JPH06345910A - Flame-retardant resin composition and heat-shrinkable tube - Google Patents

Abstract

PURPOSE:To obtain a heat-shrinkable tube for wiring having strengths and flame retardance meeting the requirements of UL specifications by producing the tubing from a resin compsn. comprising a carboxylated ethylene polymer, a metal hydroxide, and a specific organosilicon compd. CONSTITUTION:This flame-retardant resin compsn. is obtd. by compounding an ethylene polymer having repeating carboxylated monomer units, a metal hydroxide, and an organosilicon compd. of the formula (wherein X<1>, X<2>, and X<3> are each alkoxy, alkyl, or halogen provided at least one of them is alkoxy). A heat-shrinkable tube is produced by forming this compsn. into a tubing, irradiating it with an ionizing radiation, and expanding and fixing its diameter. A pref. ethylene polymer is an ethylene/vinyl acetate/acrylic acid copolymer. An example of the metal hydroxide is aluminum hydroxide pref. with a particle size of about 0.5-2.0 amum. gamma-Aminopropyltrimethoxysilane is an example of the organosilicon compd. The heat-shrinkable tubing has flame retardance and strengths meeting the requirements for wiring protection in an electronic apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant resin composition which produces little toxic gas during combustion, is excellent in mechanical strength, and is excellent in stretchability, and a heat-recoverable article made therefrom.

[0002]

2. Description of the Related Art Various heat-recoverable articles such as heat-shrinkable tubes for terminal treatment of wires and cables used for internal wiring of electronic equipment such as televisions, video equipment, office automation equipment, computers and insulation and protection of connection parts. Is used.

In general, a heat-shrinkable tube is formed by molding a thermoplastic resin such as polyethylene into a tube shape by a method such as melt extrusion, and cross-linking it by a method such as irradiating with ionizing radiation to impart shape memory property and under heating. It is manufactured by expanding the diameter of the tube by a method such as sending compressed air to the inside of the tube and then cooling and fixing the shape.

Various characteristics such as flame retardancy, mechanical strength, heat aging resistance, and heat deformation resistance are required for heat shrinkable tubes used inside electronic equipment. For example, UL (Under)
writers Laboratories In
c. ) Each standard has specific requirements.

Regarding the flame retardancy, the device shown in FIG.
The contracted product of the heat-shrinkable tube is vertically supported by a metal wire such as a nichrome wire, or the heat-shrinked sample is supported vertically around the metal rod, and the burner flame is ignited at an angle of 20 ° for 15 seconds. When repeated 5 times, the fire is extinguished within 60 seconds, and the kraft paper attached to the upper part and the absorbent cotton laid on the lower part are evaluated by a vertical combustion test to check that they do not burn by falling objects.

As a method of flame-retarding a thermoplastic resin such as polyethylene, a halogen-based flame retardant containing a bromine atom or a chlorine atom, a phosphorus-based flame retardant, or a metal hydroxide-based flame retardant is blended. The general method is

However, a resin composition flame-retarded by adding a halogen-based flame retardant causes a problem that corrosive harmful gas such as hydrogen halide is generated at the time of combustion. There are problems such as acute toxicity. Therefore,
Various practical studies have been conducted on so-called non-halogen flame-retardant resin compositions using metal hydroxide flame retardants and electric wires, cables, and heat-recoverable articles using the same.

[0008]

However, when a flame retardant is obtained by adding a metal hydrate flame retardant such as aluminum hydroxide or magnesium hydroxide to a thermoplastic resin such as polyethylene, the metal hydrate flame retardant Since the flame retardant has a smaller flame retarding effect than halogen-based flame retardants and phosphorus-based flame retardants, it is necessary to add a large amount of it, so that the mechanical strength such as tensile strength of the resin composition is significantly reduced. There is a problem that ends up.

For example, when trying to obtain a heat-shrinkable tube that passes the UL standard vertical combustion test, it cannot be said unequivocally depending on the size and wall thickness of the tube, but with respect to 100 parts by weight of a thermoplastic resin such as polyethylene, About 150 parts by weight or more of a metal hydrate flame retardant such as aluminum hydroxide or magnesium hydroxide needs to be blended.

However, in the UL standard, a heat-shrinkable tube based on a polyolefin resin such as polyethylene usually has an initial tensile strength (breaking tensile strength) of 1.05 kg.
/ Mm ² or more is required, and a resin composition containing a large amount of the metal hydrate-based flame retardant as described above cannot often meet the required value.

In order to solve the above-mentioned problem of deterioration of mechanical strength, the present inventor has proposed a thermoplastic resin such as polyethylene with aluminum hydroxide or magnesium hydroxide as proposed in Japanese Patent Application No. 3-113832. A metal hydrate flame retardant and an organosilicon compound having a (meth) acryl group (corresponding to an organosilicon compound in which R is an alkyl group having a (meth) acryl group in the general formula (1) of the present application) were blended. If it is a flame-retardant resin composition and the resin composition is irradiated with ionizing radiation such as an accelerated electron beam, flame retardance that passes the vertical combustion test in UL standard can be achieved, and the initial tensile strength can be increased. It has also been found that the breaking strength (breaking tensile strength) can satisfy 1.05 kg / mm ² or more required by the UL standard.

Then, when this flame-retardant resin composition is molded into, for example, a tube shape and irradiated with an accelerated electron beam,
A halogen-free flame-retardant tube that passes the UL standard vertical combustion test and has an initial tensile strength of 1.05 kg / mm ² or more is obtained.

However, even if an attempt is made to expand the diameter of this tube by sending compressed air to the inside of the tube at high temperature to make it a heat-shrinkable tube, since this tube has a small elongation at high temperature, it does not expand. There was a problem that could not be diameter. For heat shrink tubes, the expansion ratio (=
The inner diameter before shrinkage / inner diameter after shrinkage) is often required to be 2 or more. However, in the case of a tube using the above resin composition, even if the conditions of the diameter expansion process such as temperature conditions are changed, the expansion ratio It was very difficult to change to 2.

A heat-shrinkable tube which has passed the UL standard vertical combustion test, has an initial tensile strength of 1.05 kg / mm ² or more, and does not contain a halogen-based flame retardant or a phosphorus-based flame retardant is known. Therefore, the development of such a heat-shrinkable tube has been desired.

[0015]

Means for Solving the Problems As a result of intensive studies on the above problems, the present invention shows that an ethylene polymer having a carboxylic acid group as a repeating unit is represented by a metal hydroxide and a general formula (1). In the case of a resin composition containing an organic alkene compound, for example, when the resin composition is molded into a tube and irradiated with ionizing radiation such as an accelerated electron beam, the initial tensile strength is 1.05 kg. / Mm ² or more and a diameter expansion ratio of 2 or more, it has been found that a so-called halogen-free flame-retardant heat-shrinkable tube containing no halogen-based flame retardant, phosphorus-based flame retardant, etc. can be obtained, and based on such findings The present invention has been completed.

That is, the present invention: A flame-retardant resin obtained by mixing an ethylene polymer having a carboxylic acid group as a repeating unit with a metal hydroxide and an organosilicon compound represented by the following general formula (1). A composition is provided. Also,

[Chemical 2]

(Here, R is an alkyl group having at least one amino group, and X ¹ , X ² , and X ³ are atomic groups selected from the group consisting of an alkoxyl group, an alkyl group, and a halogen group. , X ¹ , X ² , X ³ of at least 1
Represents an alkoxyl group. ) Another feature is that an ethylene-based polymer having a carboxylic acid group as a repeating unit is mixed with a metal hydroxide surface-treated in advance with an organosilicon compound represented by the general formula (1). Further, there is provided a heat-shrinkable tube in which the tubular molded product of the flame-retardant resin composition is irradiated with ionizing radiation and then expanded in diameter and fixed.

The present invention will be specifically described below. The ethylene-based polymer having a carboxylic acid group as a repeating unit in the present invention, the first monomer component is ethylene, the second monomer component is an unsaturated carboxylic acid such as acrylic acid or methacrylic acid A certain binary copolymer; the first monomer component is ethylene, the second monomer component is vinyl acetate, acrylic acid ester such as ethyl acrylate, methacrylic acid ester such as methyl methacrylate, etc. Examples of so-called α-olefins include terpolymers or multicomponent copolymers in which the third monomer component is an unsaturated carboxylic acid such as acrylic acid or methacrylic acid. Among these, ethylene-vinyl acetate-acrylic acid copolymer and ethylene-vinyl acetate-methacrylic acid copolymer are preferable from the viewpoint of flame retardancy and the like.

Examples of the metal hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide and their complex salts. The amount of the metal hydroxide compounded is an ethylene polymer 1 having a carboxylic acid group as a repeating unit.
The amount may be approximately 100 to 250 parts by weight, preferably 125 to 225 parts by weight, relative to 00 parts by weight.

The particle size of the metal hydroxide is about 0.3 to 3 μm, preferably 0.5 to 2.0 μm.
In, 3~30m ² / g approximately the BET specific surface area, preferably those set 5 to 20 m ² / g is preferred from the viewpoint of extrusion of the case of the kneading resistance and resin composition and the resin.

As the organosilicon compound of the general formula (1), γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N-
Examples include (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane and p- [N-2-aminoethyl) aminomethyl] phenethyltrimethoxysilane.

The mixing ratio of the organosilicon compound is not necessarily limited, but is 0.1 to 10 parts by weight, preferably 0.1% by weight based on 100 parts by weight of the ethylene polymer having a carboxylic acid group as a repeating unit. It is preferable to mix it in the range of 5 to 5 parts by weight from the viewpoint of initial tensile strength and fixability for expanding the diameter in the case of a heat-shrinkable tube.

The resin composition of the present invention is produced by using an ethylene polymer having a carboxylic acid group as a repeating unit, a metal oxide, and an organosilicon compound represented by the general formula (1) in an open roll mixer, a Banbury mixer, and a pressure machine. It is also possible to collectively mix under heating with a known mixing device such as a kneader, a Henschel mixer, a single-screw mixer or a twin-screw mixer, or a metal hydroxide can be previously mixed with the organosilicon compound of the general formula (1). The surface-treated product can be kneaded with an ethylene polymer having a carboxylic acid group as a repeating unit.

As a method for surface-treating the metal hydroxide with the organosilicon compound of the general formula (1), for example, a metal hydroxide such as magnesium hydroxide is stirred in a Henschel mixer and the general formula (1) is used. ) Is added directly or diluted with an organic solvent or the like, or a metal hydroxide is dispersed in water to form a slurry, and an aqueous solution or dispersion of the organosilicon compound of the general formula (1) is added. It can be obtained by a method such as drying after treatment.

In this case, the weight ratio of the metal hydroxide to the organosilicon compound of the general formula (1) is 100.
On the other hand, the organosilicon compound of the general formula (1) is
It is preferable to set it in the range of 10 parts by weight, preferably 0.5 to 5 parts by weight, from the viewpoint of the initial tensile strength and the expandability and fixability of a heat shrinkable tube.

Ionizing radiation used as a means for crosslinking the resin composition includes accelerated electron beams, gamma rays, alpha rays,
X-rays, ultraviolet rays and the like can be exemplified, but accelerated electron beams are particularly preferable from the viewpoint of the ease of use of a radiation source, the relationship between the radiation transmission thickness, and the speed of crosslinking treatment. When it is desired to obtain a heat-shrinkable tube from the resin composition of the present invention, approximately 30
It suffices to irradiate the accelerated electron beam with a dose in the range of up to 500 kGy.

The cross-linking means of the resin composition is not limited to ionizing radiation, but a method of thermal vulcanization in which an organic peroxide is kneaded in the resin composition in advance, molded into a predetermined shape and then heated. Although applicable, in the case of thermal vulcanization, restrictions such as the balance between the decomposition start temperature of organic peroxides such as dicumyl peroxide and the molding temperature of the resin composition, and the accompanying composition of the resin composition can be freely set. Because there are problems such as decrease in degree,
From the viewpoint of industrial use, such as the production of heat-shrinkable tubes, the use of accelerated electron beams is superior in production efficiency.

The resin composition of the present invention contains polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, and a vinyl acetate graft, as long as the characteristics are not impaired. Various thermoplastic resins such as ethylene-vinyl acetate copolymer and elastomers such as EP rubber and ethylene-acrylic rubber can be blended.

Further, silica, talc, clay, antimony trioxide, calcium carbonate, basic magnesium carbonate,
It is possible to add compounding agents such as zinc borate, various fillers of hydrotalcites, antioxidants, lubricants, stabilizers, foaming agents, heavy metal deactivators, colorants, polyfunctional monomer crosslinking accelerators, etc. Needless to say.

To produce the heat-shrinkable tube according to the present invention, the flame-retardant resin composition according to the present invention is formed into a tube by molding means such as extrusion molding, and then crosslinked by, for example, electron beam irradiation, and heated under heating conditions. It is preferable to expand the diameter and fix it by cooling by blowing compressed air into the tube. Furthermore, an insulated wire can be manufactured by irradiating with ionizing radiation after extrusion-coating the resin composition of the present invention on a conductor.

[0031]

Next, the present invention will be described in more detail. For example, 100% by weight of ethylene-vinyl acetate-methacrylic acid terpolymer (vinyl acetate content 28%, methacrylic acid content 6%, melt flow index 2). Parts, 180 parts by weight of magnesium hydroxide, and 1 part by weight of γ-aminopropyltriethoxysilane were used as a main component to mold a resin composition into a sheet having a thickness of 1.0 mm using a hot press machine. The one irradiated with 100 kGy of 2 MeV electron beam had an initial tensile strength of 1.21 kg / mm ² and a breaking elongation of 245%, which was the UL standard value of 1.05 kg / mm.
^More than ^two .

Further, for the purpose of confirming the stretch fixing property of this sheet, as shown in FIG. 1, a JIS No. 3 dumbbell was punched out, and two marked lines having a distance of 30 mm were marked at the center of the dumbbell. Both ends of the dumbbell were pulled at 50 mm / min until the distance between the marked lines became 60 mm, which was twice the original distance, in a constant temperature bath at 170 ° C., and then cooled and fixed as it was.

As a result, the distance between the marked lines was kept at 60 mm even after standing at room temperature for 7 days, and this stretch-fixed sheet was heated to 150 ° C.
When left in the constant temperature bath for 5 minutes, it was found that heat recovered and the distance between the marked lines returned to the original 30 mm, exhibiting excellent stretch fixability and heat recoverability.

Further, a 2 mm thick sheet of this resin composition was irradiated with an electron beam of 100 kGy and a vertical combustion test based on UL94 was carried out. The flame spread time was 6 seconds at maximum, and the flame was excellent in flame retardancy. It was confirmed to be a thing.

[0035]

The present invention will be described in more detail with reference to the following examples, which do not limit the scope of the present invention.
The compounding compositions shown in Tables 1 to 3 were kneaded using an open roll mixer set at 120 ° C. In addition to the blended composition shown in Table 1, 2 parts by weight of pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate and 0.25 part by weight of stearic acid were used. Parts were commonly compounded.

A sheet-shaped molded product having a thickness of 1.0 mm and 2.0 mm was prepared using a hot press machine in which the above resin composition was set at 150 ° C., and 100 kGy of electron beam having an accelerating voltage of 2 MeV was irradiated. . This sheet was punched out into a JIS No. 3 dumbbell, and the initial tensile strength (breaking tensile strength) and elongation at break of a sample heat-aged in a gear oven at 158 ° C. for 168 hours were measured at tensile speed of 500 mm / min.

For the purpose of examining the stretch-fixing property and heat recovery property of the sheet, two marks with a distance between the marks of 30 mm are marked at the center of JIS No. 3 dumbbell in the same manner as in FIG.
The distance between the marked lines is 60m when the dumbbell is pulled in the constant temperature tank
An experiment was conducted in which the film was stretched at a speed of 50 mm / min so as to be m, and immediately water-cooled and fixed.

After stretching and fixing, the sample which was left at room temperature for 7 days and which had a marked line distance of 60 mm was judged to have good stretch fixing property. Further, by allowing this sample to stand in a constant temperature bath at 150 ° C. for 5 minutes, it was determined that the heat recovery property was good when the distance between marked lines was recovered to 30 mm. Further, for a sheet having a thickness of 2 mm, a vertical combustion test based on UL94 was performed, and a sheet having a spread time of 10 seconds or less after two ignitions was regarded as a pass. The results are shown in Table 1.
~ Summarized in Table 3.

(Examples 1, 2, 3, 5) Examples 1, 2,
3 and 5 are resin compositions in which magnesium hydroxide and an organosilicon compound represented by the general formula (1) are mixed with an ethylene polymer having a carboxylic acid group as a repeating unit, and the initial tensile strength is 1 of UL standard value. More than 0.05 kg / mm ² ,
It has excellent mechanical strength and its elongation is 1 even after heat aging.
It is found that the heat resistance is more than 00%, the heat aging resistance is excellent, the stretch fixing property and the heat recovery property are also good, and the flame retardance which also passes the UL94 combustion test is excellent.

(Examples 4 and 6) In Examples 4 and 6, an ethylene polymer having a carboxylic acid group as a repeating unit was used, and the general formula (1) was used.
Is a resin composition containing magnesium hydroxide which has been surface-treated in advance with an organic silicon compound, and has an initial tensile strength of U
It exceeds the L standard value of 1.05 kg / mm ² , has excellent mechanical strength, has good stretch fixing property and heat recovery property, and has excellent flame retardance that passes the UL94 combustion test. I understand.

[0041]

[Table 1]

(* 1) Vinyl acetate content 28%, methacrylic acid content 6%, MI = 2 (190 ° C., 2.16 kg) (* 2) Vinyl acetate content 33%, acrylic acid content 4
%, MI = 2 (190 ° C., 2.16 kg) (* 3) No surface treatment, average particle size 0.7 μm, BET
Magnesium hydroxide having a specific surface area of 8 m ² / g (* 4) (* 3) was previously (*
Surface-treated with the organosilicon compound of 5). (* 5) H ₂ N (CH ₂ ) ₃ Si (OC ₂ H ₅ ) ₃ (* 6) H ₂ N (CH ₂ ) ₂ NH (CH ₂ ) ₃ Si
(OC ₃ ) ₃

(Comparative Examples 1 and 2) Comparative Examples 1 and 2 are resins obtained by blending magnesium hydroxide with an ethylene polymer having a repeating unit of a carboxylic acid group without blending the organosilicon compound of the general formula (1). The composition is good in stretch fixing property and heat recovery property and has passed the UL94 combustion test, but the initial tensile strength is less than 1.05 kg / mm ² , which satisfies the UL standard value. Absent.

(Comparative Example 3) Comparative Example 3 is a resin composition prepared by blending an ethylene polymer having a carboxylic acid group as a repeating unit with magnesium hydroxide which has been surface-treated with oleate in advance. Good recovery, UL9
4 has passed the combustion test, but the initial tensile strength is 1.
It is less than 05 kg / mm ² and does not meet the UL standard value.

(Comparative Example 4) Comparative Example 4 is a resin composition in which magnesium hydroxide is mixed with an ordinary ethylene vinyl acetate copolymer having no carboxylic acid group unit, and the stretching fixability and the heat recovery property are good. However, although it has passed the UL94 combustion test, the initial tensile strength is less than 1.05 kg / mm ² and does not satisfy the UL standard value.

(Comparative Example 5) Comparative Example 5 is a resin composition in which the organosilicon compound of the general formula is blended with Comparative Example 4, has good stretch fixing property and heat recovery property, and passed the UL94 combustion test. However, the initial tensile strength is 1.05 kg / mm
^It is less than ² and does not meet the UL standard value.

Comparative Example 6 Comparative Example 6 is a resin composition prepared by blending a normal ethylene vinyl acetate copolymer having no carboxylic acid group unit with magnesium hydroxide which has been surface-treated with oleate in advance. The tensile strength is less than 1.05 kg / mm ² , and the UL standard value is not satisfied.

[0048]

[Table 2]

(* 1) Vinyl acetate content 28%, methacrylic acid content 6%, MI = 2 (190 ° C., 2.16 kg) (* 2) Vinyl acetate content 28%, MI = 2 (190
(℃, 2.16kg) (* 3) No surface treatment, average particle size 0.7μm, BET
Magnesium hydroxide having a specific surface area of 8 m ² / g (* 4) (* 3) that has been surface-treated with oleate in advance. (* 5) H ₂ N (CH ₂ ) ₃ Si (OC ₂ H ₅ ) ₃

Comparative Example 7 Comparative Example 7 is an ethylene polymer having a carboxylic acid group as a repeating unit, magnesium hydroxide, and an organosilicon compound containing a vinyl group instead of the organosilicon compound of the general formula (1). UL9 is a resin composition in which the stretch fixing property and the heat recovery property are good.
4 has passed the combustion test, but the initial tensile strength is 1.
It is less than 05 kg / mm ² and does not meet the UL standard value.

Comparative Example 8 Comparative Example 8 is an ethylene polymer having a carboxylic acid group as a repeating unit, magnesium hydroxide, and an organosilicon compound containing a methacryl group instead of the organosilicon compound of the general formula (1). A resin composition containing a compound, with an initial tensile strength of 1.05 kg / mm
² , the mechanical strength was excellent and the UL94 combustion test was passed, but in the stretch-fixing test, the distance between marked lines could not be stretched to 60 mm.

Comparative Example 9 In Comparative Example 9, a conventional ethylene vinyl acetate copolymer having no carboxylic acid group unit contains magnesium hydroxide and a vinyl group instead of the organosilicon compound of the general formula (1). It is a resin composition containing an organosilicon compound, has good stretch fixing properties and heat recovery properties, and has passed the UL94 combustion test, but its initial tensile strength is less than 1.05 kg / mm ^2. And does not meet the UL standard value.

(Comparative Example 10) In Comparative Example 10, a conventional ethylene vinyl acetate copolymer having no carboxylic acid group unit contains magnesium hydroxide and a methacryl group in place of the organosilicon compound of the general formula (1). The resin composition containing the organosilicon compound described above has an initial tensile strength of 1.
More than 05 kg / mm ² , excellent mechanical strength,
Although it passed the UL94 combustion test, in the stretch fixation test, the distance between the marked lines could not be stretched to 60 mm.

[0054]

[Table 3]

(* 1) Vinyl acetate content 28%, methacrylic acid content 6%, MI = 2 (190 ° C., 2.16 kg) (* 2) Vinyl acetate content 28%, MI = 2 (190
(℃, 2.16kg) (* 3) No surface treatment, average particle size 0.7μm, BET
A specific surface area of ^{8m 2 / g (* 4)} CH 2 = CHSi (OC 2 H 5) 3 (* 5) CH 2 = CH (CH 3) COO (CH 2) 3
Si (OCH ₃ ) ₃

As described above, a resin composition prepared by mixing magnesium hydroxide and an organosilicon compound represented by the general formula (1) into an ethylene polymer having a carboxylic acid group as a repeating unit is used, or a carboxylic acid group is added. Only the resin composition in which the ethylene polymer having a repeating unit is mixed with magnesium hydroxide which has been surface-treated with the organosilicon compound of the general formula (1) in advance has a tensile strength of 1.
It can be understood that it has a unique effect of exceeding 05 kg / mm ² and being excellent in stretch fixing property and heat recovery property, and further passing the UL94 vertical combustion test.

On the other hand, a resin composition prepared by mixing magnesium hydroxide and an organosilicon compound represented by the general formula (1) with an ordinary ethylene-based polymer having no carboxylic acid group unit or the general formula (1) is prepared in advance. The resin composition containing magnesium hydroxide surface-treated with the above organosilicon compound has an initial strength of less than 1.05 kg / mm ² and does not satisfy the UL standard value.

In the case of a resin composition containing a vinyl group-containing organosilicon compound in place of the organosilicon compound of the general formula (1), the initial tensile strength is 1. In the case of a resin composition containing less than 05 kg / mm ² and further containing an organosilicon compound containing a methacryl group instead of the organosilicon compound represented by the general formula (1), regardless of the type of the base resin, It has a tensile strength of more than 1.05 kg / mm ² , but is inferior in stretchability and is not suitable as a resin composition for producing a heat-shrinkable tube.

(Examples 7 and 8 and Comparative Examples 11 to 15)
The resin compositions of Examples 2 and 6 and Comparative Examples 2, 4, 6, 7 and 10 were pelletized with a pelletizer and a 30 mmφ melt extruder (L / D = 24, full flight screw, compression ratio 2.5). The extrusion temperature (die temperature) to 18
When set to 0 ° C, the inner diameter is 6.4 mmφ and the wall thickness is 0.50 m.
m into a tube shape.

This tube was irradiated with an electron beam having an acceleration voltage of 2 MeV at a predetermined dose. The initial tensile strength (breaking tensile strength) and breaking elongation of this tube were measured at a pulling speed of 500 mm / min. Next, this tube is cut into a length of 1.5 m, and one end of the tube is heat-sealed with a heated iron, so that the central portion of about 1 m long is heated in a constant temperature bath at 170 ° C. Set it inside and send compressed air from the other end of the tube.
An experiment was carried out in which the diameter was expanded to mmφ and the shape was fixed by water cooling immediately.

Samples that had been expanded and fixed until the tube inner diameter reached 13 mmφ were left to stand at room temperature for 7 days, and those that could hold the tube inner diameter of 13 mmφ were judged to have good expandability and fixability. , This sample 1
It was judged that the tube whose inner diameter contracted to 6.4 mmφ after being left for 5 minutes in a constant temperature bath at 50 ° C. had good heat recoverability.

On the other hand, with respect to the sample judged to have good expandability and fixability, the sample was covered with an iron rod having an outer diameter of 7.0 mmφ,
A sample that was heat-shrinked in a constant temperature bath at ℃ was prepared, and this sample was subjected to the UL standard vertical combustion test to determine whether it passed or failed. The results are summarized in Tables 4 and 5.

[0063]

[Table 4]

[0064]

[Table 5]

Example 7 is a tube using a resin composition in which an ethylene polymer having a carboxylic acid group as a repeating unit is mixed with magnesium hydroxide and an organosilicon compound represented by the general formula (1). Satisfies the UL standard value of 1.05 kg / mm ² , and a heat-shrinkable tube with excellent expandability and heat recovery is obtained. It also passed the UL standard vertical combustion test in flame retardancy. You can see that

Example 8 is a tube using a resin composition in which an ethylene polymer having a carboxylic acid group as a repeating unit is mixed with magnesium hydroxide which has been surface-treated with the organosilicon compound of the general formula (1). As in Example 7, the initial tensile strength was the UL standard value of 1.05 kg / mm.
^It was found that the heat shrinkable tube satisfying the requirement of ² and having excellent expansion fixability and heat recovery property was obtained, and also in flame retardancy, it passed the UL standard vertical combustion test.

Comparative Example 11 is a resin composition prepared by blending magnesium hydroxide with an ethylene polymer having a carboxylic acid group as a repeating unit without blending the organosilicon compound of the general formula (1). A heat-shrinkable tube that has excellent expandability and fixability, heat recovery, and passes the vertical combustion test, but has an initial tensile strength of 1.05 kg / mm ²
Is less than, and does not meet the UL standard value.

Comparative Example 12 uses a resin composition prepared by mixing magnesium hydroxide with an ordinary ethylene vinyl acetate copolymer having no carboxylic acid group unit, and is excellent in diameter expansion fixing property and heat recovery property. Moreover, a heat-shrinkable tube that passes the vertical combustion test is obtained, but the initial tensile strength is 1.
It is less than 05 kg / mm ² and does not meet the UL standard value.

Comparative Example 13 is a resin composition prepared by blending a normal ethylene vinyl acetate copolymer having no carboxylic acid group unit with magnesium hydroxide surface-treated with oleate in advance. Although a heat-shrinkable tube that is excellent in heat resistance and heat recovery and passes the vertical combustion test can be obtained, the initial tensile strength is less than 1.05 kg / mm ² and does not satisfy the UL standard value.

Comparative Example 14 is a resin in which an ethylene polymer having a carboxylic acid group as a repeating unit is mixed with magnesium hydroxide and an organosilicon compound containing a vinyl group instead of the organosilicon compound of the general formula (1). A heat-shrinkable tube that is a composition and has excellent properties for expanding and fixing the heat and recovering heat, and that has passed the vertical combustion test, but has an initial tensile strength of less than 1.05 kg / mm ^2. Does not meet the standard value.

In Comparative Example 15, magnesium hydroxide and an organosilicon compound containing a methacryl group instead of the organosilicon compound of the general formula (1) were added to an ordinary ethylene vinyl acetate copolymer having no carboxylic acid group unit. It is a tube that uses the compounded resin composition and has an initial tensile strength of more than 1.05 kg / mm ² and is excellent in mechanical strength. However, the inner diameter could only be expanded up to about 8 mmφ, and only a shrinkable tube could be obtained.

[0072]

As described above, according to the present invention,
It is possible to manufacture a heat-shrinkable tube that has excellent initial mechanical properties and that achieves vertical flame-retardant properties without containing halogen-based or phosphorus-based flame-retardant agents. The utility value is enormous.

[Brief description of drawings]

FIG. 1 is a schematic view showing a state of JIS No. 3 dumbbell for examining stretch fixing property and heat recovery property of a sheet.

FIG. 2 is a schematic diagram showing an outline of a vertical combustion test apparatus complying with the UL standard.

[Explanation of symbols]

 14 chamber 15 burner 16 kraft paper 17 absorbent cotton 18 sample

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Claims (3)

[Claims] 1. A flame-retardant composition comprising an ethylene-based polymer having a carboxylic acid group as a repeating unit and a metal hydroxide and an organosilicon compound represented by the following general formula (1). Resin composition. [Chemical 1] (Here, R is an alkyl group having at least one amino group, and X ¹ , X ² , and X ³ are an atomic group selected from the group consisting of an alkoxyl group, an alkyl group, and a halogen group, and X ¹ , X ² and X ³ represent at least one alkoxyl group.) 2. An ethylene-based polymer having a carboxylic acid group as a repeating unit, and a metal hydroxide preliminarily surface-treated with the organosilicon compound represented by the general formula (1). A flame-retardant resin composition. 3. A heat-shrinkable tube, wherein the tube-shaped molded article of the flame-retardant resin composition according to claim 1, 2 or 3 is irradiated with ionizing radiation and then expanded and fixed.