Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-03-23
2001-07-24
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S140000
Reexamination Certificate
active
06265474
ABSTRACT:
BACKGROUND
0
F THE INVENTION
The present invention broadly relates to an NBR (Nitrile Butadiene Rubber) composition, and more particularly to an NBR composition having an excellent processabiity for forming or molding various articles, and an excellent anti-fixation property to various kinds of metal.
In this regard, the term “fixation” as used herein means such a phenomenon as a hard-to-remove state when seal rubbers are removed from the place used, after a specific period of time, that is in the case of replacement of parts.
State of the Art
Sealing members such as O-rings, packings, gaskets or the like, are usually used under the condition of tight contact with various kinds of metal. When the sealing rubber and the contacting counterpart material, such as metal, are compressed and left in air or service oil at a given temperature for a given period of time, the sealing rubber and the contacting counterpart material undergo reaction and consequent strong adhesion to each other.
When these sealing members are replaced from the position used, after a sufficient time of use, sealing members are sometimes tightly fixed to the metals and, for example are difficult to remove from a counterpart made of metal. The old rubber is hard to remove away completely from the counterpart, causing decreases in sealability of newly replaced sealing members, due to incomplete removing of the old sealing members.
Therefor various means described below have been proposed for preventing such problems as tight fixing to the counterpart metals. But no satisfactory means have so far been achieved from the view point of sealing properties, productivity, manufacturing costs and the like, of these older sealing members.
Blooming or Bleeding Methods
Additives such as lubricants, plasticizer or the like which are poor in solubility with rubber are mixed into the rubber composition to bring these additives into blooming or bleeding on the surface of the rubber from within the rubber; thereby preventing direct contact between sealing rubber and the counterpart metal to prevent fixing or adhesion or sticking between the rubber and the counterpart metal. There are such shortages in this method, i.e., additives which bloom for bleed from the rubber are prone to flow away from the interface between the rubber and the counterpart metal. So the effect of preventing the rubber from fixing or adhesion or sticking to the counterpart metal is not only decreased, but also rubber physical properties are prone to deteriorate due to adding these materials, which are poor in solubility with the rubber or into the rubber.
Coating Methods
These methods include applying a solid lubricant such as graphite, molybdenum disulfide or the like on the surface of the cured rubber molding articles, or applying silicone coating agent on the surface of the rubber. This process has problems that the coating layer is prone to remove away from the surface, and has a possibility for the coating layer removed away from the surface to enter into the sealing object as a contaminant. There are also problems in cost and processing in these methods.
Surface Treatments by Chemicals
This method is a treatment of the rubber surface by using chemical agents such as halogen containing processing liquid agents which contains chlorine or fluorine, acid or alkaline liquid. The surface of the rubber is hardened to give anti-fixing or sticking property on the rubber surface. According to this method, cracking on the rubber surface tends to occur, due to hard layer on the surface of the rubber, and often there is deformation of the seal, to lower the sealing property of the rubber. And there are also problems in manufacturing cost.
OBJECT OF THE PRESENT INVENTION
One object of the present invention is to provide a new and novel NBR composition having an excellent anti-fixing property to various metals, even after a long period of time of use in contact with the metal.
Another object of the present invention is to provide an NBR composition having good processability and moldability, and having a fast cure speed, along with an excellent anti-fixing property.
SUMMARY OF THE INVENTION
These objects of the present invention can be achieved by adding the following materials, discovered herein, into an NBR composition or a rubber containing an NBR as a main rubber component:
(A) a carbocyclic phosphite represented by the following general formula,
wherein R is an alkyl group having a carbon atom of integer 8 to 24, or a mono-, di-, ti-phenyl group substituted by alkyl group having a carbon atom of integer 1 to 10;
(B) an acid phosphoric ester represented by the following general formula, and having an acid value in the range of about 150 to 800 KOHmg/g
wherein R′ is hydrogen or an alkyl group having a carbon atom integer of 1 to 13, and R″ is an alkyl group of carbon atom integer of 1 to 13;
(C) an ethylene-&agr;-olefin copolymer rubber having a number average molecular weight (Mn) of 10
4
to 10
6
; and
(D) a liquid NBR.
DETAILED DESCRIPTION OF THE PRESENT INVENTION AND BEST MODE
At least one of a polymer selected from a group consisting of an NBR, a polyvinyl chloride containing NBR, a carboxyl group containing NBR, or the like, can be used as an NBR.
As a carbocyclic phosphite represented by the general formula mentioned above, for example, cyclic neo pentane tetrail bis (octyl phosphite), cyclic neo pentane tetrail bis (tetradecyl phosphite), cyclic neo pentane tetrail bis (nona decyl phosphite), cyclic neo pentane tetrail bis (2, 4, 6-trimethyl phenyl phosphite), cyclic neo pentane tetrail bis (4-methyl-2, 6-tertiary butyl phenyl phosphite), cyclic neo pentane tetrail bis (2, 4-ditertiary butyl phenyl phosphite), or the like can be used.
As an acid phosphoric ester represented by the general formula mentioned above, for example, a compound comprising a main compound having R′, which is an alkyl group, such as methyl acid phosphate, propyl acid phosphate, butyl acid phosphate, 2-ethyl hexyl acid phosphate, iso decyl acid phosphate, tridecyl acid phosphate, mono iso decyl acid phosphate or the like; and a compound having R′, which is hydrogen, can be used. And at least one of the compounds selected from the group consisting of an alkyl acid phosphate having R″ which is an alkyl group, a mono alkyl phosphate having R″ and R′ which is an alkyl group and hydrogen respectively, such as mono butyl phosphate, and a dialkyl phosphate having R′ and R″ which is both an alkyl group, such as dibutyl phosphate, di (2-ethylhexyl) phosphate, methyl ethyl phosphate, or the like, can be used.
These acid phosphoric ester compounds must have an acid value range of about 150 to 800 KOHmg/g, preferably, about 200 to 700 KOHmg/g. If phosphoric acid having an acid value other than the range mentioned above is used, the desired aim to obtain rubber members having an excellent anti-fixing property to metal can not be achieved.
About 5 to 20, preferably about 7 to 17 weight parts, based on the 100 weight parts of NBR or a rubber having NBR as a main component, of the total of both (A) compound and (B) compound combined, is used. About 20 to 90, preferably about 40 to 80 weight percent of (A) compound, about 80 to 10, preferably 60 to 20 weight percent, based on the total amount of both (A) compound and (B) compound, is used.
This blending ratio information was discovered during the research that led to the anti-fixing property of this invention. In the case where the weight parts of the total amount of both (A) and (B) is used not less than about 20 weight parts, the physical properties of the cured rubber is not only deteriorated, but also mold staining occurs in molding process to cause a problem in productivity.
The NBR composition of the present invention further comprises (C) an ethylene-&agr;-olefin type copolymer rubber having number average molecular weight Mn of about 10
4
to 10
6
in addition to (A) component and (B) component.
As an ethylene-a-olefin copolymer rubber, copolymer of ethylene and at least one of the
Fujimoto Kenichi
Sato Takeshi
Dinnin & Dunn PC
Freudenberg-NOK General Partnership
Mulcahy Peter D.
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