Patent Publication Number: US-2005139316-A1

Title: Installation and process for continuous and intermittent production of laminates, with a multi-stage press

Description:
The invention concerns continuous installations for producing laminates of various materials.  
      Pressing and heating installations, used for sticking together two-dimensional elements of various kinds to obtain products possessing specific technical characteristics (thickness, dimensions, mechanical resistance, appearance), required for numerous structural compositions, are in common use.  
      The evolution of technology and of materials has been such that it is now possible to produce laminates of every kind, laminates made of paper, plastic, resin-impregnated fabrics, wood, rubber, multi-compositions.  
      In order to generate the physical phenomena of pressure and heat, essential for lamination, “hot” presses are used, namely, those able to generate pressure and heat at the same time.  
      Multi-plate presses have been designed for the purpose of reducing costs and to be used for a pile of packages of the material to be pressed and heated, each package, separated by a thick sheet of steel, becoming a laminate at each processing cycle.  
      While pressure is substantially applied in an equal degree to each package of the pile put into the press, considerable difficulties are encountered over providing an even amount of heat, by conduction from the heated plates, both horizontally and vertically, to all the packages in the pile and to all their components.  
      Not only does this mean that the height of the pile of packages must be limited but also that the processing cycle must be appreciably lengthened so that the difference in temperature between one package and another is not such as adversely to affect the result, namely the high quality of the product.  
      To make up for a consequently lower rate of productivity, increasingly larger presses have been built to obtain the highest possible quantity per m 2  of laminates per cycle.  
      With the same aim of lowering costs, little by little the press has been replaced by real integrated installations including not only the press but also areas and structures for preparing packages, moving them, loading and later unloading the press, dividing up packages, washing and brushing the steel separation sheets.  
      Alternative systems have been designed to obtain continuous transformation of a composite band, namely one comprising strips of different materials to be stuck together, into a laminate, subjecting the composite band to heat and pressure during its passage through a suitably sized press.  
      Results have however been unsatisfactory especially as regards the quality of the product due to complexity of the system involved. The invention here described permits a considerably greater output while ensuring maximum precision and quality of the product as will now be explained.  
      Subject of the invention is an installation and process for continuous and intermittent production of laminates, including multi-layer laminates of plastic material, using a press with fixed lower plates and movable upper plates, and a composite band comprising all the components of the laminate.  
      The press is multi-stage and executes a work cycle, the various phases, of equal length, being distributed among the stages of the press, each stage carrying out a phase following that done in the preceding stage, the composite band being moved, at the end of each phase, from one stage to another.  
      When operating at its steady rate, production of each laminate takes a time corresponding to that of the work cycle divided by the number of stages.  
      The fixed and movable plates of the press work together in the various stages.  
      The composite band comprises several strips of pre-preg associated to a copper strip on one or on both faces of said composite band.  
      The different stages are aligned to allow easy transfer of the composite band from one stage to another.  
      Constant levels of pressure and heat are generated in the stages of the press, the heat being applied so as to produce the following effects on the fractions of the composite band subjected to the specific phases of the cycle in the different stages: 
          a rise in temperature, in the fraction undergoing the first phase of the cycle in the first stage of the press, from ambient to that needed for determining, by means of a catalyst, the chemical reaction required to stick the components of the composite band together;     a rise in the first-stage temperature, in the fraction undergoing the second phase of the cycle in the second stage, sufficient to polymerize the resin;     maintenance of the temperature, reached in the preceding stages, in the fractions undergoing subsequent phases in the subsequent stages of the press, to stabilize the effects of polymerization and obtain the desired laminate;     maintenance of pressure without heat in the fraction undergoing the subsequent phase in a subsequent stage, to allow the laminate to cool.        

      The composite band, even if partially transformed into laminate, can be intermittently moved along inside the multi-stage press, by means of a metal band of high electrical conductivity that, unwinding from a reel upstream of the press and winding onto a reel downstream, practically covers the entire upper surface of the fixed lower plate, said metal band supporting the product, little by little transformed from a composite band into a cold laminate ready for use.  
      The metal band is preferably of aluminium.  
      The heat needed for carrying out the phases in the stages of the press, is generated, through Joule effect, by means of the metal band that maintains contact with the electrodes for producing electric current placed at both ends of each stage.  
      Electric power from the generator at each stage is calculated so as to produce a specific temperature, for the phase concerned, in the fraction of the composite band present in any one stage.  
      The pre-preg and copper strips are fed in from reels.  
      The metal band for heating and carrying forward the laminates is fed from and received by the respective reels.  
      All the reels are run by electric motors whose times and speeds are programmed and controlled by an electronic processor which, by coordinating the specific feed rates of the strips and bands, not only ensures precise disposition and coordination of times and speeds but also makes the correct adjustments to the tensions of the pre-preg and copper strips, coordinated with the tension created by the metal laminate-carrying band to ensure the optimum cycle of movement for each one.  
      When production makes it possible, the composite band can be heated in all the stages by a single generator that connects two electrodes placed at the beginning and end of the several stages. This single generator can be programmed to associate its effects with the specific generators for each stage.  
      In one type of execution the press comprises four heating stages, temperature of the composite band being raised in the first stage from ambient to about 130° C.; in the second stage temperature of the fraction of composite band transferred from the first stage rises to about 180° C.; in the third and fourth stages temperature in the fractions of composite band transferred from the preceding stages is maintained at about 180° there being comprised a cooling stage to lower the temperature of the fraction of composite band transferred in that stage, to about 40°.  
      Advantageously the installation can have four pairs of reels for eight strips of pre-preg and a pair of reels for two copper strips to make a composite band with eight strips of pre-preg and two of copper.  
      Alternatively the composite band in the various stages can be heated independently of the metal band, by a device chosen from among the possible electric, steam and gas heating devices. This device can advantageously be mounted in the plates of the press.  
      The press preferably comprises 5 stages each 2.5 m long.  
      As the production cycle is divided into phases carried out simultaneously in each stage, if total cycle time is 20 minutes, there will be a laminate output of 2.5 m every four minutes.  
      In one variant of the installation, upstream of the press there is a flat surface on which to slide a group, here called the lower group, of composite band components making it possible to lay a series of multi-layer laminates on said lower group.  
      Due to movement of the composite band, a group, here called the upper group, of the other components of said composite band is deposited on said lower group, so creating a regular cycle of production of multi-layer laminates in the way already described. 
    
    
      Characteristics and purposes of the invention will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figures.  
       FIG. 1  Continuous installation with a multi-stage press for plastic laminates, seen open, at the end of a cycle, longitudinal section.  
       FIG. 2  Plan view of the above.  
       FIG. 3  Installation with the press closed during a fresh cycle with a diagram of temperatures in the various stages, longitudinal section.  
       FIG. 4  Installation with the multi-stage press at the end of the new cycle, open, after the fractions of composite band have moved from one stage to the next for starting a fresh cycle, longitudinal section.  
       FIG. 5  Installation showing the multi-stage press, in the variant for multi-layer plastic laminates, open at the end of a cycle, longitudinal section. 
    
    
      The installation  10  comprises the multi-stage press  11  with five stages 1 to 5 formed by pairs of fixed and movable aligned plates, respectively 1 ( 12 - 13 ), 2 ( 14 - 15 ), 3 ( 16 - 17 ), 4 ( 18 - 19 ), 5 ( 20 - 21 ). At the longitudinal ends of the group of fixed plates are the electrodes  30  and  31  connected by wires  32  and  33  to the generator  40  of electric current.  
      At the two ends of the group of fixed plates  12 ,  14 ,  16 ,  18 ,  20  are the electrodes  35 - 37 .  
      Electrodes  30  and  35  are connected to the generator  60  of electric current by the wires  50  and  51 .  
      Electrodes  35  and  36  are connected to the generator  61  of electric current by wires  52  and  53 .  
      Electrodes  36  and  37  are connected to generator  62  of electric current by wires  54  and  55 .  
      Electrodes  37  and  31  are connected to the generator  63  of electric current by wires  56  and  57 .  
      On the upper level common to the fixed lower plates  12 ,  14 ,  16 ,  18 ,  20  the aluminium band  70  can slide in the direction indicated by the arrows, unwinding from the reel  71  and winding onto the reel  72 , through cylindrical transmissions  75  and  76 , driven by the electric motor  170  and maintaining electrical contact with the top of the electrodes  30 ,  35 - 37 ,  31 .  
      The copper strip  80 , fed in from reel  81  through transmission cylinder  85 , lies on said aluminium band  70 .  
      Substantially at the level of said copper strip  80  lying inside the press  11 , and upstream of the press there is a structure comprising coplanar slide surfaces  100  and  101 .  
      The composite band  160 , sliding partly on said surfaces  100  and  101 , coming to rest on said copper strip  80 , consists of the following pairs of pre-preg bands: 
          a pair of strips  120  and  121  that unwind from the lower reels, respectively  130  and  131 , guided by the cylindrical transmissions  140 - 142 ;     a pair of strips  122  and  123  that unwind from the lower reels respectively  132  and  133  guided by cylindrical transmissions  143 - 145 ;     a pair of strips  124  and  125  that unwind from the upper reels respectively  134  and  135  guided by cylindrical transmissions  146 - 148 ;     a pair of strips  126  and  127  that unwind from the upper reels respectively  136  and  137  guided by cylindrical transmissions  149 - 151 .        

      The copper strip  90 , fed in from the reel  91  and guided by the cylindrical transmission  95 , rests on said strip  125  of pre-preg. Adherence between the pre-preg strips in each pair is assured by heating devices  155 - 158 .  
      It follows that the composite band  160 , comprising the pre-preg strips and the copper strips on both faces, can slide inside the press drawn along by the aluminium band  70 .  
      Reels  71  and  72  for the aluminium band  70 , reels  130 - 137  for the strips of pre-preg, and reels  81 , 91  for the copper strips, are respectively driven by motors  170 - 181 .  
      These motors are programmed and operated through wires  190 - 193  from the processor  200  so as to avoid any anomalous tension in the strips of pre-preg and of copper when unwinding in syntony with movement of the aluminium band  70  which draws along the composite band  160  and therefore the laminates, produced by said band at each production cycle, as well.  
       FIGS. 1 and 2  illustrate a phase of the installation corresponding to the end of a cycle that has generated the plastic laminate G, ready to be picked up.  
      To begin a new cycle the press must obviously be closed as illustrated in  FIG. 3 .  
      At each cycle the fractions B-F of the composite band  160  move from one stage to the next so as to distribute the various phases of the cycle in a substantially even manner among the stages 1-5.  
      In said  FIG. 3 , indication XY is given, at the top of the press, of the temperatures of fractions B-F of said composite band  160  respectively corresponding to stages 1-5 indicated in the abcissae of the diagram.  
      Temperature of the composite band  160  at entry to the press ( FIG. 3 ) may be taken as ambient temperature, presumably 20° C. Power of the electricity generators  60 - 63 , respectively corresponding to press stages 1-5 and therefore to fractions B, E of the composite band  160 , is set so that during each cycle, at a stable level of operation, it will be found that: 
          in the first fraction B, there is an increase of about 130° C. in temperature from ambient level (assumed at 20° C.). At 130° a catalyst is activated that causes a chemical reaction among the components of fraction B of the composite band;     in the second stage 2, transfer has been made from stage 1 of fraction C of the composite band that, due to the effect of the preceding cycle, presents said temperature of 130°, raising it to about 180° causing polymerization of the resin;     in the third stage 3, fraction D of the composite band, transferred from stage 2 at a temperature of 180°, is kept at that temperature;     in the fourth stage 4, the temperature of fraction E, transferred from stage 3 at a temperature of 180°, is kept at that tempreature so producing the plastic laminate;     in the fifth stage 5, the fraction F transferred from stage 4 at 180°, is allowed to cool down to about 40° C.;     the plastic laminate constituted by fraction G of the composite band, that was transferred from stage 5 and therefore already cool (see  FIG. 1 ), can be removed.        

      From the foregoing it is clear that, as the phases of the cycle are carried out simultaneously in the various stages of the press for heating and cooling, the time required for the entire production cycle is divided by the number of stages.  
      If the total cycle time is 20 minutes, a laminate will be produced every 4 minutes (20+5).  
       FIG. 4  illustrates a new cycle, substantially identical with the previous one, except for movement of the composite band  160 , and therefore of all its fractions B, C, D, E of one stage, for entry of a new fraction A of composite band, and for removal of fraction F (completed plastic laminate).  
       FIG. 5  shows a variant of the press suited to production of multi-layer plastic laminates. The levels  100  and  101  are replaced by a single one  102  while the reels of pre-preg strips are limited to a lower pair  132 ,  133  of strips  122 ,  123  and to an upper pair  134 ,  135  with strips  124 , 125 .  
      During closure of the press, the operator  205  can lay a set of multi-layer laminates  206  in two rows on the pair of strips  122  and  123 . It will therefore be seen that at the start of a fresh cycle, the above mullti-layer laminates  206  will be drawn inside the multi-stage press  11  by the lower pair of pre-preg strips  122  and  123  and inserted between said pair associated to the copper strip  70  and the upper pair of pre-preg strips  124  and  125  associated to the copper strip  90 .  
      The cycle inside the press is carried out as already described.  
      The invention offers evident advantages.  
      Pressure and heat can be generated by two completely distinct entities: 
          the plates that generate pressure,     the electrothermic devices that generate heat.        

      Pressure is exerted by the plates of the press on the composite band while heat can be supplied by a thin lamina of material of high electrical conductivity which, inserted between the lower plate of the press and the laminate with electric current passing through it, Generates diffused heat due to the Joule effect.  
      In a cold press only a small part near to the laminate can be heated. The “division” of time needed for the cycle, namely passing from composite band to laminate, in several stages respectively used for increasing the temperature of the material from ambient to that of reaction, initiated by a catalyst, from that of reaction to that of polymerization and on to cooling of the laminate produced, utilizing in one stage the phase completed in the preceding stage, means an enormous saving of time even while achieving a product of very high quality.  
      The heating cycle, applied to one laminate at a time, is very quick especially in the case of plastic laminates.  
      The single-plate, multi-stage cold press can be much wider and longer, at equivalent cost, than present hot presses.  
      As the press can be fed off reels, the costly and bulky means now used for separating the packages in the pile can be eliminated, together with related equipment for loading, unloading, cleaning etc.  
      Feeding in material off reels, so making the press “continuous” even though intermittent, makes it possible to carry out all phases in sequence with simple automatic devices and few operators. Materials enter the press off reels and cut and finished laminates leave it.  
      To summarise the advantages, the process described above makes possible a very high output of top quality at costs for investment and operation much lower than those possible at present.