JP5771058B2 - Molding method of resin - Google Patents

Description

  The present invention relates to a resin molding method, for example, a resin molding method for highly transferring a mold surface state onto a surface of a molded product.

  In the molding of thermoplastic resins, the temperature of the mold is usually kept at a temperature sufficiently lower than the temperature at which the molding resin solidifies. This is necessary for cooling a resin material having extremely low thermal conductivity from a molten state to a temperature at which it can be taken out as a molded product in a short time. In addition, in order to transfer the mold surface state to a molded product highly, it is necessary to press a resin having a low viscosity against the mold with a high pressure. However, if the mold temperature is lower than the resin solidification temperature, resin filling and resin solidification proceed simultaneously, and the resin that contacts the mold near the resin flow front is rapidly cooled and has a high viscosity. At the same time, since it solidifies in a state of being pressed against the mold surface with a low pressure, it is difficult to highly transfer the mold surface state to a molded product. For this reason, normal injection molding tends to cause poor appearance such as uneven gloss, weld lines, flow marks, jetting, and fine pits in precision molded products such as optical disks, and short shots in thin-walled parts. There is also. In order to improve the transferability of the mold surface, it is necessary to prevent the resin from solidifying during the resin filling process and minimize it.

In the injection molding of thermoplastic resin and the like, it has always been required to economically improve the mold surface transferability without increasing the molding cycle time. Various methods have been proposed so far as means for improving the mold surface transferability. For example, the following methods have been proposed.
1. A method of repeatedly heating and cooling the mold surface by alternately flowing a heat medium and a refrigerant through the mold (see Non-Patent Document 1)
2. A method of selectively heating the mold surface by high-frequency induction heating immediately before molding (see Patent Document 1)
3. A method in which an insulating layer and a conductive layer are provided on the mold surface, and the conductive layer is energized and heated (see Non-Patent Document 2).
4). Method of radiant heating the mold surface (see Non-Patent Document 3)
5. A heat insulating layer coating method in which a mold surface is covered with a heat insulating layer, and the mold surface is heated with the heat of the molding resin itself (see Patent Document 2 and Patent Document 3).

  All of these molding methods are molding methods in which molding is performed while heating the mold surface during injection molding. That is, it is a molding method that improves the mold surface transferability by heating the mold surface above the solidification temperature of the resin when the injected molten resin is pressed against the mold wall surface.

  As another molding method, the present inventors have proposed a molding method using a gas that is easily dissolved in a resin such as carbon dioxide as a plasticizer for the resin (see Patent Document 4 and Patent Document 5). On the other hand, for example, a molded product and a molding method in which a fine shape having a wavelength equal to or smaller than the wavelength of visible light is transferred to the surface have been proposed (see Patent Document 6 to Patent Document 8).

U.S. Pat. No. 4,439,492 U.S. Pat. No. 5,362,226 International Publication No. 1997/04938 Pamphlet Japanese Patent No. 3349070 Japanese Patent No. 32189797 JP 2009-190276 A JP 2009-190277 A JP 2010-201842 A

Plastic Technology, VOL. 34 (June), 150 (1988) Polym.Eng.Sci., Vol.34 (11), 894 (1994) Synthetic resin, Vol.42 (1), 48 (1996)

  However, in the techniques described in Patent Document 1 and Non-Patent Document 1 to Non-Patent Document 3, there is a problem that productivity tends to be lowered because time for heating and cooling the mold surface is required. Moreover, in the technique described in patent document 2 and patent document 3, it is difficult to provide a fine functional pattern to heat insulation coating. In addition, these molding methods include: 1) the concave portions of the fine uneven pattern on the mold surface are filled with volatile components dissipated from the molten resin, and the shape transferred to the resin changes. 2) the mold and the resin It is difficult to release due to the large contact area, and the convex part of the resin fine uneven pattern is stretched at the time of mold release, and the shape of the fine uneven pattern changes, resulting in inferior transfer fidelity and productivity. is there.

  Also, in the techniques described in Patent Document 4 and Patent Document 5 proposed by the present inventors, the uneven shape present on the mold surface has an opening ratio of about 5 μm to 10 μm and an aspect ratio (depth of recess / opening). When the width is greater than 1, carbon dioxide is trapped inside the mold recess by the resin during molding, and carbon dioxide does not completely dissolve in the resin. In some cases, such as foaming by white carbon dioxide causes whitening. Further, the techniques described in Patent Document 6 to Patent Document 8 do not solve the above-described problems of continuous fidelity of transfer and productivity.

  The present invention has been made in view of such points, and an object of the present invention is to provide a resin molding method capable of highly transferring a fine uneven pattern on a metal surface to a molded product and having excellent productivity and economy. To do.

  In order to solve the above problems, the present inventors have made extensive studies in recent years to achieve nanoimprint with remarkable technological progress by injection molding. As a result, the present inventors have already filed Patent Document 4 and Patent Document 5 which have already been filed. Based on the technique shown, it has been found that a significant effect that cannot be obtained by the prior art can be obtained, and the present invention has been completed. The present inventors have developed a high aspect ratio shape that has been considered difficult to transfer in the past, such as an antireflection structure (moss-eye structure) for visible light, and a fine size having a specific size and aspect ratio. Even with an uneven pattern, by using a molding method different from the conventional mold surface heating method, it was found that the mold surface state can be transferred to the molded product with high reproducibility, and the present invention has been completed. . That is, the present invention comprises the following inventions.

The resin molding method of the present invention is a resin molding method for transferring a fine unevenness pattern provided on the mold surface to the resin surface, and the pressure of carbon dioxide is 1 MPa to 15 MPa in advance while preventing liquefaction of carbon dioxide. And filling the cavity with a liquid resin in which 0.1% by weight or more of carbon dioxide is dissolved, and the shape of the fine uneven pattern transferred to the resin surface is By filling the recess on the mold surface with resin, it is formed into a structure in which a large number of round conical protrusions are configured on the plane, or plate-like protrusions that extend in a straight line are arranged in parallel to each other, When the concave / convex pattern of the mold approximates the opening of the recess with an ellipse, the length of the short axis is 3 μm or less, and the ratio of the depth of the recess to the length of the short axis (the depth of the recess) / Length of the short axis) 0.5 above, characterized in that 4.0 or less.

  According to this method, since a liquid resin in which a predetermined amount of carbon dioxide is dissolved is filled in a cavity filled with carbon dioxide at a predetermined pressure in the resin filling step, the emission of volatile components in the resin can be suppressed. It becomes possible to suppress adhesion of volatile components of the liquid resin to the recesses of the uneven pattern. In addition, since the liquid resin in which a predetermined amount of carbon dioxide is dissolved is filled, it is possible to prevent the liquid resin from solidifying, suppress an increase in viscosity, and reduce the viscosity. Further, when the liquid resin is cooled and solidified, the fine uneven pattern is transferred and carbon dioxide is volatilized from the surface of the resin, so that the releasability of the resin from the mold is improved. Thereby, since the fine uneven | corrugated pattern of a metal surface can be highly transcribe | transferred to a molded article, the freedom degree of a product shape improves and the nanoprint which can express a various function is attained. In addition, it is possible to realize a resin molding method excellent in productivity and economy.

  In the resin molding method of the present invention, the resin is preferably a thermoplastic resin.

  In the resin molding method of the present invention, the thermoplastic resin is preferably an amorphous thermoplastic resin or a crystalline thermoplastic resin having a crystallinity of 40% or less.

  In the resin molding method of the present invention, it is preferable that the minor axis length of the opening of the dent is 1.0 μm or less.

  In the resin molding method of the present invention, it is preferable that the minor axis length of the opening of the recess is 0.3 μm or less.

  In the resin molding method of the present invention, it is preferable that the fine concavo-convex pattern is a visible light antireflection structure (moth-eye structure).

  In the resin molding method of the present invention, the fine uneven pattern preferably has a striped line and space structure.

  ADVANTAGE OF THE INVENTION According to this invention, the fine uneven | corrugated pattern of a metal surface can be highly transcribe | transferred to a molded article, and also the molding method of resin excellent in productivity and economical efficiency can be provided.

It is a schematic diagram of the fine uneven | corrugated pattern of the metal mold | die which concerns on this Embodiment. It is a schematic diagram which shows the structural example of the metal mold | die and carbon dioxide supply apparatus which concern on this Embodiment. It is a schematic diagram of the metal mold | die which concerns on this Embodiment. 3 is a scanning electron micrograph showing a cross-sectional structure of an antireflection structure (moth-eye structure) according to the present embodiment. It is a scanning electron micrograph which shows the cross-sectional structure of the line and space structure which concerns on this Embodiment.

  The inventor of the present invention paid attention to the gas in the cavity, which was conventionally considered to inhibit the transfer of the mold surface. The mechanism by which the effect of the present invention is manifested is considered as follows.

  In injection molding, the resin always flows through the cavity in a laminar flow, and when it comes into contact with the cooled mold wall surface, a solidified layer is formed at the interface. The resin to be filled later flows and advances inside the solidified layer, and flows as a fountain flow toward the mold wall surface after reaching the resin flow front end. When filling the cavity with a specific gas that is easily dissolved in a resin such as carbon dioxide and filling it with an appropriate gas pressure, the gas is absorbed at the tip of the fluidized resin or enters the interface between the mold and the resin. Dissolves in the surface layer. The gas dissolved in the resin acts as a plasticizer, selectively lowering the solidification temperature only near the resin surface, and lowering the viscosity of the resin. If only the thin resin surface layer has a solidification temperature lowered and the solidification temperature is lower than the mold surface temperature, solidification during the resin filling process does not occur, and the mold surface transferability of the molded product can be remarkably improved. Since the gas dissolved in the resin surface layer diffuses into the resin with time and the solidification temperature of the resin surface layer rises, the surface layer solidifies within a normal resin cooling time and can be taken out as a product.

  Also, if a specific amount of carbon dioxide is dissolved in the liquid resin, carbon dioxide functions as a plasticizer only during molding, and after molding, the molded product is not deformed, and carbon dioxide is diffused into the atmosphere. Since the viscosity of the liquid resin can be reduced and molding can be facilitated without changing the thickness, the transfer of the fine uneven pattern is further facilitated.

  When filling the cavity with a liquid resin, if the resin is thermoplastic, additives and impurities that are low in molecular weight and easily volatilize are diffused from the tip of the resin flow and adhere to the mold surface. When a fine uneven pattern consisting of relatively deep recesses exists on the mold surface, the recesses are filled by the adhesion of the volatile components, and the shape transferred to the resin changes. However, if the cavity is pre-pressurized with a gas such as carbon dioxide, it will be difficult for volatile components to dissipate from the tip of the resin flow, and it will be possible to prevent the recesses from being filled with volatile components. Since gas such as carbon dioxide dissolved in the resin surface layer acts as a plasticizer and volatile components are easily dissolved and absorbed in the resin, it is considered that deposition in the recesses can be prevented.

  When the molded product is released after the resin has solidified, gas such as carbon dioxide tends to be released from the resin surface, which prevents adhesion between the mold and the resin and facilitates release. It is done. As a result, in the transfer of the fine concavo-convex pattern having a specific structure, the present invention has been achieved in which the cavity is pressurized and molded with a specific gas that is easily dissolved in a resin such as carbon dioxide.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The resin molding method according to the present embodiment is a resin molding method in which a fine uneven pattern provided on the mold surface is transferred to the resin surface. In the resin molding method according to the present embodiment, the cavity is previously filled with carbon dioxide at a pressure of 1 MPa to 15 MPa, and then the resin is filled with a liquid resin in which 0.1% by weight or more of carbon dioxide is dissolved. When the fine irregular pattern of the mold has a filling step and the opening of the depression is approximated by an ellipse, the length of the minor axis is 3 μm or less, and the ratio of the depth of the depression to the length of the minor axis ( The depth of the dent / the length of the minor axis) is 0.5 or more and 4.0 or less.

(resin)
The resin used in the present invention is a thermoplastic resin that can be used for general injection molding and the like. An amorphous thermoplastic resin, a thermoplastic polymer alloy mainly composed of an amorphous resin, or a part of a crystalline thermoplastic resin having a low crystallinity can be used favorably. Examples of such resins include polypropylene, polyvinyl chloride, acrylic resin, styrene resin, polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyphenylene ether, modified polyphenylene ether resin, cycloolefin resin, wholly aromatic polyester, Thermoplastic plastic materials such as polycarbonate, polyetherimide, polyethersulfone, polyamide resin, polysulfone, polyetheretherketone, polyetherketone, and blends of these, or a mixture of two or more of these, various fillings It is a compounded material. Some crystalline thermoplastic resins having a low crystallinity include polypropylene, polybutylene terephthalate, nylon 6, and the like, and the crystallinity is preferably 40% or less. Moreover, some thermosetting resins, such as a silicone resin, a phenol resin, a urethane resin, and an epoxy resin, may be used. As the resin, an amorphous thermoplastic resin is particularly preferable from the viewpoint of lowering the solidification temperature by utilizing a plasticizer effect by gas dissolution, and the plasticizer effect is compared even with a crystalline resin solidified at the crystallization temperature. From the viewpoint of a large size, a crystalline thermoplastic resin having a crystallinity of 40% or less can be preferably used.

(gas)
In the present invention, gas (carbon dioxide) is filled in the cavity before the resin filling step of filling the cavity with resin. As this gas, a gas having a high solubility in a thermoplastic resin and having a plasticizing effect of the resin is preferable, and carbon dioxide is most preferable from the viewpoints of safety, cost, and ease of handling. The presence of the gas in the cavity allows the gas to be absorbed by the resin surface during the resin filling step, thereby reducing the solidification temperature of the resin surface in contact with the mold. As is known in the art, air having low solubility in the resin or a gas such as nitrogen only inhibits the transfer of the mold surface in the cavity, and the resin is at least twice as nitrogen as the resin solidification temperature. Solubility in is required. The gas is selected from the viewpoints of not deteriorating the resin, no danger to the mold and molding environment, and low cost. As the gas, a mixture of two or more kinds can be used as long as the solubility is high. Gases other than carbon dioxide include hydrocarbons and chlorofluorocarbons in which part of the hydrogen is substituted with fluorine, and the most suitable one is selected depending on the thermoplastic resin used.

  As the gas pressure sealed in the cavity is higher, a larger amount of gas is dissolved in the resin, so that the solidification temperature is lower, and solidification during the resin filling process can be prevented even at a low mold temperature. In practice, the required gas pressure is determined by the required degree of mold surface transferability, the type of resin or gas, the mold temperature, etc., use a highly soluble gas, and set the mold temperature high. For example, sufficient transferability can be obtained with a low gas pressure. The lower limit of the pressure is determined by the plasticizer effect of the gas dissolved in the resin, and practically about 1 MPa in the case of carbon dioxide. The upper limit of the pressure is not particularly limited, but if the pressure is too high, the force to open the mold cannot be ignored and problems such as difficulty in sealing the mold are likely to occur. Is. In order to minimize the amount of gas used in one process and simplify the structure of the mold seal and the gas supply device, the gas pressure is preferably as low as possible within the range where the required effect can be obtained.

  The air remaining in the mold when the mold is closed is preferably replaced with a gas used during the mold clamping or after the mold clamping is completed. Further, when the gas pressure used exceeds 1 MPa, the influence of air can be almost ignored. After the resin is filled, the gas pushed out of the cavity is released to atmospheric pressure. The gas is released after filling the cavity with molten resin.

  Since the mold surface state is transferred to the molded product after the resin is filled, it is desirable to apply sufficient pressure to the resin in the cavity until the surface of the molded product is solidified. In particular, when the dent of the fine unevenness pattern on the mold surface is relatively deep, it is necessary to press the resin against the mold against the gas pressure inside the dent. It is desirable to apply a high pressure to the resin.

  In the present invention, not only pressurizing the cavity with carbon dioxide, but also reducing the viscosity by dissolving carbon dioxide as a plasticizer in the liquid resin, and facilitating resin filling into the fine uneven pattern on the cavity surface. it can.

  As the type of plasticizer that dissolves in the liquid resin and lowers the viscosity, carbon dioxide is used in the present invention, but the solubility in the liquid resin is large and the resin, mold, molding machine material is not deteriorated, molding As long as there is no danger to the environment to be used, it is inexpensive, and it can satisfy any constraints such as rapid volatilization from the molded product after molding. In some cases, saturated hydrocarbons and liquids such as chlorofluorocarbon, water, and alcohol in which part of the hydrogen is substituted with fluorine can be used together, and even a mixture of two or more of these can be used together. Carbon dioxide dissolves well in the resin and becomes a good plasticizer, improving the fluidity of the liquid resin.

  In the present invention, the amount of carbon dioxide dissolved in the liquid resin is 0.1% by weight or more. In order to remarkably improve the fluidity, 0.1% by weight or more is necessary, and preferably 0.2% by weight or more. The maximum amount of carbon dioxide dissolved is about 3% by weight. This is because even if carbon dioxide is increased unnecessarily, the effect of improving the fluidity of the resin with respect to the amount of carbon dioxide may be reduced. This is because, even if the foaming is prevented by the flow front of the liquid resin during the resin filling process, the required gas pressure in the mold is remarkably increased. A preferable amount of carbon dioxide dissolved is 3% by weight or less.

  Dissolving carbon dioxide in a liquid resin is thought to tend to improve the absorbability of carbon dioxide trapped in the recesses in the fine unevenness pattern on the mold surface, and filling the resin even in recesses with a higher aspect ratio Is possible.

  As a method for dissolving carbon dioxide in the thermoplastic resin, the following two methods are preferable. One is a method in which a granular or powdery resin is placed in a carbon dioxide atmosphere in advance to absorb carbon dioxide and then supplied to the molding machine. The amount of absorption is determined by the pressure of carbon dioxide, the atmospheric temperature, and the time for absorption. . In this method, since a part of carbon dioxide in the resin is volatilized as the resin is heated during plasticization, the amount of carbon dioxide in the molten resin is less than the amount absorbed in advance. For this reason, it is desirable that the resin supply path such as the hopper of the molding machine is also in a carbon dioxide atmosphere. Another method is to plasticize the resin in the cylinder of the molding machine, or to dissolve carbon dioxide in the plasticized resin so that the vicinity of the hopper of the molding machine has a carbon dioxide atmosphere or the middle part of the screw. In this method, carbon dioxide is injected into the plasticizing resin from the tip or cylinder. When carbon dioxide is injected from the middle part of the screw or cylinder, it is preferable to increase the screw groove depth near the injection part to lower the resin pressure. Further, in order to uniformly dissolve and disperse the carbon dioxide in the resin after injecting the carbon dioxide, it is preferable to add a mixing mechanism such as a dull mage or a kneading pin to the screw, or to provide a static mixer in the resin flow path. As an injection molding machine, either an in-line screw method or a screw prep plastic method can be used, but since the screw prep plastic method is easy to change the screw design of the extruder part that plasticizes the resin and the injection position of carbon dioxide, preferable.

  In the present invention, the cavity is preliminarily pressurized with carbon dioxide above the pressure at which foaming does not occur at the flow front of the molten resin during resin filling, and then injection molding is performed. Molding is possible if the gas pressure enclosed in the cavity is higher than the minimum pressure that eliminates the foam pattern on the surface of the molded product, but if high transferability is required, the mold clamping force of the molding machine or the mold It is desirable to increase the gas pressure as much as possible according to the sealing performance. After the resin filling, in order to transfer the mold surface state to the molded product, it is desirable to pressurize the resin in the cavity with sufficient pressure until the molded product surface is solidified. Examples of the resin pressurizing method include a resin holding pressure in which a molten resin is replenished in the cavity, a method of injecting a pressure fluid such as a gas into the resin or the resin mold interface, and an injection compression method of reducing the cavity volume. Normally, the resin is pressurized at a high pressure at which the resin does not foam until the resin cools and solidifies. However, after the resin surface is solidified, the center of the molded product can be foamed by reducing the pressure.

  Carbon dioxide in the thermoplastic resin gradually diffuses into the atmosphere if the molded product is left in the atmosphere after the thermoplastic resin has solidified. Bubbles are not generated in the molded product due to the diffusion, and the performance of the molded product after the diffusion is essentially the same as that of the thermoplastic resin.

(Fine uneven pattern)
FIG. 1A is a schematic plan view of a fine pattern of a mold according to the present embodiment, and FIG. 1B is an enlarged cross-sectional view of a dashed line in FIG. 1A. In the present invention, as a method for defining the depth of the fine concavo-convex pattern existing on the mold surface (fine concavo-convex pattern forming surface 10), the opening 11 in the dent of the fine concavo-convex pattern is approximated by an ellipse. Here, a straight line passing through the two focal points inside the approximated ellipse is defined as a major axis, and a line segment obtained by drawing a perpendicular bisector of the major axis inside the ellipse is defined as a minor axis D1. At this time, the length of the minor axis D1 of the ellipse is 3 μm or less, and the ratio of the depth D2 of the recess to the length of the minor axis D1 (the depth D2 of the recess / the length of the minor axis D1, the aspect ratio) is 0. In the case of 5 or more and 4.0 or less, as described above, filling the resin after pressurizing the cavity with carbon dioxide can remarkably improve transferability and releasability while maintaining high productivity. it can. Here, when the minor axis length is as large as about 1 mm, the influence of surface solidification during the resin filling process is reduced and the transfer of the shape is relatively easy, and the effect of carbon dioxide cannot be said to be remarkable. Can also be improved by using a general-purpose silicone release agent. In addition, the length of the short axis D1 of the opening 11 is preferably 1.0 μm or less, and more preferably 0.3 μm or less from the viewpoint that the effect of carbon dioxide is remarkably obtained.

  As the minor axis length becomes smaller, the influence of surface solidification during the resin filling process cannot be ignored. In the case of forming a fine concavo-convex pattern having a minor axis length of about 10 μm to 100 μm, when the ratio of the depth of the recess to the length of the minor axis (the depth of the recess / the length of the minor axis) is 0.5 or more. In a normal molding method that keeps the mold temperature constant, transfer is difficult, and a technique such as keeping the mold surface temperature above the solidification temperature of the resin during the resin filling process is required. In particular, when the length of the short axis is 5 μm or less, further 3 μm or less, and the value of the depth of the dent / the length of the short axis is 0.5 or more, in order to transfer the fine uneven pattern with good reproducibility. In addition to preventing surface solidification during the resin filling process, it is necessary to suppress deposition of resin volatile components in the recesses of the mold. In addition, in order to maintain good mold release properties, the conventional coating mold release agent fills the dent, so a monomolecular film-forming mold release agent is required, but if the mold surface temperature is high It is difficult to maintain stable releasability, and it is necessary to pressurize the cavity with carbon dioxide. As for the lower limit of the short axis length, it is difficult to obtain a fine uneven pattern over a relatively large area of practical level such as several mm square at present, but it is estimated from an example using a short axis length of 45 nm. Then, it is considered that transfer of about 10 nm (0.01 μm) is possible.

  Here, even if the value of the depth of the dent / the length of the minor axis is less than 0.5, the effect of preventing contamination of the mold recess by the carbon dioxide and improving the releasability can be obtained, but the resin filling is relatively Since it is easy, the effect is not remarkable. Also, if the value of the depth of the dent / length of the minor axis exceeds 4.0, carbon dioxide escapes from the dent during resin filling, depending on the shape of the opening of the dent and the flow direction of the resin. It becomes difficult. In some cases, carbon dioxide may be compressed inside the dent and hinder the filling of the resin, so that the value of the dent depth / minor axis length is 4.0 or less.

(Gas supply device and mold)
In a gas supply device, a gas pipe, and a mold for supplying gas into the cavity or discharging the gas in the cavity, it is preferable to take measures to prevent gas liquefaction. This is because not only high gas pressure cannot be obtained at a temperature at which gas liquefaction occurs, but also when the liquefied gas touches the resin in the cavity, a large amount of gas dissolves in the resin, and the surface of the molded product foams after releasing the gas pressure. This is to cause an appearance defect. Measures to prevent liquefaction include heating the gas with a heater and keeping the temperature of the gas flow path and mold above the critical temperature of the gas, and significant pressure due to the gas being pushed out of the cavity during resin filling. In order to prevent the rise, a pressure release valve capable of keeping the gas pressure in the cavity and the pipe in an arbitrary range and a gas reservoir capable of backflowing the gas from the cavity can be provided.

  Normally, in order to make the mold airtight by counter pressure molding, etc., the parting surface and the O-ring between each plate are sealed, and the movable pin such as a protruding pin communicating with the cavity also has an O-ring or radial cross-sectional shape. A method such as sealing with a U-shaped rubber packing, or covering the entire protruding plate portion to which the protruding pin is fixed is hermetically sealed.

  In addition, when sealing the movable pin with packing, the pressurized gas that has entered the gap around the pin between the cavity and the packing is confined in the gap due to resin filling, and when the surface of the molded product cools away from the mold surface, it enters the cavity. The molded product surface that flows out and is not sufficiently solid may be recessed, and the molded product may expand and deform when the mold is opened. When such a problem occurs, a groove or hole that can discharge the pressurized gas that has entered the gap around the pin to the outside of the mold from a path other than the cavity is provided in the mold, and after being filled with the resin, it is pushed out of the cavity. It is desirable to exhaust at the same time as the gas is discharged.

  Gas injection into the cavity is possible by using a mold structure generally used for venting the cavity, slits provided on the parting surface on the outer periphery of the cavity, gaps between mold inserts and ejector pins, vent pins, An insert made of a porous sintered body can be used.

In FIG. 2, an example of a structure of the metal mold | die 1 and the carbon dioxide supply system 2 as a gas supply apparatus is shown.
As shown in FIG. 2, the mold 1 includes a cavity block 21 that constitutes the cavity 20 in a state in which the mold is closed, a gate 22 and a sprue 23 that introduce heat-melted resin into the cavity 20, and a cooled and solidified resin. And a protruding pin 24 that is separated from the cavity 20. The mold 1 also introduces gas (carbon dioxide gas) from the carbon dioxide supply system 2 into the cavity 20, and vents 25 for discharging the gas from the cavity 20 to the outside of the mold 1, And an O-ring 26 for improving airtightness.

  A fine uneven pattern is formed on the surface of the cavity block 21 constituting the cavity 20, and this fine pattern is transferred to the resin molded product. The gate 22 and the sprue 23 are provided so as to introduce molten resin into the cavity 20. A vent 27 is provided outside the cavity 20 as a gas supply / exhaust groove. The vent 27 communicates with the carbon dioxide supply system 2 provided outside the mold 1 through the vent slit 28 and the vent hole 25.

  FIG. 3A is a schematic plan view of the mold 1, and FIG. 3B is an enlarged cross-sectional view taken along one-dot chain line in FIG. 3A. 3A is a plan view of the inside of the cavity 20 shown in FIG. 2 as viewed from the sprue 23 side. As shown in FIG. 3A, a fine concavo-convex pattern forming surface 10 having a substantially rectangular shape in a plan view is provided in the central portion in the cavity 20. A region including the fine unevenness pattern forming surface 10 and slightly larger than the fine unevenness pattern forming surface 10 becomes a product region 41 filled with resin from the gate 22. A vent 27 as a gas supply / exhaust groove for the cavity 20 is provided outside the product region 41. The vent 27 communicates with the outside of the mold 1 through the vent hole 25. An O-ring 26 is provided outside the vent 27, and the airtightness in the cavity 20 is maintained.

The carbon dioxide supply system 2 includes a CO ₂ cylinder 31 serving as a carbon dioxide supply source, a pressure reducing valve 32 for reducing the pressure of carbon dioxide gas to a predetermined pressure, and a gas reservoir 33 for storing carbon dioxide supplied into the cavity 20. And an electromagnetic valve 34 for switching supply / stop of carbon dioxide gas into the cavity 20.

  In the carbon dioxide supply system 2, a cylinder 31 filled with liquefied carbon dioxide is kept at 50 ° C. and used as a gas supply source. The carbon dioxide gas is adjusted to a predetermined pressure by the pressure reducing valve 32 and then stored in a gas reservoir 33 kept at a temperature of about 40 ° C. Gas supply into the cavity 20 is performed by opening and closing an electromagnetic valve 34 downstream of the gas reservoir 33. During the resin filling, the gas reservoir 33 and the cavity 20 are in communication with each other. Almost simultaneously with the completion of the resin filling, the solenoid valve 34 is operated to release the gas in the vent hole 25 from the vent 27 to the outside of the mold 1.

Next, an example of a resin molding method according to the present embodiment using the mold 1 and the carbon dioxide supply system 2 will be described. First, after the mold 1 is closed and the mold is clamped, carbon dioxide is supplied from the CO ₂ cylinder 31 into the cavity 20 of the mold 1 through the pressure reducing valve 32 in the resin filling step, and the pressure in the cavity 20 is increased. Is adjusted to 1 MPa to 15 MPa. Next, the molten resin in which carbon dioxide is dissolved in advance in the molding machine cylinder is filled into the cavity 20 through the sprue 23 and the gate 22 of the mold 1. Here, since the inside of the cavity 20 is at a predetermined pressure when the liquid resin is filled, the diffusion of the volatile component contained in the resin is suppressed, and the volatile component inside the fine uneven pattern 10 in the cavity 20 is suppressed. Adhesion can be suppressed. Further, when the resin filled in the cavity 20 expands in the cavity 20, the carbon dioxide filled in the cavity 20 and the carbon dioxide previously dissolved in the resin can suppress the increase in the viscosity of the resin and solidify the resin. Prevention becomes possible.

  After the resin is filled, the resin filled in the cavity 20 is pressurized and solidified by cooling while transferring the fine uneven pattern onto the resin surface. Here, since the carbon dioxide is volatilized from the surface of the molded product that has been transferred and cooled and solidified by transferring the fine concavo-convex pattern, release of the resin from the fine concavo-convex pattern 10 is facilitated. After completion of the cooling and solidifying step, the molded product cooled and solidified is released from the cavity 20 by the protruding pins 24 of the mold 1.

  Hereinafter, the effects of the present invention will be described more specifically with reference to Examples and Comparative Examples performed to clarify the effects of the present invention. In addition, this invention is not limited at all by the following examples and comparative examples.

  In the injection molding, an acrylic resin (Delpet 80NH, manufactured by Asahi Kasei Chemicals Co., Ltd.) was used as the resin, and it was used after being dried in a hot air dryer at 80 ° C. for 5 hours before use. As the gas, carbon dioxide having a purity of 99.5% or more was used.

  As the molding machine, AMOTEC (registered trademark) specification of SG125M-HP manufactured by Sumitomo Heavy Industries, Ltd. was used. The plasticized portion was a vent type with a screw diameter of 32 mm and L / D23, and the vent could be pressurized with carbon dioxide, and the nozzle was a shut-off nozzle. In addition, a gas supply unit that supplies and exhausts carbon dioxide to the cavity is installed in conjunction with the mold clamping and injection mechanism.

  As the mold, a mold having a rectangular shape was used. The product part of the mold is 120 and 60 mm in length and width, and the thickness is 2 mm. The gate is 3 mm in width, 1 mm in thickness and 3 mm in land length, and the runner cross section has an average width of 4 mm and a depth of 4 mm. 140 mm, sprue average diameter 4 mm, length 55 mm, and nozzle touch part diameter 3.5 mm. The outer periphery of the mold cavity was sealed with O-rings around the cavity, sprue, and runner, and the cavity had an airtight structure. Carbon dioxide could be supplied to the cavity from the gas supply unit and exhausted.

  The mold was structured such that a 0.3 mm-thick Ni stamper for transferring fine uneven patterns could be fixed on the fixed side, and the surface on the moving side was a smooth mirror surface. Two types of stampers were used: an antireflection structure (moss-eye structure) and a striped line and space structure. FIG. 4 shows a scanning electron micrograph of the cross-sectional structure of the antireflection structure (moth-eye structure), and FIG. 5 shows a scanning electron micrograph of the cross-sectional structure of the line and space structure. The antireflection structure is a structure in which a large number of round conical protrusions are formed on a plane. As the surface shape of the stamper, the length of the short axis when the opening of the dent is approximated by an ellipse is about 200 nm, the depth of the dent is about 290 nm, and the pitch is about 250 nm on the surface in a hexagonal packing shape. The dents were lined up. The line-and-space structure is a structure in which long and straight plate-like protrusions are arranged in parallel to each other. The shape of the cross section perpendicular to the linearly extending axis is substantially rectangular, and as the surface shape of the stamper, the width of the opening of the grooved recess extending linearly is about 40 nm, and the depth of the recess is about 110 nm. The pitch was about 100 nm. The cylinder set temperature during injection molding was 260 ° C., and the mold cavity surface temperature was 90 ° C.

Example 1
An antireflection structure was used for the fine uneven pattern transfer stamper, an acrylic resin was put into a molding machine, and carbon dioxide was supplied to the vent portion at 6 MPa for plasticization. A cavity filled with 8 MPa of carbon dioxide was filled with molten acrylic resin in a resin filling time of 0.2 seconds. After filling the resin, the pressure was maintained at a cylinder internal pressure of 130 MPa for 5 seconds, and after cooling for 30 seconds, the molded product was taken out. . The carbon dioxide in the cavity was released into the atmosphere during the pressure holding process. This molding was performed 300 times continuously and sampled every 100 times. In order to observe the transfer uniformity of the molded product, the surface on the moving side was painted black, and the color, brightness, and unevenness of the reflected light were observed by applying white light at an incident angle of about 70 degrees. It was found that the anti-reflective structure was evenly transferred to the product. In order to measure the amount of carbon dioxide contained in the molded product, the weight of the molded product immediately after molding and the weight of the molded product when the molded product was allowed to stand for 10 days in a vacuum dryer at 90 ° C. As a result of measurement, it was found that the molded product contained 0.9% by weight of carbon dioxide, and it was estimated that the same amount of carbon dioxide was contained in the molten resin.

(Example 2)
An acrylic resin was molded in the same manner as in Example 1 by using a line and space structure for the fine uneven pattern transfer stamper. Similar to Example 1, the transfer uniformity of the molded product was observed from a direction perpendicular to the fine line, and it was found that the line-and-space structure was uniformly transferred to all the molded products.

(Comparative Example 1)
An acrylic resin was molded under the same conditions as in Example 1 using an antireflection structure for the fine uneven pattern transfer stamper and using no carbon dioxide. The continuous molding was performed 20 times and sampled every 10 times. After continuous molding, an acrylic resin was molded once under the same conditions as in Example 1. The transfer uniformity of the molded product was observed in the same manner as in Example 1. However, since the continuous molded product of 20 times has a lot of reflected light, the transfer state is insufficient, and the range of the width of about 15 mm on the gate side is as follows. In particular, it was found that there was a flow mark pattern and the transfer state was lower. The molded product under the same conditions as in Example 21 of the 21st time, although the transfer state is improved from the reflected light compared to the 20th time, the pattern on the gate side remains and the amount of reflected light is larger than that of the molded product of Example 2. From this, it was found that the height of the transferred pattern was low.

(Comparative Example 2)
A line and space structure was used as a stamper for transferring fine uneven patterns, and acrylic resin was put into a molding machine for plasticization. The mold cavity surface temperature was set to 130 ° C. in advance, and the molten acrylic resin was filled into the cavity with a resin filling time of 0.2 seconds, and then held at a cylinder internal pressure of 150 MPa for 5 seconds. Thereafter, the surface temperature of the mold cavity was cooled to 80 ° C. in about 3 minutes during pressure holding at a cylinder internal pressure of 100 MPa, and the molded product was taken out. As in Example 1, the transfer uniformity of the molded product was observed from the direction perpendicular to the fine lines, but unevenness with different glossiness occurred on the entire transfer surface. When the central part of the molded product was observed with a scanning electron microscope, it was found that the plate-like part of the line-and-space structure was irregularly stretched in the releasing direction and partially collapsed.

  In order to evaluate the fine concavo-convex pattern transfer state of the molded products obtained in Example 1, Example 2, and Comparative Example 1, using an atomic force microscope, a square part having a side of about 2 μm on the side of the central part of the molded product was used. The pattern height was measured, and the average value was obtained from the maximum and minimum heights of five consecutive uneven portions. The results of Example 1 and Example 2 are shown in Table 1 below, and the results of Comparative Example 1 are shown in Table 2 below.

  As can be seen from Tables 1 and 2, in Examples 1 and 2, high transferability was stably obtained. Further, as shown in Comparative Example 1, the transferability was lowered by a general molding method not using carbon dioxide. In Comparative Example 1, it is considered that the dents in the fine uneven pattern were partially filled with volatiles from the resin after molding 20 times.

  The present invention has an effect that a fine uneven pattern on a mold surface can be transferred to a molded product at a high level, and a molded product molding method having excellent productivity and economy can be realized. Lenses such as lenticular lenses, Fresnel lenses, etc., recording materials such as optical discs, light guide plates that are liquid crystal display components, diffuser plates, antireflection structures for visible rays (moss / eye structures) or line and space structures It can be suitably used as a nanoimprint technique in the fields of various optical components, biomimetics functional components, and the like.

DESCRIPTION OF SYMBOLS 1 Mold 2 Carbon dioxide supply system 10 Fine uneven | corrugated pattern formation surface 11 Opening 20 Cavity 21 Cavity block 22 Gate 23 Spru 24 Projection pin 25 Vent 26 O-ring 27 Vent 28 Vent slit 31 CO2 cylinder 32 Pressure reducing valve 33 Gas reservoir 34 Solenoid valve 41 product area

Claims (7)

A resin molding method for transferring a fine uneven pattern provided on a mold surface to a resin surface,
There is a resin filling step of filling the cavity with a liquid resin in which 0.1% by weight or more of carbon dioxide is dissolved after filling the cavity with carbon dioxide in advance at a pressure of 1 MPa to 15 MPa while preventing liquefaction of carbon dioxide. And
The shape of the fine concavo-convex pattern transferred to the resin surface is a structure in which a large number of round conical protrusions are formed on a flat surface or a long straight line by filling the recess in the mold surface with resin. It is formed in a structure in which plate-like protrusions are arranged in parallel with each other,
When the concave / convex pattern of the mold approximates the opening of the recess with an ellipse, the length of the short axis is 3 μm or less, and the ratio of the depth of the recess to the length of the short axis (the depth of the recess) / The length of the short axis) is 0.5 or more and 4.0 or less.   The resin molding method according to claim 1, wherein the resin is a thermoplastic resin.   The method for molding a resin according to claim 2, wherein the thermoplastic resin is an amorphous thermoplastic resin or a crystalline thermoplastic resin having a crystallinity of 40% or less.   The resin molding method according to any one of claims 1 to 3, wherein a short-axis length of the opening of the dent is 1.0 µm or less.   The resin molding method according to any one of claims 1 to 3, wherein a short axis length of the opening of the dent is 0.3 µm or less.   6. The method for molding a resin according to claim 1, wherein the fine uneven pattern is an antireflection structure (moss-eye structure) for visible light.   6. The method for molding a resin according to claim 1, wherein the fine uneven pattern has a striped line and space structure.