Method for identifying the stress relaxation temperature range of a thermoplastic resin composition, method for determining molding conditions and / or annealing conditions for a molded product, method for calculating the relaxation modulus of a thermoplastic resin composition, method for predicting deformation and / or occurrence of brittle parts in a molded body, and method for predicting residual stress in a molded body

Abstract

To simply recognize which temperature area is most effective for stress relaxation concerning a resin composition.SOLUTION: There is provided a method for identifying a stress relaxation temperature area of a thermoplastic resin composition. The composition contains a thermoplastic resin and elastomer. A fusion point of the thermoplastic resin is higher than a higher point between the fusion point and the softening point of the elastomer. In the method, temperature is changed so as to allow the following two processes to continue, i.e., a temperature raising process for raising the temperature of a test piece molded from the composition to the temperature less than the fusion point of the thermoplastic resin after lowering the temperature to be equal to or less than glass-transition temperature of the elastomer and a temperature lowering process for lowering the temperature of the test piece to the temperature equal to or less than the glass-transition temperature of the elastomer. Then, dynamic viscoelasticity of the test piece is measured, so as to identify the stress relaxation temperature area of the elastomer based on a difference in the measured dynamic viscoelasticity of the test piece between the temperature raising process and the temperature lowering process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for identifying the stress relaxation temperature range of a thermoplastic resin composition. [Background technology]

[0002] Insert moldings, which are composites of metal parts and resin, are used in automobiles, electrical and electronic parts, and other applications for various purposes, such as reducing the weight of electrical and electronic control parts and metal parts. When such insert-molded products are used in environments with large temperature changes, heat shock cracking caused by the difference in linear expansion coefficient between the resin and metal is often a problem, and research has been conducted into resin materials and processing methods to address this issue. For example, adding various elastomers to resin materials is one way to improve heat shock resistance, but the effects of various elastomers cannot be determined without actual evaluation, so selecting a resin material requires a huge amount of work.

[0003] On the other hand, a method has been proposed for obtaining resin compositions with excellent stress relaxation properties based on the results of dynamic viscoelasticity measurements (DMA). Resin compositions with excellent stress relaxation properties are thought to be less prone to the accumulation of internal strain and to have excellent heat shock resistance. For example, according to Patent Document 1, a resin composition having a tan δ peak temperature of 0 to 60°C and a peak value of 0.8 to 5 or less, obtained by dynamic viscoelasticity measurement at a frequency of 10 rad / s (1.6 Hz) in a temperature range of -40 to 150°C, is considered to have excellent stress relaxation properties. According to Patent Document 2, an automotive molded article molded from a thermoplastic resin composition containing a cross-copolymerized olefin-aromatic vinyl compound-diene copolymer is considered to have excellent stress relaxation properties when the maximum and minimum values ​​of tan δ in the temperature range of 0 to 30°C are 0.5 or more and 0.05 or more, respectively, and the difference between the maximum and minimum values ​​is 2.0 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 095683 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-265544 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the above-mentioned documents disclose the dynamic viscoelastic properties of resin compositions that are said to have excellent stress relaxation properties, it is unclear which temperature range is most effective for stress relaxation for the resin composition. Therefore, there is a problem in that the temperature range most effective for stress relaxation of the resin composition cannot be reflected in, for example, the molding conditions or annealing conditions during injection molding of the resin composition, thereby, for example, reducing residual stress in molded products of the resin composition. Furthermore, a method for determining the temperature range most effective for stress relaxation is desired to be a simple method that does not require a large number of steps for selecting a resin material.

[0006] Therefore, an object of the present invention is to provide a simple method for determining which temperature range is most effective for stress relaxation in a resin composition. [Means for solving the problem]

[0007] A first aspect of the present invention is a method for identifying the stress relaxation temperature range of a thermoplastic resin composition, wherein the composition comprises a thermoplastic resin and an elastomer, and the melting point of the thermoplastic resin is higher than the higher of the melting point or softening point of the elastomer. This method is a test piece molded from the composition is cooled to a temperature equal to or lower than the glass transition temperature of the elastomer, and then the temperature is changed so as to continuously undergo a heating process in which the temperature is raised to a temperature lower than the melting point of the thermoplastic resin, and a cooling process in which the temperature of the test piece is lowered to a temperature equal to or lower than the glass transition temperature of the elastomer, and dynamic viscoelasticity of the test piece is measured; The stress relaxation temperature range of the elastomer is The dynamic viscoelasticity of the test piece measured during the temperature rise process and the temperature fall process A specified temperature range containing the temperature at which the ratio or difference of loss tangents is greatest Identify.

[0008] A second aspect of the present invention is a method for identifying the stress relaxation temperature range of a thermoplastic resin composition using a test piece obtained by completely coating a molded piece of the composition with a coating resin that is a thermoplastic resin or a thermosetting resin, wherein the higher of the melting point or glass transition temperature of the coating resin is higher than the higher of the melting point or glass transition temperature of the composition. This method is the temperature of the test piece is lowered to a temperature not higher than the glass transition temperature of the composition, and then a temperature-raising process is carried out so as to continuously raise the temperature to a temperature lower than the higher of the melting point or the glass transition temperature of the coating resin, and a temperature-lowering process is carried out so as to continuously lower the temperature of the test piece to a temperature not higher than the glass transition temperature of the composition, and the dynamic viscoelasticity of the test piece is measured; The stress relaxation temperature range of the elastomer is The dynamic viscoelasticity of the test piece measured during the temperature rise process and the temperature fall process A specified temperature range containing the temperature at which the ratio or difference of loss tangents is greatest Identify.

[0009] A third aspect of the present invention is a method for determining molding conditions and / or annealing conditions for a molded article made from a thermoplastic resin composition, based on the stress relaxation temperature range of the composition identified by the above method.

[0010] A fourth aspect of the present invention is a method for calculating a relaxation modulus of a thermoplastic resin composition, comprising calculating the relaxation modulus of the composition based on the storage modulus and loss modulus of the composition during the temperature decrease process obtained by the above method.

[0011] A fifth aspect of the present invention is a method for predicting deformation and / or occurrence of fragile parts in a molded body, comprising: modeling the relaxation modulus of the composition calculated by the above-described method; and predicting, based on the modeled relaxation modulus of the composition, the deformation and / or occurrence of fragile parts in a molded body containing the composition as a main component when the molded body is molded.

[0012] A sixth aspect of the present invention is a method for predicting residual stress of a molded body, comprising: modeling the relaxation modulus of the composition calculated by the above-described method; and predicting residual stress of the molded body when the molded body contains the composition as a main component, based on the modeled relaxation modulus of the composition. [Effects of the Invention]

[0013] According to one aspect of the present invention, it is possible to grasp, by a simple method, which temperature range is most effective for stress relaxation in a resin composition. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 10 is a diagram showing the measurement results of DMA measurement according to one embodiment. [Figure 2] FIG. 10 is a diagram showing the measurement results of DMA measurement according to one embodiment. [Figure 3] FIG. 1 is a diagram illustrating an evaluation method using a bimetal method. [Figure 4] FIG. 10 is a diagram showing the results of evaluation using a bimetal method. [Figure 5] FIG. 1 is a diagram illustrating an evaluation method using a generated stress evaluation method. [Figure 6] FIG. 10 is a diagram showing the evaluation results obtained by a generated stress evaluation method. [Figure 7] 10A and 10B are diagrams showing the results of DMA measurements and verification results using a bimetal method according to an embodiment. [Figure 8] 10A and 10B are diagrams showing the results of DMA measurements and verification results using a bimetal method according to an embodiment. [Figure 9] FIG. 1 is a diagram illustrating a DMA measurement method according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] (1) First embodiment In the present disclosure, the term "thermoplastic resin composition" refers to a composition containing a thermoplastic resin and an elastomer. The thermoplastic resin may be a resin mixture obtained by blending multiple resin materials, and is a resin whose melting point is higher than the melting point or softening point of the elastomer, whichever is higher. Thermoplastic resin compositions (hereinafter sometimes simply referred to as "compositions") also include those to which desired properties have been imparted by adding additives such as resins other than thermoplastic resins, fillers such as glass fibers and inorganic powders, nucleating agents, colorants such as dyes and pigments, antioxidants, stabilizers, plasticizers, lubricants, mold release agents, and flame retardants. In the present disclosure, the term "stress relaxation temperature region" refers to a temperature region or temperature range that is effective for stress relaxation of a composition (i.e., where stress relaxation is likely to proceed).

[0016] The thermoplastic resin material is not limited, but examples include polyacetal (POM), polyamide (PA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether ether ketone (PEEK), styrene-based resin, acrylic-based resin, etc.

[0017] Examples of the elastomer include olefin polymers such as ethylene-ethyl acrylate copolymers, polyester elastomers, styrene elastomers, polyamide elastomers, silicone elastomers, and urethane elastomers. These elastomers may be grafted copolymers, and can be effectively used if they can be mixed into the composition of the present invention. The elastomer preferably contains a glycidyl group, and examples of the elastomer containing a glycidyl group include glycidyl group-containing olefin copolymers such as ethylene-glycidyl methacrylate copolymer and ethylene-glycidyl methacrylate-methyl acrylate copolymer (for example, Bondfast manufactured by Sumitomo Chemical).

[0018] As a result of extensive research, the inventors of the present application have discovered that the stress relaxation characteristics of an elastomer during its solidification process can be easily understood by comparing the difference in dynamic viscoelasticity between the temperature-raising process and the temperature-lowering process of a thermoplastic resin composition. More specifically, dynamic viscoelasticity measurements (DMA measurements) are performed while varying the temperature of a thermoplastic resin composition. The temperature of a test specimen molded from the composition is then lowered below the glass transition temperature of the elastomer, followed by a temperature increase process in which the temperature is increased to a temperature below the melting point of the thermoplastic resin, followed by a temperature decrease process in which the temperature of the test specimen is decreased to a temperature below the glass transition temperature of the elastomer. Because the temperature range is below the melting point of the thermoplastic resin during both the temperature increase and decrease processes, the thermoplastic resin contained in the composition during measurement is in a solid state. However, the phase (solid state, liquid state) of the elastomer contained in the composition during measurement differs between the temperature increase and decrease processes depending on the melting point or softening point. For example, if an elastomer undergoes a phase transition from a liquid state to a solid state during the temperature decrease process and remains in a nearly solid state during the temperature increase process, the dynamic viscoelasticity of the test specimen will differ between the temperature increase and decrease processes due to this phase difference. By observing this difference in dynamic viscoelasticity, the stress relaxation temperature range of the elastomer can be identified. The difference in dynamic viscoelasticity is, for example, but not limited to, the ratio or difference of the loss tangent (tanδ) between the temperature rising process and the temperature falling process of the test piece. The larger the tanδ ratio (tanδ ratio, described later), the greater the ratio of the viscous component of the elastomer, and therefore, it is thought that stress relaxation of the elastomer is more likely to proceed in this region. [Example]

[0019] An example of a DMA measurement method for a thermoplastic resin composition according to one embodiment will be described below. First, the measurement of the test piece (thermoplastic resin composition) (polyphenylene sulfide (PPS) 64%, elastomer 6%, glass fiber 30%) according to the example will be described. The PPS contained in the test specimen has a melting point of 280°C and a glass transition temperature of approximately 90°C. The elastomer contained in the test specimen is Bondfast (registered trademark) 7M manufactured by Sumitomo Chemical, which has a melting point of 52°C and a glass transition temperature of -33°C.

[0020] [DMA measurement conditions] During the heating process, the temperature of the test piece was increased from -60°C to 250°C at a rate of 2°C / min. During the cooling process, the temperature of the test piece was decreased from 250°C to -60°C at a rate of -2°C / min. During this heating and cooling process, the test piece was placed in a DMA tester and subjected to DMA measurements as specified in ISO 6721 (JIS K7244). The DMA measurements were performed in three-point bending mode (load strain: 0.02%) at a fixed frequency of 1 Hz. Based on the measurement results, the tan δ measured during the temperature rise and fall processes (tan δ during temperature rise and fall) and the tan δ ratio are plotted in Figure 1. Here, the tan δ ratio is the ratio of tan δ during the temperature fall process to tan δ during the temperature rise process (i.e., tan δ during temperature fall / tan δ during temperature rise).

[0021] Figure 2 shows tan δ (tan δ during temperature rise and tan δ during temperature fall) and the tan δ ratio (tan δ during temperature fall / tan δ during temperature rise) based on test results for a different test specimen (70% polyphenylene sulfide (PPS) and 30% glass fiber) from that shown in Figure 1. This test specimen differs from the one shown in Figure 1 in that it does not contain an elastomer (Bondfast (registered trademark) 7M). The DMA measurement conditions were the same as those shown in Figure 1.

[0022] As shown in Figure 1, the difference between tan δ during the temperature rise process and tan δ during the temperature fall process is large in the temperature range of -20°C to 60°C, and the tan δ ratio is largest in the temperature range of approximately 0°C to 20°C. On the other hand, when no elastomer is included, the difference between tan δ during the temperature rise process and tan δ during the temperature fall process is small across the entire temperature range, as shown in Figure 2. From this, it can be seen that the reason for the large difference between tan δ during the temperature rise process and tan δ during the temperature fall process in Figure 1 is the influence of the inclusion of an elastomer (Bondfast (registered trademark) 7M) in the test specimen. As mentioned above, the melting point of BondFast (registered trademark) 7M is 52°C. Therefore, in the temperature range where the tan δ ratio is large, BondFast (registered trademark) 7M is in a phase transition region from a liquid state to a solid state during the temperature drop process, and is in a nearly solid state during the temperature rise process, so it is thought that the tan δ ratio became largest in the temperature range of approximately 0°C to 20°C.

[0023] From the above test results, it is estimated that the temperature range (stress relaxation temperature range) that is effective for stress relaxation due to the elastomer contained in the test specimen, which is the basis for the test results shown in Figure 1, is approximately 0°C to 20°C. In Figure 1, it is thought that stress relaxation of the elastomer can be efficiently achieved by ensuring the time spent on stress relaxation within the temperature range of -20°C to 60°C, where the tan δ ratio is greatest, and where the difference between tan δ during the heating process and tan δ during the cooling process occurs. The inventors of the present application have verified this assumption using two methods: the bimetal method and the generated stress evaluation method.

[0024] [Verification by bimetal method] The bimetal method is a method for calculating the elastic modulus of a resin material. Generally, a bimetal is a type of composite metal material made by bonding two metal plates with different thermal expansion coefficients, and has the property of bending with temperature changes. However, the properties of a bimetal are not limited to metal plates; a bonded plate made by bonding two plates of materials with different thermal expansion coefficients exhibits similar properties. Therefore, the bimetal method calculates the elastic modulus of a resin molded product using a bonded plate made by bonding a primary plate containing a material with a thermal expansion coefficient different from that of the resin material contained in the resin molded product whose elastic modulus is to be calculated, and a secondary plate containing the same resin material as the resin molded product.

[0025] In Figure 3, the thermal expansion coefficients of the primary side plate 31 and secondary side plate 32 of the joining plate 3 are α1 and α2, respectively, and the elastic moduli (longitudinal elastic modulus) of the primary side plate 31 and secondary side plate 32 of the joining plate 3 are E1 and E2, respectively. The plate thicknesses of the primary side plate 31 and secondary side plate 32 of the joining plate 3 are h1 and h2, respectively, and the plate thickness of the joining plate 3 is h (= h1 + h2). In this case, during the cooling process after the joining plate 3 is removed from the mold, the temperature immediately after the resin-molded product of the joining plate 3 is T1, room temperature is T2, the length of the joining plate 3 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. The displacement (warpage) of the joining plate 3 can be geometrically calculated using the following equation (1): The thermal expansion coefficient α2 of the secondary side plate is equivalent to the molding shrinkage rate of the resin molded product to be evaluated.

[0026]

number

[0027] For the verification, LAPEROS (registered trademark) LCP S135 was used as the primary side plate 31, and the same thermoplastic resin composition as in Fig. 1 was used as the secondary side plate 32. Insert molding was performed using the primary side plate as an insert member, and the displacement D of the joining plate 3 was measured successively during the cooling process after removal from the mold. That is, a joining plate 3 having a predetermined shape (i.e., a shape for which h1, h2, h, and L in formula (1) are specified) was formed, and the displacement D of the joining plate was measured sequentially as the temperature was changed from temperature T1 (the same as the temperature immediately after the resin molded product was removed from the mold) to temperature T2 (e.g., room temperature). The displacement D of the joining plate is a value that reflects the relaxation modulus of the secondary side plate 32 made of the composition to be evaluated. That is, by calculating the elastic modulus of the secondary side plate based on the measured displacement D, the calculated elastic modulus of the secondary side plate takes into account the viscoelastic behavior during the cooling process after the composition to be evaluated is removed from the mold.

[0028] As shown in Figure 3, when measuring the displacement D of the bonded plate, one end of the bonded plate 3 was fixed using a fixture 4, creating a cantilever state. A vise was used as the fixture 4. The camera 27 captured an image of the bonding plate 3 from a direction perpendicular to the curved surface of the bonding plate 3 that curves in response to temperature changes. The thermograph 28 measured the amount of infrared radiation emitted from the surface of the secondary side plate 32 of the bonding plate 3 in synchronization with the image capturing timing of the camera 27, and captured an image of the temperature distribution on the surface of the secondary side plate 32.

[0029] The control device 25 calculates the amount of deformation (warpage) D of the joining plate 3 based on images successively acquired from the camera 27, and the relationship between the temperature obtained by the thermograph 28 and the amount of deformation is plotted in FIG. Figure 4 shows that the amount of deformation caused by the secondary side plate 32 made of the composition under evaluation is highest around 20°C. While the amount of deformation is greatest in the temperature range around 20°C, it decreases after reaching the maximum. This decrease in deformation can be said to be due to stress relaxation, and is consistent with the high tan δ ratio in Figure 1. In other words, the thermoplastic resin composition under evaluation undergoes a phase transition from a liquid state to a solid state around 20°C during the molding process, i.e., the cooling process, and therefore the temperature range around 20°C is effective for stress relaxation. This result is consistent with the results in Figure 1.

[0030] [Verification by generated stress evaluation method] The inventors of the present application also verified the estimation of the stress relaxation temperature range based on Figure 1 using an generated stress evaluation method. For details about the generated stress evaluation method, please refer to Japanese Patent Application Laid-Open No. 2020-159729 by the same applicant as the present application.

[0031] In the stress generation evaluation method, a cylindrical insert-molded product shown in Fig. 5(a) was molded. Fig. 5(b) is a cross-sectional view of the A-A' plane in Fig. 5(a). The insert-molded product consists of a resin composition 10 and a cylindrical insert member 12 with a strain gauge 14 attached to a position (inner wall) that does not contact the resin composition 10. The strain gauge 14 is connected to a strain measuring device (not shown) using a cable 16. The thermoplastic resin composition used to obtain the results shown in Figure 1 was used as the resin composition 10, and a uniform-walled hollow cylinder made of Ti-6Al-4V was used as the insert member 12, and the resin composition 10 was insert-molded onto the outer periphery of the insert member.

[0032] The inner wall temperature and internal stress (circumferential stress) of the insert member 12 were measured during the cooling process after the insert-molded product was removed from the mold. Specifically, the strain value (initial value A) of the inner wall of the insert member before the resin composition was molded was measured in advance using a strain gauge attached to the inner wall of the insert member. While continuing to measure the strain using the strain gauge, the resin composition was insert-molded onto the outer periphery of the insert member, and the strain value (B) of the inner wall of the insert member during the cooling process after the insert-molded product was removed from the mold was continuously measured. The internal stress (circumferential stress) of the resin composition 10 in the insert-molded product was calculated using this and the strain generated on the inner wall of the insert member 12, which was obtained by calculating the change in strain (B A) from the initial value A.

[0033] Furthermore, in the above process, a thermocouple was attached to the insert member to measure the temperature of the insert member 12 during the cooling process after removal from the mold. At this time, by synchronizing the timing of acquiring the strain value of the insert member 12 with the timing of acquiring the temperature of the insert member 12, data showing the relationship between the temperature of the insert member 12 (i.e., the surface temperature of the resin composition 10 in contact with it) and the internal stress (circumferential stress) was acquired.

[0034] The results of evaluation using the stress generation evaluation method are shown in Figure 6. Figure 6 shows the relationship between the time during insert molding, the stress generated in the inner diameter portion (resin inner diameter) of the resin composition 10 (solid line), and the temperature (dotted line) of the inner diameter portion (metal inner diameter portion) of the metal insert member 12. Figure 6 shows that the stress generated in the inner diameter portion of the resin composition 10 gradually decreases when the temperature of the metal inner diameter portion (i.e., the surface temperature of the resin composition 10 in contact with it) is around 20°C. This stress decrease can be said to be influenced by stress relaxation, and is not inconsistent with the increase in the tan δ ratio in Figure 1.

[0035] As explained above, it was confirmed that the method for identifying the stress relaxation temperature range by DMA measurement described in relation to Figure 1 also matches the results obtained by other methods, the bimetal method and the generated stress evaluation method. The method of identifying the stress relaxation temperature range by DMA measurement depends on the phase transition of the elastomer contained in the thermoplastic resin composition being measured, and therefore can be applied regardless of the elastomer material contained in the composition. For example, Figures 7 and 8 show examples for thermoplastic resin compositions different from those in Figure 1. The measurement conditions for DMA measurement are the same as those in Figure 1.

[0036] Figure 7(a) shows the results of DMA measurement on a test piece (thermoplastic resin composition) (64% polyphenylene sulfide (PPS), 6% elastomer, 30% glass fiber). The elastomer is Bondfast (registered trademark) 2C manufactured by Sumitomo Chemical, with a melting point of 105°C and a glass transition temperature of -26°C. As shown in Figure 7(a), in the temperature range of 0°C to 70°C, the difference between tan δ during the temperature rise process and tan δ during the temperature fall process is large, and the tan δ ratio is greatest in the temperature range of approximately 40°C to 60°C. Figure 7(b) plots the relationship between the temperature and the deformation of the secondary plate when the bimetal method is applied to a bonded plate in which the test piece used in the measurement shown in Figure 7(a) is used as the secondary plate. As shown in Figure 7(b), it was confirmed that the deformation does not change in the temperature range around 60°C, and that this temperature range is effective in alleviating stress.

[0037] Figure 8(a) shows the results of DMA measurement on a test piece (thermoplastic resin composition) (64% polyphenylene sulfide (PPS), 6% elastomer, 30% glass fiber). The elastomer is Bondfast (registered trademark) 7L manufactured by Sumitomo Chemical, with a melting point of 60°C and a glass transition temperature of -33°C. As shown in Figure 8(a), in the temperature range of -10°C to 70°C, the difference between tan δ during the temperature rise process and tan δ during the temperature fall process is large, and the tan δ ratio is greatest in the temperature range of approximately 10°C to 30°C. Figure 8(b) plots the relationship between temperature and deformation of the secondary plate when the bimetal method is applied to a bonded plate in which the test piece used in the measurement shown in Figure 8(a) is used as the secondary plate. As shown in Figure 8(b), the deformation reaches its maximum in the temperature range of around 30°C, but decreases after reaching the maximum. This decrease in deformation can be said to be due to stress relaxation, and is not inconsistent with the increase in the tan δ ratio mentioned above.

[0038] As described above, in one embodiment of the DMA measurement method, the phase change between the liquid state and the solid state of the elastomer contained in the thermoplastic resin composition to be evaluated is focused on, and DMA measurements are performed during the temperature increase and decrease process to observe the difference in dynamic viscoelasticity between the temperature increase and decrease process. Therefore, based on this difference in dynamic viscoelasticity, it is possible to simply determine which temperature range is most effective for stress relaxation. Therefore, when a thermoplastic resin composition containing an elastomer is used in an insert-molded product with a metal member, the number of steps required to select the elastomer material can be significantly reduced.

[0039] (2) Second embodiment Next, a method for identifying the stress relaxation temperature range of a thermoplastic resin composition according to a second embodiment will be described with reference to FIG. In the method of this embodiment, a molded piece made from the composition to be evaluated is completely coated (overmolded) with a resin. The resin that completely coats the molded piece made from the composition to be evaluated is called the "coating resin." Here, a resin whose melting point or glass transition temperature, whichever is higher, is selected as the coating resin so that the viscoelastic properties can be evaluated during the temperature drop process in which the composition to be evaluated changes from a liquid state to a solid state. The coating resin may be a thermoplastic resin or a thermosetting resin.

[0040] Referring to FIG. 9, the specific method of this embodiment is as follows. Step I: A test piece C is prepared by completely covering (overmolding) a molded piece 1 made from the thermoplastic resin composition to be evaluated with a coating resin 2. In the subsequent Step II, the temperature of test piece C is raised above the melting point of the composition (molded piece 1), so in Step I, it is necessary to completely encase molded piece 1 in the coating resin to prevent the liquid composition from leaking out.

[0041] Step II: After cooling the test piece C prepared in Step I to below the glass transition temperature of the composition, the temperature is changed so as to successively include a heating process in which the temperature is raised to a temperature below the higher of the melting point or the glass transition temperature of the coating resin 2, and a cooling process in which the temperature of the test piece C is lowered to a temperature below the glass transition temperature of the composition, and DMA measurement is performed on the test piece C. For example, after cooling to about -60°C, the temperature is changed so as to successively include a heating process in which the temperature is raised to near the melting point of the coating resin 2 at a constant heating rate, and a cooling process in which the temperature is lowered to about -60°C at the same heating rate.

[0042] Step III: Based on the difference in the dynamic viscoelasticity of test piece C measured during the temperature increase and decrease processes in Step II, the stress relaxation temperature range of the composition is identified.

[0043] In step I, in order to improve the adhesion between the molded piece and the coating resin, it is preferable to perform an adhesion improving treatment on the surface of the molded piece 1 before completely covering the molded piece 1 with the coating resin 2. There are no limitations on the adhesion improving treatment, and examples include the following treatments. (Process a) The surface of the molded piece 1 is irradiated with a laser to roughen the surface of the molded piece 1 or form grooves thereon. (Process b) The surface of the molded piece 1 is irradiated with vacuum ultraviolet light in an oxygen atmosphere to generate polar functional groups such as carboxyl groups and hydroxyl groups on the surface of the molded piece 1, thereby activating the surface. (Process c) Inorganic particles such as nano-silica are layered on the surface of the molded piece 1 to reduce the irregularities on the surface of the molded piece 1 and increase the surface area to improve adhesion. (Process d) A portion of the molded piece 1 is first joined to a small piece of thermoplastic resin.

[0044] Step III: First, DMA measurements are performed on a molded piece made from the coating resin during the temperature rise and fall process to determine the storage modulus E' of the coating resin. 2nd , and loss modulus E” 2nd Ask for. Here, the storage modulus of test piece C obtained by DMA measurement of test piece C in step II is defined as E' compand the loss modulus is E” comp It is assumed that the linear sum of the storage modulus and loss modulus shown in the following formula (2) holds when the volume content of the molded piece 1 and the coating resin 2 contained in the test piece C is V 1st , V 2nd The storage modulus and loss modulus of the thermoplastic resin composition constituting the test piece C are defined as E' 1st ,E” 1st Let's say. Then, based on the formula (2), the storage modulus E' of the thermoplastic resin composition constituting the test piece C is calculated. 1st and loss modulus E” 1st Calculate.

[0045]

number

[0046] The method for identifying the stress relaxation temperature range of a composition according to the second embodiment also makes it possible to easily determine which temperature range is most effective for stress relaxation based on the difference in DMA measurements during the temperature rise and fall processes, as in the first embodiment. In particular, the method according to the second embodiment makes it possible to perform DMA measurements up to a temperature range equal to or higher than the melting point of the composition to be evaluated.

[0047] (3) Method for determining molding conditions and / or annealing conditions for molded articles molded from the composition One embodiment is a method for determining molding conditions and / or annealing conditions for a molded article molded from a thermoplastic resin composition based on the stress relaxation temperature range determined by the method for identifying the stress relaxation temperature range of a thermoplastic resin composition. By controlling the cooling temperature and time during injection molding of an insert-molded article in which a metal member and the composition are combined, or the annealing conditions of the insert-molded article, based on the stress relaxation temperature range of the thermoplastic resin composition identified by the method according to the first or second embodiment, it is possible to efficiently perform stress relaxation and extend the product life. Furthermore, when a product is manufactured by welding a thermoplastic resin composition, residual stress can be reduced by controlling the temperature and time during the cooling step of the composition, thereby extending the life of the product.

[0048] (4) Method for calculating the relaxation modulus of a thermoplastic resin composition One embodiment is a method for calculating the relaxation modulus of a composition, in which the relaxation modulus of the composition is calculated based on the storage modulus and loss modulus of the composition during a temperature decrease, which are obtained in the method for identifying the stress relaxation temperature range of the thermoplastic resin composition. This method makes it possible to evaluate or predict residual stresses and the like during the solidification or crystallization process of a thermoplastic resin composition containing an elastomer.

[0049] Specifically, the relaxation modulus of the composition is determined by the following procedure. (i) DMA measurements are performed at different temperatures (at least three points including the reference temperature) over a specified range of time or frequency to determine the relationship between temperature and the storage modulus and loss modulus (or tan δ). Hereinafter, the storage modulus and loss modulus (or tan δ) are referred to as "viscoelastic characteristic values." DMA measurements are performed during the temperature drop process.

[0050] (ii) A time-temperature conversion rule is known in which the curves of viscoelastic characteristic values ​​against time or frequency (log-log plotted curves; hereafter referred to as "viscoelastic curves") measured at different temperatures overlap with a viscoelastic curve at a single reference temperature (referred to as "master curve") by horizontal shifting. Therefore, a master curve at the reference temperature is created from the measurement results of (i), and the WLF (Williams-Landel-Ferry) formula in equation (3) is applied to determine the relationship between the shift factor a(T) and temperature. In equation (3), T S is the reference temperature, and C1 and C2 are constants. Note that the Arrhenius equation may be applied instead of the WLF equation.

[0051]

number

[0052] Then, the horizontal shift of the viscoelastic curve measured at a temperature T other than the reference temperature is calculated by log(a(T)). S The constants C1 and C2 in equation (3) are determined (fitted) so that the viscoelastic curve overlaps with the viscoelastic curve measured in (i). Once the constants C1 and C2 are determined, the shift factor at any temperature (any temperature other than the temperature measured in (i)) can be estimated.

[0053] (iii) Finally, the relaxation modulus of the thermoplastic resin composition to be evaluated is determined from the results of (i) and (ii). By determining the relaxation modulus during the solidification or crystallization process of the composition and modeling it using CAE as described below, it becomes possible to evaluate or predict the behavior of a composition containing an elastomer during the solidification process, etc.

[0054] (5) Method for predicting deformation and / or occurrence of weak parts in molded bodies One embodiment is a method for modeling the relaxation modulus of a composition calculated by the above steps (i) to (iii), and predicting deformation and / or occurrence of fragile parts in a molded body containing the composition as a main component when the molded body is molded based on the relaxation modulus of the modeled composition. For example, Equation 4 is determined from the relaxation modulus calculated in (iii) above. Equation 4 is the spring element (elastic modulus E e and E i (i=1~N)) and dashpot element (viscosity coefficient τ i (i=1 to N)) is a series approximation of the relaxation modulus E(t) using a generalized Maxwell model.

[0055]

number

[0056] As an example of CAE analysis, for structural analysis models of resin molded products, the CAE analysis software "ANSYS Mechanical" by ANSYS, Inc. is well known. By inputting the relaxation modulus modeled by Equation (4) into this analysis software, it becomes possible to accurately predict, for example, the shrinkage behavior and the occurrence of voids (weak parts) during the solidification process of a thermoplastic resin composition.

[0057] One embodiment is a method for predicting residual stress in a molded body, which involves modeling the relaxation modulus of the composition calculated by the above steps (i) to (iii), and predicting the residual stress in the molded body when molding a molded body containing the composition as a main component, based on the relaxation modulus of the modeled composition. By inputting the relaxation modulus modeled by equation (4) into the above analysis software, the accuracy of the residual stress analysis of the molded body can be improved.

[0058] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments. Furthermore, the above-described embodiments can be improved or modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0059] 1...Molded piece 2...Coating resin C...Test piece 25...Control device 27...Camera 28...Thermography 3…Joint plate 31…Primary side plate 32…Secondary side plate 4…Fixing tool 10...Resin material 12...Insert member 14...Strain gauge 16…Cable

Claims

1. A method for identifying a stress relaxation temperature range of a thermoplastic resin composition, comprising: the composition comprises a thermoplastic resin and an elastomer, the melting point of the thermoplastic resin being higher than the melting point or softening point of the elastomer, whichever is higher; The method comprises: a test piece molded from the composition is cooled to a temperature equal to or lower than the glass transition temperature of the elastomer, and then the temperature is changed so as to continuously undergo a heating process in which the temperature is raised to a temperature lower than the melting point of the thermoplastic resin, and a cooling process in which the temperature of the test piece is lowered to a temperature equal to or lower than the glass transition temperature of the elastomer, and dynamic viscoelasticity of the test piece is measured; a predetermined temperature range including a temperature at which the ratio or difference between the loss tangents of the dynamic viscoelasticity of the test piece measured during the temperature increase process and the temperature decrease process is largest, is identified as the stress relaxation temperature range of the elastomer; A method for identifying the stress relaxation temperature range of a thermoplastic resin composition.

2. A method for identifying a stress relaxation temperature range of a thermoplastic resin composition using a test piece obtained by completely covering a molded piece molded from the composition with a coating resin that is a thermoplastic resin or a thermosetting resin, comprising: the higher of the melting point or the glass transition temperature of the coating resin is higher than the higher of the melting point or the glass transition temperature of the composition, The method comprises: the temperature of the test piece is lowered to a temperature not higher than the glass transition temperature of the composition, and then a temperature-raising process is carried out so as to continuously raise the temperature to a temperature lower than the higher of the melting point or the glass transition temperature of the coating resin, and a temperature-lowering process is carried out so as to continuously lower the temperature of the test piece to a temperature not higher than the glass transition temperature of the composition, and the dynamic viscoelasticity of the test piece is measured; a predetermined temperature range including a temperature at which the ratio or difference between the loss tangents of the dynamic viscoelasticity of the test piece measured during the temperature increase process and the temperature decrease process is largest, is identified as the stress relaxation temperature range of the elastomer; A method for identifying the stress relaxation temperature range of a thermoplastic resin composition.

3. and before completely covering a molded piece formed from the composition with the coating resin, subjecting the surface of the molded piece to an adhesion improving treatment.

3. The method of claim 2.

4. The volume content of the molded piece and the coating resin contained in the test piece is V １ｓｔ , V ２ｎｄ year, The storage modulus of the coating resin obtained by measuring the dynamic viscoelasticity of a molded piece formed from the coating resin during the temperature increase process and the temperature decrease process is defined as E' ２ｎｄ and the loss modulus is E" ２ｎｄ year, The storage modulus of the test piece obtained by measuring the dynamic viscoelasticity of the test piece is defined as E' ｃｏｍｐ and the loss modulus is E" ｃｏｍｐ When The storage modulus E' of the composition at different temperatures during the temperature increase process and the temperature decrease process １ｓｔ and loss modulus E" １ｓｔ is calculated based on formula (1), 4. The method according to claim 2 or 3. [Equation 1]

5. A method for determining molding conditions and / or annealing conditions for a molded article molded from a thermoplastic resin composition, based on the stress relaxation temperature range of the composition identified by the method described in any one of claims 1 to 4.

6. Calculating the relaxation modulus of the composition based on the storage modulus and loss modulus of the composition during the temperature decrease process obtained by the method according to claim 1 or 4. A method for calculating the relaxation modulus of a thermoplastic resin composition.

7. A method for predicting deformation and / or occurrence of fragile parts in a molded body, comprising: modeling the relaxation modulus of the composition calculated by the method described in claim 6; and predicting deformation and / or occurrence of fragile parts in a molded body containing the composition as a main component when the molded body is molded based on the modeled relaxation modulus of the composition.

8. A method for predicting residual stress in a molded body, comprising: modeling the relaxation modulus of the composition calculated by the method described in claim 6; and predicting residual stress in the molded body when the molded body contains the composition as a main component, based on the modeled relaxation modulus of the composition.

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