JP6432738B2 - Fine processing method, mold manufacturing method, and plastic molded product manufacturing method - Google Patents

Description

  The present invention relates to a technique for performing fine processing on the surface of a metal material by partially dissolving solid nitrogen on the surface of the metal material, selectively curing the surface, and then removing an uncured portion.

  Marking production information and product information on the surface of metal products and plastic products in a minute size that cannot be recognized by users, or forming many anti-slip micro patterns on the surface of mobile phones and cover cases, or designs In order to form fine three-dimensional dot images on the product surface for improving the design, it is essential to have a technology for forming micro-shaped patterns with a basic size of 1 mm or less.

The common features of the micro-texture required here are that the typical size of the unit pattern shape is 1 mm or less, the number of unit pattern shapes is well over 100, and they are highly accurate at predetermined positions on the product surface / interface. The first condition is that transfer and formation must be performed.
In addition, the second condition is that the required unit shape is an arbitrary shape including a polygonal pattern, an image pattern, and a font pattern, and the shape can be created even if the unit shape is a concavo-convex shape pattern that changes at a steep angle. Become.
Further, the third condition is that even if the material for transferring and molding the above pattern is glass, plastic, or metal, the shape can be created regardless of the type and grade.
In order to satisfy all of these requirements, a technique is required in which a necessary pattern shape is formed in a steel mold and transferred to various materials.

When micro milling or micro cutting is used as the processing method, it is necessary to create all the unit pattern shape data and shape creation data as CAM data, and create data for the number of patterns to be created.
Furthermore, in an actual cutting process, it is indispensable to use a micro tool for cutting details of a unit shape pattern without any problems and to control it with high accuracy. Even if a fragile micro tool is not damaged in the entire process, the reading time from the creation of CAM data, which has a huge amount of information, to the end of processing usually exceeds several hundred hours.
Also in the micro electric discharge machining, it is difficult to form a unit pattern having a complicated shape and a fine dimension in the electric discharge machining with a wire of a certain size.
On the other hand, in the case of die-sinking EDM, enormous time is required to create and process CAM data as described above.
JP 2006-334704 A

  The present invention has been devised to solve the above problems, and it is possible to form a minute unit pattern shape that is designed in a complex and arbitrarily designed on the surface of a metal material in a short time and with high accuracy. The purpose is to provide processing technology based on the new manufacturing science principle.

  In order to achieve the above object, the microfabrication method according to claim 1 includes a step of printing a mask on a surface of a metal material according to CAD data created in advance to form a mask, and the metal Performing a plasma nitriding process on the surface of the material, forming a hardened layer on a portion other than the mask forming portion, and performing a blasting process on the surface of the metal material to remove the mask, and on a portion other than the hardened layer And a step of forming a concave portion having a shape corresponding to the mask pattern.

  According to a second aspect of the present invention, there is provided a method of manufacturing a mold according to CAD data prepared in advance, printing a surface of a metal material with a predetermined pattern, forming a mask, and forming a mask on the surface of the metal material. Applying plasma nitriding, forming a hardened layer in a portion other than the mask forming portion, blasting the surface of the metal material, removing the mask, and forming a mask pattern in a portion other than the hardened layer And a step of forming a recess having a corresponding shape.

  According to a third aspect of the present invention, there is provided a method for producing a plastic molded product, wherein the mold according to the second aspect is used as a mold, and the microtexture is transferred to the surface during injection molding of the plastic material.

  The microfabrication method described in claim 4 uses the die of claim 2 as a press die, and performs mold press or direct press on the surface of a metal sheet, plastic sheet, metal part, plastic part, or glass part. , It is characterized by transferring microtexture to each surface.

  In the case of the microfabrication method according to the present invention, a mask pattern for microfabrication is formed by printing ink on the surface of a metal material (such as stainless steel) using a general printing technique such as ink jet printing. For this reason, it is sufficient to prepare CAD data that is relatively easy to create in advance, and it is not necessary to prepare CAM data that requires an enormous amount of time.

  In addition, a hardened layer is partially formed on the surface of the metal material, and a blasting process is performed to uniformly remove and excavate portions other than the hardened layer. Compared to conventional processing methods, much more efficient processing can be realized. As a result, the working time can be greatly shortened. This fine processing method is excellent in that no special cutting tool is required.

By using this fine processing method, it is possible to form a mold having fine concave portions on the surface.
Further, by using this die as a mold die or a press die, it becomes possible to easily form a fine processing pattern (micro texture) on the surface of various materials.

[Overview]
The plasma nitriding-assisted microfabrication technology according to the present invention comprises the following three elemental technologies, and creates a micro-texture for a plastic / glass mold press mold, a plastic / powder injection mold, and a metal press mold. To do.
(1) Design pattern printing on mold material surface and mold material interface
(2) High-density nitrogen solid solution in non-printed parts by high-density plasma nitriding
(3) Selective removal and selective excavation of printing parts by blast method

[Printing technology of the designed micro pattern]
First, as shown in FIG. 1A, a micropattern 12 designed by CAD is printed on the surface of a mold material 10 made of SUS420 or the like by inkjet printing or dot printing technology.
As the ink used for this printing, a mixture of a black ink component and an organic primer is used. Preferably, the ink includes inorganic material particles and an inorganic solvent shown in Table 1. More preferably, the ink containing the inorganic material particles and the inorganic solvent shown in Table 1 is baked and conditioned after printing.

[Selective surface hardness technology by high-concentration nitrogen solution]
As shown in FIG. 1B, the surface of the mold material 10 is subjected to a low temperature and high density plasma nitriding treatment.
At this time, since the micropattern 12 functions as a mask, only the surface of the unprinted portion 14 is selectively made into a high-concentration nitrogen solid solution and the hardened layer 16 is formed as shown in FIG.

FIG. 2 is a schematic diagram showing the structure of the RF-DC low-temperature plasma nitriding apparatus 20 according to the present invention. A stainless steel workpiece 26, a heater 28 mounted in the DC bias 24, a pair of RF electrodes 30, and an RF oscillator 32 with an output of 2 MHz arranged outside the vacuum chamber 22 are provided.
Although not shown, outside the vacuum chamber 22, a control device for the RF oscillator 32, a control device for the DC bias, and a cooling device are installed.

  A mixed gas of N2 and H2, which is a raw material, is introduced into the inside through an air supply port (not shown) of the vacuum chamber 22, a high frequency is applied between the RF electrodes 30 and 30, and a DC bias voltage is simultaneously applied. When power is supplied to 28 and the inside of the vacuum chamber 22 is heated to 450 degrees Celsius or less, the mixed gas is turned into plasma, high density nitrogen ions and NH radicals are generated as shown in FIG. Infiltrate the surface.

In the case of this apparatus 20, since RF plasma and DC plasma can be controlled independently, nitriding can be performed in a wide high pressure range (meso pressure region) of 20 Pa to 1 kPa.
The density of nitrogen ions and NH radicals in this meso pressure range is 5 × 10 17 m ⁻³ or more, and since nitriding is performed in the high nitrogen ion / high NH radical state, nitrogen remains in the workpiece 26 even at a low holding temperature. Atoms can be introduced as solute atoms.
In addition, unlike conventional plasma devices, input / output power matching is performed in the frequency domain, so input energy is not wasted and is quickly input to plasma. As a result, it is possible to stably dissolve nitrogen in the surface of the workpiece 26 without unevenness.
When the above processing is continued for a predetermined time, nitrogen is dissolved at a high concentration on the surface of the workpiece 26.

[Removal and excavation of printed parts by mechanical removal method]
Next, as shown in FIG. 4 (a), the surface of the mold material 10 is subjected to a sand blasting process in which an abrasive material 40 such as sand is sprayed, thereby removing the micropattern 12 and high concentration nitrogen solid solution. Excavation is performed on the surface of the mold material 10 that has not been made.
As a result, as shown in FIG. 4B, a mold 44 in which a large number of recesses 42 are formed in places other than the hardened layer 16 is obtained.
The mold 44 is used as follows, for example.

[Plastic material injection molding]
Using the mold 44 as a mold mold, a micro-texture is formed on the surface and interface of the plastic injection molded product at the time of injection molding of the plastic material shown in Table 2.

[Press transfer and molding to metal sheets, film materials and metal parts]
Using the metal mold 44 as a press metal mold, a micro-texture is transferred and molded by a metal press onto a metal sheet, a film material, and a metal part surface / interface.

[Press transfer and molding to plastic materials]
Using the mold 44 as a press mold, the microtexture is transferred and molded to various plastic sheets, films, and bulk component materials shown in Table 2 by mold press or direct press.

[Press transfer to glass material, molding]
The mold 44 has sufficient high temperature hardness. Using this, the microtexture is transferred and molded on the surface / interface of various glass materials, optical glass parts and general glass parts shown in Table 3 by mold press or direct press.

[Products made by transferring and molding microtextures]
The plastic products, metal products, and glass products produced as described above have characteristic changes due to the shape pattern designed on the surface / interface.

[Optimum range of high concentration nitrogen solution process]
Regarding the plasma nitridation in austenitic stainless steel, as shown in FIG. 5, in the high temperature plasma nitridation corresponding to region I, a precipitation reaction occurred at the tip of the nitride layer in parallel with the diffusion of nitrogen atoms from the surface / interface. Precipitation strengthening due to fine nitride particles and high hardness thereby are used for surface treatment.
In fact, also in the following Document 1 and Document 2, this high-temperature plasma nitriding behavior is considered to be a common nitriding phenomenon regardless of the type of plasma process.
Further, as described in Reference 3 below, in this region I, the maximum nitrogen solid solution amount is in accordance with the equilibrium diagram, and for example, in iron-chromium alloys including plasma-nitrided stainless steel and tool steel, it is at most 0.1 to 0.5 mass. It is only%. With this, high concentration nitrogen solid solution is impossible.

[Reference 1]
"Surface modification for high quality molds (book)" / Masahiko Hihara (supervised), Mold Technology Association, Life Improvement Research Committee (edited), Masahiro Anjo / Nikkan Kogyo Shimbun, March 2009 [references 2]
"High-density plasma nitriding of tool steel and its application development (paper)" / Tatsuhiko Aizawa, Yoshio Sugita / Shibaura Institute of Technology Research Report 57-1 1-10 (2013)
[Reference 3]
"Nitrogen concentration prediction technology in plasma nitriding of steel (paper)" / Yasuhira Hiraoka, Koichiro Inoue / Electric Steel, Vol. 81 No. 1 2010

On the other hand, in the low temperature plasma nitriding corresponding to the region II, no precipitation reaction for generating nitride occurs, and nitrogen diffused from the surface and interface of the steel material exists in the base material as solute nitrogen.
In particular, in FIG. 5, when the process temperature is 420 ° C. or less, it is expected that the introduced nitrogen is dissolved at a relatively high concentration without depending on the process time.
Reference 4 below reports that nitrogen is introduced into a martensitic stainless steel material, which is a mold material for injection molding, at a low temperature of 400 ° C. or less using an ion implantation method, and the concentration becomes 4 mass% or more at maximum. doing. However, in the ion implantation method, high concentration nitrogen can be dissolved in the surface layer of about 0.5 μm, but practical surface layer modification is impossible in principle. Furthermore, the surface application is also limited to a test piece shape of about 10 × 10 mm ² with a flat test piece.

[Reference 4]
"Variable lattice expansion in martensitic stainless steel after nitrogen ion implantation (paper)" / D. Manova, G. Thorwarth, etc. / Nuclear Instruments and Methods in Physics Research B 242 (2006) 285-288

Here, the cross-sectional structure after nitriding at 420 ° C. for 4 hours using the technique of the present invention is shown in FIGS.
The sample is an injection mold material, SUS420 equivalent to STAVAX. Even in a short process of 4 hours, the nitride layer thickness reaches about 40 μm, and the average nitrogen concentration also reaches 4-5 mass%.
This demonstrates that nitriding characteristics far exceeding the nitriding ability by ion implantation can be obtained by using this technique.

[Nitrogen diffusion and solution behavior in mold materials]
In high-temperature plasma nitriding, as described in Document 3, even if the surface has a nitrogen solid solution concentration of 0.1 to 0.5 mass%, it decreases exponentially from the surface toward the material deep due to the diffusion phenomenon.
On the other hand, in the low-temperature plasma nitridation, in the case of the ion implantation method in the above-mentioned document 4, some difference is recognized depending on the steel type, but the nitrogen atom distribution is a depth position (for example, uniquely determined by the energy at the time of implantation) In Reference 4, it is a Gaussian distribution shape having a maximum value (24 at% (7 mass%) at the maximum between steel types) at 0.2 to 0.3 μm), and is almost 0 mass% at a depth of about 3 μm.
Considering that the nitriding depth in the market using high-temperature plasma nitriding is 50 μm, low-temperature plasma nitriding by ion implantation is not practical in terms of the thickness of the nitride layer at this depth.

Here, FIG. 7 shows the depth distribution of nitrogen atoms in a SUS420 sample after nitriding at 420 ° C. for 2 hours and 4 hours using the technique of the present invention.
From this figure, it can be seen that there is no difference in the nitride layer depending on the location, and a uniform nitride layer is formed.
The nitride layer thickness is about 40 μm, and exhibits a sufficient depth direction distribution as a plasma nitride layer for surface treatment.
The average solid solution nitrogen concentration is 4 mass%, which is 10 times or more of the solid solution degree in the equilibrium diagram of Reference 3 above.

[Hardness of low temperature plasma nitrided SUS420]
As emphasized in the above-mentioned literature 1 and literature 2, in the surface treatment by plasma nitriding, the surface hardness value determines the pros and cons of the process.
Here, FIG. 8 shows the hardness distribution after plasma nitriding at 420 ° C. for 4 hours according to this technique. The difference between the nitrided central part and the peripheral part was clarified by masking leaving only the central part.
Since the nitriding hardly proceeds in both the vertical and horizontal directions at the mask portion, the hardness is about 200 to 250 Hv, which is similar to the base material hardness, but the hardness increases to nearly 1500 Hv at the non-mask portion.
In particular, the hardness change at the boundary between the mask part and the non-mask part is steep. This is presumed that the formation of the nitride layer, which was uniform in FIG.

[Solution of Nitrogen Dissolved in SUS420 Sample Printed with Mask]
Next, FIG. 9 shows a cross-sectional structure and nitrogen distribution in the vicinity of the print mask portion when plasma nitriding is performed under the same conditions as described above.
Under the printing mask, no nitrogen element is detected, and the printing mask completely prevents the penetration and diffusion of nitrogen atoms into the steel base material. On the other hand, except for the printing mask, a thick nitride layer (cured layer) is formed as in FIG.
In fact, in FIG. 8, the steep change in hardness occurred at the boundary between the print mask and the non-mask portion. In FIG. 9, the nitrogen atoms entered and diffused immediately from the boundary of the print mask in FIG. Because.

The selective diffusion of nitrogen atoms to areas other than the print mask portion and the anisotropic diffusion in which the nitrogen atoms do not diffuse below the mask and the diffusion proceeds only to the deep portion of the non-mask portion are phenomena inherent to the present invention.
In Reference 5 below, a CVD nitriding apparatus attempts to form a microtexture on an austenitic stainless steel material. As shown in FIG. 10, even when the nitriding time exceeds 3 hours, the nitrided layer thickness is about 10 μm. In addition, the selective nitrogen diffusion and anisotropic diffusion as shown in FIGS. 8 and 9 do not occur. That is, it is impossible to control the nitriding diffusion process by the mask shape.

[Reference 5]
"Stainless steel patterning by combination of micro-patterning and driven strain produced by plasma assisted nitriding (paper)" / Gregory Marcos, Stephane Guilet, others / Surface & Coatings Technology 205 (2011) S275-S279

[Mask pattern printing on SUS420 sample by dispenser]
By inputting micro-patterns arbitrarily designed by CAD, externally input image images, fonts, and hand-drawn pictures into Adobe Illustrator (registered trademark), which is a drawing tool software, a mask pattern is directly placed on the SUS420 sample using a dispenser. Can be printed.
FIG. 11 shows an example of printing with unit dots changed to 10 μm, 50 μm, and 100 μm. Up to 10 μm can be printed on the metal surface as dots.

[Conversion from mask pattern to hardness distribution by high-density plasma nitriding]
FIG. 12 shows the result of measuring the hardness distribution across each line mask pattern after nitriding by applying three line mask patterns on the surface of the quenched SUS420 mold (base material hardness: 300 to 400 Hv). .
As shown in the figure, the mask portion printed as a line is almost the same as the base material hardness and does not change. On the other hand, the non-mask portion is selectively hardened to 1100 to 1200 Hv.

[Three-dimensional microtexture formation by sand blasting]
Since the printed pattern on the SUS mold was converted to the hardness distribution by the plasma nitriding process, the printed pattern portion having a lower hardness was mechanically removed and excavated by the sand blast method.
FIG. 13 shows an optical microscope image when the initial μ dot diameter is 100 μm and 300 μm.
With the technology of the present invention, a microdot pattern having a high accuracy and a depth of 10 μm was dug into a stainless steel mold.

[Design design with this technology]
Unlike micro cutting, micro milling, and micro electric discharge machining, by changing the initial printing pattern, various designed patterns can be dug into the stainless steel mold.
For example, as shown in FIG. 14, each pattern of stars (FIG. (A)), triangles (FIG. (B)), and squares (c) is difficult to produce by cutting. You can dig into the surface.
The depth is 10 μm. Stars and triangle corners are also engraved at an acute angle, ensuring high shape accuracy and high alignment accuracy of each unit pattern.
Such a shape can be realized by printing ink on a portion other than the target shape (star mark or the like).

[Product example by injection molding]
As shown in FIG. 15A, a large number of fine circular recesses 54 having a diameter of 100 μm and a depth of 40 μm are formed in a constant pattern on the inner surface 52 of a cavity (female mold) 50 for a mobile phone cover jacket made of SUS420. After that, as shown in FIG. 2B, an experiment was conducted in which a polycarbonate (male) 56 having a corresponding shape was fitted, and polycarbonate was injected into a gap 58 formed therebetween.

As a result, as shown in FIG. 16, the micro boss 60 is uniformly formed on the entire surface (65 × 120 mm ² ) in contact with the hand.
FIGS. 17A and 17B show the detailed shape of the micro bosses 60 measured by the three-dimensional surface shape measuring apparatus and the arrangement pattern of the micro bosses 60 observed by the optical microscope, respectively.
As shown in the figure, the head shape corresponding to the circular recess 54 of the cavity 50 is also formed smoothly, and the array pattern (houndstooth array) is also accurately transferred.

[Comparison between this invention and existing technology]
In the above embodiment, the working time according to the technique was selected as the existing technique, and the working time was compared.
In the former case, the printing time of the micropattern on the surface of the mold material is 10 minutes including the set time, 5 hours for the plasma nitriding including the handling, heating and cooling of the mold material, and the blasting process includes the start of the apparatus 10 Minutes, a total of 5 hours and 20 minutes.
On the other hand, in the latter case, one pattern formation can be milled in a short time of 3.6 seconds, and the CAM creation time and the blade replacement time are ignored. From FIG. 15 and FIG. 16, the number of microdots is estimated to be 3.75 × 10 ⁴ (37,500). Therefore, it takes only 37 hours and 30 minutes to cut with a micro tool.
From the above, the technique can reduce the mold creation time of FIGS. 15 and 16 to 1/7.

It is a schematic diagram which shows the process of manufacturing a metal mold | die using this invention. 1 is a schematic diagram showing the structure of an RF-DC low temperature plasma nitriding apparatus according to the present invention. It is a conceptual diagram which shows a mode that a nitrogen atom osmose | permeates the surface of a workpiece. It is a schematic diagram which shows the process of manufacturing a metal mold | die using this invention. It is a graph which shows the temperature and time dependence of plasma nitriding behavior. It is a photograph which shows the cross section of the depth direction of the nitride layer formed in SUS420 material. It is a graph which shows the concentration distribution of the depth direction of the nitride layer formed in SUS420 material. It is a graph which shows the surface hardness of the nitride layer formed in SUS420 material. It is a photograph which shows the depth distribution in the mask vicinity of the nitride layer formed in SUS420 material. 6 is a photograph showing the nitrogen diffusion behavior in stainless steel in Reference 5. It is a photograph which shows the example of printing of the mask pattern based on this invention. It is a graph which shows the hardness distribution of the nitrided layer formed in SUS420 material. It is a photograph which shows the microscope image which shows the circular recessed part formed on the stainless steel type | mold material using this invention. It is a photograph which shows the microscope image which shows the recessed part of various shapes formed on the stainless steel type | mold material using this invention. It is sectional drawing which shows the state which formed the micro dot pattern in the inner surface of the cavity for cover jackets of a mobile telephone using this invention. It is the photograph which shows the state where many micro bosses were formed on the surface of the cover jacket of the cellular phone. It is the figure which shows the three-dimensional surface shape of the micro boss | hub formed in the surface of the cover jacket of a mobile telephone, and the microscope picture which shows the arrangement | sequence of each micro boss | hub.

10 type material
12 micro patterns
14 Unprinted parts
16 Hardened layer
20 Low temperature plasma nitriding equipment
22 Vacuum chamber
24 DC bias
26 Workpiece
28 Heater
30 RF electrodes
32 RF oscillator
40 abrasive
42 Recess
44 Mold
50 cavity
52 Inside the cavity
54 Circular recess
56 core
58 gap
60 Micro Boss

Claims (4)

In accordance with CAD data created in advance, printing a predetermined pattern of ink on the surface of the metal material, forming a mask,
Performing a plasma nitriding treatment on the surface of the metal material, and forming a hardened layer on a portion other than the mask forming portion;
Blasting the surface of the metal material, removing the mask, and forming a recess having a shape corresponding to the mask pattern in a portion other than the hardened layer; and
A fine processing method comprising the steps of: In accordance with CAD data created in advance, printing a predetermined pattern of ink on the surface of the metal material, forming a mask,
Performing a plasma nitriding treatment on the surface of the metal material, and forming a hardened layer on a portion other than the mask forming portion;
Blasting the surface of the metal material, removing the mask, and forming a recess having a shape corresponding to the mask pattern in a portion other than the hardened layer; and
The manufacturing method of the metal mold | die characterized by comprising.   A method for producing a plastic molded product, wherein the mold according to claim 2 is used as a mold, and the microtexture is transferred to the surface during injection molding of a plastic material.   Using the mold according to claim 2 as a press mold, a micro-texture is transferred to each surface of the metal sheet, plastic sheet, metal part, plastic part, and glass part by performing mold press or direct pressing. A fine processing method characterized by the above.

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