Patent Application
20180017450
The present invention relates to the technical field of pressure measurement, and particularly relates to a nano-conductive rubber sensing unit and a preparation method therefor.
Nano-conductive rubber is a composite material which generates electrical conductivity after a nanoscale conductive filler is added in an insulating rubber matrix. As the nano-conductive rubber has good piezoresistance characteristics, durability, fatigue resistance and flexibility, it has been researched extensively to be used as a pressure sensing material, and has been applied in the fields of robots, medical care, spaceflight, etc.
Research shows that when the nano-conductive rubber is used as a pressure sensitive material, the measuring range thereof is related to the thickness, hardness, conductive filler proportion and manufacturing process of the conductive rubber. By increasing the thickness and hardness of the nano-conductive rubber, the measuring range thereof can be increased in a suitable amount. However, the thickness of a sheet-type pressure sensor is limited frequently in some workplaces, thus the thickness of the nano-conductive rubber is limited. Moreover, a thicker nano-conductive rubber material may be torn under the effect of a higher pressure due to a larger horizontal deformation, thus sufficient mechanical strength cannot be achieved. It is an effective way to improve the conductivity and mechanical performance thereof by optimizing the composition proportion of the nano-conductive rubber or adding a modifying material and a strengthening agent. The Chinese patent publication CN 104893291 A discloses a preparation method for a silicone rubber-base force sensitive composite material, in which nanoscale metal particles are used as a filler, and the maximum pressure intensity measuring value is 2.4 MPa. In addition, by experiments, some scholars also proved that the conductivity and pressure sensitive range of the composite material can be improved effectively by adding nano SiO2 and nano Al2O3.
At present, for the research of the nano-conductive rubber, carbon-black filling type conductive rubber is used as a main type, most pressure sensors based on the nano-conductive rubber are in an experimental stage, some nano-conductive rubber sensors obtaining industrial application cannot yet realize the pressure measurement in the state of large pressure intensity in the fields of machinery, civil engineering, etc. due to the limitation of sensitivity, linearity and measuring range.
The technical problem to be solved in the invention is to provide a nano-conductive rubber sensing unit which has a large measuring range of pressure measurement, high sensitivity within the measuring range and good linearity of a piezoresistance characteristic curve, and can meet the requirement of a sheet type.
The technical problem to be solved in the invention is also to provide a method for preparing the nano-conductive rubber sensing unit.
In order to solve the technical problems, the invention adopts the following technical solution.
The invention provides a nano-conductive rubber sensing unit, which comprises at least two fabric layers, wherein nano-conductive rubber is filled between every two adjacent fabric layers, and the nano-conductive rubber is a rubber matrix in which carbon nanotubes are dispersed.
As a further improvement to the technical solution, the carbon nanotubes are multi-wall carbon nanotubes.
As a further improvement to the technical solution, the mass percent of the multi-wall carbon nanotubes in the nano-conductive rubber is between 8% and 9%.
As a further improvement to the technical solution, the nano-conductive rubber is infiltrated into fiber texture gaps of the fabric layers.
As a further improvement to the technical solution, the rubber matrix is a silicone rubber, and the proportion of basic constituents of the silicone rubber to a curing agent is 10:1.
The invention also provides a preparation method for preparing the nano-conductive rubber sensing unit as mentioned above, which comprises the following steps: S1, mixing a rubber matrix with carbon nanotubes in accordance with a mass proportion so as to make a nano-conductive rubber slurry; S2, laying flat one fabric layer, spreading the nano-conductive rubber slurry prepared in S1 over the fabric uniformly to a certain thickness, and then, laying flat the other fabric layer thereon; and S3, pressurizing and heating the nano-conductive rubber sensing unit prepared in S2 to cure the same.
As a further improvement to the technical solution, in step S2, the fabric layer located at a bottom layer is laid flat on a bottom plate of a mould, and a top plate of the mould is placed on the fabric layer located at a top layer; and in step S3, pressures are exerted on the nano-conductive rubber sensing unit by the actions of the top plate and the bottom plate of the mould.
As a further improvement to the technical solution, in step S3, the mould to which the nano-conductive rubber sensing unit is fixed is placed in a container at 60° C.
As a further improvement to the technical solution, the container is maintained in a vacuum state.
As a further improvement to the technical solution, in step S3, the mould to which the nano-conductive rubber sensing unit is fixed is placed in the container for at least 300 min.
The invention has the following beneficial effects.
1. According to the nano-conductive rubber sensing unit of the invention, by adding fabric layers as a frame, the compressive strength, tensile strength and fatigue resistance performance of the nano-conductive rubber sensing material are effectively improved, it is achieved that the nano-conductive rubber sensing unit has better sensitivity, linearity and stability of multiple cyclic loading within the measuring range of pressure intensity of 0 to 50 MPa, and the nano-conductive rubber sensing unit can be applied to a long-term pressure measurement in the state of a high pressure in the fields of mechanical manufacture, civil engineering, etc.
2. Under the effect of a vertical pressure, a resistance value measured by the nano-conductive rubber sensing unit increases with the increase of the pressure, showing a positive piezoresistance effect, which is different from the existing carbon-black filling type conductive rubber with negative piezoresistance effect. In addition, the linearity of a piezoresistance characteristic curve is good, and is suitable for manufacture of a high-accuracy pressure sensor.
3. The nano-conductive rubber sensing unit of the invention has the minimum thickness which can reach 3 mm, and can be suitable for pressure sensors of any curved surface and shape.
The conception, specific structure and generated technical effects of the invention will be clearly and fully described below in combination with embodiments and drawings for one to fully understand the purposes, features and effects of the invention. Obviously, the described embodiments are some part of embodiments of the invention and are not all embodiments; and based on the embodiments of the invention, other embodiments obtained by those skilled in the art without contributing creative work will belong to the protection scope of the invention. In addition, all linkage/connection relationships concerned in the patent do not just mean that members are directly connected, but mean that a more excellent linkage structure can be formed by adding or reducing linkage auxiliaries according to specific implementation situations. Various technical features in the invention can be combined with each other on the premise of no mutual contradiction and conflict.
Referring to
The fabric is formed by weaving elastic fibers (the higher the tex is, the thicker the fiber is) such as medium-tex or high-tex spandex, high-elasticity chinlon, etc., and the purpose of selecting large-sized yarns is to ensure that the fabric has a certain thickness to bear a pressing deformation. The elasticity of elastic fibers is required to have the following characteristics: (1) high elastic recovery percentage; (2) rapid resilience; (3) high elastic modulus (making a load required by extension thereof high). The calculation formula of the elastic recovery percentage is as follows:
elastic recovery percentage (%)=[(L1−L′1)/(L1−L0)]×100%,
where, L0 is the original length of a sample; L1 is the length when the sample is stretched to extension; and L′1 is the length after recovery of the sample.
According to the invention, the high-strength fabric layers 1 are added as a strengthening frame of the nano-conductive rubber sensing unit, thereby significantly improving the strength and toughness of the nano-conductive rubber at a high pressure of 0 to 50 MPa. In the whole using process, no cracks are generated on the surface of the nano-conductive rubber sensing unit, let alone tearing, thereby ensuring the stability and repeatability of the sensing unit at a high pressure. Therefore, the nano-conductive rubber sensing unit can be used for manufacturing a sheet-type flexible nano-conductive rubber pressure sensor having a large measuring range.
The nano-conductive rubber sensing unit according to the invention has the working principle that the sensing unit is of a sheet type in shape, when bearing the pressures of an upper surface and a lower surface (that is, pressures exerted in thickness directions of the sheet, i.e. the directions shown by arrows in
The nano-conductive rubber sensing unit of the invention is prepared mainly by a solution blending method and compression moulding, wherein the specific preparation method comprises the following steps:
S1, proportioning: weighing basic constituents of silicone rubber (PDMS), a curing agent and carbon nanotubes in accordance with a mass proportion, pouring the same into a mixer, and conducting mechanical grinding and mixing at room temperature to make sure that the carbon nanotubes are uniformly distributed in a rubber matrix, so as to make a nano-conductive rubber slurry;
S2, synthesizing: preparing many pieces of high-strength fabrics with the same size, laying flat one fabric layer on a bottom plate of a mould, spreading the nano-conductive rubber slurry prepared in S1 over the fabric uniformly to a certain thickness, and then, laying flat the other fabric layer thereon, wherein according to the thickness requirement of the nano-conductive rubber sensing element, spreading of the nano-conductive rubber slurry and a further laying of the fabric layer can be repeated successively; and
S3, curing: placing a top plate of the mold on the fabric layer located at the uppermost layer of the nano-conductive rubber sensing unit which is not cured, and exerting a certain pressure on a nano-conductive rubber material through the connection between the top plate and the bottom plate of the mold, thereby ensuring the thickness uniformity and compactness thereof; and placing the mold in a container at 60° C., evacuating the container such that a vacuum is created inside the container and keeping the mold in the container for at least 300 min.
After the nano-conductive rubber sensing unit is cured, in accordance with the design requirement of a sensor, the cured sheet-type nano-conductive rubber sensing unit can be cut to a required size and shape by using a machining cutter, and then is connected to an upper electrode and an insulating protective layer so as to complete the manufacture of a sheet-type flexible nano-conductive rubber pressure sensor having a large measuring range.
In accordance with a mass ratio, there are 100 shares of basic constituents of silicone rubber (PDMS), 10 shares of curing agent and 9.57 shares of double-wall carbon nanotubes, wherein the mass percent of the double-wall carbon nanotubes in a nano-conductive rubber mixed solution is 8%, and for fabrics, a cloth with a suitable thickness, elasticity and strength which is commercially-available is selected. The prepared nano-conductive rubber sensing unit is in the shape of a square of which the side length is 50 mm and the thickness is 3 mm, in which there are two fabric layers which are respectively located on the upper surface and the lower surface of the sensing unit. There is one conductive rubber layer, which is located between an upper fabric layer and a lower fabric layer and has a thickness of about 1 mm.
In accordance with a mass ratio, there are 100 shares of basic constituents of silicone rubber (PDMS), 10 shares of curing agent and 10.22 shares of double-wall carbon nanotubes, wherein the mass percent of the double-wall carbon nanotubes in a nano-conductive rubber mixed solution is 8.5%, and for fabrics, a cloth with a suitable thickness, elasticity and strength which is commercially-available is selected. The prepared nano-conductive rubber sensing unit is in the shape of a square of which the side length is 50 mm and the thickness is 3 mm, in which there are two fabric layers which are respectively located on the upper surface and the lower surface of the sensing unit. There is one conductive rubber layer, which is located between an upper fabric layer and a lower fabric layer and has a thickness of about 1 mm.
In accordance with a mass ratio, there are 100 shares of basic constituents of silicone rubber (PDMS), 10 shares of curing agent and 10.88 shares of double-wall carbon nanotubes, wherein the mass percent of the double-wall carbon nanotubes in a nano-conductive rubber mixed solution is 9%, and for fabrics, a cloth with a suitable thickness, elasticity and strength which is commercially-available is selected. The prepared nano-conductive rubber sensing unit is in the shape of a square of which the side length is 50 mm and the thickness is 3 mm, in which there are two fabric layers which are respectively located on the upper surface and the lower surface of the sensing unit. There is one conductive rubber layer, which is located between an upper fabric layer and a lower fabric layer and has a thickness of about 1 mm.
According to the invention, multiple layers of fabrics are adopted as frame layers, and are closely combined with nano-conductive rubber through a specific process, and the nano-conductive rubber is infiltrated into gaps in the fabrics, so as to form a stable whole. The fabric layers have good elasticity, toughness and tensile strength, can generate an elastic deformation together with the conductive rubber layer to meet the requirements of the deformation of the sensing unit, and can also limit excessive deformation of the sensing unit to protect the conductive rubber layer from being torn at a high pressure, so that the mechanical strength of the sensing unit within a pressure sensitive range is effectively improved, and the sensing unit will not be damaged even if it undergoes repeated loading and unloading under the effect of a higher pressure, thereby having good stability and repeatability and meeting the requirement of manufacturing a pressure sensor with a high measuring range and a high resistance to pressure.
The above are preferred embodiments of the invention, but the invention is not limited thereto. Those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the invention. All such equivalent modifications or replacements should fall within the scope defined by the claims of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-10571308.0 | Jul 2016 | CN | national |
