Vacuum lamination process

One of the most often used production procedures for fabricating a high-performance structural laminate is the Autoclave/Vacuum Degassing (AC/VD) laminating process. In this process, individual prepreg plies are laid up in a prescribed orientation to form a laminate. The laminate is laid against a smooth tool surface and covered with successive layers of glass bleeder fabric, Mylar or Teflon sheets, and finally a vacuum... 

The three Gulf EMA resins were experimentally evaluated and TD-938 was selected on the basis of film transparency, extrudabll-Ity, and ease of module fabrication by lamination. The TD-938-base resin sells for about 0.60/lb (April 1981). A trial formulation is shown in Table II. Modules have been fabricated with this EMA by the vacuum-bag lamination process, and have successfully passed module engineering qualification tests. Primer formulations for bonding EVA and EMA to glass and polyester film have been developed by Dow Corning and the formulations are given in Table III. 

In a vacuum lamination process, the steeper the melt viscosity/temperature curve for sheet pottant material, the better. The layers need to be dry and non-tacky during the initial evacuation step so as not to trap air between them. At the same time, the pottant must then melt to as fluid a state as possible in order to effectively penetrate and wet all the irregularities of the cell circuit. 

Unoriented Films. Unoriented multilayer films can be obtained by coextrusion of layers of 3GN and PET. Alternatively, multilayer films can be formed in a continuous lamination process using heat or optionally adhesive layers to bond the separate layers. Press lamination can also be used to form multilayer films by pressing layers of individual films at elevated temperature and pressure. Prior to film formation, the pol5miers are generally dried by heating to a temperature of 5°C below the crystallization temperature of the polymer under vacuum or inert atmosphere. The films can be rapidly cooled after extrusion to inhibit crystallization. ... 

Used as a laminate for vacuum processing and as a high-strength overwrap for heavy articles... 

In the vacuum infusion process, the fibre sheets are placed in a dry state with a plastic sheet laid over the entire form to create a vacuum. Resin is introduced at one end. The vacuum enables the flow of the resin and an even distribution of the matrix through the fibres. In comparison with the hand laminating process, a higher volume of fibre can be achieved in the composite material. However, it is difficult to control the flow of the resin along edges, comers, etc. It is also not possible to vacuum-infuse honeycomb materials for a sandwich structure. 

In general, very little data have been published on the outgassing properties of the skins for vacuum panels, even though they can contribute, in some cases, in a non-negligible way to the deterioration of the pressure inside the VIP. This can be due to the outgassing properties of the materials used as barrier layers and/or the lamination process, which may introduce volatile substances or trap gases in between the various sheets. 

Thermoset based composite laminates are generally produced bj Autoclave/Vacuum Degassing Lamination Process (38, 39). The characteristics of this inocess are shown in Fig. IS. In this process, pr eg plies of desired shape are laid up in a prescribed orientation to form a laminate. The laminate is covered with successive layers of an absorbent material (glass bleeder fabric), a fluminated film to prevent sticking, and, finally, with a vacuum bag. The mitire system is placed upon a smooth metal tool surface into an autoclave, vacuum is a Ued to the bag and the temperature is increased at a constant rate in order to promote the resin flow and polymerization. The autoclave process will be used along this section as a case study to describe the influence of the matrix characteristics on the processing behavior of hi performance conqmsites. 

In contrast, isostatic lamination uses a water-filled pressure vessel to apply heat and pressure to the ceramic layers, as illustrated in Figure 6.22. This process is more complex because contact between the water and imfired ceramic must be avoided. The pressure and temperature uniformity across the part, however, is superior to most uniaxial lamination systems. The tacked layers to be laminated are vacuum bagged to prevent introduction of water into the substrate, and metal plates may be used on either or both sides of the tape layers. A base plate is used to support the tape layers, whereas a second metal plate on top is referred to as the cover plate. Cover plates serve to distribute the pressure uniformly over the substrate, but may be omitted in some cases. As can be seen in the upper left-hand inset of Figure 6.22, the vacuum-bagged parts are often stacked inside the laminator on multiple shelves. Many parts can be laminated in one batch lamination cycle with this approach. 

Multilayer lamination processing is important to ensure good resin flow and full wetting of resin to glass in the prepreg layers. Vacuum, temperature, and pressure profiles are all important. 

The use of a dry-film PID requires only one unique piece of equipment a vacuum lamina-tor. Vacuum laminators are common at printed circuit fabrication shops in addition, the capital to obtain one is significantly less than for a curtain or slot coater. The dry-film PID has excellent planarization and does not require a leveling process dne to the film s low solvent content, low shrinkage, and vacuum lamination process. ... 

As a tme thermoplastic, FEP copolymer can be melt-processed by extmsion and compression, injection, and blow molding. Films can be heat-bonded and sealed, vacuum-formed, and laminated to various substrates. Chemical inertness and corrosion resistance make FEP highly suitable for chemical services its dielectric and insulating properties favor it for electrical and electronic service and its low frictional properties, mechanical toughness, thermal stabiUty, and nonstick quaUty make it highly suitable for bearings and seals, high temperature components, and nonstick surfaces. 

Polyester. Poly(ethylene terephthalate) [25038-59-9] (PET) polyester film has intermediate gas- and water- vapor barrier properties, very high tensile and impact strengths, and high temperature resistance (see Polyesters, thermoplastic). AppHcations include use as an outer web in laminations to protect aluminum foil. It is coated with PVDC to function as the flat or sealing web for vacuum/gas flush packaged processed meat, cheese, or fresh pasta. 

Nylon films are used in lamination or coated form to ensure heat sealabiHty and enhance barrier properties. The largest uses are as thermoforming webs for twin-web processed meat and cheese packagiag under vacuum or in an inert atmosphere. Other uses include bags for red meat, boil-ia-bags, bag-in-box for wine, and as the outer protective layer for aluminum foil in cookie and vacuum coffee packages. 

Polyacrylonitrile (PAN) films have outstanding oxygen and CO2 barrier properties, but only modest water-vapor barrier properties. They are for processed-meat and fresh pasta packaging laminations where an oxygen barrier is required for vacuum or gas flush packaging. 

Coffee vacuum-packed in flexible, bag-in-box packages has gained wide acceptance in Europe. The inner liner, usually a plastic-laminated foil, is formed into a hard brick shape during the vacuum process (30). In the United States, a printed multilaminated flexible stmcture is used to form the brick pack which is sold as is at retail. These types of packages provide a barrier to moisture and oxygen similar to that of a metal can. 

Process of molding or laminating in wliich fluid pressure is applied, usually by means of water, steam, air or vacuum, to a flexible film or bag that transmits the pressure to the material being molded. 

High pressures are commonly used during autoclave processing to provide ply compaction and suppress void formation. Autoclave gas pressure is transferred to the laminate due to the pressure differential between the autoclave environment and the vacuum bag interior. Translation of the autoclave pressure to the resin depends on several factors, including the fiber content, laminate configuration, and the amount of bleeder used. 

The pressure curves also illustrate the horizontal flow process. The resin pressure initially approaches the applied autoclave pressure and then decreases as bleeding occurs. The opposite occurs in the bleeder. The applied vacuum is measured initially, and the pressure increases as resin begins to fill the bleeder. Note that the horizontal pressure gradient is very small for a majority of the laminate but becomes large near the edges. 

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