Rubber compositions and weatherstrips

Abstract

To achieve a rubber composition with good vulcanization efficiency. [Solution] A rubber composition comprising a non-diene rubber and a boron-based surfactant, wherein the content of the boron-based surfactant per 100 parts by weight of the non-diene rubber is greater than 0.2 parts by weight and less than or equal to 1.5 parts by weight.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a weatherstrip.

Background Art

[0002] A rubber composition obtains elasticity by vulcanization and enables the molding of various rubber products. Since the vulcanization of rubber involves heating, there is a demand for a method to improve the efficiency of the vulcanization process and save the energy required for heating.

[0003] For example, Patent Document 1 describes that by containing polyethylene glycol with a high dielectric constant, the UHF (Ultra High Frequency) heating efficiency can be improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the inventors of the present invention have found that the effect of improving the UHF heating efficiency by polyethylene glycol is limited.

[0006] One aspect of the present invention aims to realize a rubber composition or the like that can carry out the vulcanization process more efficiently than before.

Means for Solving the Problems

[0007] In order to solve the above problems, a rubber composition according to one aspect of the present invention includes a non-diene rubber and a boron-based surfactant, and when the content of the non-diene rubber is 100 parts by weight, the content of the boron-based surfactant is more than 0.2 parts by weight and 1.5 parts by weight or less. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to realize a rubber composition and the like that can be vulcanized more efficiently than in the conventional method. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of an automobile fitted with a weatherstrip according to one embodiment. [Figure 2] This is a schematic diagram showing the heating position in the evaluation of UHF heat generation in the example. [Figure 3] This figure shows the evaluation results of the UHF heat generation amount obtained by heating at a set temperature of 30°C and 1kW in the example. [Figure 4] This figure shows the evaluation results of the UHF heat generation amount obtained by heating at a set temperature of 30°C and 2kW in the example. [Figure 5] This figure shows the evaluation results of the UHF heat generation amount obtained by heating at a set temperature of 100°C and 2kW in the example. [Figure 6] This figure shows the evaluation results of the UHF heat generation amount obtained by heating at a set temperature of 100°C and 3kW in the example. [Figure 7] This figure shows the evaluation results of the UHF heat generation amount obtained by heating at a set temperature of 100°C and 4kW in the example. [Figure 8] This figure shows the evaluation results of the volume resistance in the example. [Modes for carrying out the invention]

[0010] [Rubber composition] A rubber composition according to one embodiment of the present invention comprises a non-diene rubber and a boron-based surfactant, wherein the content of the boron-based surfactant is greater than 0.2 parts by weight and 1.5 parts by weight or less when the content of the non-diene rubber is 100 parts by weight. In this specification, the rubber composition according to one embodiment of the present invention may be referred to as "this rubber composition".

[0011] (Non-diene rubber) Non-diene rubber is a synthetic rubber having a polymer structure, in which the main chain of the polymer does not have double bonds, or the number of double bonds in the main chain is small. "A small number of double bonds" means, for example, that some of the monomers constituting the polymer include monomers that introduce a diene structure into the main chain, but the proportion of monomers that introduce a diene structure into the main chain is less than a predetermined proportion. In this case, the "predetermined proportion" may be, for example, 5 mol% or less, 3 mol% or less, 2 mol% or less, or 1 mol% or less of the monomers that introduce a diene structure into the main chain in the entire polymer.

[0012] One example of this is butyl rubber. Butyl rubber is obtained by copolymerizing isobutylene with isoprene, usually in an amount of 0.6 mol% to 3 mol%. Butyl rubber contains double bonds in its main chain, but because of the small number of double bonds, it has the properties of a non-diene rubber.

[0013] Furthermore, the example of "having a small number of double bonds" includes cases where, in principle, the main chain does not contain double bonds, but double bonds are introduced into the main chain due to unintended chemical reactions such as polymerization or aging.

[0014] Examples of non-diene rubbers include ethylene-α-olefin-non-conjugated diene copolymer rubber (EPDM), butyl rubber, urethane rubber, silicone rubber, acrylic rubber, and fluororubber. Among these, EPDM is preferred as the non-diene rubber because it is easier to obtain desirable physical properties when this rubber composition is used in automotive parts such as weatherstrips.

[0015] Examples of α-olefins in EPDM include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene. Examples of non-conjugated dienes include 1,4-hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene.

[0016] When the total amount of this rubber composition is 100 parts by weight, the content of the non-diene rubber may be 30 parts by weight or more, may be 40 parts by weight or more, may be 50 parts by weight or more, may be 60 parts by weight or more, or may be 70 parts by weight or more.

[0017] Since the non-diene rubber does not have a double bond in the main chain as compared with the diene rubber, it has excellent weather resistance. Further, if the non-diene rubber is a rubber having a double bond in a side chain such as EPDM, the vulcanization reaction can be carried out with sulfur, but the vulcanization reaction rate with sulfur tends to be longer than that of the diene rubber. By including a boron-based surfactant in this rubber composition, the vulcanization reaction rate of the non-diene rubber can be improved.

[0018] In the present specification, "vulcanization" is intended to mean crosslinking in general of non-diene rubber and is not limited to the reaction when sulfur is used. Crosslinking of non-diene rubber using a crosslinking agent (vulcanizing agent) other than sulfur is also included in one aspect of vulcanization.

[0019] (Boron-based surfactant) The boron-based surfactant is a surfactant containing boron. Examples of the boron-based surfactant include glycerol borate fatty acid ester. Glycerol borate may be a mode in which two glycerols or their fatty acid esters are bonded to boron. Glycerol borate only needs to have at least one glycerol having a fatty acid ester structure, and two glycerols may have a fatty acid ester structure.

[0020] The fatty acid may be a saturated fatty acid or an unsaturated fatty acid. The number of carbon atoms of the fatty acid is not particularly limited, and for example, it may be 4 or more, may be 5 or more, may be 6 or more, may be 7 or more, may be 8 or more, or may be 9 or more. When the fatty acid is an unsaturated fatty acid, it may be a monounsaturated fatty acid or a polyunsaturated fatty acid.

[0021] Examples of boron-based surfactants include glycerol borate-oleate, glycerol borate-laurate, glycerol borate-palmitate, glycerol borate-stearate, glycerol borate-isostearate, and glycerol borate-hydroxystearate. Among these, glycerol borate-oleate is preferred from the viewpoint of availability. Examples of commercially available glycerol borate-oleate include Emulbon® S-80 and Emulbon T-80 from Toho Chemical Co., Ltd.

[0022] Furthermore, examples of boron-based surfactants include various glycerol borate fatty acid esters, which are disclosed as organoboron compounds in Japanese Patent Publication No. 49-011311.

[0023] Furthermore, the boron-based surfactant may be glycerol borate-polyoxyethylene ether, or glycerol borate-polyoxyethylene ether fatty acid ester. Glycerol borate-polyoxyethylene ether fatty acid ester is an example of a glycerol borate fatty acid ester. When the boron-based surfactant is such a high-molecular-weight compound, the molecular weight of the boron-based surfactant may be between 500 and 10,000.

[0024] In this rubber composition, when the non-diene rubber content is 100 parts by weight, the content of the boron-based surfactant may be greater than 0.2 parts by weight and 1.5 parts by weight or less. Furthermore, the lower limit of the content of the boron-based surfactant may be 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, or 0.5 parts by weight or more. If the content of the boron-based surfactant relative to the non-diene rubber is greater than 0.2 parts by weight, a sufficient effect of improving the vulcanization rate of the rubber composition can be obtained. Furthermore, if the content of the boron-based surfactant relative to the non-diene rubber is 1.5 parts by weight or less, advantageous effects of the boron-based surfactant can be obtained within a range where the raw material cost of the boron-based surfactant does not become excessive.

[0025] The inventors have found that the inclusion of a boron-based surfactant in this rubber composition shortens the vulcanization rate and improves heating efficiency during vulcanization. Specifically, the boron-based surfactant shortens T90, which indicates the time required for vulcanization, as measured by a curameter according to the method compliant with JIS K6300-2:2001. Furthermore, since the boron-based surfactant also improves the UHF exothermic properties of the rubber composition, the heating time of the rubber composition can also be shortened.

[0026] Furthermore, the inclusion of boron-based surfactants does not reduce the scorch time (t5) in Mooney viscosity evaluation, which is measured according to the method compliant with JIS K6300-1:2013. Scorch time is an indicator of the time until rubber burning (scorching) occurs, and a longer scorch time is preferable. While boron-based surfactants can increase the vulcanization rate indicated by T90, they do not adversely affect the scorch time.

[0027] Furthermore, the inventors have found that the inclusion of a boron-based surfactant in this rubber composition improves the mechanical properties of the molded article after vulcanization. Specifically, the boron-based surfactant can improve Tb (tensile strength at break) and Eb (elongation at break), as measured by the method compliant with JIS K6251:2017. In addition, the value of the compression set, as measured by the method compliant with JIS K6262:2013, can also be reduced, thereby improving the restorative force (elasticity) of the rubber.

[0028] Thus, the fact that boron-based surfactants can simultaneously improve the vulcanization characteristics of rubber compositions and the mechanical properties of molded articles is a novel finding by the inventors. Specifically, boron-based surfactants can shorten the heating time in the vulcanization of rubber compositions. Shortening the heating time shortens the manufacturing time of rubber compositions, improving manufacturing efficiency, and also reduces the energy required for heating, thereby lowering manufacturing costs. Furthermore, molded articles of rubber compositions manufactured in this way have excellent mechanical properties, so a longer lifespan than conventional products can be expected.

[0029] These effects contribute, for example, to achieving United Nations Sustainable Development Goals (SDGs) Goal 7, "Improve energy efficiency," and Goal 12, "Ensure sustainable consumption and production patterns."

[0030] (Other ingredients) This rubber composition may further contain other components besides non-diene rubber and boron-based surfactants. These other components are not particularly limited, but include, for example, surfactants other than boron-based surfactants, vulcanizing agents, vulcanization accelerators, processing aids, process oils, fillers, colorants, and dehydrating agents.

[0031] Examples of vulcanizing agents include sulfur, peroxides, resins, amines, and polyols. Among these, sulfur is preferred as the crosslinking agent when using non-diene rubber having double bonds in its side chains, etc.

[0032] The vulcanization accelerator can be appropriately selected depending on the type of vulcanizing agent. When the vulcanizing agent is sulfur, examples of vulcanization accelerators include thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and guanidine-based vulcanization accelerators. This rubber composition may contain only one type of vulcanization accelerator, or it may contain two or more types.

[0033] (Method for producing this rubber composition) The method for producing this rubber composition is not particularly limited, but may include, for example, a step of mixing a non-diene rubber, a boron-based surfactant, and other components as needed. This mixing may be carried out using a kneader such as a Banbury mixer, internal mixer, kneader, or open roll.

[0034] (Uses of this rubber composition) According to this rubber composition, a molded article of this rubber composition can be obtained by vulcanization and molding. In other words, a molded article according to one embodiment of the present invention is obtained by performing the steps of vulcanizing and molding the rubber composition. In this specification, a molded article according to one embodiment of the present invention may be referred to as "this molded article".

[0035] The vulcanization reaction of this rubber composition can be carried out by adding a vulcanizing agent and, if necessary, additives such as a vulcanization accelerator, and then heating the mixture. It is preferable to carry out the heating for vulcanization and the molding process in parallel.

[0036] The molding method for this molded product is not particularly limited, but may be, for example, an extrusion molding method or a die molding method. Since the UHF heat generation properties of the rubber composition are also improved, this rubber composition can be suitably used for vulcanization molding using a vulcanization apparatus equipped with a UHF oscillator. For example, this rubber composition is suitable for extrusion molding using a vulcanization furnace.

[0037] The molded product is not particularly limited, but examples include rubber parts for automobiles. Weatherstrips are a suitable example of rubber parts for automobiles. It can also be applied to gaskets for residential use.

[0038] [Weatherstrip] Figure 1 is a schematic side view of an automobile 100 to which the molded body, the weatherstrip 102, is attached. As shown in Figure 1, the molded body may be a weatherstrip 102 attached to the door 101 of the automobile 100. In other words, the rubber composition can be suitably used for a weatherstrip 102 attached to the door 101 of the automobile 100.

[0039] The weatherstrip 102 is attached to the periphery of the door 101 and is a component that seals the space between the door 101 and the opening of the automobile 100. The door 101 is, but is not limited to, the passenger compartment door of the automobile 100. The door of the automobile 100 to which the weatherstrip 102 is attached may be, for example, a cargo compartment door, an engine compartment door (also called an engine hood or bonnet), or any other type of door.

[0040] The weatherstrip 102 may be obtained by extruding the rubber composition. The weatherstrip 102 may comprise an extruded portion and a die-molded portion. In this case, the rubber composition may be used in at least a portion of either the extruded portion or the die-molded portion, or it may be used in both. In other words, the weatherstrip 102 according to one embodiment of the present invention may have a portion made of the rubber composition.

[0041] 〔summary〕 The rubber composition according to embodiment 1 of the present invention comprises a non-diene rubber and a boron-based surfactant, wherein the content of the boron-based surfactant is 0.5 parts by weight or more and 1.5 parts by weight or less when the content of the non-diene rubber is 100 parts by weight.

[0042] In the rubber composition according to embodiment 2 of the present invention, the non-diene rubber may be an ethylene-α-olefin-non-conjugated diene copolymer rubber in embodiment 1.

[0043] In the rubber composition according to embodiment 3 of the present invention, in embodiment 1 or 2, the boron-based surfactant may be a glycerol borate fatty acid ester.

[0044] The rubber composition according to embodiment 4 of the present invention may be used in vulcanization molding using a vulcanization apparatus equipped with a UHF oscillator in any of embodiments 1 to 3.

[0045] The rubber composition according to embodiment 5 of the present invention may be used for weatherstrips attached to automobile doors in any of embodiments 1 to 4.

[0046] A weatherstrip according to embodiment 6 of the present invention is a weatherstrip that is attached to the door of an automobile, having a portion made of the rubber composition of embodiment 5.

[0047] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0048] One embodiment of the present invention is described below.

[0049] [Composition] Rubber compositions according to the examples and comparative examples were prepared. Each rubber composition was obtained by mixing the components shown in Tables 1 and 2 below using a Banbury mixer. The content of each component is listed as parts by weight, with the content of EPDM polymer, a non-diene rubber, being 100 parts by weight. PEG4000 is polyethylene glycol manufactured by NOF Corporation. Various additives include carbon black, process oil, fillers, sulfur, zinc oxide, vulcanization accelerators, processing aids, and dehydrating agents. Multiple types of vulcanization accelerators, including thiuram-based and thiazole-based ones, were added. Note that the formulations in Table 1 differ only in the presence or absence and amount of PEG4000 and Emulbon T-80 added; all other materials are the same in type, brand, and quantity. Similarly, in the formulations in Table 2, all materials except PEG4000 and Emulbon S-80 are the same in type, brand, and quantity.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Evaluation Method] The rubber compositions for each example and comparative example were evaluated as follows.

[0053] (Vulcanization properties) The vulcanization characteristics, such as the vulcanization rate, of the rubber composition were evaluated using Mooney viscosity (125°C, 10 min) according to the method conforming to JIS K6300-1:2013. Additionally, evaluation using a Curlastometer (180°C, 10 min) was performed according to the method conforming to JIS K6300-2:2001. For Mooney viscosity evaluation, Vm, t5 (min), and t35 (min) were assessed. For evaluation using the Curlastometer, ML (kgf·cm), MH (kgf·cm), T10 (min), and T90 (min) were assessed. The results are shown in Tables 1 and 2.

[0054] (pyrmogenic) The heat generation properties of rubber compositions using UHF (Ultra High Frequency) were evaluated. Specifically, test specimens (30 mm wide, 100 mm deep, 2 mm thick) were cut from molded bodies of vulcanized rubber compositions. These test specimens were placed in the position shown in Figure 2 in a batch heating chamber equipped with a UHF oscillator, and UHF was oscillated from a waveguide under the following UHF oscillation conditions to generate heat. The relationship between oscillation time and heat generation temperature was then evaluated.

[0055] The UHF oscillation conditions were set to a temperature of 30°C or 100°C, an output of 1-4kW, and oscillation times of 20, 40, and 60 seconds. The temperature was measured at the center of the depth / width of the test specimen. After the oscillation time had elapsed, the heating chamber door was opened and the temperature measurement was completed within 10 seconds. The average value for n=2 was calculated for each case. The results are shown in Figures 3 to 7.

[0056] (mechanical properties) The hardness of the molded rubber composition after vulcanization was measured according to the method in accordance with JIS K6253-3:2012. In addition, Tb (tensile strength at break, MPa) and Eb (elongation at break, %) were measured according to the method in accordance with JIS K6251:2017. Furthermore, the tear strength (N / cm) was measured according to the method in accordance with JIS K6252-1:2015. Tear strength was measured by cutting the molded rubber composition after vulcanization into an angle-shaped test piece (without cuts). Finally, the compression set was measured according to the method in accordance with JIS K6262:2013. Compression set was measured at a test temperature of 70°C with a holding time of 22 or 72 hours. The results are shown in Table 1.

[0057] (conductive) The volume resistivity of molded articles of the vulcanized rubber composition was measured according to the method compliant with JIS K6271-1:2015. The average value for n=2 was calculated for each measurement. The results are shown in Figure 8.

[0058] 〔result〕 (Regarding manufacturability) As shown in Table 1, no significant change in the t5 value was observed between Examples 1-3 and Comparative Example 1 in the Mooney viscosity evaluation. t5 is also called the scorch time, and a larger value is preferable as it indicates less scorching. It was shown that boron-based surfactants do not affect the scorch time of the rubber composition after vulcanization.

[0059] On the other hand, evaluation using a curameter showed that T90 was shortened in all three Examples 1-3 compared to Comparative Example 1, and this effect was particularly pronounced in Examples 1 and 2. T90 indicates the vulcanization rate, and a smaller value indicates a faster vulcanization rate, which is preferable. Boron-based surfactants were shown to have the effect of improving the vulcanization rate of the rubber composition through heating by thermal conduction.

[0060] Furthermore, as shown in Table 2, T90 was shortened in Examples 4 and 5 compared to Comparative Examples 2 and 3. Since Comparative Example 4 had a T90 equivalent to that of Comparative Examples 2 and 3, it was shown that the effect of boron-based surfactants on improving the vulcanization rate of rubber compositions is obtained when the amount is greater than 0.2 parts by weight per 100 parts by weight of non-diene rubber. Since Example 6 had a T90 equivalent to that of Comparative Examples 2 and 3, it was confirmed that the vulcanization rate is not adversely affected as long as the content of boron-based surfactant is at least 1.5 parts by weight or less.

[0061] Furthermore, as shown in Figures 3 to 7, in the UHF heat generation evaluation, under all UHF oscillation conditions, the heat generation temperature at the same oscillation time improved with increasing content of boron-based surfactant. In other words, it was shown that the addition of boron-based surfactant allows for heat generation at a shorter oscillation time, improving the UHF heat generation properties of the rubber composition.

[0062] Furthermore, Patent Document 1 describes that the dielectric constant increases when PEG4000 is added to a rubber compound. However, as far as can be seen by comparing Comparative Example 2 and Comparative Example 3, it was shown that the increase in dielectric constant due to PEG4000 does not substantially affect the UHF exothermic properties. This embodiment demonstrates that boron-based surfactants can provide an advantageous effect from a manufacturability standpoint, namely, improved UHF exothermic properties, which could not be obtained with conventional surfactants such as PEG.

[0063] As described above, this rubber composition containing a boron-based surfactant in an amount of more than 0.2 parts by weight and no more than 1.5 parts by weight per 100 parts by weight of non-diene rubber showed improvement in at least one of the vulcanization rate and UHF exothermic properties. A faster vulcanization rate allows for a shorter heating time during vulcanization. Furthermore, higher UHF exothermic properties allow for a more rapid increase in the temperature of the rubber composition. Since both of these effects reduce the time required for the vulcanization process of the rubber composition and improve heating energy efficiency, it is suggested that boron-based surfactants improve the vulcanization characteristics of rubber compositions, thereby enhancing manufacturability and contributing to a reduction in manufacturing costs.

[0064] (mechanical properties) As shown in Table 1, in Examples 1 to 3, the Tb and Eb values ​​were improved compared to Comparative Example 1, indicating good tensile properties as rubber. Furthermore, in Examples 1 to 3, the compression set values ​​were also smaller compared to Comparative Example 1, demonstrating good restorative force (elasticity) as rubber. Thus, it was shown that boron-based surfactants not only improve the vulcanization properties of rubber compositions and enhance manufacturability, but also improve the mechanical properties of molded articles of the vulcanized rubber compositions.

[0065] (conductive) The preferred conductivity of a rubber composition varies depending on its application. For example, when used in automotive parts such as weatherstrips, excessively high conductivity can cause problems such as door corrosion. Therefore, the effect of boron-based surfactants on the conductivity of rubber compositions was evaluated using volume resistivity.

[0066] As shown in Figure 8, the change in volume resistivity in Examples 4 and 6 was less than an order of magnitude (less than 1 / 10) compared to Comparative Examples 2 and 3, indicating no significant change. In other words, boron-based surfactants had almost no effect on the conductivity of the rubber composition and can be included without problems in both conductive and non-conductive rubbers. [Explanation of symbols]

[0067] 100 automobiles 101 Door 102 Weatherstrip

Claims

1. It contains a non-diene rubber and a boron-based surfactant. A rubber composition in which, when the content of non-diene rubber is 100 parts by weight, the content of the boron-based surfactant is greater than 0.2 parts by weight and 1.5 parts by weight or less.

2. The rubber composition according to claim 1, wherein the non-diene rubber is an ethylene-α-olefin-non-conjugated diene copolymer rubber.

3. The rubber composition according to claim 1, wherein the boron-based surfactant is a glycerol borate fatty acid ester.

4. The rubber composition according to claim 1, used for vulcanization molding using a vulcanization apparatus equipped with a UHF oscillator.

5. A rubber composition according to any one of claims 1 to 4, for use as a weatherstrip attached to the door of an automobile.

6. A weatherstrip for attaching to an automobile door, having a portion made of the rubber composition described in claim 5.

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