JP2018180358A - Mirror film, reflective optical element, method of forming reflective optical element, and method of manufacturing mirror film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mirror film which is not susceptible to cracking when combined with a molded resin product regardless of a shape thereof, a reflective optical element obtained by combining the mirror film with a molded resin product, a method of forming the reflective optical element, and a method of manufacturing the mirror film.SOLUTION: A mirror film comprises a film-like base material and a reflective layer formed on the base material. The reflective layer has a metal layer having a thickness of 50-300 nm. Looking at a cross-section of the metal layer along a thickness direction thereof, distance between adjacent grain boundaries of the metal layer is no less than 100 nm in average on a front side or back side of the cross-section.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a mirror film, a reflective optical element, a method of forming a reflective optical element, and a method of manufacturing a mirror film.

  Relatively large reflective optical elements such as fθ mirrors and folding mirrors used for laser beam printers and complex machines, and large mirrors for head-up displays and projectors, for reasons such as measures to reduce the weight and cost. Therefore, conversion from conventional glass to resin molded products has been carried out and has already been put to practical use. In these reflective optical elements, generally, a predetermined metal reflective surface is formed on a molded product obtained by transferring a high-precision mirror surface of a mold by injection molding or the like through a film forming process such as vapor deposition. doing.

  Although film formation processes such as evaporation are performed by batch processing in a film formation chamber maintained in a predetermined environment, since the size of the film formation chamber is limited, a large-sized molded article is formed over a large area. In the case of film formation, the number of molded articles that can be film-formed per batch decreases, and there is a problem that the film formation cost is significantly increased. In order to solve such problems, attempts have been made to form a reflective optical element at lower cost by combining a metal sheet, a film having a metal thin film formed thereon, and the like with a plastic molded product.

  By the way, one of the problems of the reflective optical element by such compounding is how to secure a high reflectance. The reflectance required for the large-sized optical mirror for the application as described above may be 90% or more in the visible light region.

  On the other hand, the technique of vapor-depositing silver and aluminum on a plastic film, and forming a reflection layer as a method of obtaining high reflectance is also proposed. However, in the case of a mirror film in which a reflective layer having a high reflectance is formed on a film, when stretched, there is a problem that fine cracks are formed on the surface of the reflective layer and the reflectance is lowered. In particular, in the process of integrating the mirror film into a large optical mirror-shaped molded product having curvature in three dimensions by attaching the mirror film simultaneously with injection molding using insert molding, the mirror film to be inserted is used. Since high stretchability is required, the decrease in the reflectance of the reflective layer due to cracks is a major problem.

  In order to address this problem, in Patent Document 1, a predetermined amount of nitrogen is added to the interface between the support substrate and the reflective layer in the sputter deposition method, and the adhesion between the support substrate and the reflective layer is obtained to obtain water permeability. A technique is disclosed that can prevent peeling.

JP, 2005-190611, A JP 2003-272236 A

  By the way, the reflective layer disclosed in Patent Document 1 is formed by a sputtering film forming method, the film thickness of the reflective layer is 10 nm or more and 50 nm or less, and moisture is obtained by obtaining the adhesion between the support substrate and the reflective layer. The purpose is to prevent separation due to water permeation. However, in sputter deposition, silver molecules are plasma-ionized, so that they are easily reacted with nitrogen gas to easily become silver nitride, thereby narrowing the grain boundaries. Therefore, even if such a technique is diverted to a reflective film to be compounded with a resin molded product, there is a risk that a crack may occur with respect to bending that occurs when it is compounded with a resin molded product.

  On the other hand, Patent Document 2 describes that as the nitrogen flow rate is increased in sputter deposition, the particle size is reduced. As described above, in sputtering film formation, silver molecules are plasma-ionized, so that they are easily reacted with nitrogen gas to easily become silver nitride, whereby the spacing between grain boundaries is also clogged. Therefore, even if such a technique is diverted to a reflective film to be compounded with a resin molded product, cracks will further increase with respect to bending that occurs when it is compounded with a resin molded product.

  The present invention has been made in view of the above-mentioned problems, and is a mirror film which hardly causes cracks even if it is compounded regardless of the shape of the resin molded product, a reflective optical element in which the mirror film is compounded with the resin molded product, An object of the present invention is to provide a method of forming a reflective optical element and a method of manufacturing a mirror film.

The mirror film of the present invention is a mirror film having a film-like substrate and a reflection layer formed on the substrate,
The reflective layer has a metal layer having a thickness of 50 nm to 300 nm, and when the cross section is taken along the thickness direction of the metal layer, the metal layer is formed on the front side or the back side in the cross section. The distance between adjacent grain boundaries is 100 nm or more on average.

  The method for producing a mirror film according to the present invention forms a metal layer on the substrate by causing metal molecules to collide with the substrate using a vacuum deposition method while flowing nitrogen into the processing space. .

  According to the present invention, a mirror film which hardly causes cracks even when compounded regardless of the shape of the resin molded product, a reflective optical element in which the mirror film is compounded with the resin molded product, a method of molding the reflective optical element, and a mirror film Can provide a manufacturing method of

It is the schematic of the vacuum evaporation system of a roll to roll system used in order to manufacture the mirror film concerning this Embodiment. It is the schematic of the roll coater apparatus used in order to manufacture the mirror film concerning this Embodiment. It is a figure which shows the insert molding process of a reflective optical element. (A) is a SEM (scanning electron microscope) image of the cross section in the thickness direction of the mirror film concerning a comparative example, (b) is a SEM image of the cross section in the thickness direction of a mirror film concerning an example. FIG. 4A is a view schematically illustrating the SEM image of FIG. 4A, and FIG. 4B is a view schematically illustrating the SEM image of FIG. 4B. (A) is a graph which shows the reflective characteristic of the mirror film concerning a comparative example, (b) is a graph which shows the reflective characteristic of the mirror film concerning an Example.

Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a schematic view of a roll-to-roll type vacuum deposition apparatus used to manufacture a mirror film according to the present embodiment. The roll-to-roll type vacuum deposition apparatus shown in FIG. 1 is disposed in a closed processing space in a housing 2 and is evaporated to generate a deposition flux 3 containing silver molecules or aluminum molecules as a deposition material. A film forming roller 4 for supporting a source 1 and a plastic film (base material) 8 and receiving a vapor deposition flux 3 thereon to form a thin film, and a vapor deposition flux 3 between the evaporation source 1 and the film forming roller 4 And a shielding plate 6 for shielding a part of the The housing 2 is connected to an N ₂ generation source 7, from which N ₂ gas flows into the inside.

  The present vacuum deposition apparatus is equipped with an unwinding roll and a winding roll (not shown). That is, in FIG. 1, the unwinding roll is provided further on the left side of the tension roll 5 via several rolls, and the plastic film 8 before processing is wound around the unwinding roll. As the plastic film 8, for example, PC, PET, COP material can be used, but it is not limited thereto. Further, in FIG. 1, the take-up roll is provided further on the right side of the tension roll 5 via several rolls, and the plastic film 8 after processing is wound around the take-up roll.

  The film forming roller 4 is temperature controlled by a known temperature control means. The shielding plate 6 has a function of blocking the vapor deposition flux 3 of the vapor deposition material emitted from the evaporation source 1. A pair of shielding plates 6 is disposed between the film forming roller 4 and the evaporation source 1 so as to be close to the film forming roller 4, and an opening 9 is formed therebetween.

The operation of the present vacuum deposition apparatus will be described. In FIG. 1, the degree of vacuum inside the housing 2 is 10 ^-2 Pa or more, preferably 10 ^-1 Pa (that is, it is closer to the atmospheric pressure by the amount of nitrogen inflow compared to the conventional vacuum evaporation method), The film formation pressure in the nitrogen inflow state is 10 ⁻¹ Pa. The plastic film 8 continuously supplied from the unwinding roller (not shown) is wound around the outer periphery of the film forming roll 4 and then the exposed surface passes from the evaporation source 1 to the opening 9 when passing through the opening 9. The metal layer (silver layer or aluminum layer) with a thickness of 50 nm to 300 nm (more preferably 50 nm to 200 nm) is formed by adhesion of silver molecules or aluminum molecules scattered through the film at a deposition rate of 1 Å / s. The film is formed.

  The plastic film 8 on which the metal layer is formed on one side by the film forming roll 4 is separated from the outer periphery of the film forming roll 4 and then taken up by a winding roller (not shown) and conveyed to the next step. ing. As described above, by using the roll-to-roll type vacuum deposition apparatus according to the present embodiment, a metal layer can be continuously formed on one surface of the plastic film 8.

  According to the present embodiment, the purpose is not to secure adhesion to water permeation prevention as in Patent Document 1, but by controlling grain boundaries of the silver layer or the aluminum layer, it is possible to suppress micro cracks during stretching in the surface direction. I can do it. "Grain boundary" refers to an empty wall between metal particles generated in the process of film growth. By forming a film in a nitrogen gas atmosphere, grain boundaries per unit area tend to be reduced, and in particular, grain boundaries are reduced in the thickness direction of the film cross section, so it is robust against remarkable stretching in the lateral direction. It becomes a film quality. Furthermore, since the film thickness of the silver layer or the aluminum layer is 50 nm to 300 nm, high reflectance can be secured.

  In particular, by flowing nitrogen during vacuum deposition, grain boundaries can be suppressed, and it is possible to approach a continuous film rather than granular particles. In the sputter deposition method as disclosed in Patent Document 2, silver or aluminum is plasma-ionized, so it easily reacts with nitrogen gas and tends to be silver nitride. On the other hand, in the vacuum evaporation method used in the present embodiment, since a mass of metal molecules fly toward the substrate, a chemical reaction with nitrogen gas hardly occurs, and a film quality suppressing grain boundaries advantageous for stretching It becomes.

  FIG. 2 is a schematic view of a roll coater used to manufacture the mirror film according to the present embodiment. The roll coater shown in FIG. 2 has a gravure roll 11, a pickup roll 12 and a storage tank 13. In the storage tank 13, a mixed liquid 14 using an isocyanate resin as a curing agent and a polyester or an acrylic resin as a main agent is stored. The mixed liquid 14 becomes a coating of a polyurethane resin by drying after application. The "polyurethane resin" is a polymer compound having a urethane bond in the molecule, and is usually produced by the reaction of a polyol and an isocyanate. Examples of the polyol include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination of two or more.

  The roll coater apparatus is also provided with an unwinding roll and a winding roll, which are not shown. That is, the unwinding roll is provided on the upstream side which becomes the left side in FIG. 2, and the plastic film 8 in which the metal layer is formed on one side (the lower surface in FIG. 2) is wound around the unwinding roll. Further, a take-up roll is provided on the downstream side on the right side in FIG. 2, and the plastic film 8 after processing is wound around the take-up roll.

  In FIG. 2, the mixed solution 14 stored in the storage tank 13 is transferred to the gravure roll 11 via the rubber pick-up roll 12 immersed in the mixed solution 14, and the gravure roll 11 removes the mixture from the unwinding roll. The desired thickness is applied on the metal layer of the plastic film 8 supplied continuously. Thereafter, the plastic film 8 is subjected to a drying process to obtain a plastic film 8 in which a polyurethane resin is coated as a protective layer on the metal layer, that is, a mirror film. The plastic film 8 is taken up by a take-up roller (not shown), further cut into a predetermined size, and conveyed to the next step to be combined with the molded product. In addition, the process of forming a polyurethane resin is not restricted above, It can form by various processes, such as a roll coater method, such as a gravure coater, a reverse coater, a comma coater, and a die coater method, such as slot die.

  As a modification, in the case of providing a base layer on the plastic film 8, a base layer of polyurethane resin is formed on one side of the plastic film 8 using a roll coater as shown in FIG. 2, and then as shown in FIG. A mirror film can be manufactured by forming a metal layer using a roll-to-roll type vacuum deposition apparatus and forming a protective layer of polyurethane resin using a roll coater as shown in FIG. 2 again. An adhesive layer may be provided on the side opposite to the single side provided with the metal layer regardless of whether the plastic film 8 is provided with the base layer. By providing the adhesive layer, a strong adhesive force can be secured when the plastic film 8 is attached to the molded product.

  FIG. 3 is a view showing an insert molding process of the reflective optical element. A method of manufacturing a reflective optical element using insert molding will be described with reference to FIG. In FIG. 3, the mold 21 has a convex curved transfer surface 21a, an intake hole 21b having one end opened to the transfer surface 21a, and an eject pin 21c disposed so as to be able to protrude from the transfer surface 21a. . The other end of the intake hole 21b is connected to an external negative pressure mechanism (not shown). Further, the eject pin 21c can be protruded or pulled in by the drive mechanism 21d. On the other hand, the mold 22 has a concave curved transfer surface 22a facing the transfer surface 21a.

  First, as a pre-process, the plastic film 8 on which the silver layer and the polyurethane resin are formed as described above is cut into a predetermined size. Furthermore, as shown in FIG. 3 (a), with the molds 21 and 22 separated, the cut plastic film 8 is conveyed using the conveying device 23, and the side provided with the silver layer and the protective layer is The transfer surface 21a is made to approach. At this time, if the inside of the air suction hole 21b is made negative pressure by the negative pressure mechanism, the plastic film 8 adheres to the curved transfer surface 21a by the atmospheric pressure. At this time, the silver layer and the protective layer of the polyurethane resin are bent, but no cracking or the like occurs. Furthermore, after releasing the plastic film 8, the transport device 23 retracts from between the dies.

  Thereafter, as shown in FIG. 3 (b), the molds shown in FIGS. 21 and 22 are brought close to each other and clamped, and not shown in the cavity formed between the transfer surface 21a (plastic film 8) and the transfer surface 22a. The molten resin is injected through the gate. Solidifying the injected resin results in integration with the plastic film 8. At this time, although the silver layer and the protective layer of the polyurethane resin are heated, no cracks or cracks occur due to thermal expansion or the like.

  Thereafter, as shown in FIG. 3C, the molds 21 and 22 are separated, the mold is opened, and as shown in FIG. 3D, the ejection pin 21c is protruded using the drive mechanism 21d, thereby performing transfer. The molded product can be taken out from the surface 21a. Such a molded product becomes a reflective optical element OE having a highly accurate reflective surface with high reflectance at a low cost by insert molding the plastic film 8.

The present inventors made comparative examples and examples of mirror films. Fig.4 (a) is a SEM (scanning electron microscope) image of the cross section in the thickness direction of the mirror film concerning a comparative example, FIG.4 (b) is SEM of the cross section in the thickness direction of the mirror film concerning an Example. It is an image, and let each surface be an upper surface and a back surface be a lower surface. Here, a silver layer of 150 nm in thickness was formed on the substrate by the vacuum evaporation method in both the comparative example and the example, but in the comparative example, the deposition was performed at a vacuum degree of 10 ^-3 Pa without flowing nitrogen gas. In the above, the deposition was performed while introducing nitrogen gas at a deposition pressure of 10 ⁻¹ Pa. The other film forming conditions are the same.

  FIG. 5 (a) is a schematic view of the SEM image of FIG. 4 (a), and FIG. 5 (b) is a schematic view of the SEM image of FIG. 4 (b). The grain boundaries are indicated by lines. In the comparative example shown in FIG. 5 (a), while the average distance between crystal grain boundaries on the front or back surface of the silver layer is 50 nm or less, in the embodiment shown in FIG. 5 (b), the surface of the silver layer Alternatively, the average distance between grain boundaries on the back surface is 150 nm or more, which is larger than the average distance between grain boundaries in the comparative example. By forming a metal layer by vacuum evaporation while introducing nitrogen gas, the average distance between crystal grain boundaries can be made 100 nm or more. Thereby, the reflectance fall by the crack generation at the time of mirror film bending can be controlled.

  The inventors of the present invention changed the reflectance of the mirror films of Comparative Examples and Examples when stretched at 2.5%, 5%, 7.5%, 10%, 12.5%, and 20%. Was examined. FIG. 6 is a graph showing the result. In the comparative example shown in FIG. 6A, the reflectance is less than 90% at a wavelength of less than 530 nm at a stretch ratio of 10%, and it can be seen that the reflection performance is insufficient as a mirror film that reflects visible light.

  On the other hand, in the comparative example shown in FIG. 6 (b), the reflectance is 90% or more in the visible light region of wavelength 400 nm or more at a stretching ratio of 10%, and the reflectance is at wavelength 410 nm or more even at a stretching ratio of 12.5%. It becomes 90% or more, and it turns out that it can fully use for practical use. That is, by forming silver or aluminum in a nitrogen gas atmosphere, it is difficult to generate or expand a micro crack even if it is stretched by about 10% during insert molding, thereby obtaining a mirror film capable of suppressing deterioration of reflectance. be able to.

  Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, the combination of the mirror film and the molded article is not limited to the insert molding, but includes the case where the mirror film is bonded to the resin molded article. Further, the reflective optical element of the present invention can be applied to an fθ mirror or a folding mirror used for a laser beam printer, a complex machine or the like, a large mirror for a head-up display, a projector or the like.

DESCRIPTION OF SYMBOLS 1 Evaporation source 2 Housing | casing 3 Evaporation flux 4 Film-forming roller 5 Tension roll 6 Shielding plate 7 N ₂ Source 8 Plastic film 9 Opening 11 Gravure roll 12 Pick-up roll 13 Reservoir 13 Reservoir 14 Reservoir 14 Liquid mixture 21 Mold 21a Transfer Surface 21b Intake hole 21c Ejection pin 21d Drive mechanism 22 Mold 22a Transfer surface 23 Transport device OE Reflective optical element

Claims (9)

A mirror film comprising a film-like substrate and a reflection layer formed on the substrate, the mirror film comprising
The reflective layer has a metal layer having a thickness of 50 nm to 300 nm, and when the cross section is taken along the thickness direction of the metal layer, the metal layer is formed on the front side or the back side in the cross section. The mirror film in which the distance between adjacent grain boundaries is 100 nm or more on average.   The mirror film according to claim 1, wherein the metal layer is a silver layer, and the reflectance of the reflective layer is 90% or more.   The mirror film of Claim 1 or 2 which formed the protective layer on the said reflection layer.   The mirror film in any one of Claims 1-3 which formed the base layer between the said base material and the said metal layer.   The mirror film according to any one of claims 1 to 4, wherein the base material is formed in a film shape using any of PC, PET and COP as a material.   The reflective optical element formed by sticking the mirror film in any one of Claims 1-5 on the surface of a resin molded product.   The mirror film according to any one of claims 1 to 6 is disposed in a mold, the molten resin is injected into the mold so as to be in contact with the mirror film, and the resin is solidified. A molding method of a reflective optical element in which a mirror film and the resin are integrated.   A method of manufacturing a mirror film, wherein a metal layer is formed on the substrate by causing metal molecules to collide with the substrate using a vacuum evaporation method while flowing nitrogen into the processing space. The method for producing a mirror film according to claim 8, wherein the internal pressure in the processing space is 10 ^-2 Pa or more in a nitrogen inflow state.