Patent Publication Number: US-8992204-B2

Title: Patch coating die

Description:
FIELD 
     The present invention relates to coating dies or applicator dies for applying a liquid coating material to a moving sheet or web. 
     BACKGROUND 
     A coating die is used to apply a thin layer of liquid material (e.g., thermoplastic or solvent based) to a support substrate such as a sheet or film. The most common coating process is to provide a continuous layer of coated material on the substrate by having a continuous stream of material applied to the moving substrate. However, occasionally it is desired to coat a strip or patch of material, the patch having a specific length, with uncoated areas therebetween. Such ‘patch coating’ is often desired for applications such as adhesive labels, batteries (e.g., lithium ion batteries), and for biological studies. For these instances, the application of the coating material is temporarily stopped or interrupted while the substrate continues to move, providing an area of un-coated substrate around the perimeter of the coating. 
     One attempt to provide an apparatus that can temporarily stop the flow of coating material is described in U.S. Pat. No. 4,756,271 to Maier. This patent describes a coating die that includes a rotatable cam inside, which can be rotated among different fluid chambers to select different materials or to interrupt the coating during web movement. 
     Another attempt to provide an apparatus that can temporarily stop the flow of coating material is described in U.S. Pat. No. 4,725,468 to McIntyre. This patent describes a method of co-extruding a discontinuous or sectioned coating over a continuous coating. A 3-way poppet valve (such as described in U.S. Pat. No. 4,565,217) can be intermittently shuttered by an electronic control circuit to control the flow of the discontinuous material. 
     These designs, however, can be problematic for high speed coating, because the on and off flow stopping is not fast enough or sufficiently accurate for short un-coated distances between patches. There is always room for improvement. 
     BRIEF SUMMARY 
     The present disclosure relates to a coating apparatus and more particularly to a coating die for intermittently applying liquid material onto a substrate. The coating die includes a shut-off bar located in the material flow channel within the die, the shut-off bar being activated (i.e., raised and lowered) using magnetic actuators which have fast acceleration and are highly accurate. Closing the shut-off bar stops the flow of coating material through and out of the die, thus interrupting the flow of coating material onto the substrate being coated. 
     In one particular embodiment, this invention is directed to a coating die having a die body with a flow channel therethrough, the flow channel in fluid communication with a die inlet and a die outlet. A shut-off bar in the die is moveable from an open position out of the flow channel to a closed position into the flow channel, the shut-off bar having an upstream surface, a downstream surface, and an end therebetween. When the shut-off bar is in the closed position, the downstream surface physically contacts the flow channel, and the shut-off bar end makes no contact with the walls that define the flow channel. In some embodiments, a flow channel wall may define a shoulder, so that when in the closed position, the downstream surface of the shut-off bar physically contacts the shoulder of the flow channel. The shut-off bar may move linearly from the open position out of the flow channel to the closed position in the flow channel. The shut-off bar may move orthogonally in relation to the flow channel, which may be vertically. The end of the shut-off bar may be slanted down from the upstream surface to the downstream surface. 
     In another particular embodiment, this invention is directed to a coating die having a die body with a flow channel therethrough, the flow channel in fluid communication with a die inlet and a die outlet, and with the flow channel defined by a first wall and an opposite second wall, the second wall defining a shoulder. The coating die includes a shut-off bar moveable from an open position out of the flow channel to a closed position into the flow channel, the shut-off bar having upstream surface and a downstream surface. When the shut-off bar is in the closed position, it extends across the flow channel and the downstream surface physically contacts the shoulder stopping flow through the flow channel. 
     In yet another particular embodiment, this invention is directed to a coating die having a die body with a flow channel therethrough, the flow channel in fluid communication with a die inlet and a die outlet. The die includes a shut-off bar moveable from a first position to a second position, so that when in the first position, the flow channel is open for flow of coating material therethrough and when in the second position, the flow channel is closed to flow of coating material therethrough. The seal formed by the shut-off bar is at a right angle to the flow channel. In some embodiments, the shut-off bar may move at a right angle to the flow channel, for example, linearly from the first position to the second position in the flow channel. The shut-off bar may move orthogonally in relation to the flow channel, which may be vertically. 
     These and various other features and advantages will be apparent from a reading of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which: 
         FIG. 1A  is a schematic side view of a coating die apparatus for patch coating;  FIG. 1B  is a schematic side view of another coating die apparatus for patch coating; 
         FIG. 2  is a perspective view of a coating die of the present disclosure; 
         FIG. 3  is a side view of the coating die of the present disclosure; and 
         FIG. 4  is a side view of a shut-off bar;  FIG. 4A  is an enlarged side view of the coating die of  FIG. 3  illustrating the shut-off bar of  FIG. 4  in a closed position; and  FIG. 4B  is an enlarged side view of the shut-off bar in an open position. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying set of drawings that form a part hereof and in which are shown by way of illustration at least one specific embodiment. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The present disclosure relates to coating dies that have a shut-off bar positioned to stop the flow of coating material within the flow channel of the die when the shut-off bar is in the closed position. In the closed position, the shut-off bar extends across the material flow channel, blocking flow of coating material therethrough. The shut-off bar moves essentially transverse or orthogonal to the direction of material flow and the seal formed by the shut-off bar to block the flow is essentially transverse or orthogonal to the direction of material flow. In some embodiments, the flow channel includes a shoulder against which the shut-off bar seals, the seal being essentially transverse or orthogonal to the direction of the material flow channel. Coating dies having a shut-off bar are particularly suited for patch coating applications. 
     While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below. 
       FIGS. 1A and 1B  illustrate two generic processes for manufacturing continuous webs of patch coated material. Both processes include a coating die in accordance with the present disclosure that applies a coating material (for example, a thermoplastic material, solvent based, or a high-solids liquid material) to a moving substrate or web. As used in this discussion and throughout, “length” refers to the dimension in the direction of travel of the substrate (i.e., the machine direction) past the coating outlet and “width” refers to the dimension taken transverse to the machine direction. 
     In  FIG. 1A , a continuous sheet or web of substrate  5  is provided onto which regions of coating  6  are applied. Between regions of coating  6  are substrate regions void of coating  7 . Coated regions  6  and void regions  7  are formed by coating die  10 A applying the coating material in an intermittent manner; that is, coating die  10 A starts, stops, and restarts the application of the coating material onto substrate  5  as substrate  5  passes by coating die  10 A. Coating die  10 A has a first or upper die body  12 , a second or lower die body  14  and a flow channel  15  therebetween. Coating material passes through flow channel  15  from a coating material source (not illustrated), such as an extruder, to outlet  16  where the coating material is applied to substrate  5 . In this configuration for  FIG. 1A , coating die  10 A deposits coated material on substrate  5  opposite a backup roll  9 . The apparatus of  FIG. 1A , which utilizes backup roll  9  opposite coating die  10 A, is often referred to as “supported web” or “on-roll” coating. 
     Similar to the process illustrated in  FIG. 1A , in  FIG. 1B  a continuous sheet or web of substrate  5  is provided onto which regions of coating  6  are applied. Between regions of coating  6  are substrate regions void of coating  7 . Coated regions  6  and void regions  7  are formed by coating die  10 B applying the coating material in an intermittent manner; that is, coating die  10 B starts, stops and restarts the application of the coating material onto substrate  5  as substrate  5  passes by coating die  10 B. Coating die  10 B has a first or upper die body  12 , a second or lower die body  14  and a flow channel  15  therebetween. Coating material passes through flow channel  15  from a coating material source (not illustrated), such as an extruder, to outlet  16  where the coating material is applied to substrate  5 . The apparatus of  FIG. 1B  is often referred to as “tension web” coating or “off-roll” coating. 
     In both processes illustrated in  FIGS. 1A and 1B , coated regions  6  are eventually dried or cured, resulting in an elongate product having patches of coated regions  6  extending in the machine direction or direction of substrate  5  with regions void of coating  7  between adjacent coated regions  6 . 
     Coating processes such as illustrated in  FIGS. 1A and 1B  can operate at a wide range of production speeds. For example, it is not uncommon for commercial embodiments of the above arrangement to operate at rates from a few feet per minute to 3500 feet per minute using webs having widths of less than one foot, one meter, or more. It is understood that substrates of almost any length and/or width can be used with these coating processes. Although in most embodiments the substrate being coated is a flexible substrate such as a polymeric film, rigid substrates may also be coated with the dies and processes described herein. 
     Many different coating compositions can be coated by the processes and the coating dies of this disclosure. The coating material may be, for example, hot melt or thermoplastic materials (e.g., adhesives), solvent-based materials, low VOC-based materials, emulsion-based adhesives, and high-solids materials. Furthermore, a wide variety of different liquid coatings, such as pressure sensitive adhesives, conductive coatings, insulating or non-conductive coatings, and inks, can be applied using coating dies and techniques as described herein. Two applications that are particularly conducive to patch coating are formation of battery cells (e.g., lithium ion batteries) and solar panel or photovoltaic parts. 
     Returning to  FIGS. 1A and 1B , alternating coated regions  6  and regions void of coating  7  are produced by a coating die according to this disclosure that has an internal shut-off bar that is actuated to interrupt the flow of coating material through the die. Referring now to  FIGS. 2 and 3 , a coating die  100  has a general overall configuration that is well known, having a first or upper die body  102  and a mating second or lower die body  104 . Die bodies  102 ,  104  define therebetween a flow channel  105  for passage of coating material through die  100 . Coating material enters die at an inlet (not illustrated) and exits via outlet  106 ; in the Figures, the inlet is located at the right side of the illustration and outlet  106  is on the left side, so that coating material flows through channel  105  from right to left. 
     Flow channel  105  is generically referred to herein and is not described in detail. Those skilled in the art of coating dies and coating processes understand that flow channel  105  includes a manifold downstream of the inlet, the manifold being for distributing the coating material across the width of the die. The manifold may be any suitable type, such as a horseshoe or Winter manifold, a coat hanger manifold, a fishtail manifold, or a t-manifold, and does not affect the inventive features of die  100 . Downstream of the manifold may be a preland region prior to a land region that leads to outlet  106 . Flow channel  105  may include other features, such as transition areas or run-out areas. The manifold, preland and land are arranged substantially parallel to and substantially as wide as the corresponding outlet  106  to provide a uniform delivery of liquid coating material widthwise across the web to be coated. Lands and/or outlet  106  are typically adjustable in height so that the thickness of coating applied can be adjusted as desired. The width of outlet  106  may be fixed or may be adjustable, for example, by deckling or a deckling system. 
     Coating die  100  includes an internal shut-off bar that is used to interrupt the flow of coating material in flow channel  105  through die  100 . Referring to  FIG. 4 , a shut-off bar  110  for die  100  includes a blade  112  that extends the width of at least outlet  106  and in most embodiments the width of die  100 . Blade  112  defines an upstream surface  114  and a downstream surface  11  of shut-off bar  110 . Blade  112  is sufficiently rigid to withstand the pressure of coating material pushing against it without deforming; as an example, a blade  112  about 0.1 inch (about 2.5 mm) to 0.25 inch (about 6.3 mm) thick is able to withstand fluid pressures on the order of 28 psi, although both higher and lower pressures may be encountered on blade  112 , depending on the pressure of the coating material entering die  100  and the time duration shut-off bar  110  is closed. In general, a thinner blade  112  is preferred over a thicker blade  112 , as a thinner blade will require less actuator force to overcome the fluid pressure pushing back up against blade  112  and its end  115  as it is lowered. 
     Blade  112  has an end  115  between upstream surface  114  and downstream surface  116 . In some embodiments, end  115  is an angled or slanted end, sloping down from upstream surface  114  to downstream surface  116 . Benefits of a slanted end  115  are described below. A portion of shut-off bar  110  is moveable into and out from flow channel  105  to interrupt the flow of coating material therethrough. 
       FIGS. 4A and 4B  illustrate shut-off bar  110  in a closed and an open position, respectively. To move from the open to closed position and back, shut-off bar  110  moves in a direction essentially transverse or orthogonal to flow channel  105  and to the material flowing within channel  105 . For embodiments of die  100  where flow channel  105  is essentially horizontal, shut-off bar  110  moves essentially vertically, and in preferred embodiments moves exactly vertically and in a linear motion. In the closed position,  FIG. 4A , shut-off bar  110  extends into flow channel  105  and creates a dam across flow channel  105  to inhibit (and preferably completely stop) the flow of coating material through flow channel  105 . In the open position,  FIG. 4B , shut-off bar  110  is retracted at least partially out and preferably completely out from flow channel  105  and thus allows coating material to flow through flow channel  105 . 
     In the illustrated embodiment, channel  105  has a topography that is not constant along its length. One skilled in the art of coating die design is able to readily determine the specific topography of flow channel  105 , both of upper wall  122  and lower wall  124 , needed to obtain the desired coating characteristics for the coating process. In this embodiment, both upper wall  122  of channel  105  and lower wall  124  of channel  105  are not level, so that the height of flow channel  105 , measured between upper wall  122  and lower wall  124 , varies along the length of flow channel  105 . In this embodiment, the elevation of lower wall  124  deviates more than that of upper wall  122  does. 
     Also in this illustrated embodiment, the topography of flow channel  105  includes an upstream necked region  126 , an enlarged region  127  and a downstream necked region  128 , with shut-off bar  110  positioned to extend into channel  105  proximate to the transition from enlarged region  127  to downstream necked region  128 . The transition between enlarged region  127  and downstream necked region  128  is defined by a shoulder  130  (see  FIG. 4B ). 
     No matter what the specific topography of flow channel  105 , shut-off bar  110  is located downstream from the manifold portion of flow channel  105 . In some designs, shut-off bar  110  is within the portion of flow channel  105  that is considered the preland region, upstream of the land region. In other designs, shut-off bar  110  is within the portion of flow channel  105  that is a transition region upstream of the preland region. 
     Returning to  FIG. 4A , when in the extended or closed position, shut-off bar  110  is in close proximity to and preferably abuts shoulder  130 . As indicated above, the flow of coating material through flow channel  105 , in this embodiment, is from right to left, so that downstream surface  116  of shut-off bar  110  physically contacts and provides a seal with shoulder  130 . The physical contact between shut-off bar  110  and shoulder  130 , transverse to the flow direction of material in flow channel  105 , provides a more secure and leak-free seal than would a seal that extends in the flow direction of material in flow channel  105 , such as a seal between end  115  of shut-off bar  110  and lower wall  124 . Additionally, less wear or damage occurs to a side wall (e.g., downstream surface  116 ) when sliding to form a physical seal than compared to slamming against a surface, as would a seal between end  115  and lower wall  124 . Shut-off bar  110  does not “bottom out” (i.e., end  115  does not contact lower wall  124 ). To inhibit coating material from wicking up along shut-off bar  110  and contaminating other parts of die  100 , various seals  132 ,  133  may be present. 
     In addition to the transverse physical contact between shoulder  130  and shut-off bar  110 , the fluid pressure of the coating material dammed by closed shut-off bar  110  pushes against upstream surface  114  of shut-off bar  110 , further increasing the contact and seal between shoulder  130  and downstream surface  116  of shut-off bar  110 . To allow flow of coating material through flow channel  105 , shut-off bar  110  is retracted or opened, as illustrated in  FIG. 4B . 
     One benefit of having an angled, slanted or sloped end  115  of shut-off bar  110  can be seen in  FIG. 4B . In the open, retracted position ( FIG. 4B ), the slanted end  115  creates a smooth transition in upper wall  122  between the enlarged region  127  of flow channel  105  and necked region  128 , which provides a smoother fluid flow past shut-off bar  110 . Additionally, the pressure drop distribution through the area where shut-off bar  110  is located can be easily calculated and designed when the upper wall  122  has a smooth transition. Having the slanted or sloped end  115  also decreases the force needed to overcome the fluid pressure pushing back up against blade  112  as it is lowered. Another benefit of having a slanted or sloped end  115  is that the sloped end  115  can be angled backwards, to push coating fluid back towards the die inlet. 
     As indicated above, shut-off bar  110  moves in a direction essentially transverse or orthogonal to flow channel  105  and to the material flowing within channel  105 . For embodiments of die  100  where flow channel  105  is essentially horizontal, shut-off bar  110  moves essentially vertically, and in preferred embodiments moves exactly vertically. Shut-off bar  110  can be actuated by any suitable magnetic, pneumatic, hydraulic, or mechanical means, although a magnetic actuator is preferred because of the fast acceleration and high accuracy. Some magnetic actuators are capable of the following features: travel distance 0.01 to 2 inches; acceleration 0.1 to 20 G&#39;s; peak force 0.3 to 300 lbs; continuous force 0.1 to 100 lbs; and resolution 0.0005 to 0.000004 inches. One example of a suitable magnetic actuator is a Voice Coil Positioning Stage, such as available from H2W Technologies, Inc. of Valencia, Calif. The Voice Coil Positioning Stage is particularly suited for short stroke lengths where intricate position, velocity and acceleration control is necessary. 
     To ensure consistent and even movement of shut-off bar  110  across its length, a plurality of actuators  140  is usually spaced along the length of shut-off bar  110 , although in some embodiments, a single actuator  140  may be sufficient.  FIG. 2  illustrates three actuators  140 . Although actuators  140  may be manually controlled, for precision coating it is preferred that actuators  140  are computer controlled. 
     In some designs of die  100 , a pressure relief valve and/or a material by-pass valve may be present in flow channel  105 , close to the die inlet, usually upstream of the manifold. When shut-off bar  110  opens and closes in, for example, one second or less, the build-up of back pressure on upstream surface  114  of blade  112  is minimal. However, if shut-off bar  110  is closed for several seconds, the back pressure will be much higher, due to the accumulation of stopped coating material. For these processes, a pressure relief valve and/or by-pass valve in fluid communication with flow channel  105  can be included to release undesired pressure from flow channel  105 . For example, if die  100  and the corresponding system are designed for operation at 30 psi, the relief valve would be set at 30 psi or slightly above 30 psi. If shut-off bar  110  is closed and the pressure starts to build up to undesired levels, the relief valve will open and by-pass fluid back to the die inlet, the coating material source, or to a reservoir. Maintaining a generally constant internal pressure results in a better coating. 
     To perform a patch coating operation with die  100 , material to be coating is introduced to the inlet of die  100 . A substrate, such as a film substrate, is fed in position proximate outlet  106 . Those skilled in the art of coating will be able to adjust the tension of the substrate and the distance between outlet  106  and the substrate to provide a proper coating on the substrate. Knowing the desired run speed (i.e., substrate speed), the desired length of coating (e.g., coated region  6 ) and the desired length of un-coated area (e.g., un-coated region  7 ) between coated areas, the duration of ‘coating on’ and ‘coating off’ can be calculated, usually in seconds. To begin the coating, the coating material is passed through flow channel  105  (with shut-off bar  110  in the retracted or open position) to outlet  106  and coated onto the substrate. At the previously determined time, shut-off bar  110  is extended or closed via actuator(s)  140 , blocking the flow of coating material through flow channel  105 . After the determined ‘off’ time, shut-off bar  110  is raised or opened, allowing coating material to again flow through channel  105  and out via outlet  106 . 
     As one particular example of using a coating die of this disclosure, die  100  can be used to form patch coatings on a substrate, each patch being 11.00 inches (about 28 cm) long (in the machine direction) and about 10 inches (25 cm) wide. Between adjacent patches is an uncoated region 0.787 inches (about 20 mm) long extending the width of the substrate. With the coating being done at 35 meters/minute, this requires coating material flowing for 2.09 seconds to form the patch and then the coating material flow being shut off for 0.03 second to form the uncoated region, afterwhich the coating material again flows. 
     Thus, various embodiments and features of the PATCH COATING DIE are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the various features described may be used in conjunction with any of the other features described herein above or other features other than those disclosed. For example, although the discussion and figures have place the die oriented so that the flow channel extends essentially horizontal and the shut-off bar extends essentially vertical, other orientations of the die are within the scope of this invention. For example, the die may be designed to have the flow channel extend essentially vertical and the shut-off bar extends essentially horizontal. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.