CN1363629A - Process for preparing electrically conductive high-molecular composite material by in-situ graft to modify electrically conductive filler - Google Patents

Abstract

The invention discloses a conductive polymer composite material with positive temperature coefficient (PTC) characteristics produced by filling a single or blended polymer matrix with a modified conductive filler by an in-situ grafting method. The present invention adopts the method of adding a reactive treatment agent to pretreat the conductive filler, and realizes the chemical grafting reaction of the conductive filler, the treatment agent and the polymer matrix during the processing, thereby improving the interaction between the conductive filler and the polymer matrix. Improve the bonding between the matrix, the conductive filler and the metal electrode, and finally achieve the purpose of improving the PTC effect and stability of the composite material, and provide a substrate for the manufacture of self-limiting temperature heaters and overcurrent protection components.

Description

In-Situ Grafting Modified Conductive Filler to Fabricate Conductive Polymer Composite

Technical field

The invention relates to a conductive polymer composite material with a positive temperature coefficient (PTC) which is formed by modifying a conductive filler to fill a polymer or a resin matrix of a blend thereof by using an in-situ grafting method.

Background technique

A conductive polymer composite material with positive temperature coefficient characteristics composed of a single polymer matrix filled with unmodified conductive fillers such as carbon black, has adjustable conductivity in a wide range, easy to shape, and flexible , low cost and high PTC strength (≥10 ⁵ ), etc. (see: US4,514,620; US4,732,701; US5,164,133; CN87102932; CN87102924). On this basis, the PTC composite material (Chinese patent application: CN97108956) composed of a blended polymer matrix is filled with an unmodified conductive filler, so that the stability of the PTC effect of the composite material is improved, and the comprehensive mechanical properties, especially Flexibility is significantly improved.

However, due to the weak interfacial interaction between the matrix and unmodified conductive fillers such as carbon black particles, and the carbon black particles dispersed in the matrix have strong agglomeration force, the carbon black particles in the matrix The dispersion is thermodynamically unstable. The PTC effect of PTC composites mainly depends on the degree of dispersion and distribution of carbon black in the polymer matrix and the results of changes with external conditions (oxidative degradation and crosslinking, local overheating, electric field, light and mechanical stress) , the stability of the PTC effect of the resulting composites is not very ideal whether the unmodified conductive filler is filled with a single or blended polymer matrix. Before the actual use process, it is also necessary to cross-link the composite material to improve the reproducibility of the resistance temperature behavior and eliminate the negative temperature coefficient of resistance (NTC) phenomenon. The usual cross-linking methods include chemical cross-linking, radiation cross-linking or silane cross-linking, etc. Although they are of great help to improve the electrical properties of materials, there are also some problems in practical applications: firstly, cross-linking has great influence on the process or Equipment has high requirements. For example, chemical cross-linking has strict requirements on processing technology and is difficult to control during processing. Radiation cross-linking requires high-energy radiation sources, which are not available in general factories. In addition, crosslinking can also damage the mechanical properties of composites.

Contents of Invention

The purpose of the present invention is to provide a polymer-based PTC conductive composite material manufactured by an in-situ grafting method, the interface interaction between the conductive filler and the polymer matrix is enhanced, and it has a higher PTC effect and its recurrence stability and processing performance stability, and improve the adhesion between the substrate and the metal electrode, thereby overcoming the above-mentioned shortcomings of the existing PTC composite materials, and providing a good basis for the manufacture of self-limiting temperature heaters and overcurrent protection components. material.

The conductive composite material with positive temperature coefficient of the present invention contains crystalline polymer matrix A1, conductive filler B, and other additives C, taking the weight of polymer matrix A1 as 100%, and the weight of each component in the composite material relative to the matrix The ratio is:

A1: 100wt% (A1)

B: 5-40wt% (A1)

C: 1-15wt% (A1)

Among them, A1 is a thermoplastic polymer with a crystallinity greater than 15%, B is carbon black, graphite, metal or metal oxide powder with an average particle size of 10-200nm, and C is a lubricant, antioxidant, light stabilizer, copper ion inhibitor agent, heat stabilizer, flame retardant and inorganic filler or a mixture of two or more; it is characterized in that said conductive filler B is a conductive filler that has undergone the following pretreatment: adding unmodified conductive filler to the reaction In the device, slowly add the reactive treatment agent under high-speed stirring, discharge the material after stirring evenly, and store it under airtight conditions for later use; the reactive treatment agent used is acrylic acid, methacrylic acid, acrylate and methacrylate or maleic anhydride The mixture of monomers, peroxides and azo free radical initiators, the amount of monomers is 10-50 wt% of the weight of the filler, and the amount of free radical initiators used is 0.1-5 wt% of the monomers.

The composite material of the present invention can also contain the second polymer matrix A2, and A2 and A1 form a blended matrix; A2 is a crystalline or amorphous thermoplastic polymer that is compatible or partially compatible with A1; the polymer matrix (A1+ A2) is 100, and the ratio of each component relative to the matrix in the composite material is:

A1: 50-95wt% (A1+A2)

A2: 5-50wt% (A1+A2)

B: 5-40wt% (A1+A2)

C: 1-15wt% (A1+A2)

The conductive filler B used in the composite material of the present invention is usually conductive carbon black with an average particle size of 15-100 nm (preferably oil furnace granulated conductive carbon black).

The in-situ grafting processing method adopted by the conductive composite material with a positive temperature coefficient of the present invention is to pre-process the conductive filler with reactive components (compounds containing double bonds and free radical polymerization initiators) before processing. The surface of the conductive filler is chemically grafted and modified during the mixing process with the polymer material. For example, carbon black is treated with acrylic acid (AA) and dicumyl peroxide (DCP) in a certain proportion, and then mixed with the polymer matrix in a certain order and proportion to the mixing equipment. The decomposition of DCP triggers the chemical grafting reaction of AA on the surface of carbon black, and at the same time achieves chemical bonding with the polymer matrix. AA acts as a bridge between the conductive filler and the polymer matrix, connecting the conductive filler to the polymer with chemical bonds. On the matrix, so as to adjust the balance of the interface interaction force between the conductive filler and the conductive filler, the conductive filler and the polymer matrix, so as to reduce the mobility of carbon black ions, limit their movement area, and essentially control the dispersion of the conductive filler The degree and distribution state, and improve the reproducibility of the response.

The present invention has no special restrictions on crystalline polymer A1, and all thermoplastic polymers with crystallinity greater than 15% can be used, such as: high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyvinylidene fluoride (PVDF), isotactic polypropylene (IPP), ethylene-propylene copolymer (EPM), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA) , polyamide (PA), polycarbonate (PC), polysulfone (PSF) and thermoplastic polyester. The second polymer A2 is a crystalline or amorphous thermoplastic polymer that is compatible or partially compatible with the crystalline polymer (A1); depending on the crystalline polymer, the second polymer A2 preferably contains a polar chain Thermoplastic elastomers with segments or functional groups have better toughness, flex resistance and stress crack resistance than crystalline polymers, such as: ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA ), ethylene-maleic anhydride copolymer (EMA), chlorinated polyethylene (CPE), etc., and various rubbers, such as: natural rubber (NR), nitrile rubber (NBR), etc.; amorphous resins can be Polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC) and polysulfone, etc.

Conductive fillers are generally in powder form, such as: carbon black, graphite, metal or metal oxide powder. The above-mentioned conductive fillers can be used alone, or mixed with different types and different particle sizes. The particle size of the conductive powder usually has an average particle size of 10-200 nm. Conductive fillers need to be pretreated before processing.

The pretreatment steps and process conditions for the conductive filler are as follows: add the unmodified conductive filler into the reaction device, slowly add the reactive treatment agent under high-speed stirring, discharge the material after stirring evenly, and place it under airtight conditions for later use. The reactive treatment agent used is acrylic acid (AA), methacrylic acid, ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA), and methacrylates or maleic anhydride ( MA) etc. and the mixture of peroxide, azo free radical initiator, monomer amount is 10-50wt% of carbon black weight, the amount of free radical initiator used is 0.1-5wt% of monomer consumption (preferably 0.2-2wt%).

In addition, appropriate amount of other additives can be added, such as: lubricants, antioxidants, light stabilizers, copper ion inhibitors, heat stabilizers, flame retardants, inorganic fillers, etc. to adjust the overall performance of PTC materials.

The composite material of the present invention is produced by polymer matrix A1 or A1+A2, pretreated conductive filler B and other additives C through steps such as mixing, granulation/crushing, molding, and heat treatment. The specific steps and process conditions as follows:

① Mixing: Add the raw materials of each component into the mixing equipment in a certain proportion, and mix for 5-60 minutes at a mixing temperature not lower than the melting point or softening point of the matrix. The drum or screw speed of the mixing equipment is 20 -80rpm;

②Granulation/crushing: After crushing the above-mentioned mixed material with a granulator or a pulverizer, composite material granules are obtained;

③ Molding: according to the shape of the product, the above-mentioned pellets are molded by molding, extrusion or injection molding;

④Heat treatment: The molded PTC composite material is treated for 5-15 hours at a temperature 25-30°C lower than the melting point of the polymer matrix to obtain the product composite material.

^The present invention prepares the PTC conductive polymer composite material according to the ^above -mentioned material composition formula and manufacturing ^process . The temperature at which the transition occurs can be adjusted in the range of 50-160°C. Due to the simultaneous modification of the conductive filler and the matrix resin by the method of in-situ grafting, the interfacial interaction force between the conductive filler and the polymer matrix is adjusted, so that the conductive filler is microscopically selectively dispersed, and the addition of the modifier The synergistic effect of lubrication and the like leads to a significant increase in the PTC strength and PTC effect repetition stability of the composite material, and narrows the range of resistivity transition.

The PTC material of the present invention can be used as a heating material for an electric heater, has good thermal conductivity, produces Joule heat that is evenly distributed, has good self-limiting temperature adjustment characteristics, and has a long continuous and intermittent working life (repeated power-on heating and power-off cooling cycle) ( >5000h).

Description of drawings

Fig. 1 is the relationship curve of the room temperature resistivity p ₂₅ of the composite material of embodiment 2, embodiment 3 and comparative example 1 with the number of heat cycles.

Fig. 2 is the relationship curve of the resistivity ρ changing with the temperature T of the composite material of Comparative Example 1 under the condition of multiple heat cycles.

Fig. 3 is the relationship curve of the resistivity ρ varying with the temperature T of the composite material of Example 3 under the condition of multiple heat cycles.

Detailed ways

The present invention will be further described below through embodiments and accompanying drawings.

Examples 1-11 manufactured PTC conductive composite materials according to the above-mentioned specific steps and process conditions, and Comparative Examples 1-4 except that the conductive filler was not treated, other steps and process conditions were the same as in the examples. Following table 1, table 2 are the character of each component raw material used in embodiment and comparative example, and table 3 is the charging amount (by weight) of component raw material in each embodiment and comparative example, and table 4 is each embodiment And the performance of the product composite material of comparative example.

Table 1 Types of polymer matrix properties Product name Melt index Melting point Density Manufacturer

(g/10min) (°C) (g/cm ³ ) Crystalline polymer LDPE 0.3-0.7 100-115 0.910-0.925 Beijing Yanshan Petrochemical Company (A1) HDPE 0.2-0.8 130-140 0.920-0.945

PVDF 0.1-0.5 180-195 second polymer EVA 2.0-15.0 80-95 0.930-0.980 Mitsubishi Petrochemical Corporation (A2) (VAC content

10-40%)

NBR (with AN

Quantity 15-50%)

Table 2 Conductive filler properties (carbon black) Average particle size Specific surface area DBP absorption value True density Surface element content ratio Manufacturer (nm) (m ² /g) (ml/100mg) (g/cm ³ ) [O]/[ C]15-70 150-300 120-125 1.90 0.0277 China Rubber Group Zigong

Carbon Black Research Institute

Table 3 PTC material composition ratio

A1/A2 B B C C Treatment Agent Example 1 LDPE 25 3.2 AA

100 2.5 Example 2 LDPE 25 3.2 AA

100 5 Example 3 LDPE 25 3.2 AA

100 7.5 Example 4 LDPE/EVA 25 3.2 AA

80/20 7.5 Example 5 LDPE 25 3.2 AA

100 12.5 Example 6 HDPE/NBR 30 3.2 AA

80/20 9 Example 7 PVDF 30 3.2 AA

100 9 Example 8 LDPE 25 3.2 BA

100 7.5 Example 9 LDPE/EVA 25 3.2 BA

80/20 7.5 Example 10 HDPE/NBR 30 3.2 BA

80/20 9 Example 11 PVDF 30 3.2 BA

                                                                                                                              

100 Comparative example 2 LDPE/EVA 25 3.2 0

                                                                                                     

                                                               

100

Table 4 PTC material performance comparison

Room temperature resistivity PTC strength T ₁₀ T ₁₀₀ T ₁₀₀ -T ₁₀

(Ω.cm) (°C) (°C) (°C)

Example 1 880 1.10×10 ² 72 89 17

Example 2 865 1.60×10 ² 71 87 16

Example 3 810 1.23×10 ³ 69 81 12

Example 4 805 1.26×10 ³ 65 80 15

Example 5 12000 - - - -

Example 6 450 6.0×10 ³ 102 113 11

Example 7 350 5.7×10 ³ 161 175 14

Example 8 870 7.6×10 ² 70 83 13

Example 9 855 6.4×10 ² 67 86 19

Example 10 465 3.9×10 ³ 107 119 12

Example 11 345 2.8×10 ³ 164 180 16

Comparative example 1 900 1.12×10 ² 72 90 18

Comparative example 2 860 0.97×10 ² 68 87 19

Comparative example 3 430 8.0×10 ² 107 125 18

Comparative example 4 320 7.5×10 ² 165 182 17

*In order to characterize the PTC effect of the material or the characteristics of the resistivity (ρ)-temperature (T) curve, the ratio ρ _max /ρ ₂₅ of the resistivity transition peak value ρ _max on the relationship curve to the room temperature (25°C) resistivity ρ ₂₅ is defined is the PTC strength; the temperature corresponding to the resistivity increased to ten times of ρ ₂₅ is recorded as T ₁₀ ; the temperature corresponding to the resistivity increased to one hundred times of ρ ₂₅ is recorded as T ₁₀₀ . The larger the value of ρ _max /ρ ₂₅ , the higher the PTC strength of the composite material; the smaller the difference between T ₁₀ and T ₁₀₀ T ₁₀₀ -T ₁₀ , the narrower the temperature range for the transition of the resistivity of the composite material, and the transition is more precise. steep.

Claims (3)

1. the conducing composite material with positive temperature coefficient contains crystalline polymer matrix A1, conductive filler material B and other auxiliary agent C, and getting macromolecule matrix A1 weight is 100%, each component with respect to the proportioning of matrix is in the matrix material:

A1： 100wt％(A1)

B： 5-40wt％(A1)

C： 1-15wt％(A1)

Wherein A1 is a degree of crystallinity greater than 15% thermal plastic high polymer, B is carbon black, graphite, metal or the metal oxide powder of median size 10-200nm, and C is one or more the mixture in lubricant, oxidation inhibitor, photostabilizer, copper ion inhibitor, thermo-stabilizer, fire retardant and the mineral filler; It is characterized in that said conductive filler material B is through following pretreated conductive filler material: unmodified conductive filler material is added in the reaction unit, under high-speed stirring, slowly add reactive treatment agent, the back discharging that stirs, air tight condition is transferred the usefulness of purchasing; Used reactive treatment agent is the mixture of vinylformic acid, methacrylic acid, acrylate and methyl acrylic ester or maleic anhydride monomer and superoxide, azo type free base initiator, amount of monomer is the 10-50wt% of filler weight, and the consumption of used radical initiator is the 0.1-5% of monomer consumption.

2. matrix material according to claim 1 is characterized in that this matrix material also contains the second macromolecule matrix A2, and A2 is and A1 compatible crystallinity or the amorphous thermoplastic polymer of part perhaps mutually; Getting macromolecule matrix (A1+A2) is 100, and the proportioning of the relative matrix of each component is in the matrix material:

A1： 50-95wt％(A1+A2)

A2： 5-50wt％(A1+A2)

B： 5-40wt％(A1+A2)

C： 1-15wt％(A1+A2)

3. a matrix material as claimed in claim 1 or 2 is characterized in that said conductive filler material B is the graphitized carbon black of median size 15-100nm.

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