Field Of Invention:

This invention relates to a bag made of polymer web materials, in particular polyolefines using adhesive bonding.

Background Of Invention And Known Art:

Bulk materials are packed in a variety of bags, which can be roughly divided into pillow- and box or block-shaped types. A pillow shape bag is usually created by stitching or seaming the bottoms. A box or block shape is created by folding and bonding the bottom. The box shape allows for optimal use of the material surface, good stackability and an improved utilization of volume due to its brick shape. There is also the quasi-box shape which is a pillow bag on one side and a box bag on the other.

Typically, bags have a capacity of 10, 25, 100, 500 and 1000 kg. Suitable materials include natural fibre fabric such as jute, paper, plastic sheets and plastic fabric, nonwoven web within the last decades bags made of natural fibre fabric have been replaced by bags made of paper and plastic sheets and plastic fabric, because these are cheaper and offer technical advantages. Paper does not have moisture barrier or higher strength. For this reason bags often include various layers of paper, which increases material consumption. Also, a paper bag is not suitable for storing majority of chemicals in wide use in industry. However, it can be produced at low cost and by using cheap adhesives. Plastic sheets do not have high tear strength and therefore higher thickness material is used. Further, the plastic sheets are not dimensionally stable and are more heat sensitive. The plastic sheet bag can be readily seam welded to a pillow shape, but not easily bonded to form a box- or block-shaped Bag. Plastic woven fabrics consisting of monoaxially drawn tapes have the high strength and are dimensionally stable, particularly the coated plastic woven fabrics. Compared to unstretched plastic sheets, raw material requirement of the woven fabric made from stretched tapes is much lower for the same load-bearing capacity. Bags made of plastic fabric are usually made in pillow shapes with seams. The block shape bags of plastic fabric are made by using hot air welding/seaming techniques to make joins at top and bottom side as per prior art like US5845995 are known. However, it is well known that hot air welding/seaming systems cause undesirable and uncontrolled deterioration in fabric strength. Inability to control the process parameters of hot air welding/seaming systems results in uncontrolled variation in production quality. This results in reduced production speeds.

Present invention provides alternative bonding method for polymeric webs/plastic woven fabrics/webs to form block shape bags of adequate quality of joints at higher processing speeds than the conventional systems.

Objects of Invention:

The object of the present invention is to overcome limitation of conventional box shape bag making process, particularly to establish a bag and a method for producing a bag and a machine system for producing bags by which the bags can be produce more rapidly and easily. Further, the efficiency to produce the bags has to be increased.

Another object of the invention is to provide a process of making a bag that uses surface enhancement techniques along with effective gluing patterns.

Summary of Invention:

The process disclosed here may thus be summarised as a process for bag formation which comprises the following steps: a. supplying a polymeric web material (1), optionally coated, and cutting it into piece (1 A) of suitable length; b. opening up the at least one end of said cut piece (1 A) to form hexagons, namely a first hexagon (10) and a second hexagon (10 A) at either open end of said cut piece (1A), said two hexagons (10 and 10A) having flaps (9) formed by folding of said open ends, and said second hexagon (10 A) having a first area (11) to receive outside surface (14) of a valve patch (4), and supplying and affixing the valve patch (4) onto said second hexagon (10A); c. folding said flaps (9) and forming block bottoms, namely a first block bottom (12) and a second block bottom (12A) at respective ends of said cut piece (1A), said block bottoms (12 and 12A) having a second area (11 A) to receive outside surface (14) of a cover sheet (4A); d. supplying and affixing coversheets to said block bottoms at said second area (llA).

The characterising element of the process arises from provision in each of said steps b and d, of a step of surface enhancement treatment and of a step of applying adhesives as affixing means to surfaces that are affixed or attached to each other. A further characterising aspect of the invention is in the form of a cooling roller (19A) which is also provided as a part of the apparatus following each of the sealing units (19). The cooling roller serves the dual purpose of cooling the sealed surfaces to bring them down to room temperature and also applying pressure to assist passage of the cut piece through the sealing unit (19) to the next station.

In order to carry out the aforementioned process, the invention also discloses an apparatus which has at least four stations: a first station (15), a second station (16), a third station (17), and a fourth station (18) to carry out steps a, b, c, and d, respectively, disclosed in the aforementioned process. The characterising element of the apparatus arises from the provision in each of said second, third, and fourth stations (16, 17 and 18), of a sealing unit (19) having at least one unit (3) for surface enhancement treatment and at least one adhesive applicator (8) for applying adhesives as affixing means to surfaces that are affixed to each other.

A further characterising aspect of the invention is in the form of a cooling roller (19A) which is also provided as a part of the apparatus following each of the sealing units (19). The cooling roller serves the dual purpose of cooling the sealed surfaces to bring them down to room temperature and also applying pressure to assist passage of the cut piece through the sealing unit (19) to the next station.

Brief Description Of Figures:

Figure 1 shows a schematic of the process of and apparatus for bag making Figures 2A, 2B and 2C show embodiments of the present invention Figure 3 shows a number of patterns in which adhesive may be applied

List Of Parts:

1. Web material. 1A. Cut piece of web material IB. Finished bag

2. Conveyor platform or table

3. Surface treatment unit

4. Valve patch or Cover sheet (4A)

5. Valve patch or coversheet primary delivery roller; 5 A secondary roller

6. Suction roller

7. Pressure roller

8. Adhesive applicator 8 A. Adhesive nozzle

9. Flap

10. First hexagon 10A. Second hexagon

11. First area 11 A. Second area

12. First block bottom 12A. Second block bottom 12B - comers of block bottom

13. Outside surface of block bottom 14. Outside area of valve patch or cover sheet

15. First station

16. Second station

17. Third station 18. Fourth station

19. Sealing unit

19 A. Sealing unit delivery rollers

20. Bag stacking unit/delivery unit Description Of The Invention:

The invention discloses a process of making a bag made of polymeric web materials (1) such as non-woven fabrics or woven fabrics consisting of monoaxially drawn tapes of polymer, in particular polyolefines, preferably polypropylene. Web material (1) may be optionally coated or laminated on one or both sides with thermoplastics, in particular polyolefine. The web material (1) may be either seamless tubular fabric or flat web seamed to form a tube, and wherein at least one end of the bag having in particular the shape of a box or right parallelepiped is formed by folding the fabric/web ends join together with adhesive to form a preferably rectangular bottom (or a block bottom) surface, as well as to a process for producing such a bag.

In order to produce a woven block shape bag from such web materials (1), the folded bottom is conventionally subjected to a thermal welding system. It is a complex operation for maintaining the required strength of bag and but by achieving a practically feasible but high production speed. To increase the production speed to above 120 to 150 bags per minute is a challenging task in terms of maintaining the required bag/seam strength and controlling uniform quality of production. Increasing the speed of thermal welding in order to increase the overall speed of bag manufacture could lead to increase in process temperature which cause further deterioration of fabric strength and its uniformity control at high speed.

The present invention discloses a bag production process and apparatus that uses application of adhesive onto the required bonding area of folded bottom for forming block shape bag. A person skilled in the art knows that polypropylene and polyethylene materials (which normally form the fabric) are difficult to bond firmly. Therefore, in another aspect of invention the surfaces to be bonded are subjected to pre-treatment using surface enhancement methods such as corona treatment, plasma treatment or similar thin-surface roughening treatment. The applicant has experimentally found that such pre-treatment surprisingly improves the bond strength considerably. For example, the bonding strength of joint made with web material without surface enhancing treatment was around 40 to 60% of original web/fabric strength. While, when the web material was pre-treated with surface enhancer, resultant bonding strength of joint was around 90 to 140% of original web/fabric strength, using the same adhesive and same quantity.

For the purpose of this disclosure, the terms surface enhancement treatment and pre-treatment are used synonymously.

In one aspect of the invention, the web material (1) used for making bag of present invention consists of woven fabric made from monoaxially drawn polyolefine tapes or non-woven polyolefine material or their combination. The tapes are produced from polyolefine sheets (or films) that are stretched to four to ten times their original length, whereby the molecular chains in the films’ longitudinal direction are oriented and thus attain strength in this direction which is about 6 to 10 times higher compared to the original sheet. Consequently, the tapes produced by slitting the stretched films also have a strength that is 6-10 times greater than the strength of the unstretched films. The slit film tape width is usually about 1.5 to 10 mm and has a thickness of 20-80 microns. When these tapes are woven to form fabric using circular or flat weaving looms, the fabric has uniform high tensile strength in the directions of warp and weft and also improved tear strength.

The web materials (1) can be optionally extrusion coated or laminated to achieve dust and moisture-proofness. Further, the coating layer may have the required non-skid surface for better stackability of bags manufactured from such fabric. Also, to enable filling of powdery material like cement in the block shape bag of present invention, the surface of the web material (1) or bag surface has small perforations, typically of nanometer to microns size, at required location for escape of air. In the case of filled material transported by airflow, such as cement, it may be appropriate to have an air venting system (such as perforations) in web material (1), such that entrapped air can escape after or during the filling operation. The perforations are of micrometer or nanometer size - that is the perforations are smaller than the particle size of the filled material. Thus the bags become leakproof for the stored materials but still allow air to escape.

The process and the apparatus of invention of making bag is shown schematically in Figure 1. It shows a piece of tubular web material (1) roll that has passed through series of feed rollers which take the web material (1) through several optional pre-cutting operations such as making perforation and spot holes, and inspecting the web material (1) surface for defect free portion (not shown). A suitable cutting device at a First station (15) cuts the continuously arriving web material (1) into cut-pieces (1A) of desired length. As the Figure 1 shows, the cut lengths (1A) of web material (1) are transferred onto the bag forming conveyer platform (2) with the help of suitable gripping and conveying elements (not shown). The cut piece (1A) is then passed through a Second station (16) where both cut ends of the cut piece (1A) are opened and folded to have preferably hexagonal shapes into a first and a second hexagon (10 and 10A), as per the required/predetermine size of the final bags. The terms hexagonal ends and hexagons are used synonymously in this description. The first and second hexagons (10 and 10 A) are finally converted into box shaped ends or block bottoms (12 and 12A) at one or both ends of the bag as desired. The flaps (9) of the first and second hexagons (10 and 10 A) are so folded that some part of them overlaps each other, and where the overlapping portions of the flaps (9) are joined together. In one embodiment of the invention, the surfaces of the flaps (9) that would face each other during the joining process are treated with surface enhancer treatment such as plasma treatment or corona treatment. Adhesives are applied to these areas using suitable adhesive applicator units (8), each having a nozzle (8A).

For joining the folded flaps (9) together, the cut piece (1A) with folded ends (12 and 12A) is passed through a sealing unit (19). The sealing unit may comprise two rollers - a suction roller (6) and a pressure roller (7) rotating around their axes in opposite directions such that the cut piece (1A) is pushed out of the slit or gap formed between the two rollers (6 and 7) while the rollers apply pressure on the cut piece (1A) passing through them. A separate sealing unit (19) is provided at either at one end both ends of the cut piece (1 A).

Once the basic hexagons (10 and 10A) as shown in part (b) of Figure 1 have been formed, they are folded further depending on whether a valve is required for filling the bag. In the case where a valve is provided, it is typically provided at one of the two ends of the bag. As shown in part (c) of Figure 1, a first area (11) of the second hexagon (10A) shown in part (b) is prepared at a second station (16) to receive a valve patch (4). As shown in Figure 1, the first area (11) is located straddling over the triangular part of second hexagon (10A) and the widest part of second hexagon (10A).

The pre-treatment comprises treating the first area (11) shown in Figure 1 (shaded area in part (c)) with surface enhancement treatment. Following the pre-treatment, adhesive is applied at least to the first area (11) at the second station (16). A valve patch (4) is also pre-treated and adhesive applied to the outside surface (14) of the valve patch (4) facing the first area (11) of the second hexagon (10A). As shown in part (d) of Figure 1, the valve patch (4) is then placed on the second hexagon (10A) such that it substantially covers the first area (11). Following this, at the second station (16) both hexagonal ends (10 and 10A) of the cut piece - the one with a valve patch (4) and one without - are folded to close the first and second hexagons (10 and 10A), such that there is an overlap between the flaps (9) of the hexagons (10 and 10A) after they are folded over. Adhesive is applied over the overlap area to the surfaces of the flaps (9) that face each other.

Following this step, at a third station (17), the folded ends are passed through a sealing unit (19) that has a set of suction and pressure rollers (6 and 7) so that first and second block bottoms (12 and 12 A) are formed at the respective hexagonal ends (10 and 10A) of the cut piece (1 A). Also at the third station (17), surface pre treatment is applied to the second area (11 A) of respective formed ends (12 and 12A) - indicated by hashed lines in part (f) of Figure 1. The second area (11A) is the area of the rectangle defined by four corners of first and second block bottoms (12 and 12 A).

Following this step, at a fourth station (18), a cover sheet (4A) is prepared by treating it with pre-treatment. Adhesive is applied to the outside surfaces (14) of the cover sheet (4A) and to the second area (11 A) of the block bottoms (12 and 12A). Coversheet is next placed on the pre-treated second area (11 A) of the block bottom and both block bottoms (12 and 12A) bearing cover sheets (4A) are passed through suction and pressure rollers (6, 7) of a sealing unit (19) to affix or seal the cover sheets to respective block bottoms (12 and 12 A). After the cover sheets (4A) have been applied to the block bottoms (12 and 12 A), the finished bag travels to a bag stacking/delivery unit (20) of any other suitable downstream processing station. The surface enhancer treatment according to the invention is provided using a surface enhancer treatment unit (3). A number of such surface enhancement units

(3) are provided at each sealing unit (19), which in turn are deployed at second, third and fourth stations (16, 17 and 18) of the apparatus of the invention. The surface enhancer treatment comprises treatment such as plasma or corona for activation of required area of the block bottom (12, 12A) on which the valve patch

(4) or a cover sheet (4) is pasted with help of suitable adhesive. Adhesives are applied using a suitable adhesive applicator (8) having a nozzle (8A).

As discussed in the foregoing paragraphs, the process of invention discloses a surface enhancement units (3) for web cut piece (1 A) where the cut piece (1 A) is treated using a surface enhancement treatment unit (3). It also discloses further surface enhancement units (3) for cover sheet (4 A) or valve patch (4) where the cover sheet (4A) or valve patches (4) are treated using the surface enhancement treatment units (3). It also discloses sealing units (19) for affixing two surfaces together, such as flaps (9) of the hexagons (10, 10 A), or cover sheet/valve patch (4 A/4) and the formed block bottoms (12, 12 A). These are illustrated schematically in Figures 2A, 2B, and 2C.

Figures 2A, 2B, and 2C show illustrate the parts of process where valve patches (4) and coversheets (4 A) along with first and second areas (11 and 11 A) are treated with surface enhancement treatment and passed through sealing units (19). These figures show web material (1) being delivered through a pair of primary and secondary delivery rollers (5 and 5A). The web material (1) is cut using a cutting device (not shown) into suitable pieces that work as valve patch or cover sheet (4 and 4A).

A separate sealing unit (19) is placed at second, third and fourth stations (16, 17 and 18) for the purpose of sealing together any two surfaces. Figures 2A, 2B, and 2C also show surface enhancer treatment units (3) that are provided in the process and sealing units (19) that comprise suction and pressure rollers (6 and 7) that are provided where necessary.

A separate sealing unit (19) is provided on the both end of web cut piece(lA)/bag where surface are to be sealed.

Wherever joining of surfaces is required, application of adhesives is also necessary. For that purpose, adhesive applicators (8) having nozzles (8 A) are provided. In any instances where adhesives need applying, they may be applied in continuous lines, or as dots, spots, or dashes, or in any other similar manner, as shown in Figure 2.

Figures 2A, 2B and 2C show alternative arrangements of the nozzle (8A). When two surfaces are joined together using adhesives, adhesives may be applied either to one of the two surfaces or both. For example, when two flaps (9) of each of the hexagons (10 and 10A) are joined together to form block bottoms (12, 12A) as shown in part (e) of Figure 1, only one of the two flaps (9) facing each other at each end of cut piece (1 A) may be applied with adhesives, or both of the flaps (9) at each end may be applied with adhesives. When a cover sheet (4A) is applied to the block bottom (12, 12A), either the cover sheet (4 A) or the surface of the block bottom (12, 12A), or both the coversheet (4A) and the block bottom (12, 12A) surface may be applied with adhesive.

Any one or both the surfaces that are joined together may be surface treated by surface enhancement treatment. For example, when a cover sheet (4A) is applied to the block bottom (12, 12A), the joining surface of either the cover sheet (4A) or the surface of block bottoms (12, 12A), or the joining surfaces of both the coversheet (4A) and the surfaces of block bottoms (12, 12A) may be applied treated with enhanced surface treatment. In the examples that are illustrated in Figures 2A, 2B, and 2C, a valve patch/coversheet (4/4A) is delivered using a set of primary and secondary delivery rollers (5, 5A) (only one set is show in in the figures, however, there can be more than one of these rollers), and a pair of suction and pressure rollers (6, 7).

With the help of a surface enhancer treatment unit (3), the valve patch (4) which is conveyed through the delivery system is also subject to surface activation treatment like corona or plasma, before it gets adhered to location (illustrated in parts (c) and (d) of Figure 1) on formed hexagonal shape of the cut piece (1A) of the web. The figure 2A shows a Valve patch/cover sheet (4/4A) conveying roller (5), which further has a cutting unit (not shown) and a still further surface enhancer treatment (or simply surface activation) unit (3). The surface activation unit (3), which delivers corona or plasma treatment, activates or treats the side surface of label/cover sheet which will be superimposed on the formed folded hexagonal shape of cut web length (1A).

With regards application of adhesive, the process of invention discloses a number of alternatives. Adhesive may be applied to any one of the two surfaces being joined together (as shown in Figures 2A and 2B), or to both surfaces (as shown in Figure 2C). Accordingly, as illustrated in Figure 2A, an adhesive applicator (8) having a nozzle (8A) (or optionally a roller instead of the nozzle) is provided to apply adhesive to the valve patch/coversheet (4/4A). Alternatively, as shown in Figure 2B, an adhesive applicator (8) having at least one nozzle (8A) is provided to apply adhesive to the required location (e.g. the block bottom) on the web cut piece (1 A). As a further alternative, as shown in Figure 2C, an adhesive applicator (8) having a nozzle (8A) is provided to apply adhesive to the valve patch/coversheet (4/4A) and to the required location (e.g. the block bottom) on the web cut piece (1A). As shown in these Figures 2A, 2B, and 2C, a further set of sealing unit delivery rollers (19A) that carry out cooling of the sealed surfaces are also provided. At least one cooling roller (19A) is provided at each stage as necessary. The cooling roller (19A) operates using suitable coolant like chilled water and brings the temperature of cooling roller (19A) below room temperature such that the sealed surfaces are cooled down.

Figures 2A, 2B, and 2C represent various stages of the bag making process disclosed in the invention. For this purpose, second, third and fourth stations (16, 17, and 18) are represented depending on which stage of the bag making process the cut piece is at any given time. For example, when the cut piece (1A) is at second station (16), the arrow representing the incoming cut piece shows that the cut piece is being delivered from the previous station (indicated by ‘Froml 5/16/17’). The figure also shows the specific station at which the cut piece is processed (indicated by ‘16/17/18), and at which sealing units (19) are provided. Finally, these figures also show the station to which the cut piece (1 A) travels next (indicated by ‘To 17/18/20’).

The adhesive applicators (8) are activated through an electronic control unit (not shown) for applying the adhesive/glue in required format and a predetermine quantity on to the folded surface of cut web, such that valve patch/cover sheet (4/4A) get pasted onto glued region. The control unit controls the amount of adhesive released and the rate (volume/minute) at which it is released. The pressure roller (7) and sealing unit delivery roller (19A) further facilitate the bonding of valve patch/cover sheet with the folded web structure, transforming the cut web length into block bottom bag. Optionally the delivery roller can be more than one and any one can be forced cooled. The process disclosed here may thus be summarised as a process for bag formation which comprises the following steps: a. supplying a polymeric web material (1), optionally coated, and cutting it into piece (1 A) of suitable length; b. opening up the ends of said cut piece (1A) to form hexagons, namely a first hexagon (10) and a second hexagon (10A) at either open end of said cut piece (1A), said two hexagons (10 and 10 A) having flaps (9) formed by folding of said open ends, and said second hexagon (10A) having a first area (11) to receive outside surface (14) of a valve patch (4), and supplying and affixing the valve patch (4) onto said second hexagon (10 A); c. folding said flaps (9) and forming block bottoms, namely a first block bottom (12) and a second block bottom (12A) at respective ends of said cut piece (1A), said block bottoms (12 and 12A) having a second area (11 A) to receive outside surface (14) of a cover sheet (4A); d. supplying and affixing coversheets to said block bottoms at said second area (llA).

The characterising element of the process arises from provision in each of said steps b and d, of a step of surface enhancement treatment and of a step of applying adhesives as affixing means to surfaces that are affixed or attached to each other.

Also, web material (1) is passed through any one or all pre-cutting operations such as making perforation and spot holes, and inspection of the web surface for defect free portion.

In order to carry out the aforementioned process, the invention also discloses an apparatus which is illustrated in Figure 1. It has at least four stations: a first station (15), a second station (16), a third station (17), and a fourth station (18) to carry out steps a, b, c, and d, respectively, disclosed in the aforementioned process. The characterising element of the apparatus arises from the provision in each of said second, third, and fourth stations (16, 17 and 18), of a sealing unit (19) having at least one unit (3) for surface enhancement treatment and at least one unit (8) for applying adhesives as affixing means to surfaces that are affixed to each other.

A further characterising aspect of the invention is in the form of a cooling roller (19A) which is also provided as a part of the apparatus following each of the sealing units (19). The cooling roller serves the dual purpose of cooling the sealed surfaces to bring them down to room temperature and also applying pressure to assist passage of the cut piece through the sealing unit (19) to the next station.

A number of other provisions are made in the apparatus of invention. The adhesive applicator (8) is capable of applying adhesive in a pattern selected from a group comprising dots or dashes, or lines which are either zigzag or straight, or any combination thereof. The sealing unit (19) is provided with a set of rollers comprising a suction roller (6) and a pressure roller (7) through the gap between which the said cut piece (1A) passes under pressure. For applying surface enhancement treatment with the surface enhancement treatment units (3), a number of different types of units may be selected depending on whether the chosen treatment is corona treatment, or plasma treatment or similar thin-surface roughening treatment. In the case, the chosen treatment is corona treatment, it is effected by passing said cut piece (1A) requiring corona treatment between an electrode and a metal plate in a corona treating unit (3). In the case the treatment is plasma treatment, it is effected by supplying energy in the form of radio frequency electromagnetic radiation to ionize a process gas which can be oxygen, nitrogen, argon, helium, or combinations thereof to produce a plasma of electrons, ions, and other energetic metastable species.

In the aforementioned process of bag making using the aforementioned apparatus, the web material (1) used was tubular. In another aspect of the invention, the process disclosed here may be used where the starting point is a flat web from which a tubular web would be made. In such scenario, a surface enhancer unit (3) would be used to treat the edges of the flat web, following which adhesive may be applied to the edge area of the flat web so that a tubular web may be formed by rolling up the flat web and overlapping the edge areas onto each other and passing the rolled up web through a set of pressure rollers.

The valve patch and/or coversheet (4/4A) is made same material as that of the bag or anyone of them could be alternatively made of material different from the fabric web material. The alternative material could be single ply of thermoplastic web material, or one can use composite or combination of coated or laminated with substrate like paper, fabric, printed or non-print film or non-woven web material.

The surface activation/enhancement system is applied for obtaining sufficient adhesion on polyolefine or polypropylene, especially pre-treatment of the web before the adhesion is applied. Its aim is to optimize the wetting and adhesion process. One method of accomplishing this result is to use a high frequency electric discharge towards the film surface, for example, corona treatment. The result is an improvement of the chemical bond (measured in dyne/cm) between the molecules in the plastic/polyolefme web and the applied adhesive/glue. The corona surface treatment does not reduce or change the strength of the web nor will it change the appearance of the web. Information for using corona Surface treatment on plastic film is found in many references including U.S. Pat. No. 7,074,476 which is incorporated by reference.

The effectiveness of the corona treatment depends on the specific film being used. There are no limits with regard to the materials that can be corona treated. However, the required intensity of treatment (watt/min/m ² ) may vary significantly. The treatment level can be calculated - the exact value is best determined by testing a sample of the actual web that is used for the specific application. The corona treatment can be effected by passing the web between an electrode and a metal plate in a corona treating unit (3). The electrode may have a width which corresponds to the width of the folded area/cover area so that only the required area of the web receives the treatment. The cut piece (1 A) may travel at a lengthwise direction through the corona treating unit (3). The amount of corona treatment received by the folded portion is determined by the length of the electrode, the traveling speed of the web between the electrode and the plate, and the amount of the electric potential generated between the electrode and plate.

Alternatively, the selective energy treatment surface activation may be selective plasma treatment. As described previously, in a typical plasma treating process, plasma is created by a supply energy in the form of radio frequency electromagnetic radiation to ionize a process gas which can be oxygen, nitrogen, argon, helium, or combinations thereof, to name a few. The plasma includes electrons, ions, and other energetic metastable species. The energies of individual plasma particles may range from about 3-20 electron Volts. When these energetic particles contact a surface in polyolefine web, the surface becomes energized via ionization, or chemical reaction which is typically oxidation.

The plasma may condition the substrate for receiving another material. In this instance, the substrate is a polymer, more specifically, a polyolefine polymer. The plasma treatment provides a better surface for sealing the polymer to another surface and enhances the ability of an adhesive to be retained on the polymer treated with the plasma treatment. The plasma treatment provides a secured bonding of the polymer and other materials. The plasma treatment uses only electricity and compressed air and can treat thermally sensitive materials. Thus, the plasma treatment can be readily applied to various areas of a continuous web or sheet of a polymer material that is subsequently formed into a bag. The polymeric web may also be combination of woven polymers, with non-woven polypropylene, and other materials, for example, an intermediate or extrusion layer of paper or aluminium sheet and an inner layer of material suitable for contracting the contents of the bag to be formed. The plasma treatment can be used at high speed on flat materials such as a web of polymers for forming bags. Further, the invention can intend that the valve patch and cover patch (4/4A) is bonded with surface of folded cut piece (1A) at required location wherein particularly a hot melt/glue connection or a cold glue connection exists. The hot glue/melt adhesive can comprise at least one of the following ingredients: basis polymer, resin, stabilizers, wax, nucleation means. Basis polymer may be selected from, for example, PA (polyamide), PE (polyethylene), APAO (amorphous polyalphaolefm), EVAC (ethylene vinyl acetate copolymers), TPE-E (thermoplastic polyester elastomers), TPE-U (thermoplastic polyurethane elastomers), TPE-A (thermoplastic copolyamide elastomers). As resin for example colophony and/or terpenes and/or hydrocarbon resins can be used.

According to the invention for the stabilizers for example antioxidants and/or metal deactivators and/or light stabilizers can be used. By using the hot glue the advantage results that different materials can be glued to one another. Further, unevenness of to be glued surfaces can be easily compensated.

An advantage during usage of cold glue is that high speeds of the machines can be achieved by the cold glue technique. Further, the cold glue can be applied relatively easily.

The adhesive/glue is applied onto the required substrate or predetermined area of moving web in a pattern as shown in Figure 3, including at least two spots or lines which extend transversely to each other, parallel to the direction of movement of substrate.

As per this invention the adhesive is applied in pattern which is parallel or perpendicular or their combination to the direction of substrate/web movement, by combination of operations. When the substrate web is moving below the orifice of the nozzle (8A) of the adhesive applicator (8), the adhesive is applied by extruding or hydraulically injected as per predetermined time burst in form of line or bead or whirling spray. Further, the adhesive flows out in at least the required quantity and remains in well-defined shape which maybe sharp line or beads.

The means for carrying out the adhesive application as per the invention includes a conveyor for moving the substrate through an adhesive-applying station, adhesive applying means including at least one nozzle (8A) or orifice provided to the adhesive applicator (8) located adjacent the path of movement of the substrate for depositing adhesive as a pattern parallel to the direction of substrate movement, thereby to form a required pattern. Timing means is provided for actuating this applicator (8) to operate for a period selected to provide a desired length of glue/adhesive. The timer may be pulsed or cycled so as to provide a bead-gap-bead pattern, i.e., a stitched or interrupted line. The adhesive applying means also includes a gun having a flat spray nozzle in the station for projecting adhesive as a transverse liquid sheet, directed in a plane angulated across the direction of substrate movement. Timing means is provided for actuating the adhesive orifice to operate for a period selected such that the adhesive from it will deposit as a pattern on the substrate having a width substantially less than its length. Various embodiments are shown in the Figure 3. Several patterns are shown in Figure 3 labelled as (a), (b), (c), (d), (e), and (f). Of these, patterns (b) and (c) have been found to be most effective in terms of bond strength resulting in around 1.2 to 1.5 times the fabric strength. Further, the patterns (d), (e) and (f) of Figure 3 showed adequate bonding strength with optimal usage of the adhesive measured in terms of amount of adhesive required per unit area which was around 3 to 7% lower than other patterns.

Thus, as per the invention described above it is possible to manufacture the block bottom bag made from polymeric web (1) using suitable adhesive at higher processing speed of 200 bags per minute. While in the illustrated embodiments of the invention the bag has in each case shown as being formed from single ply thermoplastic web material, it will be appreciated that one or more plies can be used without departing from scope of the invention. Further, it will also be appreciated that instead of single ply of thermoplastic web material, one can use composite or combination of coated or laminated with substrate like paper, fabric, film or non-woven web as web material (1) for bag forming.

Example: Using the process and apparatus disclosed, a block bottom bag of width 500 mm and length 600 mm was made from around 60 gsm woven polypropylene fabric, coated with 12 micron of polyolefine receipe, was sealed using generic hot melt glue, the glue spraying/application was around 10 to 12 g per square meter, showed bonding strength of around 68 to 72 kgf, at top and bottom end of block bottom bag, at production rate of around 160 to 180 bags/min.

There are a number of advantages of the invention. Some of these are listed here, however, other advantages would be apparent to a person skilled in the art. First, since there is no heat sealing involved, the coating layer thickness/linear weight on fabric can be reduced by 20 to 50% compare to heat seal block bottom bag. This results in a reduction in overall bag weight of 10 to 30% over the conventional bags, ultimately leading to a commercial advantage of around 5 to 15%. Further, as there is no external heating process involved during fabric conversion to bag, the conversion speed can be increased by 20 to 50% over heat seal block bottom conversion. Also, since polyolefins are basically hydrophobic, a person skilled in the art knows that it is essential to have surface activation for enhancing adherence of external substance like glues or adhesive, which was not possible hitherto. The system of invention allows this. Finally, the bond strength achieved using the system of present invention is around 0.75 to 1.8 times of fabric strength. While several different embodiments of the invention have been described, those persons skilled in the art will appreciate other changes and modifications that can be made without departing from the scope of the inventive claims.