Cross-linked natural rubber

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 cross-linked object of a rubber composition including, a protein-removed natural rubber and a sulfur-based cross linking agent, the cross-linked object of the rubber composition is a natural rubber cross-linked object in which, a volume change ratio after a liquid-resistance test at 180°C for 40 hours in accordance with JIS K-6258 is less than 5%. The natural rubber cross-linked object is effectively used as a rubber product which is used in contact with water, especially, an aqueous seal material, for example, a seal material for water supply.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to Cross-linked natural rubber More specifically, the present invention relates to a method for producing a cellulose acylate having a small degree of swelling and blooming (whitening) when immersed in water. Cross-linked natural rubber Regarding. [Background technology]

[0002] The rubber materials used in wet areas are generally synthetic rubbers such as EPDM, (hydrogenated) NBR, and fluororubber, but from the perspective of resource sustainability, the use of plant-derived natural rubber is desirable.

[0003] However, natural rubber has the problem that its volume increases during use because it contains hydrophilic proteins in its structure, and there is also the problem that the compound precipitates as a white deposit on the rubber surface when immersed in water, significantly impairing its appearance.

[0004] Patent Document 1 proposes protein-free natural rubber obtained by separating proteins from natural rubber, but even in this case such a tendency is still observed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO 2011 / 027739 A1 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide a method for producing a sintered product which has a small degree of swelling and blooming (whitening) when immersed in water. Cross-linked natural rubber The purpose of this invention is to provide [Means for solving the problem]

[0007] The object of the present invention is to The nitrogen content measured by the Kjeldahl method specified in JIS K-6451-2, which corresponds to ISO 1407, is 0.019% by weight or less.This is achieved by a cross-linked product of a rubber composition containing deproteinized natural rubber and a sulfur-based cross-linking agent, which has a volume change of less than 5% after a liquid resistance test at 180°C for 40 hours in accordance with JIS K-6258. Effect of the Invention

[0008] The present invention Deproteinized natural rubber made by blending deproteinized natural rubber with a sulfur-based crosslinking agent crosslinked product is the degree of expansion and blooming (whitening) when immersed in water. is small . [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an external view of Example 1 after immersion in water. [Diagram 2] FIG. 1 is an external view of Example 2 after immersion in water. [Diagram 3] FIG. 3 is an external view of Example 3 after immersion in water. [Figure 4] FIG. 4 is an external view of Example 4 after immersion in water. [Diagram 5] FIG. 1 is an external view of Comparative Example 1 after immersion in water. [Figure 6] FIG. 1 is an external view of Comparative Example 2 after immersion in water. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention natural Rubber crosslinked product comprises protein-removed natural rubber and a sulfur-based crosslinking agent.

[0011] In the present invention, deproteinized natural rubber is natural rubber having a nitrogen content of 0.01 to 0.01%, as measured by the Kjeldahl method (based on JIS K6451-2, which corresponds to ISO 1407; a 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, a strong alkali is added to the sample, and the liberated ammonia is subjected to steam distillation, introduced into an aqueous boric acid solution, and then titrated with sulfuric acid or hydrochloric acid to determine the amount of ammonia, from which the nitrogen content is calculated). 0.019% by weight or less, preferably the detection limit of 0.001 weight This refers to natural rubber that is substantially protein-free (less than 100%).

[0012] Such protein-removed natural rubber can be obtained by adding a urea compound, preferably urea represented by the general formula RNHCONH2 (R: hydrogen atom or an alkyl group having 1 to 5 carbon atoms) or a lower alkyl derivative thereof, 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 having 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 carboxylate ester having an alkyl group having 1 to 5 carbon atoms, to natural rubber latex, and then denaturing and removing the proteins in the latex.

[0013] In addition, such protein-removed natural rubber has a protein content in the solid rubber of 0.5 μg / g or less as measured by the modified Lowry method.

[0014] Kjeldahl method (JIS K6451-2): 0.1g of rubber, 0.65g of catalyst (potassium sulfate: copper(II) sulfate pentahydrate: selenium = weight ratio 15:2:1), and 2.5ml of concentrated sulfuric acid were weighed and placed in a Kjeldahl flask, and heated with a gas burner for about 30 minutes until the solution turned green. A steam distillation apparatus was assembled, and an appropriate amount of distilled water was placed in a 1L flask, which was then heated in an oil bath, and the 300ml two-neck flask and Liebig condenser were washed with steam. The contents of the Kjeldahl flask were transferred into the two-neck flask using 20ml of distilled water, and 10ml of 67w / v% sodium hydroxide aqueous solution and 10ml of distilled water were added to the two-neck flask, and steam was passed through. Ammonia was captured using an Erlenmeyer flask containing 10ml of 2w / v% boric acid aqueous solution as a receiver. The distillation was stopped when the content of the Erlenmeyer flask in the steam distillation apparatus reached about 20ml. The inside of the Liebig condenser was washed with distilled water, and the washings were poured into an Erlenmeyer flask. The nitrogen content in the rubber sample was determined by titration with 0.005 mol / L sulfuric acid using methyl red as an indicator. The nitrogen content was calculated using the following formula. Nitrogen content (%) = V / 1000(L)×N(molL -1 )×14×2(gmol -1 )×1 / w(g -1 ) x 100 Here, V is the titration amount of 0.005 mol / L sulfuric acid, w is the mass of rubber, and N is the concentration of 0.005 mol / L sulfuric acid used in the titration multiplied by a factor (1.004).

[0015] As the sulfur-based crosslinking agent, soluble or insoluble sulfur or a sulfur-containing crosslinking accelerator is used. As the sulfur, not only elemental sulfur but also polymeric sulfur and the like are used.

[0016] Examples of the sulfur-containing crosslinking accelerator that can be used include thiuram-based compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and dipentamethylenethiuram disulfide, as well as various sulfur-containing compounds such as thiazole-based compounds, sulfenamide-based compounds, guanidine-based compounds, dithiocarbamic acid-based compounds, and xanthogenic acid-based compounds.

[0017] When sulfur or a sulfur-containing crosslinking accelerator is used alone, it is used in a ratio 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, and when both are used in combination, they are used in any ratio within the above range.

[0018] Furthermore, in this case, a crosslinking aid such as zinc oxide, magnesium oxide, litharge, or stearic acid or zinc stearate can be added in an amount 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 such as p-phenylenediamines 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, and N,N'-di(1,4-dimethylpentyl)-p-phenylenediamine, and ketone-amine reaction products such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, as well as other optional ingredients may be appropriately blended and used.

[0020] The protein-removed natural rubber composition may contain up to about 90 parts by weight, preferably about 35 to 60 parts by weight, of various reinforcing agents or fillers 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 a larger proportion may impair the breaking elongation and compression set properties.

[0021] As the reinforcing agent or filler, generally, various grades of carbon black, preferably FEF carbon black, white filler such as silica produced by dry method or wet method is 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 in a sealed kneader or open roll.

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

[0024] The resulting cross-linked natural rubber composition is effectively used as a rubber product which is used in contact with water, particularly as a sealing material for water systems, for example a sealing material for water supply systems. EXAMPLES

[0025] The present invention will now be described with reference to examples.

[0026] Reference example To 100 parts by weight of natural rubber latex (product of Malaysia Golden Hope Pvt. Ltd., imported by Toyotsu Chemiplas; rubber 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 stirred at room temperature for 90 minutes.

[0027] The latex was then centrifuged at 15°C and 9000 rpm for 30 minutes to separate the upper cream layer. Distilled water was added to the cream layer, and 0.5 parts by weight of sodium dodecyl sulfate and 2.5 parts by weight of acetone were added, followed by stirring for 1 hour.

[0028] This centrifugation and redispersion process (rubber concentration was adjusted to 30% by weight using 1% anionic surfactant-0.025% ethanol aqueous solution) was repeated a total of three times to prepare protein-removed natural rubber latex, which was then dried to obtain protein-removed natural rubber.

[0029] The obtained natural rubber (PFNR) was analyzed by the Kjeldahl method (JIS K-6451 -2 ) was found to be below the detection limit of 0.001%, and the protein amount measured by the modified Lowry method was found to be below the detection limit of 0.5 μg / g.

[0030] Example 1 PFNR obtained in the reference example 100 parts by weight FEF Carbon Black 50 〃 Sulfur 1 〃 Crosslinking accelerator (Ouchi Shinko Chemical Industry Products Noccela CZ) 1.25 Same Crosslinking accelerator (Ouchi Shinko Chemical Products Noccela TT) 0.63 Same Crosslinking agent zinc oxide 5 〃 Crosslinking agent stearic acid 1 〃 Anti-aging agent (Kawaguchi Chemical Industry Products Antage RD) 2 Same 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] Example 3 In Example 1, the same amount (100 parts by weight) of deproteinized NR (imported by Toyotsu Chemiplus; nitrogen content 0.019% by weight) was used instead of the PFNR obtained in the Reference Example. However, the crosslinking accelerator Noccela CZ was changed to 1 part by weight, and the same Noccela TT was changed to 0.5 parts by weight.

[0034] Example 4 In Example 3, sulfur and the crosslinking accelerator Noccelaer CZ were not used, and the crosslinking accelerator Noccelaer TT was changed to 4 parts by weight.

[0035] Comparative Example 1 In Example 1, the same amount (100 parts by weight) of natural rubber (imported by Toyotsu Chemiplas; nitrogen content 0.480% by weight) was used in place of the PFNR obtained in the Reference Example. However, the crosslinking accelerator Noccelaer CZ was changed to 0.88 parts by weight, and the same Noccelaer TT was changed to 0.44 parts by weight.

[0036] Comparative Example 2 In Comparative 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.

[0037] The results obtained in the above examples and comparative examples are as follows: In the table As shown. table Measurement items Fruit-1 Fruit-2 Fruit-3 Fruit-4 ratio-1 ratio-2 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 brightness (%) 18 20 35 66 69 75

Claims

1. A cross-linked product of a rubber composition comprising protein-removed natural rubber having a nitrogen content of 0.019% by weight or less as measured by the Kjeldahl method specified in JIS K-6451-2, which corresponds to ISO 1407, and a sulfur-based cross-linking agent, wherein the cross-linked natural rubber has a volume change of less than 5% after a liquid resistance test at 180°C for 40 hours in accordance with JIS K-6258.

2. The cross-linked natural rubber according to claim 1, wherein the protein-removed natural rubber has 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.

3. A natural rubber cross-linked product as described in claim 1 or 2, wherein the rubber composition further contains carbon black and / or a white filler.

4. The cross-linked natural rubber according to claim 3, 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.

5. The cross-linked natural rubber according to claim 4, 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.

6. The natural rubber cross-linked product according to claim 1, which is a rubber product used in contact with water.

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