DE3038526C2 - Process for the production of shrink articles - Google Patents

Description

The present invention relates to the manufacture of short length shrink articles, in particular Shrink caps, sleeves and the like made of extrudable plastics, in which a Preform injected or extruded, then crosslinked and expanded in this crosslinked state and by cooling this expanded molding, its expanded state is fixed by "freezing" it will.

It is known in this connection (US-PS 32 77 525) that to avoid longitudinal shrinkage when shrinking a hose onto any object in continuous production energy-free during the expansion of the hose is passed through a water or steam bath. That when the hose flares up Part of its "axial length" is converted into a "radial length" which, in turn, occurs when the person is wiping of the finished article also causes longitudinal shrinkage, can by the known measure however, cannot be eliminated.

It is also known (AT-PS 188 510), for Production of heat-shrink tubing from thermoplastic masses, the extruded or injection-molded To heat a hose with a smaller diameter, to expand it by means of Drucklult and to change it Condition to be fixed by subsequent cooling. The disadvantage here, however, is that such shrink tubing made of thermoplastics, such as polyvinyl chloride, not for today's requirements are sufficiently temperature-resistant and also do not have the desired »elastic shape memory«, d. H. no longer assume their original shape in all details during the shrinking process.

Another well-known technique provides a remedy here for the manufacture of heat shrink products sold under the trade name Thermofit, in which a High density polyolefin material used for injection molding molded parts. These parts will be then exposed to high-intensity electron irradiation, so that a networked three-dimensional Mesh work of the molecules is achieved. This results in a mechanically resistant standard part, that is resistant to creep, does not tear and has an "elastic shape memory". Is z. B. a so processed Shrink tubing pulled over the object to be coated, so it shrinks when heated briefly quickly returns to its original shape via the crystallite melting point, in the known case above 135 ° and dimension back, and a strong, resilient coating for is formed Any base polymers, including modified ones, can be used in the process described above depending on the specific requirements of the application. However, this is a prerequisite in every case! the Crosslinking by irradiation before the molded articles are expanded or stretched in a heated state. This requires great care (radiation protection) and a great deal of effort by apparatus Production is made more difficult and thus more expensive.

Whide have therefore already been proposed as basic materials to use polymers for the shrink articles, which after grafting on crosslinking agents, such as organo-SUanes, before or during the shaping of the preform under the action of moisture be networked. It is also essential that the moisture exposure either by means of a special, the production of the preform downstream device is made or already due to the inherent amounts of moisture in the mold that are inherent in the polymers and additives take place or can finally be achieved by simple storage under the influence of the environment. This

Proposal is based on the idea that in contrast to the long-known and z. B. in the Cable technology in use peroxidic crosslinking under the action of heat by the Grafting of reactive low molecular weight compounds, e.g. B. of organosilanes, as a crosslinking aid on the macromolecules of the base materials, which in turn in the course of secondary reactions lead to a polyfunctional chain linkage, form "bundle-like" crosslinking points, whereby several macromolecules are fixed to one another via a cross-linking node. This particular one chemical cross-linking mechanism leads to high binding forces in the molecular range, which when heated Although loosened in the thermoplastic state and thus an expansion z. B. allow the molding, after rewarming and rapid shrinkage, however, they return to their original shape take in.

Shrink articles made from such materials also have an "elastic shape memory", they are therefore for any use possible, z. B. as hoses and caps, for example for pressure-tight and moisture-proof closure of the ends of electrical cables or as sleeves, one or more parts.

Suitable for protecting connection or connection points of electrical cables or tube bundle cables. The properties compared to radiation-crosslinked shrink articles are not b7w. only insignificantly

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changed, but the manufacturing process is significantly simplified.

Regardless of the type of base materials or the networking technology, however, this has so far been the case still difficulties in that, as already explained, e.g. B. in the production of shrink caps, So shrink articles of short length, when expanding the blank, for example when inflating, part of it "Axial length" is converted into "radial length". The ultimate consequence is that such a The cap is shortened by the amount of axial stretching entered during expansion during the shrinking process. One It is therefore difficult to maintain dimensional accuracy.

The invention is therefore based on the object of finding a possibility, in particular shrink caps manufacture that guarantee dimensional accuracy, d. H. no axial shortening in the shrunk state in relation to the not yet shrunk state.

This object is achieved according to the invention in that at least one end of the preform in the injection or extrusion process, an enlarged bag-like diameter compared to its diameter Extension is attached that when expanding after the crosslinking of the preform, the outermost Edge of the bag-like enlarged extension held and then that of the bag-like extension corresponding Area is separated.

This extension on the blank, enlarged like a bag, becomes easy when the blank is expanded turned inside out, thus forming a certain supply of material from which the "radial length" is additionally fed. The fact that the outermost edge of the bag-like enlarged extension is held is a safe one Eversion of the remaining free length ensured without influencing the axial length of the molding. The axial length remains uninvolved in the expansion process in the radial direction, with the result that the Schrunipfvorgang also takes place exclusively in the radial direction, while the axial length of the Cap remains unchanged. A high dimensional accuracy is thus guaranteed.

It is also useful in a further development of the invention if the bag-like enlarged extension in their total length is the difference in diameter between the preform and the shrink article in the expanded State corresponds. Unier overall length? is here the actual length, also taking into account the expansion, and not the axial length alone to understand. This means that sufficient material is available to allow the expansion d, - "> To be able to carry out preforms without interference.

The pure axial length of the de facto widened extension should be 5 to 15, preferably 7 to 12 mm, in order to make the expansion process efficient.

It is also advantageous if the walls of the bag-like enlargement are in the area of the extension Be trained in an S-shape. This makes turning inside out during the expansion process much easier, the expansion z. B. during inflation can run smoothly and continuously.

The invention is based on the shrink cap shown in the figure as an exemplary embodiment explained in more detail.

So far, the procedure for producing a shrink cap was such that a preform, ζ. Β. one sided closed tube of short length expanded by blowing in warm air and holding the open end and brought to bear against an external shape. This is based on the axial length of the shape lost as much material as for the expansion process is required. If this cap is now, if necessary, for. B. shrunk onto a cable or line end, if it returns to its original shape, it also takes its original dimensions again, so that although the radial dimensions are retained, the axial length compared to the original is shortened.

These disadvantages are overcome by the invention if one proceeds in accordance with the figure. In contrast to the prior art described, the preform 1 (state a) has an extension 3 enlarged in the manner of a bag at its open end 2. If, as before, the open end of the preform is held and z. B. warm air introduced for expansion, then only the extension 3 turns inside out during the radial expansion, the material required for the expansion is removed from the material storage provided by the deformation-like extension, so that the state (b) occurs. If, as previously provided, the waste 4 is removed by severing it, the length L _{2 of} the expanded molding still corresponds to the original length L 1. Nothing changes in the constant, dimensionally accurate length if, as state (d) shows, the cap is shrunk by the action of temperature. It still remains L, = L ₂ = Ls, ie the length of the shrunk cap corresponds exactly to the selected length of the preform.

Mixtures used in the practice of the invention for the manufacture of shrink articles are the following:

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50

55

60

example 1

Polyethylene copolymer

with 2 to 7 mol% vinyl acetate
Calcined clay
soot

Vinyl trimethoxysilane
peroxide
Catalyst (dibutyltin dilaurate)

Example 2

Polyethylene copolymer

with 2 to 7 moles-96 of vinyl acetate
non-hygroscopic chalk
soot

Vinyl trimethoxy silane
peroxide
Catalyst (dibutyltin dilaurate)

example 3

100 parts

20 parts 10 parts

2.0 parts 0.05 to 0.1 part

0.05 parts

100 parts

15 parts

5 parts

2.0 parts

0.05 to 0.1 parts

0.05 parts

Polyethylene Homopolymer 100

(Density 0.94 g / cm ', melt index 0.2 to 2.5) aluminum oxide hydrate 2 to 10

Soot 10

Vinyl trimethoxysilane 1.8 to 2.0

Peroxide 0.05 to 0.1

65 catalyst

Parts parts parts parts 0.05 parts

Instead of aluminum oxide hydrate, partially hydrophobized silicas can also be used.

Because of the relatively high proportion of silanes compared to the peroxides that are also provided the mixtures mentioned after the silanes have been grafted onto the base materials, in particular for moisture crosslinking suitable. If you want to network in another way, e.g. B. by radiation crosslinking or by adding suitable peroxides and in sufficient quantities, these are mixtures to change their composition with regard to the crosslinking agents and / or auxiliaries accordingly. For peroxidic crosslinking it would be e.g. B. necessary to increase the peroxide content to about tenfold.

1 sheet of drawings

Claims (3)

Patent claims: 1. Process for the production of shrink articles of short length, in particular shrink caps, -cuffs and the like, made of extensible plastics, in which initially a preform injected or extruded, then crosslinked and expanded in this state as well as by cooling this expanded form, the expanded state of which is fixed by "freezing", thereby characterized in that at least one end of the injection or extrusion process Preform is an extension that is enlarged like a bag compared to the diameter of the preform is attached that when expanding after the crosslinking of the VorformHngs the outer edge of the bag-like enlarged extension is held, and that then that of the bag-like extension corresponding area is separated. 2. The method according to claim i, characterized in that the bag-like enlarged extension in their total length the difference in diameter between the preform and the shrink article in the expanded State is adjusted. 3. The method according to claim 1 or 2, characterized in that the walls of the bag-like Enlargement in the area of the extension can be made S-shaped.