is to say "on line", while the parison is still warm. If, as is further envisaged in an extension of the inventive conception, the crosslinking reaction is effected by means of the shaping or injection-moulding process in the manufacture of the parison itself, it is then possible to dispense with a special moisture treatment at elevated temperature. The increase of temperature before distension can be effected independently of the moisture treatment, for example in the case of mixtures capable of absorbing micro-waves by means of UHF warming. The profitability of the manufacturing process can thus be further improved.

The crosslinking itself, as in the case of using moisture to crosslink cables already in use, can be effected in a kind of sauna, that is to say in a steam atmosphere at elevated temperatures. However, a warmed glycerol-water or an oil-water mixture can also be used with advantage for the same purpose in carrying out the invention, which, on the one hand provides the advantage of uniform temperature relationships without a special outlay on control and, on the other hand, ensures that the small quantities of water required for the crosslinking diffuse in more rapidly as a result of the components being more compatible than water with the polymers of the shrink articles.

As base materials it is possible to use all polymers in which an addition reaction with organo-silanes is possible as the result of grafting initiated by free radicals. Polyethylene and also ethylene copolymers with vinyl acetate andlor acrylate comonomers have proved particularly appropriate for the purposes of the invention, on grounds of processability alone. However, it is also possible to use base materials which are based on ethyl ene-propylene rubber on its own or blended with polypropylene.

It has proved particularly advantageous to add carbon black to the base material to achieve UV stability and also to improve the mechanical and rheological properties of the mixture during the manufacture of parisons. Acetylene blacks having non-hygroscopic properties are particularly suitable for this purpose.

These carbon blacks have, in addition, a high conductivity and, in contract with otherwise customary carbon blacks, even small quantities of 1.5 to 30, preferably 3.0 to 15 parts to 100 parts of polymer are sufficient to 25 impartto the shrink article anti-static properties or, if required, conductivity together with good mechanical and rheological properties. The use of non-hygroscopic acetylene blacks is also important because they do not adversely affectthe silane crosslinking. A quantity of 5 to 40, preferably 8 to 20, parts of non-hygroscopic carbon black, relative to 100 parts of polymer, therefore appears the most appropriate for the shrink articles to be manufactured in accordance with the invention.

Besides or instead of the carbon blacks which act as fillers, it is also possible to employ other non-hygroscopie fillers, such as, for example, chalk, kaolin ortalc; these fillers are advantageously used in quantities of 5 to 30, preferably 10 to 20 parts, relative to 100 parts of polymer. As well as cheapening the mixture and thus the end product, hardness, heat stability and c6mpressive strength can also be improved.

-35 In extension of the invention, it is particularly advantageous to add, combined with carbon black and/or 35 otherfillers, substances which, at elevated temperatures and in a defined manner, split off water, which then immediately induces the crosslinking through moisture in the tool. Suitable substances of this type are, in particular, silicic acids and/or silicates or hydrated aluminium oxides which have been rendered partially hydrophobic. The latter split off water at temperatures above 18WC in accordance with the equation 2AROH),-> A1103 + 3H20 IT 10 A hydrated aluminium oxide made by Messrs. Martinswerk, which is known under the tradename "Martinal A-S- or in a silanised form under the name---Martinal-A-SA 01 " has proved particularly suitable for carrying outthe invention. These fillers have an average particle size of approx. 0.4 R and have good compatibility 45 with polyethylene, particularly In the silanised form.

Afurther advantage of the carbon black already mentioned also arises in cases when, as also provided in extension of the invention, the crosslinkinglunder the influence of moisture is effected at room temperature or at a temperature slightly higherthan this and warming of this injection moulding has to take place subsequently forthe purpose of distending the parison. Then the warming can in fact be effected with great advantage via irradiation with micro-waves, since the selected carbon black is excellently suitable for the absorption of micro-waves. The temperature which can be achieved in this case depends on the intensity of the UHFfield; it can be controlled as desired. A temperature between 120'and 17WC, preferably between

130'and 15WC, has proved appropriate forthe purposes of the invention.

It is furthermore essential forthe desired crosslinking by moisture and thus the suitability by grafting on 55 crosslinking agents, that these agents, for example organo-silanes, are available in an adequate quantity, but in a weighed out quantity in relation to the peroxides, in orderto generatethe molecular bond strengths which are necessaryforthe re-shrinking from a distended condition. The molar ratio of peroxides which generate free radical points on the macromolecule to the quantity of silanes added in carrying outthe invention is, therefore, advantageously about 1: 10.

In orderto simplify known manufacturing processes,the invention is carried out in such a waythatthe distension of the hollowextrudate to the enlarged final diameterto give the shrinkable tube is effected by a multiple part-distension with the extrudate being calibrated at the conclusion of each part-distension, the distension being effected by suction pressure acting, between each calibration, on the surface of the extrudate. This measure ensures end products of high quality, firstly so far as external appearance is 65 5_ A 3 GB 2 061 967 A 3 concerned and secondly so far as shrink properties are concerned. The latter is particularlythe case if crosslinkable materials or material which have already been crosslinked at the time of the distension are employed.

In extension of the invention, it has proved advantageous if the distension of the hollow extrudate to the final diameter is effected in a bath of liquid subject to suction pressure. A particularly high surface quality of the shrinkable end product is achieved by this means. This applies above all if, in carrying out the inventive concept, this liquid, for example water, serves at the same time as the lubricant or parting agent forthe calibration process. This simple possible means of supplying lubricant or parting agent in an unassisted, maintenance-free manner is not provided in the devices hitherto disclosed for distending shrinkable products.

The distension process itself should be adapted to the polymer material used, for example polyvinyl chloride, crosslinked or non-crosslinked polyethylene orthe like. In principle it has proved appropriate in this connection to arrange forthe distension to be effected continuously, that is to say in uniform steps of enlargment of diameter. Occasionally, on the other hand, it can also be advantageous if the distension is carried out in stages.

In order to distend a hollow extrudate for the purpose of enlarging the diameter, the parison, present in a crosslinked or non-crosslinked form, should as a r ule initially be subjected to a heat treatment. For this purpose it is possible, for example, for a bath of liquid the temperature of which can be suitably controlled to be placed upstream of the distending device, but the warming can, however, also be effected by means of heat radiation from outside or by means of internal warming, say via a high frequency coil.

Occasionally, however, it can also be advantageous, particularly if a multiple enlargement of the original diameter is intended, to combine the increasing enlargement of the diameter of the extrudate with a continuously increasing warming or through-warming of the extrudate. The quantity of heat should then be appropriately metered in known manner, depending on the progress of the distension.

In the case of a distension corresponding to a multiple of the original diameter of the extrudate (parisbn), it 25 can occasionally also be advantageous if the inner surface is subjected to a so-called supporting pressure while the hollow extrudate is being distended by the suction pressure acting on the external surface. This prevents collapse of the shaped article, particularly if the wall thickness assumes very low values In relation to the total diameter. In this connection, the supporting pressure can, if desired, be applied in the interior of the extrudate, for example in the first stages of the distension, in order to support the enlargement of the 30 diameter from the inside.

A device which has proved extremely advantageous for carrying out the process according to the invention is one in which a so-called calibrator consisting of several perforated plates arranged successively in the direction of travel, having drill holes with a diameter which increases continuously or in stages, viewed in the direction of travel, serves to distend the hollow extrudate after it has been warmed or whilst it is being 35 warmed. Such calibrators, which are already known for the manufacture of plastic tubes having constant external dimensions, ensure continuous quidings over extremely small areas of contact, which enables surfaces of high quality to be achieved. Because, in accordance with a further inventive concept, the perforated discs are all arranged in one or are combined in stacks, in each case in separate containers carrying liquid which, if appropriate, can be temperature-controlled and tightly closed, satisfactory guiding 40 with imperceptibly little friction is always ensured during the flow through the perforated discs. The height of the liquid level, which can, of course, be adjusted, is appropriately so chosen that the perforated discs are completely covered, for example with water. Above this water level a suction pressure of up to 8 m head of water is adjusted, for example by means of an appropriate arrangement of suction pumps, the suction pressure ensuring that in each case between two successive perforated discs the wall of the extrudate is sucked, that is to say the ribbon is distended. The suction pressure is also exerted between the following perforated discs which have drill hole diameters enlarged in comparison with the first drill holes, so that a further distension, compared with the first distension, takes place and so on.

Because of the even weaker structure of the heat-treated extrudate when it enters the stack of perforated discs, it has also proved appropriate for the distance between the perforated discs which have an increasing 50 diameter of drill holes to increase similarly in the direction of travel. This eliminates the danger thatthe extrudate may become impressed into the perforated plates which continually limit it, while it is passing through in a still soft condition, and may tear or may even lead to the tearing off of the extrudate which is continuously passing through.

The properties of the products manufactured by the process according to the invention can be varied in 55 accordance with a further inventive concept, if the boundary walls of these shaped articles consistwholly or partially of foamed material. In addition to a considerable saving in material and thus also weight,there is a further advantage in the heat insulation and, compared with a conventional foam insulation, in the high mechanical stability under load achieved by means of the crosslinking. If the foamed part of the shrink shaped article consists of an olefine polymer or olefine copolymer which can be crosslinked under the influence of moisture and on the base molecules of which silanes or silane compounds have been grafted, a shrink shaped article having crosslinked regions is produced, with a degree of crosslinking between 30 and 80%. It thus conforms abundantly to the requirements which have been set.

In this connection the invention proceeds from the consideration that, apart from the base polymer selected, the mechanical stability under load of foamed insulation materials also depends above all on the 65 4 GB 2 061 967 A 4 number, size and distribution of the pores formed-in the foaming process. The smaller these pores are and the more uniform their distribution thro. ughout the cross-section of insulation, the better is the stability under load, or the more viscous the melt is at the time of the foaming process, the higher will be the degrees of foaming achieved at a uniform pore structure. This consideration has its basis in physical chemistry, since pore size and structure depend decisively on the two parameters; vapour pressure of the blowing agent and surface tension of the melt. The higher the viscosity of the melt, however, the greater is the surface tension. The procedure in industry hitherto has, therefore, been to reduce the temperature in order to increase the melt viscosity immediately before the foaming process. This alternative is, however, very expensive, since it requires a special process technology using long extruders.

In order to manufacture a wholly or partially foamed shrink shaped part the procedure appropriately 10 followed in carrying out the invention is first to injection-mould or extrude a parison, the boundary walls of which are wholly or partially caused to foam and are crosslinked. The shaped article is then distended in this foamed and crosslinked state and, by cooling this distended shaped article, the distended state of the latter is fixed by freezing-in. The crosslinking can in this case be effected in any desired manner, for example also by subjecting the shaped parts to high-energy radiation before, during or after the foaming process. However, it is also possible, with particular advantage, to follow a procedure in which the silane is first grafted onto the olefine polymer, then the grafted material is granulated and blowing agents are added to it and finally the material thus prepared is subjected to foam extrusion. In the course thereof the melt temperature can be adjusted in an optimum manner to the decomposition temperature of the blowing agent. As a result of this and as a result of the relatively high viscosity of the melt during the foaming process, it is possible to achieve 20 a pore structure which has fine cells and is uniform over the whole cross- section.

So-called chemical blowing agents can be used to foam the mixture which can be crosslinked in the presence of moisture. If, however, the grafting and foaming processes are carried out in the same processing stage, care must be taken in t he selection of these blowing agents that by-products formed in the course of the decomposition of the blowing agent do not have an adverse effect on the_grafting process. In order to 25 exclude this with certainty, it is possible in extension of the invention, to use physical blowing agents instead of chemical blowing agents, for example lower fluorinated andlor chlorinated hydrocarbons and also nitrogen. These blowing agents also lead to high degrees of foaming, to a uniform pore structure with fine cells and to a good mechanical stability under load of the crosslinked product, without the grafting process being affected adversely.

It can occasionally also be advantageous if, in extension of the invention, the blowing agents used for foaming are simultaneously used as carriers for at least part of the moisture required for crosslinking. Thus moist gases, for example also water vapour, can be introduced into the mi> cture,-and these gases lead to crosslinking within a short time. The time of storage in water can thus be considerably reduced.

The blowing agents - whether moisture carriers or not - can be added to the mixture in a customary manner. However, it is particularly simple if the blowing agent is mixed by tumbling in a pulverulent state.

Occasionally, however, it can also be advantageous to blend the grafted olefine polymer or olefine copolymer with a polymer batch containing blowing agent.

If, as already explained, the crosslinking of the foamed material is to be carried out under the influence of moisture, it has further proved advantageous to initiate the crosslinking process by using blowing agents 4Q which split off water. This procedure can be followed, for example in all cases in which the quantity of water automatically taken up by the insulating material during its passage through the cooling water is not sufficient for the crosslinking process.

In extension of the invention, a further possible means of introducing additional quantities of water is to add non-hygroscopic metal oxides, such as tin or zinc oxides, to the olefine polymers or copolymers. In conjunction with the so-called siloxane crosslinking, these materials lead to degrees of crosslinking of about 30% as early as immediately aftert the conclusion of the shaping operation. This crosslinking effect, obtained, for example, by the addition of zinc oxide, already causes a marked increase in the melt viscosity, which is added to the viscosity already achieved as a result of grafting. This produces a particularly viscous melt which leads to a very advantageous pore structure in the foam. In this connection, it can occasionally be advantageous if the metal oxides are not added until after the grafting process. In this way difficulties in the extrusion, caused say by incipient crosslinking during the grafting process, are prevented from the outset.

However, in addition to the improvements already mentioned, the zinc oxide employed also contributes towards further advantages Thus it is known that zinc oxide has an effect on the kinetics of the decomposition process of the customary blowing agents, that is to say that the decomposition temperatures 55 are in some cases considerably reduced in the presence of such oxides. It is thus possible to effect the decomposition of the blowing agent.at relatively low temperatures, which also has an advantageous effect on the foam structure. Further advantages arise in regard to the electrical properties of the material, since residues of undecomposed blowing agents remaining in the material are now virtually negligible.

The grafting and the foaming of the materials used can appropriately be effected in a single operation. This 60 leads to an increase in operating safety and a reduction in the susceptibility of the process to trouble. However, the same possibiliy also arises even if, as also provided in extension of the invention, layers consisting of foamed material and nonfoamed material alternate with one another in the build-up of the shrink articles.

The invention will be illustrated in greater detail with the aid of the process stages illustrated in Figures 1 to 65 GB 2 061 967 A 5 7 and the mixing examples listed below.

Example 1

A mixture of the following composition:

5 Polyethylene homopolymer (density 0.94 g/cm3; melt index 0.2 - 2.5) 100 parts Vinyltrimethoxysilane 1.0 - 1;5 parts Dicurnyl peroxide 0.03 - 0.05 part 10 Catalyst (Naftovin SN/L) 0.05 part Carbon black (acetylene black Y) 15 parts is either premixed beforehand or, as can be seen from Figure 1, is put in the form of individual components into the feed hopper 1 of the extruder 2. It is appropriate if the base polymer and the filler carbon black or 15 chalk or both - are previously dispersed homogeneously in a preliminary mixing process. In extruder 2 homogenisation is effected by melting and, in a subsequent zone of the same extruder or in the injection-moulding machine, the silane is grafted onto the polyethylene molecules at temperatures above 1400C, preferably between 1600 and 20WC. If the shrink articles manufactured are shrink caps which can be provided with outlet spouts or not, the grafted material is transferred into the shaping die 3 via the sprue 4. 20 Here, for example, or previously, foam initiators, say in the form of moist gas, can be added to the material.

In the event that shrinkable tubes or sleeves are to be manufactured, it is advantageous to follow a procedure in which continuous tubes are continuously extruded, in the manner in which elongate material is manufactured continuously, using an extruder having a tube extrusion die and vacuum calibration placed downstream thereof, and these continuous tubes are then subsequently inflated to the required dimensions 25 of the tubes or sleeves after crosslinking has been effected by means of moisture.

Independently of the type, that is to say the external shape, of the shrink articles, it is advantageous if the extrusion or injection-moulding temperature achieved is used to effect accelerated crosslinking in a moist atmosphere.

This is effected by means of the waterbath 5, indicated diagram matical ly, which contains an oil-water emulsion or a water-glycerol mixture in order, on the one hand, to ensure in a simple manner that the temperature is constant and, on the other hand, to accelerate the diffusion of water into the shaped article. After the crosslinking process, the shaped article is distended while it is still in a warm state, for example the cap 6 is distended via the mandrel 7, by means of which the cap 6 is inflated from the inside, and the shaped article is frozen-in in this distended state by cooling. Crosslinking at elevated temperature is effected in a close sequence of time with the distension, in order toutilise the heat content.

The invention is, of course, not limited to the sequence of processes described. Thus, for the purpose of crosslinking and/or distension, the shaped articles can be warmed in a separate sequence, for example as shown in Figure 2, by means of UHF irradiation 8, that is to say warming by micro-waves, subsequently to the completion of injection moulding and ejection, that is to say removal of the shaped article from the injection mould 3. Crosslinking can, however, also take place partially or completely as early as the cavity of the injection mould as a result of the moisture adhering to the polymers or the additives, and can subsequently be merely completed by means of UHF warming.

It is also possible, however, to add, at an elevated temperature. small quantities of additives which split off H20, such as certain hydrated aluminium oxides or silicates which have been rendered partially hydrophobic. The amount of H20 liberated by these additives at the temperature of injection moulding is in itself sufficient for crosslinking. The shaped article then leaves the injection moulding machine in a crosslinked state.

If caps are not being manufactured, but if, for example, tubes are being extruded continuously. it is appropriate to follow a procedure in which, as shown diagrammatically in Figure 3, the tube produced in the 50 -die 10 of the extruder 11 first passes though a vacuum calibrator 12 and is then introduced, for example, into a glycerol-water bath 13, the necessary crosslinking being effected there at temperatures between about 1300 and 1800C, preferably 160' and 180'C. In the course thereof the tube is appropriately kept in shape in a manner which is in itself known by means of an internal supporting pressure. Cooling is effected in the cooling device 14 before the shaped articles, tubes or sleeves are removed by means of a removal or cutting 55 device, not shown, and, as indicated, for example in Figure 1 and 2, are distended by warming, before cooling is effected in order to freeze-in the distended state.

Figure 4 shows diagrammatically the particular suitability of the use of materials which can be crosslinked by moisture compared with materials which can be crosslinked by peroxides, in which materials the molar ratio of the quantity of silane to the amount of peroxide is as a rule greater than 10: 1. The temperature curve 60 (a) shows the relationships in the case of crosslinking (a) shows the relationships in the case of crosslinking by moisture, while curve (b) shows crosslinking by peroxides as a function of time. In the case of crosslinking by moisture, the polyethylene mixture to be grafted is brought to the temperature required for grafting both by transfer of heat by conduction from the heated cylinder wall of the injection moulding machine and by the dissipation energy of the screw (friction) -there is no upper temperature limit -and passes at this 6 GB 2 061967 A 6 temperature into the mould, where the cooling process starts immediately.

In the case of crosslinking by peroxides, the composition must not exceed a temperature of 13WC before shaping; it passes at this temperature into the mould and must be brought to crosslinking temperature (20WC) there and this temperature must be maintained for a period before the mould is cooled forthe 5 purpose of ejection.

The outlay of energy in order to avoid, by means of cooling, temperatures higherthan 1300C in the shaping process, is higher than that required to reach 200'C in the case of crosslinking by moisture, because in the latter case the energy of the screw (dissipation) can-be utilised.

The following are further mixtures which can be used advantageously for the manufacture of shrink 1Q articles in carrying out the invention:

Example 11 - 10 Polyethylene copolymer containing 2 - 7 mol % of vinyl acetate 100 parts 15 Calcined clay (Hartkaolin M 100) 10 parts Carbon black 10 parts Viny[trimethoxysilane 2.0 parts Peroxide 0.05-0.1 part Catalyst (dibutyl-tin dilaurate 20 Naftovin SN/L 0.05 part Example 111

Polyethylene copolymer containing 25 2-7 mol % of vinyl acetate 100 parts Non-hygroscopic chalk (for example Millicarb/Omya 15 parts Carbon black 5 parts Vi nyitrimethoxysi lane 2.0 parts 30 Peroxide 0.05-0.1 part Catalyst (dibutyli-tin dilaurate (Naftovin SN/0) 0.05 part Examplell/ -35 Polyethylene homopolymer (density 0.94 g/cm3; melt index 0.2 - 2.5) 100 parts Hydrated aluminium oxide 40 (for example Martinai A-s11 01) 2A 0 parts Carbon black 10 parts Vinyltrimethoxysiiane 1.8-2.0 parts Peroxide 0.05-0.1 part Catalyst 0.05 part _45 Silicic acids which have been rendered partially hydrophobic can also be employed instead of hydrated aluminium oxide.

The mixture according to Example 1 is particularly suitableforthe manufacture of shrinktubes, and also caps and sleeves, while the mixture according. to Example W can be employed with advantage mainly for the 50 manufacture of caps which, after shaping, are already completely crosslinked.

If, as provided in the invention, the shaped articles consist of a foamed material, Examples 1 to IV of mixtures, mentioned above, are then altered as follows:.

Example I-F

Polyethylene homopolymer (density 0.94 g1CM3; melt index 0.2-2.5) 100 parts Azodicarbonamide as a chemical blowing agent 0.5-1.5 parts Vinyltrimethoxysilane 1.0-1.5 parts Dicumy] peroxide 0.03-0.05 part Catalyst (Naftovin SN/L) 0.5 part Carbon black (Acetylene black Y) 2.5 parts 7 Example II-F

GB 2 061 967 A 7 Polyethylene copolymer containing 2 - 7 mol % of vinyl acetate 100 parts Azodicarbonamide (blowing agent) 0.5 part 5 Carbon black (Ketjenblack EC) 3.0 parts Vinyltrimethoxysilane 2.0 parts Peroxide 0.05-0.1 part Catalyst (dibutyl-tin dilaurate (Naftovin SN/0) 0.05 part 10 Example III-F

Polyethylene copolymer containing 2 - 7 mol % of ethyl acrylate 100 parts 15 Azodicarbonamide (blowing agent) 0.8 part Carbon black (Ketjenblack EC) 5 parts Vinyltrimethoxysilane 2.0 parts Peroxide 0.05-0.1 part Catalyst (dibutyl-tin dilaurate 20 (Naftovin SN/0) 0.05 part Example IV-F

Polyethylene homopolymer 25 (density 0.94 g/CM3; melt index 0.2 - 2.5 100 parts Diphenol-oxide-4,4-disulpho hydrazide (blowing agent) 0.8-11.2 parts Hydrated aluminium oxide (for example 30 Martinal A-s/101) 2-10 parts Carbon black (acetylene black Noir Y 200) 10 parts Vinyltrimethoxysilane 1.8-2.0 parts Peroxide 0.05-0.1 part 35 Catalyst 0.05 part The following are further examples of mixtures for shaped articles having a foamed wall:

Example V

Ethylene-propylene rubber (for example Buna AP 407 K) 100 parts Propylene (for example Hostalen PPH 1050) 80 parts 45 Carbon black (Ketjenblack EC) 5 parts Vinyltrimethoxysi lane 1.5 parts Peroxide (Perkadox 14) 0.1 part Catalyst (dibutyl-tin dilaurate) 0.05 part Azodicarbonamide (blowing agent) 0.5-1.5 parts 50 Example V1

Polyethylene homopolymer (melt index: 1.5 - 2.0) 100 parts 55 Carbon black (Ketjenblack EC) 5 parts Physical blowing agents (for example trichlorofluoromethane or dichlorofluoromethane 0.5-2.5 parts Vinyltrimethoxysilane 1.5 parts 60 Peroxide (Luperox 270) 0.25 part Catalyst (clibutyl-tin dilaurate) 0.05 part Silicic acids which have been rendered partially hydrophobic can also be employed instead of hydrated aluminium oxide.

8 GB 2 061 967 A 8 The mixture according to Example I-F is particularly suitable forthe manufacture of shrinktubes, and also caps and sleeves, while the mixture according to Examples N-F can be employed with advantage chiefly for the manufacture of caps which are already in a completely crosslinked staie after shaping.

For the economic manufacture of shrinktubes in particular, the production of continuous extrudates having shrink properties is essential. A process for this is shown in detail and in full in Figures 5 and 7. A hollow extrudate 21, crosslinked, for example, by moisture and drawn from a stock is therefore fed firstto a warming device 22, as shown in Figure 5. This device can, for example, consist of a trough containing hot water, but it is also possible to use a radiator-heated oven. The tube thus pretreated then passes next into the vacuum calibrator 23, which is, for example, also filled with water at a controlled temperature. The water trough 24 placed upstream, which can, of course, also be replaced by spray cans or other suitable means, -10 serves the purpose of applying waterto the surface of the extrudate 21, as a lubricant or slip agent when the extrudate is introduced into the calibrator 23. The calibrator 23 contains, as an essential constituent, the stack 25 of perforated discs 26 which are arranged in tandem and are provided with drill holes for the extrudate passing through and which have a distance between them which increases in the direction of travel. The calibrator is filled with water in the sector 27; the perforated discs are thus covered. In the sector 28 there is, 15 above the water level, a vacuum of up to 8 m head of water. This vacuum acts between the perforated discs on the external wall of the extrudate, so that, if appropriate in combination with a supporting pressure within the extrudate itself, a distension is effected stage by stage in a continuous passage between the perforated discs, while the perforated disc which in each case succeeds a distension ensures calibration. The distended pipe or the tube 29 is frozen-in in its distended state after leaving the calibrator, say by being introduced into 20 the cooling basin 30. The product is then tumbled or is immediately cut into lengths readyfor sale.

Figure 6 shows the entry into the calibrator 23 again in an enlarged scale compared with that of Figure 5.

Retaining bolts 33, for example three bolts distributed uniformly over the circumference, are fastened on the base plate 31, which has a central drill hole 32 for the entry of the extrudate 21, and these bolts in turn serve as a holding device for the perforated discs 26, as supporting elements for the extrudate. These perforated 25 discs 26 are arranged close to one another at the inlet, because the extrudate 21 is even more readily deformed, and are later arranged at greater distances from one another as th e distension proceeds. The diameter of the drill holes of the discs also increases in accordance with the increase in diameter caused by progressive distension. The water, which completely surrounds the perforated discs, on the one hand supports the distension process as a result of its controlled temperature and, on the other hand, 30 continuously ensures, as a slip agent, that the distending extrudate passes through the perforated discs with continuous protection, that is to say does not jam.

In divergence from Figure 5, Figure 7 shows an illustrative embodiment in which warming and calibration are effected virtually simultaneously in the container 34 which is filled with a liquid, for example also a glycerol-water mixture, the temperature of which can be controlled. In this embodiment the calibrating element 36 which contains perforated discs 35 is located in the rear third of this container. The cooling of the extrudate 37, in order to freeze-in its distended state, is then effected, as already mentioned, in a cooling basin or cooling channel 38.

Claims

1. Process for the manufacture of shrink articles, such as shrink tubes, sleeves, caps and the like - from extrudable materials, in which a parison is first injection-moulded or extruded, is then crosslinked and, in this crosslinked state, is distended and, by cooling this distended shaped article, the distended state of the latter is fixed by freezing-in, characterised in that the base materials used for the shrink articles are polymers 45 which, after grafting crosslinking agents, such as organo-silanes, onto them, are crosslinked under the influence of moisture before or during the shaping of the parlson.

2. Process according to Claim 1, characterised in that the crossf inking of the parison is effected while the latter is treated with moisture at elevated temperatures between 80' and 20WC, preferably 140'to 18WC, and the distension to the state which is to be frozen-in is effected immediately afterwards while the parison is still 50 warm.

3. Process according to Claim 2, characterised in that a glycerol-water mixture is used for warming accompanied by simultaneous crosslinking.

4. Process according to Claim 2, characterised in that a polyalcohol miscible with water, such as ethylene glycol and homologues, is used for warming accompanied by simultaneous crosslinking.

5. Process according to Claim 1 or one of the subsequent claims, characterised in that the base materials used for the shrink articles are polyethylene or ethylene copolymers.

6. Process according to one or more of Claims 1 to4, characterised in that materials based on ethylene-propylene rubber on its own or as a component for blending with polyolefines, say polypropylene, are used for the shrink articles.

7. Process according to Claim 1 or one of the subsequent claims, characterised in'that the base materials contain fillers which split off definite small quantities of water at elevated temperatures.

8. Process according to Claim 1 or one of the subsequent claims, characterised in that a non-hygroscopic carbon black is added to the base materials ada filler ir'a quantify of 5 to 40, preferably 8 to 20, parts, relative to 100 parts of polymer.

9 GB 2 061967 A 9 9. Process according to Claim 1 or one of the subsequent claims, characterised in that inorganic fillers, such as chalk, kaolin, talc or the like, are added to the base materials in a quantity of 5 to 30 parts, preferably to 20 parts, to 100 parts of polymer.

10. Process according to Claim 1 or one of the subsequent claims, characterised in that crosslinking is effected under the influence of moisture at room temperature and the parison is subsequently warmed for 5 the purpose of distension.

11. Process according to Claim 10, characterised in that warming is effected via micro-wave irradiation.

12. Process according to Claim 11, characterised in that warming is effected at 12Tto 150T, preferably 13Tto 150T.

13. Process according to Claim 1 or one of the subsequent claims, characterised in that the molar ratio of 10 silanes or compounds thereof to peroxides is about 10: 1.

14. Process according to Claim 2, characterised in that the temperatures for crosslinking are produced by the shaping or injection-moulding process itself.

15. Process according to Claim 1 or one of the subsequent claims, characterised in that, after distension and cooling, the shrink articles are coated internally with a hot-melt adhesive, for example a hot-melt 15 adhesive based on polyamides or polyesters.

16. Process forthe manufacture of shrinktubes from extruclable materials in accordance with Claim 1 or one of the subsequent claims, in which a hollow extrudate of any desired length is first injection-moulded or extruded, is then crossRnked and, in this crosslinked state or, in the case of non-crosslinkable materials, in a non-crosslinked form, is distended by being brought into contact with surrounding shaping elements, and, 20 by cooling this distended extrudate, the distended state of the latter is fixed by freezing-in, characterised in that the distension to the enlarged final diameter of the extrudate is effected by means of a multiple part-distension, with calibration of the extrudate following each part- distension, the distension being effected by means of a suction pressure acting on the surface of the extrudate between each calibration.

17. Process according to Claim 16, characterised in that the distension of the hollow extrudate to the final 25 diameter is effected in a bath of liquid which is under suction pressure.

18. Process according to Claim 17, characterised in that the liquid serves at the same time as a lubricant or slip agent for the calibration process.

19. Process according to one or more of Claims 16 to 18, characerised in that the inner surface is subjected to a so-called supporting pressure during the distension of the hollow extrudate by means of the 30 suction pressure acting on its outer surface.

20. Device for carrying out the process according to one or more of Claims 16 to 19, characterised in that a so-called calibrator consisting of several perforated discs arranged in tandem in the direction of travel, having drill holes with a diameter which, viewed in the direction of travel, increases continuously or in stages, is used to distend the hollow extrudate after it has been warmed or while it is being warmed.

21. Device according to Claim 20, characterised in that the perforated discs, altogether as one unit or collected into stacks, are in each case located in separate containers which carry liquid and which can optionally be at a controlled temperature and can be tightly closed.

22. Shrink articles manufactured by the process according to one or more of Claims 1 to 21, which consist of a polymer material which has been crosslinked by the influence of moisture and onto the 40 macromolecules of which organo-silanes have been grafted.

23. Shrink articles according to Claim 22, characterised in that the boundary walls of these shaped articles consist wholly or partially of foamed material.

24. Shrink articles according to Claim 23, in which the walls consist partially of foamed material, characterised in that layers of foamed material and non-foamed material alternate with one another.

25. Process according to Claim 1, substantially as described with reference to any of Figures 1 to 3 and 5 to 7 of the accompanying drawings and employing a polymer composition substantially asset forth in any of the foregoing Examples 1 to V1 and IF to 1V17.

26. Shrink articles manufactured by a process according to Claim 25.

Printed for Her Majesty's Stationery Office. by Croydon Printing Company Limited, Croydon, Surrey, 1981.

Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.