Method for calculating stress relaxation rate of resin molded product, method for calculating stress relaxation rate in direction perpendicular to flow in resin molded product, method for manufacturing resin molded product, method for determining molding process capable of maximizing stress relaxation rate of resin material, method for calculating elastic modulus taking stress relaxation of resin molded product into consideration, and method for predicting life of resin molded product

Abstract

To provide a method for calculating a stress relaxation rate of a resin molded product, which enables simple and quantitative evaluation of stress relaxation that occurs during a resin solidification process.SOLUTION: A method for calculating a stress relaxation rate using a spring-in deformation during a cooling process of a resin molded product 10 includes the steps of: taking out the resin molded product having a corner part 11, and cooling the resin molded product to a predetermined temperature with a restraining jig 30 in contact with an inner surface of the corner part; cooling the resin molded product having the same resin material and shape and molded under the same conditions to the predetermined temperature without using the restraining jig in a state where the resin molded product is taken out; measuring an outer angle θorigin of the corner part before cooling, an outer angle θconst of the corner part with the restraining jig removed from the resin molded product after cooling, and an outer angle θfree of the corner part after cooling; and calculating the stress relaxation rate Relaxθ(%) of the resin molded product after cooling based on the actually measured θorigin, θconst, and θfree.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for calculating a stress relaxation rate of a resin molded product, a method for calculating a stress relaxation rate in a direction perpendicular to flow in a resin molded product, a method for manufacturing a resin molded product, a method for determining a molding process capable of maximizing the stress relaxation rate of a resin material, a method for calculating an elastic modulus of a resin molded product taking into account stress relaxation, and a method for predicting the life of a resin molded product. [Background technology]

[0002] So-called insert molded products, which are composites of metal parts and resin, are used in automobiles, electrical parts, electronic components, etc. for various purposes, such as reducing the weight of electric control parts, electronic control parts, and metal parts. When such insert molded products are used in environments with large temperature changes, the residual stress caused by the difference in linear expansion between the resin and the metal can cause early destruction and heat shock cracking of the product. For this reason, it is important to quantitatively measure the residual stress and predict the lifespan using simulation. In order to predict the residual stress after injection molding using simulation, it is necessary to obtain physical property values ​​that take into account the stress relaxation that occurs during the resin solidification process (the cooling process inside and outside the mold), and evaluation methods for stress relaxation properties for this purpose are being investigated.

[0003] For example, a method for accurately calculating the elastic modulus of a resin molded product, which changes during the cooling process after being removed from a mold, is known that involves evaluating the stress relaxation characteristics by obtaining the elastic modulus using a bimetal method and obtaining the shrinkage rate using a Thermo-DIC method (a method that uses thermography and a DIC method (digital image correlation method)) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7001874 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology of Patent Document 1, quantifying the stress relaxation characteristics requires the setup of synchronous measurements using measuring equipment for evaluation of both the bimetal method and the Thermo-DIC method, and also requires continuous measurement of changes over time during the cooling process of the resin molded product.

[0006] The present invention has been made to solve the above problems. That is, the object of the present invention is to provide a method for calculating a stress relaxation rate of a resin molded product that does not require a special measuring device or continuous measurement and can easily and quantitatively evaluate stress relaxation occurring during the cooling process of the resin molded product, a method for calculating a stress relaxation rate in a direction perpendicular to flow of a resin molded product that can easily and quantitatively evaluate stress relaxation occurring during the cooling process of the resin molded product in a direction perpendicular to the flow direction of the resin material during molding in the resin molded product, a manufacturing method for a resin molded product used to calculate the stress relaxation rate of the resin molded product, a method for determining a molding process that can maximize the stress relaxation rate of the resin material, a method for calculating an elastic modulus taking into account stress relaxation of the resin molded product, and a method for predicting the life of a resin molded product. [Means for solving the problem]

[0007] [1] A method for calculating a stress relaxation rate of a resin molded product using a spring-in deformation of the resin molded product during a cooling process of the resin molded product molded using a mold, comprising: a step of removing a first resin molded product having a molded corner portion from the metal mold, or cooling the first resin molded product to a predetermined temperature while the first resin molded product is present in the metal mold and while a restraining jig is in contact with an inner surface of the corner portion; a step of removing a second resin molded product having a corner portion molded under the same conditions as the first resin molded product, using the same resin material as the first resin molded product, and having the same shape as the first resin molded product from the metal mold, and cooling the second resin molded product to the predetermined temperature while the restraining jig is not in contact with the inner surface of the corner portion of the second resin molded product; origin(°), and in a state in which the first resin molded product is cooled to the predetermined temperature and the restraining jig is removed from the first resin molded product, the outer angle θ const (°), and measuring the outer angle θ of the corner portion of the second resin molded product after cooling to the predetermined temperature. free (°) and measuring the measured θ origin , θ const , and θ free and calculating a stress relaxation rate Relaxθ(%) of the first resin molded product in a state in which the first resin molded product has been cooled to the predetermined temperature and the restraint jig has been removed, based on the above formula (1):

number

[0008] [2] The method according to [1] above, wherein when at least one of the first resin molded product and at least one of the second resin molded product are considered as one set, there are a plurality of sets of the first resin molded product and the second resin molded product, and the cooling conditions for the cooling are different for each set in a temperature range below the higher of the crystallization temperature and the glass transition temperature of the resin material constituting the first resin molded product.

[0009] [3] The method according to [2] above, wherein the cooling conditions relate to at least one of a cooling rate and a restraining time by the restraining jig.

[0010] [4] The method according to any one of [1] to [3] above, wherein when at least one of the first resin molded product and at least one of the second resin molded product are taken as one set, there are a plurality of sets of the first resin molded product and the second resin molded product, and the molding conditions of the first resin molded product and the second resin molded product are different for each set.

[0011] [5] The method according to the above [4], wherein the molding conditions relate to at least one of the presence or absence of an insert jig, the demolding temperature from the mold, the holding pressure, and the injection speed.

[0012] [6] The method according to any one of [1] to [5] above, wherein the restraining jig is an insert jig or a mold structure itself.

[0013] [7] A method for calculating a stress relaxation rate in a direction perpendicular to the flow direction, which is a direction perpendicular to the flow direction of a resin material during molding in a resin molded product, by using a spring-in deformation of the resin molded product during a cooling process of the resin molded product molded using a metal mold, the method comprising the steps of: calculating the stress relaxation rate Relaxθ of the first resin molded product in a state in which the restraining jig is removed after cooling to the predetermined temperature by the method described in [1] above; and calculating a stress relaxation rate Relaxθ of the first resin molded product in a state in which the restraining jig is removed after cooling to the predetermined temperature by the method described in [1] above; a step of measuring a molding shrinkage rate of the third resin molded product in the flow direction and a molding shrinkage rate of the second resin molded product in the flow direction, the molding shrinkage rate being a direction perpendicular to the flow direction; a step of obtaining CAE analysis data for the first resin molded product and CAE analysis data for the second resin molded product using the measured molding shrinkage rates in the flow direction and the flow direction, the step of preparing CAE analysis models in which the first resin molded product and the second resin molded product are divided into a plurality of elements; and a step of performing a CAE analysis on each of the CAE analysis models using the CAE analysis data to obtain θ defined in the above [1]. origin , θ const , and θ free and calculating the stress relaxation rate Relaxθ of the first resin molded product and the θ calculated by the CAE analysis. origin , θ const , and θ free and calculating a stress relaxation rate in the direction perpendicular to flow of the first resin molded product in a state in which the first resin molded product has been cooled to the predetermined temperature and the restraining jig has been removed, using the above-mentioned.

[0014] [8] The CAE analysis data of the first resin molded product is a value calculated using the measured mold shrinkage rate of the third resin molded product in the flow direction and the stress relaxation rate in the flow direction obtained using a bimetal method, and a value calculated using a stress relaxation rate in the direction perpendicular to the flow direction using an arbitrary coefficient, and the CAE analysis data of the second resin molded product is a measured mold shrinkage rate of the third resin molded product in the flow direction and a measured mold shrinkage rate of the third resin molded product in the direction perpendicular to the flow, and the step of calculating the stress relaxation rate of the first resin molded product in the direction perpendicular to the flow after cooling to the predetermined temperature is performed by calculating the θ calculated by the CAE analysis. origin , θ const , and θ free to calculate a relaxation rate in the direction perpendicular to the flow of the first resin molded product from the formula (1) using the arbitrary coefficient, to obtain an approximation of the relaxation rate in the direction perpendicular to the flow of the first resin molded product corresponding to the arbitrary coefficient, and to substitute the actually measured stress relaxation rate Relaxθ of the first resin molded product into the approximation, thereby calculating the relaxation rate in the direction perpendicular to the flow of the first resin molded product at the actually measured stress relaxation rate Relaxθ of the first resin molded product.

[0015] [9] The method according to [7] or [8] above, wherein the third resin molded product is in a rectangular shape and the width of the third resin molded product is the same as the width of the first resin molded product.

[0016]

[10] A method for manufacturing a resin molded product having a corner portion used to calculate a stress relaxation rate of a resin molded product, comprising the steps of: molding a first resin molded product having a corner portion in a mold so that a side surface of an insert jig contacts the inner surface of the corner portion, cooling the first resin molded product to a predetermined temperature while keeping the side surface of the insert jig in contact with the inner surface of the corner portion of the first resin molded product, and removing the insert jig from the first resin molded product after cooling to the predetermined temperature to obtain a first resin molded product; and molding a second resin molded product having a corner portion in a mold so that the insert jig contacts the inner surface of the corner portion, cooling the second resin molded product to the predetermined temperature while removing the insert jig from the second resin molded product that has been cooled to the higher of the crystallization temperature and the glass transition temperature of a resin material constituting the second resin molded product, and removing the second resin molded product from the mold to obtain a second resin molded product.

[0017]

[11] The method for manufacturing a resin molded product described in

[10] above, wherein the molding shrinkage rate of the resin material constituting the first resin molded product is greater than the molding shrinkage rate of the material constituting the insert jig.

[0018]

[12] A method for manufacturing a resin molded product having a corner portion used to calculate a stress relaxation rate of a resin molded product, comprising the steps of: molding a first resin molded product having a corner portion in a mold so that an inner surface of the corner portion is in contact with a part of the mold, and then cooling the first resin molded product to a predetermined temperature while a part of the mold is in contact with the inner surface of the corner portion of the first resin molded product, and removing the first resin molded product from the mold after cooling to the predetermined temperature, to obtain a first resin molded product; and molding a second resin molded product having a corner portion in a mold so that a part of the mold is in contact with the inner surface of the corner portion, and then cooling the second resin molded product to the predetermined temperature while the second resin molded product is removed from the mold, to obtain a second resin molded product.

[0019]

[13] The method according to any one of

[10] to

[12] above, wherein when at least one of the first resin molded product and at least one of the second resin molded product are considered as one set, a plurality of sets of the first resin molded product and the second resin molded product are obtained, and at least one of the demolding temperature from a mold, the holding pressure, and the injection speed during molding of the first resin molded product and the second resin molded product is changed for each set.

[0020]

[14] A method for determining a molding process capable of maximizing the stress relaxation rate of a resin molded product, comprising carrying out the method for calculating a stress relaxation rate of a resin molded product described in any one of the above items [2] to [5], calculating each of the stress relaxation rates Relax θ, and comparing the calculated stress relaxation rates Relax θ to determine a molding process capable of maximizing the stress relaxation rate of the resin molded product.

[0021]

[15] A method for calculating an elastic modulus taking into account stress relaxation of a resin molded product having a corner portion, comprising the steps of: when the elastic modulus of the resin material constituting the first resin molded product defined in [1] above is E0, using the stress relaxation rate Relaxθ(%) of the first resin molded product calculated by the method defined in claim 1 and the elastic modulus E0, calculating an elastic modulus Erelaxθ(%) taking into account the stress relaxation rate Relaxθ of the first resin molded product according to the following formula (2): Erelaxθ = (1-Relaxθ)×E0…Equation (2)

[0022]

[16] A method for calculating an elastic modulus of a resin molded product having a corner portion, taking into consideration stress relaxation, comprising the steps of: freea0(%) is the molding shrinkage rate in the direction perpendicular to the flow used when calculating by CAE analysis, a(%) is the molding shrinkage rate of the first resin molded product in the direction perpendicular to the flow used when performing CAE analysis such that the stress relaxation rate Relax θ(%) of the resin molded product 10 calculated by CAE analysis has the same value as the stress relaxation rate Relax θ(%) of the actually measured first resin molded product, and a(%) is the elastic modulus of the resin material constituting the first resin molded product measured in advance, E0 is used to calculate an elastic modulus Erelaxθ(%) taking into account the stress relaxation rate Relax θ of the actually measured first resin molded product by the following formula (3).

number

[0023]

[17] A method for predicting the life of a resin molded product by CAE analysis, using a stress relaxation rate calculated by the method for calculating a stress relaxation rate of a resin molded product described in any one of [1] to [6] above, or a stress relaxation rate calculated by the method for calculating a stress relaxation rate in a direction perpendicular to flow in a resin molded product described in any one of [7] to [9] above. Effect of the Invention

[0024] According to the present invention, there are provided a method for calculating a stress relaxation rate of a resin molded product which does not require special measuring equipment or continuous measurement, and which can easily and quantitatively evaluate stress relaxation occurring during the cooling process of a resin molded product; a method for calculating a stress relaxation rate in a direction perpendicular to flow of a resin molded product which can easily and quantitatively evaluate stress relaxation in the direction perpendicular to flow, which is a direction perpendicular to the flow direction of the resin material during molding in the resin molded product, which occurs during the cooling process of the resin molded product; a manufacturing method for a resin molded product used to calculate the stress relaxation rate of a resin molded product; a method for determining a molding process which can maximize the stress relaxation rate of a resin material; a method for calculating an elastic modulus taking into account stress relaxation of a resin molded product; and a method for predicting the life of a resin molded product. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a plan view of a first resin molded product and a second resin molded product having corner portions and a restraining jig according to an embodiment. [Diagram 2] FIG. 2 is a plan view of a first resin molded product and a second resin molded product having another corner portion according to the embodiment, and a restraining jig. [Diagram 3] FIG. 3 is a plan view of the second resin molded product in FIG. 1 with a restraining jig removed from a corner portion thereof. [Figure 4] FIG. 4 is a plan view of the second resin molded product in FIG. 2 with a restraining jig removed from the corner portion. [Diagram 5] 5A is a diagram showing θorigin of the first resin molded product in FIG. 1, FIG. 5B is a diagram showing θconst and a spring-in angle of the first resin molded product in FIG. 1, and FIG. 5C is a diagram showing θfree and a spring-in angle of the second resin molded product in FIG. 1. [Figure 6] FIG. 6 is a plan view of the third resin molded product according to the embodiment. [Figure 7] 7A and 7B are diagrams for explaining an evaluation method using the bimetal method. [Figure 8] FIG. 8 is a graph showing the change in spring-in angle with time for a constrained L-shaped molded article made of the PPS resin composition 1, a constrained L-shaped molded article made of a POM resin composition, and a constrained U-shaped molded article. [Figure 9] FIG. 9 is a graph showing the change in spring-in angle with respect to elapsed time for an unconstrained L-shaped molded article made of the PPS resin composition 1, an unconstrained L-shaped molded article made of the POM resin composition, and an unconstrained U-shaped molded article. [Figure 10] FIG. 10 is a graph showing the relationship between the elastic modulus EBi-Metal at each temperature obtained by the bimetal method, the flexural modulus EBending obtained in a bending test performed at each temperature, and the molding shrinkage rate for test molded articles of PPS resin composition 1. [Figure 11] FIG. 11 is a graph used to determine the stress relaxation rate in the direction perpendicular to flow (TD) in the constrained L-shaped molded product according to Example 8. [Figure 12] FIG. 12 is a graph used to determine the stress relaxation rate in the direction perpendicular to flow (TD) in the constrained L-shaped molded article according to Example 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, a method for calculating the stress relaxation rate of a resin molded product according to an embodiment of the present invention will be described. Fig. 1 is a plan view of a first resin molded product and a second resin molded product having corner portions and a restraining jig according to this embodiment, and Fig. 2 is a plan view of a first resin molded product and a second resin molded product having another corner portion and a restraining jig according to this embodiment. Fig. 3 is a plan view of the corner portion of the second resin molded product in Fig. 1 with the restraining jig removed, and Fig. 4 is a plan view of the corner portion of the second resin molded product in Fig. 2 with the restraining jig removed. Fig. 5A shows θ of the first resin molded product in Fig. 1. origin FIG. 5B is a diagram showing the θ const 5C is a diagram showing the θ of the second resin molding product of FIG. 1 and the spring-in angle. free and the spring-in angle, FIG. 6 is a plan view of the third resin molded product according to the present embodiment, and FIGS. 7A and 7B are diagrams for explaining an evaluation method using a bimetal method.

[0027] (A) Calculation method for stress relaxation rate of resin molded products This method utilizes the spring-in deformation of a resin molded product during the cooling process immediately after molding.

[0028] First, a resin material is poured into a metal mold (not shown) and a first resin molded product 10 (hereinafter sometimes simply referred to as "resin molded product 10") having a corner portion 11 and a second resin molded product 20 (hereinafter sometimes simply referred to as "resin molded product 20") having a corner portion 21 shown in Fig. 1 are obtained by injection molding or the like. Here, the molding of the first resin molded product 10 and the second resin molded product 20 is performed with a restraining jig 30 placed in the metal mold.

[0029] The corner portions 11 and 21 have inner surfaces 11A and 21A and outer surfaces 11B and 21B, respectively, and both the inner surfaces 11A and 21A and the outer surfaces 11B and 21B are curved towards the inner surfaces 11A and 21A.

[0030] The resin molded products 10 and 20 shown in Fig. 1 have an L-shaped portion, but it is sufficient that the resin molded products 10 and 20 have one or more corner portions 11 and 21, and the resin molded products 10 and 20 may have a U-shaped portion as shown in Fig. 2. The resin molded products 10 and 20 having a U-shaped portion have two corner portions 11 and 21. The corners of the corner portions 11 and 21 may be rounded.

[0031] 1 and 2 include corner portions 11 and 21, as well as extension portions 12 and 22 extending continuously in at least one direction from the corner portions 11 and 21. In Fig. 1 and Fig. 2, linear extension portions 12 extend from both sides of the corner portion 11.

[0032] The dimensions of the resin molded products 10, 20 shown in Fig. 1 and Fig. 2 are not particularly limited. For example, the thickness of the resin molded products 10, 20 shown in Fig. 1 may be 1 mm or more and 20 mm or less, the length L from the inner corner of the corner parts 11, 21 to the tip of the extension parts 12, 22 may be 10 mm or more and 200 mm or less, and the width W1 of the corner parts 11, 21 and the extension parts 12, 22 may be 5 mm or more and 50 mm or less. Also, for example, the thickness of the resin molded products 10, 20 shown in Figure 2 may be 1 mm or more and 20 mm or less, the length L1 from the inner corner of one corner portion 11, 21 to the inner corner of the other corner portion 11, 21 may be 10 mm or more and 200 mm or less, the length L2 from the inner corner of the corner portion 11, 21 to the tip of the extension portion 12, 22 may be 10 mm or more and 200 mm or less, and the width W1 of the corner portion 11, 21 and the extension portion 12, 22 may be 5 mm or more and 50 mm or less.

[0033] The resin molded product 10 and the resin molded product 20 have the same shape. Furthermore, the resin molded product 10 and the resin molded product 20 are made of the same resin material and are molded under the same molding conditions.

[0034] The resin molded products 10 and 20 are molded products made of a resin material, but the resin material is not particularly limited. In addition, resin mixtures obtained by blending a plurality of resin materials are also included in the above resin materials. Furthermore, resin materials to which additives such as inorganic fillers such as glass fiber and carbon fiber, nucleating agents, pigments such as carbon black and inorganic calcined pigments, antioxidants, stabilizers, plasticizers, lubricants, mold release agents, and flame retardants are added to resin to impart desired properties are also included.

[0035] As the resin material, a thermoplastic resin can be used. As the thermoplastic resin, examples of the crystalline thermoplastic resin include polyolefin resin, polyester resin, polyacetal resin, polyphenylene sulfide resin, polyamide resin, and the like.

[0036] The restraining jig 30 has a side surface 30A thereof in contact with the inner side surfaces 11A, 21A of the corner portions 11, 21. The shape of the restraining jig 30 is not particularly limited as long as the side surface 30A is in contact with the inner side surface 11A of the corner portion 11, and for example, in the case of the resin molded product 10 in which the angles of the corner portions 11, 21 are right angles as shown in Fig. 1, an example of the restraining jig is one having right-angled corner portions.

[0037] The material of the restraining jig 30 is not particularly limited, but examples thereof include metal and resin. A metal restraining jig is preferable from the viewpoint of suppressing deformation of the restraining jig 30, and a resin restraining jig is preferable from the viewpoint of ease of manufacture. When the restraining jig 30 is made of resin, the resin material constituting the restraining jig 30 needs to have a melting point or softening point temperature equal to or higher than the melting point or softening point temperature of the resin material constituting the resin molded product 10, whichever is higher. The resin material constituting the restraining jig 30 and the resin material constituting the resin molded product 10 may be the same resin material.

[0038] As described later, after the resin molded product 10 is removed from the mold together with the restraining jig 30, the resin molded product 10 is cooled while being restrained by the restraining jig 30. However, if the resin molded product 10 is made of a resin material with a small molding shrinkage rate, the resin molded product 10 may be weakly attached to the restraining jig 30 and the restraining jig 30 may come off from the resin molded product 10 when the resin molded product 10 and the restraining jig 30 are removed from the mold. Therefore, it is preferable to select a combination in which the molding shrinkage rate of the constituent material of the resin molded product 10 is greater than the shrinkage rate (= temperature change ΔT × linear expansion coefficient) of the constituent material of the restraining jig 30. For example, when a resin material with an extremely small shrinkage rate such as a highly filled polyphenylene sulfide resin is used as the molding target, the contact interface between the resin molded product 10 and the restraining jig 30 can be remelted by the injection heat to create a weak welding state, so that it is possible to suppress the restraining jig 30 from coming off from the resin molded product 10.

[0039] The size of the restraining jig 30 is not particularly limited, but it is preferable that the restraining jig 30 extends to a position parallel to the tip surface 12A of the extension portion 12 of the resin molded product 10, as shown in Figures 1 and 2.

[0040] The restraining jig placed in the cavity of the mold may be washed away or damaged by the flow pressure of the resin material. For this reason, it is preferable to provide a boss portion of several mm on the restraining jig 30 in order to reliably hold the restraining jig 30 at a predetermined position in the cavity of the mold. By aligning the boss portion of the restraining jig 30 with the ejector pin of the cavity on the movable surface side of the mold and fitting it in, the restraining jig 30 can be reliably fixed in the cavity.

[0041] Next, the resin molded articles 10, 20 to be measured for stress relaxation rate are removed from the mold together with the restraining jig 30, and the resin molded articles 10, 20 are cooled.

[0042] In the case of the resin molded product 10, after the resin molded product 10 is removed from the mold together with the restraining jig 30, the resin molded product 10 is cooled to a predetermined temperature in a state in which the restraining jig 30 is in contact with the inner side surface 11A of the corner portion 11 (restrained state). When the resin molded product 10 undergoes spring-in deformation, the inner side surface 11A of the corner portion 11 is pressed against the side surface 30A of the restraining jig 30. By cooling the resin molded product 10 in a state in which the restraining jig 30 is in contact, the residual stress of the resin molded product 10 can be relaxed. The predetermined temperature is, for example, room temperature (e.g., 27°C), but is not limited to room temperature and may be a temperature (a temperature above room temperature) during cooling of the resin molded product 10 after the resin molded product 10 is removed from the mold. Whether the predetermined temperature is room temperature after cooling or a temperature above room temperature during cooling, the stress relaxation rate of the resin molded product 10 can be obtained by using the resin molded products 10 and 20.

[0043] In the case of the resin molded product 20, after the resin molded product 20 is taken out of the metal mold together with the restraining jig 30, the restraining jig 30 is removed from the resin molded product 20, and the resin molded product 20 is cooled to the above-mentioned predetermined temperature in a state where the restraining jig 30 is not in contact with the inner surface 21A of the corner portion 21 (unrestrained state). The cooling conditions are the same as those for the resin molded product 10, except that the restraining jig 30 is not used.

[0044] In the resin molded product 10, the outer angle θ of the corner portion 11 of the resin molded product 10 shown in FIG. 5A before cooling is origin After cooling, the restraining jig 30 was removed from the resin molded product 10, and the outer angle θ const In FIG. 5A, the outer angle θ origin is 90°, but is not particularly limited as long as it is in the range of more than 0° and not more than 180°. In this specification, the "outer angle of the corner portion" refers to the inner angle sandwiched between the outer surfaces of the corner portion when the resin molded product is viewed in plan as shown in Figs. 5A to 5C. In addition, in the resin molded product 20, the outer angle θ of the corner portion 21 of the resin molded product 20 shown in Fig. 5C after cooling free Measure (°).

[0045] Here, the spring-in angle (°) of the resin molded product 10 is θ origin -θ const The spring-in angle (°) of the resin molded product 20 is expressed as θ origin -θ free The spring-in angle is an index of the inward collapse of a resin molded product having a corner portion.

[0046] The θ of the resin molded product 10 origin and θ const θ of the resin molded product 20 free After measuring each, the measured θ origin , θ const , and θ free Based on this, the stress relaxation rate Relaxθ (%) of the resin molded article 10 is calculated using the following formula (1).

number

[0047] According to this embodiment, the stress relaxation rate Relaxθ of the resin molded product 10 is calculated based on formula (1), so that no special measuring equipment is required and no continuous measurement is required, and it is possible to simply and quantitatively evaluate the stress relaxation characteristics that occur during the resin solidification process (cooling process), which is important in predicting the product life.

[0048] In the above method, the stress relaxation rate of the resin molded product 10 is calculated using each of the resin molded products 10 and 20, but it is also possible to use a plurality of sets, each consisting of at least one resin molded product 10 and at least one resin molded product 20, and calculate the stress relaxation rate of the resin molded product 10 by changing at least one of the resin material, cooling conditions, and molding conditions for each set. By comparing the stress relaxation rates of the resin molded products 10 obtained by changing at least one of the resin material, cooling conditions, and molding conditions for each set, it is possible to easily quantify the influence of at least one of the resin material, cooling conditions, and molding conditions on the stress relaxation properties. When one set is composed of two or more first resin molded products 10 and two or more second resin molded products 20, the θ of the first resin molded product 10 is calculated by changing at least one of the resin material, cooling conditions, and molding conditions for each set. originand θ const is the θ of two or more first resin molded products 10 origin The arithmetic mean value of and θ const The arithmetic average value of θ of the second resin molded product 20 is free is the θ of two or more second resin molded products free The arithmetic mean value of

[0049] The cooling conditions include, for example, conditions related to the cooling rate and the restraining time by the restraining jig 30. Regarding the cooling rate, by cooling at different cooling rates (for example, slow cooling (air cooling), water cooling, and ultra-slow cooling), it is possible to easily quantify the effect of the cooling conditions on the stress relaxation properties. Here, ultra-slow cooling means a cooling rate of about 2°C / min. Regarding the restraining time, by restraining with the restraining jig 30 for different restraining times, it is possible to easily quantify the effect of the restraining time on the stress relaxation properties.

[0050] Examples of the molding conditions include conditions related to at least one of the presence or absence of an insert jig, the demolding temperature from the mold, the holding pressure, and the injection speed. Regarding the condition of the presence or absence of an insert jig, the effect of the insert jig on the stress relaxation properties can be easily quantified when molding is performed with and without the insert jig. Regarding the demolding temperature from the mold, the effect of the demolding temperature on the stress relaxation properties can be easily quantified by removing the resin molded product from the mold at different temperatures. Regarding the holding pressure conditions, the effect of the holding pressure on the stress relaxation properties can be easily quantified by holding the resin molded product at different holding pressures. Regarding the injection speed, the effect of the injection speed on the stress relaxation properties can be easily quantified by injecting the resin at different injection speeds.

[0051] In the above method, the resin molded article 10 is cooled after the resin molded article 10 and the restraining jig 30 are removed from the metal mold, but the resin molded article 10 may be cooled in the metal mold without removing the resin molded article 10 and the restraining jig 30 from the metal mold. The restraining jig 30 may be an insert jig used during molding, or may be the metal mold structure itself.

[0052] (B) Method for calculating the stress relaxation rate in the direction perpendicular to the flow of a resin molded product Residual deformation in a resin molded product having corners that contains additives such as glass fiber is believed to be mainly due to the anisotropy of molding shrinkage (the difference in shrinkage rate between the flow direction (FD) of the resin material and the direction perpendicular to the flow direction (TD) when molding the resin molded product 10) resulting from the orientation distribution of the additives (e.g., fibers). Note that even if the resin molded product having corners does not contain additives such as glass fiber, similar deformation can occur if it is molded from a resin material that exhibits anisotropy or if a temperature distribution is provided when molding the resin molded product having corners.

[0053] Furthermore, according to the theoretical formula for the spring-in angle, shown in formula (4) below, it can be understood that the spring-in angle does not depend on the elastic modulus (rigidity of the molded product), but depends on the anisotropy of molding shrinkage (difference in shrinkage rate between FD and TD) and temperature change.

number

[0054] In the above (A) method for calculating the stress relaxation rate of the resin molded article 10, the stress relaxation rate of the resin molded article 10 can be calculated, but this method expresses the stress relaxation phenomenon by reducing the apparent shrinkage rate. In other words, the calculated stress relaxation rate is a macroscopic stress relaxation rate.

[0055] In contrast, the following method makes it possible to calculate the stress relaxation rate in the direction perpendicular to the flow (TD) of the resin material during molding of the resin molded product 10, and therefore makes it possible to evaluate more microscopic effects.

[0056] (Step 1) Following the procedure described in the above section (A) Method for calculating the stress relaxation rate of the resin molded article 10, the stress relaxation rate Relax θ of the resin molded article 10 having the corner portions 11 is calculated.

[0057] (Step 2) As shown in Fig. 6, a third resin molded product 40 (hereinafter, simply referred to as "resin molded product 40") is prepared from the same resin material as the resin molded products 10 and 20, and the molding shrinkage rate of the resin molded product 40 is measured. Specifically, the molding shrinkage rates of the resin material in the flow direction (FD) and the direction perpendicular to the flow (TD) during molding of the resin molded product 40 are measured.

[0058] The resin molded product 40 is molded under the same molding conditions as the resin molded products 10 and 20, but the shape does not have to be the same as the resin molded products 10 and 20. For example, as shown in Fig. 6, the resin molded product 40 may be a rectangular shape without corners. However, it is desirable that the width W2 of the resin molded product 40 shown in Fig. 6 is the same as the width W1 of the resin molded product 10 and the width W1 of the resin molded product 20. The molding shrinkage rates of the resin molded product 40 in the flow direction (FD) and the transverse direction to flow (TD) can be measured using a dimensional measuring device or a Thermo-DIC method (a method using thermography and a DIC method (digital image correlation method)).

[0059] (Step 3) Create CAE (Computer Aided Engineering) analysis models of the resin molded products 10 and 20. The CAE analysis model of the resin molded product 10 and the CAE analysis model of the resin molded product 20 are the same, and only the input physical property values ​​are changed. The CAE analysis model can be created using general-purpose finite element software (e.g., ANSYS (registered trademark) made by ANSYS, NX NASTRAN made by Siemens, ADVENTURECluster made by Allied Engineering Co., Ltd., Abaqus made by Dassault Systèmes, etc.).

[0060] (Step 4) From the mold shrinkage rates in the flow direction (FD) and the transverse direction (TD) of the resin molded product 40 actually measured in Step 2, CAE analysis data is obtained according to the procedures of Steps 4-1 and 4-2 below, and this CAE analysis data is input into the CAE analysis model created in Step 3, and the θ origin and θ const θ of the resin molded product 20 free are calculated respectively.

[0061] (Step 4-1) In the CAE analysis of the resin molded product 20, the mold shrinkage rate in the flow direction (FD) and the mold shrinkage rate in the direction perpendicular to the flow direction (TD) obtained in step 2 are used as they are as CAE analysis data.

[0062] (Step 4-2) In the CAE analysis of the resin molded product 10, the molding shrinkage rate obtained in step 2 is reduced as in steps 4-2-1 and 4-2-2 below and used as CAE analysis data. Here, the molding shrinkage rate is reduced because, in the actual resin molded product 10, stress is alleviated due to the effect of restraint by the restraining jig 30.

[0063] (Step 4-2-1) The shrinkage rate (%) in the flow direction (FD) of the resin molded article 10 to be used as CAE analysis data is calculated from the following formula (5). Shrinkage rate of FD = (molding shrinkage rate of FD obtained in step 2) × (100 - stress relaxation rate calculated using the bimetal method) ÷ 100 ... Equation (5)

[0064] Here, the above-mentioned "bimetal method" is a method for calculating the elastic modulus of a resin material. In general, a bimetal is a type of composite metal material in which two metal plates with different thermal expansion coefficients are bonded together, and has the property of bending due to temperature changes. However, the properties of a bimetal are not limited to metal plates, and a bonded plate in which two plates of materials with different thermal expansion coefficients are bonded together has similar properties. Therefore, in the bimetal method, the elastic modulus of the resin molded product 10 is calculated using a bonded plate in which a primary side plate containing a material with a thermal expansion coefficient different from that of the resin material contained in the resin molded product 10 to be calculated for the elastic modulus is bonded to a secondary side plate containing the same resin material as the resin molded product 10.

[0065] In FIG. 7A and FIG. 7B, the thermal expansion coefficients of the primary side plate 51 and the secondary side plate 52 of the joining plate 50 are α1 and α2, respectively, and the elastic modulus (longitudinal elastic modulus) of the primary side plate 51 and the secondary side plate 52 of the joining plate 50 are E1 and E2, respectively. In addition, the plate thicknesses of the primary side plate 51 and the secondary side plate 52 of the joining plate 50 are h1 and h2, respectively, and the plate thickness of the joining plate 50 is h (= h1 + h2). At this time, in the process of removing the joining plate 50 from the mold and then cooling it, the temperature immediately after the resin molded product 10 of the joining plate 50 is removed from the mold is T1, the room temperature is T2, the length of the joining plate 50 at temperature T1 is L, and the radius of curvature at temperature T2 is r. The elastic modulus ratio m=E1 / E2, and the plate thickness ratio n=h1 / h2. At this time, the displacement (warpage) D of the joining plate 50 is geometrically calculated from the following formula (6). The thermal expansion coefficient α2 of the secondary side plate 52 is equivalent to the molding shrinkage rate in the flow direction (FD) of the resin material during molding in the resin molded product 10 to be evaluated.

number

[0066] For example, LAPEROS (registered trademark) LCP S135 is used as the primary side plate 51, and the resin material of the resin molded product 10 is used as the secondary side plate 52. Insert molding is performed using the primary side plate as an insert member, and the displacement amount D of the joining plate 50 shown in FIG. 7B is measured sequentially during the process of removing the resin molded product from the mold and cooling it. That is, the joining plate 50 having a predetermined shape (i.e., a shape in which h1, h2, h, and L in formula (6) are specified) is formed, and the displacement amount D of the joining plate is measured sequentially when the temperature is changed from temperature T1 (the same as the temperature immediately after the resin molded product is removed from the mold) to temperature T2 (for example, room temperature). The displacement amount D of the joining plate is a value that reflects the relaxation elastic modulus of the secondary side plate 52 made of the composition to be evaluated. That is, by calculating the elastic modulus of the secondary side plate based on the measured displacement amount D, the calculated elastic modulus of the secondary side plate takes into consideration the viscoelastic behavior during the process of removing the composition to be evaluated from the mold and cooling it.

[0067] The elastic modulus calculated by the bimetal method includes the effect of stress relaxation, so it is lower than the elastic modulus obtained by mechanical tests such as bending tests on solidified products. The stress relaxation rate at each temperature in the bimetal method is calculated from the following formula (7) when the elastic modulus at each temperature in the bimetal method is defined as EBi-Metal and the bending elastic modulus obtained in the bending test performed at each temperature is defined as EBending. Therefore, the stress relaxation rate at a specified temperature (room temperature) is calculated using formula (7). Note that the bending test refers to a three-point bending test in accordance with JIS K7171:2016. Stress relaxation rate (%) = (1- (EBi-Metal / EBeinding) ) × 100 …Equation (7)

[0068] (Step 4-2-2) The shrinkage rate (%) of the resin molded product 10 in the direction perpendicular to flow (TD) to be used as CAE analysis data is calculated using the following formula (8). Here, the bimetal method cannot take into account anisotropy in the same material, so it is only possible to evaluate the direction perpendicular to flow (FD) taking stress relaxation into account, and cannot evaluate the direction perpendicular to flow (TD). For this reason, the evaluation is performed using the following formula (8). Shrinkage rate of TD = (molding shrinkage rate of TD obtained in step 2) × (arbitrary coefficient: 0 to 1) ... Equation (8) In the above formula (8), when any coefficient is 1, it means that the stress relaxation rate in TD is 0%, i.e., there is no stress relaxation, and when any coefficient is 0, it means that the stress relaxation rate in TD is 100%.

[0069] (Step 5) θ of the resin molded product 10 obtained by each CAE analysis origin and θ const θ of the resin molded product 20 free The stress relaxation rate of the resin molded product 10 is calculated from the above formula (1) by CAE analysis using the above formula (8). Then, the relationship between the stress relaxation rate of the resin molded product 10 obtained by the CAE analysis and the relaxation rate in the direction perpendicular to the flow (TD) according to the arbitrary coefficient set in the above formula (8) is plotted to obtain an approximation formula.

[0070] (Step 6) By substituting the stress relaxation rate of the resin molded product 10 after cooling and with the restraint jig 30 removed, which was measured in step 1, into the above approximation equation obtained in step 5, the stress relaxation rate of the resin molded product 10 in the direction perpendicular to the flow (TD) can be calculated.

[0071] According to this method, it becomes possible to quantify the stress relaxation characteristics of the resin molded article 10 in the transverse direction (TD) to flow, which has not been possible to evaluate so far.

[0072] In the above method, one each of the resin molded products 10 and 20 is used, but at least one resin molded product 10 and at least one resin molded product 20 may be used as one set, and at least one of the resin material, cooling conditions, and molding conditions may be changed for each set. By comparing the stress relaxation rates of the resin molded products 10 calculated by changing at least one of the resin material, cooling conditions, and molding conditions for each set, it is possible to easily quantify the influence of at least one of the resin material, cooling conditions, and molding conditions on the stress relaxation properties. The cooling conditions and molding conditions are the same as those described in the above section (A) Calculation method of stress relaxation rate of resin molded product.

[0073] (C) Manufacturing method for resin molded products In the above (A) method for calculating the stress relaxation rate of a resin molded product, the resin molded products 10, 20 are cooled after being removed from the mold together with the restraining jig 30, but the resin molded product 10 may be restrained and cooled in the mold. Even when such a resin molded product 10 is obtained, the θ origin , θ const and θ of the resin molded product 20 free After measuring each, the measured θ origin , θ const and θ free Based on this, the stress relaxation rate Relax θ of the resin molded article 10 can be calculated from the formula (1) in the same manner as above.

[0074] In such a case, first, a resin molded article 10 having a corner portion 11 is molded. Specifically, the resin molded article 10 having a corner portion is molded in a metal mold so that an insert jig is in contact with the inner surface 11A of the corner portion 11. Next, the resin molded article 10 is cooled to a predetermined temperature (e.g., room temperature) in the metal mold while the insert jig is in contact with the inner surface 11A of the corner portion 11 of the resin molded article 10. After cooling, the resin molded article 10 is removed from the metal mold, and the insert jig is removed from the resin molded article 10 to obtain the resin molded article 10.

[0075] Also, a resin molded article 20 having a corner portion 21 is molded. Specifically, the resin molded article 20 having the corner portion 21 is molded in a mold with an insert jig in contact with the inner surface 21A of the corner portion 21. Next, in a state where the insert jig is removed from the resin molded article 20 that has been cooled to the higher of the crystallization temperature and the glass transition temperature of the resin material constituting the resin molded article 20, the resin molded article 20 is cooled to room temperature. After cooling, the resin molded article 20 is removed from the mold to obtain the resin molded article 20.

[0076] In the above, the resin molded product 10 is restrained by the insert jig, but the resin molded product 10 may be restrained by using a part of the metal mold.

[0077] In such a case, first, a resin molded article 10 having a corner portion 11 is molded. Specifically, the resin molded article 10 is molded in a metal mold so that an inner surface 11A of the corner portion 11 of the resin molded article 10 is in contact with a part of the metal mold. Next, the resin molded article 10 is cooled to room temperature while the inner surface 11A of the corner portion 11 of the resin molded article 10 is in contact with a part of the metal mold. After cooling, the resin molded article 10 is removed from the metal mold to obtain the resin molded article 10.

[0078] Also, a second resin molded product 20 having a corner portion 21 is molded. Specifically, the resin molded product 20 is molded in a mold so that a part of the mold comes into contact with the inner surface 21A of the corner portion 21 of the resin molded product 20. Next, the resin molded product 20 is cooled to the higher of the crystallization temperature and the glass transition temperature of the resin material constituting the resin molded product 20, and is removed from the mold. In this state, the resin molded product 20 is cooled to room temperature to obtain the resin molded product 20.

[0079] In the above manufacturing method, one each of the resin molded products 10 and 20 is obtained, but at least one resin molded product 10 and at least one resin molded product 20 may be considered as one set, and multiple sets may be used to obtain resin molded products 10 and 20 in which at least one of the resin material, cooling conditions, and molding conditions is changed for each set. The cooling conditions and molding conditions are the same as those described in the above section (A) Calculation method for stress relaxation rate of resin molded product.

[0080] (D) Method for determining molding process capable of maximizing stress relaxation rate of resin molded product First, in (B) the method for calculating the stress relaxation rate in the direction perpendicular to the flow of a resin molded product, multiple sets are used as described above, and at least one of the resin material, cooling conditions, and molding conditions is changed for each set, and the stress relaxation rate Relaxθ of the first resin molded product 10 is calculated. Then, the calculated stress relaxation rates Relaxθ are compared to determine a molding process that can maximize the stress relaxation rate of the resin molded product 10. According to this method, it is possible to efficiently find a molding process that can maximize the stress relaxation rate of the resin molded product 10.

[0081] (E) Calculation method of elastic modulus taking into account stress relaxation of resin molded products The elastic modulus taking stress relaxation of the resin molded product into consideration can be calculated as follows using the stress relaxation rate calculated by the above (A) method for calculating the stress relaxation rate of a resin molded product and the elastic modulus of the resin material constituting the resin molded product, or using the molding shrinkage rate in the direction perpendicular to flow (TD) used when calculating by CAE analysis by the above (B) method for calculating the stress relaxation rate in the direction perpendicular to flow of a resin molded product and the shrinkage rate of the resin molded product 10 used in CAE analysis such that the stress relaxation rate Relaxθ(%) of the resin molded product 10 calculated by CAE analysis has the same value as the actually measured stress relaxation rate Relaxθ(%) of the first resin molded product 10.

[0082] (E1) When the elastic modulus of the resin material constituting the resin molded product 10 is E0, the elastic modulus Erelaxθ (%) taking into account the stress relaxation rate Relaxθ of the resin molded product 10 is calculated by the following formula (2) using the stress relaxation rate Relaxθ (%) calculated by the calculation method for the stress relaxation rate of a resin molded product (A) and the elastic modulus E0. Erelaxθ = (1-Relaxθ)×E0…Equation (2)

[0083] (E2) (B) θ of the resin molded product 20 in the method for calculating the stress relaxation rate in the direction perpendicular to the flow of the resin molded product free The molding shrinkage rate in the direction perpendicular to the flow (TD) of the resin molded product 10 used in the CAE analysis to calculate the above stress relaxation rate Relaxθ(%) of the resin molded product 10 by CAE analysis is a0(%), the molding shrinkage rate in the direction perpendicular to the flow (TD) of the resin molded product 10 used in the CAE analysis to obtain the stress relaxation rate Relaxθ(%) of the resin molded product 10 of the same value as the actually measured stress relaxation rate Relaxθ(%) of the resin molded product 10 is a(%), and the elastic modulus of the resin material constituting the resin molded product 10 measured in advance is E0, the elastic modulus Erelaxθ(%) taking into account the actually measured stress relaxation rate Relaxθ of the resin molded product 10 is calculated by the following formula (3).

number

[0084] Here, it is preferable to carry out CAE analysis using the molding shrinkage rate a as a variable and to mathematically express the relationship between the molding shrinkage rate a and the stress relaxation rate Relax θ.

[0085] Stress relaxation is determined by the shrinkage rate. For this reason, in the above method (B), the shrinkage rate is multiplied by a correction coefficient. However, in reality, stress relaxation is a phenomenon in which stress (repulsive force) decreases at a certain strain (deformation), so it shows a behavior in which the apparent elastic modulus decreases. For this reason, the apparent elastic modulus can be obtained by multiplying the elastic modulus of the resin material by a correction coefficient that takes into account the effect of stress relaxation, as in the above formula (2) or (3).

[0086] (F) Method for predicting the life of a plastic molded product By using the stress relaxation rate calculated by the above (A) method for calculating the stress relaxation rate of a resin molded product or (B) method for calculating the stress relaxation rate in the direction perpendicular to the flow direction of a resin molded product, it is possible to accurately predict the life of the resin molded product against static fracture, fatigue fracture, creep fracture, heat shock fracture, stress relaxation fracture, etc. CAE analysis can be used to predict the fracture life of the resin molded product. EXAMPLES

[0087] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these descriptions. Fig. 8 is a diagram showing the change in spring-in angle with time for a constrained L-shaped molded product made of PPS resin composition 1, a constrained L-shaped molded product made of POM resin composition, and a constrained U-shaped molded product. Fig. 9 is a diagram showing the change in spring-in angle with time for an unconstrained L-shaped molded product made of PPS resin composition 1, an unconstrained L-shaped molded product made of POM resin composition, and an unconstrained U-shaped molded product. Fig. 10 is a graph showing the relationship between the elastic modulus EBi-Metal at each temperature obtained by the bimetal method, the bending elastic modulus EBending obtained in a bending test performed at each temperature, and the molding shrinkage rate in a test molded product of polyphenylene sulfide resin composition 1. Fig. 11 is a graph used to determine the stress relaxation rate in the flow perpendicular direction (TD) in the constrained L-shaped molded product of Example 8. Fig. 12 is a graph used to determine the stress relaxation rate in the flow perpendicular direction (TD) in the constrained L-shaped molded product of Example 9.

[0088] (Measurement of spring-in angle) First, two L-shaped molded products made of a polyphenylene sulfide resin composition 1 (PPS resin composition 1) containing 30% by mass of glass fiber, six L-shaped molded products made of a polyacetal resin composition (POM resin composition) containing 20% ​​by mass of glass fiber, and two U-shaped molded products were molded using a mold of the same shape and under the same molding conditions. The two L-shaped molded products made of the polyphenylene sulfide resin composition 1 had a thickness of 3 mm, a length L shown in FIG. 1 of 70 mm, and a width W1 shown in FIG. 1 of 10 mm. As the six L-shaped molded products made of the polyacetal resin composition, three types of L-shaped molded products each having a thickness of 3 mm were prepared in pairs. Specifically, two molded products each having a length L1 of 70 mm and a width W1 of 10 mm shown in FIG. 1, a length L1 of 65 mm and a width W1 of 15 mm, and a length L1 of 60 mm and a width W1 of 20 mm were prepared. The two U-shaped molded products made of the polyacetal resin composition had a thickness of 3 mm, a length L1 shown in Fig. 2 of 50 mm, a length L2 shown in Fig. 2 of 65 mm, and a width W1 shown in Fig. 2 of 15 mm. The outer angle of each corner of both the L-shaped molded products and the U-shaped molded products was 90°.

[0089] Molding was performed in a state where a restraining jig made of the polyphenylene sulfide resin composition 1 was arranged in a mold so that the restraining jig was in contact with the inner surfaces of the corners of the L-shaped molded product and the U-shaped molded product. The restraining jig used in molding the L-shaped molded product was a square with a thickness of 3 mm and a length of each side of 65 mm. The restraining jig used in molding the U-shaped molded product was a rectangular with a thickness of 3 mm, a length of one side of 65 mm, and a length of the other side of 50 mm. The restraining jig was arranged so that the other side of the restraining jig was in contact with the inner side connecting the inner corner of one corner of the U-shaped molded product and the inner corner of the other corner.

[0090] After molding, the L-shaped and U-shaped molded products were removed from the mold together with the restraining jig. Of the two L-shaped and U-shaped molded products removed from the mold, one of the L-shaped and U-shaped molded products was cooled to room temperature (27°C) with the restraining jig still attached. The restraining jigs were then removed from the L-shaped and U-shaped molded products after cooling to room temperature, and the L-shaped and U-shaped molded products (hereinafter sometimes referred to as "constrained L-shaped molded products") and U-shaped molded products (hereinafter sometimes referred to as "constrained U-shaped molded products", and the constrained L-shaped and constrained U-shaped molded products are also referred to as "constrained molded products") that were restrained by the restraining jigs during cooling were measured for a predetermined time from 0 hours to 500 hours, with the time when the restraining jig was removed being set as 0 hours. origin and θ const The measured θ origin and θ const The spring-in angle was calculated from the above.

[0091] The other L-shaped and U-shaped molded products were removed from the mold and cooled to room temperature (27°C) with the restraining jig removed. The L-shaped and U-shaped molded products that were not restrained by the restraining jig during cooling (hereinafter also referred to as "unrestrained L-shaped molded products") and U-shaped molded products (hereinafter also referred to as "unrestrained U-shaped molded products" and the unrestrained L-shaped and unrestrained U-shaped molded products are also referred to as "unrestrained molded products") were measured for a predetermined time from 0 hours to 500 hours, with the time when they reached room temperature being set as 0 hours. free The measured θ origin and θ free The spring-in angle was calculated from the above.

[0092] As shown in Figures 8 and 9, all of the restrained molded products had smaller spring-in angles than the unrestrained molded products. This shows that when the L-shaped and U-shaped molded products were cooled using a restraining jig, they were less prone to spring-in deformation than when they were cooled without using a restraining jig.

[0093] On the other hand, in the case of the unconstrained molded product, as shown in FIG. 9, a constant spring-in angle was shown over time regardless of the resin material, but in the case of the constrained molded product, as shown in FIG. 8, it can be understood that the behavior differs depending on the resin material. Specifically, the constrained L-shaped molded product made of the polyphenylene sulfide resin composition 1 showed a constant spring-in angle over time, but the constrained L-shaped molded product and the constrained U-shaped molded product made of the polyacetal resin composition showed a gradual increase in spring-in angle over time. This is considered to be due to the relationship between the glass transition temperature (Tg) of the resin material and the constraint release temperature (room temperature), which is the temperature at which the constraint jig is removed. Specifically, since the Tg of the polyacetal resin is -60°C, which is below room temperature (27°C), the stress relaxation due to the constraint by the constraint jig is released again at room temperature, and the spring-in angle gradually increases. In contrast, the Tg of the polyphenylene sulfide resin is 90°C, which is above room temperature, and therefore the spring-in angle is considered to have remained constant without change at room temperature.

[0094] <Examples 1 to 4> (Stress relaxation rate calculation) From the above results, in the molded products made of the above polyphenylene sulfide resin composition 1, the spring-in angle of the constrained L-shaped molded product and the unconstrained L-shaped molded product remains constant even after a period of time has passed since they were cooled to room temperature, so the following stress relaxation rates were determined using the above polyphenylene sulfide resin composition 1.

[0095] First, two L-shaped molded articles 1 and two U-shaped molded articles 1 made of the polyphenylene sulfide resin composition 1 were molded using a metal mold. The L-shaped molded article 1 had a length L of 65 mm and a width W1 of 15 mm as shown in Fig. 1. The U-shaped molded article 1 had a length L1 of 50 mm as shown in Fig. 2, a length L2 of 65 mm as shown in Fig. 2, and a width W1 of 15 mm as shown in Fig. 2.

[0096] Furthermore, two L-shaped molded articles 2 and two U-shaped molded articles 2 made of polyphenylene sulfide resin composition 2 containing 30% by mass of glass fiber (PPS resin composition 2) were molded using a metal mold. The dimensions of the L-shaped molded article 2 were the same as those of the L-shaped molded article 1, and the dimensions of the U-shaped molded article 2 were the same as those of the U-shaped molded article 1.

[0097] Molding was performed in a state where a restraining jig made of the polyphenylene sulfide resin composition 1 was placed in a mold so that the restraining jig was in contact with the inner surfaces of the corners of the L-shaped and U-shaped molded products. The restraining jig attached to the L-shaped molded products 1 and 2 was a square with a thickness of 3 mm and each side of 65 mm. The restraining jig attached to the U-shaped molded products 1 and 2 was a rectangular with a thickness of 3 mm, one side of 65 mm, and the other side of 50 mm. The restraining jig was attached so that the other side of the restraining jig was in contact with the inner side connecting the inner corner of one corner of the U-shaped molded products 1 and 2 and the inner corner of the other corner.

[0098] After molding, the L-shaped molded products 1, 2 and the U-shaped molded products 1, 2 were removed from the mold together with the restraining jig. Then, one of the two L-shaped molded products 1, 2 and the U-shaped molded products 1, 2 removed from the mold was cooled to room temperature (27°C) with the restraining jig still attached.

[0099] Thereafter, the restraining jigs were removed from the L-shaped molded products 1 and 2 and the U-shaped molded products 1 and 2 that had cooled to room temperature, and the restraining jigs were removed from the L-shaped molded products 1 and 2 (hereinafter referred to as "restrained L-shaped molded products 1 and 2") and the U-shaped molded products 1 and 2 (hereinafter referred to as "restrained U-shaped molded products 1 and 2") that had been restrained by the restraining jigs during cooling, and origin and θ const was actually measured.

[0100] The restraining jigs were removed from the other L-shaped molded products 1, 2 and U-shaped molded products 1, 2 that had been removed from the mold, and the L-shaped molded products 1, 2 and U-shaped molded products 1, 2 were cooled to room temperature (27°C). Then, in the L-shaped molded products 1, 2 that were not restrained by the restraining jigs during cooling (hereinafter referred to as "unrestrained L-shaped molded products 1, 2") and the U-shaped molded product (hereinafter referred to as "unrestrained U-shaped molded products 1, 2"), θ free was actually measured.

[0101] And the measured θ of the constrained L-shaped molded product 1 origin , θ const and θ of unconstrained L-shaped molded product 1 free Based on this, the stress relaxation rate Relaxθ (%) of the constrained L-shaped molded product 1 was calculated from the above formula (1). Similarly, the stress relaxation rates Relaxθ (%) of the constrained L-shaped molded product 2 and the constrained U-shaped molded products 1 and 2 were calculated from the above formula (1).

[0102] The results are shown in Table 1. [Table 1]

[0103] From the above Table 1, it was confirmed that the L-shaped molded article made of the polyphenylene sulfide resin composition 2 has a higher stress relaxation rate Relax θ than the L-shaped molded article made of the polyphenylene sulfide resin composition 1, and that the U-shaped molded article made of the polyphenylene sulfide resin composition 2 has a higher stress relaxation rate Relax θ than the U-shaped molded article made of the polyphenylene sulfide resin composition 1. Therefore, it was confirmed that the stress relaxation characteristic in the material properties can be quantified by such a method.

[0104] In the above, the stress relaxation rate of the molded products made of the polyphenylene sulfide resin compositions 1 and 2 was obtained, but it is also possible to obtain the stress relaxation rate of the molded products made of the polyacetal resin composition. The glass transition temperature (Tg) of the polyacetal resin exists in the negative temperature range, but the dashpot that causes viscoelasticity is not completely frozen, so if the restrained molded product is left in a room temperature environment after being removed from the mold, the spring-in deformation gradually recovers, that is, the stress relaxation rate decreases. The stress relaxation rate during such changes over time can also be calculated by comparing with a standard unrestrained molded product.

[0105] <Examples 5 to 7> Six L-shaped molded products (W=15, L=65) of the same shape molded in Example 1 were prepared, and three sets of two were prepared. One of each set was a constrained L-shaped molded product, and the other was an unconstrained L-shaped molded product. In each set, a constrained L-shaped molded product and an unconstrained L-shaped molded product were obtained in the same manner as in Example 1, except that the cooling conditions for obtaining the constrained L-shaped molded product and the unconstrained L-shaped molded product were changed. The cooling conditions were changed to three types: air cooling, water cooling, and ultra-slow cooling. Water cooling was performed by immersing the L-shaped molded product and the unconstrained L-shaped molded product in water. Ultra-slow cooling was performed by placing the L-shaped molded product in a thermostatic chamber and gradually cooling the temperature of the thermostatic chamber (ambient temperature) at 2°C / min.

[0106] In each group, the θ origin , θ const and θ of unconstrained L-shaped molded product free The measured θ of the restrained L-shaped molded product was origin , θ const and θ of unconstrained L-shaped molded product free Based on this, the stress relaxation rate Relaxθ (%) of the constrained L-shaped molded product was calculated from the above formula (1).

[0107] The results are shown in Table 2. [Table 2]

[0108] From Table 2 above, it was confirmed that the stress relaxation rate changes when the cooling conditions are changed, and therefore the effect of the cooling conditions on the stress relaxation properties can be easily quantified. In the case of water cooling, it is predicted that the stress relaxation rate would decrease, but it is believed that the proportion of amorphous material that is easily relaxed increases due to rapid cooling by water cooling, resulting in a stress relaxation rate equivalent to that of air cooling. On the other hand, in the case of ultra-slow cooling, crystallization is promoted, but it is believed that stress relaxation is promoted more than the promotion of crystallization, resulting in an increase in the stress relaxation rate.

[0109] <Examples 8 and 9> In Example 8, the stress relaxation rate in the direction perpendicular to the flow of the constrained L-shaped article in Example 1 was calculated, and in Example 9, the stress relaxation rate in the direction perpendicular to the flow of the constrained U-shaped article in Example 2 was calculated.

[0110] (Step 1) θ of the constrained molded product origin , θ const and θ of the unconstrained molded product free Measure the actual θ origin , θ const and θ free It is necessary to calculate the stress relaxation rate of the restrained molded product from the above. origin , θ const and θ free The stress relaxation rate of the constrained L-shaped molded product was actually measured and calculated to be 42.2% (see Table 1), so this value was used. origin , θ const and θ free The stress relaxation rate of the constrained U-shaped molded product was actually measured and calculated to be 33.7% (see Table 1), so this value was used.

[0111] (Step 2) Since the L-shaped molded product of Example 1 and the U-shaped molded product of Example 2 were composed of the polyphenylene sulfide resin composition 1, a rectangular molded product was molded using the polyphenylene sulfide resin composition 1. The thickness of the rectangular molded product was 3 mm, the length was 200 mm, and the width was 15 mm. The mold shrinkage in the flow direction (FD) and the mold shrinkage in the transverse direction (TD) of the polyphenylene sulfide resin composition 1 during molding of the rectangular molded product at each temperature were measured, and the mold shrinkage in the FD at room temperature (27°C) was 0.216% (see FIG. 10), and the mold shrinkage in the TD was 0.770% (see FIG. 10). The mold shrinkage in the flow direction (FD) and the transverse direction (TD) of the rectangular molded product were measured by a Thermo-DIC method that combines thermography and DIC. Specifically, the shrinkage behavior and temperature change of rectangular molded products were measured synchronously using the Thermo-DIC method, and the molding shrinkage rates in the flow direction (FD) and transverse direction (TD) of the rectangular molded products after cooling was completed were calculated from the results.

[0112] (Step 3) CAE analysis models of the constrained L-shaped molded product and the unconstrained L-shaped molded product of Example 1 were prepared. The CAE analysis model of the constrained L-shaped molded product and the CAE analysis model of the unconstrained L-shaped molded product were the same, and only the input physical property values ​​were changed. The CAE analysis models of the constrained L-shaped molded product and the unconstrained L-shaped molded product of Example 1 were prepared using ANSYS (manufactured by ANSYS), which is a general-purpose finite element software. Similarly, CAE analysis models of the constrained U-shaped molded product and the unconstrained U-shaped molded product of Example 2 were prepared.

[0113] (Step 4) From the mold shrinkage rate of the rectangular molded product in the flow direction (FD) and the flow transverse direction (TD) measured in Step 2, obtain CAE analysis data according to the procedures in Steps 4-1 and 4-2 below. Input this CAE analysis data into the CAE analysis model created in Step 3, and calculate the θ of the constrained L-shaped molded product of Example 1 by CAE analysis. origin , θ const and θ of unconstrained L-shaped molded productfree Similarly, the θ of the constrained U-shaped molded product of Example 2 was calculated by CAE analysis. origin , θ const and θ of unconstrained U-shaped molded product free were calculated respectively.

[0114] (Step 4-1) In the CAE analysis of the unconstrained L-shaped molded product of Example 1, the mold shrinkage rate in the flow direction (FD) and the mold shrinkage rate in the transverse direction (TD) of flow obtained in Step 2 were used as CAE analysis data as they were. Similarly, in the CAE analysis of the unconstrained U-shaped molded product of Example 2, the mold shrinkage rate in the flow direction (FD) and the mold shrinkage rate in the transverse direction (TD) of flow obtained in Step 2 were used as CAE analysis data as they were.

[0115] (Step 4-2) In the CAE analysis of the constrained L-shaped molded product of Example 1, the mold shrinkage ratio obtained in step 2 was reduced as shown in the following steps 4-2-1 and 4-2-2 and used as CAE analysis data. In the CAE analysis of the constrained U-shaped molded product of Example 2, the mold shrinkage ratio obtained in step 2 was also reduced as shown in the following steps 4-2-1 and 4-2-2 and used as CAE analysis data.

[0116] (Step 4-2-1) The shrinkage rate in the flow direction (FD) of the constrained L-shaped molded product of Example 1 used as CAE analysis data was calculated from the above formula (5) and was 0.101%. The stress relaxation rate calculated using the bimetal method was obtained as follows. Specifically, a joining plate was used to join a primary side plate made of LAPEROS (registered trademark) LCP S135 and a secondary side plate made of the above polyphenylene sulfide resin composition 1, which is the same resin material as the constrained L-shaped molded product of Example 1, to obtain the elastic modulus EBi-Metal of the molded product of the above polyphenylene sulfide resin composition 1 at each temperature (see FIG. 10). In addition, a three-point bending test was performed at each temperature in accordance with JIS K7171:2016 to obtain the bending elastic modulus EBending (see FIG. 10). The stress relaxation rate at room temperature (27°C) was calculated from the above formula (7) using the bimetal method and was 53.4%. The flow direction (FD) shrinkage rate of the constrained L-shaped molded product of Example 2 used as CAE analysis data is also 0.101%, which is the same as the flow direction (FD) shrinkage rate of the constrained L-shaped molded product of Example 1 used as CAE analysis data. This is because the constrained L-shaped molded product of Example 1 and the constrained U-shaped molded product of Example 2 are both made of the above-mentioned polyphenylene sulfide resin composition 1, and therefore the rectangular molded product used when calculating the flow direction shrinkage rate is also the same, and the secondary side plate used in the bimetal method is also the same. In other words, even if the shapes of the resin molded products are different, the same flow direction (FD) shrinkage rate is used as long as the same resin composition is used.

[0117] (Step 4-2-2) The shrinkage rate in the transverse direction (TD) of the constrained L-shaped molded product of Example 1 used as CAE analysis data was calculated using the above formula (8). Here, 11 arbitrary numbers between 0 and 1 were used as the arbitrary coefficient. Similarly, the shrinkage rate in the transverse direction (TD) of the constrained U-shaped molded product of Example 2 used as CAE analysis data was calculated using the above formula (8).

[0118] (Step 5) Using the spring-in angles of the constrained L-shaped molded product and the unconstrained L-shaped molded product of Example 1 obtained by each CAE analysis, the stress relaxation rate of the constrained L-shaped molded product was calculated from the above formula (1) by CAE analysis. Then, the relationship between the stress relaxation rate of the constrained L-shaped molded product obtained by CAE analysis and the relaxation rate in the flow orthogonal direction (TD) according to the arbitrary coefficient set in the above formula (8) was plotted, and an approximate formula (y = 0.6582x + 16.77) was obtained. Similarly, the relationship between the stress relaxation rate of the constrained U-shaped molded product of Example 2 obtained by CAE analysis and the relaxation rate in the flow orthogonal direction (TD) according to the arbitrary coefficient set in the above formula (8) was plotted, and an approximate formula (y = 0.7153x + 15.156) was obtained.

[0119] (Step 6) The stress relaxation rate of the constrained L-shaped molded product in the transverse direction (TD) of flow was calculated to be 45.5% by substituting the stress relaxation rate of the constrained L-shaped molded product in the measured direction (TD) of flow calculated in step 1 (42.2%) into the above approximation formula obtained in step 5. Similarly, the stress relaxation rate of the constrained U-shaped molded product in the transverse direction (TD) of flow calculated to be 39.4% by substituting the stress relaxation rate of the constrained U-shaped molded product in the measured direction (TD) of flow calculated in step 1 (33.7%) into the above approximation formula obtained in step 5.

[0120] Therefore, it was confirmed that the above method can calculate the flow perpendicular direction (TD) of constrained L-shaped molded products and constrained U-shaped molded products from the inclination obtained by CAE analysis and the actual measurement value.

[0121] 10...First resin molded product 11, 21…Corner section 11A, 21A…Inner side 20…Second resin molded product 30…Restraint jig 40…Third resin molded product

Claims

1. A method for calculating a stress relaxation rate of a resin molded product using a spring-in deformation of the resin molded product during a cooling process of the resin molded product molded using a metal mold, comprising: removing a first resin molded product having a molded corner portion from the metal mold, or cooling the first resin molded product to a predetermined temperature while the first resin molded product is present in the metal mold and while a restraining jig is in contact with an inner surface of the corner portion; removing from the mold a second resin molded product having a corner portion molded under the same conditions as the first resin molded product, using the same resin material as the first resin molded product, and having the same shape as the first resin molded product; and cooling the second resin molded product to the predetermined temperature in a state in which the restraining jig is not in contact with an inner surface of the corner portion of the second resin molded product; The outer angle θ of the corner portion of the first resin molded product before cooling ｏｒｉｇｉｎ (°) After cooling to the predetermined temperature, the first resin molded product is removed from the restraining jig, and the outer angle θ of the corner portion of the first resin molded product is then measured. ｃｏｎｓｔ (°) After cooling to the predetermined temperature, the outer angle θ of the corner portion of the second resin molded product ｆｒｅｅ (°) Measured θ ｏｒｉｇｉｎ , θ ｃｏｎｓｔ , and θ ｆｒｅｅ Calculating a stress relaxation rate Relaxθ (%) of the first resin molded product in a state in which the restraining jig is removed after cooling to the predetermined temperature from the following formula (1) based on the above formula: A method comprising: [0010]

2. 2. The method according to claim 1, wherein when at least one of the first resin molded product and at least one of the second resin molded product are taken as one set, there are a plurality of sets of the first resin molded product and the second resin molded product, and the cooling conditions for the cooling are different for each set in a temperature range below the higher of a crystallization temperature and a glass transition temperature of a resin material constituting the first resin molded product.

3. The method according to claim 2 , wherein the cooling conditions are conditions related to at least one of a cooling rate and a restraining time by the restraining jig.

4. 2. The method according to claim 1, wherein when at least one of the first resin molded product and at least one of the second resin molded product are considered as a set, there are a plurality of sets of the first resin molded product and the second resin molded product, and molding conditions of the first resin molded product and the second resin molded product are different for each set.

5. The method according to claim 4, wherein the molding conditions are at least any one of conditions regarding the presence or absence of an insert jig, a demolding temperature from the mold, a holding pressure, and an injection speed.

6. The method of claim 1 , wherein the restraining fixture is an insert fixture or the mold structure itself.

7. A method for calculating a stress relaxation rate in a direction perpendicular to a flow direction, which is a direction perpendicular to a flow direction of a resin material during molding in a resin molded product, by using a spring-in deformation of the resin molded product during a cooling process of the resin molded product molded using a metal mold, comprising: Calculating the stress relaxation rate Relaxθ of the first resin molded product in a state in which the first resin molded product is cooled to the predetermined temperature and the restraining jig is removed by the method according to claim 1; A step of measuring a mold shrinkage rate in a flow direction of the resin material during molding and a mold shrinkage rate in a direction perpendicular to the flow direction, which is a direction perpendicular to the flow direction, of a third resin molded product that is molded under the same conditions as the first resin molded product using the same resin material as the first resin molded product and that is cooled to the predetermined temperature; A step of obtaining CAE analysis data for the first resin molded product and CAE analysis data for the second resin molded product using the mold shrinkage rate in the flow direction and the mold shrinkage rate in the perpendicular direction to the flow direction of the third resin molded product that are actually measured; creating CAE analysis models in which the first resin molded product and the second resin molded product are divided into a plurality of elements; Using the CAE analysis data, a CAE analysis is performed on each of the CAE analysis models to obtain the θ ｏｒｉｇｉｎ , θ ｃｏｎｓｔ , and θ ｆｒｅｅ and calculating The stress relaxation rate Relaxθ of the first resin molded product and the θ calculated by the CAE analysis ｏｒｉｇｉｎ , θ ｃｏｎｓｔ , and θ ｆｒｅｅ calculating a stress relaxation rate in the direction perpendicular to flow of the first resin molded product in a state in which the restraining jig is removed after the first resin molded product is cooled to the predetermined temperature using the above-mentioned equation; A method comprising:

8. the CAE analysis data of the first resin molded product is a value calculated using a measured mold shrinkage rate of the third resin molded product in the flow direction and a stress relaxation rate in the flow direction obtained by a bimetal method, and a value calculated using a stress relaxation rate in a direction perpendicular to the flow direction using an arbitrary coefficient; and the CAE analysis data of the second resin molded product is a measured mold shrinkage rate of the third resin molded product in the flow direction and a measured mold shrinkage rate of the third resin molded product in the direction perpendicular to the flow direction, The step of calculating a stress relaxation rate in the direction perpendicular to the flow of the first resin molded product after cooling to the predetermined temperature includes calculating a stress relaxation rate in the direction perpendicular to the flow of the first resin molded product after cooling to the predetermined temperature, the stress relaxation rate being calculated based on the θ ｏｒｉｇｉｎ , θ ｃｏｎｓｔ , and θ ｆｒｅｅ to calculate a relaxation rate in the direction perpendicular to the flow of the first resin molded product from the formula (1) using the arbitrary coefficient, to obtain an approximation of the relaxation rate in the direction perpendicular to the flow of the first resin molded product corresponding to the arbitrary coefficient, and to substitute the actually measured stress relaxation rate Relaxθ of the first resin molded product into the approximation, thereby calculating the relaxation rate in the direction perpendicular to the flow of the first resin molded product at the actually measured stress relaxation rate Relaxθ of the first resin molded product.

9. 9. The method according to claim 7, wherein the third resin molded product is in a rectangular shape, and the width of the third resin molded product is the same as the width of the first resin molded product.

10. A method for producing a resin molded product having a corner portion used to calculate a stress relaxation rate of the resin molded product, comprising: a step of molding a first resin molded product having a corner portion in a mold so that an insert jig is in contact with an inner side surface of the corner portion, and then cooling the first resin molded product to a predetermined temperature while the insert jig is in contact with the inner side surface of the corner portion of the first resin molded product, and removing the insert jig from the first resin molded product after cooling to the predetermined temperature to obtain a first resin molded product; a step of molding a second resin molded product having a corner portion in a metal mold so that an insert jig is in contact with an inner surface of the corner portion, and then cooling the second resin molded product to the predetermined temperature in a state in which the insert jig is removed from the second resin molded product which has been cooled to a higher temperature than a crystallization temperature or a glass transition temperature of a resin material constituting the second resin molded product, and removing the second resin molded product from the metal mold to obtain the second resin molded product; A method for manufacturing a resin molded product comprising the steps of:

11. The method for manufacturing a resin molded product according to claim 10, wherein a molding shrinkage rate of a resin material constituting the first resin molded product is greater than a molding shrinkage rate of a material constituting the insert jig.

12. A method for producing a resin molded product having a corner portion used to calculate a stress relaxation rate of the resin molded product, comprising: a step of molding a first resin molded product having a corner portion in a metal mold so that a part of the metal mold is in contact with an inner side surface of the corner portion, and then cooling the first resin molded product to a predetermined temperature while a part of the metal mold is in contact with the inner side surface of the corner portion of the first resin molded product, and removing the first resin molded product from the metal mold after cooling to the predetermined temperature to obtain a first resin molded product; a step of molding a second resin molded product having a corner portion in a metal mold so that a part of the metal mold is in contact with an inner surface of the corner portion, and then cooling the second resin molded product to the higher of a crystallization temperature and a glass transition temperature of a resin material constituting the second resin molded product, and then cooling the second resin molded product to the predetermined temperature in a state in which the second resin molded product is removed from the metal mold to obtain a second resin molded product; A method for manufacturing a resin molded product comprising the steps of:

13. 13. The method according to claim 10, further comprising obtaining a plurality of sets of the first resin molded product and the second resin molded product when at least one of the first resin molded product and at least one of the second resin molded product is considered as one set, and varying at least one of a demolding temperature from a mold, a holding pressure, and an injection speed during molding of the first resin molded product and the second resin molded product for each set.

14. 6. A method for determining a molding process capable of maximizing the stress relaxation rate of the resin molded product by performing the method for calculating a stress relaxation rate of a resin molded product according to any one of claims 2 to 5, calculating the stress relaxation rate Relaxθ for each product, and comparing the calculated stress relaxation rates Relaxθ.

15. A method for calculating an elastic modulus of a resin molded product having a corner portion, taking into account stress relaxation, comprising the steps of: The elastic modulus of the resin material constituting the first resin molded product defined in claim 1 is E ０ When the stress relaxation rate Relaxθ (%) of the first resin molded product calculated by the method according to claim 1 and the elastic modulus E ０ and calculating an elastic modulus Erelaxθ (%) of the first resin molded product taking into account the stress relaxation rate Relaxθ by the following formula (2). Erelaxθ = (1-Relaxθ)×E 0 …Formula (2)

16. A method for calculating an elastic modulus of a resin molded product having a corner portion, taking into account stress relaxation, comprising the steps of: The method according to claim 8, wherein the θ of the second resin molded product ｆｒｅｅ The mold shrinkage rate in the direction perpendicular to the flow used in calculating the above by CAE analysis is a ０ (%), a (%) is a molding shrinkage rate of the first resin molded product in the direction perpendicular to the flow, which is used in a CAE analysis such that the stress relaxation rate Relaxθ (%) of the resin molded product 10 calculated by the CAE analysis is the same as the actually measured stress relaxation rate Relaxθ (%) of the first resin molded product, and E (%) is a previously measured elastic modulus of the resin material constituting the first resin molded product. ０ and calculating an elastic modulus Erelaxθ (%) taking into consideration the measured stress relaxation rate Relaxθ of the first resin molded product by the following formula (3). [0025]

17. A method for predicting the life of a resin molded product by CAE analysis, using a stress relaxation rate calculated by the method for calculating a stress relaxation rate of a resin molded product according to claim 1 or a stress relaxation rate calculated by the method for calculating a stress relaxation rate in a direction perpendicular to flow in a resin molded product according to claim 7.

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