JP4875070B2 - Cross-web heat distribution system and method using repositionable heater - Google Patents

Description

  This application relates to controlling thickness variations in extruded or oriented films.

  Film extrusion typically results in thickness variations along the length and width of the film. Prior art methods for controlling thickness variations include adjusting the die bolt (US Pat. No. 4,409,160, Kogo et al.) And adjusting the heating power of the stationary heater during stretching (US Pat. No. 3,347,960, Fenley; JP-A-52-047070, Tsutsui) or thick and thin areas where the roll of the finished film changes across the web so that the appearance is uniform (UK Patent No. 1,437,979, Hoechst Aktiengesellschaft; British Patent No. 1,437,980, Hoechst Aktiengesellschaft).

  The present application discloses a system and method for controlling the cross-web thickness profile of a polymeric film using a cross-web heat distribution system for providing a selectable distribution of heat to film in an orienter. The cross-web heat distribution system comprises at least one selectable and repositionable heating element. The above summary is not intended to describe each disclosed embodiment or every implementation of the present invention. The following figures and best mode for carrying out the invention more specifically illustrate the illustrative embodiments.

  The present application relates to controlling thickness variations in oriented films. Film manufacture typically results in thickness variations along the length and width of the film. This application discloses a novel system and method for finely and actively adjusting the cross-web thickness profile of an oriented film.

  The disclosed systems and methods may be used in the manufacture of films that include any polymer whose properties can benefit from stretching during film manufacture. The film may contain one or more polymers. A film having two or more constituent polymers is a miscible mixture, an immiscible mixture, a co-continuous mixture, where one polymer is a continuous phase and one or more polymers are dispersed. It may have any morphological or structural shape including, but not limited to, a polymer network penetrating each other and a layered film with any number of layers. The systems and methods currently disclosed are particularly useful for multilayer optical films. These systems and methods are also particularly useful for films comprising polyester.

  Multilayer optical films made by using this disclosed system or method include mirror films, polarizing films such as reflective polarizers, display films, optical filters, compensation films, antireflection films, or, for example, UV Or include (but are not limited to) window (energy control or solar control) films that allow infrared shielding, tinting, or shading (for architecture, automobiles, greenhouses, or other applications).

  Films made using the present system or method need not be multilayer optical films. Other high performance films may also benefit from the cross web thickness control disclosed herein. High performance film applications include magnetic media base film for audio, video, or data analog or digital recording, graphic art film, reprographic film, transparent film for overhead projector, photographic film, x-ray film, microfilm , Photographic print film, inkjet printing film, plain paper copier film, 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 base Material, polishing substrate, label film, release liner film, masking film, laminated film, packaging film, heat seal film, lid film, dual offset film Heat-resistant film for barrier, barrier film, stamping foil, metalizing film, decorative film, film for archiving and storage, wire and wire, motor, transformer, and electrical insulation film for generator, flexible printed circuit film, capacitor film, credit Cards, prepaid cards, ID cards, and card films such as “smart cards”, scratch-resistant, anti-graffiti or shutter protective windows or safety films (security films), membrane switch films, touch screen films, medical sensors and Examples include, but are not limited to, diagnostic device films, soundproof films, acoustic 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 the film die and its orifice is usually controlled by a series of die bolts. The extruded film can be subsequently oriented, for example by stretching in a ratio determined by the desired properties. As shown in FIG. 1, the longitudinal stretching can be performed by a pull roll in the length orienter 100. The length orienter typically has one or more longitudinal stretch regions. The transverse stretching can be performed in a tenter oven 200 shown in FIG. A tenter oven typically contains at least one preheat zone 210 and a transverse stretch zone 220. Often, the tenter oven also contains a heat set area 230, as shown in FIG. The system can be designed to contain one or more of any or all of these regions. If desired, the film can be biaxially oriented. Biaxial stretching can be performed sequentially or simultaneously. The film can also 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 biaxial stretching, the longitudinal and transverse stretch ratios of the product are usually in the range of 4: 1 to 60: 1. One skilled in the art will appreciate that other stretch ratios may be used as appropriate for a given film.

  For the purposes of this application, the term “transverse stretching region” refers to either a purely transverse stretching region or a simultaneous biaxial stretching region in a tenter oven. “Tenter” means any device by which a film is gripped at its edges while being conveyed in the direction of the machine. Typically, the film is stretched in a tenter. Broadly, the stretching direction in the tenter is perpendicular to the machine direction (transverse or transverse direction), but other stretching directions are also contemplated, such as directions at angles other than those perpendicular to film travel. ing. Optionally, in addition to stretching the film in a first direction that is other than the machine direction, the tenter may also stretch the film in a second direction that is either the machine direction or a direction close to the machine direction. In some cases, it can be stretched. The second direction stretching in the tenter may be performed either simultaneously with the first direction stretching or separately, or both. Stretching in the tenter may be performed in any number of steps, each of which may have stretching components in the first direction, the second direction, or both. The tenter can also be used to control the amount of lateral relaxation in the film that will shrink if not gripped at its edges. In this case, relaxation takes place in the relaxation region.

  A typical industrially useful tenter grips two edges of the film with two sets of tenter clips. Each set of tenter clips is driven by a chain, and the clips rest on two rails and can be adjusted in position so that the rails diverge from one another when traveling through the tenter. This branching results in transverse stretching. Variations on this general scheme are known and discussed herein.

  Some tenters can stretch the film in the direction of the machine or in a direction close to the direction of the machine, while at the same time they stretch the film in the transverse direction. These are often referred to as simultaneous biaxial stretching tenters. One form for driving the clip uses a mechanism such as a pantograph or scissors. This allows the clips on each rail to diverge from their nearest neighbor clips on that rail as they travel along the rail. Just like a conventional tenter, of course, the clips on each rail branch off from their counterparts on the opposite rail due to the branching of the two rails from each other. Other methods of simultaneous biaxial stretching tenters replace screws with different pitches for each chain. In this scheme, each set of clips is driven along its rail by the movement of a thread, and different pitches provide for the branching of the clips along the rail. In yet another system of simultaneous biaxial stretching tenters, the clips are individually electromagnetically driven by a linear motor, allowing the clips to branch along each rail. Simultaneous biaxial stretching tenters can also be used for stretching in the machine direction only. In this case, the machine direction stretching takes place in the machine direction stretching region. In this application, transverse stretching, relaxation, and machine directional stretching are examples of deformation, and transverse stretching, relaxation, or machine directional stretching are examples of deformation regions. Other methods of achieving deformation in two directions within the tenter may also be possible and are contemplated by this application.

  The film processing method can include extruded polymer melt through an extruder die 10. The die lip (exit part) 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. The film at this point is often called the “cast web”. During orientation, the film or cast web is stretched in the machine direction, the transverse direction, or 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.). For the sake of brevity, the term “film” is used herein to mean a film at any stage of the process, regardless of the distinction between “extruded product”, “cast web” or “finished film” And However, those skilled in the art will appreciate that films at different points in the process may be referred to by the above alternative terms, as well as other terms known in the art.

  Several factors can contribute to variations in film thickness uniformity throughout the film making process. For example, uniformity fluctuations can include die lip contour, cross web die temperature, cross web casting wheel temperature, airflow in ambient air, non-uniform tenter temperature and / or pressure, and various other factors that are obvious to those skilled in the art. May result from several variations in cross-web conditions, including variations in. Film uniformity is important in high quality multilayer films, especially multilayer optical films. In an increasing number of applications, it is desirable for these films to exhibit a high degree of physical and optical uniformity over a large area. The systems and methods disclosed in this application can provide active cross-web control to achieve such film uniformity.

  A typical method for controlling the crossweb thickness in film production involves the adjustment of 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 die bolt temperature. However, the result of die bolt adjustment on film thickness is coarse and slow. Changing the physical spacing of the die lip results in coarse adjustment due to the inflexibility of the die lip. In most cases, the effect of adjusting a single die bolt will change the film thickness in up to seven die bolt lanes in the finished film. Therefore, it is difficult to control the fine variation of the cross web thickness by adjusting the die bolt interval. Changing the die bolt temperature causes a slow change in thickness adjustment because the die bolt heater takes a considerable amount of time to warm up and cool down. In addition, the long path from the die to the winder in the film line often results in a fairly long response time from die bolt adjustment to thickness change, making thickness profile control difficult and slow.

  This disclosed system and method for controlling the cross-web thickness of an extruded film allows for active and fine control of the thickness profile as the film is being made. Cross-web thickness control can be achieved by monitoring the cross-web thickness profile and controlling the distribution profile of the heat applied to the film during stretching or deformation. Cross-web thickness profile monitoring can include measuring a physical or optical thickness profile and mapping the measurement profile to a location where heat distribution control is performed. Various systems and methods for controlling cross-web heat distribution in response to a monitoring profile 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 reached in the film. The disclosed system and method can also be used with die bolt adjustment to achieve fine control of the cross-web thickness profile.

  In some disclosed embodiments, specific techniques are utilized to control the crossweb thickness profile of the biaxially oriented polymer film. For example, a channel blocker may be used to adjust the heat distribution profile in some cases, and a pivotable heating element may be used that can be repositioned to adjust the heat distribution profile. . These techniques can be used alone or in combination during deformation, eg, longitudinal, lateral, biaxial, or controlled relaxation. For example, channel blockers can be used in a length orienter for longitudinally stretched films or in a tenter for transverse or biaxially stretched films. Similarly, repositionable, pivotable heating elements can be used in a length orienter 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 presently disclosed heat distribution systems, as well as other heating systems known in the art.

  The disclosed cross-web heat distribution system can transfer heat to the film as it is being stretched while providing adjustable position control and adjustable profile control of the transferred heat. This can provide even finer control of the crossweb thickness profile than known systems, if desired. The disclosed system can also achieve generally 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 the length orienter (LO), followed by the deformation of the film in the tenter, and the resulting crossweb thickness after the deformation region in the tenter. Rely on the measurement of the profile and adjustment of the heat distribution in the LO based on the measured thickness profile. In one embodiment, the deformation area can be just in front of the winder, the end of the line. In other embodiments, the deformation regions can be positioned between other regions, for example, as shown in FIG. Other embodiments may provide additional elements, such as a subsequent second length orienter.

  As described in more detail below, these systems and methods are used alone or in combination and in virtually any film line that produces films with improved transverse thickness uniformity. be able to. These systems and methods are also films having a cross-web thickness profile tailored to specific needs, such as in multi-layer optical film applications where color variation is preferred and film thickness variation is intentionally provided. Can also be used to manufacture.

  Two exemplary embodiments are described in detail below. The first embodiment uses a channel blocker within the length orienter. The second embodiment uses a swirlable heater that can be repositioned in a 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 blockers. Three examples of such systems are shown in FIGS. In these figures, the film is stretched in a length orienter. 2a and 2c, pull rolls 102, 104, and 106 are set up in an S wrap configuration. In FIG. 2b, the pull roll is set up in a vertical or table top configuration. The embodiment shown in FIGS. 2a-c, together with a set of channel blockers 170, provides the heating assemblies 150a-c to provide a selectable distribution of heat to the longitudinally stretched region 140 or 140b of the film 20. Use for each.

  In FIG. 2 a, the heating assembly 150 a includes three lateral infrared heating elements 160. The adjustable profile cross-web heat distribution system also includes a set of channel blockers 170 that are arranged in the machine direction of the film and positioned between the heating assembly 150a and the film 20. This particular embodiment uses three heating elements 160 and a plurality of channel blockers 170, although any number of heating elements and any number of channel blockers may be used depending on system design considerations. . For example, a system with a single heating element (heating assembly 150b) is shown in FIG. 2b, whereas a system with five heating elements (heating assembly 150c) is shown in FIG. 2c. Other embodiments may include a set of 10 heating elements and a set of 50 channel blockers. Each transverse heating element can be a single heater that spans the entire width of the controlled film area, or a plurality of miniatures, including a point heat source, arranged to provide the desired amount of heat to the controlled film area. It can be a heater. Combinations of point heat sources and extended heat sources are also intended.

  The cross-web heat distribution system of FIG. 2a provides adjustable profile control of the heat transferred by changing the position of each of the channel blockers 170 to allow for fine control of the cross-web thickness profile of the film. Transfers heat to the stretch region of the film via the heating assembly 150a. 2a-c, channel blocker 170 preferentially blocks the desired portion of heat at the desired cross-web location. As the heating element provides heat to the film, the channel blocker or a set of channel blockers can be positioned to effectively cast a shadow on the film, thereby the amount of heat transferred to the film at a particular location selected. Reduce. The location of each specific channel blocker casts a shadow at a location corresponding to the area of the film that is subject to fine control. The degree of resolution can be adjusted by the size of the channel blocker in addition to the proximity of the channel blocker to the film. In FIG. 2a, the channel blocker 170 is positioned generally horizontally and parallel to the heating element 160 of the heating assembly 150a. The film in FIG. 2a has an S wrap configuration. Thus, the channel blocker 170 is inclined with respect to the plane of the S-wrap film. In FIG. 2b, the channel blocker 170 is also generally positioned horizontally, but since the film is a table top configuration, the channel blocker is parallel to the plane of the film. In FIG. 2c, the channel blocker is angled to be parallel to the plane of the film, which is an S-wrap configuration.

  The width of each individual channel blocker can be as narrow as desired, and the blocker distance to the film can also be tailored to your needs. For example, the channel blocker can be 10 mm wide and is positioned within 50 mm from the film. Thus, the assembly of channel blockers as control elements can be subdivided and the crossweb thickness control measure can be tailored to individual needs as desired, providing excellent thickness control. In addition to this, the delay time from the channel blocker to the winder is substantially shorter than the time from the die to the winder because the control location is at a length orientation station where the web is speeding up to line speed. Therefore, the response time to control is shorter and the final thickness uniformity is achieved faster. In addition, the length orientation station is usually in an open space and is easily accessible, making the system easy to install and implement. Channel blocker embodiments can also be used in a tenter oven. In such a system, the distance between the winder and the tenter oven can be made shorter and the response time can be made faster. Access to the heating assembly including the channel blocker can be designed to be controllable from outside the tenter oven.

  The system and method of FIGS. 2a-c can rapidly change the amount of heat transferred to a particular location. As described in detail below, alternative cross-web heat distribution systems can be used in which the cross-web heat distribution profile is varied by varying the power provided to the heater array. Alternative systems may have certain benefits such as no moving parts, but may have drawbacks due to the type of heater used, such as lower spatial resolution and slower response times. For example, some industrial infrared (IR) heaters require 5 minutes to warm up and 15 minutes to cool. In contrast, systems that use movable channel blockers can be designed to have a relatively fast response time and high spatial resolution. The movement of a channel blocker or a set of channel blockers to cast a shadow on the film and thereby reduce the amount of heat transferred to the film is much faster than the response time of a conventional infrared (IR) heater. The response time of a system that uses a channel blocker is limited only by how fast the channel blocker can be moved and the time it takes for the web to respond. This depends on the specific mechanical design of the channel blocker assembly and its control mechanism. Those skilled in the art will appreciate the variety of possible designs that are suitable for mechanical control of the channel blocker assembly.

  FIG. 3 shows a plan view of one exemplary design of channel blocker assembly 300. The assembly 300 has 34 channel blockers positioned adjacent to each other, this set spanning the entire width of the controlled film. The physical dimensions of the film may extend beyond the controlled film width if desired, e.g., the outer edge of the film is trimmed and discarded leaving a usable central film portion. Or recycled. A cross-web heat distribution system incorporating a channel blocker assembly as shown in FIG. 3 can be used for the length orienter, the tenter, or both.

  The feedback mechanism repeatedly measures the physical or optical thickness profile, optionally maps the measured thickness profile to the stretch region, and cross-web heat distribution in response to the measured or mapped profile Can be used to adjust the system. The feedback mechanism is known and will not be described in detail. Simply put, the feedback mechanism can be in the form of manual control by the operator, computer controlled, or a combination of computer and manual control. For example, one such feedback mechanism can be a computer control system with manual override. Preferably, the feedback mechanism uses a computer controlled mapping algorithm using 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 that are disposed along a transverse direction in the orienter. In the exemplary embodiment described below, such a cross-web heat distribution system is used in a tenter. The deformation region of the tenter can be purely a transverse stretch region, a relaxation region, a machine direction stretch region, or a biaxial stretch region. Such cross-web heat distribution systems that include repositionable heating elements can also be used in the length orienter.

  FIG. 4 schematically illustrates one implementation of this embodiment. In FIG. 4, the film is being stretched in the transverse direction in a tenter oven 200 (see FIG. 1). In this particular implementation, the repositionable heating element is also pivotable. Cross-web heat distribution system 250 includes five repositionable rod heaters 260a-e mounted on a pair of mounting channel members 253. Other implementations are also possible, including but not limited to an array of smaller heat sources arranged in a straight line or in any other shape that is optimized for a particular desired response.

  In the embodiment of FIG. 4, the heaters are positioned in the orienter stretching region, but their location is not limited to the stretching region. The orienter can have additional or other deformation regions that may use a cross-web heat distribution system. Additional areas include, but are not limited to, a preheat area, an anneal area, and a heat set area. When used in a length orienter, 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 located at or near any of these areas. Although most of the embodiments disclosed herein refer to stretch regions, it is contemplated that cross-web heat distribution systems can also be present in or near other regions. In this application, the location where the cross-web heat distribution system is present in any embodiment 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 laterally along the attachment channel material to any position along the width of the film. Secondly, the heating element is also pivotable. The advantages of swirl heaters are described below. Other implementations and embodiments are also considered. 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.

  In order to map the lateral position to any part of the film as the film moves along the film line, virtual centerlines 22a-e are shown in FIG. 4 for each lane 40a-e, respectively. Film lanes 40a-e are bounded by imaginary lines. In FIG. 4, each of centerlines 22a-e also represents the direction of travel of each corresponding lane of the film when the film is stretched. During lateral stretching, the distance between each pair of imaginary lines increases in proportion to the amount of lateral stretching. In other words, the width of each film lane increases as the film is stretched in the lateral direction. Ideally, for example, if the film is stretched at a ratio of 3: 1, the width of each film lane will increase by a factor of 3 when measured immediately before stretch region 220 and immediately after stretch region 220. Let's go. In practice, however, the width of the film lanes is not equal due to various factors. These factors can include, for example, variations in cross-web uniformity before stretching, variations in cross-web temperature distribution within the tenter, variations in homogeneity of the extruded mixture, and edge effects in finite width film webs. .

  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. If desired, in addition to moving laterally, each rod heater can also be pivotably mounted. A swivel heater has two advantages. First, the swivel rod heater can be aligned with the travel direction of a particular lane of film above where it is located. Second, 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 from any single heating rod. This widening effect on the heat distribution profile will be discussed in more detail in the examples that follow. A swivel, repositionable heating element provides better control of the heat transferred to the film and instead 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 pivots on two parallel channel members 253 from end to end of the tenter. In this way, the cross-web location of each heater can be precisely adjusted from outside 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, the position and orientation are controlled using a pair of trade name “Acme” threaded rods 262 per rod heater. Other methods of position and swivel control can also be used, eg a pair of cables connected to each rod heater.

  FIG. 5 shows an enlarged view of a single repositionable heating element of the heat distribution system 250. The heating element 260 can be positioned at any location along the two attachment channel members 253L and 253R. If desired, the heating element 260 can also be rotated as shown by the dotted line to be in line with the line 26 to form an angle θ with respect to the machine direction 25. In one embodiment, rotation is achieved by having a single bolt 268 that is allowed to move along the sliding channel material 270 as the fixed bolt 266 and heating element 260 rotate. Fixing bolt 266 serves as a pivot point for the heating element and is positioned at the center of heating element 260 in this embodiment. If pivoting is not desired, the sliding channel material 270 can be eliminated and both bolts can be fixed. Other arrangements are also considered.

  FIG. 6 shows a perspective partial view of the heat distribution system 250 of FIG. FIG. 6 shows two heating elements 260a and 260b mounted on channel members 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. Optional rotation of heating element 260b causes nut 264b to threaded rod 262b on channel member 253R while positioning corresponding nut 264b at different locations along a corresponding threaded rod mounted on channel member 253L. This is achieved by positioning at one position along the fixed (253R) side. This can also be seen in FIG. The cross-web position of each heater 260 can be accurately 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 heater orientation angle can also be accurately adjusted from the outside of the tenter oven by the relative position of pivot points 266b and 268 controlled by the screw pair.

  A single rod heater mounted so that it can be moved laterally and, if desired, pivotable with respect to the direction of the machine, provides adjustable thermal profile control of the film as it is stretched or deformed. realizable. When used in combination, an assembly of heaters, such as heaters 260a-e, can together provide an adjustable profile of heat across any selected portion of the film or across the width of the film. .

  As in the channel blocker embodiment, this embodiment also has the effect of fast response time and fine, active control of heat distribution. When the control location is a length orientation station where the web is speeding up to line speed, the delay time from the cross web heat distribution system to the winder is substantially shorter than from the die to the winder. Accordingly, the response time for control is shortened, resulting in a shorter cycle time, achieving the desired final thickness uniformity even faster. Again, the length orientation station is often in open space and is easily accessible, making the cross-web heat distribution system easy to install. If the control location is in the tenter, the 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 cross-web heat distribution systems disclosed within the length orienter, the cross-web thickness profile can be measured downstream from the length orienter. In systems that use a cross-web heat distribution system in a tenter oven, the cross-web thickness profile can be measured downstream from the tenter oven. Alternatively, the cross web thickness profile can also be measured inside the tenter oven immediately after the deformation area where a cross web heat distribution system is present. In systems that use a cross-web heat distribution system in the length orienter but also use a tenter for subsequent transverse stretching, cross-web thickness profile measurements are taken except for the upstream of the tenter oven. Can be carried out downstream. However, as the applicant knows, the control of the crossweb heat distribution in the length orienter is followed by the deformation in the tenter, and further down the film crossweb thickness downstream from the deformation zone. The continued measurement of the profile gives unexpected results. Example 2 below describes one such system and method.

  For optical films, the total film optical thickness can be detected and monitored via an optical transmission or reflection spectrum using an optical thickness measurement gauge. For example, an on-line spectroscopic analyzer can be set up to measure its spectral transmission as the film leaves the line, thereby measuring cross-web thickness profile uniformity and providing feedback for process control. Provide necessary information. As an example of one such spectroscopic analyzer, a type U-4000 spectroscopic analyzer is manufactured by Hitachi Ltd. In some cases, the wavelength at which the transmission spectrum decays to a natural level can be used as a measure of its optical caliper. In other cases, the transmission at the characteristic wavelength can be used as a measure of the optical caliper. Other methods can include indirect methods that can be calibrated using the direct methods described below.

  The scissors scale can measure the physical thickness of the film, the optical thickness of the film, or other thickness-related properties of the film described above. In this application, cross-web thickness refers to optical thickness, physical thickness, a combination of the two, or any other thickness related property required by a particular product design. Those skilled in the art of optical or high performance films will be able to design calipers that are appropriate for a particular product. For example, measuring the physical thickness of a film is a “Measurex ™” scanner available from Honeywell International, Inc., Morristown, NJ, USA. Can be performed using an on-line transverse β-ray gauge scanner. Other caliper gauges include, but are not limited to, β-ray transmission measuring devices, x-ray transmission measuring devices, γ-ray backscattering measuring devices, contact caliper sensors, and laser caliper sensors. Such instruments are commercially available from, for example, 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 exists. In some embodiments, the film thickness profile measured after the transverse stretch region can be mapped to a film that is within the longitudinal stretch region of the length orienter. 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 done in several ways. A simple mapping method involves dividing the film width into a set of fictitious film lanes as shown, for example, by pseudolines in FIGS. In FIG. 3, the film is divided into 34 film lanes, each lane corresponding to one channel blocker. In this particular embodiment, channel blockers 301 and 334 are wider than the remaining channel blockers 302-333. Therefore, the corresponding lanes 1 and 34 are wider than lanes 2-33. In FIG. 4, five film lanes 40a to 40e are indicated by pseudo 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 is present. The film at the measurement location may not be the same width as the film at the location of the heat distribution system being controlled. A mapping algorithm is therefore used to map from one location to the other. The mapping algorithm substantially translates each crossweb location on the film at one location to the corresponding crossweb location on the film at the other location. The mapping algorithm can take into account any or all factors that can affect how the film width differs between the two locations. These factors include stretching, shrinking, warping, whether the edge of the film at one location was cut, variation in crossweb uniformity before stretching, variation in crossweb temperature distribution in the tenter, or extrusion mixture Including, but not limited to, variations in homogeneity.

  Additional mapping methods include physically marking the film with a display before stretching and measuring the location of the display after stretching. For example, the first method draws two lines 50 mm away from each edge of the film, then measures the location of those lines after stretching, and sets the width of the film between the two lines to an equal width Can be subdivided into several lanes. This method assumes that each lane is stretched or deformed by the same amount. The second method may involve drawing 50 indicator lines on the film, subsequently stretching the film, and measuring the location of each indicator line after stretching. A third method may involve selectively moving one or more of the channel blockers or repositionable heaters and measuring the effect on the stretched film thereon. This method is called active mapping or mapping by bumping. The fourth method may make use of the law of conservation of mass, where the cross-web thickness profile of the film is measured before and after stretching. Since the mass is preserved during stretching, the film volume also 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 a suitable mapping algorithm.

  For example, in FIG. 4, the film is stretched laterally within the system using a cross-web heat distribution system 250 located at the longitudinal location 60. In some embodiments, the cross web thickness profile is measured at a longitudinal location 70 where the film is wider than the film at location 60. In order to control the heat distribution at location 60, the measurement profile 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 or thin spots or irregularities in the film profile. In another example, such a system can also be equipped with 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.

  A usable cross-web heat distribution system can be any of the systems disclosed above, such as a system using a repositionable heating element, a heating element with a channel blocker, or a combination of the two. Any other known or later developed cross-web heat distribution system that can transfer heat to the web according to a cross-web profile that can be tailored to specific needs can also be used. The cross-web heat distribution system can be used in a length orienter or in a tenter. When used in a tenter, a selectable distribution of heat is provided to the deformation area of the film. When used in a length orienter, a selectable distribution of heat is provided to 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, then the corresponding channel blocker 308 is passed through, and more heat is transferred to lane 08. Can be adjusted to be transmitted to. 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 points out a low spot on the film at the location corresponding to lane 22, the channel blocker 322 will allow heat to reach the film at that location, for example as shown in FIG. Can move to block. In one embodiment, the degree of blocking or non-blocking is adjusted by channel advancement through a threaded rod that rotates with the shaft 180. Obviously, such adjustments can be made very finely and excellent control of heat distribution can be achieved.

  Similarly, as shown in Examples 3 and 4, thick spots can also be adjusted using repositionable heating elements either in the length orienter or in the tenter. If the repositionable heating element is also pivotable, these effects can be finely adjusted. As in the channel blocker 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 length-oriented film can be subsequently deformed in the tenter. In such cases, adjusting the cross-web heat distribution at the length orientation station rather than the tenter would be effective in modifying the cross-web thickness profile in the finished film downstream of the tenter. Is counterintuitive. Surprisingly in Example 2 below, more uniform biaxial stretching is possible because the crossweb thickness can be finely adjusted by selectively blocking the portion of heat transferred to the film during longitudinal stretching. It is demonstrated that a film can be provided. Example 2 uses a channel blocker heat distribution system, but this method may also be a repositionable heating element as disclosed herein, or other cross-web heat distribution system known in the art, It can be used for any other cross-web heat distribution system. The unique approach of this method of controlling heat distribution within the length orienter during longitudinal stretching to achieve a uniform cross-web thickness of the subsequently deformed film in the tenter is an exceptional result Can be provided.

Example 1
In the example shown in FIG. 7, an infrared reflective multilayer optical film was made by extruding alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polyethylene naphthalate (co-PEN). The film was first length oriented at a stretch ratio of 3.3: 1 and subsequently width oriented at a stretch ratio of 3.3: 1 in the tenter. The optical thickness of the film was measured after the tenter using an optical caliper gauge. Curve 7A shows the initial mapped optical thickness profile of the film. To control the thickness profile, a heating assembly with 3 infrared rod heaters and a set of 34 channel blockers was used in the length orienter. The infrared rod heater used was a model 5305 series parabolic strip heater made by Research, Inc. of Minneapolis, Minnesota, USA. Channel blockers 303-331 are shown at the bottom of the graph. The channel width is 12.7 mm. Channel blocker 308 was moved 25.4 mm from the start position of 35.6 mm to the final position of 10.2 mm to lower the peak, indicating the thick spot shown in curve 7A at the location corresponding to channel 308. Moving the channel blocker down allowed more heat to reach the film at the crossweb location. The more heat transferred to this location lowered the peak by allowing that portion of the film to stretch more. The resulting mapped thickness profile is shown in curve 7B at the location corresponding to channel blocker 308. Curve 7C shows the percent change from the starting thickness profile of curve 7A to the final thickness profile of curve 7B. At a location corresponding to the channel blocker 308, curve 7C shows that moving the channel blocker 308 by 25.4 mm changed the thickness profile by about −3%. Similarly, channel blocking effects are shown in curves 7A-C at locations corresponding to channel blockers 322. The starting thickness profile has an indentation indicating a thin spot at this location, as shown by curve 7A. Moving channel blocker 322 up to a final position of 61 mm up 25.4 mm prevented more heat from reaching that part of the film, allowing the film to stretch below the adjacent part It became. As a result, the thickness profile at that location increased as shown by curve 7B. The percent change at this location changed by about 3% as shown in curve 7C.

Example 2
In the example shown in FIG. 8, an infrared reflective multilayer optical film was made by extruding alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polymethyl methacrylate (co-PEN). The film was length oriented with a stretch ratio of 3.3: 1. The film was subsequently stretched in the transverse direction in the tenter at a stretch ratio of 3.3: 1. The optical thickness of the film was measured after the tenter using an optical thickness meter. Curve 8A shows the original crossweb optical thickness profile of the film mapped onto the length orientation station. A heating assembly with three infrared (IR) rod heaters and a set of 34 channel blockers was used in the length orienter to control the thickness profile. The infrared (IR) rod heater used was a model 5305 series Parabolic Strip Heaters made by Research, Inc. of Minneapolis, Minnesota, USA. It was. Channel blockers 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 blockers as indicated by the final setting of each of the channel blockers at the bottom of FIG. Table 1 shows the initial and final settings for channel blockers 303-331. The resulting optical thickness profile is shown in curve 8B. Curve 8C shows the percent change between the final and initial thickness profiles. Curve 8B demonstrates that the initial film profile shown in curve 8A can be adjusted to be more uniform using a cross-web heat distribution system having one infrared heater and one channel blocker.

Example 3
In the example shown in FIG. 9, a multilayer optical film was made by extruding alternating layers of a copolymer of polyethylene terephthalate (PET) and PMMA. The film was length oriented with a stretch ratio of 3.35: 1. The film was subsequently oriented in the transverse direction at a stretch ratio of 3.3: 1 in the tenter. The tenter was equipped with a set of swivel heating elements that could be repositioned in the transverse stretch region of the tenter. Each heating element was 325 mm long, 10 mm wide, and had a parabolic reflector with a width of 80 mm. 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 location in this example. The optical thickness of the film was measured after the tenter using an optical caliper gauge. Curves 9A, 9B, and 9C show the optical thickness variation as a function of cross-web location for different configurations of the cross-web heat distribution system, and the effect on the repositionable finished film of the swirl infrared heater Demonstrate. The heating element power and orientation angles are listed in Tables 2 and 3.

  When a single heating element is held at the same orientation angle at constant power, the change in the crossweb optical thickness profile remains the same for each of the three curves 9A, 9B, and 9C. This effect is observed as a depression in the curves 9A, 9B, and 9C at the 460 mm crossweb location corresponding to the first heating element 962. Although a single heating element is held at a constant power, a widening effect is observed when the orientation angle changes. The indentations in curves 9A, 9B, and 9C at 950 mm demonstrate the widening effect due to the single rod heater. In this example, the second heater 964 positioned at 950 mm was rotated from 0 ° in curve 9A to 12.5 ° in curve B and 25 ° in curve C.

Example 4
In the examples shown in FIGS. 10-13, multilayer optical films were made by extruding alternating layers of PET and PMMA copolymers. The film was length oriented with a stretch ratio of 3.35: 1. The film was subsequently oriented transversely with a stretch ratio of 3.3: 1. The tenter was equipped with a set of four repositionable swirl thermal elements in the transverse stretch region. Each heating element was 325 mm long, 10 mm wide, and had a parabolic reflector with a width of 80 mm. 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 in this example is shown in Tables 4 to 7 as “position, right” and the position of the movable bolt for turning as “position, left-tilt”. The optical thickness of the film was measured downstream of the tenter using an optical caliper gauge. Curve A in each of FIGS. 10-13 shows the initial optical crossweb thickness profile. 10 to 13 show successive iterations for changing the heater set value. 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 cross-web optical thickness profile of the film was then mapped to the transverse stretch region. In response to the mapped profile, heaters 1-4 were set in the first in accordance with the parameters shown in Table 4. The resulting crossweb optical thickness profile was measured and shown as curve B in FIG. The resulting optical thickness of the first bullet (curve B in FIG. 10) is then the initial thickness profile of the second bullet (curve A in FIG. 11). The steps of measuring the optical thickness profile, mapping the measured optical thickness profile to the stretch region, and adjusting the cross-web heat distribution system in response to the mapped profile form a feedback loop, which Is repeated until the desired final thickness profile is reached. In the second step, the heaters 1 to 4 are set according to the parameters listed in Table 5. The resulting optical thickness profile is plotted as curve B in FIG. This process is repeated over two or more bullets as shown in the heater settings in Tables 6 and 7, and the thickness profile is plotted in FIGS. The combined effect of a set of four repositionable swivel infrared heaters on the optical crossweb thickness profile of the finished film is illustrated by curve B in FIG. Curve B in FIG. 13, in the range of about 1300-1850 mm, yields a flat final thickness profile using four repositionable heating elements positioned in the problem regime. It is shown that. 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 amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and the best mode for carrying out the invention. 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 will be more fully understood in view of the best mode for carrying out the invention as set forth below, taken in conjunction with the accompanying drawings, wherein like reference numerals designate like elements. The accompanying drawings are intended to be illustrative examples and are not intended to be limiting.

Schematic of the film line of a biaxially oriented film. 1 is a schematic diagram of one embodiment of an adjustable profile cross-web heat distribution system within a length orienter. FIG. FIG. 4 is a schematic diagram of another embodiment of an adjustable profile cross-web heat distribution system within a length orienter. FIG. 4 is a schematic diagram of another embodiment of an adjustable profile cross-web heat distribution system within a length orienter. 1 is a schematic plan view of one embodiment of a channel blocker assembly. FIG. FIG. 3 is a schematic diagram of another embodiment of an adjustable cross-web 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 an exemplary repositionable, swivel heating element of one embodiment. FIG. The influence which the specific channel blocker in Example 1 has on optical thickness is shown. The influence which 1 set of channel blockers in Example 2 exerts on optical thickness is shown. The change of the optical thickness profile according to the cross web location in Example 3 is shown. The relative optical thickness with respect to the cross-web location corresponding to the structure of the heating element setting value in Table 4 of Example 4 is shown. The relative optical thickness with respect to the cross-web location corresponding to the structure of the heating element setting value in Table 5 of Example 4 is shown. The relative optical thickness with respect to the cross-web location corresponding to the structure of the heating element setting value in Table 6 of Example 4 is shown. The relative optical thickness with respect to the cross-web location corresponding to the structure of the heating element setting value in Table 7 of Example 4 is shown.

Claims (5)

A stretching machine for deforming a polymer film having a heat distribution region;
A cross-web heat distribution system for providing selectable heat distribution to the film in the stretcher, comprising a heating element movable in the cross-direction of the film;
A caliper gauge disposed downstream from the cross-web heat distribution system for measuring a cross-web thickness profile of the film, and for selecting the heat distribution in response to the measured cross-web thickness profile Film handling device including a feedback mechanism. The film handling apparatus according to claim 1, wherein the number of the heating elements is 2 or more, each of the heating elements is elongated, and can be swung in a plane parallel to the plane of the film. Deforming the film in a stretching machine having a cross-web direction heat distribution system;
Measuring a cross-web thickness profile of the film at a location downstream from the cross-web heat distribution system, and repositioning heating elements in the cross-web heat distribution system in the cross-direction of the film, Adjusting the cross-web heat distribution system in response to the measured cross-web thickness profile;
A method for controlling a cross-web thickness profile of a polymer film. 4. The method of claim 3, wherein the number of heating elements is two or more, each heating element being elongated and pivotable in a plane parallel to the plane of the film .   In the plane above the plane of the film and parallel to the plane of the film so that the adjusting step changes the angle between the longitudinal axis of the elongated heating element and the running direction of the lane of the film, The method of claim 4, comprising rotating the elongated heating element.

Images