Protein-removed natural rubber crosslinked product

Abstract

To provide a deproteinized crosslinked natural rubber that exhibits small volume expansion and little deterioration in physical properties when immersed in water.SOLUTION: A deproteinized crosslinked natural rubber is a crosslinked product of a rubber composition containing deproteinized natural rubber and an organic peroxide crosslinking agent, and has a volume change of 4.3% or less after a water resistance test at 80°C for 500 hours in accordance with JIS K-6258. This deproteinized crosslinked natural rubber is effectively used as a rubber product used in contact with water, such as a seal for a water system.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a protein-removed natural rubber Crosslinking material. More specifically, it relates to a natural rubber material with the removal of volume expansion and physical property degradation during water immersion Low protein material. Crosslinking

Background Art

[0002] As rubber materials used in water-related applications, synthetic rubbers such as EPDM, (hydrogenated) NBR, and fluororubber are generally used. However, from the perspective of resource sustainability, the use of plant-derived natural rubber is desired

[0003] However, since natural rubber contains hydrophilic proteins in its structure, there is a problem that its volume increases during use

[0004] Although a protein-free natural rubber obtained by separating proteins from natural rubber has been proposed in Patent Document 1, such a tendency is still observed in this case

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a natural rubber material with the removal of volume expansion and physical property degradation during water immersion Low protein material. Crosslinking

Means for Solving the Problems

[0007] ​​The object of the present invention is a crosslinked product of a rubber composition containing a protein-removed natural rubber and an organic peroxide crosslinking agent, which complies with JIS K-6258 and has a volume change rate of 4.3% or less after a water resistance test at 80°C for 500 hours. , used as a seal for water systems This is achieved by a crosslinked product of a protein-removed natural rubber.

Effects of the Invention

[0008] When an organic peroxide crosslinking agent is compounded with a protein-removed natural rubber A crosslinked product of a rubber composition, compliant with JIS K-6258, with a volume change rate of 4.3% or less after a water resistance test at 80°C for 500 hours protein-removed natural rubber Crosslinking effectively prevents volume expansion during water immersion with almost no deterioration in physical properties.

Modes for Carrying Out the Invention

[0009] The protein-removed natural rubber according to the present invention Crosslinking contains a protein-removed natural rubber and an organic peroxide crosslinking agent.

[0010] In the present invention, the protein-removed natural rubber refers to natural rubber having a nitrogen content measured by the Kjeldahl method (in accordance with JIS K6451-2 corresponding to ISO 1407; the sample is wet-decomposed using a mixed catalyst of potassium sulfate and copper(II) sulfate and sulfuric acid, the nitrogen in the sample is converted to ammonium sulfate, strong alkali is added thereto to liberate ammonia, which is steam-distilled and introduced into a boric acid aqueous solution, and then titrated with sulfuric acid or hydrochloric acid to determine the amount of ammonia, and the nitrogen content is calculated from that value). Protein removal of 0.019 wt% or less It refers to natural rubber.

[0011] Such protein-removed natural rubber is obtained by adding a urea-based compound, preferably urea represented by the general formula RNHCONH2 (R: hydrogen atom or alkyl group having 1 to 5 carbon atoms) or its lower alkyl derivative, an anionic, nonionic or cationic surfactant, and a polar organic solvent, preferably a water-miscible polar organic solvent such as an aliphatic alcohol having an alkyl group with 1 to 5 carbon atoms, a ketone having 3 to 4 carbon atoms, an aliphatic carboxylic acid having 1 to 5 carbon atoms, or a carboxylic acid ester having an alkyl group with 1 to 5 carbon atoms, to natural rubber latex, denaturing the protein in the latex, and then removing it.

[0012] In addition, such protein-removed natural rubber has a protein content in the solid rubber measured by the modified Lowry method of 0.5 μg / g or less.

[0013] Kjeldahl method (JIS K6451-2): Weighed 0.1 g of rubber, 0.65 g of catalyst (potassium sulfate: copper(II) sulfate pentahydrate: selenium = weight ratio 15:2:1), and 2.5 ml of concentrated sulfuric acid into a Kjeldahl flask, and heated with a gas burner for about 30 minutes until the color of the solution turned green. Assembled a steam distillation apparatus, put an appropriate amount of distilled water into a 1 L flask, heated it with an oil bath, and washed a 300 ml two-necked flask and a Liebig condenser with steam. Using 20 ml of distilled water, transferred the contents of the Kjeldahl flask into the two-necked flask, added 10 ml of 67 w / v% sodium hydroxide aqueous solution and 10 ml of distilled water into the two-necked flask, passed steam, and used a 10 ml of 2 w / v% boric acid aqueous solution in a triangular flask as a receiver to capture ammonia. Stopped the distillation when the volume of the contents of the triangular flask in the steam distillation apparatus reached about 20 ml. Washed the inside of the Liebig condenser with distilled water, flowed the washing solution into the triangular flask, and titrated with 0.005 mol / L sulfuric acid using methyl red as an indicator to determine the nitrogen content in the rubber sample. The following formula was used to calculate the nitrogen content. Nitrogen content (%) = V / 1000 (L) × N (mol / L -1 ) × 14 × 2 (g / mol -1 ) × 1 / w (g -1 ) × 100 Here, V is the titration volume of 0.005 mol / L sulfuric acid, w is the mass of the rubber, and N is the value obtained by multiplying the concentration of the 0.005 mol / L sulfuric acid used in the titration by the factor (1.004).

[0014] Examples of the organic peroxide crosslinking agent include dialkyl peroxides such as dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy) Hexyne-3 , 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,3-bis(tert-butylperoxyisopropyl)benzene, etc., diacyl peroxides such as benzoyl peroxide, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, peroxy esters such as tert-butylperoxyisopropyl carbonate, etc. are used, and dicumyl peroxide is preferably used.

[0015] These organic peroxide crosslinking agents are used in a proportion of about 0.1 to 10 parts by weight, preferably about 0.2 to 5 parts by weight, per 100 parts by weight of the protein-removed natural rubber.

[0016] Together with the organic peroxide crosslinking agent, polyfunctional unsaturated compounds such as triallyl isocyanurate, triallyl cyanurate trimethylolpropane trimethacrylate, etc. can also be used in combination in an amount of about 10 parts by weight or less, preferably about 0.2 to 5 parts by weight, per 100 parts by weight of the protein-removed natural rubber.

[0017] Furthermore, crosslinking aids such as zinc white, magnesium oxide, litharge, etc. or stearic acid, zinc stearate, etc. can also be added and used in a proportion of about 0.1 to 10 parts by weight, preferably about 0.2 to 5 parts by weight, per 100 parts by weight of the protein-removed natural rubber.

[0018] In addition, anti-aging agents represented by p-phenylenediamine-based compounds such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-octyl-N'-phenyl-p-phenylenediamine, N,N'-diallyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di(1,4-dimethylpentyl)-p-phenylenediamine, and ketone-amine reaction products such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and other optional components are appropriately blended and used.

[0019] Rubber composition Among them, various reinforcing agents or fillers can also be used by blending about 90 parts by weight or less, preferably about 35 to 60 parts by weight, per 100 parts by weight of the protein-removed natural rubber. The ratio of the reinforcing agent or filler improves the breaking strength and modulus of the crosslinked product, but blending at a higher ratio may impair the elongation at break and compression set characteristics.

[0020] As the reinforcing agent or filler, generally various grades of carbon black, preferably FEF carbon black, and white fillers such as silica produced by the dry method or wet method are used. When silica is used, it is preferable to use a silane coupling agent in combination.

[0021] Rubber composition is prepared by kneading the protein-removed natural rubber and other compounding components with a sealed kneader or an open roll.

[0022] Rubber composition The crosslinking is carried out by heating at about 140 to 200 °C with a hot press for about 3 to 30 minutes according to the type of crosslinking agent used.

[0023] The obtained The protein-removed natural rubber crosslinked product is is effectively used as a rubber product that comes into contact with water, particularly a sealing material for water systems, such as a sealing material for water supply.

Examples

[0024] Next, the present invention will be described with reference to examples.

[0025] Reference Example To 100 parts by weight of natural rubber latex (product of Malaysian Golden Hope Co., imported by Toyo Chemical Plus; rubber content concentration 60.2% by weight, ammonia content 0.7% by weight), 1 part by weight of sodium dodecyl sulfate and 0.1 part by weight of urea were added, and the mixture was stirred at room temperature for 90 minutes.

[0026] Thereafter, the latex was centrifuged at 15 °C and 9000 rpm for 30 minutes to separate the upper cream layer. Distilled water was added to the cream layer, 0.5 part by weight of sodium dodecyl sulfate and 2.5 parts by weight of acetone were added, and the mixture was stirred for 1 hour.

[0027] This operation of centrifugation and redispersion (adjusting the rubber content concentration to 30% by weight with a 1% anionic surfactant - 0.025% ethanol aqueous solution) was repeated a total of 3 times to prepare a protein-removed natural rubber latex, and this latex was dried to obtain a protein-removed natural rubber.

[0028] The obtained natural rubber [PFNR] was According to the above conditions measured by the Kjeldahl method (JIS K-6451) and the nitrogen content was at a level of 0.001 Weight % or less, which is the detection limit, and the protein amount measured by the modified Lowry method was at a level of 0.5 μg / g or less, which is the detection limit.

[0029] Example 1 100 parts by weight of PFNR obtained in the reference example FEF carbon black 50 〃 Dicumyl peroxide 2.5 〃 Crosslinking aid zinc oxide 5 〃 Crosslinking aid stearic acid 1 〃 Antioxidant (Antage RD, product of Kawaguchi Chemical Industry) 2 〃 Among the above components, after kneading PFNR with a sealed kneader, compounding components other than dicumyl peroxide were added and kneaded at 120 °C. Further, dicumyl peroxide was added and kneaded with an open roll to obtain a protein-removed natural rubber composition.

[0030] The obtained protein-removed natural rubber composition was heat-crosslinked at 170 °C for 7 minutes and crosslinked until the time corresponding to t90 of the vulcanization curve to obtain a crosslinked sheet with a thickness of 2 mm. The following tests were conducted on the crosslinked sheet. Normal values (hardness, tensile strength, elongation at break): Conforming to JIS K-6253 and K-6251 Water immersion test : Conforming to JIS K-6258 80 °C , 500 hours Measure the change in normal values and volume change rate after water immersion. JIS No. 6 test pieces and test pieces of 2×5 cm for measuring volume change were punched out from the rubber sheet, and three pieces were made into one set. Rubber samples were put into test tubes, 100 ml of ion-exchanged water was poured in and covered with aluminum foil. Thereafter, the test tubes were left in a constant temperature bath at a predetermined temperature. The test pieces after the test were taken out from the water, and the moisture was wiped off with a non-woven fabric. The volume was calculated using Archimedes' principle from the weight when the test piece was suspended in water, and the change rate with respect to the volume before the test was calculated. and the change rate with respect to the volume before the test was calculated. and the change rate with respect to the volume before the test was calculated.

[0031] Example 2 In Example 1, instead of the PFNR obtained in the reference example, the same amount (100 parts by weight) of protein-removed NR (imported product of Toyo Chemical Plus; nitrogen content 0.019% by weight) was used.

[0032] Comparative Example In Example 1, instead of the PFNR obtained in the reference example, the same amount (100 parts by weight) of natural rubber (imported product of Toyo Chemical Plus; nitrogen content 0.480% by weight) was used.

[0033] The results obtained in each of the above Examples and Comparative Examples are shown in the following table. Table Measurement item Example 1 Example 2 Comparative example 〔Normal value〕 Hardness (Durometer A) 53 59 61 Tensile strength (MPa) 20.3 23.4 24.5 Elongation at break (%) 340 380 350 〔After immersion in water at 80°C for 500 hours〕 Hardness change rate (%) -6 -14 -10 Tensile strength change rate (%) -10 -16 -32 Elongation at break change rate (%) +3 -8 -14 Volume change rate (%) +4.1 +4.3 +9.1

[0034] From the above results, it can be seen that when PFNR or protein - removed NR is used instead of natural rubber, the volume change rate after immersion in water at 80°C for 500 hours is small, and especially for PFNR, the change rates of various physical property values are also suppressed to be small.

Claims

1. A cross-linked product of a rubber composition comprising protein-removed natural rubber and an organic peroxide cross-linking agent, the cross-linked product being used as a seal for aqueous systems and having a volume change of 4.3% or less after a water resistance test at 80°C for 500 hours in accordance with JIS K-6258.

2. 2. The cross-linked protein-removed natural rubber according to claim 1, wherein the protein-removed natural rubber has a nitrogen content of 0.019% by weight or less as measured by the Kjeldahl method specified in JIS K-6451, which corresponds to ISO 1407.

3. 2. The cross-linked product of protein-removed natural rubber according to claim 1, wherein the rubber composition further comprises a reinforcing agent or a filler.

4. 4. The cross-linked product of protein-removed natural rubber according to claim 3, wherein the reinforcing agent or filler is blended in an amount of 90 parts by weight or less per 100 parts by weight of the protein-removed natural rubber.

5. 4. The cross-linked product of protein-removed natural rubber according to claim 3, wherein the reinforcing agent or filler is blended in an amount of 35 to 60 parts by weight per 100 parts by weight of the protein-removed natural rubber.

6. A seal for aqueous systems which is a cross-linked product of protein-removed natural rubber as described in claim 1.