Method for recovering organopolysiloxane, curable liquid silicone rubber composition and method for producing same

Abstract

To provide: a recovery method of an organopolysiloxane having a structure identical to that of a base polymer of a curable liquid silicone rubber composition from a cured product of the composition; and a production method of the curable liquid silicone rubber composition, in which the recovered organopolysiloxane is used as the base polymer of the curable liquid silicone rubber composition.SOLUTION: A recovery method of an organopolysiloxane from a silicone rubber cured product comprises a step to recover a carbinol-modified organopolysiloxane having a structure identical to a component (A) by immersing the silicone rubber cured product, formed by curing a curable liquid silicone rubber composition comprising the carbinol-modified organopolysiloxane (A), a filler (B), and a hydrolyzable organosilane compound with a specific structure (C) and / or a partially hydrolyzed condensation product thereof in a specific ratio, in an alkali solution containing an alkali aqueous solution and an alcohol.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering an organopolysiloxane having the same structure as a base polymer of a curable liquid silicone rubber composition from a cured product of the composition, a curable liquid silicone rubber composition for use in said recovery method, and a method for producing a curable liquid silicone rubber composition in which the recovered organopolysiloxane is used as the base polymer of the curable liquid silicone rubber composition. [Background technology]

[0002] Silicone compounds are made up of siloxane bonds and are relatively chemically stable, with excellent heat and chemical resistance, making them used in a wide range of fields. Room temperature vulcanizable (RTV) silicone rubber compositions, which crosslink (cure) into an elastomeric silicone rubber cured product at room temperature (23°C±15°C) due to atmospheric moisture, are easy to handle, and the silicone rubber cured product obtained by curing them has excellent weather resistance and electrical properties, making them useful in a wide range of applications, including as a sealing material for building materials and an adhesive in the electrical and electronics fields.

[0003] Furthermore, in recent years, there has been a desire to realize a recycling-oriented society, and the importance of recycling and reusing raw materials recovered from products discarded in economic activities is increasing. For this reason, even in the case of curable liquid silicone rubber compositions such as RTV silicone rubber compositions, it is desirable to recycle and reuse organopolysiloxanes having the same structure as the base polymer of the composition from the cured silicone rubber obtained by curing the composition after the product life of the composition has ended.

[0004] In response to such needs, the following recycling methods have been proposed for curable liquid silicone rubber compositions.

[0005] Patent Document 1 (JP 2000-169484 A) reports that silicone compounds are decomposed using an active hydrogen group-containing compound such as alkyl carbonate and alcohol in the presence of an acid catalyst such as sulfuric acid. Patent Document 2 (JP Patent No. 4082498 A) proposes a method of treating with an organic quaternary ammonium hydroxide and a solvent such as an amine or alcohol to decompose a part of the crosslinked structure, separating the filler, and further adding an inorganic strong base to depolymerize and recover cyclic siloxane monomers. Patent Document 3 (JP 2012-188398 A) reports that silicone compounds are decomposed using an active hydrogen group-containing compound such as acetal and alcohol in the presence of an acid catalyst such as sulfuric acid to decompose into alkoxysilanes and alkoxysilane oligomers. However, in Patent Documents 1 to 3, the siloxane bond of the silicone compound is cut, and therefore repolymerization is required for reuse.

[0006] On the other hand, Patent Document 4 (Japanese Patent No. 3721008) proposes a method of hydrolyzing crosslinked silicone rubber waste by contacting it with alcohol under supercritical conditions, and Patent Document 5 (Japanese Patent No. 3721012) proposes a method of heating it together with a mixed solvent of alcohol and water, and it is reported that the waste can be recovered as an uncrosslinked silicone rubber compound or silicone oil. Patent Documents 4 and 5 state that uncrosslinked silicone rubber compounds and recycled silicone oils can be recovered, but they do not provide details about the recovered materials, nor do they present any information about the physical properties after re-crosslinking. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-169484 A [Patent Document 2] Patent No. 4082498 [Patent Document 3] JP 2012-188398 A [Patent Document 4] Patent No. 3721008 [Patent Document 5] Patent No. 3721012 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a method for recovering an organopolysiloxane having the same structure as the base polymer of a curable liquid silicone rubber composition from a cured product of a curable liquid silicone rubber composition, which enables an organopolysiloxane having the same structure as the base polymer of the composition to be recovered from the cured product after the product life of the cured product has come to an end, and to reuse the organopolysiloxane as the base polymer of the curable liquid silicone rubber composition; a curable liquid silicone rubber composition for use in said recovery method; and a method for producing a curable liquid silicone rubber composition in which the recovered organopolysiloxane is used as the base polymer of the curable liquid silicone rubber composition. [Means for solving the problem]

[0009] As a result of intensive research by the present inventors in order to achieve the above-mentioned object, they have discovered that by using a carbinol-modified organopolysiloxane as a base polymer and immersing a silicone rubber cured product which has been cured with a crosslinking agent (curing agent) in the presence of a filler in an alkaline solution containing an aqueous alkaline solution and an alcohol under mild conditions at room temperature, it is possible to easily recover and regenerate a carbinol-modified organopolysiloxane which has the same structure as the base polymer, and that by simply mixing the recovered carbinol-modified organopolysiloxane with the necessary additives (crosslinking agent, filler) and crosslinking and curing it, a silicone rubber cured product having physical properties equivalent to those of the silicone rubber cured product before being regenerated can be obtained, i.e., recycling is possible, thereby completing the present invention.

[0010] Accordingly, the present invention provides the following method for recovering organopolysiloxanes from cured silicone rubber products, a curable liquid silicone rubber composition for use in said recovery method, and a method for producing a curable liquid silicone rubber composition using the recovered organopolysiloxane. [1] (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) filler: 0.1 to 800 parts by mass, and (C) The following general formula (1) R 1 a Six 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon radical, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or its partial hydrolysis condensate: 1 to 30 parts by mass The method for recovering organopolysiloxanes from a cured silicone rubber product comprises the step of immersing a cured silicone rubber product obtained by curing a curable liquid silicone rubber composition containing the above-mentioned in an alkaline solution containing an aqueous alkaline solution and an alcohol, and recovering a carbinol-modified organopolysiloxane having the same structure as component (A). [2] The method for recovering organopolysiloxanes from a cured silicone rubber product according to [1], wherein component (B) is silica. [3] A method for recovering organopolysiloxanes from a silicone rubber cured product obtained by curing a curable liquid silicone rubber composition as described in [1] or [2], which further contains (D) a linear organopolysiloxane (excluding component (C)) whose molecular chain is terminated at both ends with hydroxyl groups (silanol groups) bonded to silicon atoms or hydrolyzable silyl groups, in a mass ratio of component (A) to component (D) of 10:0 to 5:5. [4] The method for recovering organopolysiloxane from a cured silicone rubber product according to any one of [1] to [3], wherein the alkaline solution contains 100 mL of an aqueous alkaline solution containing 0.1 to 6.0 mol / kg of an alkaline source and 5 to 50 mL of alcohol. [5] The method for recovering organopolysiloxanes from a cured silicone rubber product according to [4], wherein the alkali source is at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, and amine compounds. [6] (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) filler: 0.1 to 800 parts by mass, and (C) The following general formula (1) R 1 a Six 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon radical, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or its partial hydrolysis condensate: 1 to 30 parts by mass A method for producing a curable liquid silicone rubber composition comprising: A method for producing a curable liquid silicone rubber composition, comprising using as component (A) a carbinol-modified organopolysiloxane recovered by the method for recovering organopolysiloxane from a cured silicone rubber product as described in any one of [1] to [5]. [7] (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) filler: 0.1 to 800 parts by mass, and (C) The following general formula (1) R 1 a Six 1 4-a (1) (In the formula, R1 is an unsubstituted or substituted monovalent hydrocarbon radical, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or its partial hydrolysis condensate: 1 to 30 parts by mass 2. A curable liquid silicone rubber composition for use in the method for recovering organopolysiloxane from a cured silicone rubber product according to claim 1, comprising: [8] The curable liquid silicone rubber composition according to [7], wherein component (B) is silica. [9] Furthermore, the composition contains (D) a linear organopolysiloxane (excluding (C)) whose molecular chain ends are blocked with hydroxyl groups (silanol groups) bonded to silicon atoms or hydrolyzable silyl groups, in a mass ratio of the components (A) and (D) of 10:0 to 5:5. The curable liquid silicone rubber composition according to [7] or [8]. Effect of the Invention

[0011] According to the present invention, a cured silicone rubber product obtained by curing a curable liquid silicone rubber composition containing a carbinol-modified organopolysiloxane as the base polymer and a filler and a crosslinking agent (curing agent) is immersed in an alkaline solution containing an aqueous alkaline solution and an alcohol under mild conditions such as room temperature, whereby the carbinol-modified organopolysiloxane, which has the same structure as the base polymer of the composition, can be easily recovered and regenerated. The recovered carbinol-modified organopolysiloxane is then mixed with the necessary additives (crosslinking agent, filler) to obtain a curable liquid silicone rubber composition, which is then crosslinked and cured to obtain a cured silicone rubber product with physical properties equivalent to those of the cured silicone rubber product before it was regenerated (i.e., the base polymer of the curable liquid silicone rubber composition can be recycled). [Brief description of the drawings]

[0012] [Figure 1] 1 is a graph showing the results of GPC measurement of the carbinol-modified organopolysiloxane before and after recycling in Example 1 (horizontal axis: elution time, vertical axis: detection intensity). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below. The present invention uses a carbinol-modified organopolysiloxane as a base polymer, and by immersing a silicone rubber cured product obtained by curing with a crosslinking agent (curing agent) in the presence of a filler in an alkaline solution containing an aqueous alkaline solution and an alcohol under mild conditions at room temperature, it is possible to easily recover and recycle a carbinol-modified organopolysiloxane having the same structure as the base polymer.

[0014] The curable liquid silicone rubber composition used in the recovery method of the present invention comprises: (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) filler: 0.1 to 800 parts by mass, and (C) The following general formula (1) R 1 a Six 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon radical, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or its partial hydrolysis condensate: 1 to 30 parts by mass The cured silicone rubber product used in the recovery method of the present invention is obtained by curing the curable liquid silicone rubber composition.

[0015] [Component (A)] The carbinol-modified organopolysiloxane of component (A) is the base polymer of the curable liquid silicone rubber composition. In the curable liquid silicone rubber composition of the present invention, the carbinol group in the carbinol-modified organopolysiloxane of component (A) and the hydrolyzable group in the hydrolyzable organosilane compound and / or its partial hydrolysis condensate, which is the crosslinking agent of component (C) described below, form a Si-OC bond at the crosslinking site, and the bond can be cleaved to C-OH and Si-OH under alkaline conditions. Therefore, by immersing the silicone rubber cured product obtained by curing the composition in an alkaline solution, only the crosslinking points of the silicone rubber cured product can be cut, so that the carbinol-modified organopolysiloxane of the same structure as component (A) contained in the composition can be easily and quantitatively recovered and recycled.

[0016] The carbinol-modified organopolysiloxane of component (A) has at least 2, preferably 2 to 6, and more preferably 2 to 4 carbinol groups (saturated aliphatic monovalent hydrocarbon groups such as alkyl groups having a terminal methylol group; -CH2OH and optionally having an ether-bonded oxygen atom (-O-)) bonded to silicon atoms of the organopolysiloxane in one molecule. Examples of carbinol groups include hydroxymethyl groups, 2-hydroxyethyl groups, 3-hydroxypropyl groups, 3-(2-hydroxyethoxy)propyl groups, and 3-(3-hydroxypropoxy)propyl groups.

[0017] In addition, the organic group other than the carbinol group bonded to the silicon atom of the organopolysiloxane is preferably an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms. For example, an unsubstituted or substituted monovalent hydrocarbon group having about 1 to 8 carbon atoms, such as an alkyl group, such as a methyl group, an ethyl group, or a propyl group; an alkenyl group, such as a vinyl group; an aryl group, such as a phenyl group; a chloromethyl group, a 2-cyanoethyl group, or a 3,3,3-trifluoropropyl group, is preferred, and an unsubstituted monovalent hydrocarbon group having about 1 to 6 carbon atoms is particularly preferred, with a methyl group or an ethyl group being particularly preferred.

[0018] The molecular structure of the carbinol-modified organopolysiloxane of component (A) may be such that the siloxane skeleton constituting the main chain is linear, branched, or cyclic; linear or branched structures are preferred, and linear structures are more preferred.

[0019] Linear carbinol-modified organosiloxanes are classified according to the position where some of the monovalent hydrocarbon groups bonded to silicon atoms are replaced (modified) with carbinol groups, and are classified into side-chain carbinol-modified linear organosiloxanes (diorganosiloxane-organo(carbinol)siloxane copolymers capped with triorganosiloxy groups at both molecular chain ends), both-end carbinol-modified linear organosiloxanes (diorganopolysiloxanes capped with diorgano(carbinol)siloxy groups at both molecular chain ends, diorganopolysiloxanes capped with organobis(carbinol)siloxy groups at both molecular chain ends), and both-end and side-chain carbinol-modified linear organosiloxanes (diorganosiloxane-organo(carbinol)siloxy groups capped with diorgano(carbinol)siloxy groups at both molecular chain ends). There are various structures such as side chain carbinol-modified linear organosiloxanes (diorganopolysiloxanes capped at one molecular end with an organobis(carbinol)siloxy group and at one molecular end with a triorganosiloxy group), and in each of the above linear carbinol-modified organosiloxanes, diol-type linear organosiloxanes having two hydroxyl groups on one carbinol-modified group. Of these, side chain carbinol-modified linear organosiloxanes (diorganosiloxane-organo(carbinol)siloxane copolymers capped at both molecular ends with triorganosiloxy groups) and both end carbinol-modified linear organosiloxanes (diorganopolysiloxanes capped at both molecular ends with diorgano(carbinol)siloxy groups) are preferred.

[0020] A method for producing a linear carbinol-modified organosiloxane having a 3-(2-hydroxyethoxy)propyl group as the carbinol group can be, for example, a method in which a linear organohydrogenpolysiloxane having a hydrogen atom bonded to a silicon atom (SiH group) is subjected to a hydrosilylation reaction with ethylene glycol capped at one end with an allyl group in the presence of a platinum catalyst.

[0021] The viscosity (kinetic viscosity) of the carbinol-modified organopolysiloxane of component (A) at 25°C is 10 to 1,000,000 mm 2 / s, and 30 to 300,000 mm 2 / s is more preferable, and 40 to 10,000 mm 2 More preferably, the range is 50 to 5,000 mm / s. 2 It is particularly preferable that the viscosity is 1 / s. If the viscosity is less than the lower limit, the cured product may not have sufficient mechanical properties, and if the viscosity is more than the upper limit, the workability may decrease. In the present invention, the viscosity is a value measured at 25°C using a kinematic viscometer (e.g., a Cannon-Fenske viscometer, an Ostwald viscometer, an Ubbelohde viscometer, etc.) (hereinafter the same).

[0022] The carbinol-modified organopolysiloxane of component (A) may use either a single compound, or a combination of two or more different compounds.

[0023] [(B) Component] The (B) component is a filler (inorganic filler and / or organic resin filler), which, when the silicone rubber cured product obtained by curing a curable liquid silicone rubber composition with a carbinol-modified organopolysiloxane as the base polymer is immersed in an alkaline solution, separates the carbinol-modified organopolysiloxane, which has the same structure as the base polymer of the composition, and plays a role in facilitating recycling. As this filler, known fillers can be used, such as fine powder silica, fumed silica, precipitated silica, glass beads, glass balloons, transparent resin beads, silica aerogel, diatomaceous earth, metal oxides such as iron oxide, zinc oxide, magnesium oxide, titanium oxide, and fumed metal oxides, wet silica or those whose surfaces are silane-treated, quartz powder, carbon black, talc, zeolite, and bentonite, reinforcing agents, asbestos, glass fiber, carbon fiber, metal carbonates such as calcium carbonate, magnesium carbonate, and zinc carbonate, glass wool, fine powder mica, fused silica powder, and synthetic resin powders such as polystyrene, polyvinyl chloride, and polypropylene. The surface may be treated or not. Surface treatment agents include fatty acids, paraffins, silanes, silazanes, low-polymerization siloxanes, organic compounds, etc. Among these fillers, inorganic fillers such as silica, calcium carbonate, carbon black, and zeolite are preferred, silica is more preferred, and fumed silica is particularly preferred.

[0024] The amount of component (B) is 0.1 to 800 parts by mass, and preferably 0.3 to 600 parts by mass, per 100 parts by mass of component (A). If it is less than 0.1 part by mass, the carbinol-modified organopolysiloxane having the same structure as the base polymer will not separate after the silicone rubber cured product is immersed in an alkali solution, while if it exceeds 800 parts by mass, the viscosity of the composition increases, making it difficult to dispense during application.

[0025] [(C) component] The curable liquid silicone rubber composition used in the present invention contains component (C) as a crosslinking agent (curing agent). That is, component (C) is a compound represented by the following general formula (1): R 1a Six 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon radical, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, provided that when a=2, R 1 may be the same or different.) and / or a partial hydrolysis condensate thereof.

[0026] In the above formula (1), R 1 is an unsubstituted or substituted monovalent hydrocarbon radical, R 1 The unsubstituted or substituted monovalent hydrocarbon group is preferably an unsubstituted or substituted monovalent hydrocarbon group having about 1 to 8 carbon atoms, such as an alkyl group, such as a methyl group, an ethyl group, or a propyl group; an alkenyl group, such as a vinyl group; an aryl group, such as a phenyl group; a chloromethyl group, a 2-cyanoethyl group, or a 3,3,3-trifluoropropyl group, and particularly preferably an unsubstituted monovalent hydrocarbon group having about 1 to 6 carbon atoms, with a methyl group, an ethyl group, a propyl group, a vinyl group, and a phenyl group being particularly preferred.

[0027] In addition, in the above formula (1), X 1 Examples of the hydrolyzable group include alkoxy groups having 1 to 6 carbon atoms, such as a methoxy group or an ethoxy group; alkenoxy groups having 2 to 6 carbon atoms, such as an isopropenoxy group; ketoxime groups having 3 to 8 carbon atoms, such as a methyl ethyl ketoxime group; and acyloxy groups having 2 to 6 carbon atoms, such as an acetoxy group. Of these, alkoxy groups and isopropenoxy groups are preferred. a is 0, 1 or 2, preferably 0 or 1.

[0028] Specific examples of the component (C) include alkoxysilanes such as methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, and methyltriethoxysilane, as well as methyltris(dimethylketoxime)silane, methyltris(methylethylketoxime)silane, ethyltris(methylethylketoxime)silane, methyltris(methylisobutylketoxime)silane, vinyltris(methylethylketoxime)silane, and phenyltris(methylethylketoxime)silane. ketoxime silanes mentioned above; isopropenoxy group-containing silanes such as methyltriisopropenoxysilane, ethyltriisopropenoxysilane, and vinyltriisopropenoxysilane; cyclopentanoxy group-containing silanes such as methyltricyclopentanoxysilane, ethyltricyclopentanoxysilane, and vinyltricyclopentanoxysilane; acetoxysilanes such as methyltriacetoxysilane, ethyltriacetoxysilane, and vinyltriacetoxysilane; and various other silanes, as well as partial hydrolysis and condensation products of these silanes.

[0029] The component (C) may use one type alone, or a mixture of two or more types. The amount of component (C) used per 100 parts by mass of component (A) is in the range of 1 to 30 parts by mass, preferably 2 to 20 parts by mass, and particularly preferably 3 to 15 parts by mass. If the amount is less than 1 part by mass, sufficient crosslinking is not obtained, and it is difficult to obtain a cured product with suitable rubber elasticity, while if the amount exceeds 30 parts by mass, the mechanical properties of the obtained cured product will be reduced.

[0030] [Other ingredients] In addition to the above components (A) to (C), various additives can also be added to the curable liquid silicone rubber composition used in the present invention, so long as they do not impede the object of the present invention. For example, in addition to the above-mentioned component (A), (D) a linear organopolysiloxane (excluding component (C)) in which both molecular chain terminals are blocked with hydroxyl groups (silanol groups) bonded to silicon atoms or hydrolyzable silyl groups can be blended as part of the base polymer in a mass ratio of component (A) to component (D) of 10:0 to 5:5, preferably 10:0 to 7:3. Other examples of the compound may include polyethers as wetters or thixotropy improvers, organotin compounds, organotitanium compounds, organozirconium compounds, and the like as catalysts, and non-reactive dimethylsilicone oil, isoparaffin, and the like as plasticizers.

[0031] Furthermore, if necessary, colorants such as pigments, dyes, and fluorescent whitening agents, antifungal agents, antibacterial agents, antistatic agents, flame retardants, and non-reactive phenyl silicone oils and fluorosilicone oils as bleed oils can also be blended. The amounts of these used are arbitrary as long as they do not impede the object of the present invention.

[0032] The curable liquid silicone rubber composition used in the present invention can be obtained by uniformly mixing the above-mentioned components (A) to (C), and optionally component (D) and / or other components, in a dry or reduced pressure atmosphere using a mixer such as a Shinagawa mixer, a planetary mixer, or a kneader.

[0033] The curable liquid silicone rubber composition obtained above can be cured under conditions of 50 to 130° C., particularly 70 to 110° C., for 10 minutes to 5 hours, particularly 30 minutes to 3 hours.

[0034] The silicone rubber cured product obtained by curing the above-mentioned curable liquid silicone rubber composition can be suitably used as a sealing material or coating agent for electronic parts, an adhesive for fixing parts, a sealing material for construction, etc.

[0035] The cured silicone rubber obtained by curing the above-mentioned curable liquid silicone rubber composition can be immersed in an alkaline solution containing an aqueous alkaline solution and an alcohol after the end of the product life of the cured silicone rubber, and a carbinol-modified organopolysiloxane having the same structure as component (A) of the above-mentioned composition can be recovered.

[0036] [Alkaline solution] The alkaline solution is used to dissolve the silicone rubber cured product obtained by curing the above-mentioned curable liquid silicone rubber composition, and to recover a carbinol-modified organopolysiloxane having the same structure as component (A) of the above-mentioned composition. The alkaline solution contains an aqueous alkaline solution and an alcohol.

[0037] Examples of the alkali source for the alkaline aqueous solution include hydroxides of alkali metals such as sodium and potassium, hydroxides of alkaline earth metals such as magnesium and calcium, carbonates of alkali metals such as sodium and potassium, and amine compounds such as triethylamine, butylamine, and tetramethylguanidine. The alkaline aqueous solution is prepared by dissolving the alkaline source in water and adjusting the concentration to 0.1 to 6.0 mol / kg, preferably 0.3 to 4.0 mol / kg. If the concentration is less than 0.1 mol / kg, the dissolution of the cured material does not proceed, and if it exceeds 6.0 mol / kg, the solution becomes too concentrated and the work becomes dangerous.

[0038] In addition, alcohol is added to the alkaline solution to promote decomposition of the hardened material. The types of alcohol include methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol, with ethanol and 2-propanol being preferred. The amount of alcohol added is 5 to 50 mL, preferably 10 to 40 mL, per 100 mL of the alkaline aqueous solution. If it is less than 5 mL, decomposition is not promoted, and if it is more than 50 mL, the alkalinity is reduced and decomposition is difficult to occur. Alternatively, for the same reason as above, the amount of alcohol added is 4 to 40 g, preferably 8 to 32 g, per 100 g of the alkaline aqueous solution.

[0039] [Method for recovering carbinol-modified organopolysiloxane] The carbinol-modified organopolysiloxane is recovered by immersing the cured product of the curable liquid silicone rubber composition (cured silicone rubber product) in an alkaline solution. Here, the amount of alkaline solution used is not particularly limited, but is preferably 700 to 1,500 parts by mass, and particularly 900 to 1,200 parts by mass, per 100 parts by mass of the silicone rubber cured product. If the amount of alkaline solution is too small, the decomposition properties will be insufficient and the silicone rubber cured product may not dissolve, whereas if the amount is too large, the recovered liquid may become strongly alkaline and a neutralization step may be required.

[0040] The immersion is carried out at room temperature (23°C ± 15°C) and the hardened material is left to dissolve for 5 hours to 7 days. The dissolution time is shorter if the hardened material is cut into small pieces. After dissolution, it separates into three layers: an upper layer (organic layer) made of carbinol-modified organopolysiloxane, a middle layer made of alkaline solution, and a lower layer (precipitation layer) made of components other than carbinol-modified organopolysiloxane (fillers, crosslinking agents, etc.).

[0041] Since the carbinol-modified organopolysiloxane having the same structure as component (A) of the above composition separates into an upper layer, the carbinol-modified organopolysiloxane having the same structure as component (A) of the above composition is recovered from the upper layer.

[0042] Specifically, the dissolution of the cured product by alkali immersion can be achieved by simply leaving the product to stand, but stirring may also be used to promote dissolution of the cured product. The oil component (carbinol-modified organopolysiloxane) naturally rises (migrates) to the top layer, making it possible to recover the oil by separation after leaving the product to stand.

[0043] The fact that the recovered carbinol-modified organopolysiloxane has the same structure as the component (A) of the composition can be confirmed by measuring the viscosity and refractive index of the recovered carbinol-modified organopolysiloxane and confirming that they are the same as the viscosity and refractive index of the component (A) before recovery. In addition, the molecular weight distribution of the recovered carbinol-modified organopolysiloxane shows the same value as the molecular weight distribution of the component (A) of the composition, so it can be reused as it is. The molecular weight distribution can be measured by GPC (gel permeation chromatography).

[0044] The recovered carbinol-modified organopolysiloxane is mixed again with the necessary additives (crosslinking agent, filler) to form a curable liquid silicone rubber composition, and by simply crosslinking and curing this composition, a cured silicone rubber with physical properties equivalent to those of the cured silicone rubber before recycling can be obtained.

[0045] The method for producing the curable liquid silicone rubber composition of the present invention comprises the steps of: (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) filler: 0.1 to 800 parts by mass, and (C) The following general formula (1) R 1 a Six 1 4-a (1) (In the formula, R 1 , X 1 , a is the same as above.) and / or its partial hydrolysis condensate: 1 to 30 parts by mass and uses, as component (A), a carbinol-modified organopolysiloxane recovered by the above-mentioned method for recovering organopolysiloxane from a cured silicone rubber.

[0046] According to the present invention, a carbinol-modified organopolysiloxane having the same structure as the base polymer can be easily recovered under mild conditions such as room temperature from a cured silicone rubber obtained by using a carbinol-modified organopolysiloxane as a base polymer and curing a curable liquid silicone rubber composition containing a filler and a crosslinking agent (curing agent). The cured silicone rubber obtained by using the recovered carbinol-modified organopolysiloxane again as a base polymer and curing a curable liquid silicone rubber composition containing a filler and a crosslinking agent (curing agent) has physical properties equivalent to those of the cured silicone rubber before recovery (regeneration), and can be easily recycled. EXAMPLES

[0047] The following examples and comparative examples are provided to specifically explain the present invention, but the present invention is not limited to the following examples. In the following examples, the viscosity is the kinetic viscosity measured at 25°C using a Cannon-Fenske viscometer.

[0048] [Example 1] The viscosity is expressed by the following formula (2) and is 70 mm 2 100 parts by mass of a carbinol-modified organopolysiloxane (dimethylpolysiloxane with both molecular chain terminals blocked by dimethyl(carbinol)siloxy groups) having a molecular weight of 100 / s, 10 parts by mass of fumed silica, and 10 parts by mass of vinyltris(methylethylketoxime)silane were mixed under reduced pressure to obtain a curable liquid silicone rubber composition 1. This composition 1 was cured at 105°C for 1 hour, and then at 23°C / 50% RH for 24 hours to obtain a silicone rubber cured product 1 having a size of 15 cm x 10 cm x 2 mm thickness. The hardness (JIS K6249, durometer type A hardness) of the obtained silicone rubber cured product 1 was measured and found to be 49. An alkaline solution was prepared by adding 80 g of 2-propanol to a 1.2 mol / kg aqueous solution of sodium hydroxide prepared by dissolving 16 g of sodium hydroxide in 320 g of water. The silicone rubber cured material 1 was immersed in this alkaline solution at 23° C. for 5 days. [ka] (n is about 40)

[0049] [Example 2] The viscosity is 70 mm as shown in the above formula (2). 2 The mixture is a carbinol-modified organopolysiloxane (dimethylpolysiloxane terminated at both ends with dimethyl (carbinol) siloxy groups) with a viscosity of 60 mm2 and a hydroxyl group (silanol group) bonded to a silicon atom at both ends. 2 25 parts by mass of linear dimethylpolysiloxane having a viscosity of 1 / s, 10 parts by mass of fumed silica, and 10 parts by mass of vinyltris(methylethylketoxime)silane were mixed under reduced pressure to obtain a curable liquid silicone rubber composition 2. This composition 2 was cured at 105°C for 1 hour, and then at 23°C / 50% RH for 24 hours to obtain a silicone rubber cured product 2 having a size of 15 cm x 10 cm x 2 mm thickness. The hardness (JIS K6249, durometer type A hardness) of the obtained silicone rubber cured product 2 was measured and found to be 58. An alkaline solution was prepared by adding 80 g of 2-propanol to a 1.2 mol / kg aqueous solution of sodium hydroxide prepared by dissolving 16 g of sodium hydroxide in 320 g of water. The silicone rubber cured material 2 was immersed in this alkaline solution at 23° C. for 5 days.

[0050] [Example 3] An alkaline solution was prepared by adding 80 g of ethanol to a 1.2 mol / kg aqueous solution of sodium hydroxide prepared by dissolving 16 g of sodium hydroxide in 320 g of water. A silicone rubber cured material 1 produced in the same manner as in Example 1 was immersed in this alkaline solution at 23° C. for 5 days.

[0051] [Comparative Example 1] Both ends are blocked with hydroxyl groups (silanol groups) bonded to silicon atoms, and the viscosity is 60 mm. 2 100 parts by mass of linear dimethylpolysiloxane having a molecular weight of 100 / s, 10 parts by mass of fumed silica, and 10 parts by mass of vinyltris(methylethylketoxime)silane were mixed under reduced pressure to obtain a curable liquid silicone rubber composition 3. This composition 3 was cured at 105°C for 1 hour, and then at 23°C / 50% RH for 24 hours to obtain a silicone rubber cured product 3 having a size of 15 cm x 10 cm x 2 mm thickness. An alkaline solution was prepared by adding 80 g of 2-propanol to a 1.2 mol / kg aqueous solution of sodium hydroxide prepared by dissolving 16 g of sodium hydroxide in 320 g of water. The silicone rubber cured material 3 was immersed in this alkaline solution at 23° C. for 5 days.

[0052] [Comparative Example 2] 100 parts by mass of a carbinol-modified organopolysiloxane (dimethylpolysiloxane terminated with dimethyl(carbinol)siloxy groups at both molecular chain terminals) represented by the above formula (2) and having a viscosity of 70 mPa s was mixed with 10 parts by mass of vinyltris(methylethylketoxime)silane under reduced pressure to obtain a curable liquid silicone rubber composition 4. This composition 4 was cured at 105°C for 1 hour, and then at 23°C / 50% RH for 24 hours to obtain a silicone rubber cured product 4 measuring 15 cm x 10 cm x 2 mm thick. An alkaline solution was prepared by adding 80 g of 2-propanol to a 1.2 mol / kg aqueous solution of sodium hydroxide prepared by dissolving 16 g of sodium hydroxide in 320 g of water. The silicone rubber cured product 4 was immersed in this alkaline solution at 23° C. for 5 days.

[0053] [Comparative Example 3] 16 g of sodium hydroxide was dissolved in 320 g of water to prepare a 1.2 mol / kg aqueous sodium hydroxide solution (alkaline aqueous solution). A silicone rubber cured material 1 produced in the same manner as in Example 1 was immersed in this alkaline aqueous solution at 23° C. for 5 days.

[0054] [Recyclability] In the examples and comparative examples, the cases where the silicone rubber cured product dissolved and the carbinol-modified organopolysiloxane layer separated were marked with an ◯, the cases where the silicone rubber cured product dissolved but the carbinol-modified organopolysiloxane layer did not separate were marked with a △, and the cases where the silicone rubber cured product did not dissolve were marked with an X. The results of the evaluation of recyclability are shown in Table 1.

[0055] [Table 1]

[0056] In all of Examples 1 to 3, the carbinol-modified organopolysiloxane component in the silicone rubber cured product was dissolved in the alkaline solution. This solution was separated into three layers: an upper layer (organic layer) consisting of the carbinol-modified organopolysiloxane, a middle layer consisting of the alkaline solution, and a lower layer (precipitate layer) consisting of components other than the carbinol-modified organopolysiloxane (filler, crosslinking agent, and in Example 2, a crosslinked product (silicone rubber cured product) between a linear dimethylpolysiloxane whose both ends are blocked with silanol groups and the crosslinking agent). The upper layer of the solution was separated and neutralized as necessary to recover the compound (carbinol-modified organopolysiloxane). When the viscosity and refractive index of the compound recovered in Example 1 were analyzed, it was confirmed that the viscosity and refractive index were the same as those of the carbinol-modified organopolysiloxane (before recycling) used in composition 1, and therefore that it had the same structure. Furthermore, when the molecular weight distribution of this carbinol-modified organopolysiloxane (after recycling) was measured by GPC, the result was the same as that of the carbinol-modified organopolysiloxane (before recycling) used in curable liquid silicone rubber composition 1, as shown in Figure 1. When Examples 2 and 3 were confirmed in the same manner as Example 1, it was confirmed that the carbinol-modified organopolysiloxane had the same structure before and after recycling, and the molecular weight distribution did not change.

[0057] In Comparative Example 1, the base polymer of the curable liquid silicone rubber composition was not a carbinol-modified organopolysiloxane, but an organopolysiloxane with both ends blocked with silanol groups, so the silicone rubber cured product did not dissolve when immersed in an alkaline solution. In Comparative Example 2, the base polymer of the curable liquid silicone rubber composition was a carbinol-modified organopolysiloxane, so the silicone rubber cured product dissolved when immersed in an alkaline solution, but because no silica filler was added, the carbinol-modified organopolysiloxane layer did not separate, making it difficult to recover. In Comparative Example 3, the alkaline solution did not contain alcohol, so even though a carbinol-modified organopolysiloxane was used as the base polymer of the curable liquid silicone rubber composition, the silicone rubber cured product did not dissolve.

[0058] [Change in hardness] Furthermore, the carbinol-modified organopolysiloxane recovered above was used as the base polymer to prepare a curable liquid silicone rubber composition similar to that described in Examples 1 to 3, and the hardness (JIS K6249, durometer type A hardness, hardness after recycling) of the silicone rubber cured product cured under the curing conditions described in Examples 1 to 3 was measured. These results are shown in Table 2 together with the hardness before recycling (hardness of the cured products obtained in Examples 1 to 3).

[0059] [Table 2]

[0060] In all of Examples 1 to 3, it was confirmed that the silicone rubber cured product obtained by curing the silicone rubber composition prepared using the recovered carbinol-modified organopolysiloxane as the base polymer had the same hardness as the silicone rubber cured product before recycling, and was therefore reusable.

Claims

1. (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) Filler: 0.1 to 800 parts by mass, and (C) a compound represented by the following general formula (1): R 1 a SiX 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon group, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or a partial hydrolysis condensate thereof: 1 to 30 parts by mass The method for recovering organopolysiloxanes from a cured silicone rubber product comprises the step of immersing a cured silicone rubber product obtained by curing a curable liquid silicone rubber composition containing the above-mentioned in an alkaline solution containing an aqueous alkaline solution and an alcohol, and recovering a carbinol-modified organopolysiloxane having the same structure as component (A).

2. 2. The method for recovering organopolysiloxanes from a cured silicone rubber product according to claim 1, wherein component (B) is silica.

3. 2. A method for recovering organopolysiloxanes from a silicone rubber cured product obtained by curing the curable liquid silicone rubber composition according to claim 1, further comprising: (D) a linear organopolysiloxane (excluding component (C)) whose molecular chain is terminated at both ends with hydroxyl groups (silanol groups) bonded to silicon atoms or hydrolyzable silyl groups, in a mass ratio of components (A) and (D) of from 10:0 to 5:

5.

4. 2. The method for recovering organopolysiloxanes from a cured silicone rubber product according to claim 1, wherein the alkaline solution comprises 100 mL of an aqueous alkaline solution containing 0.1 to 6.0 mol / kg of an alkaline source and 5 to 50 mL of an alcohol.

5. 5. A method for recovering organopolysiloxanes from cured silicone rubber according to claim 4, wherein the alkali source is at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates and amine compounds.

6. (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) Filler: 0.1 to 800 parts by mass, and (C) a compound represented by the following general formula (1): R 1 a SiX 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon group, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or a partial hydrolysis condensate thereof: 1 to 30 parts by mass A method for producing a curable liquid silicone rubber composition comprising:

6. A method for producing a curable liquid silicone rubber composition, comprising the step of: (A) using a carbinol-modified organopolysiloxane recovered by the method for recovering organopolysiloxane from a silicone rubber cured product as defined in any one of claims 1 to 5.

7. (A) Carbinol-modified organopolysiloxane: 100 parts by mass, (B) Filler: 0.1 to 800 parts by mass, and (C) a compound represented by the following general formula (1): R 1 a SiX 1 4-a (1) (In the formula, R 1 is an unsubstituted or substituted monovalent hydrocarbon group, X 1 are the same or different hydrolyzable groups, a is 0, 1 or 2, and when a=2, R 1 may be the same or different.) and / or a partial hydrolysis condensate thereof: 1 to 30 parts by mass 2. A curable liquid silicone rubber composition for use in the method for recovering organopolysiloxane from a cured silicone rubber product according to claim 1, comprising:

8. 8. The curable liquid silicone rubber composition according to claim 7, wherein component (B) is silica.

9. The curable liquid silicone rubber composition according to claim 7, further comprising (D) a linear organopolysiloxane (excluding component (C)) having both molecular chain terminals blocked with hydroxyl groups (silanol groups) bonded to silicon atoms or hydrolyzable silyl groups, in a mass ratio of components (A) and (D) of from 10:0 to 5:5.

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