Raw material for molding

The commonly used molding materials are mainly composed of resin matrix, reinforcing materials, fillers, pigments, etc., and according to the process and performance requirements, the resin matrix is also added with curing agent, thickener, internal release agent, solvent and other additives. Reinforcement material is the skeleton material of die pressing material, which mainly endows die pressing material with excellent mechanical properties and prevents the propagation of micro-cracks. The main varieties of reinforcement materials are various glass fiber felt, no twist roving, no twist coarse gauze, chopped fiber, ground fiber, glass yarn and fabric and other varieties of fiber. The main function of resin matrix in molding material is to bond the reinforcing material and filler together, which not only protects the reinforcing material, but also makes it uniform force under external load. Theoretically, most types of thermoplastic and thermosetting resins can be used as resin matrix materials. There are polyester resin, epoxy resin, amino resin and phenolic resin. A large number of various types of fillers are used in the molding material, the main function of which is to reduce the material cost, improve the process, improve the molding material some physical properties, appearance and give some characteristics. Fillers are mostly in powder form, such as clay, calcium carbonate, talcum powder and some fillers with special performance requirements.

 

The basic requirements of resin in molding are as follows: good infiltration performance of reinforcing materials and fillers to improve the bonding strength between resin and glass fiber; Resin to have the appropriate: viscosity, good fluidity, so that in the molding process of resin and glass fiber at the same time full of all corners of the cavity, to obtain a balanced strength of the molding products; Resin curing temperature is low, less volatile in the curing process, good technology (such as viscosity easy to adjust, good solubility with various solvents, easy to release mold, etc.), and can meet the mold products specific performance requirements. In addition, from the point of view of application or other point of view, the resin should also meet some other special performance requirements, such as corrosion resistance, heat resistance and so on. From the perspective of production efficiency, fast curing speed of resin is required, but for some large products with complex structure and higher requirements, the curing speed should be properly controlled. Resin curing after high mechanical strength, good toughness, avoid from the mold when taken out, in the case of bending cracking or breaking. Therefore, the selection of resin, will become a very important factor affecting the whole process.

 

Molding products are commonly used in thermosetting resin, thermoplastic resin in the molding process of the application of less. The main thermosetting resins are phenolic resin, epoxy resin, epoxy phenolic resin, polyvinyl butanal resin, unsaturated polyester resin, etc.

 

 

 

 

 

The molding process of the press automatic Moulding Machine

Is moulded plastic processing and molding the application in the city one of the oldest technology. It has a mature production technology, equipment and mold is simple, easy to forming large products, can use multiple modes to improve the production of small parts, etc, in machinery, electronics, transportation and daily life, and many other fields has been widely used.

 The market will often see a lot of kinds of Press Moulding Machine, for example: Polymer/PTFE Push press Automatic Moulding Machine, Polymer/PTFE Flange press Automatic Moulding Machine, Polymer/PTFE gasket automatic Moulding Machine, Semi-automatic Molding Machine and so on.

 Molding is widely used in the following fields:

Electrical: insulator, switch box, electrical equipment housing, insulation tools, wiring board, etc.

Automobile: lamp shade, front and rear bumper, battery bracket, engine soundproof board, etc.

Railway: window frame of vehicle, toilet components, seats, table tops, siding and roof of carriage, etc.

Construction: water tank, bath products, door panels, purification tank, building template, etc.

Bathroom: bathtub, integral bathroom equipment, integrated wash basin, etc.

And other areas of industry and agriculture.

 Molding technology is a method of putting quantitative molding materials (powder, granular or fibrous plastic) into the metal mold and forming products under the action of temperature and pressure. During the molding process, heat and pressure are required to melt (or plasticize) the molding material, fill the mold cavity with flow, and make the resin solidify. The principle is that the process of pressurizing, shaping and heating depends on the closure of the heated mold.

 Moulding Machine technology is the oldest molding method in plastic processing technology. Because of its long history, the molding technology has been quite mature, at present in thermosetting plastics and some thermoplastic plastics (fluoroplastics, uhmwpe, polyimide, etc.) processing is still the most widely used and the main position of the molding method. Moulded thermosetting plastic, placed in the cavity of the thermosetting plastic under the action of heat, first changed from solid to melt, melt flow under pressure with the shape of the cavity and cavity has given, as the crosslinking reaction, resin molecular weight increased, the curing degree rise, moulding material viscosity increase gradually and becomes solid, finally becomes demoulding products. Thermoplastic plastic mold pressure, in the previous stage of the situation and thermosetting Plastic the same, but because there is no cross-linking reaction, so in the flow of full cavity, the mold must be cooled to make its molten plastic into a solid with a constant strength can be demodulated into products. Because thermoplastic plastic mold pressing mold needs to alternately heating and cooling, production cycle is long, so thermoplastic products generally choose injection molding method more economic, only in the mold larger plane of Plastic products or because of the flow of thermoplastic plastic injection molding method is difficult to use molding.

 In the mold press material filled with the mold cavity flow process, not only the resin flow, the reinforcement material also to flow, so the mold press molding process molding pressure is higher than other process methods, belongs to the high pressure molding. Therefore, it needs not only the hydraulic press which can control the pressure, but also the high strength, high precision and high temperature resistant metal die.

 

Study on hydrophilic modification of ptfe microporous membrane

 

At present, water pollution and water shortage have seriously threatened people's life safety. For a long time, the treatment of water pollution has been the focus of environmental protection. Membrane technology has been one of the mainstream treatment methods because of its green environmental protection, sustainability, rapid and efficient separation process and other advantages, and has achieved good results. PTFE microporous membrane material has been concerned and studied by international scholars for its excellent chemical resistance, high porosity and good mechanical properties. However, PTFE microporous membrane has the characteristics of low surface energy and high hydrophobicity, which greatly limits its application in the field of water treatment. Therefore, improving the hydrophilicity of PTFE microporous membrane has become an important research direction.

 

In this paper, polyvinyl alcohol (PVA) and chitosan or oxycarboxymethyl chitosan were used as hydrophilic agents. Different crosslinking agents were used to wrap a hydrogel hydrophilic coating on PTFE microporous membrane fiber through crosslinking reaction, so as to realize the hydrophilic modification of PTFE microporous membrane.

 

Specifically, the following two parts of the study were carried out:

(1)     polyvinyl alcohol (PVA) with good hydrophilic property and chitosan (CS) with good antibacterial property were selected as materials to modify PTFE microporous membrane by combining hydrogel coating formed by epichlorohydrin crosslinking with SiO2 nanoparticles in situ under alkaline conditions.

The experimental results showed that the fiber surface of modified PTFE microporous film was coated with a layer of hydrogel, and the hydrogel coating attached a large number of solid particles to the node, which improved the surface roughness and reduced the average pore diameter and porosity slightly. Hydroxyl and amino groups appeared on the surface of modified film. New elements N,O,Si appeared on the surface of modified membrane. With the increase of PVA solution concentration, the water flux of the modified membrane first increases and then decreases, and the contact Angle of the membrane surface first decreases and then tends to be stable. With the increase of reaction time, the water flux of the modified membrane first increased and then decreased. With the increase of reaction temperature, the water flux of the modified membrane increases first and then decreases, and the contact Angle of the membrane surface decreases first and then increases. The optimal reaction conditions are :PVA solution concentration is 1wt%,CS solution concentration is 0.3wt%, the mass ratio of CS solution to PVA solution is 1:1. The reaction time is 6h, the reaction temperature is 40℃, the reaction pH is 12, and the water dilution ratio in the secondary treatment is 45 times (PBA:SiO2=1:2.5).

The contact Angle of hydrophilic modified PTFEmicroporous membrane decreased from 136° to 48°, and the pure water flux reached 3172L·m-2·h-1.The experimental results of oil in water emulsion separation of hydrophilic modified PTFE microporous membrane show that the hydrophilic modified PTFE microporous membrane has good anti-oil properties and oil retention rate of 97%.The physical and chemical stability of hydrophilic PTFE microporous membrane shows that the hydrophilic PTFE microporous membrane has good acid resistance and washing resistance.

 

(2) PTFE microporous membrane was modified with polyvinyl alcohol (PVA) and oxygen carboxymethyl chitosan (OCMCS) by crosslinking with glutaraldehyde under acidic conditions.

The results showed that the fiber surface of PTFE microporous membrane was covered with a hydrogel coating, and the surface of PTFE microporous membrane still retained the original three-dimensional network structure. Hydrophilic hydroxyl and amino groups appeared on the surface of PTFE microporous membrane. With the increase of PVA content in the reaction solution, the water flux of the modified membrane increases first and then decreases, and the contact Angle decreases first and then increases. With the increase of reaction temperature, the water flux of modified membrane increases first and then decreases, and the contact Angle decreases first and then increases. With the increase of reaction time, the water flux of modified membrane first increases and then decreases, and the contact Angle first decreases and then increases.

The optimal experimental conditions were as follows: mass ratio of OCMCS/PVA was 1:1, the amount of 5wt% glutaraldehyde and 1wt% hydrochloric acid solution was 2.5ml and 1mL, the reaction time was 6h, and the temperature was 50℃.The ptfe-pva /OCMCS membrane prepared has a larger water flux of 4480.89L·m-2·h-1 and a contact Angle of 57.48°.The anti-pollution test results of PTFE microporous membrane with hydrophilic modification showed that ptfe-pva /OCMCS membrane had good anti-bsa adsorption ability. The results of long time washing showed that ptfe-pva /OCMCS film had good physical stability.

 

Study on preparation and technology of ptfe hollow fiber membrane

Hollow fiber membrane is widely used in traditional and new membrane separation components such as ultrafiltration, microfiltration, reverse osmosis and gas separator due to its small area, high filling density, high utilization rate, easy to enlarge and easy to clean.In addition, polytetrafluoroethylene hollow fiber membrane has high mechanical strength, acid and alkali resistance, high and low temperature resistance, low friction coefficient on the surface, so it has great potential in special filtration, gas absorption, ozone dissolution filtration, membrane distillation and other fields.PTFE hollow fiber membrane was prepared by using PTFE dispersion resin as raw material and adding exxonmobil Isopar series lubricants through extrusion and stretching molding.

Average extrusion pressure, pore diameter and bubble point pressure, porosity, water flux, contact Angle, SEM and DSC were used to characterize the structure and performance of PTFE hollow fiber membrane.The experiment mainly discusses the influences of lubricants (types and ratios), extrusion process (compression ratio, length-diameter ratio and cone Angle) and tensile sintering process on PTFE structure and performance, and optimizes the process parameters to provide guidance for PTFE hollow fiber membrane production.

Specific research contents are as follows:

(a)     the experiment changed the lubricant parameters (including the type and ratio of lubricants) and prepared PTFE hollow fiber membrane through the process route of "mixing → pre-molding → extrusion → stretching → sintering → natural cooling".The experiment explored the influence of lubricant type and ratio on the structure and performance of PTFE hollow fiber membrane, and obtained the best combination of lubricant type and ratio and optimized lubricant.

(b)     by changing the parameters of extrusion process molds, the influences of RR, L/D and alpha on extrusion pressure, membrane fracture strength, average pore diameter, bubble point pressure, porosity and water flux were explored to obtain the best extrusion parameters.

(c)     By adjusting the tensile process parameters (tensile multiple and tensile temperature) and sintering process parameters (sintering temperature and sintering time), the influences of tensile sintering process on the average pore diameter, bubble point pressure, porosity and water flux of PTFE hollow fiber membrane were explored to obtain the optimal tensile sintering process parameters and optimize the tensile sintering process.

 

Experimental results show that:

 

(1)     PTFE hollow fiber membrane has small average pore diameter, high bubble point pressure and porosity, large water flux fracture strength and contact Angle, and low extrusion pressure in the extrusion process.When the lubricant content is too high or too low, the structure and properties of PTFE hollow fiber membrane will be adversely affected to some extent.

(2)     When RR=185, L/D=20, and alpha =40°, the extrusion pressure is low, the fracture strength is large, the average pore diameter is small, the bubble point pressure is high, the porosity is large, and the water flux is high, which can be used as the extrusion process parameters of excellent PTFE hollow fiber membrane.

The influences of tensile and sintering processes on the microstructure and properties of PTFE hollow fiber membrane are as follows: with the increase of tensile multiple, the average pore size and porosity of PTFE hollow fiber membrane are large, the bubble point pressure is small, and the water flux is large.With the increase of tensile temperature, the average pore diameter and water flux of PTFE hollow fiber membrane increase, the porosity increases, and the bubble point pressure decreases.With the increase of sintering temperature, the pore diameter, bubble point pressure and water flux of PTFE hollow fiber membrane decrease, and the porosity has no obvious change rule.With the increase of sintering time, the average pore diameter, porosity and water flux of PTFE hollow fiber membrane increase, and the bubble point pressure decreases.

The drawing process significantly reduces the crystallinity of PTFE products, while the sintering process further reduces the crystallinity of PTFE products.When the tensile multiple is 100%, the tensile temperature is 300℃, the sintering temperature is 320℃ and the sintering time is 5min, the average pore diameter of hollow fiber membrane is small, and the bubble point pressure, porosity and water flux are large.