[0001] In the proceeding of screen printing matrices of printing are used called frames.
These frames consist of a metallic or wood border onto which is fixed and/or stuck,
after to be put in tension, a polyester, nylon or other fabric. It is known that in
the field of the frames for screen printing has particular importance the disposition
of the elements that form the frame. In the known art said frames for screen printing
are assembled or welded and they have principally the shape of a square or rectangular
border. Said utilizations provide the perpendicularity of the elements forming the
frame. The screen printing is a proceeding in that the printing matrices, the frames,
consist of polyester, nylon or similar fabrics from which the ink pressed to the doctor
blade, or squeezer, oozes in the free meshes of the stretched weft onto the frame
and said ink makes a deposit onto the support where the printing is actuated. The
polyester, nylon or similar fabric is fixed to the border with high tensions so to
determine the deformation of the border to which it is fixed or stuck. This deformation
is present both during the tension phase of the fabric than during the removing of
the frame from the tension apparatuses. Deforming the border, also the weft of the
fabric placed in tension on the frame comes to be modified changing consequently the
geometry and the performance of the printing of the frame. The deformation of the
border of the frame has like direct consequence the lost of tension of the fabric
and so of the correct disposition of the fibres of the weft. In the conventional frames
for screen printing there is consequently a not homogeneous passing of ink in the
meshes of the weft with consequent lost of quality of the printing. The invention
refers to a new particular frame for screen printing having bond parts of the frame
elements able to obtain and to maintain the uniform and correct tension of the fibres
of the weft, so to let pass the ink in homogeneous way into the meshes of the fabric
that forms the printing matrix. Having a regular passing of ink into the meshes of
the fabric the definition and the printing quality are improved. The invented locking
fastener provides an angular element of union of the beams essentially with an angle
different to the right angle. In a preferred embodiment the union and the interface
surfaces with the beams are angulated each other with angles of eightyeight and/or
eightynine point five degrees, so to avoid, with the structure already assembled before
putting in tension the border, the perpendicularity of the elements forming the border,
and to have, instead, a border with beams curved outward of the same structure. This
disposition of the beams, obtained by means of the invented constraint element, permits
to put in tension the beams with arch elastic deformation, called preloading, with
concavity inward of the structure so to be orthogonal each other when the polyester,
nylon or similar fabric is fixed, with tensions so to bring again the beam in rectilinear
and permanent position for contrast to the fabric tension. Consequently also the fibres
and in particular the meshes of the fabric have a regular disposition, with homogeneous
spaces between the fibres and perpendicular each other and a homogeneous tension.
In this way the printing matrix let to pass the ink pushed to the doctor blade with
uniformity in the provided points with a better definition and precision of the printing.
In the principal embodiment the invented locking fastener consists of an angular element
1, having level surfaces 2 and 3, of interface between the angular elements and the
beams. The level surfaces 2 and 3 are angulated in such a way to form an angle 4 different
to the right angle. In this embodiment said angle is both of eightyeight than of eightynine
point five degrees, but its constitution changes in relation to the loads to which
is subject. For particular high tensions of the fabric fixed to the frame or for frames
of big dimension said angle may decrease of some degrees. At the contrary it is provided
with wider degrees, near at the ninety degrees, for low tensions of the polyester,
nylon or similar matrix, or for small dimensions of the frame. It is also provided
the contemporary used of angles of different degree to obtain the preloading more
suitable to the dimension and to the shape of the frame. The angulation is so determined
in such a way that the beams put to the tension of the fabric was rectilinear. The
angular element 1 is, moreover, equipped with a transversal stiffener 5 so to permit
the maintenance of the angulations of the surfaces 2 and 3 under loading. Onto said
surfaces holes 6 are realised so to permit the passing of fixing elements 7 to the
beams 8. To realize the assembling of the angular elements 1 to the beams 8 these
last have holes 9 inside the same beams corresponding to the holes 6. Ending the assembling,
jointed the angular elements 1 with the beams 8 by means of the fasteners 7, a closed
structure 10 is obtained with the arched beams that, in the subsequent phase of apposition
of the fabric, are deformed assuming the rectilinear configuration, so avoiding the
arched disposition with outward concavity typical of the previous realizations and
that determines distortions in the wefts and in the meshes where the ink passes. Possible
known realizations of frames for screen printing obtained with welding with angle
different to ninety degree, in structural and dimensional anologies, have not the
same strength and the uniform distribution of the tensions obtained with the constraint
elements of the invention such as the welding is not able to have the same characteristics
of strength and uniformity of tensions that come to form during the assembling. The
invented locking fastener is illustrated in a merely and not limiting way in the drawings
of sheets 1, 2, 3 and 4. In sheet 1 figure 1 is perspective view of the locking fastener
for frames of screen printing. In sheet 2 figure 2 is top view of the same element.
Figure 3 is lateral view of the same element. Sheets 3 and 4 are instead views of
assembled frames for screen printing. In particular in sheet 3 figure 4 is view of
a square frame for screen printing assembled before fixing the fabric. In sheet 4
figure 5 is view of a rectangular frame not having still fixed the fabric.
