JP4809426B2 - Cross-web heat distribution system and method using channel shields - Google Patents

Description

  This application relates to controlling the thickness variation of extruded and oriented films.

  Film extrusion usually causes thickness variations along the length and width of the film. Prior art methods for controlling thickness variation include die bolt adjustment (US Pat. No. 4,409,160, Kogo et al.), Adjustment of the heating power of a stationary heater during stretching (US Pat. 347,960, Fenley, Japanese Patent No. 52,047,070, Tsutsui), or thick and thin areas where the finished film roll changes across the web so that it appears to be uniform (UK Patent No. 1,437,979, Hoechst Aktiengesellschaft, UK Patent No. 1,437,980, Hoechst Corporation).

  The present application discloses a system and method for controlling the cross-web thickness profile of a polymeric film through the use of a cross-web heat distribution system that selectively distributes heat to the film in an orientation machine. The system includes a heating element proximate the heat distribution area and a plurality of channel shields, wherein at least one channel shield prevents at least a portion of the heat generated by the heating elements from reaching the film. As described above, each channel shielding member is movably arranged.

  The above summary is not intended to describe each disclosed embodiment or every implementation of the present invention. The following figures and detailed description illustrate the illustrative embodiments more specifically.

  The present application relates to controlling the thickness variation of an oriented film. Film manufacture typically causes thickness variations along the length and width of the film. The present application discloses novel systems and methods for finely and actively adjusting the cross-web thickness profile of oriented films.

  The disclosed systems and methods may be used in the manufacture of films containing any polymer that can benefit from properties during stretching during film manufacture. The film may contain one polymer or two or more polymers. Films having two or more component polymers may have any morphological or structural form, including miscible blends, one polymer in a continuous phase and one or more dispersed. Phase immiscible blends, continuous blends together, interpenetrating polymer networks, and layered films having any number of layers include, but are not limited to. The systems and methods disclosed herein are particularly useful for multilayer optical films. These systems and methods are also particularly useful for films containing polyester.

  Multilayer optical films produced using the disclosed system or method include mirror films, polarizing films such as reflective polarizers, display films, optical filters, compensation films, anti-reflection films, or for example UV or IR shielding May include, but is not limited to, window (energy control or sun control) films (for architecture, automobiles, greenhouses, or other applications) that provide coloration or sunshade.

  Films produced using the present system or method need not be multilayer optical films. Other high performance films can also benefit from the web cross-thickness control disclosed herein. High performance film applications include magnetic media base film, graphic arts film, reprographic film, transparent film for overhead, photographic film, X-ray film, microfilm, photographic printing for audio or video or data analog or digital recording Film, inkjet printing film, PPC film, printing plate film, color proofing film, digital printing film, carbon ribbon film, flexographic printing film, gravure printing film, drafting and diazo printing film, holographic film, adhesive tape substrate, abrasive Base material, label film, release liner film, masking film, laminate film, packaging film, heat sealing film, film for lid, dual observable film, bar A film, stamping foil, metallized film, decorative film, recording and storage film, electric wire and cable, insulation film for motor, transformer and generator, flexible printed circuit film, capacitor film, credit card, prepaid Films for cards such as cards, ID cards and “smart cards”, scratch-resistant, anti-graffiti or shatter protection windows or safety films (security films), membrane switch films, touch screens Examples include, but are not limited to, films, medical sensor and diagnostic device films, sound insulation films, speaker films, and drumhead films.

  In order to impart specific optical and / or physical properties to the finished film, the polymer can be extruded through a film die, which usually has its orifice controlled by a series of die bolts. The extruded film can then be oriented, for example, by stretching at a ratio determined by the desired properties. Longitudinal stretching can be performed by a pull roll in a longitudinal orientation machine 100 as shown in FIG. A longitudinal orientation machine typically has one or more longitudinal stretching regions. Transverse stretching can be performed in a tenter oven 200 shown in FIG. A tenter oven typically has at least a preheat zone 210 and a transverse stretch zone 220. The tenter oven often has a heat set area 230, as shown in FIG. The system can be designed to have one or more or all of these areas. If desired, the film can be biaxially oriented. Biaxial stretching can be performed sequentially or simultaneously. The film can be produced by longitudinal stretching alone or by transverse stretching alone. For uniaxial stretching, a stretch ratio of about 3: 1 to 10: 1 is common. In the case of biaxial stretching, the ratio of the product of longitudinal stretching and transverse stretching is usually in the range of 4: 1 to 60: 1. One skilled in the art will appreciate that other stretch ratios suitable for a given film may be used.

  For the purposes of this application, the term “cross-stretch region” refers to either a purely cross-stretch region or a simultaneous biaxial stretch region in a tenter oven. By “developing machine” is meant any device in which the film is gripped at its edges while being conveyed in the machine direction. The film is usually stretched with a tenter. The stretching direction in the tenter is generally perpendicular to the machine direction (transverse direction or lateral direction), but other stretching directions are also conceivable, for example, directions of angles other than the vertical angle for film travel. Optionally, in addition to stretching the film in a first direction that is different from the machine direction, the tenter may be capable of stretching the film in the second direction either at or near the machine direction. . Stretching in the second direction on the tenter may occur at the same time as stretching in the first direction, separately, or both. Stretching in the tenter may be performed in any number of stages, each of which may have stretching components in the first direction, in the second direction, or in both directions. The tenter can also be used to allow a controlled amount of transverse relaxation in films that may shrink if the edges are not grasped. In this case, relaxation occurs in the relaxation region.

  A typical industrially useful tenter grabs two edges of the film with two sets of tenter clips. Each set of tentering clips is driven by a chain, and the clips can be adjusted in two ways in such a way that the rails diverge from each other as they travel through the tentering machine. Riding on the rails. This branching results in transverse stretching. Variations from this general scheme are also known and are contemplated herein.

  Some tenters can stretch in the machine direction or in a direction close to the machine direction simultaneously with stretching the film in the cross direction. These are often called simultaneous biaxial stretching tenters. One type uses a pantograph or saddle-like mechanism to drive the clip. This allows the clip on each rail to branch off from the nearest adjacent clip on its rail as it travels along the rail. Since the two rails diverge from each other, of course, the clips on each rail diverge from the counterpart on the opposite rail, just as in a conventional tenter. Another type of simultaneous biaxial stretching tenter uses varying pitch screws instead of each chain. In this scheme, each set of clips is driven along its rail by the movement of a thread, and the changing pitch allows the clip to diverge along the rail. In yet another type of simultaneous biaxial stretching tenter, the clips are individually driven electromagnetically by linear motors, thus allowing the clips to be branched along each rail. The simultaneous biaxial stretching tenter can also be used to stretch only in the machine direction. In this case, the machine direction stretching occurs in the machine direction stretching region. In this application, transverse direction stretching, relaxation, and machine direction stretching are examples of deformation, and transverse stretching region, relaxation region, or machine direction stretching region are examples of deformation regions. Other ways of providing bi-directional deformation within the tenter may also be possible and are within the scope of this application.

  The film processing method can include extruding a polymer melt through an extruder die 10. The die lip profile is often adjustable with a series of die bolts. For multilayer films, multiple melt streams and multiple extruders are used. The extrudate is cooled on a rotating casting wheel 12. Films in this regard are often referred to as “cast webs”. The film or cast web is stretched during the orientation process in the machine direction, in the transverse direction, or in both directions, depending on the desired properties of the finished film. Details of film processing are described, for example, in US Pat. No. 6,830,713 (Hebrink et al.). This specification uses, for the sake of simplicity, the term “film” to denote a film at any stage of processing, regardless of the distinction between “extrudate”, “cast web”, or “finished film”. And However, one of ordinary skill in the art will appreciate that films at different points in the process may be referred to by the alternative terms listed above, as well as other terms known in the art.

  A number of factors can contribute to variations in film thickness uniformity throughout the film manufacturing process. Variations in uniformity may be due to variations in many web crossing conditions, such as die lip profile variation, web crossing die temperature variation, web cross-casting wheel temperature variation, ambient air draft variation, non-uniformity Various tenter temperatures and / or pressures, as well as various other factors apparent to those skilled in the art. Film uniformity is important in high quality multilayer films, especially in multilayer optical films. For an increasing number of applications, it is desirable for these films to exhibit a high degree of physical and optical uniformity over a wide area. The systems and methods disclosed in this application can provide active web crossing control to achieve such film uniformity.

  The usual method of controlling web cross-thickness in film production involves adjusting the die bolts in the die during the cast web forming process. These adjustments include changing the physical spacing of the die lip by physically rotating the die bolt or changing the temperature of the die bolt. However, the result of die bolt adjustment on film thickness is rough and slow. Because the die lip is inflexible, changing the physical spacing of the die lip produces a coarse adjustment. In many cases, adjusting a single die bolt will result in a change in film thickness up to 7 die bolt lanes in the finished film. Therefore, it is difficult to control minute fluctuations in the cross-web thickness by adjusting the die bolt interval. Changing the die bolt temperature creates a slow changing thickness adjustment because the die bolt heater takes a considerable amount of time to heat and cool. In addition, because the path from the die to the winder in the film line is long, the response time for thickness change from die bolt adjustment is often very long, making thickness profile control difficult and slow.

  The disclosed system and method for controlling the cross-web thickness of an extruded film allows for active and fine control of the thickness profile during film manufacture. Cross-web thickness control can be achieved by monitoring the cross-web thickness profile and controlling the heat distribution profile of the heat released to the film during stretching or deformation. Cross-web thickness profile monitoring can include measuring physical or optical thickness profiles and mapping from the measured profiles to where heat distribution control is to be performed. Various systems and methods for controlling cross-web heat distribution as a function of monitored profiles are described. The process of monitoring the thickness and adjusting the heat distribution can form a feedback loop that is used repeatedly until the desired final thickness profile is achieved in the film. The disclosed system and method can also be used with die bolt adjustment to provide fine control of the cross-web thickness profile.

  In some disclosed embodiments, special techniques are used to control the cross-web thickness profile of biaxially oriented polymer films. For example, in some cases, channel blockers are used to adjust the heat distribution profile, and in some cases, repositionable and pivotable heating elements are used to adjust the heat distribution profile. These techniques can be used alone or in combination during deformation, for example during longitudinal stretching, during transverse stretching, during biaxial stretching, or during controlled relaxation. The channel blocking material can be used, for example, in a longitudinal orientation machine for films that are stretched in the longitudinal direction, or in a tenter for films that are transverse or biaxially stretched. Similarly, repositionable and pivotable heating elements can be used in a longitudinal orientation machine or in a tenter. The method of controlling the cross-web thickness profile of a biaxially oriented polymer film can be used with any of the heat distribution systems disclosed herein, as well as other heating systems known in the art. is there.

  The disclosed cross-web heat distribution system can provide heat to the film being stretched while providing adjustable position control and adjustable profile control of the released heat. This can provide much finer cross-web thickness profile control than known systems, if desired. The disclosed systems can also generally provide faster response times compared to known systems.

  A novel method for controlling the cross-web thickness profile of a biaxially oriented film is disclosed. This method involves controlling the heat distribution in or near the stretch region of a length orienter (LO), subsequently deforming the film in a tenter, and obtaining the resulting cross-web thickness profile. It depends on measuring after the deformation area in the tenter and adjusting the heat distribution in the LO based on the measured thickness profile. In one embodiment, the deformation area can be the end of the line, just before the winder. In another embodiment, the deformation region can be placed between other regions, for example as shown in FIG. 1, and other embodiments have additional elements such as a subsequent second longitudinal orientation machine. May be.

  As described in further detail below, these systems and methods can be used alone or in combination and in virtually any film line to produce films with improved transverse thickness uniformity. can do. These systems and methods also provide for the production of films with tailored cross-web thickness profiles, such as in multi-layer optical film applications where color changes are desired and film thickness changes are intentionally provided. Can be used to produce such films.

  Two exemplary embodiments are described in detail below. The first embodiment uses a channel shield in a longitudinal orientation machine. The second embodiment uses a repositionable swivel heater in the tenter oven.

  In some embodiments, the cross-web heat distribution system includes at least one transverse heating element in combination with a plurality of channel shields. Three examples of such systems are shown in Figures 2a-2c. In these figures, the film is stretched in a longitudinal orientation machine. In FIGS. 2a and 2c, the pull rolls 102, 104, and 106 are installed in an S-wrap shape. In FIG. 2b, the pull roll is installed in a normal or table top shape. In the embodiment shown in FIGS. 2 a-c, the heating assemblies 150 a-c each have a set of channel shields 170 that selectively distribute heat to the longitudinally stretched region 140 or 140 b of the film 20. Have been used.

  In FIG. 2 a, heating assembly 150 a includes three transverse infrared heating elements 160. The profile adjustable cross-web heat distribution system also includes a set of channel shields 170 disposed between the heating assembly 150a and the film 20 and aligned in the machine direction of the film. In this particular embodiment, a set of three heating elements 160 and multiple channel shields 170 are used, but any number of heating elements and any number of channel shields may be used, depending on system design considerations. Is possible. For example, a system with a single heating element (heating assembly 150b) is shown in FIG. 2b, while a system with five heating elements (heating assembly 150c) is shown in FIG. 2c. Another example may include 10 heating element sets and 50 channel shield sets. Each transverse heating element can be a single heater that spans the entire width of the film area to be controlled, or a point heat source arranged to provide the desired amount of heat to the film area to be controlled Can be a plurality of smaller heaters. Combinations of point heat sources and extend heat sources are also considered.

  In order to allow fine control of the cross-web thickness profile of the film, the cross-web heat distribution system of FIG. 2a releases heat to the stretched region of the film via the heating assembly 150a, while the channel shield 170's By changing the respective position, an adjustable profile control of the released heat is provided. In each of FIGS. 2a-c, channel shield 170 preferentially shields the desired portion of heat at the desired cross-web location. When the heating element is providing heat to the film, the channel shield or set of channel shields can be positioned to effectively cast a shadow on the film, thereby selecting the specific The amount of heat released to the film at the location (s) is reduced. The location of each specific channel shield casts a shadow where it corresponds to the film area to be finely controlled. The degree of resolution can be adjusted by the proximity of the channel shield to the film and the dimensions of the channel shield. In FIG. 2a, the channel shield 170 is located generally horizontal and parallel to the heating element 160 of the heating assembly 150a. The film of FIG. 2a is in the S wrap shape. Therefore, the channel shielding material 170 is inclined with respect to the plane of the film formed in the S wrap. In FIG. 2b, the channel shield 170 is still generally horizontal, but since the film is in a tabletop shape, the channel shield is parallel to the film plane. In FIG. 2c, the channel shield is angled to be parallel to the film plane in the S-wrap shape.

  The width of each individual channel shield can be as narrow as desired, and the distance from the shield to the film can be adjusted. For example, the channel shield can be 10 mm wide and less than 50 mm from the film. In this way, the channel shield assembly as a control element can be finely divided and the degree of web cross-wall thickness control can be adjusted as desired to provide superior thickness control. . In addition, the delay time from the channel shield to the winder is much shorter than from the die to the winder because there is a control location at the longitudinal orientation station where the web is accelerated to the line speed. Thus, the control response time is shorter and the final thickness uniformity is achieved more quickly. In addition, the longitudinal orientation station is typically in an open space and easily accessible, making system installation and implementation easy. Channel shield embodiments can also be used in tenter ovens. In such a system, the distance between the winder and tenter oven may be even shorter and the response time may be even faster. Access to the heating assembly with the channel shield can be designed to be controlled from outside the tenter oven.

  The system and method of FIGS. 2a-c allows the amount of heat released to a particular region to be quickly changed. As discussed further below, alternative cross-web heat distribution systems can be used in which the cross-web heat distribution profile is altered by changes in power supplied to the heater array. Alternative systems may have certain effects, such as no moving parts, but depending on the type of heater used, may have disadvantages such as lower spatial resolution and slower response time There is also. For example, some industrial grade IR heaters may require as long as 5 minutes to warm up and as long as 15 minutes to cool. In contrast, systems that use movable channel shields can be designed to have a relatively fast response time and high spatial resolution. Moving the channel shield or set of channel shields to cast a shadow on the film and thereby reduce the amount of heat released to the film is much faster than the response time of conventional IR heaters. . The response time of systems that use channel shielding is limited only by how quickly the channel shielding can be moved and the time it takes for the web to respond. This depends on the specific mechanical design of the channel shield assembly and its control mechanism. Those skilled in the art will recognize a variety of possible designs suitable for mechanical control of the channel shield assembly.

  FIG. 3 shows a plan view of one exemplary design of the channel shield assembly 300. The assembly 300 has 34 channel shields positioned adjacent to each other, the set spans the full width of the film to be controlled. If desired, the physical dimensions of the film extend beyond the width of the film to be controlled, for example when the outer edge of the film is cut and discarded or reused, leaving a usable film center. May be. A cross-web heat distribution system that incorporates a channel shield assembly such as that shown in FIG. 3 can be used in a longitudinal orientation machine, a tenter, or both.

  Using a feedback mechanism, iteratively measures the physical or optical thickness profile, optionally maps the measured thickness profile to the stretched region, and heats across the web depending on the measured or mapped profile The dispensing system can be adjusted. Feedback mechanisms are known and will not be described in detail. In short, the feedback mechanism can be in the form of manual control by the operator, can be computer controlled, or can be a combination of computer and manual control. For example, one such feedback mechanism can be a computer controlled system with manual override. Preferably, the feedback mechanism uses a computer controlled mapping algorithm that uses any of the mapping methods described herein. Manual mapping algorithms can also be used.

  In some embodiments, the cross-web heat distribution system includes a set of repositionable heating elements disposed along a cross direction in an orientation machine. In the exemplary embodiment described below, such a cross-web heat distribution system is used in a tenter. The deformation area of the tenter can be purely a transverse stretching area, a relaxation area, a machine direction stretching area, or a biaxial stretching area. Such a cross-web heat distribution system that includes a repositionable heating element can also be used in a longitudinal orientation machine.

  FIG. 4 schematically shows one implementation of this embodiment. In FIG. 4, the film is stretched in the transverse direction in a tenter oven 200 (see FIG. 1). In this particular implementation, the repositionable heating element is also pivotable. The cross-web heat distribution system 250 includes five repositionable rod heaters 260a-e mounted on a pair of mounting channels 253. Other implementations are possible and include, but are not limited to, a row of small heat sources arranged in a straight line or any other shape optimized for a particular desired response.

  In the embodiment of FIG. 4, the heater is disposed in the stretching region of the orientation machine, but the location of the heater is not limited to the stretching region. The orientation machine may have additional or other deformation areas where a cross-web heat distribution system may be used. Additional areas include, but are not limited to, a preheat area, an annealing area, and a heat set area. When used in a longitudinal orientation machine, the stretch region is a longitudinal stretch region. When used in a tenter, the deformation zone can be a transverse stretch zone, a relaxation zone, a machine direction stretch zone, or a biaxial stretch zone. The cross-web heat distribution system can be placed in or near any of these areas. Although many of the embodiments disclosed herein refer to the stretch region, it is contemplated that the cross-web heat distribution system may be in or near other regions. In this application, in any embodiment, the location where the cross-web heat distribution system exists is referred to as the heat distribution area.

  In the heat distribution system 250 of FIG. 4, the heating elements can be repositioned in two ways. First, the heating element can be moved transversely along the attachment channel to any position along the width of the film. Secondly, the heating element is also pivotable. The effect of the swivel heater will be described below. Other implementations and embodiments are also contemplated. For example, the heating element can be repositionable so that it can move toward and away from the film in a plane perpendicular to the plane of the film.

  An imaginary centerline 22a-e is shown for each of each lane 40a-e in FIG. 4 for mapping to a transverse position on any part of the film moving along the film line. Film lanes 40a-e are surrounded by imaginary lines. In FIG. 4, each of the centerlines 22a-e also represents the direction of travel of each corresponding lane of the film when the film is stretched. During transverse stretching, the distance between each pair of imaginary lines increases in proportion to the amount of transverse stretching. In other words, the width of each film lane increases as the film is cross-stretched. Ideally, for example, if the film is stretched at a 3: 1 ratio, the width of each film lane is tripled when measured at the point just before the stretch region 220 and the point just after the stretch region 220. Increase. In practice, however, various factors can cause film lane width differences. These factors include, for example, variations in cross-web uniformity before stretching, variations in cross-web temperature distribution within the tenter, variation in homogeneity of the extruded mixture, and finite width film web edge effects. can do.

  The rod heaters 260a-e of the cross-web heat distribution system are mounted so that the heaters can be positioned independently of each other. Optionally, in addition to transverse movement, each rod heater can also be mounted so that it can pivot. A pivotable heater has two advantages. First, the swivel rod heater can be aligned with the travel direction of a particular lane of film on which the heater is positioned. Secondly, the swivel rod heater can be angled with respect to the direction of travel of the film lane to provide a wider heat distribution profile than any single heating rod. This expansion effect on the heat distribution profile is explained in more detail in the following examples. The swivel and repositionable heating element provides greater control over the heat released to the film, which in turn provides a more finely adjustable heat distribution profile compared to known systems.

  In FIG. 4, each of the heating elements 260a-e is mounted with pivot points on two parallel channels 253 across the tenter. In this way, the web crossing position of each heater can be accurately adjusted from the outside of the tenter oven. The position and orientation of each rod heater 260a-e can be controlled by various methods known in the art. In the embodiment of FIGS. 5-6, position and orientation are controlled through the use of a pair of Acme brand threaded rods 262 for each rod heater. Other methods of controlling position and turning can also be used, for example, a method of connecting a pair of cables to each rod heater.

  FIG. 5 shows an enlarged view of a repositionable single heating element of the heat distribution system 250. The heating element 260 can be positioned at any position along the two attachment channels 253L and 253R. Optionally, the heating element 260 can also be rotated and aligned with the line 26 as indicated by the dashed line, thereby forming an angle θ with respect to the machine direction 25. In one embodiment, the rotation is accomplished by having a single stationary bolt 266 and a single bolt 268 that is left moving along the sliding channel 270 as the heating element 260 rotates. . The stationary bolt 266 serves as a pivot point for the heating element and in this embodiment is located at the center of the heating element 260. When swiveling is not desired, the sliding channel 270 can be omitted and both bolts can be stationary. Other arrangements are also considered.

  FIG. 6 shows a partial perspective view of the heat distribution system 250 of FIG. FIG. 6 shows two heating elements 260a and 260b mounted on channels 253L and 253R. The position of the heating element 260a is controlled by a pair of threaded rods 262a. Similarly, the position of the heating element 260b is controlled by a pair of threaded rods 262b. Any rotation of the heating element 260b positions the nut 264b on the stationary side (253R) at a location along the threaded rod 262b on the channel 253R, while the corresponding nut 264b is mounted on the channel 253L. Achieved by positioning at different locations along the threaded rod. This can also be seen in FIG. The web crossing position of each heater 260 can be precisely adjusted from the outside of the tenter oven with a pair of screws (not shown) connected to each pair of threaded rods. In addition, the angle at which the heater faces can also be accurately adjusted from the outside of the tenter oven by the relative position of pivot points 266b and 268 controlled by a screw pair.

  A single rod heater is mounted movably in the transverse direction and optionally pivotable with respect to the machine direction, and can provide adjustable thermal profile control to the film when stretched or deformed. When used in combination, the heater assembly includes adjustable heat that crosses any selected portion of the film or across the entire width of the film, for example, heaters 260a-e together. A profile can be provided.

  As with the channel shield embodiment, this embodiment also has the effect of rapid response time and fine and active control of heat distribution. When there is a control location at the longitudinal orientation station where the web is accelerated to line speed, the delay time from the web cross heat distribution system to the winder is much shorter than from the die to the winder. Thus, the response time to control is shortened, resulting in a shorter cycle time, making it much faster to achieve the desired final thickness uniformity. Again, the longitudinal orientation station is often in an open space and easily accessible, simplifying the installation of the cross-web heat distribution system. When the control location is in the tenter, cycle time and response time can be even shorter.

  In general, the film thickness profile can be measured at any point downstream from the location of the cross-web heat distribution system. For example, in a system that uses any of the disclosed cross-web heat distribution systems in a longitudinal aligner, the cross-web thickness profile can be measured downstream from the longitudinal aligner. In systems where the cross-web heat distribution system is used in a tenter oven, the cross-web thickness profile can be measured downstream from the tenter oven. Alternatively, if a cross-web heat distribution system is present in the tenter oven, the cross-web thickness profile can be measured immediately after the deformation area inside the tenter oven. In systems where the cross-web heat distribution system is used in a longitudinal orientation machine but also uses a tenter for subsequent cross-stretching, the cross-web thickness profile measurement is performed downstream of the longitudinal orientation machine and in the tenter oven. Can be implemented upstream. However, controlling the cross-web heat distribution in the longitudinal orientation machine, then deforming in the tenter, and subsequently measuring the cross-web thickness profile of the film downstream from the deformation zone, will give unexpected results. Applicants found. In Example 2 below, one such system and method is described.

  In the case of optical films, the overall optical thickness of the film can be detected and monitored by visible light transmission or reflection spectra using an optical thickness meter. For example, an on-line spectrophotometer can be set up to measure the spectral transmission of the film as it exits the line, thereby providing the information necessary to measure the uniformity of the cross-web thickness profile, And the information necessary to provide feedback for process control. An example of such a spectrophotometer is the type U-4000 spectrophotometer manufactured by Hitachi Ltd. In some cases, the wavelength at which the transmission spectrum drops to a certain level can be used as a measure of its optical thickness. In other cases, transmission at a particular wavelength can be used as a measure of its optical thickness. Other methods are possible, including the indirect method, which can be converted using the direct method described above.

  The thickness gauge can measure the physical thickness of the film, the optical thickness of the film, or other properties related to the thickness of the film as described above. In this application, cross-web thickness refers to optical thickness, physical thickness, a combination of the two, or any other characteristic related to the thickness required by a particular product design. One skilled in the art of optical or high performance films will be able to design the appropriate thickness for a particular product. Measurement of the physical thickness of the film is performed, for example, on a Measurex ™ scanner available from Honeywell International, Inc., Morristown, New Jersey, USA. Such an on-line cross travel β-ray meter scanning device can be used. Other thickness meters include, but are not limited to, a β-ray transmission meter, an X-ray transmission meter, a γ-ray backscatterometer, a contact thickness sensor, and a laser thickness sensor. Such a meter can be purchased, for example, from NDC Infrared Engineering, Irwindale, California, USA.

  The measured film thickness profile is optionally mapped to the corresponding film location where the cross-web heat distribution system is present. In some embodiments, the film thickness profile measured after the transverse stretch region can be mapped to a film in the longitudinal stretch region of the longitudinal aligner. In other embodiments, the film thickness profile is measured downstream from the heat distribution system and mapped to the heat distribution area. Mapping can be implemented in several ways. A simple mapping method involves dividing the film width into a set of imaginary film lanes, for example as shown by phantom lines in FIGS. In FIG. 3, the film is divided into 34 film lanes, each lane corresponding to one channel shield. In this particular embodiment, channel shields 301 and 334 are wider than the remaining channel shields 302-333. Accordingly, the corresponding lanes 1 and 34 are wider than lanes 2-33. In FIG. 4, five film lanes 40a-e are indicated by imaginary lines. The centers of the five lanes 40a to 40e are indicated by center lines 22a to 22e, respectively.

  The cross-web thickness profile is measured downstream from the heat distribution area where the cross-web heat distribution system exists. At the measurement location, the film may not be the same width as the width of the film at the location of the heat distribution system in which the control takes place. Thus, a mapping algorithm is used to map from one place to the other. The mapping algorithm is essentially a transition from each web crossing location of the film at one location to the corresponding web crossing location on the film at another location. The mapping algorithm can take into account any or all of the factors that can affect the difference in film width between two locations, including stretching, touching, bowing, one location Include, but are not limited to, whether the film edge at has been cut, variation in cross-web uniformity before stretching, variation in temperature distribution across the web in the tenter, or variation in homogeneity of the extruded mixture. .

  Additional mapping methods can include physically marking the film before stretching with a label and measuring the position of the label after stretching. For example, the first method draws two lines 50 mm from each edge of the film, then measures the position of those lines after stretching, and sets the film width between the two lines to a number of equal widths. It can include dividing into lanes. This method assumes that each lane is stretched or deformed by an equal amount. The second method may involve drawing 50 marker lines on the film and then stretching the film and measuring the position of each labeled line after stretching. A third method may include selectively moving one or more of the channel shields or repositionable heaters to measure the effect on the stretched film. This method is called active mapping or mapping by bumping. The fourth method may use the law of conservation of mass, in which the cross-web thickness profile of the film is measured before and after stretching. Since the mass is preserved during stretching, the film volume remains the same and the width of a given number of film lanes can be calculated from the two measured thickness profiles. Any of these mapping methods can be used to design an appropriate mapping algorithm.

  For example, in FIG. 4, the film has been cross-stretched in a system that uses a cross-web heat distribution system 250 located at a longitudinal location 60. In some embodiments, the cross-web thickness profile is measured at the longitudinal location 70, but the film is wider than the film at location 60. In order to control the heat distribution at location 60, the profile measured at location 70 is mapped to the location of heat distribution system 60. The heat distribution system can then be adjusted to smooth any thick spots, thin spots, or irregularities in the film profile. In another example, such a system can also include a second cross-web heat distribution system at location 50. In that case, the cross-web thickness profile measured at location 70 can also be mapped to location 50 where the second heat distribution system is present.

  Usable cross-web heat distribution systems include any of the systems disclosed above, for example, systems that use repositionable heating elements, systems that use heating elements with channel shielding, or two It can be a system that uses a combination. Other known or later developed cross-web heat distribution systems that can release heat to the web with an adjustable cross-web profile can also be used. The cross-web heat distribution system can be used in a longitudinal orientation machine or in a tentering machine. When used in a tenter, selectable heat distribution is provided in the deformation area of the film. When used in a longitudinal orientation machine, selectable heat distribution is provided in the longitudinal stretch region of the film.

  As described in Example 1 below, if the measured film profile has a thick or high spot that is mapped to lane 08, the response is such that more heat is released to lane 08. The channel shielding material 308 to be adjusted can be adjusted. This allows the film to be stretched more in that lane, thereby reducing or eliminating thick spots in the finished film. Similarly, if the measured film profile shows a low spot on the film at a position corresponding to lane 22, for example, as shown in FIG. 3, to prevent heat from reaching the film at that position, The channel shielding material 322 can be moved. In one embodiment, the degree of blocking or unblocking is adjusted by channel advancement by a threaded rod rotated on shaft 180. Obviously, such adjustments can be made very finely, resulting in excellent heat distribution control.

  Similarly, as shown in Examples 3 and 4, the thick spot can also be adjusted using a repositionable heating element within either the longitudinal orientation machine or the tenter. If the repositionable heating element can also be swiveled, the effect can be adjusted even more finely. As in the channel shield embodiment, a repositionable heater can be used to actively control the cross-web thickness of the film to the desired final profile.

  In some embodiments, the longitudinally oriented film can subsequently be deformed in a tenter. In such a case, counter-intuitively, adjusting the cross-web heat distribution at the longitudinal orientation station rather than the tenter corrects the cross-web thickness profile of the finished film downstream of the tenter. It is effective. In Example 2 below, surprisingly, the cross-web thickness can be finely adjusted by selectively shielding the portion of heat released to the film during longitudinal stretching, and thus more uniform biaxial stretching. It has been demonstrated that films can be provided. Although Example 2 uses a channel shield heat distribution system, this method also includes other cross-web heat distribution systems, such as the repositionable heating elements disclosed herein, or the art. Other cross-web heat distribution systems known in U.S.A. can also be used. The unique approach of this method of controlling heat distribution in the longitudinal orientation machine during longitudinal stretching is very good in order to achieve a uniform cross-web thickness of the subsequently deformed film in the tenter Results.

Example 1
In the example shown in FIG. 7, an IR reflective multilayer optical film was made by extrusion of alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polyethylene naphthalate (co-PEN). The film was first longitudinally oriented at a stretch ratio of 3.3: 1 and then subsequently width oriented in a tenter at a stretch ratio of 3.3: 1. The optical thickness of the film was measured after tentering using an optical thickness meter. Curve 7A shows the optical thickness profile of the film originally mapped. To control the thickness profile, a heating assembly having a set of 3 IR rod heaters and 34 channel shields was used in the longitudinal orientation machine. The IR rod heater used was a model 5305 series Parabolic Strip Heaters manufactured by Research, Inc. of Minneapolis, Minnesota, USA. Channel shields 303-331 are shown at the bottom of the graph. The channel width is 12.7 mm. Channel shield 308 was retracted 25.4 mm from the starting position 35.6 mm to the final position 10.2 mm to lower the peak representing the thick spot shown at the position corresponding to channel 308 in curve 7A. This retraction of the channel shield allowed more heat to reach the film at its cross-web position. As more heat was released to this location, the peak dropped due to the more stretch of that portion of the film. The resulting mapped thickness profile is shown at a location corresponding to the channel shield 308 of curve 7B. Curve 7C shows the percent change from the starting thickness profile of curve 7A to the final thickness profile of curve 7B. At a position corresponding to the channel shield 308, curve 7C shows that moving the channel shield 308 by −25.4 mm changes the thickness profile by about −3%. Similarly, the effect of shielding the channel is shown at a position corresponding to the channel shielding material 322 of the curves 7A-C. The starting thickness profile has a depression at this position that represents a thin spot, as shown by curve 7A. Advancement of the channel shield 322 by 25.4 mm to a final position of 61 mm prevented more heat from reaching that part of the film and allowed the film to stretch less than the adjacent part. This resulted in the thickness profile increasing at that position, as shown by curve 7B. The percent change in this position changed by about 3% as shown in curve 7C.

Example 2
In the example shown in FIG. 8, an IR reflective multilayer optical film was made by extrusion of alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polyethylene naphthalate (co-PEN). The film was longitudinally oriented with a stretch ratio of 3.3: 1. The film was subsequently stretched in the transverse direction in a tenter with a stretch ratio of 3.3: 1. The optical thickness of the film was measured after tentering using an optical thickness meter. Curve 8A shows the initial cross-web optical thickness profile of the film mapped onto the longitudinal orientation station. To control the thickness profile, a heating assembly having a set of 3 IR rod heaters and 34 channel shields was used in the longitudinal orientation machine. The IR rod heater used was a model 5305 series Parabolic Strip Heaters manufactured by Research, Inc. of Minneapolis, Minnesota, USA. Channel shields 303-331 are shown at the bottom of the graph. The channel width was 12.7 mm.

  The film profile shown in curve 8A was adjusted by moving some of the channel shields as displayed in the final settings for each channel shield at the bottom of FIG. Table 1 shows the initial setting and the final setting of the channel shielding materials 303 to 331. The resulting optical thickness profile is shown in curve 8B. Curve 8C shows the percent change between the final thickness profile and the initial thickness profile. Curve 8B demonstrates that the initial film profile shown in curve 8A can be adjusted more uniformly with the use of a cross-web heat distribution system having an IR heater set and a channel shield set.

Example 3
In the example shown in FIG. 9, a multilayer optical film was made by extrusion of alternating layers of polyeylene terephthalate (PET) and a copolymer of PMMA. The film was longitudinally oriented with a stretch ratio of 3.35: 1. The film was subsequently oriented in the transverse direction in the tenter at a stretch ratio of 3.3: 1. The tenter was equipped with a set of repositionable and swiveling heating elements in the transverse stretch region of the tenter. Each heating element was 325 mm in length, 10 mm in width and was equipped with an 80 mm wide parabolic reflector. The heating element used was a Raymax model 1525 available from Watlow Electric, St. Louis, Missouri, USA. The center of the heating element was used as the pivot point and position location in this example. The optical thickness of the film was measured after tentering using an optical thickness meter. Curves 9A, 9B, and 9C show the optical thickness change as a function of cross-web position for different configurations of the cross-web heat distribution system, demonstrating the effect on the finished film of a repositionable swivel IR heater. Yes. The power and angles of orientation of the heating elements are listed in Tables 2 and 3.

  When a single heating element is kept at a constant power and the same angles of orientation, the change in the cross-web optical thickness profile remains the same for each of the three curves 9A, 9B, and 9C. is there. This effect is observed as a depression in the curves 9A, 9B, and 9C at the cross-web position 460 mm corresponding to the first heating element 962. A single heating element is kept at a constant power, but an expansion effect is observed when the angles of orientation change. The indentation at 950 mm of curves 9A, 9B, and 9C demonstrates this expansion effect due to the single rod heater. In this example, the second heater 964 arranged at 950 mm was rotated from 0 degrees in the curve 9A to 12.5 degrees in the curve B and 25 degrees in the curve C.

Example 4
In the examples shown in FIGS. 10-13, multilayer optical films were made by extrusion of alternating layers of PET and PMMA copolymers. The film was longitudinally oriented with a stretch ratio of 3.35: 1. The film was subsequently oriented in the cross direction at a stretch ratio of 3.3: 1. The tenter was equipped with a set of four repositionable and swivel heating elements in the transverse stretch region. Each heating element was 325 mm in length, 10 mm in width and was equipped with an 80 mm wide parabolic reflector. The heating element used was a Raymax model 1525 available from Watlow Electric, St. Louis, Missouri, USA. The center of each heating element was used as the pivot point. The center position of each heating element of this embodiment is represented as “Position, Right” in Tables 4 to 7, and the position of the movable bolt for turning is represented as “Position, Left-Inclination”. The optical thickness of the film was measured downstream of the tenter with the use of an optical thickness meter. Each curve A in FIGS. 10-13 shows the initial cross-web optical thickness profile. 10-13 represent repeated iterations with changing heater settings. Initially, the cross-web optical thickness profile of the film was measured. The measured data points are plotted as curve A in FIG. The measured web transverse optical thickness profile of the film was then mapped onto the transverse stretch region. Depending on the mapped profile, heaters 1-4 were set to the first iteration with the parameters shown in Table 4. The resulting cross-web optical thickness profile was measured and is shown as curve B in FIG. The optical thickness obtained as a result of the first iteration (curve B in FIG. 10) then becomes the initial thickness profile for the second iteration (curve A in FIG. 11). The steps of measuring the optical thickness profile, mapping the measured optical thickness profile onto the stretched region, and adjusting the cross-web heat distribution system according to the mapped profile form a feedback loop. This is repeated until the desired final thickness profile is reached. In the second iteration, heaters 1-4 are set according to the parameters listed in Table 5. The resulting optical thickness profile is plotted as curve B in Table 11. This process is reproduced through two more iterations, as shown in the heater settings in Tables 6 and 7, and the thickness profile is plotted in FIGS. The cooperative effect on the cross-web optical thickness profile of the finished film of a set of four repositionable swivel IR heaters is illustrated by curve B in FIG. Curve B in FIG. 13 shows a flat final thickness with the use of a set of four repositionable heating elements arranged in this regime of interest, in the range of approximately 1300-1850 mm. This indicates that the profile can be acquired. Note that “valleys” at cross-web positions greater than 1850 mm can be addressed by other means such as die bolt adjustment.

  While the invention is susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and the detailed description. It will be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

  The present invention is more fully understood upon consideration of the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals represent like elements. The accompanying drawings are intended as illustrative examples and are not intended to be limiting.

Schematic of the film line for biaxially oriented films. 1 is a schematic view of one embodiment of a cross-web heat distribution system in a longitudinal orientation machine with adjustable profiles. FIG. FIG. 6 is a schematic view of another embodiment of a cross-web heat distribution system in a longitudinal orientation machine with adjustable profiles. FIG. 6 is a schematic view of another embodiment of a cross-web heat distribution system in a longitudinal orientation machine with adjustable profiles. 1 is a schematic plan view of one embodiment of a channel shield assembly. FIG. FIG. 3 is a schematic diagram of another embodiment of an adjustable web cross heat distribution system. 1 is a schematic diagram of an exemplary repositionable swivel heating element of one embodiment. FIG. 1 is a partial perspective view of a repositionable swivel heating element assembly of one embodiment. FIG. The figure which shows the effect on the optical thickness of the specific channel shielding material in Example 1. FIG. The figure which shows the effect on the optical thickness of the group of the channel shielding material in Example 2. FIG. 10 is a diagram illustrating a change in an optical thickness profile with respect to a web crossing position in Example 3. FIG. 5 is a diagram showing the relative optical thickness with respect to the web crossing position corresponding to the heating element setting arrangement of Table 4 in Table 4; Example 4 The relative optical thickness with respect to the web crossing position corresponding to the heating element setting arrangement of Table 5 is shown. Example 4 The relative optical thickness with respect to the web crossing position corresponding to the heating element setting arrangement in Table 6 is shown. FIG. 9 is a diagram showing the relative optical thickness with respect to the web crossing position corresponding to the heating element setting arrangement in Table 4 in Example 4.

Claims (3)

A stretching machine or a tenter having a heat distribution region and stretching the polymer film in its longitudinal direction;
A cross-web heat distribution system that selectively distributes heat to the film in the stretcher or tenter.
A thickness meter disposed downstream from the cross-web heat distribution system for measuring a cross-web thickness profile of the film;
A feedback mechanism that selects heat distribution in response to the measured cross-web thickness profile;
The cross-web heat distribution system includes a plurality of heat shields and heating elements proximate to the heat distribution area and disposed in the cross-web direction, wherein at least a portion of the heat generated by the heating elements is Each heat shield is arranged to be movable in the longitudinal direction of the web such that at least one heat shield prevents the film from reaching the film,
Film handling device.   The film handling apparatus according to claim 1, wherein the heat distribution area is a deformation area or a preheating area. A method for controlling a thickness profile in a cross-web direction of a polymer film, comprising:
A step of deforming the film in a stretcher or a tenter that has a heat distribution system in the transverse direction of the web with a plurality of heat shields arranged in the transverse direction of the web and stretches the polymer film in the longitudinal direction thereof; ,
Measuring the cross-web thickness profile of the film at a location downstream from the cross-web heat distribution system;
Depending on the thickness profile of the measured cross-web direction, by moving at least one longitudinal selectively web heat shielding member of a plurality of heat shielding material disposed in the cross-web direction Adjusting the cross-web heat distribution system;
Including methods.

Images