An expansion microsphere foaming screening device and its application

Abstract

The present invention provides a foaming and screening device for expandable microspheres, which comprises: a cavity composed of an annular infrared heater and a stainless steel metal collar; a discharge port pipe arranged at the upper end of the cavity; a metal screen arranged at the lower end of the cavity; a feeding device arranged on the side wall of the cavity; and an aggregate box and a micro-negative pressure air extraction device connected in sequence on the discharge port pipe. When using the foaming and screening device provided by the present invention to prepare expandable microspheres, the microsphere raw materials are conveyed into the cavity through the feeding device, start to foam under the irradiation of the infrared heater, and the micro-negative pressure air extraction device is turned on to ventilate so that there is a certain wind speed in the cavity. At this time, the expanded microspheres will be drawn out of the cavity along with the air flow and thus leave the heating area, and are collected in the aggregate box, while the unexpanded microspheres with a larger density or the microspheres with incomplete expansion will settle or suspend in the cavity, and the suspended microspheres will continue to expand until the density decreases and then are separated.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a foaming and screening device for expandable microspheres, and also relates to the use of the foaming and screening device in the preparation of expandable microspheres. Background Art

[0002] Unfoamed and foamed thermoplastic microspheres can be applied in various fields. For example, dry foamed microspheres can be used as sensitizers in emulsion explosives, or as lightweight fillers in solvent-based paints, coatings and various thermosetting plastics (such as artificial marble, polyester putty, artificial wood). Wet foamed microspheres, usually stored in the form of an aqueous suspension, can be applied in many products, such as water-based coatings, thermal printing paper, porous ceramics and emulsion explosives, etc.

[0003] Transporting foamed microspheres often requires a large amount of space. For this reason, end-users of foamed microspheres often purchase unfoamed expandable microspheres and foam them on-site or directly add the unfoamed expandable microspheres to the production process to prepare the final product.

[0004] Since the high temperature required for fully foaming the thermally expandable microspheres will cause problems such as caking due to the adhesion of the thermoplastic shells of the microspheres caused by foaming, it is necessary to provide a method and equipment for preparing foamed thermally expandable microspheres, in which the degree of foaming can be controlled, so as to make it possible to provide foamed microspheres with different densities. At the same time, they are simple, only require a small space, are relatively inexpensive, and are easy to use by end-users. Moreover, since the foamed microspheres are used in-situ, transportation space and costs are saved.

[0005] Many patents have mentioned methods and devices for foaming thermoplastic expandable microspheres. For example, US Patent Nos. US5484815 and US7192989 describe methods and devices suitable for foaming dry expandable microsphere powders. US Patent No. US 4513106 proposes a method and device suitable for foaming microsphere slurries. Its principle of action is to introduce steam into the expandable microsphere slurry and generate sufficient pressure to heat the microspheres so that they expand at least to a certain extent. Then, the slightly expanded microspheres leave the pressure area at a speed of at least 1 m / s, and due to the pressure reduction, the microspheres further expand. Although the method of foaming expandable microspheres in the form of a slurry proposed in US4513106 patent can solve the problem of a large amount of surrounding dust caused by directly foaming microsphere dry powder, the microsphere slurry foaming process described in US4513106 patent still needs to be further improved. EP0348372 discloses a process for preparing foamed thermoplastic microspheres, in which foaming occurs on a conveyor belt. The process operates well, but occupies a large space and is relatively expensive. US4722943 and US5342689 describe methods for foaming microspheres, in which the microspheres are mixed with a surface barrier coating to prevent caking during the drying step. However, the amount of processing aids, such as talc, is very high, which affects the possibility of rapid cooling. This also creates difficulties in controlling the degree of foaming of the microspheres. CN1882638B, CN101263183A, and CN1729087A describe methods for foaming microspheres. Similarly, the microspheres are mixed with a surface barrier coating to prevent caking during the foaming step. At the same time, the foaming device is complex to prepare. Summary of the Invention

[0006] To solve the above problems and drawbacks of the prior art, the object of the present invention is to provide a simple, practical and easy-to-operate foaming and screening device for preparing expandable microspheres. By using the foaming and screening device of the present invention, all microsphere foaming agent raw materials can be fully foamed. The foamed microspheres are separated and sucked out under a slightly negative pressure condition, and the unfoamed microspheres will be fully heated to foam and then sucked out, which can effectively prevent the problems of insufficient foaming or non-foaming of the microsphere foaming agent. At the same time, during the foaming process, some of the microspheres are in a suspended state in the air, avoiding the phenomenon of mutual adhesion or caking, improving the product quality, and can continuously and stably obtain pure foamed microspheres, ensuring the production efficiency.

[0007] The present invention is embodied by the following technical solutions:

[0008] The present invention provides a foaming and screening device for expandable microspheres. The device includes a cylindrical foaming cavity. The lower part of the cavity wall is an annular infrared heater, and the upper part is a stainless steel metal collar. The bottom of the cavity is a metal screen, which serves as a raw material carrier and an air inlet device. The top of the cavity is provided with a discharge port pipeline. The side wall of the cavity is connected to a feeding device, such as a screw conveyor feeding device. Further, a air volume control device is provided on the discharge port pipeline. Further, the discharge port pipeline is connected to a micro-negative pressure air extraction device, such as a fan, so that the less dense expanded microspheres can slowly rise in the expansion cavity and finally be sucked out. Further, an aggregate box for collecting the expanded microspheres is arranged between the discharge port pipeline and the micro-negative pressure air extraction device. A filter screen is radially arranged in the aggregate box to prevent the expanded microspheres from entering the micro-negative pressure air extraction device.

[0009] Preferably, the inner wall of the cavity is smooth.

[0010] Preferably, the metal screen is a stainless steel screen with a pore diameter less than 20μm.

[0011] Preferably, a vibrating device, such as an automatic vibrating device, is provided at the bottom of the metal screen. It strikes the metal screen once every 30s, and can strike the unfoamed microspheres sinking on the metal screen to suspension.

[0012] Preferably, the connection between the discharge port pipeline and the cylindrical barrel of the cavity is a frustum-shaped contraction section, and the bottom angle of the frustum is 45 - 60°. The discharge port pipeline and the cavity are connected through the frustum structure, so that the surface air velocity of the air flow in the pipeline will be gradually reduced through this structure, so as to achieve the effect of slow and uniform distribution of the air flow velocity rising inside the cavity.

[0013] Preferably, a recovery device is provided at the bottom of the metal screen. The unfoamed microspheres with smaller particle size pass through the metal screen and are recovered by the recovery device, and the unfoamed microsphere raw material with smaller particle size and uniform distribution can be obtained.

[0014] Preferably, a plurality of branch pipes are provided on the discharge port pipeline, and an air volume control device with different ranges is provided on each branch pipe.

[0015] Preferably, the air volume control system can make the surface air velocity in the cavity accurate to 0.1cm / s.

[0016] Compared with the prior art, the technology of the present invention has the following beneficial effects:

[0017] (1) The present invention adopts a micro-negative pressure air extraction device, so that the less dense expanded microspheres can slowly rise in the expansion cavity and finally be sucked out, so as to be fully heated and achieve the effect of complete expansion.

[0018] (2) The present invention can precisely control the wind speed, so that the foamed microspheres can be sucked out relatively quickly, while the unfoamed microspheres will stay at the bottom of the cavity or move upward slowly, thus having enough time to expand and finally be separated from the cavity.

[0019] (3) The present invention uses a metal dense screen as the carrier and air inlet device. The air flow passes through the small holes of the metal screen and becomes a uniform upward flow, driving the microsphere particles, so that the microspheres have good dispersibility in the system, and can effectively reduce the bonding phenomenon of the microspheres during the foaming process. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of a foaming and screening device according to an embodiment of the present invention. Detailed Embodiments

[0021] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0022] In one embodiment, the present invention provides a foaming and screening device for expandable microspheres as follows. The device includes a cavity 10 composed of an annular infrared heater 1 and a stainless steel metal collar 2; a discharge port pipe 4 is provided at the upper end of the cavity 10; a metal screen 7 is provided at the lower end of the cavity 10; a feeding device 6 is provided on the side wall of the cavity 10; a collecting box 11 and a micro-negative pressure air extraction device 12 are sequentially connected to the discharge port pipe 4.

[0023] When using the foaming and screening device provided in this embodiment to prepare expandable microspheres, the microsphere raw materials are transported into the cavity 10 through the feeding device 6, and foaming starts under the irradiation of the infrared heater 1. The micro-negative pressure air extraction device 12 is turned on to ventilate so that there is a certain wind speed in the cavity 10. At this time, the expanded microspheres will be drawn out of the cavity 10 by the air flow and thus leave the heating area and enter the collecting box 11; while the unexpanded microspheres with a larger density or the microspheres that are not fully expanded will settle or suspend in the cavity 10, and the suspended microspheres will continue to expand until the density decreases and then be separated.

[0024] In another embodiment, the present invention provides a foaming and screening device for expandable microspheres, which comprises a cavity 10 formed by an annular infrared heater 1 and a stainless steel metal collar 2; the upper end of the cavity 10 is connected to a frustum-shaped contraction section 3 and a discharge port pipe 4, and the bottom angle of the frustum is 45-60°, such as 60°; the bottom end of the cavity 10 is provided with a uniformly fine metal screen 7; the side wall of the cavity 10 is provided with a feeding device 6, and the feeding port of the feeding device 6 on the side wall is located above the infrared heater 1; the discharge port pipe 4 is successively connected with an aggregate box 11 and a micro-negative pressure air extraction device 12; a plurality of air volume control devices 5 are arranged on the discharge port pipe 4; a vibration device 8 and a fine material recovery device 9 are arranged at the lower end of the metal screen 7; a filter screen 13 is radially arranged inside the aggregate box 11; in practical applications, the rising speed of the expanded microspheres in the cavity 10 is adjusted by adjusting a plurality of air volume control devices 5.

[0025] When using the foaming and screening device provided in this embodiment to prepare expandable microspheres, the microsphere raw materials are conveyed into the cavity 10 through the feeding device 6, and foaming starts under the irradiation of the infrared heater 1. The micro-negative pressure air extraction device 12 is turned on to ventilate so that there is a certain wind speed in the cavity 10. At this time, the expanded microspheres will be drawn out of the cavity 10 along with the air flow and thus leave the heating area and enter the aggregate box 11. At the same time, due to the blockage of the filter screen 13 in the aggregate box, the expanded microspheres will not enter the micro-negative pressure air extraction device 12; while the unexpanded microspheres with a larger density or the microspheres with incomplete expansion will settle or suspend in the cavity 10. The suspended microspheres will continue to expand until the density decreases and then be separated. The settled microspheres will be suspended into the air under the action of the vibration device 8 and continue to be heated and expanded. When they are expanded to a certain extent, they will be separated.

[0026] When using the foaming and screening device provided in this embodiment to prepare expandable microspheres, the air volume is adjusted by the air volume control device 5, so as to control the expansion time and separation speed of microspheres with different properties in the system:

[0027] I. Turn on the feeding switch, turn on the infrared heating device, adjust the air volume in the cavity to reach 5.5 cm / s, the residence time of the microspheres in the heating area is about 32 s, the particle size of the expanded microspheres is 80-100 μm, and they are completely expanded.

[0028] II. Turn on the feeding switch, turn on the infrared heating device, adjust the air volume in the cavity to reach 14.0 cm / s, the residence time of the microspheres in the heating area is 11 s, the particle size of the expanded microspheres is 60-80 μm, and some microspheres are not completely expanded.

[0029] III. Turn on the feeding switch, turn on the infrared heating device, adjust the air volume in the cavity to reach 23.0 cm / s, the residence time of the microspheres in the heating area is about 3 s, the particle size of the expanded microspheres is 20-40 μm, and most microspheres are not completely expanded.

[0030] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as falling within the protection scope of the present invention.

Claims

1. A foaming screening device for expandable microspheres, characterized in that, it comprises: a cavity composed of an annular infrared heater and a stainless steel metal collar; a discharge port pipe provided at the upper end of the cavity; a metal screen provided at the lower end of the cavity, and a vibration device is provided at the lower end of the metal screen; a feeding device provided on the side wall of the cavity; and an aggregate box and a micro-negative pressure air extraction device connected in sequence on the discharge port pipe, a frustum-shaped contraction section is provided between the cavity and the discharge port pipe, and an air volume control device is provided on the discharge port pipe.

2. The foaming screening device according to claim 1, characterized in that, the bottom angle of the frustum of the frustum-shaped contraction section is 45 - 60°.

3. The foaming screening device according to claim 1, characterized in that, a fine material recovery device is provided below the metal screen.

4. The foaming screening device according to claim 1, characterized in that, the metal screen is a stainless steel screen with a pore diameter less than 20μm.

5. The foaming screening device according to claim 1, characterized in that, the feeding device is a screw conveyor feeding device.

6. The foaming screening device according to claim 1, characterized in that, a plurality of branch pipes are provided on the discharge port pipe, and an air volume control device is provided on each branch pipe.

7. The foaming screening device according to claim 1, characterized in that, a filter screen is radially provided inside the aggregate box, and the diameter of the filter screen is smaller than the diameter of the expanded microspheres.

8. The use of the foaming screening device according to any one of claims 1 to 7 in the preparation of expandable microspheres, characterized in that, the microsphere raw materials are conveyed into the cavity through the feeding device, start to foam under the irradiation of the annular infrared heater, turn on the ventilation to make the cavity have a certain wind speed, at this time the expanded microspheres will be drawn away from the cavity by the air flow and thus leave the heating area, and are collected in the aggregate box, while the unexpanded microspheres with a larger density or the microspheres with incomplete expansion will settle or suspend in the cavity, and the suspended microspheres will continue to expand until the density decreases and then are separated.

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