Foam rubber molded product

Abstract

A foam rubber molded produce obtained by molding a rubber composition containing 100 parts by mass of ethylene--olefin-nonconjugated diene copolymer, 4 to 30 parts by mass of amorphous 4-methyl-1-pentene copolymer, 2 to 8 parts by mass of blowing agent, and a sulfur-based vulcanizing agent, and having a Mooney viscosity after kneading (ML1+4, 100 C.) of 54 or less. A specific gravity is 0.3 to 0.8, a compression set is less than 27%, and a foam state is an interconnected cell.

Claims

1. A foam rubber molded product obtained by molding a rubber composition containing 100 parts by mass of ethylene--olefin-nonconjugated diene copolymer, 4 to 30 parts by mass of amorphous 4-methyl-1-pentene copolymer, 2 to 8 parts by mass of blowing agent, and a sulfur-based vulcanizing agent, and having a Mooney viscosity after kneading (ML1=4, 100 C.) of 54 or less, wherein a specific gravity is 0.3 to 0.8, a compression set is less than 27%, and a foam state is an interconnected cell.

2. The foam rubber molded product according to claim 1, wherein the rubber composition further contains 45 to 87 parts by mass of process oil.

3. The foam rubber molded product according to claim 1, wherein the foam rubber molded product is a weatherstrip.

4. The foam rubber molded product according to claim 2, wherein the foam rubber molded product is a weatherstrip.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a perspective view of a weatherstrip as an example of a foam rubber molded product in Examples; FIG. 1B is a view illustrating the dimension of a foam rubber molded product produced as a sample; FIG. 1C is a view illustrating a method for testing the compression set of the foam rubber molded product; and

(2) FIG. 2 is a graph in which the horizontal axis is the amount of amorphous 4-methyl-1-pentene copolymer added, the vertical axis is the compression set, and data in Examples 1, 2, and 3 and Comparative Examples 1 and 3 are plotted.

DESCRIPTION OF EMBODIMENTS

(3) 1. Ethylene--Olefin-Nonconjugated Diene Copolymer

(4) Examples of -olefin include, but are not particularly limited to, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene. Among these, propylene is preferable.

(5) Examples of nonconjugated diene include, but are not particularly limited to, 1,4-hexadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene.

(6) 2. Blowing Agent

(7) Examples of blowing agent include, but are not particularly limited to, 4,4-oxybis(benzenesulfonyl hydrazide) (OBSH), azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), p-toluenesulfonylhydrazide (TSH),2,2-azobisisobutyronitrile (AIBN), and sodium bicarbonate.

(8) 3. Sulfur-Based Vulcanizing Agent

(9) Examples of sulfur-based vulcanizing agent include, but are not particularly limited to, sulfur, sulfur compounds, maleimides, and organic sulfur-containing vulcanizing agents. One type of the sulfur-based vulcanizing agent may be used alone, or two or more types thereof nay be used in combination.

(10) In order to promote vulcanization, a vulcanization accelerator may be appropriately added. Examples of the vulcanization accelerator include thiuram-based, dithiocarbamate-based, thiazole-based, guanidine-based, morpholine-based, sulfenamide-based, and dithiophosphoric acid-based vulcanization accelerators. One or two or more types of the vulcanization accelerators may be used.

(11) 4. Plasticizer

(12) In order to impart plasticity to the composition and facilitate processing, a plasticizer may be appropriately added. Examples of the plasticizer include, but are not particularly limited to, petroleum-based plasticizers such as process oil (paraffinic, naphthene-based, aromatic, etc.), lubricating oil, petroleum asphalt, and vaseline, coal tar-based softening agents such as coal tar and coal tar pitch, fatty oil-based plasticizers such as castor oil, linseed oil, rapeseed oil, and coconut oil, waxes such as beeswax, carnauba wax, and lanolin, fatty acid such as ricinoleic acid and palmitic acid, fatty acid salts such as barium stearate, calcium stearate, and zinc laurate, synthesis high-molecular substances such as a petroleum resin, atactic polypropylene, and a coumaroneindene resin, a tall oil, and a rubber substitute (factice).

(13) 5. Other Mixing Materials

(14) In addition to the aforementioned mixing materials, a filler, a processing aid, a cross-linking co-agent, a blowing aid, an age resistor, an acid acceptor, a scorch retarder, or a colorant may be appropriately mixed.

(15) Example of filler include carbon black, calcium carbonate, talc, silica, and baked clay.

(16) Examples of the processing aid include fatty acids such as stearic acid.

(17) Examples of the cross-linking co-agent include polyethylene glycol (PEG), fatty acid salts such as zinc oxide (ZnO, zinc white) and zinc stearate, and magnesium oxide.

(18) Examples of the blowing aid include urea and sodium benzenesulfonate.

(19) 6. Foam Rubber Molded Product

(20) Examples of application of the foam rubber molded product include, but are not particularly limited to, sealing parts (a weatherstrip of an automobile, a sealing material for a door opening and closing part of a house, etc.) and general-purpose buffer materials. In particular, a weatherstrip is suitable.

EXAMPLES

(21) Rubber compositions of Examples 1 to A and Comparative Examples 1 to 5, shown as mixing compositions in Table 1, were produced.

(22) TABLE-US-00001 TABLE 1 Type of mixing Comparative Comparative material Mixing Materials Example 1 Example 2 Example 1 Example 2 Example 3 Mixing Rubber EPDM 100 100 100 100 100 compositions Oil Process oil 90 75 85 75 65 (parts Polymer EPM 15 by mass) Amorphous 4-methyl- 5 15 25 1-pentene copolymer Compounding Carbon black 120 120 120 120 120 agent Calcium carbonate 50 50 50 50 50 Zinc white 7 7 7 7 7 Stearic acid 1 3 3 3 3 Fatty acid ester 1 1 1 1 1 processing aid Other 5 5 5 5 5 Vulcanizing agent Sulfur compounds 0.9 0.9 0.9 0.9 0.9 and Vulcanization Thiazole-based 1.8 1.8 1.8 1.8 1.8 accelerator Dithiocarbamate-based 1.3 1.3 1.3 1.3 1.3 Thiuram-based 1.2 1.2 1.2 1.2 1.2 Guanidine-based 0.6 0.6 0.6 0.6 0.6 Morpholine-based Blowing agent OBSH blowing agent 4.05 4.05 4.05 4.05 4.05 ADCA blowing agent Evaluation Physical properties Mooney viscosity 40.1 54.1 41.2 42.8 46.0 Items of kneaded product ML1 + 4, 100 C. Physical properties Specific gravity 0.6 0.7 0.6 0.6 0.7 of foam rubber 100% modulus (Mpa) 1.0 1.1 1.3 1.7 2.2 Breaking strength (Mpa) 3.0 2.7 2.9 3.4 4.2 Elongation at break (%) 240 200 200 200 180 Water absorption (%) 1.0 1.7 55.2 46.5 38.5 Compression set (%) 33.1 27.7 25.3 24.2 25.7 Comprehensive evaluation Poor Poor Good Good Good Type of mixing Comparative Comparative Comparative material Mixing Materials Example 1 Example 2 Example 5 Example 4 Mixing Rubber EPDM 100 100 100 100 compositions Oil Process oil 55 62 47 47 (parts Polymer EPM 15 by mass) Amorphous 4-methyl- 35 15 1-pentene copolymer Compounding Carbon black 120 102 102 102 agent Calcium carbonate 50 22 22 22 Zinc white 7 7 7 7 Stearic acid 3 1.5 1.5 1.5 Fatty acid ester 1 1 1 1 processing aid Other 5 2 2 2 Vulcanizing agent Sulfur compounds 0.9 2 2 2 and Vulcanization Thiazole-based 1.8 2 2 2 accelerator Dithiocarbamate-based 1.3 2 2 2 Thiuram-based 1.2 0.5 0.5 0.5 Guanidine-based 0.6 Morpholine-based 0.7 0.7 0.7 Blowing agent OBSH blowing agent 4.05 3.83 3.83 3.83 ADCA blowing agent 2.02 2.02 2.02 Evaluation Physical properties Mooney viscosity 47.9 46.1 60.8 54.0 Items of kneaded product ML1 + 4, 100 C. Physical properties Specific gravity 0.7 0.4 0.4 0.4 of foam rubber 100% modulus (Mpa) 2.8 1.0 1.2 1.6 Breaking strength (Mpa) 4.5 2.0 2.2 3.0 Elongation at break (%) 160 200 88 180 Water absorption (%) 28.5 42.9 47.8 35.8 Compression set (%) 28.0 29.0 28.0 25.0 Comprehensive evaluation Poor Poor Poor Good

(23) Herein, EPDM is trade name Mitsui EPT 8120E available from Mitsui Chemicals, Inc.

(24) A process oil is a paraffinic process oil.

(25) An ethylene-propylene rubber (EPM) is trade name EP11 available from JSR Corporation.

(26) An amorphous 4-methyl-1-pentene copolymer is trade name ABSORTOMER EP1001 available from Mitsui Chemicals, Inc.

(27) The rubber compositions were each kneaded under the following kneading condition. EPDM was placed alone in an internal mixer, and then masticated for 30 seconds. An oil, a polymer, a compounding agent, and a blowing agent shown in Table 1 were further added to the internal mixer, and the mixture was kneaded for a total of 220 seconds. At that time, the kneading temperature was increased from about 50 C. to about 150 C. The composition obtained after kneading was processed into a roll, and cooled in a tape shape. The composition after cooling, and a vulcanizing agent and a vulcanization accelerator shown in Table 1 were placed in a kneader, and kneaded for 60 seconds. At that time, the kneading temperature was about 60 C. The composition obtained after kneading was processed into a roll, kneaded by a mill blender for 60 seconds, and cooled in a tape shape. Subsequently, the Mooney viscosity (ML(1+4), 100 C.) was measured. The Mooney viscosity is shown in Table 1.

(28) From the thus kneaded rubber composition, for example, a weatherstrip 1 for an automobile shown in FIG. 1A can be molded as a foam rubber molded product. Herein, a foam rubber molded product in a shape of Type 2 dumbbell (not shown) was molded as a sample for measurement of the following specific gravity, 100% modulus, breaking strength, and elongation at break, and a foam rubber molded product 1a in a weatherstrip shape including a plate-shaped base 2 and a cylindrical hollow 3, as shown in FIG. 1B, was molded as a sample for measurement of the following water absorption and compression set. In the molding, the rubber composition was subjected to extrusion-molding using an extrusion-molding machine. The rubber composition was then subjected to UHF vulcanization in an ultra-high frequency vulcanisation (UHF) tank of 200 C., followed by HAV vulcanization through a hot air vulcanization (HAV) tank of 240 C.

(29) The specific gravity, 100% modulus, breaking strength, and elongation at break of the foam rubber molded product in a shape of Type 2 dumbbell (not shown) were measured. In the measurement of 100% modulus, breaking strength, and elongation at break, a tensile test was performed at room temperature in accordance with JIS K6251 vulcanized rubber and thermoplastic rubberDetermination of tensile properties. These physical properties are shown in Table 1.

(30) The foam rubber molded product 1a in a shape of weatherstrip shown in FIG. 1B was cut into a length of 45 mm, and the initial weight thereof was measured. The foam rubber molded product 1a was added to water of 35 C. in a beaker. The beaker was disposed under a reduced pressure of 630 mmHg, and the foam rubber molded product was immersed in water for 60 minutes, and taken out from the beaker. The weight of the foam rubber molded product 1a (after absorption) was measured. The water absorption (%) was calculated by the following expression. The results are shown in Table 1. In the present description, when the water absorption is 5% or more, the foam state is evaluated as an interconnected cell.
Water absorption=(weight after absorptioninitial weight)/(initial weight)100

(31) The foam rubber molded product 1a in a shape of weatherstrip shown in FIG. 1B was cut into a length of 45 mm as a specimen, and the heights thereof at three positions (height before a test) were measured. The specimen and a spacer 6 of which the length was 50% of the height at a center of length of the specimen were set in a compression device 5 shown in FIG. 1C, and compressed in the height direction. The specimen and the spacer 6 were disposed with the compression device 5 in a constant temperature bath (not shown) of which the temperature was set to 70 C., allowed to stand for 200 hours, and then taken out from the constant temperature bath. The foam rubber molded product 1a was rapidly released from the compression device 5, and allowed to remain at room temperature for 30 minutes. Subsequently, the heights at the three positions (height after the test) were measured. The compression set (%) (average of the heights at the three positions) was calculated by the following expression. The results are shown in Table 1.
Compression set=(height before testheight after test)/(height before testheight of spacer)100

(32) <Results of Evaluation Items>

(33) The rubber composition in Comparative Example 1 contained 90 parts by mass of process oil to secure processability. The Mooney viscosity after kneading of the rubber composition was as low as 40.1, but the compression set of the foam rubber molded product was as high as 33%. The water absorption of the foam rubber molded product was 1.0%. This shows that the foam state is a closed cell.

(34) The rubber composition in Comparative Example 2 contained 75 parts by mass of process oil, and 15 parts by mass of EPM. The Mooney viscosity after kneading of the rubber composition was as high as 54.1, and the compression set of the foam rubber molded product was 28%. The Mooney viscosity and the compression set were improved, but were not sufficient. The water absorption of the foam rubber molded product was 1.7%. This shows that the foam state is a closed cell.

(35) The rubber compositions in Examples 1 to 4 contained 47 to 85 parts by mass of process oil, and 5 to 25 parts by mass of amorphous 4-methyl-1-pentene copolymer. The Mooney viscosities after kneading of the rubber compositions were as high as 41.2 to 54.0, and the compression sets of the foam rubber molded products were 24.2 to 25.7%. The Mooney viscosities and the compression sets were improved. The water absorption of the foam rubber molded product was 35% or more. This shows that the foam state is an interconnected cell.

(36) FIG. 2 is a graph in which the horizontal axis is the amount of amorphous 4-methyl-1-pentene copolymer added, the vertical axis is the compression set, and data in Examples 1, 2, and 3 and Comparative Examples 1 and 3 are plotted on the basis of the aforementioned results. When the amount of amorphous 4-methyl-1-pentene copolymer added is 4 to 30 parts by mass, the compression set is less than 27%. This shows that excellent setting resistance is obtained.

(37) The present invention is not limited to Examples described above, and the present invention can be appropriately modified and embodied without departing from the spirit of the present invention.

REFERENCE SIGNS LIST

(38) 1 Foam rubber molded product 1a Foam rubber molded product 2 Base 3 Hollow 5 Compression device 6 Spacer