Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-02-28
2003-03-11
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S406000, C428S404000, C501S039000, C065S021400
Reexamination Certificate
active
06531222
ABSTRACT:
TECHNICAL FIELD
The present invention relates to hollow glass microspheres and a process for producing them.
BACKGROUND ART
Hollow glass microspheres are commonly called glass microballoons (hollow bodies), have a low specific gravity as compared with a conventional filler, have heat resistance, pressure resistance and impact resistance, and thereby have such an effect that when used as a filler, they contribute to weight saving of a packed product and at the same time, improve physical properties of the packed product such as strength, dimensional stability and moldability.
Accordingly, they are widely used for weight saving of resin molding components for e.g. automobiles, portable electronic equipments or electric appliance, patty/sealing materials for repairing automobiles, buoyancy materials for ships, synthetic wood and artificial marble.
Further, they are materials which are expected to develop into various applications such as heat insulating materials, insulants and dielectric constant-lowering materials. Particularly, as applications which are expected to expand by micro-sizing, not only applications for resin molding components, but also heat insulating coatings for heat insulating applications, and wire coating materials and substrates for applications for lowering dielectric constant, are mentioned.
Accordingly, hollow glass microspheres are used for various purposes and along with expectation of their expansion, ones which are micro and have more excellent particle properties and grain size properties have been strongly required in recent years.
Hollow glass microspheres and their production processes are proposed in e.g. JP-B-49-37565, JP-A-58-156551 and JP-B-4-37017.
JP-A-58-156551 discloses a process of forming hollow borosilicate glass microspheres, which comprises melting materials such as SiO
2
, H
3
BO
3
, CaCO
3
, Na
2
CO
3
, NH
4
H
2
PO
4
and Na
2
SO
4
at a high temperature of at least 1000° C. to form glass containing a sulfur component in a large amount, dry-grinding the glass, followed by classification, and dispersing and retaining impalpable glass powder thus obtained in flame so as to foam the sulfur component as a foaming agent component. However, with respect to physical properties of the hollow glass spherical bodies obtained by the process, the particle density is at a level of at most 0.50 g/cm
3
, but the average particle size is at a level of 50 &mgr;m, and they are large spherical bodies.
Further, JP-B-4-37017 discloses a process for obtaining hollow glass microspheres by baking in a furnace impalpable powder having glass forming components and a foaming agent component supported by silica gel. With respect to physical properties of the hollow glass spherical bodies obtained by the process, the particle density is at a level of 0.3 g/cm
3
, and the average particle size is at a level of 70 &mgr;m.
However, with respect to the hollow glass spherical bodies obtained by such processes, although adequate hollowness to impart e.g. weight saving effects and heat insulating effects is obtained, the average particle size is at least about 50 &mgr;m, and particles exceeding 100 &mgr;m are contained as particles with maximum particle size. Accordingly, they cannot be used for applications for which smoothness on the surface is required, in fields of e.g. heat insulating coatings and SMC (sheet molding compound) for outer jacketing laggings of automobiles, or for applications in which the thickness of a composite material is restricted, including applications for lowering dielectric constant, such being problematic.
Further, along with broadening of the particle size distribution, the particle density of particles tends to be distributed in general. Large particles having a low particle density tend to have weak particle strength, whereby they are likely to fracture due to excess stress in the processing such as kneading, in applications for fillers for thermoplastic resins, and no adequate weight saving effects, heat insulating effects and dielectric constant-lowering effects can be obtained for intended purposes, such being problematic.
The present invention has been made to overcome the above problems, and it is an object of the present invention to provide hollow glass microspheres to obtain lightweight materials having excellent heat insulating properties and high strength when used as a filler for resins, for example, and to obtain coating films which are excellent also in smoothness when used as a filler for coatings. Specifically, it is an object of the present invention to provide hollow glass microspheres having micro particle sizes, a low particle density and grain size properties with a sharp grain size distribution, having a high homogeneity and being less likely to fracture during handling such as kneading or molding, which have not been obtained yet.
DISCLOSURE OF THE INVENTION
According to a first aspect of the present invention, there is provided hollow glass microspheres which have an average particle size of at most 15 &mgr;m (based on volume), a maximum particle size of at most 45 &mgr;m, a particle density of at most 0.5 g/cm
3
, a grain size gradient of at most 2.0 as represented by the following formula, and a B
2
O
3
content contained in the glass of from 9.0 to 20.0 mass %:
grain size gradient=(
d
10
−d
90
)/
d
50
wherein d
10
, d
50
and d
90
are particle sizes with which values of volume-based oversize particle cumulative distribution become 10%, 50% and 90%, respectively, as measured by a laser scattering type grain size measuring apparatus.
As preferred embodiments of the present invention, of the hollow glass microspheres, the particle density is at most 0.4 g/cm
3
, the grain size gradient is at most 1.0, the average particle size is at most 10 &mgr;m, and the maximum particle size is at most 30 &mgr;m.
Further, as another preferred embodiment of the present invention, the B
2
O
3
content contained in the glass is from 10.0 to 15.0 mass %.
According to a second aspect of the present invention, there is provided a process for producing the above hollow glass microspheres, which comprises adding a flammable liquid to a glass preparing blend containing a foaming component, followed by wet grinding to prepare a slurry of the glass preparing blend having an average particle size of at most 3 &mgr;m, atomizing said slurry from a two-fluid nozzle under a gas pressure of from 0.2 to 2 MPa to form droplets containing the glass preparing blend, heating them to obtain hollow glass microspheres, and as the case requires, carrying out a classification treatment to bring the particle sizes to be less than 45 &mgr;m.
According to a third aspect of the present invention, there is provided a process for producing the above hollow glass microspheres, which comprises adding a flammable liquid to a glass preparing blend containing a foaming component, followed by wet grinding to prepare a slurry of the glass preparing blend having an average particle size of at most 3 &mgr;m, atomizing said slurry while applying a pressure of from 0.1 to 8 MPa to form droplets containing the glass preparing blend, heating them to obtain hollow glass microspheres, and as the case requires, carrying out a classification treatment to bring the particle sizes to be less than 45 &mgr;m.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, as mentioned above, with respect to particle properties and grain size properties as hollow glass microspheres, the average particle size is at most 15 &mgr;m, the maximum particle size is at most 45 &mgr;m, the particle density is at most 0.5 g/cm
3
, and the grain size gradient is at most 2.0 as mentioned hereinafter.
In the present invention, the average particle size is based on volume (the same applies hereinafter), and the particle size can be measured by a laser scattering type grain size measuring apparatus.
If the average particle size of the hollow glass microspheres exceeds 15 &mgr;m, or the maximum particle size exceeds 45 &mgr;m, the homogeneity tends to be impaired, the microsphere
Hirano Hachiro
Tanaka Masaharu
Yamada Kenji
Asahi Glass Company Limited
Kiliman Leszek
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Fine hollow glass sphere and method for preparing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fine hollow glass sphere and method for preparing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fine hollow glass sphere and method for preparing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3027985