Resin composition and method for producing the resin composition

Abstract

When additives are added to a base resin to improve its thermal properties, the carbon dioxide emissions originating from the manufacturing process of the additives are reduced. [Solution] The invention comprises a base resin 11 and a filler 12 kneaded into the base resin. The base resin is a polyolefin, and the filler is silk. When the filler is present inside the base resin, and the total length of the silk is divided by the shortest lengths of both ends of the silk, the relative frequency of the curvature of multiple silks contained in the base resin has a peak in the range of 1.1 to 1.3.

Description

Technical Field

[0001] The present invention relates to a resin composition and a method for producing the resin composition.

Background Art

[0002] The heat resistance of resins is an important factor in coping with the use environment. In particular, the thermal decomposition temperature of resins is directly related to the high heat stability under the use environment and serves as an index regarding the heat stability of resins. It is generally known that the heat stability of resins can be improved by adding maleic acid-modified polypropylene (MAPP) to the resins.

[0003] Patent Document 1 discloses, as a method for producing MAPP, a method in which polypropylene, an α,β-unsaturated carboxylic acid or its derivative, and an organic peroxide as a reaction initiator are supplied to an extruder and melt-mixed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, in order to promote a recycling-based society and a low-carbon society, recyclability of materials and reduction of carbon dioxide emissions have been demanded. From this perspective, in the production method of Patent Document 1 above, generation of carbon dioxide in the production process of MAPP cannot be avoided. Therefore, when adding MAPP to a resin, carbon dioxide emissions derived from the production process of MAPP cannot be avoided.

[0006] In view of the above points, an object of the present invention is to reduce the amount of carbon dioxide emissions derived from the production process of an additive when adding the additive to a base resin in order to improve its thermal properties.

Means for Solving the Problems

[0007] To achieve the above objective, the resin composition described in claim 1 comprises a base resin (11) and a filler (12) kneaded into the base resin. The base resin is a polyolefin, and the filler is silk. When the filler is present inside the base resin, and the curvature of the filler is defined as the value obtained by dividing the total length of the silk by the shortest lengths of both ends of the silk, the relative frequency of the curvature of multiple silks contained in the base resin has a peak in the range of 1.1 to 1.3.

[0008] Thus, by adding silk as a filler to a base resin and kneading it to produce a resin composition, the thermal and mechanical properties of the resin composition can be improved when the relative frequency of the degree of bending of the filler while it is present inside the base resin has a peak within the range of 1.1 to 1.3. Since the silk used as a filler is a fiber derived from natural products, carbon dioxide emissions from the filler manufacturing process can be reduced.

[0009] The symbols in parentheses for each of the above components indicate their correspondence to the specific means described in the embodiments described later. [Brief explanation of the drawing]

[0010] [Figure 1] This is an SEM image of a resin composition according to an embodiment of the present invention. [Figure 2] This is a conceptual diagram of silk contained in a resin composition. [Figure 3] This is a CT image of a resin composition. [Figure 4] This figure shows the frequency distribution of the degree of flexibility of silk contained in the resin composition after extrusion molding. [Figure 5] This figure shows the frequency distribution of the degree of flexibility of silk contained in the resin composition after injection molding and before tensile testing. [Figure 6] This figure shows the frequency distribution of the degree of flexibility of silk contained in the resin composition after injection molding and tensile testing. [Figure 7]This figure shows the results of thermogravimetric differential thermal analysis for a resin composition in which maleic acid-modified polypropylene and silk were added to polypropylene. [Figure 8] This figure shows the results of thermogravimetric differential thermal analysis for a resin composition of polypropylene with added silk. [Figure 9] This figure shows the results of thermogravimetric differential thermal analysis for a resin composition of polypropylene with added silk. [Figure 10] This figure shows the results of thermogravimetric differential thermal analysis for a resin composition in which maleic acid-modified polypropylene and silk were added to polypropylene. [Figure 11] This chart shows the thermal decomposition temperature Td of a mixed resin obtained by adding maleic acid-modified polypropylene to polypropylene, and a resin composition obtained by adding silk to the mixed resin. [Figure 12] This figure shows the stress-strain curve of a resin composition in which maleic acid-modified polypropylene and silk are added to polypropylene. [Figure 13] These are SEM images showing the fracture surface of the resin composition and the cross-section of raw silk. [Figure 14] This is a chart showing the results of dynamic viscoelasticity measurements of resin compositions. [Figure 15] This figure shows the tanδ obtained from dynamic viscoelasticity measurements of the resin composition. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will now be described with reference to the drawings. As shown in Figure 1, the resin composition 10 of this embodiment is a composite material containing a base resin 11 and a filler 12.

[0012] The base resin 11 is a polymer and is the main component of the resin composition 10. For example, polyolefins such as polypropylene and polyethylene can be used as the base resin 11. In this embodiment, polypropylene is used as the polyolefin. Hereinafter, polypropylene will also be referred to as "PP".

[0013] The filler 12 is an additive added to the resin composition 10. The filler 12 is used to improve the heat resistance and mechanical properties of the base resin 11. The filler 12 is kneaded into the base resin 11.

[0014] In this embodiment, silk is used as the filler 12. Silk is a fibrous substance derived from natural products containing organic substances. Silk mainly consists of a structural protein composed of fibroin and sericin. Silk is an animal fiber made from the cocoons of silkworms. In the process of silk production, mulberry used for raising silkworms absorbs carbon dioxide through photosynthesis. Therefore, silk can be treated as an additive with reduced carbon dioxide emissions during production.

[0015] The silk of this embodiment includes cocoon filaments taken from the cocoons produced by silkworms, raw silk obtained by bundling multiple cocoon filaments into one thread, and spun silk obtained by refining the raw silk. The cocoon filament is a thread composed of one fiber taken from a cocoon, and the fiber diameter is about 10 μm. The cocoon filament and the raw silk have fibroin and sericin, and the sericin is removed from the spun silk by refining. In this embodiment, silk in the state of raw silk or cocoon filament before removing sericin by refining is used.

[0016] The resin composition 10 may contain only the base resin 11 and the filler 12, or may contain other additives in addition to the base resin 11 and the filler 12. As other additives, for example, maleic acid-modified polypropylene can be used. Hereinafter, maleic acid-modified polypropylene is also referred to as "MAPP". Also, a material obtained by adding MAPP to PP is also referred to as "mixed resin".

[0017] In the resin composition 10, a large number of fibrous silks are dispersed and present inside the base resin 11. The resin composition 10 can be produced by kneading silk into the base resin 11. The silk added to the base resin 11 can be used with a length of about several millimeters. The kneading of the base resin 11 and silk is carried out under a high-temperature and high-pressure environment. The resin composition 10 produced by kneading can be obtained, for example, in the form of pellets.

[0018] When silk fibers of a few millimeters in length are added to the base resin 11, the silk is cut and shortened by kneading under high temperature and high pressure conditions, becoming tens to hundreds of micrometers in length. In other words, silk exists inside the base resin 11 in lengths of, for example, tens to hundreds of micrometers.

[0019] The fibrous silk has a predetermined length and exists bent within the resin composition 10. The filler 12 has a predetermined degree of bend within the resin composition 10. The degree of bend of the silk will be described later.

[0020] The color of the resin composition 10 depends on the base resin 11 and the filler 12. When raw silk is used as the filler 12, the pellets of the resin composition 10 exhibit a yellow color due to the influence of the filler 12, relative to the white, translucent base resin 11. The colors most frequently found in the resin composition 10 using raw silk are Cornsilk and #fff8dc, respectively, with HEX color codes R:255, G:248, and B:220.

[0021] The content of filler 12 in the resin composition 10 can be 0.5 to 20 wt%. By setting the content of filler 12 in the resin composition 10 to 0.5 wt% or more, the thermal properties and mechanical properties of the resin composition 10 can be improved. Furthermore, by setting the content of filler 12 in the resin composition 10 to 20 wt% or less, the disadvantages of adding filler 12 can be minimized. It is more preferable that the content of filler 12 in the resin composition 10 be 2 to 10 wt%.

[0022] Here, a method for manufacturing the resin composition 10 will be described. The resin composition 10 of this embodiment can be manufactured by adding silk as a filler 12 to a base resin 11 and performing a kneading process in a high-temperature, high-pressure environment. In the kneading process, silk is added to the base resin 11, which has been heated above its melting point to a molten state, and mixed. The added silk can be used in lengths of, for example, several centimeters. The kneading of the base resin 11 and silk can be carried out, for example, by extrusion molding using an extrusion molding machine.

[0023] In this embodiment, the "high temperature and high pressure environment" can be defined as, for example, a temperature range of 100 to 300°C and a pressure range of 0.5 MPa to 4 MPa. The temperature range is preferably 180 to 210°C, and more preferably 195 to 210°C. The pressure range is preferably 1 to 3 MPa. The resin temperature (heating temperature) during kneading is preferably above the melting point of the base resin 11 and below the thermal decomposition temperature of the base resin 11.

[0024] In this embodiment, a Process11 twin extruder from Thermo Fisher Scientific Co., Ltd. was used as the extruder. The extruder has a maximum torque of 12 N·m, a die with a 2 mm diameter extrusion port, and a water-cooled strand cooling conveyor.

[0025] In this embodiment, the mixing conditions in the extrusion molding machine were set to a die outlet pressure of 2.0 to 2.5 MPa and a screw rotation speed of 500 to 650 rpm. The measured resin temperature in the extrusion molding machine was 195 to 198°C. The resin temperature corresponds to the heating temperature.

[0026] The manufacturing process for a resin composition 10 containing a base resin 11 and a filler 12 will be described. The base resin 11 (PP) and the filler 12 (silk) were quantified so that their respective weight ratios were 95:10. The PP was then melted in an extruder and mixed with silk that had been cut to 1-5 mm. The silk used was raw silk (sericin concentration 25 wt%, 21 denier) manufactured by Miyasaka Silk Mill. Since the resin composition 10, consisting of PP and silk, emerged from the die outlet of the extruder in a thread-like form, the thread-like resin composition 10 was rapidly cooled by water cooling and then cut to obtain a pellet-like resin composition 10.

[0027] Next, the manufacturing process will be described when the resin composition 10 contains PP as a base resin 11, silk as a filler 12, and MAPP. When kneading PP, MAPP, and silk, a mixed resin is produced by kneading PP and MAPP, and then the resin composition 10 is produced by kneading the mixed resin and silk.

[0028] First, pelletized PP and pelletized MAPP were mixed in a weight ratio of 97:3 to 90:10, then supplied to an extruder for mixing in a molten state. The mixed resin of PP and MAPP came out of the die outlet of the extruder in a thread-like form. The thread-like mixed resin was rapidly cooled by water cooling and then shredded to obtain pelletized mixed resin. Here, in the mixed resin consisting of PP and MAPP, the weight ratio of MAPP can be used in the range of 3 to 10 wt%.

[0029] The mixed resin of PP and MAPP was kneaded with silk, with the weight ratio of the mixed resin to silk being determined to be 100:10. The mixed resin was then remelted in an extruder and kneaded with silk that had been cut into 1-5 mm pieces. Raw silk from Miyasaka Silk Mill was used.

[0030] Since a mixed resin of PP and MAPP comes out of the die outlet of the extrusion molding machine in the form of threads, the thread-like mixed resin is rapidly cooled by water cooling and then shredded to obtain a pellet-shaped mixed resin. Since a resin composition 10 consisting of PP, silk, and MAPP comes out of the die outlet of the extrusion molding machine in the form of threads, the thread-like resin composition 10 is rapidly cooled by water cooling and then shredded to obtain a pellet-shaped resin composition 10.

[0031] The pelletized resin composition 10 can be molded into a molded product by injection molding. Injection molding can be considered a molding process performed after the kneading process by extrusion molding. The molding process may be performed as needed. In this embodiment, a dumbbell for tensile testing of the resin composition 10 was manufactured by injection molding in order to perform a tensile test of the resin composition 10.

[0032] In this embodiment, a HAAKE MiniJet Pro piston-type injection molding machine from Thermo Fisher Scientific Co., Ltd. was used as the injection molding machine. The cylinder and mold temperatures, pressures, and holding times of the injection molding machine were set as follows: cylinder temperature 210°C, mold temperature 90°C, injection pressure 70 MPa, injection time 4 seconds, holding pressure 30 MPa, and holding time 5 seconds. The dumbbells after injection molding, like the pellets after the mixing process, exhibited a yellow color compared to the white, translucent resin. The most common colors in the molded dumbbells were Cornsilk and #fff8dc, respectively, and their HEX color codes (Hexadecimal Color Codes) were R:255, G:248, and B:220.

[0033] Injection molding can be performed using the following procedure. First, a dumbbell-shaped mold is set in the injection molding machine and preheated to a predetermined mold temperature. Then, pelletized resin composition 10 is filled into a cylinder heated to a predetermined cylinder temperature. The pelletized resin composition 10 is heated and melted inside the cylinder. After that, the cylinder is set in the apparatus and injection molding is performed.

[0034] Furthermore, injection molding can also be performed without using an injection molding machine; the molten resin extruded by the aforementioned extrusion molding machine is not cooled, and instead filled into a cylinder while still molten.

[0035] Next, the degree of flexibility of the filler 12 mixed into the base resin 11 will be described. The silk used as the filler 12 is an elongated, thread-like material, and most of it is bent inside the base resin 11.

[0036] As shown in Figure 2, if the shortest length of the silk at both ends inside the base resin 11 is La, and the total length of the silk is Lb, then the degree of flexibility of the silk can be defined as total length Lb / shortest length La. In other words, the degree of flexibility of the filler is the value obtained by dividing the total length Lb of the silk by the shortest length La at both ends of the silk.

[0037] When the silk is straight, the total length Lb and the shortest length La are equal, and the degree of curvature is the minimum value of 1. The degree of curvature of the numerous silks present inside the resin composition 10 can be determined by measuring the degree of curvature of multiple samples and determining the frequency distribution of these measurements. In this embodiment, the degree of curvature of the filler 12 present inside the base resin 11 is concentrated within a predetermined range, and the relative frequency of the degree of curvature has a peak within that predetermined range.

[0038] The shortest length La and total length Lb of the silk kneaded into the base resin 11 can be measured, for example, by analyzing a 3D image of the silk taken with an X-ray CT scanner. In this embodiment, multiple CT images obtained by scanning an object using X-rays with a computed tomography scanner (X-ray CT) were used and converted into 3D data including the inside and outside of the object by computer processing. Figure 3 shows an example of a CT image of the resin composition 10 taken with an X-CT scanner.

[0039] The X-ray CT was performed using the equipment installed at beamline BL11S3 at the Aichi Synchrotron Center. The various conditions of the equipment were as follows: Beam mode was direct (white: energy 13KeV), attenuator was Al (1mm), scan angle was 185°, step angle was 0.1°, number of measurements was 1850, exposure time was 200msec, camera was Orca-Flash4.0v3 (Hamamatsu Photonics), beam monitor was AA50 (Hamamatsu Photonics), measurement magnification was 10x (pixel size 1.33μm / voxcel) and 20x (pixel size 0.65μm / voxcel), and scintillator was LuAG 10μm.

[0040] The curvature of silk was measured by analyzing CT images of the silk. Thermo Fisher Scientific's Avizo software (ver.3D 2021.1) was used for the CT image analysis. 600 images within a 600px x 600px area were analyzed. Here, 1 pixel corresponds to 1.8 μm.

[0041] In this embodiment, the flexibility of silk was measured using a pelletized resin composition 10 after extrusion molding, a molded resin composition 10 after injection molding before tensile testing, and a molded resin composition 10 after injection molding after tensile testing. In this embodiment, the number of silk flexibility measurement samples was approximately 1000.

[0042] Figures 4 to 6 show the frequency distribution of the degree of flexibility of silk. The frequency distributions shown in Figures 4 to 6 show the results of classifying the measured values ​​of the degree of flexibility of silk into ranges divided by a predetermined width. In the resin composition 10 manufactured in this embodiment, the degree of flexibility of silk is in the range of 1.0 to 2.1. In Figures 4 to 6, the degree of flexibility of silk is divided into ranges with a width of 0.1, such as 1.0 to 1.1, 1.1 to 1.2, ..., with a class width of 0.1.

[0043] Figures 4 to 6 show the relative frequency of each range when the curvature of silk is classified into ranges with a width of 0.1. In Figures 4 to 6, the relative frequency of each range is the value obtained by dividing the number of samples belonging to each range by the total number of samples. In other words, the relative frequency of each range represents the proportion of the frequency of each range to the total.

[0044] Figure 4 shows the frequency distribution of the degree of curvature of silk in the resin composition 10 after extrusion molding. In the resin composition 10 after extrusion molding, the shortest length La and total length Lb of silk were measured using 1110 samples. The maximum value of the shortest length La was 724.7 μm, the minimum value was 19.8 μm, the mean was 120.6 μm, and the standard deviation was 110.2 μm. The maximum value of the total length Lb was 1024.9 μm, the minimum value was 20.1 μm, the mean was 135.8 μm, and the standard deviation was 138.0 μm. The maximum value of the degree of curvature (Lb / La) was 6.69, the minimum value was 1.00, the mean was 1.08, and the standard deviation was 0.24.

[0045] As shown in Figure 4, the relative frequency of the degree of curvature of silk in the resin composition 10 after extrusion molding is 92.6% (=79.4% + 13.2%) in the range of 1.1 to 1.3, which is a higher relative frequency than other ranges. In other words, the relative frequency of the degree of curvature of silk has a peak in the range of 1.1 to 1.3. More specifically, the relative frequency of the degree of curvature of silk is 79.4% in the range of 1.1 to 1.2, and the relative frequency of the degree of curvature of silk has the largest peak in the range of 1.1 to 1.2.

[0046] Figure 5 shows the frequency distribution of the degree of flexure of silk in resin composition 10 after injection molding and before tensile testing. For resin composition 10 after injection molding and before tensile testing, the shortest length La and total length Lb of silk were measured using 1184 samples. The maximum value of the shortest length La was 472.2 μm, the minimum value was 19.9 μm, the mean was 92.4 μm, and the standard deviation was 59.2 μm. The maximum value of the total length Lb was 526.0 μm, the minimum value was 20.2 μm, the mean was 99.9 μm, and the standard deviation was 71.9 μm. The maximum value of flexure (Lb / La) was 2.87, the minimum value was 1.00, the mean was 1.05, and the standard deviation was 0.10.

[0047] As shown in Figure 5, the relative frequency of the degree of bend of silk in the resin composition 10 after injection molding and before tensile testing is 94.8% (=88.4% + 6.4%) in the range of 1.1 to 1.3, which is a higher relative frequency than other ranges. In other words, the relative frequency of the degree of bend of silk has a peak in the range of 1.1 to 1.3. More specifically, the relative frequency of the degree of bend of silk is 88.4% in the range of 1.1 to 1.2, and the relative frequency of the degree of bend of silk has the largest peak in the range of 1.1 to 1.2.

[0048] Figure 6 shows the frequency distribution of the degree of flexure of silk in resin composition molded articles after injection molding and tensile testing. For resin composition molded articles after injection molding and before tensile testing, the shortest length La and total length Lb of silk were measured using 992 samples. The maximum value of the shortest length La was 352.6 μm, the minimum value was 19.7 μm, the mean was 100.1 μm, and the standard deviation was 61.3 μm. The maximum value of the total length Lb was 768.5 μm, the minimum value was 20.0 μm, the mean was 119.5 μm, and the standard deviation was 94.6 μm. The maximum value of flexure (Lb / La) was 16.24, the minimum value was 1.00, the mean was 1.16, and the standard deviation was 0.66.

[0049] As shown in Figure 6, the relative frequency of the degree of bend of silk in the resin composition 10 after injection molding and tensile testing is 95.4% (=75.2% + 10.2%) in the range of 1.1 to 1.3, and the relative frequency of the degree of bend of silk has a peak in the range of 1.1 to 1.3. More specifically, the relative frequency of the degree of bend of silk is 75.2% in the range of 1.1 to 1.2, and the relative frequency of the degree of bend of silk has the largest peak in the range of 1.1 to 1.2.

[0050] As described above, the resin composition 10 obtained by extrusion molding or injection molding has a high relative frequency of the degree of curvature of silk present inside the base resin 11 in the range of 1.1 to 1.3, and is particularly high in the range of 1.1 to 1.2. The inventors of this application have found that the thermal and mechanical properties of the resin composition 10 are improved when the peak relative frequency of the degree of curvature of silk present inside the base resin 11 is within the range of 1.1 to 1.3, and particularly within the range of 1.1 to 1.2. The thermal and mechanical properties of the resin composition 10 will be described below.

[0051] First, the thermal properties of the resin composition 10 will be explained using Figures 7 to 9. In this embodiment, the thermal decomposition temperature of the resin composition 10 was measured using a thermogravimetric differential thermal analyzer (TG-DTA). The thermogravimetric differential thermal analyzer used was a NETZSCH STA 2500 Regalus. The thermal decomposition temperature was measured under a nitrogen atmosphere in a temperature range of room temperature to 800°C at a heating rate of 10°C / min. The mass of each sample was approximately 10 mg. An open aluminum pan was used for the evaluation of all samples.

[0052] Figure 7 shows the thermal analysis results of a resin composition 10 consisting of PP (base resin 11), MAPP, and silk (filler 12). The resin composition 10 consisting of PP, MAPP, and silk used in Figure 7 was obtained by adding 10 wt% silk (resin weight ratio) to a mixed resin consisting of 95 wt% PP and 5 wt% MAPP. The ratio of silk added to the mixed resin is a weight ratio to the mixed resin, and the weight ratio of each component in the mixed resin is PP:MAPP:Silk = 95:5:10. When the total content of the resin composition 10 consisting of PP, MAPP, and silk is 100 wt%, the PP content is 86.4 wt%, the MAPP content is 4.5 wt%, and the silk content is 9.1 wt%.

[0053] Figure 7 shows the thermal analysis results for PP alone, MAPP alone, silk alone, and a mixed resin of PP and MAPP as comparative examples. In the mixed resin of PP and MAPP, the PP content is 95 wt% and the MAPP content is 5 wt%.

[0054] As shown in Figure 7, MAPP alone has a higher decomposition initiation temperature than PP alone. Furthermore, in a mixed resin containing 95 wt% PP and 5 wt% MAPP, the difference in decomposition temperature compared to MAPP alone is smaller.

[0055] Furthermore, resin composition 10, which contained 95 wt% PP, 5 wt% MAPP, and 10 wt% silk (by resin weight), showed a higher decomposition initiation temperature than the mixed resin of PP and MAPP alone, exhibiting almost the same behavior as MAPP alone. In other words, the addition of silk to the mixed resin of PP and MAPP clearly improves its thermal stability.

[0056] The resin composition 10, consisting of PP, MAPP, and silk, exhibits a slight weight loss at around 300°C. This is presumed to be due to the decomposition of silk. The organic components contained in silk are gasified by thermal decomposition. It is thought that during thermal decomposition of silk, water vapor is produced first, followed by carbon dioxide and carbon monoxide, and that the silk itself undergoes modification through the reaction of these gaseous components with the silk.

[0057] Figure 8 shows the thermal analysis results of a resin composition 10 consisting of PP (base resin 11) and silk (filler 12). The resin composition 10 used in Figure 8 consisted of 90 wt% PP and 10 wt% silk. As a comparative example, Figure 8 also shows the thermal analysis results of PP alone, MAPP alone, and silk alone.

[0058] As shown in Figure 8, resin composition 10, which contains 90 wt% PP and 10 wt% silk (by weight of the resin), exhibited a higher thermal decomposition temperature than PP alone. In other words, even without MAPP in resin composition 10, adding silk to PP can improve the decomposition initiation temperature and thus improve the thermal properties. Furthermore, resin composition 10 consisting of PP and silk showed a slight weight loss around 300°C. This is presumed to be due to the decomposition of silk, similar to the resin composition 10 consisting of PP, MAPP, and silk used in Figure 7.

[0059] Figure 9 shows the thermal analysis results of resin composition 10, which contains 10 wt% silk (by weight of resin) added to 90 wt% PP. As a comparative example, Figure 9 also shows the thermal analysis results of silk alone and a mixed resin of 95 wt% PP and 5 wt% MAPP.

[0060] As shown in Figure 9, resin composition 10, which contains 10 wt% silk (resin weight ratio) added to 90 wt% PP, exhibits similar behavior to a mixed resin of 95 wt% PP and 5 wt% MAPP, except for a weight loss that is thought to be due to the decomposition of silk around 300°C. In other words, Figure 9 shows that resin composition 10, which contains 10 wt% silk added to 90 wt% PP, has the effect of raising the thermal decomposition temperature to a similar extent as a synthetic resin of 95 wt% PP and 5 wt% MAPP.

[0061] Figure 10 shows the thermal analysis results of resin composition 10, which is a mixed resin consisting of PP and MAPP with added silk. Figure 10(A) shows the thermal analysis results of resin composition 10 in which 97 wt% PP, 3 wt% MAPP, and 10 wt% silk (resin weight ratio) are added. Figure 10(B) shows the thermal analysis results of resin composition 10 in which 95 wt% PP, 5 wt% MAPP, and 10 wt% silk (resin weight ratio) are added. Figure 10(C) shows the thermal analysis results of resin composition 10 in which 90 wt% PP, 10 wt% MAPP, and 10 wt% silk (resin weight ratio) are added.

[0062] Figure 10(A) shows the thermal analysis results of a mixed resin containing 97 wt% PP and 3 wt% MAPP as a comparative example. Figure 10(B) shows the thermal analysis results of a mixed resin containing 95 wt% PP and 5 wt% MAPP as a comparative example. Figure 10(C) shows the thermal analysis results of a mixed resin containing 90 wt% PP and 10 wt% MAPP as a comparative example.

[0063] Figure 11 shows the thermal decomposition temperatures Td of a mixed resin consisting of PP and MAPP, and resin composition 10 in which silk is added to the mixed resin. Here, Td is the onset temperature. Figure 11 shows the thermal decomposition temperatures Td when 10 wt% raw silk is added to mixed resins with MAPP weight ratios of 3 wt%, 5 wt%, and 10 wt%, and when 10 wt% thread from cut nonwoven cocoons is added to a mixed resin with a MAPP weight ratio of 5 wt%. The cut cocoon thread was used by cutting hollow cocoons, before the thread was extracted, into pieces of about a few millimeters.

[0064] As shown in Figures 10 and 11, the thermal decomposition temperature Td of the mixed resin consisting of PP and MAPP increases to 392.8°C, 398.1°C, and 401.7°C as the weight ratio of MAPP increases from 3 wt%, 5 wt%, and 10 wt%. Furthermore, in resin composition 10 in which silk is added to the mixed resin consisting of PP and MAPP, the thermal decomposition temperature Td is higher than that of the mixed resin. The increase in the thermal decomposition temperature Td of resin composition 10 is observed in all cases where the weight ratio of MAPP in the mixed resin is 3 wt%, 5 wt%, and 10 wt%. In addition, the effect of increasing the thermal decomposition temperature Td is obtained whether the silk contained in resin composition 10 is added in the form of raw silk or cocoon silk.

[0065] Next, the mechanical properties of the resin composition 10 of this embodiment will be explained using Figure 12. Figure 12 shows the stress-strain curves (SS curves) obtained by adding 5 wt% MAPP to 95 wt% PP and then adding 10 wt% silk (resin weight ratio) to the resin composition 10, and the mixed resin of 95 wt% PP and 5 wt% MAPP as results of tensile tests.

[0066] Tensile tests were performed using dumbbells made from resin composition 10 of PP, MAPP, and silk, and dumbbells made from a mixed resin of PP and MAPP. The mixed resin of PP and MAPP is a comparative example. Three samples were used for both the resin composition 10 of PP, MAPP, and silk, and the mixed resin of PP and MAPP.

[0067] Tensile tests were performed using a tensile testing machine in accordance with JIS K 7161-1 (Plastics - Determination of tensile properties - Part 1: General rules). The tensile testing machine used was a Shimadzu Autograph AG-IS (100kN) precision universal testing machine. The dumbbell used was a JIS K7161-2 1A type. The gripping distance for the tensile test was 115 mm. The tensile test was performed at room temperature (23±2℃) at a test speed of 50 mm / min.

[0068] As shown in Figure 12, the resin composition 10, consisting of PP, MAPP, and silk, exhibits improved stress and strain properties compared to a mixed resin consisting of PP and MAPP. In Figure 12, the area enclosed by the SS curve and the horizontal axis corresponds to the total amount of energy absorbed by the dumbbell corresponding to each SS curve. In other words, the resin composition 10, consisting of PP, MAPP, and silk, exhibits significantly improved mechanical properties compared to a mixed resin consisting of PP and MAPP.

[0069] Next, the interaction between the resin and silk in resin composition 10 will be explained using Figures 13 to 15.

[0070] Figures 13(A) and 13(B) are SEM images of the fracture surfaces of the resin composition 10 after tensile testing. In the fracture surface of the resin composition 10 consisting of PP and silk shown in Figure 13(A), elongated silk and holes where the silk has escaped were observed. In the fracture surface of the resin composition 10 consisting of PP, MAPP and silk shown in Figure 13(B), elongated silk and holes like those seen in the fracture surface of Figure 13(A) were not observed, and only silk that had been cut at the fracture surface was visible. This indicates that in the resin composition 10 containing MAPP shown in Figure 13(B), the resin and silk are in close contact.

[0071] These results strongly suggest that there is a difference in the magnitude of the interaction between silk and resin between the resin composition 10 consisting of PP and silk and the resin composition 10 consisting of PP, MAPP and silk.

[0072] Figure 13(C) is a cross-sectional SEM image of raw silk before it was added to the mixed resin. Figure 13(C) shows that the raw silk before being added to the mixed resin was in a bundle of about 10 silk filaments, each with a fiber diameter of about 10 μm. On the other hand, the silk diameter observed in Figures 13(A) and 13(B) was about 10 μm, close to that of a single silk filament. From this, it is thought that the raw silk added to the mixed resin, after going through the kneading and molding processes, unravels inside the resin composition 10 and becomes a single silk filament.

[0073] Figure 14 shows the results of evaluating the glass transition temperature Tg by performing dynamic viscoelasticity measurement (DMA) on resin composition 10. The storage modulus is the component of energy generated in an object by external force and strain that is stored inside the object, while the loss modulus is the component that diffuses to the outside. tanδ is the loss coefficient, which is the ratio of the loss modulus to the storage modulus.

[0074] For dynamic viscoelasticity measurements, TA Instruments' Model 2980 DMA dynamic viscoelasticity analyzer was used. The measurement conditions were: single cantilever bending mode, measurement temperature range of -70 to 50°C, and heating rate of 1 km / min. -1 The amplitude was set to 100 μm, the frequency to 1 Hz, and the sample size to L17.5 × W10.0 × T4 mm. Dynamic viscoelasticity measurements were performed on pure PP, a mixed resin of 95 wt% PP with 5 wt% MAPP added, a resin composition 10 of 90 wt% PP with 10 wt% silk (resin weight ratio) added, and a resin composition 10 of 95 wt% PP with 5 wt% MAPP and 10 wt% silk (resin weight ratio) added.

[0075] As shown in Figure 14, the resin composition 10 in which silk is added to PP shows increased loss modulus and storage modulus, as well as an increased tanδ, compared to PP alone. Similarly, the resin composition 10 in which MAPP and silk are added to PP shows increased loss modulus and storage modulus, as well as an increased tanδ, compared to the mixed resin in which MAPP is added to PP alone.

[0076] Figure 15 is a plot of the loss coefficient tanδ obtained from dynamic viscoelasticity measurements. In Figure 15, it is shown that the resin composition 10 with silk added to PP has a higher tanδ than PP alone. Similarly, it is shown that the resin composition 10 with MAPP and silk added to PP has a higher tanδ than the mixed resin with MAPP added to PP alone.

[0077] The glass transition temperature (Tg) in resin-filler composites is known to reflect the degree of interaction between the resin and the filler (Journal of Polymer Science, Vol. 65, No. 7, 2008, pp. 458-464). When the interaction between the resin and the filler is strong, the glass transition temperature (Tg) tends to be higher.

[0078] The resin composition 10 in which silk is added to PP and the resin composition 10 in which MAPP and silk are added to PP show a higher glass transition temperature Tg than PP alone and the mixed resin in which MAPP is added to PP. Therefore, it is suggested that the resin composition 10 of this embodiment is thermally stabilized because the interaction between the resin and the filler is increased by the addition of silk.

[0079] In the embodiment described above, by adding silk as a filler 12 to the base resin 11, the thermal properties and mechanical properties can be improved compared to when the base resin 11 is used alone. Silk is a fiber derived from natural products, and by using silk as the filler 12, carbon dioxide emissions from the manufacturing process of the filler 12 can be reduced.

[0080] Furthermore, even when MAPP is added to the resin composition 10 of this embodiment, the amount of MAPP added can be reduced, thereby reducing carbon dioxide emissions originating from the manufacturing process of the filler 12.

[0081] Furthermore, according to this embodiment, the thermal and mechanical properties of the resin composition 10 can be improved when the frequency of the degree of curvature of the filler 12 present inside the base resin 11 peaks within the range of 1.1 to 1.3. More specifically, the thermal and mechanical properties of the resin composition 10 can be improved when the relative frequency of the degree of curvature of the filler 12 present inside the base resin 11 peaks within the range of 1.1 to 1.2.

[0082] Furthermore, in the resin composition 10 of this embodiment, the silk added in the raw silk state is in the form of cocoon threads. This is thought to be because, as the resin composition 10 is produced through the kneading process, the bundles of raw silk unravel and become individual cocoon threads. In the resin composition 10, the silk used as filler 12 is in the form of cocoon threads, which improves the dispersibility of the filler 12 in the resin composition 10. This increases the contact area between the base resin 11 and the filler 12, thereby improving the mechanical properties.

[0083] (Other embodiments) The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of the invention. Furthermore, the means disclosed in the above embodiments may be combined as appropriate to the extent that they are feasible. [Explanation of symbols]

[0084] 10 Resin composition 11. Base resin 12 Fillers

Claims

1. Base resin (11) and The filler (12) is kneaded into the base resin, Equipped with, The aforementioned base resin is a polyolefin. The aforementioned filler is silk, A resin composition in which, when the filler is present inside the base resin, the relative frequency of the curvature of the multiple silks contained in the base resin has a peak in the range of 1.1 to 1.3, when the total length of the silk is divided by the shortest length of both ends of the silk.

2. The resin composition according to claim 1, wherein the relative frequency of the degree of curvature of the filler present inside the base resin has a peak in the range of 1.1 to 1.

2.

3. The resin composition according to claim 1, wherein the base resin is polypropylene.

4. The resin composition according to claim 1, wherein the content of the filler is in the range of 0.5 to 20 wt%.

5. The resin composition according to claim 1, wherein the silk is in the state of cocoon filaments.

6. The resin composition according to claim 1, comprising, in addition to the base resin and the filler, maleic acid-modified polypropylene.

7. A method for producing a resin composition according to any one of claims 1 to 6, A method for producing a resin composition, comprising a kneading step of adding the filler to the base resin and kneading to produce a resin composition containing the base resin and the filler.

8. The method for producing a resin composition according to claim 7, wherein in the kneading step, the base resin is heated above its melting point, and the base resin and the filler added to the base resin are kneaded at a pressure of 0.5 M to 4 MPa.

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