Patent Publication Number: US-6983860-B2

Title: Spreading head, particularly for thermoplastic material

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a spreading head, particularly for spreading thermoplastic material on an intermediate component. 
   Known spreading heads are currently used which are usually arranged transversely to the direction of movement of the intermediate component. 
   Such heads are usually composed of a laminar-flow assembly having a beak-shaped cross-section, an upper clamp block, and an underlying lower clamp block. 
   As an alternative, above the lower clamp block there can be a single device that acts as laminar-flow assembly and as upper clamp block. 
   The thermoplastic material (for example adhesives, including those known as “hot melt” or “reactive hot melt” adhesives) is first melted by means of a suitable continuous melting unit (tank) or a drum unloader and is then injected into the spreading head by means of gear pumps. 
   The transverse distribution of the adhesive is performed by means of a closed duct affected by uniformly spaced valves (modules), which allow the adhesive to reach a second laminar-flow region through channels and optionally a third region. 
   Such channels convey the adhesive directly to the laminar-flow assembly, which is directly connected to the intermediate component. 
   As mentioned, the passage of the fluid adhesive is allowed by suitable valves, usually known as modules, which are mostly actuated by electric valves of the pneumatic or magnetic type. 
   The duct is closed downstream of each valve by means of a device of the needle type, which closes onto an appropriately provided cup. 
   The ducts are opened by lifting the needle from the closed position. 
   The main drawback of this known head is the fact that sometimes the opening movement of the valve is not achieved; this can depend on various situations, including the fact that the injected hot-melt adhesives can be unstable and, if they remain at high temperature, can trigger charring (cracking) phenomena that block the valve. 
   Furthermore, if reactive hot-melts are used, the adhesive can polymerize in the head itself, consequently blocking the valve. 
   The opening movement of the valve might not be achieved also due to normal mechanical problems (hindered sliding movements) or due to wear or failure of sealing gaskets (O-rings) of the pneumatic circuit. 
   Clearly, the uncontrolled failure of a valve to open entails a severe damage for the application of the adhesive and entails, in the case of spreading heads of the known type, a reduction in the overall amount of adhesive applied to the substrate. 
   The effect in heads of the so-called “step” type (which comprise multiple regions for releasing the material in film form) is much more severe: such heads are choked transversely and each individual valve supplies a step without thereby any possibility to compensate for the adhesive that does not arrive from the unintentionally “closed” valve; the occurrence of this condition entails the uncontrolled production of rejects, since a band as wide as the step of adhesive will be missing on the strip being processed. 
   In addition to this, in many cases visual monitoring of the application is not possible owing to the small amount of adhesive that is applied: by way of example, the following application is cited:
     thickness of applied adhesive: 1.5 microns   characteristics of adhesive: transparent   width of substrate: 3,600 mm   speed of application: 400 m/min   

   In a correlated way, one can deduce that in the above cited application case the reject produced inadvertently might reach approximately 86,400 square meters/hour. 
   Moreover, one should consider that the product on which the hot melt is spread is normally coupled immediately by calendering to another film (immediately in order to utilize the ability of the hot melt to act as a bonding agent when it is at high temperature). 
   This entails the following further remarks: first of all, it is very difficult to perform visual inspection after spreading, since the region is located 300–400 mm from the calendering point (a distance that is covered in 0.0525 s in the above cited operating conditions). 
   Furthermore, it is extremely difficult to perform inspection, since the region to be examined is normally protected by barriers according to EC standards; finally, the defect (lack of adhesive on a band) is difficult to detect on the coupled material, which is wound immediately in a roll. 
   Currently, it is known, as a control measure that is usually adopted, to perform a sample check of the production, analyzing a transverse strip taken from the composite during production. 
   It is noted that this operation can occur easily only on the end portions of the rolls obtained once they have been removed from the machine; otherwise, the removal of samples would entail an inevitable machine downtime (complete cutting of the strip being processed and subsequent splicing). 
   Besides, identifying a band of defective product says nothing regarding the starting point and end point of the defect: one should bear in mind that since one is speaking of coupled products it is quite difficult to identify the head and the tail of the reject. 
   Clearly, there is the risk of not identifying a reject despite the sample check. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is therefore to solve the noted technical problems, eliminating the drawbacks of the cited known art and thus providing an invention that allows to obtain a head that allows to monitor the actual open condition of the valves (modules). 
   Within this aim, an object of the present invention is to provide a spreading head in which it is possible to detect the position of the needle in the valve, preferably detecting that it is in the open position. 
   Another important object is to provide a spreading head in which it is possible to detect immediately any failure to apply adhesive on a band. 
   Another object is to provide a spreading head that is structurally simple and has low manufacturing costs. 
   This aim and these and other objects that will become better apparent hereinafter are achieved by a spreading head, particularly for spreading thermoplastic material on an intermediate component, comprising a first duct for feeding an adhesive to a valve provided with a needle that interferes with a cup connected to a second duct for spreading said adhesive, characterized in that said valve comprises means suitable to actuate and/or visualize a selective positioning of said needle. 
   Advantageously, such means actuate the positioning of the needle in the open condition. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become better apparent from the detailed description of a particular embodiment, illustrated only by way of non-limitative example in the accompanying drawings, wherein: 
       FIG. 1  is a side view of the spreading head according to the present invention; 
       FIG. 2  is a partially sectional view, similar to  FIG. 1 ; 
       FIG. 3  is a sectional view of the valve; 
       FIG. 4  is a view, similar to  FIG. 3 , of the valve; 
       FIG. 5  is a view of the use of a capacitive sensor with the valve in the closed condition; 
       FIG. 6  is a view of the embodiment of  FIG. 5 , with the valve in the open condition. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the figures, the reference numeral  1  designates a spreading head particularly for spreading thermoplastic material on intermediate components. 
   The head  1  is preferably arranged transversely to the flow of motion of intermediate components on which for example an adhesive is to be applied, and has a first duct  2  for feeding the adhesive at a hole  3  for the transverse distribution of the adhesive at one or more valves  4 . 
   Each one of the valves  4  comprises a body  5 , rigidly coupled to the head  1 , which contains a needle  6  arranged axially thereto; the tip  7  of the needle is arranged inside the head  1  at a cup  8 , which is connected to a second duct  9  for spreading adhesive at a suitable substrate  10 . 
   At the valve  4  there are means suitable to actuate the selective positioning of the needle  6  in an open position, such means being constituted for example by a first air intake  11  obtained laterally from the body  5  and connected to a third duct  12 , which is in turn connected to a chamber  13  provided between a rear end  14  of the body  5  directed away from the cup  8  and a disk  15  to which a rear end  16  of the needle  6  is axially coupled, the disk sliding at a cover  17 , which is associated with the rear end  14  of the body  5 . 
   The disk  15 , and therefore the needle  6 , can move axially with respect to the body  5  and the cover  17  in contrast with at least one elastically deformable element, such as a spring  18 . 
   The free end of the cover  17  advantageously has a second intake  19 , which is preferably suitable to be connected to an air supply, like the first intake  11 . 
   This solution allows to move the needle  6 , for example by pneumatic actuation: it is possible to inject air at the first intake  11 , so as to force the uncoupling of the tip  7  of the needle  6  from the cup  8 , thus connecting the hole  3  to the second duct  9 , so as to allow to spread the adhesive. 
   Any injection of air at the second intake  19  instead allows to achieve the movement of the needle  6  until it is arranged in the closed condition, in which its tip  7  closes the end of the second duct  9 , so as to prevent the spreading of the adhesive. 
   As an alternative to the second intake  19 , which can also be closed, the step for closing the needle  6  can be achieved by setting the spring  18  appropriately. 
   There is also a fifth intake  26 , which is formed laterally to the body  5  at the chamber  13 : at the fifth intake  26  it is possible to arrange an additional pressure sensor or a sensor for detecting the position of the disk  15  connected to the needle  6 . 
   It is therefore again possible to control the position of the needle, as in the preceding cases. 
   It has thus been found that the invention has achieved the intended aim and objects, a head having been provided which allows to control the actual open condition of the valves, since it is possible to detect the position of the is needle. 
   It is thus possible to detect immediately any failure to apply adhesive along a band. 
   The invention is of course susceptible of numerous modifications and variations, all of which are within the scope of the same inventive concept. 
   Thus, for example, at the first intake  11  it is possible to connect an appropriate pressure sensor  20 , which is suitable to confirm the position of the disk  15  and therefore of the needle  6 , for example in the open condition in which the tip  7  of the needle does not close the second duct  9 . 
   As an alternative, as shown in  FIG. 4 , laterally to the cover  17  there is a third air intake  21 , and at the same time the second intake  19  is closed by means of a capacitive sensor  22 , suitable to provide a signal indicating the correct placement of the disk  15  and therefore of the needle  6 . 
   The capacitive sensor  22  can be of the ON/OFF type if one wishes to detect exclusively the correct opening of the needle  6 , or of the proportional type if one wishes to check, by means of the same instrument, also the correct closure of the needle  6 . 
   In this case also, the spring  18  might be omitted. 
   As an alternative to the use of a capacitive sensor, it is possible to use a sensor of the magnetic type. 
   It is also possible to use a sensor suitable to check the position assumed by the needle  6  inside the body  5 , for example a suitable optical sensor, which can be arranged at a fourth intake  23  formed radially with respect to the body  5  and adapted to connect an outer lateral surface  24  thereof with the seat in which the needle  6  slides. 
   In this case, the correct closed or open position of the needle  6  can be detected once again. 
   As an alternative, it is possible to install at the fourth intake  23  an electric position sensor, which can also be positioned, for example, at the second intake  19 . 
   It is also possible to use a suitable pressure sensor located on the air circuit upstream of the first intake  11 , the pressure sensor being suitable to confirm that the pressure that corresponds to a correct opening of the valve, and therefore to the lifting of the needle  7  with respect to the second duct  9 , has been reached. 
   It is also possible to use a pressure sensor in the adhesive circuit located downstream of the valve  4  and therefore at the second duct  9 ; such duct can in fact be connected, by means of a suitable fourth duct  25 , to the outside of the head  1 ; the fourth duct  25  is connected to a suitable pressure sensor  20  for hot-melt, which reports the correct opening of the valve because the pressure of the adhesive circuit downstream of said sensor has been reached. 
     FIGS. 5 and 6  illustrate the use of a capacitive sensor  22  in combination with the third intake  21  for the inflow of, for example, air, so as to allow the axial closure movement of the needle  6 . 
   In  FIGS. 5 and 6 , the cover  17  is elongated in order to allow to accommodate the capacitive sensor  22 , which has a suitable axial length. 
   The capacitive sensor  22  can be used to check both the closed state and the open state (of the end of the second duct  9 ) of the needle  6 ; in the first case, the capacitive sensor  22  can therefore check the closure movement of the needle  6 ; advantageously, there is a suitable amplifier for the signal that arrives from the capacitor sensor  22  and there is a visual indicator  27 , which comprises two LEDs  28   a  and  28   b  suitable, for example, to visually indicate the state of the position of the needle  6  and therefore the closure or not of the end of the second duct  9 . 
   The materials used, as well as the dimensions of the individual components of the invention, may of course be more pertinent according to specific requirements. 
   The disclosures in Italian Patent Application No. TV2001A000008 from which this application claims priority are incorporated herein by reference.