A near-pyramid microstructure on the surface of NAK80 die steel and its photolithography method

Abstract

The present invention discloses a near-pyramid-shaped micron structure on the surface of NAK80 mold steel and a photolithography method thereof. The method first uses photolithography technology to process a photoresist mask pattern on the surface of the NAK80 mold steel. Then, by regulating the composition of a wet etching solution and the etching time, a NAK80 micro mold having a near-pyramid-shaped periodic array micron structure is obtained. The micro mold can be used for micro-imprinting processing of plastic products, constructing an inverted pyramid frame structure complementary to the mold on the plastic surface. In the prior art, such pyramid-shaped periodic array structures are generally produced by photolithographically etching silicon templates, but single-crystal silicon is expensive, brittle, and has poor mechanical stability. The advantage of the present invention is that the NAK80 micro mold prepared by photolithography not only has a pyramid-shaped array microstructure similar to that obtained by wet etching of silicon wafers, but is also inexpensive and has high mechanical stability. Furthermore, the wet etching process is simple, has high etching efficiency, and can be processed in batches.

Description

Technical Field

[0001] The present invention relates to the field of micron structure processing, and in particular to a near-pyramid-shaped micron structure on the surface of a NAK80 die steel and a photoetching method thereof. Background Art

[0002] As a polymer material, plastic has a high surface energy, which often leads to many adverse phenomena at the interface of plastic products. For example, yogurt sticks to the lid, rainwater adheres to umbrellas, and dust adheres to fan blades, affecting the appearance or making it difficult to clean; ice forms in the freezer compartment of the refrigerator, causing inconvenience and wasting electricity; and plastic tableware is more difficult to clean than metal and ceramic tableware.

[0003] Inspired by the super-hydrophobic properties of lotus leaves, roses, water striders and other materials in nature, scientists discovered that their surfaces have unique micro-nano composite structures. Therefore, by constructing micro-nano composite structures, they make the surface of materials have super-hydrophobic properties. However, the current super-hydrophobic surfaces have bottleneck problems such as easy damage to the structure and poor durability.

[0004] Research has shown that a continuous inverted frame structure offers superior wear resistance and durability compared to traditional continuous columnar microstructures. In existing technology, this inverted frame structure is fabricated by photolithographically etching single-crystal silicon to create a pyramidal periodic array microstructure. This structure is then micro-embossed onto the substrate surface to create a complementary inverted frame structure to the mold. This is primarily due to the varying atomic density of single-crystal silicon, which results in anisotropy during wet etching. This allows the formation of a highly regular, periodically arranged pyramidal microstructure. However, single-crystal silicon is expensive and brittle, and larger silicon molds, in particular, are prone to shattering during embossing, making it unsuitable for large-scale production.

[0005] Microstructures fabricated using photolithography have the advantages of high precision and efficiency. A literature review of photolithographic metal etching reveals that metals such as copper, aluminum, and some carbon steels can also be photoetched to produce highly precise periodic array microstructures. Furthermore, the resulting metal micromolds exhibit greater mechanical stability than silicon molds.

[0006] NAK80 plastic mold steel offers excellent polishing properties, exceptional carving capabilities, superior discharge performance, and relatively good etching resistance. It is widely used in precision wrinkle-forming plastic molds for applications such as television filters, fan blades, and cosmetic cases. Therefore, the study of creating a periodic array of microstructures on the surface of NAK80 through photolithography, which can be used as a mold to imprint a wear-resistant inverted frame structure on plastic surfaces, is of great research significance and application value.

[0007] Currently, there are few reports on photolithographically etching NAK80 to obtain periodic array microstructures, and no relevant research results are available for reference. Therefore, it is urgent to explore an efficient, cost-effective, and versatile photolithographic method for preparing periodic array microstructures on the surface of NAK80 independent mold steel. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings and deficiencies of the above-mentioned prior art and to provide a near-pyramid-shaped micron structure on the surface of NAK80 mold steel and a photolithography method thereof.

[0009] The present invention is achieved through the following technical solutions:

[0010] A method for photolithography of a near-pyramid-shaped micron structure on the surface of NAK80 mold steel comprises the following steps:

[0011] S100. Photolithography mask pattern design: Design a periodically arranged square pattern as a photolithography mask pattern;

[0012] S200 photolithographic method to prepare a photoresist mask: by photolithographic method to prepare a pre-designed photoresist pattern on the surface of the NAK80 steel sheet as a mask;

[0013] S300. Wet etching: Immerse the NAK80 film covered with a square photoresist mask in a 1 wt.% FeCl3 + 1 wt.% HNO3 etching solution for 25-30 min to obtain a NAK80 film with a near-pyramid array microstructure covered with the photoresist mask.

[0014] S400. Removing the photoresist mask: The etched NAK80 is removed from the etching solution, rinsed with deionized water, and then ultrasonically treated in an acetone solution for 7 minutes to remove the photoresist, thereby obtaining a NAK80 micro mold having a pyramid-shaped periodic array microstructure.

[0015] S500. Embossed plastic (as a validation): PP plastic is hot-embossed using a NAK80 micro-mold fabricated using photolithography, creating an inverted pyramidal framework on the plastic surface that complements the mold.

[0016] In step S100 , the photoresist mask pattern is periodically arranged squares with a side length of 60 μm and a spacing between adjacent squares of 10 μm.

[0017] In step S200, the thickness of the NAK80 steel sheet is 1-2 mm.

[0018] In step S200, the photolithography step uses AZ4620 positive photoresist to prepare the photoresist mask. This is spin-coated onto the NAK80 mold steel surface at 3000 rpm to a thickness of 1.3 μm, with an exposure energy of 50 J and a development time of 60 seconds. In step S500, the PP plastic is hot-embossed at a temperature of 125°C and a pressure of 15 MPa.

[0019] By adopting the above method of the present invention, a micron structure of a nearly pyramidal periodic array can be obtained on NAK80 die steel.

[0020] Compared with the prior art, the present invention has the following advantages and effects:

[0021] Compared with the existing technology, the advantages and beneficial effects of the patent of the present invention include: the NAK80 mold steel of this method is cheaper than silicon wafers, the wet etching process is simple, and no heating and magnetic stirring are required. In particular, the NAK80 mold steel has high structural stability and will not crack or break after repeated use. It is an efficient and reliable method for preparing near-pyramid-shaped periodic array microstructures. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a NAK80 substrate covered with a periodic photoresist square mask; the side length (pitch) is a (b) = 60 (10);

[0023] Figure 2 Scanning electron microscope micrographs of the NAK80 micromold obtained by wet etching in 1 wt.% HNO3 etchant: (a) low-magnification microstructure morphology; (b) partial magnification of the microstructure; (c) cross-sectional view of the microstructure; (d) plastic surface morphology after embossing (Example 1);

[0024] Figure 3 Scanning electron microscope micrographs of the NAK80 micromold with a pyramid array obtained by wet etching in a mixed etchant of 1 wt.% HNO3 + 1% wt.% FeCl3: (a) low-magnification morphology of the pyramid microstructure; (b) local magnification of the microstructure; (c) cross-sectional view of the microstructure; (d) morphology of the plastic surface after imprinting (Example 2). DETAILED DESCRIPTION

[0025] The present invention is described in further detail below with reference to specific embodiments.

[0026] The present invention discloses a method for photoetching a near-pyramid-shaped micron structure on the surface of NAK80 mold steel. The technical solution of the present invention is further described in detail below in conjunction with two embodiments of wet etchants with different compositions and the accompanying drawings. However, the scope of protection of the present invention is not limited to the following.

[0027] Example 1:

[0028] S100. Photolithography mask pattern design: Design a periodically arranged square pattern as the photolithography mask pattern, with a side length a = 60 μm and a spacing b = 10 μm, as shown in the schematic diagram. Figure 1 As shown;

[0029] S200. Prepare a photoresist mask using photolithography: Use AZ4620 positive photoresist, spin-coated at 3000 rpm onto a 1 mm thick NAK80 steel mold sheet. The thickness of the spin-coated photoresist is 1.3 μm, with an exposure energy of 50 J and a development time of 60 s. Prepare a pre-designed photoresist mask pattern consisting of periodic squares with a side length of 60 μm and a spacing of 10 μm.

[0030] S300 wet etching: The NAK80 covered with a square photoresist mask was immersed in a 1wt.% HNO3 solution at room temperature and etched for 40-50min to obtain a NAK80 micro mold with a columnar periodic array microstructure covered with a photoresist mask;

[0031] S400. Removal of photoresist mask: The etched NAK80 is removed from the etching solution, rinsed with deionized water, and then ultrasonically treated in an acetone solution for 7 minutes to remove the photoresist, thereby obtaining a NAK80 micro mold with a columnar periodic array microstructure, as shown in FIG. Figure 2 (ac) shown.

[0032] S500. Embossed plastic (for effect verification): NAK80 micro mold prepared by etching in 1wt.% HNO3 etchant is used to micro-emboss PP plastic, and an inverted frame structure complementary to the mold is pressed on the plastic surface. Figure 2 (d) shown.

[0033] The surface microstructure of the NAK80 micro mold obtained by the steps in Example 1 (1wt.% HNO3 etchant) is similar to the surface microstructure of the plastic after imprinting. Figure 2 The columnar array microstructures were obtained by etching with 1 wt.% HNO3, with wide spacing between the tops (about 56 μm). The inverted frame microcavity structures obtained by imprinting plastic also had wide spacing between the tops (about 5 μm).

[0034] Example 2:

[0035] The same mask pattern, photolithography method and hot pressing method are used in Example 2 and Example 1. The only difference is that the etchant in step S300 wet etching is a 1wt.% HNO3+1wt.% FeCl3 mixed solution. The microstructure morphology of the NAK80 surface after photolithography in Example 2 is as follows: Figure 3As shown in (ac), the surface of the NAK80 micro mold presents a nearly pyramidal array microstructure, and the spacing between the tops of adjacent micro structures is narrower (about 37μm). The mold is used to emboss the plastic surface morphology as shown in Figure 3 As shown in (d), the spacing between the inverted pyramid microcavity structures on the plastic surface is narrower (about 1-2 μm).

[0036] In this invention, a NAK80 micro-template is fabricated through photolithography, resulting in a near-pyramid-shaped microstructure on the surface. This structure exhibits high dimensional accuracy, good structural stability, and is reusable. This NAK80 micro-template can be used to emboss a plastic surface to create micron-scale inverted pyramid structures. This structure exhibits resistance to external friction, low cost, high efficiency, and excellent formability.

[0037] In response to the current situation in which metal molds used for plastic embossing have low microstructure dimensional accuracy and silicon molds have low mechanical stability, the present invention uses photolithography to prepare NAK80 mold steel with high dimensional accuracy and good mechanical stability, effectively solving the difficulty of achieving high-precision, low-cost, and repeated embossing on plastics.

[0038] As described above, the present invention can be implemented well.

[0039] The implementation methods of the present invention are not limited to the above-mentioned embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A photolithography method for forming a near-pyramid microstructure on the surface of NAK80 mold steel, characterized in that: The following steps are involved: S100 photolithography mask pattern design: Design a periodically arranged square pattern as a photolithography mask pattern; Preparation of photoresist mask by S200 photolithography: A pre-designed photoresist pattern is prepared on the surface of NAK80 steel sheet by photolithography to serve as a mask; S300 wet etching: The NAK80 covered with a square photoresist mask is immersed in a 1wt.% FeCl3+1wt.% HNO3 etching solution for 25-30 minutes to obtain a NAK80 with a pyramid array microstructure covered with the photoresist mask; S400: Removal of photoresist mask: The wet-etched NAK80 is removed from the etching solution, rinsed with deionized water, and then ultrasonically treated in an acetone solution for 7 minutes to remove the photoresist, thereby obtaining a NAK80 micro mold with a pyramid-shaped periodic array microstructure. S500 Embossed Plastic: Polypropylene (PP) plastic is hot embossed using a NAK80 micro-mold prepared by photolithography, creating an inverted pyramidal framework structure that complements the mold.

2. The photolithography method for forming a near-pyramid-shaped microstructure on the surface of NAK80 mold steel according to claim 1, characterized in that: In step S100 , the photoresist mask pattern is periodically arranged squares with a side length of 60 μm and a spacing between adjacent squares of 10 μm.

3. The photolithography method for forming a near-pyramid-shaped microstructure on the surface of NAK80 mold steel according to claim 1, characterized in that: In step S200, the thickness of the NAK80 mold steel sheet is 1-2 mm.

4. The photolithography method for forming a near-pyramid-shaped microstructure on the surface of NAK80 mold steel according to claim 1, characterized in that: In step S200, AZ4620 positive photoresist is used to prepare a photoresist mask by photolithography.

5. The photolithography method for forming a near-pyramid-shaped microstructure on the surface of NAK80 mold steel according to claim 4, characterized in that: In step S200 , AZ4620 positive photoresist is spin-coated on the NAK80 surface at a speed of 3000 rpm, with a spin coating thickness of 1.3 μm, an exposure energy of 50 J, and a development time of 60 s.

6. The photolithography method for forming a near-pyramid-shaped microstructure on the surface of NAK80 mold steel according to claim 1, characterized in that: In step S500, the PP plastic hot stamping temperature is 125°C and the pressure is 15 MPa.

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