WO2017111078A1 - Polishing liquid for glass and polishing method - Google Patents

Abstract

Two-stage polishing of pre-polishing and post-polishing was conducted in the polishing of plate glass. A composition having extremely high acidity and containing hydrofluoric acid (hydrofluoric acid) and sulfuric acid is used as the polishing liquid used in conventional pre-polishing. Therefore, the need for a polishing liquid of a more manageable composition became a technical problem. A polishing liquid for plate glass wherein the polishing liquid is characterized by including hydrofluoric acid and an organic solvent having a relative dielectric constant of 10 to less than 40 makes it possible to conduct pre-polishing without causing scratches to grow and suppresses the amount of sludge generated during neutralization after use.

Description

Polishing liquid for glass and polishing method

The present invention relates to a polishing liquid and a polishing method for polishing glass of liquid crystal screens and organic EL screens used for portable terminals, FPDs (flat panel displays) and the like.

Liquid crystal display devices and organic EL display devices are widely used in products such as mobile phones, smartphones, tablet PCs, and notebook computers. And these flat display devices mainly use glass as a base material. Hereinafter, these display devices are referred to as “glass display devices”.

In a glass display device, a driving unit such as a liquid crystal, a TFT, or a light emitting layer is formed between two plate glasses serving as a base material. When the drive unit is formed, strength is required so that the glass does not break during handling. For this reason, the glass material is not soda glass used for window glass or the like, but aluminoborosilicate glass (aluminoborosilicate glass) mixed with boric acid and alumina. Further, the glass thickness is used to a certain extent.

However, after being formed into the shape of a glass display device, the thick glass is heavy and inconvenient to carry. Therefore, after manufacturing the product, the glass is polished with an etching solution for glass to reduce the thickness.

It is known that one of the problems in this polishing is that a dent (hereinafter referred to as “dimple”) occurs in the polished glass. The dimple is a recess having a diameter of about several μm to several hundred μm and a depth of several μm to several tens of μm. The dimples on the display device may be noticeable depending on the image, which may cause a problem in product quality. Accordingly, dimple suppression after polishing is one of the technical problems in glass polishing.

In Patent Document 1, in order to prevent pits and scratches at the 10 μm level from expanding to 100 μm or more by polishing, 30 to 60% by weight of hydrofluoric acid is contained as a polishing component, and inorganic substances such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. A polishing liquid containing one or more additives selected from acid, ester, phenol, amide, ether, nonion, amine and other surfactants at a polishing rate of 1 μm / sec or more. A technique for polishing is disclosed.

Patent Document 2 discloses a pre-polishing step in which a polishing solution containing 10 to 30% by weight of hydrofluoric acid and 20 to 50% by weight of sulfuric acid is brought into contact with the surface of the glass plate to pre-polish the glass plate surface at 1 μm / sec or more; After the pre-polishing step, a post-polishing step is provided in which a polishing liquid containing hydrofluoric acid is brought into contact with the glass plate surface to polish the glass plate surface at a polishing rate of 0.5 to 20 μm / min. A method for polishing a glass plate surface is disclosed.

Patent Document 3 discloses pre-polishing using 0.4 to 4% by weight hydrofluoric acid and 40 to 90% by weight sulfuric acid, and post-polishing using 2 to 30% by weight hydrofluoric acid.

JP 2003-226552 A JP 2005-343742 A JP 2007-297228 A

According to the above-mentioned prior art documents, it was first concluded that the dimples were caused by the growth of slight scratches caused by force majeure in the plate glass as a base material by etching called polishing. Yes.

Therefore, as a policy for suppressing dimples, the scratches generated on the glass plate as a base material are removed before they grow into dimples or are made difficult to grow (pre-polishing), and then the main polishing (after-polishing) Polishing). The reason why the polishing is performed in multiple stages as in Patent Documents 2 and 3 is that the polishing thickness control is not easy for polishing in which the scratches are removed before the scratches grow into dimples.

Such a polishing method is effective at the manufacturing site and is considered to be continued even now. However, the polishing liquid used for such pre-polishing has a composition with extremely strong acidity of hydrofluoric acid (hydrofluoric acid) and sulfuric acid. For this reason, in the detoxification process before discarding the polishing liquid used in the pre-polishing, inconveniences such as the generation of a large amount of sludge during the neutralization process have occurred. Accordingly, there has been a demand for a polishing liquid having a composition that is easier to handle while maintaining the effect of pre-polishing, which has been a technical problem.

The present invention has been conceived in view of the above problems. More specifically, the polishing liquid according to the present invention is a plate glass polishing liquid, and contains hydrofluoric acid and an organic solvent.

Since the polishing liquid according to the present invention has a composition of hydrofluoric acid and an organic solvent having a relative dielectric constant of 10 or more and less than 40, sulfuric acid is not used. Therefore, the acidity is weaker than the polishing liquid used for the conventional pre-polishing, and the amount of sludge generated during the neutralization treatment can be suppressed.

It is a figure which shows how to put indentation. It is a photograph which illustrates a mode that a crack grows from an indentation.

The polishing liquid according to the present invention will be described below. In addition, the following description demonstrates one form and one Example of this invention, and this invention is not limited to the following description. The following description can be modified without departing from the spirit of the present invention.

The polishing liquid according to the present invention is a polishing liquid used for pre-polishing when it is divided into pre-polishing and post-polishing when polishing a glass display device. The object of polishing is glass that can be used for glass display devices. An oxide glass containing an oxide as the main component can be suitably used. Of these, glass mainly composed of aluminosilicate glass (alumina and silicon oxide) is preferable. Aluminosilicate glass has high tensile strength and is preferable as a base material for glass display devices.

¡Aluminosilicate glass can be made in various compositions by changing the type of element added. Aluminoborosilicate glass (aluminoborosilicate glass) with B (boron) added to the main component and elements such as Mg (magnesium), Ca (calcium), Sr (strontium), and Ba (barium) added as auxiliary components ), And is particularly preferably used as a substrate of a glass display device.

Glass is handled in the form of plate glass. This is because the substrate of the glass display device is used. Therefore, although it is glass, glass that cannot be supplied as a plate glass, such as a semiconductor insulating film, is not an object of polishing.

The polishing liquid according to the present invention contains hydrofluoric acid (hydrofluoric acid) and an organic solvent. The organic solvent is easier to handle and dispose of compared to sulfuric acid that has been conventionally used. The hydrofluoric acid and the organic solvent are supplied as an anhydride or an aqueous solution.

As the organic solvent, those having a relative dielectric constant of 10 or more can be suitably used as shown in Examples described later. The reason for this is still unknown. However, in general, hydrofluoric acid is considered to be in a two-stage equilibrium state as follows.
HF ⇔ H + + F- (1)
HF + F- ⇔ HF2- (2)

As described above, the form of fluorine in the hydrofluoric acid solution is HF, F-, HF2-, and among these, the component (hereinafter referred to as active species) that contributes to the etching of glass mainly composed of SiO2 is HF2-. And HF. Furthermore, it is generally known that among active species, HF2- contributes more to etching than HF.

When an organic solvent is contained in the hydrofluoric acid solution, the equilibrium of the formula (1) shifts to the left, so that the generation of F- is suppressed, and as a result, the generation of HF2- is reduced in (2). That is, in the hydrofluoric acid solution containing an organic solvent, the HF fraction increases and the HF2- fraction decreases compared to a solution containing no organic solvent.

These tendencies depend on the relative permittivity of the organic solvent. The lower the relative permittivity, the higher the HF fraction and the lower the HF2- fraction. Therefore, in the present invention, as a result of the presence of the organic solvent having a relative dielectric constant of 10 or more and less than 40, the abundance ratio of the HF fraction and the HF2- fraction in the active species is controlled within a suitable range. Even if there is a scratch on the surface of the plate glass, it can be removed without growing into dimples. Then, it is considered that the glass surface of the glass display device can be etched by a predetermined thickness by post-polishing.

Examples of organic solvents that can be suitably used include the following. The numerical value in parentheses is the relative dielectric constant. t-butyl alcohol (12.5), benzyl alcohol (13.1), ethylene glycol monomethyl ether (16.9), 1-butanol (17.5), isobutyl alcohol (17.9), cyclohexanone (18.3) ), Ethyl methyl ketone (18.5), 2-propanol (19.9), 1-propanol (20.3), acetone (20.7), ethanol (24.6), methanol (32.7), Nitromethane (35.9), ethylene glycol (37.7), etc. are mentioned. Of these, ethanol is easy to handle and can be suitably used.

In the glass polishing method using the polishing liquid according to the present invention, the front and back surfaces of a glass display device (non-processed product) formed using plate glass are polished with the polishing liquid according to the present invention, several tens of μm in terms of one side. It comprises a polishing step, and then a post-polishing step of several hundred μm after the main polishing. In the post-polishing step, the polishing liquid contains no organic solvent.

In addition, you may put the washing process which wash | cleans a to-be-processed object between a pre-polishing process and a post-polishing process, and after a post-polishing process. This is because the polishing liquid used in the polishing step is not brought into the next step.

Hereinafter, the effects of the polishing liquid according to the present invention will be described with reference to examples. It is believed that the dimples discovered after this polishing have grown minute scratches attached to the surface of the plate glass during handling. In fact, dimples may be discovered after the final polishing even from a portion where no scratches were found by inspection using a microscope.

Therefore, in order to examine whether or not the polishing liquid can be used as a pre-polishing liquid, it is necessary to examine whether the scratches grow on the dimples after pre-polishing by scratching the glass surface in advance.

Therefore, the following method was used as an evaluation system for the polishing liquid. First, an indentation is made on the surface of an object to be processed using a micro Vickers hardness meter also used in Patent Document 2. This indentation is a substitute for scratches. The workpiece is aluminoborosilicate glass of 5 cm × 2.5 cm × 0.7 mm.

The indentation was made with a micro Vickers hardness tester under the conditions of an applied load of 500 g and an applied time of 5 seconds. The resulting indentation was a quadrangular pyramidal dent with a diagonal of 38 μm and a depth of 3.5 μm. A total of four indentations were formed at the four corners of the workpiece.

Next, immerse the workpiece in a polishing liquid for examination for a certain period of time. The fixed time was adjusted so that one side of the workpiece could be polished by 10 μm or 20 μm. The polishing liquid was 40 ° C.

Evaluation was performed by immersing the object to be processed with the impression in the object to be examined and then observing under a microscope, and whether or not a crack grew from the corner of the impression. That is, the crack generation rate was used as a guideline for evaluation. The reason is that when no crack is generated by the pre-polishing process, only the indented part is enlarged by polishing (FIGS. 2 (e) and (f)), whereas when the crack is generated from the indented, the indented part In addition to the enlargement, the inside of the crack is also etched and enlarged (FIGS. 2B and 2C). Since the crack is generated from the lower portion of the indentation, the inside of the crack is etched to grow into a deep dimple.

After performing polishing (meaning pre-polishing) according to the present invention on one side of 20 μm, after performing post-polishing on a single side of 300 μm with a hydrofluoric acid aqueous solution not containing an organic solvent, indentation when no cracks are generated in the pre-polishing. Disappears, but when the crack is generated, the indentation grows into a huge dimple having a diameter of 100 to 200 μm. The “hydrofluoric acid aqueous solution” is a solution of hydrofluoric acid and water.

Fig. 1 explains the occurrence rate of cracks. FIG. 1A shows a state in which the indentations 12 are still formed at the four corners of the workpiece 10. After being dipped in a polishing liquid for examination and polished on one side by 10 μm, if no indentation remains and no cracks are generated as before polishing, the crack generation rate was set to zero%.

FIG. 1B shows a case where crack growth is observed from two of the four indentations 12. In such a state, the crack occurrence rate was 50%. In addition, the lines 14 and 16 in FIG.1 (b) mean the growth direction of a crack. Since the indentation 12 has a square shape, it is considered that cracks grow in the same way from the four corners, but there are cases where the cracks grow only in one direction. Line 14 shows the case where cracks grow in the horizontal direction in the drawing, and line 16 shows the case where cracks grow in the vertical direction.

FIG. 1 (c) shows a case where crack growth is observed at three locations among the four indentations 12. The crack generation rate was 75%. Moreover, FIG.1 (d) and FIG.1 (e) show the case where a crack grew from four indentations 12. FIG. As shown in FIG. 1 (d), even when the crack generation direction is only one direction, it was determined that the crack grew, and the crack generation rate was set to 100%.

<Confirmation of evaluation system>
First, the degree of growth of cracks in the case where only the hydrofluoric acid aqueous solution is used for the object to be indented (Comparative Example 4 described later) and the case where ethanol is used as the organic solvent (Example described later) are shown by micrographs. In Comparative Example 4, the aqueous hydrofluoric acid solution is 3% by mass. Moreover, an Example is a case of the liquid mixture (the remainder is water) of 3 mass% hydrofluoric acid aqueous solution and 75 mass% ethanol.

2 (a), 2 (b), and 2 (c) are for the comparative example 4, and FIGS. 2 (d), 2 (e), and 2 (f) are for the example. . The lower right line of each photograph shows 100 μm. 2 (a) and 2 (d) show the case before polishing, and FIGS. 2 (b) and 2 (e) show the case where the thickness of 10 μm on one side of the workpiece is polished. 2 (c) and FIG. 2 (f) show the case where the thickness of one side of the workpiece is polished by 20 μm. 2 (a), 2 (d), 2 (e), and 2 (f), the portion where the indentation remains is circled because the photograph is thin.

Fig. 2 (a) and Fig. 2 (d) show the case of indentation only. Here, a square whose diagonal is 38 μm is shown. FIG. 2B and FIG. 2E are photographs in the case of polishing by a thickness of 10 μm on one side. In the case of Comparative Example 4 (FIG. 2B), the indentation had cracks growing from four corners, resulting in a cross-shaped scratch. The crack had a length of about 90 μm.

On the other hand, in the case of the example (FIG. 2E), the indentation did not spread. Since the polished thickness (10 μm) is larger than the depth of the indentation, if the indentation remains as it is, the indentation should not be reflected. However, the shape of the indentation remains. Therefore, although the crack did not spread around, it can be judged that the shape as it was was maintained in the depth direction. In such a state, it was determined that there was no crack growth.

FIG. 2 (c) and FIG. 2 (f) are photographs in the case of polishing by a thickness of 20 μm on one side. In Comparative Example 4 (FIG. 2C), the cracks were further grown and the length was grown to about 110 μm. Further, while maintaining the cross-shaped shape, each line was thicker than in the case of FIG. That is, the crack spread not only in the four corner directions of the indentation but also in the direction of the side.

On the other hand, in the example (FIG. 2 (f)), almost the same image as that in the case where the polishing amount was 10 μm was shown, and no crack growth was observed. Thus, it was judged that whether or not scratches grow into dimples in post-polishing can be evaluated based on the presence or absence of crack growth in the state of 10 μm on one side.

<Experimental result>
The organic solvent of the example is ethanol (relative dielectric constant 24.5). Comparative Example 1 is an organic solvent tetrahydrofuran (THF: relative permittivity 7.8), Comparative Example 2 is an organic solvent acetic acid (relative permittivity 6.2), and Comparative Example 3 is propionic acid (relative permittivity 3). .4), Comparative Example 4 is a case of only hydrofluoric acid without an organic solvent. That is, Comparative Example 4 is a simple hydrofluoric acid aqueous solution.

The concentration of hydrofluoric acid was changed to 3 mass%, 5 mass%, 7 mass%, and 10 mass%, respectively. On the other hand, the organic solvent was changed to 75% by mass, 70% by mass, 67% by mass, and 64% by mass depending on the concentration of hydrofluoric acid. The rest is water. Moreover, all are mass ratios with respect to the whole polishing liquid.

The results are shown in Table 1.

Refer to Table 1. After all, the crack occurrence rate was only 0% or 100%. That is, it can be seen that cracks always occur under conditions where they occur, and hardly occur under conditions where they do not occur.

Referring to Table 1, in a polishing liquid (Example) in which ethanol and hydrofluoric acid, which are organic solvents having a relative dielectric constant of 10 or more, were mixed, cracking was performed up to a condition where the solvent concentration was 67 mass% and hydrofluoric acid was 7 mass%. Occurrence of zero was achieved. However, when the solvent concentration was less than 67% by mass and the hydrofluoric acid concentration exceeded 7% by mass, the occurrence rate of cracks was 100%.

Although not listed in Table 1, methanol (ε = 32.7), acetone (ε = 20.6), 1-propanol (ε = 20.3), 2-propanol (ε = 19.9) However, similar results could be obtained under the conditions of a solvent concentration of 65% by mass or more and a hydrofluoric acid concentration of 3 to 7% by mass. Therefore, in the polishing liquid according to the present invention, an organic solvent having a relative dielectric constant of 10 or more and less than 40 can be suitably used.

On the other hand, cracks always occurred in THF, acetic acid, and propionic acid, which are organic solvents having a relative dielectric constant of less than 10, regardless of the concentration of the organic solvent.

In the examples shown in Table 1, when the occurrence of cracks was 0%, no dimples were generated even after post-polishing with a hydrofluoric acid aqueous solution containing no organic solvent at about 300 μm. On the other hand, when cracks occurred in the examples and comparative examples of Table 1, the cracks grew into huge dimples having a diameter of about 100 to 200 μm when post-polishing.

From the above, a polishing liquid that combines hydrofluoric acid and an organic solvent can make the growth of cracks zero, and a polishing liquid that can suppress the generation of dimples can be obtained.

The polishing liquid of the present invention can be suitably used in a pre-polishing step when polishing plate glass.

10 Object (sheet glass)
12 Indentation 14, 16 Crack

Claims (5)

1. Plate glass polishing liquid,
   A polishing liquid comprising hydrofluoric acid and an organic solvent having a relative dielectric constant of 10 or more and less than 40.
2. The polishing liquid according to claim 1, wherein the organic solvent is 65% by mass or more and 80% by mass or less.
3. The polishing liquid according to claim 1 or 2, wherein the plate glass is aluminoborosilicate glass (aluminoborosilicate glass).
4. The polishing liquid according to any one of claims 1 to 3, wherein the organic solvent is ethanol.
5. A method of polishing plate glass,
   Pre-polishing the plate glass with the polishing liquid according to any one of claims 1 to 4, and
   A method for polishing plate glass, comprising a step of further polishing the plate glass with a polishing liquid containing a hydrofluoric acid aqueous solution containing no organic solvent.

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