CA1169218A

CA1169218A - Method of making shrink articles

Info

Publication number: CA1169218A
Application number: CA000397384A
Authority: CA
Inventors: Hermann U. Voigt
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1981-03-02
Filing date: 1982-03-02
Publication date: 1984-06-19
Also published as: BE892335A; JPS57144726A; IT1142939B; GB2093760A; GB2093760B; DE3107907C2; IT8149762A0; FR2500840A1; FR2500840B1; DE3107907A1

Abstract

METHOD OF MAKING SHRINK ARTICLES

ABSTRACT OF THE DISCLOSURE

A method is proposed in which basically known cross-linking procedures for making a heat-shrink article are employ the particular feature relates to imparting radially and longitudinally elastic properties upon the article by employ-ment of suitable comonomers or elastifying blend components.

Description

` ~ 2~ 1 7l55 1 ACKGR011ND OF THE INVE:NTION

3 ¦ The present invention relates to shrink-fit objec-ts 4 ¦ ha~ing a short length, such as sleeves,,caps or the like.
5 l 6 ¦ Austrian patent 188.510 discloses a method of makiny 7 ¦ shrink hoses according to which a small-diameter hose is 8 ¦ extruded from a thermoplastic material, heated, pneumatically ¦ expanded, and cooled in the expanded state for stabllizing 10 ¦ the wide-diameter configuration. These hoses are disadvan-11 taged by an insufficient temperature resistance, particularly 12 when one uses polyvinyl chloride. Also, the elastic shape ~13 "memory" is insufficiently developed; in other words, upon 14 heating, the hose will not return to exactly its original I5 shape.

~17 The problems above have been clealt with to some extent 18 by a technique involving injection molding of a high-density 19 polyolefin; the resulting product has been traded under the description THERMOFIT*. The shapes produced here are subjected ~21 to a high-energy electron beam in order to produce a three-22 dimensional cross-linking network of the molecules. The shape 23 produced in this manner is stabile as to its contour, has a 24 high creep strength, does not tear, and has an adequate elastic shape memory. Upon slipping such a hose onto another object 26 and heating it briefly above the crystallite melting point 31 * Trade Mark.

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(e.g., above 135C), the hose shrinks rapidly down to its original shape and dimensions;and the object is now encased in a strong, resistive cover. This particular method can be practiced with many kinds of base polymers, even when modiEied, depending upon the specific purpose and its intended use. However, a precondition oE this method is cross-linking by way of irradiating the material prior to expanding the heated object to the widened, large-dimension state. This procedure requires great care, particularly regarding protection from radiation and a corresponding expensive equipment.
It has been suggested by me and another (Canadian Application No. 361,652, issued as Canadian Patent No.
1,039,666) to use polymers for the making of shrink articles which are graftad with organic silane, and prior to or during shaping the intermediate product is cross-linked by exposure - to moisture. This exposing procedure is carried out by means of particular equipment operating downstream from the maklng of the intermediate product. Alternatively, moisture is provided for in some fashion within the product itself so that cross-linking takes place during storage after shaping, augmented by environmental moisture.
This latter approach is based upon the recognition that silane cross-linking is fundamentally diferent from ~ 9 2 ~ 8 ~ -7155 1 ¦ peroxide cross-linking. Cross-linking of and by organo-2 ¦ silane is accompanied b~ secondary reactions, leading to

3 ¦ polyfunctlonal chain linking, resulting in hundle-like or

4 ¦ bunched cross-linking nodes wherein particularly several 51 macromolecules are fixed (linked) to each other by such a 6 ¦ node. This particular chemical linking and bonding mechanism 7 ¦ leads to large, local bonding forces. Upon heating and 8 ¦ establishing a thermoplastic state, these forces are reduced 9 ¦ to some extent, permitting the expansion of the material and 10 ¦ object as well as the retention of the expanded state after 11 ¦ cooling; but after reheating, the forces are sufficient 12 to cause the object to contract again to its original state.

14 It can thus be seen that objects made in this manner have an adequate elastic shape memory and are readily usable, 1~ e.g., in the form of hoses, sleeves, caps, end covers, for 17 sealing cable ends in a pressure and moisture-proof manner, 18 for protecting joints, terminal points of regular electric 19 cables or tube bundle cables, whereby one or several such shrink parts are used as the respective case requires. The 21 properties of the shrink articles so made are not or only 22 insignificantly different from articles made by cross-linking 23 through irradiation. The manufacturing, however, is consider-2~ ably simplified.

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,-7155 1¦ Independent from the type of base polymer or cross-21 linging techniques, it may be desirable in cases to have 3¦ the article exhibit rubber-eleastical properties. This may 41 be the case, for instance, for hoses or sleeves. Shrink 51 articles made as afore-described have adequate flexibility, 6¦ i.e., they can be bent and otherwise deformed. However, 71 these properties are attributable to the fact that the expanded 8¦ article has relatively thin walls. If such an article is, ¦ however, required to permit easy deformation in longitudinal 10¦ direction as well as radially, the aforementioned methods 11¦ of making do not lead ~o articles permitting these types of 12 ¦ deformation. For instance, cross-linked polyethylene exhibits 13 ¦ only a very small reversible extension and reaches readily 14 ¦ the tear strength limit.

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18 ¦ It is an object of the pxesent invention to provide 19 ¦ new and improved method of making shrink articles, permitting 20 ¦ longitudinal and radial, reversibly elastic extension to, 21 ¦ thereby, permit generally expansion of the range of geometry 22 ¦ of the type of articles made for purposes of shrink-fitting.
23 l 24 ¦ It is a particular object of the present invention to 25 ¦ improve a method of making shrink articles by means of injec-26 ¦ tion-molding or extrusion, wherein a cross-linking step 27 l ~ ,. ' l¦ concurs within parts or follows the shaping which, in turn, 21 is followed by expansion and cooling in the expanded state~

41 In accordance with the preferred embodiment of the 51 present invention, it is suggested to improve the method I as per the particular ohject by using a copolymer of ethylene 71 wherein the copolymer component (comonomer) amounts to 20~ to 40%
81 preferably 25% to 35~ (by weight), and the polymerisate is 9¦ to have rubber-elastic properties, or by using a polyolefin lO¦ or polyolefin blend which, in turn is blended with an elasti-l~¦ fying component so as to obtain rubber-elastic properties of 12 ¦ the final product. The resulting products and articles 13 ¦ (e.g., shrink hoses or sleeves) are elastic in radial and l4 ¦ axial direction, even after expan~ion and "freezing" of the 15 ¦ expanded state. Moreover, after heat-shrinking, they exert 16 ¦ rubber-elastic, inward-directed forces upon the objects onto 17 ¦ which they have been shrunk.
18 l 19 ¦ The high comonomer content, being, for example, 25%
20 ¦ to 35%, in terms of mol weight reduces the degree of crystal-21 ¦ inity of the copolymer as well as the melting temperature, 22 1 and that establishes, to a n increased extent, the rubber-23 ¦ elastic properties of the articles. It is an important 24 ¦ feature of the invention that composition (relative propor-25 ¦ tions) and/or selection of the copolymers permits, to some 26 ¦ extent, an adjustment of the shrink temperature. For instance, 31~

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~ ~ ~ 9 2 1~ -7155 l a comonomer on the basis of viny]acetate, ethylacrylate 2 or butylacrylate (the base monomer being ethylene) permits 3 shrinking at a temperature of not higher than 100C, 4 e.g. 75C.

6 Rubber-elastic shrin]c articles can also be made by 7 using an olefin polymer or a blend of polyolefins with a 8 melting range of not exceeding 120C. If -the polyolefin is 9 a low-density polyethylene, (density below 0.94 g/cm), the shrink temperature may be below 120C, e.g., 110C.
ll Alternatively, the basic polyolefin may be a high-density 12 polyethylene, i.e., the density exceeds 0.94 g/cm3. The 13 shrink temperature will ~hen be above 120C, such as 125 14 to 135C. For this case, the melting r~n~e is respectively above 120C.

A still higher shrink temperature can be provided for, 18 without abandoning rubber elasticity if isotactic poly-19 propylene is blended with an elastifier, such as a high molecular polyisobutylene with a molecular weight of 100,000 21 to 150,000.

23 The polyolefin or polyolefin blend (component A) 24 should be blended with an elastifier as outlined above (component B) at a ratio of component A to component B
26 from ~ O ~ ~C~ to ~ ~ ~ by weight.

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1 An article made on that basis begins to shrink 2 only at temperatures of from 150C to 1~0C. Another elastl-3 fying component is, for example, ethylene-propylene copolymer 4 (i.e., blended, eOg., with polye~hylene,,or isotactic poly-propylene). Such a copolymer may be ethylene-propylene-rubber 6 (EPR), or a rubber traded under the designation LAVAPR~N*
7 or others.

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1~69218 7155 l The materials mentioned above may be supplemented 2 by fillers such as carbon black (to provide for some electric 3 conductivity); or silicates or chalks in order to modify 4 the mechanical properties of the product. Amounts and fineness of the particle sizes are additional parameters 6 for such a modiEication.
8 The cross-linking can be provided for either by way 9 of radiation or silane-grafting and subsequent exposure to moisture. Peroxide cross-llnking can also be used. The ll choice is mentioned here to indicate that the invention can 12 be practiced on the basis of already existing equipment ~3 provided for that purpose. Also, the requirements for the 14 articles may lend themselves to a preference of one cross-linking method over the respective other ones. In either case, l~ the articles themselves are shaped originally in accordance l7 with usual techniques such as injection molding, extrusion, 18 blowing, etc., and cross-linking follows usually thereafter~
19 The articles are expanded subsequently, and cooled so as to "freeze" the expanded state until reheated for shrinking.
21 The residue crystallinity of the material is particularly 22 important for a retention of the shape that has been forced 23 upon such an article by the expansion.

~s was outlined above, the method as per the invention 26 permits the making of articles which shrink at different ~j 1169218 l ;-7155 l ¦ temperatures. This conceptual feature can be extended in 21 furtherance of the invention to provide shrink articles 31 in which different portions shrink at different temperatures.
4¦ For example, a rubber-elastic shrink article, such as a sleeve, 51 can be made whose one side (or half of one side) shrinks, 6 ¦ e.g., at 70C, while the other side ~(or half) remains 71 stable if the expanded dimension until, e.g., a temperature 8 ¦ of 150C to 160C has been reached.

10¦ Generally speaking, shrink articles can be constructed ll ¦ whose different functional elements shrink at different 12 ¦ temperatures. One can make such a component part by making 13 ¦ the individual components separately; and prior to cross-14 ¦ linking, the co~ponents are welded together using well 15 ¦ known synthetic or polymer welding methods. The composite 16 ¦ article is then cross-linked, expanded, and cooled.

18 ¦ EXAMPLES
, i9 The following examples show materials for making shrink 21 articles.- The compositions differ primarily by the shrink 22 temperature.

2~ _9_ ll_ ~(3~f~ 7155 1 Example I (Shrink Temperature 110C to 120C) _rts by l~1eight 2 Polyethylene homopolymer 3 (density not exceeding 0.94 y/cm3, 4 melt index 0.2 to 2.5) , 10 - 20 Ethylene-propylene-rubber 80 - 90 6 Vinyltrimethoxisilane 1.0 - 1.5 7 Dicumyl peroxide 0.03 - 0-05 8 Dibutyl-tin-dilaurate (NAFTOVIN SN/L*) 0.05 9 Carbon black (acetylene black Y) 15 11 Example II (Shrink Temperature 70C to 85C) Parts by Weight 12 Ethylene vinylacetate copolymer 13 (25 to 35 Mol. % vinylacetate) 100 14 Calcinated clay (hard Kaolin* M 100) 10 Carbon black 10 16 Vinyltrimethoxisilane 2 17 Peroxide 0.05 - 0.1 18 Dibutyl-tin-dilaurate (NAFTOVIN SN/L*) 0.05 The base components of the polymer blends (Example I) 21 or the copolymer as per Example II are grafted with silane 22 and will cross-link upon exposure to moisture. The dibutyl 23 tin dilaurate is the cross-linking catalyst and the peroxide 24 is the graft initiator. Alternatively, the silane-grafting components and the catalyst can be replaced by increasing 26 the peroxide to approximately the tenfold value of the 2~ -10-2g * Trade Mark.

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, . -` 1`1~9~8 -il55 1 stated amounts. In other words, the perioxi:de will not 2 function as yraft initiator but as cross-linking agent.
3 Still alternatively, cross-linking may be obtained by 4 irradiation, i.e., without peroxide or silane.

6 Example III (Shrink Temperature 130C to 135C~ Parts by ~eight 7 High-density polyethylene 8 (density above 0.94 g/cm3) 70 9 Polyisobutylene (Mol. weight 100,000 to 150,~00) 30 Nonhygroscopic acetylene carbon black (Noir Y) 70 11 Aging protection (e.g., VULKANOX HS*) 0.4 lZ
13 Example IV (Shrink Temperature 155C to 165C) Parts by Weight 14 Polypropylene 65 Isotactic or unsaturated etylene-propylene-16 rubber 35 17 Nonhygroscopic carbon black 30 ~18 Aging protection (VULKANOX HS*) 0.25 ~19 , These examples are specifically stated for demonstrat-21 ing the use of cross-linking by exposure to radiation.
22 Alternatively, appropriate addiny of silane, grafting, and 23 cross-linking aids (catalysts) permits the type of cross-24 linkiny by exposure to moisture. Still alternatively, one may use here peroxide cross-linking.

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~ ~921 ~ -7155 1 The examples above include particular elastifying 2 components; one may use o-ther elastomers instead. In some 3 cases, flame resistance is required and here one,may wish 4 to use chlorinated polyethylene of the ~type traded under the desiynation BAYER CM*ancl/or CPE*(by Hoechst and Dow 6 Chemical). A specific example here is the following, being 7 provided for peroxide cross-linking.
~3 9 Example V (Shrink Tempera-ture 115C) Parts by Weight _ _ High-densi~y homopoly ethylene 11 (density not below 0.94 g/cm3 50 12 Chlorinated polyethylene (BAYER CM*) 50 13 Dicumylperoxide ~ 1.5 Age protection (FLECTOL H*), possibly in the presence of filler such as 16 carbon black or calcinated clays) 0.5 ', 1~ If the heat shrink article is to be flame-retarden~
lg in the absence of hologenes, one may use exclusively aluminum oxide-hydrate in lieu of carbon black or bright fillers.
21 An example for such a composition is the following.

23 Example IV (Shrink Temperature 130C to 135C) Parts by Weight 24 High-density polyethylene (density above 0.94 g/cm3) 70 2~ Polyisobutylene (Mol. weight 100,000 to 150,000) 30 27 7~1 (O~1)3 10 28 Age protection (e.g., VULKANOX I~S*) 0.4 31 * Trade Mark ¦ 1~6g~a .-7155 1 ¦ The invention is not llmited to the embodiments 2 ¦ described above; but all changes and modifications thereof, 3 ¦ not constituting departures from the spirit and scope of :

6 the inv ntion, are intended to be included.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of making shrink articles by extruding or molding an intermediate product, causing the product to cross-link, expanding the cross-linked product and cooling it in an expanded state, the improvement of imparting upon the product rubber-elastic properties by using, as a base material, a copolymerisate of ethylene with a comonomer component of 20% to 40% by weight, the comonomer component, as a polymer, having rubber-elastic properties.

2. In a method of making shrink articles by extruding or molding an intermediate product, causing the product to cross-link, expanding the cross-linked product and cooling it in an expanded state, the improvement of imparting upon the product rubber-elastic properties by using as a base material a polyolefine or polyolefine blend, blended with an effective amount of an elastifier.

3. A method as in Claim 1, the comonomer component being 25% to 35% by weight.

4. A method as in Claim 1 or 3, the comonomer being selected on the basis of vinylacetate, ethyl-acrylate or butylacrylate.

5. A method as in Claim 2, the polyolefine or polyolefine blend having a melting temperature of not exceeding 120°C.

6. A method as in Claim 5, the polyolefine being a low-density polyethylene (not exceeding 0.94 g/cm3).

7. A method as in Claim 2, the polyolefine or polyolefine having a melting temperature of not below 120°C.

8. A method as in Claim 7, the polyolefine being a high-density polyethylene (not below 0.94 g/cm3).

9. A method as in Claim 7, the polyolefine being isotactic polypropylene.

10. A method as in Claim 7, the polyolefin being a partially crystallized copolymer of polypropylene with a melting range of above 150°C.

11. A method as in claim 7 or 8, the elastifier being a high-mole-cular polyisobutylene (Mol. weight 100,000 to 150,000).

12. A method as in claim 9 or 10, the elastifier being a high-mole-cular polyisobutylene (Mol. weight 100,000 to 150,000).

13. A method as in claim 7, the elastifier component being an ethylene-propylene copolymer.

14. A method as in claim 13, the copolymer being saturated or unsaturated ethylene-propylene-rubber.

15. A method as in claim 7, the elastifier being a chlorinated polyethylene to render the product flame-retardant.

16. A method as in claim 1 or 2, including adding aluminum oxid-hydrate as a filler.

17. A method as in claim 1 or 29 including the step of using silane cross-linking.

18. A method as in claim 1 or 2, including the step of making different portions of an article by different compositions having differ-ent shrinking temperatures and combining these portions to obtain an article in which different portions shrink at different temperatures.

19. In a method of making shrink articles by extruding or molding an intermediate product, causing the product to cross-link, expanding the cross-linked product and coding it in the expanded state, the improvement of imparting to the product rubber elastic properties by either using as a base material a copolymerisate of ethylene with a comonomer component of 20% to 40% by weight, the comonomer component, as a polymer, having rubber elastic properties or by using as a base material a polyolefin or a polyolefin blend, blended with an effective amount of an elastifier.