A gel paste, its method of preparation and use in direct write without a mold

Abstract

The application discloses a kind of gel slurry and its preparation method and application in dieless direct writing, belong to composite material preparation and additive manufacturing technical field.The composite gel slurry is made of PVDF, filler and poloxamer aqueous solution, wherein the mass fraction of PVDF and poloxamer 408 is 10%~50%, 10%~40%.On the basis of this composite gel slurry, further provides a kind of method for preparing three-dimensional functional structure using the composite gel slurry, after filling slurry into cartridge, vacuum or centrifugal defoaming is carried out, three-dimensional forming of slurry is realized using 3D printer, and the required three-dimensional structure is prepared by fusion bonding.Solve the shortcoming that traditional organic composite gel slurry needs to be cured by thermal volatilization to form, also overcome the defect that existing three-dimensional piezoelectric structure cannot be changed once forming, can be applied to the design and manufacturing field of flexible intelligent three-dimensional device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material preparation and additive manufacturing technology, in particular to a gel slurry, a preparation method thereof and application thereof in mold-free direct writing, which can be used for forming and preparing intelligent functional three-dimensional structures. BACKGROUND

[0002] Piezoelectric ceramic materials have important applications in many fields such as military and marine engineering, automobile industry, electronic industry, etc. At present, the most widely produced and used piezoelectric material is piezoelectric ceramic (such as lead zirconate titanate, barium titanate), which has excellent piezoelectric properties and high dielectric constant, but the problems of difficult ceramic processing, brittleness and poor fatigue resistance limit its further application. In recent years, with the development of intelligent robots, biomedical devices, sensing transducers and nanogenerators, improving flexibility and high sensitivity have become important research directions for the development of such devices.

[0003] Polyvinylidene fluoride (PVDF) is a polymer with excellent piezoelectric properties, and also has good flexibility, high mechanical strength, stable chemical properties and other characteristics, and is an ideal functional material for energy conversion and sensor device design. Studies have shown that compared with uniform thin film structures, PVDF piezoelectric components with three-dimensional micro-patterned film structures or complex three-dimensional structures usually exhibit higher piezoelectric properties and response sensitivity, and have wider application prospects in wearable sensing and energy supply devices.

[0004] Additive manufacturing technology, also known as 3D printing, can realize the direct forming of three-dimensional part models, and provides a convenient and fast technical path for preparing high-performance and complex three-dimensional PVDF structures. According to the forming mechanism, 3D printing technology can be divided into fused deposition modeling (FDM), selective laser sintering (SLS), and stereolithography (SLA). At present, the 3D printing of PVDF mainly adopts the FDM method, which is to pre-fabricate PVDF particles or doped fillers into printing filaments through an extruder, and then melt and extrude the filaments at the printing nozzle to accumulate layer by layer. This method can prepare PVDF components with excellent mechanical properties, but the pre-fabrication of filaments and the extrusion of nozzles need to maintain a temperature higher than the melting point of the filaments (>172℃) during the printing process, and the prepared devices have anisotropy problem.

[0005] Direct ink writing (DIW) is a new type of 3D printing technology, which is composed of a computer-aided control system, a three-dimensional motion platform system and a slurry output control system. The slurry output power is provided by air pressure or screw feeding, which can meet the molding of three-dimensional components from sub-micron to centimeter level. DIW has the characteristics of simple equipment, low cost, easy operation and low energy consumption. DIW has natural advantages in preparing functional three-dimensional structures. However, although the traditional solvent evaporation method can realize the direct writing of three-dimensional PVDF structures at room temperature, the high volatile ink has problems such as difficult preparation, poor stability and volatile gas affecting the working environment. Therefore, it is necessary to develop a composite gel slurry for DIW, which has certain viscoelasticity and shear thinning properties, and is uniform and stable in properties, and is not easy to settle and cause nozzle blockage over time or under the action of shear force. SUMMARY

[0006] The present application aims to provide a gel slurry, a preparation method thereof and an application in direct writing without mold. The preparation raw materials of the gel slurry are composed of PVDF, fillers, poloxamer and water. On the basis of the gel slurry, a method for preparing a three-dimensional functional structure by using the composite gel slurry is further provided. After the slurry is filled into the barrel, vacuum or centrifugal defoaming is carried out, and the three-dimensional molding of the slurry is realized by using a 3D printer. The required three-dimensional structure is prepared by fusion bonding. The shortcomings of the traditional organic composite gel slurry which needs to be cured by thermal volatilization are solved. At the same time, the defect that the existing three-dimensional piezoelectric structure cannot be changed after being formed is overcome. The present application can be applied to the design and manufacturing field of flexible intelligent three-dimensional devices.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A gel slurry is formed by dispersing polyvinylidene fluoride-based materials and fillers in a poloxamer hydrogel matrix. The preparation raw materials of the gel slurry are polyvinylidene fluoride-based materials, fillers, poloxamer and water. The weight content of the polyvinylidene fluoride-based materials is 10% to 50%, the weight content of the fillers is 0% to 20%, the weight content of the poloxamer is 10% to 40%, and the balance is water.

[0009] The polyvinylidene fluoride-based materials are pure polyvinylidene fluoride (PVDF) powder or polyvinylidene fluoride copolymer powder. The polyvinylidene fluoride copolymer is poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) or the like.

[0010] The filler is one or more of ceramic powder, conductive material, microporous template material and other polymer powder; the ceramic powder is barium titanate, lead zirconium titanate or titanium dioxide, the conductive material is nano-silver, graphene or carbon nanotube, etc., and the microporous template material is cellulose, paraffin or water-soluble salt.

[0011] The preparation method of the gel slurry is that the raw materials of the gel slurry, i.e., polyvinyl fluoride-based material, filler, poloxamer and water, are blended to prepare the gel slurry under the temperature condition of 0-4°C, and specifically includes the following steps:

[0012] (1) Preparation of poloxamer hydrogel matrix:

[0013] The poloxamer is dispersed and dissolved into water under the condition of ice bath and continuous stirring, and the formed gel is placed in cold storage until the gel is completely transparent and the upper floating scum is removed to obtain the poloxamer hydrogel matrix;

[0014] (2) The polyvinyl fluoride-based material and the filler powder are dispersed into the poloxamer hydrogel matrix obtained in step (1) in proportion, and are stirred at low speed under the condition of ice water bath for 1-3h and then are transferred to room temperature for magnetic stirring until the gelation; finally, the polyvinyl fluoride gel slurry (PVDF gel or PVDF and filler composite gel) is obtained after defoaming or foam removal.

[0015] In the above step (1), the continuous stirring time is at least 1h, and the stirring speed is controlled within 400rpm; the cold storage temperature is set to 0-4°C.

[0016] The gel slurry is applied to the moldless direct writing preparation of a three-dimensional structure, specifically, after the gel slurry is filled into a barrel and then vacuum defoaming or centrifugal defoaming, a direct writing needle head is installed and fixed, appropriate air pressure is adjusted, and the required three-dimensional structure is printed on a substrate by moldless direct writing.

[0017] Further, the inner diameter of the printing needle nozzle is 0.2-0.6mm, the printing layer height is 0.2-0.32mm, the printing speed is 270-900mm / min, and the printing air pressure is set to 0.25-0.60MPa; the specific process parameters are adjusted according to the components and rheological properties of the slurry.

[0018] The printed three-dimensional structure is placed in a constant temperature drying oven for constant temperature drying treatment to obtain a PVDF structure with good mechanical strength and flexibility; the constant temperature is set to 150-180°C, and the constant temperature time is set to 30-90min.

[0019] The prepared three-dimensional structure can be used for mechanical sensors, energy collection, conversion devices and piezoelectric catalytic materials.

[0020] The design mechanism and beneficial effects of the present application are as follows:

[0021] The principle of the direct writing printing PVDF structure of the present application is to use poloxamer gel reaching the critical micelle concentration as the base material, so that the printing slurry has shear thinning characteristics and certain viscoelasticity, meeting the requirements of the DIW slurry. The direct writing slurry is accompanied by drying, decomposition of the gel components and fusion bonding between the PVDF powders in the process of temperature treatment, and finally forms a three-dimensional functional structure with both strength and toughness.

[0022] In the present application, the release agent is in a liquid molten layer at a certain temperature (> 58℃), existing between the direct writing structure and the glass substrate, which is beneficial to weaken the binding effect of the substrate on the direct writing structure in the shrinkage process, so as to eliminate the structure deformation problem as much as possible, so as to ensure the printing quality.

[0023] The composite gel slurry system of the present application has good dispersibility, stable rheological properties, simple preparation process, and is easy to introduce various required functional fillers, and has wide application range.

[0024] In the present application, the slurry printing process does not need to provide heat source and curing agent to keep the structure from collapsing and deforming, and the production process is more energy-saving and environment-friendly.

[0025] The PVDF structure printed by the direct writing has both structural stability and flexibility after the fusion bonding treatment, and the anisotropy problem of the FDM printed component is weakened, which can better meet the mechanical performance requirements of the device design such as energy conversion and interactive sensing. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the slurry photo prepared in Example 1 of the present application; wherein: (a) poloxamer gel base, (b) PVDF gel slurry.

[0027] Figure 2 It is the microscopic photo of the printed structure obtained by different temperature treatment in Examples 1-3; wherein: (a) 160℃-30min, (b) 170℃-30min, (c) 170℃-60min.

[0028] Figure 3 It is the photo of the woodpile structure printed by the direct writing gel with the PVDF mass fraction of 33% in Example 3 before and after the constant temperature treatment at 170℃; wherein: (a) before treatment, (b) after treatment.

[0029] Figure 4 It is the photo of the direct writing three-dimensional lattice structure sample without barium titanate powder (left) and with the barium titanate filling mass fraction of 10% (right).

[0030] Figure 5 It is the photo of the three-dimensional functional structure with different torsion angles. DETAILED DESCRIPTION

[0031] The application is described in detail below in combination with the drawings and examples.

[0032] The application provides a method for preparing a PVDF three-dimensional structure by direct writing, comprising the following steps:

[0033] S1. uniformly mixing PVDF powder and filler powder after dispersing them into a gel matrix, and then obtaining a PVDF gel or a PVDF and filler composite gel after vacuum degassing; the PVDF accounts for 10-50% of the total weight of the gel slurry, and the filler accounts for 0-20% of the weight of the gel slurry.

[0034] S2. loading the PVDF gel slurry prepared in step S1 into a printing cartridge, and importing a model slice file into a printer for 3D printing.

[0035] S3. drying the printed three-dimensional structure in a drying oven at a constant temperature to obtain a printed structure with good mechanical strength.

[0036] Further, the gel matrix in step S1 is prepared by using poloxamer 408, which is a triblock polymer and can gel when reaching a critical micelle concentration. Preferably, a poloxamer solution with a mass fraction of 32% is prepared as the gel matrix, and the poloxamer powder is dispersed in water and then stirred at low speed in an ice water bath for at least 1 h. The obtained mixed solution is stored in a refrigerator until the solution is clear and transparent and the upper foam is removed.

[0037] Further, the PVDF powder and the filler are dispersed in the poloxamer solution which has been stored as described above, and then stirred at low speed in an ice water bath for 1 h and transferred to room temperature for magnetic stirring until gelling.

[0038] Further, the particle size of the PVDF powder and the filler in the following examples is 0.01-200 mm.

[0039] Further, the printing gel is vacuum degassed after being loaded into the cartridge, and the rotation speed is controlled at 2500-4300 rpm if centrifugal degassing is used.

[0040] Further, the gel slurry in step S2 is printed on a glass substrate coated with a release agent by using a stainless steel needle; preferably, the release agent in the following examples is a poloxamer solution with a mass fraction of 21%.

[0041] Further, the inner diameter of the 3D printing nozzle is 0.3-0.6 mm, the printing layer height is 0.2-0.4 mm, the printing speed is 270-900 mm / min, and the printing air pressure is set to 0.25-0.60 MPa.

[0042] In the present application, the process parameters of 3D printing are adjusted according to the solid content and rheological properties in the slurry; preferably, the nozzle diameter of 3D printing is 0.4 mm, the printing layer height is 0.2 mm, and the printing speed is 360 mm / min.

[0043] Further, the constant temperature treatment condition in step S3 refers to keeping the temperature in the range of 150-180 DEG C for at least 1 h, and the strength of the PVDF direct writing structure is related to the properties of the raw material powder and the holding temperature and time.

[0044] Example 1:

[0045] The PVDF gel slurry with a PVDF mass fraction of 33.3% is prepared for three-dimensional wood pile structure direct writing printing, as follows:

[0046] (1) Take 20 ml of deionized water in a 50 ml beaker and keep ice water bath stirring, weigh 9.4 g of poloxamer powder and gradually add it to the deionized water, continue to keep ice water bath stirring, the stirring speed is set to 300 rpm, stir for 1 h, transfer the completely stirred solution to the refrigerator for 8 h, remove the upper white foam, collect the lower transparent poloxamer solution as the gel matrix Figure 1 a).

[0047] (2) Weigh 5 g of poloxamer gel matrix and 2.5 g of PVDF powder under ice water bath stirring, set the stirring speed to 400 rpm, stir for 1 h, then transfer to room temperature stirring, until the gel is formed, fill the gel into the barrel for centrifugal defoaming to obtain the direct writing printing gel slurry Figure 1 b), set the centrifugal speed to 3500 rpm for 10 min during the centrifugal defoaming process. Select a stainless steel needle with an inner diameter of 0.41 mm for printing, set the air pressure to 0.4 MPa, and set the printing speed to 360 mm / min.

[0048] (3) Dry the printed gel structure in a constant temperature drying oven to make the polymer powders melt and bond, forming a printed structure with mechanical strength, the constant temperature condition is set to 160 DEG C for 30 min, and the wood pile structure micrograph is shown in Figure 2 (a).

[0049] Example 2:

[0050] The PVDF gel slurry with a PVDF mass fraction of 33.3% is prepared for three-dimensional wood pile structure direct writing printing, as follows:

[0051] (1) Take 20 ml of deionized water into a 50 ml beaker and keep it stirring in ice water bath, weigh 9.4 g of poloxamer powder and gradually add it to the deionized water, continue to keep it stirring in ice water bath, set the stirring speed to 300 rpm, stir for 1 h, transfer the completely stirred solution to the refrigerator for cold storage for 8 h, then remove the upper layer of white foam, collect the lower layer of transparent poloxamer solution as the gel matrix.

[0052] (2) Weigh 5 g of poloxamer gel matrix and 2.5 g of PVDF powder and mix them under ice water bath stirring, set the stirring speed to 400 rpm, stir for 1 h, then transfer to room temperature stirring, until the mixed solution is gelled, fill the gel into the barrel for centrifugal defoaming to obtain a direct writing printing gel slurry, set the centrifugal speed to 3500 rpm during the centrifugal defoaming process, and the time is 10 min. When printing, select a stainless steel needle with an inner diameter of 0.41 mm, set the air pressure to 0.4 MPa, and set the printing speed to 360 mm / min.

[0053] (3) Dry the printed gel structure in a constant temperature drying oven to make the polymer powders melt and bond with each other, forming a printed structure with mechanical strength, set the constant temperature conditions to 170℃, 30 min, and the micrograph of the woodpile structure is shown in Figure 2 (b).

[0054] Example 3:

[0055] Prepare a PVDF gel slurry with a PVDF mass fraction of 33.3% for three-dimensional woodpile structure direct writing printing, as follows:

[0056] (1) Take 20 ml of deionized water into a 50 ml beaker and keep it stirring in ice water bath, weigh 9.4 g of poloxamer powder and gradually add it to the deionized water, continue to keep it stirring in ice water bath, set the stirring speed to 300 rpm, stir for 1 h, transfer the completely stirred solution to the refrigerator for cold storage for 8 h, then remove the upper layer of white foam, collect the lower layer of transparent poloxamer solution as the gel matrix.

[0057] (2) Weigh 5 g of poloxamer gel matrix and 2.5 g of PVDF powder and mix them under ice water bath stirring, set the stirring speed to 400 rpm, stir for 1 h, then transfer to room temperature stirring, until the mixed solution is gelled, fill the gel into the barrel for centrifugal defoaming to obtain a direct writing printing gel slurry, set the centrifugal speed to 3500 rpm during the centrifugal defoaming process, and the time is 10 min. When printing, select a stainless steel needle with an inner diameter of 0.41 mm, set the air pressure to 0.4 MPa, and set the printing speed to 360 mm / min.

[0058] (3) The printed gel structure is dried in a constant temperature drying oven to allow the polymer powders to melt and bond, forming a printed structure with mechanical strength. The constant temperature conditions are set to 170°C for 60 minutes. The micrograph of the woodpile structure is as follows Figure 2 (c) shown, Figure 3 The photos are of the woodpile structure samples before and after constant temperature treatment.

[0059] Example 4:

[0060] A PVDF gel slurry doped with barium titanate powder is prepared for direct writing printing of a three-dimensional lattice structure. The mass fraction of barium titanate and PVDF powder in the slurry is 10% and 30%, respectively, as follows:

[0061] (1) 20 ml of deionized water is measured into a 50 ml beaker and kept in an ice water bath with stirring. 9.4 g of poloxamer powder is weighed and gradually added to the deionized water. The ice water bath is kept stirring at a speed of 300 rpm. After 1 hour of stirring, the solution is transferred to a refrigerator for 8 hours of cold storage. The upper white foam is removed, and the lower transparent poloxamer solution is collected as the gel matrix.

[0062] (2) 8 g of poloxamer gel matrix, 4 g of PVDF powder, and 1.33 g of barium titanate powder are weighed and mixed under ice water bath stirring at a speed of 400 rpm. After 1 hour of stirring, the mixture is transferred to room temperature for stirring until the gel is formed. The gel is filled into a cartridge for centrifugal defoaming to obtain a direct writing gel slurry. The centrifugal defoaming process is set to a speed of 2700 rpm for 10 minutes. A stainless steel needle with an inner diameter of 0.51 mm is selected for printing at a pressure of 0.6 MPa and a printing speed of 270 mm / min.

[0063] (3) The printed gel structure is dried in a constant temperature drying oven to allow the polymer powders to melt and bond, forming a printed structure with mechanical strength. The constant temperature conditions are set to 170°C for 1 hour, Figure 4 The photos are of a printed sample without barium titanate powder (left) and a printed sample doped with 10% mass fraction of barium titanate (right).

[0064] The above examples are for reference only. Methods for preparing polyvinylidene fluoride three-dimensional structures by direct writing of a gel, which are similar to or extended from the ideas of the present patent, are also within the scope of protection of the present patent.

Claims

1. A gel slurry characterized in that: The gel slurry is formed by dispersing polyvinylidene fluoride-based material and filler in a poloxamer hydrogel matrix; the preparation raw materials of the gel slurry are polyvinylidene fluoride-based material, filler, poloxamer and water; wherein: the weight content of polyvinylidene fluoride-based material is 10% to 50%, the weight content of filler is 0% to 20%, the weight content of poloxamer is 10% to 40%, and the balance is water; The filler is one or more of ceramic powder, conductive material and microporous template material; the ceramic powder is barium titanate, lead zirconium titanate or titanium dioxide, the conductive material is nano-silver, graphene or carbon nanotube, and the microporous template material is cellulose, paraffin or water-soluble salt.

2. The gel slurry of claim 1, wherein: The polyvinylidene fluoride-based material is pure polyvinylidene fluoride powder, or the polyvinylidene fluoride-based material is polyvinylidene fluoride copolymer powder; the polyvinylidene fluoride copolymer is poly(vinylidene fluoride-trifluoroethylene) or poly(vinylidene fluoride-hexafluoropropylene).

3. The method of claim 1, wherein: The method is to blend the preparation raw materials of the gel slurry, i.e. polyvinylidene fluoride-based material, filler, poloxamer and water, at a temperature of 0℃ to 4℃, and specifically includes the following steps: (1) Preparation of poloxamer hydrogel matrix: Disperse and dissolve poloxamer into water under the condition of ice bath and continuous stirring, and store the formed gel in a cold storage until the gel becomes completely transparent and the upper layer of foam is removed to obtain the poloxamer hydrogel matrix; (2) Disperse polyvinylidene fluoride-based material and filler powder into the poloxamer hydrogel matrix obtained in step (1) in proportion, and stir at low speed under ice water bath condition for 1-3h, then transfer to room temperature for magnetic stirring until gelation; finally, defoam or deaerate to obtain polyvinylidene fluoride gel slurry.

4. The method of claim 3, wherein: In step (1), the continuous stirring time is at least 1h, and the stirring speed is controlled within 400rpm; the cold storage temperature is set to 0℃ to 4℃.

5. Use of the gel paste according to claim 1 in direct writing without a mold, characterized by the fact that: The gel slurry is applied to moldless direct writing to prepare a three-dimensional structure, specifically, after filling the gel slurry into a barrel and performing vacuum defoaming or centrifugal deaeration, installing and fixing a direct writing needle, adjusting appropriate air pressure, and printing the required three-dimensional structure on a substrate by moldless direct writing.

6. Use of the gel paste according to claim 5 in direct writing without a mold, characterized by: The inner diameter of the printing needle nozzle is 0.2-0.6mm, the printing layer height is 0.2-0.32mm, the printing speed is 270-900mm / min, and the printing air pressure is set to 0.25-0.60MPa.

7. Use of the gel paste according to claim 5 in direct writing without a mold, characterized by the fact that: Place the printed three-dimensional structure in a constant temperature drying oven for constant temperature drying treatment to obtain a PVDF structure with good mechanical strength and flexibility; the constant temperature temperature is set to 150℃ to 180℃, and the constant temperature time is set to 30-90min.

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