Method for predicting viscoelastic characteristics of rubber material

Abstract

To be able to predict viscoelastic characteristics of a rubber material in a high frequency region with shorter hours and fewer man-hours than before.SOLUTION: A method for predicting viscoelastic characteristics of a rubber material, includes: a measuring step of deforming a rubber material while changing a frequency at one temperature to measure viscoelastic characteristic values of the rubber material at each frequency; and a predicting step of predicting the viscoelastic characteristic values of the rubber material at a frequency exceeding the frequency measured in the measuring step on the basis of a linear approximation line obtained by approximating linearly correlation data between the frequency and the viscoelastic characteristic values, determined in the measuring step.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for predicting viscoelastic properties of a rubber material. [Background technology]

[0002] Conventionally, dynamic viscoelasticity measurement has been known as a method for measuring the viscoelastic properties of rubber materials. Dynamic viscoelasticity measurement is a method for measuring the viscoelastic properties of a rubber material by applying a time-varying strain or stress to a test piece made of a rubber material and measuring the resulting stress or strain.

[0003] On the other hand, in dynamic viscoelasticity measurement, it is usually difficult to measure the viscoelastic properties of a rubber material in a wide frequency range using a single viscoelasticity tester. Therefore, Patent Document 1 discloses a method of creating a master curve using the temperature-frequency conversion rule and calculating the viscoelastic properties of a rubber material in a wide frequency range. More specifically, after measuring the frequency dispersion of the viscoelastic property values ​​of the rubber material at multiple temperatures using a viscoelasticity tester, a shift factor is calculated using the WLF formula (empirical formula (13) described in JIS K 6394), and the frequency-dependent curve at each measurement temperature is shifted according to this shift factor to create a master curve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-25891 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional methods including that described in Patent Document 1 require the measurement of viscoelastic properties of rubber materials at multiple temperatures, which is problematic in that the measurement takes time. In addition, when creating a master curve based on the measurement data, complex data processing such as conversion and interpolation of the measurement data is required, which is inefficient. [Means for solving the problem]

[0006] The method for predicting the viscoelastic properties of a rubber material according to the present invention is a method for predicting the viscoelastic properties of a rubber material, and is characterized by including a measurement step in which the rubber material is deformed while changing the frequency at one temperature, and the viscoelastic property values ​​of the rubber material are measured at each frequency, and a prediction step in which the viscoelastic property values ​​of the rubber material are predicted at frequencies higher than the frequency measured in the measurement step, based on a linear approximation line obtained by linearly approximating the correlation data between the frequency and the viscoelastic property values ​​obtained in the measurement step. Effect of the Invention

[0007] According to the method for predicting the viscoelastic properties of a rubber material of the present invention, the viscoelastic property values ​​of a rubber material in the high frequency range can be predicted in a shorter time and with fewer steps than conventional methods. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a flowchart showing a method for predicting viscoelastic properties of a rubber material according to the present invention. [Diagram 2] FIG. 1 is a diagram showing an example of correlation data between the frequency measured in the measurement step and the viscoelastic property value in the method for predicting the viscoelastic property of a rubber material of the present invention. [Diagram 3] FIG. 2 is a diagram showing an example of a linear approximation line calculated in the prediction step in the method for predicting viscoelastic properties of a rubber material according to the present invention. [Figure 4] FIG. 2 is a diagram showing a finite element model used in a simulation of the embodiment. [Diagram 5] FIG. 11 is a diagram showing the analysis results obtained in the example, in the direction perpendicular to the axis. [Figure 6]FIG. 13 is a diagram showing analysis results obtained in an example, in the axial direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] As mentioned above, conventionally, for example, 1.0×10 -2 Hz~1.0×10 6 When calculating the viscoelastic properties of a rubber material in a wide frequency range such as 100 Hz, a master curve is created using the temperature-frequency conversion rule. More specifically, the frequency dispersion of the viscoelastic property values ​​of the rubber material is measured at a plurality of temperatures using a viscoelasticity tester. In the above method, the frequency dispersion of the viscoelastic property values ​​of the rubber material is generally measured in the range of 1 Hz to several hundreds of Hz using the viscoelasticity tester. Then, the frequency-dependent curve at each measurement temperature is shifted using the temperature-frequency conversion rule to create a master curve that shows the viscoelastic properties of the rubber material in a wide frequency range.

[0010] On the other hand, when designing devices that use rubber materials, such as vibration isolation devices including engine mounts and motor mounts, the viscoelastic property values ​​of the rubber material over a wide frequency range may not necessarily be required. For example, when designing a vibration isolation device using a simulation that uses the finite element method, only the viscoelastic property values ​​of the rubber material at frequencies around 1000 Hz may be required.

[0011] However, it is difficult to directly measure the viscoelastic property value of a rubber material at a frequency of around 1000 Hz using an existing viscoelasticity tester due to the specifications of the viscoelasticity tester. Therefore, when calculating the viscoelastic property value of a rubber material at a frequency of around 1000 Hz, it is necessary to measure the viscoelastic property value of the rubber material at multiple temperatures and create a master curve as in the above method. As a result, there is a problem that it takes time to measure the viscoelastic property value of the rubber material. In addition, when creating a master curve based on measurement data at multiple temperatures, complex data processing such as conversion and complementation of the measurement data is required, which is also a problem of requiring man-hours.

[0012] As a result of the inventors' research, it was revealed that the frequency dispersion of the viscoelastic characteristic values ​​of a rubber material can be measured at one temperature using a viscoelasticity testing machine, and the viscoelastic characteristic values ​​of the rubber material can be predicted at frequencies higher than those measured using the viscoelasticity testing machine from a linear approximation line obtained by linearly approximating the correlation data between the obtained frequency and the viscoelasticity characteristic values.

[0013] According to this method, the viscoelastic property value of the rubber material is measured only at one temperature, so there is no need to measure the viscoelastic property value of the rubber material at multiple temperatures, and the measurement time can be shortened. In addition, when predicting the viscoelastic property value of the rubber material from the measurement data, the prediction can be made only by calculating a linear approximation line, so there is no need to perform complex data processing, leading to a reduction in labor hours. In addition, according to this method, as described above, there is no need to measure the viscoelastic property value of the rubber material at multiple temperatures, so the viscoelastic property value of the rubber material can be predicted using a viscoelasticity tester with a simple configuration that does not have a temperature adjustment function.

[0014] Hereinafter, an example of an embodiment of the method for predicting viscoelastic properties of a rubber material according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. In addition, in this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "numerical value A or more and numerical value B or less."

[0015] Hereinafter, the method for predicting viscoelastic properties of a rubber material according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a diagram showing a flowchart of the method for predicting viscoelastic properties of a rubber material according to this embodiment.

[0016] As shown in FIG. 1, the method for predicting the viscoelastic properties of a rubber material of this embodiment includes a preparation step S1 of preparing a test piece made of a rubber material, a measurement step S2 of measuring the viscoelastic property value of the rubber material using a viscoelasticity testing machine, and a prediction step S3 of predicting the viscoelastic property value of the rubber material.

[0017] As described above, the preparation step S1 is a step of preparing a test piece made of a rubber material. The shape, size, etc. of the test piece made of a rubber material prepared in the preparation step S1 are not particularly limited as long as they are compatible with the viscoelasticity tester used in the measurement step S2. The shape of the test piece is, for example, a sheet shape, a cylindrical shape, or a block shape.

[0018] The rubber material is a substance having rubber-like elasticity, and is a concept including not only vulcanized rubber but also elastomers such as thermoplastic elastomers. In this embodiment, vulcanized rubber is used as the rubber material.

[0019] Vulcanized rubber is a rubber material obtained by vulcanizing a rubber composition in which various compounding ingredients, including a vulcanizing agent such as sulfur, are compounded with a rubber polymer. For example, vulcanized rubber can be obtained by preparing a rubber composition by kneading each component in a mixer such as a Banbury mixer in a conventional manner, and then heating the rubber composition in a conventional manner to vulcanize and mold it.

[0020] Examples of rubber polymers contained in vulcanized rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), acrylonitrile butadiene styrene rubber (ABS), brominated butyl rubber (BR-IIR), fluororubber, silicone rubber, etc. These rubber polymers may be used alone or in combination of two or more.

[0021] In addition, the compounding agents contained in the vulcanized rubber may include various compounding agents normally used in the rubber industry, such as fillers such as carbon black and silica, softeners, antioxidants, zinc oxide, stearic acid, wax, and vulcanization accelerators.

[0022] The glass transition temperature of the rubber material is, for example, −60° C. to −20° C., and preferably −55° C. to −25° C. When the glass transition temperature is within the range of −60° C. to −20° C. or −55° C. to −25° C., the error due to the linear approximation line calculated in prediction step S3 described later is reduced, and the prediction accuracy of the viscoelastic characteristic value of the rubber material is improved.

[0023] The measurement step S2 is a step of measuring the viscoelastic property value of the test piece made of the rubber material prepared in the preparation step S1 at one temperature. More specifically, in the measurement step S2, the test piece is deformed while changing the frequency using a viscoelasticity tester, and the viscoelastic property value of the test piece at each frequency is measured. Examples of the viscoelastic property value include the storage modulus, loss modulus, complex modulus, and loss tangent (tan δ).

[0024] FIG. 2 shows an example of correlation data between the frequency measured in the measurement step S2 of the embodiment described later and the viscoelastic characteristic value (storage modulus, loss modulus) of the rubber material. Here, in the measurement step S2, it is preferable to measure the viscoelastic characteristic value of the rubber material in at least a part of the range of 50 Hz to 400 Hz using a viscoelasticity tester. If the measurement frequency is lower than 50 Hz, the viscoelastic characteristic value of the rubber material may not be linear, and an error due to a linear approximation line described later may become large. In addition, the wider the measurement range of the frequency, the smaller the error due to the linear approximation line, and the more accurate the prediction of the viscoelastic characteristic value of the rubber material is. An example of the measurement range is 60 Hz to 300 Hz. In addition, the measurement interval of the frequency is, for example, 10 Hz, preferably 8 Hz or less, and more preferably 5 Hz or less.

[0025] The measurement temperature can be set appropriately depending on the temperature conditions of the viscoelastic characteristic value of the rubber material to be predicted. That is, when predicting the viscoelastic characteristic value of a rubber material at room temperature (23°C), the viscoelastic characteristic value of the rubber material is measured at room temperature. Furthermore, as a result of the study by the present inventors, it has become clear that when the viscoelastic characteristic value of a rubber material is measured at room temperature, the error due to the linear approximation line is reduced, and the prediction accuracy of the viscoelastic characteristic value of the rubber material is improved. Therefore, when the measurement temperature is room temperature, the effect of the present invention is more remarkable.

[0026] The viscoelasticity tester used in the measurement step S2 is not particularly limited as long as it is capable of deforming the test piece at the above frequency. A specific example of the viscoelasticity tester is a viscoelasticity tester manufactured by TA Instruments (product name "RSA-G2"). As described above, the method for predicting the viscoelasticity properties of a rubber material of the present invention can predict the viscoelasticity property value of the rubber material using only the measurement results at room temperature. Therefore, the viscoelasticity tester used in the method for predicting the viscoelasticity properties of a rubber material of the present invention does not need to have a temperature adjustment function.

[0027] In the prediction step S3, the viscoelastic property value of the rubber material at a frequency exceeding the frequency measured in the measurement step S2 is predicted based on a linear approximation line obtained by linearly approximating the correlation data between the frequency and the viscoelastic property value obtained in the measurement step S2. The prediction step S3 is performed, for example, using a computer.

[0028] An example of the linear approximation line calculated in the prediction step S3 is shown in Fig. 3. The linear approximation line can be calculated, for example, by the least squares method based on correlation data between the frequency and the viscoelasticity characteristic value.

[0029] Then, using the slope and intercept of the linear approximation line obtained above, a viscoelastic property value of the rubber material at a frequency exceeding the frequency measured in the measurement step S2 is predicted. Note that, in the prediction step S3, it is preferable to predict a viscoelastic property value of the rubber material at a frequency exceeding the upper limit frequency that can be set by the measurement device (viscoelasticity tester) used in the measurement step S2.

[0030] From the viewpoint of improving the prediction accuracy of the viscoelastic property value of the rubber material, in the prediction step S3, it is preferable to predict the viscoelastic property value of the rubber material in at least a part of the range of 700 Hz to 1300 Hz, more preferable to predict the viscoelastic property value of the rubber material in at least a part of the range of 800 Hz to 1200 Hz, and even more preferable to predict the viscoelastic property value of the rubber material in at least a part of the range of 900 Hz to 1100 Hz. In other words, when the frequency exceeds 1300 Hz, the viscoelastic property value of the rubber material may not be linear, and the prediction accuracy may decrease. EXAMPLES

[0031] Examples will be shown below, but the present invention is not limited to these examples.

[0032] [Fabrication steps] Using a Banbury mixer, 100 parts by mass of styrene butadiene rubber (Asahi Kasei Corporation's "Tufden 2000") was mixed with 50 parts by mass of carbon black (Tokai Carbon Co., Ltd.'s "Seat 3"), 2 parts by mass of zinc oxide (Mitsui Mining & Smelting Co., Ltd.'s "Zinc Oxide Type 1"), 1 part by mass of stearic acid (Kao Corporation's "Lunac S-20"), 2 parts by mass of sulfur (Hosoi Chemical Industry Co., Ltd.'s "Rubber Powder Sulfur 150 Mesh"), and 1 part by mass of vulcanization accelerator (Ouchi Shinko Chemical Industry Co., Ltd.'s "Noccela CZ"), and kneaded. This prepared an unvulcanized rubber composition.

[0033] The unvulcanized rubber composition thus obtained was press-molded while being vulcanized to prepare a test piece made of a cylindrical rubber material (diameter 40 mm, height 30 mm). The hardness Hs of the test piece at a temperature of 23°C was measured using a durometer type A (model: GS-719N, manufactured by Techlock Corporation) in accordance with JIS K6253, and was found to be 51.

[0034] [Measurement step] The test pieces prepared in the above preparation steps were used to measure the frequency dependence of the storage modulus and loss modulus using a viscoelasticity tester (product name "KCH701-30") manufactured by Saginomiya Seisakusho Co., Ltd. Detailed measurement conditions are as follows. The measurement results of the storage modulus and loss modulus are shown in FIG. 2. As a result, the actual measured value of the storage modulus at 100 Hz of the rubber material of the example was 4.92 MPa, and the actual measured value of the loss modulus was 0.42 MPa.

[0035] <Measurement conditions> Measurement direction: Axial direction (see Figure 2) ·Measurement temperature: 23℃ (normal temperature) ·Load condition: 0±0.05mm vibration Measurement range: 60Hz to 300Hz (5Hz intervals)

[0036] [Prediction Step] Based on the correlation data between the frequency obtained in the above measurement step and the storage modulus and loss modulus, a linear approximation line was calculated using the least squares method. FIG. 3 shows the calculated linear approximation line. The storage modulus and loss modulus of the rubber material at 1000 Hz were predicted using the slope and intercept of the obtained linear approximation line. As a result, the predicted value of the storage modulus at 1000 Hz of the rubber material of the example was 7.35 MPa, and the predicted value of the loss modulus was 1.14 MPa.

[0037] [Simulation evaluation] Next, to evaluate the accuracy of the storage modulus and loss modulus of the rubber material at 1000 Hz calculated in the prediction step, an analytical simulation was performed using the predicted values ​​of storage modulus and loss modulus at 1000 Hz, and a comparison was made with the actual measured values. This simulation uses the finite element method to obtain the change in absolute spring constant of the rubber material contained in the motor mount with respect to the frequency of the input vibration. In the simulation, the measured values ​​of storage modulus and loss modulus at 100 Hz and the predicted values ​​of storage modulus and loss modulus at 1000 Hz were input and an analysis was performed. The simulation was performed using software named "Abaqus" manufactured by SIMULIA.

[0038] The finite element model of the motor mount used in the simulation is shown in Figure 4. As shown in Figure 4, the motor mount includes an inner cylinder, an outer cylinder that surrounds the outer periphery of the inner cylinder, and a rubber material that connects the outer cylinder and the inner cylinder.

[0039] 5 and 6 show the frequency characteristics of the absolute spring constant of the rubber material obtained by the above simulation. FIG. 5 shows the frequency characteristics of the absolute spring constant of the rubber material when the inner cylinder is vibrated in the axial direction, and FIG. 6 shows the frequency characteristics of the absolute spring constant of the rubber material when the inner cylinder is vibrated in the axial direction. As shown in FIG. 5 and FIG. 6, in the simulation of the embodiment, the rubber material shows a peak of the absolute spring constant due to surging between 600 Hz and 850 Hz. When the peak position of the absolute spring constant in the simulation is compared with the peak position of the absolute spring constant in the actual measured value, the deviation of the peak positions was 5% or less in both cases. Therefore, it can be said that the values ​​of the storage modulus and loss modulus at 1000 Hz of the rubber material calculated in the prediction step are accurate.

[0040] Although the embodiment of the present invention has been described above, the embodiment is presented as an example and is not intended to limit the scope of the invention. The embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The embodiment and its omissions, substitutions, modifications, etc. are included in the scope and gist of the invention as well as the invention and its equivalents described in the claims. [Explanation of symbols]

[0041] S1: Creation step, S2: Measurement step, S3: Prediction step

Claims

1. 1. A method for predicting viscoelastic properties of a rubber material, comprising: a measuring step of deforming the rubber material while changing a frequency at one temperature and measuring a viscoelastic characteristic value of the rubber material at each frequency; a prediction step of predicting a viscoelastic characteristic value of the rubber material at a frequency exceeding the frequency measured in the measurement step, based on a linear approximation line obtained by linearly approximating correlation data between the frequency and the viscoelastic characteristic value obtained in the measurement step; A method for predicting viscoelastic properties of a rubber material, comprising:

2. The method for predicting viscoelastic properties of a rubber material according to claim 1 , wherein the one temperature is 23° C.

3. 2. The method for predicting the viscoelastic properties of a rubber material according to claim 1, wherein in the prediction step, a viscoelastic property value of the rubber material is predicted at a frequency exceeding an upper limit frequency that can be set by a measuring device used in the measurement step.

4. In the measuring step, a viscoelastic characteristic value of the rubber material is measured in at least a part of a range of 50 Hz or more and 400 Hz or less, The method for predicting viscoelastic properties of a rubber material according to claim 1 , wherein the predicting step predicts a viscoelastic property value of the rubber material in at least a part of a range of 700 Hz or more and 1300 Hz or less.

5. The method for predicting viscoelastic properties of a rubber material, wherein the glass transition temperature of the rubber material is -60°C or higher and -20°C or lower.

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