JP4815898B2 - Injection mold and injection molding method - Google Patents

Description

  The present invention relates to an injection mold and an injection molding method, and more particularly to an injection mold for molding a small and light optical element such as a lens and a light guide plate, and an injection molding method using the mold.

  In recent years, the development of resin materials and injection molding technology has led to the development of various types of small and lightweight lenses, prism plates (LED lighting plates used in mobile devices, etc.), light guide plates, etc. There is an increasing demand for optical elements such as lenses and mobile phones. In this type of optical element, there is a demand for an injection mold that can accurately transfer a fine shape for diffraction, a fine shape such as a prism surface or a blaze surface, or a smooth surface. .

  Conventionally, in Patent Document 1, in order to achieve high-accuracy transferability, as shown in FIG. 10, a heat insulating material 53 is provided between a core mold 52 and a surface processed layer 54 disposed in the center portion of a template 51. There has been proposed a molding die 50 provided with. A resin molding space 60 is formed between the surface processed layer 54 on which the blazed surface 54 a having a fine shape is formed and the core die 55. The heat insulating material 53 is preferably a ceramic sprayed layer, and the surface treatment layer 54 is preferably a nickel plating layer.

In this mold 50, since the heat insulating material 53 is arranged on the back of the fine shape (blazed surface 54a), the heat retaining property of the blaze surface 54a after resin filling is improved, and the fine shape is transferred to the molded product with high accuracy. It became possible to do. However, in the resin molding space 51a adjacent to the blaze surface 54a, the template 51 having a relatively high thermal conductivity is exposed, and the heat radiation of the filled molten resin is large in this portion 51a, and the transfer to the fine shape is performed. The problem of adversely affecting sex was found.
JP 2002-96335 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an injection mold and an injection molding method that can further improve the transferability of a fine shape.

In order to achieve the above object, the first invention starts the filling of the molten resin material into the resin molding space and then proceeds to the pressure holding step without adjusting the temperature of the mold. In an injection molding mold for injection molding of an optical element by an injection molding method that takes out a molded product through a cooling process later, a mold core for molding an optical surface and a mold core are arranged so as to surround the mold core. The mold core is formed with a surface that forms a resin molding space by a first heat insulating material, and a second heat insulation is formed at a portion where the mold cavity faces the resin molding space. A material is provided, and the second heat insulating material faces the resin molding space without a heater. The mold core may be composed of only the first heat insulating material, or may be provided with a core mold that holds the first heat insulating material.

  In the injection mold according to the first aspect of the invention, the mold core for molding the optical surface is formed by the first heat insulating material so that the surface constituting the resin molding space is formed, so the resin molding space is filled. The heat retaining property of the resin thus obtained is good, and in particular, the transferability of the fine shape formed on the constituent surface of the resin molding space is improved. Further, since the second heat insulating material is provided in the portion where the mold cavity faces the resin molding space, the heat radiation of the resin is reduced in the portion adjacent to the fine shape, and the transferability of the fine shape is further improved.

In the second invention , the filling of the molten resin material into the resin molding space is started, and then the mold is transferred to the pressure holding process without adjusting the temperature. After the pressure holding process, the molded product is passed through the cooling process. In an injection mold for injection molding an optical element by an injection molding method to be taken out , a mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core are combined. The mold core includes a first heat insulating material, a surface that forms a resin molding space with another material is formed on the surface of the first heat insulating material, and the mold cavity is formed in the resin molding space. A second heat insulating material is provided at the facing portion, and the second heat insulating material faces the resin molding space without a heater. The mold core may be constituted only by the first heat insulating material and the resin molding space constituting surface, or may be provided with a core mold for holding the first heat insulating material.

  In the injection mold according to the second invention, the mold core for molding the optical surface is provided with the first heat insulating material, and the mold cavity faces the resin molding space. Since the second heat insulating material is provided, the heat retaining property of the resin filled in the resin molding space is good and the transferability of the fine shape is improved as in the injection mold according to the first invention.

  In the injection molds according to the first and second inventions, the thermal conductivity of the first and second heat insulating materials is preferably 20 W / m · K or less. As these materials, it is preferable to use any of stainless steel, titanium alloy, nickel alloy, ceramic, or heat resistant resin.

  An injection molding method according to a third invention is characterized in that an optical element is molded from a resin material using the injection mold according to the first or second invention. A high-performance optical element can be obtained by taking advantage of the injection mold.

  In the injection molding method according to the third invention, the temperature of the surface constituting the resin molding space and the resin molding of the second heat insulating material when the resin molding space is completely filled with the resin and the process proceeds to the pressure holding step It is preferable that the temperatures of the surfaces facing the space are both equal to or higher than the glass transition temperature. The flowability of the resin is maintained also when the process proceeds to the pressure holding process, and the resin that supplements the shrinkage in the resin molding space is replenished through the gate portion. Thereby, a higher performance optical element can be obtained.

  Hereinafter, embodiments of an injection mold and an injection molding method according to the present invention will be described with reference to the accompanying drawings. In the drawings showing the embodiments, common members are given the same reference numerals, and redundant descriptions are omitted.

(See the first embodiment, FIG. 1)
A mold 1 </ b> A according to the first embodiment includes a movable mold 10 and a fixed mold 20 as shown in FIG. 1. The movable mold 10 includes a uniformly solid template 11, a uniformly solid core mold 12, a heat insulating material 13, and a surface processed layer 14. The fixed-side mold 20 is configured by a uniformly solid core mold 22. The core mold 12, the heat insulating material 13, and the surface processing layer 14 are referred to as a mold core, and the mold plate 11 is referred to as a mold cavity.

  The surface processing layer 14 is finished corresponding to the optical surface shape of a molded product (optical element) such as a lens, a mirror, a prism plate, and a light guide plate, and has a fine shape 14a such as a diffraction grating, a prism surface, or a blaze surface. Is formed. The resin molding space 30 is composed of the surface processed layer 14, the core mold 22, and the inner peripheral upper edge of the template 11.

  The core molds 12 and 22 are made of a normal mold base material, for example, a metal material such as carbon steel or stainless steel. Carbon steel has a thermal conductivity of 50 W / m · K, and general-purpose hot die steel (JIS standard, SKD61) has a thermal conductivity of 34 W / m · K.

On the other hand, the template 11 is formed of a heat insulating material. As the heat insulating material, various materials having a thermal conductivity lower than that of the core molds 12 and 22 are used, and the thermal conductivity is preferably 20 W / m · K or less. For example, martensitic stainless steel (thermal conductivity 20 W / m · K), austenitic stainless steel (16 W / m · K), titanium alloy (Ti-6Al-4V, thermal conductivity 7.5 W / m · K) , Nickel alloy (Inconel, thermal conductivity 15 W / m · K), ceramic silicon nitride (Si ₃ N ₄ , 20 W / m · K), aluminum titanate (Al ₂ O ₃ · TiO ₂ , 1.2 W / m · K). Of course, it is possible to use materials other than these, ceramics having various compositions can be used, and metals such as stainless steel alloys, titanium alloys, and nickel alloys can be suitably used.

The heat insulating material 13 is a ceramic sprayed onto the core mold 12, an organic material (heat resistant polymer) such as polyimide resin, a sintered ceramic which is a low thermal conductive material, a titanium alloy (Ti-6Al-4V, Ti-3Al-). 2.5V, such Ti-6Al-7Nb), cermet (aluminum _{titanate, TiO 2 -Al 2 O 3)} , stainless steel (ferritic, etc. austenitic) is formed by a nickel alloy (Inconel, FeNi) Yes. As the ceramic, zirconia, silicon nitride, titanium nitride, or the like can be used. The surface processed layer 14 is formed by plating a non-ferrous metal material, for example, nickel on the heat insulating material 13.

  In addition, the heat insulating material 13 and the template 11 that is a heat insulating material are not limited to the above materials, and a material having a lower thermal conductivity than the core molds 12 and 22, for example, a thermal conductivity of 20 W / m · Any material may be used as long as it is K or less. Organic materials (heat-resistant polymer) such as polyimide resin may be used.

  According to the first embodiment, since the heat insulating material 13 is provided between the core mold 12 and the surface processed layer 14, the heat retaining property of the resin filled in the resin molding space 30 is good. The transferability of the fine shape 14a formed on the processed layer 14 is improved.

  Furthermore, although the template 11 which comprises a part of resin molding space 30 has the part 11a adjacent to the surface processing layer 14, since the whole template 11 is formed with the heat insulating material, it is fine shape. The heat radiation of the resin in the portion 11a adjacent to 14a is reduced, and the transferability of the fine shape 14a is further improved.

(See the second embodiment, FIG. 2)
As shown in FIG. 2, the mold 1 </ b> B according to the second embodiment is an inner peripheral upper edge part of the mold plate 11 constituting the movable mold 10 and a part constituting the resin molding space 30. In other words, an annular heat insulating material 15 is interposed between the template 11 and the surface processed layer 14.

In this mold 1B, the template 11 is made of a normal mold base material. The heat insulating material 15 is formed of various stainless steels, titanium alloys, and nickel alloys having low thermal conductivity shown in the first embodiment. Alternatively, it may be formed of ceramic silicon nitride (Si ₃ N ₄ , 20 W / m · K), aluminum titanate (Al ₂ O ₃ · TiO ₂ , 1.2 W / m · K), or the like. Further, it can be formed of a heat resistant polymer such as polyimide resin (thermal conductivity 0.28 W / m · K). Of course, materials other than these can be used, and ceramics having various compositions can be used. Other members and their materials are the same as those of the mold 1A according to the first embodiment.

  According to the second embodiment, since the heat insulating material 13 is provided between the core mold 12 and the surface processing layer 14, the heat retaining property of the resin filled in the resin molding space 30 is good. The transferability of the fine shape 14a formed on the processed layer 14 is improved.

  Furthermore, since the heat insulating material 15 is interposed between the template 11 constituting the part of the resin molding space 30 and the surface processed layer 14, the heat radiation of the resin in the portion adjacent to the fine shape 14a is reduced, The transferability of the fine shape 14a is further improved.

(Refer to the third embodiment, FIG. 3)
As shown in FIG. 3, the mold 1C according to the third embodiment is provided with a heat insulating material 16 instead of the heat insulating material 15 in the mold 1B according to the second embodiment. The material of the heat insulating material 16 is the same as that of the heat insulating material 15, and other structures and materials are the same as those of the second embodiment. Therefore, the effect is the same as that of the second embodiment.

(Refer to the fourth embodiment, FIG. 4)
As shown in FIG. 4, the mold 1D according to the fourth embodiment includes not only the movable mold 10 but also the fixed mold 20 with the uniformly solid mold plate 21 and the uniformly solid mold 20. A core mold 22, a heat insulating material 23, and a surface processed layer 24 are configured. Similar to the surface processed layer 14, the surface processed layer 24 is finished corresponding to the optical surface shape of the molded product (optical element), and a fine shape 24a is formed.

  The materials of the heat insulating material 23 and the surface processed layer 24 are the same as those in the first embodiment. Moreover, the template 11,21 is formed with the heat insulating material. The material is the same as that shown as the material of the template 11 in the first embodiment. The material of the core molds 12 and 22 is the same as that shown as the material of the core mold 12 in the first embodiment.

  According to the fourth embodiment, since the heat insulating materials 13 and 23 are provided between the core molds 12 and 22 and the surface processed layers 14 and 24, the heat retaining property of the resin filled in the resin molding space 30 is good. In particular, the transferability of the fine shapes 14a and 24a formed on the surface processed layers 14 and 24 is improved.

  Furthermore, although the mold plates 11 and 21 constituting a part of the resin molding space 30 have portions 11a and 21a adjacent to the surface processed layers 14 and 24, the entire mold plates 11 and 21 are made of a heat insulating material. Since it is formed, the heat radiation of the resin in the portions 11a and 21a adjacent to the fine shapes 14a and 24a is reduced, and the transferability of the fine shapes 14a and 24a is further improved. In addition, since the resin is kept warm on the front and back surfaces, there is no risk of warping of the molded product.

(Refer to the fifth embodiment, FIG. 5)
As shown in FIG. 5, the mold 1 </ b> E according to the fifth embodiment is provided with annular heat insulating materials 17 and 27 on the inner peripheral edge portions of the mold plates 11 and 21 and constituting a part of the resin molding space 30. It is provided. The materials of the heat insulating materials 17 and 27 are the same as those shown as the material of the heat insulating material 15 in the second embodiment.

  Other configurations and materials thereof are the same as those in the fourth embodiment except that the mold plates 11 and 21 are made of a normal mold base material. In addition, the effect is the same as that of the fourth embodiment.

(See the sixth embodiment, FIG. 6)
As shown in FIG. 6, the mold 1F according to the sixth embodiment is for molding a curved lens, and each component is the same as the mold 1C according to the third embodiment, and its material Is the same. Therefore, the effect is the same as that of the third embodiment.

  As shown in FIG. 7, the mold 1 </ b> G according to the seventh embodiment includes a core mold 12 made of a heat insulating material and a fine shape 12 a formed on the surface of the core mold 12. The material of the core mold 12 here is the same as that of the heat insulating material 13 described in the first embodiment, and the other configuration is the same as that of the first embodiment.

  As shown in FIG. 8, the mold 1H according to the eighth embodiment is obtained by providing a surface mold layer 14 on a core mold 12 made of a heat insulating material. The material of the core mold 12 here is the same as that of the heat insulating material 13 described in the first embodiment, and the other configuration is the same as that of the first embodiment.

  As shown in FIG. 9, the mold 1 </ b> I according to the ninth embodiment is provided with a heat insulating material 13 on a core mold 12 and a fine shape 13 a formed on the surface of the heat insulating material 13. Other configurations are the same as those of the first embodiment.

(Molding method)
Here, an outline of an injection molding method using the molds 1A to 1I will be described.

  First, a resin (for example, amorphous polyolefin resin) melted at a predetermined temperature is filled into the resin molding space 30, and immediately after the filling is completed, the pressure holding step is started. The pressure holding step is a step of maintaining a predetermined pressure on the resin in order to compensate for the amount of shrinkage of the resin filled in the resin molding space 30 due to a decrease in temperature. After the pressure-holding step, the cooling step (natural cooling) is entered, and at least when the surface of the resin (molded product) is lowered to the heat deformation temperature or lower, the mold is opened, and the molded product is ejected with an eject pin (not shown).

  In the above molding process, the resin is filled into the resin molding space 30 in a relatively high temperature molten state. At the start of filling, the surface temperature of the molding surface of each mold element facing the resin molding space 30, specifically, the surface (part 11 a or heat insulating material 15, 16 constituting the resin molding space 30 of the mold cavity). ) And the temperature Tco of the surface (such as the surface processed layer 14) constituting the core-shaped resin molding space 30 are lower than the glass transition temperature Tg of the resin.

  When filling is started, the temperature of the resin molding space 30 rises due to the heat of the filled resin, and the temperatures Tca and Tco become higher than the temperature Tg due to the heat insulation effect, and the state is maintained. The temperatures Tca and Tco are maintained at the temperature Tg or higher even when the resin filling is completed and the pressure holding process starts. Such temperature setting is also possible by adjusting the temperature of the mold, but if the mold according to the present invention is used, there is no need to further adjust the temperature of the mold due to its heat insulation effect, and pressure holding The temperatures Tca and Tco at the time of shifting to the process can be maintained at the temperature Tg or higher.

  By such temperature setting, the resin is supplied for the shrinkage in the resin molding space 30 and the transferability is improved. The temperatures Tca and Tco do not have to be the same as long as they are equal to or higher than the temperature Tg.

  In the resin molding space 30, the resin begins to decrease immediately after the completion of filling. However, in the molds 1A to 1I, since the heat insulating materials 13 and 23 are arranged on the back portions of the fine shapes 14a and 24a, the heat retaining property of the resin injected into the resin molding space 30 is good. Since at least a part of the mold constituting the resin molding space 30 is formed of a heat insulating material, the heat radiation of the resin is reduced, and the transferability of the fine shapes 14a and 24a is improved.

(Experimental result)
The inventors experimentally molded an optical element having a diffractive structure on both surfaces using the mold 1D of the fourth embodiment, and measured the optical performance. For comparison, a similar optical element was molded using a conventional mold made of a uniform material.

  The resin used for molding was ZEONEX E48R manufactured by Nippon Zeon Co., Ltd., which is an amorphous polyolefin resin, and a diffraction element for a Blu-ray / DVD / CD compatible pickup was molded. According to the mold of the present invention, the diffractive structure is well transferred when the thermal conductivity of the heat insulating material arranged around the resin molding space 30 is 20 W / m · K or less, and the diffraction efficiency is 82.5% or more. there were. In addition, the molding cycle time is the same as that of the conventional mold, so that it can be applied to mass production without any problems, and maintenance is not hindered.

  On the other hand, when molded with a conventional mold, the transferability is low, the diffraction efficiency is less than 80%, and the resin adheres to the mold, resulting in poor maintainability.

(Other examples)
The injection mold and the injection molding method according to the present invention are not limited to the above-described embodiments, and can be variously changed within the scope of the gist.

  In particular, the details of the mold structure are arbitrary, and it is needless to say that the specific materials shown in the above-described embodiments are examples. 1 to 9, the mold 10 may be a fixed side and the mold 20 may be a movable side. Alternatively, it may be a sleep rate type molding die provided with an intermediate die member.

It is sectional drawing which shows 1st Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 2nd Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 3rd Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 4th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 5th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 6th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 7th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 8th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows 9th Example of the metal mold | die which concerns on this invention. It is sectional drawing which shows the conventional metal mold | die for injection molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A-1I ... Metal mold | die 11,21 ... Template 12,22 ... Core type | mold 13,23 ... Heat insulating material 14, 24 ... Surface processed layer 14a, 24a ... Fine shape 15, 16, 17, 27 ... Heat insulating material 30 ... Resin Molding space

Claims (9)

After filling the molten resin material into the resin molding space, the mold is moved to the pressure holding process without adjusting the temperature, and after the pressure holding process, the molded product is taken out through the cooling process. In an injection mold for injection molding an element,
A mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core are combined,
The mold core has a surface forming a resin molding space formed by the first heat insulating material,
A second heat insulating material is provided in a portion where the mold cavity faces the resin molding space,
The second heat insulating material faces the resin molding space without a heater;
Mold for injection molding characterized by The injection mold according to claim 1, wherein the mold core includes a core mold that holds the first heat insulating material. After filling the molten resin material into the resin molding space, the mold is moved to the pressure holding process without adjusting the temperature, and after the pressure holding process, the molded product is taken out through the cooling process. In an injection mold for injection molding an element,
A mold core for molding an optical surface and a mold cavity arranged so as to surround the mold core are combined,
The mold core includes a first heat insulating material, and a surface that forms a resin molding space with another material is formed on the surface of the first heat insulating material,
A second heat insulating material is provided in a portion where the mold cavity faces the resin molding space,
The second heat insulating material faces the resin molding space without a heater;
Mold for injection molding characterized by   The injection mold according to claim 3, wherein the mold core includes a core mold for holding the first heat insulating material.   The injection mold according to any one of claims 1 to 4, wherein the thermal conductivity of the first and second heat insulating materials is 20 W / m · K or less.   The said 1st and 2nd heat insulating material consists of either stainless steel, a titanium alloy, a nickel alloy, a ceramic, or a heat resistant resin, For injection molding in any one of Claim 1 thru | or 5 characterized by the above-mentioned. Mold.   6. The injection molding according to claim 1, wherein the first and second heat insulating materials are made of a ceramic selected from zirconia-based, silicon nitride-based, titanium nitride, and aluminum titanate. Mold.   An injection molding method comprising molding an optical element from a resin material using the injection mold according to any one of claims 1 to 7.   When the resin filling into the resin molding space is completed and the process proceeds to the pressure holding process, the temperature of the surface constituting the resin molding space and the temperature of the surface facing the resin molding space of the second heat insulating material are both glass transition points. It is more than temperature, The injection molding method of Claim 8 characterized by the above-mentioned.

Images