Thermoplastic bag.

Thermoplastic transport bag

The invention relates to a thermoplastic transport bag having a front wall and a back wall, wherein at least one of said walls comprises a plurality of layers, the perforations of the adjacent layers being offset relative to each other, and such being used for packaging fine powders.

Plastic bags are suitable for packaging, transporting and storing a wide variety of products when the products are in the form of granules, beads or pellets. However, there are many products, such as cement, clays, powdered coal, and pigments that cannot be easily packaged in plastic bags because plastic films are unable to act as filters to release air that has trapped inside the package during a rapid filling operation. Plastic bags are known which have directly through-holes in the walls to allow the necessary air to escape. However, this can lead to widespread environmental contamination and / or loss of the product from the packaging. This means that for powdered products with a particle size of 10 micrometers or less, it has generally been resorted to use paper or paper-like packaging materials as generally acceptable finished packages. Paper bags are commonly used in these applications so that the inner layer of paper allows the necessary filtration operation. However, the use of such packaging materials limits the end use of these packaged goods in many ways.

One disadvantage is that paper bags are extremely sensitive to the extreme conditions of the environment and require special care in high humidity or low temperature. Contamination of the paper fiber can also occur when the contents of the package are emptied into sensitive chemical mixtures. Further, when the environmental safety in the workplace has been the subject of growing concern, there is a growing need for packaging which can be added and thermally or mechanically dispersed into industrial processes. Multi-walled paper bags, and to some extent plastic bags using contaminating adhesives, are generally unsuitable, especially in the plastics and rubber industries.

One of these problems can be overcome by using a plastic bag made by spinning bonded plastic from thermoplastic fibers in the form of a compressed mat, such as TYVEK (trademark), which has high strength properties and at the same time air permeable properties of the paper. Alternatively, the same results are obtained with a plastic film bag lined with paper. However, these sacks have the disadvantage of high cost and, like paper sacks, their additional disadvantage is that they are unsuitable for use in applications when both the sack and the product are thrown into rubber or plastic mixtures and the sack is expected to mix and become part of the final product.

In addition, a particularly useful bag known as a valve bag is known, which is commonly used for packaging granular materials such as fertilizers and polymeric resins. One such implementation is described in our U.S. Patent 3,833,166. An important commercial advantage of these bags is that they are easy to fill through the valve structure, and this valve structure closes on its own after filling. When filled and stored with the valve down or in the closed position, the efficiency of the valve is so good that it is difficult to get the incoming air out of the sacks. To avoid this problem, it is common practice to place a row of about 10 holes 0.6 mm in diameter down on each side of the sack to allow air to escape. This is a good solution for large-grained products, but for the finest materials with a particle size of less than 100 micrometers, this practice is not satisfactory because the product can easily leak out through the holes. This disadvantage can be somewhat overcome by placing the inner perforated layers in the bag apart from the outer layers and trapping the escaping material between the inner and outer layers of the bag when air can easily escape.

Using this system of discrete perforations, typically with perforations at 2.5 cm intervals around the entire bag, a product with a particle size of 1.0 micrometer can be packaged. However, with powders with smaller particle sizes, the product flows into these holes and forms plugs that prevent air from flowing.

It is an object of the present invention to obviate the problems described above. This object is achieved by a transport bag according to the invention, which is characterized in that this wall is bounded by a thermoplastic porous mesh with a pore size equal to or less than 1.0 mm and a pore density of at least 5 pores / cm², whereby the net forms an inner lining retaining the powdery product in the bag. This inner liner allows adequate filtration and air release during and after the filling operation.

The invention can be applied, for example, to a conventional top-open sack.

The usability of the top open sack is due to the fact that the sack can be filled so that the upper inner parts of the opposite sides of the net lining and its opposite wall are substantially in contact with each other or with the filling tube of the powder feeder. The entrained air can then exit through the thermoplastic network during the filling operation, but mainly when the bag is closed, and thus less product is lost.

The invention has a special use in a valve bag, in which case the rear wall and the front wall are connected together along all the edges of the bag, whereby a filling opening is formed in one wall to provide a valve bag.

Preferably, the back wall And the front wall are joined together along all edges of the sack, the front wall comprising a first strip and a second strip having a common width greater than the width of the back wall, and the first strip at least partially overlapping the second strip along the entire length of the sack; together along the line, substantially parallel to and spaced apart from the other end of the bag, thereby forming a self-closing filling tube having inner and outer walls extending transversely to the bag adjacent its second end, and the first strip forming the outer wall of the filling tube and the second strip also forming the inner wall of the filling tube; joined together along at least one line running from the former line to the substantially opposite end of the bag, the second strip consists of at least two layers of different sizes so that at least the inner main part of the inner wall of the filling tube consists of layers whose number is less than the total number of layers in the second strip.

The inner liner comprising the thermoplastic mesh is preferably connected to the perforated wall at the edge of the wall. However, this inner liner can be joined with intermediate fasteners, spot welds or adhesives at other selected points in the area of ​​the perforated wall area.

It can be easily seen that the advantages of the valve bag according to the invention are that the incoming air can escape through the inner liner net and pass through the perforated wall into the atmosphere instead of the filling pipe when the bag is filled and most importantly when the valve closes on its own, and the air is still in the bag.

The term thermoplastic, as used herein, refers to any polymeric material that repeatedly softens upon heating and cures upon cooling, and that can form a film, layer, or mesh of a thickness and strength suitable for transport bags. Thermoplastics of polyethylene and polybutadiene polymers have a special use. Examples which may be mentioned are high density, low density, linear low density polyethylene, ethylene-vinyl acetate copolymers and 1,2-polybutadienes.

The term mesh refers to an air-porous film or layer having pores that form discrete regular or irregular openings arranged in the shape of a mesh or screen. The mesh can generally be formed by perforating a hot thermoplastic film or by weaving a thermoplastic wire.

It is readily acceptable that the pore size selected for use in the practice of the invention depends on the particle size of the powdered product for which the bag is used and that one skilled in the art includes a porous liner suitable for a particular product to be easily selected and manufactured. The pores are of a suitable size to cause the retention of substantially all of a particular powdery product and to allow the release of incoming air. In general, the pore size is 0.1 to 1.0 mm in diameter. Pore ​​density of at least 5 pores / cm² the density is essential, preferably 25 pores / cm², and more preferably 300 pores / cm².

When the pore density (number of pores / cm²) increases, the pore size decreases to the desired lower level. However, provided that the pore size is not the size of a particular powdery product causing clogging of the pores, pore sizes of less than 0.1 mm may be used.

It has been found that the improvement in air filtration that occurs as the pore density increases is much greater than would be expected if it were simply due to an increase in the number of pores. As the pore density increases so that the adjacent pores become closer to each other, the pyramidal occlusion formation is apparently reduced by the turbulence of the air currents through the adjacent pores of the network.

Depending on the intensity of aeration of the product of the material to be bagged, the thermoplastic mesh may form the entire inner liner or only a portion thereof. Preferably, in order to accelerate the release of air, it forms the entire inner liner.

In general, the sack according to the invention comprises a simple inner lining comprising a net only on one side of the sack. However, it can be easily seen that both walls of the sack can be perforated and connected to a corresponding inner liner. However, when the valve inserts according to the invention have a mesh lining connected to the front wall of the sack, it is necessary that this lining is connected to the front wall so as not to prevent the powdered product from entering the sack, i.e. it must allow entry into the space between the rear wall and the inner mesh lining. This can be achieved, for example, by connecting the liner to the front wall under the filling pipe.

When both the front and rear walls can be perforated, provided that the wall to which the inner mesh liner is connected is perforated, this is generally sufficient to cause the release of air. The holes may be in the form of holes and / or slits, and the desired number, shapes, distributions and sizes of holes are determined by the strength and thickness of the heavy film, and the amount of air released, but should not be detrimental to the strength of the bag. Optionally, the wall further consists of two heavy layers which are torn together and then separated and moved so that the perforations of each layer are spaced apart from each other at a predetermined distance. Such an arrangement helps to prevent the ingress of moisture.

It is to be understood that the principles of the invention are also applicable to the formation of sacks whose sack walls comprise more than one layer, e.g., two layers, three layers, four layers, etc. In general, however, the back and front walls have the same number of layers, preferably two layers. An important feature is that, in addition, one or both walls must also have an internal mesh lining attached to it.

It is to be understood that the term inner liner as used herein is not limited to a liner adjacent to and in contact with a powdered product when the sack is full, but also includes a liner comprising a thermoplastic mesh separable from the product by an interposed layer interposed therebetween.

Accordingly, the scope of the present invention also includes a bag, as previously described, provided with an inner perforated film or layer comprising the actual inner layer of the bag and in contact with the powder product and allowing air and fine powder to escape through the holes before this air and the fine powder contacts the inner liner comprising a thermoplastic mesh.

It is not necessary that all the layers and the inner mesh lining of the sack be made of the same material. In the case of a two-layer sack, it may be advantageous to make the inner layer of the perforated wall and the inner mesh lining of a plastic material that melts at a different temperature than the plastic material of the outer layers. Such bags are particularly useful in applications in which materials such as crystalline or powdered chemicals or pigments are packaged when hot.

Three sack embodiments of the present invention will now be described in more detail by way of example with reference to the drawings, in which:

Fig. 1 shows a top view of a first embodiment of a valve bag according to the invention;

Fig. 2 is a sectional view taken along line II-II of Fig. 1;

Figure 3 shows a top view of another preferred valve bag according to the invention;

Fig. 4 is a cross-sectional view taken along line IV-IV of Fig. 3;

Fig. 5 is a top plan view of a third embodiment of a top open bag according to the invention; and Figure 6 is a cross-section along the line VI-VI in Figure 6.

Figures 1 and 2 show a substantially rectangular cushion-shaped sack 10 made of a thick (0.15 mm) polyethylene film with a single-layer back wall 11 and a front wall made of first and second partially overlapping panels 12 and 13. The wall 11 has a plurality of perforations forming holes 23 in diameter 23 at 2.5 cm intervals over the entire wall area. As shown, the first panel 12 is single-layered, while the second panel 13 has two layers 16 and 17. The panel 12 and the outer layer 17 of the panel 13 coincide with the back wall 11 and thus form a flat single-layer tube with the back wall closed at each end by transverse fasteners 14 and 15. The panel 13 is in an overlapping area below the panel 12, and the free edge of its inner layer 16, which is a strip of film extending the entire length of the sack and somewhat wider than the layer 17, protrudes somewhat above the free edge of the outer layer 17. Fastener 18 connects panel 13 to panel 12 of each layer, and fastener 19 connects panel 13 protruding portion of layer 16 of panel 13 to panel 12. The part left unattached in the common overlapping area at the upper end of the bag forms a tubular valve tube suitable for the installation of the filling tube. The upper end of the fasteners 18 and 19 with the point locks 20 outlines the valve tube. When the bag is filled, the protruding part of the inner layer 16 of the panel 13 acts as a sealing strip for the valve.

Also congruent with the rear wall 11, its inner edge has an inner polyethylene mesh 24 with a thickness of 1.25 mm and a pore density of 300 pores / cm² and a pore size of 0.2 mm in diameter (formed from VISPORE * film, ethylene-vinyl acetate (2%) copolymer, melt index 0.3, Ethyl Corporation). (* trademark ).

Figures 3 and 4 again show a generally rectangular cushion-shaped sack 10 made of 0.08 mm polyethylene film. It has a two-layer back wall 21, each layer of which has a plurality of holes 23 with a diameter of 0.6 mm at intervals of 2.5 cm over the entire width and surface area. The order of the holes in one layer is at a different point than the arrangement of the holes in the outer layer. The back wall 21 at the inner edge of its innermost layer is integral with the inner polyethylene mesh 24, which is 1.25 mm thick (VISPORE film).

The bag 10 also has a front wall made of two-layer 0.08 mm polyethylene, partially overlapping panels 22 and 13. The panels 22 and 13 are congruent with the back wall 21 and thus form a flat two-layer tube with the back wall closed at both ends by opposite 14 and 15. The panel 13 is in an overlapping area below the panel 22, and the free edge 16 of its inner layer protrudes somewhat above the free edge of its outer layer 17. The fastener connects the panel 22 of each panel 13 to the two layers and the fastener 19 connects the protruding portion of the panel 13 to the layer 16 to the two layers of the panel 22. The part left unattached in the overlapping common area at the upper end of the bag forms a valve pipe suitable for the installation of the filling pipe. The upper ends of the lock 18 and 19, together with the point fixings 20, outline the valve tube. When the bag is filled, the protruding end of the inner layer 16 of the panel 13 acts as a sealing strip for the valve.

Although in the specific embodiments of the invention illustrated in Figures 1-4, the valve tube end is shown to be formed from the protruding portion of the inner layer 16 of the panel 13, it should be understood that it may alternatively be formed from the outer layer 17 protruding above the edge of the inner layer 16. That is, either of the layers 16 and 17 may protrude above the other edge and form a valve closure strip. The lock 19, although not essential, prevents the contents of the filled sack from entering the space between the panels from which it would not be easy to empty. The point locks 20 can be replaced by a continuous attachment extending substantially parallel to the opposite attachment 14 from the upper end of the attachment 18 to the inner edge of the layer 16.

Although the drawings, each bag valve opening is shown as being located near the second side of the bag, it is to be understood that it may be located adjacent to any of the sack upper mounting, provided that sufficient space is left between the inside of the mouth and the bag side, which is opposite, relatively long filling tube installation to allow and for freeing the filling material therefrom. In general, it is preferred to arrange the front panels so that the valve opening is located in the second transverse half of the bag and the valve tube extends to or towards the second transverse half. The width of the wider front panel does not significantly exceed, and is preferably less than, the width of the back wall.

It is preferred that the longitudinal attachments 18 and 19 between the front panels do not intersect with the opposite attachment 15 at the bottom of the bag. Transverse travel could lead to a weakening of the final attachment at the intersections and a weakening of the bottom of the sack.

The sacks are preferably made of a thermoplastic tubular film of suitable width. Preferably, the plastic film is easily heat-sealable, or has a heat-sealable cover. Low density polyethylene film is particularly suitable due to its inherent thermal adhesion, strength and low cost.

The sacks according to the invention can be suitably constructed by contacting a sheet of thermoplastic mesh as an inner liner with a suitably perforated film of perforated size to produce a 2-layer structure, and then folding in opposite ends of the film lengths so that the mesh component is on top of each other. The heat-sealing of the overlapping portions and the mesh lining film along the length of the overlapping area and opposite the open ends of the bent film forms a sack.

By using analogous methods, but by fastening the overlapping edges of the plates along their entire length and making only a simple opposite closure, a simple access to an open sack can be formed. Such a sack is shown in Figures 5 and 6, in which a generally rectangular cushion-shaped sack 10 made of a thick (0.08 mm) polyethylene film comprises a single-layer back wall 31 and a single-layer front wall 32. The back wall 31 is perforated with a plurality of 0.6 mm diameter holes 23 at 2.5 cm intervals over the entire surface area and is connected at its edge to an inner polyethylene retina 24 having a pore density of 300 pores / cm².

In the case of a self-closing bag, part of the overlapping area is left unattached, forming a valve opening, and a second mating is made at the opposite end of the bag.

The preferred method of making the valve bag of the invention is described in U.S. Patent 3,812,769, suitably modified such that a sheet of thermoplastic mesh film is fed together with a large film to the weaving machine described therein. It is advantageous to connect the thermoplastic mesh and the thick films as the latter passes from the moving parts to the folding and bagging point, for reasons which are obvious to those skilled in the art. However, this modification can also be suitably made at the point where the thick film passes its manufacturing point, or by separate machines suitably designed for suitable hot air attachment steps and for drawing plastic films from rolls rotating freely to a point where the film can be collected again.

The sacks may be formed of one or more layers of film. When made of a two-layer film, it is convenient to use the length of the flattened tube initially as a thick film rather than two separate single-layer lengths in contact with each other.

The thermoplastic mesh that forms the inner liner can be made from the thermoplastic film by several techniques. Hot microperforation of the film with a hot air jet, laser or needle perforation is preferred when it is possible to weave thermoplastic Sten yarns.

The preferred inner liner consists of an ethylene-vinyl acetate copolymer in the form of a CIL 633 * EVA network. *(trademark ) . However, due to the elastic nature of this film, where such modification results in an inherent loss of lateral strength, it cannot be

II easily processed with high-speed transport bag manufacturing equipment. It is therefore desirable to combine this film with a thick film to facilitate passage over a suitable bending frame to complete the bagging operation.

There are several methods by which a thick membrane and a retina can be combined. They can be combined by contacting the films with a resistance-type heating element, or by using contact adhesives, or, preferably due to the relatively thin and temperature-sensitive nature of the retina, by heat-sealing with a hot air jet. Thermal fastenings with hot air jets are optionally made at the edges of the inner liner, continuously along its length, and additional fastenings parallel to and within these edges, if necessary, to secure this film are made to the heavy film before bending.

Perforation of the thick film forming the perforated wall can be done using mechanical perforators on all or any part of the film surface, preferably before it is brought into contact with the retina. Optimally, two thick layers are used, which are perforated together and then separated so that the perforations of each layer are separated from the other by a predetermined distance, continuously in the longitudinal direction of the film. This has the added advantage of reducing the ingress of moisture or other contaminant from the environment, and thus increasing the storage life, and further reducing the loss of the packaged product to the atmosphere.

In an alternative embodiment, the perforated wall of the bag has perforations only adjacent to its outer edge.

It has been shown that the preferred thermoplastic valve bag of the invention and described herein removes air after attachment in an equivalent time, generally on the order of 30 seconds, with a typical multi-walled paper bag. In contrast, a conventional thermoplastic valve bag would require a vague period of time to remove air after normal industrial filling rates with cementitious products; when a similar sack with single5-fold perforations directly through its walls would have improved air removal, but with abundant product loss and environmental contamination.