JP5742005B2 - Injection molding method for resin molded products - Google Patents

Description

  The present invention relates to an injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method.

  In general, a resin molded product molded by an injection molding method is distorted or deformed during cooling and solidification. The distortion and deformation of these resin molded products are caused by the distribution of internal pressure (residual stress), resin temperature distribution, shear force during resin flow (resin distribution), ratio distribution of melt layer and skin layer, or crystallinity. This is caused by the distribution (in the case of crystalline resin) and the like, and further by the elastic deformation of the mold at the time of clamping, but the influence of the internal pressure (residual stress) is particularly large. Among them, in a resin molded product molded with a mold cavity having a large mold projection area relative to the mold cavity thickness in the mold opening / closing direction, the larger the mold projection area, the more resin is filled into the mold cavity. The longer the resin flow length from the gate section to the mold cavity end, or the thinner the thickness, the greater the flow resistance during injection filling, and the speed of cooling and solidification accelerates the increase in flow resistance. Therefore, the residual stress in these resin molded products increases, and the uneven distribution becomes significant, and the resulting strain and deformation of the resin molded product also increase.

  As a means for suppressing such distortion and deformation of the resin molded product due to the residual stress in the resin, an injection compression molding method and an injection press molding method are aimed at equalizing the pressure in the molten resin and alleviating the residual stress in the resin. Is often used. With reference to FIG. 5, an injection molding method of an injection molded product by an injection compression molding method or an injection press molding method will be described. FIG. 5 is a schematic cross-sectional side view of a mold showing an injection molding method of a flat plate-shaped injection molded product by an injection compression molding method or an injection press molding method, and the shape of a resin molded product to be molded is simplified for explanation. Therefore, a flat plate shape is used.

  FIG. 5A shows an injection filling process. The molten resin 10b is injected and filled from the injection unit 9 into the mold cavity 10a formed by combining the fixed mold 7 and the movable mold 8 through the resin flow path 7a disposed in the fixed mold 7. . Here, in the injection compression molding method, the mold cavity that has been clamped with a weak mold clamping force is injected and filled, and the mold is opened by a distance S by the filled molten resin pressure. On the other hand, in the injection press molding method, injection filling is performed in a state where a mold is opened by a distance S in advance. In both injection molding methods, the method of micro-opening the mold at the time of injection filling is different, but by injection filling into the mold cavity whose volume is expanded in the mold opening and closing direction by micro-mold opening, The purpose of reducing the flow resistance of the molten resin, reducing the residual stress in the molten resin, preventing the uneven distribution of the residual stress, and relaxing the residual stress in the resin are common.

  FIG.5 (b) shows the time of the start of the compression process performed in the middle of the injection filling process of Fig.5 (a) or after completion. The movable mold 8 is closed to the fixed mold 7 side by a mold clamping device (not shown), and is brought into a mold-matching state with a mold thickness L, and the mold cavity 10a is also formed as a regular mold cavity thickness l (el). The At this time, the mold clamping force is not yet applied to the mold. The molten resin 10b in the mold cavity 10a is not caused by the injection filling pressure but by the mold closing operation of the movable mold 8 toward the fixed mold 7 by the mold clamping device at the start of the compression process. Since it is filled to the end, it can be shifted to the compression step in a state where unevenness of the pressure distribution in the molten resin is suppressed as compared with the filling by the injection filling pressure of the injection unit 9.

  FIG.5 (c) shows the compression process and pressure holding process performed following FIG.5 (b). When a mold clamping force is applied to the mold as it is from the mold alignment state shown in FIG. 5 (b) and the mold is clamped, the mold is compressed in the mold opening / closing direction and elastically deformed as shown in FIG. 5 (c). The mold thickness is changed from L to L ′ (L> L ′) in a state where a predetermined mold clamping force F necessary for shaping the resin molded product is applied, and the mold cavity thickness of the mold cavity 10a is also l. To l ′ (l> l ′). In a general injection compression molding method and injection press molding method, the compression step shown in FIG. 5C is maintained as it is to perform a pressure holding step, and the resin molded product is cooled and solidified.

  FIG.5 (d) is a pressure holding process performed subsequent to the compression process of FIG.5 (c) by the patent document etc. which are mentioned later, Comprising: The process performed by the general injection compression molding method and the injection press molding method However, it will be explained in advance. In this pressure holding process, a mold clamping force for reducing the mold clamping force F in the compression process to a mold clamping force f (F> f) for the purpose of reducing the internal pressure of the molten resin and alleviating the residual stress in the resin. Mitigation control is performed. By this mold clamping force relaxation control, the molten resin internal pressure in the mold cavity is lowered, and the molten resin still having fluidity inside the skin layer can be moved, and the residual stress in the resin can be relaxed. The mold thickness is changed from L ′ to L ″ (L ″> L ′) by the mold clamping force relaxation control, and the mold cavity thickness of the mold cavity 10a is also changed from l ′ to l ″ (l ″> l ′). become.

  FIG. 5E shows a product take-out process in which the flat resin molded product 10 is held by the movable mold 8 and opened after the pressure-holding process of FIG. 5C (or FIG. 5D). . The thickness of the flat resin molded product 10 is approximately l. After the mold opening, the plate-shaped resin molded product 10 is pushed out of the movable mold 8 by a product push-out means (not shown) disposed on the movable mold 8 and is carried out of the mold by a product take-out means (not shown).

  However, even if the residual stress in the molten resin is reduced by such injection compression molding method or injection press molding method, the residual stress distribution in the molten resin is reduced by preventing the uneven distribution of the residual stress distribution. Since the predetermined clamping force F necessary for shaping the resin molded product is applied to the molten resin, the uneven state of the residual stress distribution in the molten resin as described above is completely or evenly uniform. It is not necessarily converted. Here, as shown in FIG. 5 (d), the residual stress distribution in the molten resin is controlled by controlling the mold clamping force (compression force) as described above in the pressure-holding step after the compression step. It has been found that the uneven state is further relaxed and the residual stress relaxation effect in the resin is improved, and in particular, molding of optical disk substrates such as CD and DVD that require high smoothness and low refractive index properties, Various mold clamping force relaxation control methods that are employed in the injection compression molding method and the injection press molding method have been proposed for molding large panel-shaped molded products and the like for which it is difficult to suppress the amount of distortion and deformation.

  Patent Document 1 discloses a molding method in which a thin optical disk substrate such as a DVD is molded by an injection molding method or an injection compression molding method, and rapidly increases from a maximum clamping pressure or a maximum compression force (P1) to a pressure (P2). In the molding method in which cooling is performed while maintaining the pressure (P2), the pressure is rapidly reduced to a low pressure (P3) during a short period of time just before the cooling step is completed and the mold opening operation starts. An optical disk substrate forming method for performing pressure fluctuation operation is disclosed.

Patent Document 2 discloses a method for producing a polycarbonate resin substrate for an optical recording medium, which is formed by injection compression molding and has a diameter of 80 mmΦ to less than 150 mmΦ and a thickness of 1.0 mm to 1.5 mm. A first process of filling the mold, a second process of compressing and transferring a fine pattern on the stamper, a third process of holding and cooling the resin in the mold, and opening the mold to And a mold temperature is maintained at a temperature 10 to 40 ° C. lower than the glass transition point Tg of the resin, and the pressure P1 applied per unit area of the substrate in the first process is 0 ≦ P1 <. and 220 kgf / cm ^2, the pressure P2 of the second step and ^{220 ≦ P2 <430kgf / cm 2} , by controlling the pressure in two stages in the third process, the pressure P3, P4 P4 + 60 ≦ P3 <P2- 0 kgf / cm ² and,, 80 ≦ P3 <220kgf / cm 2, 0 ≦ P4 < set so that 80 kgf / cm ^2, and the time required for the first step and second step, i.e., the start injection filling The time from application of pressure P2 to the end of application of pressure P3 is set to less than 3 seconds, and the timing for changing the pressure from pressure P3 to pressure P4 is 3 seconds or more after resin filling, and 5 seconds does not pass A method for manufacturing a resin substrate for an optical information recording medium is disclosed.

  Patent Document 3 discloses an injection molding method suitable for manufacturing a large-sized panel-shaped synthetic resin molded product such as an automobile back panel, in which a synthetic resin is injected and filled into a mold cavity, and the cavity is formed by resin pressure in the mold. After the mold gate is slightly opened in the thickness direction, the mold gate is mechanically or cooled and sealed, and then compression-molded by further reducing the clamping force in the holding pressure or cooling state through the compression state. An injection molding method for a synthetic resin molded product is disclosed.

  Patent Document 4 discloses a mold clamping pressure control method suitable for injection compression molding of an optical system component that becomes a defective product when the light transmittance changes due to internal strain, and is a mold die used for injection compression molding. The opening / closing amount of the mold clamping pressure control valve, which controls the clamping pressure by adjusting the hydraulic pressure in the clamping cylinder, is controlled by an electrical signal indicating the valve opening / closing amount, and the resin temperature is detected by the resin temperature sensor and converted in advance. Whenever one of a series of electrical signals corresponding to a set of pressure switching temperature set values matches as a result of the comparison operation, a pressure switching signal is sequentially output once, and preset each time a pressure switching signal is input A series of electrical signals instructing the valve opening / closing amount corresponding to each of the set pressure values are sequentially output one by one to change the opening / closing amount of the mold clamping pressure control valve and to change the mold clamping pressure. Clamping pressure control method of the injection compression molding which is disclosed as.

JP 2002-113754 A JP-A-8-192450 JP-A-5-031774 Japanese Patent Laid-Open No. 1-146720

  In recent years, due to global environmental problems, there has been an active movement to reduce the weight of glass parts such as metal exterior panels for automobiles and sunroofs to resin-molded products such as resin exterior panels and glass resin substitutes. . Resin molded products such as exterior panels and sunroofs are required to have low distortion, high component dimensional accuracy, and high smoothness and translucency from both the design and functional aspects. Therefore, an injection compression molding method or an injection press molding method is often selected as a molding method for these resin molded products. Furthermore, in order to improve the smoothness and translucency of these resin molded products, various methods for relaxing the clamping force (compression force) during molding in the pressure-holding process as in Patent Document 1 to Patent Document 4 described above. Adoption of a mold clamping force relaxation control method is expected. However, for resin molded products having a large size that are molded with a mold cavity having a large mold projection area with respect to the thickness of the mold cavity in the mold opening / closing direction, such as exterior panels and sunroofs, the mold cavity as described above is used. In addition to the residual stress generated in the molten resin and the uneven distribution thereof, new factors of distortion and deformation of the resin molded product are generated. This is due to the use of a larger mold, unlike the molding of an optical disk substrate such as a CD or DVD, and is an elastic deformation in which the mold is compressed and deformed in the mold opening and closing direction when the mold is clamped. Under this elastic deformation, the mold cavity shape is also deformed, so that the resin molded product molded therein is also molded with a deformed mold cavity shape different from the desired shape.

As shown in the graph of Fig. 6 which gathered general data from the knowledge of the applicant who is also an injection molding machine manufacturer and has a development department that actually performs injection molding by experimental machines, the gold used for molding resin molded products The mold volume (vertical axis) increases in proportion to the product projection area (horizontal axis) of the resin molded product molded by the mold. As described above, resin molded products such as exterior panels and sunroofs for automobiles and the like have a product projection area larger than that of optical disks such as CD and DVD (144 cm ² / sheet with a diameter of 12 cm) and more than 500 cm ² . For example, taking a sunroof resin part of an automobile with a product projection area of 7000 cm ² as an example, assuming that the mold is a solid metal cube, the mold opening / closing direction during mold clamping under general preconditions The approximate amount of elastic deformation (compression amount) is shown below.
-Transparent resin material: PC (polycarbonate)
(Heat shrinkage rate = 5/1000, elastic modulus = 2300 N / mm ² )
-Size: 1000 mm x 700 mm x 5 mmt (product projected area 7000 cm ² )
・ Mold size: 1500mm x 1200 x 1800mmt
(Fixed mold + movable mold / mold volume: 3.24 × 10 ⁶ cm ³ )
-Mold steel: SKD equivalent (alloy tool steel for mold, elastic modulus 206000 N / mm ² )
-Clamping force: 28000K NTon (molding resin pressure = 40 MPa)
in this case,
-Elastic deformation of the mold (compression amount in the mold opening and closing direction) ≒ 13.6mm
-Converted into deformation amount of mold cavity thickness = 13.6mm x (5 / 1800mmt) ≒ 0.04mm
As described above, the mold cavity originally having a thickness of 5 mm is compressed 0.04 mm uniformly in the mold opening and closing direction over the entire mold cavity when the mold is clamped. This means that the mold cavity thickness is compressed by 0.8% in the mold opening and closing direction. The compression ratio 0.8% in the mold opening / closing direction is sufficiently small as a ratio, and may be within an allowable error range of the thickness of the sunroof resin-molded part. However, in actual molding, as described below, the 0.8% may be increased, but not decreased.

As shown in FIG. 5 (c), the rough estimation is that the mold clamping force is evenly applied to the plane parallel to the mold dividing surface, and the elastic deformation amount in the thickness direction of the mold and the resin molded product is the mold. Although it was calculated on the assumption that the surface is evenly distributed in the plane parallel to the dividing surface, in reality, the distribution of the mold clamping force applied to the mold and the amount of elastic deformation in the mold opening and closing direction is the same as the mold dividing surface. Not even across the parallel surfaces. That is, the compression process to obtain the mold thickness L ′ and the resin molded product thickness l ′ shown in FIG. 5C is performed in an injection molding machine 1 equipped with a general toggle type mold clamping device as shown in FIG. The fixed mold 7 and the movable mold 8 are attached to the fixed plate 2 and the movable plate 3 of the injection molding machine 1 and clamped by the toggle type mold clamping device 4, so that the fixed plate 2 and the movable mold 8 are moved by the mold clamping force. The board 3 is elastically deformed so as to be bent at the penetrating portion of the tie bar 5 like a fixed board 2 ′ and a movable board 3 ′ indicated by broken lines. Therefore, the resin molded product 10 in the mold cavity 10a of FIG. 7 is also elastically deformed so as to be curved as shown in FIG. As a result, the thickness of the resin molded product 10 after elastic deformation is l ′, l ₁ ′, l ₂ ′, l ₃ ′ (l ′> l ₁ ′> l ₂ ′> l ₃ depending on the distance from the tie bar 5. '), And the amount of elastic deformation of each thickness portion is also uneven. 7 and 8 are side (cross-sectional) views, but even in a plan (cross-sectional) view, it may be considered that the mold between the tie bars 5, the mold cavity 10a, and the resin molded product 10 are elastically deformed so as to be curved. .

  As described above, the distribution of the clamping force in the plane parallel to the mold dividing surface is such that the portion closest to the tie bar that penetrates the fixed plate and the movable plate in an injection molding machine equipped with a general toggle type clamping device. The distribution is the largest, the smaller the distance from the tie bar, and the smallest in the center. Further, in the case of an injection molding machine equipped with a direct pressure type mold clamping device, the mold clamping force at the center of the mold is larger than that of the toggle type mold clamping device. In addition, the actual mold is not a solid metal cube as assumed in the previous estimation, but various spaces are unevenly arranged inside the mold cavity of various shapes and the built-in product extrusion mechanism. Since the mold clamping device of the injection molding machine that applies the mold clamping force to the mold is not mechanically accurate, the distribution of the mold clamping force on the mold dividing surface is not good. It becomes uniform and the elastic deformation distribution of the mold becomes uneven. Therefore, the shape of the mold cavity is also elastically deformed unevenly, and the shape of the resin molded product molded therein is different from the desired shape of the resin molded product. In view of these, resin molded products such as exterior panels and sunroofs for automobiles that use larger molds than those for optical disk substrate molding such as CD and DVD are molded by an injection compression molding method or an injection press molding method. For this purpose, it is necessary to reduce the amount of elastic deformation of the mold cavity at the time of clamping to suppress the deformation of the mold cavity shape, and to approach the specification shape of the resin molded product.

  Here, in Patent Document 1 to Patent Document 4, various controls for reducing the mold clamping force (compression force) in the pressure-holding process in order to relieve the residual stress in the molten resin injected and filled into the mold cavity. Although a method is disclosed, nothing is mentioned about reducing the amount of elastic deformation of the mold cavity during mold clamping as described above and suppressing deformation of the mold cavity shape. In Patent Document 1 and Patent Document 2, the target resin molded product is an optical disk substrate or a resin substrate for an optical information recording medium (both substrates such as a CD or a DVD), and the mold is small. It is estimated that the elastic deformation of the mold cavity has little influence on the shape of the resin molded product. In Patent Document 3, the target resin molded product is a large-sized panel-shaped synthetic resin molded product such as a back panel for automobiles, but the corner portion and the inner periphery of the end portion that easily occur due to the shape of the resin molded product. There is no mention of a method for reducing sink marks and cracks, which reduces the amount of elastic deformation of the mold cavity during mold clamping and suppresses the deformation of the mold cavity shape. In Patent Document 4, the target resin molded product is not particularly specified, and it is said that it is a mold clamping pressure control method suitable for injection compression molding of optical system parts. Furthermore, nothing is mentioned about reducing the amount of elastic deformation of the mold cavity during mold clamping and suppressing the deformation of the mold cavity shape.

  The present invention has been made in view of the above-described problems. Specifically, in an injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method, a mold at the time of clamping By reducing the amount of elastic deformation of the cavity to suppress the deformation of the mold cavity shape, and by making the deformation of the mold cavity shape less than the allowable deformation amount of the resin molded product molded in the mold cavity, low distortion An object of the present invention is to provide an injection molding method for molding a resin molded product having high dimensional accuracy and having high smoothness and translucency.

The above object of the present invention is, as shown in claim 1, in an injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method.
An injection filling process in which a resin amount obtained by adding a cooling solidification shrinkage amount calculated in advance based on the resin molded product is injected and filled into a mold cavity formed by combining a set of molds;
A compression step in which the mold is clamped with a first mold clamping force necessary for shaping the resin molded product during or after the injection filling step,
Following the compression step, the amount of elastic deformation of the mold cavity based on the relationship of the amount of elastic deformation of the mold cavity with respect to the elastic deformation of the stationary platen and the movable platen due to the mold clamping force obtained in advance by analysis. A pressure holding step in which mold clamping force relaxation control is performed in which the first mold clamping force is reduced to a second mold clamping force that is equal to or less than an allowable deformation amount of the resin molded product;
It is achieved by an injection molding method characterized by comprising:

That is, in the injection compression molding method or the injection press molding method, the resin in the mold cavity is injected by an injection filling process in which a resin amount obtained by adding a cooling solidification shrinkage calculated in advance based on a resin molded product to be molded is injected and filled. Even if the cooling and solidification of the resin progresses and the resin volume shrinks, the mold cavity is filled with the resin without any gap until the mold is opened through the compression process and the pressure holding process, and the resin in the mold cavity passes through the mold. Since the mold clamping force (compression force) can be applied evenly, the adhesion between the resin molded product and the inner surface of the mold cavity is improved, and the mold can be mounted regardless of the progress of cooling and solidification shrinkage of the resin molded product. Therefore, the resin molded product can be cooled stably. In addition, following the compression process in which the mold is clamped with the first mold clamping force necessary for shaping the resin molded product, mold clamping force relaxation control is performed in which the first mold clamping force is reduced to the second mold clamping force. The pressure in the molten resin in the mold cavity is reduced by the pressure-holding step performed, and the molten resin still having fluidity inside the skin layer can be moved, and the residual stress in the resin can be relaxed. Further, the second mold clamping force is determined based on the relationship between the elastic deformation amount of the mold cavity and the elastic deformation amount of the mold cavity with respect to the elastic deformation of the fixed platen and the movable platen obtained by the analysis in advance. Since the mold clamping force is less than the allowable deformation rate of the resin molded product, the amount of elastic deformation of the mold cavity is the mold cavity at the final stage of the pressure holding process where the mold clamping force is reduced to the second mold clamping force. Therefore, the amount of distortion and deformation of the resin molded product can be reduced to the allowable deformation amount or less. In addition, since the second mold clamping force is applied to the mold until the mold opens, the mold cavity has an elastic deformation amount equal to or less than an allowable deformation amount of the resin molded product to be molded therein. The resin molded product molded with the amount of resin added with the amount of cooling solidification shrinkage calculated in advance and the adhesion between the mold cavity inner surface and the uniform clamping force application state are maintained, and the resin molded product is cooled. Regardless of the progress of solidification shrinkage, stable cooling of the resin molded product through the mold can be continued until the mold is opened.

Further, according to a second aspect of the present invention, a mold cavity thickness T at one point in the mold cavity is one end of the mold cavity in the mold opening / closing direction before the mold clamping force is applied. A distance in the mold opening and closing direction from the plane parallel to the mold dividing surface and passing through the certain point to the mold cavity surface facing the plane,
The amount of elastic deformation of the mold cavity is expressed as T′−T when the mold cavity thickness T is T ′ when the mold is elastically deformed by applying a certain clamping force. It is defined by the largest displacement TH _MAX among the displacement TH of the mold cavity thickness at the certain point,
The specified thickness t at one point of the resin molded product is a plane that is in contact with one of the end portions in the mold opening / closing direction of the mold cavity where the resin molded product is molded, and is parallel to the mold dividing surface. A distance in a direction perpendicular to the plane through the certain point to the surface of the resin molded product facing the plane or to the opposite side of the surface;
When the allowable deformation amount of the resin molded product is t ′ in the resin molded product after molding when the specified thickness t of the resin molded product is t′−t, the resin molding at the certain point represented by t′−t The injection molding method according to claim 1, wherein the injection molding method is defined by the largest allowable thickness error th _MAX among the thickness error th of the product.

  Originally, various shapes of mold cavity shapes and deformation of resin molded products molded in the mold cavities should be defined in three dimensions. However, if these deformations are defined three-dimensionally, defining this as one of the quality control values in the allowable deformation amount of the resin molded product itself is a complicated operation. Therefore, the elastic deformation amount representing the deformation amount of the mold cavity and the allowable deformation amount representing the allowable deformation amount of the resin molded product molded in the mold cavity are mainly deformations in the thickness direction. Paying attention to this, it is defined by the maximum value of the difference in the distance in the thickness direction before and after deformation from a common reference plane to the shape facing the common reference plane passing through that point at one point in the shape. For example, since each deformation is defined by the same simple one-dimensional numerical value, it is easy to specify this as one of quality control values in the allowable deformation amount of the resin molded product. Direct comparison can be made with one-dimensional numerical values obtained by definition.

  In addition, as shown in claim 3, the pressure holding step is started before reaching the glass transition temperature in the case of an amorphous resin, and before reaching the crystallization temperature in the case of a crystalline resin, It is preferable that the injection molding method according to any one of claims 1 to 2, wherein the injection molding method is completed after a predetermined time has elapsed after reaching the heat deformation temperature defined by ASTM D648.

  The pressure holding process in which mold clamping force relaxation control is performed to reduce the mold clamping force from the first mold clamping force to the second mold clamping force reduces the pressure inside the molten resin in the mold cavity and still flows inside the skin layer. In order to relieve the residual stress in the resin by moving the molten resin and supply the flowable resin to each part of the resin molded product that solidifies and shrinks as the cooling solidification progresses, In order to maintain the adhesion between the resin molded product in the mold cavity and the inner surface of the mold cavity by applying, the cooling of the resin molded product through the mold proceeds and the molding cycle time is shortened. In the case of a crystalline resin, it is necessary to start at a temperature above the glass transition temperature, and in the case of a crystalline resin, it must be started at a temperature above the crystallization temperature. In addition, the elastic deformation amount of the mold cavity is fixed below the allowable deformation amount of the resin molded product by completing the pressure holding process after a predetermined time has elapsed after reaching the heat deformation temperature defined by ASTM D648 or the like. In this state, the product can be taken out.

  According to a fourth aspect of the present invention, in the pressure holding step, the pressure is reduced in a plurality of steps from the first mold clamping force to the second mold clamping force, and the number of steps and the mold clamping in each step are determined. The injection molding method according to any one of claims 1 to 3, wherein mold clamping force relaxation control capable of arbitrarily setting, changing, and managing the force and the duration is performed. .

  If the pressure-holding process is such that mold clamping force relaxation control is performed in which the pressure is linearly reduced from the first mold clamping force to the second mold clamping force, the first mold is in addition to the first mold clamping force and the second mold clamping force. Only the time from the clamping force to the second mold clamping force can be set. However, if the mold clamping force relaxation control is configured in this way, the pressure holding process pattern in which the pressure is reduced in a plurality of steps from the first mold clamping force to the second mold clamping force is changed to the number of steps and the mold at each step. Since numerical values can be arbitrarily set, changed, and managed by the tightening force and the duration, it is possible to set, change, and manage a mold clamping force relaxation control pattern that reduces distortion and deformation for each molded product in detail.

  Next, as shown in claim 5, the mold clamping force relaxation control is performed such that a minute mold opening is performed after the pressure is reduced from the first mold clamping force to the second mold clamping force. The injection molding method according to any one of claims 1 to 4 may be used.

  At the final stage of the pressure-holding process, by performing micro mold opening just before mold opening, the mold clamping force (compression force) applied to the resin molded product is completely released, and the elastic deformation amount of the mold cavity is made zero. At the same time, the residual stress of the resin molded product can be minimized. In addition, a minute gap is formed between the inner surface of the mold cavity and the resin molded product by opening the micro mold, so that the minute gap functions as a heat insulating layer, and the amount of heat of the resin molded product moves to the inner surface of the mold cavity. In order to suppress, that is, to reduce the cooling rate of the resin molded product, the resin molded product has the same effect as the annealing treatment (heat treatment for removing stress), and can further obtain a residual stress relaxation effect in the resin. .

  Next, as shown in claim 6, the mold clamping force relaxation control is obtained by actual molding by the mold clamping force relaxation control in which the pressure is reduced from the first mold clamping force to the second mold clamping force. When the thickness error th at an arbitrary point of the resin molded product and the thickness error th ′ at the arbitrary point obtained by analysis under the same molding conditions as the actual molding are different by a predetermined amount or more, The at least one of the first mold clamping force, the second mold clamping force, the number of steps, the mold clamping force of each step, and the duration is corrected so that th = th ′. The injection molding method according to any one of Items 4 to 5 may be used.

  The relationship between the mold cavity's elastic deformation and the amount of elastic deformation of the mold cavity is obtained in advance by analysis using commercially available analysis software and a computer, etc., so the actual molding result may differ from the analysis result. It is done. If the difference is a slight difference that does not cause a problem, the analysis result is considered to have simulated the actual molding almost accurately. However, when the difference is more than a predetermined amount and the deformation amount of the resin molded product exceeds the allowable deformation amount, there is a case where it is very difficult and time consuming to clarify the cause of the difference. Many. Therefore, if the items to be compared with the items to be compared and the items to be corrected are specified in advance, even if such a difference occurs, it will not take time or cost to pursue the factors. The present invention can be carried out in a state where the correction contents are clarified.

Next, as shown in claim 7, a primary molding step in which a primary molded body is molded by injection filling a first cavity formed by combining a core mold and a first cavity mold,
The second cavity mold in which the second cavity is formed in combination with the core mold holding the primary molded body and the first cavity mold are switched relative to the core mold. In the injection molding method for molding a two-layer molded product, which has a secondary molding step of injection-filling the second cavity and laminating a secondary molded body on at least a part of the surface of the primary molded body,
The injection molding method according to any one of claims 1 to 6 is performed in at least one of the primary molding step and the secondary molding step, and a two-layer molded product is molded. It may be an injection molding method.

  Resin molded products such as automobile exterior panels and sunroofs that are molded by the injection compression molding method or injection press molding method, the rib structure portion for reinforcement, the mounting portion for assembly, etc. Often provided at the periphery. Insert molded resin parts such as automobile exterior panels and sunroofs into molds of other injection molding machines, and use them for reinforcing rib structures and assembly parts on the surface and periphery of these resin molded parts. In some cases, the mounting part and the like are laminated, and the mold for primary molding and secondary molding is switched by various methods in the mold clamping device, and the lamination is performed by a single injection molding machine. Molding-only injection molding machines have been put into practical use, and in many cases, these molding-specific injection molding machines are laminated. Since the injection molding method of the present invention does not require a special mechanism or device to be provided on the mold or the injection molding machine side, at least one of the primary molding process and the secondary molding process in these injection molding machines dedicated to lamination molding. It can be employed in an injection compression molding method or injection press molding method performed in one step.

The injection molding method according to the present invention is an injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method.
An injection filling process in which a resin amount obtained by adding a cooling solidification shrinkage amount calculated in advance based on the resin molded product is injected and filled into a mold cavity formed by combining a set of molds;
A compression step in which the mold is clamped with a first mold clamping force necessary for shaping the resin molded product during or after the injection filling step,
Following the compression step, the amount of elastic deformation of the mold cavity based on the relationship of the amount of elastic deformation of the mold cavity with respect to the elastic deformation of the stationary platen and the movable platen due to the mold clamping force obtained in advance by analysis. A pressure holding step in which mold clamping force relaxation control is performed in which the first mold clamping force is reduced to a second mold clamping force that is equal to or less than an allowable deformation amount of the resin molded product;
In the injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method, the amount of elastic deformation of the mold cavity during mold clamping is reduced to suppress the deformation of the mold cavity shape, Resin molded product with low distortion, high part dimensional accuracy, high smoothness and translucency by reducing deformation of mold cavity shape below allowable deformation amount of resin molded product molded in mold cavity Can be molded.

It is a schematic longitudinal cross-sectional view which shows the elastic deformation at the time of the mold clamping of the mold cavity and resin molded product in case the resin molded product which concerns on Example 1 of this invention is flat form. It is a schematic longitudinal cross-sectional view which shows the elastic deformation at the time of the mold clamping of a metal mold cavity and a resin molded product in case the resin molded product which concerns on Example 1 of this invention is convex shape (concave shape). It is operation | movement explanatory drawing of the control system of the mold clamping force and mold | die opening amount of the injection molding method which concerns on Example 1 of this invention. It is operation | movement explanatory drawing of the control system of the mold clamping force and mold | die opening amount of the injection molding method which concerns on Example 2 of this invention. It is a general | schematic cross-section side view of the metal mold | die which shows the injection molding method of the flat plate-shaped injection molded product by the injection compression molding method or the injection press molding method. It is a graph which shows the relationship between the product projection area of a resin molded product, and die volume. It is a schematic side view of an injection molding machine showing a state where the mold does not elastically deform evenly in the mold opening and closing direction during mold clamping. It is a schematic sectional side view which shows the elastic deformation state of the resin molded product in the metal mold cavity in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic longitudinal sectional view showing elastic deformation at the time of clamping a mold cavity and a resin molded product when the resin molded product according to Example 1 of the present invention has a flat plate shape. The left side of FIG. 1 (a) is a mold cavity in a state before a mold clamping force in which a fixed mold and a movable mold are combined, and the right side of FIG. 1 (a) is elastically deformed by the mold clamping force. The mold cavity is shown. The left side of FIG. 1 (b) shows the specification shape of the flat plate-shaped resin molded product molded in the mold cavity of FIG. 1 (a), and the right side shows the shape of the flat plate-shaped resin molded product actually molded. FIG. 2 is a schematic longitudinal sectional view showing elastic deformation at the time of clamping the mold cavity and the resin molded product when the resin molded product according to Example 1 of the present invention has a convex shape (concave shape). The left side of FIG. 2 (a) is a mold cavity in a state before the mold clamping force in which the fixed mold and the movable mold are combined, and the right side of FIG. 2 (a) is elastically deformed by the mold clamping force. The mold cavity is shown. The left side of FIG. 2 (b) is the specification shape of a convex (concave) resin molded product molded in the mold cavity of FIG. 1 (a), and the right side is the convex shape (concave shape) actually molded. The shape of a resin molded product is shown. FIG. 3 is an operation explanatory view of a mold clamping force and mold opening amount control system of the injection molding method according to Embodiment 1 of the present invention.

  First, the elastic deformation amount of the mold cavity and the allowable deformation amount of the resin molded product with respect to the mold clamping force when the resin molded product has a flat plate shape will be described with reference to FIG. As shown on the left side of FIG. 1 (a), a fixed mold 7 and a movable mold 8 are combined with each other to form a mold cavity 10a for molding a flat resin molded product 10. This shows a state in which the mold clamping force is not applied to the mold, and the mold is not just elastically deformed just by matching the mold. In this state, the mold cavity thickness at one point 20 in the mold cavity 10a is from a plane 20a that is in contact with one end of the mold cavity 10a in the mold opening / closing direction and parallel to the mold dividing surface. The distance T (arrow) in the mold opening / closing direction passes through a certain point 20 to the mold cavity surface 20b facing the flat surface 20a. Since it is a mold cavity for molding a flat resin molded product, the mold cavity thickness in the mold opening / closing direction is constant, and the mold cavity thickness is T at any point in the mold cavity 10a. Based on this assumption, the elastic deformation amount of the mold cavity with respect to the mold clamping force will be described.

In the first embodiment, the mold clamping device of the injection molding machine is a toggle type mold clamping device. When a mold clamping force is applied to the matched mold, the mold and the mold mounting plate are elastically deformed so as to bend between the tie bars as described above, so that the mold cavity 10a is also shown in FIG. (A) It is elastically deformed as shown on the right side. In this state, the mold cavity thickness at a certain point 20 in the mold cavity 10a is determined from a plane 20a that is in contact with one end of the mold cavity 10a in the mold opening / closing direction and parallel to the mold dividing surface. It is represented by a distance T ₁ ′ (arrow) in the mold opening / closing direction from a certain point 20 to the mold cavity surface 20b facing the plane 20a. As described above, since the amount of elastic deformation in the mold opening / closing direction is not uniform within the mold cavity 10a, for example, the mold cavity thickness at a different point 20 ′ is T ₂ ′ (arrow). Here, the displacement TH of the mold cavity thickness of the mold cavity 10a at a certain point 20 is defined as T ₁ '-T. The mold cavity thickness T before the mold clamping force is applied is constant, but the mold cavity thickness T ′ after mold clamping is various values such as T ₁ ′ and T ₂ ′. The amount of displacement TH also has various values. The numerical value of the displacement TH is large in the vicinity of the tie bar of the mold cavity 10a where the amount of elastic deformation in the mold opening / closing direction is large and in the portion where the rigidity of the mold is low. Therefore, in the present invention, the deformation of the mold cavity shape with respect to a certain clamping force is defined by the largest displacement amount TH _MAX among the displacement amount TH of the mold cavity thickness due to this elastic deformation, and the mold with respect to a certain clamping force is defined. This is called the amount of elastic deformation of the cavity. Therefore, the relationship of the amount of elastic deformation of the mold cavity with respect to the mold clamping force means a change in the amount of elastic deformation of the mold cavity with respect to the mold clamping force when the mold clamping force is changed.

The deformation due to the elastic deformation of the mold cavity when a certain clamping force is applied can be more accurately defined when defined in three dimensions. However, if these deformations are defined in three dimensions, as described above, it is a complicated task to define this as one of the quality control values in the allowable deformation amount of the resin molded product. Therefore, paying attention to the fact that the amount of elastic deformation representing the amount of deformation of the mold cavity is mainly the deformation in the mold opening and closing direction, the deformation of the mold cavity is the amount of elastic deformation of the mold cavity, and the elastic deformation as described above. If it is defined by the largest displacement amount TH _MAX among the displacement amount TH of the mold cavity thickness due to, it is defined by a simple one-dimensional numerical value, so as one of the quality control values in the allowable deformation amount of the resin molded product It is easy to specify this, and each deformation can be directly compared with a one-dimensional numerical value obtained by this definition. In addition, the mold cavity thickness at a certain point 20 in the mold cavity 10a is not simply the distance in the mold opening / closing direction at the certain point 20, but is a reference plane (20a) that is common to only one point at all points. Is considered in view of the correlation with the allowable deformation amount of the resin molded product, and will be described in detail later.

  Next, the allowable deformation amount of the resin molded product will be described. The left side of FIG. 1B is a specification shape of a flat resin molded product 10. In this state, the thickness of the resin molded product 10 at a certain point 30 in the resin molded product 10 is a plane that is in contact with one end of the mold opening / closing direction of the mold cavity 10a in which the resin molded product 10 is molded, and It is represented by a distance t (arrow) in a direction perpendicular to the plane 30a from the plane 30a parallel to the mold dividing surface, through a certain point 30, to the resin molded product surface 30b facing the plane 30a. This is called the specification thickness. Since it is a flat plate-shaped resin molded product, its specification thickness is constant, and the resin molded product thickness is the specified thickness t at any point in the resin molded product 10. The relationship between the resin molded product 10 and the mold cavity 10a in which the resin molded product 10 is molded is a shape except for changes from the resin molded product specifications such as cooling and solidification shrinkage that should be considered when designing the mold. And the dimensions may be considered the same. (T = t) The allowable deformation amount of the resin molded product will be described on the assumption of this.

When a mold clamping force is applied to the mold and the mold cavity 10a is elastically deformed as shown on the right side of FIG. 1A, the resin molded product 10 molded in the deformed mold cavity 10a is also shown in FIG. (B) Not the specification shape shown on the left side, but the shape shown on the right side of FIG. 1 (b), which is the same as the shape of the elastically deformed mold cavity 10a shown on the right side of FIG. 1 (a). A two-dot chain line on the right side of FIG. 1 (b) shows the specification shape of the resin molded product 10. The thickness of the resin molded product at a certain point 30 in the resin molded product 10 in this state is also a plane that is in contact with one of the end portions in the mold opening / closing direction of the mold cavity 10a in which the resin molded product 10 is molded, and the mold is divided. A distance t ₁ ′ (arrow) in a direction perpendicular to the plane 30a from the plane 30a parallel to the plane to a resin molded product surface 30b facing the plane 30a through a certain point 30 is represented. As described above, since the thickness of the resin molded product is not uniform within the resin molded product 10 in the same way as the amount of elastic deformation in the mold opening / closing direction, for example, the thickness of the resin molded product at a different point 30 ′ is t ₂ ′ (arrow). It becomes. Here, a thickness error th between the thickness of the resin molded product 10 and a specified thickness t at a certain point 30 is t ₁ ′ −t, and the specified thickness t of the resin molded product is constant. Since 'has various values such as t ₁ ' and t ₂ ', the thickness error th of the resin molded product 10 also has various values. Therefore, in the present invention, the deformation allowed for the resin molded product is defined by the largest thickness error th _MAX among the thickness errors th and is referred to as the allowable deformation amount of the resin molded product. The definition of the deformation of the resin molded product is common as one of quality control items of the resin molded product in the manufacturer of the resin molded product.

The deformation of the resin molded product can be more accurately defined if it is defined in three dimensions. However, similar to the deformation caused by the elastic deformation of the mold cavity described above, the deformation allowed for the resin molded product is the actual molded product with respect to the specified thickness of the resin molded product as the allowable deformation amount of the resin molded product. If it is defined by the largest thickness error th _MAX among the thickness errors th, it is easy to define this as one of quality control values because it is a simple one-dimensional numerical definition. In addition, the mold cavity thickness at a certain point 20 in the mold cavity 10a is not simply set as the distance in the mold thickness direction at the certain point 20, but is a reference plane (20a) that is common to only one point at all points. The definition of the deformation of the mold cavity is substantially the same as the above-described definition of the deformation of the resin molded product, which is one of the quality control items of the resin molded product in the resin molded product manufacturer. This is because each deformation can be directly compared with a one-dimensional numerical value obtained by this definition.

Next, the elastic deformation amount of the mold cavity and the allowable deformation amount of the resin molded product with respect to the clamping force when the resin molded product has a convex shape (concave shape) will be described with reference to FIG. The expression “convex shape (concave shape)” is because it can be defined as any shape depending on whether the design surface is the convex side or the concave side. Since the definition of the elastic deformation amount of the mold cavity and the allowable deformation amount of the resin molded product with respect to the clamping force when the resin molded product is a flat plate shape is basically the same, only the differences will be described. As shown on the left side of FIG. 2 (a), a mold cavity 10a for molding a convex-shaped (concave-shaped) resin molded product 10 'by aligning a fixed mold 7' and a movable mold 8 '. 'Is formed. In this state, in the case of the plate-shaped resin molded product 10, the distance T in the mold opening / closing direction of the mold cavity 10a is the same at all points in the mold cavity 10a, but a convex (concave) resin. In the case of a molded product, the mold cavity 10a ′ is a plane that is in contact with one end of the mold in the mold opening / closing direction and is parallel to the mold dividing surface, and passes through a certain point 40 to face the plane 40a. The distance T ₁ (arrow) in the mold opening / closing direction to the mold cavity surface 40b is not constant so as to be the distance T ₂ (arrow) at another point 40 ′. In an actual resin molded product, there is almost no ideal flat plate-shaped resin molded product as described above. Thus, the resin molded product having a shape in which the distance in the mold opening / closing direction from the reference flat surface 40a is not constant. Is almost. From the state shown on the left side of FIG. 2A, when a mold clamping force is applied to the mold and the mold cavity 10a ′ is elastically deformed, the state shown on the right side of FIG. 2A is obtained. (T ₁ → T ₁ ′, T ₂ → T ₂ ′) Due to the elastic deformation of the mold cavity 10 a ′, the convex (concave) resin molded product 10 ′ also has the specification shape shown on the left side of FIG. The shape shown in the right side of FIG. The mold cavity thickness of the mold cavity at a certain point, the displacement TH of the mold cavity before and after elastic deformation of the mold, and the deformation of the mold cavity shape with respect to a certain clamping force is the largest of the displacement TH The contents related to the deformation of the mold cavity, such as the amount of elastic deformation of the mold cavity defined by the displacement amount TH _MAX and referred to as the amount of elastic deformation of the mold cavity with respect to a certain clamping force, are as described above, and will not be described.

In the case of a convex (concave) resin molded product, the specification thickness t (t ₁ , t ₂ ) is not constant as in the mold cavity 10a ′ for molding the resin molded product. The specified thickness of the resin molded product 10 at a certain point, the thickness error th with the specified thickness t, and the deformation allowed for the resin molded product are defined by the largest thickness error th _MAX of the thickness error th, and the resin molded product The contents relating to the deformation of the resin molded product, such as the allowable deformation amount, are also omitted as described above.

  As described above, regardless of the shape of the resin molded product, each deformation of the mold cavity and the resin molded product is opposed to a common reference surface passing through the common reference surface at one point in the shape. If the maximum amount of difference in the thickness direction distance before and after deformation to the shape surface to be defined is defined, each deformation is defined by the same simple one-dimensional numerical value. Direct comparison can be made with the obtained one-dimensional numerical values.

  Next, an injection molding method according to Embodiment 1 of the present invention will be described with reference to FIG. First, an injection molding preparation process will be described with reference to FIG. The molding object is a flat resin molded product 10. A flat plate-shaped injection-molded product 10 to be molded, various quality control tolerance values including allowable deformation ratio of the injection-molded product 10, a molding die including a fixed die 7 and a movable die 8, and an injection molding machine 1 to be used. After the determination, first, the cooling solidification shrinkage amount of the resin molded product 10 is calculated from the resin to be used, the injection molded product 10, the mold for molding, the specifications of the injection molding machine 1, and the like. Next, using commercially available simulation software for injection molding, etc., input the molding conditions obtained from these specifications, analyze the elastic deformation of the mold cavity while changing the mold clamping force, and mold clamping force related to the mold cavity The relationship of the amount of elastic deformation to is obtained. At this time, if the amount of elastic deformation in the mold opening / closing direction of the mold cavity and the amount of deformation in the thickness direction of the resin molded product at the same point in common with the mold cavity and the resin molded product are analyzed at the same time, it is effective for the correction described later. Can be used for The obtained relationship of the elastic deformation amount to the mold clamping force related to the mold cavity is stored in the control device of the injection molding machine and is made available for use by the control program of the injection molding machine. In this analysis, it is not necessary to consider mold clamping force relaxation control in the pressure holding process described later.

  Next, an actual injection molding method will be described with reference to FIGS. FIG. 3 is an operation explanatory view of a mold clamping force and mold opening amount control system of the injection molding method according to Embodiment 1 of the present invention. As shown in FIG. 5A, an injection unit is inserted into a mold cavity 10a formed by combining a fixed mold 7 and a movable mold 8 via a resin flow path 7a arranged in the fixed mold 7. 9, an injection filling process in which the molten resin 10b is injected and filled is performed. The mold cavity is injected and filled with a mold clamping force F ′ set between mold clamping forces 0 to F, and the mold is moved by a distance S by the balance between the filling resin pressure and the mold clamping force F ′. The injection filling process of the injection compression molding method for micro-opening is the line B′-B1-B2-C shown in FIG. Further, the injection filling process of the injection press molding method in which the mold is previously opened by a distance S by a distance S is the line A'-A-C shown in FIG. The actual injection filling start point of each molding method is B1 for the former and A for the latter. In the present embodiment, the micro mold opening S in the injection compression molding method and the injection press molding method is the same for convenience. In the injection filling process of the present invention, since the resin amount obtained by adding the cooling solidification shrinkage amount calculated in advance based on the resin molded product to be molded is injection filled, the cooling solidification of the resin in the mold cavity proceeds and the resin Even if the volume shrinks, the mold cavity is filled with resin without gaps until it is opened from the compression process to the pressure holding process, so the mold clamping force is evenly applied to the resin in the mold cavity via the mold. (Compressive force) can be applied as described above. The injection compression molding method and the injection press molding method are different from each other in that the mold is opened by a distance S during injection filling, but the purpose is the same as described above. Will be omitted.

  Next, as shown by the line CK in FIG. 3, the compression process is started in the middle of the injection filling process. (It may be started after the injection filling process is completed.) As shown in FIG. 5B, the movable mold 8 is fixed by a mold clamping device (not shown) from a state where the mold is opened by a distance S. The mold is closed to the mold 7 side so that the mold is aligned with the mold thickness L, and the mold cavity 10a is also formed as a normal mold cavity thickness l (el). This is represented by the intersection K with the molding time axis in the compression step of FIG. 3, and the mold clamping force is not yet applied to the mold. The molten resin 10b in the mold cavity 10a is not due to the filling resin pressure, but the volume of the mold cavity is reduced by the mold closing operation of the movable mold 8 toward the fixed mold 7 by the mold clamping device at the start of the compression process. Therefore, the flow resistance of the molten resin in the mold cavity can be reduced as compared with the filling by the injection filling pressure of the injection unit 9, and the pressure distribution of the molten resin in the pressure distribution of the molten resin can be reduced. As described above, it is possible to shift to the compression process in a state where unevenness is suppressed.

  The compression process is continued as indicated by the line K-D-E from the line C-K in FIG. When the mold clamping force is applied to the mold as it is from the mold alignment state (point K in FIG. 3) shown in FIG. 5B and the mold is clamped, the mold clamping force applied to the mold increases, and FIG. As shown in c), the first mold clamping force F necessary for shaping the resin molded product 10 is finally reached (point D in FIG. 3) and maintained during the compression process. (Point E in FIG. 3) When the mold clamping force is applied, the mold is compressed and elastically deformed in the mold opening and closing direction, and when the mold clamping force reaches the first mold clamping force F, the mold thickness is L. To L ′ (L> L ′), and the mold cavity thickness of the mold cavity 10a also changes from l to l ′ (l> l ′). Actually, the resin molded product 10 and the mold cavity 10a are not evenly compressed and elastically deformed in the mold opening / closing direction as shown in FIG. 5 (c), but in FIG. 1, FIG. 2, FIG. 7, and FIG. As described above, the elastic deformation so as to bend between the tie bars is as described above. As the magnitude of the first mold clamping force F in this compression step, a suitable one may be selected as appropriate depending on the specifications and molding conditions of the resin molded product 10 and the molding die.

  Next, as shown by the line E-F-G in FIG. 3, a pressure holding step is performed following the compression step. In a general injection compression molding method and injection press molding method, as shown by the E-g-i line (broken line) in FIG. 3, the compression step (first clamping force F) is continued as it is and the pressure holding step. As described above, the resin molded product 10 is cooled and solidified. In the present invention, in contrast to various mold clamping force relaxation control methods for relaxing the mold clamping force (compression force) during molding, such as Patent Document 1 to Patent Document 4, during the pressure holding process, a resin molded product is used. The mold clamping force relaxation control is performed in which the first mold clamping force F necessary for the 10 shaping is reduced to a predetermined second mold clamping force f. By this mold clamping force relaxation control for reducing the pressure to a predetermined second mold clamping force f, in addition to the improvement of the residual stress relaxation effect in the resin as in Patent Document 1 to Patent Document 4, this second mold clamping force f However, based on the relationship of the amount of elastic deformation of the mold cavity to the mold clamping force obtained in advance, the mold clamping force is such that the amount of elastic deformation of the mold during mold clamping is less than the allowable deformation rate of the resin molded product. 3, in the final stage of the pressure holding process indicated by FG in FIG. 3, the elastic deformation amount of the mold cavity, that is, the deformation amount of the mold cavity is equal to or less than the allowable deformation amount of the resin molded product. The distortion amount and deformation amount of the resin molded product to be molded can be made equal to or less than the allowable deformation amount.

  Switching from the compression process to the pressure-holding process reduces the internal pressure of the molten resin in the mold cavity, moves the molten resin that is still fluid inside the skin layer, relieves residual stress in the resin, and proceeds with cooling and solidification. In order to supply a flowable resin to each part of the resin molded product that coagulates and shrinks along with, and by applying a clamping force to the mold, the resin molded product in the mold cavity and the inner surface of the mold cavity When the resin of the resin molded product 10 is an amorphous resin in order to maintain the adhesiveness and advance the cooling of the resin molded product through the mold to shorten the molding cycle time, the state is equal to or higher than the glass transition temperature. In the case of a crystalline resin, it is necessary to start at a temperature higher than the crystallization temperature. Also, after reaching the heat deformation temperature specified for each resin by ASTM D648 etc., the pressure holding process is completed after a predetermined time has elapsed, so that the elastic deformation amount of the mold cavity is the allowable deformation amount of the resin molded product. The product can be taken out in a fixed state as follows. Here, the completion timing of the pressure holding process, that is, the predetermined time after reaching the heat deformation temperature, is a balance between the effect of mold clamping force relaxation control and deformation prevention due to the product's own weight after taking out the product and the molding cycle time. In view of the above, a suitable time is selected in a timely manner.

  The present invention is not particularly specified for the resin to be used, and if it can be used for an injection compression molding method or an injection press molding method, a suitable resin that satisfies specifications such as the use, shape, cost, etc. of the resin molded product to be molded. What is necessary is just to select suitably. Specifically, the amorphous resin includes PC (polycarbonate), PMMA (polymethyl methacrylate (acrylic) resin), ABS (acrylonitrile / butadiene / styrene resin), and the crystalline resin includes POM ( Polyoxymethylene (acetal)), PET (polyethylene terephthalate), PE (polyethylene), PP (polypropylene), PA (polyamide), and the like.

  Next, as shown by the GH line in FIG. 3, following the pressure holding process, a mold opening / product taking process in which the flat resin molded product 10 is held by the movable mold 8 and opened is shown. . As shown in FIG. 5 (e), after the mold is opened, it is pushed out from the movable mold 8 by a product pushing means (not shown) arranged in the movable mold 8, and is carried out of the mold by a product taking-out means (not shown). This is as described above.

  Embodiment 2 of the present invention will be described with reference to FIG. FIG. 4 is an operation explanatory diagram of the control system for the mold clamping force and the mold opening amount of the injection molding method according to the second embodiment of the present invention. The difference between Example 2 and Example 1 is that, in the pressure holding process indicated by the line E-F-G in FIG. 3 in Example 1, the pressure is not reduced linearly as indicated by the line E-F. A micro mold opening indicated by the line h1-h2-h3 in FIG. 4 between the point where pressure is reduced in three steps indicated by the lines E-e1 to e4-F in FIG. 4 and the line FG in FIG. There are two points that are performed. Since other structural requirements and injection molding methods are basically the same as those in the first embodiment, the display of lines before point C such as the injection filling process in FIG. 4 is omitted, and only differences from the first embodiment are described. To do.

  A pressure holding process is performed following the compression process indicated by the line C-K-D-E in FIG. In the second embodiment, the second mold clamping force f that is finally reduced in pressure is the same as that in the first embodiment, but the holding pressure 1 (E−) in which the pressure holding process is reduced to the mold clamping force F1 (F> F1). e1-e2), holding pressure 2 (e2-e3-e4) for reducing the pressure to mold clamping force F2 (F1> F2), holding pressure 3 (e4-F-) for reducing the pressure to second clamping force f (F2> f) As in h1), the decompression is performed in three steps. Here, there is no significant meaning in making the pressure reduction of the mold clamping force relaxation control performed in the pressure holding process into a plurality of steps. By making the pressure reduction into a plurality of steps, the pressure reduction from the first mold clamping force F to the second mold clamping force f is not a simple linear linear pressure reduction, but the pressure reduction value, arrival timing, and maintenance time of each step. It is meaningful that the decompression process approximated to a curve shape such as a quadratic curve can be selected by setting the details and the like in detail. For example, even if the pressure reduction as shown in FIG. 4 is performed in three steps, the mold clamping forces F1 to F3 are not equal, but the pressure is increased to F1 to reduce the mold clamping force F3 from the mold clamping force F2. It is possible to reduce the pressure as a quadratic curve. Further, if the timings of e1, e3, and f1 in each step are made unequal, and the holding times e1-e2, e3-e4, and F-f1 of each mold clamping force are made unequal, the pressure is further reduced to a quadratic curve. Is possible. As described above, by reducing the pressure from the first mold clamping force F to the second mold clamping force f into a plurality of steps, the optimal mold clamping force relaxation control changes with the progress of cooling and solidification. Even if the pressure is reduced, by setting the number of steps and the respective displacement points (start point and end point) arbitrarily, it is possible to approach more optimal curved mold clamping force relaxation control. Moreover, even if complex mold clamping force relaxation control is set at the displacement point of each step (start point and end point), it is easy to set, change, and manage mold clamping force relaxation control. It can be reproduced with other injection molding machines and multiple injection molding machines.

  Next, at the final stage of the pressure holding process, as shown by the line h1-h2-h3 in FIG. Normally, if the mold cavity is filled with resin in the mold-clamped state and a predetermined mold clamping force is applied to the resin even if it is small, the resin molded product in the mold cavity and the inner surface of the mold cavity are in close contact. And a uniform clamping force application state are maintained, and cooling of the resin molded product through the mold is continued until the mold is opened. While the cooling is continued, as shown in FIG. 5 (e), when the mold opening is performed to the mold opening limit while the resin molded product 10 is held by the movable mold 8, a fixed mold for the resin molded product is obtained. Only the mold 7 side is cooled to the atmosphere at room temperature. At the time of the mold opening, the resin molded product in the mold cavity is maintained at a relatively high temperature although cooling and solidification is almost completed. Therefore, in the resin molded product 10 held by the movable mold 8, the movable mold 8 side cooled through the mold and the fixed mold 7 that is allowed to cool to the atmosphere at room temperature at once by opening the mold. A sudden temperature gradient occurs in the mold opening and closing direction. Depending on the thickness of the resin molded product 10 in the mold opening / closing direction and the projected area of the product on the mold, the generated temperature gradient in the mold opening / closing direction may induce distortion and deformation after molding.

  Therefore, in the final stage of the pressure holding process, when a minute mold opening is performed to open the mold by the distance S ′ as shown by the line h1-h2-h3 in FIG. 4 immediately before the mold opening, Two ripple effects of the mold clamping force relaxation control as shown can be obtained. One is to completely release the mold clamping force (compression force) applied to the resin molded product, thereby completely reducing the amount of elastic deformation of the mold cavity and minimizing the residual stress of the resin molded product due to the elastic deformation. Can be. The other is to form a minute gap between the resin molded product and the mold cavity by opening the mold (however, the mold cavity is kept in a sealed state). The heat transfer between the product and the mold cavity is interrupted, and the air layer is maintained at a high temperature by the heat quantity of the resin molded product, so that the resin molded product is annealed in the mold cavity (for stress relief) Most of the residual stress can be removed. Here, the degree of the annealing treatment effect is determined by the timing of opening the micro mold and the amount of micro mold opening. For example, if the mold is opened at an early timing of the pressure holding process, the heat treatment effect is great because the amount of heat of the resin molded product is large, but it is necessary to set a long cooling holding time for the resin molded product. In view of the balance between the effect and the molding cycle time, it is needless to say that a suitable one is selected as appropriate for the timing of micro mold opening and the micro mold opening amount S ′.

  The present invention is not limited to the above embodiment and can be implemented in various forms. In Example 1 and Example 2, the amount of elastic deformation of the mold cavity with respect to the mold clamping force was utilized using commercially available injection molding simulation software, etc., and the molding conditions obtained from these specifications were input to change the mold clamping force. While analyzing the elastic deformation of the mold cavity and determining the relationship between the amount of elastic deformation and the mold clamping force related to the mold cavity, the shape of the resin mold and the mold cavity where the resin mold is molded is simple. If the resin molded product is relatively small and the deformation of the mold cavity during mold clamping has little effect on the deformation of the resin molded product, the relationship between the amount of elastic deformation of the mold cavity and the mold clamping force As described above, rather than through analysis, the mold is assumed to be a solid metal cube and is calculated roughly, or the mold cavity shape is simplified from the actual shape. And or calculated in terms of the reduced load of the analysis, the present invention based on the relationship may be implemented. Furthermore, as a simple method for determining the relationship between the mold cavity's elastic deformation amount and mold clamping force, sensors for detecting the mold clamping force (extension amount) are arranged on all tie bars, and a dummy block or the like is used. After adjusting the mold clamping force (elongation amount) applied to all tie bars to be uniform, the difference in the extension amount detected by all tie bars when the actual mold is clamped with the mold clamping force F The mold clamping surface is regarded as a difference in elastic deformation distribution in the mold opening and closing direction on the mold splitting surface, and the mold clamping force is set so that the ratio is less than the ratio between the specification thickness and the allowable thickness of the resin molded product. Mold clamping force relaxation control for reducing the force from F to f may be performed.

  In Example 1 and Example 2, since the relationship between the amount of elastic deformation of the mold cavity and the mold clamping force is obtained in advance by analysis using a computer, commercially available analysis software, etc., There may be cases where the results of the analysis differ. Therefore, in preparation for the case where the difference is more than a predetermined amount and the deformation amount of the resin molded product exceeds the allowable deformation amount and becomes a problem, the mold cavity and the resin molded product at a certain point in common at the time of analysis If the amount of elastic deformation in the mold opening / closing direction of the mold cavity and the amount of deformation in the thickness direction of the resin molded product are also analyzed at the same time, the thickness error th of the resin molded product obtained by analysis at a certain point and the actual injection molding It is possible to compare the thickness error measured value th ′ at the same point of the molded resin molded product. If this comparison is performed periodically, the reliability of the analysis can be maintained. In addition, if the difference is equal to or greater than a predetermined amount as a result of this comparison and the deformation amount of the resin molded product exceeds the allowable deformation amount, there is a problem that th = th ′. If defined, the present invention can be carried out in a state where the correction contents are clarified without spending time and expense in pursuing the cause of such difference. The item to be corrected may be at least one of items related to mold clamping force relaxation control performed in the pressure holding process, which is not considered in the analysis for obtaining the relationship between the mold clamping force and the elastic deformation amount of the mold cavity. desirable.

  Furthermore, the injection molding method according to the present invention can also be adopted for laminate molding. Resin molded products such as automobile exterior panels and sunroofs that are molded by the injection compression molding method or injection press molding method, the rib structure portion for reinforcement, the mounting portion for assembly, etc. Often provided at the periphery. Insert molded resin parts such as automobile exterior panels and sunroofs into molds of other injection molding machines, and use them for reinforcing rib structures and assembly parts on the surface and periphery of these resin molded parts. In some cases, the mounting part and the like are laminated, and the mold for primary molding and secondary molding is switched by various methods in the mold clamping device, and the lamination is performed by a single injection molding machine. Various types of injection molding machines dedicated to molding have been proposed and put into practical use. In many cases, these molding machines are used for lamination molding. In the present invention, since it is not necessary to provide a special mechanism or apparatus on the mold or the injection molding machine side, at least one of the primary molding process and the secondary molding process in these lamination molding injection molding machines is performed. It can be used for injection compression molding methods and injection press molding methods, and by adopting the injection molding method according to the present invention, it is a laminate with low distortion, high component dimensional accuracy, and high smoothness and translucency. A resin molded product can be molded.

7 Fixed mold 8 Movable mold 10 Flat-shaped resin molded product 10a Mold cavity 20 One point 20a in the mold cavity A plane that is in contact with one end of the mold cavity in the mold opening / closing direction and divided into molds Mold cavity surface T facing the plane 20b 20a parallel to the surface T One mold cavity thickness T 'T when the mold is elastically deformed
TH Displacement of mold cavity (T'-T)
Elastic deformation of TH _MAX mold cavity (maximum displacement)
30 One point 30a in the resin molded product A plane 30b 30a that is in contact with one end of the mold opening / closing direction of the mold cavity in which the flat resin molded product 10 is molded and parallel to the mold dividing surface Opposite surface of the resin molded product t One specified thickness t ′ in the resin molded product t ′ of the molded resin molded product t
th Thickness error of resin molded product (t'-t)
th't 'was obtained by analysis
th _MAX resin molding allowable deformation (maximum allowable thickness error)

Claims (7)

In an injection molding method for molding a resin molded product by an injection compression molding method or an injection press molding method,
An injection filling process in which a resin amount obtained by adding a cooling solidification shrinkage amount calculated in advance based on the resin molded product is injected and filled into a mold cavity formed by combining a set of molds;
A compression step in which the mold is clamped with a first mold clamping force necessary for shaping the resin molded product during or after the injection filling step,
Following the compression step, the amount of elastic deformation of the mold cavity based on the relationship of the amount of elastic deformation of the mold cavity with respect to the elastic deformation of the stationary platen and the movable platen due to the mold clamping force obtained in advance by analysis. A pressure holding step in which mold clamping force relaxation control is performed in which the first mold clamping force is reduced to a second mold clamping force that is equal to or less than an allowable deformation amount of the resin molded product;
An injection molding method characterized by comprising: A mold cavity thickness T at a certain point in the mold cavity is a plane in contact with one of the end portions in the mold opening / closing direction of the mold cavity before the mold clamping force is applied, and the mold dividing surface The distance in the mold opening / closing direction from a parallel plane through the certain point to the mold cavity surface facing the plane,
The amount of elastic deformation of the mold cavity is expressed as T′−T when the mold cavity thickness T is T ′ when the mold is elastically deformed by applying a certain clamping force. It is defined by the largest displacement TH _MAX among the displacement TH of the mold cavity thickness at the certain point,
The specified thickness t at one point of the resin molded product is a plane that is in contact with one of the end portions in the mold opening / closing direction of the mold cavity where the resin molded product is molded, and is parallel to the mold dividing surface. A distance in a direction perpendicular to the plane through the certain point to the surface of the resin molded product facing the plane or to the opposite side of the surface;
When the allowable deformation amount of the resin molded product is t ′ in the resin molded product after molding when the specified thickness t of the resin molded product is t′−t, the resin molding at the certain point represented by t′−t 2. The injection molding method according to claim 1, wherein the thickness error th is defined as a maximum allowable thickness error th _MAX of the product thickness error th.   The pressure holding step is started before reaching the glass transition temperature in the case of an amorphous resin, and before reaching the crystallization temperature in the case of a crystalline resin, and reaches the heat deformation temperature specified by ASTM D648. The injection molding method according to claim 1, wherein the injection molding method is completed after a predetermined time has elapsed.   The pressure holding step is reduced in a plurality of steps from the first mold clamping force to the second mold clamping force, and the number of steps, the mold clamping force and the duration of each step are arbitrarily set / changed 4. The injection molding method according to claim 1, wherein controllable mold clamping force relaxation control is performed.   5. The micro mold opening is performed after the mold clamping force relaxation control is performed after the pressure is reduced from the first mold clamping force to the second mold clamping force. 6. Injection molding method.   The thickness at an arbitrary point of the resin molded product obtained by actual molding by the mold clamping force relaxation control in which the mold clamping force relaxation control is depressurized from the first mold clamping force to the second mold clamping force. When the error th and the thickness error th ′ at the arbitrary point obtained by analysis under the same molding conditions as the actual molding are compared with each other by a predetermined amount or more, the first so that th = th ′ is satisfied. 6. The method according to claim 4, wherein at least one of a mold clamping force, the second mold clamping force, the number of the steps, a mold clamping force of each step, and a duration time is corrected. The injection molding method described in 1. A primary molding step in which a primary molded body is molded by injection filling a first cavity formed by combining a core mold and a first cavity mold;
The second cavity mold in which the second cavity is formed in combination with the core mold holding the primary molded body and the first cavity mold are switched relative to the core mold. In the injection molding method for molding a two-layer molded product, which has a secondary molding step of injection-filling the second cavity and laminating a secondary molded body on at least a part of the surface of the primary molded body,
The injection molding method according to any one of claims 1 to 6 is performed in at least one of the primary molding step and the secondary molding step, and a two-layer molded product is molded. Injection molding method.

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