JPH04256581A - Composite grinding wheel - Google Patents

Abstract

PURPOSE:To obtain a composite grinding wheel which can polish a disk base with the alloy composed of a high purity aluminum and magnesium as the raw material in a high accuracy, also whose polishing force is continued longer. CONSTITUTION:It is a structure having a continuous fine pore with abrasive grain particles are combined by a synthetic resin. The synthetic resin is composed of a polyvinyl acetal resin and the body hardening a thermal hardening resin. The rate (VA/VR) of the volume (VA) of the abrasive grain particle to the volume (VR) of the synthetic resin is 0.6-1.3. The porocity is 70-85%. The swelling rate is <=2.0%.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is useful for precision polishing flat surfaces of relatively soft metals, such as aluminum alloy disk masters (hereinafter referred to as "aluminum disks") used in external storage devices for computers. Regarding synthetic whetstones.

0002

2. Description of the Related Art Rigid disk drives are used as external storage devices for computers, and their storage media are usually memory disks in which fine magnetic particles are adhered to a flat and smooth non-magnetic substrate. The surface of the disc-shaped base used in such memory disks must be precisely finished to a mirror-like state with extremely high overall flatness and no defects such as scratches, unevenness, or undulations.

[0003] Conventionally, the substrate used for memory disks is generally made of aluminum alloy, and the standard material is an alloy of about 96% aluminum with a purity of about 99% and about 4% magnesium. It was something like that.

Recently, with the miniaturization and increase in capacity of external storage devices, it has been found that it is effective to increase the purity of aluminum as an alloy raw material, and the purity of aluminum has been increased to 99.9. %, preferably 99.99%, and a substrate made of an alloy of magnesium (
(hereinafter referred to as "high-purity aluminum base") has come to be used.

[0005] A grindstone used for surface finishing processing of a substrate as described above is provided with continuous fine pores, and abrasive grain particles are bonded with a polyvinyl acetal resin and a thermosetting resin.
A polishing whetstone in which the surface hardness (H) and the abrasive grain count (G) satisfy a specific formula
No. 4, Japanese Patent Application Laid-open No. 192480/1983) are known.

[0006] The above-mentioned known grindstone is preferable for precisely finishing the surface of a base made of standard material. However, the high-purity material base has physical properties that are softer and more viscous than the standard material base, and when polished using a conventional whetstone,
Since the polishing speed is low and clogging of the grindstone surface is likely to occur, polishing efficiency and productivity are extremely low. At present, no satisfactory synthetic whetstone has yet been proposed that can efficiently polish high-purity substrates with high precision.

[0007]

[Problems to be Solved by the Invention] As a result of intensive research in view of the above-mentioned circumstances, the present inventors have discovered the requirements necessary for a grindstone for efficiently and precisely polishing a high-purity material base, and have completed the present invention. Therefore, an object of the present invention is to provide a synthetic whetstone that can perform precision surface processing with excellent flatness and smoothness on a high-purity material base, and can perform polishing with a high polishing rate and good sustainability of polishing power. It is in.

[0008]

[Means for Solving the Problems] An object of the present invention is to provide a structure having a three-dimensional network structure having continuous fine pores in which abrasive particles are bonded with a synthetic resin, the synthetic resin being polyvinyl acetal-based. It is made of a cured body of resin and thermosetting resin, and the ratio (VA/VR) of the volume occupied by the abrasive particles (VA) to the volume occupied by the synthetic resin (VR) is 0.6 to 1.3, This is achieved by a synthetic whetstone characterized by a porosity of 70 to 85% and a dimensional change between dry and wet states of 2.0% or less.

The synthetic grindstone of the present invention has a three-dimensional network structure with continuous fine pores. The average pore diameter is preferably 200 μm or less, preferably 100 μm or less, and more preferably 25 μm or less, and is preferably highly uniform. If the pore size is too large, the structure will be too sparse, and extreme pressure will be applied to that part during polishing, resulting in irregular patterns or localized streaks on the polished surface.

[0010] Examples of the abrasive particles used in the present invention include silicon carbide, fused alumina, emery, garnet,
Fine particles such as diamond, silicon nitride, chromium oxide, and cerium oxide can be used, but silicon carbide is particularly suitable for the purpose of the present invention. In addition, the size of the abrasive particles is a high-count product with a count of 1000 or more, preferably 1500 or more. Here, the abrasive grain count is one that is classified according to the particle size described in JIS standard R6001, and has a dispersion within the standard with respect to the average particle size.

As the synthetic resin for bonding the abrasive particles, a cured thermosetting resin is used in combination with a polyvinyl acetal (hereinafter abbreviated as "PVAt") resin. PVAt-based resin has excellent ability to hold fine abrasive grains, and has the property of effectively preventing abrasive grain particles from easily falling off or scattering from a synthetic whetstone. Additionally, the thermosetting resin provides the hardness, brittleness, and dimensional stability that the synthetic grindstone requires.

Examples of the thermosetting resin include melamine resin, urethane resin, phenol resin, epoxy resin, urea resin, etc. These may be used alone or in combination of two or more. good. In the present invention, a combination of a melamine resin and a phenol resin is preferred. The type and amount of the thermosetting resin may be appropriately selected depending on the hardness, brittleness, and dimensional stability required of the synthetic grindstone.

In the present invention, the mixing ratio of the abrasive particles and the synthetic resin is such that the volume occupied by each is VA,
VR, the volume ratio VA/VR (hereinafter,
(referred to as "dispersion density") is 0.6 to 1.3, preferably 0.6 to 1.2. Considering that the dispersion density of synthetic grindstones for aluminum discs that have been used in the past is smaller than 0.6, usually 0.5 or less, this can be said to be an extremely large value. That is, the present inventors have discovered that in order to finish the surface of a high-purity material base with high precision, there is a lower limit and an upper limit to the ratio of abrasive grain particles and synthetic resin, and that this is only possible within the scope of the present invention. It is something.

If the dispersion density is less than 0.6, a sufficient polishing rate cannot be obtained for the high-purity substrate, and efficient polishing cannot be achieved. Moreover, due to the synthetic resin that is the binding material,
Since the surface is rubbed unnecessarily, the surface of the object to be polished has abnormal gloss, and furthermore, shape accuracy such as flatness is reduced. On the other hand, if the dispersion density is greater than 1.3, the surface will be rough and cannot be finished with the required precision.

The synthetic grindstone of the present invention has a porous structure with continuous pores, and by having continuous pores, the heat accompanying polishing can be quickly dissipated and heat accumulation can be prevented. Furthermore, the pores play the extremely important role of holding the polishing liquid used for polishing and temporarily holding abrasive grains, polishing debris, etc. that have fallen off from the polishing surface, and preventing them from having a negative impact on the polishing surface. There is.

[0016] In order to sufficiently perform the above-mentioned effects and to achieve highly accurate surface polishing, the porosity must be 70 to 85% by volume. When the porosity is less than 70% by volume, the gripping capacity for dropped abrasive grains, polishing debris, etc. is insufficient, clogging progresses rapidly, and the number of batches that can be continuously polished with high precision decreases. As a result, the frequency of updating (dressing) the polishing surface increases, resulting in a significant decrease in productivity.

On the other hand, if the porosity is greater than 85%,
The mechanical strength of the synthetic whetstone is insufficient, the abrasion of the whetstone itself is significant, and the shape of the working surface of the whetstone tends to be distorted, making it impossible to achieve the object of the present invention.

The synthetic grindstone of the present invention has a dimensional change between dry and wet conditions, so-called swelling ratio, of 2.0% or less. The swelling ratio (Ds) referred to here is a value obtained by measuring the wet dimension (Tw) with respect to the dry dimension (Td) and using the formula Ds=(Tw-Td)/Td×100.

If the swelling ratio is greater than 2.0%, the bonding force to the abrasive grains, that is, the binding force, is so high that even after the cutting blade loses its abrasive power, it will not fall off, and the structure of the synthetic whetstone will not fall off. will remain. As a result, the synthetic whetstone not only loses its sufficient abrasive power as a whetstone and the polishing speed decreases, but also
This imparts an abnormal gloss to the polished surface and also promotes clogging of the grindstone.

[0020] Usually, a synthetic grindstone using a PVAt resin as a binder has an extremely high swelling rate. Also, PV
Although it is known that a thermosetting resin is used in combination with an At-based resin and has a low swelling rate, the reason for using a thermosetting resin in combination is mainly to impart the necessary hardness and brittleness to the grindstone. For this reason, when manufacturing such synthetic whetstones, the swelling rate has not been considered in the past, and the swelling rate is generally 2%.
It was bigger.

That is, in the present invention, it is extremely important to select the type and amount of the thermosetting resin so that the swelling ratio is 2.0% or less.

The grindstone according to the present invention is manufactured, for example, by the following method.

That is, completely saponified or partially saponified polyvinyl alcohol having an average degree of polymerization of 300 to 2000 or one or more modified products thereof is dissolved in warm water to form an aqueous solution, and a prepolymer of thermosetting resin is added to the aqueous solution. Alternatively, after adding a predetermined amount of a precursor aqueous solution, non-aqueous aqueous solution, emulsion or powder thereof, and further adding the catalyst as necessary, stir uniformly, and then add a predetermined amount of abrasive particles and an aldehyde as a crosslinking agent. A homogeneous viscous slurry is prepared by adding esters, acids as a catalyst, starch as a pore forming agent, etc., and this is poured into a desired mold.

In the above method, the amount of abrasive grains to be blended may be appropriately selected in consideration of the specific gravity of the abrasive grains so that the mixing ratio with the synthetic resin falls within the range of the present invention. In addition, the amount of the pore-forming material is such that the porosity of the resulting synthetic whetstone is between 70 and 85.
It may be appropriately selected so that the capacity is %.

[0025] Thereafter, the mixture is uniformly solidified day and night at a temperature of 40 to 100°C, and then taken out and washed with water to remove the pore-forming material and unreacted aldehydes and acids to obtain an intermediate. The resulting intermediate has the shape of a grindstone, but
The curing reaction of the resin has not yet progressed, and the physical properties are insufficient.

Next, after drying this intermediate, heat treatment (curing) is performed to harden the resin. The heat treatment conditions may be appropriately set depending on the type and amount of the thermosetting resin used, but generally the curing reaction is almost achieved by performing the heat treatment at 100 to 180°C for about 30 hours.

[0027] By curing the resin, the hardness, brittleness and dimensional stability necessary for a grindstone are imparted, and the synthetic grindstone of the present invention can be obtained.

In the above production method, the thermosetting resin may be mixed at the time of preparing the reaction stock solution as described above, but after obtaining the intermediate, the intermediate is impregnated with an aqueous solution of its precursor, and this is You can also cure it. Furthermore, when two or more types of thermosetting resins are used together, one resin may be added to the reaction stock solution and the other resin may be applied by post-impregnation, and there is no particular limitation. In particular, when using a melamine resin, a method of impregnating it into an intermediate is suitable.

After the grindstone obtained as described above is formed into a desired shape, it is used by being attached to extremely precise equipment, such as a double-sided lapping type grinder.

[0030]

[Examples] The present invention will be explained in detail with reference to Examples below. Before that, the polishing apparatus, measuring equipment, object to be polished, etc. used in this example are as follows.

○ Polishing device......Double-sided polishing machine manufactured by Speed FAM (Model 3FDL-16B-4SSG-4D) ○ Surface roughness meter...
Surface roughness meter made by Tokyo Seimitsu (model Surfcom 553A) ○ Bond degree measuring machine…Okoshi type grindstone bond degree tester made by Tokyo Koki ○Hardness meter……Rockwell hardness meter (manufactured by Matsuzawa Seiki)

[
○ Material to be polished: An annular plate made of aluminum alloy consisting of 96% high-purity aluminum and 4% magnesium with a purity of 99.9% or higher as described in JIS standard A5586 (
(manufactured by Kobe Steel).

The polishing conditions and measurement conditions are as follows.

<Polishing conditions> ○Pressure, polishing time...Polishing for 0.5 minutes at 50g/cm2, then polishing for 3 minutes at 100g/cm2○Rotation speed of upper surface plate...23.6r. p. m. (counterclockwise)
○Lower surface plate rotation speed...60.0r. p. m. (turn right)
○Carrier rotation speed...Rotation: 4.8 rpm (counterclockwise) Revolution: 19.3 rpm (clockwise) ○Polishing liquid: Bell coolant #3001 (manufactured by Kanebo) 1% aqueous solution ○Amount of polishing liquid supplied: 5 liters / minute

<Surface accuracy measurement conditions> ○Ra, Rmax, cutoff value...0.8mm or more -Measurement length...
…2.5mm ○WCM ・Cutoff value…0.8mm or less
・Measurement position: from the inner edge to the outer edge in the radial direction of the circumference. Regarding Ra, Rmax, and WCM here,
This is a parameter expressed by the following equation. Ra...Center line average roughness

[Equation 1] f(x) represents the roughness curve. Rmax...Maximum roughness Rmax=Pmax-Vmax Pmax: Maximum peak height in the roughness curve Vmin: Maximum valley depth in the roughness curve WCM...Maximum filter wave WCM=W1 - W2 W1: Maximum peak height in the filter wave curve W2: Maximum valley depth in filter wave curve

<Surface hardness measurement conditions> Rockwell Superficial 15-Y scale Working load: 1.5 kg Measuring point: 1/2 inch steel ball

<Coupling degree measurement conditions> Using a load of 7 kg, J
It was measured by a method based on IS R-6240 method.

(Examples 1-5, Comparative Examples 1-6) As the abrasive grains, silicon carbide powder No. 1500 (average particle size 7.2-8.
6 μm) and No. 3000 (average particle size 3.5 to 4.5 μm)
) were selected.

Partially saponified polyvinyl alcohol with a degree of polymerization of 500 and 1700 is made into an aqueous solution, cornstarch is used as a pore-forming material, a formaldehyde aqueous solution is used as a crosslinking agent, and melamine resin SM-700 (Showa Kobunshi Co., Ltd.) is added to the solution.
Co., Ltd.) aqueous solution and phenolic resin PR-961A (
After adding a predetermined amount of Sumitomo Bakelite (manufactured by Sumitomo Bakelite Co., Ltd.), a predetermined amount of the above-mentioned abrasive grains were mixed, and hydrochloric acid as a catalyst was further added and mixed with stirring to prepare a uniform slurry liquid.

[0040] This slurry liquid was poured into a predetermined mold, and 6
The mixture was reacted and solidified at 0°C for one day and night. Thereafter, the reaction product was taken out from the mold, washed with water to remove cornstarch, unreacted formaldehyde, hydrochloric acid, etc., and dried to obtain an intermediate for a synthetic grindstone. This was heat-treated at a temperature of 155° C. for about 9 hours, and then molded into a predetermined shape to obtain a synthetic whetstone.

[0041] The obtained synthetic whetstone was attached to a polishing device,
As a material to be polished, the high-purity aluminum substrate was polished under predetermined conditions. After polishing for a predetermined period of time, the surface shape of the material to be polished was inspected.

[0042] Also, to check the clogging condition of the grinding wheel surface,
Ten batches of grinding were performed continuously without dressing the grinding wheel surface, and the condition of the grinding surface and the polishing condition at that time were inspected.

The composition and physical properties of the obtained synthetic whetstones as well as the results of the polishing tests are shown in Tables 1 to 4 for Examples and Tables 5 to 4 for Comparative Examples.
It was as shown in Table 8.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

As is clear from Tables 1 to 4, the synthetic grindstone of the present invention can perform excellent surface polishing even on a high-purity aluminum base, which is a difficult-to-grind material, has a high polishing speed, and has a high polishing power. The durability was also good.

On the other hand, the volume ratio (V
Synthetic whetstone with A/VR) smaller than 0.6 (Comparative Example 1)
The polishing speed was low and the grindstone was easily clogged. In addition, in the case where the volume ratio (VA /VR ) was larger than 1.3 (Comparative Example 2), the grinding wheel was heavily worn and lacked durability.

[0054] In addition, the synthetic grindstones (Comparative Examples 3 and 6) with a swelling ratio of more than 2.0% had a low polishing rate and a high surface accuracy, especially the maximum filter waviness (WCM).

Furthermore, the synthetic grindstone with a porosity of less than 70% by volume (Comparative Example 4) was more likely to produce abnormal streaks on the polished surface, and the grindstone became clogged very quickly. Porosity is 85
In the case where the grinding wheel was larger than the volume percentage (Comparative Example 5), the surface precision, particularly the maximum filter wave (WCM), was extremely large, and the grinding wheel wore quickly and lacked durability.

[0056]

[Effects of the Invention] The synthetic grindstone of the present invention can efficiently polish an aluminum disk with excellent surface precision. In addition, it is resistant to clogging and maintains abrasive power well, reducing the number of times the grindstone surface needs to be resurfaced (dressed) compared to conventional products, improving work efficiency and making it possible to polish with stable quality. , the product yield will also be significantly improved.

The synthetic whetstone of the present invention is particularly effective on a high-purity aluminum base made of an alloy of high-purity aluminum and magnesium, which is considered to be an extremely difficult material to grind, and is superior to conventional products. It is possible to perform surface polishing with high precision and excellent durability.

Claims (1)

[Claims] 1. A structure having a three-dimensional network structure having continuous fine pores in which abrasive particles are bonded with a synthetic resin, wherein the synthetic resin is made of a cured product of a polyvinyl acetal resin and a thermosetting resin. The ratio (VA/VR) of the volume occupied by the abrasive particles (VA) to the volume occupied by the synthetic resin (VR) is 0.6 to 1.3, and the porosity is 70 to 85%, A synthetic whetstone, characterized in that the dimensional change between dry and wet conditions is 2.0% or less.