ANTISTATIC POLYMER COMPOSITION FIELD OF DISCLOSURE

The disclosure is related to polymeric compositions with improved antistatic properties. BACKGROUND

Thermoplastic polymers such as polyamide possess excellent mechanical properties, moldability, and chemical resistance and have therefore been used in automotive parts, electric/electronic components, and many other applications. In certain applications, it is desirable that these polymers also are antistatic. This can be achieved by the incorporation of electrically conductive additives, such as carbon black, carbon fiber, graphite, etc. However, even with the addition of such conventional additives, the resistivity of the polymer compositions is increased after thermal aging. Thus, there is still a need to develop polymer compositions with high conductivity, even post thermal aging. SUMMARY

Provided herein is an antistatic polymer composition comprising: a) at least one thermoplastic polymer; and b) about 10-25 wt% of carbon fiber, wherein, i) the carbon fiber has an average diameter in the range of about 3-15 µm, ii) the carbon fiber has an average length in the range of about 0.1-0.2 mm, with two distribution peaks at about 0.06-0.09 mm and about 0.11-0.13 mm, respectively, and iii) about 50-80 number% of the carbon fiber has a length of about 0.15 mm or lower, with the total wt% of the composition totaling to 100 wt%.

In one embodiment of the antistatic polymer composition, the

thermoplastic polymer is selected from polyamides. In a further embodiment of the antistatic polymer composition, the thermoplastic polymer is selected from aliphatic polyamide, or, the thermoplastic polymer is polyamide 6,6.

In a yet further embodiment of the antistatic polymer composition, the thermoplastic polymer is present in the composition at a level of about 55-90 wt%, or about 60-90 wt%, or about 70-90 wt%.

In a yet further embodiment of the antistatic polymer composition, the carbon fiber is present in the composition at a level of about 10-22 wt% or about 10-19 wt%.

In a yet further embodiment of the antistatic polymer composition, the carbo fiber has an average diameter of about 4-12 µm or about 5-9 µm.

In a yet further embodiment of the antistatic polymer composition, the composition further comprises additional additives at a level of about 0.005-20 wt%.

Further provided herein is an antistatic polymer composition which is prepared by compounding into a polymer matrix chopped carbon fiber and milled carbon fiber, wherein, a) the polymer matrix is formed of at least one thermoplastic polymer; b) the chopped carbon fiber has an average diameter of about 3-15 µm and an average length of about 2-9 mm, and less than about 10 number% of which has length less than about 2 mm; c) the milled carbon fiber has an average diameter of about 3-15 µm and an average length of about 0.07- 0.4 mm, and less than about 10 number% of which has length more than about 0.4 mm; and d) the weight ratio between the chopped carbon fiber and the milled carbon fiber is from about 4:6 to about 8.5:1.5, and the total amount of the chopped and milled carbon fiber is about 10-25 wt%, based on the total weight of the composition.

In a further embodiment of the antistatic polymer composition, the at least one thermoplastic polymer is polyamide. In a yet further embodiment of the antistatic polymer composition, the total amount of the chopped and milled carbon fiber is about 10-22 wt% or about 10- 19 wt%, based on the total weight of the composition. FIGURES

Figure 1 is a length distribution pattern of carbon fibers in the resins of CE1-CE3 and E1-E3. DETAILED DESCRIPTION

Disclosed herein are polymer compositions with improved antistatic property. The composition comprises at least one thermoplastic polymer and dispersed in the thermoplastic polymer matrix a mixture of carbon fiber, wherein, i) the carbon fiber has an average diameter in the range of about 3-15 µm; ii) the carbon fiber has an average length in the range of about 0.1-0.2 mm, with two distribution peaks at about 0.06-0.09 mm and about 0.11-0.13 mm, respectively; and iii) about 50-80 number% of the carbon fiber has a length of about 0.15 mm or lower.

Suitable thermoplastic polymer may include, without limitation,

polyamides, polyesters, polysulfones, polymethylmethacrylate, polyvinylchloride, polyketones, polyethers, polyphenylene sulphide, polyphenylene oxide, polyoxymethylene, polycarbonate, polylactic and its copolymers, polystyrene and its copolymers (e.g., ABS, SBS, SAN, etc.), polyolefins (e.g., polyethylene, polypropylene, copolymers of polyethylene and/or polypropylene), etc.

In one embodiment, the thermoplastic polymer used herein is selected from polyamides. Suitable polyamides include both aliphatic polyamides and aromatic polyamides.

Polyamides are (a) condensation products of one or more dicarboxylic acids and one or more diamines, or (b) condensation products of one or more aminocarboxylic acids, or (c) ring opening polymerization products of one or more cyclic lactams. The aromatic polyamides used herein may be

homopolymers, copolymers, terpolymers or higher polymers containing at least one aromatic monomer component. For example, an aromatic polyamide may be obtained by using an aliphatic dicarboxylic acid and an aromatic diamine, or an aromatic dicarboxylic acid and an aliphatic diamine as starting material and subjecting them to polycondensation.

Suitable diamines used herein may be selected from aliphatic diamines, alicyclic diamines, and aromatic diamines. Exemplary diamines useful herein include, without limitation, tetramethylenediamine; hexamethylenediamine; 2- methylpentamethylenediamine; nonamethylenediamine;

undecamethylenediamine; dodeca-methylenediamine; 2,2,4- trimethylhexamethylenediamine; 2,4,4 trimethylhexamethylenediamine; 5- methylnonamethylene-diamine; 1,3- bis(aminomethyl)cyclohexane; 1,4- bis(aminomethyl)cyclohexane; 1-amino-3 aminomethyl-3,5,5- trimethylcyclohexane; bis(4-aminocyclohexyl)methane; bis(3-methyl-4- aminocyclohexyl)methane; 2,2-bis(4-aminocyclohexyl)propane;

bis(aminopropyl)piperazine; aminoethylpiperazine; bis(p- aminocyclohexyl)methane; 2-methyloctamethylenediamine;

trimethylhexamethylenediamine; 1,8-diaminooctane; 1,9 diaminononane; 1,10- diaminodecane; 1,12-diaminododecane; m-xylylenediamine; p-xylylenediamine; and the like and derivatives thereof.

Suitable dicarboxylic acids used herein may be selected from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and aromatic dicarboxylic acids. Exemplary dicarboxylic acids useful herein include, without limitation, adipic acid; sebacic acid; azelaic acid; dodecanedoic acid; terephthalic acid; isophthalic acid; phthalic acid; glutaric acid; pimelic acid; suberic acid; 1,4- cyclohexanedicarboxylic acid; naphthalenedicarboxylic acid; and the like and derivatives thereof.

Exemplary aliphatic polyamides used herein include, without limitation, polyamide 6; polyamide 6,6; polyamide 4,6; polyamide 6,10; polyamide 6,12; polyamide 11; polyamide 12; polyamide 9,10; polyamide 9,12; polyamide 9,13; polyamide 9,14; polyamide 9,15; polyamide 6,16; polyamide 9,36; polyamide 10,10; polyamide 10,12; polyamide 10,13; polyamide 10,14; polyamide 12,10; polyamide 12,12; polyamide 12,13; polyamide 12,14; polyamide 6,14; polyamide 6,13; polyamide 6,15; polyamide 6,16; and the like.

Exemplary aromatic polyamides used herein include, without limitation, poly(m-xylylene adipamide) (polyamide MXD,6); poly(dodecamethylene terephthalamide) (polyamide 12,T); poly(undecamethylene terephthalamide) (polyamide 11,T); poly(decamethylene terephthalamide) (polyamide 10,T);

poly(nonamethylene terephthalamide) (polyamide 9,T); poly(hexamethylene terephthalamide) (polyamide 6,T); hexamethylene adipamide/hexamethylene terephthalamide copolyamide (polyamide 6,T/6,6, i.e., polyamide 6,T/6,6 having at least about 50 mol% of its repeating units derived from 6,T); hexamethylene terephthalamide/hexamethylene adipamide copolyamide (polyamide 6,6/6,T, i.e., polyamide 6,6/6,T having at least about 50 mol% of its repeating units derived from 6,6); poly(hexamethylene terephthalamide/hexamethylene isophthalamide) (polyamide 6,T/6,I, i.e., polyamide 6,T/6,I having at least about 50 mol% of its repeating units derived from 6,T); hexamethylene terephthalamide/2- methylpentamethylene terephthalamide copolyamide (polyamide 6,T/D,T);

hexamethylene adipamide/hexamethylene terephthalamide/hexamethylene isophthalamide copolyamide (polyamide 6,6/6,T/6,I); poly(caprolactam- hexamethylene terephthalamide) (polyamide 6/6,T); poly(hexamethylene isophthalamide/hexamethylene terephthalamide) (polyamide 6,I/6,T, i.e., polyamide 6,I/6,T having at least about 50 mol% of its repeating units derived from 6,I); poly(hexamethylene isophthalamide) (polyamide 6,I);

poly(metaxylylene isophthalamide/ hexamethylene isophthalamide) (polyamide MXD,I/6,I); poly(metaxylylene isophthalamide/ metaxylylene terephthalamide/ hexamethylene isophthalamide) (polyamide MXD,I/MXD,T/6,I/6,T);

poly(metaxylylene isophthalamide/dodecamethylene isophthalamide) (polyamide MXD,I/12,I); poly(metaxylylene isophthalamide) (polyamide MXD,I);

poly(dimethyldiaminodicyclohexylmethane isophthalamide/dodecanamide) (polyamide MACM,I/12); poly(dimethyldiaminodicyclohexylmethane

isophthalamide/dimethyldiaminodicyclohexylmethane

terephthalamide/dodecanamide) (polyamide MACM,I/MACM,T/12); poly(hexamethylene isophthalamide/dimethyldiaminodicyclohexylmethane isophthalamide/dodecanamide) (polyamide 6,I/MACM,I/12); poly(hexamethylene isophthalamide/hexamethylene terephthalamide/

dimethyldiaminodicyclohexylmethane isophthalamid/

dimethyldiaminodicyclohexylmethane terephthalamide) (polyamide

6,I/6,T/MACM,I/MACM,T); poly(hexamethylene isophthalamide/hexamethylene terephthalamide/dimethyldiaminodicyclohexylmethane isophthalamid/

dimethyldiaminodicyclohexylmethane terephthalamide/dodecanamide)

(polyamide 6,I/6,T/MACM,I/MACM,T/12);

poly(dimethyldiaminodicyclohexylmethane isophthalamide/

dimethyldiaminodicyclohexylmethane dodecanamide) (polyamide

MACM,I/MACM,12); and the like.

In a further embodiment, the thermoplastic polymer polyamide used herein is polyamide 6,6.

Based on the total weight of the antistatic polymer composition disclosed herein, the at least one thermoplastic polymer may be present at a level of about 55-90 wt%, or about 60-90 wt%, or about 70-90 wt%.

The carbon fiber used herein has an average diameter in the range of about 3-15 µm, or about 4-12 µm, or about 5-9 µm. The length of the carbon fiber comprised in the antistatic polymer composition are not uniformed and has certain distribution. That is, the carbon fiber has an average length of about 0.1- 0.2 mm, with two distribution peaks at about 0.06-0.09 mm and about 0.11-0.14 mm. Additionally, about 50-80 number% of the carbon fiber has a length of about 0.15 mm or lower. To obtain such measurements, the organic

components (including the polymer matrix) of the composition is removed and the length of the carbon fibers are determined using an optical microscope. Any suitable methods may be used to remove the organic components of the composition. For example, suitable solvent, such as formic acid, may be used to dissolve and remove the polymer matrix of the composition. Or, the composition may be placed in an oven with N ₂ flow protection to remove the polymer matrix. Then, under a microscope, the length of about 300-400 carbon fibers are measured and recorded. And with a step length of 20 µm, a distribution graph is drawn (as shown in Figure 1).

In order to obtain such length distribution for the carbon fibers, it is preferred that two types of carbon fibers are compounded with the base polymer. That is, a first type of carbon fiber is chopped carbon fibers having an average diameter of about 3-15 µm and an average length of about 2-9 mm (in which less than 10 number% were with length less than about 2 mm). And a second type of carbon fibers are milled carbon fibers having an average diameter of about 3-15 µm and an average length of about 0.07-0.4 mm (in which less than 10 number% are with length more than about 0.4 mm). To obtain the antistatic polymer composition disclosed herein, the weight ratio between the chopped carbon fibers and the milled carbon fibers may be from about 4:6 to about 8.5:1.5.

Based on the total weight of the antistatic polymer composition disclosed herein, the carbon fiber may be present at a level of about 10-25 wt%, or about 10-22 wt%, or about 10-19 wt%.

The antistatic polymer composition disclosed herein may further comprise other additives, such as colorants, antioxidants, UV stabilizers, UV absorbers, heat stabilizers, lubricants, viscosity modifiers, nucleating agents, plasticizers, mold release agents, scratch and mar modifiers, impact modifiers, emulsifiers, optical brighteners, antistatic agents, acid adsorbents, smell adsorbents, anti- hydrolysis agents, anti-bacterial agents, density modifiers, thermal conductive fillers, electrical conductive fillers, coupling agents, end-capping reagents and combinations of two or more thereof. Based on the total weight of the antistatic polymer composition disclosed herein, such additional additive(s) may be present at a level of about 0.005-20 wt% or about 0.01-15 wt%, or about 0.02-10 wt%, or about 0.05-5 wt%.

As demonstrated herein, the polymer composition disclosed herein possess low volume resistivity, especially after thermal aging treatment.

Further disclosed herein are articles formed of the antistatic polymer compositions disclosed herein. For example, such antistatic polymer

compositions can be used in many areas including home appliances, industrial packaging, mining, transportation, etc. Exemplary articles include, without limitation, antistatic handles, containers, connectors, etc. EXAMPLES

Materials

● Polyamide 6,6 (PA66) - polyamide 6,6 resin obtained from E.I. du Pont de Nemours and Company (U.S.A.) (hereafter“DuPont”) under the trade name Zytel® 101;

● Chopped carbon fiber (C-CF) - carbon fibers obtained from Zoltek (U.S.A.) under the tradename Panex ^TM 35 Chopped Fiber (Type -45), which has an average diameter of about 7 µm and average length of about 6 mm;

● Milled carbon fiber (M-CF) - carbon fibers obtained from Zoltek (U.S.A.) under the tradename ZOLTEK PX35 Milled Fibers, which has an average diameter of about 7 µm and average length of about 0.15 mm;

● Graphite - graphite flake with average diameter ~100 µm obtained from

Qingdao Hengsheng Graphite Company (China).

● Stearyl erucamide - obtained from Croda (U.S.A.) under the tradename

Crodamide™212. In each CE1-CE5 and E1-E3, a polymer composition (all components listed in Table 1) was prepared by compounding in a 32 mm ZSK twin screw extruder. The barrel temperatures were set at about 280°C and screw speed at about 300 rpm. After exiting the extruder, the blended compositions were cooled and cut into resin pellets, which was followed by drying overnight.

The dried resin pellets obtained in each example were injection molded into 100x100x0.8 mm test plates, with the melt temperature and mold

temperature set at about 280°C and about 90°C, respectively.

The test plates were vacuum sealed in a foil lined plastic bag to preserve them in dry-as-molded condition until they were measured with a 6517B electrometer/high-resistance meter from KEITHLEY company (U.S.A.) to obtain volume resistivity. As for volume resistivity post thermal aging, the plates were placed in an oven (model 6054 from Thermo Fisher Scientific (U.S.A.)) at 150°C for 4 hours before the volume resistivity measurements were obtained.

Further the resin in each of CE1-CE3 and E1-E3 were placed in a thermogravimetric analyzer (TGA Q500 from TA Instruments (U.S.A.)) at about 600°C under N ₂ flow protection for about 10 min to remove the polymeric components. The resulting residues were placed under optical microscope and the length of a random 350 carbon fibers were measured and recorded. Using a step length of 20 µm, the length distribution graph for each of CE1-CE3 and E1- E3 were drawn (as shown in Figure 1).

As demonstrated herein, when chopped carbon fibers and milled carbon fibers were incorporated at certain weight ratios (e.g., 4:6-8.5:1.5), the resultant polymer composition maintained low volume resistivity after thermal aging treatment.

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