Rubber composition and weather strip

Abstract

A rubber composition with good vulcanization efficiency is realized. [Solution] The rubber composition includes a non-diene rubber and a boron-based surfactant, and the content of the boron-based surfactant per 100 parts by weight of the non-diene rubber is more than 0.2 parts by weight and not more than 1.5 parts by weight.

Description

[Technical field]

[0001] The present invention relates to a rubber composition and a weather strip. [Background technology]

[0002] Rubber compositions acquire elasticity through vulcanization, enabling the molding of a variety of rubber products. Because the vulcanization of rubber involves heating, there is a demand for a method for improving the efficiency of the vulcanization process and reducing the energy required for heating.

[0003] For example, Patent Document 1 describes that the inclusion of polyethylene glycol, which has a high dielectric constant, improves the efficiency of UHF (Ultra High Frequency) heat generation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-306222 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the present inventors found that the effect of polyethylene glycol in improving UHF heat generation efficiency is limited.

[0006] An object of one aspect of the present invention is to provide a rubber composition or the like that allows a vulcanization step to be carried out more efficiently than before. [Means for solving the problem]

[0007] In order to solve the above problems, a rubber composition according to one embodiment of the present invention includes a non-diene rubber and a boron-based surfactant, and the content of the boron-based surfactant is more than 0.2 parts by weight and not more than 1.5 parts by weight when the content of the non-diene rubber is 100 parts by weight. Effect of the Invention

[0008] According to one aspect of the present invention, it is possible to realize a rubber composition or the like that allows a vulcanization step to be carried out more efficiently than before. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an automobile equipped with a weather strip according to an embodiment; [Diagram 2] FIG. 2 is a schematic diagram showing the heating position in the evaluation of UHF calorific value in the examples. [Diagram 3] FIG. 2 is a diagram showing the evaluation results of UHF calorific value when heated at a set temperature of 30° C. and 1 kW in an example. [Figure 4] FIG. 2 is a diagram showing the evaluation results of UHF calorific value when heated at a set temperature of 30° C. and 2 kW in an embodiment. [Diagram 5] FIG. 1 is a diagram showing the evaluation results of UHF calorific value when heated at a set temperature of 100° C. and 2 kW in an embodiment. [Figure 6] FIG. 1 is a diagram showing the evaluation results of UHF calorific value when heated at a set temperature of 100° C. and 3 kW in an embodiment. [Figure 7] FIG. 1 is a diagram showing the evaluation results of UHF calorific value when heated at a set temperature of 100° C. and 4 kW in an embodiment. [Figure 8] FIG. 4 is a diagram showing the evaluation results of volume resistivity in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Rubber composition] The rubber composition according to one embodiment of the present invention contains a non-diene rubber and a boron-based surfactant, and the content of the boron-based surfactant is more than 0.2 parts by weight and not more than 1.5 parts by weight when the content of the non-diene rubber is 100 parts by weight. Hereinafter, the rubber composition according to one embodiment of the present invention may be referred to as "the rubber composition".

[0011] (Non-diene rubber) A non-diene rubber is a synthetic rubber having a polymer structure, which does not have a double bond in the main chain of the polymer, or has a small number of double bonds in the main chain. For example, "having a small number of double bonds" means that, although some of the monomers constituting the polymer include a monomer that introduces a diene structure into the main chain, the proportion of the monomer that introduces 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 monomer that introduces a diene structure into the main chain in the entire polymer.

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

[0013] Furthermore, examples of "having a small number of double bonds" include cases where, in principle, the main chain does not have double bonds, but double bonds are mixed into the main chain due to unintended chemical reactions such as polymerization reactions 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 them, when the rubber composition is used for automobile parts such as weather strips, EPDM is preferred as the non-diene rubber because it is easy to obtain preferable physical properties.

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

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

[0017] Non-diene rubbers have better weather resistance than diene rubbers because they do not have double bonds in the main chain. If the non-diene rubber has double bonds in the side chain, such as EPDM, the vulcanization reaction can be carried out using sulfur, but the vulcanization reaction rate using sulfur tends to be longer than that of diene rubbers. The rubber composition contains a boron-based surfactant, which can improve the vulcanization reaction rate of the non-diene rubber.

[0018] In this specification, the term "vulcanization" refers to the general crosslinking of non-diene rubbers, and is not limited to reactions using sulfur. Crosslinking of non-diene rubbers using a crosslinking agent (vulcanizing agent) other than sulfur is also included in one aspect of vulcanization.

[0019] (Boron-based surfactants) A boron-based surfactant is a surfactant containing boron. An example of a boron-based surfactant is glycerol borate fatty acid ester. Glycerol borate may be a form in which two glycerols or their fatty acid esters are bonded to boron. Glycerol borate may be a form in which at least one glycerol has 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, but may be, for example, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, or 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 surfactants include glycerol borate-oleic acid ester, glycerol borate-lauric acid ester, glycerol borate-palmitic acid ester, glycerol borate-stearic acid ester, glycerol borate-isostearic acid ester, and glycerol borate-hydroxystearic acid ester. Among them, glycerol borate-oleic acid ester is preferred from the viewpoint of availability. Examples of commercially available glycerol borate-oleic acid ester include Emulbon (registered trademark) S-80 and Emulbon T-80 from Toho Chemical Industry Co., Ltd.

[0022] Further, examples of boron-based surfactants include various glycerol borate fatty acid esters disclosed as organic boron compounds in JP-B-49-011311.

[0023] 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 glycerol borate fatty acid ester. When the boron-based surfactant is such a polymer compound, the molecular weight of the boron-based surfactant may be 500 or more and 10,000 or less.

[0024] In the rubber composition, the content of the boron-based surfactant may be more than 0.2 parts by weight and not more than 1.5 parts by weight when the content of the non-diene rubber is 100 parts by weight. 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 more than 0.2 parts by weight, the effect of improving the vulcanization rate of the rubber composition can be sufficiently obtained. If the content of the boron-based surfactant relative to the non-diene rubber is 1.5 parts by weight or less, the advantageous effect of the boron-based surfactant can be obtained within a range in which the raw material cost of the boron-based surfactant is not excessive.

[0025] The present inventors have found that the inclusion of a boron-based surfactant in the rubber composition shortens the vulcanization rate and improves the heating efficiency during vulcanization. Specifically, the boron-based surfactant can shorten the T90, which indicates the time required for vulcanization of the rubber composition, when measured with a curastometer according to a method conforming to JIS K6300-2:2001. In addition, the boron-based surfactant improves the UHF heat generation property of the rubber composition, and therefore the temperature rise time of the rubber composition can be shortened.

[0026] The inclusion of boron-based surfactants does not reduce the scorch time (t5) in the Mooney viscosity evaluation measured by a method conforming to JIS K6300-1:2013. Scorch time is an index of the period until rubber burns (scorch) occurs, and a long scorch time is preferable. While boron-based surfactants can increase the vulcanization speed indicated by T90, they do not adversely affect the scorch time.

[0027] The present inventors have further found that the inclusion of a boron-based surfactant in the 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) measured by a method conforming to JIS K6251:2017. In addition, the value of compression set measured by a method conforming to JIS K6262:2013 can be reduced, thereby improving the restoring force (elasticity) of the rubber.

[0028] Thus, the inventors have discovered that the boron-based surfactant can improve both the vulcanization characteristics of the rubber composition and the mechanical properties of the molded article. Specifically, the boron-based surfactant can shorten the heating time in the vulcanization of the rubber composition. If the heating time can be shortened, the manufacturing time of the rubber composition can be shortened, improving the manufacturing efficiency, and the energy required for heating can be saved, and the manufacturing cost can be reduced. Furthermore, the molded article of the rubber composition manufactured in this way has excellent mechanical properties, so that it can be expected to have a longer life than before.

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

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

[0031] Examples of the vulcanizing agent include sulfur, peroxide, resin, amine and polyol. Among them, when a non-diene rubber having a double bond in a side chain or the like is used, the crosslinking agent is preferably sulfur.

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

[0033] (Method of manufacturing the rubber composition) The method for producing the rubber composition of the present invention is not particularly limited, but may include, for example, a step of mixing a non-diene rubber, a boron surfactant, and other components as necessary. The mixing may be performed using a kneading machine such as a Banbury mixer, an internal mixer, a kneader, or an open roll.

[0034] (Uses of the rubber composition) According to the present rubber composition, a molded article of the present rubber composition can be obtained by vulcanizing and molding the rubber composition. In other words, a molded article according to one embodiment of the present invention can be obtained by carrying out a step of vulcanizing the present rubber composition and a step of molding the same. Hereinafter, the molded article according to one embodiment of the present invention may be referred to as the "present molded article."

[0035] The vulcanization reaction of the rubber composition can be carried out by adding a vulcanizing agent and, if necessary, additives such as a vulcanization accelerator, and heating the mixture. Heating for vulcanization and molding are preferably carried out in parallel.

[0036] The molding method of the present molded article is not particularly limited, but may be, for example, an extrusion molding method or a mold molding method. Since the UHF heat generation property of the rubber composition is also improved, the present rubber composition can be suitably used for vulcanization molding using a vulcanizing device equipped with a UHF oscillator. For example, the present rubber composition is suitable for extrusion molding using a vulcanizing furnace.

[0037] The molded article is not particularly limited, but may be, for example, a rubber part for an automobile. A suitable example of a rubber part for an automobile is a weather strip. In addition, the molded article may be applied to a gasket for a house.

[0038] [Weather strip] Fig. 1 is a side view showing a schematic diagram of an automobile 100 to which a weather strip 102, which is the present molded article, is attached. As shown in Fig. 1, the present molded article may be a weather strip 102 to be attached to a door 101 of the automobile 100. That is, the present rubber composition can be suitably used for the weather strip 102 to be attached to the door 101 of the automobile 100.

[0039] The weather strip 102 is a member attached to the periphery of the door 101, and provides a seal between the door 101 and an opening of the automobile 100. The door 101 is a passenger compartment door of the automobile 100, but is not limited to this. The door of the automobile 100 to which the weather strip 102 is attached may be, for example, a luggage compartment door, an engine room door (also called an engine hood or bonnet), or any other door.

[0040] The weatherstrip 102 may be obtained by extrusion molding the present rubber composition. The weatherstrip 102 may have an extrusion molded portion and a molded portion. In this case, the present rubber composition may be used in at least a part of the extrusion molded portion or the molded portion, or 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 present rubber composition.

[0041] 〔summary〕 The rubber composition according to the first aspect of the present invention includes a non-diene rubber and a boron-based surfactant, and 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 a second aspect of the present invention, in the first aspect, the non-diene rubber may be an ethylene-α-olefin-non-conjugated diene copolymer rubber.

[0043] A rubber composition according to a third aspect of the present invention is the rubber composition according to the first or second aspect, wherein the boron-based surfactant is a glycerol borate fatty acid ester.

[0044] The rubber composition according to a fourth aspect of the present invention may be used in any one of the first to third aspects for vulcanization molding using a vulcanizing device equipped with a UHF oscillator.

[0045] The rubber composition according to a fifth aspect of the present invention may be for a weather strip attached to an automobile door in any one of the first to fourth aspects.

[0046] A weather strip according to a sixth aspect of the present invention is a weather strip having a portion made of the rubber composition of the fifth aspect and attached to an automobile door.

[0047] [Additional Notes] The present invention is not limited to the above-described embodiments, 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] An embodiment of the present invention will now be described.

[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 was listed as parts by weight when the content of the EPDM polymer, which is a non-diene rubber, was taken as 100 parts by weight. PEG4000 is polyethylene glycol manufactured by NOF Corporation. The various additives include carbon black, process oil, filler, sulfur, zinc oxide, vulcanization accelerator, processing aid, and dehydrating agent. Multiple types of vulcanization accelerators, including thiuram-based and thiazole-based, were added. The formulations in Table 1 differ only in the presence or absence and amount of addition of PEG4000 and Emulbon T-80, and the other materials are all the same in terms of type, brand, and amount. Similarly, the formulations in Table 2 are all the same in terms of type, brand, and amount of other materials except for PEG4000 and Emulbon S-80.

[0050] [Table 1]

[0051] [Table 2]

[0052] [Evaluation method] The rubber compositions according to the examples and comparative examples were evaluated as follows.

[0053] (Vulcanization characteristics) Regarding vulcanization characteristics such as vulcanization speed during the vulcanization reaction of the rubber composition, Mooney viscosity evaluation (125°C, 10 min) was performed according to the method in accordance with JIS K6300-1:2013. Evaluation with a curastometer (180°C, 10 min) was also performed according to the method in accordance with JIS K6300-2:2001. In the Mooney viscosity evaluation, Vm, t5 (min), and t35 (min) were evaluated. In addition, evaluation using a curastometer evaluated ML (kgf cm), MH (kgf cm), T10 (min), and T90 (min). The results are shown in Tables 1 and 2.

[0054] (Fever) The heat generation property of the rubber composition by UHF (Ultra High Frequency) was evaluated. Specifically, a test piece (width 30 mm, depth 100 mm, thickness 2 mm) was cut out from a molded body of the rubber composition after vulcanization. The test piece was placed at the position shown in FIG. 2 in a batch-type heating chamber equipped with a UHF oscillator, and UHF was oscillated from a waveguide under the following UHF oscillation conditions to generate heat, and the relationship between the oscillation time and the heat generation temperature was evaluated.

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

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

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

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

[0059] On the other hand, in the evaluation by a curastometer, T90 was shortened in all of Examples 1 to 3 compared to Comparative Example 1, and the effect was particularly remarkable in Examples 1 and 2. T90 indicates the vulcanization speed, and a smaller value indicates a faster vulcanization speed, which is preferable. It was shown that the boron-based surfactant has the effect of improving the vulcanization speed of the rubber composition by heating due to thermal conduction.

[0060] In addition, as shown in Table 2, the T90 was also shortened in Examples 4 and 5 compared to Comparative Examples 2 and 3. Comparative Example 4 had the same T90 as Comparative Examples 2 and 3, which indicated that the effect of improving the vulcanization rate of the rubber composition by the boron-based surfactant was obtained when the content was greater than 0.2 parts by weight per 100 parts by weight of the non-diene rubber. Example 6 had the same T90 as Comparative Examples 2 and 3, which confirmed that the vulcanization rate was not adversely affected as long as the content of the boron-based surfactant was at least 1.5 parts by weight or less.

[0061] 3 to 7, in the UHF heat generation evaluation, the heat generation temperature in the same oscillation time increased with an increase in the content of the boron-based surfactant under all UHF oscillation conditions. In other words, it was shown that the addition of the boron-based surfactant enables heat generation in a short oscillation time, improving the UHF heat generation property of the rubber composition.

[0062] Incidentally, Patent Document 1 describes that the addition of PEG4000 to a rubber compound increases the dielectric constant. However, a comparison between Comparative Example 2 and Comparative Example 3 shows that the increase in dielectric constant due to PEG4000 does not substantially affect the UHF heat generation. This example shows that the boron-based surfactant can improve the UHF heat generation, which is advantageous from the viewpoint of manufacturability, and cannot be achieved with conventional surfactants such as PEG.

[0063] As described above, the rubber composition containing more than 0.2 parts by weight and not more than 1.5 parts by weight of boron-based surfactant per 100 parts by weight of non-diene rubber was shown to improve at least one of the vulcanization speed and UHF heat generation. The faster the vulcanization speed, the shorter the heating time during vulcanization. Also, the higher the UHF heat generation, the faster the temperature of the rubber composition can be raised. Both of these effects reduce the time required for the vulcanization process of the rubber composition and improve the heating energy efficiency, so it was suggested that the boron-based surfactant improves the vulcanization characteristics of the rubber composition, thereby improving manufacturability and contributing to reducing manufacturing costs.

[0064] (mechanical properties) As shown in Table 1, in Examples 1 to 3, the values ​​of Tb and Eb were improved compared to Comparative Example 1, and the tensile properties of the rubber were good. Furthermore, in Examples 1 to 3, the values ​​of compression set were also smaller compared to Comparative Example 1, indicating that the restoring force (elasticity) of the rubber was good. Thus, it was shown that the boron-based surfactant not only improves the vulcanization properties of the rubber composition to increase manufacturability, but also improves the mechanical properties of the molded article of the rubber composition after vulcanization.

[0065] (Conductive) The preferred electrical conductivity of a rubber composition varies depending on the application. For example, when used in automobile parts such as weather strips, excessive electrical conductivity may cause problems such as door corrosion. Therefore, the effect of a boron-based surfactant on the electrical conductivity of a rubber composition was evaluated based on the volume resistivity.

[0066] 8, the change in volume resistivity in Examples 4 and 6 was less than one order of magnitude (less than 1 / 10) compared to Comparative Examples 2 and 3, and no significant change was observed. In other words, it was shown that the boron-based surfactant has 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 Weather strip

Claims

1. A non-diene rubber and a boron surfactant are included, A rubber composition comprising a non-diene rubber having a content of 100 parts by weight and a boron-based surfactant content of more than 0.2 parts by weight and not more than 1.5 parts by weight.

2. 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 surfactant is a glycerol borate fatty acid ester.

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

5. The rubber composition according to any one of claims 1 to 4, which is used for a weather strip attached to an automobile door.

6. A weather strip attached to an automobile door, comprising a portion made of the rubber composition according to claim 5.

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