Oiling-free capsule mold and preparation process thereof

Abstract

The invention relates to the technical field of material surface treatment, and provides an oil-coating-free capsule mold and a preparation technology thereof.The oil-coating-free capsule mold comprises a capsule mold base body and a plating layer which is plated outside the capsule mold base body and contains chromium and chromium nitride; and the thickness of the plating layer is 3-5 microns, the surface roughness is 0.06-0.09 Ra, and the hardness is 1500-2000 HV. Through the arrangement, a demolding interface with low surface energy, high strength, high wear resistance and high chemical inertness can be constructed outside a capsule mold base body, the service life of the mold is prolonged, the mirror surface level surface roughness is 0.06-0.09 Ra, the friction coefficient between a capsule and the mold can be remarkably reduced, oil-free demolding of the capsule is achieved, and the oil-free demolding efficiency of the capsule is improved. And therefore, high-efficiency and high-quality production of capsules is realized, and the economic benefit is maximized.

Description

Technical Field

[0001] This invention relates to the field of material surface treatment technology, and in particular to an oil-free capsule mold and its preparation process. Background Technology

[0002] In the capsule manufacturing industry, applying oil to the mold surface is a traditional process for capsule demolding. Currently, manufacturers generally apply grease to the mold surface, utilizing the lubricating properties of grease to reduce the adhesion between the capsule and the mold, thus facilitating smooth capsule demolding and completing the production process. This method has become a widely used demolding technique in the industry due to its simplicity and low initial investment cost.

[0003] However, in practical applications, it has been found that existing oiling and demolding technologies have significant drawbacks: Firstly, the amount of oil used is difficult to control precisely, resulting in two significant problems: when the amount of oil is insufficient, the friction between the mold and the capsule increases, making it difficult to demold the capsules. A large number of capsules are scrapped due to demolding failure, resulting in waste of raw materials and a significant increase in production costs; when the amount of oil is excessive, the excess oil will adhere to the inner wall of the capsule to form oil spots, which seriously affects the cleanliness and quality of the capsules, making it impossible for downstream pharmaceutical companies to fill drugs normally, causing large-scale returns and damaging the company's reputation and economic interests.

[0004] Secondly, during storage, the oil in the coated capsules is prone to oxidation, producing yellow spots on the inner wall of the capsules. This also provides a breeding ground for mold. As the storage time increases, the quality of the capsules deteriorates significantly, and the product qualification rate decreases markedly.

[0005] In view of this, how to achieve efficient and high-quality capsule production has become an important issue that urgently needs to be addressed. Summary of the Invention

[0006] This invention provides an oil-free capsule mold and its preparation process, which solves the problem that the quality of capsules is difficult to guarantee due to oiling during demolding in the prior art. It can achieve efficient and high-quality capsule production and maximize economic benefits.

[0007] The present invention provides an oil-free capsule mold, characterized in that it comprises: a capsule mold base, and a plating layer containing chromium and chromium nitride plated on the capsule mold base; The coating has a thickness of 3–5 μm, a surface roughness of 0.06–0.09 Ra, and a hardness of 1500–2000 HV.

[0008] According to the present invention, an oil-free capsule mold is provided, wherein the coating comprises a chromium plating layer and a chromium nitride layer; The chromium plating layer is the inner layer of the plating layer and is used to bond with the surface of the capsule mold substrate.

[0009] According to the present invention, an oil-free capsule mold is provided, wherein the chromium grain size in the chromium plating layer is 1-2 nm, and the chromium nitride grain size in the chromium nitride layer is 2-3 nm.

[0010] According to the present invention, an oil-free capsule mold is provided, wherein the surface of the capsule mold substrate is formed as an activation layer; The capsule mold substrate is bonded to the plating layer through the activation layer.

[0011] This invention also provides a process for preparing an oil-free capsule mold, used to prepare the oil-free capsule mold described in any one of the above-mentioned methods, comprising the following steps: A substrate is provided and pretreated to remove impurities from the surface of the substrate; The substrate is surface activated; A coating is applied to the activated substrate surface, comprising a coating containing chromium and chromium nitride, until the thickness of the coating is 3-5 μm. Polishing: Polish the coating to a surface roughness of 0.06 to 0.09 Ra.

[0012] According to the preparation process of an oil-free capsule mold provided by the present invention, the substrate pretreatment step includes: Impurities on the surface of the substrate are removed using a cleaning agent combined with ultrasound. After cleaning, the substrate is placed in an oven to dry.

[0013] According to the preparation process of an oil-free capsule mold provided by the present invention, the substrate surface activation step includes: The substrate was placed at a temperature of 400°C and a vacuum degree of 1.2 × 10⁻⁶. -2 Under the condition of Pa; Etching was performed with a bias voltage of 790V, a duty cycle of 70%, and argon gas introduced to a vacuum level of 2.0Pa. The bias current was set to 9.5A, and the etching process lasted for 15 minutes. After bombardment, argon gas was introduced again to achieve a vacuum level of 4.0 × 10⁻⁶. -2 At a bias voltage of 790V and a duty cycle of 70%, ion bombardment was performed for 15 minutes.

[0014] According to the present invention, a process for preparing an oil-free capsule mold includes the following coating steps: A chromium plating layer is deposited on the activated substrate surface; A chromium nitride layer is deposited on the chromium plating layer until the thickness of the plating layer is 3-5 μm.

[0015] According to the present invention, a process for preparing an oil-free capsule mold includes a chromium plating step comprising: Set the bias voltage to 200V, duty cycle to 60%, arc current to 60A, and introduce argon gas to a vacuum level of 5.0 × 10⁻⁶. -1 Pa, chromium target arc flow is turned on, and chromium plating is deposited on the substrate.

[0016] According to the present invention, a process for preparing an oil-free capsule mold includes the following steps: The first layer of chromium nitride is deposited. Argon gas is turned off, nitrogen gas is turned on, bias voltage is set to 350V, duty cycle to 60%, arc current to 60A, and nitrogen gas is used to achieve a vacuum of 5.0 × 10⁻⁶. -1 Pa, deflection 16A, deposition time 30 minutes; A second layer of chromium nitride is plated, with a bias voltage of 250V, a duty cycle of 60%, an arc current of 70A, and nitrogen gas introduced to a vacuum level of 8.0 × 10⁻⁶. -1 Pa, set the flow deflection to 20A, and the deposition time to 80 minutes; A third layer of chromium nitride is plated, with a bias voltage of 350V, a duty cycle of 60%, an arc current of 60A, and nitrogen gas introduced to a vacuum level of 5.0 × 10⁻⁶. -1 Pa, set the flow deflection to 15A, and the deposition time to 30 minutes.

[0017] According to the preparation process of an oil-free capsule mold provided by the present invention, the coating step further includes: Annealing involves heating the coated substrate to 400°C and then cooling it to 95°C under an argon atmosphere.

[0018] According to the preparation process of an oil-free capsule mold provided by the present invention, the polishing step includes: The coated surface is polished with a wool wheel and then finely polished with ceramic beads to a roughness of 0.06 to 0.09 Ra.

[0019] The oil-free capsule mold and its manufacturing process provided by this invention, by plating a layer composed of chromium and nitrogen on the surface of the capsule mold substrate, utilizes the high chemical stability of chromium and the solid solution strengthening effect of nitrogen to construct a demolding interface with low surface energy, high strength, high wear resistance, and high chemical inertness. This not only extends the service life of the mold, but also significantly reduces the friction coefficient between the capsule and the mold with a mirror-like surface roughness of 0.06–0.09 Ra, achieving oil-free demolding. The inner wall of the demolded capsule is smooth and free of oil residue, fundamentally eliminating the problems of mold growth and oxidative yellowing, and extending the shelf life of the capsule. At the same time, it improves the smoothness of the inner and outer surfaces of the capsule, reduces powder adhesion, makes subsequent powder filling smoother, improves filling quality and yield, and reduces powder loss. In addition, it eliminates the need for oiling equipment and oil consumption. Compared with related technologies, this invention achieves efficient and high-quality capsule production, maximizing economic benefits. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the oil-free capsule mold provided in an embodiment of the present invention.

[0022] Figure 2 yes Figure 1 Cross-sectional view along the AA direction.

[0023] Figure 3 This is a schematic flowchart of the oil-free capsule mold preparation process provided in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the surface activation process in the oil-free capsule mold preparation process provided in this embodiment of the invention.

[0025] Figure 5 This is a schematic diagram of the coating process in the oil-free capsule mold preparation process provided in this embodiment of the invention.

[0026] Figure label: 10. Substrate; 11. Chromium plating; 12. First chromium nitride layer; 13. Second chromium nitride layer; 14. Third chromium nitride layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0028] Furthermore, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0029] To better understand the oil-free capsule mold and its manufacturing process provided by this invention, its application background is first introduced. Oil-coated demolding has become a commonly used demolding method in the capsule manufacturing industry due to its simple operation and low initial investment cost. However, in practical applications, it has been found that oil-coated demolding technology has at least the following drawbacks: 1) The amount of oil used is difficult to control precisely; when the amount of oil is insufficient, capsules are difficult to demold, a large number of capsules are scrapped, resulting in waste of raw materials and a significant increase in production costs; when the amount of oil is excessive, a large number of oil spots adhere to the inner wall of the capsules, making it impossible for pharmaceutical companies to fill the medicines, causing a large number of returns, damaging the company's reputation and economic interests.

[0030] 2) During long-term storage, the oil in the coated capsules is prone to oxidation, which can cause yellow spots on the inner wall of the capsule. It is also prone to mold growth, which seriously affects the quality of the capsules and significantly reduces the product qualification rate.

[0031] In view of the above problems, embodiments of the present invention provide an oil-free capsule mold and its preparation process, which enables oil-free demolding of capsules, resulting in a smooth inner wall free of oil residue. This fundamentally eliminates the problems of mold growth and oxidative yellowing, extending the shelf life. Simultaneously, it improves the smoothness of the inner and outer surfaces of the capsules, reduces powder adhesion, makes subsequent powder filling smoother, improves filling quality and yield, and reduces powder loss. Furthermore, it eliminates the need for oiling equipment and oil consumption. Compared with related technologies, this achieves efficient and high-quality capsule production, maximizing economic benefits.

[0032] The following combination Figures 1 to 3 This invention describes the oil-free capsule mold and its preparation process.

[0033] An oil-free capsule mold includes a capsule mold base 10 and a plating layer containing chromium and chromium nitride plated on the capsule mold base 10; wherein the thickness of the plating layer is 3-5 μm, the surface roughness is 0.06-0.09 Ra, and the hardness is 1500-2000 HV.

[0034] In practical applications, by coating the surface of the capsule mold substrate 10 with a layer composed of chromium and nitrogen, and utilizing the high chemical stability of chromium and the solid solution strengthening effect of nitrogen, a demolding interface with low surface energy, high strength, high wear resistance, and high chemical inertness is constructed. This not only extends the service life of the mold, but also significantly reduces the coefficient of friction between the capsule and the mold due to the mirror-like surface roughness of 0.06–0.09 Ra, achieving oil-free demolding. The inner wall of the demolded capsule is smooth and free of oil residue, fundamentally eliminating the problems of mold growth and oxidative yellowing, and extending the shelf life of the capsule. Simultaneously, it improves the smoothness of the inner and outer surfaces of the capsule, reduces powder adhesion, makes subsequent powder filling smoother, improves filling quality and yield, and reduces powder loss. Furthermore, it eliminates the need for an oiling device and reduces grease consumption. Compared with related technologies, this achieves efficient and high-quality capsule production, maximizing economic benefits.

[0035] In a further example of the present invention, the above-mentioned coating includes a chromium plating layer 11 and a chromium nitride layer; wherein, the chromium plating layer 11 is the inner layer of the coating and is used to bond with the surface of the capsule mold substrate 10.

[0036] In detail, the chromium plating layer 11 has excellent physical adhesion and chemical activity. Its crystal structure and atomic arrangement enable it to undergo complex physical and chemical reactions with the surface of the capsule mold substrate 10 and the chromium nitride layer, forming a strong metallurgical bond. This effectively enhances the bonding force between the entire plating system and the substrate 10, making the entire plating system less prone to peeling off and able to function stably for a long time. The chromium nitride layer, as the outer layer of the plating, has multiple advantages such as high hardness, high wear resistance, high chemical inertness, and low coefficient of friction, thus providing reliable protection for the mold and extending its service life.

[0037] In detail, the chromium nitride layer includes a first chromium nitride layer 12, a second chromium nitride layer 13, and a third chromium nitride layer 14, which are plated in layers from the inside out.

[0038] Among them, the chromium plating layer 11 is applied under the following conditions: bias voltage 200V, duty cycle 60%, arc current 60A, and vacuum degree 5.0×10⁻⁶. -1 Under an argon atmosphere of Pa, a chromium target arc flow is activated for plating.

[0039] The first chromium nitride layer 12 is applied after the chromium plating layer 11 is deposited, with argon gas turned off and nitrogen gas turned on, and the bias voltage set to 350V, duty cycle to 60%, arc current to 60A, and nitrogen gas to a vacuum level of 5.0×10⁻⁶. -1 Pa, bias flow 16A, deposition for 30 minutes, and then plating.

[0040] The second chromium nitride layer 13 is formed after the first chromium nitride layer 12 is deposited, by adjusting the bias voltage to 250V, the duty cycle to 60%, the arc current to 70A, and introducing 1470ccm of nitrogen gas to achieve a vacuum degree of 8.0×10⁻⁶.-1 The coating was completed by setting the deflection current to 20A and the deposition time to 80 minutes.

[0041] The third chromium nitride layer 14 is formed after the second chromium nitride layer 13 is deposited, by adjusting the bias voltage to 350V, the duty cycle to 60%, the arc current to 60A, and introducing 1030ccm of nitrogen gas to achieve a vacuum degree of 5.0×10⁻⁶. -1 Pa, set the bias flow to 15A, deposit for 30 minutes, and then coat.

[0042] With this configuration, the first chromium nitride layer 12 has a high interfacial bonding strength with the chromium plating layer 11, as well as high plating toughness, which can absorb stress concentration in subsequent hard layers. The second chromium nitride layer 13 is a dense and thick layer with high hardness, constituting the main functional layer of the plating layer and providing core wear resistance. The third chromium nitride layer 14 is a fine and high-hardness layer, possessing high hardness, high wear resistance, high anti-adhesion, and high oxidation resistance, giving the plating layer a composite function of self-lubrication and protection. The combination of the chromium plating layer 11 and the three chromium nitride layers can significantly improve the adhesion, wear resistance, anti-adhesion, and oxidation resistance of the plating layer.

[0043] In a further example of the present invention, the grain size of chromium in the chromium plating layer 11 is 1-2 nm, and the grain size of chromium nitride in the chromium nitride layer is 2-3 nm.

[0044] In detail, the nanocrystal size design of the chromium plating layer 11 and the chromium nitride layer, through the gradient grain strengthening and interface synergistic protection mechanism, achieves multiple optimizations in bonding force, wear resistance, and corrosion resistance, thereby improving the service life of the capsule mold.

[0045] In a further example of the present invention, an activation layer is formed on the surface of the capsule mold substrate 10, and the film mold substrate 10 is bonded to the chromium plating layer 11 through the activation layer. With this configuration, a nanoscale active transition layer can be formed on the surface of the capsule mold substrate 10 through activation treatment (such as chemical etching, plasma bombardment, electrochemical activation, etc.), thereby improving the bonding ability between the surface of the capsule mold substrate 10 and the chromium plating layer 11, and making the plating system more firmly bonded to the capsule mold substrate 10.

[0046] The preparation process of the oil-free capsule mold provided by the present invention is described below. The preparation process of the oil-free capsule mold described below can be referred to in correspondence with the oil-free capsule mold described above.

[0047] It should be noted that the raw materials used in the following embodiments of the present invention (such as chromium targets, argon, nitrogen, etc.) are not particularly limited and can all be purchased on the market or obtained by conventional methods known to those skilled in the art. All the equipment involved (such as vacuum coating machines) are, unless otherwise specified, common equipment in the art and can be operated by those skilled in the art based on common industry knowledge and technical means.

[0048] Unless otherwise specified, the raw materials used in the following embodiments of the present invention have the following purity: chromium target ≥ 99.99%, argon gas ≥ 99.99%, and nitrogen gas ≥ 99.99%.

[0049] A process for preparing an oil-free capsule mold, used to prepare any of the oil-free capsule molds provided in the above examples, includes the following steps: Step S10: Provide a substrate 10 and pre-treat the substrate 10 to remove impurities from the surface of the substrate 10.

[0050] In detail, the capsule mold substrate 10 is generally made of stainless steel. Subsequent turning, milling, and water polishing steps remove burrs and tool marks from the surface, providing a smooth base for the plating. After these processing steps, oil and polishing wax residues may remain on the surface of the capsule mold substrate 10. In the substrate 10 pretreatment step, a cleaning agent combined with ultrasonic cleaning effectively dissolves and removes these residues, ensuring stable bonding between the plating and the substrate 10 surface. The cleaning agent can be an organic solvent, such as acetone or alcohol; specific limitations are not imposed in this embodiment. After cleaning, the substrate 10 is placed in an oven to dry.

[0051] Step S20: Surface activation of substrate 10 is performed by removing contaminants such as oxide film and oil stains from the surface of substrate 10 through physical, chemical or electrochemical means. At the same time, the surface is micro-roughened, the surface energy is increased and the potential difference is eliminated, thereby enhancing the mechanical anchoring and chemical bonding force between the coating and substrate 10.

[0052] In detail, step S20 includes: Step S200: Place the pretreated substrate 10 into the vacuum chamber of the vacuum coating machine using a fixture, then heat the temperature inside the vacuum chamber to 400°C and evacuate to 1.2 × 10⁻⁶. -2 Pa.

[0053] Step S201: Etching. Set the bias voltage to 790V, the duty cycle to 70%, introduce argon gas to a vacuum of 2.0Pa, set the bias current to 9.5A, and etch for 15 minutes.

[0054] Step S202: Bombardment, then introduce 30ccm of argon gas again to achieve a vacuum of 4.0 × 10⁻⁶. -2 At a bias voltage of 790V and a duty cycle of 70%, ion bombardment was performed for 15 minutes.

[0055] In detail, the argon gas introduced into the vacuum chamber is ionized under the action of an electric field to form an argon ion beam. The argon ion beam is accelerated in the electric field to obtain high kinetic energy, and then bombards the surface of the substrate 10 at high speed. Through physical sputtering, the contaminants, oxide layers and other atoms or molecules adsorbed on the surface of the substrate 10 are bombarded and removed, thus achieving surface cleaning. At the same time, the bombardment of the high-energy ion beam will also cause the atomic lattice of the substrate 10 surface to be distorted, forming a micro-rough structure, which enhances the bonding ability between the coating and the surface of the substrate 10.

[0056] More specifically, in step S201, under a relatively high pressure of 2.0 Pa, the plasma density generated by argon ionization is high and ion collisions are frequent. Although the kinetic energy of a single ion is relatively low, the ion flux (biased flow 9.5 A) is large. Through the collective sputtering effect, the thick oxide layer, oil stains, adsorbed impurities and other macroscopic pollutants on the surface of the substrate 10 can be quickly stripped away.

[0057] In step S202, at 4.0×10 -2 Under low atmospheric pressure, the mean free path of ions is long, the acceleration distance is longer, and the kinetic energy of individual ions is significantly improved. Through high-energy single-point bombardment, they penetrate deep into the surface lattice, effectively removing submicron-level contaminants remaining after etching. This causes lattice distortion or shallow implantation of surface atoms, forming an activated transition layer, increasing surface energy, and enhancing the bonding ability between the coating and the substrate surface.

[0058] By combining etching and bombardment in a two-step process, surface cleaning, roughening, and deep activation are achieved, significantly improving the adhesion performance of the coating.

[0059] Step S30: Plating. A plating layer containing chromium and chromium nitride is plated on the surface of the activated substrate 10. The thickness of the plating layer is 3-5 μm and the hardness is 1500-2000 HV.

[0060] In detail, step S30 includes: Step S300: Apply chromium plating 11. A chromium plating 11 is deposited on the surface of the activated substrate 10. Due to its unique crystal structure and atomic arrangement, the chromium plating 11 undergoes a physicochemical reaction with the surface of the substrate 10 and the chromium nitride layer, forming a strong metallurgical bond, enhancing the adhesion between the plating system and the substrate 10, and preventing the plating from peeling off.

[0061] More specifically, after the surface activation step is completed, the heating is turned off, the bias voltage is set to 200V, the duty cycle to 60%, the arc current to 60A, and argon gas is introduced to bring the vacuum level to 5.0 × 10⁻⁶. -1 Pa, the chromium target arc current is turned on, and the power supply induces arc discharge between the cathode chromium target and the anode. The cathode chromium target is locally evaporated and ionized at high temperature. Chromium particles are directionally transported to the surface of the substrate 10 in the vacuum field. Through physical deposition and ion bombardment, a firmly attached chromium plating layer 11 is finally formed.

[0062] More specifically, the thickness of the chromium plating 11 is 1% to 2% of the total plating thickness.

[0063] Step S301: Deposit the first layer of chromium nitride. After the chromium plating layer 11 is deposited, turn off the argon gas, turn on the nitrogen gas, set the bias voltage to 350V, duty cycle to 60%, arc current to 60A, and nitrogen gas to a vacuum degree of 5.0×10⁻⁶. -1 Pa, bias flow 16A, deposition time 30 minutes.

[0064] With this setup, when nitrogen gas is introduced into the vacuum deposition environment, it will react with the high-energy chromium particles generated by the arc discharge in the gas phase and on the surface of the substrate 10, ultimately forming a chromium nitride plating layer 11.

[0065] The lower nitrogen partial pressure and bias voltage in step S301 can avoid excessive sputtering of the underlying Cr layer, while promoting the formation of Cr-N transition bonds between Cr and N atoms at the interface, greatly improving the interfacial bonding ability between the first layer of chromium nitride and the chromium plating layer 11 as well as the toughness of the plating layer, and can absorb the stress concentration of the subsequent hard layer.

[0066] Step S302: Deposit the second layer of chromium nitride. After the first layer of chromium nitride is deposited, adjust the bias voltage to 250V, duty cycle to 60%, arc current to 70A, and introduce 1470ccm of nitrogen gas to achieve a vacuum of 8.0×10⁻⁶. -1 Pa, set the flow deflection to 20A, and the deposition time to 80 minutes.

[0067] With this setup, the higher arc current in step S301 can improve the plasma ionization rate, refine the chromium nitride grain size, and the higher nitrogen partial pressure and longer deposition time can deposit a dense, thick layer with a stoichiometric ratio, making the second chromium nitride layer the main functional layer of the coating and providing the coating with core wear resistance.

[0068] Step S303: Deposit the third layer of chromium nitride. After the second layer of chromium nitride is deposited, adjust the bias voltage to 350V, duty cycle to 60%, arc current to 60A, and introduce 1030ccm of nitrogen gas to achieve a vacuum of 5.0×10⁻⁶. -1 Pa, set the flow deflection to 15A, and the deposition time to 30 minutes.

[0069] With this setup, a chromium nitride mixed phase structure is formed on the surface by using a 350V high-energy bias voltage and a 0.5Pa medium nitrogen partial pressure. High-energy ion bombardment induces nanotwins and lattice distortion, maintaining high hardness while the surface oxidizes during friction to form a lubricating film, reducing the coefficient of friction and significantly improving anti-adhesion and anti-oxidation properties, thus giving the coating a composite function of self-lubrication and protection.

[0070] Through the above technical solution, the combination of chromium plating layer 11 and the three-layer chromium nitride layer can significantly improve the adhesion, wear resistance, anti-adhesion, and oxidation resistance of the plating layer. After the plating is completed, the arc current, nitrogen gas, and bias voltage are turned off.

[0071] In a further example of the present invention, step S30 further includes: Step S304: Annealing. The coated substrate 10 is heated to 400°C, and then 495ccm of argon gas is introduced. It is then cooled to 95°C in an argon atmosphere. This setup, through annealing, can eliminate internal stress, increase density, prevent cracking, and facilitate subsequent processing.

[0072] Step S40: Polishing. Polish the coating surface until the surface roughness is 0.06 to 0.09 Ra.

[0073] In detail, the polishing process first uses a wool wheel to polish the coating surface to achieve rapid leveling while retaining the coating thickness, and then uses ceramic beads to fine polish to a roughness of 0.06 to 0.09 Ra.

[0074] The capsule mold prepared using the above process has a coating hardness of 1500-2000 HV (HV hardness tester); a coating thickness of 3-5 μm (EDS electron microscopy test); a coating roughness of 0.06 to 0.09 Ra after fine polishing (GAUSS roughness tester test); a coating adhesion strength >86.5 N (ASTM C1624 standard test); and a service life extended by 3-5 times after coating (test of turning GCr15 bearing steel).

[0075] The capsule mold prepared using the above process was tested for demolding effect. It was found that the capsules could be demolded without oiling, eliminating the problems of discoloration and mold caused by oil residue, and greatly improving the capsule qualification rate.

[0076] It is understood that, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

[0077] The oil-free capsule mold and its preparation process provided in this invention, by coating the surface of the capsule mold substrate 10 with a layer composed of chromium and nitrogen, utilizes the high chemical stability of chromium and the solid solution strengthening effect of nitrogen to construct a demolding interface with low surface energy, high strength, high wear resistance, and high chemical inertness. This not only extends the service life of the mold, but also significantly reduces the friction coefficient between the capsule and the mold with a mirror-like surface roughness of 0.06–0.09 Ra, achieving oil-free demolding. The inner wall of the demolded capsule is smooth and free of oil residue, fundamentally eliminating the problems of mold growth and oxidative yellowing, and extending the shelf life of the capsule. At the same time, it improves the smoothness of the inner and outer surfaces of the capsule, reduces powder adhesion, makes subsequent powder filling smoother, improves filling quality and yield, and reduces powder loss. In addition, it eliminates the need for an oiling device and oil consumption. Compared with related technologies, this invention achieves efficient and high-quality capsule production, maximizing economic benefits.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A no-oil capsule mold, characterized in that, include: The capsule mold substrate, and the coating consisting of chromium and chromium nitride applied to the capsule mold substrate; The coating has a thickness of 3–5 μm, a surface roughness of 0.06–0.09 Ra, and a hardness of 1500–2000 HV.

2. The oil-free capsule mold according to claim 1, characterized in that, The coating includes a chromium plating layer and a chromium nitride layer; The chromium plating layer is the inner layer of the plating layer and is used to bond with the surface of the capsule mold substrate.

3. The oil-free capsule mold according to claim 2, characterized in that, The chromium grain size in the chromium plating layer is 1-2 nm, and the chromium nitride grain size in the chromium nitride layer is 2-3 nm.

4. The oil-free capsule mold according to any one of claims 1 to 3, characterized in that, An activation layer is formed on the surface of the capsule mold substrate; The capsule mold substrate is bonded to the plating layer through the activation layer.

5. A process for preparing an oil-free capsule mold, characterized in that, The method for preparing the oil-free capsule mold as described in any one of claims 1-4 includes the following steps: A substrate is provided and pretreated to remove impurities from the surface of the substrate; The substrate is surface activated; A coating is applied to the activated substrate surface, comprising a coating containing chromium and chromium nitride, until the thickness of the coating is 3-5 μm. Polishing: Polish the coating to a surface roughness of 0.06 to 0.09 Ra.

6. The preparation process of the oil-free capsule mold according to claim 5, characterized in that, The substrate surface activation step includes: The substrate was placed at a temperature of 400°C and a vacuum degree of 1.2 × 10⁻⁶. -2 Under the condition of Pa; Etching was performed with a bias voltage of 790V, a duty cycle of 70%, and argon gas introduced to a vacuum level of 2.0Pa. The bias current was set to 9.5A, and the etching process lasted for 15 minutes. After bombardment, argon gas was introduced again to achieve a vacuum level of 4.0 × 10⁻⁶. -2 At a bias voltage of 790V and a duty cycle of 70%, ion bombardment was performed for 15 minutes.

7. The preparation process of the oil-free capsule mold according to claim 5, characterized in that, The coating step includes: A chromium plating layer is deposited on the activated substrate surface; A chromium nitride layer is deposited on the chromium plating layer until the thickness of the plating layer is 3-5 μm.

8. The preparation process of the oil-free capsule mold according to claim 7, characterized in that, The chromium plating process includes: Set the bias voltage to 200V, duty cycle to 60%, arc current to 60A, and introduce argon gas to a vacuum level of 5.0 × 10⁻⁶. -1 Pa, chromium target arc flow is turned on, and chromium plating is deposited on the substrate.

9. The preparation process of the oil-free capsule mold according to claim 8, characterized in that, The step of plating a chromium nitride layer includes: The first layer of chromium nitride was plated. Argon gas was turned off, nitrogen gas was turned on, bias voltage was set to 350V, duty cycle to 60%, arc current to 60A, and nitrogen gas was used to achieve a vacuum of 5.0 × 10⁻⁶. -1 Pa, deflection 16A, deposition time 30 minutes; A second layer of chromium nitride is plated, with a bias voltage of 250V, a duty cycle of 60%, an arc current of 70A, and nitrogen gas introduced to a vacuum level of 8.0 × 10⁻⁶. - 1 Pa, set the flow deflection to 20A, and the deposition time to 80 minutes; A third layer of chromium nitride is plated, with a bias voltage of 350V, a duty cycle of 60%, an arc current of 60A, and nitrogen gas introduced to a vacuum level of 5.0 × 10⁻⁶. - 1 Pa, set the flow deflection to 15A, and the deposition time to 30 minutes.

10. The preparation process of the oil-free capsule mold according to claim 5, characterized in that, The coating step further includes: Annealing involves heating the coated substrate to 400°C and then cooling it to 95°C under an argon atmosphere.

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