Overview of Glass Window Film
The glass window film is a multi-layer functional polyester composite film and it is produced with the processes of dyeing, magnetron sputtering, lamination compounding and the like on a multi-layer ultra-thin high-transparency polyester film. When applied onto automotive glass and the glass of building window, door, partition, sun room, etc., it can improve the performance and the strength of the glass. It is the film with functions such as heat preservation, heat insulation, energy conservation, explosion protection, UV resistance, appearance beautification, privacy, safety and security protection. Its thickness ranges from 0.0125 mm to 0.5mm.
Classification of Glass Window Films
According to the application field, glass window films can be divided into three categories: building glass window film, automotive glass window film and dimming glassfilm.
Building Glass Window Film: It is mainly to save energy and insulate heat, together with UV resistance and safety function. This film can be further divided into heat-reflecting film and low-radiation film. The heat-reflecting film, when stuck on the surface of the glass, can allow the room to have visible light and near infrared light (other than far infrared light) to penetrate.Therefore, sufficient light enters the room, and most heat from solar energy is reflected back, so that the indoor temperature does not rise too much during the hot summer, thereby reducing the indoor air conditioning load, and achieving the effect of saving air conditioning cost and energy.The low-radiation film allows the penetration of a certain amount of short-wave solar radiation energy, so that solar radiation can enter the room and be absorbed by indoor objects; meanwhile, more than 90% long-wave infrared reflection of radiation of the indoor objects can be kept indoors.The low-radiation film can fully utilize the solar radiation and the long-wave radiation energy of indoor objects.Therefore, the heat insulation and energy-saving effect can be achieved in the cold area and the heated building.
Automotive Glass Window Film: When suck onto the inner surface of the automotive glass, this film can have the functions of energy conservation, heat insulation, ultraviolet resistance, safety and anti-theft, and the like.At the same time, the requirements on the visible light transmittance and visible light reflectivity of the window film are also high, especially the front windshield film. According to Technical Specifications for Safety of Power-driven Vehicles Operating on Road, "The visible light transmittance of the windshield glass shall not be less than 70%, and all window panes shall not apply the mirror reflective shading film". For the automotive windshield, the visible light transmittance of the film must be greater than 70%, otherwise, it will not meet the requirements of GB 7258-2004.
Dimming glass film: Namely the intelligent electric control liquid crystal film,whichis an intelligent glass film with dimming function. It is a novel energy-saving and environment-friendly film which is made by arranging different functional materials on two sides of the liquid crystal dimming film respectively.The liquid crystal dimming film is precisely processed by injecting liquid crystal and polymer mixed materials into the middle of the two-layer ITO conductive film.When the power is turned off, the liquid crystal molecules in the liquid crystal film will present anirregular scattering state, as a result, the product will appear in a light-transmitting and opaque state.When the power supply is turned on, the liquid crystal molecules in the liquid crystal film will be arranged in order, and the light rays can penetrate freely. In such case, the product instantaneously presents a transparent state.The user can control the current on or off to achieve the purpose of freely controlling the transparency and the opacity of the glass.In addition, the film has excellent resistance to ultraviolet, infrared, solar energy and sound in addition to the function of being transparent when power-on and non-transparent when power-off. And it has a wide range of color varieties and has wide application prospect in the fields of office meeting partition, hotel bathroom partition, window and cabinet exhibition hall, outdoor projection display, building exterior wall, automobile glass, and the like.
According to the production process, automotive glass window films can be divided into three main types: tinted film, primary color film and vacuum coated film.The tinted film can be further divided into common tinted film, surface layer tinted film and interlayer tinted film; and the vacuum coated film can be further divided into vacuum evaporation coated film and magnetron sputtering coated film.
Tinted Film
Common Tinted Film: Commonly known as tea paper, it is made by mixing the dye into the adhesive and then applying the mixture onto the polyethylene base material. This workmanship is the oldest. Being unable to insulate heat, resist to UV and having a very short shelf life, it is seldom used now.
Surface Layer Tinted Film: It is made by applying dye onto the surface of the PET base material. It has soft hand feeling, insufficient toughness and exposition prevention, insufficient UV resistance, easy fading and short warranty period.
Interlayer Tinted Film: It is made by applying dye onto between the two layers of PET base materials. It has soft hand feeling, certain UV and aging resistance. This film is still sold in the market due to low cost.
Characteristics of Tinted Film: low visible light reflectivity, lack of good heat control performance, easy fading, usually purple, and easy to bubble after long-term use.
Primary Color Film
Primary Color Film: It refers to a glass window film without organic dye. Up to now, the optical-grade PET films have only two color categories, i.e. gray and colorless, and the PET films of other colors must be obtained by dyeing. The primary color film is characterized by good hand feeling, being uneasy to fade, and long shelf life.
Vacuum plating velum
Vacuum Evaporation Coating Film: The film is made with the heat evaporation (for pure metals at low melting temperature) process. It can be coated with various metals, alloys, or oxidation layers. The vacuum evaporation process is usually used for the pure aluminum coated film, and can make various films with different visible light transmittance and reflectivity so that the films can have the best sunlight control performance.Vacuum Sputtering Coated Film: Generally, in a large vacuum chamber, in the inert gas environment with very low pressure and under the action of electric energy, various metal or metal composite targets are impacted by charged ions to form multilayer dense low-reflection high-heat-insulating metal film layer. Then such metal film layer is equally applied onto the surface of the PE film and then the compounding process is used. As a result, various featured films with stable color, high-level transmittance selectivity can be produced. Such films are characterized by sufficient toughness, explosion resistance, heat insulation, 99% UV rejection and long warranty period.
Depending on the materials being coated, the films are roughly divided into two major categories: ceramic film and metal film.
Ceramic Film: It is the glass film containing super-thin ceramic coating such as SiO2 and TiO2. As it does not contain metal layer, this film completely does not interfere with GPS system, radio communication and mobile phone reception in the car.At the same time, this film is not oxidized and faded. It is easier to maintain than the metal film, and is durable.It has low reflection rate and moderate light transmittance.All the above glass films must have a one-way protective function, i.e. unidirectional blocking of damage from the outside, without any obstruction to the outward damage from inside. For example, in case of fire, earthquake, traffic accident or other disasters, the people inside can easily smash through the glass for escape.
Metal Film: At present, the domestic high-end window films are mostly the magnetron sputtering metal films.Metal films have good heat insulation, especially the multilayer structure metal film produced with the magnetron sputtering technology have reached the peak of perfection in terms of heat insulation.However, metal films always have congenital defects, such as easy oxidation, shielding ETC and GPS signals, high reflection. A common single-layer metal film, although cheap in price, has ordinary heat insulation and its heat reflection effect is not as good as people imagine. More frequently, it achieves the effect of heat insulation via energy barrier.The metal film with the multi-layer film structure has good heat insulation because it is sputtered with silver, a kind of metal very easy to oxidize, to reflect heat. Although having good heat insulation, it has the most remarkable defect, i.e. oxidization. Secondly, as the metal layer is thicker than that of the common metal film, such metal film sputtered with the multi-layer film structure has a severe defect of shielding signals, even affecting mobile phone signals. Moreover, the construction for such kind of film is very difficult and the metal wire can be exposed very easily. Due to complicated production process, it is very expensive. Therefore, although having good heat insulation, metal films have some defects as mentioned above or in other forms. In the high-end film field, there are more choices for metal films. We can provide you with top-grade representative metal films.
Structure and Characteristics of Glass Window Film
The structural diagram of the glass window film is as shown below
1. Anti-wear layer: composed of wear-resistant polyurethane with hardness up to 4H;
2. PET safety substrate with color: made by melting, extruding and two-way stretching high-strength, high-transparency PET polyester and pigment. Because the pigment is sandwiched in the PET film, the oxidation and discoloration can be prevented, and the service life can be up to 8 years;
3. Metal insulation layer: the nanometer metal layer made by vacuum evaporation coating or vacuum magnetron sputtering aluminum, silver, nickel and other metals with high reflectivity to infrared ray onto PET film;
4. Composite adhesive: composed of polyurethane adhesive with high weather resistance and high transparency;
5. UV absorbing layer: composed of special UV absorber, which can obstruct 99% of ultraviolet rays;
6. Transparent PET safety substrate: composed of high-strength and high-transparency PET film, the purpose of which is to sandwich the metal layer in the middle to prevent metal oxidation and prolong the life of the metal film.
7. Mounting adhesive: composed of acrylate adhesive with high weather resistance and high transparency;
8. High-transparency PET release film.
Heat Insulation Working Principle of Glass Window Film
There are three types of heat transfer: radiation, conduction, convection. The heat-insulating film mainly use in radiation and convection to reduce heat, mainly the radiant heat of the sun.
The sunlight is composed of light waves (electromagnetic waves) in each wavelength band, and solar energy is the energy of these electromagnetic waves themselves. Filtered by the atmosphere, these energies reach the earth's surface in the form of light waves of different wavebands and convert into heat in the form of radiation. The higher the energy, the greater the amount of heat converted.
Sunlight can be divided into three spectral bands:
Ultraviolet Spectral Band: It has the wavelength ranging 280-400 nm, and characterized by strong penetrating ability. It can make human skin melanin deposit and color deepened. Excessive ultraviolet exposure can cause skin cancer and result in the fading of carpet, curtain, fabric and furniture paint.
Visible Spectral Band: It has the wavelength ranging 380~780 nm and it is only spectrum visible to the naked eye. It can be further divided into different colors (red, orange, yellow, green, indigo and violet) and it has no direct damage to the human body.
Infrared Spectral Band: It has the wavelength ranging 700~2400 nm and it is the sunshine whose "invisible" heat we can directly feel. It contains the highest heat.Of the solar energy, the far and near IRs of various wavebands take up 53%, UV 3% and visible light 44%.
Aluminum, gold, copper, silver and the like are made into multi-layer dense high-insulating metal film by vacuum spraying or magnetron sputtering technology.The electrons (free electrons) of the outer shell layer in the metal material are generally not bound by the nucleus. When the metal material is irradiated by light wave, the electric field of the light wave causes the free electrons to absorb the energy of the light, and the oscillation with the same frequency as the light is generated and such oscillation generates the light with the same frequency with the original light. This phenomenon is referred to as "reflection of light". The higher the conductivity coefficient of the metal, the shallower the penetration depth and the higher the reflectivity.These metal layers will selectively reflect the various thermal energy sources in the sunlight, including infrared, ultraviolet and visible light thermal energy, then cooperate with the colors on the film to absorb the solar heat radiation and release again, and the outdoor air flow will carry away a portion of heat.As a result, the function of heat insulation can be accomplished effectively.
Anti-Explosion Working Principle of Glass Window Film
Whether the common glass or the toughened glass, the defect that the splashing of the glass fragments can cause harm to human body exists. However, when the inner surface of the glass window is stuck with glass window film, the adhesive on the glass window film can make the glass and the film a composite material capable of bearing external force.
The safety base material in the glass window film is a transparent polyester film (PET) having a large tensile strength and impact strength, particularly when two or even three layers of PETs are bonded together by a laminating adhesive into one, the mechanical performance of such resulted film will increase by multiple and so that it can have very strong impact resistance. When subject to external force impact, the safety base layer can play an effective buffering function; even if the left and right alternating external force is applied, the special pressure-sensitive adhesive layer can ensure the glass fragments firmly stick to the surface of the window film, with only a small amount of powdery glass fragments falling off. Therefore, the external injury can be reduced to a maximum extent.
Main Performance Indicator of Glass Window Film
Visible light transmittance: The percentage of THE visible light (380-780) passing through the glass/ glass window film composite layer.
Visible light reflectivity: The percentage of visible light (380-780) reflected by the glass/ glass window composite layer.
Solar transmittance: The percentage of solar energy transmitted through the glass/ glass window composite layer.
UV rejection: The percentage of UV (280-400) reflected by the glass/ glass window composite layer.
Solar reflectivity: The percentage of solar energy reflected by the glass/ film composite layer.
Total solar energy rejection: The percentage of solar energy absorbed by the glass/ film composite layer. When the absorbed solar energy is capable of radiating more energy to both sides of the glass/ film composite layer, the side with high air flow rate will radiate more energy.
Total solar transmittance: The sum of the portion of the solar energy transmitted through the glass/ glass window film composite layer and the absorbed solar energy inward radiating. The unit of measurement for heat insulation is the amount of heat passing through per square foot per hour (BTU/Hr./Ft.2, where 1BTUs = 262 calories). The heat insulation of the transparent glass is generally 20 BTY/ Hr./ Ft.2.
Total solar reflectivity: i.e. the heat insulation, which is the sum of the portion of solar energy reflected by the glass/ glass window film composite layer and the absorbed solar energy outward radiating.
Shading coefficient: the ratio of the total solar transmittance of the glass/ glass window film composite layer to that of the glass.
U value: the amount of heat radiation through per square foot when internal and external temperature difference per hour is 1 degree. Different purpose requires different performance. In general, the main indicators are visible light transmittance, visible light reflectivity, heat insulation and UV rejection.
Technology for Manufacturing Glass Window Film
Dyeing Process: With the coating compounding process, the adhesive mixed with dye is applied onto the PET or between two layers of PET films, and the PET substrate is colored so that it can appear in different colors according to needs.This process has the advantages such as diverse colors, simple process and low cost; and also has the disadvantages: weak resistance to ultraviolet radiation, easy to fade and short shelf life.
Vacuum Sputtering Process: The film is made with the heat evaporation (for pure metals at low melting temperature) process. It can be coated with various metals, alloys, or oxidation layers.The vacuum sputtering process is usually used for the pure aluminum coated film, and can make various films with different visible light transmittance and reflectivity so that the films can have the best sunlight control performance.
Magnetron Sputtering Process: This process is an advanced technological process developed at the end of the 1970s. In a special vacuum device and under the action of electric energy, various metal or metal composite targets are impacted by charged ions to form multilayer dense low-reflection high-heat-insulating metal film layer. Then such metal film layer is equally applied onto the surface of the PE film and then the compounding process is used. As a result, various featured films with stable color, high-level transmittance selectivity can be produced. Such films are characterized by sufficient toughness, explosion resistance, heat insulation, 99% UV rejection and long warranty period.Compared with the traditional vacuum sputtering process, the magnetron sputtering process has many advantages, such as, the adhesion between the coated layer and the base material is stronger;the film with the substance of high melting point can be easily produced;a more uniform film can be produced on a large-area continuous base material;the composition of the coating can be easily controlled, and the alloy coated film with various components and proportions can be prepared.The principle of the magnetron sputtering process is that the base material is sent into a vacuum chamber provided with magnetron cathode and sputtering gas (argon), negative voltage is applied to the cathode, glow discharge in the vacuum chamber is implemented to generate plasma; as the metal target material is with negative electricity, the gas ions with positive electricity in the plasma are accelerated and strike the target surface with the energy corresponding to the target voltage drop U to cause the atoms of the metal target to be emitted to deposit on the surface of the base material, forming metal film.
Laminated Compounding Process: Glass window film is a multi-layer functional polyester composite film. With adhesive, the thin layers of different functions are compounded together, so that the resulted film can have the functions of anti-explosion, heat insulation and safety.Only a highly accurate coating system can ensure that the glass window film can be effectively controlled during the manufacturing process.
Glass Window Film Production Equipment
Magnetron Sputtering Equipment: The most famous manufacturers of magnetron sputtering coating equipment in the world are Arico of the USA and Leybold of Germany, both of which are the same in the process principle, but different in the following aspects:
(1) The vacuum pumping system used by the coating equipment of Leybold is the turbo molecular pump, while that by Arico is the oil diffusion pump. The molecular pump has high precision and short pumping time and is replaced once every two years, while the oil diffusion pump needs to be replaced once every six months, and cleaned once a year.
(2) Arico has invented C-MAG rotary target materials which can improve the utilization rate of target materials. The average utilization rate of general target materials is 20-30% while that of the rotary target material can be up to 70-80%.
(3) The sputtering chamber of Leybold in Germany consists of 17 compartments, which can be extended up to six cathodes. The sputtering chamber of Arico is composed of a single chamber (three cathodes), and if the market demand is strong, the number of the sputtering chambers can be increased; Arico is more flexible in the number of sputtering chambers.
Precise coating compounding equipment: Currently, there are many kinds of coating composite machines with different functions available in the market. The core of a coating production line for manufacturing the glass window film is the precise coating machine.
Raw Materials for Glass Window Film
PET Base Material: Polyethylene terephthalate (PET)，which was successfully researched firstly by J． tt． Whinfield and J. t Dickon from UK in 1941.PET can be prepared either by the reaction of dimethyl terephthalate (DMT) with ethylene glycol (EG) or by reaction of p-phthalic acid (PTA) with ethylene glycol. This method is called as the DMT method (or the transesterification method) and the PTA method (or the direct esterification method).Because the PTA method has more advantages than the DMT method, it is mostly adopted in the world's total PET production capacity.
Biaxially oriented polyethylene terephthalate (BOPET) film is a high-grade film which is prepared by adding titanium white powder into raw material polyester chips and then drying, melting, extruding, casting and horizontally stretching.The BOPET film has the characteristics of high strength, good rigidity, transparency, high glossiness and the like. It is odorless, tasteless, colorless, non-toxic and outstanding in toughness. Itstensile strength is 3 times of that of the PC film and the nylon film; its impact strength is 3-5 times of that of the polypropylene film, and it has excellent wear resistance and folding resistance, pinhole resistance and tear resistance. Its heat shrinkage is very small, at 120 ° C, only 1.25% shrinkage happens after 15 minutes.It has good antistatic property and is easy for vacuum coating. It also has good heat resistance, excellent cooking resistance, low temperature freezing resistance, good oil resistance and chemical resistance, etc..
The PET film used in the glass window film is the optical grade BOPET film.The glass window film has strict requirements on the performance of the base material, and requires high tensile strength and tear strength, high optical performance and more than 90% visible light transmittance.Therefore, this is one of the reasons why there are many domestic film manufacturers producing films, but there is no one producing safety filmAt present, only three companies, i.e. such as Mitsubishi, Tijen/DuPont and Toray (Japan) use PET base material for the optical glass window film.
Adhesive: Glass window film adhesives are divided into laminating composite adhesive and mounting pressure-sensitive adhesive.The laminating composite adhesive is an adhesive used for bonding thin layers of different functions, such as safety base layer, heat-insulating layer, ultraviolet-proof layer and the like.
According to U.S. patents, most of the adhesives used are polyurethane (PU) adhesives.The PU adhesive requires high heat resistance, mechanical property, adhesive property, ultraviolet aging resistance and certain water vapor transmission.It is one of the most important components of glass window films and it can directly influence the properties of glass window films, especially the optical performance and the service life. It is one of the key technologies in the manufacture of glass window films.As a result, all major foreign manufacturers have their own proprietary adhesive technology and formula, which are seldom published.
The adhesive is generally divided into dry adhesive and pressure-sensitive adhesive, and each has advantages and disadvantages.The dry adhesive has the advantages of simple installation, convenience, time saving and high adhesive strength, but it is weak in water resistance.The adhesive strength and service life of the pressure-sensitive adhesive will increase with time passing by.
The pressure-sensitive adhesive is generally a single-component solvent type acrylate pressure-sensitive adhesive. It is added with ultraviolet absorbent. It has high UV aging resistance, optical performance and weather resistance.
Development Process of Glass Window Film
The development history of the glass window film is inseparable from the development history of raw materials and process equipment, especially the development history of vacuum evaporation coating technology.
The USA began developing glass window film (tea paper) with polyethylene as the base material in the 1960s, when most of the buildings used ordinary float glass and the energy consumption caused by door and window glass accounted for more than 1/3 of the whole building. Later, people used the film materials used in the aerospace for the building doors and windows and found that it can obviously improve the thermal insulation and energy-saving characteristics of buildings.As a result, each major company began studying the glass window film, and 3M issued its first patent for the solar insulation film in 1966.The world's energy crisis in 1970 prompted people to step up the development of glass film, and vacuum evaporation coating technology was applied to PET base film so that the technology of glass window film made a great progress.
In 1977, US Deposition Technology, Inc. (which was merged by Bekaert Group, Belgium in 1991 to form a special coating company under Bekaert Group) introduced the advanced magnetron sputtering production technologies used by U.S. Air Force and NASA into the glass window film industry. In the early 1980s, it became the first manufacturer of glass window film in the world adopting magnetron sputtering technology. Compared with the vacuum evaporation coating process of the other glass film manufacturers, the film with the magnetron sputtering process has the most remarkable advantage that stainless steel, titanium, nickel, gold, silver, copper and the like can be made into a transparent heat-insulating alloy layer so that the glass window film can have high visual clarity at the same time under the condition that the heat insulation function is greatly improved, and overcome the defects of high reflection, easy fading and the like of the glass window film produced with the dyeing and vacuum evaporation coating process.In 1985, this company produced a magnetron sputtering glass window film with a width of 1,540mm.
US Southwall Technologies Inc. is mainly engaged in the development and production of the spectrum selective thin film required by military and space technology. In the mid1980s, the company turned XIR patented technology from space vehicle for civilian purpose and began the production of commercial high-performance glass window films.While selectively blocking almost all of the infrared and ultraviolet radiation, XIR is highly permeable to visible light in sunlight,creating a leading position in the field of thin film and material technology.
In the 1990s, Israel Hanita began the production of safety films, which were originally designed for military application, researched and developed by Jewish scientists in NASA under entrustment. The glass protective film can prevent the injury and damage to people and articles from bullets and explosives in the war and alleviate the damage and loss of military equipment and facilities.With the easing of the international situation, the protective film produced for military purpose is gradually converted into commercial civilian commodities, so the safety protection of people on all glass, particularly the application on the building curtain wall, plays a significant role in the application of energy-saving heat insulation and provides an ideal material.This security film production technology is transferred to various parts of the world through technology transfer, including US and Japan.
After entering the 21st century, the glass window film manufacturers made breakthroughs in technology, and had unique high-thermal control films for visible light transmittance and rejection. They use the conventional window film as a laminate, and the films are laminated by layer by layer by different effects so that the impact resistance of the glass can be improved by more than 100 times, under the premise of higher light transmittance, heat insulation ratio and UV rejection.In recent years, especially after the "September 11" Incident in the United States, the glass window film, as a brand-new building material, has been increasingly used for the safety protection of doors and windows, partition walls, ceilings and banking.