Manufacturing method for diamond grinding wheels that mimic sedimentary rock formation

Abstract

Reducing carbon dioxide emissions is a matter of urgency in order to achieve the SDGs. In the ceramics industry, where there is a firing process that heats raw materials, carbon dioxide emissions are unavoidable as long as existing fuels are used. Furthermore, while the use of hydrogen, which does not emit CO2, has been proposed as a fuel, challenges remain in procuring blue hydrogen and green hydrogen, and it is not sufficient to address the current situation. The goal is to provide firing technologies that minimize carbon dioxide emissions for each and every ceramic product. [Solution] A method for manufacturing a CSP grinding wheel containing abrasive grains having an inert grain interface, comprising impregnating the matrix containing the abrasive grains with an acid or a strong base and mixing it, enclosing the entire matrix in a substantially closed space, pressurizing it within a predetermined pressure range, heating it for a predetermined time range, and holding it for at least a predetermined time range.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sedimentary rock formation - mimicking diamond grinding wheel.

Background Art

[0002] With the evolution of semiconductor materials, it is expected that more high - performance and durable electronic devices will be realized. Gallium arsenide (GaAs), indium phosphide (InP), and silicon carbide (SiC) have attracted attention, but there are concerns about difficult processing and high costs. Furthermore, as an ultimate semiconductor material, diamond can be mentioned, but the processing difficulty is high and manufacturing with current technology is expected to face great difficulties. For processing these high - hardness materials, (i) sintered diamond grinding wheels and (ii) electrodeposited diamond grinding wheels can be mentioned.

[0003] Also, in general machining, the demand for grinding is expected to increase in the future, especially for the following reasons compared to cutting. That is, (i) Grinding can be performed with very high precision and is particularly suitable for materials with high hardness and parts with complex shapes. (ii) To meet the diversification of consumer needs, the production of small - batch, multi - variety products has increased, and the flexibility of grinding is suitable for small - batch, multi - variety production. (iii) Although the use of carbon fiber in moving bodies that require light weight and high strength is expected to increase, the processing difficulty is high, which hinders its popularization. However, by changing the processing from "cutting" to "grinding", productivity increases and the use of carbon fiber becomes easier. (iv) In gigacasting, although it is expected that conventional cutting and lapping processes will be reduced at once, grinding is required for fine adjustment after casting.

[0004] Under the circumstances described above, demand for sintered diamond grinding wheels is expected to increase in the future. However, as the name suggests, they are made by mixing diamond abrasive grains with a ceramic matrix and firing them at around 700°C to gain strength and make them usable for gripping, making them a product with high carbon dioxide emissions, which is an inherent characteristic of the ceramics industry. Furthermore, since diamonds begin to graphitize at around 600°C, firing in a special oxygen-free firing atmosphere is required, making them an energy-intensive (and therefore high-carbon dioxide emitting) product.

[0005] The inventor has been researching the cold sintering process (hereinafter referred to as "CSP") as part of efforts to conserve energy in ceramic manufacturing processes. This method mimics the formation of sedimentary rocks and involves simultaneously applying a small amount of solvent, heat below 300°C, and a pressure of several tens of MPa to the raw material powder. This reduces interparticle friction, leading to particle rearrangement and densification through dissolution and precipitation reactions via the solvent. The resulting bonding of particles increases the strength of the ceramic itself, thus enabling sintering at low temperatures (Non-Patent Documents 1 and 2).

[0006] Here, the prior art references are all research papers published by the inventors, detailing CSP. This technology uses amorphous silica as the ceramic matrix, with SiC used as an abrasive material, and furthermore, the SiC is surface-treated to have an amorphous silica layer. This was done to improve affinity with the ceramic matrix and to achieve interfacial densification. Therefore, it can be said that there is no motivation for particles like diamond abrasive grains, whose abrasive surface, i.e., interface with the ceramic matrix, is extremely stable. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Keitaro Yamaguchi, Shinobu Hashimoto, Preparation of SiC solidified bodies by CSP, Refractories, 75, [9], 1-8 (2023) [Non-Patent Document 2] Keitaro Yamaguchi, Gunik Lee, Shinobu Hashimoto “Cold sintering of SiC ceramics with the assistance of amorphous SiO surface layer”Ceramics International 48 (2022) 37362-37369 [Overview of the project] [Problems that the invention aims to solve]

[0008] In light of recent severe wind and rain disasters, reducing carbon dioxide emissions is an urgent task in order to achieve the SDGs. In the ceramics industry, which involves a firing process that heats raw materials, carbon dioxide emissions are unavoidable as long as existing fuels are used. Furthermore, while the use of hydrogen, which emits no CO2, has been proposed as a fuel, challenges remain in procuring blue and green hydrogen, and it is not yet ready to address the current situation. There is a need for firing technologies that minimize carbon dioxide emissions for each individual ceramic product. [Means for solving the problem]

[0009] The present invention, which solves the above problems, is as follows. [1] A method for manufacturing a CSP grinding wheel having a grinding wheel surface containing abrasive grains having an inert grain interface, wherein an acid or strong base is impregnated into a matrix containing the abrasive grains and mixed, the entire matrix is ​​confined in a substantially closed space that allows only gas to pass through, pressurized within a predetermined pressure range, heated within a predetermined temperature range, and held for at least a predetermined time. [2] The method for manufacturing a CSP grinding wheel as described in [1], wherein the range of the predetermined pressure is 30 to 100 MPa. [3] The method for manufacturing a CSP grinding wheel according to [1] or [2], wherein the predetermined temperature range is 130 to 200°C. [4] The method for manufacturing a CSP grinding wheel described in any one of [1] to [3], wherein the range of the predetermined time is at least 40 minutes. [5] A method for manufacturing a CSP grinding wheel according to any one of [1] to [4], wherein the surface density of the abrasive grains of the grinding wheel is 2 to 19% in terms of the projected surface area ratio with respect to the grinding wheel surface. [6] A method for manufacturing a CSP grinding wheel according to any one of [1] to [5], wherein amorphous silica is used as the matrix and the strong base impregnated therein is sodium hydroxide or potassium hydroxide. [7] The abrasive grain is a diamond abrasive grain. This is a method for manufacturing a CSP grinding wheel as described in any one of [1] to [6]. [Effects of the Invention]

[0010] CSP diamond grinding wheels, fired at low temperatures within the appropriate range, possess high rigidity and low shedding of diamond abrasive grains, making them ideal grinding tools. Compared to conventional products, they can be manufactured with extremely low carbon dioxide emissions, contributing not only to cost reduction but also to the SDGs in the future as production of these grinding wheels increases.

[0011] Furthermore, because the firing process is carried out at an extremely low temperature, it becomes easy to incorporate high-performance resins into the sintered diamond grinding wheel body, something previously unthinkable. This incorporation of high-performance resins allows for increased mechanical strength while reducing the amount of ceramic matrix, resulting in a lighter overall weight. Consequently, CSP grinding wheels of the same diameter can be operated with less power compared to conventional products, further contributing to the SDGs. [Brief explanation of the drawing]

[0012] [Figure 1] (a) This diagram schematically shows the process of placing raw materials into a mold (Process 1), and (b) the process of applying a predetermined pressure and temperature to (a) (Process 2). [Figure 2] This figure shows the relationship between molding pressure and bending strength (temperature is fixed at a mold temperature of 185°C). [Figure 3] This figure shows the relationship between mold temperature and bending strength (pressure is fixed at 50 MPa). [Figure 4]It is a diagram showing the relationship between the diamond abrasive content and the amount of friction (the temperature is 185°C of the mold temperature, and the pressure is fixed at 50 MPa). [Figure 5] It is another diagram showing the relationship between the diamond abrasive content and the amount of friction.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and modifications, corrections, and improvements can be made without departing from the scope of the invention.

[0014] Since CSP is a means of densifying particles by using a dissolution and precipitation reaction with a solvent as described above, even if the ceramic matrix itself is densified, diamond abrasive grains that are always subject to an impact external force of dropping as a grindstone have extremely stable crystal planes and cannot be assimilated and densified. That is, it was considered impossible to manufacture diamond grindstones by CSP.

[0015] Therefore, as a result of intensive research by the inventor, it has been found that the surface density of the abrasive grains on the surface of the grindstone exhibits a sufficient gripping force of the ceramic matrix against the diamond abrasive grains within a certain range in terms of the projected area ratio with respect to the grindstone surface, and the diamond abrasive grains are less likely to fall off.

[0016] This is because if the ceramic matrix between the diamond abrasive grains has a volume of a certain level or more, the ceramic matrix sandwiched between the abrasive grains is difficult to be broken because it is densified by CSP, and it is considered that it may prevent the abrasive grains from falling off. On the other hand, if the volume is too large, the number of abrasive grains per unit surface area decreases, and it is considered that the falling off is promoted by receiving excessive force per abrasive grain. That is, under severe use, if the projected area ratio of the abrasive grains is too low or too high, the falling off of the abrasive grains becomes remarkable. On the other hand, if it is within an appropriate range, it is considered that the falling off of the abrasive grains is significantly reduced even under severe use.

[0017] The manufacturing method of a CSP grinding wheel, as shown in Fig. 1(a), includes a step of putting raw material 1 into a mold 5 (hereinafter sometimes referred to as "Step 1"), and as shown in Fig. 1(b), a step of applying a predetermined pressure and a predetermined temperature to the raw material 1 for a predetermined time after Step 1 (hereinafter sometimes referred to as "Step 2"). The raw material 1 includes abrasive grains 2, a binder (matrix) 3, and a solvent 4, and the solvent 4 (not shown) is an acid solvent 4a or an alkali solvent 4b.

[0018] In Step 1, the raw material 1 is put into a space 6 formed by a first surface 5a, a second surface 5b, and a third surface 5c of the mold 5. In Step 2, the space 6 becomes a substantially closed space 6´ by a fourth surface 5d of the mold, and the substantially closed space 6´ is narrowed by the second surface 5b and the fourth surface 5d, and the raw material 1 is pressurized and heated through the first surface 5a and the third surface 5c. The pressure range is preferably 30 to 100 MPa, and the heating temperature range is preferably 130 to 200 °C.

[0019] The acid solvent 4a includes organic acids and inorganic acids. From the perspective of volatilizing from the raw material 1 by heating and not remaining in the raw material 1, for example, acetic acid and citric acid are preferred as organic acids, and phosphoric acid is preferred as an inorganic acid. On the other hand, a strong base is used as the alkali solvent 4b, and for example, NaOH and KOH are preferred.

Example

[0020] When kneading diamond abrasive grains into a ceramic matrix and manufacturing it with CSP, in order to clarify an appropriate heating temperature range, pressure range, and pressure time range, test pieces were produced in the following manner.

[0021] (Production of test pieces)

[0022] <1: Mixing> A ceramic matrix and a predetermined volume% of SiC crystal material were put into a ball mill as a substitute for diamond abrasive grains and mixed for 1 hour, and then put into a pressure vessel with a size of 45W × 45L × 50H. The SiC crystal material used here has a crystal structure up to the surface layer and does not have an amorphous surface layer. Therefore, its surface is extremely stable. Also, the SiC crystal material with an average particle size of 4 μm was used.

[0023] <2: CSP, Solvent, Strong Base> In this example, CSP was performed using either a 3M NaOH aqueous solution or a 3M KOH aqueous solution as the strong base, at a pressure of 20-100 MPa, a temperature of 80-250°C (set temperature), and a time of 40 min heating + 10 min cooling. The amount of strong base mixed was 10 wt%.

[0024] <3: Hot water treatment> After CSP treatment, the sample was kept in 50°C hot water for one day to remove residual strong bases. <4: Specimen Preparation> The specimens were cut to 7mm x 45mm for bending strength testing and dried at 110°C for more than 12 hours.

[0025] The ceramic matrix can be amorphous silica or clay mineral (kaolin), but in this example, amorphous silica was used exclusively. Furthermore, the following examples for "Determination of molding pressure" and "Determination of molding temperature" are equivalent to verification experiments to determine whether bending strength as a structure can be obtained even if the grinding wheel contains particles with low surface activity and therefore low affinity to the ceramic matrix.

[0026] (Determination of molding pressure (temperature fixed at mold temperature of 185°C)) The experimental results are shown in Figure 2. According to these results, solidification occurred at pressures above 30 MPa. At 20 MPa, the material was extremely brittle and impossible to process. If the target bending strength is 50 MPa, the preferred range is 30-100 MPa. While fabrication is possible at pressures above 100 MPa, the bending strength characteristics indicate that applying high pressure does not improve the bending strength. The results for a sample using a 3M NaOH aqueous solution and a sample using a 3M KOH aqueous solution (one point) are shown side-by-side. They show comparable values.

[0027] (Determination of molding temperature (pressure fixed at 50 MPa)) The experimental results are shown in Figure 3. According to these results, the preferred molding temperature is between 130 and 200°C, given a target bending strength of 50 MPa. The sample became brittle above 230°C. The results for samples using a 3M NaOH aqueous solution and samples using a 5M KOH aqueous solution (one point) are shown side-by-side. They show comparable values.

[0028] (Determination of abrasive surface density of grinding wheel (temperature fixed at mold temperature of 185°C, pressure fixed at 50 MPa)) This example is a verification experiment to confirm whether a grinding wheel can function with diamond abrasive grains on its surface, using diamond abrasive grains with an average particle size of 75 μm. CSP diamond grinding wheels (diamond abrasive grain ratios of 10, 30, 50, and 70 vol%) were prepared as samples, processed to a size of 7 mm x 22 mm, fixed to a sample stand with wax, and used to grind a 200 mm diameter stainless steel plate for 30 minutes, and the amount of wear of the grinding wheel was evaluated.

[0029] Figure 4 clearly shows that 70 vol% is unusable. On the other hand, the range of 10-40 vol% is unclear, so please refer to Figure 5, where the vertical axis scale has been changed.

[0030] Figure 5 shows that 30 vol% resulted in the least wear, followed by 20 vol%, and then 10 vol% and 40 vol%. This indicates that the optimal content of diamond abrasive grains in the ceramic matrix is ​​10 to 40 vol%. In this example, because the test specimens were small, it was relatively easy to mix the diamond abrasive grains to ensure uniform dispersion throughout the sample. Therefore, instead of determining the original objective of abrasive grain surface density and projected area ratio relative to the grinding wheel surface, the volume ratio was used as a substitute. Accordingly, the target projected area ratio was obtained by image processing of the grinding wheel surfaces of 10 vol% and 40 vol%, respectively. As a result, the abrasive grain surface density and projected area ratio relative to the grinding wheel surface were 2% for 10 vol% and 19% for 40 vol%, respectively. Furthermore, they were 6% for 20 vol% and 9% for 30 vol%.

[0031] Using this index, in the case of large grinding wheels, an effective diamond grinding wheel can be obtained by having diamond abrasive grains present only in the surface layer, rather than throughout the entire wheel, and by manipulating the ratio of these grains as described above. Note that the diamond abrasive grains include embedded portions that are embedded in the grinding wheel surface and protruding portions that are visible from the grinding wheel surface. [Industrial applicability]

[0032] By using CSP grinding wheels manufactured in accordance with the SDGs according to this invention to process and polish semiconductors (especially high-hardness semiconductor materials such as SiC wafers), the durability of the grinding wheels is improved, reducing the frequency of equipment maintenance. Furthermore, CSP grinding wheels can be used for processing ceramic parts and other components of semiconductor manufacturing equipment that require dimensional accuracy. Moreover, by supplying low-carbon emission tools for grinding processes, which are expected to see a dramatic increase in use in precision machining, carbon fiber processing, and fine adjustments after casting in Gigacast, this invention contributes to the SDGs. [Explanation of symbols]

[0033] 1: Raw materials 2: Abrasive grains 3: Binder (matrix) 4: Solvent 4a: Acid solvent 4b: Alkaline solvent (strong base) 5: Mold 5a: First surface of the mold 5b: 2nd side 5c:Side 3 5d: 4th side 6: Space 6': A effectively closed space

Claims

1. A method for manufacturing a CSP grinding wheel having a grinding wheel surface containing abrasive grains having an inert grain interface, comprising: impregnating a matrix containing the abrasive grains with an acid or a strong base and mixing it; enclosing the entire matrix in a substantially closed space; pressurizing it within a predetermined pressure range while simultaneously heating it within a predetermined temperature range; and holding it for at least a predetermined time.

2. The method for manufacturing a CSP grinding wheel according to claim 1, wherein the range of the predetermined pressure is 30 to 100 MPa.

3. The method for manufacturing a CSP grinding wheel according to claim 1, wherein the predetermined temperature range is 130 to 200°C.

4. The method for manufacturing a CSP grinding wheel according to claim 1, wherein the range of the predetermined time is at least 40 minutes or more.

5. The method for manufacturing a CSP grinding wheel according to claim 1, wherein the surface density of the abrasive grains of the grinding wheel is 2 to 19% in terms of the projected surface area ratio with respect to the grinding wheel surface.

6. The method for producing a CSP grinding wheel according to claim 1, wherein amorphous silica is used as the matrix, and the strong base impregnated therein is sodium hydroxide or potassium hydroxide.

7. The method for manufacturing a CSP grinding wheel according to claim 1, wherein the abrasive grains are diamond abrasive grains.

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