Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-08-11
2004-05-18
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S287110, C106S287130, C106S287140, C106S287190, C106S287100
Reexamination Certificate
active
06736891
ABSTRACT:
Particulate inorganic oxides, such as precipitated silica, are finding increasing use as reinforcing fillers in cured rubber compositions, especially tire treads. Reinforcement of rubber compositions is necessary in order to provide acceptable mechanical properties to the cured rubber compositions.
A problem associated with the use of particulate inorganic oxides in cured rubber compositions is their rather low degree of dispersion in the cured rubber, as evidenced by the relatively large percentage of white area in an optical microscope field. Grinding or milling the inorganic oxide before use in forming the cured rubber composition may produce better dispersions and hence exhibit less white area in the optical microscope field, but once the bulk of the improvement has been achieved, continued grinding or milling, even for prolonged periods, does not result in much further improvement in the degree of dispersion.
U.S. Pat. No. 5,908,660 discloses hydrophobic amorphous precipitated silica as a reinforcing and extending filler in natural rubbers and in silicone rubbers. The '660 patent describes: (1) preparing hydrophobic particulate amorphous precipitated silica from hydrophilic amorphous precipitated silica by a “pop-out” process wherein an aqueous suspension of hydrophilic particulate amorphous precipitated silica is contacted with a catalytic amount of an acid and an organosilicon compound to form an aqueous suspension of hydrophobic particulate amorphous precipitated silica, and then the aqueous suspension of hydrophobic particulate amorphous precipitated silica is contacted with water-immiscible organic solvent to transfer the hydrophobic particulate amorphous precipitated silica from the liquid aqueous phase to the liquid organic phase; (2) that the amount of organosilicon compound added to the aqueous phase should be sufficient to produce a hydrophobic particulate amorphous precipitated silica suitable for its intended use; (3) that generally the organosilicon compound should be added in an amount such that there is at least 0.04 organosilyl unit per SiO
2
unit in the precipitated silica; and (4) that the upper limit of the amount of organosilicon compound added is not critical since any amount in excess of the amount required to completely hydrophobize the precipitated silica will act as a solvent. U.S. Pat. No. 5,908,660 discloses a very broad range of hydrophobization, ranging from a small degree of hydrophobization to complete hydrophobization.
Published European Patent Application EP 0 849 320 A1 discloses amorphous precipitated silica having clusters of coupling agent chemically bonded to its surface. The coupling agent optionally also has a functional group having the capability of reacting with a rubbery thermoplastic polymer during the cure or compounding thereof to chemically bind the coupling agent to the polymer.
U.S. Pat. Nos. 5,739,197 and 5,888,467 disclose a particulate amorphous precipitated silica characterized by a Standard White Area, as therein defined, of 0.42 percent. U.S. Pat. No. 5,852,099 discloses particulate alumina as a reinforcing filler in organic rubbers.
European Patent application 721,971 A1 and Japanese Provisional Publication No. 8-176462, respectively, describe a pneumatic tire tread made from a rubber composition containing a partially hydrophobized silica and a partially hydrophobized precipitated silicic acid in which the level of hydrophobization, as measured by di-n-butylamine, is 70-180 mmol/kg.
Hydrophobic particulate inorganic oxide has now been discovered which is capable of providing an unexpectedly high degree of dispersibility in cured rubber compositions. Inasmuch as an unexpectedly high degree of dispersibility is not disclosed in the aforedescribed documents, the present invention represents a solution to the above-described dispersion problem and to be an advance in this art. The high degree of dispersibility of the hydrophobic particulate inorganic oxides of the present invention can be characterized by the M1 Standard White Area, which is hereinafter described in detail.
Hydrophobic particulate inorganic oxide used in the compositions of the present invention include the reaction product of (1) hydrophilic inorganic oxide selected from the group consisting of particulate or amorphous precipitated silica, colloidal silica, and mixtures thereof, and (2) at least one organometallic reactant selected from the group consisting of first organometallic compound represented by the formula:
R
1
a
MX
4−a
second organometallic compound represented by the formula:
R
2
2n+2
Si
n
O
n−1
third organometallic compound represented by the formula:
(R
3
3
Si)
k
NR
5
3−k
fourth organometallic compound represented by the formula:
R
4
2m
Si
m
O
m
and mixtures thereof wherein: (a) each M is independently silicon, titanium or zirconium; (b) each R
1
is independently a hydrocarbon group having no ethylenic unsaturation (e.g., a saturated aliphatic, cycloaliphatic or aromatically unsaturated hydrocarbon group) which contains from 1 to 18 carbon atoms; (c) each X is independently halo, amino, alkoxy containing from 1 to 12 carbon atoms, or acyloxy containing from 1 to 12 carbon atoms; (d) a is 1, 2, or 3; (e) each R
2
is independently halo, hydroxy, or a hydrocarbon group having no ethylenic unsaturation (as described for R
1
), which contains from 1 to 18 carbon atoms, with the proviso that at least 50 mole percent of the R
2
substituents are the hydrocarbon groups having no ethylenic unsaturation; (f) n is from 2 to 10,000; (g) each R
3
is independently halo, hydroxy, or a hydrocarbon group having no ethylenic unsaturation (as described for R
1
), which contains from 1 to 18 carbon atoms, with the proviso that at least 50 mole percent of the R
3
substituents are the hydrocarbon groups having no ethylenic unsaturation; (h) each R
5
is independently hydrogen or a hydrocarbon group having no ethylenic unsaturation (as described for R
1
), which contains from 1 to 18 carbon atoms; (i) k is 1 or 2; (j) each R
4
is independently a hydrocarbon group having no ethylenic unsaturation (as described for R
1
), which contains from 1 to 18 carbon atoms; and (k) m is a number from 3 to 20; wherein the hydrophobic particulate inorganic oxide is characterized by an M1 Standard White Area of less than 0.4 percent.
The hydrophobic particulate inorganic oxide of the present invention is also characterized by a methanol wettability of from 15 to 45 percent, preferably from 20 to 40 percent and more preferably from 25 to 35 or the methanol wettability may range between any combination of these values, inclusive of the recited values. The hydrophobic particulate inorganic oxide of the present invention is further characterized by a pH of from 3 to 10, preferably, from 4 to 8, more preferably from 5 to 7.5, and most preferably from 6 to 7, or the product pH may range between any combination of these values inclusive of the recited ranges, e.g., a pH of from 3 to 7.5.
As used herein with respect to the aforedescribed organometallic compounds, the term halo includes fluoro, chloro, bromo and iodo, preferably chloro. By “no unsaturation” is meant substantially no ethylenic unsaturation since the source of or preparative methods for some hydrocarbon groups may result in the presence of small amounts of ethylenic unsaturation in the hydrocarbon group.
For purposes of the present invention, when the organometallic reactant is an organosilicon reactant, the silicon is considered to be a metal.
The hydrophilic particulate precipitated silicas which may be used in producing the hydrophobic precipitated silicas of the invention are known and are commercially available. Processes for producing hydrophilic particulate amorphous precipitated silicas and the properties of the products are described in detail in U.S. Pat. Nos. 2,657,149; 2,940,830; 4,132,806; 4,495,167, 4,681,750, and 5,094,829.
Hydrophilic particulate or amorphous precipitated silicas are usually produced commercially by combining an aqueous solution of a soluble metal silic
Bice Jo-Ann E.
Hahn James R.
Hellring Stuart D.
Okel Timothy A.
Brunsman David
Mallak Frank P.
Marmo Carol A.
PPG Industries Ohio Inc.
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