Evaluation method for unvulcanized rubber

Abstract

This invention provides a method for evaluating unvulcanized rubber that quantitatively assesses the occurrence of warping during extrusion molding of unvulcanized rubber components, thereby eliminating variations in evaluation by operators and enabling efficient evaluation. [Solution] An evaluation method for unvulcanized rubber comprising: an unvulcanized rubber composition preparation step of preparing an unvulcanized rubber composition corresponding to an unvulcanized rubber member; a test piece extrusion molding step of extruding the prepared unvulcanized rubber composition into a test piece of a predetermined shape using an extrusion molding device; an image acquisition step of acquiring an image of the obtained test piece from the thickness direction; an image processing step of processing the acquired image of the test piece and extracting the contour of the test piece from the image; a circumference estimation step of estimating the circumference of the test piece from the extracted contour of the test piece; and a waviness condition evaluation step of evaluating the waviness condition that occurred in the test piece from the estimated circumference of the test piece.

Description

Technical Field

[0001] The present invention relates to a method for evaluating unvulcanized rubber.

Background Art

[0002] When manufacturing a pneumatic tire, an unvulcanized tire is produced using unvulcanized rubber members of various shapes.

[0003] These unvulcanized rubber members are generally formed by extrusion molding. However, if undulations occur on the surface, the shape becomes unstable, and there is a risk that a pneumatic tire cannot be provided with stable quality. Therefore, conventionally, the die shape has been devised (for example, Patent Document 1), and during extrusion molding, the occurrence of undulations has been confirmed and evaluated to prevent the occurrence of defective products.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the confirmation and evaluation of the occurrence of undulations described above have been performed by sensory evaluation based on visual observation by an operator. Therefore, variations in evaluation may occur depending on the proficiency and physical condition of the operator, and it has not been efficient.

[0006] Therefore, an object of the present invention is to provide a method for evaluating unvulcanized rubber that can quantitatively evaluate the occurrence of undulations during extrusion molding of an unvulcanized rubber member, eliminate variations in evaluation by an operator, and enable efficient evaluation.

Means for Solving the Problems

[0007] The present invention A method for evaluating unvulcanized rubber, which evaluates the state of waviness generation during extrusion molding of unvulcanized rubber components, An unvulcanized rubber composition preparation step for preparing an unvulcanized rubber composition corresponding to the unvulcanized rubber member, A test piece extrusion molding step in which the prepared unvulcanized rubber composition is extruded into a test piece of a predetermined shape using an extrusion molding apparatus, An image acquisition step is to acquire an image of the obtained test piece from the thickness direction, Image processing step of processing the acquired image of the test specimen and extracting the contour of the test specimen from the image, A perimeter estimation step in which the perimeter of the test specimen is estimated from the outline of the extracted test specimen, The method for evaluating unvulcanized rubber is characterized by comprising a step of evaluating the degree of waviness generated in the test piece based on the estimated circumference of the test piece. [Effects of the Invention]

[0008] According to the present invention, it is possible to quantitatively evaluate the state of waviness generation during the extrusion molding of unvulcanized rubber members, thereby eliminating variations in evaluation by operators and providing an efficient evaluation method for unvulcanized rubber. [Brief explanation of the drawing]

[0009] [Figure 1] This is an example of an image of a test specimen obtained in one embodiment of the present invention. [Figure 2] This diagram shows the process of extracting the outline of a test specimen from captured images. [Figure 3] This figure shows an example of evaluating the wave-like condition in one embodiment of the present invention. [Modes for carrying out the invention]

[0010] [1] Features of the evaluation method for unvulcanized rubber according to the present invention First, the features of the evaluation method for unvulcanized rubber according to the present invention will be described.

[0011] The present invention provides a method for evaluating unvulcanized rubber, which evaluates the state of waviness generation during extrusion molding of an unvulcanized rubber member, and comprises the following steps. (1) Step to prepare an unvulcanized rubber composition corresponding to an unvulcanized rubber component. (2) Test piece extrusion step: The prepared unvulcanized rubber composition is extruded into a test piece of a predetermined shape using an extrusion molding device. (3) Image acquisition step: Obtain an image of the obtained test specimen by viewing it from a direction perpendicular to the extrusion direction. (4) Image processing step of processing the acquired images of the test specimen and extracting the contour of the test specimen from the images. (5) Perimeter estimation step: Estimate the perimeter of the specimen from the contour of the extracted specimen. (6) A waviness evaluation step in which the waviness of the test specimen is evaluated based on the estimated circumference of the test specimen.

[0012] By incorporating these steps, it is possible to quantitatively evaluate the state of waviness generation during the extrusion molding of unvulcanized rubber components, eliminate variations in evaluation by operators, and provide an efficient evaluation method for unvulcanized rubber.

[0013] In other words, in this invention, instead of evaluation by the operator's sensory evaluation, an objective quantitative evaluation is performed based on the circumference estimated based on the contour obtained by image processing. This eliminates the possibility of variations in evaluation by operators, enabling efficient evaluation.

[0014] [2] Embodiment Next, a specific example of the evaluation method for unvulcanized rubber according to the present invention will be given as an embodiment, and each step will be explained.

[0015] (1) Steps for preparing an unvulcanized rubber composition In this step, an unvulcanized rubber composition corresponding to the unvulcanized rubber member to be evaluated is prepared.

[0016] Specifically, an unvulcanized rubber composition is prepared by kneading at a predetermined temperature for a predetermined time using a known (closed-type) kneader such as a Banbury mixer, a kneader, or an open roll, with a formulation adjusted to the physical properties required for the rubber member to be evaluated.

[0017] (2) Test piece extrusion molding step In this step, the unvulcanized rubber composition obtained above is extruded into a test piece having a predetermined shape using a predetermined extrusion molding apparatus.

[0018] At this time, if appropriate extrusion molding conditions are not set according to the characteristics of each unvulcanized rubber composition, undulations will occur in the test piece. Therefore, it is necessary to further evaluate the occurrence of undulations in each test piece according to the steps shown below, and appropriately adjust the setting of the extrusion molding conditions and the formulation design of the rubber composition.

[0019] In this embodiment, as the extrusion molding apparatus, it is preferable to use a capillary rheometer such as "Capilograph" (registered trademark) manufactured by Toyo Seiki Seisakusho Co., Ltd.

[0020] The above-mentioned capillary rheometer is originally a tester for measuring the melt viscosity when a polymer material or the like is sheared and flowed in a molten state, but it can also be used as an extrusion molding apparatus for an unvulcanized rubber composition. In that case, the extrusion molding conditions can be easily changed and adjusted.

[0021] In addition, the test piece obtained by the capillary rheometer is usually in a string shape and can be cut into a shape suitable for photographing and photographed. That is, since it is suitable for image evaluation of the test piece, it is preferable to use a capillary rheometer as the extrusion molding apparatus.

[0022] (3) Image acquisition step In this step, an image of the test specimen obtained above is acquired from the thickness direction. The "thickness direction of the test specimen" refers to the direction perpendicular to the "direction in which the test specimen is extruded from the extruder" when the rubber composition is extruded into the test specimen using an extrusion molding apparatus. When acquiring the image, it is preferable to capture it with a CCD camera and convert it to digital image data.

[0023] Figure 1 shows images obtained from three test specimens A, B, and C, which were extruded from three different formulations of unvulcanized rubber compositions. In Figure 1, 1 represents each test specimen.

[0024] When evaluating the occurrence of warping in each test piece using the same sensory inspection method as before, based on the three acquired images, all operators evaluated test piece A as "no warping" and all operators evaluated test piece C as "warping present." However, for test piece B, some operators evaluated it as "no warping" while others evaluated it as "warping present," resulting in variability in evaluation among operators. This may make it difficult to provide tires of consistent quality (problem with conventional technology).

[0025] Therefore, in this embodiment, the process proceeds to the next image processing step and beyond to quantitatively evaluate the occurrence of ripple.

[0026] (4) Image processing step In this step, the images of each test specimen obtained above (see Figure 2(a)) are processed according to a predetermined program, and the contours of each test specimen are extracted from the images to distinguish between the areas of the test specimen and other areas in the images.

[0027] Specifically, the first step is to load the image data into an image processing program created using a programming language such as Python, and then perform a monochrome (black and white) conversion process.

[0028] Next, an averaging filter is used on the monochrome image data to blur and smooth the image (see Figure 2(b)). This reduces image noise and emphasizes features such as edges.

[0029] Furthermore, when blurring an image, it is also preferable to use a smoothing filter instead of an averaging filter, such as a Gaussian filter that removes noise components by calculating weights within the kernel according to a Gaussian distribution, or a median filter that removes noise components while preserving edge components by using the median.

[0030] Next, the blurred image is subjected to image sharpening processing to highlight the outline of the test specimen. Specifically, a binarization process is performed, assigning each pixel in the image to either "black" or "white" (see Figure 2(c)). This eliminates intermediate tones from the image, making it possible to clearly distinguish the object from the background, easily differentiate the area of ​​the test specimen from other areas in the image, and appropriately extract the outline of the test specimen (see Figure 2(d)).

[0031] Furthermore, during the binarization process, it is preferable to perform binarization based on a pixel threshold to emphasize the contour of the test specimen, thereby enabling appropriate extraction of the specimen's contour. Note that in Figures 2(c) and (d), the original image's black and white colors are inverted by the binarization process, but this inversion is not required.

[0032] Alternatively, contour extraction can be performed without binarization. For example, contour extraction can be performed without binarization by using first-order differential filters such as Previtt filters or Sobel filters.

[0033] (5) Perimeter estimation step In this step, the circumference of the specimen is estimated from the outline of the extracted specimen.

[0034] In this case, if warping occurs in the test specimen, the circumference of the test specimen will be longer by the amount of the warping compared to when no warping occurs.

[0035] (6) Step to evaluate wave conditions In this step, the degree of waviness occurring in the test specimen is evaluated based on the estimated circumference of the test specimen.

[0036] As mentioned above, if warping occurs in the test specimen, the circumference of the specimen will be longer than when no warping occurs. Therefore, by measuring this change, the degree of warping can be evaluated.

[0037] Figure 3 shows an example of evaluating the degree of warping in this embodiment. In Figure 3, 2 is the contour of a test specimen without warping, and 3 is the contour of a test specimen with warping. From Figure 3, it can be seen that the circumference of contour 3 of the test specimen with warping is longer than the circumference of contour 2 of the test specimen without warping. Therefore, the difference between the two circumferences can be used as an indicator to evaluate the degree of warping, and whether or not warping has occurred can be evaluated based on the degree of this difference.

[0038] Specifically, by comparing the difference between the two obtained circumferences with a predetermined threshold value set for each rubber composition, it is possible to determine whether or not warping has occurred and to quantitatively evaluate the state of warping. This eliminates variations in evaluation by workers and enables efficient evaluation.

[0039] For example, when calculating the evaluation index (difference in circumference) for each test specimen shown in Figure 1, the values ​​are clearly expressed numerically: 34 for specimen A, 94 for specimen B, and 156 for specimen C. By comparing these values ​​with the threshold, it is possible to determine whether or not rippling has occurred. Therefore, unlike specimen B, which previously had varying evaluations, any operator can perform the same evaluation in a short time, eliminating evaluation variability and enabling efficient evaluation.

[0040] While the above uses the difference between two circumferences as an evaluation metric, it is not limited to this; the ratio of two circumferences, the amount of change or rate of change in two circumferences may also be used as evaluation metrics.

[0041] Furthermore, by applying the above-described evaluation method for unvulcanized rubber to conventional extrusion molding equipment, it becomes possible to perform the extrusion molding of actual unvulcanized rubber components with higher precision and efficiency.

[0042] Although the present invention has been described above based on embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equivalent scope as the present invention.

[0043] The present invention (1) is, A method for evaluating unvulcanized rubber, which evaluates the state of waviness generation during extrusion molding of unvulcanized rubber components, An unvulcanized rubber composition preparation step for preparing an unvulcanized rubber composition corresponding to the unvulcanized rubber member, A test piece extrusion molding step in which the prepared unvulcanized rubber composition is extruded into a test piece of a predetermined shape using an extrusion molding apparatus, An image acquisition step is to acquire an image of the obtained test piece from the thickness direction, Image processing step of processing the acquired image of the test specimen and extracting the contour of the test specimen from the image, A perimeter estimation step in which the perimeter of the test specimen is estimated from the outline of the extracted test specimen, The method for evaluating unvulcanized rubber is characterized by comprising a step of evaluating the degree of waviness generated in the test piece based on the estimated circumference of the test piece.

[0044] The present invention (2) is, The method for evaluating unvulcanized rubber according to the present invention (1) is characterized in that a capillary rheometer is used as the extrusion molding apparatus.

[0045] The present invention (3) is, The method for evaluating unvulcanized rubber according to (1) or (2) of the present invention is characterized in that the acquired image is converted into digital data in the image acquisition step.

[0046] The present invention (4) is, The image processing step is characterized by reading image data into an image processing program created using a predetermined programming language and performing a monochrome conversion process, and is an evaluation method for unvulcanized rubber in any combination with any of the present invention (1) to (3).

[0047] The present invention (5) is, The method for evaluating unvulcanized rubber according to the present invention (4) is characterized in that the programming language is Python.

[0048] The present invention (6) is, The method for evaluating unvulcanized rubber according to (4) or (5) of the present invention is characterized in that, in the image processing step, the image data that has been converted to monochrome is blurred and smoothed using an averaging filter.

[0049] The present invention (7) is, The method for evaluating unvulcanized rubber according to (4) or (5) of the present invention is characterized in that, in the image processing step, the image data that has been converted to monochrome is blurred and smoothed using a smoothing filter.

[0050] The present invention (8) is, The method for evaluating unvulcanized rubber according to the present invention (7) is characterized in that the smoothing filter is a Gaussian filter.

[0051] The present invention (9) is, The image processing step is characterized by applying an image enhancement process to the monochrome image data to highlight the contour of the test piece, and is a method for evaluating unvulcanized rubber in any combination with any of (5) to (8) of the present invention.

[0052] The present invention (10) is, The method for evaluating unvulcanized rubber according to the present invention (9) is characterized in that the image enhancement process is a binarization process.

[0053] The present invention (11) is, The present invention (9) is a method for evaluating unvulcanized rubber, characterized in that the image enhancement process is performed using a first-order differential filter.

[0054] The present invention (12) is, The waviness evaluation step is characterized in that it is a step of evaluating the waviness in the test piece based on the circumference of the test piece and the circumference of a test piece without waviness, and is a method for evaluating unvulcanized rubber in any combination with any of the present invention (1) to (11).

[0055] The present invention (13) is, The method for evaluating unvulcanized rubber according to the present invention (12) is characterized in that, in the step of evaluating the waviness, the difference between the circumference of the test piece and the circumference of a test piece without waviness is compared with a predetermined threshold to evaluate the waviness of the test piece. [Explanation of Symbols]

[0056] 1 Test specimen 2. Expected contour of the test specimen when no warping occurs. 3. Contour of the test specimen

Claims

1. A method for evaluating unvulcanized rubber, which evaluates the state of waviness generation during extrusion molding of unvulcanized rubber components, An unvulcanized rubber composition preparation step for preparing an unvulcanized rubber composition corresponding to the unvulcanized rubber member, A test piece extrusion molding step in which the prepared unvulcanized rubber composition is extruded into a test piece of a predetermined shape using an extrusion molding apparatus, An image acquisition step is to acquire an image of the obtained test piece from the thickness direction, Image processing step of processing the acquired image of the test specimen and extracting the contour of the test specimen from the image, A perimeter estimation step in which the perimeter of the test specimen is estimated from the outline of the extracted test specimen, A method for evaluating unvulcanized rubber, characterized by comprising a step of evaluating the degree of waviness generated in the test piece based on the estimated circumference of the test piece.

2. The method for evaluating unvulcanized rubber according to claim 1, characterized in that a capillary rheometer is used as the extrusion molding apparatus.

3. The method for evaluating unvulcanized rubber according to claim 1 or 2, characterized in that the acquired image is converted into digital data in the image acquisition step.

4. The method for evaluating unvulcanized rubber according to claim 1 or 2, characterized in that, in the image processing step, image data is read into an image processing program created using a predetermined programming language and subjected to monochrome processing.

5. The method for evaluating unvulcanized rubber according to claim 4, characterized in that the programming language is Python.

6. The method for evaluating unvulcanized rubber according to claim 5, characterized in that, in the image processing step, the image data that has been converted to monochrome is blurred and smoothed using an averaging filter.

7. The method for evaluating unvulcanized rubber according to claim 5, characterized in that, in the image processing step, the image data that has been converted to monochrome is blurred and smoothed using a smoothing filter.

8. The method for evaluating unvulcanized rubber according to claim 7, characterized in that the smoothing filter is a Gaussian filter.

9. The method for evaluating unvulcanized rubber according to claim 5, characterized in that, in the image processing step, the image data that has been converted to monochrome is subjected to an image sharpening process that highlights the contour of the test piece.

10. The method for evaluating unvulcanized rubber according to claim 9, characterized in that the image enhancement process is a binarization process.

11. The method for evaluating unvulcanized rubber according to claim 9, characterized in that the image enhancement process is performed using a first-order differential filter.

12. The method for evaluating unvulcanized rubber according to claim 1 or 2, characterized in that the step of evaluating the waviness of the test piece is a step of evaluating the waviness of the test piece based on the circumference of the test piece and the circumference of a test piece in which no waviness occurs.

13. The method for evaluating unvulcanized rubber according to claim 12, characterized in that, in the step of evaluating the waviness, the difference between the circumference of the test piece and the circumference of a test piece without waviness is compared with a predetermined threshold to evaluate the waviness of the test piece.

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