JP2006015522A - Molding machine and optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding machine capable of more simply and inexpensively molding a molded product having a fine structure of a high aspect ratio, and an optical element. <P>SOLUTION: Since an anchor part 2c is formed in a mold disc 2a so as to hold a fine shape 2b in a cyclic direction (line and space arranging direction), the deformation of at least the surface near to the mold disc 2a of a material M can be suppressed when cooling by the anchor part 2c having shearing strength higher than that of the fine shape 2b and the bending or tear of the transferred fine shape at mold release can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molding apparatus and an optical element, and more particularly to a molding apparatus and an optical element suitable for molding an optical element having a fine shape with a high aspect ratio.

  In recent years, optical elements such as objective lenses with extremely high accuracy are used in the field of optical pickup devices that are rapidly developing. When a material such as plastic or glass is molded into such an optical element using a mold, a product having a uniform shape can be quickly produced. It can be said that it is suitable for mass production.

  Furthermore, recent optical pickup devices record high-density information on recording media such as HD DVDs (High Definition DVDs) and BDs (Blu-ray Discs) using light beams from shorter-wavelength semiconductor lasers. In order to improve the aberration characteristics of the optical system, a diffractive structure which is a fine structure is provided on the optical surface. Further, even in an optical pickup device capable of recording and / or reproducing such high-density information, it is necessary to ensure the recording and / or reproducing of information even with respect to CDs and DVDs that have conventionally been supplied in large quantities. For this reason, a diffractive structure having wavelength selectivity is also provided. In addition, in an optical pickup device capable of recording and / or reproducing information in a compatible manner such as a DVD and a CD, a wave plate that gives a phase difference is used in order to share an optical system. ing.

  Here, although the diffraction structure depends on the light source wavelength to be used, for example, it is an annular structure having a step of about 2 μm at the minimum, and the wavelength plate of the type described above has a pitch less than 1/2 of the wavelength of transmitted light. Therefore, in normal injection molding, simply injecting the molten resin into the mold makes it difficult for the material to enter deeply into the steps of the microstructure formed in the mold. There is a problem that the transfer is not performed with high accuracy. If the designed fine structure is not formed due to transfer failure (sagging of the material), its optical characteristics are deteriorated, and there is a possibility that a write error or the like occurs in an optical pickup device using such an optical element. For this reason, various ideas such as selection of materials and adjustment of the temperature and pressure of the molten resin have been made. However, it is difficult to completely eliminate sagging with conventional methods.

On the other hand, Patent Document 1 below discloses a method of molding an optical element having a fine pattern on the surface by pressing a glass material in a heat-softened state.
Japanese Patent Laid-Open No. 2002-220241

  However, the technique described in Patent Document 1 is limited to molding a fine shape having a width of about 100 to 50 μm and a height of about 20 to 10 μm with an aspect ratio of about 0.2 on the surface of the glass material. . This is because the elastic modulus of inorganic glass at room temperature is as high as about 70 GPa, so even if a mold heated with a very large force of 3000 N is pressed on its surface, the glass material does not flow smoothly into the back of the microstructure, As a result, only a fine shape having an aspect ratio of about 0.2 could be formed. Therefore, for example, a molded product having a fine shape with an aspect ratio of 1 or more may exist as a prototype, but it does not yet exist as an industrial product with a uniform shape.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a molding apparatus and an optical element capable of molding a molded article having a microstructure with a high aspect ratio more easily and at low cost. And

  A molding apparatus according to a first aspect of the present invention includes a mold having a periodic fine shape and an anchor portion sandwiching the fine shape in the periodic direction, and a material having an elastic modulus of 1 to 4 (GPa) at room temperature. A holding portion for holding the die, a heater for heating the die, and a driving portion for moving the die and the holding portion relative to each other, wherein the anchor portion of the die is at least twice the pitch of the fine shape. And pressing the mold heated by the heater toward the material to transfer the fine shape and the anchor portion to the material, and then releasing the mold from the material. And

  In view of the above-mentioned problems, the present inventors have devised a molding method capable of molding a molded product having a fine shape from a completely different viewpoint as a result of intensive studies. That is, in the case of a resin material having an elastic modulus of 1 to 4 (GPa) at room temperature, when a mold having a fine shape is heated and pressed against the mold surface, the pressed surface is melted to a fine shape. As a result, it was found that, for example, even if the aspect ratio is 1 or more, a molded product in which the fine shape of the mold is accurately transferred can be obtained. In such a case, as described in Patent Document 1, a pressing force of 3000 N is unnecessary, it is sufficient to improve the conventional injection molding machine, the manufacturing equipment is reduced in cost, and a large amount of molding is performed in a short time. It becomes possible to manufacture a thing.

  Incidentally, materials having an elastic modulus of 1 to 4 (GPa) at room temperature include, for example, PMMA (elastic modulus of 1.5 to 3.3 GPa), polycarbonate (elastic modulus of 3.1 GPa), polyolefin (elastic modulus of 2). It is preferable to contain, as a composition component, a resin having an elastic modulus in the range of 1 to 4 such as .5 to 3.1 GPa). Here, room temperature means 25 ° C. These resins preferably have a glass transition point of 50 to 160 ° C. The elastic modulus can be obtained according to JIS-K7161, 7162, and the like. The glass transition temperature can be determined according to JIS R3102-3: 2001.

  Here, the present inventors faced a new problem. The new problem is that when the material is molded by the above molding method and then released, the fine shape of the transferred material is not separated from the fine shape of the mold, and a part of the fine shape of the material is torn off. This is a phenomenon that occurs. This will be specifically described with reference to the drawings.

  FIG. 1A is a view showing a state where a heated mold MD is pressed against the material M, and FIG. 1B is an enlarged view showing an arrow B portion of the mold MD and the material M. FIG. On the other hand, FIGS. 1C and 1D are views showing a state in which the mold MD is released from the material M after cooling.

  According to the study by the present inventors, the mold MD and the material M inherently have different coefficients of thermal expansion, and therefore the amount of shrinkage varies depending on the difference in thermal expansion during cooling. It was found that tensile stress was generated. Such tensile stress does not have a large influence in the vicinity of the center of the fine shape, but gives a large amount of deformation to the material M in the vicinity of the periphery. Therefore, at the time of mold release, the root of the transferred fine shape MS ′ is bent (see FIG. 1C), or the transferred fine shape MS ′ is torn off without leaving the mold MD (see FIG. 1D). ) Occurs.

  Therefore, as a result of earnest research, the present inventors have determined that if the anchor portion having a width of twice or more the pitch of the fine shape is formed in the mold so as to sandwich the fine shape in the periodic direction, the fine shape is formed. With the anchor portion having a shear strength higher than the shear strength of the shape, it is possible to suppress deformation of at least the surface of the material close to the mold at the time of cooling, thereby bending at the time of mold release of the transferred fine shape, It is derived that tearing can be suppressed.

  If the height of the anchor portion of the mold is equal to or higher than the height of the fine shape, deformation of at least the surface of the material close to the mold can be suppressed until the fine shape is completely released.

  When the anchor portion is transferred to the material to form a mark indicating the direction of the fine shape, for example, when the optical characteristic such as an optical element is biased, the direction can be indicated.

  The material is preferably a material of an optical element.

  The fine shape preferably has an aspect ratio of 1 or more and includes a plurality of lines and spaces arranged at a predetermined pitch.

  As shown in FIGS. 2A and 2B, the “aspect ratio” is represented by B / A, where A is the width of the concave or convex portion of the fine structure, and B is the depth or height. Value. “Fine shape” means a shape having a value of A of 10 μm or less. The thickness of a raw material becomes like this. Preferably it is 0.1-20 mm, More preferably, it is 1-5 mm.

  The optical element according to the second aspect of the present invention has an aspect ratio of 1 or more, a periodic fine shape arranged at a predetermined pitch, and a transfer anchor portion sandwiching the fine shape in the periodic direction of the fine shape Therefore, it is possible to suppress bending and tearing at the time of mold release of the fine shape that has been transferred and molded.

  The height of the transfer anchor portion is preferably equal to or higher than the height of the fine shape.

  The transfer anchor portion preferably has a mark indicating the direction of the fine shape.

  ADVANTAGE OF THE INVENTION According to this invention, the shaping | molding apparatus and optical element which can shape | mold the molding which has the microstructure of a high aspect ratio more simply and at low cost can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a cross-sectional view of the optical element molding apparatus according to the present embodiment. In FIG. 3, an upper mold 2 formed of SUS304 is disposed so as to be relatively movable above a lower mold 1 formed of SUS304 and fixed to a frame (not shown). The lower mold 1 serving as a holding portion fixes a material M (preferably having an elastic modulus at normal temperature of 1 to 4 (GPa)) on the upper surface.

  A silicon mold disc 2a is fixed to the lower surface of the upper mold 2, and a fine shape 2b having an aspect ratio of 1 or more is formed on the lower surface thereof by, for example, electron beam drawing for use in a wavelength plate. Yes. In this embodiment, a PMMA (molecular weight 70,000, glass transition temperature Tg 100 ° C., longitudinal elastic modulus 3.3 GPa) line and pattern having a pattern area of 1 mm × 1 mm, height 350 nm, width 200 nm, and pitch 200 nm. The fine shape of the space is transferred and formed.

  4 is a bottom view of the mold disk 2a, and FIG. 5 is an enlarged cross-sectional view of the mold disk 2a. The fine shape 2b is a line and space with a minute pitch, but the anchor portion 2c has a rectangular cross-sectional circumferential groove surrounding the fine shape 2b. However, as shown in FIG. 4, the anchor portion 2c has a discontinuous portion 2d that is cut off at one point on the circumference. The line and space of the fine shape 2b extends substantially parallel to the line connecting the center of the mold 2 to the center of the discontinuous portion 2d. The width W of the anchor portion 2c is at least twice the pitch p of the periodic fine shape 2b, and the height (depth) H of the anchor portion 2c is the height of the periodic fine shape 2b ( Depth) is more than h.

  A heater 4 is installed inside the upper mold 2. On the other hand, a cooling pipe 5 is disposed inside the lower mold 1. The upper mold 2 and the mold disc 2a constitute a mold as claimed. Although not shown, a drive unit is provided for moving the upper mold 2 relative to the lower mold 1 in the approaching / separating direction.

  The operation of the molding apparatus according to this embodiment will be described. First, as shown in FIG. 3A, the material M is fixed to the upper surface of the lower mold 1 that has been opened. Further, the heater 4 generates heat, and the upper mold 2 is heated to the glass transition temperature Tg or higher.

  When the lower surface of the mold disk 2a is heated to the glass transition temperature Tg or higher, the material M is pressed by the upper mold 2 by driving a drive unit (not shown) as shown in FIG. Then, the upper surface of the material M is rapidly heated to the glass transition temperature or higher and melted, and the fine shape 2b and the anchor portion 2c of the mold disk 2a are transferred to the surface.

  Subsequently, the heat generation of the heater 4 is stopped, the upper mold 2 is naturally cooled (may be forced cooling), and cooling water is supplied to the pipe 5 to forcibly cool the lower mold 1, thereby increasing the upper surface temperature of the material M. Lower so as to be lower than the glass transition temperature Tg. Thereafter, the optical element can be molded by releasing the upper mold 2 from the material M. Here, as shown in FIG. 5, the fine shape 2b is transferred to the material M to form the fine shape 2b ′, and the anchor portion 2c is transferred to the material M and the transfer anchor sandwiching the fine shape 2b ′. Part 2c ′ is formed.

  According to the present embodiment, in the mold disc 2a, the anchor portion 2c is formed so as to sandwich the fine shape 2b in the periodic direction (line-and-space arrangement direction: left-right direction in FIG. 5). The anchor portion 2c having a shear strength higher than the shear strength of the material can suppress deformation of at least the surface of the material M close to the mold disk 2a during cooling, thereby bending the transferred fine shape during mold release. In addition, tearing can be suppressed.

  Furthermore, according to the present embodiment, as shown in FIG. 4, since the discontinuous portion 2d of the visible anchor portion 2c is formed, when the material M is formed as an optical element, it is transferred to the material M. By using the discontinuous portion of the transferred anchor portion 2c ′ (FIG. 5) as a mark, the directionality of the fine shape 2b can be confirmed, whereby the deviation of the optical characteristics can be grasped.

  FIG. 6 is an enlarged cross-sectional view of a mold disc 2a according to a modification of the present embodiment. In this modification, the anchor part 2c has a circumferential groove shape with two rectangular cross sections. In this case, when the widths of the circumferential grooves are W1 and W2, respectively, W1 + W2> 2p (p is the pitch of the fine shape 2b) is satisfied, so the same effect as in the above embodiment can be obtained.

  FIG. 7 is an enlarged cross-sectional view of a mold disk 2a according to another modification of the present embodiment. In this modification, the anchor part 2c has a circumferential groove shape with two triangular cross sections. In this case, when the opening width of the circumferential groove is W3, W3> 2p (p is the pitch of the fine shape 2b) is satisfied, so that the same effect as the above-described embodiment can be obtained.

  FIG. 8 is an enlarged cross-sectional view of a mold disc 2a according to another modification of the present embodiment. In this modification, the anchor part 2c has a circumferential groove shape with two rectangular cross sections. In this case, since the height H of the circumferential groove exceeds the height h of the fine shape 2b (H> h), it is possible to more effectively suppress bending and tearing when the fine shape of the material M is released. . Although not shown because it is clear, the height of the transfer anchor portion in the optical element molded using this modification is higher than the height of the fine shape.

  FIG. 9 is a bottom view of a mold disk 2a according to another modification of the present embodiment. In the present modification, a triangular mark portion 2e (the height is the same as the anchor portion 2c, but may be different) is further formed in the discontinuous portion 2d with respect to the embodiment of FIG. The point is different. The mark portion 2e is also transferred to the material of the optical element, thereby forming a mark indicating the direction of the fine structure on the transfer anchor portion (not shown).

  FIG. 10 is a bottom view of a mold disc 2a according to another modification of the present embodiment. In the present modification, the discontinuous portion 2d is formed so as to be sandwiched by two in the line-and-space extending direction of the fine shape 2b and two in the arrangement direction (orthogonal direction) in the embodiment of FIG. The point is different. The discontinuous portion 2d is also transferred to the material to form a mark indicating the direction of the fine structure.

  FIG. 11 is a bottom view of a mold disc 2a according to another modification of the present embodiment. In the present modification, in view of the fact that the mold disk 2a and the region of the fine shape 2b are rectangular with respect to the embodiment of FIG. 4, the anchor portion 2c is placed around the region of the fine shape 2b. The difference is that they are arranged in a rectangular shape.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. The present invention is not limited to an optical element for an optical pickup device, but can also be applied to molding various optical elements or an inkjet printer head.

It is a figure for demonstrating the problem at the time of mold release. It is a figure for demonstrating an aspect-ratio. It is sectional drawing of the shaping | molding apparatus of the shaping | molding optical element concerning this Embodiment. It is a bottom view of the mold disk 2a. It is an expanded sectional view of the mold disk 2a. It is an expanded sectional view of the type | mold disk 2a concerning the modification of this Embodiment. It is an expanded sectional view of the type | mold disk 2a concerning the modification of this Embodiment. It is an expanded sectional view of the type | mold disk 2a concerning the modification of this Embodiment. It is a bottom view of the type | mold disk 2a concerning the modification of this Embodiment. It is a bottom view of the type | mold disk 2a concerning the modification of this Embodiment. It is a bottom view of the type | mold disk 2a concerning the modification of this Embodiment.

Explanation of symbols

1 Lower mold 2 Upper mold 2a type disk 4 Heater 5 Piping

Claims (8)

A mold in which a periodic fine shape and an anchor portion sandwiching the fine shape in the periodic direction are formed,
A holding unit for holding a material having an elastic modulus at room temperature of 1 to 4 (GPa);
A heater for heating the mold;
A drive unit that relatively moves the mold and the holding unit;
The anchor portion of the mold has a width that is twice or more the pitch of the fine shape,
A molding apparatus, wherein the mold heated by the heater is pressed toward the material to transfer the fine shape and the anchor portion to the material, and then the mold is released from the material.   The molding apparatus according to claim 1, wherein a height of the anchor portion of the mold is equal to or higher than a height of the fine shape.   The molding device according to claim 1, wherein the anchor portion forms a mark indicating the direction of the fine shape by being transferred to the material.   The molding apparatus according to claim 1, wherein the material is a material of an optical element.   The molding apparatus according to claim 1, wherein the fine shape has an aspect ratio of 1 or more and includes a plurality of lines and spaces arranged at a predetermined pitch.   An optical element having an aspect ratio of 1 or more and a periodic fine shape arranged at a predetermined pitch and a transfer anchor portion sandwiching the fine shape in a periodic direction of the fine shape.   The optical element according to claim 6, wherein a height of the transfer anchor portion is equal to or higher than a height of the fine shape. The optical element according to claim 6, wherein the transfer anchor portion has a mark indicating the direction of the fine shape.

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