Production process of non-flying plastic mircoballoons

Details Production process of non-flying plastic mircoballoons Production process of non-flying plastic mircoballoons

2001-11-19

2004-08-31

Kuhns, Allan R. (Department: 1732)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C264S051000, C264S053000

Reexamination Certificate

active

06784215

ABSTRACT:

BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to a process for producing plastic microballoons (hereinafter simply called “microballoons”) which are prevented from flying and are used as a filler in various paints, construction materials, plastics and the like to reduce their weights. Described more specifically, expanded microballoons are generally used after applying non-flying treatment because they are light, have pronounced flying tendency and are hence difficult to handle. Nonetheless, they are still accompanied by various problems, and their handling properties and the like are by no means satisfactory. The present invention is concerned with a process for producing non-flying microballoons with good handling properties.
b) Description of the Related Art
Microballoons are generally packed in containers such as plastic bags or container sacks. When microballoons are taken out of such a container for addition to a base material such as a paint, they fly up in air as they are very light in weight. Upon mixing them with stirring, they rise to the surface of the base material so that a considerable time is required until they are evenly added and mixed in the base material. Microballoons are, therefore, a material the handling of which is extremely difficult.
To overcome these problems, proposals have been made including, for example, a process featuring addition of a wetting agent to microballoons (JP 4-71664 A) and a process characterized by causing an inorganic filler to deposit on surface skins or shells of microballoons. The former process is to impart non-flying property to microballoons by a wetting agent such as a plasticizer, while the latter process is to make microballoons non-flying by fixing an inorganic filler or the like on surface skins or shells of expandable microballoons (which are unexpanded and are filled with an expanding agent) and then causing the unexpanded microballoons. The microballoons with the inorganic filler fixed on the surface skins or shells involve drawbacks such that they are lowered in collapse strength and the non-flying property is imparted at the cost of their performance as a material intended to achieve a weight reduction.
A further approach has also been proposed including, for example, the processes disclosed in JP 4-178442 A and JP 7-196813 A. Each of these processes features expansion of expandable microballoons in a wetting agent. According to the former process, a slurry with expandable microballoons dispersed in a plasticizer is heated to have the expandable microballoons expanded, and subsequent to cooling the expanded microballoons with a fresh supply of the plasticizer as needed, an excess portion of the plasticizer is removed to obtain wet microballoons. According to the latter process, on the other hand, a slurry—which is composed of expandable microballoons and a plasticizer and has been heated to a temperature close to a temperature at which the expandable microballoons start expansion—and a wetting agent (free of expandable microballoons)—which has been heated to the expansion starting temperature of the expandable microballoons—are mixed to have the expandable microballoons instantaneously expanded, and the thus-expanded microballoons are cooled to obtain wet microballoons.
These conventional processes will be described in further detail. The process disclosed in JP 4-178442 A comprises dispersing, in the form of a slurry, expandable microballoons in a wetting agent, heating the slurry until expansion to have the expandable microballoons expanded, adding a plasticizer for cooling purpose, and finally removing an excess portion of the plasticizer to obtain wet microballoons.
A problem associated with the above-described process is that, because the thermal conductivity of those expanded earlier among expandable microballoons upon expansion under heat becomes extremely low, the heating of the expandable microballoons is prevented to result in a state in which expandable microballoons in an unexpanded form and over-expanded microballoons exist in a mixed state, thereby making it difficult to obtain uniform microballoons. There is another problems in that in the cooling step, the efficiency of heat removal is too low to achieve uniform cooling.
Non-flying microballoons are obtained through the removing step of a wetting agent. As the microballoons have a large surface area and the wetting agent is viscous, it is very difficult to efficiently remove the wetting agent to a target level. Even after the removal of the wetting agent, an excess wetting agent, therefore, remains on the surfaces of the microballoons. This leads to a significant handling problem such that the microballoons have pronounced stickiness and tend to form agglomerates.
On the other hand, the process disclosed in JP 7-196813 A comprises preheating a slurry, in which expandable microballoons are dispersed in a wetting agent, until immediately before expansion; bringing the thus-preheated slurry and a wetting agent, which as a heat source needed for expansion, has been heated to a temperature higher than an expansion temperature, into contact with each other to instantaneously complete the expansion; and then immediately cooling the thus-expanded microballoons in air to obtain microballoons in a form prevented from flying.
This process does not include any factor or cause for the impairment of heat conduction, which is one of the drawbacks of the former process, and therefore, can avoid localized over-heating. Moreover, owing to the use of a wetting agent in a small proportion, cooling is facilitated. It is, therefore, possible to avoid abnormal expansion of expandable balloons and collapse of microballoons, which would otherwise occur due to bursting. Further, occurrence of fusion agglomeration of microballoons themselves can be lessened. However, it is the problems of this process that, because the resin shells forming the expandable microballoons may undergo swelling during the preheating in the wetting agent, a limitation is imposed on the combination of the wetting agent and the resin making up the shells of the expandable microballoons and the preheating has to be conducted at a temperature lower than the expansion starting temperature to avoid the swelling of the resin shells.
As the preheating temperature is lowered, it is necessary either to raise the temperature of the wetting agent as the heat source or to increase the amount of the wetting agent to be used. Because of a deterioration of the wetting agent by heat or safety consideration in the former process and because of the need for the use of the wetting agent in a large amount in the latter process, the wetting agent is obviously used in an amount greater than that needed for effectively preventing flying of microballoons. As a consequence, the microballoons have strong stickiness and tend to form agglomerates, thereby developing inconvenience or a problem in handling.
To form commercially-available, expandable microballoons into a high-flowability slurry in a wetting agent, the wetting agent is usually employed in a proportion 1.5 to 3 times as much as the weight of the expandable microballoons. To this dispersed slurry, a heating, wetting agent as a heat source for having the expandable microballoons expanded is added in substantially the same weight to have the expandable microballoons expanded, so that non-flying microballoons are obtained. As the wetting agent as the expanding heat source has to concurrently heat the wetting agent which forms the dispersed slurry, the wetting agent as the expanding heat source must be added in an amount sufficient to provide heat in a quantity many times over that basically required only for the expansion of the expandable microballoons. Therefore, the wetting agent as the heat source is used in a weight proportion at least 3 times, generally about 5 times as much as the expandable microballoons.
This means that the wetting agent is used in an amount greater than that needed for the prevention of flying of microballoons

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