JP2694705B2 - Synthetic grindstone for high-purity aluminum substrate polishing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for precision polishing a flat surface of a relatively soft metal such as an aluminum alloy disk master (hereinafter abbreviated as "aluminum disk") used for an external storage device for a computer. Regarding synthetic whetstones.

[0002]

2. Description of the Related Art There is a rigid disk drive as an external storage device of a computer, and as the storage medium, a memory disk in which magnetic fine particles are coated on a flat and smooth non-magnetic substrate is usually used. The disk-shaped substrate used for such a memory disk is required to have its surface precisely finished to a mirror-like state with excellent flatness without defects such as scratches, unevenness, and undulations.

Conventionally, a base made of an aluminum alloy has been generally used as a base for a memory disk, and a standard material thereof is an alloy of about 96% aluminum having a purity of about 99% and about 4% magnesium. It was.

Recently, it has been found that it is effective to increase the purity of aluminum as an alloy raw material in accordance with the miniaturization and large capacity of an external storage device, and the purity of aluminum is 99.9. %, Preferably 99.99%, and a base made of an alloy of magnesium (hereinafter referred to as “high-purity aluminum base”) have come to be used.

As the grindstone to be used for the surface finishing of the substrate as described above, it has continuous fine pores, and the abrasive grains are bonded by polyvinyl acetal resin and thermosetting resin,
In addition, a grinding wheel having a surface hardness (H) and an abrasive grain count (G) satisfying a specific expression (Japanese Patent Laid-Open No. 61-18277).
4 and Japanese Patent Laid-Open No. 61-192480).

The above-mentioned known grindstone is preferable for precisely finishing the surface of the base made of the standard material. However, the high-purity substrate is softer and more viscous than the standard substrate, and when polished with a conventional grindstone,
Since the polishing rate is low and the surface of the grindstone is likely to be clogged, the polishing efficiency and productivity are extremely low. At present, there is no proposal of a synthetic grindstone capable of polishing a highly pure material substrate with high accuracy and efficiency.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted intensive studies in view of the above circumstances, and as a result, found the requirements for a grindstone for efficiently and precisely polishing a high-purity material substrate, and completed the present invention. Therefore, an object of the present invention is to provide a synthetic grindstone capable of precision surface processing excellent in flatness and smoothness on a high-purity material substrate, and capable of polishing with a high polishing rate and durability of polishing power. It is in.

[0008]

An object of the present invention is to provide a structure having a three-dimensional network structure having continuous fine pores in which abrasive grains are bonded by a synthetic resin, wherein the synthetic resin is a polyvinyl acetal-based structure. It is made of a cured product of resin and thermosetting resin, and the ratio (VA / VR) of the volume (VA) occupied by the abrasive particles and the volume (VR) occupied by the synthetic resin is 0.6 to.
1.3, the porosity is 70 to 85%, and the dimensional change between dry and wet is 2.0% or less.

The synthetic grindstone of the present invention is a structure having a three-dimensional network structure having continuous fine pores. The average pore diameter is 200 μm or less, preferably 100 μm or less, more preferably 25 μm or less, and one having good uniformity is suitable. If the pore diameter is too large, the structural portion becomes too sparse, and extreme pressure is applied to the portion during the polishing work, and an irregular pattern or local scratches are generated on the polishing surface.

The abrasive grains used in the present invention include, for example, silicon carbide, fused amylna, emery, garnet,
Fine particles of diamond, silicon nitride, chromium oxide, cerium oxide and the like can be mentioned, but silicon carbide is preferable for the purpose of the present invention. The size of the abrasive grains is a high count product having a count of 1000 or more, preferably 1500 or more. Here, the grain count of the abrasive grains is classified into the grain size described in JIS standard R6001, and has a dispersion within the standard with respect to the average grain size.

As the synthetic resin for binding the above-mentioned abrasive grains, a polyvinyl acetal (hereinafter abbreviated as "PVAt") type resin and a cured body of a thermosetting resin are used together. The PVAt resin has an excellent ability to hold fine abrasive grains and has a property of effectively preventing the abrasive grains from easily falling off from the synthetic grindstone or scattering. Further, the thermosetting resin imparts the hardness, brittleness and dimensional stability required for the synthetic grindstone.

Examples of the thermosetting resin include melamine-based resins, urethane-based resins, phenol-based resins, epoxy-based resins, urea-based resins and the like. 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 suitable. The type and amount of the thermosetting resin may be appropriately selected according to the hardness, brittleness and dimensional stability required for the synthetic grindstone.

In the present invention, the mixing ratio of the abrasive grains and the synthetic resin is such that the volume occupied by each is V _A , V.
_{When R} , the volume ratio V _A / V _R (hereinafter referred to as “dispersion density”) is 0.6 to 1.3, and preferably 0.6 to 1.2. Considering that the dispersion density of the conventionally used synthetic grindstone for aluminum disks is smaller than 0.6, usually 0.5 or less, it can be said to be an extremely large value. That is, the present inventors have found that in order to finish the surface of the high-purity material substrate with high accuracy, the ratio between the abrasive particles and the synthetic resin has a lower limit and an upper limit, and it is possible for the first time within the scope of the present invention. It is a thing.

If the dispersion density is less than 0.6, a sufficient polishing rate cannot be obtained for a highly pure substrate, and efficient polishing cannot be achieved. Moreover, due to the synthetic resin that is the binder,
Since the surface is rubbed unnecessarily, the surface of the object to be polished has an abnormal gloss, and further, the shape accuracy such as flatness is lowered. On the other hand, when the dispersion density is larger than 1.3, the surface is roughened and the surface cannot be finished to the required accuracy.

The synthetic grindstone of the present invention has a porous structure having continuous pores, and by forming the continuous pores, the heat associated with polishing can be quickly dissipated, and heat accumulation can be prevented. Further, the pores have a very important role of holding the polishing liquid used for polishing and temporarily holding the abrasive grains, polishing debris, etc., which have fallen off the polishing surface, and preventing the polishing surface from being adversely affected. There is.

In order to sufficiently perform the above-mentioned actions and achieve highly accurate surface polishing, the porosity thereof needs to be 70 to 85% by volume. When the porosity is less than 70% by volume, the grasping capacity for the lost abrasive grains and polishing debris is not sufficient, the clogging progresses rapidly, and the number of batches that can be continuously polished with high accuracy decreases. For this reason, the frequency of renewal (dressing) work of the polishing surface is increased, and the productivity is significantly reduced.

On the other hand, when the porosity is larger than 85%,
The mechanical strength as a synthetic grindstone is insufficient, the grindstone itself is significantly worn, and the shape of the working surface of the grindstone is apt to change, and the object of the present invention cannot be achieved.

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

When the swelling ratio is more than 2.0%, the binding force to the abrasive grains, that is, the tie force, is too high and the cutting edge does not fall off even after the polishing force of the cutting edge is lost. Will remain. As a result, the synthetic grindstone does not lose sufficient polishing power as a grindstone, not only reduces the polishing rate, but also imparts an abnormal luster to the polished surface and further accelerates the clogging phenomenon of the grindstone.

Usually, a synthetic grindstone using a PVAt resin as a binder has an extremely large swelling rate. Also, PV
There is also known a resin having a low swelling ratio in which a thermosetting resin is used in combination with an At resin, but the reason for using the thermosetting resin in combination is mainly to impart hardness and brittleness required for a grindstone. Therefore, when manufacturing such a synthetic whetstone, the swelling ratio has not been considered so far, and the swelling ratio is generally 2%.
Was greater than%.

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

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

That is, one or two or more of completely saponified or partially saponified polyvinyl alcohol having an average degree of polymerization of 300 to 2000 or a modified product thereof is dissolved in hot water to form an aqueous solution, and a thermosetting resin prepolymer. or an aqueous solution of the precursor, non-aqueous solvent mixture was added a predetermined amount of the emulsion or a powder, after which the catalyst was added, if necessary, uniformly stirred, further predetermined amount of the abrasive grains particles as a crosslinking agent Aldehydes, acids as a catalyst, starches as a pore-forming agent, etc. are added to prepare a uniform viscous slurry, which is cast in a desired mold.

In the above-mentioned method, the blending amount of the abrasive grains may be appropriately selected in consideration of the specific gravity of the abrasive grains so that the mixing ratio with the synthetic resin is within the range of the present invention. The porosity of the obtained synthetic grindstone is 70 to 8 when the amount of the pore forming material is mixed.
It may be appropriately selected so as to be 5% by volume.

After that, the reaction solidification is carried out at a temperature of 40 to 100 ° C. for a whole day and night, and the product is taken out and washed with water to remove the pore-forming material and unreacted aldehydes and acids to obtain an intermediate. The obtained intermediate is morphologically in the shape of a grindstone, but the curing reaction of the resin has not yet proceeded and the physical properties are insufficient.

Next, after drying this intermediate, heat treatment (curing) is performed to cure 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.

By hardening the resin, the hardness, brittleness and dimensional stability necessary for the grindstone are imparted, and the synthetic grindstone of the present invention is obtained.

In the above-mentioned production method, the thermosetting resin may be mixed at the time of preparing the reaction stock solution as described above. However, after the intermediate is obtained, the aqueous solution of the precursor is impregnated into the intermediate, which is then added. Can be cured. Further, when two or more thermosetting resins are used in combination, 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 a melamine-based resin is used, a method of impregnating the intermediate is suitable.

The grindstone obtained as described above is shaped into a desired shape and then mounted on an extremely precise device such as a double-sided lapping grinder.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples. Prior to that, the polishing apparatus, the measuring instrument, the object to be polished and the like used in this example are as follows.

○ Polishing device ………… Speedfam double-sided polishing machine (model 3FDL-16B-4SSG-4D) ○ Surface roughness meter …… Tokyo Seimitsu surface roughness meter (model Surfcom 553A) ○ Coupling degree measuring machine … Tokyo Koki's Ogoshi-type grindstone bond tester ○ Hardness tester ………… Rockwell hardness tester (Matsuzawa Seiki)

Material to be polished: 96% high-purity aluminum with a purity of 99.9% or more according to JIS standard A5586
Aluminum alloy ring plate (made by Kobe Steel) consisting of 4% magnesium and magnesium.

The polishing conditions and measurement conditions are as follows.

<Polishing conditions> ○ Pressure, polishing time: polishing at 50 g / cm ^{2 for} 0.5 minutes and then at 100 g / cm ^{2 for} 3 minutes ○ Upper surface plate rotation speed: 23.6 r. p. m. (Counterclockwise) ○ Lower platen rotation speed …… 60.0r. p. m. (Clockwise) ○ Carrier rotation speed… Spinning 4.8 rpm (counterclockwise) Revolution 19.3 rpm (clockwise) ○ Polishing liquid ………… Bell coolant # 3001 (Kanebo) 1% aqueous solution ○ Polishing liquid supply amount ……… 5 l / min

<Surface accuracy measurement conditions> ○ Ra, Rmax ・ Cutoff value… 0.8 mm or more ・ Measurement length ………… 2.5 mm ○ W _CM・ Cutoff value… 0.8 mm or less ・ Measurement position ……… From the inner edge to the outer edge in the radial direction of the circumference. Note that Ra, Rmax, and W _CM referred to here are parameters represented by the following equations. Ra ... center line average roughness

(Equation 1) f (x) shows a roughness curve. Rmax ... maximum roughness Rmax = Pmax-Vmax Pmax: maximum peak height in the roughness curve Vmin: up to a maximum valley depth W _CM ... filtering in the roughness curve undulation _{W CM = W 1 -W 2 W} 1: filtered waviness Maximum peak height on curve W ₂ : Maximum valley depth on filtered wave curve

<Surface hardness measurement conditions> Rockwell Superficial 15-Y scale use load 1.5 kg probe 1/2 inch steel ball

<Condition measuring conditions> Using a load of 7 kg, J
It measured by the method based on ISR-6240 method.

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

A partially saponified polyvinyl alcohol having a degree of polymerization of 500 and 1700 was made into an aqueous solution, and cornstarch as a pore-forming material, an aqueous formaldehyde solution as a cross-linking agent, and melamine resin SM-700 (manufactured by Showa High Polymer Co., Ltd.) were used. Aqueous solution and phenol resin PR-961A
(Sumitomo Bakelite Co., Ltd.) was added in a predetermined amount, the above-mentioned abrasive grains were mixed in a predetermined amount, hydrochloric acid as a catalyst was further added, and the mixture was stirred and mixed to prepare a uniform slurry liquid.

This slurry liquid was cast into a predetermined mold, and 6
The reaction was solidified at 0 ° C for one day. Thereafter, the reaction product was taken out from the mold, washed with water to remove corn starch, unreacted formaldehyde, hydrochloric acid and the like, and then dried to obtain an intermediate of 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 grindstone.

The obtained synthetic grindstone was attached to a polishing device,
The high-purity aluminum substrate as a material to be polished was polished under predetermined conditions. After polishing for a predetermined time, the surface shape of the material to be polished was inspected.

Further, in order to confirm the clogging state of the grindstone surface,
Polishing was performed continuously for 10 batches without dressing work on the surface of the grindstone, and the state of the grinding surface and the state of polishing at that time were inspected.

The composition and physical properties of the obtained synthetic grindstone and the results of the polishing test are shown in Tables 1 to 4 in Examples and Tables 5 to 5 in Comparative Examples.
The results are 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 is capable of excellent surface polishing processing even on a highly pure aluminum base material which is a material that is difficult to grind, and has a high polishing rate and polishing power. The persistence of was also good.

On the other hand, the volume ratio of the abrasive particles to the synthetic resin (V
_The synthetic grindstone ( _A / V _R ) of less than 0.6 (Comparative Example 1) had a low polishing rate and was easily clogged with the grindstone. Further, in the case where the volume ratio (V _A / V _R ) was larger than 1.3 (Comparative Example 2), the grindstone was greatly worn and lacked in durability.

Further, the synthetic grindstones having a swelling ratio of more than 2.0% (Comparative Examples 3 and 6) had a low polishing rate and had a large surface accuracy, especially the maximum waviness (W _CM ) of the filtered wave.

Further, in the synthetic grindstone having a porosity of less than 70% by volume (Comparative Example 4), abnormal scratches were easily generated on the polished surface, and the clogging of the grindstone occurred extremely quickly. Porosity is 85
Those having a capacity of more than% by volume (Comparative Example 5) had extremely large surface accuracy, especially the maximum waviness (W _CM ) of the filtered wave, and the wheel was worn quickly and lacked in durability.

[0056]

EFFECTS OF THE INVENTION The synthetic grindstone of the present invention can efficiently polish an aluminum disk with excellent surface accuracy. In addition, clogging is less likely to occur and the durability of the polishing power is good, the number of surface renewal (dressing) of the grindstone can be reduced compared to the conventional product, the work efficiency is improved, and stable quality polishing is possible. The product yield is also significantly improved.

The synthetic grindstone of the present invention exerts its effect particularly on a high-purity aluminum base made of an alloy of high-purity aluminum and magnesium, which is extremely difficult to grind. It is possible to perform surface polishing processing with high precision and excellent durability.

Claims (1)

(57) [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 a cured product of a polyvinyl acetal resin and a thermosetting resin. The ratio (VA / VR) of the volume (VA) occupied by the abrasive grains and the volume (VR) occupied by the synthetic resin is 0.6 to 1.3, and the porosity thereof is 70.
~ 85%, and the dimensional change between dry and wet is 2.0
% Or less, a synthetic grindstone for polishing aluminum substrate of high purity material.