Curable resin composition containing dispersed particles of a cured silicone rubber

The curable resin composition of the present invention consists of a curable resin having uniformly dispersed therein particles of a cured silicone rubber obtained from an organosiloxane composition curable by a platinum-catalyzed hydrosilation reaction, wherein said organosiloxane composition contains reaction products of an ethylenically unsaturated epoxy compound and an ethylenically unsaturated aromatic compound with the organohydrogenpolysiloxane present in said organosiloxane composition. Either or both of the epoxy compound and the aromatic compound can be prereacted with a portion of the silicon-bonded hydrogen atoms of the organohydrogenpolysiloxane.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a curable resin composition. More particularly, 
this invention relates to a curable resin composition containing uniformly 
dispersed and finely divided particles of a silicone rubber. The 
composition exhibits improved flow properties during molding, and converts 
to a cured material exhibiting excellent flexibility, a low thermal 
expansion coefficient, a low mold shrinkage ratio and excellent adhesion 
between the resin matrix and dispersed silicone rubber particles. 
2. Description of the Prior Art 
Cured compositions based on organic and silicone resins have excellent 
electrical properties, including dielectric properties, volume 
resistivity, dielectric breakdown strength, and excellent mechanical 
properties that include flexural strength, compression strength, and 
impact strength. These properties make the compositions particularly 
desirable for use as insulating materials for various types of electric 
and electronic components. 
The curable resin compositions can be fabricated by transfer molding, 
injection molding, potting and casting. The compositions can be applied to 
substrates by powder coating, immersion coating or dipping. 
Cured resins prepared using the aforementioned compositions are generally 
rigid. When these resins are used, for example, to seal an electric or 
electronic component, large mechanical stresses are imparted to the 
internal elements of the component during the heating required to seal the 
component and post-cure the resin or the thermal cycling to which the 
component is subjected during testing and use. As a consequence, the 
element may not function properly or failure may occur in part of the 
element. One cause of the stresses and resultant failures is the 
difference in thermal expansion coefficient and post-molding shrinkage 
ratio between the elements of electric and electronic components and 
curable resins. The elements of electric and electronic components have 
very low thermal expansion coefficients and shrinkage ratios while the 
resins have large values for these ratios. 
These differences between the thermal expansion coefficients and shrinkage 
ratios of the resin and the coated component also result in the formation 
of cracks in the cured resin coating and gaps between the component and 
the resin. The infiltration of water and other undesirable materials into 
these gaps contributes to deterioration and subsequent failure of the 
elements comprising the components. 
Most previous attempts to modify curable resin compositions have not had as 
their objective a reduction in the thermal expansion coefficient or 
post-molding shrinkage ratio of the cured resins. For example, Japanese 
Patent Publication Number 13241/49, published on Dec. 18, 1974 relates to 
an improvement in the lubricating properties of the surfaces of resin 
moldings achieved by the addition of an organosilsesquioxane powder to 
curable phenolic resin compositions. 
Japanese Patent Application Laid Open [Kokai] Number 52-14643 [14,643/77], 
published on Feb. 3, 1977, relates to an improvement resistance of 
silicone resin to abrasion by metals. This improvement is obtained by 
filling the synthetic curable resin with finely divided particles obtained 
from a cured material based on a organopolysiloxane and an inorganic 
filler. The thermal expansion coefficient, post-molding shrinkage ratio, 
and flexural modulus are unsatisfactory in both of the aforementioned 
resin compositions following curing. 
In Japanese Laid Open Patent Application Number 58-219218 [219,218/83], 
published on Dec. 20, 1985 the present inventors propose a solution to the 
problems described in the preceding paragraph by adding to the curable 
resin a cured material containing at least 10 weight % of a straight-chain 
siloxane fraction. The material is reduced to a finely divided, i.e. 
microparticulate, form following curing. However, the problem with this 
approach that it is not always easy to reduce an elastomeric cured 
material to the desired small particle size. 
The present inventors in Japanese Laid Open Patent Application Number 
59-96122 [96,122/84], published on June 2, 1984 disclose preparing 
spherical cured particles by spraying a curable elastomer composition into 
a current of heated air. This method is quite excellent although 
expensive, due to the cost of the equipment required to produce the 
spherical particles of cured rubber. 
U.S. Pat. No. 4,743,670, which issued to K. Yoshida et al. on May 10, 1988 
describes a method for preparing a powdered form of silicone rubber by 
forming a dispersion of a liquid silicone rubber in surfactant-free water 
at a temperature of from 0 to 25 degrees C. and then mixing this 
dispersion into water at a temperature greater than 25 degrees C. Organic 
resin compositions containing these particles are less than satisfactory 
with respect to certain properties, particularly the infiltration of 
moisture into the cured resin. U.S. Pat. No. 4,778,860, which issued to 
two of the present three inventors on Oct. 18, 1988 attempts to solve 
these problems, by adding to the curable silicone rubber composition an 
aromatic hydrocarbon compound containing a substituted benzene ring where 
the substituent is a monovalent ethylenically unsaturated hydrocarbon 
radical or an alkenyloxy radical. This approach is not totally successful. 
The present inventors have now discovered that the dimensional stability 
and resistance to moisture infiltration exhibited by the resin 
compositions disclosed in the aforementioned U.S. Pat. No. 4,778,860 could 
be increased to acceptable levels by adding an ethylenically unsaturated 
epoxy compound and an ethylenically unsaturated aromatic compound to the 
curable rubber composition. 
Accordingly, an objective of the present invention is to provide a curable 
resin composition which exhibits excellent flow properties during molding, 
which will neither stain the metal mold nor exude onto the surface of the 
cured material, has an excellent mold-releasability, and converts to a 
cured material having excellent flexibility, a low thermal expansion 
coefficient, and a low mold shrinkage ratio. 
SUMMARY OF THE INVENTION 
The objectives of this invention are achieved by incorporating into the 
curable resin composition a dispersed phase of a finely divided cured 
silicone rubber that exhibits excellent compatibility with and adhesion to 
the cured resin. The organosiloxane composition used to prepare the cured 
silicone rubber particles is curable by a hydrosilylation reaction and 
contains reaction products of the organohydrogensiloxane used to cure the 
organosiloxane composition with 1) an ethylenically unsaturated epoxy 
compound and 2) an ethylenically unsaturated aromatic compound. 
Before being combined with the other ingredients of the compositions used 
to prepare the cured silicone rubber particles, one or both of the epoxy 
compound and the aromatic compound can be prereacted with a portion of the 
organohydrogenpolysiloxane that is used to cure the organosiloxane 
composition. 
DETAILED DESCRIPTION OF THE INVENTION 
This invention provides an improved curable resin composition comprising 
(I) 100 parts by weight of a curable resin selected from the group 
consisting of phenolic resins, formaldehyde resins, xylene resins, 
xylene/formaldehyde resins, ketone/formaldehyde resins, furan resins, urea 
resins, imide resins, melamine resins, alkyd resins, unsaturated polyester 
resins, aniline resins, sulfonamide resins, silicone resins, epoxy resins, 
and copolymers obtained by reacting two or more of these resins, and 
(II) from 0.1 to 100 parts by weight of uniformly dispersed, finely divided 
particles of a cured silicone rubber exhibiting a particle diameter not 
exceeding 1 millimeter, the particles having been prepared by curing an 
organosiloxane composition comprising 
(A) 100 parts by weight of an organopolysiloxane having at least two 
silicon-bonded lower alkenyl groups in each molecule, 
(B) from 0.3 to 100 parts by weight of an organohydrogenpolysiloxane having 
at least two silicon-bonded hydrogen atoms in each molecule, and 
(C) an amount of a platinum-containing catalyst sufficient to promote 
curing of said silicone rubber. 
The improvement comprises the presence in the curable organosiloxane 
composition of either 
(1) from 0.1 to 50 parts by weight of (D) an aliphatically unsaturated 
epoxide compound or a reaction product of from 0.1 to 50 parts by weight 
of said epoxide compound with a quantity of said 
organohydrogenpolysiloxane in excess of that required to react with said 
organopolysiloxane; and from 0.1 to 100 parts by weight of (E) an aromatic 
hydrocarbon containing at least one aliphatically unsaturated group per 
molecule or a reaction product of said aromatic hydrocarbon with a 
quantity of said organohydrogenpolysiloxane in excess of that required to 
react with said organopolysiloxane, or 
(2) a reaction product of from 0.1 to 50 parts by weight of said epoxide 
compound and from 0.1 to 100 parts by weight of said aromatic hydrocarbon 
with a quantity of said organohydrogenpolysiloxane in excess of that 
required to react with said organopolysiloxane. 
The two ingredients of the present curable resin compositions will now be 
explained in detail. 
I. The Curable Resin 
The curable resin comprising ingredient (I) is the base material of the 
present resin composition, and a wide variety of curable resins known in 
the art can be used here. Examples of suitable resins include but are not 
limited to: formaldehyde resins, xylene resins, xylene/formaldehyde 
resins, ketone/formaldehyde resins, furan resins, urea resins, imide 
resins, melamine resins, alkyd resins, unsaturated polyester resins, 
aniline resins, sulfonamide resins, silicone resins, epoxy resins, and 
copolymers obtained by reacting two or more of these resins. 
Phenolic, imide, epoxy, and silicone resins are preferred. It should be 
pointed out that silicone resins are typically brittle non-elastomeric 
hydrolysis reaction products of two or more organohalosilanes, and are a 
different class of materials from the finely divided cured silicone rubber 
particles the particles that constitute ingredient II of the present 
compositions. 
Ingredient I can be a single resin or a mixture of two or more resins. 
Furthermore, ingredient I encompasses not only resins which cure by the 
application of heat with or without a curing catalyst, but also those 
resins curable by exposure to radiation, for example, ultraviolet and 
gamma radiation. To facilitate blending with the finely divided silicone 
rubber particles the uncured resin is preferably either a liquid at room 
temperature or melts below about 50.degree. C. 
In addition to the resin itself, curing agents, curing catalysts, 
photosensitizers, fillers, metal salts of higher fatty acids, ester waxes, 
plasticizers, and other additives and/or modifiers can be present. 
II. The Cured Silicone Rubber Particle 
The finely divided silicone rubber particles are prepared from an 
organosiloxane composition that cures by a platinum-catalyzed 
hydrosilylation reaction. The ingredients of this curable composition will 
now be described in detail. 
The Organopolysiloxane (Ingredient A) 
The organopolysiloxane identified hereinbefore as ingredient A is the 
principal ingredient of the curable material used to prepare the cured 
silicone rubber particles referred to herein as ingredient II. This 
ingredient can be any organopolysiloxane containing at least two 
silicon-bonded lower alkenyl groups in each molecule. The molecular 
configuration of this ingredient is preferably straight chain, however 
partially branched or network configurations are also permissible. 
The viscosity of ingredient A at 25 degrees Centigrade can range from 10 
centipoise (0.01 Pa.s) up to but not including that of a gum. The cured 
silicone rubber particles are brittle when the viscosity of ingredient A 
is below 10 centipoise, and it is difficult to prepare an emulsion when 
ingredient A is a gum. To avoid either of these difficulties the viscosity 
of ingredient A is preferably from 50 to 100,000 centipoise (0.05 to 100 
Pa.s). A range of from 50 to 10,000 centipoise (0.05 to 10 Pa.s) is 
particularly preferred. 
The organic groups bonded to the silicon atoms of the siloxane units in 
ingredient A are monovalent hydrocarbon or halogenated hydrocarbon groups. 
These groups can be identical or different. The groups are exemplified by 
but not limited to alkyl such as methyl, ethyl, propyl, and butyl; 
cycloalkyl such as cyclohexyl; lower alkenyl such as vinyl, and allyl; 
aryl such as phenyl and xylyl; aralkyl such as phenylethyl; and 
halogenated hydrocarbon such as gamma-chloropropyl and 
3,3,3-trifluoropropyl. 
The required lower alkenyl groups of ingredient A can be located anywhere 
within the molecule. These groups are preferably present on at least the 
terminal positions of the molecule, although not restricted to this 
location, and are preferably vinyl. 
The terminal groups present on ingredient A are exemplified by 
triorganosiloxy groups such as trimethylsiloxy, dimethylvinylsiloxy, 
dimethylphenylsiloxy, methylvinylphenylsiloxy, hydroxyl groups and alkoxy 
groups. 
Selection of the types of monovalent hydrocarbon groups in the siloxane 
units, the type of end-blocking group on the molecular chain, and the 
viscosity of ingredient A will be based on the intended use for the 
curable organosiloxane composition. 
While the use of only straight-chain organopolysiloxane as ingredient A is 
preferred, the combination of a straight-chain organopolysiloxane and an 
organopolysiloxane resin is permitted. 
The Organohydrogenpolysiloxane (Ingredient B) 
The organohydrogenpolysiloxane is the crosslinking agent responsible for 
curing of organosiloxane composition used to obtain the cured the silicone 
rubber particles. The composition cures by the reaction of a portion of 
the silicon bonded hydrogen atoms of ingredient B with the lower alkenyl 
groups of ingredient A under the catalytic activity of ingredient C. 
The configuration of the organohydrogenpolysiloxane can be straight chain, 
cyclic or branched straight-chain, and this organohydrogenpolysiloxane can 
be a homopolymer or copolymer. It contains at least 2 silicon-bonded 
hydrogen atoms in each molecule and has a viscosity at 25.degree. C. 
within the range of 1 to 10,000 centipoise (0.001 to 10 Pa.s). Linear or 
cyclic molecules are preferred. 
The organic groups bonded to the silicon atoms of ingredient B are 
monovalent hydrocarbon and halohydrocarbon groups, as exemplified by 
methyl, ethyl, butyl, phenyl, and 3,3,3-trifluoropropyl. Methyl is 
particularly preferred among these. 
Ingredient B typically provides from 0.5 to 5, preferably from 0.7 to 2 
silicon-bonded hydrogen atoms for each silicon-bonded alkenyl group in 
ingredient A. Because ingredient B also reacts with ingredient D, an 
aliphatically unsaturated epoxide compound, and ingredient E, an 
aliphatically unsaturated aromatic compound, the concentration of 
ingredient B should be from 0.3 to 100 weight parts per 100 weight parts 
ingredient A. 
As discussed in detail in subsequent portions of this specification, the 
reaction of ingredients B, D, and E can either occur after all of the 
ingredients of the organosiloxane composition have been combined or 
ingredient D and/or E can be prereacted with the portion of the 
organohydrogenpolysiloxane. The resultant mixture containing a sufficient 
quantity of unreacted silicon-bonded hydrogen atoms to cure the 
organosiloxane composition is then combined with the other ingredients of 
this composition. 
The Platinum-Containing Catalyst (Ingredient C) 
As used in this specification the term "platinum-containing catalyst" is 
intended to include platinum, other metals from the platinum group of the 
periodic table of the elements and compounds of these platinum group 
metals. Examples of suitable catalysts include but are not limited to 
finely divided elemental platinum, finely divided platinum dispersed on 
carbon powder, chloroplatinic acid, chloroplatinic acid/olefin 
coordination compounds, chloroplatinic acid/vinylsiloxane coordination 
compounds, tetrakis(triphenylphosphine)palladium, and rhodium catalysts. 
The concentration of the platinum-containing catalyst is typically within 
the range of from 0.1 to 1,000, preferably 0.5 to 200 parts by weight, 
calculated as the metal, per 1,000,000 parts by weight of ingredient A. 
The Aliphatically Unsaturated Epoxide Compound (Ingredient D) 
The function of the aliphatically unsaturated epoxide compound is to 
increase the bonding or adhesion between the curable resin (ingredient I) 
and the finely divided particles of cured silicone rubber that constitute 
ingredient II. Any organic compound containing at least 1 aliphatically 
unsaturated group and at least 1 epoxy group in each molecule can be used 
as ingredient D. Examples of this ingredient include but are not limited 
to allyl glycidyl ether, vinylcyclohexene monoxide, glycidyl acrylate, 
glycidyl methacrylate, and compounds of the formulae 
##STR1## 
where m and n are positive integers. 
The concentration of ingredient D can range from 0.1 to 50 parts by weight 
per 100 parts by weight of ingredient A. 
In accordance with one embodiment of this invention ingredient D can be 
reacted with the stoichiometric excess of silicon-bonded hydrogen atoms in 
ingredient B before being combined with the other ingredients of the 
curable organosiloxane composition used to prepare the cured silicone 
rubber particles. This reaction is preferably conducted in the presence of 
a platinum-containing catalyst of the type described in this specification 
as ingredient C. The resultant reaction product replaces a mixture of 
ingredients B and D, and can be used in combination with ingredients A and 
C and E to prepare ingredient II. The term "stoichiometric excess" applies 
to additional silicon-bonded hydrogen atoms of ingredient B over and above 
the quantity required for reaction with ingredient A. 
The Aliphatically Unsaturated Aromatic Compound 
The aliphatically unsaturated aromatic compound (ingredient E) is the key 
component for improving the affinity between the curable resin (ingredient 
I) and the cured silicone rubber particles (ingredient II) when ingredient 
I is dispersed in ingredient II. Each molecule of ingredient E contains at 
least 1 aliphatically unsaturated group such as vinyl or allyl and at 
least 1 benzene ring. 
Ethylenically unsaturated aromatic compounds that can be used as ingredient 
E include but are not limited to 
##STR2## 
The concentration of ingredient E is typically from 0.1 to 100 weight parts 
per 100 weight parts of ingredient A. As described in the preceding 
section of this specification with respect to ingredient D, ingredient E 
can also be prereacted with a portion of the organohydrogenpolysiloxane, 
which is present in a stoichiometric excess relative to the amount 
required to react with the organopolysiloxane (ingredient A). The 
resultant mixture of reaction product and ingredient B containing 
unreacted silicon-bonded hydrogen atoms is then blended with the other 
ingredients of the curable organosiloxane composition used to prepare the 
cured silicone rubber particles (ingredient II). 
Rather than reacting ingredients D and/or E individually with ingredient B, 
a mixture of ingredients B, D and E can be reacted, preferably in the 
presence of a platinum-containing catalyst. The resultant mixture of 
reaction products and ingredient B containing unreacted silicon-bonded 
hydrogen atoms is then added to the other ingredients of the curable 
organosiloxane composition used to prepare the cured silicone rubber 
particles. 
Optional Ingredients 
In addition to ingredients A through E discussed in the preceding 
specification, the cured silicone rubber particles used as ingredient II 
may contain a filler in order to adjust the fluidity and increase the 
mechanical strength of the molded product. Such fillers are exemplified by 
reinforcing fillers such as precipitated silica, fumed silica, calcined 
silica, and fumed titanium oxide, as well as by non-reinforcing fillers 
such as quartz powder, diatomaceous earth, asbestos, aluminosilicic acid, 
iron oxide, zinc oxide, and calcium carbonate. 
These fillers can be used directly or following a surface treatment with an 
organosilicon compound such as hexamethyldisilazane, 
trimethylchlorosilane, or dimethylpolysiloxane. 
So long as the objectives of the present invention are not compromised, the 
curable organosiloxane composition used to prepare ingredient II can 
contain small or very small quantities of acetylenic compounds, 
hydrazines, triazoles, phosphines, mercaptans, or other known curing 
reaction inhibitors. Other permissible additives include but are not 
limited to pigments, heat stabilizers, flame retardants, plasticizers, and 
organopolysiloxanes having 1 alkenyl group in each molecule, the latter 
for the purpose of reducing the modulus of the cured silicone rubber. 
So long as the silicone rubber particles are cured by a hydrosilylation 
reaction, the method used to prepare these particles is not critical. For 
example, irregularly shaped particles of a cured silicone rubber can be 
obtained by first heating the curable organosiloxane composition in an 
oven to produce an elastomer, and then mechanically grinding the product 
with or without cooling, to form a powder. 
An alternative method for preparing the cured silicone rubber particles 
comprises spraying a solution of the curable organosiloxane composition 
diluted using an organic solvent into a stream of heated air using a spray 
drier or similar device. 
A second alternative method for preparing the particles comprises preparing 
a dispersion by gradually adding the curable organosiloxane composition to 
a volume of low-temperature water with stirring, optionally in the 
presence of a surfactant. This dispersion is then blended with water, 
another liquid, or a gas to produce spherical cured silicone rubber 
particles. The temperature of the medium used to cure the rubber is higher 
than the temperature of the dispersion. 
Of the preceding alternative methods, the "wet" method whereby the 
dispersed organosiloxane composition is contacted with a heated liquid has 
been found to be advantageous based on ease of production and the ability 
of the method to mass produce particles of a cured silicone rubber. The 
medium into which the organosiloxane composition is initially dispersed 
can be non-aqueous or a miscible mixture of water and a non-aqueous 
liquid. 
The particle diameter of the cured silicone rubber prepared using the 
methods described in the preceding paragraphs should generally not exceed 
1 mm. Diameters not exceeding 300 microns are preferred for use in the 
present invention. Particularly in the case of spherical particles, 
diameters not exceeding 50 microns are particularly preferred from the 
standpoint of improving fluidity of the final curable resin composition 
during molding. 
Furthermore, the spherical particles of cured silicone rubber may contain 
some modified forms, such as ovoids and ellipsoids. 
It is essential that the cured silicone rubber particles be uniformly 
dispersed into the curable resin (ingredient I) of the present 
compositions. 
The present compositions typically contain from 0.1 to 100 parts by weight 
of the cured silicone rubber particles (ingredient II) per 100 parts by 
weight of the curable resin. The beneficial effects imparted by ingredient 
II are not fully evident at concentrations below 0.1 part by weight, while 
the presence of more than 100 parts of the particles adversely affects the 
physical properties of the cured resin composition. The concentration of 
ingredient II is preferably from 0.5 to 70 parts by weight. 
A homogeneous dispersion of the cured silicone rubber particles in the 
curable resin can be prepared using any of the known types of mixing 
devices. 
The spherical or irregularly shaped particles of cured silicone rubber have 
an excellent affinity for the curable resin matrix and bond well to this 
matrix due to the presence of the unsaturated epoxide and unsaturated 
aromatic compounds. Moldings prepared using these curable resin 
composition characteristically have a lower infiltration or penetration by 
moisture than comparable moldings prepared using compositions containing 
prior cured silicone rubber particles, irrespective of the shape of the 
particles or the method used to prepare them. 
Moldings formed from the present compositions characteristically have a 
higher flexibility, a lower thermal expansion coefficient, and exhibit 
less shrinkage. 
The present compositions exhibit excellent flow properties during the 
molding operation. 
All of the foregoing advantages make the present compositions particularly 
useful for preparing moldings requiring dimensional accuracy, and as 
sealants, casting agents, liquid coatings and powder coating for various 
electric and electronic components such as transistors, integrated 
circuits, diodes, thermistors, transformer coils and resistors. 
The following examples are intended to describe preferred embodiments of 
the present invention and should not be interpreted as limiting the scope 
of the invention as defined in the accompanying claims. Unless otherwise 
specified all parts and percentages specified in the examples are by 
weight and viscosities were measured at 25 degrees C. 
The properties of the cured materials were measured using the following 
standards and methods. 
(1) Thermal expansion coefficient was determined using a sample that had 
been post-cured at 180 degrees Centigrade for 5 hours using the procedure 
described in ASTM test procedure D-696. 
(2) Flexural modulus was determined by the flexural test method of JIS 
K-6911, which can be summarized as follows: The test samples were 
rectangular strips of cured material measuring at least 80 mm in length, 
4.+-.0.2 mm thick and 10.+-.0.5 mm wide. The samples were supported at 
each end to form a span of equal to 16 times the thickness of the 
sample.+-.0.5 mm. A gradually increasing load was applied to the center of 
the span, and the deflection of the test sample as a function of amount of 
loading was measured and plotted. The flexural modulus is equal to the 
slope of the resulting plot, expressed in units of kg(f)/mm. 
(3) Mold shrinkage ratio was determined using test method described in JIS 
K-6911 on test samples prepared by compression molding the curable 
composition in a metal mold, post-curing according to the conditions in 
the particular example, and then cooling to room temperature. The test 
samples were circular in shape with an outer diameter of 90 mm. and a 
thickness of 5 mm. Each circular surface of the test sample contained a 
circular rim having an outer diameter of 80 mm., an inner diameter of 76 
mm. and a height of 3 mm, the diameters being measured from the center of 
the test sample. 
After being post cured the test samples were maintained at a temperature of 
23.degree..+-.2.degree. C. and a relative humidity of 50.+-.5% for 23-25 
hours. The outer diameter of the rim on each side of the sample was 
measured in two orthogonal directions (a total of 4 measurements) and the 
outer diameters of the corresponding grooves in the mold used to form the 
test samples were measured in a similar manner. 
The mold shrinkage (MS) of the samples was calculated using the following 
formula: 
EQU MS=1/4[(D.sub.1 -d.sub.1)/D.sub.1 +(D.sub.2 -d.sub.2)/D.sub.2 +(D.sub.3 
d.sub.3)/D.sub.3 +(D.sub.4 -d.sub.4)/D.sub.4 ].times.100 
where 
D.sub.1-4 =outer diameter of mold grooves (4 measurements) 
d.sub.1-4 =outer diameter of rim on test sample (4 measurements) 
(4) Spiral flow was measured according to the Epoxy Molding Materials 
Institute (EMMI) standard 1-66 on the curable composition prepared 
according to the conditions in the particular example. 
(5) Scanning Electron Microscope (SEM) Observations: A photomicrograph of 
the fracture surface of the test specimen from the flexural modulus 
measurement was obtained using a scanning electron microscope. The 
micrograph was inspected to determine the adhesion between the cured 
silicone rubber particles and the resin, as evidenced by the presence or 
absence of gaps or voids. 
(6) Water absorption is expressed as the weight change of a 
2.times.1/2.times.1/4 inch (50.8.times.12.7.times.6.4 mm) molding which 
had been post-cured and then immersed in boiling water for 10 hours. 
PREATIVE METHODS FOR INGREDIENT II 
Preparation of Spherical Rubber Powder F and F1 
A curable organosiloxane composition of this invention was prepared by 
adding a quantity of isopropanolic chloroplatinic acid solution equivalent 
to 20 ppm of platinum based on the total weight of ingredient A to 50 
parts of a dimethylvinylsiloxy-terminated dimethylpolysiloxane (ingredient 
A) having a viscosity of 0.8 Pa.s and maintained at a temperature of 
-10.degree. C. 18 parts of a methylhydrogenpolysiloxane (ingredient B) 
having the following structure 
##STR3## 
5 parts allyl glycidyl ether (ingredient D), and 2 parts of styrene 
monomer (ingredient E) were then added. This mixture of ingredients was 
rapidly blended to form an initial mixture and placed in a colloid mill 
that had been cooled to 5 degrees Centigrade. A homogeneous emulsion was 
obtained by the addition to this mixture of a blend of 600 parts 
ion-exchanged water and 10 parts surfactant (Tergitol(R) TMN-6 from Union 
Carbide Corporation) that had been cooled to 5 degrees C. Spherical 
particles of a cured silicone rubber were formed when this emulsion was 
introduced into stirred water maintained at a temperature of 85 degrees 
Centigrade. 
The resultant particles were isolated, washed with water, dried and then 
examined under a scanning electron microscope. The particles were found to 
be perfectly spherical with a particle diameter of 0.1 to 10 microns. This 
material will be referred to hereinafter as Powder F. 
In the comparison example, spherical particles were prepared using the 
procedure described for particles A with the following modifications: the 
allyl glycidyl ether (ingredient D) and the styrene monomer (ingredient E) 
were omitted from the above composition, and only 3 parts of the 
methylhydrogen-polysiloxane (ingredient B) was added instead of 18 parts. 
The cured silicone rubber particles were designated Powder F1. 
Preparation of Wet-Method Spherical Particles (Powders G and G1) 
Powder G was prepared using the same procedure described for Powder F using 
the following amounts and types of ingredients: 
An emulsified curable organosiloxane composition of this invention was 
prepared by blending to homogeneity 50 parts of a 
dimethylvinylsiloxy-terminated dimethylpolysiloxane with a viscosity of 
0.2 Pa.s (ingredient A), 13 parts trimethylsiloxy-terminated 
methylhydrogenpolysiloxane with a viscosity of 0.01 Pa.s (ingredient B), 5 
parts allyl glycidyl ether (ingredient D), and 5 parts alpha-methylstyrene 
(ingredient E), an amount of isopropanolic chloroplatinic acid solution 
equivalent to 20 ppm of platinum based on the total weight of ingredient 
A, 600 parts ion-exchanged water and 20 parts Tergitol TMN-6 surfactant. 
Particles of a cured silicone rubber were produced when the emulsion was 
stirred into water maintained at a temperature of 85 degrees Centigrade. 
After washing and drying the resultant powder was examined under an 
electron microscope and was found to consist of spherical particles with a 
particle diameter of from 0.1 to 8 microns. This product was designated as 
Powder G. 
As a comparison example Powder G.sup.1 was prepared using the same 
procedure described for Powder G, with the omission of the allyl glycidyl 
ether (ingredient C) and the alpha-methyl styrene (ingredient D) and the 
presence of only 3 parts of the methylhydrogenpolysiloxane instead of 13 
parts. 
Preparation of Irregularly Shaped Particles (Powders H and H.sup.1) 
A homogeneous mixture of ingredients A, B, C, D and E of the curable 
organosiloxane composition used to prepare Powder F was placed in an oven 
maintained at 100 degrees Centigrade and cured by heating for 1 hour. The 
cured product was then pulverized in a grinder to yield irregularly shaped 
particles of a cured silicone rubber. The material passing through a 
100-mesh screen was designated Powder H. 
A homogeneous mixture of the same ingredients (A, B, and E) used for Powder 
F.sup.1 was cured by heating the mixture for one hour in an oven 
maintained at 100 degrees C. The mixture of irregularly shaped cured 
particles was pulverized as described for Powder H. The material passing 
through a 100-mesh screen was designated Powder H.sup.1. Preparation of 
Dry-Method Spherical Powders I and I.sup.1 
0.1 part 3-methyl-1-butyne-3-ol as a curing reaction inhibitor was blended 
into the same ingredients A, B, C, D, and E of the curable organosiloxane 
composition used to prepare Powder G. The resultant composition was cured 
by spraying it into a spray drier wherein the air temperature was 230 
degrees Centigrade. The resultant spherical particles had particle 
diameters of 1 to 150 microns and are identified as Powder I. 
For comparative purposes particles of cured silicone rubber were prepared 
using ingredients A, B and C of the organosiloxane composition used to 
prepare Powder G.sup.1. The composition was cured by introducing it into a 
spray drier operating under the conditions described for Powder I. The 
product was designated as Powder I.sup.1.

EXAMPLE 1 
A curable resin composition of this invention was prepared by blending the 
following ingredients to homogeneity using a roller mill heated to a 
temperature of 90 degrees C.: 
31 Parts of a phenol novolac resin having a softening point of 80 degrees 
Centigrade and a hydroxyl group equivalent weight of 100, 
8 parts of Powder F, 
69 parts fused quartz powder, 
4 parts hexamethylenetetramine, and 
1 part carnauba wax. 
The resultant mixture was pulverized to yield a thermosetting phenol 
novolac resin composition (sample 1). This resin composition was then 
transfer molded at a temperature of 175.degree. C. for 3 minutes under a 
pressure of 70 Kg/cm2, followed by a 2-hour post-cure at 150 degrees 
Centigrade. 
The various properties of this molding are reported in Table 1. 
For purposes of comparison moldings were similarly prepared as above, 
either using 8 parts Powder F.sup.1 in place of Powder F of Example 1 
(comparative sample 1) or without the addition of any cured silicone 
rubber particles (comparative sample 2). The properties of these three 
moldings were measured, and the results are reported in Table 1. 
TABLE 1 
______________________________________ 
Comparative 
Sample 
Samples 
Ingredients and Properties 
1 1 2 
______________________________________ 
(i) phenol novolac resin (parts) 
30 30 30 
(ii) 
Powder F (parts) 12 -- -- 
Powder F.sup.1 (parts) 
-- 12 -- 
mold shrinkage (%) 
0.05 0.07 0.27 
spiral flow (inches) 
28 21 26 
flexural modulus (kg/mm2) 
820 930 1450 
thermal expansion coefficient 
0.2 0.3 1.4 
(.times. 10.sup.5 /.degree.C.) 
SEM observation of gaps 
absent present NE 
water absorption (%) 
0.43 0.52 0.32 
______________________________________ 
NE = Not Evaluated 
EXAMPLE 2 
The following ingredients were blended on a roll mill heated to 90 degrees 
C.: 
13 parts of a cresol novolac epoxy resin having a softening point of 80 
degrees C. and an epoxy equivalent weight of 220, 
7 parts of the phenol novolac resin described in Example 1, 
20 parts of Powder G, 
80 parts fused silica, 
0.5 parts carnauba wax, and 
0.1 part 2-methylimidazole. 
Pulverization of the resultant mixture yielded a thermosetting epoxy resin 
composition of this invention. This resin composition was transfer molded 
at 175 degrees Centigrade for 2 minutes under a pressure of 70 
kg/cm.sup.2, and post-cured for 2 hours at 180 degrees Centigrade. The 
properties of the molding (sample 2) are reported in Table 2. 
In the comparative examples, moldings were prepared using the procedure 
described in the first portion of this example, using either (1) a 
composition which contained 20 parts of Powder G.sup.1 in place of Powder 
G (comparative sample 3) or (2) a composition which did not contain any 
cured silicone rubber (comparative sample 4). The properties of the cured 
moldings are reported in Table 2. 
TABLE 2 
______________________________________ 
Comparative 
Sample Samples 
ingredients and properties 
2 3 4 
______________________________________ 
(i) cresol novolac epoxy 
13 13 13 
resin (parts) 
phenol novolac resin 
7 7 7 
(parts) 
(ii) 
Powder G (parts) 20 -- -- 
Powder G.sup.1 (parts) 
-- 20 -- 
mold shrinkage (%) 
0.13 0.15 0.39 
spiral flow (inches) 
18 14 15 
flexural modulus (kg/mm.sup.2) 
750 870 1580 
thermal expansion coefficient 
1.0 1.4 1.7 
(.times. 10.sup.5 /.degree.C.) 
SEM observation of gaps 
absent present -- 
water absorption (%) 
0.31 0.43 0.24 
______________________________________ 
EXAMPLE 3 
A curable resin composition of this invention was prepared by blending the 
following ingredients to homogeneity of a roll mill heated to a 
temperature of 90.degree. C.: 
10 parts of Powder H, 
74 parts fused silica powder, 
0.10 parts aluminum acetylacetonate, 
1 part carnauba wax, 
13 parts methylphenylpolysiloxane resin containing 5 weight percent of 
silicon-bonded hydroxyl groups, 40 mole percent CH.sub.3 SiO.sub.1.5 
units, 10 mole % C.sub.6 H.sub.5 (CH.sub.3)SiO units, 40 mole % C.sub.6 
H.sub.5 SiO.sub.1.5 units, and 10 mole % (C.sub.6 H.sub.5).sub.2 SiO 
units), and 13 parts cresol novolac epoxy resin having a softening point 
of 80.degree. C. and an epoxy equivalent weight of 220. 
The resultant mixture was removed from the mill and pulverized to yield a 
thermosetting silicone-epoxy resin composition of this invention. This 
resin composition was transfer molded at 175 degrees Centigrade for 2 
minutes under a pressure of 70 kg/cm.sup.2, and then post-cured for 12 
hours at 180 degrees Centigrade. The various properties of the molding 
(Sample 3) were measured, and these results are reported in Table 3. 
In the comparison examples, moldings were prepared using the same 
formulation described in the first part of this example, with the 
exception that one of the compositions (Comparative Sample 5) contained 10 
parts of Powder H.sup.1 in place of Powder H and the second composition 
(Comparative Sample 6) did not contain any cured silicone rubber. The 
properties of the cured moldings are reported in Table 3. 
TABLE 3 
______________________________________ 
Comparative 
Sample Samples 
Ingredients and properties 
3 5 6 
______________________________________ 
(i) silicone resin (parts) 
13 13 13 
epoxy resin (parts) 
13 13 13 
(ii) 
Powder H (parts) 10 -- -- 
Powder H.sup.1 (parts) 
-- 10 -- 
mold shrinkage (%) 
0.26 0.32 0.45 
spiral flow (inches) 
27 21 28 
flexural modulus (kg/mm.sup.2) 
820 870 1480 
thermal expansion coefficient 
1.7 1.9 2.7 
(.times. 10.sup.5 /.degree.C.) 
SEM observation of gaps 
absent present NE 
water absorption (%) 
0.38 0.49 0.39 
______________________________________ 
NE = Not Evaluated 
EXAMPLE 4 
The following ingredients were blended to homogeneity into 30 parts 
thermosetting polyimide resin (BT2480 from Mitsubishi Gas Chemical Co., 
Ltd.) using a roller mill heated to a temperature of 90.degree. C.: 
6 parts Powder I, 
70 parts fused silica powder, 
1 part carnauba wax, and 
0.32 parts aluminum benzoate. 
The resultant mixture was removed from the mill and pulverized to yield a 
thermosetting polyimide resin composition of this invention. This 
composition was transferred molded at 220 degrees Centigrade/4 minutes/70 
kg/cm.sup.2, and then post-cured at 230 degrees Centigrade for 3 hours. 
The various properties of this molding (Sample 4) were measured, and these 
results are reported in Table 4. 
In the comparison examples, molding was conducted under the same conditions 
as described in the first part of this example, but using (1) a 
composition containing 6 parts of Powder I.sup.1 in place of Powder I 
(Comparative Sample 7) and (2) a composition which contained no cured 
silicone rubber (Comparative Sample 8). The spiral flow, presence or 
absence of gaps on the SEM micrograph, and water absorption were measured, 
and these results are reported in Table 4. 
TABLE 4 
______________________________________ 
Comparative 
Sample Samples 
Ingredients and Properties 
4 7 8 
______________________________________ 
(i) polyimide resin (parts) 
30 30 30 
(ii) Powder I (parts) 
6 -- -- 
Powder I.sup.1 (parts) 
-- 6 -- 
spiral flow (inches) 
45 35 38 
SEM observation of gaps 
absent present -- 
water absorption (%) 
0.45 0.52 0.43 
______________________________________ 
The curable resin compositions of the present invention comprise a curable 
resin and either spherical or irregularly shaped particles of a cured 
silicone rubber prepared from an organosiloxane composition that is 
curable by a hydrosilylation reaction. The characterizing feature of the 
organosiloxane composition is the presence of reaction products of an 
organohydrogenpolysiloxane with 1) an aliphatically unsaturated epoxide 
compound and 2) an aliphatically unsaturated aromatic hydrocarbon. The 
reaction products can be formed in situ or prior to addition of the 
epoxide compound and/or the aromatic hydrocarbon compound to the other 
ingredients of the curable organosiloxane composition.