Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-04-06
2001-05-01
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C427S222000, C427S224000, C428S406000, C428S407000
Reexamination Certificate
active
06225361
ABSTRACT:
TECHNICAL FIELD
The present invention relates to expanded hollow micro sphere composite beads with a reduced tendency to fly. The invention further relates to an industrially advantageous process for producing such expanded hollow micro sphere composite beads.
PRIOR ART
Expandable thermoplastic polymer beads are micro spheres each comprising a thermoplastic polymer shell and a blowing agent as entrapped therein. When such expandable beads are heated at a temperature high enough to induce a sufficient degree of expansion for a certain length of time, expanded thermoplastic polymer beads are obtained. For example, when expandable micro sphere beads measuring about 15 &mgr;m in diameter and having a true specific weight of about 1.3 Kg/l are expanded by heating, expanded micro spheres measuring about 60 &mgr;m and having a true specific weight of about 0.03 kg/l may be obtained. By formulating those expanded micro spheres in various paints, coating agents, molding compounds, putty, FRP, adhesives, sealants, water-proofing materials, etc. the weights of final products can be decreased.
However, because of the extremely low specific weight of such expanded micro spheres, the micro spheres are unavoidably sent flying and adrift in the air in handling to adversely affect the working environment. Therefore, there is a demand for technology by which the fly or scattering of expanded micro spheres might be inhibited.
One of the known measures for preventing flying involves wetting expanded beads with a liquid substance such as water. The flying of expanded beads can be effectively precluded by admixing about 1-20 weight parts of a liquid such as water with each weight part of the expanded beads. This is a time-honored practice. However, this wetting method cannot be applied, of course, when the substrate material with which the expanded beads are to be formulated abhors liquids such as water.
The other measure for preventing flying involves providing expanded beads which have been coated with a particulate inorganic substance. This countermeasure has the disadvantage of increasing the specific weight of expanded beads but is still capable of reducing the weight of the final product and, at the same time, preventing scattering of the expanded beads in handling.
Heretofore, the particulate material comprising expanded beads coated with an inorganic powder has been produced basically by the technology disclosed in U.S. Pat. No. 4,722,943.
Thus, U.S. Pat. No. 4,722,943 describes a process for producing free-flowing dry beads by drying expandable micro spheres in the form of a wet cake, which comprises a step of admixing a wet cake of expandable thermoplastic polymer micro spheres (unexpanded material) with a processing aid which is a free-flowing particulate of fibrous solid having a softening or melting temperature higher than that of said expandable micro spheres; a step of continuously drying wet cake under the temperature and time conditions sufficient to thoroughly remove the water from the cake to prepare free-flowing granules each having a deposition of coating layer of said processing aid on its surface; and, a step of recovering the free-flowing dry granules.
The processing aid mentioned above includes talc, calcium carbonate, barium sulfate, alumina, silica, titanium dioxide, zinc oxide, etc.; spherical or hollow beads of ceramics, quartz or glass; glass fiber, cotton flocs, carbon or graphite fiber; and mixtures thereof.
The process described in the above-mentioned US patent involves a treatment with said processing aid in the stage of expandable thermoplastic polymer micro spheres (unexpanded material) and while it might be suited to large-scale production of a few kinds of product items, the process has the disadvantage of comparatively high costs of production when applied to the production of many kinds of products in small quantities. Moreover, in this process a certain proportion of the processing aid not adherent to the expanded product remains unbound and that the exfoliation of the processing aid from the expanded product cannot be sufficiently precluded. In addition, because the process involves expansion of expandable micro spheres at a temperature beyond their melting temperature, there is encountered the trouble of the micro spheres being broken by the deposited processing aid during expansion or, if short of breakage, low-strength grains not resistant to destruction in the stage of incorporating them for weight-reducing purposes are formed inevitably in a certain proportion.
SUMMARY OF THE INVENTION
In view of the above state of the art, the object of the present invention is to provide expanded hollow micro sphere composite beads and a process for their production, characterized in that a finely divided calcium carbonate powder can be uniformly deposited on expanded hollow thermoplastic polymer micro spheres (expanded material) by a simple procedure substantially without causing rupture of the expanded micro spheres in the course and, hence, the scattering of the expanded beads during handling can be effectively prevented.
The expanded hollow micro sphere composite beads of the present invention are characterized by comprising a composite bead (D) which comprises and expanded hollow thermoplastic polymer micro sphere (A) and, as deposited thereon, colloidal calcium carbonate (B), preferably together with the surface-treating agent or dispersing agent (C). The particularly preferred composite bead (D) comprises and expanded hollow thermoplastic polymer micro sphere (A) and, as deposited on its surface, a colloidal calcium carbonate (B) which has been surface-activated with a surface-treating agent or dispersing agent in advance.
A process for producing an expanded hollow micro sphere composite bead according to the present invention comprises admixing expanded hollow thermoplastic polymer micro spheres (A) with colloidal calcium carbonate (B) and a surface-treating agent for dispersing agent (C) to provide composite beads (D) comprising expanded hollow thermoplastic polymer micro spheres (A) and, as deposited thereon, said colloidal calcium carbonate (B) together with said surface-treating agent or dispersing agent (C).
In another aspect a process for producing expanded hollow micro sphere composite beads according to the present invention comprises dry-blending expanded hollow thermoplastic polymer micro spheres (A) with finely-divided calcium carbonate (B′) to provide composite beads each comprising said expanded hollow thermoplastic polymer micro sphere (A) and, as deposited on its surface, said calcium carbonate (B′).
REFERENCES:
patent: 4722943 (1988-02-01), Melber
patent: 5342689 (1994-08-01), Melber
Akzo Nobel N.V.
Foelak Morton
Serbin David J.
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