Method for producing polyolefin powder

Abstract

This invention provides a method for producing fine polyolefin powder in micrometer units, characterized by uniform particle shape, average particle size, and particle size distribution. [Solution] This invention relates to a method for producing polyolefin ultrafine powder and the polyolefin ultrafine powder produced thereby. Specifically, the method involves mixing and heating a polyolefin resin with a xylene mixed solvent to produce a polyolefin molten liquid, then cooling and crystallizing it, and then ultrafine grinding the crystallized reactant through a vacuum wet grinding step and a dry grinding step, in which wet grinding and drying are performed simultaneously with the solvent, thereby providing an ultrafine polyolefin powder with an average particle size of approximately 30 μm or less. A xylene mixed solvent is used as the mixed solvent for melting the polyolefin resin, and the ultrafine polyolefin powder produced thereby can be applied to general-purpose material fields such as construction, civil engineering, and chemical products, and has physical properties that are particularly advantageous for the manufacture of secondary battery electrodes.

Description

Technical Field

[0001] The present invention relates to polyolefin powder having a small and uniform size at the micrometer level and a method for producing the same. The polyolefin powder according to the present invention has an average particle size and physical properties that can be usefully used not only in general-purpose material fields such as construction, civil engineering, and chemical products but also in the production of secondary battery electrodes.

Background Art

[0002] Polyolefin-based polymer resins such as polypropylene (PP) and polyethylene (PE) are one of the typical general-purpose plastic materials that are widely used in various applications such as films, sheets, tubes, and fibers because of their low price and easy processing.

[0003] Techniques for micronizing such general-purpose polyolefin-based polymer resins to a size in the micrometer range and applying them to new fields have attracted attention.

[0004] As a method for producing existing polyolefin resins into powder, a method has been used in which pellet-shaped resins with a size of 3 to 5 mm are put into a certain pulverizer equipped with a cutter blade, and the powder is obtained by repeating cutting, impact, and abrasion by high-speed rotation. However, unlike metals and inorganic substances, polyolefin-based resins, which are plastic elastomers, are not easily mechanically pulverized due to their specific viscoelasticity, and it is difficult to produce fine particles having a size in the micrometer range, and there is also a problem of low production yield.

[0005] Particularly in the case of polypropylene, since powder of a desired size cannot be obtained by ordinary mechanical pulverization, a cryogenic pulverization method in which a polypropylene resin is cooled below its brittle temperature using liquid nitrogen, dry ice, etc. and then pulverized has been used. However, in the case of powder produced by such a cryogenic pulverization method, there are still drawbacks such as a large particle size, a non-uniform particle size distribution, irregular particle shapes, and high production costs.

Prior Art Documents

[0006] [Patent Document 1] Republic of Korea Registered Patent No. 10-1418786 (July 7, 2014) [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the problems of the prior art and provide a method for producing fine polyolefin powder in the micrometer range, in which the particle shape, average particle size, and particle size distribution are uniform.

[0008] To achieve this, a polyolefin molten liquid is produced by mixing a xylene mixed solvent adjusted to have a specific composition ratio with a polyolefin resin raw material, followed by crystallization and chemical grinding, and then a mechanical grinding process under optimal conditions. This process allows for the production of ultrafine polyolefin powder with an average particle size in the micrometer range, approximately 30 μm or less. [Means for solving the problem]

[0009] One embodiment of the present invention, which can solve the problems of the conventional technology described above, provides a method for producing polyolefin ultrafine powder, comprising: a melting step of mixing a polyolefin resin and a xylene mixed solvent and then heating to produce a polyolefin molten liquid; a crystallization step of cooling the polyolefin molten liquid to produce a crystallized mixture; a vacuum wet grinding step of stirring under reduced pressure conditions so that the crystallized mixture obtained in the crystallization step can be ground and dried simultaneously; and a fine grinding step of dry grinding the powder ground by vacuum wet grinding to grind it to an average particle size of 30 μm or less.

[0010] The polyolefin resin is preferably polyethylene and / or polypropylene.

[0011] The xylene mixed solvent may include xylene; a C6-8 aromatic component comprising ethylbenzene, benzene, and toluene, but not xylene; and a non-aromatic component not included in xylene and the C6-8 aromatic component. The xylene mixed solvent may contain a C6-8 aromatic component in an amount of less than 80 wt%.

[0012] Furthermore, it is even more preferable that the stirring speed in the reduced-pressure wet grinding stage exceeds 380 rpm, the gauge pressure in the reduced-pressure wet grinding stage is -0.05 to -0.1 MPa, and the heating temperature in the melting stage is 120 to 140°C.

[0013] The aforementioned grinding step may be performed once or repeated at least two or more times.

[0014] Another embodiment of the present invention is polyolefin ultrafine powder, in which the average particle size of the polyolefin ultrafine powder produced by the method described above and after undergoing the fine grinding step may be 30 μm or less.

[0015] Further embodiments of the present invention include secondary battery electrodes containing such polyolefin ultrafine powder. [Effects of the Invention]

[0016] The polyolefin ultrafine powder produced by the multi-stage polyolefin particle production method according to the present invention, which organically combines a chemical grinding process and a mechanical grinding process, has an average particle size in the micrometer range, particularly 30 μm or less, and a uniform particle size distribution. Therefore, it has the effect of being useful not only in general-purpose material fields such as construction, civil engineering, and chemical products, but also in the manufacture of secondary battery electrodes. [Brief explanation of the drawing]

[0017] [Figure 1] This diagram schematically illustrates the manufacturing process of polyolefin ultrafine powder according to one embodiment of the present invention.

Best Mode for Carrying Out the Invention

[0018] Before explaining the preferred embodiments of the present invention in detail below, it should be noted in advance that terms or words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that conform to the technical idea of the present invention.

[0019] Throughout this specification, when a part is said to "include" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0020] Throughout this specification, "%", which is used to indicate the concentration of a specific substance, means (weight / weight)% for solid / solid, (weight / weight)% for solid / liquid, and (weight / weight)% for liquid / liquid, unless otherwise specified.

[0021] Each step can be carried out in a different order from the described order, unless the context clearly specifies a particular order. That is, each step may be carried out in the same order as described, may be carried out substantially simultaneously, or may be carried out in the reverse order.

[0022] The embodiments of the present invention will be described below. However, the scope of the present invention is not limited to the following preferred embodiments, and those skilled in the art having ordinary knowledge in the technical field to which the present invention pertains can also implement various modified forms based on the content described in the specification.

[0023] The present invention relates to a method for producing polyolefin ultrafine powder, and provides a method that can produce polyolefin ultrafine powder having a micro-level ultrafine size and a uniform size, different from the conventional mechanical grinding method. The polyolefin ultrafine powder according to the present invention is also applicable to general-purpose material fields such as construction, civil engineering, and chemical products, and can be particularly usefully used in the production of secondary battery electrodes.

[0024] The method for producing polyolefin ultrafine powder according to the present invention includes a melting step of mixing a polyolefin resin and a xylene mixed solvent and then heating to produce a polyolefin melt; a crystallization step of cooling the polyolefin melt to produce a crystallization mixture; a reduced-pressure wet grinding step of stirring under reduced-pressure conditions so that the crystallization mixture obtained in the crystallization step can be simultaneously pulverized and dried; and a fine grinding step of dry-grinding the powder wet-grinded under reduced pressure to grind it to an average particle size of 30 μm or less.

[0025] The polyolefin resin may be polyethylene and / or polypropylene. For example, it can include at least one selected from low-density polyethylene, high-density polyethylene, linear low-density polyethylene, homopolypropylene, block polypropylene, and random polypropylene, and the polyolefin resins that can be used are not limited to these.

[0026] The xylene mixed solvent can include xylene; a C6-8 aromatic component containing ethylbenzene, benzene, and toluene but not containing xylene; and a non-aromatic component not contained in xylene and the aromatic component.

[0027] Xylene is a kind of aromatic hydrocarbon, has the same chemical structure as benzene, and is composed of three isomers. Although xylene is used as a solvent in various industries due to its high dissolving power, it has the drawback of a high evaporation rate.

[0028] The C6-8 aromatic component is an aromatic component having 6 to 8 carbon atoms, and is an aromatic substance that contains ethylbenzene, benzene, and toluene but does not contain xylene. That is, in this specification, the term "C6-8 aromatic component" means "an aromatic substance having 6 to 8 carbon atoms, which contains ethylbenzene, benzene, and toluene but does not contain xylene." The C6-8 aromatic component may contain ethylbenzene, benzene, and toluene, and as an example, the C6-8 aromatic component may consist of ethylbenzene, benzene, and toluene.

[0029] Such C6-8 aromatic components can be included in the xylene mixed solvent at a concentration of less than 80 wt%. Because the boiling point of the C6-8 aromatic components is relatively lower than that of xylene, if the C6-8 aromatic component content is 80 wt% or more, a problem arises in which the solubility of the C6-8 aromatic component in the polyolefin resin decreases during the process of mixing and heating the polyolefin resin and xylene mixed solvent at the melting stage.

[0030] Due to these issues, it is difficult to manufacture polyolefin ultrafine powder in the desired size, and problems may arise such as large particle size deviations and larger particle sizes in the powder. Therefore, it is preferable that the C6-8 aromatic component be included in the xylene mixed solvent at a concentration of less than 80 wt%.

[0031] The aforementioned melting step involves mixing the polyolefin resin with a xylene mixed solvent and then heating the mixture to produce a polyolefin molten liquid. The amounts of polyolefin resin and xylene mixed solvent mixed in this step are not particularly limited, and can be mixed in appropriate amounts with the xylene mixed solvent depending on the type and properties of the polyolefin resin.

[0032] At this stage, heating can be performed to melt the polyolefin resin, and the heating temperature can be 120 to 140°C. If heating is performed below this temperature, the polyolefin resin will not melt sufficiently, and if heating is performed above this range, the xylene mixed solvent will volatilize rapidly, changing the rheological properties, making it difficult to produce polyolefin ultrafine powder of a sufficiently fine size in subsequent steps. Therefore, it is preferable to perform the melting at the aforementioned temperature. At this stage, stirring can be performed to ensure uniform melting, and the stirring conditions are not particularly limited.

[0033] The crystallization step involves cooling the polyolefin molten liquid to produce a crystalline mixture. The cooling temperature is not particularly limited; for example, cooling can be carried out at 10 to 80°C. This cooling step causes the precipitation of polyolefin, allowing for the production of polyolefin powder. Stirring can be performed during this cooling stage, which can precipitate polyolefin powder of a more uniform size, and the stirring conditions at this time are not particularly limited.

[0034] The aforementioned vacuum wet grinding step involves stirring the crystallization mixture under reduced pressure conditions to simultaneously grind and dry the crystallization mixture. Through this step, the solvent contained in the crystallization mixture evaporates, yielding polyolefin powder.

[0035] At this stage, stirring is performed to promote the evaporation of the solvent while uniformly adjusting the size of the resulting polyolefin powder. The stirring speed may exceed 380 rpm, preferably 480 rpm or higher, and more preferably 580 rpm or higher.

[0036] If the stirring speed is too slow, a sufficiently uniform polyolefin powder may not be obtained at this stage, and the particle size of the polyolefin powder obtained in the final stage may become several hundred microns, potentially making it impossible to produce ultrafine powder. Therefore, it is preferable to stir under the stirring conditions described above.

[0037] At this stage, stirring can be carried out under reduced pressure, thereby rapidly evaporating the xylene mixed solvent and producing a more effective ultrafine powder. The reduced pressure conditions at this time are preferably a gauge pressure of -0.05 to -0.1 MPa; if the pressure falls outside this range, it becomes difficult to produce polyolefin ultrafine powder of sufficiently small and uniform size.

[0038] After this vacuum wet grinding step, if residual solvent remains, a drying step can be performed to remove the solvent, and the drying method in this step is not particularly limited.

[0039] Next, the powder that has been wet-ground under reduced pressure is subjected to a dry grinding step to finely grind the powder so that the average particle size is 30 μm or less. In this step, the powder is ground using a cutter blade that rotates at high speed under dry conditions completely free of water or solvent. Through this step, an ultrafine polyolefin powder with an average particle size of 30 μm or less can be produced.

[0040] At this stage, in order to produce the ultrafine powder with the aforementioned particle size, the rotation speed of the cutter blade is preferably 3,000 to 6,000 rpm, the internal temperature of the pulverizer is preferably 30 to 60°C, and the raw material input rate may be 30 to 60 g / min. This fine grinding step may be performed once or repeated two or more times.

[0041] Through this process, an ultrafine polyolefin powder with an average particle size of 30 μm or less can be produced. Unlike conventional methods, the method for producing ultrafine polyolefin powder according to the present invention can produce an ultrafine polyolefin powder with a very fine and uniform average particle size, and has the advantages of not being difficult to manufacture and having excellent productivity and yield.

[0042] This invention includes an ultrafine polyolefin powder with an average particle size of 30 μm or less, produced by the method described in one embodiment of the present invention. Furthermore, the present invention includes a secondary battery electrode containing the aforementioned ultrafine polyolefin powder.

[0043] The specific operation and effects of the present invention will be described below through one embodiment of the present invention. However, this is presented as a preferred example of the present invention, and the scope of the rights of the present invention is not limited by this embodiment.

[0044] [Example 1] [Manufacturing of polyolefin molten liquid]

[0045] In a 5L three-necked flask reaction vessel equipped with a stirrer, 10 wt% polypropylene (homoplypropylene with a specific gravity of 0.90) and 90 wt% xylene mixed solvent were added. The mixture was heated while stirring at a stirrer speed of 300 rpm, and the polypropylene was melted in the xylene mixed solvent at a temperature of 140°C for a residence time of 60 minutes to produce a polyolefin molten solution.

[0046] As the xylene mixed solvent, a mixed solvent containing 94.5 wt% xylene, 5.3 wt% C6-8 aromatic components (a mixture of ethylbenzene, benzene, and toluene), and 0.2 wt% non-aromatic components was prepared and used.

[0047] [Production of crystallized mixtures] The aforementioned polyolefin molten liquid was cooled to room temperature and subjected to a crystallization process to produce a crystalline mixture.

[0048] [Manufacturing of polyolefin powder] The crystalline mixture was pulverized in a vacuum chamber, and vacuum pulverization was performed, which simultaneously performed drying and wet pulverization. Inside the vacuum chamber, blades rotated to pulverize and dry the contents. During vacuum pulverization, the stirring speed was maintained at 580 rpm, and the pressure was -0.1 MPa gauge pressure for a residence time of 120 minutes, performing vacuum wet pulverization.

[0049] The pulverized material obtained through the aforementioned vacuum wet pulverization process was dried to remove any remaining xylene mixed solvent, and the polypropylene powder from which the xylene mixed solvent had been removed was then dry-pulverized to produce polypropylene ultrafine powder.

[0050] Dry grinding is a method in which raw materials are fed between a rotating body equipped with numerous cutter blades and a stationary body, and the raw materials are ground by the high-speed rotating cutter blades. Dry grinding was performed under the following conditions: rotation speed of 5,000 rpm, internal grinder temperature of 50°C, and raw material input rate of 50 g / min.

[0051] [Example 2] Polypropylene ultrafine powder was produced using the same process as in Example 1, except that the composition of the xylene mixed solvent was changed to 80.5 wt% xylene, 19.3 wt% C6-8 aromatic components, and 0.2 wt% of other non-aromatic components.

[0052] [Example 3] Polypropylene ultrafine powder was produced using the same process as in Example 1, except that the composition of the xylene mixed solvent was changed to 49.0 wt% xylene, 50.9 wt% C6-8 aromatic components, and 0.1 wt% of other non-aromatic components.

[0053] [Example 4] Polypropylene ultrafine powder was produced using the same steps as in Example 1, except that the composition of the xylene mixed solvent was changed to 35.0 wt% xylene, 64.9 wt% C6-8 aromatic components, and 0.1 wt% other non-aromatic components.

[0054] [Comparative Example 1] Polypropylene ultrafine powder was produced using the same process as in Example 1, except that the composition of the xylene mixed solvent was changed to 19.3 wt% xylene, 80.6 wt% C6-8 aromatic components, and 0.1 wt% of other non-aromatic components.

[0055] [Comparative Example 2] Polypropylene ultrafine powder was produced by the same process as in Example 1, except that the xylene mixed solvent was replaced with 100 wt% of a C6-8 aromatic component consisting of ethylbenzene, benzene, and toluene.

[0056] [Experimental Example 1] Using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern Panalytical), the particle size of the polypropylene ultrafine powders from Examples 1-4 and Comparative Examples 1 and 2, after dry grinding, was measured several times, and the particle size is shown in Table 1 in the form of "average particle size ± standard deviation". ("Mastersizer" and "Malvern" are registered trademarks of Malvern Panalytical Limited.)

[0057] [Table 1]

[0058] As can be seen in Examples 1-8 of Tables 1 and 2, it was confirmed that ultrafine polyolefin powder with an average particle size of 30 μm or less was produced by sequentially going through the chemical grinding (reduced pressure wet grinding) and mechanical grinding processes according to the present invention. In particular, it was confirmed that the average size of the final particles obtained through the same process increased as the content of C6-8 aromatic components increased during the process of producing the polyolefin melt for chemical grinding (see Examples 1-4).

[0059] Furthermore, it was found that in order to produce ultrafine polyolefin powder with an average particle size of 30 μm or less, the C6-8 aromatic component in the xylene mixed solvent must be less than 80 wt% (see Examples 1-4 and Comparative Example 1 in Table 1).

[0060] These results suggest that when the compositional components of the xylene mixed solvent include a high content of C6-8 aromatic components, such as ethylbenzene, benzene, and toluene, which have relatively lower boiling points than xylene, the dissolving power of the C6-8 aromatic components in the polyolefin resin decreases during the heating process in the melting stage of producing the polyolefin molten liquid.

[0061] In other words, the results in Table 1 show that the reduced dissolving power of the polyolefin melt resulted in an increase in the average particle size and the formation of a wider particle size distribution. Therefore, it was confirmed that for the production of ultrafine polyolefin powder with an average particle size of 30 μm or less, it is preferable that the content of C6-8 aromatic components in the xylene mixed solvent be 80 wt% or less.

[0062] [Examples 5-8] In the polyolefin melt production stage of Example 1, the polypropylene ultrafine powders of Examples 5 to 8 were produced by following the same process as in Example 1, while varying the amount of polypropylene and xylene mixed solvent added to the polyolefin resin as shown in Table 2 below.

[0063] The composition of the xylene mixed solvent used at this time was kept constant at 94.5 wt% xylene, 5.3 wt% C6-8 aromatic components, and 0.2 wt% other non-aromatic components.

[0064] [Comparative Example 3] Comparative Example 3 used the same proportions of polypropylene and xylene mixed solvent as in Example 5, but the composition of the xylene mixed solvent was changed to 19.9 wt% xylene, 80.0 wt% C6-8 aromatic components, and 0.1 wt% other non-aromatic components. Polypropylene ultrafine powder was produced in the same manner as in Example 5.

[0065] [Comparative Examples 4-6] Comparative Examples 4-6 used the same proportions of polypropylene and xylene mixed solvent as in Examples 6-8, but the composition of the xylene mixed solvent was changed as shown in Table 2 below to produce polypropylene ultrafine powder.

[0066] [Experimental Example 2] Using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern Panalytical), the particle size of the polypropylene ultrafine powders from Examples 5-8 and Comparative Examples 3-6, after dry grinding was completed, was measured several times. The particle sizes are shown in Table 2 in the form of "average particle size ± standard deviation".

[0067] [Table 2]

[0068] As can be seen in Table 2, the size of the final particles increased slightly as the polyolefin resin content increased, but it was confirmed that the xylene content in the xylene mixed solvent (i.e., C6-8 aromatic and non-aromatic components) had a greater influence. In particular, while Examples 5 to 8 could be produced as ultrafine powders with an average particle size of 30 μm or less, Comparative Examples 3 to 6 formed powders that were at least twice as large as those in the Examples. Therefore, it was confirmed that, similar to Experimental Example 1, it is preferable that the content of C6-8 aromatic components in the xylene mixed solvent be 80 wt% or less.

[0069] Furthermore, even if the content of C6-8 aromatic components is 80 wt% or less, if the polyolefin content is insufficient or the xylene mixed solvent content is excessive, the average particle size will increase and the production yield will decrease. Therefore, it was found that for the production of polyolefin ultrafine powder, it is preferable to use polyolefin resin in the range of 5 to 50 wt% and xylene mixed solvent in the range of 95 to 50 wt%. In particular, it was found to be even more preferable when the polyolefin resin and xylene mixed solvent are mixed in a weight ratio of 1:1 to 45.

[0070] [Examples 9 and 10] Using the same manufacturing method as that used for the polyolefin powder in Example 1, the polypropylene ultrafine powder of Example 9 was produced. However, the same polypropylene ultrafine powder as in Example 9 was produced, but the gauge pressure under reduced pressure conditions was changed to -0.05 MPa to produce Example 10.

[0071] [Comparative Examples 7-10] Comparative Example 7 produced the same polypropylene ultrafine powder as in Example 9, but with the vacuum removed during the vacuum wet grinding stage, while Comparative Examples 8, 9, and 10 produced polypropylene ultrafine powders with only the stirring speed adjusted to 380 rpm, 190 rpm, and 60 rpm, respectively.

[0072] [Experimental Example 3] Using a laser diffraction particle size analyzer (Mastersizer 3000, Malvern Panalytical), the particle size of the polypropylene powders from Examples 9 and 10 and Comparative Examples 7-10, which had undergone the vacuum wet grinding stage, and the particle size of the polypropylene ultrafine powders, which had undergone the drying and dry grinding stages, were measured multiple times and recorded in Table 3 in the form of "average particle size ± standard deviation".

[0073] [Table 3]

[0074] Referring to the experimental results in Table 3, it was confirmed that both the reduced pressure conditions and the rotational speed affected the final average particle size during the reduced-pressure wet grinding stage, with the effect of the rotational speed being more significant. In particular, when reduced pressure conditions were not applied, as in Comparative Example 7, the particle size increased by more than 1.5 times compared to Examples 9 and 10, where reduced pressure conditions were applied under the same conditions. This confirmed that reduced pressure conditions lower than atmospheric pressure (gauge pressure of -0.05 to -0.1 MPa) are necessary inside the reduced-pressure wet grinding chamber.

[0075] Furthermore, summarizing the results of Example 9 and Comparative Examples 8-10, it was confirmed that the final average particle size decreases as the rotation speed increases, so it is preferable that the rotation speed is at least 380 rpm or 480 rpm or higher, and most preferably 580 rpm or higher.

Claims

1. In a method for producing polyolefin powder, The melting step involves mixing polyolefin resin and a xylene mixed solvent, followed by heating to produce a polyolefin molten liquid; A crystallization step in which the molten polyolefin is cooled to produce a crystallized mixture; A vacuum wet grinding step in which the crystallized mixture obtained in the crystallization step is stirred under reduced pressure conditions so that grinding and drying can be performed simultaneously; and As the final step, the powder that has gone through the aforementioned vacuum wet grinding step is dry-ground to finely grind it down to an average particle size of 30 μm or less; A method for producing polyolefin ultrafine powder containing [the specified ingredient].

2. The method for producing polyolefin ultrafine powder according to claim 1, characterized in that the polyolefin resin is polyethylene and / or polypropylene.

3. The xylene mixed solvent is xylene; C6-8 aromatic components comprising ethylbenzene, benzene, and toluene, but not xylene; and Xylene and non-aromatic components not included in the C6-8 aromatic components; A method for producing polyolefin ultrafine powder according to claim 1, comprising:

4. A method for producing polyolefin ultrafine powder according to claim 3, wherein the xylene mixed solvent contains less than 80 wt% of the C6-8 aromatic component.

5. The method for producing polyolefin ultrafine powder according to claim 1, wherein the stirring speed in the vacuum wet grinding step exceeds 380 rpm.

6. A method for producing polyolefin ultrafine powder according to claim 1, wherein the gauge pressure in the reduced-pressure wet grinding step is -0.05 to -0.1 MPa.

7. The method for producing polyolefin ultrafine powder according to claim 1, wherein the heating temperature in the melting step is 120 to 140°C.

8. The method for producing polyolefin ultrafine powder according to claim 1, characterized in that the fine grinding step is performed once or repeated at least two or more times.

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