Hot pressing method for optical glass components

Abstract

This invention provides a hot-press forming method for optical glass elements that prevents glass preforms from sticking to molds. The method includes the following steps: depositing a boron nitride film layer on the surface of a glass preform, and then hot-pressing to form an optical glass element. The thickness of the boron nitride film layer on the surface of the glass preform is less than or equal to 15 nm. The surface of the hot-pressed optical glass element is coated with at least one atomic layer of boron nitride film, or at least 0.65 nm thick boron nitride film. This invention solves the glass adhesion problem by depositing a boron nitride film layer on the surface of the glass preform, preventing fusion, cracking, and other defects. Using PVD or CVD boron nitride film layers prevents active hydrogen from hydrogen-containing DLCs from entering the glass preform during film formation, preventing fogging, blurring, and damage to the film surface of the optical glass element. It also reduces the difficulty of mold separation during the molding process and improves production automation and molding stability.

Description

Technical Field

[0001] This invention relates to a method for manufacturing optical glass elements, and more particularly to a method for obtaining optical glass elements by thermal softening and pressing a glass preform. Background Technology

[0002] In the process of obtaining optical glass components (such as lenses) by softening glass preforms through thermal contact, carbon-based diamond-like carbon films, precious metal films, or titanium-based films are provided on the mold surface to prevent the glass preform from fusing with the mold substrate surface and achieve good mold separation performance. However, when the glass preform used is made of materials that are prone to cracking or have inherent defects during hot pressing, such as borate-based, phosphate-based, or fluorophosphate-based glass, it is difficult to obtain sufficient mold separation effect.

[0003] Forming a carbon film on the surface of a glass preform is a known technique to prevent optical glass components from sticking together, but these coatings have some drawbacks: 1) Carbon films are generally deposited using CVD (chemical vapor deposition), which uses carbon dioxide as the gas. X H Y (Hydrocarbons) are hydrogen-containing gases, and the thin film is also a hydrogen-containing DLC ​​(diamond-like carbon film). The hydrogen produced after decomposition may lead to the reduction of oxide glass; 2) The stability range of hydrogen-containing DLC ​​is below 400℃, and it is very easy to decompose during the high softening point glass molding process, leading to film failure. Both of the above defects may cause the glass preform to stick to the mold. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hot pressing method for optical glass elements that can prevent glass preforms from sticking to the mold.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a hot pressing molding method for optical glass elements, the method comprising the following steps: depositing a boron nitride film layer on the surface of a glass preform, and then forming an optical glass element by hot pressing, wherein the thickness of the boron nitride film layer on the surface of the glass preform is less than or equal to 15 nm, and the surface of the hot-pressed optical glass element is covered with at least a boron nitride film layer with an atomic layer thickness, or the surface of the hot-pressed optical glass element is covered with at least a boron nitride film layer with a thickness of 0.65 nm.

[0006] Furthermore, the thickness T of the boron nitride film layer on the surface of the glass preform satisfies:

[0007] 0.65×S(L)÷S(PF)<T≤15(nm)

[0008] In the above formula, S(PF) represents the surface area of ​​the glass preform;

[0009] S(L) represents the surface area of ​​the optical glass element.

[0010] Furthermore, the deposition of a boron nitride film on the surface of the glass preform involves: before depositing the boron nitride film, heating the glass preform at 300℃-500℃ for 30 seconds to 210 minutes, and then subjecting it to a vacuum of 5.0 × 10⁻⁶. 0 pa-1.0×10 -4 In a Pa environment, the gas is ionized and deposited on the surface of the glass preform using a voltage of 600V-1050V.

[0011] Furthermore, the boron nitride film is deposited using CVD or PVD methods, including magnetron sputtering and FCVA, and PECVD methods, including ammonia borane or urea + boric acid.

[0012] Furthermore, a monitoring agent is doped onto the surface layer of the glass preform. After hot pressing, the concentration change of the monitoring agent on the surface of the optical glass element is measured to determine the expansion rate S(L) / S(PF) of the largest part of the glass preform surface area expansion, and the thickness change of the boron nitride film layer is analyzed simultaneously.

[0013] Furthermore, the region of maximum film thickness variation was determined by simulating molding changes.

[0014] Furthermore, a series of regular patterns are used to mark each area on the glass preform. After hot pressing, the pattern is compared with the glass preform, and the surface area expansion rate of each point is calculated by the increase in the amount of each pattern.

[0015] Furthermore, before forming a boron nitride film on the surface of the glass preform, the maximum elongation of the surface area generated by the press forming is determined, and the minimum thickness of the boron nitride film to be formed on the glass preform is determined based on this elongation.

[0016] Furthermore, a mold separation film is formed on the substrate surface of the mold. The mold separation film is, for example, a diamond-like carbon film, a hydrogenated diamond-like carbon film, a tetrahedral amorphous carbon film, a hydrogenated tetrahedral amorphous carbon film, an amorphous carbon film, a hydrogenated amorphous carbon film, a carbon-based film, or an alloy film.

[0017] The beneficial effects of this invention are as follows: By depositing a boron nitride film on the surface of the glass preform, this invention can prevent fusion and the resulting fusion and cracks, thereby solving the glass adhesion problem; This invention uses a PVD or CVD boron nitride film, which can prevent active hydrogen in hydrogen-containing DLC ​​from entering the glass preform during the film formation process, and can prevent fogging, blurring and damage to the film surface of optical glass components, reduce the difficulty of mold separation in the molding process, and improve the automation capability and molding stability of production. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the hot pressing results of different boron nitride film thicknesses according to the present invention. Detailed Implementation

[0019] The hot-press forming method for optical glass elements of the present invention involves depositing a boron nitride film layer on the surface of a glass preform to prevent the glass preform from fusing with the mold substrate during the forming process, and then forming the optical glass element by hot pressing. The thickness of the boron nitride film layer on the surface of the glass preform is less than or equal to 15 nm. After hot pressing, the surface of the optical glass element is coated with at least one atomic layer of boron nitride film or at least 0.65 nm thick boron nitride film layer. The boron nitride film layer is deposited by CVD or PVD. PVD deposition methods include magnetron sputtering and FCVA (filtered vacuum cathode arc initiation), and CVD deposition methods include PECVD (plasma-enhanced chemical vapor deposition), etc. The target material is ammonia borane or urea + boric acid. Before deposition, it needs to be heated at 300℃-500℃ for 30 s-210 min, and then subjected to a vacuum of 5.0 × 10⁻⁶. 0 pa-1.0×10 -4 In a Pa environment, the gas is ionized and deposited onto the surface of the glass preform using a voltage of 600V-1050V.

[0020] The aforementioned hot pressing process involves heating a glass preform in a mold through thermal contact and radiation until it reaches its softening point. Pressure is then applied to stretch and deform the preform, transferring the mold shape to obtain the desired optical glass element. The optical glass element comprises functional and non-functional optical surfaces. The non-functional optical surfaces include discontinuous circumferential portions formed during hot pressing.

[0021] like Figure 1 As shown, when a glass preform coated with a boron nitride film extends along the mold, the boron nitride film also extends. If the film's extension cannot keep up with the preform's deformation, it will crack. This cracked film not only causes the glass preform to directly contact the mold and fuse, creating a risk of adhesion, but also leads to cracks at the crack, resulting in poor appearance of the optical glass component. Therefore, during the deformation process of the glass preform, the boron nitride film must continuously prevent the glass preform from directly contacting the mold surface.

[0022] As the glass preform is continuously formed and its thickness decreases, the surface area of ​​the glass preform increases accordingly. Consequently, the surface area of ​​the boron nitride film covering its surface also increases, and the thickness of the boron nitride film becomes increasingly thinner. When the film becomes too thin, gaps appear in the boron nitride film, resulting in cracking. The inventors conducted batch experiments and discovered that the boron nitride film exhibits a sliding phenomenon within its layer during extension. In the final stage after the glass preform is formed, the entire surface of the glass preform just slides down to a single-layer film with a thickness of 0.65 nm.

[0023] Therefore, a boron nitride film of a predetermined thickness needs to be deposited on the surface of the glass preform to ensure that at least one atomic layer or at least 0.65 nm thick boron nitride film remains on the surface of the optical glass element after hot pressing, preventing the film from cracking. Within the transfer diameter of the hot pressing process, the thickness of the boron nitride film only needs to be greater than or equal to the aforementioned minimum film thickness and does not necessarily need to be uniform. When the film thickness is non-uniform, only the thinnest part of the film needs to have an atomic layer or 0.65 nm thickness. Preforms in non-transfer diameter areas can be allowed to have no boron nitride film on their surface after molding. Furthermore, the deformation rate of the glass surface also depends on the shape of the glass preform and the shape of the mold core. Therefore, even if a nearly uniform film is deposited before hot pressing, the highly deformed portion with increased surface area during hot pressing will have a thinner boron nitride film than the slightly deformed portion with no increase in surface area. In this invention, the thinnest part of the film on the surface of the optical glass element after hot pressing must be guaranteed to be covered with at least one atomic layer or at least 0.65 nm thick boron nitride film.

[0024] Furthermore, when the boron nitride film thickness on the surface of the glass preform exceeds 15 nm, the aggregated boron nitride atoms exhibit structural regularity, and the interactions between atoms prevent the smooth movement of boron nitride atoms, causing the boron nitride film to cease extending. Therefore, even if only a portion of the boron nitride film on the glass preform is thicker than 15 nm, it is insufficient to prevent micro-fusion and cannot completely avoid defects and cracks generated during hot pressing. From this perspective, the thickness of the boron nitride film on the surface of the glass preform should be set to less than or equal to 15 nm before hot pressing. The thickness of the boron nitride film does not need to be uniform, but the thickness of the thickest part of the boron nitride film must be less than or equal to 15 nm.

[0025] The thickness of the boron nitride film layer deposited by PVD or CVD is predicted based on the surface area deformation of the glass preform. That is, the thickness of the boron nitride film layer is predicted based on the shape of the glass preform and the surface area change caused by the deformation of the glass preform during extrusion. During hot pressing, the change in surface area of ​​the glass preform will vary with the change in the surface position of the glass preform. That is, some parts may experience a large expansion, while other parts may experience a small expansion. In this case, a boron nitride film layer of a certain thickness must be provided on the glass preform so that at least one boron nitride atomic layer is retained on the formed optical glass element. Therefore, it is necessary to calculate the film layer thickness T on the glass preform. When the surface area of ​​the glass preform is extended by hot pressing to form an optical glass element, the thickness of the boron nitride film layer on the glass preform before hot pressing is T. Then T should satisfy: 0.65×S(L)÷S(PF)<T≤15(nm) (1)

[0026] In equation (1) above, S(PF) represents the surface area of ​​the glass preform;

[0027] S(L) represents the surface area of ​​the optical glass element.

[0028] To calculate the expansion ratio S(L) / S(PF) of the largest area of ​​surface expansion in a glass preform, its three-dimensional shape can be measured and analyzed. By doping the surface layer of the glass preform with a monitoring agent (colorant, isotope, etc.), and after hot pressing, the concentration change of the monitoring agent on the surface of the optical glass element can be measured to determine S(L) / S(PF), while simultaneously analyzing the thickness change of the boron nitride film, or by simulating the pressing process to determine the region of maximum film thickness change. The surface area expansion ratio of the glass preform can also be calculated using the following method: Each area on the glass preform is marked with a series of regular patterns. After hot pressing, it is compared with an unpressed glass preform. The surface area expansion ratio at each point is calculated by the increase in the size of each pattern. The material used for the pattern markings must be one that is not easily decomposed during hot pressing.

[0029] In addition, it is best to set a mold separation film on the substrate surface of the mold, such as diamond-like carbon film (DLC), hydrogenated diamond-like carbon film (DLC:H), tetrahedral amorphous carbon film (ta-C), hydrogenated tetrahedral amorphous carbon film (ta-C:H), amorphous carbon film (aC), hydrogenated amorphous carbon film (aC:H), carbon-based film, alloy film, etc.

[0030] Example 1:

[0031] A spherical glass preform with a diameter of 5 mm was used. Its glass transition temperature Tg was 522℃, softening temperature Ts was 560℃, and refractive index was 1.69384. The glass preform was bombarded with argon gas at a voltage of 1050V and a flow rate of 20sccm for 500s to obtain a better surface free energy. After molding, the diameter of the optical glass element was 7.5 mm, the radius of curvature of surface R1 was 7 mm, the radius of curvature of surface R2 was 5 mm, the edge thickness was 0.7 mm, and the area with the largest change in surface area was at the molding platform. At this point, S(L) / S(PF) was determined to be 5.2. According to the above formula (1), the thickness T of the boron nitride film was determined to be: 0.65×5.2<T≤15nm.

[0032] Therefore, a boron nitride film with a thickness of 4.5 nm was formed on the glass preform by vapor deposition. The thickness of the boron nitride film was determined using ESCA (Electron Photoelectron Spectroscopy). To maintain the cleanliness of the vapor source, 99.99% high-purity ammonia borane was used as the reaction gas. Before deposition, the preform was heated at 300°C for 30 min, and then vapor deposition was performed under a vacuum of 10⁻⁴ bar. The gas was ionized by a voltage of 600 V and deposited onto the surface of the glass preform. The resulting glass preform containing the boron nitride film was then placed in a mold and heated to 580°C in a nitrogen atmosphere for 120 s at a pressure of 0.4 kN. After releasing the pressure, the preform was transferred to a cooling stage at 480°C for cooling and shaping, then transferred to a cooling stage at approximately 300°C for secondary cooling, and finally rapidly cooled at room temperature. The final temperature of the optical glass element was below 50°C.

[0033] ESCA measurements show that the thickness of the boron nitride film on the surface of the obtained optical glass element is 0.8 nm at the maximum elongation, and around 1.7 nm on average in other areas. During the thermoforming process under the above conditions, it can be continuously molded 3000 times without any glass adhesion or cracking.

[0034] Comparative Example 1:

[0035] Vapor deposition was performed using the same glass preform as in Example 1 to obtain a glass preform with a boron nitride thickness of 25 nm (measured by ESCA). Similar to Example 1, during continuous molding, when the boron nitride film thickness of the optical glass element was measured using ESCA, some parts of the film had separated, exhibiting a discontinuous film layer. In the areas where the film layer remained, the film thickness was approximately 16 nm. During continuous hot pressing, cracks appeared on the mold surface after approximately 500 cycles. EDS analysis revealed that glass material was embedded within the cracks, making further molding impossible.

[0036] Comparative Example 2:

[0037] Vapor deposition was performed using the same glass preform as in Example 1 to obtain a boron nitride film with a thickness of 1 nm (measured by ESCA). Continuous molding was performed in the same manner as in Example 1. Cracking occurred during the initial molding process, accompanied by mold sticking. ESCA measurements were performed on the molded optical glass element, and it was found that boron nitride could not be detected in most areas of the optical glass element, indicating that the film layer was severely fractured and could not meet the requirement that the thickness of the boron nitride film after molding be greater than or equal to 0.65 nm.

[0038] Example 2:

[0039] Using the same glass preform as in Example 1, a boron nitride film was formed by the thermal decomposition of uric acid and boric acid, resulting in a glass preform with a thickness of 5 nm (measured by ESCA). Film formation was performed using a CAD device. The chamber was evacuated to a vacuum level of 0.5 Torr or below using a vacuum pump, and then heated to maintain a temperature of 480°C. Uric acid was then introduced into the chamber, and the vacuum pump speed was adjusted to maintain 160 Torr. After 30 minutes of cleaning, the uric acid flow was stopped, and boric acid was introduced and maintained for 210 minutes, with the vacuum level maintained at approximately 200 Torr. After cooling, a boron nitride film layer was obtained. When subjected to single-mold continuous molding in the same manner as in Example 1, cracking occurred after approximately 2000 cycles.

[0040] Comparative Example 3:

[0041] Vapor deposition was performed using the same glass preform and method as in Example 2 to obtain a glass preform with a boron nitride thickness of 25 nm (measured by ESCA). The verification results are shown in Table 1 below.

[0042] Comparative Example 4:

[0043] Vapor deposition was performed using the same glass preform and method as in Example 2 to obtain a glass preform with a boron nitride thickness of 1 nm (measured by ESCA). The verification results are shown in Table 1 below.

[0044] Example 3:

[0045] Boron nitride films were prepared using PVD, employing the same glass preform as in Example 1. The preform was bombarded with argon gas at 1050V and a flow rate of 20sccm for 500s to obtain good surface free energy. Film preparation was performed using FCVA, where the glass preform was placed in a loading chamber and pre-evacuated to a vacuum level of 3.5 × 10⁻⁶. -3 Pa is transferred to the process chamber, where the vacuum is further evacuated to 6.0 × 10⁻⁶. -4The boron nitride-containing glass preform was coated using a coating voltage of 1050V, a filter current of 16A, an arc current of 45A, a duty cycle of 40%, a coating scanning frequency of 15Hz, and a coating time of 30s. The preform was then removed after coating, resulting in a film thickness of approximately 4nm. The resulting boron nitride-containing glass preform was then placed in a mold and heated to 580℃ in a nitrogen atmosphere for 120s at a pressure of 0.4KN. After releasing the pressure, the preform was transferred to a 480℃ cooling stage for cooling and shaping, followed by a second-stage cooling stage at approximately 300℃, and finally rapid cooling at room temperature. The final temperature of the optical glass element was below 50℃.

[0046] ESCA measurements show that the thickness of the boron nitride film on the surface of the optical glass element is 0.7 nm at its maximum elongation, and averages around 1.5 nm in other areas. During the thermoforming process under these conditions, an average of 2600 molding cycles were performed without any glass adhesion or cracking.

[0047] Comparative Example 5:

[0048] Deposition was performed under the same conditions as in Example 3, with control conditions identical to Example 1. The deposition time was 180 seconds, resulting in a glass preform with a boron nitride thickness of 24 nm (measured by ESCA). Molding was then performed under the same conditions as in Example 3. When the boron nitride film thickness of the optical glass element was measured using ESCA, some portions of the film had separated, exhibiting a discontinuous film layer. In the portions where the film layer remained, the thickness was approximately 15 nm. During continuous hot pressing, cracks appeared on the mold surface after approximately 400 cycles.

[0049] Comparative Example 6:

[0050] Boron nitride film with a thickness of 1 nm (measured by ESCA) was deposited using the same controlled conditions as in Example 3. The deposition time was about 10 seconds. Molding was performed under the same conditions as in Example 1. After the first round of molding, the optical glass element cracked and was accompanied by mold sticking. ESCA measurement of the molded optical glass element revealed that boron nitride could not be detected in most areas of the optical glass element, indicating that the film layer was severely fractured and could not meet the requirement that the thickness of the boron nitride film layer after molding was greater than or equal to 0.65 nm.

[0051] Table 1

[0052]

[0053]

[0054] As can be seen from the above examples and comparative examples, under the condition that the materials, pretreatment, and molding methods are the same, two deposition methods were used to conduct coating and molding tests respectively. The results show that the film thickness of the glass preform needs to be less than 15nm. When it is higher than 15nm, the boron nitride film is subjected to high pressure extrusion during the molding process. The thicker film layer leads to greater internal stress, and film fracture occurs in areas with large deformation. This causes the optical glass element to directly contact the substrate surface in this area, while the rest is still protected by the boron nitride film layer. This results in uneven heating of the optical glass element, ultimately leading to appearance cracking (stress fracture). In addition, the area where the optical glass element extends the most after molding also needs to maintain a minimum film thickness of 0.65nm. When the film thickness is low, the film layer will gradually thin in this area during the film extension process. When the film layer is at its thinnest, film fracture will occur before the extension stops. The large number of fractured areas will cause the optical glass element to directly contact the substrate, resulting in uneven heating and mold sticking.

Claims

1. A hot-pressing method for forming optical glass components, characterized in that, The method includes the following steps: depositing a boron nitride film layer on the surface of a glass preform, and then forming an optical glass element by hot pressing. The thickness of the boron nitride film layer on the surface of the glass preform is less than or equal to 15 nm, and the surface of the hot-pressed optical glass element is coated with at least one atomic layer of boron nitride film layer, or the surface of the hot-pressed optical glass element is coated with at least 0.65 nm of boron nitride film layer. The deposition of the boron nitride film layer on the surface of the glass preform is as follows: before depositing the boron nitride film layer, the glass preform is heated at 300℃-500℃ for 30s-210min, and then subjected to a vacuum of 5.0×10⁻⁶. 0 Pa-1.0×10 -4 The boron nitride film is deposited on the surface of the glass preform by ionizing gas with a voltage of 600V-1050V under an environment of Pa; the boron nitride film is deposited by CVD or PVD, the PVD method includes magnetron sputtering and FCVA, the CVD method includes PECVD, and the target material is ammonia borane or urea + boric acid.

2. The hot pressing method for forming optical glass elements as described in claim 1, characterized in that, The thickness T of the boron nitride film layer on the surface of the glass preform satisfies: In the above formula, S(PF) represents the surface area of ​​the glass preform; S(L) represents the surface area of ​​the optical glass element.

3. The hot pressing method for forming optical glass elements as described in claim 1 or 2, characterized in that, A monitoring agent is doped onto the surface layer of the glass preform. After hot pressing, the concentration change of the monitoring agent on the surface of the optical glass element is measured to determine the expansion rate S(L) / S(PF) of the largest part of the glass preform surface area expansion, and the thickness change of the boron nitride film layer is analyzed simultaneously.

4. The hot pressing method for forming optical glass elements as described in claim 1 or 2, characterized in that, The region of maximum film thickness variation was determined by simulating molding changes.

5. The hot pressing method for forming optical glass elements as described in claim 1 or 2, characterized in that, A series of regular patterns are used to mark each area on the glass preform. After hot pressing, the pattern is compared with the glass preform, and the surface area expansion rate of each point is calculated by the increase in the amount of each pattern.

6. The hot pressing method for forming optical glass elements as described in claim 1 or 2, characterized in that, Before forming a boron nitride film on the surface of the glass preform, the maximum elongation of the surface area generated by the press molding is determined, and the minimum thickness of the boron nitride film to be formed on the glass preform is determined based on this elongation.

7. The hot pressing method for forming optical glass elements as described in claim 1 or 2, characterized in that, A mold separation film is set on the substrate surface of the mold.

8. The hot pressing method for forming optical glass elements as described in claim 7, characterized in that, The mold separation film is a diamond-like carbon film.

9. The hot pressing method for forming optical glass elements as described in claim 7, characterized in that, The mold separation film is: hydrogenated diamond-like carbon film, tetrahedral amorphous carbon film, hydrogenated tetrahedral amorphous carbon film, amorphous carbon film, hydrogenated amorphous carbon film, carbon-based film, or alloy film.

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