JPS6234059B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an olefinic thermoplastic elastomer compound that provides molded articles with no stickiness and improved oil resistance. Many polyolefin thermoplastic elastomer compounds are known, which are made by combining monoolefin copolymer rubber and polyolefin plastics, but these have the disadvantage of poor oil resistance. Monoolefin copolymer rubber has excellent weather resistance and cold resistance, but shows no resistance to hydrocarbon oils such as mineral oil. On the other hand, acrylonitrile-butadiene copolymer rubber (hereinafter abbreviated as NBR) shows excellent resistance to hydrocarbon oils, but has poor weather resistance and cold resistance, so monoolefin copolymer rubber and NBR There are many known techniques that attempt to obtain vulcanized rubber with excellent oil resistance, weather resistance, and cold resistance by mixing. However, co-vulcanization of mono-olefin copolymer rubber and NBR is difficult due to wide differences in solubility of the vulcanization accelerator and vulcanizing agent, and poor affinity between the two copolymers. For this reason, no effective technology has yet been obtained in the field of vulcanized rubber. Olefin thermoplastic elastomers, whose main raw materials are monoolefin copolymer rubber and polyolefin plastics, take advantage of their excellent weather resistance, cold resistance, and economical molding, and are used in automobile interior and exterior parts and electric wire coating materials. Although it is gaining demand in the field, it has no resistance at all to hydrocarbon oils, and when oil comes into contact with it, it swells significantly and deforms to the point where it no longer retains its original shape, so it has a wide range of uses. Limited in width. For example, automotive exterior parts that are installed near the gasoline filler port may be contaminated with gasoline during refueling.
If it adheres, there is a risk that the appearance and shape of the part will change significantly, so olefin-based thermoplastic elastomers cannot be used. This phenomenon is particularly remarkable in the case of highly flexible thermoplastic elastomers containing a large amount of monoolefin copolymer rubber components. This is because monoolefin copolymer rubber has significantly lower resistance to hydrocarbon oils than polyolefin plastics. In other words, it is impossible to use olefinic thermoplastic elastomers for parts that may come into contact with hydrocarbon oils, especially in applications where functional flexibility is required. As mentioned above, many attempts have been made in the vulcanized rubber field to improve the oil resistance of monoolefin copolymer rubber. In other words, the essential cause of the poor oil resistance of monoolefin copolymer rubber is due to its non-polar chemical structure; therefore, the method of adding and mixing rubbers with other polar chemical structures is generally adopted. There is. As a polar chemical structure rubber, usually
NBR is adopted. However, monoolefin copolymer rubber
When mixing NBR to obtain a vulcanized rubber with improved oil resistance, the polarity of the two rubbers is significantly different, so the solubility of the blended vulcanization accelerator and vulcanizing agent in the rubber is different, resulting in one Since the vulcanization accelerator and the vulcanizing agent are localized in the rubber, co-vulcanization is difficult, and the affinity between the two rubbers is extremely poor, resulting in a decrease in vulcanized physical properties. accordingly
Improving the oil resistance of monoolefin copolymer rubber by incorporating NBR has been taken up as an important technical issue in the rubber industry, and several publicly known techniques are known. For example, there is a method to achieve co-vulcanization using a special vulcanization accelerator (Japanese Patent Publication No. 52-19574), which has closer solubility to mono-olefin copolymer rubber and NBR, and Method of improving affinity by adding a third special polymer to polymer rubber/NBR system
67754) etc. are known. As a result of intensive research aimed at improving the oil resistance of polyolefin-based thermoplastic elastomers, the present inventors discovered that monoolefin copolymer rubber
After kneading NBR and polyolefin plastic and melting the polyolefin plastic, the monoolefin copolymer rubber and NBR were partially co-crosslinked by simultaneously causing a crosslinking reaction while dispersing the organic peroxide. It has been discovered that non-stick thermoplastic elastomer formulations with improved oil resistance are obtained. The present invention was achieved based on this knowledge, and its gist is that monoolefin copolymer rubber, acrylonitrile-butadiene copolymer rubber, and polyolefin plastics are kneaded, and the polyolefin plastics is melted. After that, the crosslinking agent is dispersed and acted upon, and the monoolefin copolymer rubber and acrylonitrile are combined.
The present invention relates to a thermoplastic elastomer compound that is characterized by partially co-crosslinking butadiene copolymer rubber and provides non-sticky molded products and improved oil resistance. In the present invention, monoolefin copolymer rubber and NBR are mixed in a closed kneader such as a Banbury mixer in the presence of a molten polyolefin plastic and a crosslinking agent such as an organic peroxide. Co-crosslinking is achieved by applying the kneaded crosslinked product to both monoolefin copolymer rubber and NBR copolymers while dispersing them. In the present invention, since the dispersion of the crosslinking agent and the crosslinking reaction are carried out simultaneously, problems with the solubility of the crosslinking agent do not occur, and a thermoplastic elastomer with improved oil resistance can be obtained. According to this method, a non-stick thermoplastic elastomer compound with improved oil resistance and less material deterioration can be obtained without using the special vulcanizing agent or the third special polymer. Compounds made by methods other than the present invention, i.e., compounds in which NBR is simply mixed with an olefin thermoplastic elastomer made from monoolefin copolymer rubber and polyolefin plastic, have the effect of improving oil resistance, but the molded product becomes sticky. gender is observed. If the molded product is sticky with plastic materials, the commercial value of the material will be drastically reduced, so when improving the oil resistance of olefin thermoplastic elastomers,
It is essential to co-crosslink the monoolefin copolymer rubber and NBR. Furthermore, if the present invention is explained in detail, a pre-heated roll mill,
A predetermined amount of polyolefin plastics, monoolefin copolymer rubber, NBR is added to an internally closed kneading machine such as a Banbury mixer or a pressure kneader.
Charge and start kneading. The charged polymer will eventually melt the polyolefin plastic due to self-heating. At this point, a small amount of crosslinking agent is added and dispersed in the polymer to ensure that almost 100% of the crosslinking agent is used, partially co-crosslinking the monoolefin copolymer rubber and NBR, resulting in a non-stick, oil-resistant product. Improved thermoplastic elastomer formulations can be obtained. After kneading, this compound is processed into a shape that can be molded using a conventional plastic molding machine, that is, into pellets or flakes. The basic method for obtaining an oil-resistant thermoplastic elastomer compound according to the present invention has been described above, but if desired, extender oil such as mineral oil, dioctyl phthalate, etc. may be used, as is generally known in the rubber industry. A plasticizer may be added, and various pigments, heat stabilizers, and weather stabilizers may be added as appropriate. Furthermore, for the oil-resistant thermoplastic elastomer obtained by the present invention, low density polyethylene,
A polyolefin resin such as high-density polyethylene or ethylene/vinyl acetate copolymer may be added to impart desired performance such as rigidity. Next, various raw materials used in the present invention will be explained. First, as a monoolefin copolymer rubber, a Ziegler-Natsuta catalyst represented by a combination of a vanadium compound and an aluminum compound is used to produce monoolefin copolymer rubber. It is an essentially amorphous random copolymer made by copolymerizing polyenes. Typically, one monoolefin is ethylene and the other is propylene, but other α
- Monoolefins (general formula CH ₂ =CHR) can also be used. This monoolefin copolymer rubber may be a saturated compound such as an ethylene/propylene two-component copolymer rubber, but by incorporating a small amount of at least one copolymerizable polyene into the copolymer,
It is usually preferred to impart unsaturation to the copolymer. As polyene, 1,4-hexadiene,
Cyclopentadiene, methylenenorbornene, ethylidenenorbornene, propenylnorbornene, cyclooctadiene, methyltetrahydroindene, etc. are used. Next, polyolefin plastics include isotactic and syndioctic polypropylene having a high degree of crystallinity, and also crystalline block copolymers of ethylene and propylene. The NBR used in the present invention is an acrylonitrile-butadiene copolymer rubber containing 15 to 50% by weight of acrylonitrile. More preferably, NBR with a lower acrylonitrile content is preferred in consideration of affinity with monoolefin copolymer rubber. That is, the acrylonitrile content is preferably 15 to 35% by weight. Furthermore, modified NBR obtained by copolymerizing 10% by weight or less of a third monomer such as an unsaturated carboxylic acid such as acrylic acid or methacrylic acid and an alkyl ester thereof may also be used. As the crosslinking agent used in the present invention, a free radical generator such as an organic peroxide is usually used. Organic peroxides used as crosslinking agents include 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di-t-butylperoxide, and 2,5-dimethyl-2. 5-di(t
-butylperoxy)hexane, α・α′-bis(t-butylperoxy)-p-diisopropylbenzene, dicumylbutylperoxide, t-butylperoxybenzoate, 1,1-bis(t-butylperoxy)hexane,
-butylperoxy)-3,3,5-trimethylcyclohexane, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, p-
Chlorbenzoyl peroxide, etc.
More preferably, a high-temperature decomposition type is selected and used. Furthermore, as for the method of adding the organic peroxide, it is preferable to adopt the technique disclosed in Japanese Patent Application Laid-Open No. 1386-1986 by the present inventors for the purpose of ensuring safety and quality stability. That is, this is a method in which a monoolefin copolymer rubber masterbatch containing an organic peroxide crosslinking agent and a crosslinking reaction retarder is added after production. Next, the proportions of monoolefin copolymer rubber, polyolefin plastics, NBR, and organic peroxide crosslinking agent will be explained. The proportion of each polymer and crosslinking agent is determined according to the required performance as a thermoplastic elastomer, but in order to maintain elasticity and thermoplasticity, the proportion of polyolefin-in plastic should be 10 to 50% by weight of the total polymer. It is necessary to adjust the rubber components of monoolefin copolymer rubber and NBR to 90 to 50% by weight. The ratio of the monoolefin copolymer rubber to NBR is determined depending on the level of oil resistance required, and is selected within the range of 5 to 700 parts by weight of NBR per 100 parts by weight of the monoolefin copolymer rubber. If NBR is less than 5 parts by weight, there is no oil resistance improvement effect, and if it exceeds 700 parts by weight, the weather resistance and heat resistance, which are the characteristics of monoolefin copolymer rubber, are impaired. Preferably 30-300
Selected within the range of parts by weight. On the other hand, the amount of the crosslinking agent is determined in the range of 0.1 to 1.0 parts by weight, and more preferably 0.3 to 0.7 parts by weight, based on 100 parts by weight of the total polymer. This is because if the amount of the crosslinking agent is too small, the co-crosslinking property will be poor, and if it is too large, the crosslinking will proceed excessively, thereby impairing the moldability of the thermoplastic elastomer and significantly deteriorating the molded appearance. The oil resistance improvement effect depends on the proportion of NBR blended and
Although it varies depending on the type of NBR, that is, the acrylonitrile content, the oil resistance ΔV, ΔW
(Volume change rate and weight change rate after immersion in kerosene at room temperature for 3 hours...according to test method JIS-K6301) are greatly improved. (Comparison of Experiment Numbers 1 to 6 and Experiment Numbers 7 to 10) Furthermore, as an effect of co-crosslinking of monoolefin copolymer rubber and NBR, as shown in Example 1 and Comparative Example 2, polyolefin plastics and monoolefin copolymer rubber were After producing an olefinic thermoplastic elastomer from a copolymer rubber and a crosslinking agent, simply
The thermoplastic elastomer blend of the present invention was tested in tensile tests (JIS-
K6301), the 100% stress (M ₁₀₀ ) and stress at break (T _B ) are large, and the injection molded product is free from stickiness. (Experiment numbers 1-3
(Comparison of Experiment Nos. 11 to 13) Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Details of each component used in Examples and Comparative Examples are as follows. Monoolefin copolymer rubber; EPM ()
(ML ₁₊₄ 100=40, propylene content 49wt%),
EPDM () (ML ₁₊₄ 100=38, propylene content
34wt%, iodine value 19...Third component ethylidene norbornene 6wt%). Crystalline polypropylene; PP () (melt flow index 12...ASTM D1238, measurement temperature
230℃, specific gravity 0.91) NBR; NBR () (ML ₁₊₄ 100 = 56, bound acrylonitrile content 26wt%), NBR () (ML ₁₊₄ =
63, bound acrylonitrile content 20wt%) Organic peroxide crosslinking agent; PO() (α・α′-bis(t-butylperoxy)p-diisopropylbenzene) Organic peroxide crosslinking reaction retarder; RE()( Dibenzothiazole disulfide) Organic peroxide master batch; MB () (EPM
() to 100 parts by weight, 40 parts of PO(),
Example 1 A thermoplastic elastomer compound was manufactured according to the formulation shown in Table 1 according to the following procedure.
The physical property evaluation results are also shown in Table 1. The manufacturing procedure for the thermoplastic elastomer compound is to preheat to 170°C.
EPDM (), PP (), NBR () in a pressure kneader (manufactured by Moriyama Seisakusho, capacity 1) preheated to
Alternatively, NBR () was added, kneading was continued for 2 minutes, PP () was brought under molten state, and organic peroxide masterbatch MB () was added. After addition,
Continue kneading for another 6 minutes until the organic peroxide is 100%
A thermoplastic elastomer compound was obtained. A portion of the resulting blend was press-molded and then evaluated for physical properties. The remaining mixture was processed into square pellets using a cube pelletizer, molded into a plate-shaped test piece using an injection molding machine, and the sticky state of the surface was observed. (Experiment No. 1-6) Comparative Example I As a comparative example, a case where NBR is not used is shown.
A thermoplastic elastomer compound was produced according to the formulation shown in Table 2 in exactly the same manner as in Example 1 except for the addition of NBR, and its physical properties were evaluated. (Experiment Nos. 7 to 10), and the formulations of Experiment Nos. 7 to 9 are referred to as TPE() to TPE(), respectively. Comparative Example 2 As a comparative example, a case where an olefin thermoplastic elastomer and NBR are simply mixed is shown. That is, the thermoplastic elastomer blend obtained in Comparative Example 1 and NBR () were simply mixed together in a pressure kneader according to the blending recipe shown in Table 3, and the physical properties of the resulting blend were evaluated. (Experiment number 11~
13) The formulations of experiment numbers 1 to 3 were controlled so that the proportions of each component were the same as those of the formulations of experiment numbers 11 to 13, respectively. Comparative Example 3 EPDM (), PP (), NBR () and
By adding PO() at the same time, approximately 360 〓 (approximately 180
℃) for 8 minutes to produce a thermoplastic elastomer blend. The physical properties of the obtained formulation were evaluated in the same manner as in Example 1, and the results are shown in Table 4. Experiment number 1 of corresponding Example 1
The oil resistance and tensile strength (M ₁₀₀ , T _B ) are considerably inferior to those of . The test methods for the test items shown in Tables 1 to 4 are listed below. Hardness JIS K-6301 (Type A) M ₁₀₀ (100% stress); JIS K6301 T _B (stress at break); E _B (elongation at break); Oil resistance △V; white kerosene, room temperature, 3hrs Volume change rate after immersion (according to JIS K6301) Oil resistance △W: White kerosene, room temperature, weight change rate after immersion for 3 hours (according to JIS K6301) ETQ; Koka type flow tester, 200℃, 300Kg load, nozzle 1mmφ Flow rate per second of 2mm sticky; Yamashiro Seiki, 1OZ injection molding machine, cylinder temperature 200℃, injection molded sheet. Determine the stickiness of the molded product by feeling it with your hands.

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Claims (1)

[Claims] 1. Knead the monoolefin copolymer rubber, acrylonitrile-butadiene copolymer rubber, and polyolefin plastics, and after the polyolefin plastics has melted, apply the crosslinking agent while dispersing it to combine the monoolefin copolymer rubber with the acrylonitrile-butadiene copolymer rubber. A thermoplastic elastomer compound which is characterized by partially co-crosslinking butadiene copolymer rubber and which prevents molded products from becoming sticky and has improved oil resistance.