Thermoplastic fluorosilicone resins, their manufacture and use.

0001This invention relates to thermoplastic fluorosilicone resins, useful e.g. for microcapsulating platinum catalysts, as a coating agent for car wax, and an additive for engineering plastics. It also relates to methods for preparing the same.

0002Conventional vehicles used for heat resistant paint and weather resistant paint include silicone resins containing a silanol or alkoxysilyl group as a functional group and having compositions: CH₃SiO_3/2, C₆H₅SiO_3/2, (C₆H₅SiO_3/2)·[(CH₃)₂SiO], and (C₆H₅SiO_3/2)·(n-C₃H₇SiO_3/2). Since these conventional silicone resins are thermosetting, the paint compositions can gel with the lapse of time.

0003It is also known to add these resins to thermoplastic molding resins for improving mold release, flame retardancy and moldability. However, addition of thermosetting silicone resins is not recommended for those resins having high molding temperatures. In this regard, Japanese Patent Application Kokai (JP-A) No. 2282/1993 proposes a thermoplastic silicone resin, in which residual silanol groups are capped.

0004For stabilizing platinum-catalyzed addition type silicone compositions during storage, JP-A 4833/1990 proposes to micro-capsulate a platinum catalyst by carrying the platinum catalyst on a thermoplastic silicone resin as mentioned above, comminuting the resin into a microparticulate powder, and washing the particulates with methanol to remove the platinum catalyst from the outer surface. Since this silicone resin, however, is soluble in vinylmethylpolysiloxane and methylhydrogenpolysiloxane, it is less effective for providing storage stability, especially in the summer season even if its softening point is elevated.

0005For the purpose of reducing solubility in vinylmethylpolysiloxane and methylhydrogenpolysiloxane, JP-A 323223/1992 proposes a thermoplastic silicone resin of the formula: (CF₃CH₂CH₂SiO_3/2)_n·((CH₃)₂SiO)_m. Since this resin, however, has a low softening point due to inclusion of a D unit, storage stability is little improved. By reducing the value of m, the softening point can be increased, but at the sacrifice of compatibility with organic solvents. Then diethyl ether, Freon 113 and other industrially undesirable solvents are necessary in order to blend a platinum catalyst with the resin in a solution form.

0006For preparing microcapsulated platinum catalysts which are insoluble in vinylmethylpolysiloxane and methylhydrogenpolysiloxane, JP-A 47442/1989 and 51140/1989 propose to use ethylenic polymers such as acrylic resin, polyvinyl alcohol, and styrene-acrylonitrile copolymers. While these vinyl polymers are substantially insoluble in siloxanes, there occurs a problem that when cured moldings are heated, the vinyl polymers can be pyrolyzed to partially discolor the moldings.

0007With respect to car wax resins, Japanese Patent Publication (JP-B) No. 58305/1990 propose to cure a methylated silicone resin with an organic titanate or organic tin catalyst to thereby form water repellent coatings. However, some functional groups (e.g., silanol or alkoxysilyl groups) are left in these silicone coatings. The coatings tend to lose gloss with the lapse of time because contaminants can attach to the silanol or alkoxysilyl groups. Moreover, the methylated silicone resin is fully water repellent, but weak to acid rain. There is a need for a car wax resin having acid resistance and stain resistance.

0008We have found that by effecting co-hydrolysis of three organic silicon compounds of the following general formulae (2), (3) and (4) or partial hydrolysates thereof in a molar ratio of x:y:z and polymerizing the co-hydrolysate, we can obtain a thermoplastic fluorosilicone resin of the following average compositional formula (1) having a softening point of 50 to 200 °C.         RfCH₂CH₂SiX₃   (2)         C₆H₅SiX₃   (3) <chemistry id="chem0001" num="0001"><img file="EP0657487A2_D0001.tif" /></chemistry> In the formulae, Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, X is a halogen atom or an alkoxy group having 1 to 6 carbon atoms, and x, y, and z are positive numbers in the range: 0.2 ≦ x ≦ 0.95, 0 &lt; y ≦ 0.8, 0 ≦ z ≦ 0.05, and x + y + z = 1.

0009The thermoplastic fluorosilicone resin of formula (1) having a softening point of 50 to 200°C can be blended with a platinum catalyst in an organic solvent and spray dried before it is added to a platinum-catalysed addition type curable composition. Since the resin is substantially insoluble in vinylmethylpolysiloxane and methylhydrogenpolysiloxane, the composition experiences little increase of viscosity even after storage, e.g. at room temperature over about one month. That is, the composition is satisfactorily storage stable. In addition, we find that the resin is also effective as a lustering and water repellent agent, e.g. for finishing wax. In particular the resin, having a high softening point, is highly resistant against staining and weathering. Since a suitable amount of a perfluoroalkyl group is contained, the resin has higher water repellency, higher acid resistance and a greater contact angle with water than the methylated silicone resins.

0010Therefore, in one aspect we provide a thermoplastic fluorosilicone resin having the following average compositional formula (1):         (RfCH₂CH₂SiO_3/2)_x(C₆H₅SiO_3/2)_y(SiO₂)_z   (1) wherein Rf, x, y, and z are as defined above and having a softening point in the range of 50 to 200 °C.

0011In another aspect, we provide a method for preparing a thermoplastic fluorosilicone resin by effecting co-hydrolysis of a first organic silicon compound of formula (2):         RfCH₂CH₂SiX₃   (2)    or a partial hydrolysate thereof, a second organic silicon compound of formula (3):         C₆H₅SiX₃   (3)    or a partial hydrolysate thereof, and a third organic silicon compound of formula (4):         SiX₄   (4)    or a partial hydrolysate thereof in a molar ratio x:y:z, and polymerising the co-hydrolysate; Rf, X, x, y and z are as defined above.

0012Use of such a composition as an encapsulant for a catalyst for use in siloxane curing reactions, especially in addition-curable organopolysiloxane compositions, is another aspect as is an addition-curable organopolysiloxane composition containing such an encapsulated catalyst. Uses for the other purposes disclosed herein are also independent aspects.

FURTHER EXPLANATIONS; OPTIONAL AND PREFERRED FEATURES

0013The thermoplastic fluorosilicone resin proposed herein may be represented by the following average compositional formula (1):         (RfCH₂CH₂SiO_3/2)_x(C₆H₅SiO_3/2)_y(SiO₂)_z   (1)

0014In the RfCH₂CH₂SiO_3/2 unit, Rf is a perfluoroalkyl group having 1 to 10 carbon atoms, usually representable by C_nF_2n+1 wherein n is an integer of 1 to 10. This perfluoroalkyl group is an essential substituent for rendering the resin incompatible with methylated polysiloxanes. The perfluoroalkyl group is also effective for imparting mold release, water repellency and lubricity. The content of perfluoroalkyl group in the resin is expressed by a molar ratio x which ranges from 0.2 to 0.95, especially from 0.5 to 0.9. If x is less than 0.2, undesirably the resin is well compatible with methylated polysiloxanes and forms a coating which is less water repellent and less releasable from the mold. If x is more than 0.95, the resin has a lower softening point. Even when a SiO₂ unit is introduced, the softening point does not exceed 50 °C insofar as the resin is produced by the method disclosed herein.

0015The resin may further contain a C₆H₅SiO_3/2 unit in a content y which is in the range: 0 &lt; y ≦ 0.8, preferably 0.1 ≦ y ≦ 0.5. The phenyl group has the effect of controlling the softening point of the resin. If the content of this unit in the resin, y, exceeds 0.8, undesirably the resin becomes compatible with methylated polysiloxanes.

0016Further the resin may contain a SiO₂ unit for the purpose of increasing the softening point of the resin. The content of SiO₂ unit in the resin is represented by z which ranges from 0 to 0.05. If z exceeds 0.05, the resin may have too high a softening point and gel when a solvent used in reaction is heated and distilled off.

0017It is understood that x, y and z represent molar ratios and amount to unity, that is, x + y + z = 1.

0018The resin should have a softening point in the range of 50 to 200 °C, preferably 70 to 150 °C. If the softening point is lower than 50 °C, the resin is poor in storage stability when a platinum catalyst is microcapsulated with the resin, or forms a too soft, stain receptive coating when used as a coating agent, e.g. suggesting that the resin is unsuitable for car wax application. If the resin has a softening point in excess of 200 °C, there arises a problem that when a platinum catalyst is microcapsulated with the resin and added to an addition type organopolysiloxane composition, the platinum catalyst is retarded from leaching out, resulting in short curing.

0019The thermoplastic fluorosilicone resin is generally soluble in methylene chloride, methyl ethyl ketone and methyl isobutyl ketone, but insoluble in toluene, hexane, and silicone oil.

0020Preferably the resin has a molecular weight of about 1,000 to 100,000 as calculated on a polystyrene basis. The molecular weight preferably ranges from about 2,000 to about 50,000 in controlling the softening point of 50 to 200 °C. An average molecular weight of less than 1,000 usually gives a softening point below 50 °C whereas an average molecular weight of more than 100,000 usually gives a softening point above 200 °C so that the resin may be less soluble in methylated polysiloxanes when heated.

0021The resin may be prepared by effecting co-hydrolysis of organic silicon compounds of formula (2), (3) and (4) or partial hydrolysates thereof in a molar ratio x:y:z, wherein x, y and z are as defined above, and polymerising the co-hydrolysate.         RfCH₂CH₂SiX₃   (2)         C₆H₅SiX₃   (3)         SiX₄   (4)

0022In the formula, Rf is as defined above, and X is a halogen atom or an alkoxy group having 1 to 6 carbon atoms, preferably the alkoxy group.

0023Examples of the organic silicon compound of formula (2): RfCH₂CH₂SiX₃ or partial hydrolysate thereof include CF₃CH₂CH₂SiCl₃, CF₃CH₂CH₂Si(OCH₃)₃, CF₃CH₂CH₂Si(OC₂H₅)₃, C₄F₉CH₂CH₂SiCl₃, C₄F₉CH₂CH₂Si(OCH₃)₃, C₄F₉CH₂CH₂Si(OC₂H₅)₃, C₈F₁₇CH₂CH₂SiCl₃, C₈F₁₇CH₂CH₂Si(OCH₃)₃ and C₈F₁₇CH₂CH₂Si(OC₂H₅)₃.

0024Included in the organic silicon compound of formula (3): C₆H₅SiX₃ or partial hydrolysate thereof are the following examples.

0025C₆H₅SiCl₃, C₆H₅Si(OCH₃)₃, C₆H₅Si(OC₂H₅)₃, <chemistry id="chem0002" num="0002"><img file="EP0657487A2_D0002.tif" /></chemistry>

0026Examples of the organic silicon compound of formula (4): SiX₄ or partial hydrolysate thereof include SiCl₄, Si(OCH₃)₄, _Si(OC₂H₅)₄, methyl polysilicate, and ethyl polysilicate.

0027When hydrolysis if carried out using chlorosilanes of formulae (2) to (4) wherein X is a chlorine atom as the starting materials, subsequent polymerization can take place without a catalyst because the hydrochloric acid by-product resulting from hydrolysis can be a catalyst. On hydrolysis, use of a solvent is effective. The useful solvent is selected from hydrocarbon solvents such as toluene, xylene, hexane, heptane, and octane and chlorinated solvents such as methylene chloride, chloroform, trichloroethylene, and perchloroethylene. It is also effective to use a polar solvent as a co-solvent during hydrolysis. Such polar solvents include methanol, ethanol, isopropyl alcohol, isobutyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ether, dibutyl ether, and tetrahydrofuran.

0028When alkoxysilanes of formulae (2) to (4) wherein X is an alkoxy group or partial hydrolysates thereof are used as the starting materials, it is recommended to prepare the resin by effecting hydrolysis in the above-mentioned organic solvent in the presence of an acid catalyst, neutralizing the acid or washing away the acid with water, and subsequently effecting polymerization in the presence of a basic catalyst. Acid catalysts usable herein include hydrochloric acid, sulfuric acid, methanesulfonic acid, acetic acid, formic acid, oxalic acid, trifluoromethanesulfonic acid, toluenesulfonic acid, and para-toluenesulfonic acid. Basic catalysts usable herein include triethylamine, sodium acetate, sodium hydroxide, potassium hydroxide, potassium siliconate, and pyridine. These catalysts are preferably used in amounts of about 0.5 to 10% by weight of the siloxanes. And at the end of the respective reactions, the catalysts are preferably removed by neutralizing with an equimolar amount of a neutralizing agent or washing with water. For hydrolysis and polymerization, a temperature from room temperature to about 120 °C is appropriate.

0029As mentioned above, the fluorosilicone resin has a softening point of 50 to 200 °C which can be controlled by a proper choice of a polymerization time, the siloxane concentration during hydrolysis, the content of SiO₂ unit and other factors.

0030Fluorosilicone resin obtained by the above-mentioned method may be silylated with hexamethyldisilazane, trimethyloximesilane or the like for the purpose of capping silanol groups remaining in the resin. This capping is effective particularly when the residual silanol groups and hydrogenpolysiloxane can be dehydrogenated in the presence of a platinum catalyst, especially for those resins having a higher softening point. The capping is effective for lowering the softening point of the resin and thus preventing the resin from gelation.

0031Preferably the silylating agent used for this capping is an organic silicon compound of the following formula (5):         (CH₃)₃SiY   (5) wherein Y is a halogen atom, amino group, dimethylamino group, diethylamino group, methyl ethyl ketoxime group, isopropenyloxy group, or acetoxy group. Examples are given below.    trimethylchlorosilane,    hexamethyldisilazane, Me₃SiNMe₂,    Me₃SiNEt₂, Me₃SiOOCMe₃, <chemistry id="chem0003" num="0003"><img file="EP0657487A2_D0003.tif" /></chemistry>

0032Among these, hexamethyldisilazane and Me₃SiNMe₂ have the highest silylating ability and are efficient.

0033The capping or silylating step may be carried out in a conventional manner. For example, the resin obtained by hydrolysis and polymerization according to the afore-mentioned method is subject to HY-removal reaction in a solventless system at room temperature. Alternatively, the resin is dissolved in a halogenated solvent such as methylene chloride, trichloroethylene and Freon solvents and subject to HY-removal reaction under reflux of the solvent. Note that Y is an organic group as previously defined.

0034The fluorosilicone resin is advantageously used for microcapsulating platinum catalysts. With a platinum catalyst carried by the resin, an addition type organopolysiloxane composition can have a pot life in excess of one month even during the summer season. Platinum catalysts relevant herein include chloroplatinic acid, zero valence platinum catalysts having vinylsiloxane coordinated thereto, and neutral platinum catalysts obtained by neutralizing chloroplatinic acid with basic compounds to remove chlorine. The platinum catalyst is preferably carried on the resin in an amount of about 1 to 50,000 ppm, more preferably about 5 to 10,000 ppm of platinum atom. The addition type organopolysiloxane composition may be comprised of conventional amounts of well-known components.

0035Another use for resins disclosed herein is as a coating agent for car wax or the like for forming a coating having good acid resistance, weather resistance, stainproof and water repellency. The resin is also useful as an additive for engineering plastics for improving mold release property and pigment dispersion. The resin finds further use as a plasticizer for shrinkable tube-forming fluoro-olefinic resins.

0036There has been described fluorosilicone resins which are useful e.g. for micro-capsulating a platinum catalyst for prolonging the pot life of an addition type organopolysiloxane composition, or as a coating agent for forming a weather resistant, stainproof, water repellent coating. The methods disclosed herein offer an efficient and simple way to produce such resins.

EXAMPLE

0037Examples of the present invention are given below together with Comparative Examples by way of illustration and not by way of limitation. All parts are by weight.

Example 1

0038To a mixture of 175 parts (1 mol of Si) of a compound of formula (a), 218 parts (1 mol of Si) of a compound of formula (b), 280 parts of methyl isobutyl ketone, and 13.9 parts of methanesulfonic acid at room temperature, 180 parts of water was added dropwise over 30 minutes. The mixture was heated for reflux at 75 °C for 2 hours. After cooling, 33 parts of triethylamine was added to the mixture, which was heated again for reflux at 75 °C for a further 2 hours. After cooling, 45 parts of citric acid was added to the mixture, which was stirred at room temperature for one hour. Subsequent water washing and solvent distillation yielded a silicone resin A.

0039Resin A had a softening point of 110 °C and a silanol content of 0.5% by weight. By NMR and IR analysis, it was identified to have the following compositional formula (A).

Source (a)

0040<chemistry id="chem0004" num="0004"><img file="EP0657487A2_D0004.tif" /></chemistry>

Source (b)

0041CF₃CH₂CH₂Si(OCH₃)₃

Resin A

0042(CF₃CH₂CH₂SiO_3/2)_0.5(C₆H₅SiO_3/2)_0.5   (A)

0043A mixture of 0.1 gram of Resin A and 99.9 grams of dimethylpolysiloxane having a viscosity of 10,000 centistokes at 25 °C (KF-96 commercially available from Shin-Etsu Chemical Co., Ltd.) was stirred at 20-25 °C for 24 hours to find that the resin was not uniformly dissolved and the mixture remained semi-suspended.

Example 2

0044A silicone resin B was prepared by the same procedure as in Example 1 except that 218 parts of the compound of formula (b) was replaced by a mixture of 209 parts of the compound of formula (B) and 6.1 parts of tetramethoxysilane Si(OCH₃)₄.

0045Resin B had a softening point of 118 °C and a silanol content of 0.3% by weight. By NMR and IR analysis, it was identified to have the following compositional formula (B). Like Resin A, Resin B was insoluble in dimethylpolysiloxane having a viscosity of 10,000 centistokes.

Resin B

0046(CF₃CH₂CH₂SiO_3/2)_0.48(C₆H₅SiO_3/2)_0.5(SiO₂)_0.02   (B)

Example 3

0047Resin B obtained in Example 2 was dissolved in methylene chloride and treated with hexamethyldisilazane for trimethylsilylating residual silanol groups, obtaining a resin C.

0048Resin C had a softening point of 105 °C and contained no detectable silanol group. It had substantially the same compositional formula as Resin B on analysis and was insoluble in the dimethylpolysiloxane.

Example 4

0049A silicone resin D was prepared by the same procedure as in Example 1 except that the amount of the compound of formula (a) was changed to 70 parts and the amount of the compound of formula (b) was changed to 349 parts.

0050Resin D had a softening point of 74 °C and contained 0.3% by weight of a silanol group. On NMR and IR analysis, it was identified to have the following compositional formula (D). It was insoluble in the dimethylpolysiloxane.

Resin D

0051(CF₃CH₂CH₂SiO_3/2)_0.8(C₆H₅SiO_3/2)_0.2   (D)

Comparative Example 1

0052A mixture of 148 parts of triphenylchlorosilane, 53 parts of propyltrichlorosilane, and 200 parts of toluene was added dropwise to 100 parts of isopropyl alcohol and 500 parts of water at room temperature over about 2 hours. The mixture was aged at 70 °C for 30 minutes, washed with water, and distilled to remove toluene, obtaining a silicone resin E having a softening point of 75 °C and a silanol content of 4.0% by weight. Resin E was substantially completely dissolved in the dimethylpolysiloxane to form a homogeneous solution.

Comparative Example 2

0053To 100 parts of methylmethoxypolysiloxane (KC-89 commercially available from Shin-Etsu Chemical Co., Ltd.) was added 5 parts of butyltitanate homopolymer (TBT-700 commercially available from Nippon Soda K.K.). They were mixed to form a resin F.

0054Using each of the foregoing resins A to F, the following experiments were carried out.

Example 5

005510 parts of each resin, 10 parts of a platinum catalyst (CAT PL-50T commercially available from Shin-Etsu Chemical Co., Ltd.), and 50 parts of methylene chloride (or 50 parts of methyl isobutyl ketone for resin D) were mixed into a homogeneous solution. The solution was atomized through a spray dryer to form platinum catalyst-containing microcapsules having a particle size of 1 to 3 µm and containing 0.5% by weight of platinum atom.

0056The microcapsules, 0.12 parts, were added to a composition of the following components. <tables id="tabl0001" num="0001"><img file="EP0657487A2_D0005.tif" /></tables> The ingredients were uniformly dispersed by means of a universal mixer. The composition as prepared was measured for viscosity (poise) at 25 °C (initial viscosity). The composition was stored at 25 °C for one month before it was examined for storage stability by measuring its viscosity again. The composition as prepared was also examined for curing property by heating the composition at 150 °C to start hydrosilylation whereupon the composition gradually increased its torque as measured by a rheometer. T10 and T90 are the times taken from the start until the torque reaches 10% and 90% of the maximum torque, respectively.

0057For comparison purposes, 0.12 parts of the platinum catalyst (PL-50T) instead of the microcapsules was added to the same composition as above. The composition was similarly examined for curing property and storage stability.

0058The results are shown in Table 1. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 1</title><tgroup cols="7" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" rowsep="0" /><entry namest="col2" nameend="col6" align="center">Microcapsulated platinum catalyst</entry><entry namest="col7" nameend="col7" rowsep="0" align="center">Platinum catalyst as such</entry></row><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">Resin A</entry><entry namest="col3" nameend="col3" align="center">Resin B</entry><entry namest="col4" nameend="col4" align="center">Resin C</entry><entry namest="col5" nameend="col5" align="center">Resin D</entry><entry namest="col6" nameend="col6" align="center">Resin E</entry><entry namest="col7" nameend="col7" /></row><row><entry namest="col1" nameend="col7" align="left">Curing property</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">T10, sec.</entry><entry namest="col2" nameend="col2" align="center">23</entry><entry namest="col3" nameend="col3" align="center">25</entry><entry namest="col4" nameend="col4" align="center">22</entry><entry namest="col5" nameend="col5" align="center">21</entry><entry namest="col6" nameend="col6" align="center">13</entry><entry namest="col7" nameend="col7" align="center">8</entry></row><row><entry namest="col1" nameend="col1" align="left">T90, sec.</entry><entry namest="col2" nameend="col2" align="center">69</entry><entry namest="col3" nameend="col3" align="center">70</entry><entry namest="col4" nameend="col4" align="center">66</entry><entry namest="col5" nameend="col5" align="center">57</entry><entry namest="col6" nameend="col6" align="center">42</entry><entry namest="col7" nameend="col7" align="center">22</entry></row></tbody></tgroup><tgroup cols="7" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="22.50mm" /><colspec colnum="2" colname="col2" colwidth="22.50mm" /><colspec colnum="3" colname="col3" colwidth="22.50mm" /><colspec colnum="4" colname="col4" colwidth="22.50mm" /><colspec colnum="5" colname="col5" colwidth="22.50mm" /><colspec colnum="6" colname="col6" colwidth="22.50mm" /><colspec colnum="7" colname="col7" colwidth="22.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col7" align="left">Storage stability</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Initial viscosity, poise</entry><entry namest="col2" nameend="col2" align="center">2500</entry><entry namest="col3" nameend="col3" align="center">2700</entry><entry namest="col4" nameend="col4" align="center">2500</entry><entry namest="col5" nameend="col5" align="center">2600</entry><entry namest="col6" nameend="col6" align="center">2600</entry><entry namest="col7" nameend="col7" align="center">2700</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Aged viscosity, poise</entry><entry namest="col2" nameend="col2" align="center">4700</entry><entry namest="col3" nameend="col3" align="center">4400</entry><entry namest="col4" nameend="col4" align="center">5000</entry><entry namest="col5" nameend="col5" align="center">5500</entry><entry namest="col6" nameend="col6" align="center">gelled after 14 days</entry><entry namest="col7" nameend="col7" align="center">gelled after 12 hours</entry></row></tbody></tgroup></table></tables>

0059As is evident from Table 1, by microcapsulating the platinum catalyst with any of silicone resin A to D within the scope of our proposals, the addition type organopolysiloxane composition is significantly improved in storage stability without adversely affecting curability.

Example 6

0060A mixture of 20 parts of each of Resins A, C, D and E and 80 parts of methyl isobutyl ketone was cast onto a steel plate to form a silicone coating having a dry thickness of about 5 µm. The coatings were measured for a contact angle with water both at the initial and after exposure in a sunshine weatherometer for 1,000 hours.

0061For comparison purposes, Resin F was cast onto a steel plate to form a coating which was similarly measured for a contact angle with water.

0062The results are shown in Table 2. <tables id="tabl0003" num="0003"><table frame="all"><title>Table 2</title><tgroup cols="6" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">Resin A</entry><entry namest="col3" nameend="col3" align="center">Resin C</entry><entry namest="col4" nameend="col4" align="center">Resin D</entry><entry namest="col5" nameend="col5" align="center">Resin E</entry><entry namest="col6" nameend="col6" align="center">Resin F</entry></row></thead><tbody valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Initial contact angle</entry><entry namest="col2" nameend="col2" align="center">89°</entry><entry namest="col3" nameend="col3" align="center">88°</entry><entry namest="col4" nameend="col4" align="center">95°</entry><entry namest="col5" nameend="col5" align="center">81°</entry><entry namest="col6" nameend="col6" align="center">90°</entry></row></tbody></tgroup><tgroup cols="6" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26.25mm" /><colspec colnum="2" colname="col2" colwidth="26.25mm" /><colspec colnum="3" colname="col3" colwidth="26.25mm" /><colspec colnum="4" colname="col4" colwidth="26.25mm" /><colspec colnum="5" colname="col5" colwidth="26.25mm" /><colspec colnum="6" colname="col6" colwidth="26.25mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col6" align="left">After weathering</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Outer appearance</entry><entry namest="col2" nameend="col2" align="center">Norma</entry><entry namest="col3" nameend="col3" align="center">Normal</entry><entry namest="col4" nameend="col4" align="center">Normal</entry><entry namest="col5" nameend="col5" align="center">Choking</entry><entry namest="col6" nameend="col6" align="center">Normal</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Contact angle</entry><entry namest="col2" nameend="col2" align="center">88°</entry><entry namest="col3" nameend="col3" align="center">87°</entry><entry namest="col4" nameend="col4" align="center">95°</entry><entry namest="col5" nameend="col5" align="center">70°</entry><entry namest="col6" nameend="col6" align="center">83°</entry></row></tbody></tgroup></table></tables>

0063As is evident from Table 2, silicone resins A, C and D within the scope of our proposals are fully resistant against weathering.

0064Japanese Patent Application No. 5-340046 is incorporated herein by reference.

0065Although some preferred embodiments have been described, many modifications and variations may be made thereto in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.