WO2010055516A1

WO2010055516A1 - System and method for configurationally heat soldering plastic bags

Info

Publication number: WO2010055516A1
Application number: PCT/IL2009/001072
Authority: WO
Inventors: Boaz Krisral
Original assignee: L.C.S. Tech Ltd
Priority date: 2008-11-14
Filing date: 2009-11-15
Publication date: 2010-05-20
Also published as: JP2012508663A; EP2365928A1

Abstract

A system and method for imprinting patterns along a seam obtained from two or more mutually attached layered plastic sheets are provided The method comprises (ι) heating selected areas of the layered plastic surface to a predefined temperature, and (ιι) forcing a molding head having a face with a plurality of fingers, associated with a desired pattern, against the heated surface A soldering head of the disclosed system has at least one such molding member with fingers, some with sharpened tips, shaped as the pattern to be imprinted A soldering head optionally comprises a pressing member with fingers for pressing against peripheries of the layered plastic sheets A soldering head may also comprise a second molding member with recesses to fit the fingers of the first molding member, with independently controllable temperatures, for embossing distinct three dimensional patterns on the soldered layered plastic sheets Tamper evident envelopes are further provided.

Description

SYSTEM AND METHOD FOR CONFIGURATIONALLY HEAT SOLDERING

PLASTIC BAGS

FIELD OF THE INVENTION

The present invention relates in general to plastic bags and in particular to configurationally heat soldering plastic sheets and manufacturing of packing bags and tamper evident envelopes.

BACKGROUND OF THE INVENTION Tamper evident envelopes made of plastic resins such as polyethylene are common in the marketplace. Normally the open edges of one folded foil, or two sheets of plastic foil laid one on top of the other are mutually attached by thermal soldering. A continuous line is typically printed along the seams providing for tamper evidence. Normally soldering is applied by contact heating and concomitantly pressing the two layers of plastic one against the other. Reference is now made to Figs 1 - 5 in which cross sectional views of a number of common soldering stations are respectively shown. Such stations provide for heat soldering the edges of the envelopes. A soldering station especially suited for soldering soft plastic layers, such as thin sheets made of polyethylene, as well as sheets of plastic foam is presented in Fig. 1. Electrically heated wire 10 activated by short pulses of electrical current heats two layers of plastic to be mutually attached when soldering heads 12 are pressed against each other while trapping the layered plastic sheets in between them. The heat capacity of soldering heads 12, which is relatively high provides for cooling off the seam by the end of each heating pulse. However the time required for heating up to a temperature suitable for soldering along each and every heating pulse provides for a relatively low soldering rate which is only of a few soldering cycles per minute. Alternative methods in which the soldering heads are kept at an almost constant temperature provide for enhanced soldering rates is demonstrated by soldering station 14 that is shown In Fig. 2. Soldering heads 16 are heated to the suitable temperature by a constant electric current conducted through embedded electrical heaters 18. The sheets to be mutually attached are simultaneously moved laterally to the soldering heads along a track passing through station 14, not shown. In another station disposed next to station 14, not shown, similar heads through which coolant streams, are pressed against the relatively wide seams to cool them off. The mutually attached sheets are further cut off along a line disposed within the region of a seam such that individual bags are separated in the following station. Such method is especially suited to laminated sheets having an inner layer, which is practically melted by such heating. A more popular method especially suited to attaching thin plastic sheets is demonstrated by the soldering station shown in Fig. 3. Soldering heads 20 retained at a suitable temperature by means of heating elements 21 are simultaneously pressed for a predefined period of time against the two layers of thin plastic sheets whilst being supported by base 22. Both layers are simultaneously cut by means of blade 24. The seams cool off by means of radiation and heat conduction to the ambient atmosphere. Another method especially suited for soldering soft and thin plastic sheets is demonstrated by the soldering station shown in Fig. 4. Cutting and soldering is applied by repeatedly pressing layers 28 while being sandwiched between soldering head 30 and cylinder 32. Soldering head 30 has tipped sharpened end 31. The hot blade formed by tip 31 practically melts both layers. Cylinder 32 rotates between successive soldering cycles, such that heating is applied each time when tip 31 presses against a different location across the surface of cylinder 32. The seams are contact cooled by cylinder 32 when the soldering head is pulled off. This method is commonly applied in manufacturing thin bags. Such soldering station provides for production rates of a few hundred soldering cycles per minute. However it is not suitable for manufacturing bags made of relatively thick sheets, plastic foam or bubbled sheets. Another method providing a relatively high rate of soldering cycles is demonstrated by the soldering station shown in Fig. 5. Both plastic sheets 38 are simultaneously pressed between pressing arm 40 and soldering head 42, such that layers 38 are forced by sharpened tip 44 against heating element 46. At this point a heating pulse is applied. The sharpened tip provides for cutting both sheets concomitantly with forming of the seams at both edges of the cut.

Linear seams are generated according to common soldering methods such as described above. Linear continuous seams that characterize common tamper evident envelopes are vulnerable to breaching. A common sealed tamper evident envelope can be opened by cutting an edge and further resealing it by heat soldering, such that the additional seam will be hardly detected. However, distinctive patterns imprinted along seams that are heat soldered along the edges of tamper evident envelopes and/or packages that are made from plastic may provide for enhanced immunity against such breaching. Therefore tamper evident envelopes and packaging that are made of plastic sheets and have configurationally heat soldered seams are beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs 1 - 5 schematically present soldering stations in accordance with various known methods for heat soldering of plastic bags;

Fig. 6A is an isometric view of two members of a soldering head providing for configurationally heat soldering layered plastic sheets according to an embodiment of the present invention;

Fig. 6B is a sectional view of the heating member shown in Fig. 6A; Fig. 6C is a sectional view of the pressing member shown in Fig. 6A;

Fig. 7A is a side view of a soldering head according to a preferred embodiment of the present invention;

Fig. 7B is an isometric view of the soldering head shown in Fig. 7A; Figs 8A - 8B schematically present segments of a soldering head providing for embossing a three dimensional pattern along a seam of a tamper evident envelope according to a preferred embodiment of the present invention; Fig. 9A is an isometric view of a segment of an embossing head that can be used for manufacturing a tamper evident envelope according to another preferred embodiment of the present invention;

Fig. 9B schematically presents another segment of the embossing head shown in Fig. 9A;

Figs 1OA - 10C are side looking views of three tamper evident envelopes in accordance with three different preferred embodiments of the present invention;

Figs 10D-10E are side looking views of the same segment of a temper evident envelope according to another preferred embodiment of the present invention;

Fig. 11 is a side looking view of a tamper evident envelope according to another preferred embodiment of the present invention;

Figs 12A is a side looking view of a temper evident envelop according to an embodiment of the present invention;

Fig. 12B is a sectional view of the envelope shown in Fig. 12A, along the line AA;

Fig. 13 is a side looking view of a molding member of a soldering head according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In accordance with the present invention tamper evident envelopes and/or packages the seams of which are generated by configurationally heat soldering of layered plastic sheets are provided. Plastic bags and/or envelopes manufactured by employing configurationally heat soldering according to the method of the present invention have at least a segment of a seam in which one layer and a second layer of one or two plastic sheets are configurationally heat soldered to each other. Each such soldered seam has a distinctive pattern embossed on, and/or perforated through, one or both layers across a significant part of the seam. In a case in which such bag is opened and resealed along one of these seams the imprinted pattern is corrupted. Therefore an unauthorized opening of such seam becomes apparent to a user of the bag. The terms tamper evident envelope or bags refer hereinafter to tamper evident sealable packages. There are two kinds of soldering heads providing for configurationally heat soldering according to the present invention. Soldering heads of the first kind are especially suitable for soldering soft plastic sheets such as bubble sheets or plastic foam. However such soldering heads successfully cope with heat soldering materials such as Tyvek^(R). Soldering heads of the second kind provide for embossing any two and/or three- dimensional patterns along the seam of a plastic bag of the invention. The soldering heads described below provide for applying three-dimensional embossed patterns onto various types of plastic sheets as further described infra. Soldering heads of the second kind are also referred hereinafter as embossing heads.

A soldering head providing for configurationally heat soldering normally comprises a molding member and a heating member. Soldering heads of the first kind optionally further include a pressing member. The heating members provide for heating the layered plastic at predefined heating rates such that their respective surfaces fuse to be mutually heat soldered when the layers are pressed against each other. The molding members provide for pressing against the heated plastic layers concomitantly with imprinting and/or perforating a pattern across the seam. The pressing members provide for further compressing the layered plastic sheets and condensing them such that their width is decreased down to a desired level as well as for dissipating the excessive heat conducted through the layered plastic to the margins of the contours imprinted across the seam. Wherever inward direction is referred to hereinbelow, it means the direction pointing from the edge towards the center of the layered plastic sheets.

Reference is first made to Figs 6A - 7B in which two soldering heads of the first kind are respectively shown. In Fig. 6A a segment of an assembly scheme of a soldering head is shown. Molding member 50 consists of body 51 from which two rows having a plurality of fingers 52 separated by elongated prism 54 extend from one face of body 51 towards a common direction. Electric heater 56 is embedded in an elongated cavity coaxially disposed within body 51. Molding member 50 provides for contact heating a surface when the faces of its fingers and prism are pressed against it. Molding member 50 serves also as the heating member of the soldering head considered as well. The pressing faces of fingers 52 may have any geometrical shape, such as pointed, circular, oval, curvilinear, or polygonal such that their footprints across the heated plastic layer have a distinct pattern. Similarly, fingers their pressing faces are shaped as alphanumeric characters, symbols, or graphical patterns are in accordance with the present invention. Optionally curvilinear elongated bulges or a series of evenly spaced fingers aligned along a linear or curvilinear line may substitute prism 54. Such series of bulges or fingers are also referred hereinafter as a prism. The rows of fingers need not be linear, but can be according to the present invention curved or wiggled at different curvature angles. One or more rows can be disposed according to the present invention at both sides of prism 54. Optionally one or more prisms with or without being interleaved with rows of fingers extend off one side of body 51.

Pressing member 58 consists of a flat body having arrays of apertures 60 conformal with the fingers and prisms of molding member 50. All these apertures are skirted with sharpened bulges protruding towards the same direction. Such sharpened bulges provide for enhancing the pressure exerted onto the layered plastic applied to the margins of the contours to be heated by means of the fingers and prisms of molding member 50. The layered plastic is sandwiched between the fingers and prisms of the molding members as well as the bulges that skirt the apertures of the pressing member and a supporting surface, not shown. In a case in which the fingers and prisms of the molding member are made of a rigid material such as stainless steel a relatively soft surface such as made of silicon or silicon rubber supports the opposite side of the layered plastic. However in cases in which the fingers and prisms are made of a soft material the supporting surface is made of a rigid material such that a distinct pattern is imprinted onto the sandwiched plastic. In Figs 6B and 6C sectional views of member 50 and 58 shown in Fig. 6A are respectively shown. The same parts shown in all of these three figures are indicated by the same numerals. Sharpened tip 63 of prism 54 provides for cutting a sheet or layered sheets of plastic when heated and forced towards the topmost layer. The pressing member is forced against the layers to be configurationally heat soldered at a predefined force that is selected in accordance with the widths and the materials from which the plastic sheets are made of. The level by which the pressing member presses the layered sheets as well as the time along which pressing is applied are crucial to the quality and distinctness of the patterns to be imprinted across a seam. Biasing springs, not shown, optionally connect pressing member 58 to molding member 50. Therefore when the molding member is moved towards the layered plastic pressing member 58 first presses the sandwiched plastic before heated fingers 52 touches its surface. Such enhanced pressing at the margins of the contours targeted for heating provides for retaining the tension applied onto the segment of the heated plastic at a constant level and condensing the layered plastic such that the width of the sandwiched plastic reduces to a desired level. Similarly when molding member is moved away from the layered plastic the pressing member continues to press it for better cooling the generated seems and avoiding shrinkage of the cooling segments.

The footprints of the fingers and/or the prisms of a molding member are referred hereinafter as features of the pattern. These features include and are not limited to according to the present invention graphical and typographical symbols and/or continuous and/or discontinuous, dashed or dotted lines, which are linear and/or curvilinear. The features are embossed on, and/or perforated through, the layered plastic. The patterns imprinted along a seam by means of the soldering heads described above are characterized by more than one continuous tier of soldered segments, each of which is successively aligned in a direction pointing inwards off the edge of the bag. Therefore even an insertion of a thin object such as a fiber-optic is involved with cutting through more than one such segment of a soldered line. In Figs 7A and 7B a side and isometric views of a molding member of a soldering head of the first kind according to a preferred embodiment of the present invention are respectively shown. The same parts shown in both figures are indicated by the same numerals. This soldering head that is shaped as a horseshoe, consists of molding member 70 and a matching pressing member, not shown, which is provided with series of skirted apertures as described above. This pressing member is connected by biasing springs to molding member 70, such that when this soldering head is moved towards the layered plastic, the bulges skirting the apertures of the pressing member first press against the layered plastic, a while later the pressing faces of the fingers touch the surface of the plastic. When the soldering head is moved in the opposite direction first the fingers of the molding member are removed from the layered plastic then a while later the tips of the pressing member are removed off the layered plastic. An inner curved prism, consisting of curved row of fingers 72 is inwardly disposed to continuous and curved prism 74. A soldering head in which any of these prisms is avoided is in accordance with the present invention. Another row of fingers the faces of which are shaped as alphanumerical symbols, provide for printing in the space between the footprint s of both prisms. The widths of the faces of fingers 72, as well as the width of prism 74 are significantly smaller compared to the distance between any of the fingers 72 to prism 74. The footprints of both prisms provide for retaining the segment of the layered plastic sheets in between them stretched. Such stretching can be also retained in cases in which the pressing member is avoided. Therefore any twisting and/or shrinking of this segment as a result of its being selectively and discontinuously heated and then cooled are significantly decreased. Optionally heat printing is further applied on top of the soldered figures by means of a foil coated with heat-transferred color disposed between the bottom faces of these fingers and the surface to be pressed and further heated. Some of the fingers according to the present invention can be slightly longer than the other fingers and can have sharpened tips at their free ends, such that the soldered layers of plastic are perforated when are pressed by the molding member. Any such perforation is skirted with a thin circular seam due to the contact with the heated finger. Such heat printing and or perforation provide for enhancing the distinctness of a seam.

A pattern having three-dimensional features embossed on both layers of plastic along a seam provides a more distinct pattern thereby the opening and resealing of a seam can be more easily recognized. Reference is now made to Figs 8A - 8B in which segments of embossing heads providing for a three-dimensional embossing in accordance with two different preferred embodiments of the present invention are respectively shown. In Fig. 8A embossing head 80 is shown. Embossing head 80 has two molding members 82 and 84. Fingers their pressing faces are shaped like alphanumeric symbols, such as finger 85, extend towards the same direction from face 81. Recesses, not shown, all of which respectively conform to the fingers are disposed on the respective face of female molding member 84. Alternatively, prisms and conformal grooves with or without fingers are disposed on the respective faces of molding members 82 and 84 respectively. The surface of a finger and the surface of the respective recess enclose a space that surrounds each finger into which the material of a segment of the heated layers of plastic is stretched and forced. The space existing between the fingers and the wall of the conformal recesses provides for structuring a three-dimensional geometrical shape that is filled with the material of the layered plastic. Embedded heaters and temperature control devices, not shown, provide for retaining the respective temperature of any of both molding members fixed, as known. The temperature of the hot member, which is preferably molding member 82, is retained fixed within a predefined temperature interval below the melting point of the plastic resins utilized. The temperature of the other member is retained at a predefined temperature difference below. Namely, the heating member of this soldering head comprises both molding members 82 and 84. For soldering a seam such as seam 86, the respective edge of the bag, such as tamper evident envelope 87, is moved along the direction of arrow 88 and placed between the jaws of soldering head 80. At this stage both molding members 82 and 84 are respectively forced to move in the direction of arrows 89 and press against the respective surfaces of the bag by a predefined force along a predefined time interval.

In Fig. 8B a segment of embossing head 90 in accordance with another preferred embodiment of a tamper evident envelope of the present invention is schematically shown. Curved fingers such as finger 91 or slim and sharpened fingers such as finger 92 protrude off the face of mail molding member 93. Matching recesses such as recess 94 and 95 are respectively located at the face of female molding member 96. The slim and sharpened fingers provide for perforating a pattern through the soldered plastic sheets. The continuously curved fingers provide for embossing typographical features across the layered plastic sheets concomitantly with mutually soldering them. (The female molding member is shown artificially tilted in the directions shown by double arrow 97 to clarify the structure of both molding members.) Preferably the temperature of a male molding member is higher than the temperature of the female molding member by a predefined temperature difference, such that the direction in which heat is conducted through the layered plastic complies with the direction of the movement of the plastic layers into the respective recesses of the female molding member. The temperature gradient generated across the widths of the layered plastic sheets that structure features of the embossed pattern provide for fine tuning the quantity of heat to be absorbed by the layered plastic and avoiding excessive heating. Furthermore the duration of the heating as well as the temperature difference provide for controlling the quantity of heat to be absorbed by the layered plastic.

A molding member of an embossing head of the invention may have a number of protruding fingers as well as another number of recesses that conform to fingers extending off the other molding member. Namely, seams in which a segment of an embossed pattern protrudes off one face of the layered plastic and the successive segment of the pattern protrudes off the opposite face of the layered plastic can be heat soldered by such soldering heads. In such a case both molding members are heated to the same temperature.

Soldering of the layered plastic and the associated embossing process are concomitantly effected with heating the layered plastic by means of the soldering head described above.

The heating and the pressing of the layered plastic need not be concomitantly effected according to the method of the present invention. The heating member and the molding member or members may be separated and incorporated in two different and independent units, as is hereby described with reference to Figs 9A - 9B, which is now made. Heating member 100 has one or more heaters such as heaters 102 disposed in front of mask 104. Mask 104 has one or more apertures such as slot 106, which are cut through diaphragm 108. The layout and geometrical shape of these apertures conform to the contours of the seams to be imprinted on the surface of the plastic bag. Beam or beams of heat radiation having a geometrical shape conformal with the geometrical shapes of these apertures impinge upon a layered plastic, not shown, disposed in front of mask 104 at the side opposing to the side facing the heaters. The layered plastic is exposed to the heat radiation for a predefined time interval. Alternatively heating can be applied by ultrasound irradiation, high frequency or radio frequency (RF) irradiation, or any combination of infrared and ultrasound irradiation. Alternatively heating can be applied by jetting heated air at predefined quantities towards the layered plastic. Following any such heating cycle the heated layered plastic is upheld still in place such that no harm involved with moving it might occur. At this stage an embossing head replaces the heating member and its molding members are further forced to press the heated contour. In Fig. 9B a segment of embossing head 110 is schematically shown at an open position following the soldering of the edges of envelope 112. Shaped fingers such as fingers 114 extend from molding member 116 towards envelope 112 and recesses conformal to the fingers, not shown, are disposed on the side of member 118 facing the envelope, as described hereinabove. Pipes 120 respectively embedded in both molding members provide for conducting coolants thereby controlling the respective temperatures of the molding members at respective desired values. In such manner the soldering of the layered plastic that results the embossed pattern is accomplished whilst the heated plastic cools off. The pattern embossed along the seam of envelope 112 includes distinct shaped bulges, such as bulges 122, conformal with the geometrical shape of the fingers of the male molding member. Recesses having similar distinct shapes are respectively disposed on the opposite face of the envelope.

For manufacturing a plastic bag according to the invention any sheet or sheets of thermoplastic resins normally utilized in manufacturing common plastic bags can be utilized. For example sheets made of high and/or low density polyethylene (HDPE, LDPE), as well as coextruded low/low, low/high and high/high density polyethylene (LLDPE, LHDPE, HHDPE) sheets made of polypropylene, PET and/or co-extruded sheets of any combination of the above mentioned material, and/or plastic foam, bubbled sheets, sheets made of PVC and/or sheets made of Tyvek®, which is made of high density polyethylene fibers, can be utilized. The plastic sheets are first layered; then segments across the surface of the layered plastic are heated to a respective predefined temperature, which is below and close to the respective melting point of the plastic considered; the heated segments are pressed by a soldering head such as described hereinabove, and then cooled again to the ambient temperature. Heating and pressing can be either successively or concomitantly effected. In cases in which heating and pressing are concomitantly effected, heating is accomplished either by contact with a body the temperature of which is regulated to equal the desired temperature or by a heat pulse such as electrically generated and further conducted through the fingers and prisms of the molding member during the time interval along which the layered plastic is pressed. In order to avoid excessive heating to temperatures above the desired temperature level the width in time of a heat pulse is predefined. The width in time of a heat pulse is selected in consideration with the heat capacity of the segment of the layered plastic and the heat capacity of the molding member the length in time separating between two successive heating pulses which depends on the rate of soldering and the ambient temperature. Similarly heating by infrared irradiation is effected along a predefined time interval along which the respective desired temperature of the targeted segments of the layered plastic is achieved to avoid full melting of the sheet at the heated zones. Optionally the layered sheets are further pressed by means of a pressing member forced at predefined level of forces prior to, and during, the time interval in which the heating member of a soldering head of the first kind presses them. Optionally a foil coated with a heat-transferred color is sandwiched between some rows of fingers and the topmost surface of the layered plastic facing them. The layered sheets to be mutually attached according to the invention are sandwiched between the jaws of an embossing head or between a soldering head of the first kind and a supporting surface. Preferably the soldering head of the first kind presses the sandwiched layers of plastic against a cylinder, which is rotated along time intervals separating in between two successive soldering cycles. Cutting along the edges of the bags can be accomplished according to the invention either by means of a sharpened prism of a heating member of a soldering head concomitantly with soldering the edges of the bags, or independently by means of a cutting knife, as known. Configurationally heat soldering plastic packaging of the present invention can be implemented in an automatic production line in which one folded, two (or more), elongated sheets of plastic are winded off two feeding drums and are stretched linearly between the jaws of an embossing head or between soldering head of the first kind and a planar or a cylindrical supporting surface.

EXAMPLE 1

Reference is now made to Fig. 10A - 10C respectively showing three tamper evident envelopes according to three different preferred embodiments of the present invention. Tamper evident envelope 140, is made of two sheets of co-extruded polyethylene (HDPE+LDPE). These sheets are attached to each other by two continuous soldered seams 142. Seams 142 are generated by means of soldering head of the first kind having an inner and outer prism extending outwards off the body of its heating member. The wiggles in-between seams 142 are generated by curved elongated fingers disposed between these prisms. Optionally the seams and/or wiggles disposed between them are further colored by heat printing as described above. Perforated tear tape 144 provides for printing data related to the content of tamper evident envelope 140. Tamper evident sealing sticker 145 has to be first removed or cut for opening the envelope and get access to its content, as known.

Tamper evident envelope 150 is made of bubbled sheet that is made of co-extruded polyethylene by means of a soldering head of the first kind. This soldering head is incorporated with a pressing unit such that the bubbles in the seam area are squeezed to give a good thermal contact between the various layers of plastic within the contour of the seam. Two continuous soldered seams 152 surround an embossed printed data 154 presented by means of imprinted alphanumerical characters. The continuous lines and the alphanumeric symbols are respectively generated with curvilinear prisms and shaped fingers of the heating member. Temper evident sticker 156 provides for sealing off the aperture of the envelope as known. The molding member employed is such structured that the outermost prisms are curved to include flap 158 as an integral part of the body of the envelope. Flap 158 provides for conveniently filling. Punched apertures 159 provide for filing envelope 150 such as within a dossier, can be either punched concomitantly with the config u rational soldering or at a later stage by means of a common punch..

Wiggly and curvy seem such as seems 160 of temper evident envelope 162 with or without additional imprinted symbols and/or data in between is another exemplary tamper evident envelope of the present invention. Envelopes having a single nonlinear and wiggly seam along their edges are in accordance with the present invention.

EXAMPLE 2

Envelopes of the present invention may have one face made of plastic sheet whereas the other face is made of a nonwoven fabric. Such envelopes are especially suitable for carrying paper money. In a soldering process the heated plastic sheet fuses and some of it further gets into the spaces separating among various fibers of the nonwoven fabric onto which it is pressed while being heat soldered. Reference is now made to Figs 10D-10E in which two opposing sides of a segment of tamper evident envelope 164 are respectively shown. Face 165 of envelope 164 is made of polyethylene. However face 166 is made of a nonwoven fabric such as Taft or Rayon. The seams along the edges shown in both figures include two continuous lines 168. A three dimensional pattern including alphanumerical characters is embossed in between lines 168. Such configurational heat soldering is accomplished by means of embossing heads such as described hereinabove. Sheets of nonwoven fabric that is utilized for manufacturing envelopes of the invention in which one of their faces is made of plastic resin whereas the other face of the envelope is made of nonwoven fabric are also referred herein after as plastic sheets

EXAMPLE 3

The inventor of the present invention has experimentally found that when a continuous region of a few millimeters square across layered Tyvek^(R) sheets is heated such that the material within the heated region fuses and further cooled off for the purpose of heat soldering, the inner material within the soldered regions becomes transparent and brittle. Although a relatively thin soldered seam circumferential to the heated zone does exist, the inner region can be easily crumpled. However the integrity of a discontinuous soldered seam across Tyvek^(R) sheets, the area of the individual segments of which is within a range of 1.5 - 2 millimeters square, remains intact. Namely, a seam consisting of an array of soldered segments that are spaced apart; which is shaped as dashed or doted line, retains almost the original integrity of a virgin Tyvek^(R) sheet. The minimal dimensions of the spaces separating between two adjacent soldered segments are such that the material within a space does not change its color in comparison with the color of a virgin Tyvek^(R) sheet. The maximal width of a soldered region as well as the minimal width separating between two adjacent soldered segments can be experimentally found according to the invention by trial. However as a rule of a thumb, the area of a soldered segment should not exceed say 1.5 - 2 mm² (one and a half up to two millimeter square), whereas the width of the spacing between two adjacent soldered segments may get down to half of the width of the soldered zone. Preferably the margin of the heated regions are further pressed by means of a pressing member concomitantly while are heated and further cooled off. In this manner an array of soldered segments is generated across the surface of the layered Tyvek^(R) sheets. By such limited heating to a predefined temperature that is lower than, however close to, the respective melting point, with, or without pressing by means of a pressing member, for example a series of points, or along segments of a dashed line, in which the area of each segment or a point does not exceed 1.5 - 2 mm², and preferably 1 mm²; a soldered seam consisting of a series of fused regions such as of point soldering is generated. Reference is now made to Fig. 11 showing a tamper evident envelope according to a preferred embodiment of the present invention. Envelope 170 is made of tyvek^(R). The edges of envelope 170 are soldered by means of a soldering head of the first kind. A company name and/or logo or any text or graphical pattern is embossed across the spacing between both seams 172. The spacing between adjacent soldered points as well as the multiple tiers of soldered points do not allow for introducing for example a fiber optic to search the content of the envelope.

EXAMPLE 4

The manufacturing time of tamper evident envelopes depends on the number of open edges per one envelope along which seams have to be heat soldered. By utilizing a folded plastic sheet one can fabricate envelopes having two open sides that have to be sealed by heat soldering. Whereas the third open side can be used as the aperture of the envelope that can be sealed off by the user by means of a tamper evident sticker as known. Reference is now made to Figs 12A - 12B. In Fig. 12A side looking view of tamper evident envelope 180 is shown. Two seams 182 each of which includes a three dimensional embossed logo disposed in between two continuous lines such as the seam shown in Figs 10D-10E. Tamper evident sticker 184 seals the aperture of the envelope. Broken line 186 designates the end of the top flap of the cover of the aperture of the envelope. Fig. 12B is a sectional view along line AA of the envelope shown in Fig 12A. An exemplary inexpensive soldering head of the present invention includes a male molding member such as molding member 190 a side looking view of which is shown in Fig. 13 to which reference is now made. Linear prism 192 and a two dimensional array of sharpened and relatively elongated pins, such as pins 194 extend off the face of molding member 190. A matching female molding member, not shown, includes an elongated groove conformal to the prism and an array of recesses that respectively conform to the elongated pins. The pins provide for perforating the tamper evident envelope such that a relatively thin circular seam is disposed circumferential to any of the punched holes made by any of the elongated pins 194. Another soldering head according to an embodiment of the present invention has a male molding member that include only a row, or a two dimensional array, of pins extending off the face of the male molding member; all of which have the same predefined temperature. A female molding member includes the respective recesses that conform to the pins. Such a soldering head can be employed for producing a seam the includes an array of holes their margins are heat soldered. Optionally such a soldering head can be added as an additional soldering station to a production line of tamper evident envelopes that include common soldering station providing for soldering linear seams as known.

Claims

1. A method for configurationally heat soldering a seam along which one folded and/or two or more layered sheets of plastic are mutually attached, said method comprising: a. heating at least one selected region disposed across the external surface of said layered plastic to a predefined temperature,; b. forcing a molding member against said layered plastic along a predefined time interval, and wherein said molding member comprises a plurality of fingers each of which has a pressing face having a distinctive geometrical shape, and wherein at least one of said pressing faces positioned within said at least one selected region, and wherein said plurality of fingers extend from said molding member pointing towards said layered plastic.

2. A method as in claim 1 , wherein said layered plastic is compressed between said molding member and a supporting surface concomitantly with said forcing.

3. A method as in claim 2, wherein said supporting surface is cylindrical.

4. A method as in claim 3, wherein said cylindrical surface is rotatable.

5. A method as in claim 1 , wherein said heating concomitantly effected with said forcing.

6. A method as in claim 5, further comprising pressing said layered plastic by means of at least one bulge protruding off a pressing member, wherein said pressing exerted onto said layered plastic at a site disposed adjacent to said at least one pressing face.

7. A method as in claim 6, wherein said heating effected along said predefined time interval which is the first time interval.

8. A method as in claim 7, further comprising continuously pressing said layered plastic adjacent to said at least one of said pressing faces starting prior to the point in time in which said predefined time interval starts and continue pressing along a second time interval immediately following the end of said first predefined time interval.

9. A method as in claim 5, wherein said molding member is a first molding member and said predefined temperature is the first temperature and the side of said layered plastic facing the first molding member is the first side, and wherein a second molding member having a second temperature is forced against said layered plastic against the side opposing said first side, and wherein said forcing of the second molding member concomitantly effected with said forcing of the first molding member, and wherein said second molding member comprises at least one recess accommodated to enclose a segment of a given length of a resprctive finger the free end of which is said at least one pressing face. .

10. A method as in claim 9, wherein said second temperature is lower 5 compared to said first temperature by a predefined temperature difference.

11. A method as in claim 9, wherein at least one finger extends off the face of said second molding member pointing towards said layered plastic, io and wherein a recess disposed on said first molding member which is accommodated to enclose a segment of said finger extending off the second molding member, and wherein said second temperature equals said first temperature.

15 12. A method as in claim 1 , wherein a heating member effects said heating, and wherein said heating member is different than said molding member.

13. A method as in claim 1 , wherein one of said layered plastic sheets is a 20 nonwoven fabric.

14. A heat soldering head for imprinting a pattern along a seam located across a surface of a layered plastic, said soldering head comprising:

• a heating member for selectively heating targeted regions 25 disposed across said surface; • a molding member, wherein said molding member comprises a body having a face and a plurality of fingers extending off said face for pressing against said surface, and wherein said fingers point towards a common direction.

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15. A heat soldering head as in claim 14, further comprising a pressing member for pressing against said surface at the periphery of at least one of said fingers.

io 16. A heat soldering head as in claim 14, wherein the temperature of said molding member is controllable.

17. A heat soldering head as in claim 14, wherein said molding member further comprises at least one prism, wherein said at least one prism

15 extends from said face towards said common direction.

18. A heat soldering head as in claim 17, wherein said at least one prism is arcuate.

20 19. A heat soldering head as in claim 17, wherein said prism comprises a sharpened tip.

20. A heat soldering head as in claim 14, wherein at least one of said fingers has a sharpened tip.

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21. A heat soldering head as in claim 14, wherein at least one of said fingers has a geometrical shape of an alphanumerical character.

22. A heat soldering head as in claim 16, further comprising a second molding member, wherein said second molding member comprises a plurality of recesses accommodated to respectively enclose a segment of any of said plurality of fingers, wherein the temperature of said second molding member is controllable.

23. A tamper evident bag made of layered plastic comprising a distinctive pattern imprinted along a seam disposed across a surface of said layered plastic, wherein said pattern generated by configurationally heat soldering, in which selected targeted regions across the surface of said layered plastic are heated and further pressed by means of a molding member, and wherein said pressing accomplished by forcing said molding member against said layered plastic such that the pressing faces of fingers of the molding member presses against said respective targeted regions, and wherein said pattern comprises geometrical shapes respectively complying with the geometrical shapes of said pressing faces.

24. A temper evident bag as in claim 23, wherein at least one feature of said pattern has a three dimensional shape.

25. A tamper evident bag as in claim 24, wherein said at least one feature comprises a bulge disposed across one face of said seam and a recess conformal with said bulge disposed across the other face of said seam.