VIBRATION-DAMPING SILICONE COMPOSITION

Technical Field [0001]

The present invention relates to a vibration-damping silicone composition and, more specifically, to a vibration-damping silicone composition that has excellent flowability even at higher values of G* which is correlated with the resonance frequency.

Background Art

[0002]

A great number of various vibration-damping compositions prepared from viscous liquids and solid powders have been proposed. For example, Japanese Unexamined Patent Application Publication (hereinafter referred to as "Kokai") S63-308241 describes a vibration-damping composition consisting of a viscous liquid such as silicone oil and a solid powder such as silica powder, glass powder, silicone resin powder, etc. Kokai H 10-251517 describes a vibration-damping composition prepared from a viscous liquid, such as silicone oil, and a silicone resin powder. Kokai Hl 0-281202 describes a viscous liquid compounded from a surface-treated wet-process fine silica powder and a silsesquioxane powder in silicone oil. Kokai Hl 1 - 182624 discloses a viscous liquid compounded from dimethylsiloxane capped at the molecular terminals with silanol groups and a wet-process fine powder silica with silsesquioxane powder in silicone oil. Kokai 2002- 161206 (equivalent to EP 129202) discloses a viscous liquid compounded from a hydrophobized wet-process fine silica powder and a silicone resin powder in silicone oil.

[0003]

Usually, small-scale vibration-damping structures require the use of materials of high resonance frequencies. This is because at low resonance frequencies, along with widening of damping frequency range, restrictions occur that dictate an increase in amplitudes and clearances. It has been found experimentally that an increase in the value of G*, which is one of the viscoelastic characteristics of materials, leads to an increase in resonance frequency. However, in vibration-damping compositions known heretofore, an increase in

the value of G* is accompanied either by an increase in viscosity that impairs handling conditions of the material.

Disclosure of Invention [0004]

It is an object of the present invention to provide a vibration-damping silicone composition that may have good fiowability even at higher values of G*.

[0005] The above object is achieved by providing a vibration-damping silicone composition obtained by uniformly mixing the below-given components at a temperature of 70°C or higher:

(A) 100 parts by weight of a silicone oil;

(B) 10 to 300 parts by weight of a silicone resin powder that contains 0.1 to 10 wt. % of silicon-bonded hydroxyl groups and/or alkoxy groups with 1 to 5 carbon atoms; and

(C) 0.5 to 50 parts by weight of an organosiloxane oligomer represented by the following average unit formula: (where R ¹ is a hydrocarbon group or a halogenated alkyl group having 1 to 10 carbon atoms, X is a hydroxyl group and/or an alkoxy group having 1 to 5 carbon atoms, "a" and "b" are positive numbers; and where the following condition is observed: 0<a<4, 0<b<4, 0<a+b<4).

[0006]

Since the vibration-damping silicone composition of the invention is prepared by uniformly mixing aforementioned components (A) through (C) in specific proportions at a temperature of 70°C or higher, the compound may possess good fiowability even if higher values of G* are required.

Best Mode for Carrying Out the Invention [0007]

Component (A), the silicone oil, functions as a medium in which component (B) is dispersed. The silicone oil is a organopolysiloxane that is liquid at room temperature. In this

organopolysiloxane, the groups bonded to the silicon atoms may be represented by univalent hydrocarbon groups having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, or similar alkyl groups; vinyl, allyl, butenyl, or similar alkenyl groups; and phenyl, tolyl, or similar aryl groups. Halogenated alkyl groups such as 3,3,3-trifluoropropyl may also be used. Small amounts of these hydrocarbon groups may be replaced by hydroxyl groups, or alkoxy groups such as methoxy, and ethoxy groups. Most preferable are alkyl groups, especially methyl groups. Alkyl groups are preferred because the composition in accordance with the present invention containing such silicone oils has a low degree of change of viscosity with respect to temperature. The aforementioned silicone oil may have a linear, partially branched linear, branched, or cyclic molecular structure. A linear molecular structure is preferred.

[0008]

The aforementioned silicone oil of component (A) is recommended to have a kinematic viscosity at 25°C of 1,000 to 1,000,000 mm ² /s, preferably from 5,000 to 500,000 mm ² /s, and even more preferably, from 10,000 to 500,000 mmVs. When the kinematic viscosity at 25 ⁰ C is less than the recommended lower limit, it is difficult to maintain the resin powder of component (B) in a uniformly dispersed state in component (A). On the other hand, when the viscosity of component (A) exceeds the recommended upper limit, handling properties deteriorate, and it becomes difficult to disperse solid powder in the silicone oil.

[0009] It is recommended to maintain the kinematic viscosity of component (A) at 25°C within the range of 10,000 to 500,000 mm ² /s because with this range it becomes possible to provide a higher value of G*. As it has been mentioned earlier, it has been found experimentally that a certain correlation exists between the value of G* and resonance frequency of a vibration- damping structure, and when the vibration-damping composition of the invention has a higher value of G*, a small-sized vibration-damping structure may have a higher resonance frequency. This is because small-sized vibration-damping structures are normally made from materials that are characterized by higher resonance frequencies.

[0010]

The silicone oil of component (A) may be exemplified by trimethylsiloxy-endblocked dimethylpolysiloxanes, trimethylsiloxy-endblocked methyloctylpolysiloxane,

vinyldimethylsiloxy-endblocked dimethylpolytsiloxane, silanol-endblocked dimethylpolysiloxanes, and trimethylsiloxy-endblocked dimethylsiloxane- methylphenylsiloxane copolymers.

[0011]

The silicone resin powder that constitutes component (B) is utilized to enhance the vibration- damping properties of the vibration-damping silicone composition of the invention and to reduce dependence of the vibration-damping properties of the composition of the invention from temperature. This component contains in its main structure RSiO _3/2 siloxane units and/or SiO _4/2 units. Arbitrarily, this component may also contain other siloxane units such as R ₂ Si0 _2/2 and R ₃ SiCv ₂ units. The use of an organopolysilsesquioxane powder containing substantially only RSiO _3/2 units is most preferred. Preferably R is a monovalent hydrocarbon group with 1 to 10 carbon atoms, for example alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl, allyl, and butenyl; and aryl groups such as phenyl and tolyl. R may also be a halogenated alkyl group with 1 to 10 carbon atoms such as 3,3,3-trifluoropropyl. The use of alkyl groups, especially methyl groups, and in particular those that contain methyl groups in an amount of more than 50%, is preferable. In addition, some of these groups may be substituted by hydroxyl groups or alkoxy groups having 1 to 5 carbon atoms, such as methoxy and ethoxy groups. Their content in component (B) should be within the range of 0.1 to 10 wt.%. Alkyl groups are preferred as the resulting composition in accordance with the invention containing such resins has only a low degree of change of viscosity with respect to temperature and has excellent storage stability. Each R may be the same or different, but it is preferred that at least 50% of the R groups are alkyl groups, most preferably methyl groups. Component B may have an average particle size of from 1 to 100 μm, preferably from 10 to 40 μm. The shape of the particles may be spherical, oblate, or irregular.

[0012]

Component (B) is an organopolysiloxane powder that is solid at room temperature. It is recommended that this powder do not have a melting point. If it has a melting point, then depending on the operation conditions of the vibration-damping silicone powder, an

undesirable situation may occur when the vibration-damping properties will depend on the operation temperature.

[0013] The amount of component (B) to be added per 100 parts by weight of component (A) may be in the range of from 10 to 300 parts by weight, preferably from 30 to 300 parts by weight. When the amount of component (B) is less than 10 parts by weight, the vibration-damping properties of the composition according to the present invention will deteriorate and will to a significant degree depend on the operation temperature, and when the amount of component (B) exceeds 300 parts by weight, this will impair workability of the composition.

[0014]

Component (C) is a surface-treating agent for the silicone resin powder of component (B).

The function of component (C) is to reduce the apparent viscosity of the silicone composition of the invention. Component (C) is a siloxane oligomer represented by the following average unit formula: R ¹ _a X _b Si0( _4-a - _b ) _/2 , where R ¹ is a monovalent hydrocarbon group with 1 to 10 carbon atoms, for example alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl, allyl, and butenyl; and aryl groups such as phenyl and tolyl. R ¹ may also be a halogenated alkyl group with 1 to 10 carbon atoms such as 3,3,3-trifluoropropyl. Methyl groups are preferable since they facilitate reaction with the silicone resin powder at a minimal steric hindrance. X is a hydroxyl group or an alkoxy group having 1 to 5 carbon atoms, such as a methoxy group, ethoxy group, or the like. Hydroxyl groups are preferable since they facilitate reaction with the silicone resin powder of component (B). In the above formula, "a" and "b" are positive numbers; and the following condition is observed: 0<a<4, 0<b<4, 0<a+b<4, preferably 1.5<a<2, 0<b<0.5, 1.5<a+b<2.5; even more preferably 1.8<a<2, 0<b<0.4, 1.8<a+b<2.4.

[0015]

The aforementioned organosiloxane oligomer may have a linear, branched, or cyclic molecular structure, of which a linear structure is preferable. If the oligomer has a linear molecular structure, it can more readily react with the silicone resin powder of component (B). The aforementioned organosiloxane oligomer has a lower viscosity than silicone oil of

component (A). And organosiloxane oligomer of component (C) is recommended to have a viscosity of 5 to 500 rnm ² /s, preferably 10 to 100 mm ² /s at 25°C. If viscosity at 25 ⁰ C is below the recommended lower limit, this will impair operative properties of this component because it will more easily evaporate. If, on the other hand, the viscosity exceeds the recommended upper limit, this will impair reactivity to the silicone resin powder. The organosiloxane oligomer of component (C) should be added in an amount of 0.5 to 50 parts by weight, preferably 0.5 to 20 parts by weight per 100 parts by weight of the aforementioned silicone oil. If it is added in an amount of less than the recommended lower limit, there will be almost no effect on lowering the apparent viscosity, and if, on the other hand, it is added in an amount exceeding the recommended upper limit, then depending on the type of component (C), it may be subject to separation.

[0016]

A preferable example of component (C) is a silanol-endblocked diorganopolysiloxane of the following formula:

where R ¹ is the same as defined above. In order to reduce a degree of polymerization, it is recommended that "n" be an integer between 0 and 100, preferably, between 2 and 20.

[0017]

The silicone composition of the invention is prepared from components (A) through (C). If necessary, however, other arbitrary components can be added, such as microfme glass powder, microfine silica powder, clay, bentonite, diatomaceous earth, quartz powder, or a similar microfine inorganic powder; microfine acrylic resin powder, microfine diatomaceous powder, microfine phenol resin powder, or a similar microfine organic powder, as well as an oxidation inhibitors, preservatives, flame retardants, pigments, dyes, or the like. These arbitrary components can be added in amounts that are not detrimental to the objects of the

invention. It is recommended that particles of microfme inorganic powders containing a large number of hydroxy 1 groups on their surfaces, i.e. micorofine silica, are not added to the silicone composition of the invention. This is because the addition to the silicone composition of the invention of a microfme inorganic powder with a large number of hydroxyl groups will increase thixotropy of the composition. This, in turn, will reduce operating properties of the composition since it will be difficult to remove air bubble during preparation of the composition and to fill sealing spaces in sealing operations. Furthermore, increase of thixotropy caused by the addition of microfme silica powder decreases tan δ in the low-frequency range and thus impairs vibration-damping properties of the composition.

[0018]

It is recommended that at room temperature the composition be in a liquid state with a viscosity from 0.01 to 10,000 Pa-s, preferably 0.1 to 4,000 Pa-s. If the viscosity exceeds the recommended upper limit, this will impair operating properties of the composition as it will be difficult to remove air bubbles from the composition and to fill sealing spaces in an inclusion body.

[0019]

A method used for the preparation of the silicone composition of the invention consists of combining and kneading aforementioned silicone oil (A), silicone resin powder (B), and organosiloxane oligomer (C) in a known mixer, such as a ball mill, a vibrating mill, kneader- mixer, screw extruder, paddle mixer, ribbon mixer, Banbury mixer, Ross mixer, Henschel mixer, flow jet mixer, Hubbard mixer, or a roll mill. In order to improve efficiency of the reaction between the silicone resin powder (B) with the organosiloxane oligomer (C), mixing should be accompanied by heating, at a temperature at least 7O ⁰ C. For improving dispersity of component (B), components (A) through (C) may be first mixed and kneaded to a uniform state of the mixture at room temperature, and then mixing may be continued at a temperature at least 70°C. The most preferable heating temperature is within the range of 70 to 200°C. While the pressure used during mixing may be atmospheric, mixing under a reduced pressure is preferred.

[0020]

The vibration-damping silicone composition of the present invention is characterized by excellent vibration-damping properties. Therefore, this composition is suitable to fill sealing spaces in an elastic inclusion body such as rubber bags or rubber tubes of a vibration- damping device. The silicone composition of the invention makes it possible to increase the value of G* without impairing handling conditions. And because the main component of the composition is a silicone-type material, it becomes possible to diminish the effect of temperature on vibration-damping properties. Therefore, the composition is suitable for use in small-sized vibration-damping devices that may be incorporated in electrical or electronic devices that require miniaturization of parts and high vibration-damping characteristics and intended for operation in environments subject to significant variations in temperature, such as compact disk players, compact disk changers, mini disk players, car navigation devices, or other devices.

Examples [0021]

The vibration-damping silicone composition of the invention will be further described in more detail with reference to application examples. In these examples, the values of kinematic viscosity were measured at 25°C and the values of viscosity were measured at 25°C with the use of a rotary-type viscosimeter from Brookfield Co. (rotor No. 14; 0.5 rpm). Vibration-damping characteristics were evaluated by measuring G* and loss tangent (tan δ) at 25°C. The loss tangent (tan δ) and G* were measured by a plate method using a dynamic analyzer (Model RDA- 700 manufactured by Rheometrics Co., Ltd.). The measurement conditions included the use of a 25-mm-diameter plate, frequencies: 0.1 Hz, 1 Hz, 10 Hz, and 40 Hz; strain: 5%; and sample thickness: 2 mm.

[0022] Example 1

A mixer was charged with the following components: 490 g of a dimethylpolysiloxane endblocked at both molecular terminals with trimethylsiloxy groups, and having a kinematic viscosity of 100,000 mm ² /s; 480 g of a methylpolysilsesquioxane powder containing siloxane units of the following formula: CH ₃ Siθ _3/2 (average particle diameter: 20μm; contents of

hydroxyl groups: 3.7 wt. %); and 30 g of a dimethylpolysiloxane endblocked at both molecular terminals with hydroxy groups and having a kinematic viscosity of 40 mm /s. The components were uniformly kneaded at 150 rpm while scraping them from the wall of the mixer and then were kneaded for 2 hr under a reduced pressure (100 mm Hg) with heating at 100°C. The vibration-damping characteristics and kinematic viscosity of the obtained silicone composition were measured. The results of measurements are shown in Table 1.

[0023] Example 2

A mixer was charged with the following components: 330 g of a dimethylpolysiloxaiie endblocked at both molecular terminals with trimethylsiloxy groups, and having a kinematic viscosity of 100,000 mm ² /s; 220 g of a dimethylpolysiloxane endblocked at both molecular terminals with trimethylsiloxy groups; 440 g of methylpolysilsesquioxane powder containing siloxane units of the following formula: CH ₃ SiO ₃ Q (average particle diameter: 20μm; contents of hydroxyl groups: 3.7 wt. %); and 50 g of a dimethylpolysiloxane encapped at both molecular terminals with hydroxy groups and having a kinematic viscosity of 40 mni ² /s. The components were uniformly kneaded at 150 rpm while scraping them from the wall of the mixer and then were kneaded for 2 hr under a reduced pressure (100 mm Hg) with heating at 100°C. The vibration-damping characteristics and kinematic viscosity of the obtained silicone composition were measured. The results of measurements are shown in Table 1.

[0024] Comparative Example 1

A mixer was charged with the following components: 490 g of a dimethylpolysiloxane endblocked at both molecular terminals with trimethylsiloxy groups, and having a kinematic viscosity of 100,000 mm ² /s; 480 g of a methylpolysilsesquioxane powder containing siloxane units of the following formula: CH ₃ Siθ _3/2 (average particle diameter: 20μm; contents of hydroxyl groups: 3.7 wt. %). The components were uniformly kneaded at 150 rpm while scraping them from the wall of the mixer and then were kneaded for 2 hr. During this period, the maximum temperature was 40°C. The vibration-damping characteristics and

kinematic viscosity of the obtained silicone composition were measured. The results of measurements are shown in Table 1.

[0025]

Comparative Example 2

A mixer was charged with the following components: 490 g of a dimethylpolysiloxane endblocked at both molecular terminals with trimethylsiloxy groups, and having a kinematic viscosity of 100,000 mm ² /s; 480 g of a methylpolysilsesquioxane powder containing siloxane units of the following formula: CH ₃ SiO ₃ Q (average particle diameter: 20μm; contents of hydroxyl groups: 3.7 wt. %), and 30 g of a dimethylpolysiloxane endblocked at both molecular terminals with hydroxy groups and having a viscosity of 40 mm ² /s. The components were uniformly kneaded at 150 rpm while scraping them from the wall of the mixer and then were kneaded for 2 hr. During this period, the maximum temperature was 4O ⁰ C. The vibration-damping characteristics and kinematic viscosity of the obtained silicone composition were measured. The results of measurements are shown in Table 1.

[0026]

[Table 1] Viscosities and Vibration-damping Characteristics of Silicone Compositions at

25°C