Method of forming a valve bag

A method of forming a valve bag suitable for filling with, for example, powder, grain, cement, animal foodstuffs, via a chute tube inserted into the valve, including forming a combined web from two webs of material, including steps of forming the combined web into a plurality of bag sections, sealing the bag sections at one side such that a valve portion is defined, separating the two webs and moving them outwardly until the bag sections are turned inside, and sealing the two webs to form a valve bag having an strong, effective seal and a valve portion for filling.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority to United Kingdom Patent Application No. 0705451.3, filed Mar. 22, 2007.

FIELD OF THE INVENTION

This invention relates to valve bags, including a method of producing valve bags.

BACKGROUND OF THE INVENTION

Valve bags, such as for carrying powder, grain, cement, animal foodstuffs, etc., are widely known. A typical valve bag is formed of thick paper having a stitched top and a valve formed in the side of the bag. The valve is opened and impaled onto a chute tube through which material is conveyed into the bag. The bag is effectively self-sealing, as once it has been removed from the chute tube, the valve closes, therefore, preventing the contents of the bag from escaping through the valve.

Disadvantages of the bag described above are the lack of resistance to moisture, such as rain or humidity, and tendency to tear.

Plastic valve bags, and a method and apparatus for making them, are also known. For example, U.S. Pat. No. 6,890,290 (Amplas) discloses a valve bag wherein a film web is formed into a continuous tube, and the tube is sealed internally by a device which is disposed within the tube of material.

The valve bag disclosed in U.S. Pat. No. 6,890,290 is more resistant to moisture and damage such as tearing than a thick paper valve bag. However, the method of forming the bag is complex, and the required equipment is expensive. Therefore, it is only commercially viable to use this method of forming a valve bag for certain applications.

Valve bags are currently used for fairly large quantities of material, and not for small quantities of discrete parts such as nuts, bolts or spare parts. The use of current valve bags for such small quantities is not economical due to the cost of equipment. The use of paper valve bags could also lead to damage of the items by moisture, or the parts themselves could cause damage to a paper valve bag. Therefore, small quantities of discrete parts are usually packaged in bags which must be further sealed after the contents have been put into the bag.

SUMMARY OF THE INVENTION

It is an aim of the present invention to overcome or at least mitigate the above problems.

Accordingly, the present invention provides, in one aspect, a method of forming a valve bag comprising steps of:

unrolling a first web of material and a second web of material, the first and second webs of material both having an upper and a lower side;

creating a combined web by contacting material from the upper side of the first web with material from the lower side of the second web, the combined web being formed of a plurality of bag sections and having a valve side and an opposing open side;

applying a sealing process to the combined web such that the first web is sealed to the second web along part of the valve side, the sealing process defining at least one valve portion in the valve side of each bag section;

separating the first web and the second web at the open side, and folding the first web and the second web outwardly, until a section of the lower side of the first web contacts a section of the upper side of the second web;

sealing together the contacting sections of the lower side of the first web and the upper side of the second web; and

separating adjacent bag sections.

Preferably, sealing lines defining the valve extend from a predefined distance from the valve side to the periphery of the valve side.

The invention provides, in a second aspect, a valve bag formed of a first web and a second web, wherein the bag has a valve side having a valve defined by sealing lines, and an opposing side, and wherein at the valve side, an upper side of the first web contacts and a lower side of the second web and is partially sealed thereto, and at the opposing side, the lower side of the first web is sealed to the upper side of the second web.

The present invention provides a much simpler and less expensive method of production than prior art methods. An advantage of the present invention is that conventional machinery can be used, therefore, providing an inexpensive and simple method of manufacture of valve bags. Therefore, various sizes and quantities of valve bag may be produced economically. Small valve bags can be produced, for example, to hold small items such as nuts, bolts or spare parts. Once the small items have been put into the bags, the bags do not need to be further sealed, thus, resulting in a time and cost saving.

A further advantage of the present invention is that various materials can be used to form the bag, thus, allowing choice of material according to required properties.

The web material used in the present invention may be a heat sealable plastic material. An advantage of a heat sealable plastics material is that it is resistant to moisture and less susceptible to damage such as tearing. The thickness of the material may be selected according to the application of the valve bag and therefore the strength required.

One or both of the webs of material may be clear. The use of one clear and one opaque web would provide easy identification of the contents of the bag, and allow for the printing of product details on the opaque web.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the present invention, a first web of material2, such as a heat sealable plastics material, is positioned in registry with to a second web of material4, as shown inFIG. 1. The first stage of production of the valve bags involves material from the first and second webs being unrolled, and the two webs of material being brought together, such that the upper side6of the first web2contacts the lower side8of the second web4, to form a combined web10.

In the second stage of production, as shown inFIG. 2, the combined web10is passed through a sealing machine (not shown) to seal the first web2and the second web4together, along initial lines of sealing12and14. The combined web10at this stage can be considered to be formed of a number of bag portions16, each bag portion16being defined by an open side18, a valve side20, a top edge22and a bottom edge24. The first and second webs2,4at the open side18are separate, i.e., have not been sealed together.

As illustrated inFIG. 2, line of sealing12is positioned at a distance X from the valve side20, and extends from the bottom edge24towards the top edge22, stopping a valve portion26. Line of sealing14is also positioned at a distance X from the valve side20, and extends from the top edge22towards the bottom edge24, stopping at valve portion26. Line of sealing12aextends from the end of line of sealing12furthest from the bottom edge24to the periphery of the valve side20. Line of sealing14aextends from the end of line of sealing14furthest from the top edge22to the periphery of the valve side20. Lines of sealing12aand14a, therefore, define the valve section26, which is unsealed between lines12aand14a.

In a third stage of production, as illustrated inFIG. 3, the first and second webs2,4at the open side18, are separated and folded fully outwardly and brought back together at the other side of the valve side20. A section of the lower side28of the first web2is brought into contact with a section of the upper side30of the second web4. Thus, the combined web10is effectively turned inside out.

The contacting sections of the lower side28of the first web2and upper side30of the second web4are then sealed together at Y in the fourth stage of production, effectively forming a tube of material36(FIG. 4). In the fifth stage of manufacture, the tube36is passed through a bottom welding machine (not shown), which forms sealing lines32,34near the top and bottom edges22,24of the bag sections16, as illustrated inFIG. 4. The bag sections16are then cut between the top edge22of one bag section and the bottom edge24of an adjacent bag section to form individual valve bags.

FIG. 5aillustrates a bag portion having a gusset40formed in the valve side20. The forming of the gusset would occur during the third stage of production, with the first and second webs being flattened together before the combined web has been turned fully inside out.FIG. 6corresponds toFIG. 5aand shows fully sealed bag portions having a gusset on the valve side.

A gusset could also be formed on the open side18, as illustrated inFIG. 5b.

Filling of the valve bags can then be achieved by usual the usual method of inserting a impaling the valve portion26of the bag onto a chute tube and flowing the contents through the chute tube into the bag. Once the chute tube is removed from the valve, the valve will be urged closed therefore preventing the escape of the contents of the bag.