JP2000239657A - Method for dustproof treatment of dust-raising powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically advantageously restore or improve in a relatively simple step a dustproofing performance of a dust-raising powder deteriorated while transported. SOLUTION: A fibrillative polytetrafluoroethylene is previously incorporated into a dust-raising powder to be dispersed therein thereby giving an initial mixture, which is, after transported by a transporting apparatus, subjected to a compression/shearing process under a temperature condition to fibrillate the fibrillative polytetrafluoroethylene. The fibrillative polytetrafluoroethylene in the initial mixture can be partially fibrillated or unfibrillated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing dust of powder such as cement which is easily scattered during handling, transportation or storage.

[0002]

2. Description of the Related Art Conventionally, as a technology for preventing powder of cement or the like which is easily scattered during handling, transportation or storage, fibrillating polytetrafluoroethylene (hereinafter referred to as poly) has been used as dust generating powder. Tetrafluoroethylene to P
A technique has been developed which suppresses dust generation by fibrillating fibrillable PTFE by adding PTFE (referred to as TFE) and stirring to apply compression and shearing force.

[0003] Fibrillable PTFE is mixed with a powdered material, and the mixture is compressed at a temperature of 20 to 200 ° C.
Japanese Patent No. 923258 (Japanese Patent Publication No. 52-32877) discloses a technique in which PTFE is fibrillated by applying a shearing action to suppress generation of dust from a powdery substance.

Japanese Patent No. 1843274 (Japanese Patent Publication No. 5-24872) contains 0.01 to 1.0 parts by weight of fibrillated PTFE per 100 parts by weight of powder containing Portland cement as a main component. There is disclosed a cement-based powder composition having good dispersibility, characterized in that: This is mainly for the purpose of uniformly dispersing water when water is added to cement, but also has a secondary effect of preventing dust generation of cement.

[0005] As described above, it is possible to prevent the generation of dust by subjecting cement powder and the like to dustproofing based on the technology disclosed in Japanese Patent Publication No. 52-32877 and Japanese Patent Publication No. 5-24872. It is possible.

A drawback of the above-mentioned method of dust-proofing with a PTFE fibril net is that the dust-proofing performance is reduced when the dust-treated powder product is transported using a commonly used powder transport device. When using a transport device such as a belt conveyor that does not apply a strong external force to the powder, the reduction in dustproof performance is slight, but for example, pressure or suction transport by a pneumatic transport device, or a screw conveyor or chain conveyor is used. When transported after being transported, the tendency of the dustproof performance to decrease is noticeable. This is due to the force received when the powder particles collide with the outer wall of the transport pipe at high speed, or a part of the PTFE fibril is torn due to the effect of excessive kneading force, or a part of the powder particle is detached from the PTFE fibril net. It is presumed to be. Therefore, in the on-site transportation process of the dust-proof powder product, there is a problem that a low-speed transportation device such as a belt conveyor which does not apply a strong external force to the powder has to be used, and the transportation efficiency is poor.

[0007]

The problem to be solved by the present invention is to recover the dust-proof performance of the dust-producing powder having reduced dust-proof performance during transportation in a relatively simple process and economically advantageously. Another object of the present invention is to provide a dust-proofing method for improving dust-proofing.

[0008]

According to the dust-proofing method of the present invention, a fibrillating polytetrafluoroethylene is previously dispersed in a dust-producing powder at a place where the dust-producing powder is produced. An initial mixture containing the mixture is prepared, and after the mixture is transported by a transportation device, the mixture is subjected to a compressive / shearing action under a temperature condition at which the fibrillable polytetrafluoroethylene is fibrillated.

The fibrillating PTFE in the initial mixture in which the fibrillating PTFE is dispersed and contained in the dusting powder
Is in a partially fibrillated state (first embodiment)
Or an unfibrillated state (second embodiment). In the first embodiment, fibrillating PTFE is added to the dusting powder at the place where the dusting powder is produced, and the temperature at which the fibrillating PTFE fibrillates, specifically 20 ° C to 200 ° C. C., preferably at 40 to 180 ° C., more preferably at 50 to 150 ° C. for an appropriate period of time (described later) by stirring.
Partially fibrillated TFE (primary fibrillation)
After preparing the prepared initial mixture and transporting the initial mixture by a transportation device, the temperature at which the fibrillable PTFE is fibrillated at the place of use or the relay station after transportation, specifically 20 ° C to 200 ° C, preferably 40 ° C ~ 180
The mixture is stirred again for an appropriate period of time at a temperature of 50 ° C., more preferably 50 to 150 ° C., to give a compression / shear action (secondary fibrillation). In a second embodiment, at the place of production of the dusting powder, the dusting powder is added with fibrillating PTFE.
Is added at a temperature at which the fibrillating PTFE does not fibrillate, specifically, under stirring at a temperature of less than 20 ° C. to prepare an initial mixture dispersed and contained, and after transporting this initial mixture by a transport device, The temperature at which the fibrillable PTFE fibrillates at the place of use or the relay station after transportation, specifically 20 ° C to 200 ° C, preferably 40 ° C.
The mixture is agitated appropriately at a temperature of from 180 to 180 ° C, more preferably from 50 to 150 ° C, to give a compressing / shearing action.

The PTFE used here is disclosed in US Pat.
It is a fibrillable product produced by an emulsion polymerization method as described in No. 59752, and any of an emulsion type or a powder type can be used.

The partially fibrillated (primary fibrillated) PTFE in the first embodiment is
This refers to PTFE in which the above-mentioned PTFE is partially fibrillated and still has room for fibrils to occur. Specifically, PTFE is added to the dust generating powder,
When subjected to compression and shearing at a temperature of 0 to 200 ° C, preferably 40 to 180 ° C, more preferably 50 to 150 ° C,
Initially, there is a stage where fibrils develop rapidly and dust generation of powder rapidly decreases, and then a plateau state with little improvement in dust prevention effect is reached, and finally a stage where re-dusting phenomenon is seen Reach. Partially fibrillated PTFE can be said to be a state of PTFE contained in dust-protected powder before and after the inflection point reaching the plateau state. The fibrillation state of the PTFE varies depending on the type of the stirrer giving the compression / shearing action, the stirring temperature and the stirring time. The appropriate stirring time for practicing the invention is
The relationship between the agitation time and the amount of dust generated at a specific temperature using an actual device can be obtained, and the relationship can be empirically determined as the time required to reach an inflection point at which a plateau state with little improvement in dust prevention effect is obtained. When the temperature is low, the stirring time is long, and when the temperature is high, the stirring time is short.

According to this method, an external force is applied such that a part of the PTFE fibril is torn during transportation of the dust-proof powder product or a part of the powder particle is detached from the PTFE fibril net. The non-fibrillated PTFE or the partially fibrillated P dispersed and contained in the dust-generating powder can be used without adding additional PTFE.
It is possible to make the dust-producing powder dust-proof by fibrillating or re-fibrillating TFE. Furthermore, during transportation such as when loading powder or bulk loading on trucks, in the final stage, for example, dust-proofing treatment to apply compression and shearing action by using a heated screw conveyor and loading operation can be performed simultaneously, There is also an advantage that it is not necessary to add a new step for dustproofing.

The equipment used when re-fibrillating (secondary fibrillation) the partially fibrillated PTFE is performed when the PTFE produced by the above-mentioned emulsion polymerization method is first fibrillated (primary fibrillation). It is desirable to use a device having a different mechanism from the device used. This is because refibrillation by a device having a different mechanism has a higher dustproof effect than using a device having the same mechanism.
That is, when the dust-producing powder is prevented by partially fibrillating (primary fibrillation) PTFE using a pug mill, the use of pug milling in the refibrillation (secondary fibrillation) treatment is more difficult. Also, there is a phenomenon that the use of a screw conveyor of a different mechanism has a higher dustproof effect.

As described above, fibrillated PTFE particles are formed into fibrils by compression / shearing force at an appropriate temperature as described above, but if an external force is applied excessively, the fibril has an aspect ratio (fibril length / cross-sectional area). ) Becomes large, and eventually the fibril diameter becomes too thin and ruptures, so that the fibril loses its ability to capture dusting powder. Microscopically speaking, all fibrillable P
Fibrillation of TFE particles does not occur simultaneously; some particles start fibrillation immediately after stirring starts, some particles begin to fibrillate with a delay, and some particles have not yet been fibrillated. Coexist. When the stirring is further continued, the fibril generated beforehand, the generation of new fibrils, and the non-fibrillated PTFE coexist. These are in a state of equilibrium is the above-mentioned plateau state. Fibril formation temperature is generally 20 to 200 ° C., but the generated fibrils are relatively hard and brittle at room temperature,
It is easily broken even with a small aspect ratio. It is presumed that the fact that the product is easily torn even under a slight external force at room temperature after the first fibrillation treatment even at a normal temperature given during short-distance transportation of the treated product may be a cause of a decrease in dustproof performance during transportation.

Therefore, the temperature at which the compressing / shearing action is applied for the secondary fibrillation (refibrillation of partially fibrillated PTFE) in the first embodiment is 40 to 180.
° C, preferably 50 to 150 ° C. According to the test results described below, at 20 ° C., no recovery or improvement of the dustproof performance was observed, while at 200 ° C., a decrease in the quality of the dust-producing powder such as pseudo-coagulation of cement was observed. In the second embodiment, the temperature at which the compression and shearing action is performed to fibrillate the unfibrillated PTFE in the final stage may be the same.

The content of PTFE is desirably 0.01 to 0.5 parts by weight per 100 parts by weight of the dusting powder. When the content of PTFE is less than 0.01 part by weight, sufficient dustproof performance cannot be obtained, and when the content is more than 0.5 part by weight, a phenomenon in which the dust-forming powder is solidified in a marshmallow shape is observed. At the place of use, it is also possible to newly add the same or different dusting powder. At this time, it is preferable to add a relatively large amount of PTFE in the first fibrillation treatment.

Although the method of the present invention can be applied to any dusting powder, particularly suitable powders are those which are produced in large quantities and which are to be transported in large quantities by ships, wagons or automobiles. There, for example, cement powder, slaked lime powder, quicklime powder, calcium carbonate powder, slag powder, fly ash,
There are talc and plaster.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a process explanatory view in which the dustproofing method of the present invention is applied to Portland cement manufactured at a cement factory.

In the Portland cement manufacturing process, the clinker that has been calcined is quenched by air, and after adding additives such as gypsum, pulverized by a finishing mill and adjusted for particle size. Has a residual heat of about 100 ° C. The fibrillating PT is added to the high-temperature cement 10 from the PTFE hopper 11.
When FE was added, and a compressive / shearing action was given by mixing and stirring using the mixer 13, fibrillation of PTFE proceeded, and the majority of the cement particles were captured by the net of partially fibrillated PTFE fibrils. A dustproof cement is obtained.

The fibrillating PTFE added here
The optimal amount depends on various conditions such as the dustproof treatment temperature, the structure of the mixer that gives compression and shearing, and the addition method.
In the case of the present embodiment, 0.0
3 parts by weight of fibrillable PTFE were added.

In this embodiment, the emulsion type trade name "Teflon (registered trademark) K-20" is used as the fibrillating PTFE, but the powder type trade name "Teflon (registered trademark) K-10" is used. ] Can also be used.

In the present embodiment, cement having a residual heat of 100 ° C. is used. However, in the case of a cement product having a lowered temperature, quick lime in the hopper 14 and water in the hopper 12 are mixed into the mixer 13. A method of adding and raising the temperature by the heat of the hydration reaction or a method of raising the temperature by a heating device can also be adopted.

In the present embodiment, the compression and shearing action is given by using the mixer 13.
The suitability of the mixer varies depending on the form of the PTFE, the method of raising the temperature, the amount of water added, and the like.
It is desirable to select a mixer having high fibrillation efficiency from a pan mixer, a two-axis bag mill mixer, a roller mixer, and the like. When using a roller mixer,
Since the cement powder can efficiently receive a composite action such as a compressing action, a shearing action, and a rolling action between the roller and the bottom surface of the mixer, the cement powder is suitable for dust-proofing the cement in which the amount of added water is to be minimized.

The dust-proof cement produced in the mixer 13 by the above-described process is stored in the product silo 16 via the chain conveyor and the bucket elevator 15, and then the cement tanker 18 or the cement tanker 18 via the pressure feed pipe 17 by air pressure. It is transported and loaded on a cement transport vehicle 19, transported in bulk to these destinations by these ships or vehicles, and again transported to the product silo 21 of the relay station via the pressure pipe 20 by pneumatic transport.

Thereafter, the dust-proof cement is applied to the product silo 21.
Through a chain conveyor and a belt conveyor 22 and subjected to a compressing / shearing action under heating by a heating screw conveyor 23, and then leave it unpackaged or packed in a fixed amount, and then transport it to a destination by a cement transport vehicle 24. Transported to Due to several degrees of pneumatic and high-speed transportation from the production of this dustproof cement to the shipment of the product,
A part of the TFE fibril may be torn or a part of the powder particles may be detached from the PTFE fibril net, and the dust-proof performance may be remarkably reduced. Heating and compression
Due to the shearing action, the partially fibrillated PTFE contained in the dust-proof cement is refibrillated, and the detached cement particles are recaptured by the fibril net.
The dustproof performance of the dustproof cement will be restored or improved.

In the above embodiment, the case where the dustproof cement produced at the production site passes through the relay station has been described. However, there is a case where the dustproof cement is directly transported from the production site to a large consumption site, for example, a dam construction site. In that case, the second fibrillation process may be performed at the dam construction site that is the place of use.

As described above, in this embodiment, 100
Fibrillable PTF to cement with residual heat of about ℃
After the addition of E and compression / shearing action in the mixer 13 to produce a dustproof cement in which the cement particles are captured by a net of partially fibrillated PTFE fibrils, a slight external force applied during short-distance transport of the treated product The decrease in dustproof performance during transportation, which is presumed to be caused by the heating and compression / shear action in the heating screw conveyor 23, causes the partially fibrillated PTFE to refibrillate, and the dustproof performance of the dustproof cement is recovered or improved. The effect occurs.

Another advantage of the present invention is that a new PTF
It is possible to recover and improve the dustproof performance in the process of transporting the dustproof cement without adding E and without adding a new dustproof treatment facility. This means that if the screw conveyor is provided with a heating device, the performance of the dust-proof cement can be easily restored even at a construction site, for example.

In the above embodiment, an example is described in which the dust-proofing method of the present invention is applied to a cement having a dust-generating property. However, the present invention is not limited to these, and therefore, the present invention is not limited thereto. It can be widely used for dusty powders.

[0030]

COMPARATIVE EXAMPLE 1 A cement having a residual heat of about 100 ° C. was stirred by a mixer 13 and 100 parts by weight of PTF was added to the cement.
E Fibrillating PTF at a solids content of 0.03 parts by weight
The dustproof cement treated by adding E emulsion is
After being housed in the product silo 16 via the chain conveyor and the bucket elevator 15, it was transported to the cement transport vehicle 19 via the pumping pipe 17 by pneumatic feeding. Then, the product was transferred from the cement transport vehicle 19 to another product silo 21 again by pneumatic pressure via the pumping pipe 20. Powder was collected at five points in this process, and the amount of dust generated was measured. Table 1 shows the measurement results. The amount of dust generated was determined by dropping 200 g of the sample from the top input port of a cylindrical container having an inner diameter of 39 cm and a height of 59 cm, and floating dust (relative concentration CP) in the container at a height of 45 cm from the bottom.
M: Count Per Minute) was measured with a scattered light digital dust meter.

[0031]

[Table 1]

As can be seen from Table 1, the dust, which is a dust-producing powder, is subjected to a dust-proofing process, and the amount of the generated dust is reduced. As the amount of dust increases, the dustproof performance of the dustproof cement is significantly reduced. This indicates that some of the fibrils have been torn or some of the cement particles have detached from the PTFE fibril net.

[0033]

EXAMPLE 1 Cement having a reduced dust-proof performance obtained by the process of Comparative Example 1 was used for a chain conveyor and a belt conveyor 22.
, And transferred to a heating screw conveyor 23, and subjected to a compression / shearing action while heating on the conveyor. The heating temperature at this time is 20 ° C., 50 ° C., 75 ° C., 100 ° C., 1
Table 2 shows the results of investigating the dustproof performance and pseudo-coagulation of the six types of dustproof cements which were set at 50 ° C. and 200 ° C. and treated at each temperature, and performed a comprehensive evaluation. The dust-proof performance was evaluated as ◎ when the amount of dust generated was less than 50 cpm, ○ when 50 to 150 cpm,
Greater than 0 cpm was represented by x. False coagulation indicates that the penetration degree of the bigger needle is less than 6 to 10 mm.
The super evaluation was indicated by x, the overall evaluation was indicated by ◎, the excellence was indicated by ○, and the conventional level was indicated by Δ.

[0034]

[Table 2]

As can be seen from Table 2, the heating temperature is 50 ° C.
If the temperature is lower, no recovery of the reduced dustproof performance is observed after the dustproof treatment, and if the temperature is higher than 150 ° C., false setting of the cement occurs. Thereby, it was confirmed that the reprocessing heating temperature for the dust-proofed cement was in the optimum range of 50 to 150 ° C.

[0036]

Example 2 A cooled cement at 15 ° C. was treated under the same conditions and with the same amount of fibrillating PTFE emulsion as in the comparative example, but the product at this time had a low processing temperature and the fibrillating PTFE was fibrillated. The amount of dust generation was 787 cpm which was the same as that of the original cement. This cement was subjected to a compressive / shearing action at a temperature of 75 ° C. in the same apparatus as in Example 1 via the same route as the comparative example. The amount of dust generated from this cement was 41 cpm.

[0037]

After the dust-proof treatment, the dust-proof performance of the dust-producing powder having reduced dust-proof performance during transportation by the transportation device can be recovered or improved economically and advantageously in a relatively simple process.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing an embodiment of a dustproofing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cement hopper 11 PTFE hopper 12 Water hopper 13 Mixer 14 Quicklime hopper 15 Chain conveyor and bucket elevator 16 Product silo 17 Pumping pipe 18 Cement tanker 19 Cement transport vehicle 20 Pumping pipe 21 Product silo 22 Chain conveyor and belt conveyor 23 Heating screw conveyor 24 Cement transport vehicle

 ──────────────────────────────────────────────────の Continuing from the front page (71) Applicant 000174851 Mitsui-Dupont Fluoro Chemical Co., Ltd. 1-18-18 Sarugaku-cho, Chiyoda-ku, Tokyo Central Research Institute of Cement Co., Ltd. (72) Inventor Teruo Urano 775-3, Ishizuka-cho, Sano City, Tochigi Pref. 1397-3 Hatsuzawa-machi, F-shi F-term (reference) 4J100 AC26P CA01 EA17 FA20 JA00 JA28

Claims (4)

[Claims] 1. An initial mixture in which fibrillating polytetrafluoroethylene is dispersed and contained in a dusting powder in advance is prepared, and the mixture is transported by a transporting device, and then the fibrillating polytetrafluoroethylene is fibrillated. A dust-proofing method for a dust-producing powder, wherein the mixture is subjected to a compressive / shearing action under a temperature condition. 2. The transportation device according to claim 1, wherein the transportation device is a pneumatic transportation device.
3. The dust-proofing method for dust-producing powder described in 1. above. 3. The dust-proofing method for dust-generating powder according to claim 1, wherein the conveying device is a rotary screw conveyor. 4. The method of claim 1, wherein the conveying device is a chain conveyor.