JP2015139861A - Coolant recycling method and recycled coolant intermediate product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coolant recycling method that enables silicon chip to be sufficiently separated from used coolant in a short period of time.SOLUTION: There is provided the coolant recycling method for separating silicon chip generated when a silicon material is cut, from a used coolant containing the silicon chip. The coolant recycling method comprises an addition step of adding a polymer coagulant to the used coolant so that the silicon chip may coagulate and a recycling step of obtaining a recycled coolant by separating the coagulated silicon chip.

Description

  The present invention relates to a coolant regeneration method and a regeneration coolant intermediate product. More specifically, the coolant regeneration method for separating the silicon cutting waste from the used coolant including the silicon cutting waste generated when the silicon material is cut to obtain the regenerated coolant, and the regeneration generated in the process of obtaining the regenerated coolant. It relates to a coolant intermediate product.

  Conventionally, silicon materials are used in various products such as semiconductor elements. The silicon material is generally in the form of a lump (silicon ingot) and is used after being cut into a size defined for each product. For the cutting of the silicon material, for example, a wire saw cutting device having an ultrafine wire is used. At this time, the coolant is used in combination so that the wire can smoothly cut the silicon material and efficiently remove the frictional heat generated during the cutting. The coolant is mainly composed of an organic solvent, and is continuously supplied to the contact portion between the wire and the silicon material to remove the generated frictional heat while smoothing the operation of the wire. The used coolant contains fine silicon chips generated when the silicon material is cut.

  The used coolant is reused to reduce costs. Specifically, silicon scraps are separated after the used coolant is collected. The used coolant from which the silicon chips are separated is reused as a regenerated coolant. Patent Document 1 proposes a technique for separating silicon cutting waste from used coolant using a separation facility (membrane filtration device).

JP 2011-173227 A

  However, fine silicon scraps are liable to cause problems in the separation equipment (for example, clogging of the filter in the membrane filtration device) and easily reduce the separation speed. Therefore, according to the technique disclosed in Patent Document 1, there is a problem that it takes a long time to sufficiently separate the fine silicon cuttings dispersed in the coolant.

  The present invention has been made in view of such conventional circumstances, and provides a coolant regeneration method and a regeneration coolant intermediate product capable of sufficiently separating silicon cutting waste from spent coolant in a short time. The purpose is to provide.

  The coolant regeneration method of one aspect of the present invention that solves the above-described problem is a coolant regeneration method that separates the silicon cutting waste from used coolant containing silicon cutting waste generated when the silicon material is cut. An addition step of adding a polymer flocculant to the used coolant so that silicon chips are aggregated, and a regeneration step of separating the aggregated silicon chips and obtaining a recycled coolant are included.

  According to such a coolant recycling method, the silicon cutting waste is agglomerated by the polymer flocculant in the addition step, and the diameter increases. Aggregated silicon chips are more easily separated from the used coolant by various separation methods (for example, a centrifugal separation operation and a filtration operation) than fine silicon chips before aggregation. As a result, according to the coolant regeneration method according to the present invention, it is easy to obtain a regeneration coolant. Moreover, according to the coolant regeneration method according to the present invention, the agglomerated silicon cutting waste is less likely to cause a malfunction of the separation equipment (for example, clogging of the filter in the filtration device) than the fine silicon cutting waste before aggregation. Therefore, according to the coolant regeneration method, the time required for regeneration is shortened.

  In the above configuration, the polymer flocculant is preferably a nitrogen-containing polymer flocculant containing nitrogen.

  According to such a configuration, the silicon cutting waste is easily aggregated. Therefore, the silicon cutting waste is easily separated from the used coolant in the regeneration process.

  In the above configuration, the nitrogen-containing polymer flocculant is preferably at least one of polyethyleneimine and polyacrylamide.

  According to such a configuration, the silicon cutting waste is more easily aggregated. Therefore, silicon cutting waste is easily separated from the used coolant in the regeneration process.

  The said structure WHEREIN: It is preferable that the said polymer flocculent is added so that it may become 100-2000 ppm with respect to the said used coolant.

  According to such a configuration, the silicon cutting waste is easily aggregated. Therefore, the silicon cutting waste is easily separated from the used coolant in the regeneration process.

  The said structure WHEREIN: The said reproduction | regeneration process contains at least any one process of a filtration process or a centrifugation process, The said filtration process filters the said used coolant, and is the process of isolate | separating into a filtrate and a concentrate. The centrifugation step is preferably a step of centrifuging the used coolant to separate it into a solid content and a diluent.

  According to such a configuration, the agglomerated silicon cutting waste is separated by a filtration process or a centrifugal separation process. When silicon cutting waste is separated by a filtration step, it is mainly present in the concentrate and is separated from the filtrate. Therefore, the filtrate can be used as a regeneration coolant. Moreover, when silicon | silicone cutting waste is isolate | separated by a centrifugation process, it exists mainly in solid content and is isolate | separated from the dilution liquid. Therefore, the diluted solution can be used as a regeneration coolant.

  In the above configuration, the regeneration step includes both the filtration step and the centrifugal separation step, the filtration step is performed on a part of the used coolant, and the centrifugal separation step is performed on the remainder. Preferably it is done.

  According to such a structure, the silicon | silicone cutting waste aggregated from the used coolant is isolate | separated not only by a filtration process but a centrifugation process. Here, according to the filtration process, the agglomerated silicon cutting waste is easily separated. However, as described above, in the filtration step, if the filter of the filtration device is clogged, the time required for regeneration may be increased. Therefore, by sending a part of the used coolant to the centrifugal separation process in this way, the amount of the used coolant sent to the filtration process can be reduced. As a result, the filter of the filtration device is less likely to be clogged, and the time required for regeneration is likely to be shortened.

  In the above configuration, the regeneration step includes both steps of the filtration step and the centrifugation step, and the filtration step is performed on the diluted solution obtained through the centrifugation step after the centrifugation step. It is preferable to carry out.

  According to such a structure, silicon | silicone cutting waste is isolate | separated previously by a centrifugation process, and is further isolate | separated further by the filtration process after that. Moreover, since silicon | silicone cutting waste is isolate | separated before the filtration process, it is hard to raise | generate clogging of the filter of a filtration apparatus in a filtration process.

  The said structure WHEREIN: It is preferable that the said reproduction | regeneration process is implemented again with respect to the said concentrate obtained through the said filtration process.

  According to such a structure, a centrifugation process or a filtration process is performed with respect to a concentrate in the reproduction | regeneration process again. As a result, silicon chips are easily separated from the used coolant. In addition, the amount of recovered coolant to be recovered increases, and the recycling efficiency is improved.

  The said structure WHEREIN: It is preferable that the said reproduction | regeneration process is implemented again with respect to the said dilution liquid obtained through the said centrifugation process.

  According to such a configuration, in the second regeneration step, the used coolant is mixed with the diluent and the fluidity is increased. Therefore, the filtration process in the re-generation process is easily performed smoothly.

  The said structure WHEREIN: It is preferable that the said used coolant is membrane-filtered at the said filtration process.

  According to such a configuration, the agglomerated silicon cutting waste is easily separated in the filtration step. Moreover, the membrane used in membrane filtration is easily regenerated by backwashing or the like, and has excellent maintainability.

  The regenerated coolant intermediate product according to another aspect of the present invention is generated in a process of separating the silicon cutting waste from the used coolant containing silicon cutting waste generated when the silicon material is cut to obtain regenerated coolant. The used coolant and a polymer flocculant that agglomerates the silicon cutting waste.

  According to such a regenerated coolant intermediate product, the silicon cutting waste is promoted to be aggregated by the polymer flocculant, and the diameter becomes large. Aggregated silicon chips are more easily separated from the used coolant by various separation methods (for example, a centrifugal separation operation and a filtration operation) than fine silicon chips before aggregation. As a result, according to the regenerated coolant intermediate product according to the present invention, regenerated coolant is easily obtained. In addition, according to the regenerated coolant intermediate product according to the present invention, since the average particle diameter of the silicon cutting waste contained is larger than that of the fine silicon cutting waste before agglomeration, the malfunction of the separation equipment (for example, the filter in the filtering device) It is difficult to cause clogging. Therefore, in the process of obtaining the regenerated coolant using such a regenerated coolant intermediate product, the time required for regeneration is shortened.

  ADVANTAGE OF THE INVENTION According to this invention, the coolant regeneration method and the regeneration coolant intermediate product which can fully isolate | separate silicon cutting waste from a used coolant within a short time can be provided.

It is a block diagram of the coolant reproduction | regeneration apparatus for enforcing the coolant reproduction | regeneration method of the 1st Embodiment of this invention. It is a block diagram of the coolant reproduction | regeneration apparatus for enforcing the coolant reproduction | regeneration method of the 2nd Embodiment of this invention. It is a block diagram of the coolant reproduction | regeneration apparatus for enforcing the coolant reproduction | regeneration method of the 3rd Embodiment of this invention.

(First embodiment)
Hereinafter, an embodiment of a coolant regeneration method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a coolant regeneration device 100 for carrying out the coolant regeneration method of the present embodiment. The coolant regeneration device 100 includes a processing tank 110, a centrifugal separator 120, a filtration device 130, a branch pipe 140, a return pipe 150, and a return pipe 160. The coolant regeneration method of this embodiment is performed using this coolant regeneration device 100.

  The processing tank 110 is a relatively large-capacity tank for temporarily storing used coolant to which a polymer flocculant is added. In the processing tank 110, an adding step S100 described later may be performed.

  In addition, in this specification, a used coolant means the coolant which is used when cutting | disconnecting a silicon material and contains the silicon | silicone cutting waste produced at the time of a cutting | disconnection. It does not specifically limit as a coolant, The general purpose coolant used for the cutting | disconnection of a silicon material is mentioned. Specifically, the coolant includes a water-soluble coolant mainly composed of various rust preventives and surfactants, a coolant obtained by mixing water and a water-soluble oil such as ethylene glycol, rust preventive oil, kerosene, and lubricating oil. An oil-based coolant based on The regenerated coolant is a coolant in which at least a part of the silicon material is separated from the used coolant. The regenerated coolant is mixed with abrasive grains and unused coolant as needed and reused.

  The branch pipe 140 is a pipe line that connects the processing tank 110, the centrifuge 120, and the filtration device 130, and introduces the used coolant from the processing tank 110 to the centrifuge 120 and the filtration device 130 in parallel. It is provided for. The processing tank 110, the centrifugal separator 120, and the filtration device 130 may be connected to the processing tank 110 by separate independent pipes (not shown) instead of the branch pipe 140.

  The centrifuge 120 is a device for centrifuging the used coolant introduced from the processing tank 110 to separate it into a solid content and a diluent. The centrifugal separator 120 performs a centrifugal separation step S210 described later.

  The type of the centrifuge is not particularly limited, and examples thereof include a vertical centrifuge having a vertical rotation axis and a horizontal centrifuge having a horizontal rotation axis. Moreover, it does not specifically limit as a method of introduce | transducing a used coolant to these centrifuges, A batch type may be sufficient and a continuous type may be sufficient. Further, such a centrifugal separator may be another device (for example, a filter press) that can separate into a solid content and a diluent.

  The centrifugal force (G) performed by the centrifugal separator 120 is not particularly limited, and is appropriately determined based on the amount of used coolant to be processed, the amount of silicon cutting waste, the viscosity of the used coolant, and the like. For example, the centrifugal force is adjusted to 500 to 5000G.

  The operation time (centrifugation time) of the centrifuge 120 is not particularly limited, and is appropriately determined based on the amount of used coolant to be processed, the amount of silicon cutting waste, the viscosity of the used coolant, and the like. For example, in the case of performing in a batch system, the centrifugation time is centrifugated at 3000 G while supplying spent coolant (containing silicon cuttings agglomerated to about 10 μm and solid content concentration of 15% by mass) at a rate of 30 L / min. In the case, it is adjusted to 15 to 120 minutes.

  The return pipe 150 is a pipe line that connects the centrifuge 120 and the processing tank 110. The diluent discharged from the centrifugal separator 120 is returned to the processing tank 110 via the return pipe 150.

  The filtration device 130 is a device for filtering the used coolant and separating it into a filtrate and a concentrate. A filtration step S220, which will be described later, is performed by the filtration device 130.

  It does not specifically limit as a kind of filtration apparatus, For example, a membrane filtration apparatus etc. are mentioned. Among these, a membrane filtration apparatus is preferable from the viewpoint of highly separating agglomerated silicon cutting waste. The membrane of the membrane filtration device is not particularly limited, and a hollow fiber membrane (internal pressure type or external pressure type), spiral membrane, tubular membrane, ceramic membrane or the like is employed. A filter press may be used instead of the membrane filtration device. Among these, by adopting a filtration method using a hollow fiber membrane, the agglomerated silicon cutting waste is highly easily separated. Moreover, the used hollow fiber membrane is easily regenerated by backwashing or the like, and has excellent maintainability.

  When a hollow fiber membrane is employed as the filtration membrane, the linear velocity of the used coolant supplied into the hollow fiber membrane can be set to 0.1 to 10 m / second.

  It does not specifically limit as a hole diameter of a filtration membrane, According to the average particle diameter of the silicon cutting waste which should be isolate | separated, it adjusts suitably. As a hole diameter of a filtration membrane, it can be set as 0.001-0.2 micrometer, for example. Moreover, it is not specifically limited as a molecular weight cut off of a filtration membrane, It adjusts suitably according to the average particle diameter of the silicon | silicone cutting waste which should be isolate | separated. The molecular weight cut off can be, for example, 1000 to 50000.

It does not specifically limit as a filtration rate, It determines suitably based on the quantity of the used coolant which should be processed, the quantity of silicon | silicone cutting waste, the kind of filtration membrane, etc. For example, the filtration rate can be 5 to 200 L / m ² · hr.

  The return pipe 160 is a pipe line that connects the filtration device 130 and the processing tank 110. The concentrated liquid discharged from the filtration device 130 is returned to the processing tank 110 through the return pipe 160.

  Next, a coolant regeneration method using the coolant regeneration apparatus 100 will be described. The coolant regeneration method according to the present embodiment is a method for obtaining regenerated coolant by separating silicon cutting waste from used coolant, and includes an addition step S100 and a regeneration step S200.

(Addition step S100)
Addition process S100 is a process of adding a polymer flocculant to a used coolant so that silicon cuttings may aggregate. The polymer flocculant should just be added with respect to the used coolant before reproduction | regeneration process S200 mentioned later is implemented. Therefore, for example, the polymer flocculant may be added to the used coolant transferred to perform the regeneration step S200, or may be added to the used coolant stored in the processing tank 110. The polymer flocculant is preferably added to the used coolant stored in the processing tank 110 so that the polymer flocculant can easily come into contact with silicon cutting waste contained in the used coolant. According to addition process S100, the reproduction | regeneration coolant intermediate product containing a used coolant and a polymer flocculent is produced | generated.

  When free abrasive grains are used during the cutting of the silicon material, it is necessary to regenerate the used coolant from a used slurry containing a large amount of free abrasive grains (a mixture of used coolant and free abrasive grains). In this case, before the addition step S100, a pretreatment for appropriately collecting the free abrasive grains may be performed on the used slurry.

  It does not specifically limit as a polymer flocculent added in addition process S100, What is necessary is just a polymer flocculent which can agglomerate the silicon | silicone cutting waste contained in an above-described coolant. Among the polymer flocculants, nitrogen-containing polymer flocculants containing nitrogen are preferable. Examples of the nitrogen-containing polymer flocculant include polyethyleneimine and polyacrylamide. The nitrogen-containing polymer flocculant is preferably used because it has excellent properties of aggregating silicon cutting waste contained in the coolant. In particular, polyethyleneimine and polyacrylamide have an excellent property of aggregating silicon cutting waste contained in the coolant. These polymer flocculants may be used alone or in combination. Moreover, it does not specifically limit as a weight average molecular weight of such a polymer flocculant, For example, 1,000-20,000,000 is mentioned.

  The polymer flocculant may be added so as to have a predetermined concentration with respect to the used coolant stored in the processing tank 110 (batch type), and with respect to the used coolant continuously introduced into the processing tank 110. You may supply continuously so that it may become a predetermined density | concentration (continuous type).

  The amount of the polymer flocculant to be added is not particularly limited, and is appropriately adjusted according to the amount and type of silicon cutting waste contained in the used coolant. That is, the amount of the polymer flocculant to be added may be an amount capable of aggregating, for example, 60% by mass or more of silicon cutting waste among all silicon cutting waste contained in the used coolant. Examples of the amount of such a polymer flocculant include 100 to 2000 ppm, preferably 200 to 800 ppm with respect to the used coolant. When a high molecular weight flocculant is added to a used coolant so that it may become 100-2000 ppm, silicon | silicone cutting waste tends to be aggregated. On the other hand, when the added amount is less than 100 ppm, the effect of aggregating silicon cutting waste is insufficient, and the filtration rate tends to decrease or the membrane life tends to be shortened. Similarly, when the addition amount exceeds 2000 ppm, the filtration rate tends to decrease. More specifically, for example, in the case where 8% by mass of silicon cutting waste is contained in the used coolant mainly composed of diethylene glycol, polyethyleneimine may be added so as to be 200 to 800 ppm. In this case, 80% by mass or more of all silicon cutting waste contained in the used coolant is aggregated. Similarly, polyacrylamide should just be added so that it may become 200-800 ppm in the case where 15 mass% silicon | silicone cutting waste is contained in the used coolant which has polyethyleneglycol as a main component. In this case, 80% by mass or more of all silicon cutting waste contained in the used coolant is aggregated.

  Moreover, it does not specifically limit as the quantity (solid content concentration) of the silicon | silicone cutting waste contained in a used coolant, For example, it is about 3-20 mass%. Moreover, it does not specifically limit as an average particle diameter of the silicon | silicone cutting waste contained in a used coolant, For example, it is about 0.01-5 micrometers.

  The average particle diameter of the silicon cutting scraps aggregated by the polymer flocculant is not particularly limited, and is, for example, 2 to 20 μm. When silicon scraps are agglomerated so as to have such an average particle diameter, they are easily separated in a regeneration step described later, and are unlikely to cause a malfunction of the separation device (for example, clogging of a filter in the filtration device).

  Regeneration process S200 is performed with respect to the used coolant (regenerated coolant intermediate product) which passed through addition process S100.

(Regeneration process S200)
The regeneration step S200 is a step of separating the silicon cutting scraps aggregated from the used coolant to obtain a regeneration coolant, and includes a centrifugal separation step S210 and a filtration step S220. In the present embodiment, the centrifugation step S210 and the filtration step S220 are performed in parallel.

(Centrifuge separation step S210)
Centrifugation step S210 is a step of centrifuging the used coolant introduced from the processing tank 110 through the branch pipe 140 into the centrifuge 120 and separating it into a solid content and a diluent. According to the centrifugation step S210, the agglomerated silicon cutting waste and the polymer flocculant are centrifuged as a solid content. Solids are discarded.

  Here, the agglomerated silicon swarf is larger in mass per silicon swarf than the conventional non-agglomerated silicon swarf, and thus is easily separated in a short time by centrifugation. Therefore, according to the centrifugal separation step S210, the silicon cutting waste is easily separated as a solid content. As a result, according to the centrifugation step S210, a diluted solution having a solid content concentration of 5% by mass or less can be obtained.

  The diluent discharged from the centrifugal separator 120 is returned to the processing tank 110 via the return pipe 150. The returned diluted solution is again subjected to the regeneration step S200. At this time, the returned diluted solution is mixed in the processing tank 110 with a used coolant or a concentrated solution having a relatively high viscosity obtained through a filtration step S220 described later.

(Filtration step S220)
Filtration process S220 is a process of carrying out the membrane filtration of the used coolant introduced into the filtration apparatus 130 (membrane filtration apparatus) via the branch piping 140 from the processing tank 110, and isolate | separating into a filtrate and a concentrate. According to the filtration step S220, the agglomerated silicon cutting waste and the polymer flocculant are mainly contained in the concentrated liquid. The filtrate is used as a regeneration coolant.

  The concentrated liquid discharged from the filtration device 130 is returned to the processing tank 110 through the return pipe 160. The reclaimed step S200 is performed again on the returned concentrated liquid. At this time, the concentrate is difficult to handle because it has a higher viscosity than the used coolant before the filtration step S220. Thus, the returned concentrated liquid is mixed with the used coolant and the diluted liquid obtained through the above-described centrifugal separation step S210 in the processing tank 110. Then, the mixed liquid is subjected to the centrifugal separation step S210 and the filtration step S220, and the regenerated coolant is further separated from the filtration device 130.

  As described above, according to the coolant regeneration method of the present embodiment, the polymer flocculant is added to the used coolant in the adding step S100. As a result, silicon chips contained in the used coolant are agglomerated. The agglomerated silicon cutting waste is well removed together with the polymer aggregating agent in the subsequent regeneration step S200. Specifically, the agglomerated silicon cutting waste is centrifuged in a short time by the centrifugal separator 120 in the centrifugal separation step S210 and separated as a solid content. Further, the agglomerated silicon cutting waste is less likely to cause a malfunction of the filtration device 130 (for example, clogging of the hollow fiber membrane of the membrane filtration device) in the filtration step S220. As a result, the performance (filtration rate and linear velocity) of the filtration device 130 is unlikely to decrease, and the time required for coolant regeneration is shortened.

  Moreover, according to the coolant regeneration method of the present embodiment, the centrifugal separation step S210 and the filtration step S220 are performed in parallel. Thus, by implementing centrifugation process S210 with respect to a part of used coolant, the quantity of the silicon | silicone cutting waste in the used coolant in which filtration process S220 is implemented is reduced. As a result, the load on the filtration device 130 is reduced, the filter of the filtration device 130 is less likely to be clogged, and the time required for regeneration is likely to be shortened.

  Furthermore, according to the coolant regeneration method of the present embodiment, the diluent discharged from the centrifugal separator 120 is returned to the processing tank 110 via the return pipe 150, and the regeneration step S200 is performed again. Therefore, in the second regeneration step S200, the used coolant is mixed with the returned diluent and the fluidity is increased. As a result, the regenerating step S200 is easily performed smoothly. Similarly, the concentrate discharged from the filtration device 130 is returned to the processing tank 110 via the return pipe 160, and the regeneration step S200 is performed again. Therefore, the amount of recovered coolant to be recovered increases and the recycling efficiency is improved.

(Second Embodiment)
A second embodiment of the coolant regeneration method of the present invention will be described with reference to FIG. FIG. 2 is a block diagram of the coolant regeneration device 101 for carrying out the coolant regeneration method of the present embodiment. The coolant regenerator 101 includes a centrifugal separator 120, a filtration device 130, an introduction pipe 170, and a return pipe 180, and the centrifugal separator 120 and the filtration device 130 are connected in series. . The coolant regeneration method of this embodiment is performed using this coolant regeneration device 101. Note that, in the following description, the same reference numerals are given to configurations common to the first embodiment, and description thereof will be omitted as appropriate. Moreover, in this embodiment, the processing tank 110 (refer FIG. 1) which stores a used coolant and a polymer flocculent temporarily may be provided in the front | former stage of the centrifuge 120, and the centrifuge 120 and A membrane treatment tank for temporarily storing the diluent may be provided between the filtration device 130 and the filter device 130.

  The introduction pipe 170 is a pipe line that connects the centrifugal separator 120 and the filtration device 130 in series. The diluent discharged from the centrifuge 120 is introduced into the filtration device 130 via the introduction pipe 170.

  The return pipe 180 is a pipe line that connects the filtration device 130 and the centrifugal separator 120. The concentrated liquid discharged from the filtration device 130 is returned to the centrifugal separator 120 via the return pipe 180.

  Next, a coolant regeneration method using the coolant regeneration apparatus 101 will be described. The coolant regeneration method of this embodiment includes an addition step S100 and a regeneration step S300. In the addition step S100, the polymer flocculant may be added to used coolant that is transferred to perform the regeneration step S300, or may be added to used coolant stored in a processing tank (not shown). In addition process S100 of this embodiment, a polymer flocculant is added with respect to the used coolant introduce | transduced into the centrifuge 120 via the introduction piping which is not shown in figure in order to implement centrifugation process S310. The regeneration step S300 includes a centrifugation step S310 and a filtration step S320. The coolant regeneration method of the present embodiment has the same configuration except that the centrifugal separation step S310 and the filtration step S320 are different from the centrifugal separation step S210 and the filtration step S220 described above as the first embodiment, respectively. Therefore, only the centrifugation step S310 and the filtration step S320 are described, and other steps are omitted.

(Centrifuge separation step S310)
Centrifugation step S310 is a step of centrifuging the used coolant and the polymer flocculant introduced into the centrifuge 120 through an introduction pipe (not shown) and separating them into a solid content and a diluent. Solids are discarded. Filtration process S320 is implemented for a dilution liquid.

(Filtration step S320)
The filtration step S320 is a step of filtering the dilute solution introduced from the centrifugal separator 120 into the filter device 130 via the introduction pipe 170 and separating it into a filtrate and a concentrated solution. The filtrate is used as a regeneration coolant. The concentrated liquid discharged from the filtration device 130 is returned to the centrifugal separator 120 via the return pipe 180. Centrifugation process S210 is implemented again for the returned concentrated liquid.

  As mentioned above, according to this embodiment, filtration process S320 is implemented with respect to the dilution liquid by which the silicon | silicone cutting waste was previously reduced by passing through centrifugation process S310. Therefore, the silicon cutting waste is easily separated. As a result, the filtrate is suitably used as a regeneration coolant. In addition, since the filtration step S320 is performed on the diluted solution in which the silicon cutting waste is reduced through the centrifugal separation step S310, the filter of the filtration device 130 (for example, the hollow fiber membrane of the membrane filtration device) is blocked by the silicon cutting waste. Hateful. As a result, the time required for regeneration of the coolant is shortened, and the life of the filtration device is extended.

(Third embodiment)
A third embodiment of the coolant regeneration method of the present invention will be described with reference to FIG. FIG. 3 is a block diagram of the coolant regeneration device 102 for carrying out the coolant regeneration method of the present embodiment. The coolant regeneration apparatus 102 has the same configuration as the coolant regeneration apparatus 101 (see FIG. 2) described above in the second embodiment, except that a return pipe 190 is provided instead of the return pipe 180. The return pipe 190 is a pipe line for returning the concentrate discharged from the filtration device 130 to the filtration device 130 again. Note that, in the following description, the same reference numerals are given to components common to the second embodiment, and description thereof will be omitted as appropriate. The coolant regeneration method of this embodiment is performed using the coolant regeneration device 102.

  The coolant regeneration method of this embodiment includes an addition step S100 and a regeneration step S400. The regeneration step S400 includes a centrifugation step S310 and a filtration step S420. The coolant regeneration method of the present embodiment has the same configuration except that the filtration step S420 is different from the filtration step S320 described above as the second embodiment. Therefore, only the filtration step S420 is described, and other steps are omitted.

(Filtration step S420)
The filtration step S420 is a step of filtering the diluted solution introduced from the centrifugal separator 120 through the introduction pipe 170 into the filtration device 130 to separate the filtrate and the concentrated solution. The filtrate is used as a regeneration coolant. The concentrated liquid is returned to the inlet of the filtration device 130 via the return pipe 190. The concentrated liquid returned is discharged from an outlet (not shown) after the concentration step is increased by performing the filtration step S420 again. Thus, since the quantity of the filtrate obtained by filtration process S420 being performed in multiple times increases, it is preferable. The concentration factor is usually about 2 to 10 times, although it varies depending on the concentration of silicon cutting waste contained in the diluent. The concentrate may be discharged when the silicon cutting waste concentration is increased to 7 to 30% by mass. The concentrated liquid may be discarded as it is without performing the filtration step S420 a plurality of times.

  As described above, according to the present embodiment, the concentrate is not returned to the centrifugation step S310. Therefore, the used coolant before the centrifugation step S310 is not mixed with the concentrated liquid and is not increased in viscosity. As a result, the used coolant is easily subjected to the regeneration step S400, and the time required for regeneration is shortened.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, For example, the following modified embodiment is employable.

  (1) In the first embodiment, the case where the regeneration step S200 includes both the centrifugation step S210 and the filtration step S220 is illustrated. Instead of this, the regeneration step S200 may include only one of the centrifugation step S210 and the filtration step S220. In this case, the diluted solution obtained through the centrifugation step S210 is used as a regeneration coolant.

  (2) In the first embodiment, the regeneration step S200 is performed again on the diluted solution that has undergone the centrifugation step S210, and the regeneration step S200 is performed again on the concentrated solution that has passed the filtration step S220. Illustrated. Instead of this, the regeneration step S200 may be performed again for only one of the concentrated solution and the diluted solution.

  (3) In 2nd Embodiment, filtration process S320 is performed with respect to the dilution liquid which passed through centrifugation process S310, and reproduction | regeneration process S300 (namely, centrifugation process S310) is performed again with respect to the concentrate which passed through filtration process S320. The case where is performed is illustrated. Instead of this, the regeneration step S300 (that is, the centrifugation step S310) may be performed again before the filtration step S320 is performed on the diluted solution that has undergone the centrifugation step S310. Further, in the case where the regeneration step S300 is performed again on the concentrated solution that has passed through the filtration step S320, the filtration step S320 may be performed again instead of performing the centrifugation step S310 on the concentrated solution. .

  (4) In the first embodiment, the case where the diluted solution that has undergone the centrifugation step S210 is returned to the processing tank 110 is illustrated. In the second embodiment and the third embodiment, the dilution that has passed through the centrifugation step S310 is illustrated. It illustrated about the case where a liquid is introduce | transduced into the filtration apparatus 130. FIG. In the present invention, instead of these, a diluting liquid may be used as a regeneration coolant.

  Hereinafter, the coolant regeneration method of the present invention will be described in detail with reference to examples. The coolant regeneration method of the present invention is not limited to the following examples.

<Example 1>
The coolant regeneration apparatus 100 shown in FIG. 1 was used, and the regeneration coolant was obtained from the used coolant. In this example, since free abrasive grains were used when the silicon ingot was cut as described below, the used slurry contained used coolant and free abrasive grains. Therefore, before adding the polymer flocculant, the following pretreatment was performed to collect free abrasive grains from the used slurry.

(Preprocessing)
The silicon ingot was cut using a wire saw cutting device. The silicon ingot was cut while supplying a polishing slurry containing a coolant and free abrasive grains to the contact area with the wire. As the coolant, a coolant composed of 98% by weight of polyethylene glycol and 2% by weight of water was used. As the free abrasive grains, silicon carbide having an average particle diameter of 10 μm was used. The obtained used slurry had a solid content concentration of 52.5% by mass. This used slurry contained 0.01 to 4 μm of silicon cutting waste. This spent slurry is put into a pretreatment tank (not shown), and 40 L is added to a vertical centrifuge (MG-50 type, manufactured by G Force Japan Co., Ltd.) adjusted to a centrifugal force of 500 G from the pretreatment tank. The circulating operation was performed for 120 minutes by supplying at a rate of / min and returning the treatment liquid to the pretreatment tank, and free abrasive grains were collected. The free abrasive grains were collected by reducing the rotational speed of the centrifugal separator every 15 to 30 minutes, pressing the scraper against the inner wall of the centrifugal separator, and scraping the deposits. After operation for 90 minutes, the liquid in the pretreatment tank had a solid content of 29% by mass. Subsequently, the centrifugal force was adjusted to 1000 G, and the abrasive grains and silicon cuttings crushed by the same method for 90 minutes were collected. The liquid in the pretreatment tank (used coolant) had a solid content concentration of 15% by mass.

(Regeneration of coolant)
Polyacrylamide (PAA, molecular weight 16 million) was added to the used coolant so that the concentration in the system was 500 ppm, and stored in the treatment tank 110 (addition process). Thereby, the silicon | silicone cutting waste was aggregated to 5-30 micrometers. The agglomerated silicon cutting waste was 90% by mass in the total silicon cutting waste. Next, the used coolant is introduced at a rate of 30 L / min from the processing tank 110 to the centrifugal separator 120 (NEO-200 type, manufactured by G Force Japan Co., Ltd.) adjusted to 3000 G through the branch pipe 140. , Separated into solid and diluent. The obtained diluted solution was returned to the processing tank 110 through the return pipe 150 and repeatedly subjected to the same centrifugal separation (centrifugation step). In the centrifugal separation process, the amount of silicon cutting waste discharged (kg / hr) was measured. At the same time as the centrifugation step, the used coolant is removed from the treatment tank 110 through the branch pipe 140 and the filtration device 130 (internal pressure membrane filtration device, hydrophilized polyvinylidene fluoride having a molecular weight cut off of 13,000). It was introduced into a hollow fiber membrane (including MU-6302HG, manufactured by Kuraray Co., Ltd., including a linear velocity of 0.4 m / sec) by a cross flow method, and separated into a filtrate and a concentrated liquid. The obtained concentrated liquid was returned to the processing tank 110 through the return pipe 160 and repeatedly subjected to membrane filtration (filtration step). In the filtration step, the membrane filtration rate (L / m ² · hr) and the membrane life were measured. The membrane lifetime was defined as the amount of membrane permeation (L / m ² ) per unit area where the membrane filtration rate was less than 60% of the initial value. In addition, although the liquid in the system was reduced by discharging the solid content generated in the centrifugation step and the filtrate generated in the filtration step, the reduced amount was newly used (500 ppm of PAA). In addition) at a predetermined rate, and the membrane filtration rate of the filtration device 130 was adjusted.

  The filtrate (regenerated coolant) was a transparent liquid from which silicon cutting waste was completely removed. The filtrate was mixed with previously recovered abrasive grains, unused coolant corresponding to the amount lost in this operation, and new abrasive grains to obtain a regenerated slurry.

<Comparative Example 1>
Except for adding the polymer flocculant to the used coolant obtained in Example 1, without introducing the polymer flocculant, the same treatment as in Example 1 was performed to obtain a regenerated coolant and a regenerated slurry. It was.

<Example 2>
The silicon ingot was cut using a wire saw cutting device provided with a wire to which silicon carbide having an average particle size of 10 μm was fixed. The silicon ingot was cut while supplying coolant to the contact area with the wire. As a coolant, what consists of 70 mass% of diethylene glycol, 29 mass% of water, and 1 mass% of other additives was used. The obtained used coolant had a solid content concentration of 8.2% by mass. Polyethyleneimine (PEI, molecular weight 70,000) was added to the used coolant so that the concentration in the system was 500 ppm, and stored in the processing tank 110 (addition process). Subsequently, the regeneration process (centrifugation process (centrifugation process) and filtration process (filtration process)) similar to Example 1 was performed, and the regeneration coolant and the regeneration slurry were obtained.

<Comparative Example 2>
Except that PEI was not added to the used coolant, the same treatment as in Example 2 was performed to obtain a regenerated coolant and a regenerated slurry.

<Example 3>
The coolant regeneration apparatus 101 shown in FIG. 2 was used, and the regeneration coolant was obtained from the used coolant. Specifically, as in Example 2, PEI is added to the used coolant so that the concentration in the system becomes 500 ppm (addition process), and a treatment tank (not shown) provided in the front stage of the centrifugal separator 120 is not shown. ). Then, it supplied to the centrifuge 120 (NEO-200 type | mold, G force Japan Co., Ltd. product) adjusted to 3000G at the speed | rate of 30 L / min, and isolate | separated into solid content and diluent (centrifugation process). The obtained diluted solution was returned to the treatment tank and repeatedly subjected to the same centrifugal separation. The solid content concentration (mass%) of the diluted solution obtained in the filtration step and the time (minute) required to achieve the solid content concentration were measured. Thereafter, the diluted solution is introduced into a membrane treatment tank (not shown) provided between the centrifugal separator 120 and the filtration device 130 via the introduction pipe 170, and then membrane filtration is performed by the filtration device 130, followed by filtration. It separated into a liquid and a diluted liquid (filtration process). The membrane filtration rate (L / m ² · hr) and membrane life immediately after the start of the filtration step were measured. Was measured. The obtained concentrated liquid was returned to the centrifugal processing tank via the return pipe 180. A new used coolant (containing 500 ppm of PEI) was mixed with the returned concentrated liquid, and then centrifugal separation and membrane filtration were performed again to obtain a regenerated coolant and a regenerated slurry. Moreover, the required time (minute) of the filtration process was measured.

<Comparative Example 3>
Except that PEI was not added to the used coolant, the same treatment as in Example 3 was performed to obtain a regenerated coolant and a regenerated slurry.

<Example 4>
Except for using the coolant regenerating apparatus 102 shown in FIG. 3, the same process as in Example 3 was performed to obtain a regenerated coolant from the used coolant. The concentrated liquid discharged from the filtration device 130 was discarded without being returned to the filtration device 130 through the return pipe 190.

<Comparative Example 4>
Except that PEI was not added to the used coolant, the same treatment as in Example 4 was performed to obtain a regenerated coolant and a regenerated slurry.

  Tables 1 and 2 show the used coolant regeneration conditions and evaluation results in Examples 1 to 4 and Comparative Examples 1 to 4.

(Evaluation results and discussion)
When silicon ingots were cut using the regenerated slurries regenerated in Examples 1 to 4 and Comparative Examples 1 to 4, it was confirmed that silicon wafers having good surface properties with no deposits and few scratches were obtained. It was.

  However, as shown in Table 1, according to the coolant regeneration methods of Example 1 and Example 2 that employ the addition step of adding the polymer flocculant, Comparative Example 1 and Comparative Example that did not employ the addition step Compared with the coolant regeneration method of 2, the solid content per unit time could be discharged in the centrifugal separation process. That is, according to the coolant regeneration method of Example 1 and Example 2, compared with the coolant regeneration method of Comparative Example 1 and Comparative Example 2, silicon chips can be separated in a short time, and the centrifugal separation process is shortened. I was able to. Moreover, according to the coolant regeneration method of Example 1 and Example 2, compared with the coolant regeneration method of Comparative Example 1 and Comparative Example 2, a large membrane filtration rate is obtained in the filtration step, and the time required for the filtration step is shortened. We were able to.

  As shown in Table 2, according to the coolant regeneration methods of Example 3 and Example 4 that employ the addition step of adding the polymer flocculant, those of Comparative Example 3 and Comparative Example 4 that did not employ the addition step Compared with the coolant regeneration method, the solid content concentration in the diluting liquid could be reduced in a short time in the centrifugal separation process, and silicon cutting waste could be separated in a short time. That is, according to the coolant regeneration method of Example 3 and Example 4, compared with the coolant regeneration method of Comparative Example 3 and Comparative Example 4, the centrifugation step could be shortened. Moreover, according to the coolant regeneration method of Example 3 and Example 4, compared with the coolant regeneration method of the comparative example 3 and the comparative example 4, the big membrane filtration rate was obtained in the filtration process. Further, in the comparison between Example 3 and Comparative Example 3 in which the presence or absence of the addition process is different, and in the comparison between Example 4 and Comparative Example 4, the coolant regeneration methods of Example 3 and Example 4 are comparative examples. Compared with the coolant regeneration methods of 3 and Comparative Example 4, the time required for membrane filtration could be shortened.

100, 101, 102 Coolant regeneration device 110 Processing tank 120 Centrifugal device 130 Filtration device 140 Branch piping 150, 160, 180, 190 Return piping 170 Introducing piping S100 Addition step S200, S300, S400 Regeneration step S210, S310 Centrifugation step S220 , S320, S420 Filtration process

Claims (11)

A coolant regeneration method for separating the silicon cutting waste from used coolant containing silicon cutting waste generated when cutting silicon material,
An addition step of adding a polymer flocculant to the used coolant so that the silicon cutting scraps aggregate;
A regeneration step of separating the agglomerated silicon cutting waste to obtain a regeneration coolant;
A coolant regeneration method including:   The coolant regeneration method according to claim 1, wherein the polymer flocculant is a nitrogen-containing polymer flocculant containing nitrogen.   The coolant regeneration method according to claim 2, wherein the nitrogen-containing polymer flocculant is at least one of polyethyleneimine and polyacrylamide.   The coolant regeneration method according to any one of claims 1 to 3, wherein the polymer flocculant is added to be 100 to 2000 ppm with respect to the used coolant. The regeneration step includes at least one of a filtration step or a centrifugation step,
The filtration step is a step of filtering the used coolant and separating it into a filtrate and a concentrate.
The coolant regeneration method according to any one of claims 1 to 4, wherein the centrifugation step is a step of centrifuging the used coolant to separate it into a solid content and a diluent. The regeneration step includes both the filtration step and the centrifugation step,
The coolant regeneration method of Claim 5 which performs the said filtration process with respect to a part of said used coolant, and performs the said centrifugation process with respect to the remainder. The regeneration step includes both the filtration step and the centrifugation step,
The coolant regeneration method of Claim 5 which performs the said filtration process with respect to the said dilution liquid obtained through this centrifugation process after the said centrifugation process.   The coolant regeneration method according to claim 6 or 7, wherein the regeneration step is performed again on the concentrate obtained through the filtration step.   The coolant regeneration method according to claim 6 or 7, wherein the regeneration step is performed again on the diluent obtained through the centrifugation step.   The coolant regeneration method according to any one of claims 5 to 9, wherein in the filtration step, the used coolant is subjected to membrane filtration. It is generated in the process of obtaining the regenerated coolant by separating the silicon cutting waste from the used coolant containing the silicon cutting waste generated when cutting the silicon material,
A regenerated coolant intermediate product comprising the used coolant and a polymer flocculant that agglomerates the silicon cutting waste.

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