Abstract:
A melt-blowing head for making polymeric material fibrils comprises at least a polymeric material inlet channel and melt-blowing die including a plurality of holes for extending fibrils therefrom and a tree-construction channel arrangement for distributing the polymeric material from the inlet channel to each hole of the melt-blowing die.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a melt-blowing head for supplying in a controlled manner either one or more polymeric materials to a melt-blowing die, either separately from one another or in a mixture thereof. 
     As known, the so-called melt-blown material, comprise a mass of polymeric material fibrils (for example polyolefine polymers, polyester polymers and copolymers thereof), extruded from a melt-blowing head having an extruding die and by using pressurized hot air jets. 
     Prior melt-blowing heads are conventionally provided with at least a suitably contoured inner chamber, receiving the mass of the polymeric material fed or supplied through an inlet channel, conveying the polymeric material inside the melt-blowing head. 
     However, the above mentioned method for supplying the polymeric material, i.e. from the mentioned inlet channel to the holes of the extruding die, does not allow to properly control the distribution of said polymeric material, thereby the polymeric material flow rate is affected by unevennesses, at the melt-blowing die level; moreover, also the holding time of the polymeric material in the melt-blowing head, and its temperature and pressure, and, in general, all the other operating parameters thereof are subjected to unevennesses. 
     Accordingly, at the outlet of the melt-blowing die, will be present a polymeric material which, for amount, temperature and melt index will be different from region to region, or through the melting die holes, thereby the fibrils generated by the air jet will have a length and a geometric shape which would be very different from region to region or from an assembly of holes to another assembly of holes of the die. 
     Accordingly, the end product (for example a non-woven fabric) formed by the mentioned fibrils would have a highly dishomogeneous construction, and, accordingly, uncontrollable chemical, physical characteristics. 
     This problem would be very serious for non woven fabric materials, of very broad diffusion, which have a lower specific gram weight. 
     SUMMARY OF THE INVENTION 
     Accordingly, the aim of the present invention is to provide a novel melt-blowing head specifically designed for providing a properly controlled supply of the polymeric material from the melt-blowing head inlet to the outlet of said polymeric material for the melt-blowing die. 
     Within the scope of the above mentioned aim, a main object of the present invention is to provide a melt-blowing head adapted to properly control the polymeric material flow-rate up to the melt-blowing die, to allow said polymeric material to be held inside the melt-blowing head for a holding time much less than that of prior melting heads, with a less risk of degrading said polymeric material. 
     The above-mentioned aim and object of the present invention, as well as yet other objects, which will become more apparent hereinafter, are achieved by the melt-blowing head as claimed in the accompanying claims. 
     Further features of the inventive melt-blowing head are defined in the dependent claims. 
     With respect to prior melt-blowing heads, the inventive melt-blowing head provide the advantage that it allows to properly control the polymeric material flow and distribution inside said melt-blowing head, thereby reducing to a minimum the holding time of said polymeric material in said melt-blowing head, and also reducing to a minimum possible degrading risks of said polymeric material. 
     Owing to the inventive melt-blowing head, in particular, the polymeric material will be supplied through a like distance from the inlet hole of the head up to any desired holes of the melt-blowing-die. 
     Thus, the polymeric material will be provided with the same heat amount and driving energy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned advantages, as well as further advantages and feature of the present invention, will become more apparent hereinafter from the following detailed disclosure of a preferred embodiment of the melt-blowing head according to the invention which are illustrated, by way of an exemplary but not limitative example, in the figures of the accompanying drawings, where: 
     FIG. 1 is a cross-sectional view illustrating a prior melt-blowing head: 
     FIG. 2 is a longitudinal cross-sectional view illustrating the melt-blowing head shown in FIG. 1; 
     FIG. 3 is a cross-sectional view illustrating a melt-blowing head according to the present invention; 
     FIG. 4 is a further longitudinal cross-sectional view illustrating the melt-blowing head of FIG. 3; and 
     FIG. 5 illustrates a further modified embodiment of the melt-blowing head according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates, at the reference number  1 , a melt-blowing head of conventional type. 
     Such a prior melt-blowing head  1  comprises an inlet  2  for the polymeric material to be melt-blown, a polymeric material delivery or distributing channel  3 , a filter  4 , a melt-blowing die  5  as well as channels  6  for supplying hot air. 
     At the outlet of the holes  7  of the melt-blowing die  5 , a plurality of fibrils  8  will be obtained by spraying. 
     As clearly shown in FIG. 2, the above mentioned polymeric material delivery channel  3  is widened in the form of a narrow chamber  9 , in which the polymeric mass supplied to a pre-die or filter  4  and then to the die  5  is expanded. 
     Thus, the path of the polymeric material from the inlet  2  to the die holes  7  would be a random and uncontrolled path. 
     Then, it should be apparent that this lacking of properly controlling the supplying of the polymeric material from the inlet  2  to the die  5  holes  7  would generate variations in the flow of the polymeric material, due to the different holding time in which said polymeric material is held in the chamber  9 . 
     Accordingly, the polymeric material will be subjected to an uncontrolled thermal processing, very different from that would be necessary and desired. 
     Moreover, the above mentioned different time and temperature would generate a degradation of the polymeric material, which will have a different melt index or fluidity, and a different flow rate through the melt-blowing die. 
     Thus, fibrils will be generated having different chemical-physical characteristics (for example length, cross-sections, consistency and so on, which would provide an end product (for example a non-woven fabric) with dishomogeneous properties (such as toughness, felting, thickness and so on). 
     The melt-blowing head according to the present invention has been indicated by the reference number  10  in FIGS. 3 and 4. 
     Said melt-blowing head comprises a polymeric material inlet channel  11 , the polymeric material being supplied by a geared volumetric or displacement pump  12 . 
     Said pump, in turn, will drive the polymeric material inside two main channels  13  and  14 , having like shapes and size, from which extend the polymeric material delivering channel arrangement, having a tree construction which will be disclosed in a more detailed manner hereinafter. 
     At the end of the main arm  13  therethrough the polymeric material is supplied to the melt-blowing die, i.e. on the first knot  15  of the above mentioned tree construction, extend two secondary side arms or branches  16  and  17 , whereas, at the end portion of the other main branch or arm  14 , i.e. at the level of the knot  18  thereof corresponding to said knot  15 , extend other two secondary side arms or branches  19  and  20 , having the same shape and size as the mentioned branches or arms  16  and  17 . 
     In particular, said branches  16 ,  17  and  19 ,  20  have, in the embodiment being illustrated, a substantially L-shape with the vertical leg downward directed, in the direction of the die  34  of the melt-blowing head  10 . 
     On the respective end portions  21 ,  22 ,  23  and  24  of the above mentioned branches, forming middle branches or arms of the polymeric material delivery channel arrangement, are formed corresponding knots of the tree construction, therefrom respective secondary side branches  25 , 26 ;  27 , 28 ;  29 , 30  and  31 , 32  extend. 
     The above mentioned branches are equal to one another for shape and size and have the same L-shape extension as that of the branches  15 ,  17  and  19 ,  20 , as above disclosed. 
     As shown, the polymeric material delivery channel extends, with a like tree construction, up to the holes  33  of the die  34  therefrom the fibrils are extruded. 
     Owing to the above disclosed polymeric material supply channel arrangement, for supplying the polymeric material to the melt-blowing die, to each of the n holes  33  of the die  34  will correspond a specifically designed path which, for shape and size, would be like to all the other path arrangements joining the polymeric material inlet channel  11  to other fibril extruding holes  33 . 
     Owing to the above disclosed construction of the polymeric material delivery channels, the holding time in which the polymeric material is held in the path from the inlet  11  to the holes  33  will be the same for all the die holes, thereby providing a homogeneous distribution of said polymeric material inside said melt-blowing head. 
     Thus, the polymeric material at the outlet of the holes  33  will be provided with the same heat amount and driving energy or power, thereby allowing to make, at the outlet of the die  34 , a plurality of fibrils having mutually homogeneous chemical and physical properties. 
     In the modified embodiment shown in FIG.  5 , the melt-blowing head has three different inlets  35 ,  36  and  37  for corresponding polymeric materials, each of said inlets supplying respective geared volumetric or displacement pumps  38 ,  39  and  40 . 
     Each of said pumps will in turn supply the corresponding polymeric material to a respective delivery channel  41 ,  42  and  43  having the tree construction disclosed with reference to FIG.  3 . 
     Thus, the different polymeric material will arrive at the melt-blowing die according to insulated path arrangements, equal to one another, thereby they will exit the die in the form of multicomponent fibrils. 
     The invention, as above disclosed and illustrated, is susceptible to several modifications and variations without departing from the inventive scope; for example, the tree construction polymeric material delivery channel arrangements can be further properly modified in their geometric and configuration parameters.