Natural stone is widely used in the home decoration industry. However, in recent years, due to the over exploitation of stone mine resources, the ecological environment has deteriorated and water and soil loss has been caused. Therefore, some countries control the development of natural stone resources and stop deforestation. Nowadays, Faux Stone Wall has become a new field to be researched and developed in the home decoration materials industry. In many traditional application fields of stone, such as wall panels, exterior walls of houses, simulation walls for interior decoration, garden landscape, cultural stone, etc., Faux Stone Wall has partially replaced natural stone. Most synthetic artificial stones can be nailed, planed and sawed. Their appearance and feel are similar to those of natural stones. They are also moisture-proof, moth proof and flame-retardant.
The raw materials used for the synthesis of Faux Stone have many different ingredients, which are generally molded with inorganic or organic fillers and adhesives. Polyurethane is common, and the organic filler is natural fiber (straw, straw and other straw, grass, hemp, bamboo silk and other agricultural and sideline products) Inorganic fillers include calcium sulfate, stone powder, etc. The comprehensive utilization of plastic instead of stone, especially waste, can save natural resources and protect resources and environment.
A few Faux Stone panels are polyurethane rigid foam products, and then through surface coating or molding process, their appearance has the typical texture and structure of lifelike natural stones, which can be used as wall decoration materials.
Polyurethane structural foam is a kind of medium and high density microporous material developed in the mid-1970s. Because it has high rigidity and mechanical strength. With simple forming process, high production efficiency and beautiful appearance, the Pu Faux Stone Wall siding can be used in various wall decoration industries instead of natural stones, which is deeply welcomed by users. With the progress of new polyurethane raw materials and the demand for natural stone substitution, the Pu Faux Stone Wall siding has developed rapidly in the housing decoration wall panels and other industries recently.
Polyurethane stone, or polyurethane synthetic stone, is a kind of medium and high-density structural rigid polyurethane foam (referred to as polyurethane rigid foam for short) from the perspective of polyurethane materials. It has a micro cell structure and has a much higher density than the conventional rigid polyurethane foam for thermal insulation. The density is usually higher than 0,2g/cm3 (200kg/m3), and the density of special foaming wallboard can also be lower than this value: the polyurethane foam of synthetic stone can produce a dense and tough surface layer through different combinations of mold and foaming process, belonging to the whole skin (or self skinning) rigid foam. The dense skin makes this synthetic material not only have realistic stone appearance and high density, but also have high strength and are not easy to scratch. The core or the part below the surface of faux stone wall can achieve low density, which can reduce the weight of the workpiece and have high overall strength: high compressive strength, tensile strength, impact strength and bending strength.
Of course, due to the anisotropy of the strength of polyurethane foam in the foaming direction in the mold, the longitudinal and transverse strength of the internal foam core of the large-scale simulated stone panel are different, but the hard skin of the whole skin rigid foam products can eliminate these differences; The lower density polyurethane Faux Stone Wall has the advantages of high thermal insulation performance of polyurethane rigid foam; In order to obtain high strength, the simulated stone used in high load-bearing occasions can be reinforced with glass fiber or natural fiber in addition to properly increasing the density, so as to double the bending strength; Rigid polyurethane foam has closed cell structure, poor air permeability and low water absorption.
Compared with natural stones, polyurethane Faux Stone panel has the obvious advantage that it can mass produce various shapes through mold design and molding, especially the typical natural stones with carved patterns, which are lifelike in shape. Stone wallboard products have excellent repeated molding performance, simple molding process, time saving and high efficiency; Good processing performance, planing, sawing, nailing and drilling; It has excellent acid and alkali resistance and corrosion resistance. In addition, it is generally necessary to add flame retardant in the manufacturing process, so the material has flame retardant performance; If the color paste of the required color is added during manufacturing, the Pu Faux Stone can be prepared without paint.
Faux Stone is a polyurethane rigid foam structure, which can be divided into three categories according to the density: the products with a density of 150-400kg/m3 are mostly used for non bearing heavy decorative materials, such as imitation wood carving decorative strips, decorative plates, Roman column carvings and other handicrafts on buildings, and the load-bearing structural synthetic wood with a density of 400-600kg/m3 can be used for manufacturing Faux Stone Wall, imitation cultural stones, tables and chairs, industrial supports, cabinets, sofa legs, and oil picture frames, Mirror frames, doors, windows, flower pots, toilet appliances, etc. The whole skin hard foam with a density of more than 600kg/m3 and medium and high density reinforced hard foam materials can be used to manufacture automobile door panels, battery boxes, trunk covers, railway sleepers, home appliance shells, and snowboards. Sleigh, golf club, etc.
The PU foam Faux Stone Wall is a kind of medium and high-density rigid polyurethane foam. Like ordinary rigid polyurethane foam, this kind of rigid polyurethane foam is a two-component raw material system Among them, the composite polyether component (white material) is also based on polyether polyols with multi-functional and high hydroxyl value, and is equipped with catalysts, foaming agents, homogenizing agents, flame retardants and other additives. The isocyanate component is generally coarse MDI, that is, Papia (polymethylene polyphenyl polyisocyanate) or coarse MDI containing modified MDI, and the functional degree is about 2.5
Foaming agents used in polyurethane foaming process can be divided into physical foaming agents and chemical foaming agents. Physical foaming agents are low boiling point compounds, such as cfc-11 HCFC-141B. Cyclopentane, the chemical foaming agent, is generally water. For wood like objects, the thermal conductivity is not a factor to be considered. High density rigid foam can be prepared without using physical foaming agent. However, it is also necessary to control the water content brought in by polyether polyols. Excessive water content may reduce the density and strength of products, and may cause core burning and cracking of foam due to the difficult control of heat release from the reaction between water and isocyanate.
During the preparation of Faux Stone panel, the dosage of foaming agent (including water) should be adjusted according to the product density requirements and whether a dense skin is required, and then determined through the molding foaming test.
Adding physical foaming agent can reduce the viscosity of combined polyether, improve the fluidity of foaming material, adjust and control the density and performance of foam products, and form a dense Faux Stone Wall siding skin. The principle of manufacturing self skinning or whole skin rigid foam is: when forming in a closed mold cavity, the exothermic reaction of foam increases the temperature of the material, but the temperature of the material close to the mold is low, and the low boiling point foaming agent condenses due to the pressure effect, so that the skin has no bubbles. The foam near the skin is also extremely fine and has a high density, thus forming a density gradient from low core density to high skin density.
In the production of polyurethane foam Faux Stone Wall siding, the selection and addition of catalysts are very important. The selection of different types and quantities of catalysts can effectively regulate the flow, foaming and gel process of materials For molding production, the catalyst with moderate reaction speed, long milky time and fast later curing speed should be selected. Even if the material has strong flow capacity during foaming, it can be cured quickly after filling the mold, with short demoulding time and improved production efficiency. Generally, composite delayed amine catalyst is used.
As a Faux Stone for home and decoration, flame retardant must be added and used to obtain good flame retardant performance. The compatibility between solid powder flame retardant and composite polyether is poor, which greatly increases the viscosity of the material, and has a certain wear effect on the metering pump of high-pressure foaming machine, so it is rarely used. Liquid phosphorus flame retardants, including halogenated phosphate flame retardants and other commonly used flame retardants for polyurethane foam, can be used. Dimethyl methylphosphonate (DMMP) with high phosphorus content has the best flame retardant effect, and the oxygen index can reach more than 26 when the addition amount is 4.5% - 5.0%. Low viscosity liquid flame retardant can significantly reduce the viscosity of the composite polyether. But at the same time, it has plasticizing effect on the products. Excessive use not only does not significantly improve the flame retardant performance, but also reduces the hardness and strength of the materials.
In addition, in order to obtain higher strength, glass fiber and other materials can be used to manufacture reinforced structural foam, so that the simulated stone has higher toughness and load-bearing performance.
Pu Faux Stone is generally produced by molding process, and some are produced by reaction molding (RIM) or reaction injection molding (RRIM), so the fluidity of materials is very important. The viscosity of the two components should not differ too much, otherwise there will be a deviation in the ratio of machine foaming, and the material mixing may not be very uniform.
Generally, the density of free foaming foam is lower than that of molding foaming. If physical foaming agent is used for polyurethane foam Faux Stone Wall, and the mold temperature is lower than the reaction material temperature, the mold limits the excessive expansion of foam, resulting in a certain pressure in the mold cavity. Therefore, there is a high to low density gradient from surface to core. If the filling coefficient is intentionally increased, and the amount of foaming agent and mold temperature are adjusted, the smooth and dense full skin foam of Faux Stone Wall is prepared. Polyurethane Faux Stone panels mostly adopt this whole skin foaming technology. The whole skin hard foam has high-density hard skin layer and low-density foam core. For the same raw materials, the higher the filling coefficient, the higher the density of the epidermis and nearby, forming a thick hard surface layer, with dense surface, higher overall density and higher strength of the material. In the actual production of Faux Stone Wall, the material filling factor should be selected according to the product use and density requirements. The filling coefficient should not be too high, otherwise the foaming pressure is too large. High pressure resistance requirements for moulds.
Both low-pressure foaming machine and high-pressure foaming machine can be used in the production of imitation stone. First, the materials must be mixed evenly. For manual foaming test and low-pressure foaming production, the mixing speed must be high enough. For high-pressure machine, a certain injection pressure must be reached to make the materials impact and mix evenly. It needs to be injected into the mold before the material starts to whiten. The material temperature affects foaming parameters such as milky time and gel time, and also affects the fluidity of the material, so it must be controlled stably; Mold temperature also affects foaming parameters, as well as skin quality and skin thickness of the product. Lower and appropriate mold temperature can reduce irregular bubbles on the surface of the product. A smooth, bubble free shell was obtained.
For large Pu Faux Stone Wall siding, open mold pouring is adopted for production, and mobile mixing head is used. Firstly, the parts with complex patterns and deep cavities are poured. Minimize the material flow distance and fill the mold. Small products should be poured by closed mold, and can be produced by RIM process of high-pressure foaming machine.
The design of the mold shall comply with the general principles of polyurethane foam products, such as the mold shall have sufficient pressure resistance, smooth surface, design demoulding slope and fillet, avoid dead corners of material flow, and set exhaust holes with reasonable location and size. For the production of Faux Stone, metal molds are generally not used, because the metal molds are bulky, inconvenient to operate, and the surface effect is poor, making and updating molds is expensive and time-consuming. Resin mold has the characteristics of fast turnover, simple process, clear turnover stone texture and realistic pattern, which can well meet the needs of the market and facilitate the timely launch of new products. According to practical experience, the best material for making molds with fine patterns is silicone, and molds made of epoxy resin can also be used. Silicon resin mold is used to produce simulation stone, which is well formed without spraying release agent.
If reinforced materials are used to produce special simulated stone products, the reinforced reaction injection molding process can be followed. The glass fiber felt can be put into the mold in advance, and short glass fiber or other reinforcement materials can also be added. It is necessary to add reinforcing fillers to reduce the fluidity of materials to ensure the yield of products.
Polyurethane Faux Stone is a kind of synthetic resin with excellent properties. Due to the diversity of raw materials and formula combinations of polyurethane materials, the performance of faux stone wall can also be designed and adjusted according to specific uses. The polyurethane structural rigid foam can be molded into some concave convex stone shapes from liquid raw materials, and the Faux Stone carving products can be mass produced. The molding process is simple. It can also be reinforced with glass fiber to make high-performance composite products. The popularization and use of this kind of imitation stone material can not only obtain beautiful and practical imitation natural products, but also achieve the purpose of saving natural stone resources and protecting the ecological environment.
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