WO2002036690A1

WO2002036690A1 - Surface treated carbon black, plastics and rubber compositions containing the same

Info

Publication number: WO2002036690A1
Application number: PCT/NO2001/000435
Authority: WO
Inventors: Steinar Lynum; Jan Hugdahl; Ketil Hox; Maria Olsson
Original assignee: Kvaerner Technology And Research Limited
Priority date: 2000-11-01
Filing date: 2001-10-31
Publication date: 2002-05-10
Also published as: AU2002224216A1; NO20011128D0; NO20011128L

Abstract

This invention relates to a method where carbon black (CB) is surface treated by means of an active processing aid (APA), which is an additive for surface treating carbon black to induce amphipathic properties. More specific, the invention relates to CB having been pre-treated with an APA as surface lubricants such as organosilanes or fluorosilicones, stabilisators, anti-static aids or silicon lubricants which in blends with plastic or rubber compounds improves the processing rheology. Further, it relates to surface treated CB (STCB) giving UV, anti-static, semiconductive and conductive properties in plastic and rubber compounds without altering any mechanical or electrical properties in the plastic and rubber compounds.

Description

Surface treated carbon black, plastics and rubber compositions containing the same

Field of the invention

This invention relates to a method where carbon black (CB) is surface treated by means of an active processing aid (APA). APA is an additive for surface treating carbon black to induce amphipathic properties. For simplicity this additive will be called APA in the following. More specific, the invention relates to CB having been pre-treated with an APA as surface lubricants such as organosilanes, stabilisators, anti-static aids or silicon lubricants which in blends with plastic or rubber compounds improves the processing rheology. Further, it relates to surface treated CB (STCB) giving UN, anti-static, semiconductive and conductive properties in plastic and rubber compounds without altering any mechanical or electrical properties in the plastic and rubber compounds.

This treated CB will be used in electrical and semiconductive polymer compound that will be processed in highly effective modern processing machines that demands material giving good rheological and mixing properties together with easy dispersion of the CB in the olymer matrix.

Background

As filler in plastics, elastomers and paints, CB is used to modify the mechanical, electrical and optical properties in the compounds and solutions. This again determines their application in a given market segment. In plastic compound, CB imparts properties such as UN-protection, electrical conductance, colour (jetness), opacity and reinforcement. In rubber, CB improves fracture behaviour, abrasion and failure properties. Of the total world-wide CB production about 90 % is going to the tire industry, in order to improve modulus and wear characteristics and enhances tear strength in the tines. In xerographic toners CB is an important pigment maintaining a suitable level of electrical charge on the toner for proper operation of the electrographic copiers and printers.

The CB properties, that is the particle- and aggregate size, the aggregate morphology and micro structure, are influencing the properties of the CB/elastomer compound. Also the surface characteristics as porosity, surface area, chemical composition are of vital importance.

CB is of nature conductive and impart conductive properties to thermoplastic polymers. The electrical and dielectrical behaviour of a CB-polymer compound are dependant on the basic nature, concentration and characteristics of the both the CB and the polymer, also on the mixing, processing and finishing conditions of production. In plastic and rubber industry CB act as colorant and enhancer of performances. More specifically, variations in the CB properties will influence the compound performance in the following manner:

• Smaller CB particle sizes (high surface areas) increases UN-protection, absorption, electrical conductivity, compound viscosity but lowers dispersibility, and both CB and compound moisture pickup are increased

• Higher structures increase electrical conductivity and compound viscosity. However this improves dispersibility

• The cleanliness of the CB is vital with regards to low levels of sulphur, ash, residues, etc.

Porosity reduces the weight of a given CB particle. At equal loading, CB with a higher porosity increases the CB particle number, which results in a reduced inter-particle distance and thus in an increased electrical conductivity,

• Higher porosities increase the compound viscosity and electrical conductivity, and enable reduced loading in conductive applications.

Conductive carbon blacks are generally distinguished by a high structure, surface area and porosity. It is important to maintain these properties fully during all processing steps where the carbon black are mixed and secured to be fully dispersed in the polymer. For conductive compounds the shear stress has to be optimised to attain maximum electrical conductivity. Too low shear stress or mixing time during processing will lead to insufficient dispersion of carbon black agglomerates in the polymer. On the other hand, too high shear stress or mixing time beyond the optimum will break the carbon black aggregates resulting in a lower electrical conductivity of the polymer. Also, high surface area and structure itself do increase the compound viscosity, leading to an excessive heat generation during mixing. This can influence the dispersion quality and stability and will in general restrict the process capacity. Basically, this puts a limitation on the maximum carbon black loading that can be used.

The various influences are summarised in Table 1, which clearly points out the difficulties which today exist in processing of conductive polymer compounds. Every CB-property that will increase the electrical conductivity will at the same time decrease the rheological properties of the compound, that is reducing the process ability due to an increase in compound viscosity and lowering of the melt index. To improve on this the industry have been working on the development of new grades of conductive CB known as "high structure low surface area conductive black". Examples here are the Ensaco grades from MMM Carbon, Belgium, and the newly developed plasma black qualities from Kvεerner Oil&Gas, Norway. These CB grades with relatively big particle sizes Table 1 Compound rheology and conductivity as a function of CB-properties increase in rheology conductivity particle size increase decrease surface area decrease increase porosity decrease increase structure decrease increase oxygen content increase decrease

(small surface area) and moderate structures are superior with regard to process ability, and maintain at the same time very good conductive properties in the polymer compound. See Table 2 for physical properties of different conductive CB grades in the market.

Table 2 Physical properties of some conductive CB-grades

1) Data taken from brochures The advantages of the new types of " high structure low surface area conductive black" from MMM and Kvεerner are: increased conductivity lower viscosity - easier dispersion of CB in the polymer(s) relatively good mechanical properties

Today there is no knowledge or use of any surface treatment of CB with APA that will provide reduction in compound viscosity or any effect on the r eology of plastic and rubber compounds.

Prior art

State of the art for after-treatment of carbon black today is that this in principle is done either by oxidative after treatment or water vapour. Oxidative after-treatment, using nitric acid, ozone, air or other oxidation agents, will increase the amount of oxygen containing groups on the carbon black surface. This is preferred for pigment vehicle systems such as lithographic inks, paints and enamels since this improves the dispersion and flow characteristics. However, conductive black need to be clean with surfaces free from oxides and organic materials. Water vapour at relatively low temperatures 300-500 °C will basically remove all extractable matter from the carbon black surface. Also, production of porous black with surface areas typically above 500 m²/g can be achieved by steam treatment.

However, none of these after-treatment methods provides any gain in the process ability of the rubber and plastic compounds.

The rubber industry have for a long time been working with the so-called "silica surface treated carbon blacks", SFTCB. In this case, the use of silica in order to adjust the reinforcing mechanism by interaction with the polymer has been the aim ending up with the "green tyre" concept. This combines tires with high abrasion resistance, good wet grip, high break strength and other performance, which at the same time improve fuel consumption and durability. This is achieved by adding sihca together with CB in the rubber compound.

Examples of this are Degusa patents EP 0447 066A1 and EP 0501 227 Al, Japanese patents (Kokai) No. 3-239737, No. 3-252431, No. 3-252433 and No. 63-63755. However, all these referred and known patents employs silica additions to improve reinforcing mechanisms, while the present invention improves the process ability/- processing parameters in compounding, mixing, extruding etc. by means of treating the CB with APA.

Object of the invention

The main object of this invention is to provide a surface treated carbon black (STCB) by means of an active processing aid (APA) which can be added to plastic and rubber compounds without altering the mechanical-, thermal- or electrical properties, but which improves the process ability, gives an easier dispersion of carbon black aggregates during compounding, increases maximum possible loading of carbon black in the compound, and improves surface characteristics/smoothness of the product. All this beneficial properties contributes to higher/increased throughput in all types of processing equipment. This relates to surface treatment of CB of all grades and polymers, including polyolefmes, copolymers, engineering thermoplastics and rubber. It is also an object of this invention to provide a method for modifying carbon black by surface treatment with an active processing aid (APA) including organosilanes, lubricant silicones and stabilisators.

Brief description of the invention

The above objects are achieved by methods which is characterised by the features presented in the patent claims and by the following description.

The aims of this invention can be achieved by directly spraying the active processing aid (APA) on the carbon black surface in an adhesion amount of 0,1-5% by weight. The APA is adsorbed on the carbon black surface, and thus adjusting the surface character to be amphipathic (two sided with a hydrophobic/hydrophilic part). This is the basic property adjustment that gives the dramatic improvement in the processing ability without altering the mechanical or electrical properties in the plastic and rubber compounds. The STCB improve the surface affinity at the carbon black/polymer melt surface interface and will act as a "surface lubricant" between the carbon black aggregates, between the carbon black and the polymer and also by establishing an adsorbed layer on the metal surfaces in the extruder and die. And thus resulting in a good dispersion of carbon black aggregates at low shear stress and low compound viscosity during mixing and processing. This enhances the processing performance and gives an improved productivity, and also allows to employ higher loadings of carbon black if desired. At the same time use of STCB improves the surface characteristics/smoothness of the product without altering the mechanical-, thermal- or electrical properties. It is preferred to employ an APA chosen form the group including any organosilane or fluorosilicon, any stabilisator of type sulphonated paraffin, any anti- static stabiliser, and/or any lubricant silicone oil. An example of organosilane is polydimethylsiloxane; fluorosilicon is polymethyltrifluoropropylsiloxane or polymethylnonafluorohexosiloxane; stabilisator is alkanesulphonate, and of lubricant silicone oil is dimethylpolysiloxane. The chemical formulas of these can be given as: polydimethylsiloxane: (CH₃)₂SiO polymethyltrifluoropropylsiloxane : CH₃ [CF₃ (CH₂)₂] SiO p olymethylnonafluorohexosiloxane : CH₃ [CF₃ (CF₂)₃ (CH₂) ] SiO Further, the invention can be employed for all known and traditional, grades produced by all known traditional processes, such as the furnace -, thermal -, gas black-, lamp black -, or acetylene black process. Included are also the novel plasma black process developed by Kvaerner ASA. It is especially preferred to employ the invention for carbon black grades specially designed for plastic and rubber applications requiring a high degree of cleanliness with regard to trace elements, ash and grit level, and low levels of hot extract- and surface oxide functional groups. From this it follows that all levels and combinations of physical properties as particle size (d), surface area (BET) and structure (DBP) are included in the invention. The STCB by means of APA is specially adapted for conductive carbon black qualities high in both surface area and structure, since both conductive and super conductive qualities without any after-treatment as per this invention only can be compounded with hmited loading due to the process ability problems following from high compound viscosity etc., see Table 1.

The polymers that may be employed in the present invention includes, but is not limited to, any polymer that are compounded with CB. That is to any polyolefine, any copolymer, any engineering thermoplastic, and any rubber. Examples of polyolefmes are PP, PE. Examples of copolymers are ENA, EB A, EEA. Examples of engineering thermoplastics are PC, PS, and examples of rubber are ΝR, SBR, CR, ΝBR, IIR, EPDM, and ENA. The different apphcation areas in which this invention may applied on includes, but are not limited to, film and sheet, extrusion coating, injection moulding, blow moulding, pipe and conduit, wire arid cable, etc.

In accordance with the invention carbon black is after-treated either directly downstream in the product stream at a location in or after the drier, alternatively in a separate after-treatment step. Also, the STCB according to the invention is not particularly limited by the production method, which can be a traditional furnace process, traditional thermal process etc. However, carbon black produced by pyrolysis or plasma processes without presence of oxygen like the novel Kvaerner plasma process is particularly well suited for this treatment. This is based on several advantages, such as giving a very clean product without functional oxygen groups, low in extracts and salts, very low moisture pick up, and a non-polar surface characteristic. The invention will now be described further by means of examples of preferred embodiments.

Examples

CB Treatment

The APA was sprayed on the CB during stirring by means of a suitable squirt with an adjustable atomising nozzle suitable to adjust the amount of spraying agent (APA) onto the CB, and the stirring was continued after spraying until a free flowing powder was achieved.

Ah CB samples were pre-treated in this manner before compounding trials with the following different polymers: - elastomers polyolefmes LLDPE, IDPE, PP copolymers polystyrenes polycarbonates

CB qualities

Three different grades of CB has been selected, that is:

— one typical super-conductive grade, Cabot XC72

— two Kvaerner Oil & Gas grades representing the new high structure low surface area conductive black; KOG CLS and KOG-5CB, respectively.

Cabot XC72 is the mostly used CB in cable applications. Two compounds have been tested here:

(1) an inner conductive layer intended for XLPE insulated power cables (2) an external semiconductive layer for XLPE insulated power cables

The KOG-5CB are a new conductive black with particle size of approximately 45 nm, that is as the MMM-grades. The conductivity are equivalent to the Cabot Nulcan P black. The KOG-CLS have an even bigger particle size of approximately 115 nm with a high nanostructure crystalline ordering, but still with a relatively high conductivity compared to Vulcan P.

Compounding Seven different polymers have been tested as follows:

— XC72 has been compounded in a Bus BP 21 and extruded in a Brabender extruder.

— Kvaerner grades were compounded in a Clextral twin-screw extruder and further tested in three processing methods:

— rolling mill — extrusion in a Brabender extruder

— injection moulding

APA tested

The following types of APA has been tested: (1) Organosilicone fluid type organo-modified polydimethylsiloxane

(2) Silicon fluid type dimethylpolysiloxane

(3) Organosilicon type alkylp oly ol-p oly alkenylester

(4) Alkanesulphonate

Test results

The test results are summarised in Table 3, from which the influence of APA on the material rheology is clearly observed on the change of the driving parameters I (ampere) representing the machine torque, and P (bar) representing the die pressure.

Table 3 Influence of active processing aid (APA) on compound rheology in processing with different polymers. ϊOljaner Carbon. Mack €B- dextrat Twin-screw extruder parameters ^■Volume Type APA grade coϊiteπt Resistivity employed

(voPA) Current (A) Pressure Output (Ωc )

- (bar) (kg/b)

EBA KOG-5CB, ref. 30 6,5 43 4 40

EBA KOG-5CB, mod. 30 6,0 9 4 40 (1)

EBA Cabot XC72, ref. 20 6,8 41 4 55

EVA KOG-5CB, ref. 30 6,5 80 4 45

EVA KOG-5CB, mod. 30 6,5 20 4 30 (1)

EVA Cabot VP, ref. 30 6,8 50 4 35

LLDPE KOG-5CB, ref. 30 7,0 72 4 10

LLDPE KOG-5CB. mod 30 6,7 21 4 8 (1)

PP KOG-5CB, ref. 30 5,4 27 4 3,5

PP KOG-5CB, mod. 30 5,5 0,3 4 3,2 (1)

PP KOG-5CB, mod. 30 5,5 0,5 6 3,0 (1)

PP KOG-5CB, mod. 30 6,6 11 8 3,1 (1)

PP KOG-5CB, mod. 30 6,6 18 4 3,6 (2)

PP KOG-5CB, mod. 30 6,4 19 4 3,7 (3)

PP KOG-5CB. mod. 30 6,8 20 4 3,7 (4)

PP Cabot VP, ref. 30 5,5 28 4 4,8

PP Ensaco 150 30 6,0 10 4 2,5

PP Ensaco 210 30 5,8 10 4 4,5

PP KOG-CLS, ref 40 5,2 13 4 80

PP KOG-CLS, mod. 40 4,7 0,1 4 250 (1)

PP KOG-CLS, mod 50 4,7 0,1 4 17 (1)

PP KOG-CLS, mod. 60 5,1 0,1 4 2,0 (1)

PP KOG-CLS, mod. 60 5,5 11 6 2,0 (1)

PP Cabot VP, ref 30 5,5 28 4 4,8

TelyttK-j. •Ouebo-i black CB- BϊsaT-endaf extruder parameters ^" Vαto-ne TypeAjPA grade content Itesistϊvity employed

(wt%) Viscosity (Fas) E-rfr . vctøcj Torque (Nm). (Dent)

EVA+NBR Cabot XC72, ref. 32 1440 511 6000 1300

EVA+NBR Cabot XC72, 32 740 800 4600 430 (1) mod.

(1) Organosilicon fluid type organomodified polymethylsiloxane (PA-1)

(2) Silicon fluid type dimethylpolysiloxane (AK)

(3) Organosilicon type alkylpolyol-polyalkylester (PC-IA)

(4) Alkenesulphonate (PS 320D)

Claims

1. A method for surface treating carbon black (CB) in order to improve the rheological properties of the CB, characterized in that an additive or active processing aid (APA) which gives the CB amphipathic properties, is added to the CB.

2. A method according to claim 1, characterized in that the amount of APA that is added is from 0,1% to 5% by weight of CB.

3. A method according to claim 1 or 2, characterized in that the addition is performed during the production process of the

CB or in a separate step.

4. An additive for surface treatment of CB, characterized in that the addition is any amphipathic additive which acts like a "surface lubricant" between the CB and polymer interface and thus giving superior dispersing properties to the CB, which originally had opposite polarity than the polymer.

5. An additive according to claim 4, characterized in that it comprises a low viscous liquid not soluble in water or with very limited and slow solubility. 6. An additive according to claim 4, characterized in that it comprises a highly viscous liquid, alternatively a solid which are soluble in an organic solution.

7. An additive according to claim 4, characterized in that it is an organosilane of type polydimethylsiloxan. 8. An additive according to claim 7, characterized in that it is bis-(3-(triethoxisyl)-propyl)-tetrasulphane.

9. An additive according to claim 4, characterized in that it is a fluorosilicon of type polymethyltrifluoropropylsiloxane or polymethylnonafluorohexosiloxane. 10. An additive according to claim 4, characterized in that it comprises an anti-static agent of type alkanosulphonate, a cationic quartener compound, and a sulphonated paraffin.

11. An additive according to claim 4, characterized in that it comprises a lubricant silicon oil.

2. Use of an AP A-treated CB according to any of the proceeding claims and which is suited to be used in any compounding with plastic and/or rubber materials.