Method for analyzing the degree of crosslinking of peroxide crosslinked rubber

Abstract

To provide a method for analyzing a crosslinking degree of peroxide crosslinked rubber.SOLUTION: There is provided a method for analyzing a crosslinking degree of peroxide crosslinked rubber obtained from an uncrosslinked rubber composition containing a rubber component and a peroxide of a crosslinking agent. Thermogravimetry in a predetermined peroxide decomposition temperature range is performed for each of the uncrosslinked rubber composition, a complete crosslinked product thereof, and peroxide crosslinked rubber to be analyzed. On the basis of a result of thermogravimetry, a difference between a weight reduction ratio of the uncrosslinked rubber composition and the complete crosslinked product is used as a consumption amount of peroxide of the crosslinking agent which is consumed in obtaining a complete crosslinked product from the uncrosslinked rubber composition, and a difference between a weight reduction ratio of the uncrosslinked rubber composition and the peroxide crosslinked rubber is used as a consumption amount of the peroxide of the crosslinking agent which is consumed in obtaining the peroxide crosslinked rubber from the uncrosslinked rubber composition, and a crosslinking degree of the peroxide crosslinked rubber is calculated.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing the degree of crosslinking of peroxide-crosslinked rubber. [Background technology]

[0002] It is known that thermogravimetry is used to analyze crosslinked rubber. Patent Document 1 describes that in multilayered polymer particles having an inner layer of crosslinked rubber and an outer layer of thermoplastic resin, if the weight loss rate in thermogravimetry is 5% or less, it is possible to suppress poor appearance and mold contamination that occur during molding processing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-130745 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a method for analyzing the degree of crosslinking of peroxide-crosslinked rubber. [Means for solving the problem]

[0005] The present invention is a method for analyzing the degree of crosslinking of a peroxide-crosslinked rubber obtained from an uncrosslinked rubber composition containing a rubber component and a peroxide crosslinking agent, wherein thermogravimetry is performed on each of the uncrosslinked rubber composition, a completely crosslinked product of the uncrosslinked rubber composition, and the peroxide-crosslinked rubber to be analyzed, and from the results of the thermogravimetry, the difference in weight loss rate between the uncrosslinked rubber composition and the completely crosslinked product is considered to be the amount of peroxide consumed as the crosslinking agent consumed when obtaining the completely crosslinked product from the uncrosslinked rubber composition, and the difference in weight loss rate between the uncrosslinked rubber composition and the peroxide-crosslinked rubber is considered to be the amount of peroxide consumed as the crosslinking agent consumed when obtaining the peroxide-crosslinked rubber from the uncrosslinked rubber composition, thereby calculating the degree of crosslinking of the peroxide-crosslinked rubber.The peroxide of the crosslinking agent is one or more of dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, n-butyl-4,4-di(t-butylperoxy)valerate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexylperoxybenzoate, and t-butylperoxybenzoate. . [Effects of the Invention]

[0006] According to the present invention, the degree of crosslinking of the peroxide-crosslinked rubber can be analyzed by using the results of thermogravimetry of the uncrosslinked rubber composition, its completely crosslinked product, and the peroxide-crosslinked rubber to be analyzed. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a graph showing the relationship between temperature and weight retention in thermogravimetry for an uncrosslinked rubber composition A, a completely crosslinked product B, and a peroxide-crosslinked rubber X. [Figure 2A] 1 is a graph showing the relationship between time and weight retention in thermogravimetry for an uncrosslinked rubber composition A and a completely crosslinked product B. [Figure 2B] 1 is a graph showing the relationship between time and weight retention in thermogravimetry for uncrosslinked rubber composition A and peroxide-crosslinked rubber X. [Figure 3A] 1 is a graph showing the relationship between the degree of crosslinking and 100% tensile stress of the completely crosslinked product B and peroxide-crosslinked rubbers X1 to X5 calculated by the first analytical method. [Figure 3B] 10 is a graph showing the relationship between the degree of crosslinking and the 100% tensile stress of the completely crosslinked product B and peroxide-crosslinked rubbers X1 to X5 calculated by the second analytical method. [Figure 4] 1 is a graph showing the relationship between the degree of crosslinking calculated by the first analysis method and the degree of crosslinking calculated by the second analysis method. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following describes the embodiments.

[0009] In the method for analyzing the degree of crosslinking of peroxide-crosslinked rubber X according to the embodiment, the peroxide-crosslinked rubber X to be analyzed is a crosslinked rubber composition obtained from an uncrosslinked rubber composition A having a known formulation containing a rubber component and a peroxide crosslinking agent.

[0010] Examples of the peroxide-crosslinkable rubber component in the uncrosslinked rubber composition A include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), ethylene-propylene-diene copolymer rubber (EPDM), ethylene-propylene copolymer rubber (EPM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), silicone rubber (Q), fluororubber (F), etc. The rubber component preferably contains one or more of these.

[0011] Examples of peroxides used as crosslinking agents include dialkyl peroxides such as dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3; peroxyketals such as 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and n-butyl-4,4-di(t-butylperoxy)valerate; and peroxyesters such as 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexylperoxybenzoate, and t-butylperoxybenzoate. The peroxide preferably contains one or more of these. The amount of peroxide compounded in the uncrosslinked rubber composition A is, for example, 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component.

[0012] The uncrosslinked rubber composition A may contain a reinforcing agent such as carbon black, a filler, a processing aid, an antioxidant, a plasticizer, a vulcanization accelerator, a vulcanization accelerator assistant, and the like.

[0013] In the method for analyzing the degree of crosslinking of peroxide-crosslinked rubber X according to the embodiment, first, thermogravimetry is performed on each of the uncrosslinked rubber composition A, the completely crosslinked product B of the uncrosslinked rubber composition A, and the peroxide-crosslinked rubber X to be analyzed.

[0014] Here, the term "completely crosslinked product B" in the present application refers to a product obtained by crosslinking an uncrosslinked rubber composition A by heating it at a predetermined crosslinking temperature for a 100% crosslinking time tc(100) determined in accordance with JIS K6300-2:2001 using a Curastometer (registered trademark).

[0015] From the viewpoint of improving analytical accuracy, the thermogravimetric measurement of the completely crosslinked product B and the peroxide crosslinked rubber X is preferably carried out after the primary crosslinking in which heating is performed by press molding or the like and before the secondary crosslinking in which heating is performed in an oven or the like.

[0016] The thermogravimetric measurement is preferably carried out in an atmosphere where an inert gas such as nitrogen is circulated. The flow rate of the inert gas is, for example, 300 ml / min to 1000 ml / min.

[0017] The temperature rise rate in thermogravimetry is preferably 1°C / min or more from the viewpoint of avoiding long measurement times, and is preferably 10°C / min or less, more preferably 5°C / min or less, and even more preferably 2°C / min or less from the viewpoint of tracking the temperature rise of the sample and improving measurement accuracy.

[0018] In the results of thermogravimetry, the difference P in the weight retention rate between the uncrosslinked rubber composition A and the completely crosslinked product B at temperature T shown in Fig. 1 coincides with the difference in the weight loss rate between the uncrosslinked rubber composition A and the completely crosslinked product B, and can therefore be regarded as the amount of peroxide consumed as the crosslinking agent when the completely crosslinked product B is obtained by heating and crosslinking the uncrosslinked rubber composition A. Similarly, the difference Q in the weight retention rate between the uncrosslinked rubber composition A and the peroxide-crosslinked rubber X at temperature T shown in Fig. 1 coincides with the difference in the weight loss rate between the uncrosslinked rubber composition A and the peroxide-crosslinked rubber X, and can therefore be regarded as the amount of peroxide consumed as the crosslinking agent when the peroxide-crosslinked rubber X is obtained by heating and crosslinking the uncrosslinked rubber composition A.

[0019] From the above, in the method for analyzing the degree of crosslinking of peroxide-crosslinked rubber X according to the embodiment, from the results of thermogravimetry, the difference P in the weight retention rate between uncrosslinked rubber composition A and completely crosslinked product B at temperature T, i.e., the difference in weight loss rate, is regarded as the amount of peroxide consumed as the crosslinking agent when completely crosslinked product B is obtained from uncrosslinked rubber composition A, and the difference Q in the weight retention rate between uncrosslinked rubber composition A and peroxide-crosslinked rubber X at temperature T, i.e., the difference in weight loss rate, is regarded as the amount of peroxide consumed as the crosslinking agent when peroxide-crosslinked rubber X is obtained from uncrosslinked rubber composition A, and the degree of crosslinking of peroxide-crosslinked rubber X is calculated based on the results. Specific analytical methods include the following first and second analytical methods.

[0020] <First analysis method> In the first analysis method, as shown in Figure 1, the difference P in the weight loss rate between the uncrosslinked rubber composition A and the completely crosslinked product B and the difference Q in the weight loss rate between the uncrosslinked rubber composition A and the peroxide-crosslinked rubber X are determined from the results of thermogravimetry at a predetermined analysis temperature T at which most of the peroxide in the crosslinking agent decomposes. Then, the ratio of the difference Q in the weight loss rate between the uncrosslinked rubber composition A and the peroxide-crosslinked rubber X to the difference P in the weight loss rate between the uncrosslinked rubber composition A and the completely crosslinked product B is calculated as the degree of crosslinking of the peroxide-crosslinked rubber X.

[0021] The analysis temperature T is preferably 200° C. or higher and 250° C. or lower, more preferably 220° C., from the viewpoint of detecting the decomposition of as much peroxide as possible to increase analytical accuracy while minimizing the influence of high-temperature decomposition components other than peroxide on weight loss. This analysis temperature T can be set by confirming the decomposition of peroxide from a DTG curve obtained by differential thermogravimetry (DTG) of the uncrosslinked rubber composition A.

[0022] This first analysis method is a simple method suitable for cases where the uncrosslinked rubber composition A has a relatively simple formulation.

[0023] <Second analysis method> In the second analysis method, as shown in FIG. 2A, the difference P in the weight retention rate between the uncrosslinked rubber composition A and the fully crosslinked product B is integrated over time from the lower limit temperature Tmin to the upper limit temperature Tmax of a predetermined peroxide decomposition temperature range, and the peroxide consumption parameter S is calculated. I (=∫Pdt) is calculated. I is an index of the amount of peroxide consumed as a crosslinking agent when a completely crosslinked product B is obtained from an uncrosslinked rubber composition A, and is the maximum value of the index.

[0024] As shown in FIG. 2B, the difference Q in the weight retention rate between the uncrosslinked rubber composition A and the peroxide-crosslinked rubber X is integrated over time from the lower limit temperature Tmin to the upper limit temperature Tmax of a predetermined peroxide decomposition temperature range, and the peroxide consumption parameter S II (=∫Qdt) is calculated. II is an index of the amount of peroxide consumed as a crosslinking agent when obtaining peroxide-crosslinked rubber X from uncrosslinked rubber composition A.

[0025] and the peroxide consumption parameter S I Peroxide consumption parameter S II The ratio is calculated as the degree of crosslinking of the peroxide crosslinked rubber X.

[0026] Here, the peroxide decomposition temperature range is a temperature range for detecting weight loss mainly caused by the decomposition of peroxide in the crosslinking agent by thermogravimetry (TGA). This peroxide decomposition temperature range can be set by confirming the decomposition of peroxide from a DTG curve obtained by differential thermogravimetry (DTG) of the uncrosslinked rubber composition A.

[0027] The lower limit temperature Tmin of the peroxide decomposition temperature range is preferably set to a temperature of 80°C or higher and 120°C or lower, from the viewpoint of detecting the decomposition of as much peroxide as possible while minimizing the influence of dissipation of low-volatile components on weight loss, and more preferably set to 100°C, particularly from the viewpoint of eliminating the influence of dissipation of water on weight loss. The upper limit temperature Tmax of the peroxide decomposition temperature range is preferably set to a temperature of 200°C or higher and 250°C or lower, and more preferably set to 220°C, from the viewpoint of detecting the decomposition of as much peroxide as possible to increase analytical accuracy while minimizing the influence of high-temperature decomposition components other than peroxide on weight loss.

[0028] Peroxide consumption parameter S I ,S II is a clarification of the amount of peroxide consumed as a crosslinking agent when obtaining a completely crosslinked product B or a peroxide-crosslinked rubber X from an uncrosslinked rubber composition A. Therefore, this second analytical method can also be used when the uncrosslinked rubber composition A has a complex blend containing a wide variety of components.

[0029] According to the method for analyzing the degree of crosslinking of peroxide-crosslinked rubber X of the above embodiment, the degree of crosslinking of the peroxide-crosslinked rubber X can be analyzed by using the results of thermogravimetry of the uncrosslinked rubber composition A, its completely crosslinked product B, and the peroxide-crosslinked rubber X to be analyzed. Moreover, since only a small amount of sample of the peroxide-crosslinked rubber X is required for thermogravimetry, for example, the degree of crosslinking can be analyzed by collecting only a small portion of a rubber product as a sample. Therefore, the method for analyzing the degree of crosslinking of the peroxide-crosslinked rubber X of the embodiment can be used in process inspection or product inspection to analyze the degree of crosslinking of samples of the peroxide-crosslinked rubber X collected from semi-finished products or finished products, by previously performing thermogravimetry of the uncrosslinked rubber composition A and its completely crosslinked product B and storing the results in a database. [Example]

[0030] (Uncrosslinked rubber composition A and fully crosslinked product B) Hydrogenated nitrile rubber (HNBR) was used as the rubber component, and 2.4 parts by mass of 1,3-di(t-butylperoxy)diisopropylbenzene, a peroxide crosslinking agent, and 30 parts by mass of carbon black were blended with 100 parts by mass of this rubber component to prepare an uncrosslinked rubber composition A.

[0031] The 100% crosslinking time tc(100) of this uncrosslinked rubber composition A was measured at 175°C using a Curastometer (registered trademark) in accordance with JIS K6300-2:2001 and was found to be 15 minutes. From this, the uncrosslinked rubber composition A was crosslinked at a crosslinking temperature of 175°C for a crosslinking time of 15 minutes to be a fully crosslinked product B.

[0032] (Peroxide cross-linked rubber X) The uncrosslinked rubber composition A was crosslinked at a crosslinking temperature of 175°C for a crosslinking time of 7 minutes to obtain peroxide-crosslinked rubber X1. In addition, peroxide-crosslinked rubbers X2 to X5 were obtained by crosslinking the uncrosslinked rubber composition A at a crosslinking temperature of 170°C, 165°C, 160°C, and 155°C, respectively, which had the same constitution as peroxide-crosslinked rubber X1.

[0033] (Thermogravimetric measurement) Thermogravimetry was carried out for each of the uncrosslinked rubber composition A, the completely crosslinked product B, and the peroxide-crosslinked rubbers X1 to X5. The thermogravimetry was carried out in a chamber containing the sample, with nitrogen circulating at a flow rate of 500 ml / min, and with the following temperature history: the sample was heated from 30°C to 50°C at a heating rate of 10°C / min, held for 5 minutes, then heated from 50°C to 80°C at a heating rate of 10°C / min, and then heated from 80°C to 220°C at a heating rate of 2°C / min.

[0034] (Degree of cross-linking) <First analysis method> The degree of crosslinking of each of the peroxide-crosslinked rubbers X1 to X5 was calculated by the first analysis method of the above embodiment, with the analysis temperature T set to 220° C. The results are shown in Table 1.

[0035] [Table 1]

[0036] <Second analysis method> For each of the peroxide-crosslinked rubbers X1 to X5, the degree of crosslinking was calculated using the second analytical method of the above embodiment, with the peroxide decomposition temperature range having a lower limit temperature Tmin of 100° C. and an upper limit temperature Tmax of 220° C. The results are shown in Table 2.

[0037] [Table 2]

[0038] (tensile stress at 100% elongation) The tensile stress at 100% elongation was measured for each of the fully cross-linked product B and the peroxide-cross-linked rubbers X1 to X5 in accordance with JIS K6251: 2010. It can be said that the tensile stress at 100% elongation is a physical property that reflects the actual degree of cross-linking of the fully cross-linked product B and the peroxide-cross-linked rubbers X1 to X5.

[0039] Fig. 3A shows the relationship between the degree of crosslinking of the completely crosslinked product B and peroxide-crosslinked rubbers X1 to X5 calculated by the first analytical method and the 100% tensile stress. Fig. 3B shows the relationship between the degree of crosslinking of the completely crosslinked product B and peroxide-crosslinked rubbers X1 to X5 calculated by the second analytical method and the 100% tensile stress. Fig. 4 shows the relationship between the degree of crosslinking calculated by the first analytical method and the degree of crosslinking calculated by the second analytical method.

[0040] 3A and 3B show that the degree of crosslinking calculated by both the first and second analytical methods has a strong correlation with the tensile stress at 100% elongation. Also, FIG. 4 shows that there is no significant difference between the degree of crosslinking calculated by both the first and second analytical methods. [Industrial Applicability]

[0041] The present invention is useful in the technical field of a method for analyzing the degree of crosslinking of peroxide-crosslinked rubber.

Claims

1. A method for analyzing the degree of crosslinking of a peroxide-crosslinked rubber obtained from an uncrosslinked rubber composition containing a rubber component and a peroxide crosslinking agent, comprising: thermogravimetry is performed on each of the uncrosslinked rubber composition, the completely crosslinked product of the uncrosslinked rubber composition, and the peroxide-crosslinked rubber to be analyzed; From the results of the thermogravimetry, the difference in weight loss rate between the uncrosslinked rubber composition and the completely crosslinked product is regarded as the amount of peroxide consumed as the crosslinking agent when obtaining the completely crosslinked product from the uncrosslinked rubber composition, and the difference in weight loss rate between the uncrosslinked rubber composition and the peroxide-crosslinked rubber is regarded as the amount of peroxide consumed as the crosslinking agent when obtaining the peroxide-crosslinked rubber from the uncrosslinked rubber composition, thereby calculating the degree of crosslinking of the peroxide-crosslinked rubber; The peroxide crosslinking agent is one or more of dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, n-butyl-4,4-di(t-butylperoxy)valerate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexylperoxybenzoate, and t-butylperoxybenzoate.

2. 2. The method for analyzing the degree of crosslinking according to claim 1, A crosslinking degree analysis method in which, from the results of the thermogravimetry, the ratio of the difference in weight loss rate between the uncrosslinked rubber composition and the peroxide-crosslinked rubber to the difference in weight loss rate between the uncrosslinked rubber composition and the completely crosslinked product at a predetermined analysis temperature is calculated as the crosslinking degree of the peroxide-crosslinked rubber.

3. 3. The method for analyzing the degree of crosslinking according to claim 2, The method for analyzing the degree of crosslinking, wherein the analysis temperature is 200°C or higher and 250°C or lower.

4. 2. The method for analyzing the degree of crosslinking according to claim 1, A crosslinking degree analysis method in which, from the results of the thermogravimetry, a ratio of a peroxide consumption parameter obtained by time-integrating the difference in weight loss rate between the uncrosslinked rubber composition and the completely crosslinked product over a period from a lower limit temperature to an upper limit temperature in a predetermined peroxide decomposition temperature range to a peroxide consumption parameter obtained by time-integrating the difference in weight loss rate between the uncrosslinked rubber composition and the peroxide-crosslinked rubber is calculated as the crosslinking degree of the peroxide-crosslinked rubber.

5. 5. The method for analyzing the degree of crosslinking according to claim 4, The method for analyzing the degree of crosslinking, wherein the lower limit temperature of the peroxide decomposition temperature range is 100°C.

6. The method for analyzing the degree of crosslinking according to claim 4 or 5, The method for analyzing the degree of crosslinking, wherein the upper limit temperature of the peroxide decomposition temperature range is a temperature of 200°C or higher and 250°C or lower.

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