KR101236591B1 - Cross-web heat distribution system and method using channel blockers - Google Patents

Abstract

A system and method for controlling web cross thickness profile of polymer film 20 is disclosed. A cross web heat distribution system 150a, 150b, 150c is disclosed that provides a selectable heat distribution for the film in the heat distribution area. The cross web heat distribution system includes at least one heating element 160 proximate the heat distribution region. The heating element provides heat to the film, and the plurality of channel blockers 170 selectively prevent at least a portion of the heat from reaching the film.

Polymer Films, Webs, Thickness, Profiles, Heat Distribution, Channel Blockers

Description

Cross-web heat distribution system and method using channel breaker {CROSS-WEB HEAT DISTRIBUTION SYSTEM AND METHOD USING CHANNEL BLOCKERS}

FIELD OF THE INVENTION The present invention relates to controlling thickness variation of extrusion oriented films.

Extrusion of the film typically causes thickness variations along the length and width of the film. The prior art method of controlling thickness fluctuations is to adjust the die bolt (US Patent No. 4,409,160 to Kogo et al.), Elongation, to make the roll of the finished film uniform in appearance. adjustment of the heating output of the fixed heater during stretching (Fenley US Pat. No. 3,347,960; Tsutsui Japanese Patent No. 52,047,070), or intentional thick areas at other points across the web. Thin area formation (British Patent No. 1,437,979 of Hoechst Aktiengesellschaft; British Patent No. 1,437,980 of Paste Aktiengesellschaft).

summary

The present invention discloses a system and method for controlling a web transverse thickness profile of a polymer film using a web transverse heat distribution system that provides a selectable heat distribution for the film in a stretcher. Includes a heating element and a plurality of channel breakers proximate the heat distribution region, each channel breaker being movable such that the at least one channel breaker blocks at least a portion of the heat generated by the heating element from reaching the film. Is located. The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The following figures and detailed description more particularly exemplify illustrative embodiments.

The invention will be more fully understood in view of the following detailed description taken in conjunction with the accompanying drawings. Like reference numerals in the accompanying drawings denote like elements. The accompanying drawings are intended to be illustrative, and not restrictive.

1 is a schematic view of a film line for biaxially stretched film.

2A is a schematic representation of one embodiment of an adjustable profile web transverse heat distribution system of a length stretcher.

2B is a schematic representation of another embodiment of an adjustable profile web transverse heat distribution system of a length stretcher.

2C is a schematic diagram of another embodiment of an adjustable profile web transverse heat distribution system of a length stretcher.

3 is a schematic plan view of one embodiment of a channel breaker assembly.

4 is a schematic representation of another embodiment of an adjustable web transverse heat distribution system.

5 is a schematic representation of an exemplary repositionable pivotal heating element of one embodiment.

6 is a partial perspective view of an assembly of the repositionable pivotal heating element of one embodiment.

FIG. 7 shows the effect of a particular channel blocker on optical thickness in Example 1. FIG.

FIG. 8 shows the effect of a set of channel blockers on optical thickness in Example 2. FIG.

FIG. 9 shows variation in optical thickness profile with web crossing point in Example 3. FIG.

FIG. 10 shows relative optical thickness versus web crossing point, corresponding to the heating element installation configuration in Table 4 of Example 4. FIG.

FIG. 11 shows relative optical thickness versus web crossing point, corresponding to the heating element installation configuration in Table 5 of Example 4. FIG.

12 shows relative optical thickness versus web cross point, corresponding to the heating element installation configuration in Table 6 of Example 4. FIG.

FIG. 13 shows relative optical thickness versus web crossing point, corresponding to the heating element installation configuration in Table 7 of Example 4. FIG.

The present invention relates to controlling the thickness variation of the stretched film. The manufacture of the film typically causes thickness variations along the length and width of the film. The present application discloses a novel system and method for finely and actively controlling the web cross thickness profile of a stretched film.

The disclosed systems and methods can be used in the manufacture of films comprising any polymer having properties that can benefit from stretching during film manufacture. The film may comprise one or more polymers. Films with more than one constituent polymer may comprise a miscible blend, an incompatible blend in which one polymer is in a continuous phase and one or more polymers in a dispersed phase, a co-continuous blend, and an interpenetrating polymer network. polymer network), and any morphological or structural form, including, but not limited to, laminated films with any number of layers. The presently disclosed systems and methods are particularly useful for multilayer optical films. Such systems and methods are also particularly useful for films comprising polyesters.

Multilayer optical films made by employing the disclosed systems or methods provide mirror films, polarizing films such as reflective polarizers, display films, optical filters, compensation films, antireflective films, or for example UV or IR blocking, coloring or shading. Which may include, but is not limited to, a window (energy or solar energy control) film (for construction, for vehicles, for greenhouses and other uses).

The film produced by employing the present system or method need not be a multilayer optical film. Other high performance films can also benefit from the web cross thickness control disclosed herein. High performance film applications include magnetic media base films, graphic art films, copy films, overhead transparent films, photographic films, X-ray films, microfilm, for analog or digital recording of audio, video or data. Photographic printing film, inkjet printing film, plain paper copy film, printing plate film, color correction film, digital printing film, carbon ribbon film, flexographic printing film, gravure printing film, drafting and diazo printing film film, holographic film, adhesive tape substrate, abrasive substrate, label film, release liner film, masking film, laminating film, packaging film, heat seal film, lidding film, for double oven Films, barrier films, stamping foils, metallizing films, decorative films, recording and storage films, Electrical insulation films for wires and cables, motors, transformers and generators, flexible printed circuit films, capacitor films, films for cards such as credit cards, prepaid cards, ID cards and "smart cards", scratch resistance, anti-scratch or Fracturing protection windows or safety films (security films), membrane switch films, touch screen films, medical sensor and diagnostic device films, sound insulation films, acoustic speaker films, and drumhead films. It is not limited.

In order to impart specific optical and / or physical properties to the finished film, the polymer may be extruded through the film die, and the orifices of the film die are typically controlled by a series of die bolts. The extruded film can then be stretched, for example by stretching, in a ratio determined by the required properties. Longitudinal stretching may be done by a pull roll of the length drawing machine 100 as shown in FIG. The length drawing machine typically has one or more longitudinal stretching regions. Transverse stretching can be done in a tenter oven 200 shown in FIG. 1. Tenter ovens typically include at least one preheating region 210 and a transverse stretching region 220. Often, the tenter oven also includes a heat set zone 230 as shown in FIG. The system may be designed to include any one or more or all of these areas. If desired, the film can be biaxially stretched. Biaxial stretching can be done sequentially or simultaneously. The film can also be produced by longitudinal stretching only or by transverse stretching only. For uniaxial stretching, a stretch ratio of approximately 3: 1 to 10: 1 is typical. For biaxial stretching, the product of the longitudinal stretching ratio and the transverse stretching ratio is typically in the range of 4: 1 to 60: 1. Those skilled in the art will appreciate that other stretch ratios may be used as appropriate for a given film.

For the purposes of the present application, the term "lateral stretching zone" refers to pure lateral stretching zones or simultaneous biaxial stretching zones in a tenter oven. "Tent" means any device that grips a film at its edge while the film is transported in the machine direction. Typically, the film is stretched in the tenter. In general, the stretching direction in Tente will be perpendicular to the machine direction (lateral or cross direction), but other stretching directions are also contemplated, for example angles other than the angle perpendicular to the film movement. Optionally, in addition to stretching the film in a first direction other than the machine direction, the tenter may also stretch the film in a second direction, which is a machine direction or a direction close to the machine direction. The second direction stretching in the tenter may occur simultaneously with the first direction stretching, or may occur separately, or both simultaneously and separately. The stretching in the tenter may be done in any number of steps, each of which may be the stretching of the component in the first direction, the second direction, or both. Tenters can also be used to allow for a controlled amount of transverse relaxation in the film that will shrink when not gripped at the edges. In this case, relaxation occurs 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, the clips move on two rails, the position of the rails can be adjusted in such a way that the rails diverge from each other when one rail is moved through the tenter. This branching causes widthwise stretching. Modifications to this general method are known and contemplated herein.

Some tenters can stretch the film in the width direction while being able to stretch the film in or near the machine direction. Such tenters are often referred to as simultaneous biaxial stretching tenters. One type uses a pantograph or scissors to drive the clip. This allows the clips on each rail to diverge from the nearest clip on the rail as it travels along the rail. Of course, as in a conventional tenter, the clips on each rail diverge from the mating clips on opposite rails because the two rails diverge from each other. Another type of simultaneous biaxial stretching tenter replaces each chain with screws of variable pitch. In this way, each set of clips is driven along the rail by the movement of the screw thread, and the variable pitch causes the clips to branch along the rail. In another type of simultaneous biaxial stretching tenter, the clips are electromagnetically driven individually by a linear motor, allowing the clips to branch along each rail. Simultaneous biaxial stretching tenters can also be used to stretch only in the machine direction. In this case, the machine direction stretch occurs in the machine direction stretch region. In the present application, transverse stretching, relaxation and machine direction stretching are examples of deformations, and transverse stretching region, relaxation region or machine direction stretching region are examples of deformation regions. Other methods of providing deformation in two directions within the tenter are also possible and are contemplated by the present application.

The film processing method may include extruding the polymer melt through the extruder die 10. The die lip profile is often adjustable with a series of die bolts. For multilayer films, a plurality of melt streams and a plurality of extruders are employed. The extrudate is cooled in the rotary casting wheel 12. The film at this point is often called the "cast web". During stretching, the film or cast web is stretched in the machine direction, transverse direction or both directions depending on the desired properties of the finished film. Details on film processing are described, for example, in US Pat. No. 6,830,713 (Hebrink et al.). For the sake of brevity, the term "film" will be used herein to refer to a film in any processing step of a process regardless of the difference between "extruded", "cast web" or "finished film". However, those skilled in the art will understand that the 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.

Throughout the film manufacturing process, many factors can contribute to variations in film thickness uniformity. For example, uniformity fluctuations are many, including die lip profile, web cross die temperature, web cross casting wheel temperature, ambient air ventilation, uneven tenter temperature and / or pressure, and many other factors apparent to those skilled in the art. Variations in web crossing conditions. Film uniformity is important for high quality multilayer films, especially multilayer optical films. For applications that increase in number, it is desirable for such films to exhibit a high degree of physical and optical uniformity over large areas. The systems and methods disclosed in this application can provide active web crossing control to achieve such film uniformity.

Typical methods of controlling web cross thickness in film manufacture include adjusting the die bolts of the die during the casting web forming process. These adjustments include changing the physical spacing of the die lips by physically turning the die bolt or changing the die bolt temperature. However, the result of die bolt adjustment on film thickness is not only precise but also slow. Changing the physical spacing of the die lips results in inaccurate control due to the inflexibility of the die lips. In most cases, the adjustment effect of a single die bolt changes the film thickness in up to seven die bolt lanes of the finished film. Thus, by adjusting the die bolt spacing, it is difficult to control fine variations in web cross thickness. Changing the die bolt temperature will cause a slow change in thickness adjustment since it takes a long time to preheat and cool the die bolt heater. In addition, since the path from the die to the winder of the film line is long, the response time of the thickness change by die bolt adjustment is often quite long, which makes the thickness profile control difficult and slow.

The disclosed systems and methods for controlling web cross thickness of extruded films allow for active fine control of the thickness profile in the manufacture of the film. Web cross thickness control can be achieved by monitoring the web cross thickness profile to control the heat distribution profile of heat transferred to the film during stretching or deformation. Monitoring the web cross thickness profile may include measuring a physical or optical thickness profile and mapping the measured profile to the point at which heat distribution control is to be made. Several different systems and methods of controlling web cross heat distribution in response to the monitored profile will be discussed. The thickness monitoring step and the heat distribution control step can form a feedback loop that is used repeatedly until the final thickness profile required for the film is reached. The disclosed systems and methods can also be used with die bolt adjustment to provide fine control of the web cross thickness profile.

In some disclosed embodiments, a specific method of controlling the web cross thickness profile of a biaxially stretched polymer film is used. For example, in some cases a channel blocker is used to adjust the heat distribution profile, and in some cases a repositionable rotatable heating element is used to adjust the heat distribution profile. These techniques can be used alone or in combination during deformation, such as longitudinal, transverse, biaxial stretching, or controlled relaxation. For example, channel blockers may be employed in length stretching machines for longitudinal stretching films, or tenters for transversely or biaxially stretching films. Similarly, a repositionable pivotable heating element can be employed in the length drawing machine or tenter. The method of controlling the web transverse thickness profile of a biaxially stretched 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 web transverse heat distribution system is capable of transferring heat to the film as it is stretched, while providing adjustable position control and adjustable profile control of the transferred heat. This can provide finer control of web cross thickness profiles compared to known systems if desired. The disclosed system can also provide faster response times compared to known systems.

A novel method of controlling web cross thickness profiles of biaxially oriented films is disclosed. This method involves controlling heat distribution in or near the stretch region of the length drawing machine LO, subsequently deforming the film in the tenter, and measuring the resulting web transverse thickness profile after the strain region of the tenter. And adjusting the heat distribution of the length drawing machine LO based on the measured thickness profile. In one embodiment, the deformation zone can be located at the end of the line just before the winder. In other embodiments, the deformation region may be located between other regions, for example as shown in FIG. 1. Other embodiments may include additional elements such as subsequent second length stretchers.

As described in more detail below, these systems and methods may be used alone or in combination in virtually any film line to produce films with improved width direction thickness uniformity. These systems and methods can also be used to make films with custom web cross thickness profiles, such as in multilayer optical film applications where color variation is desired and film thickness variation is intentionally imparted.

Two exemplary embodiments are discussed in detail below. The first embodiment employs a channel breaker in the length stretching machine. The second embodiment employs a repositionable swing heater in the tenter oven.

In some embodiments, the web cross heat distribution system includes at least one lateral heating element in combination with a plurality of channel breakers. Three embodiments of such a system are shown in FIGS. 2A-2C. In these figures, the film is stretched in the length drawing machine. 2A and 2C, the pull rolls 102, 104, 106 are installed in an S-wrap configuration. In FIG. 2B, the pull roll is installed in a conventional configuration or a tabletop configuration. The embodiments shown in FIGS. 2A-2C provide a heating assembly 150a with a set of channel breakers 170 to provide heat to the longitudinally stretched regions 140 or 140b of the film 20 for selectable heat distribution. To 150c), respectively.

In FIG. 2A, the heating assembly 150a includes three transverse infrared heating elements 160. The adjustable profile web transverse heat distribution system also includes a set of channel blockers 170 aligned in the machine direction of the film and positioned between the heating assembly 150a and the film 20. This particular embodiment employs a set of three heating elements 160 and a plurality of channel breakers 170, but any number of heating elements and any number of channel breakers may be used depending on system design considerations. Can be. For example, a system with a single heating element (heating assembly 150b) is shown in FIG. 2B, and 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 breakers. Each lateral heating element may be a single heater that spans the entire width of the film zone to be controlled, or may be a plurality of small heaters including a point heat source arranged to provide the amount of heat required for the film zone to be controlled. Can be. Combinations of point heat sources and extended heat sources are also contemplated.

In order to allow fine control of the web transverse thickness profile of the film, the web transverse heat distribution system of FIG. 2A transfers heat through the heating assembly 150a to the stretched region of the film, while at the position of each channel blocker 170. Provides adjustable profile control of the heat transferred by the change. In each of FIGS. 2A-2C, channel breaker 170 preferentially blocks the required rate of heat at the desired web crossing point. When the heating element provides heat to the film, the channel blocker or a set of channel blockers can be positioned to effectively shade the film, reducing the amount of heat delivered to the film at the particular point (s) selected. Can be. The position of each particular channel blocker shades at the point corresponding to the film zone to be finely controlled. The degree of resolution can be controlled by the size of the channel blocker as well as the proximity of the channel blocker to the film. In FIG. 2A, the channel breaker 170 is generally positioned horizontally and parallel to the heating element 160 of the heating assembly 150a. The film of FIG. 2A is an S-wrap configuration. Thus, channel blocker 170 is inclined with respect to the plane of the film in the S-wrap configuration. In FIG. 2B, the channel blocker 170 is also generally positioned horizontally but the film is in a tabletop configuration such that the channel blocker is parallel to the plane of the film. In FIG. 2C, the channel blocker is inclined parallel to the plane of the film in the S-wrap configuration.

The width of each individual channel breaker can be as narrow as desired, and the distance between the breaker and the film can also be customized. For example, the channel blocker can be 10 mm wide and can be located within 50 mm of the film. Thus, the assembly of the channel blocker as the control member can be finely divided and the web transverse thickness control scale can be customized as required, providing excellent thickness control. Also, because there is a control point in the length stretching station where the web is accelerated to line speed, the lag time from the channel breaker to the winder is substantially shorter than the delay time from the die to the winder. Thus, the response time to the control is shorter, which makes the acquisition of the final thickness uniformity quicker. In addition, the length drawing station is typically located in an open space and easily accessible, allowing the system to be easily installed and implemented. Channel breaker embodiments can also be used in tenter ovens. In such a system, the distance between the winder and the tenter oven can be much shorter and the response time can be much faster. Access to the heating assembly by the channel breaker may be designed to be controllable from outside the tenter oven.

The systems and methods of FIGS. 2A-2C allow the amount of heat delivered to a particular region to be changed quickly. As discussed further below, alternative web cross heat distribution systems may be used in which the web cross heat distribution profile is changed by varying the power provided to the array of heaters. Alternative systems may have certain benefits, such as no moving parts, but may also have disadvantages, such as low spatial resolution and slow response time, depending on the type of heater used. For example, some industrial grade IR heaters can take as long as 5 minutes to warm up and as long as 15 minutes to cool. In contrast, a system employing a movable channel blocker can be designed with relatively fast response time and high spatial resolution. The movement of a channel blocker or a set of channel blockers to shade the film to reduce the amount of heat delivered to the film is much faster than the response time of a conventional IR heater. The response time of a system using a channel breaker is limited only by how fast the channel breaker can move and the time it takes for the web to respond. This will depend on the specific mechanical design of the channel breaker assembly and its control mechanism. Those skilled in the art will recognize many different designs suitable for the mechanical control of the channel breaker assembly.

3 shows a top view of one exemplary design of channel breaker assembly 300. Assembly 300 has 34 channel blockers positioned adjacent to each other, the set spans the entire width of the film to be controlled. If desired, the physical dimensions of the film may extend beyond the width of the film to be controlled, for example if the outer edge of the film is cut and discarded or recycled to leave a usable central film portion. A web transverse heat distribution system incorporating a channel breaker assembly as shown in FIG. 3 can be used in length stretchers, tenters, or both.

A feedback mechanism can be used to repeatedly measure the physical or optical thickness profile, optionally map the measured thickness profile to the stretch region, and adjust the web transverse heat distribution system in response to the measured or mapped profile. . Feedback mechanisms are known and will not be described in detail. In short, the feedback mechanism may be in the form of manual control by an operator, may be computer controlled, or may be a combination of computer and manual control. For example, one feedback mechanism may be a computer controlled system with a manual override. Preferably, the feedback mechanism employs a computer controlled mapping algorithm using any of the mapping methods described herein. Manual mapping algorithms may also be used.

In some embodiments, the web transverse heat distribution system includes a set of repositionable heating elements disposed transversely in the stretching machine. In the exemplary embodiments discussed below, such web transverse heat distribution systems are used for tenters. The deformation region of the tenter may be a pure transverse stretching region, a relaxing region, a machine stretching region or a biaxial stretching region. Such web transverse heat distribution systems that include repositionable heating elements can also be used in length stretchers.

4 schematically shows one embodiment of the present embodiment. In FIG. 4, the film is stretched transversely in the tenter oven 200 (see FIG. 1). In this particular embodiment, the repositionable heating element is also pivotable. Web cross heat distribution system 250 includes five repositionable rod heaters 260a-260e mounted on a pair of installation channels 253. Other implementations are also possible, including, but not limited to, an array of smaller heat sources arranged linearly or in any other shape optimized for the particular response required.

In the embodiment of FIG. 4, the heater is located in the stretching region of the stretching machine, but the position of the heater is not limited to the stretching region. The stretching machine may have additional areas or other deformation areas in which a web transverse heat distribution system may be used. Additional areas include, but are not limited to, preheating areas, annealing areas and heat setting areas. When used in length stretching machines, the stretch region is a longitudinal stretch region. When used in the tenter, the deformation region may be a transverse stretching region, a relaxing region, a machine stretching region or a biaxial stretching region. The web transverse 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 intended that a web transverse heat distribution system may also be located in or near other regions. In this application, in some embodiments, the point where the web transverse heat distribution system is located is referred to as the heat distribution area.

In the heat distribution system 250 of FIG. 4, the heating element is repositionable in two ways. First, the heating element can move laterally along the mounting channel to any position along the width of the film. Secondly, the heating element is also pivotable. The benefits of the swing heater will be discussed below. Other embodiments and embodiments are also contemplated. For example, the heating element is repositionable to be moved towards and away from the film in a plane perpendicular to the plane of the film.

In order to map the transverse points on any portion of the film as the film moves along the film line, virtual centerlines 22a-22e for each lane 40a-40e are shown in FIG. 4, respectively. The film lanes 40a to 40e are bounded by virtual lines. In FIG. 4, each of the centerlines 22a-22e also represents the direction of movement of each corresponding lane of the film as the film is stretched. During transverse stretching, the distance between each pair of imaginary lines increases in proportion to the transverse stretching amount. In other words, the width of each film lane increases as the film is stretched in the transverse direction. Ideally, for example, if the film is stretched in a ratio of 3: 1, the width of each film lane will increase by three times as measured at points immediately before stretch area 220 and just after stretch area 220. . In practice, however, film lanes may not be equal in width due to various factors. These factors include, for example, variations in web cross uniformity before stretching, variations in web cross temperature distribution in the tenter, variations in homogeneity of the extruded mixture, and edge effects of finite webs. ) May be included.

The rod heaters 260a to 260e of the web cross heat distribution system are mounted so that they can be positioned independently of each other. Optionally, each bar heater can be mounted so that it can also pivot in addition to movement in the transverse direction. Rotatable heaters have two advantages. First, the swivel bar heater may be aligned with the direction of movement of the particular film lane in which the bar heater is located above. Second, the swivel bar heater can be inclined relative to the direction of movement of the film lanes to provide a wider heat distribution profile from any single heating rod. The effect of expanding this heat distribution profile will be discussed in more detail in the examples below. The pivotable repositionable heating element provides better control of the heat transferred to the film, providing a more precisely adjustable heat distribution profile compared to known systems.

In FIG. 4, each of the heating elements 260a-260e is mounted with pivots in two parallel channels 253 across the tenter. In this way, the web crossing point of each heater can be precisely adjustable from outside the tenter oven. The position and orientation of each of the rod heaters 260a-260e can be controlled by various methods known in the art. In the embodiment of FIGS. 5 and 6, the position and orientation are controlled using a pair of Acme branded threaded rods 262 for each bar heater. Other methods for position and swing control may also be used, such as for example connecting a pair of cables to each bar heater.

5 shows a detailed view of a single repositionable heating element of heat distribution system 250. The heating element 260 may be located at any position along the two mounting channels 253L and 253R. Optionally, the heating element 260 can rotate to align with the line 26 as shown by the dashed line to form an angle θ with respect to the machine direction 25. In one embodiment, this rotation is accomplished by one bolt 268 and one fixing bolt 266 that are adapted to move along the slide channel 270 as the heating element 260 rotates. Fixing bolt 266 serves as the pivot point of the heating element and is located in the center of heating element 260 in this embodiment. When no turning is required, the slide channel 270 can be omitted and both bolts can be secured. Other arrangements are also contemplated.

FIG. 6 shows a partial perspective view of the heat distribution system 250 of FIG. 4. 6 shows two heating elements 260a and 260b mounted in channels 253L and 253R. The position of the heating element 260a is controlled by a pair of threaded rods 262a. Similarly, the position of heating element 260b is controlled by a pair of screws 262b. Selective rotation of the heating element 260b causes the nut 264b to be positioned at the fixed 253R side at a point along the threaded rod 262b of the channel 253R, and the corresponding screw mounted in the channel 253L. This is accomplished by placing the nut 264b at another point along the four poles. This can also be seen in FIG. 5. The web crossing point of each heater 260 may be precisely adjustable from outside the tenter oven by a pair of screws (not shown) connected to each pair of threads. Moreover, the orientation angle of the heater can also be precisely adjusted from outside the tenter oven by the relative position of the pivot points 266b, 268 controlled by the screw pair.

A single bar heater mounted transversely and selectively pivotable relative to the machine direction can provide an adjustable thermal profile of the film as the film is stretched or deformed. When used in combination, an assembly of heaters such as, for example, heaters 260a-260e may together provide an adjustable thermal profile across any selected portion of the film or across the entire width of the film.

As in the channel breaker embodiment, the present embodiment also has the benefit of fast response time and fine active control of heat distribution. When there is a control point in the length stretching station where the web accelerates to line speed, the lag time from the web transverse heat distribution system to the winder is substantially shorter than the lag time from the die to the winder. Thus, the response time to the control is shortened, so that the cycle time is shortened, so that the required final thickness uniformity can be obtained much faster. In addition, the length drawing station is often in an open space and easily accessible, which facilitates the installation of the cross web heat distribution system. When the control point is in the tenter, the cycle time and response time can be much shorter.

In general, the thickness profile of the film can be measured at any point downstream of the point of the web transverse heat distribution system. For example, in a system employing any of the disclosed web transverse heat distribution systems in a length drawing machine, the web cross thickness profile can be measured downstream of the length drawing machine. In a system employing a web transverse heat distribution system in a tenter oven, the web transverse thickness profile can be measured downstream of the tenter oven. Alternatively, if the deformation zone is where the web cross heat distribution system is located, the web cross thickness profile can also be measured in the tenter oven immediately after the deformation zone. In a system employing a web transverse heat distribution system in a length drawing machine but also employing a tenter for subsequent transverse stretching, the measurement of the web cross thickness profile can be made downstream of the length drawing machine but upstream of the tenter oven. However, Applicants have found that measuring the cross web thickness distribution in a length drawing machine, then deforming in a tenter, and then measuring the cross web thickness profile of the film downstream of the strain area provides unexpected results. Example 2 below describes one such system and method.

For optical films, the overall film optical thickness can be detected and monitored via light transmission or light reflection spectra using an optical thickness gauge. For example, an on-line spectrophotometer can be installed to measure the spectral transmittance of the film as it comes out of the line, providing the information necessary to measure web cross thickness profile uniformity and provide feedback for process control. Done. An example of one such spectrophotometer is a type U-4000 spectrophotometer manufactured by Hitachi Ltd. In some cases, the wavelength at which the transmission spectrum falls to a certain level can be used as a measure of optical thickness. In other cases, the transmittance at a particular wavelength can be used as a measure of optical thickness. Other methods are possible, including an indirect method that can be calibrated 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 thickness related properties of the film described above. In this application, web cross 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 films or high performance films will be able to design suitable thicknesses for particular products. For example, measurement of the physical thickness of a film can be performed by on-line transverse beta gauge scanning, such as the Measurex® scanner commercially available from Honeywell International, Inc., Morristown, NJ, USA. Can be done using the device. Other thickness gauges include, without limitation, beta transmission gauges, X-ray transmission gauges, gamma backscattering gauges, contact thickness sensors, and laser thickness sensors. Such gauges are commercially available, for example, from NDC Infrared Engineering, Irwindale, CA.

The measured film thickness profile is optionally mapped to the corresponding film point where the web transverse heat distribution system is located. In some embodiments, the film thickness profile measured after the transverse stretching region can be mapped to the film in the longitudinal stretching region of the length drawing machine. In other embodiments, the film thickness profile is measured downstream of the heat distribution system and mapped to the heat distribution area. The mapping can be done in various ways. A simple mapping method involves dividing the width of the film into a set of virtual film lanes, for example as shown by the virtual lines in FIGS. 3 and 4. In FIG. 3, the film is divided into 34 film lanes, each lane corresponding to one channel blocker. In this particular embodiment, the channel blockers 301, 334 are wider than the remaining channel blockers 302-333. Thus, the corresponding lanes 1, 34 are wider than lanes 2 to 33. In Fig. 4, five film lanes 40a to 40e are shown by phantom lines. The centers of each of the five lanes 40a-40e are shown by centerlines 22a-22e, respectively.

The web cross thickness profile is measured downstream of the heat distribution area in which the web cross heat distribution system is located. At the measurement point, the width of the film may not be equal to the width of the film at the point of the heat distribution system where control is being made. Thus, a mapping algorithm is used to map one point to another. The mapping algorithm essentially moves each web crossing position of the film at one point to the corresponding web crossing point on the film at another point. Mapping algorithms include, without limitation, stretching, shrinking, bending, whether the edges of the film are cut at one point, variations in web cross uniformity before stretching, variations in web cross temperature distribution in the tenter, or extruded mixture homogeneity. Any or all of the factors that may affect how the film width differs between the two points, including variations in degrees, may be considered.

Additional mapping methods may include physically marking the film with an indicator prior to stretching and measuring the position of the indicator after stretching. For example, the first method draws two lines at a position 50 mm from each edge of the film, and then measures the position of those lines after stretching, so that the film width between the two lines has the same width Dividing into lanes. This method assumes that each lane is stretched or modified in the same amount. The second method may include drawing 50 display lines onto the film and then stretching the film to measure the position of each display line after stretching. The third method may include selectively moving one or more channel blockers 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 utilize the law of mass conservation, wherein the web cross-sectional thickness profile of the film is measured before and after stretching. Since the mass is preserved during stretching, the volume of the film 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 laterally stretched in the system using the web transverse heat distribution system 250 located at the longitudinal point 60. In some embodiments, the web cross thickness profile is measured at longitudinal point 70, at which point the film is wider than the film at point 60. In order to control the heat distribution at point 60, the measured profile at point 70 is mapped to point 60 of the heat distribution system. The heat distribution system can then be adjusted to flatten any thick or thin spots or irregularities in the film profile. In other embodiments, such a system may also have a second web transverse heat distribution system at point 50. In this case, the web transverse thickness profile measured at point 70 may also be mapped to point 50 where the second heat distribution system is located.

The usable web transverse heat distribution system can be any of the systems disclosed above, such as a repositionable heating element, a heating element with a channel breaker, or a combination of both. Any other known or later developed web cross heat distribution system capable of transferring heat to the web according to a customizable web cross profile can also be used. Web cross heat distribution systems can be used in length stretching machines or tenters. When used in tenters, a selectable heat distribution is provided to the deformation region of the film. When used in length stretching machines, a selectable heat distribution is provided in the longitudinal stretching region of the film.

As described in Example 1 below, if the measured film profile has a thick or high spot mapped to lane 08, the corresponding channel blocker 308 will allow more heat to be transferred to lane 08. Can be adjusted. This allows the film to stretch more in that lane, reducing or eliminating thick spots in the finished film. Similarly, if the measured film profile indicates a low spot on the film at a point corresponding to lane 22, then channel blocker 322 may cause the heat to reach the film at that point, for example as shown in FIG. Can be moved to prevent. In one embodiment, the blocking or non-blocking range is adjusted by the advancement of the channel through the threaded rod that rotates with the shaft 180. It is clear that such adjustments can be made with extremely fine detail, providing good control of heat distribution.

Similarly, as shown in Examples 3 and 4, thick spots can also be adjusted using repositionable heating elements in a length drawing machine or tenter. The effect can be adjusted even more finely if the repositionable heating element can also be pivoted. As in the channel breaker embodiment, the repositionable heater can be used to actively control the web cross thickness of the film to the required final profile.

In some embodiments, the length stretched film can be subsequently modified in the tenter. In such a case, it is counterintuitive that adjusting the web transverse heat distribution at the length stretching station, not the tenter, is effective in correcting the web transverse thickness profile of the finished film downstream of the tenter. Example 2 below surprisingly demonstrates that finely controlling the cross-web thickness by selectively blocking some of the heat transferred to the film during longitudinal stretching, provides a more uniform biaxial stretching film. Example 2 uses a channel breaker heat distribution system, but the method also works with any other web cross heat distribution system, such as the repositionable heating elements disclosed herein or other web cross heat distribution systems known in the art. Can be used together. The unique approach of the method, which controls the heat distribution in the length stretcher during longitudinal stretching, to achieve a uniform web thickness of the subsequently deformed film in the tenter, can provide quite good results.

Example  One

In the example shown in FIG. 7, alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polyethylene naphthalate (co-PEN) were extruded to produce an IR reflective multilayer optical film. The film was first drawn in the longitudinal direction at an elongation ratio of 3.3: 1, and subsequently stretched in the width direction at an elongation ratio of 3.3: 1 in a tenter. The optical thickness of the film was measured behind the tenter using an optical thickness gauge. Curve 7A represents the initial mapped optical thickness profile of the film. To control the thickness profile, a heating assembly with three IR bar heaters and a set of 34 channel breakers was used for the length stretcher. The IR rod heater used was a Model 5305 Series Parabolic Strip Heater manufactured by Research, Inc., Minneapolis, Minnesota, USA. Channel breakers 303 through 331 are shown at the bottom of the graph. The channel width is 12.7 mm. To lower the peak representing the thick spot shown in curve 7A at the point corresponding to channel 308, channel breaker 308 is lowered by 25.4 mm from the starting position of 35.6 mm to the final position of 10.2 mm. Moved. This downward movement of the channel blocker allowed more heat to reach the film at its web crossing point. More heat transferred to this point lowered the peak by causing that portion of the film to stretch more. The resulting mapped thickness profile is shown in curve 7B at the point 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 the point corresponding to channel blocker 308, curve 7C indicates that moving channel blocker 308 by -25.4 mm changed the thickness profile by approximately -3%. Similarly, the channel blocking effect is shown in curves 7A-7C at the point corresponding to channel blocker 322. The starting thickness profile has a dip that shows a thin spot at this point as shown by curve 7A. By moving the channel blocker 322 upwards by 25.4 mm to a final position of 61 mm, more heat is prevented from reaching that portion of the film, causing the film to stretch less than the adjacent portion. This increases the thickness profile at that point as shown by curve 7B. The percent change at this point varied by approximately 3% as shown by curve 7C.

Example  2

In the example shown in FIG. 8, alternating layers of polymethyl methacrylate (PMMA) and a copolymer of polyethylene naphthalate (co-PEN) were extruded to produce an IR reflective multilayer optical film. The film was stretched in the longitudinal direction at an elongation ratio of 3.3: 1. Subsequently, the film was stretched transversely 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 thickness gauge. Curve 8A shows the initial web transverse optical thickness profile of the film mapped to the length drawing station. To control the thickness profile, a heating assembly with three IR bar heaters and a set of 34 channel breakers was used for the length stretcher. The IR rod heater used was a Model 5305 series parabolic strip heater manufactured by Research, Inc. of Minneapolis, Minnesota, USA. Channel breakers 303 through 331 are shown at the bottom of the graph. The channel width was 12.7 mm.

The profile of the film shown in curve 8A was adjusted by moving several of the channel blockers as indicated by the final setting of each channel blocker at the bottom of FIG. 8. Table 1 shows the initial and final settings for the channel breakers 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 web transverse heat distribution system with a set of IR heaters and a set of channel breakers.

Example  3

In the example shown in FIG. 9, alternating layers of polyethylene terephthalate (PET) and a copolymer of PMMA were extruded to produce a multilayer optical film. The film was stretched in the longitudinal direction at an elongation ratio of 3.35: 1. Subsequently, the film was stretched transversely in a tenter at an elongation ratio of 3.3: 1. The tenter was equipped with a set of repositionable swivel heating elements in the transverse stretching region of the tenter. Each heating element was 325 mm long and 10 mm wide and had a parabolic reflector 80 mm wide. The heating element used was a Raymax model 1525 available from Wattlow Electric, St. Louis, Missouri. In this example, the center of the heating element was used as the pivot point and the positioning point. The optical thickness of the film was measured after the tenter using an optical thickness gauge. Curves 9A, 9B, 9C show optical thickness variation as a function of web cross point for different configurations of web cross heat distribution systems, demonstrating the effect of repositionable swiveling IR heaters on finished films. Heating element output and orientation angles are listed in Tables 2 and 3.

When a single heating element is maintained at a constant power and the same orientation angle, the change in the web cross-sectional optical thickness profile remains the same for each of the three curves 9A, 9B, 9C. This effect is observed as the descent of the curves 9A, 9B, 9C at the 460 mm web crossing point corresponding to the first heating element 962. When a single heating element is maintained at a constant output but the orientation angle changes, a broadening effect is observed. The dive of the curves 9A, 9B, 9C at 950 mm demonstrates this expansion effect due to the single bar heater. In this embodiment, the second heater 964 located at 950 mm is rotated from 0 ° of curve 9A to 12.5 ° of curve B and 25 ° of curve C.

Example  4

In the examples shown in FIGS. 10-13, alternating layers of a copolymer of PET and PMMA were extruded to produce a multilayer optical film. The film was stretched in the longitudinal direction at an elongation ratio of 3.35: 1. Subsequently, the film was stretched transversely at an elongation ratio of 3.3: 1. The tenter was provided with a set of four repositionable swivel heating elements in the transverse stretch area. Each heating element was 325 mm long and 10 mm wide and was provided with a parabolic reflector 80 mm wide. The heating element used was the Raymax Model 1525 available from Wattrow Electric, St. Louis, Missouri. The center of each heating element was used as the pivot point. The central position of each heating element in this embodiment is shown as "position, right" in Tables 4 to 7, and the position of the pivoting movable bolt is shown as "position, left-inclined". The optical thickness of the film was measured downstream of the tenter using an optical thickness gauge. Curve A in each of FIGS. 10-13 represents the initial optical web cross thickness profile. 10-13 show successive repetitions of heater setting changes. Initially, the cross web optical thickness profile of the film was measured. The measured data points are plotted as curve A in FIG. Next, the measured web transverse optical thickness profile of the film was mapped to the transverse stretch area. In response to the mapped profile, heaters 1 to 4 were set in the first iteration according to the parameters shown in Table 4. The resulting web cross optical thickness profile was measured and shown as curve B of FIG. 10. Then, the resulting optical thickness (curve B of FIG. 10) of the first iteration becomes the initial thickness profile (curve A of FIG. 11) of the second iteration. 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 are repeated until the required final thickness profile is reached. Form a feedback loop. In the second iteration, heaters 1 to 4 were set according to the parameters shown in Table 5. The resulting optical thickness profile is plotted as curve B in FIG. This process is repeated through two additional iterations as shown by the heater settings in Tables 6 and 7 and the thickness profiles are depicted in FIGS. 12 and 13. The cooperative effect of a set of four repositionable turning IR heaters on the optical web transverse thickness profile of the finished film is shown by curve B of FIG. 13. Curve B of FIG. 13 shows that a set of four repositionable heating elements located in this range of interest in the range of approximately 1300 mm to 1850 mm can be used to obtain a flat final thickness profile. It should be noted that a "valley" of web crossing points greater than 1850 mm may be handled by other means such as die bolt adjustment.

While the invention is in accordance with various modifications and alternative forms, details of the invention are set forth by way of example in the drawings and the description. It should be understood, however, that the invention is not limited to the specific embodiments described. On the contrary, the invention is intended to cover modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims (24)

Stretching apparatus having a heat distribution region and deforming the polymer film, A cross web heat distribution system providing selectable heat distribution for the film in the drawing machine, A thickness gauge positioned downstream from the web crossing heat distribution system to measure a web crossing thickness profile of the film, and A feedback mechanism for selecting a heat distribution in response to the measured web transverse thickness profile, The web transverse heat distribution system includes a heating element and a plurality of channel breakers proximate the heat distribution area, each channel breaker such that at least one channel breaker prevents at least a portion of the heat generated by the heating element from reaching the film. Is movably positioned to control the web cross thickness profile of the polymer film. The apparatus of claim 1, wherein the heat distribution zone is a strain zone or a preheat zone. Deforming the film in a drawing machine having a web crossing heat distribution system, Measuring a web cross thickness profile of the film at a point downstream from the web cross heat distribution system, and Adjusting the web transverse thickness distribution system in response to the measured web transverse thickness profile by selectively repositioning the at least one channel blocker of the web transverse heat distribution system. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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