JP2023028519A - silicone rubber composition - Google Patents

Abstract

To provide a silicone rubber composition that has excellent fire resistance and has excellent shape retentivity particularly at high temperatures.SOLUTION: A silicone rubber composition contains (A) an organopolysiloxane that has a degree of polymerization of 100-10,000 and includes, in one molecule, two or more alkenyl groups binding to a silicon atom: 100 pts.mass, (B) reinforcing silica that has a specific surface area of 50-500 m2/g as measured by the BET method: 10-100 pts.mass, (C) sintered mica with an average particle size of 0.5-20 μm: 1-100 pts.mass, (D) metalhydroxide with an average particle size of 0.5-20 μm: 0.3-15 pts.mass and (E) a curing agent: effective amount.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a silicone rubber composition having excellent fire resistance, particularly excellent shape retention under high temperature conditions such as in the event of a fire, and resistance to ignition.

2. Description of the Related Art Conventionally, materials molded from rubber materials such as chloroprene-based rubber and ethylene-propylene-diene-based rubber have been used as building refractory materials. However, although these rubber materials are excellent in flame retardancy, they emit a large amount of smoke when exposed to high temperatures in the event of a fire, obstructing visibility, and sometimes contain toxic components. Moreover, it cannot be said that the shape retainability at high temperatures is sufficient. Under these circumstances, silicone rubber has recently been used as a refractory material for construction because of its excellent heat and weather resistance and creep resistance. For the same reason, the amount of silicone rubber used as a wire coating material is also increasing.

Ordinary silicone rubber burns and ashes when exposed to high temperatures such as flames for a long period of time, and therefore does not have a sufficient function as a gasket.

Therefore, in the refractory material made of silicone rubber, in order to improve the above defects, at least one selected from zinc oxide and/or aluminum hydroxide and a platinum compound (Patent Document 1), manganese carbonate, mica, and black red iron oxide A combination of one of them and zinc oxide and/or quartz powder and a platinum compound (Patent Document 2) has been studied. Furthermore, it has been proposed to add magnesium hydroxide (Patent Document 3) or calcined mica (Patent Document 4) to organopolysiloxane to sinter it (ceramize) at a high temperature. However, these silicone rubbers have insufficient dimensional stability at high temperatures, and in some cases, the rubber partially foams and the siloxane gas contained therein burns.

JP-A-60-141778 Japanese Patent Publication No. 5-73158 JP-A-2000-169706 WO2015/011971

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a silicone rubber composition that exhibits excellent shape retention even when exposed to high temperatures for a long period of time.

As a result of intensive studies to achieve the above object, the present inventors have found that an organopolysiloxane having a degree of polymerization of 100 or more and having two or more alkenyl groups bonded to silicon atoms in one molecule can be obtained by the BET method. In a composition containing a reinforcing silica having a measured specific surface area of 50 m ² /g or more and a curing agent, furthermore, calcined mica having a specific particle size and a metal hydroxide are used in combination to improve shape retention at high temperatures. The present invention was completed based on the discovery that a silicone rubber composition having particularly excellent properties can be provided.

Accordingly, the present invention provides the following silicone rubber composition.
[1]
(A) an organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass;
(B) reinforcing silica having a specific surface area of 50 to 500 m ² /g as measured by the BET method: 10 to 100 parts by mass;
(C) calcined mica having an average particle size of 0.5 to 20 μm: 1 to 100 parts by mass,
(D) a metal hydroxide having an average particle size of 0.5 to 20 μm: 0.3 to 15 parts by mass; and (E) a curing agent: an effective amount.
[2]
The silicone rubber composition according to [1], wherein the calcined mica of component (C) is obtained by calcining pulverized muscovite mica.
[3]
The silicone rubber composition according to [1] or [2], wherein the metal hydroxide of component (D) is aluminum hydroxide or magnesium hydroxide.
[4]
The silicone rubber composition according to any one of [1] to [3], which is used for fireproof gaskets or fireproof electric wires.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide a silicone rubber composition which is excellent in fire resistance and, in particular, excellent in shape retention at high temperatures.

1 is a schematic diagram of a testing machine used for measuring breaking strength in Examples of the present invention. FIG.

The present invention will be described in more detail below.
[(A) Alkenyl Group-Containing Organopolysiloxane]
Component (A) used in the silicone rubber composition of the present invention has a degree of polymerization (or the number of silicon atoms in the molecule) of 100 to 10,000 and has two or more silicon-bonded silicon atoms in one molecule. It is an organopolysiloxane having alkenyl groups. This (A) component acts as the main ingredient (base polymer) of the present composition. Also, the alkenyl group-containing organopolysiloxane of component (A) is preferably a gum-like component (that is, highly viscous and non-liquid without self-fluidity) at room temperature (25° C.). The silicone rubber composition of the present invention, which contains such a crude rubber-like alkenyl group-containing organopolysiloxane as a main ingredient, is usually millable (i.e., raw rubber-like) and is processed under shear stress by a kneader such as a roll mill. It gives a composition that can be uniformly kneaded into As the alkenyl group-containing organopolysiloxane of component (A), for example, those represented by the following average compositional formula (I) are preferable.
R _a SiO _(4-a)/2 (I)
(In formula (I), R represents the same or different monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a number of 1.95 to 2.05.)

In the average composition formula (I), R represents the same or different monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, specifically, methyl group, ethyl group, propyl group, butyl Alkyl groups such as hexyl group and octyl group; cycloalkyl groups such as cyclopentyl group and cyclohexyl group; fluoroalkyl groups such as 3,3,3-trifluoropropyl group; alkenyl groups such as vinyl group, allyl group and propenyl group; cycloalkenyl group, phenyl group, aryl group such as tolyl group, aralkyl group such as benzyl group, 2-phenylethyl group, etc.; A methyl group and a vinyl group are preferred. It is preferable that 80% or more, particularly 90% or more of all R groups are methyl groups, and more preferably all R groups other than alkenyl groups are methyl groups.

Specific examples of the alkenyl group-containing organopolysiloxane of component (A) include those in which the main chain of the organopolysiloxane is composed of dimethylsiloxane units, or those in which a phenyl group or vinyl group is part of the main chain of the dimethylpolysiloxane. , 3,3,3-trifluoropropyl group-containing diphenylsiloxane units, methylvinylsiloxane units, methyl-3,3,3-trifluoropropylsiloxane units, etc. are preferably introduced.

The component (A) organopolysiloxane has 2 or more (usually 2 to 50, particularly about 2 to 20) alkenyl groups, preferably vinyl groups, in one molecule. Preferably, 0.01 to 10%, especially 0.02 to 5%, of all R groups in formula (I) are alkenyl groups. The alkenyl group may be bonded to a silicon atom at the terminal of the molecular chain, bonded to a silicon atom in the middle (non-terminal) of the molecular chain, or both. As the organopolysiloxane, those having at least alkenyl groups bonded to silicon atoms at both ends of the molecular chain are preferred. Specifically, it is preferable that both ends of the molecular chain are blocked with a dimethylvinylsilyl group, a methyldivinylsilyl group, a trivinylsilyl group or the like.

In the average composition formula (I) above, a is a number from 1.95 to 2.05, preferably from 1.98 to 2.02, more preferably from 1.99 to 2.01. The molecular structure of the component (A) organopolysiloxane is basically composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ) in the main chain and triorganosiloxy groups (R ₃ SiO _1/2 ), but a branched structure containing a small amount of branching units (RSiO _3/2 ) in the main chain within a range that does not impair rubber elasticity. (R is the same as above).

The degree of polymerization of the component (A) organopolysiloxane is 100 to 10,000, preferably 1,000 to 10,000, more preferably 2,000 to 10,000, still more preferably 3,000 to 8,000, particularly preferably 5,000 to 8,000. If the degree of polymerization is less than 100, sufficient rubber strength cannot be obtained. In the present invention, the degree of polymerization is the number of silicon atoms in the organopolysiloxane, and the weight average degree of polymerization (or weight average molecular weight) in terms of polystyrene in GPC (gel permeation chromatography) analysis using toluene or the like as a developing solvent. etc. In the present specification, the degree of polymerization is a value obtained as a weight average degree of polymerization from the polystyrene-equivalent number average molecular weight in gel permeation chromatography (GPC) analysis measured under the following conditions.
[Measurement condition]
Developing solvent: toluene Flow rate: 0.6 mL/min
Detector: Differential Refractive Index Detector (RI)
Column: TSK Guard column SuperH-H
TSKgel Super H5000 (6.0 mm I.D. x 15 cm x 1)
TSKgel Super H4000 (6.0mm ID x 15cm x 1)
TSKgel Super H3000 (6.0mm I.D. x 15cm x 1)
(both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (toluene solution with a concentration of 0.5% by mass)

The organopolysiloxane of component (A) may be used singly or in combination of two or more having different molecular structures and degrees of polymerization.

Such an organopolysiloxane can be obtained by a known method, for example, by (co)hydrolytic condensation of one or more organohalogenosilanes, or by ring-opening polymerization of a cyclic polysiloxane using an alkaline or acidic catalyst. can be obtained by

[(B) Reinforcing silica]
Reinforcing silica of component (B) is exemplified by fine reinforcing silica powder that is commonly used in silicone rubber compositions. For example, fumed silica, dry silica such as pyrogenic silica, wet silica such as precipitated silica, and the like can be mentioned, and among them, fumed silica is preferable from the viewpoint of heat resistance. The specific surface area measured by the BET method is 50 to 500 m ² /g, preferably 100 to 400 m ² /g, particularly preferably 100 to 300 m ² /g. If the specific surface area is less than 50 m ² /g, the mechanical strength is insufficient. Moreover, if the specific surface area is greater than 500 m ² /g, industrial production becomes difficult.

The surface of this reinforcing silica may be subjected to hydrophobic treatment with a known treating agent such as chlorosilane or hexamethyldisilazane, if necessary.

The amount of reinforcing silica (B) added is 10 to 100 parts by mass, preferably 20 to 70 parts by mass, particularly preferably 30 to 60 parts by mass, per 100 parts by mass of organopolysiloxane (A). part by mass. If the amount of component (B) added to 100 parts by mass of component (A) is less than 10 parts by mass, the amount is too small to obtain a sufficient reinforcing effect. , and the mechanical strength may decrease.

[(C) Burned mica]
Calcined mica, component (C), is a component that imparts fire resistance (that is, sinterability (shape retention) after combustion) to the silicone rubber obtained by curing the silicone rubber composition. The calcined mica used in the present invention is obtained by heat-treating wet mica or dry mica at a temperature of 800° C. or higher. Examples of such calcined mica include calcined mica manufactured by Repco Co., Ltd., which is produced by calcining pulverized muscovite mica. Non-calcined mica has the disadvantage that it tends to adhere to the surfaces of metal rolls during kneading with two rolls. Also, uncalcined mica may cause significant foaming during molding of silicone rubber or when the molded product is exposed to high temperatures.

The calcined mica has an average particle size of 0.5 to 200 μm, preferably 1 to 100 μm, particularly preferably 1 to 50 μm. If the average particle size of the calcined mica is less than 0.5 μm, it tends to agglomerate and is difficult to handle. It becomes insufficient, and the shape retention property of the ashed (sintered) silicone rubber molded article is lowered.
In the present invention, the average particle diameter is obtained as a cumulative weight average diameter (or median diameter, d50) in particle size distribution measurement by a laser diffraction method.

Component (C) is added in an amount of 1 to 100 parts by mass, preferably 10 to 80 parts by mass, per 100 parts by mass of organopolysiloxane as component (A). If the amount of component (C) added to 100 parts by mass of component (A) is less than 1 part by mass, sufficient shape retention cannot be obtained, and if it exceeds 100 parts by mass, the plasticity of the material increases, making kneading and molding difficult. It can be difficult.

[(D) metal hydroxide]
(D) Component metal hydroxide is preferably aluminum hydroxide or magnesium hydroxide. By adding an appropriate amount of metal hydroxide to the composition, it is possible to intentionally generate minute bubbles uniformly and suppress large bubbles. If a metal hydroxide is not added to the composition, large swelling (foaming) may occur when exposed to a high temperature of 500° C. or higher. This foaming is considered to be caused by moisture and low-molecular-weight siloxane derived from silica and calcined mica. Especially in the case of gaskets, a gap may be created between the glass and the gasket, allowing hot air to pass through. In addition, the bulging portion is filled with combustible siloxane gas, and there is a risk that the gas will burn if it ruptures due to high temperatures.

The average particle size of the metal hydroxide is 0.5-20 μm, preferably 1-15 μm, particularly preferably 2-10 μm. If it is smaller than 0.5 μm, the composition may be poorly filled, and if it is larger than 20 μm, foaming may become uneven at high temperatures and the strength of the silicone rubber molded article may decrease.
The average particle size is obtained, for example, as a cumulative weight average diameter (or median diameter, d50) in particle size distribution measurement by a laser diffraction method.

Component (D) is added in an amount of 0.3 to 15 parts by mass, preferably 0.5 to 10 parts by mass, per 100 parts by mass of organopolysiloxane as component (A). If the amount of component (D) added to 100 parts by mass of component (A) is less than 0.3 parts by mass, the effect is insufficient. The roll workability of the product may also deteriorate.

[(E) curing agent]
The (E) component curing agent is not particularly limited as long as it can cure the silicone rubber composition of the present invention. Therefore, known vulcanizing agents (curing agents) for silicone rubbers, such as organic peroxide vulcanizing agents (curing agents) and addition vulcanizing agents (curing agents) can be used.

Organic peroxides Examples of organic peroxides used as vulcanizing agents (curing agents) include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2 ,4-dicumyl peroxide, 2,5-dimethyl-bis(2,5-t-butylperoxy)hexane, di-t-butylperoxide, t-butylperbenzoate, 1,6-hexanediol-bis -t-butyl peroxycarbonate and the like. These may be used alone or in combination of two or more.
The amount of the organic peroxide to be added may be an effective amount sufficient to cure the silicone rubber composition. .2 to 5 parts by mass is preferred.
When an organic peroxide vulcanizing agent (curing agent) is used as a curing agent, a platinum-based catalyst, which will be described later, may be used in combination for the purpose of enhancing heat resistance. When used in combination, the amount of the platinum-based catalyst to be blended is preferably 1 to 2,000 ppm, more preferably 10 to 1,000 ppm in terms of mass of the platinum group metal per 100 parts by mass of component (A).

When curing by addition reaction (hydrosilylation addition reaction), a combination of organohydrogenpolysiloxane (curing agent or cross-linking agent) and platinum-based catalyst (curing catalyst) is used as an addition vulcanizing agent (curing agent). do.

Platinum-based catalysts include simple platinum elements, platinum compounds, platinum complexes, chloroplatinic acid, alcohol compounds of chloroplatinic acid, aldehyde compounds, ether compounds, complexes with various olefins, and rhodium similar to the platinum compounds, Platinum group metal catalysts such as palladium and ruthenium compounds are exemplified.
The amount of the platinum-based catalyst added is preferably 1 to 2,000 ppm, more preferably 10 to 1,000 ppm in terms of mass of platinum group metal relative to the organopolysiloxane of component (A).

On the other hand, the organohydrogenpolysiloxane used as a curing agent (crosslinking agent) has 2 or more per molecule (usually 2 to 200), preferably 3 or more (for example, 3 to 150, preferably and organohydrogenpolysiloxanes containing 4 to 100) silicon-bonded hydrogen atoms (hydrosilyl groups). The organohydrogenpolysiloxane may be linear, branched, cyclic, or three-dimensional network structure. The degree of polymerization of this organohydrogenpolysiloxane is preferably 300 or less, more preferably 2-300, and particularly preferably 3-150. Specific examples of the organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, 1-propyl-3,5,7 -trihydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, 1,5-dihydrogen-3,7-dihexyl-1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogen gendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, both ends trimethylsiloxy group-blocked methylhydrogenpolysiloxane, both ends trimethyl Siloxy group-blocked dimethylsiloxane/methylhydrogensiloxane copolymer, both ends of dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, both ends of dimethylhydrogensiloxy group-blocked dimethylsiloxane/methylhydrogensiloxane copolymer, both ends of trimethylsiloxy group Methylhydrogensiloxane/diphenylsiloxane copolymer blocked at both ends, methylhydrogensiloxane/diphenylsiloxane/dimethylsiloxane copolymer blocked at both ends with trimethylsiloxy groups, methylhydrogensiloxane/methylphenylsiloxane/dimethylsiloxane copolymer blocked at both ends with trimethylsiloxy groups Polymer, both terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane/dimethylsiloxane/diphenylsiloxane copolymer, both terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane/dimethylsiloxane/methylphenylsiloxane copolymer, (CH _{3 )} Copolymers _{of 2} HSiO _{1/2 units} , ₍ CH ₃ ) ₃ SiO _1/2 units and SiO _4/2 units; and copolymers composed of (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₃ SiO _1/2 units.

The amount of the organohydrogenpolysiloxane to be added as the curing agent is such that the number of hydrogen atoms (hydrosilyl groups) directly linked to silicon atoms in the organohydrogenpolysiloxane is greater than the alkenyl groups in the organopolysiloxane of component (A). It is preferably used at a molar ratio of 0.5 to 5 mol/mol. When curing the composition of the present invention, the above-mentioned organic peroxide vulcanizing agent (curing agent) and an addition vulcanizing agent (curing agent) are used in combination as the curing agent for component (D). It can also be of the sulfur type.

In addition to the components described above, the silicone rubber composition of the present invention may optionally contain (B) a reinforcing silica dispersant (e.g., α,ω-silanol group blocking low polymerization degree diorganopolysiloxane, etc.), platinum compounds (for example, platinum compounds similar to the platinum-based catalysts exemplified as components in the addition vulcanizing agent of component (D)), iron oxide and titanium oxide , Carbon, flame retardant agents such as halogen compounds, heat resistance improvers, anti-aging agents, ultraviolet absorbers, colorants, release agents, and other known additives in silicone rubber compositions can be added. .

The method for producing the silicone rubber composition of the present invention is not particularly limited, but it can be obtained by kneading predetermined amounts of the above-described components with a known kneader such as a two-roll (roll mill), kneader, Banbury mixer, or the like. . In addition, if necessary, heat treatment (kneading under heating) may be performed. Specifically, it is preferable to knead the components (A) and (B), heat-treat the mixture if necessary, and then add the component (E) at room temperature. In this case, the components (C) and (D) may be blended before or after the heat treatment. In the case of heat treatment, the heat treatment temperature and time are not particularly limited, but it is preferable to carry out at 100 to 250° C., particularly 140 to 180° C., for about 30 minutes to 5 hours.

The molding method for the silicone rubber composition of the present invention may be selected according to the required use (molded article). Specific examples include compression molding, injection molding, transfer molding, normal pressure hot air vulcanization, and steam vulcanization. Curing conditions are not particularly limited, and may be appropriately selected depending on the curing method and the molded product. Generally, the curing time is 80 to 600° C., particularly 100 to 450° C., and several seconds to several days, especially 5 seconds to 1 hour. Further, secondary vulcanization may be performed as necessary. Secondary vulcanization is usually carried out at 180 to 250° C. for about 1 to 10 hours.

The silicone rubber composition of the present invention can be used as a construction gasket material (fire-resistant gasket material), an electric wire coating material (fire-resistant electric wire material) that requires further fire resistance, a rubber material for vehicles and/or vehicles, and a battery protection. It is also useful as a material.

EXAMPLES Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples. In addition, the part in the following example shows a mass part. The degree of polymerization indicates the weight average degree of polymerization in terms of polystyrene in GPC (gel permeation chromatography) analysis using toluene as a developing solvent. The average particle diameter indicates a cumulative weight average diameter; d50 in particle size distribution measurement by a laser diffraction method.

[Examples 1 to 6, Comparative Examples 1 to 3]
100 parts of an organopolysiloxane composed of 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, and 0.025 mol% of dimethylvinylsiloxy units, having a degree of polymerization of 7,000, and a specific surface area of 200m by the BET method ² / g of fumed silica (Aerosil-200 (manufactured by Nippon Aerosil Co., Ltd.)) and 5 parts of dimethylpolysiloxane having a silanol group at both ends and a polymerization degree of 5 were blended in a kneader, C. for 2 hours to prepare a silicone rubber compound.
To 100 parts of the obtained rubber compound, calcined mica produced by calcining pulverized muscovite (manufactured by Repco Co., Ltd., average particle size 18 μm), aluminum hydroxide (manufactured by Hoover Engineered Materials, average particle size diameter 1 μm or 8 μm), magnesium hydroxide (manufactured by Kyowa Chemical Industry Co., Ltd., average particle diameter 0.8 μm or 1.7 μm), titanium oxide (manufactured by Nippon Aerosil Co., Ltd., specific surface area 50 mm ² /g by BET method). Add the parts shown in Table 1, then add 0.1 part of an alcohol solution of chloroplatinic acid (Pt concentration 2% by mass) with two rolls, and then add 1.3 parts of p-methylbenzoyl peroxide 50% by mass paste. parts were added to prepare a silicone rubber composition.

A rubber sheet having a thickness of 2 mm obtained by press-molding this composition at 120° C. for 10 minutes was further post-cured at 200° C. for 4 hours. Four sheet pieces of 3.5 cm×3.5 cm were cut out from this rubber sheet and heated at 800° C. for 5 minutes in a high-temperature furnace to obtain four sintered bodies as test pieces for each example. The obtained sintered body 2 is placed on the pedestal 3 of the testing machine with the load cell 1 shown in FIG. direction). Table 1 shows the test force measurement results of four sintered bodies (sintered body 1 to sintered body 4) in each example.

It was confirmed that the shape of the sintered body was stable in all examples. In addition, in each example, the test force values of all the test pieces of the sintered bodies 1 to 4 were stably high.
On the other hand, Comparative Example 1 in which (D) the metal hydroxide was not blended showed excellent sinterability, but the sintered body had large swellings here and there. Moreover, in Comparative Examples 2 and 3, in which aluminum hydroxide and magnesium hydroxide were respectively added in excess, the whole was greatly swollen after sintering, and the strength of all the test pieces was remarkably lowered. In addition, tackiness was observed during roll work.

1 load cell 2 sintered body 3 pedestal

Claims (4)

(A) an organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass;
(B) reinforcing silica having a specific surface area of 50 to 500 m ² /g as measured by the BET method: 10 to 100 parts by mass;
(C) calcined mica having an average particle size of 0.5 to 20 μm: 1 to 100 parts by mass,
(D) a metal hydroxide having an average particle size of 0.5 to 20 μm: 0.3 to 15 parts by mass; and (E) a curing agent: an effective amount. 2. The silicone rubber composition according to claim 1, wherein the calcined mica of component (C) is obtained by calcining pulverized muscovite mica. 3. The silicone rubber composition according to claim 1, wherein the metal hydroxide of component (D) is aluminum hydroxide or magnesium hydroxide. The silicone rubber composition according to any one of claims 1 to 3, which is used for fireproof gaskets or fireproof electric wires.

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