Protein-removed natural rubber composition

Abstract

To provide a protein-removed natural rubber composition which may provide a cross-linked object which has a small degree of expansion in immersion in water, and a low degree of whitening.SOLUTION: There is provided a protein-removed natural rubber composition which includes: a protein-removed natural rubber in which, a nitrogen content measured by a Kjeldahl method regulated by JIS K-6451-2 corresponding to ISO 1407 is 0.001% being a detection limit of the nitrogen, or lower; and a sulfur-based cross-linking agent. A natural rubber cross-linked object formed of a cross-linked object of the protein-removed natural rubber composition is effectively used as a rubber product which is used in contact with water, for example, an aqueous seal material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a protein-removed natural rubber composition. More specifically, it relates to a protein-removed natural rubber composition that provides a crosslinked product with a small degree of swelling and bloom (whitening) during water immersion.

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. In addition, there is also a problem that the formulation precipitates white on the rubber surface during water immersion, significantly damaging the appearance.

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

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 protein-removed natural rubber composition that can provide a crosslinked product with a small degree of swelling and bloom (whitening) during water immersion.

Means for Solving the Problems

[0007] The object of the present invention is to provide a protein-removed natural rubber composition containing a protein-removed natural rubber and a sulfur-based crosslinking agent, wherein the nitrogen content measured by the Kjeldahl method (JIS K-6451-2 corresponding to ISO 1407) is 0.001 Weight % or less, which is the detection limit thereof.

Advantages of the Invention

[0008] A protein-removed natural rubber composition obtained by blending a sulfur-based crosslinking agent with a protein-removed natural rubber can provide a crosslinked product with a small degree of swelling and bloom (whitening) during water immersion.

Brief Description of the Drawings

[0009]

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Modes for Carrying Out the Invention

[0010] The protein-removed natural rubber composition according to the present invention comprises a protein-removed natural rubber and a sulfur-based crosslinking agent.

[0011] In the present invention, the protein-removed natural rubber means that the 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 the value) is 0.001Weight %The following substantially protein-free natural rubber is meant.

[0012] 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 an 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, a carboxylic acid ester having an alkyl group with 1 to 5 carbon atoms, etc. to natural rubber latex, subjecting the protein in the latex to a denaturation treatment and then removing it.

[0013] Also, such protein-removed natural rubber has a protein content in the solid rubber measured by the improved Lowry method at a level of 0.5 μg / g or less.

[0014] 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 it with a gas burner for about 30 minutes until the color of the solution became 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 through it, and used a 10 ml of 2 w / v% boric acid aqueous solution in a conical flask as a receiver to capture ammonia. Stopped the distillation when the internal volume of the conical flask of the steam distillation apparatus reached about 20 ml. Washed the inside of the Liebig condenser with distilled water, flowed the washing solution into the conical 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 rate (%) = 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).

[0015] As the sulfur-based crosslinking agent, soluble or insoluble sulfur or sulfur-containing crosslinking accelerators are used. As sulfur, not only elemental sulfur but also high-molecular sulfur and the like are used.

[0016] As the sulfur-containing crosslinking accelerators, for example, thiuram-based such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and various sulfur-containing compounds such as thiazole-based, sulfenamide-based, guanidine-based, dithiocarbamic acid-based, and xanthogenic acid-based are used.

[0017] When sulfur or a sulfur-containing crosslinking accelerator is used alone, it is 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. When both are used in combination, they are used in an arbitrary proportion within the above range of proportions.

[0018] Furthermore, in this case, crosslinking aids such as zinc oxide, 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.

[0019] 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 keto-amine reaction products such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and other optional components are appropriately blended and used.

[0020] In the protein-removed natural rubber composition, various reinforcing agents or fillers can be blended and used in an amount of 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 proportion of the reinforcing agent or filler improves the breaking strength and modulus of the crosslinked product, but blending in a larger proportion may impair the elongation at break and compression set characteristics.

[0021] As the reinforcing agent or filler, generally various grades of carbon black, preferably FEF carbon black, and white fillers such as silica produced by dry or wet methods are used. When silica is used, it is preferable to use a silane coupling agent in combination.

[0022] The protein-removed natural rubber composition is prepared by kneading the protein-removed natural rubber and other compounding ingredients with a sealed kneader or an open roll.

[0023] The crosslinking of the protein-removed natural rubber composition is carried out by heating with a hot press at about 140 to 200 °C for about 3 to 30 minutes according to the type of crosslinking agent used.

[0024] The natural rubber crosslinked product composed of the crosslinked product of the obtained protein-removed natural rubber composition 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

[0025] Next, the present invention will be described with reference to examples.

[0026] Reference Example To 100 parts by weight of natural rubber latex (product of Malaysian Golden Hope, 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.

[0027] 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.

[0028] The operation of this 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.

[0029] The obtained natural rubber [PFNR] had a nitrogen content rate measured by the Kjeldahl method (JIS K-6451 -2 ) 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.

[0030] Example 1 100 parts by weight of PFNR obtained in the reference example FEF carbon black 50 〃 Sulfur 1 〃 Vulcanization accelerator (product of Ouchi Shinko Chemical Industry Co., Ltd., Nocceler CZ) 1.25 〃 Vulcanization accelerator (product of Ouchi Shinko Chemical Co., Ltd., Nocceler TT) 0.63 〃 Vulcanization aid zinc oxide 5 〃 Vulcanization aid stearic acid 1 〃 Antioxidant (product of Kawaguchi Chemical Industry Co., Ltd., Antage RD) 2 〃 Of the above components, PFNR was masticated in a closed kneader, and then the compounding components other than the vulcanization accelerator were added and kneaded at 120° C. Furthermore, the vulcanization accelerator was added and kneaded using an open roll to obtain a protein-removed natural rubber composition.

[0031] The resulting protein-removed natural rubber composition was crosslinked in a hot press at 150° C. until the time corresponding to t90 on the vulcanization curve, to obtain a crosslinked sheet having a thickness of 2 mm. The crosslinked sheet was subjected to the following tests. Volume change rate: Compliant with JIS K6258 (liquid resistance test: 180℃, 40 hours) JIS No. 6 test piece and 2 x 5 cm test piece for measuring volume change were placed on the rubber sheet. The rubber samples were punched out from the test tubes, and three pieces were cut into each set. Add 100ml of ion-exchanged water and cover with aluminum foil. After the test, the test tube was placed in a thermostatic chamber at a specified temperature. The test piece was then removed from the container and wiped with nonwoven fabric to remove the moisture. The weight of the specimen was calculated using Archimedes' principle. The rate of change in volume was calculated. Less than 5% is considered a pass, and more than 5% is considered a fail. Appearance: See Figure 1 Appearance brightness: The brightness (V) of the rubber surface is measured by photographing the surface and dividing the image into HSV space. evaluation In the above liquid resistance test, the state without bloom before immersion is 0, and the brightness is 100. % is set to 100

[0032] Example 2 In Example 1, sulfur and the crosslinking accelerator Noccelaer CZ were not used, and the crosslinking accelerator Noccelaer TT was changed to 4 parts by weight.

[0033] Comparative Example 1 In Example 1, instead of the PFNR obtained in the reference example, the same amount (100 parts by weight) of deproteinized NR (imported from Toyo Chemical Plus; nitrogen content 0.019% by weight) was used. However, the crosslinking accelerator Nocceler CZ was changed to 1 part by weight and the Nocceler TT was changed to 0.5 part by weight.

[0034] Comparative Example 2 Comparative Example 1 In, sulfur and the crosslinking accelerator Nocceler CZ were not used. Also, the crosslinking accelerator Nocceler TT was changed to 4 parts by weight.

[0035] Comparative Example 3 In Example 1, instead of the PFNR obtained in the reference example, the same amount (100 parts by weight) of natural rubber (imported from Toyo Chemical Plus; nitrogen content 0.480% by weight) was used in the same amount (100 parts by weight). However, the crosslinking accelerator Nocceler CZ was changed to 0.88 part by weight and the Nocceler TT was changed to 0.44 part by weight.

[0036] Comparative Example 4 Comparative Example 3 In, sulfur and the crosslinking accelerator Nocceler CZ were not used. Also, the crosslinking accelerator Nocceler TT was changed to 4 parts by weight.

[0037] The results obtained in each of the above examples and comparative examples are as follows In the table shown. Table Measurement item Example-1 Example-2 Ratio-1 Ratio-2 Ratio-3 Ratio-4 Volume change rate (%) 2.1 2.1 3.6 2.8 6.0 5.6 Same judgment ○ ○ ○ ○ × × Appearance Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Appearance lightness (%) 18 20 35 66 69 75

Claims

1. A protein-removed natural rubber composition comprising a protein-removed natural rubber having a nitrogen content of 0.001% by weight or less, which is the detection limit, as measured by the Kjeldahl method specified in JIS K-6451-2, which corresponds to ISO 1407, and a sulfur-based crosslinking agent.

2. The protein-removed natural rubber composition of claim 1, further comprising carbon black and / or a white filler.

3. The protein-removed natural rubber composition according to claim 2, wherein carbon black and / or white filler is blended in an amount of 90 parts by weight or less per 100 parts by weight of the protein-removed natural rubber.

4. The protein-removed natural rubber composition according to claim 3, wherein the carbon black and / or white filler is blended in an amount of 35 to 60 parts by weight per 100 parts by weight of the protein-removed natural rubber.

5. A cross-linked natural rubber product comprising a cross-linked product of the protein-removed natural rubber composition described in any one of claims 1 to 4.

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