JPH1060198A - Rubber composition having excellent resistance to chlorine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chlorine-resistant rubber product which not only is improved with respect to thermal resistance, compression set (i.e., a small set) and physical properties after aging, with a mechanical strength maintained at an original level, but also exhibits excellent resistance to chlorine, and therefore, is suitable as a sealant for use in a piping system wherein CIP washing is usually carried out. SOLUTION: This rubber product is derived from a compound comprising 100 pts.wt. of a rubber blend of an ethylene-propylene rubber and a hydrogenated acrylonitrile-butadiene rubber, 0.1 to 6 pts.wt. of an antioxidant component obtained by mixing 4,4-(α,α-dimethylbenzil)diphenylamine and 2- mercaptobenzimidazole or a zinc salt of the imidazole at a ratio of 1:1 to 0.05:1, 0.5 to 10 pts.wt of an auxiliary for crosslinking, 0.005 to 0.05 mole of a peroxide crosslinking agent and a reinforcing agent such as a carbon black.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is excellent in heat resistance, small in compression set, and excellent in chlorine resistance. Especially, the concentration of chlorine for disinfection of tap water due to recent deterioration of water quality is becoming high. Suitable as a heat exchanger, valves and other sealing materials used in the field where tap water lines are used in the field where washing and disinfection treatment with an acid or alkali aqueous solution is routinely performed as in the food industry The present invention relates to a novel chlorine-resistant rubber composition.

[0002]

2. Description of the Related Art As a method for producing a heat-resistant rubber product having excellent heat resistance and a small compression set, 4,4- (α, α-dimethylbenzyl) diphenylamine and 100% by weight of ethylene / propylene rubber are mixed. 0.1 to 6 parts by weight of an antioxidant obtained by mixing mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole in a mixing ratio of 1/1 to 0.05 / 1; 0.5 to 10 parts by weight, 0.01 to
After adding 0.05 mol and a reinforcing agent such as carbon black or the like, kneading and subjecting the rubber composition formed into a desired shape to primary vulcanization in a conventional manner, the temperature is 150 to 200 ° C.
To perform secondary vulcanization for 30 minutes to 6 hours (see Japanese Patent Application Laid-Open No. 7-138383).

[0003] The above method is based on ethylene
A propylene rubber is used, a large amount of a peroxide crosslinking agent is added to the propylene rubber together with a crosslinking aid, and 4,4 or 4 is used as an antioxidant.
-(Α, α-dimethylbenzyl) diphenylamine and 2
-Addition of a mixture of mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole, thereby improving the heat resistance and reducing the compression set of the ethylene-propylene rubber product without reducing the strength thereof. And temperature of 150-200
Since the secondary vulcanization is performed at a temperature of 30 ° C. for 30 minutes to 6 hours, residual peroxide disappears, no odor is generated, the physical properties after aging of the product are improved, and the compression set can be further reduced. .

[0004] However, when the above rubber product is used as a heat exchanger of a piping system for heat sterilization of milk or other beverages or a sealing material for valves, the above rubber product is used in a line for flowing tap water having a high chlorine concentration. The sealing material deteriorates due to the chlorine content (hypochlorite ion, chlorine ion, etc.) in the tap water,
There is a problem that this deterioration increases as the chlorine concentration is increased in order to improve the disinfecting effect.

[0005] After the beverage is heated, CIP washing is performed in which an alkaline solution and an acid solution are alternately passed through the piping system. At that time, an alkaline solution (generally, an aqueous solution of sodium hydroxide or potassium hydroxide) is used. ), Neutralization and washing with an acid solution (generally, an aqueous solution of nitric acid), and rinsing with tap water are performed. In this series of steps, ethylene-propylene rubber may be deteriorated by acid, In that case, there is a problem that the effect of deterioration due to the acid and the deterioration effect due to the chlorine content are more greatly affected, and the life of the rubber is further shortened.

[0006]

SUMMARY OF THE INVENTION The present invention is, like the above-mentioned conventional rubber product, excellent in heat resistance, small in compression set, free of odor, and CIP cleaning routinely performed in the food field. It is intended to provide a chlorine-resistant rubber composition which can be suitably used as a sealing material for piping heat exchangers and valves for heat-sterilizing beverages.

[0007]

The chlorine-resistant rubber composition according to the present invention comprises a blend rubber of ethylene / propylene rubber and hydrogenated acrylonitrile / butadiene rubber.
For 0 parts by weight, 4,4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole in a mixing ratio of 1: 1 to 0.05: 1. A total of 0.1 to 6 parts by weight of the mixed antioxidant,
-10 to 10 parts by weight, 0.005 to 0.05 of peroxide crosslinking agent
It is characterized by adding a reinforcing agent such as mol and carbon black and the like.

The above rubber composition is kneaded as described below,
The rubber product such as a sealing material is formed by performing molding and cross-linking treatment, and the obtained rubber product uses ethylene-propylene rubber such as EPM, EPDM, and a mixture thereof having excellent heat resistance and chemical resistance. In addition, since hydrogenated acrylonitrile / butadiene rubber (hydrogenated NBR) is blended with the ethylene / propylene rubber and used, the chlorine resistance is improved. Sex is maintained. Further, even when the degradation by chlorine is activated in the presence of certain metal ions such as copper ions used in water pipes or copper ions eluted from brass, the hydrogenated N
Since BR effectively captures the above-mentioned metal ions, it is considered from this point that chlorine resistance is also improved.

As in the prior art, a large amount of a peroxide crosslinking agent is added together with a crosslinking aid, and 4,4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole are used as antiaging agents. Alternatively, since a mixture with the zinc salt of 2-mercaptobenzimidazole is added, the heat resistance can be improved and the compression set can be reduced without reducing the strength of the rubber product containing EPDM as a main component. Temperature 150 as described above
By performing the secondary vulcanization at a temperature of 200 ° C. and a time of 30 minutes to 6 hours, the residual peroxide disappears, no odor is generated, and the physical properties after aging of the product are improved.

The preferred mixing ratio of the ethylene / propylene rubber and the hydrogenated NBR is 50 to 95 parts by weight of the ethylene / propylene rubber and 50 to 95 parts by weight of the hydrogenated NBR.
5 parts by weight, especially 60 parts of ethylene / propylene rubber.
Preferred is 40 to 10 parts by weight of hydrogenated NBR to 90 parts by weight. The mixing ratio of ethylene / propylene rubber is 50
If the amount is less than parts by weight, the mechanical properties of the rubber product are excessively deteriorated. If the amount is more than 95 parts by weight, the effect of blending the hydrogenated NBR is not obtained, and the rubber product is easily attacked by CIP cleaning.

As antiaging agents, 4,4- (α, α-
A mixture of (dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole is used. The mixing ratio (weight ratio) of the former and the latter is set in the range of 1/1 to 0.05 / 1, and a total of 0.1 to 6 parts by weight of both is added to the rubber. The former mixing amount is too large and the mixing ratio is 1 /
If it exceeds 1, the compression set becomes large, and if it is too small and the mixing ratio becomes less than 0.05 / 1, sufficient heat aging resistance cannot be obtained. Further, the amount added to rubber is 0.1
If the amount is less than 10 parts by weight, the desired effect cannot be obtained. On the other hand, if the amount exceeds 6 parts by weight, bloom occurs.

Examples of the crosslinking assistant include N, N-m-phenylenedimaleimide, triallyl isocyanate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and polyfunctional compounds generally used in peroxide crosslinking. Methacrylate monomers and the like can be used. The addition amount is 0.5 to 10 parts by weight. When the addition amount is less than 0.5 part by weight, heat resistance is reduced, the compression set becomes large, and when it exceeds 10 parts by weight, However, depending on the intended function, the amount is small when the amount of the crosslinking agent is large, and is large when the amount of the crosslinking agent is small.

As the peroxide crosslinking agent, 1,1-di-t is used.
-Butylperoxy-3,3,5-trimethylcyclohexane, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5
-Dimethyl-2,5-di (t-butylperoxy) hexane, 1,3 bis (t-butylperoxyisopropyl) benzene and the like can be used. The amount added is 0.
When the amount is less than 0.005 mol, the compression set becomes large. On the other hand, when the amount exceeds 0.05 mol, the composition becomes hard, elongation is reduced, and the composition is easily cracked. As the peroxide crosslinking agent, as described in claim 2, it is diluted with an acid-inactive diluent, for example, clay, calcium carbonate, ethylene / vinyl acetate copolymer (EVA) or the like. In this case, the acid resistance of the rubber product is further improved.
The dilution ratio varies depending on the type of the peroxide crosslinking agent, but is preferably 20 to 90%, particularly preferably 30 to 50%.

In addition, compounding agents commonly used in the rubber industry, such as reinforcing agents such as carbon black, zinc oxide, softeners, plasticizers, tackifiers, white fillers, etc., may be appropriately added or omitted. can do.

The rubber, antioxidant, crosslinking aid, peroxide crosslinking agent, carbon black and the like are kneaded according to a conventional method, molded into a desired shape, subjected to primary vulcanization, and then subjected to secondary vulcanization. It is commercialized by performing the next vulcanization. The conditions of the secondary vulcanization are set in the range of 150 to 200 ° C. for 30 minutes to 6 hours depending on the shape and thickness of the product. If the secondary vulcanization temperature is less than 150 ° C or the vulcanization time is less than 30 minutes, bloom tends to occur, the compression set becomes large, and conversely, the vulcanization temperature exceeds 200 ° C. If the vulcanization time exceeds 6 hours, the heat aging proceeds, and the deterioration in physical properties becomes excessive. In particular, when the vulcanization temperature is low, the decomposition of the residual peroxide is delayed, and it takes a long time to volatilize the decomposition products.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 EPDM and hydrogenated NBR are 50/50 to 95 /
5, preferably in a weight ratio of 60/40 to 90/10. For 100 parts by weight of this blend rubber, 4,
An anti-aging agent comprising a mixture of 4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or a zinc salt of 2-mercaptobenzimidazole in a weight ratio of 1/1 to 0.05 / 1. A total of 0.1 to 6 parts by weight, a crosslinking aid of 0.5 to 10 parts by weight, a peroxide crosslinking agent of 0.005 to 0.05 mol, a reinforcing agent such as carbon black and the like are added and kneaded.

After the above-mentioned kneading, the mixture is molded into a desired shape such as a heat exchanger or a sealing material for valves disposed in a piping system for heating milk or other beverages, and subjected to a primary cross-linking treatment according to a conventional method. Secondary crosslinking at a temperature of 150 to 200 ° C. for 30 minutes to 6 hours to obtain a rubber product having heat resistance and chlorine resistance. The obtained rubber product is used as a sealing material for the above heat exchangers and valves. This sealing material has excellent strength and heat resistance, low compression set, no odor, and aging of the product. Since it has good post-physical properties and excellent chlorine resistance, it can be suitably used in a piping system for heat treatment of the above-mentioned beverage which is routinely subjected to CIP cleaning.

Embodiment 2 In the same manner as in Embodiment 1, except that the peroxide cross-linking agent is diluted with an acid-inactive diluent and used, heat resistance and chlorine resistance are excellent. Get rubber products. The obtained rubber product can be used similarly to the rubber product of the first embodiment. However, the acid resistance is further improved.

[0019]

EXAMPLES The following rubbers and additives were used. EPDM: “EPT3045” manufactured by Mitsui Petrochemical Co., Ltd. Hydrogenated NBR: “Zetpol 2” manufactured by Zeon Corporation
010 "Auxiliary agent: zinc oxide Antioxidant A: zinc salt of 2-mercaptobenzimidazole" Nocrack MBZ "manufactured by Ouchi Shinko Chemical Co., Ltd. Antioxidant B: 4,4- (α, α-dimethylbenzyl)
Diphenylamine "Nocrack CD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Internal release agent A: Calcium stearate Internal release agent B: Special fatty acid amide, "Plastrogin" manufactured by Fujisawa Pharmaceutical Co., Ltd. Reinforcing agent: carbon black, Tokai Carbon Co., Ltd. Company "SEIST G-116" Activator: Synthetic hydrosaltite, Kyowa Chemical Industry Co., Ltd. "DHT-4A-2" Plasticizer: Hydrogenated polyisoprene rubber "Kuraray Co., Ltd." KURAPREN LIR-290 Cross-linking aid : Triallyl isocyanurate, "Taik" manufactured by Nippon Kasei Co., Ltd. Peroxide crosslinking agent A: Mixed powder of dicumyl peroxide diluted to 40% concentration with clay, "Di" manufactured by Hercules, USA
-Cup40KE "Peroxide crosslinking agent B: 1,3-bis (tert-butylperoxyisopropyl) benzene," Perbutyl P "manufactured by NOF Corporation Peroxide crosslinking agent C: Dicumyl peroxide in calcium carbonate at a concentration of 40% with calcium carbonate Diluted powder, "Di-Cup40C" manufactured by Hercules, USA

The above rubber and additives were kneaded with the composition shown in Table 1 (units by weight) to form a sheet having a thickness of 2 mm, and then subjected to primary vulcanization (170 ° C. × 20 minutes) and secondary vulcanization (implementation). (Example is 150 ° C x 4 hours, Comparative Example is 200 ° C x 4 hours)
To obtain samples of Examples 1 to 6 and Comparative Examples 1 to 3. However, in Table 1, the peroxide crosslinking agents A and C
13 parts was 0.019 mol (theoretical active acid amount 9.26)
%), And 3 parts of the peroxide crosslinking agent B corresponds to 0.009 mol (5.92% of the theoretically active acidic amount).

Table 1 Actual 1 Actual 2 Actual 3 Actual 4 Ratio 1 Actual 5 Ratio 2 Ratio 3 Actual 6 EPDM 50 75 90 95 100 75 100 100 75 Hydrogenated NBR 50 25 10 5 0 25 0 0 25 Zinc oxide 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Internal release agent A 1 1 1 1 1 0.5 0.5 1 1 Internal release agent B 1 1 1 1 1 0.5 0.5 1 1 Anti-aging agent A 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 Anti-aging agent B 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Carbon black 34 45 52 55 58 47 64 45 45 Plasticizer 5 5 5 5 5 5 5 5 5 5 Activator 5 5 5 5 5 5 5 5 5 5 Crosslinking aid 1 1 1 1 1 1 1 1 1 Peroxide crosslinking agent A 13 13 13 13 13 0 0 0 0 Peroxide crosslinking agent B 0 0 0 0 0 3 3 0 0 Peroxide crosslinking agent C 0 0 0 0 0 0 0 13 13

For these samples, JIS-K-63
The initial physical properties were measured according to No. 01. Next, the sample was left in an atmosphere at a temperature of 175 ° C. for 72 hours, and the physical properties after aging were measured in the same manner. The above sample was added to an aqueous solution of sodium hypochlorite (concentration: 0.1%) at 90 ° C. for 72 hours.
After soaking for a time, the physical properties (physical properties after chlorination) were tested. However, the surface area of the sample per liter of the aqueous solution of sodium hypochlorite was 350 cm ² . In addition, the adhesive surface of a commercially available cellophane tape was superimposed on the surface of the sample after immersion in the above-described aqueous solution of sodium hypochlorite, and pressed with a load of 1 kgf / cm ² , and then the cellophane tape was peeled off. The amount of carbon black deposited and attached to the tape was visually observed. Table 2 shows the results.

Table 2 Actual 1 Actual 2 Actual 3 Actual 4 Ratio 1 Actual 5 Ratio 2 Ratio 3 Actual 6 Initial physical properties Tensile strength (kgf / cm ² ) 150 179 182 193 193 193 185 185 195 183 Elongation at break (%) 210 190 170 170 180 200 180 180 170 hardness (JIS-A) 82 81 82 81 80 80 80 80 80 after aging properties tensile strength ^{(kgf / cm 2) 139 179} 188 180 177 139 177 177 147 elongation at break (%) 150 160 160 150 160 130 180 160 120 Compression set (%) 42.1 38.9 38.4 36.0 30.0 38.9 29.9 29.8 35.9 Hardness (JIS-A) 88 81 82 81 81 80 80 81 85 Physical properties after chlorination Tensile strength (kgf / cm) ² ) 108 145 159 155 159 159 177 141 161 140 Elongation at break (%) 160 170 150 140 160 170 150 150 140 Weight change rate (%) +4.9 +2.1 +2.0 +1.4 +1.0 +0.3 +2 .5 +1.3 +2.1 Hardness (JIS-A) 80 80 83 82 80 79 78 80 81 Carbon adhesion None None None Trace amount None Large amount Large amount None

As is apparent from Tables 1 and 2, Examples 1 to 6 all had good physical properties after aging and small compression set. In Examples 1, 2, 3, 5, and 6, no carbon black was precipitated after chlorination, and only a small amount of precipitation was observed in Example 4 in which the blended amount of hydrogenated NBR was 5 parts. On the other hand, in Comparative Examples 1 to 3 in which no hydrogenated NBR was blended, a large amount of precipitation was observed in each case. Further, the acid resistance test was performed on Examples 2, 5, and 6, which differed only in the type of the peroxide crosslinking agent and had substantially the same other composition. That is, it was immersed in a 5% hydrochloric acid aqueous solution at 90 ° C. for 72 hours, and the characteristics after that were compared. The acid resistance tests of Comparative Examples 1 and 3 were performed in the same manner. The results are shown in Table 3 below.

Table 3 Actual 2 Ratio 1 Actual 5 Ratio 3 Actual 6 Tensile strength (kgf / cm ² ) 146 150 117 112 124 Elongation at break (%) 180 140 190 120 120 Rate of change in weight (%) +11.3 +6. 8 +22.3 +11.7 +19.4 Hardness (JIS-A) 76 78 70 75 72

As shown in Table 3, the acid resistance was good in Examples 2 and 6 using a peroxide crosslinking agent diluted with an acid resistant diluent. In particular, a peroxide crosslinking agent A diluted with clay was used. Example 2 was the best. Note that a similar tendency was observed in the comparative example.

[0027]

As described above, according to the first aspect of the present invention, the heat resistance is excellent, the compression set is small,
Suitable for sealing materials such as pipe heat exchangers and valves that heat sterilize beverages that are routinely subjected to CIP cleaning because they can produce rubber products with no odor and excellent chlorine resistance. It is. According to the second aspect of the invention, the acid resistance is further improved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 9/02 LBG C08L 9/02 LBG

Claims (2)

[Claims] 1. A blend rubber 10 of ethylene / propylene rubber and hydrogenated acrylonitrile / butadiene rubber
With respect to 0 parts by weight, 4,4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole are mixed at a mixing ratio of 1: 1 to 0.05: 1. A total of 0.1 to 6 parts by weight of the mixed antioxidant,
-10 to 10 parts by weight, 0.005 to 0.05 of peroxide crosslinking agent
What is claimed is: 1. A chlorine-resistant rubber composition comprising a mole, a reinforcing agent such as carbon black, and the like. 2. The chlorine-resistant rubber composition according to claim 1, wherein the peroxide crosslinking agent is diluted with a diluent inert to an acid.