JP7462413B2 - Rubber foam and method for producing rubber foam - Google Patents

Description

This disclosure relates to a rubber foam and a method for producing a rubber foam.

As cylindrical rubber molded bodies, for example, hoses are disclosed in Patent Documents 1 and 2.
Patent Document 1 discloses a hose using the following rubber composition: The rubber composition contains a rubber component and a chlorine-based flame retardant, and contains less than 70 parts by mass of chloroprene rubber per 100 parts by mass of the rubber component, and contains 5 parts by mass or more of the chlorine-based flame retardant per 100 parts by mass of the rubber component.
Patent Document 2 discloses a hose using the following rubber composition: The rubber composition contains chloroprene rubber, butadiene rubber, and styrene-butadiene rubber as rubber components, and contains 60 to 80 parts by mass of chloroprene rubber per 100 parts by mass of the rubber component, and contains 5 to 25 parts by mass of silica per 100 parts by mass of the rubber component.
Incidentally, a cylindrical rubber foam is often used to surround a hose and to insulate the hose. For example, a rubber foam is used as a so-called hose heater around a hose used for an industrial robot or the like.
For example, Patent Document 3 discloses a heat insulating foam using CR (chloroprene rubber) and PVC (polyvinyl chloride).

JP 2017-2173 A JP 2013-129684 A JP 2016-74883 A

However, conventional heat insulating foams do not necessarily have sufficient durability or heat insulating properties, and improvements in these physical properties have been desired.
The present disclosure has been made in view of the above-mentioned circumstances, and has an object to provide a rubber foam having good durability and high thermal insulation properties. The present disclosure can be realized in the following aspects.

[1] A rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride,
When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less,
A rubber foam having a specific gravity of 0.05 or more and 0.15 or less.

The rubber foam disclosed herein has good durability and high thermal insulation properties.

FIG. 1 is a perspective view illustrating an example of a rubber foam. 1 is a photograph showing a rubber foam after an abrasion resistance test.

Here, a preferred example of the present disclosure is given.
[2] The rubber foam according to [1], comprising at least one selected from the group consisting of a halogen-based flame retardant and an antimony-based flame retardant.
This configuration improves the flame retardancy of the rubber foam.

[3] The rubber foam according to [1] or [2], which is cylindrical.
The cylindrical shape makes it useful as a hose heater.

[4] A method for producing a rubber foam using a mixture containing acrylonitrile-butadiene rubber, polyvinyl chloride, and azodicarboxylic acid amide particles as a raw material, comprising:
As the azodicarboxylic acid amide particles, two or more kinds of particles having different median diameters are used,
The median diameters of the two or more types of particles differ from each other by 1 μm or more and 15 μm or less,
the median diameter of any of the two or more types of particles is 5 μm or more and 40 μm or less.
This manufacturing method provides a rubber foam having good durability and high thermal insulation properties.

This disclosure is explained in detail below. Note that when a range is indicated as "x to y," it means that x and y are included in the range unless otherwise specified.

1. Rubber foam 1
The rubber foam 1 contains acrylonitrile-butadiene rubber (NBR) and polyvinyl chloride (PVC). When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less from the viewpoint of exhibiting excellent abrasion resistance while maintaining low thermal conductivity of the rubber foam 1.

(1) Specific Gravity The specific gravity of the rubber foam 1 is from 0.05 to 0.15, preferably from 0.07 to 0.13, and more preferably from 0.08 to 0.10, from the viewpoint of imparting high durability and high thermal insulation to the rubber foam 1. The specific gravity of the rubber foam 1 refers to a value measured at a temperature condition of 23° C. by JIS K7112 Method A "underwater displacement method".

(2) Acrylonitrile-butadiene rubber The acrylonitrile-butadiene rubber (NBR) is not particularly limited as long as a known acrylonitrile-butadiene rubber is appropriately selected and used. The amount of acrylonitrile (AN content) contained in the acrylonitrile-butadiene rubber (NBR) is not particularly limited. The amount of acrylonitrile (AN content) is, for example, preferably 23% by mass or more and 43% by mass or less, more preferably 28% by mass or more and 38% by mass or less.
The Mooney viscosity ML(1+4) of acrylonitrile-butadiene rubber (NBR) at 100° C. measured in accordance with JIS K6300 is not particularly limited. From the viewpoint of reducing the specific gravity and maintaining the shape of the sponge, this Mooney viscosity ML(1+4) is preferably 30 or more and 70 or less, and more preferably 40 or more and 60 or less.

(3) Flame Retardant The rubber foam 1 preferably contains a flame retardant. Any flame retardant can be used as the flame retardant. The type of flame retardant is not particularly limited, but from the viewpoint of exerting a high flame retardant effect with a small blending amount without reducing the properties such as the tensile modulus of the foam, it is preferable to use a combination of a halogen-based flame retardant and an antimony-based flame retardant.

Examples of halogen-based flame retardants include chlorine compounds and bromine compounds, and two or more of these may be used in combination.
Suitable examples of the chlorine compound include chlorinated paraffin and perchloropentacyclodecane.
Suitable examples of the bromine compound include tetrabromobisphenol A, ethylene bistetrabromophthalimide, pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, hexabromocyclododecane, and brominated polystyrene.

Examples of antimony-based flame retardants include antimony trioxide, antimony pentoxide, antimony trichloride, and antimony pentachloride.

When a halogen-based flame retardant and an antimony-based flame retardant are used in combination, the content (addition amount) of the halogen-based flame retardant per 100 parts by mass of the rubber component (the total of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass), from the viewpoint of imparting sufficient flame retardancy while maintaining high durability, is preferably 30 parts by mass or more and 80 parts by mass or less, and more preferably 45 parts by mass or more and 65 parts by mass or less.
The content (addition amount) of the antimony-based flame retardant is preferably 5 parts by mass or more and 30 parts by mass or less, and more preferably 10 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the rubber component (100 parts by mass of the total of the acrylonitrile-butadiene rubber and polyvinyl chloride), from the viewpoint of imparting sufficient flame retardancy while maintaining high durability.

(4) Filler The rubber foam 1 may contain a filler. Any filler can be used as the filler. Examples of the filler include inorganic fillers such as calcium carbonate, talc, magnesium hydroxide, mica, clay, aluminum hydroxide, magnesium hydroxide, barium sulfate, silicic acid, titanium oxide, bentonite, carbon black, mica, glass fiber, and wood powder. The amount of the filler is preferably 40 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the rubber component, from the viewpoints of processability, dimensional stability of the product, and strength of the product.

(5) Other Components Examples of other components include a softening agent, a crosslinking agent, a foaming agent, etc.
The softener may be any of vegetable oils such as lauric acid, ricinoleic acid, baltimic acid, cottonseed oil, soybean oil, castor oil, palm oil, etc., and mineral oils such as paraffinic, naphthenic, aromatic, etc. The amount of the softener is preferably 30 to 110 parts by weight per 100 parts by weight of the rubber component from the viewpoints of kneadability, product strength, etc.
The total amount of the filler and the softener added is preferably 70 to 250 parts by weight per 100 parts by weight of the rubber component. The compounding ratio of the filler and the softener is preferably 65:35 to 50:40. By setting the total amount and ratio of the filler and the softener added within the above range, compatibility is increased and moldability such as rubber kneading is excellent.

Sulfur and organic peroxides are used as crosslinking agents. Sulfur is used in the case of sulfur crosslinking, and organic peroxides are used in peroxide crosslinking. Examples of organic peroxides include dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, and t-butylcumyl peroxide. The amount of crosslinking agent is preferably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component. It is preferable to use a crosslinking accelerator or crosslinking assistant together with the crosslinking agent.

Examples of the crosslinking accelerator include benzothiazyl disulfide, 2-mercaptobenzothiazole, dipentamethylene thiuraum tetrasulfide, tetramethylthiuraum disulfide, and zinc oxide.
Examples of the crosslinking aid include divinylbenzene, ethylene dimethacrylate, trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, triallyl cyanurate, and triallyl isocyanurate.

The foaming agent may be one or more selected from organic foaming agents and inorganic foaming agents.
The organic foaming agent is not particularly limited, but azo compounds are suitable examples. The azo compounds are not particularly limited, but one or more of azodicarboxylic acid amide (ADCA), barium azodicarboxylate, azobisisobutyronitrile (AIBN), azocyclohexylnitrile, azodiaminobenzene, etc. are suitable examples.
The inorganic foaming agent is not particularly limited. For example, hydrogen carbonates such as sodium hydrogen carbonate (sodium bicarbonate) and ammonium hydrogen carbonate, carbonates such as sodium carbonate and ammonium carbonate, nitrites such as sodium nitrite and ammonium nitrite, borohydrides such as sodium borohydride, azides, and other known inorganic foaming agents can be used.
The amount of the foaming agent is preferably 5 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the rubber component.
It is also preferable to use a foaming assistant together with the foaming agent. Examples of the foaming assistant include urea compounds, organic compounds, inorganic salts, and the like.
Other components may also be added, such as processing aids, colorants, and antioxidants. Examples of processing aids include stearic acid and palmitic acid.

(6) Shape of Rubber Foam 1 There is no particular limitation on the shape of the rubber foam 1. The shape of the rubber foam 1 can be changed appropriately depending on the application. For example, a cylindrical shape can be suitably adopted as the shape of the rubber foam 1 (see FIG. 1). The cylindrical rubber foam 1 can be used as a heat insulating tube. Note that the heat insulating tube is used for insulating flexible tubes and flexible hoses for industrial robots and the like.

(7) Effects of the Rubber Foam 1 of the Embodiment The rubber foam 1 has good durability because it contains acrylonitrile-butadiene rubber and polyvinyl chloride in a specified ratio. The rubber foam 1 has a slippery surface than EPDM sponge, and therefore has excellent abrasion resistance.
The rubber foam 1 has high heat insulation properties because it contains acrylonitrile-butadiene rubber, which has low thermal conductivity, and polyvinyl chloride, which also has low thermal conductivity. The thermal conductivity of the polymer alone is 0.25 W/m K for acrylonitrile-butadiene rubber, 0.13 W/m K for polyvinyl chloride, and 0.36 W/m K for EPDM.
Moreover, the rubber foam 1 of the present embodiment has a specific gravity of not less than 0.05 and not more than 0.15, and has a particularly low thermal conductivity.

2. Manufacturing Method of Rubber Foam 1 (1) Manufacturing Method of Rubber Foam 1 In the manufacturing method of rubber foam 1, a mixture containing acrylonitrile-butadiene rubber, polyvinyl chloride, and azodicarboxylic acid amide particles is used as a raw material. Two or more types of particles having different median diameters are used as the azodicarboxylic acid amide particles. The median diameters of the two or more types of particles differ from each other by 1 μm or more and 15 μm or less. The median diameter of each of the two or more types of particles is 5 μm or more and 40 μm or less.
The reason why it is assumed that the use of two or more types of azodicarboxylic acid amide particles having different median diameters in this manner results in a rubber foam 1 having good durability and high heat insulating properties will be explained.
In this manufacturing method, it is believed that first, vulcanization proceeds moderately while the particles having a small median diameter are foamed. During this process, the foam retains gas. Thereafter, when the foaming of the particles having a small median diameter is nearly completed, the particles having a large median diameter are foamed, which is believed to lower the specific gravity of rubber foam 1.

When, among two or more types of particles having different median diameters, the particles having the smallest median diameter are designated as first particles and the particles having the largest median diameter are designated as second particles, the mass ratio of the first particles:second particles is preferably 95:5 to 20:80, more preferably 92:8 to 25:75, and even more preferably 60:40 to 25:75, from the viewpoint of slowing down the vulcanization of the rubber during foaming, thereby improving the balance between foaming and vulcanization, and suppressing gas escape to reduce the specific gravity of the rubber foam.
When there are two types of particles having different median diameters, the particles having the smaller median diameter are the first particles, and the particles having the larger median diameter are the second particles.

The total amount of azodicarboxylic acid amide particles is preferably 5 parts by mass or more and 100 parts by mass or less, and more preferably 10 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the rubber component (the total of acrylonitrile-butadiene rubber and polyvinyl chloride is 100 parts by mass), from the viewpoint of improving the balance between foaming and vulcanization, suppressing gas leakage, and lowering the specific gravity of the rubber foam.

An example of a suitable method for producing a rubber foam is shown below. First, the rubber component, compatibilizer, filler, etc. are primarily kneaded using a Banbury mixer, kneader, etc. In this case, the crosslinking agent, crosslinking accelerator, crosslinking assistant, foaming agent, and foaming assistant are not included. The conditions for the primary kneading are preferably a temperature of 50°C to 180°C and a kneading time of 3 to 30 minutes. Then, the crosslinking agent, crosslinking accelerator, crosslinking assistant, foaming agent, foaming assistant, etc. are added to the obtained primary kneaded product and the secondary kneading is performed. The conditions for the secondary kneading are preferably a temperature of 20°C to 80°C and a kneading time of 3 to 30 minutes. The obtained secondary kneaded product is formed into the desired shape using a calendar molding machine, extrusion molding machine, etc. Then, the mixture is placed in a crosslinking/foaming mold, and the primary crosslinking/foaming and secondary crosslinking/foaming are performed in sequence to obtain a rubber foam. The primary crosslinking/foaming is preferably performed at 100°C to 160°C for 3 to 20 minutes. Secondary crosslinking and foaming is preferably performed at 160°C to 220°C for 5 to 20 minutes.

(2) Effects of the Method for Producing Rubber Foam 1 of the Embodiment In the method for producing rubber foam 1 of the embodiment, two or more types of azodicarboxylic acid amide particles having different median diameters are foamed in a rubber component containing acrylonitrile-butadiene rubber and polyvinyl chloride so as to reduce the density of rubber foam 1. Therefore, in this production method, a rubber foam 1 containing acrylonitrile-butadiene rubber having low thermal conductivity as a material-specific property and polyvinyl chloride having low thermal conductivity as a material-specific property and also having a low specific gravity, and as a result, having particularly low thermal conductivity, can be produced. In addition, in this production method, a rubber foam 1 containing acrylonitrile-butadiene rubber and polyvinyl chloride can be produced which has a slippery surface and excellent abrasion resistance.

The present invention will now be described in more detail with reference to the following examples.

1. Preparation of rubber foam (Examples 1 to 8 and Comparative Examples 1 to 3)
Various rubber foams were produced according to the blending ratios shown in Table 1. In this case, the raw materials shown in Table 3 were blended in common for Examples 1 to 8 and Comparative Examples 1 to 3.
Table 2 shows the names of the raw materials and the names of the manufacturers listed in Table 1.
In Table 1, "DPT" means "N,N'-dinitrosopentamethylenetetramine."

The primary kneading was carried out using a kneader at a temperature of 160° C. for a kneading time of 5 minutes, and the secondary kneading was carried out using rolls at a temperature of 50° C. for a kneading time of 10 minutes.
The primary crosslinking and foaming was carried out by placing 70 g of the secondary kneaded product in a mold having an internal volume of 57 ^cm3 at 130°C for 10 minutes.
Secondary crosslinking and foaming were carried out at 200° C. for 5 minutes using the same mold as in the primary crosslinking and foaming.

2. Evaluation Method (1) Specific Gravity Measured at 23° C. according to JIS K7112, Method A, “Water Substitution Method”.

(2) Thermal Conductivity The thermal conductivity is a value measured in accordance with JIS-A1412-2. The thermal conductivity was measured by a probe method using a rapid thermal conductivity meter (QTM-500) manufactured by Kyoto Electronics Manufacturing Co., Ltd.

(3) Flame retardancy Flame retardancy was measured in accordance with the 20 mm vertical flame test (IEC 60695-11-10 Method B, ASTM D3801). A test piece was attached vertically to a clamp, and exposed to a 20 mm flame for 10 seconds twice. The flame behavior was evaluated as V-0, V-1, V-2, or Not.
If each of the criteria was as follows, the flammability classification was determined to be "V-0".

Burning time of each test piece: 10 seconds or less Total burning time of 5 pieces: 50 seconds or less Burning + glowing time of each test piece: 30 seconds or less Burning to clamp: None Cotton ignition by dripping: None

(4) Abrasion Resistance The abrasion resistance test method (abrasion test method) was performed as follows: After 2000 rubs, if there was no abrasion on the surface, it was rated as "good", and if there was abrasion, it was rated as "no good".
Testing device name: Gakushin type friction testing machine Testing method: JIS K 6404-4 Testing method for rubber-coated and plastic-coated fabrics Part 4: Durability test 8.3 Gakushin type friction test Load (weight of friction element): 200g
・Friction speed: 30 times/min ・Friction distance: 100 mm
・Cotton cloth was wrapped around the friction element.

(5) Overall Judgment The overall judgment was as follows:
"Good": Meets all three of the following criteria.
"Fail": Does not meet one or more of the following three criteria.
<Items>
[1] Thermal conductivity: 0.043 W/m·K or less [2] Flame retardancy: V-0 equivalent [3] Abrasion resistance test result: Good

3. Results The results are shown in Table 4.

(1) Satisfaction of Each Requirement in Examples 1 to 8 The rubber foams of Examples 1 to 8 satisfy all of the following requirements (a) to (d).
Requirement (a): A rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride.
Requirement (b): The amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less, when the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass.
Requirement (c): The specific gravity is 0.05 or more and 0.15 or less.
Requirement (d): Two types of azodicarboxylic acid amide particles having different median sizes are used.

(2) Satisfaction of Each Requirement of Comparative Examples 1 to 3 In contrast, the rubber foams of Comparative Examples 1 to 3 do not satisfy the following requirements.
Comparative Example 1 does not satisfy the requirements (a), (b), (c), and (d).
Comparative Example 2 does not satisfy the requirements (a), (b), and (d).
Comparative Example 3 does not satisfy the requirements (c) and (d).

(3) Results and Observations of Examples 1 to 8 The rubber foams of Examples 1 to 8 were evaluated as being good in the overall assessment. The rubber foams of Examples 1 to 8 had a low thermal conductivity of 0.043 W/m K or less, flame retardancy equivalent to V-0, and excellent abrasion resistance.
Fig. 2 shows the state after the abrasion resistance test of Example 2 and Comparative Example 1. There was no abrasion on the surface of Example 2 on the right side of Fig. 2, whereas there was abrasion on the surface of Comparative Example 1 on the left side.

(4) Results and Considerations of Comparative Examples 1 to 3 The rubber foam of Comparative Example 1 uses EPDM as the rubber component and has a high specific gravity. The rubber foam of Comparative Example 1 had high thermal conductivity and poor abrasion resistance.
The rubber foam of Comparative Example 2 uses only NBR as the rubber component. The rubber foam of Comparative Example 2 had poor abrasion resistance.
The rubber foam of Comparative Example 3 uses NBR and PVC as rubber components. However, the rubber foam of Comparative Example 3 is not produced using two or more types of azodicarboxylic acid amide particles having different median diameters, and has a high specific gravity. The rubber foam of Comparative Example 3 has a high thermal conductivity of 0.059 W/m·K.
From the above results, it was confirmed that the specific gravity of the rubber foam was low when a rubber foam containing acrylonitrile-butadiene rubber and polyvinyl chloride and containing 50 parts by mass or more and 90 parts by mass or less was produced using two types of azodicarboxylic acid amide particles having different median diameters as in Examples 1 to 8. It was confirmed that the rubber foams of Examples 1 to 8 had low thermal conductivity, high flame retardancy, and high abrasion resistance.

4. Effects of the Examples According to the above examples, it is possible to provide a rubber foam having low thermal conductivity, high flame retardancy, and high abrasion resistance.

The present invention is not limited to the embodiments detailed above, and various modifications and variations are possible within the scope of the claims of the present invention.

1...Rubber foam

Claims (4)

A rubber foam comprising acrylonitrile-butadiene rubber, polyvinyl chloride, a halogen-based flame retardant, and an antimony-based flame retardant,
When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less,
The content of the halogen-based flame retardant is 45 parts by mass or more and 65 parts by mass or less, and the content of the antimony-based flame retardant is 10 parts by mass or more and 20 parts by mass or less,
A rubber foam having a specific gravity of 0.05 or more and 0.15 or less (however, excluding those containing 25 to 200 parts by weight of polymethyl methacrylate per 100 parts by weight of acrylonitrile-butadiene rubber). A rubber foam comprising acrylonitrile-butadiene rubber, polyvinyl chloride, a halogen-based flame retardant, and an antimony-based flame retardant,
When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less,
The content of the halogen-based flame retardant is 45 parts by mass or more and 65 parts by mass or less, and the content of the antimony-based flame retardant is 10 parts by mass or more and 20 parts by mass or less,
A rubber foam having a specific gravity of 0.07 or more and 0.15 or less. A rubber foam comprising acrylonitrile-butadiene rubber, polyvinyl chloride, at least one selected from the group consisting of a halogen-based flame retardant and an antimony-based flame retardant, and aluminum hydroxide,
When the total amount of the acrylonitrile-butadiene rubber and the polyvinyl chloride is 100 parts by mass, the amount of the acrylonitrile-butadiene rubber is 50 parts by mass or more and 90 parts by mass or less, and the amount of the aluminum hydroxide is 40 parts by mass or more and 140 parts by mass or less,
A rubber foam having a specific gravity of 0.05 or more and 0.15 or less. A method for producing a rubber foam using a mixture containing acrylonitrile-butadiene rubber, polyvinyl chloride, and azodicarboxylic acid amide particles as a raw material, comprising:
As the azodicarboxylic acid amide particles, two or more kinds of particles having different median diameters are used,
The median diameters of the two or more types of particles differ from each other by 1 μm or more and 15 μm or less,
the median diameter of any of the two or more types of particles is 5 μm or more and 40 μm or less.

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