Patent Application
20140071392
The described embodiments relate generally to laminate bonding between two substrates and more particularly to laminate bonding two substrates with an optically clear adhesive when at least one of the substrates is relatively transparent.
Substrates can be bonded together with a variety of adhesives and techniques. Some substrates can be more difficult to laminate, particularly when the substrates are clear and the lamination process can introduce bubbles or voids between the substrates.
In some applications, the lamination between a first substrate and a second substrate can be in a critical visible area of a product. An example of a critical visible area can be a display screen for a computing device. Display screens can include multiple substrates stacked in sequence, including items such as a liquid crystal display, one or more filters to modify the light to and from the liquid crystal display and a cover glass to provide protection to display components and provide the user with a finished surface. If a bubble or void exists in the lamination area between the cover glass and the liquid crystal display, a visible defect would present itself. If the visible defect was in a central region of the display, or if the visible defect was relatively large, or if there were a plurality of visible defects, then display functionality may be compromised since visible information can be distorted by the visible defects.
Therefore, what is desired is a reliable way to laminate a first substrate to a second substrate, and avoid introducing bubbles or voids between the substrate layers.
This paper describes various embodiments that relate to forming a lamination between a first and a second substrate with a liquid optically clear adhesive such that bubbles and voids are avoided in the lamination area.
In one embodiment, a method of laminating a first substrate to a second substrate with a liquid optically clear adhesive (LOCA) can include the steps of applying a uniform layer of LOCA on the first substrate, forming only one initial contact region with LOCA dispensed separately from the uniform layer of LOCA only on one edge of the second substrate, placing the initial contact region of LOCA in contact with the uniform LOCA layer and arranging the first substrate to bond with the second substrate.
A display assembly can include a first substrate, a board assembly that can include a liquid crystal display, where the board assembly is positioned under the first substrate, a layer of LOCA placed on the liquid crystal display and a single contact region of LOCA disposed on the first substrate where the first substrate is laminated to the liquid crystal display by first contacting the single contact region of LOCA with the layer of LOCA on the liquid crystal display.
A method for laminating a cover glass to a display with LOCA can include the steps of applying a uniform layer of LOCA onto the display, creating an initial contact region with LOCA on one edge of the display disposed over the layer of LOCA, placing one edge of the cover glass in contact with the initial contact region and forming a lamination by arranging the cover glass to be parallel with the display.
Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.
The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments.
Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting.
In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments.
When laminating a first substrate to a second substrate, a bubble or a void can form in a lamination area particularly when the lamination adhesive is a liquid optically clear adhesive (LOCA). A LOCA can be selected when the lamination is positioned in a highly visible area, such as a display area for a computing device. For example, a cover glass acting as a first substrate can be laminated to a display acting as a second laminate to form a display assembly. Display assembly performance can be related to a clear and void free lamination. Laminated displays assemblies are used not only in computing devices, but also portable communication devices, media players, handheld global positioning systems and the like.
One way to help ensure a bubble free lamination is to control the initial contact between the first and the second substrate through the LOCA. Ideally the LOCA should be smooth and without waves as the LOCA is deposited onto one of the substrate surfaces. However, by controlling a first contact area between the LOCA and the substrates, the LOCA lamination area can be influenced so that bubbles are not trapped within the adhesive.
Controlling the initial contact area between the substrates can involve manipulating the LOCA in addition to the LOCA already used for lamination. Additional LOCA can be dispensed in particular area to help ensure a bubble free lamination. In another embodiment, initial contact can be controlled by slightly deforming at least one of the substrates to form the initial contact area.
Affinity between a liquid, such as a LOCA, and a solid, such as a substrate like glass can often be described as “wettability”. Those skilled in the art can appreciate that when a surface energy on a substrate is greater than a surface energy of the LOCA, then the LOCA can wet the substrate and flow more evenly and freely over the substrate. On the other hand, when the surface energy on the substrate is lower than the surface energy in the liquid, then the liquid does not wet the substrate well. Another way to help ensure a bubble free lamination addresses the surface energy on the substrates to help improve wettability and help the LOCA spread and flow evenly.
When the lamination assembly 100 includes a display, such as a liquid crystal display, the first substrate 102 can include the liquid crystal display and the second substrate 104 can include a cover glass. In the discussion herein, the term cover glass can be used when describing the second substrate and the term display can be used when describing the first substrate to help illustrate more clearly a relationship between the first and the second substrates. The selected terminology is not meant to be limiting.
When laminating the cover glass 104 to the display 102, the adhesive selected should be relatively clear so as not to occlude the view of the display 102 though the cover glass 104. In one embodiment, the adhesive 106 can be a liquid optically clear adhesive (LOCA).
In order to begin a lamination or bonding process, the edge of the cover glass 104 including the additional LOCA region 204 is held substantially parallel to one edge of the display 102. The cover glass 104 and display 102 can be positioned proximate to each other such that the additional LOCA in region 204 is brought into direct contact with LOCA 106. After initial LOCA contact is made, the edge of the cover glass remote from additional LOCA region 204 can be moved relative to the display 102 such that the cover glass 104 can be made parallel to the display 102.
In one embodiment the initial contact area can be formed by exerting a pressure with a pin 602 in a downward direction toward LOCA 106 while support rollers 604 and 606 can support cover glass 104 allowing a deformation to form in the cover glass 104. (Note that
Another approach to prevent bubble or void inclusion in the lamination area is to treat at least a portion of a surface of at least one substrate to improve wettability of the LOCA. Improved wettability of a substrate surface can enable improved flow of LOCA between the substrates involved in the lamination assembly. In one embodiment, an entire substrate surface need not be treated, but rather just a limited region. This limited region can be analogous to the initial contact area described in
Region 702 can be subjected to a plasma surface treatment to increase wettability in the area of the treatment. In one embodiment, region 702 can be treated with an inert gas plasma bombardment. Inert gases used to form plasmas can be noble gases such as helium, neon, argon and xenon. Inert gases can also include other gases that can be mostly non-reactive in a non-plasma state such as nitrogen. Treating region 702 with an inert gas plasma can increase wettability by increasing the surface energy of the substrate, particularly in region 702.
In another embodiment, region 702 can be treated with an oxygen plasma. Oxygen plasma can remove contaminants and dirt from region 702. Contaminants and dirt can cause poor wettability and low surface energy. Thus, treating region 702 with an oxygen plasma can increase wettability and improve lamination.
In yet another embodiment, an additional component can be introduced to the region 702. One example of an additional component is a hydrophilic monolayer that can be deposited on to or evaporated on to region 702. A hydrophilic monolayer can be a very thin layer that can increase wettability by causing the surface of the substrate in region 702 to become more hydrophilic. In another embodiment, a primer can be applied to region 702. One example of a primer can be LOCA particles mixed with a solvent such as either Ethanol or Methanol. The primer can be easily applied and can also have relatively lower cost compared to other alternatives such as disposing a hydrophilic monolayer. After region 702 is acted upon, as described above, bonding the first substrate to the second substrate can be performed as described in
Electronic device 1000 can also include user input device 1008 that allows a user of the electronic device 1000 to interact with the electronic device 1000. For example, user input device 1008 can take a variety of forms, such as a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of sensor data, etc. Still further, electronic device 1000 can include a display 1010 (screen display) that can be controlled by processor 1002 to display information to the user. Data bus 1016 can facilitate data transfer between at least file system 1004, cache 1006, processor 1002, and controller 1013. Controller 1013 can be used to interface with and control different manufacturing equipment through equipment control bus 1014. For example, control bus 1014 can be used to control a computer numerical control (CNC) mill, a press, an injection molding machine or other such equipment. For example, processor 1002, upon a certain manufacturing event occurring, can supply instructions to control manufacturing equipment through controller 1013 and control bus 1014. Such instructions can be stored in file system 1004, RAM 1020, ROM 1022 or cache 1006.
Electronic device 1000 can also include a network/bus interface 1011 that couples to data link 1012. Data link 1012 can allow electronic device 1000 to couple to a host computer or to accessory devices. The data link 1012 can be provided over a wired connection or a wireless connection. In the case of a wireless connection, network/bus interface 1011 can include a wireless transceiver. Sensor 1026 can take the form of circuitry for detecting any number of stimuli. For example, sensor 1026 can include any number of sensors for monitoring a manufacturing operation such as for example a Hall Effect sensor responsive to external magnetic field, an audio sensor, a light sensor such as a photometer, computer vision sensor to detect clarity, a temperature sensor to monitor a molding process and so on.
The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.
