JP5079066B2 - Rubber foam - Google Patents

Description

  The present invention relates to an ethylene / propylene rubber foam which has a low thermal compression set and is excellent in the maintenance of sealing performance.

  Rubber foams using ethylene / propylene rubber are used for home appliances as cushioning materials, padding materials, sealing materials such as airtightness and waterstop, heat insulation materials and soundproofing materials, etc. It is widely used in various fields such as indoor products, outdoor products such as automobiles, buildings such as houses, etc., and it depends on sulfur from the viewpoint of physical properties such as vulcanization foam processing workability and durability of the resulting foam. A vulcanization method is generally adopted. However, the conventional foam has a problem that the thermal compression set is large, the repulsive force (compression recovery rate) is greatly lowered after high temperature experience, and the sealing performance is significantly lowered.

  The present invention is an ethylene / propylene rubber that has low heat compression set and is excellent in maintainability of sealing performance while taking advantage of the ease of vulcanization and foaming processing by sulfur vulcanization and the good physical properties of the resulting foam. The development of rubber-based foams using styrene is an issue.

  The present invention comprises 5 to 20 parts by weight of a foaming agent, 5 to 25 parts by weight of carbon black and 90 to 200 parts by weight of a white filler, and at least a component of 100 parts by weight of ethylene / propylene rubber. A rubber-based foam comprising a foam obtained by vulcanizing and foaming an admixture, and having a compression set of 50% and a thermal compression set when left at 70 ° C. for 22 hours for 90 hours or less Is to provide.

  In the rubber foam of the present invention, it is preferable that the filler is at least one selected from the group consisting of zinc oxide, calcium carbonate, and aluminum hydroxide.

  In the rubber-based foam of the present invention, it is preferable that the filler is zinc oxide, calcium carbonate, and aluminum hydroxide.

  In the rubber foam of the present invention, the blending amount of sulfur in the blend is 0.3 to 0.8 parts by weight per 100 parts by weight of the ethylene / propylene rubber, and the blend is also a thiuram vulcanization accelerator. It is preferable to use it as a component.

Moreover, in the rubber-type foam of this invention, it is suitable that a density is 0.01-0.3 g / cm < ³ >.

  According to the present invention, ethylene propylene is excellent in maintainability of sealing performance with less heat compression set while taking advantage of the ease of vulcanization and foaming processing by sulfur vulcanization and the good physical properties of the resulting foam. A rubber-based foam using a rubber-based rubber can be obtained. Therefore, the conventional sulfur vulcanization production line can be used as it is without changing to another vulcanization method such as a peroxide type. In addition, when the above effect is achieved by reducing the amount of sulfur used, there is an advantage of effective use of resources.

  The rubber-based foam according to the present invention comprises a foam obtained by vulcanizing and foaming an ethylene / propylene-based rubber, a foaming agent, and an admixture containing at least sulfur as components, and at a compression rate of 50% for 22 hours at 70 ° C. When left standing, the heat compression set is 90% or less, especially 75% or less, particularly 60% or less.

  As the ethylene / propylene rubber, one or more suitable ones such as ethylene / propylene / diene rubber (EPDM), ethylene / propylene rubber, and ethylene / propylene terpolymer can be used without any particular limitation. Copolymerization of 5-ethylidene-2-norbornene when the copolymerization ratio of EPDM and especially propylene is 25% by weight or more, especially 40 to 49% by weight in terms of controllability of rubber properties such as compressibility and sealing performance. EPDM having a proportion of 4 to 10% by weight, particularly 6 to 8% by weight, and an ethylene / propylene system having Mooney viscosity of 100 or less (ML1 + 4, 100 ° C., the same shall apply hereinafter), especially 10 to 50, especially 20 to 40 Rubber is preferably used.

  As the foaming agent, one or more suitable ones can be used, and there is no particular limitation. Incidentally, examples include azo compounds such as azodicarbonamide (ADCA), azobisisobutyronitrile and barium azodicarboxylate, N, N′-dinitrosopentamethylenetetramine, N, N′-dimethyl-N, Examples thereof include N-nitroso compounds such as N′-dinitrosotephthalamide, and sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, and diphenylsulfone-3,3′-disulfonyl hydrazide.

  In addition, fluorinated alkanes such as trichloromonofluoromethane and dichloromonofluoromethane, hydrazine compounds such as 4,4′-oxybis (benzenesulfonylhydrazide), allylbis (sulfonylhydrazide), ρ-toluylenesulfonyl semicarbazide and 4,4 ′. -Organic foaming agents such as semicarbazide compounds such as oxybis (benzenesulfonyl semicarbazide) and triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole.

  Further examples include inorganic foaming agents such as ammonium carbonate, ammonium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, azide compounds such as calcium azide and paratoluenesulfonyl azide. In particular, ADCA is preferably used in terms of safety and non-toxicity due to self-extinguishing properties.

  The amount of the blowing agent used is preferably 5 to 20 parts by weight, particularly 10 to 15 parts by weight per 100 parts by weight of the ethylene / propylene rubber. The foaming agent used may be heat-expandable fine particles in which a heat-expandable substance is enclosed in microcapsules. The thermally expandable fine particles include commercially available products such as microspheres (trade name, manufactured by Matsumoto Yushi Co., Ltd.).

  As described above, sulfur is used as the vulcanizing agent in view of the physical properties such as the ease of the vulcanization foaming work and the durability of the obtained foam. The amount used is preferably less than the conventional amount, especially 0.3 to 0.8 parts by weight, especially 0.4 to 0.6 parts by weight per 100 parts by weight of ethylene / propylene rubber. . By setting the amount to be used in such a small amount, it is easy to obtain a foam having a small thermal compression set, which is an object of the present invention. This is thought to be because a small amount of sulfur used suppresses the formation of polysulfide bonds.

  That is, in the vulcanization treatment with sulfur, a crosslinked structure is formed by monosulfide bonds, disulfide bonds, and polysulfide bonds. In this case, the bond energy becomes smaller as the crosslinked structure becomes polysulfide. Therefore, a cross-linked structure with a monosulfide bond or a disulfide bond is generated in a rich manner, and a cross-linked structure with a large binding energy is formed to suppress the formation of a cross-linked structure with a polysulfide bond, thereby improving the thermal stability of the cross-linked product and its heat resistance. It is considered that a foam with less heat compression set can be obtained by improving the amount of polysulfide bonds by reducing the amount of sulfur used. Reduction of sulfur usage is more advantageous than efficient use of resources.

  Preparation of an admixture for forming a foam according to the present invention is performed by kneading at least a compounding component comprising an ethylene / propylene rubber, a foaming agent and sulfur, for example, an internal mixer such as a Banbury mixer, a kneader, or an intermix. It can be carried out by mixing by an appropriate method such as a method of mixing via a machine. In that case, a mixing method in which the temperature rises to such an extent that vulcanization proceeds is not preferable, and a multi-stage mixing method in which a vulcanizing agent, a foaming agent, or the like is added after mixing other components as necessary can be adopted.

  When preparing an admixture, one or more suitable compounding agents according to the prior art are required for the purpose of accelerating the vulcanization treatment and foaming treatment, adjusting the viscosity of the admixture and the physical properties of the resulting foam, etc. Can be added accordingly. Incidentally, examples of the vulcanization accelerator used for the purpose of promoting the vulcanization treatment include thiurams such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide and dipentamethylenethiuram tetrasulfide.

  Further, sulfenamides such as N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiene-2-benzothiazole sulfenamide, N, N-diisopropyl-2-benzothiazole sulfenamide, 2-mercaptobenzothiazole And thiazoles such as dibenzothiazyl disulfide, guanidines such as diphenylguanidine and diphenylguanidine phthalate, aldehyde amines and aldehyde ammonia such as acetaldehyde-aniline reactant and acetaldehyde ammonia, imidazolines such as 2-mercaptoimidazoline, thiocarbanilide, Thioureas such as diethylthiourea, dithioacid salts such as zinc dimethyldithiocarbamate and zinc diethyldithiocarbamate, dibutylxan Such xanthates Gen zinc, zinc flower be cited as examples of the vulcanization accelerator.

  One or two or more vulcanization accelerators can be used, and in particular, thiurams which have a sulfur supply ability and can function as a vulcanizing agent themselves provide a foam having a low thermal compression set. It is preferably used from the point. The amount of the vulcanization accelerator used is preferably 0.1 to 10 parts by weight, especially 0.5 to 8 parts by weight, particularly 3 to 6 parts by weight, per 100 parts by weight of the ethylene / propylene rubber. When using a vulcanization accelerator, a vulcanization accelerator aid can be used in combination.

  Examples of foaming aids used for the purpose of promoting foaming treatment include salicylic acid-based, phthalic acid-based, stearic acid-based, oxalic acid-based, organic acid-based compounds such as benzoic acid-based compounds, and urea-based compounds such as urea and its derivatives. In particular, urea is preferably used. One or two or more foaming aids can be used, and the blending of the foaming aid can lower the decomposition temperature of the foaming agent to promote foaming treatment, and is also effective for uniformizing bubbles. The amount of the foaming aid used is preferably 0.1 to 10 parts by weight, especially 0.5 to 8 parts by weight, particularly 1 to 5 parts by weight per 100 parts by weight of the ethylene / propylene rubber.

  Carbon black is added to the blend of the present invention. Carbon black is useful for reducing the thermal compression set of a foam obtained by functioning as a reinforcing agent or the like. Carbon black having a dibutyl phthalate absorption of 0.5 to 1.3 ml / g, especially 0.6 to 1.1 ml / g, is preferably used in view of the reinforcing effect and the like. The amount of carbon black used is preferably 5 to 25 parts by weight, particularly 10 to 20 parts by weight, per 100 parts by weight of the ethylene / propylene rubber, from the standpoint of appropriate reinforcement effect. If the amount used is excessive, the reinforcing effect becomes too strong, and the foaming ratio of the foam obtained is likely to be lowered.

  Examples of other compounding agents that may be added for the purpose of adjusting the viscosity of the admixture and the resulting processability and the physical properties of the resulting foam include fillers, softeners or plasticizers, flame retardants and aging. Examples thereof include an inhibitor, an antioxidant and a pigment, a colorant and an antifungal agent.

  Moreover, a filler is added to the blend of the present invention. An example of the filler is a white filler. Specific examples of such fillers include carbonates such as calcium carbonate and magnesium carbonate, wet and dry silica, talc and clay, wollastonite and bentonite, various silicates such as aluminum silicate, zinc oxide and oxide. Examples thereof include aluminum, metal oxides such as titanium oxide and magnesium oxide, mica powder and aluminum powder, and those obtained by surface treatment with a coupling agent or the like.

  In the present invention, a white filler is used as the filler from the viewpoint of suppressing blackening due to the addition of the above-described carbon black. In particular, zinc oxide, calcium carbonate, and aluminum hydroxide are preferably used as the filler. The filler is used in an amount of 90 to 200 parts by weight per 100 parts by weight of ethylene / propylene rubber from the viewpoint of improving processability such as extrudability in the blend and maintaining flexibility in the resulting foam. In particular, 95 to 190 parts by weight, particularly 100 to 180 parts by weight is preferable.

  Specific examples of softeners or plasticizers that are generally useful for adjusting the moldability of admixtures include paraffinic and naphthenic process oils, liquid paraffin and other paraffins, waxes and lubricating oils, and silicone oils. And synthetic polymer softeners such as liquid polybutene, aromas and asphalts, drying oils such as linseed oil, animal and vegetable oils, petroleum oils and various low-volume polymers, phthalic acid and adipic acid, Examples thereof include ester plasticizers such as sebacic acid and phosphoric acid, stearic acid and esters thereof, alkylsulfonic acid esters and tackifiers.

  In particular, paraffinic process oil is preferably used from the viewpoint of processability. The amount of the softener or plasticizer used is 100 parts by weight of ethylene / propylene rubber from the viewpoint of improving the processability such as extrudability in the blend and preventing the heat resistance from being reduced due to component volatilization in the resulting foam. 20 to 55 parts by weight, especially 25 to 50 parts by weight, especially 30 to 40 parts by weight are preferred.

  Other flame retardants such as the above-mentioned flame retardants, anti-aging agents, antioxidants and pigments, colorants and anti-mold agents, such as aluminum hydroxide, magnesium hydroxide, ethylene bispentabromodiphenyl, etc. An appropriate one according to the conventional method can be used. In addition, it is advantageous to use a compounding agent having a high flash point rather than improving flame retardancy. The zinc oxide described above is useful as a stabilizer, and stearic acid and its esters are useful as a lubricant. Therefore, examples of components in which various stabilizers and lubricants can be blended are listed.

  The blend may further contain one or more rubber polymers other than non-rubber polymers and ethylene / propylene rubbers for the purpose of adjusting the strength and the like of the resulting foam. Any suitable non-rubber polymer or rubber polymer can be used without any particular limitation. Incidentally, examples of non-rubber polymers include acrylic polymers such as poly (meth) acrylic acid alkyl esters, polyethylene, polypropylene, ethylene / vinyl acetate copolymers, polyvinyl acetate and polyamide, polyesters and urethane polymers, styrene. Examples thereof include silicone polymers, silicone polymers, and epoxy resins. The amount used is preferably 50% by weight or less, more preferably 30% by weight or less, and particularly preferably 15% by weight or less of the ethylene / propylene rubber from the viewpoint of maintaining the rubbery properties of the foam.

  On the other hand, examples of rubber-based polymers other than the above-described ethylene / propylene rubber include cyclic or non-cyclic polyenes having non-conjugated double bonds such as α-olefins such as butene-1, dicyclopentadiene and ethylidene norbornene. Rubber copolymer, silicone rubber, fluorine rubber, acrylic rubber, polyurethane rubber, polyamide rubber, natural rubber, polyisobutylene, polyisoprene, butyl rubber, nitrile butyl rubber, styrene-butadiene rubber, styrene-butadiene-styrene Examples thereof include rubber, styrene / isoprene / styrene rubber, styrene / ethylene / butadiene rubber, styrene / ethylene / butylene / styrene rubber, and styrene / isoprene / propylene / styrene rubber. The compounding amount of the rubber polymer other than the ethylene / propylene rubber can be the same as that of the non-rubber polymer.

  Formation of the rubber-based foam according to the present invention can be performed by heating the above-mentioned mixture and adding a foaming treatment and a vulcanization treatment, and the vulcanization foaming treatment can be performed simultaneously or in a separate process. Can also be done. In forming the rubber-based foam, if necessary, the blend may be formed into a predetermined form such as a sheet, and the molded body may be heat-treated to obtain a vulcanized foam. In that case, the molded body may be molded into an arbitrary form by an appropriate method, and the form is not particularly limited.

  Therefore, the object of vulcanization and foaming treatment may be a mixture obtained by molding the admixture into a sheet or other form by an appropriate method such as a mixing roll, a calender roll, or extrusion molding, or through a predetermined mold. Further, it may be formed into a predetermined form having irregularities by an appropriate method such as injection molding or press molding. In that case, in the formation of a foam having a concavo-convex shape, a molded sheet is placed on a mold having a concavo-convex shape and heated, and the mixture forming the sheet flows into the concavo-convex shape of the mold and vulcanized and foamed. It is also possible to adopt a method to do so.

  The method using the mold has an advantage that the uneven shape can be accurately formed even in the case of a mold having a complex deep uneven structure having a corrugated structure. Therefore, the size of the molded body is arbitrary, and can be appropriately determined according to the form of the target foam. In the case of a sheet or the like, the thickness is generally 100 mm or less, in particular, 1 μm to 80 mm, particularly 10 μm to 50 mm.

  The vulcanization foaming treatment described above can be performed under appropriate conditions according to the prior art depending on the foaming temperature, the vulcanization start temperature, and the like by the used foaming agent or vulcanizing agent. Typical processing temperatures are 450 ° C. or less, especially 100 to 350 ° C., particularly 120 to 300 ° C. By such vulcanization and foaming treatment, the admixture is softened and the foaming agent expands to form a foamed structure, and vulcanization proceeds to form the desired vulcanized foam. In this case, the foaming treatment can be performed under pressure for the purpose of adjusting the foaming ratio and the pressurizing conditions can be the same as in the past. Moreover, the vulcanization | foaming process can also perform a foaming process and a vulcanization process on different temperature conditions, and can take an appropriate process condition.

The expansion ratio (density ratio before and after foaming) of the vulcanized foam to be formed can be appropriately determined according to the purpose of use. Generally, the foaming ratio is 1.1 to 25 times, especially 1.5 to 20 times, but usually 0.01 to 0.5 g / cm ³ , especially 0.05 to 0.4 g / cm ³ , In particular, a foam having a density of 0.1 to 0.3 g / cm ³ can be preferably used for various applications. The expansion ratio can be controlled by the blending amount of the above-described foaming agent, the processing time and temperature of vulcanization foaming, and the like. In addition, by adjusting the expansion ratio, the foam structure such as the independent and continuous foams and the mixture thereof can be controlled.

  The rubber-based foam according to the present invention is preferably used in various conventional applications such as cushion materials, pad materials, sealing materials for various purposes such as airtightness and waterproofing, heat insulating materials, vibration reducing materials such as soundproofing and vibration damping. Can be used.

Example 1
100 parts of EPDM having a Mooney viscosity of 30 (parts by weight, the same applies hereinafter), carbon black 10 parts, zinc oxide 5 parts, stearic acid 2 parts, process oil 30 parts, calcium bicarbonate 150 parts and aluminum hydroxide 30 parts in a Banbury mixer After kneading, add 10 parts ADCA, 2 parts urea (foaming aid), 0.5 part sulfur, 0.8 part thiazole vulcanization accelerator, and 1.0 part dithiocarbamate vulcanization accelerator to mix. The mixture is kneaded with a roll to obtain an admixture, which is molded with an extruder to obtain an unvulcanized sheet having a thickness of 4.5 mm and a width of 150 mm, preheated in a dryer at 100 ° C. for 40 minutes, and then applied for 15 minutes. The temperature was raised to 160 ° C. and heated at that temperature for 15 minutes for vulcanization and foaming to obtain a foamed sheet.

Example 2
Except for the addition of 3 parts of thiuram vulcanization accelerator, an admixture was obtained according to Example 1, formed into an unvulcanized sheet, and then the sheet was preheated in a dryer at 100 ° C. for 25 minutes and then 15 The temperature was raised to 160 ° C. over a period of 15 minutes, and heated at that temperature for 15 minutes for vulcanization and foaming treatment to obtain a foamed sheet.

Comparative Example 1
An admixture was obtained according to Example 1 except that the amount of sulfur was changed to 1.5 parts. After forming the mixture into an unvulcanized sheet, the sheet was preheated at 100 ° C. for 15 minutes in a dryer and then 15 minutes. The temperature was raised to 160 ° C. and heated at that temperature for 15 minutes for vulcanization and foaming treatment to obtain a foamed sheet.

Comparative Example 2
An admixture was obtained in the same manner as in Example 1 except that the amount of sulfur was 1.0 part. After forming the mixture into an unvulcanized sheet, the sheet was preheated in a dryer at 100 ° C. for 25 minutes and then 15 minutes. The temperature was raised to 160 ° C. and heated at that temperature for 15 minutes for vulcanization and foaming treatment to obtain a foamed sheet.

Evaluation test About the foam sheet obtained by the Example and the comparative example, while examining the density, it investigated the thermal compression set. The thermal compression set is a spacer having a diameter of 29 mm and a thickness of 10 ± 0.15 mm (t ₀ ) on a test machine conforming to JIS K 6262 with a thickness of 5.0 mm (t ₂ ) between parallel metal plates. Sandwiched between the two and tightened with a bolt to a compression rate of 50%, left in a constant temperature bath at 50 ° C. or 70 ° C. for 22 hours, then removed from the compression device and left at room temperature for 30 minutes, The thickness of the test piece was measured with a thickness measuring instrument based on JIS K 6262, and the thermal compression set was calculated from the value (t ₁ ) according to the following equation.
Thermal compression set (%) = (t ₀ -t ₁ ) / (t ₀ -t ₂ ) × 100
The results are shown in Table 1 below.

  It can be seen from Table 1 that the thermal compression set is reduced in the example in which the amount of sulfur is reduced, and the thermal compression set is significantly reduced in Example 2 in combination with the thiuram vulcanization accelerator. .

Claims (4)

A blend comprising 5 to 20 parts by weight of a foaming agent, 5 to 25 parts by weight of carbon black and 90 to 200 parts by weight of a white filler and 100 parts by weight of sulfur with respect to 100 parts by weight of ethylene / propylene rubber. consists vulcanized foam treated foam, heat compression set if left 22 hours under 70 ° C. in a state of compression ratio 50% Ri der 90% or less,
Rubber foam density wherein 0.01 to 0.3 g / cm ³ der Rukoto. The rubber foam according to claim 1, wherein the filler is at least one selected from the group consisting of zinc oxide, calcium carbonate, and aluminum hydroxide. The rubber-based foam according to claim 1 or 2, wherein the filler is zinc oxide, calcium carbonate, and aluminum hydroxide. The amount of sulfur in the admixture is 0.3 to 0.8 parts by weight per 100 parts by weight of the ethylene / propylene rubber, and the admixture also contains a thiuram vulcanization accelerator as a component. The rubber-based foam as described in any one of 1-3 .