Patent Application
20100203395
The present invention relates to non-woven gauntlets for lead-acid batteries.
Lead acid batteries are widely used and include adjacent positive and negative electrodes immersed in an electrolyte and spaced by separators.
Lead-acid batteries of the tubular type are customarily constructed with tubular positive plates, constituent parts of which include: a grid member having a top bar; a post or burning lug and a plurality of current carrying spines; pencils of active material surrounding the current carrying spines; tubular bodies arranged to support and confine the pencils of active material and maintain such active mass in contact with the current carrying spines; and means for closing ends of the tubes.
The tubular bodies are required to provide a number of functions including: enclosure and support of the active material to maintain the active material in contact with the spines; maintenance of the dimensional stability of the pencils of active material particularly during periods of swelling of the active material; and, finally, provision of adequate communication between the electrolyte and the active material throughout the length of the tubular bodies.
From the early 1950s up to now, the tubular plate has evolved from the single tube design (PVC tubes and woven or braided tubes of C-glass fibers protected first by a perforated plastic armor, then by impregnation with phenolic resin to the more economical and productive multitube gauntlet concept. The first generation of gauntlets, still in use for some applications, were made of woven polyester fabric impregnated with phenolic and then thermoplastic acrylic resin.
Since the 1980s, the tubular gauntlet has further evolved to include modern non-woven fabrics.
Up to now the standard (and only) material used by the industry to produce non-woven gauntlets, in which the positive active mass (lead dioxide) is inserted for the production of tubular positive plates of lead-acid batteries is a point-bonded polyester spunbond material, which means that the fabric strength and cohesion is made by melting the PET filament in many points with a hot calendar. The number of points per cm2 and the point size depends on the calendar roll. The fabric is impregnated with an acrylic resin in order to protect the PET filaments from chemical attack from the sulphuric acid electrolyte or the oxidative positive active mass (Pb02).
The invention provides a new, non-woven gauntlet with a higher burst strength and a lower electrical resistance.
In order to overcome the above-mentioned problems, the present invention proposes a non-woven, cartridge belt type gauntlet for lead acid batteries comprising two sheets of spunbond, needled and flat thermobonded bicomponent PET-PBT non-woven fabric assembled together at regular intervals.
The fabric used in the present invention is a flat calendared material made of a mixture of PET and PBT filaments, the later having a lower melting point and being melted during calendaring in order to impart the fabric strength.
Surprisingly, these gauntlets have an electrical resistance of less than 180 mΩ·cm2, and a burst pressure of more than 16 bars.
Up to now it was not possible to obtain a non-woven gauntlet having such a high burst pressure and at the same time such a low electrical resistance.
Preferably, the fabric is assembled by sewing, stitching, thermal bonding, ultrasonic bonding, gluing or a combination thereof so as to form the cartridge belt type of gauntlet.
According to a preferred embodiment, the non-woven fabric is impregnated with a thermoplastic resin. The resin is chosen among the group consisting of: acrylic resins like e.g. methyl methacrylate resins or butyl acrylate/methyl acrylate copolymer resins, styrene-butadiene resins, phenolic resins or mixtures thereof. The fabric can be impregnated during the production between the calendaring and the winding steps, or the impregnation can be made off line.
Furthermore, the invention also concerns the use of spunbond, flat calendared bicomponent PET-PBT non-woven fabric for the manufacture of a non-woven, cartridge belt type gauntlet for lead acid batteries comprising two sheets of said fabric stitched together at regular intervals.
Additionally, the invention also concerns lead acid battery of the tubular type, stationary gel batteries and stationary flooded batteries comprising a gauntlet as described above.
The present invention can more fully be understood from the following description taken in conjunction with accompanying figures in which:
The process to manufacture non-woven (cartridge-belt type) gauntlets consists on joining two strips of polyester non-woven fabric at predetermined intervals with a multi-needles sewing machine, then thermo forming the multitube panel into the desired tube geometry. The thermoforming is made in an oven by inserting hot rods in between both fabric layers, between each two adjacent sewing lines.
The fabric has to have the ability to shrink around the rods at the desired temperature (typically between 160 and 200° C.) in order to keep the 3 dimensional tube shape and dimensions. The preferred shrinkage is typically around 1.5% at 160° C. and 2.5% at 200° C.:
Therefore, beside the initial fabric strip width and sewing pitch, the fabric shrinkage and applied temperature during formation are very important parameters, as they determine the final gauntlet width and tubes diameter. These dimensions are of first importance, as they will fix the final positive plate width and thickness (directly correlated to the amount of active mass entrapped and therefore to the battery capacity) to be inserted in the battery container.
Besides the shrinkage, other fabric characteristics are important for a good final gauntlet quality:
Even if gauntlets made with the current PB1 type fabric (sold e.g. by Johns Manville under the trade name Duraspun™, or by Mogul company under the trade name Moped™) improve performance of most of the industrial traction batteries compared to woven gauntlets, they keep some mechanical weaknesses which don't enable battery manufacturers to generalize their use to any type of lead-acid batteries with any type of production tools:
Different methods have been tried to reinforce the standard point bonded polyester fabric type PB1 by changing the formulation and production parameters in various ways. The best results were obtained with polyester point-bonded fabric type PB2, which is a modified version of Duraspun™ sold by Johns Manville. As mentioned in Table 1, the tensile strength in both directions have bee improved.
The impact on gauntlets properties was a slight increase of the burst strength (from 13.6 to 14.6 bars) and a slightly better elastic modulus, as illustrated by the testing results on
Unfortunately, however, beside to the improvement of the mechanical properties and elasticity, the electrical resistance has also been increased very much (from 195-250 to 405 mΩ·cm2), which is harmful for the battery electrical performance (Table 1).
The gauntlets according to the present invention have been developed with different type of non-woven polyester fabric (referred as New FC in Table 1).
The fabric is a mixture of PET (polyethylene terephthalate) and PBT (polybutylene terephtalate) filaments with a higher denier (leading to higher oxidation resistance), which are deposited on a belt using the spunbond technology, and calendared under heat and pressure in between flat rolls. Such fabrics are sold e.g. by Freudenberg Politex under the trade name Terbond™ and usually used for roofing applications.
This material has a totally different aspect than the other fabrics used in the manufacture of gauntlets. Furthermore, its physical properties do not look promising compared to the standard PB1 or reinforced PB2 materials:
Nevertheless, in spite of the apparent unsuitability of the fabric for the production of non-woven gauntlets, many efforts have been made to be able to run this fabric onto forming machines.
The oven and pre-oven equipments had to be changed and adapted to the new product requirements. A complete energetic study has been made in order to be able to shrink the fabric around the rods at temperatures adapted to the equipment. The coating of the rods had to be changed for a more resistant one. A very precise recalibration of all the machine parameters has been necessary.
The gauntlets produced with this type of fabric showed surprising results: not only the mechanical strength had been improved very much (from 13.6-14.6 bars with the point bonded fabrics to 19.5 bars with the new FC), but the electrical resistance has been reduced at the same time (157 mc·cm2 only for the gauntlets made with the new FC compared to 195 up to 405 mc·cm2 with the point-bonded technology). These enhancements in the performance could not have been foreseen from the physical properties of the starting material.
This is the first time that both the mechanical and electrical properties have been improved simultaneously.
The technologic gap is illustrated by
Additionally
A further surprising effect and a considerable advantage of the gauntlets made with the new FC fabric is the ability to come back to a narrower tube diameter after successive expansions at 10 bars (test results on
This will enable the gauntlet to constrain the positive active mass very efficiently and avoid density changes, connection loss . . . , leading to early capacity decay.
The gauntlets made with the new EC fabric can be used even in very aggressive filling technology due to their very high rigidity, without affecting the electrical properties of the battery because of their reduced electrical resistance.
The improvement of the elastic properties and the higher filament denier render possible their use even in the most demanding applications like stationary gel batteries or stationary flooded batteries. This product opens thus new markets for non-woven gauntlets.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05103651.5 | May 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/061866 | 4/27/2006 | WO | 00 | 10/30/2007 |
