Patent Application
20150065634
The present application claims the benefit of French Application No. FR 13.58248, filed on Aug. 29, 2013. The entire contents of French Application No. FR 13.58248 are hereby incorporated herein by reference in their entirety.
Embodiments of the disclosure relate to a battery gasket based on a polyamide composition as well as to a process for making same.
Electric batteries such as common consumer batteries for household use comprise a gasket for sealing the opening through which the electrolyte is introduced during the manufacturing process.
This gasket must have an appropriate mechanical flexibility and provide a required tightness. It is known to use a polyamide such as PA 6.12 as a gasket material.
Battery gaskets are generally manufactured using an injection molding process, which makes it possible to achieve mass production.
There is still a need to achieve a faster manufacturing of battery gaskets, without degrading the mechanical properties of said battery gaskets.
It is a first object of embodiments of the disclosure to provide a gasket for a battery, wherein the gasket is made from a polyamide composition comprising at least 70 wt. % of a polyamide X.Y, wherein X and Y represent respective residues from the condensation of an aliphatic diamine comprising 4 to 18 carbon atoms, and preferably 5 to 12 carbon atoms, with a (cyclo)aliphatic diacid comprising 10 to 18 carbon atoms, and wherein the polyamide composition further comprises a nucleating agent.
According to one embodiment, X+Y>12.
According to one embodiment, X is an aliphatic diamine comprising 7 to 18 carbon atoms,
According to one embodiment, the polyamide X.Y is polyamide 6.10, 6.12 or polyamide 10.12.
According to one embodiment, the polyamide composition further comprises a release agent, which is preferably an amorphous wax.
By release agent is meant without being limited to, long-chain carboxylic acids, and their soaps, esters or amides, and other materials such as polar or nonpolar polyethylene waxes.
According to one embodiment, the polyamide composition comprises at least 75 wt. %, preferably at least 80 wt. % or at least 85 wt. % or at least 90 wt. % or at least 95 wt. % or at least 98 wt. % of the polyamide X.Y.
According to one embodiment, the nucleating agent is selected from:
According to one embodiment, the nucleating agent comprises talc or consists of talc.
It must be noted that talc in embodiments of the disclosure is not used as a filler but only as a nucleating agent, but in other embodiments, the talc can be used as nucleating agent but also as filler. The function of the talc depends mainly on its amount. A filler is added for improving the mechanical properties of the final composition while a nucleating agent is used for increasing or speeding the speed or kinetic of the crystallization of the polymers. A nucleating agent is generally introduced at the beginning of the polymerisation while the fillers are generally introduced during the compounding of the composition (i.e., after the polymerisation and during the mixture of all the ingredients of the composition (polymers+fillers+stabilizer . . . ). A filler can be used at a quantity higher than the quantity of a nucleating agent, for example at a quantity up to 30%, preferably from 3% to 25%, especially from 5 to 20% while a nucleating agent is used at a quantity less than 3% and for example from 0.1 to 1%.
According to one embodiment, the nucleating agent does not contain any ethylene-acrylic acid calcium ionomer or any ethylene-acrylic acid copolymer.
According to one embodiment, the amount of talc in the polyamide composition used as a nucleating agent is from 0.05 wt. % to 1 wt. %, preferably from 0.1 wt. % to 0.5 wt. %, and more preferably from 0.1 to 0.3 wt. %, in particular approximately 0.2%.
It is another object of embodiments of the disclosure to provide a process of making a gasket for a battery, comprising the injection molding of a polyamide composition comprising at least 70 wt. % of a polyamide X.Y, wherein X and Y represent respective residues from the condensation of an aliphatic diamine comprising 4 to 18 carbon atoms, and preferably 5 to 12 carbon atoms, with a (cyclo)aliphatic diacid comprising 10 to 18 carbon atoms, and wherein the polyamide composition further comprises a nucleating agent, preferably talc.
According to embodiments of the process, the polyamide composition is as described with respect to the embodiments in the first object of the disclosure.
It is another object of embodiments of the disclosure to provide the use of a nucleating agent, the nucleating agent preferably being talc, for accelerating the crystallization of a polyamide composition in a process of making a gasket for a battery, wherein the polyamide composition comprises at least 70 wt. % of a polyamide X.Y, X and Y representing respective residues from the condensation of an aliphatic diamine comprising 4 to 18 carbon atoms, and preferably 5 to 12 carbon atoms, with a (cyclo)aliphatic diacid comprising 10 to 18 carbon atoms.
According to embodiments of the use, the polyamide composition is as described with respect to the embodiments of the first object of the disclosure.
It is another object of embodiments of the disclosure to provide a battery comprising the gasket of embodiments of the first object of the disclosure.
According to one embodiment, the battery is an alkaline battery.
Embodiments of the disclosure make it possible to overcome the drawbacks of the prior art. In particular, certain embodiments of the disclosure make it possible to achieve a faster manufacturing of battery gaskets, while maintaining the mechanical properties of said battery gaskets—or even improving said mechanical properties, according to some embodiments.
This may be achieved by using a nucleating agent such as talc or the like in the polyamide composition used for making the battery gaskets. It has been found that the use of said nucleating agent, in particular talc, significantly accelerates the crystallization of the polyamide composition (and therefore significantly accelerates the injection molding process) while preserving (or even improving) the mechanical properties of the gaskets.
Embodiments of the disclosure will now be described in more detail without limitation in the following description.
An embodiment of the disclosure makes use of a polyamide composition based on PA X.Y, where X is an integer from 4 to 18 (preferably 5 to 12) and Y is an integer from 10 to 18.
Preferably, use is made of PA6.10, PA 6.12 (polyhexamethylene dodecanamide) or of PA 10.12 (polydecamethylene dodecanamide).
The PA X.Y used for the disclosure should be crystalline at ambient temperature and should preferably have a relatively high melting point.
Mixtures of several of the above PA X.Y can also be used (for instance a mixture of PA 6.12 and of PA 10.12).
In addition to the above PA X.Y, the polyamide composition comprises a nucleating agent such as talc. The weight proportion of talc in the (total) composition may notably be: from 0.01 to 0.1%; or from 0.1 to 0.2%; or from 0.2 to 0.3%; or from 0.3 to 0.4%; or from 0.4 to 0.5%; or from 0.5 to 0.6%; or from 0.6 to 0.7%; or from 0.7 to 0.8%; or from 0.8 to 0.9%; or from 0.9 to 1.0%.
Above 1% of talc, mechanical properties of the composition may be affected.
More generally, the nucleating agent may be:
A nucleating agent is a substance able to induce nucleation of fine polymeric (polyamide) crystals.
If the above additional polyamide is present, the weight proportion of said additional polyamide in the (total) composition is from 1 to 10%, in particular from 1 to 5%.
Advantageously, when a mixture of talc and an additional polyamide is used as a nucleating agent, the weight proportion of talc in the (total) composition is from 0.1 to 0.3%, in particular approximately 0.2%, and the weight proportion of the additional polyamide is from 1 to 10%, in particular from 1 to 5%.
It must be noted that the nucleating agent can be added during the polymerization process for making the PA X.Y, or alternatively when compounding the composition.
Advantageously, the polyamide composition comprises a release agent which aims at reducing adhesion of the composition to the mold (in the context of injection molding). The release agent can in particular be an amorphous wax, such as beeswax, a silicone wax, a polyethylene wax, an oxidized polyethylene wax, an ethylene copolymer wax, a montan wax and a polyether wax.
The weight proportion of release agent in the (total) composition may notably be: from 0.01 to 0.1%; or from 0.1 to 0.2%; or from 0.2 to 0.3%; or from 0.3 to 0.4%; or from 0.4 to 0.5%; or from 0.5 to 0.6%; or from 0.6 to 0.7%; or from 0.7 to 0.8%; or from 0.8 to 0.9%; or from 0.9 to 1.0%; or from 1.0 to 1.1%; or from 1.1 to 1.2%; or from 1.2 to 1.3%; or from 1.3 to 1.4%; or from 1.4 to 1.5%; or from 1.5 to 1.6%; or from 1.6 to 1.7%; or from 1.7 to 1.8%; or from 1.8 to 1.9%; or from 1.9 to 2.0%.
According to one preferred embodiment, the polyamide composition comprises the above PA X.Y as the sole polyamide component in the composition, possibly together with an additional polyamide used as the nucleating agent (or as part of the nucleating agent). Alternatively, one or more further polyamide compounds may be included in the composition in addition to those. The weight proportion of PA X.Y in the (total) composition is at least 70%, preferably at least 75% or at least 80% or at least 85% or at least 90% or at least 95% or at least 98%.
The further polyamides, if present, can be amorphous polyamides. They can be selected from PA 11 and PA 12. Copolyamides may also be used.
Other possible additives can be present, such as:
The polyamide composition used in the disclosure may be prepared by compounding the PA X.Y with the nucleating agent, optionally the release agent as well as other optional components. The composition is usually recovered in the form of pellets or granules.
The above polyamide composition is used for making a battery gasket. The battery may be any type of battery, but preferably a primary battery (as opposed to a secondary, rechargeable battery). Preferably, it is a battery for household use, in particular a single-cell battery having a cylindrical form and commonly known as a “round battery”. It preferably has a nominal voltage of from 0.5 to 10 V, more preferably of approximately 1.5 V.
Batteries commonly designated as AAA, AA, C and D are especially appropriate. Various battery chemistries are possible. Alkaline batteries are preferred.
For instance, based on the IEC 60086 standards, the AAA batteries may be LR03 (alkaline), R03 (carbon-zinc), FR03 (Li—FeS2), HR03 (NiMH), KR03 (NiCd) or ZR03 (NiOOH); the AA batteries may be LR6 (alkaline), R6 (carbon-zinc), FR6 (Li—FeS2), HR6 (NiMH), KR6 (NiCd) or ZR6 (NiOOH); the C batteries may be LR14 (alkaline), R14 (carbon-zinc), HR14 (NiMH), KR14 (NiCd) or ZR14 (NiOOH); and the D batteries may be LR20 (alkaline), R20 (carbon-zinc), HR20 (NiMH), KR20 (NiCd) or ZR20 (NiOOH).
By way of example, and making reference to
The outer casing of the battery may comprise a steel can 3 which acts as a cathode collector and is in contact with the cathode compartment 1. It is electrically connected to a cathode cup 4 located at one (top) extremity of the cylindrical battery and acting as a cathode terminal.
An anode collector 5 may be in the shape of a metallic nail and may be disposed centrally in the anode compartment 2. It is electrically connected to an anode terminal 6 located at the (bottom) extremity of the cylindrical battery which is opposite the cathode cup 4.
The cathode compartment 1 is separated from the anode compartment 2 owing to a separator 7, which prevents mixing of the anode and cathode materials and short-circuiting of the cell. The separator 7 can be made of a non-woven layer of cellulose or a synthetic polymer soaked with the electrolyte (e.g. potassium hydroxide).
The battery gasket 8 is located at the bottom extremity of the battery. It is annularly shaped and arranged around the anode terminal 6, thus ensuring a proper sealing of the battery.
The battery gasket can be manufactured by injection molding. Injection molding consists of high pressure injection of the raw material (polyamide composition) into a mold which shapes it into the desired shape.
The polyamide composition is preferably provided in a pelletized form. It is fed through a hopper into a heated barrel with a reciprocating screw. The screw delivers the raw material forward, up through a check valve. The melted material is collected at the front of the screw. It is then forced at high pressure and velocity into the mold. The molded part is cooled. The polyamide recrystallizes during the cooling time.
The following examples illustrate the disclosure without limiting it.
In a reactor the following components are introduced under stirring:
22.06 kg dodecanedioic acid;
11.07 kg hexamethylenediamine;
103.13 g acetic acid;
2 kg water; and
1.32 g antifoaming agent (silicone oil).
The reactor is progressively heated under stirring until the inside temperature reaches 240° C., while the water formed is eliminated in order to maintain an internal pressure of 14 bar.
The internal pressure of the reactor is reduced to atmospheric pressure during 1 hour and then nitrogen flushing is performed until the required viscosity is reached.
The crystallization kinetics of PA 6.12 was investigated by differential scanning calorimetry (DSC).
The results are summarized in table 1 below.
Compositions A and C were two different compositions based on PA 6.12 produced by Arkema. Composition A was in the form of an extruded strand and composition C was in the form of granules. Composition B was a PA 6.12 formulation available on the market (PA6.12 granules from DuPont).
Talc was added to composition A at the compounding stage.
Talc was added to composition C at the polymerization stage.
The gross inherent viscosity of composition A was 1.17-1.18, while its corrected inherent viscosity was 1.17-1.18. By way of comparison, the gross inherent viscosity of composition A+0.5% talc was 1.12-1.13, while its corrected inherent viscosity was 1.13-1.14. The viscosity of the composition was therefore hardly affected by the addition of talc.
The melting point of composition C was 190° C. It was unaffected by the addition of 0.5% talc. The duration of an injection molding cycle for making a battery gasket using composition B was 15 seconds. This duration was reduced to 3 seconds by the addition of 0.5% talc.
Various mechanical properties of PA 6.12 were investigated based on the ISO 178 flexure properties test (flexure modulus and maximum strength) as well as on the ISO 527 tensile properties test (tensile modulus, stress at yield, elongation at yield, stress at break, elongation at break and tensile strength). The results are summarized in table 2 below.
Compositions E and F were two different PA 6.12 compositions:
Both compositions also comprised 0.2 wt. % of LUWAX® E as a release agent. The addition of talc was performed in an amount of 0.2 wt. % on a pilot scale.
The above results demonstrate that relevant mechanical properties are hardly affected by the addition of talc.
The process ability of PA 6.12 during injection was evaluated. Composition G according of this disclosure was: PA 6.12+0.25% acetic acid+0.4% dodecanedioic acid. Talc (LUZENAC® 10MOOS) and release agent (LUWAX® E) were added during compounding step at 0.2 wt. % and a composition G′ was thus obtained.
Injection parameters are summarized in Table 3 below.
Processing conditions were adapted for injection of this formulation. It means that no demolding or deformation issues were observed. An advantage of the disclosure was the short cycle time around 8.2 seconds. Compared to another PA 6.12 formulation without talc or release agent, cycle time can be higher than 15 seconds.
Short cycle time is directly associated with crystallization temperature. In fact, without talc or release agent, crystallization temperature of the base resin (Composition G) was 188.5° C. After compounding step to get Composition G′, crystallization temperature was increased to 195° C.
Furthermore, appearance of the molded gaskets was satisfactory. No obvious defects like holes, bubbles or central hole blocking were observed.
Battery gasket molded with Composition G′ following injection parameters cited in Table 3 (see example 4), was submitted to a metal needle punching test. The diameter of the needle used for this test was 1.35 mm. Before evaluation, injected parts were conditioned in 70° C. hot water for 2 hours and then dried by air blowing.
The goal is to check the toughness of the parts by punching a needle with a needle punching machine into the central hole of the gasket. No cracking must be observed after the metal needle had been punched. Thus, no leakage will be possible after assembly the gasket with battery.
Seventy (70) conditioned parts were tested and no cracking was observed.
Metal needle punching test explained in the previous example, is a preparation for burst pressure test. In fact, the needle punched part is put in burst pressure test machine to check the burst pressure limits.
During burst pressure test, pressurized air goes from down to top. There is a safety window in the molded gasket that cannot be broken once the internal pressure reaches a certain level. According to standard evaluation, burst pressure required for LR6 battery is between 700 to 1300 psi. The most important is to keep the results variation for a given cavity lower than 100 psi.
There is a cavity number on each needle punched part. Three samples (needle punched part molded with Composition G′) from each cavity were selected randomly and the burst pressure tested with the machine. Table 4 below summarizes burst pressure results.
aThe 1st, 5th and 8th cavities were closed.
Results showed that for each three sample from the same cavity, the burst pressure was stable and the gap was less than 100 psi.
Embodiments of the disclosure may include:
| Number | Date | Country | Kind |
|---|---|---|---|
| 13.58248 | Aug 2013 | FR | national |
