Coating on mold for glass molding and a preparation method and applications thereof

Abstract

Disclosed is a coating made of an organic material on a mold for glass molding. The coating comprises Cr.sub.xW.sub.yN.sub.(1-x-y), where 0.15<x<0.4, and 0.2≤y≤0.45. The coating has excellent high temperature resistance and anti-adhesion properties, thus being a promising coating material for molds.

Claims

1. A coating on mold for glass molding, wherein the coating comprises Cr.sub.xW.sub.yN.sub.(1-x-y), wherein 0.15<x<0.4, and 0.2≤y≤0.45.

2. The coating of claim 1, wherein the coating comprises a CrN columnar crystal.

3. The coating of claim 1, wherein the coating has a thickness of 1.4-1.8 μm.

4. A method for preparing the coating of claim 1, comprising: A: performing sputter cleaning on a substrate and a target in a vacuum or an inert gas; and B: depositing the coating on a surface of the substrate treated in step A with a Cr target and a W target in a vacuum or an inert gas.

5. The method of claim 4, wherein in step A, during the sputter cleaning, the inert gas as a working atmosphere is argon with a flow rate of 100-180 sccm, and a vacuum degree of the vacuum is 0.2-0.6 Pa; the substrate is preheated to 200-400° C.; the coating is deposited at a bias voltage of −30˜−100 V; a time for sputter cleaning of the substrate is 30-120 minutes; and a time for sputter cleaning of the target is 1-5 minutes.

6. The method of claim 4, wherein in step B, during the sputter cleaning, the inert gas as a working atmosphere is nitrogen with a flow rate of 60-120 sccm; a vacuum degree of the vacuum is 0.2-0.6 Pa; the substrate is preheated to 200-400° C.; the coating is deposited for 60-100 minutes at a bias voltage of −30˜−70 V; a power for the Cr target is 2-5 kW, and a power for the W target is 4-8 kW.

7. The method of claim 4, wherein in step B, the substrate rotates with a rotating stage of a magnetron sputtering system in the step of depositing the coating on the surface of the substrate.

8. The method of claim 7, wherein the magnetron sputtering system comprises a vacuum chamber, the rotating stage which is rotatable and is provided in the vacuum chamber, and a target provided around the rotating stage, wherein the target comprise Cr and W.

9. An application of the coating of claim 1, comprising applying the coating to the preparation of a mold for glass molding.

10. A mold for glass molding, comprising a coating which comprises Cr.sub.xW.sub.yN.sub.(1-x-y), wherein 0.15<x<0.4, and 0.2≤y<0.45.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a temperature-volume graph of optical glass;

(2) FIGS. 2A-2B are SEM images showing a surface and a cross section of a coating according to a first embodiment;

(3) FIG. 3 shows a test result of hardness of the coating according to the first embodiment;

(4) FIG. 4 shows a test result of surface roughness of the coating according to the first embodiment;

(5) FIG. 5 is an image showing morphologies of surfaces of the coating and glass according to the first embodiment, in which the glass has been molded;

(6) FIG. 6 shows an XRD result of elements of a surface of the coating according to the first embodiment;

(7) FIG. 7 shows a test result of a phase composition of the coating according to the first embodiment; and

(8) FIG. 8 shows a test result of wetability of the coating at high temperature according to the first embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The embodiments are intended to better illustrate but not to limit the present invention. Therefore, non-substantial improvements and adjustments to the embodiments based on above-mentioned inventions by those skilled in the art shall fall within the scope of the present invention.

(10) Example 1

(11) A preparation method for a coating on molds for glass molding comprises the following steps.

(12) 1) The substrate is mechanically ground and polished, and then is ultrasonically cleaned in deionized water, analytical acetone and analytical ethanol in turn for 20 minutes, respectively. Then the sample is dried in an oven at 80° C. for 30 minutes.

(13) 2) The sample is placed in a vacuum chamber which is pre-vacuumized. The vacuum of the substrate is 5×10.sup.−3 Pa, and at the same time, the vacuum chamber is heated to 300° C.

(14) 3) A substrate and a target are performed sputter cleaning in a vacuum or argon which is an inert gas. During the sputter cleaning, the working atmosphere is argon with a flow rate of 120 sccm, and a vacuum degree of the vacuum is 0.5 Pa. The substrate is preheated to 300° C. The coating is deposited at a bias voltage of −100 V. A time for the sputter cleaning of the target is 5 minutes.

(15) 4) The coating comprising Cr.sub.xW.sub.yN.sub.(1-x-y) is coated on the substrate by the magnetron method using a high-purity (99.9%) Cr target and a high-purity (99.6%) W target. During sputter cleaning, the working atmosphere is a mixture of nitrogen with a flow rate of 100 sccm and argon with a flow rate of 100 sccm, and a vacuum degree of the vacuum is 0.4 Pa. The substrate is preheated to 300° C. The coating is deposited for 100 minutes at a bias voltage of −50 V. A power of the Cr target is 2.7 kW and a power of the W target is 4 kW. The substrate rotates with a rotating stage of the magnetron sputtering system in the step of depositing the coating on the substrate surface. The magnetron sputtering system comprises a vacuum chamber, the rotating stage which is rotatable and is provided in the vacuum chamber, and target materials provided around the rotating stage.

(16) The coating in the first embodiment is tested in terms of performance such as morphologies of surface and cross section of the coating, hardness, surface roughness, surface elements, phase compositions and wetability at high temperature, and the results are shown in FIGS. 2-8.

(17) The morphologies of surface and cross section of the coating are observed by field emission scanning electron microscope (FESEM).

(18) The hardness of the coating is tested by nanoindentors using the continuous stiffness measurement (CSM). The depth of nano-indentation is set to 110 nm so as to eliminate the substrate factor on the test result. Five different areas on the sample are selected for testing, and then the hardness and elastic modulus are averaged, so that the accuracy and reliability of the data are ensured.

(19) The roughness of the surface of the coating is tested by an atomic force microscope, and the sample area to be tested is 2×2 μm.

(20) The molding pressure is tested by molding the BK7 optical glass using the self-designed mold for optical non-spherical glass molding (Chinese Patent Application No. 201710124489.7; Chinese Patent Publication No. 106946441 A), where the molding pressure is 0.5 kN; and the molding temperature is 650° C. The morphologies and colors of the glass and the coating on the mold are observed.

(21) Elements of the coating surface are tested via qualitative analysis using X-ray energy dispersive spectrometer (EDS) of the field emission scanning electron microscope (FESEM).

(22) Phase structure of the coating is tested by an X-ray diffractometer, and the crystal structure of the coating is analyzed with small angle diffraction to avoid the factor of the substrate.

(23) Through a high-temperature wetting test, the wettability of the coating at high temperature is examined at a temperature of 1000° C. by using a modified sessile drop method, where the vacuum is 5×10.sup.−3 Pa, and the glass is BK7 optical glass.

(24) As shown in FIGS. 2A-B, clusters with different sizes, fine cracks and pores are distributed on the coating surface. The morphology of cross section of the coating is in a column structure, and the coating with a thickness of 1.76 μm are closely combined with the substrate.

(25) As shown in FIG. 3, the coating prepared in Example 1 has a hardness of 12.9 GPa. Thus, the coating of the invention with good mechanical properties reaches the hardness standard for the coating on molds for glass molding.

(26) As shown in FIG. 4, the coating prepared in Example 1 has a surface roughness of 13.8 nm exhibiting good surface finishing, and is suitable for the coating on molds for precision glass molding.

(27) As shown in FIG. 5, after the molding, no significant change is observed on the glass and the coating surface. Further, the color of the glass is not changed and no bubble is generated, and the mold surface has no scratches and glass adhered thereto. It is demonstrated that the coating of the invention can meet the requirements of precision optical glass molding.

(28) As shown in FIG. 6, the coating prepared in Example 1 are mainly composed of Cr, W and N.

(29) As shown in FIG. 7, the coating prepared in Example 1 mainly has a stable CrN phase. A columnar CrN crystal can be observed in the cross-section SEM image, with (110), (200), (220), (311) and (222) orientations. Mass fractions of the Cr, W and N elements in the coating are 35%, 20% and 45%, respectively.

(30) As shown in FIG. 8, when the coating prepared in Example 1 is exposed to an ambient temperature of 1000° C. and a vacuum of 5×10.sup.−3 Pa, contact angles between the molten glass and the coating at high temperature are 116° and 133°, so a significant asymmetry occurs at left and right sides of the droplet. Therefore, the coating of the invention has a good wettability for resisting droplets of the molten glass, so it is less prone to adhesion.

(31) It should be understood that although the embodiments are illustrated in the description for clarity, each embodiment may include more than one technical solution. It is noted that the description should be taken as a whole, and various embodiments can be appropriately combined to form other embodiments that can be understood by those skilled in the art.