JP5559561B2 - Resin composition for heat-shrinkable tube, cross-linked tube and heat-shrinkable tube using the same - Google Patents

Description

  The present invention relates to a resin composition as a material of a heat shrinkable tube used as a covering material for an electric wire or a connecting member of an electric device, in particular, a resin composition for a heat shrinkable tube suitable for covering a flat electric wire (blade wire), The present invention also relates to a crosslinked tube and a heat-shrinkable tube using the resin composition.

It is known that a fluorine-based resin containing fluorine in the molecular structure of the resin is excellent in heat resistance, chemical resistance, and electrical characteristics.
Among fluorine-based resins, partially hydrogenated fluororesins such as ETFE resin (tetrafluoroethylene / ethylene copolymer resin) and PVDF resin (vinylidene fluoride resin) are perfluoro such as TFE resin (tetrafluoroethylene resin). Although it is slightly inferior to heat-resistant fluororesin, it can be melt-molded. Therefore, it is widely used as a tube material that covers and protects connection parts such as wires and cable ends and pipes.

  In resin compositions in which polyfunctional monomers such as triallyl isocyanurate and trimethylolpropane trimethacrylate are added to these partially hydrogenated fluororesins, they can be cross-linked by irradiation with electron beams, etc. A heat-shrinkable tube that can prevent melting and deformation, and further shrinks to the original diameter by heating if the tube formed by electron beam irradiation is expanded and fixed in the radial direction after crosslinking. It is also known that can be manufactured (JP-A-5-325692: Patent Document 1).

  In Patent Document 1, in order to solve the problem that a heat-shrinkable tube using an ETFE resin is likely to buckle due to the cross-linked body of the ETFE resin becoming harder than the uncrosslinked body of the ETFE resin, -It has been proposed to use a partially hydrogenated fluororesin having tetrafluoroethylene and fluorinated olefin as repeating units. Specifically, it has been proposed to use NEOFRON EP410 (trade name) and NEOFRON EP620 manufactured by Daikin Industries, Ltd.

  In addition, when a resin composition obtained by adding the above-mentioned polyfunctional monomer to ETFE resin or PVDF resin is crosslinked by electron beam irradiation, the appearance of the heat-shrinkable tube is impaired because it is colored light yellow and light brown compared to before crosslinking. It is also known that there is a problem that the problem occurs (Japanese Patent Laid-Open No. 7-33938: Patent Document 2). In Patent Document 2, it is proposed to suppress coloring by blending a phosphite compound with the composition.

JP-A-5-325692 JP 7-33938 A

When the heat-shrinkable tube is used as a covering material for connecting parts such as electric wires, it is generally required to heat shrink at 230 ° C. or lower so as not to affect the physical properties of the connecting parts.
Moreover, it is calculated | required that it is excellent in transparency so that the mode of the detail of an internal connection part can be confirmed after shrinkage | contraction.

  However, it is generally known that a partially hydrogenated fluororesin represented by ETFE resin has a melting point of 260 ° C. or higher (for example, EP-500 series catalog of NEOFRON (registered trademark) ETFE from Daikin Industries, Ltd., Dyneon (registered trademark) catalog). The EP600 series of NEOFRON (registered trademark) ETFE made by Daikin Industries, Ltd., which is known as a low melting point type ETFE resin, also has a melting point of 218 to 228 ° C. (NEOFRON (registered trademark) ETFE from Daikin Industries, Ltd.) EP-600 catalog).

  When such an ETFE resin is shrunk at 230 ° C. or lower, shrinkage may be insufficient. In recent years, in the aircraft field, flat electric wires in which fine strands are knitted in a net shape have been used. For such flat electric wire covering tubes, it is necessary to use heat-shrinkable tubes whose diameter has been expanded more than twice. There is. However, when the shrinkage is insufficient, it is difficult to make a close coating.

Therefore, in addition to heat resistance, transparency, and buckling resistance, a heat shrinkable tube used as a covering material for a flat wire is required to be able to heat shrink to ½ or less even at 230 ° C. or less.
However, none of the current heat-shrinkable tubes can satisfy all of the above requirements.

  The present invention has been made in view of such circumstances, and an object of the present invention is to thermally shrink at a temperature at which the reliability of the electrical connection component to be coated can be maintained, specifically 230 ° C. or less. It is also possible to provide a heat-shrinkable tube that can maintain transparency even after heat shrinkage and can be applied as a covering material for a flat wire, and a resin composition that is a material for the tube.

The present inventors prepared crosslinkable resin compositions for various fluorocopolymers, and examined the melt moldability and heat shrinkability at 230 ° C. or lower for the prepared compositions.
As a result of investigation, it was found that when applied to the coating of flat wire, a new problem that could not be predicted when applied to the coating of a cylindrical pipe or a thick wire formed by converging multiple pipes was found. It was. Usually, when a flat wire is to be covered with a heat-shrinkable tube, the heat-shrinkable tube 1 is usually heat-treated with the flat wire 2 inserted into the heat-shrinkable tube 1 as shown in FIG. Heat shrink. At this time, as shown in FIG. 2, the film of the tube 1 ′ after contraction may be broken at the edge portion 2 a of the flat wire 2. Further, when some of the strands constituting the flat electric wire 2 have been cut for some reason and are protruding from the blade wire, the protruding strand 3 is heated as shown in FIG. The membrane of the contracted tube 1 'may be broken.

  The present inventors have further studied the problems as shown in FIGS. 2 and 3 that occur when used for covering a flat wire, and as a result, the present invention has been completed.

That heat-shrinkable tube resin composition of the present invention, as a main constituent monomer units, Te tetrafluoroethylene, Hekisafuruo LOP propylene, and a partially hydrogenated fluorocarbon resin containing ethylene; fluorine-based resin having an and polyfunctional monomer It is a composition, The melting point of the said partially hydrogenated fluororesin is 215 degrees C or less, The said polyfunctional monomer is a compound containing an at least 2 allyl group, Comprising: 100 mass parts of said partially hydrogenated fluororesins A tube-shaped molded product (hereinafter referred to as “crosslinked tube”), which is formed by crosslinking 0.3 to 10 parts by mass of a molded product obtained by molding the resin composition into a tube shape by electron beam irradiation, After double diameter expansion at a temperature equal to or higher than the melting point of the partially hydrogenated fluororesin, a temperature equal to or higher than the melting point of the partially hydrogenated fluororesin is applied. 100% modulus in an atmosphere of 230 ° C. tubing samples were heat shrinkage (thickness 0.8mm) is 1.0 kg / cm ² or more.

Also, the cross tube, a film (thickness 0.4 mm) of the tube formed by twice enlarged inner diameter of the crosslinking tube breaks when the piercing needle (diameter 0.3 mm) at a normal temperature atmosphere The piercing load is preferably 20 g or more.

Further, the content of each constituent monomer units in the partially hydrogenated fluorocarbon resin, tetrafluoroethylene 40 to 70 mol%, ethylene 20 to 45 mol%, preferably a Hekisafuruo Lop propylene 10 to 30 mol%. The partially hydrogenated fluororesin further contains 10 mol% or less of a monomer unit represented by CH ₂ ═CF (CF ₂ ) _n H (where n is an integer of 2 to 10). Also good.

Crosslinked tube of the present invention, as a main constituent monomer units, Te tetrafluoroethylene, Hekisafuruo LOP propylene, and a partially hydrogenated fluorocarbon resin containing ethylene; and fluorine-based resin containing a polyfunctional monomer composition into a tube It is formed by extrusion and crosslinking by electron beam irradiation.

  In the heat shrinkable tube of the present invention, the cross-linked tube of the present invention is expanded at least twice the inner diameter of the cross-linked tube. More preferably, the heat-shrinkable tube of the present invention expands at least three times the internal diameter of the cross-linked tube. The tube thickness after diameter expansion is 0.5 mm or less.

  The resin composition for heat-shrinkable tube of the present invention can provide a heat-shrinkable tube that can be melt-molded at a relatively low temperature, retains transparency even after heat shrinkage, and can shrink to a diameter of ½ or less. The heat shrinkable tube of the present invention can also be applied to a wire covering having an edge portion such as a flat wire.

It is a figure for demonstrating the case where a heat contraction tube is applied to the covering of a flat type electric wire. It is a figure for demonstrating the problem at the time of applying a heat contraction tube to the covering of a flat type electric wire. It is a figure for demonstrating the problem at the time of applying a heat contraction tube to the covering of a flat type electric wire.

[Resin composition for heat shrinkable tube]
<Partially hydrogenated fluororesin>
First, the partially hydrogenated fluororesin that is the main component of the resin composition for heat-shrinkable tubes of the present invention will be described.
Partially hydrogenated fluorocarbon resin used in the present invention, as constituent monomer units are those which include at least Hekisafuruo Lop propylene (HFP), tetrafluoroethylene (TFE), and ethylene (Et). Hereinafter, the partially hydrogenated fluororesin used in the present invention is referred to as an HTE copolymer by taking the initials of constituent monomer units.

HTE based copolymer, the constituent monomer (tetrafluoroethylene, Hekisafuruo LOP propylene, and ethylene), and obtained by polymerization in the presence of a polymerization initiator.

The content of the constituent monomer units in the HTE based copolymer of tetrafluoroethylene 40 to 70 mol%, ethylene 20 to 45 mol%, is preferably in the range of Hekisafuru Oro propylene 10 to 30 mol%. The terpolymer having such a ratio can have a melting point of 215 ° C. or lower.

Wherein HTE based copolymer, as a constituent monomer units, tetrafluoroethylene, Hekisafuruo LOP propylene, and in addition to ethylene, the fluorovinyl compound may contain a monomer unit represented further by the following formula.
CH ₂ = CF (CF ₂ ) nH
In formula, n is an integer of 2-10, Preferably it is 2-5. It is preferable that the content rate of this fluorovinyl compound structural unit shall be 0-10 mol% per HTE-type copolymer.

Further, as long as the object of the present invention is not impaired, 1,1-dihydroperfluoropropene-1, 1,1-dihydroperfluorobutene-1, hexafluoro as a constituent monomer unit of the HTE copolymer. Fluorinated olefins such as propene and 3,3,3-trifluoropropene; perfluoroalkyl vinyl ether; CH ₂ ═CF (CF ₂ ) x (CH ₂ ) y OH (wherein x is 0 to 2, y is 1 to 3 A hydroxy-containing fluorinated olefin represented by an integer) may be copolymerized.

  The HTE copolymer used in the present invention has the monomer composition as described above, preferably has a melting point of 215 ° C. or lower, and has a melt index (MI) of 3 to 50 (g) at 265 ° C. and a load of 5 kg. / 10 min).

  Specific examples of HTE copolymers that satisfy the above requirements include 3M Group Dyneon HTE1510 (melting point 160 ° C., MI = 10, 265 ° C. × 5 kg), HTE 1705 (melting point 210 ° C., MI = 4, 265 ° C. × 5 kg), Daikin NEOFLON RP4020 (melting point 160 ° C., MI = 25-50, 265 ° C. × 5 kg), NEOFLON RP4040 (melting point 160 ° C., MI = 3-8, 265 ° C. × 5 kg), NEOFLON RP5000 (melting point 195 ° C., MI = 20-30, 265 ° C. × 5 kg).

  Thus, by mainly using an HTE copolymer having a melting point of 215 ° C. or less, the crosslinked product of the resin composition can be thermally shrunk at 230 ° C. or less, and the reliability of the parts to be coated, particularly 230 ° C. It becomes possible to use as a material of the heat-shrinkable tube used for coating | covering the electric wire etc. containing the components which cannot be exposed to the above high temperature.

<Multifunctional monomer>
As the polyfunctional monomer used in the present invention, various compounds having two or more carbon-carbon unsaturated bonds in the molecule can be used. For example, triallyl cyanurate, triallyl isocyanurate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolpropane tetraacrylate and the like can be mentioned. Of these, compounds having two or more allyl groups in the molecule are preferred, more preferably triallyl cyanurate, diallyl monoglycidyl isocyanurate, diallyl isocyanurate, diallylbenzyl isocyanurate, diallylcarboxymethyl isocyanurate and the like. Two or more allyl group-containing cyanurates.

  The polyfunctional monomer can function as a crosslinking aid in crosslinking by ionizing radiation irradiation described later.

What is necessary is just to select the kind and compounding quantity of a multifunctional monomer according to the kind of HTE-type copolymer so that the following physical properties may be satisfied about the prepared resin composition. The physical properties are a tube-shaped product (cross-linked tube) obtained by crosslinking a molded product obtained by molding the prepared resin composition into a tube shape by electron beam irradiation, and an HTE copolymer as a main component of the composition. The tube sample film (film thickness: 0.8 mm), which has been subjected to heat shrinkage by expanding the diameter twice at a temperature equal to or higher than the melting point, and further subjected to a temperature equal to or higher than the melting point of the HTE copolymer, is pulled in a 230 ° C. atmosphere. The 100% modulus when tested is 1.0 kg / cm ² or more.

Specifically, it is preferable to mix | blend in the ratio of 0.3-10 mass parts per 100 mass parts of HTE-type copolymers, More preferably, it is 0.4-10 mass parts.
If it is less than 0.3 part by mass, the continuous usable temperature is less than 200 ° C., and high heat resistance cannot be obtained. Moreover, since sufficient crosslinking is not performed, it is surmised that the effect of improving the strength by crosslinking is insufficient. However, problems such as those shown in FIGS. Become. On the other hand, when the compounding amount of the multi-functional monomer exceeds 10 parts by mass, the crosslinking becomes excessive and the rigidity becomes too high. Therefore, even if the obtained crosslinked product can expand twice, it is difficult to expand three times. It becomes.

<Preparation of resin composition>
The resin composition for heat-shrinkable tube of the present invention contains an HTE copolymer and a polyfunctional monomer, and is formed by crosslinking a molded product obtained by molding the prepared resin composition into a tube shape by electron beam irradiation. The tube-shaped molded article (crosslinked tube) is expanded by a factor of 2 at a temperature equal to or higher than the melting point of the HTE copolymer that is the main component of the composition, and then the temperature equal to or higher than the melting point of the HTE copolymer. The 100% modulus of the tube sample film (film thickness 0.8 mm) subjected to thermal shrinkage over a tensile test in an atmosphere at 230 ° C. is 1.0 kg / cm ² or more.

  The resin composition for heat-shrinkable tubes of the present invention can be prepared by blending an HTE copolymer and a polyfunctional monomer at a predetermined ratio. In addition to the HTE copolymer and the polyfunctional monomer, other fluorine resins may be added and mixed within a range not impairing the object of the present invention.

Examples of other fluorine resins include partially hydrogenated fluorine resins other than HTE copolymers, perfluoro fluorine resins, and fluorine resin elastomers.
Specifically, fluoroelastomers such as vinylidene fluoride-hexafluoropentene binary copolymer elastomer, vinylidene fluoride-hexafluoropentene-tetrafluoroethylene terpolymer elastomer, tetrafluoroethylene-propylene binary copolymer elastomer, etc. You may blend, Furthermore, you may blend the polymer which grafted these fluoroelastomers with the ETFE type fluoropolymer and the PVDF type fluoropolymer. When these other fluorine-based resins are contained, it is necessary to satisfy the above-described characteristics for the 100% modulus of the crosslinked film, and therefore, the content is preferably 40% by mass or less of the polymer component.

  In addition, when transparency is not so required, inorganic accelerators such as vulcanization accelerators such as zinc oxide (zinc white), magnesium oxide, calcium hydroxide, etc. have an effect of suppressing the generation of hydrofluoric acid that corrodes the conductor. You may mix | blend an acid acceptor.

  In addition to the above components, additives such as inorganic fillers such as silica, talc, and clay, lubricants, antioxidants, and plasticizers may be contained as necessary.

  The method for preparing the resin composition is not particularly limited, but the above components are mixed and mixed using a known mixing device such as an open roll mixer, a Banbury mixer, a pressure kneader, a single screw mixer, a two screw mixer or the like. Can be prepared. A twin-screw mixer is preferable.

  The resin composition for heat-shrinkable tubes of the present invention may be blended by means of kneading or the like and subjected to various moldings as it is, or may be used for various moldings after being processed into molding powder such as pellets. When using the resin composition of this invention for manufacture of a heat contraction tube, you may pelletize using a pelletizer etc., and a strand cutter, a fan cutter, etc. may be utilized.

  The resin composition for heat-shrinkable tube of the present invention can be molded by known molding means, melt extrusion molding, extrusion molding, injection molding, press molding or the like. The molding method is not particularly limited, but has a feature that it can be melt-molded at 230 ° C. or lower.

  The resin composition of the present invention having the above characteristics can expand the diameter of a cross-linked tube obtained by cross-linking a tubular molded product to 2 times, preferably 3 times or more. Furthermore, heat shrinkage is possible at 230 ° C. or less. Furthermore, it has excellent transparency even after crosslinking.

  The resin composition for heat-shrinkable tube of the present invention is preferably formed by expanding the diameter of a tube (crosslinked tube) obtained by crosslinking a molded product obtained by molding the resin composition into a tube shape by electron beam irradiation. The piercing load that breaks when the film (film thickness 0.4 mm) of the heat shrinkable tube is pierced with a needle (diameter 0.3 mm) in a room temperature atmosphere is 20 g or more.

  Here, the electron beam irradiation for crosslinking is appropriately selected depending on the specific composition of the resin composition, the film thickness of the molded body, etc., but usually the acceleration voltage is in the range of 1 to 5 MeV and the irradiation dose is 30 to 500 kGy. Is appropriately selected.

  The piercing load is measured using a thermomechanical analyzer (TMA). A push needle with a diameter of 0.3 mm is attached to this TMA, and the needle is pushed into the film at room temperature (25 ° C.) at a push speed of 5 g / min, resulting in a film thickness residual rate of 0% (penetration state). The load of time.

[Tube-shaped molded product (cross-linked tube)]
The crosslinked tube of the present invention is obtained by molding the above resin composition of the present invention into a tube shape and then crosslinking by electron beam irradiation.

The tube can be molded by known molding means, extrusion coating, extrusion molding, injection molding, press molding, or the like, and melt extrusion molding is preferably used.
The type of the extruder is not particularly limited, and any of a screw type and a non-screw type may be used, but a screw type is preferable.

  In the case of melt extrusion molding, the extrusion temperature is not particularly limited, but usually a temperature that is about 10 to 50 ° C. higher than the melting point of the partially hydrogenated fluorine copolymer contained in the resin composition that is a molding material is selected.

  The wall thickness of the tube film of the cross-linked tube of the present invention is preferably 0.01 to 0.5 mm. Usually, as the thickness of the tube film increases, it becomes easier to satisfy the puncture resistance. However, as the thickness increases, the flexibility decreases and the transparency also decreases. Since the resin composition of the present invention is excellent in mechanical strength at high temperatures, particularly puncture resistance, it can be used even when the film thickness after expansion is about 0.01 to 0.5 mm. Satisfying the puncture resistance even with this thickness is advantageous from the viewpoint of flexibility and transparency.

  Examples of electron beams used for electron beam irradiation crosslinking include accelerated electron beams, γ rays, X rays, α rays, and ultraviolet rays. Accelerated electron beams are most preferably used from the viewpoint of industrial use, such as ease of use of the radiation source, transmission thickness of ionizing radiation, and speed of crosslinking treatment.

  What is necessary is just to set the acceleration voltage of an acceleration electron beam suitably with the thickness of the tube film of a bridge | crosslinking tube. For example, in a tube having a thickness of 50 μm to 200 μm, the acceleration voltage is selected between 1 and 5 MeV. The irradiation dose is not particularly limited, but a sufficient degree of crosslinking can be obtained at 30 to 500 kGy.

  The electron beam irradiation is preferably performed in low oxygen and in the absence of oxygen. In the presence of oxygen, the decomposition of the fluororesin precedes the crosslinking reaction.

[Heat shrink tube]
The heat-shrinkable tube of the present invention is obtained by cooling and fixing the above-described crosslinked tube of the present invention.

The diameter of the cross-linked tube is expanded by a method such as introducing compressed air into the tube while being heated to a temperature equal to or higher than the melting point of the HTE copolymer that is the main component of the resin composition that is the material of the tube. be able to.
The diameter expansion and expansion are 2 times or more, preferably 3 times or more. When used for covering a flat electric wire, in order to stably insert a flat electric wire which is generally circulated, it is preferably about three times as large.

  When the diameter is expanded to a predetermined inner diameter and then cooled to fix the expanded diameter shape, a heat shrinkable tube is obtained. Although the cooling method is not particularly limited, it can be performed by leaving the tube under water cooling, cooling air, etc., preferably water cooling.

  The heat-shrinkable tube of the present invention is a tubular molded product in which the expanded state (expanded state) is fixed as described above. The heat-shrinkable tube is contracted to the original size by heating again to the melting point of the partially hydrogenated fluorocopolymer that is the main component of the composition.

  The heat-shrinkable tube of the present invention formed as described above is excellent in heat resistance and transparency, and is further excellent in mechanical strength at high temperatures, particularly puncture resistance. Therefore, it is suitable for covering a wire that requires flexibility such as a connection part or an electric wire that requires confirmation of the internal structure. Furthermore, since it has excellent puncture resistance, it is also suitable as a covering tube for electric wires formed by converging and knitting flat wire covering materials, metal wires, and fine wires that may hit the tip. Available.

  In order to achieve close contact coating with a heat-shrinkable tube, heat shrinkage may be performed in a state where solder or the like is interposed between the heat-shrinkable tube and a connecting part such as an electric wire inserted into the tube.

  The form for implementing this invention is demonstrated by an Example. The following examples are not intended to limit the scope of the invention.

[Measurement and evaluation method]
(1) Tensile properties (MPa)
(1-1) Initial stage After the resin composition is extruded into a tube shape, it is crosslinked by electron beam irradiation to produce a tubular molded product (crosslinked tube), and then this crosslinked tube has an inner diameter at the time of extrusion molding. A heat-shrinkable tube having a diameter expanded twice was produced. A sample for measurement was obtained by heating the heat-shrinkable tube to a temperature equal to or higher than the melting point of the fluororesin that is a main component of the composition. Using this measurement sample, tensile strength (MPa) and elongation at break (%) were measured in accordance with the test method of Section 3 “Tensile Test” of JIS K6301 “Physical Test Method for Vulcanized Rubber”.

(1-2) After leaving at 250 ° C. for 7 days After leaving the measurement sample prepared in (1-1) in a gear oven at 250 ° C. for 168 hours (7 days), the same as in (1-1) , Tensile strength (MPa) and elongation at break (%) were measured. Those having a tensile strength after heat aging of 8.2 MPa or more and an elongation at break after aging of 200% or more were judged to be insufficient in heat resistance.

(2) 100% modulus at high temperature (kg / cm ² )
The measurement sample prepared in (1-1) was left in a thermostat set at 230 ° C. for 3 minutes, then taken out and subjected to a tensile test at a tensile speed of 50 mm / min, and a 100% modulus was measured.

(3) Puncture strength (g)
The cross-linked tube prepared in (1-1) was expanded to twice the inner diameter of the tube at the time of extrusion molding to prepare a heat-shrinkable tube. The puncture strength of this heat shrinkable tube was measured.
The piercing load was measured using a thermomechanical analyzer (TMA). A push needle with a diameter of 0.3 mm is attached to this TMA, and the needle is pushed into the tube film at room temperature (25 ° C.) at a push speed of 5 g / min. The load (g) when

(4) Coverability Twist six tin-plated annealed copper wires with an outer diameter of 0.15 mm, twist another 16 strands, and use a flat conductor (flat conductor with a major axis of 4 mm x minor axis of 0.8 mm). Then, the covering property was examined. This flat conductor corresponds to a blade wire actually used for aircraft applications.
The flat conductor was inserted into the produced heat-shrinkable tube (length: 100 mm) as shown in FIG. 1, and heat-shrinked by leaving it in a thermostat set at 230 ° C. for 3 minutes. The heat shrinkable tube shrinks so as to cover the flat conductor. At this time, it was visually observed whether or not the heat-shrinkable tube was damaged at the edge portion of the flat conductor (see FIG. 2) and whether the heat-shrinkable tube was broken and the conductor wire was exposed (see FIG. 3). .
The above test was carried out on 10 heat-shrinkable tubes of 3 times expansion produced using each composition, and when one or more edge breaks or exposure of the strands was recognized among 10 pieces, ). When no edge breakage or wire exposure was observed, it was judged as good (◯).

(5) Transparency About the cross-linked tube, the average transmittance of light having a wavelength of 400 to 800 nm was measured using a spectrophotometer. Those showing an average transmittance of 75% or more satisfy the transparency. Below 60%, yellowing was observed.

(6) Thermal expansibility With one end of the cross-linking tube closed and a compressed air pipe connected to the other end, put in a thermostat set to the melt molding temperature of each resin composition, and send compressed air from the pipe, The tube was expanded twice, and further expanded three times (outer diameter 7.5 mm). It was observed whether the tube was cracked during the 2-fold expansion and 3-fold expansion. The case where no crack was observed was indicated as “◯”.

(7) Heat-shrinkability An aluminum rod having an outer diameter of 5 mm was inserted into a heat-shrinkable tube produced by three-fold expansion, and left in a thermostat set at 230 ° C. for 3 minutes to cause heat shrinkage. Then, it took out and visually observed the contact | adherence state of the aluminum rod of a heat-shrinkable tube, and evaluated heat-shrinkability. Those that were in close contact with the aluminum rod had good heat shrinkability, and those that did not heat shrink or those that did heat shrink but did not adhere to the aluminum rod were defined as poor heat shrinkability (x).

[Preparation of resin composition and production and evaluation of shrinkable tube]
Various fluorine-based copolymers (3 types of HTE copolymers with different melting points, 3 types of THV-based copolymers, polyvinylidene fluoride (PVDF), ETFE resin) and multi-functional monomers (triallyl isocyanurate (TAIC) ) Or trimethylolpropane trimethacrylate (TMPM)) in a mass proportion mass shown in the table below, and melted and kneaded using a biaxial mixer set at 180 ° C. (240 ° C. when using HTE 1705) Thus, a resin composition was prepared.

  The prepared resin composition was pelletized using a pelletizer. The obtained pellets are extruded into a tube shape using a single-screw melt extruder (diameter 30 mm, L / D = 24), and then crosslinked by irradiating with an acceleration voltage of 2 MeV and an electron beam at the dose shown in the table. As a result, a cross-linked tube having an inner diameter of 2.5 mm and a wall thickness of 0.8 mm was obtained. The extrusion molding temperature is 180 ° C. when using HTE copolymers 1 and 3, 240 ° C. when using HTE copolymer 2, THV copolymer, PVDF copolymer or ETFE copolymer. When a polymer is used, the temperature is 30 ° C. higher than the melting point of each copolymer.

  With one end of the resulting cross-linked tube closed and a compressed air pipe connected to the other end, put in a thermostatic bath set to the melt extrusion temperature of each resin composition, send compressed air from the pipe, After expanding the diameter to 2 times expansion (outer diameter 5 mm) and 3 times expansion (outside diameter 7.5 mm), the heat shrinkable tube was produced by immediately removing from the thermostat and water cooling.

Based on the above evaluation methods, the prepared crosslinked tube and heat-shrinkable tube were evaluated for pin puncture strength, tensile properties, coverage, 100% modulus, transparency, expansibility, and heat-shrinkability. In addition, about thermal expansibility, it evaluated by observing at the time of the expansion process performed at the time of heat shrinkable tube preparation.
Composition No. using an HTE copolymer as the fluorine-based polymer was used. The compositions and evaluation results of Nos. 1 to 10 are shown in Table 1. Table 2 shows the compositions of 11 to 18 and the evaluation results.

In addition, the fluorine-type copolymer in a table | surface is as follows.
HTE1: HTE1510 manufactured by Dynane of 3M group (melting point 160 ° C., MI 10 (265 ° C. × 5 kg))
HTE2: 3M Group Dyneon HTE1705 (melting point 210 ° C, MI 4 (265 ° C x 5 kg))
NTEFLON RP4020 manufactured by HITE3: Daikin (melting point: 160 ° C., MI: 25-50 (265 ° C. × 5 kg))
THV1: THV220 manufactured by Dyneon of 3M group (VdF (vinylidene fluoride), TFE (tetrafluoroethylene), HFP (propylene hexafluoride) terpolymer, melting point 120 ° C.))
THV2: THV610 manufactured by Dynane of 3M group (VdF (vinylidene fluoride), TFE (tetrafluoroethylene), HFP (propylene hexafluoride) terpolymer, melting point 185 ° C.))
THV3: THV815 manufactured by Dyneon of 3M Group (VdF (vinylidene fluoride), TFE (tetrafluoroethylene), HFP (propylene hexafluoride) terpolymer, melting point 225 ° C.))
PVDF: Arkema Kyner 2800 (a binary copolymer of VdF (vinylidene fluoride) and TFE (tetrafluoroethylene), melting point 145 ° C.)
ETFE: ET6235 manufactured by Dynane of 3M group, melting point 267 ° C, MI 10 (297 ° C x 5kg)
The numerical value in the parenthesis of the polymer in the table indicates the melting point of the resin.

No. 1 to 7 are resin compositions using an HTE copolymer as a partially hydrogenated fluororesin. By adjusting the blending amount of the polyfunctional monomer to an appropriate amount, the 100% modulus at 230 ° C. is 1.0 kg / cm ² or more for the tube after the diameter of the crosslinked tube is doubled and then thermally contracted. Yes, it corresponds to an embodiment of the present invention. The initial tensile properties were maintained even after the heat aging test, and the expandability, heat shrinkability, and transparency were satisfied. Furthermore, in the state of the heat-shrinkable tube formed by expanding the diameter of the crosslinked tube twice, the puncture strength is 20 g or more. Therefore, the covering property could also be satisfied.

No. 8 is a resin composition using an HTE copolymer as a partially hydrogenated fluororesin, but the 100% modulus at 230 ° C. of the tube sample heat-shrinked after diameter expansion is 1.0 kg / cm ^2. Was less than. This is probably because the degree of cross-linking became insufficient due to the low content of the polyfunctional monomer. When the crosslinking was insufficient, the heat shrinkable tube film obtained by expanding the diameter could not satisfy the puncture strength, and thus could not satisfy the covering property. On the other hand, when the content of the polyfunctional monomer is increased (No. 9), the heat-shrinkable tube after heat-expanding satisfies the 100% modulus at high temperature and expands the diameter of the heat-shrinkable tube film. Was able to satisfy the puncture resistance. However, since it has high rigidity, it can be applied to double expansion, but cannot be applied to a flat wire that requires triple expansion.

  No. No. 10 did not contain a polyfunctional monomer, so it was not crosslinked even when irradiated with an electron beam. That is, the crosslinked tube itself could not be produced. And it fuse | melted by the heat aging test heated more than melting | fusing point of a polymer. For this reason, it was not possible to evaluate 100% modulus, expansibility, and heat shrinkability at a high temperature that requires heat treatment above the melting point. No coating test was performed.

  No. 11 is a case where an ETFE resin is used as the partially hydrogenated fluororesin. Since the melting point is high, it was possible to expand two times or three times at 290 ° C., which is equal to or higher than the melting point, but it was not possible to shrink at 230 ° C., which is required by the user from the viewpoint of maintaining the quality of the wire. In addition, since the heat shrink coating by heating at 230 ° C. could not be performed, the coating property was not evaluated.

  No. 15 and 16 are cases in which a THV fluororesin having a melting point of 230 ° C. or lower is used as the partially hydrogenated fluororesin. All melted in a heat aging test in which heating was performed at a temperature higher than the melting point, despite the presence of polyfunctional monomers. Even in the presence of a polyfunctional monomer, it is considered that crosslinking by electron beam irradiation could not be performed sufficiently. Therefore, it was not possible to evaluate 100% modulus, expansibility, and heat shrinkability at a high temperature that requires heat treatment above the melting point. No coating test was performed.

  No. 17 is a case where PVDF having a melting point of 210 ° C. or lower is used as the partially hydrogenated fluororesin. Despite the coexistence of polyfunctional monomers, it melted in a heat aging test in which it was heated above its melting point. Even in the presence of a polyfunctional monomer, it is considered that crosslinking by electron beam irradiation could not be performed sufficiently. For this reason, it was not possible to evaluate 100% modulus, expansibility, and heat shrinkability at a high temperature that requires heat treatment above the melting point. No coating test was performed.

  No. It can be seen from 15-17 that a partially hydrogenated fluororesin having a melting point of 230 ° C. or lower may not be sufficiently crosslinked by electron beam irradiation even in the presence of a polyfunctional monomer.

  No. 18 is the case where the content of polyfunctional monomer is increased by using PVDF. No. No. 18 did not melt in the heat aging test, probably because the degree of crosslinking increased. Furthermore, the covering property could be satisfied. However, it could expand twice, but could not expand three times.

No. 12-14 is a composition using a THV resin having a melting point of 210 ° C. or lower as the partially hydrogenated fluororesin. The 100% modulus at 230 ° C. was 1.0 kg / cm ² or more, and there was no problem in the initial tensile properties and further the tensile properties after the heat aging test. Moreover, it was able to expand three times and heat-shrink at 230 ° C. or less. However, for the heat-shrinkable tube obtained by expanding the diameter of the crosslinked tube, the puncture strength of the tube film was less than 20 g, so that the covering property could not be satisfied. Regarding the covering property, properties other than the tensile strength at high temperature have an influence, and it is considered that the constitution of the fluororesin is involved. In addition, No. In No. 14, the content of the polyfunctional monomer is No. 14. This is the case when compared with 12 and 13, and it seems that the degree of cross-linking was increased, but the rigidity increased, and as a result, cracking occurred when attempting to expand three times. Heat shrinkability was not evaluated.

  The resin composition for heat-shrinkable tube of the present invention can be melt-molded at a relatively low temperature, has excellent mechanical strength at a high temperature, and maintains transparency. It can be used as a heat shrinkable tube material for covering electric wires and electrical equipment parts that can only be shrunk by heat treatment at 230 ° C. or lower, and a heat shrinkable tube.

Claims (7)

As a main constituent monomer units, Te tetrafluoroethylene, Hekisafuruo LOP propylene, and a partially hydrogenated fluorocarbon resin comprising ethylene; a composition of a fluorine-based resin containing, as well as multi-functional monomer,
The melting point of the partially hydrogenated fluororesin is 215 ° C. or less,
The polyfunctional monomer is a compound containing at least two allyl groups, and is contained in an amount of 0.3 to 10 parts by mass per 100 parts by mass of the partially hydrogenated fluororesin,
A tube-shaped product obtained by crosslinking a molded product of the resin composition into a tube shape by electron beam irradiation (hereinafter referred to as “crosslinked tube”) is doubled at a temperature equal to or higher than the melting point of the partially hydrogenated fluororesin. After expanding the diameter, the 100% modulus in a 230 ° C. atmosphere of a tube sample (film thickness 0.8 mm) which is further thermally contracted by applying a temperature higher than the melting point of the partially hydrogenated fluororesin is 1.0 kg / cm 2 or more. A resin composition for a heat-shrinkable tube. There is a piercing load that breaks when the needle (diameter 0.3 mm) is pierced into a tube film (thickness 0.4 mm) obtained by expanding the cross-linked tube twice the inner diameter of the cross-linked tube under a normal temperature atmosphere. The resin composition for heat-shrinkable tubes according to claim 1, wherein the resin composition is 20 g or more. The content of the constituent monomer units in the partially hydrogenated fluorocarbon resin, tetrafluoroethylene 40 to 70 mol%, ethylene 20 to 45 mol%, according to claim 1 or 2 which is Hekisafuruo Lop propylene 10 to 30 mol% Resin composition for heat shrinkable tube. The partially hydrogenated fluororesin further contains 10 mol% or less of a monomer unit represented by CH ₂ ═CF (CF ₂ ) _n H (wherein n is an integer of 2 to 10 ). The resin composition for heat-shrinkable tubes according to any one of 1 to 3 . Crosslinked and extruded compositions of fluorine-based resin containing a polyfunctional monomer into a tube, by electron beam irradiation; as a main constituent monomer units, Te tetrafluoroethylene, Hekisafuruo LOP propylene, and a partially hydrogenated fluorocarbon resins including ethylene A cross-linked tube. A heat-shrinkable tube in which the cross-linked tube according to claim 5 is expanded at least twice the inner diameter of the cross-linked tube. A heat-shrinkable tube, wherein the cross-linked tube according to claim 6 is expanded by at least three times the inner diameter of the cross-linked tube, and the tube film thickness after expansion is 0.5 mm or less.

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