CN101214722A - Method for preparing designable layered polymer-based conductive composites - Google Patents

Abstract

A layered polymer-based conductive composite material with alternating insulating layers and conductive layers was prepared using a microlayer co-extrusion device. The insulating layer and the conductive layer pellets are put into the two extruders of the micro-layer co-extrusion device to be melted and plasticized, and the two melts are stacked into two layers at the confluence, and after cutting and stacking by n stacking units , to obtain a 2 ⁽ⁿ⁺¹⁾ layer composite. The conductivity of the material is anisotropic, the number of layers and the layer thickness ratio of the conductive layer and the insulating layer are respectively determined by the number of stacked units and the speed ratio of the extruder, so the percolation value and resistivity of the conductive material can be designed sex. Compared with the traditional preparation method, the polymer conductive composite material prepared by the invention has the characteristics of low percolation value, low resistivity and high elongation at break. The equipment involved in the present invention is simple and easy to obtain, all the required raw materials are commercially available, no need to synthesize other chemicals, the operation is simple, the production cost is low, and the efficiency is high.

Description

Method for preparing designable layered polymer-based conductive composites

1. Technical field

The invention relates to the field of polymer processing, and more particularly, the invention relates to the preparation of polymer-based conductive composite materials.

2. Background technology

Polymer-based conductive composite material is a functional composite material formed by filling conductive substances into the polymer matrix in a certain way and processing technology. It can not only meet people's needs for conductive materials, but also because of its light weight, easy It is processed into various complex shapes, has good chemical stability, and the conductivity can be adjusted in a wide range, so it has been widely used, and has aroused great interest in the study of its conductive structure and properties in academia and industry, and promoted the development of The development of modern materials science. Polymer-based conductive composite materials can be widely used as antistatic materials, conductive materials, resistor materials (PTC materials), and electromagnetic wave shielding materials. Commonly used conductive fillers are divided into three categories: carbon, metal and metal oxides, among which carbon conductive fillers are mainly carbon black, graphite, carbon fiber and carbon nanotubes.

Typically, polymer-based conductive composites have a high percolation threshold. The high addition of conductive substances not only leads to a significant decrease in the toughness of the composite material, but also leads to difficulties in processing and molding, and increases the production cost. Therefore, reducing the percolation threshold of materials while meeting the requirements of electrical conductivity or improving the electrical conductivity of materials under the condition of fixing the content of conductive substances has become the goal pursued by scientific research and production workers. A large number of studies have shown that the conductivity of polymer-based conductive composites mainly depends on the conductive channels or networks formed by conductive substances in the polymer matrix related to long-range, and the formation and improvement of conductive networks in the system are related to the relaxation of polymer macromolecular chains. The behavior of carbon black is closely related to the aggregated state structure of the polymer and the distribution of carbon black in the polymer.

In practical applications, one method that can effectively reduce the percolation threshold is to use a multi-phase system for the matrix resin, the most common being a three-phase system (containing conductive substances). Add conductive substances to two incompatible polymer matrices, and through proper process control, the conductive substances are preferentially distributed in one phase of the incompatible polymer blend or at the interface of the two phases to regulate incompatible polymerization The ratio of the substance makes the phase where the conductive substance is located become a continuous phase or a co-continuous phase, realizing the percolation of the conductive substance in one continuous phase or on the continuous interface and the percolation of the continuous phase in another polymer (that is, double percolation ), thereby reducing the percolation threshold. For example, Gubbels et al. (Selective Localization of Carbon Black in Immiscible Polymer Blends: A Useful Tool To Design Electrical Conductive Composites Macromolecules; 1994; 27(7); 1972-74.) selectively filled conductive carbon black particles into polyethylene/polystyrene The polyethylene phase in the bicontinuous system, the percolation value of the prepared conductive composite material was reduced to 3wt%. Li Zhongming et al. (Preparation method of composite materials that can form in-situ conductive microfiber network: Chinese patent, CN1528816, 2004) according to the process steps of drying-masterbatch preparation-melt blending extrusion-thermal stretching-quenching-granulation The in-situ fiber-forming composite material was prepared under certain conditions. The conductive filler exists in the fiber phase with a high melting point, and these fiber phases can form a conductive network in the post-processed product. Therefore, the amount of conductive filler added is small, which greatly reduces the composite Conductive percolation value of the material.

Obviously, in the above-mentioned method, the precondition for realizing double percolation is to use a two-component polymer matrix, and the polymer phase where the conductive material is located must exist in another phase in the form of a continuous phase. Moreover, because the distribution of conductive substances in the two phases is not easy to control and calculate, the structure of the two phases is easily affected by various factors such as the ratio of components, viscosity ratio, surface tension ratio, and processing technology. From a perspective, it is difficult to obtain a repeatable and controllable ideal morphological structure through traditional blending and compounding methods, and it is difficult to prepare composite materials with designable conductive properties.

3. Contents of the invention

The purpose of the present invention is to provide a new method for preparing polymer-based conductive composite materials in view of the current situation of preparing polymer-based conductive composite materials, so as to solve the problem that the conductive composite materials prepared by the preparation method of conductive composite materials in the prior art are difficult to obtain Repeatable and controllable ideal morphological structure, conductive performance is difficult to have technical problems such as designability.

The method for preparing a designable layered polymer-based conductive composite material disclosed in the present invention is to put the conductive layer material and the insulating layer material into two extruders of a layered co-extrusion device respectively, and after melting and plasticizing, make the two strands The melt is stacked in the combiner, and after cutting and stacking of n stacked units, it flows out of the exit die to produce 2 ⁽ⁿ⁺¹⁾⁾ layers of polymer-based conductive layers that are alternately distributed with conductive layers and insulating layers. composite material. The thickness ratio of the conductive layer to the insulating layer of the polymer-based conductive composite can be adjusted by changing the speed ratio of the two extruders. .

In the above technical solution, the material of the conductive layer is a pellet obtained by mixing the filler as the conductive substance and the polymer as the matrix and extruding through an extruder. The weight content of the conductive substance in the conductive layer material is generally controlled within the range of 1-30%. The conductive substance can be one of carbon black, graphite, carbon fiber, carbon nanotube, metal and metal oxide, or two or more. The matrix polymer can also be one of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polymethyl methacrylate, polyethylene terephthalate, synthetic rubber and polyurethane, or two or more.

In the above technical scheme, the insulating layer material can be selected from polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polymethyl methacrylate, polyethylene terephthalate, A pure polymer of synthetic rubber and polyurethane, or pellets obtained by blending not less than two polymers selected from them.

In the above technical solution, when the matrix polymer of the conductive layer is incompatible with the polymer of the insulating layer, a compatibilizer for making the polymers fuse with each other is added when preparing the conductive layer material pellets or the insulating layer material pellets. The compatibilizer can be maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, SBS, etc. The specific type of compatibilizer depends on the nature of the polymer.

In the above technical solution, before preparing the layered polymer-based conductive composite material, the raw materials for preparing the layered polymer-based conductive composite material are dried to a moisture content of <0.02%.

In the above technical solution, the two extruders for preparing the layered polymer-based conductive composite material are connected to a stacking device containing n stacking units through a converging device.

The method for preparing a designable layered polymer-based conductive composite material disclosed in the present invention is characterized in that a layered composite material in which conductive layers and insulating layers are alternately distributed is prepared by using a layered co-extrusion device, and the materials of the conductive layer and the insulating layer are respectively made of Extruded by two extruders, it enters the combiner through two connectors, and enters several stacking units after being stacked at the exit of the combiner. After the number of layers is multiplied by the splitting unit, the composite material product is finally pulled under the action of the traction device. The layered unit is pulled out through the cooling device. Both the conductive layer and the insulating layer are continuous phases in the direction of extrusion. The conductive layer is a common filling system of polymers and conductive substances, and the insulating layer is pure polymer. The polymers of the conductive layer and the insulating layer may be the same polymer. Thus, double percolation in a one-component polymer matrix can be achieved using this method. The number of layers of the layered conductive composite is controlled by the number of stacked units. If the number of stacked units is n, the number of layers N is 2 ⁽ⁿ⁺¹⁾ ; the layer thickness ratio of the conductive layer and the insulating layer can be determined by Adjust the speed ratio of the two extruders to control. In this way, the structure of the layered conductive composite is programmable, resulting in controllable percolation threshold and resistivity.

Experimental results show that the percolation value and room temperature resistivity of the polymer-based conductive composite material prepared by the method of the invention are lower than those of the polymer-based conductive composite material prepared by the traditional method. The dispersed size of the conductive substance in the polymer matrix is smaller and more uniform, coupled with the unique layered structure, the elongation at break is greatly improved.

The present invention has the following advantages:

1. The equipment involved in the present invention is simple and easy to obtain. It is only necessary to connect two common extruders through a converging device, and add several stacking units at the die; the required raw materials are all commercially available, and there is no need to synthesize other chemicals . The method has the characteristics of simple and easy operation, low production cost, high efficiency and the like.

2. The polymer-based conductive composite material prepared by the present invention has a layered structure, the conductive layers and insulating layers are arranged alternately, and the electrical conductivity has anisotropy.

3. The number of layers of the polymer-based conductive composite material and the thickness ratio of the conductive layer to the insulating layer can be controlled by changing the number of stacked units and the speed ratio of the extruder, so that the percolation value and resistivity can be effectively adjusted .

4. The elongation at break of the polymer-based conductive composite material prepared by the method provided by the invention is greatly improved.

5. The polymer-based conductive composite material prepared by the method of the present invention can realize double percolation in a single-component polymer matrix.

The present invention also has some advantages in other aspects.

4. Description of drawings

Fig. 1 is a structural schematic diagram of a layered co-extrusion device involved in the present invention. In the figure, A, B: Extruder, C: Combiner D: Split unit E: Exit die

Fig. 2 is a schematic structural view of the polymer-based conductive composite material prepared in the present invention. In the figure, F: insulating layer, G: conductive layer.

5. Specific implementation

The present invention is further described in detail below by way of examples. In each of the following examples, the amounts of each component are by weight. It is necessary to point out that the following examples are only used to further illustrate the present invention, and cannot be interpreted as limiting the protection scope of the present invention. Those skilled in the art make some non-essential improvements and improvements to the present invention according to the above-mentioned contents of the present invention. Adjustment still belongs to the protection scope of the present invention.

The positive effects produced by the present invention can be illustrated with examples.

Example 1

The raw materials are polypropylene and carbon black, the insulating layer and the conductive layer are pure polypropylene and carbon black filled polypropylene respectively. Firstly, common carbon black-filled polypropylene was prepared, with a carbon black content of 11%. After the polypropylene and carbon black were dried, they were melt-mixed and granulated in a twin-screw extruder. The conductive layer and insulating layer pellets are put into the two extruders of the layered co-extrusion device respectively. The extruder speed ratio is 1:1. The temperature of each section of the extruder is controlled between 170-200 °C. The temperature of the stacking unit and the exit mold are both 200°C. Using two stacking units, the melt of the conductive composite product flows out of the exit mold under the traction of the traction device, and after being cooled by the cooling device, an 8-layer layer is prepared Polypropylene-based conductive composites. The resistivity of the material is 5.91×10 ³ Ω·cm, the PTC strength is 3.38, and the elongation at break is 416%. As a comparison, the resistivity and elongation at break of the traditional polypropylene-based conductive composite with the same carbon black content are 2.16×10 ⁴ Ω·cm and 50%, respectively.

Example 2

The raw materials are polyethylene and carbon black, and the insulating layer and conductive layer are respectively pure polyethylene and carbon black filled polyethylene. First, ordinary carbon black-filled polyethylene was prepared, with a carbon black content of 11%. After the polyethylene and carbon black were dried, they were melt-mixed and granulated in a twin-screw extruder. The conductive layer and insulating layer pellets are put into the two extruders of the micro-layer co-extrusion device respectively. The extruder speed ratio is 2:1. The temperatures of the lamination unit and the outlet die were both 200°C, and a 4-layer layered polyethylene-based conductive composite was prepared using one lamination unit. The resistivity of the material is 5.02×10 ³ Ω·cm, the PTC strength is 3.26, and the elongation at break is 316%. As a comparison, the resistivity and elongation at break of the traditional polyethylene-based conductive composite with the same carbon black content are 4.67×10 ⁴ Ω·cm and 89%, respectively.

Example 3

The raw materials are polypropylene and carbon black, the insulating layer and the conductive layer are pure polypropylene and carbon black filled polypropylene respectively. First prepare ordinary carbon black-filled polypropylene with carbon black content of 2, 4, 6, 8, 10, 12, 14, 18, 22, 30% respectively: after drying polypropylene and carbon black, extrude Melt mixing and granulation in the machine. The conductive layer and insulating layer pellets are put into the two extruders of the micro-layer co-extrusion device respectively. The extruder speed ratio is 1:1. The temperatures of the lamination unit and the outlet die were both 200°C, and a 4-layer layered polypropylene-based conductive composite was prepared using one lamination unit. The percolation value for this material is approximately 5.0 wt%. For comparison, the percolation value of conventional polypropylene-based conductive composites is about 7.0 wt%.

Example 4

The raw materials are polystyrene, carbon black and carbon nanotubes, and the insulating layer and conductive layer are respectively pure polystyrene, carbon black, and carbon nanotube-filled polystyrene. First, ordinary carbon black-filled polystyrene was prepared, and the contents of carbon black and carbon nanotubes were 14.35 and 0.55% respectively: after drying polypropylene, carbon black and carbon nanotubes, they were melt-mixed and granulated in a twin-screw extruder. The conductive layer and insulating layer pellets are put into the two extruders of the micro-layer co-extrusion device respectively. The extruder speed ratio is 1:2. The temperatures of the stacking unit and the exit die were both 200°C, and two stacking units were used to prepare an 8-layer layered polypropylene-based conductive composite. The resistivity of this material was 3.9×10 ² Ω·cm. As a comparison, when the filling content of conductive substances is the same, the resistivity of carbon black and carbon nanotube-filled polystyrene prepared by traditional methods is 7.84×10 ⁵ Ω·cm.

Example 5

The raw materials are polypropylene, carbon black and carbon nanotubes, and the insulating layer and the conductive layer are respectively pure polypropylene, carbon black, and carbon nanotube-filled polypropylene. Firstly, ordinary carbon black-filled polypropylene was prepared, and the contents of carbon black and carbon nanotubes were 12.35% and 0.65% respectively: after the polypropylene, carbon black and carbon nanotubes were dried, they were melt-mixed and granulated in a twin-screw extruder. The conductive layer and insulating layer pellets are put into the two extruders of the micro-layer co-extrusion device respectively. The extruder speed ratio is 1:1. The temperatures of the stacking unit and the exit die were both 200°C, and 3 stacking units were used to prepare a 16-layer layered polypropylene-based conductive composite. The resistivity of this material was 7.0×10 ² Ω·cm, and the elongation at break was 680%. As a comparison, when the filling content of conductive substances is the same, the resistivity of carbon black and carbon nanotube filled polypropylene prepared by traditional methods is 2.40×10 ⁶ Ω·cm, and the elongation at break is 35%.

Example 6

The raw materials are polypropylene, nylon 6, maleic anhydride grafted polypropylene (as a compatibilizer for polypropylene and nylon) and carbon black, and the insulating layer and conductive layer are respectively polypropylene (plus and carbon black filled nylon 6. First prepare Ordinary carbon black filled nylon 6 with a carbon black content of 14%: after drying nylon 6 and carbon black, melt and mix granules in a twin-screw extruder. The conductive layer and insulating layer pellets are respectively put into the micro-layer co-extrusion device Among the two extruders, the speed ratio of the extruder is 1:1, the temperature of each section of the extruder is controlled between 230 and 250 °C, and the temperature of the converging unit, the stacking unit and the outlet die are all 250 °C. Seven stacked units were prepared to obtain a layered polypropylene-based conductive composite material with 256 layers.The resistivity of the material was 2.16×10 ³ Ω·cm.

Claims (10)

1. A method for preparing a designable layered polymer-based conductive composite material is characterized in that the conductive layer material and the insulating layer material are respectively dropped into two extruders (A, B) of a layered co-extrusion device, melt plastic After melting, the two melts are superimposed in the combiner (C), and after being cut and superimposed by n split units (D), they flow out from the exit die (E) to obtain 2 ⁽ⁿ⁺¹⁾⁾ layers composed of A polymer-based conductive composite material with alternating conductive and insulating layers. 2. According to the method for preparing a designable layered polymer-based conductive composite material according to claim 1, it is characterized in that the thickness ratio of the conductive layer and the insulating layer is adjusted by the speed ratio of the two extruders. 3. according to the method for preparing designable layered polymer-based conductive composite material according to claim 1, it is characterized in that the conductive layer material is prepared by extruding through an extruder by mixing the filler as the conductive substance and the polymer as the matrix of pellets. 4. The method for preparing a designable layered polymer-based conductive composite material according to claim 3, characterized in that the weight content of the conductive substance in the conductive layer material is 1-30%. 5. The method for preparing a designable layered polymer-based conductive composite according to claim 4, wherein the conductive substance is at least one of carbon black, graphite, carbon fiber, carbon nanotube, metal and metal oxide. 6. According to the method for preparing designable layered polymer-based conductive composites according to claim 4, it is characterized in that the matrix polymer is polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polymethyl At least one of methyl acrylate, polyethylene terephthalate, synthetic rubber, and polyurethane. 7. According to the method for preparing the designable layered polymer-based conductive composite according to any one of claims 1 to 6, it is characterized in that the insulating layer material is selected from polyethylene, polypropylene, polyvinyl chloride , polystyrene, polyamide, polymethyl methacrylate, polyethylene terephthalate, synthetic rubber and polyurethane, or a polymer of not less than two selected from them Granules made by blending. 8. According to the method for preparing the designable layered polymer-based conductive composite material according to claim 7, it is characterized in that when the conductive layer matrix polymer is incompatible with the insulating layer polymer, when preparing the conductive layer material particles or/and A compatibilizer is added to make the polymers fuse with each other when the insulating layer material is granulated. 9. according to the method for preparing designable layered polymer-based conductive composite material according to claim 7, it is characterized in that before preparing layered polymer-based conductive composite material, the raw material for preparing layered polymer-based conductive composite material is dried to Moisture content <0.02%. 10. According to the method for preparing the designable layered polymer-based conductive composite material according to claim 7, it is characterized in that two extruders (A, B) for preparing the layered polymer-based conductive composite material pass through the converging device (C ) is connected with a stacking device containing n stacking units (D).

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