JP2017177599A - Manufacturing method of plastic molded products - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing technology that forms many pattern shapes in a short time and at a low cost, the pattern shapes having fineness capable of achieving water repellency on the surface of a plastic product.SOLUTION: A production method of a plastic molded article includes a step for forming a plurality of micropatterns (masks) 12 having a dimension of 30 μm or less by printing ink of a specified shape on the surface of a metal molding material 10 based on CAD data prepared in advance, a step for practicing plasma nitriding treatment on the surface of the molding material 10 to form hard layers 16 on the sites where the masks are not formed, a step for subjecting the surface of the molding material 10 to blast treatment to remove the masks and forming recesses 42 having a shape corresponding to the pattern of the masks on the sites where the hard layers 16 are not formed, and a step for forming a plurality of fine protrusions 65 on the surface of a plastic material in injection molding using the molding material 10 as a metal mold.SELECTED DRAWING: Figure 9

Description

  This invention is an application of a technique for finely processing 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 the non-cured portion. Regarding technology.

  Plastic tableware is widespread in hospitals, elderly facilities, schools, school lunch centers and restaurants. Since these are not disposable, they are reused through a process of washing, washing, drying and sterilization. Due to recent demands for reducing environmental impact and effective use of water resources, fine pattern transfer plastic tableware that combines environmental resistance and water repellency is expected as a tableware that can be washed and washed with less water consumption.

  In addition, since playground equipment, chairs, desks, and the like used outdoors are products that are directly touched by people including infants and children, it is desired to use plastics that can clean the surface with rainwater alone. For this purpose, it is necessary to commercialize a fine pattern transfer plastic that has little deterioration over time and removes dirt by a water separation effect due to water repellency.

The methods that have been adopted so far to impart water repellency to the surface of an article are roughly divided into a method of chemically modifying the surface and a method of forming a fine pattern including an air layer like a lotus leaf. There is.
For the former, it is necessary to develop an optimum chemical treatment method for each target metal, or to apply a water repellent coating or a water repellent film to the surface. These deteriorate over time during daily use, and wear out over time. Eventually, they will be damaged and peeled off. In addition, products that routinely clean their surfaces are virtually unusable due to accelerated wear. Furthermore, coating films with chemical substances involved in human body contamination such as food containers cannot be used.

  On the other hand, since the fine pattern forming method uses the product material itself, it is usually only deteriorated at the wear rate of the product even in handling such as cleaning that causes surface friction. By ensuring the safety and security of product materials, risks to the human body and the environment can be avoided.

In the shape creation method, a mechanical cutting method (Non-Patent Document 1), an electric discharge machining method (Non-Patent Document 2), a laser machining method (Non-Patent Document 3), and the like have been reported.
In the mechanical cutting method, there are limitations on the tool shape and the tool size, and it is practically difficult to form a fine pattern of 1 mm or less and to create the necessary density and number at a low production cost.
Even with the electric discharge machining method, it is impossible to form a fine pattern having a diameter smaller than the wire diameter, and at the same time, enormous machining time is required to form a complicated shape pattern.
In the case of laser processing, it is possible to create about 10,000 circular micro holes by using a high-frequency laser, but if the shape of the micro-texture becomes complicated, the micro-texture dimension that can be processed is 100 μm. Stay to the extent.

  On the other hand, in the field of cell culture, it is necessary to form discrete colonies (cell groups) while culturing cells without strongly fixing them and supplying nutrients. A cell culture sheet in which a large number of fine convex portions corresponding to the shape dimensions of cells are formed has been put into practical use (Non-patent Document 4 and Patent Document 1).

  This is to form a fine cylindrical convex portion on the plastic side by pressing a mold having a large number of fine cylindrical concave portions on the surface of the plastic softened by heating. It is presumed that enormous time and cost are required since the mold is manufactured by cutting, photolithography, electron beam direct writing, particle beam processing, scanning probe processing, or the like.

Efficient machining of micro-dimples for friction reduction. Internet URL: http://micronanomanufacturing.asmedigitalcollection.asme.org/article.aspx?articleid=1674092 Search date: March 18, 2016 Adaptive control for micro-hole EDM process with wavelet transform detecting method. Internet URL: http://link.springer.com/article/10.1007/s12206-012-0410-y Search date: March 18, 2016 Improving tribological performance of mechanical components by laser surface texturing. Internet URL: http://link.springer.com/article/10.1007/s11249-004-8081-1 Search date: March 18, 2016 Nanopillar cell culture sheet using nanoprint technology Internet URL: http://www.hitachihyoron.com/jp/pdf/2006/09/2006_09_14.pdf Search date: March 18, 2016 Japanese Patent No. 4950426

  The present invention has been devised to solve the above-described conventional problems, and can process a large number of fine pattern shapes capable of exhibiting water repellency on a plastic product surface in a short time and at a low cost. The purpose is to provide technology.

  In order to achieve the above object, the method for producing a plastic molded article according to claim 1 is performed by printing ink on the surface of a metal material in a dot shape in accordance with CAD data prepared in advance, preferably 30 μm or less (preferably A step of forming a plurality of masks having dimensions of 10 μm or less), a step of plasma nitriding the surface of the metal material to form a hardened layer on a portion other than the mask forming portion, and a blasting on the surface of the metal material A step of removing the mask and forming a recess having a shape corresponding to the mask pattern in a portion other than the hardened layer, and using the metal material as a mold die, and performing surface treatment during plastic material injection molding. A plurality of fine protrusions are formed on the substrate.

  According to a second aspect of the present invention, there is provided a method for producing a plastic molded product according to the first aspect, wherein the plastic material is made of a plastic material having a property of being deformed at room temperature.

  The method for manufacturing a plastic molded article according to claim 3 is the manufacturing method according to claim 1, wherein the common mold and the primary mold are arranged to face each other, and the first plastic material is injected into the gap between the two. Then, after removing the primary mold, the step of forming the first layer, the common mold and the secondary mold are arranged to face each other, and a second plastic material is injected into the gap between the two, Forming a second layer on the surface of the first layer, wherein the secondary mold is the mold mold, and the second plastic material has a property of deforming at room temperature. It is characterized by being made of materials.

  The method for producing a plastic molded article according to claim 4 is the production method according to claim 2 or 3, wherein the plastic material having the property of deforming at room temperature is any one of an elastomer type, a urethane type, and a rubber type. It is made of a plastic material.

  The method for producing a plastic molded product according to claim 5 is the method according to claims 1 to 4, wherein each of the masks is formed in a circular shape having a diameter of 30 μm or less (preferably 10 μm or less). It is characterized by.

  According to a sixth aspect of the present invention, there is provided a method for producing a plastic molded product according to the first to fourth aspects, wherein each of the masks is formed in a square shape having one side of 30 μm or less (preferably 10 μm or less). It is characterized by that.

  In the case of the microfabrication method according to the present invention, a mask pattern for microfabrication is obtained by printing ink on the surface of a metal material (stainless steel, etc.) using a general printing technique such as ink jet printing or dot printing. Therefore, it is sufficient to prepare in advance CAD data that is relatively easy to create, and it is not necessary to prepare CAM data that requires enormous amounts 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.
By using this die as a mold die, it becomes possible to easily form a processing pattern (micro texture) as an assembly of fine convex portions on the surface of the plastic molded product at the time of injection molding.

  Since the dimension of the processing pattern (the diameter of the cylindrical body or the side of the rectangular parallelepiped) is set to 30 μm or less, the contact angle with the droplet on the surface of the plastic molded product is increased, resulting in a decrease in wettability. It becomes possible to impart aqueous properties.

  To give elasticity and flexibility to the micro-texture formed on the surface of plastic molded products by adopting plastic materials that have the property of deforming at room temperature (elastomer, urethane, rubber). And can exhibit further water repellency due to deformation of the surface shape. Moreover, when applied to a cell culture sheet, the shape of the medium can be changed according to the cell size / colony size, and the growth / differentiation can be promoted.

  This invention uses CAD data of a water-repellent fine pattern to draw a fine pattern two-dimensionally on the surface of a metal mold (stainless steel material, tool steel, titanium and titanium alloy material, aluminum and aluminum alloy material).

Next, a die surface portion (non-drawing portion) other than drawing is subjected to low-temperature plasma nitriding, and nitrogen atoms are penetrated and diffused only in that portion to develop an initial drawing pattern inside the die.
In the non-drawing portion, nitrogen atoms are dissolved to the depth achieved by the low-temperature plasma treatment (nitriding influence layer thickness), and the hardness is selectively increased to the inside.
The drawing part maintains the same hardness as that of the metal mold without changing from that before the low temperature plasma treatment.
The boundary between the non-rendering part and the rendering part becomes the boundary of the dissolved nitrogen distribution up to the nitriding influence layer thickness.

By selectively removing only the drawing portion by the sandblast method, the boundary between the non-drawing portion and the drawing portion becomes the side surface of the micro-texture newly formed on the mold.
Further, since the portion other than the initial drawing portion is polished by the sand blasting method, dirt and unevenness of the mold surface by the low temperature plasma treatment is also removed, and the mold surface property necessary for injection molding is ensured.

  In injection molding, the plastic material flows into the microtexture formed on the mold surface and the product shape is formed simultaneously. Thereby, microtexture formation and two-color plastic product manufacture can be performed simultaneously.

  Plastic products such as plastic tableware, plastic utensils, playground equipment, cell culture / differentiation media, etc. are multi-faceted, such as expressing water repellency and developing mechanical functions such as tactile sensation and anti-slip at the required position of the product. Microtexture formation is necessary.

  The technology draws a 2D pattern of the designed microtexture on the surface of the plastic injection mold, hardens only the non-drawing area, and removes the drawing area, thereby removing the 3D negative pattern of the designed microtexture. Create a (recess).

  By inserting the mold piece into an injection mold and molding a convex portion corresponding to the concave portion formed on the mold on a predetermined surface portion of the plastic product by an injection molding process. Reproduce the designed microtexture on the product surface / interface.

  In particular, by utilizing a two-color plastic molding process and reproducing a micro-texture designed on the surface of an elastomer, urethane, or rubber system, it is possible to deform and use the micro-texture that has been transferred and molded when using the product.

This makes it possible to perform culture / differentiation by changing the shape of the medium according to the cell size / colony size when cells, regenerated tissues, etc. grow.
Furthermore, the surface characteristics such as the contact angle can be controlled by reflecting the design dimension design of the design microstructure.

First, as shown in FIG. 1A, a number of micropatterns (high-precision dot shapes) 12 designed by CAD are printed on the surface of a mold material 10 made of SUS420 or the like by ink jet printing or dot printing technology.
The micropattern 12 is formed of an ultrafine circle having a diameter of 10 μm or less, and is arranged in a matrix at a constant interval (for example, 20 μm).

As the ink used for this printing, for example, 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.

Next, 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. The vacuum chamber 22, the DC bias 24 disposed in the vacuum chamber 22, and the DC bias 24 are mounted on the vacuum chamber 22. A mold material 10, 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 disposed 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 N ² and H ^{2 as} a raw material is introduced into the inside from an air supply port (not shown) of the vacuum chamber 22, and a high frequency is applied between the RF electrodes 30 and 30 and simultaneously a DC bias voltage is applied, When the heater 28 is further powered and the inside of the vacuum chamber 22 is heated to 450 degrees Celsius or lower, the mixed gas is turned into plasma, and as shown in FIG. 3, high-density nitrogen ions and NH radicals are generated, and the nitrogen atoms become mold materials Penetrate 10 surfaces.

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 10 ¹⁷ m ⁻³ or more (preferably 5 × 10 ¹⁷ m ⁻³ or more, more preferably 10 ¹⁸ m ⁻³ ). Since nitriding is performed in a high NH radical state, nitrogen atoms can be introduced into the mold material 10 as solute atoms even at a low holding temperature.
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 mold material 10 without unevenness.
When the above processing is continued for a predetermined time, nitrogen is dissolved at a high concentration on the surface of the mold material 10.

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 40 such as sand is sprayed, thereby removing the micropattern 12 and making a high concentration nitrogen solid solution. Excavation is performed on the surface of the mold material 10 not present.
As a result, as shown in FIG. 5B, a mold 44 in which a large number of cylindrical recesses (microholes) 42 are formed in places other than the hardened layer 16 is obtained.

FIG. 5 is an electron micrograph (SEM image) obtained by photographing the plane of the mold 44, and it can be confirmed that a large number of minute recesses 42 are regularly arranged in a matrix.
The depth of each recess 42 is about 4 μm.
The mold 44 is used as a two-color molding mold piece.

Hereinafter, a method for forming a microtexture on the surface of a plastic molded product using the mold 44 will be described.
FIG. 6 is a conceptual diagram of a two-color molding machine 50 used for manufacturing this plastic molded product, and includes a base 51 on the fixed side, a primary mold 52 and a secondary mold arranged on one surface of the base 51. 53, a movable side rotary part 54, a pair of common molds 55, 55 arranged on one surface of the rotary part 54, a primary polycarbonate injection unit 56 connected to the base part 51 on the fixed side, and a secondary An elastomer injection unit 57 is provided.
The rotary unit 54 is arranged so as to be rotatable in units of 180 degrees, and so that the distance from the fixed side can be varied within a certain range (reciprocable).

First, the rotary part 54 is brought close to the base part 51 side, and a gap 60 of 500 μm is formed between the common mold 55 and the primary mold 52 as shown in FIG.
Next, as shown in FIG. 2B, polycarbonate as a primary material is injected into the gap 60 to form a polycarbonate layer 61 having a thickness of 500 μm as a base.

Next, the rotary part 54 is rotated 180 degrees away from the base part 51 to remove the primary mold 52 from the common mold 55, and as shown in FIG. Is combined with the common mold 55.
On the opposing surface of the secondary mold 53, the mold 44 is set as a piece.
A gap 62 of 500 μm is formed between the surface of the mold 44 and the surface of the polycarbonate layer 61.

By injecting an elastomer as a secondary material into the gap 62, as shown in FIG. 8 (b), the elastomer is filled in the concave portions 42 of the mold 44, and an elastomer layer 63 having a thickness of 500 μm is formed. The
Next, as shown in FIG. 9, the rotary portion 54 is separated from the base portion 51 and the common die 55 and the secondary die 53 are opened to bond the elastomer layer 63 on the polycarbonate layer 61. The plastic product 64, which is the final product, is removed.
On the surface of the elastomer layer 63, a large number of fine cylindrical convex portions 65 made of elastomer are formed.

FIG. 10 is an electron micrograph (SEM image) obtained by photographing the plane of the elastomer layer 63, and it can be confirmed that a large number of fine convex portions 65 are regularly arranged in a matrix.
The height of each convex portion 65 is about 4 μm.

  In the plastic molded product 64, the second layer is made of an elastomer having high elasticity, and a large number of convex portions 65 also have elasticity. For this reason, when this plastic molded product 64 is used as a cell culture sheet, the convex portion 65 is deformed according to the growth of the cells, and the growth and differentiation thereof can be promoted.

  In addition, since the first layer as a base is made of polycarbonate and has a certain degree of regularity, it also has convenience in handling.

  Moreover, since the diameter of each convex part 65 is 10 micrometers or less, the wettability of the surface of the plastic molded product 64 is reduced, and the surface shape is also deformable, so that a high water repellent effect can be exhibited.

FIG. 11 shows another embodiment, and shows an example in which a 5 μm × 5 μm square lattice is drawn as a micro pattern on the surface of a mold material 70 made of SUS420. The black square pattern is the drawing unit 71, and the white square pattern is the non-drawing unit 72.
Using the SUS420J2 material used as a mold material for plastic injection molding, the above two-dimensional drawing was performed using an inkjet printer after single-sided mirror polishing.

  The mold material 70 is subjected to low-temperature plasma nitriding under conditions of 420 degrees Celsius, 3 hours and 70 Pa, and then subjected to sand blasting for 5 minutes, thereby obtaining a square lattice of 5 μm × 5 μm as shown in FIG. And a fine pattern (recess 73) having a depth of 7 μm was formed. The concave portion 73 corresponds to the shape and size of the drawing portion 71 described above. Around the concave portion 73, convex portions 74 corresponding to the shape and dimensions of the non-drawing portion 72 are distributed.

  By using this mold material 70 as a mold and injecting a plastic material into the mold, the surface of the plastic molded product has fine square convex portions corresponding to the concave portions 73 and the convex portions 74. A microtexture with corresponding square-shaped fine recesses is formed.

The relationship between the micropattern according to the present invention and the contact angle of water droplets was verified.
That is, when water droplets were dropped on the surface of a plastic molded article made of Lavalon (registered trademark) in which a large number of convex portions were formed in a matrix, as shown in FIG. Compared with the flat surface (registered trademark) (registered trademark) (FIG. 5B), the contact angle is clearly enlarged.
When calculated based on the following equation 1, a contact angle sufficient for realizing water repellency of 136 degrees on the micropattern forming surface is obtained.
(Formula 1) cos θ * = − 1 + φ _s (cos θ _E +1)
theta *: Contact angle on the micro pattern formation surface theta _E: Contact angle with the flat surface phi _s: average 30μm dot diameter area ratio protrusion of the micro pattern formation surface and a non-forming surface
Pitch 50μm
Area ratio 0.396

It is a schematic diagram which shows the process of manufacturing a metal mold | die. It is a schematic diagram which shows the structure of RF-DC low temperature plasma nitriding apparatus. 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. It is the electron micrograph which image | photographed the plane of the metal mold | die. It is a conceptual diagram of the two-color molding machine used for manufacture of a plastic molded product. It is a schematic diagram which shows the process of manufacturing a plastic molded product. It is a schematic diagram which shows the process of manufacturing a plastic molded product. It is a schematic diagram which shows the process of manufacturing a plastic molded product. It is the electron micrograph which image | photographed the plane of the elastomer layer. It is a plane enlarged photograph which shows the example which drawn the square lattice as a micro pattern on the mold material surface. It is an electron micrograph which shows a mode that the square lattice-shaped recessed part was formed in the type | mold raw material surface. It is an electron micrograph which compares the contact angle of the water drop in the surface which formed the micro pattern, and the surface which does not form.

10 type material
12 micro patterns
14 Unprinted parts
16 Hardened layer
20 Low temperature plasma nitriding equipment
22 Vacuum chamber
24 DC bias
28 Heater
30 RF electrodes
32 RF oscillator
40 abrasive
42 Recess
44 Mold
50 2-color molding machine
51 Base part
52 Primary mold
53 Secondary mold
54 Rotary department
55 Common mold
56 Primary polycarbonate injection unit
57 Secondary elastomer injection unit
60 Clearance
61 Polycarbonate layer
62 Clearance
63 Elastomer layer
64 Plastic molded products
65 Cylindrical convex part
70 type material
71 Drawing part
72 Non-drawing part
73 recess
74 Convex

Claims (6)

A step of forming a plurality of masks having dimensions of 30 μm or less by printing ink in a predetermined shape on the surface of a metal material according to CAD data created in advance,
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
Using the metal material as a mold, forming a plurality of fine protrusions on the surface during injection molding of a plastic material,
A method for producing a plastic molded product comprising:   2. The method for producing a plastic molded product according to claim 1, wherein the plastic material is made of a plastic material having a property of being deformed at room temperature. A step of disposing a common mold and a primary mold opposite to each other, and injecting a first plastic material into a gap between them to form a first layer;
After removing the primary mold, the common mold and the secondary mold are arranged to face each other, a second plastic material is injected into the gap between the two, and a second layer is formed on the surface of the first layer. And forming a process,
The secondary mold is the mold;
2. The method for producing a plastic molded product according to claim 1, wherein the second plastic material is made of a plastic material having a property of being deformed at room temperature.   4. The method for producing a plastic molded product according to claim 2, wherein the plastic material having the property of deforming at room temperature is made of any one of an elastomeric material, a urethane material, and a rubber material.   Each said mask is formed in circular shape with a diameter of 30 micrometers or less, The manufacturing method of the plastic molded product in any one of Claims 1-4 characterized by the above-mentioned.   The method for producing a plastic molded product according to any one of claims 1 to 4, wherein the mask is formed in a rectangular shape with each side of 30 µm or less.

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