Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Patent
1992-04-16
1993-10-26
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
521 27, H01M 216, C08D 520
Patent
active
052565033
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for making a composite membrane and to a composite membrane, which is particularly useful as an ion-exchange membrane for use for example as an electrode separator in certain types of electrochemical device.
In certain types of electrochemical device, in particular of electrochemical cell, lifetime can be limited to migration of electrode material in particulate form and in solution onto the opposing electrode and subsequent self-discharge. Another problem arises in secondary cells on recharging when loosely attached material is deposited on the anode, often in the form of dendrites. These problems can be overcome by use of an electrode separator which provides a continuous barrier to electrode particles and which allows ionic conduction.
U.S. Pat. No. 2,965,697 (Duddy) discloses a battery diaphragm which consists of a porous matrix in which pores are filled with crosslinked polyacrylic acid. The diaphragm is made by impregnating a porous matrix, for example of polyethylene, with a mixture of methacrylic acid, divinyl benzene and benzoyl peroxide, and then applying heat to initiate polymerisation of the acid. The polymerisation reaction is exothermic and once it has been initiated, it is necessary to apply heat moderating means in order to ensure that the rate of reaction is controlled.
The process described in U.S. Pat. No. 2,965,697 is a slow and inconvenient batch process, and requires the use of the above-mentioned heat moderating means. However, even with such apparatus, the process is particularly difficult to control so as to produce diaphragms with consistent properties.
We have devised a convenient process for making a composite membrane which involves the use of irradiation, particularly using ultraviolet (UV) radiation to effect crosslinking of an ion exchange material within the pores of a porous matrix.
Accordingly in a first aspect, the present invention provides a process for making a composite polymer membrane, which comprises irradiating a membrane comprising a first material which defines a porous matrix, and a second material blocking the pores of the matrix which is crosslinkable when the membrane is irradiated as aforesaid.
The process of the invention has the advantage that it can be performed continuously on a continuous strip of the composite membrane, by passing the strip under a source of radiation rather than by exposing a membrane to heat. The sheet may be in the form of a film, tape, or ribbon, or in the form of a tube. Other sheet-like forms may be used depending upon the application. Preferably, the sheet will be flexible. The source of radiation will preferably provide UV radiation which is cheap and convenient to use with small safety risks. It is envisaged however that gamma radiation such as from a Co.sup.60 source or electron bombardment may be used as alternative radiation sources. An appropriate initiator will generally be mixed with the second material for initiation of the crosslinking reaction, and where necessary for initiation of polymerisation of the second material. When UV radiation is used, a photoinitiator will be mixed with the second material. Suitable photoinitiators are well known in the prior art such as acetophenone, propionphenone, xanthone, fluorenone, 3- or 4-methoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one and 1-hydroxycyclohexylphenyl ketone etc.
Furthermore, the use of irradiation, especially UV irradiation, has the advantage that the crosslinking step is readily controllable, it being possible to control the degree of crosslinking by selecting an appropriate exposure of the membrane to the radiation. Thus it is possible to produce continuous lengths of irradiated membrane with consistent properties, and to ensure that those properties are reproduced in subsequent lengths.
UV radiation has the further advantage that its energy is suitable for effecting the crosslinking of thin films; radiation from other sources with higher energy is absorbed only
REFERENCES:
patent: Re31824 (1985-02-01), D'Agostino et al.
patent: 2965697 (1960-12-01), Duddy
patent: 3376168 (1968-04-01), Horowitz
patent: 4230463 (1980-10-01), Henis et al.
patent: 4346142 (1982-08-01), Lazear
patent: 4468441 (1984-08-01), D'Agostino et al.
patent: 4547411 (1985-10-01), Bachot et al.
patent: 4613544 (1986-09-01), Burleigh
Extended Abstracts, vol. 80-2, 1980 (Pennington, New Jersey, USA), W. H. Philipp et al., "New Ion Exchange Membranes" pp. 1537-1538, abstract No. 618.
Chemical Abstracts, vol. 93, No. 6, Sep. 1980 (Columbus, Ohio, USA), p. 498, abstract No. 122614u & JP, A, 8032375 (Sumitomo Chemical) Mar. 7, 1980.
Cook John A.
Singleton Raymond W.
Smith Iain S.
Scimat Limited
Skapars Anthony
LandOfFree
Process for making a composite membrane does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for making a composite membrane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for making a composite membrane will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-958283