JPH0416335B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to heat-recoverable articles, and more particularly to heat-recoverable articles having dimensional recoverability against heat and uses thereof. A recoverable article is an article that substantially changes its dimensional shape when subjected to heat treatment. Typically, upon heating, these articles recover to their original shape prior to being deformed; however, as used herein, the term "heat recoverable" refers to the recovery of a new shape even if it has not been previously deformed. It also includes articles that take In its most common form, such articles consist of heat-shrinkable sleeves made from polymeric materials exhibiting elastic or plastic memory, such as those described in U.S. Pat. . For example, U.S. patent no.
As clarified in No. 2027962, the initial dimensionally heat-stable shape may be obtained by a continuous process such as expanding an extruded tube while hot into a dimensionally heat-stable shape. may be a temporary shape, but in other cases, a preformed dimensionally heat-stable article is transformed into a dimensionally heat-stable shape in another step. When manufacturing heat recoverable articles, the polymeric material may be crosslinked during any step in the manufacture of the article to enhance the desired dimensional recovery. One method of making heat recoverable articles involves forming the polymeric material into the desired heat stable shape and then crosslinking the polymeric material;
Depending on the type of polymer, the article is heated to a temperature above the crystalline melting point or the softening point of the polymer for amorphous materials, the article is deformed, and the article is kept in the deformed state by cooling it in that state. consists of doing. In use, the article in the deformed state is thermally unstable and will tend to assume its initial thermally stable shape upon application of heat. Other methods involve deforming a substantially uncrosslinked polymer at a temperature below the crystalline melting or softening point of the material to combine one or more material articles and at least one polymeric component into at least one hollow heat recoverable material. It consists of crosslinking the substantially uncrosslinked material after shaping the article. In other articles, such as those described in GB 1440524, an elastic member is held in a stretched state by a second member, and heating weakens the second member and allows the elastic member to recover. can. Heat recoverable articles have been found to have particular application in the perimeter protection of elongate substrates, such as telecommunications cables. In such applications, the heat-shrinkable article is placed around the object to be wrapped and then restored by heating its outer surface with a gas torch, such as a propane torch. U.S. Patent No. 3,669,157 (Carolina
Narrow Fabric Company) and Japanese Patent Specification No. 53-13805 (Matsushita) propose to provide a heat-shrinkable tubular knitted fabric article that can be filled with certain heat-setting resins. . However, the inventors have found that the heat-shrinkable knitted fabric of such an article has a tendency to fracture under its own recovery force as soon as the heat-recoverable fabric of the article is heat-recovered. It is very difficult to install due to the open flame from a tool or similar heating device such as a hot air gun. The present invention includes a heat-recoverable knitted fabric comprising fibers that recover in size after heating and have a tensile strength of at least 0.1 MPa at the recovery temperature, the knitted fabric comprising a polymeric material preferably having a thickness of at least 0.03 mm. at least a portion of the substrate comprising an outer surface coated with a stress-free layer of polymeric material, the polymeric material being flexible without flowing when heated and allowing thermal recovery of the article; A dimensionally heat recoverable article for wrapping is provided. "Recovery temperature" of a polymeric heat recovery material means the temperature at which recovery of the polymeric material is substantially complete. Generally, the recovery temperature is the crystalline melt transition temperature if the polymer is crystalline, or the glass transition temperature if the polymer is amorphous. The polymeric material formed in the outer layer should be softened at a temperature below the recovery temperature to allow recovery of the fibers, while the polymeric material should be melted since it would otherwise flow or flow out of the article upon heating. Not. Preferably, the layer of polymeric material is formed from a crosslinked thermoplastic polymer, either chemically crosslinked or crosslinked by radiation treatment, to render it non-fusible. The polymeric material has a dynamic complex viscosity (complex
dynamic viscosity) of at least 10 ² , more preferably at least 10 ³ , most preferably at least 10 ⁴ poise, but at the recovery temperature of the fiber preferably does not exceed 10 ⁹ , more preferably does not exceed 10 ⁸ , especially 10 Preferably no more than ⁷ whiz.
complex dynamic modulus
The specific maximum value of depends on the resilience of the fibers, but
Values significantly higher than 10 ⁹ poise may prevent the article from recovery. The dynamic complex viscosity is, for example, Van
By Wager, Lyons, Kim and Colwell:
Viscosity and flow measurement Chapter 6, H.
By Leaderman: Viscoelasticity and its
measurement Rheology Volume 12 Chapter 1, and
By FSLockett: Non−linear Viscoelastic
solids Chapter 1 (Academic press). The layer of polymeric material is preferably made from a thermoplastic polymer that has been crosslinked, either chemically or by radiation crosslinking, to render it non-fusible. The article of the invention enables advantageous properties such as high mechanical strength of knitted fabrics for use in heat-shrinkable articles on the one hand, and on the other hand for applications in gas flame implements or other previously proposed articles. It has the advantage of allowing resiliency even with the use of the harsh heating tools inherent in the process. The ability of such flame tools to recover heat-shrinkable articles can be measured in terms of torch index: The flame rate is the steady flame speed (torching
Substantially the ratio of the time it takes to damage a textile or other heat-shrinkable article for use in the invention by overheating to the time it takes to recover the textile or other heat-shrinkable article used in the present invention, when measured at be. Therefore, the higher the value of the flame rate, the more effectively the item is able to be healed by e.g. Appropriateness is low. In fact, if the flame rate is less than 2, it is essentially impossible to recover with flame tools. Articles with high flame rates are also found to have utility in high temperature environments and applications as installation methods involving such means as other harsh heating means. The inventors have discovered that although textiles made from heat-recoverable fibers exhibit relatively low values of flame rate, by laminating textiles in accordance with the present invention,
It has been found that it is possible to substantially increase the flame rate of resilient knitted fabrics. If the layer of polymeric material were to act simply as a thermal barrier, the time to damage the article due to overheating and the time to recover would be expected to increase at respective rates, and therefore the flame rate would remain constant. As such, it is difficult to fully understand the reason for the increased flame rate of articles according to the present invention. Most surprisingly, however, many articles according to the present invention are found to exhibit higher flame rates than conventional heat-shrinkable sheet products. It has been found that, in general, the flame rate of textile composite structures increases as the thickness of the polymeric material layer increases. The thickness of the polymeric material layer is preferably at least 0.05 mm, more preferably at least 0.07 mm, especially at least 0.1 mm, more particularly at least 1.5 mm, most particularly at least
It is 0.2mm. In practice, the maximum thickness of the layer is 2 mm, preferably 1 mm and most preferably 0.6 mm. If this layer has a thickness substantially greater than 2 mm, there is a risk that the outer layer will scorch before the fabric reaches its recovery temperature. The layer of polymeric material can be selected from a wide range of polymers, provided that it is softened after heating so that recovery of the textile fabric takes place conveniently. In order to facilitate recovery of the fibers, the polymeric material is preferably heated at a softening point of not more than 20°C above the recovery temperature of the fibers, more preferably at a temperature not higher than the recovery temperature of the fibers themselves, especially at least below the recovery temperature. It has a softening point of 10°C. However, preferably this softening point is 40° below the recovery temperature of the fiber.
The temperature should not be lower than ℃. Examples of thermoplastic polymers that can be used to form such layers include ethylene/vinyl acetate copolymers, ethylene/ethyl acrylate copolymers, linear low density,
polyethylenes, polypropylene, polybutylene, polyesters, polyamides, polyetheramides, including low density and high density grades;
Examples include perfluoroethylene/ethylene copolymer and polyvinylidene fluoride. Considering additional classes of these materials, this includes acrylic elastomers, including acrylonitrile butadiene styrene block copolymers, acrylic esters, methacrylic esters, and copolymers thereof, such as polybutyl acrylate or poly 2-ethylhexyl acrylate. , high vinyl acetate
Includes ethylene copolymers (VAES), polynorbornenes, polyurethanes, and silicone resin elastomers. The polymer material used to make the polymer layer is
If it is fusible, it can be cross-treated, e.g. by chemical cross-linking agents or by high-energy electron beam irradiation.
It can be made non-fusible by radiation treatment such as gamma irradiation or ultraviolet irradiation. The polymer material used to make the polymer layer is
It may be transparent (at least to visible radiation) or completely opaque, or it may have an opacity somewhere between these extremes. If the opacity is increased, for example by incorporating a small amount, say 5% by weight, of carbon black into the polymeric material, both the recovery and damage times of the textile will be reduced, possibly due to increased heating from the absorption of infrared radiation. appears to decrease, so that the flame rate does not change significantly. As will be appreciated, the matrix material is selected in view of various other favorable properties inherent in the polymeric material itself, and may be loaded with various additives such as antioxidants, UV stabilizers, anti-tracking agents, etc. Can be manufactured with adducts. As mentioned above, the polymeric material of the composite structure softens to allow fiber recovery. This material preferably has a secant modulus of 20%
at least 10 ⁻² MPa, and an elongation to break of at least 50%, preferably at least 100%, both properties measured at the recovery temperature of the fiber. In addition, the textile composite preferably satisfies the following inequality at the fiber recovery temperature: X(1-R)/YR is less than 1, preferably less than 0.5, especially less than 0.05. where X is the 20% secant modulus of the polymeric material (measured at a pull rate of 300%/min), Y is the recovery stress of the fiber, and R is the total capacity of the composite structure in a given direction. represents the average effective volume fraction or related fraction of heat recoverable fibers in a composite structure along the In another composite structure of the invention, the resilient knitted fabric provides resilient fibers in the resilient composite structure, the composite structure comprising a cross-linked polymeric material that imparts resilience and a resilient fabric. It is possible to contain cross-linked fibers. Such resilient composite structures can be produced by applying a polymeric material to resilient crosslinked fibers and then crosslinking the polymeric material. This fiber can be cross-linked to increase its strength after recovery, and the recovery stress is at least
A suitable pressure is 1 MPa, preferably 1.5 to 5 MPa. The polymeric material is preferably cross-treated to prevent it from running down or escaping during the heat recovery process, particularly by the flame implement. However, if the degree of cross-linking of the polymeric material is too high, it will reduce the recovery ratio of the composite. This can be problematic as different cross-linking treatments may be required for fibers and polymeric materials. The reason for this is that the two-step bridging process is performed separately. This problem arises due to the different cross-linking responses (beam response in the case of radiation cross-linking) of the materials used for the fibers and polymer materials, as well as the processing history of the fibers and polymers. This second effect involves a reduction in the fiber's beam response resulting from the orientation created by stretching the fiber to make it resilient. Nevertheless, if the beam response of the recoverable fiber compared to the beam response of the polymeric material decreases before the recovery ratio of the composite structure decreases to a value of 70% of that of the non-radiation treated composite structure, the fiber A single bridging step can be used to form a composite structure, provided the beam response is such that it can achieve an own radiative recovery stress of at least 1 MPa. The relative beam response can be created by the presence of prorads in the resilient fibers and/or antirads of polymeric materials. In a preferred embodiment of the invention, the textile is combined into a pliable, resilient composite structure comprising a resilient textile and a polymeric matrix applied thereto. In this embodiment, (a) the resilient knit fabric is comprised of a cross-linked resilient polyolefin having a recovery stress of 1.5 to 5 MPa, and (b) the matrix has a recovery ratio that applies to the composite and a recovery ratio that applies to the free knit fabric. The polymeric matrix material itself, after radiation treatment, has a room temperature elongation of 400 to 700%, measured at a tensile rate of 300%/min. In addition to providing a method of bridging, radiation treatment can impart other properties to composite structures. Radiation treatment of the fibers, especially in the presence of oxygen, before the application of the polymeric substance causes changes in the surface properties of the fibers (such as oxidation), which improve the adhesion between the fibers and the polymeric substance. . An irradiation step after application of the polymeric material can also aid in bonding by forming cross-links between the two components in the composite structure. Alternatively, instead of relying on the conditions applied to the polymeric material, some type of mechanical bond between the fiber and the polymeric material can be provided. The fibers preferably have a minimum recovery stress of 10 ^-1 MPa at a temperature above the transition temperature of the fibers, more preferably 5×
10 ^-1 MPa, usually at least 1 MPa, especially 1.5×
Has 5MPa. In theory, there is no upper limit to the recovery stress, but in practice the highest value that can typically be achieved for polymeric fibers is 200 MPa, more usually 100 MPa. Heat recoverable fibers are preferably made from polymeric materials that impart good physical properties and especially good creep resistance to the fibers. Olefin polymers such as polyethylene, ethylene copolymers, polyamides, polyesters, acrylic polymers and other polymers that can be crosslinked can be used. A particularly preferred polymeric material for fibers has a density of 0.94-0.97 g/cc, Mw80
x10 ³ to 200 x 10 ³ and Mn 15 x 10 ³ to 30 x 10 ³ . The recovery temperature of the fibers is preferably 60°C or higher, most preferably 80-250°C, such as 120-250°C.
The temperature is 150℃. When crosslinking fibers by radiation, it is advantageous to incorporate the crosslinking step into the fiber manufacturing process. The fibers are extruded and drawn preferably 800-2000% at a temperature below their melting point and then treated with radiation to effect cross-linking. Less preferred methods of manufacture include extruding the fibers, cross-linking them with radiation treatment, then heating the fibers preferably above their melting point, drawing the fibers, and cooling the drawn fibers. The high density polyethylene fibers are preferably radiation treated with a radiation dose of about 5 to 35 Megarads, preferably about 5 to 25 Megarads, especially about 7 to 18 Megarads, especially about 10 to 18 Megarads. Usually, the gel content in cross-linked fibers is
20% or more, preferably 30% or more, most preferably
40% or more. In practice, gel contents of more than 90% are not easily achieved. The heat-recoverable knitted fabric may be manufactured from only the above-mentioned heat-recoverable fibers, or may contain other fibers in addition to the above-mentioned heat-recoverable fibers, if necessary. When the knitted fabric contains fibers other than heat-recoverable fibers, R in inequality (1) above relates only to the heat-recoverable fiber component. The knitted fabric can be knitted, woven, nonwoven, braided, etc. In a preferred embodiment, the knitted fabric is a woven fabric. The fabric may contain only heat recoverable fibers or heat recoverable fibers along with non-heat recoverable fibers or filaments. For example, the fabric may contain recoverable fibers in one direction and non-recoverable fibers in the other direction. This is to produce a heat recovery fabric that is recoverable in only one direction of the fabric. Non-recoverable fibers include glass fibers, carbon fibers, wire or other metal fibers, polyesters, aromatic polymers or imides, and ceramics. Particularly preferred fabrics are those described in British Patent Application No. 8300219 and British Patent Application No. 8300222. The woven fabric may be of any type, such as twill weave, broken pattern weave, satin, satin weave, karami weave, plain weave, hops weave, satsuku, matte, and various types of single-layer weave or multi-layer weave, such as 2- to 3-layer weave. It can be woven with a similar combination of textile structures. Recoverable fibers with many floats (e.g. 6-20) as can be obtained by satin weaving
Fabrics containing . The article can also have multiple layers, such as two or three layers of fabric, separated by one or more layers of polymeric material. If desired, the layer of polymeric material may be bonded to only one side of the heat-recoverable fabric, either by adhesive bonding, i.e., chemical or physical surface interaction, or by a mechanical interlocking process. Preferably, however, a heat-recoverable knitted fabric is included in the polymeric material. That is, the polymeric material surrounds the main part of the fiber surface area. Most preferably, the fabric is entirely surrounded by polymeric material, or in particular so that there is a limited thickness of polymeric material on each side of the fabric. In this case, the thickness of the polymer layer for the purposes of the invention is defined as the thickness of that part of the layer present on the textile. In preferred articles according to the invention, the thickness of the polymeric material on the inner surface of the article on the side of the fabric opposite to the side receiving the flame is greater than the thickness of the polymeric material on the outer surface. The polymeric materials forming the layers on opposite sides of the fabric may be the same or different from each other, and laminates of different polymer layers can be used on one or both sides of the fabric. The differences between the polymeric materials on either side of the fabric can be any one or more of the following: differences in thickness, differences in chemical type of polymer, and differences in chemically similar types of polymers. Differences in combination or processing methods. There are two possibly contradictory schools of thought regarding the configuration of polymeric materials. First, it is possible to set a polymer layer on the side facing the heating source to increase the flame rate of the knitted fabric, and second, it is possible to set a matrix material that should not interfere with the inherent recovery of the knitted fabric. (for example, to make knitted fabrics opaque). The heat-facing layer is preferably bridging to prevent its escape or run-off, but bridging of the matrix generally inhibits recovery. Therefore, in a preferred embodiment of the invention, varying degrees of crosslinking are provided between the flame exposed surface and the remaining surface of the polymeric material.
This is achieved, for example, by forming a cross-linked thin layer on the outside or by forming a cross-linked layer on one side of the fabric and a non-cross-linked layer on the other side. Such an outer thin layer can be formed using radiation with very low penetrating power, such as electron curtain radiation, or if the matrix is uncrosslinked or crosslinked to a lesser extent. This can be achieved by laminating a thin cross-linked layer onto the surface of a composite material. Different crosslinking treatments in any of these embodiments can be achieved by separate crosslinking steps for each layer to be crosslinked to a different degree. However, it is preferable to obtain the above result by a single crosslinking step, in particular by radiation treatment, which can be done if the beam responses of the different layers are suitably different (or made different). For example, the majority of the matrix can be polypropylene (which is not crosslinked in this method) and only the surface layer (or only one side of the fabric) is polyethylene (which is crosslinked). Other methods include prorads and/or antirads in various layers.
This is a method of applying an appropriate load. As a further feature, an adhesive or sealant (eg, a hot melt adhesive) or mastic that can be melted may be applied on the inner surface of the article. It has been discovered that increasing the thickness of the polymeric material on the interior surface of the article and/or applying a sealant or adhesive to the interior surface increases the flame rate of the article. Examples of hot melt adhesives that can be used include ethylene and vinyl acetate copolymer-based adhesives and polyamide-based adhesives. Such adhesives are well known and are disclosed, for example, in US Pat. No. 4,018,733 and US Pat. No. 4,181,775. If desired, a heat cureable adhesive can be used as the adhesive. An example of such an adhesive is disclosed in British Patent Publication No. 2104800. Since the heat recovery properties of the articles of the invention are attributable to the recovery properties of the fabrics that make up the knitted fabric, the articles as a whole need not be stretched during manufacture, and the layers of such polymeric material are substantially The layer may be stress-free, ie the layer exhibits little or no tendency to spontaneously recover when heated. The article of the invention therefore has the further significant advantage of being highly insensitive to the presence of small scratches on its surface, which may occur due to rough handling prior to its assembly. . For comparison, conventional heat-shrinkable articles formed, for example, by cross-processing and then stretching a polymer sheet, are damaged by tearing during heat recovery even with very small scratches on their surface. It was discovered that Heat-recoverable textiles can be coated with layers of polymeric material in a number of ways. For example, articles formed on each substrate piece may be preferably formed by applying the polymeric material to a textile fabric by press lamination, or if the article can be made from a textile fabric of variable length. It is preferred to use an extrusion lamination process in which the hot polymeric material is pressed onto the fabric and immediately quenched to prevent recovery of the fabric, and this operation is carried out as a continuous process. In either case, sufficient heat and pressure must be applied to bond or interlock the polymeric material to at least a major portion of the fabric, and substantially all portions thereof. Other methods of coating knitted fabrics with polymeric substances include
For example, saturated, solution coatings, slurry coatings, powder coatings, reactive prepolymers (eg, UV or peroxide activated acrylic prepolymers), etc. can be used. Unless the knitted fabric is adequately inhibited from recovery in any bonding method employed,
Sufficient heating to cause significant recovery of the textile should be avoided. Of the coating processes used, extrusion lamination is preferred for that reason, as it appears to produce articles exhibiting particularly high flame rates. After coating the textile with the polymeric material, the polymeric material is preferably treated with high-energy electron beam irradiation or gamma irradiation, preferably from 0.5 to 15 Megarads, especially from 1 to 10 Megarads, especially from 3 to 7 Megarads, most preferably from 1 to 7 Megarads. Cross-linking treatment can be performed with a radiation dose of 5 megarads. The article of the invention can be formed into many shapes depending on its intended use. Preferred applications include perimeter protection of cables and pipes or their joints or junctions.
The article of the invention can thus be tubular in shape or have multiple tubular sections, such as in the case of cable breaks. If the article is designed to wrap around an elongated substrate with ends that cannot be easily reached, the article may be manufactured as a so-called wraparound article in which the covering fabric has an open cross-section. can do. For example, it is substantially sheet-shaped and has two opposite end sections extending perpendicular to the direction of recovery, which end sections are held together against the recovery forces of the fabric. can be something that can be done. The article can simply be wrapped around the substrate to be encapsulated, and the end portions are held together so as to wrap around the sleeve-shaped substrate after the article has been heated. Wrapping articles made from knitted fabrics and suitable closure arrangements thereof are disclosed in further detail in British Patent Application No. 8300223. In the case of a wrapped article in which the coated textile is in the form of a sheet, the outer surface of the textile is confined to face outwardly once the article surrounds the substrate and the opposite end portions are constrained. In general, the ability of a textile or textile composite to be penetrated without tearing allows portions to be joined together (eg, to form an hemlock) by mechanical bonding arrangements that extend through the textile. Preferred arrangements are stitches or clasps. Two types of articles of the invention are illustrated by way of example with reference to the accompanying drawings, in which: FIG. FIG. 1 is a partially sectional perspective view of one type of article of the invention. FIG. 2 is a partially sectional perspective view of a second type of article of the invention. FIG. 3 is a partial cross-sectional view of a third type of article of the invention. FIG. 4 is a graphical representation of recovery power versus time for a knitted fabric of the present invention and a conventional heat recovery article. With reference to the accompanying figures 1-3, figure 1 shows a fabric 1 consisting of heat-recoverable warp fibers 1 and heat-stable weft fibers 2.
1 shows a type of knitted article having a heat-softening polymer layer 3 coated on its outer surface. FIG. 2 shows a fabric similar to that of FIG. 1, but additionally having a lower layer 4 of adhesive. Figure 3 shows an article of a similar type as described above, but in which a thermosoftening polymer layer 3 extends beneath the fabric so as to completely encapsulate the fabric. In articles of this type, the corresponding thickness of the polymer layer is the thickness of that portion of the layer overlying the fabric. The flame rate in the examples below is determined by the following procedure: A square coated fabric sample of dimensions 100 mm x 100 mm is placed between the fixtures of an Instron® tensile tester so that its resilient fibers are placed in the tensile tester. and with the outer surface of the fabric facing a propane gas flame located approximately 128 mm away from it. The vertical edges of the fabric sample are protected from the flame by a metal plate and only the 96 mm wide center area is exposed to the flame. Before lighting the flame tool, a temporary metal plate is placed to completely darken the sample from the flame. Ignite the flame tool, travel length approximately 260mm,
The flame is moved continuously across the face of the sample from one side to the other at a rate of about 1 pass/second at which the flame passes along the sample. The force exerted by the resilient fabric on the regularly spaced sample fixtures of the tensile tester, excluding the temporary metal plate, is plotted as a function of time. Typical graphs of resiliency versus time are shown in the accompanying drawings as a heat-recoverable fabric (plot) and a conventional heat-shrinkable sheet (plot). This graph effectively represents the forces exerted by the heat-shrinkable seam portion on the center of the seam, where the seam is unable to recover to any significant degree due to the relatively large diameter of the center. As the article is heated by the flame, the resilience of the article increases until it reaches a maximum value (points A, A'), then the resilience decreases, and the degree of decrease in the resilience is such that the specimen is damaged. Before, the minimum value in a short time (points B, B')
reach. Damage in conventional sheet-type articles is observed as a sudden decrease in the recovery force (point C') when the article tears, whereas damage in articles of the present invention is observed as the fibers recover as they are progressively damaged. Observed as a substantially linear decrease in force (region C). The point on the time axis corresponding to the horizontal tangent section where the curve at the maximum recovery force and the extrapolated straight line of the maximum slope of the curve (points D, D') touch is recorded as the recovery time. For regular items, the recovery power suddenly decreases (points
E') or, in the case of the articles of the invention, the intersection between the tangent at the minimum recovery reduction rate and the tangent of recovery reduction after the fibers begin to damage (point E). Consider it as time. The flame rate of an article, as used herein, is defined as the ratio of damage time to recovery time (or Y/X value as shown in the graph) for that article. Next, preferred embodiments of the present invention will be specifically described with reference to Examples. Examples 1 to 6 Torn oblique fabrics are made using high-density polyethylene monofilament with a diameter of 0.29 mm as the warp yarn and 75ECG glass yarn as the weft yarn. This fabric has a weave density of 80/12 (i.e., warp fibers per inch).
80 pieces/12 weft fibers per inch or 31.5/4.7
(per cm)). The fabric is irradiated with a 1.5 MeV electron beam of 15 megarads at an irradiation rate of about 100 megarads/min. The resulting polyethylene fibers had a gel content of 37.3%, measured after refluxing in xylene, and
The secant modulus of elasticity was 0.50 MPa at 150°C. The thickness of the fabric was 0.6 mm. This fabric was flame treated as described above, and the flame rate was measured, and the results are shown in the table. On each side of the fabric, an equal thickness of pure low density polyethylene (MFI = 3.0), number average molecular weight Mn
= 14800, weight average molecular weight Mw = 114800) is pressed to form a laminate and then irradiated with high energy electrons to a further dose of 3 Megarads to give the products of Examples 2-6. The flame rate values are shown in the table. It can be seen from the table that the coated fabric is substantially more flameable than the uncoated fabric and that the flame rate increases with the thickness of the polyethylene coating.

Table: The uncoated fabric (Example 1) shows a low flame rate and the fabric recovers and damages over a period of only a few seconds, which becomes practically unacceptable. Examples 6 to 9 Prior to the press lamination process in Examples 2 to 6 above, each side of the fabric was similarly extrusion laminated with pure low density polyethylene (melting point from 260°C) and immediately quenched to form the fabric. Processing to prevent recovery is performed, and the operations in Examples 2 to 6 are repeated for the rest. The thickness of the extrusion laminated fabric is 0.75 mm. The results are shown in the table. From this it can be seen that extrusion laminated samples generally exhibit significantly higher flame rate values than purely press laminated samples.

[Table] Examples 10 to 14 Low-density polyethylene was press-laminated on the fabric, and 2% by weight of carbon black was added on the fabric.
(so that it is black and completely opaque) and otherwise repeating Examples 6 to 9. The results are shown in the table.

[Table] Examples 15 to 16 The operation of Example 10 was repeated using fabrics with two different texture designs (plain weave and satin weave). The results are shown in the table. It can be seen from this that the satin weave article exhibits the highest flame rate.

[Table] Example 17 Using a medium-density polyethylene press laminate forming layer instead of a low-density polyethylene press laminate forming layer,
Otherwise, the operations in Example 15 are repeated. The flame rate was 3.2. Examples 18-20 The operation of Example 10, plus before flame treatment, 0.13
Using a 405 g load with a smooth surface with a sharp knife edge protruding ~0.14 mm, a 5-6 cm length is applied to the outer surface of the fabric by pulling it across the fabric in a direction perpendicular to its direction of recovery. The same operation as in Example 10 was repeated except that scratches were formed. For comparison, ordinary heat-shrinkable sheets used for joints in telecommunications cables were flame treated under similar conditions. This heat-shrinkable sheet is either scratched and not scratched (Example 19) or scratched and scratched (Example 20). The results are shown in the table. from now,
Not only does the scratch-free woven article of the present invention have a higher flame rate than a conventional sheet, but the woven article is also considerably less sensitive to the presence of scratches, whereas a conventional sheet cannot recover when injured.

【table】 [Brief explanation of drawings]

1 to 3 are drawings showing the article of the present invention,
FIG. 1 is a partial sectional perspective view of a first type of article, FIG. 2 is a partial sectional perspective view of a second type of article, and FIG. 3 is a partial sectional view of a third type of article. FIG. 4 is a graph showing the resilience of the article over time. 1... warp fiber, 2... weft fiber, 3... polymer layer.

Claims (1)

[Scope of Claims] 1. At least a portion of a base material comprising a pipe or cable or a joint or seam portion thereof is surrounded by a dimensional heat recoverable article, and the article is heated to recover and engage the portion. (a) the article comprises a knitted fabric having fibers that recover upon heating and have a tensile strength of at least 0.1 MPa at the recovery temperature; the knitted fabric has an outer surface coated with a layer of a polymeric material at least 0.03 mm thick, the polymeric material being softened without flowing upon heating to accommodate recovery of the article; (b) a layer of polymeric material is bonded to the fiber;
and (c) the article is heated by a torch flame directed against the coated surface. 2. The method of claim 1, wherein the polymer layer has a thickness of at least 0.1 mm. 3. A method according to claim 1 or 2, wherein the polymer layer has a thickness not exceeding 2 mm. 4. A method according to any one of claims 1 to 3, wherein the knitted fabric has a layer of polymeric material on each side thereof. 5. The layer of polymeric material on the outer surface of the knitted fabric is
5. A method according to any of claims 1 to 4, comprising an ethylene homopolymer or copolymer having a density not exceeding 0.94 g/cm ^<3> . 6. The method according to any one of claims 1 to 5, wherein the polymer layer is applied to the knitted fabric by extrusion coating, spray coating, dip coating, or sheet lamination. 7. A method according to any of claims 1 to 6, wherein the knitted fabric includes dimensionally thermostable fibers. 8. The method of claim 7, wherein the dimensionally heat-stable fibers are substantially perpendicular to the heat-recoverable fibers. 9. The method according to any one of claims 1 to 8, wherein the knitted fabric is woven in a plain weave, twill weave, broken pattern weave, or satin weave. 10. A method according to any of claims 1 to 9, wherein the layer of polymeric material is substantially stress-free. 11. The method according to any one of claims 1 to 10, wherein the article has a tubular shape. 12. Any one of claims 1 to 10, wherein the article is in the form of a wraparound device having opposing ends extending substantially perpendicular to the direction of recovery of the article and capable of being kept in engagement. Method described. 13 by surrounding at least a portion of a substrate comprising a pipe or cable or a joint or seam portion thereof with a dimensional heat recoverable article and heating the article to recover and engage the portion; A method of environmentally protecting a part, comprising: (a) an article comprising a layer of heat-recoverable fibers and a polymeric matrix material, between the surface of the polymeric material facing heating and the remainder; different degrees of cross-linking are provided; (b) the fibers of the composite are bonded to the polymer matrix material; and (c) the article is heated by a torch flame directed against the outwardly facing surface. A method characterized by: 14. The method of claim 13, wherein the matrix material is crosslinked by radiation irradiation. 15. The method of claim 14, wherein the different degrees of crosslinking result from different beam responses of different regions of the matrix material. 16 A knitted fabric having fibers that recover when heated and has a tensile strength of at least 0.1 MPa at the recovery temperature, the knitted fabric having at least
having an outer surface coated with a layer of polymeric material 0.03 mm thick, which polymeric material is softened without flowing upon heating to accommodate recovery of the article;
A dimensional heat recoverable article for enclosing at least a portion of a substrate. 17. The article of claim 16, wherein the polymer layer has a thickness of at least 0.1 mm. 18. An article according to claim 16 or 17, wherein the polymer layer has a thickness not exceeding 2 mm. 19. An article according to any of claims 16 to 18, wherein the knitted fabric has a layer of polymeric material on each side thereof. 20. Article according to any of claims 16 to 19, wherein the layer of polymeric material on the outer surface of the knitted fabric comprises an ethylene homopolymer or copolymer having a density not exceeding 0.94 g/cm ³ . 21. The article according to any one of claims 16 to 20, wherein the polymer layer is applied to the knitted fabric by extrusion coating, spray coating, dip coating, or sheet lamination. 22. The article according to any one of claims 16 to 21, wherein the heat-recoverable fiber is formed from high-density polyethylene. 23. An article according to any of claims 16 to 22, wherein the knitted fabric includes dimensionally thermostable fibers. 24. The article of claim 23, wherein the dimensionally heat-stable fibers are substantially perpendicular to the heat-recoverable fibers. 25 Claims 16 to 25, wherein the knitted fabric is woven into a plain weave, twill weave, broken pattern weave, or satin weave.
Articles described in any of Item 24. 26. An article according to any of claims 16 to 25, wherein the layer of polymeric material is substantially stress-free. 27. The article according to any one of claims 16 to 26, wherein the article has a tubular shape. 28. Any of claims 16 to 26, wherein the article is in the form of a wrap-around device with opposing ends extending substantially perpendicular to the direction of recovery of the article and capable of being kept in engagement. Items listed. 29 Composite structures comprising layers of heat-recoverable fibers and polymeric matrices, providing different degrees of cross-linking between the surface of the polymeric material facing the heating and the remainder. Heat recoverable articles. 30. An article according to claim 29, wherein the layer on the externally facing surface of the matrix material is crosslinked to a greater extent than the rest. 31. An article according to claim 29 or 30, wherein the different degrees of crosslinking result from different beam responses of different regions of the matrix material.