DESCRIPTION Curable Silicone Resin Composition and Cured Product [0001] The present invention relates to a curable silicone resin composition and to a cured product, and more specifically, to a curable silicone composition suitable for forming a transparent cured product with a non-tacky surface, as well as to the aforementioned product itself.

[0002] Curable silicone compositions which cure by means of an addition reaction can be quickly cured into a gel-like or a rubber-like cured product by heating at a relatively low temperature such as from 30°C to 350°C. Therefore such compositions find application for the preparation of adhesive agents, coating agents, and potting agents. On the other hand, some of these curable silicone compositions are intended for forming products of high hardness. Such a composition may comprise, e. g. , an organosilicon resin consisting of SiO4/2 units, R3SiOl/2 units and (CH2=CH) R2SiOl/2 units where R is a monovalent hydrocarbon, organohydrogen <BR> <BR> polysiloxane, silica filler, ceramics, and a platinum catalyst (see, e. g. , Japanese Patent Application Publication (hereinafter referred to as Kokai) S51-82319), or an organosilicon resin consisting of R'3SiOl/2 units and Si04/2 units where R'is a monovalent organic radical with less than 10 carbon atoms and containing at least two alkenyl groups and at least two alkoxy groups in one molecule, a linear or a partially- branched organopolysiloxane having at least two alkenyl groups in one molecule, an organohydrogen polysiloxane, ceramic-type substance, and an addition reaction catalyst (see Kokai S55-118958). However, these curable silicone resin compositions have to be cured at temperatures exceeding 500°C to be suitable for forming only high- hardness products. This is because they are cured into low-hardness rubber-like products if curing is carried out at relatively low temperatures from 30°C to 350°C.

Therefore such compositions cannot be used for forming cured bodies of high hardness on substrates of low thermal resistance. Furthermore, when the compositions are used for producing cured bodies, e. g. , in the form of thick films, a large number of cracks are formed on surfaces of such films.

[0003] On the other hand, it has been proposed (see Kokai H8-176447) to prepare a curable silicone resin composition for forming cured bodies of high hardness from an organohydrogencyclosiloxane, organosilicon resin composed of C6HsSiO3/2 units and (CH2=CH) CH3SiO2/2 units, and an addition-reaction catalyst. However, when this composition is used for the formation of transparent films, the obtained films have insufficient resistance to tackiness on their surfaces. Furthermore, since the organohydrogencyclosiloxane as the cross-linking agent is volatile, the ratio of the alkenyl groups to the silicon-bonded hydrogen atoms in the composition can be easily changed, and therefore it becomes very difficult to control the process of curing.

[0004] It is an object of the present invention to provide a curable silicone composition for forming a transparent cured product with a non-tacky surface, as well as a cured product obtained from this composition.

[0005] The present invention relates to a curable silicone resin composition, comprising: (A) an organosilicon resin represented by the following average unit formula: (C6HSSi03/2) x(RlaSiO (4 a)/2) y and having at least two alkenyl groups in one molecule, where Rl is an alkyl group, alkenyl group, or a phenyl group, 0 < a <3, x>0, y>0, and (x+y) =1, (B) a cyclic siloxane having the following general formula: where R2 is an alkyl group or a phenyl group, and m and n are numbers equal to or greater than 2, or a silicone resin represented by the following average unit formula: ( (CH3) 2HSiOi/2) p (C6H5Si03/2) q ( (CH3) C6H5Si02/2) r (Si04/2) s

where p>0, q, r, and s are each numbers which are equal to or greater than 0, and at least q or s is a number exceeding 0; (q + r + s) > 0; (p + q + r + s) =l, the mole ratio of silicone-bonded hydrogen atoms of component (B) to alkenyl groups of component (A) being within the range from 0.5 to 5; (C) a hydrosilation reaction catalyst; and (D) a hydrosilation reaction inhibitor.

[0006] The invention also relates to a cured product obtained from the aforementioned composition.

[0007] Component (A) is an organosilicon resin described by the average unit formula (C6H5Si03/2) x (RlaSiO (4aa)/2) y. In this formula, Rl designates an alkyl group, alkenyl group, or a phenyl group. The alkyl group can be exemplified by methyl, ethyl, propyl, and butyl. The most preferable is methyl. It is preferable to have an alkenyl group with 12 or less carbon atoms, such as vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecyl, and dodecenyl. The preferable among the above are vinyl, butenyl, hexenyl. The more preferable among the above are butenyl, hexenyl, or a similar alkenyl group having 4 or above carbon atoms. The most preferable among the above is hexenyl. Two or more such alkenyl groups should be in one molecule. The alkenyl groups can be one type or different types. The following conditions should be observed: 0 S a _< 3 ; x should be greater than 0, preferably between 0.2 and 0.9, more preferably between 0.4 and 0.9 ; y should be a number greater than 0, e. g. , preferably between 0.1 and 0.8, more preferably between 0.1 and 0.6. The sum of x and y should be equal to 1. It is recommended that the number average molecular weight of the aforementioned silicone resin be within the range of 800 to 80000, preferably from 1000 to 20000. Component (A) may be a silicone resin of one type or may be a mixture of silicone resins of two or more types. At 25°C, the silicone resin may be a liquid or a solid. In the case of a solid, the silicone resin can be uniformly mixed with other components by utilizing an organic solvent.

[0008] Examples of Component (A) include the silicone resins described by the formulae given below, where x > 0, z > 0, and w > 0: (C6H5Si03/2) x ( (CH3) 2Si02/2) z ( (CH2=CH) CH3Si02/2) w (C6H5Si03/2) x ( (CH3) 2Si02/2) z ( (CH2= CHC4Hg) CH3Si02/2) w

(C6H5Si03/2) x ( (CH2=CH) CH3Si02/2) z (C6H5Si03/2) x ( (CH2-CHC4H8) CH3Si02/2) z (C6H5si°3/2) x (CH3sio3l2) z ( (CH2= CH) CH3SiO2/2) w (C6H5SiO3/2) x (CH3SiO3/2) z ( (CH2=CHC4Hg) CH3 Si02/2) w [0009] Component (A) can be prepared by various methods. According to one method, a phenyltrichlorosilane and a chlorosilane that contains an alkenyl group, such as vinyltrichlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, allylmethyldichlorosilane, butenylmethyldichlorosilane, methylpentenyldichlorosilane, hexenyltrichlorosilane, hexenylmethyldichlorosilane, hexenyldimethylchlorosilane, heptenylmethyldichlorosilane, methyloctenyldichlorosilane, methylnonenyldichlorosilane, decenylmethyldichlorosilane, methylundecenyldichlorosilane, dodecenylmethyldichlorosilane are cohydrolyzed and condensed, if necessary, in the presence of tetrachlorosilane, methyltrichlorosilane, dimethyldichlorosilane, or trimethylchlorosilane. According to another method, a phenyltrimethoxysilane and an alkoxysilane that contains an alkenyl group, such as vinyltrimethoxysilane, methylvinyldimethoxysilane, dimethylvinylmethoxysilane, allylmethyldimethoxysilane, butenylmethyldimethoxysilane, methylpentenyldimethoxysilane, hexenyltrimethoxysilane, hexenylmethyldimethoxysilane, hexenyldimethylmethoxysilane, heptenylmethyldimethoxysilane, methyloctenyldimethoxysilane, methylnonenyldimethoxysilane, decenylmethyldimethoxysilane, methylundecenyldimethoxysilane, dodecenylmethyldimethoxysilane are cohydrolyzed and condensed, if necessary, in the presence of tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, or trimethylmethoxysilane. Other methods suitable for the invention are the following: subjecting the silanol groups contained in silicone resins prepared by the methods described above to a condensation reaction in the presence of an acidic or basic catalyst; subjecting silicone resin composed of C6HsSiO3/2 units and methylvinylsiloxane having both molecular terminals capped with trimethylsiloxy unit to reequilibrium polymerization in the presence of an acidic or a basic polymerization catalyst; subjecting cyclic methylvinylsiloxane and silicone resin composed of C6H5Si03/2 units to reequilibrium

polymerization in the presence of an acidic or a basic catalyst; subjecting silicone resin composed of CgHSiO units, cyclic methylvinylsiloxane, and cyclic dimethylsiloxane to reequilibrium polymerization in the presence of an acidic or a basic catalyst ; subjecting silicone resin composed of C6HsSiO3/2 units and methylhexenylsiloxane having both molecular terminals capped with silanol groups to reequilibrium polymerization in the presence of an acidic or a basic catalyst; subjecting cyclic hexenylmethylsiloxane and a silicone resin composed of C6HsSiO3/2 units to reequilibrium polymerization in the presence of an acidic or a basic catalyst; and subjecting cyclic hexenylmethylsiloxane, cyclic methylvinylsiloxane, and a silicone resin composed of C6HsSiO3/2 units to reequilibrium polymerization in the presence of an acidic or a basic catalyst.

[0010] The cyclic siloxane or the silicone resin as component (B) is a cross-linking agent. Component (B) is characterized by excellent miscibility with component (A) and is intended for improving the transparency of a cured body obtained from the composition and for decreasing tackiness on the surface of this body.

[0011] In the cyclic siloxane described by the aforementioned general formula, R2 designates an alkyl group or a phenyl group. Examples of the alkyl group include methyl, ethyl, propyl, or butyl. An alkyl group having at least two carbon atoms is preferable, and ethyl group is the most preferable. In the aforementioned general formula, m and n are numbers each being equal to or greater than 2. It is recommended that (m + n) be a number within the range from 4 to 20, preferably from 4 to 10, and the boiling point of the cyclic siloxane is at least 150°C at normal pressure.

Component (B) may comprise a cyclic siloxane of one type or a mixture of cyclic siloxanes of two or more types. Such cyclic siloxanes are commercially produced and easily obtainable.

[0012] In the silicone resin represented by the average unit formula, ( (CH3) 2HSiOi/2) p (C6H5Si03/2) q ( (CH3) C6HsSi02/2) r (Si04/2) s,, P>0, q, r, and s are numbers equal to or greater than 0, but at least one of q and s exceeds 0; (q + r + s) > 0; and (p + q + r + s) =1. The ratio p : (q + r + s) is within the range from 0.2 to 0.9 : 0.8 to 0.1, preferably from 0.4 to 0.9 : 0.6 to 0.1. The number average molecular weight of this silicone resin is preferably from 500 to 20000, more preferably from 800 to 10000.

Eamples of these silicone resins include the following average unit formulae, where p > 0, b > 0, c > 0, d > 0, and e > 0 : ((CH3) 2HSiO I/2) p (SiO4I2) b ((CH3) 2HSiO 1/2) p (C6H5 siO3/2) C ( (CH3) 2HSiO1/2) p ( (CH3) C6H5Si02/2) d siOq./2) e [0013] The silicone resin as component (B) may be prepared by adding alkylsilicate into a mixed system of an aqueous solution of a hydrochloric acid of a specific concentration and an organic silicon compound, such as 1,1, 3,3-tetramethyldisiloxane, dimethylchlorosilane, or dimethylalkoxysilane. In this case, the value of the molecular weight of the silicone resin can be freely controlled by the amount of the alkylsilicate added by dripping, but in general component (B) may have an arbitrarily chosen molecular weight.

[0014] It is recommended to use component (B) in such an amount that the mole ratio of silicon-bonded hydrogen atoms contained in component (B) to alkenyl groups of component (A) is within the range of 0.5 to 5, preferably 0.5 to 3, and even more preferably 0.8 to 1.5. This is because, if the ratio of silicon-bonded hydrogen atoms contained in component (B) to alkenyl groups of component (A) is below 0.5, it will be difficult to ensure sufficient curing of the composition. If, on the other hand, the ratio of silicon-bonded hydrogen atoms contained in component (B) to alkenyl groups of component (A) exceeds 5, air bubbles may occur in the cured product, and the material of the cured product may have a reduced mechanical strength.

[0015] Component (C), a hydrosilation reaction catalyst, is intended for acceleration of curing of the composition. This component may comprise a platinum- type catalyst, rhodium-type catalyst, or a palladium-type catalyst. Examples include platinum black, platinum on a finely powdered carbon carrier, platinum on a finely powdered silica powder, chloroplatinic acid, an alcoholic solution of a chloroplatinic acid, a platinum-olefin complex, and a platinum-vinylsiloxane complex. Component (C) should be used in a catalytic quantity, preferably (if measured in weight units), in a metal amount of 0.1 to 1000 ppm relative to component (A). If component (C) is used in an amount of less than 0.1 ppm, curing of the composition will occur very slowly, while the use of component (C) in an amount exceeding 1000 ppm practically

will not accelerate curing but will make the use of the catalyst economically unjustifiable.

[0016] Component (D), a hydrosilation reaction inhibitor, is used to improve storage stability and conditions for handling of the composition of the invention.

Examples of useful inhibitors are: 3-methyl-l-butyn-3-ol, 3, 5-dimethyl-1-hexyn-3-ol, 2-phenyl-3-butyn-2-ol, or a similar alkyne alcohol; 3-methyl-3-penten-1-yne, 3,5- dimethyl-3-hexen-1-yne, or a similar enyne; 1, 3,5, 7-tetramethyl-1, 3-5,7- tetravinylcyclotetrasiloxane, 1, 3,5, 7-tetramethyl-1, 3,5, 7-tetrahexenylcyclotetrasiloxane, and benzotriazol. Although there are no special restrictions with regard to the amount in which component (D) can be used, it is recommended to use this component in an amount to inhibit curing of the composition at room temperature and to enable heat- curing of the composition, and concretely in an amount from 0.0001 to 10 parts by weight, preferably from 0. 001 to 5 parts by weight for each 100 parts by weight of component (A).

[0017] It has been shown that the composition of the invention may be composed of components (A) through (D). However, if it is necessary to improve adherence of the cured body of the composition to a substrate, an adhesion-imparting agent can be added to the composition as component (E). Examples of compounds suitable for use as component (E) include silane coupling agents, such as 3- methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, or a similar acryloxy-containing organoalkoxysilane ; 3-aminopropyl trimethoxysilane, 3- (2- aminoethyl) -aminopropyltrimethoxysilane, or a similar amino-containing organoalkoxysilane; 3-glycidoxypropyltrimethoxysilane, or similar epoxy-containing organoalkoxysilane; as well as products of a condensation reaction between y- glycidoxypropyltrialkoxysilane and a silanol-capped dimethylpolysiloxane, a condensation reaction between y-glycidoxypropyltrialkoxysilane and a silanol-capped methylvinylpolysiloxane, and a condensation reaction between y- glycidoxypropyltrialkoxysilane and a copolymer of a silanol-capped dimethylsiloxane and methylvinylsiloxane. When added to the composition, it is recommended to use component (E) in an amount of 0.1 to 50 parts by weight, preferably 0.1 to 30 parts by weight for each 100 parts by weight of component (A).

[0018] If it is desirable to obtain a cured body having improved mechanical properties and higher hardness, it is recommended to combine the composition of the invention with fumed silica, precipitated silica, titanium dioxide, carbon black, alumina, quartz powder, or similar inorganic filler, or with the aforementioned inorganic fillers subjected to hydrophobic surface treatment with the use of an organoalkoxysilane, organochlorosilane, organosilazane, or a similar organic silicon compound. When it is required to obtain a cured body that possesses transparency, the aforementioned fillers should be added in amounts that do not impair transparency of the product.

Furthermore, if necessary, the following additives can also be used: tetramethoxysilane, tetraethoxysilane, dimethyldimethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, phenyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, or a similar alkoxysilane; hexane, heptane, or a similar aliphatic solvent; tolyene, xylene, or a similar aromatic solvent; methylethylketone, methylisobutylketone, or a similar ketone-type solvent, or other organic solvents.

[0019] The composition of the invention is prepared by uniformly mixing components (A) through (D), if necessary, in combination with other optional additives.

Mixing can be carried out for example with the use of Rose mixer, planetary mixer, or Hobart mixer.

[0020] The cured body of the invention is obtained by curing the aforementioned curable silicone resin composition. Although the curing temperature is not specifically limited, it is recommended to carry out the curing at a relatively low temperature, e. g., between 30 and 350°C. It is recommended that hardness of the cured body measured by means of a Type A durometer in accordance with JIS K 6249 be higher than 30, and preferably higher than 50 units. The cured body of the invention may used in the form of a coating firmly attached to a substrate or can be used independently in the form of sheets or films. The substrate can be made, e. g. , from rubber, such as silicone rubber, butyl rubber, natural rubber, from plastic, such as acrylic resin, polycarbonate resin, ABS resin, PPS resin, or from glass, ceramic, and metal. There are no special restrictions with regard to the thickness of the cured body, however, a thickness of the body exceeding even 5 mm will not lead to the formation of surface cracks, while a thickness even below 5 mm can provide sufficient mechanical strength.

[0021] As has been mentioned above, the composition of the present invention is characterized by the low curing temperature which produces a transparent cured body having high hardness and low tackiness. One advantage of the aforementioned composition is that prevention of evaporation of component (B) makes it possible to control the curing. The composition of the invention is suitable for such applications as a coating for electric and electronic circuit substrates, a protective coating for bottles, a key-top coating, etc.

[0022] The invention will now be described in more detail with reference to practical examples. In these examples, values of viscosity correspond to 25°C and were obtained on EMD rotary-type viscometer of Tokyo Keiki Co. , Ltd. Refractive indices also correspond to 25°C and were obtained on a refractometer of Elmer Co.

Light transmittance was measured on a spectrophotometer (UV-265FW, the product of Shimazu Seisakusho) at 450 nm with a 10 mm volume cell. Hardness was measured on the aforementioned Type A durometer in accordance with the provisions of JIS K 6249.

[0023] Reference Example 1: A 10 L flask equipped with a stirrer, a reflux condenser, a thermometer, and a dripping funnel was loaded with 2843.2 g toluene, 598.2 g 2-propanol (IPA), and 977.5 g (54. 2mol) ion-exchange water (hereinafter referred to simply as water). The flask was then cooled with icy water, and the contents were combined with a mixture of 2701.5 g (12.8 mol) phenyltrichlorosilane, 134.9 g (1.04 mol) dimethyldichlorosilane, 681.2 g (3.45 mol) hexenylmethyldichlorosilane, and 623.3 g toluene added by dripping. Upon completion of the addition, the flask was heated by means of a mantle heater and subjected to 1 hour refluxing at 80°C. After cooling to room temperature, the water layer was removed by means of a separation funnel, 3 kg of water were added, the mixture was stirred for 10 min. , and the water layer was separated for the second time. After the above-described procedure was repeated three times, the product was combined with 1.08 kg of 7.4 wt. % aqueous solution of sodium hydrogencarbonate. The mixture was then subjected to refluxing for 1 hour at 85 to 87°C. After cooling to room temperature, the water layer was separated, and the organic layer was filtered under vacuum (filter paper GC-90, the <BR> <BR> product of Advantech Toyo Co. ). The obtained filtrate was loaded into a 10 L flask equipped with a stirrer, a reflux condenser, a Dean-Stark tube, and a thermometer. The

contents were combined with 14.1 g of 46. 8 wt. % aqueous solution of potassium hydroxide, and the mixture was heated at a reflux temperature of 88 to 115°C and subjected to azeotropic dehydration. The reaction solution was sampled in an amount of 3 g, placed onto an aluminum plate, left intact for 5 min. , then heated for 30 min. in an oven at 150°C, and measured with regard to a non-evaporatable component. As the non-evaporatable component was 41.2%, the product was heated at 115 to 122°C until the aforementioned component reach 50%, and then 1146 g of toluene were removed.

After stirring for 3 hours at 122°C, the product was cooled to 100°C, combined with 7.9 g of acetic acid and neutralized. After neutralization, the product was stirred for 1 hour at 90 to 100°C, cooled to room temperature, and the potassium acetate was removed by filtering through filter paper GC-90 (the product of Advantech Toyo Co.).

The obtained filtrate was loaded into a 10 L separable flask equipped with an evaporator, and the toluene and acetic acid were removed by evaporation under vacuum at 100°C/30 mm Hg to 150°C/7 mm Hg. The product was obtained in a yield of 95.9% and comprises 2125 g of an organosilicon resin with an average unit formula given below. The number-average molecular weight was 2300.

(C6H5 Si03/2) o. 74 ((CH3) 2Sio2l2) 0. 06 ((CH2 = CHC4H8) CH3si°2/2) 0. 20 [0024] Reference Example 2: A 5 L flask equipped with a stirrer, a reflux condenser, a thermometer, and a dripping funnel was loaded with 1004.1 g toluene, 166.0 g IPA, and 363.6 g (20.2 mol) water. The flask was then cooled with icy water, and the contents were combined with a mixture of 740.4 g (3.50 mol) phenyltrichlorosilane, 271. 1 g (2. 10 mol) dimethyldichlorosilane, 275. 7 g (1. 40 mol) hexenylmethyldichlorosilane, and 425.0 g toluene added by dripping. Upon completion of the addition, the flask was heated by means of a mantle heater and subjected to 1 hour refluxing at 80°C. After cooling to room temperature, the water layer was removed by means of a separation funnel, 2 kg of water were added, the mixture was stirred for 10 min. , and the water layer was separated for the second time.

After the above-described procedure was repeated three times, the product was combined with 529g of 5.6 wt. % aqueous solution of sodium hydrogencarbonate. The mixture was then subjected to refluxing for 1 hour at 80 to 83°C. After cooling to

room temperature, the water layer was separated, and the organic layer was filtered <BR> <BR> under vacuum (filter paper GC-90, the product of Advantech Toyo Co. ). The obtained filtrate was loaded into a 5 L flask equipped with a stirrer, a reflux condenser, a Dean- Stark tube, and a thermometer. The contents were combined with 18.6 g of 14.1 wt. % aqueous solution of potassium hydroxide, and the mixture was heated at a reflux temperature of 83 to 110°C and subjected to azeotropic dehydration. The reaction solution was sampled in an amount of 3 g, placed onto an aluminum plate, left intact for 5 min. , then heated for 30 min. in an oven at 150°C, and measured with regard to a non- evaporatable component. As the non-evaporatable component was 33.0%, the product was heated at 115 to 122°C until the aforementioned component reach 50%, and then 780 g of toluene were removed. After stirring for 3 hours at 122°C, the product was cooled to 100°C, combined with 3.1 g of acetic acid and neutralized. After neutralization, the product was stirred for 1 hour at 90 to 100°C, cooled to room temperature, and the potassium acetate was removed by filtering through filter paper <BR> <BR> GC-90 (the product of Advantech Toyo Co. ). The obtained filtrate was loaded into a 2 L separable flask, and the toluene and acetic acid were removed by evaporation under vacuum at 100°C/30 mm Hg to 150°C/7 mm Hg. The product was obtained in a yield of 93.2% and comprised 751. 0 g of an organosilicon resin with an average unit formula given below. The number-average molecular weight was 1300.

(C6H5 Si03/2) 0. 50 ((CH3) 2 Si02/2) 0. 30 ( (CH2 = CHC4Hg) CH3Si02/2) o. 20 [0025] Reference Example 3: A 5 L flask equipped with a stirrer, a reflux condenser, a thermometer, and a dripping funnel was loaded with 1005.2 g toluene, 240.4 g IPA, and 344.2 g (19.1 mol) water. The flask was then cooled with icy water, and the contents were combined with a mixture of 735.2 g (3.47 mol) phenyltrichlorosilane, 358. 9 g (2. 78 mol) dimethyldichlorosilane, 136. 9 g (0. 694 mol) hexenylmethyldichlorosilane, and 401.8 g toluene added by dripping. Upon completion of dripping, the flask was heated by means of a mantle heater and subjected to 1 hour refluxing at 80°C. After cooling to room temperature, the water layer was removed by means of a separation funnel, 2 kg of water were added, the mixture was stirred for 10 min. , and the water layer was separated for the second time. After the

above-described procedure was repeated three times, the product was combined with 529g of 5.5 wt. % aqueous solution of sodium hydrogencarbonate. The mixture was then subjected to refluxing for 1 hour at 80 to 83°C. After cooling to room temperature, the water layer was separated, and the organic layer was filtered under vacuum (filter paper GC-90, the product of Advantech Toyo Co. ). The obtained filtrate was loaded into a 5 L flask equipped with a stirrer, a reflux condenser, a Dean- Stark tube, and a thermometer. The content was combined with 5. 5 g of 41. 8 wt. % aqueous solution of potassium hydroxide, and the mixture was heated at a reflux temperature of 84 to 110°C and subjected to azeotropic dehydration. The reaction solution was sampled in an amount of 3 g, placed onto an aluminum plate, left intact for 5 min. , then heated for 30 min. in an oven at 150°C, and measured with regard to a non- evaporatable component. As the non-evaporatable component was 34. 8%, the product was heated at 115 to 122°C until the aforementioned component reached 50%, and then 655 g of toluene were removed. After stirring for 3 hours at 122°C, the product was cooled to 100°C, combined with 2.7 g of acetic acid and neutralized. After neutralization, the product was stirred for 1 hour at 90 to 100°C, cooled to room temperature, and the potassium acetate was removed by filtering through filter paper GC-90 (the product of Advantech Toyo Co. ). The obtained filtrate was loaded into a 2 L separable flask, and the toluene and acetic acid were removed by evaporation under vacuum at 100°C/30 mm Hg to 150°C/7 mm Hg. The product was obtained in a yield of 94.0% and comprises 706.7g of an organosilicon resin with an average unit formula given below. The number-average molecular weight was 1700.

(C6H5Sio3/2) o. 50 ((CH3) 2Sio2l2) 0. 40 ((CH2 = CHC4Hg) CH3 Si°2/2) 0. l 0 [0026] Reference Example 4: A 2 L flask equipped with a stirrer, a reflux condenser, a thermometer, and a dripping funnel was loaded with 268 g (2.00 mol) of 1,1, 3, 3-tetramethyldisiloxane and 134 g (7. 44 mol) of water. After the components were mixed, the flask was cooled, and the contents were combined with 90 g of a concentrated hydrochloric acid slowly added by dripping. Upon completion of dripping, 11 g of methanol were added. The mixture was then combined with 335 g

(2.20 mol) of tetramethoxysilane slowly added by dripping at a temperature of 20°C.

Upon completion of this stage of dripping, water was added in an amount of 280 g, the mixture was stirred for 5 min. , and left intact for 5 min. A low-molecular-weight polymer layer (a) formed in the aforementioned process was removed by separation and poured into an Erlenmeyer flask. Meanwhile, the reaction solution obtained after removal of low-molecular-weight polymer layer (a) was combined with 280 g of n- hexane. The mixture was stirred for 10 min. and then left intact for 5 min. After separation of a water layer, the contents were combined with the aforementioned low- molecular-weight polymer layer (a) and 280g of water. The mixture was stirred for 5 min. and then left intact for 5 min. After separation of a water layer, n-hexane was removed by distillation. The resulting product comprised 394 g of a silicone resin with an average unit formula given below and was obtained with a yield of 95. 1%. A number-average molecular weight was 1000.

((CH3) 2HSiO 1/2) 0. 62 (si°4/2) 0. 38 [0027] Practical Example 1: A mixture was prepared under normal pressure and 95°C temperature from 2125 g of the organosilicon resin obtained in Reference Example 1,590 g of cyclic siloxane represented by the following general formula: (where Me is a methyl group, Et is an ethyl group, and a mole ratio of SiH to hexenyl groups in the silicone resin was equal to 1.2. Boiling point: 200°C), 27.7 g of the product of a condensation reaction between a. m-dihydroxypolydimethylsiloxane and y- glycidoxypropyltrimethoxysilane, and 0.277 g of phenyl butynol. After mixing for 1 hour at 80 to 90°C, the mixture was cooled to room temperature. The reaction solution <BR> <BR> was filtered through a filter paper GC-90 (the product of Advantech Toyo Co. ). As a result, 2650 g of a silicone resin composition was obtained. This resin composition was mixed in a weight ratio of 99: 1 with a mixture of 1.25 g of a complex of platinum with 1, 3-divinyl-1, 1, 3,3-tetramethyldisiloxane (4 wt. % content of metallic platinum) and 98.75 g of a cyclic methylvinylsiloxane of the following formula where Me is methyl and n is 4-5:

As a result, a curable silicone resin composition was obtained. This composition was measured with regard to viscosity, refractive index, light transmittance, and hardness of a cured body obtained by pressure curing for 15 min. at 150°C and under pressure of 10 MPa. The results of measurement are shown in Table 1. Furthermore, the aforementioned curable silicone resin composition was placed onto an aluminum plate, and heated for 30 min. in an oven at 150°C to produce a transparent cured body. The surface of this cured body was tested by finger touch. This tactile test showed that the surface of the cured body is absolutely not tacky. Furthermore, the aforementioned curable silicone resin composition was applied onto a glass plate and heated for 30 min. in an oven at 150°C. The obtained cured coating film showed strong adhesion to the glass plate.

[0028] Practical Example 2: A mixture was prepared under normal pressure and a 80°C temperature from 698 g of the organosilicon resin obtained in Reference Example 2,127g of the silicone resin obtained in Reference Example 4 and represented by the following average unit formula: ((CH3) 2HSiO 1/2) 0. 62 (Si°4/2) 0. 38 (with the mole ratio of SiH to hexenyl groups in the silicone resin obtained in Reference Example 2 equal to 1.0), 8.4 g of the product of a condensation reaction between a, co- dihydroxypolydimethylsiloxane and y-glycidoxypropyltrimethoxysilane, and 0.84 g of phenyl butynol. After mixing for 1 hour at 72 to 81°C, the mixture was cooled to room temperature. The reaction solution was filtered through a filter paper GC-90 (the product of Advantech Toyo Co. ). As a result, 834 g of a silicone resin composition was obtained. This resin composition was mixed in a weight ratio of 99: 1 with a

mixture of 1.25 g of a complex of platinum with 1, 3-divinyl-1, 1,3, 3- tetramethyldisiloxane (4 wt. % content of metallic platinum) and 98.75 g of the silicone resin obtained in Reference Example 2. As a result, a curable silicone resin composition was obtained.

[0029] The obtained curable silicone resin composition was measured with regard to viscosity, refractive index, and light transmittance. Hardness of a cured body obtained by pressure curing of the above composition for 15 min. at 150°C and under pressure of 10 MPa also was measured. The results of measurement are shown in Table 1. Furthermore, the aforementioned curable silicone resin composition was placed onto an aluminum plate, and heated for 30 min. in an oven at 150°C to produce a transparent cured body. The surface of this cured body was tested by finger touch.

This tactile test showed that the surface of the cured body is absolutely not tacky.

Furthermore, the aforementioned curable silicone resin composition was applied onto a glass plate and heated for 30 min. in an oven at 150°C. The obtained cured coating film showed strong adhesion to the glass plate.

[0030] Practical Example 3: A mixture was prepared under normal pressure and a 80°C temperature from 225.0 g of the silicone resin obtained in Reference Example 3, 337. 5 g of the silicone resin obtained in Reference Example 2, 139. 7 g of silicone resin having a number-average molecular weight equal to 900 and represented by the following average unit formula: ((CH3) 2HSiO 1/2) 0. 52 (C6H5si°3/2) 0. 48 (with the mole ratio of SiH to hexenyl groups in the silicone resins obtained in Reference Example 2 and Reference Example 3 equal to 1.0), 7.2 g of the product of a condensation reaction between oc, (D-dihydroxypolydimethylsiloxane and y- glycidoxypropyl trimethoxysilane, and 0.72 g of phenyl butynol. After mixing for 1 hour at 73 to 83°C, the mixture was cooled to room temperature. The reaction solution was filtered through a filter paper GC-90 (the product of Advantech Toyo Co. ). As a result, 667. 1g of a silicone resin composition were obtained. This resin composition was mixed in a weight ratio of 99: 1 with a mixture of 0.090 g of a complex of platinum with 1, 3-divinyl-l, 1,3, 3-tetramethyldisiloxane (4 wt. % content of metallic platinum)

and 7.07 g of the silicone resin obtained in Reference Example 2. As a result, a curable silicone resin composition was obtained.

[0031] The obtained curable silicone resin composition was measured with regard to viscosity, refractory index, and light transmittance. Hardness of a cured body obtained by pressure curing of the above composition for 15 min. at 150°C and under pressure of 10 MPa also was measured. The results of measurement are shown in Table 1. Furthermore, the aforementioned curable silicone resin composition was placed onto an aluminum plate, and heated for 30 min. in an oven at 150°C to produce a transparent cured body. The surface of this cured body was tested by finger touch.

This tactile test showed that the surface of the cured body is absolutely not tacky.

Furthermore, the aforementioned curable silicone resin composition was applied onto a glass plate and heated for 30 min. in an oven at 150°C. The obtained cured coating film showed strong adhesion to the glass plate.

[0032] Practical Example 4: A mixture was prepared under normal pressure and 95°C temperature from 417.2 g of the organosilicon resin obtained in Reference Example 1, 115.9 g of cyclic siloxane represented by the following general formula: (where Me is a methyl group, Et is an ethyl group, and the mole ratio of SiH to hexenyl groups in the silicone resin was equal to 1.2. Boiling point: 200°C), and 0.54 g of phenyl butynol. After mixing for 1 hour at 85 to 90°C, the mixture was cooled to room temperature. The reaction solution was filtered through a filter paper GC-90 (the <BR> <BR> product of Advantech Toyo Co. ). As a result, 520 g of a silicone resin composition was obtained. This resin composition was mixed in a weight ratio of 99: 1 with a mixture of 1.25 g of a complex of platinum with 1, 3-divinyl-1, 1,3, 3- tetramethyldisiloxane (4 wt. % content of metallic platinum) and 98.75 g of a cyclic methylvinylsiloxane of the following formula:

[0033] As a result, a curable silicone resin composition was obtained. This composition was measured with regard to viscosity, refractive index, light transmittance, and hardness of a cured body obtained by pressure curing for 15 min. at 150°C and under pressure of 10 MPa. The results of measurement are shown in Table 1.

Furthermore, the aforementioned curable silicone resin composition was placed onto an aluminum plate, and heated for 30 min. in an oven at 150°C to produce a transparent cured body. The surface of this cured body was tested by finger touch. This tactile test showed that the surface of the cured body is absolutely not tacky.

[0034] Comparative Example 1: A mixture was prepared under normal pressure and 60°C temperature from 656 g of the organosilicon resin obtained in Reference Example 2,69 g of methylhydrogencyclosiloxane represented by the following general formula: Boiling point : 134°C 7.4 g of a product of a condensation reaction between a, m-dihydroxypolydimethyl- siloxane and y-glycidoxypropyltrimethoxysilane, and 0.74 g of phenyl butynol.

[0035] After mixing for 1 hour at 60°C, the mixture was cooled to room temperature. The reaction solution was filtered through a filter paper GC-90 (the product of Advantech Toyo Co.).. As a result, 834 g of a silicone resin composition was obtained. This resin composition was mixed with a hydrosilation reaction catalyst

in the same manner as in Practical Example 2. As a result, a curable silicone resin composition was obtained.

[0036] The obtained composition was placed onto an aluminum plate and heated for 30 min. in an oven at 150°C to produce a transparent cured body. The surface of this cured body was tested by finger touch. This tactile test showed that the surface of the cured body was tacky.

[Table 1]

Pr. Ex. 1 Pr. Ex. 2 Pr. Ex. 3 Pr. Ex. 4 Viscosity (mPa * s) 5900 5950 4200 5300 Refractive index 1. 509 1. 495 1. 508 1. 509 Light transmittance (%) 99. 8 99. 8 99. 9 99. 6 Hardness 90 ? 90 ? 74 90 ?

*Light transmittance recalculated to 1 mm thickness.

[0037] When the composition of the invention is prepared from aforementioned components (A) through (D), especially when a specific cyclic siloxane or silicone resin such as component (B) is used as a cross-linking agent, it is possible to obtain a transparent cured body with the surface free of tackiness.