JPH0573717B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is particularly applicable to low-pollution engines that purify exhaust gas by oxidizing or reducing harmful components such as carbon monoxide, hydrocarbons, and nitrogen oxides emitted from automobile engines. The present invention relates to a heat expansion resistant member suitable as a holding material for a ceramic honeycomb monolithic catalyst constituting a converter. [Prior art] Carbon monoxide emitted from automobile engines,
It is well known that ceramic honeycomb monolith catalysts, which have excellent high-temperature properties, are suitable as catalysts for purifying exhaust gas by oxidizing or reducing harmful components such as hydrocarbons and nitrogen oxides, and for obtaining low-pollution engines. It is being By the way, since ceramics are brittle and have poor toughness, a retaining material with cushioning properties is used to prevent them from being damaged by mechanical shocks such as vibrations that occur when a car is running. It is rolled and attached to a metal casing. Since the ceramic honeycomb monolith catalyst is exposed to high-temperature exhaust gas during engine operation, the holding material is naturally required to have excellent heat resistance, that is, conditions that do not reduce high-temperature strength. Moreover, as the engine is operated continuously and the exhaust gas gradually becomes hotter, even if the holding material expands correspondingly to each temperature range, the holding power and cushioning properties for the ceramic honeycomb monolith catalyst decrease. Conditions that do not apply are required. Conventionally, as a holding material for monolithic catalysts that can satisfy these conditions, for example,
-40% to 65% by weight of treated unexpanded vermiculite treated with an aqueous solution of ammonium dihydrogen phosphate, as disclosed in Publication No. 35143, inorganic fiber material
Heat-expandable sheets are known that contain 25% to 50% by weight and 5% to 15% by weight of a binder selected from inorganic binders. For example, as disclosed in Japanese Patent Publication No. 62-38397, instead of the inorganic binder, natural rubber latex, styrene-butadiene latex,
Heat-expandable sheet materials using organic binders such as butadiene-acrylonitrile latex, latexes of polymers or copolymers of acrylic esters and methacrylic esters are also known. [Problems to be Solved by the Explanation] However, as is clear from Table 2 and the graph in FIG. 3, which are based on the experimental results by the present inventors, in the heat-expandable sheet made using the above-mentioned inorganic binder, A relatively large negative expansion occurs due to the creep phenomenon in the vicinity of 200℃ to 300℃, which corresponds to the low temperature region (more specifically, 200℃ to 325℃), and the amount of thermal expansion is extremely large in the 350℃ to 400℃ region, which corresponds to the medium temperature region. Because of its small size, it causes wobbling, and the holding power of the ceramic honeycomb monolith catalyst decreases significantly.
It was found that the amount of thermal expansion was suppressed and the holding power of the ceramic honeycomb monolith catalyst in the high temperature range was significantly reduced. In other words, with conventional heat-expandable sheets, it is not possible to expect high retention strength in both low-temperature and high-temperature regions, resulting in wobbling.Furthermore, bonding only with inorganic binders allows for shape retention. As a result, the parts exposed to exhaust gas flowing down at high temperatures and high speeds gradually disappear, and the retention function of the monolithic catalyst disappears over time. That is, it has problems such as extremely poor gas attack resistance. It is also known to treat the aforementioned untreated unexpanded vermiculite with sodium dihydrogen phosphate, but with this heat-expandable sheet, negative expansion in the low-temperature region is suppressed, but Sufficient holding force cannot be expected due to the small thermal expansion in Tables 2 and 3.
(see figure). Furthermore, as is clear from Table 5 below, which is based on the experimental results of the present inventors, the heat-expandable sheet material made using the above-mentioned organic binder has low tensile strength at room temperature, and Due to its lack of flexibility, it is prone to cracking over a long range when bent, making it undesirable for this type of heat-expansion-resistant member that is often used in a bent state, such as when wound. The present invention was made in view of these circumstances, and it is possible to secure a sufficiently large holding force from low temperature to high temperature ranges, improve gas attack resistance, and improve tensile strength and flexibility. It is an object of the present invention to provide a heat-expandable member that can be used in various ways. [Means for Solving the Problems] In order to achieve the above object, the heat expansion resistant member of the present invention comprises sepiolite mineral, unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, This is a heat expansion resistant member made by blending ceramic fibers and an organic binder in a predetermined ratio, and uses an ethylene vinyl acetate acrylate ester copolymer as the organic binder. In addition, the blending ratio of each of the constituent materials is 3 to 5% by weight of sepiolite mineral, 49 to 59% by weight of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, and ceramic fiber.
25 to 30% by weight, and 10 to 15% by weight of the organic bonding material using ethylene vinyl acetate acrylate copolymer. Furthermore, the blending ratio of each of the constituent materials is 3 to 5% by weight of sepiolite mineral, 23 to 33% by weight of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, and 50 to 60% by weight of ceramic fiber. , 10-15% by weight organic binder using ethylene vinyl acetate acrylate copolymer
It is set to . [Function] According to the present invention, sepiolite mineral, unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, ceramic fiber,
By blending organic binders using ethylene vinyl acetate acrylic acid ester copolymer at predetermined ratios, we can reduce negative expansion in low-temperature ranges, improve heat resistance strength in high-temperature ranges, and reduce mechanical shocks such as vibrations. Not only does it provide a moderate balance of cushioning properties and shape retention properties at room temperature, but it also ensures a sufficiently large holding force in a wide temperature range from low to high temperatures, as well as gas attack resistance. can be increased. In particular, by using ethylene vinyl acetate acrylate copolymer, which has excellent elongation, adhesiveness, and weather resistance, as an organic binder, it has improved tensile strength and flexibility at room temperature, and is resistant to bending. The occurrence of accompanying cracks is suppressed. In addition, by treating untreated unexpanded vermiculite with a solution of sodium ammonium hydrogen phosphate, the vermiculite that easily exchanges ions with Na+ and the one that easily exchanges ions with NH4+ were able to exchange both of these ions. The containing solution effectively exchanges ions, increasing the swelling amount and swelling power of vermiculite. [Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a catalytic converter. In the figure, 1 is a monolithic catalyst made of ceramic honeycomb, and a heat-expandable sheet 2 is wound around the outer periphery of the monolithic catalyst, and a metal casing 3 is divided into two parts. The outer periphery of the metal casing 3 is tightened with a metal band 4. The heat-expandable sheet 2 contains 3 to 5% by weight, preferably 4% by weight of sepiolite mineral, 49 to 59% by weight, preferably 54% by weight of unexpanded vermiculite, and 25 to 35% by weight, preferably ceramic fiber. teeth
30% by weight and 10 to 15% by weight, preferably 12% by weight of ethylene vinyl acetate acrylate copolymer as an organic binder, and is manufactured by a papermaking method. The two-split metal casing 3 and metal band 4 are each made of SUS304. There are two types of sepiolite minerals that make up the heat-expandable sheet 2, depending on their degree of crystallinity: α-type sepiolite is a fibrous type with high crystallinity, and α-type sepiolite is a type with low crystallinity or amorphous powder. It is called β-type sepiolite. Since β-type sepiolite is in powder form, it has poor entanglement with ceramic fibers, unexpanded vermiculite, etc.
Alpha-type sepiolite is used. However, α type and β type may be used together. Moreover, sepiolite mineral solidifies when kneaded with water and dried. moreover,
Light sinterability is obtained at temperatures of 400 to 800°C, and α-type sepiolite in particular entangles well with ceramic fibers and vermiculite, and it does not break like glass fibers or ceramic fibers even when rubbed or tightened. There is no. For this purpose, the heat-expandable sheet 2 containing sepiolite mineral is
Negative expansion at around 300°C is prevented to improve the holding power of the ceramic honeycomb monolith catalyst 1. The treated unexpanded vermiculite is treated with an aqueous solution of sodium ammonium hydrogen phosphate. In this way, by immersing the untreated unexpanded vermiculite in the aqueous solution, the
Those that are easily ion-exchanged with Na+ and those that are easily ion-exchanged with NH4+ are effectively ion-exchanged by the aqueous solution containing both ions, increasing the amount of expansion and expansion power of vermiculite. Ceramic fibers not only improve heat resistance strength but also play a role in preventing negative expansion around 300℃.
Particularly in high-temperature regions where the organic binder completely disappears, it exhibits a bonding function and improves shape retention. As the organic binder, use an ethylene vinyl acetate acrylate copolymer (for example, Sumikaflex 900 manufactured by Sumitomo Chemical Co., Ltd.), and if it is less than 10% by weight, the strength and flexibility at room temperature will be insufficient, Must be in the range of 15% by weight. After immersing 1000 g of unexpanded vermiculite from South Africa in the aqueous solution shown in Table 1 for 120 hours at room temperature,
Wash with running water and dry for 2 hours at 105℃.
After performing the prescribed heat treatment for 30 minutes, the specific volume of the vermiculite was measured using a measuring cylinder. The measurement results are shown in Table 2 and FIG. 3.

【table】

[Table] In Table 2, the numbers in parentheses indicate the coefficient of thermal expansion (%). Further, vermiculite No. 1 has a particle size of 0.5 to 2 mm. In Table 2, sodium ammonium hydrogen phosphate does not shrink at 200 to 300°C, that is, does not undergo negative expansion, as seen in ammonium dihydrogen phosphate treatment. It also shows a higher degree of expansion (amount of expansion) compared to sodium hydrogen phosphate treatment, and the expansion start temperature is as early as 275°C. α-type sepiolite (Milcon MS of Showa Mining Co., Ltd.)
-2-2) 4% by weight, unexpanded vermiculite (No. 0 produced in South Africa) treated with an aqueous solution of sodium ammonium hydrogen phosphate (54 weight), ceramic fiber (SC1260D2 from Shin Nikka Co., Ltd.) 30 weight %,
By using 12% by weight of ethylene vinyl acetate acrylic ester copolymer emulsion (Sumikaflex 900, manufactured by Sumitomo Chemical Co., Ltd.) as an organic binder, the thickness was 4.9%.
A heat-expandable mat with a density of 0.5 to 0.8 g/cm ³ , preferably 0.7 g/cm ³ is manufactured by a papermaking method, and a sample A with a diameter of 15 mm and a thickness of 4.9 mm is prepared from this mat. As shown in FIG. 2, the material was compressed to a thickness of 3 mm with quartz rods 7A, 7A using a load cell 6 in a heating furnace 5, and the thermal expansion force was measured while the temperature was raised to 750° C. in about 50 minutes. The results are shown in Table 3 below.

[Table] From Table 3, it can be seen that high expansion power is obtained even in the high temperature range. In particular, vermiculite (No. 0), which has a small particle size, has a higher expansion power and less decrease in expansion power at high temperatures, so it can be used as a holding material for ceramic catalysts for automobiles, etc., and has high expansion power even at high temperatures. Table 2 above shows that vermiculite (No. 1), which has a large particle size, has a slightly lower expansion force than vermiculite (No. 0), which has a small particle size. As can be seen, materials with a large expansion amount are suitable for use as fireproof sealing materials, for example, to be wound around the outer periphery of power transmission cables inserted through through holes in construction walls. The heat expansion resistant sheet 2 according to the present invention or the heat expansion resistant sheet of the conventional example (Japanese Patent Publication No. 61-35143) is wound around the outer periphery of a cylindrical catalyst 10 with an outside diameter of 76 mm as shown in FIG. After being loaded into a metal cylindrical casing 11 and subjected to heat treatment,
A cylindrical catalyst 1 is compressed at a compression speed of 5 m/min by a load cell 14 via a rubber plate 12 and a metal plate 13.
0 in the direction of the arrow to measure the pressing force required to extrude the cylindrical catalyst 10, that is, the holding force of the heat-expandable sheet 2. The results are shown in Table 4 below and the graph in FIG.

[Table] According to the graphs in Table 4 and Figure 5, in the conventional heat-expandable sheet 2, the holding power at 325°C is significantly reduced due to the above-mentioned negative expansion, and furthermore, the holding power at 600°C is
Although the holding force in the above high temperature range is small, according to the heat expansion resistant sheet 2 according to the present invention, the holding force is not significantly low even in the negative expansion range at 325°C, and in the high temperature range of 600°C or higher. It can be seen that a large holding force can be secured. This can be said to be due to the synergistic effect of the expansion amount and expansion power possessed by vermiculite treated with sodium ammonium hydrogen phosphate and sepiolite mineral, which is not included in conventional sheets. . In addition, matte (example) manufactured by the papermaking method with the above-mentioned blending ratio and NBR as an organic binder were also used.
The tensile strength and bending resistance of conventional pine (Comparative Examples 1 and 2) manufactured using latex (Nippon Zeon Co., Ltd.'s 1562 and 1571) at the same blending ratio were measured, and the organic binder The effectiveness of using ethylene vinyl acetate acrylic ester copolymer was confirmed. The test results are shown in Table 5. Tensile test is 25mm wide x 160mm long x 4.9mm thick.
It was pulled using a joint test mat with a gage distance of 100 mm and a pulling speed of 20 mm/min. In addition, the bending resistance test was carried out when a sample mat A of width (W) 25 mm x length (L) 80 mm x thickness (t) 4.9 mm was bent at 180° as shown in Figure 6. The crack length (l) generated on the outer surface of the bent portion was measured.

Table 5 shows that the tensile strength is approximately 2.3 to 3.5 times higher than that of conventional heat expansion resistant mats, and the bending resistance is also significantly superior. In the above embodiment, like the exhaust system of a four-wheeled vehicle, the distance from the engine exhaust port to the catalytic converter is long and the exhaust gas is exposed to a slightly slower speed, so that the gas attack on the heat-expandable sheet is relatively small. We have shown a thermal expansion resistant material with a blending ratio suitable for use in small and highly rigid catalytic converters, but because the distance from the engine exhaust port to the catalytic converter is short, such as in the exhaust system of motorcycles, In cases where the catalytic converter is exposed to exhaust gas flowing down at high speed and the gas attack on the thermal expansion resistant sheet is severe, it is desirable to use a thermal expansion resistant member with a blending ratio that emphasizes gas attack resistance rather than the amount of expansion. The blending ratio of each constituent material for this is 3 to 5% by weight of sepiolite mineral, preferably 4% by weight,
Unexpanded vermiculite 23-33% by weight, preferably 28% by weight, treated with a solution of sodium ammonium hydrogen phosphate, ceramic fibers 50-60%
% by weight, preferably 56% by weight, ethylene vinyl acetate acrylate copolymer as organic binder
The amount is 10 to 15% by weight, preferably 12% by weight, and in this case, the amount of expansion is reduced by lowering the blending ratio of unexpanded vermiculite compared to the example suitable for the exhaust system of a four-wheeled vehicle. On the other hand, it is possible to increase the blending ratio of ceramic fibers that contribute to improving heat resistance strength, thereby preventing cracking of the monolithic catalyst 1 and abnormal deformation of the metal casing 3 due to excessive expansion. [Effects of the Invention] As described above, according to the present invention of claim 1, the low negative expansion range in the low temperature region, the improvement in heat resistance strength in the high temperature region, and the cushioning property that effectively alleviates mechanical shocks such as vibrations are achieved. The ceramic honeycomb monolith catalyst, which has a suitable balance of shape retention and poor toughness, can be held properly without wobbling with a large holding power regardless of the low temperature or high temperature range. Therefore, it is possible to prevent the inconvenience of damage to the ceramic honeycomb monolith catalyst due to mechanical shocks such as vibrations generated when the automobile is running. Furthermore, by using ethylene vinyl acetate acrylate copolymer, which has excellent elongation, adhesiveness, and weather resistance, as an organic binder, it is possible to improve tensile strength at room temperature, improve flexibility, and improve durability. Flexibility can be increased, cracking caused by bending during actual use can be suppressed, and durability can be significantly improved. Furthermore, by treating unexpanded vermiculite with a solution of sodium ammonium hydrogen phosphate, the expansion amount and expansion force of unexpanded vermiculite are significantly increased from the low temperature range, and the holding power is significantly increased. can be increased. In the heat expansion resistant member according to claim 2, the blending ratio of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate is sufficiently higher than the blending ratio of sepiolite mineral, so that the amount of expansion and the expansion are particularly improved. Although the compressive strength of the honeycomb monolith catalyst is high and the metal casing is formed with a thick wall and has high rigidity, it is designed to increase the force and ensure appropriate gas attack resistance. Suitable for catalytic converters for four-wheeled vehicles that are exposed to exhaust gas with a slightly slower flow rate. In the heat expansion resistant member according to claim 3, the blending ratio of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate is lowered, while the blending ratio of ceramic fibers is increased, thereby increasing the amount of expansion and expansion. Although the compressive strength of the honeycomb monolith catalyst is low and the metal casing is formed thin and has low rigidity, it is possible to improve the heat resistance strength and ensure sufficient gas attack resistance while suppressing the force. Suitable for catalytic converters for motorcycles that are exposed to high-flowing exhaust gas.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view showing an example of a catalytic converter to which the thermal expansion resistant member of the present invention is applied, Fig. 2 is a schematic front view showing a thermal expansion force measuring device, and Fig. 3 differs depending on the processing liquid. A graph showing the degree of expansion of vermiculite, Fig. 4 is an explanatory cross-sectional view of the holding force measurement device for heat-expandable sheets, Fig. 5 is a comparison graph showing the holding force measurement results, and Fig. 6 is the state of the bending test. FIG. 2... Heat expansion resistant sheet (heat expansion resistant member)

Claims (1)

[Claims] 1. A heat-resistant expansion product made by blending sepiolite mineral, unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, ceramic fiber, and an organic binder in a predetermined ratio. 1. A heat-expandable member characterized in that the organic binder is an ethylene-vinyl acetate acrylate copolymer. 2 3-5% by weight of sepiolite mineral, 49-59% by weight of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, 25-30% by weight of ceramic fibers, and 10-15% of organic binder.
% by weight. The heat expansion resistant member according to claim 1. 3-5% by weight of sepiolite mineral, 23-33% by weight of unexpanded vermiculite treated with a solution of sodium ammonium hydrogen phosphate, 50-60% by weight of ceramic fibers, and 10-15% by weight of an organic binder.
% by weight. The heat expansion resistant member according to claim 1.