Heat-shrinkable article

Details Heat-shrinkable article Heat-shrinkable article

1996-03-27

1998-06-09

Bell, James J.

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

174120R, 174121A, 442 60, 442 85, H01B 700

Patent

active

057630321

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an article having improved heat-shrink characteristics, in particular to one combining improved heat-shrink characteristics and excellent mechanical properties. Heat-shrink articles find particular use in environmental protections of substrates such as cables and pipes, particularly splices in telecommunications cables. For example, a cable splice case is expected to have a life-time comparable to that of the cables it joins, typically 25 years, under unfavourable environmental conditions. Products for use as cable splice cases must pass rigorous temperature and pressure cycling tests if their purchaser is to have confidence that they will perform satisfactorily over these long life times. Designing a splice case is therefore a difficult matter, and careful choice of materials must be made.
Heat-shrinkable materials have been widely used for environmental protection because they can be produced over-sized, easily installed, and then shrunk into tight, sealing engagement with the substrate to be protected. They are frequently internally coated with a heat-activatable adhesive such that the heating required for installation causes both shrinkage of the article and activation of the adhesive. In this way, an excellent environmental seal can be produced.
Recently, heat-shrinkable composite materials have begun to replace monolithic heat-shrinkable sleeves in particular in the telecommunications cable accessories market. Such composite materials have the advantage of superior mechanical properties, in particular split-resistance. They are manufactured by incorporating a heat-shrinkable fabric within a matrix material; shrinkable fibres of the fabric drive shrinkage of the product and provide split-resistance perpendicular to the shrink direction, glass fibres of the fabric provide additional strength, and the matrix material renders the product impervious.
Whilst such composite products are ideal for many applications, there are occasions when the temperature and quantity of heat required for installation are too great. Problems may therefore arise where an open-flame torch, which can supply vast quantities of heat, is considered undesirable, and/or where the cable or other substrate around which the heat shrinkable article is to be shrunk is easily damaged by heat. For example, optical fibre cables are generally rather small and do not carry a large mass of highly heat-conducting copper. They are therefore easily damaged by heat. It is desirable therefore that a technique be found for joining or sealing them that avoids high temperature and prolonged heating.
It is generally recognised that of the few broad types of materials used for the formation of heat-shrinkable articles, LLDPE thin film has advantages where low shrink temperatures are required. Unfortunately, that information is not very helpful since a vast number of materials of widely differing properties are known as LLDPE, and what applies to thin film for temporary packaging cannot be assumed to apply to the generally thick-walled materials required for long-term environmental protection of, for example, outside telecommunications cable plant.
Nonetheless, a brief review of LLDPE may be made. The table below shows just some of the LLDPEs available.


TABLE 1 ______________________________________ Supplier Trade Name Grade Density ______________________________________ DSM Teamex Cast Film 0.902 DSM Stamylex 08-026F Cast Film 0.91 DSM Stamylex 08-076F Cast Film 0.911 DSM Stamylex 09-046F Cast Film 0.915 DSM Stamylex 09-016F Blown Film 0.914 DSM Stamylex 1016F Blown Film 0.919 DSM Stamylex 1026F Blown Film 0.919 DSM Stamylex 1046F Cast film 0.919 DSM Stamylex 1066F Cast film 0.919 DSM Stamylex 09-258 Injection 0.917 DSM Stamylex 2258 Injection 0.927 DSM Stamylex 3026F Cast film 0.932 DSM Stamylex 4026F Cast film 0.936 DSM Stamylex 4046F Cast film 0.935 Quantum Petrothene GA501 Film 0.918 Quantum Petrothene GA502 Film 0.918 Quantum Petrothene GA601 Film 0.918

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patent: 4554202 (1985-11-01), Kamei et al.
patent: 4590124 (1986-05-01), Schoenberg
patent: 4617241 (1986-10-01), Mueller
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patent: 5079051 (1992-01-01), Garland et al.
patent: 5110686 (1992-05-01), Taka et al.
patent: 5266392 (1993-11-01), Land et al.

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