JP5742432B2 - Method for predicting deterioration of molded product, method for producing molded product based on design obtained thereby, and molded product - Google Patents

Description

  The present invention relates to a method for predicting material deterioration of a molded product by computer simulation based on a small amount of experimental data.

  Resin material (plastic) molded articles are used for various purposes as structural members and machine parts, and are used in various environments depending on the applications. In order to ascertain whether or not the resin material molded product maintains sufficient performance for the expected lifetime of the product, an environmental resistance test is performed. Conventionally, in the environmental resistance test, a test piece or an actual product is generally prepared, and an accelerated test under conditions severer than the normal use environment is generally performed.

  However, the deterioration of the test piece and the deterioration of the actual molded product in use are often not always the same. This is considered to be because the evaluation by the test piece is suitable for relative evaluation such as comparison between materials, but the progress of deterioration is different when the shape of the molded product is different.

  Therefore, each time the usage environment or the part structure is changed, it is necessary to perform an environmental resistance test to estimate the product life and to take measures to prevent deterioration. In recent years, the product life has been extended, and it has become questionable whether the results obtained by conventional accelerated tests are sufficiently reliable.

  On the other hand, for designers and developers in the position of designing and developing molded products, test piece deterioration data can be used to predict the actual life of molded products by simply giving a relative evaluation of the materials as described above. It is not a thing. Even if it is preferable to actually make a molded product and perform an environmental resistance test, the environmental resistance test takes time even for an accelerated test. In addition, changing the shape of the parts requires changing the mold and is very expensive, so it is difficult to try various types of design changes. For this reason, there is a great restriction in designing a molded product, and therefore, there has often been an excessive design with a margin for deterioration in advance.

  With regard to material deterioration prediction, Patent Document 1 (Japanese Patent Laid-Open No. 2011-21903) describes a method for predicting quality deterioration of a compound. However, the prediction method of Patent Document 1 does not predict environmental degradation of a molded product.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 7-214629) describes a method for predicting the degree of deterioration during molding of a thermally deteriorated resin. However, the prediction method of Patent Document 2 deals with deterioration at the time of molding, and does not predict deterioration of a molded product in a use environment.

JP 2011-21903 A JP 7-214629 A

  An object of the present invention is to provide a method for freeing a designer / developer from excessive experimentation and quickly and easily predicting deterioration of a resin material molded product.

  The present invention relates to the following matters.

1. A method of predicting deterioration due to one or more deterioration factors of a molded product made of a resin material,
Obtaining a one-dimensional penetration-time function of each deterioration factor into the resin material (S1);
Obtaining shape data of the molded product (S2);
Obtaining use environment data of the molded product (S3);
Calculating a three-dimensional penetration profile of each deterioration factor into the molded product based on the shape data and environmental data (S4);
Obtaining a relational expression between each deterioration factor concentration and deterioration (S5);
A step of calculating a three-dimensional deterioration profile inside the molded product by applying the relational expression between the respective deterioration factor concentrations and deterioration to the three-dimensional penetration profile of each deterioration factor (S6).
A method for predicting deterioration of a molded product, comprising:

  2. 2. The deterioration prediction method according to 1 above, further comprising a step (S7) of predicting mechanical performance after deterioration of the molded product based on the obtained three-dimensional deterioration profile.

  3. 3. The deterioration prediction method according to claim 1 or 2, wherein in the step (S1), the one-dimensional penetration-time function is predicted by a material diffusion equation.

  4). In any one of the above items 1 to 3, wherein the deterioration factor is 2 or more, and in step (S6), the sum of the deterioration based on each deterioration factor is multiplied by a weighting factor, and the sum is set as the deterioration degree. Deterioration prediction method described.

  5. A method for producing a resin material molded product, characterized in that a molded product is produced based on the design obtained by the deterioration prediction method according to any one of 1 to 4 above.

  6). The molded article manufactured based on the design obtained by the deterioration prediction method of any one of said 1-4.

  7). The apparatus which performs the deterioration prediction method of any one of said 1-4, Comprising: The apparatus which has a function to perform each said step.

  8). The computer program which performs the deterioration prediction method of any one of said 1-4.

  ADVANTAGE OF THE INVENTION According to this invention, the method of estimating rapidly deterioration of a plastic molded product can be provided. Therefore, by using the present invention, it is possible to easily predict the deterioration of molded products of various shapes without performing a long-term environmental test. Since it is possible to predict deterioration without manufacturing an actual molded product, it is a useful guide for designing molded products such as material selection and shape design, and it is easy to design molded products that meet the required performance. be able to. Therefore, a molded product can be provided in a short development period, and the development speed of new products and improved products can be improved.

  Moreover, the molded product manufactured based on the prediction result by this invention becomes the thing excellent in the balance of cost and performance.

It is a flowchart explaining the deterioration prediction method of this invention. It is a figure which shows a two-layer deterioration model typically. It is a figure which shows the density | concentration of the deterioration factor in the resin material inside. It is a graph which shows the time change of the thickness of a deterioration layer in a two-layer deterioration model. It is a graph which shows the example of a use environment. It is a graph which shows the relationship between a deterioration factor density | concentration and a mechanical characteristic. It is a graph which shows the relationship between a deterioration factor density | concentration and a mechanical characteristic in a two-layer deterioration model. It is a figure which shows the example of the fracture | rupture which should be considered which may arise in the laminated structure of a degradation layer and an undegraded layer. It is a graph which shows typically a mode that a mechanical characteristic changes (deteriorates) with water absorption. It is a figure which shows the shape of the prediction object molded article. It is a figure which shows the result of having actually measured the relationship between the load and the amount of pushing of the molded article of prediction object. It is a graph which shows the osmosis | permeation (diffusion) of the water | moisture content inside the resin material. It is a figure which shows the example of the internal profile of a degradation factor which applied the multilayer degradation model to the molded article. It is a figure which shows the relationship between prediction by simulation, and actual measurement.

A typical embodiment of the present invention will be described with reference to the flowchart shown in FIG. The method for predicting deterioration of a molded article according to this embodiment includes the following steps:
Obtaining a one-dimensional penetration-time function into the resin material (bulk) of each degradation factor (S1),
Obtaining shape data of the molded product (S2);
Obtaining the usage environment data of the molded product (S3);
Calculating a three-dimensional penetration profile of each degradation factor into the interior of the molded product based on the shape data and the environmental data (S4);
Obtaining a relational expression between each deterioration factor concentration and deterioration (S5);
Applying the relational expression between each deterioration factor concentration and deterioration to the three-dimensional penetration profile of each deterioration factor to calculate a three-dimensional deterioration profile inside the molded article (S6), and the obtained three-dimensional deterioration; Predicting mechanical performance after deterioration of the molded product based on the profile (S7)
Have

  The “resin material” as used herein means the whole material constituting the molded article, and usually includes a base polymer and various additives added in addition to the base polymer as necessary.

  The term “degradation factor concentration” is used to indicate the strength of the degradation factor in the target medium. For substances, it means “concentration” as it is, for temperature it means “temperature ° K”, or for light it means “light intensity W”, etc. Is selected.

  The terms “function” and “relational expression” mean two or more parameters that indicate the mutual relationship between the parameters, and may be expressed as a mathematical expression or obtained from measurement such as graph data. The relationship may be good.

  As a pre-stage of step S1, first, a degradation factor is selected for a specific target resin. The deterioration factor causes the resin material to deteriorate, and varies depending on the environment in which the molded product is used. For example, oxygen, moisture, temperature, lubricant, fuel, refrigerant, snow melting agent, ozone, light (ultraviolet ray, etc.), and various other factors can be cited as factors. In the present invention, in the environment where the molded product is used, the simulation may be performed in consideration of all the factors that cause the degradation, but in general, the cause of the degradation in the environment where the molded product is used. The main factors that should be considered are as follows. For example, even if a factor is present in a large amount in the usage environment, if it has less influence as a cause of deterioration compared to other factors, or has a negligible presence in the usage environment, ignore its presence. Also good. The deterioration factor to be selected varies depending on the type of resin material.

  After selecting at least one degradation factor, a penetration-time function of the degradation factor into the resin material is acquired for each degradation factor (S1).

  The penetration, that is, the diffusion of the deterioration factor into the resin material occurs from the environment exposed to the environment. The penetration of the deterioration factor into the resin material flake 10 will be described with reference to FIGS. As schematically shown in FIG. 2, the permeation layer (deterioration layer) 12 penetrates into the resin material 10 over time, and the inner non-permeation layer (undegradation layer) 11 shrinks. FIG. 3A shows a cross-section of the resin material flake, and FIG. 3B is a schematic diagram showing the diffusion of the deterioration factor into the resin material flake 10 with the concentration of the deterioration factor as the vertical axis.

  As shown in FIG. 3B, the deterioration factor concentration is high at the interface and low inside. The degradation factor concentration varies with time. If the region where the deterioration factor concentration is equal to or higher than a specific critical value is defined as the deterioration layer 12, the thickness of the deterioration layer 12 increases with time as shown in FIG.

  That is, the “permeation of deterioration factor into the resin material—time function” to be prepared in step S1 is the time change of the diffusion profile of the deterioration factor, that is, the permeation behavior of the deterioration factor, as shown in FIG. It is. In a very simplified model in which the material deterioration is a two-layer structure of a deteriorated layer and a non-degraded layer, the thickness of the deteriorated layer may be obtained as a time function as shown in FIG.

  The penetration-time function can all be determined experimentally using a sample flake of resin material. However, since it is cumbersome to obtain all the experiments experimentally over a long period of time, the known substance diffusion equation (1):

（式中、Ｃ：質量濃度、 ρ：密度、 Ｄｍ：物質拡散係数、 ｄ：湧き出し、 ｕ：流速）
に従うと仮定し、実験的に求めた物質拡散係数Ｄｍ、または文献記載の物質拡散係数Ｄｍを当てはめることができる。

(Where C: mass concentration, ρ: density, Dm: material diffusion coefficient, d: springing out, u: flow velocity)
The material diffusion coefficient Dm determined experimentally or the material diffusion coefficient Dm described in the literature can be applied.

  In the deterioration factor penetration experiment using resin material flakes, the diffusion coefficient Dm can be obtained from the penetration (diffusion) profile obtained experimentally with d = 0 and u = 0.

  In step S2, the shape data of the molded product is acquired. For example, data is created by general-purpose CAD software.

  In step S3, usage environment data is prepared. As an example of the usage environment data, as shown in FIG. 5, a graph (function) showing a temporal change in the concentration (intensity) of the deterioration factor in the usage environment can be mentioned. Further, when the concentration of the deterioration factor varies depending on the position of the outer surface of the molded product, use environment data is prepared for each position together with the shape data.

  Next, in step S4, the deterioration factor penetration-time function is applied to the shape data of the molded product based on the usage environment data, and a three-dimensional profile of the deterioration factor concentration in the molded product after a desired time has elapsed. Ask. The calculation is performed using general-purpose finite element analysis software (FEM), for example, MSC. This can be done using MARC (trademark) or the like.

  The three-dimensional profile of deterioration factor concentration obtained in step S4 is the basis for deterioration of mechanical properties (elastic modulus, strength, elongation, etc.) calculated in the following steps. Further, the three-dimensional profile of the deterioration factor concentration is obtained for all of the deterioration factors selected in the previous stage of step S1.

  Next, as step S5, as a pre-stage for calculating mechanical characteristics (elastic modulus, strength, elongation, etc.), the relationship between each deterioration factor concentration and deterioration is acquired. Ideally, as shown in FIG. 6, a change in mechanical properties is prepared as a function of the concentration of the deterioration factor. As a simple model, in a two-layer model of an undegraded layer and a degraded layer, as shown in FIG. It is only necessary to determine the mechanical characteristics in an undegraded region where the degradation factor concentration is less than the critical concentration and in a degraded region where the degradation factor concentration is higher than the critical concentration.

  The correlation data between each deterioration factor and deterioration may be obtained experimentally, or literature values may be adopted for known data. For experimental determination, for example, using a thin test piece, measure the mechanical characteristics after placing in a predetermined environment (for example, multiple environments with different deterioration factor concentrations), and determine the deterioration factor concentration from the internal deterioration factor concentration. And a relationship between mechanical properties (that is, a relationship with deterioration) can be obtained.

  In addition to or in place of measuring each of the deteriorated layer (multi-stage deteriorated layer) and the undegraded layer, there is a deteriorated layer (multi-stage deteriorated layer) and an undegraded layer in the test piece. It is also useful to measure the mechanical properties in the state or in the presence of a significant concentration gradient in the test piece. For example, as shown in FIG. 8, when the deteriorated layer 12 breaks first and a notch crack is generated on the surface, the undegraded layer 11 may break early due to a so-called notch effect. It is useful to make such measurements in order to obtain more realistic results.

  The mechanical properties are selected from, for example, elastic modulus (for example, tensile and bending elastic modulus), strength (for example, tensile strength and bending strength), elongation, tan δ, etc., melting point, softening temperature, Tg, crystallization temperature, and the like. . These are merely examples, and it is sufficient that the physical properties required for the use of the molded product can be evaluated without excess or deficiency.

In step S6, a mechanical characteristic profile in the molded product, that is, a deterioration profile is calculated. The degree of deterioration of mechanical properties (for example, elastic modulus) at a certain point in the molded product is expressed by, for example, the formula (2)
C _total = A ₁ C ₁ + A ₂ C ₂ + A ₃ C ₃ +... + C ₀ (2)
(Where C _total is the degree of deterioration of mechanical characteristics at a certain point, C _{i is the} degree of deterioration based on the deterioration factor i, A _{i is a} coefficient, C _{0 is a} constant, where i = 1, 2, 3,... .)
Can be expressed as

The concentration of the deterioration factor i at a certain point in the molded product is obtained in step S4. Further, the relationship between the concentration of the deterioration factor i and the mechanical characteristics is obtained in step S5. The deterioration degree C _i is, for example, a reduction value from the initial characteristic of the mechanical characteristics, and when deterioration due to a plurality of deterioration factors is superimposed, a weighting coefficient A _i of the influence degree of each deterioration factor is multiplied by C _i . By taking the total sum together, it is possible to obtain the degree of deterioration at a specific point (that is, the characteristic deterioration value at that point). Here, C ₀ is based on deterioration not depending on the deterioration factor, and if there is no such element, C ₀ = 0 can be set. From the degree of deterioration at each point of such a molded product, a degradation level profile in the molded product and a mechanical property (for example, elastic modulus) profile after degradation are obtained.

The weighting coefficient A _i can be experimentally obtained from a test piece placed in an environment where a plurality of deterioration factors exist. Also, A _i can be determined from the calculation so as to match the deterioration data already possessed.

  In this way, since a mechanical property (for example, elastic modulus) profile after deterioration of the molded product is obtained in step S6, the post-degradation performance as a part is calculated for the entire molded product in step S7.

  The performance as a part is selected and calculated as appropriate depending on the application in which the molded product is used. For example, pulling, compression, bending in a specific direction, strength against vibration, deformation, destruction, etc. at a specific part are predicted by calculation. This calculation is also performed by general-purpose finite element analysis software (FEM), for example, MSC. This can be done using MARC (trademark) or the like.

  Based on the predicted post-degradation performance obtained in this way, the designer and developer perform an assessment of the shape and material of the molded product. When the result is unsatisfactory for the application or further improvement is required, the simulation of the present invention can be performed again by changing the shape or the resin material. For example, a molded article using a resin material containing a large amount of an expensive deterioration preventing agent as an additive may be less deteriorated but is expensive. According to the present invention, the post-deterioration performance can be predicted quickly based on a small number of experiments, so that a molded product with a good balance between performance and cost can be easily designed.

  Although the deterioration prediction method of the present invention has been described above, the present invention further relates to computer software that executes the deterioration prediction method and an apparatus that has a function of executing each step of the deterioration prediction method of the present invention.

Further, one-dimensional penetration-time function acquired in step S1, a relational expression of deterioration factor concentration and deterioration acquired in step S5, and one coefficient A _i for calculating a deterioration profile in the molded article in step S6. The above can be stored in advance in a storage device as a database, and can be executed more easily by executing a simulation by executing the steps. Further, when new deterioration data on a product or a test piece is newly obtained, it is preferable to add new actual measurement data to correct and update each basic data, thereby enabling a more accurate simulation.

  Moisture (moisture absorption) was selected as the deterioration factor, and the simulation results were compared with the actual measurement results.

  First, in order to obtain a correlation between moisture absorption and changes in mechanical properties (corresponding to step S5), a dumbbell-type test piece (JIS No. 2 test piece) was produced using polyamide 6 resin. After the test pieces were completely dried (water absorption rate≈0) under humidity control conditions, a predetermined number of test pieces were immersed in water at a predetermined temperature for a predetermined time. The test piece after immersion was put in a water-vapor impermeable bag, sealed and left. After leaving to the extent that the moisture distribution in the test piece reached equilibrium, the mechanical properties were tested. Test pieces having different water absorption rates were obtained by changing the immersion time and immersion temperature in water. The water absorption was determined from the weight change.

  FIG. 9 schematically shows a strain-stress curve obtained from the measurement of the test piece. From this result, the relational expression between the deterioration factor concentration in step S5 and the mechanical characteristics is obtained.

  Next, the predicted molded product for which mechanical characteristics are to be obtained was formed into a U-shaped cross section shown in FIG. 10 (corresponding to step S2). For the usage environment data (corresponding to step S3), the immersion conditions in water shown in Table 1 were used. In addition, in order to compare simulation and actual measurement, a molded product having the same shape was produced. All molded articles were completely dried (water absorption ≈ 0) under humidity control conditions, and a predetermined number of molded articles were immersed in water under the conditions shown in Table 1.

  A load was applied to the test piece from above the test piece using a three-point bending tester, and data on the load and the amount of indentation were obtained. The obtained results are shown in FIG. In this figure, the average water absorption rate of the entire molded product is also shown for reference.

  On the other hand, moisture penetration was predicted using the material diffusion equation (corresponding to step S1). The results are shown in FIGS. 12 (a) and 12 (b).

  Next, the mechanical properties of the molded product to be predicted will be obtained. Here, for the sake of simplicity, the penetration profile of the deterioration factor in the molded product (corresponding to step S4) is determined from the penetration profile predicted in step S1. As shown in FIG. 13, the calculation is performed using a multilayer deterioration model. As described above, the usage environment data (step S3) is as shown in Table 1. Therefore, FIG. 12 shows a penetration profile corresponding to the usage environment data.

  By applying the relationship between the deterioration factor obtained from FIG. 9 and the mechanical characteristics for such a multilayer deterioration model, the mechanical characteristics of the molded product are predicted (corresponding to step S6). Here, the relationship between the pushing amount and the reaction force was obtained. Prediction data and actual measurement data are shown in FIG. The actual measurement data is obtained by correcting the previous FIG. From this result, the result predicted by the simulation agreed with the actual measurement within a range of ± 10%.

  In the examples, a molded article having a simple structure was used only with moisture as a deterioration factor. However, according to the principle of the present invention, even when there are a plurality of deterioration factors, a complex product is obtained based on data obtained from a small number of experiments. Deterioration can also be predicted for shaped molded products.

  The present invention is advantageously used for designing a molded article of a resin material.

10 Resin material flake 11 Undegraded layer 12 Degraded layer

Claims (6)

A method of predicting deterioration due to one or more deterioration factors of a molded product made of a resin material,
Obtaining a one-dimensional penetration-time function of each deterioration factor into the resin material (S1);
Obtaining shape data of the molded product (S2);
Obtaining use environment data of the molded product (S3);
Calculating a three-dimensional penetration profile of each deterioration factor into the molded product based on the shape data and environmental data (S4);
Obtaining a relational expression between each deterioration factor concentration and deterioration (S5);
Applying the relational expression between each deterioration factor concentration and deterioration to the three-dimensional penetration profile of each deterioration factor to calculate a three-dimensional deterioration profile inside the molded article (S6) ;
Predicting mechanical performance after deterioration of the molded product based on the obtained three-dimensional deterioration profile (S7)
A method for predicting deterioration of a molded product, comprising: 2. The deterioration prediction method according to claim 1 , wherein in the step (S <b> 1), the one-dimensional penetration-time function is predicted by a material diffusion equation. 3. The deterioration prediction according to claim 1, wherein the deterioration factor is 2 or more, and in step (S <b> 6), a deterioration sum is obtained by multiplying deterioration based on each deterioration factor by a weighting coefficient. Method. The manufacturing method of the resin material molded product characterized by manufacturing a molded product based on the design obtained by the deterioration prediction method of any one of Claims 1-3 . Equipment for executing the deterioration prediction method according to any one of claims 1-3. The computer program which performs the deterioration prediction method of any one of Claims 1-3 .

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