Preparation and application of polyurethane mould adhesive
People have been using moulds since they had written records. The earliest use of the mold was the ancient Egyptians, dating back thousands of years. After many years of application, people found, many materials can be used to die from practical experience such as sand, wax, wood, plaster, metal, and plastic, rubber and other natural and synthetic polymer materials such as polyurethane cushion.
For today's mold manufacturing industry, although some materials are still in use, more and more functional polymer materials have brought unprecedented prospects for development. Emulsion, epoxy resin, unsaturated polyester resin, application, polysulfide rubber, silicone rubber, polyurethane material has gained popularity, because these materials have good repeatability in processing, and good tensile strength and elongation, and materials with low cost, simple production process, so they are ideal die material.
In these materials, because of the difference in performance, it also has different disadvantages in mold application.
Latex is a kind of natural rubber extracted from rubber tree. It has good wear resistance, resilience and elongation. It can be used as mould glue after processing. Latex may also be the earliest use of mold materials. However, the use of latex manufacturing mold more trouble, in order to achieve the required thickness and tensile strength of the mold, the general latex mold should be painted about 1 times 20, and each brush to dry about 4 hours. In that case, it would take about a week to make a latex mold. And some latex products, there is still a certain amount of ammonia. The mold made of lower hardness, is not conducive to stereotypes.
Polysulfide materials used in the manufacture of molds are generally two-component. The utility model has the advantages that the mould made of the material has good flexibility and is suitable for producing products with fine grain, and the utility model is convenient to use. The disadvantage is poor wear resistance, and there is a certain odor, poor pollution resistance.
Silicone rubber is the most widely used material in the field of mold. Silicone rubber mold material is also used in two-component form. Mold manufacturing methods can be brushed, can also be poured. Can be cured at room temperature in the presence of catalyst product has low hardness, resistance to chemicals has very good performance and high temperature performance (the highest up to 250 DEG C) 2. The most valuable is the mold mold made of silicone rubber is very good, do not need to mold internal pre coating demoulding agent, so can be suitable for a variety of resin casting, instead of pouring products after surface cleaning. Good chemical resistance and high temperature resistance also allows silicone molds to be used in the casting of some low melting point metal mixtures. But the high viscosity silicone rubber material, must be vacuum defoamation treatment before use, to prevent the surface defects of products caused by bubbles. In addition, the price of silicone rubber material is higher.
Polyurethane material is a kind of macromolecule material developed in recent years. Because of its wide range of raw materials, formulations and processing methods varied, adjustable range, performance ranging from plastic to rubber materials, the entire range of 3, so it is one of the fastest growing materials in recent years.
With polyurethane material, the mold is also divided into two components, which can be brushed or poured, and also can be sprayed according to the construction needs. The hardness of the die can be adjusted easily, ranging from Shaw's A15 degrees to Shao's D85 degrees. The viscosity of the material is low, without pre deaeration treatment, easy to use, the price is lower than the silicon rubber material. The disadvantage is that the adhesion of polyurethane material is very good, the mold should be pre - painted release agent, will not cause the pouring of products adhere to the mold. In addition, because polyurethane material is very sensitive to moisture, it is necessary to avoid the influence of moisture in the air on the polyurethane material. Otherwise, the product will react with moisture during the curing process to produce bubbles.
Here we simply introduce a mold that can be used to make polyurethane mold.
I. raw materials
1.B component (isocyanate component)
Polyether diol (molecular weight 1000) 75
Polyether diol (molecular weight 2000) 85
Polyether three yuan alcohol (molecular weight 3000) 85 parts
56 parts of toluene diisocyanate
Two methylene diphenyl diisocyanate 35 copies
2.A component (polyol component)
Polyether diol (molecular weight 2000) 68
Polyether three yuan alcohol (molecular weight 1000) 12 parts
Two chlorine - two amino group, two benzene methane 15 parts
2 copies of catalyst
Two, mold adhesive production
The prepolymer of -NCO group was prepared by reaction of polyether polyol with isocyanate and dehydration at high temperature. The percentage content of NCO group was analyzed and sealed.
The two chloro two amino two phenyl methane in the formula is dissolved in polyether polyol, and the auxiliary agent and catalyst are adopted to seal.
Three, mold production
1., to deal with the surface of the model, painted release agent, it is best to dry, avoid moisture caused by the mold glue curing bubble.
2. put the model in the container, put it in place and fix it. Release the release agent carefully in the container.
3. weigh the A and B components in a certain proportion (as accurately as possible) and mix them. Stir evenly, pay attention to the stirring process, try to avoid producing more bubbles.
4., the mixing of good glue into the container, dumping attention, it is best to inject from the side of the container, so that it naturally flows to the other side, or from the bottom of the container flowing to high-end.
5. fill the container (or when required) and stand still for 1~2 hours