Silicone heat-shrinkable tube

Abstract

The present invention is a silicone heat-shrinkable tube characterized by being a product of thermosetting a silicone rubber composition containing: (A) 100 parts by mass a linear organopolysiloxane which has two or more alkenyl groups bonded to silicon atoms in a molecule thereof, which has an average polymerization degree of 3,000-50,000, and in which among all substituents, 50 mol% or greater are methyl groups and 0.05-5.0 mol% are alkenyl groups; (B) 5-60 parts by mass a fine powder silica having a BET specific surface area of 100 m2 / g or greater; (C) 0.2-100 parts by mass at least one, or two or more, inorganic pigments selected from among metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and ferrite powders; (D) 10-100 parts by mass a thermoplastic resin; (E) an effective amount of a curing agent; and (F) 3-100 parts by mass a filler dispersant. Thereby provided is a silicone heat-shrinkable tube having colorability to a prescribed color and good flame-retardant properties.

Description

Silicone heat shrink tubing

[0001] This invention relates to silicone heat shrink tubing.

[0002] Conventionally, heat-shrinkable molded articles obtained from silicone rubber compositions, which are made by blending silicone raw rubber with thermoplastic resins such as polyethylene or silicone resin, as well as fillers, have been known. A typical example of a heat-shrinkable molded article is silicone heat-shrinkable tubing (Patent Document 1).

[0003] In the automotive sector, conventional vehicles include multiple cables for transmitting power or data signals from one end to the other. However, with the increasing performance of electric vehicles and other high-performance vehicles in recent years, there has been a growing demand for busbars that can achieve high voltage and high output in a small space. Therefore, there is a need to cover the busbars with materials that are colored in orange, red, or yellow and exhibit good flame retardancy in the parts that become hot during operation. One method of covering them is the use of heat shrink tubing (Patent Document 2).

[0004] Silicone rubber has a main skeleton made of siloxane bonds and has a lower proportion of organic components (hydrocarbon components) compared to ordinary organic rubber, making it flame-retardant. However, under harsh conditions such as direct contact with flames, silicone rubber can ignite and burn. To solve the above problem, it is known that triazole compounds are added to silicone rubber compositions as flame retardants to platinum compounds or reaction products of platinum compounds with alkynyl groups and alcoholic hydroxyl groups (Patent Document 3).

[0005] Japanese Patent Publication No. Hei 8-157727, International Publication No. 2019 / 189469, Japanese Patent Publication No. 2023-130798

[0006] Conventional technology has a problem in that when silicone heat-shrinkable tubing is colored, the flame retardancy may be impaired depending on the coloring component.

[0007] The present invention was made to solve the above problems, and aims to provide a silicone heat-shrinkable tube that is formed into a tube shape, vulcanized, and heat-stretched radially, and has colorability to a predetermined color and good flame retardancy.

[0008] To solve the above problems, the present invention provides: (A) a linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 3,000 to 50,000, wherein 50 mol% or more of the total substituents are methyl groups and 0.05 to 5.0 mol% are alkenyl groups: 100 parts by mass; (B) a BET specific surface area of ​​100 m² ２ The present invention provides a silicone heat-shrinkable tube characterized by being obtained by heat curing a silicone rubber composition containing: (C) fine powder silica with a concentration of 5 to 60 parts by mass, (D) at least one or more inorganic pigments selected from metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and ferrite powders, (E) thermoplastic resin, (F) effective amount of curing agent, and (F) dispersant for fillers, (C) 3 to 100 parts by mass.

[0009] Such silicone heat shrink tubing possesses the heat shrinkage characteristics of conventional silicone heat shrink tubing, as well as the ability to be colored to a predetermined color and good flame retardancy.

[0010] In the silicone heat shrinkable tube of the present invention, it is preferable that the (C) component is one or more selected from iron oxide, iron hydroxide, and magnesium ferrite.

[0011] Silicone heat-shrinkable tubing containing such (C) component results in molded products that combine orange, red, and yellow coloring with good flame retardancy.

[0012] Furthermore, in the silicone heat-shrinkable tube of the present invention, it is preferable that the (D) component is an organopolysiloxane resin.

[0013] Silicone heat-shrinkable tubing containing such component (D) results in a molded product that retains its heat-shrinkability.

[0014] Furthermore, it is preferable that the silicone heat-shrinkable tubing of the present invention satisfies the flame retardancy requirement of VW-1 in the UL-224 standard.

[0015] Such silicone heat-shrinkable tubing has excellent flame retardancy.

[0016] The silicone heat shrinkable tube of the present invention further comprises a component (G) with a BET specific surface area of ​​50 to 400 m². ２ It is preferable that the mixture contains 5 to 300 parts by mass of inorganic fillers other than the above-mentioned components (B) and (C) at a concentration of / g.

[0017] Silicone heat-shrinkable tubing containing such (G) component exhibits superior physical strength.

[0018] In the silicone heat-shrinkable tube of the present invention, it is preferable that the (G) component is one or more inorganic fillers selected from crystalline silica, precipitated silica, quartz powder, and titanium white.

[0019] Silicone heat-shrinkable tubing containing such (G) component exhibits excellent flame retardancy and physical strength.

[0020] The silicone heat-shrinkable tubing of the present invention can be used as a covering material for busbars that are connected to distribution boards, control panels, or batteries and conduct large amounts of current.

[0021] Such silicone heat-shrink tubing makes it possible to create busbars that can achieve high voltage and high power output in a small space.

[0022] As described above, the silicone heat shrink tube of the present invention has the heat shrinkage characteristics of conventional silicone heat shrink tubes, and also has the ability to be colored to a predetermined color and has good flame retardancy, so its effects are remarkable.

[0023] As mentioned above, silicone heat shrink tubing is widely used in various industrial fields because it can easily cover objects and can be tightly sealed by shrinking through heating. However, when a specific color is applied, the flame retardancy may be impaired depending on the coloring component. Therefore, there has been a need for the development of silicone heat shrink tubing that can achieve both good colorability and good flame retardancy.

[0024] As a result of diligent research into the above-mentioned problems, the present inventors have discovered that by heat-curing a silicone rubber composition containing the following components (A) to (F), it is possible to provide a silicone heat-shrinkable tube with colorability to a predetermined color and high flame retardancy, thus completing the present invention.

[0025] That is, the present invention comprises: (A) a linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 3,000 to 50,000, wherein 50 mol% or more of the total substituents are methyl groups and 0.05 to 5.0 mol% are alkenyl groups: 100 parts by mass; (B) a BET specific surface area of ​​100 m² ２ This silicone heat-shrinkable tube is characterized by being a silicone rubber composition that has been heat-cured, containing: (C) fine powder silica with a concentration of 5 to 60 parts by mass, (D) at least one or more inorganic pigments selected from metals, metal oxides, metal hydroxides, metal nitrides, metal carbides, and ferrite powders, (E) a sufficient amount of curing agent, and (F) a dispersant for fillers, in a silicone rubber composition of 3 to 100 parts by mass.

[0026] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0027] <Component (A)> Component (A) is a linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 3,000 to 50,000, wherein 50 mol% or more of the total substituents are methyl groups and 0.05 to 5.0 mol% are alkenyl groups.

[0028] The aforementioned component (A) is the main component of the silicone rubber composition that constitutes the silicone heat shrinkable tube of the present invention.

[0029] The linear organopolysiloxane has two or more alkenyl groups bonded to silicon atoms, preferably 2 to 10,000, per molecule.

[0030] (A) Examples of alkenyl groups bonded to silicon atoms in component (A) include those typically having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms. Specific examples include vinyl groups, allyl groups, propenyl groups, butenyl groups, pentenyl groups, hexenyl groups, cyclohexenyl groups, heptenyl groups, etc., with vinyl groups being particularly preferred.

[0031] Other substituents bonded to the silicon atom besides alkenyl groups include C1-C10 alkyl groups, C6-C10 aryl groups, and C7-C10 aralkyl groups. Specifically, these include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; aryl groups such as phenyl and tolyl groups; and aralkyl groups such as benzyl and 2-phenylethyl groups. Among these, methyl and phenyl groups are preferred.

[0032] Furthermore, of the total substituents of the linear organopolysiloxane, 50 mol% or more, preferably 80 to 95 mol%, are methyl groups, and more preferably, all substituents other than alkenyl groups are methyl groups, and 0.05 to 5.0 mol%, preferably 0.1 to 3.0 mol%, are alkenyl groups.

[0033] Furthermore, the average degree of polymerization of the linear organopolysiloxane is characterized by being 3,000 to 50,000, and preferably 4,000 to 20,000. The average degree of polymerization in this invention is a value obtained from the weight-average molecular weight, which is calculated by converting polystyrene with a known molecular weight as a standard substance using gel permeation chromatography (GPC) analysis measured under the conditions shown below.

[0034] [Measurement Conditions] Developing Solvent: Tetrahydrofuran (THF) Flow Rate: 0.6 mL / min Detector: Differential Refractometer (RI) Column: TSK Guardcolumn SuperH-H TSKgel SuperH4000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH3000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH2000 (6.0 mm I.D. × 15 cm × 1) (All manufactured by Tosoh Corporation) Column Temperature: 40°C Sample Injection Volume: 50 μL (THF solution with a concentration of 2.0 mass%)

[0035] The kinematic viscosity of this linear organopolysiloxane is preferably 1,000 mm ２ / s or more at 25°C measured using a Cannon-Fenske viscometer described in JIS Z8803:2011, and particularly preferably 100,000 to 10,000,000 mm ２ / s.

[0036] <Component (B)> Component (B) is fumed silica (dry silica) having a BET specific surface area of 100 m ２ / g or more, fine powder silica such as wet silica, or fine powder silica obtained by hydrophobically treating the surfaces thereof with silane, silazane, siloxane, etc. The measurement method for the BET specific surface area is the BET method. The upper limit of the BET specific surface area in component (B) is not particularly limited, but can be, for example, 400 m ２ / g or less.

[0037] The blending amount of component (B) is 5 to 60 parts by mass, preferably 10 to 50 parts by mass, based on 100 parts by mass of the linear organopolysiloxane of component (A). If this blending amount is less than 5 parts by mass, the strength required for stretching cannot be obtained, and if it is more than 60 parts by mass, physical properties such as the elongation required for stretching may not be obtained.

[0038] <Component (C)> Component (C) is an inorganic pigment, and examples include metal oxides such as cobalt oxide, copper oxide, copper carbonate, yellow iron oxide, red iron oxide, chromium oxide, magnesium oxide, manganese oxide, nickel oxide, tin oxide, titanium oxide, zircon silicate, beryllium oxide, and zinc oxide; metallic iron hydroxides such as iron hydroxide, copper(II) hydroxide, aluminum hydroxide, ammonium hydroxide, and magnesium hydroxide; metallic nitrides such as aluminum nitride, zinc nitride, yttrium nitride, indium nitride, gallium nitride, silicon nitride, and calcium nitride; metallic carbides such as titanium carbide and chromium carbide; ferrite powders such as magnesium ferrite, manganese ferrite, zinc ferrite, and lithium ferrite; metals such as copper, iron, zinc, and aluminum; and mixtures thereof. In particular, when an orange, red, or yellow coloring is required for the silicone rubber composition, it is preferable to use metal, metal oxide, metal hydroxide, metal nitride, metal carbide, and ferrite powder, or mixtures thereof, such as yellow, brown, or red. Specifically, it is preferable to use one or more selected from the group consisting of iron hydroxide, iron oxide such as red iron oxide or yellow iron oxide, and magnesium ferrite.

[0039] Furthermore, iron hydroxide, red iron oxide, yellow iron oxide, and magnesium ferrite are suitable as inorganic coloring pigments because they have relatively good compatibility with component (A), a wide range of varieties are available industrially, they are readily available as resources, and they are available at relatively low cost.

[0040] The amount of component (C) is 0.2 to 100 parts by mass, preferably 1 to 50 parts by mass, and more preferably 10 to 40 parts by mass, per 100 parts by mass of the linear polyorganopolysiloxane of component (A). If the amount of component (C) is less than 0.2 parts by mass, the coloring of the silicone rubber layer tends to be insufficient, and if it is more than 100 parts by mass, the rubber strength may decrease, the two-roll processability may decrease, and the moldability may worsen.

[0041] <Component (D)> Component (D) is a thermoplastic resin, and may be the same as those used in known silicone heat shrink tubing. Examples include methyl methacrylate, polyethylene, polypropylene, polystyrene, polyvinyl chloride, and various thermoplastic silicone resins. Considering the miscibility with silicone resins, component (D) is preferably an organopolysiloxane resin, and more preferably an organopolysiloxane resin represented by the following formula (1).

[0042] The amount of component (D) is 10 to 100 parts by mass, more preferably 20 to 60 parts by mass, per 100 parts by mass of the linear polyorganopolysiloxane of component (A). If the amount of component (D) is less than 10 parts by mass, a molded product with the desired heat shrinkage properties cannot be obtained, and if it is more than 100 parts by mass, a product with rubber elasticity cannot be obtained.

[0043] <Component (E)> Component (E) is a curing agent (crosslinking agent and / or curing catalyst), and conventionally known agents that are normally used for curing silicone rubber can be used. For example, when curing by radical reaction, organic peroxides such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide can be used, and when curing by addition reaction, an addition reaction crosslinking agent consisting of an organohydrodiene polysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule and a platinum catalyst such as platinum element and chloroplatinic acid can be used.

[0044] The amount of component (E) added is an effective amount, but typically, for radical reactions, the amount of peroxide is preferably 0.1 to 3 parts by mass per 100 parts by mass of organopolysiloxane. For addition reactions, the amount of organohydrodienepolysiloxane is preferably such that the molar ratio of silicon atom-bonded hydrogen atoms (hydrosilyl groups) to alkenyl groups in component (A) is 0.5 to 5, and for the platinum catalyst, the amount of platinum metal is preferably 0.1 to 2,000 ppm.

[0045] <(F) component> The (F) component is a dispersant for fillers. When mixing the above components with a commonly used mixer such as a two-roll mill, kneader, Banbury mixer, etc., in order to facilitate uniform mixing as needed, a low molecular weight siloxane with both ends sealed with hydroxyl groups, an alkoxysilane, a silazane, diphenylsilanediol, or a dimethylpolysiloxane represented by the following general formula (2) and having a trialkoxysilyl group at one end of the molecular chain fragment is included. The (F) component functions as a surface treatment agent for uniformly dispersing the (C) component in the matrix composed of the (A) component during the preparation of the composition.

[0046] In the above general formula (2), R ５ is, independently of each other, an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100. The alkyl group having 1 to 6 carbon atoms is, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, and a hexyl group, etc. R ５ is preferably an alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, a propyl group, etc., and more preferably a methyl group.

[0047] The amount of the (F) component is 3 to 100 parts by mass, preferably 5 to 50 parts by mass, based on 100 parts by mass of the (A) component. By blending within the range of 3 to 100 parts by mass, the (C) component can be uniformly dispersed in the matrix composed of the (A) component. If the amount of the (F) component relative to the (A) component exceeds 100 parts by mass, it may induce oil separation, which is not preferable. Also, when the amount of the (F) component is less than 3 parts by mass, the wettability of the (A) component and the (C) component decreases, and there is a possibility that the composition cannot be formed.

[0048] [Other components] <(G) Inorganic filler> The silicone heat-shrinkable tube of the present invention may contain, in addition to the above (A) to (F) components, 5 to 300 parts by mass of an inorganic filler other than the above (B) and (C) components having a BET specific surface area of 50 to 400 m ２ / g as the (G) component.

[0049] The (G) component has a BET specific surface area of 50 to 400 m２ Preferably, it is 100 to 350 mg / g. ２ It is more preferable that the BET specific surface area is 50 m². ２ If the amount is 1 / g or more, the reinforcing effect is sufficiently exerted, and the physical strength of the silicone heat shrink tubing does not decrease, 400m ２ If the amount is less than / g, there are no manufacturing issues.

[0050] The amount of component (G) is 5 to 300 parts by mass, preferably 20 to 200 parts by mass, per 100 parts by mass of component (A). If the amount is 5 parts by mass or more, sufficient rubber strength can be obtained, and if the amount is 300 parts by mass or less, there is no problem with the formulation.

[0051] Component (G) is not particularly limited as long as it is different from the fine silica powder of component (B) and the inorganic pigment of component (C). Examples of inorganic fillers include fumed silica, crystalline silica, precipitated silica, silsesquioxane, fumed titanium dioxide, magnesium oxide, zinc oxide, iron oxide, aluminum hydroxide, magnesium carbonate, calcium carbonate, zinc carbonate, layered mica, carbon black, diatomaceous earth, glass fiber, titanium white, quartz powder, and talc, among which crystalline silica, precipitated silica, quartz powder, and titanium white are preferred. These fillers may also be used after being surface-treated with organosilicon compounds such as organoalkoxysilane compounds, organochlorosilane compounds, organosilazane compounds, and low molecular weight siloxane compounds.

[0052] It is preferable that the aforementioned component (G) is one or more inorganic fillers selected from crystalline silica, precipitated silica, quartz powder, and titanium white.

[0053] In addition to the components (A) to (G) described above, the silicone heat shrinkable tube of the present invention may contain optional components such as degradation inhibitors, heat resistance improvers, heat-resistant agents such as titanium dioxide and cerium oxide, internal mold release agents such as zinc stearate and dimethyl silicone oil, and pigments other than component (C) in any proportion.

[0054] The silicone heat-shrinkable tube of the present invention is obtained by forming the above-mentioned silicone rubber composition into a tube shape, vulcanizing it, and further heating and stretching it radially (i.e., expanding it). In this case, it is preferable to extrude the above-mentioned composition into a tube shape with a draw-down ratio of preferably 150% to 250%, more preferably 170% to 200%, relative to the nipple diameter.

[0055] Vulcanization conditions are appropriately selected according to the curing method, but in this invention, a method of thermocuring at a temperature of 100°C or higher at atmospheric pressure is employed. Furthermore, by stretching this tubular molded product radially under heating at 120 to 220°C and then cooling it in that state, a heat-shrinkable tubular molded product can be obtained.

[0056] The silicone heat-shrinkable tube obtained in this way shrinks almost completely back to its original shape when heated to 120°C or higher using hot air or other heating means.

[0057] [Flame Retardancy] The silicone heat shrink tubing of the present invention can satisfy the flame retardancy of VW-1 in the UL-224 standard, for example.

[0058] [Covering Material] The silicone heat shrink tubing of the present invention can be used, for example, as a covering material for busbars connected to distribution boards, control panels, or batteries, which conduct large amounts of current.

[0059] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0060] [Example 1] (A) 100 parts by mass of dimethylpolysiloxane having a vinyl group content of 0.4 mol% relative to the total monovalent hydrocarbon groups, with both ends of the molecular chain sealed with dimethylvinylsilyl groups, (B) specific surface area (BET method) of 200 m ２(D) 50 parts by mass of fumed silica (average degree of polymerization 8,000) / g, 30 parts by mass of methylphenylpolysiloxane resin represented by the following formula (1), (G-1) 19 parts by mass of crystalline silica (Crystalite VX-S, Ryumori Co., Ltd.), (G-2) 9.5 parts by mass of titanium dioxide (P-25, Ishihara Sangyo Co., Ltd.), and (F) 20 parts by mass of dimethylpolysiloxane represented by the following formula (3), with an average degree of polymerization of 30 and one end sealed with a trimethoxysilyl group are mixed in a kneader, and for every 100 parts by mass of this compound, (C-1) 10 parts by mass of 50% iron hydroxide paste and (C-2 A silicone rubber composition was prepared by mixing 0.7 parts by mass of 50% iron oxide paste, 0.02 parts by mass of (E-1) 5% 2-ethylhexanol chloroplatinate solution, and 1.4 parts by mass of (E-2) a linear dimethylsiloxane-methylhydrogensiloxane copolymer (hydrosilyl group content: 0.0076 mol / g) in which both ends of the molecular chain are sealed with trimethylsiloxy groups, the average degree of polymerization is 38, the average number of hydrosilyl groups per molecule is 20, and the viscosity is 20 mPa·s. This composition was formed into a sheet and press-cured at 120°C for 10 minutes, followed by post-curing at 200°C for 4 hours to cure.

[0061] Next, the cured sheet obtained in this manner was stretched to twice its original size under heating at 200°C, cooled to room temperature, and then the stress was removed. The stretch retention rate, heat shrinkage rate, and the properties of the resulting cured sheet as a heat-shrinkable tube were then evaluated. The results are shown in Table 1.

[0062] [Example 2] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that the amount of component (C) used in Example 1 was changed to 10 parts by mass of 50% paste of (C-2) red iron oxide. Each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0063] [Example 3] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that the amount of component (C) used in Example 1 was changed to 10 parts by mass of 50% magnesium ferrite paste (C-3). Each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0064] [Comparative Example 1] Except for changing the amount of inorganic pigment added to the inorganic pigment used in Example 1, the addition was changed to 2.2 parts by mass of 30% paste of (C-4) organic dye (Pariotol Yellow K0961HD, Morishita Sangyo Co., Ltd.) and 0.8 parts by mass of 50% paste of (C-5) organic dye (Seika First Orange 2900, Dainichi Seika Kogyo Co., Ltd.). A cured sheet was manufactured under the same formulation and molding conditions as in Example 1, and each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0065] [Comparative Example 2] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that component (C) used in Example 1 was omitted, and each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0066] [Comparative Example 3] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that the amount of (C-1) iron hydroxide 50% paste added was changed to 150 parts by mass. Each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0067] [Comparative Example 4] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that the amount of component (F) (dispersant for filler) used in Example 1 was changed to 2 parts by mass. Each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0068] [Comparative Example 5] A cured sheet was manufactured using the same formulation and molding conditions as in Example 1, except that the amount of component (D) (methylphenylpolysiloxane resin) used in Example 1 was changed to 5 parts by mass. Each property was measured in the same manner as in Example 1. The results are shown in Table 1.

[0069] Method for evaluating silicone compositions (1) Stretch retention rate The stretch retention rate was determined as follows: if the composition could withstand stretching to 200% after being placed in the jig, and the stretch retention rate after being removed from the jig was 60% or higher, it was marked as "○".

[0070] (2) Heat shrinkage Heat shrinkage was assessed as "○" if the heat shrinkage rate after heating at 100°C for 3 minutes was 50% or more.

[0071] The stretch retention rate and heat shrinkage rate were calculated using the following formulas. L ０: Original length of the marking line L １ : The length between the markings when heated to 200°C, stretched to 200%, and fixed to a jig. (L) ２ : Length between markings when removed from the jig L ３ : Remove from the jig and measure the distance between the markings after heating at 100°C for 3 minutes and then cooling.

[0072] (3) Flame retardancy The VW-1 vertical combustion test described in the UL-224 standard was performed on five samples. Each sample was ignited for 15 seconds five times. A sample was considered acceptable if it was extinguished within 60 seconds, the cotton wool placed underneath was not burned by the burning material, and the kraft paper attached to the top of the sample did not burn or char. If even one of the five samples did not meet the acceptable level, it was considered a failure.

[0073] (4) Color tone In this embodiment, the color tone was evaluated by visual inspection.

[0074] (5) Two-roll compounding In this embodiment, the evaluation method for the two-roll compounding was as follows: If the roll wrapping properties were good and the ends were smooth, it was marked with a "○" to indicate good processability. If the roll wrapping properties were poor (for example, the rubber slipped on the rolls and did not wrap around them, or the rubber that passed between the rolls did not connect), and the ends were rough in shape, it was marked with a "×" to indicate that processing was not possible.

[0075]

[0076] From the results in Table 1, it was found that the silicone compositions of the present invention (Examples 1-3) have good color tone and high flame retardancy, and that they can be used as heat-shrinkable molded articles with stretch and shrink properties.

[0077] This specification includes the following embodiments: [1]: (A) A linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 3,000 to 50,000, wherein 50 mol% or more of the total substituents are methyl groups and 0.05 to 5.0 mol% are alkenyl groups: 100 parts by mass; (B) A BET specific surface area of ​​100 m² ２A silicone heat shrink tube characterized by being obtained by heat curing a silicone rubber composition containing: (C) fine powder silica having a concentration of 5 to 60 parts by mass, (D) at least one or more inorganic pigments selected from metals, metal oxides, metal hydroxides, metal nitrides, metal carbides and ferrite powders, (E) a sufficient amount of curing agent, and (F) a dispersant for fillers, in a silicone rubber composition of 3 to 100 parts by mass. [2]: The silicone heat shrink tube according to [1], characterized in that the (C) component is one or more selected from iron oxide, iron hydroxide and magnesium ferrite. [3]: The silicone heat shrink tube according to [1] or [2], characterized in that the (D) component is an organopolysiloxane resin. [4]: ​​The silicone heat shrink tube according to any one of [1] to [3], characterized in that it satisfies the flame retardancy of VW-1 in the UL-224 standard. [5]: Furthermore, as component (G), the BET specific surface area is 50 to 400 m ２ A silicone heat shrinkable tube according to any one of [1] to [4], characterized in that it contains 5 to 300 parts by mass of an inorganic filler other than the aforementioned components (B) and (C) at a concentration of / g. [6]: A silicone heat shrinkable tube according to [5], characterized in that the aforementioned component (G) is one or more inorganic fillers selected from crystalline silica, precipitated silica, quartz powder, and titanium white. [7]: A silicone heat shrinkable tube according to any one of [1] to [6], characterized in that it is used as a covering material for busbars that are connected to a power distribution board, control panel, or battery and conduct a large amount of current.

[0078] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. (A) A linear organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, with an average degree of polymerization of 3,000 to 50,000, wherein 50 mol% or more of the total substituents are methyl groups and 0.05 to 5.0 mol% are alkenyl groups: 100 parts by mass; (B) A BET specific surface area of ​​100 m² ２ A silicone heat-shrinkable tube characterized by being obtained by heat curing a silicone rubber composition containing: (C) fine powder silica with a concentration of 5 to 60 parts by mass, (D) at least one or more inorganic pigments selected from metals, metal oxides, metal hydroxides, metal nitrides, metal carbides and ferrite powders, (E) thermoplastic resin, (F) effective amount of curing agent, and (F) dispersant for filler, (C) 3 to 100 parts by mass.

2. The silicone heat shrinkable tube according to claim 1, characterized in that the (C) component is one or more selected from iron oxide, iron hydroxide, and magnesium ferrite.

3. The silicone heat shrinkable tube according to claim 1, characterized in that the (D) component is an organopolysiloxane resin.

4. The silicone heat shrink tubing according to claim 1, characterized in that it satisfies the flame retardancy of VW-1 in the UL-224 standard.

5. Furthermore, as component (G), the BET specific surface area is 50 to 400 m². ２ A silicone heat shrinkable tube according to any one of claims 1 to 4, characterized in that it contains 5 to 300 parts by mass of an inorganic filler other than the aforementioned components (B) and (C) at a concentration of / g.

6. The silicone heat shrinkable tube according to claim 5, characterized in that the (G) component is one or more inorganic fillers selected from crystalline silica, precipitated silica, quartz powder, and titanium white.

7. The silicone heat shrink tubing according to claim 1, characterized in that it is used as a covering material for busbars that are connected to a distribution board, control panel, or battery and conduct a large amount of current.

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