JPH0434570B2 - - Google Patents

Description

[Detailed description of the invention]

Cured Rubber Compounds and Process for Producing the Same Field of the Invention The present invention provides a method for preparing blends of (a) highly unsaturated rubbers and (b) saturated rubbers with sulfur, sulfur cure accelerators, zinc oxide, and peroxide cured rubber compounds. It relates to a rubber composition made by curing using a curing agent consisting of: In another aspect, the invention relates to a method of manufacturing the rubber composition. BACKGROUND OF THE INVENTION The rubber industry has long sought to provide rubber formulations that combine the toughness of highly unsaturated rubbers (e.g., diene rubbers) with the ozone resistance of saturated rubbers (e.g., ethylene-propylene elastomers). The goal was to In the past, it has been difficult to produce cured blends of highly unsaturated and saturated rubbers.
The resulting product typically exhibits physical properties that are inferior to those of such rubber alone. This phenomenon is generally attributed to the co-curing incompatibility of unsaturated and saturated rubbers due to their polarity and different degrees of saturation. Moreover, curing migration between saturated and unsaturated components can also lead to curing difficulties. One important factor in the field of rubber processing is scorch time. Scorch is an early vulcanization of a rubber stock in which the stock is partially vulcanized before the product is in its final form and ready for vulcanization. Scorch reduces the plasticity of the compound so that it can no longer be processed as such. "Scorch time" refers to the time before such premature vulcanization occurs and is measured using a Mooney viscometer as described in ASTM Standard Method D-1646. Therefore, it is desirable that the method of curing the rubber composition has a relatively long scorch time. U.S. Pat. No. 3,299,175 [Marchesini et al.] discloses (A) a saturated amorphous copolymer of ethylene and a different alpha olefin; and (B)
A method for vulcanization of a mixture of polymer fillers obtained by free radical polymerization of divinylbenzene in the presence of a polymer of conjugated diolefins is presented. Marchesini et al. disclose that mixtures of peroxide and sulfur can be used as vulcanizing agents, and indicate that the amount of sulfur is generally about 0.1 to 3 gram atoms per mole of peroxide. The use of such mixed vulcanizing agents will cure mixtures of highly unsaturated and saturated rubbers, as shown in the table below, but from 0.1 to 0.1 per mole peroxide. 3
Mooniscorch times for such hardeners consisting of gram atom sulfur are relatively low. US Pat. No. 4,350,795 [Bohm]
et al. disclose a method for partially curing blends of 1-olefins, random styrene-butadiene rubber copolymers, and highly unsaturated elastomers. Bohm et al. show that combinations of sulfur and peroxide curatives can be utilized as is well known to those skilled in the art. Baum et al. further indicate that other additives, including accelerators, can be used, but the description in that patent is largely in addition to the Marchesini patent with respect to curing agents for formulations of rubbers with different degrees of saturation. There is no place. It would therefore be desirable to have a rubber composition that exhibits the toughness of highly unsaturated rubbers and the ozone resistance of saturated rubbers, while reducing the risk of scorch. It is therefore an object of the present invention to provide rubber compositions which exhibit desirable strength and resistance to oxidation and which can be produced with reduced risk of scorch. Another object of the present invention is to provide a method for producing such a rubber composition. The above objects and additional objects will become clearer in more detail from the description and examples below. DESCRIPTION OF THE INVENTION In one aspect, the present invention comprises: (a) at least one highly unsaturated rubber; (b) at least one saturated rubber; and (c) an effective amount of () sulfur. Rubber compositions made by curing a formulation comprising a curing accelerator, () at least one peroxide curing agent, and () a curing agent comprising zinc oxide, wherein the peroxide There is between about 5 and about 150 gram atoms of sulfur per mole. In another aspect of the invention, the following steps include: (a) at least one highly unsaturated rubber; (b) at least one saturated rubber; (c) an effective amount of () sulfur; A formulation is prepared consisting of () at least one sulfur cure accelerator, () at least one peroxide curetate, and () a curing agent consisting of zinc oxide, in which one peroxide
between about 5 and about 150 gram atoms per mole of sulfur are present; and () subjecting said formulation to curing conditions. As used herein, the term "highly unsaturated rubber" refers to rubber having an iodine number of 50 or higher. The term "saturated rubber" refers to rubbers with an iodine number of less than 50 and thus includes rubbers with low degrees of unsaturation as well as truly unsaturated rubbers. The iodine value of each rubber compound is S.
G. Gearo, Etsuchi. Kay. Weeds, and J.A. F. Nelson (SGGallo, Hk
Wiese, and JF Nelson), “Unsaturation in isoprene-isobutylene copolymers”
(“Unsaturation in Isoprene−Isobutylene
Copolymers”), Industrial and Engineering Chemistry (Industrial and
Engineering Chemistry), Vol. 40, Paragraphs 1277-80 (1948). Furthermore, as used herein, the term "peroxide" includes hydroperoxide curates as well as peroxide curates. Representative examples of highly unsaturated rubbers that can be used in the practice of this invention are diene rubbers. Such rubbers typically have an iodine number between about 100 and about 250, but can have higher or lower (i.e., 50
~100) Highly unsaturated rubbers with iodine numbers can also be used. Examples of diene rubbers that can be used include polymers based on conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc. Also included are copolymers of such conjugated dienes and monomers such as styrene, alpha-methylstyrene, acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, and the like. Particularly suitable highly unsaturated rubbers include natural rubber, cis-
Included are polyisoprene, polybutadiene, poly(styrene-butadiene) and poly(acrylonitrile-butadiene). Furthermore, mixtures of two or more highly unsaturated rubbers can also be used. Examples of saturated rubbers that may be used include copolymers of ethylene and copolymerizable monomers having the formula CH2=CHR, where R is _C1 - _C10 alkyl. Such copolymers include non-conjugated dienes such as dicyclopentadiene, 5-
Unsaturation can be included by incorporating ethylidene-2-norbornene, 1,4-hexadiene, and the like. The non-conjugated diene content of the saturated rubber used is 0.
ranging from approximately 20% by weight. Alternatively, other polymers such as butyl rubber can also be used. Furthermore, mixtures of two or more saturated rubbers can also be used. A particularly suitable saturated rubber is ethylene-propylene-diene terpolymer ("EPDM"). Sulfur curing accelerators that can be used include thioureas such as N,N'-dibutylthiourea, 2-methycaptoimidazoline, tetramethylthiourea, guanidine derivatives such as N,N'-diphenylguanidine, xanthates, dithiocarbamates such as zinc dibutylxanthate, dithiocarbamates such as zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, sodium diethyldithiocarbamate, thiuram sulfides such as dipentamethylenethiuram disulfide, dipentamethylene Heterocyclic compounds such as thiuram hexane sulfide, tetrabutylthiuram monosulfide, tetramethylthiuram monosulfide, tetraethylthiuram monosulfide, tetraethylthiuram disulfide, such as mercaptobenzimidazole, mercaptobenzthiazole, 2,2'-dibenzothiazyl disulfide, 2
- such as zinc mercaptobenzothiazole, and sulfenamides, such as N-oxydiethylene-2-benzothiazole sulfenamide, N-
t-Butylbenzothiazylsulfenamide, N
-cyclohexyl-2-benzothiazylsulfenamide, N,N-diisopropyl-2-benzothiazylsulfenamide, and the like. Furthermore, mixtures of two or more sulfur curing accelerators can also be used in the curing agent according to the invention. Particularly suitable accelerators are thiazoles and sulfenamides,
Particularly preferred are sulfenamides. Examples of peroxides that can be used include benzoyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, butyl 4,4-bis(t-butylperoxy)valerate, pperoxide
-chlorobenzoyl, cumene hydroperoxide, t-butylcumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t
-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butyl-peroxy-3-hexyne, 4-methyl-2,2-di-t-butylperoxypentane, and the like. Mixtures of two or more peroxides can also be used. Particularly suitable peroxides are dicumyl peroxide and 2,5-dimethyl-
2,5-di-t-butylperoxyhexane. The curing agent according to the invention consists of sulfur, at least one sulfur curing accelerator, zinc oxide and at least one peroxide curative. Between about 5 and about 150, preferably between about 6 and about 14, sulfur are present in the curing agent per mole of peroxide. The sulfur cure accelerator may be present in an amount between about 0.1 and about 5 grams per 100 grams of rubber, but preferably between about 0.3 and about 3.0 grams of accelerator per 100 grams of rubber. good. Most preferably about 0.3 grams and about 1.0 grams per 100 grams of rubber.
Accelerators between grams are used. It is preferred to use between about 2 and about 10 grams of zinc oxide per 100 grams of rubber, although amounts in excess of 10 grams can also be used. most preferably rubber
There may be between about 3 and about 5 grams of zinc oxide per 100 grams. between about 0.2 grams and about 5 grams, more preferably between about 0.5 grams and about 3 grams, and most preferably between about 0.5 grams and about 3 grams per 100 grams of rubber.
Use between 1.5 grams of sulfur. Using the sulfur to peroxide ratios discussed above, one skilled in the art can readily calculate the corresponding amount of a particular peroxide to be used. The weight ratio of highly unsaturated rubber to saturated rubber will generally vary between about 10/90 and about 90/10. A ratio between about 85/15 and about 60/40 is preferred for most applications, but as will be appreciated by those skilled in the art, ratios between about 85/15 and about 60/40 may be particularly suitable depending on the particular application to which the product is intended. The ratio will change. In addition to the highly unsaturated rubbers, saturated rubbers and curing agents mentioned above, the formulations according to the invention also contain reinforcing agents,
It can further include fillers, processing aids, extender oils, plasticizers, antioxidants, UV stabilizers, etc., and all of these additional ingredients are well known to rubber industry professionals. . Formulations according to the present invention are typically prepared by first mixing all ingredients except the curing agent in suitable mixing equipment (e.g., Banbury(TM) type internal mixer, two-roll mill, etc.). . Such mixing typically requires about 5 minutes, although shorter or longer mixing times can be used. This mixing can be carried out at room temperature or temperatures ranging from very low temperatures to about 180°C. If a mixing temperature above the activation temperature of the curing agent is used, after mixing is complete the compounded rubber is cooled to a temperature below such activation temperature or allowed to cool. The curing agent is then incorporated into the formulation by subsequent mixing or milling. Alternatively, formulations according to the invention can be prepared by formulating the saturated and unsaturated components and blending the desired amounts of these two components together. In this alternative embodiment, there is no particular limitation on the location of the components of the curing agent (i.e., peroxide, zinc oxide, sulfur, and sulfur cure accelerator), and any or all of such components may be substituted with the saturated component. , unsaturated components, or both. Vulcanization of the formulation can be carried out in a press, oven or other suitable equipment until cross-bonding occurs to a satisfactory degree of cure. EXAMPLES The following examples are intended to further illustrate the invention and are not intended to limit the scope of the invention in any way. Examples 1-6 and Comparative Experiments A and B Several rubber compositions were prepared as follows using the ingredients shown in the table (listed in parts per 100 parts by weight). Highly unsaturated rubber (Standard Malaysian Natural Rubber, Type 5CV) and saturated rubber (52 weight percent ethylene, 39 weight percent propylene, and 5-
EPDM consisting of 9 percent by weight of ethylidene-2-norbornene) in total (in the relative amounts listed in the table), together with 3 parts by weight of zinc oxide and 2 parts by weight of an antioxidant (reaction product of diphenylamine and acetone). , Banbury
(trademark) type B internal mixer.
Next, we started blending. After 2 minutes, add 50 parts by weight of N326 carbon black, extender oil [Type 103
oil (ASTM D2226)] 5.0 parts and stearic acid
1.0 part was introduced into the mixer. After continuing mixing for an additional 2 minutes, the inside of the mixer was cleaned and mixing continued for an additional minute. The formulation was then removed from the mixer. In the mill, hardener [1.0 part sulfur, 40% by weight active dicumyl peroxide on clay (Dicup 40KE)
3.5 parts and the amount and type of sulfur curing agent indicated in the table] was added to the mixture, taking care that the temperature of the mixture did not exceed 105°C.
In this way, 6.03 gram atoms of sulfur were used per mole of peroxide. The raw materials thus produced were made into thin plates and samples were cut. The samples were cured at 171° C. for 20 minutes and the physical properties of these samples were determined according to ASTM D412. The results of such tests are listed in the table.

[Table] The above data shows that using the method of the present invention, blends of highly unsaturated and saturated rubbers can be produced;
The results show that this formulation exhibits desirable physical properties. Examples 7 to 9 Further rubber compositions are made analogously to Examples 1 to 6, except that mixtures of highly unsaturated rubbers [Standard Malaysian natural rubber, type 5CV and polybutadiene rubber, cis content 91 %] in Examples 1 to 6
Blended with EPDM as described. Ratio of rubber used (100
The number of parts per part by weight) is listed in the table. Antioxidant, carbon black, zinc oxide and stearic acid components were added in the amounts described in Examples 1-6 as described. However, the extender oil [type
103 oil (ASTM D2226)], sulfur, sulfur cure accelerator (Nt-butyl-2-benzothiazole sulfenamide) and dicumyl peroxide were varied as indicated in the table. Samples were prepared as described in Examples 1-6. The samples were cured for 20 minutes at 171°C and their physical properties were determined according to ASTM D412.
Record the results for such samples in a table.

【table】

[Table] * All component data is expressed in parts by weight.
The above results further demonstrate that by using the method of the present invention, formulations can be made that are comprised of mixtures of various saturated and highly unsaturated rubbers and exhibit desirable physical properties. Examples 10 to 12 and Comparative Experiment C Highly unsaturated standard Malaysian natural rubber (type
5CV), highly unsaturated polybutadiene rubber (91% cis content), and saturated EPDM rubber (ethylene
52 weight percent, 39 weight percent propylene, and 9 weight percent 5-ethylidene-2-norbornene.
Several rubber compositions were prepared using the following procedure. 50 parts by weight of natural rubber and 50 parts by weight of butadiene rubber are charged to a Banbury Type B internal mixer along with 3 parts of zinc oxide and 2.0 parts of an antioxidant (reaction product of diphenylamine and acetone); Mixed for 2 minutes. 50 parts N326 carbon black, 5 parts extender oil (Type 103 oil - ASTM D2226), and 1.0 part stearic acid were added and mixing continued for an additional 2 minutes.
The inside of the mixer was cleaned and blending continued for an additional minute. The resulting formulation is introduced into a mill where it contains 2.0 parts of sulfur and a sulfur cure accelerator (Nt-butyl-2-benzothiazole sulfenamide).
Added 1.0 part. Highly unsaturated component A was made by compounding the mixture, taking care to keep the temperature of the compound below 105°C. 100 parts by weight of EPDM were charged to a Banbury™ Model B internal mixer with 3 parts of zinc oxide and mixed for 2 minutes. 50 parts N326 carbon black, extender oil (type 103 oil)
5 parts ASTM D2226) and 1.0 part stearic acid were added and mixing continued for an additional 2 minutes. The inside of the mixer was cleaned and blending continued for an additional minute. The resulting formulation was introduced into a mill where 7.0 parts of 40 percent active dicumyl peroxide on clay was added. Saturated component B was made by blending the mixture, taking care to keep the blend temperature below 105°C. Several rubber compositions were made by blending various amounts of highly unsaturated component A and saturated component B at the rubber ratios shown in the table. 171% of this formulation
Cure for 20 minutes at °C. As a comparison, Sample C was prepared using a sulfur to peroxide ratio outside the range of the present invention. Its elastomeric properties, curative properties and mooniscorch properties were measured. The results of such tests are summarized in the table.

TABLE The above results demonstrate that compositions of the invention can be made by combining preformed saturated and unsaturated components. Examples 13 and 14 and Comparative Experiments D and E Highly unsaturated nitrile rubber (acrylonitrile content 33%) and as described in Examples 1 to 6 above
Several compositions were made using blends of EPDM. The composition of Example 13 was prepared according to the method of Examples 1-6 except that nitrile rubber was used in place of natural rubber. The composition of Example 14 was prepared according to the method of Examples 10-12, except that the highly unsaturated rubber component consisted of nitrile rubber instead of natural rubber and butadiene rubber. The compositions were cured for 20 minutes at 171°C and their physical properties were measured as described above. The results of such measurements are shown in the table. As comparative examples, a sample made from the highly unsaturated component of Example 14 (Comparative Run D) and a sample made from the saturated component of Example 14 (Comparative Run E) were similarly cured and tested. The results of this test are also shown in the table.

TABLE The above data demonstrate that highly unsaturated nitrile rubbers can be co-cured with saturated rubbers using the method of the present invention. Examples 15-18 and Comparative Experiment H Using the same methods and ingredients as used in Examples 1-6, several rubber compositions were prepared using the following parts by weight.

Table: The compositions were cured for 20 minutes at 171°C and their physical properties were determined as described above. The results of such tests are shown in the table.

【table】

TABLE The above results show that increased mooniscorch times are obtained by using the sulfur to peroxide ratio according to the present invention compared to the ratios published in the prior art.

Claims (1)

[Claims] 1. (a) at least one highly unsaturated rubber having an iodine value of 50 or more, (b) at least one saturated rubber, and (c) an effective amount of () sulfur. () at least one sulfur curing accelerator; () at least one peroxide curing agent; and () a curing agent comprising zinc oxide. per mole of substance,
The above cured composition characterized in that between 5 and 150 gram atoms of sulfur are present. 2. The composition of claim 1, wherein between 6 and 14 gram atoms of sulfur are present per mole of peroxide. 3. The composition according to claim 1, wherein component (a) is a diene rubber and component (b) is an ethylene-propylene non-conjugated diene terpolymer. 4. A patent claim in which component (a) is at least one member selected from the group consisting of natural rubber, cis-polyisoprene rubber, polybutadiene rubber, poly(styrene-butadiene) rubber, and poly(acrylonitrile-butadiene) rubber. A composition according to scope 1. 5. The composition according to claim 1, wherein component (b) is an ethylene-propylene-(5-ethylidene-2-norbornene) terpolymer. 6 Claims in which the sulfur curing accelerator is at least one member selected from the group consisting of thioureas, guanadine derivatives, xanthates, dithiocarbamates, thiuram sulfides, heterocyclic compounds, and sulfenamides. The composition according to item 1. 7. The composition according to claim 1, wherein the sulfur curing accelerator is a thiazole or sulfenamide sulfur curing accelerator. 8 The peroxide curative is benzoyl peroxide,
1,3-bis(t-butylperoxyisopropyl)benzene, butyl 4,4-bis(t-butylperoxy)valerate, p-chlorobenzoyl peroxide, cumene hydroperoxide, t-butylcumyl peroxide, t-butyl perbenzoate,
Di-t-butyl peroxide, dicumyl peroxide, 2,5
-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-
The composition according to claim 1, which is at least one member selected from the group consisting of butylperoxy-3-hexyne and 4-methyl-2,2-di-t-butylperoxypentane. 9. The composition according to claim 1, wherein the peroxide curetate is dicumyl peroxide or 2,5-dimethyl-2,5-di-t-butylperoxyhexane. 10 Component (a) is selected from the group consisting of natural rubber, polybutadiene rubber or poly(acrylonitrile-butadiene) rubber, and component (b) is ethylene-propylene-(5-ethylidene-2-norbornene).
terpolymer, the sulfur cure accelerator is a thiazole or sulfenamide cure accelerator, and the peroxide curative is dicumyl peroxide or 2,5-dimethyl-2,5-di-t-butylperoxyhexane. A composition according to claim 1. 11 Component (a) is selected from the group consisting of natural rubber, polybutadiene rubber or poly(acrylonitrile-butadiene) rubber, and component (b) is ethylene-propylene-(5-ethylidene-2-norbornene).
terpolymer, and the sulfur curing accelerator is N-t-
Claim 1: Butyl-2-benzothiazolesulfenamide, tetramethylthiuram monosulfide, benzothiazole disulfide, or di-O-tolylguanidine, and the peroxide curate is dicumyl peroxide. Compositions as described. 12. A step of: () (a) at least one highly unsaturated rubber having an iodine value of 50 or more; (b) at least one saturated rubber; and (c) an effective amount of () sulfur; () at least one sulfur curing accelerator; () at least one peroxide curing agent; and () a curing agent consisting of zinc oxide (5 and 150 g atoms per mole of peroxide) sulfur between
and () subjecting said formulation to curing conditions. 13 Claims in which step () consists of 1. blending the unsaturated rubber (a) with the saturated rubber (b) to form a mixture, and 2. blending the mixture of step 1 with a curing agent (c). The method according to paragraph 12. 14 Step () 1 forms a saturated component consisting of at least one saturated rubber; 2 forms a highly unsaturated component consisting of at least one highly unsaturated rubber having an iodine value of 50 or more; 13. The method of claim 12, comprising the steps of: blending a mixture of said saturated component and said highly unsaturated component. 15. The method of claim 12, wherein between 6 and 14 gram atoms of sulfur are present per mole of peroxide. 16 Component (a) is diene rubber, and component (b)
13. The method of claim 12, wherein is an ethylene-propylene-nonconjugated diene terpolymer. 17 Component (a) is natural rubber, cis-polyisoprene rubber, polybutadiene rubber, poly(styrene-butadiene) rubber and poly(acrylonitrile-
13. The method according to claim 12, wherein the at least one member is selected from the group consisting of (butadiene) rubber. 18. The method according to claim 12, wherein component (b) is an ethylene-propylene-(5-ethylidene-2-norbornene) terpolymer. 19 The sulfur curing accelerator is at least one member selected from the group consisting of thioureas, guanadine derivatives, xanthates, dithiocarbamates, thiuram sulfides, heterocyclic compounds, and sulfenamides. Range 12th
The method described in section. 20. The method according to claim 12, wherein the sulfur curing accelerator is a thiazole or sulfenamide sulfur curing accelerator. 21 Peroxide curate is benzoyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, butyl 4,4-bis(t-butylperoxy)valerate, p-chlorobenzoyl peroxide, cumene hydroperoxide , t-butylcumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide,
2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butyl-peroxy-3-hexyne and 4-methyl-2,2-di- 13. The method according to claim 12, wherein the at least one member is selected from the group consisting of t-butylperoxypentane. 22 Claim 12, wherein the peroxide curetate is dicumyl peroxide or 2,5-dimethyl-2,5-di-t-butylperoxyhexane.
The method described in section. 23 Component (a) is natural rubber, polybutadiene rubber,
or poly(acrylonitrile-butadiene) rubber, and component (B) is ethylene-propylene-(5-ethylidene-2-norbornene).
terpolymer, the sulfur cure accelerator is a thiazole or sulfenamide cure accelerator, and the peroxide curative is dicumyl peroxide or 2,5-dimethyl-2,5-di-t-butylperoxyhexane. The method according to claim 12. 24 Component (a) is selected from the group consisting of natural rubber, polybutane diene rubber, or poly(acrylonitrile-butadiene) rubber, and component (b) is an ethylene-propylene-(5-ethylidene-2-norbornene) terpolymer. and the sulfur curing accelerator is N-t-butyl-2-benzothiazole sulfenamide, tetramethylthiuram monosulfide, benzothiazole disulfide or di-O
- tolylguanidine and the peroxide curate is dicumyl peroxide.