WO2017017519A1

WO2017017519A1 - Bag with hybrid wall

Info

Publication number: WO2017017519A1
Application number: PCT/IB2016/001059
Authority: WO
Inventors: Constantinos Xenopoulos; Darshan BAIJNATH; Nicolas GEORGE; Xavier CIEREN
Original assignee: Lafarge
Priority date: 2015-07-29
Filing date: 2016-07-27
Publication date: 2017-02-02
Also published as: FR3039524A1; FR3039524B1

Abstract

This invention refers to a bag (1) with a multi-ply wall (2) forming an enclosure (3) designed to contain powdery substances (4), in particular hydraulic cementing materials such as cement, and where the multi-ply wall (2) is composed of: - an external ply (10) made from woven polypropylene; - an internal ply (20) made from paper with an inner surface (21) facing the enclosure (3) of the bag (1) and an outer surface (22) facing the external ply (10); the bag being characterised by the internal paper ply (20) comprising a water resistant composition (23) on all or part of its outer surface (22).

Description

Bag with hybrid wall

This invention relates to packaging technology for powdery materials, and more specifically, a bag with a multi-ply wall that forms an enclosure around powdery substances, especially hydraulic cementing materials such as cement.

There are different types of cement bags currently availa- ble, which vary based on the geographical region in which they are intended to be used.

For example, bags with a paper wall are commonly used in Europe and North America, whilst those with a woven polypropylene wall are mostly used in certain African and Asian countries .

A paper-lined bag generally has two plies of paper. These plies may be perforated to allow ventilation inside the bag while it is being filled, or they may be unperforated if the bag is required to be impermeable.

There is also the option to .. extend the shelf life of the cement inside the bag by placing a polyethylene film in between the two paper plies, in order to reduce the amount of moisture entering the bag. Usually, this film is perfo^¬ rated or has slits so as not to impede de-aeration of the bag during the filling process.

Bags with paper walls can be manufactured relatively cheaply.

However, paper-lined bags can only withstand humidity for a limited period of time before deteriorating or exposing their contents to the moisture, which can leave the contents unfit for sale or use.

Furthermore, a paper wall is less mechanically resistant than a polypropylene one, especially in terms of tensile strength and tear strength.

This means that bags with paper walls may become damaged when handled at any point between production and delivery to the end customer.

That said, some bags have paper wall with a formulation that enables them to better resist liquid water and, optionally, steam, thus bringing their properties more in line with polypropylene bags.

An example of a bag that can withstand liquid water but not vapour is made by Mondi and marketed as Splash Bag^®.

Bags with woven polypropylene walls generally only have one ply.

This ply is either laminated with polyethylene on one of the two sides, or on both sides.

It is also possible for this ply not to be laminated at all.

Where both sides of the ply are laminated with polyethylene, the polyethylene edges render the bag wall airtight.

To ensure continued de-aeration during the filling process, these polyethylene edges must be perforated prior to the bag being filled. However, this entails also perforating the polypropylene ply and therefore the wall of the bag.

This perforation may result in powdery materials leaking from the enclosure inside the bag.

In addition, it also substantially reduces the bag's moisture resistance and therefore the shelf life of the cement.

Some bags with a wall including an external ply of polypropylene can also be equipped with an internal paper ply.

The purpose of this internal paper ply is to reduce the amount of moisture able to enter the bag. Such bags are used on a seasonal basis, notably in winter, in order to prolong the shelf life of the cement stored inside the bag.

A bag with a wall including a polypropylene ply has several advantages over a paper-lined bag.

In particular, a bag with a wall including a polypropylene ply has better tensile, elongation and tear strength, meaning it can withstand a high degree of forceful handling.

For bags with unperforated walls, resistance to liquid water is also higher.

However, once moisture has entered the bag, it either comes into direct contact with the cement if the bag has only one single polypropylene ply, or into contact with the paper wall if the bag is equipped with one polypropylene ply and one paper ply. The paper used for the internal ply in bags with an external ply of woven polypropylene has a relatively high Cobb 60 value, typically in the region of or above 28 grams/m², meaning that the material has a high water absorption capacity, and it provides no protection against water impregnation.

This invention aims to resolve all or some of the aforementioned disadvantages, in particular by improving the shelf life of the cement stored within the enclosure of a bag that has a wall including a polypropylene ply in conditions where it is exposed to liquid water and humidity.

To this end, this invention relates to a multi-ply wall forming an enclosure to contain powdery substances, especially hydraulic cementing materials such as cement, and where this multi-ply wall includes an external woven polypropylene ply and an internal paper ply with one side facing the inside of the bag's enclosure and the other facing the external ply, and where this bag is characterised by the internal paper ply with a water resistant composition on all or part of its external surface.

The term water resistant means that with such a composition the paper acquires a superior resistance of the passage of water than without such a composition, in particular in wet conditions, the paper resists better to impregnation and retains a better strength.

The addition of the water resistant composition makes the outside surface of the internal ply water repellent.

The combination of the two plies in the wall improves the bag's overall resistance to liquid water and moisture. In fact, there is a striking improvement in moisture resistance compared to bags with a wall of an external woven polypropylene ply and an untreated internal paper ply.

This combination therefore helps prolong the shelf life of the cement contained within the bag's enclosure.

One aspect of the invention is that the paper used to form the internal ply is kraft paper.

This provision ensures the paper wall has increased tensile strength .

One aspect of the invention is that the paper used to form the internal ply has a grammage of at least 70 g/m² and a tensile strength of at least 6,0 kN/m in the machine direc^¬ tion and of at least 4,4 kN/m in the cross direction as determined according to ISO 1924-3 standard dated July 2005, as well as a wet tensile strength of at least 1,8 kN/m in the cross direction as determined according to ISO 3781 standard dated September 2011.

One aspect of the invention is that the multi-ply wall is permeable to gases.

This provision ensures de-aeration remains possible during the filling process.

The present invention relates also to the use of a paper comprising a water resistant composition as protection from moisture for a woven polypropylene bag. In any case, the following description will ensure the invention is understood correctly, in reference to the appended schematic that shows, as a non-limiting example, a sample bag as per the invention.

Figure 1. shows a bag as per the invention.

Figure 2 shows a bag as per the invention during the filling stage, with a view of the inside of the bag.

Figure 3 is a cross-section of the bag's multi-ply wall as per the invention.

Figures 1 and 2 show a bag 1 with a wall 2 that constitutes an enclosure 3 to receive, store and transport powdery substances 4.

The powdery substance 4 can be any material that is composed of granules small enough to form a powder.

It is most likely such a substance will be cement, plaster, or another hydraulic cementing material.

The bag 1 may be any size, and may come in other shapes than the rectangular one shown in the illustrations.

As shown in figure 3, the wall 2 of the bag 1 is composed of a first ply 10 backed onto a second ply 20.

The first ply 10 is placed between the second ply 20 and the outside environment. The first ply may therefore be referred to as the external ply 10. This external ply 10 is made from woven polypropylene, thus rendering it naturally permeable to gases, especially air.

The second ply 20 is placed between the external ply 10 and the enclosure 3 of the bag 1. The second ply may therefore be referred to as the internal ply 20.

This internal ply 20 is composed of an inner surface 21 and an outer surface 22 and is made from paper, preferably kraft paper.

This paper has a density of at least 70 g/m² and a tensile strength of at least 5, 6 kN/m.

The paper is naturally permeable to gases due to the pores formed by cellulose fibres crossing over each other.

Optionally, the paper can micro or nano-perforated in a process by which holes of diameter of a few microns are distributed over the surfa as a means of optimising de- aeration and minimizing ai impact on mechanical perfor- mance .

These pores are large enough to allow air to pass through, but small enough to retain the powdery material 4 inside the enclosure 3.

Besides this, the internal ply 20 comprises a water resistant composition 23 on all or part of its outer surface 22.

The water resistant composition 23 is the result of a surface treatment on all or part of the outer surface 22 of the internal ply 20, and not the addition of an extra ply backed onto or affixed to the paper used to make the internal ply 20.

This water resistant composition 23 may be the result of superposing a number of plies.

For example, the composition 23 may be similar to that described in US patent 5,837,383.

In addition, the paper is naturally permeable to gases and the areas of the paper that have been treated with the water resistant composition remain so.

Thus, the internal ply 20 is largely permeable to gases, especially air.

As a result, the entirety of the wall 2 of the bag 1 is permeable to gases, especially air.

In the example shown, the bag 1 is equipped with a valve 5 for filling it with powdery material 4.

This valve 5 is housed in a bottom cap 6 of the folded and empty bag 1.

The bag 1 can be filled with powdery material 4 when it is placed vertically as shown in figure 2.

When filling the bag 1, a filling head 7 is placed across the filling valve 5.

The powdery material 4 is injected into the enclosure 3 in the bag 1 via the filling head 7 and filling valve 5. As the bag 1 is filled, the volume of the enclosure 3 increases until the bag 1 takes on its final shape.

The powdery material 4 is injected into the enclosure 3 of the bag 1 until the bag 1 is considered sufficiently full.

Whilst filling the enclosure 3 of the bag 1 with powdery material 4, the air that was initially contained within the enclosure 3 of the bag 1 is expelled through the wall 2 of the bag 1, which is permeable to air.

The filling valve 5 closes when the filling head 7 is removed and the bag 1 goes from a vertical position to a hor^¬ izontal position.

The cement bag 1 can now be stored pending use.

During its use on site, the cement bag 1 may be exposed to adverse weather conditions.

Liquid water may enter the bag 1 through the gaps in the woven polypropylene external ply 10, and then reach the outer surface 22 of the internal ply 20. The water resistant composition 23 then prevents the liquid water from reaching the cement 4 for a period of up to 2 hours .

It is also possible that the cement bag 1 will be placed in a wet environment in the worksite, such as on a pile of wet sand. Moisture may then enter the bag 1 through the pores in the woven polypropylene external ply 10, and reach the outer surface 22 of the internal ply 20.

The water resistant composition 23 then prevents the moisture from reaching the cement 4 for a period of up to 12 hours.

Beyond these durations, the internal paper ply 20 is able to maintain its shape during handling because of the presence of the woven polypropylene external ply 10, which is chiefly responsible for conferring its strength to the bag 1.

Although this invention has been described in relation to specific examples, it is of course not limited to these and may include any technical equivalents of the methods described, as well as their combinations.

Examples illustrating the improvements brought by the invention, without compromising the degree of protection, are described below.

EXAMPLES

The examples below are based on water vapour transmission rate (WVTR) measurements from a number of samples carried out using the walls for these bags.

The water vapour transmission coefficient is the mass of water vapour transmitted per unit of area and unit of time in defined temperature and humidity conditions. This coefficient is expressed in grams per square metre per 24 hours [g/ (m². day) ] . These measurements were taken in accordance with the ISO 2528 standard dated September 2001, regarding the determination of the water vapour transmission rate of sheet materials, and in accordance with Appendix A in particular, which provides a method for determining the water vapour transmission rate for folded and therefore multi-ply materials.

As prescribed by this method, capsules containing a desic- cant and sealed using the material submitted for testing are placed in a controlled environment.

These capsules are weighed at suitable time intervals. When the increase in mass is proportional to the time interval, it is possible to determine the water vapour transmission rate of the material being tested.

Tables 1 and 2 show the results of water vapour transmission rate measurements for 48 different samples.

The tests were carried out using four air humidity values: 7,75 g/kg of air, 14,8 g/kg of air, 23,6 g/kg of air and 37,8 g/kg of air.

In each of these tests, the capsule depth was 13 mm, the exchange surface area was 49,51 cm², and the desiccant used was silica gel, the height of which at the bottom of the capsule was less than 4 mm and the mass of which was between 15 and 20 g.

Table 1 shows the WVTR values for 12 samples tested using woven polypropylene only. These 12 samples are labelled in table 1 as representing the wall of bag A. Table 1 also gives the_. WVTR values of the same 12 woven polypropylene samples with an additional ply of standard paper. These 12 samples are labelled in table 1 as repre- senting the wall of bag A' .

Table 2 also gives the WVTR values for 12 samples tested using woven polypropylene only. These 12 samples are labelled in table 2 as representing the wall of bag B.

Table 2 also gives the WVTR values of the same 12 woven polypropylene samples with an additional ply of paper where there is a water resistant composition on its outer surface. These 12 samples are labelled in table 2 as repre- senting the wall of bag B'.

Of course, the sides of the woven polypropylene ply are set up in the same way as they would be in the bag wall,, with the inside of the capsule representing the enclosure 3 of the bag 1.

Similarly, the surfaces of the paper ply where it is used and especially the surfaces of the paper ply when it has a water resistant composition are placed in the same way as they would be in the bag wall, with the inside of the capsule representing the enclosure 3 of the bag 1.

The final column in tables 1 and 2 shows the increase gained from the addition of the paper ply to the woven pol- ypropylene ply. Bag A' = bag A

Bag A =

wall + interwoven PP

nal standard

wall

paper ply

Absolute

humidity

in g of WVTR (g/(m².day) Increase water per

kg of air

7,75 170, 4 159,2 -6, 57%

7,75 159, 1 149, 5 -6, 03%

7,75 194, 8 181,3 -6, 93%

14,8 335, 6 321, 4 -4,23%

14,8 230, 7 223,2 -3,25%

14,8 271, 4 260, 8 -3, 91%

23,6 482, 9 486, 4 0, 72%

23,6 511, 9 491, 4 -4,00%

23,6 622, 9 589,2 -5,41%

37,8 1011, 5 960, 8 -5,01%

37,8 827, 6 793 -4,18%

37,8 803, 1 767, 9 -4, 38%

AVERAGE -4,43%

Table 1: WVTR measurements of bag A polypropylene wall

Bag B' = bag B

Bag B = wall + interwoven PP nal water- wall resistant

paper ply

Absolute

humidity in

g of water WVTR (g/(m².day) Increase per kg of

air

7,75 100, 7 97, 3 -3,4%

7,75 _.158, 3 147, 3 -6, 9%

7,75 104, 8 102,9 -1,8%

14,8 301, 3 274, 8 —8,8%

14,8 336, 5 300, 3 -10, 8%

14,8 291, 7 268, 6 -7,9%

23,6 348,3 333, 1 -4,4%

23,6 463, 8 447,4 ^—3 ^ 5%

23,6 477,5 459, 7 -3, 7%

37,8 988, 9 874,5 -11, 6%

37,8 1052, 2 938, 1 -10, 8%

37,8 793,7 731, 6 -7,8%

AVERAGE -6, 79%

Table 2: WVTR measurements of bag A ' polypropylene wall

The arithmetic mean of the increases in the bag A' wall compared to the bag A wall, and the arithmetic mean of the increases in the bag B' wall compared, to the bag B wall, show us that the bag B' wall with a paper ply comprising a water re- sistant composition is more resistant to moisture than the bag A' wall comprising a standard paper ply.

Fig. 4 shows the water vapour transmission rates (WVTR) for bags A' and B ¹. The WVTR values of the 48 samples are plotted in Fig. 4, where the x-axis is the WVTR values of the bag A or B wall samples and the y-axis is the WVTR values of the bag A' or B' wall samples .

A linear representation is given for each group of points belonging to bags A¹ and B¹.

It can be noted from Fig. 4 that the slopes of the two lines obtained are less than 1.

It is therefore beneficial to add a paper ply beneath the woven polypropylene ply in the wall of the bag 1 in order to improve its resistance to moisture.

It can also be observed that the slope for bag B' is less than that of bag A' .

It is therefore beneficial to add a paper ply with a water re- sistant composition to the wall of the bag 1 in order to improve its resistance to moisture.

Claims

Claims :

1. A bag (1) with a multi-ply wall (2) forming an enclosure (3) for containing powdery substances (4), in particular hydraulic cementing materials such as cement, and where the multi-ply wall (2) is composed of:

- an external ply (10) made from woven polypropylene;

- an internal ply (20) made from paper with an inner surface (21) facing the enclosure (3) of the bag (1) and an outer surface (22) facing the external ply (10);

the bag being characterised by the internal paper ply (20) comprising a water resistant composition (23) on all or part of its outer surface (22) .

2. A bag (1) according to claim 1, comprising an internal paper ply (20) where the paper used is kraft paper.

3. The bag (1) according to claims 1 or 2, where the paper used to form the internal ply (20) has a grammage of at least 70 g/m² and a tensile strength of at least 6,0 kN/m in the machine direction and of at least 4,4 kN/m in the cross direction as determined according to ISO 1924-3 standard dated July 2005, as well as a wet tensile strength of at least 1,8 kN/m in the cross direction as determined according to ISO 3781 standard dated September 2011.

4. A bag (1) according to one of claims 1 to 3, where the multi-ply wall (2) is permeable to gases.

5. Use of a paper comprising a water resistant composition (23) as protection from moisture for a woven polypropylene bag (1) .