Method for evaluating stability and quality control of resin compositions

Abstract

To provide a stability evaluation method and a quality control method for resin composition that are adaptive regardless of whether or not a resin composition is colored or whether or not additives which are thermally unstable are blended, and can evaluate, in a short time, long-period stability of the resin composition.SOLUTION: A stability evaluation method for a resin composition comprises: a first step of accelerating deterioration of the resin composition; a second step of obtaining a resin extract having a yellow component, generated through the deterioration, extracted through solvent extraction of the deteriorated resin composition obtained in the first step; a third step of measuring an absorbance of the resin extract obtained in the second step at an absorption wavelength of the yellow component; and a fourth step of evaluating long-period stability of the resin composition based upon a measured value of the absorbance obtained in the third step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the stability and quality control of a resin composition. [Background technology]

[0002] Currently, home appliances such as air conditioners, televisions, refrigerators, and washing machines, office automation equipment such as copiers, and information devices such as personal computers are widely used, and resin compositions are widely used for the housings and mechanical parts of these appliances.

[0003] Examples of the resin composition include olefin-based, styrene-based, and acrylonitrile-based resin compositions. Polyolefin resin compositions such as polypropylene resins, which have excellent strength, rigidity, chemical resistance, and moldability, are often used in durable consumer goods such as the above-mentioned products.

[0004] Resin compositions gradually deteriorate over time after production due to exposure to degradation factors such as heat, oxygen, and ultraviolet light, so it is necessary to evaluate in advance the stability of the produced resin composition over long-term use.In particular, it is important to evaluate the stability of resin compositions (recycled materials) produced using resin compositions (post-consumer waste materials) that were used in discarded products as starting materials, since the composition of the starting materials varies.

[0005] Patent Document 1 describes a test method for early detection of yellowing due to thermal degradation of molten resin in contact with heated metal material, in which a resin is pressed against a heated metal to melt it, and the results are measured using a Fourier transform infrared spectrophotometer (FTIR) in the range of 1500 to 1900 cm before and after the test. -1 (C=O), 1000–1300 cm -1 (CO), 0-1300 cm -1 A test method is disclosed in which measurements are made in the wave number range of (-OH) and the intensity ratio before and after the test is calculated to determine whether or not there is a possibility of yellowing.

[0006] Non-Patent Document 1 discloses that the effect of an antioxidant added to polyethylene used in the coating material of an electric wire can be evaluated by measuring the oxidation induction time using a DSC (differential scanning calorimeter).

[0007] Non-patent document 2 discloses that the degree to which the physical properties of CNF (cellulose nanofiber) composite resins are retained was confirmed by examining the relationship between the mechanical properties of the resin and yellowing degree, the correlation between tensile stress retention rate and yellowing degree, and the progression of yellowing degree due to molding thermal history, etc., in order to confirm the degree to which CNF composite resins were selected and recycled from shredder dust (mixed resins, etc.) generated when used home appliances that use CNF composite resins were dismantled. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-31739 [Non-patent literature]

[0009] [Non-Patent Document 1] UBE Scientific Analysis Center, Inc., "Measurement of Oxidation Induction Time (OIT) of PE," [online], [Retrieved March 31, 2021], Internet<URL:https: / / www.ube-ind.co.jp / usal / documents / p201_141.htm> [Non-patent document 2] Panasonic Corporation, Production Technology Headquarters, "Report on the FY2017 Commissioned Work on Performance Evaluation of Cellulose Nanofiber Recycling (Development of High-Speed ​​Sorting and High-Strength Processing Methods for Cellulose Nanofiber Composite Resins)," pp. 4-5, [online], March 2018, [Retrieved March 31, 2021], Internet<URL:https: / / www.env.go.jp / earth / ondanka / cnf / mat47_panasonicH29recycle.pdf> Summary of the Invention [Problem to be solved by the invention]

[0010] However, in order to evaluate the long-term stability of the mechanical properties of a resin composition, a high-temperature aging method using a test piece of the resin composition is used. However, since the evaluation test cannot be performed at a temperature higher than the melting point of the resin composition, the evaluation test temperature is low, which causes a problem in that it takes a long time to complete the evaluation.

[0011] The method of evaluating the stability of resin molded products such as plates and pellets by measuring the yellowness using a color difference meter has the problem that if the resin molded product is colored, the color difference between the deteriorated sample and the initial sample is small, and the yellowness may not change.

[0012] Furthermore, the oxidation induction time measurement method requires specialized equipment, such as a TG / DTA (thermogravimetric / differential thermal analyzer) or DSC, which can measure weight and observe heat generation, and requires evaluation testing for each sample. For heat-sensitive samples, the evaluation temperature may need to be lowered. Lowering the evaluation temperature increases the evaluation time required to complete the analysis, and when evaluating multiple samples, additional evaluation time is required for each sample. This makes the method impractical for use in lot management, where many samples are tested. Furthermore, when evaluating resin compositions containing heat-labile additives, this method, which monitors the heat generation of the sample, may simultaneously observe heat exchange due to the decomposition of the additives while the heat generation due to the oxidation of the resin may occur, resulting in an inaccurate assessment of the time it takes for the resin composition to deteriorate.

[0013] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a method for evaluating the stability of a resin composition and a method for quality control, which can be used regardless of whether the resin composition is colored or whether a heat-unstable additive is blended, and which can evaluate the long-term stability of the resin composition in a short period of time. [Means for solving the problem]

[0014] The method for evaluating the stability of a resin composition of the present invention, which has been devised to solve the above-mentioned problems, comprises: a first step of accelerating the deterioration of a resin composition; a second step of obtaining a resin extract by extracting the yellow component produced by deterioration through solvent extraction of the deteriorated resin composition obtained in the first step; a third step of measuring the absorbance of the resin extract obtained in the second step at the absorption wavelength of the yellow component; and a fourth step of evaluating the long-term stability of the resin composition based on the measured absorbance value obtained in the third step.

[0015] According to the stability evaluation method described above, compounds (yellow components) formed by degradation from a resin composition subjected to an accelerated degradation test (first step) are separated by solvent extraction, and the concentration of the compounds (yellow components) in the resin extract is determined by absorbance, thereby evaluating the degree of degradation of the resin composition (long-term stability of the resin composition). Since the long-term stability of a resin composition is evaluated based on the yellow components formed by degradation of the resin composition, the accelerated degradation test can be performed at a temperature above the melting point of the resin composition in the first step, allowing the long-term stability of the resin composition to be evaluated in a short period of time. Furthermore, by using the solvent-extracted resin extract for evaluation, the long-term stability of the resin composition can be evaluated without being affected by the pigments or dyes that color the resin composition. Furthermore, because the resin extract after the accelerated degradation test is used to evaluate long-term stability, the time-consuming accelerated degradation test can be performed simultaneously on multiple samples, allowing the long-term stability to be evaluated in a short period of time.

[0016] In addition, the quality control method for a resin composition of the present invention, which has been devised to solve the above-mentioned problems, involves extracting a portion of a resin composition from the same lot of resin composition produced by the same manufacturing process as an evaluation sample, evaluating the extracted evaluation sample using the above-mentioned stability evaluation method, and determining that the lot can be shipped as a product if the evaluation sample is an acceptable product, and determining that the lot should be suspended from shipping if the evaluation sample is an unacceptable product.

[0017] According to the above quality control method, the resin composition stability evaluation method of the present invention is used to distinguish between acceptable and unacceptable products, so it is possible to handle the situation regardless of whether the resin composition is colored or whether it contains heat-unstable additives, and it is possible to sort acceptable and unacceptable products in a short period of time. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a method for evaluating the stability of a resin composition and a method for quality control, which can be used regardless of whether the resin composition is colored or whether it contains a heat-unstable additive, and which can evaluate the long-term stability of the resin composition in a short period of time. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a graph showing the relationship between the absorbance difference and the concentration of the primary antioxidant and the heating time in Example 1. [Figure 2] 1 is a graph showing the relationship between the absorbance difference and the concentration of the primary antioxidant and the heating time in Example 3. [Figure 3] 1 is a graph showing the relationship between the absorbance difference and the concentration of the primary antioxidant and the heating time in Example 2. [Figure 4] 1 is a graph showing the relationship between the absorbance difference and the concentration of the primary antioxidant and the heating time in Example 4. [Figure 5] 1 is a graph showing the relationship between the formulation amount of a primary antioxidant in a resin composition and discoloration time. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention includes a method for evaluating the stability and quality control of a resin composition. The method for evaluating the stability of a resin composition of the present invention includes a first step of accelerating the deterioration of the resin composition, a second step of subjecting the deteriorated resin composition obtained in the first step to solvent extraction to obtain a resin extract containing a yellow component produced by the deterioration, a third step of measuring the absorbance of the resin extract obtained in the second step at the absorption wavelength of the yellow component, and a fourth step of evaluating the long-term stability of the resin composition based on the measured absorbance value obtained in the third step.

[0021] The first step is a step of accelerating the deterioration of the resin composition. Examples of methods for accelerating the deterioration of the resin composition include a method of heat-treating the resin composition at a certain temperature (a method of placing the resin composition in a high-temperature environment), a method of heat-treating the resin composition in a high-concentration ozone atmosphere, a method of heating the resin composition in a high-concentration oxygen atmosphere, and a method of irradiating the resin composition with ultraviolet light.

[0022] When evaluating the long-term stability (long-term durability) of a resin composition used in home appliances, etc., it is preferable to use a method in which the resin composition, which allows observation of indicators of oxidative degradation, is heat-treated at a constant temperature (a method in which the resin composition is placed in a high-temperature environment; hereinafter, simply referred to as "heat treatment"), because the ambient gas is the same as the environment in which the resin composition is used.

[0023] Here, when a method of heat-treating a resin composition at a constant temperature (a method of placing the resin composition in a high-temperature environment) is used, the heating temperature to be used in the long-term stability evaluation in step 4 can be determined by appropriately selecting from the following methods: a method of setting the temperature by conducting a preheating test on the resin composition; a method of determining the 5% weight loss temperature of the resin composition or additive and setting the temperature from a temperature at least 80°C lower than the lowest temperature; a method of setting the temperature from the oxidation induction time at the heating temperature using DSC or TG / DTA; etc. The heating temperature is preferably set so that the discoloration time is in the range of 10 hours or more but less than 100 hours in order to stabilize the pass / fail judgment of long-term stability.

[0024] The resin composition used in the first step may be in the form of an injection-molded test piece, pellets, or fine powder obtained by freeze-pulverizing these. Since the greater the number of heat treatment steps such as extrusion molding or injection molding, the more rapid the deterioration may be, it is preferable to use pellets or fine powder obtained by freeze-pulverizing.

[0025] In the first step, when the resin composition is heat-treated at a temperature above the melting point of the resin composition, it is necessary to place the resin composition in a heating container and treat it. The material of the heating container may be any material that does not react with the resin composition and the additives contained therein, and containers such as heat-resistant glass containers, aluminum pans, and platinum pans can be used.

[0026] The weight of the resin composition used in the first step is not particularly limited, but when a heating container is used in the heat treatment, it is preferable to use an amount of resin composition that is 80% or less of the volume of the heating container so that the resin composition does not spill.

[0027] In the present invention, a resin extract is obtained by solvent extraction in the second step, and the degree of deterioration of the resin composition is determined by measuring the absorbance at the absorption wavelength of the yellow component in the resin extract in the third step. In order to determine the degree of deterioration of the resin composition, a temperature above the melting point can be used in the step of heat-treating the resin composition at a certain temperature.

[0028] As described above, in the stability evaluation method of the present invention, the first step can be carried out simultaneously on multiple samples in parallel, thereby enabling the long-term stability of a resin composition to be evaluated in a short period of time.

[0029] The second step is a step of extracting the deteriorated resin composition obtained in the first step with a solvent to obtain a resin extract in which the yellow component produced by deterioration is extracted.

[0030] As the solvent extraction method in the second step, Soxhlet extraction, ultrasonic extraction, dissolution-reprecipitation, etc. can be selected. However, when multiple samples are processed simultaneously, such as in lot control, it is preferable to select the dissolution-reprecipitation method, which requires simple extraction equipment.

[0031] When the dissolution-reprecipitation method is used in the second step, any colorless and transparent extraction solvent can be used as long as it can dissolve the resin composition. For example, if the resin composition to be evaluated is a polypropylene resin composition, an extraction solvent that is colorless and transparent and dissolves polypropylene at temperatures of 80°C or higher can be used. Specific examples include benzene, toluene, xylene, decahydronaphthalene (decahydronaphthalene), tetrahydronaphthalene (tetrahydronaphthalene), and chlorobenzene.

[0032] When the dissolution and reprecipitation method is performed on the resin composition in the second step, it is preferable to set the processing amount of the resin composition per 10 mL of extraction solvent to 0.5 g or less to avoid leaving any undissolved resin, and it is more preferable to set the processing amount of the resin composition per 10 mL of extraction solvent to 0.125 g or less, as this is the processing amount that makes it easy to remove the precipitate.

[0033] When the dissolution and reprecipitation method is performed on the resin composition in the second step, it is preferable to reflux the resin composition at the boiling point of the extraction solvent for 20 minutes or more to prevent any undissolved resin composition from remaining. However, if the reflux time is too long, the extracted additives will decompose and turn yellow, so it is preferable to reflux the resin composition for no more than 2 hours.

[0034] It is necessary to remove the precipitated resin from the resin extract obtained using the dissolution-reprecipitation method. From the viewpoint of the solid matter removal rate, it is preferable to remove the precipitated resin composition by filtration using a membrane filter having a pore size of 0.2 μm to 3 μm and made of a material that is not corroded by the extraction solvent, and filtration using a 3 μm membrane filter is more preferable from the viewpoint of filtration speed.

[0035] The filtrate obtained by filtering the resin extract obtained by the dissolution and reprecipitation method through a membrane filter may contain fine precipitates of the resin composition, and the precipitates may be removed using a centrifuge.

[0036] The third step is a step of measuring the absorbance of the resin extract obtained in the second step at the absorption wavelength of the yellow component.

[0037] The absorbance at the absorption wavelength of the yellow component corresponds to the concentration of compounds produced by deterioration in the resin extract, so by measuring this absorbance it is possible to determine the degree of deterioration of the resin composition.

[0038] The absorbance of the yellow component is the value obtained by subtracting the absorbance measured using only the extraction solvent from the absorbance of the extract of the deteriorated resin composition obtained in the second step.

[0039] When measuring the concentration of a yellow component produced by thermal degradation of a resin composition, the wavelength range that can be used as the absorption wavelength of the yellow component is 350 nm to 400 nm, and more preferably 365 nm to 380 nm, which is the complementary color of yellow and in which the amount of change in absorbance is greatest.

[0040] Absorbance can be measured using a general spectrophotometer, and many different types of sample measurement units are available, including a general rectangular cell holder for measuring solution samples, and a microcell holder or microflow cell holder for measuring trace samples.

[0041] The light source of the spectrophotometer is not particularly limited as long as it emits light with a wavelength of 350 nm to 400 nm, and can be appropriately selected from a deuterium discharge tube, a tungsten-halogen lamp, a xenon lamp, a xenon flash lamp, etc.

[0042] The fourth step is a step of evaluating the long-term stability of the resin composition based on the measured absorbance value obtained in the third step.

[0043] The standard for determining discoloration is the absorbance converted to a resin extract with a resin concentration of 12.5 mg / mL. A resin composition that shows an increase of 0.05 or more compared to the absorbance of the yellow component before heating is considered discolored. If the actual resin concentration is not 12.5 mg / mL, the amount of absorbance change that serves as the threshold for discoloration can be calculated using the Beer-Lambert law and the following equation (1). Y = 0.05 × C ÷ 12.5 (1) In formula (1), Y represents the amount of change in absorbance that is the threshold for discoloration, and C represents the resin concentration of the measured solution.

[0044] If the discoloration time is defined as the time it takes for the deteriorated resin composition to first be judged to have discolored, then the antioxidant concentration and the discoloration time show a linear relationship.

[0045] The discoloration time at different temperatures can be calculated by, for example, preparing a plurality of resin compositions with different antioxidant concentrations in advance, and conducting an accelerated deterioration test (accelerated test) for each antioxidant concentration to determine the discoloration time, as in Examples 1 to 4 described below, and then calculating the acceleration factor based on the following formula (2). L=exp(Ea / kT2) / exp(Ea / kT1) ···(2) In formula (2), L is the temperature acceleration coefficient, Ea is the activation energy, k is the Boltzmann coefficient, and T1 and T2 are the heat treatment temperatures.

[0046] In this example, the time until the antioxidant is completely consumed is used as the criterion for judging long-term durability, but the criterion is not limited to the antioxidant concentration, and it is possible to select a necessary index depending on the application of the resin composition.

[0047] For example, at temperatures below the melting point, there is a correlation between the time it takes for physical properties such as flexural strength, tensile strength, and impact strength to suddenly decrease and the time it takes for discoloration to occur, so physical properties can be used as a criterion for long-term stability.

[0048] By using the relationship between these long-term stability criteria and the above-mentioned discoloration time, it is possible to determine, as a stability criterion, the length of time required for a resin composition to discolor at high temperatures in order to ensure the minimum required long-term stability in lot management, etc., and to determine whether the target resin composition complies with the long-term stability criteria.

[0049] The resin composition to be evaluated for stability in the present invention is not particularly limited, but is preferably a polyolefin resin composition. Polyolefin resin compositions are widely used in housings and mechanical parts of durable consumer goods such as home appliances such as air conditioners, televisions, refrigerators, and washing machines, office automation equipment such as copiers, and information devices such as personal computers.

[0050] When the starting material for a resin composition is a used polyolefin resin obtained from at least one product or device selected from the group consisting of home appliances, office automation equipment, information equipment, and communication equipment (when the resin composition is a recycled product), the composition of the starting material varies, resulting in variation in the long-term stability of the resin composition. The stability evaluation method of the present invention is more suitable for such resin compositions because it can evaluate the long-term stability of the resin composition in a short period of time.

[0051] Examples of polyolefin resins include polyethylene, polypropylene, polybutene, propylene-ethylene block copolymers, propylene-ethylene random copolymers, propylene-butene block copolymers, propylene-butene random copolymers, propylene-α-olefin block copolymers, and propylene-α-olefin graft copolymers. Examples of the α-olefins include α-olefins having 3 to 20 carbon atoms, such as propylene, butene, and pentene. The polyolefin resin may also be a mixture of these resins.

[0052] Additives contained in the resin composition to be evaluated for stability in the present invention include antioxidants (phenolic, phosphorus-based, sulfur-based, etc.), flame retardants (bromine-based, phosphorus-based, sulfur-based, inorganic metal-based, etc.), flame retardant aids (antimony oxide, etc.), anti-drip agents (fluorine-based resins, etc.), UV absorbers (benzophenone-based, hindered amine-based, etc.), fillers (glass fiber, mica, calcium carbonate, barium sulfate, etc.), lubricants, plasticizers, stabilizers, release agents, antistatic agents, colorants (pigments, dyes, etc.), metal deactivators, neutralizers, dispersants, etc. In the stability evaluation method of the present invention, long-term stability is evaluated based on the absorbance of the yellow component in the resin extract obtained by solvent extraction of the resin composition as described above, so stability evaluation can be performed without any problems even if the resin composition to be evaluated is colored with a colorant, etc. [Example]

[0053] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0054] First, the polyolefin resin, phenolic antioxidant, phosphorus-based antioxidant, bromine-based flame retardant, and flame retardant aid used as raw materials in the examples will be described.

[0055] <Polyolefin resin> Used polypropylene resin: Crushed polypropylene resin separated and recovered from used home appliances (washing machines, refrigerators, and air conditioners) <Phenol-based antioxidants (primary antioxidants)> Adeka Stab AO-60 (product name, manufactured by ADEKA Corporation) <Phosphorus-based antioxidant (secondary antioxidant)> ADK STAB 2112 (product name, manufactured by ADEKA Corporation) <Brominated flame retardants> Pyroguard SR-720N (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) The main component of Pyroguard SR-720N is TBBA-bis(dibromopropyl ether). <Flame retardant synergist> Hiromaster A390 (product name, manufactured by Suzuhiro Chemical Co., Ltd.) Hiromaster A390 is a masterbatch whose base resin is polypropylene and contains 90% antimony trioxide.

[0056] <Preparation of Resin Composition> Next, the method for producing the resin composition in the examples will be described.

[0057] First, the above components were mixed in the mass ratios shown in Table 1 below as raw materials, and the mixture was obtained by mixing them using a tumbler mixer.

[0058] This mixture was melt-kneaded at a set temperature of 200°C in a twin-screw kneading extruder (KZW27TW-45MG-NH(-500) manufactured by Technovel Co., Ltd.) with a screw diameter of 27 mm and an effective screw length L / D of 45, and formed into a strand shape, which was then cut into pellets using a pelletizer to produce the resin compositions of Examples 1 to 4. The extrusion conditions were such that the screw rotation speed and the feed rate from the hopper were adjusted so that the pellet yield was 12 kg per hour.

[0059] [Table 1]

[0060] <Heat treatment of resin composition> (Examples 1 and 2) The prepared pellet-shaped resin composition was placed on a stainless steel sieve and placed in a thermostatic bath (Yamato Scientific Co., Ltd., constant temperature incubator DKM600) at 140°C for heat treatment.

[0061] (Examples 3 to 4) The resin composition was freeze-pulverized to a fine powder, and 12.50±0.05 mg (n=3) of the resin composition was weighed onto an aluminum pan for TG / DTA (thermogravimetric / differential thermal analyzer). The powder was then placed in a thermostatic chamber at 180°C, a temperature set to accelerate degradation, which is at least 80°C lower than the 5% weight loss temperature of the brominated flame retardant TBBA·bis(dibromopropyl ether), 290°C.

[0062] In this example, due to experimental constraints, a resin composition that has been freeze-pulverized into a fine powder form is used in the heating evaluation at 180°C to reduce the amount of sample, but there is no particular restriction on using a pellet-shaped resin composition in the heating evaluation at 180°C or a fine powder-shaped resin composition in the heating evaluation at 140°C.

[0063] <Solvent extraction> The resin composition for each heat treatment time was dissolved in 6 mL of xylene by refluxing and stirring. The solution was purified by suction filtration using a PTFE membrane filter with a pore size of 3 μm and centrifugal separation to obtain a resin extract.

[0064] <Absorbance measurement> The absorbance of the obtained resin extract was measured using a spectrophotometer ASV11D-H manufactured by AS ONE Corporation.

[0065] <Measurement of antioxidant (AO-60) concentration> Ten microliters of the resulting resin extract (resin concentration 6.25 mg / mL or 12.5 mg / mL) was taken and placed in a pyrolyzer sample cup. The sample was heated for 10 minutes on a hot plate at 75°C under a nitrogen stream to remove the xylene. After the solvent was dried, 5 μL of a 25% methanol solution of tetramethylammonium hydroxide was added to the sample cup and heated in a constant temperature bath at 50°C for 10 minutes. The sample was then measured by pyrolysis gas chromatography / mass spectrometry (pyrolysis gas chromatography / mass spectrometry) under the following conditions, and the AO-60 concentration was determined from the peak at m / z = 291 at a retention time of 8.6 minutes.

[0066] (Measurement conditions) Gas chromatography: Agilent Technologies 7890A Mass spectrometry detector: Agilent Technologies 5975C Pyrolyzer: Frontier Labs PY-2020iD Injection method: Pyrolyzer → GC / MS split injection port (split ratio 30:1) Pyrolyzer temperature: 290℃ Sample volume: 10 μL of extract + 5 μL of 25 wt% tetramethylammonium hydroxide in methanol (TMAH, manufactured by Nacalai Tesque, Inc.) ·GC inlet temperature: 300℃ GC oven temperature rise conditions: 50°C, hold for 1 minute, heat at 20°C / min, then 210°C, then post-run at 350°C for 5 minutes Carrier flow rate: 2mL / min Column: Frontier Labs UA1 (MS / HT) Total length 15 m, inner diameter 0.25 mm, film thickness 0.25 μm MSD transfer line: 320℃ MSD measurement mode: SIM mode (m / z=291,306, dwell time 100,140msec) MS ion source: 230°C ·MS quadrupole: 150℃

[0067] <Stability evaluation> The results of the above measurements on the resin extracts of Examples 1 to 4 are shown in Figures 1 to 4. Figure 1 shows the results for Example 1 (antioxidant concentration 0.05%, heating temperature 140°C), Figure 2 shows the results for Example 3 (antioxidant concentration 0.05%, heating temperature 180°C), Figure 3 shows the results for Example 2 (antioxidant concentration 0.20%, heating temperature 140°C), and Figure 4 shows the results for Example 4 (antioxidant concentration 0.20%, heating temperature 180°C). Based on these results, the relationship between the discoloration time at 140°C and the initial antioxidant concentration, and the relationship between the discoloration time at 180°C and the antioxidant concentration, the discoloration time at 180°C of the sample corresponding to the antioxidant concentration at which discoloration occurred was determined, setting the criterion for long-term stability at 140°C for 1,000 hours. This was used as the stability standard value for lot management, allowing us to determine whether the produced resin composition is able to absorb the variation in heat resistance caused by variations in raw materials, which is a challenge for recycled materials.

[0068] For simplicity, in this test, lot control criteria were determined for two temperature conditions, but it is more preferable to calculate the temperature acceleration coefficient as follows and determine the evaluation time at 180°C, which is equivalent to 1000 hours at 140°C. (1) Change the heating temperature and determine the discoloration time at three or more temperatures, and then calculate the activation energy based on the Arrhenius equation. (2) Using the activation energy thus determined, the temperature acceleration coefficient is determined, which indicates how much faster the oxidation reaction (discoloration of the resin) occurs when heated at 180°C compared to when heated at 140°C. The temperature acceleration coefficient is calculated using the following formula (2) in accordance with the JEITA standard EIAJ ED-4701. L=exp(Ea / kT2) / exp(Ea / kT1) ···(2) In formula (2), L is the temperature acceleration coefficient, Ea is the activation energy, k is the Boltzmann coefficient, and T1 and T2 are the heat treatment temperatures (in this case, T1 is 140° C. and T2 is 180° C.).

[0069] In addition, for a resin extract with a resin concentration of 12.5 mg / mL, the time when the absorbance increased by 0.05 or more compared to before heating was defined as the discoloration time. In the examples, a resin extract with a resin concentration of 6.25 mg / mL was prepared, which is half the resin concentration, and the absorbance was also halved, so the time when the absorbance at 370 nm increased by 0.025 or more was defined as the discoloration time.

[0070] 5 is a graph showing the relationship between the formulation amount of the primary antioxidant in a resin composition and the discoloration time. The stability standard in a 180°C heat treatment test, which corresponds to the long-term stability standard (1000 hours at 140°C) in the lot management described above, can be determined as follows. (1) The time it takes for samples containing different amounts of primary antioxidant to change color when heated at 140°C is determined, and the amount of primary antioxidant required to change color in the reference time (1,000 hours) is estimated (arrow 1 in Figure 5). (2) The discoloration time of samples with different amounts of primary antioxidants when heated at 180°C was determined, and the discoloration time for the amount of primary antioxidants estimated in (1) was estimated and used as the stability standard for the 180°C heat treatment test (arrow 2 in Figure 5).

[0071] Here, in the examples, the stability standard is a discoloration time of 30 hours or more at 180°C. Therefore, a portion is taken as an evaluation sample from a lot of resin composition produced by the same manufacturing method, and if the discoloration time at 180°C is 30 hours or more, the lot of resin composition is deemed to have passed the long-term stability and can be shipped.

[0072] The melting point of the resin composition in this example is 160°C to 170°C, but by setting stability standards for an 180°C heat treatment test, performing an 180°C heat treatment test on an evaluation sample, and examining whether the evaluation sample meets these stability standards using the above-mentioned procedures (steps 2 to 4), the long-term stability of the resin composition can be evaluated even when an accelerated deterioration test is performed at a temperature above the melting point.

[0073] <Other embodiments> It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the claims. The technical scope of the present invention also includes all modifications within the scope and meaning equivalent to the claims.

Claims

1. a first step of accelerating deterioration of a resin composition; A second step of extracting the deteriorated resin composition obtained in the first step with a solvent to obtain a resin extract in which a yellow component produced by deterioration is extracted; a third step of measuring the absorbance of the resin extract obtained in the second step at the absorption wavelength of the yellow component; a fourth step of evaluating the long-term stability of the resin composition based on the absorbance measurement value obtained in the third step; Equipped with the resin composition is a polyolefin resin composition, The extraction solvent used in the second step is a solvent that can dissolve the resin composition and is colorless and transparent, The method for evaluating the stability of a resin composition, characterized in that the wavelength range of absorbance measured in the third step is 350 nm to 400 nm.

2. The method for evaluating the stability of a resin composition according to claim 1, A method for evaluating the stability of a resin composition, characterized in that the starting material of the resin composition is a used polyolefin resin obtained from at least one product or device selected from the group consisting of home appliances, office automation equipment, information equipment, and communication equipment.

3. A method for evaluating the stability of the resin composition according to claim 1 or 2, A method for evaluating the stability of a resin composition, characterized in that in the first step, the resin composition is heat-treated at a constant temperature to accelerate deterioration of the resin composition.

4. A method for evaluating the stability of a resin composition according to any one of claims 1 to 3, A method for evaluating the stability of a resin composition, characterized in that the first step is carried out simultaneously in parallel on a plurality of resin compositions.

5. A portion of the resin composition produced in the same manufacturing process and from the same lot is extracted as an evaluation sample. The extracted evaluation sample is evaluated by the stability evaluation method according to any one of claims 1 to 4, A quality control method for a resin composition, characterized in that if the evaluation sample is an acceptable product, the lot is judged to be eligible for shipment as a product, and if the evaluation sample is an unacceptable product, the lot is judged to be suspended from shipment.

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