JP5313538B2 - Injection mold and injection molding method - Google Patents

Description

The present invention relates to an injection mold and an injection molding method.

  Various optical devices such as cameras and other imaging devices have resin optical elements formed by injection molding because of the low cost of materials and the ease of forming special optical surfaces typified by aspheric surfaces. Has become indispensable.

  Injection molding of the resin optical element is performed using a “mirror surface piece” in order to accurately mold the optical surface. For example, in the case of injection molding of a resin lens, one of the lens surfaces is formed as a mirror surface molding portion on each of a pair of mirror surface frames, and each mirror surface frame is set on the template so that these mirror surface molding portions face each other. Is done. The facing portion of the mirror surface forming portion constitutes a “cavity”, and molding is performed by injecting molten resin into the cavity.

In this case, if the “positional relationship between the central axes” of both lens surfaces of the molded lens is shifted, a so-called “lens with shifted optical axis” is formed, and such a lens cannot be used as an optical element. For this reason, in the injection molding of the resin optical element, “adjustment for matching the central axes of the mirror surface molding portions of the pair of opposing mirror surface pieces” is required. The “adjustment for matching the central axis” is called “alignment operation”.
As described above, the alignment operation is an extremely important operation step in the injection molding of the resin optical element, and the labor of the alignment operation has been one of the difficulties in improving the efficiency of the optical element molding.

  As an injection molding method that can save the labor of the alignment operation, a method described in Patent Document 1 is known.

  That is, in this injection molding method, the mirror surface piece having the mirror surface forming portion for forming the cavity is integrated with the piece main body having the mirror surface forming portion and “the central axis of the piece main body coincides with the central axis. And a thermal expansion member formed of a material having a thermal expansion coefficient larger than the thermal expansion coefficient of the main body of the piece, and is formed as an integrated state, and these mirror surface pieces have a clearance with respect to the mold surface. After setting, heat is applied by the heating means, and the thermal expansion member is expanded to “adhere the outer peripheral portion of the thermal expansion member to the mold surface”, and the molten resin is put into the cavity in a state where the clearance disappears. Injection into the mold.

  In this injection molding method, when the molten resin is injected into the cavity, the thermal expansion member that forms a part of the mirror surface piece is thermally expanded to be in close contact with the mold surface of the mold plate, thereby eliminating the clearance. The center axis of the thermal expansion member automatically matches the “center axis of the mold surface of the template”. Since the center axis of the thermal expansion member coincides with the center axis of the piece body, the center axis of the mirror molding part automatically matches the “center axis of the mold surface” and is automatically “aligned”. State "is realized.

This method is excellent as an automatic alignment operation.
However, in the injection molding method described in Patent Document 1, the mirror piece is composed of “a frame body having a mirror surface molding part” and “a thermal expansion member”, and the thermal expansion member has a “thermal expansion coefficient larger than that of the frame body. In order to eliminate clearance from the mold surface due to thermal expansion due to heating, the coefficient of thermal expansion must be greater than that of the template material. I must.

  As described above, since “the frame main body and the thermal expansion member constituting the mirror surface piece are different materials”, a “step of integrating the frame main body and the thermal expansion member” is required when manufacturing the mirror surface piece. Patent Document 1 discloses “coupling by a fastening member such as a bolt” and “coaxial fitting and integration of the piece body to the thermal expansion member” as an integration mode of the piece body and the thermal expansion member.

  The coupling by the fastening member requires a special member called “fastening member”, and it is necessary to have a structure for engaging the fastening member with the frame main body and the thermal expansion member. It is difficult to increase manufacturing efficiency.

  In addition, when “the body of the piece is coaxially fitted and integrated with the thermal expansion member”, when the heating means heats up, the “fitting portion has a clearance due to the difference in thermal expansion coefficient between the piece main body and the thermal expansion member. In order to avoid this, it is necessary to “press-fit” the frame body into the thermal expansion member by “shrink fitting”. “Existence of the press-in process for integration” makes it difficult to improve the efficiency of mirror surface piece production. .

  In addition, the piece main body and the thermal expansion member are different materials, but the size of the piece main body varies depending on the size of the “mirror surface forming part”, and causes the thermal expansion member to exhibit a desired “clearance elimination effect”. Therefore, there is a problem that it is necessary to individually design the size and material of the thermal expansion member according to the piece body.

Japanese Patent No. 3850112

  The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to realize an injection mold / injection molding method that does not require a troublesome alignment operation and has a high production efficiency of a mirror piece.

The injection mold of the present invention is used for injection molding of a resin optical element, and has a pair of mold plates, a pair of specular pieces, and a heating means.
The “mirror surface piece” has “mirror surface forming portions” for forming an optical surface, and is used as a pair, and the mirror surface forming portions of the pair of mirror surface pieces facing each other form a cavity.
The “heating means” is means for heating a pair of mirror pieces and a pair of templates.
Each of the pair of “templates” has a mirror piece set and held during injection molding.
The injection mold according to claim 1 has the following characteristics.
That is, each of the pair of mirror pieces forming the cavity is a “single structure”. A single structure is a structure that is configured as a single unit. Therefore, each mirror piece is formed of “homogeneous material”. The homogeneous material is not limited to a “single material” but may be a composite material such as an alloy.

Each of the pair of specular pieces has a small diameter portion and a large diameter portion.
The “small diameter part” has a “predetermined small diameter” in which a “mirror surface forming part” is formed in a single axial part of the piece.
The small diameter portion has a cylindrical shape whose diameter is the predetermined small diameter.
The “large diameter portion” is a cylindrical shape having a predetermined large diameter larger than the small diameter portion, and forms a step in the axial direction at the boundary with the small diameter portion. The small diameter part and the large diameter part are coaxial. That is, the central axis of the cylindrical portion formed by the small diameter portion coincides with the central axis of the cylindrical portion formed by the large diameter portion.

Each mirror piece is formed of a “material having a higher coefficient of thermal expansion” than the material of the template on which they are set.
Each of the template plates on which the specular pieces are set is a cylindrical shape having a step due to two inner diameters corresponding to the small diameter portion and the large diameter portion of the specular piece to be set coaxially in the central axis direction, and the large inner diameter portion side is closed. Has a set hole.

  Each of the mirror surface pieces is in a state in which heating by the heating means is not performed. In the template, “the peripheral surface of the large diameter portion has a first clearance with respect to the mold surface, and the peripheral surface of the small diameter portion becomes the mold surface. “Set with a second clearance”. Corresponding to the fact that the mirror piece has a “small diameter portion and a large diameter portion”, one side of the template has a step between “a portion facing the large diameter portion and a portion facing the small diameter portion”.

When heating of the template / specular piece by the heating means is performed, the shape of the template surface and the shape of each of the template plate are set so that the first clearance disappears and the second clearance does not disappear due to the thermal expansion of each specular piece. The “shape of the small-diameter portion and the large-diameter portion” of the mirror surface piece is defined.
When heating is performed, the large-diameter portion of the mirror piece set in the set hole of each template comes into contact with the back side surface of the set hole.

As described above, optical insert for use in injection molding die of the present invention is a small diameter portion having a predetermined diameter having a "mirror surface molding portion, with the central axis coaxial with the small diameter portion, larger predetermined than the small diameter portion And a “single structure made of a material having a coefficient of thermal expansion greater than that of the template material”.

  And the mirror piece is “in a state where heating by the heating means is not performed, the peripheral surface of the large diameter portion has a first clearance with respect to the mold surface in the template, and the peripheral surface of the small diameter portion is the mold surface. In order to prevent the first clearance from disappearing and the second clearance from disappearing due to the thermal expansion of each specular piece when the heating means is used to set the second clearance with respect to the second clearance. The shapes of the small-diameter portion and the large-diameter portion are determined according to the mold surface shape / template material of the template.

Such a mirror piece is preferably formed by “cutting the large diameter portion and then cutting the small diameter portion coaxially” .

  As described in the prior art, the mirror surface piece that is “integrated by forming the piece main body and the thermal expansion member from different materials” is, as described in Patent Document 1, the piece main body and the thermal expansion member are separated from each central axis. Can be manufactured by cutting the outer peripheral portion at the same time, but as a pre-process for cutting the outer peripheral portion, the central axis of the piece body and the thermal expansion member are matched. Assembling process "is necessary.

On the other hand, the mirror piece according to the present invention is easy to manufacture because it can be formed by “cutting a large diameter portion into a single material and then cutting a small diameter portion coaxially”.

In the injection molding method of the present invention, in the state where the injection mold according to claim 1 is used, heating is performed by heating means, each mirror piece is thermally expanded, and the first clearance of each mirror piece is lost. The molten resin is injected into the cavity and molded.

  As described above, according to the present invention, a novel injection mold, a mirror piece used for the mold, and an injection molding method using these can be realized. The injection molding die / injection molding method of the present invention is easy to manufacture because the mirror piece used is a single structure, and the first clearance between the large diameter portion and the mold surface disappears during molding. By doing so, an automatically aligned state is realized, so that there is no troublesome alignment operation.

FIG. 1 is a diagram illustratively showing one embodiment of an injection mold. This injection mold is used for injection molding of a resin lens as a “resin optical element” .
The “fixed mold” indicated by reference numeral 10 in FIG. 1 has a configuration in which the fixed-side mold plate 14 is attached to the fixed-side attachment plate 12, and the movable mold indicated by reference numeral 20 has a spacer 23 on the movable-side attachment plate 22. A movable-side template 24 is attached to the movable platen. A protruding plate 25 is attached to the movable side mounting plate 22, and the tip of an ejector pin 26 attached to the protruding plate 25 is slidably inserted into the movable side template 24.

  Cylindrical set holes 141 and 241 having “steps due to two large and small inner diameters” are formed in the fixed side mold plate 14 and the movable side mold plate 24 so as to face each other in the vertical direction in FIG. The fixed-side mirror surface piece 30 and the movable-side mirror surface piece 40 are respectively set in the set holes 141 and 241. The opposing surfaces of the pair of mirror pieces 30 and 40 that have been set form a mold cavity 60 by being clamped.

Temperature adjusting holes 143 and 243 as "heating means" are formed in the fixed side mold plate 14 and the movable side template 24 around the mirror surface pieces 30 and 40, respectively. The pieces 30 and 40 and the templates 14 and 24 are heated.
A spool 50 for supplying molten resin is passed through the fixed side mounting plate 12 and the fixed side mold plate 14 and extends to a part of the movable side mold plate 24. A runner 51 communicating with the spool 50 is formed, and the runner 51 communicates with the cavity 60. The front end surface of the ejector pin 26 faces the “lower end surface in the drawing” of the spool 50.

  FIG. 2A shows a state in which the mirror pieces 30 and 40 are set on the templates 14 and 24 in FIG. In the state of FIG. 2A, “heating by the heating means” is not performed.

  The mirror piece 30 is a single structure formed such that a cylindrical small-diameter portion and a large-diameter portion “make a step in the central axis direction”. As shown in FIG. 2 (a), the small-diameter portion 31 has a mirror surface molding portion 33 formed at its end as an end surface shape. The large-diameter portion 32 of the mirror piece 30 has a predetermined large diameter larger than that of the small-diameter portion 31. And the small diameter part 31 and the large diameter part 32 make a level | step difference in the direction of the central axis CL. The central axis CL is “an axis common to the small diameter part 31 and the large diameter part 32”.

  The mirror piece 40 is a single structure in which a cylindrical small-diameter portion and a large-diameter portion are formed so as to “make a step in the central axis direction”. As shown in FIG. 2A, the small-diameter portion 41 is formed with a mirror surface molding portion 43 as an end surface shape at the end thereof. The large diameter portion 42 of the mirror piece 40 has a predetermined large diameter larger than that of the small diameter portion 41. And the small diameter part 41 and the large diameter part 42 make a level | step difference in the direction of the central axis CL. The central axis CL is “a common axis for the small diameter portion 41 and the large diameter portion 42”. The mirror surface molding portions 33 and 43 are surfaces for forming both surfaces of the lens.

  The set hole 141 of the template 14 in which the mirror piece 30 is set has a cylindrical shape having “a step due to two large and small inner diameters” corresponding to the small diameter portion 31 and the large diameter portion 32 of the mirror surface piece 30 in the central axis CL direction. The mirror piece 30 is set in the set hole 141. The inner peripheral surface of the set hole 141 is a “mold surface” of the template 14.

  The mirror piece 30 has a set hole 141 of the template 14, the peripheral surface of the large-diameter portion 32 has a first clearance CL <b> 1 with respect to the mold surface, and the peripheral surface of the small-diameter portion 31 is the first with respect to the mold surface. 2 so as to have a clearance CL2.

  The set hole 241 of the template 24 on which the mirror piece 40 is set has a cylindrical shape having “a step due to two large and small inner diameters” in the direction of the central axis CL according to the small diameter portion 41 and the large diameter portion 42 of the mirror surface piece 40. The mirror piece 40 is set in the set hole 241. The inner peripheral surface of the set hole 241 is the “mold surface” of the template 24.

  In the mirror surface piece 40, the peripheral surface of the large diameter portion 42 has a first clearance CL3 with respect to the mold surface in the set hole 241 of the template 24, and the peripheral surface of the small diameter portion 41 is the first with respect to the mold surface. 2 so as to have a clearance CL4 of 2.

  The first clearance CL1 (radius difference between the mold surface with the large inner diameter of the set hole 141 and the large diameter portion 32 of the mirror piece 30) and CL3 (the mold surface with the large inner diameter of the set hole 241 and the large diameter portion 42 of the mirror piece 40) Is the same in this embodiment. Further, the second clearance CL2 (radius difference between the mold surface having a small inner diameter of the set hole 141 and the small diameter part 31 of the mirror piece 30) and CL4 (mold surface having a small inner diameter of the set hole 241 and the small diameter part 41 of the mirror piece 40). Is also the same in this embodiment.

  These clearances CL1 to CL4 may be the same or different from each other.

  In this embodiment, the mirror pieces 30 and 40 are made of the same material, and the templates 14 and 24 are also made of the same material. As the material of the mirror pieces 30 and 40, a material having a thermal expansion coefficient larger than the “thermal expansion coefficient of the material of the template plates 14 and 24” is selected.

  When injection molding is performed, a thermal fluid is supplied to the temperature adjusting holes 143 and 243 (see FIG. 1) forming the “heating means”, and the mirror pieces 30 and 40 and the template plates 14 and 24 are heated.

  By this heating, the mirror surface pieces 30 and 40 are thermally expanded, and both the small diameter portion and the large diameter portion “increase the diameter”. In addition, the mold plates 141 and 241 are also thermally expanded, and accordingly, the diameters of the mold surfaces of the set holes 141 and 241 are increased.

  The radius of the small-diameter portion 31 of the mirror piece 30 is r11, the radius of the large-diameter portion 32 is r12, the radius of the small inner diameter of the mold surface in the set hole 141 is R11, and the radius of the large inner diameter is R12. When the coefficient (linear expansion coefficient) is α1, the coefficient of thermal expansion (linear expansion coefficient) of the template 14 is β1, and the temperature rise due to heating is T, the small diameter portion 31 is caused by the thermal expansion of the mirror piece 30 and the template 14. Is “r11 (1 + α1 · T)”, and the radius of the large diameter portion 32 is “r12 ((1 + α1 · T)).

  Further, the radius of the small inner diameter of the mold surface in the set hole 141 is “R11 (1 + β1 · T)”, and the radius of the large inner diameter is “R12 (1 + β1 · T)”.

Therefore, due to this thermal expansion, the clearance CL1 becomes CL1- {R12 (1 + β1 · T) −r12 ((1 + α1 · T))}.
= CL1- {R12-r12} + {r12 · α1-R12 · β1} T
= {R12 · α1-R12 · β1} T = ΔCL1
become.

On the other hand, the clearance CL2 is calculated by the same calculation.
{R11 · α1-R11 · β1} T = ΔCL2
It becomes.

Accordingly, for the temperature T to be raised by the heating means when molding is performed:
ΔCL1 ≦ 0, and
ΔCL2> 0
When the above-mentioned amounts: r11, r12, R11, R12, α1, and β1 are set, the mirror piece 30 has a large diameter portion 32 with a large surface portion of the set hole 141 when molding is performed. The first clearance CL1 disappears and the second clearance CL2 does not disappear by being in close contact with or crimped to the inner mold surface.

  The relationship between the mirror piece 40 and the set hole 241 of the template 24 is the same.

  Thus, when injection molding is performed, the mirror surface pieces 30 and 40 and the template plates 14 and 24 are heated by a predetermined temperature: T by the heating means, so that “corresponding to the large diameter portions of the mirror surface pieces 30 and 40”. The first clearance with the large-inner-diameter mold surface of the set hole disappears, and the central axis CL of the mirror surface pieces 30 and 40 automatically enters the “aligned state”.

  FIG. 2B shows this state. The first clearance disappears, and the second clearances CL2 ′ and CL4 ′ (“CL2 ′ = CL4 ′” in the example in the description) are smaller than the sizes CL2 and CL4 before heating. However, it has a finite size. As described above, since the second clearances CL2 ′ and CL4 ′ are minute but not zero, no stress due to thermal expansion is applied to the small-diameter portion, and the surface shape of the mirror surface molding portion is well transferred and “optical axis misalignment” is achieved. No good resin lens "can be obtained.

  Since the mirror surface pieces 30 and 40 have the shapes as described above, in order to manufacture them, first, after forming the large diameter portion by cutting, the small diameter portion is cut by coaxial as it is, and then the mirror surface molding is performed. What is necessary is just to process a part into a desired surface shape.

  The actual size of the first and second clearances CL1 to CL4 is about 2 to 5 μm. When the mirror pieces 30 and 40 are set in the setting holes 141 and 241, since the clearances CL <b> 1 and CL <b> 2 are provided in the large diameter portion, the setting is easy.

  In addition, due to the thermal expansion of the mirror surface pieces 30 and 40, the mirror surface molding part also expands due to the expansion, and the surface shape of the mirror surface molding part differs strictly before and after heating. In many cases, it can be ignored. If the difference in the surface shape of the mirror surface forming part before and after heating becomes a problem, the deformation due to thermal expansion is anticipated in advance, and the “surface shape of the mirror surface forming part” after heating becomes the desired surface shape. The surface shape may be produced as described above.

As the material of the mold plates 14 and 24, for example, a stainless material having a linear expansion coefficient of 11.1 × 10 ⁻⁶ / ° C. at room temperature and 11.6 × 10 ⁻⁶ / ° C. at a molding temperature (about 120 ° C.) Can be used. In this case, examples of the material of the mirror pieces 30 and 40 include a linear expansion coefficient of about 22.0 × 10 ⁻⁶ / ° C. at room temperature and about 23.3 × 10 ⁻⁶ at a molding temperature (about 120 ° C.). A material having a larger linear expansion coefficient than the material of the mold plates 14 and 24, such as an aluminum material at / ° C., can be used.

  The injection mold shown in FIG. 1 for explaining the embodiment has mold plates 14 and 24 and a mirror surface molding part for forming a cavity, and is set in the mold plate with a clearance. In an injection mold having a pair of mirror pieces 30 and 40 and heating means 143 and 243 for heating the mirror pieces and the template, each of the mirror pieces 30 and 40 has a mirror forming portion 33 and 43. The small diameter portions 31 and 41 having a predetermined small diameter and the large diameter portions 32 and 42 having a predetermined large diameter that is coaxial with the central axis of the small diameter portion and larger than the small diameter portion are stepped in the central axis direction. Each of the mirror pieces 30 and 40 is a single structure made of a material having a coefficient of thermal expansion larger than that of the template material and is not heated by the heating means 143 and 243. In the plates 14 and 24, the peripheral surfaces of the large diameter portions 32 and 42 are mold surfaces. 41 and 241 have first clearances CL1 and CL3, and the peripheral surfaces of the small diameter portions 31 and 41 are set with second clearances CL2 and CL4 with respect to the mold surfaces 141 and 241 to heat the heating means. When the heating by is performed, the mold surface shapes and the mold plate materials of the mold plates 14 and 24 are not lost by the thermal expansion of each mirror piece so that the first clearances CL1 and CL3 disappear and the second clearance does not disappear. This is a configuration in which the shapes of the small-diameter portions 31 and 41 and the large-diameter portions 32 and 42 of each mirror surface piece 30 and 40 are defined (Claim 1).

The mirror pieces 30 and 40 are formed by cutting the large diameter portions 32 and 42 and then cutting the small diameter portions 31 and 41 coaxially .

Further, by using the injection mold shown in FIG. 1, heating by the heating means 143 and 243 was performed to thermally expand the mirror surface pieces 30 and 40, thereby eliminating the first clearances CL1 and CL3 of each mirror surface piece. In this state, an injection molding method ( Claim 2 ) is performed in which molten resin is injected into the cavity 60 and molded.

It is a figure for demonstrating one Embodiment of an injection mold. It is a figure for demonstrating the state (a) before a heating which set a pair of mirror surface piece to the template, and the state (b) after a heating.

Explanation of symbols

14, 24 Template 30, 30 Mirror face 143, 243 Heating means 60 Cavity

Claims (2)

An injection mold used for injection molding of resin optical elements,
A pair of templates,
A mirror surface forming portion for forming a cavity, a pair of mirror surface pieces set in the pair of template plates with a clearance, and a heating means for heating the mirror surface pieces and the template plate. In injection mold,
Each of the mirror surface pieces includes a small diameter portion having the mirror surface forming portion and a predetermined small diameter, and a large diameter portion having a predetermined large diameter that is coaxial with the central axis of the small diameter portion and larger than the small diameter portion. A shape having a step in the central axis direction, and a single structure made of a material having a larger coefficient of thermal expansion than the template material,
Each of the template plates on which the specular pieces are set has a cylindrical shape having a step with two inner diameters corresponding to the small diameter portion and the large diameter portion of the specular piece to be set coaxially in the central axis direction, and the large inner diameter portion side is closed. Set holes,
In a state where the heating by the heating means is not performed, each of the optical insert is in the set hole of the mold plate, the peripheral surface of the large diameter portion has a first clearance relative to the mold surface, the small The peripheral surface of the part is set with a second clearance with respect to the mold surface,
In addition, the pair of stencils are closely contacted with each other so as to match the central axes with the small inner diameter portions of the respective set holes.
When heating by the heating means is performed , the large-diameter portion of each mirror piece comes into contact with the back side surface of the set hole, and the first clearance disappears due to the thermal expansion of each mirror piece, and the second The mold surface shape and template material of the pair of mold plates and the shapes of the small diameter portion and the large diameter portion of each mirror piece are determined so that the clearance of the pair is not lost . Using the injection mold according to claim 1,
An injection molding method characterized by performing heating by a heating means to thermally expand each mirror piece and injecting molten resin into the cavity in a state where the first clearance of each mirror piece is lost. .

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