Silicon dioxide which bears partially or fully silylated...

Details Silicon dioxide which bears partially or fully silylated... Silicon dioxide which bears partially or fully silylated...

1998-12-16

2001-02-06

Le, Hoa T. (Department: 1773)

Stock material or miscellaneous articles

Coated or structually defined flake, particle, cell, strand,...

Particulate matter

C428S404000, C428S407000

Reexamination Certificate

active

06183867

ABSTRACT:

TECHNICAL FIELD
The invention relates to silicon dioxide which bears partially or fully silylated polysilicic acid chains on its surface and to a process for its preparation, and also to toners and silicone elastomers in which it is present.
BACKGROUND ART
DE 1163784 and DE 3211431, DEGUSSA AG, describes processes for hydrophobicizing silicon dioxide at elevated temperature. For this purpose, the silicon dioxide is activated and predried at high temperatures, giving a hydrophobic product.
DE 4240741, Wacker-Chemie GmbH, describes a process for silylating silicon dioxide with chlorosilanes with addition of lower alkyl alcohols. A uniformly hydrophobic product is obtained.
DE 2344388, Wacker-Chemie GmbH, describes a process for hydrophobicizing silicon dioxide with mechanical compaction. A completely hydrophobic material is obtained.
DE 2403783, BAYER AG, describes a process for preparing a silicon dioxide filler for use in silicone compositions. A completely hydrophobic silica is obtained.
DE 3839900 and EP 0378785, Wacker-Chemie GmbH, describe a process for hydrophobicizing a particulate solid containing Si—OH groups by means of hydrophobicizing agents. This gives a hydrophobic filler which is suitable for use in curable compositions based on diorganopolysiloxanes.
The prior art products are, in general, homogeneously hydrophobic, and are not well suited for some applications. Partially or fully silylated polysilicic acid chains on a silicon dioxide surface have not been previously prepared.
DISCLOSURE OF INVENTION
It is an object of the invention to overcome the disadvantages of the prior art by providing silicon dioxide which bears partially or fully silylated polysilicic acid chains on its surface, wherein the sum of silanol groups of the silicon dioxide surface (SiOH) and grafted-on silylating agent radicals (SiR
a
) is greater than the number of silanol groups on the surface of untreated silicon dioxide, where a can be 1, 2 or 3 and the R groups can be identical or different and are each a substituted or unsubstituted hydrocarbon radical.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hydrophobicization of silicon dioxide, in particular pyrogenic silicon dioxide, is practiced as described by the prior art, by the reaction of the silanol groups of silicon dioxide with organosilicon radicals. Thus, according to the prior art, the hydrophobicization proceeds as a condensation reaction between the silanol groups of the silicon dioxide with SiX groups (X is a reactive leaving group) of a silylating agent. As a consequence, the hydrophobicized silicon dioxide has fewer silanol groups on its surface than the initial, hydrophilic silicon dioxide which has at most two silanol groups per nm
2
of silicon dioxide surface.
The silicon dioxide of the invention has chemically bound, partially or fully silylated polysilicic acids on its surface. The silylating agent layer therefore comprises partially or fully silylated polysilicic acid structures which are bound to the silicon dioxide surface and comprise units of the structure
R
a
(OH)
b
SiO
c
and (OH)
d
SiO
e
,
where R can be identical or different and are preferably each a substituted or unsubstituted hydrocarbon radical,
a is 1, 2 or 3, preferably 3,
b is 0, 1 or 2, preferably 0,
and c is 1, 2 or 3, preferably 1,
where a+b+c is 4,
d is 0, 1, 2 or 3, preferably 0, 1 or 2,
e is 1, 2, 3 or 4
and d+e is 4.
Preferably, R are identical or different, substituted or unsubstituted hydrocarbon radicals having from 1 to 18 carbon atom(s), and may be saturated or unsaturated aliphatic, or aromatic, preferably substituted by halogen or pseudohalogen.
Examples of R are alkyl radicals such as the methyl radical, the ethyl radical; propyl radicals such as the iso- or n-propyl radical; butyl radicals such as the t- or n-butyl radical; pentyl radicals such as the neo-, iso- or n-pentyl radical; hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl radical; octyl radicals such as the 2-ethylhexyl or n-octyl radical; decyl radicals such the n-decyl radical; dodecyl radicals such as the n-dodecyl radical; hexadecyl radicals such as the n-hexadecyl radical; and octadecyl radicals such as the n-octadecyl radical; alkenyl radicals such as the vinyl, 2-allyl, and 5-hexenyl radicals; aryl radicals such as the phenyl, biphenyl, and naphthenyl radicals; alkylaryl radicals such as the benzyl, ethylphenyl, tolyl, and xylyl radicals; halogenated alkyl radicals such as the 3-chloropropyl, 3,3,3-trifluoropropyl, and perfluorohexylethyl radicals; and halogenated aryl radicals such as the chlorophenyl and chlorobenzyl radicals.
Preferred examples of R are, for reasons of industrial availability, the methyl radical, the vinyl radical and the 3,3,3-trifluoropropyl radical.
The content of active and acid SiOH on the SiO
2
surface of the silicon dioxide of the invention is preferably less than 25 mol %, based on the total content of active and acid SiOH of an untreated hydrophilic silicon dioxide.
The partially or fully silylated polysilicic acid structures which are chemically bound to the silicon dioxide surface preferably contain at least two and at most 20 Si atoms.
The molar proportion of the partially or fully silylated polysilicic acid structures which are bound to the silicon dioxide surface and comprise units of the structure
R
a
(OH)
b
SiO
c
in the total silylating agent layer is less than or equal to 75 mol %, but greater than or equal to 25 mol %, where R, a, b and c are as defined above.
Examples of silylated polysilicic acid radicals on the silicon dioxide surface are set forth below. In these formulae, Z is a silicon atom of the silicon dioxide surface. The silicon dioxide surface is preferably not occupied by merely one type of silylated polysilicic acid radical, but by a variety of silylated polysilicic acid radicals.
Z—O—Si[OSiR
3
]
3
Z—O—SiOH[OSiR
3
]
2
Z—O'Si(OH)
2
[OSiR
3
]
{Z—O—}
2
Si[OSiR
3
]
2
{Z—O—}
2
SiOH[OSiR
3
]
Z—O—Si[OSiR
3
]
2
—O—Si[OSiR
3
]
3
Z—O—SiOH[OSiR
3
]—O—Si[OSiR
3
]
3
Z—O—Si(OH)
2
—O—Si[OSiR
3
]
3
Z—O—Si[OSiR
3
]
2
—O—SiOH[OSiR
3
]
2
Z—O—Si[OSiR
3
]
2
—O—Si(OH)
2
[OSiR
3
]
Z—O—SiOH[OSiR
3
]—O—SiOH[OSiR
3
]
2
Z—O—Si{OSi[OSiR
3
]
3
}
3
Z—O—SiOH{OSi[OSiR
3
]
3
}
2
Z—O—Si[OSiOH{OSiR
3
]
2
}
3
,
where R are identical or different and are as defined above.
Preferred examples are:
Z—O—Si[OSi(CH
3
)
3
]
3
Z—O—SiOH[OSi(CH
3
)
3
]
2
Z—O—Si(OH)
2
[OSi(CH
3
)
3
]
{Z—O—}
2
Si[OSi(CH
3
)
3
]
2
{Z—O—}
2
SiOH[OSi(CH
3
)
3
]
Z—O—Si[OSi(CH
3
)
3
]
2
—O—Si[OSi(CH
3
)
3
]
3
Z—O—SiOH[OSi(CH
3
)
3
]—O—Si[OSi(CH
3
)
3
]
3
Z—O—Si(OH)
2
—O—Si[OSi(CH
3
)
3
]
3
Z—O—Si[OSi(CH
3
)
3
]
2
—O—SiOH[OSi(CH
3
)
3
]
2
Z—O—Si[OSi(CH
3
)
3
]
2
—O—Si(OH)
2
[OSi(CH
3
)
3
]
Z—O—SiOH[OSi(CH
3
)
3
]—O—SiOH[OSi(CH
3
)
3
]
2
Z—O—Si{OSi[OSi(CH
3
)
3
]
3
}
3
Z—O—SiOH{OSi[OSi(CH
3
)
3
]
3
}
2
Z—O—Si{OSi[OSiOH(CH
3
)
3
]
2
}
3
The invention further provides a process for preparing silicon dioxide which bears partially or fully silylated polysilicic acid chains on its surface, wherein the silylating agent is added in a molar excess, based on the silanol groups present on the silicon dioxide.
The silicon dioxides used in the process of the invention are preferably silicon dioxides such as silicon dioxide prepared by wet chemical precipitation or, particularly preferably, pyrogenic silicon dioxide prepared by flame hydrolysis, e.g. from tetrachlorosilane or methyltrichlorosilane or methyldichlorosilane. The silicon dioxides which are preferably used have a hydrodynamic diameter of the silicon dioxide aggregates of less than 10 &mgr;

Affiliated with

Also associated with

Rating

Silicon dioxide which bears partially or fully silylated... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Silicon dioxide which bears partially or fully silylated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silicon dioxide which bears partially or fully silylated... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2563235