LOW-E glass

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Low-E glass, also known as low emissivity glass, is a film product consisting of multi-layer metals or other compounds coated on the glass surface. The coating layer has visible light High penetration and centering infrared The high reflection characteristic makes it Ordinary glass And traditional building Coated glass Compared with, it has excellent heat insulation effect and good Light transmittance 。

Glass It is an important building material Decorative With the continuous improvement of requirements, the use of glass in the construction industry is also increasing. However, when people choose the glass doors and windows of a building today, they pay more attention to its heat control, cooling cost and comfortable balance of internal sunlight projection, in addition to its aesthetic and appearance characteristics. This makes Coated glass Low-E glass, the new rich in the family, stands out and becomes the focus of attention.

Chinese name: Low-E glass
Foreign name: Low emissivity glass
Other Expressions: Low emissivity glass

Interpretation: An Energy saving Glass with Relative Heat Reflective Glass
Production method: two types
Basic color: varied

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performance

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Excellent Thermal performance

Low-E glass

Of exterior door window glass Heat loss It is the main part of building energy consumption, accounting for more than 50% of building energy consumption. of research data It indicates that the glass Internal surface The heat transfer of glass is mainly radiation, accounting for 58%, which means that the most effective way to reduce the heat loss is to restrain the radiation of its inner surface by changing the performance of glass. ordinary Float glass Of Emissivity As high as 0.84, when a layer of silver based low radiation film is plated, its emissivity can be reduced to below 0.15. Therefore, building doors and windows made of Low-E glass can greatly reduce the transmission of indoor heat energy caused by radiation to the outside, and achieve ideal energy-saving effect.

Another significant benefit brought by the reduction of indoor heat loss is environmental protection. CO2 SO2 etc. Harmful gas Emissions are important Pollution source 。 If Low-E glass is used, the fuel consumed for heating can be greatly reduced due to the reduction of heat loss, thus reducing the emission of harmful gases.

The heat passing through the glass is bidirectional, which means that the heat can be transferred from indoor to outdoor, and vice versa, and it is carried out at the same time, which is just a problem of poor heat transfer. In winter, the indoor temperature is higher than the outdoor temperature, so insulation is required. In summer, the indoor temperature is lower than the outdoor temperature, so the glass is required to be insulated, that is, the outdoor heat is transferred to the indoor as little as possible. Low-E Glass can meet the requirements of winter and summer. It can not only keep warm but also insulate heat, and has the effect of environmental protection and low carbon.

Good optical performance

Low-E glass visible light Transmissivity From 0% - 95% in theory (6mm white glass is difficult to do), the visible light transmittance represents the indoor daylighting. outdoor reflectivity From about 10% - 30%, the outdoor reflectivity is visible light reflectance , representing the reflective intensity or dazzling degree. At present, China requires that the visible light reflectance of curtain walls be no more than 30%.

Low-e special cleaning brush for glass

The above characteristics of Low-E glass make it developed country Has been increasingly widely used. China is a country with relatively scarce energy resources, and the per capita share of energy is very low Building energy consumption It has accounted for about 27.5% of the country's total energy consumption. Therefore, we should vigorously develop the Production technology And promote it application area , which will bring significant social results and economic performance 。 During the production of Low-E glass, due to the particularity of material Cleaning machine There are high requirements for cleaning the brush. Brush silk It must be high-grade nylon brush wire such as PA1010 、 PA612 The diameter of the wire should be 0.1-0.15mm. Because the brush wire has good softness, strong elasticity, acid and alkali resistance, and temperature resistance, it can easily remove the dust on the glass surface without causing scratches on the surface.

Application development

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In the United States and Europe, low emission (Low-E) coated glass has received great attention due to its superior performance. In particular, Germany's Wschvo regulations have made Low-E glass develop rapidly.

European manufacturers started in the late 1960s Laboratory research "Low-E". In 1978, Interqane of the United States successfully applied "Low-E" glass to buildings.

The superiority of "Low-E" is unquestionable. Since 1990, the use of "Low-E" has increased at an annual rate of 5% in the United States. In the future, will "Low-E" become the window glass leading role I don't know, but both the owner and the door and window company attach great importance to energy-saving doors and windows. At present, most buildings are evaluated by their energy-saving effects.

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Two current Low-E glasses Production method

Online high-temperature pyrolysis deposition method:

"Low-E" glass produced by online high-temperature pyrolysis deposition method has products from several companies in the United States. For example, Surgate200 of PPG Company and Sunglas H.R "P" of Ford Company. These products are Float glass cooling Process Completed in. Liquid metal Or metal powder Direct injection On the surface of hot glass, as the glass cools, Metallic film The layer becomes part of the glass. Therefore, the film is hard and durable. The "Low-E" glass produced by this method has many advantages: it can Hot bending It is tempered and does not need to be used in the hollow state. It can be stored for a long time. Its disadvantage is poor thermal performance. Unless the film is very thick, its "u" value is only "Low-E" by sputtering method Coated glass Half of. If you want to improve its thermal performance by increasing the film thickness, its transparency is very poor.

Off-line vacuum sputtering

The production of Low-E glass by off-line method is currently widely used in the world Magnetron sputtering coating Technology. Unlike high-temperature pyrolytic deposition, sputtering is off-line. It can be horizontal or vertical according to different glass transmission positions.

To produce "Low-E" glass by sputtering process, a layer of pure silver film is required as a functional film. Pure silver film on the second layer metallic oxide Between membranes. The metal oxide film provides protection for the pure silver film, and acts as the intermediate layer between the film layers to increase the purity of color and light transmission Degrees.

Vertical Production process In the middle, the glass is placed vertically on the shelf and fed into 10-1 Pa Order of magnitude Of Vacuum environment Medium, inject proper process gas（ inert gas Ar Or reaction gas O2 、 N2 ）, and keep vacuum degree stable. take Target material Ag, Si, etc. are embedded in the cathode, and horizontal direction A magnetic field is inserted to form a magnetic control target. Take magnetic control target as cathode, add DC or AC power supply , on high voltage The process gas is ionized under the action of Plasma 。 Among them, the electrons are high-speed under the joint action of electric field and magnetic field Spiral movement Colliding with gas molecules to produce more Positive ion And electronics; Under the action of electric field, positive ions hit the cathode target after reaching a certain energy, and the splashed target is deposited on the glass Substrate A thin film is formed on the. In order to form a uniform film, the cathode target moves back and forth near the glass surface. In order to obtain Multilayers Multiple cathodes must be used. Each cathode moves back and forth on the glass surface to form a certain film thickness.

The horizontal method is similar to the vertical method to a large extent. The main difference lies in the placement of glass. The glass is transmitted by horizontally arranged wheels. Through the cathode, the vacuum degree changes after the glass passes through a series of pin valves. When the glass reaches the main sputtering chamber, the coating pressure reaches, the metal cathode target is fixed, and the glass moves. When the glass passes through Cathode process Medium, film formation.

At present, the target products of the domestic and most of the imported magnetron sputtering coating production lines are solar control film glass, which is mainly used for plating single film and metal film. This kind of product has relatively simple process and low requirements for equipment. Therefore, these production lines cannot meet the requirements of LOW-E plating Glass Requirements.

Sputtering production of "Low-E" glass has the following characteristics:

Because there are many Metal target Selection, and combination of multiple metal targets. Therefore, the sputtering production of "Low-E" glass can have a variety of configurations. In terms of color and purity, Sputter plating Also better than Thermal spraying , and since it is an offline method new product development It is also flexible. The main advantage lies in the "Low-E" produced by sputtering Hollow glass Its "u" value is better than Pyrolysis The "u" value of the product, but its disadvantage is Silver oxide The film is very fragile, so it cannot be like Ordinary glass Same use. It must be made into hollow glass, and it is not suitable for long-distance transportation before being made into hollow products.

Features and functions

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solar radiation 97% of the energy is concentrated in the wavelength range of 0.3-2.5um, which comes from outdoor; For objects below 100 ℃ Radiant energy Concentrated in the long wave band above 2.5um, this part of energy mainly comes from indoor.

If the window is the boundary, in winter High latitude We want outdoor radiant energy Measure in, and do not let out the indoor radiant energy. If the wavelength of radiation is taken as the boundary, the dividing point of indoor and outdoor radiant energy is at the wavelength of 2.5 um. Therefore, it is critical to select a window with certain functions.

3mm thick ordinary transparent glass pair Solar radiant energy It has a transmissivity of 87%, and most of the radiation energy from outdoor in the daytime can be transmitted; However, at night or in rainy weather, 89% of the heat radiation energy from indoor objects is absorbed by them, which makes the glass temperature rise, and then dissipates its heat through indoor and outdoor radiation and convection exchange, so it cannot effectively block the indoor heat from leaking to the outside.

The thermal insulation performance of window glass is generally expressed by "u" value, which is directly related to the emissivity of glass.

The "u" value is defined as: ASHRAE Standard Condition, due to glass heat conduction And the temperature difference between indoor and outdoor, which forms the heat transfer from air to air. his English units In English heat unit Every hour every square foot each fahrenheit ， Metric Units For: Watts per square meter each Celsius temperature The lower the "u" value, the lower the heat transfer through the glass, and the better the thermal insulation performance of the window glass. The emissivity is the ratio of the radiant heat per unit area of an object to the radiant heat per unit area of a blackbody at the same temperature and under the same conditions. Radiosity is defined as the ability of an object to absorb or reflect heat. Theoretically, the complete blackbody has 100% absorption of all wavelengths. I.e reflectivity Is zero. Therefore, Blackbody radiation The rate is 1.0.

Generally, Float The emissivity of white glass is 0.84. Most of them are online Thermal polymerization The emissivity of "Low-E" coated glass is between 0.25 and 0.35. The emissivity of magnetron vacuum sputtered "Low-E" coated glass is between 0.08 and 0.15. It is worth noting that the low emissivity directly corresponds to the low "u" value. The closer the emissivity of glass is to zero, the better its thermal insulation performance will be.

The advantage of an "energy-saving daylighting system" must be reflected in the highest possible total solar energy transmission, while having the lowest "u" value. By considering both energy gain and heat loss energy balance Equation, Ueg=UF-RFg. The best lighting system with energy balance characteristics is vacuum Magnetron sputtering "Low-E" coated insulating glass. Although the solar energy transmission of single-layer glass is the largest, its "u" and "Ueg" values are the worst. Therefore, the demand for a good energy balance cannot be met.

Pure high solar energy transmission cannot be considered as Energy saving materials 。 "Low-E" coated insulating glass is a better energy-saving daylighting material. It has a high solar energy transmission, a very low "u" value, and because of the effect of coating, the heat reflected by the "Low-E" glass returns to the room, making the temperature near the window glass higher, and people will not feel too uncomfortable near the window glass. The building with "Low-E" window glass has relatively high indoor temperature, so it can keep relatively high indoor temperature in winter without frost, so people in the room will feel more comfortable. "Low-E" glass can block a small amount of ultraviolet rays Transmission, slightly helps to prevent indoor objects from fading.

colour

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In terms of technology, low-E can be divided into online deposition coating method and offline vacuum magnetic sputtering method. According to the color, there are three basic colors: blue, green and gray. Different processes can be made according to the combination of different thicknesses and materials. for instance Neutral , Gold（ rose gold ）, silver and other relatively distinctive colors.

Problem solving

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At present, Low-E glass is divided into two types: online Low-E glass, offline Low-E glass and online LOW-E glass.

The offline Low-E glass has a variety of varieties. According to different climatic characteristics, it can be made into products with high, medium and low transmittance, and the colors are silver gray, light gray, light blue and colorless transparent Tinted glass It can also be made in green and other colors. The thickness can be made from 3~12mm. Note:

1. Online Low-E glass will bear close to glass during tempering softening point At this time, the color of the film may have some changes, resulting in color difference. In addition, the online Low-E glass is tempered with a film. The existence of the film makes the heating on both sides of the glass asymmetric, and the tempering process is difficult to control, which may cause a series of problems such as large tempering deformation. The off-line Low-E glass is tempered before coating, so there is no problem. In order to avoid the above tempering problem of online Low-E glass, some people use the untempered online Low-E glass as the inner sheet of insulating glass, and place the tempered transparent glass on the outside. This usage will not only have a certain impact on the effect of Low-E glass in the south, but also may toughen the outer side of the white glass Stress spot It is magnified by the inner Low-E glass and becomes heavier. In contrast, the tempered offline Low-E glass is placed on the outdoor side without this problem.

2. Low-E glass single piece offline Low-E Glass film The surface is soft, and will be affected by moisture and some oxidants Slow oxidation 。

3. Online Low-E glass is "hard coating", film quality guarantee period 30 years. Offline Low-E glass is "soft coating" Firmness Poor, almost can not be preserved naked.

4. Offline Low-E glass must be processed into insulating glass in a short time, and the edge coating must be removed when forming the insulating glass. Due to the weakness of insulating glass Respiration ， steam 、 sulfide 、 oxide After entering the cavity, the thermal insulation performance of off-line Low-E glass will gradually lose, and the appearance will become dark, discolored, and gradually appear a lot Mildew spot 。

Low-E glass is also called Low emissivity coated glass As far as the world is concerned, the production and application of Low-E glass is in a period of rapid growth. from Ministry of Construction According to the requirements of Energy saving building To become the mainstream of domestic architecture, Ministry of Construction Energy saving sign certification and corresponding Preferential tax policies To promote energy-saving buildings. Therefore, whether new buildings and existing buildings can save energy is not only related to alleviating the tension of energy supply and demand in China, but also related to the 11th Five Year Plan Energy Saving Achievement of goals. As the construction industry in the three major energy use fields, the energy conservation situation is very serious, and energy conservation and consumption reduction are urgent.

According to market analysis and prediction, by 2015, Low-E glass international market requirement It will exceed 1 billion square meters. In the next decade, the world's Low-E glass Market demand It will grow at an average annual rate of more than 18%.

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Single silver Low-E glass

Single silver Low-E Coated glass It usually contains only one functional layer (silver layer), plus other metal and compound layers, film The total number reaches 5 floors.

Double silver Low-E glass

Double silver Low-E coated glass has two functional layers (silver layer), plus other metal and compound layers, the total number of film layers reaches 9. However, the double silver Low-E glass Technical process The control difficulty is much greater than that of single bank.

Comparison between single silver LOW-E glass and double silver LOW-E glass

Any coating Glass In limiting the sun thermal radiation The transmission of visible light will be limited to some extent at the same time. Double silver Low-E glass can block more solar heat radiation than single silver Low-E glass. In other words, in Transmittance In the same case, Double Silver Low-E has lower Sunshade coefficient Sc， Can more effectively sunlight Filter into Cold light source 。

Double silver Low-E glass Heat transfer coefficient Lower than single silver Low-E, which can be further improved Exterior window The heat preservation performance can truly achieve warm winter and cool summer. In short, the double silver Low-E glass greatly reduces the indoor External environment Heat exchange through glass, so when the air conditioner is heating or cooling, the indoor temperature reaches setting temperature After that, the air conditioner can stay in the position in readiness To save power consumption.

The advantages of double silver Low-E glass can be simply summarized as follows:

1. Under the same glass combination, double silver Low-E glass has lower Emissivity And lower heat transfer coefficient（ U value ）。

2. Double silver Low-E glass has lower shading coefficient, namely Sc value.

3. Under the same shading coefficient (Sc value), visible light Transmissivity Higher than single silver Low-E. In short, the double silver Low-E glass highlights Glass pair The shielding effect of solar thermal radiation will reduce the height of glass Light transmittance And low solar thermal radiation Penetrability By ingenious combination, the problem of coexistence of high light transmittance and low U value and Sc value has been successfully solved, so it has better energy-saving effect, which is an advantage that no other glass can have.

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