Patent Application
20230340255
The present invention relates to the field of copolyetheresters, particularly flame-retardant copolyetheresters.
Several patents, patent applications and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents, patent applications and publications is incorporated by reference herein.
Copolyetheresters are a group of elastomeric polyesters having hard segments comprising polyester blocks and soft segments comprising long-chain polyether diols. They are widely used in applications in which resilience and elasticity are required.
A typical copolyetherester is made by reacting one or more diacid moieties with a short-chain diol and a long-chain polyether diol.
Copolyetheresters show excellent elasticity, maintenance of mechanical properties at low temperature and good fatigue performance.
There is an ongoing need for non-halogen-containing fire resistant (“NHFR”) copolyetheresters. Dialkyl phosphinate salts are well-known, non-halogenated flame retardant molecules. U.S. Pat. No. 7,420,007 [Clariant Produkte (Deutschland) GmbH] describes the use of dialkylphosphinic salts of the formula (I):
where R1, R2 are identical or different and are C1-C6-alkyl linear or branched;
M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Fe, Zr, Zn, Ce, Bi, Sr, Mn, Li, Na, K and/or is a protonated nitrogen base; and m is from 1 to 4; as flame-retardants in many different polymers, including polyetheresters. US2013/0190432 describes the use of aluminium diethyl phosphinate together with the aluminium salt of phosphorous acid as a flame-retardant stabilizer combination in nylon-6,6, nylon-6T/6,6, nylon-4,6, and PBT.
While the use of flame retardants in polymer resins can significantly reduce flammability, it can unfortunately result in high smoke production upon exposure to heat or flame. This is of concern since smoke can be a significant contributor to damage and mortality in fires.
There is a need for resin and flame-retardant combinations that show not only reduced flammability but also reduced smoke production on exposure to heat and/or flames.
In a first aspect, the invention provides a flame-retardant polymer composition comprising:
In a second aspect, the invention provides a flame-retardant copolyetherester composition comprising:
In a third aspect, the invention provides a shaped article made from a flame-retardant copolyetherester composition comprising:
In a fourth aspect, the invention provides a cable comprising a light or electrical conducting core and at least one sheath made from a flame-retardant copolyetherester composition comprising:
In a fifth aspect, the invention provides a method for making a composition of the invention, comprising the step of:
Copolyetheresters suitable for the compositions of the invention are polymers made by reacting a C2-C6 diol with an aromatic diacid moiety and a poly(alkyleneoxide)diol.
The poly(alkyleneoxide)diol is preferably selected from poly(ethyleneoxide)diol, poly(propyleneoxide)diol, poly(tetramethyleneoxide)diol (“PTMEG”), and mixtures of two or more of these. The poly(propyleneoxide)diol, poly(tetramethylene-oxide)diol may be straight-chain or branched. If they are branched at a carbon containing the terminal hydroxyl, they are preferably end-capped with ethylene glycol or poly(ethyleneoxide)diol. Particularly preferred are poly(propyleneoxide)diol and poly(tetramethyleneoxide)diol (“PTMEG”), and mixtures of these, with PTMEG being more particularly preferred.
The C2-C6 diol is preferably selected from ethylene glycol, propylene glycol, butylene glycol, and mixtures of two or more of these, with butylene glycol being more preferred.
The aromatic diacid is preferably selected from terephthalate, iso-phthalate, and mixtures of these, with terephthalate being particularly preferred.
Particularly preferred copolyetheresters are selected from:
Particularly preferred is a copolyetherester made from butylene diol, terephthalate and PTMEG.
Particularly preferred is a copolyetherester made from butylene diol, terephthalate, isophthalate and PTMEG.
The softness of copolyetheresters is affected by the chain-length (i.e. molecular weight) of the poly(alkyleneoxide)diol and by the relative amount of poly(alkyleneoxide)diol that is used to make the polymer.
In a preferred embodiment, the poly(alkyleneoxide)diol has a molecular weight of at or about 2000 g/mol.
In another preferred embodiment, the poly(alkyleneoxide)diol constitutes from 40 wt % to 80 wt % of the copolyetherester based on the total weight of the copolyetherester, more preferably 50 to 75 wt %, particularly preferably 72.5 wt %.
In a particularly preferred embodiment, the copolyetherester comprises a poly(alkyleneoxide)diol having a molecular weight of at or about 2000 g/mol at 40 wt % to 80 wt % of the copolyetherester, based on the total weight of the copolyetherester, more preferably 50 to 75 wt %, particularly preferably 72.5 wt %.
A particularly preferred copolyetherester comprises at or about 72.5 weight percent of polytetramethylene oxide, preferably having an average molecular weight of about 2000 g/mol, as polyether block segments, the weight percentage being based on the total weight of the copolyetherester elastomer, the short chain ester units of the copolyetherester being polybutylene terephthalate segments.
In addition to at least one copolyetherester, the compositions of the invention comprise aluminium diethyl phosphinate (“DEPAI”).
The total phosphinate concentration is 2 to 25 wt %, more preferably 10 to 20 wt %, particularly 15 wt %, based on the total weight of the copolyetherester composition.
In a preferred embodiment, the DEPAI has a D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns.
The compositions of the invention comprise at least one aluminium salt of phosphorous acid (“Al phosphite”). Phosphorous acid is also referred to as phosphonic acid, HP(═O)(OH)2.
Phosphorous acid has tautomeric forms as shown below:
Salts of phosphorous acid are also referred to as phosphites.
Preferred aluminium phosphites are those having the CAS numbers [15099 32-8], [119103-85-4], [220689-59-8], [56287-23-1], [156024-71-4], [71449-76-8] and [15099-32-8]. Particularly preferred are aluminium phosphites of the type Al2(HPO3)3*0.1-30 Al2O3*0-50H2O, more preferably of the type Al2(HPO3)3*0.2-20 Al2O3*0-50H2O, most preferably of the type Al2(HPO3)3*1-3 Al2O3*0-50H2O.
Particularly preferred are mixtures of aluminium phosphite and aluminium hydroxide having the composition of 5-95% by weight of Al2(HPO3)3*nH2O and 95-5% by weight of Al(OH)3, more preferably 10-90% by weight of Al2(HPO3)3*nH2O and 90-10% by weight of Al(OH)3, most preferably 35-65% by weight of Al2(HPO3)3*nH2O and 65-35% by weight of Al(OH)3 and in each case n=0 to 4.
Particularly preferred is the aluminium phosphite having the CAS number [56287-23-1].
In a preferred embodiment, the aluminium phosphite has a D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns.
Particularly preferred is aluminium phosphite [56287-23-1] having a D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns.
The compositions of the invention may additionally comprise a zinc salt of phosphorous acid (Zn phosphite). Phosphorous acid is also referred to as phosphonic acid, HP(═O)(OH)2.
Phosphorous acid has tautomeric forms as shown below:
Salts of phosphorous acid are also referred to as phosphites.
Zinc and aluminium phosphites comprise reaction products of phosphorous acid with compounds of the respective metal.
Zinc salts of phosphorous acid are also referred to herein as zinc phosphites. Particularly preferred is zinc phosphite having CAS number [14332-59-3], depicted below.
In a preferred embodiment, the zinc phosphite has a particle size of D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns. Alternatively, the zinc phosphite preferably has particle sizes from 0.1 to 100 μm and particularly preferably from 0.1 to 30 μm.
Particularly preferred is zinc phosphite [14332-59-3] having a D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns.
In a preferred embodiment, the composition of the invention comprises zinc phosphite having CAS number [14332-59-3] and aluminium phosphite having the CAS number [56287-23-1].
In a particularly preferred embodiment, the composition comprises aluminium phosphite having the CAS number [56287-23-1] and having a D95 (volume %, measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone) of ≤10 microns.
In compositions of the invention the total phosphite concentration is preferably greater than 0.5 wt %. Preferably the total phosphite concentration is from 3 to 15 wt %, more preferably 5 to 8 wt %, based on the total weight of the copolyetherester composition.
Aluminium phosphite is preferably used at a concentration of from 3 to 10 wt %, more preferably 5 to 8 wt %. Preferably the aluminium phosphite having CAS number [CAS 56287-23-1] is used at 3 to 10 wt %, more preferably 5 to 8 wt %.
The copolyetherester compositions of the invention additionally comprise component (D) at least one melamine derivative, selected from melamine salts with organic or inorganic acids and mixtures of these. Particularly preferred are salts of melamine with boric acid, cyanuric acid, phosphoric acid, pyrophosphoric acid, polyphosphoric acid, and mixtures of two or more of these.
Component (D) is preferably present at 1 to 15 wt %, more preferably 2 to 15 wt %, more particularly preferably 5 to 12 wt %, based on the total weight of the copolyetherester composition. Particularly preferred as component (D) is melamine pyrophosphate, particularly at 2 to 15 wt %, more preferably at 5 to 12 wt %, particularly preferably 8 wt %, based on the total weight of the copolyetherester composition.
Component (D) preferably has a mean particle diameter of less than 20 microns, more preferably 15 microns or less, as measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone. Particularly preferred is melamine pyrophosphate having a mean particle diameter of 15 microns, as measured using laser diffraction technology with a Malvern Mastersizer 2000 particle size analyser instrument, in acetone, particularly at 2-15 wt %, more preferably 4 to 12 wt %, based on the total weight of the copolyetherester composition.
Some particularly preferred compositions comprise the ingredients listed below, or consist of the ingredients listed below:
The copolyetherester compositions described herein may additionally comprise (B′) 0.2 to 16% by weight of aluminum salts of ethylbutylphosphinic acid, dibutylphosphinic acid, ethylhexylphosphinic acid, butylhexylphosphinic acid and/or dihexylphosphinic acid, or mixtures of two or more of these.
Component (B′), when present, is preferably selected from aluminium salts of ethylbutylphosphinic acid, dibutylphosphinic acid, ethylhexylphosphinic acid, and mixtures of two or more of these.
The copolyetherester compositions described herein may additionally comprise (E) 0 to 10% by weight of one or more inorganic synergists selected from zinc borate, zinc stannate, boehmite and hydrotalcite.
The copolyetherester compositions described herein may additionally comprise (F) 0 to 3% by weight of an organic phosphonite and/or a mixture of an organic phosphonite and an organic phosphite.
The copolyetherester compositions described herein may additionally comprise (G) 0 to 3% by weight of an ester and/or salt of long-chain aliphatic carboxylic acids (fatty acids) which typically have chain lengths of C14 to C40. Particularly preferred are stearic acid and its esters and/or salts, and esters and/or salts of montanic acid, in particular calcium salts.
The term “flame-retardant mixture” as used herein refers to all of the components of the copolyether composition, excluding only the copolyetherester.
In a particularly preferred embodiment, the copolyetherester composition comprises a flame-retardant mixture comprising the following components:
In a particularly preferred embodiment, the copolyetherester composition comprises a flame-retardant mixture comprising the following components:
In a particularly preferred embodiment, the copolyetherester composition comprises a flame-retardant mixture comprising the following components:
In a particularly preferred embodiment, the copolyetherester composition comprises a flame-retardant mixture comprising the following components:
In a particularly preferred embodiment, the copolyetherester composition comprises a flame-retardant mixture comprising the following components:
The copolyetherester compositions described herein may further comprise one or more optional additives that include, but are not limited to, one or more of the following components as well as combinations of two or more of these: metal deactivators, such as hydrazine and hydrazide; heat stabilizers; antioxidants; modifiers; colorants, lubricants, fillers and reinforcing agents, impact modifiers, flow enhancing additives, antistatic agents, crystallization promoting agents, conductive additives, viscosity modifiers, nucleating agents, plasticizers, mold release agents, scratch and mar modifiers, drip suppressants, adhesion modifiers and other processing aids known in the polymer compounding art. Preferably, the additives are selected from the group consisting of stabilizers, processing agents, metal deactivators, antioxidants, UV stabilizers, heat stabilizers, dyes and/or pigments. When used, the total amount of these additives is preferably about 0.05 to about 10 weight percent, based on the total weight of the copolyetherester formulation.
The compositions of the invention show excellent flammability performance. Flammability can be assessed by methods known to one skilled in the art. One method is Limiting Oxygen Index (“LOI”) according to test method ISO 4589-1/-2, using test bars in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm.
Preferably the compositions of the invention show an LOI of 19 or greater, more preferably 21 or greater, more particularly preferably 23 or greater or 25 or greater when measured according to test method ISO 4589-1/-2, using test bars in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm.
Preferably the compositions of the invention show a ratio of LOI of the composition incorporating the DEPAI and metal phosphite(s) and component (D) to LOI of the composition without component (D) of about 0.75 or greater, more preferably 0.8 or greater, more particularly preferably 0.86 or greater when measured according to test method ISO 4589-1/-2, using test bars in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm.
Often compositions showing good flammability performance produce excessive smoke on exposure to heat and/or flame. The compositions of the invention achieve a superior combination of good flammability performance and reduced smoke production.
Smoke density testing can be performed according to ISO 5659 test standard inside a NBS smoke chamber. Test specimens are prepared as plaques having an area of 75 mm×75 mm and thickness of 2 mm. The specimens are mounted horizontally within the chamber and exposed to a constant thermal irradiance on their upper surface of 25 kW/m2 via a radiator cone and heat flux meter and in the presence of a pilot flame for a period of about 10 min. The smoke evolved over time is collected in the chamber, and the attenuation of a light beam passing through the smoke is measured with a photometric system including a 6.5 V incandescent lamp, a photomultiplier tube, and a high accuracy photodetector. The results are measured in terms of light transmission over time and reported in terms of specific optical density, Ds. Ds is inversely proportional to light transmission and is given for a specific path length equal to the thickness of the molded specimen. Smoke production is measured as max specific optical density, and the total smoke production during the first 4 min of the test, VOF4. VOF4 is calculated as: Ds1min+Ds2min+Ds3min+(Ds4min/2), where Ds1min, Ds2min, Ds3min, and Ds4min are the values of the specific optical density recorded at the 1st, 2nd, 3rd and 4th minutes respectively. Any dripping from the plaque test specimen occurring during the test is recorded. The weight of the dripped material is subtracted from the weight of the 75 mm×75 mm×2 mm test plaque. This difference is reported in grams as the “mass retained” during experiment time. A normalised Ds,max can be calculated by dividing Ds,max over the mass retained during the experiment time, and is reported as Ds, max, ret.
Low values of Ds,max, ret and VOF4 are desirable and indicative of material that will less distract visibility in the event of fire, thus allowing rapid escape of people from confined spaces. Without any smoke light transmittance is 100% and Ds is 0.
The parameters VOF4 and Ds,max, ret can be used to evaluate smoke performance.
The compositions of the invention preferably show a VOF4 measured according to ISO 5659 test standard and using plaques having an area of 75 mm×75 mm and thickness of 2 mm, of not greater than 800, more preferably not greater than 600, more particularly not greater than 500.
The compositions of the invention preferably show a Ds,max, ret measured according to ISO 5659 test standard and using plaques having an area of 75 mm×75 mm and thickness of 2 mm, of not greater than 45, more preferably not greater than 35, more particularly not greater than 30.
The compositions of the invention preferably show a ratio of Ds,max, ret, ex of the composition including the DEPAI and metal phosphite(s) and component (D) to Ds,max, ret, 0 of the composition without component (D) measured according to ISO 5659 test standard and using plaques having an area of 75 mm×75 mm and thickness of 2 mm, of not greater than 0.8, more preferably not greater than 0.6, more particularly not greater than 0.5.
In a more particularly preferred embodiment, the compositions of the invention have an LOI of 21 or greater, more preferably 23 or greater, more particularly preferably 25 or greater when measured according to test method ISO 4589-1/-2, using test bars in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm, and a Ds,max, ret measured according to ISO 5659 test standard and using plaques having an area of 75 mm×75 mm and thickness of 2 mm, of not greater than 45, more preferably not greater than 35, more particularly not greater than 30.
In a more particularly preferred embodiment, the compositions of the invention have a ratio of LOI of the composition incorporating the DEPAI and metal phosphite(s) and component (D) to LOI of the composition with DEPAI alone of about 0.75 or greater, more preferably 0.9 or greater, more particularly preferably 1.0 or greater when measured according to test method ISO 4589-1/-2, using test bars in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm, and a ratio of Ds,max, ret, ex of the composition including the DEPAI and metal phosphite(s) and component (D) to Ds,max, ret, 0 of the composition DEPAI alone measured according to ISO 5659 test standard and using plaques having an area of 75 mm×75 mm and thickness of 2 mm, of not greater than 0.7, more preferably not greater than 0.6, more particularly not greater than 0.5.
The compositions of the invention are made by melt blending the ingredients until a homogeneous blend is obtained. Melt-blending can be carried out, for example, in a twin-screw extruder.
The compositions of the invention are suited to any use in which flame retardancy and reduced smoke production are important. In particular, the compositions of the invention are suitable for making moulded articles (injection moulding, blow-moulding), extruded articles, films, filaments and/or fibres. The compositions of the invention are particularly suited to housings for electrical connectors, parts in contact with current in power distributors, circuit boards, casting compounds, current plugs, circuit breakers, lamp housings, LED lamp housings, capacitor housings, bobbins, fans, protective contacts, plugs, in/on circuit boards, housings for plugs, cables, flexible printed circuit boards, charging cables, and motor covers. Some particularly preferred applications include wire and cable sheathing (including optical cables), automotive uses, trains and aeronautic uses.
A particularly preferred application is wire and cable, in which a light-conducting element or an electrically conductive element or both are surrounded by a sheath made from a composition of the invention. The invention thus extends to wires and cables comprising an electrically conductive element as core, such as a metal wire (for example copper, silver, etc.) and a sheath made from a composition of the invention. The invention also extends to optical cables, comprising a light-conducting element as core and a sheath made from a composition of the invention.
A preferred method for making cables or wires according to the invention is co-axial extrusion. In this method, the conductive element is fed through a die while the sheath of composition is extruded around it. The wire or cable may comprise other elements in the core, such as reinforcing structures or fibers. It may additionally comprise additional sheathing materials both interior to the sheath of the composition of the invention or exterior to the sheath of the composition of the invention. The sheath of the composition of the invention may serve as the insulation, the jacket or both.
The invention is further illustrated by certain embodiments in the examples below which provide greater detail for the compositions, uses and processes described herein. These examples, which set forth a preferred mode presently contemplated for carrying out the invention, are intended to illustrate and not to limit the invention.
Materials
The following materials were used to prepare the flame-retardant polymer compositions described herein and the compositions of the comparative examples.
Copolyetherester (TPC): a copolyetherester elastomer comprising about 72.5 weight percent of copolymerized polytetramethylene oxide having an average molecular weight of about 2000 g/mol as polyether block segments, the weight percentage being based on the total weight of the copolyetherester elastomer, the short chain ester units of the copolyetherester being polybutylene terephthalate segments. The copolyetherester elastomer contained up to 6 weight percent of heat stabilizers, antioxidants and metal deactivators.
Test Methods
Flame Retardance
Flammability testing was performed according to Limiting Oxygen Index (“LOI”) Test method ISO 4589-1/-2. Test specimen were prepared from the compositions of the tables by melt-extruding narrow flat strips in a standard extruder having barrel temperatures set at about 170° C. to about 190° C. and cutting test specimens, in the shape of rectangular bars of dimension 125 mm long by 13 mm wide and having an average thickness of about 1.7±0.1 mm, from the thus-obtained flat strips. Test specimens were conditioned for at least 72 hours at room temperature and 50% relative humidity before testing. According to this test, the specimen is clamped vertically at the centre of a glass chimney at room temperature in an atmosphere of a mixture of oxygen and nitrogen slowly fed into the glass column upwards, where the relative concentration of oxygen and nitrogen can be changed. The upper end of the test sample is ignited with a pilot flame and burns downward. The burning behaviour of the specimen is observed to compare the period for which burning continues. LOI is the minimum concentration of oxygen, expressed as a volume percentage, required to sustain the combustion of the sample indicated by a target burning time after ignition of less than 180 sec. High values of LOI are desirable and indicative of less easily ignited and less flammable material.
Smoke Density
Smoke density testing was performed according to ISO 5659 test standard inside a NBS smoke chamber, supplied by Fire Testing Technologies. Test specimens were prepared from the compositions of the tables by melt-extruding narrow flat strips in a standard extruder having barrel temperatures set at about 170° C. to about 190° C. and compression molding the strips to form plaques having an area of 75 mm×75 mm and thickness of 2 mm. The specimens were mounted horizontally within the chamber and exposed to a constant thermal irradiance on their upper surface of 25 kW/m2 via a radiator cone and heat flux meter and in the presence of a pilot flame for a period of about 40 min. The smoke evolved over time was collected in the chamber, and the attenuation of a light beam passing through the smoke was measured with a photometric system including a 6.5 V incandescent lamp, a photomultiplier tube, and a high accuracy photodetector. The results were measured in terms of light transmission over time and reported in terms of specific optical density, Ds. Ds is inversely proportional to light transmission and is given for a specific path length equal to the thickness of the molded specimen. Comparison between the material compositions is made via the measurement of max specific optical density, Ds,max and the total smoke production during the first 4 min of the test, VOF4. VOF4 is calculated as: Ds1min+Ds2min+Ds3min+(Ds4min/2), where Ds1min, Ds2min, Ds3min, and Ds4min are the values of the specific optical density recorder at the 1st, 2nd, 3rd and 4th minutes respectively. Any dripping from the plaque test specimen occurring during the test is recorded. The weight of the dripped material is subtracted from the weight of the 75 mm×75 mm×2 mm test plaque. This difference is reported in grams as the “mass retained” during experiment time. A normalised Ds,max can be calculated by dividing Ds,max over the mass retained during the experiment time, and is reported as Ds, max, ret.
Ds,max and VOF4 values were calculated automatically by the software of the NBS smoke chamber. The software is consistent with the applicable ISO standard. Low values of Ds,max,ret and VOF4 are desirable and indicative of material that will have a less adverse effect on visibility in the event of fire, and thus will present a lesser obstacle to the rapid escape of people from confined spaces. Without any smoke, light transmittance is 100% and Ds is 0.
Experimental Data
Compositions designated with “CE” are comparative, and compositions designated with “E” are inventive.
Table 1
Table 1 shows comparative copolyetherester compositions CE3 (DEPAI alone) and CE4 (DEPAI+Al phosphite) as well as a composition according to the invention (DEPAI+Al phosphite+melamine pyrophosphate).
The inventive compositions have good flame retardancy as evidenced by an LOI of 25.
In Table 1, LOIex LOI0 means the ratio of the LOI of the experimental material (i.e., containing DEPAI plus phosphite plus MDP), to the LOI of the control material (i.e., containing DEPAI alone).
In Table 1, Ds, max, ret, ex/Ds, max, ret, 0 means the ratio of the Ds, max, ret of the experimental material (i.e., containing DEPAI plus phosphite plus MDP), to the Ds, max, ret of the control material (i.e., containing DEPAI alone).
While certain of the preferred embodiments of this invention have been described and specifically exemplified above, it is not intended that the invention be limited to such embodiments. Various modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.
This application claims priority under 35 U.S.C. § 365 to U.S. Provisional Application Nos. 63/039,098; 63/039,133; and 63/039,171, each of which was filed on Jun. 15, 2020, and each of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/037379 | 6/15/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63039171 | Jun 2020 | US | |
| 63039098 | Jun 2020 | US | |
| 63039133 | Jun 2020 | US |
