JP4815897B2 - 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 an injection molding method using the mold.

  In recent years, various small and light resin lenses have been developed due to the development of resin materials and injection molding technology, and the demand for optical elements such as optical pickup devices and mobile phones is increasing. In this type of resin lens, there is a demand for a mold that can accurately transfer a fine shape and a smooth surface such as a diffractive optical element.

  Generally, since the gate portion located between the resin molding space of the mold and the runner portion is thin, the resin filled in the gate portion in the pressure-holding step after the resin filling into the resin molding space is completed is the resin molding space. It solidifies relatively quickly than the molded product. Therefore, the holding pressure to the resin in the resin molding space is reduced and the supply of resin to compensate for the shrinkage is insufficient, and in the molded product, the surface fine shape and the smooth surface are deteriorated (transferability is reduced), There have been problems such as an increase in birefringence due to a tensile stress applied to the central portion due to resin shrinkage.

Patent Document 1 discloses a mold for obtaining an optical element with high surface accuracy and low residual distortion. In this mold, the mold member constituting the other side surface portion excluding the side surface portion where the gate is arranged has a slide structure so that the molded product can be released smoothly. However, this mold cannot cope with a decrease in transferability due to the solidification of the resin at the gate portion and an increase in tensile stress due to the shrinkage of the resin in the resin molding space.
JP 2002-187168 A

  Accordingly, an object of the present invention is to provide an injection mold that can improve the transferability by suppressing the temperature drop of the resin at the gate portion and can alleviate the stress due to the shrinkage of the resin. There is to do.

To achieve the above object, a first invention is an injection mold comprising a resin molding space, a runner portion, and a gate portion positioned between the resin molding space and the runner portion, Of the resin molding space, the runner part, and the gate part, at least the surface part of only the gate part is constituted by a heat insulating material, and the gate part is made of a heat insulating material fitted in a mold, and the heat insulating material It is characterized by a sleeve-like der Rukoto surrounding a core constituting a chip-shaped member or a resin molding space. The surface which comprises a gate part with another raw material may be formed in the surface of the said heat insulating material.

In the injection mold according to the first invention, since at least the surface portion of only the gate portion is thermally insulated, the gate portion is filled in the pressure holding step after filling the resin molding space with the resin. The temperature drop of the resin is suppressed, and the time for solidification is slightly delayed. This means that the resin in the gate portion has fluidity in the pressure-holding step, and the resin that compensates for the shrinkage in the resin molding space is supplied. Therefore, in the molded product, the fine shape of the surface and the surface accuracy of the smooth surface are not lowered, and the transferability is improved. Further, the tensile stress to the central portion due to the shrinkage of the resin is alleviated, and the birefringence is reduced, so that a high-performance molded article (optical element) can be obtained.

Further, it is preferable that the thermal conductivity of the sectional heat material is less 20W / m · K. As such a heat insulating material, any of stainless steel, titanium alloy, nickel alloy, or ceramic can be used.

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

  In the injection molding method according to the second invention, when the molten resin is allowed to flow into the mold, the thickness center temperature of the molded product is equal to or higher than the glass transition temperature even when the resin filling into the resin molding space is completed. It is preferable. Alternatively, when the molten resin is allowed to flow into the mold, the thickness center temperature of the gate portion maintains the glass transition temperature even when the thickness center temperature of the molded article is equal to or lower than the glass transition temperature. It is preferable that the thickness center temperature of the molded product becomes the glass transition temperature, and at the same time the thickness center temperature of the gate portion becomes the glass transition temperature.

  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.

(Refer to the first embodiment, FIGS. 1 and 2)
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, and a sleeve-like heat insulating material 13. The fixed-side mold 20 includes a uniformly solid mold plate 21, a uniformly solid core mold 22, and a sleeve-like heat insulating material 23. The resin molding space 30 is configured by end faces of the core molds 12 and 22 facing each other and edges of the heat insulating materials 13 and 23. The core molds 12 and 22 and the heat insulating materials 13 and 23 are referred to as mold cores, and the mold plates 11 and 21 are referred to as mold cavities.

  A runner 15 is formed on one side of the dividing surfaces of the templates 11 and 21. A gate 16 extending from the runner 15 to the resin molding space 30 is formed in the heat insulating materials 13 and 23. That is, the gate 16 is formed as a recess on the end surfaces of the heat insulating materials 13 and 23 facing each other.

  The surface of the resin molding space 30 is finished corresponding to a predetermined shape of a molded product such as a lens, and a surface processing layer may be formed by nickel plating or the like.

  The mold plates 11 and 21 and the core molds 12 and 22 are made of a metal material such as carbon steel, which is a normal mold base material. For example, when general-purpose hot die steel (JIS standard, SKD61) is used as a material, the thermal conductivity is 34 W / m · K.

For the heat insulating materials 13 and 23, various materials having lower thermal conductivity than the mold plates 11 and 21 and the core molds 12 and 22 are used. 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) and aluminum titanate (Al ₂ O ₃ · TiO ₂ , 1.2 W / m · K). Of course, materials other than these can be used, ceramics having various compositions can be used, and metals such as stainless alloys, titanium alloys, and nickel alloys can be suitably used. Further, it may be an organic material (heat resistant polymer) such as polyimide resin.

  FIG. 2 shows a modification of the mold 1A according to the first embodiment. In this mold 1A ′, a sleeve-like heat insulating material 13 is provided only on the movable mold 10, and the heat insulating material is omitted from the fixed mold 20.

  The effects of the present invention described below are exhibited by providing the heat insulating materials 13 and 23, but are also exhibited when the heat insulating material 13 is provided only on the movable mold 10. Conversely, the heat insulating material 23 may be provided only on the fixed mold 20.

(Refer to the second embodiment, FIG. 3)
As shown in FIG. 3, the mold 1 </ b> B according to the second embodiment is provided with chip-like heat insulating materials 14 and 24 in grooves formed in the mold plates 11 and 21. The resin molding space 30 is constituted by end faces of the core molds 12 and 22 facing each other.

  The gate 16 extending from the runner 15 formed on one side of the dividing surfaces of the mold plates 11 and 21 to the resin molding space 30 is formed as a recess on the end surfaces of the heat insulating materials 14 and 24 facing each other.

  The materials of the mold plates 11 and 21 and the core molds 12 and 22 are as described in the first embodiment. As the material of the chip-like heat insulating materials 14 and 24, the stainless steel, titanium alloy, nickel alloy, ceramic, etc., which have a relatively low thermal conductivity described in the first embodiment, can be used.

  Also in the second embodiment, similarly to the modification shown in FIG. 2, the chip-like heat insulating material 14 may be provided only on the movable mold 10. The effects of the present invention described below are exhibited by providing the heat insulating materials 14 and 24, but are also exhibited when the heat insulating material 14 is provided only on the movable mold 10. Conversely, the heat insulating material 24 may be provided only on the fixed mold 20.

(Refer to the third embodiment, FIG. 4)
As shown in FIG. 4, the mold 1 </ b> C according to the third embodiment is formed by forming a heat insulating material as a coating on the inner surface of the gate 16 formed as a recess in the mold plates 11 and 21. This thermal insulation coating is a ceramic sprayed film, a metal plating film such as nickel or cobalt, a titanium-based deposition film such as titanium nitride, a titanium-based (TiN etc.) coating film, a polyimide resin (thermal conductivity 0.28 W / m · It is formed as a coating film of a heat-resistant polymer such as K). The film thickness can be arbitrarily set. The materials of the mold plates 11 and 21 and the core molds 12 and 22 are as described in the first embodiment.

  Also in the third embodiment, the heat insulating coating may be provided only on the movable mold 10 as in the modification shown in FIG. The operational effects of the present invention described below are exhibited by providing the heat insulating coating, but are also exhibited even when the heat insulating coating is provided only on the movable mold 10. Conversely, a heat insulating coating may be provided only on the fixed mold 20.

  Furthermore, the surface which comprises the gate 16 with the raw material different from this heat insulating material may be formed in the surface of the said heat insulating material. For example, the heat insulating material may be formed of a ceramic sprayed film and the surface thereof may be nickel-plated.

(Refer to the fourth to seventh embodiments, FIGS. 5 to 8)
The following fourth to seventh embodiments mainly relate to the configuration of the resin molding space 30. Basically, it will be described as a modification of the mold 1A shown as the first embodiment, but it can also be applied as a modification of the second and third embodiments.

  FIG. 5 shows a fourth embodiment. In this mold 1A, the core molds 12 and 22 are provided with heat insulating materials 31 and 41, and the surfaces of the heat insulating materials 31 and 41 are used as surface processed surfaces of molded products. .

  FIG. 6 shows a fifth embodiment. In this mold 1A, surface processed layers 32 and 42 are formed on heat insulating materials 31 and 41 provided on the core molds 12 and 22, respectively. The surface processed layers 32 and 42 are formed by plating a non-ferrous metal material, for example, nickel.

  FIG. 7 shows a sixth embodiment. In this mold 1A, the core mold is composed of heat insulating materials 31 and 41, and the surfaces of the heat insulating materials 31 and 41 are the surface processed surfaces of the molded product.

  FIG. 8 shows a seventh embodiment. In the mold 1A, surface processed layers 32 and 42 are formed on heat insulating materials 31 and 41 which are core types. The material of the surface processed layers 32 and 42 is as shown in the fifth embodiment.

  As described above, by disposing the heat insulating materials 31 and 41 around the resin molding space 30, the surface temperature of the resin molding space when the molten resin is filled into the resin molding space 30 is kept high. The temperature difference between the surface portion (skin layer) and the center portion of the resin is small, and the residual stress generated in the subsequent pressure holding step and cooling step is reduced.

(See molding process, FIG. 9 and FIG. 10)
Next, the injection molding method according to the present invention will be described. Here, an injection molding process using the molds 1A to 1C will be described.

  FIG. 9 shows the change in the temperature of the resin in the mold along the time (horizontal axis). In FIG. 9, the curve “a” indicates the temperature change of the resin at the center portion of the gate 16, and the curve “b” indicates the temperature change of the resin at the center portion of the resin molding space 30. Further, for comparison, a curve c shows the temperature change of the resin in the central portion of the gate of the conventional mold not provided with a heat insulating material.

  In the molding, first, a resin (for example, amorphous polyolefin resin) melted at a predetermined temperature is filled into the resin molding space 30 from the runner 15 through the gate 16, and immediately after the filling is completed, the pressure holding step is started. The pressure holding step is a step of holding a predetermined pressure on the resin for a predetermined time in order to compensate for the amount of the resin filled in the resin molding space 30 slightly shrinking due to a temperature drop. 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 less, the molded product is taken out from the mold.

  The resin temperature begins to decrease immediately after filling. In a conventional mold not provided with a heat insulating material, as indicated by a curve c in FIG. 9, the resin in the gate 16 portion is lowered to a glass transition temperature or lower during the pressure-holding process (see point B) and solidifies. start. This state is shown in FIG. 10 (B), and the resin in the central portion 31 of the runner 15 and the central portion 33 of the resin molding space 30 has a glass transition temperature or higher and maintains fluidity. However, since the resin in the gate 16 portion is solidified and almost loses fluidity, no pressure is applied to the resin in the resin molding space 30, and the resin that compensates for the shrinkage is not supplied. Therefore, in the molded product, the transferability of the surface shape is lowered, and the birefringence increases due to the tensile stress to the central portion due to the shrinkage.

  On the other hand, since the metal molds 1A to 1C are provided with a heat insulating material in the gate 16 portion, as shown by a curve a in FIG. Drops below the glass transition temperature and begins to solidify. FIG. 10A shows the state of the resin at the time difference ΔA from the point B to the point A, and not only the resin in the central portion 31 of the runner 15 and the central portion 33 of the resin molding space 30 but also the central portion of the gate 16. The resin No. 32 has a glass transition temperature or higher and retains fluidity. It should be noted that the central portion 32 of the gate 16 may become the glass transition temperature at the same time that the resin of the central portion 33 becomes the glass transition temperature.

  As described above, since the resin in the gate 16 portion maintains fluidity in the pressure holding step, the resin that supplements the shrinkage in the resin molding space 30 is replenished through the gate 16. Therefore, in the molded product, the transferability is improved without deteriorating the fine shape of the surface and the surface accuracy of the smooth surface. Further, the tensile stress to the central portion due to the shrinkage of the resin is alleviated, and the birefringence is reduced, so that a high-performance molded article (optical element) can be obtained.

  Incidentally, specific examples of the glass transition temperature of the amorphous polyolefin resin are, for example, 139 ° C for ZEONEX and E48R manufactured by Nippon Zeon, and 123 ° C for ZEONEX and 330R. Further, APEL and APL5014 manufactured by Mitsui Petrochemical Industries, Ltd. are 135 ° C., and ARTON and FX4727 manufactured by JSR are 125 ° C.

  In addition, with respect to the heat insulating material provided on the gate 16, experiments were performed using various materials having thermal conductivity of 4 W / m · K, 7 W / m · K, 17 W / m · K, and 20 W / m · K. As a result, preferable transferability was obtained.

(Insulating material only on one side)
In addition, the form which provides a heat insulating material in the gate 16 part is preferable to provide in both the movable mold 10 and the fixed mold 20 as shown in FIG.1, FIG3 and FIG.4. However, as shown in FIG. 2, even if it is provided only on either the movable side or fixed side mold, it has the effect of suppressing the temperature drop of the resin in the gate portion.

  The shape of the gate 16 is usually distributed in equal sizes on the movable side and the fixed side, but this distribution may be uneven. When the heat insulating material is provided only on either the movable side or the fixed side mold, it is preferably provided on the movable side or fixed side mold in which the shape of the gate 16 is largely distributed.

(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 8, 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.

The 1st Example of the metal mold | die which concerns on this invention is shown, (A) is sectional drawing, (B) is a top view of a movable side metal mold | die. It is sectional drawing which shows the modification of the said 1st Example. The 2nd Example of the metal mold | die which concerns on this invention is shown, (A) is sectional drawing, (B) is a top view of a movable side metal mold | die. The 3rd Example of the metal mold | die which concerns on this invention is shown, (A) is sectional drawing, (B) is a top view of a movable side metal mold | die. It is sectional drawing which shows 4th Example of a metal mold | die . It is sectional drawing which shows 5th Example of a metal mold | die . It is sectional drawing which shows 6th Example of a metal mold | die . It is sectional drawing which shows 7th Example of a metal mold | die . It is a graph showing the temperature change of the resin definitive into a mold in an injection molding process using a mold according to the present invention. The state of the resin in the pressure-holding process of injection molding is shown, (A) is an explanatory view when the mold according to the present invention is used, and (B) is an explanatory view when a conventional mold is used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A-1C ... Metal mold | die 11,21 ... Template 12,22 ... Core type | mold 13,23 ... Sleeve-like heat insulating material 14, 24 ... Chip-shaped heat insulating material 15 ... Runner 16 ... Gate 30 ... Resin molding space 31,41 ... Heat insulation Material 32, 42 ... Surface processed layer

Claims (7)

An injection mold having a resin molding space, a runner portion, and a gate portion located between the resin molding space and the runner portion,
At least the surface portion of only the gate portion of the resin molding space, the runner portion, and the gate portion is composed of a heat insulating material ,
The gate portion is made of a heat insulating material fitted in a mold,
The insulation sleeve der Rukoto surrounding a core constituting a chip-shaped member or a resin molding space,
Mold for injection molding characterized by   2. The injection mold according to claim 1, wherein a surface constituting the gate portion is formed of another material on the surface of the heat insulating material. The injection mold according to claim 1 or 2 , wherein the heat conductivity of the heat insulating material is 20 W / m · K or less. The insulation is stainless steel, titanium alloy, injection mold according to any one of claims 1 to 3, characterized in that it consists either of a nickel alloy or a ceramic. An injection molding method, wherein an optical element is molded using the injection mold according to any one of claims 1 to 4 . The molten resin when causing to flow into the mold, the molded article even when completed resin filling into the resin molding space center thickness temperature according to claim 5, characterized in that the glass transition temperature or higher Injection molding method. When the molten resin flows into the mold, the thickness center temperature of the gate portion maintains the glass transition temperature even when the thickness center temperature of the molded product is equal to or lower than the glass transition temperature. The injection according to claim 5 or 6 , wherein the thickness center temperature of the molded product becomes the glass transition temperature and at the same time the thickness center temperature of the gate portion becomes the glass transition temperature. Molding method.

Images