CN104672704A - Method for preparing PVC conductive composite material through mechanical milling method - Google Patents

Abstract

The invention relates to the field of conductive composite material processing, in particular to a method for preparing PVC conductive composite material by mechanical ball milling. The method is to place the graphite in absolute ethanol containing a coupling agent, stir at a constant temperature until the graphite is dispersed in the ethanol, filter with suction, dry the graphite to obtain modified graphite, and mix the modified graphite and PVC by 15-20% : The proportion of 80-85% is put into a circulating water type high-energy ball mill for mechanical ball milling for 0.5-2.5h to obtain a mixture, which is filled in the mold of a flat vulcanizer, and demolded after high-temperature hot pressing to obtain a PVC conductive composite material. The preparation method of the present invention eliminates the interface difference between graphite and PVC, makes the graphite evenly dispersed in the PVC matrix, forms a denser conductive network inside the composite material, significantly enhances the conductivity of the composite material, and the method has high reaction efficiency, Energy saving, no industrial waste, low production cost.

Description

Method for preparing PVC conductive composite material by mechanical ball milling

technical field

The present invention relates to the field of conductive composite material processing, specifically a method for preparing PVC conductive composite material by mechanical ball milling.

Background technique

PVC (polyvinyl chloride) is one of the five general-purpose plastics, with a huge production volume at home and abroad and a wide range of applications. A large part of products in daily life are made of PVC, but some of its own defects, such as electrical insulation, greatly limit its application range. Preparation of insulating PVC into a composite material with good electrical conductivity will expand the application of PVC in integrated circuits, chemical equipment, outer packaging materials, aerospace and other fields.

Conductive plastics can be classified into structural conductive plastics and composite conductive plastics according to the production method. Structural conductive plastics, also known as intrinsic conductive plastics, refer to plastics that are electrically conductive or chemically modified, mainly including: (1) π-conjugated polymers: such as polyacetylene, (Sr) n. Linear polyphenylene, layered polymers, etc.; (2) Metal chelates: such as polyketone phthalocyanine; (3) Charge-moving polymer complexes: such as polycations, CQ complexes. The production cost of structural conductive plastics is high and the process is difficult. So far, there is no mass production. The widely used conductive plastics are generally composite conductive plastics. This kind of material is simple to prepare and low in cost, and is suitable for industrial production. The conductive fillers of composite conductive plastics mainly include: (1) metal dispersion system; (2) carbon black system; (3) organic complex dispersion system. The price of this type of conductive filler is relatively high, which is not conducive to reducing the cost of materials. Graphite is a good conductor and is widely used in the electrical industry to manufacture electrodes, brushes, carbon rods, carbon tubes, positive electrodes of mercury positive current devices, graphite gaskets, telephone parts, coatings for television picture tubes, etc., and Graphite has a wide range of sources and low price, and is very suitable as a filler for conductive plastics.

In terms of the preparation method of composite conductive plastics, the traditional method is to use an internal mixer to mix and plasticize the plastic matrix and conductive fillers in a certain proportion, then put them into a twin-screw open mixer to extrude and granulate, and use a flat vulcanizer to heat press them. . Chinese patent CN201410566862 discloses an ultra-low resistance conductive plastic and its preparation method. The ultra-low resistance conductive plastic is mainly prepared from the following raw materials according to the weight percentage of each component: 30-45% plastic carrier, 45-65% Conductive fillers, 2-5% surfactants, 0.5-2% lubricants and 0.3-0.5% antioxidants, the invention mixes the components uniformly according to the weight percentage, and then adopts a banbury mixer Refining and forming, extruding and granulating to make conductive plastic products. This method easily leads to uneven mixing of the plastic matrix and the conductive filler, resulting in uneven and weak electrical conductivity of the material.

In recent years, a variety of processing methods for preparing composite conductive plastics have emerged, which can be divided into: melt mixing, solution blending, powder mixing, etc. according to different processing methods and raw material requirements.

Melt mixing is to mix conductive filler powder and molten plastic with the help of mixing equipment, and then process it into shape. Chinese patent CN200910010679 discloses a preparation method for melt blending of PVC/EPR foam conductive NTC material filled with special carbon black, using special carbon black (HG-1P) as the conductive filler, polyvinyl chloride (PVC) and ethylene-propylene Rubber (EPR) is the polymer matrix, dioctyl phthalate (DOP) is the plasticizer, stearic acid (St) is the lubricant, azodicarbonamide (AC) is the foaming agent, stearic acid Zinc (Zn-St) is a foaming synergist, dicumyl peroxide (DCP) is a crosslinking agent, and calcium/zinc Ca/Zn composite stabilizer is a heat stabilizer. Made PVC/EPR foam conductive NTC material. This method requires high temperature and long time for mixing in the process of melting and mixing, so toxic gases such as _Cl will be released, which is not conducive to environmental protection, and requires high temperature and high energy consumption. From an economic point of view, the cost is relatively high. High, this method is now widely used in the plastic products industry, its technology is mature, and the mechanical properties of the plate are good.

Solution blending: This method is to dissolve plastics and conductive fillers in an appropriate solvent, and obtain a mixture of plastics and conductive fillers after uniform dispersion. The mixture is melt-cast, extruded or molded. Chinese patent CN201310270671 discloses a polyvinyl chloride semiconductive soft composite material and its preparation method and application. The preparation method of the composite material is: (1), pour the plasticizer into a stainless steel container with a stirrer, and Stir evenly at a constant speed, control the temperature between 20°C and 30°C, slowly pour in superconducting carbon black, mix and soak for more than 20 hours; (2), put the soaking mixture and polyvinyl chloride resin into a rotating And in the mixer with built-in stirring, under the condition that the rotation speed is 80~100 rpm and the stirring speed is 50-60 rpm, mix to obtain black particles with a size of 1~3mm; (3), Put the black granules and other raw materials into the Buss mixer, carry out reciprocating mixing, granulate, dry, and the product is ready. This method has high pollution, and the recovery and detoxification of the solvent are very difficult technical difficulties to overcome, and the environmental protection effect is poor.

Powder mixing: The powder mixing method is to grind the plastic and conductive filler into very fine powder, mix them evenly, and then melt and cast them. Powder mixing is the most promising application technology at present, and has strong environmental protection effect. Chinese patent CN201410547858 discloses a graphene silicone resin conductive composite material, which belongs to the technical field of conductive materials. The graphene silicone resin conductive composite material described in this invention is ground by adding graphene and methylphenyl silicone resin into a ball mill It is prepared by mixing evenly, and the weight ratio of graphene to methylphenyl silicone resin is 1:20-500. This method often has the problem of uneven dispersion of fillers, resulting in uneven material composition and unstable performance.

To sum up, there are many deficiencies in the existing methods for preparing composite conductive plastics, which limit the industrial production and large-scale application of this material. Therefore, developing an economical, practical, safe, environmentally friendly, convenient and effective method to prepare conductive plastics with excellent electrical conductivity is of great significance for improving plastic properties, expanding plastic application fields, and saving metal resources.

Contents of the invention

The purpose of the present invention is to overcome the problems of non-uniform filler dispersion, non-uniform material composition and unstable performance in the existing powder mixing method for preparing conductive materials, and provide a method for preparing PVC conductive composite materials by mechanical ball milling.

Scheme of the present invention is achieved by:

(1) Put the graphite in absolute ethanol containing a coupling agent, the amount of the coupling agent is 1-3% of the weight of the graphite, stir at a constant temperature until the graphite is evenly dispersed in the ethanol, filter with suction, and dry the graphite to obtain the improved After the surface modification of graphite by coupling agent, it can reduce the surface chemical energy of graphite particles, eliminate the interface difference between graphite and PVC, so that graphite can be evenly dispersed in PVC matrix, which is conducive to the formation of graphite inside the matrix. A denser conductive network improves the conductivity of the composite.

(2) Mix the modified graphite and PVC at a weight ratio of 15-20%:80-85%, put them into a circulating water type high-energy ball mill for mechanical ball milling, the temperature of the mechanical ball milling is 45-50°C, and the speed is 100- 300 rpm, the time is 0.5-2.5 h, so that the graphite is evenly dispersed into the PVC matrix to obtain a mixture; the ball mills used in the market basically do not have circulating water, and the applicant initially used ordinary ball mills for research and development, but obtained The color of the product is uneven, and the performance of the product is also very unstable. The circulating water high-energy ball mill can take away a large amount of heat energy generated during the ball milling process through circulating water, and control the ball milling at a suitable temperature to avoid the performance or color of PVC as the temperature rises. change.

(3) Take out the mixture, fill it in the mold of a flat vulcanizer, heat press it at a temperature of 160-180°C and a pressure of 5-8 MPa for 10-20 minutes, and demould to obtain a PVC conductive composite material.

Preferably, the amount of the coupling agent is 2% of the graphite weight.

Preferably, the coupling agent is any one of silane KH570, aluminate and titanate.

Preferably, the weight ratio of the modified graphite to PVC is 20%:80%.

Preferably, the temperature of the mechanical ball milling is 50°C.

Preferably, the rotating speed of described mechanical ball mill is 150 rpm.

Preferably, the time of said mechanical ball milling is 1.0 h.

Preferably, the temperature of the hot pressing is 165°C.

Preferably, the pressure of the hot pressing is 5 MPa.

Preferably, the time of the hot pressing is 15 min.

Under the above preferred conditions, the PVC conductive composite material prepared by the present invention has the lowest resistivity and excellent electrical conductivity.

The technical principle realized by the present invention is that the coupling agent consists of two parts: one part is an inorganic group, which can interact with inorganic fillers or reinforcing materials, and the other part is an organic group, which can interact with synthetic resins. After the graphite is treated with a coupling agent (silane KH570, aluminate, titanate), the inorganic group of the coupling agent forms a polar group with the graphite through a strong chemical bond, the surface properties of the graphite are changed, and the surface chemical energy is reduced. The interface difference between it and PVC is eliminated, and at the same time, the organophilic group of the coupling agent is combined with PVC, so that the coupling agent acts as a "bridge" to connect graphite and PVC. After mechanical ball milling by a circulating water type high-energy ball mill, Graphite is evenly dispersed in the PVC matrix, and a denser conductive network is formed inside the composite material, and the conductive performance is enhanced.

The present invention has the following good effects:

(1) The present invention is an improvement on the basis of the traditional powder mixing method for preparing conductive composite materials, using a coupling agent to modify the surface of graphite, reducing the surface chemical energy of graphite particles, and eliminating the interface difference between graphite and PVC. The graphite can be evenly dispersed in the PVC matrix to form very fine and evenly mixed mixed powder particles, which ultimately shortens the ball milling time of the material, improves the reaction efficiency, and saves various energy sources.

(2) The ball mills currently used in the market basically do not have circulating water. The applicant also used ordinary ball mills for research and development at first, but the obtained products had uneven color and unstable product performance. Therefore, the applicant self-developed a belt mill. There is a circulating water high-energy ball mill. After the circulating water-type high-energy ball mill is used, a large amount of heat energy generated during the ball milling process is taken away by circulating water, and the ball mill is controlled at a suitable temperature to avoid PVC performance or color loss as the temperature rises. change, maintaining the good quality of the composite.

(3) The present invention uses the optimized preparation method and product formula to form a denser conductive network inside the obtained conductive composite material, and the conductive performance is significantly enhanced. The conductive permeation threshold is lower than 6%, and the resistivity is as low as 0.169Ω·cm, the mechanical properties of the product are tested according to the national standard GB1040-1992 and GB9341-2000, the tensile strength is above 20MPa, and the bending strength is above 16MPa.

(4) The conductive composite material prepared by the present invention has the advantages of easy adjustment of resistivity, light weight, easy processing, wear resistance and corrosion resistance.

(5) Compared with the current commonly used methods such as melt mixing, solution blending, and powder mixing to prepare conductive composite materials, in the preparation process of the present invention, on the basis of introducing the mechanical activation method, except for the basic raw materials, no Toxic and harmful chemical reagents such as plasticizers, lubricants, and foaming agents need to be added, so no toxic waste gas is emitted, the environmental protection effect is strong, the raw materials used are all cheap, and the production cost of PVC conductive composite materials is reduced.

Description of drawings

Fig. 1. the flow chart of the method for preparing PVC conductive composite material by mechanical ball milling method of the present invention.

Detailed ways

A method for preparing PVC conductive composite material by mechanical ball milling method of the present invention will be described below in conjunction with examples, and these descriptions are not intended to further limit the content of the present invention.

Example 1

The preparation method of the PVC conductive composite material in this embodiment is firstly to place the graphite in absolute ethanol with the addition of coupling agent silane KH570, the amount of silane KH570 is 2% of the graphite weight, and stir at a constant temperature until the graphite is dispersed in ethanol , suction filtration, dry the graphite to obtain modified graphite, put the modified graphite and PVC in the ratio of 20%:80% into a circulating water type high-energy ball mill, and mechanically ball mill at a speed of 150 rpm and a temperature of 50°C for 1 h , disperse the graphite evenly into the PVC matrix to obtain a mixture, fill the mixture into the mold of a flat vulcanizer, heat press at a pressure of 5 MPa and a temperature of 165°C for 15 minutes, and demould to obtain a PVC conductive composite material.

The product prepared in this example has a conductive percolation threshold lower than 6%, a resistivity of 0.169 Ω cm, a tensile strength of 20.63 MPa, and a bending strength of 16.88 MPa.

Example 2

The preparation method of this PVC conductive composite material in the present embodiment, at first is that graphite is placed in the dehydrated alcohol that adds coupling agent aluminate, and the consumption of aluminate is 2.5% of graphite weight, is stirred at constant temperature until graphite is dispersed in In ethanol, filter with suction, dry the graphite to obtain modified graphite, put the modified graphite and PVC in the ratio of 15%:85% into a circulating water-type high-energy ball mill, and mechanically ball mill at a speed of 100 rpm and a temperature of 45°C After 2.0 h, the graphite was evenly dispersed into the PVC matrix to obtain a mixture, which was filled in the mold of a flat vulcanizer, hot-pressed at a pressure of 6 MPa and a temperature of 160°C for 20 minutes, and demolded to obtain a PVC conductive composite material.

The product prepared in this example has a conductive permeation threshold lower than 6%, a resistivity of 0.499 Ω cm, a tensile strength of 21.25 MPa, and a bending strength of 17.36 MPa.

Example 3

The preparation method of the PVC conductive composite material in this embodiment is firstly to place the graphite in absolute ethanol with the addition of coupling agent titanate, the amount of titanate is 1% of the weight of the graphite, and stir at a constant temperature until the graphite is dispersed in In ethanol, filter with suction, dry the graphite to obtain modified graphite, put the modified graphite and PVC in the ratio of 18%:82% into a circulating water-type high-energy ball mill, and mechanically ball mill at a speed of 300 rpm and a temperature of 48°C After 0.5 h, the graphite was evenly dispersed into the PVC matrix to obtain a mixture, which was filled into the mold of a flat vulcanizer, and hot-pressed at a pressure of 7 MPa and a temperature of 180°C for 10 minutes, and demolded to obtain a PVC conductive composite material.

The product prepared in this example has a conductive permeation threshold lower than 6%, a resistivity of 0.252 Ω cm, a tensile strength of 20.95 MPa, and a bending strength of 17.04 MPa.

Example 4

The preparation method of the PVC conductive composite material in this embodiment is firstly to place the graphite in absolute ethanol with the addition of coupling agent silane KH570, the amount of silane KH570 is 3% of the graphite weight, and stir at a constant temperature until the graphite is dispersed in ethanol , suction filtration, dry the graphite to obtain modified graphite, put the modified graphite and PVC in the ratio of 16%:84% into a circulating water type high-energy ball mill, and mechanically ball mill at a speed of 250 rpm and a temperature of 46°C for 1.5h , disperse the graphite evenly into the PVC matrix to obtain a mixture, fill the mixture into the mold of a flat vulcanizer, heat press at a pressure of 8 MPa and a temperature of 170°C for 16 minutes, and demould to obtain a PVC conductive composite material.

The product prepared in this example has a conductive permeation threshold lower than 6%, a resistivity of 0.370 Ω cm, a tensile strength of 21.16 MPa, and a bending strength of 16.95 MPa.

comparative example

Chinese patents CN201410566862, CN200910010679, CN201310270671, and CN201410547858 respectively adopt banbury plasticization, melt blending, solution blending, and powder mixing methods to prepare conductive composite materials. The resistivity of the conductive composite materials prepared by these methods is similar to that of PVC conductive materials prepared by the present invention. Composite material resistivity comparison is shown in Table 1:

Table 1 Resistivity of conductive composites prepared by different methods

processing method Minimum resistivity (Ω·cm) Mixing and plasticizing 0.5 melt mixing 0.22 solution blending 5.6 powder mix 287 this invention 0.17

It can be seen from Table 1 that the resistivity of the PVC conductive composite material prepared by the mechanical ball milling method of the present invention is obviously lower than that of the conductive composite material prepared by other methods. Therefore, compared with the prior art, the method for preparing the PVC conductive composite material by the mechanical ball milling method of the present invention has significantly more excellent conductivity.

The present invention is created through long-term work experience accumulated by a number of conductive composite material processing personnel and created through creative labor, and has outstanding substantive features and remarkable progress. This method uses PVC as the base material, graphite as the conductive filler, and uses a coupling agent to eliminate the interface difference between graphite and PVC, so that the graphite is evenly dispersed in the PVC matrix, and a denser conductive network is formed inside the composite material. , the electrical conductivity of the composite material is significantly enhanced, and the method has high reaction efficiency, energy saving, no industrial waste, low production cost, and can realize a win-win situation of economic benefit and environmental protection.

Claims (10)

1. a method for preparing PVC conductive composite material by mechanical ball milling, is characterized in that, may further comprise the steps: (1) Put the graphite in absolute ethanol containing a coupling agent, the amount of the coupling agent is 1-3% of the weight of the graphite, stir at a constant temperature until the graphite is evenly dispersed in the ethanol, filter with suction, and dry the graphite to obtain the improved Sexual graphite; (2) Mix the modified graphite and PVC at a weight ratio of 15-20%:80-85%, put them into a circulating water type high-energy ball mill for mechanical ball milling, the temperature of the mechanical ball milling is 45-50°C, and the speed is 100- 300 rpm, the time is 0.5-2.5 h, so that graphite is evenly dispersed into the PVC matrix to obtain a mixture; (3) Take out the mixture, fill it in the mold of a flat vulcanizer, heat press it at a temperature of 160-180°C and a pressure of 5-8 MPa for 10-20 minutes, and demould to obtain a PVC conductive composite material. 2. mechanical ball milling method according to claim 1 prepares the method for PVC conductive composite material, is characterized in that, described coupling agent consumption is 2% of graphite weight. 3. The method for preparing PVC conductive composites by mechanical ball milling according to claim 1 or 2, wherein the coupling agent is any one of silane KH570, aluminate, titanate. 4. mechanical ball milling method according to claim 3 prepares the method for PVC conductive composite material, is characterized in that, the weight ratio of described modified graphite and PVC is 20%:80%. 5. The method for preparing PVC conductive composite material by mechanical ball milling according to claim 4, characterized in that, the temperature of said mechanical ball milling is 50°C. 6. mechanical ball milling method according to claim 5 prepares the method for PVC conductive composite material, is characterized in that, the rotating speed of described mechanical ball milling is 150 rpm. 7. mechanical ball milling method according to claim 6 prepares the method for PVC conductive composite material, is characterized in that, the time of described mechanical ball milling is 1.0 h. 8. The method for preparing PVC conductive composite material by mechanical ball milling according to claim 7, characterized in that, the temperature of the hot pressing is 165°C. 9. mechanical ball milling method according to claim 8 prepares the method for PVC conductive composite material, is characterized in that, the pressure of described hot pressing is 5 MPa. 10. mechanical ball milling method according to claim 9 prepares the method for PVC conductive composite material, is characterized in that, the time of described hot pressing is 15 min.