Modified fluororesin and process for producing the same

Details Modified fluororesin and process for producing the same Modified fluororesin and process for producing the same

2001-06-08

2003-04-22

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S150000, C522S155000, C525S192000, C525S193000, C525S326200

Reexamination Certificate

active

06552099

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a modified fluororesin comprising a functional group-containing organic compound grafted onto the surface of a crosslinked fluororesin, and more particularly to a modified fluororesin which has been improved in ion-exchange property, hydrophilicity, adhesive property, abrasion resistance or other properties by graft copolymerizing a specific side-chain monomer onto a backbone polymer in a crosslinked fluororesin.
BACKGROUND OF THE INVENTION
Among fluororesins, tetrafluoroethylene polymers (hereinafter referred to as “PTFE”), tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymers (hereinafter referred to as “PFA”), and tetrafluoroethylene-hexafluoropropylene copolymers (hereinafter referred to as “FEP”) are known as radiation-degradable resins. The mechanical strength of these resins is known to be significantly lowered upon exposure to a very small quantity of an ionizing radiation to such an extent that the resins no longer can be used as materials. For example, in the case of PTFE, upon exposure to a &ggr; radiation in air at a radiation dose of 5 kGy, the mechanical strength at break is reduced to not more than 10 MPa and the elongation is reduced to not more than 100%, and, upon exposure to the &ggr; radiation in vacuo at a radiation dose of 15 kGy, the mechanical strength at break is reduced to not more than 15 MPa and the elongation is reduced to not more than 100%.
In general, grafted resins cannot be put to practical use when resins used as the base have low mechanical strength. Therefore, when a functional group-containing radiation-graftable organic compound (a functional monomer) is grafted onto the above fluororesins by the application of an ionizing radiation, the mechanical strength of the resins is lowered unless a graft reaction takes place at a very low radiation dose of about 10 kGy. Thus, in the conventional radiation grafting of fluororesins, the mechanical strength of the resin is incompatible with the graft level of the functional organic compound. That is, when the radiation dose is decreased, the graft reaction becomes unsatisfactory and, consequently, the properties of the functional group cannot be satisfactorily provided. On the other hand, when the radiation dose is increased to a level which causes a satisfactory graft reaction, the mechanical strength and elongation of the fluororesin as the base resin are lowered, and, consequently, the grafted fluororesin cannot be put to practical use.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a modified fluororesin which has satisfactory mechanical strength and, at the same time, has, imparted thereto, for example, satisfactory ion-exchange capacity, hydrophilicity, adhesive property, or abrasion resistance, and a process for producing the same.
According to the first feature of the invention, a modified fluororesin comprises: a crosslinked fluororesin produced by exposing a fluororesin at a temperature at or above the melting point of the resin to an ionizing radiation to crosslink the fluororesin; and a functional group-containing organic compound which has been grafted onto the crosslinked fluororesin by ionizing radiation irradiation. Thus, the modified fluororesin according to the invention comprises a functional group-containing organic compound which has been radiation grafted onto a crosslinked fluororesin. In the modified fluororesin according to the invention, various properties could have been imparted to the fluororesin without sacrificing the mechanical properties of the fluororesin, and a tensile strength at break of not less than 10 MPa and an elongation of not less than 50% can be realized. Here the tensile strength at break and the elongation were measured according to JIS K 7161 using an IA-type test piece specified in JIS K 7162 at a tensile speed of 200 mm/min.
According to the second feature of the invention, a process for producing a modified fluororesin comprises the steps of: exposing a fluororesin heated at a temperature at or above the melting point of the resin in an inert gas atmosphere having an oxygen concentration of not more than 10 Torr to an ionizing radiation at a radiation dose of 0.1 kGy to 10 MGy to prepare a crosslinked fluororesin; exposing the crosslinked fluororesin to an ionizing radiation at a radiation dose of 10 kGy to 5 MGy; and then bringing the crosslinked fluororesin into contact with a functional group-containing organic compound to cause a graft reaction.
According to the third feature of the invention, a process for producing a modified fluororesin comprises the steps of: exposing a fluororesin heated at a temperature at or above the melting point of the resin in an inert gas atmosphere having an oxygen concentration of not more than 10 Torr to an ionizing radiation at a radiation dose of 0.1 kGy to 10 MGy to prepare a crosslinked fluororesin; and exposing the crosslinked fluororesin to an ionizing radiation at a radiation dose of 10 kGy to 5 MGy in the presence of a functional group-containing organic compound to cause a graft reaction.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the invention will be described. The above-described PTFE, PFA, and FEP may be mentioned as fluororesins usable in the invention. The form of the fluororesin is not particularly limited, and examples thereof include particles, sheets, films, blocks, and fibers. Further, a laminate or a composite formed of two or more of these materials or a laminate or a composite formed of at least one of these materials and other material(s) may also be used.
The above-described PTFE embraces those containing not more than 1% by mole of polymer units based on a comonomer, such as perfluoro(alkyl vinyl ether), hexafluoropropylene, (perfluoroalkyl)ethylene, or chlorotrifluoroethylene. In the case of the fluororesin in a copolymer form, a minor amount of a third component may be contained in the molecular structure.
The crosslinked fluororesin according to the invention may be produced by exposing a fluororesin heated at a temperature at or above the melting point of the fluororesin in an inert gas atmosphere having an oxygen concentration of not more than 10 Torr to an ionizing radiation at a radiation dose of 0.1 kGy to 10 MGy. When the oxygen concentration of the atmosphere exceeds 10 Torr, the crosslinking effect is unsatisfactory. When the radiation dose of the ionizing radiation is less than 0.1 kGy, the crosslinking effect is unsatisfactory, while when the radiation dose exceeds 10 MGy, the elongation or the like is significantly lowered. The crosslinked fluororesin may be produced by exposing a sheet or a block of a fluororesin to an ionizing radiation. Alternatively, the crosslinked fluororesin may be produced by molding a fluororesin powder, which has been exposed to an ionizing radiation, for example, by compression molding into a sheet or a block.
Ionizing radiations usable in crosslinking the fluororesin include &ggr; radiation, electron beams, X radiation, neutrons, and high energy ions. In applying the ionizing radiation, the fluororesin should be previously heated at a temperature at or above the crystalline melting point of the fluororesin. For example, when PTFE is used as the fluororesin, the fluororesin should be exposed to an ionizing radiation in such a state that the fluororesin has been heated to a temperature of 327° C. (the crystalline melting point of this material) or above. When PFA is used, this fluororesin is exposed to an ionizing radiation in such a state that the fluororesin has been heated to a temperature of 310° C. (the crystalline melting point of this material) or above. When FEP is used, this fluororesin is exposed to an ionizing radiation in such a state that the fluororesin has been heated to a temperature of 275° C. (the crystalline melting point of this material) or above. Heating the fluororesin at a temperature at or above the melting point of the fluororesin can energize the molecular motion of the backbone constituting the fluororesin an

Affiliated with

Also associated with

Rating

Modified fluororesin and process for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Modified fluororesin and process for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modified fluororesin and process for producing the same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3094294