Composition and molded article

Abstract

This technology provides a method for achieving a good appearance in molded products. [Solution] A composition comprising ethylene propylene diene rubber (EPDM), a sulfur-containing vulcanizing agent, and a plasticizer, wherein the SP value of the plasticizer is 8.5 or higher.

Description

[Technical Field]

[0001] The present disclosure relates to a composition and a molded article. [Background Art]

[0002] Patent Document 1 discloses a rubber composition containing a rubber component, a plasticizer, and sulfur. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-204504 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] When ethylene propylene diene rubber (EPDM) is used as the rubber component, a whitening phenomenon in which the surface turns white may sometimes be observed when sulfur crosslinking is performed to obtain a molded article. Occurrence of whitening on the surface of the molded article results in poor appearance. Accordingly, there is a need for a technique capable of improving the appearance of a molded article containing ethylene propylene diene rubber (EPDM).

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a technique that can improve the appearance of a molded article. The present disclosure can be implemented in the following modes. [Means for Solving the Problem]

[0006] A composition containing ethylene propylene diene rubber (EPDM), a vulcanizing agent containing sulfur, and a plasticizer, wherein the composition has an SP value of the plasticizer of 8.5 or more. [Effect of the Invention]

[0007] This disclosure provides a technology that can result in a molded article with a good appearance. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows photographs of molded articles after the bloom acceleration test. (A) is a molded article without plasticizers with an SP value of 8.5 or higher. (B) is a molded article containing a plasticizer (ether ester compound). (C) is a molded article containing a plasticizer (di(2-ethylhexyl) adipate (DEHA)). (D) is a molded article containing a plasticizer (di(2-ethylhexyl) phthalate (DEHP)). [Modes for carrying out the invention]

[0009] Herein lies a preferred example of this disclosure. [1] A composition containing ethylene propylene diene rubber (EPDM), a sulfur-containing vulcanizing agent, and a plasticizer, A composition in which the SP value of the plasticizer is 8.5 or higher.

[0010] [2] A molded article obtained by crosslinking the composition described in [1] with sulfur.

[0011] The disclosure is described in detail below. In this specification, when a numerical range is described using "-", it includes both the lower and upper limits unless otherwise specified. For example, the description "10-20" includes both the lower limit "10" and the upper limit "20". In other words, "10-20" has the same meaning as "10 or more and 20 or less". Furthermore, in this specification, the upper and lower limits of each numerical range can be combined in any way.

[0012] 1. Composition The composition disclosed herein contains ethylene propylene diene rubber (EPDM), a sulfur-containing vulcanizing agent, and a plasticizer. The SP value of the plasticizer is 8.5 or higher. A molded article is formed by sulfur crosslinking of the composition.

[0013] 1-1. Ethylene Propylene Diene Rubber (EPDM) Ethylene propylene diene rubber (EPDM) is a rubber obtained by copolymerizing ethylene, propylene, and dienes. EPDM is made possible by introducing unsaturated bonds into the ethylene-propylene copolymer by further copolymerizing dienes, thereby enabling vulcanization with vulcanizing agents.

[0014] The dienes are not particularly limited, but non-conjugated dienes are preferred, for example, 5-ethylidene-2-norbornene, 1,4-hexadiene, dicyclopentadiene, etc. are used. From the viewpoint of obtaining the properties of this disclosure, 5-ethylidene-2-norbornene is preferred as the diene.

[0015] The content of dienes in ethylene propylene diene rubber (EPDM) is not particularly limited. From the viewpoint of sulfur crosslinking reactions and the influence of mechanical properties, the content of dienes is preferably 4% to 17% by mass, and more preferably 7% to 15% by mass.

[0016] The ethylene content in ethylene propylene diene rubber (EPDM) is not particularly limited. From the viewpoint of heat resistance and resistance to permanent deformation, the ethylene content is preferably 40% by mass or more and 80% by mass or less, and more preferably 45% by mass or more and 60% by mass or less.

[0017] The SP value (solubility parameter) of ethylene propylene diene rubber (EPDM) is, for example, around 7.8-8.0. The SP value of ethylene propylene diene rubber (EPDM) can be measured using the Hoy method.

[0018] Ethylene propylene diene rubber (EPDM) may be used alone or in a mixture of two or more types.

[0019] 1-2. Vulcanizing agent The vulcanizing agent contains sulfur. Sulfur is not particularly limited. For example, powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur and the like are suitably used as sulfur.

[0020] The content of the vulcanizing agent is not particularly limited. From the viewpoint of securing physical properties after sulfur crosslinking, when the content of ethylene propylene diene rubber (EPDM) is 100 parts by mass, the content of the vulcanizing agent is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and still more preferably 0.3 parts by mass or more. From the viewpoint of allowing sulfur crosslinking to proceed appropriately and suppressing the occurrence of blooming (a phenomenon in which excess material bleeds to the product surface) after sulfur crosslinking, the content of the vulcanizing agent is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and still more preferably 1.0 part by mass or less. From these viewpoints, the content of the vulcanizing agent is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, more preferably 0.2 parts by mass or more and 3.0 parts by mass or less, and still more preferably 0.3 parts by mass or more and 1.0 part by mass or less.

[0021] 1-3. Plasticizer Examples of the plasticizer (softener) include oil and fatty acid amide.

[0022] Various oils such as synthetic oils can be used as the oil. Examples of synthetic oils include ether ester compounds, adipate ester compounds, phthalate ester compounds, and the like. Examples of the adipate ester compounds include Di(2-ethylhexyl) adipate (DEHA), diisodecyl adipate (DIDA) and the like. Examples of the phthalate ester compounds include Di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) and the like.

[0023] From the viewpoint of making it easier for the oil to seep out as a liquid so as to make the solid precipitated in the molded article less noticeable, the oil content as a plasticizer is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, when the ethylene propylene diene rubber (EPDM) content is 100 parts by mass. From the viewpoint of suppressing variations in physical properties, the oil content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less. From these viewpoints, the oil content is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 7 parts by mass or less, and even more preferably 1 part by mass or more and 4 parts by mass or less.

[0024] The viscosity of the oil used as a plasticizer is preferably 5 mPa·s to 70 mPa·s, more preferably 10 mPa·s to 40 mPa·s, and even more preferably 15 mPa·s to 25 mPa·s. Here, the viscosity of the plasticizer can be measured at 25°C using an E-type viscometer in accordance with JIS K1557-5.

[0025] Examples of fatty acid amides include stearic acid amide, oleic acid amide, erucic acid amide, ethylenebisstearyl amide, ethylenebisoleyl amide, N-stearylstearate amide, and N-stearylerucic acid amide.

[0026] From the viewpoint of making the precipitated solids in the molded article less noticeable, the content of fatty acid amide as a plasticizer is preferably 0.03 parts by mass or more, and more preferably 0.04 parts by mass or more, when the content of ethylene propylene diene rubber (EPDM) is 100 parts by mass. From the viewpoint of suppressing variations in physical properties, the content of fatty acid amide is preferably 2 parts by mass or less, and more preferably 1 part by mass or less. From these viewpoints, the content of fatty acid amide is preferably 0.03 parts by mass or more and 2 parts by mass or less, and more preferably 0.04 parts by mass or more and 1 part by mass or less.

[0027] The SP value (solubility parameter) of the plasticizer is preferably 8.5 or higher, more preferably 8.6 or higher, and more preferably 8.8 or higher, from the viewpoint of facilitating the plasticizer's leaching (bleeding) to the surface of the molded article. From the viewpoint of obtaining desired physical properties in the molded article, the SP value of the plasticizer is preferably 10 or lower, more preferably 9.5 or lower, and even more preferably 9 or lower. From these viewpoints, the SP value of the plasticizer is preferably 8.5 or higher, more preferably 8.5 to 10, more preferably 8.6 to 9.5, and even more preferably 8.8 to 9. Here, the SP value of the plasticizer can be measured by the Hoy method.

[0028] The molecular weight of the plasticizer is preferably 250 to 600, more preferably 300 to 550, and even more preferably 350 to 500.

[0029] 1-4. Sulfurization accelerators (crosslinking accelerators) The composition preferably contains a vulcanization accelerator. Using a vulcanization accelerator can increase the crosslinking rate during the production of the molded article.

[0030] As long as the purpose and effects of this disclosure are not impaired, one or more vulcanization accelerators that can be used in general rubber compositions may be freely selected and used. Examples of vulcanization accelerators include thiazoles (e.g., 2-mercaptobenzothiazole, dibenzothiadyl disulfide, etc.), dithiocarbamates (e.g., zinc dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, etc.), guanidines (e.g., diphenylguanidine, di-o-tolylguanidine, etc.), sulfenamides (e.g., N-cyclohexyl-2-benzothiadylsulfenamide, benzothiadyl-2-diethylsulfenamide, etc.), and thiurams (e.g., tetra Examples of vulcanization accelerators include methyl thiuram disulfide, tetramethyl thiuram monosulfide, tetraethyl thiuram disulfide, N,N'-dipentamethylenethiuram tetrasulfide, etc., xanthogenic acids (e.g., sodium isopropyl xanthogenic acid, zinc isopropyl xanthogenic acid, etc.), aldehyde ammonia (e.g., acetaldehyde ammonia, hexamentylenetetramine, etc.), aldehyde amines (e.g., n-butyraldehyde aniline, butyraldehyde monobutylamine, etc.), thioureas (e.g., diethyl thiourea, trimethyl thiourea, etc.), and dithiophosphide-based vulcanization accelerators. Among these, it is preferable that the vulcanization accelerator includes thiazoles, sulfenamides, and thiurams.

[0031] The content of the vulcanization accelerator is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, more preferably 0.5 parts by mass or more and 3.0 parts by mass or less, and even more preferably 1.0 part by mass or more and 2.0 parts by mass or less, when the content of ethylene propylene diene rubber (EPDM) is 100 parts by mass.

[0032] 1-5. Sulfurization accelerators (crosslinking accelerators) The composition may contain a vulcanization accelerator. By using the vulcanization accelerator in combination with the above-mentioned vulcanization accelerator, improvements in crosslinking efficiency and rubber strength (degree of crosslinking) can be achieved.

[0033] As long as the purpose and effects of this disclosure are not impaired, one or more vulcanization accelerators that can be used in general rubber compositions may be freely selected and used. Examples of vulcanization accelerators include zinc oxide, stearic acid, magnesium oxide, zinc stearate, magnesium stearate, calcium stearate, and the like.

[0034] Zinc oxide is also called zinc oxide. From the viewpoint of increasing the specific surface area, it is preferable that the zinc oxide is one selected from the group consisting of fine particle zinc oxide, composite zinc oxide, and mixtures thereof. Fine particle zinc oxide is zinc oxide particles having a smaller particle size than general zinc oxide.

[0035] Composite zinc oxide is zinc oxide particles in which zinc oxide is laminated on the surface of solid particles. The solid particles include, for example, clay minerals such as clay, talc, sericite, white clay, and mica; natural products such as silica, silica sand, diatomaceous earth, limestone, magnesite, dolomite, shirasu, perlite, gypsum, and fluorite, which are appropriately crushed; or chemically synthesized solid particles used as rubber fillers, such as precipitated calcium carbonate, basic magnesium carbonate, calcium sulfate, precipitated barium sulfate, fine silicic acid, artificial silicates, alumina, and alumina hydrate; or inorganic basic solid particles that promote the vulcanization of rubber, such as calcium hydroxide, magnesium hydroxide, calcium oxide, and magnesium oxide.

[0036] The fine zinc oxide particles and composite zinc oxide may have a rough surface and may have voids inside.

[0037] The content of the vulcanization accelerator is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 0.5 parts by mass or more and 8.0 parts by mass or less, and even more preferably 1.0 part by mass or more and 5.0 parts by mass or less, when the content of ethylene propylene diene rubber (EPDM) is 100 parts by mass.

[0038] 1-6. Antioxidants (anti-aging agents) The composition may contain antioxidants. Using antioxidants (anti-aging agents) can improve the weather resistance of the molded article. Examples of antioxidants include amine compounds, imidazole compounds, monophenol compounds, bisphenol compounds, trisphenol compounds, polyphenol compounds, and waxes. Antioxidants may be used individually or in combination of two or more.

[0039] Examples of amine compounds include amine derivatives such as diphenylamines (4,4'-bis(α,α-dimethylbenzyl)diphenylamine, p-(p-toluenesulfonylamide)-diphenylamine, octylated diphenylamine, etc.) and p-phenylenediamines (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-phenyl-N'-isopropyl-p-phenylenediamine (IPPD), N,N'-di-2-naphthyl-p-phenylenediamine). Among these, 6PPD is preferred.

[0040] Examples of imidazole compounds include 2-mercaptobenzimidazole and its zinc salt.

[0041] Examples of monophenol compounds include 2,6-di-t-butyl-4-methylphenol.

[0042] The wax is not particularly limited and includes petroleum-based waxes such as paraffin wax and microcrystalline wax, natural waxes such as plant-based waxes and animal-based waxes, and synthetic waxes such as polymers of ethylene and propylene.

[0043] The antioxidant content is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, more preferably 0.3 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 1.5 parts by mass or less, based on the ethylene propylene diene rubber (EPDM) content being 100 parts by mass.

[0044] 1-7. Fillers The composition may contain fillers. Examples of fillers include carbon black, aluminum hydroxide powder, aluminum short fibers, and barium titanate powder.

[0045] The filler content is preferably 10 parts by mass or more and 100 parts by mass or less, more preferably 30 parts by mass or more and 90 parts by mass or less, and even more preferably 50 parts by mass or more and 80 parts by mass or less, when the ethylene propylene diene rubber (EPDM) content is 100 parts by mass.

[0046] 1-8. Other ingredients The composition may also contain other components such as paraffinic oils, fillers, flame retardants, fibers, wood flour, pigments, colorants, and fungicides.

[0047] 2. Molded body The molded articles of this disclosure are formed by sulfur crosslinking the above composition (ethylene propylene diene rubber (EPDM), vulcanizing agent, plasticizer, vulcanization accelerator, and other components). For example, the above composition can be molded into a desired shape by extrusion using an extruder or the like in an uncrosslinked state, and the molded articles can be manufactured by heating them in a vulcanizer.

[0048] 3. Physical properties of the molded product The hardness of the molded article (Type A durometer hardness) is preferably 75 or less, more preferably 70 or less, and even more preferably 65 or less. The hardness of the molded article (Type A durometer hardness) can be measured according to JIS K 6253-3:2023 "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness".

[0049] 4. Applications of molded products The molded articles of this disclosure are useful for a variety of applications. For example, the molded articles can be used in vehicle interior parts (grommets for column hole covers, rubber waterproof covers for steering shafts, grommets for wire harnesses, etc.).

[0050] 5. Effects of this Disclosure According to this disclosure, the appearance of the molded article can be improved. When ethylene propylene diene rubber (EPDM) is used as the rubber component, a whitening phenomenon may occur when the molded article is formed by sulfur crosslinking. This is thought to be due to the precipitation of components contained in the composition onto the surface of the molded article. Therefore, in this disclosure, a plasticizer with an SP value of 8.5 or higher is included in the composition. Because there is a discrepancy between the SP value of the plasticizer and the SP value of ethylene propylene diene rubber (EPDM) (for example, around 7.8-8.0), it is thought that the plasticizer may seep out from the molded article. As a result, it is thought that the presence of the plasticizer makes the solid precipitates on the surface of the molded article less noticeable, as they are less likely to crystallize by dissolving in the plasticizer.

[0051] It is known that when a composition contains vulcanization accelerators (thiazoles, thirams, etc.), these accelerators can be detected on the surface of the molded body by measuring the absorption spectrum with a Fourier transform infrared spectrometer (FT-IR). Therefore, it is assumed that the surface of the molded body may whiten due to the vulcanization accelerators (thiazoles, thirams, etc.) in the composition, and it is thought that including a plasticizer in the composition will make the vulcanization accelerators (thiazoles, thirams, etc.) on the surface less noticeable due to the presence of the plasticizer. [Examples]

[0052] 1. Fabrication of molded body For the examples and comparative examples, molded articles were prepared by crosslinking compositions prepared in the proportions shown in Table 1 with sulfur. Specifically, the compositions were kneaded, formed into sheets by extrusion, and heated in a vulcanizer at 160°C for 10 minutes to produce the molded articles.

[0053] [Table 1]

[0054] Details of each ingredient are as follows: • EPDM: Ethylene propylene diene rubber, SP value: 7.9 (Product name: EPT3092M, manufactured by Mitsui Chemicals, Inc.) • Sulfurizing agent: Sulfur (Product name: Renogran S-80, manufactured by Rhein Chemie) • Vulcanization accelerator 1: Zinc dibutyldithiocarbamate (Product name: Renogran ZDBC-80, manufactured by Rhein Chemie) • Vulcanization accelerator 2: N-cyclohexyl-2-benzothiadylsulfenamide (product name: Noxellar CZ-Z, manufactured by Ouchi Shinko Chemical Co., Ltd.) • Vulcanization accelerator 3: Tetramethylthiuram disulfide (Product name: Sunmix TT-75, manufactured by Sanshin Chemical Co., Ltd.) • Sulfurization accelerator 4: Dithiocarbamate type (Product name: Renogran TETD, manufactured by Rhein Chemie) • Vulcanization accelerator 5: Thiuram-based vulcanization accelerator (Product name: Sunmix TRA-70, manufactured by Sanshin Chemical Co., Ltd.) • Vulcanization accelerator 1: Zinc oxide (Product name: Meta Z L-40, manufactured by Inoue Lime Industry Co., Ltd.) • Vulcanization accelerator 2: Stearic acid (manufactured by NOF Corporation) • Antioxidant 1: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (product name: Nowguard 445, manufactured by Si Group) • Antioxidant 2: Benzimidazole-based antioxidant (Product name: Renogran MBI-80, manufactured by Rhein Chemie) • Filler 1: Carbon Black (Product Name: HS45, manufactured by Orion Co., Ltd.) • Filler 2: Aluminum hydroxide (Product name: C301N, manufactured by Sumika Alchem ​​Co., Ltd.) • Oil: Paraffin-based oil, SP value: 7.9 (Product name: PS-430, manufactured by Idemitsu Kosan Co., Ltd.) • Plasticizer 1: Ether ester compound, molecular weight: 434, SP value: 8.8 (Product name: W-260, manufactured by DIC Corporation) • Plasticizer 2: Di(2-ethylhexyl) phthalate (DEHP), molecular weight: 390, SP value: 8.9 (Product name: Sanso-sizer DOP, manufactured by Shin-Nippon Rika Co., Ltd.) • Plasticizer 3: Di(2-ethylhexyl) adipate (DEHA), molecular weight: 371, SP value: 8.5 (product name: DOA, manufactured by Daihachi Chemical Industry Co., Ltd.)

[0055] 2. Physical property evaluation (1) Evaluation of the whitening phenomenon after the bloom acceleration test Bloom acceleration tests were conducted on the molded articles of the examples and comparative examples. One cycle consisted of leaving the articles at 70°C and 95% relative humidity for 4 hours, then cooling them to 0°C over 1.5 hours, leaving them at 0°C for 1.5 hours, and finally heating them to 70°C over 1 hour. This cycle was repeated 20 times. Afterward, the presence or absence of whitening on the surface of the molded articles was visually inspected and evaluated according to the following criteria. The results are shown in Table 1. "A": Almost no bleaching phenomenon was observed. "B": Whitening was observed.

[0056] (2)Hardness The hardness (Type A durometer hardness) of the molded articles of the examples and comparative examples was measured according to JIS K 6253-3:2023, "Vulcanized rubber and thermoplastic rubber - Method for determining hardness - Part 3: Durometer hardness". The measured hardness was used as an indicator of the degree of crosslinking.

[0057] (3) Detection of surface components of the molded body Absorption spectra were measured for the molded articles of the examples and comparative examples using a Fourier transform infrared spectrometer (FT-IR). Measurement of the absorption spectra of the surface of the molded articles revealed the presence of thiazoles and thiram-derived components from vulcanization accelerators as components of the surface.

[0058] 3. Evaluation Results Examples 1-5 satisfy requirement (A) below. Comparative Example 1 does not satisfy requirement (A) below. (A) A composition containing a plasticizer with an SP value of 8.5 or higher is used. As shown in Figure 1(A), Comparative Example 1 received a "B" rating for the whitening phenomenon after the bloom acceleration test, indicating that whitening was observed. As shown in Figures 1(B)-(D), Examples 1-5 all received an "A" rating for the whitening phenomenon after the bloom acceleration test, indicating that almost no whitening was observed.

[0059] The whitening phenomenon is thought to be caused by the precipitation of components contained in the composition onto the surface of the molded body. Specifically, since components derived from thiazoles and thiram-based vulcanization accelerators have been detected as components on the surface of the molded body, it is assumed that the precipitation of at least thiazoles and thiram-based vulcanization accelerators is causing the whitening phenomenon.

[0060] In Examples 1-5, by including a plasticizer with an SP value of 8.5 or higher in the composition, the SP value of the plasticizer differs from that of ethylene propylene diene rubber (EPDM) (7.9), which may cause the plasticizer to seep out of the molded article. As a result, solid precipitates (components derived from vulcanization accelerators, etc.) on the surface of the molded article are less likely to dissolve in the plasticizer and crystallize, making the solid precipitates less noticeable.

[0061] In Examples 1-5, one of the following was used as a plasticizer: an ether ester compound, di(2-ethylhexyl) phthalate (DEHP), or di(2-ethylhexyl) adipate (DEHA). Therefore, it was found that the occurrence of whitening on the surface of the molded article could be suppressed regardless of whether an ether ester compound, di(2-ethylhexyl) phthalate (DEHP), or di(2-ethylhexyl) adipate (DEHA) was used as the plasticizer.

[0062] In Examples 1-3, the ether ester compound plasticizer was contained in 1 part by mass, 2 parts by mass, and 4 parts by mass, respectively. Therefore, it was found that the whitening phenomenon on the surface of the molded article could be suppressed when the content of the ether ester compound plasticizer was at least 1-4 parts by mass.

[0063] The hardness (Type A durometer hardness) of the molded articles in Examples 1-5 was 61-63. The hardness (Type A durometer hardness) of the molded article in Comparative Example 1 was 63. The hardness (Type A durometer hardness) values ​​are similar for the molded articles in Examples 1-5 and Comparative Example 1, suggesting that there is no significant difference in the degree of crosslinking.

[0064] 4. Effects of the Examples According to this embodiment, in a molded article using ethylene propylene diene rubber (EPDM), a good appearance was achieved by using a plasticizer with an SP value of 8.5 or higher.

[0065] This disclosure is not limited to the embodiments detailed above, and various modifications or changes are possible within the scope of this disclosure.

Claims

1. A composition containing ethylene propylene diene rubber (EPDM), a sulfur-containing vulcanizing agent, and a plasticizer, A composition in which the SP value of the plasticizer is 8.5 or higher.

2. A molded article obtained by crosslinking the composition described in claim 1 with sulfur.

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