CA1237263A - Heat recoverable polymeric articles - Google Patents

Abstract

HEAT RECOVERABLE POLYMERIC ARTICLES
Ramsey/Rowlands/Schott/Siden ABSTRACT
Heat recoverable articles prepared from semi-crystalline polymers having a glass transition temperatures, Tg, above about 25°C exhibit unexpectedly high recovery stress under certain conditions. A preferred method of preparing such a heat recoverable article comprises heating the article above its glass transition temperature, Tg, deforming the article while it is above Tg but below the crystalline melting temperature, Tm, and cooling the article to a temperature below Tg while maintaining it in the deformed state.

Description

~L237~63

-2- 27065-103 This invention relates to dimensionally heat-recoverable polymeric articles having high recovery stress and to the preparation of such articles.

s It is well known to make dimensionally heat-recoverabie articles from various polymeric raterials.

A dimensionally heat recoverable article is an article the dimensional configuration of which may be made substan-tially to change when subjected to heat treatment. Usually these articles recover towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating~ adopts a new configuration, even if it lS has not been previously deformed.

In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example, U.S.
Patent 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst 2s hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage.

Typically, such articles are prepared from polymers that are capable of being cross-linked, For example, poly-ethylene, polybutene-1, poly 4-methyl pentene and fluorinated polyolefins for example, ethylene-trifluorochloroethylene ~7263 MP 09 OB

copolymers, ethylenetetrafluoroethylene copolymers, and vinylidene fluoride polymers, especially polyvinylidene fluoride, and blends thereuf, for example, the fluorinated olefin blends as described and claimed in British Patent No.
1,120,131, and the like.

In the production of heat recoverable articles, from cross-linkable polymers, the polymer material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article compris~s shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed stste of the article is heat-unstable, whereafter application of heat will cause the article to assume its original heat-stable shape.

Heat recoverable articles frùm cross-linkable crystal-line polymers can be prepared by deforming the uncrosslinked polymer below the crystalline melting point and without cross-linking, cooling the deformed article. Subsequent heating of .he article to the deformation temperature causes the article to recover toward the undeformed configuration but it does so with a relatively low recovery stress. As a result such recoverable articles are generally unsuitable for use as mechanical devices, such as couplings, where a ~ 237263 high recovery stress is required. Further, the use of such devices requires not only a high recovery stress but that the high stress be maintained after the device has been recoYered against the substrate and subsequently cooled to ambient tempersture. Heat recoverable devices disclosed in ths art do not meet this requirement.

Summary of the Invention It has been unexpectedly discovered that dimensionally heat-recoverable articles of semi-crystalline polymers having a glass transition temperature above about 25C
exhibit exceptionally high recovery stress under certain conditions. Further, after the article has been recovered lS agains~ a substrate, the recovery stress is substantially retained and in some instances is increased. Such an effect is totally unexpected and not predicted from the known behavior of dimensionally recoverable polymeric articles taught and used prior to this invention.
One aspect of this invention comprise a dimensionally heat-recoverable article of a semi-crystalline polymer having a glass transition temperature, Tg, aboYe about 25~C, said article having a recovery stress of above about 1100 X
(E-1)0~5 pounds per square inch, wherein E is the unresolved recovery ratio when heated above Tg.

Another aspect of this invention comprises a method of producing a dimensionally heat-recoverable article of a semi-crystalline polymer having a glass transition temperature, Tg, above 25~C by:

~23726~
MP09OB .-a) heating a shaped article of a semi-crystalline polymer to a temperature above the Tg of the polymer;

s b) deforming the article; and c) cooling the article while maintaining the article in the deformed state, thereby producing an article which, when heated to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer, recovers with a recovery stress above about 1100 X (E-1)0-5 pounds per square inch, wherein E
is the unresolved recovery ratio snd substantially retains such stress on cooling of the article to a lS temperature below Tg.

A further aspect of this invention comprises a method of producing a heat-shrinkable article of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25C which comprises:

a) stretching a film or fiber of said polymer at a temperature above the Tg of said polymer;

b) cooling the stre'ched film or fiber to a temperature below the Tg of the polymer; and c) forming a shaped article from the stretched film or fiber, thereby forming an article which when heated to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer, shrinks with a stress of above about 11ûO X (E-1)0-5 pounds per square inch, wherein E is the unresolved recovery ratio.

~237263 MP0908 Yet another aspect of this invention comprises a method of recovering a dimensionally heat-recoverable device against a substrate which comprises:

a) selecting a heat-recoverable article of a semi- ::
crystalline polymer having a glass transition temperature, Tg, above about 25~C;

b) positioning a tubular heat-recoverable article lo adjacent such that on recovery the substrate restrains the article to a recovery of less than sbout 25~, based on the dimension of the deformed article;

c) heating said article to a temperature between Tg and the crystslline melting temperature, Tm, of the poiymer thereby causing the article to recover about said substrate exerting a recovery stress of at least about 11ûû X (E-1)0-5 pounds per square inch, wherein E is the unresolved recovery ratio on said substrate; and d) cooling said article.

2S Another aspect o~ this invention comprises a method of joining cylindrical articles which comprises:

a) positioning said cylindrical substrates in end-to-end abutting relationship;
b) positioning a heat-shrinkable tubular article such that it surrounds the ends of said cylindrical substrates, said article being of a semi-crystalline polymer having a glass transition temperature, Tg, 3S above about 25C; and ~ 23'7263 c) hesting said article to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer to cause it to shrink and exert a stress of at least 1100 X (E-1)0-5 pounds per square inch, wherein E is the unresolved recovery ratio on the cylindrical substrates thereby joining the substrates together; and d) cooling the recovery article and joined substrates.

Brief Description of the Drawing These and other features, aspects and advantages of the present invention will become better understood with reference to the appended claims, the following description and accompanying drawings, where:

FIG. 1 is a graph of the peak values of unresolved recovery stress divided by the expansion stress vs. the 2~ difference between the recovery and expansion temperatures for 4 materials useful for preparing articles of the invention and for one material (lowest curve) incapable of providing articles of the present invention;

FIG. 2 is a graph of the unresolved recovery stress after 1 minute at the recovery te~perature divided by the expansion stress vs. the difference between the recovery and expansion temperatures for 4 materials useful for preparing articles of the invention and for one material (lowest curve) incapable of providing articles of the present .
invention;

9 %37;2~;3 FIG. 3 is a graph of the unresolved recovery stress vs. the unresolved recovery ratio for 4 materials useful for preparing articles of the present invention and for 2 materials (lowest 2 curves) incapable of providing articles s of the present invention;

FIG. 4 is a graph of the unresolved recovery stress vs. percentage recovery for 4 materials useful for preparing articles of the present invention and for 1 material (PE) incapable of providing articles of the present invention;

FIG. 5 shows 2 tubes or rods of similar dimensions joined together with a high recovery stress tube according to the teachings of the present invention;
1~
FIG. 6 shows overlapping concentric tubular members joined with a high recovery stress tube according to the teachings of the present invention; and FIG. 7 shows a braid joined to a rod with a high recovery stress ring according to the teachings of the present invention.

Detailed Descri~tion of the Invention The heat-recoverable articles of this invention are prepared using a semi-crystalline polymer having a glass transition temperature, Tg, above about 25C. Preferably the polymer used to make the article ha.~ a Tg above about 1û0C and most preferably above about 150C. The polymer used should be a polymer having crystalline melting tempera-ture of above about 150C, preferably above about 180C and ~23~Z63 _9_ most preferably above about 290C. Such polymers include for example, polyamides, such as polycaprolactam, nylon 6, and poly(11-iminoundecanoyl), nylon 11, crystalline polyesters, su.h as crystalline polyethylene terephthalate, polybutylene terephthalate and the like, other crystalline or crystallizable aromatic polymers, such as polyphenylene sulfide and polyaryl ethers, in particular polyaryl ether ketones. Blends of these polymers with each other and/or with other polymers can also be utilized.

Semi-crystalline polyaryl ether ketones are particularly preferred polymers for the preparstion of heat recoverable articles of this invention. Such polymers typically have a glass transition temperature in the range of between about 140C to about 25ûC and a crystalline melting temperature between about 270C and 450C.

Polyaryl ether ketones comprise repeat units of the formula:

-O-E-O-El _ wherein E and E1 are aromatic radicals at least one of which is a polynuclear aromatic moiety having two aromatic nuclei joined by a ketone group, the other of E and E1 is an aromatic moiety containing at least one aromatic ring.
The polymer can contain other polynuclear moieties joined by other functional grcups such as sulfone, sulfide, alkylene, etc.

~23'72~i3 Poly(aryl ether ketones) suitable for use in this invention may be better defined as having repeat units of the formula:
-CO-Ar-CO-Ar'-wherein Ar and Ar' are aromatic moieties at least one of which contains a diaryl ether linkase forming part of the polymer backbone and wherein both Ar and Ar' are covalently linked to the carbonyl qroups through aromatic carbon atoms.

Preferably, Ar and Ar' are inde?endently selected from substituted and unsubstituted phenylene and substituted and unsubstituted polynuclear aromatic moieties. The term polynuclear aromatic moieites is used to mean aromatic moieties containing at least two aromatic rings. The rings can be fused, joined by a direct bond or by a linking group.
Such linking groups include for example, carbonyl, ether sulfone, sulfide, amide, imide, azo, alkylene, perfluoro-alkylene and the like. As mentioned above, at least one of Ar and Ar' contains a diaryl ether linkage.

- 9a ~;~3726;3 The phenylene and polynuclear aroma~ic moieties can contain substituents on the aromatic rings. These substi-tuents should not inhibit or otherwise interfere with the polymerization reaction to any significant extent. Such substituents include, for example, phenyl, haloqen, nitro, cyano, alkyl, 2-alkynyl and the like.

- 9b -~2372~63 Poly(aryl ether ketones) having the following repeat units (the simplest repeat ur.it bein~ designated for a given polymer) are preferred:

@ o ~ c o o <~o ~ o @ c ~, c ~ C --@ O --~3 ~ C ~ ~ ~ C--_ @ - D - ~ D - @ -C -@ o @ c ~> c ~o ~ o ~ c ~ o @

gc -Poly(aryl ether ketones) can be prepared by knowr methods of qynthesis. Preferred poly(aryl ether ~etones) can be prepared by Friedel-Crafts polymerization of a monomer system comprising:

I) (i) phosgene or an aromatic diacid dihalide tosether with (ii) a polynuclear aromatic comonomGr comprising:

(a) H-Ar-O-Ar-H

(b) H-(Ar-O)n-Ar-H
wherein n is 2 or 3 (c) H-Ar-O-Ar-(CO-Ar-O-Ar)m~~
wherein m is 1, 2 or 3 or II) an acid halide o. the formula:
H-Arn--O--~ (Arn-CO)p-(Arn-O)q(ARn-CO)r]k-Arn-CO-Z
wherein Z is halogen, k is 0, 1 or 2, p is 1 or 2, q is 0, 1 or 2 and r is 0, 1 or 2;

or III) an acid halide of the formula:
H-(Ar~-O)n-Ar~-Y
wherein n is 2 or 3 and Y is CO-Z or CO-Ar~-CO-Z
where Z is halogen;

- 9d -~L23~72~3 whereir, ea-h Ar" is independently selec~ed from substi-tuted or unsubstituted phenylene, and s~bstituted and unsubstitu~ed polynuclear aromatic moieties free of ketone carbonyl or ether oxygen groups, in the presence of a reaction medium comprising:

A) A Lewis acid in an amount of one equivalent per equivalent of carbonyl groups present, plus one equivalent per equivalent of Lewis base, plus an amount effective to act as a catalys~ for the polymerization;

B) a Lewis base in an amount from O to about 4 equi~alents per equivalent of acid halide gro~ps present in the monomer system;

C) a non-protic diluent in an amount from O to about 93% by weigh~, based on the weigh~ of the total reaction mixture.

- 9e -~ he aromatic diacid dihalide employed is preferabl~ a dichloride or dibro~.ide. Illustratlve diacid dihalides w~lich can be used include, for example ~CC~cnu ~C~ eD~CI c~-~C

C,C~ CC~ 1' 0 ~9 ~1' e~c C 1I 11 ~hGr~in 11 i~l 0~

9f _ Illustrated polynuclear aromatic comonomers which can be used with such diacid halides are:

(a) H-Arn-O-Arn-H, which includes, for example:

~ -D~ ~ ~ _ (b) H-(Ar~-O)n-Arn-H, which incluAe, for exa~.,?le:
~ O ~ O ~

ond ~0 ~ ~ o_~

(c) H-Arn-O-Ar" (CO-Arn-O-Arn)m-H, which includes, for example:

~ O -~ C ~- ~~ O ~ ~

and (d) H-(Ar~-O)n-Ar~-CO-Ar~-(O-Ar~)m-H which includes, for example:

~~0~~~0 ~ 3_C~~ O-~

gg _ ~37263 Mor,omer systems II and III comprise an acid halide. (,,~G
term acid halide is used herein to refer to a mor,oacid mGr.c~allde.
In monomer system II, the acid halide is of the fcr~ula:

H-Ar~-O-[tAr~-CO)p-(Arr-O)q-(Ar~-CO)r~k-Ar"-CO-Z

Such monomers include for example, whe e k = O

cC~ o ~ CC1 , ~ ~3~3 0 ~D~) nnd ~hsr~ k ~ 1 o ~/c\~

~~0~ ~ C ~ CC1 - 9h -123~7263 In monomer system III, the acid halide is of t~e formula H-(Arn-O)n-Arn-Y

Examples of such acid halides include o ~nd ~c~

I' is to be understood that combi~ations of monomers can be employed. For example, one or more diacid dihalides can be used with one or more polynuclear aromatic comonomers as long as the correct stoichiometry is maintained. Further, one or more acid halides can be included. In addition monomers which contain other linkages such as those specified above, can be employed as long a one or more of the comonomers used contains at least one ether oxygen linkage. Such comonomers include for example:

C I~
- 9i -372~;3 9j 27065-103 which can be used as the sole comonomer with an ether containing diacid dihalide or with phosgene or any diacid dihalide when used in addition to a polynuclear aromatic comonomer as defined in I(ii) (a), I(ii)(b), I(ii)(c) or I(ii)(d). Similarly [~ CH2~

CCl can be used as a comonomer together with an ether-containing poly-nuclear aromatic acid halide or as an additional comonomer together with a monomer system as defined in I.
The monomer system can also contain up to about 30 mole of a comonomer such as a sulfonyl chloride which polymerizes under Friedel-Crafts conditions to provide ketone/sulfone copolymers.
Further details of this process for producing poly(aryl ether ketones) can be found in published European Patent application 0124276.
Other processes for preparing these polymers can be found in United States Patent Nos. 3,953,400, 3,956,240, 3,928,295, 4,176,222 and 4,320,224.

_ 9j _ . 12~7~63 The extent to which other functional groups can be present depend on the nature of the particular group. For example, if sulfone groups are present the ratio of sulfone to ketone groups generally should be below about 30:70 as polymers containing a higher sulfone content are generally amorphous and non-crystallizable.

Other semi~crystalline aromatic polymers or polymers which can be rendered semi-crystalline include polyphenylene lo sulfide, polyphenylene ethers, and the like. Blends of these polymers with each other and with other polymers can be used.

As mentioned above, the polymer used in making the heat recoverable articles of this invention is semi-crystalline polymers or polymers capable of being rendered crystalline, that i5 are crystallizable. To exhibit the exceptional recovery stress the polymer should have a crystallinity of above about 5~. The degree of crystallinity varies depending on the particular polymer~ It is generally desirable that the crystallinity of the polymer used is at a maximum.
However, high recovery stresses can be obtained using semi-crystalline polymers with lower crystallinity. The polymer can be treated, for example by snnealing, solvent swelling or the like to increase the crystallinity.

The dimensionally heat-recoverable articles of this invention are produced by deforming the polymeric material at a temperature above the glass transition temperature of the polymer but below the melting temperature of the polymer.
By the glass transition temperature is meant the temperature which is the approximate midpoint of the temperature range over which a reversible change in the amorphous region of ~237263 the polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one (see ASTM
D883). The crystalline melting temperature of the polymer is the temperature at which the last trace of crystallinity disappears as the temperature of the polymer is raised. The glass transition temperature is designated in the specification and claims of this patent application as Tg and the crystalline melting temperature as Tm.

The dimensionally heat-recoverable article can be produced by forming an article such as a tube, ring or the like of the polymeric material. Such articles cnn be produced by conventional techniques such as injection molding, extruding, rotation molding and the like. The article is then rendered dimensionally heat-recoverable by heating the article to a temperature T1 between Tg and Tm of the polymer then deforming the article, for example, expanding it by passing it over a tapered mandrel or the like resulting in a heat shrinkable article, or compressing it by swaging or the like resulting in a heat expandable article. It is to be noted that when a rod shaped or filamentary article is rendered heat-shrinkable along its long axis, it is also rendered radially heat expandable.

The temperature at which the deformation step takes place is preferably abo~t 5C above Tg of the polymer.
Following the deformation step the article is cooled, for example, to a temperature, T2, below the glass transition temperature of the polymer. Generally the article is cooled to ambient temperature.

~;~37263 Another method of producing the article is to take a film of the polymer, the film being produced by extrusion, casting, or the like. The film is then heated to a tempera-ture between Tg and Tm of the polymer and stretched. While S maintained in the stretched configuration the film is cooled, generally to a temperature below the Tg of the polymer. The film can then converted to the dimensionally recoverable tubular article, for example, by wrapping it over a mandrel or by otherwise fnrming it and securing the ends. . The article is then removed. Alternatively, the film can be wrapped around the substrate to be covered. On application of heat to a temperature above Tg but below Tm the article recovers with high recovery stress.

l; Another method of producing a heat-shrinkable article of this invention is to produce a heat-shrinkable fiber of a semi-crystalline aromatic polymer. The fiber can be prepared by conventional spinning techniques, slit film processes and the like. The fiber is heated to a temperature between Tg and Tm of the polymer and stretched by conventional fiber stretching techniques. The fiber is cooled, for example to a temperature below Tg of the polymer. It is to be understood that the fiber (or film or tape as described above) is in itself a heat-recoverable article within the scope of this invention. To form a ring or tubular article the fiber can be wound around a mandrel and the ends thereof secured. The resulting article is removed from the mandrel. Alternatively, the film can be wrapped around the substrate to be covered.
Upon application of heat to a temperature between Tg and Tm of the polymer, the article will shrink with a high recovery stress.

~23721~3 : MP0908 -13- .

The term recovery stress is used herein to mean the recovery stress per unit area exhibited by a heat-recoverable article during constrained or unconstrained recovery. It is generally estimated by measuring the stress necessary to juat prevent recovery at the given recovery temperature.
Measurement of the recovery stress retention of recovery stress on cooling to room temperature is set forth in more detail hereinafter in the examples.

The term high recovery stress is used herein to mean a recovery stress of at least sbout 1100 X (E-1)0-5 pounds per square inch (psi), preferably at least about 15ûO X
(E-1)0-5 psi and most preferably 2000 X (E-1), wherein E
is the unresolved recovery ratio. The unresolved recovery ratio, E, is equal to Rr/Ro wherein Rr is the size of the heat recoverable article in a direction of recovery and Ro is the size of the article in that directisn before the article is rendered heat-recoverable.

For a heat-shrinkable elongate articie, this ratio is the ratio of the length after expansion or during recovery to the original length before expansion. For a thin walled tubular article this ratio is approximately the ratio of the corresponding diameters. For the thick walled tubular article this ratio is given by (ro2~(X2-1)ri2)0 5-ri .
(rO-xri ) where x is the ratio of the internal diameter of the heat-recoverable article to the diameter (ri) of the original article before being rendered heat-recoverable and rO is the external diameter of the heat recoverable article.

~23'7263 .

The high recovery stress is exhibited by articles of this invention when the article is constrained from complete recr!very, that is, is prevented from recovering to its original dimensions. Generally, the high recovery stress is exhibited when the article is recovered less than 25~, based on the dimension of the deformed article. Preferably the article is prevented by the substrate against which it is recovered from recovery of more than about 20~ and particularly more than about 15~, based on the dimension of the deformed article.

The articles of this invention sre typicslly used by recovering the srticle sgsinst a substrate. The article, for example can be used to cost the inside or outside of a lS pipe against which it is recovered, i.e. expanded or shrunk.
It can also be used to join a pair of substrates. Typical uses o~ hest recoversble articles of this inventisn sre illustrated in Figures 5, 6 snd 7. In Figure 5, a heat recoverable coupling, 1, is used to join substrates 2 and 3, which are metal pipes of similar diameter. The coupling, 1, is of heat shrinkable poly(oxy-e-phenylenecarbonyl-e-phenylene) having a diameter about 20~ greater than the diameter of the pipes 2 and 3. The coupling, 1, is positioned over the abutting ends of the pipes and heated to a temperature of about 250 C which causes the coupling to shrink into contact with the pipes with sufficient force to couple the pipes securely together.

In Figure 5, the coupling, 2, is recovered into direct contact with the substrates. An intermediate layer, for example a layer of sealant or sdhesive such as a hot melt adhesive or epoxy or a low modulus metal which is deformed s by the recovery stress of the coupling may also be used in this and the other embodiments.

Figure 6 illustrates the use of a coupling, 10, which is used to join substrates, 11 and 12 toyether. In this case substrste 11 is a pipe of smaller diameter than substrate 12 a pipe of a low modulus metal such as aluminum. The pipes are positioned so that pipe 11 is inserted into pipe 12 forming an area of overlap. Coupling 10 is positioned over the area of overlap and recovered. The recovery stress of coupling 10 is sufficient to deform the end of pipe 12 into contact with pipe 11 securely joining the substrates together.

Figure 7 illustrates joining a braid onto a metal rod~
~raid, 22, is positioned over the end of rod 21. A heat recoverable ring of poly(oxy-e-phenylenecarbonyl-e-phenylene) is positioned over the braid and rod and recovered~ The recovery stress is sufficiently high to securely attach the braid to the rod.
In each of these embodiments the stress the polymeric ring exerts on the substrate is maintained on cooling.

Other uses of heat recoverable articles of this 3C invention include heat expandable as well as heat shrinkable applications. It is also to be noted that srticles other than rings and tubular articles can be render~d heat recoverable and recovered in accordance with this invention.

. ~237263 Example 1 Poly(oxy-~-phenylenecarbonyl-e-phenylene) (Stilan), poly(oxy-p-phenyleneoxy-e-phenylenecarbonyl-p-phenylene) (PEEK), polyethylene terephthalate (PET), poly(11-iminoundecanoyl) (nylon 11) and polyethylene (PE) were extruded 8S tape of about the same thickness (0.03 in.), width (1 rS in.) and melt draw ratio under the conditions described in Table 1.
Tapes of the first four polymers, which have glass transition temperatures above 25C, were cut into 5 in. X 1/4 in.
strips with the long dimension in the extrusion direction and then annealed for the times stated in Table 1 to ensure each polymer was at a significant level of crystallinity.
Strips of each polymer were mounted in the jaws of an lS Instron Tensile Tester and equilibrated for 3 minutes at a temperature 100~C above the Tg of the pDlymer in a preheated oven before being stretched at a jaw separation spePd of 5 in. per minute to give a predetermined expansion. For the polyarylene ether ketones this expansion was 100~. Nylon 11 and crystalline PET undergo necking and drawing at the expansion temperatures selected so these polymers were drawn to their natural draw ratios (that is, to the extent thst the entire strip between the jaws had necked). As soon as the desired elongation had been attained, the drawing was stopped and the drawn strip was quenched by placing two pieces of dsmp sponge in contact with either side of the strip and then removed from the Instron Tensile Tester.

Specimens about 3 in. long were cut from the center of the stretched samples and their cross-sectional ~reas measured. The specimens were placed in thermally insulated clips of such dimensions that only the ends of the samples projected out, which ends were clamped in sn Instron Tensile ~237263 tester jaws mounted inside the oven which was maintained at the appropriate recovery temperature. The insulating clip was then removed allowing the specimen to rapidly warm up to the oven temperature. The recovery stress exerted by the specimen was measured at its peak value and also after one, two and five minutes after removal of the insulating clip.
The values of the true expansion stress at the selected expansion ratio and of the recovery stress at various tempera-tures above the Tg but below the Tm and at the above mentioned lo times after the specimens were placed in the oven are shown in Table 2.

In figures 1 and 2 the ratio of the recovery stress to the original expansion stress has been plotted as a function of the difference between the temperature of expansion and of recovery. Fi~ure 1 shows the peak values of this ratio and figure 2 the values obtained one minute after the specimens were positioned in the oven. This ratio represents the fraction of the expansion stress that is available at these recovery temperatures and at that expansion ratio.
These figures also show the fraction of the expansion stress that is expressed on exposure to the recovery temperature for polyethylene rendered heat recoverable according to the teachings of the prior art as described in Example 2.
-Example 2 This example illustrates the teachings of the prior art regarding heat recoverable articles and is outside the scope of the instant invention. The polyethylene tape described in Table 1 was rendered heat recoverable at a temperature of 85C by the natural draw technique described above (we have found that drawing at 85C yields heat recoverable articles with the highest recovery stresses). The recovery stress exerted ~;~37%63 by the polyethylene when maintained at temperatures between 40 and 100C was at a maximum value of 850 psi at ~5C. A
polyethylene strip expanded at 85C which after cooling to room temperature had an expansion of 100~ was heated to 85C
whilst clamped in the jaws of the Instron tester. On cooling down to room temperature the stress was found to increase 9~ that is to 930 psi. In another embodiment taught by the prior art, polyethylene terephthalate amorphous tape extruded as described in example 1 was stretched at 100C this being the maximum temperature that we found could be used without cryst~llization of the amorphous tape during the drawing. The heat recoverable polyethylene terephthalate when tested as desribed in exsmple 1 achieved a maximum recovery stress of 677 psi at 100~C recovery temperature after having previously been expanded 555~'. In another embodiment outside the scope of this invention a strip of crystalline Stilan was placed in the jaws of an Instron Tensile Tester and elongated at room temperature. We found that the strip necked non-uniformly and broke at a low elongation well before the strip had completely drawn.

Fxample 3 Strips of crystalline tapes prepared and annealed as described in example 1 were expanded 100~ at a temperature 50C above the Tg of each polymer, cooled to room temperature and specimens cut from the expanded strips were heated tD a temperature 50C above their Tg while clamped in the jaws of an Instron Tensile tester. Table ~ shows t~he values of the recovery stress obtained after 1 minute of exposure to the hot oven.

lZ37263 - 1 g -Example 4 Strips of crystaliine tapes prepared and annealed as described in example 1 were expandecl to various degrees at a 5 temperature 10ûC above the Tg of each polymer and cooled to room temperature. Specimens cut from the expanded strips were then heated to the temperature of expansion while clamped in the jaws of an Instron Tensile tester. Table 4 shows the peak recovery stresss generated within the first five minute5 of exposure to the hot oven. Figure 3 shows the peak recovery stress for these specimens plotted as a function of unresolved recovery. The lowest two curves in Figure 3 show the peak recovery stresses observed with materials incapable of use in the present invention (see Table 4, amorphous PET and PE).

Example 5 The expanded specimens of Example 3 were heated to Tg +
50C and allowed to shrink to varying degrees, the recovery stress being measured as a function of the degree of recovery.
Table 5 shows the values obtained; the vsriation of shrinkage stress with percent recovery is plotted in figure 4. The recoverable articles of the instant invention exhibit significant recovery stresss after shrinkages of as much as ~6~ based on the expanded dimensions. Figure 6 also shows the variation of recovery stress with percent recovery for polyethylene, material incapable of use in the instant inventi D n.

-~72~3 MP0908 Example 6 The expanded specimens of Example 1 were reheated to their expansion temperature while clamped in the jaws of an Instron Tensile tester then cooled to room temperature in,:
the way described in Example 1, the percentage change in stress on cooling to room temperature being recorded. The results obtained are given in Table 6 and show that heat recoverable articles of the instant invention retain a substantial proportion of or even increase the force which they exert on any substrate they are recovered onto on cooling.

Example 7 Tubular rings of engineering thermoplastics useful in this invention were injection molded using the conditions stated in Table 7, annealed as necessary to develop substantial crystallinity and preheated in an oven for ten minutes at Tg + 50~C. The preheated rings were removed from the oven and expanded over a mandrel (similarly preheated) as rapidly as possible and quenched in water, then removed from the mandrel. The mandrel size wa- chosen so that each expanded ring had 2 diameter twice that of the unexpanded rings after removal from the mandrel. The expanded rings were recovered over tinned copper braid placed on mandrels of varying size so that the braid extended beyond the end of each mandrel.
The braid used is typical of that used to electrically shield signal csbles used in electronic equipment. The temperature of recovery was the same as that used to expand each ring. Each assembly was allowed to cool to room temperature. The free end of the braid was clamped in one ~237263 jaw of the Instron Tensile tester and the mandrel in the other. The jaws were separated at a rate of 0.2 in. per :minute. The peak force required to pull off the braid is given in table B. Table 8 also shows the force required to pull of a polyethylene (Marlex 6003) ring expanded at 85C
as taught by the prior art. Table B shows that considerably greater force was required to pull of the heat recoverable rings of the instant invention than thst required to remove the rings made following a teaching of the prior srt.

Example B

Annealed crystalline rings of Stilan were expanded onto a mandrel at room temperature. In every instance the rings expanded non-uniformly and broke at an elongation of about 30~.
k ~1.23~726~
MP09D~

Table 1 PolymerStilan PEEK PET Nylon-11 Nylon-6 PE
Tradename Marlex 6003 S Extruder Size Temperature Profile:
Zone 1 360 338 220 230 150C
Zone 2 360 350 240 250 175C
Zone 3 372 38Z 260 270 175C
Zone 4 382 382 260 290 200C
Die 1 382 388C
Die 2 400 388C
Cl~p 382 388C
l~ S~rew type 1 1 2 2 2 Head 30D0 1800 N/A N/A N/A N/A
Pressure Throat On On N/A N/A N/A N/A
water Roller 177 177 3B 65 93C
Temperature Roller Speed N/A 4 FPM N/~ N/A N/A N/A
Annealing (C) 250 250 125 100 0 N/A
2~ Conditions (hrs) 4 4 0.5 1 hours N/A
Expansion Tg~10aTg+100 Tg+100 Tg+100 Tg~100 Tem?erature 265 245 175 155 150 85C
Expansion 2:1 2:1 2.95:1 2.95:1 2:1 2:1 (1~ Die dimensions were 2 in. X 0,065 in.

(2) Screw type 1 was a linear low density polyethylene screw.
Screw type 2 was a low density polyethylene screw.

3;
(3, ~ylon 6 was in the form of injection-molded dumbells, ~ST~' D638 Type IV. For injection molding conditions ~.~7Z63 MPo908 TABLE 2 Recovery Stress Versus Recovery Temperature Reeovery Temp. Time StilanPEEK PETNylon 11 Nylon 6 s TE-80 1m 6,8531,211 882 2m 6,9061,288 882 5m 7,û221,355 882 TE-50 1m 4,537 8,4003,012 1,491 2m 4,578 8,4763,019 1,469 5m 4,603 8,5353,019 1,413 801 TE-40 1m 2m 5m TE-20 1m 4,741 9,2783,303 2,175 2m 4,741 9,3513,303 2,126 5m 4,741 9,2073,303 2,û56 TE* Peak 4,628 9,3493,383 2,475 1m 4,476 9,3012,975 2,406 2m 4,349 9,2332,924 2,207 5m 4,214 9,0992,848 2,121 1,9B1 TE+20 Peak 4,674 9,3583,32B 2,646 1m 3,710 8,5591,788 1,212 2m 3,621 8,3691,749 1,057 5m 3,451 8,0941,696 1,003 TE+50 Peak 4S406 8,8752,817 1m 2,514 6,496 370 2m 2,408 6,279 358 5m 2,236 5,920 332 198 Expansion Stress 6,10415,1885,254 3,266 I TE = Expansion temperature 123~7Z63 MP0908 TABLE 3 Recovery Stress After Expansion at Tq 1 50C

Expansion Recovery Recovery Temp.(C)Ratio Temp.(C)Stress (psi) Stilan 215 100,c 215 5,653 PEEK 195 100~ 195 10,332 PET 125 100~ 125 1,933 Nylon 11 105 100V 105 2,039 - . ~237263 TABLE 4 Recovery Stress And Expansion Expansion Recovery Recovery Polymer Temp.(C) Elonqation Temp.('C) StrPss (psi) Stilan 265 100~ 265 5,214 265 166,Vo 265 9,531 PEEK 245 100~ 245 8,465 PET 175 225~ 175 2,019 175 285~ 175 4,426 175 350Z 175 5,063 Nylon 11 155 195V 175 2,696 155 220X 175 3,967 155 280Z 175 5,417 155 350X 175 7,854 B5 370~ 85 956 880X 85 2,191 Amorphous 100 100X 100 27 PET 100 260X 100 ?11 123~263 MP09OB

TABLE 5 Recovery Stress Versus Percent Shri~

Recovery Stress_(psi) S Percent Shrink StilanPEEK P Nylon 11 PE ' 0 5,50610,174 1,794 2,0i4 8B7 3,472 6,108 1,285 1,220 710 1D 2,166 3,062 733 725 556 1,209 1,212 307 55 lS 20 433 128 0 0 208 1;~3726;~

TABLE 6 Chanqe in Recovery Stress on Coolinq to Room Tempersture Expansion Recov ry Chanqes in Stress on 5Temperature Elonqation Temperature Coolinq Stilan 265DC 100~D 265C +1 3o PEEK 245~C 1000 245C +16o PET 175C 200~ 175C +27Do Nylon 11 155C 195o 155C -75 Nylon 6 150 C 150~ 150~C -20o ~;~3~72~i;3 Table 7 Molding Conditions s Stilan PE PET Nylon 11 PE ' Nylon 6 8arrel Temperatures (C) Rear 380C 370C 250C 190C 140C 240C
Front 395C 380C 260C 200C 145C 260C
Mold Temperatures (C) Sprue Side 200C 165C *cold *cold *cold 45C
Ejector Side 200C 165C *cold *cold *cold 45C

Cycle Times (seconds) Injection 21 21 22 22 22 10 Mbld Close 51 51 52 52 52 30 . Mold Clnse 04 04 04 04 04 03 20Injection Pressure ~psi) 1200 1200 1200 1200 1200 800 ~Cold-No mold heating used ~237~63 TABLE B Pull-Dff Force - Pound/Inch Width Mandrel Size_ 0.375 0.395 0.4150.435 0.455 0-475 Stilan 289 382 484 623 725~ ~

PEEK 277 369 469 642 738+ *

Pet 115 198 265 399 525 691 Nylon 11 57 86 112 164 233 346 PE (Marlex 6003) 11 21 66 83 10B 14B

Results are an average of three samples~

~ Braid tore before pulling off fnr all three samples.

1 ~raid tore before pulling off for 1 sample for PEEK and 2 samples for Stilan.

Claims (17)

We Claim:

1. A dimensionally heat-recoverable article of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25°C, said article having a recovery stress of above about 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio.

2. An article in accordance with Claim 1 wherein said polymer is poly(oxy-p-phenylenecarbonyl-p-phenylene).

3. An article in accordance with Claim 1 in the form of a ring.

4. An article in accordance with Claim 1 in the form of a tube.

5. An article in accordance with Claim 1 in the form of a ring.

6. An article in accordance with Claim 1 in the form of a fiber.

7. An article in accordance with Claim 1 in the form of a film.

8. A method of producing a dimensionally heat-recoverable article of a semi-crystalline polymer having a glass transition temperature, Tg, above 25°C by:

a) heating a shaped article of a semi-crystalline polymer to a temperature above the Tg of the polymer;

b) deforming the article; and c) cooling the article while maintaining the article in the deformed state, thereby producing an article which, when heated to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer, recovers with a recovery stress above about 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio, and substantially retains such stress on cooling of the article to ambient temperature.

9. A method in accordance with Claim 8 wherein the step of deforming the article comprises expanding the article.

10. A method in accordance with Claim 9 wherein said.
article is in the form of a ring and is expanded by passing the ring over a tapered mandrel.

11. A method of producing a heat-shrinkable article of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25°C which comprises:

a) stretching a film or fiber of said polymer at a temperature above the Tg of said polymer;

b) cooling the stretched film or fiber to a temperature below the Tg of the polymer; and c) forming a shaped article from the stretched film or fiber, thereby forming an article which when heated to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer, shrinks with a stress of above about 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio.

12. A method in accordance with Claim 11, wherein said shaped article is formed by winding said film or fiber around a mandrel to form a tubular article.

13. A method of recovering a dimensionally heat-recoverable device against a substrate which comprises:

a) selecting a heat-recoverable article of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25°C;

b) positioning a tubular heat-recoverable article adjacent such that on recovery the substrate restrains the article to a recovery of less than about 25%, based on the dimension of the deformed article;

c) heating said article to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer thereby causing the article to recover about said substrate exerting a stress of at least about 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio on said substrate; and d) cooling said article.

14. A method of joining cylindrical articles which comprises:

a) positioning said cylindrical substrates in end-to-end abutting relationship;

b) positioning a heat-shrinkable tubular article such that it surrounds the ends of said cylindrical substrates, said article being of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25°C;

c) heating said article to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer to cause it to shrink and exert a stress of at least 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio on the cylindrical substrates thereby joining the substrates together; and d) cooling the recovered article and joined substrates.

15. A method in accordance with Claim 14 wherein an intermediate layer is positioned between the heat shrinkable article and the substrates.

16. A method in accordance with Claim 15 wherein said intermediate layer comprises an adhesive.

17. A method of securing a braid to a cylindrical substrate which comprises:

a) placing the braid over the substrate in abutting relationship;

b) positioning a heat-shrinkable ring such that it surrounds braid and substrate, said article being of a semi-crystalline polymer having a glass transition temperature, Tg, above about 25°C; and c) heating said ring to a temperature between Tg and the crystalline melting temperature, Tm, of the polymer to cause it to shrink and exert a stress of at least 1100 X (E-1)0.5 pounds per square inch, wherein E is the unresolved recovery ratio on the braid and securing the braid to the substrate;
and d) cooling the recovered ring.