Resin magnetic compound and molded article thereof

A resin magnetic compound is disclosed, comprising (i) from 65 to 77% by weight of a magnetic powder having been surface treated with from 0.01 to 5% by weight, based on the magnetic powder, of a mercaptosilane represented by the following formula (I) or a hydrolysis product of the mercaptosilane: EQU (RO).sub.n R'.sub.(3-n) SiR"SH (I) wherein R and R' each represents an alkyl group having 1 or 2 carbon atoms; R" represents an alkylene group having from 2 to 6 carbon atoms; and n represents 2 or 3, (ii) from 14 to 30% by weight of polyphenylene sulfide resin, and (iii) from 9 to 21% by weight of glass fiber. The resin magnetic compound and a molded article obtained from the compound are excellent in thermal shock resistance, magnetic characteristics, and heat resistance.

FIELD OF THE INVENTION 
This invention relates to a resin magnetic compound comprising a 
polyphenylene sulfide resin as a binder and a molded article thereof with 
high thermal shock resistance and excellent magnetic force. 
BACKGROUND OF THE INVENTION 
A compound comprising a polyphenylene sulfide resin and a magnetic powder 
reflects the characteristics essential to polyphenylene sulfide resin, 
such as heat resistance, chemical resistance, and low water absorption, 
and has been increasing its importance in the fields of automobiles, 
electric and electronic parts, and industrial machinery. The outstanding 
problem associated with molded articles obtained from the polyphenylene 
sulfide resin/magnetic powder compound consists in unsatisfactory 
resistance to thermal shock, i.e., the molded articles suffer from 
cracking with drastic changes in temperature. 
Thermal shock resistance of the compound may be improved by incorporation 
of glass fiber as described in JP-A-62-176103 and JP-A-4-44304 (the term 
"JP-A" as used herein means an "unexamined published Japanese patent 
application"). However, addition of glass fiber in an amount sufficient 
for obtaining an appreciably improved thermal shock resistance interferes 
with dispersion of a magnetic powder and extremely deteriorates fluidity 
of the compound, resulting in a reduction of magnetic force. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a resin magnetic compound 
which, even when compounded with a larger proportion of glass fiber than 
in conventional techniques, provides a high thermal shock resistant molded 
article without being accompanied with a reduction in magnetic force. 
Another object of the present invention is to provide a molded article 
obtained from such a resin magnetic compound. 
The present invention provides a resin magnetic compound comprising 
(i) from 65 to 77% by weight of a magnetic powder having been subjected to 
a surface treatment with from 0.01 to 5% by weight, based on the magnetic 
powder, of a mercaptosilane represented by the following formula (I) or a 
hydrolysis product of the mercaptosilane: 
EQU (RO).sub.n R'.sub.(3-n) SiR"SH (I) 
wherein R and R' each represents an alkyl group having 1 or 2 carbon 
atoms; R" represents an alkylene group having from 2 to 6 carbon atoms; 
and n is an integer of 2 or 3; 
(ii) from 14 to 30% by weight of polyphenylene sulfide resin; 
(iii) from 9 to 21% by weight of glass fiber wherein the resin magnetic 
compound is prepared by dry blending and melt-kneading the magnetic 
powder, the polyphenylene sulfide resin and the glass fiber. 
Further, the present invention provides a molded article obtained from the 
resin magnetic compound.

DETAILED DESCRIPTION OF THE INVENTION 
The magnetic powder which can be used in the present invention is a 
magnetic powder having been subjected to a surface treatment with a 
specific mercaptosilane represented by formula (I) or a hydrolysis product 
of the mercaptosilane. 
In formula (I), examples of R and R' include methyl and ethyl groups, and 
examples of R" include ethylene, propylene and trimethylene groups. 
The mercaptosilane represented by formula (I) preferably includes 
3-mercaptopropylmethyldimethoxysilane, 
3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropyltrimethoxysilane, 
and 3-mercaptopropyltriethoxysilane. More preferred are 
3-mercaptopropylmethyldimethoxysilane and 
3-mercaptopropylmethyldiethoxysilane. 
The mercaptosilane or the hydrolysis product thereof is used in an amount 
of 0.01 to 5% by weight, preferably 0.5 to 2% by weight, based on the 
magnetic powder. If the amount of mercaptosilane is less than 0.01% by 
weight, the fluidity of the resin is markedly reduced, causing a reduction 
in magnetic force. If it is more than 5% by weight, foaming will occur on 
molding. 
The method of surface treatment with the mercaptosilane or the hydrolysis 
product thereof is not particularly restricted. The treatment is 
preferably carried out by agitating a magnetic powder in an alcoholic 
aqueous solution (e.g., methyl alcohol, ethyl alcohol, isopropyl alcohol) 
of a mercaptosilane or a mercaptosilane aqueous solution adjusted to a pH 
of 3 to 7, preferably 4.5 to 5, followed by drying. 
In case of using 3-mercaptopropylmethyldimethoxysilane or 
3-mercaptopropylmethyldiethoxysilane, there is no need to conduct 
hydrolysis beforehand, and there is obtained a compound excellent in 
mechanical strength and fluidity by simply mixing with polyphenylene 
sulfide resin, a magnetic powder, and glass fiber. 
The magnetic powder to be treated is not particularly limited but 
preferably includes magneto-plumbite type ferrites such as barium ferrite 
and strontium ferrite, and rare earth magnetic powders such as 
samarium-cobalt alloy magnetic powder and neodymium-iron-boron magnetic 
powder. 
The compound of the present invention contains from 65 to 77% by weight, 
preferably from 67 to 76% by weight, and more preferably from 68 to 74% by 
weight, of the magnetic powder. If the amount of the magnetic powder is 
less than 65% by weight, the magnetic characteristics of the resulting 
molded article are reduced. If it is more than 77% by weight, fluidity of 
the compound on molding is reduced. 
The compound of the present invention contains from 14 to 30% by weight, 
preferably from 15 to 28% by weight, and more preferably from 16 to 26% by 
weight, of polyphenylene sulfide resin. If the amount of polyphenylene 
sulfide resin is less than 14% by weight, the fluidity of the compound is 
reduced to make molding difficult. If it is more than 30% by weight, the 
resulting molded article cannot possess sufficient magnetic 
characteristics. 
Polyphenylene sulfide resin which can be used in the present invention as a 
binder includes both homopolymers comprising a p-phenylene sulfide unit 
and copolymers mainly comprising a p-phenylene sulfide unit. Polyphenylene 
sulfide resin copolymer preferably contains 60% by weight or more, and 
more preferably contains 90% by weight or more, of a p-phenylene sulfide 
unit. 
Of polyphenylene sulfide resin, those substantially having a linear 
structure which are obtained from monomers mainly comprising bifunctional 
monomers are particularly preferred because of their excellent toughness. 
Partially crosslinked polyphenylene sulfide resins or polyphenylene 
sulfide resins having the melt viscosity increased by oxidative 
crosslinking (i.e., curing) may be employed as far as the mechanical 
characteristics of polyphenylene sulfide resin are retained. 
The melt viscosity of polyphenylene sulfide resin is not particularly 
limited as long as polyphenylene sulfide resin may be stably melt-kneaded 
with a magnetic powder to provide a compound applicable to melt 
processing, such as melt extrusion or injection molding. The melt 
viscosity of polyphenylene sulfide resin measured at 310.degree. C. and 
200 sec.sup.-1 is preferably from 15 to 500 Pa.s, more preferably from 20 
to 400 Pa.s. 
Glass fiber which can be used in the present invention usually has a 
diameter of 6 to 13 .mu.m. The compound of the present invention contains 
from 9 to 21% by weight, preferably from 10 to 18% by weight, and more 
preferably from 11 to 16% by weight, of glass fiber. If the amount of 
glass fiber is less than 9% by weight, the resulting molded article has 
insufficient thermal shock resistance and reduced heat resistance. If it 
is more than 21% by weight, the fluidity of the compound is reduced, and 
the magnetic characteristics of the resulting molded article are reduced. 
The resin magnetic compound is prepared by dry blending and melt-kneading 
the magnetic powder which has been subjected to surface treatment with the 
mercaptosilane, along with the polyphenylene sulfide resin, and the glass 
fiber. 
The present invention will now be illustrated in greater detail with 
reference to Examples, but it should be understood that the present 
invention is not construed as being limited thereto. 
Physical properties of the molded articles obtained were measured according 
to the following methods. 
1) Thermal Shock Resistance 
A resin magnetic compound was molded at 150.degree. C. into a hollow 
cylinder having an outer diameter of 16 mm, an inner diameter of 8 mm, and 
a thickness of 5 mm around a metal shaft having a diameter of 8 mm and a 
length of 20 mm to prepare a specimen for a thermal shock test. Ten 
specimens per sample were immersed in a liquid phase and subjected to 500 
thermal cycles, one cycle comprising -65.degree. C. for 5 minutes and then 
150.degree. C. for 5 minutes. Ten specimens were experimented, and the 
number of specimens which underwent cracking after 500 thermal cycles was 
obtained. 
2) Flexural Strength 
A flexural strength of a rectangular parallelopiped specimen (3 mm.times.13 
mm.times.130 mm) was measured according to ASTM D-790. 
3) Maximum Energy Product 
A maximum energy product of a molded article was measured according to JIS 
C2501. 
EXAMPLE 1 
3-Mercaptopropyltrimethoxysilane was mixed with an equal portion of water 
and a double portion of methyl alcohol to hydrolyze the mercaptosilane. 
Strontium ferrite powder ("NP-20" produced by Nippon Bengara Kogyo Co., 
Ltd.) in an amount 100 times as much as the mercaptosilane was put in a 20 
l Henschel mixer, and the hydrolyzed mercaptosilane was added thereto 
while stirring. 
In a 20 l Henschel mixer were mixed 2.4 kg of linear polyphenylene sulfide, 
10.35 kg of the above-prepared silane-treated strontium ferrite, and 2.25 
kg of glass fiber having a diameter of 9 .mu.m, and the compound was fed 
to a twin-screw extruder having a diameter of 45 mm to prepare specimens 
for measurement of physical properties. The results of measurements are 
shown in Table 1 below. 
EXAMPLE 2 
The same procedure as in Example 1 was repeated, except for changing the 
amounts of strontium ferrite and glass fiber to 10.95 kg and 1.65 kg, 
respectively. The results of measurements are shown in Table 1 below. 
EXAMPLE 3 
The same procedure as in Example 1 was repeated, except for changing the 
amounts of linear polyphenylene sulfide, strontium ferrite, and glass 
fiber to 3.0 kg, 10.35 kg, and 1.65 kg, respectively. The results of 
measurements are shown in Table 1 below. 
EXAMPLE 4 
In a 20 l Henschel mixer were put 2.4 kg of linear polyphenylene sulfide, 
10.25 kg of strontium ferrite, and 2.25 kg of glass fiber having a 
diameter of 9 .mu.m, and 100 g of 3-mercaptopropylmethyldimethoxysilane 
was added thereto while stirring. The resulting compound was fed to a 
twinscrew extruder having a diameter of 45 mm to prepare specimens. The 
results of measurements are shown in Table 1 below. 
EXAMPLE 5 
The same procedure as in Example 1 was repeated, except for replacing 
3-mercaptopropyltrimethoxysilane with 
3-mercaptopropylmethyldimethoxysilane. The results of measurements are 
shown in Table 1 below. 
COMATIVE EXAMPLE 1 
The same procedure as in Example 1 was repeated, except for changing the 
amounts of strontium ferrite and glass fiber to 11.85 kg and 0.75 kg, 
respectively. The results of measurements are shown in Table 1 below. 
COMATIVE EXAMPLE 2 
The same procedure as in Example 1 was repeated, except for changing the 
amounts of strontium ferrite and glass fiber to 11.4 kg and 1.2 kg, 
respectively. The results of measurements are shown in Table 1 below. 
COMATIVE EXAMPLE 3 
The same procedure as in Example 1 was repeated, except for changing the 
amounts of polyphenylene sulfide resin, strontium ferrite, and glass fiber 
to 5.25 kg, 8.25 kg, and 1.5 kg, respectively. The results of measurements 
are shown in Table 1 below. 
COMATIVE EXAMPLE 4 
The same procedure as in Example 1 was repeated, except that the magnetic 
powder was not treated with a mercaptosilane. The results of measurements 
are shown in Table 1 below. 
TABLE 1 
__________________________________________________________________________ 
Thermal Shock 
Resistance 
Maximum 
Compound (wt %) Flexural 
(Number of 
Energy 
Melt 
Example Magnetic 
Glass 
Mercapto- 
Mixing 
Strength 
cracked Product 
Viscosity.sup.2) 
No. PPS.sup.1) 
Powder 
Fiber 
silane 
Method 
(MPa) 
specimens) 
(kJ/m.sup.3) 
(10 Pa .multidot. 
__________________________________________________________________________ 
s) 
Example 1 
16 69 15 MPTMS.sup.3) 
.sup. A.sup.5) 
178 0 8 39 
Example 2 
16 73 11 MPTMS A 166 0 10 38 
Example 3 
20 69 11 MPTMS A 162 0 8 37 
Example 4 
16 69 15 MPDMS.sup.4) 
.sup. B.sup.6) 
186 0 8 29 
Example 5 
16 69 15 MPDMS A 183 0 8 32 
Comparative 
16 79 5 MPTMS A 146 10 11 39 
Example 1 
Comparative 
16 76 8 MPTMS A 157 2 10 38 
Example 2 
Comparative 
35 55 10 MPTMS A 155 0 2 31 
Example 3 
Comparative 
16 69 15 -- B 142 10 7 59 
Example 4 
__________________________________________________________________________ 
Note: 
.sup.1) PPS: polyphenylene sulfide homopolymer 
.sup.2) Measured at 330.degree. C. and 1000 sec.sup.-1. 
.sup.3) MPTMS: 3Mercaptopropyltrimethoxysilane 
.sup.4) MPDMS: 3Mercaptopropylmethyldimethoxysilane 
.sup.5) A: The magnetic powder was sprayed with an alcoholic aqueous 
solution of the mercaptosilane, agitated, and then dried. 
.sup.6) B: The mercaptosilane (not hydrolyzed) was mechanically mixed wit 
polyphenylene sulfide, magnetic powder, and glass fiber. 
In the above examples, the practical range of the flexural strength is 147 
MPa or more. The practical range of the maximum energy product is 4.8 
kJ/m.sup.3 or more. When the number of cracked specimens by the thermal 
shock test is 0 or 1, the molded article can be practical. 
As is apparent from Table 1 above, the resin magnetic compound according to 
the present invention provides a molded article excellent in thermal shock 
resistance, magnetic characteristics, and heat resistance. The resin 
magnetic compound and molded articles thereof are applicable to parts 
requiring thermal shock resistance, magnetic characteristics and heat 
resistance, such as automobile revolution sensors, speed sensors, and 
position sensors of various motors. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.