Polymer/Carbon Black Composite: Method for Its Preparation and Use Thereof
20170045837 · 2017-02-16
Inventors
Cpc classification
G03G9/0806
PHYSICS
International classification
Abstract
There is provided a process for preparing a polymer/carbon black composite material. The process comprises a mini emulsion polymerization (MEP) process involving a reactive co-stabilizer. Optionally, the co-stabilizer is a long alkyl chain methacrylate or a mixture of long alkyl chain methacrylates.
Claims
1. A process for preparing a polymer/carbon black composite material, comprising a mini emulsion polymerization (MEP) process involving a reactive co-stabilizer.
2. The process according to claim 1, wherein the co-stabilizer is a long alkyl chain methacrylate or a mixture of long alkyl chain methacrylates.
3. The process according to claim 1, wherein the co-stabilizer is a long alkyl chain methacrylate of general formula I below ##STR00017## wherein R is a C.sub.6 to C.sub.22 linear, branched, saturated or unsaturated alkyl group, or the co-stabilizer is a mixture of two or more of the long alkyl chain methacrylates.
4. The process according to claim 1, wherein the co-stabilizer is a long alkyl chain methacrylate of general formula I below ##STR00018## wherein R is a C.sub.10 to C.sub.20 linear, branched, saturated or unsaturated alkyl group, or the co-stabilizer is a mixture of two or more of the long alkyl chain methacrylates.
5. The process according to claim 1, wherein the co-stabilizer is stearyl methacrylate (SteaMA) of formula II below ##STR00019##
6. The process according to claim 1, wherein the MEP process further involves monomers of one type or more and carbon black.
7. The process according to claim 1, wherein the MEP process further involves monomers of one type or more, carbon black and a charge control agent.
8. The process according to claim 1, wherein the MEP process further involves monomers of one type or more and carbon black, and wherein the monomers are selected from the group consisting of styrene (St), alkyl esters of acrylic and methacrylic acids, vinyl esters of aliphatic acids, and monomers containing sulfonate groups including sodium styrene sulfonate (NaSS).
9. The process according to claim 1, wherein the MEP process further involves styrene (St) monomers and carbon black.
10. The process according to claim 1, wherein the MEP process further involves styrene (St) monomers, carbon black and a charge control agent.
11. The process according to claim 1, wherein the amount of co-stabilizer is about 0.5 to 15 mol % based on the amount of the monomers.
12. The process according to claim 1, wherein the MEP process further involves monomers of one type or more, carbon black and a charge control agent, and wherein an amount of the charge control agent is about 0.1 to 10 mol % based on the amount of the monomers.
13. A polymer/carbon black composite material obtained by a mini emulsion polymerization process (MEP) involving: a co-stabilizer which is a long alkyl chain methacrylate of general formula I below ##STR00020## wherein R is a C.sub.6 to C.sub.22 linear, branched, saturated or unsaturated alkyl group, or the co-stabilizer is a mixture of two or more of the long alkyl chain methacrylates; monomers of one type or more; and carbon black.
14. The polymer/carbon black composite material according to claim 13, further involving a charge control agent.
14. The polymer/carbon black composite material according to claim 13, having particles size in the range of about 20 to 1000 nm.
15. The polymer/carbon black composite material according to claim 13, having a carbon black content in the range of about 0.5 to 20 wt %.
16. A polystyrene/carbon black or polystyrene copolymer/carbon black obtained by a mini emulsion polymerization process (MEP) involving styrene (St) monomers, stearyl methacrylate (SteaMA) of general formula II below, and a charge control agent ##STR00021##
Description
BRIEF DESCRIPTION OF DRAWINGS
[0040] Example embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:
[0041]
[0042]
[0043] Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.
DETAILED DESCRIPTION
[0044] In order to provide a clear and consistent understanding of the terms used in the present specification, a number of definitions are provided below. Moreover, unless defined otherwise, all technical and scientific terms as used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains.
[0045] The use of the word a or an when used in conjunction with the term comprising in the claims and/or the description may mean one, but it is also consistent with the meaning of one or more, at least one, and one or more than one. Similarly, the word another may mean at least a second or more.
[0046] As used herein, the words comprising (and any form of comprising, such as comprise and comprises), having (and any form of having, such as have and has), including (and any form of including, such as include and includes) or containing (and any form of containing, such as contain and contains), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.
[0047] As used herein, when referring to numerical values or percentages, the term about includes variations due to the methods used to determine the values or percentages, statistical variance and human error. Moreover, each numerical parameter in this application should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
[0048] The present disclosure is drawn to a mini emulsion polymerization (MEP) process for preparing a polymer/carbon black composite material. The process involves a reactive hydrophobic co-stabilizer. The composite material of the invention may be used in various applications. Such applications include for example applications where it is desired to have a material with low volatile organic content (VOC), such as for example toners, coatings, ingredients in polymer blends.
[0049] The reactive hydrophobic co-stabilizer used in the process of the invention is polymerizable. It may be for example a long alkyl chain methacrylate or a mixture of such methacrylates. An example of a general chemical formula of a long alkyl chain methacrylate is depicted below (Formula I) wherein R is a C.sub.6 to C.sub.22 linear, branched, saturated or unsaturated alkyl group. An example of such long alkyl chain methacrylate is stearyl methacrylate (SteaMA), the chemical formula of which is also depicted below (Formula II).
##STR00007##
[0050] The co-stabilizer of the invention allows for an adjustment of the glass transition temperature (T.sub.g) of the composite material obtained. Indeed, the co-stabilizer is covalently incorporated into the polymeric matrix through copolymerization. Accordingly, the polymer/carbon black composite material may also be useful in applications where it is desired to have a material a with low T.sub.g.
[0051] Information on the various chemicals used in this invention is outlined in Table 1 below.
TABLE-US-00001 TABLE 1 Chemical name Abbreviation CAS# Supplier Formula Monomer Styrene St 100-42-5 99% Aldrich
[0052] The MEP of hydrophobic monomers such as St with a long chain alkyl acrylate as co-stabilizer is described in the literature and may be successfully performed in the presence of SDS. As indicated above, MEP processes generally use hydrophobic hexadecane (HD) as co-stabilizer. In this invention, HD is replaced by a long chain methacrylate. The size of the particles in the composite material obtained is comparable to the size of the particles in a material obtained by a classic MEP using HD as co-stabilizer. The long chain alkyl co-stabilizer forms copolymers with styrene. Modulated DSC investigations show two T.sub.g of 62 and 93 C. pointing to the existence in the particles of a copolymer as well as pure PSt. These results were found for samples with high amount of co-stabilizer such as in Examples 1 and 2 outlined below.
[0053] The T.sub.g of the particles, as well as the particle size and the particle size distribution depend on the amount of reactive long alkyl chain methacrylate used.
[0054] Preparation of St/CB composite particles was performed successfully in the presence of a reactive long chain alkyl methacrylate, SteaMA, as co-stabilizer. The St/CB composite particles were stable (Examples 4-10), similarly to particles in a MEP process performed in the presence of HD as co-stabilizer (Example 3). No unmodified CB was observed, as shown by scanning electron microscopy (SEM) investigations presented in
[0055] The content of CB in the composite material varied between 5 and 10 wt %. In all cases, and using various types of CB, stable composite particles were obtained with a particle size of >90 nm and with often bimodal size distribution. High monomer conversion rates >95% were obtained and the resulting polymers showed high molar masses with Mn >100,000 g/mol.
[0056] In toner applications, it is known that charge control agents (CCAs) play an important role. Therefore, the formation of PSt/CB composites was studied in the presence of CCA. The investigated CCA were bi-salicylates of Al or Zr. The use of HD as co-stabilizer did not give positive results in the formulations. Significant amount of unmodified CB was observed by SEM. Replacement of HD by SteaMA showed an improvement in the quality of the composite particles obtained. No unmodified CB was found by SEM investigations for the two CCA types used (Examples 13 and 14). In all of the experiments a conversion rate of the monomers of >93% was obtained. Thus, the use of a reactive co-stabilizer such as SteaMA instead of HD in the MEP process for the preparation of a polymer/CB composite is advantageous.
[0057] The commonly used low molecular weight co-stabilizers such as HD or hydrophobic oils has a drawback in that such stabilizers physically bound to the products only after the polymerization reaction. Consequently, the polymeric particles obtained still contain volatile substances. Despite the fact that the boiling point of HD is relatively high, about 287 C., the thermogravimetric analysis of pure HD showed evaporation at temperatures of up to 200 C. with a T.sub.onset of 89 C. and T.sub.10% of 133 C. (TGA under N.sub.2, 10 K/min). Thus liberation of volatile substances cannot be excluded in applications such as printer applications where high temperatures are common. Replacing volatile HD with a reactive co-stabilizer reduces the VOC. The reactive co-stabilizer is incorporated by covalent bonds into the polymer chain after the polymerization thus avoiding liberation of any volatile substances.
[0058] Furthermore, the formation of copolymers resulted in products with lower T.sub.g as the original PSt. A lowering of T.sub.g of up to 62 C. was observed by modulated DSC for products with the highest content of SteaMA.
[0059] Furthermore, preparation of PSt/CB composite material having a CB content of up to 10 wt % is possible, and the composite material may be prepared in the presence of CCA. It was even noted that in this case, the particles presented a higher stability.
EXAMPLES
MEP of St using SteaMA as Co-Stabilizer
Examples 1 and 2
[0060] Details of the experiments performed and the results of the analytical investigations are summarized in Table 2 below.
[0061] 4.27 g of purified St, 0.929 g SteaMA (98%), and 0.146 g AIBN were weighted. After mixing by shaking the organic phase, the required amounts of surfactant SDS (0.056 g) and water (41.6 g) were added. Then the mixture was slowly stirred at about 150 rpm under N.sub.2 (the needle for purging with N.sub.2 was not in the mixture, very small stream of N.sub.2) for 15 minutes. During this time, the SDS was dissolved in water. A formation of pre-emulsion was not observed because of the slow stifling. Then the mixture was stirred under N.sub.2 at 800 min.sup.1 for 30 minutes to prepare the pre-emulsion using a glass stirrer. The distance between top side fastener stirrer and lower side of the fastener motor was measured and used in further experiments. So the stifling conditions were comparable.
[0062] After 30 minutes, the mixture was transferred to the sonifier. During the transfer, a moderate stream of N.sub.2 was applied. The mini emulsion was prepared by sonication of the pre-emulsion for 600 s (level 7, pulse, duty cycle 50%) with an ultrasonic disintegrator Branson 450W using a minitip. The connection between vessel and tip was realized by a special Teflon adapter. Due to the adapter, a tight connection between minitip and vessel could be realized. During all operations the vessel was purged with a slight stream of nitrogen. A cooling of the reaction vessel by ice water was performed during the sonication in order to avoid a heating of the mixture. The reaction vessel with the formed mini emulsion was transferred to the preheated thermostat (66 C.). The reaction was performed at 400 min.sup.1 for 3 hours. Then the mixture was cooled to room temperature within 5 minutes using ice-water. Before the storage of the dispersion, about 200 mg of a 1 wt % solution of HQ in water was added and the mixture was shaken.
Removal of Coagulum
[0063] After the polymerization, the formed dispersion was poured through a mesh (pore size 20 m20 m) and then used for the analytical investigations. Finally, the rest in the mesh and the rests from the stirrer and the vessel were transferred into a frit using water. The coagulum was washed with water and dried in vacuum at room temperature in order to determine the quantity of coagulum.
Determination of Conversion Rate
[0064] Three samples of 2 g of the formed dispersion were weighted in a petri dish and kept overnight at room temperature. The air dried products were dried in vacuum at room temperature until the weight was constant. P.sub.4O.sub.10 was used as drying agent in the vacuum oven.
Size Exclusion Chromatography (SEC)
[0065] SEC measurements were performed with an apparatus of the Agilent Series 1100 (RI detection, 1PL_MIXED-B-LS-column [7,5300 mm] and 10 m PSt gel Agilent column, Chloroform 1.0 mL/min). Polystyrene was used as standard. This was the standard method for all of the samples. The samples containing CB were filtrated to remove the CB before the analysis. The error of the method is about 10%.
Particle Size Measurement
[0066] The particle size measurements were performed with a Zetasizer NANO S (Malvern) at a fixed scattering angle of 173. The given values are the z.sub.ave (intensity based). The error of the measurements is about 5%. Higher values of PDI mean that the particle size distribution becomes broader.
Preparation of Samples for the DLS Measurements
[0067] The measurements were performed in 0.01 N NaCl solutions according to the Malvern recommendation for the measurements of latex standards. For the experiments with 20 wt % solid content, about 250 mg of the dispersion was weighted and about 20 g of 0.01 N NaCl solution was added. For the samples with lower solid content (10 or 15 wt %) the amount of NaCl solution was proportionally reduced to keep the concentration of the thinned dispersions nearly constant. The particle sizes of 3 samples were estimated, each sample was consecutively measured twice. In few cases the application of NaCl solution led to a precipitation of the dispersion. Therefore, the dispersion was thinned only with pure Millipore water.
Scanning Electron Microscopy (SEM)
[0068] The SEM investigations were performed with an Ultra 55 plus (Zeiss). The thinned dispersions from the DLS measurements were used to prepare the samples. One drop was placed on a C-pad or a wafer. After air drying, the samples were sputtered with 3 nm Pt.
Preparation of PSt/CB Composites using SteaMA and Different Surfactants
[0069] Two different CB types, NIPex 35 and NIPex 150 (Evonik) were selected for the preparation of PSt/CB composites. But the invention is not limited to these CB types. NIPex 35 is a non-oxidized, low structure furnace black with a mean primary particle size of about 31 nm and a pH value of about 9 (according to DIN ISO 787/9). NIPex 150 is a high structure oxidized gas black with a mean primary particle size of about 25 nm and a pH value of about 4 (according to DIN ISO 787/9). As will be understood by a skilled person, other suitable types of carbon black may also be used.
[0070] The procedure described above was repeated using the recipe described in the 2.sup.nd part of Table 2 which relates to Example 3. The CB was added to the organic phase at the beginning and the organic phase was shaken. Then water and the surfactant were added to the mixture which was processed as described above.
TABLE-US-00002 TABLE 2 Table 2. Recipes for the MEP of styrene using SteaMA as co-stabilizer Water Styrene Surfactant Co-stabilizer AIBN Filler CCA Sample [g] [g] Type [mg] Type [mg] [mg] Type [mg] wt %.sup.# Type [mg] 0 (Reference) 37.7 8.6 SDS 103 HD 359 269 Without 0 without 0 1 (Reference) 41.6 4.3 SDS 56 SteaMA 929 146 Without 0 without 0 2 (Reference) 41.6 4.3 SDS 52 SteaMA 955 140 without 0 without 0 3* 28.09 6.4 SDS 76 HD 264 199 CB150 344 5.4 without 0 (Reference) 4 41.6 4.3 SDS 52 SteaMA 979 133 CB150 214 5.0 without 0 5 41.6 4.3 SDS 52 SteaMA 959 134 CB150 344 8.0 without 0 6 41.6 4.3 SDS 53 SteaMA 927 135 CB150 345 10.0 without 0 8 41.6 4.3 SDS 53 SteaMA 934 136 CB150 429 5.0 without 0 9 41.6 4.3 SDS 52 SteaMA 935 134 CB35 214 5.0 without 0 10 41.6 4.3 SDS 54 SteaMA 932 137 CB90 215 5.0 without 0 11 37.7 8.6 SDS 103 HD 356 268 CB150 428 5.0 MEC-88 86 12 37.7 8.6 SDS 103 HD 357 268 CB150 428 5.0 MEC-105 86 13 41.6 4.3 SDS 51 SteaMA 926 134 CB150 214 5.0 MEC-88 467 14 41.6 4.3 SDS 52 SteaMA 926 134 CB150 214 5.0 MEC-105 429 *sonication 20 minutes at 90% duty, polymerization for 6 hours .sup.#based on styrene.
[0071] Table 3 below outlines the results for the MEP of St in the presence of SteaMA. Table 4 below outlines the results obtained for PSt/CB composites using HD or SteaMA as co-stabilizer in the presence of CCA. In this invention, bi-salicylates of Al and Zr were used as charge control agents. As will be understood by a skilled person, other suitable charge control agents may also be used.
TABLE-US-00003 TABLE 3 Results for the MEP of St in the presence of SteaMA Particle size DLS SEC Conversion z-ave M.sub.n M.sub.w rate Coagulum Example [nm] PDI [g/mol] [g/mol] M.sub.w/M.sub.n [%] [%] 0 78 0.06 149000 693000 4.7 94 0.3 (Reference) 1 72 0.06 121000 1370000 11.3 96 0.2 (Reference) 2 73 0.05 105000 889000 8.5 97 0.2 (Reference) 3 98 0.18 105000 571000 5.4 95 1.0 (Reference) 4 92 96000 1375000 14.3 96 0.2 6 100 169000 1820000 10.8 94 1.6 8 103 157000 1690000 10.8 93 1.6 9 96 178000 1870000 10.5 96 0.7 10 90 148000 1675000 11.3 93 2.1
TABLE-US-00004 TABLE 4 Results obtained for PSt/CB composites using HD or SteaMA as co-stabilizer in the presence of CCA Particle size DLS SEC Conversion Coag- z-ave M.sub.n M.sub.w rate ulum [nm] PDI [g/mol] [g/mol] M.sub.w/M.sub.n [%] [%] 11 109.sup.a 115000 517000 4.5 96 2.4 12 103.sup.a 115000 473000 4.1 96 0.6 13 94.sup.b 145000 1633000 11.3 104 0.7 14 118.sup.b 109000 1677000 15.4 97 0.1 .sup.aUnmodified CB and larger agglomerates could be observed by SEM. .sup.bUnmodified, non-encapsulated CB could not be identified by SEM. Few agglomerates in of about 200 nm were observed.
Description of the SEM Images of Particles Obtained with the SteaMA
Preparation of the Samples for SEM Measurements
[0072] After the polymerization, a part of the resultant dispersion was thinned with 0.01 normal NaCl solution in deionized water (200-250 mg dispersion were thinned with 10 g of NaCl solution). These thinned dispersions were used for the particle size measurements as well as for the SEM investigations. The SEM investigations were performed with an Ultra 55 plus (Zeiss). The thinned dispersions from the DLS measurements were used to prepare the samples. One drop was placed on a purified silicon wafer mounted at a sample holder. After air drying, the samples were sputtered with 3 nm Pt.
[0073] Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. The present disclosure refers to a number of documents, the content of which is herein incorporated by reference in their entirety.
INDUSTRIAL APPLICABILITY
[0074] The polymer/carbon black composite material of the invention may be used in various applications. Such applications include for example toner applications. In these applications, the composite material of the invention leads to a reduction in the volatile organic content (VOC). Accordingly, the polymer/carbon black composite material of the invention is environmentally friendly and potentially less harmful for the health. The polymer/carbon black composite material of the invention may also be useful in applications where it is desired to have a material with a low T.sub.g.
[0075] It will be appreciated that the polymer/carbon black composite material, toners comprising such material, use of the material and the toners, and processes for preparing the material and the toners disclosed herein may be embodied in various combinations to produce environmentally friendly and cost efficient toners. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.