JP4994405B2 - Method for determining quality of release film of press mold and method for manufacturing optical element - Google Patents

Description

The present invention relates to a method for determining the quality of a release film formed on a molding surface of a molding die used for manufacturing a glass optical element such as a lens or a prism by press molding a glass material. .
Furthermore, the present invention relates to a method for manufacturing an optical element, which includes performing pass / fail determination of a release film by the pass / fail determination method.

  By pressing the softened glass material with a mold, when the optical element such as a lens is obtained, the glass material is used in order to prevent the molding surface of the mold and the glass material from fusing and to obtain releasability. A coating made of a carbon-based material is provided on the surface (see Patent Document 1), and a release film such as a carbon-based thin film, a metal nitride-based thin film, or a metal carbide-based thin film is provided on the molding surface of the mold. (For example, see Patent Documents 2 to 6).

JP 2004-231505 A Japanese Patent Laid-Open No. 3-50127 JP 2003-313046 A JP 2008-1572 A Japanese Patent Laid-Open No. 7-138033 JP 2001-335331 A

  The release film provided on the molding die is required to have an effect of suppressing cracking (cracking of a molded product that occurs during press molding) during press molding. For example, Patent Documents 5 and 6 describe that the surface shape of a release film is measured by an atomic force microscope or a stylus-type shape measuring instrument. It is difficult to determine whether it has the desired performance.

  Therefore, an object of the present invention is to provide a means for determining the quality of a release film on a press mold.

As a result of intensive studies to achieve the above object, the present inventor has obtained the following knowledge.
The smaller the frictional force acting between the press mold and the material to be molded (glass material), the smaller the deformation stress applied between the mold and the molding material during press molding. It is thought to be suppressed. Therefore, the present inventor tried to obtain a correlation with the occurrence frequency of cracking of the optical element by measuring the friction coefficient with a general commercially available friction coefficient measuring device, but could not obtain a good correlation. It was. In this regard, the present inventor has found that the measurement conditions in a general friction coefficient measurement apparatus are significantly different from the conditions in which a release film is placed during press molding. The reason is that a good correlation cannot be obtained with the coefficient.
As a result of further studies based on the above knowledge, the present inventor determined the compressive stress applied to the film to be measured at the time of measuring the friction coefficient based on the surface pressure generated on the release film at the time of press molding, and the object to be measured By determining the relative movement speed between the film and the probe on the basis of the shear rate generated at the interface between the release film and the glass material during press molding, the measured friction coefficient value and crack The inventors have newly found that a good correlation is established with the occurrence of the above, and have completed the present invention.

That is, the above object was achieved by the following means.
[1] A method for determining pass / fail of a release film formed on a molding surface of a press mold used for press-molding a glass material to be molded,
The friction coefficient is obtained by sliding either the film or the measuring element against the other in a state where the measuring element is pressed against the release film or the film formed under the same conditions as the release film. If the measured friction coefficient is less than or equal to a preset reference value, the release film is determined as a non-defective product, and if the measured value exceeds the reference value, the release film is determined as a defective product. Determining the quality of the release film, and
Setting the compressive stress applied to the film at the time of pressing in the range of 5 to 80 MPa, and setting the relative movement speed when sliding between the film and the probe to 0.2 mm / sec or less,
A quality determination method for a release film of a press mold, characterized by
[2] A compressive stress applied to the film at the time of pressing is determined based on a surface pressure generated on the release film at the time of press molding, and a relative moving speed at the time of sliding between the film and the measuring element is determined by pressing The quality determination method for a release film of a press mold according to [1], including determining based on a shear rate generated at an interface between the release film and the glass material to be molded at the time of molding.
[ 3 ] The method according to [1], wherein the measuring element is made of the same material as that of the glass material to be formed in a portion that contacts the film when the pressing is performed.
[ 4 ] For the pass / fail judgment, the measured value of the friction coefficient after repeated sliding, the minimum value of the friction coefficient during repeated sliding, and the amount of change over time of the friction coefficient during repeated sliding are below a preset reference value. The method according to any one of [1] to [ 3 ], which is performed by determining a product as a non-defective product and determining a product exceeding the value as a defective product.
[ 5 ] The method according to [ 4 ], wherein the number of times of repeated sliding is determined based on a desired number of times of use of the press mold.
[ 6 ] A method for producing a glass optical element, comprising supplying a glass material to be molded to a mold, and then press-molding the supplied glass material to be molded with the mold.
Performing pass / fail judgment of the release film formed on the molding surface of the mold by the method according to any one of [1] to [ 5 ],
Using the mold in which the release film is determined to be non-defective by the determination, for the press molding,
A method for producing a glass optical element.

According to the method of determining the quality of the release film of the press mold of the present invention, the quality of the release film can be determined with high reliability.
According to the method for producing a glass optical element of the present invention, by using a press mold having a good release film determined to be non-defective as a result of pass / fail judgment, productivity improvement by press molding and defective product rate reduction are achieved. The production cost can be suppressed by the above.

It is a perspective view of a press mold and a glass material to be molded. It is explanatory drawing of the film-forming apparatus. It is explanatory drawing of the aspect simultaneously formed into a press mold and a sample. It is explanatory drawing of the compressive load and frictional force which are applied to a release film. It is a perspective view which shows the structure of a friction coefficient measuring apparatus. It is a graph which shows a response | compatibility with the friction coefficient in Example 1, and the incidence rate of crack. It is a graph which shows a response | compatibility with the friction coefficient in the comparative example 1, and the incidence rate of crack. It is a graph which shows the relationship between the friction coefficient in Example 2, and the incidence rate of cracking. It is a graph which shows the measurement result of a reference example.

[How to judge the quality of the release film of a press mold]
The present invention
A method for determining the quality of a release film formed on a molding surface of a press mold used for press molding a glass material to be molded,
The friction coefficient is obtained by sliding either the film or the measuring element against the other in a state where the measuring element is pressed against the release film or the film formed under the same conditions as the release film. If the measured friction coefficient is less than or equal to a preset reference value, the release film is determined as a non-defective product, and if the measured value exceeds the reference value, the release film is determined as a defective product. Determining the quality of the release film, and
The compressive stress applied to the film at the time of pressing is determined based on the surface pressure generated on the release film at the time of press molding, and the relative moving speed at the time of sliding between the film and the probe is determined at the time of press molding. Determining based on the shear rate generated at the interface between the release film and the glass material to be molded,
And a quality determination method for a release film of a press mold (hereinafter referred to as “quality determination method 1”). Hereinafter, the quality determination method 1 and the quality determination method 2 described later may be collectively referred to as the quality determination method of the present invention.

  FIG. 1 shows a perspective view of a press mold and a glass material to be molded. As shown in FIG. 1, the glass material to be molded and the molding surface of the mold are in direct contact during press molding. Here, when a chemical reaction occurs at the interface between the glass material to be molded and the molding surface, glass cracking occurs due to fusion or high deformation stress. Therefore, a carbon film is used to suppress the chemical reaction and relieve the deformation stress. It is widely performed to provide a release film such as a mold on the molding surface of a mold. The quality determination method of the present invention is for determining the quality of the release film formed on the molding surface of the press mold used for press-molding the glass material to be molded.

The pass / fail judgment method of the present invention comprises the step of pressing the measuring element against a release film formed on a molding surface of a press mold or a film formed under the same conditions as the release film. Measuring the friction coefficient by sliding one of the measurements with respect to the other (hereinafter referred to as “friction coefficient measurement process”), and if the measured friction coefficient is less than a preset reference value The release film is determined to be a non-defective product, and if the value exceeds the reference value, the release film is determined to be a defective product, thereby determining the quality of the release film (hereinafter referred to as “good / bad determination step”). Included).
Hereinafter, the detail of the said process is demonstrated sequentially.

Friction coefficient measurement process The friction coefficient measurement target in this step may be the release film itself to be a pass / fail judgment target, or a film formed under the same conditions as the release film (hereinafter also referred to as “sample film”). ). There is no restriction | limiting in particular as said mold release film, The various coating films provided for the purpose of mold release improvement on the molding surface of a press mold are mentioned. Examples of such coatings include diamond-like carbon films, hydrogenated diamond-like carbon films, tetrahedral amorphous carbon films, hydrogenated tetrahedral amorphous carbon films, amorphous carbon films, hydrogenated amorphous carbon films, and nitrogen. Carbon-based films such as carbon films, platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), ruthenium (Ru), rhenium (Re), tungsten (W), and An alloy film containing at least one metal selected from tantalum (Ta) can be given. The thickness of these release films is not particularly limited. Further, the release film is formed by DC-plasma CVD method, RF-plasma CVD method, microwave plasma CVD method, ECR-plasma CVD method, plasma CVD method such as photo-CVD method, laser CVD method, ion plate, etc. Techniques such as ionizing vapor deposition such as a coating method, sputtering, ion plating, vapor deposition, and FCA (Filtered Cathodic Arc) can be used.

The sample film is a film formed under the same conditions as the release film to be judged as good or bad. Here, “deposited under the same conditions” means, for example, that the films were simultaneously formed in the same film forming apparatus as the release film. In the batch type film forming method, the film was formed in the same film forming lot. Say it was filmed.
For example, in film formation by sputtering, as shown in FIG. 2, a press mold is placed in a film forming apparatus so as to face a film forming material (target), and the inside of the apparatus is evacuated, and then argon or the like is used. A release film is formed on the molding surface of the press mold by applying a DC or AC electric field to the sputtering gas in a state where the inside of the apparatus is maintained at a predetermined pressure with the sputtering gas. Here, as shown in FIG. 2, the sample film can be formed on the surface of the sample substrate by arranging the sample substrate together with the press mold in the film forming apparatus. As a sample base material, the base material which has the same shape as a press-molding die may be sufficient, and arbitrary-shaped base materials, such as a flat plate, may be sufficient. From the viewpoint of ease of measuring the coefficient of friction described later, it is preferable to use a sample base material having a flat surface. On the surface of the sample substrate, it is desirable from the viewpoint of the reliability of pass / fail judgment that a film having the same quality, thickness, etc. as the press mold and the film (release film) is formed. From this point of view, it is preferable to preliminarily determine a region (a prescribed film formation region) where the sample base material is arranged as shown in FIG. 3 by performing a preliminary experiment prior to actual film formation. For example, an area where the film thickness distribution of the film to be formed is 10% or less can be set as the prescribed film formation area.

  In the present invention, the friction coefficient is obtained by sliding at least one of the film (release film or sample film) or the measuring element with respect to the other while pressing the measuring element against the release film or the sample film. Measure. For example, the film may be slid with respect to the probe, or the probe may be slid with respect to the film. Hereinafter, the film (release film or sample film) to be measured for the friction coefficient is also referred to as “measuring film”.

FIG. 4 is an explanatory diagram of the friction coefficient measurement. As shown in FIG. 4, the friction coefficient is determined from the frictional force generated when the probe is slid on the pressed surface in a state where a compressive load (vertical load) is applied in the vertical direction to the pressed surface.
Coefficient of friction = friction force / compressive load. In the quality determination method 1, the compressive stress applied to the measurement target film at the time of pressing is determined based on the surface pressure generated on the release film at the time of press molding, and the relative movement during sliding between the measurement target film and the measuring element is determined. The speed is determined based on the shear rate generated at the interface between the release film and the glass material to be molded during press molding. Hereinafter, this point will be described in more detail.

As described above, the smaller the frictional force acting between the press mold and the glass material to be molded, the smaller the deformation stress applied between the mold and the mold material during press molding. It is considered that cracking of the element is suppressed. Therefore, the inventors measured the coefficient of friction with a commercially available general coefficient of friction measuring device and tried to correlate it with the frequency of cracking of the optical element, but a good correlation could not be obtained. There wasn't. In this regard, the inventor of the present invention is that the measurement conditions in a general friction coefficient measuring device are significantly different from the conditions under which the release film is placed during press molding.
(1) The compression stress generated by the load applied to the object to be measured in a general friction coefficient measuring apparatus, that is, the surface pressure is significantly larger than the surface pressure generated in the release film during press molding, and
(2) The relative movement speed at the time of sliding between the object to be measured and the measuring element in a general friction coefficient measuring device is the shear rate generated at the interface between the release film and the glass material to be molded at the time of press molding. Is significantly larger than
However, it was inferred that a general coefficient of friction measurement device cannot obtain a good correlation between the occurrence frequency of cracks and the coefficient of friction. According to the study of the present inventors, the surface pressure generated on the release film during normal press molding was about 5 to 80 MPa, and the shear rate was about 0.2 mm / sec or less. On the other hand, the normal compressive stress applied to the surface to be measured in a general friction coefficient measuring apparatus is at least 685 MPa or more, and the relative movement speed when sliding between the surface to be measured and the measuring element is at least 10 mm / sec or more. Yes, it is significantly different from the conditions under which the release film is placed during press molding.
Therefore, as described above, in the quality determination method of the present invention, the compressive stress applied to the measurement target film during the pressing is determined based on the surface pressure generated on the release film during press molding, and the measurement target film and the measuring element are determined. Is determined based on the shear rate generated at the interface between the release film and the glass material to be molded during press molding. Since a good correlation can be established between the friction coefficient measured in this way and the occurrence frequency of cracks, it is possible to determine the quality of the release film based on the measurement result of the friction coefficient.

  Hereinafter, although the friction coefficient measuring apparatus used suitably in the quality determination method of this invention is demonstrated, this invention is not limited to the following aspect.

  FIG. 5 is a schematic diagram of a friction coefficient measuring apparatus that is preferably used in the quality determination method of the present invention. The apparatus shown in FIG. 5 includes a frictional force generating means and a compressive load generating means for generating a compressive load. Details of each means will be described below.

(i) Friction force generating means The frictional force generating means functions as a sample holding table for fixing and holding a sample having a measurement target film on the outermost surface and as a moving table for moving the sample in an arbitrary direction. For example, the frictional force can be generated by moving the sample in the horizontal direction (Y direction in FIG. 5) with respect to the measurement target surface in a state where the measurement piece is pressed against the measurement target surface. By making the frictional force generating means reciprocally movable in an arbitrary direction, for example, the Y direction in FIG. 5, the probe can be repeatedly slid on the surface to be measured. In the apparatus shown in FIG. 5, the shearing Y stage 2 is moved in the Y direction in a state where the measuring element 3 is pressed against the surface to be measured of the measured object 1 of the release film formed fixedly held on the sample support 4. By repeating the reciprocating movement, the probe can be repeatedly slid on the measurement target surface. Alternatively, it is possible to repeatedly slide the probe on the surface to be measured by moving the probe 3 back and forth regardless of the reciprocation of the Y stage 2 for shearing operation.

(ii) Compressive load generating means The compressive load generating means has a configuration capable of reciprocating in an arbitrary direction, for example, the X direction in FIG. can do. In order to adjust the position of the probe, a two-stage configuration for coarse movement and fine adjustment can be used. For example, in the apparatus shown in FIG. 5, the upper surface pressure application X stage 5 is a fine movement (fine adjustment) stage, and the lower surface pressure application X stage 5 is a coarse movement (rough movement) stage.

  In the apparatus shown in FIG. 5, the compressive load generating means can fix the measuring element 3 via the X-direction elastic deformation member and the Y-direction elastic deformation member. Although both elastic deformation members can be configured as a single sheet, it is preferable to employ a pair of leaf springs. This is because that a pair of leaf springs can avoid torsion of the elastically deformable member due to vertical compressive stress and shear stress. In FIG. 5, the surface pressure displacement leaf spring 6 corresponds to a pair of leaf springs as X-direction elastic deformation members, and the frictional force displacement leaf spring 8 corresponds to a pair of leaf springs as Y-direction elastic deformation members.

  It is closer to the state where the release film is placed at the time of press molding, as the measuring element, the part that contacts the measurement target film at the time of pressing is made of the same material as the glass material to be molded used at the time of press molding. It is preferable because the friction coefficient can be measured in the state. From this point, it is more preferable to use the glass material of the same shape made of the same material as the glass material to be molded itself or the glass material to be molded used at the time of press molding.

  As described above, the measurement target film may be a release film itself provided on a press mold used for press molding, or a sample provided on a sample substrate having the same shape as the press mold. It may be a film, or may be a sample film provided on a sample base material having an arbitrary shape different from the press mold. From the viewpoint of simplification of friction coefficient measurement (in FIG. 5, simplification of measurement of frictional force generated by applying a compressive load in the X direction and movement in the Y direction of the probe), a sample formed on a plane It is preferable to measure the coefficient of friction of the film. In addition, in order to correspond to a measurement target surface having a curved surface (concave surface or convex surface) shape such as a molding surface shape, contact position adjusting means (X direction in FIG. The means capable of moving in the direction and the Z direction) can also be provided in the compression load generating means. In FIG. 5, the measurement position change Z stage 10 and the measurement position change Y stage 11 correspond to the contact position adjusting means.

As the compressive load and shear stress measuring means, a displacement sensor capable of measuring the amount of displacement can be disposed in each of the X and Y direction elastically deformable members. The displacement amount of each elastically deformable member is detected by a displacement sensor, and the vertical compressive stress applied to the surface to be measured and the generated shear stress, that is, the frictional force are measured by a calibration curve (correlation data between the displacement amount and the stress). it can. Alternatively, the vertical compressive stress and the frictional force can be measured by using a strain measuring device such as a load cell. In the apparatus shown in FIG. 5, the surface pressure detecting displacement sensor 7 and the frictional force detecting displacement sensor 9 correspond to the displacement sensor.
Moreover, the relative movement speed at the time of sliding between the measurement target film and the probe can be controlled by using a servo motor or the like.
As described above, it is possible to obtain correlation data between the operating state of the friction coefficient measuring apparatus, the vertical compressive stress applied to the measurement target surface, and the generated frictional force.

  Next, a method for measuring the friction coefficient of the measurement target film based on the obtained correlation data will be described.

  First, the sample is fixedly held in the friction coefficient measuring apparatus shown in FIG. 5 so that the measurement target film is disposed on the outermost surface. Next, the compression load generating means is adjusted so that the measurement comes into contact with a desired position of the sample.

  In the pass / fail judgment method 1, the compressive stress applied to the measurement target film when the measurement piece is pressed is determined based on the surface pressure generated on the release film during press molding, and the sliding between the measurement target film and the measurement piece is performed. The relative movement speed at the time is determined based on the shear rate generated at the interface between the release film and the glass material to be molded during press molding, that is, the speed at which the glass material to be deformed is deformed with respect to the release film.

  In order to determine the measurement conditions when measuring the friction coefficient, it is preferable to conduct a preliminary experiment in which press forming is performed under the same conditions as actual press forming. The surface pressure and shear rate in the region where cracking of the molded optical element was likely to occur as a result of repeating the press molding multiple times in the preliminary experiment, should be used as the reference values for determining the conditions in the quality determination method. Is preferred.

  From the viewpoint of the reliability of the pass / fail judgment result, the compressive stress applied to the film to be measured at the time of measuring the friction coefficient is preferably set to a value of about ± 20% of the surface pressure generated on the release film at the time of press molding. The relative movement speed during sliding between the target film and the probe is preferably set to a value of about ± 0.1 mm / sec of the shear rate generated at the interface between the release film and the glass material to be molded during press molding. . Note that the upper limit of the relative moving speed between the measurement target film and the measuring element is preferably about 1 mm / sec, and the lower limit is that if there is a relative moving speed during sliding (if it is not 0) Although measurement is possible, considering the measurement time, that is, measurement efficiency, a practical value up to about 0.01 mm / sec is an appropriate setting. In consideration of general press molding conditions, the compressive stress is preferably set in a range of 5 to 80 Mpa, and the relative movement speed is preferably set in a range of 0.2 mm / sec or less.

After determining the measurement conditions at the time of measuring the coefficient of friction, the measuring element is pressed against the surface to be measured so that the determined compressive stress is applied in a direction perpendicular to the surface to be measured (X direction in FIG. 5). In this state, a frictional force is generated (for example, in the Y direction in FIG. 5) by reciprocating the probe on the measurement target surface at the determined relative movement speed. The frictional force generated here can be calculated, for example, by multiplying the spring constant of the leaf spring by the amount of bending obtained by the displacement sensor. The friction coefficient can be calculated by the following formula as described above.
Friction coefficient = calculated friction force / measured normal compressive stress

In the pass / fail judgment process 1, the pass / fail judgment of the release film formed on the molding surface of the press mold used for press molding is performed based on the friction coefficient thus obtained. In order to determine pass / fail, a reference value for pass / fail determination is set in advance prior to the measurement of the friction coefficient. For setting the reference value, for example, the following preliminary experiment can be performed. In addition, if the temperature and humidity conditions at the time of friction coefficient measurement are normal temperature and a relative humidity of 60% or less, the influence on a measured value will be very small. Therefore, in the present invention, it is not essential that the friction coefficient measurement step be performed in the same temperature and humidity environment as the preliminary experiment for setting the reference value.
(1) A preliminary experiment is performed to obtain a correlation between the measured value of the coefficient of friction after sliding the release film and the measuring element repeatedly and the frequency of cracking of the optical element. Based on the result of this preliminary experiment, a reference value for pass / fail determination is determined for the measured value of the coefficient of friction after repeated sliding.
(2) A preliminary experiment is performed to obtain a correlation between the minimum value of the coefficient of friction during repeated sliding and the frequency of cracking of the optical element after the release film and the measuring element are repeatedly slid. Based on the result of this preliminary experiment, a reference value for pass / fail judgment is determined for the minimum value of the friction coefficient during repeated sliding.
(3) After sliding the release film and the measuring element repeatedly, a preliminary experiment is performed to obtain the correlation between the amount of change in the friction coefficient with time during repeated sliding and the frequency of cracking of the optical element. Based on the result of this preliminary experiment, a reference value for pass / fail judgment is determined for the amount of change over time of the friction coefficient during repeated sliding.

Note that the minimum value in the above (2) is not necessarily the friction coefficient immediately after the start of measurement. This is because there is a roughness on the surface of the release film at the start of measurement, and a decrease in the coefficient of friction may be seen at the beginning of the measurement due to the fact that this roughness is used (adapted) by contact and sliding of the probe. Because there is. In such a case, the amount of change with time in (3) above is the minimum value and the maximum value of the friction coefficient during repeated sliding (usually, the friction coefficient increases as the number of times of sliding increases so It is preferable from the point of reliability of pass / fail judgment to take a difference from the coefficient.

  The number of times of repeated sliding is preferably determined based on a desired number of times the press mold is used. In the quality determination method of the present invention, the measuring element can be slid on the surface to be measured in a state very close to the state where the release film is placed at the time of press molding. It is considered that the state of the measurement target surface approximates the state of the release film that has been press-molded twice. In consideration of this point, for example, the sliding can be repeatedly performed with the number of sliding times of about ½ of the desired number of times of use of the press mold. That is, it is preferable to repeatedly slide 50 times in a reciprocating manner for a specification that performs press molding 100 times. The preliminary experiment is preferably performed under the same measurement conditions as the friction coefficient measurement conditions for pass / fail judgment. In addition, the preliminary experiment may be performed under film formation conditions different from those of the release film formed on the mold that actually performs press molding. From the viewpoint of obtaining, it is preferable that the film is formed under the same conditions as the release film formed on the mold for actually performing press molding.

Furthermore, the present invention provides
A method for determining the quality of a release film formed on a molding surface of a press mold used for press molding a glass material to be molded,
The friction coefficient is obtained by sliding either the film or the measuring element against the other in a state where the measuring element is pressed against the release film or the film formed under the same conditions as the release film. If the measured friction coefficient is less than or equal to a preset reference value, the release film is determined as a non-defective product, and if the measured value exceeds the reference value, the release film is determined as a defective product. Determining the quality of the release film, and
Setting the compressive stress applied to the film at the time of pressing in the range of 5 to 80 MPa, and setting the relative movement speed when sliding between the film and the probe to 0.2 mm / sec or less,
A quality determination method for a release film of a press mold (hereinafter referred to as “quality determination method 2”)
About.

  The quality determination method 1 described above determines the measurement conditions for the friction coefficient based on the actual press forming conditions. On the other hand, according to the study of the present inventor, the surface pressure generated on the mold release film is about 5 to 80 MPa and the shear rate is about 0.2 mm / sec or less in the press molding of a normal glass optical element. Met. Therefore, in the quality determination method 2, the surface pressure and the shear rate in the normal press molding are adopted as the conditions for measuring the friction coefficient, and the quality of the release film is determined. The quality determination method 1 is advantageous in terms of the reliability of the quality determination because the friction coefficient can be measured under conditions closer to the actual press molding conditions. On the other hand, the quality determination method 2 is advantageous in terms of simplicity because it is easy to determine the measurement conditions for the friction coefficient. The friction coefficient measurement conditions employed in the pass / fail judgment method 2 are conditions that are not employed by a general friction coefficient measurement apparatus, but are approximate to the conditions under which a release film is placed during press molding. According to the pass / fail determination method 2, it is possible to accurately determine that the release film is likely to crack by performing pass / fail determination based on the values obtained under the above measurement conditions. The compressive stress in the pass / fail judgment method 2 is in the range of 5 to 80 MPa, and preferably in the range of 10 to 60 MPa. The relative movement speed in the pass / fail judgment method 2 is 0.2 mm / sec or less, and preferably in the range of 0.1 to 0.2 mm / sec. The other details of the quality determination method 2 are as described above for the quality determination method 1.

When the release film formed on the molding surface of the mold is formed in a batch-type film forming apparatus, the performance of the release film is improved between the film forming lots even if the film forming conditions are set the same. Variations may occur. This is because, for example, in sputtering, when a new film-forming raw material is used, impurities are present on the surface of the film-forming raw material. If the use of the film material is continued, it is considered that the substrate material holding the film formation material starts to be blown off and impurities are mixed into the release film. Such variations in the film formation results are thought to affect the ease of cracking of the molded optical element, but it is difficult to determine by visually observing the release film. If it is an expensive sputtering device, it is possible to manage the film forming conditions to be constant, but in an inexpensive sputtering device, the film forming conditions are managed to be constant due to the influence of temperature change depending on the season of the device cooling water. It can be difficult. In addition, in order to form a release film having a desired specification using an inexpensive sputtering apparatus, in order to avoid contamination with impurities, the film forming raw material is wasted at the start of use for stabilization, and at the end of film formation Although the film forming raw material still exists, it is possible to cope with the problem by exchanging it with the following, but this method is disadvantageous in terms of cost because the number of unused film forming raw materials increases.
On the other hand, according to the quality determination method of the present invention, it is actually confirmed that the release film formed on the molding surface of the mold is a release film that is likely to crack the optical element to be molded. Since determination can be made without performing press molding, a molding die having a release film that is easily cracked can be excluded from actual molding as a defective product. Thereby, according to this invention, the effective utilization of the film-forming raw material and the trouble between the film-forming lots can be solved easily and reliably.

[Method for producing glass optical element]
The method for producing the glass optical element of the present invention comprises:
A glass optical element manufacturing method comprising supplying a glass material to be molded to a mold and then press-molding the supplied glass material to be molded with the mold,
Performing pass / fail determination of a release film formed on the molding surface of the mold by the pass / fail determination method of the present invention,
Using the mold in which the release film is determined to be non-defective by the determination, for the press molding,
It is characterized by.

  In the manufacturing method of the glass optical element of the present invention, the occurrence of cracking of the press-molded glass optical element can be suppressed by using the molding die determined to be non-defective by the quality determination method of the present invention. Conventionally, it has been difficult to determine in advance the ease of cracking of optical elements during repeated press molding, so if a defective product is actually generated by press molding, the defective product is removed from the product element. It was dealt with by eliminating. However, it is difficult to reduce the defective product rate of the glass optical element in this correspondence. On the other hand, according to the present invention, it is possible to eliminate molds that are prone to cracking before press molding, and therefore it is possible to reduce the defective rate of glass optical elements.

  The glass material to be molded may be preformed into a shape such as a spherical shape, a flat spherical shape, or a flat plate shape. However, the glass material used in the production method of the present invention is not limited to these shapes. In addition, it is preferable that the glass material having the above-mentioned shape that is hot-formed by flowing a predetermined weight out of the molten glass is directly subjected to press-molding because it is simple and economical. The method for producing a glass optical element of the present invention is suitable as a precision press molding method for obtaining a glass optical element without providing a polishing step that approximates the shape of the glass optical element to be molded. It is also possible to obtain a glass glass optical element by performing post-processing such as polishing.

As the base material of the molding die, for example, SiC, WC, TiC, TaC, BN, TiN, AlN, Si ₃ N ₄ , SiO ₂ , Al ₂ O ₃ , ZrO ₂ , W, Ta, Mo, cermet, sialon, A material selected from mullite, carbon composite (C / C), carbon fiber (CF), WC-Co alloy, glass material including crystallized glass, stainless steel, and high heat-resistant metal can be used effectively. The release film provided on the molding surface of the mold is as described above.

  In the manufacturing method of the glass optical element of the present invention, the quality of the release film formed on the molding surface of the mold is determined by the quality determination method of the present invention, and the release film is determined to be non-defective by the determination. A mold is used for press molding of a glass material to be molded. The details of the quality determination of the release film are as described above.

Press molding using a mold having a release film determined to be non-defective by the quality determination can be performed by a known means. For example, a glass material to be molded is introduced between an upper mold and a lower mold of a mold, and the glass material to be molded is heated and softened to a temperature corresponding to a viscosity equivalent to 10 ⁸ to 10 ¹² poise. By pressing with a mold, the molding surfaces of the upper and lower molds are transferred to the glass material to be molded. Or, by introducing a glass material whose viscosity has been raised to a temperature corresponding to 10 ⁸ to 10 ¹² poises in advance between the upper mold and the lower mold of the mold, and pressing it with the upper and lower molds, The upper and lower mold surfaces are transferred to the glass material to be molded. In order to prevent the release film from being oxidized, the molding atmosphere is preferably non-oxidizing. Thereafter, the mold and the glass material are cooled, and when the temperature is preferably Tg or less, the mold is released and the molded optical element can be taken out.

  The glass optical element manufacturing method of the present invention can be effectively applied to the manufacture of optical elements such as lenses, mirrors, gratings, prisms, microlenses, and laminated diffractive optical elements. Moreover, there is no restriction | limiting in particular in the glass type of glass applicable to this invention. In particular, the application of the present invention is effective for borate-based glasses, phosphate-based glasses, borophosphate-based glasses, fluorophosphate-based glasses, and the like that are easily broken.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to the aspect shown in an Example. In addition, the friction coefficient measurement described below was performed in an environment having a relative humidity of 60% or less at normal temperature (about 20 to 25 ° C.) unless otherwise specified.

[Example 1]
(1) Measurement of surface pressure and shear rate during press molding Using a mold having a molding surface shape to obtain a convex meniscus glass lens, repeated press molding as a preliminary experiment, on the release film, Calculate the surface pressure at the time of press molding of the part corresponding to the area where cracks are most likely to occur in the molded optical element by dividing the press load by the area calculated from the distance from the lens center of the cracked part. The shear rate was calculated from the displacement rate of the press shaft. As a result, the surface pressure was 37 MPa and the shear rate was 0.2 mm / sec.

(2) Preparation of friction coefficient measurement sample Ten molds having the same shape as the mold used in the preliminary experiment were prepared, sputtered under the same conditions, and carbon as a release film on the molding surface of each mold. A film was formed. However, the film thickness of the carbon film formed was changed by changing the film formation time.

(3) Measurement of friction coefficient The sample prepared in (2) above is placed in the friction coefficient measuring apparatus shown in FIG. 5 and is made of the same material as the glass material to be molded that was press-molded in (1) above as a measuring element Glass materials with the same shape were placed. The relative moving speed between the sample surface and the probe at the time of measuring the friction coefficient is 0.16 mm / sec, and the friction coefficient after 50 times sliding in the Y direction is measured. , 25 MPa, 33 MPa, 50 MPa or 75 MPa, and the average friction coefficient was calculated. Using a mold produced under the same conditions as each sample, a step of press-molding a glass material having the same shape as the glass material used as the measuring element was performed 100 times to obtain a convex meniscus lens. Crack generation in the obtained lens was visually observed, and the crack generation rate was calculated as (lens confirmed crack / all lenses) × 100. FIG. 6 shows the relationship between crack occurrence rate and average friction coefficient.

[Comparative Example 1]
Except for using a commercially available friction coefficient measuring device, the relationship between the crack occurrence rate and the average friction coefficient was determined in the same manner as in Example 1. The results are shown in FIG. The relative moving speed between the sample surface and the measuring element in a commercially available friction coefficient measuring apparatus was 10 mm / sec. Since the vertical compressive stress could be set in three stages of 685 MPa, 720 MPa, and 1000 MPa, the vertical compressive stress was changed to 685 MPa, 720 MPa, or 1000 MPa, and each sample was measured three times to calculate the average friction coefficient.

Evaluation results As shown in FIG. 6, the friction coefficient measured at normal stress approximated to the surface pressure and relative movement speed approximated to the shear rate based on the surface pressure and shear rate at the time of press forming was good with the crack generation rate. Showed a good correlation. From the result of FIG. 6, in order to manufacture a glass lens with a crack occurrence rate of 40% or less, for example, a release film having a friction coefficient of 0.2 or less can be determined as a non-defective product with a friction coefficient of 0.2 as a reference value. .
On the other hand, as shown in FIG. 7, in the commercially available friction coefficient measuring device, no correlation was found between the value of the friction coefficient and the crack occurrence rate.
From the above results, according to the present invention, it is possible to determine the quality of the release film by using the value of the coefficient of friction measured under the conditions set based on the surface pressure and shear rate during press molding. Indicated.

[Example 2]
A plurality of molds having a release film formed in the same lot as in Example 1 were prepared, and the friction coefficient of the release film was measured in the same manner as in Example 1. Thereafter, each mold was used and press molding was performed 100 times under the same molding conditions as in Example 1. As a result, 100 glass lenses were obtained for each mold. The obtained glass lens was observed visually to determine the presence or absence of cracks. FIG. 8 shows the relationship between the crack occurrence rate and the value of the friction coefficient of the release film. The bar graph in FIG. 8 represents an average value, and a line indicating the width of the bar graph tip indicates an error bar (error range). From the results of FIG. 8, the friction coefficient value measured in the present invention shows a good correlation with the crack occurrence rate, and the reference value 0.2 of the friction coefficient set in Example 1 is adopted. If it determines, it can confirm that a shaping | molding die with a low crack incidence can be selected.

[Reference example]
Change with time of friction coefficient due to repeated sliding Three samples (samples 1 to 3) in which an amorphous carbon film having a thickness of about 40 nm was formed on a SiC substrate by sputtering using the same film forming apparatus were prepared. .
For each sample, the friction coefficient was measured by repeatedly sliding the measuring element and the amorphous carbon film under the following conditions. The measurement results are shown in FIG.
Measurement conditions Compressive stress: 30 MPa, Shear rate: 0.16 mm / sec
Measuring element: Optical lens material (borate silicate glass (HOYA Co., Ltd. glass type BACD12)
Measurement environment: In the atmosphere (room temperature, humidity about 50% RH)

  Samples 1 to 3 are samples formed under the same conditions so as to have the same film thickness although the film formation lots are different. As shown in FIG. 9, the cause of the difference in the measurement result of the coefficient of friction in each sample may be a change over time in the deposition of the deposition material. In each sample, as described above, a decrease in the coefficient of friction is seen at the beginning of measurement. This repeated sliding is preferably set according to the number of press moldings. For example, in the case of a specification that performs 100 press moldings, it is possible to measure the friction coefficient at least 50 reciprocations, that is, 100 times. preferable. In the measurement result of the friction coefficient, the reference value for the quality determination may be set according to the specifications required for the mold. For example, with respect to the sample shown in FIG. 9, it is conceivable that the desired number of presses is set to 100 and that the coefficient of friction at the final sliding is 0.2 or less is determined as a non-defective product. According to the above criteria, in FIG. 9, sample 1 can be determined to be a defective product, sample 2 can be determined to be a good product that can be used in practice, and sample 3 can be determined to be a good product having extremely good quality. Or, when the coefficient of friction after the decrease of the coefficient of friction at the beginning of the measurement is 0.1 or less, and the amount of change (increase) of the coefficient of friction after 50 reciprocations thereafter is 0.1 or less, it is determined as a non-defective product. It is also possible.

  The present invention is useful in the field of manufacturing glass optical elements such as glass lenses.

1 DUT film-formed object 2 Y stage for shearing action 3 Measuring element 4 Sample support 5 X stage for surface pressure application (2 types / coarse movement, fine movement)
6 Surface pressure displacement leaf spring 7 Surface pressure detection displacement sensor 8 Friction force displacement leaf spring 9 Friction force detection displacement sensor 10 Measurement position change Z stage 11 Measurement position change Y stage

Claims (6)

A method for determining the quality of a release film formed on a molding surface of a press mold used for press molding a glass material to be molded,
The friction coefficient is obtained by sliding either the film or the measuring element against the other in a state where the measuring element is pressed against the release film or the film formed under the same conditions as the release film. If the measured friction coefficient is less than or equal to a preset reference value, the release film is determined as a non-defective product, and if the measured value exceeds the reference value, the release film is determined as a defective product. Determining the quality of the release film, and
Setting the compressive stress applied to the film at the time of pressing in the range of 5 to 80 MPa, and setting the relative movement speed when sliding between the film and the probe to 0.2 mm / sec or less,
A quality determination method for a release film of a press mold, characterized by The compressive stress applied to the film at the time of pressing is determined based on the surface pressure generated on the release film at the time of press molding, and the relative moving speed at the time of sliding between the film and the probe is determined at the time of press molding. The quality determination method of the release film of the press mold of Claim 1 including determining based on the shear rate which arises in the interface of a release film and the said to-be-molded glass raw material. 3. The method according to claim 1, wherein the measuring element is made of the same material as the glass material to be molded at a portion that abuts on the film at the time of pressing. 4. For the above pass / fail judgment, the measured value of the coefficient of friction after repeated sliding, the minimum value of the coefficient of friction during repeated sliding, and the amount of change over time of the coefficient of friction during repeated sliding are less than a preset reference value. The method according to any one of claims 1 to 3 , wherein the method is performed by determining that a value exceeding the value is a defective product. The method according to claim 4 , wherein the number of sliding times of the repeated sliding is determined based on a desired number of times the press mold is used. A glass optical element manufacturing method comprising supplying a glass material to be molded to a mold and then press-molding the supplied glass material to be molded with the mold,
Performing pass / fail judgment of a release film formed on the molding surface of the mold by the method according to any one of claims 1 to 5 .
Using the mold in which the release film is determined to be non-defective by the determination, for the press molding,
A method for producing a glass optical element.