Apparatus and method for precision manufacturing of solvent-laminated retarder stacks

Abstract

A laminator for high precision solvent bonded delay films is disclosed. The laminator is capable of producing laminates with high orientation repeatability and low in-plane stress that can otherwise create a gap between the best theoretical performance and the physically achievable performance. The batch mode laminator is scalable to large area master sheets and is suitable for high volume manufacturing.

Description

[0001] Cross-referencing

[0002] This application claims priority to U.S. Provisional Application 63 / 041,978, filed June 21, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to equipment and methods for the precision manufacture of solvent-laminated delayer stacks. Background Technology

[0004] The most common adhesive family used for laminating optical retardation (also known as phase retarding) films is acrylic pressure-sensitive adhesive (PSA). PSA (sometimes called optically-clear adhesive, OCA) is typically 25 to 50 micrometers thick, has a refractive index of approximately 1.46, and can form large-area bonds between substrates such as cellulose triacetate (CTA or TAC), polycarbonate (PC), and cyclic-olefin polymers (COP or COC). Pre-lamination surface activation (e.g., plasma or corona) is typically used to promote adhesion, and post-lamination autoclaving is usually used to eliminate haze and microbubbles. Batch-mode laminators (which differ from roll-to-roll laminators), such as those used to laminate polarizers and retardation films to liquid crystal displays, televisions, and monitors, are common. Modern techniques using vacuum membranes to provide in-plane support for the entire membrane during lamination minimize stress for two important reasons: first, the membrane is bonded to the membrane via vacuum, thus minimizing lateral non-uniformity of pressure that may occur during the formation of the bonded zone; second, the membrane, combined with translational lamination rollers, minimizes stress in the machine-direction that may occur, for example, when the membrane is pulled away from the vacuum platform. Strain is minimized by maintaining a small gap between the two membranes during lamination. XY-θ manipulation platforms incorporating machine vision cameras are also useful for precise, high-volume film-to-display and film-to-film lamination.

[0005] Solvent bonding of delayed films is also described for bonding polycarbonate layers, offering all the benefits of not requiring adhesives. A solvent bonding apparatus is described in which a reference guide on a transport device parallel to the lamination direction is used to determine position in the transverse direction and also to determine orientation. Position in the longitudinal direction (or lamination direction) can be set by a reference stop on a motion control platform. The laminator forms a pressing zone by pressing the lower part of the membrane, suspended below the membrane transport device, against the membrane on a movable backing surface. This pressing zone determines the initial conditions for lamination initiation, which can affect the overall quality of the lamination. These initial conditions for lamination initiation include precise input membrane orientation and pressure distribution in the transverse direction.

[0006] Retarder stacks, such as those required for linear-to-circular polarization conversion (and vice versa) over a wide wavelength range, can exhibit near-ideal theoretical inverse dispersion. For example, designed retarder stacks can produce ellipticity field-ratios exceeding 0.99 across the entire visible spectrum (400 nm to 700 nm), which may be desirable in high-performance optical systems. There is a growing demand for lamination devices and methods that offer high precision and minimal induced stress in optic-axis alignment. Summary of the Invention

[0007] This disclosure describes batch-mode solvent lamination apparatus and methods for minimizing uncertainties in the fabrication of precision optical retarder stacks. The optical retarder stacks consist of oriented transparent film layers capable of achieving a designed pulse response that can resolve a wide range of polarization control functions. These techniques seek to minimize the uncertainty in the position / orientation of each layer in a solvent-bonded retarder stack lamination method. These techniques also seek to minimize internal in-plane stresses within the retarder stack at the lamination points that may occur in prior art lamination methods. These embodiments typically introduce process control in the manipulation of the input or feed film of the bonding process. In particular, these embodiments attempt to control the leading edge of the feed film up to the critical steps including the lamination zone forming the laminate.

[0008] This paper describes solvent lamination apparatus and methods that minimize uncertainties in film orientation and optimally preserve statistical data during the fabrication of the underlying retarder film. The former refers to methods that achieve high repeatability in the orientation setup of the feed film (or input film) based on reliable mechanical references (e.g., film edges). The latter refers to the uniformity of pressure along the roller axis in the lamination zone, which is established during lamination zone formation. In the presence of such non-uniformity, localized in-plane compressive loads may exist on the input film, potentially impairing optical axis and phase difference statistics. Furthermore, this non-uniformity can propagate along the longitudinal direction during lamination, affecting the performance of the entire master sheet. Because solvent lamination does not involve adhesives that could potentially introduce mechanical compliance, any such stresses can be permanently frozen into the structure at the moment of bond formation. The techniques described herein aim to overcome uncertainties in lamination zone formation and other potential lamination stresses that could impair the performance of the retarder stack.

[0009] The apparatus and methods disclosed herein ideally provide exemptions from many specific properties of the input (feed) membrane, making the process more robust. This can be achieved by placing a preloading mechanism at / near the leading edge of the input membrane, allowing the input membrane to be supported during the critical pressing zone formation step. The formation of the pressing zone involves at least four elements. In a single-roller configuration, these elements include the input membrane, pressure roller, build plate, and build membrane (work-in-progress, WIP stack) attached to the build plate. Embodiments use some form of reference surface to support as much of the input membrane area as possible to flatten the membrane before the pressing zone is formed. This is achieved while minimizing in-plane stress (particularly in the area forming the pressing zone). In another embodiment, a fifth element (a deformable support member) is introduced to provide complete support for the feed membrane.

[0010] The performance of the retarder stack fabricated according to the teachings of this paper depends on maintaining the in-plane optical path length difference (also known as R) during the fabrication of each base film. e ) and optical axis orientation. High peel strength solvent bonding uses a method suitable for softening the substrate surface almost instantaneously without significantly damaging R. e The solvent has a specific value. Under sufficient pressure / time (or energy), this bond can be formed. A uniform downward force applied to the lamination does not impair the functional properties of the resulting stack. However, any in-plane stresses occurring during lamination can severely compromise these properties. This paper describes several sources of in-plane stresses that can affect retarder stacks, as well as non-uniform downward forces, and the apparatus / methods for minimizing the effects on these retarder stacks. Attached Figure Description

[0011] Figure 1: Existing apparatus for solvent bonding of polycarbonate delayed film together.

[0012] Figure 2: In existing bonding devices, the uncertainty of the angle between the edge of the feed film and the roller axis may be caused by the unsupported film.

[0013] Figure 3: Localized in-plane compressive stress that may occur in existing bonding devices when forming a pressing zone with an unsupported membrane.

[0014] Figure 4 : A feed plate structure that minimizes the unsupported length (D) of the membrane leading edge.

[0015] Figure 5 : A transverse view of the feed plate, wherein (A) is a membrane in a relaxed state, (B) is a membrane conformal to the feed plate, and (C) is the leading edge of the membrane captured between the retaining rod and the feed plate.

[0016] Figure 6 A method for forming an exemplary pressing zone according to the invention, the method comprising: (A) mechanically aligning an input film onto a feed plate, (B) forcing the film to conform to the feed plate, (C) capturing the leading edge of the film with a retaining rod, (D) partially winding the film around a laminating roller, (E) forming the pressing zone, and (F) removing the retaining rod and moving the stage to a starting position.

[0017] Figure 7 : Top view of the laminator structure of the present invention using a segmented feed plate.

[0018] Figure 8 Method steps for constructing an alternative laminator of the present invention using a single three-position feed plate.

[0019] Figure 9 : An enlarged view of the end of the feed plate of the present invention, which has a contoured upper surface to which a vacuum bending force is applied.

[0020] Figure 10 The solvent laminator of the present invention uses deformable support members.

[0021] Figure 11 Method steps of the solvent laminator of the present invention using deformable support members.

[0022] Figure 12 Side view of the pressed zone constructed using two solvent-laminated laminators with deformable support members (DSMs), wherein (A) is a narrow gap and conventional uniform strain on the DSM, and (B) is a wide gap and two-piece DSM, wherein the outer portion relieves most of the strain. Detailed Implementation

[0023] These technologies are driven by the need for high-precision, large-area, manufacturable optical retarder stacks for polarization control. These stacks are needed for augmented reality or virtual reality headsets (e.g., polarization-based thin lenses and optical isolators), direct-view displays (e.g., ambient light control, sunlight readability, and OLED display isolators), stray light mitigation, image capture filters, wavelength-selective polarization control, polarization measurement, sunglasses, color-deficient glasses, and other custom-designed optical components. These stacks are typically transparent stretched polymers with one or more of longitudinal, transverse, or diagonal in-plane stretching. Thicknesses typically range from 25 micrometers to 100 micrometers. While most substrates (e.g., polycarbonate or cycloolefins) tend to exhibit increased refractive index (positive anisotropy) in the stretching direction, other, less common substrates exhibit negative anisotropy (e.g., polystyrene). Polycarbonate retarders are well-suited for applications requiring large in-plane optical path length differences (R0). e In cases where the wavelength range is 400 nm to 2,000 nm, or where price is very sensitive (e.g., 3D cinema glasses), manufacturers include Teijin and Kaneka. Cycloolefins (e.g., cycloolefin polymers from Zeon, or cycloolefin copolymers such as Arton from JSR) are optically transparent, planar, have low refractive index, low birefringence dispersion, low hygroscopicity, and are well-suited for applications requiring low in-plane optical path length differences (R0). e In the case of <300 nm), COP (Cyclic Optical Array) is generally preferred for manufacturing robust, high-performance retarder stacks due to factors such as manufacturing statistics, low stress optical coefficient, low tensile elongation (i.e., high Young's modulus), and environmental robustness (e.g., stress due to hygroscopic expansion). For example, multilayer achromatic circular polarizers require optical path length differences in the range of 100 nm to 300 nm, which falls within the manufacturing range of COP. The impact of any in-plane stress generated by the solvent laminator on the COP stack is less than that from similar PC stacks.

[0024] Retarding films are manufactured in a continuous web process by heating a uniformly thick cast / extruded transparent film to (near) its glass transition temperature and stretching the film to achieve a predetermined spatially uniform optical path length difference. Web widths range from 500 mm to over 1,300 mm, and lengths can reach hundreds of meters. Manufacturers can provide one or more longitudinal slit edges, although there may be some uncertainty in the orientation of the optical axis relative to the slit edges. Since uniformity is never perfect, testing may be required to precisely position the optical axis. The statistical variation of optical retardation / optical axis in the cross-web direction is often greater than that in the down-web direction. Retarder stacks typically use multiple optical axis orientations, and therefore, these stacks are usually manufactured via a batch process using one or two retardation values. These techniques specifically involve methods that support batch processes. Each layer of the master sheet is cut from the web at an appropriate angle using mechanical or laser methods, depending on the requirements of the specific design. The size of the master sheet can be, for example, A4, but scaling to, for example, A2 is preferred to reduce manufacturing costs. The machine design assumes that the base film delay / optical axis statistics, testing protocols, and master sheet cutting processes collectively optimize the statistical characteristics of the input master sheet. Each master sheet has at least one reference edge with sufficient straightness (or equivalent reliable registration features), a reliable optical axis orientation relative to that edge, and a sufficient in-plane optical path length difference (R0). e )Statistical data. Therefore, it is assumed that the mother stack produced by the laminator has high repeatability in terms of edge orientation alignment and has a minimum R caused by lamination. e When the changes occur, the best possible performance of the delayer stack is achieved.

[0025] Even after fabrication (i.e., in the glassy state), the retardation film remains susceptible to any elastic deformation resulting from the lamination process. The degree of this susceptibility depends on the amount of stress applied (σ, or force per unit cross-sectional area) and the stress-optical coefficient (C, or birefringence (Δn) per unit stress). For a film with thickness d, the resulting difference in optical path length can be expressed as follows:

[0026] Δn d=σC d

[0027] A membrane subjected to a small force F along its length (the cross-sectional area of ​​which is defined by the product of d and width w) has an optical path length difference per unit force, given by the following formula:

[0028]

[0029] For example, if a vacuum is applied to the feed platform during lamination, the input film can be under quasi-uniform tension in the longitudinal direction at the lamination point. This process can also (e.g., due to fixation) generate more localized forces, which may be more influential than forces uniformly distributed across the width. Furthermore, solvent bonding of low-stress-optical-coefficient polymers is generally preferred according to the above equation. If an in-plane force is applied at the lamination point (i.e., in the lamination zone), this force can become permanent during solvent-lamination. Conversely, the PSA layer provides some compliance that may alleviate stress, and post-processing heat treatment can potentially alleviate some of the stresses associated with the lamination process. If a small uniaxial in-plane stress (positive anisotropy) is applied along the slow-axis retardation film, the optical retardation increases proportionally with the increase of the slow-axis refractive index, and the optical axis orientation remains stable. Similarly, if a small stress is applied perpendicular to the slow-axis retardation film, the optical retardation decreases proportionally with the increase of the refractive index perpendicular to the slow axis, and the optical axis stabilizes again. If stress is applied at ±45° to the slow axis, the optical retardation is essentially stable, and the optical axis rotates with a sign that depends on the stress orientation. At other angles, there is a mixture of optical retardation and optical axis orientation variations. Therefore, a lamination method is sought that minimizes in-plane elastic deformation at the lamination point, thereby optimizing the performance of the resulting stack.

[0030] When the membrane conforms to the lamination roll, it can also deform elastically. For single-roll lamination methods with planar backing surfaces, the input membrane can conform to the roll at the lamination point, where the build-up side (or stack) can be substantially free from in-plane stress. For a roll with radius R, the in-plane stress at the contact point is given by:

[0031]

[0032] Here, E is the Young's modulus of the film. This stress can be frozen into solvent bonds that may cause curling. However, even without significant curling, the polarization function can change significantly. Fortunately, most delayed films in the thickness range of 25 μm to 100 μm are soft enough that the bending stress at the lamination point is acceptable for rollers with a diameter greater than 30 mm (>30 mm).

[0033] In a single-roll lamination method, the formation of the lamination zone involves combining four elements: (1) a lamination roll, (2) an input film (including any protective substrate), (3) a build film (including any lower protective substrate), and (4) a build plate. The handling of the input film during lamination zone formation is often the most problematic due to the flexibility and flatness of the sheet. The entire area of ​​the built stack is rigidly supported by the build plate, thus the entire area of ​​the built stack is relatively well supported, and the roll only needs to extend to form the lamination zone. Various embodiments share the common objective of supporting the input film during lamination zone formation and subsequent lamination.

[0034] The construction of the master sheet can vary significantly depending on the substrate's chemical properties, surface energy, thickness, flatness, molecular weight / hardness, the type / thickness of any protective substrate, the application process, and the typical flat-lay characteristics of the input film. The film may have a roll-set, thus exhibiting an upward / downward curling tendency after being cut to master sheet dimensions. The precise axis of the curl can depend on the orientation of the optical axis relative to the edge. The film may have an anti-reflective coating, which may cause stress-induced curling. The film may have a protective substrate, which may cause curling or be laminated under mechanical loads, thus affecting the film's flatness. The film may absorb moisture, causing curling. The film may have a high surface energy, thus tending to form discrete optical contacts when it is close to a film on a build plate. The film manufacturing process may cause, for example, lateral width variations during flat-laying, such as corrugations. All of the above-mentioned variables in the master sheet characteristics can introduce uncertainties in prior art solvent lamination methods, which may affect the performance of the resulting retarder stack. First and foremost, these indicators include the repeatability of lamination orientation and the non-uniformity of in-plane stress in the input membrane.

[0035] Ideally, each master sheet should be laid flat when not subjected to significant external loads (e.g., gravity alone). Since the finished retarder stack typically needs to be planar, any bending force required to flatten each sheet could alter the in-plane stress at the lamination points. A base film requiring minimal bending force to produce a flat sheet (e.g., a flat sheet conformally to the lamination rolls is typically required) is more preferable. Furthermore, the protective substrate present during lamination should not significantly degrade the flatness characteristics of the retarder film.

[0036] In solvent lamination methods, the fixation of the input film controls the physical orientation of the film and the R... eMaintaining the uniformity of the optical axis can be crucial. According to prior art methods, the diaphragm can be inserted onto a vacuum feed plate, slid into the pressing zone, and aligned with a reference guide. If the vacuum is strong enough (e.g., if there is a strong vacuum clamping between the membrane and the feed plate), the alignment relative to the guide can be reliable. However, a certain length of unsupported membrane hanging over the end of the feed plate for the purpose of establishing the pressing zone can be problematic. The unsupported length, including the hanging portion (the minimum length required to extend into the pressing zone), and the potential length lacking vacuum support at the end of the feed plate, can introduce uncertainty in membrane alignment. This can occur even if the membrane is precisely aligned with the reference guide. Figure 1 shows a side view of a prior art device (US 6,638,583, or '583) for solvent-laminated polycarbonate delayed films. This disclosure indicates in the figure the minimum unsupported length D of the membrane, which extends from the end of the membrane conveying device to the contact point. As shown, this distance is approximately equal to the diameter of the roller.

[0037] The lamination control in the '583 apparatus of Figure 1 is affected by the characteristics of the input film and the unsupported length. For example, if the film tends to curl upwards, the unsupported length may tend to spontaneously form one or more localized contacts with the film on the build side. In this case, the surface energy of the film may be sufficient to create a location for forming an optical contact, and the input film is "suspended" on the build film when it slides into place. When this occurs, the film can be lifted relative to the feed plate, and the lift height may be a function of the position in the transverse (roller axis) direction. If the associated force on the film is sufficient to break the vacuum clamping near the end of the feed plate, the unsupported length can be effectively increased, and the problem may be exacerbated. If laminating A4 sheets (210 mm transverse width) and a required orientation tolerance of 0.1° is required, the associated height difference in the transverse direction is 367 micrometers. If this height difference persists after the laminating rollers extend, the 0.1° error in film orientation is "carried over" into the finished laminate.

[0038] If the membrane tends to curl downwards in the '583 apparatus, the unsupported length may not make initial contact with the build-side membrane when it slides into the lamination position. If over-curling occurs, the membrane may make initial contact with the rollers. In either case, the membrane only contacts the build-side membrane after the rollers have extended and formed the lamination zone. In this case, the rollers may again partially lift the membrane upwards while it is trapped in the lamination zone, introducing orientation uncertainty. Note that the axis of the curl (which can be a function of the orientation of the optical axis relative to the edge) can affect the position where the rollers make initial contact with the membrane. For example, this may preferably cause one corner to be lifted more than the other.

[0039] Figure 2 illustrates a first problem that may occur in the prior art ('583) apparatus of Figure 1. The figure shows a view of the membrane conveying device and the rollers. Edge lifting of the input membrane can occur by interaction with the rollers during extension, or via contact between the input membrane and the build membrane before the rollers extend, or both. As shown, random manipulation of the leading edge of the input membrane can produce uncertainty in the angle between the transverse edge of the membrane and the roller axis. Although the longitudinal edge of the membrane may appear to align precisely with the reference guide, orientation errors may still exist when the bonding zone is formed, and these errors can become permanent orientation errors in the bonded stack.

[0040] Figure 3 illustrates a second problem that may occur in the prior art ('583) apparatus of Figure 1. As previously mentioned, the unsupported leading edge of the input membrane may initially contact the surface of the build membrane, the roller, or not until the roller extends. In any case, in the prior art apparatus, the unsupported length of the membrane is essentially unrestricted until the membrane is captured in the pressing zone. At the point where the pressing zone is formed, the leading edge may randomly contact the build membrane at one or more locations. This contact may alter the membrane orientation, but it may also create localized in-plane stress zones. Figure 3(A) shows the input membrane on the feed plate before vacuum is applied, with the three contact points in the figure being spontaneously formed between the input and build membranes. Figure 3(B) illustrates the in-plane stresses that occur when the roller extends and the input membrane is captured. The input membrane may have a high surface energy, such that after contact with the build membrane, there may be no further slippage, which would otherwise release stress and create uniform pressure (i.e., only downward force). Without slippage, the input membrane may experience localized in-plane compressive stress between the aforementioned contact points. This stress may not be released when solvent is dispensed and bonding begins, and this initial condition can extend to the entire length of the mother sheet. Similarly, this situation is caused by the unconstrained leading edge of the input membrane.

[0041] Figure 4This is a side view of a portion of an exemplary feed plate. An input membrane is shown, conformally fitted to the feed plate, with a minimum length D of unsupported membrane overhanging. The feed plate may have a low surface energy coating (e.g., Teflon, PTFE, or parylene coating), or the input membrane may have a low surface energy protective substrate, or both, so that the conformal action of the input membrane to the feed plate does not cause significant in-plane stress. The feed plate preferably provides a downward force across the entire surface of the input membrane, making the input membrane effectively infinitely rigid as close as possible to the lamination zone. The underside of the feed plate may thin near its ends so that the roller is as close as possible to the ends of the feed plate. For a lamination roller with radius R, the length of the unsupported feed membrane is preferably less than R or more preferably close to R / 2. The top of the roller may be substantially coplanar with the feed plate, or slightly above the feed plate for easy contact. The roller can be made of a low surface energy material, or the roller can have a low surface energy coating, such that when the feed plate applies a downward force to the input membrane, the leading edge of the input membrane makes uniform contact with the top of the roller.

[0042] Figure 5 The process for capturing the leading edge of the feed membrane and retaining it during the formation of the compression zone is illustrated. The normal direction in the figure represents the longitudinal direction, and the X direction is along the transverse direction. Figure 5 (A) shows the feed film on the feed plate before the clamping force is applied. Figure 5 (B) shows the feed membrane after a downward force has been applied, where the feed membrane conforms to the feed plate as previously described. Figure 5 (C) illustrates a retainer bar (RB) actuated to the top of the leading edge of the feed film. The retainer bar captures the feed film between the retainer bar and the roller, thus maintaining the established orientation without introducing significant in-plane stress. The retainer bar may have a low surface energy coating, or it may be made of a low surface energy material. The profile of the retainer bar can be selected to provide a strong and uniform clamping of the feed film without introducing any deformation as the feed film is pressed against the roller. For example, the retainer bar may have a profile that matches the profile of the roller to distribute pressure uniformly. The retainer bar may be substantially parallel to the roller axis throughout the transverse direction, such that the pressure in the transverse direction is uniform throughout the capture of the feed film. Alternatively, the retainer bar may have a profile in the transverse direction that facilitates the spread of the feed film in the transverse direction (e.g., crown-shaped), thereby achieving uniform contact between the feed film and the roller without introducing in-plane stress. In this configuration, the retaining rod can initially contact the feed film near the center of the roller in the transverse direction, and then, as the pressure increases, the pressure can diffuse outward in both directions in the transverse direction. Similarly, the roller can have a uniform diameter, or the roller can have a profile (such as a crown) that controls the local pressure in the pressing zone.

[0043] Figure 6 The diagram illustrates a six-step process for supporting the leading edge of the feed film during the formation of the pressing zone. The figure is a side view, with the normal to the diagram along the roller axis. Figure 6 (A) to (C) are similar Figure 5 ,only Figure 6 (A) through (C) present different perspectives. Figure 5 As shown in the figure, Figure 6 (A) shows a membrane resting on a platform. Figure 6 (B) shows the film conformally to the feed plate, wherein the minimum length of the unsupported film extends beyond the top of the roller, and Figure 6 (C) shows the leading edge of the membrane captured by the retaining rod (RB). Figure 6 The stage is shown in a horizontal position, although it can also be tilted. If tilted, it is preferable that the tilt angle is small enough that the membrane will not slide into the pressing zone under the influence of gravity when no manual or vacuum pressing is applied. Figure 6 (D) illustrates the steps of partially advancing the film around the laminating roller. This can be accomplished by driving a retaining rod and using an idle laminating roller, or by using a driven laminating roller. As the film is advanced around the roller, some tension may be applied to the film via vacuum, air, or electrostatic discharge from the feed platen. This is done to ensure uniform contact between the film and the entire surface of the roller. Similar to the feed platen, ensuring uniform conformity of the film to the roller effectively increases the film thickness and thus eliminates uncertainties. The goal is to achieve complete conformity between the film and the roller without introducing in-plane stress. While in-plane stress can be applied during the process of advancing the film around the roller, this in-plane stress can be significantly reduced or completely eliminated when the pressed zone is formed. The amount of tension required depends on the tendency of the film to physically separate from the roller, which may leave the film unsupported and potentially lead to the uncertainties described earlier.

[0044] The benefit of conforming the membrane to the roller is that it eliminates the degrees of freedom that exist when the membrane is not under any load. For example, it is easy to introduce curvature along one axis into a flexible membrane using a very small bending force, but when the membrane is already bent around the roller axis, a large force is required to introduce curvature along one axis into the membrane. The desired single-axis curvature can be introduced using conventional rollers, where a rubber / silicone layer is cast onto the shaft and machined / polished. A retainer can be used to hold the membrane, and the above process allows the leading edge to conform to the roller. Alternatively, a vacuum roller can be used to force the membrane to conform to the roller without a retainer. In this case, the vacuum should be applied uniformly so that no in-plane stress is induced when the vacuum is turned on or when the membrane is advanced around the roller. In this case, the roller can be driven. One concern with vacuum rollers is that perforations or features that allow air to pass through the roller medium to apply force to the membrane may introduce small pressure non-uniformities during lamination. For example, porous ceramic vacuum chucks often have localized surface depressions, even after polishing, and if the film is conformal, subsequent lamination processes can transfer these surface irregularities into the laminate. In the case of optical films, this "read-through" caused by uneven pressure or localized irregularities in the reference surface flatness can render the retarder stack optically unacceptable. A second concern with using vacuum rollers is that a vacuum may be applied to the underside of the protective substrate. If the substrate adhesion to the retarder is insufficient, the substrate may detach from the retarder as the film is advanced around the roller.

[0045] Other methods for conformal bonding of the membrane to the roller include downward forces applied via air pressure, electrostatics, or low-tack adhesives. Downward forces from compressed air are functionally most similar to retainers, although the relatively robust attachment of the membrane to the roller using retainers alleviates any concerns about slippage. Other methods raise the same concerns about substrate-membrane separation as discussed above. Electrostatic clamping also introduces concerns about aesthetic issues caused by the potential for dust attraction due to electrostatic discharge.

[0046] Regardless of the mechanism, the amount by which the film roll advances is the minimum amount required to expose the pressing zone of the feed film while avoiding mechanical interference problems. Figure 6 (D) shows that the retaining rod has advanced far enough that the feed plate / roller assembly can contact the build plate without mechanical interference. Figure 6 (E) illustrates the formation of the lamination zone, where the feed plate / roller assembly translates horizontally and the rollers press the feed film onto the build film. Again, this lamination zone is optimally formed by the feed film in uniform contact with the rollers and with minimal in-plane tension. Once the initial state of lamination has been established through the lamination zone, the retaining rods can be removed, as... Figure 6As shown in (F). With the retaining rod removed, the build plate can be moved to the starting position for improved material utilization. At this point, solvent can be dispensed, the vertical stage can be moved downwards, and lamination is completed.

[0047] Since the initial state of the lamination zone determines the lamination axis and the uniformity of the two films being joined together, precision mechanisms (e.g., guides) are not required to control the lamination process. However, as the input film passes through the feed platen, it may be useful to continue providing loose support for the input film. This can be accomplished using, for example, a small vacuum clamping, or it may be sufficient to place a rod (not shown) above the film to ensure that the film remains conformally aligned with a portion of the rollers in the lamination zone as it advances. As previously stated, any vacuum clamping during lamination should not affect the in-plane statistics of the delayed film. For this reason, a rod slightly suspended above the input film may be preferred. Since the rod can contact the surface of the film, it must be kept clean (i.e., free of solvents and dust), and the rod must not scratch the surface. Near the end of lamination, the trailing edge of the input film tends to detach from the feed platen. Without a clamping mechanism in place, the material may suffer greater exposure to solvents and thus functional damage. To maximize the yield of the master sheet, the clamping mechanism can support the trailing edge of the input film as close as possible to the lamination zone. The clamping rod can be fixed, or it can rotate as the membrane advances. Note that if the clamping rod remains stationary throughout the build process, it may pose some challenges to the removal of the substrate from the feed membrane. Preferably, the rod is raised relative to the feed stage during membrane loading and substrate removal, and lowered directly above the membrane during the lamination process. Alternatively, the rod can be held near the build plate, away from the substrate removal process.

[0048] Figure 7This is a top view of an exemplary batch solvent laminator. This design uses a segmented feed plate, rather than translating the entire feed plate / roller assembly, to form the pressing zone. The operator places the input film (the dashed outline of a rectangular master sheet) substantially on the first segment, with a small portion extending onto the second segment. Mechanical alignment features on the first segment (which could simply be adhesive tape) are used for coarse alignment of the film with the stage. The (coplanar) second vacuum stage segment is part of an assembly that may include laminating rollers. The master sheet spans the entire length of the second vacuum stage segment and extends onto the laminating rollers, with a small portion extending beyond the laminating rollers. After the master sheet is aligned on the feed stage, it is vacuum-pressed. The operator can remove the protective substrate from the top side of the input film. An antistatic air knife can blow air onto the input film to remove any debris. A vision system, including lighting, a camera, a translation platform, and image processing software, quickly and accurately locates the longitudinal edges of the master sheet. In cases where there is any "drift" in the straightness of the mother sheet edge due to cutting, an algorithm can be used to best fit the edge data. Alternatively, a single camera with a sufficient field of view, or two or more cameras in fixed positions, can be used to locate the membrane edge. If the operator does not place the input membrane on the platform with sufficient precision, an alarm can notify the operator that the membrane must be repositioned. The vision system can rely on data from a portion of the membrane scanned on the first vacuum stage segment, in which case vacuum may not be applied to the second vacuum stage segment. Alternatively, the entire length can be scanned, in which case vacuum can be applied to both segments.

[0049] After positioning the membrane edge, fine repositioning of the input membrane can be achieved using a motion stage on the first vacuum stage segment. The most critical type of motion is orientation, where coarse positioning in the lateral and longitudinal directions may be sufficient. For example, an operator can position the membrane with an XY accuracy of ±500 micrometers, which may have no impact on the performance of the resulting stack. However, a 500-micrometer wedge on the A4 mother sheet represents an angular error of 0.1°, which is unacceptable in many cases. By applying vacuum only to segment 1, the membrane is repositioned and (at least) the orientation tolerance can be significantly improved. Alternatively, a platform mounted on the build-side can be used to compensate for uncertainties in the feed plate position. If any orientation uncertainty exists during membrane capture, the adjustment of the build plate orientation can be corrected by scanning the edge (or an image forming the edge) after capture. In the case shown, the gap between the first and second vacuum stage segments allows the first segment to rotate (e.g.) ±1° without mechanically interfering with the second segment. The stage supporting the A2 laminate can have a width of approximately 450 mm. Therefore, a rotation of ±1° requires a gap of approximately 8 mm between the two sections. If the membrane is flexible enough to sag within this gap, the flexible material supporting the membrane can span this gap. The current state-of-the-art accuracy for edge alignment in vision systems is ±50 micrometers. When using A4 master sheet, this translates to an orientation tolerance of ±0.01°.

[0050] Once the membrane is repositioned, a vacuum can be applied to the second section, and the membrane is fully compressed, except for a small length extending onto the roller. As previously described, a retaining rod (RB) suspended above the roller (not shown) can then capture the leading edge by pressing the retaining rod evenly against the laminating roller. The retaining rod can be attached to a mechanism that drives the input membrane partially around the laminating roller, as previously described. Once the membrane conforms to the roller and membrane stress is minimized, the membrane in contact with the roller is provided to the build plate, and the roller translates horizontally to form a pressing zone. In one configuration, the second vacuum stage section travels to the build plate with the roller. In this case, the vacuum applied to the first vacuum stage section is cut off, while the vacuum on the second section can be maintained during translation. Thus, the second section can be used to maintain some tension during the formation of the pressing zone, and even during lamination. Alternatively, the clamping rod can be part of this translation assembly.

[0051] Translational components can have one or more motion mechanisms. For example, the amount of working distance required between the feed platform and the build platform for protecting substrate removal after lamination may require a fast two-position platform with a relatively large translation distance. Once the platform is moved into the lamination position, the roller can extend a relatively short distance using different mechanisms. For example, a cylinder or servo motor can cause the roller to translate (e.g.) 10 mm to 20 mm to form the bonding zone.

[0052] The solvent dispensing head can then travel laterally and dispense one or more sprays into the bonding zone. The motion control platform on the build side can then move downwards and form a bond. At the end of the cycle, the feed platform and build platform return to the starting position. If a protective substrate is located below the feed film, it can be removed manually or using a robot. An air knife can be used to blow air onto the build side, and this process can be repeated until the stack is complete.

[0053] The laminate of the present invention has other embodiments, which are similar in reducing orientation errors and in-plane lamination stress. The above examples illustrate a practical solution that minimizes the amount and complexity of motion of the various components. As an alternative, Figure 8 The demonstration uses a single-segment feeding station. After the feeding membrane is vacuum-fixed, as... Figure 8 As shown in (A), the entire feed plate assembly can be translated / rotated to a second position as needed to optimally provide the leading edge of the feed membrane to the construction membrane. In the second position, as... Figure 8 As shown in (B), the feed plate can provide the leading edge of the feed film to the build film in a quasi-parallel manner, with a small controlled gap between the two films before the rollers extend. In this case, the roller assembly can be stationary, with the pressing zone formed only by horizontal translation via a cylinder or servo motor. Moreover, this configuration may not require a retaining rod. After the rollers extend and the pressing zone is formed, as... Figure 8 As shown in (C), the feed plate can be rotated / translated to a third position that allows solvent dispensing and feed film clamping without mechanical interference. Figure 8 (D) shows a feed plate with the angle between the feed plate and the build plate open to allow solvent injection. Once the lamination zone is formed, relative film orientation and in-plane pressure are essentially established, allowing the feed plate to function as a low-precision surface providing support. Similarly, a guide rod mounted above the feed film can function as a low-precision device to prevent film lifting as it travels along the feed stage. After lamination is complete, both platforms can return to the starting position. This design offers some design simplification, although it may also require more complex movements from a single, substantially larger feed plate assembly.

[0054] Figure 9 This is an enlarged view of the area near the end of a feed plate, as presented in one embodiment. In this case, a profile exists at the upper end of the plate, on which a vacuum can be applied. Vacuum zones can be sequentially joined (e.g., from left to right) to ensure uniform adhesion of the membrane to the plate. When a vacuum is applied at the end of the feed plate, the membrane is subjected to a bending force that reorients it to a downward position. This can reduce or eliminate the impact on… Figure 8(B) illustrates the need to rotate the feed plate. In this case, the film can conform to the profile of the feed plate, with a smaller overhang length D at the leading edge. The preloaded film can be substantially tangential to the roller (with radius R) at the leading edge. As previously stated, the peel strength of any released substrate must be sufficient to prevent the preloaded film from delaminating under bending forces. Once the film is in the downward position in contact with the roller, a pressing zone can be formed. This can be accomplished by translating the roller and keeping the feed plate stationary, or by translating the roller and feed plate together, or both. As discussed earlier, a roller and feed plate pair with a large stroke, and a short roller translation to create the pressing zone, may have advantages in terms of working distance.

[0055] Solvent lamination can, in principle, be performed on any orientation of the lamination zone, provided the (low viscosity) solvent distribution is well controlled. A particularly practical method for solvent lamination is to perform it vertically or near vertically. After the lamination zone is formed, the solvent can be dispensed and a solvent reservoir can be formed, which remains in a quasi-stable position until the lamination stage moves. The time delay allows capillary forces from the film to distribute the solvent uniformly in the lamination zone, after which lamination can proceed. Because local bonding may require very little solvent, and because this can occur quickly enough that evaporation may be insignificant, a single dispensing at the start of lamination may be sufficient to laminate sheets with lengths from 600 mm to 1000 mm. Alternatively, when it is impractical to dispense enough solvent to complete lamination using only pre-lamination dispensing, solvent can be dispensed during lamination to replenish the solvent reservoir.

[0056] In another single-roll lamination method, the formation of the pressing zone involves combining five elements: (1) a lamination roll, (2) a deformable support member (DSM), (3) an input film (including any protective substrate), (4) a build film (or an unfinished stack including any lower protective substrate), and (5) a build plate. The deformable support member is added to support the entire area of ​​the input film during lamination without introducing in-plane stress. The deformable support member can effectively increase the thickness of the input film and make it more mechanically stable. A potential advantage of this method is that the film is fully supported even where the pressing zone is formed. Figure 10A solvent laminator 20 is shown, comprising a feed assembly 22 and build assemblies 32, 34. The feed assembly is shown substantially horizontal during membrane loading, and the build assemblies are shown substantially vertical. While one consideration is the convenience of horizontal membrane loading, some flexibility in angle is also possible. A second consideration is that lamination should be performed at a sufficiently steep angle so that the solvent does not flow in the lamination direction without the influence of rollers. The feed assembly may be a quasi-sealed box containing rollers mounted to a Z-translation platform (e.g., a cylinder or servo motor), wherein the entire assembly travels on a Y-translation platform (e.g., a worm gear drive) 26. A deformable support member 28 substantially covers the upper side (XY plane) of the box. The deformable support member is under tension so that it can hold the feed membrane 30 planarly prior to lamination. The deformable support member may be a polymer (e.g., polyester film), or it may be a metal (e.g., stainless steel). Appropriate material / thickness allows the pressure from the rollers to be uniformly transmitted to the material being laminated.

[0057] After the feed film 30 (e.g., using tape defining two axes) is loaded and roughly aligned, it can be secured by applying a vacuum to the feed assembly 22, and the protective substrate can then be removed. A deformable support member can transfer the vacuum to the feed film and hold it firmly in place, thus supporting the feed film over the entire area. Care must be taken to ensure that this vacuum feature does not locally compromise the lamination. As in the previous embodiment, the vision system can locate the film edges by scanning (e.g.) along the longitudinal direction. A platform for precise alignment of the film can be located on the feed side or the build side. In this case, a positioning platform 34 for precise alignment is mounted on a vertical fixing plate 32 (build assemblies 32, 34 include the vertical fixing plate 32 and the positioning platform 34). A build plate (e.g., a flat glass plate) 36 can be rigidly held to the positioning platform using vacuum or mechanical means. The build film (or stack) 38 is attached to the build plate via tape, optical contact, or a low-tack adhesive. Once secured and aligned, the hinge mechanism 40 can elevate the feed assembly, locking it in place in the same surface-normal direction as the building assembly.

[0058] Figure 11 Demonstrated the use of Figure 10 The lamination process of the solvent laminator. Figure 11 (A) shows a state as Figure 10 The laminator at the loading position in the middle. Figure 11(B) illustrates a feed plate hinged to a vertical position about the X-axis. After the feed plate is locked in place, a uniform gap is formed between the feed film and the build film. This gap facilitates solvent introduction, takes into account the maximum thickness of the stack, and also affects the angle between the feed film and the build film at the lamination point. If the gap is small, the angle between the two films is also small, and capillary forces may cause the solvent to rise too far before the lamination point, damaging both films. When the gap is increased, the roller also translates further in the Y direction to form a bonding zone, but the angle between the two films increases. If rigidly fixed at the boundary, the strain in the deformable support member increases with the gap, and the pressure applied by the roller's cylinder or servo motor can also be increased to maintain a constant bonding zone pressure. Other factors affecting the angle between the two films after the bonding zone is formed include the Young's modulus, thickness, and tension of the deformable support member before the roller extends. If the desired angle necessitates large strain in the deformable support member, it is important that the deformable support member does not transfer in-plane strain to the input film at the lamination point.

[0059] One method to mitigate in-plane stress on the input membrane caused by strain in a deformable support member is to provide some slip during the formation of the lamination zone. For example, if the membrane is fixed only at the beginning / end of lamination, the vacuum can be weak enough to allow the membrane to slip during the initial formation of the lamination zone, thereby releasing stress. Another method to mitigate strain in a deformable support member is to introduce flexible boundary conditions. If the strain is introduced near the boundary, rather than in the portion of the support membrane of the deformable support member, a relatively low stress may be applied to the input membrane. Figure 12 for Figure 11 Enlarged view of the pressing zone of (C). Figure 12 (A) shows an example of a gap whose width W1 forms an approximate angle θ1 between the two membranes. In this case, as the roller extends, there is a single deformable support member layer under quasi-uniform strain. This strain can be partially transferred to the input membrane. Figure 12 (B) illustrates the case where the gap between the two membranes is increased to W2 to produce a larger angle θ2. If the deformable support members have the same construction, greater strain will be introduced to form the compression zone, and the input membrane may be subjected to increased tension. However, as Figure 12 As shown in (B), the deformable support member may include an inner portion supporting the feed membrane and an outer portion that substantially releases tension. The inner portion may be made of a material with a higher modulus than the outer portion, the inner portion may be thicker relative to the outer portion, or both. Thus, the purpose of the outer portion is to generate most of the strain required to induce the desired compression zone geometry, thereby supporting the input membrane without in-plane stress.

[0060] Figure 11 (C) shows the extension of the roller (in the Y direction) to form the pressing zone. The low-profile dispenser can be positioned before or after the lifting feed stage. After the pressing zone is formed, the injection needle can dispense one or more jets as it retracts, creating a solvent reservoir. The solvent dispensing pressure can be minimized to avoid splashing and associated film damage. Figure 11 (D) illustrates the translation of the roller in the Z direction, thereby bonding the two films together. At the end of the stroke, the roller retracts and returns to the starting position, and the feed table returns to the loading position.

[0061] In this configuration, there may be concerns about the impact of deformable support members on lamination quality. If the deformable support members (e.g., through holes) provide a vacuum to hold the feed membrane in place, there may be areas where the pressure required to form a bond is insufficient. In this case, the membrane may be overexposed to the solvent, and reliable bonding may not occur without sufficient pressure. In one configuration, vacuum holes may exist only on sacrificial portions of the mother sheet. For example, vacuum holes may exist only along the transverse direction at the top and bottom of the laminate. This can provide adequate support for the membrane without significantly affecting yield.

[0062] Because the deformable support member is an integral part of the lamination process, it should possess excellent thickness uniformity and surface quality. Otherwise, pressure non-uniformity may result in through-texture and localized in-plane stress. To ensure pressure uniformity within the lamination zone, a different tension in the longitudinal direction than in the transverse direction is also required. Preferably, the deformable support member is substantially conformal to the roller during lamination, and the tension present in the deformable support member at the roller ends can be destructive. This can be overcome by extending the length of the roller / deformable support member sufficiently beyond the width of the film, or by relieving some of the transverse stress. The latter can be achieved by making the area of ​​the deformable support member outside the lamination zone more flexible, either by thinning this area or by using a different material to make it more flexible. This is similar to the methods described above for minimizing longitudinal strain in the deformable support member during roller bonding.

[0063] Typically, the materials and tolerances of components in close contact with the lamination zone must be carefully selected. Optical quality standards are generally preferred to avoid through-printing or read-through textures in the laminate that may result from localized pressure inhomogeneities and solvent exposure. These inhomogeneities can arise from in-plane and normal effects on the sheet. Roll density, thickness, and surface inhomogeneities must be carefully examined, including material uniformity, roll casting / machining processes, and associated defects (e.g., bubbles or inclusions in the cast roll material). The roll axis must be precisely aligned with the build plate to avoid lateral pressure skew. The uniformity of the protective substrate thickness and the cleanliness of the protective substrate lamination must be carefully examined. The thickness uniformity and surface quality of the build plate must be carefully examined. Exemplary build plate materials include polished glass, polished metal, and possibly (e.g., unit-cast) polymers. The latter can contribute to single-use build plates or reduce build plate weight in large-area laminates. The flatness of the build platform must be carefully examined. If a vacuum is used to hold the build plate to the build platform, the vacuum feature cannot be printed through to the laminate. This can be achieved by placing vacuum features outside the lamination area, making these vacuum features small enough, or using a build plate with sufficient rigidity so that these vacuum features do not affect the lamination quality. Of course, all components constituting the lamination area must be free of debris. Particles trapped in the lamination process affect appearance yield, with the area affected by solvents typically much larger than that of physical particles. Particles outside the laminate can affect the local flatness / transmission wavefront quality of the finished stack. The latter can manifest as dents or pits when one surface of the finished stack is subsequently bonded to another optical surface, and these dents or pits are particularly problematic.

[0064] The method used to attach (i.e., temporarily fix) the first delayed film sheet to the build plate must be carefully examined. This process is preferably performed using a laminator (e.g., with adhesive solvent dispensing turned off) so that the machine vision system can place all films with the same accuracy, the same convenience, and minimal handling. The attachment method can be an adhesive applied to a sacrificial area of ​​the mother sheet or the build plate (e.g., double-sided tape along the transverse direction at the start / end of lamination), or the attachment method can be a full bond. The adhesive can preferably be transferable without requiring the transfer of the carrier substrate to the build plate (e.g., with adhesive tape). The functional purpose of the adhesive is to secure the first sheet to some of the same requirements as the bonding process (i.e., maintaining orientation accuracy with minimal in-plane stress). If discrete attachment is performed at the top / bottom, the film cannot move significantly in-plane during subsequent lamination steps. If excess solvent is expelled at the end of lamination in subsequent solvent bonding, the excess solvent cannot be wicked under the stack and could damage the stack. Discrete attachment methods can have some benefits in allowing the membrane to mechanically “float” in the laminated region, which can help reduce in-plane stress.

[0065] If the protective substrate is located on the underside of the retardation film, it preferably has a low surface energy. The protective substrate (or the unprotected retarder) can have a high surface energy, thus creating random optical contacts when in contact with the build plate, resulting in in-plane stress. Furthermore, any air trapped at the interface between these surfaces during the attachment of the first layer can create localized pressure inhomogeneities and texture in the finished stack. As in all previous analyses regarding bonding, any in-plane stresses from the attachment of the first layer can be introduced when the first layer is bonded to the second layer.

[0066] For more complete support, the adhesive previously applied to the first-layer protective substrate or build plate can be used to achieve full bonding of the first-layer sheet to the build plate. This can be done by impregnating or spraying the lamination side of the build plate and then attaching a release protective substrate, which can be removed when the build plate is mounted in the laminator. If the build plate must be cleaned and reused, the adhesive preferably has chemical properties that make it easy to remove with water or a non-corrosive solvent (e.g., isopropanol). The adhesive is ideally applied at a precise thickness and / or has a minimum thickness (<1 micrometer) such that any non-uniformity in the adhesive thickness does not affect the flatness of the laminate. An extreme example of the latter is a water-soluble self-assembling monolayer (SAM), in which head / tail groups provide sufficient adhesion between the build plate material and the protective substrate. The tackiness may preferably be sufficient to reliably hold the stack during lamination, but this tackiness is lower than the tackiness of the protective substrate to the build plate. The latter allows for easy removal of the finished stack (with protective substrates on both sides) from the build plate. If the adhesive layer is extremely thin (e.g., SAM), it may not provide compliance when the first sheet is laminated. This differs from solvent bonding in that there may be no liquid in the lamination zone during attachment. Ideally, the lamination process does not rely on compliance at the build plate to minimize in-plane stress. However, some mechanical isolation between the first sheet and the build plate can be achieved via the mechanical properties (thickness / modulus / surface energy) of the protective substrate. In some cases, the adhesive can be in liquid form when attaching the first sheet, thus providing some lubrication and minimizing in-plane stress. For example, a low-viscosity cyanoacrylate adhesive can be dispensed into the lamination zone and rolled to attach the first sheet.

[0067] Other possible methods exist for attaching the first layer to the build plate. This can be accomplished using a vacuum transferred from the build platform through the build plate. These vacuum features can be located only on sacrificial portions of the mother sheet. As discussed with reference to vacuum rollers, very small features capable of achieving vacuum compaction can compromise the optical properties of the retarder stack. Full attachment can also be achieved using electrostatic attraction between the first layer and the build plate. Attachment can also be achieved via van der Waals attraction force between the protective substrate (or bare retarder) and the build plate chemicals. A suitable liquid can be dispensed in the pressing zone to promote chemical bonding that is strong enough for fixation but easily broken when the completed stack is peeled off.

Claims

1. An apparatus for precisely solvent-laminating two or more delayed films with low in-plane stress, the apparatus comprising: A feed plate adapted to fix a monolayer retardation film, the feed plate including mechanical features for substantially positioning and oriented the monolayer retardation film; Construction board, the construction board being adapted to fix one or more layers of a delayer stack; A vision system adapted to locate the position and orientation of the feed sheet; A first motion stage is attached to the feed plate or the build plate, and the first motion stage is adapted to use information transmitted through the vision system to correct relative errors in position and orientation between the retardation film and the retarder stack. A second motion table and a laminating roller, the second motion table and the laminating roller being adapted to laminate the feed sheet onto the one or more sheets of the retarder stack, wherein the laminating roller is further adapted to be positioned close to the feed plate such that the unsupported length of the retarding film between the feed plate and the laminating roller is less than the radius of the laminating roller; Solvent dispensing head, the solvent dispensing head being adapted to deliver solvent to the pressing zone; and A mechanism adapted to convey the leading edge of the feed sheet to the retarder stack, and the mechanism substantially maintains the relative orientation between the feed sheet and the retarder stack and minimizes the in-plane stress on the feed sheet.

2. The apparatus according to claim 1, wherein, The feed plate is positioned in a substantially horizontal plane, and the construction plate is positioned in a substantially vertical plane.

3. The apparatus according to claim 1, wherein, The angle of the feed plate relative to the horizontal direction is less than 40°, and the angle of the building plate relative to the vertical direction is less than 20°.

4. The apparatus according to claim 1, wherein, The feed plate includes two sections: a first static section that supports the retardation film during vision system alignment; and a second section that conveys the leading edge of the feed sheet to the retarder stack to form the pressing zone.

5. The apparatus according to claim 1, further comprising an in-plane stress relief mechanism, wherein, The leading edge of the feed sheet is captured between the laminating roller and the retaining rod.

6. The apparatus according to claim 5, wherein, The device is configured such that the retaining rod can advance around the laminating roller to provide the feed sheet to the carrier substrate or the delayer stack without mechanical interference.

7. The apparatus according to claim 6, wherein, The device is configured such that the laminating stage is driven to the lamination start position after forming the pressing zone and retracting the retaining rod, thereby maximizing the area yield of the delayer stack.

8. The apparatus according to claim 1, wherein, Vacuum fixation is used during alignment to hold the feed sheet in place.

9. The apparatus according to claim 1, wherein, The retarder stack is received by an optically flat, rigid carrier substrate attached to the build plate using vacuum or mechanical fasteners, wherein the carrier substrate and the retarder stack can be removed from the laminator after the solvent lamination process is completed.

10. The apparatus according to claim 9, wherein, The rigid carrier substrate includes polished glass or polymer.

11. A method for solvent-laminating two delayed films with low in-plane stress and high orientation accuracy, the method comprising: Align the first layer of delayed film on a feed plate with mechanical registration features; Load the carrier substrate onto the construction board; Use a vision system to locate the edge of the first layer of the retardation film; The position and orientation of the first layer of delayed film are selected using a motion table attached to the feed plate; The first layer of delayed film is transferred to the carrier substrate using a lamination stage that is attached to the construction plate; Align the second layer of retardation film with the feed plate and keep the second layer of retardation film against the feed plate; The vision system is used to locate the edge of the second layer of the retardation film. The second layer of retardation film is aligned with the first layer of retardation film using the motion table attached to the feed plate; The leading edge of the second layer of delayed film is captured between the retaining rod and the laminating roller; By translating a section of the feed plate, the second layer of delayed film is supplied to the first layer of delayed film, thereby forming a pressing zone; Dispensing the solvent into the pressing zone; and The second layer of delayed film is solvent-bonded to the first layer of delayed film using the lamination table. The laminating roller is adapted to be positioned close to the feed plate such that the unsupported length of the first sheet delayed film between the feed plate and the laminating roller is less than the radius of the laminating roller.

Images