Method for shaping synthetic paper, holding strip formed by such a method, and sheet holding device

Abstract

A method for thermoforming synthetic paper is provided, more concretely for thermoforming holding strips of synthetic paper, the strips being used to produce sheet-holding devices of a specific configuration. The devices can be used in the assembly of sheet holders such as calendars, white sheet dispensers or information cards.

Claims

1. A sheet fastener comprising: two fastening strips (1), each one having: a body (2A), a tab (1A) provided on an upper part of said body (2A), a hinged pullout tab (P) provided on a lower part of said body (2A), and a curved area (G) provided on said upper part of said body (2A) between said tab (1A) and said hinged pullout tab (P); a base (3) having a length approximately equal to half the length of each fastening strip (1); and an additional base (9) including two windows (15) provided on an upper part of said additional base (9), two slots (19A) provided on a lower part of said additional base (9) opposite to the windows (15), and a support section consisting of: a first folding line (16), a second folding line (17), and a third folding line (18) provided between said two windows (15) and said two slots (19A), wherein said base (3) is positioned between the fastening strips (1) and the additional base (9) so that the hinged pullout tab (P) of each fastening strip (1) serve as a positioning guide and a locking mechanism for the support section when said sheet fastener is in use.

2. The sheet fastener of claim 1, wherein said support section of the additional base (9) serves as a standing base of the sheet fastener by folding said first folding line (16), said second folding line (17) and said third folding line (18) so that said two slots (19A) face a rear wall of said additional base (9) and the lower parts of the two fastening strips (1) are inserted through said two windows (15), respectively, until the hinged pullout tabs (P) of each fastening strip (1) is latched against said two slots (19A), respectively.

3. The sheet fastener of claim 1, wherein the base (3) further includes two semicircular indents (20) provided on a lower part of said base (3), serving as guides for the fastening strips (1) when said fastening strips (1) are inserted through said two windows (15).

4. The sheet fastener of claim 3, wherein the base (3) further includes two below slots (10) so that the two tabs (1A) are inserted through said below slots (10) and remain hidden between said base (3) and said additional base (9).

5. The sheet fastener of claim 1, wherein said fastening strips (1), said base (3) and said additional base (9) are joined together by double-sided adhesive.

6. The sheet fastener of claim 1, wherein pre-slotted sheets are fastened to said sheet fastener by inserting the curved area (G) of each fastening strip (1) through each slot of said sheets.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a flow chart of the process by which the laminated thermoplastic of synthetic paper is thermoformed.

(2) FIG. 2 shows a schematic of the components for the equipment used to perform the thermoforming.

(3) FIG. 3 shows an exploded view of the novel fastener device with the fastening strip and its base printed.

(4) FIG. 4 is a variation of the device in FIG. 3.

(5) FIGS. 5A and 5B show details of the thermal behavior of the thermoforming process in the fastening strip.

(6) FIG. 6A is an exploded view of the device of the prior art, FIG. 6B is a lateral view showing that when a force is applied, the ring gets deformed for not having restriction on its movement.

(7) FIG. 7A is an exploded view of the device, object of this invention.

(8) FIG. 7B is a schematic representation showing that a second base provides more rigidity to the ring aiding in the correct functioning of the system.

(9) FIGS. 8A-8C show views of the sheets fastener built using the fastening strip and the sheet-fastening device of the present invention.

(10) FIGS. 9A to 9F show several views of the assembly process of the fastener shown in FIGS. 8A-8C. The fastener comprises a base, a fastening device and two fastening strips.

DETAILED DESCRIPTION OF THE INVENTION

(11) In FIG. 1, it can be seen that the process begins by printing 101 the synthetic paper templates with the shape of the strips, to later apply in 102 a double-sided adhesive and then cut 103 the formed template in order to obtain individual pieces. The synthetic paper fastening strip 1 is printed in 104 (see FIG. 3) with the corresponding indicia 2 such as logos, means to improve fastening such as points of relief, assembly instructions, etc. It is noted that the ink used was selected so that it withstands the operating temperature of the thermoforming. In step 102 a double-sided adhesive strip is placed, which has also been selected in order to withstand the temperatures generated in the thermoforming process without losing properties or dripping on the sides of the fastening strip 1. This adhesive strip will serve to join, on one side, the fastening strip 1 with a base 3. The adhesive is placed on the opposite side of the indicia 2.

(12) Once the adhesive and the indicia 2 are placed on the strips 1, these are placed 105 in individual molds with the surface having the adhesive facing towards the heat source and are heated by a heat source that can be for example infrared radiation (thermoforming) exclusively in the zone G to be thermoformed. For this procedure, a thin mesh 4 is placed (106) with fine squares between the infrared lamp 5 and the zone to be heated or hook G (see FIGS. 3, 5A and 5B, among others).

(13) It should be noted that this process is described in relationship to a curved zone G; however, other configurations are applicable depending on the final application of the thermoformed product. This mesh 4 is used to spread the heat and avoid an excessive concentration of heat on the zone to be thermoformed G. The temperature for the thermoforming process should be controlled within a range of 193 C.1 C. On 107 the lamp is placed at a distance from the strip of approximately 1.4 cm. The mesh must be right in the middle. The exposition time of the strip to heat emitted by the lamp varies according to environmental conditions from 17 to 20 seconds. The mesh is built from stainless steel threads and the opening of its squares is from 0.1 mm to 0.4 mm, preferably 0.1 mm.

(14) Once at the operating temperature, the next step follows in 108 consisting in removing the lamp, lowering the counter-mold 6, pressing and curing the synthetic paper. This stage must be performed quickly to avoid the strip 1 from getting cold; the lamp 5 should be removed in a way that will not interfere with the movement of the counter-mold 6 over the mold 7. It must be mentioned that the counter-mold is cooled at a temperature of 25 C.+5 C. The counter-mold comprises the male part 6a, formed by an elastomeric insert, while mold 7 comprises the female part (not shown), in order to form hook B (see FIGS. 2 and 5A).

(15) Once thermoformed and cured, the counter-mold 6 is removed and and the strip 1 is taken out of the mold, already formed as shown for example in FIGS. 3 and 7A.

(16) During the manufacturing of the device described in document WO'021, a burr was formed that had to be eliminated, which produced a reduction, time consumption and loss of properties. It was surprisedly found that the best way to manufacture this device was individually and avoiding the burr that usually stays around the pieces made by the conventional thermoforming process. Fastening strip 1 requires, for functioning reasons, a very particular cyclical retractable capacity since its design is oriented to withstand thousand of flexions without losing its original shape. The thermoforming process provided the end product a retractable memory (flexion) of unique and very efficient characteristics.

(17) A process that would not produce a burr was searched. Literature does not provide that such a process exists and manufacturers and distributors of synthetic paper could not offer help in that regards either, so the development of a propietary process was initiated.

(18) Printing of the synthetic paper strip can be printed by means of printing techniques known in the art such as silk-screen printing, flexography, off-set, digital printing, etc.

(19) At the end of the thermoforming process, the printings on the fastening strip should not show any variations and the double-sided adhesive should retain its properties.

(20) The forming process of the adhesive strip provides a great benefit that consists of a perfect register of the printing on the piece, regular thickness, burr-free pieces and most importantly, a precise and constant mechanical function.

(21) Pressing of the strip is done in a way such that the thickness of hook G is not decreased, but that at the same time it is enough to permanently deform the material. Also, the pressing process must take care not to produce deformations in any part of hook G or the adjacent parts.

(22) Applying of abrupt cooling to hook G with the cold mold, but at the same time keeping the shape of the hook provides it with the anatomical stability properties in conjunction with a great elasticity of the hook.

(23) Once the strip is formed, the cover of the double-sided adhesive strip is removed, located in the back of the fastening strip to adhere this strip to the base 3 (see FIGS. 2 and 3).

(24) Considering now FIGS. 5A and 5B, it can be noted that the thermal behavior of the strip is as follows: when applying heat with the infrared lamp 5 through the mesh 4, the zone or hook G receives a certain amount of heat that dissipates towards the upper part of the strip and to the lower part of the same (that is, towards the double-sided adhesive).

(25) Another of the important inconveniences was the thermal expansion undergone by the zone exposed to the heat. Is important to remember that the hook is not fastened to a frame that will keep it steady at the time of heat exposure, as a consequence, at the time of exposure, the zone experiences a certain degree of thermal expansion, enough to move the piece inside of the mold cavity, causing failures in register at the time of closing the matrix.

(26) It was necessary to make millimetric modifications to the cavities to provide the necessary space for the expansion of the material.

(27) Since synthetic paper is a bad heat conductor, a great amount of it will dissipate towards the upper part due to the reduced area of the tab and a smaller amount towards the lower part due to the joint of three materials (synthetic paper, double-sided adhesive and cover with double-sided adhesive). This phenomenon implied developing a method that would help to distribute heat homogeneously on the desired area to thermoform. The method consisted on introducing a mesh between the heat source and the material to thermoform.

(28) Once the forming process was found, the strip 1 with caliber 12 and a larger diameter R of 0.7 cm to a diameter of 1.2 cm (FIG. 3) was worked on. However, once it was thermoformed, this strip showed deformation during operation.

(29) Then it was decided to try with a different caliber, maintaining the diameter R of 0.7 cm and experimenting with different diameters up to 1.2 cm. The results obtained were optimal for the objectives of this invention since the piece did not deform, maintained its shape and improved greatly the amount of work cycles from 5,000 to 9,000 cycles.

(30) FIGS. 6A and 6B show the fastener of the prior art where it is shown that the arrangement of the sheets is not ideal because they do not sit correctly on their base since the curve of the strip does not posses the adequate configuration for lack of an additional base and where it is also noted that the hook of the plastic strip does not sit correctly on the rear part of the base stop functioning as planned. It was noted during the operation of the device of the prior art, that in absence of a second base or support base, it was difficult to open the tab (of the prior art) since when pressuring the curved body g of the strip with the finger to open the system, this doesn't find a stop and submerges, difficulting the opening. In other words, it simply does not work. Another important factor is aesthetics, the product in all its variations looks of a better quality when the tab 1a (of the present invention) of the strip stays hidden between the base 3 and the additional base 9 (as shown in FIGS. 7A and 8A). The curved body of the strip looks firm and with a good shape, the sheets find a better support over a well-defined curve and the functioning of the system is the ideal.

(31) Once the material and its process were determined, it was proceeded to design a fastening device 8. This design led to the one shown in FIG. 7A and comprises the fastening strip 1, the base 3 (or a variation of the same as the one shown in FIG. 4) and an additional base 9.

(32) The fastening strip 1 formed as described above, comprises an adhesive strip (not shown) that will join this strip to the base 3, such joint is indicated by the dotted reference 11. This base 3 is joined to the additional base 9 where its joint is represented by dotted reference 12. The joint between these two bases is again done by a double-sided adhesive strip (not shown). The base 3 also comprises a slot 10 for introducing tab 1A through said slot 10. It is important to point out that this slot has a greater height than the one indicated in document WO'021 because another defect found was that during use, the tab got continuously stuck due to the narrowness of the slot height. Note and compare the dimensions of both slots shown schematically in FIGS. 6A and 7A. The width of both slots is the same; however, the height is significantly different being at least 20% of the length of the slot for the novel slot. The widths of the slots can vary from 1.5 cm to 5.0 cm maximum (this parameter also applies for the width of the strip and for the fastener hook). In the case of the height of the opening, it should be a minimum of 0.6 mm to a maximum of 1 cm (the height of the opening in document WO'021 was 0.3 mm so it increased 100%).

(33) In an embodiment of the invention, base 3 covers only approximately half of the length of the fastening strip. Strip 1 comprises a tab 1A and a body 2A that optionally includes in its lower part a pullout tab P in the shape of a half circle or half rectangle that works as a guide to position the fastener in the right way and as a work mechanism for its use in other devices as will be shown later. A preferred embodiment is the device shown in FIG. 8A that comprises a base 3 and two devices 1 placed next to each other.

(34) Described below is an exemplary embodiment of an application of the fastener strip 1 by means of a sheet fastener product represented by a desk calendar.

Example 1

(35) Device 13 shown in FIGS. 8A and 9F is a sheet fastener represented for description purposes and is not limited to a calendar.

(36) Fastener 13 comprises the fastening strip 1, the base 3 and the additional base 9. The sheets, besides having the shape of a calendar, can be sheets with advertisement or technical information, blank sheets or similar. Such sheets are previously slotted according to the amount of fastening strips 1 provided in fastener 13.

(37) Fastener 13, in the embodiment illustrated, comprises two fastening strips 1 joined by double-sided adhesive to base 3, which in turns is to the additional base 9. Base 3 has a length approximately equal to half the length of the fastening strip 1.

(38) As shown in FIGS. 8A to 9F, the additional base 9 comprises two windows 15, a first folding line 16, a second intermediate folding line 17, a third folding line 18 and two slots or cuts 19A, placed on the lower part, opposite to windows 15.

(39) In the case of base 3, it has under the slots 10 two semicircular indents 20, which will serve as guides for strips 1, as described below.

(40) The fastener is built (see FIGS. 8A-8C) by joining the fastening strips 1 to the base 3, making sure that they are aligned with slots 10 and indents 20. The strips have double-sided adhesive, one of the sides is joined to the same strip 1 and the other side is joined to the base 3. Once base 3 is joined to the fastening strip by means of this adhesive, it is placed, on the side opposite to the base 3, another double-sided adhesive to be joined with the front side of the additional base 9.

(41) After this, the piece shown in FIG. 8C is obtained.

(42) To form the calendar, the steps shown in FIGS. 9A to 9F are followed. The assembled piece is folded on the intermediate folding line 17 extending it towards the rear side of the same. The folding continues until the lower edge of the lower part 19 makes contact with the fastening strips that have been previously folded for passing through windows 15 towards the rear side of the assembled piece as shown in FIG. 9B. Then the lower part of the fastening strips 1 are introduced into slots 19A sliding the strip until the pullout tab P, of each strip, passes through slot 19A (see FIG. 9C). Once the pullout tab P passes through slot 19A, the calendar is assembled and locked to avoid disassembling by its handling.

(43) FIG. 9E shows the calendar completely assembled in a left frontal isometric view and image 9F shows a rear isometric view of the same where the locking effect that pullout tab P provides in conjunction with slots 19A is appreciated in more detail. The lower part of the fastening strips is shown in a dotted line. This locking mechanism prevents that the intermediate folding line 17 recovers its initial position and deforms the calendar. Folding lines 16 and 18 are now the support base of the calendar.

(44) The invention has been described making reference especially to one of its embodiments and that consists in the final production of an article such as a desk calendar; however, the final product produced can take different forms. It is requested that in as much as these forms are evident to a person with average knowledge in the art, they are included within the scope of this invention.