Silicone rubber composition and silicon heat-shrinkable tube

Abstract

To provide a silicone rubber composition capable of forming a silicone heat-shrinkable tube showing excellent shrinkability even under low-temperature heating and having conventional shape retention during storage at room temperature.SOLUTION: A silicone rubber composition for forming a silicone heat-shrinkable tube, comprises: (A) 100 pts.mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule, an average degree of polymerization of 3,000 to 50,000, at least 50 mol.% of all substituents being methyl groups, and 0.05 to 5.0 mol.% being vinyl groups; (B) 10 to 100 pts.mass of an organopolysiloxane resin different from the component (A) having a softening point of 100 to 200°C, and an endothermic peak of 50°C to 80°C in differential scanning calorimetry; (C) 5 to 50 pts.mass of powdered silica having a BET specific surface area of 100 m2 / g or more; and (D) an effective amount of a curing agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicone rubber composition and a silicone heat-shrinkable tube. [Background technology]

[0002] Conventionally, heat-shrinkable molded articles have been known that are made from silicone rubber compositions containing silicone raw rubber, a filler, and a thermoplastic resin such as polyethylene or a silicone resin. A typical example of a heat-shrinkable molded article is heat-shrinkable tubing (see, for example, Patent Documents 1 and 2).

[0003] Heat-shrinkable tubes that have been proposed up to now require heating to 120° C. or higher, preferably 150° C. or higher, when shrinking.

[0004] However, in recent years, there has been an increase in applications that cannot be subjected to high temperatures and a growing demand for reducing energy costs in the heating process. This has led to a desire to develop heat-shrinkable tubing that can be shrunk in a short time even when heated at low temperatures and that retains its shape as conventional tubing when stored at room temperature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-157727 [Patent Document 2] Japanese Patent Application Publication No. 6-340018 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a silicone rubber composition that can be used to form silicone heat-shrinkable tubing that exhibits good shrinkability even when heated at low temperatures and that retains its shape during storage at room temperature, as well as a silicone heat-shrinkable tubing that is a molded article of the composition. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a silicone rubber composition for forming silicone heat-shrinkable tubing, comprising: (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which 50 mol % or more of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) 10 to 100 parts by mass of an organopolysiloxane resin other than the component (A), which has a softening point of 100 to 200°C and an endothermic peak of 50 to 80°C in differential scanning calorimetry; (C) BET specific surface area is 100m 2 / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount The present invention provides a silicone rubber composition comprising:

[0008] Such a silicone rubber composition can provide a silicone heat-shrinkable tube that can be shrunk in a short time by heating at a low temperature and that retains its shape as well as conventional silicone heat-shrinkable tubes when stored at room temperature.

[0009] Furthermore, (E) BET specific surface area is 50 to 400 m 2 It is preferable that the inorganic filler content is 5 to 300 parts by mass / g.

[0010] By including such component (E), it is possible to impart higher rubber strength to the heat-shrinkable tubing obtained from the silicone rubber composition.

[0011] The component (E) may be, for example, a cellulose ester having a BET specific surface area of ​​50 m 2 / g or more 100m 2 / g, crystalline silica with a BET specific surface area of ​​50m 2 / g or more 100m 2The inorganic filler may be selected from precipitated silica, quartz powder, and titanium white, having a saturation of less than 1 / g.

[0012] The type of inorganic filler used as component (E) is not particularly limited, but the above-mentioned fillers can be used, for example.

[0013] Furthermore, it is preferable that the composition contains a dispersant for fillers as component (F).

[0014] By including such a filler dispersant, the powdered silica or other filler can be sufficiently dispersed, and the strength required for stretching can be uniformly imparted to molded articles of the silicone rubber composition of the present invention.

[0015] The present invention also provides a silicone heat-shrinkable tube, which is a molded article made from the silicone rubber composition of the present invention.

[0016] The silicone heat-shrinkable tubing of the present invention is a molded article made from the silicone rubber composition of the present invention, and therefore can be shrunk in a short time by heating at a low temperature, and can retain its shape as well as conventional tubing when stored at room temperature. [Effects of the Invention]

[0017] As described above, the silicone rubber composition of the present invention can provide silicone heat-shrinkable tubing that can be shrunk in a short time by heating at a low temperature and that retains its shape during storage at room temperature, similar to conventional methods. In other words, the silicone rubber composition of the present invention is suitable for use in the manufacture of silicone heat-shrinkable tubing.

[0018] Furthermore, the silicone heat-shrinkable tubing of the present invention can be shrunk in a short time by heating at a low temperature, and is suitable as a heat-shrinkable tubing that retains its shape like conventional tubing when stored at room temperature, and its effects are remarkable. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a schematic diagram illustrating an example of a silicone heat-shrinkable tube of the present invention. [Figure 2] 2 is a schematic view showing a state in which a part of the silicone heat-shrinkable tube shown in FIG. 1 has been heat-shrunk. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] As described above, there has been a demand for the development of a heat-shrinkable tube that can be shrunk in a short time by heating at a low temperature and that retains its shape as well as conventional tubes when stored at room temperature.

[0021] As a result of extensive research into the above-mentioned problems, the present inventors have come to the conclusion that (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which 50 mol % or more of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) 10 to 100 parts by mass of an organopolysiloxane resin other than the component (A), which has a softening point of 100 to 200°C and an endothermic peak of 50 to 80°C in differential scanning calorimetry; (C) BET specific surface area is 100m 2 / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount The present inventors have found that a silicone heat-shrinkable tube made of a silicone rubber composition containing the above compound can be shrunk by low-temperature heating and can maintain the same shape as conventional tubes when stored at room temperature, thereby completing the present invention.

[0022] That is, the present invention provides a silicone rubber composition for forming a silicone heat-shrinkable tube, comprising: (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which 50 mol % or more of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) 10 to 100 parts by mass of an organopolysiloxane resin other than the component (A), which has a softening point of 100 to 200°C and an endothermic peak of 50 to 80°C in differential scanning calorimetry; (C) BET specific surface area is 100m 2 / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount The silicone rubber composition is characterized by comprising:

[0023] The present invention also relates to a silicone heat-shrinkable tube, which is a molded article made from the silicone rubber composition of the present invention.

[0024] The present invention will be described in detail below, but the present invention is not limited thereto.

[0025] [Silicone rubber composition] The silicone rubber composition of the present invention is a silicone rubber composition for forming a silicone heat-shrinkable tube, (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which 50 mol % or more of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) 10 to 100 parts by mass of an organopolysiloxane resin other than the component (A), which has a softening point of 100 to 200°C and an endothermic peak of 50 to 80°C in differential scanning calorimetry; (C) BET specific surface area is 100m 2 / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount It contains:

[0026] The silicone rubber composition of the present invention may further contain optional components in addition to the above components (A) to (D).

[0027] The essential components and optional components of the silicone rubber composition of the present invention will be described in detail below.

[0028] <Component (A)> The silicone rubber composition of the present invention contains component (A), which is a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which at least 50 mol % of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups.

[0029] The component (A) is the main component of the silicone rubber composition that constitutes the silicone heat-shrinkable tubing of the present invention.

[0030] The organopolysiloxane has two or more, preferably 2 to 10,000, vinyl groups bonded to silicon atoms in one molecule.

[0031] Examples of substituents other than vinyl groups include alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms. Specific examples 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. Of these, methyl and phenyl groups are preferred.

[0032] Furthermore, of all the substituents on the organopolysiloxane, 50 mol % or more, preferably 80 to 95 mol %, are methyl groups, and more preferably, all substituents other than vinyl groups are methyl groups.Another characteristic of component (A) contained in the silicone rubber composition of the present invention is that 0.05 to 5.0 mol %, preferably 0.1 to 3.0 mol %, are vinyl groups.

[0033] The organopolysiloxane is characterized by having an average degree of polymerization of 3,000 to 50,000, and preferably 4,000 to 20,000. The average degree of polymerization in the present invention is a value determined from the weight average molecular weight determined by gel permeation chromatography (GPC) analysis measured under the conditions shown below, using polystyrene of known molecular weight as a standard substance.

[0034] [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6mL / min Detector: Refractive index detector (RI) Column: TSK Guardcolumn SuperH-H TSKgel SuperH4000(6.0mmI.D.×15cm×1) TSKgel SuperH3000(6.0mmI.D.×15cm×1) TSKgel SuperH2000(6.0mmI.D.×15cm×1) (All manufactured by Tosoh Corporation) Column temperature: 40℃ Sample injection volume: 50 μL (2.0% by mass THF solution)

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

[0036] <(B) component> Component (B) contained in the silicone rubber composition of the present invention is an organopolysiloxane resin different from component (A), which has a softening point of 100 to 200° C. and an endothermic peak in differential scanning calorimetry (DSC) of 50 to 80° C. Component (B) is a component that imparts shape retention at room temperature and shrinkability upon heating to the silicone rubber composition that constitutes the silicone heat-shrinkable tubing of the present invention.

[0037] The blending amount of component (B) is characterized by being 10 to 100 parts by mass, preferably 20 to 60 parts by mass, per 100 parts by mass of the linear organopolysiloxane of component (A). If the blending ratio of organopolysiloxane resin to linear organopolysiloxane is less than 10 parts by mass, a molded product having the desired heat shrinkability cannot be obtained, whereas if the blending ratio of polysiloxane resin is more than 100 parts by mass, a product having raw rubber elasticity cannot be obtained.

[0038] The softening point of the organopolysiloxane resin is characterized by being 100 to 200°C, preferably 120 to 180°C. In the present invention, the softening point refers to a value measured by the method described in JIS K2207:2006. If the softening point of the organopolysiloxane resin is lower than 100°C, it becomes difficult to maintain the shape at room temperature. On the other hand, if the softening point of the organopolysiloxane resin is higher than 200°C, the temperature required for shrinkage becomes too high, which can damage other substrates and increase the energy required for the process.

[0039] The organopolysiloxane resin is characterized by an endothermic peak in differential scanning calorimetry (DSC) of 50°C to 80°C, preferably 60°C to 75°C. In the present invention, the DSC endothermic peak refers to a value measured at a temperature rise rate of 5°C / min from 25°C to 200°C. If the DSC endothermic peak of the organopolysiloxane resin is lower than 50°C, it becomes difficult to maintain its shape at room temperature. On the other hand, if the DSC endothermic peak of the organopolysiloxane resin is higher than 80°C, the temperature required for shrinkage becomes too high, which can damage other substrates and increase the energy required for the process.

[0040] By including component (B) that satisfies these two conditions (softening point and endothermic peak conditions), it is possible to realize a silicone heat-shrinkable tube that can both retain its shape when stored at room temperature and shrink well when heated at low temperatures.

[0041] Furthermore, it is preferable that the substituent of the organopolysiloxane resin is not a functional group having hydrosilylation reactivity, such as an alkenyl group. Examples include alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl and 2-phenylethyl. Of these, methyl and phenyl groups are preferred.

[0042] Specific examples of component (B) include organopolysiloxanes containing trifunctional siloxane units (T units) and / or tetrafunctional siloxane units (Q units). Among these, it is preferable that the T units contain siloxane units having phenyl groups, and it is more preferable that the organopolysiloxane contains difunctional siloxane units (D units) having phenyl groups in addition to the T units having phenyl groups.

[0043] <(C) component> The powdered silica of component (C) has a BET specific surface area of ​​100m 2 / g or more.

[0044] As a specific example, the specific surface area of ​​100 m2, which has been used conventionally for silicone rubber, 2 Examples of suitable silica include powdered silica such as fumed silica or crystalline silica (dry silica) or precipitated silica (wet silica) having a surface hydrophobicity of 1 / g or more, and powdered silica obtained by subjecting the surface of such silica to hydrophobic treatment with silane, silazane, siloxane, or the like.

[0045] The blending amount of component (C) is 5 to 50 parts by mass, and particularly 10 to 40 parts by mass, per 100 parts by mass of the diorganopolysiloxane of component (A). If the blending amount is less than 5 parts by mass, the strength required for stretching cannot be obtained, and if the blending amount is more than 50 parts by mass, the physical properties such as elongation required for stretching may not be obtained.

[0046] The powdered silica may be, for example, powdered silica having a number-based average particle size in the range of 1 to 100 μm. Powdered silica having such an average particle size may also be called finely powdered silica. Here, the number-based average particle size is a value measured by D50.

[0047] <(D) component> Component (D) is a curing agent, which may be a crosslinking agent or a curing catalyst.

[0048] The crosslinking agent and / or curing catalyst can be any of the conventional crosslinking agents and / or curing catalysts typically used for curing silicone rubber. For example, when curing by radical reaction, organic peroxides such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide are used. When curing by addition reaction, an addition reaction crosslinking agent consisting of an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule and a platinum catalyst such as platinum element or chloroplatinic acid is used. The amount of peroxide added is typically 0.1 to 3 parts by mass per 100 parts by mass of diorganopolysiloxane in the case of radical reaction. In the case of addition reaction, the organohydrogenpolysiloxane is preferably added in an amount such that the molar ratio of hydrosilyl groups (SiH groups) to vinyl groups (SiVi) in component (A) is SiH / SiVi = 0.5 to 5, and the platinum catalyst is preferably added in an amount of 0.1 to 2,000 ppm as platinum metal.

[0049] <(E) Inorganic filler> In addition to the components (A) to (D), the silicone rubber composition of the present invention may further comprise, as an optional component, (E) a specific surface area measured by the BET method (BET specific surface area) of 50 to 400 m 2 / g, especially 100-350m 2 It is preferable to compound an inorganic filler having a viscosity of 1 / g.

[0050] BET specific surface area is 50 to 400 m 2 By compounding an inorganic filler having a content of 0.1g / g, it is possible to prevent manufacturing difficulties while exerting a sufficient reinforcing effect on the silicone heat-shrinkable tubing made of the silicone rubber composition, and to impart sufficient physical strength to the heat-shrinkable tubing.

[0051] The amount of inorganic filler blended is preferably 5 to 300 parts by mass, and more preferably 20 to 200 parts by mass, per 100 parts by mass of component (A). By blending an amount of 5 parts by mass or more, sufficient rubber strength can be obtained, and by blending an amount of 300 parts by mass or less, blending becomes easier.

[0052] The inorganic filler component (E) is not particularly limited as long as it is different from the powdered silica component (C). Examples of inorganic filler components include: 2 / g or more 100m 2 / g, BET specific surface area of ​​50m 2 / g or more 100m 2 / g, crystalline silica with a BET specific surface area of ​​50m 2 / g or more 100m 2 / g, 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, alumina, quartz powder, talc, and other inorganic fillers, among which those having a BET specific surface area of ​​50 m 2 / g or more 100m 2 / g, crystalline silica with a BET specific surface area of ​​50m 2 / g or more 100m 2 Precipitated silica, quartz powder, and titanium white, which have a density of less than 1 / g, are preferably used. These fillers may be surface-treated with an organosilicon compound such as an organoalkoxysilane compound, an organochlorosilane compound, an organosilazane compound, or a low-molecular-weight siloxane compound.

[0053] <(F) Component> The silicone rubber composition of the present invention preferably further contains a filler dispersant as component (F).

[0054] The inclusion of such a filler dispersant allows for sufficient dispersion of the powdered silica (component (C)) and fillers such as the inorganic filler (component (E)), and makes it possible to uniformly impart the strength required for stretching to articles molded from the silicone rubber composition of the present invention.

[0055] The filler dispersant of component (F) is not particularly limited, but examples thereof include low molecular weight siloxanes, alkoxysilanes, silazanes, diphenylsilanediols, and the like, both ends of which are blocked with hydroxyl groups.

[0056] The blending amount of component (F) is preferably 1 to 50 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of component (C), or per 100 parts by mass of component (C) and optional component (E) combined.

[0057] <Other ingredients> In addition to the essential components (A) to (D) and the optional components (E) and (F), the silicone rubber composition of the present invention can contain further optional components, such as an anti-degradant, a heat resistance improver, a heat resistance agent such as titanium oxide or cerium oxide, an internal mold release agent such as zinc stearate or dimethyl silicone oil, and a pigment, in any proportion.

[0058] <Manufacturing method> The above components can be mixed using a commonly used mixer such as a two-roll mill, kneader, or Banbury mixer. If necessary, a known dispersing aid (component (F) above; filler dispersant) such as a low-molecular-weight siloxane, alkoxysilane, silazane, or diphenylsilanediol, both of which are terminated with hydroxyl groups, can be optionally added to facilitate uniform mixing.

[0059] [Silicone heat shrink tubing] The silicone heat-shrinkable tubing of the present invention is a molded article made from the silicone rubber composition of the present invention.

[0060] The silicone heat-shrinkable tubing of the present invention is a molded article made from the silicone rubber composition of the present invention, and therefore can be shrunk by low-temperature heating, and can retain its shape as well as conventional tubing when stored at room temperature.

[0061] An example of the silicone heat-shrinkable tubing of the present invention is shown schematically in Fig. 1. Fig. 2 also shows a schematic view of the silicone heat-shrinkable tubing of Fig. 1 after a portion of the tubing has been heat-shrunk.

[0062] The silicone heat-shrinkable tube 1 shown in Fig. 1 has a tubular shape. When the silicone heat-shrinkable tube 1 is heated, the heated portion 2 shrinks (for example, shrinks in the radial direction) as shown in Fig. 2.

[0063] The silicone heat-shrinkable tubing of the present invention can be produced, for example, by the following production method.

[0064] First, the silicone rubber composition of the present invention is molded into a tubular shape by extruding the composition at a drawdown ratio of preferably 150% to 250%, more preferably 170% to 200%, relative to the nipple diameter.

[0065] The silicone rubber composition molded into a tube is then vulcanized. Vulcanization conditions are appropriately selected depending on the curing method. For example, thermal curing can be performed at a temperature of 100°C or higher under normal pressure.

[0066] The tubular silicone rubber composition that has been subjected to vulcanization is then heated and stretched (i.e., expanded) in the radial direction. For example, the tubular molded article is stretched in the radial direction under heating at 120 to 220°C, and then cooled in that state to obtain a heat-shrinkable tubular molded article.

[0067] The silicone heat-shrinkable tubing thus obtained exhibits good shrinkability even when heated with hot air or other heating means at 100°C, which is lower than the conventional heating temperature. [Example]

[0068] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0069] Example 1 The following components (A) and (B) were prepared.

[0070] Component (A): a dimethylpolysiloxane (average degree of polymerization: 8000) whose molecular chain ends are blocked with dimethylvinylsilyl groups and whose vinyl group content is 0.4 mol% based on all monovalent hydrocarbon groups;

[0071] Component (B): A polysiloxane resin (having a structure represented by the following formula) having a softening point of 128°C and an endothermic peak of 68°C in differential scanning calorimetry (DSC)

[0072] [ka]

[0073] (C) Component: specific surface area (BET method) of 200 m 2 / g fumed silica;

[0074] Component (D) (hardener): 2,4-dichlorobenzoyl peroxide

[0075] Next, 100 parts by mass of component (A), 24 parts by mass of component (C), and 10 parts by mass of component (B) were mixed in a kneader, and the resulting mixture was kneaded using a twin roll mill to produce a compound. 100 parts by mass of this compound were mixed with 1.5 parts by mass of component (D), yielding the silicone rubber composition of Example 1.

[0076] Next, the silicone rubber composition of Example 1 was formed into a sheet, press-cured at 200°C for 10 minutes, and then post-cured at 200°C for 1 hour to harden it.

[0077] The cured sheet thus obtained was then stretched to 2 times its original size under heating at 150°C, and cooled to room temperature in that state, after which the stress was removed.

[0078] The rubber physical properties of the resulting cured sheet were measured in accordance with JIS K6249:2003, including stretch retention and heat shrinkage at 120° C. and 100° C. The results are shown in Table 1.

[0079] The obtained silicone rubber composition was extruded in an extrusion molding machine using an extrusion die of 7.5φ and a nipple of 4.0φ to set the tube inner diameter to 2.7φ, and passed through a heated vulcanization tower (450°C) to produce a vulcanized tube with a drawdown ratio of 150% of the nipple diameter ((nipple diameter / tube inner diameter) × 100). The orientation of the tube (the direction in which the tube is most likely to tear) was always axial.

[0080] Next, the tube was placed in a stainless steel pipe with an inner diameter of 6.8φ and a length of 1 m, which was heated to 200°C, and air was blown into the tube at 3.0 kg / cm. 2 The silicone heat-shrinkable tubing thus obtained had an inner diameter of 5.3φ, and the orientation at this time was axial, similar to that of the extrusion-molded product.

[0081] When this silicone heat-shrinkable tube was stored at 23° C., no shrinkage was observed. Based on this result, the tube retention was judged to be acceptable.

[0082] The silicone heat-shrinkable tubing was then heated to 100°C and shrunk. The inside diameter of the tubing after shrinkage was 2.8φ, and the orientation was axial, similar to that of the extruded and stretched products. Based on these results, the tubing was judged to have acceptable shrinkability.

[0083] Examples 2 and 3 Cured sheets of Examples 2 and 3 were produced using the same formulations and molding conditions as in Example 1, except that the amount of polysiloxane resin (component (B)) added in Example 1 was changed to 18 parts by mass and 30 parts by mass, respectively, and the properties of the cured sheets of Examples 2 and 3 were measured in the same manner as in Example 1. The results are shown in Table 1.

[0084] Furthermore, silicone heat-shrinkable tubing was produced using the silicone rubber compositions used in Examples 2 and 3 in the same manner as in Example 1, and the same evaluations were carried out. As a result, in all Examples, both the tubing shrinkability and tubing retention were judged to be acceptable.

[0085] Comparative Example 1 The cured sheet of Comparative Example 1 was produced using the same formulation and molding conditions as in Example 2, except that the polysiloxane resin (component (b1)) used in Example 2, component (B), was replaced with a polysiloxane resin having a softening point of 89°C and an endothermic peak of 45°C in differential scanning calorimetry (DSC), and the properties of the cured sheet of Comparative Example 1 were measured using the same methods as in Example 1. The results are shown in Table 1.

[0086] The structure of the polysiloxane resin (b1) used in Comparative Example 1 is shown below. [ka]

[0087] Comparative Example 2 A cured sheet of Comparative Example 2 was produced using the same formulation and molding conditions as in Example 2, except that the polysiloxane resin (component (b2)) used in Example 2, component (B), was replaced with a polysiloxane resin having a softening point of 126°C and an endothermic peak in differential scanning calorimetry (DSC) of 82°C. The properties of the cured sheet of Comparative Example 2 were measured using the same methods as in Example 1. The results are shown in Table 1.

[0088] The structure of the polysiloxane resin (b2) used in Comparative Example 2 is shown below. [ka]

[0089] Furthermore, silicone heat-shrinkable tubes were prepared using the silicone rubber compositions used in Comparative Examples 1 and 2 in the same manner as in Example 1, and the same evaluations were carried out.

[0090] As a result, in Comparative Example 1, when the silicone heat-shrinkable tubing was heated to 100°C and shrunk, the tubing inner diameter after shrinkage was 2.8φ, and the orientation was axial, similar to the extruded and stretched products. Based on these results, the tubing shrinkability was judged to be acceptable. However, when the silicone heat-shrinkable tubing was stored at 23°C, shrinkage was confirmed, indicating poor retention, so the tubing retention was judged to be unacceptable.

[0091] In Comparative Example 2, the silicone heat-shrinkable tubing was heated to 100°C and shrunk. The shrunk tube inner diameter was 4.0φ, and the orientation was axial, similar to the extruded and stretched products. Based on these results, it was determined that the tubing had not shrunk sufficiently, and the tubing shrinkability was judged to be unacceptable. However, when the silicone heat-shrinkable tubing was stored at 23°C, no shrinkage was observed. Based on these results, the tubing retention was judged to be acceptable.

[0092] Comparative Example 3 A cured sheet of Comparative Example 3 was produced using the same formulation and molding conditions as in Example 1, except that the polysiloxane resin, component (B), used in Example 1, was not added, and the properties of the cured sheet of Comparative Example 3 were measured using the same methods as in Example 1. The results are shown in Table 1.

[0093] The stretch retention rate and heat shrinkage were calculated according to the following formulas.

[0094]

number

[0095] [Table 1]

[0096] From the results in Table 1, it was found that the cured sheets according to the present invention (Examples 1 to 3) exhibit good shrinkage at 100°C, which is lower than conventional ones, and also have excellent retention properties at room temperature, resulting in stretchability that allows them to be used without problems as heat-shrinkable molded products.

[0097] On the other hand, in Comparative Example 1, in which component (B) was replaced with polysiloxane resin (b1) having a softening point of 89°C and an endothermic peak in DSC of 45°C, the results showed poor retention at room temperature.

[0098] In addition, in Comparative Example 2, in which component (B) was replaced with polysiloxane resin (b2), which has a softening point of 126°C but an endothermic peak in DSC of 82°C, sufficient shrinkage was not exhibited when heated at 100°C.

[0099] In Comparative Example 3, in which component (B) was not used, stretch molding was not possible.

[0100] The present invention includes the following aspects. [1] A silicone rubber composition for forming a silicone heat-shrinkable tube, (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 3,000 to 50,000, in which 50 mol % or more of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) 10 to 100 parts by mass of an organopolysiloxane resin other than the component (A), which has a softening point of 100 to 200°C and an endothermic peak of 50 to 80°C in differential scanning calorimetry; (C) BET specific surface area is 100m 2 / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount A silicone rubber composition comprising: [2] Furthermore, (E) BET specific surface area is 50 to 400 m 2 The silicone rubber composition according to [1], characterized in that it contains 5 to 300 parts by mass of inorganic filler in an amount of 100 to 1000 parts by mass / g. [3] The component (E) has a BET specific surface area of ​​50 m 2 / g or more 100m 2 / g, crystalline silica with a BET specific surface area of ​​50m2 / g or more 100m 2 The silicone rubber composition according to [2], characterized in that the inorganic filler is selected from precipitated silica, quartz powder, and titanium white, and has a water solubility of less than 10 ... [4] The silicone rubber composition according to any one of [1] to [3], further comprising a filler dispersant as component (F). [5] A silicone heat-shrinkable tube, which is a molded article made from the silicone rubber composition according to any one of [1] to [4].

[0101] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0102] 1...Silicone heat shrink tubing, 2...Heated part.

Claims

1. A silicone rubber composition for forming a silicone heat shrinkable tube, comprising: (A) 100 parts by mass of a linear organopolysiloxane having two or more vinyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 3,000 to 50,000, in which at least 50 mol % of all substituents are methyl groups and 0.05 to 5.0 mol % are vinyl groups; (B) an organopolysiloxane resin other than the component (A) having a softening point of 100 to 200° C. and an endothermic peak of 50 to 80° C. in differential scanning calorimetry: 10 to 100 parts by mass; (C) BET specific surface area is 100 m ２ / g or more: 5 to 50 parts by mass of powdered silica; and (D) Curing agent: effective amount A silicone rubber composition comprising:

2. Furthermore, (E) the BET specific surface area is 50 to 400 m ２ 2. The silicone rubber composition according to claim 1, further comprising 5 to 300 parts by mass of inorganic filler / g.

3. The component (E) has a BET specific surface area of ​​50 m ２ / g or more 100m ２ / g, BET specific surface area of ​​50 m ２ / g or more 100m ２ 3. The silicone rubber composition according to claim 2, wherein the inorganic filler is selected from the group consisting of precipitated silica, quartz powder and titanium white, the inorganic filler having a viscosity of less than 1000 s / g.

4. 2. The silicone rubber composition according to claim 1, further comprising a filler dispersant as component (F).

5. 5. A silicone heat shrinkable tube which is a molded article made of the silicone rubber composition according to claim 1.

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