Advanced control system and method for making polyethylene terephthalate sheets and objects

ES 2 811 774 T3

DESCRIPTION

Advanced control system and method for manufacturing polyethylene terephthalate sheets and objects

Field of the invention

The present invention relates to a system and method for manufacturing polyethylene terephthalate sheets and objects.

Problem

As described in US Patent No. 5,756,032, polyesters such as polyethylene terephthalate (PET) are known to possess good chemical stability, physical and mechanical strength, durability, and heat resistance. Therefore, polyester has been widely used in the manufacture of various items, including packaging and labeling devices. The good performance of polyester is very important and the ability to reduce the cost of materials with this polymer will generalize its use to a great extent. Polyester is divided into general purpose plastics and engineering plastics, and has been shown to be used in many applications. Polyester foil packaging materials are being used more and more and have a tendency to penetrate applications with which they have not been associated. Therefore, advancements to reduce your manufacturing cost in PET sheet applications and enhance your mechanical and optical performance attributes in a wide variety of applications is an important step in overcoming cost and performance barriers to competing polymers and polymers. in this way, increase the interest it arouses in new applications. In particular, the stiffness and impact resistance of the PET sheet is an important functional attribute, as it allows the gauge of the PET sheet to be reduced. These sheets can be made into rolls of different diameters or cut directly into sheets. PET and amorphous polyethylene terephthalate (APET) resin are used interchangeably as the resin used to make APET rigid film.

Under the traditional manufacturing process, the final PET or APET product is produced by a multi-stage process. Initially, a relatively low molecular weight precursor polymer is prepared by melt phase polymerization techniques commonly known in the art. As explained in the US patent. No. 5,736,621, the common route for manufacturing polyester resin involves polycondensation, the first step being carried out down to a moderate molecular weight that corresponds to an average intrinsic or inherent viscosity (VI) of about 0.5- 0.7 deciliters / gram (dl / g) in the melt and additional solid phase condensation taking place. For solid stage condensation, the polyester chips are heated at a reduced temperature until they reach the desired molecular weight.

The precursor is then cooled and pelletized, and then possibly crystallized and subjected to further solid phase polymerization at a lower temperature. Gases can be used to remove glycols, aldehydes and other reaction by-products from PET pellets, which also contributes to increasing the VI value. This is followed by the storage of PET pellets normally in ambient air, where hygroscopic pellets absorb moisture from the air, therefore, it is necessary to dry the pellets before reheating and melting them in an extruder connected to a die. Normally, PET pellets are dried to a moisture content of less than 0.025%. If the resin is dried prior to supply to the rolling mill, the material will have to be stored under dry nitrogen.

The means of preparing PET sheets from various forms of PET with various viscosities are known to require the use of PET pellets. Each grade of PET resins has its own problems due to the hygroscopicity of the PET material and its deterioration during the extrusion process. However, this technique requires the use of transport and intermediate manufacturing processes. Articles produced by the extrusion system or the rotary die method produce parts of various gauges.

The resin is extruded through an extruder, and the extruder barrel can have a vacuum purge in order to remove the moisture generated during the extrusion process. A melt pump is used in order to achieve uniform melt production as it is pushed into the extrusion die. The molten resin is then formed into a sheet by passing it through an extrusion die. In the case of the rotary die, the objects are manufactured directly on the rotary die and do not go through the rolling phase. The sheet is then polished on a stack of rollers or passed through a stack of calenders, where the sheet is sized to the appropriate thickness. The sheet can be surface treated with silicone on one or both sides. In the case of strap material, the sheet is typically cut to produce strap material. Finally, the sheet is then rolled into a roll or cut into finished sheets. In the case of thick sheets, the sheets are not normally rolled, but rather laminated. (The key parameter to keep the pressure entering the die constant. The pressure variation should be less than +/- 1 bar).

These various processes affect the performance of PET pellets when they are sheet-shaped or injected into a rotary die. In general, the physical properties of PET, such as its hygroscopicity in pelletized form, adversely affect the optical properties of polyester in the finished product if it is not properly conditioned. When extruded, side reactions result in degradation of the polyester chain, 2

ES 2 811 774 T3 which adversely affects the properties. Furthermore, it has been a common practice to compensate for some of the negative performances of PET pellets relative to hygroscopicity and the decrease in IV grades during the extrusion process.

Additionally, during melt phase processing of polyesters, certain unwanted by-products are formed. One such product is acetaldehyde, which is continuously formed as a by-product during polymerization and subsequent melt processing of polyesters. Acetaldehyde is known to contaminate food or beverage products when present in a food or beverage container. Therefore, it is desirable to produce molded polyester packages with acetaldehyde content in low or no concentrations. Residence time at elevated temperatures is the main cause of acetaldehyde formation.

In addition, there are methods that describe the attachment of a reactor to a ram system to inject the polymer into a mold. Other patents refer to a continuous system, but the production of uniform parts in multiple streams is not possible.

Information pertinent to attempts to address these problems can be found in the following US Patents: 5,656,719, issued August 12, 1997 to Stibal et al .; No. 5,980,797, issued Nov. 9, 1999 to Shelby et al .; No. 5,968,429, issued Oct. 19, 1999 to Treec et al .; No. 5,756,032, issued May 26, 1998 to Stibal et al .; No. 6,099,778, issued Aug. 8, 2000 to Nelson et al .; and published US patent application. US No. 10 / 996,352, filed October 14, 2004 by Otto et al.

An apparatus and method for producing molded polyester articles with a low acetaldehyde content from a melt prepared by continuous reaction of polyester precursors is described in US Patent No. 5,968,429. A central controller associated with the molding machine minimizes excessive wall temperatures, provides uniform heating conditions, and reduces residence time in the extruder.

Solution

The problems described above are solved and technical advancement is achieved by the present system and method for making single-layer or multi-layer polyethylene terephthalate ("PET") sheets ("system for making PET sheets") at a cost lower and exhibiting excellent mechanical and optical properties by eliminating certain steps in the manufacturing process and by passing the PET melt directly from the reactor through a die and onto a surface, instead of melting the PET resin into pellets through an extruder and then onto a surface.

According to a first aspect, the present invention provides a method for manufacturing PET objects comprising: reacting a first PET precursor and a second PET precursor to produce a PET melt; flowing said PET melt into a distribution system having multiple outlets; flowing said PET melt from the distribution system having multiple outlets to a die-forming system and a side stream of chips; individually control the mass flow of the PET melt in the die forming system and in the chip side stream using a combined feed and feedback control system in the die forming system and the chip side stream , wherein said individual control of the mass flow of the PET melt comprises controlling the pressure of said PET melt with pressure control loops prior to said shaping of said PET objects; forming said PET objects from said PET melt; and wherein the method further comprises: flowing said PET from one of the multiple outlets into the side stream of chips to form pellets.

According to a second aspect, the present invention provides a system for manufacturing PET objects comprising:

means for reacting a first PET precursor and a second PET precursor at a temperature in the range of about 200 ° C to about 330 ° C to produce a PET melt; means for flowing said PET melt into a distribution system having multiple outlets; means for flowing said PET melt from at least two outlets of the multiple outlets to at least one die-forming system (121) and a side stream of chips to produce pellets;

means for individually controlling the mass flow of the PET melt in each of at least said two forming lines independently of the other of said lines, wherein said means for individually controlling the mass flow of the PET melt comprise means for controlling the pressure of said PET melt with pressure control loops prior to said shaping of said PET objects; and means for forming said PET objects from said PET melt.

By avoiding a series of manufacturing steps by which the PET melt is conditioned and altered during the preparation and extrusion process, the optical and mechanical properties of the original PET melt exiting the reactor are not impaired, and neither is it. traps moisture. These are very important steps as these intermediate steps above are eliminated as the PET resin is already in the molten phase and therefore does not have to be melted through an extruder and also because it is not required. transportation, which due to nature 3

ES 2 811 774 T3 hygroscopic of the pellet requires a treatment with nitrogen. Additionally, multilayer PET can be manufactured using other substrates in one or more of the layers. The present system for making PET sheets allows the preparation of PET sheets of particularly high quality under mild reaction conditions, as PET is never pelleted or remelted through an extruder.

The present system makes it possible to manufacture PET sheets that can be efficiently thermoformed into containers and cut to produce strapping material, and that when made into thick sheets can be used as display material for interior and exterior signage. Since the present system for making PET sheets pertains to making items directly from the extruder die onto a sheet forming system or a rotary die, the results are the same, a product superior to a lower gauge without going through the pellet stage, thus maintaining its VI grade and inherent stiffness, resulting in superior mechanical performance. The present system for manufacturing PET sheets is a process by which a system of continuous reactors for PET is coupled to a series of forming subsystems while maintaining a constant pressure in each subsystem regardless of the operating conditions of the other subsystems. In this way, speed changes, start-up, stops and breakdowns are all solved by the present system for the manufacture of PET sheets. In one aspect, the present system for making PET sheets extrudes products such as sheets or objects with a rotary die directly from the PET melt prepared in the polymerization reactor. The uniqueness of this present system for making PET sheets resides in the handling of the melt stream from the reactor to the die. In order to extrude the cast through a die and maintain part thickness control, strict control of the pressure entering each die must be maintained at a uniform set pressure and within a range. tight tolerance. The present system for the manufacture of PET sheets is applied to control the pressure entering the die or dies feeding the forming device or devices. A side stream of chips is added to the multiple forming lines, as well as a plurality of pumps before the die (s). These new additions allow the shaping of a uniform piece.

The present system for manufacturing PET sheets produces high quality PET sheets in continuous and discontinuous forms where the PET melt is obtained directly from the esterification and after the polymerization stage in the PET reactor using pure terephthalic acid ( PTA) or dimethyl terephthalate (DMT) and monoethylene glycol (MEG), and is passed through the die directly onto a receiving surface without being pelletized. In another aspect, other types of glycols can be used, such as diethylene glycol and the like. The PET sheets produced by the above methods are manufactured at a lower cost, have high structural homogeneity, improved optical properties, and excellent mechanical strength. In the case of the manufacture of articles directly from the reactor to a rotating die, the results are the same, except that the manufactured products are not previously transformed into sheets, but are shaped according to their final configuration.

Furthermore, the extruder, when coupled to a melt reactor and properly controlled, provides a material that does not require preconditioning and has minimal thermal history. This coupling simplifies the process and results in a better finished product. Denying intermediate process steps, such as pelletizing and drying, reduces the overall cost of manufacturing. Furthermore, the present system for making PET sheets simplifies the manufacturing process for making PET sheets and articles on a rotary die where the polymer does not have to be processed before being processed through the extrusion die.

Also, the lack of moisture in the PET melt enhances the PET resin's optical properties and performance at the rigid film manufacturing stage. Both of the end-use properties achieved through this manufacturing process produce sheet quality, which is very important to thermoformers and end users. Likewise, the trimmings and other residues generated in the process are of high quality in terms of VI readings and can be mixed with virgin PET resins in the preparation process.

The PET sheets produced by the above methods are manufactured at a lower cost, have high structural homogeneity, improved optical properties, and excellent mechanical strength. In the case of the manufacture of articles directly from the reactor to a rotating die, the results are the same, except that the manufactured products are not previously transformed into sheets, but are shaped according to their final configuration.

Summary

Preferably, the system for making PET objects includes means for reacting a first PET precursor and a second PET precursor to produce a PET melt; means for flowing the PET melt into a distribution system that channels the melt to the appropriate final process. The final process represents means of forming the PET objects from the PET melt. The system further includes means for flowing PET from one of at least two outlets to a side stream of chips to form pellets. Preferably, the means for the reaction take place within a temperature range of from about 200 ° C to about 330 ° C.

Preferably, the first PET precursor is selected from the group consisting of pure terephthalic acid (PTA) or 4

ES 2 811 774 T3 diethylterephthalate (DMT) and the second PET precursor is monoethylene glycol (MEG) or diethylene glycol (DEG). In another aspect of the present invention, secondary precursors, such as cyclohexanedimethanol (CHDM), can be used in combination with the primary precursors, such as MEG. In this aspect, the end product is polyester glycol (PETG). Preferably, the system further includes means to reduce the acetaldehyde content in the PET melt. Preferably, the means for individually controlling the mass flow of the PET melt includes means for controlling the pressure of the PET melt with pressure control loops prior to shaping of the PET objects. Preferably, the PET objects are selected from the group consisting of PET articles, PET sheets, strapping and architectural articles. Preferably, the means for forming PET objects further includes means for adding at least one side extruder in order to produce a multilayer PET object or sheet. Preferably, the system further includes means for producing a laminate structure which is selected from the group consisting of a sheet and an EVOh structure. Preferably, the system further includes means for filtering said PET melt prior to forming the PET objects.

Brief description of the drawings

A block diagram of the system for making PET sheets according to one embodiment of the present invention is illustrated in Figure 1;

Figure 2 illustrates a block diagram detailing the main control loop;

An outline of the detailed control system for the sheet and knife lines producing the product is shown in Figure 3;

A block diagram of a die and a coextruder of the system for making PET sheets according to an embodiment of the present invention is illustrated in Figure 4;

A block diagram of a die and laminated sheet subsystem of the system for making PET sheets according to an embodiment of the present invention is illustrated in Figure 5;

A flow chart of a process for making PET sheet according to one embodiment of the present invention is illustrated in Figure 6.

Detailed description of the drawings

By the term PET films it is generally meant a rigid PET or APET film of at least 5 thousandths of an inch (0.0254 mm). This sheet can be made into rolls of different diameters or it can be cut directly into sheets. PET and APET resin are used interchangeably as the resin used to make APET rigid film. Similar reference numbers are used to indicate like parts throughout the drawings. An embodiment 100 of a system for making PET sheets is illustrated in Figure 1. The precursors or raw materials are fed to the reactor 106 of the system for making PET sheets 100. In one embodiment, the precursors include a raw material of pure terephthalic acid ("PTA") or dimethyl terephthalate ("DMT") 102 and a material Monoethylene glycol ("mEg") cousin 104. In another embodiment, another glycol may be used, such as DEG. In another aspect of the present invention, secondary precursors, such as cyclohexanedimethanol (CHDM), can be used in combination with the primary precursors, such as MEG. In this aspect, the end product is polyester glycol (PETG).

In one embodiment, the two raw materials 102 and 104 produce a bis (2-hydroxyethyl) terephthalate intermediate, which can be converted to polyethylene terephthalate by heating to a temperature above the boiling point of ethylene glycol or the reaction mixture under conditions that produce removal of glycol or water. Raw materials 102 and 104 are reacted in reactor 106 by esterification and polymerization to produce the PET melt. If desired, heating in reactor 106 can take place at a temperature of up to 325 ° C. During heating, the pressure is reduced to provide rapid distillation of excess glycol or water. The final polyethylene terephthalate polymer can have an IV, measured in orthochlorophenol at 25 ° C, of ​​more than 0.3 dl / g. More preferably, the IV of the polymer is in the range of from about 0.4 to about 1.0 dl / g, measured in orthochlorophenol at 25 ° C. Even more preferably, the polyethylene terephthalate used in the present system to make PET 100 sheets has an IV of about 0.5 to about 0.7 dl / g, measured in orthochlorophenol at 25 ° C. The polyester-containing thermoplastic polymers of this present system for making PET 100 sheets have a preferred melting point in the range of from about 200 ° C to about 330 ° C, or more preferably, from about 220 ° C to about 290 ° C. ° C, and even more preferably, from about 250 ° C to about 275 ° C.

In one aspect of the present system the PET sheet is manufactured. In another aspect, the present PET 100 sheet making system is used to produce all types of products, including sheets, with all other types of molten polymers. Another example of a molten polymer is a linear low density polyethylene (LLDPE) polymer. In addition to homopolymers, the present system for making PET 100 sheets can be used with

ES 2 811 774 T3 PET copolymers, such as by adding cyclohexanedimethanol (CHDM) in place of ethylene glycol or isophthalic acid in place of some of the terephthalate units. These are examples of suspension copolymers that are not part of the base reaction and that can be used in this manufacturing process.

Many different kinds of additives can also be added to the PET melt, depending on the type of properties desired in the finished article. Such additives may include, but are not limited to, colorants, antioxidants, acetaldehyde reducing agents, stabilizers, for example UV radiation and heat stabilizers, impact resistance enhancers, polymerization catalyst deactivators, corrosion resistance enhancers. fusion, chain extenders, antistatic agents, lubricants, nucleating agents, solvents, fillers, plasticizers, and the like. Preferably, these additives are added to reactor 106, but can be added to other locations in the present system to make PET sheets 100.

The PET melt is then fed via line 108 to a master pump 110 where it is pumped to a filter 114 via line 112. In this embodiment, the main pump 110 feeds the PET melt throughout the system. of distribution. The PET melt is passed through filter 114 to remove any foreign particles introduced through the feed stream or produced by the reaction from the PET melt. Preferably, filter 114 is used to screen any large gels, degraded particles, or foreign material that may harm subsequent melt pumps or the final product. Filter media of various grades (mechanical sieves, sand, sintered metal, etc.) can be used. The proper design (volume, pressure drop, and residence time) of filter 114 is important to maintain proper pressure throughout the present system for making PET 100 sheets.

The PET melt is then fed to a process discharge pump with distribution vessel 118 via line 116. In this particular embodiment, the process discharge pump with distribution vessel 118 has a distribution box. with multiple outputs. Preferably, dispensing container 118 may have any number of outlets to suit a desired application. As shown, two streams 119 and 120 produce PET pellets 126. This material can be sold directly for bottles or used in a coextrusion process (Figure 2) to produce a multilayer film. Additionally, the process discharge pump system 118 also feeds the PET melt to three sheet production processes or die-forming units, 121, 122 and 123. Although only three lamination lines are indicated, multiple lines could be added. Two lines of knives are required to maintain maximum control. The two blades are sized so that these blades can handle the maximum output of reactor 106. The design of the system is such that melt flow is minimized so degradation and acetaldehyde are not a problem. All individual processes have control valves that are used in the final control stream, as well as allowing a branch to be completely stopped.

In one embodiment, the system for making PET sheets 100 is a continuous process that does not stop once it is started. One way to control the mass flow of the PET melt flowing through the present system for making PET sheet 100 is by adjusting the mass flow of raw materials 102 and 104 entering reactor 106. A loop can be used feedback switch to control pressure feedback pump 118. As shown in Figure 1, the pump 118 that goes to the side or bypass chip stream 119 can be opened more or less to modulate the PET melt going to each section of the process of the entire system. The pumps 110 and 118 are controlled by continuous feedback of the calculated flow necessary to maintain the pressure in each of the branches of the system. These values ​​are collected from the branches, fed back to the main PLC, and then used as main speed control. Pressure loops within the system cut speeds. In this way, sufficient flow is distributed into the system. The pumps in each subsystem will then modulate the pressure to the final value. Excess flow is always introduced into the system to allow one line of knives to operate. As the flow in the sheeting systems is decreased or increased, the blade system reacts to keep the flow and pressure entering the sheeting lines within operating parameters.

The control loop for pumps 110 and 118 is depicted in Figure 2. Fusion pumps operate according to the constant volume theory at each revolution of the pump. When melt pumps are used for plastic melts, the compressibility of the material becomes a factor. For any given polymer, at a given temperature and inlet / outlet pressure setting, the output for a given pump can be calculated. In order to precisely control the production on the rolling lines in the process, we have developed a control system in which the calculated flow of all the pumps is used as the control parameter.

As depicted in Figure 2, if we have three rolling mill lines in operation, we would also have at least one of the knife lines in operation. The calculated flow parameters (501) would be calculated on each of the operating lines and fed back to the main system control (502, 503 and 504). The main system controllers would then control the main product discharge pump (118) and pump (110) to discharge enough polymer melt into the system to keep the suction side of all pumps running. The pressure can be cut off by operating pressure valves within the loops. This main control loop is constantly monitored to compensate for any speed changes on any of the rolling lines. As the lines change speed, he heads for more or 6

ES 2 811 774 T3 less material to the cutting process. The main system continuously cuts the speeds of the blades (506) in order to maintain optimum quality of the pellets through the blades.

The individual loops used to control the output of the last pump are detailed in Figure 3 to maintain quality in both the blade loop and the roll line loop. The input into each of the loops is controlled by the main loop, while the output speed of the individual loops is used to maintain the pressure within the specified value of 1 bar by the 525 speed controls and the 526 motor speeds . The speeds of the rolling line depend on the speed of the rolling line and the width and gap of the die. The thickness of the sheet is the important parameter. As the speed of the rolling line increases or decreases, the speed of the last pump must follow the changes to maintain thickness accuracy.

The main process pump feeds material into the system based on the calculated flow values. The values ​​within the system help direct the appropriate flow to each of the branches. The flow from the main pump is directed to the main sheeting line pump (507). The speed of this pump is controlled by the feedback loop, which mainly comprises the inlet pressure (508) to the outlet pump (509). To effectively control flows and pressure, the system also includes numerous 527 flow controllers and indicators, 528 flow indicators, 529 pressure indicators, 531 pressure indicators and controllers, 530 speed indicators, and 525 speed controllers. Pressure Suction entering the outlet pump is maintained at a constant pressure. If the speed of the rolling line is changed, then the loop is designed to feed back to all three pumps, the main pump, the primary pump and the outlet pump. If the roll line slows down substantially, then the material can be diverted to the knife line to prevent the roll line from being massively flooded. Similarly, if the roll line accelerates from there, material from the blade can be diverted back to the roll line. The use of this higher order control current allows the system to maintain a constant pressure and a tolerance margin for thickness of less than 1%. Preferably, the multiple pumps provide highly dependent thickness control with constant pressure entering the sheet production processes or die-forming units 121, 122, and 123. The first pump will modulate any large variations in pressure. The second pump and each subsequent pump will further reduce any modulation to less than + 1-1 bar leaving the final pump. This allows the forming lines (outputs) to remain independent so that they can be slowed down, started, stopped or accelerated independently of the other die forming units. Pressure control loops with side or bypass chip stream 119 will provide this function.

The blade loop is flow dependent. The knife line can accommodate a minimum production as well as a maximum production. There are two lines of knives available, so as one line approaches maximum flow the second line can be brought into line. Flow and speed are controlled so that the blades keep the size of the pellets uniform. Material from the main process pump is pumped to the manifold; Properly positioned valves allow flow to be diverted to the primary knife pump (510). In one embodiment, the present system for making PET sheets 100 continuously produces PET sheets from PTA and MEG directly from the molten phase of reactor 106 to an extrusion die without going through a nitrogen treatment, an extruder and others. steps, and rolled or not in the longitudinal direction. In another embodiment, the present system for making PET sheets 100 flows the PET melt directly from reactor 106 and an extruder die over rotating dies for the manufacture of packaging material and other items.

In one embodiment, the sheet production processes or die-forming units 121, 122, and 123 are a three-roll stack or air knife system. Most preferably, the die forming units are a three horizontal roll stack system. Normally, behind the stack of rollers there are auxiliary systems, such as coaters, treaters, cutting devices, etc., which are fed to a winder. These units are suitably specified to the individual section of the system and the overall capacity of the reactor 106.

In another embodiment, another type of unit would be a low-pull rotary die that forms parts such as bottle caps or caps directly on the rotary die from the formed sheet. In one embodiment, there is a pump 110 that feeds the systems 119 to 123. Preferably, at the end of each run, before the die and the sheet or rotary die, there are one or two individual pumps 507 and 509, respectively. Preferably, pump 118 maintains pressure in the system. This pump 118 is controlled by the main PLC that uses continuous flow information from the branch pumps in the system. If the pressure decreases, the pump 118 will increase the pressure. If the pressure increases, then the pump 118 slows down or the PET melt is diverted to the side or bypass chip stream 119. Preferably, if either system is to have lower production for an extended period of time, such as for several hours, then a flow system value signal will be provided to main pump 110 and reactor 106 to slow feed to in order to compensate for the lower production. When the 507 and 509 pumps include two pumps in series, the first pump in the multi-pump set is used to modulate the pressure in the total system. In this arrangement, the first pump in the series of pumps comprising pumps 507 and 509 maintains a constant pressure head entering the second pump in the series of pumps. Preferably, the multiple pumps provide highly dependent thickness control with constant pressure in the chip side streams and the die-forming units 119 to 123. The first pump will modulate any large variations

ES 2 811 774 T3 in pressure. The second pump and each subsequent pump will further reduce any modulation to less than +/- 1 bar exiting the final pump and entering the forming die. This allows the forming lines (outputs) to remain independent so that they can be slowed down, started, stopped or accelerated independently of the other die forming units. Pressure control loops with side or bypass chip stream 119 will provide this function. In one embodiment, the pumps are volumetric pumps as described herein.

The pressure control logic controls the continuous reactor 106, whose response time is generally greater in magnitude than at the outlet ends in the side streams of chips and the die-forming units 119 to 123, to control the output. thickness of the final product or sheet. In one embodiment, this is accomplished while each exit leg remains independent of the other exit legs. In one embodiment, the control loop allows for sudden disturbances to the process, such as starting or stopping one of the output legs. In this embodiment, a side or bypass chip stream 119 allows chip production to increase or decrease depending on any disturbance in the process. The disturbance can be a planned disturbance, such as shutting down a line for maintenance, etc., or an unplanned disturbance, such as equipment malfunction.

In addition to the above, the control loop preferentially compensates for the increase or decrease in speed in a span while continuing the overall system for manufacturing the PET sheets 100 under stationary conditions. Pump 118 and associated valves (not shown) will react by diverting to or from the side stream of chips. This can cause a brief rise or change in pressure to which the pumps 507 and 509 at the end of each branch of the system will react. In this embodiment, the individual pumps comprising pumps 507 and 510 will experience the pressure rise and react to it while the second pump in the series 509 and 511 will experience modulation of the magnitude of the disturbance, which will be low enough to to be modulated by an order of magnitude less than one second. In another embodiment, each line configuration is going to be different, so individual schemes will apply to that system.

Shown in Figure 4 is one embodiment 200 of a coextrusion subsystem for producing a multilayer sheet by adding a coextruder 204 to the PET melt contained in line 138 or 150. The coextruded material is fed from coextruder 204 to a feed block 212 via line 202 along with the PET melt from the flow channels as described above. The feed block 212 then extends the materials suitably into the flat die 208. This feed block 212 directs the streams that produce a multilayer stream, which is fed to a flat die 208 via tubing 206 where it is extruded forming the section that forms the sheet or the PET 210 sheet. Coextruder 204 may use resin pellets 126 from side or bypass chip stream 119 or be a different material, such as an adhesive tie layer or barrier resin, but is not limited to these examples. This coextrusion process can be added to any of the processes or to all sheet production processes or die-forming units 121, 122 or 123. In one embodiment, the size of the coextruder 204 is designed according to the required kilogram output. When a coextruder 204 is used in the present system to make PET 100 sheets, the kilograms of material added to the system should preferably be taken into account to provide the cooling capacity required in the section of the present system to make PET 100 sheets. .

An embodiment 300 of a subsystem for generating a multilayer laminated structure or PET sheet is shown in Figure 5. The PET melt (either single layer or coextruded multilayer) is fed through flat die 208 via tubing 206 to forming rolls 310 and 312. In one embodiment, additional film 304 is fed to shaping rollers 308 and 310. Heat from the PET melt stream binds additional film 304 to form a coherent laminate structure 316. Additional rollers 306 and 308 can be used to guide additional film from feed spool 302 to forming rollers 312. In another embodiment , other materials such as metallic foil or EVOH film can be added to the laminating process. In yet another embodiment, other types of materials can be added to the laminating process. Each of these unique structures can then be used for specific end applications.

Preferably, the design criteria for 300, the subsystem for creating a multilayer laminated structure or a PET sheet, are to provide a sheet of the highest quality from the lowest capital investment. The high melt throughput of PET through the 100 PET sheet making system requires good chill roll design so that no drift occurs. The ability to monitor and control the thickness of PET sheets during cooling is important. In addition, the ability to change the sizes and thicknesses of the PET sheets is also important. Other downstream operations such as rolling and cutting are also considered when using the multi-layer laminated structure or the PET sheet.

As demonstrated, the resulting product or the PET sheet is determined by the sheet production processes or the die-forming units 121 to 123. The present system for making PET 100 sheets controls the sheet production processes or die-forming units 121 to 123 with such precision (as well as an extrusion system) that the objects produced by this system are limited to only 8

ES 2 811 774 T3 for the creativity of the manufacturer. Similarly, the number of die-forming units can vary from the three shown to any number that does not exceed the capacity of reactor 106.

In one embodiment, the present system for making PET sheets 100 controls the pressure going from a continuous reactor 106 to multiple flow channels. Each channel is attached to a shaping section that produces different objects. Each flow channel acts as an individual extruder without an extruder. In another embodiment, a single pump can be used if the dynamics of the pump is accounted for in the process control algorithm.

In one embodiment, the present system for making PET 100 sheets favorably affects the mechanical and optical properties of the PET sheet being manufactured, which will allow the PET sheet to be manufactured at a lower gauge when manufactured to packaging or other application such as sheet, strip or architectural items.

The present system for manufacturing PET 100 sheets produces PET objects and articles that have scrap quality, and other waste generated in the manufacturing process will be of high quality, so that they can be mixed in high percentages with the virgin PET melt. without negatively affecting the quality of the final sheet and without the need to increase the gauge.

In addition to the above-mentioned embodiments and aspects of the present system for making PET sheets 100, the present invention further includes methods for making these PET sheets.

A flow chart of an embodiment 400 of such a process is illustrated in Figure 6. In step 402, a first PET precursor and a second PET precursor as described above are reacted in a reactor to produce a pEt melt. Preferably, in this step, the known reactor capacity and a certain mixture of products with various foil thicknesses and widths are determined. From this information the number of sections is determined taking into account the cooling capacity of each of the die-forming units. The cooling capacity preferably determines the maximum production of each subsequent run. In one aspect, a side or bypass chip stream 119 may be introduced into reactor 106 in this step. In another aspect, a side stream of scraps from the previous operation may be introduced into reactor 106 in this step.

In step 404, the PET melt is filtered to remove impurities from the PET melt. In step 406, the PET melt is flowed through a positive or negative displacement apparatus, such as a pump, to a valve that preferably has multiple outlets. In step 408, the PET melt is flowed from the valve outlets to the individual valve outlet. The outlet sections are connected to individual die-forming systems, additionally a distribution section is connected to a blade (pelletizing) system. In step 410, the pressure or mass flow of the PET melt is controlled. Flow and pressure are controlled by a combined feed-forward and feedback system. The feed-forward system uses the flow parameter calculated from each of the individual systems to calculate a total flow that is fed forward to the process discharge pump and blade runs. Then, in each of the sections of the system, a feedback system is used between two fusion pumps to keep the outlet pressure within +/- 1 bar. This is then fed to an article making extruder (PET forming die) 412.

Although what are presently considered preferred embodiments of the system for making PET sheets have been described, it will be understood that the present system for making PET sheets can be incorporated in other specific forms. For example, additional pumps or different combinations of pumps, other than those described herein, could be used. Therefore, the present embodiments are to be considered illustrative in all respects and are not restrictive. The scope of the present system for the manufacture of PET sheets is indicated by the appended claims and not by the foregoing description.