Abstract:
A unit for making pre-shaped absorbent pads for sanitary items is equipped with a continuous conveyor belt with an operating branch which defines a line for pad forming and feed; the branch extends along a straight path, along which there are three successive stations for feeding absorbent material and a plurality of seats designed to accept and retain a given quantity of the absorbent material.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a unit for making pre-shaped absorbent pads for sanitary items. 
     In particular, the present invention relates to a unit of the above-mentioned type which can advantageously be used for the production of diapers, sanitary towels and similar items. 
     The following description refers, without limiting the scope of the invention, to units for making pre-shaped absorbent pads for diapers. 
     As is known, diapers contain an absorbent pad which is normally sealed between an inner permeable layer of spun-bonded material and an impermeable polyethylene outer layer. 
     In the past, absorbent pads for diapers were relatively thick and were obtained by cutting into sections a continuous web consisting of a collection of absorbent material, normally cellulose fiber. Then, in response to new market demands, diaper manufacturers began to make anatomically shaped diapers. This meant that the pads had to be shaped, according to the desired anatomical shape, before being sealed between the above-mentioned inner and outer layers. 
     For a lengthy period the best solution consisted in the use of a pad forming drum, the outside of which was equipped with a plurality of vacuum seats shaped according to the desired anatomical shape for the pad, said outer surface being fed with absorbent material. A forming drum of the above-mentioned type is known, for example, from U.S. Pat. No. 4,674,966. 
     However, in recent years, on one hand the market demand has been for diapers with pads that are increasingly thin and absorbent, and on the other, diaper manufacturers requested increasingly fast production units. This led to a gradual reduction in the depth of the shaped vacuum seats and, at the same time, an increase in the peripheral speed of the above-mentioned forming drums. 
     The reduction of diaper pad thickness to extremely low levels and the improvement in diaper absorption were made possible by using super-absorbent materials inserted, according to a multi-layer structure, between layers of the collection of cellulose fiber. An absorbent pad of the aforesaid multi-layer type is known, for example, from U.S. Pat. No. 5,919,178. 
     The increase in the peripheral speed of the forming drums is obtained by increasing both the angular velocity of rotation and the external diameter of the drums. The increase in the angular velocity was possible up to a speed limit beyond which it was found that the layers of super-absorbent material and collections of cellulose fiber, subjected to excessive centrifugation, tended to break up and penetrate one another. Moreover, the increase in external diameter made the forming drums increasingly bulky, heavy and expensive. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to provide a unit for making pre-shaped absorbent pads for sanitary items, such as diapers, sanitary towels or similar products, with a relatively high production speed and, at the same time, free of the disadvantages indicated with reference to the prior art. 
     Accordingly, the present invention provides a unit for making pre-shaped absorbent pads for sanitary items. The unit comprises conveyor means defining at least one line for the formation and feed of said absorbent pads and at least one absorbent material feed station located along the forming and feed line. The conveyor means comprise a plurality of seats evenly distributed along the forming and feed line. The seats are designed to accept and retain a given quantity of the absorbent material; wherein the conveyor means comprise a continuous conveyor belt, which has at least one operating branch defining the forming and feed line. The operating branch extends along a straight path and moves at a given speed and in a given direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is now described with reference to the accompanying drawings, which illustrate a preferred embodiment of the invention without limiting its scope of application and in which: 
     FIG. 1 is a schematic side view of a unit for making pre-shaped absorbent pads, in accordance with the present invention; 
     FIG. 2 is a side view of a detail in FIG. 1; 
     FIG. 3 is a plan view of another detail in FIG. 1; 
     FIG. 4 is a cross-section along the line IV—IV in FIG. 3; 
     FIG. 5 is a perspective view of the detail in FIG. 3; and 
     FIG. 6 is a perspective view of a pre-shaped diaper pad made by the unit in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 6, the numeral  1  indicates a unit for making pre-shaped and multi-layer absorbent pads  2  for sanitary items, in particular for diapers (not illustrated) as a whole. 
     The lower part of the unit  1  comprises a conveyor  3  which, in turn, comprises a continuous belt  4  closed in a loop over a plurality of pulleys  5 ,  6 ,  7  and  8  with a horizontal axis, one of which, pulley  7 , is driven by a motor  9  so as to draw the belt  4  in a given direction D of feed. 
     Pulley  5  is connected to a tensioner  10  in order to maintain a given belt  4  tension. 
     As is better illustrated in FIGS. 3,  4  and  5 , the belt  4  consists of a metal mesh  11 , on top of which a relatively thin layer  12  of a flexible material is joined, the material having a plurality of through-holes  13 , the edge  14  of each defining the perimeter. 
     The edge  14  and a portion  15  of the metal mesh  11  delimited by the edge  14  respectively constitute a perimeter wall  14  and a base wall of a seat  16  for forming the pads  2 . 
     The seats  16  are evenly distributed at constant intervals along the entire length of the belt  4 . 
     Pulleys  5  and  6  together and on the belt  4  define an operating branch  4   a  defining a pad  2  forming and feed line L 1 . This branch  4   a  extends along a straight, horizontal path P and is mobile along the path P and in direction D at a given speed V. 
     Pulleys  6  and  7  together and on the belt  4  define a branch  4   b  which is angled downwards, defining a pad  2  outfeed line L 2 . 
     A first unit  17   a  which feeds a web of a first absorbent material  18 , unwound from a reel  19   a , is connected to a first mill  20   a , of the known type, for breaking up the web into fibrous particles  21 . 
     In particular, the above-mentioned web of first absorbent material  18  is a web of cellulose. 
     The mill  20   a  unloads the fibrous particles  21  onto the operating branch  4   a  of the belt  4  through a first pipe  22   a , opposite which, on the other side of the belt  4 , there is a first suction outlet  23 . 
     Downstream of the mill  20   a , in the above-mentioned direction D, there is a unit  24  which distributes a second absorbent material  25 , consisting, in particular, of granules of a super-absorbent material of the known type. 
     The unit  24  comprises a storage tank  26  for the material  25  and a feeder device  27  for the material  25 . 
     In particular, the feeder device  27  is located below the tank  26  and above the operating branch  4   a.    
     The feeder device  27 , as is clearly illustrated in FIG. 2, comprises a hopper  28  which collects the second material  25  arriving from the tank  26  and a material  25  dosing device  29 . The dosing device  29  comprises a conveyor belt  30  located below the hopper  28  and mobile on two pulleys  31  and  32  with a horizontal axis, one of which is driven by a motor of the known type which is not illustrated. 
     The feeder device  27  also comprises a material  25  accelerator brush  33 , positioned below the dosing device  29  and designed to generate a flow F of granules of material  25  in substantially the same direction D and at the same feed speed V as the operating branch  4   a.    
     The accelerator brush  33  comprises a plurality of accelerator elements  34  extending radially from the edge of a drum  35  with a horizontal axis, driven by a motor of the known type which is not illustrated. The brush  33  is partially surrounded by a first and a second containment and channeling wall  36  and  37 , which define, for the brush  33 , a feed zone  38  for the material  25  arriving from the conveyor belt  30  and an outfeed zone  39  for the flow F from the accelerator brush  33  to the operating branch  4   a  of the belt  4 . 
     At the flow F outfeed zone  39 , on the opposite side of the belt  4 , there is a suction outlet  40 . 
     Downstream of the distribution unit  24 , in direction D, there is a second feed unit  17   b  for the above-mentioned web of first absorbent material  18 , unwound from a reel  19   b , which is connected to a second mill  20   b , of the known type, for breaking up the web into fibrous particles  21 . 
     Like the first mill  20   a , the second mill  20   b  unloads the fibrous particles  21  onto the operating branch  4   a  of the belt  4  through a second pipe  22   b , opposite which, on the other side of the belt  4 , there is a suction outlet  41 . 
     Downstream of the second mill  20   b , in direction D, there is a rotary refining and cleaning brush  42 , driven by a motor of the known type which is not illustrated and substantially at a tangent to the belt  4 , in order to remove any excess particles of the materials  18  and  25  from the pad  2  forming seats  16 . 
     The brush  42  rotates about a horizontal axis  42   a  along which it extends over the entire width of the belt  4 . The brush  42  comprises a plurality of brushing elements  43  distributed on the edge of a drum  44 , coaxial with the axis  42   a . The edge is shaped by a circular containing wall  45 , with the exception of a portion  46  opposite the operating branch  4   a.    
     At this portion  46 , the brush  42  operates together with an air-jet pipe  47 , supplied by a compressed air source  48  and with an infeed end  49  of a recovery pipe  50 , located on the opposite side of the pipe  47  relative to the brush  42 . 
     On the opposite side to the infeed end  49 , the recovery pipe  50  has a discharge outlet  51 , which is located opposite the operating branch  4   a  in a position between the above-mentioned first mill  20   a  and distribution unit  24 . On the opposite side of the belt  4  to the discharge outlet  51 , there is a suction outlet  52 . 
     The above-mentioned suction outlets  23 ,  40 ,  41  and  52  are connected, by relative pipes  53 , to a suction well  54 . The suction outlets  23 ,  40 ,  41  and  52  are also connected to one another by a shared suction manifold  55  below the belt  4 , along the lines L 1  and L 2  and opposite the belt  4 . 
     In practice, the motor  9  causes the pulley  7  to rotate. The pulley drives the belt  4  in direction D at the above-mentioned speed V. 
     During belt  4  feed, the seats  16  are fed along the forming and feed line L 1 , passing in succession beneath the first pipe  22   a  from the first mill  20   a , where a first layer  56  of fibrous particles  21  of the first material  18  is deposited on the base  15  of each seat  16 . The particles  21  are deposited on the base  15  following suction through the wall  15 , which is permeable to air, originating from the vacuum created in the manifold  55  by the suction well  54 . The methods with which the mill  20   a  breaks the absorbent material  18  into fibrous particles  21  and doses the particles  21  are known and, therefore, do not require explanation. 
     When it has left the first pipe  22   a , each seat  16  is fed under the recovery pipe  50  discharge outlet  51 , where the particles of material  18  and  25  removed by the brush  42  are deposited on the first layer  56 . 
     Then, each seat  16  is fed under the outfeed zone  39  of the flow F of material  25  from the feeder device  27 . The material  25  is deposited in the seat  16 , depending on the quantity dosed by the conveyor belt  30 , constituting a second layer  57  of absorbent material, on top of the first layer  56  and the particles of material  18  and  25  recovered using the pipe  50 . 
     In particular, it should be noticed that the particles of material  25  which constitute the layer  57  are delicately placed in each seat  16  according to a flow F with substantially the same speed V and direction D of feed as the seat  16  itself. 
     Continuing along the forming and feed line L 1 , each seat  16  is positioned under the second pipe  22   b  from the second mill  20   b , where a third layer  58  of fibrous particle  21  of the first material  18  is deposited on the second layer  57 . Again, the methods with which the mill  20   b  breaks the absorbent material  18  into fibrous particles  21  and doses the particles  21  are known and, therefore, do not require explanation. 
     After leaving the pipe  22   b , each seat  16  passes below the brush  42 , which removes from the belt  4  any excess particles of material  18  and  25  projecting from the seat  16 . In particular, it should be noticed that in addition to helping to recover the above-mentioned excess particles, the brush  42  also has a finishing function, which consists in leveling the third layer  58 . 
     Finally, the seats  16 , containing the completed pads  2 , are fed along the outfeed line L 2  towards an operating line which is not illustrated, along which, in a way that is known and therefore not illustrated, each seat  16  is closed between a permeable inner layer of spun-bound material and an impermeable outer layer of polyethylene, to form the relative diaper, which is not illustrated. 
     Obviously, the manifold  55  retains the absorbent material  18 ,  25  as it is deposited in the seats  16  along the length of the lines L 1  and L 2 . 
     It is also obvious how the seats  16 , together with the shape and thickness of the perimeter walls  14 , give the pads  2  the desired shape. 
     Finally, it should be noticed that the walls  14  are extremely thin. As a result, the belt  4  is relatively thin and can be wound, without disadvantages, over pulleys  5 ,  6 ,  7  and  8  with relatively small diameters, having evident advantages in terms of the size of the conveyor  3 .