Formula, raw materials, process and manufacturing technology of polyurethane plate

1. Types of polyurethane plates

In terms of building board, polyurethane board can be divided into ordinary polyurethane board and composite polyurethane board according to the product condition; According to the foaming process, it can be divided into continuous plate and intermittent plate.

Intermittent sheet requires that the foaming material should fill the thin large-volume mold cavity in a short time, and that the foaming system should have excellent activity, good density distribution and excellent dimensional stability. The continuous sheet requires that the foaming parameters have a proper match with the production line speed, and that it has excellent demoulding property in the later stage.

2. Features

2.1 Stability

Light weight, high strength and good dimensional stability.

We produce intermittent plates, and the foam properties of rigid polyurethane foam are tested after one week of curing. The foam properties are shown in Table 1.

2.2 Strong adhesion

Polyurethane rigid foam has good bonding strength to metals such as steel, aluminum and stainless steel, and most plastic materials such as wood, concrete, asbestos, asphalt, paper, polyethylene and polypropylene. The adhesive strength between foamed plastics and surface materials directly affects the practical effect of composite plates.

2.3 Excellent thermal performance

Polyurethane rigid foam has high closed cell rate and extremely low thermal conductivity, so polyurethane rigid foam has the best thermal performance among current building materials. The data show that the heat collection cost of the operation can be reduced by 60% compared with that of the external wall without thermal insulation. Taking the composite of steel plate and rigid polyurethane foam as an example, the thermal conductivity of the composite plate is listed in Table 3.

3. Production and technology

3.1 Intermittent Plate

3.1.1 Production of Injection Plate

This manufacturing method is injection molding in a mold, which is an intermittent processing method. The metering pump in the foaming machine pumps two components of polyurethane into the mixing head, and after mixing evenly, the raw materials are injected into the mold cavity through the injection hole of the mold. The cavity of the mold has been pre-placed with face material. After foaming and curing, the plate can be taken out of the mold.

The advantage of this processing method is that the equipment is simple and it is suitable for multi-variety production. According to the needs of application, plane or concave-convex surface materials are selected as the surface layer of composite plates, which can also be applied. When this method is used to produce plates, we should pay attention to adjusting the parameters of foaming time. For plates with different lengths, we should choose different formulas to meet the requirements of the forming process of plates with different specifications. For plates with longer lengths, it is very important to adjust the formulas. When producing plates, the two components of raw materials must be completely filled in the mold cavity before they can gel, otherwise, it is difficult to make products with uniform foam density. If the gel solidifies too fast, it may cause the filling density near the injection port to be too high, and the filling density far away from the injection port to be insufficient, resulting in the cavity. At this time, it is particularly important to adjust the formula of polyether composition.

3.1.2 Selection of raw materials

The isocyanate (PAPI) component is yantai wanhua PM-200, which is fixed. With the increase of PAPI content, the crosslinking degree of foam increases, and its strength and stiffness also improve. However, if PAPI content is too high, the foam will become brittle and the core material will easily crack.

Firstly, it is most important to choose polyether polyol, which is one of the basic raw materials for polyurethane rigid foam, and it affects the physical and mechanical properties, dimensional stability and foaming process performance of foam core material. After determining the polyether model according to the initiator, hydroxyl value and viscosity, the content of potassium ions in polyether is low.

It is advisable to choose foam stabilizer with strong emulsifying ability. It mainly controls the cell size, maintains the cell stability and prevents the cell collapse. Silicone ketone foam stabilizer has a good effect on this, and its dosage can be adjusted within 1.5 ~ 2.5 (mass fraction)

The kind and dosage of foaming agent have a direct influence on the physical properties such as density and strength of polyurethane rigid foam. Foaming agent can not only adjust and control the density and properties of foam products, but also reduce the viscosity of combined polyether, improve its foaming process, improve the activity of foam, and be beneficial to foam molding. Considering the need of sustainable development strategy, the use of CFC, which seriously damages the ecological environment, has been restricted.

11 fluorocarbon compounds, using alternative foaming agents.

The delayed catalytic system can be selected as the catalyst, which can make the interval between milky white time and gel time longer, effectively improve the activity of foaming system and improve foam performance, so as to be suitable for production process control. Factors such as the uniformity of foam in the cavity, the fineness of foam and the closed cell rate of foam have great influence on the overall thermal insulation performance of the board, which are related to the firm adhesion between foam and the cavity wall and the dimensional stability of foam.

Flame retardant can improve the fire resistance of foam plastics, but it can destroy the foam during the foaming process. Under the condition of ensuring the improved flame retardant effect, the use performance and dimensional stability of foam plastics can be guaranteed.

3.1.3 Production of Box-type Thermal Insulation Plate

Using a mold similar to the box-type soft foam production, the combined polyether is delivered to the working kettle of the box-type foaming machine, stirred for a few minutes, then delivered to the foaming stirring barrel, and then delivered to the calculated isocyanate component. After high-speed stirring for 30 seconds, the stirring barrel is lifted and the bottom cover of the barrel is opened at the same time, so that the mixed black and white materials flow into the box-type mold (the mold surface is coated with a release agent or the surface is spread with a polyethylene plastic film), and the mixture is foamed. After standing for 20min minutes, the four side plates of the box can be opened, and the rigid polyurethane foam can be taken out, naturally cured for 24 hours and then cut.

The following aspects should be paid attention to in the production of box-type thermal insulation board rigid foam composition: (1) selecting polyether polyol with high functionality; ⑵ The water quantity should be controlled between 0.1% and 0.5% to avoid foam core burning caused by excessive heat release; ⑶ Control the viscosity of the mixture not to be too large. If the viscosity is too large, use a delayed catalyst to appropriately extend the mixing time and milky time, which is beneficial to the uniform mixing of a large number of raw materials, complete reaction in a large mold and improved activity. ⑷ Under the condition of definite formula, the temperature of raw materials is the main factor affecting the foaming speed. Generally, the material temperature should be controlled at about 15℃. The material temperature is too high, and the reaction speed is too fast. In the case of intense heat release, and the thermal conductivity of polyurethane foam itself is low, the accumulated heat is not easy to spread, and a large amount of heat concentration will cause core burning of foam.

In China, a large number of compartments are needed for cold-storage and heat-preservation vehicles, and the demand is increasing. The main material of the compartments is polyurethane rigid foam. The method of intermittent plate production has always been used in Henan Bingxiong Cold Shelter Factory. With the great progress of the national requirements for the safety and environmental protection performance and service life of sandwich panel products, it is estimated that the demand for polyurethane panels will reach 30 million m3 in the next five years, with a market share of over 60%.

3.1.4 Block cutting and sticking method

Sawing, grinding and other processing methods suitable for woodworking can be used to process block rigid polyurethane foam. Hard foam is processed into a certain shape and size and then adhered to the upper layer material to become a composite plate. Adhesives such as polyurethane, epoxy resin, unsaturated polyester and polyvinyl acetate can all be used to stick hard foam. Be sure to remove the dust left by cutting the hard foam surface before sticking. Vacuum cleaning and powder removal method is more effective. The pressure and heating degree in the sticking process vary with the type of adhesive. Some adhesives contain solvents, and it is necessary to identify whether these solvents will damage hard foam and surface materials in advance. Glass fiber reinforced polyester or epoxy resin can be bonded to foam plastics as surface materials. The advantages of material cutting and sticking method are: the production device is relatively simple, and it is convenient and economical to manufacture curved plates and change the shape and size of plates. Products are usually used as curved parts on buildings, boats and other sports equipment. The disadvantage is that marginal waste is born, which wastes foam plastics, and it is more troublesome to add a pasting process, which consumes more labor.

3.2 continuous plate

Continuous production of composite plates can greatly improve production efficiency. The continuous forming process of horizontal composite board: the foaming machine evenly mixes the raw materials and sends them to the surface material moving at a constant speed for foaming. At the same time, the upper surface material is combined with foam plastic, and the composite board with surface materials on both sides is born. Most of the materials used as surface materials are aluminum foil and metal materials. In the process of foam transmission, the foam is cured in the double-layer pressure panel and cut according to the required length to produce the required specifications of the board.

The thickness of the sandwich panel can be adjusted by changing the interval between the upper and lower metal plate conveyor belts and the thickness of the side sealing blocks. The thickness can be adjusted from 20 to 250 mm, the conveyor belt speed can be adjusted steplessly from 1.0 to 25 m/min as required, and the plate width can also be adjusted from 600 to 1200 mm as required.

In the production of continuous composite forming of plates, the distribution of reaction materials must be uniform. The mixing head simply pours materials back and forth. When the width of the plate is about 1.25m, the production speed is generally limited to 9 ~ 10 m/min. Above this speed, when the mixing head moves and reverses direction, the reaction material is easy to be excessive at the edge of the plate. In addition, the round-trip speed is too high and the operation is not safe. If more than two mixing heads are used to inject materials jointly, the pouring amount of each mixing head can be reduced, but the mixing heads do not move back and forth, and are fixed in the center, connected with a pressing roller or other batching devices that can make the materials distribute evenly quickly. The production process of high-speed continuous composite molding is very sensitive to the temperature and the reaction speed of a foam, especially the polyisocyanurate foam system. In order to weaken the sensitivity, high viscosity polymeric MDI should be used.

At present, there are more than 50 continuous polyurethane sheet production lines in China. Due to the current market demand and other factors, most continuous plate production lines are not running at full capacity. With the increase of market demand and technical update, continuous sheet will become the mainstream production mode in the near future.

4. Conclusion

To sum up, rigid polyurethane foam is a kind of building energy-saving and thermal insulation material with excellent comprehensive performance. Polyurethane board can be divided into two ways according to the production process, one is intermittent board and the other is continuous board. In the application process, intermittent plate production technology is simple to operate and low in cost, which is widely used in China; The continuous plate is widely used in central air conditioning cold air duct and other fields, but the equipment investment is huge, and the research and development efforts need to be strengthened from the aspects of formula, raw materials, technology and manufacturing, and obvious progress has been made in recent years.

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