CN114286791A

CN114286791A - Method and apparatus for bag forming

Info

Publication number: CN114286791A
Application number: CN202080059989.7A
Authority: CN
Inventors: 高雷夫·罗希亚
Original assignee: Lohia Corp Ltd
Current assignee: Lohia Corp Ltd
Priority date: 2019-08-24
Filing date: 2020-08-19
Publication date: 2022-04-05
Anticipated expiration: 2040-08-19
Also published as: EP4017808A1; EP4017808A4; CN114286791B; WO2021038387A1

Abstract

The present invention relates to a process and apparatus for making bags from polymeric web materials, particularly polyolefins, using adhesive bonding. It is well known that the hot air welding/sewing system used in such processes results in an undesirable and uncontrolled deterioration of the fabric strength. A process is disclosed in which surface enhancement techniques are used on the surfaces to be joined prior to joining the surfaces together by the use of an adhesive. The bag weight is reduced overall, production speed is increased, and joint bond strength is increased. The invention also discloses an apparatus having at least four stations: a first station (15), a second station (16), a third station (17) and a fourth station (18), wherein in each of said second (16), third (17) and fourth (18) stations a sealing unit (19) is provided, which sealing unit (19) has at least one unit (3) for surface enhancement treatment and at least one adhesive applicator (8) for applying adhesive as attachment means to surfaces to be attached to each other.

Description

Method and apparatus for bag forming

Technical Field

The present invention relates to a bag made of a polymeric web material, in particular a bag made of polyolefin bonded with an adhesive.

Background

Bulk materials are contained in various bags, which can be broadly classified as pillow-type and box-type or block-type. Pillow bags are typically made by sewing or sewing the bottom. The box-shaped or block-shaped form is made by folding and gluing the bottom. The box shape allows for optimal utilization of the material surface, good stackability and improved volume utilization due to its brick shape. There is also a quasi-box shape, one side is a pillow bag and the other side is a box bag.

Typically, the bags have a capacity of 10kg, 25kg, 100kg, 500kg and 1000 kg. Suitable materials include natural fiber fabrics (such as jute, paper), plastic sheets and fabrics, non-woven webs. Over the last decades, bags made of natural fiber fabrics have been replaced by bags made of paper and plastic sheets and fabrics, since these bags are cheaper and offer technical advantages. The paper has no moisture barrier or greater strength. For this reason, bags often comprise various paper layers, which increases the material consumption. Furthermore, paper bags are not suitable for storing most chemicals widely used in industry. However, it can be produced at low cost by using an inexpensive binder. Plastic sheets do not have high tear strength and therefore thicker materials are used. Further, the plastic sheet is dimensionally unstable and is sensitive to heat. Plastic sheet bags can be seam welded into pillows easily, but are not easily bonded into box or block shaped bags.

Woven plastic fabrics comprising uniaxially drawn tapes are of high strength and dimensionally stable, in particular coated woven plastic fabrics. The raw material requirements for a woven fabric made of stretched tapes are much lower for the same load-bearing capacity compared to unstretched plastic sheets. Bags made of plastic fabric are usually made in pillow shape with seams. A block-shaped bag of plastic fabric is made by using hot air welding/sewing techniques to form connections at the top and bottom sides, as known in the prior art from US 5845995. However, it is well known that hot air welding/sewing systems cause undesirable and uncontrolled deterioration of the fabric strength. The inability to control the process parameters of a hot air welding/sewing system results in uncontrolled variations in production quality. This results in a reduction in production speed.

Disclosure of Invention

The present invention provides an alternative bonding method for a polymer web/plastic woven fabric/web to form a block-shaped bag with sufficient joint quality at higher processing speeds than conventional systems.

The object of the present invention is to overcome the limitations of the traditional box-shaped pouch manufacturing process, in particular to create a pouch and a method for producing a pouch and a machine system for producing a pouch by means of which the pouch can be produced faster and easier. Further, the efficiency of producing the bag is improved.

It is another object of the present invention to provide a process for manufacturing bags that uses surface enhancement techniques and an efficient gluing pattern.

Accordingly, the process disclosed herein may be summarized as a process for bag forming, comprising the steps of:

a. supplying an optionally coated polymeric web material (1) and cutting it into pieces (1A) of suitable length;

b. opening at least one end of the cutter (1A) to form hexagons, a first hexagon (10) and a second hexagon (10A), at either open end of the cutter (1A), the two hexagons (10, 10A) having flaps (9) formed by folding the open end, and the second hexagon (10A) having a first area (11) to receive an outer surface (14) of a valve pad (4), and supplying and affixing the valve pad (4) onto the second hexagon (10A);

c. folding the flap (9) and forming a block bottom, a first block bottom (12) and a second block bottom (12A), at both ends of the cutting member (1A), the block bottoms (12 and 12A) having a second area (11A) to receive the outer surface of a cover sheet (4A);

d. cover sheets are supplied at the second area (11A) and affixed to the block bottom.

The characteristic elements of the process result from the step of providing a surface enhancing treatment in each of said steps b and d and the step of applying an adhesive as attachment means to the surfaces to be attached or attached to each other. Another characterizing aspect of the invention is the form of a cooling roller (19A), which cooling roller (19A) is also provided as part of the apparatus after each of the sealing units (19). The double function of the cooling rollers is to cool the sealing surface down to room temperature and also to apply pressure, helping the cut pieces to pass through the sealing unit (19) to the next station.

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

Another characterizing aspect of the invention is the form of a cooling roller (19A), which cooling roller (19A) is also provided as part of the apparatus after each of the sealing units (19). The double function of the cooling rollers is to cool the sealing surface to bring it to room temperature and also to apply pressure, helping the cut pieces to pass through the sealing unit (19) to the next station.

Drawings

Fig. 1 shows a schematic view of a process and apparatus for bag manufacturing.

Fig. 2A, 2B and 2C illustrate an embodiment of the present invention.

Fig. 3 shows a number of patterns in which adhesive may be applied.

List of parts:

1. a web material. A cut of web material. 1B finished product bag

2. Conveyor platforms or tables

3. Surface treatment unit

4. Valve pad or cover (4A)

5. A valve plate or cover plate main conveying roller; 5A. Secondary roller

6. Suction roll

7. Pressure roller

8. Adhesive applicator 8a adhesive nozzle

9. Wing panel

10. The first hexagon 10A. Second hexagon

11. A first region. 11A. second region

12. First block bottom 12A, second block bottom 12B-corner of block bottom

13. Outer surface of bottom of block

14. Outer region of valve pad or cover sheet

15. First station

16. Second station

17. Third station

18. Fourth station

19. Sealing unit

19a sealing unit transfer roller

20. Bag stacking/transfer unit

Detailed Description

The invention discloses a process for manufacturing bags made of a polymeric web material (1), such as a non-woven or woven fabric comprising uniaxially stretched tapes of a polymer, in particular a polyolefin, preferably polypropylene. The web material (1) can optionally be coated or laminated on one or both sides with a thermoplastic, in particular a polyolefin. The web material (1) may be a seamless tubular fabric or a flat web sewn to form a tube, and where at least one end of a bag, particularly having the shape of a box or a right parallelepiped, is made by folding the fabric/web ends together with an adhesive to form a preferably rectangular bottom (or block bottom) surface, and a process for producing such a bag.

To produce woven block-shaped bags from such a web material (1), the folded bottom is usually subjected to a thermal welding system. Maintaining the required strength of the bag in turn requires achieving a practical and high production speed, which is a complicated operation. Increasing production speeds to 120 to over 150 bags per minute is a challenging task in view of maintaining the required bag/stitch strength and controlling uniform production quality. Increasing the rate of thermal welding in order to increase the overall speed of bag manufacture may result in an increase in processing temperature, which leads to further deterioration in fabric strength and its uniformity control at high speeds.

A bag production process and apparatus is disclosed which uses adhesive applied to the desired adhesive areas at the bottom of the folds to form a block-shaped bag. Those skilled in the art know that polypropylene and polyethylene materials (typically formed into fabrics) are difficult to bond strongly. Thus, in another aspect of the invention, the surfaces to be bonded are pre-treated using a surface enhancement method, such as corona treatment, plasma treatment or similar thin surface roughening treatment. The applicant has found through experimentation that such a pre-treatment surprisingly greatly improves the bond strength. For example, the bond strength of joints made with web material that has not been surface enhanced is about 40% to 60% of the original web/fabric strength. Whereas when the web material is pretreated with a surface enhancing agent, the final bond strength of the joint is about 90% -140% of the original web/fabric strength using the same binder and the same amount.

For the purposes of this disclosure, the terms surface enhancement treatment and pretreatment are used synonymously.

In one aspect of the invention, the web material (1) used to make the bags of the invention comprises a woven or non-woven polyolefin material made from uniaxially stretched polyolefin tapes or a combination thereof. The tape is produced from a polyolefin sheet (or film) stretched to 4 times to 10 times its original length, whereby molecular chains in the longitudinal direction of the film are oriented to obtain a strength in that direction of about 6 times to 10 times that of the original sheet. Therefore, the tape produced by slitting the stretched film also has a strength 6 times to 10 times that of the unstretched film. Slit film tapes are typically about 1.5mm to 10mm wide and 20 microns to 80 microns thick. When these tapes are woven using a circular or flat loom to form a fabric, the fabric has uniformly high tensile strength in the warp and weft directions, and tear strength is also improved.

The web material (1) may optionally be extrusion coated or laminated to achieve dust and moisture protection. Furthermore, the coating may have a desired non-slip surface to achieve a better stackability of the bag made of such a fabric. Furthermore, in order to be able to fill the block-shaped bags of the invention with a powdery material like a binding agent, the surface of the web material (1) or the bag surface has small perforations, typically of nanometer to micrometer size, at the locations required for the air to escape. In case the filling material, such as binding agent, is transported by an air flow, it may be suitable to have a venting system, such as perforations, in the web material (1) so that air trapped after or during the filling operation can escape. The size of the perforations is micro-or nano-meter, that is, the perforation size is smaller than the particle size of the filler material. Thus, the bag becomes leak proof to the stored material, but still allows air to escape.

FIG. 1 schematically illustrates the bag-making process and apparatus of the present invention. It shows a roll of tubular web material (1), which has passed through a series of feed rollers that subject the web material (1) to several optional pre-cutting operations, such as perforation and spot holes, and inspect the surface of the web material (1) for non-defective portions (not shown). Suitable cutting devices at the first station (15) cut the web material (1) arriving continuously into cuts (1A) of the desired length. As shown in fig. 1, the cut length (1A) of web material (1) is transferred onto a bag-forming conveyor platform (2) with the aid of suitable gripping and conveying elements (not shown). The cut piece (1A) then passes through a second station (16), where at the second station (16) the two cut ends of the cut piece (1A) are opened and folded into a shape, preferably hexagonal, forming a first hexagon (10) and a second hexagon (10A) according to the desired/predetermined size of the final bag. The terms hexagonal end and hexagonal are used synonymously in this specification.

The first hexagon (10) and the second hexagon (10A) are finally converted into box-shaped end portions or block bottoms (12 and 12A) at one or both ends of the bag as required. The flaps (9) of the first hexagon (10) and the second hexagon (10A) are folded so that portions thereof overlap each other, and the overlapping portions of the flaps (9) are joined together. In one embodiment of the invention, the surfaces of the fins (9) facing each other in the joining process are treated with a surface enhancing agent treatment, such as a plasma treatment or a corona treatment. Adhesive is applied to these areas using suitable adhesive applicator units (8), each having a nozzle (8A).

In order to connect the folded flaps (9) together, the cutting member (1A) with the 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), the suction roller (6) and the pressure roller (7) rotating about their axes in opposite directions so that the cutting member (1A) is pushed away from the slit or gap formed between the two rollers (6 and 7) while the rollers exert pressure on the cutting member (1A) passing through the rollers. A separate sealing unit (19) is provided at one or both ends of the cutting member (1A).

Once the basic hexagons (10 and 10A) as shown in part (b) of fig. 1 are formed, they are further folded depending on whether a valve is required for filling the bag. Where a valve is provided, the valve is typically provided at one of the two ends of the bag. As shown in part (c) of fig. 1, the first region (11) of the second hexagon (10A) shown in part (b) is ready to receive the valve pad (4) at the second station (16). As shown in fig. 1, the first region (11) is positioned across the triangular portion of the second hexagon (10A) and the widest portion of the second hexagon (10A).

The pre-processing includes processing the first region (11) (the shaded region in section (c)) shown in fig. 1 with a surface enhancement process. After the pre-treatment, an adhesive is applied at least to the first region (11) at a second station (16). The valve pad (4) is also pre-treated and an adhesive is applied to the outer surface (14) of the valve pad (4) facing the first region (11) of the second hexagon (10A). As shown in part (d) of fig. 1, the valve pad (4) is then placed on the second hexagon (10A) such that it substantially covers the first region (11). Subsequently, at a second station (16), the two hexagonal ends (10 and 10A) of the cut piece-one with the valve pad (4) and one without the valve pad (4) -are folded to close the first hexagon (10) and the second hexagon (10A) so that there is an overlap between the flaps (9) of the hexagons (10 and 10A) after the flaps (9) are folded. Adhesive is applied to the surfaces of the flaps (9) facing each other on the overlapping area.

After this step, at a third station (17), the folded end passes through a sealing unit (19) having a set of suction (6) and pressure (7) rollers, so that the first (12) and second (12A) bottom pieces are formed at the respective hexagonal ends (10 and 10A) of the cut piece (1A). Furthermore, at the third station (17), a surface preparation is applied to the second zone (11A) of the respective shaped end (12 and 12A) -indicated by the broken line in part (f) of fig. 1. The second region (11A) is a rectangular region defined by four corners of the first block bottom (12) and the second block bottom (12A).

After this step, at a fourth station (18), the coverslip (4A) is prepared by pre-treating the coverslip (4A). Adhesive is applied to the outer surface (14) of the coversheet (4A) and to the second region (11A) of the tile base (12 and 12A). The cover sheet is next placed on the pre-treated second area (11A) of the block bottom and the two block bottoms (12 and 12A) carrying the cover sheet (4A) are passed over a suction roller (6) and a pressure roller (7) of a sealing unit (19) to affix or seal the cover sheet to the respective block bottoms (12 and 12A). After the flap (4A) has been applied to the block bottom (12 and 12A), the finished bag proceeds to the bag stacking/conveying unit (20) of any other suitable downstream processing station.

A surface enhancer treatment unit (3) is used to provide the surface enhancer treatment according to the present invention. A plurality of such surface enhancing units (3) is provided at each sealing unit (19), which surface enhancing units (3) are in turn arranged at the second station (16), the third station (17) and the fourth station (18) of the apparatus of the present invention. The surface enhancing agent treatment comprises a treatment, such as plasma or corona, for activating the desired area of the block bottom (12, 12A) to which the valve pad (4) or cover sheet (4) is affixed by means of a suitable adhesive. The adhesive is applied using a suitable adhesive applicator (8) having a nozzle (8A).

As discussed in the preceding paragraphs, the process of the present invention discloses a surface enhancing unit (3) for a web cutter (1A), wherein the cutter (1A) is treated using the surface enhancing treatment unit (3). A further surface enhancing unit (3) for the cover sheet (4A) or the valve pad (4) is also disclosed, wherein the cover sheet (4A) or the valve pad (4) is treated using the surface enhancing treatment unit (3). Also disclosed is a sealing unit (19) for attaching two surfaces together, such as a hexagonal (10, 10A) flap (9), or a cover/valve pad (4A/4) and a shaped block base (12, 12A). These are schematically illustrated in fig. 2A, 2B and 2C.

Fig. 2A, 2B and 2C show a part of the process in which the valve pad (4) and the cover sheet (4A) together with the first region (11) and the second region (11A) are treated with a surface enhancing treatment and passed through the sealing unit (19). These figures show that the web material (1) is conveyed by a pair of main conveyor rolls (5) and secondary conveyor rolls (5A). The web material (1) is cut into suitable pieces using a cutting device (not shown), which pieces serve as valve pads or cover sheets (4 and 4A).

Separate sealing units (19) are placed at the second station (16), the third station (17) and the fourth station (18) for the purpose of sealing any two surfaces together. Fig. 2A, 2B and 2C also show a surface-enhancing agent treatment unit (3) provided in the process, and a sealing unit (19) including a suction roll (6) and a pressure roll (7) provided as necessary.

Separate sealing units (19) are provided at both ends of the web cutter (1A)/bag, wherein the surfaces are to be sealed.

Application of adhesive is also necessary wherever a surface needs to be joined. For this purpose, an adhesive applicator (8) with a nozzle (8A) is provided. In any case where it is desired to apply the adhesive, they may be applied in a continuous line, or in dots, spots, dashes, or any other similar manner, as shown in FIG. 2.

Fig. 2A, 2B and 2C show an alternative arrangement of the nozzles (8A). When two surfaces are joined together using an adhesive, the adhesive may be applied to one or both of the surfaces. For example, as shown in part (e) of fig. 1, when the two flaps (9) of each of the hexagons (10 and 10A) are connected together to form the block bottom (12, 12A), only one of the two flaps (9) facing each other at each end of the cutter (1A) may be applied with adhesive, or both of the two flaps (9) at each end may be applied with adhesive. When the cover sheet (4A) is applied to the block bottom (12, 12A), the surface of the cover sheet (4A) or the block bottom (12, 12A), or the surfaces of the cover sheet (4A) and the block bottom (12, 12A) may be applied with an adhesive.

Either or both surfaces joined together may be surface treated by a surface enhancement treatment. For example, when the cover sheet (4A) is applied to the block bottom (12, 12A), the joining surface of the cover sheet (4A) or the surface of the block bottom (12, 12A), or both the joining surface of the cover sheets (4A) and the surface of the block bottom (12, 12A) may be treated with an enhanced surface treatment.

In the example illustrated in fig. 2A, 2B and 2C, the valve pad/flap (4/4a) is conveyed using one set of main conveying rollers (5) and secondary conveying rollers (5A) (only one set is shown in the figure, however, there may be more than one set of these rollers) and a pair of suction rollers (6) and pressure rollers (7).

The valve pad (4) conveyed through the conveying system is also subjected to a surface activation treatment, such as corona or plasma, with the aid of the surface enhancer treatment unit (3), before its position adhering to the shaped hexagonal shape of the cut piece (1A) of the web, as shown in parts (c) and (d) of fig. 1. Fig. 2A shows a valve pad/flap (4/4a) that feeds a roller (5) that further has a cutting unit (not shown) and a further surface enhancer treatment (or simply surface activation) unit (3). A conveyor corona or plasma treated surface activation unit (3) activates or treats the side surfaces of the labels/coversheets which will be superimposed on the formed folded hexagonal shape with the cut web length (1A).

The process of the present invention discloses many alternatives with respect to the application of the adhesive. The adhesive may be applied to either of the two surfaces that are joined together (as shown in fig. 2A and 2B), or to both surfaces (as shown in fig. 2C). Thus, as illustrated in fig. 2A, an adhesive applicator (8) having a nozzle (8A) (or alternatively, a roller in place of a nozzle) is provided to apply adhesive to the valve pad/flap (4/4 a). Alternatively, as shown in fig. 2B, an adhesive applicator (8) having at least one nozzle (8A) is provided to apply adhesive to a desired location (e.g., the bottom of a block) on the web cutter (1A). As another alternative, as shown in fig. 2C, an adhesive applicator (8) with a nozzle (8A) is provided to apply adhesive to the valve pad/flap (4/4a) and to the desired location (e.g., the bottom of the block) on the web cutter (1A).

As shown in these fig. 2A, 2B and 2C, another set of sealing unit conveying rollers (19A) that cool the sealing surface is also provided. If necessary, at least one cooling roller (19A) is provided at each stage. The cooling roller (19A) is operated with a suitable coolant, such as chilled water, and the temperature of the cooling roller (19A) is brought below room temperature so that the sealing surface is cooled.

Fig. 2A, 2B and 2C illustrate various stages of the bagging process disclosed herein. For this purpose, the second station (16), the third station (17) and the fourth station (18) are indicated according to which stage of the bag-making process the cutter is at any given time. For example, when the cut piece (1A) is at the second station (16), the arrow representing the input cut piece shows that the cut piece is being delivered from the previous station (indicated by 'from 15/16/17'). The figure also shows a specific station (denoted by' 16/17/18) for processing the cut pieces and providing the sealing unit (19). Finally, these figures also show the station to which the cutting member (1A) next travels (indicated with "to 17/18/20").

The adhesive applicator (8) is activated by an electronic control unit (not shown) for applying the required gauge and predetermined amount of adhesive/glue onto the folded surface of the cut web so that the valve pad/flap (4/4a) sticks to the gluing area. The control unit controls the amount and rate (volume/minute) of release of the binder.

The pressure roller (7) and sealing unit transfer rollers (19A) further promote adhesion of the valve pad/cover sheet to the folded web structure, converting the cut web length into bulk bottom pockets. Alternatively, there may be more than one transfer roll, and any one may be forcibly cooled.

Accordingly, the process disclosed herein may be summarized as a process for bag forming comprising the steps of:

b. opening the ends of the cutter (1A) to form hexagons, a first hexagon (10) and a second hexagon (10A), at either open end of the cutter (1A), the two hexagons (10 and 10A) having flaps (9) formed by folding the open end, and the second hexagon (10A) having a first area (11) to receive an outer surface (14) of a valve pad (4), and supplying and affixing the valve pad (4) onto the second hexagon (10A);

c. folding the flaps (9) and forming a block bottom, a first block bottom (12) and a second block bottom (12A), at the respective ends of the cut piece (1A), the block bottoms (12 and 12A) having a second area (11A) to receive the outer surface (14) of a cover sheet (4A);

The characteristic elements of the process result from the step of providing a surface enhancing treatment in each of said steps b and d and the step of applying an adhesive as attachment means to the surfaces to be attached or attached to each other.

Furthermore, the web material (1) is passed through any or all pre-cutting operations, such as perforating and spot-holing, and inspected for non-defective portions of the web surface.

To carry out the above process, the present invention also discloses an apparatus as exemplified in FIG. 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 perform steps a, b, c and d respectively, disclosed in the above process. The characterizing feature of the apparatus comes from providing a sealing unit (19) in each of said second (16), third (17) and fourth (18) stations, which sealing unit (19) has at least one unit (3) for surface-enhancing treatment and at least one unit (8) for applying adhesive as attachment means to surfaces to be attached to each other.

Another characterizing aspect of the invention is the form of a cooling roller (19A) which is also provided as part of the apparatus after each of the sealing units (19). The double function of the cooling rollers is to cool the sealing surface down to room temperature and also to apply pressure, helping the cut pieces to pass through the sealing unit (19) to the next station.

Many other configurations are made in the apparatus of the present invention. The adhesive applicator (8) is capable of applying adhesive in a pattern selected from the group consisting of dots or dashes, or zig-zag or straight lines, 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), the cutting member (1A) passing under pressure through a gap between the suction roller (6) and the pressure roller (7). In order to apply a surface enhancing treatment with the surface enhancing treatment unit (3), many different types of units may be selected depending on whether the selected treatment is a corona treatment, or a plasma treatment, or a similar thin surface roughening treatment. In this case, the selected treatment is a corona treatment, which is carried out by passing the cutting member (1A) requiring corona treatment between an electrode and a metal plate in a corona treatment unit (3). Where the process is a plasma process, this is carried out by supplying energy in the form of radio frequency electromagnetic radiation to ionize a process gas, which may be oxygen, nitrogen, argon, helium or combinations thereof, to produce a plasma of electrons, ions and other high energy metastable species.

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

The valve pad and/or flap (4/4A) are made of the same material as the bag, or either of them may alternatively be made of a material different from the fabric web material. The alternative material may be a single layer of thermoplastic web material, or one may use a composite material or a combination coated or laminated with a substrate such as paper, fabric, printed or non-printed film, or a non-woven web material.

The surface activation/enhancement system is applied to obtain sufficient adhesion on the polyolefin or polypropylene, in particular to pretreat the web before applying the adhesion. The aim is to optimize the wetting and adhesion process. One way to achieve this result is to apply a high frequency discharge, such as a corona treatment, towards the surface of the film. The result is an improvement in the chemical bonds (in dynes/cm) between the plastic/polyolefin web and the molecules in the applied adhesive/glue. The corona surface treatment does not reduce or change the strength of the web nor does it change the appearance of the web. Information for using corona surface treatments on plastic films can be found in a number of references, including U.S. patent No.7,074,476, which is incorporated herein by reference.

The effectiveness of the corona treatment depends on the particular film used. There is no limitation on the material that can be corona treated. However, the required treatment intensity (watts/min/square meter) may vary significantly. The treatment level can be calculated-the exact value can best be determined by testing the actual web sample for a particular application. The corona treatment may be carried out by passing the web between an electrode and a metal plate in a corona treatment unit (3). The width of the electrodes may correspond to the width of the fold/footprint so that only the desired area of the web receives treatment. The cutting member (1A) may travel in a longitudinal direction through the corona treatment unit (3). The amount of corona treatment received by the folded portion is determined by the length of the electrode, the speed of travel of the web between the electrode and the plate, and the amount of electrical potential generated between the electrode and the plate.

Alternatively, the selective energy treatment surface activation may be a selective plasma treatment. As previously mentioned, in a typical plasma treatment process, the plasma is generated from a supply energy in the form of radio frequency electromagnetic radiation to ionize a process gas, which may be, for example, oxygen, nitrogen, argon, helium, or a combination thereof. The plasma includes electrons, ions, and other high energy metastable species. The energy of the individual plasma particles may be in the range of about 3 ev to about 20 ev. When these energetic particles contact the surface of the polyolefin web, the surface is energized via ionization or a chemical reaction (usually oxidation).

The plasma may condition the substrate for receiving other materials. In this case, the substrate is a polymer, more specifically, a polyolefin polymer. Plasma treatment provides a better surface for sealing the polymer to other surfaces and enhances the ability of the adhesive to remain on the polymer treated with plasma. Plasma treatment provides strong adhesion of polymers and other materials. The plasma treatment uses only electricity and compressed air, and can treat heat-sensitive materials. Thus, plasma treatment can be readily applied to various regions of a continuous web or sheet of polymeric material that is subsequently formed into a bag. The polymeric web may also be a combination of woven polymer with non-woven polypropylene and other materials, such as an intermediate or extruded layer of paper or aluminium sheet and an inner layer of material suitable for shrinking the contents of the bag to be formed. Plasma treatment can be used at high speed on flat materials, such as polymeric webs used to form bags.

Further, the present invention may be intended to bond the valve pad and the cap pad (4/4a) to the surface of the folded cutter (1A) at a desired position, particularly where there is a hot/adhesive or cold adhesive bond. The hot melt adhesive/melt adhesive may include at least one of the following ingredients: base polymer, resin, stabilizer, wax, nucleating device. The base polymer may be selected from, for example, PA (polyamide), PE (polyethylene), APAO (amorphous polyalphaolefin), EVAC (ethylene vinyl acetate copolymer), TPE-E (thermoplastic polyester elastomer), TPE-U (thermoplastic polyurethane elastomer), TPE-A (thermoplastic copolyamide elastomer). For example, rosin and/or terpenes and/or hydrocarbon resins may be used as resins.

In accordance with the invention, stabilizers, for example antioxidants and/or metal deactivators and/or light stabilizers, may be used. By using a hot glue, the advantage is that different materials can be glued to each other. Further, unevenness of the surface to be glued can be easily compensated.

The advantage of using cold glue is that the cold glue technique allows high speed operation of the machine. Further, cold glue can be applied relatively easily.

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

According to the present invention, the adhesive is applied in a pattern parallel or perpendicular to the direction of substrate/web movement or a combination thereof by a combination of operations. The adhesive is applied by extrusion or hydraulic injection in the form of a line or bead or a rotating spray burst at a predetermined time as the substrate web moves under the orifice of a nozzle (8A) of the adhesive applicator (8). Further, the adhesive flows out in at least the desired amount and maintains a clear shape, which may be a sharp line or bead.

The device for applying adhesive according to the invention comprises a conveyor for moving the substrate through the adhesive application station, the adhesive application device comprising at least one nozzle (8A) or orifice provided to the adhesive applicator (8) adjacent to the path of movement of the substrate for depositing adhesive in a pattern parallel to the direction of movement of the substrate to form the desired pattern. Timing means are provided for actuating the applicator (8) for a selected period of time to provide a desired length of glue/adhesive. The timer may be pulsed or cycled to provide a bead-space-bead pattern, i.e., a stitched or discontinuous thread. The adhesive application device also includes a gun having a flat spray nozzle in a station for spraying adhesive as a transverse liquid sheet directed at a plane at an angle to the direction of substrate movement. A timing device is provided for actuating the adhesive orifices to operate for a selected period of time such that adhesive from the adhesive orifices will be deposited as a pattern on the substrate with a width substantially less than its length. Various embodiments are shown in fig. 3. Fig. 3 shows several patterns, labeled (a), (b), (c), (d), (e), and (f). Among them, the patterns (b) and (c) have been found to be most effective in terms of adhesive strength, resulting in about 1.2 to 1.5 times the strength of the fabric. Further, patterns (d), (e) and (f) in fig. 3 show sufficient adhesive strength, the optimum use of the adhesive is about 3% to 7% lower than other patterns, measured as the amount of adhesive required per unit area.

Thus, according to the above invention, bulk-bottom bags made from a polymer web (1) can be made at a relatively high processing speed of 200 bags per minute using a suitable adhesive. Although in the exemplified embodiments of the invention the bag is in each case shown as being formed from a single layer of thermoplastic web material, it will be appreciated that one or more layers may be used without departing from the scope of the invention. Further, it is also understood that instead of a single layer of thermoplastic web material one may use a composite material or a combination coated or laminated from a substrate such as paper, fabric, film or non-woven web as the web material (1) for bag formation.

Example (c): using the disclosed process and apparatus, a bottom block bag of 500mm width and 600mm length was made from about 60gsm woven polypropylene fabric, coated with 12 micron polyolefin receiver, sealed using a common hot melt adhesive, sprayed with glue/applied at about 10 to 12 grams per square meter, showed an adhesive strength of about 68 to 72kgf at the top and bottom ends of the bottom block bag, and produced at a rate of about 160 to 180 bags per minute.

The present invention has many advantages. Some of which are listed here, however, other advantages will be apparent to those skilled in the art. First, since no heat sealing is involved, the coating thickness/linear weight on the fabric can be reduced by 20% to 50% compared to heat sealing the block bottom bag. This results in a 10% to 30% reduction in the overall weight of the bag over conventional bags, ultimately resulting in a commercial advantage of about 5% to 15%. Further, since no external heating process is involved during the conversion of the fabric into bags, the conversion rate can be increased by 20% to 50% over the heat seal block bottom conversion. Furthermore, since polyolefins are substantially hydrophobic, the skilled person knows that surface activation has to be carried out to enhance the adhesion of foreign substances such as glues or adhesives, which has not been possible so far. The system of the present invention allows this. Finally, the bond strength achieved using the system of the present invention is about 0.75 to 1.8 times the strength of the fabric.

Although several different embodiments of the present invention have been described, those skilled in the art will appreciate that other changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A process for bag forming, the process comprising the steps of:

a. supplying a tubular polymeric web material and cutting it into suitable length of cutting members (1A);

b. opening the ends of the cutter (1A) to form hexagons, a first hexagon (10) and a second hexagon (10A), at either open end of the cutter (1A), the two hexagons (10, 10A) having flaps (9) formed by folding the open end, and the second hexagon (10A) having a first area (11) to receive the outer surface of a valve pad (4), and supplying and affixing the valve pad (4) onto the second hexagon (10A);

d. -supplying and affixing the cover sheet (4A) to the sheet bottom (12 and 12A) at the second area (11A);

characterized in that it is introduced in each of said steps b and d that the step of applying a surface enhancing treatment to said first and second areas (11, 11A) and to the outer surface (14) of said valve pad (4) and said cover sheet (4A) and the step of applying adhesive as affixing means to said first and second areas (11, 11A) and to the outer surface (14) of said valve pad (4) and said cover sheet (4A).

2. The process of claim 1, wherein the first region (11) is positioned across a triangular portion of the second hexagon (10A) and a widest portion of the second hexagon (10A), and the second region (11A) is a rectangular region defined by four corners of the first block bottom (12) and the second block bottom (12A).

3. A process according to claim 2, wherein the step of surface enhancing treatment comprises the step of providing at least one surface enhancing treatment unit (3) capable of providing corona treatment, or plasma treatment or similar thin surface roughening treatment.

4. Process according to claim 3, wherein the surface-enhancing treatment unit (3) is provided at the stage of forming the bottom of the block, wherein the surface-enhancing treatment unit (3) treats those regions of the flaps (9) of the hexagon (10, 10A) formed at the ends of the cut (1A), which regions of the flaps (9) overlap each other after folding the flaps (9) of the hexagon (10, 10A).

5. Process according to claims 3 and 4, wherein the surface-enhancing treatment unit (3) is provided to treat the first area (11) before folding the flaps (9) to form the block bottoms (12 and 12A).

6. Process according to claims 3 to 5, wherein said at least one surface enhancing treatment unit (3) is provided to treat the outer surface (14) of said valve pad (4) or said cover sheet (4A).

7. Process according to claims 3 to 6, wherein said at least one surface enhancing treatment unit (3) is provided to treat the outer surface of the block bottom (12, 12A) to which the cover sheet (4A) is affixed.

8. Process according to claims 1 to 7, wherein the predetermined adhesion areas comprise the overlapping areas of the flaps (9), the outer surface of the block bottom (12, 12A) formed and the outer surface of the valve pad/flap (4/4A).

9. Process according to claims 1 to 8, wherein the actual affixing in step b and step d is performed in separate sealing units (19), said sealing units (19) being provided in each of said steps b and d and at each end of the cut piece (1A).

10. A process as claimed in claim 9, wherein the sealing unit comprises a set of rollers comprising a suction roller (6) and a pressure roller (7), the cutting member (1A) passing under pressure through a gap between the suction roller (6) and the pressure roller (7).

11. Process according to claims 1 to 10, wherein the adhesive is applied by an adhesive applicator (8), the adhesive applicator (8) being provided in each of the steps b and d.

12. Process according to claim 11, wherein the adhesive applicator (8) is provided with at least one nozzle (8A), said nozzle (8A) being capable of discharging adhesive at a desired rate (ml/min) and in a desired pattern, such as dots or dashes, or zigzags or straight lines, or any combination thereof.

13. The process according to claims 1 to 12, wherein the binder comprises at least one of the following components: base polymer, resin, stabilizer, wax, nucleating device.

14. The process according to claims 1 to 13, wherein the base polymer is selected from the group comprising polyamides, polyethylene, amorphous poly-alpha-olefins, ethylene vinyl acetate copolymers, thermoplastic polyester elastomers, thermoplastic polyurethane elastomers and thermoplastic copolyamide elastomers.

15. The process according to claims 1 to 14, wherein the resin is selected from the group comprising rosin, terpenes and hydrocarbon resin compounds.

16. A process according to claims 1 to 15 wherein the corona treatment is carried out by passing the cut piece requiring corona treatment between an electrode and a metal plate in a corona treatment station to ensure that only the required area of the cut piece is subjected to the corona treatment.

17. The process of claims 1 to 15, wherein said plasma treatment is carried out 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 high energy metastable species.

18. The process according to claims 1 to 17, wherein in step 'a' of claim 1, the web material (1) can be a flat fabric, which is converted into a tubular web before being cut into pieces of suitable length for further processing according to said step 'b'.

19. The process of claims 1 to 18, wherein the adhesive can be a hot or cold melt adhesive.

20. Process according to claims 1 to 19, wherein at least one cooling roller (19A) cools the sealing surface of the cut pieces (1A) coming out of the sealing unit (19).

21. The process according to claims 1 to 20, wherein the polymeric web material (1) is pre-coated or laminated on one or both sides with a thermoplastic, in particular a polyolefin.

22. An apparatus for bag forming, the apparatus comprising:

-a first station (15) for supplying the web material (1) and cutting it into suitable lengths of cutting members (1A);

-a second station (16) to open the ends of the cutting member (1A) to form a first hexagon (10) and a second hexagon (10A) at the respective ends of the cutting member (1A), the hexagons (10, 10A) having flaps (9), and to supply a valve pad (4) and to affix the valve pad (4) onto the second hexagon (10A);

-a third station (17) for folding the flaps (9) and forming a first bottom (12) and a second bottom (12A) at the respective ends of the cut piece (1A);

-a fourth station (18) for supplying cover sheets (4A) and affixing said cover sheets (4A) to said block bases (12, 12A) at predetermined positions;

characterized in that in each of said second station (16), said third station (17) and said fourth station (18) there is provided (i) at least one surface enhancing treatment unit (3) for applying a surface enhancing treatment to said cutter (1), said valve pad (4) and said cover sheet (4A), and (ii) a separate sealing unit (19) provided for each end of said cutter (1A), said sealing unit (19) comprising at least one adhesive applicator (8) for applying adhesive as affixing means to the first area (11) and the second area (11A) and to the outer surface (14) of said valve pad (4) and said cover sheet (4A).

23. The apparatus of claim 22, wherein the adhesive applicator (8) is capable of applying adhesive in a pattern selected from the group consisting of dots or dashes, or zigzags or straight lines, or any combination thereof.

24. Apparatus according to claims 22 and 23, wherein at least one cooling roller (19A) is provided to cool the sealing area of a cover sheet (4A) coming out of the sealing unit (19).

25. Apparatus according to claims 22 to 24, wherein said sealing unit comprises a set of rollers comprising a suction roller (6) and a pressure roller (7), said cutting member (1A) passing under pressure through a gap between said suction roller (6) and said pressure roller (7).

26. The apparatus according to claims 22 to 25, wherein the surface enhancing treatment unit (3) is a corona treatment, or a plasma treatment or a similar thin surface roughening treatment.

27. Apparatus according to claim 26, wherein the corona treatment is carried out by passing the cutting member (1A) requiring corona treatment between an electrode and a metal sheet in a corona treatment station.

28. The apparatus of claim 26, wherein said plasma treatment of said cutting element (1A) is carried out 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 high energy metastable species.

29. The apparatus according to claims 22-28, wherein said adhesive applicator (8) is activated by an electronic control unit for applying adhesive/glue in a desired pattern and in predetermined amounts and rates (ml/min).