JPS617343A - Low-specific gravity rubber composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition of good molding processability capable of giving cured products with high spring hardness and both large tensile strength and elongation, by homogeneously incorporating specific polyolefin powder in natural or synthetic rubber. CONSTITUTION:The objective composition giving a stress <=4MPa at 50% elongation can be obtained by homogeneously incorporating (A) 5-150pts.wt. of crystalline polyolefin powder with a density 0.920-0.970g/cm<3> and a size <=74mum (pref. 44-0.3mum) in (B) 100pts.wt. of at least one sort of either natural or synthetic rubber. Said polyolefin is pref. polyethylene esp. with a viscosity-average molecular weight (determined by the ASTMD2857) >=50,000 pref. >=300,000.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a low specific gravity rubber composition, and more particularly, a composition comprising a specific polyolefin powder mixed and dispersed in at least one type of natural rubber or synthetic rubber at a temperature below its melting point. The present invention relates to a low specific gravity rubber composition.

Since the vulcanizate obtained from the low specific gravity rubber composition of the present invention has high spring hardness, large tensile strength and large tensile elongation, it can be used for window frames, liquid feeding hoses, waterproof sheets, etc.
Suitable as cushioning materials, backings, roof ink sheets, sponge rubber materials, sealing materials, etc.

Prior Art Conventionally, as a method for obtaining a vulcanizable low specific gravity rubber composition,
It is extremely common to minimize the amount of carbon black and inorganic fillers, which have a higher specific gravity than rubber, or to add low specific gravity additives such as tackifiers and process oils to the outside. .

However, in the former method, if a compound that yields a product with high hardness is adopted, the resulting rubber composition has poor fluidity, resulting in extremely poor extrusion moldability, calender moldability, and injection molding properties. There is.

Furthermore, although the latter method improves fluidity, the resulting rubber composition has low hardness due to the blending of a large amount of softening agent such as process oil, and its use is limited to rubber products within a very specific range. It has the disadvantage of being added.

In addition, as a method to improve these drawbacks, for example, ethylene-propylene-nonconjugated diene copolymer rubber (EpD
(M) is ethylene-vinyl acetate copolymer (EVA), low-density polyethylene (LDPE), or (c) amorphous ethylene-α-olefin copolymer, carbon black, and process oil at a temperature above the melting point of the resin. A method of adding it has been proposed (Japanese Unexamined Patent Publication No. 177039/1983).

However, the rubber compositions obtained by this method generally have poor extrusion moldability at temperatures below the melting point of the resin, and also have problems in mechanical stability under heat, since the resins are melt-mixed.

As described above, it is extremely difficult to obtain a rubber product with high hardness and low specific gravity while maintaining rubber elasticity.

Object and Summary of the Invention The object of the present invention is to solve the above-mentioned problems, to provide a low specific gravity rubber composition that has excellent moldability and can be vulcanized without impairing the physical properties of the vulcanized rubber. It is on offer.

According to the essence, 0.920 to 0.970 j! /
5 to 150 parts of crystalline polyolefin powder having a particle size of 74 μm or less is mixed and dispersed in 100 parts of at least one kind of natural rubber or synthetic rubber, and has a particle size of 4 MPα or less when pulled at 50 cm. A low specific gravity rubber composition with improved hardness characterized by exhibiting stress is provided.

Structure and effect of the invention The crystalline polyolefin used in the present invention has 1-
It is an olefin homopolymer or a copolymer, and has a crystallinity of usually 20 inches or more, preferably 60 degrees or more, as determined by X-ray diffraction. The polymerization type may be either random polymerization or block polymerization. For random copolymers, it is preferable that the smaller 1-olefin units are usually less than 40 moles, preferably less than 60 moles.

The 1-olefins include ethylene, propylene, 1-olefin,
-butene, 1-pentene, 1-hexene, 4-methyl-
It can be one or more of 1-pentene, 1-octene, 1-decene, 1-dodecene, etc.

In addition, the crystalline polyolefin is not limited to the above polymers or copolymers, and other olefin polymers may be used at 40% by weight based on the composition.
The composition may contain ff4 or less.

Among the above-mentioned crystalline polyolefins, polyethylene is preferably used, and in particular, polyethylene is used according to the viscosity method (ASTMD2857).
average molecular weight of 50,000 or more, preferably 300
,000 or more, it is possible to obtain an oleic acid compound for vulcanized rubber that has high mechanical strength and hardness, a low coefficient of friction, and excellent wear resistance.

The polyethylene powder has a much lower true specific gravity than either carbon black or inorganic fillers, and also has a great effect on increasing the hardness of vulcanized rubber - even more so than inorganic fillers. The present inventors discovered this surprising fact.

The polyolefin used in the present invention is ASTM
D 1505 test method, 0.920 to 0.9
75 jl, /cIfL”, especially 0.925 to 0.9
7['/c! Let's calculate the density of rL3.

If a low-density polyolefin with a density of less than 0.920 g/cm is used, the hardness and tensile strength will be unsatisfactory when vulcanized. Although this does not cause any problems in terms of physical properties, it does not meet the objective of lowering the specific gravity.

In addition, the melting point of the polyolefin used in the present invention is measured by the test method according to 1,4STM D 2117,
The temperature is usually 120°C or higher, particularly 125°C or higher.

If the melting point is lower than 120°C, it will be difficult to mix with a practical mixing machine such as a Banbury mixer even at temperatures below the melting point, and the thermal properties of the vulcanized rubber will be insufficient. accompanied by.

Furthermore, in the present invention, among the above-mentioned crystalline polyolefins, Coulter Counter (model ZM, C
A polyolefin powder having a particle diameter of 74 μm or less, particularly 44 to 0.6 μm, as measured by a method manufactured by Counter Electronics, Inc., is used. If the particle size exceeds 74 μm, the resulting rubber composition will have a rough extruded surface, a calendered surface, etc., and the tensile strength of the vulcanized rubber will significantly decrease.

According to the present invention, 5 to 150 parts by weight, preferably 10 to 100 parts by weight of the polyolefin powder, particularly polyethylene powder, is mixed and dispersed in 100 parts by weight of natural rubber or various synthetic rubbers.

If the amount of polyolefin powder is less than 5 parts by weight, the effects of lowering the specific gravity of the rubber composition and increasing the hardness of the vulcanized rubber will not be achieved, and if it exceeds 150 parts by weight, the processability of the rubber composition will be impaired. It is undesirable because it deteriorates the mechanical properties, especially the permanent elongation, after vulcanization.

Furthermore, in the present invention, it is important that the polyolefin powder be mixed and dispersed at a temperature below its melting point, that is, that the polyolefin powder be dispersed in the composition without forming a continuous phase.

When polyolefin powder is mixed with rubber at a temperature above its melting point, the powder forms a continuous phase or becomes compatible with the rubber, resulting in a reduction in the rubber bullet t1 of the resulting composition. In this case, the viscosity of the composition increases significantly due to the melting point of the polyurethane resin used, for example, polyethylene, and when the roll processing and extrusion processing temperature is below 120°C, which is practical in the rubber industry, the composition This makes molding extremely difficult.

Mixing and dispersion is performed using a mixed wire mill for various rubbers.

For example, an intensive mixer such as a Panburi mixer, a roll mill such as a two-roll mill, and an extruder such as a screw-mounted or multi-screw extruder are used.

In addition, during this mixing and dispersion, the polyolefin powder such as polyethylene to be used is wetted using various petroleum-based or synthetic oils, various plasticizers such as phthalic acid derivatives, adipic acid derivatives, phosphoric acid derivatives, and polyester derivatives. Good too.

Rubbers used in the present invention include natural rubber, polyisoprene rubber, styrene-butadiene copolymer-t)1
, phthalene rubber, chloroprene rubber, isoprene-isobutylene copolymer rubber, acrylonitrile-butadiene copolymer rubber, ethylene-propylene copolymer rubber, ethylene-propylene diene copolymer rubber, acrylic rubber, urethane rubber, silicone rubber, fluororubber, and modifications thereof Various natural or synthetic rubbers such as comb, chlorosulfonated polyethylene, and halogenated polyethylene may be used, and polyolefin rubbers are particularly preferably used.

In addition, in the present invention, various fillers usually added to rubber, such as carbon black, silica, clay, Merck, aluminum, magnesium, calcium, zinc, etc.
Oxides such as titanium, mineral-based or synthetic softeners, vulcanizing agents, vulcanization accelerators, anti-aging agents, coloring agents, lubricants, etc. can be blended as necessary.

The 50mm tensile stress of the rubber composition of the present invention is JISK660
1 tensile test, using a No. 6 dumbbell test piece under standard conditions (204-:°C), 50 ynm/rnin
4 MPa or less when measured at tD tensile speed,
Preferably 2 MPα or less, more preferably 1 kiPα
The following must be true. If the 50% tensile stress exceeds 4 MPa, it will be extremely difficult to mold the composition at rolling and extrusion temperatures of 120° C. or lower, which are practical in the rubber industry.

In order to suppress the 50 mm tensile stress to 4 MPa or less, it is beneficial to cross-wire the polyethylene powder at a temperature lower than its melting point, for example.

The rubber composition of Kienori J can be easily molded using ordinary rubber molding machines, such as extruders, calendar rolls, injection molding machines, compression molding machines, etc., and can be molded by heating and/or electron beams, microwaves, etc. Can be vulcanized by electromagnetic radiation, etc.

Example 1 1500 tons of rhudecane was placed in a polymerization vessel with an internal volume of 27501 mm)
15Q Q mtyuyl of ethylaluminum and 15rrLWlOt of particulate titanium catalyst component were added, and the temperature was raised to 70°C. Afterwards, add 600 ethylene gas
It was introduced into the polymerization vessel at a rate of NM/Hr. Polymerization pressure is 1
~6 kg/l the G.

When the cumulative amount of ethylene introduced reached 180 NM'', the ethylene feed was cut, and after polymerization was carried out for 10 minutes, cooling and depressurization were performed to obtain a slurry of ultra-high molecular weight polyethylene.This slurry The slurry was subjected to high-speed shearing using a commercially available homomitsukline mill.
It was carried out for an hour. The obtained polymer and solvent were separated by a centrifuge, and dried under reduced pressure at 75° C. under a stream of air.

The yield of the obtained polyethylene powder was 255 kg, and the molecular weight was measured in decalin at 165°C, and the intrinsic viscosity was 23.5.
di/g, density 0.940 g/cm3, melting point 166
°C and its shape (ζ diameter was small spheres of 20 μm to 60 μm. Also, the average particle size (c) was 26 μm, and the bulk density was 0.2 μm.
89/crIL” and the angle of repose was 50°.

OOC using this high-density polyethylene powder with the following formulation
The mixture was kneaded for 5 minutes under strong cooling using a Banbury mixer (manufactured by Kobe Steel, Ltd.). The crosstalk temperature (rubber composition temperature, same hereinafter) was 118°C.

Mixed polyethylene powder 60 parts by weight No. 6 zinc white 5 parts by weight Stearin (R) 1 part by weight The mixture was cooled to room temperature, a part of it was re-milled in an 8-inch open mill with a surface temperature of 50°C, It was divided into sheets with a thickness of about 6 mm.From this divided sheet, approximately 140 x 125 x 2.5 iTI
Cut out a L sheet piece, sandwich it between 150 μm aluminum foil, insert it into a mold with internal dimensions of 140 x 125 x 2.5, and
Pressure molding was carried out for 10 minutes using a hot press at 0°C to create 50 sheet pieces for tensile stress (v50) measurement.

After leaving this sheet piece in the standard state for 2 hours, the aluminum foil was removed, and a JIS 3 bow-shaped dumbbell-shaped test piece was punched out from it, and the piece was pulled at a tensile rate of 5 Q 12/1 ninn) to measure the 50% tensile stress. .

On the other hand, the remaining mixed material was wound around a 14-inch open mill with a surface temperature of 60°C, and 1.5 parts by weight of mercaptobenzothiazole (NET) and zinc di-louptyldithiocarbamate (ZrLEDC) were added as vulcanization accelerators. 0 parts by weight, TETD (tetraethylthiuram disulfide)
0.7 parts by weight, 0.5 parts by weight of EU (ethylene thiourea), and 1.5 parts by weight of sulfur were mixed. At this time, roll workability was visually observed.

In addition, the Mooney viscosity of the obtained vulcanized rubber composition was determined according to JIS
Measured according to K6500. In addition, the surface roughness of the 1-inch-thick roll sheet, which eliminates unevenness caused by air inclusion, was measured using a surface roughness meter (Surfcom 200B model, manufactured by Tokyo Seimitsu Co., Ltd.), and the 10-point average roughness Rz was measured. Indicated.

Next, the composition for vulcanized rubber was heated at 150°C at 25°C using a hot press.
The physical properties of the vulcanized rubber were determined according to JISK6501.
Measured according to. Also, the specific gravity is JIS 28807.
It was measured using the method described in Section 4.

The results are shown in Table 1.

Example 2 High-density polyethylene powder with a density of 0.940 g/cc, a melting point of 156°C, and a particle size of 44 to 56 μm was used.
A rubber composition was produced in the same manner as in Example 1, except that it was kneaded at a mixed temperature of 20°C, and the same measurements of roll processability, Mooney tenacity, etc. were performed. The measurement results are shown in Table 1.

Example 6゜density 0.931/cc, melting point 122℃, particle size 67
10 pieces of linear low-density polyethylene powder of ~44μ7
A rubber composition was prepared in the same manner as in Example 1, except that it was kneaded at a cross-mixing temperature of 5° C., and the same measurements were performed. The measurement results are shown in Table 1.

Implementation f(・1) 4゜density 0.968 jl/cc, 7 melting point 164℃, particle size 67-144μm using high-density polyethylene powder, 1
A rubber composition was produced in the same manner as in Example 1, except that it was kneaded at a cross-mixing temperature of 20° C., and the same measurements were performed. The measurement results are shown in Table 1.

Comparative Example 1 A rubber composition was produced in the same manner as in Example 1, except that high-density polyethylene powder with a particle size of 105 to 250 μm was used and the cross-wire temperature was 121°C, and the same measurements were performed. . The redundancy measurement results are shown in Table 1.

The obtained rubber composition had a rough surface and was unsuitable for use as extruded products or calendered products.

Comparative Example 2゜ Same as Example 1 except that a frozen pulverized product of low density polyethylene with a density of 0.91797 cc and a melting point of 108°C and a polyethylene powder with a particle size of 56 to 66 μm was used, and crosstalk was performed at a crosstalk temperature of 100°C. A rubber composition was prepared using the same method, and the same measurements were performed. The measurement results are shown in Table 1. The rubber composition obtained showed a significantly large permanent elongation.

Example 5゜The polyethylene powder of Example 1 was made into 10 parts by weight, and 120 parts by weight
A rubber composition was produced using the same pile as in Example 1, except that cross-wire was conducted at a cross-wire temperature of .degree. C., and the same measurements were performed. The results are shown in Table 2.

Implementation fa116゜50 parts by weight of the polyethylene powder of Example 1, 120 parts by weight
A rubber composition was produced in the same manner as in Example 1, except that the crosstalk temperature was set at .degree. C., and the same measurements were performed. The results are shown in Table 2.

Example Z The polyethylene powder of Example 1 was 100 parts by weight, and 12
A rubber composition was produced in the same manner as in Example 1, except that the crosstalk temperature was 2° C., and the same measurements were performed. The results are shown in Table 2.

Comparative Example 3 A rubber composition was produced in the same manner as in Example 1, except that no polyethylene powder was blended, and the same measurements were performed. The results are shown in Table 2.

The obtained vulcanized rubber had insufficient hardness.

Comparative Example 4 A rubber composition was produced in the same manner as in Example 1, except that the polyethylene powder of Example 1 was used at 170 parts by weight, and the cross wire temperature was set at 121° C., and the same measurements were performed. The results are shown in Table 2.

The obtained rubber composition had poor processability and a large permanent elongation.

Comparative Example 5 A rubber composition was produced in the same manner as in Example 1, except that the crosstalk temperature was 146°C, and the same measurements were performed. The results are shown in Table 2.

The obtained rubber composition exhibited drawbacks such as extremely poor processability, high M2O content, and extremely high surface roughness.

Example 8゜Using the polyethylene powder of Example 1, 1 was prepared with the following composition.
A rubber composition was produced in the same manner as in Example 1 at a crosstalk temperature of 19°C.

Blended polyethylene powder 50 parts by weight Natural rubber (No. R551) 100 parts by weight Zinc white
5 parts by weight Stearic acid 1 part by weight 4A
Yellow 1 part by weight Regarding the obtained rubber composition, various physical properties were measured in the same manner as in Example 1, and the measurement results are shown in Table 6.

Example 9 Using the polyethylene powder of Example 1, a rubber composition was produced in the same manner as in Example 1 with the following formulation.

Blended polyethylene powder 60 parts by weight Zinc Flower 5 parts by weight Stearic acid 1 part by weight FEF carbon black (Asahi 60) 80 parts by weight Process oil (A
', 5100) 40 parts by weight Dipenzothiazyl disulfide 1.2 parts by weight Diorthotolylguanidine 0.2 parts by weight Sulfur
Regarding the rubber composition obtained in an amount of 1.75 parts by weight, various physical properties were measured in the same manner as in Example 1, and the measurement results are shown in Table 6.

Comparative Example 6 A rubber composition was produced in the same manner as in Example 8, except that no polyethylene powder was blended, and the same measurements were carried out. The measurement results are shown in Table 6.

Comparative Example Z A rubber composition was produced in the same manner as in Example 9 except that polyethylene powder was not blended, and the same measurements were carried out. The measurement results are shown in Table 6.

Example 1 The same procedure as in Example 1 was carried out except that the amount of 0° polyethylene powder was changed to 20 parts by weight. The results are shown in Table 4.

Comparative Example 8 The same procedure was carried out as in Example 10 except that FEF carbon black was added in place of the polyethylene powder. The results are also shown in Table 4.

Comparative Example 9 The same procedure as in Example 10 was carried out except that talc was added in place of the polyethylene powder. The results are also shown in Table 4.

Claims (2)

[Claims] (1) 5 to 150 parts by weight of a crystalline polyolefin powder having a density of 0.920 to 0.970 g/cm^3 and a particle size of 74 μm or less is mixed and dispersed in 100 parts by weight of at least one type of natural rubber or synthetic rubber. 50%
A low specific gravity rubber composition with improved hardness, characterized in that it exhibits a stress of 4 MPa or less when stretched. (2) The rubber composition according to claim 1, wherein the polyolefin is polyethylene.